JP2017082222A - Nonaqueous pigment ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve low ink viscosity capable of applying a nonaqueous pigment ink to power saving and to achieve excellent low temperature suitability and storage stability, suppression of striking-through and high printing density.SOLUTION: There is provided a nonaqueous pigment ink containing a pigment, a nonaqueous solvent, a nonaqueous resin and a water soluble resin, wherein the nonaqueous resin is an acrylic polymer consisting of a copolymer of a monomer mixture containing at least alkyl (meth)acrylate having an alkyl group with 8 to 18 carbon atoms (A) and a monomer having a β-diketone group or a β-keto acid ester group (B).SELECTED DRAWING: None

Description

  The present invention is a non-aqueous pigment ink suitable for use in an ink jet recording apparatus, and in particular, can contribute to power saving, can suppress back-through, and achieve a high printing density. It relates to a possible non-aqueous pigment ink.

  Inkjet recording is a method in which high-fluidity inkjet ink is ejected from fine head nozzles as ink particles, and an image is recorded on a recording medium placed opposite to the nozzle, enabling high-speed printing with low noise. Therefore, it has been spreading rapidly in recent years. As an ink used in such an ink jet recording system, a so-called non-aqueous pigment ink in which a pigment is finely dispersed in a water-insoluble solvent is known.

  In recent years, it has been desired to reduce the power consumption of devices such as printers as much as possible from the viewpoint of resource environment and energy saving, and the demand for power saving is increasing more and more in ink-jet printing in order to save power.

  In an ink jet recording apparatus, pressure is applied to an ink chamber provided in an ink jet head, and ink in the ink chamber is ejected from a nozzle. A time difference or a speed difference occurs between the head part and the tail part of the head. Since the viscosity of the ink increases under a low temperature environment, it is necessary to increase the drive voltage of the inkjet head in order to eject a desired amount of ink, which increases power consumption. Further, if discharge is performed with a high driving voltage, satellites are likely to be generated. Satellites adhere to the recording medium and reduce the print quality. For this reason, conventionally, under a low temperature environment in which satellites are likely to occur, recording is started after performing a so-called warm-up operation for heating the inkjet head in order to ensure print quality.

  That is, in a low temperature environment in which satellites are likely to be generated, recording is started after the warm-up operation is performed, so that power necessary for warm-up is also consumed. Further, the longer the warm-up operation is required, the longer it takes to record an image. This causes a problem not only from the viewpoint of power but also from the viewpoint of the user's work time. Therefore, it is effective for power saving if the viscosity of the ink in a low temperature environment can be reduced from the side of the ink. As a means for that purpose, it is extremely effective to reduce the viscosity of the ink. It is possible to reduce the ink viscosity by reducing the amount of the color material and the amount of powder in the ink. However, if this is done, the print density will decrease and the image quality will deteriorate.

  For example, Patent Document 1 includes two or more primary and / or secondary amino groups in one molecule chemically bonded to a dispersant by reacting with a pigment, a dispersant, and a reactive functional group of the dispersant. There has been proposed an ink using a colorant which is a composite of a water-soluble resin. This ink has high storage stability, pigment dispersibility, and ejection stability that does not cause clogging at the nozzle portion. In general, the dispersant is in an equilibrium state by repeating adsorption and desorption on the pigment surface to stabilize the ink. However, with the colorant described in Patent Document 1, the ink is used in a low temperature environment. In order to stabilize, it is necessary to increase the amount of the dispersant, and the viscosity cannot be lowered to such an extent that the satellite is suppressed.

  For this reason, in the ink of Patent Document 1, it is necessary to increase the power consumption by heating the ink and reducing the ink viscosity. In particular, when the ink jet recording apparatus is used in a circulation type ink jet recording apparatus, the amount of ink that needs to be heated increases, so that power consumption is increased and the time required for heating further increases. On the other hand, in order to reduce the viscosity, it is necessary to reduce the amount of the dispersant. However, it is difficult to ensure the pigment dispersion stability.

  By the way, it is possible to reduce the viscosity of the ink by using a hydrocarbon-based high boiling point and low-viscosity nonpolar solvent (hereinafter simply referred to as a hydrocarbon-based nonpolar solvent). The use of a hydrocarbon-based non-polar solvent as the ink solvent changes the polarity of the ink solvent and may deteriorate the pigment dispersion stability. This is considered to be solved by changing the composition of the dispersant. . In the patent document 2, the applicant has proposed a non-aqueous pigment ink containing water-insoluble resin-dispersed fine particles having pigment dispersing ability.

JP 2008-019333 A JP 2010-1452 A

  However, the water-insoluble resin-dispersed fine particles described in Patent Document 2 have a functional group (urethane group) that adsorbs to the pigment inside the hydrocarbon-based nonpolar solvent and has an affinity for the hydrocarbon-based nonpolar solvent. In this case, the water-insoluble resin-dispersed fine particles are difficult to adsorb on the pigment, and a sufficient amount of pigment dispersibility cannot be ensured with a small amount. For this reason, there is a problem that it is necessary to preliminarily prescribe a large amount of water-insoluble resin-dispersed fine particles for the pigment, and the ink viscosity becomes high. On the other hand, the pigment dispersibility needs to have good affinity between the hydrocarbon-based nonpolar solvent and the pigment. If the affinity is too high, the pigment disperses when the hydrocarbon-based nonpolar solvent penetrates into the recording medium. However, there is a tendency to be easily pulled into the recording medium. As a result, the print density is lowered and the show-through tends to occur.

  That is, in order to reduce the viscosity of the ink, it is better to use a small amount of the dispersant. For this purpose, the pigment adsorbing group is not in the shape of particles oriented inward, but is dissolved in a non-aqueous solvent. It is necessary. In addition, as described above, the pigment dispersant is in an equilibrium state by repeating adsorption and desorption on the pigment surface to stabilize the ink system. However, if the pigment dispersant can be immobilized on the pigment surface, less pigment dispersion is achieved. It is possible to stabilize the ink with an agent.

  Further, the water-soluble resin described in Patent Document 2 can stabilize the ink system, but the water-soluble resin is mixed with the water-insoluble resin dispersed fine particles described in Patent Document 1. It has been found that the obtained ink has high wettability with respect to the nozzle plate used in the ink jet head, so that bending or non-ejection occurs when the ink is ejected. In addition, the ink attached to the nozzle plate may be transferred to paper or the like to contaminate the printed matter.

  The present invention has been made in view of the above circumstances, realizes a low ink viscosity that can contribute to power saving and is excellent in storage stability (pigment dispersion stability), and at the same time, it is possible to suppress strikethrough. It is an object of the present invention to provide a non-aqueous pigment ink capable of realizing a high printing density.

The non-aqueous pigment ink of the present invention is a non-aqueous pigment ink containing a pigment, a non-aqueous solvent, a water-insoluble resin, and a water-soluble resin, wherein the water-insoluble resin has at least 8 to 18 carbon atoms. It is an acrylic polymer comprising a copolymer of a monomer mixture containing an alkyl (meth) acrylate (A) having an alkyl group and a monomer (B) having a β-diketone group or β-keto ester group. It is what.
Here, the water-insoluble resin means a resin having a solubility in water at 23 ° C. of 0.5% by mass or less at 20 ° C.

  The acrylic polymer preferably has a comb structure having urethane groups as side chains with respect to the main chain of the acrylic polymer.

  The water-soluble resin is a polyethyleneimine having a mass average molecular weight of 200 to 2000, or a modified polyethyleneimine obtained by addition reaction of the polyethyleneimine with either an acrylate ester or a vinyl compound, wherein the modified polyethyleneimine is a polyethyleneimine. When the total amine value is 1 molar equivalent, the acrylic acid ester or the vinyl compound is preferably reacted in a ratio of 0.3 molar equivalent or more and less than 1 molar equivalent.

The content of the acrylic polymer is preferably 0.1 to 1.0 in terms of mass ratio with respect to the pigment.
The content of the acrylic polymer is preferably 0.1 to 20 by mass ratio with respect to the water-soluble resin.
The content of the water-soluble resin is preferably 0.01 to 0.5 in terms of mass ratio to the pigment.

  The non-aqueous pigment ink of the present invention is a non-aqueous pigment ink containing a pigment, a non-aqueous solvent, a water-insoluble resin, and a water-soluble resin, and the water-insoluble resin is an alkyl having at least 8 to 18 carbon atoms. Since it is an acrylic polymer comprising a copolymer of a monomer mixture containing an alkyl (meth) acrylate (A) having a group and a monomer (B) having a β-diketone group or β-keto ester group, It is possible to reduce the viscosity, and while ensuring low-temperature suitability and pigment dispersion stability, it is possible to simultaneously suppress the show-through and achieve a high printing density.

  Therefore, the non-aqueous pigment ink of the present invention can be suitably used as an inkjet ink. Further, since the non-aqueous pigment ink of the present invention has a low ink viscosity even in a low temperature environment, it can be suitably used particularly for a circulation type ink jet recording apparatus that requires time and power for warm-up.

  When the water-soluble resin is a modified polyethyleneimine obtained by addition reaction with polyethyleneimine and either an acrylic acid ester or a vinyl compound, and the modified polyethyleneimine has a total amine value of polyethyleneimine of 1 molar equivalent, the acrylic acid ester Or when the vinyl compound is reacted in a ratio of 0.3 molar equivalent or more and less than 1 molar equivalent, the printing density improvement effect is sufficiently high compared with polyethyleneimine, although the printing density improvement effect is slightly small. In addition, the amino group —N—H active hydrogen is alkylated (—N—R), and the affinity to the nozzle plate is suppressed, resulting in an increase in ink repellency of the nozzle plate. For this reason, even if wiping is not performed frequently, bending or non-ejection is suppressed when ink is ejected, so the ink attached to the nozzle plate is transferred to paper or the like and printed matter It is less likely to get dirty.

The non-aqueous pigment ink of the present invention (hereinafter also simply referred to as ink) contains a pigment, a non-aqueous solvent, a water-insoluble resin, and a water-soluble resin.
The water-insoluble resin is a monomer mixture comprising an alkyl (meth) acrylate (A) having an alkyl group having at least 8 to 18 carbon atoms and a monomer (B) having a β-diketone group or a β-keto ester group. It is an acrylic polymer made of a copolymer.

  The alkyl group having 8 to 18 carbon atoms of the functional group is highly compatible with the non-aqueous solvent hydrocarbon non-polar solvent described later, thereby being dissolved in the non-aqueous solvent, and the other functional group β- By including a diketone group or a β-keto acid ester group, the viscosity of the ink can be lowered, and the low-temperature suitability can be further improved. In addition, by suppressing the increase in viscosity, it contributes to electrostatic aggregation and fixing of the ink when the ink lands on the recording medium. As a result, the printing density is improved and the back-through is suppressed. be able to.

  When the carbon number of the alkyl group is 19 or more, the water-insoluble resin is easily solidified at a low temperature and the low-temperature suitability is deteriorated. On the other hand, when the number of carbon atoms is 7 or less, the compatibility with the hydrocarbon-based nonpolar solvent is lowered, and the pigment cannot be stably dispersed, so that the storage stability is deteriorated and the viscosity of the ink is high. turn into. Further, in a low temperature environment, the ink viscosity is further increased, and the low temperature aptitude is deteriorated. More desirably, it is preferably composed of an alkyl group having 12 to 18 carbon atoms.

  The alkyl group having 8 to 18 carbon atoms constituting the functional group may be linear or branched. Specifically, an octyl group, a nonyl group, a decyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, and the like may be mentioned, and these may include a plurality of types. .

  Examples of the β-diketone group or β-keto acid ester group constituting the functional group include acetoacetyl group, propion acetyl group and the like as preferable examples, and examples of the β-keto acid ester group include acetoacetoxy as a preferable example. Group, propionacetoxy group and the like.

The molecular weight (mass average molecular weight) of the acrylic polymer is not particularly limited, but when used as an ink jet ink, it is preferably about 5000 to 50000, and preferably about 10,000 to 30000 from the viewpoint of ink ejection. Is more preferable.
The glass transition temperature (Tg) of the acrylic polymer is preferably normal temperature or lower, and more preferably 0 ° C. or lower. Thereby, when the ink is fixed on the recording medium, the film formation can be promoted at room temperature.

  The alkyl (meth) acrylate (A) is an alkyl (meth) acrylate having an alkyl group having 8 to 18 carbon atoms, and forms a main chain of the acrylic polymer together with the monomer (B). The alkyl group is a functional group of the main chain. Configure the group. Examples of the alkyl (meth) acrylate (A) include palmityl / stearyl methacrylate (C16 / C18), cetyl acrylate (C16), dodecyl methacrylate (C12), dodecyl acrylate (C12), 2-ethylhexyl methacrylate (C8), 2 -Ethylhexyl acrylate (C8) can be preferably mentioned. These can be used singly or appropriately mixed.

  The monomer (B) is a (meth) acrylate or (meth) acrylamide having a β-diketone group or a β-keto ester group, and forms the main chain of the acrylic polymer together with the alkyl (meth) acrylate (A). -A diketone group or a β-keto ester group constitutes a functional group of the main chain. By including this monomer (B), the viscosity of the ink can be lowered, and the low-temperature suitability can be further improved. In addition, by suppressing the increase in viscosity, it contributes to electrostatic aggregation and fixing of the ink when the ink lands on the recording medium. As a result, the printing density is improved and the back-through is suppressed. be able to.

  Preferred examples of the monomer (B) include (meth) acrylates and (meth) acrylamides containing a β-diketone group or a β-keto acid ester group in the ester chain. More specifically, acetoacetoxyalkyl (meth) acrylates such as acetoacetoxyethyl (meth) acrylate, acetoacetoxyalkyl (meth) acrylamides such as hexadione (meth) acrylate, acetoacetoxyethyl (meth) acrylamide, and the like can be mentioned. These may be used alone or in combination of two or more.

  In the monomer mixture (alkyl (meth) acrylate (A) and monomer (B)), the alkyl (meth) acrylate (A) is preferably contained in an amount of 30% by mass or more, and preferably 40 to 95% by mass. More preferably, it is 50-90 mass%. It is preferable that a monomer (B) is 3-30 mass%, and it is more preferable that it is 5-20 mass%.

  Each of the above monomers can be easily polymerized by known radical copolymerization. The reaction system is preferably carried out by solution polymerization or dispersion polymerization. In this case, in order to make the molecular weight of the acrylic polymer after polymerization within the above preferred range, it is effective to use a chain transfer agent in combination during the polymerization. Examples of the chain transfer agent include thiols such as n-butyl mercaptan, lauryl mercaptan, stearyl mercaptan, and cyclohexyl mercaptan.

  Examples of the polymerization initiator include azo compounds such as AIBN (azobisisobutyronitrile), t-butylperoxybenzoate, t-butylperoxy-2-ethylhexanoate (Perbutyl O, manufactured by NOF Corporation), etc. Known thermal polymerization initiators such as peroxides can be used. In addition, a photopolymerization initiator that generates radicals upon irradiation with active energy rays can be used. As a polymerization solvent used for solution polymerization, for example, a petroleum solvent (aroma free (AF) system) or the like can be used. As the polymerization solvent, it is preferable to select one or more kinds of solvents (described later) that can be used as they are as a non-aqueous solvent for the ink. In the polymerization reaction, other commonly used polymerization inhibitors, polymerization accelerators, dispersants and the like can also be added to the reaction system.

  The acrylic polymer of the present invention preferably has a comb structure having a urethane group as a side chain with respect to the main chain of the acrylic polymer composed of the alkyl (meth) acrylate (A) and the monomer (B). By the alkyl group having 8 to 18 carbon atoms of the alkyl (meth) acrylate (A), the affinity of the non-aqueous solvent described later with a hydrocarbon non-polar solvent is improved, and the solubility in the solvent is ensured. On the other hand, the pigment can be adsorbed by the side chain of the urethane group to improve the storage stability.

  The side chain urethane group is a functional group capable of reacting with an amino group by using (meth) acrylate having a functional group capable of reacting with an amino group in addition to the alkyl (meth) acrylate (A) and the monomer (B). And an amino alcohol and a polyvalent isocyanate compound, which will be described later, can be introduced. Preferable examples of the functional group capable of reacting with an amino group include a glycidyl group, a vinyl group, and a (meth) acryloyl group.

  Examples of the (meth) acrylate having a glycidyl group include glycidyl (meth) acrylate, and examples of the (meth) acrylate having a vinyl group include vinyl (meth) acrylate and 2- (2-vinyloxyethoxy) ethyl (meth). An acrylate etc. are mentioned preferably. Examples of the (meth) acrylate having a (meth) acryloyl group include dipropylene glycol di (meth) acrylate and 1,6-hexanediol di (meth) acrylate. These (meth) acrylates may contain multiple types. In addition, (meth) acrylate having a functional group capable of reacting with these amino groups can be used even when a urethane group is not introduced.

An amino alcohol reacts with a functional group capable of reacting with an amino group and binds, and an isocyanate group (R ¹ N═C═O) of a polyvalent isocyanate compound is added to the hydroxy group of the amino alcohol as shown below. Then, a urethane group (urethane bond) (carbamic acid ester: R ¹ NHCOOR) is introduced. Here, R- represents an amino alcohol part bonded to a functional group of the copolymer.
R ¹ N═C═O + R—OH → ROCONHR ¹
By the above, the urethane group which acts as a pigment adsorption group is introduced.

Examples of amino alcohols include monomethylethanolamine, diethanolamine, and diisopropanolamine. Among them, those having two hydroxy groups can increase the number of urethane groups to be formed, and therefore dialkanolamines (secondary) represented by the general formula (HOR) ₂ NH (R is a divalent hydrocarbon group). Alkanolamine) is preferable. These amino alcohols can also be used in combination of multiple types.

  In the case of introducing a urethane group, from the viewpoint of introducing a urethane group, this amino alcohol is reacted at 0.05 to 1 molar equivalent with respect to a functional group capable of reacting with the amino group of the (meth) acrylate. It is more preferable to make it react by 0.1-1 molar equivalent. When the amino alcohol is less than 1 molar equivalent, an unreacted functional group remains in the (meth) acrylate having a functional group capable of reacting with an amino group, but the remaining functional group acts as an adsorbing group for the pigment. Conceivable.

  Examples of the polyvalent isocyanate compound include aliphatic compounds such as 1,6-diisocyanate hexane, 1,3-bis (isocyanatemethyl) benzene, 1,3-bis (isocyanatemethyl) cyclohexane, 1,5-naphthalene diisocyanate, and fats. A cyclic type and an aromatic type are mentioned, and multiple types can also be used. In order to prevent unreacted raw materials from remaining when the urethane group is introduced by the reaction with the hydroxy group, the polyvalent isocyanate compound is approximately equivalent to the hydroxy group contained in the charged raw material (0.98 to 0.98 to (1.02 molar equivalent) is preferable.

  The mass ratio of the copolymer part and the introduced urethane base part in the acrylic polymer is preferably 80:20 to 99: 1, and more preferably 85:15 to 95: 5. The mass of the copolymer part in the acrylic polymer is the total mass of the monomers used in the copolymerization, and the mass of the introduced urethane base is the total mass of the amino alcohol and polyvalent isocyanate compound used in the reaction. . Since the urethane base has a high pigment adsorbing capacity, the higher the mass ratio of the urethane base, the higher the pigment adsorption rate. However, if the mass ratio is higher than 20, the compatibility with the solvent becomes worse. However, the amount of free water-insoluble resin increases, and the adsorption rate of the pigment decreases.

  The content of the acrylic polymer with respect to the total amount of the ink is preferably 0.1% by mass or more, and more preferably 1% by mass or more from the viewpoint of ensuring pigment dispersibility. On the other hand, if the content of the acrylic polymer is too high, not only the viscosity of the ink is increased, but also the storage stability in a high temperature environment may be deteriorated. It is more preferable that the amount is not more than mass%. That is, the content of the acrylic polymer with respect to the total amount of the ink is preferably 1 to 10% by mass, and more preferably 2 to 8% by mass.

  The content of the acrylic polymer with respect to the pigment is preferably 0.1 to 1.0 in terms of a mass ratio with respect to the pigment from the viewpoint of ensuring storage stability. When the content of the acrylic polymer with respect to the pigment is too small as less than 0.1 by mass ratio with respect to the pigment, or when it is too large with more than 1.0, it is difficult to ensure storage stability.

  The content of the acrylic polymer with respect to the water-soluble resin is preferably 0.1 to 20 and more preferably 0.4 to 10 in terms of mass ratio. When the content of the acrylic polymer is as small as less than 0.1 by mass ratio with respect to the water-soluble resin, or when it is greater than 20 in terms of mass ratio, it is difficult to ensure storage stability.

  The mass of the resin relative to the mass of the pigment (the total amount of the acrylic polymer and the water-soluble resin) is preferably 0.2 or more from the viewpoint of ensuring the pigment dispersibility effect, assuming that the mass of the pigment is 1. It is preferably 1.5 or less from the viewpoint of improvement and ejection failure due to aging.

The content of the water-soluble resin is preferably 0.01 to 0.5, more preferably 0.05 to 0.3, and preferably 0.1 to 0.2 in terms of a mass ratio to the pigment. Is most preferred.
The water-soluble resin is preferably contained in an amount of about 0.1 to 5% by mass, and more preferably 0.5 to 1.5% by mass with respect to the total amount of ink.

  Examples of the water-soluble resin include basic polymer electrolytes such as polyethyleneimine (PEI), polyvinylamine, and polyvinylpyridine, or derivatives thereof. Particularly, polyethyleneimine having a mass average molecular weight of 200 to 2000, or mass. A modified polyethyleneimine obtained by addition reaction with polyethyleneimine having an average molecular weight of 200 to 2,000 and either an acrylate ester or a vinyl compound can be suitably used. The modified polyethyleneimine has a ratio of 0.3 mol equivalent to less than 1 mol equivalent to the acrylic ester or vinyl compound when the total amine value of polyethyleneimine is 1 mol equivalent (hereinafter, simply referred to as modified polyethyleneimine). Is preferred). Here, the amine value is determined by the amine titration method (KOHmg / g) by (2) indicator titration method of JIS K-7237-1995 (total amine value test method for amine curing agent of epoxy resin), and the molecular weight of KOH is 56. It is calculated in terms of 11 mg / mmol.

  When the weight average molecular weight of polyethyleneimine is less than 200, the effect of increasing the density with respect to plain paper is low, and when it is 2000 or more, the storage stability deteriorates depending on the storage environment. The mass average molecular weight of polyethyleneimine is more preferably 300 to 1800 because the effect of increasing the concentration is great, and the pour point is −5 ° C. or lower and the storage stability at low temperatures is good. .

  Polyethyleneimine can use a commercially available thing, for example, Nippon Shokubai Co., Ltd. SP-006, SP-012, SP-018, SP-200; BASF Corporation Lupasol FG, Lupasol G20 Waterfree, Lupasol A preferred example is PR8515.

  In the modified polyethyleneimine, an acrylic acid ester and a vinyl compound may be used together. In this case, the ratio of the acrylic acid ester to the vinyl compound is 0.1 when the amine value of polyethyleneimine is 1 molar equivalent. 3 molar equivalents or more. When the amount is less than 0.3 molar equivalent, the effect of improving the ink repellency of the nozzle plate is weakened.

The mechanism for improving the ink repellency of the nozzle plate when modified polyethyleneimine is used is presumed as follows. That is, imino groups and amino groups (—NH, —NH ₂ ) present in inks using polyethyleneimine tend to stick to the nozzle plate of the inkjet head. By using a modified polyethyleneimine obtained by Michael addition of an acrylate ester or vinyl compound to the imino group or amino group of polyethyleneimine, the ink repellency is increased and the wettability to the nozzle plate is improved.

Preferred examples of the acrylate ester include methyl acrylate, ethyl acrylate, t-butyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, and the like.
Preferable examples of the vinyl compound include vinyl halides such as acrylonitrile, vinyl chloride and vinyl fluoride, and vinyl acetate.

  The modified polyethyleneimine can be obtained by Michael addition of an acrylate ester or a vinyl compound to the imino group or amino group of polyethyleneimine. In detail, it is manufactured by dropping polyethyleneimine and an acrylic ester or vinyl compound into diethanolamine heated to 50 to 60 ° C. while stirring, and then maintaining at 50 to 60 ° C. for 1 to 3 hours. Can do.

  Even in the case of an acrylic polymer that does not have a functional group having a high pigment adsorbing ability such as a urethane group, a combination of an acrylic polymer having a β-diketone group or a β-keto acid ester group and a water-soluble resin, Strong pigment adsorption ability can be obtained. It is presumed that pigment dispersion can be stabilized by the interaction of the β-diketone group or β-keto acid ester group of the water-insoluble resin, the polar group of the water-soluble resin, and the pigment. Since the elimination of the water-insoluble resin from the pigment is suppressed by the interaction between the β-diketone group or β-keto acid ester group, the polar group of the water-soluble resin and the pigment, the amount of the water-insoluble resin to be used As a result, the viscosity can be kept low while ensuring the pigment dispersion stability, and the low temperature suitability can be improved.

  In addition, the comb-type acrylic polymer with urethane groups as side chains increases the pigment adsorption capacity by the urethane groups, but the higher the mass ratio of the urethane groups, the worse the compatibility with the solvent and the lower the pigment adsorption rate. As a result, free water-insoluble resin increases and ink viscosity increases. However, when the comb-type acrylic polymer having a urethane group as a side chain further has a β-diketone group or β-keto ester group, it can interact with the pigment by using a water-soluble resin in combination. It is possible to reduce the amount of free water-insoluble resin, and the ink viscosity can be lowered.

  Furthermore, the alkyl group having 8 to 18 carbon atoms of the acrylic polymer improves the affinity of the non-aqueous solvent with the hydrocarbon non-polar solvent and ensures solubility in the solvent. If the affinity is too high, the pigment tends to be drawn into the recording medium when the non-aqueous solvent penetrates into the recording medium. However, the combination of acrylic polymer and water-soluble resin ensures pigment dispersion stability even if the amount of acrylic polymer is reduced, so the amount of acrylic polymer can be reduced and pigment penetration is suppressed. Is done. As a result, show-through can be suppressed and a high print density can be realized.

As the non-aqueous solvent, a hydrocarbon non-polar solvent or a polar solvent can be used, and these can be used alone or in admixture of two or more. From the viewpoint of lowering the viscosity, it is preferable to use a hydrocarbon-based nonpolar solvent.
The content of the hydrocarbon-based nonpolar solvent is preferably 20% by mass or more, more preferably 50% by mass or more, and further preferably 80% by mass or more with respect to the total mass of the ink solvent. When the content of the hydrocarbon-based nonpolar solvent is less than 50% by mass with respect to the total amount of the solvent, the viscosity of the ink cannot be sufficiently reduced although it depends on the use environment.

  When the content of the hydrocarbon-based nonpolar solvent is 50% by mass or more based on the total amount of the ink solvent, it is possible to obtain the effect of further reducing the ink viscosity and further improving the storage stability. When the content of the hydrocarbon-based nonpolar solvent is 50% by mass or more based on the total amount of the ink solvent, the water-soluble resin and the water-insoluble resin are hardly released in the ink solvent but gather in the vicinity of the pigment, and the pigment surface It comes to adsorb strongly. For this reason, not only can the viscosity of the solvent itself be lowered, but also the effect of lowering the viscosity can be obtained by reducing the amount of free resin in the solvent, and the dispersion stability of the pigment can be further improved. It is estimated that

  Preferred examples of the hydrocarbon nonpolar solvent include aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, aromatic hydrocarbon solvents, and the like. Examples of the aliphatic hydrocarbon solvent and alicyclic hydrocarbon solvent include, for example, “Teclean N-16, Teclean N-20, Teclean N-22, Nisseki Naphthezol L, Nissho Naphthezol M, manufactured by Nippon Petroleum Corporation. Nisseki Naphthezol H, No. 0 Solvent L, No. 0 Solvent M, No. 0 Solvent H, Nisseki Isosol 300, Nisseki Isosol 400, AF-4, AF-5, AF-6, AF-7 ", manufactured by Exxon “Isopar G, Isopar H, Isopar L, Isopar M, Exxsol D40, Exxsol D80, Exxsol D100, Exxsol D130, Exxsol D140” and the like can be preferably exemplified. Preferred examples of the aromatic hydrocarbon solvent include “Nisseki Clean Sol G” (alkylbenzene) manufactured by Nippon Petroleum Corporation, “Solvesso 200” manufactured by Exxon, and the like.

  As the polar solvent, polar solvents such as ester solvents, alcohol solvents, higher fatty acid solvents and ether solvents can be used. More specifically, methyl laurate, isopropyl laurate, hexyl laurate, isopropyl myristate, isopropyl palmitate, isostearyl palmitate, methyl oleate, ethyl oleate, isopropyl oleate, butyl oleate, methyl linoleate , Isobutyl linoleate, ethyl linoleate, isopropyl isostearate, soybean oil methyl, soybean oil isobutyl, tall oil methyl, tall oil isobutyl, diisopropyl adipate, diisopropyl sebacate, diethyl sebacate, propylene glycol monocaprate, tri 2- Ester solvents having 14 or more carbon atoms in one molecule, such as trimethylolpropane ethylhexanoate and glyceryl tri-2-ethylhexanoate; isomyristyl alcohol, isopa Alcohol solvents having 12 or more carbon atoms in one molecule, such as mytyl alcohol, isostearyl alcohol, and oleyl alcohol; higher fatty acids such as isononanoic acid, isomustic acid, hexadecanoic acid, isopalmitic acid, oleic acid, isostearic acid Preferred solvents include ether solvents such as diethyl glycol monobutyl ether, ethylene glycol monobutyl ether, propylene glycol monobutyl ether and propylene glycol dibutyl ether. These non-aqueous solvents can be used alone or in admixture of two or more.

  Examples of the pigment include carbon blacks such as furnace black, lamp black, acetylene black, and channel black; metals or metal oxides such as copper, iron, and titanium oxide; and organic pigments such as orthonitroaniline black. These may be used alone or in combination as appropriate. As pigments for color inks, Watching Red, Toluidine Red, Permanent Carmine FB, Disazo Orange PMP, Lake Red C, Brilliant Carmine 6B, Quinacridone Red, Dioxane Violet, Ortho Nitroaniline Orange, Dinitroaniline Orange, Vulcan Orange, Toluidine Red, Chlorinated Parared, Brilliant First Scarlet, Naphthol Red 23, Virazolone Red, Barium Red 2B, Calcium Red 2B, Strontium Red 2B, Manganese Red 2B, Barium Resome Red, Pigment Scar Red 3B Lake, Lake Bordeaux 10B, Anthosine 3B Lake , Anthosine 5B rake, rhodamine 6G rake, eosin rake, bengara, phatol red GR, Rhodamine B Lake, Methyl Bio Red Lake, Dioxazine Bio Red, Naphthol Carmine FB, Naphthol Red M, Fast Yellow AAA, Fast Yellow 10G, Disazo Yellow AAMX, Disazo Yellow AAOT, Disazo Yellow AAOA, Disazo Yellow HR, Isoindoline Yellow, Fast Yellow G, Disazo Yellow AAA, Phthalocyanine Blue, Pictoria Pure Blue, Basic Blue 5B Lake, Basic Blue 6G Lake, Fast Sky Blue, Alkali Blue R Toner, Peacock Blue Lake, Bituminous Blue, Ultraviolet, Reflex Blue 2G, Reflex Blue R, Alkali Blue G Toner, Brilliant Green Lake, Diamond Green Thioflavin Lake, Lid Cyanine green G, green gold, phthalocyanine green Y, iron oxide powder, rust, zinc white, titanium oxide, calcium carbonate, clay, barium sulfate, alumina white, aluminum powder, bronze powder, daylight fluorescent pigment, pearl pigment, etc. It can be illustrated. These can be used alone or in combination.

  The content of the pigment in the ink is usually 0.01 to 20% by mass, preferably 1 to 15% by mass from the viewpoint of printing density and ink viscosity, and more preferably 5 to 10% by mass. .

  In addition to the above components, the ink of the present invention may contain conventional additives. Additives include surfactants such as anionic, cationic, amphoteric or nonionic surfactants, antioxidants such as dibutylhydroxytoluene, propyl gallate, tocopherol, butylhydroxyanisole, and nordihydroguaiare. And tic acid.

  In the case of an ink jet recording system, the viscosity of the ink varies depending on the nozzle diameter of the ejection head, the ejection environment, and the like, but in general, it is preferably 5 to 30 mPa · s at 23 ° C., preferably 5 to 15 mPa · s. It is more preferable that the pressure is about 10 mPa · s, which is suitable for an inkjet recording apparatus. Here, the viscosity represents a value at 10 Pa when the shear stress is increased from 0 Pa at a rate of 0.1 Pa / s at 23 ° C.

  In the ink of the present invention, a pigment, a water-insoluble resin, a non-aqueous solvent, and a water-soluble resin are mixed, and the pigment is dispersed by using any dispersing means such as a ball mill or a bead mill. It can be prepared by passing through a filter. When polyethyleneimine is used as the water-soluble resin, polyethyleneimine is often slightly soluble or hardly soluble in general-purpose non-aqueous solvents. Therefore, it is desirable to use a device capable of applying a share such as a bead mill and mix in a state where the share is applied. When the water-soluble resin is soluble in the non-aqueous solvent to be used, such a share is unnecessary, but it is preferable to mix them under stirring.

The average particle size of the pigment in the obtained ink is preferably about 500 nm or less, more preferably 200 nm or less, and even more preferably 150 nm or less. On the other hand, it is preferable that the average particle diameter is about 50 nm or more in order to suppress the back-through of the printed matter. Here, the average particle diameter of the pigment is a value measured by a dynamic light scattering particle size distribution analyzer LB-500 manufactured by Horiba, Ltd.
Examples of the non-aqueous inkjet ink of the present invention are shown below.

(Synthesis of resin solutions a to d)
A 300 ml four-necked flask was charged with 75 g of AF-7 (naphthenic solvent; manufactured by JX Nippon Oil & Energy Corporation), heated to 110 ° C. while aerated with nitrogen gas and stirred. Subsequently, 16.7 g of AF-7 and perbutyl O (t-butylperoxy 2-ethylhexanoate; manufactured by NOF Corporation) were added to each monomer mixture having the composition shown in Table 1 while maintaining the temperature at 110 ° C. 2 g of the mixture was added dropwise over 3 hours. Thereafter, 0.2 g of perbutyl O was added after 1 hour and 2 hours while maintaining at 110 ° C. Further, aging was carried out at 110 ° C. for 1 hour, and diluted with 10.7 g of AF-7 to obtain colorless and transparent resin solutions a to d having a nonvolatile content of 50%. The mass average molecular weight (GPC method, standard polystyrene conversion) of each obtained resin solution was 20000-23000.

(Synthesis of resin solution e)
Each monomer mixture having the composition shown in Table 1 was mixed in a 500 ml four-necked flask, and further 1.29 g of V-65 (Wako Pure Chemical Industries, Ltd.) as a polymerization initiator and stearyl mercaptan ( Wako Pure Chemical Industries, Ltd.) 0.97 g, AF7 (AF Solvent No. 7, naphthenic solvent, JX Nippon Oil & Energy Corporation) 260.2 g was added and refluxed under the conditions of 61 ° C. ± 3 ° C. Then, the reaction was carried out for 5 hours to obtain a resin solution e (solid content 25%). After the reaction, a small amount of methoquinone (p-methoxyphenol) was added as a polymerization inhibitor. The obtained resin solution had a mass average molecular weight (GPC method, standard polystyrene conversion) of 21,800.

(Synthesis of resin solutions D1 and D2)
In a 500 mL four-necked flask, 200 g of the resin solution a obtained above (solid content in AF-7 solvent 50%), Michael adduct (diethanolamine / 2-ethylhexyl acrylate adduct) 4.0 g, diethanolamine (Nippon Shokubai) 2.8 g) was charged, and the temperature was raised to 110 ° C. while agitating with nitrogen gas. By maintaining at 110 ° C. for 1 hour, the reaction between the glycidyl group of the resin solution a and diethanolamine was completed. Then, 0.2 g of dibutyltin dilaurate was added, Takenate 600 (1,3-bis (isocyanatomethyl) cyclohexane, manufactured by Mitsui Chemicals Polyurethane Co., Ltd.) and Exepal HL (hexyl laurate, Kao Corporation) (Product made) 72.0 g of the mixture was added dropwise over 1 hour. After the dropwise addition, the temperature was raised to 120 ° C. and reacted for 6 hours, followed by cooling to obtain a resin solution D1 having a solid content of 40%.
Similarly, a resin solution D2 was produced with the composition shown in Table 2. Each acrylic polymer obtained had a mass average molecular weight (GPC method, standard polystyrene conversion) of 22000 to 26000.

(Preparation of modified polyethyleneimine)
A 300 ml four-necked flask was charged with 50 g of Epomin SP-006 (polyethyleneimine molecular weight 600, manufactured by Nippon Shokubai Co., Ltd.) and heated to 60 ° C. while stirring. 13.27 g of acrylonitrile (manufactured by Wako Pure Chemical Industries, Ltd.) was added dropwise over about 30 minutes. After the dropwise addition, the mixture was kept at 60 ° C. for 2 hours to complete the Michael addition reaction to obtain modified polyethyleneimine PEI-3. Similarly, modified polyethyleneimines of PEI-4 to PEI-12 were prepared according to the formulation shown in Table 3. In the case of PEI-3, the Michael addition equivalent shown in Table 3 includes 20 mmol of amino groups in 1 g of polyethyleneimine (SP-006), so 20 mmol × 0.5 molar equivalent = 10 mmol vinyl compound Means that it has reacted.

(Preparation of ink)
4 g of the obtained resin solution a, 1.5 g of polyethyleneimine (Nippon Shokubai Co., Ltd. SP-012), 10 g of pigment (carbon black, MA100 manufactured by Mitsubishi Chemical Corporation), 17.25 g of AF-7, hexyl laurate 17.25 g was mixed, zirconia beads (diameter 0.5 mm) were added, and dispersed for 120 minutes by a rocking mill (manufactured by Seiwa Giken Co., Ltd.). After dispersion, the zirconia beads are removed, and AF-7 (25 g) and Exepearl HL (25 g) are added and diluted, and then filtered through 3 μm and 0.8 μm membrane filters in order to remove dust and coarse particles to obtain the ink of Example 1. It was.
Similarly, inks of respective examples and comparative examples were obtained in the same manner as in Example 1 with the formulations shown in Tables 4 to 8.

  About the obtained ink, the dispersion average particle diameter of the pigment and the viscosity of the ink were measured. The dispersion average particle size of the pigment was measured with a dynamic light scattering particle size distribution device LB-500 manufactured by Horiba, Ltd. The viscosity of the ink is a viscosity at 10 Pa when the shear stress is increased from 0 Pa at a rate of 0.1 Pa / s at 23 ° C., and is a stress-controlled rheometer RS75 (cone angle: 1 °, diameter: 60 mm) manufactured by Harke. It was measured.

(Evaluation method)
(Print density)
The obtained ink was loaded into HC5500 (made by Riso Kagaku Kogyo Co., Ltd.), and the OD values of the solid image printed on plain paper (ideal paper thin mouth, Oki Kagaku Kogyo Co., Ltd.) were used as the optical density. It measured using the meter (RD920, Macbeth company make), and evaluated with the following references | standards. If the OD value on the front surface is high, the image density is high, and if the OD value on the back surface is low, there is little show-through.
Print density (Table OD)
S: 1.20 or more A: 1.15 or more and less than 1.20 B: 1.10 or more and less than 1.15 C: 1.05 or more and less than 1.10 D: Less than 1.05 Print density (back OD)
S: Less than 0.20 A: More than 0.20 and less than 0.25 B: More than 0.25 and less than 0.30 C: More than 0.30

(Ink storage stability (70 ° C))
Each ink was put in an airtight container and allowed to stand in an environment of 70 ° C. for 4 weeks. Thereafter, changes in the viscosity of the ink and changes in the dispersion average particle diameter of the pigment were measured, and the measurement results were evaluated as follows. The viscosity after standing and the dispersion average particle diameter of the pigment were measured by the above methods.
Viscosity change rate:
[(Viscosity after 4 weeks × 100) / (initial value of viscosity)] − 100 (%)
Change rate of dispersion average particle size of pigment:
[(Dispersion average particle diameter after 4 weeks × 100) / (initial value of dispersion particle diameter)] − 100 (%)
S: Viscosity and pigment dispersion average particle size change rate are both less than ± 3% A: Viscosity and pigment dispersion average particle size change rate are either ± 3% or more and less than ± 5% B: Viscosity and pigment dispersion Either the average particle size change rate is ± 5% or more and less than ± 10% C: Either the viscosity or the dispersion average particle size change rate of the pigment is 10% or more

(Low temperature aptitude)
The obtained ink was allowed to stand at −5 ° C. for 4 weeks, and then the ink viscosity at −5 ° C. was measured and evaluated according to the following criteria.
A: Less than 50 mPa · s B: 50 mPa · s or more and less than 100 mPa · s C: 100 mPa · s or more

(Discharge stability)
After the ink is left in a sealed state in an environment of 70 ° C. for one month, a solid image (main scanning 318 dots / sub scanning 3000 dots) is continuously printed 100 times using the ink jet head (CF1) manufactured by Toshiba TEC. The image was visually confirmed and evaluated according to the following criteria.
A: Uniform solid image B: Uniform solid image is obtained in the initial stage, but the image is disturbed after printing several tens of times. C: The image is disturbed from the initial stage.

(satellite)
In ORPHIS-X (manufactured by Riso Kagaku Kogyo Co., Ltd.), printing is performed on A4 paper under the printing conditions of a head gap of 3 mm, an environmental temperature of 15 ° C., a printing speed of 120 ppm, a resolution of 300 dpi * 300 dpi 1-6 drop (6 pl per drop). Evaluated by criteria.
A: Satellites can hardly be confirmed B: Satellites can be confirmed slightly C: Satellites are prominent

(Wettability to nozzle plate)
Put the inkjet ink in a 30 ml container, pinch one end of the nozzle plate (length 5 cm, width 5 mm) used in the inkjet printer HC5500 (trade name: Riso Kagaku Kogyo Co., Ltd.) with tweezers, and use the other end 2 cm for the ink. Soaked. The wettability was evaluated after standing for 1 week in an environment of 60 ° C. The nozzle plate was quickly pulled up, and the time until the ink film remaining on the nozzle plate became ink droplets without wiping was measured 10 times, the average value was calculated, and the ink repelling time was evaluated according to the following criteria. In addition, the used nozzle plate used the polyimide film as the base material, and the surface was fluorine-processed.
S: Time required for ink droplets is less than 3.5 seconds A: Time required for ink droplets is 3.5 seconds or more and less than 1 minute B: Time required for ink droplets is 1 minute or more The evaluation results are shown in Tables 4 to 8 together with the ink prescriptions.

  As shown in Tables 4 and 5, the inks of Examples 1 to 15 are acrylics made of a monomer mixture copolymer in which Examples 1 to 13 include alkyl (meth) acrylate (A) and monomer (B). Polymer, Examples 14 and 15 include an acrylic polymer having a comb structure having a urethane group as a side chain with respect to the main chain of the acrylic polymer. It can be seen that it has a particle size, both of which are excellent in low-temperature suitability and storage stability, and can suppress show-through and achieve a high printing density. Even when the mass ratio of the water-insoluble resin (solid content) to the pigment is as low as 20%, the pigment dispersion stability can be obtained, the penetration of the pigment is suppressed, and the strikethrough is suppressed. It can be seen that the printing density can be realized, and that low temperature suitability can be obtained by using a water-insoluble resin and a water-soluble resin in combination.

  On the other hand, the inks of Comparative Examples 1 to 4 and Comparative Examples 7 to 11 shown in Table 8 do not contain a water-soluble resin. In Comparative Example 1, since the pigment dispersion stability is ensured by the water-insoluble resin, storage stability is ensured. , Low-temperature suitability, and ejection stability are good, satellites are suppressed, but the affinity between the non-aqueous solvent and the pigment is high, so when the non-aqueous solvent penetrates into the recording medium, the pigment is inside the recording medium. The print density was lowered due to drawing through. In Comparative Example 2, since the mass ratio of the water-insoluble resin to the pigment was half that of Comparative Example 1, the pigment dispersion stability deteriorated. Since Comparative Examples 7 and 8 had no urethane group side chain, Comparative Example 7 had poor pigment dispersion stability, and Comparative Example 8 was not dispersed. In Comparative Examples 9 and 10, since the water-insoluble resin of the present invention was not included, it was not dispersible. In Comparative Example 11 in which the water-insoluble resin was doubled, the dispersion was achieved but the stability was poor and the printing density was low. .

  In Comparative Example 3, the carbon number of the alkyl group constituting the functional group of the water-insoluble resin is 22 and 8, and the storage stability was ensured because the carbon number of the alkyl group was long. Became easy to solidify, and the low-temperature suitability deteriorated, and the satellite could not be suppressed. In Comparative Example 4, the pigment could not be dispersed because the content of the water-insoluble resin was small.

  Comparative Examples 5 and 6 include a water-soluble resin but no β-diketone group or β-keto acid ester group of the water-insoluble resin. In Comparative Example 5, the mass ratio of the water-insoluble resin to the pigment is high. Therefore, although dispersibility of the pigment was obtained even without the β-diketone group or β-keto ester group, the viscosity increased and the low-temperature suitability and the ejection stability were both poor. -Since there is no diketone group or β-keto ester group, the adsorption of the pigment is not sufficient, so that the back-through cannot be suppressed, and the printing density is lowered. In Comparative Example 6A, the mass ratio of the water-insoluble resin was halved in Comparative Example 5A. In this case, however, pigment adsorptivity was not obtained and the pigment could not be dispersed.

  Comparative Examples 12 and 13 are water-soluble resins, but are acrylic polymers having no β-diketone group or β-keto ester group, so that the image quality is poor at low environmental temperatures, the printing density is low, and the stability is high. It was bad too.

  As is clear from the above examples, the combination of the β-diketone group or β-keto acid ester group of the water-insoluble resin and the water-soluble resin enables stable pigment dispersion even when the amount of the water-insoluble resin used is small. Therefore, the viscosity can be kept low while securing the properties, and the low temperature suitability can be improved. In addition, since the pigment dispersion stability is ensured by the water-soluble resin, it is possible to reduce the amount of the water-insoluble resin, and the penetration of the pigment is suppressed. Can be realized.

  On the other hand, as shown in Tables 6 and 7, the inks of Examples 16 to 22 can simultaneously suppress low-through while ensuring low-temperature suitability and pigment dispersion stability, and can achieve high printing density. did it. In addition, the ink repellency was high, and the wettability of the nozzle plate was improved.

  In Examples 23 and 24, since the polyethyleneimine was unmodified, the ink repellency of the nozzle plate without wiping was not sufficient. In Examples 25 to 27, since the modification of polyethyleneimine was less than 0.3 equivalent, the ink repellency of the nozzle plate without wiping was not sufficient.

  As described above, the non-aqueous pigment ink of the present invention is suitable as an ink-jet ink because it can suppress low-through through while ensuring low-temperature suitability and pigment dispersion stability, and can achieve a high printing density. Can be used for Further, since the non-aqueous pigment ink of the present invention has a low ink viscosity even in a low temperature environment, it can be suitably used particularly for a circulation type ink jet recording apparatus that requires time and power for warm-up.

The non-aqueous pigment ink of the present invention is a non-aqueous pigment ink containing a pigment, a non-aqueous solvent, a water-insoluble resin, and a water-soluble resin, wherein the water-insoluble resin has at least 8 to 18 carbon atoms. It is an acrylic polymer comprising a copolymer of a monomer mixture containing an alkyl (meth) acrylate (A) having an alkyl group and a monomer (B) having a β-diketone group or β-keto ester group. It is what.
Here, the water-insoluble resin, solubility in water at 23 ° C. refers to 0.5 mass% of the resin.

Claims (7)

A non-aqueous pigment ink comprising a pigment, a non-aqueous solvent, a water-insoluble resin, and a water-soluble resin,
A monomer mixture in which the water-insoluble resin contains an alkyl (meth) acrylate (A) having at least an alkyl group having 8 to 18 carbon atoms and a monomer (B) having a β-diketone group or a β-keto ester group. A non-aqueous pigment ink comprising an acrylic polymer made of a copolymer.   The non-aqueous pigment ink according to claim 1, wherein the acrylic polymer has a comb structure having urethane groups as side chains with respect to the main chain of the acrylic polymer.   The non-aqueous pigment ink according to claim 1, wherein the water-soluble resin is polyethyleneimine having a mass average molecular weight of 200 to 2,000.   The polyethyleneimine is a modified polyethyleneimine obtained by addition reaction with either an acrylate ester or a vinyl compound, and the acrylic acid ester or the vinyl compound when the modified polyethyleneimine has the total amine value of polyethyleneimine as 1 molar equivalent. The non-aqueous pigment ink according to claim 3, wherein the non-aqueous pigment ink is reacted in a ratio of 0.3 to 1 molar equivalent.   The non-aqueous pigment ink according to any one of claims 1 to 4, wherein the content of the water-soluble resin is 0.01 to 0.5 in terms of a mass ratio to the pigment.   6. The non-aqueous pigment ink according to claim 1, wherein a content of the acrylic polymer is 0.1 to 1.0 by mass ratio with respect to the pigment.   7. The non-aqueous pigment ink according to claim 1, wherein a content of the acrylic polymer is 0.1 to 20 in a mass ratio with respect to the water-soluble resin.