Reactive hot-melt adhesive, structure, and electronic device

Abstract

To provide a reactive hot-melt adhesive showing superior initial bonding performance, as well as a structure and an electronic device produced by using this adhesive.SOLUTION: A reactive hot-melt adhesive comprises a urethane prepolymer and a non-reactive urethane compound that contains a monovalent aliphatic hydrocarbon group.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a reactive hot melt adhesive, a structure, and an electronic device. [Background technology]

[0002] Hot melt adhesives are solvent-free adhesives that are gentle on the environment and the human body and are used as adhesives that can bond quickly. Hot melt adhesives can be broadly divided into two types: those that use thermoplastic resin as the main component and those that use reactive resin as the main component. Urethane prepolymers with isocyanate groups at the terminals are mainly used as reactive resins. Hereinafter, hot melt adhesives that use reactive resin as the main component will also be referred to as "reactive hot melt adhesives."

[0003] Reactive hot melt adhesives, whose main component is urethane prepolymer, develop a certain degree of adhesive strength (initial adhesion) in a short period of time by cooling and solidifying from the molten state at the time of application. The terminal isocyanate groups of the urethane prepolymer then react with moisture (in the air or on the surface of the adherend) to increase the molecular weight and form crosslinks, thereby developing even stronger adhesive properties. These adhesives are also called "moisture-curing reactive hot melt adhesives." In order to improve the initial adhesion of reactive hot melt adhesives whose main component is a urethane prepolymer, adhesive compositions containing a multifunctional polyol as a polyol component and adhesive compositions containing Diels-Alder crosslinking units are also known (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-16691 [Patent Document 2] Japanese Patent Application Publication No. 2023-73658 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, as electronic device terminals have become smaller, the adhesive area between parts has become smaller and the shapes of the parts that make up the terminal have become more complex. As a result, research is underway into using reactive hot melt adhesives instead of double-sided tape as a method of bonding terminal parts together.

[0006] Reactive hot melt adhesives have room for improvement in initial adhesion compared to conventional adhesives such as double-sided tapes. An object of the present disclosure is to provide a reactive hot melt adhesive that exhibits excellent initial adhesion, as well as a structure and electronic device obtained using this adhesive. [Means for solving the problem]

[0007] The means for solving the above problems include the following embodiments. <1> A reactive hot melt adhesive comprising a urethane prepolymer and a non-reactive urethane compound containing a monovalent aliphatic hydrocarbon group. <2> The number of monovalent aliphatic hydrocarbon groups contained in the urethane compound is 1 to 4. <1> The reactive hot melt adhesive according to claim 1. <3> the number of urethane bonds contained in the urethane compound is 1 to 4; <1> or <2> The reactive hot melt adhesive according to claim 1. <4> The number of monovalent aliphatic hydrocarbon groups contained in the urethane compound is 2, and the number of urethane bonds is 1 to 4. <1> ~ <3> The reactive hot melt adhesive according to any one of claims 1 to 10. <5> The urethane compound is a reaction product of a monool containing a monovalent aliphatic hydrocarbon group and a polyisocyanate. <1> ~ <4> The reactive hot melt adhesive according to any one of claims 1 to 10. <6> The content of the urethane compound is 0.1% by mass to 5% by mass of the total reactive hot melt adhesive. <1> ~ <5> The reactive hot melt adhesive according to any one of claims 1 to 10. <7> Two or more objects are bonded together <1> ~ <6> and a cured product of the reactive hot melt adhesive according to any one of claims 1 to 4. <8> <7> An electronic device comprising the structure described above. [Effects of the Invention]

[0008] According to the present invention, there are provided a reactive hot melt adhesive that exhibits excellent initial adhesion, and a structure and an electronic device obtained using this adhesive. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present disclosure will be described in detail, but the present disclosure is not limited to the following embodiments.

[0010] In the present disclosure, "polyol" refers to a compound having 1.8 or more hydroxyl groups in the molecule. In the present disclosure, "polyisocyanate" means a compound having two or more isocyanate groups in the molecule. In this disclosure, "urethane prepolymer" refers to a compound that is a reaction product of a polyol and a polyisocyanate and has an isocyanate group at the end of the molecule. That is, "urethane prepolymer" refers to a compound that contains a polymer chain that includes a structural unit derived from a polyol and a structural unit derived from a polyisocyanate, and has an isocyanate group as the terminal group of the polymer chain.

[0011] In the present disclosure, a numerical range indicated using "to" indicates a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In numerical ranges described in stages in this specification, the upper or lower limit of a numerical range in one stage may be replaced with the upper or lower limit of a numerical range in another stage. In numerical ranges described in this specification, the upper or lower limit of that numerical range may be replaced with a value shown in an example. In the present disclosure, "A or B" means including at least one of A and B, and may include both. Unless otherwise specified, the materials exemplified in this disclosure can be used alone or in combination of two or more. In this disclosure, when multiple substances corresponding to each component are present in the composition, the content of each component in the composition means the total amount of the multiple substances present in the composition, unless otherwise specified.

[0012] <Reactive hot melt adhesive> The reactive hot melt adhesive of the present disclosure comprises a urethane prepolymer and a non-reactive urethane compound containing a monovalent aliphatic hydrocarbon group.

[0013] The reactive hot melt adhesive of the present disclosure contains a urethane prepolymer as a reactive component, and therefore exhibits excellent adhesive strength due to the reaction between the urethane prepolymer and moisture in addition to the adhesiveness due to cooling and solidification from a molten state.

[0014] Furthermore, the reactive hot melt adhesive of the present disclosure includes a non-reactive urethane compound containing a monovalent aliphatic hydrocarbon group. Hereinafter, the non-reactive urethane compound containing a monovalent aliphatic hydrocarbon group is also referred to as a "specific urethane compound." As shown in the results of the examples described below, reactive hot melt adhesives containing a specific urethane compound together with a urethane prepolymer exhibit superior initial adhesion compared to reactive hot melt adhesives that do not contain the specific urethane compound.

[0015] One possible reason why the reactive hot melt adhesive of the present disclosure exhibits excellent initial adhesion is that, for example, when the molten reactive hot melt adhesive solidifies, the specific urethane compound functions as a crystal nucleus, promoting the crystallization of the urethane prepolymer. The components used in the reactive hot melt adhesive of the present disclosure will be described below.

[0016] (Polyol) In the urethane prepolymer contained in the reactive hot melt adhesive of the present disclosure, the type of structural unit derived from a polyol is not particularly limited, and may be a structural unit derived from a polyol such as a polyester polyol, a polyether polyol, a polybutadiene polyol, or a polycarbonate polyol. In the present disclosure, "polyester polyol" means a polyol having an ester bond in the molecule, "polyether polyol" means a polyol having an ether bond in the molecule, "polycarbonate polyol" means a polyol having a carbonate bond in the molecule, and "polybutadiene polyol" means a polyol containing a polymer chain derived from butadiene in the molecule. The urethane prepolymer may contain structural units derived from one type of polyol, or may contain structural units derived from two or more types of polyols.

[0017] The polyol may be crystalline or non-crystalline. In the present disclosure, crystalline polyol means a polyol that is in a crystalline state at 25°C, and amorphous polyol means a polyol that is in an amorphous state at 25°C.

[0018] From the viewpoint of adjusting the solidification time and viscosity of the reactive hot melt adhesive, the urethane prepolymer preferably contains structural units derived from polyester polyol. The type of polyester polyol used as a raw material for the urethane prepolymer is not particularly limited. For example, the polyester polyol may be a reaction product of a polyhydric alcohol and a polycarboxylic acid. For example, the polyester polyol may be a reaction product of a polyhydric alcohol having 2 to 15 carbon atoms and 2 or 3 hydroxyl groups with a polycarboxylic acid having 2 to 14 carbon atoms (including the carbon atoms in the carboxyl groups) and 2 to 6 carboxyl groups.

[0019] Specific examples of polyhydric alcohols include cyclic or acyclic aliphatic polyhydric alcohols such as ethylene glycol, propylene glycol (1,2-propanediol), 1,3-propanediol, isomers of butanediol, isomers of pentanediol, isomers of hexanediol, neopentyl glycol (2,2-dimethyl-1,3-propanediol), 2-methylpropanediol, 2,4,4-trimethyl-1,6-hexanediol, 2,2,4-trimethyl-1,6-hexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, glycerin, and trimethylolpropane; and aromatic polyhydric alcohols such as 4,4'-dihydroxydiphenylpropane, bisphenol A, bisphenol F, pyrocatechol, resorcinol, and hydroquinone. The polyhydric alcohol used in the synthesis of the polyester polyol may be one kind or two or more kinds.

[0020] Specific examples of polycarboxylic acids include aromatic polycarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, and 1,2,4-benzenetricarboxylic acid; and cyclic or acyclic aliphatic polycarboxylic acids such as maleic acid, fumaric acid, aconitic acid, 1,2,3-propanetricarboxylic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, azelaic acid, sebacic acid, cyclohexane-1,2-dicarboxylic acid, and 1,4-cyclohexanediene-1,2-dicarboxylic acid. The polycarboxylic acids used in the synthesis of the polyester polyol may be one kind or two or more kinds.

[0021] Instead of the above-mentioned polycarboxylic acids, polycarboxylic acid derivatives such as carboxylic acid anhydrides and compounds in which a portion of the carboxyl group is esterified can also be used. Examples of polycarboxylic acid derivatives include dodecyl maleic acid and octadecenyl maleic acid.

[0022] When a bifunctional polyester polyol is used as a raw material for the urethane prepolymer, the bifunctional polyester polyol may be a polyester diol which is a reaction product of a diol and a dicarboxylic acid. When a trifunctional polyester polyol is used as a raw material for the urethane prepolymer, the trifunctional polyester polyol may be a polyester triol that is a reaction product of a triol and a dicarboxylic acid, or a polyester triol that is a reaction product of a diol and a tricarboxylic acid.

[0023] The polyester polyol used as the raw material for the urethane prepolymer may be one type only, or two or more types. The polyester polyol used as a raw material for the urethane prepolymer may be one containing an aromatic ring (hereinafter also referred to as an aromatic polyester polyol) or one not containing an aromatic ring (hereinafter also referred to as a non-aromatic polyester polyol).

[0024] The number average molecular weight (Mn) of the polyester polyol is preferably in the range of 300 to 10,000, more preferably in the range of 350 to 8,000, and even more preferably in the range of 400 to 5,000, from the viewpoint of improving the waterproofness and adhesive strength of the cured product of the reactive hot melt adhesive.

[0025] In the present disclosure, the number average molecular weight of a polyol is measured by gel permeation chromatography (GPC) and is a value converted into standard polystyrene. GPC measurement can be performed under the following conditions. Column: "Gelpack GLA130-S," "Gelpack GLA150-S," and "Gelpack GLA160-S" (packed columns for HPLC, manufactured by Showa Denko Materials Co., Ltd.) Eluent: tetrahydrofuran Flow rate: 1.0mL / min Column temperature: 40℃ Detector: RI

[0026] From the viewpoints of workability during application of the reactive hot melt adhesive and adhesive properties, waterproofness and flexibility after curing, it is preferred that the urethane prepolymer contain structural units derived from polyether polyol.

[0027] The type of polyether polyol used as a raw material for the urethane prepolymer is not particularly limited. For example, the polyether polyol may be a compound obtained by addition polymerization of an alkylene oxide with an initiator in the presence of a basic catalyst. The initiator may be a polyhydric alcohol, a polyhydric amine, or the like. Examples of the polyhydric alcohol include the polyhydric alcohols exemplified as raw materials for the polyester polyol. Examples of polyamines include ethylenediamine and triethanolamine. Examples of the alkylene oxide include alkylene oxides having 1 to 4 carbon atoms, such as ethylene oxide, propylene oxide, butylene oxide, and tetramethylene oxide. When the polyether polyol contains a structure in which a plurality of alkylene oxides are linked (polyalkylene oxide), the number of linked alkylene oxides is not particularly limited and can be set according to the desired molecular weight of the polyether polyol.

[0028] When a difunctional polyether polyol is used as a raw material for the urethane prepolymer, the difunctional polyether polyol may be a polyether diol which is a reaction product of a diol or a diamine with an alkylene oxide. When a trifunctional polyether polyol is used as a raw material for the urethane prepolymer, the trifunctional polyether polyol may be a polyether triol which is a reaction product of a triol or a triamine with an alkylene oxide.

[0029] The polyether polyol used as the raw material for the urethane prepolymer may be one type only, or two or more types. The polyether polyol used as a raw material for the urethane prepolymer may be one containing an aromatic ring (hereinafter also referred to as an aromatic polyether polyol) or one not containing an aromatic ring (hereinafter also referred to as a non-aromatic polyether polyol).

[0030] Specific examples of aromatic polyether polyols include polyether polyols having a bisphenol skeleton. Specific examples of non-aromatic polyether polyols include polyalkylene glycols such as polyethylene glycol, polypropylene glycol, polybutylene glycol, polytetramethylene glycol, and ethylene oxide-modified polypropylene glycol, as well as triol compounds thereof.

[0031] The number average molecular weight (Mn) of the polyether polyol is preferably in the range of 300 to 2000, more preferably in the range of 350 to 1500, and even more preferably in the range of 400 to 1000, from the viewpoints of initial adhesive strength, adhesive strength after curing, and appropriate open time after application.

[0032] From the viewpoint of improving the hydrolysis resistance of the reactive hot melt adhesive, the urethane prepolymer preferably contains a structural unit derived from a polycarbonate polyol. Polycarbonate polyols can be obtained, for example, by reacting a carbonate compound with a polyol or phosgene, or by ring-opening polymerization of a cyclic carbonate compound having 3 to 18 carbon atoms with a polyol such as a low-molecular-weight polyol, a polyether polyol, a polyester polyol, or a polycarbonate polyol.

[0033] The carbonate compound used in producing the polycarbonate polyol is preferably a carbonate compound having 3 to 18 carbon atoms, more preferably a carbonate compound having 3 to 13 carbon atoms. Specific examples of the carbonate compound include dimethyl carbonate, diethyl carbonate, ethylene carbonate, and diphenyl carbonate. These carbonate compounds may be used alone or in combination.

[0034] The polyol used in the production of the polycarbonate polyol is preferably a polyol having 2 to 18 carbon atoms, more preferably a polyol having 4 to 12 carbon atoms.

[0035] The polycarbonate polyol is preferably an aliphatic polycarbonate polyol, more preferably an aliphatic polycarbonate diol.

[0036] From the viewpoints of initial adhesive strength, adhesive strength after curing, and an appropriate open time after application, the number average molecular weight of the polycarbonate polyol is preferably 500 to 6000, more preferably 700 to 5000, and even more preferably 1000 to 4000. One type of polycarbonate diol may be used alone, or two or more types may be used in combination.

[0037] From the viewpoint of improving the impact resistance and adhesive properties of the reactive hot melt adhesive after moisture curing, the urethane prepolymer preferably contains structural units derived from polybutadiene polyol. The polybutadiene polyol may be a compound having a hydroxyl group at the end of a polymer chain derived from butadiene, or may be a liquid butadiene copolymer having a hydroxyl group at the molecular end. The number average molecular weight of the polybutadiene polyol is preferably 1000 to 5000, more preferably 1000 to 4000, and even more preferably 1200 to 3000. When the number average molecular weight of the polybutadiene polyol is 1000 or more, impact resistance is more easily improved, and when it is 5000 or less, adhesion is less likely to decrease.

[0038] (Polyisocyanate) The polyisocyanate used as a raw material for the urethane prepolymer may be one containing an aromatic ring (hereinafter also referred to as an aromatic polyisocyanate) or one not containing an aromatic ring (hereinafter also referred to as a non-aromatic polyisocyanate).

[0039] Specific examples of aromatic polyisocyanates include diphenylmethane diisocyanate, dimethyldiphenylmethane diisocyanate, tolylene diisocyanate, xylylene diisocyanate, and p-phenylene diisocyanate. Specific examples of non-aromatic polyisocyanates include cyclic or acyclic aliphatic polyisocyanates such as dicyclohexylmethane diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate. From the viewpoint of the reactivity and adhesiveness of the reactive hot melt adhesive, the polyisocyanate is preferably an aromatic polyisocyanate, and more preferably diphenylmethane diisocyanate.

[0040] The polyisocyanate used as the raw material for the urethane prepolymer may be one type only, or two or more types.

[0041] The equivalent ratio (NCO / OH) of the isocyanate groups (NCO) of the polyisocyanate to the hydroxyl groups (OH) of the polyol used as a raw material for the urethane prepolymer is greater than 1, preferably 1.3 to 3.0, and more preferably 1.5 to 2.0. When the NCO / OH ratio is greater than 1, a urethane prepolymer having an isocyanate group at the end of the polymer chain can be obtained. When the NCO / OH ratio is 1.3 or more, the viscosity of the resulting urethane prepolymer does not become too high, maintaining good workability.When the NCO / OH ratio is 3.0 or less, foaming is less likely to occur during the moisture curing reaction of the adhesive composition, and a decrease in adhesive strength is suppressed.

[0042] (Specific urethane compounds) The specific urethane compound is a non-reactive urethane compound containing a monovalent aliphatic hydrocarbon group. In the present disclosure, the term "urethane compound" refers to a compound containing a urethane bond in the molecule. The term "non-reactive urethane compound" refers to a urethane compound that does not contain a reactive functional group such as a hydroxyl group or an isocyanate group in the molecule.

[0043] The monovalent aliphatic hydrocarbon group contained in the specific urethane compound may or may not contain a branched or cyclic structure. The monovalent aliphatic hydrocarbon group contained in the specific urethane compound may or may not contain an unsaturated double bond. The monovalent aliphatic hydrocarbon group is preferably an alkyl group that does not contain a branched or cyclic structure and does not contain an unsaturated double bond. Preferred examples of the alkyl group that does not contain a branched or cyclic structure and does not contain an unsaturated double bond include an n-pentyl group (carbon number: 5), an n-hexyl group (carbon number: 6), an n-heptyl group (carbon number: 7), an n-octyl group (carbon number: 8), an n-nonyl group (carbon number: 9), an n-decyl group (carbon number: 10), an n-undecyl group (carbon number: 11), an n-dodecyl (lauryl) group (carbon number: 12), an n-tetradecyl group (carbon number: 14), an n-hexadecyl group (carbon number: 16), an n-octadecyl (stearyl) group (carbon number: 18), and an n-eicosyl group (carbon number: 20).

[0044] The number of carbon atoms in the monovalent aliphatic hydrocarbon group contained in the specific urethane compound is not particularly limited and can be selected, for example, from between 1 and 36. The number of carbon atoms in the monovalent aliphatic hydrocarbon group may be 5 or more, 8 or more, or 10 or more. The number of carbon atoms in the monovalent aliphatic hydrocarbon group may be 30 or less, 25 or less, or 20 or less. The above-mentioned "number of carbon atoms in the monovalent aliphatic hydrocarbon group" refers to the number of carbon atoms per monovalent aliphatic hydrocarbon group.

[0045] The number of monovalent aliphatic hydrocarbon groups contained in the specific urethane compound is preferably 1 to 4, and more preferably 2. When the specific urethane compound contains a plurality of monovalent aliphatic hydrocarbon groups, the structures of the plurality of monovalent aliphatic hydrocarbon groups may be the same or different. The number of urethane bonds contained in the specific urethane compound is preferably 1 to 4, and more preferably 2.

[0046] The specific urethane compound may be a compound represented by the following general formula (1).

[0047] [ka]

[0048] In general formula (1), R 1 and R 2 are each independently a monovalent aliphatic hydrocarbon group, and R 3 is a divalent organic group. R 3 Examples of the divalent organic group represented by the formula (I) include a divalent aromatic hydrocarbon group, a divalent aliphatic hydrocarbon group, and a combination thereof. The number of carbon atoms in the divalent organic group is not particularly limited and can be selected from, for example, between 1 and 36. The number of carbon atoms in the divalent organic group may be 3 or more, 4 or more, or 5 or more. The number of carbon atoms in the divalent organic group may be 30 or less, 20 or less, or 15 or less. Specific examples of the divalent organic group include a hexamethylene group and a diphenylmethane group.

[0049] The specific urethane compound may be a reaction product of a monool containing a monovalent aliphatic hydrocarbon group and a polyisocyanate. For example, a specific urethane compound having two monovalent aliphatic hydrocarbon groups and two urethane bonds can be obtained by reacting a monool containing a monovalent aliphatic hydrocarbon group with a bifunctional polyisocyanate. As the monool, the above-mentioned monool containing a monovalent aliphatic hydrocarbon group may be used. As the polyisocyanate, the polyisocyanate described above as a raw material for the urethane prepolymer may be used. Specific examples of reaction products of monools containing a monovalent aliphatic hydrocarbon group and polyisocyanates include a reaction product of stearyl alcohol and diphenylmethane diisocyanate, a reaction product of stearyl alcohol and hexamethylene diisocyanate, a reaction product of stearyl alcohol and diphenylmethane diisocyanate, and a reaction product of lauryl alcohol and hexamethylene diisocyanate. The reactive hot melt adhesive may contain only one type of specific urethane compound or two or more types of specific urethane compounds.

[0050] From the viewpoint of the initial adhesiveness of the reactive hot melt adhesive, it is preferable that the specific urethane compound is in a crystalline state at 25°C. From the viewpoint of miscibility with the urethane prepolymer, the melting point of the specific urethane compound is preferably 150°C or lower, and more preferably 135°C or lower.

[0051] From the viewpoint of the initial adhesiveness of the reactive hot melt adhesive, the content of the specific urethane compound contained in the reactive hot melt adhesive is preferably 0.1 mass% of the entire reactive hot melt adhesive, and may be 0.3 mass% or more, 1 mass% or more, 2 mass% or more, or 2.5 mass% or more. The content of the specific urethane compound in the reactive hot melt adhesive may be 5% by mass or less, 4% by mass or less, 3.5% by mass or less, or 3% by mass or less of the total reactive hot melt adhesive.

[0052] (Other ingredients) The reactive hot melt adhesive may contain other components (other components) in addition to the urethane prepolymer and the specific urethane compound, as needed, such as thermoplastic polymers, tackifying resins, catalysts, pigments, UV absorbers, surfactants, flame retardants, and fillers. The content of each component may be, for example, 0.1% by mass to 5% by mass of the entire reactive hot melt adhesive.

[0053] Thermoplastic polymers include polyurethanes, ethylene-based copolymers, propylene-based copolymers, vinyl chloride-based copolymers, acrylic copolymers, and styrene-conjugated diene block copolymers. Examples of tackifying resins include rosin resins, rosin ester resins, hydrogenated rosin ester resins, terpene resins, terpene phenol resins, hydrogenated terpene resins, petroleum resins, hydrogenated petroleum resins, coumarone resins, ketone resins, styrene resins, modified styrene resins, xylene resins, and epoxy resins. Catalysts include dibutyltin dilaurate, dibutylthione octoate, dimethylcyclohexylamine, dimethylbenzylamine, and trioctylamine.

[0054] Methods for producing a reactive hot melt adhesive as a mixture of a urethane prepolymer and a specific urethane compound include the following methods 1 and 2. Method 1: A method of obtaining a urethane prepolymer by reacting a polyol with a polyisocyanate in the presence of a specific urethane compound. Method 2: A method comprising the steps of reacting a polyol with a polyisocyanate to obtain a urethane prepolymer, and mixing the urethane prepolymer with a specific urethane compound.

[0055] The temperature when the polyol and the polyisocyanate are reacted may be, for example, 85° C. to 135° C. The temperature when the urethane prepolymer and the specific urethane compound are mixed may be, for example, 85° C. to 135° C. During the mixing, degassing under reduced pressure may be performed.

[0056] From the viewpoint of workability during application, the viscosity of the reactive hot melt adhesive measured using a rotational viscometer is preferably 10 Pa s or less, more preferably 8 Pa s or less, and even more preferably 7 Pa s or less at 120°C. There are no restrictions on the lower limit of the viscosity, but it may be, for example, 1 Pa s or more at 120°C.

[0057] The reactive hot melt adhesive of the present disclosure is in a solid state before use. The form of the solid reactive hot melt adhesive is not particularly limited. For example, it may be in the form of a pellet, a block, a powder, a sheet, or the like.

[0058] The reactive hot melt adhesive of the present disclosure is solid at room temperature and is liquefied by heating when used. The method for applying the liquefied reactive hot melt adhesive to an object is not particularly limited. For example, the reactive hot melt adhesive liquefied by heating may be brought into contact with the object using a dispenser or the like, or an unliquefied reactive hot melt adhesive, such as an adhesive sheet, may be heated and liquefied while in contact with the object.

[0059] The type of object with which the reactive hot melt adhesive of the present disclosure comes into contact is not particularly limited, and can be selected from metals, plastics, ceramics, glass, and the like. Specific examples of metals include stainless steel and aluminum. Specific examples of plastics include polycarbonate, polyamide, polybutylene terephthalate, and polyetherimide.

[0060] <Structure> The structure of the present disclosure includes two or more objects and a cured product of the reactive hot melt adhesive described above that bonds the two or more objects together.

[0061] The method for producing the structure of the present disclosure is not particularly limited. For example, a reactive hot melt adhesive that has been liquefied by heating is brought into contact with a predetermined area of ​​one object, and another object is brought into contact with the reactive hot melt adhesive, and the reactive hot melt adhesive is cooled and solidified in this state. Next, a curing reaction of the urethane prepolymer contained in the reactive hot melt adhesive is caused. This allows for the production of a structure in which two or more objects are bonded together with the cured product of the reactive hot melt adhesive. In the above method, the reactive hot melt adhesive is heated before being brought into contact with a predetermined area of ​​one of the objects, but it may also be heated after contact to liquefy it. The heating temperature may be, for example, 80°C to 180°C.

[0062] Reactive hot melt adhesives cure when the isocyanate groups of the urethane prepolymer react with moisture in the air or on the surface of an object with which the reactive hot melt adhesive is in contact. The reactive hot melt adhesive can be cured, for example, over 24 hours in an environment with a temperature of 20 to 30°C and a relative humidity of 40 to 60%.

[0063] In the structure of the present disclosure, the materials of the two or more objects are not particularly limited and can be selected from metal, plastic, ceramic, glass, etc. The materials of the two or more objects may be the same or different. Specific examples of metals include stainless steel and aluminum. Specific examples of plastics include polycarbonate, polyamide, polybutylene terephthalate, and polyetherimide.

[0064] The use of the structure of the present disclosure is not particularly limited, and examples of the use of the structure include electronic devices, semiconductor devices, seamless clothing, and the like.

[0065] <Electronic equipment> The electronic device of the present disclosure includes the structure of the present disclosure described above. The electronic device of the present disclosure may be an electronic device including a glass display and a metal or resin housing. In this case, the portion where the glass display and the metal or resin housing are bonded may be the structure of the present disclosure described above. Specific examples of electronic devices according to the present disclosure include electronic devices equipped with displays, such as smartphones, smartwatches, and personal computers. [Example]

[0066] The present disclosure will be specifically described below based on examples, but the present invention is not limited to these.

[0067] (Synthesis of urethane prepolymer) Polyol, a raw material for the urethane prepolymer, was added to a reaction vessel in the blending amount (parts by mass) shown in Table 1 and mixed. Next, polyisocyanate was further added to the reaction vessel in the blending amount (parts by mass) shown in Table 1 and mixed, followed by reaction at 110°C for 1 hour. Thereafter, the mixture was stirred at 110°C under reduced pressure and degassed for another 1 hour to synthesize a urethane prepolymer.

[0068] The details of the materials shown in Table 1 are as follows: Polyol 1: Crystalline polycarbonate polyol obtained by reacting 1,6-hexanediol, number of hydroxyl groups: 2, Mn: 2000, manufactured by Ube Industries, Ltd., product name: UH-200J Polyol 2: Polytetramethylene glycol, number of hydroxyl groups: 2, Mn: 2000, manufactured by Hodogaya Chemical Co., Ltd., product name: PTG-2000SN Polyol 3: Bisphenol A polyether polyol, number of hydroxyl groups: 2, Mn: 160, manufactured by ADEKA Corporation, BPX-11 Polyol 4: Polypropylene glycol, number of hydroxyl groups: 2, Mn: 2000, manufactured by AGC Inc., EXCENOLL2020 Polyisocyanate: Diphenylmethane diisocyanate, Number of isocyanate groups: 2

[0069] (Synthesis of specific urethane compounds) Hexamethylene diisocyanate-based polyisocyanate (79 parts by mass, Duranate D101, manufactured by Asahi Kasei Corporation) was added to stearyl alcohol (100 parts by mass, Conol 30SS, manufactured by New Japan Chemical Co., Ltd.), which had been previously dehydrated using a vacuum dryer, and mixed. The resulting mixture was then reacted at 110°C for 1 hour, and further stirred and degassed under reduced pressure at 110°C for 1 hour, synthesizing Specific Urethane Compound 1 having a melting point of 120°C. Specific urethane compound 2 having a melting point of 130°C was synthesized in the same manner as specific urethane compound 1, except that diphenylmethane diisocyanate (46 parts by mass, Millionate MT, manufactured by Tosoh Corporation) was used instead of hexamethylene diisocyanate.

[0070] (Preparation of reactive hot melt adhesive) The specific urethane compound shown in Table 1 was mixed with the resulting urethane prepolymer to obtain a reactive urethane adhesive.

[0071] (Viscosity measurement) The viscosity of the reactive hot melt adhesive when melted was measured under the following conditions using a BH-HH type small volume rotational viscometer (manufactured by Toki Sangyo Co., Ltd.). Rotor: No. 4 rotor Sample amount: 15g Rotor rotation speed: 50 min -1 Temperature: 120℃

[0072] (Evaluation of initial adhesion) As an index for evaluating initial adhesion, the time T until the viscosity of the molten reactive urethane adhesive became constant was measured. The shorter the time T, the faster the adhesive strength of the reactive urethane adhesive developed, and the better the initial adhesion. Specifically, the temperature of the reactive urethane adhesive was lowered from 120°C to 20°C at a rate of -40°C / min, and then held at 20°C for 30 minutes, and the time T until the viscosity of the reactive urethane adhesive became constant was measured. The results are shown in Table 1. In Table 1, if the time T is 2000 seconds or less, the actual measured value is recorded, and if it is greater than 2000 seconds, it is recorded as >2000 sec.

[0073] The viscosity measurement conditions are as follows. Apparatus: Rotational rheometer, DHR-2 (TA Instruments Japan Co., Ltd.) Geometry: Φ20mm parallel plate Gap: 200μm Frequency: 1Hz ·Distortion: 0.3%

[0074] [Table 1]

[0075] As shown in Table 1, the reactive hot melt adhesives of Examples 1 to 6, which contain a specific urethane compound together with a urethane prepolymer, exhibit superior initial adhesion compared to the reactive hot melt adhesives of Comparative Examples 1 to 3, which contain a urethane prepolymer but no specific urethane compound. Furthermore, the reactive hot melt adhesives of the examples have sufficiently low viscosities when melted and exhibit excellent applicability.

Claims

1. A reactive hot melt adhesive comprising a urethane prepolymer and a non-reactive urethane compound containing a monovalent aliphatic hydrocarbon group.

2. 2. The reactive hot melt adhesive according to claim 1, wherein the number of monovalent aliphatic hydrocarbon groups contained in the urethane compound is 1 to 4.

3. 2. The reactive hot melt adhesive according to claim 1, wherein the number of urethane bonds contained in the urethane compound is 1 to 4.

4. 2. The reactive hot melt adhesive according to claim 1, wherein the number of monovalent aliphatic hydrocarbon groups contained in the urethane compound is 2 and the number of urethane bonds is 1 to 4.

5. 2. The reactive hot melt adhesive of claim 1, wherein the urethane compound is a reaction product of a monool containing a monovalent aliphatic hydrocarbon group and a polyisocyanate.

6. The reactive hot melt adhesive according to claim 1, wherein the content of the urethane compound is 0.1% by mass to 5% by mass of the total reactive hot melt adhesive.

7. A structure comprising two or more objects and a cured product of the reactive hot melt adhesive according to any one of claims 1 to 6, which bonds the two or more objects.

8. An electronic device comprising the structure of claim 7.

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