U.S. patent application number 11/922684 was filed with the patent office on 2009-12-03 for ink composition containing magenta solid solution pigment and ink jet recording method using the same.
Invention is credited to Miharu Kanaya, Nagatoshi Kasahara.
Application Number | 20090297712 11/922684 |
Document ID | / |
Family ID | 37570443 |
Filed Date | 2009-12-03 |
United States Patent
Application |
20090297712 |
Kind Code |
A1 |
Kasahara; Nagatoshi ; et
al. |
December 3, 2009 |
Ink Composition Containing Magenta Solid Solution Pigment and Ink
jet Recording Method Using the Same
Abstract
Disclosed is an ink composition for ink jet recording that can
realize excellent printing quality on various recording media, has
a high level of color developing properties particularly on plain
papers, and can realize excellent gloss for glossy paper and, at
the same time, is excellent in ink reliability such as ejection
stability, storage stability, and recovery from clogging. The ink
composition is characterized by comprising at least a magenta solid
solution pigment, a polymer, which can render the pigment
dispersible in the ink composition, and water, the polymer having
been produced by copolymerizing a monomer composition comprising at
least a styrene macromer (A) and a salt forming group-containing
monomer (B).
Inventors: |
Kasahara; Nagatoshi;
(Nagano-ken, JP) ; Kanaya; Miharu; (Nagano-ken,
JP) |
Correspondence
Address: |
LADAS & PARRY LLP
26 WEST 61ST STREET
NEW YORK
NY
10023
US
|
Family ID: |
37570443 |
Appl. No.: |
11/922684 |
Filed: |
June 20, 2006 |
PCT Filed: |
June 20, 2006 |
PCT NO: |
PCT/JP2006/312354 |
371 Date: |
June 1, 2009 |
Current U.S.
Class: |
427/256 ;
524/90 |
Current CPC
Class: |
C09D 11/30 20130101;
C09D 11/326 20130101; C09D 11/322 20130101 |
Class at
Publication: |
427/256 ;
524/90 |
International
Class: |
B05D 5/06 20060101
B05D005/06; C09D 11/10 20060101 C09D011/10 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 20, 2005 |
JP |
2005-179433 |
Claims
1. An ink composition comprising at least a magenta solid solution
pigment, a dispersant polymer, which can render the pigment
dispersible in the ink composition, and water, wherein the
dispersant polymer is produced by copolymerizing a monomer
composition comprising at least a styrene macromer (A) and a salt
forming group-containing monomer (B).
2. The ink composition according to claim 1, wherein the dispersant
polymer further comprises a polyoxyalkylene group-containing
monomer (C).
3. The ink composition according to claim 2, wherein the
polyoxyalkylne group-containing monomer (C) comprises one or more
monomers selected from the group consisting of monomer C1
represented by formula (I): ##STR00011## wherein R.sup.1 represents
a hydrogen atom or a methyl group; R.sup.2 represents a hydrogen
atom, an alkyl group having 1 to 20 carbon atoms or an alkylphenyl
group having 1 to 9 carbon atoms; and m is a number of 1 to 30,
monomer C2 represented by formula (II): ##STR00012## wherein
R.sup.1 and R.sup.2 are as defined in formula (I); and n is a
number of 1 to 30, monomer C3 represented by formula (III):
##STR00013## wherein R.sup.1, R.sup.2, and m are as defined in
formula (I); n is as defined in formula (II); and the oxyethylene
groups and the oxypropylene groups in [ ] are attached as a block
polymer or a random polymer, and monomer C4 represented by formula
(IV): ##STR00014## wherein R.sup.1, R.sup.2, and m are as defined
in formula (I); n is as defined in formula (II); and the
oxypropylene groups and the oxytetramethylene groups in [ ] are
attached as a block polymer or a random polymer.
4. The ink composition according to claim 2, wherein the dispersant
polymer further comprises a monomer (D) which is copolymerizable
with the styrene macromer (A), the salt forming group-containing
monomer (B), and the polyoxyalkylene group-containing monomer
(C).
5. The ink composition according to claim 4, wherein the
copolymerizable monomer (D) comprises at least one monomer selected
from the group consisting of aromatic ring-containing monomers and
macromers.
6. The ink composition according to claim 5, wherein the aromatic
ring-containing monomer is at least one monomer selected from the
group consisting of styrene, .alpha.-methylstyrene, vinyltoluene,
and vinylnaphthalene.
7. The ink composition according to claim 1, which exhibits a UV
visible absorption spectrum wherein at least one absorption peak is
present at a wavelength of 510 nm to 535 nm and at least one
absorption peak is present at a wavelength of 550 nm to 570 nm, and
the maximum value A of the absorbance in the wavelength range of
510 to 535 nm and the maximum value B of the absorbance in the
wavelength range of 550 nm to 570 nm satisfies a relationship of
0.9<A/B<1.0.
8. The ink composition according to claim 1, wherein the magenta
solid solution pigment is a solid solution pigment comprising at
least two quinacridone compounds selected from the group consisting
of unsubstituted quinacridone, 3,10-dichloroquinacridone,
2,9-dimethyl quinacridone, and 2,9-dichloroquinacridone.
9. The ink composition according to claim 1, which further
comprises a vinyl polymer produced by polymerizing a monomer
composition comprising a polyoxyalkylene group-containing monomer
(1) a salt forming group-containing monomer (2), and a monomer (3)
copolymerizable with the polyoxyalkylene group-containing monomer
and the salt forming group-containing monomer.
10. The ink composition according to claim 1, wherein the
polyoxyalkylene group-containing monomer (1) comprises at least one
monomer selected from the group consisting of monomer M1
represented by the following formula: ##STR00015## wherein R.sup.1
represents a hydrogen atom or a methyl group; R.sup.2 represents a
hydrogen atom, an alkyl group having 1 to 20 carbon atoms or an
alkylphenyl group having 1 to 9 carbon atoms; and m is a number of
1 to 30, monomer M2 represented by the following formula:
##STR00016## wherein R.sup.1 represents a hydrogen atom or a methyl
group; R.sup.2 represents a hydrogen atom, an alkyl group having 1
to 20 carbon atoms or an alkylphenyl group having 1 to 9 carbon
atoms; and n is a number of 1 to 30, and monomer M3 represented by
the following formula: ##STR00017## wherein R.sup.1 represents a
hydrogen atom or a methyl group; R.sup.2 represents a hydrogen
atom, an alkyl group having 1 to 20 carbon atoms or an alkylphenyl
group having 1 to 9 carbon atoms; m and n are a number of 1 to 30;
and the oxyethylene groups and the oxypropylene groups in [ ] are
attached as a block polymer or a random polymer.
11. The composition according to claim 10, wherein the
polyoxyalkylene group-containing monomer (1) is monomer M1.
12. The ink composition according to claim 9, wherein the vinyl
polymer has a weight average molecular weight of 150,000 to
500,000.
13. The ink composition according to claim 9, wherein the
copolymerizable monomer (3) comprises at least one monomer selected
from the group consisting of higher alkyl group-containing
monomers, aromatic ring-containing monomers, and macromers.
14. The ink composition according to claim 9, which further
comprises a surfactant which comprises both a compound represented
by formula (a): ##STR00018## and a compound represented by formula
(b): ##STR00019## wherein m and n satisfy a requirement of
m+n=10.
15. The ink composition according to claim 14, wherein the two
surfactants are contained at a weight ratio of (a):(b)=2:1 to
1:4.
16. A method for ink jet recording, comprising ejecting droplets of
an ink composition and depositing the droplets onto a recording
medium to performing printing, wherein the ink composition is one
according to claim 1.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of Invention
[0002] The present invention relates to an ink composition for ink
jet recording, which exhibits excellent printing quality on various
recording media, can develop a high level of color developing
properties particularly on plain papers, and, at the same time, can
exhibit high gloss on gloss paper and is excellent in ink
reliability such as ejection stability, storage stability, and
recovery from clogging, a recording method using this ink
composition, and a recorded matter.
[0003] 2. Background Art
[0004] Ink jet recording is a method wherein ink is ejected as
droplets through fine nozzle heads to record letters or figures
onto the surface of recording media such as paper. Ink jet
recording methods which have been put to practical use include a
method wherein an electric signal is converted to a mechanical
signal using an electrostrictive element to intermittently eject
droplets of ink reservoired in a nozzle head section, thereby
recording letters or symbols on the surface of a recording medium,
and a method wherein an ink liquid, reservoired in a nozzle head
section, in its portion very close to the ejection portion is
rapidly heated to create a bubble and droplets of the ink are
intermittently ejected by volume expansion created by the bubble to
record letters or symbols on the surface of a recording medium.
[0005] In recent years, there is an increasing tendency toward the
use of printed matter, formed by printing with an ink jet printer,
as a display in an indoor environment as well as in an outdoor
environment for advertisement or appreciation purposes, and the
development of an ink having excellent fastness properties such as
excellent lightfastness, gasfastness, and waterfastness has been
demanded. To meet this demand, an ink using a pigment having
excellent fastness properties such as excellent lightfastness,
waterfastness, and gasfastness as a colorant has been
developed.
[0006] JP H11(1999)-209672 proposes a water-based pigment ink
comprising a pigment covered with a specific polymer, which
water-based pigment ink has a high level of color developing
properties and excellent lightfastness. JP H10(1998)-120956
proposes an ink set comprising a combination of specific pigments.
Further, JP H10(1998)-219166 and JP H11(1999)-49998 propose an ink
composition using a quinacridone pigment or a magenta solid
solution pigment as a pigment for use for a magenta color, which
ink composition has color rendering properties comparable with
magenta dyes and, at the same time, is excellent in lightfastness
and gasfastness.
[0007] Further, a water-based ink containing a surfactant and a
polymeric dispersant added thereto and having excellent pigment
dispersion, and an ink comprising a pigment as a colorant covered
with a dispersing resin have been proposed. Inks with fine
particles of pigment having a given particle diameter dispersed
therein exhibit excellent color developing properties on various
recording media, particularly on plain papers.
[0008] When the ink with fine particles of pigment dispersed
therein is printed on recording media having a smoothly processed
surface such as gloss paper, however, glossiness of the recorded
part is sometimes deteriorated by irregular reflection of
light.
[0009] Further, in the water-based ink with a surfactant and a
polymeric dispersant added thereto, upon the vaporization of water
and other volatile components in the course of drying of the ink
after deposition of the ink onto the recording medium, the
dispersion stable system of the ink is broken, often
disadvantageously leading to the aggregation of the pigment. As a
result, the aggregate of this pigment deteriorates the gloss of the
recorded part, renders the gloss of the printed image uneven, and
sometimes results in deteriorated printing quality.
SUMMARY OF THE INVENTION
[0010] The present inventors have now found that, in an ink using a
magenta solid solution pigment as a colorant, a combination of the
ink with a dispersant polymer having a specific structure can
realize an ink composition for ink jet recording that can realize
excellent printing quality on various recording media, has a high
level of color developing properties particularly on plain papers,
and can realize excellent gloss for glossy paper and, at the same
time, is excellent in ink reliability such as ejection stability,
storage stability, and recovery from clogging. The present
invention has been made based on such finding.
[0011] Accordingly, an object of the present invention is to
provide an ink composition for ink jet recording that can realize
excellent printing quality on various recording media, has a high
level of color developing properties particularly on plain papers,
and can realize excellent gloss for glossy paper and, at the same
time, is excellent in ink reliability such as ejection stability,
storage stability, and recovery from clogging.
[0012] The above object can be attained by an ink composition
comprising at least a magenta solid solution pigment, a dispersant
polymer, which can render the pigment dispersible in the ink
composition, and water, wherein the dispersant polymer has been
produced by copolymerizing a monomer composition comprising at
least a styrene macromer (A) and a salt forming group-containing
monomer (B).
[0013] The present invention can realize an ink composition for ink
jet recording that can realize excellent printing quality on
various recording media, has a high level of color developing
properties particularly on plain papers, and can realize excellent
gloss for glossy paper and, at the same time, is excellent in ink
reliability such as ejection stability, storage stability, and
recovery from clogging.
BRIEF DESCRIPTION OF THE DRAWING
[0014] FIG. 1 is a diagram showing a UV visible light absorption
spectra of inks prepared in Examples 1, 6 and 7.
DETAILED DESCRIPTION OF THE INVENTION
Magenta Solid Solution Pigment
[0015] According to the present invention, a combination of a
magenta solid solution pigment with a dispersant polymer, which
will be described later, can realize an ink composition for ink jet
recording that has a high level of color developing properties
particularly on plain papers, and can realize excellent gloss for
glossy paper and, at the same time, is excellent in ink reliability
such as ejection stability, storage stability, and recovery from
clogging.
[0016] The magenta solid solution pigment used in the ink
composition according to the present invention is preferably a
solid solution pigment comprising two or more quinacridone
compounds selected from the group consisting of unsubstituted
quinacridone, 3,10-dichloroquinacridone, 2,9-dimethylquinacridone,
and 2,9-dichloroquinacridone. Specifically, the magenta solid
solution pigment is a solid solution pigment comprising two or more
quinacridone compounds selected from four quinacridone compounds,
that is, unsubstituted quinacridone represented by the following
formula:
##STR00001##
3,10-dichloroquinacridone of which the 3- and 10-positions have
been substituted by chlorine, 2,9-dimethylquinacridone of which the
2- and 9-positions have been substituted by methyl group, and
2,9-dichloroquinacridone of which the 2- and 9-positions have been
substituted by chlorine.
[0017] The quinacridone compounds may be commercially available
products. Specifically, the unsubstituted quinacridone may be one
commercially available as C.I. Pigment Violet 19;
3,10-dichloroquinacridone may be one commercially available as C.I.
Pigment Red 209; 2,9-dimethylquinacridone may be one commercially
available as C.I. Pigment Red 122; and 2,9-dichloroquinacridone may
be one commercially available as C.I. Pigment Red 202.
[0018] The combination of the two or more quinacridone compounds is
not particularly limited. In the present invention, however, a
solid solution pigment comprising a combination of unsubstituted
quinacridone with 3,10-dichloroquinacridone, a combination of
unsubstituted quinacridone with 2,9-dimethylquinacridone, or a
combination of unsubstituted quinacridone with
2,9-dichloroquinacridone is preferred. In particular, the use of a
combination of the solid solution pigment, comprising the above
combination, with an acetylene compound having a specific structure
which will be described later, can contribute to a further
improvement in color developing property on plain papers.
[0019] The mixing ratio between the unsubstituted quinacridone and
the 3,10-dichloroquinacridone in the solid solution pigment is
preferably unsubstituted quinacridone:
3,10-dichloroquinacridone=10:90 to 90:10, more preferably 15:85 to
85:15. Further, the mixing ratio between the unsubstituted
quinacridone and 2,9-dimethylquinacridone is unsubstituted
quinacridone: 2,9-dimethylquinacridone=10:90 to 90:10, more
preferably 15:85 to 85:15. The mixing ratio between the
unsubstituted quinacridone and 2,9-dichloroquinacridone is
unsubstituted quinacridone 2,9-dichloroquinacridone=10:90 to 90:10,
more preferably 15:85 to 85:15.
[0020] The magenta solid solution pigment may be produced by any
method without particular limitation, and conventional production
processes may be used. Specific examples of such processes include
those disclosed in Japanese Patent Laid-Open No. 49998/1999,
Japanese Patent Laid-Open No. 319534/2000, and Japanese Patent
Laid-Open No. 253150/2003.
[0021] In the present invention, preferably, the magenta solid
solution pigment has an average particle diameter of 10 to 200 nm,
more preferably 50 to 150 nm. When the average particle diameter is
in the above-defined range, good weathering resistance and good
ejection stability can be advantageously realized.
[0022] In a preferred embodiment of the present invention, the ink
composition according to the present invention exhibits a UV
visible absorption spectrum wherein
[0023] at least one absorption peak is present at a wavelength of
510 nm to 535 nm and at least one absorption peak is present at a
wavelength of 550 nm to 570 nm, and the maximum value A of the
absorbance in the wavelength range of 510 to 535 nm and the maximum
value B of the absorbance in the wavelength range of 550 nm to 570
nm satisfies a relationship of 0.9<A/B<1.0. The above light
absorption spectrum can be realized by the selection and ratio of
pigment species in the magenta solid solution pigment, and the
selection of other ink composition.
[0024] Dispersant Polymer
[0025] In the present invention, the dispersant polymer is produced
by copolymerizing a monomer composition comprising at least a
styrene macromer (A) and a salt forming group-containing monomer
(B).
[0026] Styrene macromer (A) is a styrenic macromonomer having a
number average molecular weight of 500 to 500,000.
[0027] An example of preferred styrene macromer (A) is a macromer
which has a polymerizable functional group at its one end and
preferably has a number average molecular weight of 500 to 500,000,
more preferably 1,000 to 10,000.
[0028] Specific examples of preferred styrene macromer (A) include
styrenic macromers having a polymerizable functional group at one
end thereof and styrene-acrylonitrile macromers having a
polymerizable functional group at one end thereof. Among them,
styrenic macromers having a polymerizable functional group at one
end thereof are preferred from the viewpoint of satisfactorily
incorporating the magenta solid solution pigment into the vinyl
polymer.
[0029] Acrylonitrile may be mentioned as a monomer other than
styrene constituting the styrenic macromonomer having a
polymerizable functional group at its one end. The content of
styrene is preferably not less than 60% by weight, more preferably
not less than 70% by weight, from the viewpoint of satisfactorily
incorporating the pigment in the vinyl polymer.
[0030] Among styrenic macromers having a polymerizable functional
group at one end thereof, those having an acryloyloxy or
methacryloyloxy group as the polymerizable functional group at one
end thereof are preferred.
[0031] Commercially available styrenic macromers include, for
example, AS-6, AN-6, AN-6S, HS-6S, and HS-6, manufactured by
TOAGOSEI Co., Ltd.
[0032] The content of the styrene macromer in the dispersant
polymer is preferably 0.1 to 40% by weight, more preferably 1 to
30% by weight, from the viewpoints of waterfastness and
scratch/rubbing resistance.
[0033] Preferred salt forming group-containing monomers (B) as a
comonomer component in the dispersant polymer are anionic monomers
or cationic monomers. The anionic monomers and the cationic
monomers may be used either solely or as a mixture of two or
more.
[0034] A specific example of the anionic monomer is at least one
monomer selected from the group consisting of unsaturated
carboxylic acid monomers, unsaturated sulfonic acid monomers, and
unsaturated phosphoric acid monomers.
[0035] Specific examples of unsaturated carboxylic acid monomers
include, for example, acrylic acid, methacrylic acid, crotonic
acid, itaconic acid, maleic acid, fumaric acid, citraconic acid,
and 2-methacryloyloxymethylsuccinic acid. They may be used either
solely or as a mixture of two or more.
[0036] From the viewpoint of ink viscosity and ejection stability,
preferred anionic monomers are unsaturated carboxylic acid
monomers, and acrylic acid and methacrylic acid are more
preferred.
[0037] Cationic monomers include polyvinylamine, polyallylamine,
N,N-dimethylaminoethylacrylate, and
N,N-dimethylaminopropylacrylamide. Among them,
N,N-dimethylaminoethylacrylate and
N,N-dimethylaminopropylacrylamide are preferred.
[0038] The content of the salt forming group-containing monomer (B)
in the dispersant polymer is 3 to 40% by weight, preferably 5 to
30% by weight, from the viewpoint of dispersion stability and
ejection stability.
[0039] In a preferred embodiment of the present invention, the
dispersant polymer further comprises a polyoxyalkylene
group-containing monomer (C).
[0040] Preferably, the polyoxyalkylne group-containing monomer (C)
comprises one or more monomers selected from the group consisting
of monomer C1 represented by formula (I):
##STR00002##
[0041] wHerein R.sup.1 represents a hydrogen atom or a methyl
group; R.sup.2 represents a hydrogen atom, an alkyl group having 1
to 20 carbon atoms or an alkylphenyl group having 1 to 9 carbon
atoms; and m is a number of 1 to 30,
[0042] monomer C2 represented by formula (II):
##STR00003##
[0043] wherein R.sup.1 and R.sup.2 are as defined in formula (I);
and n is a number of 1 to 30,
[0044] monomer C3 represented by formula (III):
##STR00004##
[0045] wherein R.sup.1, R.sup.2, and m are as defined in formula
(I); n is as defined in formula (II); and the oxyethylene groups
and the oxypropylene groups in [ ] are attached as a block polymer
or a random polymer, and
[0046] monomer C4 represented by formula (IV):
##STR00005##
[0047] wherein R.sup.1, R.sup.2, and m are as defined in formula
(III); n is as defined in formula (IV); and the oxypropylene groups
and the oxytetramethylene groups in [ ] are attached as a block
polymer or a random polymer.
[0048] Polyethylene glycol mono(meth)acrylate may be mentioned as a
specific example of monomer C1. Specific examples of commercially
available monomer A include: NK Ester M-20G, NK Ester M-40G, NK
Ester M-90G, and NK Ester M-230G, manufactured by Shin-Nakamura
Chemical Co., Ltd.; and Blemmer PE series, Blemmer PME-100, Blemmer
PME-200, Blemmer PME-400, and Blemmer PME-1000, manufactured by
Nippon Oils & Fats Co., Ltd.
[0049] Specific examples of monomer C2 include polypropylene glycol
mono(meth)acrylate.
[0050] Specific examples of monomer C3 include ethylene
glycol/propylene glycol (meth)acrylate, poly(ethylene
glycol/propylene glycol) mono(meth)acrylate, octoxy polyethylene
glycol/polypropylene glycol mono(meth)acrylate, octoxy
poly(ethylene glycol/propylene glycol) mono(meth)acrylate, stearoxy
polyethylene glycol/polypropylene glycol mono(meth)acrylate,
stearoxy poly(ethylene glycol/propylene glycol) mono(meth)acrylate,
nonylphenoxy polyethylene glycol/polypropylene glycol
mono(meth)acrylate, and nonylphenoxy poly(ethylene glycol/propylene
glycol) mono(meth)acrylate. They may be used either solely or as a
mixture of two or more.
[0051] Specific examples of monomer C4 include propylene
glycol/tetramethylene glycol mono(meth)acrylate, poly(propylene
glycol/tetramethylene glycol) mono(meth)acrylate, propylene
glycol/polybutylene glycol mono(meth)acrylate, and poly(propylene
glycol/butylene glycol) mono(meth)acrylate. They may be used either
solely or as a mixture of two or more.
[0052] Among monomers C1 to C4, polyethylene glycol
mono(meth)acrylate, polypropylene glycol mono(meth)acrylate,
ethylene glycol/propylene glycol (meth)acrylate, and poly(ethylene
glycol/propylene glycol) mono(meth)acrylate are preferred from the
viewpoints of ink viscosity and ejection stability.
[0053] Specific examples of commercially available monomers C2 to
C4, include, for example, Blemmer PP-1000, Blemmer PP-500, Blemmer
PP-800, Blemmer AP-150, Blemmer AP-400, Blemmer AP-550, Blemmer
AP-800, Blemmer 50 PEP-300, Blemmer 70 PEP-350B, Blemmer AEP
series, Blemmer 30 PPT-800, Blemmer 50 PPT-800, Blemmer 70 PPT-800,
Blemmer APT series, Blemmer 10 PPB-500B, Blemmer 10 APB-500B,
Blemmer 50 POEP-800B, Blemmer 50 AOEP-800B, Blemmer ASEP series,
Blemmer PNEP series, Blemmer PNPE series, Blemmer 43 ANEP-500, and
Blemmer 70 ANEP-550, manufactured by Nippon Oils & Fats Co.,
Ltd.
[0054] The content of polyoxyalkylen group-containing monomer (C)
in the dispersant polymer is preferably 5 to 45% by weight,
preferably 5 to 35% by weight, from the viewpoints of print density
and ink viscosity.
[0055] In the present invention, preferably, the dispersant polymer
further comprises a monomer (D) copolymerizable with the styrene
macromer (A), the salt forming group-containing monomer (B), and
the polyoxyalkylene group-containing monomer (C).
[0056] Copolymerizable monomers (D) include (meth)acrylic esters,
aromatic ring-containing monomers, and macromers. These monomers
may be used either solely or as a mixture of two or more. Monomer
(D) preferably contains at least one monomer selected from the
group consisting of aromatic ring-containing monomers and macromers
from the viewpoints of waterfastness and scratch/rubbing
resistance.
[0057] (Meth)acrylic esters include, for example, (meth)acrylic
esters in which the ester part is an alkyl group having 1 to 18
carbon atoms, for example, methyl (meth)acrylate, ethyl
(meth)acrylate, (iso)propyl (meth)acrylate, (iso or tertiary)butyl
(meth)acrylate, (iso)amyl (meth)acrylate, cyclohexyl
(meth)acrylate, benzyl (meth)acrylate, 2-ethylhexyl (meth)acrylate,
(iso)octyl (meth)acrylate, (iso)decyl (meth)acrylate, (iso)dodecyl
(meth)acrylate, and (iso)stearyl (meth)acrylate. They may be used
either solely or as a mixture of two or more.
[0058] The term "(iso or tertiary)" and the term "(iso)" as used
herein mean both the case where these groups are present and the
case where these groups are absent. When these groups are absent,
the compounds are normal.
[0059] The aromatic ring-containing monomer is preferably at least
one monomer selected from the group consisting of styrene,
vinylnaphthalene, .alpha.-methylstyrene, vinyltoluene, ethyl
vinylbenzene, 4-vinylbiphenyl, 1,1-diphenylethylene, benzyl
(meth)acrylate, phenoxyethyl (meth)acrylate,
2-hydroxy-3-phenoxypropyl acrylate,
2-methacryloyloxyethyl-2-hydroxypropyl phthalate,
2-acryloyloxyethylphthalic acid, and neopentyl glycol acrylate
benzoate from the viewpoint of waterfastness. Among them, at least
one monomer selected from the group consisting of styrene,
.alpha.-methylstyrene, vinyltoluene, and vinylnaphthalene is more
preferred from the viewpoints of waterfastness and scratch/rubbing
resistance.
[0060] Macromers include those that have a polymerizable functional
group on one end thereof and preferably have a number average
molecular weight of 500 to 500,000, more preferably 1,000 to
10,000.
[0061] Specific examples of macromers include styrenic macromers
having a polymerizable functional group on one end thereof,
silicone macromers having a polymerizable functional group on one
end thereof, methyl methacrylate macromers having a polymerizable
functional group on one end thereof, styrene-acrylonitrile
macromers having a polymerizable functional group on one end
thereof, butyl acrylate macromers having a polymerizable functional
group on one end thereof, and isobutyl methacrylate macromers
having a polymerizable functional group on one end thereof. Among
them, styrenic macromers having a polymerizable functional group on
one end thereof are preferred from the viewpoint of satisfactorily
incorporating the magenta solid solution pigment into the
dispersant polymer.
[0062] A styrene homopolymer having a polymerizable functional
group on its one end and a copolymer of styrene with another
monomer having a polymerizable functional group on its one end may
be mentioned as the styrenic macromer containing a polymeriable
functional group on its one end.
[0063] In the copolymer of styrene with another monomer having a
polymerizable functional group on its one end, examples of another
monomers include acrylonitrile. The content of styrene is
preferably not less than 60% by weight, more preferably not less
than 70% by weight, from the viewpoint of satisfactorily
incorporating the magenta solid solution pigment in the dispersant
polymer.
[0064] Among styrenic macromers having a polymerizable functional
group on one end thereof, those having an acryloyloxy or
methacryloyloxy group as the polymerizable functional group on one
end thereof are preferred.
[0065] Commercially available styrenic macromers include, for
example, AS-6, AN-6, AN-6S, HS-6S, and HS-6, manufactured by
TOAGOSEI Co., Ltd.
[0066] The content of copolymerizable monomer (D) in the dispersant
polymer is 15 to 87% by weight, preferably 15 to 75% by weight,
more preferably 15 to 50% by weight, from the viewpoints of print
density and waterfastness.
[0067] The content of the aromatic ring-containing monomer in the
dispersant polymer is preferably 0.1 to 70% by weight, more
preferably 1 to 50% by weight, from the viewpoints of
waterfastness, scratch/rubbing resistance, ink viscosity, and
ejection stability.
[0068] The content of the macromer in the dispersant polymer is
preferably 0.1 to 40% by weight, more preferably 1 to 30% by
weight, from the viewpoints of waterfastness and scratch/rubbing
resistance.
[0069] The content of each monomer in the monomer composition
comprising styrene macromer (A), salt forming group-containing
monomer (B), polyoxyalkylene group-containing monomer (C), and
copolymerizable monomer (D) is 0.1 to 40% by weight (preferably 1
to 30% by weight) for styrene macromer (A), 3 to 40% by weight
(preferably 5 to 30% by weight) for salt forming group-containing
monomer (B), 5 to 45% by weight (preferably 5 to 35% by weight) for
polyoxyalkylene group-containing monomer (C), and 15 to 87% by
weight (preferably 15 to 75% by weight) for copolymerizable monomer
(D).
[0070] The weight average molecular weight of the dispersant
polymer is preferably 3,000 to 300,000, more preferably 5,000 to
200,000, from the viewpoints of print density and ejection
stability.
[0071] Synthesis of Dispersant Polymer
[0072] The dispersant polymer may be synthesized by polymerizing
the above monomer-containing composition by the following
method.
[0073] The polymerization may be carried out by a conventional
polymerization method such as a bulk polymerization method, a
solution polymerization method, a suspension polymerization method,
or an emulsion polymerization method. Among these polymerization
methods, the solution polymerization method is preferred.
[0074] A polar organic solvent is preferably used as the solvent in
the solution polymerization method. When the polar organic solvent
is miscible with water, the polar organic solvent may be used as a
mixture with water.
[0075] Polar organic solvents include, for example, aliphatic
alcohols having 1 to 3 carbon atoms such as methanol, ethanol, and
propanol; ketones such as acetone and methyl ethyl ketone; and
esters such as ethyl acetate. Among them, methanol, ethanol,
acetone, methyl ethyl ketone, or a mixed liquid composed of the
above solvent with water is preferred.
[0076] Further, in the polymerization of monomer composition, a
radical polymerization initiator may be used. Radical
polymerization initiators include azo compounds such as
2,2'-azobisisobutyronitrile,
2,2'-azobis(2,4-dimethylvaleronitrile),
dimethyl-2,2'-azobisbutyrate, 2,2'-azobis(2-methylbutyronitrile),
and 1,1'-azobis(1-cyclohexanecarbonitrile); and organic peroxides
such as t-butylperoxyoctoate, di-t-butylperoxide, and
dibenzoyloxide.
[0077] The addition amount of the polymerization initiator per mole
of monomer composition is preferably 0.001 to 5 moles, more
preferably 0.01 to 2 moles.
[0078] In the polymerization of monomer composition, in addition to
the radical polymerization initiator, a polymerization chain
transfer agent may be added. Polymerization chain transfer agents
usable herein include mercaptanes such as octylmercaptan,
n-dodencylmercaptan, t-dodecylmercaptan, n-tetradecylmercaptan, and
2-mercaptoethanol; xanthogen disulfides such as dimethylxanthogen
disulfide and diisopropylxanthogen disulfide; thiuram disulfides
such as tetramethyl thiuram disulfide and tetrabutyl thiuram
disulfide; halogenated hydrocarbons such as carbon tetrachloride
and ethylene bromide; hydrocarbons such as pentaphenylethane;
unsaturated cyclic hydrocarbon compounds such as acrolein,
methacrolein, allyl alcohol, 2-ethylhexyl thioglycolate,
turbinolene, .alpha.-terpinene, .gamma.-terpinene, dipentene,
.alpha.-methylstyrene dimmer, 9,10-dihydroanthracene,
1,4-dihydronaphthalene, indene, and 1,4-cyclohexadiene; and
unsaturated hetetrocyclic compounds such as 2,5-dihydrofuran. These
polymerization chain transfer agents may be used either solely or
as a mixture of two or more.
[0079] Polymerization conditions for monomer composition vary
depending, for example, upon radical polymerization initiators,
monomers, and the type of solvents used. In general, the
polymerization temperature is preferably 30 to 100.degree. C., more
preferably 50 to 80.degree. C. The polymerization time is
preferably 1 to 20 hr. The polymerization atmosphere is preferably
an inert gas atmosphere such as nitrogen gas.
[0080] After the completion of the polymerization reaction, the
produced vinyl polymer is isolated from the reaction solution by a
conventional method such as reprecipitation from the reaction
solution or removal of the solvent by evaporation. The vinyl
polymer thus obtained may be purified by removing the unreacted
monomer and the like, for example, by the repetition of
reprecipitation, membrane separation, chromatography, or
extraction.
[0081] Preparation of Magenta Solid Solution Pigment Dispersion
Liquid
[0082] The magenta solid solution pigment dispersion liquid may be
prepared, for example, by a method described in Japanese Patent
Laid-Open No. 247810/2001. Specifically, a polymer solution
dissolved in a water soluble organic solvent, a pigment, and
optionally a neutralizing agent are mixed together to prepare a
solvent dispersion liquid which is developed in an aqueous phase to
prepare an aqueous suspension. Thereafter, the water soluble
organic solvent added in the preparation of the solvent dispersion
liquid is removed by distillation to cover the pigment with
dispersant polymer particles.
[0083] The neutralizing agent may be properly determined, and
alkalis usable as the neutralizing agent include tertiary amines
such as trimethylamine and triethylamine, ammonia, sodium
hydroxide, and potassium hydroxide. Acids usable as the
neutralizing agent include inorganic bases such as hydrochloric
acid and sulfuric acid and organic acids such as acetic acid,
propionic acid, lactic acid, succinic acid, glycolic acid, glyconic
acid, and glyceric acid.
[0084] Preferred organic solvents are water soluble organic
solvents, and examples thereof include alcohols such as methanol,
ethanol, and isopropanol, ketones such as acetone, methyl ethyl
ketone, diethyl ketone, and methyl isobutyl ketone, and ethers such
as dibutyl ether, tetrahydrofuran, and dioxane.
[0085] A dispergator may be used in the step of covering the
pigment with the dispersant polymer. For example, the dispersion
may be carried out with dispergators such as ball mills, sand
mills, attritors, roll mills, agitator mills, Henschel mixers,
colloid mills, ultrasonic homogenizers, jet mills, and Ong mills.
More preferred are high-pressure homogenizers in which milling
debrises of dispersing media and the like are less likely to be
included.
[0086] The dispersant polymer particles thus obtained preferably
have a diameter of about 25 to 250 nm. More preferably, the lower
limit of the particle diameter is about 30 nm, and the upper limit
of the particle diameter is about 175 nm.
[0087] The weight ratio of the magenta solid solution pigment to
the dispersant polymer containing the pigment is preferably 5:95 to
95:5, more preferably 10:90 to 90:10. The addition amount of the
pigment is preferably 0.5 to 15% by weight, more preferably 1 to
10% by weight, in terms of the weight of only the pigment, based on
the total amount of the ink composition, in such as state that the
pigment is covered with the dispersant polymer.
[0088] Vinyl Polymer
[0089] In a preferred embodiment of the present invention, the ink
composition according to the present invention may comprise a vinyl
polymer produced by copolymerizing a monomer composition comprising
(1) a polyoxyalkylene group-containing monomer, (2) a salt forming
group-containing polymer, and (3) a monomer copolymerizable with
the polyoxyalkylene group-containing monomer and the salt forming
group-containing monomer (hereinafter often referred to simply as a
copolymerizable monomer). This polymer may be added in the
preparation of the dispersion liquid of the magenta solid solution
and the dispersant polymer, or alternatively may be added after the
preparation of the dispersion liquid. Preferably, the polymer is
added after the preparation of the dispersion liquid.
[0090] The composition ratio of the monomers is not particularly
limited. The monomer composition preferably comprises (1) 5 to 50
parts by weight of the polyoxyalkylene group-containing monomer,
(2) 3 to 40 parts by weight of the salt forming group-containing
monomer, and (3) 15 to 90 parts by weight of the copolymerizable
monomer.
[0091] (1) Polyoxyalkylene Group-Containing Monomer
[0092] The polyoxyalkylene group-containing monomer preferably
comprises at least one monomer selected from the group consisting
of
[0093] monomer M1 represented by the following formula:
##STR00006##
[0094] wherein R.sup.1 represents a hydrogen atom or a methyl
group; R.sup.2 represents a hydrogen atom, an alkyl group having 1
to 20 carbon atoms or an alkylphenyl group having 1 to 9 carbon
atoms; and m is a number of 1 to 30,
[0095] monomer M2 represented by the following formula:
##STR00007##
[0096] wherein R.sup.1 represents a hydrogen atom or a methyl
group; R.sup.2 represents a hydrogen atom, an alkyl group having 1
to 20 carbon atoms or an alkylphenyl group having 1 to 9 carbon
atoms; and n is a number of 1 to 30, and monomer M3 represented by
the following formula:
##STR00008##
[0097] wherein R.sup.1 represents a hydrogen atom or a methyl
group; R.sup.2 represents a hydrogen atom, an alkyl group having 1
to 20 carbon atoms or an alkylphenyl group having 1 to 9 carbon
atoms; m and n are a number of 1 to 30; and the oxyethylene groups
and the oxypropylene groups in [ ] are attached as a block polymer
or a random polymer.
[0098] An ink composition having excellent gloss of printed images,
ink storage stability, and recovery from clogging can be produced
by using the water soluble monomer M1 as the polyoxyalkylene
group-containing monomer. The reason for this has not been fully
elucidated yet but it is considered that the excellent properties
are based on spreading of a hydrophilic hydration layer of a highly
hydrophilic oxyethylene group possessed by monomer M1 in the
ink.
[0099] When monomer M2 is used as the polyoxyalkylene
group-containing monomer, an ink composition having excellent
ejection properties can be obtained. The reason for this has not
been fully elucidated yet but it is considered that strong
hydrophobic interaction occurs between the highly hydrophobic
oxypropylene group of monomer M2 and the magenta solid solution
pigment as the colorant and the vinyl polymer develops a high level
of adsorption to the colorant, and, consequently, the
hydrophobicity of the polymer particles containing the colorant is
increased resulting in lowered viscosity of the ink
composition.
[0100] Further, when monomer M3 is used as the polyoxyalkylene
group-containing monomer, excellent dispersion stability can be
imparted to the colorant. The reason for this has not been fully
elucidated yet but is believed to reside in that the hydrophilic
hydration layer of the highly hydrophilic oxyethylene group or
oxytetramethylene group is spread in the ink.
[0101] In the above monomers M1 to M3, R.sup.1 represents a
hydrogen atom or a methyl group; and R.sup.2 represents a hydrogen
atom, an alkyl group having 1 to 20 carbon atoms, or an alkylphenyl
group having 1 to 9 carbon atoms. R.sup.2 preferably represents an
octyl group or a nonyl phenyl group from the viewpoints of
waterfastness and rubbing/scratch resistance.
[0102] m is a number of 1 to 30, and, from the viewpoint of
ejection stability and print density, m is preferably 2 to 25. n is
a number of 1 to 30, and, from the viewpoint of ejection stability
and print density, n is preferably 2 to 25.
[0103] Polyethylene glycol mono(meth)acrylate and the like may be
mentioned as monomer M1 represented by formula (I). Specific
examples of monomer M1 as commercially available monomer M1
include: NK Ester M-20G, NK Ester M-40G, NK Ester M-90G, and NK
Ester M-230G, manufactured by Shin-Nakamura Chemical Co., Ltd.; and
Blemmer PE series, Blemmer PME-100, Blemmer PME-200, Blemmer
PME-400, and Blemmer PME-1000, manufactured by Nippon Oils &
Fats Co., Ltd.
[0104] Specific examples of monomer M2 represented by formula (II)
include polypropylene glycol mono(meth)acrylate.
[0105] Specific examples of monomer M3 represented by formula (III)
include ethylene glycol/propylene glycol (meth)acrylate,
poly(ethylene glycol/propylene glycol) mono(meth)acrylate, octoxy
polyethylene glycol/polypropylene glycol mono(meth)acrylate, octoxy
poly(ethylene glycol/propylene glycol) mono(meth)acrylate, stearoxy
polyethylene glycol/polypropylene glycol mono(meth)acrylate,
stearoxy poly(ethylene glycol/propylene glycol) mono(meth)acrylate,
nonylphenoxy polyethylene glycol/polypropylene glycol
mono(meth)acrylate, and nonylphenoxy poly(ethylene glycol/propylene
glycol) mono(meth)acrylate. They may be used either solely or as a
mixture of two or more.
[0106] Among them, monomers M2 and M3 are preferably polypropylene
glycol mono(meth)acrylate, ethylene glycol/propylene glycol
(meth)acrylate, or poly(ethylene glycol/propylene glycol)
mono(meth)acrylate from the viewpoints of ink viscosity and
ejection stability.
[0107] Commercially available monomers M2 and M3, include, for
example, Blemmer PP-1000, Blemmer PP-500, Blemmer PP-800, Blemmer
AP-150, Blemmer AP-400, Blemmer AP-550, Blemmer AP-800, Blemmer 50
PEP-300, Blemmer 70 PEP-350B, Blemmer AEP series, Blemmer 30
PPT-800, Blemmer 50 PPT-800, Blemmer 70 PPT-800, Blemmer APT
series, Blemmer 10 PPB-500B, Blemmer 10 APB-500B, Blemmer 50
POEP-800B, Blemmer 50 AOEP-800B, Blemmer ASEP series, Blemmer PNEP
series, Blemmer PNPE series, Blemmer 43 ANEP-500, and Blemmer 70
ANEP-550, manufactured by Nippon Oils & Fats Co., Ltd.
[0108] The content of the polyoxyalkylene group-containing monomer
in the water insoluble polymer is preferably 5 to 50% by weight,
more preferably 10 to 40% by weight, from the viewpoints of
improving the ejection stability of the ink composition and the
gloss of the printed image and suppressing the lowering of the
color developing property and fixation on gloss paper.
[0109] (2) Salt Forming Group-Containing Monomer
[0110] Preferred salt forming group-containing monomers are anionic
monomers and cationic monomers. The anionic monomers and the
cationic monomers may be used either solely or as a mixture of two
or more.
[0111] At least one monomer selected from the group consisting of
unsaturated carboxylic acid monomers, unsaturated sulfonic acid
monomers, and unsaturated phosphoric acid monomers may be mantioned
as the anionic monomer.
[0112] Unsaturated carboxylic acid monomers include, for example,
acrylic acid, methacrylic acid, crotonic acid, itaconic acid,
maleic acid, fumaric acid, citraconic acid, and
2-methacryloyloxymethylsuccinic acid. They may be used either
solely or as a mixture of two or more.
[0113] Unsaturated sulfonic acid monomers include, for example,
styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid,
3-sulfopropyl (meth)acrylate, and bis-(3-sulfopropyl) itaconate.
They may be used either solely or as a mixture of two or more.
[0114] Unsaturated phosphoric acid monomers include, for example,
vinylphosphonic acid, vinyl phosphate, bis(methacryloxyethyl)
phosphate, diphenyl-2-acryloyloxyethyl phosphate,
diphenyl-2-methacryloyloxyethyl phosphate, and
dibutyl-2-acryloyloxyethyl phosphate. They may be used either
solely or as a mixture of two or more.
[0115] Among the anionic monomers, unsaturated carboxylic acid
monomers are preferred from the viewpoints of ink viscosity and
ejection stability, and acrylic acid and methacrylic acid are more
preferred.
[0116] At least one monomer selected from the group consisting of
unsaturated tertiary amine-containing vinyl monomers and
unsaturated ammonium salt-containing vinyl monomer may be mentioned
as the cationic monomer.
[0117] Unsaturated tertiary amine-containing monomers include, for
example, N,N-dimethylaminoethyl (meth)acrylate,
N,N-dimethylaminopropyl (meth)acrylate, N, N-diethylaminoethyl
(meth)acrylate, N,N-dimethylaminopropyl (meth)acrylamide,
N,N-dimethylarylamine, vinylpyrrolidone, 2-vinylpyridine,
4-vinylpyridine, 2-methyl-6-vinylpyridine, and
5-ethyl-2-vinylpyridine. They may be used either solely or as a
mixture of two or more.
[0118] Unsaturated ammonium salt-containing monomers include, for
example, quaternalized N,N-dimethylaminoethyl (meth)acrylate,
quaternalized N,N-diethylaminoethyl (meth)acrylate, and
quaternalized N,N-dimethylaminopropyl (meth)acrylate. They may be
used either solely or as a mixture of two or more.
[0119] Among the cationic monomers, N,N-dimethylaminoethyl
(meth)acrylate, N,N-dimethylaminopropyl (meth)acrylamide, and
vinylpyrrolidone are preferred.
[0120] The content of the salt forming group-containing monomer in
vinyl polymer is preferably 3 to 40% by weight, more preferably 5
to 30% by weight, from the viewpoints of dispersion stability and
ejection stability.
[0121] (3) Copolymerizable Monomer
[0122] Monomers copolymerizable with the polyoxyalkylene
group-containing monomer and the salt forming group-containing
monomer include, for example, higher alkyl group-containing
monomers, aromatic ring-containing monomers, macromers, and
(meth)acrylic esters. Among them, one or more of higher alkyl
group-containing monomers, aromatic ring-containing monomers, and
macromers are preferably used. The monomer copolymerizable with the
polyoxyalkylene group-containing monomer and the salt forming
group-containing monomer can suppress a change in viscosity of the
ink caused by a wetting agent and a dispersant added in the
preparation of the ink. Further, the storage stability of the ink
can be enhanced. They may be used either solely or as a mixture of
two or more.
[0123] In the higher alkyl group-containing monomer, the number of
carbon atoms of the higher alkyl group is preferably 16 to 30, more
preferably 18 to 22 from the viewpoint of, because they are easily
available. For example, compounds represented by the following
formula may be mentioned as representative examples of the higher
alkyl group-containing monomer, wherein R.sup.1 represents a
hydrogen atom or a lower alkyl group having 1 to 4 carbon atoms;
R.sup.2 represents a hydrocarbon group optionally having a hetero
atom and having 16 to 30 carbon atoms.
##STR00009##
[0124] In the above formula, preferably, R.sup.2 represents an
optionally heteroatom-containing monovalent hydrocarbon group
having 18 to 30 carbon atoms, more preferably 18 to 22 carbon
atoms.
[0125] Specific examples of higher alkyl group-containing monomers
include (meth)acrylic esters such as (iso)cetyl (meth)acrylate,
(iso)stearyl (meth)acrylate, and (iso)behenyl (meth)acrylate. They
may be used either solely or as a mixture of two or more. Among
them, (iso)stearyl (meth)acrylate and/or (iso)behenyl
(meth)acrylate are particularly preferred. When the higher alkyl
group-containing monomer is used, a change in viscosity of the ink
caused by a wetting agent or a dispersant added in the preparation
of the ink can be advantageously suppressed to satisfactorily
improve the storage stability. In this case, the total amount of
stearyl (meth)acrylate and behenyl (meth)acrylate in the monomer
mixture is preferably 5 to 50% by weight, more preferably 10 to 30%
by weight, from the viewpoints of suppressing a change in ink
viscosity and satisfactorily enhancing storage stability.
[0126] The aromatic ring-containing monomer is preferably at least
one monomer selected from the group consisting of styrene,
vinyinaphthalene, .alpha.-methylstyrene, vinyltoluene, ethyl
vinylbenzene, 4-vinylbiphenyl, 1,1-diphenylethylene, benzyl
(meth)acrylate, phenoxyethyl (meth)acrylate,
2-hydroxy-3-phenoxypropyl acrylate,
2-methacryloyloxyethyl-2-hydroxypropyl phthalate,
2-acryloyloxyethylphthalic acid, and neopentyl glycol acrylate
benzoate from the viewpoint of imparting waterfastness. Among them,
one or more monomers selected from the group consisting of styrene,
.alpha.-methylstyrene, vinyltoluene, and vinylnaphthalene is more
preferred from the viewpoints of waterfastness and scratch/rubbing
resistance.
[0127] (Meth)acrylic esters include, for example, (meth)acrylic
esters in which the ester part is an alkyl group having 1 to 18
carbon atoms, for example, methyl (meth)acrylate, ethyl
(meth)acrylate, (iso)propyl (meth)acrylate, (iso or tertiary)butyl
(meth)acrylate, (iso)amyl (meth)acrylate, cyclohexyl
(meth)acrylate, benzyl (meth)acrylate, 2-ethylhexyl (meth)acrylate,
(iso)octyl (meth)acrylate, (iso)decyl (meth)acrylate, (iso)dodecyl
(meth)acrylate, and (iso)stearyl (meth)acrylate. They may be used
either solely or as a mixture of two or more.
[0128] An example of the macromer as one of the copolymerizable
monomers is a macromer having a polymerizable functional group at
its one end and preferably having a number average molecular weight
of 500 to 500,000, more preferably 1,000 to 10,000.
[0129] Specific examples of macromers include styrenic macromers
having a polymerizable functional group at one end thereof,
silicone macromers having a polymerizable functional group at one
end thereof, methyl methacrylate macromers having a polymerizable
functional group at one end thereof, styrene-acrylonitrile
macromers having a polymerizable functional group at one end
thereof, butyl acrylate macromers having a polymerizable functional
group at one end thereof, and isobutyl methacrylate macromers
having a polymerizable functional group at one end thereof. Among
them, styrenic macromers having a polymerizable functional group at
one end thereof are preferred from the viewpoint of satisfactorily
incorporating the colorant into the vinyl polymer.
[0130] A styrene homopolymer having a polymerizable functional
group at its one end and a copolymer of styrene with another
monomer having a polymerizable functional group at its one end may
be mentioned as the styrenic macromer containing a polymeriable
functional group on its one end.
[0131] In the copolymer of styrene with another monomer having a
polymerizable functional group at its one end, examples of another
monomers include acrylonitrile. The content of styrene is
preferably not less than 60% by weight, more preferably not less
than 70% by weight, from the viewpoint of satisfactorily
incorporating the pigment in the vinyl polymer.
[0132] Among styrenic macromers having a polymerizable functional
group at one end thereof, those having an acryloyl or methacryloyl
group as the polymerizable functional group at one end thereof are
preferred. Commercially available styrenic macromers include, for
example, AS-6, AS-6S, AN-6, AN-6S, HS-6S, and HS-6, manufactured by
TOAGOSEI Co., Ltd.
[0133] The number average molecular weight of the macromer is
measured by gel chromatography using 1 mmol/L
dodecyldimethylamine-containing chloroform as the solvent and
polystyrene as a standard material.
[0134] The content of the macromer in the vinyl polymer is
preferably 0.1 to 40% by weight, more preferably 1 to 30% by
weight, from the viewpoints of waterfastness and scratch/rubbing
resistance.
[0135] The use of the macromer as a monomer for constituting the
vinyl polymer can realize the provision of an ink composition
having excellent ejection properties. The reason for this has not
been fully elucidated yet but is believed to reside in that the
hydrophobic interaction between the highly hydrophobic macromer and
the magenta solid solution pigment as the colorant is so strong
that the vinyl polymer develops a high level of adsorption to the
colorant and, thus, the hydrophobicity of the colorant-containing
polymer particles is enhanced resulting in lowered viscosity of the
water-based ink.
[0136] The content of the copolymerizable monomer in the vinyl
polymer is 15 to 90% by weight, preferably 35 to 80% by weight,
from the viewpoints of print density and waterfastness.
[0137] The vinyl polymer may be produced by mixing a predetermined
amount of the polyoxyalkylene group-containing monomer (1), a
predetermined amount of the salt forming group-containing monomer
(2), and a predetermined amount of the copolymerizable monomer (3)
together and copolymerizing them. The polymerization may be carried
out by a conventional polymerization method such as a bulk
polymerization method, a solution polymerization method, a
suspension polymerization method, or an emulsion polymerization
method. Among these polymerization methods, the solution
polymerization method is preferred.
[0138] A polar organic solvent is preferably used as the solvent in
the solution polymerization method. When the polar organic solvent
is miscible with water, the polar organic solvent may be used as a
mixture with water.
[0139] Polar organic solvents include, for example, aliphatic
alcohols having 1 to 3 carbon atoms such as methanol, ethanol,
propanol, and isopropyl alcohol; ketones such as acetone and methyl
ethyl ketone; and esters such as ethyl acetate. Among them,
methanol, ethanol, isopropyl alcohol, acetone, methyl ethyl ketone,
or a mixed liquid composed of the above solvent with water is
preferred.
[0140] In the polymerization, a radical polymerization initiator
may be used. Suitable radical polymerization initiators include azo
compounds such as 2,2'-azobisisobutyronitrile,
2,2'-azobis(2,4-dimethylvaleronitrile),
dimethyl-2,2'-azobisbutyrate, 2,2'-azobis(2-methylbutyronitrile),
and 1,1'-azobis(1-cyclohexanecarbonitrile). Organic peroxides such
as t-butylperoxyoctoate, di-t-butylperoxide, and dibenzoyloxide may
also be used.
[0141] The addition amount of the polymerization initiator per mole
of monomer composition is preferably 0.001 to 5 moles, more
preferably 0.01 to 2 moles.
[0142] In the polymerization, in addition to the radical
polymerization initiator, a polymerization chain transfer agent may
be added. Specific examples of polymerization chain transfer agents
usable herein include mercaptanes such as octylmercaptan,
n-dodencylmercaptan, t-dodecylmercaptan, n-tetradecylmercaptan, and
2-mercaptoethanol; xanthogen disulfides such as dimethylxanthogen
disulfide and diisopropylxanthogen disulfide; thiuram disulfides
such as tetramethyl thiuram disulfide and tetrabutyl thiuram
disulfide; halogenated hydrocarbons such as carbon tetrachloride
and ethylene bromide; hydrocarbons such as pentaphenylethane;
unsaturated cyclic hydrocarbon compounds such as acrolein,
methacrolein, allyl alcohol, 2-ethylhexyl thioglycolate,
turbinolene, .alpha.-terpinene, .gamma.-terpinene, dipentene,
.alpha.-methylstyrene dimmer, 9,10-dihydroanthracene,
1,4-dihydronaphthalene, indene, and 1,4-cyclohexadiene; and
unsaturated hetetrocyclic compounds such as 2,5-dihydrofuran. These
polymerization chain transfer agents may be used either solely or
as a mixture of two or more.
[0143] Polymerization conditions for monomer composition vary
depending, for example, upon radical polymerization initiators,
monomers, and the type of solvents used. In general, the
polymerization temperature is preferably 30 to 100.degree. C., more
preferably 50 to 80.degree. C. The polymerization time is
preferably 1 to 20 hr. The polymerization atmosphere is preferably
an inert gas atmosphere such as nitrogen gas.
[0144] After the completion of the polymerization reaction, the
produced vinyl polymer is isolated from the reaction solution by a
conventional method such as reprecipitation from the reaction
solution or removal of the solvent by evaporation. The vinyl
polymer thus obtained may be purified by removing the unreacted
monomer and the like, for example, by the repetition of
reprecipitation, membrane separation, chromatography, or
extraction.
[0145] The weight average molecular weight of the vinyl polymer is
preferably 150,000 to 500,000. When the weight average molecular
weight of the vinyl polymer is in the above-defined range, printing
stability in continuous printing is improved. The average molecular
weight of the polymer can be controlled by a conventional procedure
in which a chain transfer material such as mercaptan is added.
[0146] The weight average molecular weight of the vinyl polymer may
be determined by drying a part of the polymer solution under the
reduced pressure at 150.degree. C. for 2 hr, to remove the solvent
to isolate the vinyl polymer, and subjecting the vinyl polymer to
gel permeation chromatography using polystyrene as the standard
substance and 60 mmol/L phosphoric acid and 50 mmol/L lithium
bromide-containing dimethylformamide as the solvent.
[0147] In the present invention, the vinyl polymer is preferably
present in the form of polymer particles in the ink. The polymer
particles may be produced, for example, by adding a solvent such as
methyl ethyl ketone to the polymer solution, adding an aqueous
electrolyte solution such as potassium hydroxide thereto to
neutralize the polymer salt forming group, adding ion exchanged
water thereto, stirring the mixture, further carrying out stirring
with a microfluidizer or the like, removing the organic solvent and
water from the resultant emulsification product.
[0148] The average particle diameter of the vinyl polymer is
preferably regulated to approximately 10 to 200 nm, more preferably
60 to 200 nm. When the average particle diameter is less than 10
nm, the recovery from clogging is deteriorated. On the other hand,
when the average particle diameter exceeds 300 nm, the gloss on
gloss paper is deteriorated. The diameter of the polymer particles
may be measured by observation under an electron microscope, a
coulter counter, or a light scattering method. For example, the
measurement by the coulter counter can be carried out with Coulter
Counter N4 (manufactured by Coulter Electronics K.K.), the
measurement by the light scattering method can be carried out with
a laser particle diameter analysis system LPA-3000/3100
(manufactured by Otsuka Electronics Co., Ltd.) or a laser
diffraction-type particle size distribution measuring device
SALD-2000A (manufactured by Shimadzu Seisakusho Ltd.).
[0149] The amount of the vinyl polymer particles added to the ink
composition is preferably not less than 0.1% by weight from the
viewpoint of the fixation and is preferably not more than 3.0% by
weight, more preferably 0.2 to 2.0% by weight, from the viewpoint
of preventing a deterioration in recovery from clogging.
[0150] Surfactant
[0151] In a preferred embodiment of the present invention, the ink
composition according to the present invention comprises two
compounds represented by formulae (a) and (b):
##STR00010##
[0152] wherein m and n satisfy a requirement of m+n=10.
[0153] An improvement in recovery from clogging and ejection
stability while improving color developing properties on plain
papers can be realized by using the compound having a low balance
(HLB) value between hydrophilicity and lipophilicity (compound of
formula (a)) and the compound having a high HLB value (compound of
formula (b)) in combination at a weight ratio of 2:1 to 1:4,
preferably 5:7 to 5:13.
[0154] In the present invention, the incorporation of the compound
having a low HLB value (compound of formula (a)) and the compound
having a high HLB value (compound of formula (b)) at a
predetermined ratio in the ink composition can simultaneously
realize an improvement in color developing properties on plain
papers and an improvement in recovery from clogging and ejection
stability.
[0155] The total addition amount of the compound of formula (a) and
the compound of formula (b) may be properly determined. Preferably,
however, the total amount of the compound of formula (a) and the
compound of formula (b) added to the ink composition is preferably
0.03 to 5% by weight, more preferably 0.3 to 3% by weight.
[0156] The compound of formula (a) may be a commercially available
product, and specific examples thereof include Olfine STG
(manufactured by Nissin Chemical Industry Co., Ltd.) and Surfynol
104 (manufactured by Air Products and Chemicals, Inc.).
[0157] The compound of formula (b) may be a commercially available
product, and examples thereof include Surfynol 400 series
(manufactured by Air Products and Chemicals, Inc.) and Olfine E1010
(manufactured by Nissin Chemical Industry Co., Ltd.).
[0158] Water and Other Components
[0159] Water
[0160] The ink composition according to the present invention
comprises water as a main solvent. Water may be pure water or
ultrapure water obtained by ion exchange, ultrafiltration, reverse
osmosis, distillation or the like. Water, which has been
sterilized, for example, by ultraviolet irradiation or by addition
of hydrogen peroxide, is preferred, because this treatment can
prevent the growth of mold or bacteria and, thus, the ink
composition can be stored for a long period of time.
[0161] pH Adjustor
[0162] Preferably, the ink composition according to the present
invention further comprises a pH adjuster. Specific examples of pH
adjustors include: hydroxides of alkali metals such as lithium
hydroxide, potassium hydroxide, sodium hydroxide and amines such as
ammonia, triethanolamine, tripropanolamine, diethanolamine, and
monoethanolamine. More preferably, the pH adjustor is selected from
the group consisting of triethanolamine, tripropanolamine, and a
mixture of triethanolamine with tripropanolamine.
[0163] In the present invention, the pH value of the ink
composition is preferably 8.0 to 11. Better gloss can be realized
by adjusting the ink composition to the above-defined pH range. The
use of the above pH adjustor is advantageously for the adjustment
of the ink composition to the above-defined pH range.
[0164] Water Soluble Organic Solvent
[0165] The ink composition according to the present invention
preferably further comprises a water soluble organic solvent. The
water soluble organic solvent functions mainly as a penetrating
agent, a humectant, a viscosity modifier and the like of the ink
composition.
[0166] Specific examples of water soluble organic solvents include
monohydric alcohols such as methanol, ethanol, n-propanol,
iso-propanol, n-butanol, sec-butanol, tert-butanol, iso-butanol,
and n-pentanol, and glycol monoalkyl 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-iso-propyl ether, diethylene glycol mono-iso-propyl ether,
ethylene 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-iso-propyl ether, dipropylene glycol monomethyl ether,
dipropylene glycol monoethyl ether, dipropylene glycol
mono-n-propyl ether, and dipropylene glycol mono-iso-propyl
ether.
[0167] In a preferred embodiment of the present invention, the ink
composition comprises a component selected from water soluble
polyols, glycol-type butyl ether, pyrrolidone, and mixtures
thereof. Among them, a combination of a water soluble polyol, a
glycol-type butyl ether, and pyrrolidone is more preferred. The
incorporation of the combination can realized a further improvement
in ink reliability of the ink composition, for example, print
quality, ejection stability, and recovery from clogging.
[0168] Specific examples of water soluble polyols include ethylene
glycol, diethylene glycol, triethylene glycol, tetraethylene
glycol, propylene glycol, dipropylene glycol, tripropylene glycol,
polyethylene glycol, 1,3-propylene glycol, 1,3-butanediol,
1,5-pentanediol, 1,6-hexanediol, glycerin, metherythritol,
pentaerythritol, thiodiglycol, trimethylolpropane,
trimethylolpropane, and pentaerythritol. Among them, diethylene
glycol, triethylene glycol, 1,5-pentanediol, glycerin, and
trimethylolpropane are preferred. These water soluble polyols may
be used either solely or as a mixture of two or more.
[0169] An example of a preferred glycol-type butyl ether is a ether
selected, for example, from ethylene glycol mono-n-butyl ether,
diethylene glycol mono-n-butyl ether, triethylene glycol
mono-n-butyl ether, propylene glycol mono-n-butyl ether, or
dipropylene glycol mono-n-butyl ether. Among them, ethylene glycol
mono-n-butyl ether and triethylene glycol mono-n-butyl ether are
preferred. These glycol-type butyl ethers may be used either solely
or as a mixture of two or more.
[0170] The addition amount of the water soluble organic solvent is
preferably 0.25 to 15% by weight, more preferably 0.5 to 10% by
weight, based on the total amount of the ink.
[0171] 1,2-Alkanediol
[0172] In the present invention, preferably, the ink composition
further comprises an 1,2-alkanediol.
[0173] The 1,2-alkanediol is preferably selected from the group
consisting of 1,2-alkanediols having 4 to 10 carbon atoms. In this
case, a mixture of a plurality of 1,2-alkanediols may be added.
[0174] In a preferred embodiment of the present invention, the
1,2-alkanediol is selected from the group consisting of
1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,2-heptenediol,
and mixtures thereof. They are advantageous because of their
excellent penetration into the recording medium.
[0175] In a more preferred embodiment of the present invention, the
1,2-alkanediol is preferably 1,2-hexanediol or 1,2-pentanediol,
more preferably 1,2-hexanediol.
[0176] The addition amount of the 1,2-alkanediol is preferably not
less than 0.25% by weight and not more than 15% by weight based on
the total amount of the ink composition. More preferably, the upper
limit of the addition amount of the 1,2-alkanediol is 10% by
weight, and the lower limit of the addition amount of the
1,2-alkanediol is 0.5% by weight.
[0177] Other Components
[0178] In a preferred embodiment of the present invention, the ink
composition preferably contains polyols from the viewpoint of
preventing nozzle clogging of an ink jet recording head. Preferred
polyols include water soluble polyols, and examples thereof include
ethylene glycol, diethylene glycol, triethylene glycol,
tetraethylene glycol, propylene glycol, dipropylene glycol,
tripropylene glycol, polyethylene glycol, 1,3-propylene glycol,
isopropylene glycol, isobutylene glycol, 1,4-butanediol,
1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, glycerin,
metherythritol, pentaerythritol, thiodiglycol, trimethylolpropane,
trimethylolethane, 1,2,6-hexantriol, trimethylolethane,
trimethylolpropane, and pentaerythritol.
[0179] Further, lactams such as 2-pyrrolidone,
N-methyl-2-pyrrolidone, and .epsilon.-caprolactam, and ureas such
as urea, thiourea, ethyleneurea, and 1,3-dimethylimidazolidinone
may also be used. Furthermore, for example, glucose, mannose,
fructose, ribose, xylose, arabinose, galactose, aldonic acid,
glucitol, (sorbit), maltose, cellobiose, lactose, sucrose,
trehalose, and maltotriose may be added as monosaccharides,
dissacharides, oligosaccharides, and polysaccharides. Further,
derivatives of these saccharides may also be used. For example,
reducing sugars, oxidizing sugars, amino acids, and thiosugars may
also be used. Among them, sugar alcohols are particularly
preferred, and specific examples thereof include maltitol and
sorbit. Commercially available products, for example, HS-500 and
HS-300 manufactured by Hayashibara Biochemical Laboratories, Inc.,
may also be used. They may be used either solely or as a mixture of
two or more.
[0180] The addition amount of the clogging preventive component is
preferably not less than 5% by weight and not more than 40% by
weight based on the total amount of the ink composition. More
preferably, the upper limit of the addition amount of the clogging
preventive component is 30% by weight, and the lower limit of the
addition amount of the clogging preventive component is 10% by
weight.
[0181] Further, these components in combination with other ink
additives is preferably added in such an amount that bring the ink
viscosity to not more than 25 cPs at 25.degree. C.
[0182] The ink composition according to the present invention may
if necessary contain pH buffers, antioxidants, ultraviolet
absorbers, preservatives or fungicides, chelating agents and the
like.
[0183] Specific examples of pH adjustors include collidine,
imidazole, phosphoric acid, 3-(N-morpholino)propanesulfonic acid,
tris(hydroxymethyl)aminomethane, and boric acid.
[0184] Specific examples of antioxidants or ultraviolet absorbers
include allophanates such as allophanate and methyl allophanate,
biurets such as biuret, dimethylbiuret and tetramethylbiuret,
L-ascorbic acid and its salts, Tinuvin328, Tinuvin900, Tinuvini130,
Tinuvin384, Tinuvin292, Tinuvin123, Tinuvin144, Tinuvin622,
Tinuvin770, Tinuvin292, Irgacor252, Irgacor153, Irganox1010,
Irganox1076, Irganox1035, and MD1024 (manufactured by CIBA-GEIGY
Ltd.), or lanthanide oxides.
[0185] Specific examples of preservatives or fungicides include
sodium benzoate, sodium pentachlorophenolate, sodium
2-pyridinethiol-1-oxide, sodium sorbate, sodium dehydroacetic acid,
and 1,2-dibenzothiazolin-3-one (ProxelCRL, ProxelBDN, ProxelGXL,
ProxelXL-2, and ProxelTN, manufactured by Avecia). Specific
examples of chelating agents include ethylenediaminetetraacetic
acid (EDTA).
[0186] Preparation of Ink Composition
[0187] The ink composition according to the present invention may
be prepared by supplying the above components into a
dispersing/mixing machine (for example, a ball mill, a sand mill,
an attritor, a basket mill, or a roll mill) and dispersing the
mixture. In a preferred embodiment of the present invention, the
ink stock solution thus prepared by the dispersing/mixing machine
is filtered, for example, through a membrane filter or a mesh
filter to remove coarse particles.
[0188] Ink Jet Recording Method and Apparatus
[0189] The ink jet recording method in which the ink composition
according to the present invention is used, comprises ejecting
droplets of an ink composition and depositing the droplets onto a
heated recording medium to perform printing. Examples of methods
for ejecting droplets of the ink composition include a method
wherein an electric signal is converted to a mechanical signal
using an electrostrictive element to intermittently eject ink
reservoired in a nozzle head section, thereby recording letters or
symbols on the surface of a recording medium, and a method wherein
ink, reservoired in a nozzle head section, in its portion very
close to the ejection portion is rapidly heated to create a bubble
and the ink are intermittently ejected by volume expansion created
by the bubble to record letters or symbols on the surface of a
recording medium. In a preferred embodiment of the present
invention, the ink composition according to the present invention
is preferably used in ink jet recording using an electrostrictive
element. The ejection of droplets of the ink composition is
preferably carried out by a recording head through which ink
droplets are ejected by taking advantage of the dyanamical action
of the piezoelectric element.
[0190] Further, according to the present invention, there is also
provided a recorded matter recoded by the above recording
method.
EXAMPLES
[0191] The present invention is further illustrated by the
following Examples that are not intended as a limitation of the
invention.
[0192] Preparation of Magenta Solid Solution Pigment (a)
[0193] A crude pigment of C.I. Pigment Violet 19 (10 parts), 100
parts of sodium chloride, and 1 part of a high-boiling point
alicyclic hydrocarbon are charged into a ball mill, and the mixture
was milled for 10 hr. Subsequently, the milled mixture was
subjected to post treatments such as pigment formation, filtration,
and washing according to the conventional method to provide a
pressed cake having a solid content of 30% by weight.
[0194] A crude pigment of C.I. Pigment Red 209 (10 parts), 100
parts of sodium chloride, and 1 part of a high-boiling point
alicyclic hydrocarbon are charged into a ball mill, and the mixture
was milled for 10 hr. Subsequently, the milled mixture was
subjected to post treatments such as pigment formation, filtration,
and washing according to the conventional method to provide a
pressed cake having a solid content of 30% by weight.
[0195] Next, the solid matter of the pressed cake of C.I. Pigment
Violet 19 (2 parts) and the solid matter of the pressed cake of
C.I. Pigment Red 209 (8 parts) were added, and the mixture was
milled, and the solid solution pigment was converted to a pigment
by organic solvent treatment, followed by filtration, washing,
drying and grinding to prepare a solid solution pigment of C.I.
Pigment Violet 19/C.I. Pigment Red 209 (weight ratio: 3/1). The hue
was a magenta color. The produced solid solution pigment had an
average particle diameter of not more than 200 nm.
[0196] Preparation of Magenta Solid Solution Pigment (b)
[0197] A crude pigment of C.I. Pigment Violet 19 (10 parts), 100
parts of sodium chloride, and 1 part of a high-boiling point
alicyclic hydrocarbon are charged into a ball mill, and the mixture
was milled for 10 hr. Subsequently, the milled mixture was
subjected to post treatments such as pigment formation, filtration,
and washing according to the conventional method to provide a
pressed cake having a solid content of 30% by weight.
[0198] A crude pigment of C.I. Pigment Red 122 (10 parts), 100
parts of sodium chloride, and 1 part of a high-boiling point
alicyclic hydrocarbon are charged into a ball mill, and the mixture
was milled for 10 hr. Subsequently, the milled mixture was
subjected to post treatments such as pigment formation, filtration,
and washing according to the conventional method to provide a
pressed cake having a solid content of 30% by weight.
[0199] Next, the solid matter of the pressed cake of C.I. Pigment
Violet 19 (7.5 parts) and the solid matter of the pressed cake of
C.I. Pigment Red 122 (2.5 parts) were added, and the mixture was
milled, and the solid solution pigment was converted to a pigment
by organic solvent treatment, followed by filtration, washing,
drying and grinding to prepare a solid solution pigment of C.I.
Pigment Violet 19/C.I. Pigment Red 122 (weight ratio: 3/1). The hue
was a magenta color. The produced solid solution pigment had an
average particle diameter of not more than 200 nm.
[0200] Preparation of Magenta Solid Solution Pigment (c)
[0201] Magenta solid solution pigment (c) was produced in the same
manner as in magenta solid solution pigment (b), except that the
weight ratio between C.I. Pigment Red 19 and C.I. Pigment Red 122
is 1:1. The hue was a magenta color, and the average particle
diameter was not more than 200 nm.
[0202] Preparation of Magenta Solid Solution Pigment (d)
[0203] Magenta solid solution pigment (d) was produced in the same
manner as in magenta solid solution pigment (b), except that the
weight ratio between C.I. Pigment Red 19 and C.I. Pigment Red 122
is 2:8. The hue was a magenta color, and the average particle
diameter was not more than 200 nm.
[0204] Preparation of Dispersant Polymer
[0205] Methyl ethyl ketone (20 parts by weight), 0.03 part by
weight of a polymerization chain transfer agent
(2-mercaptanethanol), and 10% by weight in total of the monomers
specified in Table 1 below were charged into a reaction vessel and
were mixed together. Thereafter, the air in the vessel was replaced
by nitrogen gas. On the other hand, the remaining 90% by weight of
the monomer composition was charged into a dropping device.
[0206] A polymerization chain transfer agent (2-mercaptanethanol)
(0.27 part by weight), 60 parts by weight of methyl ethyl ketone,
and 1.2 parts by weight of 2,2'-azobis(2,4-dimethylvaleronitrile)
are then added to the dropping device, followed by mixing.
Thereafter, the air in the dropping device was replaced by nitrogen
gas.
[0207] Under a nitrogen atmosphere, the mixed solution within the
reaction vessel was heated to 65.degree. C. with stirring, and the
mixed solution in the dropping device was gradually added dropwise
to the contents of the reaction vessel over a period of 3 hr. After
the completion of the dropwise addition, the temperature of the
mixed solution was maintained at 65.degree. C. for 2 hr. A solution
of 0.3 part by weight of 2,2'-azobis(2,4-dimethylvaleronitrile)
dissolved in 5 parts by weight of methyl ethyl ketone was added to
the mixed solution, and the mixture was ripened at 65.degree. C.
for 2 hr and at 70.degree. C. for 2 hr to prepare a polymer
solution.
[0208] A part of the polymer solution thus obtained was provide,
and the solvent was removed by distillation under the reduced
pressure for drying for isolation to give polymer particles.
[0209] The weight average molecular weight was determined by gel
permeation chromatography using polystyrene as a standard substance
and 60 mmol/L phosphoric acid and 50 mmol/L lithium
bromide-containing dimethylformamide as a solvent and was found to
be 70,000.
TABLE-US-00001 TABLE 1 Addition amount (wt %) Monomer A B C
Polypropylene glycol 0 15 15 monomethacrylate (n = 9) Poly(ethylene
glycol/propylene 0 0 8 glycol) monomethacrylate Methacrylic acid 22
14 14 Styrene monomer 63 48 48 Styrene macromer 15 15 15 n-Butyl
methacrylate 0 0 0 n-Butyl acrylate 0 0 0 Stearyl methacrylate 0 8
0 Degree of neutralization (%) 60 60 60
[0210] Polypropylene glycol monomethacrylate (n=9):
[0211] tradename: Blemmer PP-500, manufactured by Nippon Oils &
Fats Co., Ltd.
[0212] Styrene macromer: tradename: AS-6S (styrene macromer),
manufactured by TOAGOSEI Co., Ltd., number average molecular
weight: 6000, polymerizable functional group: methacryloyl
group.
[0213] Poly(ethylene glycol/propylene glycol) monomethacrylate:
tradename: Blemmer 50PEP-300, manufactured by Nippon Oils &
Fats Co., Ltd.
[0214] Preparation of Pigment Dispersion Liquids 1 to 6
TABLE-US-00002 TABLE 2 Pigment Magenta solid Dispersant dispersion
liquid solution pigment polymer 1 (a) A 2 (a) B 3 (a) C 4 (b) C 5
(c) C 6 (d) C
[0215] As described above, the magenta solid solution pigment was
used in combination with the dispersant polymer to prepare a
pigment dispersion liquid. The vinyl polymer (5 parts by weight)
was dissolved in 45 parts by weight of methyl ethyl ketone. A
predetermined amount (specified in Table 1) of a neutralizing agent
(a 20% aqueous sodium hydroxide solution) was added to the solution
to neutralize the salt forming group. The magenta solid solution
pigment prepared above (20 parts by weight) was then added, and the
mixture was kneaded with a bead mill for 2 hr.
[0216] Ion-exchanged water (120 parts by weight) was added to the
kneaded product prepared above, and the mixture was stirred. Methyl
ethyl ketone was removed under the reduced pressure at 60.degree.
C. Further, a part of water was removed. Thus, pigment dispersion
liquids 1 to 6 having a solid content of 20% by weight were
prepared. The average particle diameter of the polymer particles in
the pigment dispersion liquid was measured with Coulter Counter N4
(manufactured by Coulter Electronics) and, for all the pigment
dispersion liquids, was found to be 100 nm.
Preparation of Ink Compositions
Examples 1 to 7
[0217] The components were mixed together according to the
formulations specified in Table 2 below, and the mixture was
stirred for 2 hr. Subsequently, the stirred mixture was filtered
through Membrane Filter (tradename, manufactured by NIHON
MILLIPORE, LTD.) having a pore diameter of about 8 .mu.m. Thus,
magenta inks were prepared. In Table 2, the addition amount of each
composition is in % by weight.
TABLE-US-00003 TABLE 3 Example 1 2 3 4 5 6 7 Composition Addition
amount (wt %) Pigment 1 40 40 40 -- -- -- -- dispersion liquid 2 --
-- -- 40 -- -- -- 3 -- -- -- -- 40 -- -- 4 -- -- -- -- -- 40 -- 5
-- -- -- -- -- -- 40 Trimethylolpropane 5 5 5 5 5 5 5 Glycerin 5 5
5 5 5 5 5 Triethylene glycol 10 10 10 10 10 10 10 TEGmBE 2 2 2 2 2
2 2 1,2-Hexanediol 3 3 3 3 3 3 3 Olfine E1010 0.6 0.4 0.9 0.7 0.6
0.6 0.6 Surfynol 104 0.3 0.9 0.2 0.3 0.4 0.3 0.3 Emulgen 120 -- --
-- -- -- -- -- Emulgen 408 -- -- -- -- -- -- -- 2-Methylpyrrolidone
2 2 2 2 2 2 2 Triethanolamine 1 1 1 1 1 1 1 Ultrapure water Balance
Balance Balance Balance Balance Balance Balance In the table,
TEGmBE represents triethylene glycol monobutyl ether Emulgen 120
(manufactured by Kao Corp.) is a surfactant which is
polyoxyethylene lauryl ether and has an HLB value substantially
equal to Olfine E1010. Emulgen 480 (manufactured by Kao Corp.) is a
surfactant which is polyoxyethylene oleyl ether and has an HLB
value substantially equal to Surfynol 104.
[0218] Preparation of Vinyl Polymer
[0219] Methyl ethyl ketone (20 parts by weight), 10% by weight of
the amount (parts by weight) of each monomer of Preparations 1 to 3
specified in the table below, and 2-mercaptoethanol (polymerization
chain transfer agent) in an amount shown in the table below were
placed and were mixed together in a reaction vessel, followed by
thorough replacement of the air in the reaction vessel by nitrogen
gas to prepare a mixed solution. Thus, three types of mixture
liquids were prepared.
[0220] On the other hand, the remaining 90% by weight of the amount
(parts by weight) of each monomer specified in the table below was
charged into a dropping funnel. Next, a polymerization chain
transfer agent (2-mercaptoethanol) in an amount specified in the
table, 60 parts by weight of methyl ethyl ketone and 1.2 parts by
weight of 2,2'-azobis(2,4-dimethylvaleronitrile) were added to and
mixed with the solution in the dropping funnel, followed by
thorough replacement of the air in the dropping funnel by nitrogen
gas. Thus, three types of mixture liquids were produced.
[0221] Under a nitrogen atmosphere, the mixed solution within the
reaction vessel was heated to 65.degree. C. with stirring, and the
mixed solution in the dropping funnel was gradually added dropwise
to the contents of the reaction vessel over a period of 3 hr. After
the completion of the dropwise addition, the temperature of the
mixed solution was maintained at 65.degree. C. for 2 hr. A solution
of 0.3 part by weight of 2,2'-azobis(2,4-dimethylvaleronitrile)
dissolved in 5 parts by weight of methyl ethyl ketone was added to
the mixed solution, and the mixture was ripened at 65.degree. C.
for 2 hr and at 70.degree. C. for 2 hr. Thus, polymer solutions of
Preparations 1 to 3 were produced.
[0222] A part of each polymer solution of Preparations 1 to 3 thus
obtained was dried under the reduced pressure at 105.degree. C. for
2 hr to remove the solvent for isolation of the polymer. The weight
average molecular weight of the polymer was determined by
gel-permeation chromatography using polystyrene as a standard
substance, and 60 mmol/L of phosphoric acid and 50 mmol/L of
lithium bromide-containing dimethylformamide as solvents.
TABLE-US-00004 TABLE 4 Preparation No.. Starting materials for
polymer synthesis 1 2 3 Monomer Polyethylene glycol 0 8 8
monomethacrylate (m = 23) Polypropylene glycol 15 15 15
monomethacrylate (n = 9) Poly(ethylene 8 0 0 glycol/propylene
glycol) monomethacrylate Methacrylic acid 14 14 14 Styrene monomer
48 48 48 Styrene macromer 15 15 15 Stearyl methacrylate 0 0 0
2-Mercaptoethanol Within reaction vessel 0.030 0.030 0.010
(polymerization Within dropping 0.270 0.270 0.100 chain transfer
funnel agent) weight average molecular weight of 60,000 60,000
250,000 polymer
[0223] The detail of main starting compounds specified in the table
are as follows.
[0224] Polyethylene glycol monomethacrylate (m=23): tradename; NK
ester M230G, manufactured by Shin-Nakamura Chemical Co., Ltd.; a
compound represented by formula (I) wherein m is 23 and R.sup.1 and
R.sup.2 represent a methyl group.
[0225] Polypropylene glycol monomethacrylate (n=9): tradename;
Blemmer PP-500, manufactured by Nippon Oils & Fats Co., Ltd.; a
compound represented by formula (II) wherein n is 9, R.sup.1
represents a methyl group, and R.sup.2 represents a hydrogen
atom.
[0226] Poly(ethylene glycol/propylene glycol) monomethacrylate:
tradename; Blemmer 50PEP-300, manufactured by Nippon Oils &
Fats Co., Ltd.; a monomer represented by formula (III) wherein m is
3.5, n is 2.5, R.sup.1 represents a methyl group, R.sup.2
represents hydrogen, and oxypropylene groups and oxyethylene groups
are added to each other randomly.
[0227] Styrene macromer: tradename; AS-6S (styrene macromer),
manufactured by TOAGOSEI Co., Ltd., number average molecular
weight: 6000, polymerizable functional group: methacryloyl
group.
[0228] Preparation of Vinyl Polymer Particles
[0229] Methyl ethyl ketone (64.0 parts by weight) was added to 14.0
parts by weight of the polymer obtained by drying each polymer
solution of Preparations 1 to 3 synthesized above in vacuo. A
predetermined amount of a 1 mol/L aqueous potassium hydroxide
solution was added thereto to neutralize the salt forming group of
the polymer to a degree of neutralization of 70% and thus to
provide a degree of neutralization (60%) specified in Table 1
above. Ion exchanged water (200 parts by weight) was added thereto,
and the mixture was stirred, followed by emulsification with
Microfluidizer (tradename, manufactured by Microfluidics) for 20
min.
[0230] An organic solvent was removed from each emulsion thus
obtained under the reduced pressure at 60.degree. C., and water was
further removed for concentration to give polymer particles 1 to 3
having a solid content of 20% by weight. The average particle
diameter of polymer particles 1 to 3 thus obtained was measured
with Coulter Counter N4 (tradename, manufactured by Coulter
Electronics) and was found to be 110 nm.
Production of Ink Compositions
Examples 8 to 10
[0231] The components were mixed together according to the
formulations specified in the table below, and the mixture was
stirred for 2 hr. Subsequently, the stirred mixture was filtered
through Membrane Filter (tradename, manufactured by NIHON
MILLIPORE, LTD.) having a pore diameter of about 8 .mu.m. Thus,
magenta inks of Examples 8 to 10 were prepared. In the table, the
addition amount of each composition is in % by weight.
TABLE-US-00005 TABLE 5 Example 8 9 10 Composition Addition amount
(wt %) Pigment 3 40 -- -- dispersion liquid 6 -- 40 40 Vinyl
polymer 1 2.5 -- -- particles 2 -- 2.5 -- 3 -- -- 2.5
Trimethylolpropane 5 5 5 Glycerin 5 5 5 Triethylene glycol 10 10 10
TEGmBE 2 2 2 EGmBE -- -- -- 1,2-Hexanediol 3 3 3 Olfine E1010 1 1 1
Surfynol 104 1 1 1 N-Methylpyrrolidone -- 3 -- 2-Methylpyrrolidone
3 -- 3 Triethanolamine 1 1 1 Ultrapure water Balance Balance
Balance In the table, TEGmBE represents triethylene glycol
monobutyl ether. EGmBE represents ethylene glycol monobutyl
ether.
Production of Ink Compositions
Examples 11 to 16
[0232] Ink compositions 11 to 16 were produced according to the
formulations specified in the table below in the same manner as in
Examples 1 to 7.
TABLE-US-00006 TABLE 6 Example 11 12 13 14 15 16 Composition
Addition amount (wt %) Pigment 1 40 40 -- -- -- -- dispersion
liquid 3 -- -- 40 40 40 40 Trimethylolpropane 5 5 5 5 5 5 Glycerin
5 5 5 5 5 5 Triethylene glycol 10 10 10 10 10 10 TEGmBE 2 2 2 2 2 2
1,2-Hexanediol 3 3 3 3 3 3 Olfine E1010 1.0 -- 1.0 -- 0.6 --
Surfynol 104 -- 1.0 -- 1.0 -- 0.3 Emulgen 120 -- -- -- -- -- 0.6
Emulgen 408 -- -- -- -- 0.3 -- 2-Methylpyrrolidone 2 2 2 2 2 2
Triethanolamine 1 1 1 1 1 1 Ultrapure water Balance Balance Balance
Balance Balance Balance In the table, TEGmBE represents triethylene
glycol monobutyl ether. Emulgen 120 (manufactured by Kao Corp.) is
a surfactant which is polyoxyethylene lauryl ether and has an HLB
value substantially equal to Olfine E1010. Emulgen 480
(manufactured by Kao Corp.) is a surfactant which is
polyoxyethylene oleyl ether and has an HLB value substantially
equal to Surfynol 104.
[0233] Evaluation of Ink Compositions
[0234] (1) Gloss
[0235] Blotted image printing was carried out with an ink jet
printer EM-930C (manufactured by Seiko Epson Corporation) at a
resolution of 1440 dpi. In this case, PM photographic paper
(tradename; model number KA 420 PSK, manufactured by Seiko Epson
Corporation) was used as the recording medium. The printed matter
thus obtained was allowed to stand under an environment of
24.degree. C. for 24 hr and was then measured for the 20-degree
gloss of the blotted image part with a gloss meter GM-268
(manufactured by KONICA MINOLTA).
[0236] The results of the measurement were evaluated according to
the following criteria.
[0237] A: 20-degree gloss of not less than 60
[0238] B: 20-degree gloss of not less than 50 and less than 60
[0239] C: 20-degree gloss of less than 50
[0240] The results were as shown in the table below.
[0241] (2) Color Developing Property
[0242] Blotted image printing was carried out with an ink jet
printer EM-930C (manufactured by Seiko Epson Corporation) at a
resolution of 720 dpi. In this case, four types of plain papers,
i.e., Xerox P (tradename, manufactured by FUJI XEROX OFFICE SUPPLY
Co., Ltd.), Xerox R (tradename, manufactured by FUJI XEROX OFFICE
SUPPLY Co., Ltd.), Xerox 4024 (tradename, manufactured by Xerox
Corporation), and Recycle Cut R-100 (manufactured by Oji Paper Co.,
Ltd.), were used as the recording medium. The printed matter was
allowed to stand under an environment of 24.degree. C. for 24 hr
and was measured for the OD value of the blotted image part with a
Gretag densitometer (manufactured by Gretag Macbeth).
[0243] The results of the measurement were evaluated according to
the following criteria.
[0244] A: Print density of not less than 1.2
[0245] B: Print density of not less than 1.1 and less than 1.2
[0246] C: Print density of less than 1.1
[0247] The results were as shown in the table below.
[0248] (3) Ejection Stability
[0249] Blotted images and line patterns were continuously printed
at room temperature with the above ink jet printer. The number of
times of cleaning operations of a printer nozzle necessary for
recovery to normal printing from dot missing or ink droplet
trajectory directionality problems caused during printing on 100
sheets or less was determined. The results were evaluated according
to the following criteria.
[0250] A: Any cleaning operation was not necessary for the
recovery.
[0251] B: Cleaning operation was necessary once to four times for
the recovery.
[0252] C: Cleaning operation was necessary five times or more for
the recovery.
[0253] The results were as shown in the table blow.
[0254] (4) Storage Stability of Ink
[0255] The ink compositions (50 g) were placed in aluminum bags.
The bags were allowed to stand under an environment of 70.degree.
C. for one week. After the standing, each ink composition was
inspected for the presence of foreign matter (sediment). The ink
composition free from the presence of foreign matter was further
inspected for a change in properties (viscosity, surface tension,
pH, and particle diameter of resin particles).
[0256] The results were evaluated according to the following
criteria.
[0257] A: There was neither foreign matter nor a change in
properties.
[0258] B: There was a slight change in properties, although no
foreign matter occurred.
[0259] C: There was foreign matter or a significant change in
properties.
[0260] The results were as shown in the table below.
[0261] (5) Recovery from Clogging
[0262] Printing was continuously carried out for 10 min using the
above ink cartridge and ink jet printer. After normal ejection of
the ink through all nozzles was confirmed, in order to accelerate
drying in nozzles, the ink cartridge was removed, and the recording
head was removed from the head cap, followed by standing in this
state under an environment of 40.degree. C. and 20% RH for one
week.
[0263] After the one-week standing, cleaning operation was repeated
to determine the number of cleaning operations required for all the
nozzles to normally eject the ink as in the initial state. The
recovery from nozzle clogging was evaluated based on the number of
cleaning operations according to the following criteria.
[0264] A: Recovered to the initial state by performing the cleaning
operation once.
[0265] B: Recovered to the initial state by performing the cleaning
operation twice to five times.
[0266] C: Recovered to the initial state by performing the cleaning
operation six times or more.
[0267] The results were as shown in the table below.
[0268] (6) Fixation
[0269] On the recorded matter obtained above, the backside of the
same type of a recording medium was put. A weight (200 g/size A4)
was placed on the recording medium, and the printed face was rubbed
twenty times by the weight.
[0270] The results were evaluated according to the following
criteria.
[0271] A: No scratch mark was observed.
[0272] B: Some scratch mark caused by the rubbing was observed on
such a level that is not substantially noticeable.
[0273] C: Noticeable scratch mark caused by the rubbing was
observed.
[0274] The results were as shown in the table below.
[0275] (7) Hue
[0276] A solution prepared by diluting 0.5 g of the ink composition
with 1000 ml of water was measured for UV spectral characteristics
with U-3000 (manufactured by Hitachi, Ltd.). FIG. 1 shows
absorption spectra for Examples 1, 6 and 7. Further, the value of
A/B was calculated wherein A represents the maximum value of the
absorbance in the wavelength range of 510 nm to 535 nm and B
represents the maximum value of the absorbance in the wavelength
range of 550 to 570 nm. The results were as shown in the table
below.
TABLE-US-00007 TABLE 7 Results of evaluation tests Recovery Color
Ejection Storage from Ex. Gloss development stability stability
clogging Fixation Hue 1 B A A A A B 0.98 2 B B A A A B 0.98 3 B B A
A A B 0.98 4 A A A A B B 0.98 5 A A A A A B 0.98 6 A B A A A B 0.90
7 A A A A A B 0.95 8 A A B A B A 0.98 9 A A B A A A 0.98 10 A A A A
A A 0.98 11 B B B A A B 0.98 12 B B B B B B 0.98 13 B B B A A B
0.98 14 B B B B B B 0.98 15 B B B B B B 0.98 16 B B B B B B
0.98
* * * * *