Ink set

Abstract

To provide an ink set which is excellent in pinning speed, beading, bleeding, and discharge stability.SOLUTION: An ink set is composed of a pretreatment liquid and pigment ink, wherein the pretreatment liquid contains water, a coagulant, and an organic solvent, a content of the coagulant in the pretreatment liquid is 1.0 mass% or more and 20.0 mass% or less, the pigment ink contains an organic solvent containing water, a coloring material and a glycol ester compound, polyoxyethylene alkyl ether, and a resin, a content of the polyoxyethylene alkyl ether in the pigment ink is 1.0 mass% or more and 5.0 mass% or less, a content of the glycol ether compound is 10.0 mass% or more and 20.0 mass% or less, a ratio P / R of a content P of the coloring material in the pigment ink to a content R of the resin is 0.25 or more and 3.0 or less, a mixture SP value of the organic solvent in the pigment ink is different from a mixture SP value of the organic solvent in the pretreatment liquid, and the difference therebetween is 2.0 (cal / cm3)0.5 or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an ink set.

Background Art

[0002] In recent years, in the fields of commercial printing and industrial printing where analog printing such as offset printing and flexographic printing is mainstream, the need for inkjet printers as digital printing that can print small quantities and multiple varieties of designs without the need for plates has been increasing.

[0003] In the fields of commercial printing and industrial printing, high productivity is required compared to home printing, so high-speed printing is performed. In order to cope with this high-speed printing, an increase in the speed (pinning speed) from the diffusion to the fixation of the ink on the recording medium is required.

[0004] In the prior art, when recording aqueous ink on a recording medium having a coating layer used for offset printing paper, there has been a problem that beading occurs on offset printing paper with poor absorbency of the aqueous ink, resulting in a decrease in image quality. In addition, since color inks of different colors are successively overlaid, the color ink bleeds at the color boundary portion and mixing occurs (hereinafter referred to as bleeding), and there has been a problem that the image quality is greatly reduced.

[0005] In order to solve this problem, a method of applying a pretreatment liquid that promotes the aggregation of ink pigments and imparts a function of preventing bleeding has been proposed (see, for example, Patent Document 1).

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the method disclosed in Patent Document 1, although a polyvalent metal salt is used in the pretreatment liquid for inkjet recording to improve image quality (beading, bleeding), the speed from the diffusion of the ink on the recording medium to its fixation (pinning speed) when assuming high-speed printing has not been studied.

[0007] An object of the present invention is to provide an ink set that is excellent in pinning speed, beading, bleeding, and ejection stability when assuming high-speed printing.

Means for Solving the Problems

[0008] The present invention relates to an ink set as described below. An ink set comprising a pretreatment liquid and a pigment ink, wherein the pretreatment liquid contains water, a flocculant, and an organic solvent, and the content of the flocculant in the pretreatment liquid is 1.0% by mass or more and 20.0% by mass or less, the pigment ink contains water, a colorant, an organic solvent containing at least a glycol ether compound, a polyoxyethylene alkyl ether, and a resin, the content of the polyoxyethylene alkyl ether in the pigment ink is 1.0% by mass or more and 5.0% by mass or less, the content of the glycol ether compound is 10.0% by mass or more and 20.0% by mass or less, when the content of the colorant in the pigment ink is P and the content of the resin is R, P / R is 0.25 or more and 3.0 or less, the mixed SP value of the organic solvent contained in the pigment ink is different from the mixed SP value of the organic solvent contained in the pretreatment liquid, and the difference is 2.0 (cal / cm 3 ) 0.5 or more An ink set characterized by the above.

Advantages of the Invention

[0009] According to the present invention, it is possible to provide an ink set that is excellent in pinning speed, bleeding, bleeding, and ejection stability when high-speed printing is assumed.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0011] In the prior art as described in Patent Document 1, a polyvalent metal salt is used in the pretreatment liquid to improve image quality (bleeding, bleeding), but the speed from the diffusion to the fixation of the ink on the offset recording medium when high-speed printing is assumed (pinning speed) has not been studied. Therefore, the pinning speed was measured with the ink formulation of the prior art, but it did not satisfy the pinning speed required at the time of high-speed printing (frequency 40 kHz). Therefore, an attempt was made to improve the pinning speed by adjusting the addition amount of the penetrant and surfactant contained in the ink, but the required level was not achieved.

[0012] As a result of intensive studies by the present inventors, in an ink set composed of a pretreatment liquid and a pigment ink, when the pretreatment liquid and the pigment ink have the following configurations, it is possible to provide an ink set that is excellent in pinning speed, bleeding, bleeding, and ejection stability when high-speed printing is assumed. (Pretreatment Liquid) The pretreatment liquid contains water, a flocculant, and an organic solvent, and the content of the flocculant in the pretreatment liquid is 1.0% by mass or more and 20.0% by mass or less. (Pigment Ink) The pigment ink contains water, a coloring material, an organic solvent containing at least a glycol ether compound, a polyoxyethylene alkyl ether, and a resin. The content of the polyoxyethylene alkyl ether in the pigment ink is 1.0% by mass or more and 5.0% by mass or less, and the content of the glycol ether compound is 10.0% by mass or more and 20.0% by mass or less. When the content of the coloring material in the pigment ink is P and the content of the resin is R, P / R is 0.25 or more and 3.0 or less. The mixed SP value of the organic solvent contained in the pigment ink is different from the mixed SP value of the organic solvent contained in the pretreatment liquid, and the difference is 2.0 (cal / cm 3 ) 0.5 or more. Hereinafter, "pigment ink" may be referred to as "ink".

[0013] By applying a pretreatment liquid to the substrate before applying the ink, bleeding and color unevenness due to mixing of ink droplets can be improved, and beading and bleeding of the ink layer on the pretreatment liquid on the offset recording paper can be improved. This effect is due to the effect of a flocculant such as a polyvalent metal salt contained in the treatment liquid. Among the flocculants, polyvalent metal salts are preferable because they have a low molecular weight and the cation component moves easily compared to cationic resins and organic acids used as flocculants, and they dissolve instantaneously in water and generate a cation component that causes aggregation of solid components. When the ink is applied on the substrate coated with the treatment liquid, the cation component can instantaneously move throughout the layer and cause aggregation of the pigment.

[0014] Furthermore, by adding an organic solvent containing at least a glycol ether compound and a polyoxyethylene alkyl ether to the color ink, the penetration rate and the wetting rate can be increased, and the pinning rate can be improved. At that time, the difference in the mixed SP value of the organic solvent contained in the ink from the mixed SP value of the organic solvent contained in the pretreatment liquid reduces the compatibility, and the pinning rate can be improved.

[0015] The mixing SP value of the organic solvents contained in the pigment ink is 10.0 (cal / cm 3 ) 0.5 or more and 12.0 (cal / cm 3 ) 0.5 or less, and the mixing SP value of the organic solvents contained in the pretreatment liquid is 13.0 (cal / cm 3 ) 0.5 or more and 15.0 (cal / cm 3 ) 0.5 or less, which is preferable. Also, by adjusting the content ratio of the coloring material to the resin in the pigment ink, the penetration rate and the wetting rate can be further increased, and the pinning rate can be improved. Note that the definition of the "mixing SP value" will be described later.

[0016] Hereinafter, the present invention will be specifically described.

[0017] (Ink) The ink in the present invention contains water, a coloring material, an organic solvent, a surfactant, and a resin, and may contain other components as necessary. The ink in the present invention refers to a material using a colored coloring material other than white for the coloring material. Hereinafter, the organic solvent, coloring material, surfactant, resin, etc. used in the ink of the present invention will be described.

[0018] <Organic Solvent> The organic solvent used in the present invention is not particularly limited, and a water-soluble organic solvent can be used. For example, polyhydric alcohols, ethers such as polyhydric alcohol alkyl ethers and polyhydric alcohol aryl ethers, nitrogen-containing heterocyclic compounds, amides, amines, sulfur-containing compounds can be mentioned. Specific examples of the water-soluble organic solvent include, for example, polyhydric alcohols such as ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 3-methyl-1,3-butanediol, triethylene glycol, polyethylene glycol, polypropylene glycol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 2,4-pentanediol, 1,5-pentanediol, 1,2-hexanediol, 1,6-hexanediol, 1,3-hexanediol, 2,5-hexanediol, 1,5-hexanediol, glycerin, 1,2,6-hexanetriol, 2-ethyl-1,3-hexanediol, ethyl-1,2,4-butanetriol, 1,2,3-butanetriol, 2,2,4-trimethyl-1,3-pentanediol, petriol, etc.; polyhydric alcohol alkyl ethers such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, propylene glycol monoethyl ether, etc.; polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, etc.; nitrogen-containing heterocyclic compounds such as 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, ε-caprolactam, γ-butyrolactone, etc.; amides such as formamide, N-methylformamide, N,N-dimethylformamide, 3-methoxy-N,N-dimethylpropionamide, 3-butoxy-N,N-dimethylpropionamide, etc.; amines such as monoethanolamine, diethanolamine, triethylamine, etc.; sulfur-containing compounds such as dimethyl sulfoxide, sulfolane, thiodiethanol, etc.; and propylene carbonate, ethylene carbonate, etc. Since it not only functions as a wetting agent but also provides good drying properties, it is preferable to use an organic solvent having a boiling point of 250 °C or lower.

[0019] As the organic solvent, polyol compounds having 8 or more carbon atoms and glycol ether compounds are also preferably used, and the present invention includes at least a glycol ether compound. Specific examples of the polyol compound having 8 or more carbon atoms include 2-ethyl-1,3-hexanediol and 2,2,4-trimethyl-1,3-pentanediol. Specific examples of the glycol ether compound include polyhydric alcohol alkyl ethers such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, and propylene glycol monoethyl ether; and polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether.

[0020] The polyol compound having 8 or more carbon atoms and the glycol ether compound can improve the ink permeability when paper is used as the recording medium.

[0021] "SP value" means "solubility parameter", and is generally widely used as an index of affinity and solubility with materials used by dissolving or dispersing in water or solvents such as solvents, resins, and pigments. Regarding the method for obtaining the SP value, various methods have been proposed, such as a method of measuring by experiment, a method of calculating from the measurement of physical properties such as immersion heat, and a method of calculating from the molecular structure. In the present invention, the method of calculating from the molecular structure proposed by Fedors is used. This method is effective in that the SP value can be calculated if the molecular structure is known and the difference from the measured value by experiment is small. In the present invention, based on the Fedors method, the SP value calculated from the molecular structure is used, and its unit is (cal / cm 3 ) 0.5 is used. The SP value can be calculated using the Fedors method described in the literature "R.F. Fedors: Polym. Eng. Sci., 14〔2〕, 147-154".

[0022] [Definition of mixed SP value] The mixed SP value in the mixed solution of organic solvents in the pretreatment liquid can be calculated by the following formula (1) based on the molar fraction of each organic solvent in the pretreatment liquid. The mixed SP value (cal / cm in the mixed solution of organic solvents in the pretreatment liquid 3 ) 0.5 =[SP value of organic solvent A × molar fraction of organic solvent A] + [SP value of organic solvent B × molar fraction of organic solvent B] + ······ Formula (1)

[0023] Examples of organic solvents include 3-ethyl-3-oxetanemethanol (SP value: 11.31 (cal / cm 3 ) 0.5 ), 3-methyl-3-oxetanemethanol (SP value: 11.79 (cal / cm 3 ) 0.5 ), β-methoxy-N,N-dimethylpropionamide (3-methoxy-N,N-dimethylpropionamide) (SP value: 9.19 (cal / cm 3 ) 0.5 ), β-butoxy-N,N-dimethylpropionamide (3-butoxy-N,N-dimethylpropionamide) (SP value: 10.27 (cal / cm 3 ) 0.5 ), 1,2-hexanediol (SP value: 12.59 (cal / cm 3 ) 0.5 ), 2-ethyl-1,3-hexanediol (SP value: 11.72 (cal / cm 3 ) 0.5 ), 2,2,4-trimethyl-1,3-pentanediol (SP value: 10.8 (cal / cm 3 ) 0.5 ), diethylene glycol monoethyl ether (SP value: 10.94 (cal / cm 3 ) 0.5 ), 3-methoxy-1-butanol (SP value: 9.64 (cal / cm3 ) 0.5 ) 3-methoxy-3-methyl-1-butanol (SP value: 10.92 (cal / cm 3 ) 0.5 ) 3-methyl-1,5-pentanediol (SP value: 11.8 (cal / cm 3 ) 0.5 ) methylpropylene triglycol (SP value: 9.43 (cal / cm 3 ) 0.5 ) diethylene glycol mono-n-butyl ether (SP value: 10.7 (cal / cm 3 ) 0.5 ) diethylene glycol monomethyl ether (SP value: 11.23 (cal / cm 3 ) 0.5 ) triethylene glycol monomethyl ether (SP value: 10.12 (cal / cm 3 ) 0.5 ) propylene glycol monopropyl ether (SP value: 9.82 (cal / cm 3 ) 0.5 ) propylene glycol monomethyl ether (SP value: 10.19 (cal / cm 3 ) 0.5 ) propylene glycol monobutyl ether (SP value: 9.69 (cal / cm 3 ) 0.5 ) 3-methoxy-1-butanol (SP value: 10.65 (cal / cm 3 ) 0.5 ) 3-methoxy-1-propanol (SP value: 10.41 (cal / cm 3 ) 0.5 ) dipropylene glycol monomethyl ether (SP value: 9.84 (cal / cm 3 ) 0.5 ) and 3-methyl-1,5-pentanediol (SP value: 11.8 (cal / cm 3 ) 0.5 ) and the like exist.

[0024] SP value is 8.0 (cal / cm 3 ) 0.5 or more and 20.0 (cal / cm 3 ) 0.5It is preferable to use the following organic solvents. These may be used individually or in combination of two or more. There is no particular limitation on the content of the organic solvent having an SP value within the above range, and it can be appropriately set according to the purpose. From the viewpoint of ejection stability, 20.0 mass% or more and 40.0 mass% or less with respect to the total amount of the ink is preferable.

[0025] <Water> The water content in the ink is not particularly limited and can be appropriately selected according to the purpose. From the viewpoints of the drying property and ejection reliability of the ink, 10 mass% or more and 90 mass% or less is preferable, and 20 mass% or more and 60 mass% or less is more preferable.

[0026] <Colorant> The colorant is not particularly limited, and pigments and dyes can be used. As the pigment, an inorganic pigment or an organic pigment can be used. These may be used individually or in combination of two or more. Also, mixed crystals may be used. As the pigment, for example, black pigments, yellow pigments, magenta pigments, cyan pigments, white pigments, green pigments, orange pigments, metallic pigments such as gold and silver, and metallic pigments can be used. As the inorganic pigment, in addition to titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, and chrome yellow, carbon black produced by known methods such as the contact method, the furnace method, and the thermal method can be used. Also, as the organic pigment, azo pigments, polycyclic pigments (for example, phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc.), dye chelates (for example, basic dye type chelates, acid dye type chelates, etc.), nitro pigments, nitroso pigments, aniline black, etc. can be used. Among these pigments, those having good affinity with the solvent are preferably used. In addition, the use of resin hollow particles and inorganic hollow particles is also possible. As specific examples of pigments, for black pigments, there are carbon blacks (C.I. Pigment Black 7) such as furnace black, lamp black, acetylene black, and channel black, or metals such as copper, iron (C.I. Pigment Black 11), titanium oxide, and organic pigments such as aniline black (C.I. Pigment Black 1). Furthermore, for color pigments, there are C.I. Pigment Yellow 1, 3, 12, 13, 14, 17, 24, 34, 35, 37, 42 (yellow iron oxide), 53, 55, 74, 81, 83, 95, 97, 98, 100, 101, 104, 108, 109, 110, 117, 120, 138, 150, 153, 155, 180, 185, 213, C.I. Pigment Orange 5, 13, 16, 17, 36, 43, 51, C.I. Pigment Red 1, 2, 3, 5, 17, 22, 23, 31, 38, 48:2, 48:2 (Permanent Red 2B (Ca)), 48:3, 48:4, 49:1, 52:2, 53:1, 57:1 (Brilliant Carmine 6B), 60:1, 63:1, 63:2, 64:1, 81, 83, 88, 101 (vermilion), 104, 105, 106, 108 (cadmium red), 112, 114, 122 (quinacridone magenta), 123, 146, 149, 166, 168, 170, 172, 177, 178, 179, 184, 185, 190, 193, 202, 207, 208, 209, 213, 219, 224, 254, 264, C.I. Pigment Violet 1 (rhodamine lake), 3, 5:1, 16, 19, 23, 38, C.I. Pigment Blue 1, 2, 15 (phthalocyanine blue), 15:1, 15:2, 15:3, 15:4 (phthalocyanine blue), 16, 17:1, 56, 60, 63, C.I. Pigment Green 1, 4, 7, 8, 10, 17, 18, 36, etc. As dyes, there are no particular limitations, and acid dyes, direct dyes, reactive dyes, and basic dyes can be used. They can be used alone or in combination of two or more. Examples of the dye include C.I. Acid Yellow 17, 23, 42, 44, 79, 142, C.I. Acid Red 52, 80, 82, 249, 254, 289, C.I. Acid Blue 9, 45, 249, C.I. Acid Black 1, 2, 24, 94, C.I. Food Black 1, 2, C.I. Direct Yellow 1, 12, 24, 33, 50, 55, 58, 86, 132, 142, 144, 173, C.I. Direct Red 1, 4, 9, 80, 81, 225, 227, C.I. Direct Blue 1, 2, 15, 71, 86, 87, 98, 165, 199, 202, C.I. Direct Black 19, 38, 51, 71, 154, 168, 171, 195, C.I. Reactive Red 14, 32, 55, 79, 249, C.I. Reactive Black 3, 4, 35.

[0027] From the viewpoints of improving image density, good fixability, and ejection stability, the content of the coloring material in the ink is preferably 0.1% by mass or more and 15% by mass or less, more preferably 1% by mass or more and 10% by mass or less.

[0028] In order to obtain ink by dispersing a pigment, methods such as introducing a hydrophilic functional group into the pigment to make a self-dispersible pigment, coating the surface of the pigment with a resin and dispersing it, and dispersing it using a dispersant can be mentioned. Examples of the method of introducing a hydrophilic functional group into the pigment to make a self-dispersible pigment include a method of making it dispersible in water by adding a functional group such as a sulfone group or a carboxyl group to the pigment (for example, carbon). Examples of the method of coating the surface of the pigment with a resin and dispersing it include a method of including the pigment in microcapsules to make it dispersible in water. This can be paraphrased as a resin-coated pigment. In this case, not all of the pigments blended in the ink need to be coated with the resin, and uncoated pigments or partially coated pigments may be dispersed in the ink as long as the effects of the present invention are not impaired. Examples of the method of dispersing using a dispersant include methods of dispersing using a known low-molecular-weight dispersant or a high-molecular-weight dispersant typified by a surfactant. As the dispersant, for example, an anionic surfactant, a cationic surfactant, an amphoteric surfactant, a nonionic surfactant, etc. can be used according to the pigment. RT-100 (nonionic surfactant) manufactured by Takemoto Yushi Co., Ltd. and sodium naphthalene sulfonate formalin condensate can also be suitably used as the dispersant. The dispersant may be used alone or in combination of two or more.

[0029] <Pigment dispersion> It is possible to obtain ink by mixing a pigment with materials such as water or an organic solvent. Also, it is possible to manufacture ink by mixing a pigment and other materials such as water or a dispersant to form a pigment dispersion and then mixing a material such as water or an organic solvent. The pigment dispersion is obtained by mixing, dispersing water, a pigment, a pigment dispersant, and other components as necessary, and adjusting the particle size. It is advisable to use a disperser for dispersion. There is no particular limitation on the particle size of the pigment in the pigment dispersion. However, from the viewpoints of good dispersion stability of the pigment and high image quality such as ejection stability and image density, the maximum frequency in terms of the maximum number is preferably 20 nm or more and 500 nm or less, and more preferably 20 nm or more and 150 nm or less. The particle size of the pigment can be measured using a particle size analyzer (NanoTrack Wave-UT151, manufactured by Microtrac Bell Co., Ltd.). The content of the pigment in the pigment dispersion is not particularly limited and can be appropriately selected according to the purpose. However, from the viewpoints of obtaining good ejection stability and increasing the image density, it is preferably 0.1% by mass or more and 50% by mass or less, and more preferably 0.1% by mass or more and 30% by mass or less. The pigment dispersion is preferably filtered to remove coarse particles and degassed using a filter, a centrifugal separator, etc. as necessary.

[0030] <Resin> The type of resin contained in the ink is not particularly limited and can be appropriately selected according to the purpose. For example, urethane resin, polyester resin, acrylic resin, vinyl acetate resin, styrene resin, butadiene resin, styrene-butadiene resin, vinyl chloride resin, acrylic styrene resin, acrylic silicone resin, etc. can be mentioned. Resin particles composed of these resins may be used. It is possible to obtain an ink by mixing the resin particles with materials such as colorants and organic solvents in the state of a resin emulsion in which water is used as a dispersion medium. As the resin particles, those appropriately synthesized may be used, or commercially available products may be used. Further, these may be used alone or in combination of two or more kinds of resin particles.

[0031] The resin contained in the pigment ink preferably has a glass transition point of 30°C or higher. Further, it is more preferable to use in combination a resin having a glass transition point of 30°C or higher and a resin having a glass transition point of less than 0°C. When the content of the resin is in the range of 4.0% by mass or more and 15.0% by mass or less, the drying property is excellent. Hereinafter, the glass transition point may be referred to as Tg.

[0032] The type of resin contained in the color ink is not particularly limited and can be appropriately selected according to the purpose. For example, urethane resin, polyester resin, acrylic resin, vinyl acetate resin, styrene resin, butadiene resin, styrene-butadiene resin, vinyl chloride resin, acrylic styrene resin, acrylic silicone resin, etc. can be mentioned. Resin particles composed of these resins may be used. It is possible to obtain an ink by mixing the resin particles with materials such as organic solvents in the state of a resin emulsion in which water is used as a dispersion medium. As the resin particles, those appropriately synthesized may be used, or commercially available products may be used. For example, under the trade name, DAOTAN series TW1225, VTW1265, VTW1686, VTW6450, VTW6460, VTW6462, VTW6463, TW6464, etc. manufactured by Daicel Ornex Co., Ltd. can be mentioned.

[0033] The volume average particle diameter of the resin particles is not particularly limited and can be appropriately selected according to the purpose. However, from the viewpoints of good fixability and high image hardness, it is preferably 10 nm or more and 1,000 nm or less, more preferably 10 nm or more and 200 nm or less, and particularly preferably 10 nm or more and 100 nm or less. The volume average particle diameter can be measured, for example, using a particle size analyzer (NanoTrack Wave-UT151, manufactured by Microtrac Bell Co., Ltd.).

[0034] The content of the resin is not particularly limited and can be appropriately selected according to the purpose. However, from the viewpoints of fixability and storage stability of the ink, it is preferably 1% by mass or more and 30% by mass or less, more preferably 5% by mass or more and 20% by mass or less, based on the total amount of the ink.

[0035] Regarding the particle diameter of the solid content in the ink, there is no particular limitation and it can be appropriately selected according to the purpose. However, from the viewpoint of improving image quality such as ejection stability and image density, the maximum frequency in terms of the maximum number conversion is preferably 20 nm or more and 1,000 nm or less, more preferably 20 nm or more and 150 nm or less. The solid content includes resin particles, pigment particles, etc. The particle diameter can be measured using a particle size analyzer (NanoTrack Wave-UT151, manufactured by Microtrac Bell Co., Ltd.).

[0036] <Additive> Surfactants, defoamers, antiseptics, rust preventives, pH adjusters, etc. may be added to the ink as necessary.

[0037] <Surfactant> In the present invention, as the surfactant, a nonionic surfactant can be used. There is no particular limitation on the nonionic surfactant, and it can be appropriately selected according to the purpose. For example, polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene alkyl ester, polyoxyethylene alkyl amine, polyoxyethylene alkyl amide, polyoxyethylene propylene block polymer, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, ethylene oxide adduct of acetylene alcohol, etc. may be mentioned. These may be used alone or in combination of two or more. Among these, it contains at least polyoxyethylene alkyl ether represented by the following general formula (1). [Chemical formula] (In general formula (1), R1, R2, R3, and R4 each independently represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and n is an integer of 4 or more and 10 or less.) As the alkyl group having 1 to 5 carbon atoms, it may be a branched alkyl group or an unbranched alkyl group. For example, methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, s-butyl group, isobutyl group, t-butyl group, pentyl group, isopentyl group, neopentyl group, etc. may be mentioned.

[0038] From the viewpoint of compatibility with the ink, the polyoxyethylene alkyl ether preferably has an HLB value of 7 or more, and more preferably 9 or more. The HLB value is an index representing the degree of hydrophilicity and lipophilicity of the surfactant calculated by the Griffin method. It indicates that the smaller the HLB value, the higher the lipophilicity, and the larger the HLB value, the higher the hydrophilicity. The polyoxyethylene alkyl ether can be used alone or in combination of two or more.

[0039] The polyoxyethylene alkyl ether is not limited by the number of carbon atoms in the alkyl group and the average number of moles of ethyleneoxy groups added. For example, it is preferably about 11 to 15 carbon atoms in the alkyl group, more preferably about 12 to 15 carbon atoms, and preferably about 3 to 15 average moles of ethyleneoxy groups added, and more preferably about 5 to 10 average moles of ethyleneoxy groups added.

[0040] Examples of the polyoxyethylene alkyl ether include trade names: "Emulgen 705", "Emulgen 707", "Emulgen 709", "Emulgen 1108", "Emulgen 1118S-70", "Emulgen 1135S-70", "Emulgen 1150S-60" (manufactured by Kao Corporation), trade names: "Adekatoru LA-675B", "Adekatoru LA-775" (manufactured by ADEKA Corporation), trade name: "TRITON (registered trademark) HW1000" (manufactured by Dow), trade name: "Sunonic SS70" (manufactured by Sanyo Chemical Industries, Ltd.), and the like.

[0041] The content of the surfactant in the ink is not particularly limited and can be appropriately selected according to the purpose. However, from the viewpoints of excellent wettability and ejection stability and improved image quality, it is preferably 0.001% by mass or more and 5% by mass or less, and more preferably 0.05% by mass or more and 5% by mass or less.

[0042] <Antifoaming agent> The antifoaming agent is not particularly limited, and examples include silicone-based antifoaming agents, polyether-based antifoaming agents, fatty acid ester-based antifoaming agents, and the like. These may be used alone or in combination of two or more. Among these, silicone-based antifoaming agents are preferred because of their excellent defoaming effect.

[0043] <Preservative and mildew preventive> The preservative and mildew preventive is not particularly limited, and examples include 1,2-benzisothiazolin-3-one and the like.

[0044] <Rust preventive> There are no particular restrictions on the rust preventive agent, and examples thereof include acid sulfite, sodium thiosulfate, and the like.

[0045] <pH adjuster> There are no particular restrictions on the pH adjuster as long as it can adjust the pH to 7 or higher, and examples thereof include amines such as diethanolamine and triethanolamine.

[0046] There are no particular restrictions on the physical properties of the ink, and it can be appropriately selected according to the purpose. For example, it is preferable that the viscosity, surface tension, pH, etc. are within the following ranges. The viscosity of the ink at 25°C is preferably 5 mPa·s or more and 30 mPa·s or less, more preferably 5 mPa·s or more and 25 mPa·s or less, from the viewpoints of improving the printing density and the quality of characters and obtaining good ejection properties. Here, for example, a rotational viscometer (RE-80L manufactured by Toki Sangyo Co., Ltd.) can be used to measure the viscosity. The measurement conditions are as follows: at 25°C, using a standard cone rotor (1°34’×R24), a sample liquid volume of 1.2 mL, a rotation speed of 50 rpm, and it can be measured in 3 minutes. The surface tension of the ink is preferably 35 mN / m or less, more preferably 32 mN / m or less at 25°C, from the viewpoints of the ink being preferably leveled on the recording medium and shortening the drying time of the ink. The pH of the ink is preferably 7 to 12, more preferably 8 to 11, from the viewpoint of preventing corrosion of the metal members in contact with the liquid.

[0047] <Pretreatment liquid> The pretreatment liquid contains a flocculant, an organic solvent, and water, and may contain a surfactant, an antifoaming agent, a pH adjuster, an antiseptic and antifungal agent, a rust preventive agent, etc. as necessary. As the organic solvent, surfactant, antifoaming agent, pH adjuster, antiseptic and antifungal agent, and rust preventive agent, the same materials as those used in the ink can be used, and in addition, materials used in known treatment liquids can be used. The type of the flocculant is not particularly limited, and examples thereof include water-soluble cationic polymers, acids, polyvalent metal salts, and the like.

[0048] <Flocculant> The flocculant associates with the coloring material in the ink through a charge-based action, forms aggregates of the coloring material, separates the coloring material from the liquid phase, and promotes fixing and pinning to the recording medium. Further, by including a flocculant in the pretreatment liquid, bleeding and bleeding can be suppressed even when using a recording medium with low ink absorbency, and a high-quality image can be formed. The pretreatment liquid contains a flocculant.

[0049] The content of the flocculant in the pretreatment liquid in the present invention is 1.0% by mass or more and 20.0% by mass or less. When the content of the flocculant is 1.0% by mass or more based on the total amount of the treatment liquid, the color developability can be improved. When the content of the flocculant is 20.0% by mass or less based on the total amount of the treatment liquid, the ejection stability can be improved. Examples of the flocculant include cationic polymers, polyvalent metal salts, acids, etc., and polyvalent metal salts are preferred.

[0050] - Polyvalent metal salt - From the viewpoint of improving color developability, the polyvalent metal salt is preferably a divalent metal salt or a trivalent metal salt. The divalent metal salt can be selected as appropriate without particular limitation according to the purpose, and examples include calcium carbonate, calcium nitrate, calcium chloride, calcium acetate, calcium sulfate, magnesium chloride, magnesium acetate, magnesium sulfate, etc. The trivalent metal salt can be selected as appropriate without particular limitation according to the purpose, and examples include aluminum sulfate, aluminum silicate, aluminum lactate, etc.

[0051] As the polyvalent metal salt, those synthesized as appropriate may be used, or commercially available products may also be used. Examples of commercially available polyvalent metal salts include, for example, calcium acetate monohydrate (substance name: calcium acetate, manufactured by Fujifilm Wako Pure Chemical Corporation, valence: divalent), magnesium acetate tetrahydrate (substance name: magnesium acetate, manufactured by Fujifilm Wako Pure Chemical Corporation, valence: divalent), aluminum silicate (substance name: aluminum silicate, manufactured by Fujifilm Wako Pure Chemical Corporation, valence: trivalent), potassium acetate (substance name: potassium acetate, manufactured by Fujifilm Wako Pure Chemical Corporation, valence: monovalent), and the like.

[0052] As the cationic polymer, a quaternary ammonium salt type cationic polymer is preferable, and examples thereof include dialkyl allyl ammonium chloride polymers, dialkyl aminoethyl (meth) acrylate quaternary ammonium salt polymers, modified polyvinyl alcohol dialkyl ammonium salt polymers, dialkyl diallyl ammonium salt polymers, and the like. Examples of other water-soluble cationic polymers include cationic epichlorohydrin condensates, cationic special modified polyamine compounds, cationic polyamide polyamine compounds, cationic urea-formalin resin compounds, cationic polyacrylamide compounds, cationic alkyl ketene dimers, cationic dicyandiamide compounds, cationic dicyandiamide-formalin condensation compounds, cationic dicyandiamide-polyamine condensation compounds, cationic polyvinyl formamide compounds, cationic polyvinyl pyridine compounds, cationic polyalkylene polyamine compounds, cationic epoxy polyamide compounds, and the like.

[0053] As the acid, a water-soluble aliphatic organic acid is preferable, and examples thereof include lactic acid, malic acid, citric acid, tartaric acid, oxalic acid, malonic acid, succinic acid, adipic acid, acetic acid, propionic acid, butyric acid, valeric acid, gluconic acid, pyruvic acid, fumaric acid, and the like. Further, amine salts of these organic acids may also be used.

[0054] <Surfactant> As the surfactant, any of silicone-based surfactants, fluorine-based surfactants, amphoteric surfactants, nonionic surfactants, and anionic surfactants can be used. The silicone-based surfactant is not particularly limited and can be appropriately selected according to the purpose. Among them, those that do not decompose even at high pH are preferred. For example, side-chain modified polydimethylsiloxane, both-terminal modified polydimethylsiloxane, one-terminal modified polydimethylsiloxane, side-chain and both-terminal modified polydimethylsiloxane, etc. can be mentioned. Those having a polyoxyethylene group or a polyoxyethylene-polyoxypropylene group as the modifying group are particularly preferred because they exhibit good properties as an aqueous surfactant. Further, as the silicone-based surfactant, a polyether-modified silicone-based surfactant can also be used. For example, compounds in which a polyalkylene oxide structure is introduced into the Si part side chain of dimethylsiloxane can be mentioned. As the fluorine-based surfactant, for example, perfluoroalkyl sulfonic acid compounds, perfluoroalkyl carboxylic acid compounds, perfluoroalkyl phosphate ester compounds, perfluoroalkyl ethylene oxide adducts, and polyoxyalkylene ether polymer compounds having a perfluoroalkyl ether group in the side chain are particularly preferred because of their low foaming properties. Examples of the perfluoroalkyl sulfonic acid compounds include perfluoroalkyl sulfonic acid, perfluoroalkyl sulfonate, etc. Examples of the perfluoroalkyl carboxylic acid compounds include perfluoroalkyl carboxylic acid, perfluoroalkyl carboxylate, etc. Examples of the polyoxyalkylene ether polymer compounds having a perfluoroalkyl ether group in the side chain include sulfate esters of polyoxyalkylene ether polymers having a perfluoroalkyl ether group in the side chain, salts of polyoxyalkylene ether polymers having a perfluoroalkyl ether group in the side chain, etc. Examples of the counter ions of the salts in these fluorine-based surfactants include Li, Na, K, NH4, NH3CH2CH2OH, NH2(CH2CH2OH)2, NH(CH2CH2OH)3, etc. Examples of the amphoteric surfactant include lauryl aminopropionate, lauryldimethyl betaine, stearyldimethyl betaine, lauryldihydroxyethyl betaine, etc. Examples of nonionic surfactants include polyoxyethylene alkyl phenyl ethers, polyoxyethylene alkyl esters, polyoxyethylene alkyl amines, polyoxyethylene alkyl amides, polyoxyethylene propylene block polymers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and ethylene oxide adducts of acetylene alcohols. Examples of anionic surfactants include polyoxyethylene alkyl ether acetates, dodecylbenzene sulfonates, laurates, salts of polyoxyethylene alkyl ether sulfates, and the like. These may be used alone or in combination of two or more.

[0055] The content of the surfactant in the pretreatment liquid is not particularly limited and can be appropriately selected according to the purpose. However, from the viewpoints of excellent wettability and ejection stability and improved image quality, it is preferably 0.001% by mass or more and 5% by mass or less, and more preferably 0.05% by mass or more and 5% by mass or less.

[0056] <Recording medium> The recording medium used for recording is not particularly limited, and examples include plain paper, glossy paper, special paper, cloth, film, OHP sheet, general-purpose printing paper, and the like.

[0057] <Recorded matter> The ink recording of the present invention has an image formed on a recording medium using the ink of the present invention. Recording can be performed by an inkjet recording apparatus and an inkjet recording method to obtain a recorded matter.

[0058] <Recording apparatus, recording method> The ink of the present invention can be suitably used in various recording apparatuses using an inkjet recording method, such as printers, facsimile apparatuses, copying apparatuses, printer / fax / copier multifunction machines, and three-dimensional modeling apparatuses. In the present invention, a recording apparatus and a recording method are an apparatus capable of discharging ink, various processing liquids, etc. onto a recording medium, and a method of performing recording using the apparatus. The recording medium means something onto which ink or various processing liquids can adhere even temporarily. This recording apparatus can include not only a head portion that discharges ink, but also means related to feeding, conveying, and discharging the recording medium, and other apparatuses referred to as a preprocessing apparatus, a postprocessing apparatus, etc. The recording apparatus and the recording method may have heating means used in the heating process and drying means used in the drying process. The heating means and the drying means include, for example, means for heating and drying the printing surface or the back surface of the recording medium. The heating means and the drying means are not particularly limited, but for example, a warm air heater, an infrared heater can be used. Heating and drying can be performed before printing, during printing, after printing, etc. Also, the recording apparatus and the recording method are not limited to those in which significant images such as characters and figures are visualized by ink. For example, those that form patterns such as geometric patterns, and those that create three-dimensional images are also included. Also, the recording apparatus includes, unless otherwise particularly limited, both a serial type apparatus that moves the discharge head and a line type apparatus that does not move the discharge head. Furthermore, this recording apparatus includes not only desktop types, but also wide-width recording apparatuses capable of printing on A0-sized recording media, and continuous printers that can use, for example, continuous paper wound in a roll as the recording medium. An example of a recording apparatus will be described with reference to FIGS. 1 to 2. FIG. 1 is a perspective explanatory view of the apparatus. FIG. 2 is a perspective explanatory view of the main tank. An image forming apparatus 400 as an example of the recording apparatus is a serial type image forming apparatus. A mechanism unit 420 is provided inside an exterior 401 of the image forming apparatus 400. Each ink storage unit 411 of main tanks 410 (410k, 410c, 410m, 410y) for each color of black (K), cyan (C), magenta (M), and yellow (Y) is formed of a packaging member such as an aluminum laminate film. The ink storage unit 411 is housed, for example, in a plastic storage container case 414. Thereby, the main tank 410 is used as an ink cartridge for each color. On the other hand, a cartridge holder 404 is provided on the back side of the opening when the cover 401c of the apparatus main body is opened. The main tank 410 is detachably attached to the cartridge holder 404. Thereby, each ink discharge port 413 of the main tank 410 communicates with a discharge head 434 for each color via a supply tube 436 for each color, and ink can be discharged from the discharge head 434 onto a recording medium.

[0059] This recording apparatus can include not only a portion that discharges ink but also apparatuses referred to as a preprocessing apparatus and a postprocessing apparatus. As one aspect of the preprocessing apparatus and the postprocessing apparatus, similar to the case of inks such as black (K), cyan (C), magenta (M), and yellow (Y), a liquid storage unit having a preprocessing liquid and a postprocessing liquid and a liquid discharge head are added, and there is an aspect of discharging the preprocessing liquid and the postprocessing liquid by an inkjet recording method. As another aspect of the preprocessing apparatus and the postprocessing apparatus, there is an aspect of providing a preprocessing apparatus and a postprocessing apparatus by a method other than the inkjet recording method, for example, a blade coating method, a roll coating method, or a spray coating method.

[0060] In addition, the method of using the processing liquid or ink is not limited to the inkjet recording method and can be widely used. In addition to the inkjet recording method, for example, blade coating method, gravure coating method, gravure offset coating method, bar coating method, roll coating method, knife coating method, air knife coating method, comma coating method, U-comma coating method, AKKU coating method, smoothing coating method, microgravure coating method, reverse roll coating method, four-roll coating method, five-roll coating method, dip coating method, curtain coating method, slide coating method, die coating method, etc. can be mentioned.

Example

[0061] Hereinafter, the present invention will be described more specifically by showing examples and comparative examples, but the present invention is not limited by these examples. In addition, in the following description, unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass".

[0062] (Production Example 1 of Pigment Dispersion) (Production of Cyan Pigment Dispersion) A cyan pigment dispersion was obtained in the same manner as the method described in "-Method A-" of [Pigment Surface Modification Treatment] in JP-A-2012-207202. Specifically, 20 g of C.I. Pigment Blue 15:3 (trade name: Chromophine Blue, manufactured by Dainichi Seika Kogyo Co., Ltd.), 20 mmol of the compound of the following structural formula (2), and 200 mL of ion-exchanged water are mixed at room temperature using a Silverson mixer (6,000 rpm (0.6%)) to obtain a slurry. If the pH of the obtained slurry is higher than 4, 20 mmol of nitric acid is added. After 30 minutes, sodium nitrite (20 mmol) dissolved in a small amount of ion-exchanged water is slowly added to the above slurry. Further, the mixture is heated to 60 °C with stirring and reacted for 1 hour. A modified pigment with the compound of the following structural formula (2) added to the surface of C.I. Pigment Blue 15:3 was obtained. Then, by adjusting the pH to 10 with an aqueous NaOH solution, a modified pigment dispersion was obtained after 30 minutes. Ultrafiltration using a dialysis membrane was performed using the modified pigment dispersion and ion-exchanged water, and further ultrasonic dispersion was performed to obtain a [cyan pigment dispersion] (self-dispersing type) having a bisphosphonic acid group as a hydrophilic functional group with a pigment concentration of 15%.

Chemical formula

[0063] (Preparation Example 2 of Pigment Dispersion) <Preparation of Magenta Pigment Dispersion> In the preparation of the cyan pigment dispersion, a [magenta pigment dispersion] with a pigment concentration of 15% was prepared in the same manner as the preparation of the cyan pigment dispersion, except that 20 g of C.I. Pigment Blue 15:3 was changed to 20 g of C.I. Pigment Red 122 (trade name: Toner Magenta EO02, manufactured by Clariant Japan K.K.).

[0064] (Preparation Example 3 of Pigment Dispersion) <Preparation of Yellow Pigment Dispersion> In the preparation of the cyan pigment dispersion, a [yellow pigment dispersion] with a pigment concentration of 15% was prepared in the same manner as the preparation of the cyan pigment dispersion, except that 20 g of C.I. Pigment Blue 15:3 was changed to 20 g of C.I. Pigment Yellow 74 (trade name: First Yellow 531, manufactured by Dainichi Seika Kogyo Co., Ltd.).

[0065] (Preparation Example 4 of Pigment Dispersion) (Preparation of Black Pigment Dispersion) In the preparation of the cyan pigment dispersion, a [black pigment dispersion] with a pigment concentration of 15% was prepared in the same manner as the preparation of the cyan pigment dispersion, except that 20 g of C.I. Pigment Blue 15:3 was changed to 20 g of carbon black (NIPEX 160, manufactured by Degussa).

[0066] (Preparation Example 1 of Resin Particles) (Preparation of Polycarbonate-based Urethane Resin Particle Liquid) Into a reaction vessel equipped with a stirrer, a reflux condenser, and a thermometer, 1,500 g of polycarbonate diol (reaction product of 1,6-hexanediol and dimethyl carbonate (number average molecular weight (Mn): 1,200)), 220 g of 2,2-dimethylolpropionic acid (hereinafter sometimes referred to as "DMPA"), and 1,347 g of N-methylpyrrolidone (hereinafter sometimes referred to as "NMP") were charged under a nitrogen stream and heated to 60 °C to dissolve DMPA. Next, 1,445 g of 4,4'-dicyclohexylmethane diisocyanate and 2.6 g of dibutyltin dilaurate (catalyst) were added and heated to 90 °C, and a urethanization reaction was carried out over 5 hours to obtain an isocyanate-terminated urethane prepolymer. This reaction mixture was cooled to 80 °C, 149 g of triethylamine was added thereto, 4,340 g was withdrawn from the mixture, and added to a mixed solution of 5,400 g of water and 15 g of triethylamine under strong stirring. Next, 1,500 g of ice was added, 626 g of a 35% aqueous solution of 2-methyl-1,5-pentanediamine was added to carry out a chain extension reaction, and the solvent was distilled off so that the solid content concentration became 40% to obtain a [polycarbonate-based urethane resin particle liquid]. Regarding the obtained [polycarbonate-based urethane resin particle liquid], when the Tg of the resin was measured, the Tg was -20 °C.

[0067] (Preparation Example 2 of Resin Particles) (Preparation of Polyester-based Urethane Resin Particle Liquid) In Preparation Example 1 of the resin particles, except that polycarbonate diol (the reaction product of 1,6 - hexanediol and dimethyl carbonate (number average molecular weight (Mn): 1,200)) was changed to polyester polyol ("Polyolite OD - X - 2251", manufactured by DIC Corporation, weight average molecular weight: 2,000), a [polyester - based urethane resin particle liquid] with a solid content concentration of 30% was obtained in the same manner as in Preparation Example 1 of the resin particles. Regarding the obtained [polyester - based urethane resin particle liquid], the Tg measured in the same manner as in Preparation Example 1 of the polycarbonate - based urethane resin particle liquid 1 was 57°C.

[0068] (Preparation of Color Ink 1) [Cyan Pigment Dispersion] (pigment solid content concentration 15%) 20%, [Polycarbonate - based Urethane Resin Particle Liquid] (solid content concentration 40%) 2.5%, [Polyester - based Urethane Resin Particle Liquid] (solid content concentration 30%) 33.3%, 3 - methoxy - N,N - dimethylpropanamide (manufactured by Tokyo Chemical Industry Co., Ltd.) 15.0%, 1,2 - hexanediol (manufactured by Tokyo Chemical Industry Co., Ltd.) 5.0%, propylene glycol monomethyl ether (manufactured by Tokyo Chemical Industry Co., Ltd.) 5.0%, diethylene glycol monobutyl ether (manufactured by Tokyo Chemical Industry Co., Ltd.) 10.0%, polyoxyethylene alkyl ether (trade name: TRITON HW - 1000: manufactured by DOW CHEMICAL) 3.0%, defoaming agent with trade name: Surfynol AD01 (manufactured by Nissin Chemical Industry Co., Ltd.) 1.0%, 2 - amino - 2 - ethyl - 1,3 - propanediol (manufactured by Tokyo Chemical Industry Co., Ltd.) 0.25% as a pH adjuster, 2 - cyclohexylaminoethanesulfonic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) 0.05% as a pH buffer, antibacterial agent (preservative) with trade name: Proxel LV (manufactured by Arch Chemicals Japan Co., Ltd.) 0.1%, and high - purity water was added to make up the balance, mixed and stirred, and then filtered through a polypropylene filter with an average pore size of 1.0 μm to prepare [Color Ink 1].

[0069] (Preparation of Color Inks 2 - 41) Using the formulations shown in Table 1-1 to Table 1-4, [Color Ink 2] to [Color Ink 41] were prepared in the same manner as [Color Ink 1]. The unit of the numerical value of each component in the table is "mass%".

[0070] (Preparation of Pretreatment Liquid 1) 1,2 - propanediol (manufactured by Tokyo Chemical Industry Co., Ltd.) 18.0%, 3 - methoxy - 3 - methyl - 1 - butanol (manufactured by Tokyo Chemical Industry Co., Ltd.) 15.0%, 2,3 - butanediol (manufactured by Tokyo Chemical Industry Co., Ltd.) 5.0%, 2 - ethyl - 1,3 - hexanediol (manufactured by Tokyo Chemical Industry Co., Ltd.) 3.0%, polyether - modified surfactant (product name: WET270, manufactured by TEGO) 2.0%, silicone - based surfactant (product name: Silface SAG503A, manufactured by Nissin Chemical Industry Co., Ltd.) 3.0%, defoaming agent with trade name: Surfynol AD01 (manufactured by Nissin Chemical Industry Co., Ltd.) 1.0%, magnesium acetate tetrahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) 10.0% as a flocculant, 2 - amino - 2 - ethyl - 1,3 - propanediol (manufactured by Tokyo Chemical Industry Co., Ltd.) 0.25% as a pH adjuster, 2 - cyclohexylaminoethanesulfonic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) 0.05% as a pH buffer, product name: Proxel LV (manufactured by Arch Chemicals Japan Co., Ltd.) 0.1% as an antibacterial agent (preservative), and high - purity water was added to make up the balance, mixed and stirred, and then filtered through a polypropylene filter with an average pore size of 1.0 μm to prepare [Pretreatment Liquid 1].

[0071] (Preparation of Pretreatment Liquids 2 - 16) Using the formulations shown in Table 2 - 1 and Table 2 - 2, [Pretreatment Liquid 2] to [Pretreatment Liquid 16] were prepared in the same manner as [Pretreatment Liquid 1]. The unit of the numerical value of each component in the table is "mass%".

[0072]

Table 1 - 1

Table 1 - 2

Table 1 - 3

[0073] [Table 2-1] [Table 2-2]

[0074] (Example 1) As shown in Table 3-1, [Pretreatment Liquid 1] and [Color Ink 1] were combined to form an ink set, and an image was formed as follows. [Pretreatment Liquid 1] and [Color Ink 1] were filled into an offset coated paper (OK Top Coat + (basis weight 127.9 g / m 2 ), manufactured by Oji Paper Co., Ltd.) of an inkjet printer (device name: IPSiO GXe5500 modified machine, manufactured by Ricoh Company, Ltd.). After printing a halftone image with a print rate of 10 to 90% at a resolution of 600 × 600 dpi with a volume of 21 pL per drop of the pretreatment liquid, the printed matter was passed through a hot air drying unit at 80°C to be dried and fixed. Next, [Color Ink 1] was printed on the offset coated paper on which [Pretreatment Liquid 1] was printed. After printing a full-tone color solid image with a volume of 21 pL per drop of the color ink at a resolution of 600 × 600 dpi, the printed matter was passed through a hot air drying unit at 80°C to be dried and fixed, thereby obtaining the printed matter of Example 1.

[0075] Next, regarding the ink in Example 1, the "contact angle of the color ink with respect to the pretreatment liquid", "beading", "bleeding", "pinning speed", and "discharge stability" were evaluated by the methods described below. The results are shown in Table 3-1.

[0076] (Examples 2 to 35, Comparative Examples 1 to 15) In Example 1, prints of Examples 2 to 35 and Comparative Examples 1 to 15 were obtained in the same manner as in Example 1, except that [Color Ink 1] and [Pretreatment Liquid 1] were changed to the combinations shown in Tables 3-1 and 3-2. For the obtained prints, "contact angle of color ink with respect to the pretreatment liquid", "beading", "bleeding", "pinning speed", and "discharge stability" were evaluated in the same manner as in Example 1. The results are shown in Tables 3-1 and 3-2.

[0077] <Method for obtaining contact angle θ of color ink> The method for obtaining the contact angle θ of the color ink with respect to the offset coated paper will be described in detail below. The color ink is dropped onto the surface of the offset coated paper, and the contact angle is the value at 1,000 ms after dropping. For the measurement of the contact angle, a contact angle meter (DMo-501, manufactured by Kyowa Interface Science Co., Ltd.) was used. With this contact angle meter, the contact angle of the color ink can be measured from the image of the droplet of the measurement sample (color ink) dropped onto the surface of the offset coated paper. The measurement of the contact angle is performed in an environment at 25°C. A droplet of the color ink to be dropped is formed at the tip of a syringe, and the dropping amount is adjusted to 3.0 μL. The sample stage on which the offset coated paper is placed is gently raised, and the color ink is dropped onto the surface of the offset coated paper. An image of the droplet formed on the surface of the offset coated paper at 500 ms after dropping is captured, and the contact angle is obtained by the θ / 2 method using the analysis software "FAMAS (interFAce Measurement & Analysis System)" attached to the apparatus. Also, the measurement is performed three or more times, and the average value is taken as the contact angle of the sample.

[0078] <Method for obtaining contact angle θ of color ink with respect to the coating film surface of the pretreatment liquid> The method for obtaining the contact angle θ of the ink landed on the surface of the pretreatment liquid will be described in detail below. The pretreatment liquid is applied to the offset coated paper with a coating amount of 9.0 g / m 2After coating with a bar coater so as to achieve the specified value, it is dried with a dryer at 80°C. Then, the ink is dropped onto the coating film, and the contact angle adopted is the value at 500 ms after the drop is made.

[0079] <Beading> The printing mode was changed to a mode in which the "glossy paper - clean" mode attached to the printer was modified to "no color correction" using the driver attached to the printer. A solid image was printed in the same way as the image density, and the density unevenness (beading) of the solid image was visually observed and judged according to the following evaluation criteria. 〔Evaluation Criteria〕 A: None at all B: Slightly present C: Considerably present D: Severely present *Since the black solid image is very difficult to see visually, it was observed under a 40 - fold magnification with an optical microscope.

[0080] <Bleeding> The printing mode was changed to a mode in which the "glossy paper - clean" mode attached to the printer was modified to "no color correction" using the driver attached to the printer. The boundary part of the solid image formed by mixing the black ink and the color ink on the offset coated paper was visually evaluated for "color boundary bleeding" based on the following evaluation criteria. Note that a level of "C" or higher is a level with no practical problems. 〔Evaluation Criteria〕 A: There is no bleeding at the boundary part, or it is hardly noticeable, and it is a high - quality image. B: Slight bleeding is seen at the boundary part, but it is an image of acceptable quality. C: Bleeding is seen at the boundary part, and it is an image that can be actually used. D: Extreme bleeding is seen at the boundary part, and it is an image of poor quality.

[0081] <Pinning Speed> The pretreatment liquid was applied to the offset coated paper with a bar coater so that the coating amount was 9.0 g / m 2 After that, it was dried with a dryer at 80°C. Then, the color ink was applied onto the coating film with a coating amount of 9.0 g / m 2After coating with a bar coater so as to achieve [a certain state], a laser was irradiated onto the coating film using CurinScan Classic (manufactured by Sanyo Trading Co., Ltd.), and the drying and film-forming state of the sample was measured in real time by analyzing the image of the interference wave of the reflected scattered light. The time from when the color inks 1 to 41 were coated with the bar coater until the reflected scattered light intensity became stable was defined as the pinning time. 〔Evaluation Criteria〕 A: The time until the color ink pins is 10 seconds or less. B: The time until the color ink pins is more than 10 seconds and 20 seconds or less. C: The time until the color ink pins is more than 20 seconds and 30 seconds or less. D: The time until the color ink pins is more than 30 seconds and 60 seconds or less.

[0082] <Discharge Stability> Loaded into an inkjet discharge device (manufactured by Ricoh Co., Ltd.) equipped with an inkjet head GEN5 (manufactured by Ricoh Printing Systems), the discharge state from the nozzles after continuous discharge for 30 minutes was observed with a camera (ARTCAM-036MI, manufactured by ArtRay Co., Ltd.). Evaluation was performed according to the following evaluation criteria. 〔Evaluation Criteria〕 A: Discharging from all nozzles. B: The number of nozzles with non-discharge observed is less than 10. C: The number of nozzles with non-discharge observed is 10 or more and less than 30. D: The number of nozzles with non-discharge observed is 30 or more.

[0083]

Table 3-1

[0084]

Table 3-2

[0085] Aspects of the present invention are, for example, as follows. (1) An ink set comprising a pretreatment liquid and a pigment ink, wherein the pretreatment liquid contains water, a flocculant, and an organic solvent, and the content of the flocculant in the pretreatment liquid is 1.0% by mass or more and 20.0% by mass or less, the pigment ink contains water, a coloring material, an organic solvent containing at least a glycol ether compound, a polyoxyethylene alkyl ether, and a resin, the content of the polyoxyethylene alkyl ether in the pigment ink is 1.0% by mass or more and 5.0% by mass or less, and the content of the glycol ether compound is 10.0% by mass or more and 20.0% by mass or less, when the content of the coloring material in the pigment ink is P and the content of the resin is R, P / R is 0.25 or more and 3.0 or less, the mixed SP value of the organic solvent contained in the pigment ink is different from the mixed SP value of the organic solvent contained in the pretreatment liquid, and the difference is 2.0 (cal / cm 3 ) 0.5 or more characterized ink set. (2) The ink set according to (1) above, wherein the polyoxyethylene alkyl ether is a compound represented by the following general formula (1). [Chemical formula] (In general formula (1), R1, R2, R3, and R4 each independently represent a hydrogen atom or an alkyl group having 1 or more and 5 or less carbon atoms, and n is an integer of 4 or more and 10 or less.) (3) The ink set according to (1) above, wherein the glycol ether compound contains a glycol ether compound having 8 or more carbon atoms. (4) The ink set according to (1) above, wherein the organic solvent contained in the pretreatment liquid and the organic solvent contained in the pigment ink are alcohol-based solvents having a boiling point of 250°C or less. (5) The mixed SP value of the organic solvent contained in the pigment ink is 10.0 (cal / cm 3 ) 0.512.0 (cal / cm or less), and the mixed SP value of the organic solvent contained in the pretreatment liquid is 13.0 (cal / cm 3 ) or more and 15.0 (cal / cm 0.5 ) or less. The ink set according to (1) above. 3 ) 0.5 15.0 (cal / cm or less), and the mixed SP value of the organic solvent contained in the pretreatment liquid is 13.0 (cal / cm 3 ) or more and 15.0 (cal / cm 0.5 ) or less. The ink set according to (1) above. (6) The content of the organic solvent contained in the pigment ink is 20.0% by mass or more and 40.0% by mass or less. The ink set according to (1) above. (7) The resin contained in the pigment ink contains a resin having a glass transition temperature (Tg) of 30°C or more. The ink set according to (1) above. (8) The resin contained in the pigment ink contains a resin having a glass transition temperature (Tg) of less than 0°C. The ink set according to (7) above. (9) When the contact angle of the pigment ink with respect to the recording medium coated with the pretreatment liquid is θ1, and the contact angle of the pigment ink with respect to the recording medium not coated with the pretreatment liquid is θ2, θ1 and θ2 satisfy the following relational expression (A). The ink set according to (1) above. 20° < θ1 - θ2 < 30° (A)

Explanation of Signs

[0086] 400 Image forming apparatus 401 Exterior of image forming apparatus 401c Cover of apparatus main body 404 Cartridge holder 410 Main tank 410k, 410c, 410m, 410y Main tanks for each color of black (K), cyan (C), magenta (M), yellow (Y) 411 Ink storage section 413 Ink discharge port 414 Storage container case 420 Mechanism section 434 Discharge head 436 Supply tube

Prior Art Documents

Patent Document

[0087]

Patent Document 1

Claims

1. An ink set comprising a pretreatment liquid and a pigment ink, the pretreatment liquid contains water, a flocculant, and an organic solvent, and the content of the flocculant in the pretreatment liquid is 1.0 mass % or more and 20.0 mass % or less; The pigment ink contains water, a coloring material, an organic solvent containing at least a glycol ether compound, a polyoxyethylene alkyl ether, and a resin, a content of the polyoxyethylene alkyl ether in the pigment ink is 1.0% by mass or more and 5.0% by mass or less, and a content of the glycol ether compound in the pigment ink is 10.0% by mass or more and 20.0% by mass or less, a P / R ratio is 0.25 or more and 3.0 or less, where P is the content of the color material in the pigment ink and R is the content of the resin in the pigment ink; The mixed SP value of the organic solvent contained in the pigment ink is different from the mixed SP value of the organic solvent contained in the pretreatment liquid, and the difference is 2.0 (cal / cm ３ ) ０．５ That's all. An ink set characterized by:

2. The ink set according to claim 1 , wherein the polyoxyethylene alkyl ether is a compound represented by the following general formula (1): 【Chemistry 1】 (In general formula (1), R １ , R ２ , R ３ , and R ４ each independently represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and n is an integer of 4 to 10.

3. The ink set according to claim 1 , wherein the glycol ether compound comprises a glycol ether compound having 8 or more carbon atoms.

4. The ink set according to claim 1 , wherein the organic solvent contained in the pretreatment liquid and the organic solvent contained in the pigment ink are alcohol-based solvents having a boiling point of 250° C. or lower.

5. The mixed SP value of the organic solvent contained in the pigment ink is 10.0 (cal / cm ３ ) ０．５ More than 12.0 (cal / cm ３ ) ０．５ The pretreatment liquid has a mixed SP value of 13.0 (cal / cm ３ ) ０．５ More than 15.0 (cal / cm ３ ) ０．５ 2. The ink set of claim 1, wherein:

6. The ink set according to claim 1 , wherein the content of the organic solvent in the pigment ink is 20.0% by mass or more and 40.0% by mass or less.

7. The ink set according to claim 1 , wherein the resin contained in the pigment ink contains a resin having a glass transition temperature (Tg) of 30° C. or higher.

8. The ink set according to claim 7 , wherein the resin contained in the pigment ink contains a resin having a glass transition temperature (Tg) of less than 0° C.

9. 2. The ink set according to claim 1, wherein when a contact angle of the pigment ink with respect to a recording medium to which the pretreatment liquid has been applied is θ1 and a contact angle of the pigment ink with respect to a recording medium to which the pretreatment liquid has not been applied is θ2, θ1 and θ2 satisfy the following relational expression (A): 20°<θ1-θ2<30° (A)

Images