Reactive hot-melt adhesive and structure

Abstract

This reactive hot-melt adhesive contains a urethane prepolymer and satisfies at least one of the following condition A or condition 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 °C or less.

Description

Reactive hot melt adhesives and structures

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

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

[0003] Hot melt adhesives are solid at room temperature, liquefied by heating and brought into contact with an adherend, and develop adhesive strength upon cooling and solidification. Hot melt adhesives can be broadly divided into two types: those containing a thermoplastic resin as the main component and those containing a reactive resin. Known hot melt adhesives containing reactive resins (hereinafter also referred to as reactive hot melt adhesives) include hot melt adhesives containing urethane prepolymers. Hot melt adhesives containing urethane prepolymers not only develop a certain degree of adhesive strength upon cooling and solidification in a short period of time, but also cure when the terminal isocyanate groups of the urethane prepolymer react with moisture present in the air or on the surface of the adherend. As a result, they develop a strong adhesive strength that cannot be achieved with hot melt adhesives containing thermoplastic resins.

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

[0005] Reactive hot melt adhesives are promising materials for use as adhesives for clothing, taking advantage of their high-speed adhesion and excellent adhesive strength. However, reactive hot melt adhesives still have room for improvement in properties such as elasticity 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.

[0006] Means for solving the above problems include the following embodiments. <1> A reactive hot melt adhesive containing a urethane prepolymer and satisfying 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; and Condition B: The glass transition temperature in the cured state is 25°C or less. <2> The reactive hot melt adhesive according to <1>, in which the proportion of structural units derived from amorphous polyol among the structural units derived from polyol in the urethane prepolymer is 70 mass% or more. <3> The reactive hot melt adhesive according to <1> or <2>, in which 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. <4> The reactive hot melt adhesive according to any one of <1> to <3>, for bonding stretchable objects. <5> 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 <4>, which bonds the two or more objects together. <6> The structure according to <5>, wherein the two or more objects are fabrics. <7> The structure according to <5>, wherein the two or more objects are clothing.

[0007] Hereinafter, embodiments of the present disclosure will be described, but the present disclosure is not limited to the following embodiments.

[0008] In this disclosure, "polyol" refers to a compound having two or more hydroxyl groups in the molecule. In this disclosure, "polyisocyanate" refers to a compound having two or more isocyanate groups in the molecule. In this disclosure, "urethane prepolymer" refers to a compound that is a reaction product of a polyol and a polyisocyanate and has an isocyanate group at the end of the molecule. In other words, "urethane prepolymer" refers to a compound that contains a polymer chain containing a structural unit derived from a polyol and a structural unit derived from a polyisocyanate, and has an isocyanate group as the end group of the polymer chain.

[0009] <Reactive Hot Melt Adhesive> The reactive hot melt adhesive of the present disclosure is a reactive hot melt adhesive that 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 the cured state is 25°C or less.

[0010] The reactive hot melt adhesive of the present disclosure contains a urethane prepolymer as a reactive component. Therefore, the adhesive exhibits excellent adhesive strength by not only solidifying upon cooling after heating and melting but also by curing reaction between the urethane prepolymer and moisture. Furthermore, the reactive hot melt adhesive of the present disclosure has a ratio of aromatic rings to the total amount of urethane prepolymer (hereinafter also referred to as the aromatic ring ratio of the urethane prepolymer) of 22 mass% or less, or a glass transition temperature in the cured state of 25°C or less.

[0011] As a result of investigations by the present inventors, it has become clear that reactive hot melt adhesives in which the aromatic ring ratio of the urethane prepolymer is 22 mass% or less or the glass transition temperature in the cured state is 25°C or less have superior elasticity after curing compared to reactive hot melt adhesives that do not satisfy either of these conditions.

[0012] 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 may be 20% by mass or less. There is no particular lower limit for the aromatic ring ratio of the urethane prepolymer. For example, the aromatic ring ratio of the urethane prepolymer may be 5% by mass or more.

[0013] In the aromatic ring-containing urethane prepolymer, both the structural unit derived from the polyol and the structural unit derived from the polyisocyanate may contain an aromatic ring, or only either the structural unit derived from the polyol or the structural unit derived from the polyisocyanate may contain an aromatic ring. The aromatic ring-containing urethane prepolymer may contain, as the structural unit derived from the polyol, a structural unit containing an aromatic ring and a structural unit not containing an aromatic ring, or may contain only one of them. The aromatic ring-containing urethane prepolymer may contain, as the structural unit derived from the polyisocyanate, a structural unit containing an aromatic ring.

[0014] The aromatic ring ratio of the urethane prepolymer is a value calculated using the following formula. In the formula, "total mass of the raw materials for the urethane prepolymer" means the mass including raw materials that do not contain aromatic rings. If polyester polyol or polyether polyol is not used as the 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).

[0015] Aromatic ring ratio (%) of urethane prepolymer = {(aromatic ring ratio of polyester polyol having aromatic ring × mass of polyester polyol having aromatic ring) + (aromatic ring ratio of polyether polyol having aromatic ring × mass of polyether polyol having aromatic ring) + (aromatic ring ratio of polyisocyanate having aromatic ring × mass of polyisocyanate) / total mass of raw materials for urethane prepolymer} × 100

[0016] 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 an aromatic ring = (molecular weight of aromatic ring x molar composition ratio (%) of polycarboxylic acid having an aromatic ring in the raw material carboxylic acid) / (molecular weight of each polycarboxylic acid x molar composition ratio (%) in the raw material carboxylic acid) + (molecular weight of each polyhydric alcohol x molar composition ratio (%) in the raw material alcohol).

[0017] 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 the polyether polyol having an aromatic ring = Molecular weight of aromatic ring x Number of moles of aromatic rings per mole of polyether polyol / Molecular weight of polyether polyol

[0018] 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 the polyisocyanate having an aromatic ring = Molecular weight of aromatic ring x Number of moles of aromatic ring per mole of polyisocyanate / Molecular weight of polyisocyanate

[0019] From the viewpoint of elasticity after curing, the glass transition temperature of the reactive hot melt adhesive in the cured state is preferably 25° C. or lower. If the glass transition temperature in the cured state is 25° C. or lower, the cured product of the reactive hot melt adhesive will become rubbery in an environment of 25° C. or higher and will exhibit excellent elasticity. The glass transition temperature of the reactive hot melt adhesive in the cured state is measured by the method shown in the examples.

[0020] As a result of investigations by the present inventors, it was found 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 the aromatic ring ratio of the urethane prepolymer contained in the reactive hot melt adhesive.

[0021] From the viewpoint of elasticity after curing, it is preferable that the polyol-derived structural units of the urethane prepolymer include structural units derived from an amorphous polyol. In the present disclosure, crystalline polyol refers to a polyol that exhibits an endothermic peak (melting point Tm) accompanied by melting when measured by DSC, and amorphous polyol refers to a polyol that does not exhibit an endothermic peak (melting point Tm) accompanied by melting when measured by DSC. The proportion of the amorphous polyol-derived structural units in the polyol-derived structural units of the urethane prepolymer may be 70% by mass or more, 80% by mass or more, or 95% by mass.

[0022] From the viewpoint of adjusting the solidification time and viscosity of the reactive hot melt adhesive, the urethane prepolymer preferably contains a structural unit derived from a polyester polyol as a structural unit derived from a polyol. That is, the raw material of the urethane prepolymer preferably contains a polyester polyol as a polyol.

[0023] The polyester polyol may be a compound produced by a polycondensation reaction between a polyhydric alcohol and a polycarboxylic acid. 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 with a polycarboxylic acid having 2 to 14 carbon atoms (including the carbon atoms in the carboxyl groups) and 2 to 6 carboxyl groups.

[0024] The polyester polyol may be a linear polyester diol produced from a diol and a dicarboxylic acid, or a branched polyester triol produced from a triol and a dicarboxylic acid. The branched polyester triol can also be obtained by reacting a diol with a tricarboxylic acid.

[0025] Examples of polyhydric alcohols include aliphatic or alicyclic diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, isomers of butanediol, isomers of pentanediol, isomers of hexanediol, 2,2-dimethyl-1,3-propanediol, 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. The polyhydric alcohols 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.

[0026] 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. One type of polycarboxylic acid may be used alone, or two or more types may be used in combination.

[0027] Instead of the above-mentioned polycarboxylic acids, polycarboxylic acid derivatives such as carboxylic acid anhydrides and compounds in which a portion of the carboxyl group is esterified can also be used. Examples of polycarboxylic acid derivatives include dodecyl maleic acid and octadecenyl maleic acid.

[0028] The polyester polyol used as the raw material for the urethane prepolymer may be one type only, or two or more types.

[0029] 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, from the viewpoint of improving the waterproofness and adhesive strength of the cured product of the reactive hot melt adhesive.

[0030] In the present disclosure, the number average molecular weight of a polyol is measured by gel permeation chromatography (GPC) and is a value converted into standard polystyrene. GPC measurement can be performed under the following conditions. Column: "Gelpack GLA130-S," "Gelpack GLA150-S," and "Gelpack GLA160-S" (packed columns for HPLC, manufactured by Showa Denko Materials Co., Ltd.) Eluent: tetrahydrofuran Flow rate: 1.0 mL / min Column temperature: 40°C Detector: RI

[0031] 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.

[0032] From the viewpoints of workability during application of the reactive hot melt adhesive and adhesion, waterproofness, and flexibility after curing, the urethane prepolymer preferably contains a structural unit derived from a polyether polyol as a structural unit derived from a polyol, i.e., the raw material of the urethane prepolymer preferably contains a polyether polyol as the polyol.

[0033] Examples of polyether polyols 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.

[0034] The polyether polyol used as the raw material for the urethane prepolymer may be one kind or two or more kinds.

[0035] 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, from the viewpoints of initial adhesive strength, adhesive strength after curing, and an appropriate open time after application.

[0036] 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.

[0037] The polyisocyanate used as a raw material for the urethane prepolymer is not particularly limited. Examples of polyisocyanates include aromatic isocyanates such as diphenylmethane diisocyanate, dimethyldiphenylmethane diisocyanate, tolylene diisocyanate, xylylene diisocyanate, and p-phenylene diisocyanate; alicyclic isocyanates such as dicyclohexylmethane diisocyanate and isophorone diisocyanate; and aliphatic isocyanates such as hexamethylene diisocyanate. From the viewpoints of reactivity and adhesiveness, aromatic diisocyanates are preferred as polyisocyanates, and diphenylmethane diisocyanate is more preferred.

[0038] The polyisocyanate used as the raw material for the urethane prepolymer may be one type only, or two or more types.

[0039] 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 during the reaction of the polyol and the polyisocyanate is suppressed, and good stretchability is maintained after curing.

[0040] 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 more. When the NCO / OH ratio is 1.6 or more, the viscosity of the resulting urethane prepolymer when melted does not become too high, and good workability is maintained.

[0041] 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 carried out.

[0042] The reactive hot melt adhesive may further contain a catalyst to promote the curing reaction of the urethane prepolymer. Examples of catalysts include dibutyltin dilaurate, dibutylthione 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 entire reactive hot melt adhesive.

[0043] 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. Examples of the thermoplastic polymer include polyurethane, ethylene copolymer, propylene copolymer, vinyl chloride copolymer, acrylic copolymer, and styrene-conjugated diene block copolymer.

[0044] The reactive hot melt adhesive may further contain a tackifying resin to impart stronger adhesiveness to the cured product. Examples of tackifying resins include rosin resins, rosin ester resins, hydrogenated rosin ester resins, terpene resins, terpene phenol resins, hydrogenated terpene resins, petroleum resins, hydrogenated petroleum resins, coumarone resins, ketone resins, styrene resins, modified styrene resins, xylene resins, and epoxy resins.

[0045] The reactive hot melt adhesive may contain components such as antioxidants, pigments, ultraviolet absorbers, surfactants, flame retardants, silane coupling agents, and fillers, as needed.

[0046] The method for obtaining a cured product of the reactive hot melt adhesive is not particularly limited. For example, the cured product may be obtained by causing a curing reaction of the urethane prepolymer in an environment at a temperature of 20°C to 30°C and a relative humidity of 40% to 60%.

[0047] From the viewpoint 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. The lower limit of the viscosity of the reactive hot melt adhesive measured using a rotational viscometer at 120°C is not limited, but may be, for example, 1 Pa s or more.

[0048] The reactive hot melt adhesive of the present disclosure is in a solid state before use. The form of the solid reactive hot melt adhesive is not particularly limited. For example, it may be in the form of a pellet, a block, a powder, a sheet, or the like.

[0049] The reactive hot melt adhesive of the present disclosure is solid at room temperature and is liquefied by heating when used. The method for applying the liquefied reactive hot melt adhesive to an object is not particularly limited. For example, the liquefied reactive hot melt adhesive may be brought into contact with the object using a dispenser or the like, or an unliquefied reactive hot melt adhesive, such as an adhesive sheet, may be heated in contact with the object to be liquefied.

[0050] The reactive hot melt adhesive of the present disclosure has excellent elasticity after curing. Therefore, the reactive hot melt adhesive of the present disclosure is useful as an adhesive for bonding elastic objects. The material of the elastic object is not particularly limited. For example, it may be natural fiber, synthetic fiber, plastic, etc. In one embodiment, the elastic object may be a fabric such as a knitted fabric or woven fabric, or may be a fabric for clothing.

[0051] <Structure> The structure of the present disclosure is a structure including 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.

[0052] In the structure of the present disclosure, the cured product of the reactive hot melt adhesive bonding two or more objects exhibits excellent stretchability. The material of the stretchable objects is not particularly limited. For example, it may be natural fiber, synthetic fiber, plastic, etc. In one embodiment, the stretchable objects may be fabrics such as knitted fabrics, woven fabrics, nonwoven fabrics, etc., and may be fabrics for clothing.

[0053] The method for producing the structure of the present disclosure is not particularly limited. For example, a heated reactive hot melt adhesive is brought into contact with a predetermined area of ​​one object, and another object is brought into contact with the reactive hot melt adhesive, and the reactive hot melt adhesive is cooled and solidified in this state. Next, a curing reaction of the urethane prepolymer contained in the reactive hot melt adhesive is caused. This allows a structure in which two or more objects are bonded together with the cured reactive hot melt adhesive to be obtained.

[0054] The present disclosure will be specifically described below based on examples, but the present invention is not limited to these.

[0055] <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, to obtain a composition containing a urethane prepolymer.

[0056]

[0057] Details of the polyols and polyisocyanates shown in Table 1 are as follows: Polyol 1: Amorphous polyester polyol having an aromatic ring, primarily 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 an aromatic ring: 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)) Polyol 2: Crystalline polyether polyol having an aromatic ring (bisphenol A / PO type) (manufactured by ADEKA Corporation, trade name: BPX-11, number of hydroxyl groups: 2, melting point: 3°C) Polyol 3: Amorphous polyester polyol having no aromatic ring, primarily composed of dicarboxylic acids (adipic acid) and diols (1,4-butanediol and neopentyl glycol) (number of hydroxyl groups: 2, number average molecular weight: 5000) Polyol 4: A crystalline polyester polyol having no 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) Polyol 5: Amorphous polyester polyol having no aromatic ring, mainly composed of a dicarboxylic acid (adipic acid) and a diol (methylpentanediol) (number of hydroxyl groups: 2, number average molecular weight: 4000) Polyisocyanate: Diphenylmethane diisocyanate (manufactured by Tosoh Corporation, trade name: Millionate MT, number of isocyanate groups: 2)

[0058] (Glass Transition Temperature) The glass transition temperature of the urethane prepolymer was determined as the peak top temperature of tan δ measured by dynamic mechanical analysis (DMA) under the following conditions: Testing equipment: RSA-G2 manufactured by TA instruments Testing mode: Tensile Testing temperature: -100°C to 250°C Heating rate: 5°C / min Frequency: 1 Hz Strain: 0.05% Atmosphere: Nitrogen

[0059] (Elongation Force Damping Rate) A cured coating approximately 100 μm thick was formed from the prepared composition, and a dumbbell-shaped No. 1 test specimen was prepared. Using this test specimen, the elongation force damping rate (%) was measured by 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 grippers of a tensile tester (grip spacing: 100 mm), and the test specimen was stretched at a tensile speed of 300 mm / min until the elongation rate of the test specimen reached 40% (Step 1). The grippers were then returned to their original positions at the same tensile speed (Step 2). The elongation force damping rate (%) of the test specimen was calculated using the load (Load 1) at which the elongation rate of the test specimen reached 30% in Step 1 and the load (Load 2) at which the elongation rate of the test specimen reached 30% in Step 2, using the following formula. The results are shown in Table 1. Extension force attenuation rate (%) = (Load 2 / Load 1) x 100

[0060] As shown in Table 1, the compositions of Examples 1 to 6, which satisfy the conditions for a reactive hot melt adhesive of the present disclosure, exhibited greater elongation force attenuation rates and superior stretchability of the cured films than the compositions of Comparative Examples 1 and 2, which do not satisfy the conditions for a reactive hot melt adhesive of the present disclosure.

[0061] The disclosure of Japanese Patent Application No. 2022-200325 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

1. It contains a urethane prepolymer and satisfies the following conditions A and B, A reactive hot melt adhesive, wherein the proportion of structural units derived from amorphous polyester polyol in the structural units derived from polyol of the urethane prepolymer is 70 mass % or more. 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 the cured state is 25°C or lower

2. 2. 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.

3. The reactive hot melt adhesive of claim 1 for bonding elastic objects.

4. A structure comprising two or more stretchable objects and a cured product of the reactive hot melt adhesive according to any one of claims 1 to 3, which bonds the two or more objects.

5. The structure of claim 4 , wherein the two or more objects are fabrics.

6. 5. The structure of claim 4, which is an article of clothing.