WO2025173753A1 - Reactive hot melt adhesive and structure - Google Patents

Abstract

A reactive hot melt adhesive containing a urethane prepolymer, wherein the urethane prepolymer contains a structural unit derived from a trifunctional polyol.

Description

Reactive hot melt adhesives and structures

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

Technology has been proposed for producing clothing such as innerwear and sportswear using adhesives rather than sewing. For example, Patent Document 1 describes a sheet or tape-type hot melt adhesive for bonding stretchy materials.

Hot melt adhesives are solid at room temperature, liquefied by heating when brought into contact with the adherend, and develop adhesive strength when cooled and solidified. Hot melt adhesives can be broadly divided into two types: those containing thermoplastic resins as the main component and those containing reactive resins. Hot melt adhesives containing urethane prepolymers are known as hot melt adhesives containing reactive resins (hereinafter also referred to as reactive hot melt adhesives). Hot melt adhesives containing urethane prepolymers not only develop a certain degree of adhesive strength in a short period of time when cooled and solidified, but also harden when the terminal isocyanate groups of the urethane prepolymer react with moisture 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.

JP 2017-179195 A

Reactive hot melt adhesives are promising materials for use in clothing due to their high-speed adhesion and excellent adhesive strength. However, there is still room for improvement in properties such as elasticity, which are required for adhesives for clothing.
In view of the above circumstances, one aspect of the present disclosure aims to provide a reactive hot melt adhesive that has excellent elasticity after curing, and a structure obtained using the reactive hot melt adhesive that has excellent elasticity after curing.

Means for solving the above problems include the following embodiments.
<1> A reactive hot melt adhesive comprising a urethane prepolymer, the urethane prepolymer comprising a structural unit derived from a trifunctional polyol.
<2> The reactive hot melt adhesive according to <1>, wherein the proportion of structural units derived from the trifunctional polyol is 1% by mass to 20% by mass of all structural units derived from the polyol contained in the urethane prepolymer.
<3> The reactive hot melt adhesive according to <1> or <2>, wherein the proportion of aromatic rings in the total amount of the urethane prepolymer is 22 mass% or less.
<4> The reactive hot melt adhesive according to any one of <1> to <3>, wherein the urethane prepolymer contains a structural unit derived from a polyester polyol.
<5> The reactive hot melt adhesive according to any one of <1> to <4>, wherein the equivalent ratio (NCO/OH) of the isocyanate group (NCO) of the polyisocyanate to the hydroxyl group (OH) of the polyol used as a raw material for the urethane prepolymer is 2.0 or less.
<6> The reactive hot melt adhesive according to any one of <1> to <5>, for bonding stretchable objects.
<7> A structure comprising two or more stretchable objects and a cured product of the reactive hot melt adhesive according to any one of <1> to <6>, which bonds the two or more objects.
<8> The structure according to <7>, wherein the two or more objects are fabrics.
<9> The structure according to <7> or <8>.

The following describes embodiments of the present disclosure. However, the present disclosure is not limited to the following embodiments.

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

<Reactive hot melt adhesive>
The reactive hot melt adhesive of the present disclosure is a reactive hot melt adhesive that includes a urethane prepolymer, and the urethane prepolymer includes structural units derived from a trifunctional polyol.

The reactive hot melt adhesive of the present disclosure contains a urethane prepolymer as a reactive component, and therefore exhibits excellent adhesive strength by not only exhibiting adhesiveness due to cooling and solidification after heating and melting, but also adhesiveness due to the curing reaction between the urethane prepolymer and moisture.
Furthermore, the urethane prepolymer contained in the reactive hot melt adhesive of the present disclosure contains structural units derived from a trifunctional polyol.
As a result of investigations by the present inventors, it has become clear that reactive hot melt adhesives containing urethane prepolymers containing structural units derived from trifunctional polyols have superior elasticity after curing compared to reactive hot melt adhesives that do not satisfy this condition. The reasons for this are thought to be, for example, as follows.

When a urethane prepolymer contains structural units derived from a trifunctional polyol, a branched structure is formed in the molecular chain of the urethane prepolymer. This increases the number of urethane bonds and chemical crosslinking points contained in the urethane prepolymer, which is thought to improve the cohesive strength between the hard segments of the polyurethane obtained by polymerizing the urethane prepolymer.

From the viewpoint of exhibiting good stretchability, the proportion of structural units derived from trifunctional polyols in all structural units derived from polyols in the urethane prepolymer is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 5% by mass or more.
From the viewpoint of balance with other properties of the reactive hot melt adhesive, the proportion of structural units derived from trifunctional polyols in all structural units derived from polyols in the urethane prepolymer is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less.

From the viewpoint of a balance with other properties of the reactive hot melt adhesive, it is preferable that the urethane prepolymer further contains structural units derived from a bifunctional polyol.
From the viewpoint of exhibiting good stretchability, the proportion of structural units derived from bifunctional polyols in all structural units derived from polyols in the urethane prepolymer is preferably less than 99% by mass, more preferably less than 98% by mass, and even more preferably less than 95% by mass.
From the viewpoint of balance with other properties of the reactive hot melt adhesive, the proportion of structural units derived from bifunctional polyols in all structural units derived from polyols in the urethane prepolymer is preferably more than 80 mass%, more preferably more than 85 mass%, and even more preferably more than 90 mass%.

From the viewpoint of adjusting the solidification time and viscosity of the reactive hot melt adhesive, the urethane prepolymer preferably contains structural units derived from polyester polyol.
When the urethane prepolymer contains structural units derived from polyester polyol, the proportion thereof may be within a range of 70% by mass to 100% by mass of all structural units derived from polyol.
When the urethane prepolymer contains a structural unit derived from a polyester polyol, the urethane prepolymer preferably contains a structural unit derived from a polyester polyol as a structural unit derived from a bifunctional polyol. In this case, the structural unit derived from a trifunctional polyol contained in the urethane prepolymer may be a structural unit derived from a polyester polyol or a structural unit derived from a polyether polyol.
In the present disclosure, "polyester polyol" means a polyol having an ester bond in the molecule, and "polyether polyol" means a polyol having an ether bond in the molecule.

There are no particular restrictions on the type of polyester polyol used as a raw material for the urethane prepolymer. For example, the polyester polyol may be a reaction product of a polyhydric alcohol and a polycarboxylic acid. The polyester polyol may be, for example, a reaction product of a polyhydric alcohol having 2 to 15 carbon atoms and 2 or 3 hydroxyl groups with a polycarboxylic acid having 2 to 14 carbon atoms (including the carbon atoms in the carboxy groups) and 2 to 6 carboxy groups.

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

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

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

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

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

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 300 to 10,000, more preferably in the range of 350 to 8,000, and even more preferably in the range of 400 to 5,000.

In the present disclosure, the number average molecular weight of a polyol is a value measured by gel permeation chromatography (GPC) and converted into standard polystyrene. GPC measurement can be performed under the following conditions. Column: "Gelpack GLA130-S,""GelpackGLA150-S," and "Gelpack GLA160-S" (packed columns for HPLC, manufactured by Showa Denko Materials Co., Ltd.)
Eluent: tetrahydrofuran Flow rate: 1.0 mL/min Column temperature: 40°C
Detector: RI

From the viewpoint of adjusting the solidification time and viscosity of the reactive hot melt adhesive, the polyol used as a raw material for the urethane prepolymer preferably contains a polyester polyol.
The amount of polyester polyol used as a raw material for the urethane prepolymer may be, for example, within the range of 70% by mass to 100% by mass of the total polyol.

From the standpoint of workability during application of the reactive hot melt adhesive and adhesion, waterproofness, and flexibility after curing, it is preferable that the urethane prepolymer contain structural units derived from polyether polyol as structural units derived from polyol. In other words, it is preferable that the raw material for the urethane prepolymer contain polyether polyol as the polyol.

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

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

The polyether polyol used as the raw material for the urethane prepolymer may be one kind or two or more kinds.
The polyether polyol used as a raw material for the urethane prepolymer may be one containing an aromatic ring (hereinafter also referred to as an aromatic polyether polyol) or one not containing an aromatic ring (hereinafter also referred to as a non-aromatic polyether polyol).

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

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

The amount of polyether polyol used as a raw material for the urethane prepolymer may be, for example, within the range of 0% to 30% by mass, 0% to 20% by mass, or 0% to 10% by mass of the total polyol.

The polyisocyanate used as a raw material for the urethane prepolymer may contain an aromatic ring (hereinafter also referred to as an aromatic polyisocyanate) or may not contain an aromatic ring (hereinafter also referred to as a non-aromatic polyisocyanate).

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

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

(Aromatic ring ratio)
From the viewpoint of elasticity after curing, the proportion of aromatic rings in the total amount of urethane prepolymer contained in the reactive hot melt adhesive (hereinafter also referred to as the aromatic ring ratio of the urethane prepolymer) is preferably 22% by mass or less, more preferably 17% by mass or less, and even more preferably 12% by mass or less. The aromatic ring ratio of the urethane prepolymer may be 0% by mass.
From the viewpoint of a balance between physical properties other than stretchability, the aromatic ring ratio of the urethane prepolymer may be 0% by mass, 1% by mass or more, 5% by mass or more, or 10% by mass or more.

When the urethane prepolymer contains an aromatic ring, each of the structural units derived from the polyol and the structural units derived from the polyisocyanate of the urethane prepolymer may contain an aromatic ring, or only one of the structural units derived from the polyol and the structural units derived from the polyisocyanate may contain an aromatic ring.
When the structural units derived from a polyol of the aromatic ring-containing urethane prepolymer contain an aromatic ring, all of the structural units derived from the polyol may contain an aromatic ring, or only some of the structural units derived from the polyol may contain an aromatic ring.
When the structural units derived from a polyisocyanate of the aromatic ring-containing urethane prepolymer contain an aromatic ring, all of the structural units derived from the polyisocyanate may contain an aromatic ring, or only a portion of the structural units derived from the polyisocyanate may contain an aromatic ring.

The aromatic ring ratio of a urethane prepolymer is a value calculated using the formula below. In the formula below, "total mass of urethane prepolymer raw materials" means the mass including raw materials that do not contain aromatic rings. If polyester polyol or polyether polyol is not used as a raw material polyol, the item for the polyol not used can be omitted. The molecular weight of the aromatic ring is 78 (in the case of a benzene ring).

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

In the above formula, the aromatic ring ratio of the polyester polyol having an aromatic ring is calculated by the following formula.
Aromatic ring ratio of polyester polyol having aromatic ring=(molecular weight of aromatic ring×molar composition ratio (%) of polycarboxylic acid having aromatic ring in raw material carboxylic acid)/(molecular weight of each polycarboxylic acid×molar composition ratio (%) in raw material carboxylic acid)+(molecular weight of each polyhydric alcohol×molar composition ratio (%) in raw material alcohol)

In the above formula, the aromatic ring ratio of the polyether polyol having an aromatic ring is calculated by the following formula.
Aromatic ring ratio of polyether polyol having aromatic rings = molecular weight of aromatic rings x number of moles of aromatic rings per mole of polyether polyol / molecular weight of polyether polyol

In the above formula, the aromatic ring ratio of the polyisocyanate having an aromatic ring is calculated by the following formula.
Aromatic ring ratio of polyisocyanate having aromatic ring = molecular weight of aromatic ring × number of moles of aromatic ring per mole of polyisocyanate / molecular weight of polyisocyanate

From the viewpoint of stretchability after curing, the structural units derived from polyol in the urethane prepolymer preferably contain structural units derived from amorphous polyol.
In the present disclosure, a crystalline polyol refers to a polyol that exhibits an endothermic peak (melting point Tm) accompanying melting when measured by DSC, and an amorphous polyol refers to a polyol that does not exhibit an endothermic peak (melting point Tm) accompanying melting when measured by DSC.
The proportion of structural units derived from amorphous polyol in the structural units derived from polyol of the urethane prepolymer may be 70% by mass or more, 80% by mass or more, 95% by mass or more, or 100% by mass.

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 2.0 or less. When the NCO/OH ratio is 2.0 or less, the amount of unreacted polyisocyanate remaining when the polyol and polyisocyanate are reacted is suppressed, and good elasticity is maintained after curing.

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 1.6 or higher. When the NCO/OH ratio is 1.6 or higher, the viscosity of the resulting urethane prepolymer when melted does not become too high, maintaining good workability.

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.

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, or 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.

The reactive hot melt adhesive may contain additives such as antioxidants, antifoaming agents, nucleating agents, pigments, ultraviolet absorbers, surfactants, flame retardants, silane coupling agents, and fillers, as necessary.
The content of each additive may be, for example, 0% to 0.5% by mass of the entire reactive hot melt adhesive.

The reactive hot melt adhesive may further contain a thermoplastic polymer to enhance the rubber elasticity of the cured product and further improve impact resistance. Specific examples of thermoplastic polymers include polyurethane, ethylene copolymers, propylene copolymers, vinyl chloride copolymers, acrylic copolymers, and styrene-conjugated diene block copolymers.

The reactive hot melt adhesive may further contain a tackifying resin to impart stronger adhesive properties to the cured product. Specific 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, and epoxy resin.

There are no particular restrictions on the method for obtaining a cured reactive hot melt adhesive. For example, a cured product can be obtained by causing a curing reaction of the urethane prepolymer in an environment with a temperature of 20°C to 30°C and a relative humidity of 40% to 60%.

From the standpoint of workability during application, the viscosity of the reactive hot melt adhesive measured using a rotational viscometer at 120°C is preferably 20 Pa·s or less, more preferably 15 Pa·s or less, and even more preferably 10 Pa·s or less. There is no lower limit to the viscosity of the reactive hot melt adhesive measured using a rotational viscometer at 120°C, but it may be, for example, 1 Pa·s or more.

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 pellets, blocks, powder, sheets, etc.

The reactive hot melt adhesive of the present disclosure is solid at room temperature and is liquefied by heating when in use. There are no particular limitations on the method for applying the liquefied reactive hot melt adhesive to the object. 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 while in contact with the object to be liquefied.

The reactive hot melt adhesive of the present disclosure has excellent elasticity after curing, and is therefore useful as an adhesive for bonding elastic objects.
The material of the stretchable object is not particularly limited, and may be, for example, natural fiber, synthetic fiber, plastic, or the like.
In one embodiment, the stretchable article may be a fabric such as a knitted fabric, woven fabric, or nonwoven fabric, and may be a fabric for clothing.

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

In the structure of the present disclosure, the cured reactive hot melt adhesive that bonds two or more objects exhibits excellent stretchability.
The material of the stretchable object is not particularly limited, and may be, for example, natural fiber, synthetic fiber, plastic, or the like.
In one embodiment, the stretchable article may be a fabric such as a knitted fabric, woven fabric, or nonwoven fabric, and may be a fabric for clothing.

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 together with a cured reactive hot melt adhesive can be produced by a method including contacting a predetermined area of one object with 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.

The present disclosure will be explained in detail below based on examples, but the present invention is not limited to these.

<Preparation of Composition>
Polyol, a raw material for the urethane prepolymer, was added to a reaction vessel in the blending amount (parts by mass) shown in Table 1 and mixed. Next, polyisocyanate was further added to the reaction vessel in the blending amount (parts by mass) shown in Table 1 and mixed, followed by reaction at 110°C for 1 hour. Thereafter, the mixture was further stirred at 110°C under reduced pressure and degassed for 1 hour, yielding a composition containing a urethane prepolymer.

<Measurement of extension force decay rate>
A cured coating approximately 100 μm thick was formed from the prepared composition, and a strip-shaped test specimen (10 mm wide, 12 cm long) was prepared. Using this test specimen, the extension force decay rate (%) was measured using a repeated constant-rate extension method in accordance with JIS L 1096:2010 (Testing Methods for Woven and Knit Fabrics). Specifically, both ends of the test specimen were gripped with the grippers of a tensile tester (grip spacing: 100 mm), and the test specimen was stretched at a tensile speed of 100 mm/min until the elongation of the test specimen reached 50% (grip spacing after stretching: 150 mm, step 1). The test specimen was then held in this state for 1 minute, and the grippers were then returned to their original position at the same tensile speed (step 2). The elongation force attenuation rate (%) of the test piece was calculated using the following formula from the load (load 1) when the elongation rate of the test piece reached 50% in step 1 and the load (load 2) when the elongation rate of the test piece reached 50% in step 2. The results are shown in Table 1.
Extension force attenuation rate (%) = (Load 2/Load 1) x 100

The details of the materials shown in Table 1 are as follows.
Bifunctional polyol 1: Amorphous polyester polyol containing an aromatic ring (number average molecular weight: 2000), mainly composed of dicarboxylic acids (isophthalic acid and adipic acid) and diols (ethylene glycol and neopentyl glycol)
Bifunctional polyol 2: Amorphous polyester polyol containing no aromatic ring, mainly composed of a dicarboxylic acid (adipic acid) and a diol (1,4-butanediol and neopentyl glycol) (number average molecular weight: 5000)

Trifunctional polyol 1: Amorphous polyester polyol (number average molecular weight: 500) containing no aromatic ring and composed mainly of dicarboxylic acid (adipic acid) and triol (trimethylolpropane)
Trifunctional polyol 2: Amorphous polyester polyol containing no aromatic ring, mainly composed of dicarboxylic acid (adipic acid) and triol (trimethylolpropane) (number average molecular weight: 1000)
Trifunctional polyol 3: Amorphous polyester polyol containing no aromatic ring, mainly composed of a dicarboxylic acid (adipic acid) and a triol (trimethylolpropane) (number average molecular weight: 2000)
Trifunctional polyol 4: Amorphous polyester polyol containing no aromatic ring, mainly composed of dicarboxylic acid (adipic acid) and triol (trimethylolpropane) (number average molecular weight: 3000)
Trifunctional polyol 5: Amorphous polyether polyol (number average molecular weight: 400) containing no aromatic ring and composed mainly of alkylene oxide (propylene oxide) and triol (glycerin)
Trifunctional polyol 6: Amorphous polyether polyol (number average molecular weight: 600) containing no aromatic ring and composed mainly of alkylene oxide (propylene oxide) and triol (glycerin)

As shown in Table 1, the compositions of Examples 1 to 8, which meet the conditions for a reactive hot melt adhesive as disclosed herein, exhibited a greater elongation force attenuation rate and superior stretchability in the cured films than the composition of Comparative Example 1, which does not meet the conditions for a reactive hot melt adhesive as disclosed herein.

The disclosure of Japanese Patent Application No. 2024-019714 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards mentioned herein are incorporated by reference into this specification to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims (9)

A reactive hot melt adhesive comprising a urethane prepolymer, the urethane prepolymer comprising structural units derived from a trifunctional polyol. The reactive hot melt adhesive according to claim 1, wherein the proportion of structural units derived from the trifunctional polyol is 1% by mass to 20% by mass of all structural units derived from the polyol contained in the urethane prepolymer. The reactive hot melt adhesive according to claim 1, wherein the proportion of aromatic rings in the total amount of the urethane prepolymer is 22 mass% or less. The reactive hot melt adhesive according to claim 1, wherein the urethane prepolymer contains structural units derived from a polyester polyol. The reactive hot melt adhesive according to claim 1, wherein 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 2.0 or less. The reactive hot melt adhesive according to claim 1, for bonding elastic objects. A structure comprising two or more stretchable objects and a cured product of the reactive hot melt adhesive described in any one of claims 1 to 6, which bonds the two or more objects together. The structure described in claim 7, wherein the two or more objects are fabrics. The structure described in claim 7, which is an article of clothing.