Water-based ink composition, laminate and absorbent article

Abstract

Provided are an aqueous ink composition that can form an ink layer that has excellent adhesion to a plastic film and also has excellent resolubility, a laminate that includes the ink layer, and an absorbent article that includes the laminate. [Solution] The aqueous ink composition for the back sheet of an absorbent article contains a binder resin (A), a pigment (B), and an aqueous medium (C), wherein the binder resin (A) contains an aqueous (meth)acrylic emulsion resin (A1), the aqueous (meth)acrylic emulsion resin (A1) has a minimum film-forming temperature of 40°C or less, and the mass ratio of the pigment (B) to the binder resin (A) calculated as the non-volatile content is 0.3 to 1.0.

Description

[Technical Field]

[0001] The present invention relates to a water-based ink composition, a laminate, and an absorbent article. [Background technology]

[0002] Absorbent articles such as diapers are subjected to printing processes using gravure printing, flexographic printing, etc. to impart design and functionality to them. In view of recent environmental issues and the fact that absorbent articles are worn, there has been an increasing demand for water-based inks (hereinafter also referred to as "water-based inks") for use in printing processes. Absorbent articles are generally configured such that, with the side that comes into contact with the human body being the innermost layer, a surface material, an absorbent material, and a waterproof material (back sheet) are arranged in this order from the innermost layer side. In order to make the design visible from the outside, surface printing is usually performed on the surface of the substrate that constitutes the back sheet, which is the outermost layer, and an ink layer is provided.

[0003] The substrate used for backsheets is typically a milky white polyethylene film composed of calcium carbonate and polyethylene resin. The substrate is manufactured by stretching and processing a polyethylene film containing calcium carbonate, or by applying other special processes. These processes create micropores on the substrate surface, allowing air and water vapor to pass through while blocking water, thereby imparting breathability, waterproofing, and flexibility. To ensure breathability and flexibility, the substrate is designed to be thin, approximately 10–20 μm thick. Corona treatment is sometimes applied to substrates to improve adhesion to the ink layer, but if the substrate is thin, corona treatment with a high discharge rate can cause problems such as holes in the substrate. For this reason, substrates such as milky white polyethylene films used for backsheets are generally not corona-treated or have a low degree of corona treatment.

[0004] The properties required for the water-based ink used in the backsheet include adhesion to the substrate such as milky white polyethylene film, and resolubility to realize excellent printability.

[0005] As an example of a water-based ink, Patent Document 1 discloses a water-based varnish composition containing an acrylic resin emulsion with a minimum film-forming temperature of less than 5°C, which is used for plastic labels on beverage packaging containers. Patent Document 2 discloses an aqueous flexographic printing ink composition that contains a binder resin such as a styrene-acrylic emulsion resin, a pigment, water, and the like, and is used for food packaging paper. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 7348416 [Patent Document 2] Patent Publication No. 2021-038022 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the aqueous varnish composition described in Patent Document 1 and the aqueous flexographic printing ink composition described in Patent Document 2 are not intended for use in absorbent articles such as diapers, and do not necessarily have satisfactory resolubility. Furthermore, the ink layers formed from these water-based inks have insufficient adhesion to plastic films, particularly plastic films that have not been corona-treated or have been only lightly corona-treated.

[0008] The present invention aims to provide an aqueous ink composition that can form an ink layer that has excellent adhesion to plastic films and also has excellent resolubility, a laminate that includes the ink layer, and an absorbent article that includes the laminate. [Means for solving the problem]

[0009] The present invention has the following aspects. [1] An aqueous ink composition for a back sheet of an absorbent article, comprising a binder resin (A), a pigment (B), and an aqueous medium (C), the binder resin (A) contains an aqueous (meth)acrylic emulsion resin (A1), the minimum film-forming temperature of the aqueous (meth)acrylic emulsion resin (A1) is 40°C or lower, The water-based ink composition has a mass ratio of the pigment (B) to the binder resin (A) calculated as nonvolatile matter of 0.3 to 1.0. [2] The aqueous ink composition according to [1] above, wherein the aqueous (meth)acrylic emulsion resin (A1) is a self-crosslinking type. [3] The water-based ink composition according to [1] or [2], wherein the content of the binder resin (A) in terms of non-volatile content is 15 to 35 mass % relative to the total mass of the water-based ink composition. [4] The water-based ink composition according to any one of [1] to [3], wherein the binder resin (A) further contains a water-soluble styrene-(meth)acrylic resin (A2). [5] The aqueous ink composition according to any one of [1] to [4] above, wherein the minimum film-forming temperature of the aqueous (meth)acrylic emulsion resin (A1) is 15°C or lower. [6] Further containing wax (D), The water-based ink composition according to any one of [1] to [5] above, wherein the wax (D) has an average particle size of 8 μm or less and a penetration of 5 or less. [7] The water-based ink composition according to any one of the above [1] to [6], further comprising a silicone (E). [8] The aqueous ink composition according to any one of [1] to [7] above, which is for flexographic printing. [9] A plastic film and an ink layer provided on the plastic film, A laminate, wherein the ink layer is a layer formed using the water-based ink composition according to any one of [1] to [8] above.

[10] An absorbent article comprising the laminate described in [9]. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an aqueous ink composition that can form an ink layer that has excellent adhesion to a plastic film and also has excellent resolubility, a laminate that includes the ink layer, and an absorbent article that includes the laminate. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view schematically illustrating an example of a laminate of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in detail below. The following embodiments are merely examples for explaining the present invention, and are not intended to limit the present invention to these embodiments. The present invention can be implemented in various forms without departing from the spirit of the present invention. In the present invention, the term "aqueous" in the aqueous ink composition means that the composition contains an aqueous medium. "Aqueous medium" means a liquid medium that contains water. The contents of the binder resin (A), pigment (B), wax (D), silicone (E), and optional components in the aqueous ink composition are each expressed as amounts calculated on a non-volatile basis (also referred to as "solids content"). "Non-volatile content" refers to the components contained in the aqueous ink composition excluding volatile components such as the aqueous medium, and is the component that will ultimately form the ink layer. Specifically, it is measured in accordance with JIS K 5601-1-2:2008. The term "coated film" refers to the ink coating film before drying obtained by applying the aqueous ink composition of the present invention onto a substrate. The "ink layer" refers to a layer formed by the aqueous ink composition of the present invention, and is a dried product obtained by drying a coating film and removing volatile components such as the aqueous medium (C) in the coating film. The term "(meth)acrylic" is meant to include both the terms "acrylic" and "methacrylic." The term "(meth)acrylate" is meant to include both the terms "acrylate" and "methacrylate." The term "(meth)acryloyl" is meant to include both the terms "acryloyl" and "methacryloyl." "Self-crosslinking" refers to the formation of a crosslinked structure by reaction between functional groups of the same kind or between different functional groups without the use of a crosslinking agent or the like. "Resolubility" refers to the ability of a coating liquid (aqueous ink composition) remaining on a printing plate such as a flexographic plate to be redissolved in a solvent (such as an aqueous medium (C)) contained in the coating liquid (aqueous ink composition) before it dries and becomes a state that would cause poor transfer when the aqueous ink composition is applied by a printing method. The more easily the coating film dissolves in a solvent (such as an aqueous medium (C)) contained in the coating liquid (aqueous ink composition), the better the resolubility of the aqueous ink composition. Resolubility can be considered one of the important printing suitabilities. In this specification, when the term "excellent printability" is used simply, it means that the printing suitability is excellent due to factors other than resolubility, such as excellent dispersibility of components such as pigments and waxes and excellent transferability to the substrate. The symbol "to" indicating a range of values ​​means that the values ​​before and after it are included as the lower and upper limits. For example, A to B is equivalent to A or more and B or less. The lower and upper limits of the ranges disclosed in this specification can be combined in any way to create new ranges.

[0013] The glass transition temperature of the binder resin (A) is measured as follows in accordance with JIS K 7121:2012: That is, using a differential scanning calorimeter, 10 mg of the binder resin (A) is heated from −100° C. to 160° C. at a rate of 20° C. / min to obtain a curve (DSC curve), and the glass transition temperature of the binder resin (A) is determined from the intersection of the baseline and the tangent to the endothermic curve. The acid value of the binder resin (A) is the amount of potassium hydroxide required to neutralize acid groups such as carboxyl groups per 1 g of the nonvolatile content (solid content) of the sample, expressed in milligrams, and is measured in accordance with JIS K 5601-2-1:1999. The minimum film-forming temperature of the binder resin (A) is measured in accordance with JIS K 6828-2:2003.

[0014] The penetration of the wax (D) is measured by a method conforming to JIS K 2235:2009. The measurement temperature is 25°C. The average particle size of wax (D) is the particle size at 50% cumulative frequency (median size: D50) calculated from the particle size distribution measured by the Coulter Counter method. The Coulter Counter method is a method for electrically measuring the particle size and particle size distribution of wax particles dispersed in a solution by passing them through a fine hole and observing the change in the electrical signal as the particles pass through.

[0015] The pH of the aqueous ink composition is measured using a pH meter while the temperature of the aqueous ink composition is maintained at 25°C.

[0016] [Water-based ink composition] An aqueous ink composition according to one embodiment of the present invention contains a binder resin (A), a pigment (B), and an aqueous medium (C) as shown below. The water-based ink composition preferably further contains one or more selected from the following wax (D) and silicone (E). The water-based ink composition may further contain a basic compound (F) shown below. The aqueous ink composition may further contain components (optional components) other than the binder resin (A), pigment (B), aqueous medium (C), wax (D), silicone (E), and basic compound (F) as necessary, as long as the effects of the present invention are not impaired.

[0017] <Binder resin (A)> The binder resin (A) contains the aqueous (meth)acrylic emulsion resin (A1) shown below. For the purpose of further improving the resolubility and pigment dispersibility of the aqueous ink composition, the binder resin (A) preferably further contains a water-soluble styrene-(meth)acrylic resin (A2) shown below. The binder resin (A) may further contain a resin (hereinafter also referred to as "another resin (A3)") other than the (meth)acrylic emulsion resin (A1) and the water-soluble styrene-(meth)acrylic resin (A2) as necessary, as long as the effects of the present invention are not impaired.

[0018] (Water-based (meth)acrylic emulsion resin) The aqueous (meth)acrylic emulsion resin (A1) (hereinafter simply referred to as "resin (A1)") is a type of water-dispersible acrylic resin. Examples of such resins include emulsion-type resins having a core-shell structure.

[0019] When the resin (A1) has a core-shell structure, the mass ratio of the core portion to the shell portion (core portion:shell portion) is preferably 20:80 to 80:20, more preferably 25:75 to 75:25, and even more preferably 30:70 to 70:30. If the mass ratio of the core portion to the shell portion is greater than the above range and the amount of the shell portion is less than the above range, the ink stability and leveling ability of the aqueous ink composition will decrease. If the mass ratio of the core portion to the shell portion is less than the above range and the amount of the shell portion is greater than the above range, the rub resistance, water rub resistance, ammonia resistance, and oil resistance of the ink layer will decrease.

[0020] When the resin (A1) has a core-shell structure, the core preferably contains a hydrophobic acrylic resin, more preferably a resin containing a (meth)acrylate unit, and the shell preferably contains a hydrophilic resin, more preferably a hydrophilic resin containing a carboxy group, even more preferably a hydrophilic acrylic resin containing a carboxy group. Examples of the core portion include a homopolymer of a (meth)acrylate monomer, a copolymer of two or more types of (meth)acrylate monomers, and a copolymer of a (meth)acrylate monomer and a monomer other than a (meth)acrylate monomer. Examples of the shell portion include a homopolymer of a carboxy group-containing monomer, a copolymer of two or more types of carboxy group-containing monomers, and a copolymer of a carboxy group-containing monomer and a monomer other than the carboxy group-containing monomer. The core and shell may be bonded together by a crosslinking agent.

[0021] Examples of the (meth)acrylate monomer include alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and lauryl (meth)acrylate; cycloalkyl (meth)acrylates such as cyclohexyl (meth)acrylate; aryl (meth)acrylates such as phenyl (meth)acrylate; aralkyl (meth)acrylates such as benzyl (meth)acrylate; and hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate. These (meth)acrylate monomers may be used alone or in combination of two or more.

[0022] The carboxy group-containing monomer is not particularly limited as long as it is a monomer having a carboxy group, and examples thereof include (meth)acrylic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, and itaconic anhydride. These carboxyl group-containing monomers may be used alone or in combination of two or more.

[0023] Examples of the monomer other than the (meth)acrylate monomer and the monomer other than the carboxy group-containing monomer include conjugated diene compounds such as 1,3-butadiene, isoprene, and chloroprene; styrene-based monomers such as α-methylstyrene, halogenated styrene, and vinylstyrene; vinyl cyanide compounds such as acrylonitrile and methacrylonitrile; acrylamides such as N,N-dimethyl(meth)acrylamide and N,N-diethyl(meth)acrylamide; and unsaturated carboxylic acid esters such as diethyl maleate, dibutyl maleate, dibutyl fumarate, diethyl itaconate, and dibutyl itaconate. These (meth)acrylate monomers may be used alone or in combination of two or more. These monomers may be used alone or in combination of two or more.

[0024] The resin (A1) can be obtained by polymerizing the monomers that constitute the resin (A1). The method for polymerizing the monomer is not particularly limited, and examples thereof include radical polymerization such as bulk polymerization, solution polymerization, emulsion polymerization, and suspension polymerization; anionic polymerization; and cationic polymerization. Of these, emulsion polymerization is preferred. Emulsion polymerization is a method in which the monomers to be used for polymerization are polymerized in an aqueous medium in the presence of an emulsifier and a polymerization initiator. Resin (A1) may be produced by separately producing the core and shell portions and then combining them. Alternatively, it may be produced by multi-stage emulsion polymerization. Specifically, first, a monomer or a mixture of monomers constituting the core portion is polymerized to obtain the core portion, and then a monomer or a mixture of monomers constituting the shell portion is polymerized in the presence of the core portion to produce resin (A1) having a core-shell structure. The polymerization mode is not particularly limited, and may be any of random copolymerization, block copolymerization, and graft copolymerization, i.e., the resin (A1) may be any of a random copolymer, a block copolymer, a graft copolymer, etc.

[0025] The resin (A1) may be a self-crosslinking resin. The use of a self-crosslinking resin (A1) improves the blocking resistance of the coating film, and the abrasion resistance, water abrasion resistance, ammonia resistance, and oil resistance of the ink layer. The self-crosslinking resin (A1) preferably contains a structural unit derived from the following monomer (x). Examples of the monomer (x) include an alkoxysilyl group-containing monomer, a hydrazine group-containing monomer, an epoxy group-containing monomer, a methylol group-containing monomer, an alkoxymethyl group-containing monomer, adipic acid dihydrazide, diacetone acrylamide, vinyl acetoacetate, allyl acetoacetate, and acetoacetoxyalkyl (meth)acrylate. Examples of epoxy group-containing monomers include glycidyl (meth)acrylate, 2,3-epoxycyclohexyl (meth)acrylate, 3,4-epoxycyclohexyl (meth)acrylate, and allyl glycidyl ether. Examples of acetoacetoxyalkyl(meth)acrylates include acetoacetoxyethyl(meth)acrylate, acetoacetoxypropyl(meth)acrylate, acetoacetoxybutyl(meth)acrylate, and 2,3-di(acetoacetoxy)propyl(meth)acrylate. These monomers (x) may be used alone or in combination of two or more.

[0026] The minimum film-forming temperature of resin (A1) is 40°C or lower, preferably 30°C or lower, and more preferably 15°C or lower. Furthermore, the minimum film-forming temperature of resin (A1) is preferably -20°C or higher, more preferably -10°C or higher, and even more preferably -5°C or higher. The above upper and lower limits can be combined arbitrarily. For example, the minimum film-forming temperature of resin (A1) is preferably -20 to 40°C, more preferably -10 to 30°C, and even more preferably -5 to 15°C. When the minimum film-forming temperature of the resin (A1) is equal to or lower than the above upper limit, the film-forming properties of the aqueous ink composition, the blocking resistance of the coating film, and the adhesion of the ink layer to substrates such as plastic films, abrasion resistance, water abrasion resistance, ammonia resistance, and oil resistance are further improved.

[0027] The acid value of the resin (A1) is preferably 0 to 200 mgKOH / g, more preferably 0 to 180 mgKOH / g, and even more preferably 0 to 160 mgKOH / g. If the acid value of the resin (A1) is at least the lower limit, the resolubility of the aqueous ink composition is improved, and if it is at most the upper limit, the water rub resistance and ammonia resistance of the ink layer are improved.

[0028] The glass transition temperature of the resin (A1) is preferably 0 to 60° C., more preferably 2 to 40° C., and even more preferably 5 to 30° C. If the glass transition temperature of the resin (A1) is at least the lower limit above, the blocking resistance of the coating film and the heat resistance of the ink layer are improved, and if it is no more than the upper limit above, the adhesion of the ink layer to a substrate such as a plastic film and the abrasion resistance are improved.

[0029] As the resin (A1), a synthetic product or a commercially available product may be used. Commercially available resins (A1) include, for example, the "Hiros-X Series" manufactured by Seiko PMC Corporation, the "Joncryl Series" manufactured by BASF Japan Ltd., and the "Neocryl Series" manufactured by Covestro Coating Resins. These resins (A1) may be used alone or in combination of two or more.

[0030] (Water-soluble styrene-(meth)acrylic resin (A2)) The water-soluble styrene-(meth)acrylic resin (A2) (hereinafter also referred to simply as "resin (A2)") is a copolymer containing a structural unit derived from a styrene-based monomer, a structural unit derived from a carboxyl group-containing monomer, and a structural unit derived from a (meth)acrylate monomer, and is soluble in alkaline water. The resin (A2) may further contain structural units derived from monomers other than styrene-based monomers, carboxyl group-containing monomers, and (meth)acrylate monomers (hereinafter also referred to as "other monomers").

[0031] The styrene-based monomer is not particularly limited as long as it has a styrene structure and is copolymerizable with at least one of a carboxy group-containing monomer and a (meth)acrylate monomer, and examples thereof include α-methylstyrene, halogenated styrene, and vinylstyrene. These styrene-based monomers may be used alone or in combination of two or more.

[0032] The carboxy group-containing monomer is not particularly limited as long as it has a carboxy group and is copolymerizable with at least one of a styrene-based monomer and a (meth)acrylate monomer, and examples thereof include the carboxy group-containing monomers exemplified above in the description of resin (A1). The carboxyl group-containing monomer may be used alone or in combination of two or more kinds.

[0033] The (meth)acrylate monomer is not particularly limited as long as it is a monomer having a (meth)acryloyl group, and examples thereof include the (meth)acrylate monomers exemplified above in the description of resin (A1). The (meth)acrylate monomers may be used alone or in combination of two or more.

[0034] The other monomer is not particularly limited as long as it is a monomer copolymerizable with one or more of a carboxy group-containing monomer, a (meth)acrylate monomer, and a (meth)acrylate monomer, and examples thereof include conjugated diene compounds such as 1,3-butadiene, isoprene, and chloroprene; vinyl cyanide compounds such as acrylonitrile and methacrylonitrile; acrylamides such as N,N-dimethyl(meth)acrylamide and N,N-diethyl(meth)acrylamide; and unsaturated carboxylic acid esters such as diethyl maleate, dibutyl maleate, dibutyl fumarate, diethyl itaconate, and dibutyl itaconate. These other monomers may be used alone or in combination of two or more.

[0035] The resin (A2) can be obtained by polymerizing a monomer mixture containing a styrene-based monomer, a carboxyl group-containing monomer, a (meth)acrylate monomer, and, if necessary, other monomers. The method for polymerizing the monomer mixture is not particularly limited, and examples thereof include the polymerization methods exemplified above in the explanation of resin (A1). For example, in the case of solution polymerization, a monomer mixture is polymerized in the presence of a suitable organic solvent and a polymerization initiator, and then a basic compound is added to neutralize the mixture, and water is further added to remove the organic solvent, thereby obtaining resin (A2). As the polymerization initiator, known initiators can be used, for example, azo initiators such as 2,2-azobisisobutyronitrile, 2,2-azobis(2-methylbutyronitrile), and 1,1-azobis(cyclohexanecarbonitrile); and peroxide initiators such as dialkyl peroxide, diacyl peroxide, peroxydicarbonate, ketone peroxide, and peroxyketal. The polymerization mode is not particularly limited, and may be any of random copolymerization, block copolymerization, and graft copolymerization. That is, the resin (A2) may be any of a random copolymer, a block copolymer, a graft copolymer, etc. The resin (A2) may also be a self-crosslinking type.

[0036] The acid value of the resin (A2) is preferably 140 to 300 mgKOH / g, more preferably 180 to 290 mgKOH / g, and even more preferably 200 to 280 mgKOH / g. If the acid value of the resin (A2) is at least the lower limit, the resolubility and pigment dispersibility of the aqueous ink composition are improved, and if it is at most the upper limit, the water rub resistance and ammonia resistance of the ink layer are improved.

[0037] The glass transition temperature of resin (A2) is preferably 20 to 150° C., more preferably 50 to 135° C., and even more preferably 80 to 120° C. If the glass transition temperature of resin (A2) is at least the above lower limit, the blocking resistance of the coating film and the heat resistance of the ink layer are improved, and if it is at most the above upper limit, the adhesion of the ink layer to substrates such as plastic films and the abrasion resistance are further improved.

[0038] As the resin (A2), a synthetic product or a commercially available product may be used. Commercially available resins (A2) include, for example, the "Hiros-X Series" manufactured by Seiko PMC Corporation, the "Joncryl Series" manufactured by BASF Japan Ltd., and the "Neocryl Series" manufactured by Covestro Coating Resins. These resins (A1) may be used alone or in combination of two or more.

[0039] (Other resins (A3)) Examples of the other resin (A3) include aqueous (meth)acrylic emulsion resins, water-soluble (meth)acrylic resins, aqueous (meth)acrylic urethane resins, aqueous urethane resins, aqueous polyester resins, aqueous polyamide resins, aqueous vinyl chloride-vinyl acetate copolymer resins, aqueous cellulose resins, aqueous epoxy resins, and aqueous olefin resins, all of which have a minimum film-forming temperature of more than 40°C. These other resins (A3) may be used singly or in combination of two or more.

[0040] <Basic Compound (F)> When the resin (A1) has a core-shell structure and the shell contains a hydrophilic resin containing a carboxy group, the carboxy group in the shell of the resin (A1) is preferably neutralized with a basic compound (F), and the carboxy group in the resin (A2) is preferably neutralized with a basic compound (F). Neutralization of the carboxy groups of these resins (A1) and (A2) further improves the resolubility of the aqueous ink composition.

[0041] Examples of the basic compound (F) capable of neutralizing the carboxy groups of the resin (A1) and the resin (A2) include ammonia, triethylamine, morpholine, monoethanolamine, N-methylethanolamine, N,N-dimethylaminoethanol, N,N-diethylaminoethanol, etc. Among these, ammonia and N,N-dimethylaminoethanol are preferred. These basic compounds (F) may be used alone or in combination of two or more.

[0042] <Pigment (B)> As the pigment (B), known pigments used as colorants etc. can be used, including, for example, organic pigments and inorganic pigments. Examples of organic pigments include azo pigments such as monoazos and condensed azos; threne pigments such as anthraquinones, perinones, perylenes, and thioindigos; phthalocyanine pigments such as phthalocyanine blue and phthalocyanine green; quinacridone pigments; dioxazine pigments; isoindolinone pigments; pyrrolopyrrole pigments; aniline black; and organic fluorescent pigments. Examples of inorganic pigments include natural products such as clay, baryte, mica, and talc; ferrocyanides such as Prussian blue, sulfides such as zinc sulfide; sulfates such as barium sulfate; oxides such as chromium oxide, zinc white, titanium oxide, and iron oxide; hydroxides such as aluminum hydroxide; silicates such as calcium silicate and ultramarine; carbonates such as calcium carbonate and magnesium carbonate; carbon such as carbon black and graphite; metal powders such as aluminum powder, bronze powder, and zinc powder; and calcined pigments. These pigments (B) may be used alone or in combination of two or more.

[0043] <Aqueous medium (C)> Examples of the aqueous medium (C) include water and mixed solvents of water and organic solvents. The organic solvent is not particularly limited as long as it is soluble in water, and examples thereof include alcohol-based solvents such as methanol, ethanol, n-propanol, i-propanol, n-butanol, and i-butanol; ketone-based solvents such as acetone; and glycol ether-based solvents such as propylene glycol monomethyl ether. These aqueous media (C) may be used alone or in combination of two or more. As the aqueous medium (C), water is preferred from the viewpoint of reducing the impact on the environment and volatile organic compounds (VOCs).

[0044] <Wax (D)> When the water-based ink composition contains the wax (D), the blocking resistance of the coating film and the water rub resistance and rub resistance of the ink layer are improved. The wax (D) is preferably a water-based wax. Aqueous wax is a wax dispersed in water to form an emulsion or dispersion. Known waxes can be used as the wax to be dispersed in water, including polyethylene wax, polypropylene wax, modified paraffin wax, carnauba wax, and polytetrafluoroethylene wax. Among these, polyethylene wax and polypropylene wax are preferably used. These waxes (D) may be used alone or in combination of two or more.

[0045] The average particle size of wax (D) is preferably 8 μm or less, more preferably 7.5 μm or less, and even more preferably 7 μm or less. The average particle size of wax (D) is preferably 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more. The above upper and lower limits can be combined arbitrarily. For example, the average particle size of wax (D) is preferably 0.1 to 8 μm, more preferably 0.5 to 7.5 μm, and even more preferably 1 to 7 μm. When the average particle size of the wax (D) is equal to or greater than the lower limit, the blocking resistance of the coating film and the rub resistance of the ink layer are improved. When the average particle size of the wax (D) is equal to or less than the upper limit, poor transfer of the wax (D) to the substrate can be suppressed, and the printability of the aqueous ink composition can be maintained at a good level. In addition, the water rub resistance, oil resistance, and color development of the ink layer are improved.

[0046] The penetration of the wax (D) is preferably not more than 5, more preferably not more than 4, and even more preferably not more than 3. The lower limit of the penetration of the wax (D) is not particularly limited, but is, for example, 0.1 or more. When the penetration of the wax (D) is equal to or less than the upper limit, the blocking resistance of the coating film and the rub resistance of the ink layer are improved.

[0047] <Silicone (E)> When the water-based ink composition contains the silicone (E), the abrasion resistance and water abrasion resistance of the ink layer are further improved. The silicone (E) is a compound having a siloxane bond. Examples of the silicone (E) include polyorganosiloxanes such as polydimethylsiloxane. The polyorganosiloxane may be partially modified with an organic group or may not be modified, but organic modification is preferred because it improves solubility and dispersibility in an aqueous medium. The polyorganosiloxane may be reactive or non-reactive. The polyorganosiloxane may be in the form of an oil, emulsion, or dispersion. The silicone (E) may be copolymerized with an acrylic resin skeleton. In this specification, polyorganosiloxanes partially modified with organic groups are also referred to as "modified polyorganosiloxanes" or "modified silicones."

[0048] Examples of modified polyorganosiloxanes include polyether-modified polyorganosiloxanes, amino-modified polyorganosiloxanes, epoxy-modified polyorganosiloxanes, alkyl-modified polyorganosiloxanes, polyester-modified polyorganosiloxanes, polyetherester-modified polyorganosiloxanes, and phenyl-modified polyorganosiloxanes. Among these, polyether-modified polyorganosiloxanes are preferred from the viewpoint of improving compatibility with components other than silicone. Furthermore, amino-modified polyorganosiloxanes and epoxy-modified polyorganosiloxanes are preferred from the viewpoint of improving dispersibility in the aqueous medium (C).

[0049] As the silicone (E), polydimethylsiloxane is preferred, and polyether-modified polydimethylsiloxane, amino-modified polydimethylsiloxane, and epoxy-modified polydimethylsiloxane are more preferred. These silicones (E) may be used alone or in combination of two or more.

[0050] As the silicone (E), a commercially available product may be used. Examples of commercially available silicone (E) products include the "BYK series" manufactured by BYK; the "KF series," "KP series," "KM series," "X series," "PAM-E," and "POLON series" manufactured by Shin-Etsu Chemical Co., Ltd.; the "DOWSIL series" manufactured by Dow-Toray Industries, Inc.; and the "TEGOGLIDE series" manufactured by EVONIK.

[0051] <Optional ingredients> As the optional components, known additives can be used. Specific examples of additives include thickeners, anti-settling agents, ultraviolet absorbers, antioxidants, leveling agents, viscoelasticity modifiers, surface tension modifiers, rheology modifiers, light stabilizers, antifoaming agents, lubricants, dispersants, stabilizers, fillers, anti-mold agents, antistatic agents, metal fine particles, and magnetic powders. These optional components may be used alone or in combination of two or more.

[0052] <Content> The content of the binder resin (A) in terms of nonvolatile content is preferably 15 to 35 mass %, more preferably 18 to 32 mass %, and even more preferably 20 to 30 mass %, based on the total mass of the aqueous ink composition. The content of the binder resin (A) in terms of nonvolatile content is preferably 40 to 70 mass %, more preferably 45 to 68 mass %, and even more preferably 50 to 65 mass %, based on the total mass of the nonvolatile content of the aqueous ink composition. If the content of the binder resin (A) is at least the above lower limit, the adhesion of the ink layer to a substrate such as a plastic film, as well as the abrasion resistance, water abrasion resistance, ammonia resistance, and oil resistance, will be further improved. If the content of the binder resin (A) is at most the above upper limit, the resolubility of the aqueous ink composition and the blocking resistance of the coating film will be further improved.

[0053] The content of the resin (A1) in terms of nonvolatile content is preferably from 12 to 35 mass %, more preferably from 15 to 32 mass %, and even more preferably from 17 to 30 mass %, relative to the total mass of the aqueous ink composition. The content of the resin (A1) in terms of nonvolatile content is preferably 40 to 70 mass %, more preferably 45 to 68 mass %, and even more preferably 50 to 65 mass %, based on the total mass of the nonvolatile content of the aqueous ink composition. If the content of resin (A1) is at least the above lower limit, the abrasion resistance, water abrasion resistance, and ammonia resistance of the ink layer are improved, and if it is at most the above upper limit, the resolubility of the aqueous ink composition is improved.

[0054] The content of the resin (A2) in terms of nonvolatile content is preferably 10% by mass or less, more preferably 0.1 to 10% by mass, even more preferably 0.5 to 5% by mass, and particularly preferably 1 to 3% by mass, relative to the total mass of the aqueous ink composition. The content of the resin (A2) in terms of nonvolatile content is preferably 15 mass % or less, more preferably 0.5 to 15 mass %, even more preferably 1 to 10 mass %, and particularly preferably 2 to 5 mass %, based on the total mass of the nonvolatile content of the aqueous ink composition. When the content of resin (A2) is equal to or greater than the above lower limit, the pigment dispersibility and resolubility of the aqueous ink composition are further improved, and when the content is equal to or less than the above upper limit, the abrasion resistance, water abrasion resistance, and ammonia resistance of the ink layer are further improved.

[0055] The content of the pigment (B) in terms of nonvolatile content is preferably from 1 to 50 mass %, more preferably from 1 to 45 mass %, and even more preferably from 1 to 40 mass %, relative to the total mass of the aqueous ink composition. The content of the pigment (B) in terms of nonvolatile content is preferably 1 to 60 mass %, more preferably 1 to 55 mass %, and even more preferably 1 to 50 mass %, based on the total mass of the nonvolatile content of the aqueous ink composition. If the content of pigment (B) is equal to or greater than the above lower limit, the hiding power and color development of the ink layer will be improved, and if it is equal to or less than the above upper limit, the fluidity of the aqueous ink composition and the adhesion of the ink layer to a substrate such as a plastic film will be improved.

[0056] The mass ratio of pigment (B) to binder resin (A) calculated as nonvolatile content (hereinafter also referred to as "B / A ratio") is 0.3 to 1.0, preferably 0.35 to 0.8, and more preferably 0.4 to 0.7. If the B / A ratio is equal to or greater than the lower limit, the resolubility of the aqueous ink composition and the blocking resistance of the coating film are improved, while if the B / A ratio is equal to or less than the upper limit, the adhesion of the ink layer to substrates such as plastic films, as well as rub resistance, water rub resistance, ammonia resistance, and oil resistance are improved.

[0057] The content of the aqueous medium (C) is preferably 20 to 84 mass %, more preferably 30 to 80 mass %, and even more preferably 40 to 70 mass %, based on the total mass of the aqueous ink composition. If the content of the aqueous medium (C) is equal to or greater than the lower limit, the fluidity of the aqueous ink composition is improved, and if it is equal to or less than the upper limit, the drying properties of the coating film are improved.

[0058] The sum of the content of the binder resin (A) and the pigment (B) in terms of nonvolatile content and the content of the aqueous medium (C) is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, relative to the total mass of the aqueous ink composition, and may be 100% by mass. The total content of the binder resin (A) and the pigment (B) in terms of nonvolatile content is preferably 16 to 70 mass %, more preferably 20 to 60 mass %, and even more preferably 30 to 50 mass %, relative to the total mass of the aqueous ink composition. The total content of the binder resin (A) and the pigment (B) in terms of nonvolatile content is preferably 75% by mass or more, more preferably 80% by mass or more, and even more preferably 85% by mass or more, relative to the total mass of the nonvolatile content of the aqueous ink composition, and may be 100% by mass.

[0059] When the aqueous ink composition contains wax (D), the content of wax (D) in terms of non-volatile matter is preferably 0.1 to 10 mass %, more preferably 0.5 to 8 mass %, and even more preferably 1 to 5 mass %, relative to the total mass of the aqueous ink composition. When the aqueous ink composition contains wax (D), the content of wax (D) in terms of non-volatile content is preferably 1 to 20 mass %, more preferably 1.5 to 10 mass %, and even more preferably 2 to 8 mass %, based on the total mass of the non-volatile content of the aqueous ink composition. When the content of wax (D) is equal to or greater than the above lower limit, the blocking resistance of the coating film and the abrasion resistance of the ink layer are improved, and when the content is equal to or less than the above upper limit, the printability of the aqueous ink composition and the color development of the ink layer are improved.

[0060] When the aqueous ink composition contains a silicone (E), the content of the silicone (E) in terms of non-volatile content is preferably 0.01 to 5 mass %, more preferably 0.05 to 1 mass %, and even more preferably 0.1 to 0.5 mass %, relative to the total mass of the aqueous ink composition. When the aqueous ink composition contains a silicone (E), the content of the silicone (E) in terms of non-volatile content is preferably 0.05 to 5 mass %, more preferably 0.1 to 3 mass %, and even more preferably 0.2 to 1 mass %, relative to the total mass of the non-volatile content of the aqueous ink composition. If the content of silicone (E) is equal to or greater than the above lower limit, the abrasion resistance and water abrasion resistance of the ink layer are further improved, and if it is equal to or less than the above upper limit, the abrasion resistance of the ink layer is improved.

[0061] When the aqueous ink composition contains a basic compound (F), the content of the basic compound (F) is preferably 0.1 to 5 mass %, more preferably 0.1 to 4 mass %, and even more preferably 0.1 to 3 mass %, relative to the total mass of the aqueous ink composition. If the content of the basic compound (F) is equal to or greater than the above lower limit, the resolubility of the aqueous ink composition is further improved, and if it is equal to or less than the above upper limit, the water rub resistance of the ink layer is further improved.

[0062] The sum of the contents of the binder resin (A), pigment (B), wax (D) and silicone (E) calculated as nonvolatile components, the content of the aqueous medium (C), and the content of the basic compound (F) is preferably 80% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more, relative to the total mass of the aqueous ink composition, and may be 100% by mass. The total content of the binder resin (A), pigment (B), wax (D) and silicone (E) in terms of nonvolatile content is preferably 85% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, based on the total mass of the nonvolatile content of the aqueous ink composition, and may be 100% by mass.

[0063] The content of optional components is not particularly limited as long as it is within a range that does not impair the effects of the present invention, but for example, it is preferably 0 to 20 mass % relative to the total mass of the aqueous ink composition, more preferably 0 to 15 mass %, and even more preferably 0 to 10 mass %. When the aqueous ink composition contains optional components, the content of the optional components is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.5% by mass or more, relative to the total mass of the aqueous ink composition. When the content of the optional components is equal to or greater than the above lower limit, the effects of the optional components are fully exhibited.

[0064] <Physical properties> The pH of the aqueous ink composition at 25°C is preferably 7 to 11, more preferably 7.5 to 11, and even more preferably 8 to 11. When the pH of the aqueous ink composition is equal to or higher than the above lower limit, the storage stability of the aqueous ink composition is improved, and when the pH is equal to or lower than the above upper limit, good workability can be maintained when the aqueous ink composition is applied to a substrate or the like.

[0065] <Manufacturing method> The aqueous ink composition of this embodiment can be obtained, for example, by mixing the binder resin (A), the pigment (B), and the aqueous medium (C) with one or more of the wax (D), the silicone (E), the basic compound (F), and the optional components, as needed, so that the desired content of each component is achieved, and then, as needed, by performing a dispersion treatment. The method for mixing the components is not particularly limited, and the components can be mixed by various methods. The dispersion treatment method is not particularly limited, and can be carried out using a known dispersing machine. Examples of dispersing machines include a paint shaker, ball mill, attritor, sand mill, bead mill, dyno mill, roll mill, ultrasonic mill, and high-pressure collision dispersing machine. In this case, the dispersion treatment can be carried out once or multiple times using one type of dispersing machine, or multiple times using two or more types of dispersing machines in combination.

[0066] <Action and effect> The aqueous ink composition of the present embodiment described above contains the binder resin (A) including the resin (A1) and the pigment (B) in a specific mass ratio, and therefore has excellent resolubility and therefore excellent printability. Furthermore, by using the aqueous ink composition of the present embodiment, an ink layer having excellent adhesion to a substrate such as a plastic film can be formed. The ink layer formed from the aqueous ink composition of this embodiment has excellent adhesion to substrates, and also has excellent adhesion to plastic films that have not been corona-treated or have been only lightly corona-treated, for example. For example, in the case of a milky white polyethylene film, which is an example of a plastic film, the wet tension is usually less than 35 mN / m when not subjected to a corona treatment, and the wet tension is 35 mN / m or more and 38 mN / m or less when subjected to a low level of corona treatment. The wet tension is measured in accordance with JIS K 6768:1999.

[0067] Furthermore, by using the water-based ink composition of this embodiment, a coating film with excellent blocking resistance can be formed. In addition, the ink layer formed from the water-based ink composition of this embodiment also has excellent abrasion resistance, water abrasion resistance, ammonia resistance, and oil resistance. As described above, the aqueous ink composition of the present embodiment has excellent printability and coating film properties, and can form an ink layer that has excellent adhesion, water friction resistance, friction resistance, ammonia resistance, and oil resistance, even on plastic films that have not been corona-treated or have been only slightly corona-treated.

[0068] <Applications of water-based ink compositions> The aqueous ink composition of this embodiment is suitable as an ink for the backsheet of an absorbent article, and is particularly suitable as an ink for printing on the surface of a substrate such as a plastic film (if an optional layer is formed on the surface of the substrate, on the surface of this optional layer) by gravure printing or flexographic printing. Among these, it is particularly suitable as an ink for printing on the surface of a substrate or the surface of the optional layer by flexographic printing. That is, the aqueous ink composition of this embodiment is particularly suitable for flexographic printing. The aqueous ink composition may be used as it is as ink, or may be diluted with water or the like to be used as ink.

[0069] [Laminate] An example of a laminate according to one embodiment of the present invention is shown in Figure 1. Note that the dimensional ratio in Figure 1 is different from the actual ratio for the sake of convenience of explanation. The laminate 10 in FIG. 1 is a printed matter comprising a plastic film 11 as a substrate and an ink layer 12 provided on one surface of the plastic film 11.

[0070] <Plastic film> Examples of resins that can be used to make up the plastic film 11 include polyolefins such as polyethylene (PE), milky white polyethylene, and polypropylene (PP); polyesters such as polyethylene terephthalate (PET); polystyrene (PS); oriented polypropylene (OPP); and polyamide (NY). These plastic films 11 may be used alone or in combination of two or more.

[0071] The plastic film 11 may have a single layer structure or a laminated structure. That is, the plastic film 11 may be a single layer film or a laminated film. When the plastic film 11 is a laminated film, it may be configured by laminating two or more films of the same type, or by laminating two or more films of different types.

[0072] The plastic film 11 may or may not be subjected to a corona treatment. The thickness of the plastic film 11 is preferably 10 to 30 μm, more preferably 12 to 25 μm, and even more preferably 14 to 20 μm.

[0073] <Ink layer> In the illustrated laminate 10, the ink layer 12 is provided on one surface of the plastic film 11. The ink layer 12 is a layer formed using the above-mentioned water-based ink composition of the present invention. The ink layer 12 may have a single layer structure or a multilayer structure. The thickness of the ink layer 12 is preferably 0.01 to 3 μm, more preferably 0.05 to 2 μm, and even more preferably 0.1 to 1 μm.

[0074] <Method of manufacturing laminate> The method for producing the laminate 10 of this embodiment includes a step of forming an ink layer 12 on one surface of a plastic film 11 using the water-based ink composition of this embodiment. In the manufacturing method of the laminate 10 of this embodiment, for example, the aqueous ink composition of the present invention is applied to one side of a plastic film 11 to form a coating film to form a laminate precursor, and then the coating film is dried to form an ink layer 12. The aqueous ink composition of the present invention may be applied to one surface of a plastic film 11, the resulting coating film may be dried to form an ink layer 12, and then the aqueous ink composition of the present invention may be applied (reapplied) and the resulting coating film may be dried one or more times to form an ink layer with a laminated structure. When the aqueous ink composition of the present invention is applied in multiple coats, the color tones of the respective aqueous ink compositions may be the same or different.

[0075] The method for applying the aqueous ink composition is not particularly limited, and known application methods such as gravure printing, flexographic printing, brush coating, gravure coating, die coating, bar coating, spray coating, flow coating, dip coating, spin coating, and curtain coating can be used. Among these, gravure printing and flexographic printing are preferred from the viewpoint of excellent quality and productivity. Among these, flexographic printing is more preferred from the viewpoint of particularly excellent suitability for high-speed printing.

[0076] The method for drying the coating film is not particularly limited as long as it can remove the organic solvent contained in the aqueous ink composition coated on one side of the plastic film 11, and may be natural drying or forced drying such as reduced pressure drying, pressure drying, heat drying, or air drying. When drying is performed by heating, the drying temperature is preferably 30 to 90°C, more preferably 35 to 85°C.

[0077] <Action and effect> The laminate of the present embodiment described above has an ink layer formed using the above-mentioned aqueous ink composition of the present invention on one surface of a plastic film, and has excellent water friction resistance, friction resistance, ammonia resistance, and oil resistance. In addition, the ink layer has excellent adhesion to the plastic film.

[0078] <Application> The laminate of this embodiment is suitable as a back sheet (waterproof material) for absorbent articles.

[0079] <Other embodiments> The laminate is not limited to the above-described embodiment. For example, in the case of the laminate 10 shown in Figure 1, the ink layer 12 is provided over the entire surface of one side of the plastic film 11, but the ink layer 12 may also be provided over only a portion of one side of the plastic film 11. As long as the effects of the present invention are not impaired, an optional layer (also referred to as an "intermediate layer") may be provided between the plastic film 11 and the ink layer 12. A protective layer may be provided on the surface of the ink layer 12 opposite to the plastic film 11.

[0080] [Absorbent articles] An absorbent article according to one embodiment of the present invention includes the above-described laminate of the present invention as a backsheet (waterproof material). The absorbent article may include a surface material and an absorbent material in addition to the laminate of the present invention. In this case, the surface material, the absorbent material, and the laminate of the present invention are preferably laminated in this order. The surface material is the side that comes into contact with liquid, i.e., the innermost layer. The ink layer that constitutes the laminate of the present invention is the outermost layer. The surface material and absorbent material are not particularly limited and may be any known surface material and absorbent material used in absorbent articles.

[0081] The absorbent article of the present invention can be used for applications intended to absorb liquids such as body fluids, and can be used, for example, as disposable diapers for infants, adults, and pets, sanitary napkins, panty liners (discharge sheets), urine pads, and light incontinence pads. The ink layer formed from the aqueous ink composition of the present invention has excellent ammonia resistance. Absorbent articles equipped with the laminate of the present invention having this ink layer are suitable for applications expected to come into contact with urine, specifically, disposable diapers, urine absorption pads, and light incontinence pads. In particular, the ink layer has excellent oil resistance, making it particularly suitable for applications expected to come into contact with baby oil, specifically, disposable diapers. [Example]

[0082] The present invention will be explained in more detail below by way of examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention.

[0083] [Raw materials used] <Water-based (meth)acrylic emulsion resin (A1)> The following compounds were used as resin (A1) or a substitute therefor. A1-1: Water-based (meth)acrylic emulsion resin (manufactured by BASF Japan Ltd., product name "Joncryl", non-volatile content: 47% by mass, minimum film formation temperature: 8°C, glass transition temperature: 9°C, self-crosslinking type). A1-2: Water-based (meth)acrylic emulsion resin (manufactured by Covestro Coating Resins, product name "Neocryl", non-volatile content: 18.3% by mass, minimum film formation temperature: less than 0°C, glass transition temperature: 13°C, self-crosslinking type). A1-3: Water-based (meth)acrylic emulsion resin (manufactured by Covestro Coating Resins, product name "Neocryl", non-volatile content: 45% by mass, minimum film formation temperature: 31°C, glass transition temperature: 21°C, self-crosslinking type). A1-4: Water-based (meth)acrylic emulsion resin (manufactured by BASF Japan Ltd., product name "Joncryl", non-volatile content: 41.4 mass%, minimum film-forming temperature: less than 5°C, glass transition temperature: 12°C, non-self-crosslinking type). A1-5: Water-based (meth)acrylic emulsion resin (manufactured by BASF Japan Ltd., product name "Joncryl", non-volatile content: 38% by mass, minimum film formation temperature: 44°C, glass transition temperature: 30°C, self-crosslinking, substitute for resin (A1)). A1-6: Water-based (meth)acrylic emulsion resin (manufactured by Covestro Coating Resins, product name "Neocryl", non-volatile content: 43% by mass, minimum film formation temperature: 50°C, glass transition temperature: 56°C, non-self-crosslinking, alternative to resin (A1)).

[0084] <Water-soluble styrene-(meth)acrylic resin (A2)> The following compound was used as the resin (A2). A2-1: Water-soluble styrene-(meth)acrylic resin (manufactured by BASF Japan Ltd., trade name "Joncryl", non-volatile content: 30% by mass).

[0085] <Pigment (B)> As the pigment (B), the following compound was used. B-1: Dainichiseika Color & Chemicals Mfg. Co., Ltd., product name "Cyanine Blue ZCA-350-EP", non-volatile content: 100% by mass. B-2: Product name "Yellow AP22" manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd., non-volatile content: 100% by mass. B-3: Manufactured by DIC Corporation, product name "Shimura Brilliant Carmine 6B 410", non-volatile content: 100% by mass. B-4: Tokai Carbon Co., Ltd., product name "Touka Black #7240F", non-volatile content: 100% by mass.

[0086] <Aqueous medium (C)> As the aqueous medium (C), the following compounds were used. ·B-1: Water.

[0087] <Wax (D)> As the wax (D), the following compound was used. D-1: Mitsui Chemicals, Inc., product name "Chemipearl W-308", non-volatile content: 40% by mass, penetration: less than 1, average particle size: 6 μm. D-3: Mitsui Chemicals, Inc., trade name "Chemipearl W-400", non-volatile content: 40% by mass, penetration: 3, average particle size: 4 μm. D-3: Mitsui Chemicals, Inc., trade name "Chemipearl W-310", non-volatile content: 40% by mass, penetration: less than 1, average particle size: 9.5 μm. D-4: Mitsui Chemicals, Inc., product name "Chemipearl W-500", non-volatile content: 40% by mass, penetration: 10, average particle size: 2.5 μm.

[0088] <Silicone (E)> As the silicone (E), the following compound was used. E-1: Manufactured by Dow Toray Industries, Inc., product name "DOWSIL 52 Additive", non-volatile content: 65% by mass.

[0089] <Basic Compound (F)> As the basic compound (F), the following compound was used. F-1: Ammonia water with a concentration of 25% by mass.

[0090] <Optional ingredients> As optional components, the compounds shown below were used. Antifoaming agent: BYK, product name "BYK-024", non-volatile content: 100% by mass. Dispersant: BYK, product name "DISPERBYK-190", non-volatile content 40% by mass.

[0091] [Evaluation method] <Evaluation of Adhesion> After applying cellophane tape (manufactured by Nichiban Co., Ltd.) to the surface of the ink layer of the laminate, the cellophane tape was quickly peeled off and the condition of the ink layer remaining on the plastic film (milky white polyethylene film) was visually inspected, and the adhesion of the ink layer to the plastic film was evaluated according to the following evaluation criteria. 5: The ink layer is not peeled off at all. 4: The ratio of the area of ​​the peeled ink layer to the adhesive area of ​​the cellophane tape is more than 0% and less than 20%. 3: The ratio of the area of ​​the peeled ink layer to the adhesive area of ​​the cellophane tape is 20% or more but less than 50%. 2: The ratio of the area of ​​the peeled ink layer to the adhesive area of ​​the cellophane tape is 50% or more but less than 70%. 1: The ratio of the area of ​​the peeled ink layer to the adhesive area of ​​the cellophane tape is 70% or more.

[0092] <Evaluation of blocking resistance> Two laminate precursors were prepared. Two laminate precursors were stacked together so that the surface of the coating film side (printed surface) of one laminate precursor was in contact with the surface of the plastic film side (non-printed surface) of the other laminate precursor, and a pressure of 4 kg / cm was applied. 2 The test piece was stored for 24 hours in a thermostatic chamber at a temperature of 40°C and a humidity of 80% under a load of 1000 kJ / cm2. Thereafter, the two laminate precursors were peeled from each other, and the blocking resistance was evaluated according to the following evaluation criteria. 5: The proportion of the area of ​​the coating film that has transferred to the non-printed surface is less than 5% of the total area of ​​the coating film. 4: The proportion of the area of ​​the coating film that has migrated to the non-printed surface is 5% or more and less than 20% of the total area of ​​the coating film. 3: The proportion of the area of ​​the coating film that has transferred to the non-printed surface is 20% or more and less than 50% of the total area of ​​the coating film. 2: The proportion of the area of ​​the coating film that has transferred to the non-printed surface is 50% or more and less than 80% of the total area of ​​the coating film. 1: The proportion of the area of ​​the coating film that has transferred to the non-printed surface is 80% or more of the total area of ​​the coating film.

[0093] <Evaluation of abrasion resistance> A white cloth (golden No. 3) was placed on the surface of the ink layer of the laminate, and a friction test was performed using a Gakushin-type friction fastness tester (manufactured by Tester Sangyo Co., Ltd., product name "AB-301") by rubbing 50 times with a load of 200 gf. After the friction test, the appearance of the ink layer was visually inspected, and the friction resistance was evaluated according to the following evaluation criteria. 5: The area of ​​the ink layer that has transferred to the white cloth (gold cloth No. 3) is less than 10% of the total area of ​​the ink layer. 4: The area of ​​the printed layer that has migrated to the white cloth (gold cloth No. 3) is 10% or more but less than 20% of the total area of ​​the ink layer. 3: The area of ​​the printed layer that has migrated to the white cloth (gold cloth No. 3) is 20% or more but less than 50% of the total area of ​​the ink layer. 2: The area of ​​the printed layer that has migrated to the white cloth (gold cloth No. 3) is 50% or more but less than 80% of the total area of ​​the ink layer. 1: The area of ​​the printed layer that has migrated to the white cloth (gold cloth No. 3) is 80% or more of the total area of ​​the ink layer.

[0094] <Evaluation of water friction resistance> A water-moistened white cloth (No. 3 gold cloth) was placed on the surface of the ink layer of the laminate, and a friction test was performed using a Gakushin-type friction fastness tester (manufactured by Tester Sangyo Co., Ltd., product name "AB-301") by rubbing 20 times back and forth under a load of 200 gf. After the friction test, the appearance of the ink layer was visually inspected, and the water-rub resistance was evaluated according to the following evaluation criteria. 5: The area of ​​the ink layer that has transferred to the white cloth (gold cloth No. 3) is less than 10% of the total area of ​​the ink layer. 4: The area of ​​the ink layer that has transferred to the white cloth (gold cloth No. 3) is 10% or more but less than 20% of the total area of ​​the ink layer. 3: The area of ​​the ink layer that has transferred to the white cloth (gold cloth No. 3) is 20% or more but less than 50% of the total area of ​​the ink layer. 2: The area of ​​the ink layer that has transferred to the white cloth (gold cloth No. 3) is 50% or more but less than 80% of the total area of ​​the ink layer. 1: The area of ​​the ink layer that has transferred to the white cloth (gold cloth No. 3) is 80% or more of the total area of ​​the ink layer.

[0095] <Evaluation of resolubility> One drop of water was dropped onto the surface of the coating film of the laminate precursor using a dropper every minute, and 10 seconds after the drop, the drop was wiped off with gauze to check whether the coating film had adhered to the gauze. The process of dropping water and wiping off was repeated until the coating film no longer adhered to the gauze, i.e., until the coating film no longer redissolved in water. The time required for the coating film to no longer redissolve in water was measured, and the resolubility was evaluated according to the evaluation criteria shown below. 5: It takes 10 minutes or more for the coating film to no longer redissolve in water. 4: The time required for the coating film to no longer redissolve in water is 5 minutes or more but less than 10 minutes. 3: The time required for the coating film to no longer redissolve in water is 3 minutes or more but less than 5 minutes. 2: The time required for the coating film to no longer redissolve in water is 1 minute or more but less than 3 minutes. 1: The time required for the coating film to no longer redissolve in water is less than 1 minute.

[0096] <Evaluation of ammonia resistance> The laminate was immersed in ammonia water (pH = 9.5, liquid temperature 25°C) for 48 hours, then removed, and the condition of the ink layer remaining on the plastic film (milky white polyethylene film) was visually inspected, and the ammonia resistance was evaluated according to the evaluation criteria shown below. 5: Neither dissolution nor discoloration of the ink layer was observed. 4: No dissolution of the ink layer was observed, but slight discoloration was observed. 3: Slight dissolution or discoloration of the ink layer was observed. 2: Dissolution of the ink layer or significant discoloration was confirmed. 1 The entire ink layer was dissolved.

[0097] <Evaluation of oil resistance> A white cloth (golden cloth No. 3) with three drops of baby oil (Johnson & Johnson, product name "Johnson Baby Oil, Lightly Fragranced") was placed on the surface of the ink layer of the laminate, and a friction test was performed using a Gakushin-type friction fastness tester (Tester Sangyo Co., Ltd., product name "AB-301") by rubbing 10 times with a load of 200 gf. After the friction test, the appearance of the ink layer was visually inspected, and the oil resistance was evaluated according to the following evaluation criteria. 5: The area of ​​the ink layer that has transferred to the white cloth (gold cloth No. 3) is less than 10% of the total area of ​​the ink layer. 4: The area of ​​the ink layer that has transferred to the white cloth (gold cloth No. 3) is 10% or more but less than 20% of the total area of ​​the ink layer. 3: The area of ​​the ink layer that has transferred to the white cloth (gold cloth No. 3) is 20% or more but less than 50% of the total area of ​​the ink layer. 2: The area of ​​the ink layer that has transferred to the white cloth (gold cloth No. 3) is 50% or more but less than 80% of the total area of ​​the ink layer. 1: The area of ​​the ink layer that has transferred to the white cloth (gold cloth No. 3) is 80% or more of the total area of ​​the ink layer.

[0098] [Examples 1 to 18, Comparative Examples 1 to 5] <Preparation of Water-Based Ink Composition> According to the compositions shown in Tables 1 to 4, resin (A1), resin (A2), pigment (B), aqueous medium (C), wax (D), silicone (E), basic compound (F), and optional components were mixed, and the resulting mixture was then kneaded with a paint shaker to obtain an aqueous ink composition.

[0099] <Preparation of laminate> The prepared aqueous ink composition was diluted with water to prepare a coating liquid (diluted liquid) so that the viscosity at 25°C, measured using Zahn cup #4, was 15 seconds. The plastic film used was a milky white polyethylene film (manufactured by Mitsui Chemicals, Inc., product name "ESPOIR", thickness: 15 μm) before or after corona treatment. For the corona treatment, a corona discharge surface treatment device (manufactured by Wedge Corporation, product name "CTW-0212") was used. The treatment degree (wet tension) of the plastic film was 34 mN / m before corona treatment and 38 mN / m after corona treatment. The treatment degree (wet tension) of the plastic film was measured in accordance with JIS K 6768:1999 using a mixture for wet tension testing (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.).

[0100] The corona-treated surface of the plastic film is coated with a coating weight of 1.0 g / m after drying. 2 A flexographic hand proofer equipped with an anilox roll with a cell volume of 13 cc was used as an applicator to apply the coating solution by flexographic printing, yielding a laminate precursor in which a coating film was formed on a plastic film. The laminate precursor was then dried at 20°C for 24 hours to obtain a laminate (printed product) in which an ink layer was formed on a plastic film. The laminate precursor (before drying) was used to evaluate blocking resistance and redissolution, and the laminate (after drying) was used to evaluate adhesion, abrasion resistance, water abrasion resistance, ammonia resistance, and oil resistance. The results are shown in Tables 1 to 4.

[0101] [Table 1]

[0102] [Table 2]

[0103] [Table 3]

[0104] [Table 4]

[0105] The amounts of each component other than the aqueous medium (C) and the basic compound (F) in the table are calculated as nonvolatile content. A blank cell in the table means that the component was not blended (amount blended: 0 mass %). The "balance" in the table is the amount of water (C-1) added so that the total amount (mass %) of all ingredients contained in the aqueous ink composition becomes 100 mass %. The "B / A ratio" in the table is the mass ratio expressed as pigment (B) / binder resin (A) in terms of nonvolatile content.

[0106] As is clear from the results in Tables 1 to 3, the aqueous ink compositions obtained in each Example were excellent in resolubility. Furthermore, the coating films formed from these aqueous ink compositions were excellent in blocking resistance, and the ink layers were excellent in adhesion to plastic films, abrasion resistance, water abrasion resistance, ammonia resistance, and oil resistance.

[0107] On the other hand, as is clear from the results in Table 4, the coating films formed from the aqueous ink compositions obtained in Comparative Examples 1 and 2, which used aqueous (meth)acrylic emulsion resins with a minimum film-forming temperature of 44° C. or 50° C., were poor in blocking resistance, and the ink layers were poor in adhesion to plastic films, water rub resistance, ammonia resistance, and oil resistance. In the case of Comparative Example 2, the ink layer was also poor in rub resistance. The aqueous ink composition obtained in Comparative Example 3, which had a B / A ratio of 0.20, was poor in resolubility, and the coating film formed from this aqueous ink composition was poor in blocking resistance. The ink layer formed from the water-based ink composition obtained in Comparative Example 4, in which the B / A ratio was 1.15, was poor in adhesion to plastic films, ammonia resistance, and oil resistance. The aqueous ink composition obtained in Comparative Example 5, which did not contain pigment (B), was poor in resolubility, and the coating film formed from this aqueous ink composition was poor in blocking resistance. [Industrial Applicability]

[0108] The aqueous ink composition of the present invention has excellent resolubility and can form an ink layer that has excellent adhesion to plastic films, abrasion resistance, water abrasion resistance, ammonia resistance, and oil resistance, and is useful as an ink for the backsheet of absorbent articles. [Explanation of symbols]

[0109] 10 Laminate 11 Plastic Film 12 Ink layer

Claims

1. An aqueous ink composition for a back sheet of an absorbent article, comprising a binder resin (A), a pigment (B), and an aqueous medium (C), the binder resin (A) contains an aqueous (meth)acrylic emulsion resin (A1), the minimum film-forming temperature of the aqueous (meth)acrylic emulsion resin (A1) is 40°C or lower, The water-based ink composition has a mass ratio of the pigment (B) to the binder resin (A) calculated as nonvolatile matter of 0.3 to 1.

0.

2. The aqueous ink composition according to claim 1, wherein the aqueous (meth)acrylic emulsion resin (A1) is a self-crosslinking type.

3. 2. The water-based ink composition according to claim 1, wherein the content of the binder resin (A) in terms of non-volatile content is 15 to 35 mass % relative to the total mass of the water-based ink composition.

4. 2. The water-based ink composition according to claim 1, wherein the binder resin (A) further contains a water-soluble styrene-(meth)acrylic resin (A2).

5. 2. The aqueous ink composition according to claim 1, wherein the aqueous (meth)acrylic emulsion resin (A1) has a minimum film-forming temperature of 15°C or lower.

6. Further containing a wax (D), 2. The water-based ink composition according to claim 1, wherein the wax (D) has an average particle size of 8 μm or less and a penetration of 5 or less.

7. The aqueous ink composition according to claim 1 , further comprising a silicone (E).

8. The aqueous ink composition according to any one of claims 1 to 7, which is for flexographic printing.

9. A plastic film and an ink layer provided on the plastic film, A laminate, wherein the ink layer is a layer formed using the aqueous ink composition according to claim 8.

10. An absorbent article comprising the laminate of claim 9.

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