Resin composition, hot-melt adhesive, and adhesive

Abstract

To provide a resin composition which retains a suitable open time and cures within a short period, exhibiting superior initial bonding strength, and to provide a hot-melt adhesive and an adhesive comprising the resin composition.SOLUTION: A resin composition includes a urethane prepolymer having an isocyanate group and an acrylic polymer containing a structural unit derived from ethyl (meth)acrylate and having a glass transition temperature of 15°C or more and 100°C or less. The resin composition retains a suitable open time and cures within a short period, exhibiting superior initial bonding strength. A hot-melt adhesive and an adhesive comprising the resin composition are also provided.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a resin composition, a hot melt adhesive, and an adhesive. [Background technology]

[0002] Hot melt adhesives are solid or semi-solid at room temperature and become fluid when heated. Reactive hot melt adhesives are those whose main component is a prepolymer containing reactive functional groups such as isocyanate groups or alkoxysilyl groups. Most of these are moisture-curing urethane adhesives, usually in the form of an isocyanate-containing urethane prepolymer formed by condensation polymerization of a polyol component and an isocyanate component.

[0003] These reactive hot melt adhesives are applied to a substrate in a heated, molten state, and after cooling and solidifying, moisture curing occurs through a chemical crosslinking reaction between the isocyanate groups and water, forming a coating (adhesive layer) that is tough, heat-resistant, and chemical-resistant.

[0004] Conventional reactive hot melt adhesives exhibit excellent adhesive properties when chemical crosslinks are formed by moisture curing. However, reactive hot melt adhesives have issues with insufficient initial adhesive strength to substrates because almost no chemical crosslinking occurs immediately after application, and the adhesive temperature is high immediately after heating and melting, and the thermoplastic polymer has fluidity. Note that initial adhesive strength refers to the adhesive strength 2 to 5 minutes after application to the substrate.

[0005] One known method for increasing initial adhesive strength is to incorporate a thermoplastic resin such as an acrylic resin into a urethane hot melt adhesive to improve initial cohesive strength, as shown in Patent Document 1. Furthermore, in recent years, as the applications of reactive hot melt adhesives have become more diverse, there has been an increasing demand for reactive hot melt adhesives with even higher initial adhesive strength. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2008-500406 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made to solve these problems. That is, an object of the present invention is to provide a resin composition that can be cured in a short time while maintaining an appropriate open time and has excellent initial adhesive strength, and a hot melt adhesive and adhesive that use the resin composition. [Means for solving the problem]

[0008] The present invention is summarized as follows [1] to [9]. [1] A resin composition comprising a urethane prepolymer having an isocyanate group and an acrylic polymer having structural units derived from ethyl (meth)acrylate and having a glass transition temperature of 15°C or higher and 100°C or lower. [2] The resin composition according to [1], wherein the urethane prepolymer having an isocyanate group is a reaction product of a polyester polyol, a polyether polyol, and an isocyanate. [3] The resin composition according to [2] above, wherein the polyether polyol is a polyalkylene glycol. [4] The resin composition according to [3], wherein the polyalkylene glycol has a number average molecular weight of 200 or more and 5,000 or less, or a mass average molecular weight of 200 or more and 5,000 or less. [5] The resin composition according to any one of [1] to [4], wherein the acrylic polymer has a mass average molecular weight of 10,000 or more and 100,000 or less. [6] The resin composition according to any one of [1] to [5], wherein the acrylic polymer has a molecular weight distribution of 1 or more and 10 or less. [7] The resin composition according to any one of [1] to [6] above, wherein the acrylic polymer has a biobased content defined in ISO 16620-2 of 1% or more and 100% or less. [8] A hot melt adhesive comprising the resin composition according to any one of [1] to [7] above. [9] An adhesive comprising the resin composition according to any one of [1] to [7] above. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a resin composition that exhibits excellent short-time curing and initial adhesive strength while maintaining a moderate open time compared to conventional products, and a hot melt adhesive and adhesive that use the resin composition. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described in detail below. Unless otherwise specified, in this specification, a numerical range expressed using "to" means a range that includes the numerical values written before and after "to" as the lower and upper limits. "(Meth)acrylic" is a general term for acrylic and methacrylic.

[0011] <Resin composition> The resin composition of the present invention contains a urethane prepolymer having an isocyanate group and an acrylic polymer having a structural unit derived from ethyl (meth)acrylate and having a glass transition temperature (hereinafter also referred to as "Tg") of 15°C or more and 100°C or less.

[0012] (acrylic polymer) The acrylic polymer contains a structural unit derived from ethyl (meth)acrylate, and preferably further contains a structural unit derived from a (meth)acrylic acid ester other than ethyl (meth)acrylate, since this makes it easier to adjust the glass transition temperature.

[0013] Examples of the other (meth)acrylic acid esters include (meth)acrylic acid esters having a linear or branched hydrocarbon skeleton, such as alkyl (meth)acrylate esters, such as methyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, stearyl (meth)acrylate, and isostearyl (meth)acrylate; (meth)acrylic acid esters having an alicyclic skeleton, such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate (meth)acrylate; (meth)acrylic acid esters having a glycidyl group, such as glycidyl (meth)acrylate and hydroxybutyl (meth)acrylate glycidyl ether; phenoxy (meth)acrylate, benzoyl (meth)acrylate; Examples of suitable (meth)acrylic acid esters include (meth)acrylic acid esters having an aromatic ring such as phenyl (meth)acrylate; (meth)acrylic acid esters having a cyclic ether such as tetrahydrofurfuryl (meth)acrylate; ethylene oxide-modified (meth)acrylic acid esters such as 2-methoxyethyl (meth)acrylate; (meth)acrylic acid esters having an amino group such as N-dimethylaminoethyl (meth)acrylate and N-diethylaminoethyl (meth)acrylate; (meth)acrylic acid esters having a phosphate group such as 2-(meth)acryloyloxyethyl acid phosphate and 2-(meth)acryloyloxyethyl acid phosphate monoethanolamine salt; and (meth)acrylic acid esters having a hydroxyl group such as 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate. Among these, structural units derived from (meth)acrylic acid alkyl esters in which the alkyl group has 1 to 6 carbon atoms are preferred, with methyl (meth)acrylate, n-butyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate being more preferred. The other (meth)acrylic acid esters may be used singly or in combination of two or more.

[0014] The proportion of structural units derived from ethyl (meth)acrylate in the acrylic polymer is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, and particularly preferably 30% by mass or more. It is also preferably 100% by mass or less, more preferably 80% by mass or less, even more preferably 60% by mass or more, and particularly preferably 40% by mass or less. When the proportion of structural units derived from ethyl (meth)acrylate is equal to or greater than the lower limit, the initial adhesive strength of the hot melt adhesive is improved. When the proportion of structural units derived from ethyl (meth)acrylate is equal to or less than the upper limit, the hot melt adhesive can maintain an appropriate open time.

[0015] It is preferable that the acrylic polymer contains a structural unit derived from a monomer having a carboxyl group, since this can promote the reaction between the isocyanate and the polyol when preparing the resin composition, and also improves the initial adhesion to the substrate when the hot melt adhesive is applied and the adhesive strength after curing.

[0016] Examples of the monomer having a carboxyl group include (meth)acrylic acid, 2-(meth)acryloylhexahydrophthalic acid, 2-(meth)acryloyloxypropylhexahydrophthalic acid, 2-(meth)acryloyloxyethyltetrahydrophthalic acid, 2-(meth)acryloyloxypropyltetrahydrophthalic acid, 5-methyl-2-(meth)acryloyloxyethylhexahydrophthalic acid, 2-(meth)acryloyloxyethylphthalic acid, 2-(meth)acryloyloxypropyltetrahydrophthalic acid, Examples of α,β-unsaturated carboxylic acids include methacrylic acid, 2-(meth)acryloyloxyethyl maleic acid, 2-(meth)acryloyloxypropyl maleic acid, 2-(meth)acryloyloxyethyl succinic acid, 2-(meth)acryloyloxypropyl succinic acid, 2-(meth)acryloyloxyethyl oxalic acid, 2-(meth)acryloyloxypropyl oxalic acid, crotonic acid, isocrotonic acid, cinnamic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, mesaconic acid, and glutaconic acid. Among these, it is preferable to have a structural unit derived from methacrylic acid because of its good copolymerizability with ethyl (meth)acrylate.

[0017] The acrylic polymer may contain structural units derived from other monomers copolymerizable with the (meth)acrylic acid ester and the monomer having a carboxyl group. Examples of the other monomers include (meth)acrylates such as ammonium (meth)acrylate, sodium (meth)acrylate, and potassium (meth)acrylate; (meth)acrylamide derivatives such as (meth)acrylamide, (meth)acrylamide diacetone acrylamide, N-methylol (meth)acrylamide, N-methoxymethyl (meth)acrylamide, N-ethoxymethyl (meth)acrylamide, N-butoxymethyl (meth)acrylamide, and (meth)acryloylmorpholine; styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, and Examples of the other monomers include aromatic vinyl monomers such as acrylonitrile, methacrylonitrile, α-cyanoacrylate, dicyanovinylidene, and fumaronitrile; vinyl cyanide monomers such as vinyl sulfonic acid and 2-acrylamido-2-methylpropanesulfonic acid; monomers having a sulfonic acid group such as divinylbenzene, divinylnaphthalene, and divinyl ether; vinyl monomers such as vinyl acetate and vinyl propionate; and structural units derived from conjugated diene monomers such as 1,3-butadiene, isoprene, 2-chloro-1,3-butadiene, and chloroprene. The other monomers may be used alone or in combination of two or more.

[0018] In the polymerization, a chain transfer agent or a radical polymerization initiator may also be used. Examples of chain transfer agents include, but are not limited to, hydrogen, mercaptans, α-methylstyrene dimer, dimers to 20-mers of (meth)acrylic monomers, terpenoids, and cobalt chain transfer agents. The chain transfer agents can be used alone or in combination of two or more. Specific examples of mercaptans suitable for use as chain transfer agents include, but are not limited to, n-octyl mercaptan, n-dodecyl mercaptan, tert-dodecyl mercaptan, n-octyl mercaptan, n-tetradecyl mercaptan, n-hexyl mercaptan, and 2-ethylhexyl thioglycolate.

[0019] The amount of chain transfer agent used is preferably 0.01 to 5 parts by mass per 100 parts by mass of the total monomers used. When the amount of chain transfer agent used is equal to or greater than the lower limit, the molecular weight of the acrylic polymer decreases due to chain transfer of radicals, improving adhesion to the substrate. When the amount of chain transfer agent used is equal to or less than the upper limit, the amount of unreacted monomer and chain transfer agent remaining decreases, reducing odor.

[0020] Examples of the radical polymerization initiator include, but are not limited to, organic peroxides, azo compounds, persulfate compounds, etc. The radical polymerization initiators may be used alone or in combination of two or more. Specific examples of suitable organic peroxides used as radical polymerization initiators include, but are not limited to, t-butyl peroxypivalate, o-methylbenzoyl peroxide, bis-3,5,5-trimethylhexanoyl peroxide, octanoyl peroxide, cyclohexanone peroxide, benzoyl peroxide, methyl ethyl ketone peroxide, dicumyl peroxide, lauroyl peroxide, diisopropylbenzene hydroperoxide, t-butyl hydroperoxide, di-t-butyl peroxide, t-butylperoxy-2-ethylhexanoate, and 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate. Specific examples of azo compounds include, but are not limited to, 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), and 2,2'-azobis(2,4-dimethyl-4-methoxyvaleronitrile). Specific examples of persulfate compounds include, but are not limited to, ammonium persulfate and potassium persulfate.

[0021] As the radical polymerization initiator, benzoyl peroxide, lauroyl peroxide, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile) and 2,2'-azobis(2,4-dimethylvaleronitrile) are preferred because they provide good polymerizability of the monomer. The amount of radical polymerization initiator used is preferably 0.0001 to 10 parts by mass per 100 parts by mass of the total of the monomers used, since this improves the polymerizability of the monomers and reduces production costs.

[0022] During polymerization, a dispersant or dispersion aid may be used to stabilize the oil droplets of the monomer. Examples of dispersants include surfactants that stably disperse the monomer in water. Specific examples include copolymers of 2-sulfoethyl sodium methacrylate, potassium methacrylate, and methyl methacrylate, copolymers of 3-sodium sulfopropyl methacrylate and methyl methacrylate, copolymers of sodium methacrylate and methacrylic acid, polyvinyl alcohol, polyvinylpyrrolidone, hydroxyethyl cellulose, hydroxypropyl cellulose, anionic emulsifiers (sodium dodecylbenzenesulfonate, sodium lauryl sulfonate, sodium lauryl sulfate, dipotassium alkenyl succinate, sodium dialkyl sulfosuccinate, etc.), anionic emulsifiers containing polyoxyethylene groups, nonionic emulsifiers (polyoxyethylene nonylphenyl ether, polyoxyethylene lauryl ether, etc.), and reactive emulsifiers having a vinyl polymerizable double bond in the molecule. Examples of the dispersing aid include sodium sulfate, sodium carbonate, sodium dihydrogen phosphate, disodium hydrogen phosphate, potassium chloride, calcium acetate, magnesium sulfate, and manganese sulfate.

[0023] The acrylic polymer may have any structure, such as a homopolymer, a random copolymer, a graft copolymer, or a block copolymer.

[0024] In this specification, the Tg of an acrylic polymer means a value (unit: ° C.) calculated by the Fox formula shown in the following formula (1).

[0025]

number

[0026] In formula (1), Wi represents the mass fraction of monomer i, and Tgi represents the Tg (° C.) of the homopolymer of monomer i. For the Tg of a homopolymer, the values described in "Polymer Handbook, 4th Edition, published by John Wiley & Sons" can be used.

[0027] The glass transition temperature (Tg) of the acrylic polymer is 15° C. or higher, preferably 30° C. or higher and more preferably 50° C. or higher in order to improve the initial adhesive strength of the hot melt adhesive. The Tg of the acrylic polymer is 100° C. or lower, preferably 90° C. or lower and more preferably 85° C. or lower in order to facilitate handling during formulation of the adhesive.

[0028] The mass average molecular weight (hereinafter also referred to as "Mw") of the acrylic polymer is preferably 10,000 or more and 100,000 or less, and more preferably 30,000 or more and 80,000 or less. When Mw is equal to or more than the lower limit, the initial adhesive strength of the adhesive tends to be good. When Mw is equal to or less than the upper limit, the adhesive is easy to handle when blended.

[0029] The molecular weight distribution (hereinafter also referred to as "Mw / Mn") of the acrylic polymer is preferably 1 or more and 10 or less, more preferably 1.2 or more and 5 or less, and even more preferably 1.5 or more and 3 or less.

[0030] In this specification, the terms "mass average molecular weight (Mw)" and "number average molecular weight (Mn)" refer to the polystyrene-equivalent mass average molecular weight and number average molecular weight measured by the GPC-LS method (Gel Permeation Chromatography-Light Scattering Method: GPC-light scattering method).

[0031] The biobased content of the acrylic polymer as defined by ISO 16620-2 is preferably 1% or more, more preferably 5% or more, and even more preferably 10% or more. If the biobased content is equal to or greater than the lower limit, the environmental impact can be reduced.

[0032] In the present invention, "bio-based content" refers to the weight percentage (unit: %) of the number of carbon atoms derived from biomass-derived (meth)acrylate relative to the total carbon of an acrylic polymer produced using biomass-derived (meth)acrylate as a raw material. ISO 16620-2 specifies the standard for bio-based content, and uses the ratio of carbon from biomass-derived (meth)acrylate relative to the total carbon of the dried acrylic polymer. For example, in biomass-derived ethyl methacrylate, there are two carbon atoms in the molecule that come from the raw material bioethanol, which accounts for 33.3% of the total carbon atom count of six in the molecule, so the bio-based content of the ethyl methacrylate homopolymer is 33.3%.

[0033] (Urethane prepolymer having isocyanate groups) The urethane prepolymer having an isocyanate group is preferably a reaction product of polyester polyol, polyether polyol and isocyanate, since it provides high adhesive strength due to moisture curing.

[0034] As the polyether polyol, polyalkylene glycol is preferred because it can be used as a material for hot melt adhesives. Examples of polyalkylene glycols include polymethylene glycol, polyethylene glycol, polypropylene glycol, polyoxytetramethylene glycol, polyhexamethylene glycol, polyalkylene glycols having structural units derived from two or more glycols, such as a copolymer of ethylene oxide and propylene oxide, and branched polyalkylene glycols using polyfunctional alcohols, such as glycerin. These may be used alone or in combination of two or more.

[0035] The number average molecular weight of the polyalkylene glycol is preferably 200 to 5000, more preferably 700 to 3000. When the number average molecular weight of the polyalkylene glycol is equal to or greater than the lower limit, the adhesive strength of the hot melt adhesive after curing is good. When the number average molecular weight of the polyalkylene glycol is equal to or less than the upper limit, the viscosity of the resin composition is low, and the coatability is good. For the same reason, the mass average molecular weight of the polyalkylene glycol is preferably 200 to 5,000, and more preferably 700 to 3,000.

[0036] Known polyester polyols include crystalline polyester polyols and amorphous polyester polyols, and specific examples thereof include aliphatic polyester polyols and aromatic polyester polyols. Crystalline polyester polyols and amorphous polyester polyols can also be easily distinguished by differential scanning calorimetry (DSC). More specifically, the melting point of a crystalline polyester polyol is observed by DSC as an endothermic peak during heating and as an exothermic peak during cooling. In contrast, when measuring the melting point of an amorphous polyester polyol by DSC, no clear endothermic or exothermic peak is observed, making it possible to distinguish it from a crystalline polyester polyol.

[0037] Aliphatic polyester polyols can be obtained by reacting an aliphatic dicarboxylic acid with a diol. Specific examples of the aliphatic dicarboxylic acid include adipic acid, sebacic acid, azelaic acid, and decamethylenedicarboxylic acid. The aliphatic dicarboxylic acid may be used alone or in combination of two or more. Specific examples of diols include low-molecular-weight diols having 2 to 12 carbon atoms, such as ethylene glycol, 1-methylethylene glycol, 1-ethylethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, heptanediol, octanediol, nonanediol, decanediol, dodecanediol, neopentyl glycol, 2-methyl-1,3-propanediol, cyclohexanedimethanol, and 2,4-dimethyl-1,5-pentanediol. Among these, one or more of ethylene glycol, butanediol, hexanediol, octanediol, and decanediol are preferred. One diol may be used alone, or two or more may be used in combination.

[0038] Specific examples of the aliphatic polyester polyol include polyhexamethylene adipate, polyhexamethylene sebacate, polyhexamethylene dodecanate, and polybutylene adipate.

[0039] The aromatic polyester polyol is preferably a compound obtained by reacting an aromatic polycarboxylic acid or an aromatic dicarboxylic acid with the above-mentioned diol. Specific examples of aromatic polycarboxylic acids or aromatic dicarboxylic acids include phthalic acid, isophthalic acid, and terephthalic acid, which may be used alone or in combination of two or more. Specific examples of aromatic polyester polyols include polyalkylene phthalate, polyalkylene isophthalate, and polyalkylene terephthalate.

[0040] Polyester polyols have low viscosity and good handleability. In addition, polyester polyols have high heat resistance, high solvent resistance, and high strength, so it is preferable to use polyalkylene glycols and polyester polyols in combination.

[0041] Specific examples of isocyanates include ethylene diisocyanate, ethylidene diisocyanate, propylene diisocyanate, butylene diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, cyclopentylene-1,3-diisocyanate, cyclohexylene-1,4-diisocyanate, cyclohexylene-1,2-diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,2-diphenylpropane-4,4'-diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, xylylene diisocyanate, and 1,4-naphthalene diisocyanate. Examples include ethylene diisocyanate, 1,5-naphthylene diisocyanate, diphenyl-4,4'-diisocyanate, azobenzene-4,4'-diisocyanate, diphenylsulfone-4,4'-diisocyanate, dichlorohexamethylene diisocyanate, furfuridene diisocyanate, 1-chlorobenzene-2,4-diisocyanate, 4,4',4"-triisocyanate-triphenylmethane, 1,3,5-triisocyanate-benzene, 2,4,6-triisocyanate-toluene, and 4,4'-dimethyldiphenylmethane-2,2',5,5'-tetraisocyanate.

[0042] From the viewpoint of high adhesive strength after moisture curing, the isocyanate is preferably a compound containing an average of 1 to 3 isocyanate groups per molecule, and more preferably a bifunctional isocyanate, or so-called diisocyanate. Among these, 4,4'-diphenylmethane diisocyanate is particularly preferred from the viewpoint of high adhesive strength after moisture curing. One type of isocyanate may be used alone, or two or more types may be used in combination.

[0043] Although monools, monoisocyanates, trifunctional polyols, and trifunctional isocyanates can also be used, a combination of a difunctional polyol (diol) and a difunctional isocyanate (diisocyanate) is preferred in terms of the viscosity of the resin composition. It is preferable to use 2 moles of a difunctional isocyanate per mole of a difunctional polyol, since this allows the desired urethane prepolymer to be produced relatively easily.

[0044] The urethane prepolymer having an isocyanate group may be produced by reacting a polyol with an isocyanate in the presence of an acrylic polymer, or the polyol may be reacted with an isocyanate in advance and then mixed with the acrylic polymer.

[0045] The resin composition of the present invention may contain other additives to the extent that they do not adversely affect the reaction between the polyol and the isocyanate that forms the urethane prepolymer. Specific examples of additives include plasticizers, antioxidants, pigments, light stabilizers, flame retardants, curing catalysts, and waxes. Furthermore, wetting agents, thickeners, defoamers, rheology modifiers, etc. may also be added as needed. The proportion of the additives relative to the total mass of the resin composition of the present invention is preferably 0 to 5% by mass. The adhesive of the present invention is preferably a moisture-curable urethane-based hot-melt adhesive, since it can be cured in a short time while maintaining an appropriate open time and provides excellent initial adhesive strength. The moisture-curing urethane-based hot melt adhesive refers to a hot melt adhesive that has the property of being cured by atmospheric humidity and that contains a urethane prepolymer.

[0046] <Hot melt adhesive> In the present invention, the term "hot melt adhesive" refers to an adhesive that is melted by heating at 80 to 150°C before use. The hot melt adhesive of the present invention comprises the resin composition of the present invention. By including the resin composition of the present invention in the hot melt adhesive of the present invention, the initial adhesive strength of the adhesive tends to be good. The hot melt adhesive of the present invention is particularly useful as a moisture-curing urethane-based hot melt adhesive.

[0047] In the hot melt adhesive, the acrylic polymer is preferably 1 part by mass or more and 50 parts by mass or less, and the urethane prepolymer having an isocyanate group is preferably 50 parts by mass or more and 99 parts by mass or less, relative to a total of 100 parts by mass of the acrylic polymer and the urethane prepolymer having an isocyanate group. It is more preferable that the acrylic polymer is 5 parts by mass or more and 30 parts by mass or less, and the urethane prepolymer having an isocyanate group is 70 parts by mass or more and 95 parts by mass or less. When the acrylic polymer is at or above the lower limit, the initial adhesive strength tends to be good. When the acrylic polymer is at or below the upper limit, the adhesive strength after curing tends to be improved.

[0048] The hot melt adhesive of the present invention can be used in the same manner as conventional hot melt adhesives, and the method of use is not particularly limited. The heating temperature for melting the hot melt adhesive is preferably 80 to 140°C, more preferably 90 to 110°C. Within this temperature range, the components dissolve well, the viscosity of the hot melt adhesive decreases, and handling becomes easy. Furthermore, the reaction between the isocyanate and the polyalkylene glycol proceeds sufficiently. The heating time is not particularly limited, but is preferably 30 to 300 minutes, more preferably 60 to 180 minutes.

[0049] The initial adhesive strength of the hot melt adhesive is preferably 200 kPa or more, more preferably 300 kPa or more, and even more preferably 400 kPa or more. The initial adhesive strength of the hot melt adhesive can be measured by the method described in the examples.

[0050] The open time of the hot melt adhesive is preferably 15 to 40 minutes, more preferably 20 to 30 minutes. With an open time of this value, the bonding process can be shortened while maintaining sufficient working time. The open time of the hot melt adhesive can be measured by the method described in the examples.

[0051] The hot melt adhesive of the present invention can be used in fields where hot melt adhesives have traditionally been used, such as the field of architectural interiors (or construction), the field of electronic materials, the field of automotive interiors, etc. Specifically, it can be used, for example, for attaching automotive interior components, attaching decorative materials to architectural interior components, for woodworking, paper processing, fiber processing, and as a general-purpose adhesive.

[0052] For example, when attaching an adherend to a substrate, the hot melt adhesive may be applied to one or more surfaces of the substrate side and the adherend side. The adherend and substrate may be any commonly used material, such as a molding material, a film sheet, or a fibrous material made by weaving synthetic or natural fibers in a spinning machine into a sheet.

[0053] The raw materials for the molding material, film, and sheet are not particularly limited, but thermoplastic resins are preferred. Specific examples of the raw materials for the molding material, film, and sheet include polyolefin resin, polyester resin, acetate resin, polystyrene resin, ABS resin, vinyl chloride resin, and polycarbonate resin. Specific examples of the polyolefin resin include polyethylene and polypropylene. Specific examples of the polyester resin include polyethylene terephthalate.

[0054] Laminates obtained by bonding an adherend and a substrate with the hot melt adhesive of the present invention can be used in a variety of applications, including construction, electronic materials, and automotive. No special equipment is required to produce laminates; they can be produced using commonly known manufacturing equipment, including a conveyor, coater, press, heater, and cutter. For example, laminates can be produced as follows: While the substrate and adherend are conveyed by a conveyor, the hot melt adhesive of the present invention is applied to the substrate or adherend using a coater. The temperature during application is controlled to a predetermined temperature using a heater. The adherend is lightly pressed against the substrate using a press, and the adherend and substrate are bonded together via the hot melt adhesive. The bonded adherend and substrate are then allowed to cool and then conveyed by a conveyor to solidify the hot melt adhesive. The substrate with the adherend attached is then cut to an appropriate size using a cutter.

[0055] The hot melt adhesive of the present invention has a high initial adhesive strength and excellent heat resistance after moisture curing, making it difficult for the substrate and the adherend to separate even in summer. It is also possible to produce a laminate by applying the adhesive without using a coater. [Example]

[0056] EXAMPLES The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited to the following descriptions. <Measurement of mass average molecular weight (Mw) and molecular weight distribution (Mw / Mw)> The mass-average molecular weight and molecular weight distribution were measured using a Tosoh high-speed GPC system, model HLC-8320GPC (detector: RI detector). Two Tosoh TSKgel SuperHZM-M (4.6 mm ID x 15 cm L) columns and one Tosoh TSKgel HZ2000 (4.6 mm ID x 15 cm L) columns were connected together. Tetrahydrofuran (containing the stabilizer dibutylhydroxytoluene) was used as the eluent, with a flow rate of 0.35 mL / min, an inlet temperature of 40°C, an oven temperature of 40°C, and an RI detector temperature of 40°C. A 10 μL sample was injected, with the composition concentration adjusted to 0.2% by mass with tetrahydrofuran.

[0057] (Production Example 1) Acrylic Polymer P-1 A polymerization apparatus equipped with a stirrer, condenser, and thermometer was charged with 145 g of deionized water, 0.10 g of sodium sulfate (NaSO), and 0.020 g of a copolymer of potassium methacrylate and methyl methacrylate as dispersants, and a copolymer of 2-sulfoethyl sodium methacrylate, potassium methacrylate, and methyl methacrylate. The contents were stirred to form a uniform aqueous solution. Next, the ingredients shown in Table 1 (unit: g) were added to form a dispersion. The atmosphere inside the polymerization apparatus was then thoroughly purged with nitrogen, and the dispersion was heated to 80°C with continued stirring and held there for approximately 80 minutes, then further heated to 90°C and held there for 60 minutes, yielding a suspension containing the composition. The suspension was then filtered through a filter cloth, and the residue remaining on the filter cloth was washed with deionized water, dehydrated, and dried at 40°C for 16 hours to obtain acrylic polymer (P-1).

[0058] (Production Examples 2 to 11) Acrylic Polymers (P-2 to P-11) Acrylic polymers (P-2 to P-11) were produced in the same manner as in Production Example 1, except that the amounts of the monomer and chain transfer agent (OTG) were changed to those shown in Table 1.

[0059] (Production Example 12) Acrylic polymer (P-12) A polymerization apparatus equipped with a stirrer, condenser, and thermometer was charged with 200 g of deionized water, 0.50 g of sodium sulfate (NaSO), and 0.020 g of a copolymer of potassium methacrylate and methyl methacrylate as dispersants, and a copolymer of 2-sulfoethyl sodium methacrylate, potassium methacrylate, and methyl methacrylate. The contents were stirred to form a uniform aqueous solution. Next, the ingredients shown in Table 1 (unit: g) were added to form a dispersion. The atmosphere inside the polymerization apparatus was then thoroughly purged with nitrogen, and the dispersion was heated to 80°C with continued stirring and held there for approximately 80 minutes, then further heated to 90°C and held there for 60 minutes, yielding a suspension containing the composition. The suspension was then filtered through a filter cloth, and the residue remaining on the filter cloth was washed with deionized water, dehydrated, and dried at 10°C for 16 hours to obtain acrylic polymer (P-12).

[0060] [Table 1]

[0061] The abbreviations listed in Table 1 are as follows: MMA: Methyl methacrylate (Mitsubishi Chemical Corporation) nBMA: n-butyl methacrylate (Mitsubishi Chemical Corporation) EMA: Ethyl methacrylate (Mitsubishi Chemical Corporation) MAA: methacrylic acid (Mitsubishi Chemical Corporation) BA: Butyl acrylate (Mitsubishi Chemical Corporation) HEMA: 2-hydroxyethyl methacrylate (Mitsubishi Chemical Corporation) AMBN: 2,4-azobis(2-methylbutyronitrile) (Otsuka Chemical Co., Ltd.) OTG: 2-ethylhexyl thioglycolate (Yodo Chemical)

[0062] (Example 1) Hot melt adhesive [Dissolution process] A 300 mL four-neck flask equipped with a thermometer, a stirrer, and a condenser was charged with 41.1 g of polypropylene glycol (product name "ADEKA Polyether P-2000", manufactured by ADEKA) having a mass-average molecular weight of approximately 2000, 3.0 g of polypropylene glycol (product name "ADEKA Polyether P-400", manufactured by ADEKA) having a mass-average molecular weight of approximately 400, 24.5 g of polyester polyol "HS 2H-351A" (manufactured by Toyokuni Oil Co., Ltd., a polyester polyol of hexanediol and adipic acid, molecular weight 3500, melting point 55°C, hydroxyl value = 32 mgKOH / g), 0.3 g of "MODAFLOW 2100" (manufactured by Allnex Co., Ltd.) as a defoamer, and 23.7 g of acrylic polymer (P-1). The flask was heated to 140°C and stirred for 1 hour to obtain a homogeneous resin solution.

[0063] [Decompression dehydration process] The resin composition was heated and stirred at 15 kPa and 140°C for 1 hour and then dehydrated under reduced pressure. Then, 14.0 g of 4,4'-diphenylmethane diisocyanate as an isocyanate and 0.1 g of 2,2'-dimorpholinodiethyl ether (manufactured by Mitsui Fine Chemicals) as a curing catalyst were added, and the mixture was stirred at 15 kPa and 100°C for 90 minutes. After cooling, the resulting hot melt adhesive was recovered, sealed, and stored.

[0064] (Examples 2 to 10, Comparative Examples 1 and 2) Hot melt adhesives were produced in the same manner as in Example 1, except that the type of acrylic polymer was changed as shown in Table 2.

[0065] (Method for measuring open time) The hot melt adhesive was applied to a dried wooden flat bar (1.7 cm wide, 7.5 cm long, 1.5 mm thick) and heated to 120°C in a Geer oven. Then, at room temperature, pieces of kraft paper were attached by applying pressure with fingers at 1-minute intervals, and the kraft paper pieces were quickly peeled off. The open time was the time from when the hot melt adhesive was applied to the flat bar until no paper fibers remained on the adhesive surface when the kraft paper pieces were peeled off. (Evaluation criteria) A: 20 minutes or more but less than 30 minutes B: 15 minutes or more but less than 20 minutes, or 30 minutes or more but less than 35 minutes C: Less than 15 minutes or more than 35 minutes

[0066] (Initial adhesive strength) Two wooden flat bars (1.7 cm wide, 7.5 cm long, 1.5 mm thick) were prepared, and a hot melt adhesive that had been heated to 120°C was applied to one of the bars to a thickness of 0.36 mm over an area of 1.5 cm x 1.7 cm. The other bar was placed on top of the other bar, clamped with a double clip, and left to stand at 23°C for 5 minutes to allow the hot melt adhesive to cool and solidify. After leaving it to stand, the double clips were removed, and a tensile shear test was performed under the following measurement conditions using a precision universal testing machine (product name: AGS-X, manufactured by Shimadzu Corporation) as the tensile tester, to measure the initial adhesive strength. <Measurement conditions> Tensile speed: 5.0 mm / min Chuck distance: 50mm Measurement temperature: 23℃ (Evaluation criteria) A: Initial adhesive strength 400kPa or more B: Initial adhesive strength: 300 kPa or more and less than 400 kPa C: Initial adhesive strength less than 300 kPa

[0067] [Table 2]

[0068] As shown in Table 2, Examples 1 to 10 contain an acrylic polymer containing structural units derived from ethyl methacrylate, resulting in excellent initial adhesive strength and a short curing time. On the other hand, Comparative Example 1, which does not contain an acrylic polymer containing structural units derived from ethyl methacrylate, resulted in poor initial adhesive strength and a long curing time. Furthermore, Comparative Example 2, which contains structural units derived from ethyl methacrylate but uses an acrylic polymer with a glass transition temperature of less than 15°C, resulted in poor initial adhesive strength and a long curing time. [Industrial Applicability]

[0069] According to the present invention, a resin composition suitable for hot melt adhesives having excellent initial adhesive strength while maintaining a suitable open time can be provided. Therefore, the resin composition of the present invention can be suitably used in fields where hot melt adhesives have traditionally been used, such as the fields of architectural interiors, electronic materials, and automotive interiors, and is therefore extremely important industrially.

Claims

1. A resin composition comprising a urethane prepolymer having an isocyanate group and an acrylic polymer having structural units derived from ethyl (meth)acrylate and having a glass transition temperature of 15°C or higher and 100°C or lower.

2. 2. The resin composition according to claim 1, wherein the urethane prepolymer having an isocyanate group is a reaction product of a polyester polyol, a polyether polyol, and an isocyanate.

3. The resin composition according to claim 2 , wherein the polyether polyol is a polyalkylene glycol.

4. The resin composition according to claim 3 , wherein the polyalkylene glycol has a number average molecular weight of 200 or more and 5,000 or less, or a mass average molecular weight of 200 or more and 5,000 or less.

5. The resin composition according to claim 1 or 2, wherein the acrylic polymer has a mass average molecular weight of 10,000 or more and 100,000 or less.

6. The resin composition according to claim 1 or 2, wherein the acrylic polymer has a molecular weight distribution of 1 or more and 10 or less.

7. The resin composition according to claim 1 or 2, wherein the acrylic polymer has a biobased content defined in ISO 16620-2 of 1% or more and 100% or less.

8. A hot melt adhesive comprising the resin composition according to claim 1 or 2.

9. An adhesive comprising the resin composition according to claim 1 or 2.

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