Aqueous ink for inkjet recording

Abstract

To provide a water-based ink for inkjet recording that can form a recorded material having superior gloss even on a recording medium such as mat paper, and an inkjet recording method.SOLUTION: The present invention provides [1] a water-based ink for inkjet recording containing a pigment and a polymer emulsion, the polymer emulsion containing crosslinked polymer particles that are crosslinked with polyalkylene glycol diglycidyl ether and [2] an inkjet recording method for performing recording onto mat paper using the water-based ink.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an aqueous ink for inkjet recording and an inkjet recording method.

Background Art

[0002] The inkjet recording method is a recording method in which ink droplets are directly ejected from fine nozzles and adhered to a recording medium to obtain printed matter or the like on which characters and images are recorded. This method has many advantages such as being easy to achieve full color and being inexpensive, being able to use plain paper as a recording medium, and being non-contact with the recording medium, so it has become extremely popular. In particular, from the viewpoints of weather resistance and water resistance of the recorded matter, those using pigments as colorants have become the mainstream. Since pigment particles are dispersed in the ink liquid in pigment ink, when the ink adheres to the recording medium and then dries, when moisture, organic solvents, etc. evaporate, the stable dispersion system collapses and pigment aggregation easily occurs. When the aggregated pigments precipitate on the recording medium, there is a problem that the smoothness of the surface is lost, resulting in a decrease in glossiness and deterioration of the recorded image.

[0003] On the other hand, in order to achieve the color tone and texture assumed by users, various recording media with different surface characteristics are used. As recording media, plain paper, coated paper, etc. are widely used, and for coated paper that is strongly required to have high image quality and high quality, various textures such as glossy paper with a mirror surface having excellent glossiness and matte paper with a dull finish are used. Here, when performing inkjet recording using pigment ink, the glossiness can be adjusted by appropriately changing the recording conditions according to the surface characteristics of the recording medium to be used, but the range is limited, and changing the recording conditions every time the type of recording medium is changed has an adverse effect on productivity. Therefore, there is a demand for an inkjet recording ink with high versatility regardless of the type of recording medium such as matte paper, and various proposals have been made.

[0004] For example, Patent Document 1 discloses an aqueous ink containing water-insoluble crosslinked polymer particles (A) containing a pigment and a polymer emulsion (B), wherein the crosslinked polymer constituting the crosslinked polymer particles (A) is a polymer having a structural unit derived from a carboxylic acid monomer having an acid value of 200 mgKOH / g or more and a structural unit derived from a hydrophobic monomer, which is crosslinked with an epoxy compound, and the polymer constituting the polymer emulsion (B) contains a structural unit derived from a carboxylic acid monomer and a structural unit derived from a hydrophobic monomer.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Mat paper is widely used for papers such as pamphlets, posters, catalogs, and business cards. Mat paper is paper with a matte coating on the surface, which has the advantages of suppressing the glossiness, being easy to read characters, and having a crispy texture. Also, mat paper has the merit that the ink adheres well, the color reproducibility is high, and when using both characters and photos, the photo does not float unnaturally but forms a well-balanced and calm atmosphere. However, there is a desire to increase the gloss of the printed image part as much as possible even for mat paper. The aqueous inks such as those in Patent Document 1 have insufficient glossiness of the images obtained by inkjet recording on mat paper or the like and cannot meet the above-mentioned desire. An object of the present invention is to provide an aqueous ink for inkjet recording capable of obtaining a recording with excellent glossiness even on a recording medium such as mat paper, and an inkjet recording method using the aqueous ink.

Means for Solving the Problems

[0007] The inventors have found that an aqueous ink containing a pigment and a polymer emulsion containing crosslinked polymer particles having a polyalkylene oxide chain can solve the above problems. That is, the present invention provides the following [1] and [2]. [1] An aqueous inkjet recording ink containing a pigment and a polymer emulsion, wherein the polymer emulsion contains crosslinked polymer particles crosslinked with polyalkylene glycol diglycidyl ether. [2] An inkjet recording method for recording on matte paper using the aqueous ink according to [1]. [Advantages of the Invention]

[0008] According to the present invention, it is possible to provide an aqueous inkjet recording ink capable of obtaining a recording having excellent glossiness even on a recording medium such as matte paper, and an inkjet recording method using the aqueous ink. [Embodiments for Carrying Out the Invention]

[0009] [Aqueous Inkjet Recording Ink] The aqueous inkjet recording ink of the present invention (hereinafter also referred to as "the ink of the present invention") is an aqueous ink containing a pigment and a polymer emulsion, and the polymer emulsion is characterized by containing crosslinked polymer particles crosslinked with polyalkylene glycol diglycidyl ether. Here, "aqueous" means that water occupies the largest proportion in the medium for dispersing the pigment. Further, "recording" is a concept including printing and printing for recording characters and images.

[0010] According to the ink of the present invention, when inkjet recording is performed on a recording medium such as matte paper, a recording having excellent glossiness can be obtained. The reason is not clear, but it is considered as follows. When aqueous ink is ejected onto a recording medium in inkjet recording, the moisture in the ink on the recording medium evaporates, and the concentrated ink becomes a hydrophobic system containing a large amount of organic solvent. Here, since the ink of the present invention contains a polymer emulsion containing crosslinked polymer particles crosslinked with polyalkylene glycol diglycidyl ether, there is a polymer having a polyalkylene oxide chain. The polyalkylene oxide chain is localized on the outermost shell of the polymer emulsion particles, and since water is solvated with the polyalkylene oxide chain, the steric repulsive force suppresses the aggregation of the pigment and the polymer particles. In addition, the polyalkylene oxide chain has an affinity for both water and the organic solvent in the ink, and even in the ink in which water has evaporated and concentrated, the steric repulsive force due to solvation is maintained, suppressing the aggregation of the pigment and the polymer particles. As a result, when recording on matte paper or the like, in the conventional ink, during the drying process on the recording surface, the pigment particles and the polymer particles immediately aggregate and solidify quickly, whereas in the ink of the present invention, aggregation is less likely to occur, resulting in a time margin for smoothing by the gravity of the polymer particles on the recording surface, improving the effect of filling the irregularities on the surface of the recording medium such as matte paper, forming a uniform polymer film on the recording medium, and it is considered that the glossiness is also improved for the recording medium such as matte paper.

[0011] <Pigment> The pigment used in the present invention may be either an inorganic pigment or an organic pigment. Examples of the inorganic pigment include carbon black, metal oxides, etc. In black ink, carbon black is preferred. Examples of carbon black include furnace black, lamp black, acetylene black, channel black, etc. In white ink, metal oxides such as titanium dioxide, zinc oxide, silica, alumina, magnesium oxide, etc. are mentioned. Examples of the organic pigment include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, quinophthalone pigments, and the like. The hue is not particularly limited. In the case of achromatic inks, achromatic pigments such as white, black, and gray can be used, and in the case of chromatic inks, 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.

[0012] Preferable forms of the pigment used in the ink of the present invention include (i) a pigment capable of maintaining a dispersed state without a dispersant, that is, a self-dispersing pigment form, (ii) a form of pigment particles obtained by dispersing the pigment with a surfactant, and (iii) a form of polymer particles containing the pigment. Among these, from the viewpoint of improving the glossiness of the obtained recording, the form of polymer particles containing the pigment is preferable. Here, the "polymer particles containing a pigment" (hereinafter also referred to as "pigment-containing polymer particles") means particles in which the polymer contains the pigment, particles in which a part of the pigment is exposed on the surface of the particles composed of the polymer and the pigment, particles in which the polymer is adsorbed on a part of the pigment, and mixtures thereof. Among these, particles in which the polymer contains the pigment are more preferable.

[0013] [Pigment-containing polymer particles] The polymer (hereinafter also referred to as "polymer a") constituting the pigment-containing polymer particles is not particularly limited as long as it has at least pigment dispersibility. Examples of the polymer a include vinyl resins obtained by addition polymerization of vinyl monomers, polyester resins, polyurethane resins, and the like. Among these, vinyl resins are preferable from the viewpoints of dispersion stability and storage stability of the pigment. The polymer a may be appropriately synthesized or a commercially available product may be used. The pigment-containing polymer particles are more preferably crosslinked polymer particles containing a pigment (hereinafter also referred to as "pigment-containing crosslinked polymer particles") obtained by further crosslinking polymer particles containing a pigment with a crosslinking agent.

[0014] The polymer a before crosslinking may be a water-soluble polymer or a water-insoluble polymer, but a water-insoluble polymer is more preferable. Even if the polymer used is a water-soluble polymer, the polymer becomes a water-insoluble polymer by crosslinking treatment. In this specification, "water-insoluble" of a polymer means that when a polymer dried at 105 °C for 2 hours to reach a constant weight is dissolved in 100 g of water at 25 °C, the dissolved amount is less than 10 g. When the polymer is an anionic polymer, the dissolved amount is the dissolved amount when the anionic groups of the polymer are 100% neutralized with sodium hydroxide.

[0015] [Polymer a] When the polymer a is a vinyl-based resin, the polymer a preferably contains a structural unit derived from an (a-1) ionic monomer, more preferably further contains a structural unit derived from an (a-2) hydrophobic monomer and / or an (a-3) nonionic monomer, and more preferably contains a structural unit derived from an (a-1) ionic monomer and a structural unit derived from an (a-2) hydrophobic monomer.

[0016] [(a-1) Ionic monomer] As the (a-1) ionic monomer, an anionic monomer is preferable, and examples thereof include carboxylic acid monomers and sulfonic acid monomers, and carboxylic acid monomers are more preferable. Examples of the carboxylic acid monomer include one or more selected from (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid, and preferably (meth)acrylic acid. "(Meth)acrylic acid" means at least one selected from acrylic acid and methacrylic acid.

[0017] [(a-2) Hydrophobic monomer] (a-2) The "hydrophobicity" of the hydrophobic monomer means that when the monomer is dissolved until saturated in 100 g of ion-exchanged water at 25°C, the dissolved amount is less than 10 g. (a-2) Specific examples of the hydrophobic monomer include those described in paragraphs

[0020] to

[0022] of JP-A-2018-83938. Among these, one or more selected from alkyl (meth)acrylates having an alkyl group with 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms, and aromatic group-containing monomers having an aromatic group with 6 to 22 carbon atoms, preferably 6 to 18 carbon atoms, are preferred, and one or more selected from ethyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, styrene, α-methylstyrene, and benzyl (meth)acrylate are more preferred.

[0018] [(a-3) Nonionic monomer] (a-3) The nonionic monomer is a monomer having a high affinity for water and water-soluble organic solvents, and is, for example, a monomer containing a hydroxyl group or a polyalkylene glycol chain. (a-3) Specific examples of the component include those described in paragraph

[0018] of JP-A-2018-83938. 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 preferred. The above components (a-1) to (a-3) can be used by individually using the monomer components contained in each component or by mixing two or more thereof.

[0019] (Content of each structural unit in the vinyl resin) The content of the structural units derived from the components (a-1) to (a-3) in the vinyl resin is as follows from the viewpoint of improving the glossiness of the obtained recording. The content of component (a-1) is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more, and is preferably 45% by mass or less, more preferably 40% by mass or less, still more preferably 35% by mass or less. The content of component (a-2) is preferably 35% by mass or more, more preferably 40% by mass or more, still more preferably 45% by mass or more, and is preferably 90% by mass or less, more preferably 85% by mass or less, still more preferably 80% by mass or less. When component (a-3) is contained, its content is preferably 30% by mass or less, more preferably 20% by mass or less, still more preferably 5% by mass or less. The mass ratio of component (a-1) to component (a-2) [(a-1) component / (a-2) component] is preferably 0.05 or more, more preferably 0.1 or more, and is preferably 0.8 or less, more preferably 0.6 or less.

[0020] (Production of Polymer a) Polymer a can be produced by copolymerizing a mixture of the above monomer components (a-1) to (a-3) by a known polymerization method. As the polymerization method, solution polymerization is preferred. There is no limitation on the solvent used in the solution polymerization method, but polar solvents such as water, aliphatic alcohols, ketones, ethers, and esters are preferred, and water, methanol, ethanol, acetone, methyl ethyl ketone, etc. are more preferred. During the polymerization, a polymerization initiator or 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, etc., and examples of the polymerization chain transfer agent include mercaptans, etc. The polymerization temperature varies depending on the type of polymerization initiator, monomer, solvent, etc. used, but is preferably 40°C or more, more preferably 50°C or more, and is preferably 95°C or less, more preferably 90°C or less. The polymerization atmosphere is preferably a nitrogen gas or inert gas atmosphere. The vinyl resin is preferably neutralized with a neutralizing agent as described later.

[0021] From the viewpoint of improving the glossiness of the resulting recording material, the weight average molecular weight of polymer a is preferably 5,000 or more, more preferably 10,000 or more, still more preferably 15,000 or more, and preferably 80,000 or less, more preferably 60,000 or less, still more preferably 40,000 or less. The weight average molecular weight of the polymer is measured by the method described in the examples. From the viewpoint of improving the glossiness of the resulting recording material, the acid value of polymer a is preferably 50 mgKOH / g or more, more preferably 100 mgKOH / g or more, still more preferably 150 mgKOH / g or more, and preferably 350 mgKOH / g or less, more preferably 300 mgKOH / g or less, still more preferably 250 mgKOH / g or less. The acid value of the polymer is measured by the method described in the examples.

[0022] 〔Production of pigment-containing polymer particles〕 The pigment-containing polymer particles can be efficiently produced by a method having the following steps 1 and 2 as a pigment aqueous dispersion and, if necessary, further step 3. Step 1: A step of subjecting a pigment mixture containing a pigment, polymer a, an organic solvent, and water to a dispersion treatment to obtain a dispersion-treated product Step 2: A step of removing the organic solvent from the dispersion-treated product obtained in Step 1 to obtain an aqueous dispersion of pigment-containing polymer particles A (hereinafter, also referred to as "pigment aqueous dispersion (i)") Step 3: A step of adding a crosslinking agent to the pigment aqueous dispersion (i) obtained in Step 2 to crosslink the pigment-containing polymer particles to obtain an aqueous dispersion (I) of pigment-containing crosslinked polymer particles (hereinafter, also referred to as "pigment aqueous dispersion (I)") The pigment-containing polymer particles according to the present invention also include the pigment-containing crosslinked polymer particles obtained in Step 3.

[0023] (Step 1) The pigment mixture in Step 1 is preferably obtained by dissolving Polymer a in an organic solvent, adding a pigment, water, and, if necessary, a neutralizing agent, a surfactant, etc. to the obtained organic solvent solution, and mixing them to obtain an oil-in-water dispersion. There is no limitation on the organic solvent used in Step 1, but ketones, ethers, esters, aliphatic alcohols having 1 to 3 carbon atoms, etc. are preferable. From the viewpoint of improving the wettability to the pigment and the adsorptivity of Polymer a to the pigment, ketones having 4 to 8 carbon atoms are more preferable, and methyl ethyl ketone is even more preferable. When a vinyl resin is synthesized as Polymer a by solution polymerization, the solvent used in the polymerization may be used as it is.

[0024] When Polymer a has an acid group, at least a part of the acid group is preferably neutralized using a neutralizing agent. It is considered that this increases the charge repulsive force generated after neutralization, suppresses the aggregation of pigment particles in the aqueous ink, and improves the dispersion stability of the pigment. When neutralizing, it is preferable to neutralize so that the pH becomes 7 or more and 11 or less. Examples of the neutralizing agent include bases such as sodium hydroxide, potassium hydroxide, ammonia, and various amines, and sodium hydroxide and ammonia are preferable. Also, Polymer a may be neutralized in advance. From the viewpoint of improving dispersion stability, the equivalent amount of the neutralizing agent used is preferably 20 mol% or more, more preferably 30 mol% or more, still more preferably 40 mol% or more, and preferably 120 mol% or less, more preferably 100 mol% or less, still more preferably 80 mol% or less. Here, when the equivalent amount of the neutralizing agent used is calculated with Polymer a before neutralization as "Polymer a'", it can be obtained by the following formula. Equivalent amount of neutralizing agent used (mol%) = [{mass of neutralizing agent added (g) / equivalent of neutralizing agent} / [{acid value of Polymer a' (mgKOH / g) × mass of Polymer a' (g)} / (56×1,000)]]×100

[0025] In the dispersion process in Step 1, the pigment particles can be atomized to the desired particle size only by this dispersion due to shear stress. However, from the viewpoint of obtaining a uniform pigment aqueous dispersion, it is preferable to pre-disperse the pigment mixture and then further perform this dispersion. As the disperser used for pre-dispersion, a generally used mixing and stirring device such as an anchor blade or a dispersing blade can be used. Examples of the means for applying shear stress used for this dispersion include kneaders such as a roll mill and a kneader, high-pressure homogenizers such as a microfluidizer, and media-type dispersers such as a paint shaker and a bead mill. Among these, from the viewpoint of reducing the particle size of the pigment, it is preferable to use a high-pressure homogenizer or a bead mill. When performing the dispersion process using a high-pressure homogenizer, the average particle size of the pigment particles in the pigment aqueous dispersion can be adjusted by controlling the processing pressure and the number of passes. From the viewpoints of productivity and economy, the processing 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.

[0026] (Step 2) The removal of the organic solvent in Step 2 can be performed by a known method. Although it is preferable that the organic solvent in the obtained pigment aqueous dispersion (i) is substantially removed, it may remain as long as the object of the present invention is not impaired. Also, for the purpose of removing coarse particles and the like, after centrifuging the aqueous dispersion from which the organic solvent has been removed, the liquid layer portion is filtered through a filter or the like, and what passes through the filter or the like is preferably obtained as the pigment aqueous dispersion (i).

[0027] (Step 3) Step 3 is optional. A crosslinking agent is added to the pigment aqueous dispersion (i) obtained in Step 2 to crosslink a part of the carboxy groups of polymer a constituting the pigment-containing polymer particles, and a crosslinked structure is formed in the surface layer portion of the pigment-containing polymer particles to obtain a pigment aqueous dispersion (I) of pigment-containing crosslinked polymer particles. As a result, the polymer formed by crosslinking polymer a is strongly adsorbed or immobilized on the pigment surface, aggregation of the pigment is suppressed, and as a result, it is considered that the dispersion stability of the resulting ink is further improved.

[0028] As the crosslinking agent, a polyfunctional epoxy compound having two or more epoxy groups in the molecule is preferable, a compound having two or more glycidyl ether groups is more preferable, and a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group having 3 to 4 carbon atoms is still more preferable. The epoxy equivalent (g / eq) of the crosslinking agent is preferably 90 or more, more preferably 100 or more, and preferably 300 or less, more preferably 200 or less. Preferable 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.

[0029] From the viewpoint of improving the glossiness of the obtained recording, the degree of crosslinking in Step 3 is the ratio of the molar equivalent number of the crosslinkable functional groups of the crosslinking agent to the molar equivalent number of the carboxy groups of polymer a, preferably 8 mol% or more, more preferably 10 mol% or more, and preferably 70 mol% or less, more preferably 50 mol% or less. From the viewpoint of the crosslinking reaction efficiency, the temperature of the crosslinking treatment is preferably 40°C or higher, more preferably 50°C or higher, and preferably 90°C or lower, more preferably 85°C or lower. The acid value after crosslinking of polymer a is preferably 40 mgKOH / g or more, more preferably 60 mgKOH / g or more, still more preferably 80 mgKOH / g or more, and is preferably 250 mgKOH / g or less, more preferably 200 mgKOH / g or less, still more preferably 150 mgKOH / g or less.

[0030] From the viewpoint of improving the dispersion stability of the pigment dispersion, the non-volatile component concentration (solid content concentration) of the obtained pigment 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 35% by mass or less. The solid content concentration is measured by the method described in the examples. From the viewpoint of dispersion stability, the content of the pigment in the pigment dispersion (I) is preferably 7% by mass or more, more preferably 10% by mass or more, and is preferably 30% by mass or less, more preferably 20% by mass or less. From the viewpoint of dispersion stability, the content of the (crosslinked) polymer in the pigment dispersion (I) is preferably 4% by mass or more, more preferably 5% by mass or more, and is preferably 15% by mass or less, more preferably 10% by mass or less. The mass ratio of the (crosslinked) polymer to the pigment [(crosslinked) polymer / pigment] constituting the pigment-containing (crosslinked) polymer particles in the pigment dispersion (I) is preferably 0.1 or more, more preferably 0.2 or more, and is preferably 1.2 or less, more preferably 0.8 or less. From the viewpoint of improving the glossiness of the obtained recording, the average particle diameter of the pigment-containing (crosslinked) polymer particles is preferably 50 nm or more, more preferably 80 nm or more, and is preferably 300 nm or less, more preferably 200 nm or less. The average particle diameter is measured by the method described in the examples.

[0031] <Polymer emulsion> The polymer emulsion is used to fill the voids of the unevenness on the surface of the recording medium and improve the smoothness and glossiness as the ink dries after aqueous ink ejection. In the present invention, the polymer emulsion contains crosslinked polymer particles crosslinked with polyalkylene glycol diglycidyl ether. That is, the crosslinked polymer particles crosslinked with polyalkylene glycol diglycidyl ether are composed of a constituent component derived from a polymer (hereinafter also referred to as "polymer b") and a constituent component derived from polyalkylene glycol diglycidyl ether. Specific examples of polymer b include vinyl resins, urethane resins, polyester resins, etc. Among these, vinyl resins and urethane resins are preferred, and vinyl resins are more preferred. The vinyl resin preferably contains a structural unit derived from an ionic monomer (b-1) and a structural unit derived from a hydrophobic monomer (b-2), and may further contain a structural unit derived from a nonionic monomer (b-3). Specific examples and preferred examples of the above components (b-1) to (b-3) are the same as the components (a-1) to (a-3) described in the column of the polymer (polymer a) constituting the pigment-containing polymer particles.

[0032] Also, the production method of the vinyl resin is the same as the production method of the polymer a. When the polymer emulsion is produced by emulsion polymerization, since carboxyl groups are present on the surface of the polymer particles, the pH tends to be on the acidic side, and viscosity increase and aggregation are likely to occur. Therefore, neutralization with a basic substance such as sodium hydroxide is usually carried out. The addition amount of the neutralizing agent is appropriately determined so that the pH of the polymer emulsion is in the range of 7.5 to 9.5, preferably in the range of 7.5 to 8.5. From the viewpoints of reaction completion and economy, the reaction temperature is preferably 40°C or higher, more preferably 50°C or higher, and preferably 95°C or lower, more preferably 90°C or lower.

[0033] Examples of the urethane resin as polymer b include polyester-based urethane resins having an ester bond, polycarbonate-based urethane resins having a carbonate bond, polyether-based urethane resins having an ether bond, etc. Among them, polyester-based urethane resins are preferred. The polyester-based urethane resin means a urethane resin obtained by reacting a polyester polyol with a polyisocyanate. For the polyester-based urethane resin, a synthesized one may be used, or a commercially available product may be used. As a method for producing a polyester-based urethane resin, for example, a polyol containing a polyester polyol is reacted with a polyisocyanate to produce an isocyanate-terminated urethane prepolymer, and then the anionic group in the isocyanate-terminated urethane prepolymer is neutralized with a neutralizing agent such as ammonia or an organic amine, and then further reacted with a polyamine (chain extender) and a reaction terminator as needed. Examples of commercially available products of polyester-based urethane resins include BYRON UR-3500, UR-3600, etc. manufactured by Toyobo Co., Ltd., and NeoRez R-9660, R-2170, etc. manufactured by DSM Coating Resins.

[0034] From the viewpoint of improving the glossiness of the obtained recording material, the acid value of polymer b is preferably 5 mgKOH / g or more, more preferably 20 mgKOH / g or more, still more preferably 35 mgKOH / g or more, and even more preferably 90 mgKOH / g or more, and is preferably 250 mgKOH / g or less, more preferably 200 mgKOH / g or less. When polymer b is a vinyl-based resin, from the viewpoint of improving the glossiness of the obtained recording material, the acid value is preferably 50 mgKOH / g or more, more preferably 90 mgKOH / g or more, still more preferably 100 mgKOH / g or more, and even more preferably 180 mgKOH / g or more, and is preferably 250 mgKOH / g or less, more preferably 230 mgKOH / g or less, and still more preferably 200 mgKOH / g or less. When polymer b is a urethane resin, from the viewpoint of improving the glossiness of the obtained recording material, the acid value is preferably 10 mgKOH / g or more, more preferably 20 mgKOH / g or more, still more preferably 30 mgKOH / g or more, and is preferably 100 mgKOH / g or less, more preferably 50 mgKOH / g or less, and still more preferably 40 mgKOH / g or less.

[0035] The polyalkylene glycol diglycidyl ether as the crosslinking agent may be any diglycidyl ether capable of introducing a polyalkylene oxide chain into polymer b, but those containing an alkylene group having preferably 2 or more and 8 or less carbon atoms, more preferably 2 or more and 4 or less carbon atoms are preferred. Also, from the viewpoints of hydrophilizing and stabilizing the polymer emulsion, imparting flexibility, and forming a smooth polymer coating film on the recording medium, the number of repeating units n of the alkylene oxide group is preferably 2 or more and 30 or less, more preferably 4 or more and 20 or less, still more preferably 6 or more and 15 or less, and even more preferably 8 or more and 12 or less.

[0036] From the same viewpoints as above, the epoxy equivalent (g / eq) of the polyalkylene glycol diglycidyl ether is preferably 200 g / eq or more, more preferably 215 g / eq or more, still more preferably 250 g / eq or more, and even more preferably 270 g / eq or more, and is preferably 600 g / eq or less, more preferably 560 g / eq or less, still more preferably 530 g / eq or less, even more preferably 500 g / eq or less, and even more preferably 350 g / eq or less. Specific examples of the polyalkylene glycol diglycidyl ether preferably include one or more selected from polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and polytetramethylene glycol diglycidyl ether, etc., and more preferably one or more selected from polyethylene glycol diglycidyl ether and polypropylene glycol diglycidyl ether.

[0037] Examples of commercially available polyalkylene glycol diglycidyl ethers include polyethylene glycol diglycidyl ethers manufactured by Nagase ChemteX Corporation, trade names: EX-821 (n = 4, epoxy equivalent: 185), EX-830 (n = 9, epoxy equivalent: 268), EX-841 (n = 14, epoxy equivalent: 372), EX-861 (n = 22, epoxy equivalent: 551), polypropylene glycol diglycidyl ethers, trade name: EX-931 (n = 11, epoxy equivalent: 471), polyethylene glycol diglycidyl ethers manufactured by Kyoeisha Chemical Co., Ltd., trade name: Epolite 200E (n = 4, epoxy equivalent: 215), Epolite 400E, n = 9, epoxy equivalent 290), and the like.

[0038] The mass ratio of polyalkylene glycol diglycidyl ether (crosslinking agent) to the polymer constituting the polymer emulsion (crosslinking agent / polymer) is preferably 0.05 or more, more preferably 0.1 or more, still more preferably 0.2 or more, even more preferably 0.5 or more, and preferably 1.5 or less, more preferably 1.2 or less, still more preferably 1.1 or less, even more preferably 1 or less. From the viewpoint of the crosslinking reaction efficiency, the temperature for crosslinking the polymer emulsion is preferably 40°C or higher, more preferably 50°C or higher, and preferably 90°C or lower, more preferably 85°C or lower.

[0039] From the viewpoint of improving the glossiness of the obtained recording material, the degree of crosslinking of the polymer constituting the polymer emulsion is preferably 8 mol% or more, more preferably 10 mol% or more, still more preferably 15 mol% or more, even more preferably 30 mol% or more, even more preferably 40 mol% or more, and preferably 90 mol% or less, more preferably 85 mol% or less, still more preferably 80 mol% or less, even more preferably 60 mol% or less. The degree of crosslinking is the apparent degree of crosslinking calculated from the acid value of the polymer and the equivalent of the epoxy group of the crosslinking agent. That is, the degree of crosslinking is "the molar equivalent number of epoxy groups of the epoxy compound / the molar equivalent number of carboxyl groups of the polymer before crosslinking".

[0040] From the viewpoint of improving the glossiness of the resulting recording material, the acid value of the crosslinked polymer after crosslinking that constitutes the polymer emulsion is preferably 4 mgKOH / g or more, more preferably 8 mgKOH / g or more, and preferably 180 mgKOH / g or less, more preferably 150 mgKOH / g or less. When the crosslinked polymer is a vinyl resin, its acid value is preferably 8 mgKOH / g or more, more preferably 15 mgKOH / g or more, still more preferably 20 mgKOH / g or more, even more preferably 45 mgKOH / g or more, and preferably 180 mgKOH / g or less, more preferably 160 mgKOH / g or less, still more preferably 140 mgKOH / g or less, even more preferably 120 mgKOH / g or less, even more preferably 100 mgKOH / g or less, even more preferably 80 mgKOH / g or less. When the crosslinked polymer is a urethane resin, its acid value is preferably 4 mgKOH / g or more, more preferably 6 mgKOH / g or more, and preferably 60 mgKOH / g or less, more preferably 40 mgKOH / g or less, still more preferably 30 mgKOH / g or less.

[0041] From the viewpoint of improving the glossiness of the resulting recording material, the average particle diameter of the crosslinked polymer particles in the polymer emulsion is preferably 30 nm or more, more preferably 50 nm or more, still more preferably 70 nm or more, and preferably 200 nm or less, more preferably 150 nm or less, still more preferably 120 nm or less. The average particle diameter of the crosslinked polymer particles is measured by the method described in the examples.

[0042] [Method for producing the ink of the present invention] The ink of the present invention can be produced by mixing an aqueous pigment dispersion containing pigment-containing (crosslinked) polymer particles obtained by the above method, the polymer emulsion, an organic solvent, water, and, if necessary, various additives such as a surfactant. There is no particular limitation on the mixing method of the above components.

[0043] From the viewpoint of improving the storage stability of the aqueous ink, etc., the organic solvent preferably has a boiling point of 110°C or higher, preferably 150°C or higher, and preferably 240°C or lower, more preferably 220°C or lower, and preferably contains one or more organic solvents. Specific examples of the organic solvent include polyhydric alcohols, polyhydric alcohol alkyl ethers, nitrogen-containing heterocyclic compounds, amides, amines, sulfur-containing compounds, etc. Among these, one or more selected from polyhydric alcohols and polyhydric alcohol alkyl ethers are preferred, and one or more selected from ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, trimethylolpropane, and diethylene glycol diethyl ether are more preferred, and one or more selected from propylene glycol, glycerin, triethylene glycol, and trimethylolpropane are even more preferred. Examples of the surfactant include nonionic surfactants, anionic surfactants, amphoteric surfactants, silicone-based surfactants, fluorine-based surfactants, etc., and nonionic surfactants are more preferred. Examples of the nonionic surfactant include, for example, acetylene glycol-based surfactants, polyoxyalkylene alkyl ether type surfactants, polyhydric alcohol type surfactants, fatty acid alkanolamides, etc., and acetylene glycol-based surfactants and polyoxyalkylene alkyl ether type surfactants are more preferred. Other additives used in the method for producing the ink of the present invention include humectants, wetting agents, penetrants, viscosity modifiers, defoamers, preservatives, fungicides, rust preventives, etc.

[0044] (Content of each component in the ink of the present invention) The content of each component in the ink of the present invention is as follows from the viewpoint of improving the glossiness of the obtained recording material, etc. (Content of pigment) From the perspective of improving the printing density of the aqueous ink, the pigment content in the ink of the present invention is preferably 1% by mass or more, more preferably 2% by mass or more, still more preferably 3% by mass or more, and from the perspective of improving the storage stability, it is preferably 15% by mass or less, more preferably 10% by mass or less, still more preferably 8% by mass or less. (Content of (crosslinked) polymer particles containing pigment) The content of (crosslinked) polymer particles containing pigment in the ink of the present invention, in total with the pigment and the (crosslinked) polymer, is preferably 2% by mass or more, more preferably 4% by mass or more, still more preferably 5% by mass or more, and is preferably 17% by mass or less, more preferably 12% by mass or less, still more preferably 10% by mass or less.

[0045] (Content of polymer emulsion) The polymer emulsion is preferably 2% by mass or more, more preferably 4% by mass or more, still more preferably 6% by mass or more as a solid content in the aqueous ink, and is preferably 12% by mass or less, more preferably 10% by mass or less, still more preferably 9% by mass or less. The mass ratio (pigment / polymer) of the pigment and the polymer (the total amount of polymer a constituting the pigment-containing polymer particles and polymer b constituting the polymer emulsion) in the ink of the present invention is preferably 0.1 or more, more preferably 0.2 or more, still more preferably 0.3 or more from the perspective of improving the glossiness of the obtained recording, and is preferably 2 or less, more preferably 1 or less, still more preferably 0.8 or less. The mass ratio [pigment-containing (crosslinked) polymer particles / crosslinked polymer particles] of the (crosslinked) polymer particles containing pigment in the ink of the present invention and the crosslinked polymer particles (solid content of the polymer emulsion) in the polymer emulsion is preferably 0.1 or more, more preferably 0.15 or more, still more preferably 0.18 or more from the perspective of improving the glossiness of the obtained recording, and is preferably 1 or less, more preferably 0.8 or less, still more preferably 0.6 or less, even more preferably 0.4 or less.

[0046] (Content of organic solvent) From the viewpoint of improving the ejection stability of the ink, the content of the organic solvent in the ink of the present invention is preferably 5% by mass or more, more preferably 8% by mass or more, still more preferably 10% by mass or more, and preferably 50% by mass or less, more preferably 30% by mass or less, still more preferably 20% by mass or less. (Water content) From the viewpoint of improving the ejection stability and the like, the water content in the ink of the present invention is preferably 40% by mass or more, more preferably 50% by mass or more, still more preferably 60% by mass or more, and preferably 85% by mass or less, more preferably 80% by mass or less, still more preferably 75% by mass or less.

[0047] (Physical properties of the ink of the present invention) From the viewpoint of improving the storage stability of the ink, the viscosity of the ink of the present invention at 32 °C is preferably 2 mPa·s or more, more preferably 4 mPa·s or more, and preferably 12 mPa·s or less, more preferably 8 mPa·s or less. From the viewpoint of improving the storage stability of the ink, the pH of the ink of the present invention is preferably 7 or more, more preferably 7.5 or more. Also, from the viewpoints of member resistance and skin irritation, the pH is preferably 11 or less, more preferably 10 or less.

[0048] [Inkjet recording method] The inkjet recording method of the present invention is characterized by recording on matte paper using the ink of the present invention. The ink of the present invention can be loaded into a known inkjet recording apparatus, ejected as ink droplets onto a recording medium, and an image or the like excellent in glossiness can be recorded. Examples of the inkjet recording apparatus include thermal and piezo types, but it is more preferably used as an aqueous ink for piezo-type inkjet recording. From the viewpoint of the efficiency of high-speed recording and the like, the applied voltage of the recording head during inkjet recording is preferably 10 V or more, more preferably 20 V or more, and preferably 40 V or less, more preferably 30 V or less. The temperature inside the recording head is preferably 20°C or higher, more preferably 25°C or higher, and preferably 45°C or lower, more preferably 40°C or lower, from the viewpoint of reducing the viscosity of the ink. The ink of the present invention can be applied to recording papers such as plain paper, coated paper, and resin film. However, in the inkjet recording method of the present invention, coated paper is preferred, and the effects of the present invention are more significantly manifested particularly when recording on matte paper.

Examples

[0049] In the following production examples, preparation examples, examples, and comparative examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified. The measurement methods for each physical property are as follows.

[0050] (1) Measurement of the weight average molecular weight (Mw) of the polymer Using a solution prepared by dissolving phosphoric acid and lithium bromide in N,N-dimethylformamide at concentrations of 60 mmol / L and 50 mmol / L, respectively, as the eluent, gel permeation chromatography [manufactured by Tosoh Corporation, GPC apparatus (HLC-8320GPC), columns manufactured by Tosoh Corporation (TSKgel SuperAWM-H, TSKgel SuperAW3000, TSKgel guardcolumn Super AW-H), flow rate: 0.5 mL / min], a monodisperse polystyrene kit with known molecular weight [manufactured by Tosoh Corporation, PStQuick B (F-550, F-80, F-10, F-1, A-1000), PStQuick C (F-288, F-40, F-4, A-5000, A-500)] was used as the standard substance for measurement. The measurement sample was prepared by mixing 0.1 g of the polymer with 10 mL of the above eluent in a glass vial, stirring at 25°C for 10 hours with a magnetic stirrer, and filtering through a syringe filter (manufactured by Advantec Co., Ltd., DISMIC-13HP, PTFE, 0.2 μm).

[0051] (2) Measurement of the average particle diameter of pigment-containing polymer particles and crosslinked polymer particles Using a laser particle analysis system (manufactured by Otsuka Electronics Co., Ltd., product name: ELS-8000), the particle size was measured by the dynamic light scattering method and calculated by cumulant method analysis. The measurement conditions were a temperature of 25°C, an angle of 90° between the incident light and the detector, and an integration number of 100 times. The refractive index of water (1.333) was input as the refractive index of the dispersion solvent. For the measurement sample, an aqueous dispersion was weighed into a screw tube (manufactured by Maruemu Co., Ltd., No. 5), and water was added so that the solid content concentration became 2×10 -4 mass%, and the mixture was stirred at 25°C for 1 hour using a magnetic stirrer.

[0052] (3) Measurement of acid value of polymer 2 g of the polymer before crosslinking or 2 g of the aqueous dispersion of the polymer after crosslinking was diluted with 50 g of ion-exchanged water, and 3 ml of 0.1 N sodium hydroxide solution was added. Then, 0.1 N hydrochloric acid was gradually added dropwise, and the inflection points of pH were measured at two places. The number of moles of acid calculated from the difference in the amount of 0.1 N hydrochloric acid dropped between the two points corresponded to the number of moles of carboxylic acid in the polymer, and this number of moles was converted to the acid value.

[0053] (4) Measurement of solid content concentration of aqueous dispersion 10.0 g of sodium sulfate that had been made constant in a desiccator was weighed into a 30 mL polypropylene container (φ: 40 mm, height: 30 mm), and about 1.0 g of the sample was added thereto. After mixing, it was weighed, maintained at 105°C for 2 hours to remove the volatile matter, and then 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 mass of the added sample to obtain the solid content concentration.

[0054] Production Example 1 (Preparation of aqueous dispersion of vinyl polymer P1) (1) Production of polymer P1 Into a reaction vessel equipped with a dropping funnel, the monomers shown in the "Initial Charge Monomer Solution" described in Table 1 and an organic solvent (methyl ethyl ketone (MEK)) were put and mixed, and nitrogen gas substitution was performed to obtain the "Initial Charge Monomer Solution". On one hand, the monomers shown in the "dropwise monomer solution" in Table 1, MEK, a polymerization initiator (2,2'-azobis(2,4-dimethylvaleronitrile), manufactured by Fujifilm Wako Pure Chemical Corporation, trade name: V-65), and a polymerization chain transfer agent (2-mercaptoethanol: manufactured by Fujifilm Wako Pure Chemical Corporation, reagent) were mixed to obtain a "dropwise monomer solution", which was placed in a dropping funnel and purged with nitrogen gas. Under a nitrogen atmosphere, the "initial charge monomer solution" in the reaction vessel was maintained at 77 °C while being stirred, and the "dropwise monomer solution" in the dropping funnel was gradually dropped into the reaction vessel over 3 hours. After the dropping was completed, the mixed solution in the reaction vessel was stirred at 77 °C for 0.5 hour. Next, a polymerization initiator solution prepared by dissolving 0.6 part of the polymerization initiator in 27.0 parts of MEK was added to the mixed solution, and aging was carried out by stirring at 77 °C for 1 hour. The preparation, addition, and aging of the polymerization initiator solution were carried out 5 more times. Then, after maintaining the reaction solution in the reaction vessel at 80 °C for 1 hour, the reaction solution in the reaction vessel was transferred to a stainless-steel vat and MEK was distilled off using a vacuum dryer to obtain polymer P1. The weight-average molecular weight of the obtained polymer P1 was 28,700, and the acid value was 200 mgKOH / g. The results are shown in Table 1.

[0055] (2) Preparation of an aqueous dispersion of polymer P1 128.6 parts of the polymer P1 obtained in (1) above was dissolved in 192.9 parts of MEK to obtain a MEK solution of polymer P1 (solid content concentration: 40%). The MEK solution of polymer P1 was charged into a reaction vessel with a volume of 3 L, and while stirring the solution, a mixture of 1091.2 parts of ion-exchanged water and 48.9 parts of a 5N aqueous sodium hydroxide solution (equivalent amount of neutralizing agent used: 45 mol%) was dropped over 2 hours. After the dropping, the contents of the reaction vessel were placed in a 3 L eggplant flask, and using a rotary distillation apparatus (manufactured by Tokyo Rika Kikai Co., Ltd., trade name: Rotary Evaporator N-1000S), at a rotation speed of 50 rpm, in a warm bath adjusted to 32 °C, and held at a pressure of 0.09 MPa for 3 hours to remove the organic solvent. Further, the warm bath was adjusted to 62 °C, the pressure was reduced to 0.07 MPa, and the solution was concentrated until the solid content concentration reached 25% to obtain an aqueous dispersion of polymer P1.

[0056] Production Example 2 (Preparation of Aqueous Dispersion of Vinyl Polymer P2) In Production Example 1(1), a polymer P2 was obtained in the same manner as in Production Example 1, except that the monomer compositions of the initial charge monomer solution and the dropping monomer solution were changed to the amounts shown in Table 1. The weight average molecular weight of the obtained polymer P2 was 20,200, and the acid value was 100 mgKOH / g. Furthermore, in Production Example 1(2), an aqueous dispersion of polymer P2 was obtained in the same manner as in Production Example 1(2), except that the above polymer P2 was used instead of polymer P1, and 24.5 parts of 5N aqueous sodium hydroxide solution (equivalent amount of neutralizing agent used: 45 mol%) was used.

[0057] [Table 1]

[0058] Production Example 3 (Preparation of Aqueous Dispersion of Vinyl Polymer P3) Into a glass container, 96.34 parts of ion-exchanged water, 18.46 parts (solid content) of a surfactant (sodium polyoxyethylene alkyl ether sulfate, manufactured by Kao Corporation, emulsifier for emulsion polymerization, trade name: Latemul E-118B, solid content concentration: 26%), 0.32 part of a water-soluble polymerization initiator (potassium persulfate: manufactured by Fuji Film Wako Pure Chemical Industries, Ltd., reagent), 10.0 parts of a polymerization chain transfer agent (n-dodecyl mercaptan, manufactured by Kao Corporation, trade name: Thiokol 20), 30.0 parts of methacrylic acid, 40.0 parts of 2-ethylhexyl acrylate, and 130.0 parts of styrene were added as monomers, and the mixture was stirred at 500 rpm for 30 minutes using a Teflon (registered trademark) stirring blade to obtain a pre-emulsion. Next, 96.3 parts of ion-exchanged water, 4.6 parts (solid content) of the above surfactant, 5.3 parts of the above water-soluble polymerization initiator, and 15.5 parts of the pre-emulsion prepared in advance were added to a glass reactor equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet tube. After nitrogen substitution, the temperature was raised to 80 °C in a water bath while stirring at 250 rpm. After reaching 80 °C, the remaining pre-emulsion (309.62 parts) was added dropwise over 2 hours to carry out emulsion polymerization. The acid value of the polymer constituting the obtained emulsion was 97 mgKOH / g. After completion of the dropping, aging was carried out at 80 °C for 2 hours. After cooling to room temperature, 36.9 parts of a 5N aqueous sodium hydroxide solution (an amount corresponding to 45 mol% based on the total amount of methacrylic acid in the obtained polymer emulsion: neutralization degree 45%) was added, and further ion-exchanged water was added so that the polymer solid content concentration became 25%, to obtain an aqueous dispersion of polymer P3.

[0059] Preparation Example 1 (Preparation of Emulsion A1 of Crosslinked Polymer P1) 227 parts of the aqueous dispersion of polymer P1 (50.0 parts as polymer P1) obtained in Production Example 1(2) and 25.8 parts of crosslinking agent X1 (polyethylene glycol diglycidyl ether, manufactured by Kyoeisha Chemical Co., Ltd., trade name: Epolite 400E, n = 9, epoxy equivalent: 290 g / eq) (crosslinking ratio: 50 mol%) were stirred at 80 °C for 2 hours in a container that could be sealed. After cooling to 5 °C, it was filtered through the 5 μm filter to remove coarse particles, and further ion-exchanged water was added so that the solid content concentration became 22%, to obtain Emulsion A1 of crosslinked polymer P1 (acid value: 66 mgKOH / g) containing no pigment. The results are shown in Table 2. The compositions (parts) in Table 2 are the amounts of solids (active ingredients).

[0060] Preparation Examples 2 to 11, Comparative Preparation Example 1 (Preparation of Crosslinked Polymer Emulsions A2 to A11, AC1) Instead of the aqueous dispersion of polymer P1 obtained in Production Example 1(2), the aqueous dispersion of polymer P2 obtained in Production Example 2, the aqueous dispersion of polymer P3 obtained in Production Example 3, or emulsions of commercially available urethane resins P4 and P5 were used in the amounts shown in Table 2, and crosslinked polymer emulsions A2 to A11 and AC1 containing no pigment were obtained in the same manner as in Preparation Example 1, except that the type and amount of the crosslinking agent were used in the amounts shown in Table 2. The acid values of the crosslinked vinyl polymers P2 and P3 were 40 mgKOH / g, respectively. In addition, commercially available urethane resins are as follows. · Urethane resin P4: Polyester urethane resin (manufactured by Toyobo Co., Ltd., trade name: Baylon UR-3500, acid value 35 mgKOH / g (catalog value), solid content concentration: 40%) · Urethane resin P5: Polyester urethane resin (manufactured by Toyobo Co., Ltd., trade name: Baylon UR-3600, acid value 20 mgKOH / g (catalog value), solid content concentration: 40%)

[0061] Details of the crosslinking agents X2 to X6 described in Table 2 are as follows. · X2: Polyethylene glycol diglycidyl ether (manufactured by Nagase ChemteX Corporation, trade name: Denacol EX-841, n = 14, epoxy equivalent: 372 g / eq) · X3: Polypropylene glycol diglycidyl ether (manufactured by Nagase ChemteX Corporation, trade name: Denacol EX-931, n = 11, epoxy equivalent: 471 g / eq) · X4: Polyethylene glycol diglycidyl ether (manufactured by Kyoeisha Chemical Co., Ltd., trade name: Epolite 200E, n = 4, epoxy equivalent: 215 g / eq) · X5: Polyethylene glycol diglycidyl ether (manufactured by Nagase ChemteX Corporation, trade name: Denacol EX-861, n = 22, epoxy equivalent: 551 g / eq) · X6: 1,6-Hexanediol diglycidyl ether (manufactured by Nagase ChemteX Corporation, trade name: Denacol EX212, epoxy equivalent: 151 g / eq)

[0062]

Table 2

[0063] Preparation Example 20 (Preparation of Pigment Dispersion) 128.6 parts of the polymer P1 obtained in Production Example 1(1) was mixed with 308 parts of MEK to obtain a MEK solution of the polymer P1. Into a high-speed disperser (manufactured by Primix Corporation, trade name: T.K. Robomix, stirring section: Homodisper 2.5 type (blade diameter 40 mm)) having a receiver with a volume of 3 L, a MEK solution of the polymer P1 was charged, and while stirring under the condition of 1,400 rpm, 893.8 parts of ion-exchanged water and 56.6 parts of a 5N aqueous sodium hydroxide solution (neutralization degree: 52 mol%) were added, and while cooling in a water bath at 0 °C, stirring was carried out at 1,400 rpm for 15 minutes. Next, 300 parts of carbon black (manufactured by Cabot Corporation, trade name: MONARCH717) as a pigment was added, and stirring was carried out at 20 °C and 7,000 rpm for 3 hours. Further, 399.6 parts of ion-exchanged water was added, and the obtained pigment mixture was subjected to a dispersion treatment of 20 passes at a pressure of 150 MPa using a microfluidizer (manufactured by Microfluidics, trade name: M-110EH-30XP) to obtain a dispersion-treated product. 2,000 parts of the obtained dispersion-treated product was placed in a 4 L eggplant flask, 800 parts of ion-exchanged water was added, and using a rotary evaporator (manufactured by Tokyo Rika Kikai Co., Ltd., trade name: Rotary Evaporator N-1000S), at a rotation speed of 50 rpm, in a warm bath adjusted to 32 °C, the pressure was maintained at 0.09 MPa for 3 hours to remove the organic solvent. Further, the warm bath was adjusted to 62 °C, the pressure was reduced to 0.07 MPa, and concentration was carried out until the solid content concentration reached 25%. The obtained concentrate was put into a 500 mL angle rotor, centrifuged at 7,000 rpm for 20 minutes using a high-speed cooling centrifuge (manufactured by Hitachi Koki Co., Ltd., trade name: himac CR22G, set temperature 20 °C), and then the liquid layer portion was filtered through a 5 μm membrane filter (manufactured by Sartorius, trade name: Minisart) to obtain an aqueous dispersion (i) of pigment-containing polymer particles. To 100 parts of the obtained aqueous dispersion (containing 17.2% pigment and 7.4% polymer P1), 13.7 parts of ion-exchanged water was added. Further, 0.22 part of Proxel LVS (manufactured by Arch Chemicals Japan K.K., mildew preventive, active ingredient 20%) and 0.27 part of a crosslinking agent (trimethylolpropane polyglycidyl ether, manufactured by Nagase ChemteX Corporation, trade name: Denacol EX321L, epoxy equivalent: 129 g / eq) were added so that the crosslinking degree became 40 mol%, and the mixture was stirred at 80 °C for 2 hours. After cooling to 25 °C, it was filtered through the 5-μm filter, and ion-exchanged water was further added so that the solid content concentration became 22% (15.4% pigment, 6.6% crosslinked polymer) to obtain an aqueous dispersion (I) of pigment-containing polymer particles. The average particle diameter of the pigment-containing polymer particles in the pigment aqueous dispersion (I) was 94.7 nm, and the acid value of the crosslinked polymer constituting the particles was 120 mgKOH / g.

[0064] Example 1 (Preparation of Aqueous Ink 1) 26.3 parts of the pigment aqueous dispersion obtained in Preparation Example 20 (4.5 parts of pigment, 1.9 parts of polymer P1), 34.5 parts of a crosslinked polymer aqueous dispersion (A1) not containing pigment (5.0 parts of polymer P1, 2.6 parts of crosslinking agent), 12.0 parts of propylene glycol, 0.6 part of a nonionic surfactant (50% solution of 2,4,7,9-tetramethyl-5-decyne-4,7-diol in propylene glycol, manufactured by Nissin Chemical Industry Co., Ltd., trade name: Surfynol 104PG50), and 0.6 part of a nonionic surfactant (polyoxyethylene lauryl ether, manufactured by Kao Corporation, trade name: Emulgen 120) were mixed, and ion-exchanged water was added to make a total of 100 parts. The obtained mixture was filtered through a 25-mL syringe without a needle equipped with a 1.2-μm filter (acetyl cellulose membrane, outer diameter: 2.5 cm, manufactured by Fujifilm Corporation) to remove coarse particles, thereby obtaining aqueous ink 1 (pigment in the ink: 4.5%, crosslinked polymer not containing the pigment in the ink: 7.6%). The results are shown in Table 3. The numerical values of the compositions in Table 3 are the amounts of solid content (active ingredient).

[0065] Examples 2 to 11 and Comparative Example 1 (Preparation of Aqueous Inks 2 to 11 and 21) Except for changing the types and amounts of the crosslinked polymer emulsions containing no pigments obtained in Preparation Examples 2 to 11 and Comparative Preparation Example 1 as shown in Table 3, aqueous inks 2 to 11 and 21 were prepared in the same manner as in Example 1.

[0066] <Evaluation method> The glossiness of the matte paper of the aqueous inks obtained in Examples 1 to 11 and Comparative Example 1 was evaluated by the following method. The results are shown in Table 3.

[0067] (Printing method) Using a piezo printer (manufactured by Kyocera Corporation, product name: KJ4B-1200), solid printing was performed on matte paper (manufactured by UPM, product name: UPM Finesse Matt, basis weight: 115 g / m 2 , 60° glossiness: 5.6, water absorption: 4.4 g / m 2 ). The recording conditions of the printer were set to a recording head voltage of 26 V, a recording head temperature of 32 °C, a resolution of 600 dpi, a pre-discharge flushing frequency of 200 shots, and a negative pressure of -4.0 kPa, respectively. Then, the printed matter was left at 25 °C for 24 hours to obtain the final printed matter.

[0068] (Measurement of matte paper glossiness) The final printed matter was measured for 60° glossiness 5 times with a gloss meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name: HANDY GLOSSMETER PG-1), and the average value was taken as the glossiness. 〔Evaluation criteria〕 5: The 60° glossiness is 30 or more. 4: The 60° glossiness is 27 or more and less than 30. 3: The 60° glossiness is 24 or more and less than 27. 2: The 60° glossiness is 21 or more and less than 24. 1: The 60° glossiness is less than 21. If the evaluation result of the glossiness is 3 or more, it is practically satisfactory.

[0069]

Table 3

[0070] From Table 3, it can be seen that the aqueous inks of Examples 1 to 11 are superior in the glossiness of matte paper compared to the aqueous ink of Comparative Example 1.

Claims

1. An aqueous ink containing a pigment and a polymer emulsion, wherein the polymer emulsion contains crosslinked polymer particles composed of a urethane resin crosslinked with a polyalkylene glycol diglycidyl ether, the aqueous ink for inkjet recording.

2. The aqueous ink for inkjet recording according to Claim 1, wherein the repeating unit number n of the alkylene oxide groups of the polyalkylene glycol diglycidyl ether is 2 or more and 30 or less.

3. The aqueous ink for inkjet recording according to Claim 1 or 2, wherein the epoxy equivalent of the polyalkylene glycol diglycidyl ether is 200 g / eq or more and 600 g / eq or less.

4. The aqueous ink for inkjet recording according to any one of Claims 1 to 3, wherein the polyalkylene glycol diglycidyl ether is at least one selected from polyethylene glycol diglycidyl ether and polypropylene glycol diglycidyl ether.

5. The aqueous ink for inkjet recording according to any one of Claims 1 to 4, wherein the acid value of the crosslinked polymer constituting the polymer emulsion is 4 mgKOH / g or more and 180 mgKOH / g or less.

6. The aqueous ink for inkjet recording according to any one of Claims 1 to 5, wherein the pigment is in the form of polymer particles containing the pigment.

7. The aqueous ink for inkjet recording according to Claim 6, wherein the polymer particles containing the pigment are crosslinked polymer particles containing the pigment.

8. The aqueous ink for inkjet recording according to Claim 7, wherein the acid value of the crosslinked polymer constituting the crosslinked polymer particles containing the pigment is 100 mgKOH / g or more and 140 mgKOH / g or less.

9. An inkjet recording method of recording on matte paper using the aqueous ink according to any one of Claims 1 to 8.

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