JPH1060345A - Water-base pigment ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a water-base pigment ink excellent in shelf stability and prevented from clogging at a printer head particularly when used as an ink for ink jet recording by using a specified polymeric dispersant. SOLUTION: This ink comprises mainly a pigment, a polymeric dispersant, a water-soluble solvent and water, and the polymeric dispersant used comprises a copolymer obtained by using 10-50wt.% polyalkylene glycol mono(meth) acrylate monomer represented by formula I (R<1> is H or methyl; R<2> is a 2-4C alkylene; R<3> is H, a 1-5C alkyl or alkenyl; and n is 2 to 300), 50-89wt.% (meth) acrylic monomer represented by formula II (R<4> is H or methyl; and X is H, a monovalent metal, a divalent metal, ammonium or an organic amine) and 1-50wt.% monomer copolymerizable therewith, or a copolymer obtained by neutralizing this copolymer with an alkaline substance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aqueous pigment ink excellent in storage stability of an ink, and more particularly to an aqueous pigment ink in which clogging in a printer head is prevented when used as an ink for ink jet recording. It is about.

[0002]

2. Description of the Related Art Dye inks and pigment inks are mainly used as water-based inks conventionally used. Of these inks, pigment inks are known to be excellent in water resistance and light resistance of printed images as compared with dye inks, but are insufficient in pigment dispersibility.

[0003] For example, as a water-based pigment ink, a water-based pigment ink having excellent coating and writing surface leveling properties comprising a pigment, a binder, a surfactant, and water has been known (JP-A-59-199780). . However, such water-based pigment inks still have insufficient dispersion stability of pigments, particularly dispersion stability under long-term storage. In particular, the low dispersion stability of the pigment is a major problem that causes clogging of the head when such an aqueous pigment ink is used as an ink for inkjet recording.

Accordingly, an object of the present invention is to provide a water-based pigment ink having excellent storage stability. Another object of the present invention is to provide a water-based pigment ink in which clogging in a printer head is prevented particularly when used as an ink for inkjet recording.

[0005]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that an aqueous pigment ink which can achieve the above object can be obtained by using a specific polymer dispersant.

The present invention has been made based on the above-mentioned findings. In an aqueous pigment ink containing a pigment, a polymer dispersant, a water-soluble solvent and water as main components, the polymer dispersant represented by the following general formula (I) A polyalkylene glycol mono (meth) acrylate monomer (a) represented by:
The (meth) acrylic acid-based monomer (b) represented by the following general formula (II) and the monomer (c) copolymerizable with the monomers (a) and (b) are Body (a) 10 to 50% by weight,
50 to 89% by weight of the monomer (b) and the monomer (c) 1
５０50% by weight [However, the total of the monomers (A), (B) and (C) is 100% by weight. A water-based pigment ink characterized by using a copolymer (A) obtained by using the copolymer in the ratio described above or a copolymer (B) obtained by neutralizing the copolymer (A) with an alkaline substance. The above object has been achieved by providing

[0007]

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[0008]

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[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The water-based pigment ink of the present invention contains a pigment, a polymer dispersant, a water-soluble solvent and water as essential components as described above, and uses a specific copolymer as the polymer dispersant. It is characterized by having been. Hereinafter, each of the above components constituting the water-based pigment ink of the present invention will be described.

The polymer dispersant is a polyalkylene glycol mono (meth) acrylate monomer (a) represented by the general formula (I), and a polyalkylene glycol mono (meth) acrylate monomer (a) represented by the following general formula (II) A) an acrylic acid-based monomer (b) and a monomer (c) copolymerizable with the monomers (a) and (b), 10 to 50% by weight of the monomer (a), Multimer (b) 50-8
9% by weight and 1 to 50% by weight of the monomer (c) [where the total of the monomers (a), (b) and (c) is 100% by weight
It is. ] The copolymer (A) obtained by using at a ratio
Or a copolymer (B) obtained by neutralizing the copolymer (A) with an alkaline substance. By using the copolymer (A) or the copolymer (B), storage stability is improved, and in particular, when used as an inkjet recording ink, anti-clogging property of a printer head is improved. .

The polyalkylene glycol mono (meth) acrylate-based monomer (a) represented by the general formula (I) (hereinafter simply referred to as “monomer (a)”) is prepared by a known method. Specific examples thereof include polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, polybutylene glycol mono (meth) acrylate, methoxypolyethylene glycol mono (meth) acrylate, and methoxy polypropylene. Glycol mono (meth) acrylate, methoxy polybutylene glycol mono (meth) acrylate, ethoxy polyethylene glycol mono (meth) acrylate, ethoxy polypropylene glycol mono (meth) acrylate, ethoxy polybutylene glycol Roh (meth) acrylate. These monomers (a) can be used alone or in combination of two or more.

In the above monomer (a), the number of additions per molecule of ethylene oxide or propylene oxide represented by n is 2 to 3 independently as described above.
00, preferably 3 to 200, and more preferably 4 to 1
More preferably, it is 50. If the number of additions of ethylene oxide or propylene oxide is less than 2, the pigment cannot be stably dispersed. On the other hand, if it exceeds 300, the viscosity of the ink increases and the handleability is poor, and it is not particularly suitable as an ink for inkjet recording. It will be.
In the above monomer (a), only one of ethylene oxide and propylene oxide may be added as the alkylene oxide, or both may be added. Further, when n is 2 or more (that is, when a polyalkylene oxide chain is formed), the polyalkylene oxide chain may be formed from only one of ethylene oxide and propylene oxide, or may be formed from both. It may be. in this case,
The addition form of both may be any of block addition, alternate addition and random addition, and the addition molar ratio of ethylene oxide and propylene oxide (former: latter) is 10:90 to
90:10 is desirable, and 10: 90-60:
More preferably, it is 40.

Examples of the (meth) acrylic acid-based monomer (II) represented by the above general formula (II) (hereinafter simply referred to as “monomer (II)”) include acrylic acid, methacrylic acid and These include monovalent metal salts, divalent metal salts, ammonium salts and organic amine salts. These monomers (b)
They can be used alone or in combination of two or more.

A monomer (c) copolymerizable with the above monomers (a) and (b) (hereinafter simply referred to as "monomer (c)")
Examples of the ester include an ester of an aliphatic alcohol having 1 to 20 carbon atoms and (meth) acrylic acid; (meth) acrylamide; maleic acid, fumaric acid, or an acid thereof and an aliphatic alcohol having 1 to 20 carbon atoms. Or a monoester or diester with an aliphatic glycol having 2 to 4 carbon atoms or a polymer of the aliphatic glycol (that is, a polyalkylene glycol (addition number is about 2 to 100 per molecule)); vinyl acetate, propenyl acetate, etc. Alkenyl acetate; aromatic vinyl such as styrene, p-methylstyrene, and styrenesulfonic acid; and vinyl chloride. These monomers (c) can be used alone or in combination of two or more.

In the copolymers (A) and (B), the total of the monomers (a), (b) and (c) is 10
When the amount is 0% by weight, the monomer (a) is contained in an amount of 10 to 50% by weight, preferably 15 to 45% by weight, and more preferably 20 to 40% by weight. The monomer (b) is contained in an amount of 50 to 89% by weight, preferably 55 to 8%.
The content is 5% by weight, more preferably 60 to 80% by weight. The monomer (c) is contained in an amount of 1 to 50% by weight, preferably 1 to 30% by weight, and more preferably 1 to 1% by weight.
0% by weight. When the amount of the monomer (a) is less than 10% by weight, the storage stability of the ink is inferior, and when it exceeds 50% by weight, the viscosity of the ink is remarkably increased, and the handleability is inferior. Viscosity is too high and performance does not appear. When the amount of the monomer (b) is 5
If the amount is less than 0% by weight, the solubility in water is significantly reduced, while if it exceeds 90% by weight, the ability to disperse the pigment is reduced.

The above monomer (c) is used in an amount such that the resulting copolymer (A) or copolymer (B) becomes water-soluble in the amounts of the monomers (a) and (b). It is preferably used in an amount of 1 to 50% by weight based on the total of (b) and the monomer (c).

The copolymerization mode of the monomers (a), (b) and (c) can be a random copolymerization, a block copolymerization, an alternating copolymerization, a graft copolymerization,
There is no particular limitation as long as the functions of the obtained copolymers (A) and (B) as a polymer dispersant are not impaired.

The copolymers (A) and (B) have a weight average molecular weight of 5,000 to 200,000. If the molecular weight of the copolymers (A) and (B) is too high beyond the above range, the viscosity increases and the handleability becomes poor. In addition, when the ink is used as an ink, the viscosity of the ink increases and the performance of the ink decreases. I will. The weight average molecular weight is desirably 5,000 to 70,000.

The method for preparing the copolymer (A) is not particularly limited as long as the function of the copolymer (A) as a polymer dispersant is not impaired, and a conventionally known preparation method is used.
Specific examples of the preparation method include the method described in JP-B-59-18338, column 5, line 4 to column 6, line 1. The copolymer (B) neutralizes the copolymer (A) with an alkaline substance, for example, a hydroxide, chloride and carbonate of a monovalent metal or a divalent metal; ammonia; It can be obtained by:

The reason why the dispersibility of the pigment is improved by using the copolymer (A) or (B) as the polymer dispersant in the aqueous pigment ink of the present invention is not clear, but is as follows. It is inferred. That is, in the above-mentioned copolymers (A) and (B), in the ink, a site having a charge (polarity) in the molecule (for example, a carbonyl site) is adsorbed on the pigment surface, and a polyoxyalkylene group in the side chain is added to the outside. Facing the surface of the pigment. Since the polyoxyalkylene group has a long chain length and high steric hindrance, aggregation between the pigments is inhibited by the polyoxyalkylene group. As a result, it is considered that the dispersibility and storage stability of the pigment are improved, and clogging in the printer head is prevented, particularly when used as an ink for inkjet recording. Since the steric hindrance caused by the polyoxyalkylene group is particularly noticeable when the pH of the aqueous pigment ink of the present invention is high, the pH of the aqueous pigment ink of the present invention may be set to a high range as described later. preferable.

The copolymer (A) or (B) used as a polymer dispersant is preferably incorporated in the aqueous pigment ink of the present invention in an amount of 0.05 to 10% by weight. If the blending amount of the copolymer is less than 0.05% by weight, the blending amount does not reach the level sufficient to stabilize the pigment, so that storage stability may be lacking. The storage stability is preferably not further improved, and the viscosity of the ink may be increased. The blending amount of the copolymer is more preferably 0.1 to 4% by weight, and even more preferably 0.5 to 3% by weight. In the present invention, the above copolymers (A) and (B) may be used in combination.

Next, in the aqueous pigment ink of the present invention,
The essential components other than the polymer dispersant will be described. The pigment used in the water-based pigment ink of the present invention is not particularly limited in its kind, and includes, for example, carbon black;
C. I. Pigment Yellow 1, 5, 12, 14, 1
7, 24, 42, 53, 83, 95, 97, 98 and 1
00; I. Pigment Red 1, 3, 4, 5, 1
7, 22, 31, 48, 49, 53, 63, 64, 8
1: 1, 88 and 101; I. Pigment Blue 1, 15, 16, 27, 28, 29, 56, 60 and 6
3 and; I. Pigment Black 1 and 11 can be used, and carbon black is particularly preferable. The pigment is preferably blended in the water-based pigment ink of the present invention in an amount of 1 to 15% by weight.
More preferably, it is added at 0% by weight. If the amount of the pigment is less than 1% by weight, the printing density is insufficient and
Even if it is used in an amount exceeding 5% by weight, the print density cannot be significantly improved, so it is preferable to be within the above range. Also,
The pigment preferably has an average particle size of 0.05 to 3 μm from the viewpoint of improving the storage stability of the ink.
It is more preferred that the thickness be from 0.5 to 1 μm.

When color printing is performed by the subtractive color mixture method using the aqueous pigment ink of the present invention, black, yellow,
It is preferable to use a water-based pigment ink set including four types of inks (black ink, yellow ink, magenta ink, and cyan ink) containing magenta and cyan pigments. In this case, carbon black is used as a black pigment, and C.I. I. Pigment Yellow 17 and 83,
As a magenta pigment, C.I. I. Pigment Red 48:
3, 83 and 122, and C.I. I. Pigment Blue 15: 3 is preferred because color reproducibility is improved.

The water-soluble solvent used in the water-based pigment ink of the present invention is not particularly limited as long as it has a function as a wetting agent or a humectant. Examples thereof include ethylene glycol, propylene glycol, diethylene glycol, and triethylene glycol. Glycols such as glycol, tetraethylene glycol and polyethylene glycol; glycerin; diethylene glycol diethyl ether, diethylene glycol monobutyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, methyl carbitol, ethyl carbitol, butyl carbitol , Ethyl carbitol acetate, diethyl carbitol, triethylene glycol monomethyl ether, triethyl Ethers of polyhydric alcohols such as tylene glycol monoethyl ether and propylene glycol monomethyl ether, acetates; thiodiglycol; N-methyl-2-pyrrolidone; 1,3-dimethylimidazolidinone; triethanolamine; formamide; One or two or more of nitrogen-containing compounds such as dimethylformamide and dimethylsulfoxide can be used. These water-soluble solvents are preferably contained in the water-based pigment ink of the present invention in an amount of 0.1 to 30% by weight, more preferably 0.1 to 15% by weight.

In the water-based pigment ink of the present invention (particularly when used as an ink for ink jet recording), water is used as a medium, and is preferably contained in an amount of 70 to 98% by weight, more preferably 85 to 95% by weight. More preferably,

In addition to the above-mentioned essential components, the water-based pigment ink of the present invention may optionally contain various components as described below.

In the water-based pigment ink of the present invention, it is preferable to use a dispersibility improver together with the above-mentioned polymer dispersant. As the dispersibility improver, an anionic surfactant,
Various surfactants such as a cationic surfactant, a nonionic surfactant, and an amphoteric surfactant can be used. The surfactant is contained in the aqueous pigment ink of the present invention in a total amount of 0.1%.
It is preferable that the content is 0.1 to 10% by weight.
-10% by weight, more preferably 0.05% by weight.
-5% by weight, more preferably 0.1% by weight.
Most preferably, it is blended in an amount of about 5% by weight.

Examples of the above-mentioned anionic surfactant include alkyl benzene sulfonate, alkyl naphthalene sulfonate, alkane or olefin sulfonate, alkyl sulfate, polyoxyethylene alkyl or alkyl aryl ether sulfate, alkyl phosphate. , An alkyl diphenyl ether disulfonate, an ether carboxylate, an alkyl sulfosuccinate, an α-sulfofatty acid ester, and a surfactant selected from the group consisting of a fatty acid salt, a condensate of a higher fatty acid and an amino acid, a naphthenate, and the like. Can be used. Anionic surfactants preferably used include alkyl benzene sulfonates (especially linear alkyl), alkanes or olefin sulfonates (especially secondary alkane sulfonates, α-olefin sulfonates), alkyl sulfates Polyoxyethylene alkyl or alkyl aryl ether sulfate (especially polyoxyethylene alkyl ether sulfate), alkyl phosphate (especially monoalkyl), ether carboxylate, alkyl sulfosuccinate, α-sulfofatty acid ester And surfactants selected from the group consisting of fatty acid salts, and particularly preferred are alkylbenzene sulfonates (especially those of linear alkyl), polyoxyethylene alkyl or alkylaryl ether sulfates Ester salts (especially polyoxyethylene alkyl ether sulfate salts), and alkyl sulfate salts. These can be used alone or in combination of two or more.

As the above-mentioned cationic surfactant, aliphatic amine salts, quaternary ammonium salts, sulfonium salts, phosphonium salts and the like can be used. These can be used alone or in combination of two or more.

Examples of the nonionic surfactant include polyoxyethylene alkyl ether, polyoxyethylene alkyl aryl ether, sorbitan fatty acid ester,
A surfactant selected from the group consisting of polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester, polyoxyethylene fatty acid ester and alkyl (poly) glycoxide can be used. Nonionic surfactants preferably used are surfactants selected from polyoxyethylene alkyl ethers and polyoxyethylene alkyl aryl ethers. These can be used alone or in combination of two or more.

As the amphoteric surfactant, amino acid type compounds, betaine type compounds and the like can be used.

In particular, when the above surfactant is used,
Either an anionic surfactant or a combination of an anionic surfactant and a nonionic surfactant is used, and the amount of each is 0.01 to 5% by weight (particularly 0.01 to 3% by weight,
In particular, 0.05 to 2% by weight), and the mixing ratio of both is anionic surfactant: nonionic surfactant = 10
It can be used in a weight ratio of 0: 1 to 1: 100 (especially 90: 1 to 1:70, especially 70: 1 to 1:50), and the print density of the printed image and the long-term storage It is preferable from the viewpoint of improving dispersion stability.

When an anionic surfactant is used as the surfactant, the mixing ratio of the polymer dispersant and the anionic surfactant is such that the polymer dispersant and the anionic surfactant are mixed. = 1: 2 to 30: 1 by weight. If the amount of the polymer dispersant exceeds the above range, the wettability to the pigment may be insufficient and the dispersibility may be reduced. On the other hand, if the amount of the anionic surfactant is more than the above range, the foaming property of the ink is increased and the handleability may be poor. The mixing ratio of the two is more preferably the polymer dispersant: the anionic surfactant = 1: 1 to 15: 1, and 1: 1.
More preferably, the ratio is from 10 to 10: 1.

In the water-based pigment ink of the present invention, polypropylene glycol is used in order to balance the improvement of the permeability of the ink into the recording paper and the prevention of strikethrough (ink seepage to the back side of the recording paper). It is preferable to mix them. Polypropylene glycol has a molecular weight of 400
It is preferably from 3,000 to 3,000, and more preferably from 400 to 2,000. The polypropylene glycol is preferably incorporated in the water-based pigment ink of the present invention in an amount of 0.01 to 3% by weight, more preferably 0.01 to 1% by weight.

Further, in order to improve the drying property of the ink, it is preferable to blend an aliphatic monohydric alcohol with the aqueous pigment ink of the present invention. As the aliphatic monohydric alcohol, it is preferable to use one or more of ethyl alcohol, 1-propyl alcohol, and 2-propyl alcohol, and it is particularly preferable to use 1-propyl alcohol. The aliphatic monohydric alcohol is preferably incorporated in the aqueous pigment ink of the present invention in an amount of 0.01 to 10% by weight, more preferably 0.1 to 8% by weight. In particular, in relation to the amount of the aliphatic monohydric alcohol and the amount of the polymer dispersant, the compounding ratio of the both is such that the polymer dispersant: the aliphatic monohydric alcohol = 1: 10.
By adjusting the ratio to １1: 1, the drying property of the ink is further improved.

Further, the water-based pigment ink of the present invention has a molecular weight of 400 to 3 particularly in order to improve the intermittent ejection property when used as an ink jet recording ink.
A polyethylene glycol disulfate salt of 500 (particularly, 400 to 2,000) can be blended.
The polyethylene glycol disulfate salt is preferably incorporated in the aqueous pigment ink of the present invention in an amount of 0.01 to 3% by weight, more preferably 0.01 to 1% by weight.

Similarly, in order to improve the intermittent ejection property,
Sugars can be blended in the aqueous pigment ink of the present invention. As the saccharide, D-glucose, fructose,
It is preferable to use one or more of maltose and saccharose, and it is particularly preferable to use saccharose. The saccharide is preferably contained in the water-based pigment ink of the present invention in an amount of 0.1 to 5% by weight, more preferably 0.1 to 3% by weight. In particular, when the compounding amount of the saccharide is related to the compounding amount of the polymer dispersant, the compounding ratio of the two is such that the polymer dispersant: the saccharide = 20: 1 to 1: 5.
The intermittent ejection property is further improved by adjusting such that.

Similarly, in order to improve the intermittent ejection property, a nitrogen-containing heterocyclic compound such as N-methyl-2-pyrrolidone or 1,3-dimethyl-2-imidazolidinone is added to the aqueous pigment ink of the present invention. It can also be blended. The nitrogen-containing heterocyclic compound is preferably incorporated in the aqueous pigment ink of the present invention in an amount of 0.01 to 10% by weight, more preferably 0.1 to 5% by weight.

Similarly, in order to improve the intermittent ejection property, an aprotic polar solvent can be added to the aqueous pigment ink of the present invention. As the aprotic polar solvent, it is preferable to use one or more of dimethyl sulfoxide and sulfolane. The aprotic polar solvent is preferably incorporated in the aqueous pigment ink of the present invention in an amount of 0.01 to 10% by weight, and more preferably 0.1 to 10% by weight.
-5% by weight.

The polyethylene glycol disulfate salt, saccharide, nitrogen-containing heterocyclic compound, and aprotic polar solvent capable of improving the intermittent ejection property are used in combination with a pigment having an average particle diameter of 0.05 to 3 μm. Thereby, the intermittent ejection property is further improved.

In the water-based pigment ink of the present invention, it is preferable to incorporate an acryl-urethane copolymer emulsion in order to improve the fixing property of the ink. As the emulsion, it is preferable to use an acryl-urethane block copolymer (a copolymer obtained by adding a polyurethane polymer to a polyacrylic acid polymer). The weight average molecular weight of the copolymer in the emulsion is preferably from 10,000 to 300,000, and more preferably from 20,000 to 250,000. The emulsion is preferably contained in the aqueous pigment ink of the present invention in a solid content concentration of 0.01 to 10% by weight, more preferably 0.05 to 5% by weight.

Similarly, in order to improve the fixing property of the ink, the water-based pigment ink of the present invention has a weight average molecular weight of 800.
Polyethyleneimine of up to 300,000 may be blended. As the polyethyleneimine, it is preferable to use one or more of polyethyleneimine grafted to the side chain of the main chain composed of an acrylic chain, polyethyleneimine subjected to hydroxylation treatment, and polyethyleneimine zwitterionized. It is particularly preferable to use hydroxylated polyethyleneimine. The polyethyleneimine is present in the aqueous pigment ink of the present invention in an amount of 0.01%.
-10% by weight, preferably 0.05-5%
More preferably, it is blended by weight.

In the water-based pigment ink of the present invention, if necessary, an antifoaming agent such as a silicone compound, a fungicide such as a chloromethylphenol compound, a chelating agent such as EDTA, and an oxygen absorbing agent such as a sulfite are used. Etc. can also be blended.

The water-based pigment ink of the present invention preferably has a pH of 9.5 to 13.0, from the viewpoint of improving the print density of a printed image, particularly the black print density.
More preferably, it is 0 to 12.0. In order to keep the pH within the above range, a pH adjuster, for example, amino alcohol may be added to the aqueous pigment ink of the present invention. As the amino alcohol, it is preferable to use monoethanolamine (for example, 2-aminoethanol), triethanolamine, or the like.

The method for preparing the water-based pigment ink of the present invention by mixing the above-mentioned components is not particularly limited, and is prepared using a conventionally known apparatus such as a ball mill, a sand mill, an attritor, a basket mill, a roll mill and the like. can do. In preparing the water-based pigment ink of the present invention, it is preferable to remove coarse particles. For example, the ink obtained by blending the above components is centrifuged (2500 G, 20 minutes) with a centrifuge to remove particles of preferably 2000 nm or more, more preferably 1000 nm or more. This is preferable because ink without clogging can be obtained.

The water-based pigment ink of the present invention is used as an ink for ordinary writing implements such as a fountain pen, a ball-point pen, a magic pen, and a felt-tip pen, and is particularly preferably used as an ink for ink-jet recording. When the water-based pigment ink of the present invention is used as an inkjet recording ink,
If the printer uses the inkjet recording method,
It can be used in any printer. For example, a thermal jet recording type printer that performs recording using thermal energy from a heater or the like of a heating resistance element disposed in a printer head, and a piezoelectric element recording that performs recording using a piezoelectric element disposed in the printer head Any type of printer can be used.

[0047]

The following examples illustrate the effectiveness of the present invention. However, the scope of the present invention is not limited to such an embodiment. In the following examples, "parts" and "%" represent parts by weight and% by weight, respectively, unless otherwise specified.

[Example 1] 15 parts of pigment A 3 parts of polymer dispersant A 5 parts of diethylene glycol 1 part of 2-aminoethanol 76 parts of water The above components were dispersed in a sand mill for 4 hours. did. Next, the dispersion A and the following components were diluted with a dissolver so as to have the following mixing ratio. -33 parts of dispersion A-4 parts of diethylene glycol-63 parts of water After blending the above components, centrifugation is performed with a centrifuge (2500
G, 20 minutes) to remove coarse particles to obtain an aqueous pigment ink. The storage stability of this aqueous pigment ink and the clogging of the ink at the tip of the printer head were measured according to the following [measurement method]. Table 3 shows the results. The details of the pigment A and the polymer dispersant A in the above components are as shown in Table 2.

[Measurement method] Storage stability The obtained ink was stored at 60 ° C for 120 hours, and then stored for 25 hours.
The ink was centrifuged at 00 G for 20 minutes, and the solid content concentration (wt%) of the ink after the centrifugation was measured. In the same manner, the solid content concentration (w of the ink stored at room temperature (25 ° C., 120 hours)
t%). The measured value was substituted into the following formula (I) to calculate the change in the solid content (%) of the ink. The storage stability of the ink was evaluated from the calculated solid content change value of the ink according to the following criteria.

[0050]

(Equation 1)

Evaluation Criteria 0 ≦ Ink Solids Concentration Change ≦ 3... ◎ 3 <Ink Solids Concentration Change ≦ 5... 5 <Ink Solids Concentration Change ≦ 10... Change in solid concentration

The clogged ink is applied to a thermal jet printer (BJ-10 Lite manufactured by Canon) in which a printer head is provided with a heater of a heating resistance element, and an ink jet printer in which a piezoelectric element is provided to a printer head. (Epson MJ-500C), solid printing was performed on recycled paper for PPC [manufactured by Nippon Kaishi Paper Co., Ltd.]
The clogging of the ink at the tip of the printer head after standing for 0 days was evaluated according to the following criteria. Evaluation criteria S: All nozzles discharged without cleaning. A: The ejection failure was recovered by one cleaning. B: The ejection failure was recovered by cleaning within three times. C: Some nozzles did not discharge even after five cleanings.

Examples 2 to 5 and Comparative Examples 1 and 2 A water-based pigment ink was obtained in the same manner as in Example 1 except that the types and amounts of the pigment and the polymer dispersant were as shown in Table 1. Was. Example 1 about the obtained water-based pigment ink
The same measurement was performed. Table 3 shows the results. The details of the pigment and the polymer dispersant used in Examples 2 to 5 and Comparative Examples 1 and 2 are as shown in Table 2.

[0054]

[Table 1]

[0055]

[Table 2]

[0056]

[Table 3]

As is clear from the results shown in Table 3, the aqueous pigment inks of the present invention using the specific polymer dispersant (Examples 1 to 5) had better storage stability than the aqueous pigment inks of Comparative Examples. It is clear that clogging in the printer head is prevented particularly when used as an ink for ink jet recording. In addition, it can be seen that the water-based pigment ink of the present invention can provide good results in any of the ink jet recording methods in which recording is performed using thermal energy and a piezoelectric element.

[0058]

According to the present invention, a water-based pigment ink having excellent storage stability can be obtained. Further, according to the present invention, there is obtained an aqueous pigment ink in which clogging in a printer head is prevented particularly when used as an ink for inkjet recording.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hideki Yanagi 2606, Kabashi-cho, Akaga-cho, Haga-gun, Tochigi Prefecture (72) Inventor Shigemi Wakabayashi 2606, Kabaka-cho, Akaba-cho, Haga-gun, Tochigi Prefecture, Kao Corporation ( 72) Inventor Yoshiaki Tsujii 2606 Kabane-cho, Akaga-cho, Haga-gun, Tochigi Pref. (72) Inventor Kenji Aida 2606 Kabashi-cho, Akabane-cho, Haga-gun, Tochigi Pref.

Claims (2)

[Claims] 1. An aqueous pigment ink containing a pigment, a polymer dispersant, a water-soluble solvent and water as main components, wherein the polymer dispersant is a polyalkylene glycol mono (meta) represented by the following general formula (I). ) Acrylic acid ester monomer (a), (meth) acrylic acid monomer (b) represented by the following general formula (II) and copolymerizable with the above monomers (a) and (b) 10 to 50% by weight of the monomer (C), 50 to 89% by weight of the monomer (B) and 1 to 50% by weight of the monomer (C) [however, The total of the monomers (a), (b) and (c) is 100% by weight. A water-based pigment ink using the copolymer (A) obtained by using the copolymer in the ratio described above or the copolymer (B) obtained by neutralizing the copolymer (A) with an alkaline substance. . Embedded image Embedded image 2. The aqueous pigment ink according to claim 1, which is an ink jet recording ink.