Water-based ink for ink-jet printing

Abstract

To provide a water-based ink for inkjet recording that has excellent continuous dischargeability and can give a recorded material with excellent image density.SOLUTION: The present invention provides [1] a water-based ink for ink jet recording that contains polymer particles containing pigment, dispersed with a polymer dispersant (A), polymer particles containing wax, dispersed with a polymer dispersant (B), and organic solvent, where the constituent polymers of the polymer particles containing wax have an acid value of 20-110 mgKOH / g, and the wax has a melting point of 80°C or higher.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a water-based ink for ink-jet printing. [Background technology]

[0002] Inkjet recording is a method of directly ejecting ink droplets from fine nozzles and depositing them on a recording medium to obtain a recorded matter on which characters or images are recorded. This method has become extremely popular due to its many advantages, including the ease and low cost of producing full-color images, the ability to use plain paper as a recording medium, and the fact that the recording medium is not in contact with the ink. In recent years, inks that use pigments as colorants have come to be widely used in terms of the weather resistance and water resistance of recorded matter. However, unlike dyes, pigment molecules cannot be uniformly dissolved in the ink vehicle. Therefore, it is necessary to maintain the dispersion state of the pigment in the ink until the ink is ejected from the nozzle to form an image on the recording medium, and further to improve the continuous ejection properties during inkjet recording. This is because pigment inks tend to clog the nozzles of the head, and when printing is performed over a long period of time, some of the nozzles become clogged. In addition, with pigment inks, only the surface molecular parts of the pigment in the ink contribute to color development, so the image density is lower than with dye inks, in which the entire dye molecule in the ink contributes to color development, and this aspect must also be improved.

[0003] Various proposals have been made to improve the above problems. For example, Patent Document 1 discloses an inkjet recording method that achieves both image transferability and robustness, which repeats a first image formation step including a liquid component containing water and a high-boiling-point water-soluble organic solvent and a solid component formed by mixing the reaction liquid and the ink by passing through a step of applying a reaction liquid containing a high-viscosity component and a step of applying an ink containing water, a coloring material, and a wax onto a transfer body, a step of contacting a porous body with the first image to form a second image from which a part of the liquid component has been removed, and a transfer step of heating the second image to transfer it onto a recording medium, and in which the temperature of the first image and the second image are controlled under specific conditions. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-144736 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the technique of Patent Document 1 is not satisfactory in terms of continuous ejection properties and image density. An object of the present invention is to provide a water-based ink for ink-jet printing which has excellent continuous ejection properties and can give recorded matter with excellent image density. [Means for solving the problem]

[0006] The present inventors have found that the above problems can be solved by incorporating wax particles, which are obtained by dispersing a high-melting wax in a polymer dispersant having a specific acid value, into a water-based ink. That is, the present invention provides a water-based ink for ink-jet printing, which contains polymer particles containing a pigment dispersed with a polymer dispersant (A), polymer particles containing a wax dispersed with a polymer dispersant (B), and an organic solvent, wherein the acid value of the polymer constituting the wax-containing polymer particles is 20 mgKOH / g or more and 110 mgKOH / g or less, and the melting point of the wax is 80° C. or more. Effect of the Invention

[0007] According to the present invention, there is provided a water-based ink for ink-jet printing which has excellent continuous ejection properties and can give recorded matter having excellent image density. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] [Water-based ink for inkjet printing] The water-based ink for ink-jet printing of the present invention (hereinafter also referred to as "the ink of the present invention") is a water-based ink for ink-jet printing comprising polymer particles containing a pigment dispersed with a polymer dispersant (A), polymer particles containing a wax dispersed with a polymer dispersant (B), and an organic solvent, The acid value of the polymer constituting the wax-containing polymer particles is 20 mgKOH / g or more and 110 mgKOH / g or less, and the melting point of the wax is 80° C. or more.

[0009] In this specification, the term "water-based" means that water accounts for the largest proportion by mass of the medium in which the pigment is dispersed. In addition, "recording" is a concept that includes printing and printing out characters and images, and "recorded matter" is a concept that includes printed matter and printed matter on which characters and images are recorded.

[0010] The water-based ink for ink-jet printing of the present invention is excellent in continuous ejection property and can give recorded matter having excellent image density. Although the reason for this is not clear, it is believed to be as follows. In inkjet recordings using pigment inks, a large amount of pigment remains on the surface of the recording medium after recording, and the pigment is easily peeled off from the surface of the recording medium, and this effect is particularly noticeable in recordings with higher image density. It is known that when a wax is added to a water-based ink, the friction resistance of the ink coating film when rubbed is reduced. It is preferable that the wax is dispersed using a polymer. By making the acid value of the polymer 110 mgKOH / g or less, the wax will quickly coagulate when the ink is exposed to the surface of the recording medium, allowing a moderate amount of wax to remain on the surface of the recording medium, making the surface of the recording medium hydrophobic, and by allowing a moderate amount of ink to remain on the recording medium, it is possible to increase the image density of the recorded matter.

[0011] Furthermore, when water-based inks for inkjet printing are exposed to strong shear conditions near the ejection nozzle during continuous ejection, the pigment particles and wax particles form aggregates near the nozzle edge, causing problems such as nozzle blockage and ejection distortion, and worsening continuous ejection. Here, by setting the acid value of the polymer dispersant (B) that disperses the wax to 20 mgKOH / g or more, even when exposed to strong shear conditions near the ejection nozzle, the wax particles in the ink have a sufficient repulsive force between themselves or between the pigment particles and the wax particles, which is thought to solve problems such as clogging and improve continuous ejection. Furthermore, the strong shear force generated when the ink is ejected can cause some of the wax particles to melt, and the molten wax can be adsorbed onto the pigment surface, promoting the aggregation of the pigment particles. However, since the melting point of the wax is 80°C or higher, it is believed that the partially molten wax does not promote the aggregation of the pigment particles, thereby further improving the continuous ejection properties.

[0012] <Pigments> The pigment used in the present invention may be either an inorganic pigment or an organic pigment. Examples of inorganic pigments include carbon black and metal oxides, and carbon black is preferred for black inks. Examples of carbon black include furnace black, lamp black, acetylene black, channel black, etc. Examples of white inks include titanium dioxide, zinc oxide, silica, alumina, magnesium oxide, and other metal oxides. Examples of organic pigments include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments. The hue is not particularly limited, and in the achromatic ink, achromatic pigments such as white, black, and gray can be used, while in the chromatic ink, chromatic pigments such as yellow, magenta, cyan, red, blue, orange, and green can be used. The above pigments can be used alone or in combination of two or more kinds.

[0013] The pigment used in the present invention is used in the form of polymer particles containing the pigment dispersed with a polymer dispersant (A) from the viewpoint of improving continuous dischargeability and image density. Here, "polymer particles containing a pigment" (hereinafter also referred to as "pigment-containing polymer particles") means particles in which the polymer dispersant (A) encapsulates the pigment, particles in which part of the pigment is exposed on the surface of particles consisting of the polymer dispersant (A) and the pigment, particles in which the polymer dispersant (A) is adsorbed to part of the pigment, and mixtures thereof. Among these, particles in which the polymer dispersant (A) encapsulates the pigment are more preferred.

[0014] [Pigment-containing polymer particles] The polymer dispersant (A) (hereinafter also referred to as "polymer (a)") constituting the pigment-containing polymer particles is not particularly limited as long as it has at least the ability to disperse pigments. Examples of the polymer (a) include vinyl resins obtained by addition polymerization of vinyl monomers, polyester resins, polyurethane resins, etc. Among these, vinyl resins are preferred from the viewpoints of pigment dispersion stability, storage stability, etc. The polymer (a) may be a non-crosslinked polymer, and may be appropriately synthesized or a commercially available product. The pigment-containing polymer particles are more preferably crosslinked polymer particles containing a pigment (hereinafter also referred to as "pigment-containing crosslinked polymer particles") made of a polymer (a) having a crosslinked structure. The "polymer (a) having a crosslinked structure" means that the polymer (a) has a constitutional unit derived from a crosslinking agent in addition to the constitutional unit derived from the polymer (a) described above.

[0015] When the polymer dispersant (A) does not have a crosslinked structure, the polymer (a) may be a water-soluble polymer or a water-insoluble polymer, but is preferably a water-insoluble polymer. When the polymer dispersant (A) has a crosslinked structure, it necessarily becomes a water-insoluble polymer by having both the structural unit of the polymer (a) and the structural unit derived from the crosslinking agent. In this specification, the term "water-insoluble" of a polymer means that when a polymer that has been dried at 105° C. for 2 hours and has reached a constant weight is dissolved in 100 g of water at 25° C., the amount of dissolution is less than 10 g. When the polymer is an anionic polymer, the amount of dissolution is the amount of dissolution when 100 mol % of the anionic groups of the polymer are neutralized with sodium hydroxide.

[0016] [Polymer (a)] When the polymer (a) is a vinyl resin, the polymer (a) preferably contains (a-1) a structural unit derived from an ionic monomer, and more preferably further contains (a-2) a hydrophobic monomer and / or (a-3) a structural unit derived from a nonionic monomer.

[0017] [(a-1) Ionic Monomer] As the (a-1) ionic monomer, anionic monomers are preferred, such as carboxylic acid monomers and sulfonic acid monomers, with carboxylic acid monomers being more preferred. The carboxylic acid monomer may be at least one selected from (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid, and is preferably (meth)acrylic acid. "(Meth)acrylic acid" means at least one selected from acrylic acid and methacrylic acid.

[0018] [(a-2) Hydrophobic Monomer] The term "hydrophobic" in (a-2) hydrophobic monomer means that when the monomer is dissolved in 100 g of ion-exchanged water at 25° C. until saturation, the amount of the monomer that dissolves is less than 10 g. Specific examples of the (a-2) hydrophobic monomer include alkyl (meth)acrylates and aromatic group-containing monomers. The alkyl (meth)acrylate preferably has an alkyl group having 1 to 22 carbon atoms, and more preferably has an alkyl group having 6 to 18 carbon atoms. Examples of the alkyl (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, (iso)propyl (meth)acrylate, (iso- or tert-)butyl (meth)acrylate, (iso)amyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, (iso)octyl (meth)acrylate, (iso)decyl (meth)acrylate, (iso)dodecyl (meth)acrylate, and (iso)stearyl (meth)acrylate. Incidentally, "(iso or tert-)" and "(iso)" refer to both the case where these groups are present and the case where they are not present, and when these groups are not present, it refers to normal.

[0019] The aromatic group-containing monomer is preferably a vinyl monomer having an aromatic group with 6 to 22 carbon atoms, which may have a substituent containing a hetero atom, and more preferably at least one selected from a styrene monomer and an aromatic group-containing (meth)acrylate. The molecular weight of the aromatic group-containing monomer is preferably less than 500. As the styrene-based monomer, styrene, 2-methylstyrene, α-methylstyrene, vinyltoluene, and divinylbenzene are preferred, and styrene is more preferred. As the aromatic group-containing (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, etc. are preferred, with benzyl (meth)acrylate being more preferred. Among these, preferred are alkyl (meth)acrylates having an alkyl group having 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms, and more preferably 1 to 8 carbon atoms, and aromatic group-containing monomers having an aromatic group having 6 to 22 carbon atoms, preferably 6 to 18 carbon atoms, more preferably one or more selected from alkyl (meth)acrylates having an alkyl group having 1 to 4 carbon atoms and aromatic group-containing monomers having an aromatic group having 6 to 12 carbon atoms, and even more preferably one or more selected from ethyl acrylate, styrene, and α-methylstyrene.

[0020] [(a-3) Nonionic Monomer] (a-3) The nonionic monomer is a monomer that has a high affinity for water or a water-soluble organic solvent, and is, for example, a monomer that contains a hydroxyl group or a polyalkylene glycol chain. Specific examples of the (a-3) component include those described in paragraph

[0018] of JP 2018-83938 A. Hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate and 3-hydroxypropyl (meth)acrylate; polyalkylene glycol (meth)acrylates such as polyethylene glycol (meth)acrylate (n = 2 to 30, n indicates the average number of moles of oxyalkylene groups added. The same applies below) and polypropylene glycol (n = 2 to 30) (meth)acrylate; alkoxypolyalkylene glycol (meth)acrylates such as methoxypolyethylene glycol (n = 1 to 30) (meth)acrylate; phenoxy (ethylene glycol-propylene glycol copolymer) (n = 1 to 30, ethylene glycol therein: n = 1 to 29) (meth)acrylate, and the like. Among these, one or more selected from methoxypolyethylene glycol (n=1 to 30) (meth)acrylate and polypropylene glycol (n=2 to 30) (meth)acrylate are preferable. The monomer components contained in each of the above components (a-1) to (a-3) can be used alone or in combination of two or more kinds.

[0021] (Content of each structural unit in polymer a) From the viewpoint of improving the continuous dischargeability and image density, the contents of the structural units derived from the components (a-1) to (a-3) in the polymer a are as follows. The content of the (a-1) component is preferably 5 mass% or more, more preferably 8 mass% or more, even more preferably 10 mass% or more, and preferably 45 mass% or less, more preferably 40 mass% or less, even more preferably 35 mass% or less. The content of the (a-2) component is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, and preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 88% by mass or less.

[0022] When the (a-3) component is contained, the content thereof is preferably 2 mass% or more, more preferably 5 mass% or more, even more preferably 10 mass% or more, and preferably 45 mass% or less, more preferably 40 mass% or less, even more preferably 35 mass% or less. The mass ratio of the component (a-1) to the component (a-2) [component (a-1) / component (a-2)] is preferably 0.1 or more, more preferably 0.15 or more, even more preferably 0.2 or more, and is preferably 1 or less, more preferably 0.8 or less, even more preferably 0.5 or less.

[0023] (Production of polymer (a)) The polymer (a) can be produced by copolymerizing a mixture of the above monomer components (a-1) to (a-3) by a known polymerization method, preferably a solution polymerization method. The solvent used in the solution polymerization method is not limited, but polar solvents such as water, aliphatic alcohols, ketones, ethers, and esters are preferred, and water, methanol, ethanol, acetone, methyl ethyl ketone, and the like are more preferred. In the polymerization, a polymerization initiator and a polymerization chain transfer agent can be used. Examples of the polymerization initiator include persulfates such as ammonium persulfate and potassium persulfate, and water-soluble azo polymerization initiators, and examples of the polymerization chain transfer agent include mercaptans. The polymerization temperature varies depending on the types of polymerization initiator, monomer, solvent, etc. used, but is preferably 30° C. or higher, more preferably 50° C. or higher, and is preferably 95° C. or lower, more preferably 80° C. or lower. The polymerization atmosphere is preferably a nitrogen gas atmosphere or an inert gas atmosphere. The polymer (a) is preferably neutralized with a neutralizing agent as described below.

[0024] When the polymer (a) does not have a crosslinked structure, from the viewpoint of improving the continuous dischargeability, the number average molecular weight is preferably 5,000 or more, more preferably 10,000 or more, even more preferably 20,000 or more, and is preferably 80,000 or less, more preferably 60,000 or less, even more preferably 40,000 or less. The number average molecular weight of the polymer is measured by the method described in the Examples.

[0025] [Preparation of pigment-containing polymer particles] The pigment-containing polymer particles can be efficiently produced as a pigment aqueous dispersion by a method having the following steps 1 and 2, and it is preferable to further carry out the following step 3. Step 1: A step of dispersing a pigment mixture containing a pigment, a polymer (a), an organic solvent, and water to obtain a dispersion. Step 2: A step of removing the organic solvent from the dispersion obtained in step 1 to obtain an aqueous dispersion of pigment-containing polymer particles A (hereinafter also referred to as "aqueous pigment dispersion (i)"). Step 3: A step of adding a crosslinking agent to the pigment water dispersion (i) obtained in step 2 to crosslink the pigment-containing polymer particles to obtain a pigment-containing crosslinked polymer particle water dispersion (I) (hereinafter also referred to as "pigment water dispersion (I)").

[0026] (Process 1) The pigment mixture in step 1 is preferably obtained by a method in which the polymer (a) is dissolved in an organic solvent, and the pigment, water, and, if necessary, a neutralizing agent, a surfactant, and the like are added to the obtained organic solvent solution and mixed to obtain an oil-in-water dispersion. Although there is no limitation on the organic solvent used in step 1, ketones, ethers, esters, aliphatic alcohols having 1 to 3 carbon atoms, etc. are preferred, and from the viewpoint of improving the wettability to the pigment and the adsorption of polymer (a) to the pigment, ketones having 4 to 8 carbon atoms are more preferred, and methyl ethyl ketone is even more preferred. When a vinyl resin is synthesized as polymer (a) by solution polymerization, the solvent used in the polymerization may be used as it is.

[0027] When the polymer (a) has acid groups, it is preferable that at least a part of the acid groups is neutralized with a neutralizing agent, which is believed to increase the charge repulsion force exhibited after neutralization, suppress the aggregation of pigment particles in the water-based ink, and improve the dispersion stability of the pigment. In the case of neutralization, it is preferable to neutralize so that the pH is 7 or more and 11 or less. Examples of the neutralizing agent include bases such as sodium hydroxide, potassium hydroxide, ammonia, and various amines, with sodium hydroxide and ammonia being preferred. The polymer (a) may be neutralized in advance. From the viewpoint of improving dispersion stability and storage stability, the amount of the neutralizing agent used is preferably 10 mol % or more, more preferably 15 mol % or more, even more preferably 20 mol % or more, and is preferably 150 mol % or less, more preferably 120 mol % or less, even more preferably 100 mol % or less. Here, the equivalent amount of the neutralizing agent used can be calculated by the following formula, where the polymer (a) before neutralization is regarded as the "polymer (a')". Equivalent amount of neutralizing agent used (mol%)=[{weight of neutralizing agent added (g) / equivalent amount of neutralizing agent} / [{acid value of polymer (a') (mg KOH / g) × weight of polymer a' (g)} / (56 × 1,000)]] × 100

[0028] In the dispersion treatment in step 1, the pigment particles can be atomized to a desired particle size only by main dispersion using shear stress. However, from the viewpoint of obtaining a uniform aqueous pigment dispersion, it is preferable to pre-disperse the pigment mixture and then further carry out main dispersion. As a dispersing machine used for preliminary dispersion, a commonly used mixing and stirring device such as an anchor blade or a dispersing blade can be used. Examples of means for applying shear stress used in the present dispersion include kneaders such as roll mills and kneaders, high-pressure homogenizers such as microfluidizers, and media-type dispersers such as paint shakers and bead mills. Among these, it is preferable to use high-pressure homogenizers and bead mills from the viewpoint of reducing the particle size of the pigment. When the dispersion treatment is carried out using a high-pressure homogenizer, the average particle size of the pigment particles in the pigment aqueous dispersion can be adjusted by controlling the treatment pressure and the number of passes. From the viewpoints of productivity and economy, the treatment pressure is preferably 60 MPa or more and 300 MPa or less, and the number of passes is preferably 3 or more and 30 or less.

[0029] (Process 2) The organic solvent can be removed by a known method in step 2. It is preferable that the organic solvent in the obtained pigment water dispersion (i) has been substantially removed, but it may remain as long as it does not impair the object of the present invention. In addition, for the purpose of removing coarse particles and the like, it is preferable to further centrifuge the aqueous dispersion from which the organic solvent has been removed, and then filter the liquid layer portion through a filter or the like, and obtain the pigment aqueous dispersion (i) that has passed through the filter or the like.

[0030] (Step 3) Step 3 is optional, but a crosslinking agent is added to the pigment water dispersion (i) obtained in step 2, and reacted with a part of the carboxyl group of the polymer a constituting the pigment-containing polymer particle to form a crosslinked structure in the surface layer of the pigment-containing polymer particle, thereby obtaining a pigment water dispersion (I) of pigment-containing crosslinked polymer particles. This makes it possible to have a crosslinking agent-derived structural unit in addition to the structural unit of the polymer (a), and the polymer formed by crosslinking the polymer a is firmly adsorbed or fixed on the pigment surface, suppressing the aggregation of the pigment, which is considered to result in further improved dispersion stability and storage stability of the obtained ink.

[0031] The crosslinking agent is preferably a polyfunctional epoxy compound having two or more epoxy groups in the molecule, more preferably a compound having two or more glycidyl ether groups, and even more preferably a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group having 3 to 4 carbon atoms. The epoxy equivalent of the crosslinking agent is preferably 90 or more, more preferably 100 or more, and is preferably 300 or less, more preferably 200 or less. Suitable examples of the crosslinking agent include one or more selected from polyglycidyl ethers such as 1,6-hexanediol diglycidyl ether, trimethylolpropane polyglycidyl ether, and pentaerythritol polyglycidyl ether.

[0032] From the viewpoint of improving continuous dischargeability, image fastness, etc., the degree of crosslinking in step 3 is preferably 8 mol % or more, more preferably 10 mol % or more, even more preferably 15 mol % or more, in terms of the ratio of the molar equivalent number of the crosslinkable functional group of the crosslinking agent to the molar equivalent number of the carboxy group of polymer a, and is preferably 70 mol % or less, more preferably 60 mol % or less, even more preferably 50 mol % or less. When the polymer dispersant (A) has a crosslinked structure, it is difficult to measure its number average molecular weight. However, it is preferable that the number average molecular weight is larger than the number average molecular weight of the polymer (a) before the crosslinked structure is formed, from the viewpoints of improving the dispersibility of the pigment in an aqueous medium and the storage stability of the ink. From the viewpoint of crosslinking reaction efficiency, the temperature of the crosslinking treatment is preferably 40° C. or higher, more preferably 50° C. or higher, and is preferably 90° C. or lower, more preferably 80° C. or lower.

[0033] From the viewpoint of improving dispersion stability, the non-volatile component concentration (solid content concentration) of the resulting pigment water dispersion (I) is preferably 10% by mass or more, more preferably 15% by mass or more, and is preferably 45% by mass or less, more preferably 40% by mass or less. The solids concentration is measured by the method described in the Examples. From the viewpoint of improving dispersion stability, the content of the pigment in the pigment water dispersion (I) is preferably 5% by mass or more, more preferably 8% by mass or more, and is preferably 40% by mass or less, more preferably 30% by mass or less. The mass ratio of the polymer dispersant (A) constituting the pigment-containing (crosslinked) polymer particles in the pigment water dispersion (I) to the pigment [(polymer dispersant (A) / pigment)] is preferably 0.05 or more, more preferably 0.1 or more, and is preferably 1 or less, more preferably 0.5 or less. In the present invention, when the polymer constituting the pigment-containing (crosslinked) polymer particles has a crosslinked structure, the mass of the constituent units derived from the crosslinking agent of the crosslinked polymer is also included when calculating the mass ratio of the polymer dispersant (A) to the pigment.

[0034] From the viewpoint of improving the continuous ejection properties of the ink and the image density, the acid value of the polymer constituting the pigment-containing (crosslinked) polymer particles before dispersion treatment (before crosslinking) is preferably 50 mgKOH / g or more, more preferably 80 mgKOH / g or more, even more preferably 100 mgKOH / g or more, still more preferably 120 mgKOH / g or more, and is preferably 350 mgKOH / g or less, more preferably 300 mgKOH / g or less, and even more preferably 250 mgKOH / g or less. From the same viewpoints as above, the acid value after dispersion treatment (after crosslinking) of the polymer constituting the pigment-containing (crosslinked) polymer particles is preferably 50 mgKOH / g or more, more preferably 80 mgKOH / g or more, even more preferably 100 mgKOH / g or more, still more preferably 120 mgKOH / g or more, and is preferably 200 mgKOH / g or less, more preferably 150 mgKOH / g or less, and even more preferably 110 mgKOH / g or less. The acid value of the polymer is measured by the method described in the Examples.

[0035] From the viewpoint of storage stability, etc., the average particle size of the pigment-containing (crosslinked) polymer particles is preferably 50 nm or more, more preferably 70 nm or more, even more preferably 80 nm or more, and is preferably 400 nm or less, more preferably 300 nm or less, even more preferably 200 nm or less. The average particle size is measured by the method described in the Examples.

[0036] <Wax> In the present invention, the wax may be either a natural wax or a synthetic wax. Examples of natural waxes include petroleum waxes such as paraffin wax and microcrystalline wax; vegetable waxes such as carnauba wax, candelilla wax and rice wax; and animal waxes such as lanolin and beeswax. Examples of synthetic waxes include synthetic hydrocarbon waxes such as polyolefin wax and Fischer-Tropsch wax, silicone waxes, and modified waxes such as paraffin wax derivatives, montan wax derivatives, and microcrystalline wax derivatives. Among these, polyolefin waxes containing an olefin monomer as a main component are preferred. The above waxes can be used alone or in combination of two or more.

[0037] From the viewpoint of improving the continuous ejection properties of the ink, the melting point of the wax used in the present invention is 80°C or higher, preferably 100°C or higher, more preferably 105°C or higher, even more preferably 108°C or higher, and preferably 150°C or lower, more preferably 145°C or lower, even more preferably 140°C or lower. The melting point of the wax is measured by the method described in the Examples.

[0038] [Wax-containing polymer particles] The wax used in the present invention is used in the form of polymer particles containing wax dispersed with a polymer dispersant (B) (hereinafter also referred to as "wax-containing polymer particles") in order to improve the continuous ejection properties of the ink. Here, the term "wax-containing polymer particles" refers to particles in which the polymer dispersant (B) contains wax, particles in which part of the wax is exposed on the surface of particles made of the polymer dispersant (B) and wax, particles in which the polymer dispersant (B) is adsorbed on part of the wax, and mixtures thereof. Among these, particles in which part of the wax is exposed on the surface of particles made of the polymer dispersant (B) and wax, or particles in which the polymer dispersant (B) is adsorbed on part of the wax are more preferred.

[0039] The polymer dispersant (B) (hereinafter also referred to as "polymer (b)") constituting the wax-containing polymer particles preferably has (b-1) a constituent unit derived from a carboxylic acid monomer and (b-2) a constituent unit derived from a hydrophobic monomer. Examples of the polymer (b) include vinyl resins obtained by addition polymerization of vinyl monomers, polyester resins, polyurethane resins, etc. Among these, vinyl resins are preferred from the viewpoints of pigment dispersion stability, storage stability, etc. The polymer (b) may be a non-crosslinked polymer, and may be appropriately synthesized or a commercially available product. The wax-containing polymer particles are more preferably crosslinked polymer particles containing wax (hereinafter also referred to as "wax-containing crosslinked polymer particles") in which wax is dispersed with a polymer dispersant (B) having a crosslinked structure. "Polymer dispersant (B) having a crosslinked structure" means that the polymer dispersant (B) is a polymer having a constitutional unit derived from a crosslinking agent in addition to the constitutional unit of the above-mentioned polymer (b).

[0040] [Polyolefin wax] Examples of the olefin monomer that is the main component of the polyolefin wax include linear olefins and cyclic olefins. Preferably, the main component is a linear olefin having 2 to 6 carbon atoms. More preferably, the polyolefin wax is mainly composed of ethylene or propylene. More preferably, the polyethylene wax is mainly composed of ethylene. Here, "containing ethylene or propylene as a main component" means that the content of ethylene or propylene relative to the total components constituting the wax is preferably 50 mass% or more, more preferably 65 mass% or more, and even more preferably 80 mass% or more. Oxidized polyolefin waxes are included in the category of polyolefin waxes, and can be obtained by introducing oxygen atoms or the like into the molecules of high molecular weight polyolefin polymers while adjusting the molecular weight to a desired value by thermal decomposition or the like. That is, the polyolefin wax is preferably at least one selected from polyethylene wax, polypropylene wax, and oxidized polyethylene wax, and polyethylene wax is more preferable.

[0041] From the same viewpoints as above, the weight average molecular weight of the polyolefin wax is preferably 400 or more, more preferably 600 or more, and even more preferably 800 or more, and is preferably 10,000 or less, more preferably 8,000 or less, and even more preferably 6,000 or less. From the same viewpoint as above, the density of the polyolefin wax is preferably 0.890 g / cm 3 More preferably, 0.900 g / cm 3 More preferably, 0.910 g / cm 3 and preferably 0.985 g / cm 3 Less than or equal to 0.980 g / cm 3 More preferably, 0.975 g / cm 3 The following is the result. In the present invention, waxes other than the polyolefin wax may be contained within the range that does not impair the effects of the present invention. The content of the polyolefin wax in the total amount of wax is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and still more preferably 100% by mass.

[0042] [Polymer (b)] The polymer (b) preferably contains at least (b-1) a structural unit derived from a carboxylic acid monomer and (b-2) a structural unit derived from a hydrophobic monomer, and may further contain (b-3) a structural unit derived from a nonionic monomer.

[0043] Specific examples and preferred examples of the (b-1) carboxylic acid monomer are the same as those of the (a-1) ionic monomer described in the section on the polymer (a). That is, the (b-1) component is preferably at least one selected from acrylic acid and methacrylic acid. Specific examples and preferred examples of the hydrophobic monomer (b-2) are the same as those of the hydrophobic monomer (a-2) described in the section on polymer (a). That is, the component (b-2) is preferably at least one selected from alkyl (meth)acrylates having an alkyl group with 1 to 4 carbon atoms and aromatic group-containing monomers having an aromatic group with 6 to 12 carbon atoms, and more preferably at least one selected from ethyl acrylate, styrene, and α-methylstyrene. Specific examples and preferred examples of the (b-3) nonionic monomer are the same as the specific examples and preferred examples of the (a-3) nonionic monomer explained in the section on the polymer (a).

[0044] The content of the structural units derived from the components (b-1) to (b-3) in the polymer b is the same as the content of the structural units derived from the components (a-1) to (a-3) in the polymer (a), from the viewpoint of improving continuous ejection properties and image fastness. That is, the content of the (b-1) component is preferably 5 mass% or more, more preferably 10 mass% or more, even more preferably 12 mass% or more, and preferably 45 mass% or less, more preferably 40 mass% or less, even more preferably 35 mass% or less. The content of the (b-2) component is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, and preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 88% by mass or less.

[0045] The polymer (b) can be produced in the same manner as in the above (production of polymer (a)). When the polymer (b) has acid groups, it is preferable that at least a part of the acid groups is neutralized with a neutralizing agent, which is believed to increase the charge repulsion force exhibited after neutralization, suppress the aggregation of wax particles in the water-based ink, and improve the dispersion stability of the wax. The amount of the neutralizing agent used is the same as that described above (Production of polymer (a)), and is preferably 10 mol% or more, more preferably 15 mol% or more, even more preferably 20 mol% or more, and is preferably 150 mol% or less, more preferably 120 mol% or less, even more preferably 100 mol% or less.

[0046] [Preparation of wax-containing crosslinked polymer particles] Examples of methods for producing wax-containing crosslinked polymer particles include (i) a method in which a dispersion containing a (crosslinked) polymer obtained by copolymerizing a monomer mixture containing the above-mentioned components (b-1), (b-2), and, if necessary, the component (b-3) is subjected to a dispersion treatment, and wax is subjected to a dispersion treatment; (ii) a method in which a crosslinking agent is added to a dispersion containing a non-crosslinked polymer obtained by copolymerizing a monomer mixture containing the above-mentioned components (b-1), (b-2), and, if necessary, the component (b-3), and wax is subjected to a crosslinking treatment. The dispersion treatment method and crosslinking treatment method are the same as those in the above-mentioned [Production of Pigment-Containing Polymer Particles], and specific examples and preferred examples are also basically the same. Suitable examples of the crosslinking agent include one or more selected from polyglycidyl ethers such as 1,6-hexanediol diglycidyl ether, trimethylolpropane polyglycidyl ether, and pentaerythritol polyglycidyl ether.

[0047] Among the above-mentioned manufacturing methods, from the viewpoint of improving the continuous ejection property of the ink and the fastness of the image, (ii) a method of adding a crosslinking agent to a dispersion containing an uncrosslinked polymer obtained by copolymerizing a monomer mixture containing the above-mentioned (b-1), (b-2), and if necessary, (b-3) components, and crosslinking the dispersion is preferred. The reason for this is that in the step of dispersing the polyolefin wax, it is considered that the uncrosslinked polymer is more likely to be adsorbed quickly and uniformly on the wax surface than the crosslinked polymer. By obtaining wax-containing crosslinked polymer particles by the method (ii), it is possible to obtain a crosslinked polymer having a constitutional unit derived from the crosslinking agent in addition to the constitutional unit of the polymer (b). The crosslinking reaction of the polymer (b) may be carried out in a system containing or not containing a pigment, but is preferably carried out in a system not containing a pigment, because if the crosslinking reaction is carried out in a system containing both an aqueous pigment dispersion and an aqueous dispersion of wax-containing polymer particles, the balance of electrostatic repulsion between dispersed particles in the system may change in the early stage of the crosslinking reaction, which may cause the pigment in the aqueous pigment dispersion to aggregate.

[0048] From the viewpoint of improving the storage stability and continuous ejection property of the ink, the degree of crosslinking of the polymer (b) is preferably 2 mol % or more, more preferably 5 mol % or more, even more preferably 10 mol % or more, and is preferably 75 mol % or less, more preferably 70 mol % or less, even more preferably 65 mol % or less. The degree of crosslinking is the equivalent weight of the crosslinking sites in all the monomers constituting the polymer, and is calculated by the following formula: Degree of crosslinking=[(molar equivalent of monomer forming crosslinking site)×(number of crosslinking sites in monomer backbone forming crosslinking site) / (molar equivalent of all monomers constituting polymer)]×100

[0049] From the viewpoint of improving the continuous ejection property of the ink, the image density, and the image fastness, the acid value of the polymer before crosslinking that constitutes the wax-containing crosslinked polymer particles is preferably 50 mgKOH / g or more, more preferably 80 mgKOH / g or more, even more preferably 100 mgKOH / g or more, still more preferably 120 mgKOH / g or more, and is preferably 350 mgKOH / g or less, more preferably 300 mgKOH / g or less, and even more preferably 250 mgKOH / g or less. From the same viewpoints as above, the acid value of the crosslinked polymer constituting the wax-containing crosslinked polymer particles is preferably 40 mgKOH / g or more, more preferably 50 mgKOH / g or more, even more preferably 60 mgKOH / g or more, still more preferably 70 mgKOH / g or more, and is preferably 250 mgKOH / g or less, more preferably 200 mgKOH / g or less, even more preferably 150 mgKOH / g or less.

[0050] From the viewpoint of improving the continuous ejection property of the ink and the image density, it is preferable that the difference in acid value between the polymer constituting the pigment-containing polymer particles and the polymer constituting the wax-containing polymer particles is small. Specifically, the difference in acid value is more preferably within 20 mgKOH / g, even more preferably within 15 mgKOH / g, and even more preferably within 5 mgKOH / g, and it is most preferable that there is substantially no difference and that the acid values ​​are the same. That is, it is preferable that the polymer constituting the pigment-containing polymer particles is the same as the polymer constituting the wax-containing polymer particles. In the present invention, it is preferred that both the polymer constituting the pigment-containing polymer particles and the polymer constituting the wax-containing polymer particles are crosslinked.

[0051] The mass ratio of wax to polymer (b) in the wax-containing (crosslinked) polymer particles [wax / polymer (b)] is, from the viewpoint of improving the continuous ejection properties of the resulting wax dispersion and ink, preferably 1 or more, more preferably 2 or more, even more preferably 3 or more, and is preferably 30 or less, more preferably 20 or less, even more preferably 10 or less, and still more preferably 6 or less. In the present invention, when calculating the mass ratio of the wax to the polymer (b) in the wax-containing crosslinked polymer particles, the mass of the constituent units derived from the crosslinking agent is also included.

[0052] From the viewpoint of improving the continuous ejection properties of the ink and the image density, the average particle size of the wax-containing (crosslinked) polymer particles is preferably 20 nm or more, more preferably 40 nm or more, even more preferably 80 nm or more, and is preferably 250 nm or less, more preferably 200 nm or less, even more preferably 150 nm or less. The average particle size of the polymer particles is measured by the method described in the Examples.

[0053] <Organic solvent> The organic solvent used in the present invention mainly plays a role in imparting wetting and spreading properties of the ink to the recording medium. The organic solvent may be liquid or solid at 25° C., but a water-soluble organic solvent that dissolves in 100 mL of water at 25° C. in an amount of 10 mL or more is preferred. From the viewpoint of improving the continuous ejection properties of the ink and the image density, the boiling point of the water-soluble organic solvent is preferably 110°C or higher, more preferably 130°C or higher, even more preferably 150°C or higher, and is preferably 250°C or lower, more preferably 240°C or lower, even more preferably 235°C or lower. From the same viewpoint as above, the water-soluble organic solvent is preferably one or more selected from polyhydric alcohols and polyhydric alcohol alkyl ethers, and more preferably a polyhydric alcohol. Examples of polyhydric alcohols include ethylene glycol, propylene glycol, 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,2-octanediol, 1,8-octanediol, 1,2-decanediol, 1,3-propanediol, 1,4-butanediol, 2-ethyl-1,3-hexanediol, diethylene glycol, dipropylene glycol, and glycerin. Among these, one or more selected from 1,2-pentanediol, 1,2-hexanediol, 1,2-octanediol, dipropylene glycol, and glycerin are preferred, and one or more selected from 1,2-hexanediol, dipropylene glycol, and glycerin are more preferred.

[0054] Examples of polyhydric alcohol alkyl ethers include ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monobutyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, and tripropylene glycol monomethyl ether. Of these, one or more selected from dipropylene glycol monomethyl ether, dipropylene glycol monobutyl ether, diethylene glycol monoisopropyl ether, and diethylene glycol monobutyl ether are preferred, and one or more selected from dipropylene glycol monomethyl ether and diethylene glycol monobutyl ether are more preferred. The organic solvent may further contain organic solvents other than those mentioned above, within the range that does not impair the effects of the present invention.

[0055] The ink of the present invention may further contain a surfactant, if necessary, from the viewpoint of improving the wettability to the recording medium. Examples of the surfactant include nonionic surfactants, silicone-based surfactants, and fluorine-based surfactants, with nonionic surfactants being more preferred. Examples of nonionic surfactants include acetylene glycol surfactants, polyoxyalkylene alkyl ether surfactants, polyhydric alcohol surfactants, fatty acid alkanolamides, etc. Among these, acetylene glycol surfactants and polyoxyalkylene alkyl ether surfactants are preferred, and for example, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, polyoxyethylene alkyl ether, etc. are more preferred. Examples of commercially available nonionic surfactants include the "Surfynol" series manufactured by Nissin Chemical Industry Co., Ltd. and Air Products & Chemicals, the "Acetylenol" series manufactured by Kawaken Fine Chemicals Co., Ltd., and the "Emulgen" series manufactured by Kao Corporation. The above surfactants can be used alone or in combination of two or more.

[0056] (Content of each component in the ink of the present invention) The contents of the various components in the ink of the present invention are as follows, from the viewpoint of improving the continuous ejection properties of the ink and the image density.

[0057] (Pigment content) The content of the pigment in the ink of the present invention is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 4% by mass or more, and is preferably 12% by mass or less, more preferably 10% by mass or less, even more preferably 8% by mass or less. The content of the pigment-containing polymer particles in the ink of the present invention is preferably 2% by mass or more, more preferably 3% by mass or more, even more preferably 5% by mass or more, and preferably 15% by mass or less, more preferably 12% by mass or less, even more preferably 10% by mass or less.

[0058] (Wax content) The content of wax, particularly polyolefin wax, in the ink of the present invention is preferably 0.5% by mass or more, more preferably 0.8% by mass or more, even more preferably 1% by mass or more, and preferably 4% by mass or less, more preferably 3% by mass or less, even more preferably 2.5% by mass or less. The content of the wax-containing crosslinked polymer particles in the ink of the present invention is preferably 0.6% by mass or more, more preferably 1% by mass or more, even more preferably 1.5% by mass or more, and preferably 6% by mass or less, more preferably 5% by mass or less, even more preferably 4% by mass or less.

[0059] The mass ratio of pigment to wax in the water-based ink (pigment / wax) is preferably 1 or more, more preferably 2 or more, even more preferably 2.5 or more, and preferably 6 or less, more preferably 5 or less, even more preferably 4 or less.

[0060] (Contents of polymer dispersants (A) and (B) in the ink of the present invention) The content of the polymer dispersant (A) in the ink of the present invention is preferably 0.5% by mass or more, more preferably 1% by mass or more, even more preferably 1.5% by mass or more, and preferably 5% by mass or less, more preferably 4% by mass or less, even more preferably 3% by mass or less. The content of the polymer dispersant (B) in the ink of the present invention is preferably 0.1 mass% or more, more preferably 0.2 mass% or more, even more preferably 0.3 mass% or more, and preferably 3 mass% or less, more preferably 2 mass% or less, even more preferably 1 mass% or less. The mass ratio of the pigment to the total content of the polymer dispersants (A) and (B) in the water-based ink [pigment / polymer dispersant [(A)+(B)]] is preferably 0.5 or more, more preferably 1 or more, even more preferably 1.5 or more, and is preferably 8 or less, more preferably 6 or less, even more preferably 4 or less. In the present invention, when the polymer dispersants (A) and (B) in the water-based ink are crosslinked polymers, the mass ratio of the pigment to the total content of the polymer dispersants (A) and (B) is calculated by taking into account the mass of the constituent units derived from the crosslinker in the polymer dispersants (A) and (B).

[0061] (Organic solvent content) The content of the organic solvent in the ink of the present invention is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less.

[0062] The content of the surfactant in the ink of the present invention is preferably 0.2% by mass or more, more preferably 0.4% by mass or more, even more preferably 0.6% by mass or more, and is preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 2% by mass or less. (Acetylene glycol surfactant content) From the viewpoint of improving the wettability of the ink onto a recording medium, the content of the acetylene glycol surfactant in the water-based ink is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.15% by mass or more, and from the viewpoint of improving the ejection stability of the ink, the content is preferably 1.2% by mass or less, more preferably 1% by mass or less, and even more preferably 0.8% by mass or less. (Content of other nonionic surfactants) The content of other nonionic surfactants in the water-based ink, for example polyoxyalkylene alkyl ether surfactants, is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.2% by mass or more, and is preferably 3% by mass or less, more preferably 2% by mass or less, even more preferably 1.5% by mass or less.

[0063] The water content in the ink of the present invention is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, and preferably 80% by mass or less, more preferably 75% by mass or less, even more preferably 70% by mass or less. The ink of the present invention may contain various additives such as preservatives, pH adjusters, viscosity adjusters, defoamers, and rust inhibitors as optional components depending on the application. In such cases, a portion of the water content may be replaced with the various additives.

[0064] (Physical properties of the ink of the present invention) From the viewpoint of improving the continuous ejection properties of the ink and the image density, the average particle size of the polymer particles, including the pigment-containing polymer particles and the wax-containing polymer particles, in the ink of the present invention is preferably 40 nm or more, more preferably 60 nm or more, even more preferably 80 nm or more, and is preferably 250 nm or less, more preferably 200 nm or less, even more preferably 150 nm or less. From the viewpoint of improving continuous jetting ability, the viscosity of the ink of the present invention at 32°C is preferably 2 mPa s or more, more preferably 3 mPa s or more, even more preferably 5 mPa s or more, and is preferably 12 mPa s or less, more preferably 9 mPa s or less, even more preferably 7 mPa s or less. The viscosity of the water-based ink can be measured using an E-type viscometer. From the viewpoint of improving continuous jetting property, the pH of the ink of the present invention is preferably 7 or more, more preferably 7.5 or more, and even more preferably 8 or more. From the viewpoint of member resistance and skin irritation, the pH is preferably 11 or less, more preferably 10 or less, and even more preferably 9.5 or less. The pH of the water-based ink is measured by the method described in the Examples.

[0065] [Inkjet recording method] The ink of the present invention can be loaded into a known ink jet recording device and ejected as ink droplets onto a recording medium to record an image or the like. Ink droplets are ejected in inkjet recording using a piezoelectric method, a thermal method, or an electrostatic method, with the piezoelectric method being preferred. In the piezoelectric method, a large number of nozzles are each connected to a pressure chamber, and ink droplets are ejected from the nozzles by vibrating the walls of the pressure chambers using a piezoelectric element. Examples of recording media include inkjet-specific paper having an ink-absorbing layer, plain paper used for copying, paper substrates such as art paper, ordinary uncoated paper, coated paper in which both sides of a base paper are coated with a resin or the like, various laminated papers, synthetic paper, and various non-absorbent resin films used in so-called soft packaging. Examples of plain paper include high-grade printing paper, medium-grade printing paper, low-grade printing paper, thin printing paper, lightly coated printing paper, special printing paper such as colored wood-free paper, form paper, PPC paper (copy paper), and other information paper. EXAMPLES

[0066] In the following Production Examples, Preparation Examples, Examples and Comparative Examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified. The methods for measuring each physical property are as follows.

[0067] (1) Measurement of polymer number average molecular weight The measurement was performed by gel permeation chromatography (GPC apparatus (HLC-8320GPC) manufactured by Tosoh Corporation, columns (TSKgel SuperAWM-H, TSKgel SuperAW3000, TSKgel guardcolum Super AW-H) manufactured by Tosoh Corporation, flow rate: 0.5mL / min) using a solution of phosphoric acid and lithium bromide dissolved in N,N-dimethylformamide to a concentration of 60mmol / L and 50mmol / L, respectively, as an eluent, and using a monodisperse polystyrene kit with known molecular weight (PStQuick B (F-550, F-80, F-10, F-1, A-1000), PStQuick C (F-288, F-40, F-4, A-5000, A-500), manufactured by Tosoh Corporation) as a standard substance. The measurement sample was prepared by mixing 0.1 g of polymer with 10 mL of the eluent in a glass vial, stirring with a magnetic stirrer at 25° C. for 10 hours, and filtering with a syringe filter (DISMIC-13HP, PTFE, 0.2 μm, Advantec Co., Ltd.).

[0068] (2) Measurement of the acid value of the polymer The acid value of the polymer was measured by dissolving the resin in a titration solvent of toluene and acetone (2:1) in an automatic potentiometric titrator (Kyoto Electronics Manufacturing Co., Ltd., electric burette, model number: APB-610) and titrating it with 0.1N potassium hydroxide / ethanol solution by potentiometric titration, with the inflection point on the titration curve as the end point. The acid value (mgKOH / g) was calculated from the titration amount of the potassium hydroxide solution up to the end point. The acid value of the wax dispersion or the pigment-containing polymer particle dispersion was measured by diluting 2 g of the dispersion with 50 g of ion-exchanged water, adding 3 ml of 0.1 N sodium hydroxide solution, slowly dripping 0.1 N hydrochloric acid thereto, and measuring the pH inflection points at two points by potentiometric titration. The number of moles of acid calculated from the difference in the amount of 0.1 N hydrochloric acid dripped between the two points corresponds to the number of moles of carboxylic acid in the polymer, and this number of moles was converted into the acid value (mg KOH / g).

[0069] (3) Measurement of solids concentration in aqueous dispersion 10.0 g of sodium sulfate, which had been kept constant in a desiccator, was weighed out into a 30 mL polypropylene container (φ: 40 mm, height: 30 mm), and about 1.0 g of the sample (water dispersion) was added thereto and mixed, then accurately weighed, maintained at 105°C for 2 hours to remove volatile matter, and left in the desiccator for another 15 minutes, and the mass was measured. The mass of the sample after removing the volatile matter was taken as the solid content, and divided by the initial mass of the sample to obtain the solid content concentration.

[0070] (4) Measurement of the melting point of wax The melting point of the wax was measured using an apparatus conforming to JIS K 0064. Specifically, using a differential scanning calorimeter (Q20, manufactured by TA Instruments), the sample was heated to 200°C and cooled from that temperature to 0°C at a rate of 10°C / min. Next, the sample was heated at a rate of 10°C / min, and the amount of heat was measured up to 200°C. Among the observed heat of fusion peaks, the temperature of the peak with the largest peak area was determined as the maximum peak temperature of melting, and this peak temperature was determined as the melting point.

[0071] (5) Measurement of the average particle size of polymer particles in pigment dispersion The particle size was measured by dynamic light scattering using a laser particle analysis system (manufactured by Otsuka Electronics Co., Ltd., product name: ELS-8000), and calculated by cumulant method analysis. The measurement conditions were a temperature of 25°C, an angle between the incident light and the detector of 90°, and 100 cumulative measurements. The refractive index of water (1.333) was entered as the refractive index of the dispersion solvent. For the measurement sample, a water-based pigment dispersion was weighed into a screw tube (Maruemu Co., Ltd., No. 5) and the solids concentration was 2 × 10 -4 Water was added so as to obtain the desired mass %, and the mixture was stirred at 25° C. for 1 hour using a magnetic stirrer.

[0072] (6) Measurement of the average particle size of polymer particles in wax dispersion The average particle size (average dispersed particle size) of the polymer particles in the wax dispersion was measured using a Microtrack particle size analyzer UPA manufactured by Nikkiso Co., Ltd.

[0073] (7) pH measurement The pH of the ink at 20° C. was measured using a tabletop pH meter (manufactured by Horiba Ltd., product name: F-71) equipped with a pH electrode (manufactured by Horiba Ltd., product name: 6337-10D).

[0074] Production Example 1 (Preparation of Water-Insoluble Polymer (i)) A monomer mixture was prepared by mixing 29 parts of acrylic acid, 60 parts of styrene, and 11 parts of ethyl acrylate. In a reaction vessel, 10 parts of MEK, 0.2 parts of 2-mercaptoethanol (polymerization chain transfer agent), and 10% of the monomer mixture were mixed and thoroughly purged with nitrogen gas. Meanwhile, a mixture of the remaining 90% of the monomer mixture, 0.2 parts of the polymerization chain transfer agent, 30 parts of MEK, and 1.1 parts of an azo-based radical polymerization initiator (2,2'-azobis(2,4-dimethylvaleronitrile, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product name: V-65) was placed in a dropping funnel, and the monomer mixture in the reaction vessel was heated to 65°C under a nitrogen atmosphere while being stirred, and the mixture in the dropping funnel was dropped over 3 hours. After 2 hours at 65°C from the end of the dropping, a solution in which 0.1 parts of the polymerization initiator was dissolved in 2 parts of MEK was added, and the mixture was further aged at 65°C for 2 hours and at 70°C for 2 hours, and then dried under reduced pressure to obtain a water-insoluble polymer (i) (number average molecular weight: 32000, acid value: 226 mgKOH / g). The results are shown in Table 1.

[0075] Production Examples 2 to 6 (Preparation of Water-Insoluble Polymers (ii) to (vi)) Water-insoluble polymers (ii) to (vi) were obtained in the same manner as in Production Example 1, except that the conditions in Production Example 1 were changed to those shown in Table 1. The results are shown in Table 1.

[0076] [Table 1]

[0077] Preparation Example I-1 (Preparation of Wax Dispersion W1) As the polymer dispersant (B), 25 parts of the water-insoluble polymer (i) obtained in Production Example 1 was neutralized by adding 9.70 parts of a 5N aqueous sodium hydroxide solution (NaOH solid content: 16.9%) as a neutralizing agent for neutralizing the carboxyl group of the polymer (i) (use equivalent of the neutralizing agent: 40 mol %). Further, 240 parts of ion-exchanged water was added, and polyethylene wax (HW110P: manufactured by Mitsui Chemicals, Inc., product name: Hiwax 110P, melting point: 109°C, density: 0.920 g / cm 3100 parts by mass of a tertiary glycerin-based polymer (weight average molecular weight: 1000, softening point: 113°C) was heated and dissolved at 85 to 95°C, and the resulting mixture was dispersed for 30 minutes using an ultrasonic homogenizer while being maintained at 90 to 95°C. The mixture was then cooled to room temperature and dispersed three times using a Microfluidizer (trade name, manufactured by Microfluidics Corp.) at a pressure of 200 MPa to obtain a dispersion. Ion exchange water was added to the obtained dispersion, and 6.32 parts (corresponding to a crosslinking degree of 45 mol%) of an epoxy crosslinker (trimethylolpropane polyglycidyl ether, Nagase ChemteX Corporation, product name: Denacol EX-321, epoxy value: 140) was added, and the mixture was sealed and heated at 70°C for 5 hours while stirring with a stirrer to obtain a dispersion W1 of crosslinked polymer particles containing wax [(mass ratio of the contents of dispersion W1; wax: 20.0%, polymer dispersant (B): 6.2% (component derived from epoxy crosslinker in dispersion W1 is 0.2%), sodium hydroxide: 0.33%, the remainder is water.), average particle size: 92 nm, pH: 7.9, acid value of polymer dispersant (B): 96 mgKOH / g]. The results are shown in Table 2.

[0078] Preparation Examples I-2 to I-14 (Preparation of Wax Dispersions W2 to W14) Wax dispersions W2 to W14 were obtained in the same manner as in Preparation Example I-1, except that the type of wax, the type of polymer dispersant (B), the amount of 5N aqueous sodium hydroxide solution, and the amount of crosslinking agent were changed as shown in Table 2. The results are shown in Table 2. In addition, since the wax dispersions W9 and W11 do not use an epoxy crosslinking agent, the wax-containing polymer particles contained in the wax dispersions W9 and W11 do not have a crosslinked structure.

[0079] Details of the waxes used in the Examples and Comparative Examples in Table 2 are as follows. HW110P: Hiwax 110P (polyethylene wax, melting point: 109°C, density: 0.920g / cm 3 Weight average molecular weight: 1000, manufactured by Mitsui Chemicals, Inc. HW200P: Hiwax 200P (polyethylene wax, melting point: 122°C, density: 0.970g / cm 3 Weight average molecular weight: 2000, manufactured by Mitsui Chemicals, Inc. HWNP055: Hiwax NP055 (polypropylene wax, melting point: 136°C, density: 0.900g / cm 3 Weight average molecular weight: 7400, manufactured by Mitsui Chemicals, Inc. TW131: TOWAX-131 (Carnauba wax, melting point: 109°C, density: 0.997g / cm 3 , low molecular weight mixture, manufactured by Toa Kasei Co., Ltd.) PW155: Paraffin wax 155 (Paraffin wax, melting point: 69°C, density: 0.927g / cm 3 , low molecular weight mixture, manufactured by Nippon Seiro Co., Ltd.)

[0080] [Table 2]

[0081] Preparation Example II-1 (Preparation of Pigment Dispersion P1) As the polymer dispersant (A), 100 parts of the water-insoluble polymer (i) obtained in Production Example 1 was mixed with 78.6 parts of MEK, and then 38.8 parts of a 5N aqueous sodium hydroxide solution (NaOH solid content: 16.9%) was added as a neutralizing agent for neutralizing the carboxyl groups of the polymer (i) to neutralize the mixture (neutralizing agent equivalent: 40 mol %). Further, 500 parts of ion-exchanged water was added, to which was then added 300 parts of carbon black pigment (CB, CI Pigment Black 7, manufactured by Cabot Chemical Corporation, product name: Monarch 800), and the mixture was stirred for 60 minutes using a Disper (manufactured by Asada Iron Works Co., Ltd., product name: Ultra Disper) at 20°C with the Disper blade rotating at 7000 rpm. The resulting mixture was subjected to a dispersion treatment using a Microfluidizer (trade name, manufactured by Microfluidics) at a pressure of 200 MPa for 10 passes to obtain a pigment dispersion (solid content concentration: 26.7%, pigment: 20%, polymer: 6.7%). 1000 parts of ion-exchanged water was added to the obtained pigment dispersion, and after stirring, MEK was completely removed at 60°C under reduced pressure, and further a part of the water was removed to make the solid concentration 20% (pigment: 15.0%), and then 25.3 parts (corresponding to a crosslinking degree of 45 mol%) of an epoxy crosslinker (trimethylolpropane polyglycidyl ether, Nagase ChemteX Corporation, product name: Denacol EX-321, epoxy value: 140) was added, the container was sealed, and heated at 70°C for 5 hours while stirring with a stirrer to obtain a pigment-containing crosslinked polymer particle dispersion P1 [(The mass ratio of the contents of dispersion P1 is pigment: 15.0%, polymer dispersant (A): 6.3% (the amount of the component derived from the epoxy crosslinker in dispersion P1 is 1.3%), sodium hydroxide: 0.33%, and the remainder is water.), average particle size: 96 nm, pH: 7.9, acid value of polymer dispersant (A): 96 mgKOH / g]. The results are shown in Table 3.

[0082] Preparation Examples II-2 to II-10 (Preparation of Pigment Dispersions P2 to P10) Pigment dispersions P2 to P10 were obtained in the same manner as in Preparation Example II-1, except that the type of polymer dispersant (A), the amount of 5N sodium hydroxide aqueous solution, and the amount of crosslinking agent in Preparation Example II-1 were changed as shown in Table 3. The results are shown in Table 3. In addition, since the pigment dispersions P6 and P8 do not use an epoxy crosslinking agent, the polymer particles containing the pigment contained in the pigment dispersions P6 and P8 do not have a crosslinked structure.

[0083] [Table 3]

[0084] Example 1 (Preparation of Water-Based Ink) Dispersion W1 of crosslinked polymer particles containing wax 10 parts, Dispersion P1 of crosslinked polymer particles containing pigment 40 parts, dipropylene glycol 16.0 parts, 1,2-hexanediol 4.0 parts, glycerin 4.0 parts (all organic solvents are manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., total amount 24.0 parts), acetylene glycol-based nonionic surfactant (2,4,7,9-tetramethyl-5-decyne-4,7-diol: manufactured by Nissin Chemical Industry Co., Ltd., trade name: Surfynol 104) 0.2 parts, nonionic surfactant (polyoxyethylene alkyl ether Water-based ink 1 (solid concentration: 11.1%, pigment: 6%, polymer dispersant (A): 2.5%, wax: 2.0%, polymer dispersant (B): 0.6%) was obtained by adding 1.0 part of Emulgen 120 (manufactured by Kao Corporation) (total amount of surfactants: 1.2 parts), 0.52 parts of triethanolamine (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a pH adjuster so that the pH of the water-based ink was 9.0, and ion-exchanged water was added to make a total amount of 100 parts.

[0085] Examples 2 to 15 and Comparative Examples 1 to 3 (Production of Water-Based Inks) In the same manner as in Example 1, water-based inks 2 to 15 and 21 to 23 were obtained according to the formulations shown in Table 4.

[0086] The resulting water-based ink was evaluated for image density and continuous ejection property by the following methods. The results are shown in Table 4.

[0087] (1) Evaluation of continuous discharge In an environment of temperature 25±1°C and relative humidity 30±5%, an inkjet ejection evaluation device (ImageXpert, product name: JetXpert) equipped with an inkjet head (FUJIFILM Corporation, product name: Samba G3L, piezo type) was filled with water-based ink. The head voltage was set to 30V, the frequency to 50kHz, the push-pull type driving waveform, the appropriate amount of ejected liquid to 2.5pl, and the negative pressure to -4.0kPa, and an ink ejection command was transferred to the ejection evaluation device, and the number of nozzles from which ink was normally ejected was confirmed. Continuous ejection was performed for 30 minutes under the same conditions, and the number of nozzles from which ink was normally ejected after 30 minutes was reconfirmed. The continuous ejection property (%) was calculated by the following formula to evaluate the continuous ejection property. Continuous dischargeability (%) = [(number of nozzles discharging normally after 30 minutes / number of nozzles discharging normally at the beginning)] x 100 The higher the continuous dischargeability (%), the better the ink is considered to be. A value of 90% or more is considered to be practically usable.

[0088] (2) Evaluation of image density An image was formed on A4-size high-quality plain paper (form paper, product name: NPi Form Next-IJ70, manufactured by Nippon Paper Industries Co., Ltd.) using a water-based ink by the following inkjet recording method. (Inkjet recording method) In an environment of temperature 25±1°C and relative humidity 30±5%, a printing evaluation device (manufactured by Tritec Co., Ltd.) equipped with an inkjet head (manufactured by Kyocera Corporation, product name: KJ4B-HD06MHG-STDV, piezo type) was filled with water-based ink. The head voltage was set to 26V, frequency to 10kHz, suitable amount of ejected liquid to 12pl, head temperature to 32°C, resolution to 600dpi, number of flushings before ejection to 200, and negative pressure to -4.0kPa, and the recording medium was fixed to the conveying table under reduced pressure so that the longitudinal direction of the recording medium was the same as the conveying direction. A printing command was transferred to the printing evaluation device, a solid image with a duty of 100% was printed, and the paper was left to stand for 24 hours after printing, and the image density was measured using a spectrophotometer (manufactured by Sakata Inx Engineering Co., Ltd., product name: Spectroeye). The higher the image density, the better the image fastness is judged to be, and a value of 1.1 or more is practically usable.

[0089] [Table 4]

[0090] From Table 4, it can be seen that the water-based inks obtained in the Examples have excellent continuous ejection properties and can provide recorded matter with excellent image density, compared to the water-based inks obtained in the Comparative Examples.

Claims

1. 1. A water-based ink for ink-jet printing, comprising: polymer particles containing a pigment dispersed with a polymer dispersant (A); polymer particles containing a wax dispersed with a polymer dispersant (B); and an organic solvent, The polymer constituting the wax-containing polymer particles is crosslinked, the acid value of the polymer constituting the wax-containing polymer particles is 20 mgKOH / g or more and 110 mgKOH / g or less; The water-based ink for ink-jet printing, wherein the wax has a melting point of 80° C. or higher.

2. A water-based ink for ink-jet recording, comprising polymer particles containing a pigment dispersed with a polymer dispersant (A), polymer particles containing a wax dispersed with a polymer dispersant (B), and an organic solvent, the polymer constituting the pigment-containing polymer particles is crosslinked, the acid value of the polymer constituting the wax-containing polymer particles is 20 mgKOH / g or more and 110 mgKOH / g or less; The water-based ink for ink-jet printing, wherein the wax has a melting point of 80° C. or higher.

3. 3. The water-based ink for ink-jet printing according to claim 1, wherein a difference between an acid value of the polymer constituting the pigment-containing polymer particles and an acid value of the polymer constituting the wax-containing polymer particles is within 20 mgKOH / g.

4. 4. The water-based ink for ink-jet printing according to claim 1, wherein the acid value of the polymer constituting the pigment-containing polymer particles is from 50 mgKOH / g to 200 mgKOH / g.

5. 5. The water-based ink for ink-jet printing according to claim 1, wherein both the polymer constituting the pigment-containing polymer particles and the polymer constituting the wax-containing polymer particles are crosslinked.

6. 6. The water-based ink for ink-jet printing according to claim 1, wherein the wax is a polyolefin wax.

7. 7. The water-based ink for ink-jet printing according to claim 1, wherein the organic solvent is a polyhydric alcohol.

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