Water-based white ink and dried film

Abstract

To provide an environmentally friendly water-based white ink for label printing which has good adhesion to a printing base material such as a plastic film, excellent blocking resistance, water resistance and water abrasion resistance and can form a dried film which is a printed layer with a high white density and maintains adhesion to a printing base material even when the printing base material shrinks.SOLUTION: There is provided a water-based white ink used for label printing, which contains a white pigment and a polymer dispersant, wherein the polymer dispersant is a polymer which contains a constitutional unit (i) derived from methacrylic acid and a constitutional unit (ii) derived from a first methacrylate of biological material origin in which at least a portion of the carboxy groups is neutralized with alkali, the polymer has an acid value of 30 to 250 mgKOH / g and the content of the constitutional unit (ii) in the polymer is 50 mass% or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a water-based white ink and dried film used in label printing. [Background technology]

[0002] On flexible packaging films used for food packaging, beverage bottles such as PET bottles, and daily necessities, images and characters are printed with gravure ink or flexographic ink from the viewpoints of design, content display, aesthetic appeal, content protection, functionality, etc. The mainstream method for printing images on plastic films such as flexible packaging films has been to use solvent-based gravure ink (Patent Document 1).

[0003] However, when solvent-based gravure ink is used, the organic solvent in the ink is released into the environment when it dries after printing, which raises concerns about global warming, an increase in carbon dioxide, and environmental pollution. Therefore, in consideration of the environment, there has been a shift to printing methods that use water-based inks, which use water as the main liquid medium (Patent Documents 2 to 4). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-30611 [Patent Document 2] Japanese Patent Application Publication No. 11-172168 [Patent Document 3] Patent No. 4151801 [Patent Document 4] Special Publication No. 2005-518459 Summary of the Invention [Problem to be solved by the invention]

[0005] In the case of aqueous inks, it is necessary to dissolve or disperse the film-forming polymer and the polymer dispersant for dispersing the pigment in the aqueous medium. However, these polymers and polymer dispersants are highly hydrophilic, and there are issues with the adhesion of the formed print layer (dried film) to the printing substrate such as plastic film, as well as durability such as water resistance and abrasion resistance, and further performance improvements are required.

[0006] Furthermore, in order to improve hiding power and image color development, water-based white inks containing white pigments are used as reverse printing inks. Inorganic pigments with high specific gravity, such as titanium dioxide and zinc dioxide, are used as white pigments. However, these white inorganic pigments have a high specific gravity and tend to settle in the ink and form a hard cake. Therefore, water-based white inks have issues in terms of storage stability, pigment dispersibility, hard cake redispersibility, and sedimentation recovery, and also have the issue of making it difficult to increase the optical density (white density) of the images formed.

[0007] Label printing inks are sometimes used, for example, to print on shrink film that constitutes shrink labels used on beverage bottles and the like. The shrink film must be suitable for attachment to the bottle. Furthermore, the printed layer (dried film) printed on the shrink film must adapt to the shrinkage of the shrink film. In other words, there is a demand for water-based inks that can withstand the heat generated when the shrink film shrinks, do not detach even after shrinkage, and are capable of forming a printed layer that is resistant to deterioration in adhesion and abrasion resistance.

[0008] Furthermore, in recent years, there has been a demand for carbon-neutral and sustainable materials from the perspective of preventing global warming and reducing carbon dioxide emissions, and there is also a demand for the active use of bio-derived materials as constituent materials for water-based white inks.

[0009] The present invention has been made in consideration of the problems associated with the prior art, and an object of the present invention is to provide an environmentally friendly water-based white ink for label printing that has good adhesion to printing substrates such as plastic films, is excellent in blocking resistance, water resistance, and water abrasion resistance, maintains adhesion to the printing substrate even when the printing substrate shrinks, and is capable of forming a dried film that is a printed layer with a high white density.Another object of the present invention is to provide a dried film using the water-based white ink. [Means for solving the problem]

[0010] That is, according to the present invention, there is provided the following water-based white ink. [1] An aqueous white ink used for label printing, comprising a white pigment, water, a water-soluble organic solvent, a resin binder, and a polymeric dispersant for dispersing the white pigment, wherein the polymeric dispersant is a polymer in which at least a portion of the carboxyl groups have been neutralized with an alkali, the polymer comprising a structural unit (i) derived from methacrylic acid and a structural unit (ii) derived from a first methacrylate derived from a biological material, the polymer having an acid value of 30 to 250 mg KOH / g, the content of the structural unit (ii) in the polymer being 50% by mass or more, the number average molecular weight of the polymer being 5,000 to 20,000, and the molecular weight distribution (weight average molecular weight / number average molecular weight) being 2.5 or less, and the first methacrylate being at least one of tetrahydrofurfuryl methacrylate and isobornyl methacrylate. [2] The water-based white ink according to [1], wherein the polymer further contains a structural unit (iii) derived from polyethylene glycol monomethyl ether (molecular weight 400 to 4,000) methacrylate, and the content of the structural unit (iii) in the polymer is 10 to 30 mass%. [3] The water-based white ink according to [1] or [2], wherein the polymer further comprises a structural unit (iv) derived from a second methacrylate derived from a biological material, the content of the structural unit (iv) in the polymer being 10 to 30 mass %, and the second methacrylate being at least one of dodecyl methacrylate and octadecyl methacrylate. [4] The water-based white ink according to any one of [1] to [3], wherein the alkali is at least one selected from the group consisting of ammonia, dimethylaminoethanol, and 2-amino-2-methyl-1-propanol. [5] The water-based white ink according to any one of [1] to [4], wherein the resin binder is at least one resin dispersion selected from the group consisting of an acrylic emulsion, a styrene-acrylic emulsion, an acrylic-urethane emulsion, and a urethane aqueous dispersion, containing resin particles made of a resin, the acid value of the resin being 80 mgKOH / g or less, and the number average particle size of the resin particles being 30 to 200 nm. [6] The water-based white ink according to any one of [1] to [5], further comprising at least one crosslinking agent selected from the group consisting of an epoxy-based crosslinking agent, an aziridine-based crosslinking agent, a carbodiimide-based crosslinking agent, and an isocyanate-based crosslinking agent. [7] The water-based white ink according to any one of [1] to [6] above, which is used for printing labels for beverages.

[0011] The present invention also provides the following dry film. [8] A dried film which is a dried product of the water-based white ink according to any one of [1] to [7] above. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide an environmentally friendly water-based white ink for label printing that has good adhesion to printing substrates such as plastic films, excellent blocking resistance, water resistance, and water abrasion resistance, maintains adhesion to the printing substrate even when the printing substrate shrinks, and is capable of forming a dried film that is a printed layer with a high white density.Furthermore, according to the present invention, it is possible to provide a dried film using the water-based white ink. DETAILED DESCRIPTION OF THE INVENTION

[0013] <Water-based white ink> Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments. Various physical property values in this specification are values at room temperature (25°C) unless otherwise specified. One embodiment of the water-based white ink of the present invention (hereinafter also simply referred to as "white ink" or "ink") is a water-based white ink used for label printing, and contains a white pigment, water, a water-soluble organic solvent, a resin binder, and a polymer dispersant that disperses the white pigment.

[0014] (white pigment) As the white pigment, conventionally known white pigments can be used. Examples of white pigments include titanium dioxide pigments, zinc oxide pigments, calcium carbonate pigments, basic barium sulfate pigments, barium carbonate, diatomaceous earth, talc, clay, and alumina white. Among these, titanium dioxide pigments are preferred from the viewpoints of hiding power and whiteness. Furthermore, from the viewpoint of environmental friendliness, uncalcined shell powder of shellfish such as scallops and oysters can also be used.

[0015] The white pigment may be surface-treated, such as silica treatment, alumina treatment, silica-alumina treatment, silane coupling agent treatment, organic acid treatment, or polymer treatment. The amount of surface treatment is preferably 10% by mass or less of the white pigment. From the viewpoint of color development and hiding power, the number-average particle diameter (primary particle diameter) of the white pigment is preferably 100 to 500 nm. The content of the white pigment in the ink is preferably 10 to 60% by mass based on the total mass of the ink.

[0016] (water) The ink of this embodiment is a water-based ink and contains water as an essential component. Deionized water, distilled water, purified water, etc. are preferably used as the water. The content of water in the ink is preferably 30 to 90 mass % based on the total amount of the ink.

[0017] (Water-soluble organic solvent) The water-soluble organic solvent is a component that has effects such as leveling on the substrate, film-forming properties, and viscosity adjustment. Examples of water-soluble organic solvents that can be used include alcohol-based solvents, glycol-based solvents, amide-based solvents, urea-based solvents, carbonate-based solvents, sulfoxide-based solvents, ionic liquids, and glycerin-based solvents. Among these, it is preferable to use a solvent that easily volatilizes by drying after printing, and it is preferable to use a water-soluble organic solvent with a boiling point of 250°C or less. Examples of suitable solvents include alcohol-based solvents such as methanol, ethanol, and isopropanol, and glycol-based solvents such as propylene glycol, propylene glycol monomethyl ether, propylene glycol monopropyl ether, ethylene glycol monobutyl ether, and diethylene glycol monobutyl ether. Of these, low-boiling alcohols such as isopropyl alcohol are preferred.

[0018] When the polymer used as the polymer dispersant is produced by solution polymerization, it is preferable to use the same water-soluble organic solvent used in the solution polymerization in the ink. The content of the water-soluble organic solvent in the ink is preferably 30 mass% or less based on the total weight of the ink.

[0019] (resin binder) The ink of this embodiment contains a resin binder, which is a film-forming component. Examples of resin binders that can be used include a resin solution containing a dissolved resin, and an emulsion or aqueous dispersion in which resin particles are emulsified or dispersed in an aqueous medium. Among these, it is preferable to use an emulsion or aqueous dispersion with low viscosity in order to reduce the viscosity of the ink. Examples of emulsions include polymer emulsions obtained by emulsion polymerization of a monomer in the presence of a surfactant; protective colloid emulsions using a water-soluble polymer as a protective colloid; and aqueous dispersions obtained by neutralizing with an alkali, ionizing, and self-emulsifying a polymer chain containing carboxylic acid groups or sulfonic acid groups.

[0020] Examples of the resin binder include resin dispersions such as styrene-acrylic emulsions, acrylic emulsions, styrene-acrylic-methacrylic emulsions, styrene-methacrylic emulsions, acrylic-methacrylic emulsions, vinyl acetate emulsions, vinyl chloride emulsions, styrene-olefin emulsions, olefin-based aqueous dispersions, polyester-based aqueous dispersions, urethane-based aqueous dispersions, and urethane-acrylic emulsions.

[0021] From the viewpoint of improving adhesion to the substrate and abrasion resistance, the resin binder is preferably at least one resin dispersion selected from the group consisting of acrylic emulsions, styrene-acrylic emulsions, acrylic-urethane emulsions, and urethane aqueous dispersions. Acrylic emulsions are emulsions obtained by emulsion polymerization of acrylates such as ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate in the presence of a surfactant. Styrene-acrylic emulsions are emulsions obtained by polymerizing styrene-based monomers such as styrene and vinyltoluene with the above-mentioned acrylates.

[0022] The resin binder can also be an emulsion obtained by adding a styrene-based monomer or an acrylate-based monomer dropwise to an aqueous polymer solution obtained by neutralizing a styrene-maleic acid copolymer or a styrene-acrylic acid copolymer with an acid value of 100 mgKOH / g or more with an alkali and polymerizing the aqueous polymer solution.Furthermore, an emulsion in which a resin having a hydroxyl group is dispersed, obtained by copolymerizing a (meth)acrylate having a hydroxyl group, can also be used.

[0023] A urethane-based aqueous dispersion can be obtained, for example, by reacting a diisocyanate component, a polyol component, a low-molecular-weight diol, and a diol component having a carboxy group to produce a polyurethane oligomer, neutralizing the resulting polyurethane oligomer with an alkali, chain-extending the resulting polyurethane oligomer with a chain extender, and then self-emulsifying the resulting polyurethane oligomer in water. Examples of the diisocyanate component include isophorone diisocyanate and hexamethylene diisocyanate. Examples of the polyol component include polycarbonate polyols such as polyhexamethylene carbonate diol; polyether polyols such as polytetramethylene glycol; and polyester polyols such as condensates of adipic acid and diols. Examples of the low-molecular-weight diol include ethylene glycol and butanediol. Examples of the diol component having a carboxy group include dimethylol ethanoic acid and dimethylol butanoic acid.

[0024] The resin used as the resin binder may be a polymer having a crosslinked structure and having structural units derived from a polyfunctional monomer; or a polymer having a structure that self-crosslinks upon drying and containing a compound having an alkoxysilyl group or a hydrazine group and diacetone acrylamide as copolymerization components. Furthermore, from the viewpoint of environmental consideration, it is preferable to use a polymer having structural units derived from a monomer derived from a biological material.

[0025] The resin dispersion used as the resin binder contains resin particles. The number-average particle diameter of the resin particles in the resin dispersion, measured by dynamic light scattering, is preferably 30 to 200 nm, and more preferably 80 to 150 nm. If the number-average particle diameter of the resin particles is less than 30 nm, the viscosity of the ink may increase excessively. On the other hand, if the number-average particle diameter of the resin particles exceeds 200 nm, problems such as plate fogging may easily occur during printing.

[0026] The acid value of the resin constituting the resin particles is preferably 80 mgKOH / g or less, and more preferably 0 to 50 mgKOH / g. If the acid value of the resin exceeds 80 mgKOH / g, the resulting printed layer (dried film) will contain many hydrophilic carboxyl groups. This may result in a slight decrease in the water resistance and water abrasion resistance of the printed layer. The content of the resin binder (solid content) in the ink is preferably 3 to 60 mass % based on the total amount of ink, and more preferably 5 to 50 mass %.

[0027] (polymer dispersant) The polymer dispersant is a polymer containing a constitutional unit (i) derived from methacrylic acid and a constitutional unit (ii) derived from a first methacrylate derived from a biological material, in which at least a portion of the carboxyl groups have been neutralized with an alkali.

[0028] The structural unit (i) is a structural unit derived from methacrylic acid. That is, the structural unit (i) is a structural unit having a carboxy group derived from methacrylic acid. By neutralizing this carboxy group with an alkali, the polymer (polymer dispersant) can be dissolved in water. The acid value of the polymer is 30 to 250 mgKOH / g, preferably 50 to 150 mgKOH / g. If the acid value of the polymer is less than 30 mgKOH / g, it may not be possible to dissolve it in water even after neutralization and ionization with an alkali. On the other hand, if the acid value of the polymer is more than 250 mgKOH / g, the polymer will be too hydrophilic, resulting in excessively high viscosity when dissolved in water and reduced water resistance of the printed layer (dried film).

[0029] The structural unit (ii) is a structural unit derived from a first methacrylate derived from a biological material. In other words, having a structural unit derived from a monomer derived from a carbon-neutral biological material can contribute to reducing carbon dioxide emissions. The first methacrylate is at least one of tetrahydrofurfuryl methacrylate and isobornyl methacrylate. Tetrahydrofurfuryl methacrylate is an ester of tetrahydrofurfuryl alcohol and methacrylic acid. Tetrahydrofurfuryl alcohol is an alcohol obtained by modifying a furan derivative obtained from corn or the like. Isobornyl methacrylate is an ester of isoborneol and methacrylic acid. Isoborneol is a plant-derived material derived from camphene obtained from pine resin or the like.

[0030] By using the first methacrylate, it is possible to introduce an ester residue with excellent adsorption to the pigment into the polymer. For example, tetrahydrofurfuryl methacrylate has a cyclic ether group that can exhibit adsorption by forming a hydrogen bond with the pigment. Also, isobornyl methacrylate has a hydrophobic isobornyl group that can adsorb to the pigment through hydrophobic interaction.

[0031] Furthermore, the homopolymer of the first acrylate has a high glass transition temperature (Tg). For example, the Tg of a homopolymer of tetrahydrofurfuryl methacrylate is 60°C, and the Tg of a homopolymer of isobornyl methacrylate is 155°C. It is believed that by using a polymer into which a structural unit with a high Tg has been introduced as a polymer dispersant, it is possible to obtain an ink capable of forming a printed layer with improved abrasion resistance and adhesion. Furthermore, since all of the first acrylates have a cyclic structure, it is believed that they have good shrinkage properties. The content of the structural unit (ii) in the polymer is 50% by mass or more, preferably 60% by mass or more.

[0032] The number-average molecular weight (Mn) of the polymer used as the polymer dispersant is 5,000 to 20,000, preferably 6,000 to 15,000. If the polymer number-average molecular weight (Mn) is less than 5,000, it will easily detach from the white pigment, resulting in insufficient dispersion stability of the white pigment. On the other hand, if the polymer number-average molecular weight (Mn) is more than 20,000, the ink viscosity will be excessively high due to the residue not adsorbed to the white pigment, and the white pigment particles will easily adsorb to each other, resulting in poor dispersibility. The number-average molecular weight (Mn) of the polymer in this specification is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0033] The molecular weight distribution (weight average molecular weight / number average molecular weight) of the polymer is 2.5 or less, preferably 2.0 or less. If the molecular weight distribution (PDI) exceeds 2.5, the dispersion stability of the white pigment becomes insufficient and the physical properties of the ink deteriorate.

[0034] The polymer may further contain structural units derived from other monomers, such as vinyl monomers such as styrene and vinyl toluene; (meth)acrylic acid monomers; and the like. Examples of the (meth)acrylic acid monomer include monofunctional (meth)acrylates having a substituent such as methyl, ethyl, propyl, butyl, hexyl, 2-ethylhexyl, octyl, decyl, dodecyl, tridecyl, hexadecyl, octadecyl, isostearyl, behenyl, cyclohexyl, trimethylcyclohexyl, t-butylcyclohexyl, benzyl, methoxyethyl, butoxyethyl, phenoxyethyl, nonylphenoxyethyl, isobornyl, dicyclopentanyl, dicyclopentenyl, dicyclopentenyloxyethyl, glycidyl, 2-hydroxyethyl, 2-hydroxypropyl, 4-hydroxybutyl, dimethylaminoethyl, diethylaminoethyl, polyethylene glycol, polypropylene glycol, polyethylene glycolyl monomethyl ether, polypropylene glycol monomethyl ether, polyepsilon caprolactone, and polydimethylsiloxane.

[0035] The polymer preferably further contains a structural unit (iii) derived from polyethylene glycol monomethyl ether methacrylate (molecular weight 400 to 4,000). The use of a polymer further containing this structural unit (iii) as a polymer dispersant can improve the leveling properties of the ink coating. The polyethylene glycol monomethyl ether methacrylate may be a polyethylene glycol monomethyl ether methacrylate of a single molecular weight, or a combination of multiple polyethylene glycol monomethyl ether methacrylates with different molecular weights. For example, a polyethylene glycol monomethyl ether methacrylate with a molecular weight of 400 and a polyethylene glycol monomethyl ether methacrylate with a molecular weight of 4,000 can be combined in a 95 / 5 mass ratio.

[0036] The content of the structural unit (iii) in the polymer is preferably 10 to 30% by mass, and more preferably 10 to 20% by mass. If the content of the structural unit (iii) is less than 10% by mass, the effect of improving leveling may be insufficient. On the other hand, if the content of the structural unit (iii) is more than 30% by mass, the polymer itself becomes more soluble in water, which may slightly reduce the water resistance of the printed layer. Furthermore, since the polyethylene glycol chain in polyethylene glycol monomethyl ether methacrylate is easily decomposed in the environment, polymers containing the structural unit (iii) are environmentally friendly materials.

[0037] The polymer used as the polymer dispersant preferably further contains a structural unit (iv) derived from a second methacrylate derived from a biological material. The second methacrylate is at least one of dodecyl methacrylate and octadecyl methacrylate. Both dodecyl methacrylate and octadecyl methacrylate are highly hydrophobic. Therefore, by using a polymer further containing a structural unit (iv) derived from the second methacrylate as the polymer dispersant, a printed layer with improved chemical resistance and ethanol resistance can be formed.

[0038] In addition, both dodecyl methacrylate and octadecyl methacrylate have low Tg homopolymers. Therefore, by further incorporating a structural unit (iv) derived from a second methacrylate, the polymer can be plasticized, further improving the adhesion of the resulting printed layer to the substrate. Furthermore, both dodecyl methacrylate and octadecyl methacrylate are compounds derived from biological materials. Specifically, dodecyl methacrylate and octadecyl methacrylate are methacrylic acid esters of dodecanol and octadecyl alcohol, which are obtained from palm oil, coconut oil, etc., and are environmentally friendly materials.

[0039] The content of the structural unit (iv) in the polymer is preferably 10 to 30% by mass, and more preferably 10 to 20% by mass. If the content of the structural unit (iv) is less than 10% by mass, the effect of improving hydrophobicity may be insufficient. On the other hand, if the content of the structural unit (iv) is more than 30% by mass, the polymer itself becomes softer due to the long alkyl chain, and the scratch resistance of the resulting printed layer may be slightly reduced.

[0040] The polymer dispersant (polymer) can be produced by a conventionally known polymerization method. For example, it is preferable to polymerize a monomer in the same water-soluble organic solvent as the one used in the ink, since the resulting polymer can be directly incorporated into the ink. The polymer may be produced by a radical polymerization method using an azo-based initiator or a peroxide-based initiator, or a polymer with a uniform molecular weight may be produced by a living radical polymerization method. Alternatively, the structure may be controlled by living radical polymerization to produce a block polymer.

[0041] After polymerization, the carboxyl groups derived from methacrylic acid can be neutralized with an alkali to ionize the polymer and dissolve it in water. Examples of alkalis that can be used include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; ammonia; and organic amines such as trimethylamine, triethylamine, dimethylaminoethanol, diethanolamine, and 2-amino-2-methyl-1-propanol. Among these, volatile alkalis are preferred, with ammonia, dimethylaminoethanol, and 2-amino-2-methyl-1-propanol being particularly preferred. When an ink containing a polymer (polymer dispersant) with carboxyl groups neutralized with a volatile alkali dries after printing, the alkali evaporates, generating the original carboxyl groups, rendering the polymer water-insoluble, further improving the water resistance and water abrasion resistance of the printed layer. Furthermore, the generated carboxyl groups are preferred because they react with the optional crosslinking agent described below, improving the physical properties of the resulting printed layer.

[0042] (Other ingredients) The ink may further contain other components. In particular, adding a crosslinking agent to the ink is preferred because it can further improve the durability and abrasion resistance of the printed layer. The crosslinking agent used is preferably one that can react with carboxy groups in the polymer dispersant or with carboxy and hydroxy groups in the resin binder. Of these, at least one crosslinking agent selected from the group consisting of epoxy-based crosslinking agents, aziridine-based crosslinking agents, carbodiimide-based crosslinking agents, and isocyanate-based crosslinking agents, which can be incorporated into aqueous inks, is preferred. These crosslinking agents contain one or more functional groups, such as epoxy groups, aziridine groups, carbodiimide groups, and isocyanate groups, that react with carboxy and hydroxy groups, and two or more of these functional groups per molecule.

[0043] Commercially available epoxy crosslinking agents include those under the trade name "jER" (manufactured by Mitsubishi Chemical Corporation) and those under the trade name "Denacol" (manufactured by Nagase Chemtec Corporation). Commercially available aziridine crosslinking agents include those under the trade name "Chemitaite" (manufactured by Nippon Shokubai Co., Ltd.). Commercially available carbodiimide crosslinking agents include those under the trade name "Carbodilite" (manufactured by Nisshinbo Chemical Co., Ltd.). Specific examples of isocyanate crosslinking agents include hexamethylene diisocyanate, isophorone diisocyanate, and their adducts and biuret-modified derivatives. Specific examples also include those having a structure in which these are blocked with oxime or the like. Commercially available isocyanate crosslinking agents include those under the trade name "Duranate" (manufactured by Asahi Kasei Corporation).

[0044] The content of the crosslinking agent (solid content) in the ink is preferably 0.1 to 10 mass % based on the total amount of the ink, and more preferably 0.5 to 5 mass %.

[0045] Examples of other components besides the crosslinking agent include organic solvents other than the above-mentioned water-soluble organic solvents, leveling agents, surface tension adjusters, surfactants, pH adjusters, ultraviolet absorbers, light stabilizers, antioxidants, dyes, fillers, waxes, plasticizers, matting agents, antifoaming agents, antisettling agents, thickeners, antifungal agents, antibacterial agents, antistatic agents, etc. Among these, from the viewpoint of further improving the adhesion of the dried film (printed layer) to the substrate and the abrasion resistance, it is preferable for the ink to further contain a wax component.

[0046] (Method for manufacturing water-based white ink) The ink of this embodiment can be produced according to a conventional method. For example, the desired ink can be obtained by mixing a white pigment, water, a water-soluble organic solvent, a resin binder, and a polymer dispersant. Alternatively, water, a white pigment, and a polymer dispersant can be blended, and a water-soluble organic solvent can be further blended as needed, and the resulting mixture can be thoroughly dispersed using a disperser such as a bead mill to obtain a pigment dispersion. The desired ink can also be obtained by using the resulting pigment dispersion and adding water or a water-soluble organic solvent to achieve a predetermined pigment concentration, as well as further adding and mixing other additives including a resin binder and a crosslinking agent. After blending and thoroughly mixing the various materials, it is preferable to remove dust and impurities by filtering or the like.

[0047] The crosslinking agent may be blended into the ink in advance, but is preferably blended into the ink immediately before printing. If ink containing a crosslinking agent is left to stand for a long period of time, the functional groups of the crosslinking agent may react with water, functional groups in the polymer dispersant or resin binder, water-soluble organic solvents, alkalis, etc., resulting in gelation or loss of the crosslinking groups, which may make it difficult to exert the crosslinking effect.

[0048] (Physical properties of water-based white ink) The viscosity of the ink measured at 25°C using Zahn cup #4 is preferably 5 to 30 seconds, and the surface tension of the ink at 25°C is preferably 20 to 50 mN / m.

[0049] (printing base material) The ink of this embodiment is a water-based white ink used for label printing. Therefore, labels made of any material can be used as the printing substrate. Examples of labels include polyester films such as polyethylene terephthalate and polylactic acid; polyamide films such as nylon 6; polyolefin films such as polypropylene and polyethylene; polystyrene films; polyimide films; polycarbonate films; and polyvinyl chloride films. These films may be surface-treated by corona treatment, plasma treatment, or the like. They may also be provided with an anchor coating agent layer or adhesive layer to improve adhesion. These films may also be stretched. Other examples include films provided with a metal vapor deposition layer such as aluminum, and films provided with a transparent vapor deposition layer such as alumina or silica.

[0050] The ink of this embodiment is suitable as a water-based white ink used for printing beverage labels attached to beverage bottles. The printed layer, which is a dried film formed using the ink of this embodiment, has excellent water resistance. Therefore, a printed layer that is difficult to peel off can be formed even if water droplets adhere to the bottle or the bottle is cooled by pouring water on it. Furthermore, shrink labels for beverages such as PET bottles are also suitable as beverage labels. Even if the film is shrunk by applying heat after the ink is applied, the printed layer is unlikely to be disturbed, and its adhesion to the film and abrasion resistance are unlikely to decrease.

[0051] The various films mentioned above can be used as the substrate for the shrink label. The shrink film that constitutes the shrink label is preferably a film that is oriented uniaxially, biaxially, or multiaxially.

[0052] <Dry film> One embodiment of the dried film of the present invention is a dried product of the above-mentioned water-based white ink. The dried film of this embodiment is a printed layer formed by applying the above-mentioned ink to a substrate such as a film, printing, and then drying to remove water and water-soluble organic solvents. The thickness of the dried film is preferably 0.1 to 20 μm. The dried film has good adhesion to the substrate, excellent abrasion resistance, designability, and hiding power, and also has a high white density. Furthermore, the dried film is environmentally friendly because it contains components derived from biological materials, making it a carbon-neutral printed layer. [Example]

[0053] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. In the examples and comparative examples, "parts" and "%" are by mass unless otherwise specified.

[0054] <Production of polymer dispersants> (Synthesis Example 1) 50 parts of isopropyl alcohol (IPA) and 50 parts of diethylene glycol monomethyl ether (BDG) were placed in a reaction vessel and heated to 80°C while bubbling with nitrogen. In a separate vessel, 40 parts of tetrahydrofurfuryl methacrylate (THFMA), 40 parts of isobornyl methacrylate (IBXMA), 20 parts of methacrylic acid (MAA), and 3 parts of 2,2'-azobis(2-methylbutyronitrile) (V-59) (trade name "V-59"; Fujifilm Wako Pure Chemical Industries, Ltd.) were mixed uniformly to prepare a monomer mixture. THFMA is a bio-derived methacrylate, a reaction product of tetrahydrofurfuryl alcohol, a hydrogenated form of furfural obtained from corn cobs, with methacrylic acid. IBXMA is a bio-derived methacrylate, a reaction product of borneol, obtained as camphene by isomerization of α-pinene from pine resin and pine essential oil, with methacrylic acid. The prepared monomer mixture was added dropwise to the reactor over 2 hours, and polymerization was carried out at 80°C for 5 hours to obtain a polymer solution.

[0055] A sample was dried in a dryer at 150°C, and the solids content calculated from the residue at the time of constant weight was 49.8%, confirming that most of the polymer had polymerized. The number average molecular weight (Mn) of the polymer, calculated in terms of polystyrene, was 14,000, and the molecular weight distribution (PDI = weight average molecular weight (Mw) / number average molecular weight (Mn)) was 2.04, as measured by gel permeation chromatography (GPC) using tetrahydrofuran as the developing solvent. The acid value of the polymer was measured by dissolving it in a 1 / 1 toluene / ethanol solution and titrating it with 0.1N potassium hydroxide ethanol solution using phenolphthalein as an indicator, and was found to be 130.0 mgKOH / g.

[0056] 14.2 parts of 28% aqueous ammonia and 85.8 parts of ion-exchanged water were added to neutralize the carboxyl groups and convert the polymer into an aqueous solution, yielding a pale yellow, transparent liquid solution of polymer dispersant PD-1. The solids content of the resulting solution was 39.5%. The pH of the solution, measured after diluting 10 times with ion-exchanged water, was 8.9.

[0057] (Synthesis Examples 2 to 11) Solutions of polymer dispersants PD-2 to PD-11 were obtained in the same manner as in the above-described Example 1, except that various materials were used in the types and amounts (unit: parts) shown in Table 1. Various physical properties are shown in Table 1. The meanings of the abbreviations in Table 1 are as follows: PEGMA: Polyethylene glycol monomethyl ether (molecular weight 400) methacrylate LMA: Lauryl methacrylate StMA: Stearyl methacrylate AMP: 2-amino-2-methyl-1-propanol DMAE: N,N-dimethylaminoethanol

[0058] TIFF0007727604000001.tif106170

[0059] (Comparative Synthesis Example 1) A solution of polymer dispersant HPD-1 was obtained in the same manner as in Example 1, except that 15 parts of methyl methacrylate (MMA), 20 parts of butyl methacrylate (BMA), 30 parts of 2-ethylhexyl methacrylate (2EHMA), 20 parts of 2-hydroxyethyl methacrylate (HEMA), 15 parts of MAA, and 3 parts of AIBN were used for polymerization. The Mn of the resulting polymer dispersant (polymer) was 13,600, the PDI was 2.01, and the acid value was 97.6 mg KOH / g. The pH of the resulting solution was 8.6, and the solids content was 40.0%.

[0060] (Comparative Synthesis Example 2) A reaction vessel was charged with 100 parts of a monoamino compound (a methyl ether-terminated polyethylene glycol (EO) / polypropylene glycol (PO) random copolymer, a monoamino group at one end (amine value = 27.9 mg KOH / g, EO / PO = 3 / 1 (molar ratio)), and 10 parts of polystyrene / maleic acid (1 / 1 molar ratio, Mn 2,300). The mixture was heated to 130 °C and homogenized. The reaction was continued for 3 hours while dehydrating, until the acid value reached 29.0 mg KOH / g. After cooling to 100 °C, the mixture was diluted with ion-exchanged water to obtain a solution of polymer dispersant HPD-2 with a solids content of 40.0%. The resulting polymer dispersant (polymer) had an Mn of 12,000 and a PDI of 1.85. The pH of the resulting solution was 4.6. The obtained polymer dispersant HPD-2 is a polymer having a structure in which polystyrene / maleic acid is grafted with polyalkylene glycol via amide bonds, cyclic imide bonds, and ionic bonds between carboxylic acid and amino groups.

[0061] <Preparing various materials> (binder) The following binders were prepared: A-1: Water-based styrene-acrylic emulsion, manufactured by BASF Japan Ltd., trade name "Joncryl PDX-7430", Mw 200,000, Tg 30°C, minimum film formation temperature 44°C, acid value 20 mg KOH / g, non-volatile content 38% A-2: Water-based styrene-acrylic emulsion, manufactured by BASF Japan Ltd., trade name "Joncryl PDX-7356", Mw 100,000-200,000, Tg 40°C, acid value 78 mg KOH / g, non-volatile content 45.5% A-3: Water-based acrylic-urethane emulsion, manufactured by Taisei Fine Chemical Co., Ltd., product name "WEM-200U", Tg 27°C, acid value 6mgKOH / g, non-volatile content 38% A-4: Aqueous urethane resin dispersion, manufactured by Mitsui Chemicals, Inc., product name "Takelac W-6010", 100% modulus 14 MPa, Tg 90°C, number average particle size 0.06 μm, solid content 30%) A-5: Water-based acrylic emulsion, manufactured by Daicel Allnex Corporation, product name "VIACRYL VSC 6254W / 40WA", minimum film-forming temperature 53°C, acid value 0mgKOH / g, hydroxyl value 60mgKOH / g, number average particle size 0.11μm

[0062] (Crosslinking agent) The following crosslinking agents were prepared: B-1: Epoxy crosslinking agent, Nagaze Chemtech Co., Ltd., product name "Denacol EX-612", non-volatile content 100% B-2: Carbodiimide crosslinking agent, manufactured by Nisshinbo Chemical Co., Ltd., trade name "Carbodilite E-02", non-volatile content 40% B-3: Aziridine-based crosslinking agent, manufactured by Nippon Shokubai Co., Ltd., trade name "ChemiTite DZ-22E", non-volatile content 30% B-4: Isocyanate crosslinking agent, manufactured by Asahi Kasei Corporation, product name "Duranate WB40-100", non-volatile content 100%

[0063] (Other additives) The following other additives were prepared: Wax: Polyethylene wax: BASF Japan, trade name "Joncryl Wax 26", volume average particle size 0.05 μm, non-volatile content 25%, melting point 130°C Thickener: Urethane associative thickener, manufactured by San Nopco, product name "SN Thickener 612", non-volatile content 40% Antifoaming agent: Evonik, product name "Tegoformex 805N", non-volatile content 20% Surfactant: Evonik, product name "Tegowet 500", non-volatile content 100%

[0064] <Manufacturing of water-based flexographic white ink> Example 1 A mixture of 40 parts of titanium dioxide (trade name "R-960" manufactured by DuPont), 7.5 parts of water, and 5.1 parts of a solution of polymer dispersant PD-1 (2 parts as solids) was kneaded and dispersed in a bead mill. Then, 31.4 parts of binder A-1 (12 parts as solids), 2.4 parts of crosslinker B-1 (2.4 parts as solids), 5 parts of wax, 0.08 parts of thickener (0.08 parts as solids), 0.04 parts of defoamer (0.04 parts as solids), and 0.2 parts of surfactant were added. The mixture was thoroughly mixed using a disperser and then diluted with water to a viscosity of 16 seconds (25°C) in a Zahn Cup #4 (manufactured by Rigo Co., Ltd.) to obtain a water-based flexographic ink, white ink W-1.

[0065] (Examples 2 to 16, Comparative Examples 1 and 2) White inks W-2 to 16, HW-1, and HW-2, which are water-based flexographic inks, were obtained in the same manner as in Example 1 above, except that the materials shown in Table 2 were used.

[0066] TIFF0007727604000002.tif136170

[0067] <Production of printed materials> A plastic film (uniaxially shrinkable PET film, trade name "Toyobo Space Clean S7053", manufactured by Toyobo Co., Ltd., thickness 40 μm) was prepared. The cell volume was 6.0 cm. 3 / m 2 A flexo hand proofer equipped with an anilox roll was used as the applicator, and the coating weight after drying was 1.0 g / m. 2 Each white ink was applied to a plastic film. After application, the film was dried at 25°C for 72 hours to obtain a printed matter in which a printed layer, a dry film with a thickness of approximately 0.85 μm, was formed on one side of the plastic film.

[0068] <Evaluation> The following evaluations were carried out, and the evaluation results are shown in Table 3. In the evaluation criteria shown below, "◎", "◯", and "△" were considered to be acceptable, and "×" was considered to be unacceptable.

[0069] (white density) The white density (optical density (OD value)) of the printed matter (printed layer) was measured using a transmission densitometer (product name "361T", manufactured by X-Rite). The OD values were measured at three random locations, and the average value was used. The larger the OD value, the higher the whiteness. An OD value of 0.185 or higher was considered to be acceptable.

[0070] (blocking resistance) A uniaxially shrinkable PET film (product name "Toyobo Space Clean S7053", manufactured by Toyobo Co., Ltd., thickness 40 μm) was placed on the printed material so as to contact the printed layer, and the film was compressed at 4 kg / cm 2 The printed matter was left in a thermostatic chamber at 40° C. for 24 hours with a load of 1000 kJ / s applied. Thereafter, the PET film was peeled off from the printed matter, and the blocking resistance was evaluated according to the following evaluation criteria. ⊚: There was no peel resistance and no transfer of the printed layer to the PET film was observed. ◯: Very slight resistance to peeling was felt, but no transfer of the printed layer to the PET film was observed. Δ: Some resistance to peeling was felt, but no transfer of the printed layer to the PET film was observed. ×: Considerable resistance to peeling was felt, and transfer of the printed layer to the PET film was observed.

[0071] (water resistance) A water resistance test was conducted by immersing the printed material in a sealed container filled with tap water and storing it at 40°C for 24 hours. After the water resistance test, the changes in the printed layer were visually observed, and the water resistance was evaluated according to the evaluation criteria shown below. ○: The printed layer was unchanged. Δ: The printed layer was whitened and slightly detached from the film. ×: The printed layer was whitened and detached from the film.

[0072] (adhesion) After printing, 18 mm wide cellophane tape (manufactured by Nichiban Co., Ltd.) was applied to the surface of the printed layer of the printed matter 15 minutes, 30 minutes, 1 hour, and 3 hours after printing at room temperature and pressed with a finger. The pressed cellophane tape was then quickly peeled off. The condition of the printed layer remaining on the film was visually confirmed, and the adhesion of the printed layer to the substrate was evaluated according to the following evaluation criteria. ⊚: The printed layer was not peeled off at all. ◯: The ratio of the area of the printed layer peeled off from the film to the adhesive area of the cellophane tape was more than 0% and less than 20%. Δ: The ratio of the area of the printed layer peeled off from the film to the adhesive area of the cellophane tape was 20% or more and less than 70%. ×: The ratio of the area of the printed layer peeled off from the film to the adhesive area of the cellophane tape was 70% or more.

[0073] (Water abrasion resistance) The surface of the printed layer of test pieces cut out from the printed matter was rubbed back and forth 50 times with a water-soaked cotton cloth at a load of 200 g using a Gakushin-type rub fastness tester (product name "AB-301", manufactured by Tester Sangyo Co., Ltd.). The degree of peeling of the printed layer from each test piece was then visually confirmed, and the water rub resistance of the printed layer was evaluated according to the following evaluation criteria. ○: No ink peeling from the printed layer. ×: Ink peeled off from the printed layer.

[0074] (Adhesion after shrinkage) A 20 cm long print was immersed in hot water at 90°C for 30 seconds and shrunk to a length of 15 cm. After shrinkage, an 18 mm wide piece of cellophane tape (manufactured by Nichiban Co., Ltd.) was applied to the surface of the printed layer of the printed matter and pressed with a finger. The cellophane tape was then quickly peeled off. The condition of the printed layer remaining on the film was visually confirmed, and the adhesion of the printed layer to the substrate (adhesion after shrinkage) was evaluated according to the following evaluation criteria. ⊚: The printed layer was not peeled off at all. ◯: The ratio of the area of the printed layer peeled off from the film to the adhesive area of the cellophane tape was more than 0% and less than 20%. Δ: The ratio of the area of the printed layer peeled off from the film to the adhesive area of the cellophane tape was 20% or more and less than 70%. ×: The ratio of the area of the printed layer peeled off from the film to the adhesive area of the cellophane tape was 70% or more.

[0075] TIFF0007727604000003.tif148170 [Industrial Applicability]

[0076] The water-based white ink of the present invention is capable of forming a printed layer (dried film) that exhibits excellent water resistance, blocking resistance, and water abrasion resistance, and is useful as a white ink for label printing on a printing substrate such as a plastic film. Furthermore, since it is capable of forming a printed layer that exhibits excellent water resistance and water abrasion resistance, it is useful as a white ink for printing on beverage labels that frequently come into contact with moisture. Furthermore, since it is capable of forming a printed layer that maintains adhesion even when the printing substrate shrinks, it is useful as a white ink for printing on shrink labels for beverages. Furthermore, since it can use monomers derived from biological materials, it is environmentally friendly, leading to increased environmental awareness among consumers, and taking into consideration the prevention of global warming, making it useful as a non-petroleum product.

Claims

1. A water-based white ink used for label printing, The ink contains a white pigment, water, a water-soluble organic solvent, a resin binder, and a polymer dispersant that disperses the white pigment, the polymer dispersant is a polymer in which at least a portion of the carboxy groups are neutralized with an alkali, the polymer comprising a structural unit (i) derived from methacrylic acid and a structural unit (ii) derived from a first methacrylate derived from a biological material; The acid value of the polymer is 30 to 250 mg KOH / g; the content of the structural unit (ii) in the polymer is 50% by mass or more, the number average molecular weight of the polymer is 5,000 to 20,000, and the molecular weight distribution (weight average molecular weight / number average molecular weight) is 2.5 or less; the first methacrylate is at least one of tetrahydrofurfuryl methacrylate and isobornyl methacrylate; the polymer further comprises a structural unit (iii) derived from polyethylene glycol monomethyl ether (molecular weight 400 to 4,000) methacrylate; The water-based white ink has a content of the structural unit (iii) in the polymer of 10 to 30 mass %.

2. the polymer further comprises a constitutional unit (iv) derived from a second methacrylate derived from a biological material; the content of the structural unit (iv) in the polymer is 10 to 30% by mass, 2. The water-based white ink according to claim 1, wherein the second methacrylate is at least one of dodecyl methacrylate and octadecyl methacrylate.

3. 3. The water-based white ink according to claim 1, wherein the alkali is at least one selected from the group consisting of ammonia, dimethylaminoethanol, and 2-amino-2-methyl-1-propanol.

4. the resin binder is at least one resin dispersion selected from the group consisting of an acrylic emulsion, a styrene-acrylic emulsion, an acrylic-urethane emulsion, and a urethane aqueous dispersion, containing resin particles made of a resin; The acid value of the resin is 80 mg KOH / g or less, 3. The water-based white ink according to claim 1, wherein the number average particle diameter of the resin particles is 30 to 200 nm.

5. 3. The water-based white ink according to claim 1, further comprising at least one crosslinking agent selected from the group consisting of an epoxy-based crosslinking agent, an aziridine-based crosslinking agent, a carbodiimide-based crosslinking agent, and an isocyanate-based crosslinking agent.

6. 3. The water-based white ink according to claim 1, which is used for printing labels for beverages.

7. A dried film which is a dried product of the water-based white ink according to claim 1 or 2.

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