JP2015124356A - Non-aqueous pigment ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-aqueous pigment ink having decreased viscosity and excellent pigment dispersion stability.SOLUTION: The non-aqueous pigment ink comprises a pigment, a non-aqueous solvent, a water-insoluble resin, a water-soluble resin, and water. The water-insoluble resin is an acrylic polymer comprising a copolymer of a monomer mixture that includes at least an alkyl (meth)acrylate (A) having an alkyl group having 8 to 18 carbon atoms and a monomer (B) having a β-ketone group or β-keto acid ester group. The water-soluble resin is insoluble with a non-aqueous solvent and has two or more primary and/or secondary amino groups in one molecule. The content of the water-soluble resin is 0.005 to 0.4 in a mass ratio relative to the pigment. The water content of the ink, measured by a Karl-Fischer process, is 0.2 mass% or more relative to the whole amount of the ink, and up to a level equal to the solubility with the ink.

Description

  The present invention relates to a non-aqueous pigment ink suitable for use in an ink jet recording apparatus.

  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.

  Lowering the viscosity of non-aqueous pigment inks is important from the viewpoint of resource stability and energy saving in recent years because it leads to reduction of warm-up operation in a low temperature environment from the viewpoint of ejection stability. If the amount of color material or powder in the ink is reduced, the ink viscosity can be lowered. However, if this is done, the print density is lowered and the image quality is lowered.

  As a method for reducing the viscosity of ink without reducing the amount of color material and powder in the ink, a hydrocarbon-based high boiling point, low-viscosity nonpolar solvent (hereinafter simply referred to as petroleum hydrocarbon solvent) is used. Use. By using a petroleum hydrocarbon solvent as the ink solvent, the polarity of the ink solvent is changed, and the pigment dispersion stability may be deteriorated. This can be solved by changing the constitution of the dispersant. In Patent Document 1, the applicant has proposed a non-aqueous pigment ink containing water-insoluble resin-dispersed fine particles having a pigment-dispersing ability.

JP 2010-1452 A

  However, the water-insoluble resin-dispersed fine particles described in Patent Document 1 have a high affinity for petroleum-based hydrocarbon solvents, with the functional groups (urethane groups) adsorbed to the pigment inside the petroleum-based hydrocarbon solvents. Since the alkyl group is dispersed in the outward direction, the pigment adsorbing power is somewhat weak and sufficient pigment dispersibility cannot be ensured with a small amount. For this reason, in order to ensure the pigment dispersibility, it is necessary to prescribe many water-insoluble resin-dispersed fine particles in advance. Therefore, if the ink viscosity is to be lowered, the pigment dispersibility must be sacrificed to some extent.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a non-aqueous pigment ink that can reduce the ink viscosity and is excellent in pigment dispersion stability (storage stability). Is.

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, a water-soluble resin, and water, and the water-insoluble resin has at least 8 carbon atoms. It is an acrylic polymer comprising a copolymer of a monomer mixture containing an alkyl (meth) acrylate (A) having an alkyl group of ˜18 and a monomer (B) having a β-diketone group or a β-keto ester group. The water-soluble resin is insoluble in a non-aqueous solvent and contains two or more primary and / or secondary amino groups in one molecule, and the content of the water-soluble resin is 0.005 by mass ratio to the pigment. The water content based on the Karl Fischer method is in the range of 0.2% by mass or more of the total amount of ink and below the solubility in ink.
Here, the water-insoluble resin refers to a resin having a solubility in water at 23 ° C. of 0.5% by mass or less.

  The water-soluble resin is preferably polyethyleneimine.

  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, a water-soluble resin, and water, and the water-insoluble resin has at least 8 to 8 carbon atoms. An acrylic polymer comprising a copolymer of a monomer mixture containing an alkyl (meth) acrylate (A) having 18 alkyl groups and a monomer (B) having a β-diketone group or β-keto ester group, The water-soluble resin is insoluble in a non-aqueous solvent and contains two or more primary and / or secondary amino groups in one molecule, and the content of the water-soluble resin is 0.005 to 0.4 by mass ratio to the pigment. Since the moisture content based on the Karl Fischer method is in the range of 0.2% by mass or more of the total amount of ink and below the solubility in the ink, the pigment dispersion stability is ensured at the same time while reducing the viscosity of the ink. be able to.

  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, a water-soluble resin, and water, and has a water content based on the Karl Fischer method. It is characterized by being in the range of 0.2 mass% or more of the total amount of ink and not more than the solubility in ink. The ink moisture content is preferably adjusted to be in the range of 0.2 to 2 mass%, more preferably 0.5 to 1.5 mass%.

  When the water content of the ink is in the above range, it is possible to reduce the ink viscosity without reducing the amount of color material and the amount of powder in the ink. Usually, it is considered that when water is added to non-aqueous ink, the viscosity of the ink increases because the structural viscosity increases. However, the ink of the present invention contains a predetermined water-soluble resin, and a small amount of water is compatible with the water-soluble resin, so that the viscosity of the ink can be reduced without increasing the structural viscosity. it is conceivable that.

The water-soluble resin is insoluble in a non-aqueous solvent and contains two or more primary and / or secondary amino groups in one molecule, and the content thereof is 0.005 to 0.00 by mass ratio to the pigment. 4 range. When the content of the water-soluble resin is less than 0.005 by mass ratio with respect to the pigment, the water-soluble resin with respect to water is small, so that the viscosity does not decrease. On the other hand, if the content of the water-soluble resin is larger than 0.4 by mass ratio to the pigment, the viscosity cannot be lowered even if water is contained, and the pigment dispersion stability cannot be ensured. The content of the water-soluble resin is preferably in the range of 0.05 to 0.2, more preferably in the range of 0.1 to 0.15, by mass ratio to the pigment.
The water-soluble resin is preferably contained in an amount of about 0.1 to 4.5% by mass, more preferably 0.5 to 3% by mass, and more preferably 1 to 2% by mass with respect to the total amount of ink. More preferably.

  Examples of the water-soluble resin include basic polymer electrolytes such as polyethyleneimine (PEI), polyvinylamine, and polyvinylpyridine, or derivatives thereof. In particular, polyethyleneimine is preferable. The mass average molecular weight of polyethyleneimine is preferably 200 to 2,000. A modified polyethyleneimine obtained by addition reaction with polyethyleneimine having a mass average molecular weight of 200 to 2000 and either an acrylate ester or a vinyl compound can also be suitably used.

  If the weight average molecular weight of the polyethyleneimine is less than 200, the effect of increasing the density with respect to plain paper may be lowered, and if it exceeds 2000, the pigment dispersion stability may be deteriorated depending on the storage environment. The mass average molecular weight of polyethyleneimine is 300 to 1800 because the effect of increasing the concentration is great, the pour point is −5 ° C. or less, and the pigment dispersion stability at low temperatures is good. preferable.

  Polyethyleneimine can use a commercially available thing, for example, Epomin SP-003, Epomin SP-006, Epomin SP-012, Epomin SP-018, Epomin SP-200 (all manufactured by Nippon Shokubai Co., Ltd.) And Lupasol FG, Lupasol G20 Waterfree, Lupasol PR8515 (all manufactured by BASF) and the like can be preferably mentioned.

  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.

  This water-insoluble resin containing an alkyl group having 8 to 18 carbon atoms as a functional group is highly compatible with a non-aqueous solvent petroleum hydrocarbon solvent, which will be described later, thereby being dissolved in the non-aqueous solvent. The viscosity can be lowered. The other functional group, β-diketone group or β-keto acid ester group, has a high adsorptivity to the pigment, whereby the pigment dispersibility is improved and the viscosity of the ink can be lowered. By including these functional groups, the viscosity of the ink can be lowered, so that the low temperature suitability can be further improved. In addition, because it has low viscosity and excellent low-temperature suitability, it contributes to electrostatic aggregation and fixing of ink when landing on a recording medium, and as a result, it can improve printing density and achieve back-through suppression. it can.

  When the carbon number of the alkyl group of the alkyl (meth) acrylate (A) 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 petroleum hydrocarbon solvent is lowered, the pigment cannot be stably dispersed, and the viscosity of the ink is increased. 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 constituting the functional group include acetoacetyl group and propionacetyl group as preferred examples. Examples of the β-keto acid ester group include acetoacetoxy group and propionacetoxy group as preferred examples. Can be mentioned.

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 23 ° C. or lower, and more preferably 0 ° C. or lower. Thereby, the film formation can be promoted when the ink is fixed on the recording medium.

  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 methacrylate (alkyl group having 16 carbon atoms, the same shall apply hereinafter), stearyl methacrylate (18), cetyl acrylate (16), dodecyl methacrylate (12), dodecyl acrylate (12 ), 2-ethylhexyl methacrylate (8), and 2-ethylhexyl acrylate (8). 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.

  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). The affinity of the non-aqueous solvent, which will be described later, with the petroleum hydrocarbon solvent is improved by the alkyl group having 8 to 18 carbon atoms of the alkyl (meth) acrylate (A), and the solubility in the solvent is ensured. On the other hand, the pigment dispersion stability can be improved by adsorbing the pigment by the side chain of the urethane group.

  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 pigment dispersion stability in a high temperature environment may be deteriorated. More preferably, it is 10 mass% or less. 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 from 0.1 to 1.0 in terms of a mass ratio to the pigment from the viewpoint of ensuring pigment dispersion stability. Whether the content of the acrylic polymer with respect to the pigment is too small as less than 0.1 in terms of the mass ratio to the pigment, or when it is too large with more than 1.0, it is difficult to ensure the pigment dispersion stability in a high temperature environment.

  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. Whether the acrylic polymer content is as small as less than 0.1 by mass ratio to the water-soluble resin or more than 20 in mass ratio, it is difficult to ensure the pigment dispersion stability in a high temperature environment.

  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.

  As the non-aqueous solvent, any of a non-polar organic solvent and a polar organic solvent can be used. These may be used alone or in combination of two or more as long as they form a single phase.

  Preferable examples of the nonpolar organic solvent include petroleum hydrocarbon solvents such as aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents. Examples of the aliphatic hydrocarbon solvent and alicyclic hydrocarbon solvent include paraffinic, isoparaffinic, and naphthenic solvents. For example, what is sold with the following brand names is mentioned. Teclean N-16, Teclean N-20, Teclean N-22, Naphthezol L, Naphthezol M, Naphthezol H, No. 0 Solvent L, No. 0 Solvent M, No. 0 Solvent H, Isosol 300, Isosol 400, AF Solvent No. 4, AF Solvent No. 5, AF Solvent No. 6, and AF Solvent No. 7 (all manufactured by JX Nippon Oil & Energy Corporation); Isopar G, Isopar H, Isopar L, Isopar M, Exol D40, Exol D80, Exol D100, Exol D130 and Exol D140 (both manufactured by TonenGeneral Sekiyu KK). Examples of the aromatic hydrocarbon solvent include grade alkene L, grade alkene 200P (all manufactured by JX Nippon Oil & Energy Corporation), Solvesso 200 (manufactured by TonenGeneral Sekiyu KK), and the like.

  Preferable examples of the polar organic solvent include ester solvents, higher alcohol solvents, higher fatty acid solvents, and the like. For example, methyl laurate, isopropyl 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, trimethylolpropane tri-2-ethylhexanoate, tri Ester solvent having 14 or more carbon atoms in one molecule such as glyceryl 2-ethylhexanoate; isomyristyl alcohol, isopalmityl alcohol, isostear Higher alcohol solvents with 8 or more carbon atoms in one molecule such as alcohol, oleyl alcohol, etc .; carbon in one molecule such as isononanoic acid, isomyristic acid, hexadecanoic acid, isopalmitic acid, oleic acid, isostearic acid And higher fatty acid solvents having a number of 9 or more.

  Among these non-aqueous solvents, it is preferable to use petroleum hydrocarbon solvents from the viewpoint of reducing the viscosity. The content of the petroleum hydrocarbon solvent is preferably 20% by mass or more, more preferably 50% by mass or more, and further preferably 80% by mass or more based on the total mass of the ink solvent. When the content of the petroleum hydrocarbon 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 petroleum hydrocarbon 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 pigment dispersion stability. When the content of the petroleum hydrocarbon 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 are collected on the pigment surface. Adsorbs firmly. 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

  As the pigment, organic pigments such as azo pigments, phthalocyanine pigments, polycyclic pigments, dyed lake pigments, and inorganic pigments can be used. Examples of the azo pigments include soluble azo lake pigments, insoluble azo pigments, and condensed azo pigments. Examples of phthalocyanine pigments include metal phthalocyanine pigments and metal-free phthalocyanine pigments. Polycyclic pigments include quinacridone pigments, perylene pigments, perinone pigments, isoindoline pigments, isoindolinone pigments, dioxysazine pigments, thioindigo pigments, anthraquinone pigments, quinophthalone pigments, metal complex pigments. And diketopyrrolopyrrole (DPP). Representative examples of inorganic pigments include carbon black and titanium oxide. These pigments may be used alone or in combination of two or more.

  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. preferable.

  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 discharge head, the discharge environment, and the like, but in general, it is preferably 5 to 20 mPa · s at 23 ° C., and preferably 5 to 15 mPa · s. It is suitable for an ink jet recording apparatus that the degree is about. 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.

  The ink of the present invention is a mixture of a pigment, a water-insoluble resin, a non-aqueous solvent, a water-soluble resin, and water, and the pigment is dispersed using an arbitrary dispersing means such as a ball mill or a bead mill. Can be prepared by passing through a known filter. In addition, since the water-soluble resin in the present invention is insoluble in a non-aqueous solvent, it is desirable to use a device capable of applying a shear such as a bead mill and to mix in a sheared state.

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 solution a)
In a four-necked flask, 75 parts by mass of Isopar G (manufactured by TonenGeneral Sekiyu KK) was charged, and the temperature was raised to 110 ° C. while aerated with nitrogen gas and stirred. Next, while maintaining the temperature at 110 ° C., 16.7 parts by mass of Isopar G, perbutyl O (t-butylperoxy 2-ethylhexanoate; manufactured by NOF Corporation) 2 was added to each monomer mixture shown in Table 1. Part by weight of the mixture was added dropwise over 3 hours. Thereafter, 0.2 parts by mass 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 10.6 parts by mass of Isopar G to obtain a colorless and transparent resin solution a having a nonvolatile content of 50%. The mass average molecular weight (GPC method, standard polystyrene conversion) of the obtained resin solution a was 21,500.

(Synthesis of resin solution D1)
In a four-necked flask, 200 parts by mass g of the resin solution a obtained above (solid content 50% in Isopar G solvent), 4.0 parts by mass of propylene glycol (Wako Pure Chemical Industries, Ltd.), diethanolamine (Japan Co., Ltd.) 2.8 parts by mass of catalyst) was charged, and the temperature was raised to 110 ° C. while aerated and stirred 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. Thereafter, 0.2 parts by mass of dibutyltin dilaurate was added, and 7.8 parts by mass of Takenate 500 (manufactured by Mitsui Chemicals Polyurethane Co., Ltd.) and 72.0 parts by mass of ISPV (isostearyl palmitate, manufactured by Nikko Chemicals) 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%. The weight average molecular weight (GPC method, standard polystyrene conversion) of the obtained acrylic polymer was 24000. Table 2 shows the formulation of the resin solution D1.

(Preparation of pigment dispersion)
According to the formulations shown in Tables 3 to 5, resin solution D1, water-soluble resin, pigment (carbon black, MA8 manufactured by Mitsubishi Chemical Corporation), solvent are mixed, zirconia beads (diameter 0.5 mm) are added, and a bead mill (Rocking mill RMO5S type, manufactured by Seiwa Giken Co., Ltd.) for 120 minutes. After dispersion, the zirconia beads were removed to obtain pigment dispersions of Examples and Comparative Examples.

(Preparation of ink)
The pigment dispersions obtained above were diluted with the diluents shown in Tables 3 to 5 to obtain inks of Examples and Comparative Examples.

(Evaluation method)
(Pigment dispersion stability)
Each ink was put in a sealed container and allowed to stand for 10 days to 1 month in an environment at 70 ° C., and then the change in viscosity of the ink was measured. The measurement result was evaluated as follows. 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 Hake. ).
Viscosity change rate:
[(Viscosity after 10 days or 1 month × 100) / (initial value of viscosity)] − 100 (%)
A: Viscosity change rate less than 5% even after 1 month at 70 ° C. B: Viscosity change rate after 10 days at 70 ° C. is less than 5%, 5% or more after 1 month C: Viscosity change rate after 10 days at 70 ° C. is 5% or more The evaluation results are shown in Tables 3 to 5 together with the pigment dispersion and the ink formulation. Table 6 shows the decrease in the initial viscosity of the same ink with the same formulation other than the addition of water (described in terms of the viscosity when the viscosity of the ink containing no water in the same formulation with the addition of water is 100).

  As shown in Table 3, it can be seen that all of the inks of Examples 1 to 7 have ensured pigment dispersibility. The inks of Comparative Examples 1 to 5 shown in Table 4 contain a water-soluble resin, but these had a high viscosity because they did not contain water, although the pigment dispersibility was ensured by the acrylic polymer and the water-soluble resin. The ink of Comparative Example 6 is a water-soluble resin not containing two or more primary and / or secondary amino groups in one molecule, but in this case, the pigment dispersion stability was lowered. Further, since the inks of Comparative Examples 7 and 8 have a high water-soluble resin content, the ink of Comparative Example 9 has a water content higher than the solubility in the ink, and the inks of Comparative Examples 10 to 13 are water-soluble. In any case, no pigment dispersion stability was obtained.

  Further, as is apparent from Table 6, it can be seen that in any of the inks of Examples 1 to 7 of the present invention, the viscosity can be lowered simultaneously by adding water. On the other hand, even when water is added, the water-soluble resin does not contain two or more primary and / or secondary amino groups in one molecule (contrast with Comparative Examples 5 and 6), and does not contain a water-soluble resin. In the case of the product (contrast with Comparative Examples 12 and 13), the viscosity did not decrease. Even when a predetermined water-soluble resin was contained, the viscosity was not reduced even when the water content was too high (comparative to Comparative Examples 9 and 1). Further, even if a predetermined water-soluble resin is contained in too much content (comparative to Comparative Examples 7 and 8), the viscosity decreases relatively, but the initial viscosity of the ink is high and pigment dispersion stability is obtained. I couldn't.

  As described above, the non-aqueous pigment ink of the present invention can ensure pigment dispersibility with a predetermined acrylic polymer and water-soluble resin, and can lower the ink viscosity by containing a predetermined amount of water-soluble resin and water. And 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.

Claims (2)

A non-aqueous pigment ink comprising a pigment, a non-aqueous solvent, a water-insoluble resin, a water-soluble resin, and water,
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. An acrylic polymer made of a copolymer,
The water-soluble resin is insoluble in a non-aqueous solvent and contains two or more primary and / or secondary amino groups in one molecule, and the content of the water-soluble resin is 0.005 by mass ratio to the pigment. 0.4,
A non-aqueous pigment ink characterized in that the water content based on the Karl Fischer method is in the range of 0.2 mass% or more of the total amount of ink and below the solubility in ink.   The non-aqueous pigment ink according to claim 1, wherein the water-soluble resin is polyethyleneimine.