Inkjet ink, image forming method

Abstract

This invention provides an inkjet ink and an image forming method that can improve friction fastness even when the ink is stored over time. [Solution] The inkjet ink comprises water, a water-dispersible resin, and a blocked isocyanate compound. The blocked isocyanate compound contains three or more blocked isocyanate groups in which the isocyanate groups are blocked by dimethylpyrazole.

Description

[Technical Field]

[0001] The present invention relates to an inkjet ink and an image forming method. [Background technology]

[0002] In recent years, inkjet recording, which forms images on substrates using the inkjet method, has become widely used as an image formation method due to its ability to stain in a short time and its high production efficiency.

[0003] While dye-based inks have been the mainstream inkjet inks used in inkjet recording (hereinafter also simply referred to as "ink"), the use of pigment-based inks, which eliminate the need for post-processing steps such as washing away dyes that did not dissolve or react, is being considered.

[0004] Pigment inks exhibit high color development by retaining pigment particles on the surface of the substrate, but tend to have lower pigment particle fixation and inferior friction fastness compared to dye inks. Therefore, adding crosslinking agents to inks is being considered from the viewpoint of improving image fastness, etc. (for example, Patent Documents 1-3). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2019-31611 [Patent Document 2] Japanese Patent Publication No. 2023-66349 [Patent Document 3] Japanese Patent Publication No. 2014-129617 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, according to the inventors' findings, when the inks described in these patent documents were stored over time, the images formed using the aged inks exhibited unsatisfactory friction fastness.

[0007] The present invention has been made in view of the above problems, and an object thereof is to provide an inkjet ink and an image forming method capable of enhancing rubbing fastness even when the ink is stored over time.

Means for Solving the Problems

[0008] The present invention relates to the following inkjet ink and image forming method.

[0009] [1] An inkjet ink containing water, a water-dispersible resin, and a blocked isocyanate compound, wherein the blocked isocyanate compound contains three or more blocked isocyanate groups in which isocyanate groups are blocked by dimethylpyrazole, an inkjet ink. [[ID=二十]]

[0010] [[ID=二十一]] [[ID=二十二]] [2] The blocked isocyanate compound has no cyclic structure, The inkjet ink according to [1].

[0011] [3] The blocked isocyanate compound is a compound in which isocyanate groups of hexamethylene diisocyanate biuret are blocked, The inkjet ink according to [1] or [2].

[0012] [4] The water-dispersible resin is an ether-based urethane resin, The inkjet ink according to any one of [1] to [3].

[0013] [5] The content of the blocked isocyanate compound is 0.10% by mass to 1.00% by mass based on the total mass of the inkjet ink, The inkjet ink according to any one of [1] to [4].

[0014] [6] An inkjet ink for printing, The inkjet ink according to any one of [1] to [5].

[0015] [7] A step of applying the inkjet ink according to any one of [1] to [6] onto a substrate by an inkjet method is included. Image forming method.

Effect of the Invention

[0016] According to the present invention, it is possible to provide an inkjet ink and an image forming method capable of enhancing friction fastness even when the ink is stored over time.

Mode for Carrying Out the Invention

[0017] Hereinafter, embodiments of the present invention will be described in detail. Note that the present invention is not limited to the following embodiments.

[0018] In this specification, a numerical range represented by "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value.

[0019] Also, in this specification, "(meth)acrylate" means either one or both of acrylate and methacrylate, and "(meth)acrylic" means either one or both of acrylic and methacrylic.

[0020] 1. Inkjet Ink The inkjet ink according to the present embodiment (hereinafter, also simply referred to as "ink") includes water, a water-dispersible resin, and a blocked isocyanate compound.

[0021] 1-1. Blocked Isocyanate Compound Blocked isocyanate compounds are compounds containing blocked isocyanate groups, which are functional groups that become isocyanate groups when the blocking agent is removed by heat. The isocyanate groups then form crosslinks with the hydroxyl moieties of the water-dispersible resin and / or the hydroxyl moieties of the substrate, which can improve the wet friction fastness of the image. The hydroxyl moiety may be the -OH moiety of a hydroxyl group, or it may be the -OH moiety contained in a carboxyl group, phosphonic acid group, sulfonic acid group, etc.

[0022] The blocked isocyanate compound according to this embodiment is not particularly limited as long as it is a compound containing three or more blocked isocyanate groups in which the isocyanate groups are blocked by dimethylpyrazole. The dimethylpyrazole used as the blocking agent is preferably one in which a methyl group has been introduced to a cyclic carbon atom, and more preferably 3,5-dimethylpyrazole.

[0023] The elimination of dimethylpyrazole from blocked isocyanate groups is an equilibrium reaction, and dimethylpyrazole has a relatively high boiling point. Therefore, even if some dimethylpyrazole is eliminated during storage of the ink over time, it does not easily evaporate from the ink, making it easier to maintain the equilibrium reaction and allowing the isocyanate groups to be reblocked. As a result, the deactivation of isocyanate groups by water is less likely to occur, and the wet friction fastness of the resulting image tends to improve even when the ink is stored over time.

[0024] Furthermore, having three or more blocked isocyanate groups facilitates the formation of a dense crosslinked structure. Also, if the ink is stored over time and some of the isocyanate groups are deactivated by water, for example, in a compound with two blocked isocyanate groups, even if only one isocyanate group is deactivated, the compound will no longer be able to contribute to the crosslinked structure. On the other hand, if there are three or more blocked isocyanate groups, even if some functional groups are deactivated, two blocked isocyanate groups may remain and thus contribute to the crosslinked structure. Therefore, even when the ink is stored over time, it is possible to form a sufficient crosslinked structure, which is thought to improve wet friction fastness.

[0025] Furthermore, during image formation, the blocking agent may volatilize once the aqueous solvent has dried to some extent and the ink has lost its fluidity. This can lead to the formation of pinholes in the image, reducing its robustness. On the other hand, as mentioned above, dimethylpyrazole has a relatively high boiling point, which helps to suppress the volatilization of the blocking agent during image formation. This makes it less likely for pinholes to form in the image, thus improving wet friction fastness.

[0026] The number of blocked isocyanate groups in the blocked isocyanate compound is three or more, preferably three to five, and more preferably three. With three or more groups, as described above, it is possible to form a sufficient crosslinked structure even when the ink is stored over time, which tends to improve wet friction fastness. With five or fewer groups, it is possible to control the crosslinked structure so that it does not become too dense, so the resulting image is less likely to be fragile, and the texture tends to improve, especially when a fabric is used as the substrate.

[0027] As the isocyanate compound used in the blocked isocyanate compound, known isocyanate compounds with three or more functions may be used. The isocyanate compound may be a trifunctional or more isocyanate compound in which a diisocyanate compound is trimerized. Among these, trifunctional isocyanate compounds in which a diisocyanate compound is trimerized to form a biuret structure, or trifunctional isocyanate compounds in which a diisocyanate compound is trimerized to have an isocyanurate structure are preferably used.

[0028] The diisocyanate compound used to obtain a trifunctional or more isocyanate compound by increasing the amount of the above-mentioned compound is not particularly limited, but examples include hexamethylene diisocyanate, tolylene diisocyanate, lysine diisocyanate, isophorone diisocyanate, hydrogenated xylylene diisocyanate, xylene diisocyanate, and diphenylmethane diisocyanate. Among these, hexamethylene diisocyanate and isophorone diisocyanate are preferred, as they have moderately flexible linking chains, making the resulting image less brittle, and especially when fabric is used as the base material, the texture is more easily improved.

[0029] The isocyanate compound may or may not have a cyclic structure, but it is preferable that the isocyanate compound contains 0 to 4 cyclic structures, more preferably 0 to 1, and even more preferably 0. When a cyclic structure is present, the movement of the molecular chains is constrained to some extent, so when a cross-linked structure is formed, the resulting image tends to be hard and brittle. On the other hand, the fewer cyclic structures the isocyanate compound contains, the more flexible the resulting image becomes when a cross-linked structure is formed, making it less brittle, and especially when a fabric is used as the base material, the more likely it is to have a good texture.

[0030] From the viewpoint of not containing a cyclic structure and easily enhancing the texture when a fabric is used as the base material, it is preferable that the isocyanate compound used in the blocked isocyanate compound is a trifunctional isocyanate compound in which a diisocyanate compound is trimerized to form a biuret structure. Furthermore, from the viewpoint of further enhancing the texture, it is even more preferable that it is a trifunctional isocyanate compound (hexamethylene diisocyanate biuret) in which hexamethylene diisocyanate is trimerized to form a biuret structure.

[0031] The lower limit of the content of the blocked isocyanate compound is preferably 0.01% by mass or more, more preferably 0.04% by mass or more, even more preferably 0.10% by mass or more, even more preferably 0.40% by mass or more, and most preferably 0.75% by mass or more, based on the total mass of the ink. Increasing the amount of blocked isocyanate compound added tends to improve wet friction fastness.

[0032] On the other hand, the upper limit of the content of the blocked isocyanate compound is preferably 5.00% by mass or less, more preferably 2.50% by mass or less, even more preferably 1.75% by mass or less, even more preferably 1.25% by mass or less, and most preferably 1.00% by mass or less, relative to the total mass of the ink. By reducing the amount of blocked isocyanate compound added, the resulting image becomes less fragile, and the texture tends to improve, especially when using fabric as the substrate.

[0033] Among these, from the viewpoint of easily improving wet friction fastness, it is preferable that the amount be 0.40% to 5.00% by mass, more preferably 0.75% to 5.00% by mass, and even more preferably 0.75% to 2.50% by mass. Furthermore, from the viewpoint of making the image less fragile and especially when the base material is a fabric, it is preferable that the amount be 0.01% to 1.75% by mass, more preferably 0.01% to 1.25% by mass, and even more preferably 0.04% to 1.25% by mass. Furthermore, in terms of improving wet friction robustness and making the image less prone to brittleness, a concentration of 0.01% to 5.00% by mass is preferred, 0.04% to 2.50% by mass is more preferred, 0.10% to 1.75% by mass is even more preferred, 0.10% to 1.25% by mass is even more preferred, 0.10% to 1.00% by mass is even more preferred, 0.40% to 1.00% by mass is even more preferred, and 0.75% to 1.00% by mass is most preferred.

[0034] 1-2.Water dispersible resin Water-dispersible resins facilitate the fixation of pigments and other materials to the substrate. Water-dispersible resins can be included as resin particles in ink. These resins may be self-emulsifying resin particles with hydrophilic groups introduced, or forced-emulsifying resin particles that become water-dispersible through the use of an external emulsifier. From the viewpoint of suppressing bleed-out, self-emulsifying resins are preferred.

[0035] A low glass transition temperature (Tg) of a water-dispersible resin is preferable from the viewpoint of preventing image brittleness and better maintaining the texture when using a fabric as the substrate. The Tg of a water-dispersible resin is preferably -80°C to 50°C, and more preferably -70°C to 10°C. The Tg of a water-dispersible resin can be measured at a heating rate of 10°C / min in accordance with JIS K7121:2012.

[0036] The water-dispersible resin may have cationic groups or anionic groups. For example, since the pretreatment solution preferably contains a resin having cationic groups (hereinafter also referred to as "cationic resin"), it is preferable that the water-dispersible resin contained in the ink contains a resin having anionic groups (hereinafter also referred to as "anionic resin"). Examples of anionic groups include carboxyl groups, sulfonic acid groups, and phosphonic acid groups.

[0037] Examples of water-dispersible resins include (meth)acrylic resins, styrene resins, urethane resins, and ester resins, which have anionic groups. Among these, (meth)acrylic resins or urethane resins having anionic groups are preferred, and urethane resins having anionic groups are more preferred, from the viewpoint of having a moderately low Tg of the resin and flexibility.

[0038] (Anionic (meth)acrylic resin) An anionic group-containing (meth)acrylic resin is a polymer of (meth)acrylic monomer, or a copolymer thereof with another monomer copolymerizable thereto. At least one of the (meth)acrylic monomer and the other monomer, preferably the (meth)acrylic monomer, has anionic groups. The (meth)acrylic monomer is a monomer having a (meth)acryloyl group. The concept of (meth)acrylic includes both methacrylic and acrylic.

[0039] Examples of (meth)acrylic monomers having anionic groups include acrylic acid and methacrylic acid. Examples of other (meth)acrylic monomers include (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, and hydroxyethyl (meth)acrylate; (meth)acrylamides; and (meth)acrylic monomers without anionic groups such as (meth)acrylonitrile.

[0040] Other examples of copolymerizable monomers include monofunctional monomers such as ethylenically unsaturated carboxylic acids (e.g., maleic acid, itaconic acid); styrenes (e.g., styrene, α-methylstyrene, vinyltoluene); saturated fatty acid vinyls (e.g., vinyl acetate, vinyl propionate); vinyl compounds (e.g., 1,4-divinyloxybutane, divinylbenzene, etc.); and allyl compounds (e.g., diallyl phthalate, triallyl cyanurate, etc.); as well as bifunctional or more functional monomers such as polyfunctional (meth)acrylates (e.g., diethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, propylene glycol di(meth)acrylate, N,N'-methylenebis(acrylamide), etc.) and polyfunctional acrylamides.

[0041] In particular, from the viewpoint of lowering the Tg of the water-dispersible resin, the (meth)acrylic monomer preferably contains acrylic acid or an alkyl acrylate. The alkyl acrylate is preferably a C4-12 alkyl acrylate, and more preferably n-butyl acrylate or 2-ethylhexyl acrylate.

[0042] (Urethane resin having anionic groups) Examples of urethane resins having anionic groups include ether-based urethane resins, ester-based urethane resins, and carbonate-based urethane resins. Among these urethane resins, ether-based urethane resins are preferred because they have a flexible alkylene oxide skeleton, the resulting image is less likely to be brittle, and the texture is easily enhanced when the substrate is a fabric. Furthermore, it is preferable that the urethane resin having anionic groups be of the self-emulsifying type. Self-emulsifying urethane resins can be, for example, polyaddition reaction products of a polyhydric alcohol having anionic groups and a polyhydric isocyanate.

[0043] Examples of commercially available urethane resins include Takelac(R) W-6010 (polycarbonate-based / anionic type), Takelac(R) W-6110 (polycarbonate-based / anionic type), Takelac(R) W-6020 (ether-based / anionic type), Takelac(R) W-6061 (ether-based / anionic type), Takelac(R) W-405 (ester-based / anionic type), Takelac(R) W-605 (ester-based / anionic type), Takelac(R) WS-5000 (polyester-based / anionic type), and Takelac(R) WS-4000 (polycarbonate-based). This includes products such as (nate / anionic type) (all manufactured by Mitsui Chemicals, Inc.), Superflex(R) 126 (ether / ester type, anionic type), Superflex(R) 130 (ether type, anionic type), Superflex(R) 150 (ether / ester type, anionic type), Superflex(R) 300 (ether / ester type, weak anionic type), Superflex(R) 420 (polycarbonate type / anionic type), and Superflex(R) 460 (polycarbonate type / anionic type) (all manufactured by Daiichi Kogyo Seiyaku Co., Ltd.).

[0044] (General) The average particle size of the water-dispersible resin is preferably 80 nm to 400 nm, and more preferably 150 nm to 300 nm. The average particle size of the water-dispersible resin can be measured in the same way as the average particle size of the pigment particles.

[0045] The water-dispersible resin content in the ink is preferably 1.0% to 20.00% by mass, and more preferably 5.0% to 15.0% by mass, relative to the total mass of the ink. If the water-dispersible resin content is above the lower limit, the ink's adhesion to the substrate is more easily improved. If the water-dispersible resin content is below the upper limit, the substrate does not become too hard, and the texture is less likely to be damaged when using fabric as the substrate. There may be one type of water-dispersible resin or two or more types.

[0046] 1-3. Pigments The ink according to this embodiment may or may not contain a pigment, but it is preferable to include a pigment. When the blocked isocyanate compound forms a crosslinked structure, the pigment is incorporated into the crosslinked structure, which tends to increase the wet friction fastness.

[0047] Any known pigment may be used, but for example, organic or inorganic pigments with the following numbers listed in the color index may be used.

[0048] Examples of orange pigments include CIPigment Orange 31, 43, and 47.

[0049] Examples of red or magenta pigments include: Pigment Red 3, 5, 19, 22, 31, 38, 43, 48:1, 48:2, 48:3, 48:4, 48:5, 49:1, 53:1, 57:1, 57:2, 58:4, 63:1, 81, 81:1, 81:2, 81:3, 81:4, 88 , 104, 108, 112, 122, 123, 144, 146, 149, 166, 168, 169, 170, 177, 178, 179, 184, 185, 202, 208, 216, 226, 254, 257, Pigment Violet 3, 19, 23, 29, 30, 37, 50, 88, Pigment Orange 13, 16, 20, 36 It includes.

[0050] Examples of blue or cyan pigments include: Pigment Blue 1, 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 17-1, 22, 27, 28, 29, 36, 60 It includes.

[0051] Examples of green or yellow pigments include Pigment Green 7, 26, 36, and 50.

[0052] Examples of yellow pigments include: Pigment Yellow 1, 3, 12, 13, 14, 15, 17, 34, 35, 37, 55, 74, 81, 83, 93, 94, 95, 97, 108, 109, 110 , 128, 137, 138, 139, 151, 153, 154, 155, 157, 166, 167, 168, 180, 185, 193, 213 It includes.

[0053] Examples of black pigments include Pigment Black 7, 28, and 26.

[0054] Examples of white pigments include titanium dioxide.

[0055] From the viewpoint of improving dispersibility in the ink, it is preferable that the pigment is further dispersed with a pigment dispersant. Pigment dispersants will be described later.

[0056] Furthermore, the pigment may be a self-dispersing pigment. A self-dispersing pigment has a surface modified with a hydrophilic group, and comprises pigment particles and a hydrophilic group bonded to its surface.

[0057] Examples of hydrophilic groups include carboxyl groups, sulfonic acid groups, and phosphorus-containing groups. Examples of phosphorus-containing groups include phosphate groups, phosphonic acid groups, phosphinic acid groups, phosphite groups, and phosphate groups.

[0058] Examples of commercially available self-dispersing pigments include Cabot's Cab-O-Jet® 200K, 250C, 260M, and 270V (sulfonic acid group-containing self-dispersing pigments), Cab-O-Jet® 300K (carboxylic acid group-containing self-dispersing pigment), and Cab-O-Jet® 400K, 450C, 465M, 470V, and 480V (phosphate group-containing self-dispersing pigments).

[0059] The pigment content is not particularly limited, but from the viewpoint of easily adjusting the ink viscosity within the above range and enabling the formation of high-density images, it is preferably 0.3% to 10.0% by mass relative to the ink, and more preferably 0.5% to 5.0% by mass. If the pigment content is above the lower limit, the image colors tend to become even more vivid. If the pigment content is below the upper limit, the ink viscosity does not become too high, and the ejection stability is less likely to be impaired.

[0060] 1-4. Aqueous solvents The inkjet ink according to this embodiment preferably contains at least water and is an aqueous solvent further containing a water-soluble organic solvent.

[0061] Water-soluble organic solvents are not particularly limited as long as they are miscible with water, but examples include polyhydric alcohols (e.g., dihydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, and polypropylene glycol, and trihydric or higher alcohols such as glycerin, trimethylolpropane, and hexanetriol); polyhydric alcohol ethers (e.g., ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monophenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether) This includes methyl ethers, propylene glycol monomethyl ether, propylene glycol monoethyl ether; monohydric alcohols (e.g., methanol, ethanol, propanol, pentanol, hexanol, cyclohexanol, benzyl alcohol); amines (e.g., ethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenediamine, triethylenetetramine); amides (e.g., formamide, N,N-dimethylformamide, N,N-dimethylacetamide); heterocyclic compounds (e.g., 2-pyrrolidone, N-methyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidine); sulfoxides (e.g., dimethyl sulfoxide); and sulfones (e.g., sulfolanes).

[0062] Furthermore, from the viewpoint of further improving the injection stability by inkjet printing, it is preferable to include a high-boiling-point solvent with a boiling point of 180°C or higher. The boiling point of the high-boiling-point solvent is preferably 190°C or higher, and more preferably 200°C or higher. Examples of solvents with a boiling point of 200°C or higher include divalent alcohols such as 1,3-butanediol (boiling point 208°C), 1,6-hexanediol (boiling point 223°C), and polypropylene glycol; and trivalent or higher alcohols such as glycerin (boiling point 290°C) and trimethylolpropane (boiling point 295°C).

[0063] The water content is preferably 30.0% to 85.0% by mass, and more preferably 40.0% to 75.0% by mass, relative to the total mass of the ink. The total mass of the water-soluble organic solvent is preferably 10.0% to 70.0% by mass, and more preferably 20.0% to 60.0% by mass, relative to the total mass of the ink.

[0064] 1-5. Other ingredients The ink may contain other components as needed. Examples of other components include pigment dispersants, surfactants, preservatives, fungicides, and pH adjusters.

[0065] (Surfactants) Surfactants can lower the surface tension of inkjet compositions, thereby increasing their wettability to the substrate. The type of surfactant is not particularly limited, but examples include acetylene glycol-based surfactants, silicone-based surfactants, and fluorine-based surfactants. Examples of commercially available surfactants include Olfin E1010 (manufactured by Nisshin Chemical Industry Co., Ltd.) and TEGOWET250 (manufactured by Evonik).

[0066] (Preservative or fungicide) Examples of preservatives or fungicides include aromatic halogen compounds (e.g., Preventol CMK), methylenedithiocyanates, halogenated nitrogen-sulfur compounds, and 1,2-benzisothiazolin-3-one. Another example of a preservative or fungicide is Proxel GXL(S) (manufactured by Lonza).

[0067] (Pigment dispersant) The pigment dispersant exists in the ink either surrounding the surface of the pigment particles or adsorbed onto the surface of the pigment particles to form a pigment dispersion, thereby effectively dispersing the pigment. The pigment dispersant is preferably a polymeric dispersant, and more preferably an anionic polymeric dispersant.

[0068] Anionic polymer dispersants are polymer dispersants having hydrophilic groups such as carboxyl groups, phosphate groups, and sulfonic acid groups, and are preferably polymer dispersants having carboxyl groups.

[0069] A polymeric dispersant having a carboxyl group may contain structural units derived from an unsaturated carboxylic acid monomer or a salt of an unsaturated carboxylic acid monomer. Examples of unsaturated carboxylic acid monomers include acrylic acid or its derivatives, maleic acid or its derivatives, itaconic acid or its derivatives, and fumaric acid or its derivatives. Anionic polymeric dispersants may be copolymers containing structural units derived from the aforementioned unsaturated carboxylic acid monomer or a salt of an unsaturated carboxylic acid monomer, and structural units derived from other monomers. Examples of other monomers include styrene, butyl acrylate, and vinyl naphthalene.

[0070] From the viewpoint of sufficiently dispersing pigment particles, the anionic group equivalent of an anionic polymer dispersant is preferably, for example, 1.1 meq / g to 3.8 meq / g. When the anionic group equivalent is within the above range, high pigment dispersibility can be easily obtained without increasing the molecular weight of the anionic polymer dispersant. The anionic group equivalent of an anionic polymer dispersant can be determined from the acid value. The acid value can be measured in accordance with JIS K 0070:1992.

[0071] The weight-average molecular weight (Mw) of the polymeric dispersant is not particularly limited, but is preferably between 5,000 and 30,000. If the Mw of the polymeric dispersant is 5,000 or higher, the pigment particles are easily dispersed, and if it is 30,000 or lower, the ink does not become excessively thickened, so the permeability to the substrate is not easily impaired. The Mw of the polymeric dispersant can be measured by the same method as described above. The weight-average molecular weight (Mw) of the polymeric dispersant can be measured in polystyrene equivalent by gel permeation chromatography.

[0072] The content of the polymeric dispersant is not particularly limited, as long as it is within a range that sufficiently disperses the pigment particles and has a viscosity that does not impair the permeability to the substrate. The content of the polymeric dispersant is preferably 20% to 100% by mass, and more preferably 25% to 60% by mass, relative to the mass of pigment.

[0073] 1-6. Physical Properties The viscosity of the ink at 25°C is not particularly limited, as long as it is sufficient for good ejection by the inkjet method, but it is preferably 3 mPa·s to 20 mPa·s, and more preferably 4 mPa·s to 12 mPa·s. The viscosity of the ink can be measured at 25°C using an E-type viscometer.

[0074] 2. Image forming method An image forming method according to one embodiment of the present invention may include at least the step of 1) applying the above-mentioned ink to a substrate using an inkjet method.

[0075] If the ink described above contains a pigment, step 2) may include a step of applying a treatment solution to the substrate. Step 2) may be performed before step 1) using a pre-treatment solution as the treatment solution, or after step 1) using a post-treatment solution as the treatment solution. Alternatively, step 2) may be performed before or after step 1) using both a pre-treatment solution and a post-treatment solution.

[0076] Furthermore, if the ink mentioned above is a clear ink that does not contain pigment, the ink may be used as a processing solution, and the process may include a step of applying an inkjet ink containing pigment separately from step 1).

[0077] 2-1. Step 1) Ink application process The ink according to this embodiment is applied to the substrate by an inkjet method.

[0078] The type of substrate is not particularly limited, but it may be a highly absorbent paper substrate, a non-absorbent substrate such as a film or plastic board (flexible polyvinyl chloride, rigid polyvinyl chloride, acrylic sheet, polyolefin, etc.), or a cloth. Among these, if the substrate contains a material having hydroxyl groups, such as cellulose, the blocked isocyanate compound and the substrate can form a crosslinked structure, which tends to increase wet friction fastness.

[0079] Examples of woven fabrics include natural fibers such as cotton (cellulose fibers), linen, wool, and silk; chemical fibers such as rayon, vinylon, nylon, acrylic, polyurethane, polyester, or acetate; and blends thereof. Of these, the resin constituting the woven fabric may be a hydrophilic fiber such as cotton, a hydrophobic fiber such as polyester, or a blend thereof. Furthermore, the woven fabric may be made from these fibers in any form, such as woven, nonwoven, or knitted fabric. In addition, the woven fabric may be a blended woven fabric or a blended nonwoven fabric of two or more types of fibers.

[0080] If the ink contains pigment, the substrate may have a flocculant attached to it to help the pigment and other components coagulate. That is, a substrate containing both the substrate and the flocculant attached to it may be used. This makes it easier to coagulate the pigment and water-dispersible resin in the ink on the substrate.

[0081] Furthermore, if the ink does not contain pigment, the substrate may have pigment attached to it, and a substrate containing both the substrate and the pigment attached to it may be used.

[0082] Next, the ink applied to the substrate may be dried further, or, if a post-treatment solution is to be applied, the post-treatment solution may be applied using a wet-on-wet method after the ink has been applied, and then all the materials may be dried together after the post-treatment solution has been applied.

[0083] The ink is dried by removing the aqueous solvents and other substances contained in each liquid applied to the substrate. The drying method is not particularly limited and may be carried out at room temperature or by heating. The heating method may be a method using a heater, a hot air dryer, a heating roller, etc., and preferably a method using a hot air dryer and a heater to heat both sides of the substrate.

[0084] The drying temperature is not particularly limited, but may be, for example, 80°C to 180°C. A drying temperature of 110°C to 170°C or lower is preferable. If the temperature is above 110°C, the blocking agent will be more easily detached, allowing the crosslinking reaction to proceed more efficiently. If the temperature is below 170°C, deterioration such as fabric burning and substrate shrinkage will be reduced. The drying time may also depend on the drying temperature, but may be, for example, 1 to 10 minutes.

[0085] 2-2. Step 2) Step of applying the processing solution 2-2-1. Step of applying pretreatment solution In the step of applying the pretreatment solution, for example, the substrate can be brought into contact with the pretreatment solution containing the flocculant, and then dried to obtain a substrate to which the flocculant has adhered.

[0086] (Pretreatment solution) The pretreatment solution contains at least a coagulant and an aqueous solvent.

[0087] The type of coagulant can be any one that coagulates the pigments contained in the ink, and may utilize a change in pH or an electrical effect.

[0088] Examples of the flocculant that causes flocculation due to a change in pH include organic acids. Examples of the organic acid include saturated fatty acids such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, and hexanoic acid, and hydroxy acids such as lactic acid, malic acid, and citric acid, as carboxylic acids having 6 or less carbon atoms.

[0089] Examples of the flocculant that causes flocculation by an electric action include polyvalent metal salts and compounds having a cationic group or an anionic group. For example, when the pigment dispersant contained in the ink is anionic, the flocculant preferably contains a polyvalent metal salt or a compound having a cationic group.

[0090] The polyvalent metal salt may be a water-soluble compound having a divalent or higher polyvalent metal ion and an anion bonded thereto. Examples of the polyvalent metal ion include divalent metal ions such as Ca 2+ , Cu 2+ , Ni 2+ , Mg 2+ , Zn 2+ , Ba 2+ ; and trivalent metal ions such as Al 3+ , Fe 3+ , Cr 3+ . Examples of the anion include Cl - , I - , Br - , SO4 2- , ClO3 - , NO3 - , and HCOO - , CH3COO - . Among them, calcium salts and magnesium salts are preferable, and calcium nitrate and calcium chloride are preferable.

[0091] Examples of the cationic group in the compound having a cationic group include a secondary amino group, a tertiary amino group, a quaternary ammonium base, and the like. Examples of the compound having a cationic group include the above-mentioned cationic urethane compound. In addition, cationic resins such as cationic urethane resins, cationic olefin resins, and cationic allylamine resins, and quaternary salts of alkylamine-epichlorohydrin adducts may be used.

[0092] The aqueous solvent can be the same as the solvent exemplified for the ink. The pretreatment solution may also contain known pH adjusters, preservatives, etc., as needed.

[0093] The method of contacting the material with the pretreatment solution can be the same as the method of applying the ink. The amount of coagulant applied is not particularly limited, but for example, 0.1 g / m 2 ~5.0g / m 2 It could be considered that...

[0094] 2-2-2. Step of applying post-treatment solution In the process of applying the post-treatment solution, the solution is applied to the ink that has been applied to the substrate. This makes it easier to improve the fixation of the pigment and to improve the slipperiness of the surface.

[0095] The method of applying the post-treatment solution is not particularly limited and may be immersion, spray, or inkjet, but inkjet is preferred.

[0096] To reduce the viscosity of the post-treatment solution, thereby stabilizing inkjet injection and suppressing fluctuations in ejection temperature due to temperature fluctuations of the inkjet head, it is preferable to apply the post-treatment solution at a controlled temperature. Specifically, the heating temperature of the post-treatment solution is preferably 20°C to 35°C, and more preferably 30°C to 35°C.

[0097] After applying the post-treatment solution, the inkjet composition applied to the substrate may be further dried. The drying method and conditions for the post-treatment solution can be the same as those for drying the ink.

[0098] (Post-treatment solution) The post-treatment solution contains a resin and an aqueous solvent.

[0099] The type of resin may be the same as the "water-dispersible resin" used in the ink, or it may be a known overcoat material, or, if the process includes a step of applying a pretreatment solution, it may be a resin that interacts with the flocculant contained in the pretreatment solution. Furthermore, the type of resin is not particularly limited as long as it enhances the fixation of pigments, etc.

[0100] Examples of overcoat materials include materials containing anionic resin fine particles. From the viewpoint of suppressing stickiness of the image and deterioration of the texture of the substrate on which the image is formed, the glass transition temperature Tg of the anionic resin fine particles is preferably 50°C or higher, and more preferably 100°C or higher. The glass transition temperature Tg of the anionic resin fine particles can be measured by differential scanning calorimetry in accordance with JIS K 7121:2012 at a heating rate of 10°C / min.

[0101] Examples of anionic resin nanoparticles include polymer nanoparticles having functional groups that can have a negative charge. Examples of such functional groups include carboxyl groups, hydroxyl groups, and sulfate groups.

[0102] Examples of commercially available products containing anionic resin microparticles include AQUACER507 from BYK and Hi-Tec E-4A from Toho Chemical Co., Ltd.

[0103] Furthermore, the resin contained in the post-treatment solution interacts with the flocculant contained in the pre-treatment solution. If the pre-treatment solution contains a cationic flocculant, it is preferable that the post-treatment solution contains an anionic flocculant. This configuration suppresses electrostatic repulsion between the flocculants contained in the pre-treatment solution, thereby increasing the cohesiveness of pigments and other materials, and improving the robustness of the image-forming product. In this case, a resin similar to the anionic resin exemplified in the water-dispersible resin of the ink can be used.

[0104] The amount of inkjet composition applied is preferably such that the amount of resin adhered is 0.3 g / m². 2 ~3.0g / m 2 More preferably 0.3 g / m 2 ~1.5g / m2 It can be set to be such. If the amount of resin attached is within the above range, the image is less likely to become brittle, and the texture can be further enhanced when a fabric is used as the base material. [Examples]

[0105] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0106] 1. Preparation of pretreatment solution The following components were mixed in a total amount of 100.00 parts by mass to prepare a pretreatment solution. -------------------------------------------------- Composition of pretreatment solution -------------------------------------------------- Quaternary salt of alkylamine epichlorohydrin adduct: 2.00 parts by mass Glycerin: 10.00 parts by mass Propylene glycol: 20.00 parts by mass Proxel GXL(S) (manufactured by Lonza, preservative): 0.05 parts by mass Surfinol E1010 (manufactured by Nisshin Chemical Industry Co., Ltd., surfactant): 0.10 parts by mass Deionized water: Remaining portion --------------------------------------------------

[0107] 2. Ink preparation 2-1. Preparation of Pigment Dispersion As a pigment dispersant, 7 parts by mass of styrene-butyl acrylate-methacrylic acid copolymer (anionic dispersant) was mixed with 63 parts by mass of water, then heated and stirred. Sodium hydroxide equivalent to a 50% degree of neutralization was added to prepare a neutralized pigment dispersant. 30 parts by mass of carbon black was added to this mixture, and after pre-mixing, the mixture was dispersed using a sand grinder filled with 0.5 mm zirconia beads at a volume percentage of 50% to obtain a black pigment dispersion with a pigment concentration of 30% by mass and a solid content concentration of 37% by mass. The weight-average molecular weight of the pigment dispersant used was 16000, and the anionic group equivalent was 3.5 meq / g.

[0108] 2-2. Water-dispersible resin As dispersions of water-dispersible resins, we prepared Takelac(R)W-6061 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., a dispersion with a solid content of 30% by mass using water as the dispersion medium) and Takelac(R)W-6110 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., a dispersion with a solid content of 32% by mass using water as the dispersion medium).

[0109] 2-3. Blocked Isocyanate Compounds Blocked isocyanate compounds 1 to 6 were prepared by blocking all isocyanate groups of the following isocyanate compounds (1) to (5) with the respective blocking agents shown in Table 1 below.

[0110] [Table 1]

[0111] [ka]

[0112] [ka]

[0113] [ka]

[0114] [ka]

[0115] [ka]

[0116] 2-4. Ink preparation Ink 1 was prepared by mixing the following components in a total amount of 100.00 parts by mass. Note that the amounts of pigment dispersion and water-dispersible resin dispersion listed below include volatile components (solvents). -------------------------------------------------- Composition of Ink 1 -------------------------------------------------- Pigment dispersion prepared by the above method: 9.00 parts by mass Takerack(R)W-6061: 30.00 units by mass Blocked isocyanate compound 1: 1.00 parts by mass Glycerin: 10.00 parts by mass Propylene glycol: 20.00 parts by mass Proxel GXL(S) (manufactured by Lonza, preservative): 0.05 parts by mass Surfinol E1010 (manufactured by Nisshin Chemical Industry Co., Ltd., surfactant): 0.10 parts by mass Deionized water: Remaining portion --------------------------------------------------

[0117] Inks 2-13 were prepared in the same manner, except that the formulations were changed as shown in Table 2.

[0118] The compositions of inks 1-13 are shown in Table 2.

[0119] [Table 2]

[0120] 3. Preparation of post-treatment solution A post-treatment solution was prepared in the same manner as with ink 1, except that the amount of deionized water added was adjusted so that the total amount was 100.00 parts by mass, without adding the blocked isocyanate compound and pigment dispersion.

[0121] 4. Image Formation and Evaluation 4-1. Image formation for initial evaluation Using the pre-treatment solution, ink, and post-treatment solution prepared above, images were formed for each ink. In this process, inks that had not been stored for extended periods after preparation were used.

[0122] First, a simple printing test machine equipped with a Konica Minolta KM1024i head was prepared as the image forming apparatus. This head had a pre-treatment solution head, an ink head, and a post-treatment solution head installed adjacent to each other, and the prepared pre-treatment solution, each ink, and the post-treatment solution were set in each of them. The application of the pre-treatment solution, each ink, and the post-treatment solution was carried out continuously so that the timing of impact on the substrate was in the order of pre-treatment solution, ink, and post-treatment solution.

[0123] (1) Application of pretreatment solution Cotton satin (100% cotton) was prepared as the base material. Next, the pretreatment solution was discharged from the head onto this base material to apply the pretreatment solution to the base material and obtain a treated base material. The amount of treatment solution applied was 12 g / m². 2 That's what I decided.

[0124] (2) Ink application A solid image measuring 200 mm x 200 mm was formed on the substrate that had undergone the above processing. Ink ejection was performed at a main scan speed of 540 dpi and a sub-scan speed of 720 dpi. Note that dpi represents the number of ink droplets (dots) per 2.54 cm. The ejection frequency was set to 22.4 kHz.

[0125] (3) Application of post-treatment solution The post-treatment solution was applied to the substrate to which the ink had been applied as described above by discharging it from the head. Then, the substrate was dried at 150°C for 3 minutes in a belt-type dryer to obtain an image-formed product. The amount of treatment solution applied was 12 g / m². 2 That's what I decided.

[0126] 4-2. Image formation for evaluating storage stability Except for using ink that had been stored at 50°C for 7 days, the image formation for storage stability evaluation was performed in the same manner as in "4-1. Image Formation for Initial Evaluation".

[0127] 4-3. Evaluation The wet friction fastness and texture of the image formations obtained for initial evaluation, and the wet friction fastness of the image formations for storage stability evaluation, were evaluated using the following method.

[0128] (1) Wet friction resistance The wet friction fastness of the image formations used for initial evaluation was assessed using a clock meter (friction tester type I) in accordance with the wet test specified in JIS L 0849:2013.

[0129] Specifically, friction was applied to a 100mm x 100mm area of ​​the formed image by moving a 100mm length white cotton cloth back and forth 10 times with a load of 9N. The white cotton cloth used for friction was moistened with water to approximately 100% moisture. After applying friction, color transfer to the white cotton cloth was observed, and wet friction fastness was evaluated according to the following criteria (wet friction fastness in the initial stages of storage). A score of 3 or higher was considered acceptable.

[0130] Furthermore, wet friction fastness was evaluated in the same manner, except that an image formation used for storage stability evaluation was used instead of an image formation used for initial evaluation (wet friction fastness after storage over time). Similarly, for wet friction fastness after storage over time, the following criteria were used, with a value of 3 or higher being considered acceptable.

[0131] 5: No color transfer. 4: There is almost no color transfer. 3: Some color transfer occurs, but it is within acceptable limits. 2: Color transfer occurred, exceeding acceptable limits. 1: Significant color transfer occurs.

[0132] (2) Texture Image-forming material for initial evaluation was cut into 5 × 20 cm pieces to serve as sample pieces. Using a KES-FB2-A pure bending tester (manufactured by Kato Tech Co., Ltd.), the bending stress B-MEAN [gf*cm] of the unused substrate and the image-forming substrate was measured. 2 The [cm] was measured. Then, the difference in bending stress △B between the unprocessed substrate and the image-forming substrate was calculated and evaluated based on the following criteria.

[0133] The width of the substrate was set to 20 cm. Furthermore, an unused substrate refers to a substrate to which neither ink nor processing solution has been applied, while a processed image-forming substrate refers to a substrate (image-forming object) to which pre-treatment solution, ink, and post-treatment solution have been applied. A value of 3 or higher was considered acceptable.

[0134] 5: △B is 0.06 or less. 4: △B is greater than 0.06 and less than or equal to 0.09. 3: △B is greater than 0.09 and less than or equal to 0.12. 2: △B is greater than 0.12 and less than or equal to 0.15. 1: △B is greater than 0.15.

[0135] (3) Results Table 3 shows the evaluation results of the image formations from Examples 1-9 and Comparative Examples 1-4 corresponding to each ink 1-13.

[0136] [Table 3]

[0137] As shown in Table 3, the image formations in Examples 1-9, which use a blocked isocyanate compound containing three or more blocked isocyanate groups in which the isocyanate groups are blocked by dimethylpyrazole, demonstrate improved friction fastness even when the ink is stored over time.

[0138] Furthermore, comparing Example 6, which uses a blocked isocyanate compound without a cyclic structure, with Examples 1 and 2, it can be seen that the less cyclic structure the blocked isocyanate compound contains, the better the texture. In particular, Example 6, which uses a blocked isocyanate compound without a cyclic structure, shows particularly excellent texture. [Industrial applicability]

[0139] According to the present invention, it is possible to provide an inkjet ink that can improve friction fastness even when the ink is stored over time.

Claims

1. It contains water, a water-dispersible resin, and a blocked isocyanate compound. The blocked isocyanate compound contains three or more blocked isocyanate groups, each in which an isocyanate group is blocked by dimethylpyrazole. Inkjet ink.

2. The aforementioned blocked isocyanate compound does not have a cyclic structure. The inkjet ink according to claim 1.

3. The aforementioned blocked isocyanate compound is a compound in which the isocyanate group of hexamethylene diisocyanate biuret is blocked. The inkjet ink according to claim 1.

4. The water-dispersible resin is an ether-based urethane resin. The inkjet ink according to claim 1.

5. The content of the blocked isocyanate compound is 0.10% to 1.00% by mass relative to the total mass of the inkjet ink. The inkjet ink according to claim 1.

6. Inkjet ink for textile printing, The inkjet ink according to claim 1.

7. The process includes applying an inkjet ink according to any one of claims 1 to 6 onto a substrate using an inkjet method. Image forming method.

Images