Inkjet ink

Abstract

To provide an inkjet ink capable of forming an image having excellent ejection stability, rubfastness, and adhesion to a recording medium.SOLUTION: An inkjet ink includes a pigment, resin particles, and an aqueous medium. The resin particles include a specific urethane resin. A content ratio of the resin particles is 2.5 mass% or more and 9.0 mass% or less. A breaking elongation at 25°C of the specific urethane resin is 60% or less. A glass transition temperature of the specific urethane resin is 40°C or more and 110°C or less. The aqueous medium includes water and a specific organic solvent. A content ratio of the specific organic solvent is 0.3 mass% or more and less than 2.0 mass%. A boiling point of the specific organic solvent is 200°C or more and 275°C or less. An 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.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] Some inkjet recording apparatuses use an aqueous inkjet ink containing a pigment and an aqueous medium. The inkjet ink is required to have excellent ejection stability. Further, the inkjet recording apparatus may form 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 an image formed on a non-permeable recording medium using an inkjet recording apparatus comes into contact with other members (for example, other recording media), a phenomenon may occur in which the pigment contained in the image adheres to the other members, or a phenomenon may occur in which the image peels off from the recording medium. Therefore, the inkjet ink used for such applications is required to be able to form an image excellent in rubbing resistance and adhesion to the recording medium even when forming an image on a non-permeable recording medium.

[0004] In response to such requirements, for example, an inkjet ink containing a pigment, fine particles of a polyester resin having a particle diameter of 30 to 300 nm, and a water-soluble epoxy compound has been proposed (Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, even with the ink for inkjet described in Patent Document 1, it is difficult to form an image that exhibits excellent ejection stability and is excellent in scratch resistance and adhesion to a recording medium.

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

Means for Solving the Problems

[0008] The ink for inkjet according to the present invention contains a pigment, resin particles, and an aqueous medium. The resin particles contain a specific urethane 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 urethane resin at 25°C is 60% or less. The glass transition point of the specific urethane 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 and 26.0 (J / cm 3 ) 1 / 2 or less.

Effects of the Invention

[0009] The ink for inkjet according to the present invention is excellent in ejection stability and can form an image that is excellent in scratch resistance and adhesion to a recording medium.

Modes for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described. In the following, 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)

[0011] The breaking elongation can be measured by a tensile test using a tensile testing machine at 25°C in accordance with "JIS (Japanese Industrial Standards) K7127-1999".

[0012] If there is no specific regulation, the measured value of the glass transition temperature (Tg) is the value measured in accordance with "JIS (Japanese Industrial Standards) K7121-2012" using a differential scanning calorimeter (for example, "DSC-60" manufactured by Shimadzu Corporation). In the endothermic curve measured by the differential scanning calorimeter (vertical axis: heat flow (DSC signal), horizontal axis: temperature, heating rate 5°C / min), 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).

[0013] If there is no specific regulation, the SP value indicates the value calculated by "Hansen Solubility Parameter in Practice (HSPiP) Ver.5.2.06" (developed by Prof. Steven Abbott et al.), which is software for calculating and estimating SP values.

[0014] In this specification, acrylic and methacrylic may be collectively referred to as "(meth)acrylic" inclusively. Each component described in this specification may be used alone or in combination of two or more. "At least one of A and B" means "A, B, or A and B".

[0015] <Ink for Inkjet> Hereinafter, an ink for inkjet (hereinafter, may be simply referred to as ink) according to an embodiment of the present invention will be described. The ink according to this embodiment contains a pigment, resin particles, and an aqueous medium. The resin particles contain a specific urethane resin. The content ratio of the resin particles in the ink according to this embodiment is 2.5% by mass or more and 9.0% by mass or less. The elongation at break of the specific urethane resin at 25°C is 60% or less. The urethane glass transition point of the specific urethane 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 according to 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.

[0016] By having the above-described configuration, the ink according to this embodiment is excellent in ejection stability and can form an image excellent in scratch resistance and adhesion to a recording medium. The reason why the ink according to this embodiment exhibits the above-described effects is presumed as follows.

[0017] The ink according to this embodiment contains resin particles containing a specific urethane resin at a certain ratio (specifically, 2.5% by mass or more and 9.0% by mass or less). The specific urethane resin is a urethane resin having an elongation at break of 60% or less and a glass transition point of 40°C or more and 110°C or less. The resin particles function as a binder and ensure the scratch resistance of the image formed by the ink according to this embodiment and the adhesion to the recording medium. In particular, since the urethane resin has a polar group, the adhesion between the image formed by the ink according to this embodiment and the recording medium can be optimized.

[0018] In addition, the lower the elongation at break of the urethane resin, the higher the film strength, and an ink coating film excellent in scratch resistance can be formed. Therefore, the lower the elongation at break of the urethane resin, the better the scratch resistance of the formed image. Furthermore, the higher the glass transition point of the urethane resin, the better the film-forming property of the ink coating film. On the other hand, the lower the elongation at break of the urethane resin, the harder the formed ink coating film becomes, and the adhesion between the image formed by the ink and the recording medium decreases. Furthermore, resin particles containing a urethane resin with an excessively high elongation at break or an excessively low glass transition point may cause the particles to collapse and aggregate during ejection, reducing the ejection stability of the ink.

[0019] By setting the elongation at break of the urethane resin contained in the resin particles of the ink according to this embodiment to 60% or less and the glass transition point to 40°C or higher and 110°C or lower, while optimizing the ejection stability, sufficient strength can be effectively imparted to the formed image.

[0020] In addition, the ink according to this embodiment contains a specific organic solvent in a certain ratio (specifically, 0.3% by mass or more and less than 2.0% by mass). The specific organic solvent has a boiling point of 200°C or higher and 275°C or lower, and an SP value of 19.5 (J / cm 3 ) 1 / 2 or higher and 26.0 (J / cm 3 ) 1 / 2 or lower. It is the following organic solvent. The SP value is 19.5 (J / cm 3 ) 1 / 2 or higher and 26.0 (J / cm 3 ) 1 / 2The following organic solvents have high solubility for resin particles containing the above-specified urethane resin. Also, inks containing organic solvents with a boiling point of 200°C or higher are difficult to dry. Therefore, if the ink contains a certain amount of an organic solvent having a boiling point of 200°C or higher, drying of the ink within 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 occurrence of ink dripping from the recording head can be suppressed. Further, if 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, if 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.

[0021] As a result of these, the ink according to the present embodiment is excellent in ejection stability and can form an image excellent in scratch resistance and adhesion to the recording medium.

[0022] The ink according to the present embodiment is preferably used for front printing. Here, front printing means printing on the front side surface (the surface visible to the viewer) of the recording medium in printing on a transparent recording medium. The front-printed recording medium has a positional relationship of "viewer, image, recording medium", and the image (ink coating) exists on the outermost layer on the viewer side. On the other hand, in printing on a transparent recording medium, printing on the back side surface (the surface opposite to the side visible to the viewer) of the recording medium is called back printing. The back-printed recording medium has a positional relationship of "viewer, recording medium, image".

[0023] Therefore, when performing front printing, compared with the case of performing back printing, there is a tendency that particularly excellent scratch resistance and adhesion to the recording medium are required for the formed image. Since the ink according to the present embodiment can form an image excellent in scratch resistance and adhesion to the recording medium as described above, it can be used for front printing, and it is also conceivable to use the printed matter without lamination.

[0024] Moreover, the ink according to this embodiment is preferably used for a circulation type recording head. An inkjet recording apparatus equipped with a circulation type recording head is required to have excellent ejection stability even when the ink is circulated for a long time. As described above, the ink according to this embodiment is excellent in ejection stability and can be suitably used even when the recording head is a circulation type recording head.

[0025] Hereinafter, the ink according to this embodiment will be described in more detail. As described above, the ink according to this embodiment contains a pigment, resin particles, and an aqueous medium. Note that the ink according to this embodiment preferably further contains a pigment-coated resin. Also, the ink according to this embodiment preferably further contains a surfactant.

[0026] In the ink according to this embodiment, the pigment constitutes pigment particles together with, for example, a pigment-coated resin. The pigment particles are composed of, for example, a core containing a pigment and a pigment-coated resin covering the core. The pigment-coated resin is present, for example, dispersed in a solvent. From the viewpoint of optimizing the color density, hue, or stability of the ink according to the embodiment, the volume median diameter of the pigment particles is preferably 30 nm or more and 200 nm or less, and more preferably 70 nm or more and 130 nm or less.

[0027] [Pigment] 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).

[0028] In the ink according to this embodiment, the content ratio of the pigment is preferably 0.5% by mass or more and 10.0% by mass or less, and more preferably 1.5% by mass or more and 5.0% by mass or less. By setting the content ratio of the pigment to 0.5% by mass or more, the ink according to this embodiment can form an image having a desired image density. Further, by setting the content ratio of the pigment to 10.0% by mass or less, the fluidity of the ink according to this embodiment can be ensured.

[0029] [Pigment-coated resin] The pigment-coated resin is a resin soluble in an aqueous medium. A part of the pigment-coated resin exists, for example, 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 dissolved state in the aqueous medium of the ink according to this embodiment.

[0030] As the pigment-coated resin, a styrene-(meth)acrylic resin is preferred. The styrene-(meth)acrylic resin has repeating units derived from at least one monomer of (meth)acrylic acid alkyl ester and (meth)acrylic acid, and styrene units. Examples of the (meth)acrylic acid alkyl ester include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, and butyl (meth)acrylate. As the styrene-(meth)acrylic resin, a copolymer (X) of styrene, methyl methacrylate, methacrylic acid, and butyl acrylate is preferred. The copolymer (X) is preferably neutralized in equal amounts with a base (for example, potassium hydroxide and sodium hydroxide).

[0031] 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.

[0032] In the ink according to 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, and more preferably 0.5% by mass or more and 1.5% by mass or less. By setting the content ratio of the pigment-coated resin to 0.1% by mass or more and 4.0% by mass or less, the ejection stability of the ink according to the present embodiment can be further optimized.

[0033] In the ink according to this embodiment, the content of the pigment-coated resin with respect 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, and more preferably 20.0 parts by mass or more and 30.0 parts by mass or less. By setting the content of the pigment-coated resin to 10.0 parts by mass or more and 60.0 parts by mass or less, the ejection stability of the ink according to this embodiment can be further optimized.

[0034] [Resin particles] The resin particles exist in a state of being dispersed in an aqueous medium. The resin particles contain a specific urethane resin. The content ratio of the specific urethane resin in the resin particles is preferably 85.0% by mass or more, more preferably 90.0% by mass or more, and still more preferably 100.0% by mass.

[0035] The volume median diameter (D 50 ) of the resin particles is preferably 8 nm or more and 100 nm or less, more preferably 15 nm or more and 50 nm or less, and still more preferably 25 nm or more and 40 nm or less. By setting the volume median diameter of the resin particles to 8 nm or more, the storage stability of the ink according to this embodiment can be optimized. By setting the volume median diameter of the resin particles to 100 nm or less, the ejection stability of the ink according to this embodiment can be further optimized.

[0036] The content ratio of the resin particles in the ink according to this embodiment is 2.5% by mass or more and 9.0% by mass or less, and preferably 4.0% by mass or more and 6.0% by mass or less. By setting the content ratio of the resin particles to 2.5% by mass or more, the ink according to this embodiment can optimize the scratch resistance of the formed image and the adhesion to the recording medium. By setting the content ratio of the resin particles to 9.0% by mass or less, the ejection stability of the ink according to this embodiment can be optimized.

[0037] [Specific urethane resin] The urethane resin is, for example, a copolymer of a diol compound or a bisphenol compound and a polyisocyanate.

[0038] Examples of the diol compounds 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.

[0039] Examples of the bisphenol compounds include bisphenol A, hydrogenated bisphenol A, bisphenol A ethylene oxide adduct (e.g., polyoxyethylene(2,2)-2,2-bis(4-hydroxyphenyl)propane), and bisphenol A propylene oxide adduct.

[0040] Examples of the polyisocyanate include diisocyanate. Examples of the diisocyanate include aliphatic diisocyanate, alicyclic diisocyanate, and aromatic diisocyanate.

[0041] Examples of the aliphatic diisocyanate include ethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, and 1,6-hexamethylene diisocyanate.

[0042] Examples of the alicyclic diisocyanate include hydrogenated 4,4'-diphenylmethane diisocyanate, 1,4-cyclohexane diisocyanate, methylcyclohexylene diisocyanate, isophorone diisocyanate, and norbornane diisocyanate.

[0043] Examples of the aromatic diisocyanate include 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate, toluene diisocyanate, and naphthalene diisocyanate.

[0044] The specific urethane resin is a urethane resin having an elongation at break at 25°C of 60% or less and a glass transition point of 40°C or higher and 110°C or lower.

[0045] As described above, the elongation at break of the specific urethane resin at 25°C is 60% or less, preferably 4% or more and 60% or less, and more preferably 4% or more and 10% or less. By including a specific urethane resin having an elongation at break at 25°C of 60% or less in the ink according to the present embodiment, the ejection stability of the ink according to the present embodiment can be optimized, and the abrasion resistance of the image formed by the ink according to the present embodiment can be optimized.

[0046] As described above, the glass transition point of the specific urethane resin is 40°C or higher and 110°C or lower, preferably 45°C or higher and 90°C or lower, and more preferably 65°C or higher and 85°C or lower. By including a specific urethane resin having a glass transition point of 40°C or higher and 110°C or lower in the ink according to the present embodiment, the ejection stability of the ink according to the present embodiment can be optimized, and the adhesion of the image formed by the ink according to the present embodiment to the recording medium can be optimized.

[0047] [Surfactant] The surfactant optimizes the compatibility and dispersion stability of each component contained in the ink according to the present embodiment. Further, the surfactant optimizes the permeability (wettability) of the ink according to the present embodiment to the recording medium. Examples of the surfactant include nonionic surfactants.

[0048] Examples of the nonionic surfactant include acetylene glycol surfactants (surfactants containing acetylene glycol compounds), silicone surfactants (surfactants containing silicone compounds), and fluorine surfactants (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 according to the present embodiment preferably contains a silicone surfactant as the surfactant.

[0049] As for the content ratio of the surfactant in the ink according to this embodiment, it is preferably 0.1 mass% or more and 2.0 mass% or less, and more preferably 0.2 mass% or more and 0.6 mass% or less.

[0050] [Aqueous medium] The aqueous medium contained in the ink according to this embodiment includes water and a specific organic solvent. The specific organic solvent is a water-soluble organic solvent. The aqueous medium may function as a solvent or as a dispersion medium. The aqueous medium may further contain other water-soluble organic solvents (hereinafter sometimes referred to as other organic solvents) other than the specific organic solvent. Examples of the specific organic solvent and other organic solvents include glycol compounds, glycol ether compounds, lactam compounds, nitrogen-containing compounds, acetate compounds, thiodiglycol, and dimethyl sulfoxide.

[0051] (Water) In the ink according to this embodiment, the content ratio of water is preferably 40.0 mass% or more and 85.0 mass% or less, and more preferably 50.0 mass% or more and 70.0 mass% or less. By setting the content ratio of water to 40.0 mass% or more and 85.0 mass% or less, the ejection stability of the ink according to this embodiment can be optimized.

[0052] The specific organic solvent has a boiling point of 200°C or more and 275°C or less, and an SP value of 19.5 (J / cm 3 ) 1 / 2 or more and 26.0 (J / cm 3 ) 1 / 2 or less and is the following organic solvent.

[0053] The boiling point of the specific organic solvent is 200°C or more and 275°C or less as described above, preferably 200°C or more and 250°C or less, and 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 in the ink according to this embodiment, the ejection stability of the ink according to this embodiment can be optimized, and the rubbing resistance of the image formed by the ink according to this embodiment and the adhesion to the recording medium can be optimized.

[0054] The SP value of the specific organic solvent is, as described above, 19.5 (J / cm 3 ) 1 / 2 or more and 26.0 (J / cm 3 ) 1 / 2 or less, and 20.0 (J / cm 3 ) 1 / 2 or more and 25.5 (J / cm 3 ) 1 / 2 or less is preferable, and 23.0 (J / cm 3 ) 1 / 2 or more and 25.5 (J / cm 3 ) 1 / 2 or less is more preferable. 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, the ejection stability of the ink according to the present embodiment can be optimized, and the scratch resistance of the image formed by the ink according to the present embodiment and the adhesion to the recording medium can be optimized.

[0055] As the specific organic solvent, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, tripropylene glycol, or 3-methyl-1,3-butanediol is preferable.

[0056] As other organic solvents, organic solvents having a boiling point of less than 200°C or more than 275°C, and organic solvents having an SP value of less than 19.5 (J / cm 3 ) 1 / 2 or more than 26.0 (J / cm 3 ) 1 / 2 can be mentioned. As an example, as other organic solvents, for example, those having a boiling point of less than 200°C or more than 275°C and an SP value of less than 19.5 (J / cm 3 ) 1 / 2 or more than 26.0 (J / cm 3 ) 1 / 2Among them, polyhydric alcohols or glycol ether compounds that meet at least one of the conditions can be mentioned. Examples of polyhydric alcohols that meet the above-mentioned conditions include propylene glycol, triethylene glycol, tripropylene glycol, 3-methyl-1,3-butanediol, glycerin, and the like. Examples of glycol ether compounds that meet the above-mentioned conditions include dipropylene glycol methyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, and the like.

[0057] Polyhydric alcohols function as, for example, humectants. Humectants can suppress the volatilization of liquid components from the ink according to the present embodiment and stabilize the viscosity. Therefore, it is preferable that the ink according to the present embodiment further contains a humectant. By further containing a humectant in the ink according to the present embodiment, the volatilization of liquid components from the ink according to the present embodiment can be suppressed, and the ejection stability can be further optimized.

[0058] In addition, glycol ether compounds function as, for example, wetting agents that enhance the wettability of the substrate used as the recording medium. Wetting agents can enhance the wet spreading property of the ink according to the present embodiment on the recording medium (substrate) and further optimize the adhesion of the formed image to the recording medium. Therefore, it is preferable that the ink according to the present embodiment further contains a wetting agent.

[0059] As the humectant, the above-mentioned polyhydric alcohols can be used, and among them, propylene glycol is preferable. As the wetting agent, the above-mentioned glycol ether compounds can be used, and among them, triethylene glycol monobutyl ether glycol is preferable. Therefore, it is preferable that the ink according to the present embodiment further contains propylene glycol and triethylene glycol monobutyl ether glycol as other organic solvents.

[0060] In the ink according to this embodiment, the content ratio of the specific organic solvent 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 setting the content ratio of the specific organic solvent to 0.3% by mass or more and less than 2.0% by mass, the scratch resistance of the image formed by the ink according to this embodiment and the adhesion to the recording medium can be optimized.

[0061] As the content ratio of the other organic solvent in the ink according to this embodiment, 10.0% by mass or more and 50.0% by mass or less is preferable, and 20.0% by mass or more and 40.0% by mass or less is more preferable.

[0062] When the ink according to this embodiment contains a humectant, the content ratio of the humectant in the ink of this embodiment is preferably 7.0% by mass or more and 35.0% by mass or less, and more preferably 15.0% by mass or more and 25.0% by mass or less.

[0063] When the ink according to this embodiment contains a wetting agent, the content ratio of the wetting agent in the ink of this embodiment is preferably 3.0% by mass or more and 15.0% by mass or less, and more preferably 5.0% by mass or more and 15.0% by mass or less.

[0064] The aqueous medium preferably contains only water, a specific organic solvent, propylene glycol, and triethylene glycol monobutyl ether glycol. The total content ratio of water, the specific organic solvent, propylene glycol, and triethylene glycol monobutyl ether glycol in the aqueous medium is preferably 90.0% by mass or more, more preferably 95.0% by mass or more, and still more preferably 100.0% by mass.

[0065] [Other components] The ink according to this embodiment may further contain known additives (for example, a dissolution stabilizer, an anti-drying agent, an antioxidant, a viscosity modifier, a pH adjuster, and a fungicide) as necessary.

[0066] [Preferred composition] The ink according to this embodiment preferably has any one of Compositions 1 to 11 shown in Tables 1 to 3 below. In Table 1 below, "ratio" indicates the numerical range of the preferred content ratio [% by mass]. For example, "2.7 - 3.3", which is the ratio of the pigment in Composition 1, indicates that the pigment is contained in an amount of 2.7% by mass or more and 3.3% by mass or less. "Resin" indicates a pigment coating resin. "r-1", ~ "r-4" of the types of specific urethane resins respectively indicate the specific urethane resin particles (r-1) ~ (r-4) used in the examples. "DEGMBE" of the type of specific organic solvent indicates diethylene glycol monobutyl ether. "TEGMME" indicates triethylene glycol monomethyl ether. "TPG" indicates tripropylene glycol. "3M-1,3BD" indicates 3-methyl-1,3-butanediol. "PG" of the type of other organic solvents indicates propylene glycol. "TEGMBE" indicates triethylene glycol monobutyl ether. "PG (ratio)" indicates the numerical range of the preferred content ratio [% by mass] of propylene glycol. "TEGMBE (ratio)" indicates the numerical range of the preferred content ratio [% by mass] of triethylene glycol monobutyl ether.

[0067]

Table 1

[0068]

Table 2

[0069]

Table 3

[0070] [Method for Manufacturing Ink] The ink according to this embodiment can be produced by uniformly mixing, with a stirrer, for example, a pigment dispersion containing a pigment, a urethane resin emulsion containing resin particles including a specific urethane resin, an aqueous medium containing water and a specific organic solvent, and other components (for example, a surfactant) blended as necessary. In the production of the ink according to this embodiment, after uniformly mixing each component, foreign matters and coarse particles may be removed by a filter (for example, a filter having a pore size of 5 μm or less).

[0071] (Pigment dispersion) The pigment dispersion is a dispersion containing a pigment. The pigment dispersion preferably further contains a pigment coating resin. As the dispersion medium of the pigment dispersion, water is preferable.

[0072] The content ratio of the pigment in the pigment dispersion is preferably 5.0% by mass or more and 25.0% by mass or less, and more preferably 10.0% by mass or more and 20.0% by mass or less. The content ratio of the pigment coating resin in the pigment dispersion is preferably 1.0% by mass or more and 10.0% by mass or less, and more preferably 2.0% by mass or more and 6.0% by mass or less.

[0073] The pigment dispersion can be prepared by wet-dispersing a pigment, a pigment coating resin, a dispersion medium (for example, water), and components (for example, a surfactant) added as necessary with a media-type wet disperser. In the wet dispersion by the media-type wet disperser, as the media, for example, small-diameter beads (for example, beads with D 50 of 0.5 mm or more and 1.0 mm or less) can be used. The material of the beads is not particularly limited, but a hard material (for example, glass and zirconia) is preferable.

[0074] When adding the pigment dispersion in the production of the ink according to this embodiment, the ratio of the pigment dispersion to all the raw materials of the ink is, for example, 10.0% by mass or more and 40.0% by mass or less.

[0075] (Urethane resin emulsion) A urethane resin emulsion is a dispersion containing resin particles containing a urethane resin. Water is preferred as the dispersion medium of the urethane resin emulsion.

Examples

[0076] Hereinafter, examples of the present invention will be described. However, the present invention is not limited to the following examples.

[0077] [Preparation of Pigment Dispersion] A pigment dispersion (C) used for the preparation of the ink was prepared. The components contained in the pigment dispersion (C) and their amounts are shown in Table 4.

[0078]

Table 4

[0079] In Table 4, "Resin A-Na" indicates Resin A (pigment coating resin) neutralized with sodium hydroxide (NaOH). As the pigment, "Black Pigment" ("MONARCH (registered trademark) 800" manufactured by Cabot Corporation) was used.

[0080] [Preparation of Resin A] Resin A for obtaining "Resin A-Na" in Table 4 was prepared by the following method. Specifically, a four-necked flask was set with a stirrer, a nitrogen introduction tube, a condenser, and a dropping funnel. Next, 100.0 parts by mass of isopropyl alcohol and 300.0 parts by mass of methyl ethyl ketone were placed in the flask. While bubbling nitrogen through the contents of the flask, heating reflux was carried out at 70°C.

[0081] 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, which is a monomer solution. With the contents of the flask heated to reflux at 70 °C, solution L1 was added dropwise to the flask over 2 hours. After the addition, the contents of the flask were further heated to reflux at 70 °C for 6 hours.

[0082] 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 to reflux at 70 °C for 5 hours. Thus, resin A (styrene-(meth)acrylic resin) was obtained. The obtained resin A had a mass average molecular weight (Mw) of 20,000 and an acid value of 100 mgKOH / g.

[0083] Here, the mass average molecular weight Mw of resin A was measured using gel permeation chromatography ("HLC-8020GPC" manufactured by Tosoh Corporation) under the following conditions. Column: "TSKgel SuperMultipore HZ-H" (semi-micro column with 4.6 mm I.D. × 15 cm) manufactured by Tosoh Corporation Number of columns: 3 Eluent: Tetrahydrofuran Flow rate: 0.35 mL / min Sample injection volume: 10 μL Measurement temperature: 40 °C Detector: IR detector

[0084] The calibration curve was prepared by selecting seven types, F-40, F-20, F-4, F-1, A-5000, A-2500, and A-1000, and n-propylbenzene from TSKgel standard polystyrene manufactured by Tosoh Corporation.

[0085] Also, the acid value of Resin A was measured by a method compliant with "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)".

[0086] [Preparation of Pigment Dispersion (C)] While heating Resin A in a warm bath at 70 °C, an aqueous sodium hydroxide solution in an amount necessary for neutralizing Resin A was added to Resin A. More specifically, an aqueous sodium hydroxide solution with a mass 1.1 times the neutralization equivalent was added to Resin A. In this way, 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 became 8.

[0087] Into the vessel of a media-type disperser ("Dyno (registered trademark) Mill" manufactured by Willy E. Bachofen Co., Ltd. (WAB)) so as to achieve the compounding amounts shown in Table 4, the above-mentioned 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 put, and the total amount was made 100.0 parts by mass. Note that water was added so that the mass of water, including the mass of water contained in the aqueous sodium hydroxide solution used for neutralizing Resin A and the mass of water generated in the neutralization reaction, became 80.0 parts by mass.

[0088] Next, media (zirconia beads with a diameter of 1.0 mm) were filled into the vessel so that the filling rate became 70% by volume with respect to the capacity of the vessel. Using the media-type disperser, the contents of the vessel were subjected to a dispersion treatment. In this way, Pigment Dispersion (C), which is a pigment dispersion for black ink, was obtained.

[0089] Pigment Dispersion (C) was diluted 300-fold with water to obtain a diluted solution. Using a dynamic light scattering particle size distribution measuring device ("Zetasizer Nano ZS" manufactured by Malvern), the diluted solution was measured to determine the volume median diameter (D 50 ) of the pigment particles contained in Pigment Dispersion (C). And 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 Pigment Dispersion (C).

[0090] [Urethane resin emulsion] As resin emulsions used for the preparation of inks, urethane resin emulsions (R-1) to (R-8) shown in Table 5 below were prepared. The urethane resin emulsions (R-1) to (R-8) were all manufactured by Daiichi Kogyo Seiyaku Co., Ltd. The urethane resin emulsions (R-1) to (R-8) each contained urethane resin particles (r-1) to (r-8). In Table 5 below, "Tg" indicates the glass transition point. "(R)" indicates that it is a registered trademark. Note that the urethane resin particles (r-1) to (r-4) were resin particles of a specific urethane resin.

[0091] [Table 5] [Organic solvent]

[0092] As organic solvents used for the preparation of inks, the organic solvents shown in Table 6 below were prepared. Note that diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, tripropylene glycol, and 3-methyl-1,3-butanediol were specific organic solvents.

[0093] [Table 6]

[0094] [Preparation of ink] Inks of Examples 1 to 11 and Comparative Examples 1 to 9 were prepared by the following method.

[0095] [Example 1] 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 urethane resin emulsion (R-1) (urethane 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 silicone surfactant ("Silface (registered trademark) SAG503A" manufactured by Nissin Chemical Co., Ltd., polyether-modified siloxane compound) were placed in 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. Using a stirrer ("Three One Motor BL-600" manufactured by Shin-Tong Science Co., Ltd.), the contents of the beaker were mixed at a rotational speed of 400 rpm to obtain a mixed solution. The mixed solution was filtered using a filter (pore size 5 μm) to remove foreign substances and coarse particles contained in the mixed solution. Thus, the ink of Example 1 was obtained.

[0096] [Examples 2 to 11 and Comparative Examples 1 to 9] Inks of Examples 2 to 11 and Comparative Examples 1 to 9 were prepared in the same manner as the preparation of the ink of Example 1, except that the types and amounts of each component were changed as shown in Tables 7 to 9.

[0097] In Tables 7 to 9, the numerical values indicate the content ratio [mass%]. "DPGME" indicates dipropylene glycol methyl ether. "DEGMBE" indicates diethylene glycol monobutyl ether. "TEGMME" indicates triethylene glycol monomethyl ether. "TPG" indicates tripropylene glycol. "3M-1,3BD" indicates 3-methyl-1,3-butanediol. "TEG" indicates triethylene glycol. "PG" indicates propylene glycol. "TEGMBE" indicates triethylene glycol monobutyl ether. "-" indicates that the corresponding material is not used.

[0098]

Table 7

[0099]

Table 8

[0100]

Table 9

[0101] [Evaluation] In the following manner, the rub resistance of the images formed, the adhesion to the recording medium, and the ejection stability of the inks of Examples 1 to 11 and Comparative Examples 1 to 9 were evaluated. Also, the ejection stability of the ink was evaluated by the presence or absence of the occurrence of sagging in the non-printed area. The evaluation results are shown in Tables 10 to 11 below. In addition, the evaluation was carried out at a temperature of 25°C and a humidity of 60%RH unless otherwise specified.

[0102] [Preparation of Evaluation Film] The evaluation film for adhesion and rub resistance was prepared by the following method. First, on a non-permeable recording medium, the ink to be evaluated (any one of the inks of Examples 1 to 11 and Comparative Examples 1 to 9) was applied to form a black solid image with a wet film thickness of about 6 μm of the ink coating film immediately after application. As the non-permeable recording medium, a corona-discharged PET film (「FE2001」manufactured by Futamura Chemical Co., Ltd., one-sided corona discharge treatment) was used. Specifically, the ink coating film was formed on the surface of the PET film that had been subjected to corona discharge treatment. For the application of the ink, a bar coater (「K303S Multi Coater」manufactured by Matsu Ink Ozawa Sangyo Co., Ltd.) was used. For the bar of the bar coater, the bar of bar No. 1 was used. The printing speed was set at 30 m / min. Next, the non-permeable recording medium on which the solid image was formed was dried at 100°C for 10 minutes and then allowed to stand for 12 hours to obtain the evaluation film.

[0103] [Adhesion] An adhesive tape ("Cellotape (registered trademark) CT-18S" manufactured by Nichiban Co., Ltd., width 18 mm) was attached to the solid image of the evaluation film, and the adhesive tape was peeled off at an angle of approximately 60 degrees. The peeling of the adhesive tape was performed at a speed such that the time from the start of peeling to the end of peeling was 1 second. After peeling the adhesive tape, the evaluation film was visually observed to confirm the presence or absence of peeling of the solid image. Then, when the area where the adhesive tape was attached in the solid image was set to 100 area%, the ratio of the area of the solid image peeled off together with the adhesive tape (peeling rate [area%]) was calculated. The adhesion of the formed image to the recording medium was determined according to the following criteria.

[0104] (Adhesion evaluation criteria) A (Good): There is no peeling of the solid image (peeling rate 0 area%). B (Slightly poor): The peeling rate is more than 0 area% and less than 50 area%. C (Poor): The peeling rate is 50 area% or more.

[0105] [Scratch resistance] According to the friction tester type II (Gakushin type) method described in JIS L-0849:2013 (Test method for color fastness to rubbing), the solid image formed on the evaluation film was rubbed back and forth 100 times with a load of 200 g using a friction cloth (cotton flannel). After rubbing with the friction cloth, the evaluation film was visually observed to confirm the presence or absence of peeling of the solid image. Then, when the area of the solid image on the evaluation film before rubbing was set to 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 determined according to the following criteria.

[0106] (Scratch resistance evaluation criteria) A (Good): There is no peeling of the solid image (peeling rate 0 area%). B (Slightly poor): The peeling rate is more than 0 area% and less than 5 area%. C (Poor): The peeling rate is 5 area% or more.

[0107] [Discharge stability (waviness of non-printed area)] The evaluation of ejection stability (waviness in the non-printing area) was carried out in a normal temperature and high humidity environment (environment at a temperature of 25°C and a humidity of 80% RH) in order to suppress the influence of ink nozzle drying.

[0108] As the evaluation apparatus, an image forming apparatus (an inkjet recording apparatus equipped with a line head, a testing machine manufactured by Kyocera Document Solutions Inc.) was used. The ink to be evaluated (ink of any one of Examples 1 to 11 and Comparative Examples 1 to 9) was set in the line head of the evaluation apparatus.

[0109] Regarding the above-mentioned evaluation apparatus, ink purge from the line head and wiping of the line head were performed (purge wipe process). One minute after the purge wipe process, a single horizontal line (a line along the main scanning direction) was formed on A4 glossy paper ("Super Fine Paper" manufactured by Seiko Epson Corporation) using the evaluation apparatus. At this time, the line width of the horizontal line was set to 1 dot (the amount of one drop of ink). The volume per dot of the ink ejected from each nozzle of the line head (the volume per drop) was set to 3 pL. Next, the deviation amount of the above-mentioned horizontal line was determined using an optical microscope ("MM-800" manufactured by Nikon Corporation). Specifically, the maximum distance (deviation amount) in the sub-scanning direction of each dot constituting the above-mentioned horizontal line was measured using the application software attached to the above-mentioned optical microscope. The larger the deviation amount, the more distortion occurred in the above-mentioned horizontal line due to waviness in the non-printing area. The ejection stability (waviness in the non-printing area) was determined according to the following criteria.

[0110] (Evaluation criteria for ejection stability) A (good): The deviation amount is 20 μm or less. B (bad): The deviation amount exceeds 20 μm.

[0111]

Table 10

[0112]

Table 11

[0113] [Evaluation] As shown in Tables 10 to 11, the inks of Examples 1 to 11 contained a pigment, resin particles, and an aqueous medium. The resin particles contained a specific urethane resin. The content ratio of the resin particles was 2.5% by mass or more and 9.0% by mass or less. The elongation at break of the specific urethane resin at 25°C was 60% or less. The glass transition point of the specific urethane resin was 40°C or more and 110°C or less. The aqueous medium contained water and a specific organic solvent. The content ratio of the specific organic solvent was 0.3% by mass or more and less than 2.0% by mass. The boiling point of the specific organic solvent was 200°C or more and 275°C or less. The SP value of the specific organic solvent was 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 were excellent in ejection stability, and the formed images were excellent in scratch resistance and adhesion to the recording medium.

[0114] On the other hand, in the ink of Comparative Example 1, since the content ratio of the resin particles was less than 2.5% by mass, the scratch resistance of the formed image and the adhesion to the recording medium were poor or slightly poor.

[0115] In the ink of Comparative Example 2, since the content ratio of the resin particles exceeded 9.0% by mass, the ejection stability was poor.

[0116] In the inks of Comparative Examples 3 to 5, since the elongation at break of the urethane resin contained in the resin particles exceeded 60%, the scratch resistance was poor.

[0117] Also, in the inks of Comparative Examples 4 and 6, since the glass transition point of the urethane resin contained in the resin particles was less than 40°C, the ejection stability was poor.

[0118] In the ink of Comparative Example 7, the boiling point of dipropylene glycol methyl ether used for comparison with the specific organic solvent was less than 200°C and the SP value was 19.5 (J / cm 3 ) 1 / 2Since it was less than, the abrasion resistance of the formed image and the adhesion to the recording medium were slightly poor.

[0119] The ink of Comparative Example 8 had a boiling point of more than 275°C and an SP value of 26.0 (J / cm 3 ) 1 / 2 more than, so the abrasion resistance of the formed image and the adhesion to the recording medium were poor or slightly poor.

[0120] The ink of Comparative Example 9 had a content ratio of the specific organic solvent of 2.0 mass% or more, so the abrasion resistance of the formed image and the adhesion to the recording medium were poor or slightly poor.

Industrial Applicability

[0121] The ink of the present invention can be used for forming an image.

Claims

1. containing a pigment, resin particles, and an aqueous medium, wherein the resin particles contain a specific urethane 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 urethane resin at 25°C is 60% or less, the glass transition point of the specific urethane 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 and the following is an ink for inkjet.

2. The inkjet ink 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 inkjet ink 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. further containing a surfactant, The inkjet ink according to claim 1 or 2, wherein the surfactant contains a silicone surfactant.

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

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

Images