U.S. patent application number 10/990508 was filed with the patent office on 2005-04-28 for inkjet ink composition, method for manufacturing the inkjet ink composition and image forming method using the inkjet ink composition.
This patent application is currently assigned to RICOH COMPANY, LTD.. Invention is credited to Hatada, Shigeo, Taniguchi, Keishi.
Application Number | 20050087105 10/990508 |
Document ID | / |
Family ID | 19188866 |
Filed Date | 2005-04-28 |
United States Patent
Application |
20050087105 |
Kind Code |
A1 |
Taniguchi, Keishi ; et
al. |
April 28, 2005 |
Inkjet ink composition, method for manufacturing the inkjet ink
composition and image forming method using the inkjet ink
composition
Abstract
A method for manufacturing a composition including: mixing a
basic material with a pigment dispersion including at least a
pigment and water; and then subjecting the mixture of the basic
material and pigment dispersion to a heat treatment. This
composition is useful as an inkjet ink composition. An inkjet ink
composition including at least pigment, water and a basic material,
and has a pH of from 6.5 to 11.0 is also provided. An image forming
method including discharging the composition from a nozzle to form
an ink image on a receiving material is provided.
Inventors: |
Taniguchi, Keishi;
(Susono-shi, JP) ; Hatada, Shigeo; (Numazu-shi,
JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
RICOH COMPANY, LTD.
Tokyo
JP
|
Family ID: |
19188866 |
Appl. No.: |
10/990508 |
Filed: |
November 18, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10990508 |
Nov 18, 2004 |
|
|
|
10310061 |
Dec 5, 2002 |
|
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Current U.S.
Class: |
106/401 ;
106/31.6; 106/31.86; 106/499; 347/100; 428/195.1 |
Current CPC
Class: |
C09D 11/30 20130101;
C09C 1/48 20130101; C01P 2004/62 20130101; C09C 1/56 20130101; C09D
11/322 20130101; Y10T 428/24802 20150115 |
Class at
Publication: |
106/401 ;
106/031.6; 106/499; 106/031.86; 347/100; 428/195.1 |
International
Class: |
C08K 005/00; C09D
011/00; B41J 002/01 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 26, 2001 |
JP |
2001-394425 |
Claims
1-16. (canceled).
17. A composition comprising: at least one surface-treated pigment;
water; at least one water-soluble organic solvent; and a basic
material, wherein the composition has an initial pH of from 6.5 to
11.
18. The composition according to claim 17, wherein the composition
has a final pH not less than 6.5 after being heated at 70.degree.
C. for 3 weeks.
19. The composition according to claim 18, wherein a ratio of the
final pH to the initial pH is not less than 0.90.
20. An image forming method comprising: discharging an inkjet ink
from a nozzle to form an ink image on a receiving material, wherein
the inkjet ink comprises: at least one surface treated pigment; at
least one water-soluble organic solvent: water; and a basic
material, wherein the inkjet ink composition has an initial pH of
from 6.5 to 11.
21. The image forming method according to claim 20, wherein the
inkjet ink has a final pH not less than 6.5 after being heated at
70.degree. C. for 3 weeks.
22. The image forming method according to claim 21, wherein a ratio
of the final pH to the initial pH is not less than 0.90.
23. An image formed on a receiving material in accordance with the
method of claim 20.
24. The composition of claim 17, wherein the surface-treated
pigment has at least one of --COONa or --SO.sub.3Na groups
chemically reacted with the surface of the pigment.
25. An inkjet ink comprising the composition claimed in claim
17.
26. The composition of claim 17, wherein the pigment is present in
an amount of from 1 to 20% by weight.
27. The composition of claim 17, further comprising at least one
selected from the group consisting of lithium hydroxide, sodium
hydroxide and potassium hydroxide.
28. The composition of claim 17, comprising at least one selected
from the group consisting of glycerin, diethylene glycol, and
1,2-butanediol.
29. The composition of claim 17, wherein the solvent is present in
an amount not greater than 50% by weight relative to the total
weight of the composition.
30. The method of claim 20, wherein the surface-treated pigment has
at least one of --COONa or --SO.sub.3Na groups chemically reacted
with the surface of the pigment.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a composition and
particularly to an inkjet ink composition for use in ink jet
printing. In addition, the present invention relates to a method
for manufacturing the composition, and to an image forming method
using the composition.
[0003] 2. Discussion of the Background
[0004] As having been disclosed in published Japanese Patent
Applications Nos. 63-51485, 63-56575 and 01-198671, inkjet inks,
which are prepared by dissolving one or more water-soluble dyes in
water or a mixture solvent including water and a water-soluble
solvent and optionally adding an additive to the solution, have
been mainly developed and used. However, these inkjet inks
(hereinafter referred to as dye type inkjet inks) have the
following drawbacks:
[0005] (1) recorded images have so poor water resistance as to be
blurred when contacting water; and
[0006] (2) recorded images have poor light resistance such that
when the recorded images are exposed to light, the color tones of
the images change or the image density thereof decreases.
[0007] In attempting to solve these problems of the dye type inkjet
inks, pigment type inkjet inks, which use one or more pigments
(e.g., carbon black and organic pigments) instead of the dyes, have
been disclosed in published Japanese Patent Applications Nos.
57-10660, 57-10661 and 02-255875.
[0008] When pigment type inkjet inks are used for inkjet printing,
the resultant images, which have dried on a receiving material,
have good water resistance. Therefore when the images contact
water, the images do not blur (i.e., the images have good water
resistance). This is because pigments do not dissolve in water. In
addition, since the reactivity of pigments with light is lower than
that of dyes, the images formed of pigment type inks have better
light resistance than those formed of dye type inks.
[0009] Such pigment type inkjet inks are typically prepared by the
following method:
[0010] (1) a mixture including one or more pigments, a dispersing
medium and a dispersant is subjected to a dispersing treatment
using a dispersing machine such as ball mills and sand mills;
and
[0011] (2) the thus prepared pigment dispersion is optionally mixed
with one or more additives to prepare a pigment type inkjet
ink.
[0012] When the pigment dispersion for use in an inkjet ink
includes pigment particles having a relatively large particle
diameter, the nozzles from which the ink is to be discharged are
clogged with the large pigment particles included in the resultant
inkjet ink, resulting occurrence of a problem in that the ink is
not discharged from the nozzles (hereinafter referred to as a
clogging problem). In addition, when large pigment particles are
present in the inkjet ink, image qualities of the recorded images,
such as clearness, resolution and color reproducibility (i.e.,
transparency) deteriorate. Therefore, the pigment dispersion is
typically prepared such that the pigment particles dispersed
therein have a particle diameter not greater than 200 nm to prevent
the clogging problem and to produce images having good clearness,
color reproducibility (in particular, color reproducibility of
secondary colors (i.e., overlaid color images)) and
transparency.
[0013] Recently, self-dispersion type pigments which are prepared
by chemically reacting the surface of a pigment with a specific
functional group which can dissociate in water and which can be
dispersed without using a dispersant have been practically
used.
[0014] Since a specific group such as --COONa and --SO.sub.3Na is
chemically reacted with the surface of a pigment in such
self-dispersion pigments, the self-dispersion pigments can be
stably dispersed in water without a dispersant due to electrostatic
repulsion of the functional group dissociated in water.
[0015] Black pigments such as carbon black, and yellow (Y), magenta
(M) and cyan (C) color pigments such as Pigment Yellow 74, Pigment
Red 122 and Pigment Blue 15:4 are preferably applied to the
self-dispersion pigments.
[0016] However, both pigment type inkjet inks which use a pigment
dispersion including a dispersant and pigment type inkjet inks
which use a pigment dispersion including a self-dispersion pigment
have a drawback in that the pH of the inks greatly changes (i.e.,
decreases) when the inks are preserved at 70.degree. C. in a closed
place.
[0017] If the degree of decrease in pH of an ink is large, a
problem in that metal elements of an inkjet printer which contacts
the inkjet ink and which are designed so as to be suitable for the
original inkjet ink dissolve in or are corroded by the pH-changed
inkjet ink occurs.
[0018] Because of these reasons, a need exists for a pigment type
inkjet ink capable of producing good images without causing
problems such as the clogging problem and pH changing problem even
when used and preserved under various conditions.
SUMMARY OF THE INVENTION
[0019] Accordingly, an object of the present invention is to
provide a composition (particularly a pigment type inkjet ink
composition), which has good pH stability even when preserved at a
high temperature.
[0020] Another object of the present invention is to provide a
method for manufacturing the composition (the pigment type inkjet
ink composition).
[0021] Yet another object of the present invention is to provide an
image forming method by which images having good image qualities
can be stably produced without causing a discharge problem such as
the clogging problem even when the image forming ink is used or
preserved under high temperature conditions.
[0022] Briefly these objects and other objects of the present
invention as hereinafter will become more readily apparent can be
attained by a method for manufacturing a composition (a pigment
type inkjet ink composition), including:
[0023] mixing a basic material with a pigment dispersion including
at least a pigment and water to prepare a basic material containing
pigment dispersion; and
[0024] then subjecting the basic material containing pigment
dispersion to a heat treatment to control a pH thereof in a
predetermined pH range to prepare a composition (a pigment type
inkjet ink composition).
[0025] The method may further include the step of:
[0026] adding at least one of water and a water soluble organic
solvent to the pigment type inkjet ink composition (i.e., the
heat-treated basic material containing pigment dispersion).
[0027] The pH of the thus prepared composition (inkjet ink
composition) hardly changes even after the inkjet ink composition
is preserved under high temperature conditions because the acidic
materials adsorbed on the surface of the pigment are neutralized by
the basic material added. Therefore, a pigment type inkjet ink
composition having an improved stability is provided.
[0028] The pigment content of the pigment dispersion is preferably
from 5 to 30% by weight to prevent the pigment dispersion from
having a high viscosity and to impart good dispersion stability to
the resultant composition (inkjet ink composition).
[0029] The pigment content of the composition (inkjet ink
composition) is preferably from 1 to 20% by weight to prevent the
ink composition from having a high viscosity and to prepare a
composition (an inkjet ink composition) capable of producing clear
images.
[0030] The pigment preferably includes a pigment selected from the
group consisting of carbon black, and color pigments. The pigment
is preferably a self-dispersion pigment.
[0031] The basic material preferably includes a material selected
from the group consisting of lithium hydroxide, sodium hydroxide,
potassium hydroxide, and basic organic compounds. These basic
materials are preferably added to the pigment dispersion as an
aqueous solution thereof. By using these basic materials or the
technique, the acidic materials adsorbed on the surface of the
pigment can be well-neutralized, resulting in formation of a
pigment type inkjet ink composition having good pH stability.
[0032] The heat treatment is preferably performed at a temperature
from 30 to 95.degree. C. to sufficiently dissolve the acidic
materials adsorbed on the surface of the pigment in the ink
composition to be neutralized, thereby preventing increase of the
viscosity of the composition (inkjet ink composition).
[0033] The initial pH of the inkjet ink composition preferably
ranges from 6.5 to 11 after the heat treatment.
[0034] The thus prepared composition (inkjet ink composition)
preferably has a final pH not less than 6.5 even after being 0.6
preserved in a closed place at 70.degree. C. In addition, the ratio
of the final pH of the composition (inkjet ink composition) after
the preservation test to the initial pH thereof before the
preservation test is preferably not less than 0.90 (i.e., 90%) By
using the thus prepared inkjet ink composition, the problem in that
the inkjet ink composition corrodes the members of inkjet printers,
which members contact the inkjet ink composition, can be
prevented.
[0035] In this regard, the "initial pH" is defined as the pH of the
composition measured just after making the composition. The "final
pH" is defined as a certain pH of the composition obtained after
subjecting the composition to a heat-treatment test of 70.degree.
C. for 3 weeks.
[0036] The average particle diameter of the pigment dispersed in
the thus prepared inkjet ink composition is preferably from 20 to
200 nm to prevent occurrence of the clogging problem.
[0037] In another aspect of the present invention, an inkjet ink
composition is provided which includes at least a pigment, water
and a basic material and which has a pH of from 6.5 to 11. The
inkjet ink composition preferably has a pH not less than 6.5 even
after being preserved in a closed place at 70.degree. C. for 3
weeks. It is preferable that the final pH of the inkjet ink
composition after the preservation test (i.e., the preservation at
70.degree. C. for 3 weeks) to the initial pH of the ink composition
before the preservation test is not less than 0.90. The ink
composition is preferably prepared by one of the methods mentioned
above.
[0038] The ink composition has good pH stability even when used or
preserved at high temperature conditions for a long period of
time.
[0039] In yet another aspect of the present invention, an image
forming method is provided which includes the step of:
[0040] discharging an ink from a nozzle to form an image on a
receiving material to form an ink image thereon, wherein the ink is
the composition (inkjet ink composition) of the present
invention.
[0041] By using this image forming method, clear images can be
formed on the receiving material without causing a problem in that
the ink corrodes the members of the inkjet printer used.
[0042] These and other objects, features and advantages of the
present invention will become apparent upon consideration of the
following description of the preferred embodiments of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0043] The composition (pigment type inkjet ink composition) of the
present invention is prepared by mixing a basic material with a
pigment dispersion including at least a pigment and water or a
pigment ink liquid including a pigment dispersion and at least one
of a water soluble organic solvent and an additive such as
surfactants, pH adjusters, antiseptics and resins to prepare a
basic material containing pigment ink dispersion (or a basic
material containing pigment ink liquid); then subjecting the basic
material containing pigment dispersion to a heat treatment to
control the pH thereof in a predetermined range (6.5 to 11) to
prepare a heat-treated basic material containing liquid dispersion;
and then optionally adding water and/or a water soluble organic
solvent thereto. The thus prepared inkjet ink composition has good
pH stability (i.e., good preservation stability) even when used or
preserved under high temperature conditions.
[0044] In the present application, the pigment dispersion is
defined as a dispersion including at least a pigment and water, and
optionally an additive such as dispersants. The pigment ink liquid
is defined as a liquid including at least a pigment dispersion, and
at least one of a water soluble organic solvent and an additive
such as surfactants, pH adjusters, antiseptics and resins.
[0045] A basic material containing pigment dispersion is defined as
a pigment dispersion which is mixed with a basic material. A basic
material containing pigment ink liquid is defined as a pigment ink
liquid which is mixed with a basic material.
[0046] A heat treated basic material containing pigment dispersion
is defined as a basic material containing pigment dispersion which
is subjected to a heat treatment. A heat treated basic material
containing pigment ink liquid is defined as a basic material
containing pigment ink liquid which is subjected to a heat
treatment.
[0047] The present invention will be explained in detail.
[0048] The reason why the pH of conventional pigment type inkjet
ink compositions decreases particularly when the ink compositions
are preserved under high temperature conditions is considered to be
that the acidic impurities adsorbed on the surface of primary
particles of the pigment therein gradually dissolve in the ink.
[0049] In general, the particles of a pigment included in a pigment
dispersion for use in an inkjet ink composition are secondary
particles which are aggregation of from a few to a few hundred
primary particles and which have an average particle diameter of
from 20 to 200 nm. A large number of surfaces of such primary
particles are present inside the secondary particles.
[0050] In general, the acidic impurities present on such surfaces
of the primary particles, which impurities are included in raw
materials of the pigment or which are generated during pigment
production processes, hardly contact the liquid components of the
ink composition. Even when the acidic impurities contact the liquid
components of the ink composition, the liquid components hardly
flow. Therefore, the acidic impurities hardly dissolve into the ink
composition.
[0051] However, when such ink composition is preserved at a high
temperature for a certain time or more, the water molecules in the
ink composition actively move and invade into the secondary
particles. Therefore the acidic materials present inside the
secondary particles, which hardly dissolve into the ink composition
under normal conditions, dissolve into the ink composition,
resulting in decrease of the pH of the ink composition.
[0052] In view of this point, it is important that the acidic
impurities adsorbed on the surfaces of the primary pigment
particles are previously dissolved into the ink and neutralized, in
order to prevent decrease of the pH of the ink composition or lower
the degree of decrease of the pH even after the ink composition is
preserved under high temperature conditions.
[0053] In particular, it is preferable that the ink composition is
prepared as follows:
[0054] (1) a pigment dispersion or a pigment ink liquid is mixed
with a basic material to prepare an ink composition; and
[0055] (2) the basic material containing pigment dispersion or a
basic material containing pigment ink liquid is subjected to a heat
treatment to prepare a heat-treated basic material containing
pigment dispersion or basic material containing pigment ink liquid
(i.e., an inkjet ink composition if a material such as water and
water soluble organic material is not further added thereto) having
a pH in a predetermined range.
[0056] The thus prepared inkjet ink composition does not cause the
above-mentioned pH decrease problem.
[0057] The pigment in the pigment dispersion or the pigment ink
liquid for use in the inkjet ink composition of the present
invention is not particularly limited, and the following known
black and colored pigments can be exemplified.
[0058] Specific examples of such black pigments include carbon
blacks such as furnace black, lamp black, acetylene black and
channel black; powders including one or more metals such as copper
powders, iron powders and titanium oxide powders; and organic
pigments such as o-nitroaniline black and the like.
[0059] Specific examples of the yellow pigments include Pigment
Yellows 1, 2, 3, 12, 13, 14, 16, 17, 73, 74, 75, 83, 93, 95, 97,
98, 114, 120, 128, 129, 138, 150, 151, 154, 155, 180, etc.
[0060] Specific examples of the magenta pigments include Pigment
Reds 5, 7, 12, 48 (Ca), 48 (Mn), 57 (Ca), 57:1, 112, 122, 123, 168,
184, 202, etc.; Pigment Violet 19; etc.
[0061] Specific examples of the cyan pigments include Pigment Blue
1, 2, 3, 15, 15:3, 15:4, 16, 22 and 60; Vat Blue 4 and 60; etc.
[0062] Specific examples of other color pigments include toluidine
red, Permanent Carmine FB, Fast Yellow AAA, Disazo Orange PMP, Lake
Red C, Brilliant Carmine 6B, Phthalocyanine Blue, Quinacridone Red,
Dioxane Violet, Victoria Pure Blue, Alkali Blue Toner, Fast Yellow
10G, Disazo Yellow AAMX, Disazo Yellow AAOT, Disazo Yellow AAOA,
yellow iron oxide, Disazo Yellow HR, o-nitroaniline orange,
dinitroaniline orange, Vulcan orange, chlorinated Para Red,
Brilliant Fast Scarlet, Naphthol Red 23, Pyrazolone red, Barium Red
2B, Calcium Red 2B, Strontium Red 2B, Manganese Red 2B, Barium
Rithol Red, Pigment Scarlet 3B Lake, Lake Bordeaux 10B, Anthocyne
3B Lake, Anthocyne 5B Lake, Rhodamine 6G Lake, Eosin Lake, red iron
oxide, Fanatol Red FGR, Rhodamine B Lake, Methyl Violet Lake,
dioxazine violet, Basic Blue 5B Lake, Basic Blue 6G Lake, Fast Sky
Blue, Alkali Blue R Toner, Peacock Blue Lake, Prussian Blue,
ultramarine blue, Reflex Blue 2G, Reflex Blue R, Brilliant Green
Lake, Diamond Green, Thioflavine Lake, Phthalocyanine Green G,
Green Gold, Phthalocyanine Green Y, iron oxide powders, red rust,
zinc oxide, titanium oxide, calcium carbonate, clay, barium
sulfate, alumina, alumina white, aluminum powders, bronze powders,
fluorescent pigments, pearl pigments, Naphthol Carmine FB, Naphthol
Red M, Fast Yellow G, Disazo Yellow AAA, dioxane violet, Alkali
Blue G Toner and the like. In addition, process pigments which are
prepared by grafting a resin on a pigment can also be used. These
pigments can be used alone or in combination.
[0063] Among these pigments, carbon blacks, Pigment Yellow 74,
Pigment Red 122 and Pigment Blues 15:3 are preferably used as a
black color pigment, a yellow color pigment, a magenta color
pigment and a cyan color pigment, respectively, because of having
good dispersion stability, color reproducibility and light
resistance.
[0064] The pigment dispersion for use in the inkjet ink composition
of the present invention includes at least one or more pigments and
water as essential components and optionally includes a water
soluble organic solvent and an additive such as dispersants. The
mixture is dispersed with a dispersing machine such as sand mills,
pearl mills, DYNO mills, ball mills, roll mills, nanomizers, and
homogenizers.
[0065] The pigment ink liquid for use in the pigment type inkjet
ink composition of the present invention is typically prepared by
optionally adding water, a water soluble organic solvent and/or an
additive such as surfactants to the above-mentioned pigment
dispersion and mixing them to impart desired properties to the
resultant ink.
[0066] The pigment type inkjet ink composition of the present
invention is typically prepared by a method in which a basic
material is added to the pigment dispersion mentioned above; and
the mixture is subjected to a heat treatment to adjust the pH
thereof.
[0067] Alternatively, the pigment type inkjet ink composition can
be prepared by a method in which a basic material is added to the
pigment ink liquid mentioned above; and the mixture is subjected to
a heat treatment to adjust the pH thereof.
[0068] After the heat treatment, the resultant pigment type inkjet
ink composition is typically subjected to a filtering treatment
using a screen or a centrifugal separator to remove large particles
therefrom, which is followed by a deaeration treatment, if
desired.
[0069] The above-mentioned pigment dispersion may include a water
soluble organic solvent.
[0070] Specific examples of such water soluble organic solvents for
use in the pigment dispersion and pigment ink liquid mentioned
above include alcohols having from 1 to 4 carbon atoms such as
methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol,
n-butyl alcohol, sec-butyl alcohol and tert-butyl alcohol: amides
such as dimethylformamide and dimethylacetamide; ketones or ketone
alcohols such as acetone and diacetone alcohol; ethers such as
tetrahydrofuran and dioxane; polyhydric alcohols such as ethylene
glycol, propylene glycol, 1,2-propanediol, 1,2-butanediol,
1,3-butanediol, 1,4-butanediol, diethyleneglycol,
triethyleneglycol, 1,2,6-hexanetriol, thiodiglycol, hexyleneglycol,
and glycerin; polyalkylene glycols such as polyethylene glycol and
polypropylene glycol; alkyl ethers of a polyhydric alcohol, such as
ethylene glycol monomethyl ether, ethylene glycol monoethyl ether,
triethylene glycol monomethyl ether and triethylene glycol
monoethyl ether; alkanol amines such as monoethanol amine,
diethanol amine and triethanol amine; and other solvents such as
N-methyl-2-pyrrolidone, 2-pyrrolidone and
1,3-dimethyl-2-imidazolydinone.
[0071] Among these water-soluble solvents, glycerin, diethylene
glycol and 1,3-butanediol are preferably used.
[0072] In addition, polyhydric alcohols such as diethylene glycol,
and lower alkyl ethers of a polyhydric alcohol such as triethylene
glycol monomethyl ether and triethylene glycol monoethyl ether are
preferably used for the pigment ink liquid mentioned above for use
in the inkjet ink composition of the present invention.
[0073] The content of the water soluble organic solvent in pigment
type inkjet ink composition of the present invention is preferably
not greater than 50% by weight in view of environmental
protection.
[0074] In order to prepare a self-dispersion pigment, a pigment
such as pigments mentioned above is subjected to a chemical
treatment such that one or more functional groups are connected
with the surface of the pigment in a desired amount. Thus, a
self-dispersion pigment which can be stably dispersed in water
while the particles repulse each other due to electrostatic
repulsion thereof.
[0075] Methods for manufacturing a self-dispersion pigment have
been disclosed in U.S. Pat. Nos. 5,571,311, 5,630,868 and
5,707,432; J. E. Johnson, Imaging Science and technology's 50th
Annual Conference (1997); Yuan Yu, Imaging Science and technology's
53th Annual Conference (2000); and Polyfile, 12 48(1996),
incorporated by reference.
[0076] The pigment particles dispersed in the pigment dispersion,
pigment ink liquid and inkjet ink composition preferably have an
average particle diameter of from 20 nm to 200 nm and more
preferably from 20 to 100 nm. When the average particle diameter is
greater than 200 nm, the clogging problem tends to occur in inkjet
printing nozzles, and in addition clear color images cannot be
obtained. To the contrary, when the average particle diameter is
less than 20 nm, the preservability of the inkjet ink and the light
resistance of the resultant recorded images tend to deteriorate.
Further, the manufacturing costs of the pigment dispersion, pigment
ink liquid and inkjet ink composition increase because it takes a
long time to prepare a pigment dispersion (or a pigment ink liquid)
including such small pigment particles. In the present invention,
the average particle diameter of a pigment is measured by an
instrument, MICROTRACK UPA manufactured by Nikkiso Co., Ltd.
[0077] The pigment content of the pigment dispersion is preferably
from 5 to 30% by weight, and more preferably from 10 to 20% by
weight. When the pigment content is too low, the productivity of
the pigment dispersion is low. In contrast, when the pigment
content is too high, the resultant dispersion has too high
viscosity, and thereby it becomes difficult to disperse the pigment
dispersion.
[0078] The pigment content of the pigment ink liquid, which depends
on the pigment used, is preferably from 3 to 20% by weight, and
more preferably from 3 to 15% by weight.
[0079] The pigment content of the inkjet ink composition of the
present invention is preferably from 1 to 20% by weight, and more
preferably from 2 to 15% by weight. When the pigment content is too
low, the resultant printed images has low image density, and
therefore clear color images cannot be obtained. To the contrary,
when the pigment content is too high, the viscosity of the
resultant inkjet ink tends to increase. In addition, the clogging
problem tends to occur.
[0080] Suitable basic material to be added to the pigment
dispersion or the pigment ink liquid for use in the ink composition
of the present invention include alkali compounds such as
hydroxides of an alkali metal and hydroxides of an alkali earth
metal; organic basic compounds such as aliphatic amines and
aromatic amines; etc., but are not limited thereto.
[0081] Among these materials, lithium hydroxide (anhydrate or
hydrate), sodium hydroxide and potassium hydroxide are preferably
used because of exerting good effects even at a low
concentration.
[0082] In addition, among the basic organic compounds, monoethanol
amine, diethanol amine, triethanol amine, aminomethyl propanol and
choline are preferably used.
[0083] When a basic material is added to a pigment dispersion or an
ink, it is preferable that the basic material is preliminarily
dissolved in water to prepare a solution of the basic material. The
solution of the basic material is added to the pigment dispersion
or pigment ink liquid. When a basic material is directly added to a
pigment dispersion or a pigment ink liquid, the pH of a portion of
the pigment dispersion or pigment ink liquid locally increases for
a short period of time, and thereby problems in that the pigment
dispersion or pigment ink liquid is damaged (coagulation or the
like) and viscosity of the pigment dispersion or ink seriously
increases occur.
[0084] After mixed with a basic material, the dispersion or pigment
ink liquid is subjected to a heat treatment. The temperature of the
heat treatment is preferably from 30 to 95.degree. C., more
preferably from 40 to 90.degree. C., and even more preferably from
50 to 80.degree. C. When the temperature is too low, it takes a
long time to dissolve the acidic materials, which are adsorbed on
the surface of the primary pigment particles inside the secondary
pigment particles of the pigment used, into the resultant ink
composition, and thereby it takes a long time to neutralize the
acidic materials.
[0085] In contrast, when the temperature is too high, problems in
that the pigment dispersion or pigment ink liquid is damaged
(occurrence of coagulation or the like) and the viscosity of the
pigment dispersion or pigment ink liquid seriously increases
occur.
[0086] The time of the heat treatment, which is determined
depending on the heating temperature, the amount of the acidic
materials included in the pigment dispersion or pigment ink liquid,
and the species of the basic material to be added, is typically
from 30 minutes to 1 month, preferably from 1 hour to 3 weeks, and
more preferably from 3 hours to 2 weeks.
[0087] When the treating time is too short, the acidic materials
adsorbed on the surface of the primary pigment particles inside the
secondary pigment particles are insufficiently dissolved in the
resultant ink composition, and thereby a problem in that the pH of
the produced inkjet ink composition decreases after long term use
or preservation. When the treating time is too long, not only the
productivity of the inkjet ink composition deteriorates but also
the viscosity of the inkjet ink composition (i.e., the pigment
dispersion or ink to which a basic material has been added)
seriously increases.
[0088] The pH of the inkjet ink composition after the heat
treatment is preferably from 6.5 to 11, more preferably from 7.0 to
10 and even more preferably from 7.5 to 9.5. When the pH is too
low, it is likely that members of the inkjet printer, which contact
the ink, are corroded. To the contrary, when the pH is too high,
the ink is dangerous to handle because of being highly basic.
[0089] The ratio of the pH of the thus prepared pigment type inkjet
ink composition after preserved at 70.degree. C. for 3 weeks to the
initial pH of the thus prepared pigment type inkjet ink composition
before the preservation testis preferably not less than 90%, more
preferably not less than 95% and even more preferably not less than
98%. That the ratio is too low means that the acidic materials
adsorbed on the surface of the primary particles of the pigment
used are insufficiently dissolved into the ink even after the heat
treatment. Namely, such resultant inkjet ink composition has poor
preservability.
[0090] The inkjet ink composition of the present invention is
typically prepared by any one of the methods mentioned above.
However, it is possible to further add a basic material or an
acidic material after performing the heat treatment, to finally
adjust the pH of the inkjet ink composition.
[0091] The inkjet ink composition of the present invention can be
used for continuously-projecting type inkjet printing methods and
on-demand type inkjet printing methods. The on-demand type inkjet
printing methods include piezoelectric inkjet recording methods,
thermal inkjet recording methods and electrostatic inkjet recording
methods.
[0092] Having generally described this invention, further
understanding can be obtained by reference to certain specific
examples which are provided herein for the purpose of illustration
only and are not intended to be limiting. In the descriptions in
the following examples, the numbers represent weight ratios in
parts, unless otherwise specified.
EXAMPLES
Example 1
[0093] The following components were mixed to prepare a pigment ink
liquid (1) for use in a pigment type inkjet ink composition.
1 Formula of pigment ink liquid (1) for pigment type inkjet ink
composition Glycerin 80 Diethylene glycol 240 2-pyrrolidone 30
2-ethyl-1,3-hexanediol 30 Antiseptic (PROXEL LV(S), solid content
of 20%) 3 Distilled water 436 Self-dispersion carbon black 600
(CAB-O-JET300 manufactured by CABOT CORP., average particle
diameter of 136 nm and pigment content of 15% by weight)
[0094] Then 80 parts of a 1% aqueous solution of lithium hydroxide
(monohydrate) were added to the pigment ink liquid (1) drop by drop
while the mixture was agitated to prepare an inkjet ink composition
(1a) (i.e., a basic material containing pigment ink liquid (1)).
The pH of the inkjet ink composition (1a) was 10.91.
[0095] The thus prepared inkjet ink composition (1a) was contained
in a polyethylene container and then the container was sealed. The
inkjet ink composition (1a) in the container was set in an oven
heated at 70.degree. C. to be subjected to a heat treatment. When
the inkjet ink composition (1a) was heat-treated while the pH
thereof was measured, the pH gradually decreased over a period of
time. After the inkjet ink composition (1a) was subjected to the
heat treatment for 7 days, the inkjet ink composition (1a) was
taken out from the oven. The pH thereof was 8.19.
[0096] The heat-treated inkjet ink composition (1a) was then
subjected to a filtering treatment using PROFILE II manufactured by
Nihon Pall Ltd. and having openings of 1.0 .mu.m. Thus, a final
inkjet ink composition (1b) was prepared. The average particle
diameter of the carbon black in the inkjet ink composition (1b) was
138 nm and the pH thereof was 8.20.
[0097] When the pH of the final inkjet ink composition (1b) was
measured after the final inkjet ink composition (1b) was preserved
at 70.degree. C. for 3 weeks while contained in a sealed container,
the pH was 7.88. The pH ratio was 96% (i.e., 7.88/8.19).
Comparative Example 1
[0098] The procedure for preparation of the inkjet ink composition
(1b) in Example 1 was repeated except that the 1% aqueous solution
of lithium hydroxide was not added and the heat treatment for 7
days at 70.degree. C. was not performed. Thus, a comparative inkjet
ink composition (1) was prepared. The average particle diameter of
the carbon black in the comparative inkjet ink composition (1) was
136 nm, and the pH thereof was 7.80.
[0099] When the pH of the comparative inkjet ink composition (1)
was measured after the comparative inkjet ink composition (1) was
preserved at 70.degree. C. for 3 weeks while contained in a sealed
container, the pH was 6.47. The pH ratio was 83% (i.e.,
6.47/7.80).
Comparative Example 2
[0100] The procedure for preparation of the inkjet ink composition
(1b) in Example 1 was repeated except that the 1% aqueous solution
of lithium hydroxide was not added, the heat treatment for 7 days
at 70.degree. C. was not performed and a 10% aqueous solution of
sodium hydroxide was added thereto to control the pH thereof so as
to be 8.17. Thus, a comparative inkjet ink composition (2) was
prepared. The average particle diameter of the carbon black in the
comparative inkjet ink composition (2) was 136 nm.
[0101] When the pH of the comparative inkjet ink composition (2)
was measured after the comparative inkjet ink composition (2) was
preserved at 70.degree. C. for 3 weeks while contained in a sealed
container, the pH was 6.70. The pH ratio was 82% (i.e.,
6.70/8.17).
Example 2
[0102] The procedure for preparation of the inkjet ink composition
(1a) in Example 1 was repeated except that the addition amount of
the 1% aqueous solution of lithium hydroxide was changed from 80
parts to 110 parts. Thus an inkjet ink composition (2a) (i.e., a
basic material containing pigment ink liquid) was prepared. The pH
of the inkjet ink composition (2a) was 11.46.
[0103] The thus prepared inkjet ink composition (2a) was contained
in a polyethylene container and then the container was sealed. The
inkjet ink composition (2a) in the container was set in an oven
heated at 80.degree. C. to be subjected to a heat treatment. When
the inkjet ink composition (2a) was heat-treated while the pH
thereof was measured, the pH gradually decreased over a period of
time. After the inkjet ink composition (2a) was subjected to the
heat treatment for 16 days, the inkjet ink composition (2a) was
taken out from the oven. The pH thereof was 8.36.
[0104] The heat-treated inkjet ink composition (2a) was then
subjected to a filtering treatment using PROFILE II manufactured by
Nihon Pall Ltd. and having openings of 1.0 .mu.m. Thus a final
inkjet ink composition (2b) was prepared. The average particle
diameter of the carbon black in the inkjet ink composition (2b) was
140 nm and the pH thereof was 8.37.
[0105] When the pH of the final inkjet ink composition. (2b) was
measured after the final inkjet ink composition (2b) was preserved
at 70.degree. C. for 3 weeks while contained in a sealed container,
the pH was 8.24. The pH ratio was 98.4% (i.e., 8.24/8.37).
Example 3
[0106] Twenty (20) parts of a 10% aqueous solution of sodium
hydroxide were added drop by drop to the following pigment
dispersion (1) while the mixture was agitated to prepare a basic
material containing pigment dispersion (3a) (hereinafter referred
to as a dispersion (3a)). The pH of the dispersion (3a) was
10.50.
2 Formula of pigment dispersion (1) for pigment type inkjet ink
composition Self-dispersion carbon black 600 (CAB-O-JET300
manufactured by CABOT CORP., average particle diameter of 136 nm
and pigment content of 15% by weight)
[0107] The thus prepared dispersion (3a) was contained in a
polyethylene container and then the container was sealed. The
dispersion (3a) in the container was set in an oven heated at
50.degree. C. to be subjected to a heat treatment. When the pigment
dispersion (3a) was heat-activated while the pH thereof was
measured, the pH gradually decreased over a period of time. After
the dispersion (3a) was subjected to the heat treatment for 5 days,
the dispersion (3a) was taken out from the oven. Thus, the
dispersion (3a) was heat-treated (hereinafter this heat-treated
dispersion (3a) is referred to as a dispersion (3b)).
[0108] The pH of the dispersion (3b) was 8.23 and the average
particle diameter of the carbon black therein was 151 nm.
[0109] Then the following components were mixed to prepare an
inkjet ink composition (3a).
3 Formula of inkjet ink composition (3a) Glycerin 80 Diethylene
glycol 240 2-pyrrolidone 30 2-ethyl-1,3-hexanediol 30 Antiseptic
(PROXEL LV(S), solid content of 20%) 3 Distilled water 436
Dispersion (3b) 600
[0110] The inkjet ink composition (3a) was subjected to a filtering
treatment using PROFILE II manufactured by Nihon Pall Ltd. and
having openings of 1.0 .mu.m. Thus a final inkjet ink composition
(3a) was prepared. The average particle diameter of the carbon
black in the final inkjet ink composition (3a) was 150 nm and the
pH thereof was 8.26.
[0111] When the pH of the final inkjet ink composition (3a) was
measured after the inkjet ink composition (3a) was preserved at
70.degree. C. for 3 weeks while contained in a sealed container,
the pH was 7.59. The pH ratio was 92% (i.e., 7.59/8.26).
Example 4
[0112] The following components were mixed to prepare a pigment ink
liquid (2) for use in a pigment type inkjet ink composition.
4 Formula of pigment ink liquid (2) for pigment type inkjet ink
composition Glycerin 80 Diethylene glycol 240
2-ethyl-1,3-hexanediol 30 Antiseptic (PROXEL LV(S), solid content
of 20%) 3 Distilled water 436 Self-dispersion magenta pigment 600
(IJX-266 manufactured by CABOT, average particle diameter of 109.5
nm and pigment content of 14.3% by weight)
[0113] Then 70 parts of a 1% aqueous solution of lithium hydroxide
(monohydrate) were added to the pigment ink liquid (2) drop by drop
while the mixture was agitated to prepare an inkjet ink composition
(4a) (i.e., a basic material containing pigment ink liquid (2)).
The pH of the inkjet ink composition (4a) was 10.01.
[0114] The thus prepared inkjet ink composition (4a) was contained
in a polyethylene container and then the container was sealed. The
inkjet ink composition (4a) in the container was set in an oven
heated at 70.degree. C. to be subjected to a heat treatment. When
the inkjet ink composition (4a) was heat-treated while the pH
thereof was measured, the pH gradually decreased over a period of
time. After the inkjet ink composition (4a) was subjected to the
heat treatment for 9 days, the inkjet ink composition (4a) was
taken out from the oven. The pH thereof was 7.71.
[0115] The heat-treated inkjet ink composition (4a) was then
subjected to a filtering treatment using PROFILE II manufactured by
Nihon Pall Ltd. and having openings of 1.0 .mu.m. Thus a final
inkjet ink composition (4b) was prepared. The average particle
diameter of the magenta pigment in the inkjet ink composition (4b)
was 112 nm and the pH thereof was 7.71.
[0116] When the pH of the final inkjet ink composition (4b) was
measured after the final ink composition (4b) was preserved at 70
CC for 3 weeks while contained in a sealed container, the pH was
7.56. The pH ratio was 98% (i.e., 7.56/7.71).
Comparative Example 3
[0117] The procedure for preparation of the final inkjet ink
composition (4b) in Example 4 was repeated except that the 1%
aqueous solution of lithium hydroxide was not added and the heat
treatment for 9 days at 70.degree. C. was not performed. Thus, a
comparative inkjet ink composition (3) was prepared. The average
particle diameter of the magenta pigment in the comparative inkjet
ink composition (3) was 110 nm, and the pH thereof was 7.70.
[0118] When the pH of the comparative inkjet ink composition (3)
was measured after the comparative inkjet ink composition (3) was
preserved at 70.degree. C. for 3 weeks while contained in a sealed
container, the pH was 5.89. The pH ratio was 76% (i.e.,
5.89/7.70).
Example 5
[0119] The following components were mixed to prepare a pigment ink
liquid (3) for use in a pigment type inkjet ink composition.
5 Formula of pigment ink liquid (3) for pigment type inkjet ink
composition Glycerin 80 Diethylene glycol 240 2-pyrrolidone 30
2-ethyl-1,3-hexanediol 30 Antiseptic (PROXEL LV(S), solid content
of 20%) 3 Distilled water 436 Self-dispersion carbon black 600
(LIOJET BLACK BASE manufactured by Toyo Ink Mfg. Co., Ltd., average
particle diameter of 71.8 nm and pigment content of 16.6% by
weight)
[0120] Then 50 parts of a 1% aqueous solution of lithium hydroxide
(monohydrate) were added to the pigment ink liquid (3) drop by drop
while the mixture was agitated to prepare an inkjet ink composition
(5a). The pH of the inkjet ink composition (5a) was 11.55.
[0121] The thus prepared inkjet ink composition (5a) was contained
in a polyethylene container and then the container was sealed. The
inkjet ink composition (5a) in the container was set in an oven
heated at 70.degree. C. to be subjected to a heat treatment. When
the inkjet ink composition (5a) was heat-treated while the pH
thereof was measured, the pH gradually decreased over a period of
time. After the inkjet ink composition (5a) was subjected to the
heat treatment for 14 days, the inkjet ink composition (5a) was
taken out from the oven. The pH thereof was 8.20.
[0122] The heat-treated inkjet ink composition (5a) was then
subjected to a filtering treatment using PROFILE II manufactured by
Nihon Pall Ltd. and having openings of 1.0 .mu.m. Thus a final
inkjet ink composition (5b) was prepared. The average particle
diameter of the magenta pigment in the final inkjet ink composition
(5b) was 75.2 nm and the pH thereof was 8.21.
[0123] When the pH of the inkjet ink composition (5b) was measured
after the final inkjet ink composition (5b) was preserved at
70.degree. C. for 3 weeks while contained in a sealed container,
the pH was 7.55. The pH ratio was 92% (i.e., 7.55/8.21).
Comparative Example 4
[0124] The procedure for preparation of the inkjet ink composition
(5b) in Example 5 was repeated except that the 1% aqueous solution
of lithium hydroxide was not added and the heat treatment for 14
days at 70.degree. C. was not performed. Thus, a comparative inkjet
ink composition (4) was prepared. The average particle diameter of
the carbon black in the comparative inkjet ink composition (4) was
72 nm, and the pH thereof was 8.12.
[0125] When the pH of the comparative inkjet ink composition (4)
was measured after the comparative inkjet ink composition (4) was
preserved at 70.degree. C. for 3 weeks while contained in a sealed
container, the pH was 5.60. The pH ratio was 69% (i.e.,
5.60/8.12).
Example 6
[0126] The procedure for preparation of the inkjet ink composition
(1a) in Example 1 was repeated except that the 1% aqueous solution
of lithium hydroxide of 80 parts was replaced with 15 parts of a
15.8% aqueous solution of choline. Thus an inkjet ink composition
(6a) was prepared. The pH of the inkjet ink composition (6a) was
11.02.
[0127] The thus prepared inkjet ink composition (6a) was contained
in a polyethylene container and then the container was sealed. The
inkjet ink composition in the container was set in an oven heated
at 70.degree. C. to be subjected to a heat treatment. When the
inkjet ink composition was heat-treated while the pH thereof was
measured, the pH gradually decreased over a period of time. After
the inkjet ink composition (6a) was subjected to the heat treatment
for 12 days, the inkjet ink composition (6a) was taken out from the
oven. The pH thereof was 8.40.
[0128] The heat-treated inkjet ink composition (6a) was then
subjected to a filtering treatment using PROFILE II manufactured by
Nihon Pall Ltd. and having openings of 1.0 .mu.m. Thus, a final
inkjet ink composition (6b) was prepared. The average particle
diameter of the carbon black in the inkjet ink composition (6b) was
138 nm and the pH thereof was 8.40.
[0129] When the pH of the final inkjet ink composition (6b) was
measured after the final inkjet ink composition (6b) was preserved
at 70.degree. C. for 3 weeks while contained in a sealed container,
the pH was 7.64. The pH ratio was 91% (i.e., 7.64/8.40).
[0130] As mentioned above, the thus prepared inkjet ink
compositions (1b) to (6b) in Examples 1 to 6 have good pH stability
(i.e., the pH ratio is not less than 90%) even when the inkjet ink
compositions are preserved at 70.degree. C. for 3 weeks. Therefore,
the inkjet ink compositions do not corrode metallic members of the
inkjet printers for which the inkjet ink compositions are used. To
the contrary, the comparative inkjet ink compositions (1) to (4)
have poor pH stability (i.e., the pH ratio is low) when the
comparative inkjet ink compositions are preserved at 70.degree. C.
for 3 weeks. Therefore, the comparative inkjet ink compositions
cause a problem in that metallic members of the inkjet printers for
which the inkjet ink compositions are used are corroded.
[0131] The ink discharging property of each of inkjet ink
compositions (1b) to (6b) before and after the preservation test
for 3 weeks at 70.degree. C. was evaluated as follows.
[0132] Each inkjet ink composition was set in each of printers,
MJ-930C manufactured by Seiko Epson Corp. and using a piezoelectric
inkjet recording method, and DESK JET 880C manufactured by
Hewlett-Packard Co. and using a thermal inkjet recording method to
evaluate the ink discharging property of the inkjet ink
compositions.
[0133] As a result, each of the inkjet ink compositions was stably
discharged from nozzles without causing the clogging problem.
[0134] Effects of the Present Invention
[0135] As can be understood from the above description, the pigment
type inkjet ink composition of the present invention has good
stability (such as pH stability) even when preserved under high
temperature conditions. Therefore the inkjet ink composition can be
stably discharged from inkjet printers, thereby stably forming
images having good image qualities.
[0136] Additional modifications and variations of the present
invention are possible in light of the above teachings. It is
therefore to be understood that within the scope of the appended
claims the invention may be practiced other than as specifically
described herein.
[0137] This document claims priority and contains subject matter
related to Japanese Patent Application No. 2001-394425, filed on
Dec. 26, 2001, the entire contents of which are herein incorporated
by reference.
* * * * *