Reactive hot melt adhesives and structures

Abstract

This invention provides a reactive hot-melt adhesive that exhibits excellent dispensing properties from a jet dispenser and superior elasticity after curing. [Solution] The reactive hot melt adhesive contains a urethane prepolymer which is a reaction product of a polyol and a polyisocyanate, and the urethane prepolymer satisfies the following conditions: A: the proportion of amorphous polyol in the total polyol is 50% by mass or more; B: the equivalent ratio (NCO / OH) of isocyanate groups (NCO) of the polyisocyanate to the hydroxyl groups (OH) of the polyol is 1.6 or more; C: the proportion of aromatic rings derived from the polyol in the total urethane prepolymer is 15% by mass or less; and D: the viscosity of the urethane prepolymer at 120°C is 30 Pa·s or less.

Description

Technical Field

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

Background Art

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

[0003] A hot melt adhesive is a solid at room temperature, which is brought into contact with an adherend in a liquefied state by heating, and develops an adhesive force by cooling and solidifying. Hot melt adhesives can be roughly classified into two types: those containing a thermoplastic resin as the main component and those containing a reactive resin. As a hot melt adhesive containing a reactive resin (hereinafter also referred to as a reactive hot melt adhesive), a hot melt adhesive containing a urethane prepolymer is known. The hot melt adhesive containing a urethane prepolymer not only develops a certain adhesive force in a short time by cooling and solidifying, but also the terminal isocyanate groups of the urethane prepolymer react with moisture present in the air or on the surface of the adherend and cure. As a result, a strong adhesive force that cannot be achieved with hot melt adhesives containing thermoplastic resins is developed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Existing reactive hot melt adhesives still have room for improvement in stretchability after curing. Furthermore, when applying reactive hot-melt adhesive to a substrate using a device such as a jet dispenser, excellent dispensing performance from the jet dispenser is desirable. In view of the above circumstances, one aspect of this disclosure aims to provide a reactive hot-melt adhesive that exhibits excellent dispensing properties from a jet dispenser and excellent elasticity after curing, and a structure obtained using this reactive hot-melt adhesive. [Means for solving the problem]

[0006] The means for solving the above problems include the following embodiments. <1> A reactive hot-melt adhesive comprising a urethane prepolymer, which is a reaction product of a polyol and a polyisocyanate, wherein the urethane prepolymer satisfies the following conditions A, B, C, and D. Condition A: The proportion of amorphous polyol in the total polyol is 50% by mass or more. Condition B: The equivalent ratio (NCO / OH) of the isocyanate groups (NCO) of the polyisocyanate to the hydroxyl groups (OH) of the polyol is 1.6 or higher. Condition C: The proportion of aromatic rings derived from polyols in the total urethane prepolymer is 15% by mass or less. Condition D: The viscosity of the urethane prepolymer at 120°C is 30 Pa·s or less. <2> For bonding objects that are stretchable, <1> The reactive hot melt adhesive described above. <3> Two or more objects that are stretchable, and the two or more objects that are bonded together. <1> or <2> A structure comprising a cured product of a reactive hot melt adhesive as described in [reference]. <4> The two or more objects mentioned above are fabrics. <3> The structure described above. <5> Clothing items, <3> or <4> The structure described above. [Modes for carrying out the invention]

[0007] The embodiments of this disclosure are described below. However, this disclosure is not limited to the embodiments described below.

[0008] In this disclosure, "polyol" means a compound having two or more hydroxyl groups in its molecule. In this disclosure, "polyisocyanate" means a compound having two or more isocyanate groups in its molecule. In this disclosure, "urethane prepolymer" means 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" means a compound that includes a polymerization chain containing structural units derived from a polyol and structural units derived from a polyisocyanate, and has an isocyanate group as the terminal group of the polymerization chain. The polymerization chain of the urethane prepolymer is a state in which structural units derived from polyol and structural units derived from polyisocyanate are linked by urethane bonds formed by the reaction of the hydroxyl groups of the polyol and the isocyanate groups of the polyisocyanate. The "polyol-derived structural units" contained in urethane prepolymers refer to the portion of the polyol molecular structure used as a raw material for urethane prepolymers that excludes the hydroxyl group that contributes to the reaction with the isocyanate group of polyisocyanate. The "polyisocyanate-derived structural units" contained in urethane prepolymers refer to the portion of the polyisocyanate molecular structure used as a raw material for urethane prepolymers, excluding the isocyanate group that contributes to the reaction with the hydroxyl group of the polyol.

[0009] In this disclosure, crystalline polyols refer to polyols that exhibit an endothermic peak (melting point Tm) associated with melting when measured by DSC, and amorphous polyols refer to polyols that do not exhibit an endothermic peak (melting point Tm) associated with melting when measured by DSC.

[0010] <Reactive hot melt adhesive> The reactive hot melt adhesive of this disclosure is The material contains a urethane prepolymer which is a reaction product of a polyol and a polyisocyanate, and the urethane prepolymer satisfies the following conditions A, B, C, and D. Condition A: The proportion of amorphous polyol in the total polyol is 50% by mass or more. Condition B: The equivalent ratio (NCO / OH) of the isocyanate groups (NCO) of the polyisocyanate to the hydroxyl groups (OH) of the polyol is 1.6 or higher. Condition C: The proportion of aromatic rings derived from polyols in the total urethane prepolymer is 12% by mass or less. Condition D: The viscosity of the urethane prepolymer at 120°C is 30 Pa·s or less.

[0011] In this disclosure, the equivalent ratio of the isocyanate groups (NCO) of the polyisocyanate to the hydroxyl groups (OH) of the polyol (NCO / OH) is also referred to as the "NCO / OH ratio". In this disclosure, the proportion of aromatic rings derived from polyols in the entire urethane prepolymer is also referred to as the "polyol-derived aromatic ring ratio."

[0012] If the raw materials for the urethane prepolymer contain multiple types of polyols, the polyol conditions described above refer to the combined conditions for all of the multiple types of polyols. If the raw materials for the urethane prepolymer contain multiple polyisocyanates, the polyisocyanate condition described above refers to the total amount of multiple types of polyisocyanates.

[0013] The reactive hot-melt adhesive of this disclosure contains a urethane prepolymer as a reactive component. Therefore, it exhibits excellent adhesive strength, as it exhibits adhesiveness due to both the cooling and solidification after liquefaction by heating and the curing reaction between the urethane prepolymer and water.

[0014] Furthermore, the urethane prepolymer contained in the reactive hot melt adhesive of the present disclosure satisfies Condition A, Condition B, Condition C, and Condition D respectively. As shown in the examples described later, the reactive hot melt adhesive containing a urethane prepolymer that satisfies Condition A, Condition B, Condition C, and Condition D respectively has excellent dischargeability from a jet dispenser and excellent elasticity after curing.

[0015] (Condition A) The reactive hot melt adhesive of the present disclosure contains a urethane prepolymer in which the proportion of amorphous polyol in the total polyol is 50% by mass or more. From the viewpoint of elasticity after curing, the proportion of amorphous polyol in the polyol of the urethane prepolymer is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more. The upper limit of the proportion of amorphous polyol in the polyol of the urethane prepolymer is not particularly limited and may be 100% by mass or less than 100% by mass.

[0016] (Condition B) The reactive hot melt adhesive of the present disclosure contains a urethane prepolymer having an NCO / OH ratio of 1.6 or more. From the viewpoint of dischargeability from a jet dispenser, the NCO / OH ratio of the urethane prepolymer is preferably 1.7 or more, more preferably 1.8 or more, and even more preferably 1.9 or more.

[0017] From the viewpoint of reducing the amount of unreacted polyisocyanate, the NCO / OH ratio of the urethane prepolymer is preferably 2.2 or less, more preferably 2.1 or less, and even more preferably 2.0 or less.

[0018] (Condition C) The reactive hot melt adhesive of the present disclosure contains a urethane prepolymer in which the aromatic ring ratio derived from polyol is 12% by mass or less. From the viewpoint of elasticity after curing, the proportion of aromatic rings derived from the polyol in the urethane prepolymer is preferably 11% by mass or less, more preferably 10% by mass or less, even more preferably 9% by mass or less, and still more preferably 8% by mass or less.

[0019] From the viewpoint of elasticity after curing, the proportion of aromatic rings derived from the polyol in the urethane prepolymer is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 7% by mass or more.

[0020] In this disclosure, the aromatic ring ratio derived from the polyol in the urethane prepolymer is a value calculated by the following formula. In the following formula, "total mass of raw materials for the urethane prepolymer" means the total mass of the polyol and polyisocyanate that are used as raw materials for the urethane prepolymer. If polyester polyol or polyether polyol is not used as the raw material polyol, the item for the polyol that is not used can be omitted. The molecular weight of the aromatic ring is 78 (in the case of a benzene ring).

[0021] The percentage of aromatic rings derived from polyols in urethane prepolymers (%) = {(percentage of aromatic rings of polyester polyols containing aromatic rings × mass of polyester polyols containing aromatic rings) + (percentage of aromatic rings of polyether polyols containing aromatic rings × mass of polyether polyols containing aromatic rings) / total mass of raw materials for urethane prepolymers} × 100

[0022] In the above formula, the aromatic ring ratio of the polyester polyol having an aromatic ring is calculated by the following formula. The aromatic ring ratio of a polyester polyol containing aromatic rings = (molecular weight of the aromatic ring × molar proportion of the polycarboxylic acid containing aromatic rings in the starting carboxylic acid (%)) / (molecular weight of each polycarboxylic acid × molar proportion in the starting carboxylic acid (%)) + (molecular weight of each polyhydric alcohol × molar proportion in the starting alcohol (%))

[0023] In the above formula, the aromatic ring ratio of polyether polyols having aromatic rings is calculated by the following formula. Aromatic ring ratio of polyether polyols containing aromatic rings = Molecular weight of aromatic ring × Number of moles of aromatic rings in 1 mole of polyether polyol / Molecular weight of polyether polyol

[0024] The percentage of aromatic rings derived from the polyol in the urethane prepolymer may be adjusted, for example, by using polyols without aromatic rings and polyols with aromatic rings as raw materials for the urethane prepolymer, and by changing the blending ratio of these.

[0025] When the polyol and polyisocyanate used as raw materials for the urethane prepolymer contain aromatic rings, it is acceptable if each of the polyol and polyisocyanate contains aromatic rings, or if only one of them contains aromatic rings.

[0026] (Condition D) The reactive hot-melt adhesive of this disclosure comprises a urethane prepolymer having a viscosity of 30 Pa·s or less at 120°C. A reactive hot-melt adhesive containing a urethane prepolymer with a viscosity of 30 Pa·s at 120°C exhibits excellent dispensing properties from a jet dispenser. From the viewpoint of dispensing performance from a jet dispenser, the viscosity of the urethane prepolymer at 120°C is preferably 25 Pa·s or less, more preferably 20 Pa·s or less, and even more preferably 15 Pa·s or less. There is no particular lower limit to the viscosity of the urethane prepolymer at 120°C, but from the viewpoint of penetration into fabric, it is preferably 1 Pa·s or higher, more preferably 2 Pa·s or higher, and even more preferably 5 Pa·s or higher. In this disclosure, the viscosity of the urethane prepolymer at 120°C is measured by the method described in the examples.

[0027] From the viewpoint of adjusting the solidification time and viscosity of reactive hot-melt adhesives, it is preferable that the urethane prepolymer contains structural units derived from polyester polyol as structural units derived from polyol. In other words, it is preferable that the raw material for the urethane prepolymer contains polyester polyol as the polyol.

[0028] As the polyester polyol, a compound produced by the polycondensation reaction of a polyhydric alcohol and a polycarboxylic acid can be used. 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 carbon atoms in the carboxyl groups) and 2 to 6 carboxyl groups.

[0029] 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, branched polyester triols can also be obtained by the reaction of a diol and a tricarboxylic acid.

[0030] Examples of polyhydric alcohols include isomers of ethylene glycol, 1,2-propanediol, 1,3-propanediol, and butanediol, isomers of pentanediol, isomers of hexanediol, aliphatic or alicyclic diols such as 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, and 1,4-cyclohexanedimethanol; and aromatic diols such as 4,4'-dihydroxydiphenylpropane, bisphenol A, bisphenol F, pyrocatechol, resorcinol, and hydroquinone. Polyhydric alcohols may be used individually or in combination of two or more. Among these, aliphatic diols are preferred, and more preferably aliphatic diols having 2 to 6 carbon atoms.

[0031] Examples of polycarboxylic acids 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-cyclohexanediene-1,2-dicarboxylic acid. Polycarboxylic acids may be used individually or in combination of two or more.

[0032] Instead of the polycarboxylic acids mentioned above, polycarboxylic acid derivatives such as carboxylic acid anhydrides and compounds in which some of the carboxyl groups are esterified can also be used. Examples of polycarboxylic acid derivatives include dodecyl maleic acid and octadecenyl maleic acid.

[0033] The polyester polyol used as a raw material for the urethane prepolymer may be of one type only, or it may be of two or more types.

[0034] The number-average molecular weight (Mn) of the polyester polyol is preferably in the range of 500 to 10000, more preferably in the range of 1000 to 8000, and even more preferably in the range of 1500 to 6000, from the viewpoint of improving the waterproofness and adhesive strength of the cured product of the reactive hot-melt adhesive.

[0035] In this disclosure, the number-average molecular weight of polyols is measured by gel permeation chromatography (GPC) and converted to standard polystyrene equivalent. GPC measurements can be performed under the following conditions. Columns: "Gelpack GL A130-S", "Gelpack GL A150-S", and "Gelpack GL A160-S" (manufactured by Resonaq Corporation, packed columns for HPLC) Eluent: Tetrahydrofuran Flow rate: 1.0mL / min Column temperature: 40℃ Detector: RI

[0036] The amount of polyester polyol used as a raw material for the urethane prepolymer may be, for example, within the range of 70% to 100% by mass of the total polyol.

[0037] The urethane prepolymer may contain structural units derived from polyether polyols as structural units derived from polyols. In other words, the raw material for the urethane prepolymer may contain polyether polyols as polyols.

[0038] Examples of polyether polyols include aromatic polyether polyols containing aromatic rings and non-aromatic polyether polyols that do not contain aromatic rings. Examples of aromatic polyether polyols include polyether polyols having a bisphenol skeleton. Examples of non-aromatic polyether polyols include polyethylene glycol, polypropylene glycol, polybutylene glycol, polytetramethylene glycol, and ethylene oxide-modified polypropylene glycol.

[0039] The polyether polyol used as a raw material for the urethane prepolymer may be of one type only, or of two or more types.

[0040] The manganese content of the polyether polyol is preferably in the range of 500 to 3000, more preferably in the range of 700 to 2500, and even more preferably in the range of 1000 to 2000, from the viewpoint of initial adhesive strength, adhesive strength after curing, and dispensability from a jet dispenser.

[0041] The amount of polyether polyol used as a raw material for the urethane prepolymer may be, for example, within the range of 0% to 10% by mass of the total polyol.

[0042] 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 viewpoint of reactivity and adhesion, aromatic diisocyanates are preferred as polyisocyanates, and diphenylmethane diisocyanate is more preferred.

[0043] The polyisocyanate used as a raw material for the urethane prepolymer may be of one type only, or it may be of two or more types.

[0044] The temperature and time for reacting the polyol and polyisocyanate may be, for example, 85 to 120°C and 1 minute to 48 hours. When mixing the polyol and polyisocyanate, degassing under reduced pressure may be performed.

[0045] Reactive hot-melt adhesives may further contain a catalyst to promote the curing reaction of the urethane prepolymer. Examples of catalysts include dibutyltin dilaurate, dibutylthion octate, dimethylcyclohexylamine, dimethylbenzylamine, trioctylamine, and dimorpholinodiethyl ether (bis(2-morpholinoethyl) ether). The catalyst content may be, for example, 0% to 0.5% by mass of the total reactive hot melt adhesive.

[0046] Reactive hot-melt adhesives may further contain thermoplastic polymers to enhance the rubber elasticity of the cured product and improve its impact resistance. Examples of thermoplastic polymers include polyurethane, ethylene copolymers, propylene copolymers, vinyl chloride copolymers, acrylic copolymers, and styrene-conjugated diene block copolymers.

[0047] Reactive hot-melt adhesives may further contain a tackifying resin to provide stronger adhesion to the cured product. Examples of tackifying resins include rosin resin, rosin ester resin, hydrogenated rosin ester resin, terpene resin, terpene phenol resin, hydrogenated terpene resin, petroleum resin, hydrogenated petroleum resin, coumarone resin, ketone resin, styrene resin, modified styrene resin, xylene resin, epoxy resin, and the like.

[0048] Reactive hot melt adhesives may contain, as needed, components such as antioxidants, pigments, UV absorbers, surfactants, flame retardants, silane coupling agents, and fillers.

[0049] The method for obtaining a cured product of a reactive hot-melt adhesive is not particularly limited. For example, the curing reaction of a urethane prepolymer may be carried out in an environment with a temperature of 20°C to 30°C and a relative humidity of 40% to 60%, and the cured product may be obtained.

[0050] The reactive hot melt adhesive of this disclosure is in a solid state before use. The form of the reactive hot melt adhesive in its solid state is not particularly limited. For example, it may be in the form of pellets, blocks, powder, sheets, etc.

[0051] The reactive hot-melt adhesive of this disclosure is solid at room temperature and is heated to liquefy it before use. The method of 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, or a non-liquefied reactive hot-melt adhesive, such as an adhesive sheet, may be heated in contact with the object to liquefy it.

[0052] The reactive hot-melt adhesives of this disclosure are preferably used in a method of contacting a substrate using a dispenser. There are two types of dispensers: contact and non-contact, and jet dispensers fall under the non-contact category. A jet dispenser is a machine that dispenses liquid from a syringe, tank, etc., towards an object to be coated. Jet dispensers are superior in that they accurately dispense small and consistent amounts of liquid. In the method using a jet dispenser, reactive hot-melt adhesive is dispensed onto a substrate located at a distance from the nozzle. Therefore, for example, a desired pattern made of reactive hot-melt adhesive can be formed on the substrate.

[0053] The type of application pattern using reactive hot-melt adhesive is not particularly limited and can be selected from bead-like, dot-like, spiral-like, spray-like, stripe-like, etc. Because the reactive hot-melt adhesive of this disclosure exhibits excellent elasticity after curing, it is also suitable for use when applying the reactive hot-melt adhesive to a substrate in a spiral pattern.

[0054] The reactive hot-melt adhesive of this disclosure exhibits excellent elasticity after curing. Therefore, the reactive hot-melt adhesive of this disclosure is useful as an adhesive for bonding stretchable objects. The material of the stretchable object is not particularly limited. For example, it may be natural fibers, synthetic fibers, plastics, etc. In one embodiment, the stretchable object may be a fabric such as a knitted or woven fabric, or a fabric for clothing.

[0055] <Structure> The structure of the present disclosure comprises two or more stretchable objects and a cured product of the reactive hot-melt adhesive described above that is used to bond the two or more objects together.

[0056] In the structures of this disclosure, the cured product of a reactive hot-melt adhesive bonding two or more objects exhibits excellent elasticity. The material of the stretchable object is not particularly limited. For example, it may be natural fibers, synthetic fibers, plastics, etc. In one embodiment, the stretchable object may be a fabric such as a knitted fabric, woven fabric, or nonwoven fabric, and may also be a fabric for clothing.

[0057] The method for fabricating the structures of this disclosure is not particularly limited. For example, a structure in which object A and object B are bonded together with a cured product of a reactive hot-melt adhesive may be fabricated by the following method. A heated reactive hot-melt adhesive is brought into contact with a predetermined area of ​​object A, and object B is brought into contact with the reactive hot-melt adhesive. In this state, the reactive hot-melt adhesive is allowed to cool and solidify. Next, the curing reaction of the urethane prepolymer contained in the reactive hot-melt adhesive is allowed to occur. In the above method, the reactive hot-melt adhesive may be in a cooled and solidified state when it comes into contact with object B. In this case, the reactive hot-melt adhesive may be reheated and then cooled and solidified again after coming into contact with object B. [Examples]

[0058] The present disclosure will be described in detail below based on examples, but the present invention is not limited thereto.

[0059] <Preparation of urethane prepolymer> Polyols, as raw materials for urethane prepolymers, were added to the reaction vessel in the amounts (parts by mass) shown in Table 1 and mixed. Next, polyisocyanate was added to the reaction vessel in the amounts (parts by mass) shown in Table 1 and mixed, and the mixture was reacted at 110°C for 1 hour. Subsequently, the mixture was defoamed and stirred under reduced pressure at 110°C for another 1 hour to obtain the urethane prepolymer.

[0060] [Table 1]

[0061] Details of the polyols and polyisocyanates shown in Table 1 are as follows.

[0062] Polyester Polyol 1: An amorphous polyester polyol having aromatic rings, mainly composed of dicarboxylic acids (isophthalic acid and adipic acid) and diols (ethylene glycol and neopentyl glycol) (Hydroxyl group count: 2, number average molecular weight: 2000, Content of constituent units derived from aromatic ring compounds: 25 mol% (based on the total amount of constituent units constituting the amorphous polyester polyol), 50 mol% (based on the total amount of constituent units derived from dicarboxylic acids)).

[0063] Polyester polyol 2: An amorphous polyester polyol without aromatic rings, mainly composed of dicarboxylic acid (adipic acid) and diols (1,4-butanediol and neopentyl glycol) (number of hydroxyl groups: 2, number average molecular weight: 5000).

[0064] Polyester polyol 3: A crystalline polyester polyol without aromatic rings, mainly composed of dicarboxylic acid (adipic acid) and diol (1,6-hexanediol) (number of hydroxyl groups: 2, number average molecular weight: 5500).

[0065] Polyester polyol 4: A crystalline polyester polyol without aromatic rings, mainly composed of dicarboxylic acid (sebacic acid) and diol (1,6-hexanediol) (number of hydroxyl groups: 2, number average molecular weight: 5000).

[0066] Polyester polyol 5: A crystalline polyester polyol without aromatic rings, mainly composed of dicarboxylic acid (adipic acid) and diol (1,6-hexanediol) (number of hydroxyl groups: 2, number average molecular weight: 3000).

[0067] Polyether polyol 1: Polypropylene glycol (manufactured by Sanyo Chemical Industries, Ltd., "PP-2000", number of hydroxyl groups: 2, number average molecular weight: 2000) as an amorphous polyether polyol without aromatic rings.

[0068] Polyether polyol 2: A crystalline polyether polyol having an aromatic ring, specifically a bisphenol A·PO-based polyether polyol (ADEKA Corporation's "BPX-11", number of hydroxyl groups: 2, number average molecular weight: 360).

[0069] Polyisocyanate: Diphenylmethane diisocyanate (manufactured by Tosoh Corporation, product name: Myrionate MT, number of isocyanate groups: 2)

[0070] (Viscosity measurement) The viscosity of urethane prepolymer at 120°C was measured according to the method compliant with JIS Z 8803:2011. Specifically, a Type B viscometer (TVB-25H, manufactured by Toki Sangyo Co., Ltd.) was fitted with a No. 4 rotor to measure the viscosity of urethane prepolymer (15g) at 120°C. The rotor rotation speed was set to 20 rpm (revolutions per minute) when the viscosity was between 5 Pa·s and 50 Pa·s, and reduced to less than 20 rpm when the viscosity exceeded 50 Pa·s.

[0071] (Evaluation of elasticity) Test specimens were prepared from urethane prepolymer, consisting of strip-shaped cured material (100 mm x 10 mm, 100 μm thick). These specimens were evaluated by hand; "○" indicated elasticity, and "×" indicated no elasticity.

[0072] As shown in Table 1, the urethane prepolymers of Examples 1 to 5, in which the proportion of amorphous polyol in the polyol is 50% by mass or more, the NCO / OH ratio is 1.6 or more, the proportion of aromatic rings derived from the polyol is 15% by mass or less, and the viscosity at 120°C is 30 Pa·s or less, exhibit excellent elasticity after curing. Comparative Example 1, a urethane prepolymer in which the proportion of amorphous polyol in the polyol is 50% by mass or more, the proportion of aromatic rings derived from the polyol is 15% by mass or less, but the NCO / OH ratio is less than 1.6, has a high viscosity at 120°C and its discharge performance from a jet dispenser is inferior to that of the Examples. Comparative Example 2, a urethane prepolymer having an NCO / OH ratio of 1.6 or higher, an aromatic ring ratio derived from polyol of 15% by mass or less, a viscosity of 30 Pa·s or less at 120°C, but with an amorphous polyol content of less than 50% by mass in the polyol, exhibits inferior elasticity after curing compared to the example. Comparative Example 3, a urethane prepolymer in which the proportion of amorphous polyol in the polyol is 50% by mass or more, the NCO / OH ratio is 1.6 or more, and the viscosity at 120°C is 30 Pa·s or less, but the proportion of aromatic rings derived from the polyol exceeds 15% by mass, exhibits inferior elasticity after curing compared to the example.

Claims

1. A reactive hot-melt adhesive comprising a urethane prepolymer which is a reaction product of a polyol and a polyisocyanate, wherein the urethane prepolymer satisfies the following conditions A, B, C, and D. Condition A: The proportion of amorphous polyol in the total polyol is 50% by mass or more. Condition B: The equivalent ratio (NCO / OH) of the isocyanate groups (NCO) of the polyisocyanate to the hydroxyl groups (OH) of the polyol is 1.6 or higher. Condition C: The proportion of aromatic rings derived from polyols in the total urethane prepolymer is 15% by mass or less. Condition D: The viscosity of the urethane prepolymer at 120°C is 30 Pa·s or less.

2. A reactive hot-melt adhesive according to claim 1 for bonding stretchable objects.

3. A structure comprising two or more stretchable objects and a cured product of a reactive hot-melt adhesive according to claim 1 or claim 2 that is used to bond the two or more objects.

4. The structure according to claim 3, wherein the two or more objects are fabrics.

5. The structure according to claim 3, which is a garment.

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