JPH1060328A - Water-based pigment ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the long-term dispersion stability and storage stability at high temps. of water-base pigment ink mainly comprising a carbon black, a polymeric dispersant, a water-soluble solvent, and water by specifying the volatile content of the carbon black. SOLUTION: A carbon black having a volatile content of 9-25wt.%, pref. 9.5-20wt.%, still pref. 10-15wt.%, is used. The amt. of the black compounded is pref. 1-15wt.% still pref. 2-10wt.%, of the ink. The polymeric dispersnant used in pref. a (meth)acrylic acid deriv. copolymer obtd. by copolymeizing a monomer represented by formula I (R1 and R2 are each H or lower alkyl; m1 is 0-2; AO is 2-3C oxyalkylene; n is 1-300; and X is R1 ) and a monomer (including its acid anhydride) represented by formula II [R3 to R5 are each R1 or (CH2 )m2 COOM2 ; M1 and M2 are each H, an alkali or alkaline earth metal, ammonium, or an amine; and m2 is m1 ].

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 having improved long-term storage stability at high temperatures, and more particularly to an aqueous pigment having improved print quality by preventing feathering when used as an ink for ink jet recording. Regarding ink.

[0002]

2. Description of the Related Art
As a technique relating to the volatile matter of carbon black in the ink, for example, a technique described in JP-A-3-210373 is known. The publication states that the volatile content is 3.5-8.
It is described that by combining a weight percent of acidic carbon black with a specific water-soluble resin, the density of printed matter is high, and the ejection stability and long-term storage stability of the ink are improved.

However, the ink described in the above publication has low long-term storage stability at high temperatures, and especially when used as an ink for ink jet recording, so-called feathering (adhesion to a recording member). (A phenomenon in which ink droplets trail)), which has not yet been satisfactory in terms of print quality.

Accordingly, it is an object of the present invention to provide a water-based pigment ink having improved long-term storage stability at high temperatures. Another object of the present invention is to provide a water-based pigment ink in which feathering and the like are prevented and print quality is improved, 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 setting the volatile matter content of carbon black within a specific range.

The present invention has been made based on the above findings. In a water-based pigment ink containing carbon black, a polymer dispersant, a water-soluble solvent and water as main components, the carbon black has a volatile content of 9 to 10. The above object has been achieved by providing a water-based pigment ink characterized by being 25% by weight.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The water-based pigment ink of the present invention contains carbon black, a polymer dispersant, a water-soluble solvent and water as essential components, and uses a carbon black having a specific volatile content. It is characterized by the following.

The carbon black having a specific volatile content is a carbon black having a volatile content of 9 to 25% by weight. By using the carbon black, the long-term storage stability of the ink at high temperatures is improved, and in particular, when the water-based pigment ink of the present invention is used as an inkjet recording ink, the occurrence of feathering and bleeding is prevented. Printing quality is improved. More specifically, if the volatile content of the carbon black is less than 9% by weight, the long-term storage stability of the ink at high temperatures is poor, and if it exceeds 25% by weight, the water-based pigment ink of the present invention is particularly suitable for inkjet recording. When used as ink, deposits are formed on the electrode portion in the printer head, causing problems such as ejection failure and clogging of the head. The volatile matter of the carbon black is preferably 9.5 to 20% by weight,
More preferably, it is 0 to 15% by weight. The volatile content of the carbon black is measured by the method described in JP-A-3-210373, page 4, lower left column, line 9 to last line.

Carbon black having a volatile content within the above range is, for example, High Color Channel, M
edium Color Channel and Reg
Channels such as the Ultra Color Channel
It can be manufactured using the el method. Further, as the carbon black, Printex 15 manufactured by Degussa Co., Ltd.
Commercial products such as OT, Special Black 4, 4A, 5, and 6, Color Black FW2, FW2V, and FW200 can also be used.

The above-mentioned carbon black is preferably blended in the water-based pigment ink of the present invention in an amount of 1 to 15% by weight, more preferably 2 to 10% by weight. If the amount of the carbon black is less than 1% by weight, the print density is insufficient, and even if the carbon black is used in excess of 15% by weight, the print density may not be significantly improved. Is preferred.

The carbon black preferably has an oil absorption in a powder state of 250 to 800 g / 100 g. When the oil absorption does not satisfy the above conditions,
Agglomeration of carbon black is likely to occur, and the storage stability of the ink may be reduced. In particular, when the water-based pigment ink of the present invention is used as an ink for inkjet recording, ink ejection failure may occur. The oil absorption is 300
７００700 g / 100 g, more preferably 40 g / 100 g.
More preferably, it is 0 to 600 g / 100 g. Carbon black having an oil absorption within the above range is, for example, H
high ColorChannel, Medium C
color Channel and Regular Co
It can be manufactured using a Channel method such as lor Channel. In addition, the above oil absorption is based on JIS K
It is a value measured according to 6221-1982.

The average particle size of the carbon is preferably from the viewpoint of further improving the long-term storage stability of the ink at high temperatures and further improving the printing quality particularly when used as an ink for ink jet recording. It is preferably from 0.05 to 3 μm, more preferably from 0.05 to 1 μm. In particular, the carbon black has a particle size distribution of 60 to 98% by volume of particles having a particle size of less than 0.2 μm,
Preferably, it is composed of particles having a particle diameter of 0.6 μm or more and 5% by volume or less. By using carbon black having such a particle size distribution, as a result of forming a coarse coating layer on the printer head with a small amount of coarse particles, carbon black particles are prevented from further adhering,
The long-term ejection stability of the ink is improved. In addition, when particles having a narrow particle size distribution are used, the particles are likely to aggregate, but by using the carbon black particles having the above particle size distribution, aggregation of the particles is prevented, so that the dispersibility of the carbon black particles is reduced. This further improves the long-term storage stability of the ink at high temperatures. The carbon black is 75 to 98% by volume of particles having a particle size of less than 0.2 μm;
Particles having a particle size of 0.2 μm or more and less than 0.6 μm 0.5 to 2
More preferably, it is composed of 0% by volume and 3% by volume or less of particles having a particle size of 0.6 μm or more, and 85 to 98% by volume of particles having a particle size of less than 0.2 μm, and particles having a particle size of 0.2 μm or more and less than 0.6 μm. More preferably, the particles comprise 0.5 to 10% by volume of particles having a diameter of 1.5% by volume or less and particles having a particle size of 0.6 μm or more. The particle size distribution of the carbon black can be measured using, for example, a centrifugal sedimentation type distribution measuring device (manufactured by Shimadzu Corporation).

Next, essential components other than the above-mentioned carbon black in the water-based pigment ink of the present invention will be described. Examples of the above-mentioned polymer dispersants include proteins such as gelatin and casein, natural rubber such as gum arabic, and glucoxides such as saponin. , Cellulose derivatives such as alkylcellulose, carboxyalkylcellulose and hydroxyalkylcellulose, natural polymers such as ligninsulfonate and shellac, polyacrylates, styrene-acrylic acid copolymer salts, vinylnaphthalene-acrylic acid copolymers Salt, styrene-maleic acid copolymer salt, vinylnaphthalene-maleic acid copolymer salt, sodium salt of β-naphthalenesulfonic acid formalin condensate, anionic polymer such as polyphosphoric acid, polyvinyl alcohol, polyvinylpyrrolidone, polyalkylene It can be used non-ionic polymers such as glycol. These can be used alone or in combination of two or more.

In particular, when a copolymer of a (meth) acrylic acid derivative is used as the polymer dispersant, the dispersibility of the carbon black is further improved, and the long-term storage stability of the ink at a high temperature is further improved. It is preferred. The copolymer of the (meth) acrylic acid derivative may be one in which only acrylic acid or methacrylic acid or a derivative thereof is used as a copolymer component, or may be a copolymer of acrylic acid or methacrylic acid or a derivative thereof. And a polymerizable monomer may be used as a copolymerization component. As the derivatives of (meth) acrylic acid, alkali metal salts, alkaline earth metal salts, ammonium salts or amine salts and esters thereof, and hydrogen atoms bonded to the double bond carbon may have various functional groups (for example, carboxyl group and carboxyalkyl group). (For example, maleic acid, itaconic acid, citraconic acid, and fumaric acid). In particular, a derivative of (meth) acrylic acid capable of introducing a side chain having a chain length sufficient to exhibit steric hindrance into the copolymer is preferable.

Particularly preferred as the copolymer of the (meth) acrylic acid derivative are a monomer (a) represented by the following general formula (A) and a monomer (a) represented by the following general formula (B). And a copolymer obtained by polymerizing the monomer (b) [hereinafter, this copolymer is referred to as “copolymer (I)”].

[0016]

Embedded image

The copolymer (I) is described in detail below.
In the general formula (A), R ₁ and R ₂ represent a hydrogen atom or a lower alkyl group (preferably C 1 to C
3), which may be the same or different. In particular, it is preferred that both R ₁ and R ₂ are hydrogen atoms, or that R ₁ is a hydrogen atom and R ₂ is a methyl group. m ₁ is, 0-2
And preferably 0 or 1. AO represents an oxyalkylene group having 2 to 3 carbon atoms (that is, an oxyethylene group or an oxypropylene group), and is preferably an oxyethylene group. n represents an integer of 1 to 300, preferably an integer of 2 to 150, more preferably 4 to
It is an integer of 130. If n is 0, the dispersion stability cannot be sufficiently exhibited, and if n exceeds 300, the viscosity of the ink increases, which may adversely affect the ejection behavior, for example, when used in an ink jet printer. X represents a hydrogen atom or a lower alkyl group (preferably C1 to C5), and is preferably a hydrogen atom, a methyl group or an ethyl group.

Specific examples of preferred compounds represented by the above general formula (A) include methoxy polyethylene glycol, methoxy polyethylene polypropylene glycol, ethoxy polyethylene glycol, ethoxy polyethylene polypropylene glycol, propoxy polyethylene glycol, and propoxy polyethylene polypropylene glycol. Ethylene oxide, propylene oxide to esterified product of dealkylated (oxidized) reactant of acrylic acid, methacrylic acid or fatty acid, or to dehydrogenated (oxidized) reactant of acrylic acid, methacrylic acid or fatty acid Adducts. In the compound represented by the general formula (A),
When both ethylene oxide and propylene oxide are added, any of random addition, block addition, alternate addition and the like can be used. In this case, the addition molar ratio between ethylene oxide and propylene oxide (the former: the latter) is preferably from 10:90 to 90:10, and more preferably from 10:90 to 60:40.

Examples of the compound represented by the general formula (B) include unsaturated monocarboxylic acids and salts thereof, and unsaturated dicarboxylic acids and salts thereof. Specifically, acrylic acid, methacrylic acid and crotonic acid and metal salts thereof, and maleic acid which is an unsaturated dicarboxylic acid monomer,
Examples include itaconic acid, citraconic acid and fumaric acid and their alkali metal salts, alkaline earth metal salts, ammonium salts and amine salts, and their acid anhydrides, maleic anhydride, itaconic anhydride and citraconic anhydride.

In the copolymer (I), the molar ratio of the monomers (a) and (b) [monomer (a) / monomer (b)] is 0.1 / 100-100. / 100, more preferably 1/100 to 70/100. If the ratio of the monomer (a) is smaller than this, the dispersion storage stability is impaired. If the ratio of the monomer (a) is larger than this, the solubility in water is reduced and the dispersibility is reduced. There is a risk of doing so. That is, it is preferable to set the molar ratio of the monomers (a) and (b) within such a range, since a polymer dispersant having excellent dispersibility and excellent storage stability can be obtained.

In the copolymer (I), another copolymerizable monomer may be further used as a copolymer component as long as its function as a polymer dispersant is not impaired. The monomer includes (meth) acrylonitrile, (meth)
Acrylamide, styrene, styrene sulfonic acid and the like can be mentioned.

The copolymerization mode of the above monomers (a) and (b) can be random copolymerization, block copolymerization, alternating copolymerization, or graft copolymerization. There is no particular limitation as long as the function of the polymer dispersant (I) is not impaired.

When the copolymer (I) has a high molecular weight, the viscosity increases and the handleability is deteriorated. In addition, when the ink is used as an ink, the viscosity of the ink may increase and the performance of the ink may be reduced. Weight average molecular weight of 5000 to 20
It is preferably 10,000, and more preferably 5000 to 70,000.

In particular, among the above copolymers (I), from the viewpoint of dispersibility and storage stability of the dispersion, preferably 1 to 300, more preferably 2 to 150 oxyalkylene groups per molecule are used. More preferably, 4 to 130 polyalkylene glycol monoester monomers (particularly, a polyalkylene glycol ester of (meth) acrylic acid or an alkoxypolyalkylene glycol ester) and a (meth) acrylic acid monomer are introduced. It is desirable to use a copolymer obtained by polymerization.

The method for preparing the copolymer (I) is not particularly limited as long as the function of the copolymer (I) 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-A-7-223852, column 4, line 42 to column 5, line 11.

The reason why the dispersibility of the carbon black is particularly improved by using a copolymer of a (meth) acrylic acid derivative, particularly the above-mentioned copolymer (I), as the above-mentioned polymer dispersant is not clear. It is presumed to be as follows. That is, in the above-mentioned copolymer (I), in the ink, a site having a charge (for example, a carbonyl site) in the molecule is adsorbed on the surface of the carbon black particles, and the polyoxyalkylene group of the side chain is directed outward. It surrounds the surface of the carbon black particles in a state. Since the polyoxyalkylene group has a long chain length and high steric hindrance, aggregation of the carbon black particles is inhibited by the polyoxyalkylene group. As a result, it is considered that the dispersibility of carbon black and the storage stability of the ink are improved. Since the steric hindrance caused by the polyoxyalkylene group is particularly noticeable when the pH of the ink is high, it is preferable to set the pH of the water-based pigment ink of the present invention to a high range as described later.

The above-mentioned 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 amount of the polymer dispersant is less than 0.05% by weight, the amount does not reach the amount sufficient to stabilize the carbon black, so that storage stability may be lacking. Dispersibility and storage stability may not be further improved, and the viscosity of the ink may be increased. The compounding amount of the polymer dispersant is more preferably from 0.1 to 4% by weight, and even more preferably from 0.5 to 3% by weight.

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, water (preferably ion-exchanged water) is used as a medium, and is preferably contained in an amount of 70 to 98% by weight, and is preferably 85 to 85% by weight.
More preferably, it is blended in an amount of up to 95% by weight.

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 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 preferably added in an amount of from 0.05 to 10% by weight.
More preferably, it is blended at 5% by weight.

Examples of the anionic surfactant include alkyl benzene sulfonate, alkyl naphthalene sulfonate, alkane or olefin sulfonate, alkyl sulfate, polyoxyethylene alkyl or alkyl aryl ether sulfate, and 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, etc. 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 carbon black 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 compounding ratio of the two is more preferably the polymer dispersant: the anionic surfactant = 1: 1 to 15: 1, and further preferably 1: 1 to 10: 1.

In the water-based pigment ink of the present invention, polypropylene glycol is used in order to balance the improvement in 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 mix 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 3500 (particularly 400 to 2000) in order to improve the intermittent ejection property of the ink, particularly when used as an ink for ink jet recording. A polyethylene glycol disulfate salt can also be included. 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, 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 to improve the intermittent ejection property. 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, an aprotic polar solvent can be added to the aqueous pigment ink of the present invention in order to improve the intermittent ejection property. 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 and nitrogen-containing heterocyclic compound capable of improving the intermittent ejection property can be used in combination with the above carbon black having an average particle size of 0.05 to 3 μm to improve the intermittent ejection property. Even better.

Further, in the water-based pigment ink of the present invention, in order to improve the fixing property of the ink, an acrylic-based pigment ink is used.
It is preferable to mix emulsions such as aqueous urethane, styrene-butadiene, and polyester. In particular, it is preferable to mix an acrylic-urethane copolymer emulsion. As the emulsion, it is preferable to use an acryl-urethane block copolymer (a copolymer in which urethane is grafted on a side chain of a main chain composed of an acrylic chain). The weight average molecular weight of the copolymer in the emulsion is 10,000 to 300,000
And more preferably 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 fixability 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 aqueous 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 may be used. Etc. can also be blended.

The water-based pigment ink of the present invention, particularly when used as an ink for ink jet recording, prevents the ink from clogging at the leading end of the printer head due to drying or scorching due to thermal energy during printing. Therefore, specific heat exceeds 4.00 J / gK to 4.1.
5 J / gK and thermal conductivity of 0.1 × 10 ⁻³ to 50 × 1
It is preferably 0 ⁻³ W / (cm · deg). In this case, it is preferable to mix the carbon black in an amount of 2 to 5% by weight and the polymer dispersant in an amount of 0.5 to 6% by weight. In order to keep the specific heat and the thermal conductivity of the ink within the above ranges, the amount of water (preferably ion-exchanged water) as a medium and the amount of the water-soluble solvent may be appropriately adjusted.

The water-based pigment ink of the present invention has a viscosity at 25 ° C. of from 0.3 to 0.3, particularly when used as an ink for ink-jet recording, because it can improve the ejection behavior.
It is preferably 30 cps, more preferably 1 to 10 cps. In order for the viscosity to be within the above range, for example, the water-based pigment ink of the present invention is adjusted so that the thickness of the polymer dispersant adsorption layer (the layer formed by adsorbing the carbon black) becomes optimal. The pH may be adjusted, the solid content in the ink may be optimized, or the amount of the aliphatic monohydric alcohol may be adjusted.

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, (eg, 2-aminoethanol), triaminoethanol, or the like.

Further, the water-based pigment ink of the present invention can improve the ejection stability, particularly when used as an ink for ink jet recording, so that the Ross Miles method (JIS K 3362) known as a foaming test method can be used. ), The stability of the foam after 5 minutes is preferably from 5 mm to 50 mm, more preferably from 10 mm to 40 mm, even more preferably from 15 mm to 30 mm. In order to keep the stability of the foam of the ink within the above range, for example, the various surfactants described above may be blended into the ink.

Similarly, in order to improve the ejection stability,
The water-based pigment ink of the present invention has a surface tension at 25 ° C. of 3
0 to 60 dyne / cm is preferable, and 30 to
More preferably, it is set to 50 dyne / cm. In order to keep the surface tension within the above range, various surfactants may be blended into the ink as in the case of the stability of the foam of the ink described above.

In the water-based pigment ink of the present invention, an ultracentrifugal separation operation (50,000 G, 4 hours) is performed to improve the fixability to a recording member such as plastic (especially OHP sheet), metal and cloth. ), The water-soluble resin component in the supernatant liquid of the ink after the carbon black is precipitated [the polymer dispersant, and the acryl-urethane copolymer emulsion and the polyethylene imine used as needed (both are fixed). Resin component)] is 2 to 7% by weight.

The method for preparing the water-based pigment ink of the present invention is not particularly limited, and a conventionally known apparatus such as a ball mill,
It can be prepared using a sand mill, attritor, basket mill, roll mill, or the like. In preparing the 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 2 μm or more, more preferably 1 μm or more. This is preferable because ink without clogging can be obtained.

The water-based pigment ink of the present invention is a thermal jet recording type printer that performs recording by using thermal energy from a heater or the like of a heating resistor element disposed in a printer head, and a piezoelectric element disposed in the printer head. An excellent effect is exhibited when printing is performed by using any of the piezoelectric element recording type printers that perform recording by using.

[0056]

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" indicates parts by weight unless otherwise specified.

Example 1-5 parts of carbon black A-2 parts of polymer dispersant A-2 parts of sodium lauryl sulfate-7 parts of diethylene glycol-1 part of 2-diaminoethanol-83 parts of water Centrifuge with a centrifuge (2500
G, 20 minutes) to remove coarse particles to obtain an ink.
The details of the carbon black A and the polymer dispersant A are as shown in Tables 1 and 2. With respect to this ink, the storage stability of the ink at a high temperature and the print quality were evaluated according to the following [Evaluation criteria]. Table 3 shows the results.

[Measurement method] Storage stability The obtained ink was stored at 60 ° C for 2 months,
The ink was centrifuged at 0 G for 20 minutes, and the solid content (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.

[0059]

(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

Print Quality <Print Density> A thermal jet printer (Canon-made printer) in which a heater for a heat-generating resistor is provided on the printer head
BJ-10 Lite) and an ink jet printer (MJ-500C manufactured by Epson) in which a piezoelectric element is arranged in the printer head, and solid printing is performed on recycled paper for PPC [manufactured by Nippon Kaishi Paper Co., Ltd.]. After standing for more than an hour, the optical density of the solid print area was measured using a Macbeth densitometer RD91.
8 (manufactured by Macbeth). <Feathering / Bleeding> The test chart shown in FIG. 1 was printed in the same manner as the above-described print density measuring method, and it was visually determined how far the levels 1 to 5 were printed. In the test chart shown in FIG. 1, level 1 is the best and level 5 is the worst. And level 3
The above is the generally accepted print quality.

[Examples 2 and 3 and Comparative Examples 1 and 2]
An aqueous ink was obtained in the same manner as in Example 1 except that the carbon black and the polymer dispersant shown in Tables 1 and 2 were used. The same evaluation as in Example 1 was performed on the obtained ink. Table 3 shows the results. The carbon black E in Comparative Example 2 was the same as that in Example 1 of JP-A-3-210373.

[0063]

[Table 1]

[0064]

[Table 2]

[0065]

[Table 3]

As is clear from the results shown in Table 3, the water-based pigment inks of the present invention (Examples 1 to 3), particularly the water-based pigment inks of Examples 1 and 2, using carbon black having a specific volatile content, It can be seen that, compared to the ink of the comparative example, the storage stability at high temperatures and the printing quality were excellent. In particular, it can be seen that the water-based pigment ink of the present invention has good print quality in any of the ink jet recording methods in which recording is performed using thermal energy and a piezoelectric element.

[0067]

According to the water-based pigment ink of the present invention, long-term dispersion stability and storage stability at high temperatures are improved. Further, according to the water-based pigment ink of the present invention, particularly when used as an ink for inkjet recording, feathering and bleeding are prevented, and print quality is improved.

[Brief description of the drawings]

FIG. 1 is a test chart used for evaluating print quality in Examples and Comparative Examples.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shoichi Suzuki 2606 Kabane-cho, Akaga-cho, Haga-gun, Tochigi Pref. (72) Inventor Yoshiaki Tsujii 2606 Kabane-cho, Akaga-cho, Haga-gun, Tochigi Pref. (72) Inventor Kenji Aida 2606 Kabane-cho, Akabane-cho, Haga-gun, Tochigi Pref.

Claims (5)

[Claims] 1. An aqueous pigment ink containing carbon black, a polymer dispersant, a water-soluble solvent and water as main components,
The carbon black has a volatile content of 9 to 25% by weight.
An aqueous pigment ink, characterized in that: 2. The carbon black according to claim 1, wherein the oil absorption in a powder state is 250 to 800 g / 100 g.
The water-based pigment ink according to the above. 3. The aqueous pigment ink according to claim 1, wherein the polymer dispersant is a copolymer of a (meth) acrylic acid derivative. 4. The polymer dispersant according to the following general formula (A)
And a copolymer obtained by polymerizing a monomer (b) represented by the following general formula (B):
The aqueous pigment ink according to claim 3. Embedded image 5. The aqueous pigment ink according to claim 1, which is an ink for inkjet recording.