Water dispersion and laminate

Abstract

To provide a water dispersion that can form a coating film having excellent low-temperature heat sealability and a reduced feeling of tackiness.SOLUTION: A water dispersion has an ethylenic polymer (A1) with a density of 900 kg / m3 or more, an ethylene-α-olefin copolymer (A2) with a density of 895 kg / m3 or less, an unsaturated carboxylic acid copolymer (B) and water, with a mass ratio between the ethylenic polymer (A1) and ethylene-α-olefin copolymer (A2) [(A1) / (A2)] of 95 / 5-40 / 60.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an aqueous dispersion and a laminate, and more particularly to an aqueous dispersion and a laminate obtained by using the aqueous dispersion. [Background technology]

[0002] Conventionally, in various industrial fields, it has been known to bond substrates such as plastic films, vapor-deposited films, metal foils, paper, and nonwoven fabrics together, or to bond a substrate to another adherend, by heat and pressure (i.e., heat sealing). In heat sealing, a method of directly bonding the substrates together or the substrate to the adherend is usually used, but in order to improve the heat sealability between the substrate and the adherend, a method has also been used in which a heat seal agent (adhesive) layer is formed on the substrate in advance, and the substrates are bonded together or the substrate to the other adherend via the adhesive layer.

[0003] As an adhesive for use in such heat sealing agents, for example, an aqueous dispersion containing at least one type of high-crystallinity polyolefin having a crystallinity of more than 50%, at least one type of dispersant, and water has been proposed (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-52124 Summary of the Invention [Problem to be solved by the invention]

[0005] Laminates for heat-sealing applications are required to have good heat-sealing properties at low temperatures (for example, about 80 to 100°C) (hereinafter also referred to as "low-temperature heat-sealing properties"), and further, the coating film formed by applying the aqueous dispersion must have a low tackiness (stickiness) on the surface.

[0006] An object of the present invention is to provide an aqueous dispersion capable of forming a coating film having excellent low-temperature heat-sealing properties and little tackiness, and a laminate having a coating film having excellent low-temperature heat-sealing properties and little tackiness. [Means for solving the problem]

[0007] The present invention relates to the following [1] to [7]. [1] Density is 900 kg / m 3 The ethylene polymer (A1) above, having a density of 895 kg / m 3 An aqueous dispersion comprising the following ethylene-α-olefin copolymer (A2), unsaturated carboxylic acid copolymer (B), and water, wherein the mass ratio of the ethylene polymer (A1) to the ethylene-α-olefin copolymer (A2) [(A1) / (A2)] is in the range of 95 / 5 to 40 / 60.

[0008] [2] The aqueous dispersion of [1] above, wherein the ethylene polymer (A1) has a melting point of 95°C or higher, and the ethylene-α-olefin copolymer (A2) has a melting point of 80°C or lower. [3] The aqueous dispersion according to [1] or [2], wherein the unsaturated carboxylic acid polymer (B) is at least one polymer selected from the group consisting of an ethylene-unsaturated carboxylic acid copolymer (b1) and / or a salt thereof (B1) and a (meth)acrylic acid ester polymer (B2).

[0009] [4] The aqueous dispersion according to any one of [1] to [3] above, wherein the ethylene-α-olefin copolymer (A2) is an ethylene-1-butene copolymer. [5] A laminate comprising a substrate and an adhesive layer laminated on at least a portion of at least one surface of the substrate, the adhesive layer being made of a dried product of any one of the aqueous dispersions [1] to [4] above.

[0010] [6] The laminate of [5] above further comprises an adherend layer laminated on the surface of the adhesive layer opposite to the substrate side. [7] The laminate according to [5] or [6], wherein the substrate is made of aluminum. [Effects of the Invention]

[0011] The aqueous dispersion of the present invention can form a coating film that has excellent low-temperature heat-sealing properties and little tackiness. The coating film of the laminate of the present invention also has excellent low-temperature heat-sealing properties and little tackiness. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will now be described in further detail. [Water dispersion] The aqueous dispersion according to the present invention comprises an ethylene polymer (A1), an ethylene-α-olefin copolymer (A2), an unsaturated carboxylic acid polymer (B), and water, and is characterized in that the mass ratio of the polymer (A1) to the copolymer (A2) is within a predetermined range.

[0013] <Ethylene polymer (A1)> The ethylene polymer (A1), which is one of the components forming the aqueous dispersion of the present invention, is an ethylene homopolymer or a copolymer of ethylene and an α-olefin, the copolymer comprising ethylene as the main component.

[0014] The density of the ethylene polymer (A1) is 900 kg / m 3 or more, preferably 905 kg / m 3 More preferably, 910 kg / m 3 The upper limit is not particularly limited, but is usually 940 kg / m 3 Less than or equal to 935 kg / m 3 The following is the result.

[0015] The melting point of the ethylene polymer (A1), measured by differential scanning calorimetry (DSC) under the following conditions, is usually 95° C. or higher, preferably 100° C. or higher, and more preferably 105° C. or higher. The upper limit of the melting point of the ethylene polymer (A1) may be 140° C. or lower, or even 130° C. or lower.

[0016] [DSC measurement conditions] Using a differential scanning calorimeter, approximately 5.0 mg of a sample is heated from 30°C to 200°C at a heating rate of 10°C / min under a nitrogen atmosphere and held at that temperature for 10 minutes. The sample is then cooled to 30°C at a heating rate of 10°C / min, held at that temperature for 5 minutes, and then heated to 200°C at a heating rate of 10°C / min. The endothermic peak observed during this second heating is taken as the melting peak, and the temperature at which the melting peak appears is taken as the melting point. If the melting peak is multimodal, the temperature at which the highest melting peak appears is taken as the melting point.

[0017] Examples of the α-olefin in the ethylene-α-olefin copolymer include α-olefins having 3 to 12 carbon atoms, such as propylene, 1-butene, 3-methyl-1-butene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-heptene, 1-hexene, 1-decene, and 1-dodecene. The content (mol %) of structural units derived from α-olefins in the ethylene-α-olefin copolymer is determined by the following formula: 3 There are no particular limitations as long as the content is equal to or greater than the above, but it is, for example, 0.01 to 10 mol %. As long as the density and other properties of the ethylene polymer (A1) are within the above ranges, the method for producing the same is not particularly limited.

[0018] <Ethylene-α-olefin copolymer (A2)> The ethylene-α-olefin copolymer (A2), which is one of the components forming the aqueous dispersion of the present invention, has a density of 895 kg / m 3 Less than or equal to 890 kg / m 3 Less than or equal to 880 kg / m 3The ethylene-α-olefin copolymer (A2) is an ethylene-α-olefin copolymer having a density of 860 kg / m or less. 3 or more, preferably 865 kg / m 3 That's all.

[0019] The melting point of the ethylene-α-olefin copolymer (A2), as measured by DSC under the above conditions, is usually 80° C. or lower, and preferably 70° C. or lower. In the present invention, the term "° C. or lower" also includes polymers that do not have a melting point, as described below.

[0020] The ethylene / α-olefin copolymer (A2) may be amorphous, that is, it may have no melting point, or may have a melting point of 40° C. or higher, or 50° C. or higher. Examples of the α-olefin constituting the ethylene-α-olefin copolymer (A2) include α-olefins having 3 to 12 carbon atoms, such as propylene, 1-butene, 3-methyl-1-butene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-heptene, 1-hexene, 1-decene, and 1-dodecene.

[0021] The content (mol %) of structural units derived from α-olefins in the ethylene-α-olefin copolymer (A2) is not particularly limited as long as the density of the ethylene-α-olefin copolymer (A2) satisfies the above range, but is usually in the range of 5 to 50 mol %.

[0022] <Unsaturated Carboxylic Acid Polymer (B)> The unsaturated carboxylic acid polymer (B), which is one of the components forming the aqueous dispersion of the present invention, is a polymer and / or a salt thereof containing, as a structural unit, an unsaturated carboxylic acid or a derivative of an unsaturated carboxylic acid, such as an ester or an acid anhydride.

[0023] Examples of the unsaturated carboxylic acid polymer (B) include an ethylene-unsaturated carboxylic acid copolymer (b1) which is a copolymer of ethylene and an unsaturated carboxylic acid and / or a salt thereof (B1), and a (meth)acrylic acid ester polymer (B2) which is a derivative of an unsaturated carboxylic acid.

[0024] (Ethylene-unsaturated carboxylic acid copolymer (b1) and / or its salt (B1)) The ethylene-unsaturated carboxylic acid copolymer (b1) is a copolymer of ethylene and an unsaturated carboxylic acid.

[0025] The unsaturated carboxylic acid is a monomer having both at least one ethylenically unsaturated bond and a carboxy group in one molecule, and examples thereof include monobasic acids such as acrylic acid, methacrylic acid, and crotonic acid, and dibasic acids such as maleic acid, fumaric acid, and itaconic acid.

[0026] These unsaturated carboxylic acids may be used alone or in combination of two or more. As the unsaturated carboxylic acid, from the viewpoint of water resistance, preferably, a monobasic acid is used, and more preferably, acrylic acid or methacrylic acid is used.

[0027] The ethylene-unsaturated carboxylic acid copolymer (b1) contains structural units derived from ethylene (hereinafter also referred to as "ethylene units") and structural units derived from unsaturated carboxylic acid (hereinafter also referred to as "unsaturated carboxylic acid units") in a proportion of, relative to their total amount (100% by mass of the total amount of ethylene and unsaturated carboxylic acid), the ethylene units account for, for example, 75% by mass or more, preferably 78% by mass or more, and for example, 90% by mass or less, preferably 88% by mass or less. The unsaturated carboxylic acid units account for, for example, 10% by mass or more, preferably 12% by mass or more, and for example, 25% by mass or less, preferably 22% by mass or less.

[0028] When the content ratio of ethylene units and unsaturated carboxylic acid units in the ethylene-unsaturated carboxylic acid copolymer (b1) is within the above range, a coating film formed from the aqueous dispersion can exhibit excellent adhesive strength and blocking resistance.

[0029] The polymerization of ethylene and unsaturated carboxylic acid is not particularly limited, and known polymerization methods can be used. Examples of the polymerization method include a method in which ethylene and unsaturated carboxylic acid are brought into contact with a known polymerization initiator such as a peroxide under high temperature and high pressure conditions.

[0030] The ethylene-unsaturated carboxylic acid copolymer (b1) can be obtained as a dispersion (aqueous dispersion) in which its single particles (hereinafter referred to as resin particles (I)) are dispersed in water. In such cases, polymerization can be carried out by methods described, for example, in Japanese Patent Publication Nos. 7-008933, 5-039975, 4-030970, 42-000275, 42-023085, 45-029909, and 51-062890. The ethylene-unsaturated carboxylic acid copolymer (b1) has self-emulsifying properties.

[0031] In the production of the ethylene-unsaturated carboxylic acid copolymer (b1), an emulsifier (surfactant) described below can be added as needed to improve production stability. The proportion of the emulsifier added is appropriately determined.

[0032] In the production of the ethylene-unsaturated carboxylic acid copolymer (b1), known additives such as pH adjusters, sequestering agents such as ethylenediaminetetraacetic acid and salts thereof, and molecular weight regulators (chain transfer agents) such as mercaptans and low-molecular-weight halogen compounds may be blended in appropriate proportions in order to improve production stability.

[0033] As the ethylene-unsaturated carboxylic acid copolymer (b1) and / or its salt (B1), a salt of the ethylene-unsaturated carboxylic acid copolymer (b1) is preferred from the viewpoint of improving dispersion stability and printability of the laminate (described later).

[0034] The salt of the ethylene-unsaturated carboxylic acid copolymer (b1) can be prepared, for example, by adding a base to the ethylene-unsaturated carboxylic acid copolymer (b1), specifically, to a dispersion of the ethylene-unsaturated carboxylic acid copolymer (b1).

[0035] Examples of the base include inorganic bases such as sodium hydroxide and potassium hydroxide, and organic bases such as amines such as ammonia, triethylamine, triethanolamine and dimethylethanolamine.

[0036] These bases may be used alone or in combination of two or more. The base is preferably an inorganic base, more preferably sodium hydroxide.

[0037] The amount of base added (i.e., amount of substance / valence) is, from the viewpoint of improving dispersion stability and printability of the laminate (described later), for example, 5 moles or more, preferably 30 moles or more, more preferably 50 moles or more, and for example, 100 moles or less, preferably 95 moles or less, relative to 100 moles of carboxy groups in the ethylene-unsaturated carboxylic acid copolymer (b1).

[0038] When the amount of base added is equal to or greater than the lower limit, the dispersion stability of the aqueous dispersion is excellent and the printability of the laminate is excellent. When the amount of base added is equal to or less than the upper limit, the viscosity of the aqueous dispersion is not too high and the workability is excellent.

[0039] After the base is added to the ethylene-unsaturated carboxylic acid copolymer (b1), the mixture is preferably maintained at a predetermined temperature for a predetermined time. The temperature is, for example, 40°C or higher, preferably 50°C or higher, and for example, 190°C or lower, preferably 180°C or lower. The maintenance time is, for example, 30 minutes or longer, preferably 1 hour or longer, and for example, 12 hours or shorter, preferably 10 hours or shorter.

[0040] By maintaining the above conditions, the ethylene-unsaturated carboxylic acid copolymer (b1) is neutralized, and the dispersion stability and printability of the laminate (described later) can be improved. When the ethylene-unsaturated carboxylic acid copolymer (B1) is a salt of the ethylene-unsaturated carboxylic acid copolymer (b1), the degree of neutralization thereof is, for example, 30% or more, preferably 50% or more, and for example, 100% or less, preferably 95% or less.

[0041] If the degree of neutralization is within the above range, excellent adhesive strength and blocking resistance can be obtained. The degree of neutralization is calculated by the following method. The infrared absorption spectrum of the sample was measured, and the peak at 1700 cm corresponding to the carboxyl group was -1 Calculate the absorption peak height (peak height is a).

[0042] The sample is then brought into contact with hydrochloric acid to remove the metal ions in the resin (demetallation), yielding an acid copolymer free of ionic bonds (intramolecular crosslinking). The infrared absorption spectrum of this acid copolymer sample is measured, and the peak at 1700 cm -1 Calculate the absorption peak height (peak height is b).

[0043] The peak height a corresponds to the number of carboxyl groups that are not ionically bonded in the resin. The peak height b corresponds to the number of all carboxyl groups in the resin. Therefore, the degree of neutralization (%) is calculated using the following formula. Neutralization degree (%)=100-100×a / b

[0044] The weight average molecular weight of the ethylene-unsaturated carboxylic acid copolymer (b1) and / or its salt (B1) is, in terms of standard polystyrene measured by gel permeation chromatography (GPC), for example, 5,000 or more, preferably 10,000 or more, and for example, 1,000,000 or less, preferably 500,000 or less.

[0045] The melting point of the ethylene-unsaturated carboxylic acid copolymer (b1) and / or its salt (B1) measured by DSC under the above conditions is, for example, 55°C or higher, preferably 65°C or higher, and for example, 110°C or lower, preferably 100°C or lower.

[0046] The solids concentration of the ethylene-unsaturated carboxylic acid copolymer (b1) and / or its salt (B1) in the dispersion of the ethylene-unsaturated carboxylic acid copolymer (b1) and / or its salt (B1) is, for example, 10 mass% or more, preferably 20 mass% or more, and for example, 60 mass% or less, preferably 50 mass% or less.

[0047] The dispersion of the ethylene-unsaturated carboxylic acid copolymer (b1) and / or its salt (B1) is also available as a commercial product. The ethylene-unsaturated carboxylic acid copolymer (b1) and / or its salt (B1) may be used alone or in combination of two or more.

[0048] <(Meth)acrylic acid ester polymer (B2)> The (meth)acrylic acid ester polymer (B2) has, as a structural unit, at least a structural unit (hereinafter also referred to as "(meth)acrylic acid ester unit") obtained from a (meth)acrylic acid ester (a (meth)acrylic acid ester monomer). The (meth)acrylic acid ester is defined as an acrylic acid ester and / or a methacrylic acid ester.

[0049] Examples of the (meth)acrylic acid ester include (meth)acrylic acid esters having an alkyl moiety having 1 to 12 carbon atoms, such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, iso-butyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and lauryl (meth)acrylate. The (meth)acrylic acid esters may be used alone or in combination of two or more.

[0050] The (meth)acrylic acid ester is preferably methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, iso-butyl (meth)acrylate, t-butyl (meth)acrylate, or 2-ethylhexyl (meth)acrylate, more preferably methyl (meth)acrylate or n-butyl (meth)acrylate, and even more preferably methyl methacrylate, n-butyl methacrylate, or butyl acrylate.

[0051] The (meth)acrylic acid ester polymer (B2) may contain, as an optional component, polymerized units obtained from a copolymerizable monomer copolymerizable with a (meth)acrylic acid ester. Examples of the copolymerizable monomer include functional group-containing vinyl monomers, aromatic vinyl monomers, N-substituted unsaturated carboxylic acid amides, heterocyclic vinyl compounds, vinylidene halide compounds, α-olefins, and dienes.

[0052] Examples of functional group-containing vinyl monomers include carboxy group-containing vinyl monomers, hydroxy group-containing vinyl monomers, amino group-containing vinyl monomers, glycidyl group-containing vinyl monomers, cyano group-containing vinyl monomers, sulfonic acid group-containing vinyl monomers and salts thereof, acetoacetoxy group-containing vinyl monomers, phosphoric acid group-containing compounds, amide group-containing vinyl monomers, and vinyl esters.

[0053] Examples of the carboxy group-containing vinyl monomer include (meth)acrylic acid, maleic anhydride, maleic acid, fumaric acid, itaconic acid, and crotonic acid. Examples of the hydroxyl group-containing vinyl monomer include 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate.

[0054] Examples of amino group-containing vinyl monomers include 2-aminoethyl (meth)acrylate, 2-(N-methylamino)ethyl (meth)acrylate, and 2-(N,N-dimethylamino)ethyl (meth)acrylate.

[0055] An example of the glycidyl group-containing vinyl monomer is glycidyl (meth)acrylate. An example of the cyano group-containing vinyl monomer is (meth)acrylonitrile.

[0056] Examples of sulfonic acid group-containing vinyl monomers include allyl sulfonic acid and methallyl sulfonic acid. Examples of salts thereof include alkali metal salts of the sulfonic acid group-containing vinyl monomers, such as sodium salts and potassium salts, and ammonium salts. Specific examples include sodium allyl sulfonate, sodium methallyl sulfonate, and ammonium methallyl sulfonate.

[0057] An example of an acetoacetoxy group-containing vinyl monomer is acetoacetoxyethyl (meth)acrylate. An example of the phosphate group-containing compound is 2-methacryloyloxyethyl acid phosphate.

[0058] An example of the amide group-containing vinyl monomer is (meth)acrylamide. Examples of vinyl esters include vinyl propionate (but excluding vinyl acetate).

[0059] Examples of aromatic vinyl monomers include styrene, α-methylstyrene, and divinylbenzene. An example of the N-substituted unsaturated carboxylic acid amide is N-methylol (meth)acrylamide.

[0060] An example of the heterocyclic vinyl compound is vinylpyrrolidone. Examples of the vinylidene halide compound include vinylidene chloride and vinylidene fluoride.

[0061] Examples of the α-olefins include ethylene and propylene. An example of the dienes is butadiene. Furthermore, the copolymerizable monomer may also include a crosslinkable vinyl monomer.

[0062] Examples of crosslinkable vinyl monomers include compounds containing two or more vinyl groups, such as methylenebis(meth)acrylamide, divinylbenzene, and polyethylene glycol chain-containing di(meth)acrylate.

[0063] These copolymerizable monomers may be used alone or in combination of two or more. As the copolymerizable monomer, preferably, a functional group-containing vinyl monomer is used. As the (meth)acrylic acid ester, from the viewpoint of water resistance, methacrylic acid ester is preferred among acrylic acid ester and methacrylic acid ester.

[0064] The content of the (meth)acrylic acid ester units and structural units derived from other copolymerizable monomers (hereinafter also referred to as "copolymerizable monomer units") in the (meth)acrylic acid ester polymer (B2) is, when the total of these is taken as 100 mass%, for example, 50 mass% or more, preferably 70 mass% or more, more preferably 77 mass% or more of the (meth)acrylic acid ester units. Also, the content of the copolymerizable monomer units is, for example, 50 mass% or less, preferably 30 mass% or less, more preferably 23 mass% or less.

[0065] When the content ratio of the (meth)acrylic acid ester unit and the copolymerizable monomer unit is within the above range, a coating film formed from an aqueous dispersion containing the (meth)acrylic acid ester polymer (B2) can have excellent adhesive strength and blocking resistance.

[0066] That is, the (meth)acrylic acid ester polymer (B2) may be composed only of (meth)acrylic acid ester units without containing any copolymerizable monomer units, or may be composed of (meth)acrylic acid ester units and copolymerizable monomer units in the above-mentioned ratio. The polymer (B2) is preferably composed only of (meth)acrylic acid ester units, or composed of (meth)acrylic acid ester units and copolymerizable monomer units in the above-mentioned ratio.

[0067] When the polymer (B2) is composed of only (meth)acrylic acid ester units, the (meth)acrylic acid ester preferably consists of only a (meth)acrylic acid ester having an alkyl moiety with 4 carbon atoms, or a combination of methyl (meth)acrylate and a (meth)acrylic acid ester having an alkyl moiety with 4 carbon atoms.

[0068] When the (meth)acrylic acid ester is composed solely of a (meth)acrylic acid ester having an alkyl moiety having 4 carbon atoms, the (meth)acrylic acid ester particularly preferably consists solely of n-butyl methacrylate, or consists of a combination of n-butyl methacrylate and n-butyl acrylate.

[0069] Furthermore, when the (meth)acrylic acid ester is a combination of methyl (meth)acrylate and a (meth)acrylic acid ester having an alkyl moiety with 4 carbon atoms, the (meth)acrylic acid ester is particularly preferably a combination of methyl methacrylate and n-butyl methacrylate, or a combination of methyl methacrylate and n-butyl acrylate.

[0070] When the (meth)acrylic acid esters are used in such a combination, the glass transition temperature of the (meth)acrylic acid ester polymer (B2) can be adjusted to fall within the range described below. When the other copolymerizable monomer is a carboxyl group-containing vinyl monomer, the proportion of structural units derived from the carboxyl group-containing vinyl monomer in the polymer (B2) is, for example, 5% by mass or less, preferably 3% by mass or less, from the viewpoint of production stability.

[0071] The method for producing the polymer (B2) is not particularly limited, and any known production method can be used. An example of the production method is a method in which water, a (meth)acrylic acid ester, and a polymerization initiator are mixed together, and the (meth)acrylic acid ester is polymerized in water.

[0072] The polymerization initiator is not particularly limited, but examples thereof include: hydrogen peroxide; persulfates such as ammonium persulfate, potassium persulfate, and sodium persulfate; Organic peroxides such as cumene hydroperoxide, t-butyl hydroperoxide, benzoyl peroxide, t-butyl peroxy-2-ethylhexanoate, t-butyl peroxybenzoate, and lauroyl peroxide; and azo compounds such as azobisisobutyronitrile, and Redox initiators that combine these with metal ions such as iron ions and reducing agents such as sodium sulfoxylate, formaldehyde, sodium pyrosulfite, sodium hydrogen sulfite, L-ascorbic acid, and Rongalit These polymerization initiators may be used alone or in combination of two or more.

[0073] The mixing ratio of the polymerization initiator is set appropriately, and is, for example, 0.1% by mass or more and 5% by mass or less relative to the total amount of the monomer components. In the polymerization, a molecular weight modifier can be added as needed.

[0074] Examples of molecular weight modifiers include mercaptans such as t-dodecyl mercaptan and n-dodecyl mercaptan, and allyl compounds such as allyl sulfonic acid, methallyl sulfonic acid, and sodium salts thereof. These molecular weight modifiers may be used alone or in combination of two or more. The blending ratio of the molecular weight modifiers is appropriately set.

[0075] When polymerization is carried out under normal pressure, the polymerization temperature is, for example, 30° C. or higher, preferably 50° C. or higher, and for example, 95° C. or lower, preferably 85° C. or lower. The polymerization time is, for example, 1 hour or higher, preferably 2 hours or higher, and for example, 30 hours or lower, preferably 20 hours or lower.

[0076] In the production of the polymer (B2), an emulsifier (surfactant) may be added as needed in order to improve production stability. Examples of emulsifiers (surfactants) include anionic surfactants, nonionic surfactants, and cationic surfactants.

[0077] Examples of anionic surfactants include sodium dodecylbenzenesulfonate, sodium lauryl sulfate, sodium alkyldiphenyl ether disulfonate, sodium alkylnaphthalenesulfonate, sodium dialkylsulfosuccinate, sodium stearate, potassium oleate, sodium dioctyl sulfosuccinate, sodium polyoxyethylene alkyl ether sulfate, sodium polyoxyethylene alkyl ether sulfate, sodium polyoxyethylene alkylphenyl ether sulfate sodium dialkylsulfosuccinate, sodium stearate, sodium oleate, and sodium t-octylphenoxyethoxypolyethoxyethyl sulfate.

[0078] Examples of nonionic surfactants include polyoxyethylene lauryl ether, polyoxyethylene octylphenyl ether, polyoxyethylene oleylphenyl ether, polyoxyethylene nonylphenyl ether, oxyethylene-oxypropylene block copolymer, t-octylphenoxyethyl polyethoxyethanol, and nonylphenoxyethyl polyethoxyethanol.

[0079] Examples of cationic surfactants include lauryltrimethylammonium chloride and stearyltrimethylammonium chloride. These emulsifiers (surfactants) may be used alone or in combination of two or more kinds.

[0080] The emulsifier (surfactant) is preferably an anionic surfactant, more preferably sodium dodecylbenzenesulfonate. The blending ratio of the emulsifier (surfactant) is not particularly limited, but from the viewpoint of production stability, it is, for example, 0.02 parts by mass or more, for example, 5 parts by mass or less, per 100 parts by mass of the total amount of the (meth)acrylic acid ester and any other copolymer monomer.

[0081] In the production of the (meth)acrylic acid ester polymer (B2), from the viewpoint of improving production stability, known additives such as pH adjusters, sequestering agents such as ethylenediaminetetraacetic acid and salts thereof, and molecular weight regulators (chain transfer agents) such as mercaptans and low-molecular-weight halogen compounds may be blended in appropriate proportions.

[0082] The weight average molecular weight of the (meth)acrylic acid ester polymer (B2) is, for example, 5,000 or more, preferably 10,000 or more, and for example, 1,000,000 or less, preferably 500,000 or less, as calculated in terms of standard polystyrene by gel permeation chromatography (GPC).

[0083] The (meth)acrylic acid ester polymer (B2) has a glass transition temperature of, for example, −28° C. or higher, preferably −10° C. or higher, and for example, 80° C. or lower, preferably 60° C. or lower. When the (meth)acrylic acid ester polymer (B2) has a glass transition temperature within the above range, excellent adhesive strength and blocking resistance can be obtained.

[0084] In particular, from the viewpoint of improving adhesive strength, the glass transition temperature of the (meth)acrylic acid ester polymer (B2) is preferably 20°C or lower, more preferably 10°C or lower.

[0085] From the viewpoint of improving blocking resistance, the glass transition temperature of the (meth)acrylic acid ester polymer (B2) is preferably above 0°C, and more preferably 10°C or higher.

[0086] <Other ingredients> The aqueous dispersion of the present invention may contain a polymer (such as an ethylene-vinyl acetate copolymer) or an additive other than the above components (A1), (A2) and (B).

[0087] Examples of additives include the above-mentioned emulsifiers, as well as known additives such as curing agents, crosslinking agents, film-forming aids, antifoaming agents, anti-cising agents, leveling agents, tackifiers, hardness-imparting agents, preservatives, thickeners, antifreeze agents, dispersants, inorganic pigments, and organic pigments. These additives may be used alone or in combination of two or more. The blending ratio and blending timing of the additives are appropriately determined depending on the purpose and application.

[0088] <Water dispersion> The aqueous dispersion of the present invention is a dispersion containing the ethylene polymer (A1), the ethylene-α-olefin copolymer (A2), the unsaturated carboxylic acid copolymer (B), and water, and the mass ratio of the ethylene polymer (A1) to the ethylene-α-olefin copolymer (A2) [(A1) / (A2)] is from 95 / 5 to 40 / 60, and preferably from 90 / 10 to 50 / 50.

[0089] When the total amount of the ethylene polymer (A1), the ethylene-α-olefin copolymer (A2), and the unsaturated carboxylic acid copolymer (B) is taken as 100% by mass, the content of the unsaturated carboxylic acid copolymer (B) in the aqueous dispersion of the present invention is preferably 30% by mass or more, more preferably 35% by mass or more, even more preferably 40% by mass or more, and is preferably 55% by mass or less, more preferably 50% by mass or less, even more preferably 45% by mass or less.

[0090] When the content ratio of ethylene (A1), ethylene-α-olefin copolymer (A2) and unsaturated carboxylic acid copolymer (B) is within the above range, a coating film having excellent low-temperature heat-sealing properties and low tackiness can be obtained from the aqueous dispersion of the present invention.

[0091] <Method of producing aqueous dispersion> Methods for producing the aqueous dispersion of the present invention include a method in which the above components are mixed in the above-mentioned predetermined ratio and emulsified all at once, and a method in which the individual components are emulsified and then mixed in the above-mentioned predetermined ratio.

[0092] The aqueous dispersion of the present invention may contain the above components in a non-particulate form or in a particulate form. Preferably, the above components are contained in a particulate form. The weight average particle diameter of the particles (measurement method: light scattering measurement) is, for example, 10 nm or more, and, for example, 10 μm or less, preferably 1 μm or less.

[0093] When the above-mentioned components are contained in the aqueous dispersion in the form of particles, the components may be single particles of each polymer, or composite particles made of two or more types of polymers. The particles of the unsaturated carboxylic acid polymer (B) may be composite particles formed by an ethylene-unsaturated carboxylic acid copolymer (b1) and / or a salt thereof (B1) and a (meth)acrylic acid ester polymer (B2). The method for producing such composite particles is not particularly limited, and known methods can be used.

[0094] The form of the composite particles is not particularly limited, and examples thereof include a core / shell structure, a composite structure, a localized structure, a potbellied structure, an octopus-like structure, a raspberry-like structure, a multi-particle composite structure, and an IPN structure.

[0095] The solids concentration of the aqueous dispersion is, for example, 10% by mass or more, preferably 20% by mass or more, and for example, 60% by mass or less, preferably 50% by mass or less. The pH of the aqueous dispersion is, for example, 7 or more, preferably 8 or more, and for example, 11 or less, preferably 10 or less.

[0096] The aqueous dispersion of the present invention can quickly exhibit low friction properties after being applied to a substrate. When the aqueous dispersion of the present invention is used to form an adhesive layer (heat seal layer) of a laminate, a laminate having excellent adhesive strength can be obtained.

[0097] Therefore, the aqueous dispersion can be suitably used as an adhesive composition for forming an adhesive layer in a laminate comprising a substrate and an adhesive layer laminated on at least one surface of the substrate.

[0098] <Laminate> The laminate of the present invention comprises a substrate and an adhesive layer laminated on at least a portion of at least one surface of the substrate.

[0099] Examples of the substrate include a resin substrate, a metal substrate, and a composite substrate. Examples of resin substrates include plastic films, containers, cups, and the like made of plastic materials such as cellophane, polyethylene, ethylene-vinyl acetate copolymer, ionomer, polypropylene, polyamide (nylon), polyester, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, polycarbonate, polystyrene, and polyacrylonitrile copolymer.

[0100] Examples of metal substrates include metal plates, metal foils, containers, and cups, and examples of metals include aluminum, gold, silver, copper, nickel, zinc, titanium, cobalt, indium, and chromium.

[0101] Examples of composite substrates include vapor-deposited films in which a metal (aluminum, gold, silver, copper, nickel, zinc, titanium, cobalt, indium, chromium, etc.) or its oxide (aluminum oxide, silicon oxide, etc.) is vapor-deposited onto the above-mentioned plastic film.

[0102] Furthermore, examples of the substrate include paper and nonwoven fabric. These substrates may be used alone or in combination of two or more. The substrate is preferably a metal substrate, more preferably a metal substrate made of aluminum, and even more preferably a metal foil made of aluminum.

[0103] The substrate may be surface-treated as needed. Examples of surface treatments include ink (solvent-based or water-based) coating, plating, coupling, and vacuum plasma treatment, preferably ink coating, and more preferably solvent-based ink coating.

[0104] The adhesive layer is a dried product of the above-mentioned aqueous dispersion, and can be obtained by applying (coating) the above-mentioned aqueous dispersion to one surface of a substrate and drying it. The aqueous dispersion may be applied to the entire surface of one side of the substrate, or, if the aqueous dispersion is used to form a heat seal layer, it may be applied to a portion of one side of the substrate where the laminate and another material are heat sealed (bonded).

[0105] The method for applying (coating) the aqueous dispersion is not particularly limited, and known methods such as gravure roll coating, triple roll coating, dip coating, and spray coating can be used. When the applied coating film of the aqueous dispersion is dried, the drying temperature is, for example, 100 to 200° C., and the drying time is, for example, 10 seconds to 30 minutes.

[0106] Furthermore, before coating and drying, in order to improve adhesion between the substrate and the aqueous dispersion, the substrate may be coated with a primer (such as titanate or polyethyleneimine), or may be subjected to pretreatment such as corona discharge treatment or chemical conversion treatment.

[0107] According to such a laminate, since the above-mentioned aqueous dispersion is used in the heat seal (adhesive) layer, excellent adhesive strength and low friction can be obtained. Furthermore, since the aqueous dispersion of the present invention is not a dispersion in which particles are dispersed in an organic solvent such as ethyl acetate or toluene, the amount of residual organic solvent in the adhesive layer can be preferably 100 ppm or less, more preferably 10 ppm or less.

[0108] Therefore, the laminate of the present invention is used as a heat-sealing material in various industrial fields. During heat sealing, the dried product of the aqueous dispersion formed on the substrate (that is, the adhesive layer) and the adherend layer are adhered together.

[0109] The adherend layer is made of a material that is heat sealed (adhered) to the base layer via the dried product of the aqueous dispersion, and examples of the material include resin materials, metal materials, and composite materials. Examples of resin materials include plastic films, containers, cups, etc. made from plastic materials such as cellophane, polyethylene, ethylene-vinyl acetate copolymer, ionomer, polypropylene, polyamide (nylon), polyester, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, polycarbonate, polystyrene, and polyacrylonitrile copolymer.

[0110] Examples of metal materials include metal plates, metal foils, containers, and cups, and examples of metals include aluminum, gold, silver, copper, nickel, zinc, titanium, cobalt, indium, and chromium.

[0111] Examples of composite materials include vapor-deposited films in which a metal (aluminum, gold, silver, copper, nickel, zinc, titanium, cobalt, indium, chromium, etc.) or its oxide (aluminum oxide, silicon oxide, etc.) is vapor-deposited onto the above-mentioned plastic film.

[0112] Furthermore, examples of the adherend layer include paper and nonwoven fabric. These adherend layers may be used alone or in combination of two or more. The adherend layer may be surface-treated as needed. Examples of surface treatments include ink (solvent-based or water-based) coating, plating, coupling, and vacuum plasma treatment, preferably ink coating, and more preferably solvent-based ink coating.

[0113] The adherend layer may also be a laminate comprising a substrate and an adhesive layer. These adherend layers can be used alone or in combination of two or more kinds. From the viewpoint of adhesive strength and ease of adhesion, the adherend layer is preferably a plastic film made of polyvinyl chloride or polyvinylidene chloride.

[0114] The method for heat-sealing the substrate and the adherend layer is not particularly limited, and known methods can be used. For example, the substrate and the adherend layer are laminated via an adhesive layer, and then heated and pressurized. When a laminate is used as the adherend layer, the adhesive layers are bonded together, and the two substrates are laminated via the two adhesive layers, and then heated and pressurized.

[0115] The heating temperature is, for example, 80° C. or higher, preferably 100° C. or higher, and for example, 250° C. or lower, preferably 200° C. or lower. The pressure is, for example, 50 kPa or higher, preferably 100 kPa or higher, and for example, 500 kPa or lower, preferably 300 kPa or lower.

[0116] As a result, the substrate and the adherend layer are heat sealed (thermocompression bonded). The adhesive strength between the substrate and the adherend layer can be measured by the peel strength between the substrate and the adherend layer. The laminate in which an adherend layer is laminated on one surface of the dried product layer of the aqueous dispersion in this manner is included in the present invention regardless of the heat-sealed state (i.e., before or after heat-sealing).

[0117] Such a laminate is obtained using the above-mentioned aqueous dispersion, and therefore has excellent low friction properties. Furthermore, such laminates have excellent adhesive strength.

[0118] Therefore, the laminate is suitable for use as a packaging material in various industrial fields. The items to be packaged with the laminate are not particularly limited, and examples thereof include various industrial products such as confectionery, food, daily necessities, pharmaceuticals, and paper.

[0119] In particular, in the fields of pharmaceutical and food packaging, the adhesive is expected to have the effect of suppressing deterioration of packaging materials and packaged items during heat sealing, improving productivity by increasing filling speed and reducing power consumption, etc. In addition, because the adhesive composition used to form the adhesive layer is an aqueous dispersion, it has the advantage of being environmentally friendly. [Example]

[0120] EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to these. [Evaluation method] The aqueous dispersions and laminates produced in the examples were evaluated by the following methods.

[0121] <Evaluation of tackiness of coating film> The aluminum substrate was attached to the dried coating film of the laminate produced in the examples, and the laminate was sealed using a heat sealer at a temperature of 50°C and a pressure of 3 kgf / cm. 2 The test piece was then cooled to room temperature, and the presence or absence of adhesion was judged based on whether or not a sound was generated when peeling the aluminum substrate from the dried coating film of the laminate. The evaluation criteria were as follows: ×: There is a feeling of adhesion (tackiness) and noise is generated when peeling off. Good: No adhesion (tackiness) and no noise when peeling off.

[0122] <Evaluation of heat sealability> The laminates produced in the examples were left overnight at room temperature, then cut into 15 mm wide strips. Two strips of laminate were placed with the dried coating films facing each other, and heated at a temperature of 95°C and a pressure of 2 kgf / cm. 2 The test piece was heat-sealed for 0.5 seconds under the conditions of 180° peel strength was measured using the test piece obtained at a pulling speed of 200 mm / sec.

[0123] [Comparative Example 1] <Production of aqueous dispersion> Using the kneading apparatus shown in FIG. 1 of JP-A-63-46273, a low-density polyethylene (trade name: Mirason (registered trademark) FL60 (density 915 kg / m), manufactured by Mitsui-Dow Polychemicals Co., Ltd.) was mixed as an ethylene polymer (A1). 3 (melting point 102°C) and an ethylene-acrylic acid copolymer (B) [manufactured by Mitsui-Dow Polychemicals Co., Ltd., trade name: Nucrel® (ethylene content: 72% by mass), hereinafter also referred to as "EAA"] were charged into the hopper of a kneading machine so that the mass ratio of the ethylene polymer (A1) to the unsaturated carboxylic acid polymer (B) was 50 / 50, and melt-kneaded. During melt-kneading, an aqueous potassium hydroxide solution was added to the kneader to neutralize the acrylic acid units in the ethylene-acrylic acid copolymer to a degree of neutralization of 50%. Water was then added to the kneader, and the mixture in the kneader was cooled to room temperature. Finally, additional water was added to obtain an aqueous dispersion with a solids concentration of 40% by mass.

[0124] <Production of laminate> The obtained aqueous dispersion was adjusted to a solids concentration of 24% by adding deionized water, and then the dispersion was applied to the entire surface of one side of a soft aluminum foil (thickness: 40 μm) in a coating amount of 3 g / m 2 The solution was applied with a wire bar so that the coating became thicker, and then dried at 120°C for 10 seconds to obtain a laminate consisting of a soft aluminum foil and a dried coating film of the aqueous dispersion.

[0125] The evaluation results of the laminate are shown in Table 1. [Examples 1 to 3, Comparative Examples 2 and 3] Together with the ethylene polymer (A1) and the unsaturated carboxylic acid polymer (B), an ethylene-α-olefin copolymer (A2) was prepared using an ethylene-1-butene copolymer (manufactured by Mitsui Chemicals, Inc., trade name: Tafmer (registered trademark) DF740, density: 870 kg / m 3 , melting point: 55° C.] in the proportions shown in Table 1, the same procedure as in Comparative Example 1 was repeated to obtain an aqueous dispersion having a solid content concentration of 40% by mass.

[0126] [Table 1]

Claims

1. Density is 900 kg / m 3 an ethylene polymer (A1) having a density of 895 kg / m or more and 940 kg / m or less; 3 An aqueous dispersion comprising the following ethylene / α-olefin copolymer (A2), an unsaturated carboxylic acid copolymer (B), and water, wherein the mass ratio of the ethylene polymer (A1) to the ethylene / α-olefin copolymer (A2) [(A1) / (A2)] is in the range of 95 / 5 to 40 / 60.

2. The ethylene polymer (A1) is a low-density polyethylene, and the density of the ethylene / α-olefin copolymer (A2) is 860 kg / m 3 The aqueous dispersion according to claim 1 .

3. 3. The aqueous dispersion according to claim 1, wherein the ethylene polymer (A1) has a melting point of 95°C or higher, and the ethylene / α-olefin copolymer (A2) has a melting point of 80°C or lower.

4. The aqueous dispersion according to any one of claims 1 to 3, wherein the unsaturated carboxylic acid polymer (B) is at least one polymer selected from the group consisting of an ethylene-unsaturated carboxylic acid copolymer (b1) and / or a salt thereof (B1) and a (meth)acrylic acid ester polymer (B2).

5. The aqueous dispersion according to any one of claims 1 to 4, wherein the ethylene / α-olefin copolymer (A2) is an ethylene / 1-butene copolymer.

6. A laminate comprising a substrate and an adhesive layer laminated on at least a portion of at least one surface of the substrate, wherein the adhesive layer comprises a dried product of the aqueous dispersion according to any one of claims 1 to 5.

7. The laminate according to claim 6 , further comprising an adherend layer laminated on the surface of the adhesive layer opposite to the substrate side.

8. 8. The laminate according to claim 6, wherein the substrate is made of aluminum.

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