Heat sealant and laminate

Abstract

To provide a heat sealant that allows for the formation of a heat seal layer with good heat sealability and blocking resistance by combining polyurethane resin and wax, and that also has excellent stability. [Solution] A heat sealant comprising a polyurethane resin (A) containing structural units derived from an acid group-free polyether polyol (a-1), a structural unit derived from an acid group-containing polyol (a-2), a structural unit derived from a polyisocyanate (a-3), and a structural unit derived from a chain extender (a-4), and a wax (B), wherein the acid group-free polyether polyol (a-1) contains at least one structural unit selected from the group consisting of plant-derived polyethylene glycol, polypropylene glycol, and polytetramethylene glycol.

Description

Technical Field

[0001] The present invention relates to a heat-sealing agent and a laminate.

Background Art

[0002] Conventionally, paper and plastic films have been used as packaging materials for packaging clothes, food, drugs, etc. After packaging the contents, heat sealing is often used to seal the opening (hereinafter also referred to as "sealing"). Plastic film packaging materials often have heat-sealing properties themselves, but paper packaging materials do not have heat-sealing properties themselves. Therefore, a plastic film such as a polyethylene film having heat-sealing properties is laminated on the entire inner surface of the packaging material or the opening to be sealed, so that heat-sealing properties are often imparted.

[0003] In recent years, from the viewpoints of resource saving, plastic reduction, and ease of recycling, the use of paper packaging materials has been remarkably increasing. However, a paper packaging material laminated with a plastic film needs to be separated from the plastic film during recycling, which is a burden in the recycling process. Therefore, instead of laminating a plastic film on a paper substrate, consideration has been given to obtaining a packaging material having a paper substrate by forming a heat-sealing layer by coating a heat-sealing agent having heat-sealing properties on the substrate.

[0004] However, when the seal strength of the opening is not sufficient, there may occur a problem that the opening of the sealed packaging material opens during transportation or handling of the package. In addition, when a heat-sealing layer is formed by coating a heat-sealing agent, there is a problem that a so-called "blocking" phenomenon occurs in which a portion that is not intended to be sealed adheres to the heat-sealing layer. This blocking leads to a decrease in workability and a decrease in the quality of the packaging material. It is generally recognized among those skilled in the art that the ease of this blocking (blocking property) is a property contrary to heat-sealing property.

[0005] Furthermore, while commonly used heat sealants are mainly olefin and acrylic materials derived from petroleum, there is ongoing research into designing heat sealants using plant-derived materials, similar to paper substrates, from an environmental perspective.

[0006] Patent Document 1 discloses a coating agent using polylactic acid, a plant-derived raw material, which exhibits good heat-sealability and blocking resistance. However, the aqueous dispersion of polylactic acid has poor stability over time and is insufficient for distribution as a product with stable quality. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] International Publication No. 2022 / 097708 [Overview of the project] [Problems that the invention aims to solve]

[0008] The problem that this invention aims to solve is to provide a heat sealant that can form a heat seal layer with good heat sealability and blocking resistance using a combination of polyurethane resin and wax, and that is also highly stable. [Means for solving the problem]

[0009] The inventors of this invention have diligently conducted research to solve the above problems, and as a result, have arrived at the present invention. In other words, the present invention relates to a heat sealant containing a polyurethane resin (A) and a wax (B) which include structural units derived from an acid group-free polyether polyol (a-1), a structural unit derived from an acid group-containing polyol (a-2), a structural unit derived from a polyisocyanate (a-3), and a structural unit derived from a chain extender (a-4).

[0010] Furthermore, the present invention relates to the above-mentioned heat sealant wherein the above-mentioned acid group-free polyether polyol (a-1) contains at least one structural unit selected from the group consisting of polyethylene glycol, polypropylene glycol, and polytetramethylene glycol, which are of plant origin.

[0011] Furthermore, the present invention relates to the above-mentioned heat sealant wherein the acid value of the polyurethane resin (A) is 5 mg KOH / g or more and 30 mg KOH / g or less.

[0012] Furthermore, the present invention relates to the heat sealant described above, wherein the polyurethane resin (A) is in particulate form and has an average particle diameter of 30 nm or more and 300 nm or less.

[0013] Furthermore, the present invention relates to the heat sealant described above, wherein the wax (B) contains a plant-derived wax.

[0014] Furthermore, the present invention relates to a laminate having a heat-seal layer formed from the above-mentioned heat-seal agent on a substrate. [Effects of the Invention]

[0015] The present invention makes it possible to form a heat seal layer with good heat sealability and blocking resistance using a combination of polyurethane resin and wax, and to provide a heat sealant with excellent stability. [Modes for carrying out the invention]

[0016] The heat sealant of the present invention contains a polyurethane resin (A) and a wax (B) which include structural units derived from an acid group-free polyether polyol (a-1), a polyol containing an acid group (a-2), a polyisocyanate (a-3), and a chain extender (a-4).

[0017] The polyurethane resin (A) contains structural units derived from an acid group-free polyether polyol (a-1), structural units derived from an acid group-containing polyol (a-2), structural units derived from a polyisocyanate (a-3), and structural units derived from a chain extender (a-4).

[0018] Examples of the acid group-free polyether polyol (a-1) include polyethylene glycol, polypropylene glycol, and polytetramethylene glycol, which are polymers or copolymers of cyclic ethers such as ethylene oxide, propylene oxide, and tetrahydrofuran. From the perspective of environmental compatibility, it is preferable to use plant-derived polyether polyols, and among them, it is more preferable to use plant-derived polytetramethylene glycol. By using polytetramethylene glycol, the stability when the polyurethane resin (A) is made aqueous becomes good.

[0019] The number average molecular weight (Mn) of the above polyether polyol (a-1) is preferably 500 or more and 4000 or less, and more preferably 1000 or more and 3000 or less. By using a polyether polyol with Mn of 500 or more and 4000 or less, the concentration of urethane bonds becomes an optimal ratio, and it becomes easier to achieve both heat sealability and blocking resistance.

[0020] Examples of the acid group-containing polyol (a-2) include dimethylolalkanoic acids such as dimethylolacetic acid, dimethylolpropionic acid, dimethylolbutanoic acid, and dimethylolpentanoic acid, and dihydroxysuccinic acid and dihydroxybenzoic acid. From the perspective of reactivity during the synthesis of the polyurethane resin (A) and stability when the polyurethane resin (A) is dispersed in water, dimethylolpropionic acid and dimethylolbutanoic acid are preferable.

[0021] As the polyisocyanate (a-3), aromatic isocyanates, aliphatic isocyanates, alicyclic isocyanates, or mixtures thereof can be used.

[0022] Examples of aromatic isocyanates include aromatic polyisocyanates such as 1,5-naphthalene diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-diphenyldimethylmethane diisocyanate, dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, tolylene diisocyanate, and xylylene diisocyanate.

[0023] Examples of aliphatic isocyanates include aliphatic polyisocyanates such as 1,5-pentamethylene diisocyanate, butane-1,4-diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, and lysine diisocyanate.

[0024] Examples of alicyclic isocyanates include alicyclic polyisocyanates such as cyclohexane-1,4-diisocyanate, isophorone diisocyanate, norbornane-2,6-diylbis(methylene)diisocyanate, bis(4-isocyanatocyclohexyl)methane, 1,3-bis(isocyanatomethyl)cyclohexane, and methylcyclohexane diisocyanate.

[0025] In the present invention, it is preferable to use isophorone diisocyanate or 1,5-pentamethylene diisocyanate among these.

[0026] As the chain extender (a-4), it is preferable to use a polyamino compound having good reactivity with a urethane resin having an isocyanate group, which is a precursor of the polyurethane resin (A) (sometimes referred to as a urethane prepolymer). Polyamino compounds can include ethylenediamine, propylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, isophoronediamine, dicyclohexylmethane-4,4'-diamine, norbornanediamine, as well as amines having hydroxyl groups such as 2-(2-aminoethylamino)ethanol, 2-hydroxyethylethylenediamine, 2-hydroxyethylpropylenediamine, di-2-hydroxyethylethylenediamine, and di-2-hydroxypropylethylenediamine. However, from the viewpoint of stability when polyurethane resin (A) is dispersed in water, it is preferable to use ethylenediamine, diethylenetriamine, or isophoronediamine.

[0027] When urethane-forming polyether polyols (a-1) that do not contain acidic groups, polyols (a-2) that contain acidic groups, and polyisocyanates (a-3), catalysts and organic solvents as reaction solvents can be used as needed. While the catalysts are not particularly limited, examples include metal catalysts such as dibutyltin dilaurate (DTD), alkyl titanates, organosilicon titanates, stanus octoate, lead octoate, zinc octoate, bismuth octoate, bismuth neodecanoate, dibutyltin diorthophenylphenoxide, and reaction products of tin oxide with ester compounds (such as dioctyl phthalate), as well as amine catalysts such as monoamines (such as triethylamine), diamines (such as N,N,N',N'-tetramethylethylenediamine), triamines (such as N,N,N',N”,N”-pentamethyldiethylenetriamine), and cyclic amines (such as triethylenediamine).

[0028] Examples of organic solvents include aliphatic hydrocarbons such as hexane and octane, alicyclic hydrocarbons such as cyclohexane and methylcyclohexane, ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, esters such as ethyl acetate, propyl acetate and butyl acetate, glycol ether esters such as ethylene glycol ethyl ether acetate, propylene glycol monomethyl ether acetate, 3-methyl-3-methoxybutyl acetate and ethyl-3-ethoxypropionate, ethers such as dioxane, halogenated hydrocarbons such as methylene iodide and monochlorobenzene, amide solvents such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide and hexamethylphosphonylamide, and dimethyl sulfoxide.

[0029] From an environmental perspective, the polyurethane resin (A) is preferably dispersed in water to form a heat sealant. From the viewpoint of stability after water dispersion, the acid value of the polyurethane resin (A) is preferably 5 mg KOH / g or more and 30 mg KOH / g or less, and more preferably 5 mg KOH / g or more and 20 mg KOH / g or less.

[0030] Furthermore, from the viewpoint of stability after aqueous dispersion, it is preferable to neutralize the acidic groups derived from the acidic group-containing polyol (a-2). While not particularly limited, examples of neutralizing agents include ammonia, organic amine compounds, and inorganic basic compounds. Examples of organic amine compounds include alkylamines such as triethylamine, isopropylamine, propylamine, ethylamine, diethylamine, and sec-butylamine; alkoxyamines such as 3-ethoxypropylamine and 3-methoxypropylamine; alkanolamines such as N,N-dimethylethanolamine, N,N-diethylethanolamine, ethanolamine, N-methyl-N,N-diethanolamine, monoethanolamine, diethanolamine, and triethanolamine; and morpholines such as morpholine, N-methylmorpholine, and N-ethylmorpholine. From the viewpoint of drying properties, it is preferable to use ammonia or triethylamine.

[0031] The polyurethane resin (A) in the present invention is preferably used as an aqueous dispersion, and can be obtained, for example, as follows. Specifically, a precursor of polyurethane resin (A) having isocyanate groups at its termini is obtained by addition reaction of an acid-free polyether polyol (a-1), an acid-containing polyol (a-2), and a polyisocyanate (a-3). This precursor is neutralized with a neutralizing agent and dispersed in water. Furthermore, a chain extender (a-4) is added and reacted with the isocyanate groups of the precursor to obtain an aqueous dispersion of polyurethane resin (A) in which the precursor is chain-extended by the chain extender (a-4).

[0032] As for the method of neutralization, the neutralizing agent may be added after the synthesis of the precursor to neutralize it, or the neutralizing agent may be added by dissolving it in water when dispersing the precursor with water. By adding water to the neutralized precursor, the precursor can be dispersed in water. In this dispersed state in water, by gradually adding the chain extender (a-4), the terminal isocyanate groups of the precursor react to obtain polyurethane resin (A).

[0033] When obtaining an aqueous dispersion of polyurethane resin (A), it is preferable to use a surfactant to improve stability. Examples of surfactants include anionic surfactants, cationic surfactants, nonionic surfactants, and amphoteric surfactants, but from the viewpoint of safety and good coating film properties, it is preferable to use anionic or nonionic surfactants. To avoid adverse effects on blocking resistance, the surfactant is preferably included in an amount of 0.1 parts by mass or more and 5.0 parts by mass or less, and more preferably 0.2 parts by mass or more and 3.0 parts by mass or less, based on 100 parts by mass of the total amount of polyurethane resin (A). The surfactant can be used alone or in combination of two or more types.

[0034] Examples of anionic surfactants that can be used include higher fatty acid salts such as sodium oleate, alkylaryl sulfonates such as dodecylbenzenesulfonic acid, alkyl sulfate esters such as sodium lauryl sulfate, polyoxyethylene alkyl ether sulfate esters such as sodium polyoxyethylene lauryl ether sulfate, alkyl sulfosuccinate esters such as sodium monooctyl sulfosuccinate, sodium dioctyl sulfosuccinate, sodium polyoxyethylene lauryl sulfosuccinate and their derivatives, and polyoxyethylene distyrenated phenyl ether sulfate esters. However, from the viewpoint of the stability of the aqueous dispersion, among the above, the surfactant is preferably an alkyl sulfate ester or an alkyl sulfosuccinate ester, and more preferably the alkyl sulfate ester is lauryl sulfate, and the alkyl sulfosuccinate ester is dioctyl sulfosuccinate.

[0035] Examples of nonionic surfactants include polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether and polyoxyethylene stearyl ether, polyoxyethylene alkylphenyl ethers such as polyoxyethylene octylphenyl ether and polyoxyethylene nonylphenyl ether, sorbitan higher fatty acid esters such as sorbitan monolaurate, sorbitan monostearate, and sorbitan trioleate, polyoxyethylene sorbitan higher fatty acid esters such as polyoxyethylene sorbitan monolaurate and polyoxyethylene sorbitan monostearate, polyoxyethylene higher fatty acid esters such as polyoxyethylene monolaurate and polyoxyethylene monostearate, glycerin higher fatty acid esters such as oleic acid monoglyceride and stearate monoglyceride, polyoxyethylene polyoxypropylene block copolymer, polyvinyl alcohol, polyvinylpyrrolidone, and polyoxyethylene distyleninated phenyl ether.

[0036] The weight-average molecular weight of the polyurethane resin (A) is preferably 500,000 or more. A molecular weight of 500,000 or more results in excellent coating film strength, making it easier to achieve both heat-sealability and blocking resistance. The weight-average molecular weight of the polyurethane resin can be measured by dissolving the dried resin in tetrahydrofuran (THF), preparing a 0.2% by mass solution, and then filtering it through a membrane filter (ADVANTEC 13HP045AN; pore size 0.45 μm) using the following apparatus and measurement conditions. Note that if the resin does not completely dissolve in THF, or if it dissolves but does not pass through the filter, it is considered to have an ultra-high molecular weight, and its weight-average molecular weight is determined to be 500,000 or more. Equipment: HLC-8320-GPC system (manufactured by Tosoh Corporation) Column: TSKgel-SuperMultiporeHZ-M0021488 4.6mm I.D. × 15cm × 3 pieces (Molecular weight measurement range: 2000 to approximately 2,000,000) Elution solvent: tetrahydrofuran Standard material: Polystyrene (manufactured by Tosoh Corporation) Flow rate: 0.6mL / min Sample solution volume: 10 μL Column temperature: 40℃

[0037] Due to limitations in the molecular weight range that can be measured by the above-mentioned GPC (gel permeation chromatography) apparatus, a preferred upper limit for the weight-average molecular weight of polyurethane resin (A) is not specified. It can be used as long as it does not impair the stability and applicability of the resulting heat sealant or the performance of the laminate with the heat seal layer.

[0038] The average particle size of the polyurethane resin (A) after water dispersion is preferably 30 nm to 300 nm, and more preferably 40 nm to 200 nm. Adjusting the particle size to 30 nm to 300 nm improves film formation and heat sealability, as well as providing excellent stability as a heat sealant.

[0039] The non-volatile content concentration of the aqueous dispersion of polyurethane resin (A) is preferably 10% by mass or more and 70% by mass or less, and more preferably 20% by mass or more and 50% by mass or less. If the non-volatile content concentration is 10% by mass or more, the thickness of the dried coating film after application can be increased, thereby obtaining a tough coating film. If the non-volatile content concentration is 70% by mass or less, sufficient inter-particle distance can be ensured in the dispersion, resulting in good dispersion stability.

[0040] Examples of waxes (B) include plant-derived waxes such as carnauba wax, candelilla wax, rice wax, wood wax, and soy wax; animal-derived waxes such as beeswax, shellac wax, and privet wax; crude oil-derived waxes such as paraffin wax, microcrystalline wax, and slacks wax; mineral-derived waxes such as montan wax, ceresin, and osogelite; and synthetic waxes such as polyethylene wax, oxidized polyethylene wax, modified polyethylene wax, polypropylene wax, oxidized polypropylene wax, modified polypropylene wax, ethylene vinyl acetate copolymer wax, modified ethylene vinyl acetate copolymer wax, fatty acid amides, polytetrafluoroethylene, and Fischer-Tropsch wax. However, it is preferable to use plant-derived waxes from the viewpoint of improving blocking resistance.

[0041] Based on a total amount of 100 parts by mass of polyurethane resin (A), it is preferable to use wax (B) in a proportion of 1 to 100 parts by mass, and more preferably 2 to 50 parts by mass. Using wax (B) in a proportion of 1 to 100 parts by mass makes it easier to achieve both heat sealability and blocking resistance.

[0042] Heat sealants may contain additives such as fillers, colorants, defoamers, aqueous organic solvents, preservatives, and crosslinking agents as optional components.

[0043] The filler is not particularly limited as long as it is a known material, and examples include talc, silica, calcium carbonate, barium sulfate, titanium dioxide, diatomaceous earth (white carbon), cellulose powder, etc.

[0044] As colorants, known organic pigments, inorganic pigments, dyes, etc., can be used.

[0045] Examples of defoaming agents include polysiloxane-based defoaming agents, mineral oil-based defoaming agents, and nonionic surfactants. Among these, polysiloxane-based defoaming agents are preferred due to their strong defoaming power. Polysiloxane-based defoaming agents with a polydimethylsiloxane structure can be used. Polysiloxane-based defoaming agents mixed with hydrophobic silica or mineral oil may be used as needed.

[0046] Examples of aqueous organic solvents include monohydric alcohols such as ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, 2-butanol, and 2-methyl-2-propanol; glycols such as ethylene glycol, 1,3-propanediol, propylene glycol, 1,2-butanediol, 1,4-butanediol, pentylene glycol, 1,2-hexanediol, 1,6-hexanediol, diethylene glycol, triethylene glycol, and tetraethylene glycol; ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monoethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, and diethylene glycol. Examples of glycol ethers include monoisopropyl ether, triethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, diethylene glycol monoisobutyl ether, triethylene glycol monoisobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monohexyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol dimethyl ether, and tripropylene glycol monomethyl ether.

[0047] The preservatives are not particularly limited and include, for example, sodium dehydroacetate, dichlorophene, sorbic acid, sodium benzoate, p-hydroxybenzoic acid esters, and isothiazolinone compounds.

[0048] Suitable crosslinking agents include polyfunctional compounds that are reactive to carboxyl groups, such as polyfunctional carbodiimides, polyfunctional isocyanates, polyfunctional epoxys, and polyfunctional oxazolines.

[0049] The heat-sealing agent of the present invention can be applied to a substrate such as a plastic film or paper to form a heat-seal layer, and the laminate of the present invention can be obtained by performing molding or other processing as necessary.

[0050] Examples of substrates include paper, nonwoven fabric, sheets with a porous surface for woven fabrics, polyethylene film, polypropylene film, polyester film, nylon film, and aluminum foil, but paper is preferred. When the substrate is paper, the coating agent wets the substrate sufficiently and penetrates into the substrate, resulting in a stronger bond between the substrate and the coating agent. Therefore, the heat sealability of the laminate can be improved.

[0051] Coating equipment includes knife coaters, comma coaters, roll coaters, bar coaters, gravure coaters, and flexo coaters.

[0052] The heat sealant of the present invention is particularly suitable for use with paper substrates. Furthermore, the heat sealant of the present invention may be applied in multiple layers as needed to obtain the desired heat sealability and water resistance. [Examples]

[0053] The present invention will be specifically described below with reference to examples. In the examples, unless otherwise specified, "parts" refers to "parts by mass," and "%" refers to "mass%."

[0054] <Acid value> For dried polyurethane resin (A), potentiometric titration with potassium hydroxide-ethanol solution was performed according to the method described in JIS K2501, and the results were calculated.

[0055] <Average particle size> The aqueous dispersion of resin obtained in each example was diluted 500 times with water, and approximately 5 ml of the diluted solution was measured using dynamic light scattering (measurement device: NanoTrac UPA; MicroTrac Bell). The median diameter (median value) based on volume was defined as the average particle size.

[0056] [Example 1] In a reaction vessel (reaction tank) equipped with a stirrer, thermometer, dropping funnel, and reflux apparatus, 18.8 parts of BioPTMG2000, a plant-derived raw material used as an acid-free polyether polyol (a-1), and 0.6 parts of dimethylolpropionic acid and 0.6 parts of dimethylolbutanoic acid were charged as acid-containing polyols (a-2). The internal temperature of the reaction vessel was raised to 60°C while purging with nitrogen. Next, 8.7 parts of isophorone diisocyanate (a-3) were added to the reaction vessel, the internal temperature of the reaction vessel was raised to 100°C, and the reaction was carried out at 100°C for 1 hour while stirring. After the reaction, it was cooled to 50°C and neutralized with 0.7 parts of triethylamine. Furthermore, 0.7 parts of Perex OT-P (sodium dioctyl sulfosuccinate, active ingredient 70%, manufactured by Kao Corporation) were added, and an aqueous dispersion was prepared by gradually adding 56 parts of water to the reaction vessel. Subsequently, 1.3 parts of ethylenediamine and 10 parts of water were placed in a dropping funnel as a chain extender (a-4) and added dropwise over 10 minutes. After the addition was complete, the mixture was reacted at 50°C for 1 hour to obtain an aqueous dispersion of polyurethane resin (A). The acid value of the nonvolatile content of the obtained polyurethane resin (A) was 16.0 mgKOH / g, and the average particle size of the aqueous dispersion of polyurethane resin (A) was 80 nm. To the obtained aqueous dispersion of polyurethane resin (A), 20 parts of AQUACER2650 (aqueous dispersion of carnauba wax manufactured by BYK, nonvolatile content concentration: 30%, melting point: 84°C) and a predetermined amount of water were added as wax (B) to adjust the nonvolatile content concentration to 30% to obtain the desired heat sealant. The resulting heat sealant is applied to a base material of single-sided glossy bleached kraft paper (basis weight 50g / m²). 2 One side of the material was coated using a bar coater #8. After coating, a laminate was obtained by drying in a hot air oven set to 100°C for 30 seconds.

[0057] [Examples 2-22, Comparative Examples 2-4] Polyurethane resins were prepared using the same method as in Example 1, with the formulations shown in Tables 1 and 2. The acid value and average particle size of the obtained polyurethane resins were measured, and laminates were fabricated, in the same manner as in Example 1. The amount of water was adjusted so that the non-volatile content of the heat sealant was 30%. In Tables 1 and 2, blank spaces indicate that the ingredient is not included or is not present. In Example 15, Topscreen BW200 (aqueous dispersion of plant-derived wax manufactured by Solenis, with a non-volatile content of 40% and a melting point of 57°C) was used as wax (B) instead of AQUACER2650, and in Example 18, AQUACER497 (aqueous dispersion of modified paraffin wax manufactured by BYK, with a non-volatile content of 50% and a melting point of 55°C) was used as wax (B) instead of AQUACER2650.

[0058] [Comparative Example 1] In a reaction vessel (reaction tank) equipped with a stirrer, thermometer, dropping funnel, and reflux valve, 93 parts of ε-caprolactone and 7 parts of dimethylolpropionic acid were charged, and the mixture was heated to 180°C under a nitrogen atmosphere with stirring and reacted for 5 hours. After that, the unreacted cyclic ester component was removed by distillation under reduced pressure with a pump to obtain a polyester polyol. The number-average molecular weight of the obtained polyester polyol was 2000. 21.3 parts of the obtained polyester polyol and 0.6 parts of dimethylolbutanoic acid as an acidic group-containing polyol (a-2) were charged into the reaction vessel, and the internal temperature of the reaction vessel was raised to 60°C while purging with nitrogen. Next, 7.1 parts of isophorone diisocyanate as polyisocyanate (a-3) were added to the reaction vessel, and the internal temperature of the reaction vessel was raised to 100°C and reacted at 100°C for 1 hour. After the reaction, it was cooled to 50°C and neutralized with 1.5 parts of triethylamine. Furthermore, 0.8 parts of Perex OT-P (sodium dioctyl sulfosuccinate solution, 70% active ingredient, manufactured by Kao Corporation) were added, and 56 parts of water were gradually added to the reaction vessel to prepare an aqueous dispersion. Then, 1.0 part of ethylenediamine and 10 parts of water were charged into a dropping funnel as a chain extender (a-4) and added dropwise over 10 minutes. After the addition was complete, the mixture was reacted at 50°C for 1 hour. The acid value of the nonvolatile content of the obtained polyurethane resin was 28.4 mgKOH / g, and the average particle size of the aqueous dispersion of polyurethane resin was 60 nm. To the obtained aqueous dispersion of polyurethane resin, 20 parts of AQUACER2650 as wax (B) and a predetermined amount of water were added to adjust the nonvolatile content concentration to 30% to obtain the target heat sealant. Using the obtained heat sealant, a laminate was prepared in the same manner as in Example 1.

[0059] The raw materials in Tables 1 and 2 are as follows. "NV" represents the non-volatile content concentration, and "Mn" represents the number-average molecular weight. • AQUACER2650: Manufactured by BYK, an aqueous dispersion of carnauba wax (melting point 84°C) (NV30%) • Topscreen BW200: Aqueous dispersion of plant-derived wax (melting point 57°C) manufactured by Solenis (NV 40%). • AQUACER497: Manufactured by BYK, aqueous dispersion of modified paraffin wax (melting point 55°C) (NV50%) • Perex OT-P: Manufactured by Kao Corporation, sodium dioctyl sulfosuccinate solution (NV 70%) • Neoperex G-25: Manufactured by Kao Corporation, sodium dodecylbenzenesulfonate aqueous solution (NV 26%) • BioPTMG1000: Manufactured by Mitsubishi Chemical Corporation, polytetramethylene glycol, Mn1000, made from plant-derived raw materials. • BioPTMG2000: Manufactured by Mitsubishi Chemical Corporation, polytetramethylene glycol, Mn2000, made from plant-derived raw materials. • BioPTMG3000: Manufactured by Mitsubishi Chemical Corporation, polytetramethylene glycol, Mn3000, made from plant-derived raw materials. • ECOTRION H2000: Manufactured by SK Chemicals, using plant-derived raw materials, polypropylene glycol, Mn2000 • Polyglykol 3350 SG Vita: Manufactured by CLARIANT, a polyethylene glycol made from plant-derived raw materials, Mn3350

[0060] [Table 1]

[0061] [Table 1]

[0062] [Table 2]

[0063] Evaluation items and evaluation methods The evaluation items and evaluation methods for the heat sealant and laminate obtained in each example and comparative example are as follows.

[0064] <Stability of heat sealant> The heat-sealing agent obtained above was placed in a screw-top bottle and left to stand at 50°C for one month. The presence or absence of sediment formation over time and the redispersibility when the screw-top bottle was shaken vertically several times were then checked. [Evaluation Criteria] A: No sediment has formed (good). B: Although sediment has formed, it can be easily redispersed by shaking a few times (usable). C: Sediment has formed and cannot be redistributed (unusable).

[0065] <Blocking resistance> The resulting laminates were stacked so that the coated surfaces (heat sealant layers) were in contact with each other, and evaluated using the following test equipment and conditions. Test equipment: CO-201 permanent strain tester (manufactured by Tester Industries Co., Ltd., upper and lower plate heating) Pressure: 4 kg / cm² 2 [Evaluation Criteria] S: After compression for 24 hours in a 40℃-80%RH environment, there was no resistance during delamination, and the laminate was intact (extremely good). A: After compression for 24 hours in a 40℃-40%RH environment, there was no resistance during delamination, and the laminate was intact (good). B: After compression for 24 hours in a 40℃-40%RH environment, there is some resistance during delamination, but the laminate is not damaged (usable). C: After compression for 24 hours in a 40℃-40%RH environment, there was resistance during delamination and the laminate was damaged (unusable).

[0066] <Heat seal strength> Two test pieces were prepared by cutting the obtained laminate to a width of 15 mm. The coated surface of one test piece was placed on top of the coated surface of the other test piece, and a heatsheel and impulse tester (manufactured by Nichiri Kagaku Kogyo Co., Ltd., with upper and lower plate heating) was used at 100°C and 2 kgf / cm². 2 Samples crimped under the -1 second condition were used for evaluation. For this evaluation sample, the peel strength was measured under the following conditions, and the heat seal strength (heat sealability) was evaluated. Testing equipment: Tensile testing machine (manufactured by Tester Industries Co., Ltd.) Peeling conditions: 180° peeling, 300 mm / min [Evaluation Criteria] S: 6N or higher (extremely good) A: 4N or higher, less than 6N (good) B: 2N or more, less than 4N (usable) C: Less than 2N (unusable)

[0067] As can be seen from Tables 1 and 2, the heat sealants obtained in Examples 1 to 22 exhibited excellent stability, heat sealability of the laminate, and blocking resistance, demonstrating performance that fully met practical requirements. On the other hand, the heat sealants obtained in Comparative Examples 1 to 4 exhibited extremely poor physical properties in terms of stability, heat sealability of the laminate, and blocking resistance, making it difficult to say that they met practical standards.

Claims

1. A heat sealant comprising a polyurethane resin (A) containing structural units derived from an acid-free polyether polyol (a-1), an acid-containing polyol (a-2), a polyisocyanate (a-3), and a chain extender (a-4), and a wax (B).

2. The heat sealant according to claim 1, wherein the acid group-free polyether polyol (a-1) comprises at least one structural unit selected from the group consisting of polyethylene glycol, polypropylene glycol, and polytetramethylene glycol, which are of plant origin.

3. The heat sealant according to claim 1, wherein the acid value of the polyurethane resin (A) is 5 mg KOH / g or more and 30 mg KOH / g or less.

4. The heat sealant according to claim 1, wherein the polyurethane resin (A) is in particulate form and has an average particle diameter of 30 nm or more and 300 nm or less.

5. The heat sealant according to claim 1, wherein the wax (B) comprises a plant-derived wax.

6. A laminate having a heat-seal layer formed from a heat-seal agent according to any one of claims 1 to 5 on a substrate.

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