Inkjet ink manufacturing method

Abstract

This invention provides a method for manufacturing inkjet ink that can form highly water-resistant images immediately after printing. [Solution] A method for manufacturing an inkjet ink, wherein the inkjet ink comprises a binder resin, a water-insoluble organic solvent X1, a water-soluble organic solvent Y1, and 1.0% by mass or more of water relative to the total amount of the inkjet ink, and the method comprises synthesizing the binder resin in a solvent SS containing a water-insoluble organic solvent X2.

Description

Technical Field

[0001] Embodiments of the present invention relate to a method for manufacturing inkjet ink.

Background Art

[0002] The inkjet recording method involves ejecting highly fluid inkjet ink as droplets from a fine nozzle and recording an image on a substrate placed opposite the nozzle. Due to its low noise and ability to print at high speeds, it has rapidly spread in recent years. As inks used in such inkjet recording methods, there are known aqueous inks containing water as the main solvent, ultraviolet curable inks (UV inks) containing a high content of polymerizable monomers as the main component, hot melt inks (solid inks) containing a high content of wax as the main component, and so-called non-aqueous inks containing a non-aqueous solvent as the main solvent. Non-aqueous inks can be classified into solvent inks (solvent-based inks) whose main solvent is a volatile organic solvent and oil-based inks (oil-based inks) whose main solvent is a low-volatile or non-volatile organic solvent. Solvent inks mainly dry on the substrate by evaporation of the organic solvent, while oil-based inks mainly dry by penetration into the substrate.

[0003] Patent Document 1 describes an ink having glycol ether dialkyl ethers as the main solvent and containing an acrylic resin obtained by solution polymerization using a radical polymerization initiator in a glycol ether dialkyl ether solvent.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] For example, even when using inks containing low-boiling-point, highly volatile organic solvents such as solvent inks, the slow drying time immediately after printing can cause the printed image to peel off easily when rubbed with water. Similarly, when using inks containing binder resins synthesized in water-soluble organic solvents, the printed image may peel off easily when rubbed with a water-based substance.

[0006] The object of the embodiments of the present invention is to provide a method for manufacturing inkjet ink that can form a highly water-resistant image immediately after printing. [Means for solving the problem]

[0007] One embodiment of the present invention relates to a method for manufacturing an inkjet ink, wherein the inkjet ink comprises a binder resin, a water-insoluble organic solvent X1, a water-soluble organic solvent Y1, and 1.0% by mass or more of water relative to the total amount of the inkjet ink, and the method comprises synthesizing the binder resin in a solvent SS containing a water-insoluble organic solvent X2. [Effects of the Invention]

[0008] According to embodiments of the present invention, it is possible to provide a method for manufacturing inkjet ink that can form highly water-resistant images immediately after printing. [Modes for carrying out the invention]

[0009] The present invention will be described below using embodiments. The examples in the following embodiments are not intended to limit the present invention. In the following description, inkjet ink may be simply referred to as "ink".

[0010] In the method for producing an inkjet ink according to the embodiment, the inkjet ink comprises a binder resin, a water-insoluble organic solvent X1, a water-soluble organic solvent Y1, and 1.0% by mass or more of water relative to the total amount of inkjet ink, and the method for producing the inkjet ink comprises synthesizing the binder resin in a solvent SS containing a water-insoluble organic solvent X2.

[0011] Using the manufacturing method of this embodiment, it is possible to produce inkjet ink capable of forming highly water-resistant images immediately after printing. Although not bound by any particular theory, the reason is presumed to be as follows.

[0012] By synthesizing a binder resin in a solvent containing a water-insoluble organic solvent, a binder resin is produced in which water-insoluble organic solvent molecules are bonded to the ends of the resin. Because the binder resin contains structures derived from the water-insoluble organic solvent, it develops a high affinity for the water-insoluble organic solvent. Since water-insoluble organic solvents have low affinity for water, a binder resin synthesized in a solvent containing a water-insoluble organic solvent will have low affinity for water. This can impart water resistance to the binder resin.

[0013] Furthermore, because the ink contains water, which has a low boiling point, as a component that evaporates after printing, the proportion of easily volatile components in the ink increases. Also, even if the ink contains volatile components that are less volatile than water, the water azeotropically forms with these less volatile components, allowing the ink to dry quickly after printing and forming a coating that is less likely to peel off immediately after printing.

[0014] In this way, it is presumed that it will be possible to form images with high water resistance immediately after printing.

[0015] <Inkjet ink> In a method for manufacturing inkjet ink, the inkjet ink may contain a binder resin, a non-water-soluble organic solvent X1, a water-soluble organic solvent Y1, and 1.0% by mass or more of water relative to the total amount of inkjet ink.

[0016] Examples of binder resins include (meth)acrylic resin, styrene-(meth)acrylic resin, styrene-maleic acid resin, ethylene-(meth)acrylic resin, urethane resin, vinyl chloride resin, vinyl chloride-vinyl acetate resin, polyester resin, polyvinyl alcohol resin, epoxy resin, and polyvinylpyrrolidone resin.

[0017] From the viewpoint of improving the adhesion of the image to the substrate, (meth)acrylic resin is preferred as the binder resin. More preferably, (meth)acrylic resin is a binder resin that is soluble in the organic solvent contained in the ink. When (meth)acrylic resin is used, the adhesion of the image to plastic substrates such as olefin resin can be improved. In particular, olefin resins tend to have low affinity for organic solvents commonly used in inks, and it can be difficult to obtain good image adhesion, but when (meth)acrylic resin is used, it is easier to improve the adhesion of the image to the substrate.

[0018] The (meth)acrylic resin may be a resin comprising, for example, at least one unit selected from the group consisting of units derived from (meth)acrylic acid and units derived from (meth)acrylic acid esters. In this disclosure, (meth)acrylic acid means acrylic acid and methacrylic acid collectively, (meth)acrylic acid ester means acrylic acid ester and methacrylic acid ester collectively, and (meth)acrylate means acrylate and methacrylate collectively.

[0019] Examples of (meth)acrylic acid esters include alkyl (meth)acrylates, benzyl (meth)acrylates, and hydroxyalkyl (meth)acrylates. Examples of alkyl (meth)acrylates include alkyl (meth)acrylates having an alkyl group with 1 to 8, 1 to 6, or 1 to 4 carbon atoms, specifically including methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[0020] (Meta)acrylic resin may be, for example, a polymer of one or more monomers selected from the group consisting of (meta)acrylic acid and (meta)acrylic acid esters.

[0021] (Meta)acrylic resins include, for example, poly(meth)acrylic acid, poly(meth)acrylic acid esters (such as polymethyl (meth)acrylate, polyethyl (meth)acrylate, polybutyl (meth)acrylate, etc.), (meth)acrylic acid ester copolymer resins, (meth)acrylic acid-(meth)acrylic acid ester copolymer resins, and the like.

[0022] (Meta)acrylic resin preferably contains, for example, units derived from (meta)acrylic acid alkyl esters. The units derived from (meta)acrylic acid alkyl esters may be, for example, 50.0% by mass or more, 70.0% by mass or more, or 90.0% by mass or more based on all the units of the (meta)acrylic resin. (Meta)acrylic resin may contain, for example, units derived from (meta)acrylic acid alkyl esters and units derived from (meta)acrylic acid. The units derived from (meta)acrylic acid may be, for example, 50.0% by mass or less, 30.0% by mass or less, or 10.0% by mass or less based on all the units of the (meta)acrylic resin.

[0023] Specific examples of (meta)acrylic resin include, for example, polymers of methyl (meta)acrylate, copolymers of methyl (meta)acrylate and at least one selected from the group consisting of (meta)acrylic acid, ethyl (meta)acrylate, butyl (meta)acrylate, 2-ethylhexyl (meta)acrylate, 2-hydroxyethyl (meta)acrylate, and benzyl (meta)acrylate (such as copolymers of 100 parts by mass of methyl methacrylate and 0.1 to 200 parts by mass, 1 to 180 parts by mass, or 10 to 150 parts by mass of at least one selected from the group consisting of methacrylic acid, butyl methacrylate, and benzyl methacrylate), and the like.

[0024] The glass transition temperature (Tg) of the (meth)acrylic resin may be, for example, 10°C or higher or 60°C or higher, and from the viewpoint of improving the adhesion of the image to the substrate, 80°C or higher is preferred, and 100°C or higher is more preferred. The glass transition temperature of the (meth)acrylic resin may be, for example, 200°C or lower. The glass transition temperature of the (meth)acrylic resin may be, for example, 10-200°C, 60-200°C, 80-200°C, or 100-200°C. In this disclosure, the glass transition temperature is an estimated value according to FOX's formula.

[0025] The weight-average molecular weight of the (meth)acrylic resin is preferably 5,000 to 150,000, and more preferably 10,000 to 100,000. From the viewpoint of water resistance and durability, the weight-average molecular weight of the (meth)acrylic resin is preferably 5,000 or more, and more preferably 10,000 or more. From the viewpoint of ink viscosity and discharge properties, the weight-average molecular weight of the (meth)acrylic resin is preferably 150,000 or less, and more preferably 100,000 or less. In this disclosure, the weight-average molecular weight is the value obtained by the GPC method on a standard polystyrene basis.

[0026] From the viewpoint of water resistance of the image, the binder resin is preferably, for example, 1.0% by mass or more, more preferably 3.0% by mass or more, and even more preferably 5.0% by mass or more, relative to the total amount of ink. On the other hand, the binder resin may be, for example, 40.0% by mass or less, 30.0% by mass or less, or 20.0% by mass or less, relative to the total amount of ink. The binder resin may be, for example, 1.0 to 40.0% by mass, 3.0 to 30.0% by mass, or 5.0 to 20.0% by mass, relative to the total amount of ink.

[0027] Ink can contain water.

[0028] While there are no particular restrictions on the type of water used, it is preferable to use water that contains as few ionic components as possible. In particular, from the viewpoint of the storage stability of the ink, it is preferable to use water with a low content of polyvalent metal ions such as calcium. For example, deionized water, distilled water, or ultrapure water may be used.

[0029] From the viewpoint of water resistance of the image immediately after printing, the amount of water is preferably 1.0% by mass or more, more preferably 2.0% by mass or more, even more preferably 3.0% by mass or more, even more preferably 4.0% by mass or more, and even more preferably 4.5% by mass or more, relative to the total amount of ink. When the amount of water in the ink is 1.0% by mass or more, good quick-drying properties can be easily obtained, and water resistance immediately after printing can be improved. On the other hand, the amount of water may be, for example, 10.0% by mass or less, 9.0% by mass or less, or 8.0% by mass or less, relative to the total amount of ink. The amount of water may be, for example, 1.0 to 10.0% by mass, 2.0 to 10.0% by mass, 3.0 to 10.0% by mass, 4.0 to 9.0% by mass, or 4.5 to 8.0% by mass, relative to the total amount of ink.

[0030] The amount of water in the ink may be the same as the amount of water actively added to the ink. On the other hand, when an organic solvent that has an affinity for water is added to the ink, such an organic solvent may absorb water vapor or other substances contained in the atmosphere, and in such cases, the amount of water added to the ink may not be the same as the amount of water in the ink. The amount of water in the ink may be measured, for example, using the Karl Fischer method.

[0031] The ink may contain a non-water-soluble organic solvent X1 and a water-soluble organic solvent Y1. In this disclosure, a water-soluble organic solvent is defined as a mixture that, when gently stirred with the same volume of pure water at 1 atmosphere and a temperature of 20 degrees Celsius, maintains a uniform appearance even after the flow has subsided. In this disclosure, any organic solvent that does not meet these conditions for a water-soluble organic solvent is defined as a non-water-soluble organic solvent.

[0032] Because ink contains water, if the ink contains only a non-water-soluble organic solvent X1 as an organic solvent and no water-soluble organic solvent Y1, the ink may not be uniform, and separation of the non-water-soluble organic solvent and water, as well as resin precipitation, may occur. When water-soluble organic solvent Y1 is included in the ink, it is easier to obtain a uniform ink.

[0033] Examples of non-water-soluble organic solvents X1 and water-soluble organic solvents Y1 include ketone-based organic solvents, alcohol-based organic solvents, glycol ether-based organic solvents, acetate-based organic solvents, carboxylic acid ester-based organic solvents, amide-based organic solvents, etc. These may be used individually or in combination of two or more.

[0034] The boiling point of the water-insoluble organic solvent X1 is preferably, for example, 70 to 300°C, and more preferably 100 to 250°C. Examples of water-insoluble organic solvents X1 include, for example, ethylene glycol monobutyl ether acetate, ethylene glycol diacetate, propylene glycol diacetate, dipropylene glycol dimethyl ether, propylene glycol 1-monobutyl ether, butyl lactate, hexyl propionate, ethyl 3-ethoxypropionate, γ-hexanolactone, ethyl acetoethyl, and the like. These water-insoluble organic solvents may be used individually or in combination of two or more.

[0035] The water-insoluble organic solvent X1 may include a water-insoluble organic solvent X2 used in the synthesis of the binder resin. For example, if the ink contains two or more organic solvents as the water-insoluble organic solvent X1, only one of them may be used as the water-insoluble organic solvent X2.

[0036] The boiling point of the water-soluble organic solvent Y1 is preferably 70 to 300°C, and more preferably 100 to 250°C. Examples of water-soluble organic solvent Y1 include diethylene glycol diethyl ether, diethylene glycol ethyl methyl ether, diethylene glycol isopropyl methyl ether, diethylene glycol dimethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monomethyl ether, dipropylene glycol monomethyl ether, 3-methoxy-3-methyl-1-butanol, 3-methoxy-1-butanol, ethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, 1,2-propanediol, ethyl lactate, ethylene glycol, ethylene glycol monoacetate, γ-butyrolactone, 2-pyrrolidone, etc. These water-soluble organic solvents may be used individually or in combination of two or more.

[0037] For example, if the solvent SS used in the synthesis of the binder resin contains a water-soluble organic solvent Y2, the water-soluble organic solvent Y1 may also contain the water-soluble organic solvent Y2 used in the synthesis of the binder resin. For example, if the ink contains two or more organic solvents as the water-soluble organic solvent Y1, only one of them may be used as the water-soluble organic solvent Y2.

[0038] The non-water-soluble organic solvent X1 may be, for example, 1% by mass or more, 10% by mass or more, or 20% by mass or more, relative to the total amount of ink. The water-soluble organic solvent Y1 may be, for example, 70% by mass or less, 60% by mass or less, or 50% by mass or less, relative to the total amount of ink. The non-water-soluble organic solvent X1 may be, for example, 1 to 70% by mass, 10 to 60% by mass, or 20 to 50% by mass, relative to the total amount of ink.

[0039] The water-soluble organic solvent Y1 may be, for example, 10% by mass or more, 20% by mass or more, or 30% by mass or more, relative to the total amount of ink. The water-soluble organic solvent Y1 may be, for example, 80% by mass or less, 70% by mass or less, or 60% by mass or less, relative to the total amount of ink. The water-soluble organic solvent Y1 may be, for example, 10-80% by mass, 20-70% by mass or 30-60% by mass, relative to the total amount of ink.

[0040] The total amount of the non-water-soluble organic solvent X1 and the water-soluble organic solvent Y1 may be, for example, 60% by mass or more, 70% by mass or more, or 75% by mass or more, relative to the total amount of ink. The total amount of the non-water-soluble organic solvent X1 and the water-soluble organic solvent Y1 may be, for example, 95% by mass or less, 90% by mass or less, or 85% by mass or less, relative to the total amount of ink. The total amount of the non-water-soluble organic solvent X1 and the water-soluble organic solvent Y1 may be, for example, 60-95% by mass, 70-90% by mass or 75-85% by mass, relative to the total amount of ink.

[0041] Ink may contain colorants. Ink may contain pigments, dyes, or combinations thereof as colorants.

[0042] As pigments, organic pigments such as azo pigments, phthalocyanine pigments, polycyclic pigments, and blue-green lake pigments, and inorganic pigments such as carbon black and metal oxides can be used. Examples of azo pigments include soluble azo lake pigments, insoluble azo pigments, and condensed azo pigments. Examples of phthalocyanine pigments include metallic phthalocyanine pigments and metal-free phthalocyanine pigments. Examples of polycyclic pigments include quinacridone pigments, perylene pigments, perinone pigments, isoindoline pigments, isoindolinone pigments, dioxazine pigments, thioindigo pigments, anthraquinone pigments, quinophthalone pigments, metal complex pigments, and diketopyrrolopyrrole (DPP). Examples of carbon black include furnace carbon black, lamp black, acetylene black, and channel black. Examples of metal oxides include titanium dioxide and zinc oxide. These pigments may be used individually or in combination of two or more types.

[0043] From the viewpoint of ejection stability and storage stability, the average particle size of pigment particles in the ink is preferably 1 μm or less, more preferably 500 nm or less, and even more preferably 300 nm or less, as the volume-based average value of the particle size distribution measured by dynamic light scattering.

[0044] Pigments may be incorporated into the ink as pigment dispersions. The pigment dispersions should be such that the pigment is dispersible in a solvent and the pigment is dispersed in the ink. For example, a dispersion in which the pigment is dispersed in a dispersion medium with a pigment dispersant, or a dispersion in which microencapsulated pigments coated with resin are dispersed in a dispersion medium can be used.

[0045] The dispersion form of the pigment may be a so-called encapsulated pigment in which the pigment is coated with a non-oil-soluble resin, or a dispersion in which colored resin particles are dispersed with a pigment dispersant, but it is preferable that the dispersion is in which the pigment dispersant is directly adsorbed onto the surface of the pigment and dispersed.

[0046] Any dye commonly used in the relevant art can be used. It is preferable to use an oil-soluble dye because it exhibits affinity for the non-aqueous solvent of the ink, resulting in better storage stability.

[0047] Examples of oil-soluble dyes include azo dyes, metal complex dyes, naphthol dyes, anthraquinone dyes, indigo dyes, carbonium dyes, quinoneimine dyes, xanthene dyes, cyanine dyes, quinoline dyes, nitro dyes, nitroso dyes, benzoquinone dyes, naphthoquinone dyes, phthalocyanine dyes, and metal phthalocyanine dyes. These may be used individually or in combination.

[0048] From the viewpoint of print density and ink viscosity, the colorant content is preferably 0.1 to 20% by mass, more preferably 1 to 15% by mass, and even more preferably 5 to 10% by mass, relative to the total amount of ink.

[0049] When an ink contains a pigment, a pigment dispersant can be used together with the pigment to stably disperse the pigment in the ink. The pigment dispersant is not particularly limited as long as it can stably disperse the pigment in the ink, but examples of preferred dispersants include hydroxyl group-containing carboxylic acid esters, salts of long-chain polyaminoamides and high molecular weight acid esters, salts of high molecular weight polycarboxylic acids, salts of long-chain polyaminoamides and polar acid esters, high molecular weight unsaturated acid esters, copolymers of vinylpyrrolidone and long-chain alkenes, modified polyurethanes, modified polyacrylates, polyether ester-type anionic surfactants, polyoxyethylene alkyl phosphates, and polyester polyamines.

[0050] It is preferable to use a polymeric dispersant as the pigment dispersant. The polymeric dispersant may be synthesized or commercially available. Examples of commercially available pigment dispersants include "Solspers J180," "Solspers J200," "Solspers 71000," "Solspers 74000," "Solspers 86000," "Solspers 87000," and "Solspers M387" from Lubrizol Japan Co., Ltd., and "BYKJET-9151," "BYKJET-9152," and "BYKJET-9170" from BYK Chemie Japan Co., Ltd. (all are product names). These may be used individually or in combination of two or more.

[0051] The pigment dispersant is preferably included in a mass ratio of 0.2 to 1.0 per unit of pigment. The pigment dispersant content in the total amount of ink is preferably 0.5 to 15% by mass, and more preferably 1 to 5% by mass.

[0052] Ink preferably contains a surfactant. For example, it is preferable for the ink to contain a surfactant in order to improve the wetting and spreading of the ink even on hydrophobic substrate surfaces, increase the drying speed, and form a good image. Examples of surfactants include silicone-based surfactants, fluorine-based surfactants, and nonionic surfactants such as polyoxyethylene derivatives.

[0053] Examples of silicone-based surfactants include polyester-modified silicones and polyether-modified silicones. Examples of commercially available silicone-based surfactants include "BYK-307," "BYK-313," "BYK-330," "BYK-333," "BYK-342," "BYK-370," "BYK-377," "BYK-378," "BYK-3550," "BYK-3750," "BYK-3761," "BYK-3762," "BYK-3764," and "BYK-SILCLEAN 3700" from BIC Chemie Japan Co., Ltd., and "Sylface SAG005," "Sylface SAG008," and "Sylface SAG503A" from Nisshin Chemical Industry Co., Ltd. (all are product names).

[0054] Examples of commercially available fluorine-based surfactants include "BYK-340" from BIC Chemie Japan Co., Ltd., and "Surflon S-241," "Surflon S-242," "Surflon S-242L," "Surflon S-243," "Surflon S-420," and "Surflon S-431" from AGC Inc. (all are product names).

[0055] As the polyoxyethylene derivative, it is preferable to use an acetylene glycol-based surfactant. Examples of commercially available acetylene glycol-based surfactants include, for example, "Surfinol 420," "Surfinol 440," "Surfinol 465," and "Surfinol 485" from Evonik Industries, and "Orfin E-1004" and "Orfin-1010" from Nisshin Chemical Industry Co., Ltd. (all are trade names).

[0056] From the standpoint of continuous ink ejection during printing and image color reproduction, it is preferable that the ink contains a silicone-based surfactant.

[0057] Surfactants may be used individually or in combination of two or more types. The surfactant is preferably present in an amount of 0.05 to 2% by mass, and more preferably 0.1 to 1% by mass, relative to the total amount of ink.

[0058] Depending on the application, the ink may contain various additives. Examples of additives include UV absorbers, light stabilizers, antioxidants, and plasticizers.

[0059] The ink may contain a colorant or it may not contain a colorant. For example, the ink may be a colored ink or a colorless, transparent ink.

[0060] The viscosity of an inkjet ink varies depending on the nozzle diameter of the inkjet recording system's ejection head and the ejection environment, but generally, it is preferably 3 to 30 mPa·s at 23°C, more preferably 3 to 15 mPa·s, and even more preferably 4 to 10 mPa·s. In this disclosure, the ink viscosity is a value measured at 23°C. For example, a rheometer MCR302 manufactured by Anton Paar Japan Co., Ltd. can be used as a viscosity measuring device.

[0061] The printing method using inkjet ink is not particularly limited and may be any method, such as piezo, electrostatic, or thermal. When using an inkjet recording device, it is preferable to eject ink according to one embodiment from the inkjet head based on a digital signal and to adhere the ejected ink droplets to the substrate.

[0062] In this embodiment, the substrate is not particularly limited and can be printing paper such as plain paper, coated paper, or specialty paper, cloth, inorganic sheets, films, OHP sheets, or adhesive sheets with an adhesive layer on the back surface using these as substrates. For example, the ink of this embodiment can also be preferably used on plastic substrates such as polyvinyl chloride resin or olefin resin. Examples of olefin resins include polypropylene resin. Such plastic substrates may be absorbent substrates that can absorb the applied ink, such as substrates having an ink-receiving layer, or they may be non-absorbent substrates that do not have an ink-receiving layer. The ink of this embodiment can also be preferably used on substrates that are difficult for ink to penetrate. Furthermore, olefin resins tend to have low affinity for organic solvents in inks, and it may be difficult to obtain good image adhesion to the substrate, but when using the ink of this embodiment, it is possible to obtain good image adhesion even on substrates made of olefin resin. The ink of this embodiment can also be preferably used on synthetic paper made of olefin resin such as polypropylene resin.

[0063] <Inkjet ink manufacturing method> In the method for manufacturing an inkjet ink according to the embodiment, the inkjet ink is as described above, and this method for manufacturing an inkjet ink may include synthesizing the binder resin in a solvent SS containing a water-insoluble organic solvent X2.

[0064] The method for synthesizing the binder resin is not particularly limited. The binder resin can be obtained, for example, by polymerizing one or more radical polymerizable monomers. Examples of radical polymerizable monomers include (meth)acrylic acid and (meth)acrylic acid esters mentioned above. For example, in the case of (meth)acrylic resin, at least one monomer selected from the group consisting of (meth)acrylic acid and (meth)acrylic acid esters can be polymerized.

[0065] The polymerization method is not particularly limited, as long as it allows synthesis in a solvent SS containing a non-water-soluble organic solvent X2. Solution polymerization is preferred as the polymerization method.

[0066] The solvent SS is preferably an organic solvent. The solvent SS is preferably a non-water-soluble organic solvent X2. The solvent SS may further contain a water-soluble organic solvent Y2. For example, the non-water-soluble organic solvent X2 may contain a non-water-soluble organic solvent contained in the non-water-soluble organic solvent X1. For example, the water-soluble organic solvent Y2 may contain a water-soluble organic solvent contained in the water-soluble organic solvent Y1. The solvent SS is preferably capable of dissolving the binder resin obtained by polymerization.

[0067] Examples of water-insoluble organic solvents X2 include those listed as examples of water-insoluble organic solvents X1. Water-insoluble organic solvents X2 can be used as one of these water-insoluble organic solvents alone or in combination of two or more.

[0068] The non-water-soluble organic solvent X2 is preferably capable of dissolving the binder resin obtained by polymerization. From the viewpoint of compatibility between the obtained binder resin and the organic solvent in the ink, and thereby preparing a low-viscosity ink, the non-water-soluble organic solvent X1 contained in the ink may be used as the non-water-soluble organic solvent X2. For example, if the ink contains two or more organic solvents as the non-water-soluble organic solvent X1, one or more of them may be used as the non-water-soluble organic solvent X2. For example, if the ink contains two or more organic solvents as the non-water-soluble organic solvent X1, only one of them may be used as the non-water-soluble organic solvent X2.

[0069] From the viewpoint of superior image water resistance, the non-water-soluble organic solvent X2 is preferably 30% by mass or more, more preferably 50% by mass or more, even more preferably 70% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 99% by mass or more, based on the total amount of solvent SS. The non-water-soluble organic solvent X2 may be, for example, 100% by mass, based on the total amount of solvent SS. From the viewpoint of superior image water resistance, the non-water-soluble organic solvent X2 is preferably 30 to 100% by mass, more preferably 50 to 100% by mass, even more preferably 90 to 100% by mass or more, even more preferably 95 to 100% by mass, and even more preferably 99 to 100% by mass, based on the total amount of solvent SS.

[0070] Examples of water-soluble organic solvents Y2 include those listed as examples of water-soluble organic solvents Y1. Water-soluble organic solvents Y2 can be used individually or in combination of two or more of these solvents.

[0071] The water-soluble organic solvent Y2 is preferably one that can dissolve the binder resin obtained by polymerization. From the viewpoint of compatibility between the obtained binder resin and the organic solvent in the ink, and thereby preparing a low-viscosity ink, the water-soluble organic solvent Y1 contained in the ink may be used as the water-soluble organic solvent Y2. For example, if the ink contains two or more organic solvents as the water-soluble organic solvent Y1, one or more of them may be used as the water-soluble organic solvent Y2. For example, if the ink contains two or more organic solvents as the water-soluble organic solvent Y1, only one of them may be used as the water-soluble organic solvent Y2.

[0072] From the viewpoint of superior image water resistance, the water-soluble organic solvent Y2 may be, for example, 70% by mass or less, 50% by mass or less, 30% by mass or less, 10% by mass or less, 5% by mass or less, or 1% by mass or less, relative to the total amount of solvent SS. The water-soluble organic solvent Y2 may not be included in the solvent SS, for example. If the water-soluble organic solvent Y2 is included in the solvent SS, the amount of water-soluble organic solvent Y2 may be, for example, 1 to 70% by mass, 1 to 50% by mass, 1 to 30% by mass, 1 to 10% by mass, 1 to 5% by mass, or 1% by mass or less, relative to the total amount of solvent SS.

[0073] In the synthesis of binder resins, polymerization initiators such as radical polymerization initiators may be used during the polymerization reaction.

[0074] As radical polymerization initiators, known radical polymerization initiators such as azo compounds like 2,2'-azobis(isobutyronitrile) (AIBN), 2,2'-azobis(2,4'-dimethylvaleronitrile), and dimethyl 2,2'-azobisisobutyrate, and organic peroxides such as hydroperoxides, dialkylperoxides, peroxyesters, and diallylperoxides (e.g., t-butylperoxy-2-ethylhexanoate) can be used. These may be used individually or in combination of two or more.

[0075] The amount of polymerization initiator may be, for example, 0.1 to 20 parts by mass, or 1 to 10 parts by mass, per 100 parts by mass of the total amount of monomer used in the synthesis. The polymerization initiator may be added in its entirety at once, or in two or more separate additions. For example, the polymerization initiator may be added at the start of the polymerization reaction, and then the polymerization reaction may be carried out further by adding the polymerization initiator one or two or more times.

[0076] In the synthesis of binder resins, it is preferable to perform solution polymerization of a radically polymerizable monomer with a radical polymerization initiator in a solvent SS containing a water-insoluble organic solvent X2.

[0077] In the process of synthesizing the binder resin, for example, a binder resin solution containing the binder resin and an organic solvent may be obtained. The concentration of this binder resin solution may be adjusted by adding further organic solvents as needed. When diluting the binder resin solution with an organic solvent, it is preferable that the organic solvent used for dilution be one or more of the organic solvents contained in the solvent SS used in the synthesis of the binder resin. For example, solvent SS may be used as the organic solvent used to dilute the binder resin solution. The resulting binder resin solution may contain the binder resin and a non-water-soluble organic solvent contained in a non-water-soluble organic solvent X1, a water-soluble organic solvent contained in a water-soluble organic solvent Y1, or a combination thereof. When using the binder resin solution in the manufacture of ink, the amount of binder resin (solid content) relative to the total amount of the binder resin solution may be, for example, 20-70% by mass, 30-60% by mass, or 35-55% by mass.

[0078] The method for manufacturing the ink may further include a step of mixing and stirring a binder resin, a water-insoluble organic solvent X1, a water-soluble organic solvent Y1, water, and other components such as pigments as needed. For example, the binder resin may be subjected to the mixing and stirring step in the form of a binder resin solution containing the binder resin and the water-insoluble organic solvent contained in the water-insoluble organic solvent X1, the water-soluble organic solvent contained in the water-soluble organic solvent Y1, or a combination thereof. These components may be mixed and stirred all at once or in separate portions. Specifically, for example, all components can be introduced all at once or in separate portions into a disperser such as a bead mill and dispersed. After that, if desired, the mixture can be passed through a filter such as a membrane filter.

[0079] For example, a pigment dispersion may be prepared by first mixing and stirring the pigment with a pigment dispersant and an organic solvent to disperse the pigment. The organic solvent used in the pigment dispersion may be a non-water-soluble organic solvent contained in a non-water-soluble organic solvent X1, a water-soluble organic solvent contained in a water-soluble organic solvent Y1, or a combination thereof.

[0080] <Manufacturing methods for printed materials> Printed materials can be manufactured using the ink produced by the method described above. The method for manufacturing printed materials may include, for example, applying the ink produced by the method described above to a substrate using an inkjet method. As the substrate, the substrates described above as substrates that can use the ink can be used.

[0081] In the process of applying ink to the substrate, it is preferable that the ink is applied to the substrate by an inkjet method. The inkjet method is not particularly limited and may be any method such as a piezo method, electrostatic method, or thermal method.

[0082] The amount of ink applied to the substrate is 1 to 500 g / m². 2 Preferably, 3-100 g / m 2 More preferably, 5-50 g / m 2 More preferably, 10-30 g / m 2 Most preferable.

[0083] The method for manufacturing printed materials may include steps such as pretreatment and heating.

[0084] This disclosure includes the following embodiments. <1> A method for manufacturing inkjet ink, The inkjet ink comprises a binder resin, a non-water-soluble organic solvent X1, a water-soluble organic solvent Y1, and 1.0% by mass or more of water relative to the total amount of the inkjet ink. The method for producing an inkjet ink comprises synthesizing the binder resin in a solvent SS containing a water-insoluble organic solvent X2. <2> The non-water-soluble organic solvent X2 is present in an amount of 50 to 100% by mass relative to the total amount of the solvent SS. <1> The method for manufacturing inkjet ink as described above. <3> The binder resin is 5.0% by mass or more relative to the total amount of the inkjet ink. <1> or <2> The method for manufacturing inkjet ink as described above. <4> The amount of water is 3.0% by mass or more relative to the total amount of inkjet ink. <1> ~ <3> A method for manufacturing inkjet ink as described in any one of the items. [Examples]

[0085] The present invention will be described in detail below with reference to examples. The present invention is not limited to the following examples.

[0086] <Manufacturing of pigment dispersions> Each material listed in Table 1 was measured into a beaker in the proportions shown in Table 1, premixed, and then transferred to a plastic container with a lid. Zirconia beads with a diameter of 0.8 mm were added, and the mixture was dispersed for 60 minutes using a rocking mill RM-05 (manufactured by Seiwa Giken Co., Ltd.). The beads were then separated from the dispersion to produce pigment dispersions D1 to D5 with a pigment concentration of 20% by mass.

[0087] Details of the materials listed in Table 1 will be described later.

[0088] [Table 1]

[0089] <Synthesis of binder resin and production of binder resin solution> Binder resins and binder resin solutions were manufactured as described below. In the following, the weight-average molecular weight of the manufactured binder resins was determined using the GPC method on a standard polystyrene basis. A GPC measuring instrument manufactured by Shimadzu Corporation was used for the measurement. The glass transition temperature (Tg) was calculated using the FOX formula.

[0090] (Synthesis of binder resin A1 and production of binder resin solution A1) In a 1 L flask, 317.8 g of propylene glycol diacetate (manufactured by Tokyo Chemical Industry Co., Ltd.) (non-water-soluble organic solvent 1), maintained at 90°C, was mixed with 335.0 g of methyl methacrylate, a radical polymerizable monomer, and 10.1 g of 2,2'-azobis(isobutyronitrile) (AIBN) (manufactured by Tokyo Chemical Industry Co., Ltd.) (polymerization initiator 1), a polymerization initiator, dissolved in 85.0 g of propylene glycol diacetate. This mixture was added dropwise over 2 hours. After the dropwise addition was complete, 1.1 g of AIBN was added after 30 minutes while maintaining the liquid temperature at 90°C. The mixture was further reacted at 90°C for 1 hour, and then diluted with propylene glycol diacetate to obtain binder resin solution A1, which is a solution of binder resin A1. The active ingredient concentration in the obtained binder resin solution A1 is 40% by mass. The Tg of binder resin A1 was 105°C, and its weight-average molecular weight was 20,000.

[0091] (Synthesis of binder resins A2-A10 and A12-A14, and production of binder resin solutions A2-A10 and A12-A14) In the synthesis of binder resin A1 and the production of binder resin solution A1, the same procedure was followed except that the solvent, monomer, initiator, and their amounts were changed to the raw materials and amounts listed in Tables 2 and 3 to obtain binder resin solutions A2-A10 and A12-A14. The active ingredient concentrations in binder resin solutions A2-A10 and A12-A14, as well as the Tg and weight-average molecular weight of binder resins A2-A10 and A12-A14, are shown in Tables 2 and 3.

[0092] (Synthesis of binder resin A11 and production of binder resin solution A11) In a 1 L flask, 317.8 g of propylene glycol diacetate (manufactured by Tokyo Chemical Industry Co., Ltd.), maintained at 90°C, was mixed with 336.1 g of methyl methacrylate, a radical polymerizable monomer, and 10.1 g of 2,2'-azobis(isobutyronitrile) (AIBN) (manufactured by Tokyo Chemical Industry Co., Ltd.), a polymerization initiator, dissolved in 85.0 g of propylene glycol diacetate. This mixture was added dropwise over 2 hours. The mixture was then stirred at 90°C for 1 hour and diluted with propylene glycol diacetate to obtain binder resin solution 1, which is a solution of binder resin A11, with an active ingredient concentration of 40.0% by mass. The active ingredient concentration of binder resin solution A11 in the obtained binder resin solution 1 is 40% by mass. The Tg and weight-average molecular weight of binder resin A11 are shown in Table 3.

[0093] [Table 2]

[0094] [Table 3]

[0095] <Ink Manufacturing> Each material listed in Tables 4-7 was measured out in the proportions shown in Tables 4-7, mixed and stirred using a three-one motor, and then filtered through a 3 μm pore size membrane filter to obtain the ink. Details of the raw materials listed in Tables 4-7 will be described later.

[0096] Tables 4-7 show the amount of water and binder resin in the ink, expressed as a percentage (mass %) of the total ink volume. The amounts of water in the ink listed in Tables 4-7 were measured using the Karl Fischer method, with a KF-31 volumetric titration moisture meter manufactured by Nitto Seiko Analytech Co., Ltd. used for the measurement.

[0097] Details of the materials listed in Tables 1-7 are shown below. The monomers listed in Tables 2 and 3 (methyl methacrylate, n-butyl methacrylate, and methacrylic acid) are all available from Tokyo Chemical Industry Co., Ltd.

[0098] (Pigment) Pigment 1: Carbon black, "MOGUL L" (product name), manufactured by Cabot Corporation. Pigment 2: Copper phthalocyanine, "Fastogen Blue LA5380" (product name), manufactured by DIC Corporation.

[0099] (Pigment dispersant) Polymeric dispersant: "Solspers J180" (product name), manufactured by Lubrizol Japan Co., Ltd., active ingredient 100% by mass

[0100] (Non-water-soluble organic solvents) Non-water-soluble organic solvent 1: Propylene glycol diacetate, manufactured by Tokyo Chemical Industry Co., Ltd., boiling point 191℃ Non-water-soluble organic solvent 2: Ethylene glycol diacetate, manufactured by Tokyo Chemical Industry Co., Ltd., boiling point 190℃ Non-water-soluble organic solvent 3: γ-hexanolactone, manufactured by Tokyo Chemical Industry Co., Ltd., boiling point 220℃ Non-water-soluble organic solvent 4: Ethyl acetoethyl, manufactured by Tokyo Chemical Industry Co., Ltd., boiling point 184℃ (Water-soluble organic solvent) Water-soluble organic solvent 1: Diethylene glycol diethyl ether, manufactured by Tokyo Chemical Industry Co., Ltd., boiling point 188℃ Water-soluble organic solvent 2:2-pyrrolidone, manufactured by Tokyo Chemical Industry Co., Ltd., boiling point 245℃

[0101] (Polymerization initiator) Polymerization initiator 1: 2,2'-Azobis(isobutyronitrile) (AIBN), manufactured by Tokyo Chemical Industry Co., Ltd. Polymerization initiator 2: t-butylperoxy-2-ethylhexanoate (perbutyl O), manufactured by NOF Corporation.

[0102] (Pigment dispersion) Pigment dispersions D1-D5: Manufactured as described above.

[0103] (Binder resin) Binder resin solution A1: A solution of binder resin A1, manufactured as described above. Binder resin solution A2: A solution of binder resin A2, manufactured as described above. Binder resin solution A3: A solution of binder resin A3, manufactured as described above. Binder resin solution A4: A solution of binder resin A4, manufactured as described above. Binder resin solution A5: Solution of binder resin A5, manufactured as described above. Binder resin solution A6: Solution of binder resin A6, manufactured as described above. Binder resin solution A7: A solution of binder resin A7, manufactured as described above. Binder resin solution A8: Solution of binder resin A8, manufactured as described above. Binder resin solution A9: Solution of binder resin A9, manufactured as described above. Binder resin solution A10: A solution of binder resin A10, manufactured as described above. Binder resin solution A11: A solution of binder resin A11, manufactured as described above. Binder resin solution A12: A solution of binder resin A12, manufactured as described above. Binder resin solution A13: Solution of binder resin A13, manufactured as described above. Binder resin solution A14: A solution of binder resin A14, manufactured as described above.

[0104] (Surfactants) Surfactant: Silicone-based surfactant, "BYK-333" (product name), manufactured by Bic Chemie Japan Co., Ltd.

[0105] <Rating> The water resistance of the ink manufactured as described above was evaluated as follows.

[0106] (water resistance) Ink was introduced into the ink path of a commercially available solvent inkjet printer ("ValueJet VJ-628" (product name) manufactured by Mutoh Industries, Ltd.). A solid color image measuring 25 cm vertically x 18 cm horizontally was printed onto A4 size polypropylene synthetic paper ("New Yupo FGS110" (product name) manufactured by Yupo Corporation) to obtain a printed material. At 10 seconds and 1 day after printing, the solid image area of ​​the printed material was rubbed 100 times with a cotton swab soaked in water. The image and cotton swab after rubbing were observed, and the water resistance of the image was evaluated according to the evaluation criteria below. The results are shown in Tables 4-7. A: No peeling in the image B: Some ink has transferred to the cotton swab after rubbing, but there is no noticeable peeling of the image. C: Some parts of the image are peeling.

[0107] [Table 4]

[0108] [Table 5]

[0109] [Table 6]

[0110] [Table 7]

[0111] Examples 1 to 18 showed excellent results in water resistance evaluation starting 10 seconds after printing. On the other hand, Comparative Examples 1 to 3, in which the binder resin was not synthesized in a solvent containing a non-water-soluble organic solvent, and Comparative Example 4, which contained a small amount of water in the ink, all showed poor water resistance after 10 seconds of printing.

Claims

1. A method for manufacturing inkjet ink, The inkjet ink comprises a binder resin, a non-water-soluble organic solvent X1, a water-soluble organic solvent Y1, and 1.0% by mass or more of water relative to the total amount of the inkjet ink. The above method is a method for producing an inkjet ink, comprising synthesizing the binder resin in a solvent SS containing a non-water-soluble organic solvent X2.

2. The method for producing an inkjet ink according to claim 1, wherein the non-water-soluble organic solvent X2 is 50 to 100% by mass relative to the total amount of the solvent SS.

3. The method for manufacturing an inkjet ink according to claim 1 or 2, wherein the binder resin is 5.0% by mass or more of the total amount of the inkjet ink.

4. The method for producing an inkjet ink according to claim 1 or 2, wherein the amount of water is 3.0% by mass or more relative to the total amount of the inkjet ink.

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