Reactive hot melt adhesive, structure, and electronic device

Abstract

Provided is a reactive hot melt adhesive which contains a urethane prepolymer that is a reaction product of a polyol and a polyisocyanate, wherein: the polyol contains a crystalline polyester polyol and a polyalkylene glycol; the crystalline polyester polyol contains a crystalline polyester polyol having a melting point of 30°C to 52°C; the polyalkylene glycol comprises a structural unit that is derived from an alkylene glycol having 4 to 10 carbon atoms; the proportion of the crystalline polyester polyol having a melting point of 30°C to 52°C in the polyol is 30 mass% to 80 mass%; and the proportion of the polyalkylene glycol in the polyol is 30 mass% or less.

Description

Reactive hot melt adhesives, structures and electronic devices

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

[0002] Hot melt adhesives are solid at room temperature, liquefied by heating and brought into contact with an adherend, and develop adhesive strength upon cooling and solidification. Hot melt adhesives can be broadly divided into two types: those containing a thermoplastic resin as the main component and those containing a reactive resin. Known hot melt adhesives containing reactive resins (hereinafter also referred to as reactive hot melt adhesives) include hot melt adhesives containing urethane prepolymers (see, for example, Patent Documents 1 to 3). Hot melt adhesives containing urethane prepolymers not only develop a certain degree of adhesive strength in a short time upon cooling and solidifying, but also cure when the terminal isocyanate groups of the urethane prepolymer react with moisture present in the air or on the surface of the adherend. As a result, they develop strong adhesive strength that cannot be achieved with hot melt adhesives containing thermoplastic resins.

[0003] JP 06-122860, JP 64-054089, JP 52-037936

[0004] In recent years, the display area of ​​wearable devices such as mobile phones has tended to increase compared to the dimensions of the device's housing. As a result, the adhesive area between the display and the housing has become smaller, making it difficult to obtain sufficient adhesive strength using conventional double-sided tape. For this reason, the use of reactive hot melt adhesives as a material for adhering the display and the housing has been investigated.

[0005] Since wearable devices may be accidentally dropped while being carried or used, excellent impact resistance is required at the adhesive joint between the display and the housing. Existing reactive hot melt adhesive compositions have room for further improvement in impact resistance at the adhesive joint between the display and the housing. In view of the above circumstances, one aspect of the present disclosure aims to provide a reactive hot melt adhesive with excellent impact resistance and a structure obtained using this reactive hot melt adhesive.

[0006] Means for solving the above problems include the following embodiments. <1> A reactive hot melt adhesive comprising a urethane prepolymer that is a reaction product of a polyol and a polyisocyanate, wherein the polyol comprises a crystalline polyester polyol and a polyalkylene glycol, wherein the crystalline polyester polyol comprises a crystalline polyester polyol having a melting point of 30°C to 52°C, and the polyalkylene glycol comprises a structural unit derived from an alkylene glycol having 4 to 10 carbon atoms, wherein the crystalline polyester polyol having a melting point of 30°C to 52°C accounts for 30% to 80% by mass of the polyol, and wherein the polyalkylene glycol accounts for 30% by mass or less of the polyol. <2> The reactive hot melt adhesive according to <1>, wherein the crystalline polyester polyol having a melting point of 30°C to 52°C comprises a structural unit derived from a polyhydric alcohol having an aliphatic hydrocarbon group having 4 to 10 carbon atoms. <3> The reactive hot melt adhesive according to <1> or <2>, wherein the crystalline polyester polyol having a melting point of 30°C to 52°C contains a structural unit derived from 1,4-butanediol. <4> The reactive hot melt adhesive according to any one of <1> to <3>, wherein the crystalline polyester polyol having a melting point of 30°C to 52°C accounts for 50% by mass to 100% by mass of the crystalline polyester polyol. <5> The reactive hot melt adhesive according to any one of <1> to <4>, wherein the polyalkylene glycol contains a structural unit derived from tetramethylene glycol. <6> The reactive hot melt adhesive according to any one of <1> to <5>, further comprising a silane coupling agent. <7> A structure comprising two or more objects and a cured product of the reactive hot melt adhesive according to any one of <1> to <6>, bonding the two or more objects together. <8> The structure according to <7>, wherein at least one of the two or more objects is made of glass and at least one is made of metal or resin. <9> An electronic device comprising the structure according to any one of <1> to <8>.

[0007] According to one aspect of the present disclosure, there are provided a reactive hot melt adhesive having excellent impact resistance and a structure obtained using this reactive hot melt adhesive.

[0008] Hereinafter, embodiments of the present disclosure will be described, but the present disclosure is not limited to the following embodiments.

[0009] In this disclosure, "polyol" refers to a compound having two or more hydroxyl groups in the molecule. In this disclosure, "polyisocyanate" refers to 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. In other words, "urethane prepolymer" refers to a compound that contains a polymer chain containing a structural unit derived from a polyol and a structural unit derived from a polyisocyanate, and has an isocyanate group as the end group of the polymer chain.

[0010] In the present disclosure, "crystalline polyester polyol" means a polyester polyol that is in a crystalline state at 25°C, and "non-crystalline polyester polyol" means a polyester polyol that is not in a crystalline state at 25°C.

[0011] In the present disclosure, the melting point of a crystalline polyol means the temperature corresponding to the apex of the peak of the heat of crystallization or heat of fusion in DSC (differential scanning calorimetry) in accordance with JIS K 7121:2012.

[0012] In the present disclosure, the number average molecular weight of a compound is measured by gel permeation chromatography (GPC) and is a value converted to standard polystyrene. GPC measurements are performed using tetrahydrofuran as an eluent at a flow rate of 1.0 ml / min, using a series of Hitachi Chemical HPLC packed columns "Gelpack GLA130-S," "Gelpack GLA150-S," and "Gelpack GLA160-S," at a column temperature of 40°C, and using an RI detector.

[0013] <Reactive Hot Melt Adhesive> The reactive hot melt adhesive of the present disclosure is a reactive hot melt adhesive comprising: a urethane prepolymer that is a reaction product of a polyol and a polyisocyanate; the polyol comprising a crystalline polyester polyol and a polyalkylene glycol; the crystalline polyester polyol comprising a crystalline polyester polyol having a melting point of 30°C to 52°C; the polyalkylene glycol comprising a structural unit derived from an alkylene glycol having 4 to 10 carbon atoms; the proportion of the crystalline polyester polyol having a melting point of 30°C to 52°C in the polyol being 30% by mass to 80% by mass; and the proportion of the polyalkylene glycol in the polyol being 30% by mass or less.

[0014] The reactive hot melt adhesive of the present disclosure contains a urethane prepolymer as a reactive component. Therefore, it exhibits excellent adhesive strength, as well as adhesiveness resulting from cooling and solidification after heating and melting, as well as adhesiveness resulting from the curing reaction between the urethane prepolymer and moisture. Furthermore, the reactive hot melt adhesive of the present disclosure contains, as the polyol raw material for the urethane prepolymer, a crystalline polyester polyol having a melting point of 30°C to 52°C and a polyalkylene glycol containing a structural unit derived from an alkylene glycol having 4 to 10 carbon atoms. Furthermore, in the reactive hot melt adhesive of the present disclosure, the proportion of the crystalline polyester polyol having a melting point of 30°C to 52°C in the polyol is 30% to 80% by mass, and the proportion of the polyalkylene glycol in the polyol is 30% by mass or less. As shown in the results of the examples described below, reactive hot melt adhesives in which the raw materials for the urethane prepolymer satisfy the above conditions exhibit superior impact resistance compared to reactive hot melt adhesives in which the raw materials for the urethane prepolymer do not satisfy the above conditions.

[0015] In the reactive hot melt adhesive of the present disclosure, the proportion of the crystalline polyester polyol in the polyol is not particularly limited. From the viewpoint of improving impact resistance, the proportion of the crystalline polyester polyol in the polyol is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more. The proportion of the crystalline polyester polyol in the polyol is not particularly limited as long as it is less than 100% by mass, and may be less than 99% by mass, less than 98% by mass, or less than 95% by mass.

[0016] In the reactive hot melt adhesive of the present disclosure, the proportion of the crystalline polyester polyol having a melting point of 30°C to 52°C in the polyol is not particularly limited as long as it is 30% by mass to 80% by mass. From the viewpoint of improving impact resistance, the proportion of the crystalline polyester polyol having a melting point of 30°C to 52°C in the polyol is preferably 40% by mass or more, more preferably 45% by mass or more, and even more preferably 50% by mass or more. The proportion of the crystalline polyester polyol having a melting point of 30°C to 52°C in the polyol may be 75% by mass or less, 70% by mass or less, or 60% by mass or less.

[0017] In the reactive hot melt adhesive of the present disclosure, the crystalline polyester polyol may be a crystalline polyester polyol having a melting point of 30°C to 52°C alone, or a combination of a crystalline polyester polyol having a melting point of 30°C to 52°C with a crystalline polyester polyol having a melting point below 30°C or above 52°C. From the viewpoint of improving impact resistance, the proportion of the crystalline polyester polyol having a melting point of 30°C to 52°C in the crystalline polyester polyol is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. The proportion of the crystalline polyester polyol having a melting point of 30°C to 52°C in the crystalline polyester polyol may be 100% by mass, 90% by mass or less, or 80% by mass or less.

[0018] In the reactive hot melt adhesive of the present disclosure, the melting point of the crystalline polyester polyol having a melting point of 30° C. to 52° C. is not particularly limited as long as it is in the range of 30° C. to 52° C. From the viewpoint of improving impact resistance, the melting point of the crystalline polyester polyol having a melting point of 30° C. to 52° C. is preferably 35° C. to 52° C., and more preferably 40° C. to 52° C.

[0019] In the reactive hot melt adhesive of the present disclosure, the proportion of polyalkylene glycol in the polyol is not particularly limited as long as it is 30% by mass or less. From the viewpoint of improving impact resistance, the proportion of polyalkylene glycol in the polyol is preferably 25% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less. The proportion of polyalkylene glycol in the polyol is not particularly limited as long as it is a value greater than 0, and may be 1% by mass or more, 2% by mass or more, or 5% by mass or more.

[0020] (Polyester Polyol) In the present disclosure, the polyester polyol may be a compound produced by a polycondensation reaction between a polyhydric alcohol and a polycarboxylic acid. That is, the polyester polyol may be a compound having a structural unit derived from a polyhydric alcohol and a structural unit derived from a polycarboxylic acid.

[0021] The polyester polyol may be, for example, a polycondensate of a polyhydric alcohol having 2 to 15 carbon atoms and 2 or 3 hydroxyl groups and a polycarboxylic acid having 2 to 14 carbon atoms (including the carbon atoms in the carboxyl groups) and 2 to 6 carboxyl groups.

[0022] The polyester polyol may be a linear polyester diol produced from a diol and a dicarboxylic acid, or a branched polyester triol produced from a triol and a dicarboxylic acid. The branched polyester triol can also be obtained by reacting a diol with a tricarboxylic acid.

[0023] Examples of polyhydric alcohols include polyhydric alcohols having an aliphatic hydrocarbon group and polyhydric alcohols having an aromatic hydrocarbon group. The aliphatic hydrocarbon group may be cyclic or acyclic, and the acyclic aliphatic hydrocarbon group may be linear or branched. The aromatic hydrocarbon group may be a benzene ring. Examples of polyhydric alcohols having an aliphatic hydrocarbon group include aliphatic diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, isomers of butanediol, isomers of pentanediol, isomers of hexanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 2-methylpropanediol, 2,4,4-trimethyl-1,6-hexanediol, 2,2,4-trimethyl-1,6-hexanediol, 1,4-cyclohexanediol, and 1,4-cyclohexanedimethanol. Examples of polyhydric alcohols having an aromatic hydrocarbon group include aromatic diols such as 4,4'-dihydroxydiphenylpropane, bisphenol A, bisphenol F, pyrocatechol, resorcinol, and hydroquinone. The polyhydric alcohols used as raw materials for the polyester polyol may be one type alone or a combination of two or more types.

[0024] Examples of polycarboxylic acids include polycarboxylic acids having an aliphatic hydrocarbon group and polycarboxylic acids having an aromatic hydrocarbon group. The aliphatic hydrocarbon group may be cyclic or acyclic, and the acyclic aliphatic hydrocarbon group may be linear or branched. The aromatic hydrocarbon group may be a benzene ring. Examples of polycarboxylic acids having an aliphatic hydrocarbon group include 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. Examples of polycarboxylic acids having an aromatic hydrocarbon group include aromatic polycarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, and 1,2,4-benzenetricarboxylic acid. One type of polycarboxylic acid may be used alone, or two or more types may be used in combination. Anhydrides of polycarboxylic acids may also be used as polycarboxylic acids. The polycarboxylic acids used as raw materials for the polyester polyol may be one type alone or a combination of two or more types.

[0025] The polyol used as a raw material for the urethane prepolymer contains at least a crystalline polyester polyol as a polyester polyol. From the viewpoint of improving impact resistance, the crystalline polyester polyol preferably contains a structural unit derived from a polyhydric alcohol having an aliphatic hydrocarbon group having 4 to 10 carbon atoms. The aliphatic hydrocarbon group preferably contains 4 to 8 carbon atoms, more preferably 4 to 6 carbon atoms, and even more preferably 4 carbon atoms. The aliphatic hydrocarbon group is preferably acyclic, and more preferably linear. The crystalline polyester polyol particularly preferably contains a structural unit derived from a polyhydric alcohol having a linear aliphatic hydrocarbon group having 4 carbon atoms, i.e., 1,4-butanediol (tetramethylene glycol).

[0026] When the crystalline polyester polyol contains structural units derived from a polyhydric alcohol having an aliphatic hydrocarbon group having 4 to 10 carbon atoms, the proportion of the structural units derived from the polyhydric alcohol in the crystalline polyester polyol is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, and even more preferably 80% by mass to 100% by mass.

[0027] From the viewpoint of improving impact resistance, the crystalline polyester polyol preferably contains structural units derived from a polycarboxylic acid having an aliphatic hydrocarbon group having 4 to 10 carbon atoms. The aliphatic hydrocarbon group preferably contains 4 to 8 carbon atoms, more preferably 4 to 6 carbon atoms, and even more preferably 4 carbon atoms. The aliphatic hydrocarbon group is preferably acyclic, and more preferably linear. It is particularly preferable that the crystalline polyester polyol contains structural units derived from a polycarboxylic acid having a linear aliphatic hydrocarbon group having 4 carbon atoms, i.e., adipic acid.

[0028] When the crystalline polyester polyol contains structural units derived from polycarboxylic acid having an aliphatic hydrocarbon group having 4 to 10 carbon atoms, the proportion of these structural units is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, and even more preferably 80% by mass to 100% by mass of all structural units derived from polycarboxylic acid in the crystalline polyester polyol.

[0029] The number average molecular weight of the crystalline polyester polyol is not particularly limited and can be selected depending on the application of the reactive hot melt adhesive, etc. From the viewpoint of waterproofness and adhesiveness, the number average molecular weight of the crystalline polyester polyol is preferably in the range of 500 to 10,000, more preferably in the range of 1,000 to 8,000, and even more preferably in the range of 2,000 to 7,000.

[0030] The polyol used as a raw material for the urethane prepolymer may contain a polyester polyol that does not fall under the category of crystalline polyester polyol (hereinafter also referred to as amorphous polyester polyol). When the polyol contains amorphous polyester polyol, the proportion of amorphous polyester polyol in the polyol may be 1% by mass or more, 2% by mass or more, or 5% by mass or more. The proportion of amorphous polyester polyol in the polyol may be 50% by mass or less, 40% by mass or less, or 35% by mass or less.

[0031] Examples of the amorphous polyester polyol include polyester polyols containing structural units derived from polyhydric alcohols having branched aliphatic hydrocarbon groups, such as 2,2-dimethyl-1,3-propanediol (neopentyl glycol).

[0032] The number average molecular weight of the amorphous polyester polyol is not particularly limited and can be selected depending on the application of the reactive hot melt adhesive, etc. From the viewpoint of adhesiveness, the number average molecular weight of the amorphous polyester polyol is preferably in the range of 500 to 3000, more preferably in the range of 1000 to 3000. From the viewpoint of flexibility and impact resistance, the number average molecular weight of the amorphous polyester polyol is preferably in the range of 5000 to 12000, more preferably in the range of 5000 to 7000.

[0033] The proportion of polyester polyol in the polyol (i.e., the proportion including crystalline polyester polyol and amorphous polyester polyol) is preferably 30% by mass or more, more preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more. The proportion of polyester polyol in the polyol is not particularly limited as long as it is less than 100% by mass, and may be less than 99% by mass, less than 98% by mass, or less than 95% by mass.

[0034] (Polyalkylene Glycol) In the present disclosure, a compound having a structure (polyether) in which alkylene glycol is polymerized can be used as the polyalkylene glycol. The alkylene glycol is a compound having an aliphatic hydrocarbon group having two or more carbon atoms and two hydroxyl groups bonded to the aliphatic hydrocarbon.

[0035] The polyalkylene glycol functions as a soft segment of the polyurethane formed by polymerization of the urethane prepolymer, and contributes to the development of adhesive properties and flexibility of the reactive hot melt adhesive.

[0036] Examples of alkylene glycols that can be used as raw materials for polyalkylene glycol include ethylene glycol, propylene glycol, butylene glycol, tetramethylene glycol, etc. The polyalkylene glycol may be a polymer of one type of alkylene glycol or a polymer of two or more types of alkylene glycols.

[0037] In the present disclosure, the polyalkylene glycol contains a structural unit derived from an alkylene glycol having 4 to 10 carbon atoms. From the viewpoint of improving impact resistance, the alkylene glycol having 4 to 10 carbon atoms preferably has 4 to 8 carbon atoms, more preferably 4 to 6 carbon atoms, and even more preferably 4 carbon atoms. The alkylene glycol is preferably acyclic, and more preferably linear. It is particularly preferable that the polyalkylene glycol contains a structural unit derived from a linear alkylene glycol having 4 carbon atoms, i.e., tetramethylene glycol.

[0038] When the polyalkylene glycol contains structural units derived from alkylene glycol having 4 to 10 carbon atoms, the proportion of the structural units derived from alkylene glycol is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, and even more preferably 80% by mass to 100% by mass.

[0039] In the present disclosure, the polyalkylene glycol used as the polyol may be one type or two or more types. When two or more types of polyalkylene glycols are used as the polyol, it is preferable that the proportion of structural units derived from alkylene glycols having 4 to 10 carbon atoms contained in the two or more polyalkylene glycols as a whole is within the above-mentioned range. When two or more types of polyalkylene glycols are used as the polyol, the structural units derived from alkylene glycols having 4 to 10 carbon atoms may be contained in each of the two or more polyalkylene glycols, or may be contained in only at least one of the two or more polyalkylene glycols.

[0040] From the viewpoint of improving impact resistance, the polyalkylene glycol preferably contains polytetramethylene glycol. In the present disclosure, polytetramethylene glycol means a polyalkylene glycol in which the proportion of structural units derived from tetramethylene glycol to all structural units derived from alkylene glycol is 100 mass%.

[0041] When the polyalkylene glycol contains polytetramethylene glycol, the proportion thereof is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, and even more preferably 80% by mass to 100% by mass of the entire polyalkylene glycol.

[0042] The number average molecular weight of the polyalkylene glycol is not particularly limited and can be selected depending on the application of the reactive hot melt adhesive, etc. From the viewpoint of adhesiveness and flexibility, the number average molecular weight of the polyalkylene glycol is preferably in the range of 200 to 10,000, more preferably in the range of 500 to 5,000, and even more preferably in the range of 1,000 to 4,000.

[0043] (Polyisocyanate) The polyisocyanate used as a raw material for the urethane prepolymer is not particularly limited. Examples of polyisocyanates include aromatic isocyanates such as diphenylmethane diisocyanate, dimethyldiphenylmethane diisocyanate, tolylene diisocyanate, xylylene diisocyanate, and p-phenylene diisocyanate; alicyclic isocyanates such as dicyclohexylmethane diisocyanate and isophorone diisocyanate; and aliphatic isocyanates such as hexamethylene diisocyanate. From the viewpoints of reactivity and adhesiveness, the polyisocyanate is preferably an aromatic diisocyanate, and more preferably diphenylmethane diisocyanate. One type of polyisocyanate may be used alone, or two or more types may be used in combination.

[0044] 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 preferably 2.2 or less. NCO / OH is preferably greater than 1.4. When the NCO / OH ratio is greater than 1.4, the viscosity of the resulting urethane prepolymer does not become too high, and good application workability is maintained. NCO / OH is preferably 2.5 or less. When the NCO / OH ratio is 2.5 or less, foaming is less likely to occur during the moisture curing reaction, and good adhesion is maintained. NCO / OH is more preferably 1.5 to 2.5, and even more preferably 1.6 to 2.2.

[0045] The temperature and time for reacting the polyol and polyisocyanate may be, for example, 85° C. to 120° C. and 1 minute to 48 hours. When mixing the polyol and polyisocyanate, degassing under reduced pressure may be carried out.

[0046] (Silane Coupling Agent) The reactive hot melt adhesive may further contain a silane coupling agent to improve adhesiveness. The silane coupling agent is an organosilicon compound that has both a functional group capable of reacting with organic materials and a hydrolyzable group in one molecule.

[0047] The type of silane coupling agent is not particularly limited. For example, a compound represented by the following general formula (1) may be used as the silane coupling agent. In general formula (1), R represents an alkoxy group or an alkyl group, at least one R is an alkoxy group, E represents a functional group capable of reacting with an organic material, and n represents a number of 1 or more. In general formula (1), multiple R may be the same or different, and are preferably methoxy groups, ethoxy groups, methyl groups, or ethyl groups. n is preferably 3. E may be a group containing a nitrogen atom or a group containing a sulfur atom, or may be an isocyanate group or a mercapto group.

[0048]

[0049] Specific examples of the compound represented by general formula (1) include 3-mercaptopropyltrimethoxysilane and 3-mercaptopropylmethyldimethoxysilane. The silane coupling agent contained in the reactive hot melt adhesive may be a single type or a combination of two or more types. The silane coupling agent contained in the reactive hot melt adhesive may be a single type or a combination of two or more types.

[0050] When the reactive hot melt adhesive contains a silane coupling agent, the content thereof is preferably 0.1 to 3.0 parts by mass, and more preferably 0.5 to 2.0 parts by mass, per 100 parts by mass of the total amount of the urethane prepolymer.

[0051] The reactive hot melt adhesive may further contain a catalyst to accelerate the curing reaction of the urethane prepolymer, such as dibutyltin dilaurate, dibutyltin dioctate, dimethylcyclohexylamine, dimethylbenzylamine, trioctylamine, etc.

[0052] The reactive hot melt adhesive may further contain additives other than the silane coupling agent and the catalyst, such as pigments, antioxidants, ultraviolet absorbers, surfactants, flame retardants, and fillers.

[0053] The method for obtaining a cured product of the reactive hot melt adhesive is not particularly limited. For example, the cured product may be obtained by causing a curing reaction of the urethane prepolymer for 24 hours or more in an environment at a temperature of 20°C to 30°C and a relative humidity of 40% to 60%.

[0054] From the viewpoint of workability when applying the molten reactive hot melt adhesive, the viscosity of the reactive hot melt adhesive measured using a rotational viscometer at 110°C is preferably 20 Pa s or less, more preferably 15 Pa s or less, and even more preferably 10 Pa s or less. The lower limit of the viscosity of the reactive hot melt adhesive measured using a rotational viscometer at 110°C is not limited, but may be, for example, 1 Pa s or more.

[0055] 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.

[0056] 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 liquefied reactive hot melt adhesive may be brought into contact with the object using a dispenser or the like. Alternatively, an unliquefied reactive hot melt adhesive, such as an adhesive sheet, may be heated in contact with the object to be liquefied.

[0057] <Structure> The structure of the present disclosure is a structure including two or more objects and a cured product of the reactive hot melt adhesive described above that bonds the two or more objects together.

[0058] The method for producing the structure of the present disclosure is not particularly limited. For example, a structure in which two or more objects are bonded with a cured product of the reactive hot melt adhesive can be produced by a method including contacting a predetermined area of ​​one object with a heated reactive hot melt adhesive, contacting another object with the reactive hot melt adhesive, cooling and solidifying the reactive hot melt adhesive, and causing a curing reaction of the urethane prepolymer contained in the reactive hot melt adhesive.

[0059] In the structure of the present disclosure, the materials of the two or more objects are not particularly limited. For example, they may be inorganic materials such as metal, glass, ceramic, etc., or organic materials such as resin. The materials of the two or more objects may be the same or different. Specific examples of metals include SUS (stainless steel), aluminum, titanium, etc. Specific examples of resins include polycarbonate, polyamide, polyetherimide, polybutylene terephthalate, etc.

[0060] In the structure of the present disclosure, at least one of the two or more objects may be made of glass, and at least one may be made of metal or resin. As shown in the examples described below, the structure of the present disclosure exhibits sufficient impact resistance even when a glass object and a metal or resin object are bonded together.

[0061] <Electronic Device> 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 the electronic device of the present disclosure include electronic devices including displays such as smartphones, smartwatches, and personal computers.

[0062] The present invention will be described in detail below based on examples, but the present invention is not limited to these. Unless otherwise specified, parts are parts by mass.

[0063] <Preparation of Reactive Hot Melt Adhesives> Various polyols that had been previously dehydrated were added to a reaction vessel in the amounts (parts by mass) shown in Table 1 and mixed uniformly. Next, polyisocyanate was further added to the reaction vessel in the amount (parts by mass) shown in Table 1, mixed uniformly, and reacted at 110°C for 30 minutes. A silane coupling agent was added to the resulting mixture in the amount (parts by mass) shown in Table 1 and mixed uniformly. Subsequently, the mixture was stirred at 110°C for 45 minutes under reduced pressure to degas and obtain the reactive hot melt adhesives of Examples 1 to 9 and Comparative Examples 1 to 3. Details of the components shown in Table 1 are as follows.

[0064] A: Crystalline polyester polyol A-1: ​​Crystalline polyester polyol mainly composed of adipic acid, 1,4-butanediol, and propylene glycol (number of hydroxyl groups: 2, number average molecular weight: 2800, melting point: 49°C) A-2: Crystalline polyester polyol mainly composed of adipic acid and 1,6-hexanediol (number of hydroxyl groups: 2, number average molecular weight: 3000, melting point: 55°C) A-3: Crystalline polyester polyol mainly composed of adipic acid, 1,4-butanediol, and ethylene glycol (number of hydroxyl groups: 2, number average molecular weight: 2000, melting point: 25°C)

[0065] B: Amorphous polyester polyol B-1: Amorphous polyester polyol composed mainly of adipic acid, neopentyl glycol, and 1,4-butanediol (number of hydroxyl groups: 2, number average molecular weight: 5000) B-2: Amorphous polyester polyol composed mainly of adipic acid, neopentyl glycol, and propylene glycol (number of hydroxyl groups: 2, number average molecular weight: 2000)

[0066] C: Polyalkylene glycol C-1: Polytetramethylene glycol (hydroxyl value: 110 mg KOH / g, number average molecular weight: 1000) C-2: Polytetramethylene glycol (hydroxyl value: 55 mg KOH / g, number average molecular weight: 2000) C-3: Polytetramethylene glycol (hydroxyl value: 35 mg KOH / g, number average molecular weight: 3000) C-4: Polypropylene glycol (hydroxyl value: 56 mg KOH / g, number average molecular weight: 2000)

[0067] D: Polyisocyanate D-1: Diphenylmethane diisocyanate (number of isocyanate groups: 2)

[0068] E: Silane coupling agent E-1: 3-mercaptopropyltrimethoxysilane (trade name: "KBM-803", manufactured by Shin-Etsu Silicones Co., Ltd.)

[0069] <Viscosity measurement of reactive hot melt adhesive> A TVB-25H viscometer (torque balance servo type, manufactured by Toki Sangyo Co., Ltd.) was used with a No. 4 rotor at a rotor rotation speed of 20 rpm (min －１ The viscosity (melt viscosity) of the reactive hot melt adhesive (sample amount: 15 g) was measured at 110° C. The results are shown in Table 1.

[0070] <Evaluation of Impact Resistance> The reactive hot melt adhesive was melted at 100° C. and placed in a syringe container (PSY-30E manufactured by Musashi Engineering Co., Ltd.) equipped with a precision nozzle (SHN-0.25N manufactured by Musashi Engineering Co., Ltd.) having an inner diameter of 0.40 mm. Next, using a dispenser (SHOTMASTER 200DS manufactured by Musashi Engineering Inc.) preheated to 100°C, the reactive hot melt adhesive was applied to adherend A in a circular pattern with an inner diameter of 26 mm around the hole in the center. Next, adherend B was laminated to adherend A so that the adhesive width was 1.0 mm and the thickness was 0.15 mm. This state was left in an environment of 23°C and 50% RH (relative humidity) for two days to obtain a laminate for impact resistance evaluation. Details of the adherends used are as follows: Adherend A was an aluminum (Al) or polybutylene terephthalate (PBT) plate measuring 50 mm wide x 90 mm long with a hole in the center with an inner diameter of 12 mm. Adherend B was an ink glass (IG) plate measuring 50 mm wide x 50 mm long.

[0071] The laminate was fixed to a DuPont impact tester under an environment of 23°C and 50% RH (relative humidity) with the surface of adherend B facing downward. Next, a hammer (10 mm diameter) was placed so that it would pass through the hole in adherend A of the laminate and contact the adhesive-coated surface of adherend B from above. A 200 g weight was then dropped from a height of 200 mm above the laminate, repeatedly impacting the hammer, thereby applying a vertically downward force to adherend B of the laminate. The weight was repeatedly dropped until adherend B peeled off, and impact resistance was evaluated according to the following criteria based on the number of times the weight was dropped before adherend B peeled off. Impact resistance was evaluated separately for adherend A (Al / IG) and adherend A (PBT / IG). The results are shown in Table 1. A: The number of drops is 50 or more. B: The number of drops is 30 or more but less than 50. C: The number of drops is 30 or less.

[0072]

[0073] As shown in Table 1, Examples 1 to 9 using reactive hot melt adhesives in which the proportion of crystalline polyester polyol having a melting point of 30 ° C. to 52 ° C. in the polyol is 30% to 80% by mass and the proportion of polyalkylene glycol is 30% by mass or less, had good impact resistance evaluations. In contrast, Comparative Example 1 using a reactive hot melt adhesive in which the proportion of crystalline polyester polyol having a melting point of 30 ° C. to 52 ° C. in the polyol exceeds 80% by mass, Comparative Example 2 in which the proportion of polyalkylene glycol in the polyol exceeds 30% by mass, Comparative Example 3 using a reactive hot melt adhesive in which the polyol does not contain polyalkylene glycol, Comparative Examples 4 and 5 using a reactive hot melt adhesive in which the polyol does not contain a crystalline polyester polyol having a melting point of 30 ° C. to 52 ° C, and Comparative Example 6 using a reactive hot melt adhesive using polypropylene glycol as the polyalkylene glycol, the impact resistance evaluations are lower than those of the Examples.

[0074] The above results suggest that the reactive hot melt adhesive of the present disclosure is useful for manufacturing structures that require excellent impact resistance, and in particular, for bonding glass objects to metal or resin objects.

Claims

1. A reactive hot melt adhesive comprising a urethane prepolymer which is a reaction product of a polyol and a polyisocyanate, wherein the polyol comprises a crystalline polyester polyol and a polyalkylene glycol, wherein the crystalline polyester polyol comprises a crystalline polyester polyol having a melting point of 30°C to 52°C, and the polyalkylene glycol comprises a structural unit derived from an alkylene glycol having 4 to 10 carbon atoms, wherein the proportion of the crystalline polyester polyol having a melting point of 30°C to 52°C in the polyol is 30% to 80% by mass, and wherein the proportion of the polyalkylene glycol in the polyol is 30% by mass or less.

2. The reactive hot melt adhesive according to claim 1, wherein the crystalline polyester polyol having a melting point of 30°C to 52°C contains structural units derived from a polyhydric alcohol having an aliphatic hydrocarbon group having 4 to 10 carbon atoms.

3. The reactive hot melt adhesive according to claim 1, wherein the crystalline polyester polyol having a melting point of 30°C to 52°C contains structural units derived from 1,4-butanediol.

4. The reactive hot melt adhesive according to claim 1, wherein the proportion of the crystalline polyester polyol having a melting point of 30°C to 52°C in the crystalline polyester polyol is 50% by mass to 100% by mass.

5. The reactive hot melt adhesive of claim 1, wherein the polyalkylene glycol comprises structural units derived from tetramethylene glycol.

6. The reactive hot melt adhesive of claim 1, further comprising a silane coupling agent.

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 together.

8. The structure according to claim 7, wherein at least one of the two or more objects is made of glass and at least one is made of metal or resin.

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

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