U.S. patent application number 15/269319 was filed with the patent office on 2017-01-05 for uv curable ink jet recording ink composition, ink container and ink jet recording apparatus.
This patent application is currently assigned to Seiko Epson Corporation. The applicant listed for this patent is Seiko Epson Corporation. Invention is credited to Hiroshi Fukumoto, Hiroaki Kida, Toyohiko Mitsuzawa, Keitaro Nakano.
Application Number | 20170002221 15/269319 |
Document ID | / |
Family ID | 50681301 |
Filed Date | 2017-01-05 |
United States Patent
Application |
20170002221 |
Kind Code |
A1 |
Kida; Hiroaki ; et
al. |
January 5, 2017 |
UV CURABLE INK JET RECORDING INK COMPOSITION, INK CONTAINER AND INK
JET RECORDING APPARATUS
Abstract
The UV curable ink jet recording ink composition contains a
thioxanthone-based photopolymerization initiator and a hindered
amine compound. The dissolved oxygen content in the ink composition
is 20 ppm or less.
Inventors: |
Kida; Hiroaki;
(Shiojiri-shi, JP) ; Fukumoto; Hiroshi;
(Shiojiri-shi, JP) ; Nakano; Keitaro;
(Matsumoto-shi, JP) ; Mitsuzawa; Toyohiko;
(Shiojiri-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Seiko Epson Corporation |
Tokyo |
|
JP |
|
|
Assignee: |
Seiko Epson Corporation
Tokyo
JP
|
Family ID: |
50681301 |
Appl. No.: |
15/269319 |
Filed: |
September 19, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14081281 |
Nov 15, 2013 |
9493667 |
|
|
15269319 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B41J 2/2107 20130101;
C09D 11/107 20130101; B41J 2/17523 20130101; C09D 11/322 20130101;
C09D 11/38 20130101; C08F 2/50 20130101; B41J 2/175 20130101; C09D
11/101 20130101; B41J 2/19 20130101; B41J 2/195 20130101; B41J
2/17513 20130101 |
International
Class: |
C09D 11/38 20060101
C09D011/38; B41J 2/175 20060101 B41J002/175; C09D 11/322 20060101
C09D011/322; C08F 2/50 20060101 C08F002/50; C09D 11/107 20060101
C09D011/107; C09D 11/101 20060101 C09D011/101 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 15, 2012 |
JP |
2012-250940 |
Claims
1-20. (canceled)
21. A UV curable ink jet recording ink composition comprising: a
polymerizable compound containing a monofunctional (meth)acrylate
having a vinyl ether group; a thioxanthone-based
photopolymerization initiator; and a hindered amine compound,
wherein the ink composition has an dissolved oxygen content of 20
ppm or less.
22. The UV curable ink jet recording ink composition according to
claim 21, wherein the thioxanthone-based photopolymerization
initiator content is 0.5% to 4% by mass.
23. The UV curable ink jet recording ink composition according to
claim 21, wherein the hindered amine compound has a
2,2,6,6-tetramethylpiperidine-N-oxyl skeleton.
24. The UV curable ink jet recording ink composition according to
claim 21, wherein the thioxanthone-based photopolymerization
initiator contains at least one compound selected from the group
consisting of thioxanthone, diethylthioxanthone,
isopropylthioxanthone, and chlorothioxanthone.
25. The UV curable ink jet recording ink composition according to
claim 21, wherein the thioxanthone-based photopolymerization
initiator contains diethylthioxanthone.
26. The UV curable recording ink composition according to claim 21,
further containing an acylphosphine oxide-based photopolymerization
initiator.
27. An ink container comprising: the UV curable ink jet recording
ink composition as set forth in claim 21; and a member in contact
with the ink composition.
28. An ink container comprising: the UV curable ink jet recording
ink composition as set forth in claim 22; and a member in contact
with the ink composition.
29. An ink container comprising: the UV curable ink jet recording
ink composition as set forth in claim 23; and a member in contact
with the ink composition.
30. An ink container comprising: the UV curable ink jet recording
ink composition as set forth in claim 24; and a member in contact
with the ink composition.
31. An ink container comprising: the UV curable ink jet recording
ink composition as set forth in claim 25; and a member in contact
with the ink composition.
32. An ink container comprising: the UV curable ink jet recording
ink composition as set forth in claim 26; and a member in contact
with the ink composition.
33. An ink container comprising: the UV curable ink jet recording
ink composition as set forth in claim 27; and a member in contact
with the ink composition.
34. The ink container according to claim 27, wherein the member is
made of a material having an oxygen permeation rate of 5.0 cc20
.mu.m/(m.sup.2dayatm) or less at a temperature of 23.degree. C. and
a relative humidity of 65%.
35. The UV curable recording ink composition according to claim 21,
wherein the monofunctional (meth)acrylate having a vinyl ether
group contains one or more of 2-vinyloxyethyl (meth)acrylate,
3-vinyloxypropyl (meth)acrylate, 1-methyl-2-vinyloxyethyl
(meth)acrylate, 2-vinyloxypropyl (meth)acrylate, 4-vinyloxybutyl
(meth)acrylate, 1-methyl-3-vinyloxypropyl (meth)acrylate,
1-vinyloxymethyl propyl (meth)acrylate, 2-methyl-3-vinyloxypropyl
(meth)acrylate, 1,1-dimethyl-2-vinyloxyethyl (meth)acrylate,
3-vinyloxybutyl (meth)acrylate, 1-methyl-2-vinyloxypropyl
(meth)acrylate, 2-vinyloxybutyl (meth)acrylate,
4-vinyloxycyclohexyl (meth)acrylate, 6-vinyloxyhexyl
(meth)acrylate, 4-vinyloxymethylcyclohexylmethyl (meth)acrylate,
3-vinyloxymethylcyclohexylmethyl (meth)acrylate,
2-vinyloxymethylcyclohexylmethyl (meth)acrylate,
p-vinyloxymethylphenylmethyl (meth)acrylate,
m-vinyloxymethylphenylmethyl (meth)acrylate,
o-vinyloxymethylphenylmethyl (meth)acrylate,
2-(vinyloxyethoxy)ethyl (meth)acrylate, 2-(vinyloxyisopropoxy)ethyl
(meth)acrylate, 2-(vinyloxyethoxy)propyl (meth)acrylate,
2-(vinyloxyethoxy)isopropyl (meth)acrylate,
2-(vinyloxyisopropoxy)propyl (meth)acrylate,
2-(vinyloxyisopropoxy)isopropyl (meth)acrylate,
2-(vinyloxyethoxyethoxy)ethyl (meth)acrylate,
2-(vinyloxyethoxyisopropoxy)ethyl (meth)acrylate,
2-(vinyloxyisopropoxyethoxy)ethyl (meth)acrylate,
2-(vinyloxyisopropoxyisopropoxy)ethyl (meth)acrylate,
2-(vinyloxyethoxyethoxy)propyl (meth)acrylate,
2-(vinyloxyethoxyisopropoxy)propyl (meth)acrylate,
2-(vinyloxyisopropoxyethoxy)propyl (meth)acrylate,
2-(vinyloxyisopropoxyisopropoxy)propyl (meth)acrylate,
2-(vinyloxyethoxyethoxy)isopropyl (meth)acrylate,
2-(vinyloxyethoxyisopropoxy)isopropyl (meth)acrylate,
2-(vinyloxyisopropoxyethoxy)isopropyl (meth)acrylate,
2-(vinyloxyisopropoxyisopropoxy)isopropyl (meth)acrylate,
2-(vinyloxyethoxyethoxyethoxy)ethyl (meth)acrylate,
2-(vinyloxyethoxyethoxyethoxyethoxy)ethyl (meth)acrylate,
2-(isopropenoxyethoxy)ethyl (meth)acrylate,
2-(isopropenoxyethoxyethoxy)ethyl (meth)acrylate,
2-(isopropenoxyethoxyethoxyethoxy)ethyl (meth)acrylate,
2-(isopropenoxyethoxyethoxyethoxyethoxy)ethyl (meth)acrylate,
polyethylene glycol monovinyl ether (meth)acrylate, polypropylene
glycol monovinyl ether (meth)acrylate.
36. The UV curable recording ink composition according to claim 21,
wherein the content of the monofunctional (meth)acrylate having a
vinyl ether group is 10% to 70% by mass relative to the total mass
of the ink composition.
37. The UV curable recording ink composition according to claim 21,
wherein the polymerizable compound contains one or more of
bifunctional or higher polyfunctional (meth)acrylate.
38. The UV curable recording ink composition according to claim 37,
wherein the content of the bifunctional or higher (meth)acrylate is
5% to 60% by mass relative to the total mass of the ink
composition.
39. The UV curable recording ink composition according to claim 21,
wherein the content of the photopolymerization initiator is 5% to
20% by mass relative to the total mass of the ink composition.
40. An ink jet recording method comprising ejecting the UV curable
ink jet recording ink composition according to claim 21 from a head
in a state where the dissolved oxygen content is 20 ppm or less.
Description
BACKGROUND
[0001] 1. Technical Field
[0002] The present invention relates to a UV curable ink jet
recording ink composition, an ink container containing the ink
composition, and an inkjet recording apparatus.
[0003] 2. Related Art
[0004] Various techniques are applied to recording processes for
forming images on a recording medium, such as paper, according to
image data signals. Among such techniques is an ink jet technique
in which images are formed directly on a recording medium by
ejecting an ink only onto desired image portions, using an
inexpensive apparatus. In the ink jet technique, inks are
efficiently used, and accordingly running cost can be reduced. In
addition, little noise is produced when the ink jet technique is
used, and the ink jet technique is thus advantageous as a recording
method.
[0005] In order to form an image having high fastness to water,
solvents, rubbing and so forth on the surface of a recording
medium, UV curable ink jet recording inks that can be cured by
being irradiated with UV radiation have been used in an ink jet
recording method in recent years.
[0006] For example, JP-A-2007-138070 discloses an ink jet ink
containing a coloring material, water, and an active energy
radiation-crosslinkable polymer that includes a hydrophilic main
chain having a plurality of side chains and can form a cross link
between the side chains by being irradiated with active energy
radiation. In this ink, the dissolved oxygen content is 0.05 to 1.8
ppm at 25.degree. C. According to the disclosure, the ink can be
easily discharged and can form highly glossy images having high rub
fastness without bleeding (paragraph 0023 in JP-A-2007-138070).
[0007] For example, JP-A-2004-196936 discloses a UV curable ink jet
ink containing a water-soluble solvent, and at least a coloring
material, a UV polymerizable compound and a photopolymerization
initiator in the water-soluble solvent, and having a dissolved
oxygen content of 0.1 to 2 ppm at 25.degree. C. According to this
disclosure, the ink can be stably discharged over a long time
(paragraph 0017 and 0019 in JP-A-2004-196936)).
[0008] However, the inks disclosed in the above-cited patent
documents are undesirably inferior in at least any of curability,
storage stability and ejection stability.
SUMMARY
[0009] An advantage of some aspects of the invention is that it
provides a UV curable ink jet recording ink composition superior in
curability, storage stability and ejection stability.
[0010] Another advantage of the invention is that it provides an
ink container containing the UV curable ink jet recording ink
composition, and an ink jet recording apparatus that uses the UV
curable ink jet recording ink composition.
[0011] The present inventors have conducted intensive research to
solve the above issue. The inventors first used thioxanthone-based
photopolymerization initiators advantageous in solubility, safety
and cost. However, it was found that ink compositions containing a
thioxanthone-based photopolymerization initiator tend to exhibit
markedly low ejection stability when the dissolved oxygen content
is high. The inventors thought that it might be effective in
improving the ejection stability to suppress the occurrence of air
bubbles by reducing the dissolved oxygen content in the ink
composition to a specific value or less. However, a UV curable ink
composition having a low dissolved oxygen is inferior in storage
stability because the oxygen in such an ink composition cannot
sufficiently inhibit the polymerization (dark reaction) of the ink.
The inventors then found that an ink composition further containing
a hindered amine polymerization inhibitor can be stably stored.
Thus, the inventors found that an ink composition can overcome the
above-described issue, which contains thioxanthone-based
photopolymerization initiator and a hindered amine compound and has
a dissolved oxygen content (dissolved air content) reduced to a
specific value or less.
[0012] According to an aspect of the invention, a UV curable ink
jet recording ink composition having the following features is
provided.
[0013] The UV curable ink jet recording ink composition contains a
thioxanthone-based photopolymerization initiator and a hindered
amine compound. The dissolved oxygen content in the ink composition
is 20 ppm or less.
[0014] The thioxanthone-based photopolymerization initiator content
in the ink composition may be 0.5% to 4% by mass.
[0015] The hindered amine compound may have a
2,2,6,6-tetramethylpiperidine-N-oxyl skeleton.
[0016] The thioxanthone-based photopolymerization initiator may
contain at least one compound selected from the group consisting of
thioxanthone, diethylthioxanthone, isopropylthioxanthone, and
chlorothioxanthone.
[0017] Preferably, the thioxanthone-based photopolymerization
initiator contains diethylthioxanthone.
[0018] The UV curable ink jet recording ink composition may further
contain an acylphosphine oxide-based photopolymerization
initiator.
[0019] The dissolved oxygen content in the UV curable ink jet
recording ink composition may be in the range of 5 to 20 ppm.
[0020] According to another aspect of the invention, an ink
container is provided which includes the UV curable ink jet
recording ink composition and a member in contact with the ink
composition.
[0021] The member may be made of a material having an oxygen
permeation rate of 5.0 cc20 .mu.m/(m.sup.2dayatm) or less at a
temperature of 23.degree. C. and a relative humidity of 65%.
[0022] According to still another aspect of the invention, an ink
jet recording apparatus is provided which includes an ejection
device that ejects the UV curable ink jet recording ink composition
from a head in a state where the dissolved oxygen content is 20 ppm
or less.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The invention will be described with reference to the
accompanying drawings, wherein like numbers reference like
elements.
[0024] FIG. 1 is a perspective view of an ink bag that is an ink
container according to an embodiment of the invention.
[0025] FIG. 2 is a representation of the structure around the head
of an ink jet recording apparatus according to an embodiment of the
invention.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0026] Embodiments of the invention will now be described in
detail. The invention is not limited to the following embodiments,
and various modifications may be made within the scope and spirit
of the invention.
[0027] The term "curability" mentioned herein is a property of an
ink composition that represents the degree in which the ink can be
cured by responding to light. Also, the term "storage stability" is
a property of an ink composition that represents the degree in
which the viscosity of the ink does not vary during storage. The
term "ejection stability" is a property of an ink composition that
represents the degree in which the ink is stably ejected in the
form of droplets through nozzles without clogging the nozzles.
[0028] In the description, the term "(meth)acrylate" refers to at
least either an acrylate or the corresponding methacrylate, and
"(meth)acrylic" compound refers to at least either an acrylic
compound or the corresponding methacrylic compound.
"(Meth)acryloyl" refers to at least either an acryloyl or the
corresponding methacryloyl.
UV-Curable Ink Jet Recording Ink Composition
[0029] The UV curable ink jet recording ink composition of an
embodiment of the invention (hereinafter simply referred to as the
ink composition) contains a thioxanthone-based photopolymerization
initiator and an hindered amine compound, and has a dissolved
oxygen content of 20 ppm or less.
[0030] Possible constituents of the ink composition will now be
described.
Thioxanthone-Based Photopolymerization Initiator
[0031] The ink composition of the present embodiment contains a
thioxanthone-based photopolymerization initiator, which is
advantageous in solubility, safety, and cost. The
thioxanthone-based photopolymerization initiator is used for curing
the ink composition on the surface of the recording medium by
photopolymerization caused by UV irradiation, thereby forming
printed images or characters. The use of the thioxanthone-based
photopolymerization initiator can enhance the curability of the ink
composition. Ultraviolet (UV) light may be used as radiation. UV
light is superior in safety, and the use of UV light reduces the
cost of light source.
[0032] Thioxanthone-based photopolymerization initiators suitably
used in the ink composition include, but are not limited to,
thioxanthone, diethylthioxanthone, isopropylthioxanthone, and
chlorothioxanthone. These may be used singly or in combination.
Preferred diethylthioxanthone may be, but is not limited to,
2,4-diethylthioxanthone; preferred isopropylthioxanthone may be,
but is not limited to, 2-isopropylthioxanthone; and preferred
chlorothioxanthone may be, but is not limited to,
2-chlorothioxanthone. The ink composition containing such a
thioxanthone-based photopolymerization initiator tends to exhibit
high curability, storage stability, and ejection stability. A
thioxanthone-based photopolymerization initiator containing
diethylthioxanthone is particularly advantageous.
Diethylthioxanthone can change the polymerizable compound in the
ink composition into an active species with UV radiation in a wide
range of wavelengths.
[0033] Commercially available thioxanthone-based
photopolymerization initiators may be used. These include, but are
not limited to, Speedcure DETX (2,4-diethylthioxanthone) and
Speedcure ITX (2-isopropylthioxanthone), each produced by Lambson,
and KAYACURE DETX-S (2,4-diethylthioxanthone) produced by Nippon
Kayaku Co., Ltd.
[0034] The thioxanthone-based photopolymerization initiator content
is preferably 0.5% to 4% by mass, more preferably 1% to 4% by mass,
relative to the total mass (100% by mass) of the ink composition.
When the thioxanthone-based photopolymerization initiator content
is 0.5% by mass or more, the ink composition tends to exhibit high
curability. When this content is 4% by mass or less, the ink
composition tends to maintain good ejection stability more
effectively. However, the use of a thioxanthone-based
photopolymerization initiator in an ink composition having a high
dissolved oxygen content markedly reduces the stability of ejecting
the ink composition from the recording head. This is probably
because the thioxanthone-based photopolymerization initiator
present in the form of fine particles in the ink composition acts
as cores of air bubbles and thus helps the ink composition to
release dissolved oxygen as it bubbles. This is merely a
conjecture, and there may be other causes.
Additional Photopolymerization Initiator
[0035] The ink composition may further contain other
photopolymerization initiators. Any photopolymerization initiator
can be used as long as it can produce an active species, such as a
radical or a cation, with light (UV) energy, and thus initiate a
polymerization of the polymerizable compound in the ink
composition. For example, a photo-radical polymerization initiator
or a photo-cationic polymerization initiator may be used, and
preferably, a photo-radical polymerization initiator is used.
[0036] Examples of the photo-radial polymerization initiator
include, but are not limited to, aromatic ketones, acylphosphine
oxides, aromatic onium salts, organic peroxides, thio compounds
(such as thiophenyl group-containing compounds),
.alpha.-aminoalkylphenone compounds, hexaaryl biimidazole
compounds, ketoxime ester compounds, borates, azinium compounds,
metallocene compounds, active ester compounds, compounds having a
carbon-halogen bond, and alkylamine compounds.
[0037] Among these, acylphosphine oxide-based photopolymerization
initiators such as acylphosphine oxides are preferably used.
Combined use of an acylphosphine oxide-based photopolymerization
initiator and a thioxanthone-based photopolymerization initiator is
suitable for UV-LED curing processes and can enhance the curability
of the ink composition.
[0038] Acylphosphine oxide-based photopolymerization initiators
include, but are not limited to,
bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide,
(2,4,6-trimethylbenzoyl)diphenylphosphine oxide, and
bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide.
[0039] Commercially available acylphosphine oxide-based
photopolymerization initiators include, but are not limited to,
IRGACURE 819 (bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide) and
DAROCUR TPO ((2,4,6-trimethylbenzoyl)diphenylphosphine oxide.
[0040] Other photo-radical polymerization initiators may be used
without particular limitation. Examples of such a photo-radical
polymerization initiator include acetophenone, acetophenone
benzylketal, 1-hydroxycyclohexylphenyl ketone,
2,2-dimethoxy-2-phenylacetophenone, xanthone, fluorenone,
benzaldehyde, fluorene, anthraquinone, triphenylamine, carbazole,
3-methylacetophenone, 4-chlorobenzophenone,
4,4'-dimethoxybenzophenone, 4,4'-diaminobenzophenone, Michler's
ketone, benzoin propyl ether, benzoin ethyl ether,
benzyldimethylketal,
1-(4-isopropylphenyl)-2-hydroxy-2-methylpropane-1-one,
2-hydroxy-2-methyl-1-phenylpropane-1-one, and
2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropane-1-one.
[0041] Commercially available photo-radical polymerization
initiators include, but are not limited to, IRGACURE 651
(2,2-dimethoxy-1,2-diphenylethane-1-one), IRGACURE 184
(1-hydroxycyclohexyl phenyl ketone), DAROCUR 1173
(2-hydroxy-2-methyl-1-phenylpropane-1-one), IRGACURE 2959
(1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propane-1-one),
IRGACURE 127
(2-hydroxy-1-{4-[4-(2-hydroxy-2-methylpropionyl)benzyl]phenyl}-2-methylpr-
opane-1-one), IRGACURE 907
(2-methyl-1-(4-methylthiophenyl)-2-morpholinopropane-1-one),
IRGACURE 369
(2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone-1),
IRGACURE 379
(2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-
-1-butanone), IRGACURE 784
(bis(.eta.5-2,4-cyclopentadiene-1-yl)-bis(2,6-difluoro-3-(1H-pyrrole-1-yl-
)phenyl) titanium), IRGACURE OXE 01 (1,2-octanedione,
1-[4-(phenylthio)phenyl]-, 2-(O-benzoyloxime)), IRGACURE OXE 02
(ethanone, 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazole-3-yl]-,
1-(O-acetyloxime)), and IRGACURE 754 (mixture of oxyphenyl acetic
acid, 2-[2-oxo-2-phenylacetoxyethoxy]ethyl ester and
2-(2-hydroxyethoxy)ethyl ester) (each produced by BASF); Speedcure
TPO (produced by Lambson); Lucirin TPO, LR 8893 and LR 8970 (each
produced by BASF); and Ubecryl P36 (produced by UCB).
[0042] Photo-cationic polymerization initiators include, but are
not limited to, sulfonium salts and iodonium salts.
[0043] Commercially available photo-cationic polymerization
initiators include, but are not limited to, Irgacure 250 and
Irgacure 270.
[0044] The above photopolymerization initiators may be used singly
or in combination.
[0045] The photopolymerization initiator content is preferably 5%
to 20% by mass relative to the total mass (100% by mass) of the ink
composition. When the photopolymerization initiator content is in
such a range, the ink composition can be rapidly cured with UV
light, completely dissolved in the ink composition without
remaining in an insoluble state, and prevented from being stained
by the photopolymerization initiator.
Hindered Amine Compound
[0046] The ink composition of the present embodiment contains a
hindered amine compound. In general, as the dissolved oxygen
content in a UV curable ink composition is reduced, the storage
stability of the ink composition decreases because the oxygen in
such an ink composition cannot sufficiently inhibit the
polymerization (dark reaction) of the ink. However, the presence of
a hindered amine-based polymerization inhibitor in the ink
composition allows the ink composition to be stably stored even if
the dissolved oxygen content is low.
[0047] Examples of the hindered amine compound include, but are not
limited to, compounds having a 2,2,6,6-tetramethylpiperidine-N-oxyl
skeleton, compounds having a 2,2,6,6-tetramethylpiperidine
skeleton, compounds having a 2,2,6,6-tetramethylpiperidine-N-alkyl
skeleton, and compounds having a
2,2,6,6-tetramethylpiperidine-N-acyl skeleton.
[0048] Hindered amine compounds are commercially available.
Examples of such a hindered amine compound include ADK STAB series
LA-7RD (2,2,6,6-tetramethyl-4-hydroxypiperidin-1-oxyl), LA-52,
LA-57, LA-62, LA-63P, LA-68LD, LA-77Y, LA-77G, LA-81, LA-82
(1,2,2,6,6-pentamethyl-4-piperidyl methacrylate), and LA-87 (each
produced by ADEKA); IRGASTAB UV 10
(4,4'-[1,10-dioxo-1,10-decanediyl)bis(oxy)]bis[2,2,6,6-tetramethyl]-1-pip-
eridinyloxy, CAS. 2516-92-9), TINUVIN 123
(4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl), TINUVIN 111FDL,
TINUVIN 144, TINUVIN 152, TINUVIN 292, TINUVIN 765, TINUVIN 770DF,
TINUVIN 5100, SANOL LS-2626, CHIMASSORB 119FL, CHIMASSORB 2020 FDL,
CHIMASSORB 944 FDL, and TINUVIN 622 LD (each produced by BASF); and
FA-711HM and FA-712HM (2,2,6,6-tetramethylpiperidinyl methacrylate,
produced by Hitachi Chemical Company, Ltd).
[0049] Among the above-cited compounds, LA-82 is a compound having
a 2,2,6,6-tetramethylpiperidine-N-methyl skeleton, and ADK STAB
LA-7RD, IRGASTAB UV 10 and TINUVIN 123 are compounds having a
2,2,6,6-tetramethylpiperidine-N-oxyl skeleton.
[0050] Compounds having a 2,2,6,6-tetramethylpiperidine-N-oxyl
skeleton are particularly advantageous because such compounds allow
the ink composition to maintain its high curability and can enhance
the storage stability of the ink composition.
[0051] Other compounds having a
2,2,6,6-tetramethylpiperidine-N-oxyl skeleton include, but are not
limited to, bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) sebacate
and bis(2,2,6,6-tetramethyl-1-(octyloxy)-4-piperidinyl)
decanedioate.
[0052] Hindered amine compounds may be used singly or in
combination.
[0053] The hindered amine compound content is preferably 0.05% to
0.5% by mass, more preferably 0.1% to 0.5% by mass, relative to the
total mass (100% by mass) of the ink composition. When it is 0.05%
by mass or more, the ink composition can exhibit high storage
stability, and when it is 0.1% by mass or more, the storage
stability can be still higher. In addition, when it is 0.5% by mass
or less, the ink composition can exhibit high curability.
Additional Polymerization Inhibitor
[0054] The ink composition of the present embodiment may further
contain additional polymerization inhibitor other than hindered
amine compounds. Examples of such a polymerization inhibitor
include, but are not limited to, p-methoxyphenol, hydroquinone
monomethyl ether (MEHQ), hydroquinone, cresol, t-butylcatechol,
3,5-di-t-butyl-4-hydroxytoluene,
2,2'-methylene-bis(4-methyl-6-t-butylphenol),
2,2'-methylene-bis(4-ethyl-6-butylphenol), and
4,4'-thio-bis(3-methyl-6-t-butylphenol).
[0055] These additional polymerization inhibitors may be used
singly or in combination. The additional polymerization inhibitor
content depends on the content of other constituents and is not
particularly limited.
Dissolved Oxygen Content
[0056] In the ink composition of the present embodiment, the
dissolved oxygen content is limited to 20 ppm or less. In an ink
composition containing a thioxanthone-based photopolymerization
initiator, the thioxanthone-based photopolymerization initiator is
present in the form of fine particles, and the particles act as
cores of air bubbles and thus help the ink composition to release
dissolved oxygen as air bubbles. When the dissolved oxygen content
is 20 ppm or less, however, air bubbles are not much generated even
though a thioxanthone-based photopolymerization initiator is
contained. Thus, the ink composition can be stably ejected. The
dissolved oxygen content can be reduced to 20 ppm or less by
deaeration.
[0057] The ink composition of the present embodiment exhibits high
ejection stability and is accordingly suitable for use in ink jet
recording apparatuses. When an ink passes through the ink flow
channels in an ink jet recording apparatus, air may dissolve in the
ink to increase the dissolved oxygen content in the ink. In the
present embodiment, however, the dissolved oxygen content in the
ink composition is as low as 20 ppm or less. Accordingly, it is not
increased to the extent that the storage stability is adversely
affected even if air dissolves in the ink composition flowing
through the ink flow channels. Consequently, the ink composition
can exhibit high ejection stability and curability when an ink jet
recording apparatus charged with the ink composition transferred
from an ink container performs recording.
[0058] The dissolved oxygen content is preferably 1 to 20 ppm, more
preferably 3 to 20 ppm, and still more preferably 5 to 20 ppm. In
particular, when the dissolved oxygen content is 1 ppm or more,
preferably 5 ppm or more, polymerization of the polymerizable
compound is inhibited more effectively. Accordingly, the ink
composition is likely to be more stably stored. The ink composition
of the present embodiment contains any of the above-described
hindered amine compounds as a polymerization inhibitor and has a
dissolved oxygen content limited to a specific range, thereby
exhibiting extremely high storage stability.
[0059] The dissolved oxygen content is not always in the above
range, as long as the ink composition has such a dissolved oxygen
content when it is transferred into an ink jet recording apparatus.
More specifically, the dissolved oxygen content is in the above
range desirably in the period between the time when an ink
container containing the ink composition has been shipped and the
time immediately before the ink container or the ink composition
therein is used or transferred to a recording apparatus. If the
recording apparatus includes a deaeration mechanism, the dissolved
oxygen content can be reduced in the recording apparatus. However,
since the capability of deaeration is likely to be limited even in
such a case, it is desirable that the dissolved oxygen content in
the ink composition be within the above range in an ink container.
On the other hand, a recording apparatus that hardly varies the
dissolved oxygen content need not have a deaeration mechanism, as
long as the dissolved oxygen content of the ink composition is
controlled in the above range in the ink container.
[0060] The dissolved oxygen content can be measured by a known
method, and the dissolved oxygen content mentioned herein is a
value measured by the method described in Examples below for the
sake of convenience.
[0061] The dissolved oxygen content in an ink composition before
deaeration, which is intended to reduce the dissolved oxygen
content, is generally about 50 to 60 ppm. Therefore, deaeration is
performed to control the dissolved oxygen content to 20 ppm or
less. For deaeration, a deaeration mechanism may be used, or
bubbling with an inert gas may be applied.
Polymerizable Compound
[0062] The ink composition may contain a polymerizable compound.
The polymerizable compound, by itself or with a function of the
photopolymerization initiator, is polymerized by irradiation with
light and thus cures the ink composition deposited on a recording
medium. Examples of the polymerizable compounds include, but are
not limited to, known monofunctional, bifunctional, trifunctional
and higher polyfunctional monomers and oligomers. These
polymerizable compounds may be used singly or in combination.
Polymerizable compounds will be further described below.
[0063] Monofunctional, bifunctional, trifunctional and higher
polyfunctional monomers include, but are not limited to,
(meth)acrylic acid, itaconic acid, crotonic acid, isocrotonic acid,
maleic acid and other unsaturated carboxylic acids, and their
salts; esters, urethanes, amides and anhydrides of those
unsaturated carboxylic acids; and acrylonitrile, styrene,
unsaturated polyesters, unsaturated polyethers, unsaturated
polyamides, and unsaturated urethanes. Monofunctional,
bifunctional, trifunctional and higher polyfunctional oligomers
include oligomers produced from the above monomers, such as linear
acrylic oligomers, epoxy (meth)acrylates, oxetane (meth)acrylates,
aliphatic urethane (meth)acrylates, aromatic urethane
(meth)acrylates, and polyester (meth)acrylates.
[0064] The polymerizable compound may contain an N-vinyl compound
as another monofunctional or polyfunctional monomer. Examples of
the N-vinyl compound include, but are not limited to,
N-vinylformamide, N-vinylcarbazole, N-vinylacetamide,
N-vinylpyrrolidone, N-vinylcaprolactam and acryloyl morpholine, and
derivatives of these N-vinyl compounds.
[0065] Among the above-described polymerizable compounds,
(meth)acrylic acid esters, that is, (meth)acrylates, are
particularly suitable.
[0066] Monofunctional (meth)acrylates include, but are not limited
to, isoamyl (meth)acrylate, stearyl (meth)acrylate, lauryl
(meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate,
isomyristyl (meth)acrylate, isostearyl (meth)acrylate,
2-ethylhexyl-diglycol (meth)acrylate, 2-hydroxybutyl
(meth)acrylate, butoxyethyl (meth)acrylate, ethoxydiethylene glycol
(meth)acrylate, methoxydiethylene glycol (meth)acrylate,
methoxypolyethylene glycol (meth)acrylate, methoxypropylene glycol
(meth)acrylate, phenoxyethyl (meth)acrylate, tetrahydrofurfuryl
(meth)acrylate, isobornyl (meth)acrylate, 2-hydroxyethyl
(meth)acrylate, 2-hydroxypropyl (meth)acrylate,
2-hydroxy-3-phenoxypropyl (meth)acrylate, flexible lactone-modified
(meth)acrylate, t-butylcyclohexyl (meth)acrylate, dicyclopentanyl
(meth)acrylate, and dicyclopentenyloxyethyl (meth)acrylate. Among
these, phenoxyethyl (meth)acrylate is preferred.
[0067] Preferably, the monofunctional (meth)acrylate content is 30%
to 85% by mass, more preferably 40% to 75% by mass, relative to the
total mass (100% by mass) of the ink composition. By controlling
this content in such a range, the initiator can be satisfactorily
dissolved, and the ink composition can exhibit higher curability,
storage stability and ejection stability.
[0068] The monofunctional (meth)acrylate may contain a vinyl ether
group. Examples of such a monofunctional (meth)acrylate include,
but are not limited to, 2-vinyloxyethyl (meth)acrylate,
3-vinyloxypropyl (meth)acrylate, 1-methyl-2-vinyloxyethyl
(meth)acrylate, 2-vinyloxypropyl (meth)acrylate, 4-vinyloxybutyl
(meth)acrylate, 1-methyl-3-vinyloxypropyl (meth)acrylate,
1-vinyloxymethyl propyl (meth)acrylate, 2-methyl-3-vinyloxypropyl
(meth)acrylate, 1,1-dimethyl-2-vinyloxyethyl (meth)acrylate,
3-vinyloxybutyl (meth)acrylate, 1-methyl-2-vinyloxypropyl
(meth)acrylate, 2-vinyloxybutyl (meth)acrylate,
4-vinyloxycyclohexyl (meth)acrylate, 6-vinyloxyhexyl
(meth)acrylate, 4-vinyloxymethylcyclohexylmethyl (meth)acrylate,
3-vinyloxymethylcyclohexylmethyl (meth)acrylate,
2-vinyloxymethylcyclohexylmethyl (meth)acrylate,
p-vinyloxymethylphenylmethyl (meth)acrylate,
m-vinyloxymethylphenylmethyl (meth)acrylate,
o-vinyloxymethylphenylmethyl (meth)acrylate,
2-(vinyloxyethoxy)ethyl (meth)acrylate, 2-(vinyloxyisopropoxy)ethyl
(meth)acrylate, 2-(vinyloxyethoxy)propyl (meth)acrylate,
2-(vinyloxyethoxy)isopropyl (meth)acrylate,
2-(vinyloxyisopropoxy)propyl (meth)acrylate,
2-(vinyloxyisopropoxy)isopropyl (meth)acrylate,
2-(vinyloxyethoxyethoxy)ethyl (meth)acrylate,
2-(vinyloxyethoxyisopropoxy)ethyl (meth)acrylate,
2-(vinyloxyisopropoxyethoxy)ethyl (meth)acrylate,
2-(vinyloxyisopropoxyisopropoxy)ethyl (meth)acrylate,
2-(vinyloxyethoxyethoxy)propyl (meth)acrylate,
2-(vinyloxyethoxyisopropoxy)propyl (meth)acrylate,
2-(vinyloxyisopropoxyethoxy)propyl (meth)acrylate,
2-(vinyloxyisopropoxyisopropoxy)propyl (meth)acrylate,
2-(vinyloxyethoxyethoxy)isopropyl (meth)acrylate,
2-(vinyloxyethoxyisopropoxy)isopropyl (meth)acrylate,
2-(vinyloxyisopropoxyethoxy)isopropyl (meth)acrylate,
2-(vinyloxyisopropoxyisopropoxy)isopropyl (meth)acrylate,
2-(vinyloxyethoxyethoxyethoxy)ethyl (meth)acrylate,
2-(vinyloxyethoxyethoxyethoxyethoxy)ethyl (meth)acrylate,
2-(isopropenoxyethoxy)ethyl (meth)acrylate,
2-(isopropenoxyethoxyethoxy)ethyl (meth)acrylate,
2-(isopropenoxyethoxyethoxyethoxy)ethyl (meth)acrylate,
2-(isopropenoxyethoxyethoxyethoxyethoxy)ethyl (meth)acrylate,
polyethylene glycol monovinyl ether (meth)acrylate, polypropylene
glycol monovinyl ether (meth)acrylate, phenoxyethyl (meth)acrylate,
isobornyl (meth)acrylate, and benzyl (meth)acrylate. Among these,
preferred are 2-(vinyloxyethoxy)ethyl (meth)acrylate, phenoxyethyl
(meth)acrylate, isobornyl (meth)acrylate, and benzyl
(meth)acrylate.
[0069] In particular, 2-(vinyloxyethoxy)ethyl (meth)acrylates, that
is, 2-(vinyloxyethoxy)ethyl acrylate and 2-(vinyloxyethoxy)ethyl
methacrylate, are preferred, and 2-(vinyloxyethoxy)ethyl acrylate
is more preferred. The use of these polymerizable compounds reduces
the viscosity of the ink composition and enhances the curability of
the ink composition. Also, these compounds have high flash points.
In particular, since 2-(vinyloxyethoxy)ethyl acrylate and
2-(vinyloxyethoxy)ethyl methacrylate have simple structures and low
molecular weights, the viscosity of the ink composition can be
significantly reduced. Examples of the 2-(vinyloxyethoxy)ethyl
(meth)acrylate include 2-(2-vinyloxyethoxy)ethyl methacrylate,
2-(1-vinyloxyethoxy)ethyl methacrylate, 2-(2-vinyloxyethoxy)ethyl
acrylate, and 2-(1-vinyloxyethoxy)ethyl acrylate. In terms of
curability, 2-(vinyloxyethoxy)ethyl acrylate is superior to
2-(vinyloxyethoxy)ethyl methacrylate.
[0070] The content of the (meth)acrylate having a vinyl ether
group, particularly the 2-(vinyloxyethoxy)ethyl (meth)acrylate
content, is preferably 10% to 70% by mass, more preferably 30% to
50% by mass, relative to the total mass (100% by mass) of the ink
composition. The ink composition containing 10% by mass or more of
such a (meth)acrylate can have a low viscosity and exhibit high
curability. Also, when the content of such a (meth)acrylate is 70%
by mass or less, the ink composition can be stably stored.
[0071] Exemplary bifunctional (meth)acrylates include triethylene
glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate,
polyethylene glycol di(meth)acrylate, dipropylene glycol
di(meth)acrylate, tripropylene glycol di(meth)acrylate,
polypropylene glycol di(meth)acrylate, 1,4-butanediol
di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol
di(meth)acrylate, neopentyl glycol di(meth)acrylate,
dimethylol-tricyclodecane di(meth)acrylate, bisphenol A ethylene
oxide adduct di(meth)acrylate, bisphenol A propylene oxide adduct
di(meth)acrylate, hydroxypivalic acid neopentyl glycol
di(meth)acrylate, and polytetramethylene glycol di(meth)acrylate,
and diethylene glycol di(meth)acrylate. Trifunctional or higher
polyfunctional (meth)acrylates may have a pentaerythritol or
dipentaerythritol skeleton. Among these, preferred are dipropylene
glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate,
diethylene glycol di(meth)acrylate, triethylene glycol
di(meth)acrylate, and trifunctional and higher polyfunctional
(meth)acrylates having a pentaerythritol or dipentaerythritol
skeleton. Preferably, the ink composition contains a polyfunctional
(methacrylate in addition to a monofunctional (meth)acrylate.
[0072] Preferably, the content of the bifunctional or higher
polyfunctional (meth)acrylate is 5% to 60% by mass, more preferably
15% to 60% by mass, still more preferably 20% to 50% by mass,
relative to the total mass (100% by mass) of the ink composition.
By controlling this content in such a range, the ink composition
can exhibit higher curability, storage stability and ejection
stability.
[0073] Examples of the trifunctional and higher polyfunctional
(meth)acrylates include trimethylolpropane tri(meth)acrylate,
ethylene oxide-modified trimethylolpropane tri(meth)acrylate,
pentaerythritol tri(meth)acrylate, pentaerythritol
tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate,
ditrimethylolpropane tetra(meth)acrylate, glycerinpropoxy
tri(meth)acrylate, caprolactone-modified trimethylolpropane
tri(meth)acrylate, pentaerythritolethoxy tetra(meth)acrylate, and
caprolactam-modified dipentaerythritol hexa(meth)acrylate.
[0074] Preferably, the polymerizable compound contains a
monofunctional (meth)acrylate. In this instance, the viscosity of
the ink composition is reduced, and the photo-polymerization
initiator and other constituents can be sufficiently dissolved in
the ink. Also, the ink composition can exhibit satisfactory
ejection stability during ink jet recording. More preferably, a
monofunctional (meth)acrylate and a bifunctional (meth)acrylate are
used in combination. The combined use of these compounds enhances
the toughness, heat resistance and chemical resistance of the
coating of the ink composition. Still more preferably, phenoxyethyl
(meth)acrylate and dipropylene glycol di(meth)acrylate are used in
combination.
[0075] The polymerizable compound content is preferably 5% to 95%
by mass, more preferably 15% to 90% by mass, relative to the total
mass (100% by mass) of the ink composition. By controlling the
polymerizable compound content in such a range, the viscosity and
odor of the ink composition can be reduced, and the solubility and
reactivity of the photopolymerization initiator can be
increased.
Coloring Material
[0076] The ink composition may further contain a coloring material.
The coloring material may be either one or both of a pigment and a
dye.
Pigment
[0077] A pigment used as a color material can enhance the light
fastness of the ink composition. The pigment may be selected from
inorganic pigments or organic pigments.
[0078] Exemplary inorganic pigments include carbon blacks (C.I.
Pigment Black 7), such as furnace black, lamp black, acetylene
black, and channel black; iron oxide; and titanium oxide.
[0079] Exemplary organic pigments include azo pigments, such as
insoluble azo pigments, condensed azo pigments, azo lake, and
chelate azo pigments; polycyclic pigments, such as phthalocyanine
pigments, perylene and perinone pigments, anthraquinone pigments,
quinacridone pigments, dioxane pigments, thioindigo pigments,
isoindolinone pigments, and quinophthalone pigments; dye chelates,
such as basic dye chelates and acid dye chelates; dye lakes, such
as basic dye lakes and acid dye lakes; and nitro pigments, nitroso
pigments, aniline black, and daylight fluorescent pigments.
[0080] Carbon blacks may be used for black inks. Examples of such a
carbon black include No. 2300, No. 900, MCF 88, No. 33, No. 40, No.
45, No. 52, MA7, MA8, MA100, and No. 2200B (each produced by
Mitsubishi Chemical Corporation); Raven 5750, Raven 5250, Raven
5000, Raven 3500, Raven 1255, and Raven 700 (each produced by
Carbon Columbia); Regal 400R, Regal 330R, Regal 660R, Mogul L,
Monarch 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000,
Monarch 1100, Monarch 1300, and Monarch 1400 (each produced by
CABOT); and Color Black FW1, Color Black FW2, Color Black FW2V,
Color Black FW18, Color Black FW200, Color Black S150, Color Black
S160, Color Black S170, Printex 35, Printex U, Printex V, Printex
140U, Special Black 6, Special Black 5, Special Black 4A, and
Special Black 4 (each produced by Degussa).
[0081] Pigments that can be used in a white ink include C.I.
Pigment whites 6, 18, and 21.
[0082] Pigments that can be used in a yellow ink include C.I.
Pigment Yellows 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 16, 17,
24, 34, 35, 37, 53, 55, 65, 73, 74, 75, 81, 83, 93, 94, 95, 97, 98,
99, 108, 109, 110, 113, 114, 117, 120, 124, 128, 129, 133, 138,
139, 147, 151, 153, 154, 167, 172 and 180.
[0083] Pigments that can be used in a magenta ink include C.I.
Pigment Reds 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17,
18, 19, 21, 22, 23, 30, 31, 32, 37, 38, 40, 41, 42, 48(Ca), 48(Mn),
57(Ca), 57:1, 88, 112, 114, 122, 123, 144, 146, 149, 150, 166, 168,
170, 171, 175, 176, 177, 178, 179, 184, 185, 187, 202, 209, 219,
224 and 245, and C.I. Pigment Violets 19, 23, 32, 33, 36, 38, 43
and 50.
[0084] Pigments that can be used in a cyan ink include C.I. Pigment
Blues 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:34, 15:4, 16, 18, 22, 25,
60, 65 and 66, and C.I. Vat Blues 4 and 60.
[0085] Pigments that can be used for colors other than magenta,
cyan and yellow include C.I. pigment greens 7 and 10, C.I. Pigment
Browns 3, 5, 25, and 26, and C.I. Pigment Oranges 1, 2, 5, 7, 13,
14, 15, 16, 24, 34, 36, 38, 40, 43, and 63.
[0086] The above pigments may be used singly or in combination.
[0087] If a pigment is used in the ink composition, the average
particle size of the pigment is preferably 300 nm or less, and more
preferably 50 to 200 nm. Such a pigment can be stably dispersed in
the ink composition, and the ink composition can be reliable in,
for example, ejection stability, and can form high-quality images.
The average particle size mentioned herein is a value measured by
dynamic light scattering.
Dye
[0088] A dye may be used as a coloring material. Any dye, including
acid dyes, direct dyes, reactive dyes, and basic dyes, may be used
without particular limitation. Examples of these dyes include C.I.
Acid Yellows 17, 23, 42, 44, 79 and 142, C.I. Acid Reds 52, 80, 82,
249, 254 and 289, C.I. Acid Blues 9, 45 and 249, C.I. Acid Blacks
1, 2, 24 and 94, C.I. Food Blacks 1 and 2, C.I. Direct Yellows 1,
12, 24, 33, 50, 55, 58, 86, 132, 142, 144 and 173, C.I. Direct Reds
1, 4, 9, 80, 81, 225 and 227, C.I. Direct Blues 1, 2, 15, 71, 86,
87, 98, 165, 199 and 202, C.I. Direct Blacks 19, 38, 51, 71, 154,
168, 171 and 195, and C.I. Reactive Reds 14, 32, 55, 79 and 249,
and C.I. Reactive Blacks 3, 4 and 35.
[0089] The above dyes may be used singly or in combination.
[0090] The coloring material content is preferably 1% to 20% by
mass relative to the total mass (100% by mass) of the ink
composition. Such a content results in a high hiding power and a
high color reproduction.
Dispersant
[0091] If the ink composition contains a pigment, a dispersant may
be added so that the pigment can be sufficiently dispersed. The
dispersant may be, but is not limited to, a compound that is
generally used for preparing a pigment dispersion, such as a
polymer dispersant. Examples of polymer dispersant include
polyoxyalkylene polyalkylene polyamines, vinyl polymers and
copolymers, acrylic polymers and copolymers, polyesters,
polyamides, polyimides, polyurethanes, amino polymers,
silicon-containing polymers, sulfur-containing polymers,
fluorine-containing polymers, and epoxy resins. The dispersant may
contain these compound singly or in combination. The polymer
dispersant is commercially available. Examples of such a dispersant
include AJISPER series produced by Ajinomoto Fine-Techno, Solsperse
series such as Solsperse 36000, available from Avecia or Noveon,
Disper BYK series produced by BYK, and DISPARLON series produced by
Kusumoto Chemicals.
Other Additives
[0092] The ink composition may further contain other additives or
constituents. Possible additives or constituents include, but are
not limited to, a known slip agent (surfactant), polymerization
promoter, penetration enhancer, and wetting agent (moisturizing
agent). In addition, other additives may be added, such as a fixing
agent, a fungicide, a preservative, an antioxidant, an ultraviolet
absorbent, a chelating agent, a pH adjuster, and a thickener.
Ink Container
[0093] The ink container of an embodiment of the invention contains
a UV curable ink jet recording ink composition. The ink container
may be, but is not limited to, an ink cartridge, a bag, a bottle, a
tank, or a can. Among these, preferred are the ink cartridge, bag,
bottle and tank because their oxygen permeation (descried later)
can be easily controlled to a desired level. More preferably, bags,
particularly plastic film bags, are used.
[0094] In the present embodiment, the ink container may be used in
any of the following forms of: (A) an ink cartridge apart from the
recording apparatus, which is mounted in the recording apparatus so
as to deliver the ink composition sequentially to the recording
apparatus; (B) a bottle or any other container apart from the
recording apparatus, from which the ink is transferred to the
recording apparatus before use; and (C) a tank or any other
container that contains an ink and is installed in the recording
apparatus in advance.
[0095] The forms of (A) and (B) each function as an ink container
in the period from the time when it has been shipped to the time
immediately before the ink is delivered to the recording apparatus.
The form of (C) functions as an ink container in the period from
the time when it has been shipped until the ink composition is used
in the recording apparatus for the first time.
[0096] In the use of an ink container in the form of (A) or (C),
the recording apparatus performs printing while the ink composition
is supplied from the ink container through an ink tube or any other
member connected to the ink container.
[0097] Also, in the use of an ink container in the form of (B), the
recording apparatus performs printing after the ink composition has
been transferred to the recording apparatus from the ink container.
In the case of form (B), the ink composition is transferred to a
tank or the like mounted in the recording apparatus.
[0098] The ink container may be made of, but not limited to,
plastics, such as polyethylene terephthalate (PET) and polyolefins
including polyethylene ethylene-vinyl acetate copolymer and
polypropylene, or metals including alloys. Alternatively, the ink
container may be made of, for example, a film of a mixture or a
composite produced by mixing or laminating some of these
polymers.
[0099] The material of the ink container that will come in contact
with the ink composition preferably has an oxygen permeation rate
of 5.0 cc20 .mu.m/(m.sup.2dayatm) or less, more preferably 2.0 cc20
.mu.m/(m.sup.2dayatm) or less. When the oxygen permeation rate is
within these values, the dissolved oxygen content in the ink
composition does not vary much during storage. Such a material is
not particularly limited. If the ink container is in the form of an
ink bag, the ink bag may be made by forming a plastic film into a
bag by heat sealing. The plastic film forming the ink bag may be a
drawn film made of a high-density, low-density or linear
low-density polyethylene, polypropylene, ethylene-vinyl alcohol
copolymer, or polystyrene. The plastic film may be a composite film
having a plurality of layers. The ink bag may be made of only such
a plastic film when the film satisfies the above-described
requirement for oxygen permeation, or the film may be provided with
a gas barrier layer to obtain an oxygen permeation rate within the
above value. The gas barrier layer may be formed of a metal such as
aluminum, an inorganic oxide such as silicon oxide or aluminum
oxide, or a low oxygen permeation plastic such as ethylene-vinyl
alcohol copolymer or polyvinyl alcohol. The plastic film has a
thickness of, preferably, 50 .mu.m or more, more preferably 70
.mu.m or more, and still more preferably 70 to 200 .mu.m. When the
plastic film has such a thickness, the dissolved oxygen content in
the ink composition does not vary much during storage, and the ink
bag has high strength and flexibility. Among the materials of the
film of the ink bag, ethylene-vinyl alcohol copolymer is
advantageous because it has a low oxygen permeation rate and high
strength. If the ink container is in a form other than the ink bag,
it may be made of, for example, synthetic resin, glass, or
metal.
[0100] The unit of oxygen permeation rate used herein is cc20
.mu.m/(m.sup.2dayatm), wherein "atm" represents the pressure (atm)
at a temperature of 23.degree. C. and a relative humidity of 65%.
The oxygen permeation rate can be determined by measuring the
permeation rate of oxygen permeating the film by a method specified
in ISO 14663-2: 1999 (Annex C), that is, by using a coulometric
sensor (when the relative humidity reaches a state of
equilibrium).
[0101] The capacity of the ink container is not particularly
limited, and is preferably 100 to 2,000 mL, more preferably 100 to
1,000 mL, and still more preferably 200 to 800 mL. Such a capacity
helps the ink composition exhibit high curability, storage
stability and ejection stability.
[0102] When the capacity of the ink container is in such a range,
the ink composition can be consumed without varying the dissolved
oxygen content in the ink composition after the beginning of the
use of the ink container, and the dissolved oxygen does not vary
much during storage. Preferably, the ink container is made of a
material having an oxygen permeation rate in the above range and
can contain a volume of ink composition in the above ranges. In the
description herein, the terms "capacity" and "volume" have the same
meaning.
[0103] An ink bag that is an embodiment of the ink container of the
invention will now be described. FIG. 1 is a perspective view of an
ink bag 1. The ink bag 1 includes an ink outlet 2 and a film member
10. The film member 10 may be made of any of the above-described
materials. The ink bag 1 may be packed in a box or any other
container (not shown) for protection during transport. The ink bag
1 may be used as, but not limited to, an ink cartridge in the
above-described form (A).
[0104] As described above, an embodiment of the invention can
provide an ink container containing a UV curable ink jet recording
ink composition superior in storage stability, curability and
ejection stability.
Ink Jet Recording Apparatus
[0105] The ink jet recording apparatus according to an embodiment
of the invention includes an ejection device that ejects the UV
curable ink jet recording ink composition from a head in a state
where the dissolved oxygen content of the ink composition is 20 ppm
or less. The ink jet recording apparatus may further include a
curing device that irradiates the ink composition ejected to the
recording medium with UV radiation to cure the ink composition.
Ejection Device
[0106] The ejection device ejects the UV curable ink jet recording
ink composition from the head in a state where the dissolved oxygen
content of the ink composition is 20 ppm or less. The ejection
device will be further described in detail with reference to a
drawing, but is not limited to the following embodiment. FIG. 2 is
a schematic diagram of the structure around the head of an ink jet
recording apparatus according to an embodiment of the invention. An
ink composition is supplied to a sub tank 200 from an ink cartridge
(not shown), and is then delivered to a plurality of heads 100 by a
pressure pump 202 through a deaeration module 204, which is a
mechanism for deaerating the ink composition, and a heater 220 in
that order.
[0107] The head 100 ejects the ink composition onto a recording
medium (not shown). A pressure control valve 108 is opened by a
valve-opening actuator 320 to control the pressure of the ink
composition that will be delivered to the heads 100 from the sub
tank 200.
[0108] When the pressure control valve 108 is open, the ink
composition having passed through the deaeration module 204 flows
into a branch connection 106. The flow channel 214 going to the
heads 100 is divided into a plurality of paths in the branch
connection 106 and connected to the heads 100.
[0109] The ink composition remaining in the heads 100 without being
discharged returns to the sub tank 200 through an integration joint
210 and a return channel 216 when a switching valve 212 is open. By
circulating the ink composition between the sub tank 200 and the
heads 100, the ink composition can recover from separation or
settling that may be caused by being retained for a long time, and
keep the temperature constant. The ink composition may be heated
with heaters 218, 220 and 222 to reduce the viscosity to a degree
at which the ink composition can be suitably ejected from the heads
100.
[0110] These devices are disposed on a main scan transfer table 64
that moves relative to the recording medium, and the ink
composition is ejected onto a recording medium from the heads 100
while the main scanning transfer table is moving.
[0111] The deaeration module 204 has therein a deaeration chamber
(not shown) into which the ink composition flows, and a
decompression chamber (not shown) adjacent to the deaeration
chamber with a separation membrane therebetween which can be
permeated by air, but cannot by liquid. By reducing the pressure of
the decompression chamber by a vacuum pump (not shown), gas such as
air babbles trapped or oxygen dissolved in the ink composition is
removed in the deaeration chamber, so that the ink composition
having a lower dissolved oxygen content than the ink composition in
the deaeration module 204 can be delivered to the heads 100, and
the heads 100 eject the ink composition having such a low dissolved
oxygen content. The deaeration module 204 can continuously deaerate
the ink composition while delivering the ink composition to the
heads 100 from the sub tank 200.
[0112] The recording apparatus may have the structure shown in, for
example, FIG. 2. The recording apparatus may have a structure like
a line printer, which is configured so that the head ejects ink
onto a recording medium moving relative to the head instead of
moving the above-described transfer table. As an alternative to the
deaeration module that continuously deaerates the ink composition
as described above, an intermittent type not provided with a
separation membrane may be used which alternately perform the
operations of deaerating the ink composition by reducing the
pressure of the decompression chamber with the pressure control
valve closed, and of subsequently delivering the ink composition to
the heads with the decompression chamber in a normal state and with
the pressure control valve 108 open. The continuously deaerating
type is advantageous in continuously deaerating the ink
composition, and the intermittently deaerating type is advantageous
in deaeration power.
[0113] When the ink composition contained in the ink cartridge has
a dissolved oxygen content of 20 ppm or less, it is preferable that
the dissolved oxygen content in the ink composition be not
increased while the ink composition is delivered in the recording
apparatus. Thus the ink composition can be highly stably ejected.
However, even if the dissolved oxygen content increases during the
delivery of the ink composition, the deaeration module can reduce
the dissolved oxygen content. Even if the performance of the
deaeration module is limited, the head 100 can eject the ink
composition in which the dissolved oxygen content is kept 20 ppm or
less as long as the dissolved oxygen content of the ink composition
in the ink cartridge is 20 ppm or less. The dissolved oxygen
content is increased depending on the length and material of the
tube or pipe in the recording apparatus through which the ink
composition is delivered to the heads, the time taken for
delivering the ink composition, and the conditions for applying
pressure for delivering the ink composition. The ink container of
the present embodiment is therefore advantageous in designing a
recording apparatus as desired.
Recording Medium
[0114] A recorded article is produced by an ink jet recording
method as described below, for example, by ejecting an ink
composition onto a recording medium. The recording medium may be
absorbent or non-absorbent. The ink jet recording method described
below can be widely applied to various recording media from a
non-absorbent recording medium into which water-soluble ink
compositions cannot penetrate to an absorbent recording medium into
which ink compositions easily penetrate. If the ink composition of
the above embodiment is used for a non-absorbent recording medium,
the medium may be required to be dried after curing the ink
composition by UV irradiation.
[0115] Absorbent recording media include, but are not limited to,
plain paper such as electrophotographic paper having high
permeability to inks, ink jet paper having an ink absorbing layer
containing silica particles or alumina particles or an ink
absorbing layer made of a hydrophilic polymer such as polyvinyl
alcohol (PVA) or polyvinyl pyrrolidone (PVP), and art paper, coat
paper and cast-coated paper that are used for ordinary offset
printing and have relatively low permeability to inks.
[0116] Nonabsorbent recording media include, but are not limited
to, plastic films or plates, such as those of polyvinyl chloride,
polyethylene, polypropylene, and polyethylene terephthalate (PET);
metal plates, such as those of iron, silver, copper, and aluminum;
metal-coated metal plates or plastic films formed by
vapor-depositing those metals on a metal plate or plastic film; and
alloy plates, such as those of stainless steel and brass.
Ink Jet Recording Method
[0117] The UV curable ink jet recording ink composition contained
in an ink container according to an embodiment may be used in an
ink jet recording method including ejecting the ink composition
onto a recording medium and curing the ink composition by UV
irradiation. The ink composition thus forms a coating (cured film)
on the recording medium.
Ejection of Ink Composition
[0118] For ejecting the ink composition, an ink jet recording
apparatus as described above may be used. The ink composition to be
ejected may be adjusted to a viscosity of, preferably, 25 mPas or
less, more preferably 5 to 20 mPas. An ink composition having a
viscosity in such a range can be ejected at room temperature or
without being heated. Alternatively, the ink composition may be
heated to a predetermined temperature so that the viscosity of the
ink composition is adjusted to a level suitable to be ejected. Thus
the ink composition is stably ejected.
[0119] UV curable ink compositions have a higher viscosity than
aqueous ink compositions generally used for ink jet recording.
Accordingly, the viscosity of the UV curable ink composition is
significantly varied by temperature change during ejection. Such
variation in the viscosity of the ink composition affects the size
of the ink droplets and the ejection speed of the droplets and may
result in a degraded image quality. Accordingly, it is preferable
that the ink composition be kept at a constant temperature while
being ejected.
Curing of Ink Composition
[0120] Subsequently, the ink composition deposited on the recording
medium is cured by being irradiated with UV radiation. In other
words, the coating of the ink composition formed on the recording
medium is turned into a cured film by UV irradiation. More
specifically, the photopolymerization initiator in the ink
composition is decomposed to produce an initiation species, such as
a radical, an acid or a base, by the irradiation with UV radiation,
and the initiation species induces polymerization of the
polymerizable compound. Alternatively, the polymerizable compound
may initiate a photopolymerization reaction by irradiation with UV
radiation. At this time, if a sensitizing dye is present in the ink
composition together with the photopolymerization initiator, the
sensitizing dye is excited by absorbing UV light. The excited
sensitizing dye then comes into contact with the
photopolymerization initiator and promotes the decomposition of the
photopolymerization initiator, and thus, a highly sensitive curing
reaction can be performed.
[0121] A mercury lamp or a gas or solid laser is generally used as
a UV light source. For curing the UV curable ink jet ink
composition, a mercury lamp or a metal halide lamp is widely used.
However, since the light source is desired to be mercury-free from
the viewpoint of environmental protection, the use of GaN-based
semiconductor UV emission devices is advantageous in view of
industry and environment. Also, UV light-emitting diodes (UV-LEDs)
and UV laser diodes (UV-LDs), which are small and inexpensive and
have long life and high efficiency, are considered to be a useful
light source for UV curing ink jet recording. UV-LEDs are
advantageous.
[0122] Preferably, the ink composition is cured by being irradiated
with UV radiation having an emission peak wavelength in the range
of 365 to 405 nm, more preferably 380 to 400 nm. The irradiation is
performed at an energy of, preferably, 50 to 500 mJ/cm.sup.2, more
preferably 100 to 400 mJ/cm.sup.2.
[0123] When irradiation is performed under such conditions, the ink
composition can be rapidly cured at a low energy, depending on the
constituents and their contents in the ink composition. The
irradiation energy is calculated by multiplying irradiation time by
irradiation intensity. The irradiation time can be reduced by
altering the ink composition, thus increasing the recording speed.
Also, the irradiation intensity can be reduced by altering the ink
composition. In this instance, the size and cost of the recording
apparatus can be reduced. For UV irradiation, a UV-LED is
preferably used as described above. The ink composition used in
this case contains a photopolymerization initiator that will be
decomposed by irradiation with UV radiation having a wavelength in
the above range and a polymerizable compound that will initiate a
polymerization by irradiation with UV radiation having a wavelength
in the above range. The number of emission peak wavelengths of the
UV radiation may be one or two or more. Even if it is plural, the
irradiation energy of the UV radiation refers to the entire
irradiation energy of UV light having emission peak wavelengths in
the above range.
EXAMPLES
[0124] The above-described embodiments of the invention will now be
further described in detail with reference to Examples. However,
the invention is not limited to the Examples.
Raw Materials
[0125] The following materials were used in the Examples and
Comparative Examples.
Coloring Material:
[0126] C.I. Pigment Black 7 (Microlith Black C-K, produced by BASF,
represented as black pigment in the Tables)
Dispersant:
[0127] Solsperse 36000 (produced by Noveon)
Vinyl Ether-Containing (Meth)Acrylic Acid Ester
[0128] VEEA (2-(2-vinyloxyethoxy)ethyl acrylate, produced by Nippon
Shokubai, abbreviated as VEEA in the Tables)
Other Polymerizable Compounds:
[0129] Biscoat #192 (phenoxyethyl acrylate, produced by Osaka
Organic Chemical Industry Ltd., abbreviated as PEA in the
Tables)
[0130] SR 508 (dipropylene glycol diacrylate, produced by Sartomer,
abbreviated as DPGDA in the Tables) Hindered Amine Compound
(Polymerization Inhibitor)
[0131] ADK STAB LA-82 (1,2,2,6,6-pentamethyl-4-piperidyl
methacrylate, produced by ADEKA, abbreviated as LA-82 in the
Tables)
[0132] ADK STAB LA-7RD
(2,2,6,6-tetramethyl-4-hydroxypiperidin-1-oxyl, produced by ADEKA,
abbreviated as LA-7RD in the Tables)
Photopolymerization Initiator:
[0133] DAROCURE TPO (produced by BASF, solid content: 100%)
[0134] IRGACURE 369 (produced by BASF, solid content: 100%)
[0135] Speedcure DETX (produced by Lambson, solid content:
100%)
[0136] Speedcure ITX (produced by Lambson, solid content: 100%)
Examples 1 to 21, Comparative Examples 1 to 6
Preparation of Pigment Dispersion
[0137] Before preparing ink compositions, pigment dispersions were
prepared. First, 18% by mass of the above-described black pigment
and 9% by mass of a dispersant were mixed, followed by stirring for
an hour. The resulting mixture was agitated in a bead mill to
disperse the pigment, thus yielding a pigment dispersion. The
dispersion was performed using zirconia beads of 0.65 mm in
diameter with a filling rate of 70% for 2 to 4 hours at a
peripheral speed of 9 m/s.
UV Curable Ink Jet Recording Ink Composition
[0138] Materials were mixed in a proportion (unit: mass %, percent
by mass) according to the composition shown in the Tables. The
mixture was agitated with a high-speed water-cooling agitator to
prepare a black UV curable ink jet recording ink composition. After
the preparation, the ink composition was deaerated. The longer the
deaeration time is, the lower the dissolved oxygen content is.
Thus, the deaeration time was adjusted so that the dissolved oxygen
content would be the value shown in Table 1 or 2.
Measurement of Dissolved Oxygen Content
[0139] The dissolved oxygen in the ink composition was measured
with a gas chromatograph Agilent 6890 (manufactured by Agilent
Technologies). Helium (He) gas was used as carrier gas.
[0140] The features of the Examples and Comparative Examples will
now be described. Examples 1 to 5 used the same ink composition,
but the dissolved oxygen in the ink composition was varied.
Comparative Example 1 also used the same ink composition as
Examples 1 to 5, but the dissolved oxygen content in the ink
composition was very high (30 ppm) relative to that in Examples 1
to 5. Comparative Example 2 was different from Examples 1 to 5 in
that the ink composition had a very high dissolved oxygen content
(30 ppm) and did not contain a thioxanthone compound.
[0141] Examples 6 to 11 used ink compositions having different
contents of photopolymerization initiator, namely, thioxanthone
compound, and the difference among these ink compositions was
evaluated. Comparative Examples 5 and 6 were substantially the same
as Example 6 except that the thioxanthone compound was not added
for comparison with Examples 6 to 11.
[0142] Examples 12 to 16 used ink compositions in which the VEEA
content was varied, and the difference among these ink compositions
was evaluated.
[0143] Examples 17 to 21 used ink compositions in which the type
and content of the hindered amine compound were varied, and the
difference among these ink compositions was evaluated. Comparative
Examples 3 and 4 were different from Examples 17 to 21 in that the
ink composition did not contain any hindered amine compound.
TABLE-US-00001 TABLE 1 Example 1 2 3 4 5 6 7 8 9 10 11 12 Black
pigment -- -- -- -- -- 2.0 2.0 2.0 2.0 2.0 2.0 -- Solsperse36000 --
-- -- -- -- 1.0 1.0 1.0 1.0 1.0 1.0 -- VEEA 30.0 30.0 30.0 30.0
30.0 30.0 30.0 30.0 30.0 30.0 30.0 10.0 PEA -- -- -- -- -- 54.9
54.9 54.9 54.9 54.9 54.9 47.9 DPGDA 57.9 57.9 57.9 57.9 57.9 -- --
-- -- -- -- 30.0 LA-82 -- -- -- -- -- -- -- -- -- -- -- -- LA-7RD
0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 DAROCURE TPO 10.0
10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 9.0 8.0 10.0 IRGACURE 369
-- -- -- -- -- 1.5 1.0 1.0 -- -- -- -- SpeedcureDETX 2.0 2.0 2.0
2.0 2.0 0.5 1.0 -- 1.0 1.5 2.0 -- SpeedcurelTX -- -- -- -- -- -- --
1.0 1.0 1.5 2.0 2.0 Total 100 100 100 100 100 100 100 100 100 100
100 100 Dissolved oxygen 20 15 10 5 1 10 10 10 10 10 10 10 content
Curability A A A A A B A A A A A B Storage stability A A A B C A A
A A A A A Ejection stability C A A A A A A B B C C A Example 13 14
15 16 17 18 19 20 21 Black pigment -- -- -- -- 2.0 2.0 2.0 2.0 2.0
Solsperse36000 -- -- -- -- 1.0 1.0 1.0 1.0 1.0 VEEA 30.0 50.0 70.0
80.0 30.0 30.0 30.0 30.0 30.0 PEA 27.9 7.9 -- -- 24.9 24.9 24.5
24.95 54.90 DPGDA 30.0 30.0 17.9 7.9 30.0 30.0 30.0 30.0 -- LA-82
-- -- -- -- -- 0.1 0.5 0.05 -- LA-7RD 0.1 0.1 0.1 0.1 0.1 -- -- --
0.1 DAROCURE TPO 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0
IRGACURE 369 -- -- -- -- -- -- -- -- 1.5 SpeedcureDETX -- -- -- --
1.0 1.0 1.0 1.0 0.5 SpeedcurelTX 2.0 2.0 2.0 2.0 1.0 1.0 1.0 1.0 --
Total 100 100 100 100 100 100 100 100 100 Dissolved oxygen 10 10 10
10 10 10 10 10 20 content Curability A A A A A A B A B Storage
stability A A B C A C A B A Ejection stability A A A A A A A A
C
TABLE-US-00002 TABLE 2 Comparative Example 1 2 3 4 5 6 Black
pigment -- -- 2.0 2.0 2.0 2.0 Solsperse36000 -- -- 1.0 1.0 1.0 1.0
VEEA 30.0 30.0 10.0 30.0 30.0 30.0 PEA -- -- 45.0 25.0 54.9 54.9
DPGDA 57.9 57.9 30.0 30.0 -- -- LA-82 -- -- -- -- -- -- LA-7RD 0.1
0.1 -- -- 0.1 0.1 DAROCURE TPO 10.0 10.0 10.0 10.0 10.0 10.0
IRGACURE 369 -- 2.0 -- -- 2.0 2.0 SpeedcurelDETX 2.0 -- 1.0 1.0 --
-- SpeedcurelTX -- -- 1.0 1.0 -- -- Total 100.0 100.0 100.0 100.0
100.0 100.0 Dissolved oxygen 30 30 10 10 20 10 content Curability B
C A A C C Storage stability A A D E A A Ejection stability E C A A
B A
Evaluation
[0144] The curability, storage stability and ejection stability of
the UV curable ink jet recording ink compositions prepared in the
Examples and Comparative Examples, in which the dissolved oxygen
content was controlled by adjusting the deaeration time, were
evaluated as below. The evaluation of curability and ejection
stability and the measurement of the dissolved oxygen content were
performed on the ink composition that had been stored under the
conditions for the evaluation of storage stability.
1. Storage Stability
[0145] Ink bags as shown in FIG. 1 were prepared as the ink
containers. The ink compositions of the Examples and Comparative
Examples were each enclosed in the ink bags and stored in an oven
of 60.degree. C. for 20 days. After the storage, the increase in
viscosity was determined. The ink bag had a capacity of 700 mL, and
was made of an ethylene-vinyl alcohol copolymer film (oxygen
permeation rate: 2.0 cc20 .mu.m/(m.sup.2dayatm) having a thickness
of 100 .mu.m. The evaluation criteria were as follows, and the
results are shown in the Tables:
[0146] A: 3% or less
[0147] B: more than 3% and 6% or less
[0148] C: more than 6% and 9% or less
[0149] D: more than 9% and 12% or less
[0150] E: more than 12%
2. Curability
[0151] Coatings having a thickness of 10 .mu.m were formed by
applying each of the ink compositions of the Examples and
Comparative Examples to a PET film (PET 50A PL series manufactured
by LINTEC) using a bar coater. Then, the coating was cured by
irradiated with UV radiation having an irradiation intensity of
1,100 mW/cm.sup.2 and a wavelength of 395 nm. The cured coating
(cured film) was rubbed 10 times at a load of 100 g with a cotton
swab, and the irradiation energy (curing energy) at the time when
the coating was hardened to the extent that the rubbing did not
cause abrasion was measured.
[0152] Irradiation energy (mJ/cm.sup.2) were calculated as a
product of the irradiation intensity (mW/cm.sup.2) at a surface
irradiated from the light source and the time (s) for which the
irradiation had been continued. Irradiation intensity was measured
with a UV intensity meter UM-10 and a light receiver UM-400 (each
produced by Konica Minolta Sensing, Inc.) The evaluation criteria
were as follows, and the results are shown in the Tables:
[0153] A: 150 mJ/cm.sup.2 or less
[0154] B: more than 150 mJ/cm.sup.2 and 200 mJ/cm.sup.2 or less
[0155] C: more than 200 mJ/cm.sup.2 and 250 mJ/cm.sup.2 or less
[0156] D: more than 250 mJ/cm.sup.2 and 300 mJ/cm.sup.2 or less
[0157] E: more than 300 mJ/cm.sup.2
3. Ejection Stability
[0158] An ink jet apparatus (trial model) for evaluation was
prepared which had 180 nozzles that had a diameter of 20 .mu.m and
were adjusted so as to be operated at a frequency of 24 kHz to
eject 5 ng of ink for each ejection. The ink composition was
continuously ejected from the apparatus, and the number of the
nozzles that had caused ejection failure was counted. The
evaluation criteria were as follows, and the results are shown in
the Tables:
[0159] A: None (0)
[0160] B: 1 to 5
[0161] C: 6 to 10
[0162] D: 11 to 15
[0163] E: 16 or more
[0164] The results show that the ink compositions (of the Examples)
containing a thioxanthone-based photopolymerization initiator and a
hindered amine compound and has a dissolved oxygen content of 20
ppm or less were superior in curability, storage stability and
ejection stability to other ink compositions (Comparative
Examples).
[0165] Also, the ink composition of Example 2 was further examined
in the same manner as above after being stored in an oven of
60.degree. C. for 20 days, except that the capacity of the ink bag
was 50 mL. The results are that the dissolved oxygen content was 18
ppm; the storage stability was A; the curability was A; and the
ejection stability was B.
[0166] Furthermore, the ink composition of Example 2 was still
further examined in the same manner as above after being stored in
an oven of 60.degree. C. for 20 days, except that the ink
composition was enclosed in an ink bag of a polyacrylonitrile film
(oxygen permeation rate: 10.0 cc20 .mu.m/(m.sup.2dayatm) having a
thickness of 70 .mu.m. The results are that the dissolved oxygen
content was 20 ppm; the storage stability was A; the curability was
A; and the ejection stability was C.
[0167] These results suggest that the ink composition containing no
thioxanthone-based photopolymerization initiator and having a high
dissolved oxygen content is inferior in curability, and that the
ink composition containing a thioxanthone-based photopolymerization
initiator and having a high dissolved oxygen content exhibits
improved ejection stability, but is inferior in curability. The
comparison between Comparative Examples 1 and 2 show that the ink
composition containing a thioxanthone compound is inferior in
ejection stability when both ink compositions have the same
dissolved oxygen content.
[0168] The ink bag containing the ink composition was loaded as an
ink cartridge in the recording apparatus shown in FIG. 2, and the
ink composition was delivered to the heads 100. Then, the dissolved
oxygen contents of the ink composition in the sub tank 200 and the
heads 100 were measured. The results are that the dissolved oxygen
contents of the ink composition of Example 1 were 27 ppm in the sub
tank 200 and 20 ppm in the heads 100, and that those of the ink
composition of Comparative Example 1 were 36 ppm in the sub tank
200 and 31 ppm in the heads 100.
[0169] The entire disclosure of Japanese Patent Application No.:
2012-250940, filed Nov. 15, 2012 is expressly incorporated by
reference herein.
* * * * *