Water-based ink composition, laminate and absorbent article

Abstract

Provided are an aqueous ink composition capable of forming an ink layer having excellent adhesion to a plastic film and also having excellent re-solubility, a laminate having the ink layer, and an absorbent article having 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 lower, and the mass ratio of the pigment (B) / 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 printed using gravure printing, flexographic printing, etc., to impart design and functionality to the articles. In view of recent environmental issues and the fact that absorbent articles are worn, there is an increasing demand for water-based inks (hereinafter also referred to as "water-based inks") for the inks used in the printing process. Absorbent articles are generally configured such that, from the innermost layer, the surface material, absorbent material, and waterproof material (back sheet) are arranged in this order, with the side that comes into contact with the human body being the innermost layer. In order to make the design visible from the outside, surface printing is usually performed on the surface of the substrate constituting the back sheet, which is the outermost layer, and an ink layer is provided.

[0003] As the substrate for the back sheet, a so-called milky polyethylene film composed of calcium carbonate and polyethylene resin is generally used. The substrate is manufactured by stretching and processing a polyethylene film containing calcium carbonate or by applying other special processing. These processes create fine holes on the surface of the substrate, which allows air and water vapor to pass through while blocking water, making it possible to impart functions such as breathability, waterproofness, and flexibility. In addition, in order to ensure breathability and flexibility, the film thickness of the substrate is designed to be thin, about 10 to 20 μm. Corona treatment may be applied to the substrate for the purpose of increasing adhesion to the ink layer, but if the substrate is thin, corona treatment with a high discharge amount will cause problems such as holes being formed in the substrate. Therefore, substrates such as milky polyethylene films used for back sheets are generally not corona treated or have a low degree of corona treatment.

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

[0005] As an example of a water-based ink, Patent Document 1 discloses an aqueous varnish composition that contains an acrylic resin emulsion having a minimum film-forming temperature of less than 5° C. and is used for plastic labels of 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 re-solubility. Furthermore, the ink layers formed from these water-based inks have insufficient adhesion to plastic films, particularly to plastic films that have not been subjected to corona treatment or have been subjected to a low degree of corona treatment.

[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 re-solubility, a laminate comprising the ink layer, and an absorbent article comprising 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, A water-based ink composition, wherein a mass ratio of the pigment (B) to the binder resin (A) calculated as non-volatile content is 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] above, wherein the content of the binder resin (A) in terms of non-volatile matter is 15 to 35 mass% based on the total mass of the water-based ink composition. [4] The water-based ink composition according to any one of [1] to [3] above, wherein the binder resin (A) further contains a water-soluble styrene-(meth)acrylic resin (A2). [5] The water-based ink composition according to any one of [1] to [4] above, wherein the water-based (meth)acrylic emulsion resin (A1) has a minimum film-forming temperature of 15° C. or lower. [6] Further containing a wax (D), The water-based ink composition according to any one of the above [1] to [5], 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 printing apparatus comprising: a plastic film; and an ink layer provided on the plastic film; 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]. Effect of the Invention

[0010] According to the present invention, it is possible to provide an aqueous ink composition capable of forming an ink layer having excellent adhesion to a plastic film and also having excellent re-solubility, a laminate having the ink layer, and an absorbent article having the laminate. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view illustrating a schematic example of a laminate of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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 calculated as a non-volatile content (also called "solid content"). The "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 an 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." The term "self-crosslinking" refers to the formation of a crosslinked structure by reaction between functional groups of the same type or between different functional groups without the use of a crosslinking agent or the like. "Resolubility" refers to the ability of the coating liquid (aqueous ink composition) remaining on a printing plate such as a flexographic plate to be redissolved in a solvent (such as aqueous medium (C)) contained in the coating liquid (aqueous ink composition) before it dries and becomes a cause of poor transfer when the aqueous ink composition is applied by a printing method. The more easily the coating film dissolves in the solvent (such as aqueous medium (C)) contained in the coating liquid (aqueous ink composition), the more excellent the resolubility of the aqueous ink composition. Resolubility can be said to be one of the important printing suitabilities. In this specification, when it is simply said that the printing suitability is excellent, 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 a substrate. The symbol "~" 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 numerical ranges disclosed in this specification can be combined in any manner to create new numerical ranges.

[0013] The glass transition temperature of the binder resin (A) is measured in accordance with JIS K 7121:2012 as follows: 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 between 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 gram of nonvolatile matter (solid matter) 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 particles by passing wax particles dispersed in a solution through a fine hole and measuring the change in the electrical signal when the particles pass through the hole.

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

[0016] [Water-based ink composition] The 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. It is preferable that the water-based ink composition 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) described 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, within a range that does not impair the effects of the present invention.

[0017] <Binder resin (A)> The binder resin (A) contains the following aqueous (meth)acrylic emulsion resin (A1). For the purpose of further improving the resolubility and pigment dispersibility of the aqueous ink composition, it is preferred that the binder resin (A) further contains a water-soluble styrene-(meth)acrylic resin (A2) described below. The binder resin (A) may further contain a resin (hereinafter also referred to as "other resin (A3)") other than the (meth)acrylic emulsion resin (A1) and the water-soluble styrene-(meth)acrylic resin (A2) as necessary, within a range that does not impair the effects of the present invention.

[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 part to the shell part (core part:shell part) 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 part to the shell part is greater than the above range, and the shell part is smaller than the above range, the ink stability and leveling properties of the aqueous ink composition are reduced. If the mass ratio of the core part to the shell part is less than the above range, and the shell part is greater than the above range, the abrasion resistance, water abrasion resistance, ammonia resistance, and oil resistance of the ink layer are reduced.

[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, and 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 kinds 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 kinds 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 kinds.

[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, chloroprene, etc.; styrene-based monomers such as α-methylstyrene, halogenated styrene, vinylstyrene, etc.; vinyl cyanide compounds such as acrylonitrile, methacrylonitrile, etc.; acrylamides such as N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, etc.; unsaturated carboxylate esters such as diethyl maleate, dibutyl maleate, dibutyl fumarate, diethyl itaconate, dibutyl itaconate, etc. 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. Among these, emulsion polymerization is preferred. Emulsion polymerization is a method in which monomers to be used in polymerization are polymerized in an aqueous medium in the presence of an emulsifier and a polymerization initiator. Resin (A1) may be produced by producing the core and shell parts separately and then compounding them. It may also be produced by multi-stage emulsion polymerization. Specifically, the monomer or monomer mixture constituting the core part may first be polymerized to obtain the core part, and then the monomer or monomer mixture constituting the shell part may be polymerized in the presence of the core part 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. That is, 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 type. The use of a self-crosslinking type 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 monomer (x) shown below. 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 the epoxy group-containing monomer 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 the resin (A1) is 40° C. or lower, preferably 30° C. or lower, and more preferably 15° C. or lower. The minimum film-forming temperature of the 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 the 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 a substrate such as a plastic film, the 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. When the acid value of the resin (A1) is equal to or more than the lower limit, the resolubility of the aqueous ink composition is improved, and when it is equal to or less than 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. When the glass transition temperature of the resin (A1) is not less than the above lower limit, the blocking resistance of the coating film and the heat resistance of the ink layer are improved, and when it is not more than the above upper limit, 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 "Hi-Los-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 simply referred to as "resin (A2)") is a copolymer containing a structural unit derived from a styrene-based monomer, a structural unit derived from a carboxy group-containing monomer, and a structural unit derived from a (meth)acrylate monomer, and is soluble in alkaline water. Resin (A2) may further contain a structural unit derived from a monomer other than the styrene-based monomer, the carboxy group-containing monomer, and the (meth)acrylate monomer (hereinafter also referred to as "other monomer").

[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 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. Examples of the carboxy group-containing monomer include the carboxy group-containing monomers exemplified above in the description of the 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 explanation of resin (A1). The (meth)acrylate monomer may be used alone or in combination of two or more kinds.

[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, chloroprene, etc.; vinyl cyanide compounds such as acrylonitrile, methacrylonitrile, etc.; acrylamides such as N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, etc.; unsaturated carboxylic acid esters such as diethyl maleate, dibutyl maleate, dibutyl fumarate, diethyl itaconate, dibutyl itaconate, etc. 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 the 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), 1,1-azobis(cyclohexanecarbonitrile), etc.; peroxide initiators such as dialkyl peroxide, diacyl peroxide, peroxydicarbonate, ketone peroxide, peroxyketal, etc. 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. When the acid value of the resin (A2) is equal to or more than the lower limit, the resolubility and pigment dispersibility of the aqueous ink composition are improved, and when it is equal to or less than 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. When the glass transition temperature of resin (A2) is not less than the above lower limit, the blocking resistance of the coating film and the heat resistance of the ink layer are improved, and when it is not more than the above upper limit, the adhesion of the ink layer to a substrate such as a plastic film 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 "Hi-Los-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, each of which has a minimum film-forming temperature of more than 40°C. These other resins (A3) may be used alone or in combination of two or more.

[0040] <Basic Compound (F)> When the above-mentioned resin (A1) has a core-shell structure and the shell portion contains a hydrophilic resin containing a carboxy group, the carboxy group in the shell portion 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). By neutralizing the carboxy groups of these resins (A1) and (A2), the resolubility of the aqueous ink composition is further improved.

[0041] Examples of the basic compound (F) capable of neutralizing the carboxyl 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), any known pigment used as a colorant or the like can be used, and examples thereof include 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, and sulfides such as zinc sulfide; sulfates such as barium sulfate; oxides such as chromium oxide, zinc oxide, 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 kinds.

[0043] <Aqueous medium (C)> Examples of the aqueous medium (C) include water; a mixed solvent of water and an organic solvent, and the like. 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 kinds. As the aqueous medium (C), water is preferred from the viewpoints of, for example, the impact on the environment and the reduction of volatile organic compounds (VOCs).

[0044] <Wax (D)> By including the wax (D) in the water-based ink composition, 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. Any known wax can be used as the wax dispersed in water, including, for example, polyethylene wax, polypropylene wax, modified paraffin wax, carnauba wax, polytetrafluoroethylene wax, etc. Among these, it is preferable to use polyethylene wax or polypropylene wax. These waxes (D) may be used alone or in combination of two or more kinds.

[0045] The average particle size of the 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 the 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 arbitrarily combined. For example, the average particle size of the 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. If the average particle size of the wax (D) is equal to or larger than the lower limit, the blocking resistance of the coating film and the rub resistance of the ink layer are improved. If the average particle size of the wax (D) is equal to or smaller 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 above upper limit, the blocking resistance of the coating film and the abrasion resistance of the ink layer are improved.

[0047] <Silicone (E)> By including the silicone (E) in the water-based ink composition, 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 it is preferable to modify it with an organic group because it enhances the 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 one 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 increasing compatibility with components other than silicone. Furthermore, amino-modified polyorganosiloxanes and epoxy-modified polyorganosiloxanes are preferred from the viewpoint of increasing 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. Commercially available silicones (E) include, for example, 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, UV 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 non-volatile matter is preferably from 15 to 35 mass %, more preferably from 18 to 32 mass %, and even more preferably from 20 to 30 mass %, based on the total mass of the water-based ink composition. The content of the binder resin (A) in terms of non-volatile 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 non-volatile content of the aqueous ink composition. When the content of the binder resin (A) is not less than 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 are further improved. When the content of the binder resin (A) is not more than the above upper limit, the resolubility of the aqueous ink composition and the blocking resistance of the coating film are further improved.

[0053] The content of the resin (A1) in terms of non-volatile content is preferably from 12 to 35 mass %, more preferably from 15 to 32 mass %, and even more preferably from 17 to 30 mass %, based on the total mass of the water-based ink composition. The content of the resin (A1) in terms of non-volatile content is preferably from 40 to 70 mass %, more preferably from 45 to 68 mass %, and even more preferably from 50 to 65 mass %, based on the total mass of the non-volatile content of the aqueous ink composition. When the content of the resin (A1) is at least the lower limit, the abrasion resistance, water abrasion resistance and ammonia resistance of the ink layer are improved, and when it is no more than the upper limit, the resolubility of the aqueous ink composition is improved.

[0054] The content of the resin (A2) in terms of non-volatile content is preferably 10 mass % or less, more preferably 0.1 to 10 mass %, even more preferably 0.5 to 5 mass %, and particularly preferably 1 to 3 mass %, based on the total mass of the aqueous ink composition. The content of the resin (A2) in terms of non-volatile 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 non-volatile content of the aqueous ink composition. When the content of resin (A2) is equal to or more 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 non-volatile matter is preferably from 1 to 50 mass %, more preferably from 1 to 45 mass %, and even more preferably from 1 to 40 mass %, based on the total mass of the aqueous ink composition. The content of the pigment (B) in terms of nonvolatile content is preferably from 1 to 60 mass %, more preferably from 1 to 55 mass %, and even more preferably from 1 to 50 mass %, based on the total mass of the nonvolatile content of the aqueous ink composition. When the content of pigment (B) is equal to or more than the above lower limit, the hiding power and color development of the ink layer are improved, and when the content 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 are improved.

[0056] The mass ratio (hereinafter also referred to as "B / A ratio") expressed in terms of non-volatile content, expressed as pigment (B) / binder resin (A), is 0.3 to 1.0, preferably 0.35 to 0.8, and more preferably 0.4 to 0.7. When 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, whereas when the B / A ratio is equal to or less than the upper 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 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. When the content of the aqueous medium (C) is equal to or more than the lower limit, the fluidity of the aqueous ink composition is improved, and when it is equal to or less than the upper limit, the drying property of the coating film is improved.

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

[0059] When the aqueous ink composition contains a wax (D), the content of the 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%, based on the total mass of the aqueous ink composition. When the aqueous ink composition contains a wax (D), the content of the wax (D) in terms of non-volatile matter 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 matter of the aqueous ink composition. When the content of the wax (D) is equal to or more 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 matter 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 matter is preferably 0.05 to 5 mass%, more preferably 0.1 to 3 mass%, and even more preferably 0.2 to 1 mass%, based on the total mass of the non-volatile matter in the aqueous ink composition. When the content of silicone (E) is equal to or more than the above lower limit, the abrasion resistance and water abrasion resistance of the ink layer are improved, and when 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 %, based on the total mass of the aqueous ink composition. If the content of the basic compound (F) is equal to or more than the lower limit, the resolubility of the aqueous ink composition is further improved, and if it is equal to or less than the upper limit, the water friction resistance of the ink layer is further improved.

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

[0063] The content of the 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 %, more preferably 0 to 15 mass %, and even more preferably 0 to 10 mass %, relative to the total mass of the aqueous ink composition. When the aqueous ink composition contains an optional component, the content of the optional component 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, based on the total mass of the aqueous ink composition. When the content of the optional component is equal to or more than the lower limit, the effect of the optional component is sufficiently 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 the present embodiment can be obtained, for example, by mixing the binder resin (A), the pigment (B), and the aqueous medium (C) with, as required, one or more of the wax (D), the silicone (E), the basic compound (F), and the optional components so that each component has a desired content, and, as required, performing a dispersion treatment. The method for mixing the components is not particularly limited, and the components can be mixed by various methods. The method of dispersion treatment is not particularly limited, and can be carried out using a known dispersing machine. Examples of dispersing machines include paint shakers, ball mills, attritors, sand mills, bead mills, dyno mills, roll mills, ultrasonic mills, and high-pressure collision dispersing machines. In this case, one type of dispersing machine can be used to carry out dispersion treatment once or multiple times, or two or more types of dispersing machines can be used in combination to carry out dispersion treatment multiple times.

[0066] <Action and effect> The aqueous ink composition of the present embodiment described above contains the binder resin (A) including the above-mentioned resin (A1) and the pigment (B) in a specific mass ratio, and therefore has excellent resolubility and excellent printability. In addition, 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 for example, has excellent adhesion to plastic films that have not been subjected to corona treatment or have been subjected to a low degree of corona treatment. 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 corona treatment, and the wet tension is 35 mN / m or more and 38 mN / m or less when the degree of corona treatment is low. 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 having excellent blocking resistance can be formed. In addition, the ink layer formed from the water-based ink composition of this embodiment is also excellent in 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, while being capable of forming an ink layer that has excellent adhesion, water abrasion resistance, abrasion resistance, ammonia resistance, and oil resistance, even on a plastic film that has not been subjected to corona treatment or has been subjected to a low degree of corona treatment.

[0068] <Applications of water-based ink composition> The aqueous ink composition of the present embodiment is suitable as an ink for the back sheet of an absorbent article, and is particularly suitable as an ink for printing on the surface of a substrate such as a plastic film (when an optional layer is formed on the surface of the substrate, on the surface of the optional layer) by gravure printing or flexographic printing. Among them, it is 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 the present 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 and used as ink.

[0069] [Laminate] An example of a laminate according to an embodiment of the present invention is shown in Fig. 1. Note that the dimensional ratio in Fig. 1 is different from the actual one 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 may be used to form the plastic film 11 include polyolefins such as polyethylene (PE), milky 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 kinds.

[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 a structure in which two or more films of the same type are laminated, or a structure in which two or more films of different types are laminated.

[0072] The plastic film 11 may be either not subjected to a corona treatment or may be subjected to a corona treatment. The thickness of the plastic film 11 is preferably from 10 to 30 μm, more preferably from 12 to 25 μm, and even more preferably from 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 from 0.01 to 3 μm, more preferably from 0.05 to 2 μm, and even more preferably from 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 onto one surface of a plastic film 11 to form a coating film to serve as a laminate precursor, and then the coating film is dried to form the 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 having 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 coater, die coater, bar coater, 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 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, pressurized drying, heat drying, or air drying. When drying is performed by heating, the drying temperature is preferably from 30 to 90°C, more preferably from 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 side 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 FIG. 1, the ink layer 12 is provided over the entirety of one surface of the plastic film 11, but the ink layer 12 may also be provided over only a portion of one surface of the plastic film 11. As long as the effects of the present invention are not impaired, an arbitrary layer (also called 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-mentioned laminate of the present invention as a back sheet (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, it is preferable that the surface material, the absorbent material, and the laminate of the present invention are laminated in this order. The surface material is on the side that comes into contact with liquid, i.e., the innermost layer. The ink layer constituting 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, pets, etc., sanitary napkins, panty liners (discharge sheets), urine pads, light incontinence pads, etc. The ink layer formed from the above-mentioned aqueous ink composition of the present invention is also excellent in ammonia resistance. The absorbent article having the laminate of the present invention having this ink layer is suitable for applications that are expected to come into contact with urine, specifically, disposable diapers, urine pads, and light incontinence pads. In particular, since the ink layer has excellent oil resistance, it is particularly suitable for applications that are expected to come into contact with baby oil, etc., specifically, disposable diapers. EXAMPLES

[0082] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples as long as it does not depart from the gist of the present invention.

[0083] [Raw materials used] <Water-based (meth)acrylic emulsion resin (A1)> The compounds shown below 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-forming 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 mass%, minimum film-forming 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 mass%, minimum film formation temperature: 44°C, glass transition temperature: 30°C, self-crosslinking type, alternative to resin (A1)). A1-6: Water-based (meth)acrylic emulsion resin (manufactured by Covestro Coating Resins, product name "Neocryl", non-volatile content: 43 mass%, minimum film formation temperature: 50°C, glass transition temperature: 56°C, non-self-crosslinking type, alternative to resin (A1)).

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

[0085] <Pigment (B)> As the pigment (B), the compound shown below was used. B-1: Manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd., product name "Cyanine Blue ZCA-350-EP", non-volatile content: 100% by mass. B-2: Manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd., product name "Yellow AP22", 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: Manufactured by 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 compound was used. ·B-1: Water.

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

[0088] <Silicone (E)> As the silicone (E), the compound shown below 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 compound shown below 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. Defoamer: 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 attaching 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 has 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 and 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 and 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 the laminate was heated at 4 kg / cm 2 A load of 10 ... 5: The percentage 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 percentage of the area of ​​the coating film that has transferred to the non-printed surface is 5% or more and less than 20% of the total area of ​​the coating film. 3: The percentage 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 percentage 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 ratio 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 width No. 3) was placed on the surface of the ink layer of the laminate, and a friction test was performed by rubbing it back and forth 50 times under a load of 200 gf using a Gakushin-type friction fastness tester (manufactured by Tester Sangyo Co., Ltd., product name "AB-301") After the friction test, the appearance of the ink layer was visually confirmed, and the friction resistance was evaluated according to the following evaluation criteria. 5: The percentage of 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 percentage of the area of ​​the printed layer that has transferred to the white cloth (gold cloth No. 3) is more than 10% and less than 20% of the total area of ​​the ink layer. 3: The percentage of the area of ​​the printed layer that has transferred to the white cloth (gold cloth No. 3) is more than 20% and less than 50% of the total area of ​​the ink layer. 2: The percentage of the area of ​​the printed layer that has transferred to the white cloth (gold cloth No. 3) is more than 50% and less than 80% of the total area of ​​the ink layer. 1: The area of ​​the printed layer that has transferred 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-dampened white cloth (golden cloth No. 3) was placed on the surface of the ink layer of the laminate, and a friction test was performed by rubbing it back and forth 20 times under a load of 200 gf using a Gakushin-type friction fastness tester (manufactured by Tester Sangyo Co., Ltd., product name "AB-301") After the friction test, the appearance of the ink layer was visually confirmed, and the water friction resistance was evaluated according to the following evaluation criteria. 5: The percentage of 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 percentage of the area of ​​the ink layer that has transferred to the white cloth (gold cloth No. 3) is more than 10% but less than 20% of the total area of ​​the ink layer. 3: The percentage of the area of ​​the ink layer that has transferred to the white cloth (gold cloth No. 3) is 20% or more and less than 50% of the total area of ​​the ink layer. 2: The percentage of the area of ​​the ink layer that has transferred to the white cloth (gold cloth No. 3) is more than 50% and 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 redissolution> A drop of water was dropped onto the surface of the coating film of the laminate precursor with a dropper every minute, and 10 seconds after the drop, the water was wiped off with gauze to check whether the coating film 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 following evaluation criteria. 5: The time required for the coating film to no longer redissolve in water is 10 minutes or longer. 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 dissolve 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> After immersing the laminate in ammonia water (pH = 9.5, liquid temperature 25°C) for 48 hours, the laminate was 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 observed. 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 Light Fragrance") was placed on the surface of the ink layer of the laminate, and a friction test was performed by rubbing it back and forth 10 times under a load of 200gf using a Gakushin type friction fastness tester (Tester Sangyo Co., Ltd., product name "AB-301"). After the friction test, the appearance of the ink layer was visually confirmed, and the oil resistance was evaluated according to the following evaluation criteria. 5: The percentage of 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 percentage of the area of ​​the ink layer that has transferred to the white cloth (gold cloth No. 3) is more than 10% but less than 20% of the total area of ​​the ink layer. 3: The percentage of the area of ​​the ink layer that has transferred to the white cloth (gold cloth No. 3) is 20% or more and less than 50% of the total area of ​​the ink layer. 2: The percentage of the area of ​​the ink layer that has transferred to the white cloth (gold cloth No. 3) is more than 50% and 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, the resin (A1), the resin (A2), the pigment (B), the aqueous medium (C), the wax (D), the silicone (E), the 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 so that the viscosity at 25° C., measured using a Zahn cup #4, was 15 seconds, thereby preparing a coating liquid (diluted liquid). 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. A corona discharge surface treatment device (manufactured by Wedge Corporation, product name "CTW-0212") was used for the corona treatment. The treatment degree (wet tension) of the plastic film was 34 mN / m before corona treatment and 38 mN / m after corona treatment. The degree of treatment (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 / m2 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 liquid by flexographic printing to obtain 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 material) in which an ink layer was formed on a plastic film. The laminate precursor (before drying) was used to evaluate the blocking resistance and redissolution property, and the laminate (after drying) was used to evaluate the 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 non-volatile contents. 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 the components contained in the aqueous ink composition was 100 mass %. The "B / A ratio" in the table is the mass ratio expressed as pigment (B) / binder resin (A) in terms of non-volatile 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 using 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, in which the B / A ratio was 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 the 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 back sheet 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 absorbent article is for absorbing body fluids including urine, 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) in terms of non-volatile content 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 % based on the total mass of the water-based ink composition.

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

5. 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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