Reactive hot melt adhesive and structure

Abstract

A reactive hot-melt adhesive which contains a urethane prepolymer and satisfies at least one of the following conditions A and B, condition A: the proportion of aromatic rings in the total amount of the urethane prepolymer is 22 mass% or less; condition B: The glass transition temperature in a cured state is 25 DEG C or less.

Description

Technical Field

[0001] The present invention relates to reactive hot melt adhesives and structures. Background Art

[0002] There has been proposed a technique for producing clothing products such as underwear and sportswear using adhesives instead of sewing. For example, Patent Document 1 describes a sheet-shaped or tape-shaped hot-melt adhesive for bonding stretchable materials.

[0003] Hot melt adhesive is a solid adhesive at room temperature, which contacts with an adherend under a liquefied state by heating and shows adhesive strength by cooling and solidifying. Hot melt adhesive can be roughly divided into two types: a hot melt adhesive comprising a thermoplastic resin as a main component and a hot melt adhesive comprising a reactive resin as a main component. As a hot melt adhesive comprising a reactive resin (hereinafter also referred to as a reactive hot melt adhesive), a hot melt adhesive comprising a carbamate prepolymer is known. The hot melt adhesive comprising a carbamate prepolymer shows a certain degree of adhesive strength in a short period of time by cooling and solidifying, and the terminal isocyanate group of the carbamate prepolymer reacts with the moisture present in the air or on the surface of the adherend and solidifies. As a result, the hot melt adhesive comprising a thermoplastic resin shows a firm adhesive strength that cannot be achieved.

[0004] Patent Document 1: Japanese Patent Application Laid-Open No. 2017-179195 Summary of the Invention

[0005] Problems to be solved by the invention

[0006] Reactive hot-melt adhesives hold great promise as adhesives for clothing, effectively utilizing their high-speed adhesiveness and excellent adhesive strength. However, reactive hot-melt adhesives still have room for improvement in properties such as stretchability required for clothing adhesives.

[0007] In view of the above circumstances, an object of one aspect of the present disclosure is to provide a reactive hot-melt adhesive having excellent stretchability after curing, and a structure obtained by using the reactive hot-melt adhesive having excellent stretchability after curing.

[0008] Means for solving problems

[0009] Means for solving the above-mentioned problems include the following embodiments.

[0010] <1> A reactive hot-melt adhesive comprises a urethane prepolymer and satisfies at least either one of the following conditions A or B.

[0011] Condition A: The proportion of aromatic rings in the total amount of urethane prepolymer is 22% by mass or less. Condition B: The glass transition temperature in the cured state is 25°C or less.

[0012] <2> according to <1> In the reactive hot-melt adhesive, the proportion of the structural units derived from the amorphous polyol in the structural units derived from the polyol in the urethane prepolymer is 70% by mass or more.

[0013] <3> according to <1> or <2> In the reactive hot-melt adhesive, the equivalent ratio (NCO / OH) of the isocyanate group (NCO) of the polyisocyanate used as a raw material of the urethane prepolymer to the hydroxyl group (OH) of the polyol is 2.0 or less.

[0014] <4> according to <1> ~ <3> The reactive hot-melt adhesive described above is used for bonding stretchable objects.

[0015] <5> A structure comprising: two or more objects having elasticity; and a bonding member for bonding the two or more objects. <1> to <4> A cured product of any one of the reactive hot-melt adhesives.

[0016] <6> according to <5> In the structure, the two or more objects are cloths.

[0017] <7> according to <5> The structure is a clothing product. DETAILED DESCRIPTION

[0018] Hereinafter, embodiments of the present disclosure will be described, but the present disclosure is not limited to the following embodiments.

[0019] In the present disclosure, "polyol" refers to a compound having two or more hydroxyl groups in the molecule.

[0020] In the present disclosure, "polyisocyanate" refers to a compound having two or more isocyanate groups in the molecule.

[0021] In this disclosure, a "urethane prepolymer" is a reaction product of a polyol and a polyisocyanate, and refers to a compound having an isocyanate group at the end of the molecule. Specifically, a "urethane prepolymer" refers to a compound comprising a polymer chain containing structural units derived from a polyol and structural units derived from a polyisocyanate, and having an isocyanate group as the terminal group of the polymer chain.

[0022] <Reactive Hot Melt Adhesive>

[0023] The reactive hot-melt adhesive of the present disclosure contains a urethane prepolymer and satisfies at least either one of the following conditions A or B.

[0024] Condition A: The proportion of aromatic rings in the total amount of urethane prepolymer is 22% by mass or less. Condition B: The glass transition temperature in the cured state is 25°C or less.

[0025] The reactive hot-melt adhesive disclosed herein contains a urethane prepolymer as a reactive component. Therefore, it exhibits adhesiveness due to solidification upon cooling after heating and melting, as well as adhesiveness due to the curing reaction of the urethane prepolymer with water, and exhibits excellent adhesive strength.

[0026] Furthermore, in the reactive hot melt adhesive of the present disclosure, the ratio of aromatic rings in the total amount of the urethane prepolymer (hereinafter also referred to as the aromatic ring ratio of the urethane prepolymer) is 22% by mass or less, or the glass transition temperature in the cured state is 25° C. or less.

[0027] The present inventors have studied and found that reactive hot melt adhesives having an aromatic ring ratio of 22% by mass or less in the urethane prepolymer or a glass transition temperature of 25°C or less in the cured state have superior stretchability after curing compared to reactive hot melt adhesives that do not meet either of these conditions.

[0028] The aromatic ring ratio of the urethane prepolymer can be set in consideration of the balance with properties other than stretchability. For example, the aromatic ring ratio of the urethane prepolymer can be 20% by mass or less.

[0029] The lower limit of the aromatic ring ratio of the urethane prepolymer is not particularly limited. For example, the aromatic ring ratio of the urethane prepolymer may be 5% by mass or more.

[0030] In the urethane prepolymer containing an aromatic ring, the structural unit derived from the polyol and the structural unit derived from the polyisocyanate may each contain an aromatic ring, or only one of the structural unit derived from the polyol and the structural unit derived from the polyisocyanate may contain an aromatic ring.

[0031] The urethane prepolymer containing an aromatic ring may contain a structural unit containing an aromatic ring and a structural unit not containing an aromatic ring as a structural unit derived from a polyol, or may contain only one of the structural unit containing an aromatic ring and the structural unit not containing an aromatic ring.

[0032] The aromatic ring-containing urethane prepolymer may contain an aromatic ring-containing structural unit as a structural unit derived from polyisocyanate.

[0033] The aromatic ring ratio of the urethane prepolymer is calculated using the following formula. In the following formula, "the total mass of the raw materials for the urethane prepolymer" refers to the mass of the raw materials that do not contain aromatic rings. If polyester polyols or polyether polyols are not used as the raw polyols, the unused polyols can be omitted. The molecular weight of the aromatic rings is 78 (in the case of benzene rings).

[0034] Aromatic ring ratio (%) of urethane prepolymer = {(aromatic ring ratio of polyester polyol having aromatic rings × mass of polyester polyol having aromatic rings) + (aromatic ring ratio of polyether polyol having aromatic rings × mass of polyether polyol having aromatic rings) + (aromatic ring ratio of polyisocyanate having aromatic rings × mass of polyisocyanate) / total mass of raw materials of urethane prepolymer} × 100

[0035] In the above formula, the aromatic ring ratio of the polyester polyol having an aromatic ring is calculated by the following formula.

[0036] Aromatic ring ratio of polyester polyol having an aromatic ring = (molecular weight of aromatic ring × molar composition ratio of polycarboxylic acid having an aromatic ring in raw carboxylic acid (%)) / (molecular weight of each polycarboxylic acid × molar composition ratio in raw carboxylic acid (%)) + (molecular weight of each polyol × molar composition ratio in raw alcohol (%))

[0037] In the above formula, the aromatic ring ratio of the polyether polyol having an aromatic ring is calculated by the following formula.

[0038] Aromatic ring ratio of polyether polyol having an aromatic ring = molecular weight of aromatic ring × number of moles of aromatic ring in 1 mole of polyether polyol / molecular weight of polyether polyol

[0039] In the above formula, the aromatic ring ratio of the polyisocyanate having an aromatic ring is calculated by the following formula.

[0040] Aromatic ring ratio of polyisocyanate having an aromatic ring = molecular weight of aromatic ring × number of moles of aromatic ring in 1 mole of polyisocyanate / molecular weight of polyisocyanate

[0041] From the perspective of post-curing stretchability, the glass transition temperature of the reactive hot-melt adhesive in its cured state is preferably 25°C or lower. When the glass transition temperature in its cured state is 25°C or lower, the cured reactive hot-melt adhesive becomes rubbery in an environment of 25°C or higher, exhibiting excellent stretchability.

[0042] The glass transition temperature of the reactive hot-melt adhesive in a cured state is measured by the method described in Examples.

[0043] Research by the present inventors has revealed that the glass transition temperature of a reactive hot-melt adhesive in a cured state tends to decrease as the aromatic ring ratio of the urethane prepolymer contained in the reactive hot-melt adhesive decreases. Therefore, the glass transition temperature can be controlled by adjusting the aromatic ring ratio of the urethane prepolymer contained in the reactive hot-melt adhesive.

[0044] From the viewpoint of stretchability after curing, the structural unit derived from the polyol in the urethane prepolymer preferably includes a structural unit derived from an amorphous polyol.

[0045] In the present disclosure, a crystalline polyol refers to a polyol having an endothermic peak (melting point Tm) associated with melting when measured by DSC, and an amorphous polyol refers to a polyol having no endothermic peak (melting point Tm) associated with melting when measured by DSC.

[0046] The ratio of the structural unit derived from the amorphous polyol in the structural unit derived from the polyol in the urethane prepolymer may be 70% by mass or more, 80% by mass or more, or 95% by mass.

[0047] From the viewpoint of adjusting the curing time and viscosity of the reactive hot-melt adhesive, the urethane prepolymer preferably contains a polyester polyol-derived structural unit as the polyol-derived structural unit. That is, the raw material of the urethane prepolymer preferably contains a polyester polyol as the polyol.

[0048] As polyester polyols, compounds produced by the polycondensation reaction of a polyol and a polycarboxylic acid can be used. For example, the polyester polyol can be a polycondensation product of a polyol having 2 to 15 carbon atoms and 2 or 3 hydroxyl groups and a polycarboxylic acid having 2 to 14 carbon atoms (including carbon atoms in the carboxyl group) and 2 to 6 carboxyl groups.

[0049] 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. Furthermore, a branched polyester triol may be obtained by reacting a diol with a tricarboxylic acid.

[0050] Examples of polyols include aliphatic or alicyclic diols such as ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, isomers of butanediol, isomers of pentanediol, isomers of hexanediol, 2,2-dimethyl-1,3-propanediol, 2-methylpropanediol, 2,4,4-trimethyl-1,6-hexanediol, 2,2,4-trimethyl-1,6-hexanediol, 1,4-cyclohexanedimethanol, and aromatic diols such as 4,4'-dihydroxydiphenylpropane, bisphenol A, bisphenol F, catechol, resorcinol, and hydroquinone. Polyols may be used alone or in combination of two or more. Among these, aliphatic diols are preferred, and aliphatic diols having 2 to 6 carbon atoms are more preferred.

[0051] Examples of the polycarboxylic acid include aromatic polycarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, and 1,2,4-benzenetricarboxylic acid; and aliphatic or alicyclic 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-cyclohexadiene-1,2-dicarboxylic acid. The polycarboxylic acid may be used alone or in combination of two or more.

[0052] In place of the above-mentioned polycarboxylic acids, polycarboxylic acid derivatives such as carboxylic anhydrides and compounds in which a part of the carboxyl groups is esterified may be used. Examples of the polycarboxylic acid derivatives include lauryl maleate and octadecenyl maleate.

[0053] The polyester polyol used as a raw material of the urethane prepolymer may be only one kind or two or more kinds.

[0054] From the viewpoint of improving the waterproofness and adhesive strength of the cured product of the reactive hot-melt adhesive, the number average molecular weight (Mn) of the 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 1,500 to 6,000.

[0055] In the present invention, the number average molecular weight of the polyol is a value obtained by measuring by gel permeation chromatography (GPC) and converting it into standard polystyrene. The GPC measurement can be performed under the following conditions.

[0056] Chromatography columns: "Gelpack GLA130-S", "Gelpack GLA150-S", and "Gelpack GLA160-S" (manufactured by Showa Denko Materials Co., Ltd., packed columns for HPLC)

[0057] Eluent: tetrahydrofuran

[0058] Flow rate: 1.0 mL / min

[0059] Column temperature: 40°C

[0060] Detector: RI

[0061] The amount of the polyester polyol used as a raw material of the urethane prepolymer can be, for example, within a range of 70% by mass to 100% by mass of the entire polyol.

[0062] From the perspectives of workability during application of the reactive hot-melt adhesive and adhesiveness, water resistance, and flexibility after curing, the urethane prepolymer preferably contains a polyether polyol-derived structural unit as the polyol-derived structural unit. That is, the raw material of the urethane prepolymer preferably contains a polyether polyol as the polyol.

[0063] Examples of the polyether polyol include aromatic polyether polyols such as polyether polyols having a bisphenol skeleton, polyethylene glycol, polypropylene glycol, polybutylene glycol, polytetramethylene glycol, and ethylene oxide-modified polypropylene glycol.

[0064] The polyether polyol used as a raw material of the urethane prepolymer may be only one kind or two or more kinds.

[0065] From the viewpoint of initial adhesive strength, adhesive strength after curing, and appropriate open time after coating, the Mn of the polyether polyol is preferably in the range of 500 to 2000, more preferably in the range of 700 to 2000, and even more preferably in the range of 1000 to 2000.

[0066] The amount of the polyether polyol used as a raw material of the urethane prepolymer may be within a range of, for example, 0% by mass to 10% by mass of the entire polyol.

[0067] 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, methylphenylene diisocyanate, xylylenediisocyanate, and p-phenylene diisocyanate; alicyclic isocyanates such as dicyclohexylmethane diisocyanate and isophorone diisocyanate; and aliphatic isocyanates such as hexamethylene diisocyanate. From the perspective of reactivity and adhesion, aromatic diisocyanates are preferred, and diphenylmethane diisocyanate is more preferred.

[0068] The polyisocyanate used as a raw material of the urethane prepolymer may be only one kind or two or more kinds.

[0069] The equivalent ratio (NCO / OH) of the isocyanate group (NCO) of the polyisocyanate used as a raw material for the urethane prepolymer to the hydroxyl group (OH) of the polyol is preferably 2.0 or less. If the NCO / OH ratio is 2.0 or less, the residual unreacted polyisocyanate can be suppressed when the polyol and the polyisocyanate are reacted, and the elasticity after curing can be well maintained.

[0070] The equivalent ratio (NCO / OH) of the isocyanate group (NCO) of the polyisocyanate used as the raw material of the urethane prepolymer to the hydroxyl group (OH) of the polyol is preferably 1.6 or greater. If the NCO / OH ratio is 1.6 or greater, the viscosity of the resulting urethane prepolymer when melted will not be too high, and good workability can be maintained.

[0071] The temperature and time for reacting the polyol and the polyisocyanate may be, for example, 85 to 120° C. and 1 minute to 48 hours. When the polyol and the polyisocyanate are mixed, degassing may be performed under reduced pressure.

[0072] From the perspective of promoting the curing reaction of the urethane prepolymer, the reactive hot-melt adhesive may further contain a catalyst. Examples of the catalyst include dibutyltin dilaurate, dibutyltin octoate, dimethylcyclohexylamine, dimethylbenzylamine, trioctylamine, and dimorpholinodiethyl ether (bis(2-morpholinoethyl)ether).

[0073] The content of the catalyst may be, for example, 0% by mass to 0.5% by mass of the entire reactive hot-melt adhesive.

[0074] From the viewpoint of improving the rubber elasticity of the cured product and further improving the impact resistance, the reactive hot melt adhesive may further contain a thermoplastic polymer. Examples of the thermoplastic polymer include polyurethane, ethylene copolymers, propylene copolymers, vinyl chloride copolymers, acrylic copolymers, and styrene-conjugated diene block copolymers.

[0075] From the viewpoint of imparting stronger adhesion to the cured product, the reactive hot-melt adhesive may further contain a pressure-sensitive tackifier resin. Examples of the pressure-sensitive tackifier resin include rosin resin, rosin ester resin, hydrogenated rosin ester resin, terpene resin, terpene phenolic resin, hydrogenated terpene resin, petroleum resin, hydrogenated petroleum resin, coumarone resin, ketone resin, styrene resin, modified styrene resin, xylene resin, and epoxy resin.

[0076] The reactive hot-melt adhesive may further contain ingredients such as an antioxidant, a pigment, an ultraviolet absorber, a surfactant, a flame retardant, a silane coupling agent, and a filler as needed.

[0077] The method for obtaining the cured product of the reactive hot melt adhesive is not particularly limited. For example, the cured product can be obtained by causing a curing reaction of a urethane prepolymer under an environment with a temperature of 20° C. to 30° C. and a relative humidity of 40% to 60%.

[0078] From the perspective of workability during coating, the viscosity of the reactive hot-melt adhesive, as measured at 120°C using a rotational viscometer, 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, as measured at 120°C using a rotational viscometer, is not particularly limited and may be, for example, 1 Pa·s or greater.

[0079] The reactive hot-melt adhesive disclosed herein 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 granules, blocks, powders, or sheets.

[0080] The reactive hot-melt adhesive disclosed herein is solid at room temperature and is heated to liquefy during use. 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 an unliquefied reactive hot-melt adhesive such as an adhesive sheet may be brought into contact with the object and then heated to liquefy it.

[0081] The reactive hot-melt adhesive of the present disclosure has excellent stretchability after curing. Therefore, the reactive hot-melt adhesive of the present disclosure is useful as an adhesive for bonding stretchable objects.

[0082] The material of the stretchable object is not particularly limited and may be, for example, natural fiber, synthetic fiber, plastic, etc.

[0083] In one embodiment, the stretchable object may be a fabric such as a knitted or woven fabric, or may be a fabric for clothing.

[0084] <structure>

[0085] The structure disclosed herein is a structure comprising two or more stretchable objects and a cured product of the reactive hot-melt adhesive for bonding the two or more objects together.

[0086] In the structure disclosed herein, the cured product of the reactive hot-melt adhesive used to bond two or more objects exhibits excellent stretchability.

[0087] The material of the stretchable object is not particularly limited and may be, for example, natural fiber, synthetic fiber, plastic, etc.

[0088] In one embodiment, the stretchable object may be a fabric such as a knitted fabric, a woven fabric, or a non-woven fabric, or may be a fabric for clothing.

[0089] The method for producing the structure disclosed herein is not particularly limited. For example, a heated reactive hot-melt adhesive is brought into contact with a predetermined area of one object, and then brought into contact with another object. The reactive hot-melt adhesive is then cooled and solidified. The urethane prepolymer contained in the reactive hot-melt adhesive is then subjected to a curing reaction. This produces a structure in which two or more objects are bonded together by a cured product of the reactive hot-melt adhesive.

[0090] Example

[0091] Hereinafter, the present disclosure will be described in detail based on Examples, but the present invention is not limited thereto.

[0092] <Preparation of Composition>

[0093] The polyol, a raw material for the urethane prepolymer, was added to a reaction vessel in the amounts (parts by mass) shown in Table 1 and mixed. Subsequently, polyisocyanate was further added to the reaction vessel in the amounts (parts by mass) shown in Table 1, mixed, and reacted at 110°C for 1 hour. Degassing and stirring were then performed under reduced pressure at 110°C for another hour to obtain a composition containing a urethane prepolymer.

[0094] Table 1

[0095]

[0096] The details of the polyols and polyisocyanates shown in Table 1 are as follows.

[0097] Polyol 1: Amorphous polyester polyol with an aromatic ring, mainly composed of dicarboxylic acids (isophthalic acid and adipic acid) and diols (ethylene glycol and neopentyl glycol) (number of hydroxyl groups: 2, number average molecular weight: 2000, content of structural units derived from compounds having aromatic rings: 25 mol% (based on the total amount of structural units constituting the amorphous polyester polyol), 50 mol% (based on the total amount of structural units derived from dicarboxylic acids))

[0098] Polyol 2: Crystalline polyether polyol having an aromatic ring (bisphenol A-PO type) (manufactured by ADEKA Co., Ltd., trade name: BPX-11, number of hydroxyl groups: 2, melting point: 3°C)

[0099] Polyol 3: Amorphous polyester polyol (number of hydroxyl groups: 2, number average molecular weight: 5000) with no aromatic rings and composed mainly of dicarboxylic acid (adipic acid) and diols (1,4-butanediol and neopentyl glycol)

[0100] Polyol 4: A crystalline polyester polyol without an aromatic ring, mainly composed of a dicarboxylic acid (adipic acid) and a diol (1,6-hexanediol) (number of hydroxyl groups: 2, number average molecular weight: 5500)

[0101] Polyol 5: Amorphous polyester polyol with no aromatic rings and composed mainly of dicarboxylic acid (adipic acid) and diol (methylpentanediol) (number of hydroxyl groups: 2, number average molecular weight: 4000)

[0102] Polyisocyanate: diphenylmethane diisocyanate (manufactured by Tosoh Corporation, trade name: Millionate MT, number of isocyanate groups: 2)

[0103] (Glass transition temperature)

[0104] The glass transition temperature of the urethane prepolymer is set to the peak top temperature of tan δ when measured by dynamic viscoelasticity measurement (DMA: Dynamic Mechanical Analysis) under the following conditions.

[0105] Test equipment: RSA-G2 manufactured by TA Instruments

[0106] Test mode: tensile

[0107] Test temperature: -100℃~250℃

[0108] Heating rate: 5℃ / min

[0109] Frequency: 1Hz

[0110] Strain: 0.05%

[0111] Atmosphere: Nitrogen

[0112] (elongation attenuation rate)

[0113] A cured film having a thickness of about 100 μm was formed from the prepared composition to prepare a dumbbell No. 1 type test piece. Using this test piece, the elongation attenuation rate (%) was measured by the repeated constant speed elongation method according to JIS L 1096:2010 (Test methods for textile and knitted fabrics). Specifically, the two ends of the test piece were clamped with the clamps of the tensile testing machine (clamping interval: 100 mm), and the test piece was stretched at a tensile speed of 300 mm / min until the elongation of the test piece reached 40% (process 1). Then, the clamp was returned to its original position at the same tensile speed (process 2). Based on the load (load 1) when the elongation of the test piece reached 30% in process 1 and the load (load 2) when the elongation of the test piece reached 30% in process 2, the elongation attenuation rate (%) of the test piece was calculated by the following formula. The results are shown in Table 1.

[0114] Elongation attenuation rate (%) = (load 2 / load 1) × 100

[0115] As shown in Table 1, the compositions of Examples 1 to 6, which meet the requirements of the reactive hot-melt adhesive of the present disclosure, have a larger elongation attenuation rate of the cured films than the compositions of Comparative Examples 1 and 2, which do not meet the requirements of the reactive hot-melt adhesive of the present disclosure, and exhibit excellent stretchability.

[0116] The entire disclosure of Japanese Patent Application No. 2022-200325 is incorporated into this specification by reference.

[0117] All documents, patent applications, and technical standards described in this specification are herein incorporated by reference to the same extent as if each individual document, patent application, or technical standard were specifically and individually indicated to be incorporated by reference.

Claims

1. A reactive hot melt adhesive comprising a urethane prepolymer and satisfying at least one of the following conditions A or B: Condition A: The proportion of aromatic rings in the total amount of the urethane prepolymer is 22% by mass or less; Condition B: The glass transition temperature in the cured state is 25° C. or lower.

2. The reactive hot-melt adhesive according to claim 1, wherein The ratio of the structural unit derived from the amorphous polyol in the structural units derived from the polyol in the urethane prepolymer is 70% by mass or more.

3. The reactive hot-melt adhesive according to claim 1, wherein The equivalent ratio of the isocyanate group NCO of the polyisocyanate used as a raw material of the urethane prepolymer to the hydroxyl group OH of the polyol is 2.0 or less in terms of NCO / OH. The reactive hot-melt adhesive according to claim 1 , which is used for bonding stretchable objects.

5. A structure comprising: Two or more objects with stretchability; and A cured product of the reactive hot-melt adhesive according to any one of claims 1 to 4, which is used to bond the two or more objects together.

6. The structure according to claim 5, wherein The two or more objects are cloths. The structure according to claim 5 , which is an article of clothing.

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