U.S. patent application number 11/373687 was filed with the patent office on 2006-07-13 for microencapsulated pigment, production process therefor, aqueous dispersion, and ink jet recording ink.
This patent application is currently assigned to SEIKO EPSON CORPORATION. Invention is credited to Hidehiko Komatsu, Toshiyuki Miyabayashi, Hiroto Nakamura, Masahiro Yatake.
Application Number | 20060155006 11/373687 |
Document ID | / |
Family ID | 28795102 |
Filed Date | 2006-07-13 |
United States Patent
Application |
20060155006 |
Kind Code |
A1 |
Nakamura; Hiroto ; et
al. |
July 13, 2006 |
Microencapsulated pigment, production process therefor, aqueous
dispersion, and ink jet recording ink
Abstract
Provided are ink jet ink excellent in dispersion stability and
ejection stability and capable of forming images with fastness,
abrasion resistance, color developability, and high density with
little feathering; a microencapsulated pigment (MCP) providing the
ink and a process of making the same; and an aqueous dispersion of
the MCP. The MCP comprises pigment particles having a hydrophilic
group on their surface (hydrophilized pigment particles) and coated
with a polymer by emulsion polymerization. The process comprises
emulsion polymerization in the presence of the hydrophilized
pigment particles. The ink essentially contains the MCP and
water.
Inventors: |
Nakamura; Hiroto; (Nagano,
JP) ; Miyabayashi; Toshiyuki; (Nagano, JP) ;
Yatake; Masahiro; (Nagano, JP) ; Komatsu;
Hidehiko; (Nagano, JP) |
Correspondence
Address: |
LADAS & PARRY
26 WEST 61ST STREET
NEW YORK
NY
10023
US
|
Assignee: |
SEIKO EPSON CORPORATION
|
Family ID: |
28795102 |
Appl. No.: |
11/373687 |
Filed: |
March 10, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10228162 |
Aug 26, 2002 |
|
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11373687 |
Mar 10, 2006 |
|
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Current U.S.
Class: |
523/160 ;
523/205 |
Current CPC
Class: |
C09D 11/326 20130101;
Y10T 428/29 20150115; C09C 3/10 20130101; C09C 1/56 20130101; C09D
11/322 20130101; Y10T 428/2998 20150115; C09B 68/44 20130101; Y10T
428/2991 20150115; C09B 68/4475 20130101; Y10T 428/2993 20150115;
C09B 67/0097 20130101; C01P 2004/54 20130101; B01J 13/04 20130101;
C09B 68/4253 20130101; B01J 13/14 20130101; C09D 17/001 20130101;
Y10T 428/2982 20150115; C09B 67/0013 20130101 |
Class at
Publication: |
523/160 ;
523/205 |
International
Class: |
C08K 9/00 20060101
C08K009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 27, 2001 |
JP |
P.2001-256025 |
Aug 27, 2001 |
JP |
P.2001-256033 |
Feb 15, 2002 |
JP |
P.2002-038793 |
Aug 23, 2002 |
JP |
P.2002-242979 |
Claims
1. A microencapsulated pigment comprising a plurality of pigment
particles, each of the pigment particles having a hydrophilic group
on the surface thereof and being coated with a polymer by emulsion
polymerization, wherein said polymer comprises a repeating unit
derived from a polymerizable surface active agent having a
hydrophilic group, a hydrophobic group and a polymerizable
group.
2. The microencapsulated pigment according to claim 1, which has an
aspect ratio of 1.0 to 1.3 and a Zingg index of 1.0 to 1.3.
3. (canceled)
4. The microencapsulated pigment according to claim 13, wherein
said polymer is a copolymer further comprising a repeating unit
that is derived from a comonomer copolymerizable with said
polymerizable surface active agent.
5. The microencapsulated pigment according to claim 4, wherein said
comonomer is at least one of a hydrophilic monomer and a
hydrophobic monomer.
6. The microencapsulated pigment according to claim 5, wherein said
hydrophobic monomer has at least a hydrophobic group and a
polymerizable group per its molecule, said hydrophobic group being
selected from the group consisting of an aliphatic hydrocarbon
group, an alicyclic hydrocarbon group and an aromatic hydrocarbon
group.
7. The microencapsulated pigment according to claim 1, wherein said
polymer coating is prepared by adding said polymerizable surface
active agent and a polymerization initiator to an aqueous
dispersion having said pigment particles dispersed therein and
subjecting the system to emulsion polymerization.
8. The microencapsulated pigment according to claim 1, wherein said
polymer coating is prepared by adding said polymerizable surface
active agent, a comonomer copolymerizable with said polymerizable
surface active agent, and a polymerization initiator to an aqueous
dispersion having said pigment particles dispersed therein and
subjecting the system to emulsion polymerization.
9-14. (canceled)
15. The microencapsulated pigment according to claim 5, wherein
said hydrophilic monomer has at least a hydrophilic group and a
polymerizable group in its molecule thereof, said hydrophilic group
being selected from the group consisting of a sulfonic acid group
or a salt thereof, a sulfinic acid group or a salt thereof, a
carboxyl group or a salt thereof, a carbonyl group or a salt
thereof, a hydroxyl group, an oxyethylene group, an amido group,
and an amino group.
16. The microencapsulated pigment according to claim 6, wherein
said polymerizable group is a radically polymerizable unsaturated
hydrocarbon group and is selected from the group consisting of a
vinyl group, an allyl group, an acryloyl group, a methacryloyl
group, a propenyl group, a vinylidene group, and a vinylene
group.
17-21. (canceled)
22. The microencapsulated pigment according to claim 1, wherein the
pigment constituting said pigment particles is carbon black or an
organic pigment.
23. The microencapsulated pigment according to claim 1, wherein
said hydrophilic group on the surface of the pigment particles is
at least one of a sulfonic acid group (--SO.sub.3H) and a sulfinic
acid group --RSO.sub.2H; wherein R represents an alkyl group having
1 to 12 carbon atoms, or a phenyl or its derivative group.
24. The microencapsulated pigment according to claim 1, wherein
said hydrophilic group on the surface of the pigment particles is
at least one of a sulfonic acid anion (--SO.sub.3--) and a sulfinic
acid anion --RSO.sub.2--; wherein R represents an alkyl group
having 1 to 12 carbon atoms, or a phenyl or its derivative
group.
25. The microencapsulated pigment according to claim 1, wherein
said hydrophilic group on the surface of the pigment particles is
at least one of a carboxyl group (--COOH) and a carboxylate anion
(--COO--).
26-28. (canceled)
29. A process for producing a microencapsulated pigment, comprising
coating pigment particles having a hydrophilic group on the surface
thereof with a polymer, wherein said polymer is prepared by
emulsion polymerization in the presence of said pigment particles,
said emulsion polymerization comprising polymerizing a
polymerizable surface active agent having a hydrophilic group, a
hydrophobic group and a polymerizable group and, optionally, a
comonomer copolymerizable with the polymerizable surgical active
agent, in an aqueous dispersion having said pigment particles
dispersed therein.
30. (canceled)
31. The process according to claim 29, comprising polymerizing the
polymerizable surface active agent having the hydrophilic group,
the hydrophobic group and the polymerizable group, and the
comonomer copolymerizable with said polymerizable surface active
agent in the aqueous dispersion having said pigment particles
dispersed therein.
32. The process according to claim 29, comprising: mixing a
polymerization initiator having a cationic group with an aqueous
dispersion having dispersed therein pigment particles having an
anionic group as said hydrophilic group under a condition that does
not activate said polymerization initiator; adding a hydrophilic
monomer and a surface active agent to the dispersion; and
activating said polymerization initiator to carry out
polymerization.
33-45. (canceled)
46. An aqueous dispersion containing a microencapsulated pigment
according to claim 1.
47. An ink jet recording ink containing an aqueous dispersion
according to claim 46.
48. An ink jet recording ink comprising a microencapsulated pigment
according to claim 1 and water.
49. The ink jet recording ink according to claim 47, further
comprising a water-soluble organic solvent.
50. The ink jet recording ink according to claim 49, wherein said
water-soluble organic solvent is a high-boiling water-soluble
organic solvent having a boiling point of 180.degree. C. or
higher.
51. The ink jet recording ink according to claim 49, wherein said
water-soluble organic solvent contains at least one compound
selected from the group consisting of glycerol, an alkyl ether of a
polyhydric alcohol, and a 1,2-alkyldiol.
52. The ink jet recording ink according to claim 47, which further
comprises a solid wetting agent in an amount of 3 to 20% by weight
based on the total weight of the ink.
53. The ink jet recording ink according to claim 52, wherein said
solid wetting agent is at least one of trimethylolpropane and
1,2,6-hexanetriol.
54. The ink jet recording ink according to claim 47, further
comprising a surface active agent.
55. The ink jet recording ink according to claim 54, wherein said
surface active agent is at least one of an acetylene glycol surface
active agent and an acetylene alcohol surface active agent.
56. The ink jet recording ink according to claim 47, which further
comprises a saccharide.
57. The microencapsulated pigment according to claim 1, wherein the
polymer on each of the pigment particles has a first surface that
is disposed on the surface of the pigment particle and a second
surface that is spaced form the surface of the pigment
particle.
58. The microencapsulated pigment according to claim 57, wherein
the hydrophilic group of the pigment particle extends above the
second surface of the pigment particle.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a microencapsulated pigment, a
production process therefor, an aqueous dispersion, and an ink jet
recording ink.
BACKGROUND OF THE INVENTION
[0002] Ink jet recording is an image forming technique comprising
ejecting ink droplets from fine nozzles of a recording head to form
letters or figures on a recording medium such as paper. Ink jet
recording technologies that have been implemented include
drop-on-demand techniques, such as a method in which electrical
signals are converted to mechanical signals by a piezoelectric
actuator to discontinuously eject ink droplets stored in the nozzle
head and a method in which part of ink is rapidly heated to
generate a bubble near the nozzle of a recording head to
discontinuously eject ink droplets by the volume expansion of the
bubble.
[0003] Aqueous pigment inks having a pigment dispersed in water
have recently been developed for use in ink jet recording systems.
Compared with inks containing water-soluble dyes, aqueous pigment
inks are characterized by excellent water resistance and light
resistance. It is a generally followed practice that such aqueous
pigment ink is prepared by dispersing a pigment in an aqueous
medium with the aid of a dispersant, such as a surface active agent
or a polymeric dispersant.
[0004] For example, JP-A-3-157464 proposes using a polymeric
dispersant for helping pigment particles be dispersed and using a
mixture of water, a non-volatile organic solvent, and a lower
alcohol as an aqueous medium in a pigment ink formulation
containing an acetylene glycol-based penetrant thereby to secure
dispersion stability of the pigment. However, use of a dispersant
for pigment particles leads to an increased number of elements
involved in ink preparation, which makes it difficult to control
ink physical properties such as viscosity within designed ranges.
Besides this, the proposed pigment ink still has the problem that a
sufficient image density is hard to obtain.
[0005] Further, aqueous pigment ink containing a dispersant has the
dispersant merely adsorbed on the surface of pigment particles.
Since a strong shear force is applied to ink ejected through a fine
nozzle of a recording head, the dispersant can come off the surface
of pigment particles to lose its dispersing capability, which can
result in instable ink ejection. Destabilization can also occur
when the aqueous pigment ink is stored for a long time.
[0006] Introducing a sulfonic acid group on the surface of pigment
particles has been proposed as a successful technique for
dispersing pigment particles in water. For example, JP-A-10-110129
discloses a pigment ink containing a surface-sulfonated organic
pigment which is obtained by treating an organic pigment dispersed
in a solvent having no active protons with a sulfonating agent
(referred to as related art (1)). The inventors of the related art
1 allege that the pigment ink has excellent dispersion stability
and exhibits satisfactory ejection stability from the nozzle of a
recording head (the property of being stably ejected from the
recording head in a fixed direction).
[0007] JP-A-11-49974 teaches that a positively chargeable organic
pigment mass is prepared by treating a sulfonated organic pigment
mass with a monovalent metallic ion and that a pigment prepared
from the positively chargeable organic pigment mass is formulated
together with a dispersant and water into an aqueous ink
composition-having high storage stability (dispersion stability)
(referred to as related art (2)).
[0008] Although the ink compositions of the related arts (1) and
(2) which contain surface-treated pigment particles as a colorant
are excellent in dispersion stability and ejection stability as
compared with conventional ink jet recording inks, the images
printed with them on recording media such as plain paper or inkjet
recording media (recording media having an ink receiving layer
designed for ink jet recording ink) have insufficient abrasion
resistance. This seems to be due to insufficient fixability of the
surface-treated pigment particles on the recording media.
[0009] Application of polymer-encapsulated pigments to ink jet
recording technologies is known for improved fixability of pigments
on a recording medium. JP-B-7-94634 and JP-A-8-59715 disclose
encapsulated pigment particles. JP-A-5-339516, JP-A-8-302227,
JP-A-8-302228, and JP-A-8-81647 propose pigment particles having a
polymer grafted on their surface. JP-A-5-320276 suggests a method
of microencapsulating hydrophobic powder with an amphiphilic graft
polymer, which has turned out to involve the problem that use of
such a previously polymerized material for encapsulation results in
too large a particle diameter. Additionally, JP-A-8-218015,
JP-A-8-295837, JP-A-9-3376, JP-A-8-183920, JP-A-10-46075,
JP-A-10-292143, JP-A-11-80633, JP-A-11-349870, and JP-A-12-7961
disclose inks containing pigment particles coated with a resin
capable of forming film at room temperature by phase reversal of
emulsion. JP-A-9-31360, JP-A-9-217019, JP-A-9-316353,
JP-A-9-104834, JP-A-9-151342, JP-A-10-140065, JP-A-11-152424,
JP-A-11-166145, JP-A-11-166145, JP-A-11-199783, and JP-A-11-209672
propose inks containing pigment particles coated with an anionic
group-containing organic polymer by acid precipitation.
JP-A-9-286939, JP-A-12-44852, JP-A-12-53897, JP-A-12-53898,
JP-A-12-53899, and JP-A-12-53900 propose inks comprising a polymer
emulsion having polymer particles impregnated with a colorant by
phase inversion of emulsion (referred to related art 3). Even in
ink compositions containing such a colorant as obtained by phase
inversion of emulsion or acid precipitation, the polymer adsorbed
on the pigment particles can separate and dissolve in ink,
resulting in insufficient performance in terms of dispersion
stability, ejection stability, image quality, and the like, which
depends on the kind of organic solvents used as, for example, a
penetrant, though. Because the ink according to the related art 3
not a little suffers from separation of polymer from pigment
particles, the pigment content in ink is of necessity limited for
assuring dispersion stability. As a result, the ink only provides
recorded matter with low image densities and, when printed on plain
paper, easily feathers and attains only low color
developability.
SUMMARY OF THE INVENTION
[0010] An object of the present invention is to provide a
microencapsulated pigment capable of providing an ink jet recording
ink satisfying all the requirements: (1) high dispersion stability,
(2) high stability when ejected from a recording head, (3)
capability of providing images with excellent fastness, (4)
capability of providing images with high density, (5) capability of
providing images with excellent abrasion resistance, and (6)
capability of providing images which hardly feather and show high
color developability even when formed on plain paper.
[0011] Another object of the present invention is to provide a
process for producing the microencapsulated pigment.
[0012] A still other object of the invention is to provide an
aqueous dispersion.
[0013] A yet other object of the invention is to provide an ink jet
recording ink which satisfies all the requirements (1) to (6)
supra.
[0014] As a result of extensive investigations, the present
inventors have surprisingly found that an ink jet recording ink
satisfying all the requirements (1) to (6) supra can be obtained by
preparing a specific microencapsulated pigment and using the
microencapsulated pigment as a colorant. The present invention has
been completed based on this finding.
[0015] The present invention provides:
[0016] (1) A microencapsulated pigment comprising pigment particles
having a hydrophilic group on the surface thereof and being coated
with a polymer by emulsion polymerization.
[0017] (2) The microencapsulated pigment according to item (1),
which has an aspect ratio of 1.0 to 1.3 and a Zingg index of 1.0 to
1.3.
[0018] (3) The microencapsulated pigment according to item (1) or
(2), wherein said polymer comprises a repeating unit derived from a
polymerizable surface active agent having a hydrophilic group, a
hydrophobic group and a polymerizable group.
[0019] (4) The microencapsulated pigment according to item (3),
wherein said polymer is a copolymer further comprising a repeating
unit that is derived from a comonomer copolymerizable with said
polymerizable surface active agent.
[0020] (5) The microencapsulated pigment according to item (4),
wherein said comonomer is at least one of a hydrophilic monomer and
a hydrophobic monomer.
[0021] (6) The microencapsulated pigment according to item (5),
wherein said hydrophobic monomer has at least a hydrophobic group
and a polymerizable group per its molecule, and is selected from
the group consisting of an aliphatic hydrocarbon group, an
alicyclic hydrocarbon group and an aromatic hydrocarbon group.
[0022] (7) The microencapsulated pigment according to any one of
items (1) to (6), wherein said polymer coating is prepared by
adding said polymerizable surface active agent and a polymerization
initiator to an aqueous dispersion having said pigment particles
dispersed therein and subjecting the system to emulsion
polymerization.
[0023] (8) The microencapsulated pigment according to any one of
items (1) to (7), wherein said polymer coating is prepared by
adding said polymerizable surface active agent, a comonomer
copolymerizable with said polymerizable surface active agent, and a
polymerization initiator to an aqueous dispersion having said
pigment particles dispersed therein and subjecting the system to
emulsion polymerization.
[0024] (9) The microencapsulated pigment according to item (1) or
(2), wherein said hydrophilic group on the surface of the pigment
particles is an anionic group, and said polymer is one prepared by
polymerizing a hydrophilic monomer in the presence of a
polymerization initiator having a cationic group.
[0025] (10) The microencapsulated pigment according to item (1) or
(2), wherein said hydrophilic group on the surface of the pigment
particles is an anionic group, and said polymer is one prepared by
polymerizing a hydrophilic monomer and a comonomer copolymerizable
with said hydrophilic monomer in the presence of a polymerization
initiator having a cationic group.
[0026] (11) The microencapsulated pigment according to item (1) or
(2), wherein said hydrophilic group on the surface of the pigment
particles is an anionic group, and said polymer coating is prepared
by mixing a polymerization initiator having a cationic group with
an aqueous dispersion having the pigment particles dispersed
therein under a condition that does not activate said
polymerization initiator; adding a hydrophilic monomer and a
surface active agent to the dispersion; and activating said
polymerization initiator to carry out emulsion polymerization.
[0027] (12) The microencapsulated pigment according to item (1) or
(2), wherein said hydrophilic group on the surface of the pigment
particles is an anionic group, and said polymer coating is prepared
by mixing a polymerization initiator having a cationic group with
an aqueous dispersion having the pigment particles dispersed
therein under a condition that does not activate said
polymerization initiator; adding a hydrophilic monomer, a comonomer
copolymerizable with said hydrophilic monomer, and a surface active
agent to the dispersion; and activating said polymerization
initiator to carry out emulsion polymerization.
[0028] (13) The microencapsulated pigment according to item (11) or
(12), wherein said surface active agent is a polymerizable surface
active agent having a hydrophilic group, a hydrophobic group, and a
polymerizable group.
[0029] (14) The microencapsulated pigment according to any one of
items (9) to (13), wherein said polymerization initiator is at
least one member selected from the group consisting of
2,2'-azobis[2-(5-methyl-2-imidazolin-2-yl)propane]dihydrochloride,
2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride,
2,2'-azobis[2-(2-imidazolin-2-yl)propane]disulfite dihydrate,
2,2'-azobis[2-(3,4,5,6-tetrahydropyrimidin-2-yl)propane]dihydrochloride,
2,2'-azobis[2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane]dihydrochlori-
de, and 2,2'-azobis(2-amidinopropane) dihydrochloride.
[0030] (15) The microencapsulated pigment according to any one of
items (5) to (14), wherein said hydrophilic monomer has at least a
hydrophilic group and a polymerizable group in its molecule
thereof, and said hydrophilic group is selected from the group
consisting of a sulfonic acid group or a salt thereof, a sulfinic
acid group or a salt thereof, a carboxyl group or a salt thereof, a
carbonyl group or a salt thereof, a hydroxyl group, an oxyethylene
group, an amido group, and an amino group.
[0031] (16) The microencapsulated pigment according to any one of
items (6) to (8) and (15), wherein said polymerizable group is a
radically polymerizable unsaturated hydrocarbon group and is
selected from the group consisting of a vinyl group, an allyl
group, an acryloyl group, a methacryloyl group, a propenyl group, a
vinylidene group, and a vinylene group.
[0032] (17) The microencapsulated pigment according to item (1) or
(2), wherein said polymer is polymerized by a process comprising:
polymerizing at least one of a polymerizable surface active agent
having a hydrophilic group, a hydrophobic group and a polymerizable
group, and a hydrophilic monomer in the presence of a polymeric azo
initiator comprising a repeating unit represented by formula (I):
##STR1## wherein D represents a portion having at least a
hydrophobic segment; L.sup.1 and L.sup.2, which may be the same or
different, each represent a linking group; R.sup.1, R.sup.2,
R.sup.3, and R.sup.4 each represent an alkyl group having 1 to 4
carbon atoms or a cyano group; and n represents an integer of 1 or
greater.
[0033] (18) The microencapsulated pigment according to item (1) or
(2), wherein said polymer coating is prepared by mixing
[0034] a polymeric azo initiator comprising a repeating unit
represented by formula (I): ##STR2## wherein D represents a portion
having at least a hydrophobic segment; L.sup.1 and L.sup.2, which
may be the same or different, each represent a linking group;
R.sup.1, R.sup.2, R.sup.3, and R.sup.4 each represent an alkyl
group having 1 to 4 carbon atoms or a cyano group; and n represents
an integer of 1 or greater,
[0035] with an aqueous dispersion having said pigment particles
dispersed therein under a condition that does not activate said
polymeric azo initiator;
[0036] adding at least one of a polymerizable surface active agent
having a hydrophilic group, a hydrophobic group and a polymerizable
group, and a hydrophilic monomer to the mixture; and
[0037] activating said polymeric azo initiator to carry out
emulsion polymerization.
[0038] (19) The microencapsulated pigment according to item (18),
wherein said polymer coating is prepared by: mixing said polymeric
azo initiator with said aqueous dispersion of the pigment particles
under a condition that does not activate said polymeric azo
initiator; and subjecting the system to emulsion polymerization in
the presence of at least one of said polymerizable surface active
agent and said hydrophilic monomer, and a hydrophobic monomer.
[0039] (20) The microencapsulated pigment according to item (18),
wherein said polymer coating is prepared by: mixing said polymeric
azo initiator with said aqueous dispersion of the pigment particles
under a condition that does not activate said polymeric azo
initiator; and subjecting the system to emulsion polymerization in
the presence of at least one of said polymerizable surface active
agent and said hydrophilic monomer, and a crosslinking agent.
[0040] (21) The microencapsulated pigment according to any one of
items (17) to (20), wherein said polymeric azo initiator is a
compound represented by formula (Ic): ##STR3## wherein R.sup.1 and
R.sup.3 each represent an alkyl group having 1 to 4 carbon atoms;
R.sup.2 and R.sup.4 each represent a cyano group; and .alpha.,
.beta., h, j, and n each represent an integer of 1 or greater.
[0041] (22) The microencapsulated pigment according to any one of
items (1) to (21), wherein the pigment constituting said pigment
particles is carbon black or an organic pigment.
[0042] (23) The microencapsulated pigment according to any one of
items (1) to (22), wherein said hydrophilic group on the surface of
the pigment particles is at least one of a sulfonic acid group
(--SO.sub.3H) and a sulfinic acid group (--RSO.sub.2H; wherein R
represents an alkyl group having 1 to 12 carbon atoms, or a phenyl
or its derivative group).
[0043] (24) The microencapsulated pigment according to any one of
items (1) to (23), wherein said hydrophilic group on the surface of
the pigment particles is at least one of a sulfonic acid anion
(--SO.sub.3.sup.-) and a sulfinic acid anion (--RSO.sub.2.sup.-;
wherein R represents an alkyl group having 1 to 12 carbon atoms, or
a phenyl or its derivative group).
[0044] (25) The microencapsulated pigment according to any one of
items (1) to (24), wherein said hydrophilic group on the surface of
the pigment particles is at least one of a carboxyl group (--COOH)
and a carboxylate anion (--COO.sup.-).
[0045] (26) The microencapsulated pigment according to any one of
items (3) to (8) and (13) to (25), wherein said polymerizable group
of said polymerizable surface active agent is selected from the
group consisting of a vinyl group, an allyl group, an acryloyl
group, a methacryloyl group, a propenyl group, a vinylidene group,
and a vinylene group.
[0046] (27) The microencapsulated pigment according to any one of
items (3) to (8) and (13) to (26), wherein the hydrophilic group of
the polymerizable surface active agent is selected from the group
consisting of a sulfonic acid group or a salt thereof, a sulfinic
acid group or a salt thereof, a carboxyl group or a salt thereof,
and a carbonyl group or a salt thereof.
[0047] (28) The microencapsulated pigment according to any one of
items (3) to (8) and (13) to (27), wherein said hydrophobic group
of said polymerizable surface active agent is selected from the
group consisting of an alkyl group, an aryl group, and a group
composed of a combination thereof.
[0048] (29) A process for producing a microencapsulated pigment,
comprising
[0049] coating pigment particles having a hydrophilic group on the
surface thereof with a polymer,
[0050] wherein said polymer is prepared by emulsion polymerization
in the presence of said pigment particles.
[0051] (30) The process according to item (29), comprising
polymerizing a polymerizable surface active agent having a
hydrophilic group, a hydrophobic group and a polymerizable group in
an aqueous dispersion having said pigment particles dispersed
therein.
[0052] (31) The process according to item (29), comprising
polymerizing a polymerizable surface active agent having a
hydrophilic group, a hydrophobic group and a polymerizable group
and a comonomer copolymerizable with said polymerizable surface
active agent in an aqueous dispersion having said pigment particles
dispersed therein.
[0053] (32) The process according to item (29), comprising: mixing
a polymerization initiator having a cationic group with an aqueous
dispersion having dispersed therein pigment particles having an
anionic group as said hydrophilic group under a condition that does
not activate said polymerization initiator; adding a hydrophilic
monomer and a surface active agent to the dispersion; and
activating said polymerization initiator to carry out
polymerization.
[0054] (33) The process according to item (29), comprising: mixing
a polymerization initiator having a cationic group with an aqueous
dispersion having dispersed therein pigment particles having an
anionic group as said hydrophilic group under a condition that does
not activate said polymerization initiator; adding a hydrophilic
monomer, a comonomer copolymerizable with said hydrophilic monomer
and a surface active agent to the dispersion; and activating said
polymerization initiator to carry out polymerization.
[0055] (34) The process according to item (32) or (33), wherein
said polymerization initiator is at least one member selected from
the group consisting of
2,2'-azobis[2-(5-methyl-2-imidazolin-2-yl)propane]dihydrochloride,
2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride,
2,2'-azobis[2-(2-imidazolin-2-yl)propane]disulfite dihydrate,
2,2'-azobis[2-(3,4,5,6-tetrahydropyrimidin-2-yl)propane]dihydrochloride,
2,2'-azobis[2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane]dihydrochlori-
de, and 2,2'-azobis(2-amidinopropane) dihydrochloride.
[0056] (35) The process according to any one of items (32) to (34),
wherein said surface active agent is a polymerizable surface active
agent having a hydrophilic group, a hydrophobic group, and a
polymerizable group.
[0057] (36) The process according to any one of items (30), (31),
(34) and (35), wherein said polymerizable group of said
polymerizable surface active agent is selected from the group
consisting of a vinyl group, an allyl group, an acryloyl group, a
methacryloyl group, a propenyl group, a vinylidene group, and a
vinylene group.
[0058] (37) The process according to any one of items (30), (31)
and (34) to (36), wherein said hydrophilic group of said
polymerizable surface active agent is at least one of: an anionic
group selected from the group consisting of a sulfonic acid group
or a salt thereof, a sulfinic acid group or a salt thereof, a
carboxyl group or a salt thereof, and a carbonyl group or a salt
thereof; and a nonionic group selected from the group consisting of
a hydroxyl group, and an oxyethylene group.
[0059] (38) The process according to any one of items (30), (31)
and (34) to (37), wherein said hydrophobic group of said
polymerizable surface active agent is selected from the group
consisting of an alkyl group, an aryl group, and a group composed
of a combination thereof.
[0060] (39) The process according to any one of items (29) to (38),
wherein said hydrophilic group of said pigment particles is at
least one of a sulfonic acid group (--SO.sub.3H) and a sulfinic
acid group (--RSO.sub.2H; wherein R represents an alkyl group
having 1 to 12 carbon atoms, or a phenyl or its derivative
group).
[0061] (40) The process according to any one of items (29) to (38),
wherein said hydrophilic group of said pigment particles is at
least one of a sulfonic acid anion (--SO.sub.3.sup.-) and a
sulfinic acid anion (--RSO.sub.2.sup.-; wherein R represents an
alkyl group having 1 to 12 carbon atoms, or a phenyl or its
derivative group).
[0062] (41) The process according to any one of items (29) to (38),
wherein said hydrophilic group of said pigment particles is at
least one of a carboxyl group (--COOH) and a carboxylate anion
(--COO.sup.-).
[0063] (42) The process according to any one of items (31) and (33)
to (41), wherein said comonomer is at least one of a hydrophilic
monomer and a hydrophobic monomer.
[0064] (43) The process according to item (42), wherein said
hydrophobic monomer has at least a hydrophobic group and a
polymerizable group per its molecule, and is selected from the
group consisting of an aliphatic hydrocarbon group, an alicyclic
hydrocarbon group and an aromatic hydrocarbon group.
[0065] (44) The process according to item (42) or (43), wherein
said hydrophilic monomer has at least a hydrophilic group and a
polymerizable group in its molecule thereof, and said hydrophilic
group is selected from the group consisting of a sulfonic acid
group or a salt thereof, a sulfinic acid group or a salt thereof, a
carboxyl group or a salt thereof, a carbonyl group or a salt
thereof, a hydroxyl group, an oxyethylene group, an amido group,
and an amino group.
[0066] (45) The process according to item (43) or (44), wherein
said polymerizable group is a radically polymerizable unsaturated
hydrocarbon group and is selected from the group consisting of a
vinyl group, an allyl group, an acryloyl group, a methacryloyl
group, a propenyl group, a vinylidene group, and a vinylene
group.
[0067] (46) An aqueous dispersion containing a microencapsulated
pigment according to any one of items (1) to (28).
[0068] (47) An ink jet recording ink containing an aqueous
dispersion according to item (46).
[0069] (48) An ink jet recording ink comprising a microencapsulated
pigment according to any one of items (1) to (28) and water.
[0070] (49) The ink jet recording ink according to item (47) or
(48), further comprising a water-soluble organic solvent.
[0071] (50) The ink jet recording ink according to item (49),
wherein said water-soluble organic solvent is a high-boiling
water-soluble organic solvent having a boiling point of 180.degree.
C. or higher.
[0072] (51) The ink jet recording ink according to item (49) or
(50), wherein said water-soluble organic solvent contains at least
one compound selected from the group consisting of glycerol, an
alkyl ether of a polyhydric alcohol, and a 1,2-alkyldiol.
[0073] (52) The ink jet recording ink according to any one of items
(47) to (51), which further comprises a solid wetting agent in an
amount of 3 to 20% by weight based on the total weight of the
ink.
[0074] (53) The ink jet recording ink according to item (52),
wherein said solid wetting agent is at least one of
trimethylolpropane and 1,2,6-hexanetriol.
[0075] (54) The ink jet recording ink according to any one of items
(47) to (53), further comprising a surface active agent.
[0076] (55) The ink jet recording ink according to item (54),
wherein said surface active agent is at least one of an acetylene
glycol surface active agent and an acetylene alcohol surface active
agent.
[0077] (56) The ink jet recording ink according to any one of items
(47) to (55), which further comprises a saccharide.
BRIEF DESCRIPTION OF THE DRAWINGS
[0078] By way of example and to make the description clearer,
reference is made to the accompanying drawing, in which:
[0079] FIG. 1 schematically illustrates a first disperse state in
which a pigment particle having a hydrophilic group on the surface
thereof is dispersed in an aqueous medium and is coexistent with a
polymerizable surface active agent.
[0080] FIG. 2 schematically illustrates the first disperse state in
which the polymerizable surface active agent has been
polymerized.
[0081] FIG. 3 schematically shows a second disperse state in which
a pigment particle having a hydrophilic group on the surface
thereof is dispersed in an aqueous medium and is coexistent with a
polymerizable surface active agent.
[0082] FIG. 4 schematically illustrates the second disperse state
in which the polymerizable surface active agent has been
polymerized.
[0083] FIG. 5 schematically depicts a disperse state in which a
pigment particle having an anionic group on the surface thereof is
dispersed in an aqueous medium and is coexistent with an azo
compound having a cationic group, a hydrophilic monomer, and a
comonomer.
[0084] FIG. 6 schematically shows the disperse state of FIG. 5 in
which the polymerizable monomer and the comonomer have been
copolymerized.
REPRESENTATION OF REFERENCE NUMERALS
[0085] 1, 101: pigment particles
[0086] 2: polymerizable surface active agent
[0087] 10: hydrophilic group
[0088] 11: hydrophilic group
[0089] 12, 12': hydrophobic group
[0090] 13, 13': polymerizable group
[0091] 60, 61, 150: polymer layer (polymer)
[0092] 100, 200, 300: microencapsulated pigment
[0093] 102: azo compound (polymerization initiator)
[0094] 103: hydrophilic monomer
[0095] 104: comonomer
[0096] 110: anionic group
[0097] 111: cationic group
[0098] 112: hydrophilic group
[0099] 113: polymerizable group
DETAILED DESCRIPTION OF THE INVENTION
[0100] The microencapsulated pigment according to an embodiment of
the present invention is characterized in that pigment particles
having a hydrophilic group on the surface thereof are coated with a
polymer by emulsion polymerization techniques.
[0101] In the emulsion polymerization system, there is produced a
polarized state due to the surface hydrophilic group of the pigment
particles and the polar group of an emulsifier (surface active
agent) or a polymerization initiator used to carry out emulsion
polymerization. As a result, the configuration of monomer molecules
existing around the pigment particles on standby for polymerization
is under highly accurate control by the polarization. Upon
polymerizing the monomer in this state, there is obtained the
microencapsulated pigment according to the invention. The
microencapsulated pigment of the present invention is capable of
providing an ink jet recording ink satisfying all the requirements:
(1) high dispersion stability, (2) high ejection stability, (3)
capability of providing images with excellent fastness, (4)
capability of providing images with high density, (5) capability of
providing images with excellent abrasion resistance, and (6)
capability of providing images which hardly feather and show high
color developability even when formed on plain paper. In contrast,
it seems that coating of pigment particles with a previously
polymerized material by means of emulsion phase inversion or acid
precipitation fails to provide coated pigment particles that
fulfill all the requirements (1) to (6) supra presumably because of
a limited coating state achievable with the previously polymerized
material.
[0102] The microencapsulated pigment of the present invention
preferably has an aspect ratio (a ratio of the major diameter to
the minor diameter) of 1.0 to 1.3 and a Zingg index of 1.0 to 1.3,
particularly 1.0 to 1.2, for securing fulfillment of the
requirements (1), (2), (4), and (6).
[0103] Taking the minor diameter, major diameter, and thickness of
a particle taken as b, l, and t, respectively, provided that
1.gtoreq.b.gtoreq.t>0, the aspect ratio and the flatness of the
particle are represented by l/b (.gtoreq.1) and b/t (.gtoreq.1),
respectively, and the Zingg index of the particle is represented by
aspect ratio/flatness=(lt)/b.sup.2. According to these
representations, a true sphere has an aspect ratio of 1 and a Zingg
index of 1.
[0104] Microencapsulated pigments with Zingg indices greater than
1.3 tend to fail to exhibit satisfactory results with respect to
the requirements (1), (2), (4), and (6), which may be ascribable to
a flatter shape and lower the isotropy of the microencapsulated
pigments. While methods for controlling the aspect ratio and Zingg
index within the above ranges are not particularly restricted, it
is notable that a microencapsulated pigment in which the pigment
particles having a hydrophilic group on their surface are coated
with a polymer by emulsion polymerization readily satisfis these
conditions. For securely obtaining microencapsulated pigments
having the above-specified aspect ratio and Zingg index, it is
particularly preferred to adopt the modes according to first to
third embodiments hereinafter described. Where techniques other
than emulsion polymerization, such as acid precipitation and
emulsion phase inversion, are followed, it is difficult to obtain
microencapsulated pigments having an aspect ratio and a Zingg index
controlled within the recited ranges.
[0105] The microencapsulated pigment whose aspect ratio and Zingg
index fall within the respective recited ranges is like a true
sphere. Inks containing such microencapsulated pigments easily
exhibit Newtonian flow behavior and excellent ejection stability.
Being like a true sphere, it is assured that the ejected
microcapsules are arranged on a recording medium such as paper at a
high density to realize image density and color development with
high efficiency. Also, being like a true sphere, superiority in
dispersibility and dispersion stability is promised.
[0106] The preferred first to third embodiments of the
microencapsulated pigment according to the present invention are
described below.
[I] First Embodiment
[0107] The microencapsulated pigment according to the first
embodiment comprises pigment particles having a hydrophilic group
on the surface thereof and being coated with a polymer, wherein the
polymer comprises a repeating unit derived from a polymerizable
surface active agent having a hydrophilic group, a hydrophobic
group, and a polymerizable group. The microencapsulated pigment of
the first embodiment is conveniently produced by a process
comprising the steps of adding a polymerizable surface active agent
and a polymerization initiator to an aqueous dispersion having
pigment particles dispersed therein and subjecting the system to
emulsion polymerization. The disperse states the pigment particles
could take in this process will herein be called "a first disperse
state" and "a second disperse state", which will be illustrated
hereunder by way of FIGS. 1 through 4. Note that the description
contains theoretical assumptions.
First Disperse State:
[0108] FIG. 1 illustrates a first disperse state in which a pigment
particle 1 having a hydrophilic group 10 on its surface is
dispersed in a solvent mainly comprising water (hereinafter
referred to as an aqueous medium) in the presence of a
polymerizable surface active agent 2 having a hydrophilic group 11,
a hydrophobic group 12, and a polymerizable group 13. The pigment
particle 1 has on its surface hydrophilic groups 10 bonded through
chemical bonding at a specific density and hydrophobic regions 50
among the hydrophilic groups 10. The molecules of the polymerizable
surface active agent 2 enter between the hydrophilic groups 10 with
their hydrophobic groups 12 facing the pigment particle 1 by the
interaction between the hydrophobic groups 12 and the hydrophobic
regions 50. The hydrophilic groups 11 of the polymerizable surface
active agent 2 are directed toward the aqueous medium, i.e., away
from the pigment particle 1.
[0109] In this disperse state, when the polymerizable groups 13 of
the polymerizable surface active agent 2 are polymerized by, for
example, addition of a polymerization initiator, there is produced
a microencapsulated pigment 100 comprising the pigment particle 1
encapsulated with a polymer layer 60 as shown in FIG. 2. Since the
polymer layer 60 has the hydrophilic groups 10 and/or the
hydrophilic groups 11 on its surface, the microencapsulated pigment
100 is dispersible in the aqueous medium. If desired, a comonomer
copolymerizable with the polymerizable surface active agent 2 may
be present in the disperse system in the step of polymerization. In
this case, the polymer layer 60 is a copolymer layer comprising the
polymerizable surface active agent 2 and the comonomer.
Second Disperse State:
[0110] FIG. 3 illustrates a second disperse state in which a
pigment particle 1 having a hydrophilic group 10 on its surface is
dispersed in an aqueous medium and is coexistent with a
polymerizable surface active agent 2 having a hydrophilic group 11,
a hydrophobic group 12, and a polymerizable group 13 and another
polymerizable surface active agent 2' having a hydrophilic group
11', a hydrophobic group 12', and a polymerizable group 13'. The
polymerizable surface active agent 2 forms a monomolecular layer A
in which the hydrophilic groups 11 face the hydrophilic groups 10
of the pigment particle 1 because of their interaction while the
hydrophobic groups 12 face away from the pigment particle 1. The
polymerizable surface active agent 2' forms a monomolecular layer B
in which the hydrophobic groups 12' face the monomolecular layer A
because of the interaction with the hydrophobic groups 12 of the
monomolecular layer A while the hydrophilic groups 11' face the
aqueous medium.
[0111] In this second disperse state, when the polymerizable groups
13 and 13' of the polymerizable surface active agents 2 and 2' are
polymerized by, for example, addition of a polymerization
initiator, there is produced a microencapsulated pigment 200
comprising the pigment particle 1 encapsulated with a polymer layer
61 as shown in FIG. 4. Since the polymer layer 61 has the
hydrophilic groups 11' on its outer surface, the microencapsulated
pigment 200 is dispersible in an aqueous medium. If desired, a
comonomer copolymerizable with the polymerizable surface active
agents 2 and 2' may be present in the disperse system in carrying
out polymerization. In this case, the polymer layer 61 can be a
copolymer layer copolymerized from the polymerizable surface active
agents 2 and 2' and the comonomer.
[0112] Either of the first and second disperse states begins with
the pigment particle 1 being in a dispersed state in an aqueous
medium by virtue of its surface hydrophilic groups 10. The pigment
particles 1 achieve a highly dispersed state in an aqueous medium
compared with pigment particles having no hydrophilic groups on
their surface dispersed in an aqueous medium with the aid of a
dispersant. According to the first embodiment, in which pigment
particles having a hydrophilic group on their surface are covered
with a polymer, improved stability of pigment dispersion in an
aqueous medium can be achieved since the microencapsulated pigment
particles have hydrophilic groups regularly and densely orientated
toward the aqueous medium as illustrated in FIGS. 2 and 4.
Therefore, application of the microencapsulated pigment of the
first embodiment as a colorant of water-based ink jet recording ink
provides an ink jet recording ink formulation which can have an
increased pigment concentration and yet exhibits excellent
dispersion stability equal to conventional microencapsulated
pigment inks. Excellent dispersion stability of microencapsulated
pigment leads to reduction of clogging the nozzle of a recording
head, thus promising ejection stability. That is, the
microencapsulated pigment of the first embodiment provides a
pigment ink excellent in dispersion stability and ejection
stability and having a higher pigment concentration than the
conventional microencapsulated pigment inks. Ink jet recording
using the microencapsulated pigment ink having the increased
pigment concentration will produce recorded matter enjoying high
image density as well as excellent image fastness.
[0113] The mechanism of action of the first embodiment will further
be considered. It is believed that the microencapsulated pigment
has the hydrophilic groups originated in the polymerizable surface
active agent regularly and densely orientated toward the aqueous
medium to produce electrostatic repulsive force among the
encapsulated particles which is effective to stabilize the disperse
state. Besides the electrostatic repulsion, the steric hindrance of
the homo- or copolymer of the polymerizable surface active agent
covering the pigment particles (polymer effect) seems to contribute
to the excellent dispersion stability of the microencapsulated
pigment in an aqueous medium.
[0114] Suppression of feathering on plain paper and the high image
density achievable are considered to owe largely to the action of
the hydrophilic groups regularly and densely orientated to the
aqueous medium for the following reason. Upon landing of ink
ejected from a recording head onto plain paper, the ink solvent
swiftly soak paper. Conventional pigment particles dispersed with
the aid of a dispersant, being coated with the dispersant, tend to
spread randomly rather than be adsorbed on the surface cellulose
fibers of paper. This is presumably partly because the hydrophilic
group content on the pigment surface is lower than that of the
microencapsulated pigment of the present embodiment and partly
because the hydrophilic groups are not orientated regularly and
densely. As a result, the image density is low, and the color
developability is insufficient.
[0115] By contrast, the microencapsulated pigment according to the
present invention is easily adsorbed onto the cellulose fiber of
plain paper for the following reasons. The microencapsulated
pigment easily agglomerate upon mutual action between the surface
hydrophilic groups (especially anionic groups) and various metal
ions present in plain paper, e.g., magnesium, calcium or aluminum
ions. The microencapsulated pigment easily agglomerate and is
adsorbed on plain paper upon mutual action between the hydrophilic
groups (especially anionic groups) and cationic starch or a
cationic polymer that has been used together with a size in sizing
plain paper. Additionally, the hydrophilic groups (especially
anionic groups) also exert interaction with the cellulose fibers of
plain paper. Thus, when the microencapsulated pigment ink is
ejected from a recording head and lands onto plain paper, the
colorant readily stays at the landing position to give a high image
density with little feathering.
[0116] Further, since the pigment particles are coated with a
polymer, an ink jet printing ink according to the first embodiment
exhibits higher fixability on a recording medium to form an image
with higher abrasion resistance than inks comprising conventional
surface-treated pigment particles.
[0117] Components constituting the microencapsulated pigment of the
first embodiment will be described in detail.
[0118] The pigment particles having a hydrophilic group on their
surface (hereinafter sometimes referred to as hydrophilized pigment
particles) are conveniently prepared by treating pigment particles
with a hydrophilic group-imparting agent. Therefore the pigment
itself is not particularly limited as long as it is insoluble in
the hydrophilic group-imparting agent chosen. Pigments for use in
the ink of the present invention are divided into inorganic
pigments and organic pigments.
[0119] Suitable inorganic pigments include carbon blacks (C.I.
Pigment Black 7), such as furnace black, lamp black, acetylene
black, and channel black, and iron oxide pigments. Suitable organic
pigments include azo pigments, such as azo lakes, insoluble azo
pigments, condensed azo pigments, and chelate azo pigments;
polycyclic pigments, such as phthalocyanine pigments, perylene
pigments, perinone pigments, anthraquinone pigments, quinacridone
pigments, dioxane pigments, thioindigo pigments, isoindolinone
pigments, and quinofranone pigments; dye chelates, such as basic
dye chelates and acidic dye chelates; nitro pigments, nitroso
pigments, and aniline black.
[0120] Specific examples of inorganic pigments used for black
include carbon blacks, such as No. 2300, No. 900, MCF88, No. 33,
No. 40, No. 45, No. 52, MA7, MA8, MA100 and No. 2200B, all
available from Mitsubishi Chemical Corp.; Raven series 5750, 5250,
5000, 3500, 1255, and 700 from Columbian Carbon; Regal series 400R,
330R, and 660R, Mogul L, and Monarch series 700, 800, 880, 900,
1000, 1100, 1300, and 1400 from Cabot Corp.; and Color Black series
FW1, FW2, FW2V, FW18, FW200, S150, S160, and S170, Printex series
35, U, V, and 140U, and Special Black series 6, 5, 4A, and 4 from
Degussa Corp.
[0121] Specific examples of organic pigments for black include
aniline black (C.I. Pigment Black 1).
[0122] Specific examples of organic pigments for yellow include
C.I. Pigment Yellow 1 (Hansa Yellow), 2, 3 (Hansa Yellow 10G), 4, 5
(Hansa Yellow 5G), 6, 7, 10, 11, 12, 13, 14, 16, 17, 24
(Flavanthrone Yellow), 34, 35, 37, 53, 55, 65, 73, 74, 75, 81, 83,
93, 94, 95, 97, 98, 99, 108 (Anthrapyrimidine Yellow), 109, 110,
113, 117 (copper complex salt pigment), 120, 124, 128, 129, 133
(Quinophthalone), 138, 139 (Isoindolinone), 147, 151, 153 (nickel
complex pigment), 154, 167, 172, and 180.
[0123] Specific examples of organic pigments for magenta ink
include C.I. Pigment Red 1 (Para Red), 2, 3 (Toluidine Red), 4, 5
(ITR Red), 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 21, 22,
23, 30, 31, 32, 37, 38 (Pyrazolone Red), 40, 41, 42, 48 (Ca), 48
(Mn), 57 (Ca), 57:1, 88 (Thioindigo), 112 (Naphthol AS), 114
(Naphthol AS), 122 (Dimethylquinacridone), 123, 144, 146, 149, 150,
166, 168 (Anthoanthrone Orange), 170 (Naphthol AS) 171, 175, 176,
177, 178, 179 (Perylene Maroon), 184, 185, 187, 202, 209
(Dichloroquinacridone), 219, 224 (perylene), and 245 (Naphthol AS);
and C.I. Pigment Violet 19 (Quinacridone), 23 (Dioxazine Violet),
32, 33, 36, 38, 43, and 50.
[0124] Specific examples of organic pigments for cyan ink include
C.I. Pigment Blue 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:34, 15:4, 16
(metal-free phthalocyanine), 18 (alkali blue toner), 22, 25, 60
(Threne Blue), 65 (Violanthrone), and 66 (Indigo); and C.I. Vat
Blue 4 and 60.
[0125] Other organic pigments used for color inks other than
magenta, cyan or yellow inks include C.I. Pigment Green 7
(Phthalocyanine Green), 10 (Green Gold), 36, and 37; C.I. Pigment
Brown 3, 5, 25, and 26; and C.I. Pigment Orange 1, 2, 5, 7, 13, 14,
15, 16, 24, 34, 36, 38, 40, 43, and 63.
[0126] These pigments can be used either individually or as a
combination of two or more thereof in the microencapsulated pigment
of the invention.
[0127] The hydrophilic group-imparting agents which can be used to
surface treat the pigment particles include sulfur-containing
treating agents, such as sulfuric acid, fuming sulfuric acid,
sulfur trioxide, chlorosulfuric acid, fluorosulfuric acid,
amidosulfuric acid, sulfonated pyridine salts, and sulfamic acid.
Preferred of them are sulfonating agents, such as sulfur trioxide,
sulfonated pyridine salts, and sulfamic acid, which can be used
either individually or as a mixture of two or more thereof. The
term "sulfonating agent" as used herein denotes a treating agent
capable of introducing at least one of a sulfonic acid group
(--SO.sub.3H) and a sulfinic acid group (--RSO.sub.2H; wherein R is
an alkyl group having 1 to 12 carbon atoms, or a phenyl or its
derivative group).
[0128] Complexes of sulfur trioxide formed with a mixed solvent of
a solvent capable of forming a complex with sulfur trioxide, such
as basic solvents (e.g., N,N-dimethylformamide, dioxane, pyridine,
triethylamine, and trimethylamine), nitromethane or acetonitrile,
and at least one solvent described below are also effective
sulfonating agents. In particular, where the reactivity of sulfur
trioxide is so high that the pigment itself may be decomposed or
denatured or where use of a strong acid such as sulfuric acid is
unsuitable due to difficulty of reaction control, it is advisable
to use a tertiary amine-sulfur trioxide complex to accomplish the
surface treatment (sulfonation in this case) of pigment
particles.
[0129] Where a strong acid, such as sulfuric acid, fuming sulfuric
acid, chlorosulfuric acid or fluorosulfuric acid, is used alone,
the pigment particles easily dissolve to undergo reaction molecule
by molecule. In this case, the reaction must be performed under
control, giving due consideration to the kind and amount of a
solvent used.
[0130] The solvent which can be used in the surface treatment
reaction is selected from those which are inert to the
sulfur-containing treating agent and in which the pigment is
insoluble or sparingly soluble. Examples are sulfolane,
N-methyl-2-pyrrolidone, dimethylacetamide, quinoline,
hexamethylphosphoric triamide, chloroform, dichloroethane,
tetrachloroethane, tetrachloroethylene, dichloromethane,
nitromethane, nitrobenzene, liquid sulfur dioxide, carbon
disulfide, and trichlorofluoromethane.
[0131] The treatment with the sulfur-containing treating agent is
carried out by dispersing pigment particles in the solvent, adding
the treating agent to the dispersion, and heating the mixture while
stirring at 60 to 200.degree. C. for 3 to 10 hours. It is advisable
that the mixture be slurried prior to the reaction by high shear
dispersion in a high-speed mixer, etc. or impact dispersion in a
bead mill, a jet mill, etc. The resulting slurry is then stirred
gently, and the sulfur-containing treating agent is added thereto
to introduce the hydrophilic group onto the surface of the pigment
particles. The amount of the hydrophilic group that can be
introduced largely depends on the reaction conditions and the kind
of the sulfur-containing treating agent. After heating the reaction
mixture under the above-recited conditions, the solvent and the
residual sulfur-containing treating agent are removed from the
pigment slurry by washing with water, ultrafiltration, reverse
osmosis, repetition of centrifugation and filtration, or like
means.
[0132] The pigment particles having a sulfonic acid group
(--SO.sub.3H) and/or a sulfinic acid group (--RSO.sub.2H; wherein R
is as defined above) introduced thereon can further be treated with
an alkali compound to convert the sulfonic acid group and/or the
sulfinic acid group to a sulfonate anion (--SO.sub.3.sup.-) and/or
a sulfinate anion (--RSO.sub.2.sup.-; wherein R is as defined
above).
[0133] The alkali compound is selected from those capable of
dissociating an alkali metal cation or a monovalent cation
represented by formula: (R.sub.1R.sub.2R.sub.3R.sub.4N).sup.+,
wherein R.sub.1, R.sub.2, R.sub.3, and R.sub.4, which may be the
same or different, each represent a hydrogen atom, an alkyl group,
a hydroxyalkyl group or a halogenated alkyl group. Preferred alkali
compounds are those capable of dissociating a lithium ion
(Li.sup.+), a potassium ion (K.sup.+), a sodium ion (Na.sup.+), an
ammonium ion (NH.sub.4.sup.+) or an alkanolamine cation, e.g., a
triethanolamine cation.
[0134] The anion of the alkali compound is preferably a hydroxide
ion. Examples of alkali compounds include ammonia, alkanolamines
(e.g., monoethanolamine, diethanolamine, N,N-butylethanolamine,
triethanolamine, propanolamine, aminomethylpropanol, and
2-aminoisopropanol), and monovalent alkali metal hydroxides (e.g.,
LiOH, NaOHO, and KOH).
[0135] The alkali compound is preferably added in amounts equal to
or more than the neutralization equivalent for the sulfonic acid
group and/or the sulfinic acid group on the pigment particles.
Volatile alkali compounds, such as ammonia and alkanolamines, are
preferably added in amounts at least 1.5 times the neutralization
equivalent. The treatment is conducted by adding the pigment
particles having the sulfonic acid group and/or the sulfinic acid
group chemically bonded thereto into the alkali compound, followed
by shaking in a paint shaker, etc.
[0136] The hydrophilic group-imparting agents for treating the
pigment particles surface also include carboxylating agents. The
term "carboxylating agent" as used herein denotes a treating agent
capable of introducing a carboxyl group (--COOH).
[0137] Techniques for introducing a carboxyl group include chemical
treatment with an oxidizing agent, such as hypohalogenous acid
salts (e.g., sodium hypochlorite and potassium hypochlorite), which
severs part of the bonds (C.dbd.C or C--C) on the pigment particles
surface to achieve oxidation, and physical oxidation such as a
plasma treatment. Various techniques are applicable as long as a
stable dispersed state in an aqueous medium is achieved as a
result. The above-described treatments for carboxyl introduction
are sometimes accompanied by introduction of a quinone group, etc.,
while not much in quantity. Such cases are included under the scope
and spirit of the present invention unless the dispersion stability
of the microencapsulated pigment in an aqueous medium is
spoiled.
[0138] The following describes an example of the treatment with a
carboxylating agent. Pigment particles are previously dispersed in
an aqueous medium by high shear dispersion in a high-speed mixer,
etc or impact dispersion in a bead mill, a jet mill, etc. to
prepare a pigment slurry. The slurry is mixed with a hypohalogenous
acid salt, such as sodium hypochlorite, having an effective halogen
concentration of 10 to 30% in an adequate amount of water. The
mixture is heated with stirring at 60 to 80.degree. C. for about 5
to 10 hours, preferably 10 hours or longer. Accompanied by
considerable heat generation, the reaction should be carried out
with due care about safety. After the reaction, the solvent and the
residual carboxylating agent are removed from the slurry by heat
treatment. If necessary, the resulting dispersion is further worked
up by washing with water, ultrafiltration, reverse osmosis,
repetition of centrifugation and filtration, or like means to
obtain a desired aqueous dispersion.
[0139] Similarly to the pigment particles having a sulfonic acid
group and/or a sulfinic acid group, the pigment particles having a
carboxyl group (--COOH) can be treated with an alkali compound to
convert the carboxyl group to a carboxylate anion (--COO.sup.-).
The kind of the alkali compound and the method of treating with the
alkali compound are the same as described above.
[0140] A preferred amount of the hydrophilic group to be introduced
on the surface of pigment particles and a method of investigating
the introduced state of the hydrophilic group will then be
described.
[0141] Where hydrophilization of pigment particles is achieved by a
sulfonating agent, the amount of the hydrophilic group to be
introduced on the pigment particles surface is preferably
10.times.10.sup.-6 equivalent or more per gram of the pigment
particles. Amounts less than 10.times.10.sup.-6 equivalent tend to
result in agglomeration of the pigment particles in the step of
microencapsulating the pigment particles in an aqueous medium,
which tends to result in an increased average particle size of the
resulting encapsulated pigment. As the average particle size of
microencapsulated pigment particles increases, it becomes harder to
obtain ink jet recording ink excellent in dispersion stability and
ejection stability and capable of forming images with high
density.
[0142] The upper limit of the amount of the hydrophilic group
introduced is not particularly limited but is preferably not more
than 150.times.10.sup.-6 equivalent per gram of the pigment
particles. Seeing that introduction of more than
150.times.10.sup.-6 equivalent of a hydrophilic group does not
always bring about a reduction in average particle size,
150.times.10.sup.-6 equivalent can be seen as an advisable upper
limit from the standpoint of cost performance.
[0143] Where hydrophilization is achieved with a carboxylating
agent by the surface treating method adopted in the present
invention, it is impossible to directly measure the amount of the
carboxyl group (--COOH) and/or the carboxylate anion (--COO.sup.-)
which are believed to be introduced by the method. Instead, the
amount is estimated from the content of surface active hydrogen.
Details of the method of measuring the surface active hydrogen
content will be described later.
[0144] The active hydrogen content of the surface treated pigment
is preferably 1.0 mmol/g or higher, still preferably 1.5 mmol/g or
higher. With active hydrogen contents lower than 1.0 mmol/g, the
pigment particles tend to have poor dispersibility in an aqueous
medium and are liable to agglomerate in the step of
microencapsulation.
[0145] According to the above-described techniques of
hydrophilization, it is easy to obtain hydrophilized pigment
particles with an average particle size of 150 nm or smaller. It is
still preferred to control the average particle size in a range of
20 to 80 nm by properly selecting the kinds of the pigment and the
hydrophilic group-imparting agent, the amount of a hydrophilic
group introduced, and so forth. The preferred average particle size
is more effective in providing an ink jet recording ink having
excellent dispersion stability, excellent ejection stability, and
capability of forming ink images with an increased density. The
term "average particle size" as referred to in the present
invention means a value measured by a laser light scattering
method.
[0146] The resulting hydrophilized pigment particles are then
coated with a polymer having a repeating unit derived from a
polymerizable surface active agent having a hydrophilic group, a
hydrophobic group, and a polymerizable group to become a
microencapsulated pigment according to the first embodiment. As
stated previously, such a microencapsulated pigment is conveniently
prepared by adding the polymerizable surface active agent and a
polymerization initiator to an aqueous dispersion of the
hydrophilized pigment particles and subjecting the system to
emulsion polymerization.
[0147] The hydrophilic group of the polymerizable surface active
agent is preferably an anionic group selected from the group
consisting of a sulfonic acid group or a salt thereof, a sulfinic
acid group or a salt thereof, a carboxyl group or a salt thereof,
and a carbonyl group or a salt thereof. The hydrophobic group of
the polymerizable surface active agent is preferably selected from
the group consisting of an alkyl group, an aryl group, and a group
composed of a combination thereof.
[0148] The polymerizable group of the polymerizable surface active
agent is preferably an unsaturated hydrocarbon group and is still
preferably selected from the group consisting of a vinyl group, an
allyl group, an acryloyl group, a methacryloyl group, a propenyl
group, a vinylidene group, and a vinylene group. Particularly
preferred of them are an acryloyl group and a methacryloyl
group.
[0149] Examples of such polymerizable surface active agents are
anionic allyl derivatives described, e.g., in JP-B-49-46291,
JP-B-1-24142, and JP-A-62-104802; anionic propenyl derivatives
described, e.g., in JP-A-62-221431; anionic acrylic acid
derivatives described, e.g., in JP-A-62-34947 and JP-A-55-11525;
anionic itaconic acid derivatives described, e.g., in JP-B-46-34898
and JP-A-51-30284; anionic maleic acid derivatives described, e.g.,
in JP-B-51-4157 and JP-A-51-30284; nonionic allyl derivatives
described, e.g., in JP-A-62-104802; nonionic propenyl derivatives
described, e.g, in JP-A-62-100502; nonionic acrylic acid
derivatives described, e.g., in JP-A-56-28208; nonionic itaconic
acid derivatives described, e.g., in JP-B-59-12681; and nonionic
maleic acid derivatives described, e.g., in JP-A-59-74102.
[0150] The polymerizable surface active agents which can be used in
the invention include acrylic acid-modified polyoxyethylene alkyl
ethers, acrylic acid-modified polyoxyethylene alkylphenyl ethers,
allylic acid-modified polyoxyethylene alkyl ethers, allylic
acid-modified polyoxyethylene alkylphenyl ethers; allylic
acid-modified polyoxyethylene polystyrylphenyl ether; acrylic
acid-modified polyoxyethylene polystyrylphenyl ether, and
polyoxyethylene-polyoxypropylene glycol monoacrylate.
[0151] Preferred polymerizable surface active agents for use in the
invention include compounds represented by formula (31): ##STR4##
wherein R.sup.21 and R.sup.31 each represent a hydrogen atom or a
hydrocarbon group having 1 to 12 carbon atoms; Z.sup.1 represents a
carbon-carbon single bond or --CH.sub.2--O--CH.sub.2--: x
represents an integer of 2 to 20; X represents a hydrogen atom or
--SO.sub.3M.sup.1; and M.sup.1 represents an alkali metal atom, an
ammonium salt residue or an alkanolamine residue; and compounds
represented by formula (32): ##STR5## wherein R.sup.22 and R.sup.32
each represent a hydrogen atom or a hydrocarbon group having 1 to
12 carbon atoms; Z.sup.2 represents a carbon-carbon double bond or
--CH.sub.2--O--CH.sub.2--; y represents an integer of 2 to 20; Y
represents a hydrogen atom or --SO.sub.3M.sup.2; M.sup.2 represents
an alkali metal atom, an ammonium salt residue or an alkanolamine
residue.
[0152] The compounds of formula (31) are disclosed in JP-A-5-320276
and JP-A-10-316909. The hydrophilicity or hydrophobicity of the
compound of formula (31) can be adjusted to match the
hydrophilicity or hydrophobicity of the pigment particle surface by
appropriately selecting the group for R.sup.21 and the value of x.
Preferred polymerizable surface active agents of formula (31) are
represented by formulae (31a) to (31d) shown below. ##STR6##
[0153] Some of the polymerizable surface active agents supra are
commercially available, which can be made use of in the present
invention. Examples of useful commercial products are Aqualon HS
series (HS-05, HS-10, HS-20 and HS-1025), Aqualon RN series (RN-10,
RN-20, RN-30, RN-50, and RN-2025), and New Frontier series (N-177E
and S-510), all available from Daiichi Kogyo Yakuhin Co., Ltd.; and
Adeka Reasope SE series and Adeka Reasope NE series both available
from Asahi Denka Co., Ltd.
[0154] Preferred polymerizable surface active agents for use in the
invention also include compounds represented by formula (33):
##STR7## wherein n represents 9 or 11; m represents an integer of 2
to 20; A represents a hydrogen atom or --SO.sub.3M.sup.3; M.sup.3
represents an alkali metal atom, an ammonium salt residue or an
alkanolamine residue.
[0155] The compounds of formula (33) include compounds represented
by formula: ##STR8## wherein n is 9 or 11; and m is 5 or 10.
[0156] The polymerizable surface active agents supra which are
commercially available, such as Aqualon KH-05 and Aqualon KH-10
from Daiichi Kogyo Yakuhin Co., Ltd., can be made use of.
[0157] Compounds represented by formula (A) shown below are also
preferred polymerizable surface active agents. ##STR9## wherein
R.sup.1 represents a hydrogen atom or a hydrocarbon group having 1
to 12 carbon atoms; n represents 2 to 20; X represents a hydrogen
atom or --SO.sub.3M; and M represents an alkali metal atom, an
ammonium salt residue or an alkanolamine residue.
[0158] The above-enumerated polymerizable surface active agents can
be used either individually or as a mixture of two or more
thereof.
[0159] The polymerizable surface active agent is preferably used in
an amount of about 5 to 70% by weight, particularly about 10 to 50%
by weight, based on the pigment. Amounts of 5% or more assure
excellent dispersibility of the encapsulated particles and
excellent ejection stability, adsorbability to paper fiber, image
density, and color developability of the resulting ink. When added
in amounts exceeding 70%, part of the polymerizable surface active
agent tends to remain unadsorbed onto the pigment particles, and
polymer particles containing no core substance tend to be
produced.
[0160] In the first embodiment, the polymer layer coating the
pigment particles may be a copolymer comprising a repeating unit
derived from the above-described polymerizable surface active agent
having a hydrophilic group, a hydrophobic group, and a
polymerizable group and a repeating unit derived from a comonomer
copolymerizable with the polymerizable surface active agent. The
microencapsulated pigment having such a copolymer layer is
conveniently produced by adding the polymerizable surface active
agent, a comonomer copolymerizable therewith, and a polymerization
initiator to an aqueous dispersion of the hydrophilized pigment
particles and subjecting the system to emulsion polymerization to
coat the pigment particles with a copolymer. This modification is
particularly effective to control the fixability, abrasion
resistance, and solvent resistance of recorded images and storage
stability of the ink. In particular, the fixability and abrasion
resistance of recorded images can be controlled by selecting an
appropriate glass transition point (Tg) of the copolymer. A
preferred Tg of the copolymer is -20.degree. to 30.degree. C. A Tg
higher than 30.degree. C. tends to result in reduction of
fixability and abrasion resistance. A Tg lower than -20.degree. C.
tends to result in reduction of solvent resistance.
[0161] The comonomer copolymerizable with the polymerizable surface
active agent includes hydrophilic monomers and hydrophobic
monomers.
[0162] The hydrophobic monomers are compounds having at least a
hydrophobic group and a polymerizable group in the molecule
thereof. The hydrophobic group is preferably selected from the
group consisting of aliphatic hydrocarbon groups, alicyclic
hydrocarbon groups, and aromatic hydrocarbon groups. The
hydrophilic monomers are compounds having at least a hydrophilic
group and a polymerizable group in the molecule thereof. The
hydrophilic group is preferably selected from the group consisting
of a sulfonic acid group or a salt thereof, a sulfinic acid group
or a salt thereof, a carboxyl group or a salt thereof, a carbonyl
group or a salt thereof, a hydroxyl group, an oxyethylene group, an
amido group, and an amino group.
[0163] The polymerizable group possessed by the comonomer, whether
hydrophilic or hydrophobic, is preferably a radically polymerizable
unsaturated hydrocarbon group selected from the group consisting of
a vinyl group, an allyl group, an acryloyl group, a methacryloyl
group, a propenyl group, a vinylidene group, and a vinylene
group.
[0164] As for the hydrophobic monomer, the aliphatic hydrocarbon
groups include methyl, ethyl, and propyl. The alicyclic hydrocarbon
groups include cyclohexyl, dicyclopentenyl, and isobornyl. The
aromatic hydrocarbon groups include benzyl, phenyl, and
naphthyl.
[0165] Examples of the hydrophobic monomers having a radically
polymerizable group are styrene; styrene derivatives, such as
methylstyrene, dimethylstyrene, chlorostyrene, dichlorostyrene,
bromostyrene, p-chloromethylstyrene, and divinylbenzene;
monofunctional acrylic esters, such as methyl acrylate, ethyl
acrylate, n-butyl acrylate, butoxyethyl acrylate, benzyl acrylate,
phenyl acrylate, phenoxyethyl acrylate, cyclohexyl acrylate,
dicyclopentanyl acrylate, dicyclopentenyl acrylate,
dicyclopentenyloxyethyl acrylate, tetrahydrofurfuryl acrylate,
isobornyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl
acrylate, caprolactone acrylate, and glycidyl acrylate;
monofunctional methacrylic esters, such as methyl methacrylate,
ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl
methacrylate, butoxymethyl methacrylate, benzyl methacrylate,
phenyl methacrylate, phenoxyethyl methacrylate, cyclohexyl
methacrylate, dicyclopentanyl methacrylate, dicyclopentenyl
methacrylate, dicyclopentenyloxyethyl methacrylate,
tetrahydrofurfuryl methacrylate, isobornyl methacrylate,
2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate,
2-hydroxybutyl methacrylate, glycerol methacrylate, caprolactone
methacrylate, and glycidyl methacrylate; allyl compounds, such as
allylbenzene, allyl-3-cyclohexane propionate,
1-allyl-3,4-dimethoxybenzene, allylphenoxy acetate, allylphenyl
acetate, allylcyclohexane, and allyl polycarboxylates; esters of
fumaric acid, maleic acid or itaconic acid; acrylonitrile,
methacrylonitrile, N-substituted maleimides, and cyclic
olefins.
[0166] The hydrophilic monomers are compounds having at least a
hydrophilic group and a polymerizable group in the molecule
thereof. The hydrophilic group is preferably selected from the
group consisting of a sulfonic acid group or a salt thereof, a
sulfinic acid group or a salt thereof, a carboxyl group or a salt
thereof, a carbonyl group or a salt thereof, a hydroxyl group, an
oxyethylene group, an amido group, and an amino group.
[0167] Of these, anionic groups, such as a sulfonic acid group, a
sulfinic acid group, a carboxyl group, a carbonyl group, and their
salts, easily exert interaction with various metal ions (e.g., Mg,
Ca or Al ions) and cationic starch or a cationic polymer which are
usually contained in plain paper and also with cellulose fiber of
paper. Microencapsulated pigments having a copolymer layer
comprising a repeating unit derived from a polymerizable monomer
having such an anionic hydrophilic group, when formulated into ink
jet recording ink and ejected onto plain paper, readily stay at the
landing position on the paper to form an image with high density
and little feathering.
[0168] From this viewpoint, preferred hydrophilic monomers include
methacrylic acid, acrylic acid, 2-hydroxymethacrylates,
ethyldiethylene glycol acrylate, polyethylene glycol
monomethacrylate, methoxypolyethylene glycol methacrylate,
phosphoric group-containing (meth)acrylates, N-vinyl-2-pyrrolidone,
sodium vinylsulfonate, 2-sulfoethyl methacrylate, and
2-acrylamido-2-methylpropanesulfonic acid. Still preferred of them
are methacrylic acid, acrylic acid, sodium vinylsulfonate,
2-sulfoethyl methacrylate, 2-acrylamido-2-methylpropanesulfonic
acid, and phosphoric group-containing (meth)acrylates.
[0169] Where the polymerizable surface active agent is a highly
electron-donating compound, such as one represented by formula (1)
described supra, it is preferred to use a highly electron-accepting
compound as a comonomer. Highly electron-accepting comonomers
include acrylonitrile, fumaronitrile, fumaric diesters (e.g.,
dibutyl fumarate), maleic diesters (e.g., dibutyl maleate),
maleimides (e.g., N-phenylmaleimide), and vinylidene cyanide. They
can be used either individually or as a mixture of two or more
thereof.
[0170] The comonomer is preferably used in an amount of about 2 to
15 mol, particularly about 3 to 12 mol, per mole of the
polymerizable surface active agent. By using at least double the
molar quantity of the comonomer, the resulting microencapsulated
pigment exhibits particularly high dispersion stability in an
aqueous medium. When used in amounts of 15 mol or less, the
comonomer completely copolymerizes with the polymerizable surface
active agent with a reduced fear that excess of the comonomer may
homopolymerize to produce a water-insoluble polymer. After the
polymerization, the mixture is preferably worked up by, for
example, micro-filtration to remove coarse particles which may clog
the nozzle of a recording head.
[0171] The polymerization of the polymerizable surface active agent
or copolymerization of the polymerizable surface active agent and
the comonomer is preferably initiated by addition of a
polymerization initiator. It is preferable to use a water-soluble
polymerization initiator, such as potassium persulfate, ammonium
persulfate, sodium persuflate, 2,2-azobis(2-methylpropionamidine)
dihydrochloride or 4,4-azobis(4-cyanovaleric acid).
[0172] In a preferred example, the microencapsulated pigment
according to the first embodiment is obtained as follows. An
aqueous dispersion of the hydrophilized pigment particles and, if
necessary, an aqueous solvent is/are put into a reaction vessel
equipped with an ultrasonic generator, a stirrer, a reflux
condenser, a dropping funnel, and a temperature controller and
mixed by stirring. The polymerizable surface active agent is added
thereto, and the system is ultrasonicated for a prescribed period
of time. The comonomer, if used, is added here, followed by
ultrasonication for a prescribed time. The system is heated to a
predetermined polymerization temperature, and a solution of the
water-soluble polymerization initiator in pure water is added
dropwise to carry out polymerization under ultrasonication. After
completion of the polymerization, the reaction mixture is
preferably adjusted to a pH of 7.0 to 9.0 and filtered. The aqueous
solvent (aqueous medium) used here is a solvent mainly comprising
water as previously defined. The aqueous medium may further
comprise other water-soluble solvents, such as glycerols and
glycols. The polymerization temperature preferably ranges
60.degree. to 90.degree. C. In case the hydrophilized pigment
particles are not in the form of an aqueous dispersion, they are
preferably previously subjected to a dispersion operation by use of
a general dispersing machine, such as a ball mill, a roll mill, an
Eiger mill or a jet mill.
[0173] It is considered that the microencapsulated pigment of the
first embodiment has a structure in which pigment particles with a
small average particle size are completely coated with a polymer
layer, and the hydrophilic groups of the polymer layer are
regularly orientated toward the aqueous medium as shown in FIGS. 2
and 4. Therefore, the microencapsulated pigment exhibits high
dispersion stability in an aqueous medium.
[II] Second Embodiment
[0174] The microencapsulated pigment according to the second
embodiment of the invention is characterized in that pigment
particles having an anionic group as a hydrophilic group on their
surface are coated with a polymer produced by polymerizing a
hydrophilic monomer with the aid of a polymerization initiator
having a cationic group. The microencapsulated pigment of the
second embodiment is conveniently produced by a process comprising
the steps of mixing a polymerization initiator having a cationic
group with an aqueous dispersion of pigment particles having an
anionic hydrophilic group on their surface under a condition that
does not activate the polymerization initiator, adding a
hydrophilic monomer and a surface active agent to the dispersion,
and activating the polymerization initiator to carry out emulsion
polymerization to thereby coat the pigment particles with a
polymer. The process will be described with reference to a disperse
state the pigment particles could take in the process. Note that
the description contains theoretical assumptions. FIGS. 5 and 6 are
referred to.
[0175] FIG. 5 illustrates a disperse state in which a pigment
particle 101 having an anionic group 110 on the surface thereof is
dispersed in an aqueous medium in the presence of an azo compound
102 having a cationic group 111 as a polymerization initiator
having a cationic group, a hydrophilic monomer 103 having a
hydrophilic group 112 and a polymerizable group 113, and a
comonomer 104 copolymerizable with the hydrophilic monomer 103. The
azo compound 102 is orientated with its cationic groups 111 facing
the anionic groups 110 of the pigment particle 101. The hydrophilic
monomer 103 is orientated with its hydrophilic group 112 directed
toward the aqueous medium and its polymerizable group 113
positioned near the azo group (-M=N--) of the azo compound 102. The
comonomer 104 is in the same position as the hydrophilic monomer
103 with respect to the pigment particle 101.
[0176] In this disperse state, when the hydrophilic monomer 103 and
the comonomer 104 are copolymerized by, for example, heating or
irradiation, there is produced a microencapsulated pigment 300
comprising the pigment particle 101 encapsulated with a polymer
layer 150 as shown in FIG. 6. Since the polymer layer 150 has the
hydrophilic groups 112 on its surface, the microencapsulated
pigment 300 is dispersible in an aqueous medium.
[0177] Since the pigment particles 101 are in a dispersed state in
an aqueous medium by virtue of their surface hydrophilic groups
101. The pigment particles 101 achieve a high dispersed state in an
aqueous medium compared with pigment particles having no
hydrophilic groups on their surface dispersed in an aqueous medium
with a dispersant. Since the hydrophilic groups originated in the
hydrophilic monomer are considered to be regularly and densely
orientated toward the aqueous medium, there seems to be produced
electrostatic repulsive force among the encapsulated particles.
Besides the electrostatic repulsion, the polymer covering the
pigment particles seems to produce a polymer effect.
[0178] Accordingly, the microencapsulated pigment of the second
embodiment, in which pigment particles having an anionic group on
their surface are coated with a polymer, is capable of providing a
microencapsulated pigment ink excellent in dispersion stability and
ejection stability and having a higher pigment concentration than
the conventional microencapsulated pigment inks. Ink jet recording
using the microencapsulated pigment ink having the increased
pigment concentration will produce recorded matter enjoying high
image density as well as excellent image fastness. Compared with
inks comprising conventional surface-treated pigment particles as a
colorant, the ink jet recording ink of the present invention, in
which the pigment is coated with a polymer, exhibits high
fixability on a recording medium to provide recorded matter with
excellent abrasion resistance.
[0179] Components constituting the microencapsulated pigment of the
second embodiment will be described in detail.
[0180] The pigment particles having an anionic group as a
hydrophilic group on their surface (hereinafter referred to as
anionic-hydrophilized pigment particles) are conveniently prepared
by treating the surface of pigment particles with an anionic
group-imparting agent. The anionic group-imparting agent includes
the hydrophilic group-imparting agents recited with respect to the
first embodiment. Accordingly, the anionic-hydrophilized pigment
particles include the hydrophilized pigment particles described
with respect to the first embodiment.
[0181] A preferred amount of the anionic group to be introduced
onto the surface of pigment particles and a method of investigating
the introduced state of the anionic groups will then be
described.
[0182] Where hydrophilization with an anionic group (hereinafter
referred to as anionic hydrophilization) is achieved with a
sulfonating agent, the amount of the anionic group to be introduced
on the pigment particles surface is preferably 1.0 mmol or more per
gram of the pigment particles. Amounts less than 1.0 mmol/g tend to
result in agglomeration of the pigment particles in the step of
microencapsulating the pigment particles in an aqueous medium,
which tends to result in an increased average particle size of the
resulting encapsulated pigment. As the average particle size of
microencapsulated pigment particles increases, it becomes harder to
obtain an ink jet recording ink excellent in dispersion stability
and ejection stability and capable of forming images with high
density.
[0183] The upper limit of the amount of the anionic group
introduced is not particularly limited but is preferably not more
than 15 mmol/g. Seeing that introduction of more than 15 mmol/g of
an anionic group does not always bring about a reduction in average
particle size, 15 mmol/g can be seen as an advisable upper limit
from the standpoint of cost performance.
[0184] Where anionic hydrophilization is achieved with a
carboxylating agent by the surface treating method adopted in the
present invention, it is impossible to directly measure the amount
of the carboxyl group (--COOH) and/or the carboxylate anion
(--COO.sup.-) which are believed to be introduced by the method.
Instead, the amount is estimated from the content of surface active
hydrogen. Details of the method of measuring the surface active
hydrogen content will be described later.
[0185] The active hydrogen content of the surface treated pigment
is preferably 1.0 mmol/g or higher, still preferably 1.5 mmol/g or
higher. With active hydrogen contents lower than 1.0 mmol/g, the
pigment particles tend to have poor dispersibility in an aqueous
medium and are liable to agglomerate in the step of
microencapsulation.
[0186] According to the above-described techniques of anionic
hydrophilization, it is easy to obtain pigment particles having a
hydrophilic anionic group on their surface with an average particle
size of 150 nm or smaller. It is preferred to control the average
particle size in a range of 20 to 80 nm by properly selecting the
kinds of the pigment and the anionic group-imparting agent, the
amount of an anionic group introduced, and so forth. The preferred
average particle size is more effective in providing an ink jet
recording ink having excellent dispersion stability, excellent
ejection stability, and capability of forming ink images with an
increased density.
[0187] The resulting anionic-hydrophilized pigment particles are
then coated with a polymer to become a microencapsulated pigment
according to the second embodiment. The polymer is one obtained by
polymerizing a hydrophilic monomer in the presence of a
polymerization initiator having a cationic group. As stated
previously, such a microencapsulated pigment is conveniently
prepared by adding a polymerization initiator having a cationic
group to an aqueous dispersion of the anionic-hydrophilized pigment
particles under such a condition that does not activate the
polymerization initiator having a cationic group, adding a
hydrophilic monomer and a surface active agent to the mixture, and
activating the polymerization initiator having a cationic group to
carry out emulsion polymerization.
[0188] Suitable examples of the polymerization initiator having a
cationic group include
2,2'-azobis[2-(5-methyl-2-imidazolin-2-yl)propane]dihydrochloride
(VA-041, available from Wako Pure Chemical Industries, Ltd.),
2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride (VA-044,
from Wako Pure Chemical),
2,2'-azobis[2-(2-imidazolin-2-yl)propane]disulfite dihydrate
(VA-046B, from Wako Pure Chemical),
2,2'-azobis[2-(3,4,5,6-tetrahydropyrimidin-2-yl)propane]dihydrochloride
(VA-058, from Wako Pure Chemical),
2,2'-azobis[2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane]dihydrochlori-
de (VA-060, from Wako Pure Chemical), and
2,2'-azobis(2-amidinopropane) dihydrochloride (V-50, from Wako Pure
Chemical).
[0189] The amount of the polymerization initiator having a cationic
group to be used is preferably about 0.5 mol, still preferably from
0.1 to 0.5 mol, per the amount of the anionic group content of the
hydrophilized pigment particles. In other words, the amount of the
polymerization initiator having a cationic group to be added is
arbitrarily selected within the above-recited range according to
the anionic group content of the hydrophilized pigment particles
and the amount of the pigment charged. With amounts less than 0.1
mol of the polymerization initiator, the resulting polymer has
difficulty in uniformly covering the individual pigment particles.
When the polymerization initiator is added in amounts more than 0.5
mol, the excess remains free in water without being adsorbed on the
surface of pigment particles. It would follow that an increased
amount of polymer molecules is free in water, which may lead to
insufficient performance of resulting ink jet recording ink such as
ejection stability.
[0190] The hydrophilic monomer which can be used in the second
embodiment includes those described as for the first embodiment.
The hydrophilic monomer is preferably used in a weight ratio of
from about 5/100 to 50/100, particularly about 5/100 to 30/100, to
the pigment. The hydrophilic monomer/pigment weight ratio of 5/100
or higher assures excellent dispersibility in water. Where the
hydrophilic monomer is added at a weight ratio exceeding 30/100,
the hydrated layer may tend to extend to increase the diameter of
the particles, or water-soluble oligomers or polymers may tend to
be generated and dissolved in water without being adsorbed onto the
pigment particles.
[0191] The polymer coating the pigment particles may be a copolymer
produced from the hydrophilic monomer and a comonomer
copolymerizable with the hydrophilic monomer with the aid of the
polymerization initiator having a cationic group. The
microencapsulated pigment having such a copolymer layer is
conveniently produced by a process comprising the steps of mixing
the polymerization initiator having a cationic group with an
aqueous dispersion of the anionic-hydrophilized pigment particles
under a condition that does not activate the polymerization
initiator having a cationic group, adding the hydrophilic monomer
and a comonomer copolymerizable with the hydrophilic monomer to the
mixture, and activating the polymerization initiator to carry out
emulsion polymerization to thereby coat the pigment particles with
a copolymer. This modification is particularly effective to control
the fixability, abrasion resistance, and solvent resistance of
recorded images and storage stability of the ink. In particular,
the fixability and abrasion resistance of recorded images can be
controlled by appropriately selecting the glass transition point
(Tg) of the copolymer. A preferred Tg of the copolymer is
-20.degree. to 30.degree. C. A Tg higher than 30.degree. C. tends
to result in reduction of fixability and abrasion resistance. A Tg
lower than -20.degree. C. tends to result in reduction of solvent
resistance.
[0192] The comonomer copolymerizable with the hydrophilic monomer
includes the hydrophobic monomers recited above with reference to
the first embodiment.
[0193] The comonomer to be added is chosen according to the
performance required of the resulting polymer, such as water
resistance, solvent resistance, and Tg.
[0194] The surface active agent which can be used in the second
embodiment includes anionic surface active agents, such as sulfonic
acid types, e.g., alkanesulfonic acid salts, .alpha.-olefinsulfonic
acid salts, alkylbenzenesulfonic acid salts,
alkylnaphthalenesulfonic acids, acylmethyltaurines, and
dialkylsulfosuccinic acids; alkylsulfuric ester salts, sulfated
oils, sulfated olefins, polyoxyethylene alkyl ether sulfuric ester
salts; carboxylic acid types, e.g., fatty acid salts and
alkylsarcosine salts; and phosphoric acid ester types, e.g.,
alkylphosphoric ester salts, polyoxyethylene alkyl ether phosphoric
ester salts, and glycerophosphoric ester salts; and nonionic
surface active agents, such as ethylene oxide adduct types, e.g.,
polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers,
polyoxyethylene alkyl esters, and polyoxyethylene alkylamides;
polyol ester types, e.g., glycerol alkyl esters, sorbitan alkyl
esters, and sugar alkyl esters; polyether types, e.g., polyhydric
alcohol alkyl ethers; and alkanolamide types, e.g., alkanolamine
fatty acid amides.
[0195] The surface active agent is preferably added in
concentrations of about 0.01 to 10% by weight, particularly about
0.1 to 5% by weight, in the aqueous dispersion.
[0196] In the second embodiment, it is preferred to use a
polymerizable surface active agent having a hydrophilic group, a
hydrophobic group, and a polymerizable group. In this case, the
polymerizable surface active agent copolymerizes with the
hydrophilic monomer to bring about marked improvements in
dispersibility in an aqueous medium and long-term storage
stability. The polymerizable surface active agents useful in the
second embodiment include those recited with respect to the first
embodiment.
[0197] The polymerizable surface active agent is preferably added
at a weight ratio to the pigment of about 1/100 to 50/100,
particularly 5/100 to 30/100. A polymerizable surface active
agent/pigment weight ratio of 1/100 or higher assures excellent
dispersibility. When used at a weight ratio exceeding 50/100 to the
pigment, part of the polymerizable surface active agent tends to
remain unadsorbed onto the pigment particles and to produce polymer
particles containing no core substance.
[0198] Where the polymerizable surface active agent is a highly
electron-donating compound, such as one represented by formula (1)
described below, it is preferred to use a highly electron-accepting
compound as the comonomer. Highly electron-accepting comonomers
include acrylonitrile, fumaronitrile, fumaric diesters (e.g.,
dibutyl fumarate), maleic diesters (e.g., dibutyl maleate),
maleimides (e.g., N-phenylmaleimide), and vinylidene cyanide. These
comonomers can be used either individually or as a mixture of two
or more thereof.
[0199] In a preferred example, the microencapsulated pigment
according to the second embodiment is obtained as follows. An
aqueous dispersion of the anionic-hydrophilized pigment particles
in an aqueous medium and the polymerization initiator having a
cationic group are mixed by stirring at a low temperature
(0.degree. C. or lower, preferably -5 to -20.degree. C.) and
ultrasonicated. The resulting mixture is put into a reaction vessel
equipped with an ultrasonic generator, a stirrer, a reflux
condenser, a dropping funnel, and a temperature controller.
Separately, an emulsified monomer mixture is prepared by mixing the
hydrophilic monomer, the polymerizable surface active agent and, if
desired, the comonomer by stirring. The monomer mixture is slowly
added through the dropping funnel to the reaction vessel, the inner
temperature of which is set to a prescribed polymerization
temperature, and the system is allowed to undergo polymerization
under ultrasonication for a prescribed period of time. After
completion of the polymerization, the reaction mixture is
preferably adjusted to a pH of 7.0 to 9.0 and filtered. The aqueous
medium used here is a solvent mainly comprising water as previously
defined. The aqueous medium may further comprise other
water-soluble solvents, such as glycerols and glycols. The
polymerization temperature preferably ranges 60.degree. to
90.degree. C. In case the hydrophilized pigment particles are not
in the form of an aqueous dispersion, they are preferably
previously subjected to a dispersion operation by use of a general
dispersing machine, such as a ball mill, a roll mill, an Eiger mill
or a jet mill.
[0200] In more detail, the anionic-hydrophilized pigment particles
having an anionic group content of 1 mmol/g or more, ion-exchanged
water, and a glycerol aqueous solution are put into a stirring
apparatus equipped with an ultrasonic generator, and the mixture is
dispersively stirred under ultrasonication for a prescribed period
of time. The resulting dispersion is put into a reaction vessel
equipped with an ultrasonic generator, a stirrer, a temperature
controller, a reflux condenser, and a dropping funnel. The cationic
polymerization initiator is added thereto in an amount of 0.1 to
0.5 mol per the amount of the anionic group content of the
hydrophilized pigment particles, and the mixture is stirred at -20
to 0.degree. C. for a prescribed period of time under
ultrasonication. Then, the polymerizable surface active agent is
added thereto, followed by mixing with stirring for a prescribed
time. The inner temperature of the reaction vessel is set to a
prescribed temperature while slowly adding an emulsified monomer
mixture that has been prepared by stirring the hydrophilic monomer,
the polymerizable surface active agent, water, and, if desired, a
comonomer from the dropping funnel to carry out polymerization for
a prescribed period of time. During the reaction, the reaction
system is preferably ultrasonicated. The resulting
microencapsulated pigment dispersion is adjusted to a pH 7.0 to 9.0
with an appropriate pH adjuster, e.g., potassium hydroxide or
ammonia, followed by filtration to remove coarse particles. The
filtrate is further subjected to ultrafiltration to remove
oligomers or unreacted monomers to obtain a desired
microencapsulated pigment dispersion.
[0201] It is considered that the microencapsulated pigment of the
second embodiment has a structure in which pigment particles with a
small average particle size are completely coated with a polymer
layer, and the hydrophilic groups of the polymer layer are
regularly orientated toward the aqueous medium as shown in FIG. 6.
Therefore, the microencapsulated pigment exhibits high dispersion
stability in an aqueous medium.
[III] Third Embodiment
[0202] The microencapsulated pigment according to the third
embodiment of the present invention is characterized in that
pigment particles having a hydrophilic group on their surface
(hydrophilized pigment particles) are coated with a polymer
obtained by polymerizing a polymerizable surface active agent
having a hydrophilic group, a hydrophobic group and a polymerizable
group and/or a hydrophilic monomer by using a polymeric azo
initiator comprising a repeating unit represented by formula (I):
##STR10## wherein D represents a portion having at least a
hydrophobic segment; L.sup.1 and L.sup.2, which may be the same or
different, each represent a linking group; R.sup.1, R.sup.2,
R.sup.3, and R.sup.4 each represent an alkyl group having 1 to 4
carbon atoms or a cyano group; and n represents an integer of 1 or
greater.
[0203] The microencapsulated pigment of the third embodiment is
conveniently produced by a process comprising the steps of mixing
the polymeric azo initiator comprising a repeating unit represented
by formula (I) into an aqueous dispersion having hydrophilized
pigment particles dispersed therein under a condition that does not
activate the initiator, adding a polymerizable surface active agent
having a hydrophilic group, a hydrophobic group, and a
polymerizable group and/or a hydrophilic monomer to the mixture,
and activating the polymeric azo initiator to carry out emulsion
polymerization.
[0204] The resulting encapsulated pigment of the third embodiment
has a structure in which hydrophilized pigment particles are
substantially completely coated with a polymer layer, i.e.,
completely encapsulated in a polymer layer.
[0205] The pigment particles before encapsulation is in a dispersed
state in an aqueous medium by virtue of their surface hydrophilic
groups. The aqueous dispersion of the hydrophilized pigment
particles has a highly dispersed state as compared with an aqueous
dispersion prepared by dispersing pigment particles having no
hydrophilic groups on their surface with the aid of a
dispersant.
[0206] Similarly to the microencapsulated pigments of the first and
second embodiments, the microencapsulated pigment of the third
embodiment, having the individual hydrophilized pigment particles
coated with a polymer, is excellent in dispersion stability and
ejection stability. Seeing that the hydrophilic groups originated
in the polymerizable surface active agent and/or the hydrophilic
monomer are considered orientated regularly and densely toward the
aqueous medium, it seems that an effective electrostatic repulsive
force is generated. Besides the electrostatic repulsion, it is
believed that a polymer effect due to the polymer coating the
pigment particles is exerted.
[0207] Thus, the microencapsulated pigment of the third embodiment
provides a microencapsulated pigment ink having an increased
colorant concentration as compared with conventional
microencapsulated pigment inks. Application of such a
microencapsulated pigment ink having a high colorant concentration
to ink jet recording makes it feasible to provide images with not
only excellent fastness but high density. Further, the ink jet
recording ink containing the microencapsulated pigment of the third
embodiment exhibits superior fixability on a recording medium to
provide images with excellent abrasion resistance compared with
inks containing conventional surface-treated pigment particles.
[0208] Although the mechanism of the hydrophilized pigment
particles' being completely encapsulated in a polymer layer
according to the third embodiment has not been elucidated clearly,
the following assumption can be presented.
[0209] The preparation of the aqueous dispersion of hydrophilized
pigment particles starts with addition of the hydrophilized
pigments to an aqueous medium in the presence of the polymeric azo
initiator comprising the repeating unit of formula (I). Having both
a hydrophobic moiety and a hydrophilic moiety in the repeating
unit, the polymeric azo initiator is adsorbed to the surface of a
hydrophilized pigment particle with the hydrophobic moiety thereof
being adsorbed to the hydrophobic regions of the pigment particle
and with the hydrophilic moiety thereof being adsorbed to the
hydrophilic groups of the pigment particle. In the region of the
polymeric azo initiator that does not participate in the
adsorption, the hydrophilic moiety appears to face the aqueous
medium to form a loop projection. In this state, when the
polymerizable surface active agent and/or the hydrophilic monomer
is/are added to the dispersion under ultrasonication, the
hydrophobic moiety of the polymerizable surface active agent and/or
the hydrophilic monomer is directed to the regions of the
hydrophobic moiety of the polymeric azo initiator, while the
hydrophilic moiety is directed to the aqueous medium. This
configuration is favorable for assuring a satisfactory disperse
state. The step of dispersing the hydrophilized pigment particles
should be conducted under a condition that does not activate the
polymeric azo initiator, i.e., a condition that does not cause the
azo group of the polymeric azo initiator to decompose to generate a
radical. Such a condition that does not activate the polymeric azo
initiator includes a cooling condition.
[0210] Upon being activated, the polymeric azo initiator cleaves
its azo group to generate nitrogen (N.sub.2) and offer a radical.
The radical attacks the polymerizable group of the polymerizable
surface active agent and/or the hydrophilic monomer thereby
inducing polymerization. The polymerizable surface active agent
and/or the hydrophilic monomer bond(s) to the cleaved site of the
polymeric azo initiator to produce a polymer having block chains
originated in the polymeric azo initiator, with which the pigment
particle is coated.
[0211] The polymer coating the pigment particles can further
comprise a repeating unit derived from a hydrophobic comonomer.
Useful hydrophobic comonomers include the above-recited hydrophobic
monomers. By using a hydrophobic comonomer, the chain length from
the pigment particle surface to the hydrophilic group regions
increases to ensure satisfactory dispersibility.
[0212] It is a preferred modification of the third embodiment to
add a crosslinking agent to the polymerization system. A
crosslinking agent crosslinks the polymer to form a polymer layer
which is bonded to the surface of a pigment particle more
firmly.
[0213] As stated above, the microencapsulated pigment of the third
embodiment is assumed to have a structure in which the individual
pigment particles are completely coated with a polymer layer, but
the present invention is not restricted by this assumption.
[0214] The components constituting the microencapsulated pigment of
the third embodiment will be described in more detail below.
[0215] The pigment particles having a hydrophilic group on their
surface (hydrophilized pigment particles) include those described
in the first embodiment.
[0216] The polymeric azo initiator, polymerizable surface active
agent and/or hydrophilic monomer, hydrophobic monomer, and
crosslinking agent, and furthermore other additives, which can be
used in the third embodiment are illustrated in order.
[0217] The polymeric azo initiator for use in the third embodiment
can be prepared by, for example, copolymerizing an azo compound
represented by formula (II): ##STR11## wherein L.sup.11 and
L.sup.12 each represent a group capable of forming a linking group
L.sup.1 or L.sup.2 in formula (I) on bonding to a linking group
L.sup.21 or L.sup.22 in formula (III) shown infra; and R.sup.1,
R.sup.2, R.sup.3, and R.sup.4 each represent an alkyl group having
1 to 4 carbon atoms or a cyano group, and a compound represented by
formula (III): L.sup.21-D-L.sup.22 (III) wherein L.sup.21 and
L.sup.22 each represent a group capable of forming a linking group
L.sup.1 or L.sup.2 in formula (I) on bonding to a linking group
L.sup.11 or L.sup.12 in formula (II); and D is a portion containing
at least a hydrophobic segment.
[0218] The polymeric azo initiator used in the third embodiment
includes a compound having the structure of formula (I) wherein D
is a hydrophobic segment, and L.sup.1 and L.sup.2, which may be the
same or different, each represent a hydrophilic linking group, such
as an ester linkage or an amido linkage. In this compound the
portion between the hydrophilic linking groups L.sup.1 and L.sup.2
is a hydrophilic moiety.
[0219] The polymeric azo initiator used in the third embodiment
also includes a compound having the structure of formula (I)
wherein D is a copolymer segment represented by formula (11):
-B.sup.1-A.sup.1- (11) wherein A.sup.1 is a hydrophilic segment;
and B.sup.1 is a hydrophobic segment. The copolymer segment of
formula (11) includes an ethylene oxide-propylene oxide copolymer
segment represented by formula (11a): ##STR12## wherein h and j
each represent an integer of 1 or greater, preferably 1 to 30,
still preferably 1 to 20, particularly preferably 4 to 20.
[0220] The polymeric azo initiator used in the third embodiment
also includes a compound having the structure of formula (I)
wherein D is a copolymer segment represented by formula (12):
-A.sup.2-B.sup.2-A- (12) wherein A.sup.2 and A.sup.3, which may be
the same or different, each represent a hydrophilic segment; and
B.sup.2 represent a hydrophobic segment. The copolymer segment of
formula (12) includes an
.alpha.,.omega.-bis(polyoxyethylene)polydimethylsiloxane segment
represented by formula (12a): ##STR13## wherein R.sup.11 and
R.sup.12 each represent a methyl group; Y represents an ethylene
group; and a, b, and c each represent an integer of 1 or greater (a
is preferably 1 to 24; b is preferably 1 to 20; and c is preferably
1 to 24).
[0221] The hydrophobic segment in the repeating unit represented by
formula (I) is not limited as long as it has adsorbability to
pigment particles. Preferred hydrophobic segments include a
polysiloxane segment, a polyaryl segment, a polyalkyl segment, a
polyalkylene oxide segment having 3 or more carbon atoms in the
alkylene moiety thereof, and a combination thereof.
[0222] The polysiloxane segment includes a polydialkylsiloxane
segment (preferably a polydimethylsiloxane segment) represented by
formula (13): ##STR14## wherein R.sup.6, R.sup.7, R.sup.8, and
R.sup.9 each represent an alkyl group having 1 to 4 carbon atoms
(preferably a methyl group) or an aryl group having 6 to 10 carbon
atoms (preferably a phenyl group); d represents 0 or 1 (preferably
1); and e represents an integer of 1 or greater, preferably 1 to
20, still preferably 1 to 10.
[0223] The hydrophilic segment in the repeating unit of formula (I)
is not particularly limited as long as it is not adsorbed to the
pigment particles but protrudes toward an aqueous medium in a loop.
A polyethylene oxide segment is a preferred hydrophilic segment. A
polyethylene oxide segment includes one represented by formula
(21): --(CH.sub.2CH.sub.2O).sub.t-- (21) wherein t represents an
integer of 1 or greater, preferably 1 to 30, still preferably 1 to
20, particularly preferably 4 to 20.
[0224] The polymeric azo initiator having the repeating unit of
formula (I) includes a compound represented by formula (Ia), a
compound represented by formula (Ib), and a compound represented by
formula (Ic): ##STR15## wherein R.sup.1 and R.sup.3 each represent
an alkyl group having 1 to 4 carbon atoms; R.sup.2 and R.sup.4 each
represent a cyano group; R.sup.6, R.sup.7, R.sup.8, and R.sup.9
each represent an alkyl group having 1 to 4 carbon atoms or an aryl
group having 6 to 10 carbon atoms; d represents 0 or an integer of
1 or greater; and e, n, p, q, r, and s each represent an integer of
1 or greater (In formula (Ia), R.sup.1 and R.sup.3 each preferably
represent a methyl group; e is preferably 1 to 20; n is preferably
1 to 20; p is preferably 1 to 5; q is preferably 1 to 30; r is
preferably 1 to 5; and s is preferably 1 to 5); ##STR16## wherein
R.sup.1 and R.sup.3 each represent an alkyl group having 1 to 4
carbon atoms; R.sup.2 and R.sup.4 each represent a cyano group;
R.sup.11 and R.sup.12 each represent an alkyl group having 1 to 4
carbon atoms or an aryl group having 6 to 10 carbon atoms; a, b, c,
f, g, and n each represent an integer of 1 or greater (In formula
(Ib), R.sup.1 and R.sup.3 each preferably represent a methyl group;
R.sup.11 and R.sup.12 each preferably represent a methyl group; a
is preferably 1 to 24; b is preferably 1 to 20; c is preferably 1
to 24; f is preferably 1 to 5; g is preferably 1 to 5; and n is
preferably 1 to 20); ##STR17## wherein R.sup.1 and R.sup.3 each
represent an alkyl group having 1 to 4 carbon atoms; R.sup.2 and
R.sup.4 each represent a cyano group; and .alpha., .beta., h, j,
and n each represent an integer of 1 or greater (In formula (Ic),
R.sup.1 and R.sup.3 each preferably represent a methyl group;
.alpha. is preferably 1 to 5; .beta. is preferably 1 to 5; h is
preferably 1 to 30; j is preferably 1 to 30; and n is preferably 1
to 20).
[0225] While the amount of the polymeric azo initiator to be added
is not particularly limited provided that it is sufficient for
covering all the surface of the hydrophilized pigment particles, it
preferably ranges from 1 to 30% by weight, particularly from 3 to
10% by weight, based on the total weight of the hydrophilized
pigment particles. Use of 1% or more of the polymeric azo initiator
ensures the improvement on dispersion stability of the
hydrophilized pigment particles. With amounts of not more than 30%,
existence of the polymeric azo pigment remaining unadsorbed to the
pigment particles is suppressed, and production of a
water-insoluble polymer or polymer particles having no core is
prevented. Amounts of 3% or more further ensures the improvement on
the dispersion stability of the pigment particles, and amounts of
10% or less assure suppression of an increase of the encapsulated
pigment particle size.
[0226] The polymerizable surface active agents which can be used in
the third embodiment preferably include those illustrated with
respect to the first embodiment.
[0227] The hydrophilic monomer which can be used in the third
embodiment include those described as for the first embodiment.
[0228] The hydrophilic monomers can be used either individually or
as a mixture of two or more thereof. One or more of the
polymerizable surface active agents and one or more of the
hydrophilic monomers can be used in combination.
[0229] The amount of the polymerizable surface active agent and/or
the hydrophilic monomer to be added preferably ranges 5 to 70% by
weight, particularly 10 to 50% by weight, based on the total weight
of the hydrophilized pigment particles. Use of 5% or more of the
polymerizable surface active agent and/or the hydrophilic monomer
brings about improved dispersion stability of the encapsulated
pigment. With the amount being not more than 70%, production of
polymer particles having no core or a water-soluble polymer can be
prevented. Amounts of 10% or more result in further improvement on
the dispersion stability of the encapsulated pigment. With amounts
not more than 50% by weight, an increase in the encapsulated
pigment particle size can be suppressed. The hydrophobic monomers
which can be used in the third embodiment include those recited
with respect to the first embodiment. The hydrophobic monomers can
be used either individually or as a mixture of two or more
thereof.
[0230] In the third embodiment, a crosslinking agent may be used to
form a crosslinked polymer layer on the hydrophilized pigment
particles.
[0231] Crosslinkable groups include a glycidyl group, an isocyanate
group, a hydroxyl group, and an unsaturated hydrocarbon group
(e.g., vinyl, allyl, acryloyl, methacryloyl, propenyl, vinylidene
or vinylene).
[0232] The crosslinking agent that can be used is not particularly
limited provided that it is highly reactive with the polymerizable
surface active agent and/or the hydrophilic monomer. Crosslinking
agents having at least two functional groups reactive with the
crosslinkable group are preferred.
[0233] Such functional groups include an amino group, a carboxyl
group, a hydroxyl group, a mercapto group, a glycidyl group, an
isocyanate group, an N-methylol group, an N-methyl ether group, and
a vinyl group.
[0234] Suitable crosslinking agents include (meth)acrylic ester
monomers having a blocked isocyanate group, (meth)acrylic ester
monomers having a glycidyl group, and (meth)acrylic ester monomers
having a 1,3-dioxolan-2-one-4-yl group.
[0235] Specific examples are 2-methacryloyloxyethyl isocyanate,
glycidyl (meth)acrylate, (1,3-dioxolan-one-4-yl)methyl
(meth)acrylate, ethylene glycol diacrylate, diethylene glycol
diacrylate, triethylene glycol diacrylate, tetraethylene glycol
diacrylate, polyethylene glycol diacrylate, allyl acrylate,
bis(acryloxyethyl)hydroxyethyl isocyanurate, bis(acryloxyneopentyl
glycol) adipate, 1,3-butylene glycol diacrylate, 1,6-hexanediol
diacrylate, neopentyl glycol diacrylate, propylene glycol
diacrylate, polypropylene glycol diacrylate,
2-hydroxy-1,3-diacryloxypropane,
2,2-bis[4-(acryloxy)phenyl]propane,
2,2-bis[4-(acryloxyethoxy)phenyl]propane,
2,2-bs[4-(acryloxyethoxy-diethoxy)phenyl]propane,
2,2-bis[4-(acryloxyethoxy-polyethoxy)phenyl]propane, hydroxypivalic
acid neopentyl glycol diacrylate, 1,4-butanediol diacrylate,
dicyclopentanyl diacrylate, dipentaerythritol hexaacrylate,
dipentaerythritol monohydroxypentaacrylate, ditrimethylolpropane
tetraacrylate, pentaerythritol triacrylate, tetrabromobisphenol A
diacrylate, triglycerol diacrylate, trimethylolpropane triacrylate,
tris(acryloxyethyl) isocyanurate, ethylene glycol dimethacrylate,
diethylene glycol dimethacrylate, triethylene glycol
dimethacrylate, tetraethylene glycol dimethacrylate, polyethylene
glycol dimethacrylate, propylene glycol dimethacrylate,
polypropylene glycol dimethacrylate, 1,3-butylene glycol
dimethacrylate, 1,4-butanediol dimethacrylate, 1,6-hexanediol
dimethacrylate, neopentyl glycol dimethacrylate,
2-hydroxy-1,3-dimethacryloxypropane,
2,2-bis[4-(methacryloxy)phenyl]propane,
2,2-bis[4-(methacryloxyethoxy)phenyl]propane,
2,2-bis[4-(methacryloxyethoxy-diethoxy)phenyl]propane,
2,2-bis[4-(methacryloxyethoxy-polyethoxy)phenyl]propane,
tetrabromobisphenol A dimethacrylate, dicyclopentanyl
dimethacrylate, dipentaerythritol hexamethacrylate, glycerol
dimethacrylate, hydroxypivalic acid neopentyl glycol
dimethacrylate, dipentaerythritol monohydroxypentamethacrylate,
ditrimethylolpropane tetramethacrylate, pentaerythritol
trimethacrylate, pentaerythritol tetramethacrylate, triglycerol
dimethacrylate, trimethylolpropane trimethacrylate,
tris(methacryloxyethyl) isocyanurate, allyl methacrylate,
divinylbenzene, diallyl phthalate, diallyl terephthalate, diallyl
isophthalate, and diethylene glycol bisallyl carbonate.
[0236] The aqueous dispersion containing the microencapsulated
pigment according to the third embodiment is prepared by a process
comprising the steps of:
[0237] (1) allowing the polymeric azo initiator to be adsorbed onto
the hydrophilized pigment particles in the presence of the
polymeric surface active agent and/or the hydrophilic monomer under
a condition that does not activate the polymeric azo initiator, and
subsequently
[0238] (2) activating the polymeric azo initiator to polymerize the
polymerizable surface active agent and/or the hydrophilic
monomer.
[0239] In the step (1), a mixture comprising the hydrophilized
pigment particles, the polymeric azo initiator, the polymerizable
surface active agent and/or the hydrophilic monomer, and a
water-soluble organic solvent and/or water is ultrasonicated under,
if necessary, cooling. Alternatively, a mixture of the
hydrophilized pigment particles, the polymeric azo initiator, and a
water-soluble organic solvent and/or water is ultrasonicated under,
if necessary, cooling, and the polymerizable surface active agent
and/or the hydrophilic monomer are added to the dispersion,
followed by ultrasonication. If desired, a hydrophobic monomer
and/or a crosslinking agent can be added to the system. The cooling
is effected by, for example, circulating cooling water by means of
a circulator. The cooling temperature, which depends on the
decomposition (cleavage) temperature of the polymeric azo
initiator, is preferably 20.degree. C. or lower, still preferably
10.degree. C. or lower.
[0240] Subsequently, the obtained mixture is put into a reaction
vessel equipped with an ultrasonic generator, a stirrer, a
temperature controller, a reflux condenser, and a dropping funnel.
A water-soluble organic solvent and/or water is added to give a
post-reaction solids content of 10 to 30% by weight, followed by
stirring well. The system is then heated up to the decomposition
temperature of the polymeric azo initiator to thereby activate the
initiator and induce radical polymerization. If desired,
crosslinking reaction by the crosslinking agent follows. The
heating temperature, while varying with the kind of the polymeric
azo initiator, preferably ranges from 60.degree. to 80.degree.
C.
[0241] Addition of ink formulation components (described later) to
the system in the above described step results in direct
preparation of ink, for example, an ink jet recording ink.
[0242] The microencapsulated pigment according to the first,
second, and third embodiments preferably has a particle size of 400
nm or smaller, particularly 300 nm or smaller, especially 50 to 200
nm. An embodiment in which the hydrophilized pigment particles are
dispersed in an aqueous medium with the aid of a general
non-polymerizable surface active agent, such as sodium
dodecylbenzenesulfonate, sodium dodecyl sulfate or sodium lauryl
sulfate, and a monomer is emulsion polymerized in the aqueous
dispersion is also included under the scope of the present
invention. Comparing with such an embodiment, the first to third
embodiments are preferred in that foaming of the aqueous dispersion
is suppressed.
[Aqueous Dispersion]
[0243] The aqueous dispersion according to an embodiment of the
present invention contains the microencapsulated pigment according
to the embodiments of the invention, preferably the liquid
resulting from the emulsion polymerization as carried out according
to the first, second or third embodiments described supra. Mixing
the aqueous dispersion of the invention with ink components for ink
jet recording provides an ink jet recording ink according to an
embodiment of the present invention.
[Ink Jet Recording Ink]
[0244] In an embodiment of the invention, the ink jet recording ink
contains the aqueous dispersion of the invention as stated.
[0245] In another embodiment, the ink jet recording ink contains
the microencapsulated pigment of the invention and water. The
microencapsulated pigment content is preferably 1 to 20% by weight,
still preferably 3 to 15% by weight, based on the total ink
composition. A content of 5 to 15% by weight is particularly
recommended for securing high image density and high color
developability.
[0246] The solvent of the ink jet recording ink preferably
comprises water and a water-soluble organic solvent. If desired,
other solvents may be added.
[0247] Suitable water-soluble organic solvents include alkyl
alcohols having 1 to 4 carbon atoms, such as ethanol, methanol,
butanol, propanol, and 2-propanol; glycol ethers, such as ethylene
glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene
glycol monobutyl ether, ethylene glycol monomethyl ether acetate,
diethylene glycol monomethyl ether, diethylene glycol monoethyl
ether, diethylene glycol mono-n-propyl ether, ethylene glycol
mono-isopropyl ether, diethylene glycol mono-isopropyl ether,
ethylene glycol mono-n-butyl ether, diethylene glycol mono-n-butyl
ether, triethylene glycol mono-n-butyl ether, ethylene glycol
mono-t-butyl ether, diethylene glycol mono-t-butyl ether,
1-methyl-1-methoxybutanol, propylene glycol monomethyl ether,
propylene glycol monoethyl ether, propylene glycol mono-t-butyl
ether, propylene glycol mono-n-propyl ether, propylene glycol
mono-isopropyl ether, dipropylene glycol monomethyl ether,
dipropylene glycol monoethyl ether, dipropylene glycol
mono-n-propyl ether, dipropylene glycol mono-isopropyl ether,
propylene glycol mono-n-butyl ether, and dipropylene glycol
mono-n-butyl ether; formamide, acetamide, dimethyl sulfoxide,
sorbitol, sorbitan, glycerol monoacetate, glycerol diacetate,
glycerol triacetate, and sulfolane.
[0248] The ink jet recording ink preferably contains a high-boiling
water-soluble organic solvent as a water-soluble organic solvent
which can serve as a wetting agent for imparting water retentivity
and wetting properties to the ink composition. Such a high-boiling
water-soluble organic solvent includes one having a boiling point
of 180.degree. C. or higher.
[0249] Examples of the water-soluble organic solvent having a
boiling point of 180.degree. C. or higher are ethylene glycol,
propylene glycol, diethylene glycol, pentamethylene glycol,
trimethylene glycol, 2-butene-1,4-diol, 2-ethyl-1,3-hexanediol,
2-methyl-2,4-pentanediol, tripropylene glycol monomethyl ether,
dipropylene glycol monoethyl glycol, dipropylene glycol monoethyl
ether, dipropylene glycol monomethyl ether, dipropylene glycol,
triethylene glycol monomethyl ether, tetraethylene glycol,
triethylene glycol, diethylene glycol monobutyl ether, diethylene
glycol monoethyl ether, diethylene glycol monomethyl ether,
tripropylene glycol, polyethylene glycols having molecular weights
of 2000 or lower, 1,3-propylene glycol, isopropylene glycol,
isobutylene glycol, 1,4-butanediol, 1,3-butanediol,
1,5-pentanediol, 1,6-hexanediol, glycerol, mesoerythritol, and
pentaerythritol. Preferred of them are those having boiling points
of 200.degree. C. or higher. They can be used either individually
or as a mixture of two or more thereof. Use of the high-boiling
organic solvents provides ink jet recording inks which retain
flowability and re-dispersibility for an extended period of time
even when left to stand in an open state (in contact with air at
room temperature) and which exhibit high ejection stability, hardly
clogging nozzles during printing or on resuming printing after
suspension.
[0250] The water-soluble organic solvent content in the ink jet
recording ink is preferably about 10 to 50% by weight, still
preferably 10 to 30% by weight, based on the total ink
composition.
[0251] Useful water-soluble organic solvents further include polar
solvents, such as 2-pyrrolidone, N-methylpyrrolidone,
.epsilon.-caprolactam, dimethyl sulfoxide, sulfolane, morpholine,
N-ethylmorpholine, and 1,3-dimethyl-2-imidazolidinone. These polar
solvents can be used either individually or as a combination of two
or more thereof. Use of the polar solvent is effective on
dispersibility, bringing about satisfactory ejection stability.
[0252] The amount of the polar solvent is preferably 0.1 to 20% by
weight, still preferably 1 to 10% by weight, based on the total ink
composition.
[0253] The ink jet recording ink preferably contains a penetrant
for accelerating penetration of the aqueous medium into recording
media. Accelerated penetration of the aqueous medium into a
recording medium assures formation of images with little
feathering. Penetrants suitable for this purpose include polyhydric
alcohol alkyl ethers (glycol ethers) and 1,2-alkyldiols. Examples
of the polyhydric alcohol alkyl ethers are ethylene glycol
monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol
monobutyl ether, ethylene glycol monomethyl ether acetate,
diethylene glycol monomethyl ether, diethylene glycol monoethyl
ether, ethylene glycol mono-n-propyl ether, ethylene glycol
mono-isopropyl ether, diethylene glycol mono-isopropyl ether,
ethylene glycol mono-n-butyl ether, diethylene glycol mono-n-butyl
ether, triethylene glycol mono-n-butyl ether, ethylene glycol
mono-t-butyl ether, diethylene glycol mono-t-butyl ether,
1-methyl-1-methoxybutanol, propylene glycol monomethyl ether,
propylene glycol monoethyl ether, propylene glycol mono-t-butyl
ether, propylene glycol mono-n-propyl ether, propylene glycol
mono-isopropyl ether, dipropylene glycol monomethyl ether,
dipropylene glycol monoethyl ether, dipropylene glycol
mono-n-propyl ether, dipropylene glycol mono-isopropyl ether,
propylene glycol mono-n-butyl ether, and dipropylene glycol
mono-n-butyl ether. Examples of the 1,2-alkyldiols are
1,2-pentanediol and 1,2-hexanediol. The penetrant may also be
selected from straight-chain hydrocarbon diols, such as
1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol,
1,7-heptanediol, and 1,8-octanediol.
[0254] Particularly preferred penetrants are propylene glycol
monobutyl ether, dipropylene glycol monobutyl ether, diethylene
glycol monobutyl ether, triethylene glycol monobutyl ether,
1,2-pentanediol, and 1,2-hexanediol. The penetrant is preferably
used in an amount of 1 to 20% by weight, particularly 1 to 10% by
weight, based on the total ink composition. Less than 1% of the
penetrant is substantially ineffective. More than 20% of the
penetrant rather results in disadvantages such as feathering or an
increased viscosity. Use of the 1,2-alkyldiol, such as
1,2-pentanediol or 1,2-hexanediol, is particularly effective in
improving drying properties after recording and feathering
resistance.
[0255] It is particularly preferred for the ink jet printing ink to
contain at least one compound selected from the group consisting of
glycerol, a polyhydric alcohol alkyl ether, and a 1,2-alkyldiol to
improve penetrability of ink solvent components into a recording
medium while sufficiently securing ejection reliability
(non-clogging properties) and storage stability of the ink. These
effects in cooperation with the effects of the microencapsulated
pigment bring about remarkably improved image quality with greatly
reducing feathering even when plain paper or regenerated paper is
used as a recording medium.
[0256] In using the glycol ethers supra, they are preferably used
in combination with an acetylene glycol compound hereinafter
described as a surface active agent.
[0257] The ink jet recording ink of the invention preferably
contains a surface active agent, especially an anionic surface
active agent and/or a nonionic surface active agent. Useful anionic
surface active agents include sulfonic acid types, such as
alkanesulfonic acid salts, .alpha.-olefinsulfonic acid salts,
alkylbenzenesulfonic acid salts, alkylnaphthalenesulfonic acids,
acylmethyltaurines, and dialkylsulfosuccinic acids; alkylsulfuric
ester salts, sulfated oils, sulfated olefins, polyoxyethylene alkyl
ether sulfuric ester salts; carboxylic acid types, e.g., fatty acid
salts and alkylsarcosine salts; and phosphoric acid ester types,
such as alkylphosphoric ester salts, polyoxyethylene alkyl ether
phosphoric ester salts, and glycerophosphoric ester salts. Useful
nonionic surface active agents include ethylene oxide adduct types,
such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl
ethers, polyoxyethylene alkyl esters, and polyoxyethylene
alkylamides; polyol ester types, such as glycerol alkyl esters,
sorbitan alkyl esters, and sugar alkyl esters; polyether types,
such as polyhydric alcohol alkyl ethers; and alkanolamide types,
such as alkanolamine fatty acid amides.
[0258] Examples of the anionic surface active agents are sodium
dodecylbenzenesulfonate, sodium laurate, and a polyoxyethylene
alkyl ether sulfate ammonium salt. Examples of the nonionic surface
active agents are ethers such as polyoxyethylene nonylphenyl ether,
polyoxyethylene octylphenyl ether, polyoxyethylene dodecylphenyl
ether, polyoxyethylene alkylallyl ether, polyoxyethylene oleyl
ether, polyoxyethylene lauryl ether, and polyoxyalkylene alkyl
ethers (e.g., polyoxyethylene alkyl ethers); and esters, such as
polyoxyethylene oleate, polyoxyethylene oleate ester,
polyoxyethylene distearate, sorbitan laurate, sorbitan
monostearate, sorbitan mono-oleate, sorbitan sesquioleate,
polyoxyethylene mono-oleate, and polyoxyethylene stearate.
[0259] It is still preferred for the ink jet recording ink of the
invention to contain an acetylene glycol surface active agent
and/or an acetylene alcohol surface active agent to improve the
penetrability of the aqueous medium into recording media thereby
achieving printing with little feathering.
[0260] The acetylene glycol surface active agent which is
preferably used includes one represented by formula (6): ##STR18##
wherein R.sup.1, R.sup.2, R.sup.3, and R.sup.4 each represent an
alkyl group (preferably having 6 or fewer carbon atoms); and m and
n are numbers satisfying the relationship:
0.ltoreq.m+n.ltoreq.50.
[0261] Of the compounds represented by formula (6) particularly
preferred are 2,4,7,9-tetramethyl-5-decyne-4,7-diol,
3,6-dimethyl-4-octyne-3,6-diol, and 3,5-dimethyl-1-hexyn-3-ol. The
acetylene glycol surface active agents represented by formula (6)
which are commercially available can be made use of. Examples
include Surfynol series 104, 82, 465, 485 and TG, produced by Air
Products and Chemicals, Inc., and Olfine series STG and E1010,
supplied by Nisshin Chemical Industry Co., Ltd.
[0262] The acetylene alcohol surface active agents that are
commercially available include Surfynol 61 from Air Products and
Chemicals, Inc.
[0263] These surface active agents are preferably used in amounts
of 0.01 to 10% by weight, particularly 0.1 to 5% by weight, based
on the total ink composition.
[0264] The ink jet recording ink can contain a pH adjuster for
adjusting its pH preferably to 7 to 9, still preferably 7.5 to
8.5.
[0265] Suitable pH adjusters include potassium metal compounds,
such as sodium hydroxide, potassium hydroxide, lithium hydroxide,
sodium carbonate, sodium hydrogencarbonate, potassium carbonate,
lithium carbonate, sodium phosphate, potassium phosphate, lithium
phosphate, potassium dihydrogenphosphate, dipotassium
hydrogenphosphate, sodium oxalate, potassium oxalate, lithium
oxalate, sodium borate, sodium tetraborate, potassium
hydrogenphthalate, and potassium hydrogentartrate; ammonia; and
amines, such as methylamine, ethylamine, diethylamine,
trimethylamine, triethylamine, tris(hydroxymethyl)aminomethane
hydrochloride, triethanolamine, diethanolamine,
diethylethanolamine, triisopropenolamine, butyldiethanolamine,
morpholine, and propanolamine.
[0266] Inter alia, an alkali metal hydroxide or an amine alcohol is
contributory to the improvement of dispersion stability of the
pigment particles.
[0267] The alkali metal hydroxide is preferably used in an amount
of 0.01 to 5% by weight, particularly 0.05 to 3% by weight, based
on the total ink composition.
[0268] The amine alcohol is preferably used in an amount of 0.1 to
10% by weight, particularly 0.5 to 5% by weight, based on the total
ink composition.
[0269] The ink jet recording ink can contain antifungals,
antiseptics, and rust inhibitors, such as benzoic acid,
dichlorophene, hexachlorophene, sorbic acid, p-hydroxybenzoic
esters, ethylenediaminetetraacetic acid (EDTA), sodium
dehydroacetate, 1,2-benthiazolin-3-one (commercially sold under a
trade name "Proxel" from Avecia), 3,4-isothiazolin-3-one, and
4,4-dimethyloxazolidine.
[0270] The ink jet recording ink can contain urea, thiourea and/or
ethylene urea for preventing the ink from drying at nozzles of a
recording head.
[0271] A particularly preferred formulation of the ink jet
recording ink according to the invention comprises at least:
[0272] (1) the microencapsulated pigment according to the present
invention,
[0273] (2) an acetylene glycol surface active agent and/or an
acetylene alcohol surface active agent,
[0274] (3) at least one compound (penetrant) selected from the
group consisting of diethylene glycol monobutyl ether, triethylene
glycol monobutyl ether, and a 1,2-alkyldiol having 4 to 10 carbon
atoms,
[0275] (4) glycerol, and
[0276] (5) water.
[0277] The ink jet recording ink having the above formulation is
excellent in dispersion stability and ejection stability and
assures stable recording without causing nozzle clogging for a
prolonged period of time. It has satisfactory drying properties
after ejected to form high-quality ink images with high density and
excellent color developability and with little feathering even on
plain paper, regenerated paper or coated paper.
[0278] In general, pigments are dispersed in the presence of
surface active agents or polymeric dispersants. However, because
these dispersing aids are simply adsorbed by pigment particles,
they are liable to separate from the surface of pigment particles
by some environmental factors. In the present invention, to the
contrary, the (crosslinked) polymer layer completely encapsulates
the hydrophilized pigment particles and hardly comes off the
surface of the particles because, as is believed, the polymer layer
is very firmly adsorbed onto the surface of the pigment
particles.
[0279] Conventional ink compositions comprising a pigment
dispersion prepared by dispersing pigment particles with a surface
active agent or a polymeric dispersant, the above-described
acetylene glycol surface active agent and/or the acetylene alcohol
surface active agent, and a penetrant, such as diethylene glycol
monobutyl ether, triethylene glycol monobutyl ether, propylene
glycol monobutyl ether, dipropylene glycol monobutyl ether or a
1,2-alkyldiol, are apt to undergo reduction of dispersion
stability, which leads to instable ejection, because the dispersant
is easily released from the pigment surface due to the strong shear
force imposed when the ink is ejected through fine nozzles.
[0280] Such a phenomenon is not at all observed with the ink jet
recording ink of the present invention. Since the (crosslinked)
polymer layer encapsulates the pigment particles to exhibit
satisfactory solvent resistance, the penetrant is prevented from
accelerating separation of the polymer from the pigment particles
or swelling the polymer. The ink of the invention therefore
maintains excellent dispersion stability for a prolonged period of
time.
[0281] Further, the conventional ink compositions containing a
pigment dispersion prepared by dispersing pigment particles with a
surface active agent or a polymeric dispersant and a penetrant
generally tend to have an increased viscosity on account of the
existence of a free dispersant which has failed to be adsorbed by
the pigment particles in the very beginning of dispersion or which
has separated from the particles later and is dissolved in the ink
solvent. The amount of the pigment that is allowed to exist in inks
is therefore limited of necessity. As a result, these conventional
ink compositions often fail to provide images with sufficient
density and satisfactory color developability particularly on plain
paper or regenerated paper. The ink jet recording ink of the
present invention enjoys low viscosities in the absence of the
viscosity increase problem because the encapsulating (crosslinked)
polymer layer hardly comes off the pigment particles. This allows
the ink composition to contain an increased amount of a colorant,
leading to obtaining sufficient image densities on plain paper or
regenerated paper.
[0282] In the particularly preferred formulation of the ink jet
recording ink described supra, the total amount of the acetylene
glycol surface active agent and/or the acetylene alcohol surface
active agent as component (2) is preferably 0.01 to 10% by weight,
particularly 0.1 to 5% by weight, based on the total ink
composition.
[0283] In the particularly preferred formulation of the ink jet
recording ink described supra, diethylene glycol monobutyl ether
and/or triethylene glycol monobutyl ether, which are added as
component (3) (penetrant), are preferably added in an amount of 10%
by weight or less, particularly from 0.5 to 5% by weight, based on
the total ink composition. Addition of diethylene glycol monobutyl
ether or triethylene glycol monobutyl ether produces remarkable
effects on ink penetrability. Addition of diethylene glycol
monobutyl ether and/or triethylene glycol monobutyl ether is
effective in improving solubility of the acetylene glycol surface
active agent and image quality.
[0284] In the particularly preferred formulation of the ink jet
recording ink described supra, the 1,2-alkylene glycol having 4 to
10 carbon atoms as component (3) (penetrant) is preferably used in
an amount of 15% by weight or less based on the total ink
composition. 1,2-Alkylene glycols having 3 or fewer carbon atoms
are not so effective, and 1,2-alkylene glycols having 15 or more
carbon atoms hardly dissolve in water. Addition of more than 15% by
weight of the 1,2-alkylene glycol tends to result in an increase of
viscosity. The 1,2-alkylene glycol is preferably 1,2-pentanediol
and/or 1,2-hexanediol. 1,2-Pentanediol is preferably added in an
amount of 3 to 15% by weight. Less than 3% fails to secure
satisfactory penetrability. 1,2-Hexanediol is preferably added in
an amount of 0.5 to 10% by weight. Less than 0.5% fails to obtain
satisfactory penetrability.
[0285] In order to improve reliability against clogging and to
prevent generation of undesired white blanks in image areas, it is
preferred for the ink jet recording ink of the invention to contain
a solid wetting agent in amounts of 3 to 20% by weight based on the
total ink composition.
[0286] The term "solid wetting agent" as used herein means a
water-soluble substance which has a water-retaining function and is
solid at ambient temperature (25.degree. C.). Preferred solid
wetting agents include saccharides, saccharide derivatives such as
sugar alcohols, hyaluronic acid salts, trimethylolpropane, and
1,2,6-hexanetriol. The saccharides include monosaccharides,
disaccharides, oligosaccharides (including trisaccharides and
tetrasaccharides), and polysaccharides. Examples of the saccharides
are glucose, mannose, fructose, ribose, xylose, arabinose,
galactose, aldonic acids, glucitol (or sorbitol), maltose,
cellobiose, lactose, sucrose, trehalose, and maltotriose. The term
"polysaccharide" as used herein is intended to mean saccharide in
its broad sense and to include substances widely occurring in
nature such as alginic acid, .alpha.-cyclodextrin, and cellulose.
The saccharide derivatives include reduced sugars, such as sugar
alcohols represented by formula: HOCH.sub.2(CHOH).sub.nCH.sub.2OH,
where n is an integer of 2 to 5), oxidized sugars, such as aldonic
acids and uronic acids, amino acid, and thiosugars, with sugar
alcohols being preferred. Examples of sugar alcohols are maltitol,
sorbitol, and xylitol. The hyaluronic acid salt can be a
commercially available 1% aqueous solution of sodium hyaluronate
(molecular weight: 350,000). These solid wetting agents can be used
either individually or as a mixture of two or more thereof.
[0287] Having a water retaining function, the solid wetting agent
suppresses water evaporation to prevent a viscosity increase in the
ink flow passageways or near the nozzles and film formation. As a
result, the ink hardly clogs. The above-described solid wetting
agents are chemically stable. They do not decompose in ink and
retain the performance for a long time. Addition of the solid
wetting agent does not make the ink wet the nozzle plate and
therefore does not adversely affect the ejection stability.
[0288] The solid wetting agent or agents is/are preferably added in
a total amount of 3 to 20% by weight, particularly 3 to 10% by
weight, based on the total ink composition. Where two or more solid
wetting agents are used in combination, it is preferred to combine
at least one of saccharides, sugar alcohols, and hyaluronic acids
and at least one of trimethylolpropane and 1,2,6-hexanetriol. These
combinations are favorable for suppressing an increase of viscosity
that may have resulted from addition of solid wetting agents.
Addition of less than 3% of the solid wetting agent results in
insubstantial effect on clogging prevention. Addition of more than
20% tends to result in too high a viscosity to assure stable
ejection.
[0289] Since the microencapsulated pigment used as a colorant in
the ink jet recording ink of the invention has a truly spherical
shape as previously described, the ink easily exhibit Newtonian
behavior. Further, it is considered that the hydrophilic groups on
the encapsulated pigment particles are regularly and densely
orientated to face the aqueous medium, which would result in
effective electrostatic repulsive force. Therefore, the ink jet
recording ink of the invention is superior in ejection stability,
high dispersibility, and dispersion stability and is allowed to
have an increased colorant content compared with the conventional
microencapsulated pigment inks.
[0290] Ink jet recording using the ink of the present invention is
conveniently carried out by loading a known ink jet printer with
the ink of the invention and printing on plain paper or other ink
jet recording media. Ink jet recording using the ink of the
invention can be continued with high ink ejection stability and
provides recorded images with excellent fastness and abrasion
resistance, satisfactory color developability, high density, and
less feathering. Even on plain paper, the ink hardly feathers and
exhibits high color developability.
[0291] The present invention will now be illustrated in greater
detail with reference to Examples and Comparative Examples, but it
should be understood that the invention is not construed as being
limited thereto. Unless otherwise noted, all the parts and percents
are by weight. In Examples, the amounts of hydrophilic groups
introduced on the surface of pigment particles were measured as
follows.
Quantitative Determination of Introduced Hydrophilic (Anionic)
Group Content:
(a) Hydrophilic Group Content Introduced by Sulfonating Agent
[0292] Pigment particles having been surface treated with a
sulfonating agent by the oxygen flask combustion method. The
combustion gas was absorbed by a 0.3% hydrogen peroxide aqueous
solution. The sulfate ion (SO.sub.4.sup.-2) content of the solution
was determined by ion chromatography (Model 2000i, supplied by
Dionex Corp.), converted to a sulfonic acid group (--SO.sub.3H)
content, and expressed in terms of equivalent per gram of the
pigment.
(b) Hydrophilic Group Content Introduced by Carboxylating Agent
[0293] A solution of diazomethane in an appropriate solvent was
dropped into a hydrophilized pigment dispersion to convert all the
active hydrogen to a methyl group, which was to be quantitatively
determined by making use of the Zeisel method. Hydroiodic acid
(specific gravity: 1.7) was added to the treated pigment, followed
by heating to convert methyl groups into methyl iodide, which was
vaporized. The methyl iodide vapor was trapped in a standard silver
nitrate solution and precipitated as silver iodide. The amount of
the methyl group, i.e., active hydrogen was calculated from the
weight of the silver iodide and expressed in terms of molar
quantity per gram of the pigment (mmol/g).
Preparation of Anionic-Hydrophilized Black Pigment Particles
P1:
[0294] Fifteen parts of carbon black (MA-7, available from
Mitsubishi Chemical Corp.) were dispersed in 200 parts of sulfolane
in Eiger Motor Mill M250 (supplied by Eiger Japan) at a bead
loading of 70% and an agitation speed of 5000 rpm for 1 hour. The
pigment dispersion was transferred to an evaporator, where it was
heated to 120.degree. C. under a reduced pressure of -30 mmHg or
lower to remove as much water present in the system as possible.
The temperature was then kept at 150.degree. C., and 25 parts of
sulfur trioxide was added and allowed to react for 6 hours. After
completion of the reaction, the reaction mixture was washed several
times with excess sulfolane and poured into water. Filtration
yielded anionic-hydrophilized black pigment particles P1.
[0295] The amount of the hydrophilic group (anionic group)
introduced on the surface of the pigment particles was found to be
120.times.10.sup.-6 eq./g-pigment (12 mmol/g).
Preparation of Anionic-Hydrophilized Black Pigment Particles
P2:
[0296] Three hundred grams of acidic carbon black (MA-100, from
Mitsubishi Chemical Corp.) were mixed well with 1000 ml of water,
and 450 g of sodium hypochlorite (effective chlorine concentration:
12%) was added thereto dropwise, followed by stirring at 80.degree.
C. for 15 hours. The resulting slurry was purified by repetition of
washing with ion-exchanged water and filtration through filter
paper (Toyo Roshi No. 2) until addition of a 0.1N silver nitrate
aqueous solution to a filtrate no longer caused turbidity. The
washed pigment slurry was re-dispersed in 2500 ml of water and
desalted through a reverse osmosis membrane until the conductivity
of the desalted product was decreased to 0.2 ms or lower. The
dispersion was concentrated to give a pigment concentration of
about 15%.
[0297] The hydrophilized pigment dispersion was treated with a
hydrochloric acid aqueous solution, concentrated, dried, and
pulverized to powder. The surface active hydrogen content of the
hydrophilized pigment particles, as determined by the method
described supra, was 2.8 mmol/g.
Preparation of Anionic-Hydrophilized Cyan Pigment Particles P3:
[0298] Twenty parts of phthalocyanine pigment (C.I. Pigment Blue
15:3) were dispersed in 500 parts of quinoline in Eiger Motor Mill
M250 (from Eiger Japan) at a bead loading of 70% and an agitation
speed of 5000 rpm for 2 hours. The pigment dispersion was
transferred to an evaporator, where the mixture was heated to
120.degree. C. under a reduced pressure of 30 mmHg or lower to
remove as much water present in the system as possible. The
temperature was maintained at 160.degree. C., and 20 parts of a
sulfonated pyridine complex was added and allowed to react for 8
hours. After completion of the reaction, the reaction mixture was
washed several times with excess quinoline and poured into water.
Filtration yielded anionic-hydrophilized cyan pigment particles
P3.
[0299] The amount of the hydrophilic group (anionic group)
introduced on the surface of the pigment particles was found to be
40.times.10.sup.-6 eq./g-pigment (4 mmol/g).
Preparation of Anionic-Hydrophilized Yellow Pigment Particles
P4:
[0300] Anionic-hydrophilized yellow pigment particles P4 were
obtained in the same manner as for the hydrophilized cyan pigment
particles P3, except for replacing the phthalocyanine pigment with
the same amount of an isoindolinone pigment (C.I. Pigment Yellow
110).
[0301] The resulting yellow pigment particles P4 were found to have
a hydrophilic (anionic) group content of 45.times.10.sup.-6
eq./g-pigment (4.5 mmol/g).
Preparation of Anionic-Hydrophilized Magenta Pigment Particles
P5:
[0302] Anionic-hydrophilized magenta pigment particles P5 were
obtained in the same manner as for the hydrophilized cyan pigment
particles P3, except for replacing the phthalocyanine pigment with
the same amount of an isoindolinone pigment (C.I. Pigment Red
122).
[0303] The resulting yellow pigment particles P5 were found to have
a hydrophilic (anionic) group content of 60.times.10.sup.-6
eq./g-pigment (6 mmol/g).
Preparation of Microencapsulated Pigments MCP 1-1 to 1-8 and 1-13
to 1-15:
[0304] A mixture consisting of hydrophilized pigment particles, a
polymerizable surface active agent, and an aqueous medium
(optionally including glycerin or glycol) was prepared according to
the formulation shown in Table 1 below. A polymerization initiator
of the amount shown in Table 1 was added, and the mixture was
allowed to react at 80.degree. C. for 10 hours for encapsulation
while applying ultrasonic waves from an ultrasonic generator. The
resulting dispersion of the encapsulated pigments was adjusted to a
pH of 7 to 9 with a potassium hydroxide aqueous solution. The
dispersion was purified by filtration to remove coarse particles
and by ultrafiltration to remove the unreacted polymerizable
surface active agent and comonomer to obtain microencapsulated
pigments MCP 1-1 to -8 and -13 to -15. The aspect ratio and the
Zingg index of the microencapsulated pigments are shown in Table 1.
TABLE-US-00001 TABLE 1 MCP MCP MCP MCP MCP MCP MCP MCP MCP MCP MCP
1-1 1-2 1-3 1-4 1-5 1-6 1-7 1-8 1-13 1-14 1-15 Hydrophilized P1 10
5 -- -- -- -- -- -- -- -- -- Pigment (part) P2 5 10 -- -- -- -- --
-- -- -- -- P3 -- -- 7 15 -- -- -- -- 7 -- -- P4 -- -- -- -- 7 --
15 -- -- 7 -- P5 -- -- -- -- -- 7 -- 15 -- -- 7 Polymerizable Adeka
Reasope SE-10N 7.5 -- 2 -- 2 -- -- 5 -- -- -- Surface Active
Aqualon HS-1025 -- 10 -- 0.75 -- 3.5 10.5 5 -- -- -- Agent (part)
Aqualon KH-10 -- -- -- -- -- -- -- -- 3 3 3 Comonomer Methylstyrene
2.5 -- -- -- 1 1 -- 2 -- -- -- (part) 2-Ethylhexyl methacrylate --
-- 1 0.5 1 -- -- -- 1 1 1 Benzyl methacrylate -- -- -- -- -- -- --
-- 1 1 1 Aqueous Medium Glycerin 10 -- -- -- -- -- 5 8 -- -- --
(part) Diethylene glycol -- 15 -- 10 -- -- 5 -- -- -- --
Ion-exchanged Water 65 60 30 38.75 33 34.5 51.5 100 40 40 40
Initiator Potassium persulfate 0.5 0.5 0.5 0.2 0.3 0.3 0.5 0.5 0.5
0.5 0.5 (part) Aspect ratio 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
1.0 Zingg index 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
Preparation of Microencapsulated Pigment MCP 2-1:
[0305] A hundred grams of anionic-hydrophilized black pigment
particles P1 (anionic sulfonic acid group and anionic sulfinic acid
group content: 12 mmol/g) were stirred in a solution of 50 g of
glycerin in 250 g of ion-exchanged water in a stirring machine
equipped with an ultrasonic generator for 2 minutes under
ultrasonication. The resulting dispersion was poured into a
reaction vessel equipped with an ultrasonic generator, a stirrer, a
temperature controller, a reflux condenser, and a dropping funnel,
and to the dispersion was added 1.63 g of a cationic polymerization
initiator V-50 (from Wako Pure Chemical Industries, Ltd.; 10-hour
half-life temperature: 56.degree. C.; molecular weight: 411), which
corresponded to 0.5 mol per mole of the anionic group content of
the hydrophilized black pigment particles P1. The mixture was
stirred at -10.degree. to 0.degree. C. under ultrasonication. Then,
10 g of a polymerizable surface active agent Adeka Reasope SE-10N
(from Asahi Denka Co., Ltd.) was added, followed by stirring for 1
hour. While the inner temperature of the reaction vessel was heated
up to 70.degree. C., an emulsified monomer mixture that had
separately been prepared by stirring 3 g of methacrylic acid, 5 g
of 2-sulfoethyl methacrylate, 10 g of styrene, 10 g of n-butyl
methacrylate, 1.2 g of a polymerizable surface active agent Adeka
Reasope SE-10N (from Asahi Denka Co., Ltd.), and 150 g of
ion-exchanged water was slowly added dropwise from the dropping
funnel to the reaction mixture. The reaction was continued for 24
hours under ultrasonication. The resulting dispersion of the
encapsulated pigments was adjusted to a pH of 7 to 9 with a
potassium hydroxide aqueous solution. The dispersion was filtered
through a membrane filter of 1 .mu.m to remove coarse particles and
then subjected to ultrafiltration to remove the unreacted monomers
and oligomers to obtain a dispersion of microencapsulated pigment
MCP 2-1.
Preparation of Microencapsulated Pigment MCP 2-2 to 2-9:
[0306] Microencapsulated pigments MCP 2-2 to -9 were obtained in
the same manner as for microencapsulated pigment MCP 2-1 according
to the formulation given in Table 2 below. As described with
respect to the preparation of microencapsulated pigment MCP 2-1,
the amount of the cationic polymerization initiator to be added was
decided based on the molecular amount of the anionic group content
possessed by 100 g of the pigment particles P2 to P5 as
follows.
Microencapsulated Pigment MCP 2-2:
[0307] 0.58 g of VA-060 (Wako Pure Chemical; 10-hour half-life
temperature: 60.degree. C.; molecular weight: 411) equivalent to
0.5 mol of the anionic group content of 100 g of pigment particles
P2 was added.
Microencapsulated Pigment MCP 2-3:
[0308] 0.70 g of VA-058 (Wako Pure Chemical; 10-hour half-life
temperature: 58.degree. C.; molecular weight: 351) equivalent to
0.5 mol of the anionic group content of 100 g of pigment particles
P3 was added.
Microencapsulated Pigment MCP 2-4:
[0309] 0.75 g of VA-046B (Wako Pure Chemical; 10-hour half-life
temperature: 47.degree. C.; molecular weight: 250) equivalent to
0.5 mol of the anionic group content of 100 g of pigment particles
P4 was added.
Microencapsulated Pigment MCP 2-5:
[0310] 0.73 g of VA-044 (Wako Pure Chemical; 10-hour half-life
temperature: 44.degree. C.; molecular weight: 323) equivalent to
0.5 mol of the anionic group content of 100 g of pigment particles
P5 was added.
Microencapsulated Pigment MCP 2-6:
[0311] 1.48 g of VA-060 equivalent to 0.1 mol of the anionic group
content of 100 g of pigment particles P1 was added.
Microencapsulated Pigment MCP 2-7:
[0312] 0.1 g of VA-058 equivalent to 0.1 mol of the anionic group
content of 100 g of pigment particles P3 was added.
Microencapsulated Pigment MCP 2-8:
[0313] 0.15 g of VA-046B equivalent to 0.1 mol of the anionic group
content of 100 g of pigment particles P4 was added.
Microencapsulated Pigment MCP 2-9:
[0314] 0.73 g of VA-044 equivalent to 0.5 mol of the anionic group
content of 100 g of pigment particles P5 was added.
[0315] The aspect ratio and Zingg index of the resulting
microencapsulated pigment MCP 2-1 to -9 are shown in Table 2.
TABLE-US-00002 TABLE 2 (unit of amount of component: g) MCP MCP MCP
MCP MCP MCP MCP MCP MCP 2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-8 2-9
Anionic-Hydrophilized P1 (black) 100 100 Pigment P2 (black) 100 100
P3 (cyan) 100 100 P4 (yellow) 100 100 P5 (magenta) 100 Cationic
V-50 1.63 Polymerization VA-060 0.58 1.48 Initiator VA-058 0.70
0.10 VA-046B 0.75 0.15 VA-044 0.73 0.73 Hydrophilic Monomer
Methacrylic acid 3 5 3 5 2-Sulfoethyl methacrylate 5 10 7 5 5
2-Acrylamido-2- 7 5 8 6 methylpropanesulfonic acid Vinylsulfonic
acid 5 5 5 2-Hydroxyethyl 5 10 methacrylate Tetraethylene 7 4
glycol monomethacrylate N-vinylpyrrolidone 2 3 Comonomer Styrene 10
15 10 10 5 Benzyl methacrylate 7 20 15 7 Phenoxyethyl methacrylate
7 3 5 n-Butyl acrylate 10 10 5 5 2-Ethylhexyl methacrylate 10 10 10
10 3 10 Butoxymethyl methacrylate 10 5 3 10 Polymerizable surface
Adeka Reasope SE-10N 10 5 5 5 3 active agent Aqualon HS-10 10 5 5 5
3 Polymerizable surface Adeka Reasope SE-10N 1.2 1.1 0.9 0.5 0.7
active agent (for Aqualon HS-10 0.72 0.94 0.66 0.82 monomer
emulsification) Ion-exchanged water 400 400 400 400 400 400 400 400
400 Glycerin 50 50 50 50 50 50 50 50 50 Aspect ratio 1.0 1.0 1.0
1.0 1.0 1.0 1.0 1.0 1.0 Zingg index 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
1.0
Preparation of Microencapsulated Pigment MCP 1-9 to -12:
[0316] MCP 1-9 (microencapsulated black pigment), MCP 1-10
(microencapsulated cyan pigment), MCP 1-11 (microencapsulated
magenta pigment), and MCP 1-12 (microencapsulated yellow pigment)
were prepared in accordance with the process taught in
JP-A-10-140065 as follows.
Preparation of MCP 1-9:
[0317] Into a flask was put 250 g of methyl ethyl ketone and heated
up to 75.degree. C. while stirring in a nitrogen stream. A mixture
consisting of 85 g of n-butyl methacrylate, 90 g of n-butyl
acrylate, 40 g of 2-hydroxyethyl methacrylate, 25 g of methacrylic
acid, and 20 g of a polymerization initiator Perbutyl O (t-butyl
peroxyoctoate available from NOF Corp.) was added thereto dropwise
over a period of 2 hours. After the dropwise addition, the reaction
was continued for 15 hours to obtain a solution of a vinyl
polymer.
[0318] In a stainless steel beaker were charged 8 g of the polymer
solution, 0.4 g of dimethylethanolamine, and 8 g of a black pigment
(MA-100 from Mitsubishi Chemical Corp.), and ion-exchanged water
was added to make 40 g. The mixture was kneaded in a sand mill
together with 250 g of zirconia beads having an average particle
size of 0.5 mm for 4 hours. The zirconia beads were separated by
filtration to give an aqueous dispersion in which a dispersion of
the base-neutralized carboxyl-containing polymer and the pigment
was dispersed in water. The dispersion was put into a dispersing
machine, and a 1N hydrochloric acid aqueous solution was added
thereto while stirring at room temperature until the resin was
insolubilized and adsorbed onto the pigment. The pH of the system
was 3 to 5. The aqueous medium containing the polymer-adsorbed
pigment was filtered by suction, and the filter cake was washed
with water. A 10% sodium hydroxide aqueous solution was added to
the wet cake while stirring in a disperser until the pH rose to 8.5
to 9.5. After stirring for an additional 1 hour period,
ion-exchanged water was added to give a solids content of 20% to
obtain microencapsulated black pigment MCP 1-9, which was found to
have an aspect ratio of 1.4 and a Zingg index of 1.4.
Preparation of MCP 1-10:
[0319] Into a flask was put 250 g of methyl ethyl ketone and heated
up to 75.degree. C. while stirring in a nitrogen stream. A mixture
consisting of 155 g of n-butyl methacrylate, 20 g of n-butyl
acrylate, 35 g of 2-hydroxyethyl methacrylate, 40 g of methacrylic
acid, and 5 g of a polymerization initiator Perbutyl O was added
thereto dropwise over a period of 2 hours. After the dropwise
addition, the reaction was continued for 15 hours to obtain a
solution of a vinyl polymer.
[0320] Ten grams of the polymer solution, 7 g of a cyan pigment
(C.I. Pigment Blue 15:3), 40 g of methyl ethyl ketone, and 150 g of
ceramic beads having an average particle size of 0.5 mm were put
into a stainless steel container of a bead mill and dispersed. The
ceramic beads were separated by filtration to obtain a paste for
microencapsulated pigment preparation.
[0321] Twenty grams of the resulting paste and 0.2 g of
diethanolamine were mixed to make an organic solvent phase. While
the organic solvent phase was stirred under ultrasonication, 25 g
of ion-exchanged water was added thereto dropwise over 20 minutes
to cause phase inversion of emulsion to obtain an aqueous
dispersion of a microencapsulated pigment.
[0322] The resulting dispersion was distilled at 85.degree. C. to
remove the solvent to yield microencapsulated cyan pigment MCP
1-10, which was found to have an aspect ratio of 1.4 and a Zingg
index of 1.4.
Preparation of MCP 1-11:
[0323] Into a flask was put 250 g of methyl ethyl ketone and heated
up to 75.degree. C. while stirring in a nitrogen stream. A mixture
consisting of 70 g of n-butyl methacrylate, 58 g of n-butyl
acrylate, 35 g of 2-hydroxyethyl methacrylate, 35 g of acrylic
acid, and 20 g of a polymerization initiator Perbutyl O was added
thereto dropwise over a period of 2 hours. After the dropwise
addition, the reaction was continued for 15 hours to obtain a vinyl
polymer solution.
[0324] In a stainless steel beaker were charged 15 g of the polymer
solution, 0.8 g of dimethylethanolamine, and 15 g of a magenta
pigment (C.I. Pigment Red 122), and ion-exchanged water was added
to make 75 g. The mixture was kneaded in a sand mill together with
250 g of zirconia beads having an average particle size of 0.5 nm
for 4 hours. The zirconia beads were separated by filtration to
give an aqueous dispersion in which a dispersion of the
base-neutralized carboxyl-containing polymer and the pigment was
dispersed in water. A 1N hydrochloric acid aqueous solution was
added to the dispersion while stirring at room temperature in a
disperser until the resin was insolubilized and adsorbed onto the
pigment. The pH of the system was 3 to 5. The aqueous medium
containing the polymer-adsorbed pigment was filtered by suction,
and the filter cake was washed with water to obtain a
water-containing cake. A 10% sodium hydroxide aqueous solution was
added to the wet cake while stirring in a disperser until the pH
rose to 8.5 to 9.5. The stirring was continued for an additional 1
hour, and ion-exchanged water was added to give a solids content of
20% to obtain microencapsulated magenta pigment MCP 1-11, which was
found to have an aspect ratio of 1.4 and a Zingg index of 1.4.
Preparation of MCP 1-12:
[0325] Into a flask was put 250 g of methyl ethyl ketone and heated
up to 75.degree. C. while stirring in a nitrogen stream. A mixture
consisting of 170 g of n-butyl methacrylate, 5 g of n-butyl
acrylate, 35 g of 2-hydroxyethyl methacrylate, 35 g of acrylic
acid, and 20 g of a polymerization initiator Perbutyl O was added
thereto dropwise over 2 hours. After the dropwise addition, the
reaction was continued for an additional 15 hour period to obtain a
vinyl polymer solution.
[0326] In a stainless steel beaker were charged 15 g of the polymer
solution, 0.8 g of dimethylethanolamine, and 15 g of a yellow
pigment (C.I. Pigment Yellow 110), and ion-exchanged water was
added to make 75 g. The mixture was kneaded in a sand mill together
with 250 g of zirconia beads having an average particle size of 0.5
mm for 4 hours. The zirconia beads were separated by filtration to
give an aqueous dispersion in which a dispersion of the
base-neutralized carboxyl-containing polymer and the pigment was
dispersed in water. While the dispersion was stirred in a disperser
at ambient temperature, a 1N hydrochloric acid aqueous solution was
added thereto until the resin was insolubilized and adsorbed onto
the pigment. The pH of the system was 3 to 5. The aqueous medium
containing the polymer-adsorbed pigment was filtered by suction,
and the filter cake was washed with water to obtain a
water-containing cake. A 10% sodium hydroxide aqueous solution was
added to the wet cake while stirring in a disperser until the pH
rose to 8.5 to 9.5. The stirring was continued for an additional 1
hour, and ion-exchanged water was added to give a solids content of
20% to obtain microencapsulated yellow pigment MCP 1-12, which was
found to have an aspect ratio of 1.4 and a Zingg index of 1.4.
<Preparation of Polymeric Azo Initiator>
(1) Preparation of Polymeric Azo Initiator 1:
[0327] Polymeric azo initiators for use in the invention were
synthesized by the process disclosed in Example 1 of JP-A-12-53716.
Specifically, 4,4'-Azobis(4-cyanopentanoic acid),
.alpha.,.omega.-bis(polyoxyethylene)polydimethylsiloxane (number
average molecular weight: 1400), and 4-dimethylaminopyridine were
dissolved in acetonitrile, and dicyclohexylcarbodiimide was added
thereto. The system was allowed to react at room temperature. The
precipitated crystals were removed by filtration. The filtrate was
concentrated to dryness to give a polymeric azo initiator having an
organopolysiloxane moiety and a polyoxyalkylene moiety in its
molecule (designated polymeric azo initiator 1).
(2) Preparation of Polymeric Azo Initiator 2:
[0328] 4,4'-Azobis(4-cyanopentanoic acid), a polyethylene
glycol-polypropylene glycol block copolymer represented by formula
(11b): ##STR19## and 4-dimethylaminopyridine were dissolved in
acetonitrile, and dicyclohexylcarbodiimide was added thereto. The
system was allowed to react at room temperature. The precipitated
crystals were removed by filtration. The filtrate was concentrated
to dryness to give a polymeric azo initiator having a polyethylene
glycol moiety and a polypropylene glycol moiety in its molecule
(designated polymeric azo initiator 2). Preparation of
Microencapsulated Pigments MCP 3-1 to -15: (1) Preparation of
Microencapsulated Pigment MCP 3-1:
[0329] A hundred grams of hydrophilized black pigment particles P1,
30 g of polymeric azo initiator 1, and 500 g of ion-exchanged water
were put into a reaction vessel equipped with an ultrasonic
generator, a stirrer, a temperature controller, a reflux condenser,
and a dropping funnel. The mixture was stirred under
ultrasonication. To the mixture were added 15 g of a polymerizable
surface active agent represented by formula (31a) (SE-10N,
available from Asahi Denka Co., Ltd.), 15 g of 2-sulfoethyl
methacrylate as a hydrophilic monomer, and 300 g of ion-exchanged
water. After the mixture was stirred well, the monomers were
copolymerized at 70.degree. C. for 2 hours while stirring and
ultrasonicating. The resulting microencapsulated pigment dispersion
was adjusted to a pH of 7 to 9 with a potassium hydroxide aqueous
solution. The dispersion was filtered through a 1 .mu.m membrane
filter to remove coarse particles to obtain a dispersion of
microencapsulated black pigment (designated microencapsulated
pigment MCP 3-1), which was found to have an aspect ratio of 1.0
and a Zingg index of 1.0.
(2) Preparation of Microencapsulated Pigment MCP 3-2:
[0330] A hundred grams of hydrophilized black pigment particles P1,
30 g of polymeric azo initiator 2, and 500 g of ion-exchanged water
were put into a reaction vessel equipped with an ultrasonic
generator, a stirrer, a temperature controller, a reflux condenser,
and a dropping funnel. The mixture was stirred under
ultrasonication. To the mixture were added 15 g of a polymerizable
surface active agent represented by formula (31a) (SE-10N,
available from Asahi Denka Co., Ltd.), 10 g of sodium
vinylsulfonate as a hydrophilic monomer, 5 g of diethylene glycol
dimethacrylate as a crosslinking agent, and 300 g of ion-exchanged
water. After the mixture was stirred well, the monomers were
copolymerized at 70.degree. C. for 2 hours while stirring and
ultrasonicating. The resulting microencapsulated pigment dispersion
was adjusted to a pH of 7 to 9 with a potassium hydroxide aqueous
solution. The dispersion was filtered through a 1 .mu.m membrane
filter to remove coarse particles to obtain a dispersion of
microencapsulated black pigment (designated microencapsulated
pigment MCP 3-2), which was found to have an aspect ratio of 1.0
and a Zingg index of 1.0.
(3) Preparation of Microencapsulated Pigment MCP 3-3:
[0331] A hundred grams of hydrophilized black pigment particles P1,
30 g of polymeric azo initiator 1, and 500 g of ion-exchanged water
were put into a reaction vessel equipped with an ultrasonic
generator, a stirrer, a temperature controller, a reflux condenser,
and a dropping funnel. The mixture was stirred under
ultrasonication. To the mixture were added 15 g of a polymerizable
surface active agent represented by formula (31a) (SE-10N,
available from Asahi Denka Co., Ltd.), 5 g of
2-acrylamido-2-methylpropanesulfonic acid as a hydrophilic monomer,
4.2 g of methacrylic acid as a hydrophilic monomer, 6.3 g of
glycidyl methacrylate as a crosslinking agent, and 300 g of
ion-exchanged water. After the mixture was stirred well, the
monomers were copolymerized at 70.degree. C. for 3 hours while
stirring and ultrasonicating. The resulting microencapsulated
pigment dispersion was adjusted to a pH of 7 to 9 with a potassium
hydroxide aqueous solution. The dispersion was filtered through a 1
.mu.m membrane filter to remove coarse particles to obtain a
dispersion of microencapsulated black pigment (designated
microencapsulated pigment MCP 3-3), which was found to have an
aspect ratio of 1.0 and a Zingg index of 1.0.
(4) Preparation of Microencapsulated Pigment MCP 3-4:
[0332] Pigment microencapsulation was carried out in the same
manner as for microencapsulated pigment MCP 3-1, except for
replacing hydrophilized black pigment P1 with hydrophilized black
pigment P2. The resulting microencapsulated pigment dispersion was
adjusted to pH 7 to 9 with a potassium hydroxide aqueous solution.
The dispersion was filtered through a 1 .mu.m membrane filter to
remove coarse particles to obtain a dispersion of microencapsulated
black pigment (designated microencapsulated pigment MCP 3-4), which
was found to have an aspect ratio of 1.0 and a Zingg index of
1.0.
(5) Preparation of Microencapsulated Pigment MCP 3-5:
[0333] Pigment microencapsulation was carried out in the same
manner as for microencapsulated pigment MCP 3-2, except for
replacing hydrophilized black pigment P1 with hydrophilized black
pigment P2. The resulting microencapsulated pigment dispersion was
adjusted to pH 7 to 9 with a potassium hydroxide aqueous solution.
The dispersion was filtered through a 1 .mu.m membrane filter to
remove coarse particles to obtain a dispersion of microencapsulated
black pigment (designated microencapsulated pigment MCP 3-5), which
was found to have an aspect ratio of 1.0 and a Zingg index of
1.0.
(6) Preparation of Microencapsulated Pigment MCP 3-6:
[0334] Pigment microencapsulation was carried out in the same
manner as for microencapsulated pigment MCP 3-3, except for
replacing hydrophilized black pigment P1 with hydrophilized black
pigment P2. The resulting microencapsulated pigment dispersion was
adjusted to pH 7 to 9 with a potassium hydroxide aqueous solution.
The dispersion was filtered through a 1 .mu.m membrane filter to
remove coarse particles to obtain a dispersion of microencapsulated
black pigment (designated microencapsulated pigment MCP 3-6), which
was found to have an aspect ratio of 1.0 and a Zingg index of
1.0.
(7) Preparation of microencapsulated pigment MCP 3-7:
[0335] A hundred grams of hydrophilized cyan pigment particles P3,
30 g of polymeric azo initiator 1, and 500 g of ion-exchanged water
were put into a reaction vessel equipped with an ultrasonic
generator, a stirrer, a temperature controller, a reflux condenser,
and a dropping funnel. The mixture was stirred under
ultrasonication. To the mixture were added 15 g of a polymerizable
surface active agent (New Frontier N-177E, available from Daiichi
Kogyo Yakuhin Co., Ltd.), 15 g 2-sulfoethyl methacrylate as a
hydrophilic monomer, and 300 g of ion-exchanged water. After the
mixture was stirred well, the monomers were copolymerized at
70.degree. C. for 2 hours while stirring and ultrasonicating. The
resulting microencapsulated pigment dispersion was adjusted to a pH
of 7 to 9 with a potassium hydroxide aqueous solution. The
dispersion was filtered through a 1 .mu.m membrane filter to remove
coarse particles to obtain a dispersion of microencapsulated cyan
pigment (designated microencapsulated pigment MCP 3-7), which was
found to have an aspect ratio of 1.0 and a Zingg index of 1.0.
(8) Preparation of Microencapsulated Pigment MCP 3-8:
[0336] A hundred grams of hydrophilized magenta pigment particles
P5, 30 g of polymeric azo initiator 2, and 500 g of ion-exchanged
water were put into a reaction vessel equipped with an ultrasonic
generator, a stirrer, a temperature controller, a reflux condenser,
and a dropping funnel. The mixture was stirred under
ultrasonication. To the mixture were added 15 g of a polymerizable
surface active agent Aqualon HS-10 (available from Daiichi Kogyo
Yakuhin Co., Ltd.), 10 g sodium vinylsulfonate as a hydrophilic
monomer, 5 g of 1,6-hexanediol diacrylate as a crosslinking agent,
and 300 g of ion-exchanged water. After the mixture was stirred
well, the monomers were copolymerized at 70.degree. C. for 2 hours
while stirring and ultrasonicating. The resulting microencapsulated
pigment dispersion was adjusted to a pH of 7 to 9 with a potassium
hydroxide aqueous solution. The dispersion was filtered through a 1
.mu.m membrane filter to remove coarse particles to obtain a
dispersion of microencapsulated magenta pigment (designated
microencapsulated pigment MCP 3-8), which was found to have an
aspect ratio of 1.0 and a Zingg index of 1.0.
(9) Preparation of Microencapsulated Pigment MCP 3-9:
[0337] A hundred grams of hydrophilized yellow pigment particles
P4, 30 g of polymeric azo initiator 1, and 500 g of ion-exchanged
water were put into a reaction vessel equipped with an ultrasonic
generator, a stirrer, a temperature controller, a reflux condenser,
and a dropping funnel. The mixture was stirred under
ultrasonication. To the mixture were added 15 g of a polymerizable
surface active agent represented by formula (31a) (SE-10N,
available from Daiichi Kogyo Yakuhin Co., Ltd.), 5 g of
N-vinyl-2-pyrrolidine as a hydrophilic monomer, 4.2 g of
methacrylic acid as a hydrophilic monomer, 6.3 g of glycidyl
methacrylate as a crosslinking agent, and 300 g of ion-exchanged
water. After the mixture was stirred well, the monomers were
copolymerized at 70.degree. C. for 3 hours while stirring and
ultrasonicating. The resulting microencapsulated pigment dispersion
was adjusted to a pH of 7 to 9 with a potassium hydroxide aqueous
solution. The dispersion was filtered through a 1 .mu.m membrane
filter to remove coarse particles to obtain a dispersion of
microencapsulated yellow pigment (designated microencapsulated
pigment MCP 3-9), which was found to have an aspect ratio of 1.0
and a Zingg index of 1.0.
(10) Preparation of Microencapsulated Pigment MCP 3-10:
[0338] A hundred grams of carbon black (Raven C, available from
Columbian Carbon) and 30 g of polymeric azo initiator 1 were
dispersed in 500 g of ion-exchanged water in Eiger Motor Mill M250
(from Eiger Japan) at a bead loading of 70% and an agitation speed
of 5000 rpm for 1 hour while cooling with cooling water. The
resulting dispersion was put into a reaction vessel equipped with
an ultrasonic generator, a stirrer, a temperature controller, a
reflux condenser, and a dropping funnel, followed by stirring and
ultrasonication. To the dispersion were added 15 g of a
polymerizable surface active agent of formula (31a) (SE-10N, from
Asahi Denka Co., Ltd.), 15 g of 2-sulfoethyl methacrylate as a
hydrophilic monomer, and 300 g of ion-exchanged water, followed by
stirring well. The reaction system was allowed to polymerize at
70.degree. C. for 2 hours while stirring and ultrasonicating. The
resulting microencapsulated pigment dispersion was adjusted to a pH
of 7 to 9 with a potassium hydroxide aqueous solution. The
dispersion was filtered through a 1 .mu.m membrane filter to remove
coarse particles to obtain a dispersion of microencapsulated carbon
black pigment (designated microencapsulated pigment MCP 3-10),
which was found to have an aspect ratio of 1.0 and a Zingg index of
1.0.
(11) Preparation of Microencapsulated Pigment MCP 3-11:
[0339] A hundred grams of carbon black (Raven C, available from
Columbian Carbon) and 30 g of polymeric azo initiator 2 were
dispersed in 500 g of ion-exchanged water in Eiger Motor Mill M250
(from Eiger Japan) at a bead loading of 70% and an agitation speed
of 5000 rpm for 1 hour while cooling with cooling water. The
resulting dispersion was put into a reaction vessel equipped with
an ultrasonic generator, a stirrer, a temperature controller, a
reflux condenser, and a dropping funnel and stirred under
ultrasonication. To the dispersion were added 15 g of a
polymerizable surface active agent of formula (31a) (SE-10N, from
Asahi Denka Co., Ltd.), 10 g of sodium vinylsulfonate as a
hydrophilic monomer, 5 g of diethylene glycol dimethacrylate as a
crosslinking agent, and 300 g of ion-exchanged water, followed by
stirring well. The reaction system was allowed to polymerize at
70.degree. C. for 2 hours while stirring and ultrasonicating. The
resulting microencapsulated pigment dispersion was adjusted to a pH
of 7 to 9 with a potassium hydroxide aqueous solution. The
dispersion was filtered through a 1 .mu.m membrane filter to remove
coarse particles to obtain a dispersion of microencapsulated black
pigment (designated microencapsulated pigment MCP 3-11), which was
found to have an aspect ratio of 1.0 and a Zingg index of 1.0.
(12) Preparation of Microencapsulated Pigment MCP 3-12:
[0340] A hundred grams of carbon black (Raven C, available from
Columbian Carbon) and 30 g of polymeric azo initiator 1 were
dispersed in 500 g of ion-exchanged water in Eiger Motor Mill M250
(from Eiger Japan) at a bead loading of 70% and an agitation speed
of 5000 rpm for 1 hour while cooling with cooling water. The
resulting dispersion was put into a reaction vessel equipped with
an ultrasonic generator, a stirrer, a temperature controller, a
reflux condenser, and a dropping funnel and stirred under
ultrasonication. To the dispersion were added 15 g of a
polymerizable surface active agent of formula (31a) (SE-10N, from
Asahi Denka Co., Ltd.), 5 g of 2-acrylamido-2-methylpropanesulfonic
acid as a hydrophilic monomer, 4.2 g of methacrylic acid as a
hydrophilic monomer, 6.3 g of glycidyl methacrylate as a
crosslinking agent, and 300 g of ion-exchanged water, followed by
stirring well. The reaction system was allowed to polymerize at
70.degree. C. for 3 hours while stirring and ultrasonicating. The
resulting microencapsulated pigment dispersion was adjusted to a pH
of 7 to 9 with a potassium hydroxide aqueous solution. The
dispersion was filtered through a 1 .mu.m membrane filter to remove
coarse particles to obtain a dispersion of microencapsulated black
pigment (designated microencapsulated pigment MCP 3-12), which was
found to have an aspect ratio of 1.0 and a Zingg index of 1.0.
(13) Preparation of Microencapsulated Pigment MCP 3-13:
[0341] A hundred grams of C.I. Pigment Blue 15 (Fastgen Blue TGR,
available from Dainippon Ink & Chemicals, Inc.) and 30 g of
polymeric azo initiator 1 were dispersed in 500 g of ion-exchanged
water in Eiger Motor Mill M250 (from Eiger Japan) at a bead loading
of 70% and an agitation speed of 5000 rpm for 1 hour while cooling
with cooling water. The resulting-dispersion was put into a
reaction vessel equipped with an ultrasonic generator, a stirrer, a
temperature controller, a reflux condenser, and a dropping funnel
and stirred under ultrasonication. To the dispersion were added 15
g of a polymerizable surface active agent New Frontier N-177E (from
Daiichi Kogyo Yakuhin Co., Ltd.), 15 g of 2-sulfoethyl methacrylate
as a hydrophilic monomer, and 300 g of ion-exchanged water,
followed by stirring well. The reaction system was allowed to
polymerize at 70.degree. C. for 2 hours while stirring and
ultrasonicating. The resulting microencapsulated pigment dispersion
was adjusted to a pH of 7 to 9 with a potassium hydroxide aqueous
solution. The dispersion was filtered through a 1 .mu.m membrane
filter to remove coarse particles to obtain a dispersion of
microencapsulated cyan pigment (designated microencapsulated
pigment MCP 3-13), which was found to have an aspect ratio of 1.0
and a Zingg index of 1.0.
(14) Preparation of Microencapsulated Pigment MCP 3-14:
[0342] A hundred grams of C.I. Pigment Red 122 (Fastgen Super
Magenta RTS, available from Dainippon Ink & Chemicals Inc.) and
30 g of polymeric azo initiator 2 were dispersed in 500 g of
ion-exchanged water in Eiger Motor Mill M250 (from Eiger Japan) at
a bead loading of 70% and an agitation speed of 5000 rpm for 1 hour
while cooling with cooling water. The resulting dispersion was put
into a reaction vessel equipped with an ultrasonic generator, a
stirrer, a temperature controller, a reflux condenser, and a
dropping funnel and stirred under ultrasonication. To the
dispersion were added 15 g of a polymerizable surface active agent
Aqualon HS-10 (from Daiichi Kogyo Yakuhin Co., Ltd.), 10 g of
sodium vinylsulfonate as a hydrophilic monomer, 5 g of
1,6-hexanediol diacrylate as a crosslinking agent, and 300 g of
ion-exchanged water, followed by stirring well. The reaction system
was allowed to polymerize at 70.degree. C. for 2 hours while
stirring and ultrasonicating. The resulting microencapsulated
pigment dispersion was adjusted to a pH of 7 to 9 with a potassium
hydroxide aqueous solution. The dispersion was filtered through a 1
.mu.m membrane filter to remove coarse particles to obtain a
dispersion of microencapsulated magenta pigment (designated
microencapsulated pigment MCP 3-14), which was found to have an
aspect ratio of 1.0 and a Zingg index of 1.0.
(15) Preparation of Microencapsulated Pigment MCP 3-15:
[0343] A hundred grams of C.I. Pigment Yellow 17 (Fastgen (Symuler
Fast Yellow 8GF, available from Dainippon Ink & Chemicals Inc.)
and 30 g of polymeric azo initiator 1 were dispersed in 500 g of
ion-exchanged water in Eiger Motor Mill M250 (from Eiger Japan) at
a bead loading of 70% and an agitation speed of 5000 rpm for 1 hour
while cooling with cooling water. The resulting dispersion was put
into a reaction vessel equipped with an ultrasonic generator, a
stirrer, a temperature controller, a reflux condenser, and a
dropping funnel and stirred under ultrasonication. To the
dispersion were added 15 g of a polymerizable surface active agent
represented by formula (31a) (SE-10N, available from Asahi Denka
Co., Ltd.), 5 g of N-vinyl-2-pyrrolidone as a hydrophilic monomer,
4.2 g of methacrylic acid as a hydrophilic monomer, 6.3 g of
glycidyl methacrylate as a crosslinking agent, and 300 g of
ion-exchanged water, followed by stirring well. The reaction system
was allowed to polymerize at 70.degree. C. for 3 hours while
stirring and ultrasonicating. The resulting microencapsulated
pigment dispersion was adjusted to a pH of 7 to 9 with a potassium
hydroxide aqueous solution. The dispersion was filtered through a 1
.mu.m membrane filter to remove coarse particles to obtain a
dispersion of microencapsulated yellow pigment (designated
microencapsulated pigment MCP 3-15), which was found to have an
aspect ratio of 1.0 and a Zingg index of 1.0.
[0344] It is seen that the microencapsulated pigments of the
present invention (MCP 1-1 to -8, -13 to -15, MCP 2-1 to -9, and
MCP 3-1 to -9) had an aspect ratio of 1.0 and a Zingg index of 1.0,
i.e., a truly spherical shape, whereas the comparative
microencapsulated pigments (MCP 1-9 to -12) had an aspect ratio
greater than 1.3 and a Zingg index of 1.3 or greater, i.e., a
non-truly spherical shape. The aspect ratio and the Zingg index
were obtained from the major and minor diameters and the thickness
of dispersed particles (the aqueous dispersion was 100-fold diluted
with ion-exchanged water and dried) as observed under a
transmission electron microscope and a scanning electron
microscope.
Preparation of Ink Jet Recording Ink:
EXAMPLES 1-1 TO 1-11 AND 2-1 TO 2-13
[0345] Ink jet recording inks were prepared according to the
formulations shown in Tables 3 and 4 below. TABLE-US-00003 TABLE 3
(unit: wt %) Example 1-1 1-2 1-3 1-4 1-5 1-6 1-7 1-8 1-9 1-10 1-11
Micro- MCP 1-1 8 encapsulated MCP 1-2 6 Pigment MCP 1-3 4 MCP 1-4 6
MCP 1-5 10 MCP 1-6 8 MCP 1-7 6 MCP 1-8 8 MCP 1-13 8 MCP 1-14 8 MCP
1-15 8 Wetting Agent Glycerin 15 12 15 15 12 10 10 10 12 12 12
Diethylene glycol 5 2 5 Penetrant Diethylene glycol monobutyl ether
5 5 3 3 5 3 3 3 1,2-Hexanediol 6 6 3 3 5 3 3 3 Surfactant Surfynol
465 1 0.5 1 0.5 1 0.5 1 1 1 1 1 Polyoxyethylene nonylphenyl ether
0.5 1 0.5 0.5 pH Adjuster Potassium hydroxide 0.2 0.2 0.1 0.1 0.1
0.1 Propanolamine 3 3 3 2 2 Antiseptic Proxel XL 0.05 0.05 0.05
0.05 0.05 0.05 0.05 4,4-Dimethyloxazolidine 1 1 1 1 Solid wetting
Trimethylolpropane 8 10 agent 1,2,6-Hexanetriol 3 Water
Ion-exchanged water bal. bal. bal. bal. bal. bal. bal. bal. bal.
bal. bal.
[0346] TABLE-US-00004 TABLE 4 (unit: wt %) Example 2-1 2-2 2-3 2-4
2-5 2-6 2-7 2-8 2-9 2-10 2-11 2-12 2-13 Micro- MCP 2-1 (black) 8 8
encapsulated MCP 2-2 (black) 6 pigment MCP 2-3 (cyan) 6 MCP 2-4
(yellow) 6 MCP 2-5 (magenta) 10 MCP 2-6 (black) 8 MCP 2-7 (cyan) 6
8 MCP 2-8 (yellow) 8 8 MCP 2-9 (magenta) 8 8 Glycerin 15 15 12 15
15 12 13 12 15 15 15 15 15 Diethylene glycol 5 2 5 5
Trimethylolpropane 3 3 8 10 Diethylene glycol monobutyl ether 3 3 3
Triethylene glycol monobutyl ether 3 5 5 5 3 3 3 1,2-Hexanediol 5 5
5 5 5 3 4 4 4 1,2-Pentanediol 3 2 3 2 4
1,3-Dimethyl-2-imidazolidinone 4 5 2-Pyrrolidone 6 4 2 3 3 4 2 2 2
Maltitol 3 3 3 3 Xylitol 5 2 3 2 5 1 1 Sorbitol 3 3 2 1 2 Surfynol
465 1 1 1 1 1 1 3 Olfine E1010 1 1 1 1 1 1 1 1,2,6-Hexanetriol 3 3
3 Potassium hydroxide 0.1 0.2 0.2 0.1 0.1 0.2 0.1 0.1 0.1
Triethanolamine 3 2 3 3 2 2 2 Proxel XL-2 0.05 0.05 0.05 0.05 0.05
0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 Ion-exchanged water bal.
bal. bal. bal. bal. bal. bal. bal. bal. bal. bal. bal. bal.
EXAMPLE 3-1
[0347] A mixture consisting of 8 g (solid basis) of
microencapsulated pigment MCP 3-1, 12 g of glycerin, 5 g of
1,2-hexanediol, 0.3 g of an acetylene glycol surface active agent
Surfynol 104, and 0.7 g of an acetylene glycol surface active agent
Surfynol 485 was mixed with ion-exchanged water to make 100 g. The
mixture was adjusted to a pH of 7.5 by addition of
triethanolamine.
[0348] The mixture was stirred for 2 hours and filtered through a
stainless steel filter having a pore size of about 5 .mu.m to
prepare an ink jet printing ink.
EXAMPLES 3-2 TO 3-10
[0349] Ink jet printing inks were prepared in the same manner as in
Example 3-1 according to the formulations given in Table 5 below.
TABLE-US-00005 TABLE 5 (unit: wt %) Example 3-1 3-2 3-3 3-4 3-5 3-6
3-7 3-8 3-9 3-10 Micro-encapsulated MCP 3-1 8 8 pigment MCP 3-2 8
MCP 3-3 8 MCP 3-4 8 MCP 3-5 8 MCP 3-6 8 MCP 3-7 8 MCP 3-8 8 MCP 3-9
8 Glycerin 12 10 10 12 10 10 10 10 0 12 1,2-Hexanediol 5 5 3 5 5 3
5 5 3 5 Diethylene glycol monobutyl ether 5 5 5 Triethylene glycol
monobutyl ether 5 5 5 5 3 2-Pyrrolidone 2 2 2 2 Surfynol 104 0.3
0.3 Surfynol 485 0.7 0.7 Surfynol 465 1 1 1 1 1 Olfine E1010 1 1 1
Trimethylolpropane 10 Triethanolamine 0.4 0.4 0.4 0.4 KOH 0.1 0.1
0.1 0.1 0.1 0.1 Ion-exchanged water bal. bal. bal. bal. bal. bal.
bal. bal. bal. bal.
COMPARATIVE EXAMPLES 1-1 TO 1-13 AND 2-1 TO 2-13
[0350] Ink jet printing inks were prepared in accordance with the
formulations shown in Tables 6 to 9. TABLE-US-00006 TABLE 6 (unit:
wt %) Comparative Example 1-1 1-2 1-3 1-4 1-5 1-6 1-7 1-8 Micro-
MCP 1-9 4 8 encapsulated MCP 1-10 2 4 pigment MCP 1-11 2 8 MCP 1-12
2 6 Wetting Glycerin 15 15 12 12 15 10 10 15 agent Diethylene
glycol 5 5 Penetrant Diethylene glycol monobutyl ether 6 6 7.5 6
1,2-Hexanediol 6 6 7.5 6 Surface Surfynol 465 1 0.5 1 0.5 1 1 1 1
active agent Polyoxyethylene nonylphenyl ether 0.5 0.5 pH Adjuster
Potassium hydroxide 0.1 Propanolamine 2 3 3 3 3 3 3 Antiseptic
Proxel XL 0.05 0.05 0.05 0.05 4,4-Dimethyloxazolidine 1 1 1 1 Water
Ion-exchanged water bal. bal. bal. bal. bal. bal. bal. bal.
[0351] TABLE-US-00007 TABLE 7 (unit: wt %) Comparative Example 1-9
1-10 1-11 1-12 1-13 Pigment P1 8 P2 4 P3 6 P4 10 P5 8 Wetting
Glycerin 15 10 10 12 15 agent Diethylene glycol 2 2 Penetrant
Diethylene glycol 6 3 7.5 monobutyl ether 1,2-Hexanediol 3 6 7.5
Surface Surfynol 465 1 1 1 1 1 active agent Polyoxyethylene 0.5 0.5
nonylphenyl ether pH Adjuster Potassium hydroxide 0.5 0.5
Propanolamine 1 1 1 Antiseptic Proxel XL 0.05 0.05 0.05 4,4- 1 1
Dimethyloxazolidine Water Ion-exchanged water bal. bal. bal. bal.
bal.
[0352] TABLE-US-00008 TABLE 8 (unit: wt %) Comparative Example 2-1
2-2 2-3 2-4 2-5 Pigment Carbon black 8 8 C.I. Pigment Red 122 6
C.I. Pigment Blue 15:3 6 C.I. Pigment Yellow 185 6 Styrene-acrylic
acid copolymer 1 1 1 1 1 ammonium salt (mol. wt.: 7000; polymer
component: 38%) Glycerin 15 10 10 15 10 Diethylene glycol 10 8 8 10
8 1,2-Hexanediol 5 2-Pyrrolidone 2 2 2 Olfine E1010 1 1 Potassium
hydroxide 0.1 0.1 0.1 0.1 0.1 Proxel XL-2 0.05 0.05 0.05 0.05 0.05
Ion-exchanged water bal. bal. bal. bal. bal.
[0353] TABLE-US-00009 TABLE 9 (unit: wt %) Comparative Example 2-6
2-7 2-8 2-9 2-10 2-11 2-12 2-13 Microencapsulated MCP 1-9 (black) 4
8 Pigment MCP 1-10 (cyan) 3 8 MCP 1-11 (magenta) 3 8 MCP 1-12
(yellow) 3 8 Glycerin 15 15 15 15 15 10 10 15 Diethylene glycol 5 5
Trimethylolpropane 6 6 6 Diethylene glycol monobutyl ether 8
1,3-Dimethyl-2-imidazolidione 2 2 2-Pyrrolidone 2 2 Surfynol 465 1
1 1 1 1 1 1 1 Potassium hydroxide 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1
Proxel XL-2 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 Ion-exchanged
water bal. bal. bal. bal. bal. bal. bal. bal.
COMPARATIVE EXAMPLES 3-1 TO 3-12
[0354] Ink jet recording inks were prepared in the same manner as
in Example 3-1 according to the formulations given in Tables 10 and
11 below.
COMPARATIVE EXAMPLE 3-13
[0355] A hundred grams of carbon black (Raven C, from Columbian
Carbon), 70 g of a dispersant Joncryl J-62 (from Johnson Polymer),
40 g of a 10% sodium hydroxide aqueous solution, and 150 g of water
were mixed and dispersed in a ball mill together with zirconia
beads for 10 hours. The resulting dispersion was filtered through a
stainless steel filter having a pore size of about 5 .mu.m. The
filtrate was diluted with water to a pigment concentration of 20%
to prepare a carbon black dispersion. Thirty grams of the pigment
dispersion, 10 g of glycerin, 5 g of 2-pyrrolidone, and 4 g of
ethanol were mixed, and ion-exchanged water was added to make 100
g. The mixture was stirred for 2 hours and filtered through a
stainless steel filter having a pore size of about 5 .mu.m to
prepare an ink jet recording ink.
COMPARATIVE EXAMPLE 3-14
[0356] Thirty grams of the pigment dispersion prepared in
Comparative Example 3-1, 10 g of glycerin, and 7 g of triethylene
glycol monobutyl ether were mixed and adjusted to pH 7.5 with
triethanolamine. The mixture was stirred for 2 hours and filtered
through a stainless steel filter having a pore size of about 5
.mu.m to prepare an ink jet recording ink. TABLE-US-00010 TABLE 10
Comparative Example 3-1 3-2 3-3 3-4 3-5 3-6 Micro- MCP 3-10 8
encapsulated MCP 3-11 8 pigment MCP 3-12 8 MCP 3-13 8 MCP 3-14 8
MCP 3-15 8 Glycerin 12 10 10 10 10 10 1,2-Hexanediol 5 5 3 5 5 3
Diethylene glycol monobutyl 5 5 ether Triethylene glycol monobutyl
5 5 5 ether 2-Pyrrolidone 2 2 Surfynol 104 0.3 Surfynol 485 0.7
Surfynol 465 1 1 1 1 Olfine E1010 1 Triethanolamine 0.4 0.4
Potassium hydroxide 0.1 0.1 0.1 0.1 Ion-exchanged water bal. bal.
bal. bal. bal. bal.
[0357] TABLE-US-00011 TABLE 11 Comparative Example 3-7 3-8 3-9 3-10
3-11 3-12 Micro- MCP 3-10 4 encapsulated MCP 3-11 4 pigment MCP
3-12 4 MCP 3-13 4 MCP 3-14 4 MCP 3-15 4 Glycerin 12 10 10 10 10 10
1,2-Hexanediol 5 5 3 5 5 3 Diethylene glycol monobutyl 5 5 ether
Triethylene glycol monobutyl 5 5 5 ether 2-Pyrrolidone 2 2 Surfynol
104 0.3 Surfynol 485 0.7 Surfynol 465 1 1 1 1 Olfine E1010 1
Triethanolamine 0.4 0.4 Potassium hydroxide 0.1 0.1 0.1 0.1
Ion-exchanged water bal. bal. bal. bal. bal. bal.
[0358] The ink jet recording inks of Examples and Comparative
Examples and images printed with these inks were evaluated
according to the following methods. The results obtained are shown
in Tables 12 to 17.
1-1) Dispersibility-1
[0359] An ink sample was set in a rheometer (Physica MCR300,
supplied by Paar Physica), and the storage modulus (Pa) was
measured using a corn/plate measuring system CP 75-1 (Paar Physica)
having a radius of 37.5 mm and an angle of measuring corn of
1.degree.. The gap was set at 0.05 mm. Measurement was taken at
20.degree. C. at an angular speed varying from 0.5 to 5 rad/sec.
The storage moduli at 0.6 rad/sec (G'.sub..omega.=0.6) and 0.8
rad/sec (G'.sub..omega.=0.8) were recorded. The ink dispersibility
was rated A to D according to the following standard. [0360] A:
(log G'.sub..omega.=0.8-log G'.sub..omega.=0.6)/(log 0.8-log
0.6)=1.8 to 2.0 [0361] B: (log G'.sub..omega.=0.8-log
G'.sub..omega.=0.6)/(log 0.8-log 0.6)=1.6 to 1.8 [0362] C: (log
G'.sub..omega.=0.8-log G'.sub..omega.=0.6)/(log 0.8-log 0.6)=1.2 to
1.6 [0363] D: (log G'.sub..omega.=0.8-log G'.sub..omega.=0.6)/(log
0.8-log 0.6)<1.2 1-2) Dispersibility-2
[0364] The viscosity of an ink sample was measured with a rolling
ball viscometer AMVn (Anton Paar) at 20.degree. C. using a steel
ball having a diameter of 0.794 mm and a density of 7.850
g/cm.sup.3 and a capillary having an inner diameter of 0.9 mm
inclined at an angle of 70.degree., 60.degree., 50.degree.,
40.degree., and 30.degree.. The sin .theta. was plotted as abscissa
and the viscosity as ordinate. The dispersibility of the ink was
evaluated from the slope of the resulting sin .theta.-viscosity
curve and rated as follows. [0365] A: The slope is 0 to -0.05,
indicating Newtonian flow behavior and excellent dispersibility of
the sample. [0366] B: The slope is -0.05 to -0.1, indicating nearly
Newtonian flow behavior and good dispersibility of the sample.
[0367] C: The slope is -0.1 to -0.15, indicating non-Newtonian flow
behavior but slightly good dispersibility of the sample. [0368] D:
The slope is smaller than -0.15, indicating non-Newtonian flow
behavior. The sample fluid easily settles due to poor
dispersibility. 2) Dispersion Stability
[0369] An ink sample was put into a glass bottle, sealed, and
allowed to stand at 60.degree. C. for 2 weeks. The viscosity of the
sample before and after the standing was measured with Physica MCR
300 (Paar Physica) using a corn/plate measuring system CP 75-1
(Paar Physica) having a radius of 37.50 mm and an angle of
measuring corn of 1.degree.. The gap was set at 0.05 mm.
Measurement was taken at 20.degree. C. at a shear rate of 150
s.sup.-1. The dispersion stability was evaluated from the change in
viscosity and rated as follows. [0370] A: The change is smaller
than +0.1 mPas. [0371] B: The change is +0.1 mPas or greater and
smaller than +0.3 mPas. [0372] C: The change is +0.3 mPas or
greater. 3) Non-Settling Properties
[0373] Non-settling properties of the colorant in an ink were
evaluated from the back scattered and transmitted light intensity
distributions in the height direction of a sample as measured at
20.degree. C. with Turbiscan 2000, supplied by Formulaction.
Turbiscan 2000 comprises a reading head that vertically moves along
a cylindrical cell to scan the sample length, the reading head
having a transmission detector which monitors light transmitted
through the sample and a backscattering detector which receives
light backscattered by the sample. The reading head acquires
transmission and backscattering date every 40 .mu.m along the
sample height. The acquisition scan is then repeated over and over
at an arbitrary frequency so that any movement of particles or
change in particle diameter can be observed on the transmission and
backscattering data. The non-settling properties of the sample were
ranked A or B based on the following standard. [0374] A: No
settling occurs for more than 2 weeks. [0375] B: Settling occurs
after 2 weeks. 4) Image Density
[0376] Plain paper Xerox P (from Xerox Corp.) was printed solid on
an inkjet printer PM-720C (supplied by Seiko Epson Corp.) loaded
with an ink cartridge filled with each of the inks prepared in
Examples and Comparative Examples. The optical density (OD) of the
solid printed area was measured with a spectrophotometer Gretag
SPM-50 (supplied by GretagMacbeth GmbH) and rated as follows.
[0377] A: The OD of black ink is 1.4 or higher, or the OD of color
ink is 1.2 or higher. [0378] B: The OD of black ink is 1.3 or
higher and lower than 1.4, or the OD of color ink is 1.15 or higher
and lower than 1.2. [0379] C: The OD of black ink is lower than
1.3, or the OD of color ink is lower than 1.15. 5) Print
Quality
[0380] Large and small alphabet letters A,a to Z,z were printed on
various kinds of paper using the Epson inkjet printer PM-720C
loaded with an ink cartridge filled with each of the inks prepared
in Examples and Comparative Examples. The printed letters were
observed with the naked eye and ranked AA, A, B or C based on the
following standard. Printing papers used were Conqueror, Favorit,
Modo, Rapid Copy, EPSON EPP, Xerox P, Xerox 4042, Xerox 10, Neenha
Bond, Ricopy 6200, Yamayuri (regenerated paper), and Xerox R
(regenerated paper). All the papers except Yamayuri and Xerox R are
plain papers. [0381] AA: No feathering occurs on any paper. [0382]
A: Slight feathering is observed on two or three papers. [0383] B:
Slight feathering is observed on all papers. [0384] C: Appreciable
feathering is observed on all papers. 6) Color Developability
[0385] MC Semigloss Photo Paper (available from Seiko Epson Corp.)
and plain paper Xerox P (from Xerox Corp.) were each printed solid
on the Epson inkjet printer PM-720C loaded with an ink cartridge
filled with each of the inks prepared in Examples and Comparative
Examples. The C* value of the solid printed area was measured. The
color developability on plain paper was evaluated from the ratio of
the C* value on Xerox P to that on MC Semigloss Photo Paper
according to the following standard. [0386] A: 0.9 or higher [0387]
B: 0.8 or higher and lower than 0.9 [0388] C: lower than 0.8 7)
Abrasion Resistance
[0389] Super Fine Glossy Film (designed for inkjets, available from
Seiko Epson) was printed solid (printing duty ratio: 100%) in an
area of 10 mm.times.10 mm on the Epson inkjet printer PM-720C
loaded with an ink cartridge filled with each of the inks of
Examples and Comparative Examples. After the printed matter was
left to stand at 25.degree. C. for 1 hour, the printed area was
abraded with a water-based, fluorescent yellow marker pen ZEBRA PEN
2 (available from Zebra Pen Corp.) under a load of 500 g at a
stroke speed of 10 mm/sec, and occurrence of smearing was observed
and rated as follows. [0390] A: Two strokes causes no smearing.
[0391] B: One stroke causes no smearing, but two strokes causes
smearing. [0392] C: One stroke causes smearing. 8) Water
Resistance
[0393] One milliliter of ion-exchanged water was dropped on the
printed image of the printed matter obtained in (4) above
(evaluation of image density). After 20 minutes, the condition of
the printed image was observed with the naked eye and rated as
follows. [0394] A: No change occurs on all papers. [0395] B: The
colorant slightly dissolves but leaves letters legible. [0396] C:
The colorant dissolves and spreads to make letters illegible. 9)
Ejection Stability
[0397] Ruling lines 1 mm thick were printed on Super Fine (paper
designed for inkjets, available from Seiko Epson) by use of the
Epson inkjet printer PM-720 loaded with each ink of Examples and
Comparative Examples. Print defects, such as dot missing and dot
placement errors, were observed with the naked eye and rated on the
following basis. [0398] A: No dot missing nor dot placement errors
occur in obtaining 10000 or more prints. [0399] B: Dot missing or
dot placement errors occur in obtaining 1000 or more prints and
less than 10000 prints. [0400] C: Dot missing or dot placement
errors occur in obtaining 100 or more prints and less than 1000
prints. [0401] D: Dot missing or dot placement errors occur in
obtaining less than 100 prints. 10) Non-Clogging Properties
[0402] After the printing test in (5) above (evaluation of print
quality), the inkjet printer was switched off. After one week
suspension, the same printing test was carried out. The condition
of ink ejection was observed with the naked eye and rated as
follows. [0403] A: Printing is resumed normally on inputting image
signals without requiring a cleaning operation. [0404] B: Normal
printing starts after three or fewer cleaning operations. [0405] C:
Normal printing starts after six or fewer cleaning operations.
[0406] D: Normal printing does not start even after seven or more
cleaning operations. 11) Freedom from White Blank
[0407] Each of the plain papers used in (5) above (evaluation of
print quality) was printed solid on the Epson ink jet printer
PM-720C loaded with an ink cartridge filled with the ink of
Examples and Comparative Examples. The solid printed area was
inspected for what we call white blanks with the naked eye and
ranked as follows. White blanks as referred to herein are small
spots where the background color of the paper is exposed without
attachment of ink. [0408] A: White blanks are not observed. [0409]
B: White blanks are slightly observed. [0410] C: White blanks are
observed.
[0411] D: Many white blanks are observed. TABLE-US-00012 TABLE 12
Exam- Dis- Non- Print Water Non- ple persion settling Image qual-
Color Abrasion Resis- Ejection clogging White No. Dispersibility-1
Dispersibility-2 Stability Properties Density ity Developability
Resistance tance Stability Properties blanks 1-1 A A A A A AA A B A
A B A 1-2 A A A A A AA A B A A B A 1-3 B B B A A A A A A B B B 1-4
A A A A A AA A A A A B A 1-5 A A A A A AA A A A A B A 1-6 A A A A A
AA A B A A B A 1-7 A A A A A AA A B A A B A 1-8 A A A A A AA A B A
A B A 1-9 A A A A A AA A A A A A A 1-10 A A A A A AA A A A A A A
1-11 A A A A A AA A A A A A A
[0412] TABLE-US-00013 TABLE 13 Exam- Dis- Non- Print Water Non- ple
persion settling Image qual- Color Abrasion Resis- Ejection
clogging White No. Dispersibility-1 Dispersibility-2 Stability
Properties Density ity Developability Resistance tance Stability
Properties blanks 2-1 A A A A A AA -- A A A B A 2-2 B B A A A AA --
A A A A A 2-3 A A A A A AA -- A A A A A 2-4 A A A A A AA A A A A A
A 2-5 A A A A A AA A A A A B A 2-6 A A A A A AA A A A A A A 2-7 A A
A A A AA A A A A A A 2-8 A A A A A AA A A A A A A 2-9 A A A A A AA
A A A A B A 2-10 A A A A A AA A A A A B A 2-11 A A A A A AA A A A A
A A 2-12 A A A A A AA A A A A A A 2-13 A A A A A AA A A A A A A
[0413] TABLE-US-00014 TABLE 14 Exam- Dis- Non- Print Water Non- ple
persion settling Image qual- Color Abrasion Resis- Ejection
clogging White No. Dispersibility-1 Dispersibility-2 Stability
Properties Density ity Developability Resistance tance Stability
Properties blanks 3-1 A A A A A AA A A A A B A 3-2 A A A A A AA A A
A A B A 3-3 A A A A A AA A A A A B A 3-4 A A A A A AA A A A A B A
3-5 A A A A A AA A A A A B A 3-6 A A A A A AA A A A A B A 3-7 A A A
A A AA A A A A B A 3-8 A A A A A AA A A A A B A 3-9 A A A A A AA A
A A A B A 3-10 A A A A A AA A A A A A A
[0414] TABLE-US-00015 TABLE 15 Comp. Exam- Dis- Non- Print Water
Non- ple persion settling Image qual- Color Abrasion Resis-
Ejection clogging White No. Dispersibility-1 Dispersibility-2
Stability Properties Density ity Developability Resistance tance
Stability Properties blanks 1-1 B B B A C C -- B A B C C 1-2 A A A
A C C B B A A B C 1-3 A A A A C C B B A A B C 1-4 A A A A C C B B A
A B C 1-5 C C C B B C -- A A C C C 1-6 B B B A B C B A A B C C 1-7
C C C B B C B A A C C C 1-8 B B B A B C B A A B C C 1-9 A A A A A A
-- C A A A A 1-10 A A A A A A -- C A A A A 1-11 A A A A A A A C A A
A A 1-12 A A A A A A A C A A A A 1-13 A A A A A A A C A A A A
[0415] TABLE-US-00016 TABLE 16 Comp. Exam- Dis- Non- Print Water
Non- ple persion settling Image qual- Color Abrasion Resis-
Ejection clogging White No. Dispersibility-1 Dispersibility-2
Stability Properties Density ity Developability Resistance tance
Stability Properties blanks 2-1 D D C B B B -- C A D C C 2-2 C C C
B C C -- C A C C D 2-3 C C C B C C C C A C C D 2-4 D D C B B B B C
A D C C 2-5 C B C B C C C C A C C D 2-6 B B B A C C -- B A B C C
2-7 B B B A C C B B A B C C 2-8 B B B A C C B B A B C C 2-9 B C B A
C C B B A B C C 2-10 C C C B B C -- A A C C C 2-11 C C C B B C B A
A C B B 2-12 C C C B B C B A A C B B 2-13 C C C B B C B A A C B
B
[0416] TABLE-US-00017 TABLE 17 Comp. Exam- Dis- Non- Print Water
Non- ple persion settling Image qual- Color Abrasion Resis-
Ejection clogging White No. Dispersibility-1 Dispersibility-2
Stability Properties Density ity Developability Resistance tance
Stability Properties blanks 3-1 B B B A A A -- A A B C B 3-2 B B B
A A A -- A A B C B 3-3 B B B A A A -- A A B C B 3-4 B B B A A A B A
A B C B 3-5 B B B A A A B A A B C B 3-6 B B B A A A B A A B C B 3-7
A A B A B A -- A A A C B 3-8 A A A A B A -- A A A C B 3-9 A A A A B
A -- A A A C B 3-10 A A A A B A B A A A C B 3-11 A A A A B A B A A
A C B 3-12 A A A A B A B A A A C B 3-13 D D C B B B -- C A D C C
3-14 C C C B C C -- C A C C D
[0417] As shown in Tables 12 through 17, the ink jet printing inks
of Examples were proved superior in all the tested attributes.
[0418] The inks of Examples 1-9 to 1-11, Comparative Examples 2-11
to 2-13 and Comparative Example 3-10, which contain a solid wetting
agent, gave particularly satisfactory results in the test of
non-clogging properties.
[0419] The inks of Comparative Examples 2-1 to 2-5, 3-13, and 3-14,
in which the pigment is dispersed by a dispersant, are found
insufficient in dispersibility, dispersion stability, image
density, print quality, color developability, abrasion resistance,
and ejection stability. The inks of Comparative Examples 1-1 to 1-4
and 2-6 to 2-9, which comprise a conventional microencapsulated
pigment obtained by coating pigment particles that have not been
treated with an anionic group-imparting agent with a polymer and
which have a lower pigment content than the inks of Examples, are
excellent in dispersion stability and ejection stability but fail
to achieve sufficient print quality in terms of image density,
print quality, abrasion resistance, and color developability.
[0420] The inks of Comparative Examples 1-5 to 1-8 and 2-10 to
2-13, which comprise the conventional microencapsulated pigment and
has the same pigment content as the inks of Examples, are
particularly inferior in dispersibility, dispersion stability, and
ejection stability. The inks of Comparative Examples 3-1 to 3-12
have markedly poor reliability against clogging. The inks of
Comparative Examples 1-9 to 1-13 containing pigment particles
having been treated with an anionic group-imparting agent are,
while superior in dispersion stability and ejection stability,
inferior in abrasion resistance.
[0421] As described above, the present invention provides a
microencapsulated pigment, a process for producing the
microencapsulated pigment, and an aqueous dispersion, with which to
provide an ink jet recording ink satisfying all the requirements:
(1) high dispersion stability, (2) high ejection stability, (3)
capability of forming images with excellent fastness, (4)
capability of forming images with high density, (5) capability of
forming images with excellent abrasion resistance, and (6)
capability of forming images which hardly feather and show high
color developability even on plain paper.
[0422] Accordingly, the present invention provides an ink jet
recording ink satisfying all the above requirements (1) to (6).
[0423] While the invention has been described in detail and with
reference to the specific embodiments thereof, it will be apparent
to those skilled in the art that various changes and modifications
can be made therein without departing from the spirit and the scope
thereof.
[0424] This application is based on Japanese Patent Application No.
2001-256025 filed Aug. 27, 2001, No. 2001-256033 filed Aug. 27,
2001, No. 2002-38793 filed Feb. 15, 2002, and No. 2002-242979 filed
Aug. 23, 2002, the entire contents thereof being hereby
incorporated by reference.
* * * * *