Water-based varnish compositions, laminates, and packaging materials

Abstract

To provide a water-based varnish composition that can form a coating film with excellent properties such as water resistance and friction resistance, and also exhibits excellent stability, thereby suppressing the deterioration of the coating film's properties over time. [Solution] An aqueous varnish composition comprising an aqueous binder resin (A), an aziridine-based curing agent (B), and an aqueous medium (C), wherein the aqueous binder resin (A) contains an emulsion-type (meth)acrylic resin (A1), the acid value of the emulsion-type (meth)acrylic resin (A1) is 2 to 60 mgKOH / g, the average particle size is 0.04 μm to 0.2 μm, and the ratio of the total number of aziridine rings derived from the aziridine-based curing agent (B) to the total number of carboxyl groups derived from the aqueous binder resin (A) is 0.30 to 6.0.

Description

Technical Field

[0001] The present invention relates to an aqueous varnish composition, a laminate, and a packaging material.

Background Art

[0002] In soft packaging materials such as plastic films used for packaging foods, daily necessities, etc., printing is performed by gravure printing or flexographic printing using ink or varnish for the purpose of information display, design, functionality, etc. Conventionally, the main type of ink and varnish for soft packaging has been an oil-based type using organic solvents, but in recent years, there has been a strong demand for an aqueous type from the perspective of environmental problems and the like.

[0003] One of the uses of soft packaging materials is a packaging label attached to containers such as plastic containers, metal containers, and paper containers. Examples of packaging labels include roll labels attached by wrapping around the container and fastening with an adhesive, and shrink labels attached by heating and shrinking to a shape suitable for the container. As a typical configuration of the packaging label, an ink layer serving as a pattern layer is laminated on the inside of the plastic film, that is, on the container side, and a varnish layer for protecting the ink layer from contact with the container or the like is laminated on the surface of the ink layer. Further, in such a configuration, a typical example is also a configuration in which a varnish layer for protecting the plastic film from external contact such as human hands or the like is further laminated on the outside of the plastic film, that is, on the side opposite to the container. Furthermore, in recent years, there is also known a configuration in which the outer varnish layer is a matte ink layer for the purpose of not only protecting the plastic film from external contact but also improving the design. The varnish layer, ink layer, and matte ink layer are each a coating film formed by printing using varnish, ink, and matte ink. Hereinafter, these are also collectively referred to as a printed coating film.

[0004] The required coating properties for printed labels on packaging include adhesion to the substrate, abrasion resistance, blocking resistance, and heat resistance, but water and abrasion resistance are particularly important. Packaging labels, especially those for food and beverages, are often exposed to water. Therefore, the printed coating is frequently exposed to external contact and friction while in contact with water. Water-based varnishes inherently have poor water and abrasion resistance. Therefore, to compensate for this drawback and further improve the properties of the coating film, it is known that measures such as incorporating a hardening agent are taken. In particular, it is known that using aziridine-based hardening agents can improve the properties of the coating film compared to hardening agents that have been commonly used in the past (Patent Documents 1-3). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2024-097580 [Patent Document 2] Japanese Patent Publication No. 2024-151995 [Patent Document 3] Japanese Patent Publication No. 2024-158313 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, while the aqueous ink compositions described in Patent Documents 1 to 3 yield good coating film properties, their water abrasion resistance is insufficient. Furthermore, there are still many challenges regarding the stability of these aqueous ink compositions, and their use has been limited to the time immediately after adding the aziridine-based curing agent. In water-based varnish compositions containing (meth)acrylic resin as a binder resin, the addition of an aziridine-based curing agent significantly impairs the stability of the water-based varnish composition due to its high reactivity. After time has passed since the addition of the aziridine-based curing agent, the stability of the water-based varnish composition is compromised, and consequently, various coating properties, including water abrasion resistance, are also significantly impaired.

[0007] The present invention has been made in view of these circumstances, and its objective is to provide an aqueous varnish composition that can form a coating film with excellent properties such as water resistance and friction resistance, has excellent stability, and consequently suppresses the deterioration of the coating film properties over time, as well as a laminate and a packaging material using the same. [Means for solving the problem]

[0008] The present invention has the following aspects. [1] an aqueous varnish composition, It contains an aqueous binder resin (A), an aziridine-based curing agent (B), and an aqueous medium (C), The aqueous binder resin (A) contains an emulsion-type (meth)acrylic resin (A1), The aforementioned emulsion-type (meth)acrylic resin (A1) has an acid value of 2 to 60 mgKOH / g and an average particle size of 0.04 μm to 0.2 μm. An aqueous varnish composition characterized in that the ratio of the total number of aziridine rings derived from the aziridine curing agent (B) to the total number of carboxyl groups derived from the aqueous binder resin (A) is 0.30 to 6.0. [2] The aqueous varnish composition according to [1], wherein the content of the emulsion-type (meth)acrylic resin (A1) on an amount of non-volatile matter basis is 70% by mass or more relative to the total non-volatile matter of the aqueous varnish composition. [3] The aqueous varnish composition according to [1] or [2], wherein the minimum film-forming temperature of the emulsion-type (meth)acrylic resin (A1) is 50°C or less. [4] The aqueous varnish composition according to any one of [1] to [3], wherein the acid value of the emulsion-type (meth)acrylic resin (A1) is 3 to 50 mg KOH / g. [5] Furthermore, it contains wax (D), The aqueous varnish composition according to any one of [1] to [4], wherein the penetration of the wax (D) is 12 or less and the average particle size is 6 μm or less. [6] Furthermore, it contains a thickening agent (E), The aqueous varnish composition according to any one of [1] to [5], wherein the thickening agent (E) contains an associated polyurethane-based thickening agent. [7] An aqueous varnish composition according to any of [1] to [6], for use in flexographic printing. [8] A laminate comprising a plastic film and a printed layer formed on one surface of the plastic film using the aqueous varnish composition described in any of [1] to [7]. [9] The laminate according to [8], further comprising a pattern layer between the plastic film and the printed layer. A packaging material comprising the laminate described in

[10] [9]. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an aqueous varnish composition that can form a coating film with excellent properties such as water resistance and friction resistance, has excellent stability, and consequently suppresses the deterioration of the coating film properties over time, as well as laminates and packaging materials using the same. [Modes for carrying out the invention]

[0010] The present invention will now be described in detail. The following embodiments are merely illustrative for illustrating 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 its spirit. In the present invention, "water-based" in an aqueous varnish composition means that it contains water as a medium. The proportion of water in the medium of the aqueous varnish composition is preferably 50% by mass or more, more preferably 70% by mass or more, and particularly preferably 90% by mass or more, based on the total mass of the medium. "Medium" refers to volatile components such as water and organic solvents. The "non-volatile content" of a water-based varnish composition refers to the components of the water-based varnish composition excluding the medium, and is the component that ultimately forms the coating film (printed layer). Specifically, it is measured in accordance with JIS K 5601-1-2:2008. "(Meth)acrylic" is a general term for "acrylic" and "methacrylic". "Water-based binder resin" is a general term encompassing both "water-soluble binder resin" and "water-dispersible binder resin." Examples of water-dispersible binder resins include emulsion type and dispersion type. The medium of the water-based binder resin is assumed to be included in the medium of the water-based varnish composition. The weight-average molecular weight of the aqueous binder resin is the weight-average molecular weight converted to the standard polystyrene molecular weight and is measured by gel permeation chromatography (GPC). The glass transition temperature of aqueous binder resin is measured in accordance with JIS K 7121:2012 as follows: Using a differential scanning calorimeter, 10 mg of aqueous binder resin is heated from -100°C to 160°C at a rate of 20°C / min. The glass transition temperature is determined from the intersection point of the baseline and the tangent to the endothermic curve in the resulting curve (DSC curve). The acid value of an aqueous binder resin is expressed in milligrams as the amount of potassium hydroxide required to neutralize acidic groups such as carboxyl groups per gram of non-volatile matter in the sample, and is measured in accordance with JIS K 5601-2-1:1999. The average particle diameter of paraffin wax (C) is the particle diameter at 50% cumulative frequency (median diameter: D50) calculated from the volume-based particle diameter distribution obtained by measuring the volume-based particle diameter distribution using the dynamic light scattering method, and is also called the volume-average particle diameter. The average particle size of emulsion-type (meth)acrylic resin (A1) is the particle size at which the volume-based cumulative frequency reaches 50% (median diameter: D50) calculated from the volume-based particle size distribution obtained by dynamic light scattering. The average particle size of wax (D) is the particle size at which the cumulative frequency of particles reaches 50% (median diameter: D50) is calculated from the particle size distribution obtained by measuring the particle size distribution on a number basis using the Coulter counter method. The Coulter counter method is a method of electrically measuring the particle size and particle size distribution of particles by passing particles dispersed in a medium through pores and observing the change in electrical signals as the particles pass through. The penetration of wax (D) is determined in accordance with JIS K 2235. The measurement temperature is 25°C. The "~" indicating a numerical range means that the numerical values described before and after it are included as the lower limit value and the upper limit value.

[0011] 〔Water-based varnish composition〕 The water-based varnish composition of the present embodiment contains an aqueous binder resin (A), an aziridine-based curing agent (B), and an aqueous medium (C). The water-based varnish composition may further contain a wax (D). The water-based varnish composition may further contain a thickener (E). The water-based varnish composition may further contain other components (hereinafter also referred to as other optional components) other than the aqueous binder resin (A), the aziridine-based curing agent (B), the aqueous medium (C), the wax (D), and the thickener (E) as long as the effects of the present invention are not impaired.

[0012] <Aqueous binder resin (A)> The aqueous binder resin (A) contains an emulsion-type (meth)acrylic resin (A1). The aqueous binder resin (A) may further contain other aqueous binder resins other than the emulsion-type (meth)acrylic resin (A1) in accordance with various required physical properties as long as the effects of the present invention are not impaired.

[0013] 「Emulsion-type (meth)acrylic resin (A1)」 The emulsion-type (meth)acrylic resin (A1) (hereinafter also referred to as resin (A1)) is a kind of water-dispersible (meth)acrylic resin. Typically, the resin (A1) has a core-shell structure. The core part of the core-shell structure is preferably a hydrophobic (meth)acrylic resin. The shell part of the core-shell structure is preferably a hydrophilic (meth)acrylic resin. The core part and the shell part may be bonded by a crosslinking agent.

[0014] The hydrophobic (meth)acrylic resin of the core is typically a resin containing constituent units based on (meth)acrylate monomers. Examples of such resins include homopolymers of (meth)acrylate monomers, copolymers of two or more (meth)acrylate monomers, and copolymers of (meth)acrylate monomers and monomers other than (meth)acrylate monomers. The (meth)acrylate monomer is preferably one that does not have a carboxyl group.

[0015] The hydrophilic (meth)acrylic resin of the shell portion is typically a resin containing constituent units based on carboxyl group-containing monomers. Examples of such resins include homopolymers of carboxyl group-containing monomers, copolymers of two or more carboxyl group-containing monomers, and copolymers of carboxyl group-containing monomers and monomers other than carboxyl group-containing monomers. The monomers other than carboxyl group-containing monomers can be any monomer that does not have a carboxyl group, and may be (meth)acrylate monomers or monomers other than (meth)acrylate-based monomers.

[0016] Examples of (meth)acrylate monomers 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. (Meth)acrylate monomers may be used individually or in combination of two or more.

[0017] Examples of monomers containing carboxyl groups include (meth)acrylic acid, maleic acid (maleic anhydride), fumaric acid, and itaconic acid (itaconic anhydride). Carboxyl group-containing monomers may be used individually or in combination of two or more.

[0018] Examples of monomers other than (meth)acrylate monomers and carboxyl group-containing monomers include conjugated diene compounds such as 1,3-butadiene, isoprene, and chloroprene; aromatic vinyl compounds such as styrene, α-methylstyrene, halogenated styrene, and divinylbenzene; 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 monomers may be used individually or in combination of two or more.

[0019] The resin (A1) may be self-crosslinking. If the resin (A1) is self-crosslinking, the resin (A1) typically contains structural units based on reactive functional group-containing monomers. These structural units may be contained in the core, the shell, or both. Examples of monomers containing reactive functional groups include monomers containing alkoxysilyl groups, monomers containing hydrazine groups, monomers containing epoxy groups, monomers containing methylol groups, monomers containing alkoxymethyl groups, dihydrazide adipate, 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. Reactive functional group-containing monomers may be used individually or in combination of two or more.

[0020] In resin (A1), 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. When the mass ratio of the core portion to the shell portion is within the above range, the stability, film-forming properties, adhesion of the printed layer to the substrate, abrasion resistance, water abrasion resistance, and blocking resistance of the aqueous varnish composition are better. If the amount of core portion is greater and the amount of shell portion is less than the above range, stability, film-forming properties, and adhesion to the substrate may decrease. If the amount of core portion is less and the amount of shell portion is greater than the above range, abrasion resistance, water abrasion resistance, and blocking resistance may decrease.

[0021] The acid value of resin (A1) is 60 mgKOH / g or less, preferably 50 mgKOH / g or less, more preferably 30 mgKOH / g or less, and 2 mgKOH / g or more, preferably 3 mgKOH / g or more, and more preferably 5 mgKOH / g or more. The above upper and lower limits can be combined as appropriate. When the acid value of resin (A1) is below the above upper limit, the stability of the water-based varnish composition, the water-based varnish layer's abrasive resistance, and heat resistance are excellent. When the acid value of resin (A1) is above the above lower limit, the water-based varnish composition's printability and the resolubility of the printed layer are excellent.

[0022] The average particle size of resin (A1) is 0.04 μm to 0.2 μm, preferably 0.045 μm to 0.15 μm, and more preferably 0.05 μm to 0.12 μm. When the average particle size of resin (A1) is below the above upper limit, the adhesion, abrasion resistance, and water abrasion resistance of the printed layer to the substrate are excellent. When the average particle size of resin (A1) is above the above lower limit, the stability of the aqueous varnish composition and the blocking resistance of the printed layer are excellent.

[0023] The glass transition temperature of resin (A1) is preferably -10 to 90°C, more preferably -5 to 70°C, and even more preferably 0 to 60°C. If the glass transition temperature of resin (A1) is above the lower limit, the heat resistance and blocking resistance are better, and if it is below the upper limit, the adhesion of the printed layer to the substrate, abrasion resistance, and water abrasion resistance are better.

[0024] The minimum film-forming temperature of resin (A1) is preferably 50°C or lower, more preferably 30°C or lower, and even more preferably 10°C or lower. When the minimum film-forming temperature of resin (A1) is below the above upper limit, the film-forming properties of the aqueous varnish composition, the adhesion of the printed layer to the substrate, abrasion resistance, water abrasion resistance, and heat resistance are better. The minimum film formation temperature is measured in accordance with JIS K 6828-2:2003.

[0025] The resin (A1) may be one manufactured by a known manufacturing method, or a commercially available product may be used. In the production of resin (A1), the polymerization method of the monomer is not particularly limited, but examples include radical polymerization, anionic polymerization, cationic polymerization, etc. In particular, radical polymerization includes bulk polymerization, solution polymerization, emulsion polymerization, suspension polymerization, etc. Among these, emulsion polymerization is preferred. Emulsion polymerization is a method of polymerization in which the monomers 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 compounding the core and shell parts after producing them separately, or it may be produced by multi-step emulsion polymerization. The polymerization mode may be any of random copolymer, block copolymer, graft copolymer, etc.

[0026] Examples of commercially available resins (A1) include the "Hyros-X series" manufactured by Seikoh PMC Co., Ltd., the "Joncryl series" manufactured by BASF Japan Ltd., and the "Neocryl series" manufactured by Covestro. Resin (A1) may be used alone or in combination of two or more types.

[0027] "Other water-based binder resins" Other aqueous binder resins are not particularly limited, but examples include water-soluble (meth)acrylic resins, dispersion-type (meth)acrylic resins, aqueous polyurethane resins, aqueous polyolefin resins, and aqueous polyester resins. Aqueous polyurethane resins, aqueous polyolefin resins, and aqueous polyester resins may each be of the following types: water-soluble, emulsion, or dispersion.

[0028] <Aziridine-based hardener (B)> The aziridine-based curing agent (B) (hereinafter also simply referred to as curing agent (B)) is a compound containing two or more aziridine groups in one molecule. The aziridine groups react with the carboxyl groups in the aqueous binder resin (A), causing the crosslinking reaction (curing reaction) of the aqueous binder resin (A) to proceed. The number of aziridine groups (functional groups) contained in one molecule of the curing agent (B) is preferably 3 or more, from the viewpoint that a network structure is formed when a crosslinking reaction occurs with the aqueous binder resin (A), which is expected to further improve physical properties, and from the viewpoint of stability when added, it is preferably 4 or less.

[0029] Examples of curing agents (B) include 2,2-bishydroxymethylbutanol-tris[3-(1-aziridinyl)propionate], pentaerythritol-tris[3-(1-aziridinyl)propionate], and 4,4'-bis(ethyleneiminocarbonylamino)diphenylmethane. Examples of commercially available hardening agents (B) include the "Chemitite" series from Nippon Shokubai Co., Ltd. and the "Picassian" series from Stahl. The hardening agent (B) may be used alone or in combination of two or more types.

[0030] <Aqueous medium (C)> Examples of aqueous media (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, but examples 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. One organic solvent may be used alone, or two or more may be used in combination. The aqueous medium (C) preferably does not contain an organic solvent.

[0031] <Wax (D)> To improve the water resistance, abrasion resistance, and blocking resistance of the printed layer, the water-based varnish composition may further contain wax (D). A water-based wax is preferred as the wax (D). Aqueous wax is a wax that has been dispersed in water to form an emulsion or dispersion. The wax dispersed in water may be any conventionally known wax, such as polyethylene wax, polypropylene wax, modified paraffin wax, carnauba wax, or polytetrafluoroethylene wax. Among these, polyethylene wax and polypropylene wax are preferred. Wax (D) may be used alone or in combination of two or more types.

[0032] The average particle size of wax (D) is preferably 6 μm or less, more preferably 5 μm or less, and even more preferably 4 μm or less. When the average particle size of wax (D) is below the above upper limit, water friction resistance, friction resistance, and color development are better. If wax (D) is an aqueous wax, the average particle size of the dispersed particles in the aqueous wax can be considered as the average particle size of wax (D) in the aqueous varnish composition.

[0033] The penetration degree of wax (D) is preferably 10 or less, more preferably 5 or less, and even more preferably 3 or less. When the penetration degree of wax (D) is below the above upper limit, water resistance, abrasion resistance, and blocking resistance are better.

[0034] <Thickening agent (E)> For the purpose of increasing the viscosity of the water-based varnish composition and improving its stability, the water-based varnish composition may contain an additional thickener (E). Examples of thickeners (E) include polyurethane-based thickeners, polyacrylic-based thickeners, polyamide-based thickeners, cellulose-based thickeners, and clay minerals such as bentonite. Among these, associated polyurethane-based thickeners are preferred because they have an excellent effect in improving stability. Examples of commercially available polyurethane-based thickeners include the "SN Thickener Series" manufactured by Sunopco. Thickening agent (E) may be used alone or in combination of two or more types.

[0035] <Other optional components> Other optional components not listed above may include known additives. Examples of additives include defoamers, surfactants, anti-settling agents, UV absorbers, antioxidants, leveling agents, surface tension modifiers, rheology modifiers, light stabilizers, lubricants, dispersants, stabilizers, pH adjusters, fillers, antifungal agents, antistatic agents, metal nanoparticles, magnetic powders, and the like. Other optional components may be used individually or in combination of two or more.

[0036] <Content of each ingredient> The content of the water-based binder resin (A) on a non-volatile matter basis is preferably 26 to 44% by mass, more preferably 29 to 41% by mass, and even more preferably 32 to 38% by mass, relative to the total mass of the water-based varnish composition. The content of the aqueous binder resin (A) on a non-volatile content basis is preferably 80 to 97% by mass, more preferably 85 to 95% by mass, and even more preferably 87 to 93% by mass, relative to the total non-volatile content of the aqueous varnish composition. When the content of the water-based binder resin (A) is above the lower limit, adhesion to the substrate and blocking resistance are better, and when it is below the upper limit, moisture friction resistance, friction resistance, heat resistance, and printability are better.

[0037] The content of resin (A1) on a non-volatile matter basis is preferably 28% by mass or more, more preferably 30% by mass or more, even more preferably 32% by mass or more, and preferably 42% by mass or less, more preferably 39% by mass or less, and even more preferably 38% by mass or less, based on the total mass of the aqueous varnish composition. The content of resin (A1) on a non-volatile content basis is preferably 70% by mass or more, more preferably 76% by mass or more, even more preferably 80% by mass or more, and preferably 95% by mass or less, more preferably 94% by mass or less, and even more preferably 92% by mass or less, relative to the total non-volatile content of the aqueous varnish composition. When the resin (A1) content is above the lower limit, the heat resistance, moisture resistance, abrasion resistance, and blocking resistance are superior. When the resin (A1) content is below the upper limit, the blocking resistance is superior. The upper and lower limits can be combined as appropriate.

[0038] The amount of curing agent (B) is such that the ratio of the total number of aziridine rings derived from curing agent (B) to the total number of carboxyl groups derived from aqueous binder resin (A) (hereinafter also referred to as Az / COOH) is 0.30 to 6.0. Az / COOH is preferably 0.40 to 5.0, and more preferably 0.50 to 4.0. If Az / COOH is above the lower limit, the water abrasion resistance, abrasion resistance, and heat resistance of the printed layer are excellent, and if it is below the upper limit, the stability of the aqueous varnish composition and the blocking resistance of the printed layer are excellent.

[0039] The content of the aqueous medium (C) is preferably 20 to 90% by mass, more preferably 30 to 80% by mass, and even more preferably 40 to 70% by mass, relative to the total mass of the aqueous varnish composition. When the content of the aqueous medium (C) is above the lower limit, the fluidity and printability are better, and when it is below the upper limit, the blocking resistance and drying properties are better.

[0040] If the aqueous varnish composition contains wax (D), the content of wax (D) in terms of non-volatile matter is preferably 0.1 to 5% by mass, more preferably 0.2 to 3% by mass, and even more preferably 0.3 to 1% by mass, based on the total mass of the aqueous varnish composition. When the aqueous varnish composition contains wax (D), the amount of wax (D) in terms of non-volatile content is preferably 0.1 to 10% by mass, more preferably 0.5 to 5% by mass, and even more preferably 1 to 3% by mass, relative to the total non-volatile content of the aqueous varnish composition. When the wax (D) content is above the lower limit, the effects of wax (D) on improving water resistance, abrasion resistance, and blocking resistance are fully realized, and when it is below the upper limit, printability and color development are even better.

[0041] If the aqueous varnish composition contains a thickener (E), the amount of thickener (E) in terms of non-volatile content is preferably 0.01 to 1% by mass, more preferably 0.02 to 0.5% by mass, and even more preferably 0.03 to 0.1% by mass, relative to the total mass of the aqueous varnish composition. When the aqueous varnish composition contains a thickener (E), the amount of thickener (E) in terms of non-volatile content is preferably 0.01 to 3% by mass, more preferably 0.05 to 1% by mass, and even more preferably 0.1 to 0.5% by mass, relative to the total non-volatile content of the aqueous varnish composition. When the content of the thickener (E) is above the lower limit, the viscosity-improving and stability-improving effects of the thickener (E) are fully realized, and when it is below the upper limit, printability, color development, water-resistance, and abrasion resistance are superior.

[0042] The content of other optional components is not particularly limited as long as it does not impair the effects of the present invention, but for example, it is preferably 0 to 20% by mass, more preferably 0 to 15% by mass, and even more preferably 0 to 10% by mass, relative to the total mass of the aqueous varnish composition. If the aqueous varnish composition contains other optional components, the content of these other 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 varnish composition. When the content of these other optional components is above the above lower limit, the effects of the other components are fully expressed.

[0043] <Manufacturing method> The aqueous varnish composition of this embodiment can be obtained, for example, by mixing an aqueous binder resin (A), a hardener (B), an optional additional aqueous medium (C), an optional wax (D), an optional thickener (E), and an optional other optional component. The method of mixing each component is not particularly limited, and the components can be mixed by various methods. For example, one method is to dissolve or disperse an aqueous binder resin (A), a curing agent (B), a wax (D) if necessary, a thickener (E) if necessary, and other optional components in an aqueous medium (C). The method for dissolving or dispersing each component in an aqueous medium is not particularly limited and can be carried out using known dispersers. Examples of dispersers include paint shakers, ball mills, attritors, sand mills, bead mills, dyno mills, roll mills, ultrasonic mills, and high-pressure impact dispersers. In this case, the dispersion treatment may be performed once or multiple times using one type of disperser, or multiple dispersion treatments may be performed using two or more types of dispersers in combination.

[0044] <Effects and Effects> The aqueous varnish composition of this embodiment described above contains the above-mentioned resin (A1), curing agent (B), and aqueous medium (C), and has an Az / COOH ratio of 0.30 to 6.0, thereby enabling the formation of a coating film with excellent properties such as water resistance and friction resistance, as well as excellent stability, and consequently suppressing the deterioration of the coating film properties over time.

[0045] The inventors have found that the stability of an aqueous varnish composition containing a resin (A1), a curing agent (B), and an aqueous medium (C) is greatly influenced by three factors: the acid value and average particle size of the resin (A1), and the Az / COOH ratio. The crosslinking reaction between the carboxyl group-containing resin (A1) and the curing agent (B) is thought to proceed relatively slowly when they coexist in an aqueous medium (C), and mainly proceeds during the drying process (film formation) after coating. This is because, as the aqueous medium (C) volatilizes during the drying process, its concentration increases, bringing the reaction sites closer together, and the heat applied during drying promotes the crosslinking reaction. However, if the formulation does not satisfy the three elements mentioned above, the crosslinking reaction is more likely to proceed even in the aqueous varnish composition before coating, leading to thickening, gelation, and a decrease in various physical properties. The inventors initially found that a high acid value of resin (A1) leads to poor stability of the aqueous varnish composition. Resin (A1) generally adopts a structure in which hydrophobic groups face inward and hydrophilic groups face outward in order to maintain an emulsion state. Taking the core-shell structure as an example, the core is hydrophobic and the shell is hydrophilic, and in order to be stabilized in water, the hydrophilic groups (carboxyl groups) present in the shell face outward. Therefore, it is considered that the acid value of resin (A1) is particularly sensitive to the proximity of reaction sites with aziridine groups. The inventors further discovered that the stability of resin (A1) deteriorates when the average particle size is small. This is thought to be because a smaller average particle size results in a larger surface area, which similarly greatly affects the proximity of the reaction site with the aziridine group. Assuming the use of a resin (A1) with an appropriate acid value and average particle size, we further found that stability decreases as the Az / COOH ratio increases. Even when using a resin (A1) with an appropriate acid value and average particle size, it is thought that crosslinking reactions will proceed in the aqueous varnish composition if there is an excess of aziridine groups.

[0046] When the minimum film-forming temperature of resin (A1) is 50°C or lower, film-forming properties, adhesion to the substrate, abrasion resistance, water abrasion resistance, and heat resistance are improved. One of the contributing factors is that, as is already known, a low minimum film formation temperature makes film formation defects less likely, and as a result, the resin (A1) can perform to its full potential. Furthermore, in the aqueous varnish composition of this embodiment, the crosslinking reaction of the curing agent (B) is thought to proceed mainly during the drying process (film formation) after coating, as described above. Therefore, the lower the minimum film formation temperature, the earlier film formation begins in the drying process. That is, film formation begins while the aqueous medium (C) has not completely evaporated and the fluidity of the coating remains. This allows for good compatibility between the resin (A1) and the curing agent (B), enabling the crosslinking reaction to proceed evenly and efficiently, thus producing the above-mentioned effects.

[0047] The stability of the water-based varnish composition is further improved when it contains a thickening agent (E), and especially when the thickening agent (E) contains an associated polyurethane-based thickening agent. When the viscosity of the aqueous varnish composition is increased by the thickening agent (E), it becomes more difficult for the aziridine groups contained in the curing agent (B) and the carboxyl groups contained in the aqueous binder resin (A) to come into contact in the aqueous varnish composition, and it is thought that this can suppress the crosslinking reaction in the aqueous varnish composition. Associative polyurethane thickeners are compounds that contain urethane bonds and hydrophilic polyether chains in their main skeleton, with hydrophobic functional groups at both ends. The hydrophobic functional groups of the associateative polyurethane thickener interact with each other and associate, or the hydrophobic functional groups associate with dispersed particles of the emulsion, thereby constructing a mesh-like network and thickening the aqueous varnish composition. It is believed that the expression of thickening by constructing this mesh-like network inhibits the approach of aziridine groups contained in the curing agent (B) and carboxyl groups contained in the aqueous binder resin (A) in the aqueous varnish composition, thereby more efficiently suppressing the crosslinking reaction in the aqueous varnish composition.

[0048] <Application> The aqueous varnish composition of this embodiment is printed onto any substrate to form a printed layer. Hereinafter, the printed layer formed using the aqueous varnish composition will also be referred to as the varnish layer. The thickness of the varnish layer is, for example, 0.1 to 1 μm. If the varnish layer contains particles (e.g., wax (D) particles) and some of these particles protrude from the surface of the varnish layer, the thickness of the varnish layer shall be the thickness of the portion where the particles do not protrude.

[0049] Examples of substrates include plastic films. Examples of plastic films include polyolefins (e.g., polyethylene (PE), milky polyethylene, polypropylene (PP), etc.), polyesters (e.g., polyethylene terephthalate (PET), etc.), polystyrene (PS), stretched polypropylene (OPP), and polyamide (NY), etc. (base films). Plastic films may be used individually or two or more types may be laminated together. The thickness of the plastic film (or the thickness after lamination if two or more types are used together) is, for example, 10 to 50 μm.

[0050] The method for forming the varnish layer may be any known printing method. For example, the varnish layer may be formed by applying an aqueous varnish composition to a substrate and drying it. The coating method may be any known coating method, 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. Among these, flexographic printing is preferred due to its high quality and productivity. Therefore, the aqueous varnish composition of this embodiment is preferably for flexographic printing. The drying method may be any known drying method, such as vacuum drying, pressure drying, heat drying, or air drying. The drying temperature is not particularly limited, as long as it can remove the aqueous medium (C), but is for example 60 to 100°C. The varnish layer may be formed on one side of the plastic film, or on both the one side and the other side of the plastic film. Typically, it is formed on one side of the plastic film.

[0051] A laminate comprising a plastic film and a varnish layer formed on one surface of the plastic film using the aqueous varnish composition of this embodiment is suitable as a packaging material, particularly as a packaging label. Packaging labels are attached to containers such as plastic containers, metal containers, and paper containers. Examples of packaging labels include roll labels, which are attached by wrapping them around the container and securing them with adhesive, and shrink labels, which are attached by applying heat to shrink them to a shape that fits the container. When the laminate is used for packaging labels, it is preferable that one of the surfaces on which the varnish layer is formed is the inner surface of the packaging label, i.e., the surface facing the container.

[0052] The laminate may further include a pattern layer between the plastic film and the varnish layer. The pattern layer is typically a printed layer formed using ink. The ink may be a known ink. The ink typically contains a pigment. The method for forming the ink layer may be a known printing method, similar to the method for forming the varnish layer.

[0053] The laminate may further comprise other layers on the other surface of the plastic film. Examples of other layers include a varnish layer and a matte ink layer. The varnish layer on the other surface may be formed using the aqueous varnish composition of this embodiment, or using a known varnish. The matte ink layer is a printed layer formed using a matte ink. The matte ink may be a known matte ink. The matte ink typically contains a matting agent. The method for forming the matte ink layer may be a known printing method, similar to the method for forming the varnish layer. [Examples]

[0054] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the invention.

[0055] [Raw materials used] <Resin (A1)> A1-1: Manufactured by Seikoh PMC Co., Ltd., product name "Hyros-X M-141", non-volatile content: 46%, acid value: 19 mg KOH / g, average particle size: 0.07 μm, minimum film formation temperature: less than 5℃. A1-2: Manufactured by Seikoh PMC Co., Ltd., product name "Hyros-X KE-1148", non-volatile content: 43%, acid value: 31 mg KOH / g, average particle size: 0.08 μm, minimum film formation temperature: less than 5℃. A1-3: Manufactured by BASF Japan Ltd., product name "Joncryl 352D", non-volatile content: 45%, acid value: 51 mg KOH / g, average particle size: 0.1 μm, minimum film formation temperature: 10℃. A1-4: Manufactured by BASF Japan Ltd., product name "Joncryl PDX-7164", non-volatile content: 47%, acid value: 4 mg KOH / g, average particle size: 0.17 μm, minimum film formation temperature: 8℃. A1-5: Manufactured by BASF Japan Ltd., product name "Joncryl PDX-7780", non-volatile content: 48%, acid value: 46 mg KOH / g, average particle size: 0.1 μm, minimum film formation temperature: over 50°C. A1-6: Manufactured by Seikoh PMC Co., Ltd., product name "Hyros-X RE-218", non-volatile content: 40%, acid value: 49 mg KOH / g, average particle size: 0.035 μm, minimum film formation temperature: less than 5℃. A1-7: Manufactured by Seikoh PMC Co., Ltd., product name "Hyros-X TE-1124", non-volatile content: 60%, acid value: 25 mg KOH / g, average particle size: 0.33 μm, minimum film formation temperature: less than 5℃. A1-8: Manufactured by Seikoh PMC Co., Ltd., product name "Hyros-X TE-1336", non-volatile content: 39%, acid value: 64 mg KOH / g, average particle size: 0.15 μm, minimum film formation temperature: less than 5℃.

[0056] <Water-based polyurethane resin (A2)> A2-1: Covestro product, product name "NeoRez R-600", non-volatile content: 33%, acid value: 7 mg KOH / g.

[0057] <Water-based polypropylene resin (A3)> A3-1: Manufactured by Mitsubishi Chemical Corporation, product name "Aptrock BW-5596", non-volatile content: 30%, acid value: 15 mg KOH / g.

[0058] <Hardening agent (B)> • B-1: Manufactured by Nippon Shokubai Co., Ltd., product name "Chemitite PZ-33", non-volatile content: 99%, molecular weight 425.24 g / mol, number of functional groups 3.

[0059] <Aqueous medium (C)> Water: Tap water.

[0060] <Wax (D)> • D-1: Manufactured by Mitsui Chemicals, Inc., product name "Chemipearl W-401", non-volatile content: 40%, penetration: 3, average particle size: 1 μm. • D-2: Manufactured by Mitsui Chemicals, Inc., product name "Chemipearl W-410", non-volatile content: 40%, penetration degree: 3, average particle size: 9.5 μm. D-3: Polyolefin wax, non-volatile content: 15%, penetration: 13, average particle size: 2.2 μm.

[0061] <Thickening agent (E)> • E-1: Associative polyurethane-based thickener, manufactured by Sunopco Corporation, product name "SN Thickener 612", non-volatile content: 40%. E-2: Polyacrylic thickener, manufactured by BASF Japan Ltd., product name "Rheovis AS1130", non-volatile content: 30%.

[0062] <Other optional components> • Surfactant: Evonik brand, product name "TEGO WET 240", non-volatile content: 100%. • Defoaming agent: Manufactured by BYK, product name "BYK-018", non-volatile content: 97%.

[0063] [Examples 1-18, Comparative Examples 1-7] <Preparation of water-based varnish composition> Aqueous varnish compositions with the compositions shown in Tables 1-5 were prepared using the following procedure. The components other than the hardener (B) were mixed and kneaded in a paint shaker. The hardener (B) was added to the resulting mixture to obtain an aqueous varnish composition. The hardener (B) was added immediately before preparing the varnish for printing in the following <Preparation of Printed Materials> or <Evaluation of Stability>.

[0064] <Creating printed materials> The prepared aqueous varnish composition was diluted with water to a viscosity of 15 seconds at 25°C, as measured using a Zahn cup #4, to prepare a printing varnish. Using an anilox roll with a cell volume of 6cc, the prepared printing varnish was applied to the treated surface of an OPP film (Futamura Chemical Co., Ltd., product name "FOR", thickness: 30μm) that had been corona-discharged on one side, or to the treated surface of a PET film (Toyobo Co., Ltd., product name "E5102", thickness: 12μm) that had been corona-discharged on one side, or to the inner surface of a PS film (Gunze Corporation, product name "Fancy Wrap GMGS", thickness: 50μm). The printed layer (varnish layer) was then formed by drying at 20°C for 24 hours to obtain a printed material. For corona treatment, a corona discharge surface treatment device (product name "CTW-0212") manufactured by Wedge Co., Ltd. was used.

[0065] <Stability Evaluation> Printing varnish was prepared by diluting it with water so that its viscosity at 25°C, as measured using a Zahn cup #4, was 15 seconds. The varnish was then allowed to stand at 25°C for 12 hours. After that, the viscosity of the printing varnish was measured again at 25°C using a Zahn cup #4, and its stability was evaluated according to the evaluation criteria shown below. A score of 3 to 5 is considered acceptable. 5. The increase in viscosity after standing is 5 seconds or less compared to before standing. 4. The increase in viscosity after standing is more than 5 seconds but less than 10 seconds compared to before standing. 3. The increase in viscosity after standing is more than 10 seconds but less than 15 seconds compared to before standing. 2: The increase in viscosity after standing is more than 15 seconds but less than 30 seconds compared to before standing. 1: After standing, an increase in viscosity was observed for more than 30 seconds compared to before standing, or gelation was confirmed.

[0066] <Evaluation of adhesion to the substrate> After applying cellophane tape (manufactured by Nichiban Co., Ltd.) to the varnish-coated surface (printed side) of the obtained printed material, the cellophane tape was quickly removed, and the condition of the varnish layer remaining on the substrate was visually inspected. The adhesion of the varnish layer to the substrate was evaluated according to the following evaluation criteria. A score of 3 to 5 is considered acceptable. 5: The varnish layer has not peeled off at all. 4. The ratio of the area of ​​the peeled varnish layer to the total area of ​​the varnish layer is greater than 0% and less than or equal to 10%. 3. The ratio of the area of ​​the peeled varnish layer to the total area of ​​the varnish layer is greater than 10% but less than or equal to 30%. 2: The ratio of the area of ​​the peeled varnish layer to the total area of ​​the varnish layer is greater than 30% but less than or equal to 50%. 1: The area of ​​the peeled varnish layer is more than 50% of the total area of ​​the varnish layer.

[0067] <Evaluation of blocking resistance> The printed side of the printed material immediately after production (before drying) is placed on top of the unprinted side of the same film, and the temperature is measured at 5 kg / cm². 2 The specimens were subjected to a load and stored in a constant temperature chamber at 40°C and 50% humidity for 24 hours. Afterward, the test specimens were peeled off, and their blocking resistance was evaluated according to the following evaluation criteria. A score of 3 to 5 is considered acceptable. "Varnish removal" means that the varnish layer adhered to the opposing surface (the non-printed surface in this evaluation) while peeling from the substrate. 5: No varnish is applied to non-printed surfaces. 4. The amount of varnish removed from the non-printed surface is greater than 0% and less than or equal to 10% of the total area of ​​the varnish layer. 3: The amount of varnish removed from the non-printed surface is between 10% and 30% of the total area of ​​the varnish layer. 2: The amount of varnish removed from the non-printed surface is between 30% and 50% of the total area of ​​the varnish layer. 1: The amount of varnish removed from the non-printed surface exceeds 50% of the total area of ​​the varnish layer.

[0068] <Evaluation of water and friction resistance> The printed surface of the obtained printed material was subjected to a friction test using a JSPS-type friction fastness tester (manufactured by Tester Sangyo Co., Ltd., product name "AB-301"), in which a water-moistened white cloth (Kanahaba No. 3) was rubbed back and forth 200 times under a load of 200 gf. Afterwards, the appearance of the varnish layer was visually inspected, and the water resistance friction was evaluated according to the evaluation criteria shown below. A score of 3 to 5 is considered acceptable. 5: The percentage of the varnish layer that has migrated to the white cloth (gold cloth No. 3) side is 0%. 4. The percentage of the varnish layer that has migrated to the white cloth (gold cloth No. 3) side is greater than 0% and less than or equal to 5%. 3. The percentage of the varnish layer that has migrated to the white cloth (gold cloth No. 3) side is greater than 5% and less than or equal to 10%. 2: The percentage of the varnish layer that has migrated to the white cloth (gold cloth No. 3) side is greater than 10% and less than or equal to 30%. 1: The area of ​​the varnish layer that has moved to the white cloth (gold cloth No. 3) side exceeds 30%.

[0069] <Heat resistance evaluation> The printed surface of the resulting printout is placed on top of a soft aluminum foil, and a heat seal tester (Tester Industries Co., Ltd., product name "TP-701-C Heat Seal Tester") is used to seal the aluminum foil at 120, 130°C, 140°C, or 150°C at a rate of 2 kg / cm². 2 The product was heated for 3 seconds under the specified conditions. Afterward, the condition of the varnish layer was checked, and its heat resistance was evaluated according to the following criteria. A score of 3 to 5 is considered acceptable. Even at 5:150℃, the varnish didn't peel off. At 4:140℃, there was no varnish removal, but at 150℃, varnish removal occurred. At 3:130℃, there was no varnish removal, but at 140℃, varnish removal occurred. 2. There was no varnish removal at 120℃, but there was varnish removal at 130℃. At 1:120℃, the varnish was removed.

[0070] For Example 18 and Comparative Examples 6 and 7, printed materials were prepared and evaluated in the same manner using the printing varnish after its stability had been evaluated. Note that Example 18 corresponds to the varnish from Example 1 after its stability evaluation, Comparative Example 6 corresponds to the varnish from Comparative Example 3 after its stability evaluation, and Comparative Example 7 corresponds to the varnish from Comparative Example 5 after its stability evaluation.

[0071] [Table 1]

[0072] [Table 2]

[0073] [Table 3]

[0074] [Table 4]

[0075] [Table 5]

[0076] In the table, the amounts listed for each component represent the amounts of the active ingredients. The unit of the amount is mass %. The "residue" of water is the amount that makes the total of all components equal 100 mass %. The unit of the acid value is mgKOH / g. "Particle size" indicates the average particle diameter (μm). "NV." indicates non-volatile content. "MFT" indicates the minimum film-forming temperature (°C). "Pe" indicates the penetration degree.

[0077] <Application Examples> A laminate was obtained by forming a pattern layer on the treated surface of an OPP film (manufactured by Futamura Chemical Co., Ltd., product name "FOR", thickness: 30 μm) that had been corona-discharge treated on one side, using an aqueous white ink composition consisting of an emulsion-type (meth)acrylic resin as an aqueous binder resin, titanium dioxide as a pigment, water as an aqueous medium, an aziridine-based curing agent, wax, a thickener, and a surfactant, and then forming a varnish layer on the surface of the pattern layer using the varnish composition of Example 1. The obtained laminate was confirmed to have excellent adhesion to the substrate, blocking resistance, and heat resistance. Next, the resulting laminate was wrapped around a water-soaked plastic bottle with the printed side facing inward, and then secured with adhesive to create a packaging material. A transport test was conducted on the resulting packaging material to confirm its excellent water and abrasion resistance, and to verify that there were no problems with its use. [Industrial applicability]

[0078] The aqueous varnish composition of the present invention can form a coating film with excellent properties such as water resistance and friction resistance, and also exhibits excellent stability, thereby suppressing the deterioration of the coating film properties over time, making it useful as a varnish for packaging materials, especially for packaging labels.

Claims

1. A water-based varnish composition, It contains an aqueous binder resin (A), an aziridine-based curing agent (B), and an aqueous medium (C), The aqueous binder resin (A) contains an emulsion-type (meth)acrylic resin (A1), The aforementioned emulsion-type (meth)acrylic resin (A1) has an acid value of 2 to 60 mgKOH / g and an average particle size of 0.04 μm to 0.2 μm. An aqueous varnish composition characterized in that the ratio of the total number of aziridine rings derived from the aziridine curing agent (B) to the total number of carboxyl groups derived from the aqueous binder resin (A) is 0.30 to 6.

0.

2. The aqueous varnish composition according to claim 1, wherein the content of the emulsion-type (meth)acrylic resin (A1) on a non-volatile content basis is 70 to 95% by mass relative to the total non-volatile content of the aqueous varnish composition.

3. The aqueous varnish composition according to claim 1, wherein the minimum film-forming temperature of the emulsion-type (meth)acrylic resin (A1) is 50°C or lower.

4. The aqueous varnish composition according to claim 1, wherein the acid value of the emulsion-type (meth)acrylic resin (A1) is 3 to 50 mgKOH / g.

5. Furthermore, it contains wax (D), The aqueous varnish composition according to claim 1, wherein the penetration of the wax (D) is 12 or less and the average particle size is 6 μm or less.

6. Furthermore, it contains a thickening agent (E), The aqueous varnish composition according to claim 1, wherein the thickening agent (E) contains an associated polyurethane-based thickening agent.

7. An aqueous varnish composition according to any one of claims 1 to 6, for use in flexographic printing.

8. A laminate comprising a plastic film and a printed layer formed on one surface of the plastic film using the aqueous varnish composition described in claim 7.

9. The laminate according to claim 8, further comprising a pattern layer between the plastic film and the printed layer.

10. A packaging material comprising the laminate described in claim 9.

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