JP4623549B2 - Ink for inkjet printer - Google Patents

Description

  The present invention relates to an aqueous ink for an ink jet printer.

  As inks for inkjet printers, which are widely used with the spread of computers, water-based inks are the mainstream in terms of safety, and water-based inks that use water-soluble dyes are particularly color-forming. It is most popular because of its superiority. However, the water-based ink using the water-soluble dye has poor water resistance because the dye is water-soluble, and because the dye is molecular, light, ozone, etc. There is a problem that deterioration due to gas is fast.

  In order to solve these problems, an ink using an insoluble colorant such as a pigment that takes a form in which a plurality of molecules are aggregated instead of a molecular form is being studied. Images formed from these dispersed inks are superior to images using water-soluble dyes in so-called image fastness such as water resistance, light resistance, and gas resistance. In order to improve the ink ejection stability and the sharpness of the hue of an image when used in a printer, it is required to further increase the dispersion of pigment particles.

  Various resin (polymer) dispersants are used to stably disperse fine colorants in an aqueous medium. These resin dispersants have affinity for colorants and affinity for aqueous media. In addition, stability of the molecular skeleton and strong film-forming property at the time of printing are required. In order to satisfy such a requirement, it is usual to use a copolymer in which monomer units having different properties are combined. For example, in Patent Document 1, a hydrophilic block and a hydrophobic block are used. A block copolymer having a block content of 10 to 90% by mass is disclosed.

  In addition, in order to optimize the water solubility, the acid value of the resin is also adjusted. In Patent Document 2, a resin having an acid value of 250 mg-KOH / g or less is suitable for dispersing carbon black. In Patent Document 3, the acid value is 300 mg-KOH / g or less, 50% or more of the acidic groups are neutralized with ammonia or amine, the hydrophilic part is 20 to 60 mol%, and the hydrophobic part is 40 to 80. Resins that are mole percent are disclosed. Patent Document 4 discloses an ink comprising a colorant encapsulated in a resin in which an acid value is 50 mg-KOH / g or more and 280 mg-KOH / g or less and 60% or more of acid groups are neutralized. .

The range of monomer composition and acid value of the resins shown in these examples is extremely wide, and further optimization is desired. In particular, in order to realize sufficient ink ejection stability when applied to an ink jet printer, further detailed examination is required. In addition, these parameters are not related to each other but are related to each other, and it is important to search for the optimal combination including not only the monomer composition and acid value, but also the type of neutralizing agent for acidic groups. is there.
JP 7-53841 A JP 2000-290554 A JP 2003-171590 A JP-A-8-183920

  In view of the above situation, the present invention examines the optimal combination of the monomer composition and acid value of the polymer (resin) dispersant and the neutralizing agent, and stables the fine colorant having excellent image fastness in an aqueous medium. It is an object to provide ink for inkjet printers (hereinafter simply referred to as “ink”) having excellent ejection stability.

  The above problems are solved by the present invention described below. That is, the present invention comprises at least a water-insoluble colorant, a polymer, and an aqueous medium, wherein the polymer is at least one monomer unit (A) selected from the group consisting of methyl methacrylate and ethyl methacrylate, 2 to 10% by mass of a hydrophobic monomer unit (B) other than the monomer unit (A), 5 to 15% by mass of a monomer unit (C) having a nonionic hydrophilic group, and a monomer unit (D) having an acidic group And an acid value of 90 to 200 mg-KOH / g, and at least a part of the acidic group is neutralized with a base.

  In the ink of the present invention, the content of the hydrophobic monomer unit (B) is 2 to 10% by mass and the acid value is 110 to 200 mg-KOH / g; the hydrophobic monomer unit ( The content of B) is 2 to 7% by mass, the acid value is 110 to 150 mg-KOH / g, and at least a part of the base is ammonia; the acid value is 130 to 200 mg- Preferably, KOH / g, at least a portion of the base is an alkanolamine; and the water-insoluble colorant is a pigment.

  According to the present invention, by using a polymer dispersant comprising a combination of an optimized monomer structure and acid value, and a neutralizing agent, a fine particle colorant having excellent image fastness can be stably dispersed in an aqueous medium. Thus, it is possible to provide an ink having excellent ejection stability.

Next, the present invention will be described in more detail with reference to the best mode for carrying out the invention.
The polymer used in the present invention comprises at least one monomer unit (A) selected from the group consisting of methyl methacrylate and ethyl methacrylate, a hydrophobic monomer unit (B) other than the monomer unit (A), and a nonionic A monomer unit (C) having a hydrophilic group and a monomer unit (D) having an acidic group. Methyl methacrylate and / or ethyl methacrylate constitutes the basic skeleton of the polymer and serves to interconnect other components in the polymer molecule.
The content of the monomer unit (A) in the polymer is preferably 54 to 72% by mass. If the content of the monomer unit (A) is less than 54% by mass, inconvenience may occur in that the particle diameter of the resulting color material dispersion tends to increase. On the other hand, when the content of the monomer unit (A) exceeds 72% by mass, there is a disadvantage in that the dispersion stability of the colorant dispersion is lowered, particularly the dispersion stability during long-term storage is likely to be lowered. There is a case.

  The hydrophobic monomer unit (B) mainly has a function of interacting with the fine particle colorant, and various esters such as acrylic acid ester or methacrylic acid ester, crotonic acid ester, itaconic acid ester, maleic acid ester, and fumaric acid ester ( The ester group is a substituted or unsubstituted aliphatic ester group having 3 or more carbon atoms, or a substituted or unsubstituted aromatic ester group, and specifically includes an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group. Group, sec-butyl group, tert-butyl group, pentyl group, hexyl group, 2-ethylhexyl group, tert-octyl group, cyclohexyl group, cyclooctyl group, bornyl group, isobornyl group, 2-chloroethyl group, 4-bromobutyl group , Phenyl group, benzyl group, 4-butylphenyl group), Kurylamides, methacrylamides (n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, 2-ethylhexyl, tert-octyl, cyclohexyl Group, cyclooctyl group, bornyl group, isobornyl group, 2-chloroethyl group, 4-bromobutyl group, phenyl group, benzyl group, 4-butylphenyl group, N-monosubstituted acrylamide, N-disubstituted acrylamide, N-monosubstituted methacrylamide, N-disubstituted methacrylamide), olefins (ethylene, propylene, 1-butene, 1-pentene, vinyl chloride, vinylidene chloride, butadiene, styrene, methylstyrene, dimethylstyrene, trimethylstyrene, Ethyl styrene Isopropyl styrene) is derived from such.

  The content of these hydrophobic monomer units (B) in the polymer molecule is preferably 2 to 10% by mass, and more preferably 2 to 7% by mass. When the amount of the hydrophobic monomer unit (B) is less than 2% by mass, the adhesion of the polymer to the colorant particles is weakened, and the probability that the surface of the naked colorant particles is exposed increases. Is likely to occur. Conversely, when the amount of the hydrophobic monomer unit is too large, the hydrophilicity of the polymer is insufficient, and aggregation between the polymer molecules or between the polymers including the colorant particles tends to occur.

  The monomer unit (C) having a nonionic hydrophilic group helps to stably disperse the polymer in the aqueous medium, and at the same time provides good film-forming properties when printed on a paper medium. Acrylic acid ester or methacrylic acid ester having an alkylene oxide chain in the chain is preferred. The content of the monomer unit having a nonionic hydrophilic group in the polymer molecule is suitably 5 to 15% by mass. When it is less than this, the hydrophilicity of the polymer is lowered, and the dispersion stability of the colorant particles is impaired. Increasing the amount of monomer units having acidic groups to compensate for the lack of hydrophilicity will cause problems such as deterioration of the water resistance of the printed matter, so the presence of more than a certain amount of nonionic hydrophilic monomer units It is essential. On the other hand, if the amount of the nonionic hydrophilic monomer unit exceeds 15% by mass, the interaction between the hydrophobic monomer unit and the colorant particles is hindered, which also hinders stable dispersion of the colorant particles.

The monomer unit (D) having an acidic group has a function of imparting high water solubility to the polymer by neutralization with an alkali and stably dispersing the colorant particles in an aqueous medium. Specific examples include acrylic acid, methacrylic acid, acrylic acid ester having a carboxyl group, a sulfone group, a phosphone group, and the like at the ester site, and methacrylic acid ester. It is preferable that the monomer unit having an acidic group contains an amount such that the acid value of the polymer is 90 to 200 mg-KOH / g, and an amount such that the acid value is 110 to 200 mg-KOH / g. More preferably. When the acid value is less than the above range, the solubility of the polymer in the aqueous medium is insufficient, and the colorant particles cannot be stably dispersed. The hydrophilicity due to the acidic group-containing monomer unit cannot be supplemented by the nonionic hydrophilic monomer unit, and a certain amount or more of the acidic group-containing monomer unit is required. On the other hand, if there are many acidic group-containing monomer units and the acid value is too high, the water resistance of the printed matter deteriorates, and the water solubility of the polymer becomes too high and the polymer alone dissolves, resulting in dispersion of the colorant particles. It may not contribute.
The content of the monomer unit (D) in the polymer is an amount that the polymer has the above acid value. Specifically, the content of the monomer unit (D) is preferably 15 to 30% by mass.

  The polymer used in the present invention can be produced by a known polymerization method. For example, various methods such as solution polymerization, emulsion polymerization, suspension polymerization, bulk polymerization and the like can be adopted. From the physical properties of the monomer (A) to monomer (D), solution polymerization using an appropriate radical polymerization initiator is possible. Is preferred. The monomer used in the present invention is not limited to the monomer (A) to the monomer (D). Monomers other than those described above may be used as a part of the monomer (A) within a range that does not hinder the achievement of the object of the present invention. It can be polymerized.

  In order to develop the hydrophilicity of the polymer containing an acidic group, it is necessary to neutralize it by adding an alkali. As the kind of alkali, sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonia, alkanolamine and the like can be used. In particular, neutralization with ammonia or alkanolamine is suitable for realizing long-term stable ejection in an ink jet printer and enhancing the water resistance of printed matter. The addition amount of the alkali needs to be adjusted so that the final colorant dispersion has a pH of about 7 to 9, and an equivalent amount to 2 times equivalent to the acid value of the polymer is appropriate.

  When ammonia is used as the alkali, the acid value of the polymer is preferably 110 to 150 mg-KOH / g, and when alkanolamine is used as the alkali, the acid value of the polymer is 130 to 200 mg-KOH / g. Is preferred. The reason why the optimum acid value varies depending on the type of alkali used for neutralization is not clear, but considering that the amount of acidic groups substantially dissociated affects ink ejection stability, ammonia It is presumed that the difference in the degree of ionization of the acidic group affects the neutralization and neutralization with alkanolamine.

  A pigment is preferable as the color material used in the present invention. Specifically, it is as follows, but the present invention is not limited to these.

Black pigment
Raven760Ultra, Raven1060Ultra, Raven1080Ultra, Raven1100Ultra, Raven1170, Raven1200, Raven1250, Raven1255, Raven1500, Raven2000, Raven2500Ultra, Raven3500, Raven5250, Raven5750, Raven7000, Raven5000UltraII, Raven1190UltraII (Golden-Carbon L, MO) Rega1400R, Rega1660R, Rega1330R, Monarch800, Monarch880, Monarch900, Monarch1000, Monarch1300, Monarch1400 (manufactured by Cabot); Color Black FW1, Color Black FW2, Color Black FW200, Color Black 18, Color Black S160, Color Black S170, Special Black 4, Special Black 4A, Special Black 6, Special Black 550, Printex35, Printex45, Printex55, Printex85, Printex95, PrintexU, Printex140U, PrintexV, Printex140V (made by Degussa); No.25, No.33, No.40, No.45, No.47, No.52, No.900, No.970, No.2200B, No.2300, No.2400B, MCF-88, MA600, MA77, MA8, MA100, MA220, MA230 (Mitsubishi) Etc.)

Blue pigment C.I. I. Pigment blue-1, C.I. I. Pigment blue-2, C.I. I. Pigment blue-3, C.I. I. Pigment blue-15, C.I. I. Pigment blue-15: 2, C.I. I. Pigment blue-15: 3, C.I. I. Pigment blue-15: 4, C.I. I. Pigment blue-16, C.I. I. Pigment blue-22, C.I. I. Pigment Blue-60 etc.

Red pigment C.I. I. Pigment red-5, C.I. I. Pigment red-7, C.I. I. Pigment red-12, C.I. I. Pigment red-48, C.I. I. Pigment red-48: 1, C.I. I. Pigment red-57, C.I. I. Pigment red-112, C.I. I. Pigment red-122, C.I. I. Pigment red-123, C.I. I. Pigment red-146, C.I. I. Pigment red-168, C.I. I. Pigment red-184, C.I. I. Pigment red-202, C.I. I. Pigment Red-207 etc.

Yellow pigment C.I. I. Pigment yellow-12, C.I. I. Pigment yellow-13, C.I. I. Pigment yellow-14, C.I. I. Pigment yellow-16, C.I. I. Pigment yellow-17, C.I. I. Pigment yellow-74, C.I. I. Pigment yellow-83, C.I. I. Pigment yellow-93, C.I. I. Pigment yellow-95, C.I. I. Pigment yellow-97, C.I. I. Pigment yellow-98, C.I. I. Pigment yellow-114, C.I. I. Pigment yellow-128, C.I. I. Pigment yellow-129, C.I. I. Pigment yellow-151, C.I. I. Pigment yellow-154 and the like.

  In addition, titanium oxide, zinc oxide, iron oxide, zirconium oxide, silica, alumina, silicon nitride, silicon carbide, and other inorganic oxides, nitrides, carbide particles, and composite particles in which these are coated with an organic pigment are also included. Applicable.

  The amount of the colorant in the ink of the present invention is preferably 1 to 20% by mass, and the mass ratio of the polymer and the colorant is preferably 9: 1 to 1: 9. If the amount of the colorant is less than 1% by mass, the coloring power as an ink is not sufficient, and as described above, a sufficient density cannot be obtained in the printed image. If the amount of the colorant exceeds 20% by mass, the image density becomes too high. Although it does not increase significantly, the dispersion of the colorant tends to become unstable, and it causes a decrease in ejection stability such as ink clogging in the nozzle. Further, when the ratio of the polymer to the total amount of the colorant and the polymer is less than 10% by mass, the dispersion of the colorant becomes unstable, and the scratch resistance of the printed matter when printed as an ink also deteriorates. On the other hand, when the ratio of the polymer to the total amount of the colorant and the polymer exceeds 90% by mass, the coloring power of the printed matter is reduced, and at the same time, ejection failure due to an increase in ink viscosity is caused.

  The main liquid medium of the aqueous ink of the present invention is water, but may contain other water-soluble organic substances. These organic substances serve to prevent solidification of the ink due to drying at the nozzle portion when the ink of the present invention is used in an ink jet printer. Specifically, alcohols such as isopropanol and butanol; ethylene Glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, thiodiglycol, neopentyl Diols such as glycol, 1,4-cyclohexanediol and polyethylene glycol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether Alkylene glycol monoalkyl such as ethylene glycol monoallyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether Ethers; polyols such as glycerin, 1,2,4-butanetriol, 1,2,5-pentanetriol, 1,2,6-hexanetriol, trimethylolethane, trimethylolpropane, pentaerythritol; tetrahydrofuran, dioxane Cyclic ethers such as dimethyl sulfoxide, diacetone alcohol, Phosphorus monoallyl ether, N-methyl-2-pyrrolidone, 2-pyrrolidone, γ-butyrolactone, 1,3-dimethyl-2-imidazolidinone, sulfolane, urea, β-dihydroxyethylurea, acetonylacetone, dimethylformamide, Examples thereof include dimethylacetamide and phenoxyethanol.

  Such a substance may be solid or liquid as long as it is water-soluble. Further, since it is required to remain in the ink even under conditions where water evaporates, it is desirable that the boiling point is higher than that of water, and it is desirable that the temperature be 120 ° C. or higher, but there is an interaction with the polymer. Therefore, since it becomes harder to evaporate than a single case, it is not necessarily limited to a high boiling point substance. These organic substances may be used alone or in combination of two or more. The proportion of these organic substances in the ink is 5 to 50% by mass, preferably 10 to 30% by mass, based on the total mass of the ink.

  In addition to the components described above, various additives such as surfactants, pH adjusters, antioxidants, and antifungal agents may be added to the ink of the present invention.

  The ink in the present invention can be produced by kneading a colorant and a polymer, adding and dispersing in a predetermined liquid medium, and further adding dilution water or the above-mentioned additives. A kneader or a roll mill can be used for kneading, and a dispersing machine such as an ultrasonic wave application or a bead mill or a ball mill can be used for dispersion. Neutralization of acidic groups in the polymer by addition of alkali may be performed before or after mixing the colorant and the polymer, but it is preferable to perform after mixing.

  The ink of the present invention can be suitably used in an ink jet recording method in which energy is applied to the ink to cause it to fly. As energy, thermal energy or mechanical energy can be used, but a method using thermal energy is particularly preferable.

  As a printer for inkjet recording, it can be applied to a printer for general households mainly using A4 size paper, a printer for printing business cards and cards, or a large printer for business use. It is suitably used for large machines that require a large amount of ink.

  As a recording medium to be recorded with the ink of the present invention, plain paper without a special coating, so-called inkjet exclusive paper coated with a layer for receiving ink on at least one surface, postcards, business card paper, label paper, cardboard Examples include paper and inkjet films.

Specific examples of the present invention will be described below. However, the present invention is not limited by these examples. In the following description, all “parts” and “%” are based on mass.
[Synthesis of Polymer A]
A glass four-necked flask equipped with a reflux tube, a dropping funnel, a thermometer, and a stirrer was charged with 300 parts of methyl ethyl ketone, and heated while stirring until reflux was constantly emitted from the reflux tube. The internal temperature at this time was 84 ° C. To this solution, a mixture 400 of ethyl methacrylate (A), hydrophobic monomer (B) (isobornyl methacrylate), hydrophilic monomer (C) (carbitol acrylate) and monomer (D) (methacrylic acid) having an acidic group A mixed solution of 24 parts of a polymerization initiator and 24 parts of a polymerization initiator (ABN-E manufactured by Wako Pure Chemical Industries, Ltd.) was dropped at a constant rate over 180 minutes. After aging for another 30 minutes, a mixed solution of 100 parts of methyl ethyl ketone and 2 parts of ABN-E was added dropwise at a constant rate over 120 minutes. After completion of the dropping, the internal temperature was maintained for 60 minutes, followed by cooling, and 100 parts of methyl ethyl ketone was added to prepare polymer A. Table 1 shows a series of polymers A prepared by changing the amount of each monomer. In addition, all of the weight average molecular weights of the obtained polymers were about 15,000.

[Synthesis of Polymer B]
A glass four-necked flask equipped with a reflux tube, a dropping funnel, a thermometer, and a stirrer was charged with 300 parts of methyl ethyl ketone, and heated while stirring until reflux was constantly emitted from the reflux tube. The internal temperature at this time was 84 ° C. In this solution, methyl methacrylate (A), hydrophobic monomer (B) (tert-octyl methacrylate), hydrophilic monomer (C) (triethylene glycol ethyl ether acrylate), monomer having acidic group (D) (methacrylic acid) A mixed solution of 400 parts of a mixture and 24 parts of a polymerization initiator (ABN-E manufactured by Wako Pure Chemical Industries, Ltd.) was added dropwise at a constant rate over 180 minutes. After aging for another 30 minutes, a mixed solution of 100 parts of methyl ethyl ketone and 2 parts of ABN-E was added dropwise at a constant rate over 120 minutes. After completion of the dropping, the internal temperature was maintained for 60 minutes, followed by cooling, and 100 parts of methyl ethyl ketone was added to prepare polymer B. Table 2 shows a series of polymers B prepared by changing the amount of each monomer. In addition, all of the weight average molecular weights of the obtained polymers were about 15,000.

[Synthesis of Polymer C-1]
A four-necked flask equipped with a reflux tube, a thermometer and a stirrer is charged with 56 parts of ethylene glycol, 200 parts of isophorone diisocyanate, 144 parts of dimethylolpropionic acid, and 300 parts of methyl ethyl ketone until the internal temperature reaches 60 ° C. while stirring. Heated, aged over 120 minutes, then cooled. When the internal temperature became 40 ° C. or lower, 200 parts of methyl alcohol was added, and the reaction was further terminated by stirring for 60 minutes to obtain a polymer C-1 having a urethane skeleton. The weight average molecular weight of the obtained polymer was 15,000, and the acid value was 150 mg-KOH / g.

[Synthesis of Polymer C-2]
A four-necked flask equipped with a rectifying tube, a reflux tube, a thermometer and a stirrer is charged with 100 parts of diethylene glycol and 156 parts of terephthalic acid together with a transesterification catalyst and heated. When the raw material starts to melt, stirring is started. Heating was continued. Heat and stirring were continued until water and the reflux liquid of the raw material were separated in the rectifying tube and no water was released. The internal temperature at this time was 140 ° C. Further, 144 parts of dimethylolpropionic acid was added, and heating and stirring were continued until no water was released. The obtained liquid was charged into a depressurizable flask equipped with a rectifying tube, heated while reducing the pressure, and diethylene glycol was removed with the rectifying tube. The obtained polymer C-2 having an ester skeleton had a weight average molecular weight of 14,000 and an acid value of 150 mg-KOH / g.

[Preparation of dispersion]
The methyl ethyl ketone solution of the polymer synthesized by the above method and a copper phthalocyanine pigment were charged into a kneader having a biaxial screw and kneaded until uniform, and then the solvent was distilled off under reduced pressure while maintaining the internal temperature at 80 ° C. . This kneaded product was formed into a sheet using two rolls, and a predetermined amount of ion-exchanged water and a neutralizing agent were added and stirred to obtain a dispersion having a pigment concentration of 10% by mass and a polymer concentration of 10% by mass.

[Preparation of ink]
2 parts of glycerin and 2 parts of diethylene glycol were added to 8 parts of a liquid obtained by diluting the dispersion with ion-exchanged water so that the pigment concentration was 5% by mass to obtain an ink.

[Examples 1 to 20]
Ink of the combinations shown in Table 3 was prepared by the above method.

[Comparative Examples 1-19]
Ink of the combinations shown in Table 4 was prepared by the above method.

[Evaluation]
Dispersion stability of the dispersion:
With respect to the aqueous dispersion used for the preparation of the ink, the average particle size immediately after preparation and after storage at 60 ° C. for 4 weeks was measured with a PAR-III dynamic light scattering measurement apparatus manufactured by Otsuka Electronics Co., Ltd. The results are shown in Table 5. The increase rate of the average particle size is [BA / A] × 100 (%) (where A is the average particle size (nm) immediately after preparation, and B is the average particle size after storage (nm). )).

Ink ejection characteristics:
Each ink was mounted on an ink jet recording apparatus BJF-660 (manufactured by Canon) having an on-demand type multi-recording head that discharges ink by applying thermal energy corresponding to a recording signal to the ink. Continuously printing a 100% solid image on plain paper, the number of printed sheets in which ejection failure (a state in which white streaks are regularly observed) occurred was examined. The evaluation results are shown in Table 6.

  According to the present invention, by using a polymer dispersant comprising a combination of an optimized monomer structure and acid value, and a neutralizing agent, a fine particle colorant having excellent image fastness can be stably dispersed in an aqueous medium. Thus, it is possible to provide an ink having excellent ejection stability.

Claims (5)

  At least one monomer unit (A) selected from the group consisting of methyl methacrylate and ethyl methacrylate, and at least one monomer unit (A), comprising at least a water-insoluble colorant, a polymer, and an aqueous medium. 2 to 10% by mass of the hydrophobic monomer unit (B), 5 to 15% by mass of the monomer unit (C) having a nonionic hydrophilic group, and the monomer unit (D) having an acidic group, An ink for an ink jet printer, having a value of 90 to 200 mg-KOH / g, wherein at least a part of the acidic group is neutralized with a base.   2. The ink for an ink jet printer according to claim 1, wherein the content of the hydrophobic monomer unit (B) is 2 to 10% by mass and the acid value is 110 to 200 mg-KOH / g.   The content of the hydrophobic monomer unit (B) is 2 to 7% by mass, the acid value is 110 to 150 mg-KOH / g, and at least a part of the base is ammonia. Ink for inkjet printers.   The ink for an ink jet printer according to claim 3, wherein the acid value is 130 to 200 mg-KOH / g, and at least a part of the base is an alkanolamine.   The ink for an inkjet printer according to any one of claims 1 to 4, wherein the water-insoluble colorant is a pigment.