Adhesive, cured product thereof, and structure

Abstract

The purpose of the present disclosure is to provide an adhesive that is suitable for adhering an aluminum substrate and another substrate together, and achieves both high adhesive strength, and cohesive failure of the adhesive and long-term moist heat resistance, without a primer.　By using a polyol main agent and a polyisocyanate curing agent in combination, said polyol main agent including a polyol, a phosphoric acid compound, and a monoalcohol, when the adhesive is used, adhesion to aluminum is ensured due to the phosphoric acid compound, and the adhesive strength is improved. Additionally, by using the monoalcohol to adjust the degree of crosslinking in a coating film, a starting point for cohesive failure of the adhesive is created, whereby stable adhesive strength can be demonstrated.

Description

Adhesive, cured product thereof, and structure

[0001] The present disclosure relates to a primerless adhesive that is suitable for bonding aluminum substrates to other substrates and that combines high adhesive strength with cohesive failure and long-term moist heat resistance, as well as a cured product and structure made from the adhesive.

[0002] In recent years, in the fields of automobiles and aircraft, the use of lightweight materials such as light metals (e.g., aluminum and magnesium) and fiber-reinforced plastics (hereinafter referred to as FRP) has been increasing in order to reduce the weight of vehicle bodies. However, when bonding materials with different linear expansion coefficients, such as aluminum and FRP, the difference in the expansion coefficients between the materials caused by temperature changes during the manufacturing process or in the operating temperature environment tends to impart high stress to the adhesive layer, accelerating the destruction or deterioration of the adhesive layer. Therefore, methods of imparting flexibility to adhesives have been widely studied as a stress relief design, and urethane adhesives, which combine high adhesive strength and flexibility, have attracted particular attention.

[0003] When using urethane adhesives, a pretreatment step is typically performed by applying a primer or activator to the substrate to promote long-term adhesion of the adhesive composition. In fields such as automotive, productivity and safety considerations require both sufficient adhesive strength without primer and cohesive failure of the adhesive. However, conventional urethane adhesives may not be able to achieve sufficient adhesive strength without primer, which can lead to interfacial failure of the adhesive.

[0004] For example, Patent Document 1 discloses a solventless urethane adhesive composition having excellent breaking elongation, which is composed of a base agent containing a urethane prepolymer and a cured product of a curing agent containing a compound having an active hydrogen group. However, the adhesive described in Patent Document 1 tends to have a high crosslink density because it uses a polyol component containing a macropolyol having a number average molecular weight of 500 to 10,000 and an average number of hydroxyl groups of 1.9 to 4.0. As a result of investigations by the present inventors, it has been found that cohesive failure may not occur on aluminum substrates.

[0005] For example, Patent Document 2 discloses a primerless adhesive comprising an adhesive composition containing a urethane prepolymer and a monofunctional alkylene glycol. However, because it is a one-component type, it tends to cure slowly, and as a result of investigations by the present inventors, it has become clear that the adhesive strength to aluminum substrates tends to be low.

[0006] For example, Patent Document 3 discloses a primerless adhesive that consists of a base agent containing a urethane prepolymer and a curing agent cured product containing a compound having an active hydrogen group, and that adheres to a polypropylene substrate by flame treatment. However, as a result of investigations by the present inventors, it became clear that the primerless adhesive tends to have low adhesive strength to an aluminum substrate even when flame treatment is performed.

[0007] International Publication No. 2021 / 132094 Special Publication No. 2021-528524 International Publication No. 2018 / 100674

[0008] An object of the present disclosure is to provide a primerless adhesive that is suitable for bonding aluminum substrates to other substrates, and that combines high adhesive strength with cohesive failure of the adhesive and long-term resistance to moist heat.

[0009] The present inventors have conducted extensive research and found that the above-mentioned problems can be solved. The present disclosure relates to an adhesive comprising a polyol base agent (A) and a polyisocyanate curing agent (B), wherein the polyol base agent (A) contains a polyol (C), a phosphoric acid compound (D), and a monoalcohol (E).

[0010] The present disclosure also relates to the adhesive, which satisfies at least one of the following formulas (1) and (2): (1) 0.002≦P / M≦0.1 (2) 0.002≦P / N≦0.1 P: absolute value of the content (mass%) of the phosphoric acid compound (D) in 100 mass% of the adhesive M: absolute value of the breaking strength (MPa) measured in accordance with JIS K 6251 for a cured product obtained by curing the adhesive for 7 days in an environment of 23°C and 50% relative humidity N: absolute value of the breaking strength (MPa) measured in accordance with JIS K 6251 for a cured product obtained by curing the adhesive for 24 hours at 80°C

[0011] The present disclosure also relates to the above adhesive, wherein the cured product obtained by curing the adhesive for 7 days in an environment of 23°C and 50% relative humidity, or the cured product obtained by curing the adhesive for 24 hours at 80°C, has a breaking strength of 3 to 40 MPa, as measured in accordance with JIS K 6251.

[0012] The present disclosure also relates to the above adhesive, wherein the monoalcohol (E) contains a monoalcohol having an aromatic ring.

[0013] The present disclosure also relates to the adhesive, which contains 1 to 50% by mass of the monoalcohol (E) relative to 100% by mass of the polyol (C).

[0014] The present disclosure also relates to the above adhesive, wherein the polyol (C) does not include a polyester polyol.

[0015] The present disclosure also relates to the adhesive, wherein the polyol (C) includes at least one selected from the group consisting of polyether polyols, polycarbonate polyols, polybutadiene polyols, acrylic polyols, and polyurethane polyols.

[0016] The present disclosure also relates to the adhesive, wherein the polyol (C) comprises a polyol (C1) having a number average molecular weight of 2,000 or more and a polyol (C2) having a number average molecular weight of 100 or more and less than 2,000.

[0017] The present disclosure also relates to the adhesive, wherein the mass proportion of the polyol (C1) relative to the total mass of the polyol (C1) and the polyol (C2) is 10 to 70 mass%.

[0018] The present disclosure also relates to the above adhesive, wherein the polyisocyanate curing agent (B) comprises at least one selected from the group consisting of aromatic polyisocyanates, araliphatic polyisocyanates, aliphatic polyisocyanates, alicyclic polyisocyanates, and modified products thereof.

[0019] The present disclosure also relates to the above adhesive, wherein the polyisocyanate curing agent (B) comprises at least one selected from the group consisting of diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, carbodiimide-modified diphenylmethane diisocyanate, and modified products thereof.

[0020] The present disclosure also relates to the adhesive, which contains the polyol having a urethane bond in an amount ranging from 30 to 70 mass % based on the mass of the polyol.

[0021] The present disclosure also relates to a cured product obtained by curing the above adhesive.

[0022] The present disclosure also relates to a structure comprising an adhesive layer between a first substrate and a second substrate, wherein the adhesive layer is the above-described cured product.

[0023] The present disclosure provides a primerless adhesive that is suitable for bonding aluminum substrates to other substrates, and that combines high adhesive strength with cohesive failure of the adhesive and long-term resistance to moist heat.

[0024] The adhesive, its cured product, and structures according to the present disclosure are described in detail below. Other embodiments are also within the scope of the present disclosure as long as they are consistent with the spirit of the present disclosure. Furthermore, in this specification, a numerical range specified using "to" includes the numerical values ​​before and after "to" as the lower and upper limits of the range. Furthermore, a numerical value specified using "≦" includes the numerical value to the left of "≦" as the lower limit and the numerical value to the right of "≦" as the upper limit. Furthermore, in numerical ranges described in stages in this specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in numerical ranges described in this specification, the upper or lower limit of that numerical range may be replaced with a value shown in an example.

[0025] The adhesive according to the present disclosure (hereinafter also referred to as the present adhesive) comprises a polyol base (A) and a polyisocyanate curing agent (B), wherein the polyol base (A) comprises a polyol (C), a phosphoric acid compound (D), and a monoalcohol (E). By using such an adhesive, adhesion to aluminum is ensured, improving adhesive strength and enabling stable adhesive strength to be exhibited. Furthermore, the adhesive also exhibits good cohesive failure and long-term moist heat resistance.

[0026] The adhesive is preferably solvent-free, since it does not require a drying step during the curing process. However, it may contain a solvent if it contains a solvent contained in an antifoaming agent or a diluting solvent used when adding a solid additive.

[0027] From the viewpoints of adhesive strength and flexibility, the adhesive preferably has a breaking strength of 3 to 40 MPa as measured in accordance with JIS K 6251 for a cured product obtained by curing for 7 days in an environment of 23°C and 50% relative humidity, or a cured product obtained by curing for 24 hours at 80°C. From the same viewpoint, the breaking elongation as measured in accordance with JIS K 6251 is preferably 20 to 500%. From the same viewpoint, the adhesive more preferably has a breaking strength of 5 to 30 MPa, and more preferably has a breaking elongation of 50 to 300%. In particular, in fields such as automobiles, from the viewpoints of productivity and energy conservation, the breaking strength of a cured product obtained by curing for 7 days at 23°C and 50% RH is preferably 3 to 40 MPa.

[0028] <Polyol Base (A)> The polyol base (A) contains a polyol (C), a phosphoric acid compound (D), and a monoalcohol (E). The phosphoric acid compound (D) improves initial strength and adhesion to metals when cured at room temperature, ensuring adhesion to aluminum substrates and other substrates without the need for a primer, and improving adhesive strength. Furthermore, the monoalcohol (E) adjusts the degree of crosslinking of the coating film, creating a starting point for cohesive failure of the adhesive, thereby achieving stable adhesive strength.

[0029] <Polyol (C)> The polyol (C) is not particularly limited as long as it is a compound having two or more hydroxyl groups in the molecule. Examples of such polyol (C) include polyester polyols, polyether polyols, polyurethane polyols, polyesteramide polyols, acrylic polyols, polycarbonate polyols, polycaprolactone polyols, polyvalerolactone polyols, polybutadiene polyols, polyolefin polyols, polyhydroxyalkanes, castor oil, and mixtures thereof. From the viewpoint of long-term moist heat resistance, it is preferable that the polyol (C) does not contain a polyester polyol. Furthermore, from the viewpoint of long-term moist heat resistance, it is preferable that the polyol (C) is selected from the group consisting of polyether polyols, polyurethane polyols, acrylic polyols, polycarbonate polyols, and polybutadiene polyols, which have high hydrolysis resistance even when used in combination with the phosphoric acid compound (D). From the same viewpoint, it is particularly preferable that the polyol (C) contains at least one of a polyether polyol and a polycarbonate polyol. These polyols (C) may be used alone or in combination of two or more.

[0030] The polyol (C) preferably contains a polyol (C1) having a number-average molecular weight of 2,000 or more and a polyol (C2) having a number-average molecular weight of 100 or more but less than 2,000. The combined use of the polyol (C1) and the polyol (C2) makes it possible to easily achieve both the elongation and adhesive strength of the cured adhesive. The number-average molecular weight is a value measured by gel permeation chromatography (GPC) and converted into standard polystyrene.

[0031] The mass ratio of the polyol (C1) to the total mass of the polyols (C1) and (C2) is preferably 10 to 70 mass%, more preferably 10 to 50 mass%, since such a mass ratio of the polyol (C1) results in even better adhesive strength and extensibility of the cured coating film when cured at room temperature, which is preferred.

[0032] [Polyol (C1)] The polyol (C1) is not particularly limited as long as it has a number average molecular weight of at least 2,000. The upper limit of the number average molecular weight may be any value within a producible range, but as a guideline, it is preferably 200,000 or less.

[0033] The polyol (C1) preferably has a primary hydroxyl group at its terminal. Having a primary hydroxyl group at its terminal results in better initial adhesive strength at room temperature, better foaming suppression of the coating film, and better strength after curing. As the polyol (C1) having a primary hydroxyl group at its terminal, a polyol having a urethane bond in the molecule (hereinafter referred to as a urethane polyol) is preferred. By including such a urethane polyol, sagging of the adhesive when applied to a vertical surface and better extensibility of the cured coating film are suppressed.

[0034] The method for producing the urethane polyol is not particularly limited, and for example, a reaction product of a polyol and a polyisocyanate can be suitably used. As the polyol, for example, the compounds exemplified in the section on polyol (C) above can be used.

[0035] Examples of the polyisocyanate include aromatic, aliphatic, or alicyclic diisocyanates (hereinafter also referred to as polyisocyanate monomers); dimers, trimers, biurets, and allophanates derived from polyisocyanate monomers; and polyisocyanates having a 2,4,6-oxadiazinetrione ring obtained from carbon dioxide gas and the above-mentioned polyisocyanate monomers. These may be used alone or in combination of two or more.

[0036] Examples of aromatic diisocyanates include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, tolidine diisocyanate, xylylene diisocyanate, m-tetramethylxylene diisocyanate, p-tetramethylxylene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, 3,3'-dimethoxy-4,4'-biphenylene diisocyanate, 3,3'-dichloro-4,4'-biphenylene diisocyanate, and 1,5-tetrahydronaphthalene diisocyanate.

[0037] Examples of aliphatic diisocyanates include xylylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 1,2-propylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, dodecamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, lysine ester triisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate tetramethylene diisocyanate, pentamethylene diisocyanate, and trimethylhexamethylene diisocyanate.

[0038] Examples of alicyclic diisocyanates include isophorone diisocyanate, 1,3-cyclopentane diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), 1,4-bis(isocyanatomethyl)cyclohexane, hydrogenated xylylene diisocyanate, dimer acid diisocyanate, and norbornene diisocyanate.

[0039] The number average molecular weight of the urethane polyol is not particularly limited, but is preferably 3,000 to 200,000. When the number average molecular weight is 3,000 or more, the extensibility of the coating film after curing is superior, and when it is 200,000 or less, the adhesive strength when cured at room temperature and the dispenser dischargeability after mixing in adhesive coating are superior.

[0040] The polyurethane polyol may further have a urea bond in the molecule. The presence of a urea bond in the molecule improves heat resistance durability and adhesive strength. As a urethane polyol having such a urea bond, for example, a compound obtained by reacting an isocyanato group of a urethane polymer having an isocyanato group at a terminal, which is a reaction product of a polyol and a polyisocyanate, with an amino group of a monoamine compound having a molecular weight of less than 200 and having a hydroxyl group in the molecule, is preferred from the viewpoints of viscosity and sagging property during ejection and adhesive strength.

[0041] [Polyol (C2)] The polyol (C2) is not particularly limited as long as it has a number-average molecular weight of 100 or more and less than 2,000. Examples of the polyol (C2) include glycols such as 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, methylpentane glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, bishydroxyethoxybenzene, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, and triethylene glycol; polyalkylene glycols with a number-average molecular weight of 100 or more and less than 2,000; trifunctional or tetrafunctional aliphatic alcohols such as glycerin, trimethylolpropane, and pentaerythritol; and polyols in which the above-mentioned glycols or polyols are added to the above-mentioned trifunctional or tetrafunctional aliphatic alcohols. It is particularly preferable that the polyol (C2) contains a polyether polyol or a polycarbonate polyol, from the viewpoint of long-term resistance to moist heat. From the viewpoint of adhesive strength and viscosity reduction effect when cured at room temperature, it is preferable to use one polyol (C2) selected from the group consisting of 1,5-pentanediol, 3-methyl-1,5-pentanediol, and 1,6-hexanediol in combination. These polyols (C2) may be used alone or in combination of two or more.

[0042] <Phosphoric Acid Compound (D)> The phosphoric acid compound (D) may be any compound having at least one free oxygen acid. Examples of the phosphoric acid compound (D) include phosphoric acids such as hypophosphorous acid, phosphorous acid, orthophosphoric acid, and hypophosphoric acid; condensed phosphoric acids such as metaphosphoric acid, pyrophosphoric acid, tripolyphosphoric acid, polyphosphoric acid, and ultraphosphoric acid; and phosphonic acids. Derivatives of phosphoric acid compounds may also be used as the phosphoric acid compound (D). Examples of such derivatives include phosphonic acid esters, which are esters of the phosphorus oxygen acids partially esterified with an alcohol while leaving at least one free oxygen acid in the phosphorus oxygen acid. Examples of such alcohols include aliphatic alcohols such as methanol, ethanol, ethylene glycol, and glycerin; and aromatic alcohols such as phenol, xylenol, hydroquinone, catechol, and phloroglucinol. The phosphoric acid compound (D) may be used alone or in combination of two or more.

[0043] The amount of the phosphoric acid compound (D) to be added preferably satisfies at least one of the following formulae (1) and (2), from the viewpoints of achieving both adhesion to metals and cohesive failure, and suppressing hydrolysis of the cured product. (1) 0.002≦P / M≦0.1 (2) 0.002≦P / N≦0.1 P: Absolute value of the content (mass%) of the phosphoric acid compound (D) in 100 mass% of the adhesive M: Absolute value of the breaking strength (MPa) of the cured product obtained by curing the adhesive for 7 days in an environment of 23°C and 50% relative humidity, measured in accordance with JIS K 6251 N: Absolute value of the breaking strength (MPa) of the cured product obtained by curing the adhesive for 24 hours at 80°C, measured in accordance with JIS K 6251 When used in applications where materials with different linear expansion coefficients are to be bonded, such as bonding an aluminum substrate to another substrate, it is more preferable that formula (1) be satisfied. When used in applications where curing must be accelerated by heat curing during the manufacturing process, it is more preferable that formula (2) be satisfied.

[0044] <Monoalcohol (E)> The monoalcohol (E) is not particularly limited as long as it is a compound having one hydroxyl group in the molecule. The main chain of the monoalcohol (E) is not particularly limited, and examples thereof include vinyl resins, acrylic resins, polyesters, epoxy resins, and urethane resins having one hydroxyl group. Aliphatic alcohols, alkyl alkylene glycols, and the like can also be used. The main chain of the monoalcohol (E) may be linear or branched. The bonding position of the hydroxyl group is not particularly limited, but it is preferably present at the terminal of the molecular chain.

[0045] Specific examples of such monoalcohols (E) include methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, lauryl alcohol, myristyl alcohol, pentadecanol, cetyl alcohol, heptadecanol, stearyl alcohol, nonadecanol, other alkanols (C20-50), oleyl alcohol, and aliphatic monools such as isomers thereof, cyclohexanol, methyl ... cyclohexanol, 4-butylcyclohexanol, 4-pentylcyclohexanol, 4-hexylcyclohexanol, cyclodecanol, cyclododecanol, cyclopentadecanol, 4-isopropylcyclohexanol, 3,5,5-trimethylcyclohexanol, menthol, 2-norbornanol, borneol, 2-adamantanol, dicyclohexylmethanol, decitol, 2-cyclohexylcyclohexanol, 4-cyclohexylcyclohexanol, 4-(4-propanol) (4-propylcyclohexyl)cyclohexanol, 4-(4-pentylcyclohexyl)cyclohexanol, α-ambrinol, desoxycorticosterone, 11-dehydrocorticosterone, cholesterol, β-sitosterol, campesterol, stigmasterol, brassicasterol, lanosterol, ergosterol, β-cholestanol, testosterone, estrone, digitoxigenin, dehydroepiandrosterone, coprostanol, pregnenolone, epicholesterol Examples of the monoalcohol (E) include alicyclic monools such as ethanol, 7-dehydrocholesterol, estradiol benzoate, tigogenin, hecogenin, methandienone, cortisone acetate, stenolone, and isomers thereof, aromatic aliphatic monools such as benzyl alcohol, and polyoxyalkylene monools obtained by ring-opening addition polymerization of alkylene oxides such as ethylene oxide, propylene oxide, butylene oxide, and tetrahydrofuran using an alkyl compound containing one active hydrogen as an initiator. One type of monoalcohol (E) may be used alone, or two or more types may be used in combination.

[0046] Among these, from the viewpoint of adhesiveness, it is preferable to use a monoalcohol having an aromatic ring as the monoalcohol (E), and it is particularly preferable to use benzyl alcohol or phenoxyethanol.

[0047] The blending amount of the monoalcohol (E) is preferably 1 to 50% by mass, more preferably 5 to 20% by mass, based on 100% by mass of the polyol (C). When the blending amount of the monoalcohol (E) is within the above range, it becomes possible to easily achieve both stable adhesive strength and heat resistance.

[0048] <Polyisocyanate Curing Agent (B)> The polyisocyanate curing agent (B) is not particularly limited and may be, for example, an aromatic polyisocyanate, an araliphatic polyisocyanate, an aliphatic polyisocyanate, an alicyclic polyisocyanate, or a modified product thereof. These may be used alone or in combination of two or more.

[0049] Examples of modified polyisocyanates include allophanate-type modified products, isocyanurate-type modified products, biuret-type modified products, and adduct-type modified products, as well as reaction products having an isocyanate group and a urethane bond, which are obtained by reacting the above-mentioned polyisocyanate component with a polyol under conditions of excess isocyanate groups. The polyol that forms the above-mentioned modified polyisocyanate is not particularly limited and can be selected from known polyols, such as polyester polyols, polyester urethane polyols, polycarbonate polyols, polycaprolactone polyols, polyether polyols, polyether urethane polyols, polyolefin polyols, acrylic polyols, silicone polyols, castor oil-based polyols, and fluorine-based polyols.

[0050] The polyisocyanate curing agent (B) preferably contains at least one selected from the group consisting of aromatic polyisocyanates and modified products thereof, and more preferably contains at least one selected from the group consisting of diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, carbodiimide-modified diphenylmethane diisocyanate, and modified products thereof.

[0051] The polyisocyanate curing agent (B) is preferably blended so that the molar ratio [NCO / OH] of the hydroxyl groups in the polyol base resin (A) to the isocyanato groups in the polyisocyanate curing agent (B) is 0.9 to 1.5, and more preferably the molar ratio [NCO / OH] is 1.0 to 1.3.

[0052] <Filler> The adhesive may contain a known filler. Examples of fillers include inorganic fillers and organic fillers. Examples of inorganic fillers include talc, zeolite, silica, microballoons, clay, calcium carbonate, and carbon black. Examples of organic fillers include acrylic particles, carbon nanotubes, graphite, starch, natural organic fibers, and synthetic fibers. These fillers may be used alone or in combination of two or more. Among these, from the viewpoints of adhesiveness and foaming suppression, it is preferable to use talc, zeolite, and silica as fillers.

[0053] <Additives> The adhesive may further contain known additives such as reaction accelerators, silane coupling agents, leveling or defoaming agents, fillers, propellants, plasticizers, superplasticizers, wetting agents, flame retardants, viscosity modifiers, preservatives, stabilizers, and colorants. These additives may be used alone or in combination of two or more.

[0054] Examples of the reaction accelerator include metal catalysts such as dibutyltin diacetate, dibutyltin dilaurate, dioctyltin dilaurate, and dibutyltin dimaleate. The amount of the reaction accelerator added is preferably 0.005 to 1% by mass based on the total mass of the polyol.

[0055] Examples of silane coupling agents include trialkoxysilanes having a vinyl group, such as vinyltrimethoxysilane and vinyltriethoxysilane; trialkoxysilanes having an amino group, such as 3-aminopropyltriethoxysilane and N-(2-aminoethyl)3-aminopropyltrimethoxysilane; trialkoxysilanes having a glycidyl group, such as 3-glycidoxypropyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane and 3-glycidoxypropyltriethoxysilane; trialkoxysilanes having an isocyanato group, such as 3-isocyanatepropyltriethoxysilane; and trialkoxysilanes having a mercapto group, such as 3-mercaptopropylmethyldimethoxysilane and 3-mercaptopropyltrimethoxysilane. The amount of silane coupling agent added is preferably 0.05 to 10% by mass, based on the total mass of the adhesive.

[0056] Examples of leveling agents include polyether-modified polydimethylsiloxane, polyester-modified polydimethylsiloxane, aralkyl-modified polymethylalkylsiloxane, polyester-modified hydroxyl group-containing polydimethylsiloxane, polyetherester-modified hydroxyl group-containing polydimethylsiloxane, acrylic copolymer, methacrylic copolymer, polyether-modified polymethylalkylsiloxane, acrylic acid alkyl ester copolymer, methacrylic acid alkyl ester copolymer, and lecithin.

[0057] Examples of the antifoaming agent include known antifoaming agents such as silicone resin, silicone solution, copolymers of alkyl vinyl ether, alkyl acrylate ester and alkyl methacrylate ester.

[0058] Examples of the plasticizer include known plasticizers such as phthalate ester compounds, alkylsulfonate ester compounds, adipate ester compounds, partially hydrogenated terpenes, trioctyl phosphate, and epoxy plasticizers.

[0059] <Cured Product> The cured product according to the present disclosure (hereinafter also referred to as the present cured product) is obtained by curing the present adhesive. For example, the present cured product can be obtained by curing the present adhesive at 23°C and 50% relative humidity for 7 days or at 80°C for 24 hours.

[0060] <Structure> The structure according to the present disclosure (hereinafter also referred to as the present structure) is characterized by comprising an adhesive layer between a first substrate and a second substrate, the adhesive layer being the present cured product. The method for producing the present structure is not particularly limited. For example, the present structure can be obtained by applying the present adhesive to one surface of the first substrate, then placing a second substrate on the uncured adhesive surface, and carrying out a curing reaction at approximately 20 to 80°C to cure the present adhesive. The thickness of the adhesive layer after curing is preferably 0.1 μm to 300 mm.

[0061] <First Substrate, Second Substrate> The present adhesive can be used to bond a wide variety of substrates. Suitable substrates that can be used as the first and second substrates include, for example, metals such as aluminum, thermoplastic polymers such as polyethylene, polypropylene, polyurethane, polyacrylate, polycarbonate, and copolymers thereof, thermosetting polymers such as vulcanized rubber, urea-formaldehyde foam, melamine resin, wood, carbon fiber reinforced plastic, glass fiber reinforced plastic, and other fiber reinforced plastics. The first substrate and second substrate may be the same or different.

[0062] This adhesive does not require a primer and achieves both high adhesive strength and cohesive failure of the adhesive on aluminum substrates. Structures using this adhesive are useful as structural components (panel parts, frame parts, suspension parts, etc.) for automobiles, building materials, ships, aircraft, and other transportation equipment.

[0063] The adhesive will be described in more detail below using examples, but the following examples are not intended to limit the scope of the present disclosure. Unless otherwise specified, "parts" and "%" in the examples represent "parts by mass" and "% by mass."

[0064] <Average Molecular Weight> The number average molecular weight (Mn) and mass average molecular weight (Mw) of each component were determined by gel permeation chromatography (GPC) as converted values ​​using standard polystyrene. Measurements were performed using a GPC-8020 (manufactured by Tosoh Corporation) GPC apparatus, tetrahydrofuran as an eluent, and three TSKgel Super HM-M (manufactured by Tosoh Corporation) columns connected in series, under conditions of a flow rate of 0.6 ml / min, an injection volume of 10 μl, and a column temperature of 40°C.

[0065] Abbreviations for compounds used in this specification are as follows: <Polyols> P-1000: bifunctional polypropylene glycol, number average molecular weight 1,000, manufactured by ADEKA Corporation GI-2000: polybutadiene polyol, number average molecular weight 2,000, manufactured by Nippon Soda Co., Ltd. UH-2041: acrylic polyol, number average molecular weight 2,500, manufactured by Toagosei Co., Ltd. T5652: bifunctional polycarbonate polyol, number average molecular weight 2,000, trade name "Duranol T5652", manufactured by Asahi Kasei Corporation T5651: bifunctional polycarbonate polyol, number average molecular weight 1,000, trade name "Duranol T5650E", manufactured by Asahi Kasei Corporation T5650E: bifunctional polycarbonate polyol, number average molecular weight 500, trade name "Duranol T5650E", manufactured by Asahi Kasei Corporation P-400: Bifunctional polypropylene glycol, number average molecular weight 400, manufactured by ADEKA Corporation. P-2000: Bifunctional polypropylene glycol, number average molecular weight 2,000, manufactured by ADEKA Corporation. T-400: Trifunctional polypropylene glycol, number average molecular weight 400, manufactured by Mitsui Chemicals, Inc. TMP: Trimethylolpropane.

[0066] <Polyisocyanate> TDI: Tolylene diisocyanate XDI: Xylylene diisocyanate IPDI: Isophorone diisocyanate 4,4'-MDI: 4,4'-diphenylmethane diisocyanate Liquid MDI: Millionate NM, manufactured by Tosoh Corporation Crude MDI: PM-200, manufactured by Wanka Chemical Co., Ltd.

[0067] <Epoxy plasticizers> JP-100: Epoxidized polybutadiene, manufactured by Nippon Soda Co., Ltd. O-130P: Epoxidized soybean oil, manufactured by ADEKA Corporation

[0068] <Synthesis of Polyol (C1-1) Having a Number Average Molecular Weight of 2,000 or More> (Polyol (C1-1)) A reaction vessel equipped with a nitrogen gas inlet tube, a stirrer, a thermometer, and a reflux condenser was charged with 100 parts of T5651 as a polyol and 13.7 parts of tolylene diisocyanate, and after stirring uniformly, the mixture was reacted at 110°C for 5 hours under a nitrogen atmosphere to obtain a urethane-modified polyol (C1-1) having a number average molecular weight of 5,000.

[0069] (Polyol (C1-2)) A reaction vessel was charged with 100 parts of T5651 as a polyol and 30.5 parts of isophorone diisocyanate, and after uniform stirring, the mixture was reacted for 5 hours at 90°C under a nitrogen atmosphere to obtain a urethane prepolymer. Next, the mixture was cooled to 80°C, and 4.8 parts of ethanolamine was added, and the mixture was reacted for 2 hours at 75°C to obtain a polyurethane urea polyol (C1-2) having a number average molecular weight of 6,000.

[0070] (Polyol (C1-3)) A reaction vessel was charged with 100 parts of P-1000 as a polyol and 13.9 parts of tolylene diisocyanate TDI, and the mixture was reacted at 110°C for 5 hours under a nitrogen atmosphere, to obtain a urethane-modified polyol (C1-3) having a number average molecular weight of 5,000.

[0071] (Polyol (C1-4)) A reaction vessel was charged with 100 parts of P-1000 as a polyol and 30.5 parts of isophorone diisocyanate, and after uniform stirring, the mixture was reacted for 5 hours at 90°C under a nitrogen atmosphere to obtain a urethane prepolymer. Next, the mixture was cooled to 80°C, 4.8 parts of ethanolamine was added, and the mixture was reacted for 2 hours at 75°C to obtain a polyurethane urea polyol (C1-4) having a number average molecular weight of 6,500.

[0072] <Production of Polyol Base> (Polyol Base A1) To 20 parts of urethane-modified polyol (C1-1), 80 parts of T5651, 5 parts of 3-methyl-5-pentanediol, 5 parts of benzyl alcohol, 0.5 parts of 3-glycidoxypropyltrimethoxysilane, 1 part of polyphosphoric acid, and 100 parts of talc were added, and the mixture was stirred and degassed using a planetary centrifugal mixer (Awatori Rentaro, manufactured by Thinky Corporation), to obtain polyol base A1.

[0073] (Polyol bases A2 to A23, A'1 to A'3) Except for changing the compounding ratio of each component to that shown in Tables 1 and 2, polyol bases A2 to A23 and A'1 to A'3 were obtained by mixing in the same manner as polyol base A1.

[0074]

[0075]

[0076] <Production of Polyisocyanate Curing Agent> (Polyisocyanate Curing Agent B1) A reaction vessel was charged with 12.5 parts of P-400, 12.6 parts of P-2000, and 1.7 parts of T-400, and after stirring uniformly, 31.2 parts of 4,4'-MDI was charged and reacted for 3 hours at 90°C under a nitrogen atmosphere to carry out a urethane reaction. After cooling to 50°C, 30 parts of crude MDI, 12 parts of liquid MDI, and 10 parts of JP-100 were added and stirred for 15 minutes to obtain polyisocyanate curing agent (B1).

[0077] (Polyisocyanate curing agent B2) A reaction vessel was charged with 7.6 parts of P-400 and 6.1 parts of TMP and stirred uniformly, after which 76.3 parts of liquid MDI was charged and reacted for 3 hours at 90°C under a nitrogen atmosphere to carry out a urethane reaction. After that, the mixture was cooled to 50°C, and 10 parts of crude MDI and 10 parts of JP-100 were added and stirred for 15 minutes to obtain polyisocyanate curing agent (B2).

[0078] (Polyisocyanate curing agent B3) A reaction vessel was charged with 23.4 parts of P-400 and 46.6 parts of 4,4'-MDI, and the mixture was reacted for 3 hours at 90°C under a nitrogen atmosphere to carry out a urethane reaction. After that, the mixture was cooled to 50°C, and 18 parts of crude MDI, 12 parts of liquid MDI, and 10 parts of JP-100 were added and stirred for 15 minutes to obtain polyisocyanate curing agent (B3).

[0079] (Polyisocyanate curing agent B4) A reaction vessel was charged with 23.4 parts of P-400 and 46.6 parts of 4,4'-MDI, and the mixture was reacted for 3 hours at 90°C under a nitrogen atmosphere to carry out a urethane reaction. After that, the mixture was cooled to 50°C, and 18 parts of crude MDI, 12 parts of liquid MDI, and 10 parts of O-130P were added and stirred for 15 minutes to obtain polyisocyanate curing agent (B4).

[0080] (Polyisocyanate curing agent B5) A reaction vessel was charged with 14.4 parts of P-400, 14.6 parts of P-2000, and 1.9 parts of T-400, and after uniform stirring, 27.1 parts of XDI was charged and reacted at 90°C for 3 hours under a nitrogen atmosphere to carry out a urethane reaction. After cooling to 50°C, 30 parts of crude MDI, 12 parts of liquid MDI, and 10 parts of JP-100 were added and stirred for 15 minutes to obtain polyisocyanate curing agent (B5). The formulation of each curing agent is shown in Table 3 below.

[0081]

[0082] <Preparation of Adhesive> [Examples 1 to 28, Comparative Examples 1 to 3]

[0083] The polyol base agent and the polyisocyanate curing agent were mixed with stirring at room temperature in the formulations shown in Tables 4 and 5 to prepare the respective adhesives.

[0084] [Preparation of test pieces for measuring breaking strength and breaking elongation] A 2 mm thick mold was filled with the adhesive prepared in each example, the surface was smoothed, and the adhesive was cured under one of the conditions shown below, and then punched out with a No. 3 dumbbell mold to prepare test pieces. See Tables 4 and 5 for the curing conditions of each example. Curing condition I: Cured for 7 days in an environment of 23°C and 50% relative humidity. Curing condition II: Cured for 24 hours at 80°C.

[0085] [Break Strength and Break Elongation of Cured Coating Film] Using the test pieces obtained above, tensile tests were performed at a tensile speed of 500 mm / min in an environment of 25°C to measure break strength (MPa) and break elongation (%) in accordance with JIS K 6251. The results are shown in Tables 4 and 5.

[0086] <Evaluation of Adhesive> The adhesive obtained was evaluated as follows. The results are shown in Tables 4 and 5.

[0087] [Adhesion to Aluminum Substrate] Each adhesive obtained was applied to an aluminum A5052 substrate (length 100 mm, width 25 mm, thickness 2 mm) to a width of 25 mm, length 10 mm, and thickness of 0.3 mm. The adhesive was then bonded to the same aluminum A5052 substrate and pressed to maintain a thickness of 0.3 mm. The adhesive was cured for 7 days at 23°C and a relative humidity of 50%, or cured and aged for 24 hours at 80°C to obtain a test specimen. The shear adhesive strength of the obtained test specimen was measured using a tensile tester at 25°C and a pulling rate of 10 mm / min. (Evaluation Criteria) A: Shear adhesive strength of 20 MPa or more (very good) B: Shear adhesive strength of 10 MPa or more but less than 20 MPa (good) C: Shear adhesive strength of 3 MPa or more but less than 10 MPa (usable) D: Shear adhesive strength of less than 3 MPa (unusable)

[0088] [Cohesive Failure] After the evaluation of [Adhesion to Aluminum Substrate] above, the test piece was visually inspected, and the percentage of the area where the adhesive had cohesively failed and remained on the test piece was evaluated as the cohesive failure rate. (Evaluation Criteria) A: Cohesive failure rate of 80% or more (very good) B: Cohesive failure rate of 60% or more but less than 80% (good) C: Cohesive failure rate of 40% or more but less than 60% (usable) D: Cohesive failure rate of less than 40% (unusable)

[0089] [Long-term moist heat resistance] Test pieces prepared in the same manner as in [Adhesion to aluminum substrate] above were stored for 1000 hours in an environment of 85°C and 85% relative humidity. For the test pieces before and after storage, the shear strength was measured using a tensile tester at a tensile speed of 10 mm / min under conditions of 25°C, and the shear strength retention was calculated using the following formula, and the long-term moist heat resistance was evaluated according to the following criteria: Shear strength retention (%) = (shear strength after storage / shear strength before storage) x 100 A: Shear strength retention of 75% or more (good) B: Shear strength retention of 50% or more but less than 75% (usable) C: Shear strength retention of less than 50% (unusable)

[0090]

[0091]

[0092] According to Tables 4 and 5, the adhesive, which uses a combination of a polyol base containing a polyol, a phosphoric acid compound, and a monoalcohol, with a polyisocyanate curing agent, achieved the following effects: During use, the phosphoric acid compound contained in the adhesive provided high adhesion to aluminum, and the monoalcohol provided the starting point for cohesive failure of the adhesive, thereby providing stable adhesive strength.

[0093] The present disclosure is not limited to the above-described embodiment, and can be appropriately modified without departing from the spirit and scope of the present disclosure. Furthermore, the present disclosure may be implemented by appropriately combining the above-described embodiment and examples thereof.

[0094] This application claims priority based on Japanese Patent Application No. 2023-188430, filed November 2, 2023, the disclosure of which is incorporated herein by reference in its entirety.

Claims

1. An adhesive comprising a polyol base agent (A) and a polyisocyanate curing agent (B), the polyol base agent (A) comprising a polyol (C), a phosphoric acid compound (D) and a monoalcohol (E).

2. The adhesive according to claim 1, which satisfies at least one of the following formulas (1) and (2): (1) 0.002≦P / M≦0.1 (2) 0.002≦P / N≦0.1 P: absolute value of the content (mass%) of the phosphoric acid compound (D) in 100 mass% of the adhesive M: absolute value of the breaking strength (MPa) of the cured product obtained by curing the adhesive for 7 days in an environment of 23°C and relative humidity of 50%, measured in accordance with JIS K 6251 N: absolute value of the breaking strength (MPa) of the cured product obtained by curing the adhesive for 24 hours at 80°C, measured in accordance with JIS K 6251 3. The adhesive according to claim 2, wherein the cured product obtained by curing the adhesive at 23°C and a relative humidity of 50% for 7 days or the cured product obtained by curing the adhesive at 80°C for 24 hours has a breaking strength of 3 to 40 MPa, as measured in accordance with JIS K 6251.

4. The adhesive according to any one of claims 1 to 3, wherein the monoalcohol (E) contains a monoalcohol having an aromatic ring.

5. The adhesive according to any one of claims 1 to 4, comprising 1 to 50 mass% of the monoalcohol (E) relative to 100 mass% of the polyol (C).

6. The adhesive according to any one of claims 1 to 5, wherein the polyol (C) does not include a polyester polyol.

7. The adhesive according to any one of claims 1 to 6, wherein the polyol (C) comprises at least one selected from the group consisting of polyether polyols, polycarbonate polyols, polybutadiene polyols, acrylic polyols, and polyurethane polyols.

8. The adhesive according to any one of claims 1 to 7, wherein the polyol (C) comprises a polyol (C1) having a number average molecular weight of 2,000 or more, and a polyol (C2) having a number average molecular weight of 100 or more and less than 2,000.

9. The adhesive according to claim 8, wherein the mass ratio of the polyol (C1) to the total mass of the polyol (C1) and the polyol (C2) is 10 to 70 mass %.

10. The adhesive according to any one of claims 1 to 9, wherein the polyisocyanate curing agent (B) comprises at least one member selected from the group consisting of aromatic polyisocyanates, araliphatic polyisocyanates, aliphatic polyisocyanates, alicyclic polyisocyanates, and modified products thereof.

11. The adhesive according to claim 10, wherein the polyisocyanate curing agent (B) comprises at least one member selected from the group consisting of diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, carbodiimide-modified diphenylmethane diisocyanate, and modified versions thereof.

12. A cured product obtained by curing the adhesive according to any one of claims 1 to 11.

13. A structure comprising an adhesive layer between a first substrate and a second substrate, the adhesive layer being the cured product according to claim 12.

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