Inkjet ink

Abstract

The present invention provides an inkjet ink containing a pigment, resin particles, and an aqueous medium. The resin particles contain a specific polyurethane resin. The content ratio of the resin particles is 2.5 mass% or more and 9.0 mass% or less. The specific polyurethane resin has an elongation at break of 60% or less at 25 DEG C. The specific polyurethane resin has a glass transition temperature of from 40 DEG C to 110 DEG C (inclusive). The aqueous medium contains water and a specific organic solvent. The content ratio of the specific organic solvent is 0.3% by mass or more and less than 2.0% by mass. The boiling point of the specific organic solvent is from 200 DEG C to 275 DEG C (inclusive). The SP value of the specific organic solvent is 19.5 (J / cm3) 1 / 2 or more and 26.0 (J / cm3) 1 / 2 or less.

Description

Technical Field

[0001] The present invention relates to an ink for inkjet use. Background Art

[0002] Some inkjet recording devices use an aqueous ink for inkjet containing a pigment and an aqueous medium. Excellent ejection stability is required for the ink for inkjet. In addition, the inkjet recording device sometimes forms an image on a non-permeable recording medium such as an OPP (biaxially oriented polypropylene) film or a PET (polyethylene terephthalate) film.

[0003] In addition, when the image formed on the non-permeable recording medium by the inkjet recording device comes into contact with other members (for example, other recording media), there sometimes occur a phenomenon in which the pigment contained in the image adheres to other members and a phenomenon in which the image peels off from the recording medium. Therefore, for the ink for inkjet used for such purposes, even when forming an image on a non-permeable recording medium, it is required to form an image excellent in scratch resistance and adhesion to the recording medium.

[0004] In response to such requirements, for example, an ink for inkjet containing a pigment, fine particles of a polyester resin having a particle size of 30 to 300 nm, and a water-soluble epoxy compound has been proposed (Japanese Patent Laid-Open No. 2003-313468). Summary of the Invention

[0005] Problems to be Solved by the Invention

[0006] However, even with the ink for inkjet described in Japanese Patent Laid-Open No. 2003-313468, it is difficult to exhibit excellent ejection stability and form an image excellent in scratch resistance and adhesion to the recording medium.

[0007] The present invention has been made in view of the above problems, and an object thereof is to provide an ink for inkjet that has excellent ejection stability and can form an image excellent in scratch resistance and adhesion to the recording medium.

[0008] Means for Solving the Problems

[0009] The ink for inkjet of the present invention contains a pigment, resin particles, and an aqueous medium. The above resin particles contain a specific polyurethane resin. The content ratio of the above resin particles is 2.5% by mass or more and 9.0% by mass or less. The elongation at break of the above specific polyurethane resin at 25°C is 60% or less. The glass transition temperature of the above specific polyurethane resin is 40°C or more and 110°C or less. The above aqueous medium contains water and a specific organic solvent. The content ratio of the above specific organic solvent is 0.3% by mass or more and less than 2.0% by mass. The boiling point of the above specific organic solvent is 200°C or more and 275°C or less. The SP value of the above specific organic solvent is 19.5 (J / cm 3) 1 / 2 or more and 26.0 (J / cm 3 ) 1 / 2 or less.

[0010] Advantages of the Invention

[0011] The ink for inkjet of the present invention can form an image excellent in scratch resistance and adhesion to a recording medium while having excellent ejection stability. Detailed Description of the Invention

[0012] Hereinafter, embodiments of the present invention will be described. In addition, hereinafter, unless otherwise specified, the measured value of the volume median diameter (D 50 ) is a value measured using a dynamic light scattering particle size distribution measuring device (for example, "Zetasizer Nano ZS" manufactured by Malvern).

[0013] The elongation at break can be measured by a tensile test using a tensile tester at 25°C in accordance with "JIS (Japanese Industrial Standards) K7127-1999".

[0014] Unless otherwise specified, the measured value of the glass transition temperature (Tg) is a value measured using a differential scanning calorimeter (for example, "DSC-60" manufactured by Shimadzu Corporation) in accordance with "JIS (Japanese Industrial Standards) K7121-2012". In the endothermic curve measured by the differential scanning calorimeter (vertical axis: heat flow (DSC signal), horizontal axis: temperature, heating rate 5°C / minute), the temperature of the inflection point caused by the glass transition (specifically, the temperature of the intersection of the extrapolated line of the baseline and the extrapolated line of the descending line) corresponds to Tg (glass transition temperature).

[0015] Unless otherwise specified, the SP value represents a value calculated using the SP value calculation and prediction software "Hansen Solubility Parameter in Practice (HSPiP) Ver.5.2.06" (developer: Prof. Steven Abbott, etc.).

[0016] In addition, in this specification, acrylic acid and methacrylic acid are sometimes collectively referred to as "(meth)acrylic acid". Each component described in this specification can be used alone or in combination of two or more. "At least one of A and B" means "A, B, or A and B".

[0017] <Ink for Inkjet>

[0018] Hereinafter, the ink for inkjet (hereinafter sometimes simply referred to as ink) of the embodiment of the present invention will be described. The ink of this embodiment contains a pigment, resin particles, and an aqueous medium. The resin particles contain a specific polyurethane resin. The content ratio of the resin particles in the ink of this embodiment is 2.5% by mass or more and 9.0% by mass or less. The elongation at break of the specific polyurethane resin at 25°C is 60% or less. The glass transition temperature of the specific polyurethane resin is 40°C or more and 110°C or less. The aqueous medium contains water and a specific organic solvent. The content ratio of the specific organic solvent in the ink of this embodiment is 0.3% by mass or more and less than 2.0% by mass. The boiling point of the specific organic solvent is 200°C or more and 275°C or less. The SP value of the specific organic solvent is 19.5 (J / cm 3 ) 1 / 2 or more and 26.0 (J / cm 3 ) 1 / 2 or less.

[0019] Due to the above configuration, the ink of this embodiment has excellent ejection stability and can form an image with excellent scratch resistance and adhesion to the recording medium. The reason for the ink of this embodiment to exhibit the above effects is presumably as follows.

[0020] The ink of this embodiment contains resin particles containing a specific polyurethane resin in a certain proportion (specifically, 2.5% by mass or more and 9.0% by mass or less). The specific polyurethane resin is a polyurethane resin with an elongation at break of 60% or less and a glass transition temperature of 40°C or more and 110°C or less. The resin particles function as a binder to ensure the scratch resistance and adhesion to the recording medium of the image formed by the ink of this embodiment. In particular, since the polyurethane resin has polar groups, the adhesion between the image formed by the ink of this embodiment and the recording medium can be optimized.

[0021] In addition, the lower the elongation at break of the polyurethane resin, the higher the film strength of the ink film and the more excellent the abrasion resistance of the ink film. Therefore, the lower the elongation at break of the polyurethane resin, the more excellent the abrasion resistance of the formed image. Furthermore, the higher the glass transition temperature of the polyurethane resin, the more excellent the film-forming property of the ink film. On the other hand, the lower the elongation at break of the polyurethane resin, the harder the formed ink film and the lower the adhesion between the image formed by the ink and the recording medium. Furthermore, resin particles containing a polyurethane resin with an excessively high elongation at break or a polyurethane resin with an excessively low glass transition temperature may sometimes fragment and aggregate during ejection, reducing the ejection stability of the ink.

[0022] By setting the elongation at break of the polyurethane resin contained in the resin particles of the ink of this embodiment to 60% or less and the glass transition temperature to 40°C or more and 110°C or less, the ejection stability can be optimized and sufficient strength can be effectively imparted to the formed image.

[0023] In addition, the ink of the present embodiment contains a specific organic solvent in a certain proportion (specifically, 0.3% by mass or more and less than 2.0% by mass). The boiling point of the specific organic solvent is 200°C or higher and 275°C or lower, and the SP value is 19.5 (J / cm 3 ) 1 / 2 or more and 26.0 (J / cm 3 ) 1 / 2 or less. The resin particles containing the above-mentioned specific polyurethane resin have high solubility in an organic solvent having an SP value of 19.5 (J / cm 3 ) 1 / 2 or more and 26.0 (J / cm 3 ) 1 / 2 or less. In addition, an ink containing an organic solvent having a boiling point of 200°C or higher is difficult to dry. Therefore, when the ink contains a certain amount of an organic solvent having a boiling point of 200°C or higher, drying of the ink in the nozzles of the recording head and drying of the ink adhering to the ejection surface of the recording head can be suppressed. As a result, aggregation of the ink components can be suppressed, and ejection deviation of the ink liquid from the recording head can be suppressed. In addition, when the boiling point of the organic solvent contained in the ink is 275°C or lower, the ink dries appropriately on the surface of the recording medium. Therefore, when the boiling point of the organic solvent contained in the ink is 275°C or lower, the scratch resistance of the formed image can be ensured.

[0024] As a result, the ink of the present embodiment has excellent ejection stability, and an image having excellent scratch resistance and adhesion to the recording medium can be formed.

[0025] The ink of the present embodiment is preferably used for surface printing. Here, surface printing refers to printing on the surface side (the side viewed by the viewer) of a transparent recording medium during printing. The recording medium for surface printing has a positional relationship of "viewer, image, recording medium", and the image (ink coating film) exists on the outermost layer on the viewer side. On the other hand, in the printing of a transparent recording medium, printing on the back side (the side opposite to the side viewed by the viewer) of the recording medium is called reverse printing. The recording medium for reverse printing has a positional relationship of "viewer, recording medium, image".

[0026] Therefore, in the case of surface printing, compared with the case of reverse printing, the formed image is more likely to be required to have particularly excellent scratch resistance and adhesion to the recording medium. As described above, since the ink of the present embodiment can form an image having excellent scratch resistance and adhesion to the recording medium, it is considered that it can be used for surface printing and can also be used for printed products without a laminating material.

[0027] In addition, the ink of the present embodiment is preferably used for a circulation type recording head. For an inkjet recording apparatus having a circulation type recording head, excellent ejection stability is required even when the ink is circulated for a long time. As described above, the ejection stability of the ink of the present embodiment is excellent, and it can also be applied to the case where the recording head is a circulation type recording head.

[0028] Hereinafter, the embodiments of the present invention will be described in further detail. As described above, the ink of the present embodiment contains a pigment, resin particles, and an aqueous medium. In addition, the ink of the present embodiment preferably further contains a pigment-coated resin. Furthermore, the ink of the present embodiment preferably further contains a surfactant.

[0029] In the ink of the present embodiment, the pigment, for example, forms pigment particles together with the pigment-coated resin. The pigment particles are composed of, for example, a core containing the pigment and a pigment-coated resin coating the core. The pigment-coated resin is, for example, dispersed in a solvent. From the viewpoint of optimizing the color density, hue, or stability of the ink of the embodiment, the volume median diameter of the pigment particles is preferably 30 nm or more and 200 nm or less, more preferably 70 nm or more and 130 nm or less.

[0030] [Pigment]

[0031] Examples of the pigment include a yellow pigment, an orange pigment, a red pigment, a blue pigment, a purple pigment, and a black pigment. Examples of the yellow pigment include C.I. Pigment Yellow (74, 93, 95, 109, 110, 120, 128, 138, 139, 151, 154, 155, 173, 180, 185, and 193). Examples of the orange pigment include C.I. Pigment Orange (34, 36, 43, 61, 63, and 71). Examples of the red pigment include C.I. Pigment Red (122 and 202). Examples of the blue pigment include C.I. Pigment Blue (15, more specifically 15:3). Examples of the purple pigment include C.I. Pigment Violet (19, 23, and 33). Examples of the black pigment include C.I. Pigment Black (7).

[0032] In the ink of the present embodiment, the content ratio of the pigment is preferably 0.5% by mass or more and 10.0% by mass or less, more preferably 1.5% by mass or more and 5.0% by mass or less. By making the content ratio of the pigment 0.5% by mass or more, the ink of the present embodiment can form an image having a desired image density. In addition, by making the content ratio of the pigment 10.0% by mass or less, the fluidity of the ink of the present embodiment can be ensured.

[0033] [Pigment-coated resin]

[0034] The pigment-coated resin is a resin soluble in an aqueous medium. A part of the pigment-coated resin, for example, exists on the surface of the pigment particles to optimize the dispersibility of the pigment particles. A part of the pigment-coated resin exists, for example, in a state dissolved in the aqueous medium of the ink of the present embodiment.

[0035] As the pigment-coated resin, a styrene-(meth)acrylic resin is preferred. The styrene-(meth)acrylic resin has repeating units of monomers from at least one of (meth)acrylic acid alkyl esters and (meth)acrylic acid and a styrene unit. As the (meth)acrylic acid alkyl ester, for example, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, and butyl (meth)acrylate can be mentioned. As the styrene-(meth)acrylic resin, a copolymer (X) of styrene, methyl methacrylate, methacrylic acid, and butyl acrylate is preferred. In addition, the copolymer (X) is preferably neutralized equally with a base (such as potassium hydroxide and sodium hydroxide).

[0036] In all the repeating units of the copolymer (X), the content ratio of the repeating units derived from styrene is preferably 10.0% by mass or more and 20.0% by mass or less. In all the repeating units of the copolymer (X), the content ratio of the repeating units derived from methyl methacrylate is preferably 10.0% by mass or more and 20.0% by mass or less. In all the repeating units of the copolymer (X), the content ratio of the repeating units derived from methacrylic acid is preferably 35.0% by mass or more and 45.0% by mass or less. In all the repeating units of the copolymer (X), the content ratio of the repeating units derived from butyl acrylate is preferably 25.0% by mass or more and 35.0% by mass or less.

[0037] In the ink of the present embodiment, the content ratio of the pigment-coated resin is preferably 0.1% by mass or more and 4.0% by mass or less, more preferably 0.5% by mass or more and 1.5% by mass or less. By making the content ratio of the pigment-coated resin 0.1% by mass or more and 4.0% by mass or less, the ejection stability of the ink of the present embodiment can be further optimized.

[0038] In the ink of the present embodiment, the content of the pigment-coated resin relative to 100.0 parts by mass of the pigment is preferably 10.0 parts by mass or more and 60.0 parts by mass or less, more preferably 20.0 parts by mass or more and 30.0 parts by mass or less. By making the content of the pigment-coated resin 10.0 parts by mass or more and 60.0 parts by mass or less, the ejection stability of the ink of the present embodiment can be further optimized.

[0039] [Resin particles]

[0040] The resin particles exist in a state of being dispersed in an aqueous medium. The resin particles contain a specific polyurethane resin. As the content ratio of the specific polyurethane resin in the resin particles, it is preferably 85.0% by mass or more, more preferably 90.0% by mass or more, and further preferably 100.0% by mass.

[0041] As the volume median diameter (D 50 ) of the resin particles, it is preferably 8 nm or more and 100 nm or less, more preferably 15 nm or more and 50 nm or less, and further preferably 25 nm or more and 40 nm or less. By making the volume median diameter of the resin particles 8 nm or more, the ejection stability of the ink of the present embodiment can be optimized. By making the volume median diameter of the resin particles 100 nm or less, the ejection stability of the ink of the present embodiment can be further optimized.

[0042] The content ratio of the resin particles in the ink of the present embodiment is 2.5% by mass or more and 9.0% by mass or less, preferably 4.0% by mass or more and 6.0% by mass or less. By making the content ratio of the resin particles 2.5% by mass or more, the scratch resistance of the formed image and the adhesion to the recording medium of the ink of the present embodiment can be optimized. By making the content ratio of the resin particles 9.0% by mass or less, the ejection stability of the ink of the present embodiment can be optimized.

[0043] [Specific Polyurethane Resin]

[0044] The polyurethane resin is, for example, a copolymer of a diol compound or a bisphenol compound and a polyisocyanate.

[0045] Examples of the diol compound include ethylene glycol, diethylene glycol, triethylene glycol, 1,2 - propanediol, 1,3 - propanediol, 1,4 - butanediol, neopentyl glycol, 2 - butene - 1,4 - diol, 1,5 - pentanediol, 2 - pentene - 1,5 - diol, 1,6 - hexanediol, 1,4 - cyclohexanedimethanol, dipropylene glycol, 1,4 - benzenediol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol.

[0046] Examples of the bisphenol compound include bisphenol A, hydrogenated bisphenol A, bisphenol A ethylene oxide adduct (for example, polyoxyethylene(2,2) - 2,2 - bis(4 - hydroxyphenyl)propane), and bisphenol A propylene oxide adduct.

[0047] Examples of the polyisocyanate include diisocyanate. Examples of the diisocyanate include aliphatic diisocyanate, alicyclic diisocyanate, and aromatic diisocyanate.

[0048] Examples of the aliphatic diisocyanate include ethylene diisocyanate, 2,2,4 - trimethylhexamethylene diisocyanate, and 1,6 - hexamethylene diisocyanate.

[0049] Examples of the alicyclic diisocyanate include hydrogenated 4,4'-diphenylmethane diisocyanate, 1,4-cyclohexane diisocyanate, methylcyclohexylidene diisocyanate, isophorone diisocyanate, and norbornane diisocyanate.

[0050] Examples of the aromatic diisocyanate include 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate, tolylene diisocyanate, and naphthalene diisocyanate.

[0051] The specific polyurethane resin is a polyurethane resin having an elongation at break at 25°C of 60% or less, a glass transition temperature of 40°C or higher and 110°C or lower.

[0052] As described above, the elongation at break of the specific polyurethane resin at 25°C is 60% or less, preferably 4% or more and 60% or less, more preferably 4% or more and 10% or less. By containing the specific polyurethane resin having an elongation at break at 25°C of 60% or less, the ink of the present embodiment can optimize the ejection stability of the ink of the present embodiment and can optimize the scratch resistance of the image formed by the ink of the present embodiment.

[0053] The glass transition temperature of the specific polyurethane resin is 40°C or higher and 110°C or lower as described above, preferably 45°C or higher and 90°C or lower, more preferably 65°C or higher and 85°C or lower. By containing the specific polyurethane resin having a glass transition temperature of 40°C or higher and 110°C or lower, the ink of the present embodiment can optimize the ejection stability of the ink of the present embodiment and can optimize the adhesion of the image formed by the ink of the present embodiment to the recording medium.

[0054] [Surfactant]

[0055] The surfactant optimizes the compatibility and dispersion stability of the respective components contained in the ink of the present embodiment. In addition, the surfactant optimizes the permeability (wettability) of the ink of the present embodiment to the recording medium. Examples of the surfactant include nonionic surfactants.

[0056] Examples of the nonionic surfactant include acetylene glycol surfactants (surfactants containing acetylene glycol compounds), polysiloxane surfactants (surfactants containing polysiloxane compounds), and fluorosurfactants (surfactants containing fluororesins or fluorine-containing compounds). Examples of the acetylene glycol surfactant include ethylene oxide adducts of acetylene glycol and propylene oxide adducts of acetylene glycol. The ink of the present embodiment preferably contains a polysiloxane surfactant as the surfactant.

[0057] The content ratio of the surfactant in the ink of the present embodiment is preferably 0.1% by mass or more and 2.0% by mass or less, more preferably 0.2% by mass or more and 0.6% by mass or less.

[0058] [Aqueous medium]

[0059] The aqueous medium contained in the ink of the present embodiment includes water and a specific organic solvent. The specific organic solvent is a water-soluble organic solvent. The aqueous medium can function as a solvent or as a dispersion medium. The aqueous medium may further include other water-soluble organic solvents (hereinafter, sometimes referred to as other organic solvents) in addition to the specific organic solvent. Examples of the specific organic solvent and other organic solvents include glycol compounds, ethylene glycol ether compounds, lactam compounds, nitrogen-containing compounds, acetate compounds, thiodiglycol, and dimethyl sulfoxide.

[0060] (Water)

[0061] In the ink of the present embodiment, the content ratio of water is preferably 40.0% by mass or more and 85.0% by mass or less, more preferably 50.0% by mass or more and 70.0% by mass or less. By making the content ratio of water 40.0% by mass or more and 85.0% by mass or less, the ejection stability of the ink of the present embodiment can be optimized.

[0062] The boiling point of the specific organic solvent is 200 °C or more and 275 °C or less, and the SP value is 19.5 (J / cm 3 ) 1 / 2 or more and 26.0 (J / cm 3 ) 1 / 2 or less.

[0063] As described above, the boiling point of the specific organic solvent is 200 °C or more and 275 °C or less, preferably 200 °C or more and 250 °C or less, more preferably 200 °C or more and 220 °C or less. By including a specific organic solvent having a boiling point of 200 °C or more and 275 °C or less, the ink of the present embodiment can optimize the ejection stability of the ink of the present embodiment, and can optimize the scratch resistance of the image formed by the ink of the present embodiment and the adhesion to the recording medium.

[0064] As described above, the SP value of the specific organic solvent is 19.5 (J / cm 3 ) 1 / 2 or more and 26.0 (J / cm 3 ) 1 / 2 or less, preferably 20.0 (J / cm 3 ) 1 / 2 or more and 25.5 (J / cm 3 ) 1 / 2 or less, more preferably 23.0 (J / cm3 ) 1 / 2 or more and 25.5 (J / cm 3 ) 1 / 2 or less. The ink of the present embodiment can optimize the ejection stability of the ink of the present embodiment and can optimize the scratch resistance and adhesion to the recording medium of the image formed by the ink of the present embodiment by including a specific organic solvent having an SP value of 19.5 (J / cm 3 ) 1 / 2 or more and 26.0 (J / cm 3 ) 1 / 2 or less.

[0065] As the specific organic solvent, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, tripropylene glycol, or 3-methyl-1,3-butanediol is preferred.

[0066] As other organic solvents, organic solvents having a boiling point less than 200°C or greater than 275°C, an SP value less than 19.5 (J / cm 3 ) 1 / 2 or greater than 26.0 (J / cm 3 ) 1 / 2 can be cited. As an example, as other organic solvents, polyhydric alcohols or ethylene glycol ether compounds that meet at least one of the conditions of a boiling point less than 200°C or greater than 275°C and an SP value less than 19.5 (J / cm 3 ) 1 / 2 or greater than 26.0 (J / cm 3 ) 1 / 2 can be cited. As polyhydric alcohols that meet the above conditions, for example, propylene glycol, triethylene glycol, tripropylene glycol, 3-methyl-1,3-butanediol, glycerol, etc. can be cited. In addition, as ethylene glycol ether compounds that meet the above conditions, for example, dipropylene glycol methyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, etc. can be cited.

[0067] Polyhydric alcohols function as, for example, humectants. Humectants can inhibit the volatilization of liquid components from the ink of the present embodiment and stabilize the viscosity. Therefore, the ink of the present embodiment preferably further contains a humectant. By further including a humectant in the ink of the present embodiment, the volatilization of liquid components from the ink of the present embodiment can be inhibited, and the ejection stability can be further optimized.

[0068] In addition, ethylene glycol ether compounds function as, for example, wetting agents that improve the wettability of the substrate used as the recording medium. Wetting agents can improve the wetting spreadability of the ink of the present embodiment on the recording medium (substrate) and further optimize the adhesion of the formed image to the recording medium. Therefore, the ink of the present embodiment preferably further contains a wetting agent.

[0069] As a humectant, the above-mentioned polyols can be used, and propylene glycol is particularly preferred. In addition, as a wetting agent, the above-mentioned ethylene glycol ether compound can be used, and triethylene glycol monobutyl ether is particularly preferred. Therefore, the ink of the present embodiment preferably further contains propylene glycol and triethylene glycol monobutyl ether as other organic solvents.

[0070] The content ratio of the specific organic solvent in the ink of the present embodiment is 0.3% by mass or more and less than 2.0% by mass, preferably 1.0% by mass or more and 1.7% by mass or less. By making the content ratio of the specific organic solvent 0.3% by mass or more and less than 2.0% by mass, the scratch resistance of the image formed by the ink of the present embodiment and the adhesion to the recording medium can be optimized.

[0071] As the content ratio of the other organic solvent in the ink of the present embodiment, it is preferably 10.0% by mass or more and 50.0% by mass or less, more preferably 20.0% by mass or more and 40.0% by mass or less.

[0072] In addition, when the ink of the present embodiment contains a humectant, as the content ratio of the humectant in the ink of the present embodiment, it is preferably 7.0% by mass or more and 35.0% by mass or less, more preferably 15.0% by mass or more and 25.0% by mass or less.

[0073] When the ink of the present embodiment contains a wetting agent, as the content ratio of the wetting agent in the ink of the present embodiment, it is preferably 3.0% by mass or more and 15.0% by mass or less, more preferably 5.0% by mass or more and 15.0% by mass or less.

[0074] The aqueous medium preferably contains only water, a specific organic solvent, propylene glycol, and triethylene glycol monobutyl ether. As the total content ratio of water, a specific organic solvent, propylene glycol, and triethylene glycol monobutyl ether in the aqueous medium, it is preferably 90.0% by mass or more, more preferably 95.0% by mass or more, and further preferably 100.0% by mass.

[0075] [Other components]

[0076] The ink of the present embodiment may further contain known additives (for example, dissolution stabilizers, anti-drying agents, antioxidants, viscosity regulators, pH regulators, and fungicides) as needed.

[0077] [Preferred composition]

[0078] The ink of this embodiment preferably has any one of Compositions 1 to 11 shown in Tables 1 to 3 below. In Table 1 below, "proportion" represents the numerical range of the preferred content proportion [% by mass]. For example, "2.7 - 3.3" of the proportion of the pigment in Composition 1 means that the pigment content is 2.7% by mass or more and 3.3% by mass or less. "Resin" represents the pigment-coated resin. "r-1" to "r-4" of the types of specific polyurethane resins respectively represent the specific polyurethane resin particles (r-1) to (r-4) used in the examples. "DEGMBE" of the type of specific organic solvent represents diethylene glycol monobutyl ether. "TEGMME" represents triethylene glycol monomethyl ether. "TPG" represents tripropylene glycol. "3M-1,3BD" represents 3-methyl-1,3-butanediol. "PG" of the type of other organic solvents represents propylene glycol. "TEGMBE" represents triethylene glycol monobutyl ether. "PG (proportion)" represents the numerical range of the preferred content proportion [% by mass] of propylene glycol. "TEGMBE (proportion)" represents the numerical range of the preferred content proportion [% by mass] of triethylene glycol monobutyl ether.

[0079] [Table 1]

[0080]

[0081] [Table 2]

[0082]

[0083] [Table 3]

[0084]

[0085] [Method for manufacturing ink]

[0086] The ink of this embodiment can be manufactured, for example, by uniformly mixing a pigment dispersion containing a pigment, a resin emulsion containing resin particles containing a specific polyurethane, an aqueous medium containing water and a specific organic solvent, and other components (for example, a surfactant) as required using a stirrer. In the manufacture of the ink of this embodiment, after uniformly mixing the respective components, foreign matters and coarse particles can be removed through a filter (for example, a filter with a pore size of 5 μm or less).

[0087] (Pigment dispersion)

[0088] The pigment dispersion is a dispersion containing a pigment. The pigment dispersion preferably further contains a pigment-coated resin. As the dispersion medium of the pigment dispersion, water is preferred.

[0089] The content ratio of the pigment in the pigment dispersion liquid is preferably 5.0% by mass or more and 25.0% by mass or less, more preferably 10.0% by mass or more and 20.0% by mass or less. The content ratio of the pigment-coated resin in the pigment dispersion liquid is preferably 1.0% by mass or more and 10.0% by mass or less, more preferably 2.0% by mass or more and 6.0% by mass or less.

[0090] The pigment dispersion liquid can be prepared by wet-dispersing a pigment, a pigment-coated resin, a dispersion medium (e.g., water), and components added as needed (e.g., a surfactant) using a medium-type wet disperser. In the wet dispersion using a medium-type wet disperser, for example, small-diameter beads (e.g., beads with a diameter of 0.5 mm or more and 1.0 mm or less) can be used as the medium. The material of the beads is not particularly limited, and a hard material (e.g., glass and zirconia) is preferred. 50 As the beads, those having a diameter of 0.5 mm or more and 1.0 mm or less are used. The material of the beads is not particularly limited, and a hard material (e.g., glass and zirconia) is preferred.

[0091] When adding the pigment dispersion liquid in the production of the ink of the present embodiment, the ratio of the pigment dispersion liquid to all the raw materials of the ink is, for example, 10.0% by mass or more and 40.0% by mass or less.

[0092] (Polyurethane resin emulsion)

[0093] The polyurethane resin emulsion is a dispersion liquid containing resin particles, and the above resin particles contain a polyurethane resin. As the dispersion medium of the polyurethane resin emulsion, water is preferred.

[0094] Examples

[0095] Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the following examples.

[0096] [Preparation of pigment dispersion liquid]

[0097] A pigment dispersion liquid (C) for preparing an ink is prepared. The components contained in the pigment dispersion liquid (C) and their amounts are shown in Table 4.

[0098] [Table 4]

[0099]

[0100] In Table 4, "Resin A-Na" represents Resin A (pigment-coated resin) neutralized with sodium hydroxide (NaOH). As the pigment, "black pigment" (Cabot Corporation's "MONARCH (registered trademark) 800") is used.

[0101] [Preparation of Resin A]

[0102] Resin A for obtaining "Resin A - Na" in Table 4 was prepared by the following method. Specifically, a stirrer, a nitrogen inlet tube, a condenser, and a dropping funnel were set in a four-necked flask. Then, 100.0 parts by mass of isopropyl alcohol and 300.0 parts by mass of methyl ethyl ketone were added to the flask. While bubbling nitrogen through the contents of the flask, the mixture was heated under reflux at 70 °C.

[0103] Next, Solution L1 was prepared. Specifically, 40.0 parts by mass of styrene, 10.0 parts by mass of methacrylic acid, 40.0 parts by mass of methyl methacrylate, 10.0 parts by mass of butyl acrylate, and 0.4 parts by mass of azobisisobutyronitrile (AIBN, polymerization initiator) were mixed to obtain Solution L1 as a monomer solution. Solution L1 was added dropwise to the flask over 2 hours while maintaining the contents of the flask at 70 °C under reflux. After the addition, the contents of the flask were further heated under reflux at 70 °C for 6 hours.

[0104] Next, Solution L2 was prepared. Specifically, 0.2 parts by mass of AIBN and 150.0 parts by mass of methyl ethyl ketone were mixed to obtain Solution L2. Solution L2 was added dropwise to the flask over 15 minutes. After the addition, the contents of the flask were further heated under reflux at 70 °C for 5 hours. By performing in this way, Resin A (styrene-(meth)acrylic resin) was obtained. The weight-average molecular weight (Mw) of the obtained Resin A was 20,000, and the acid value was 100 mg KOH / g.

[0105] Here, the weight-average molecular weight Mw of Resin A was measured under the following conditions using gel permeation chromatography ("HLC-8020GPC" manufactured by Tosoh Corporation).

[0106] Chromatographic column: "TSKgel SuperMultipore HZ-H" (semi-micro column of 4.6 mm I.D. × 15 cm) manufactured by Tosoh Corporation

[0107] Number of columns: 3

[0108] Eluent: Tetrahydrofuran

[0109] Flow rate: 0.35 ml / min

[0110] Sample injection volume: 10 μL

[0111] Measurement temperature: 40 °C

[0112] Detector: IR detector

[0113] The calibration curve was made by selecting 7 kinds of F-40, F-20, F-4, F-1, A-5000, A-2500, and A-1000 in TSKgel standard polystyrene manufactured by Tosoh Corporation and n-propylbenzene.

[0114] In addition, the acid value of Resin A was measured according to the method of "JIS (Japanese Industrial Standards) K0070-1992 (Test Methods for Acid Value, Saponification Value, Ester Value, Iodine Value, Hydroxyl Value and Unsaponifiable Matter of Chemical Products)".

[0115] [Preparation of Pigment Dispersion (C)]

[0116] While heating Resin A in a warm bath at 70°C, an aqueous sodium hydroxide solution in an amount required to neutralize Resin A was added to Resin A. More specifically, an aqueous sodium hydroxide solution having a mass 1.1 times the neutralization equivalent was added to Resin A. By doing so, an aqueous solution of Resin A neutralized with sodium hydroxide (Resin A-Na) was obtained. The pH of the aqueous solution of Resin A-Na was 8.

[0117] The above aqueous solution containing 5.0 parts by mass of Resin A-Na, 15.0 parts by mass of C.I. Pigment Blue 15:3 and water were added to the container of a media-type disperser ("DYNO (registered trademark) MILL" manufactured by Willy A Bachofen Co., Ltd. (WAB Co., Ltd.)) so as to be in the blending amounts shown in Table 4, and the total amount was made 100.0 parts by mass. In addition, water was added so that the mass of water including the water contained in the aqueous sodium hydroxide solution used to neutralize Resin A and the water generated in the neutralization reaction became 80.0 parts by mass.

[0118] Next, media (zirconia beads with a diameter of 1.0 mm) were filled into the container so that the filling rate was 70% by volume with respect to the capacity of the container. The content of the container was dispersed using a media-type disperser. By doing so, Pigment Dispersion (C) as a pigment dispersion for black ink was obtained.

[0119] The Pigment Dispersion (C) was diluted 300 times with water to obtain a diluted solution. The diluted solution was measured using a dynamic light scattering type particle size distribution measuring device ("Zetasizer Nano ZS" manufactured by Malvern Co., Ltd.), and the volume median diameter (D 50 ) of the pigment particles contained in the Pigment Dispersion (C) was determined. Then, it was confirmed that pigment particles in the range of 70 nm or more and 130 nm or less in volume median diameter were dispersed in the Pigment Dispersion (C).

[0120] [Polyurethane Resin Emulsion]

[0121] As a resin emulsion for preparing ink, polyurethane resin emulsions (R-1) to (R-8) shown in Table 5 below were prepared. The polyurethane resin emulsions (R-1) to (R-8) were all manufactured by Daiichi Kogyo Seiyaku Co., Ltd. The polyurethane resin emulsions (R-1) to (R-8) contained polyurethane resin particles (r-1) to (r-8) respectively. In Table 5 below, "Tg" represents the glass transition temperature. "(R)" represents a registered trademark. In addition, the polyurethane resin particles (r-1) to (r-4) were resin particles of a specific polyurethane resin.

[0122] [Table 5]

[0123]

[0124] [Organic solvent]

[0125] As an organic solvent for preparing ink, the organic solvents shown in Table 6 below were prepared. In addition, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, tripropylene glycol, and 3-methyl-1,3-butanediol were specific organic solvents.

[0126] [Table 6]

[0127]

[0128] <Preparation of ink>

[0129] Inks of Examples 1 to 11 and Comparative Examples 1 to 9 were prepared by the following method.

[0130] [Example 1]

[0131] Water, 20.0 parts by mass of pigment dispersion (C) (pigment: 3.0 parts by mass, resin A-Na: 1.0 part by mass), 16.7 parts by mass of polyurethane resin emulsion (R-1) (polyurethane resin particles (r-1): 5.0 parts by mass), 1.5 parts by mass of 3-methyl-1,3-butanediol, 20.0 parts by mass of propylene glycol, 8.0 parts by mass of triethylene glycol monobutyl ether, and 0.3 part by mass of a polysiloxane surfactant ("SILFACE (registered trademark) SAG503A", a polyether-modified silicone compound manufactured by Nisshin Chemical Industry Co., Ltd.) were added to a beaker. The amount of water added was such that the total amount of the mixture in the beaker was 100.0 parts by mass. The contents of the beaker were mixed at a rotation speed of 400 rpm using a stirrer ("Three-One Motor BL-600" manufactured by Shin-Tong Science Co., Ltd.) to obtain a mixed solution. The mixed solution was filtered using a filter (pore size 5 μm) to remove foreign matters and coarse particles contained in the mixed solution. By doing so, the ink of Example 1 was obtained.

[0132] [Examples 2 to 11 and Comparative Examples 1 to 9]

[0133] The types and amounts of the respective components were changed as shown in Tables 7 to 9, and in other respects, in the same manner as in the preparation of the ink of Example 1, inks of Examples 2 to 11 and Comparative Examples 1 to 9 were prepared.

[0134] In addition, in Tables 7 to 9, the values represent the content ratio [% by mass]. "DPGME" represents dipropylene glycol methyl ether. "DEGMBE" represents diethylene glycol monobutyl ether. "TEGMME" represents triethylene glycol monomethyl ether. "TPG" represents tripropylene glycol. "3M-1,3BD" represents 3-methyl-1,3-butanediol. "TEG" represents triethylene glycol. "PG" represents propylene glycol. "TEGMBE" represents triethylene glycol monobutyl ether. "-" indicates that the corresponding material was not used.

[0135] [Table 7]

[0136]

[0137] [Table 8]

[0138]

[0139] [Table 9]

[0140]

[0141] [Evaluation]

[0142] By the following method, the scratch resistance, adhesion to the recording medium, and ejection stability of the images formed from the inks of Examples 1 to 11 and Comparative Examples 1 to 9 were evaluated. In addition, the ejection stability of the ink was evaluated by the presence or absence of deviation in the non-printing portion. The evaluation results are shown in Tables 10 to 11 below. In addition, unless otherwise specified, the evaluation was carried out at a temperature of 25°C and a humidity of 60% RH.

[0143] [Production of Evaluation Film]

[0144] The film for evaluating adhesion and scratch resistance is produced by the following method. First, the ink to be evaluated (any one of the inks in Examples 1 to 11 and Comparative Examples 1 to 9) is applied onto a non-permeable recording medium to form a black solid image with a wet film thickness of about 6 μm of the ink coating film just after application. As the non-permeable recording medium, a PET film after corona discharge treatment ("FE2001" manufactured by FUTAMURA CHEMICAL CO., LTD., single-sided corona discharge treatment) is used. Specifically, the ink coating film is formed on the surface of the PET film that has been subjected to corona discharge treatment. For the application of the ink, a bar coater ("K303S Multicoater" manufactured by Matsuo Sangyo Co., Ltd.) is used. The bar of the bar coater uses bar No. 1. The printing speed is set at 30 m / minute. Then, the non-permeable recording medium on which the solid image is formed is dried at 100 °C for 10 minutes and then left standing for 12 hours to obtain the film for evaluation.

[0145] [Adhesion]

[0146] An adhesive tape ("Cellotape (registered trademark) CT-18S" manufactured by Mitsubang Co., Ltd., width 18 mm) is pasted onto the solid image of the film for evaluation, and the adhesive tape is peeled off at an angle of about 60 degrees. The peeling of the adhesive tape is carried out at a speed such that the time from the start of peeling to the end of peeling is 1 second. After peeling off the adhesive tape, the film for evaluation is visually observed to confirm whether there is peeling of the solid image. Then, the ratio (peeling rate [area%]) of the area of the solid image peeled off together with the adhesive tape is calculated when the area of the region of the solid image where the adhesive tape is pasted is 100 area%. The adhesion of the formed image to the recording medium is judged according to the following criteria.

[0147] (Evaluation criteria for adhesion)

[0148] A (Good): There is no peeling of the solid image at all (peeling rate 0 area%).

[0149] B (Slightly poor): The peeling rate is greater than 0 area% and less than 50 area%.

[0150] C (Poor): The peeling rate is 50 area% or more.

[0151] [Scratch resistance]

[0152] According to the friction tester II-shaped (Gakushin-shaped) method described in JIS L-0849:2013 (Test method for color fastness to rubbing), the solid image formed on the evaluation film was repeatedly rubbed 100 times with a load of 200 g using a friction cloth (cotton broadcloth). After rubbing with the friction cloth, the evaluation film was visually observed to confirm whether there was any peeling of the solid image. Then, when the area of the solid image in the evaluation film before rubbing was taken as 100 area%, the ratio of the area of the solid image peeled off after rubbing (peeling rate [area%]) was calculated. The scratch resistance of the formed image was judged according to the following criteria.

[0153] (Evaluation criteria for scratch resistance)

[0154] A (Good): There is no peeling of the solid image at all (peeling rate 0 area%).

[0155] B (Slightly poor): The peeling rate is greater than 0 area% and less than 5 area%.

[0156] C (Poor): The peeling rate is 5 area% or more.

[0157] [Spray stability (offset of non-printing part)]

[0158] To suppress the influence of drying of the ink nozzles, the evaluation of spray stability (offset of non-printing part) was carried out in a normal temperature and high humidity environment (environment with a temperature of 25 °C and a humidity of 80% RH).

[0159] As the evaluation equipment, an image forming apparatus (an inkjet recording apparatus equipped with a line head, a testing machine manufactured by Kyocera Office Information Systems Co., Ltd.) was used. The ink to be evaluated (any one of the inks in Examples 1 to 11 and Comparative Examples 1 to 9) was set on the line head of the evaluation equipment.

[0160] For the above evaluation equipment, ink was removed from the line head and the line head was wiped (cleaning and wiping treatment). One minute after the cleaning and wiping treatment, a horizontal line (a line along the main scanning direction) was formed on A4 glossy paper (''SuperFine Paper'' manufactured by Seiko Epson Corporation) using the evaluation equipment. At this time, the line width of the horizontal line was set to 1 dot (the amount of 1 drop of ink). The volume of each dot of ink ejected from each nozzle of the line head (the volume of each drop) was set to 3 pL. Then, an optical microscope (''MM-800'' manufactured by Nikon Corporation) was used to judge the offset amount of the above horizontal line. Specifically, the maximum distance (offset amount) in the sub-scanning direction of each point constituting the above horizontal line was measured through the application software attached to the above optical microscope. The larger the offset amount, the greater the deformation of the above horizontal line caused by the offset in the non-printing part. The spray stability (offset of non-printing part) was judged according to the following criteria.

[0161] (Evaluation Criteria for Inkjet Stability)

[0162] A (Good): The offset is 20 μm or less.

[0163] B (Poor): The offset is greater than 20 μm.

[0164] [Table 10]

[0165]

[0166] [Table 11]

[0167]

[0168] [Evaluation]

[0169] As shown in Tables 10 to 11, the inks of Examples 1 to 11 contain a pigment, resin particles, and an aqueous medium. The resin particles contain a specific polyurethane resin. The content ratio of the resin particles is 2.5% by mass or more and 9.0% by mass or less. The elongation at break of the specific polyurethane resin at 25°C is 60% or less. The glass transition temperature of the specific polyurethane resin is 40°C or more and 110°C or less. The aqueous medium contains water and a specific organic solvent. The content ratio of the specific organic solvent is 0.3% by mass or more and less than 2.0% by mass. The boiling point of the specific organic solvent is 200°C or more and 275°C or less. The SP value of the specific organic solvent is 19.5 (J / cm 3 ) 1 / 2 or more and 26.0 (J / cm 3 ) 1 / 2 or less. The inks of Examples 1 to 11 have excellent inkjet stability, and the scratch resistance and adhesion to the recording medium of the formed images are excellent.

[0170] On the other hand, since the content ratio of the resin particles in the ink of Comparative Example 1 is less than 2.5% by mass, the scratch resistance and adhesion to the recording medium of the formed image are poor or slightly poor.

[0171] Since the content ratio of the resin particles in the ink of Comparative Example 2 is greater than 9.0% by mass, the inkjet stability is poor.

[0172] Since the elongation at break of the polyurethane resin contained in the resin particles of the inks of Comparative Examples 3 to 5 is greater than 60%, the scratch resistance is poor.

[0173] In addition, since the glass transition temperature of the polyurethane resin contained in the resin particles of the inks of Comparative Examples 4 and 6 is less than 40°C, the inkjet stability is poor.

[0174] Since the boiling point of dipropylene glycol methyl ether, which is used to compare with a specific organic solvent in the ink of Comparative Example 7, is less than 200 °C and the SP value is less than 19.5 (J / cm 3 ), 1 / 2 the scratch resistance of the formed image and the adhesion to the recording medium are slightly poor.

[0175] Since the boiling point of triethylene glycol, which is used to compare with a specific organic solvent in the ink of Comparative Example 8, is greater than 275 °C and the SP value is greater than 26.0 (J / cm 3 ), 1 / 2 the scratch resistance of the formed image and the adhesion to the recording medium are poor or slightly poor.

[0176] Since the content ratio of the specific organic solvent in the ink of Comparative Example 9 is 2.0 mass% or more, the scratch resistance of the formed image and the adhesion to the recording medium are poor or slightly poor.

Claims

1. An ink for inkjet, which contains a pigment, resin particles, and an aqueous medium, wherein the resin particles contain a specific polyurethane resin, the content ratio of the resin particles is 2.5% by mass or more and 9.0% by mass or less, the elongation at break of the specific polyurethane resin at 25°C is 60% or less, the glass transition temperature of the specific polyurethane resin is 40°C or more and 110°C or less, the aqueous medium contains water and a specific organic solvent, the content ratio of the specific organic solvent is 0.3% by mass or more and less than 2.0% by mass, the boiling point of the specific organic solvent is 200°C or more and 275°C or less, The SP value of the specific organic solvent is 19.5 (J / cm 3 ) 1 / 2 or more and 26.0 (J / cm 3 ) 1 / 2 or less.

2. The ink for inkjet according to claim 1, wherein, the volume median diameter of the resin particles is 8 nm or more and 100 nm or less.

3. The ink for inkjet according to claim 1 or 2, wherein, The specific organic solvent contains at least one of diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, tripropylene glycol, and 3-methyl-1,3-butanediol.

4. The ink for inkjet according to claim 1 or 2, wherein, The ink for inkjet further contains a surfactant, the surfactant contains a polysiloxane surfactant.

5. The ink for inkjet according to claim 1 or 2, wherein, The ink for inkjet is used to form an image on a non-permeable recording medium.

6. The ink for inkjet according to claim 1 or 2, wherein, The ink for inkjet is used for surface printing.

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