Ink set and image forming method

Abstract

An ink set having: an ink composition containing a particle having a polymerizable group and water; and a maintenance liquid containing a pH buffering agent and water.

Description

Technical Field

[0001] This invention relates to an ink set and an image forming method. Background Technology

[0002] In inkjet technology, an image recording technology for recording color images, there is a known ink group comprising: ink (ink composition) containing pigment; and a maintenance fluid that, in addition to continuously (maintaining) the inkjet head that ejects the ink composition and its ejection performance in an initial state or close to such a state, also cleans the inkjet head.

[0003] In Japanese Patent Application Publication No. 2013-146952, a maintenance solution was disclosed that contains nitrogen-containing compounds and nitrogen-containing heterocyclic compounds, and has a pH set to 5.0 to 9.0, addressing problems such as ink agglomeration caused by contact between the maintenance solution and ink during storage with a decreased pH, corrosion of metal parts by the maintenance solution with a decreased pH, and deterioration of the hydrophobic film applied to the inkjet head. Furthermore, Japanese Patent Application Publication No. 2013-64074 discloses an ink group comprising: a water-based curable ink containing pigments, water, resin particles, a polymerizable compound having a (meth)acrylamide structure, and a polymerization initiator; and a maintenance solution that improves the cleaning properties based on the maintenance solution by making the solubility parameter (SP value) of a specific polymerizable compound forming the resin particles close to the SP value of the compound contained in the maintenance solution.

[0004] These maintenance solutions disclosed in Japanese Patent Application Publication Nos. 2013-146952 and 2013-64074 are improved maintenance solutions that address the difficulty of cleaning ink compositions containing pigments and resin particles. In the ink compositions disclosed in Japanese Patent Application Publication Nos. 2013-146952 and 2013-64074, so-called self-dispersing resin particles are used as resin particles. On the other hand, unlike the ink compositions containing self-dispersing resin particles disclosed in Japanese Patent Application Publication Nos. 2013-146952 and 2013-64074, an ink composition is known to contain particles with polymerizable groups, including polymerizable compounds and polymerization initiators (e.g., International Publication No. 2023 / 053593). Summary of the Invention

[0005] The technical problem to be solved by the invention However, regarding ink compositions containing particles with polymerizable groups, as disclosed in International Publication No. 2023 / 053593, the pH sometimes decreases over time due to their susceptibility to hydrolysis. This also lowers the pH of the entire system, including the cleaning solution, sometimes resulting in reduced cleaning performance based on the cleaning solution. Even if the reduction in cleaning performance is prevented by increasing the pH of the cleaning solution, aggregation of the ink composition in contact with the cleaning solution may occur, sometimes leading to ink stability problems.

[0006] Therefore, in view of the above-mentioned actual situation, the object of the present invention is to provide an ink group and an image forming method, wherein the ink group contains a maintenance liquid with excellent cleaning properties and excellent ink stability for an ink composition containing particles with polymerizable groups.

[0007] means for solving technical problems The inventors conducted in-depth research to achieve the above objectives and obtained the following insights: for ink compositions containing particles with polymerizable groups, by using a maintenance liquid containing a pH buffer that has the function of inhibiting pH changes, it is possible to balance cleanliness and ink stability, and based on this insight, the present invention was completed.

[0008] That is, the present invention includes the following methods.

[0009] <1> An ink group comprising: an ink composition containing particles having polymerizable groups and water; and a maintenance liquid containing a pH buffer and water.

[0010] <2> According to the ink group described in <1>, the pH buffer is an alkaline compound with a pKa of 7.6 to 9.0.

[0011] <3> The ink group according to <1> or <2>, wherein the pH of the maintenance solution is 8.0 to 9.0.

[0012] <4> The ink group according to any one of <1> to <3>, wherein the maintenance liquid further contains a surfactant.

[0013] <5> According to the ink group described in <4>, the surfactant comprises R 1 -O-(CH2CH2O) m -H represents polyoxyethylene alkyl ether, R 1 The group represents a hydrocarbon group with 6 to 16 carbon atoms, and m represents an integer from 3 to 15.

[0014] <6> The ink group according to <4>, wherein the HLB value of the surfactant is 12.6 to 17.0.

[0015] <7> According to the ink group described in <4>, the molecular weight of the surfactant is 200 to 400.

[0016] <8> According to the ink group described in <4>, the value obtained by subtracting the polarity term of the solubility parameter of the surfactant contained in the maintenance liquid from the value of the polarity term of the solubility parameter of the particle polymer having polymeric groups is in the range of -1.5 to 0.5.

[0017] <9> The ink group according to any one of <1> to <7>, wherein the particles having polymerizable groups are resin particles having urethane bonds.

[0018] <10> The ink group according to any one of <1> to <9>, wherein the particles having polymerizable groups are resin particles having constituent units derived from acrylate compounds.

[0019] <11> The ink group according to any one of <1> to <10>, wherein the ink composition contains a polymeric compound that is different from the particles having polymeric groups.

[0020] <12> The ink group according to any one of <1> to <11>, wherein the particles having polymerizable groups contain either or both of a polymerizable compound and a polymerization initiator, and are dispersed in water.

[0021] <13> An image forming method using any one of <1> to <12>, the image forming method comprising: an ink application step of ejecting an ink composition contained in the ink group from an inkjet head and applying it to a recording medium; and an ink removal step of removing an ink composition adhering to the inkjet head using a maintenance fluid contained in the ink group.

[0022] Invention Effects According to the present invention, an ink composition with excellent cleanability and excellent ink stability can be provided for ink compositions containing particles with polymerizable groups and water.

[0023] Furthermore, according to the present invention, an image forming method can be provided that uses an ink composition that exhibits excellent cleanability and ink stability to ink compositions containing particles with polymerizable groups and water, and can stably form an image even if the pH of the ink composition decreases over time. Detailed Implementation

[0024] The ink group and image forming method of the present invention will be described in detail below.

[0025] In this specification, the numerical range represented by “~” indicates the range included by taking the values ​​before and after “~” as the minimum and maximum values, respectively.

[0026] In this specification, the amount of each component in the composition, when there are multiple substances in the composition equivalent to each component, means the total amount of those multiple substances in the composition, unless otherwise stated.

[0027] In this specification, the term "process" includes not only independent processes, but also processes that can be clearly distinguished from other processes, as long as the intended purpose of the process can be achieved.

[0028] In this specification, "image" refers to the entire film formed by ink. The concept of "image" includes not only patterned images (e.g., characters, symbols, or graphics) but also solid images.

[0029] In this specification, "light" is a concept that includes active energy rays such as gamma rays, beta rays, electron beams, ultraviolet rays, and visible light.

[0030] In this specification, ultraviolet light is sometimes referred to as "UV (Ultra Violet) light".

[0031] In this specification, light generated from an LED (Light Emitting Diode) light source is sometimes referred to as "LED light".

[0032] In this specification, "(meth)acrylic acid" is a concept that includes both acrylic acid and methacrylic acid, "(meth)acrylate" is a concept that includes both acrylate and methacrylate, and "(meth)acryloyl" is a concept that includes both acryloyl and methacryloyl.

[0033] <<Ink Group>> The ink assembly of the present invention comprises: an ink composition containing particles having polymerizable groups and water; and a maintenance liquid containing a pH buffer and water. Even when using an ink composition containing particles having polymerizable groups, the ink assembly of the present invention exhibits excellent cleanability due to the maintenance liquid, and also excellent ink stability. Furthermore, excellent ink stability means that it does not cause agglomeration or other phenomena in the pigments or other particles contained in the ink composition.

[0034] The following sections will describe the maintenance fluid and ink composition in turn.

[0035] <Maintenance Fluid> The maintenance fluid involved in this invention refers to a solution that, in addition to maintaining the inkjet head that ejects the ink composition and its ejection performance in an initial or near-initial state, is also used to clean the inkjet head to prepare and maintain it in a better condition. For example, in this invention, when referred to as "cleaning property," it refers to the ability to remove ink compositions (e.g., ink adherence, dried ink film).

[0036] (pH buffer) The maintenance solution of this invention contains a pH buffer and water. The pH buffer is not particularly limited, and refers to a compound that exhibits pH buffering properties when in solution. Examples of pH buffers include weak acidic compounds, combinations of weak acidic compounds and their salts, weak basic compounds, and combinations of weak basic compounds and their salts. pH buffering refers to the ability to suppress drastic changes in pH and maintain the pH of the solution within a specific range, even when a certain amount of other acid or base is added to the solution. Therefore, a solution containing a pH buffer can maintain the pH within a specific range even when a specified amount of acid or base is added. While not particularly limited, a weak basic compound with a pKa (acid dissociation constant) of 7.6 to 9.0 is preferred, and a weak basic compound with a pKa of 7.8 to 8.3 is particularly more preferred. By using a pH buffer with a pKa value within this range, excellent cleaning properties can be achieved, and excellent ink stability can be maintained.

[0037] Furthermore, the maintenance solution of the present invention preferably contains, in addition to the aforementioned pH buffer, an alkaline or acidic compound that neutralizes the weakly acidic or weakly basic compounds contained in the pH buffer. By containing these alkaline or acidic compounds, the pH of the maintenance solution can be maintained within a desired range, achieving excellent cleaning properties and maintaining excellent ink stability. Here, if the pH of the maintenance solution is too low, the cleaning properties will decrease; if it is too high, the ink stability will decrease. Therefore, it is preferable to set it within a desired range. The reason for this is that the higher the pH of the maintenance solution, the more some of the charged repulsive groups of the polymerizable particles become acidic groups over time, thus becoming anionic groups, thereby making the polymer as a whole water-soluble and improving cleaning properties. The reason for this is that if the pH of the maintenance solution is too high, the hydrolysis of the polymerizable particles will accelerate, and stability will deteriorate. On the other hand, it is speculated that if the pH of the maintenance solution is too low, the charged repulsive groups of particles with polymerizable groups will be deactivated (replaced by acid), thus deteriorating the cleaning properties and stability when mixed with the cleaning solution.

[0038] Therefore, for example, the lower limit of the pH of the maintenance solution can be set to 6.5 or higher, particularly preferably 7.0 or higher, more preferably 7.5 or higher, even more preferably 8.0 or higher, and most preferably 8.5 or higher. Furthermore, for example, the upper limit of the pH of the maintenance solution can be set to 11.0 or lower, particularly preferably 10.5 or lower, more preferably 10.0 or lower, even more preferably 9.5 or lower, even more preferably 9.0 or lower, and most preferably 8.9 or lower. Among these, the pH of the maintenance solution is preferably 8.0 to 9.0.

[0039] In this invention, pH refers to the value measured using a pH meter after adjusting the liquid temperature to 25℃±0.2℃.

[0040] There are no particular limitations on the pH buffers that can be used in maintenance solutions. Examples include succinate, dimethylarsine, 2-morpholinoethanesulfonic acid, 2,2-bis(hydroxymethyl)-2,2',2''-nitrotriethanol, phosphate, N-(2-acetamide)iminodiacetic acid, N-(2-acetamide)-2-aminoethanesulfonic acid, 1,4-piperazine diethanesulfonic acid, imidazole, hydroxypropanesulfonic acid, 3-morpholinopropanesulfonic acid, N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid, N-(2-hydroxyethyl)piperazine-N′-(2-ethanesulfonic acid), N-tris(hydroxymethyl)methyl-2-aminoethanesulfonic acid, 4-(N-morpholinyl)butyric acid, 3-[N,N-bis(2-hydroxyethyl)amino]-2-hydroxypropanesulfonic acid, N-tris(hydroxyethyl)methoxy ... Methyl-3-aminopropanesulfonic acid, 4-(2-hydroxyethyl)-1-piperazine propanesulfonic acid, piperazine-1,4-bis(2-hydroxypropanesulfonic acid), triethanolamine, 4-(2-hydroxyethyl)-1-piperazine-1-propanesulfonic acid, tris(hydroxymethyl)aminomethane, tris(hydroxymethyl)glycine, glycylglycine, dihydroxyethylglycine, hydroxyethylpiperazine ethanesulfonic acid, N-tris(hydroxymethyl)methyl-3-aminopropanesulfonic acid, 2-amino-2-methyl-1,3-propanediol, N-tris(hydroxymethyl)methyl-3-aminopropanesulfonic acid, 2-hydroxyethyl)amino-1-propanesulfonic acid, boric acid, 2-cyclohexylaminoethanesulfonic acid, glycine, sodium 3-cyclohexylamino-2-hydroxypropanesulfonate, 3-cyclohexylaminopropanesulfonic acid, 4-(cyclohexylamino)-1-butanesulfonic acid, etc. From these pH adjusters, solutions that exhibit buffering effects within the target pH range can be appropriately selected.

[0041] Among these pH adjusters, particularly concerning 3-[N,N-bis(2-hydroxyethyl)amino]-2-hydroxypropanesulfonic acid (also known as DIPSO), N-tris(hydroxymethyl)methyl-3-aminopropanesulfonic acid (also known as TAPSO), 4-(2-hydroxyethyl)-1-piperazine propanesulfonic acid (also known as HEPPSO), piperazine-1,4-bis(2-hydroxypropanesulfonic acid) (also known as POPSO), triethanolamine (also known as TEA), 4-(2-hydroxyethyl)-1-piperazine-1-propanesulfonic acid (also known as EPPS), and tris(hydroxymethyl)amino Methane (also known as Tris), tris(hydroxymethyl)glycine, glycylglycine, di(hydroxyethyl)glycine, hydroxyethylpiperazine ethanesulfonic acid (also known as HEPBS), N-tris(hydroxymethyl)methyl-3-aminopropanesulfonic acid (also known as TAPS), 2-amino-2-methyl-1,3-propanediol (also known as AMPD), N-tris(hydroxymethyl)methyl-3-aminopropanesulfonic acid (also known as TABS), and 2-hydroxyethyl)amino-1-propanesulfonic acid (also known as AMPSO) are preferred because their pKa values ​​are in the range of 7.6 to 9.0. Table 1 summarizes whether these listed pH buffers are neutralized with base or acid, the pH range in which they exhibit buffering effect, and their pKa values. These pH buffers are available from Tokyo Chemical Industry Co., Ltd.

[0042] [Table 1]

[0043] (surfactant) In addition, the maintenance solution preferably contains a surfactant in addition to the pH buffer mentioned above. Using a maintenance solution containing a surfactant can further improve cleaning performance. The content of the surfactant in the maintenance solution is not particularly limited, but it is preferably 0.1% to 10% by mass relative to the total mass of the maintenance solution, more preferably 0.5% to 5% by mass, and even more preferably 0.8% to 1.2% by mass. If the surfactant content is within the above range, it is advantageous in terms of cleaning performance.

[0044] There are no particular limitations on the surfactant contained in the maintenance fluid, but it is preferred to be composed of R 1 -O-(CH2CH2O) m -H indicates polyoxyethylene alkyl ether. In the case of R... 1 -O-(CH2CH2O) m -H represents the formula where R 1 The hydrocarbon group can be a hydrocarbon group with 6 to 16 carbon atoms, and is particularly preferred to be a hydrocarbon group with 6 to 12 carbon atoms. Furthermore, in the case of R... 1 -O-(CH2CH2O) mIn the formula represented by -H, m can be set to 3 to 15, and is preferably set to 4 to 8.

[0045] As a surfactant for polyoxyethylene alkyl ethers, commercially available products can be used appropriately. For example, examples include NOVEL6-3 (manufactured by Novel Corporation), NOVEL6-6 (manufactured by Novel Corporation), TAKESURF D1004 (manufactured by Takemoto Oil & Fat Co., Ltd.), TAKESURF D1006 (manufactured by Takemoto Oil & Fat Co., Ltd.), TAKESURF D1007 (manufactured by Takemoto Oil & Fat Co., Ltd.), CAFLON NE0400 (manufactured by UNIVAR Corporation), CAFLON NE0500 (manufactured by UNIVAR Corporation), Takesafu D-1706N (manufactured by Takemoto Oil & Fat Co., Ltd.), CAFLON NE0800 (manufactured by UNIVAR Corporation), Takesafu D-1715 (manufactured by Takemoto Oil & Fat Co., Ltd.), Emulgen 104P (manufactured by Kao Corporation), Emulgen 106 (manufactured by Kao Corporation), and Emulgen 108 (manufactured by Kao Corporation). CAFLON TD0500 (manufactured by UNIVAR), Synperonic 13 / 7-85-L (manufactured by CRODA), CAFLON TD0800 (manufactured by UNIVAR), Emulgen 709 (manufactured by Kao Corporation), CAFLON TD1000 (manufactured by UNIVAR), Emulgen 120, Tergitol 15-S-7 (manufactured by Dow), Neodol 25 / 7 (manufactured by Shell Chemicals), Emulgen 210 (manufactured by Kao Corporation), Emulgen220 (manufactured by Kao Corporation), Surfynol 420 (manufactured by Evonik), Surfynol 440 (manufactured by Evonik), etc.

[0046] Furthermore, the surfactant contained in the maintenance solution is not particularly limited, and can be a surfactant with an HLB value of 8.0 to 17.0, preferably 10.0 to 17.0, more preferably 11.5 to 17.0, and even more preferably 12.6 to 17.0. If the HLB value is below this range, the ink stability may deteriorate. Furthermore, if the HLB value exceeds this range, the surface activity decreases, and the cleaning performance may deteriorate. Therefore, by using a surfactant with an HLB value within this range, cleaning performance and ink stability can be maintained particularly well. HLB is an abbreviation for Hydrophobic Lipophile Balance, and the HLB value is a numerical value representing the balance between hydrophobicity and hydrophilicity, calculated by the following formula 1.

[0047] HLB = 20 × (formula weight of hydrophilic portion) / (molecular weight) ... Formula 1 Furthermore, when the surfactant has a polyoxyethylene structure, the "matrix weight of the hydrophilic part" in Formula 1 above can be set as the "matrix weight of the polyoxyethylene alkyl group".

[0048] Examples of surfactants with HLB values ​​of 12.6 to 17.0 among the aforementioned commercially available polyoxyethylene alkyl ethers include NOVEL 6-6 (HLB value: 14.4), TAKESURF D1006 (HLB value: 13.4), TAKESURF D1007 (HLB value: 14.1), CAFLON NE0800 (HLB value: 13.5), Takesafu D-1715 (HLB value: 16.1), CAFLON TD0800 (HLB value: 12.8), Emulgen 709 (HLB value: 13.3), CAFLON TD1000 (HLB value: 13.5), Emulgen 120 (HLB value: 15.3), Emulgen 220 (HLB value: 14.2), and Surfynol 440 (HLB value: 14.0). These surfactants are particularly preferred as surfactants contained in maintenance solutions.

[0049] Furthermore, the surfactant contained in the maintenance solution is preferably a surfactant with a molecular weight of 200 to 900, more preferably a surfactant with a molecular weight of 200 to 600, even more preferably a surfactant with a molecular weight of 200 to 500, and most preferably a surfactant with a molecular weight of 200 to 400. By using surfactants with molecular weights within this range, the surfactant can easily penetrate into the ink film, achieving excellent cleaning properties and maintaining excellent ink stability.

[0050] Examples of surfactants with molecular weights of 200 to 400 among the commercially available polyoxyethylene alkyl ethers mentioned above include NOVEL6-3 (molecular weight: 234), NOVEL6-6 (molecular weight: 366), TAKESURF D1004 (molecular weight: 306), TAKESURF D1006 (molecular weight: 394), CAFLON NE0400 (molecular weight: 334), CAFLON NE0500 (molecular weight: 378), and Emulgen 104P (molecular weight: 362). These surfactants are particularly preferred as surfactants contained in maintenance solutions.

[0051] Furthermore, as the surfactant contained in the maintenance solution, it is preferable to use a surfactant whose value of the polarity term of the solubility parameter (called the SP(P) value, and sometimes also referred to as δP of the SP value) differs slightly from the SP(P) value of the polymer constituting the particles having polymeric groups, as described later. Specifically, the surfactant contained in the maintenance solution can be set in the range of -2.5 to 1.0, particularly preferably in the range of -2.0 to 0.5, and more preferably in the range of -1.5 to 0.5. By using a surfactant whose difference from the SP(P) value of the polymer constituting the particles having polymeric groups is within this range, the compatibility with the ink composition is excellent, and therefore, particularly excellent cleanability can be maintained.

[0052] Regarding the commercially available polyoxyethylene alkyl ether surfactants mentioned above, their SP(P) values ​​are as follows. Based on the SP(P) values ​​measured for the polymers constituting the polymeric groups, surfactants whose SP(P) values ​​differ from those of the polymers constituting the polymeric groups are within the aforementioned range can be appropriately selected. NOVEL 6-3 has an SP(P) value of 5.6 MPa. 1 / 2 The SP (P) value of NOVEL 6-6 is 5.6 MPa. 1 / 2 The SP (P) value of TAKESURF D1004 is 5.0 MPa. 1 / 2 The SP (P) value of TAKESURF D1006 is 5.1 MPa. 1 / 2 The SP (P) value of TAKESURF D1007 is 5.2 MPa. 1 / 2 The SP (P) value of CAFLON NE0400 is 4.8 MPa. 1 / 2 The SP (P) value of CAFLON NE0500 is 4.9 MPa. 1 / 2 The SP (P) value of Takesafu D-1706N is 4.9 MPa. 1 / 2The SP (P) value of CAFLON NE0800 is 5.0 MPa. 1 / 2 The SP (P) value of Takesafu D-1715 is 5.4 MPa. 1 / 2 The SP (P) value of Emulgen 104P is 4.5 MPa. 1 / 2 The SP (P) value of Emulgen 106 is 4.6 MPa. 1 / 2 The SP (P) value of Emulgen 108 is 4.6 MPa. 1 / 2 The SP (P) value of CAFLON TD0500 is 4.4 MPa. 1 / 2 The SP (P) value of Synperonic 13 / 7-85-L is 4.6 MPa. 1 / 2 The SP (P) value of CAFLON TD0800 is 4.6 MPa. 1 / 2 The SP (P) value of Emulgen 709 is 4.7 MPa. 1 / 2 The SP (P) value of CAFLON TD1000 is 4.7 MPa. 1 / 2 The SP (P) value of Emulgen 120 is 4.9 MPa. 1 / 2 The SP (P) value of TERGITOL 15-S-7 is 4.5 MPa. 1 / 2 The SP (P) value of Neodol 25 / 7 is 4.4 MPa. 1 / 2 The SP (P) value of Emulgen 210 is 4.3 MPa. 1 / 2 The SP (P) value of Emulgen 220 is 4.5 MPa. 1 / 2 The SP (P) value of Surfynol 420 is 4.2 MPa. 1 / 2 The SP (P) value of Surfynol 440 is 4.4 MPa. 1 / 2 .

[0053] In solubility parameters, the Hansen solubility parameter (HSP value) is an index that takes into account the polarity of physical properties by dividing the Hildebrand solubility parameter (SP value) into three components: dispersion force term δD, polarity term δP, and hydrogen bonding term δH. Detailed information on the HSP value can be found in Hansen, Charles (2007). Hansen Solubility Parameters: Auser's handbook, Second Edition. Boca Raton, Fla: CRC Press. ISBN 9780849372483. Furthermore, the HSP value is calculated by inputting the structural formula of the compound into the following software. The software used is HSPiP (Hansen Solubility Parameters in Practice) ver4.1.07.

[0054] (Organic solvent) In the maintenance fluid of this invention, water or a water-soluble organic solvent is preferably used as the solvent. Water solubility, as used herein, means a solubility in water of 1% by mass or more at 25°C.

[0055] Examples of water-soluble organic solvents used in the maintenance fluids involved in this invention include, for example, alkyl diols (polyols) such as glycerol, ethylene glycol, and propylene glycol; sugar alcohols; alkyl alcohols with 1 to 4 carbon atoms such as ethanol, methanol, butanol, propanol, and isopropanol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-propyl ether, and ethylene glycol monomethyl ether. Isopropyl ether, diethylene glycol monoisopropyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol mono-tert-butyl ether, diethylene glycol mono-tert-butyl ether, triethylene glycol monoethyl ether, 1-methyl-1-methoxybutanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-tert-butyl ether, propylene glycol mono-n-propyl ether, propylene glycol monoisopropyl ether, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, dipropylene glycol monoisopropyl ether, tripropylene glycol monomethyl ether, and other glycol ethers. Water-soluble organic solvents can be used alone or in combination of two or more of these.

[0056] Furthermore, as a water-soluble organic solvent, for example, known water-soluble organic solvents described in Japanese Patent Application Publication No. 2011-074150, paragraphs 0124 to 0135, or Japanese Patent Application Publication No. 2011-079901, paragraphs 0104 to 0119, can also be used.

[0057] (Other ingredients) In addition to the pH buffer and surfactant mentioned above, the maintenance liquid involved in this invention may, as needed, contain other additives such as humectants, anti-fading agents, emulsion stabilizers, penetration enhancers, ultraviolet absorbers, preservatives, antifungals, defoamers, and viscosity modifiers.

[0058] (Moisturizer) In the maintenance solution of this invention, a humectant may be included to prevent drying or improve wettability. Preferably, the maintenance solution of this invention contains at least one humectant. By including a humectant, drying caused by the evaporation of water from the maintenance solution can be suppressed, and the deterioration of the composition of the maintenance solution during long-term storage can be prevented. The humectant refers to a water-soluble compound with low volatility and relatively high water-retention capacity.

[0059] Examples of moisturizers include, for instance, polyols (e.g., glycerin, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, pentaerythritol, etc.), lactams (e.g., 2-pyrrolidone, N-methyl-2-pyrrolidone, etc.), and water-soluble solid moisturizers (e.g., urea, thiourea, N-ethylurea and other nitrogen compounds, 1,6-hexanediol, 1,8-hexanediol, etc.). - Diols such as octanediol, 2,2-dimethyl-1,3-propanediol, and 2,2-diethyl-1,3-propanediol; trimethylolethane, trimethylolpropane, etc.; glucose, mannose, fructose, ribose, xylose, arabinose, galactose, aldose, glucosyl alcohol (sorbitol), maltose, cellobiose, lactose, sucrose, trehalose, maltotriose, etc. (monosaccharides, disaccharides, oligosaccharides, and polysaccharides, as well as reducing sugars, oxidized sugars, amino acids, and sulfose derivatives of these sugars). As a humectant used in this invention, polyols are preferred, more preferably glycerol, ethylene glycol, diethylene glycol, and triethylene glycol, with diethylene glycol being the most preferred.

[0060] The content of the humectant in the maintenance solution is preferably in the range of 1% to 20% by mass relative to the total amount of the maintenance solution. By having a humectant content of 1% by mass or more, drying caused by the evaporation of water from the maintenance solution is suppressed. Furthermore, by having a humectant content of 20% by mass or less, a decrease in fluidity due to increased viscosity can be prevented, and good cleanability is ensured. For the same reason, the humectant content is preferably 5% to 16% by mass.

[0061] (Physical properties of maintenance fluid, etc.) From an operational point of view, the viscosity of the maintenance fluid involved in this invention at 20°C is preferably 1 mPa·s or more and 1000 mPa·s or less, more preferably 1 mPa·s or more and less than 500 mPa·s, and even more preferably 2 mPa·s or more and less than 100 mPa·s. The viscosity can be measured using a VISCOMETER TV-22 (manufactured by TOKI SANGYO CO.,LTD) at 20°C.

[0062] The maintenance solution involved in this invention is preferably a colorless liquid without pigments. Furthermore, the content of solid components (at 25°C) in the maintenance solution is not particularly limited, but from the viewpoint of preventing solid residues after cleaning, it is preferably 5% by mass or less, more preferably 2% by mass or less.

[0063] <Ink Composition> The ink compositions constituting the ink group of the present invention contain particles having polymerizable groups (hereinafter also referred to as "specific particles") and water. Examples of specific particles having polymerizable groups include the following.

[0064] Method 1: The resin contained in specific particles does not have polymerizable groups, but contains polymeric compounds that do have polymerizable groups. Method 2: The resin contained in specific particles has polymerizable groups, and further contains polymeric compounds with polymerizable groups. Method 3: Only resins containing polymerizable groups in specific particles. (polymeric groups) In the ink composition of this invention, specific particles possess polymerizable groups. These polymerizable groups can be polymerizable groups of a resin containing polymerizable groups. That is, the resin contained in the specific particles can possess polymerizable groups. As described later, if the specific particles contain polymerizable monomers, the resin may not possess polymerizable groups. Therefore, the resin does not necessarily have to possess polymerizable groups. The resin may contain only one type of polymerizable group, or it may contain two or more types. The presence of polymerizable groups in the resin can be confirmed, for example, by Fourier transform infrared spectroscopy (FT-IR) analysis.

[0065] The polymerizable groups that may be contained in the resin are preferably photopolymerizable groups, and more preferably photoradical polymerizable groups. The photoradical polymerizable groups are preferably (meth)acryloyl, allyl, styrene, or vinyl, and (meth)acryloyl is more preferred from the viewpoint of free radical polymerization reactivity and the hardness of the formed film. Preferably, the polymerizable groups that may be contained in the resin include olefinic double bonds.

[0066] When the number of millimoles of olefinic double bonds in 1g of resin is set as the C=C value of the resin, from the viewpoint of further improving the hardness of the formed film, the C=C value of the resin is preferably 0.05 mmol or more, more preferably 0.10 mmol / g or more, even more preferably 0.30 mmol / g or more, and particularly preferably 0.50 mmol / g or more.

[0067] On the other hand, from the viewpoint of dispersion stability, the C=C value of the resin is preferably 3.00 mmol / g or less, more preferably 2.50 mmol / g or less, even more preferably 2.00 mmol / g or less, and particularly preferably 1.50 mmol / g or less.

[0068] (Resin) The resin can be a chain polymer or a cross-linked polymer. In this invention, a chain polymer refers to a polymer without a cross-linked structure, and a cross-linked polymer refers to a polymer with a cross-linked structure. Chain polymers can have cyclic structures or branched structures. For details regarding specific particles containing chain polymers, please refer, for example, to Japanese Patent No. 6584677.

[0069] As a preferred method for specific particles when the resin is a crosslinked polymer, examples include microcapsules comprising a shell composed of polymer P, which is a crosslinked polymer, and a core comprising a polymeric monomer. For example, Japanese Patent No. 6510681 can be consulted regarding specific particles comprising a crosslinked polymer.

[0070] From the viewpoint of extrusion properties, the resin is preferably a chain polymer without cross-linking structure. Preferably, the resin comprises structural units derived from isocyanate compounds and structural units derived from compounds containing active hydrogen groups. The resin of the preferred embodiment described above comprises bond U formed by the reaction of isocyanate groups of the isocyanate compound with the active hydrogen groups of the compound containing active hydrogen groups.

[0071] The active hydrogen group is preferably a hydroxyl, primary amino, or secondary amino group. For example, a urethane bond is formed by the reaction of the isocyanate group with the hydroxyl group. Furthermore, a urea bond is formed by the reaction of the isocyanate group with the primary or secondary amino group. In particular, as a specific particle, i.e., a particle having polymerizable groups, a resin containing urethane bonds is preferred.

[0072] Hereinafter, the isocyanate compound and the compound containing an active hydrogen group, which are raw materials for the resin having the preferred structure described above, will sometimes be referred to as raw material compounds. The isocyanate compound used as a raw material compound may be only one type or may be two or more types. The compound containing an active hydrogen group used as a raw material compound may be only one type or may be two or more types.

[0073] At least one isocyanate compound is preferred among the starting material compounds, preferably an isocyanate compound with two or more functional groups. At least one compound containing an active hydrogen group is preferred among the starting material compounds, preferably a compound containing two or more active hydrogen groups.

[0074] In the raw material compounds, at least one of the isocyanate compounds and compounds containing active hydrogen groups preferably contains anionic groups. This facilitates the manufacture of resins containing anionic groups. In this case, at least a portion of the anionic groups in the final resin can be neutralized groups from the anionic groups in the raw material compounds.

[0075] A more preferred method is that at least one of the compounds containing active hydrogen groups in the raw material compound is a compound containing both active hydrogen groups and anionic groups.

[0076] When the resin contains polymerizable groups, at least one of the isocyanate compound and the compound containing active hydrogen groups in the raw material compound preferably contains polymerizable groups. Therefore, it is easy to manufacture a resin containing polymerizable groups.

[0077] A more preferred embodiment is that at least one of the compounds containing active hydrogen groups in the raw material compound is a compound containing both active hydrogen groups and polymerizable groups.

[0078] When the resin is a chain polymer, it can be manufactured, for example, by reacting a difunctional isocyanate compound with a compound containing two active hydrogen groups. When the resin is a crosslinked polymer, it can be manufactured, for example, by reacting a trifunctional or more isocyanate compound with a compound containing two or more active hydrogen groups. When the resin is a crosslinked polymer, it can also be manufactured, for example, by reacting a difunctional isocyanate compound with a compound containing three or more active hydrogen groups.

[0079] Regarding preferred raw material compounds, for example, compounds disclosed in International Publication No. 2023 / 053593 can be used.

[0080] (Compounds for introducing polymeric groups) Particles with polymerizable groups can also be prepared by introducing polymerizable groups into the resin that constitutes specific particles. When introducing polymerizable groups into the resin, a compound for introducing polymerizable groups can be used. As a compound for introducing polymerizable groups, a compound having both polymerizable groups and active hydrogen groups can be used.

[0081] As a compound for introducing polymerizable groups, it is preferable to use a compound having one or more polymerizable groups and two or more active hydrogen groups.

[0082] There are no particular limitations on the method of introducing polymerizable groups into the resin, but in the synthesis of the resin, it is particularly preferred to react at least one of the group consisting of difunctional isocyanate compounds, at least one of the group consisting of water, glycol compounds, diamine compounds, and dithiol compounds, and at least one of the polymerizable group introducing compounds. The monomer for introducing polymerizable groups can be used alone or in combination of two or more.

[0083] As a compound for introducing polymerizable groups, compounds described in paragraphs 0075 to 0089 of International Publication No. 2016 / 052053 may also be used, for example.

[0084] As a compound for introducing polymerizable groups, a compound represented by the following formula (ma) is preferred.

[0085] L 1 Lc m Z n (ma) In the formula (ma), L 1 The group represents a linking group with an m+n valence, where m and n are independent integers selected from 1 to 100, Lc represents a monovalent olefinic unsaturated group, and Z represents an active hydrogen group.

[0086] L 1 Preferably, it is an aliphatic group or aromatic group or aromatic group or aromatic group or aromatic group or a heterocyclic group or aromatic group or aromatic group or aromatic group or aromatic group or aromatic group or a combination thereof, with a valence of 2 or more.

[0087] m and n are each preferably 1 to 50, more preferably 2 to 20, even more preferably 3 to 10, and especially preferably 3 to 5.

[0088] Examples of monovalent olefinic unsaturated groups represented by Lc include allyl, vinyl, acryloyl, and methacryloyl.

[0089] The active hydrogen group represented by Z is more preferably a hydroxyl or primary amino group, and even more preferably a hydroxyl group.

[0090] In particular, acrylate compounds can be cited as compounds for introducing polymerizable groups. By using acrylate compounds, it is possible to introduce the constituent units (acryloyl groups) derived from acrylate compounds into the synthesized resin.

[0091] (Resin properties) From the viewpoint of dispersion stability of aqueous dispersions (i.e., dispersion stability of specific particles), the weight-average molecular weight (Mw) of the resin is preferably 5,000 or more, more preferably 7,000 or more, and even more preferably 8,000 or more.

[0092] There is no specific limit to the upper limit of Mw; for example, 150,000, 100,000, 70,000, or 50,000 can be given.

[0093] In this invention, number-average molecular weight and weight-average molecular weight were determined using gel permeation chromatography (GPC). For example, an HLC-8220 GPC (manufactured by TOSOH CORPORATION) was used as the GPC column, with three TSKgel SuperMultipore HZ-H (manufactured by TOSOH CORPORATION, 4.6 mm ID × 15 cm) columns used as the eluent, and THF (tetrahydrofuran) as the eluent. The conditions were set as follows: sample concentration 0.45% by mass, flow rate 0.35 mL / min, sample injection volume 10 μL, measurement temperature 40 °C, and detection using a differential refractive index (RI) detector. Calibration curves were prepared using eight samples manufactured by Tosoh Corporation under the product name "TSK Standard Polystyrene": "F-40", "F-20", "F-4", "F-1", "A-5000", "A-2500", "A-1000", and "n-propylbenzene" as standard samples.

[0094] The glass transition temperature of the resin is preferably below 90°C, more preferably below 70°C. There is no particular limitation on the lower limit of the glass transition temperature; for example, it can be -50°C.

[0095] If the glass transition temperature of the resin is below 90°C, the resin's mobility increases, thereby increasing the polymerization rate. Furthermore, when specific particles contain polymerizable monomers, if the resin's glass transition temperature is below 90°C, the polymerizable monomers' mobility increases, further increasing the polymerization rate. As a result, migration can be suppressed.

[0096] The glass transition temperature (Tg) of a resin is a value determined using differential scanning calorimetry (DSC).

[0097] The glass transition temperature was determined according to the methods described in JIS K 7121 (1987) or JIS K 6240 (2011).

[0098] The glass transition temperature in this invention is the extrapolated glass transition initiation temperature (Tig).

[0099] The glass transition temperature is determined by the following method.

[0100] When determining the glass transition temperature, first maintain the temperature at a level approximately 50°C lower than the expected glass transition temperature of the resin until the apparatus stabilizes. Then, heat at a rate of 20°C / minute until the temperature is approximately 30°C higher than the end of the glass transition, in order to produce a differential thermal analysis (DTA) curve or a DSC curve.

[0101] The extrapolated glass transition onset temperature (Tig) is determined by the temperature at the intersection of the straight line drawn from the low-temperature side of the DTA or DSC curve to the high-temperature side and the tangent line drawn at the point where the slope of the curve in the stepwise change portion of the glass transition is the largest.

[0102] When the aqueous dispersion contains two or more resins, the glass transition temperature (Tg) of the resins refers to the weighted average of the glass transition temperatures of each resin.

[0103] From the viewpoint of dispersion stability, the resin content relative to the total solid content of specific particles is preferably 20% to 95% by mass, more preferably 30% to 90% by mass, and even more preferably 40% to 85% by mass.

[0104] (Polymerization initiator) The specific particles involved in this invention contain at least one polymerization initiator. The polymerization initiator is a compound that generates free radicals upon light irradiation.

[0105] Examples of polymerization initiators include, for instance, intramolecular cleavage photopolymerization initiators that produce intramolecular cleavage (sometimes simply called "cleavage photopolymerization initiators") and intramolecular hydrogen abstraction photopolymerization initiators that abstract hydrogen from the molecule (sometimes simply called "hydrogen abstraction photopolymerization initiators").

[0106] Examples of intramolecular cleavage-type photopolymerization initiators include alkyl phenyl ketone-based photopolymerization initiators, acylphosphine oxide-based photopolymerization initiators, and oxime ester-based photopolymerization initiators. Among these, acylphosphine oxide-based photopolymerization initiators are preferred.

[0107] Examples of acylphosphine oxide compounds include monoacylphosphine oxide compounds and diacylphosphine oxide compounds, with diacylphosphine oxide compounds being preferred.

[0108] Examples of monoacylphosphine oxide compounds include, for example, isobutyryl diphenylphosphine oxide, 2-ethylhexanoyl diphenylphosphine oxide, 2,4,6-trimethylbenzoyl diphenylphosphine oxide, (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide, o-toluyl diphenylphosphine oxide, p-tert-butylbenzoyl diphenylphosphine oxide, 3-pyridylcarbonyl diphenylphosphine oxide, acryloyl diphenylphosphine oxide, benzoyl diphenylphosphine oxide, and neopentyl phenylphosphine. Vinyl ester, adipyl bis(diphenylphosphine oxide), neopentyl diphenylphosphine oxide, p-toluyl diphenylphosphine oxide, 4-(tert-butyl)benzoyl diphenylphosphine oxide, terephthalyl bis(diphenylphosphine oxide), 2-methylbenzoyl diphenylphosphine oxide, neodecanoyl diphenylphosphine oxide, 2-methyl-2-ethylhexanoyl diphenylphosphine oxide, 1-methyl-cyclohexanoyl diphenylphosphine oxide, methyl neopentyl phenylphosphine and isopropyl neopentyl phenylphosphine.

[0109] Examples of diacylphosphine oxide compounds include, for example, bis(2,6-dichlorobenzoyl)phenylphosphine oxide, bis(2,6-dichlorobenzoyl)-2,5-dimethylphenylphosphine oxide, bis(2,6-dichlorobenzoyl)-4-ethoxyphenylphosphine oxide, bis(2,6-dichlorobenzoyl)-4-propylphenylphosphine oxide, bis(2,6-dichlorobenzoyl)-2-naphthylphosphine oxide, and bis(2,6... (-dichlorobenzoyl)-1-naphthylphosphine oxide, bis(2,6-dichlorobenzoyl)-4-chlorophenylphosphine oxide, bis(2,6-dichlorobenzoyl)-2,4-dimethoxyphenylphosphine oxide, bis(2,6-dichlorobenzoyl)decylphosphine oxide, bis(2,6-dichlorobenzoyl)-4-octylphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, bis(2,4,6- (trimethylbenzoyl)-2,5-dimethylphenylphosphine oxide, bis(2,6-dichloro-3,4,5-trimethoxybenzoyl)-2,5-dimethylphenylphosphine oxide, bis(2,6-dichloro-3,4,5-trimethoxybenzoyl)-4-ethoxyphenylphosphine oxide, bis(2-methyl-1-naphthoyl)-2,5-dimethylphenylphosphine oxide, bis(2-methyl-1-naphthoyl)-4- Ethoxyphenyl phosphine oxide, bis(2-methyl-1-naphthoyl)-2-naphthyl phosphine oxide, bis(2-methyl-1-naphthoyl)-4-propylphenyl phosphine oxide, bis(2-methoxy-1-naphthoyl)-4-ethoxyphenyl phosphine oxide, bis(2-chloro-1-naphthoyl)-2,5-dimethylphenyl phosphine oxide, and bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentyl phosphine oxide.

[0110] The preferred acylphosphine oxide compound is bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (product name "Omnirad 819", manufactured by IGM Resins BV), 2,4,6-trimethylbenzoyl diphenylphosphine oxide (product name "Omnirad TPO H", manufactured by IGM Resins BV), or (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide (product name "Omnirad TPO-L", manufactured by IGM Resins BV).

[0111] Examples of intramolecular hydrogen abstraction photopolymerization initiators include thioxanone compounds.

[0112] Examples of thioxanthone compounds include thioxanthone, 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2-chlorothioxanthone, 2,4-dichlorothioxanthone, 2-dodecylthioxanthone, 2,4-diethylthioxanthone, 2,4-dimethylthioxanthone, 1-methoxycarbonylthioxanthone, 2-ethoxycarbonylthioxanthone, 3-(2-methoxyethoxycarbonyl)thioxanthone, 4-butoxycarbonylthioxanthone, 3-butoxycarbonyl-7-methylthioxanthone, 1-cyano-3-chlorothioxanthone, 1-ethoxycarbonyl-3-chlorothioxanthone, 1-ethoxycarbonyl-3-ethoxythioxanthone, 1-ethoxycarbonyl-3-aminothioxanthone, 1-ethoxycarbonyl-3-phenylsulfonylthioxanthone, 3,4-bis[2-(2-methoxyethoxy)ethoxycarbonyl]thioxanthone, 1-ethoxycarbonyl- 3-(1-Methyl-1-morpholinylethyl)thioxanthone, 2-methyl-6-dimethoxymethylthioxanthone, 2-methyl-6-(1,1-dimethoxybenzyl)thioxanthone, 2-morpholinylmethylthioxanthone, 2-methyl-6-morpholinylmethylthioxanthone, N-allylthioxanthone-3,4-dicarboxylic acid imide, N-octylthioxanthone-3,4-dicarboxylic acid imide, N-(1,1, 3,3-Tetramethylbutyl)thioxanthone-3,4-dicarboxylic imide, 1-phenoxythioxanthone, 6-ethoxycarbonyl-2-methoxythioxanthone, 6-ethoxycarbonyl-2-methylthioxanthone, thioxanthone-2-polyethylene glycol ester and 2-hydroxy-3-(3,4-dimethyl-9-oxo-9H-thioxanthone-2-yloxy)-N,N,N-trimethyl-1-propaneammonium chloride.

[0113] Thioxanone compounds can be commercially available products. Examples of commercially available products include the SPEEDCURE series manufactured by Lambson (e.g., SPEEDCURE 7010, SPEEDCURE CPTX, and SPEEDCURE ITX).

[0114] The polymerization initiator preferably includes both intramolecular cleavage photopolymerization initiators and intramolecular hydrogen abstraction photopolymerization initiators. In the photoradical generator, the mass ratio of intramolecular cleavage photopolymerization initiator to intramolecular hydrogen abstraction photopolymerization initiator (intramolecular cleavage photopolymerization initiator: intramolecular hydrogen abstraction photopolymerization initiator) is preferably 50:50 to 95:5, more preferably 70:30 to 90:10.

[0115] (polymeric compounds) The specific particles involved in this invention preferably contain at least one polymerizable compound. In this invention, "polymerizable compound" refers to a monomer having polymerizable groups, which is different from the resin having polymerizable groups that constitute the specific particles.

[0116] When an ink composition applied to a substrate or similar material is cured, polymerizable compounds help to link specific particles together, thereby improving the scratch resistance of the resulting film.

[0117] As a polymeric compound contained in a specific particle, the compound described in paragraphs 0097 to 0105 of International Publication No. 2016 / 052053 may be used.

[0118] The polymerizable compounds that can be contained in specific particles are preferably photopolymerizable monomers, more preferably photoradical polymerizable monomers. Photopolymerizable monomers are compounds that have the property of polymerizing upon irradiation by light.

[0119] The molecular weight of the polymerizable compound is preferably 100–4000, more preferably 100–2000, even more preferably 100–1000, even more preferably 100–900, even more preferably 100–800, and particularly preferably 150–750. The molecular weight of the polymerizable compound can be calculated based on the types and amounts of elements constituting the polymerizable compound.

[0120] The preferred manner in which the polymerizable compound possesses polymerizable groups is the same as the preferred manner in which the polymerizable groups that the resin described above can contain. That is, the polymerizable compound is preferably a compound containing an olefinic double bond. Examples of polymerizable compounds include acrylate compounds, methacrylate compounds, styrene compounds, vinylnaphthalene compounds, N-vinyl heterocyclic compounds, unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, and unsaturated urethanes.

[0121] Examples of acrylate compounds include 2-hydroxyethyl acrylate, butoxyethyl acrylate, carbitol acrylate, cyclohexyl acrylate, tetrahydrofurfuryl acrylate, benzyl acrylate, tridecyl acrylate, 2-phenoxyethyl acrylate (PEA), bis(4-acryloyloxypolyethoxyphenyl)propane, low-polyester acrylates, epoxy acrylates, isobornyl acrylate (IBOA), dicyclopentenyl acrylate, dicyclopentenyloxyethyl acrylate, dicyclopentyl acrylate, cyclic trimethylolpropane formaldehyde acrylate, 2-(2-ethoxyethoxy)ethyl acrylate, 2-(2-vinyloxyethoxy)ethyl acrylate, octyl acrylate, decyl acrylate, isodecyl acrylate, lauryl acrylate, 3,3,5-trimethylcyclohexyl acrylate, and so on. Monofunctional acrylate compounds including 4-tert-butylcyclohexyl acrylate, isoamyl acrylate, stearyl acrylate, isostearyl acrylate, 2-ethylhexyl diethylene glycol acrylate, 2-hydroxybutyl acrylate, 2-acryloyloxyethyl hexahydrophthalic acid, ethoxydiethylene glycol acrylate, methoxydiethylene glycol acrylate, methoxypolyethylene glycol acrylate, methoxypropylene glycol acrylate, 2-hydroxy-3-phenoxypropyl acrylate, vinyl ether acrylate, 2-acryloyloxyethyl succinate, 2-acryloyloxyethyl phthalate, 2-acryloyloxyethyl-2-hydroxyethyl phthalate, lactone-modified acrylates, acryloylmorpholine, acrylamide, and substituted acrylamides (e.g., N-hydroxymethylacrylamide and diacetone acrylamide). Polyethylene glycol diacrylate, polypropylene glycol diacrylate, polytetramethylene glycol diacrylate, 1,3-butanediol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate (HDDA), 1,9-nonanediol diacrylate (NDDA), 1,10-decanediol diacrylate (DDDA), 3-methylpentanediol diacrylate (3MPDDA), neopentyl glycol diacrylate, tricyclodecanedimethylethanol diacrylate, bisphenol A ethylene oxide (EO) adduct diacrylate, bisphenol A propylene oxide (PO) adduct The compounds include diacrylates such as ethoxylated bisphenol A diacrylate, hydroxyneopentyl glycol diacrylate, propoxylated neopentyl glycol diacrylate, alkoxylated dihydroxymethyltricyclodecane diacrylate, alkoxylated cyclohexanone dimethyl diacrylate, alkoxylated hexanediol diacrylate, dioxanediol diacrylate, cyclohexanone dimethyl diacrylate, diethylene glycol diacrylate, tetraethylene glycol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate (TPGDA), and neopentyl glycol propylene oxide adduct diacrylate; Trimethylolpropane triacrylate, pentaerythritol triacrylate, dipentaerythritol tetraacrylate, ethoxylated isocyanurate triacrylate, ε-caprolactone-modified tri-(2-acryloyloxyethyl)isocyanurate, ditrimethylolpropane tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, ethoxylated trimethylolpropane triacrylate, propoxylated trimethylolpropane triacrylate, caprolactone-modified trimethylolpropane triacrylate, pentaerythritol tetraacrylate, pentaerythritol ethoxylated tetraacrylate, glycerol propoxylated triacrylate, ethoxylated dipentaerythritol hexaacrylate, caprolactone-modified dipentaerythritol hexaacrylate, propoxylated glycerol triacrylate, and other acrylate compounds with three or more functionalities.

[0122] In particular, among the above-mentioned monofunctional acrylate compounds, one compound selected from the group consisting of stearyl acrylate and isostearyl acrylate is preferred.

[0123] Examples of monofunctional methacrylate compounds include methyl methacrylate, n-butyl methacrylate, allyl methacrylate, glycidyl methacrylate, benzyl methacrylate, dimethylamino methacrylate, methoxy polyethylene glycol methacrylate, methoxy triethylene glycol methacrylate, hydroxyethyl methacrylate, phenoxyethyl methacrylate, and cyclohexyl methacrylate. Difunctional methacrylate compounds such as polyethylene glycol dimethacrylate, polypropylene glycol dimethacrylate, 2,2-bis(4-methacryloyloxypolyethoxyphenyl)propane, and tetraethylene glycol dimethacrylate.

[0124] Examples of styrene compounds include styrene, p-methylstyrene, p-methoxystyrene, β-methylstyrene, p-methyl-β-methylstyrene, α-methylstyrene, and p-methoxy-β-methylstyrene.

[0125] Examples of vinylnaphthalene compounds include 1-vinylnaphthalene, methyl-1-vinylnaphthalene, β-methyl-1-vinylnaphthalene, 4-methyl-1-vinylnaphthalene, and 4-methoxy-1-vinylnaphthalene.

[0126] Examples of N-vinyl heterocyclic compounds include N-vinylcarbazole, N-vinylpyrrolidone, N-vinylethylacetamide, N-vinylpyrrole, N-vinylphenthiazide, N-vinylacetanilide, N-vinylethylacetamide, N-vinylsuccinimide, N-vinylphthalimide, N-vinylcaprolactam, and N-vinylimidazolium.

[0127] Other polymerizable compounds include allyl glycidyl ether, diallyl phthalate, trimellitic acid trimellitate, N-vinylformamide, and other N-vinylamides.

[0128] From the viewpoint of further improving the adhesion between the film and the substrate, the polymeric compound that can be contained in the specific particles preferably contains a polymeric compound with a cyclic structure.

[0129] Examples of monofunctional polymerizable compounds with cyclic structures include 2-phenoxyethyl acrylate, cyclohexyl acrylate, tetrahydrofurfuryl acrylate, benzyl acrylate, isobornyl acrylate, dicyclopentenyl acrylate, dicyclopentenoxyethyl acrylate, dicyclopentyl acrylate, ethoxylated isocyanuric acid triacrylate, and ε-caprolactone-modified tri-(2-acryloyloxyethyl)isocyanurate.

[0130] Furthermore, examples of difunctional polymerizable compounds with cyclic structures include tricyclodecanediethanol di(meth)acrylate, bisphenol A ethylene oxide (EO) adduct di(meth)acrylate, bisphenol A propylene oxide (PO) adduct di(meth)acrylate, ethoxylated bisphenol A di(meth)acrylate, alkoxylated dihydroxymethyl tricyclodecanedi(meth)acrylate, alkoxylated cyclohexanone diethanol di(meth)acrylate, and cyclohexanone diethanol di(meth)acrylate.

[0131] In addition to the polymerizable compounds mentioned above, commercially available products and free radical polymerizable monomers known in the industry can also be used, as described in Shinzo Yamashita's "Crosslinking Agent Handbook" (Taiseisha, 1981); Kiyoshi Kato's "UV / EB Curing Handbook (Raw Materials)" (Polymer Journal, 1985); RadTech Japan's "Application and Market of UV / EB Curing Technology," p. 79 (CMC Publishing Co., Ltd., 1989); and Eiichiro Ryuzan's "Polyester Resin Handbook" (Nikkan Kogyo Shimbun, 1988).

[0132] Furthermore, as photopolymerizable compounds, there are known photocurable polymerizable compounds used in photopolymerizable compositions as described in Japanese Patent Application Publication No. 7-159983, Japanese Patent Application Publication No. 7-31399, Japanese Patent Application Publication No. 8-224982, Japanese Patent Application Publication No. 10-863, Japanese Patent Application Publication No. 9-134011, and Japanese Patent Application Publication No. 2004-514014. These can also be used as polymerizable compounds that can be contained in specific particles.

[0133] Commercially available photopolymerizable compounds can be used. Examples of commercially available photopolymerizable compounds include AH-600 (2-functional), AT-600 (2-functional), UA-306H (6-functional), UA-306T (6-functional), UA-306I (6-functional), UA-510H (10-functional), UF-8001G (2-functional), DAUA-167 (2-functional), LIGHT ACRYLATENPA (2-functional), and LIGHT ACRYLATE 3EG-A (2-functional) (the above are from KYOEISHA CHEMICAL). Co., Ltd.), SR339A (PEA, monofunctional), SR506 (IBOA, monofunctional), CD262 (dual-functional), SR238 (HDDA, dual-functional), SR341 (3MPDDA, dual-functional), SR508 (dual-functional), SR306H (dual-functional), CD560 (dual-functional), SR833S (dual-functional), SR444 (trifunctional), SR454 (dual-functional), SR492 (dual-functional), SR499 (dual-functional), CD501 (dual-functional), SR502 ( SR9020 (3-functional), CD9021 (3-functional), SR9035 (3-functional), SR494 (4-functional), SR399E (5-functional) (all from Sartomer Company, Inc.), A-NOD-N (NDDA, 2-functional), A-DOD-N (DDDA, 2-functional), A-200 (2-functional), APG-400 (2-functional), A-BPE-10 (2-functional), A-BPE-20 (2-functional), A-9300 (3-functional), A-9300-1CL (3-functional), A-TMPT (3-functional), A-TMM-3L (3-functional), A-TMMT (4-functional), AD-TMP (4-functional) (all from Shin-Nakamura Chemical Co., Ltd.), UV-7510B (3-functional) (Nippon Synthetic Chemical Industry) KAYARAD DPCA-30 (6-functional), KAYARAD DPEA-12 (6-functional) (the above are products of Nippon Kayaku Co., Ltd.), etc.

[0134] In addition, as polymerizable compounds, commercially available products such as NPGPODA (neopentyl glycol propylene oxide adduct diacrylate), SR531, SR285, SR256 (all from Sartomer Company, Inc.), A-DHP (dipentaerythritol hexaacrylate, Shin-Nakamura Chemical Co., Ltd.), ARONIX (registered trademark) M-156 (TOAGOSEI CO.,LTD.), V-CAP (BASF), and VISCOAT#192 (Osaka Organic Chemical Industry Co., Ltd.) can be preferably used.

[0135] The content of the polymeric compound relative to the total solid content of the specific particles is preferably 5% to 75% by mass, more preferably 10% to 65% by mass, even more preferably 15% to 55% by mass, and particularly preferably 20% to 50% by mass.

[0136] (Other ingredients) The ink composition of this invention may contain components other than specific particles and water. Examples of other components include pigments and water-soluble organic solvents. Furthermore, the aqueous dispersion of this invention may contain surfactants, polymerization inhibitors, ultraviolet absorbers, etc., which are commonly added to inks as additives. These other components may or may not be contained within the specific particles.

[0137] In the case where the ink composition of the present invention contains colorant, the ink composition of the present invention preferably contains colorant outside the specific particles (i.e., the specific particles do not contain colorant).

[0138] There are no particular restrictions on the pigment used; any known pigments such as pigments, water-soluble dyes, and disperse dyes can be selected. However, from the viewpoint of excellent weather resistance and rich color reproduction, pigments are preferred.

[0139] There are no particular limitations on pigments; they can be appropriately selected according to the purpose. Examples include well-known organic and inorganic pigments. Furthermore, examples include resin particles dyed with dyes, commercially available pigment dispersions, or surface-treated pigments (e.g., pigments dispersed in water, liquid compounds, or insoluble resins as a dispersion medium, and pigments whose surfaces have been treated with resins or pigment derivatives). Examples of organic and inorganic pigments include, for instance, yellow pigments, red pigments, magenta pigments, blue pigments, cyan pigments, green pigments, orange pigments, purple pigments, brown pigments, black pigments, and white pigments.

[0140] When using pigments as colorants, pigment dispersants can be used as needed. Furthermore, when using pigments as colorants, self-dispersing pigments with hydrophilic groups on the surface of the pigment particles can be used. For information on colorants and pigment dispersants, please refer to paragraphs 0180-0200 of Japanese Patent Application Publication No. 2014-040529 and paragraphs 0122-0129 of International Publication No. 2016 / 052053.

[0141] When the ink composition involved in this invention contains a colorant, the content of the colorant relative to the total amount of water dispersion is preferably 0.1% to 20% by mass, more preferably 0.5% to 10% by mass, and particularly preferably 0.5% to 5% by mass.

[0142] The ink composition of the present invention is preferably used as an inkjet ink. When using the ink composition of the present invention as an inkjet ink, from the viewpoint of improving ejectibility, the ink composition of the present invention preferably contains a water-soluble organic solvent on the exterior of specific particles.

[0143] Here, "water-soluble" refers to the property of dissolving more than 1g of a substance relative to 100g of distilled water at 25°C. When the ink composition according to this invention contains a water-soluble organic solvent, the content of the water-soluble organic solvent relative to the total amount of the ink composition is preferably 0.1% to 30% by mass, more preferably 1.0% to 20% by mass.

[0144] Specific examples of water-soluble organic solvents are as follows.

[0145] • Alcohols (e.g., methanol, ethanol, propanol, isopropanol, butanol, isobutanol, sec-butanol, tert-butanol, pentanol, hexanol, cyclohexanol, benzyl alcohol, etc.) • Polyols (e.g., ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butanediol, hexanediol, pentanediol, glycerol, glyceryl glycerol, thiodiethylene glycol, 2-methylpropanediol, etc.) • Polyol ethers (e.g., ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, tripropylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol dimethyl ether, ethylene glycol monomethyl ether acetate, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, ethylene glycol monophenyl ether, propylene glycol monophenyl ether, etc.) • Amines (e.g., ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine, etc.) • Amides (e.g., formamide, N,N-dimethylformamide, N,N-dimethylacetamide, etc.) Heterocyclic compounds (e.g., 2-pyrrolidone, N-methyl-2-pyrrolidone, cyclohexylpyrrolidone, 2-oxazolidinone, 1,3-dimethyl-2-imidazolone, γ-butyrolactone, etc.) • Sulfoxide compounds (e.g., dimethyl sulfoxide, etc.) • Sulfones (e.g., sulfolane, etc.) Others (urea, acetonitrile, acetone, etc.) [Methods for manufacturing specific particles] The method for manufacturing the specific particles involved in this invention is not particularly limited. For example, the method for manufacturing the specific particles can be achieved by mixing an oil phase component containing an organic solvent and the aforementioned resin with an aqueous phase component containing water and emulsifying the mixture to obtain the specific particles as a dispersion.

[0146] Examples of organic solvents contained in the oil phase include ethyl acetate and methyl ethyl ketone. Preferably, at least a portion of the organic solvent is removed during or after the formation of the specific particles.

[0147] Furthermore, in addition to the components mentioned above, the oil phase component may also contain, for example, any one or both of the aforementioned polymerizable compounds and polymerization initiators. In this case, specific particles contain any one or both of the aforementioned polymerizable compounds and polymerization initiators and are dispersed in water.

[0148] In the process of obtaining specific particles, the method of mixing the oil phase component and the aqueous phase component is not particularly limited; for example, mixing based on stirring can be cited. In the process of obtaining an aqueous dispersion of specific particles, the emulsification method is not particularly limited; for example, emulsification based on an emulsification device (e.g., a disperser) such as a homogenizer can be cited. The rotational speed of the disperser in emulsification is, for example, 5000 rpm to 20000 rpm, preferably 10000 rpm to 15000 rpm.

[0149] The rotation time during emulsification is, for example, 1 minute to 120 minutes, preferably 3 minutes to 60 minutes, more preferably 3 minutes to 30 minutes, and even more preferably 5 minutes to 15 minutes.

[0150] Emulsification in the process of obtaining specific particles can be performed under heating. Emulsification under heating allows for more efficient formation of specific particles. Furthermore, emulsification under heating facilitates the removal of at least a portion of the organic solvent from the oil phase component of the mixture. The heating temperature for emulsification under heating is preferably 35°C to 70°C, more preferably 40°C to 60°C.

[0151] Furthermore, the process for obtaining specific particles may include: an emulsification process, which emulsifies a mixture of oil phase and aqueous phase components (e.g., at a temperature below 35°C); and a heating process, which heats the emulsion obtained by the emulsification process (e.g., at a temperature above 35°C). In a process for obtaining specific particles that includes both an emulsification process and a heating process, the specific particles can be formed more effectively, particularly in the heating process. Furthermore, in a process for obtaining an aqueous dispersion of specific particles that includes both an emulsification process and a heating process, at least a portion of the organic solvent in the oil phase component is easily removed from the mixture, particularly in the heating process. The heating temperature in the heating process is preferably 35°C to 70°C, more preferably 40°C to 60°C. The heating time in the heating process is preferably 6 hours to 50 hours, more preferably 12 hours to 40 hours, and even more preferably 15 hours to 35 hours.

[0152] Furthermore, the method for manufacturing specific particles according to the present invention can include other steps besides the step of obtaining specific particles, as needed. Examples of other steps include adding other components (colorants, etc.) after the step of obtaining specific particles.

[0153] <<Image Formation Methods>> The image forming method of the present invention uses the ink group of the present invention described above. The image forming method includes: an ink application step, in which an ink composition contained in the ink group is ejected from an inkjet head and applied to a recording medium; and an ink removal step, in which an ink composition adhering to the inkjet head is removed using a maintenance fluid. The image forming method of the present invention may further include other steps as needed.

[0154] <Ink application process> The ink application process is the process of ejecting the ink composition of the present invention, as described in the inkjet head, from the inkjet head and applying it to the recording medium.

[0155] In this process, the ink composition can be selectively applied to the recording medium, enabling the formation of a desired visible image. Furthermore, details regarding the ink composition, including its specific features and preferred embodiments, have been described in the accompanying description.

[0156] Specifically, image recording using inkjet technology involves supplying energy to eject a liquid composition onto a desired recording medium, such as ordinary paper, resin-coated paper, inkjet-specific paper, film, general-purpose electronic photographic paper, cloth, glass, metal, ceramics, etc. Furthermore, as a preferred inkjet recording method in this invention, the method described in paragraphs 0093 to 0105 of Japanese Patent Application Publication No. 2003-306623 is applicable.

[0157] There are no particular limitations on inkjet printing methods; any known method can be used. For example, it can be a charge-controlled method that uses electrostatic attraction to eject ink, a drop-on-demand method (pressure pulse method) that uses the oscillating pressure of a piezoelectric element, an acoustic inkjet method that converts an electrical signal into a sound beam to irradiate the ink and ejects the ink using radial pressure, or a thermal inkjet method (BUBBLE JET (registered trademark)) that heats the ink to form bubbles and uses the resulting pressure. In particular, the inkjet method described in Japanese Patent Application Publication No. 54-59936 can be used effectively, where the ink undergoes a rapid volume change under heat, and the force generated by this change in state is used to eject the ink from the nozzle.

[0158] In addition, inkjet printing includes methods such as spraying large amounts of low-concentration ink called photo ink in small volumes, improving image quality by using multiple inks with basically the same hue but different concentrations, or using colorless and transparent inks.

[0159] Furthermore, the inkjet head used in inkjet printing can be either an on-demand inkjet head or a continuous inkjet head. Specific examples of the ejection method include electromechanical conversion methods (e.g., single-cavity, dual-cavity, beender, piston, shear-mode, common-wall, etc.), electrothermal conversion methods (e.g., thermal inkjet, BUBBLEJET, etc.), electrostatic attraction methods (e.g., electric field control, slit jet, etc.), and discharge methods (e.g., spark jet, etc.), and any of these ejection methods can be used.

[0160] Furthermore, there are no particular restrictions on the ink nozzles used when recording using inkjet technology, and the appropriate selection can be made according to the purpose.

[0161] The following are specific examples of inkjet recording methods.

[0162] As an inkjet recording method, (1) there is a method called electrostatic suction method. The electrostatic suction method is as follows: a strong electric field is applied between the nozzle and the acceleration electrode arranged in front of the nozzle, and droplet-shaped ink is continuously ejected from the nozzle. When the ink droplet passes between the deflection electrodes, a printing information signal is given to the deflection electrodes, thereby causing the ink droplet to fly toward the recording medium and fixing the ink onto the recording medium and recording an image. Alternatively, the ink droplet is ejected from the nozzle toward the recording medium according to the printing information signal without deflecting the ink droplet, thereby fixing the image onto the recording medium and recording an image.

[0163] Furthermore, (2) there is a method that applies pressure to the ink liquid by a small pump and mechanically vibrates the inkjet nozzle by a crystal oscillator or the like, thereby forcibly ejecting ink droplets from the nozzle. The ink droplets ejected from the nozzle are charged at the same time as they are ejected, and as the ink droplets pass between the deflection electrodes, printing information signals are assigned to the deflection electrodes, causing the ink droplets to fly toward the recording medium, thereby recording an image on the recording medium.

[0164] Next, (3) there is a method that simultaneously applies pressure and printing information signal to ink liquid by a piezoelectric element, causing ink droplets to be ejected from the nozzle toward the recording medium and an image to be recorded on the recording medium (piezoelectric), and (4) there is a method that uses a microelectrode to heat ink liquid according to the printing information signal to make it foam, and causes ink liquid to be ejected from the nozzle toward the recording medium by expanding the bubble and an image to be recorded on the recording medium (Bubble Jet (registered trademark)).

[0165] As inkjet heads, there are reciprocating methods that use short-sized serial printheads to scan and record simultaneously across the width of the recording medium, and linear methods that use linear printheads with recording elements arranged over an entire area corresponding to one side of the recording medium. In the linear method, by scanning the recording medium in a direction orthogonal to the arrangement direction of the recording elements, image recording can be performed on the entire surface of the recording medium, eliminating the need for a transport system such as a carriage for scanning short-sized printheads. Furthermore, since complex scanning control of carriage movement and the recording medium is not required, only the recording medium is moved, thus enabling higher recording speeds compared to the reciprocating method. The image forming method of the present invention can be applied to any of these methods, but it generally has a greater effect on improving printout accuracy and image scratch resistance when applied to the linear method without spurious ejection.

[0166] From the viewpoint of obtaining high-definition images, the amount of ink droplets ejected from the inkjet head is preferably 1 to 10 picoliters, and more preferably 1.5 to 6 picoliters. Furthermore, from the viewpoint of improving image uniformity and continuity, it is also effective to combine different droplet amounts for ejection, and even in this case, the present invention can be preferred.

[0167] <Ink Removal Process> The ink removal process in this invention is a process of removing the ink composition (including ink composition adherents (ink adherents)) adhering to the inkjet head using the maintenance fluid involved in this invention. The same applies hereinafter.

[0168] In the ink removal process, a protective liquid is applied to the printhead (e.g., the printhead periphery and ink flow path; hereinafter also referred to as "printhead, etc.") in order to remove the ink composition from the nozzle surface of the printhead. By applying the protective liquid to the printhead, the ink composition (e.g., ink adherence) dissolves, swells, etc.

[0169] The application of maintenance fluid can be achieved, for example, by inkjet-based ejection, roller coating, spraying, etc.

[0170] Furthermore, it is preferable to remove the ink composition by scraping with a doctor blade or wiping with a cloth or paper before or after applying the maintenance fluid. Preferred methods include: wiping the nozzle surface with a doctor blade (wiping) to remove the ink composition after applying the maintenance fluid; removing the ink composition by using air pressure or hydraulic pressure such as maintenance fluid; and wiping the ink composition with a cloth or paper.

[0171] The preferred material for the wiper blade is elastic rubber. Specific materials include butyl rubber, neoprene rubber, ethylene propylene rubber, silicone rubber, polyurethane rubber, and nitrile rubber. To impart ink-dispensing properties to the wiper blade, a wiper blade coated with a fluororesin or similar material can also be used.

[0172] The amount of the maintaining fluid provided is not particularly limited, as long as it is sufficient to dissolve and swell the ink composition. Preferably, it can be set to 1 g / m³. 2 ~100g / m 2 .

[0173] In the ink removal process of this invention, by using the maintenance liquid of this invention described above, ink deposits can be removed in a shorter time compared to conventional methods. Furthermore, in the ink removal process of this invention, it is preferable to apply the maintenance liquid of this invention to the nozzle surface before scraping with a scraper or wiping with a cloth or paper. This dissolves the ink deposits and prevents them from scraping the printhead surface due to scraping with a scraper or wiping with a cloth or paper.

[0174] <Processing fluid application process> The image forming method of the present invention preferably further includes a process of applying a processing liquid containing a coagulant that causes components in the ink composition to agglomerate onto a recording medium.

[0175] In this process, the processing liquid applied to the recording medium comes into contact with the ink composition applied to the recording medium in the ink application process to form an image. In this case, dispersed particles such as pigments or resin particles in the ink composition agglomerate, and the image is fixed on the recording medium.

[0176] The application of the treatment solution can be performed using known methods such as coating, inkjet printing, and dipping. As for coating methods, known methods such as doctor blade coaters, extrusion coaters, air knife coaters, scraper coaters, bar coaters, doctor blade coaters, extrusion coaters, and reverse roller coaters can be used. Details regarding inkjet printing are as described above.

[0177] The treatment liquid application process can be set before or after the ink application process using the ink composition.

[0178] In this invention, it is preferable to perform the ink application step after the processing liquid application step. In other words, it is preferable that the ink application step is performed after the processing liquid application step, and that the ink composition is applied to the processing liquid applied to the recording medium by the processing liquid application step. Specifically, it is preferable to pre-apply the processing liquid before applying the ink composition to the recording medium, and to apply the ink composition in contact with the processing liquid applied to the recording medium for imaging. As a result, inkjet recording can be accelerated, and even with high-speed recording, images with high density and resolution can be obtained.

[0179] Furthermore, in this invention, it is preferable to perform an ink application step after the treatment liquid application step, and to further perform a heat drying step of heating and drying the treatment liquid on the recording medium during the period from the application of the treatment liquid to the application of the ink composition. By preheating and drying the treatment liquid before the ink application step, ink colorability such as bleeding is prevented, and visual images with good color concentration and hue can be recorded.

[0180] Heating and drying can be performed using known heating methods such as heaters, air supply methods such as dryers, or combinations thereof. Examples of heating methods include heating the recording medium from the side opposite to the surface to which the processing liquid is applied using a heater, blowing warm or hot air onto the surface to which the processing liquid is applied on the recording medium, and heating using an infrared heater. Multiple methods can also be combined.

[0181] <Curing Process> The image forming method of the present invention preferably further includes a curing step of irradiating an ink composition applied to a recording medium by an ink application step with active energy rays to cure the ink composition.

[0182] Examples of active energy rays used here include alpha rays, gamma rays, electron beams, X-rays, ultraviolet light, visible light, and infrared light. Among these, ultraviolet light is preferred.

[0183] The curing process reliably polymerizes and cures the monomeric components (polymeric compounds) in the ink composition. At this point, if a light source irradiating the recording surface of the recording medium is positioned facing the recording surface and irradiates the entire recording surface, the entire image formed by the ink composition can be cured. Furthermore, the light source irradiating the recording surface can also be an ultraviolet lamp, a halogen lamp, a high-pressure mercury lamp, a laser, an LED, an electron beam irradiation device, etc.

[0184] The curing step is performed after the ink application step, but in the case where the image forming method of the present invention includes a processing liquid application step, it is preferable to perform the curing step after both the ink application step and the processing liquid application step.

[0185] As for the irradiation conditions of the active energy rays, there are no particular limitations as long as the polymerizable compound can polymerize and solidify. For example, the wavelength of the active energy rays is preferably 200-600 nm, more preferably 300-450 nm, and even more preferably 350-420 nm.

[0186] The preferred irradiation dose for active energy rays is 5000 mJ / cm². 2 The following values ​​are more preferably 10–4000 mJ / cm². 2 Further preferred is 20–3000 mJ / cm 2 .

[0187] <Recording Media> The image forming method of the present invention is a method of recording images on a recording medium. The recording medium is not particularly limited, and can be any common printing paper used in offset printing, such as high-quality cellulose-based paper, coated paper, or art paper. In image recording using water-based inkjet printing on cellulose-based printing paper, ink absorption and drying are relatively slow, and pigment migration easily occurs after the ink droplets are ejected, which can easily lead to a decrease in image quality. However, according to the image forming method of the present invention, pigment migration can be suppressed, and high-quality images with excellent color density and hue can be recorded.

[0188] As a recording medium, commercially available recording media can be used, such as high-quality paper (A) such as "OK PRINCE JOSHITSU" manufactured by OJI PAPER CO.,LTD., "SHIRAOI" manufactured by Nippon Paper Industries Co.,Ltd., and "NEW NPI JOSHITSU" manufactured by Nippon Paper Industries Co.,Ltd.; micro-coated paper such as "OK EVERLIGHT COAT" manufactured by OJI PAPER CO.,LTD., and "AURORA S" manufactured by Nippon Paper Industries Co.,Ltd.; lightweight coated paper such as "OK COAT L" manufactured by OJI PAPER CO.,LTD., and "AURORA L" manufactured by Nippon Paper Industries Co.,Ltd.; and "OK TOP COAT+" manufactured by OJI PAPER CO.,LTD., and "AURORA" manufactured by Nippon Paper Industries Co.,Ltd. Coated papers such as "COAT" (A2, B2), "OK KANTO+" manufactured by OJI PAPER CO.,LTD., and "Tokubishi Art" coated paper (A1) manufactured by Mitsubishi Paper MillsLimited are also available. In addition, various special photo papers for inkjet recording can also be used.

[0189] In recording media, coated paper, commonly used in offset printing, is preferred. Coated paper is paper with a coating formed by applying a coating to the surface of high-quality paper or neutral paper, which is generally untreated and primarily composed of cellulose. In conventional water-based inkjet image formation, coated paper is prone to quality problems such as image gloss or abrasion resistance. However, in the image formation method of the present invention, uneven gloss can be suppressed, thereby obtaining images with good gloss and abrasion resistance. In particular, coated paper having a base paper and a coating containing inorganic pigments is preferred, and coated paper having a base paper and a coating containing kaolin and / or heavy calcium carbonate is more preferred. More specifically, art paper, coated paper, lightweight coated paper, or micro-coated paper is more preferred.

[0190] Example The present invention will now be described in more detail through embodiments, but the technical scope of the present invention is not limited to the following embodiments. Furthermore, in the following description, unless otherwise stated, "room temperature" means 25°C.

[0191] [Preparation of Polymer P1] Polymer P1 with polymerizable groups was prepared. First, 187.9 g of methyl ethyl ketone, 116.4 g of isophorone diisocyanate, 13.9 g of cyclohexanediol, 82.9 g of epoxy acrylate (product name "EBECRYL600", manufactured by DAICEL-ALLNEX LTD.), 26.0 g of 2,2-bis(hydroxymethyl)propionic acid, 45.6 g of a hydroxyl-containing silicone compound (product name "SILAPLANE FM-DA11", manufactured by JNC Corporation), and 0.01 g of 2-tert-butyl-1,4-benzoquinone were added to a 1-liter three-necked flask equipped with a stirrer, thermometer, and reflux condenser. The temperature was raised to 70°C, and 0.5 g of tris(2-ethylhexanoate) bismuth (product name "NEOSTANN U-600", manufactured by DAICEL-ALLNEX LTD.) was added. Then, the reaction mixture was stirred for 8 hours while maintaining the temperature at 70°C.

[0192] Next, a solution consisting of 64.4 g of methyl ethyl ketone and 221.1 g of 2-propanol was added to the reaction vessel and stirred for 2 hours. Then, the temperature was lowered to 40°C and 25.1 g of N,N-diisopropylethylamine was added. While maintaining the temperature inside the reaction vessel at 40°C, the mixture was stirred for 1 hour to obtain a polymer P1 solution (polymer P1 content: 40% by mass, SP(P) value of polymer P1 = 6.5).

[0193] [Preparation of Polymer P2] Polymer P2, which lacks polymerizable groups, was prepared. First, 187.9 g of methyl ethyl ketone, 116.4 g of isophorone diisocyanate, 33.8 g of cyclohexanediol, 26.0 g of 2,2-bis(hydroxymethyl)propionic acid, 45.6 g of a hydroxyl-containing silicone compound (product name "SILAPLANE FM-DA11", manufactured by JNC Corporation), and 0.01 g of 2-tert-butyl-1,4-benzoquinone were added to a 1-liter three-necked flask equipped with a stirrer, thermometer, and reflux condenser. The mixture was heated to 70°C, and 0.5 g of tris(2-ethylhexanoate) bismuth (product name "NEOSTANN U-600", manufactured by DAICEL-ALLNEX LTD.) was added. The mixture was then stirred for 8 hours while maintaining the temperature in the reaction vessel at 70°C.

[0194] Next, a solution consisting of 64.4 g of methyl ethyl ketone and 221.1 g of 2-propanol was added to the reaction vessel and stirred for 2 hours. Then, the temperature was lowered to 40°C, and 25.1 g of N,N-diisopropylethylamine was added. While maintaining the temperature in the reaction vessel at 40°C, the mixture was stirred for 1 hour to obtain a polymer P2 solution (polymer P2 content: 40% by mass, SP(P) value of polymer P2 = 7.1).

[0195] [Preparation of Polymer P3] Referring to the example of WO2021 / 107104A1, a polymer P3 having polymerizable groups was prepared. First, 126 g (0.4 mol) of hexamethylene diisocyanate trimer, 262 g (0.8 mol) of pentaerythritol pentaacrylate and 510 g (0.4 mol) of polyethylene glycol monoallyl ether (n=30~40 in general formula (1) of WO2021 / 107104A1) were reacted to produce polymer P3 as a nonionic UV-curable polymer (SP (P) value of polymer P3 = 4.7).

[0196] [Preparation of Aqueous Dispersion 1 of Specific Particles] -Preparation of oil phase components- The following components were mixed and stirred at room temperature for 30 minutes to obtain the oil phase.

[0197] A 40% by mass solution of polymer P1…98.77 g UV3520EA (difunctional urethane oligomer, manufactured by Mitsubishi Chemical Corporation)...13.37g SR833 (a dual-functional monomer, manufactured by Arkema)...9.38g STA (monofunctional monomer, manufactured by OSAKA ORGANIC CHEMICAL INDUSTRY LTD.)...12.48g Polymerization initiator 1…2.4g Polymerization initiator 2…2.4g Sensitizer: SpeedCure DETX (manufactured by Arkema)...4.0g Ethyl acetate…58.85g Methyl ethyl ketone…117.38g In the above, polymerization initiator 1 is (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide (product name "Omnirad TPO-L", manufactured by IGM Resins BV). Furthermore, polymerization initiator 2 is phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (product name "Omnirad 819", manufactured by IGM Resins BV). Also, in the above, UV3520EA and SR833 are equivalent to polymerizable compounds.

[0198] -Preparation of aqueous dispersions of specific particles- The above oil phase components were mixed with 303.59 g of distilled water, and the resulting mixture was emulsified at 7000 rpm for 30 minutes at room temperature using a homogenizer to obtain an emulsion. The obtained mixture was heated to 50°C and stirred at 50°C for 4 hours, thereby distilling off ethyl acetate and methyl ethyl ketone from the mixture. The liquid from which ethyl acetate and methyl ethyl ketone were removed by distillation was diluted with distilled water to make the solids concentration 25% by mass, thereby obtaining an aqueous dispersion 1 of specific particles (specific particle content: 25% by mass). The volume average dispersed particle size of the specific particles was 90 nm.

[0199] [Preparation of Aqueous Dispersion 2 of Specific Particles] -Preparation of oil phase components- The following components were mixed and stirred at room temperature for 30 minutes to obtain the oil phase.

[0200] A 40% by mass solution of polymer P2…98.77 g UV3520EA (difunctional urethane oligomer, manufactured by Mitsubishi Chemical Corporation)...13.37g SR833 (a dual-functional monomer, manufactured by Arkema)...9.38g STA (monofunctional monomer, manufactured by OSAKA ORGANIC CHEMICAL INDUSTRY LTD.)...12.48g Polymerization initiator 1…2.4g Polymerization initiator 2…2.4g Sensitizer: SpeedCure DETX (manufactured by Arkema)...4.0g Ethyl acetate…58.85g Methyl ethyl ketone…117.38g In the above, polymerization initiator 1 and polymerization initiator 2 are the same as those used in [the preparation of aqueous dispersion 1 of specific particles].

[0201] -Preparation of aqueous dispersions of specific particles- The above oil phase components were mixed with 303.59 g of distilled water, and the resulting mixture was emulsified at 7000 rpm for 30 minutes at room temperature using a homogenizer to obtain an emulsion. The obtained emulsion was heated to 50°C and stirred at 50°C for 4 hours, thereby distilling off ethyl acetate and methyl ethyl ketone from the emulsion. The liquid from which ethyl acetate and methyl ethyl ketone were removed by distillation was diluted with distilled water to make the solids concentration 25% by mass, thereby obtaining an aqueous dispersion 2 of specific particles (specific particle content: 25% by mass). The volume average dispersed particle size of the specific particles was 90 nm.

[0202] [Preparation of Aqueous Dispersion 3 of Specific Particles] The polymer P3 obtained above was kept at 60°C and added dropwise to ion-exchange water preheated to 60°C with stirring to obtain an aqueous dispersion 3 of specific particles (specific particle content: 25% by mass). The average particle size (D50) of the specific particles in this aqueous dispersion was determined to be 36 nm using a MICROTRAC UPA particle size analyzer (MODEL: 9340-UPA, manufactured by Nikkiso Co., Ltd.).

[0203] [Preparation of Black Ink 1] Black ink 1 was prepared by mixing the following components.

[0204] • Aqueous dispersion of the above-mentioned specific particles 1 (specific particle content 25% by mass) ... 44 parts by mass • Pigment dispersion: Product name "Pro-jet Black APD1000", manufactured by FUJIFILM ImagingColorants, pigment concentration 15% by weight...20 parts by weight Surfactant: Polyoxyethylene alkyl ether (product name "EMULGEN 707", manufactured by Kao Corporation, solid content concentration 100% by mass)... 0.9 parts by mass Surfactant: Acetylene glycol (product name "Surfynol 440", manufactured by EVONIK, solid content 100% by mass)...0.9 parts by mass Surfactant: Acetylene glycol (product name "Surfynol 420", manufactured by EVONIK, solid content 100% by mass)...0.9 parts by mass • Water-soluble organic solvent: Propylene glycol (PG) … 14 parts by weight Water…the ink as a whole constitutes a balance of 100 parts by weight. [Preparation of Black Ink 2] Aqueous dispersion 2 using the aforementioned specific particles was used, and black ink 2 was prepared in the same manner as in [Preparation of black ink 1].

[0205] [Preparation of Black Ink 3] Using the aqueous dispersion 3 of the aforementioned specific particles, 0.2 parts by mass of GENOPOL TX-2 manufactured by RAHN and 0.4 parts by mass of Omnipol 910 manufactured by IGM were added, and black ink 3 was prepared in the same manner as in [Preparation of black ink 1].

[0206] [Preparation of maintenance fluid 1] As a surfactant, TAKESURF D1006 (molecular weight = 366, HLB = 14.4, SP (P) value = 5.6) was used, and maintenance solutions were prepared using various pH buffers shown in Tables 2 and 3.

[0207] [Preparation of maintenance fluid 2] As a pH buffer, a maintenance solution was prepared using tris(hydroxymethyl)aminomethane (Tris) and 1 mol / L nitric acid, along with various surfactants shown in Tables 5 and 6. Additionally, the surfactants used were derived from R... 1 -O-(CH2CH2O) m -H indicates polyoxyethylene alkyl ether.

[0208] [Evaluation of Maintenance Fluid - Cleaning Performance] For the various maintenance solutions prepared in [Preparation of Maintenance Solution 1] or [Preparation of Maintenance Solution 2], the cleaning properties were evaluated using black ink 1 to black ink 3. Specifically, initial ink or aged ink was sprayed onto the surface of the test piece using a sprayer to create an ink deposit with a droplet diameter of 50 μm, and then dried at 50°C for 1 hour. The surface material of the test piece used in this example is the same as the hydrophobic film with fluorinated alkyl groups on the surface of the printhead substrate of the inkjet recording device.

[0209] The dried test pieces with ink residue were immersed in 1 mL of the prepared maintenance solution for 1 hour. Then, the test pieces were removed from the maintenance solution, and the ink residue was observed using an optical microscope to determine the area of ​​the ink residue after immersion. Additionally, ink that had been stored at 70°C for 3 days was used as a time-resistant ink.

[0210] ~Evaluation Criteria~ 5…No ink residue was detected on the surface of the test piece.

[0211] 4…The area of ​​ink adhesion is less than 5% of the area of ​​ink adhesion before immersion.

[0212] 3…The area of ​​the ink-adhered material is more than 5% and less than 10% of the area of ​​the ink-adhered material before immersion.

[0213] 2…The area of ​​the ink-adhered material is more than 10% and less than 20% of the area of ​​the ink-adhered material before immersion.

[0214] 1…The area of ​​the ink-adhered material is more than 20% of the area of ​​the ink-adhered material before immersion.

[0215] [Evaluation of Maintenance Fluid - Stability] For the various maintenance solutions prepared in [Preparation of Maintenance Solution 1] or [Preparation of Maintenance Solution 2], the stability was evaluated using black ink 1 to black ink 3. Specifically, the ink and maintenance solution were mixed at a mass ratio of 10:90 and stored at 60°C for 7 days. Then, the particle size of the ink was observed using an optical microscope, and the change in particle size after storage was evaluated.

[0216] ~Evaluation Criteria~ 5…Particle size change rate is less than 5%.

[0217] 4… The particle size variation rate is greater than 5% and less than 10%.

[0218] 3… The particle size variation rate is greater than 10% and less than 20%.

[0219] 2… The particle size variation rate is greater than 20% and less than 30%.

[0220] 1…Particle size variation rate is over 30%.

[0221] [Evaluation Results] The cleaning properties and stability of the maintenance solutions obtained by changing the pH buffer used for black ink 1 are shown in Tables 2 and 3. Furthermore, the 21 maintenance solutions shown in Tables 2 and 3 are designated as Examples 1 to 21.

[0222] [Table 2]

[0223] [Table 3]

[0224] Furthermore, the maintenance solution that does not contain pH buffer was designated as Comparative Examples 1 to 3, and the results of the cleaning performance and stability were evaluated using black ink 1 in the same way, as shown in Table 4.

[0225] [Table 4]

[0226] As can be seen from the results in Tables 2 to 4, Examples 1 to 21, which used a combination of ink containing specific particles and water and a maintenance solution containing a pH buffer (i.e., ink group), showed superior cleanability for both initial and aged inks compared to Comparative Examples 1 to 3, where the maintenance solution in the ink group did not contain a pH buffer. Furthermore, the inks also exhibited superior stability.

[0227] Furthermore, the results from Examples 1 to 14 show that the ink stability is particularly excellent when the pH of the maintenance solution is set to 8.0–9.0 (Examples 3–5, 11, and 12). This is presumably because the hydrolysis of specific particles can be further suppressed when the pH of the maintenance solution is 8.0–9.0. As an example, to set the pH of the maintenance solution to 8.0–9.0, an alkaline compound with a pKa of 7.6–9.0 was used as a pH buffer in the maintenance solution. The results show that by using this alkaline compound as a pH buffer, the pH of the maintenance solution can be controlled at 8.0–9.0, thereby balancing ink cleanliness and ink stability.

[0228] Furthermore, as shown in Example 8, the pH of the maintenance solution can be set to the desired range using only a pH buffer. However, when the pH buffer is an alkaline compound, an acid (nitric acid in this example) can be used to control the pH of the maintenance solution within a more preferred range to prevent the pH from becoming too high. Conversely, when the pH buffer is an acidic compound, an alkali (sodium hydroxide in this example) can be used to control the pH of the maintenance solution within a more preferred range to prevent the pH from becoming too low. Thus, the maintenance solution can achieve superior cleaning properties and superior ink stability for inks.

[0229] Furthermore, the results from Examples 15 to 21 show that, when the total amount of the maintenance solution is 100% by mass, setting the surfactant content in the maintenance solution within the range of 0.5% to 5% by mass achieves both excellent cleaning properties and excellent ink stability. Additionally, as shown in Example 15, even maintenance solutions without surfactants exhibit excellent ink stability and good ink cleaning properties as long as the pH is within the above range via a pH buffer.

[0230] Next, the results of evaluating the cleaning properties and stability of the maintenance solutions used for black ink 1, with the surfactants changed, are shown in Tables 5 and 6. Furthermore, the 25 maintenance solutions shown in Tables 5 and 6 are designated as Examples 22 to 46. Example 25 has the same composition as Example 4 shown in Table 2. In the tables, R... 1 The m column represents R respectively. 1 -O-(CH2CH2O)m -H is from R 1 The number of carbon atoms in the hydrocarbon group and the value of m.

[0231] [Table 5]

[0232] [Table 6]

[0233] As shown in Tables 5 and 6, it can be seen that the maintenance solutions designated as Examples 22 to 46, due to the presence of a pH buffer, exhibit excellent cleaning properties for black ink 1 containing water dispersions of specific particles both initially and over time, and also demonstrate excellent stability.

[0234] Furthermore, the results of evaluating the cleaning properties and stability of the maintenance solution used for black ink 2 with a different surfactant are shown in Table 7. Additionally, the 10 maintenance solutions shown in Table 7 are designated as Examples 47 to 56.

[0235] [Table 7]

[0236] As shown in Table 7, it can be seen that the maintenance solutions designated as Examples 47 to 56, due to the presence of a pH buffer, exhibit excellent cleaning properties for black ink 2 containing specific particles in water dispersions, both initially and over time, and also demonstrate excellent stability.

[0237] Furthermore, the results of evaluating the cleaning properties and stability of the maintenance solutions used for black ink 3, with different surfactants, are shown in Tables 8 and 9. Additionally, the 25 maintenance solutions shown in Tables 8 and 9 are designated as Examples 57 to 81.

[0238] [Table 8]

[0239] [Table 9]

[0240] As shown in Tables 8 and 9, it can be seen that the maintenance solutions of Examples 57 to 81 contain a pH buffer, and therefore exhibit excellent cleaning properties and stability for black ink 3 containing aqueous dispersions of specific particles, both initially and over time.

[0241] If the results shown in Tables 5 to 9 above are verified, as in Examples 23, 25, 26, 30, 31, 38 to 40, 41, 46, 48, 50, 51, 55, 56, 58, 60, 61, 65, 66, 73 to 75, 79 and 81, it can be seen that the stability of the ink is better in the maintenance liquid containing surfactants with HLB values ​​in the range of 12.6 to 17.0.

[0242] Furthermore, based on the evaluation results of the cleaning properties of initial ink and aged ink shown in Tables 5-9, it can be seen that surfactants with smaller molecular weights exhibit superior cleaning properties, and surfactants with smaller values ​​of [SP(P) value of surfactant in maintenance solution] - [SP(P) value of specific particles] exhibit superior cleaning properties. This is presumably because surfactants with smaller molecular weights can more easily penetrate the dried ink film, and a smaller value of [SP(P) value of surfactant in maintenance solution] - [SP(P) value of specific particles] indicates better compatibility with the ink film.

[0243] In particular, excellent detergency is exhibited when the molecular weight of the surfactant is 400 or less, and especially excellent detergency is exhibited when the value of [SP(P) value of surfactant in maintenance liquid] - [SP(P) value of specific particles] is in the range of -1.5 to 0.5. These surfactant molecular weights and the value of [SP(P) value of surfactant in maintenance liquid] - [SP(P) value of specific particles] are independent variables in surfactants. Therefore, it is preferable to use a surfactant that satisfies either a molecular weight of 400 or less or a value of [SP(P) value of surfactant in maintenance liquid] - [SP(P) value of specific particles] within the range of -1.5 to 0.5. In particular, it is most preferable to use a surfactant with a molecular weight of 400 or less and a value of [SP(P) value of surfactant in maintenance liquid] - [SP(P) value of specific particles] within the range of -1.5 to 0.5.

[0244] The disclosure of Japanese Patent Application No. 2024-54591, filed on March 28, 2024, is incorporated herein by reference in its entirety.

[0245] All documents, patent applications and technical references described in this specification are incorporated herein by reference to the same extent as the specific and individually described documents, patent applications and technical references incorporated herein by reference.

Claims

1. An ink assembly comprising: An ink composition containing particles with polymerizable groups and water; and The maintenance solution contains a pH buffer and water.

2. The ink assembly according to claim 1, wherein, The pH buffer is an alkaline compound with a pKa of 7.6 to 9.

0.

3. The ink assembly according to claim 1, wherein, The pH of the maintenance solution is 8.0 to 9.

0.

4. The ink assembly according to claim 1, wherein, The maintenance fluid also contains surfactants.

5. The ink assembly according to claim 4, wherein, The surfactant comprises R 1 -O-(CH2CH2O) m -H represents polyoxyethylene alkyl ether, R 1 It represents a hydrocarbon group with 6 to 16 carbon atoms, and m represents an integer from 3 to 15.

6. The ink group according to claim 4, wherein, The surfactant has an HLB value of 12.6 to 17.

0.

7. The ink assembly according to claim 4, wherein, The surfactant has a molecular weight of 200 to 400.

8. The ink group according to claim 4, wherein, The value obtained by subtracting the polarity value of the solubility parameter of the surfactant contained in the maintenance solution from the value of the polarity value of the solubility parameter of the polymer particles with polymeric groups is in the range of -1.5 to 0.

5.

9. The ink assembly according to claim 1, wherein, The particles with polymerizable groups are resin particles with urethane bonds.

10. The ink assembly according to claim 1, wherein, The particles having polymerizable groups are resin particles having constituent units derived from acrylate compounds.

11. The ink set according to claim 1, wherein, The ink composition contains a polymeric compound that is different from the particles having polymeric groups.

12. The ink assembly according to claim 1, wherein, The particles having polymerizable groups contain one or both of a polymerizable compound and a polymerization initiator, and are dispersed in water.

13. An image forming method using the ink set according to any one of claims 1 to 12, the image forming method comprising: The ink application process involves ejecting the ink composition contained in the ink group from the inkjet head and applying it to the recording medium; and The ink removal process uses a maintenance fluid contained in the ink assembly to remove the ink composition adhering to the inkjet head.

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