Adhesive, cured product of the same and structure

Abstract

To provide an adhesive which achieves high adhesive strength without a primer and cohesive fracture and long-term moisture heat resistance of an adhesive and is suitable for bonding an aluminum substrate and other substrate.SOLUTION: The combination use of a polyol main agent containing a polyol, a phosphoric acid-based compound and a mono-alcohol and a polyisocyanate curing agent secures adhesiveness to aluminum by the phosphoric acid-based compound when the adhesive is used, thereby improving adhesive strength. In addition, stable adhesive strength can be exhibited by creating the starting point of cohesive fracture of an adhesive by adjusting the cross-linking degree of a coating film by a mono-alcohol.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] In recent years, in the fields of automobiles and aircraft, the proportion of lightweight materials used, such as light metals such as 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, there is a problem that the difference in the expansion coefficients between the materials caused by temperature changes during the manufacturing process or the temperature environment in which they are used places high stress on the adhesive layer, accelerating the destruction or deterioration of the adhesive layer. For this reason, methods of imparting flexibility to adhesives have been widely studied as a way to design stress relief, and urethane adhesives that combine high adhesive strength and flexibility have attracted attention.

[0003] When using urethane adhesives, a pretreatment step must generally be performed by applying a primer or activator to the substrate to promote long-term adhesion of the adhesive composition. In the automotive and other fields, from the standpoint of productivity and safety, it is required to achieve both sufficient adhesive strength without primers and cohesive failure of the adhesive, but conventional urethane adhesives cannot achieve sufficient adhesive strength without primers, resulting in interfacial failure of the adhesive.

[0004] For example, Patent Document 1 discloses a solvent-free urethane adhesive composition with 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 uses a polyol component containing a macropolyol with a number average molecular weight of 500 to 10,000 and an average number of hydroxyl groups of 1.9 to 4.0, so the crosslink density is high, and as a result of the inventors' investigation, there is a problem that it does not cause cohesive failure on aluminum substrates.

[0005] For example, Patent Document 2 discloses a primerless adhesive consisting of an adhesive composition containing a urethane prepolymer and a monofunctional alkylene glycol. However, because it is a one-component type, it cures slowly, and the inventors' investigations revealed that it has low adhesive strength to aluminum substrates.

[0006] For example, Patent Document 3 discloses a primerless adhesive consisting of a base agent containing a urethane prepolymer and a curing agent cured product containing a compound having an active hydrogen group, and discloses that the adhesive is bonded to a polypropylene substrate by flame treatment. However, as a result of the inventors' investigation, it became clear that the adhesive strength to an aluminum substrate is low in the primerless adhesive even when flame treatment is performed. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2021 / 132094 [Patent Document 2] Special table number 2021-528524 [Patent Document 3] International Publication No. 2018 / 100674 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide an adhesive which is suitable for bonding an aluminum substrate to another substrate, and which is primer-free and which combines high adhesive strength with cohesive failure and long-term resistance to moist heat. [Means for solving the problem]

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

[0010] The present invention also relates to the above adhesive, which satisfies at least one of the following formulae (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: The absolute breaking strength (MPa) of the adhesive cured for 7 days at 23°C and 50% relative humidity, measured according to JIS K 6251. N: The absolute value of the breaking strength (MPa) of the adhesive cured at 80°C for 24 hours, measured in accordance with JIS K 6251

[0011] The present invention also relates to the above adhesive, wherein a cured product obtained by curing the adhesive for 7 days in an environment of 23°C and a relative humidity of 50% or a 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 invention also relates to the above adhesive, wherein the monoalcohol (E) contains a monoalcohol having an aromatic ring.

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

[0014] The present invention also relates to the above adhesive, wherein the polyol (C) contains a polyether polyol or a polycarbonate polyol.

[0015] The present invention 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.

[0016] The present invention also relates to the above adhesive, 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 %.

[0017] The present invention also relates to the above adhesive, which contains the polyol having a urethane bond in a range of 30 to 70 mass % based on the mass of the polyol.

[0018] The present invention also relates to a cured product obtained by curing the above adhesive.

[0019] The present invention also relates to a structure comprising an adhesive layer between a first substrate and a second substrate, the adhesive layer being the above-mentioned cured product. Effect of the Invention

[0020] The present invention provides an adhesive that is suitable for bonding an aluminum substrate to another substrate, and that is primer-free and combines high adhesive strength with cohesive failure and long-term resistance to moist heat. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The present invention will be described in detail below. Other embodiments are also included in the scope of the present invention as long as they are consistent with the gist of the present invention. In addition, a numerical range specified using "~" in this specification includes the numerical values ​​before and after "~" as the lower limit and upper limit range. In addition, a numerical value specified using "≦" includes the numerical value written to the left of "≦" as the lower limit and the numerical value written to the right of "≦" as the upper limit.

[0022] <Adhesive> The adhesive of the present invention comprises a polyol base agent (A) and a polyisocyanate curing agent (B), and is characterized in that the polyol base agent (A) contains a polyol (C), a phosphoric acid compound (D), and a monoalcohol (E). By using such an adhesive, adhesion to aluminum is ensured, and the adhesive strength is improved and stable adhesive strength can be exerted.

[0023] The adhesive of the present invention is preferably solvent-free since it does not require a drying step in the curing process. However, there is no problem if the adhesive contains a solvent such as that contained in an antifoaming agent or a dilution solvent used when adding a solid additive.

[0024] From the viewpoint of adhesive strength and flexibility, the adhesive of the present invention 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 relative humidity of 50% or for a cured product obtained by curing for 24 hours at 80°C. Also, the breaking elongation of the adhesive of the present invention is preferably 20 to 500% as measured in accordance with JIS K 6251. More preferably, the breaking strength is 5 to 30 MPa and the breaking elongation is 50 to 300%, respectively. Particularly in the field of automobiles and the like, from the viewpoints of productivity and energy saving, it is preferable that the breaking strength of the cured product obtained after being left at 23° C. and 50% RH for 7 days is 3 to 40 MPa.

[0025] <Polyol base (A)> The polyol base (A) contains 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, and ensures adhesion to aluminum substrates and other substrates without the need for a primer, improving adhesive strength. In addition, the monoalcohol (E) adjusts the degree of crosslinking in the coating film to create the starting point for cohesive failure of the adhesive, allowing for stable adhesive strength.

[0026] <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 polyols (C) that can be used 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 resistance to moist heat, the polyol (C) is preferably selected from the group consisting of polyether polyol, polyurethane polyol, acrylic polyol, polycarbonate polyol and polybutadiene polyol. In particular, it is preferable to include at least one of polyether polyol and polycarbonate polyol. These polyols (C) may be used alone or in combination of two or more kinds.

[0027] 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 and less than 2,000. By using the polyol (C1) and the polyol (C2) in combination, it is possible to achieve both good elongation and good adhesive strength of the cured product of the adhesive. The number average molecular weight is a value measured by gel permeation chromatography (GPC) and converted into a polystyrene standard.

[0028] 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%, which is preferable because such a mass ratio of the polyol (C1) results in excellent adhesive strength at room temperature curing and excellent extensibility of the cured coating film.

[0029] [Polyol (C1)] The polyol (C1) is not particularly limited as long as it has a number average molecular weight of at least 2000. The upper limit of the number average molecular weight may be within a producible range, but as a guideline, it is preferably 200,000 or less.

[0030] The polyol (C1) preferably has a primary hydroxyl group at the end. If the polyol has a primary hydroxyl group at the end, the initial adhesive strength at room temperature, the foaming inhibition of the coating film, and the strength after curing are excellent. As the polyol (C1) having a primary hydroxyl group at the end, a polyol having a urethane bond in the molecule (hereinafter, urethane polyol) is preferable. By containing such a urethane polyol, the adhesive is prevented from sagging when applied to a vertical surface, and the cured coating film has excellent extensibility.

[0031] 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.

[0032] 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 polyisocyanate monomers. These may be used alone or in combination of two or more.

[0033] 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.

[0034] Examples of the aliphatic diisocyanate include 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.

[0035] 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(isocyanatemethyl)cyclohexane, hydrogenated xylylene diisocyanate, dimer acid diisocyanate, and norbornene diisocyanate.

[0036] 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 coating film after curing is excellent in extensibility, 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 excellent.

[0037] The polyurethane polyol may further have a urea bond in the molecule. By having a urea bond in the molecule, heat resistance durability and adhesive strength are improved. As the 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 preferable from the viewpoints of viscosity and sagging property during ejection and adhesive strength.

[0038] [Polyol (C2)] The polyol (C2) is not limited in any way as long as it is a polyol (C2) having a number average molecular weight of 100 or more and less than 2,000. For example, 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 having 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; and the like can be used. In particular, from the viewpoint of long-term wet heat resistance, it is preferable to contain polyether polyol or polycarbonate polyol, and from the viewpoint of adhesive strength and viscosity reduction effect at room temperature curing, it is preferable to use one 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 kinds.

[0039] <Phosphate Compounds (D)> The phosphoric acid compound (D) may be any compound having at least one free oxygen acid, and examples thereof 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. Also, a derivative of a phosphoric acid compound may be used as the phosphoric acid compound (D). Examples of such derivatives include phosphonic acid esters, which are partially esterified with alcohol in a state where at least one free oxygen acid remains in the oxygen acid of phosphorus. Examples of the alcohol include aliphatic alcohols such as methanol, ethanol, ethylene glycol, and glycerin; aromatic alcohols such as phenol, xylenol, hydroquinone, catechol, and phloroglucinol; and the like. The phosphoric acid compound (D) may be used alone or in combination of two or more kinds.

[0040] The amount of the phosphoric acid compound (D) to be blended 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: The absolute breaking strength (MPa) of the adhesive cured for 7 days at 23°C and 50% relative humidity, measured according to JIS K 6251. N: The absolute value of the breaking strength (MPa) of the adhesive cured at 80°C for 24 hours, measured in accordance with JIS K 6251 When the adhesive is used for bonding materials with different linear expansion coefficients, such as bonding an aluminum substrate to another substrate, it is more preferable that the adhesive satisfies formula (1). When the adhesive is used for applications requiring accelerated curing by heating during the manufacturing process, it is more preferable that the adhesive satisfies formula (2).

[0041] <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 and alkyl alkylene glycols 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 end of the molecular chain.

[0042] 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 isomers thereof, aliphatic monools, 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, decatol, 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 polyoxyalkylene monools include polyoxyalkylene monools obtained by ring-opening addition polymerization of alkylene oxides such as ethylene oxide, propylene oxide, butylene oxide, and tetrahydrofuran using as an initiator 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 alkyl compounds containing one active hydrogen atom. The monoalcohol (E) may be used alone or in combination of two or more kinds.

[0043] Among these, from the viewpoint of adhesion, aromatic monoalcohols are preferred, and it is particularly preferred to use benzyl alcohol or phenoxyethanol.

[0044] The blending amount of the monoalcohol (E) is preferably 1 to 50 mass %, and more preferably 5 to 20 mass %, based on 100 mass % of the polyol (C). When the amount of the monoalcohol (E) is within the above range, it is possible to achieve both stable adhesive strength and heat resistance.

[0045] <Polyisocyanate hardener (B)> The polyisocyanate curing agent (B) is not particularly limited, and examples thereof include aromatic polyisocyanates, araliphatic polyisocyanates, aliphatic polyisocyanates, alicyclic polyisocyanates, and modified products thereof. These may be used alone or in combination of two or more.

[0046] Examples of the modified polyisocyanate include allophanate modified products, isocyanurate modified products, biuret modified products, adduct modified products, and reaction products having an isocyanate group and a urethane bond, which are produced by reacting the polyisocyanate component with a polyol under conditions of excess isocyanate group. The polyol forming the 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.

[0047] The polyisocyanate curing agent (B) preferably contains an aromatic polyisocyanate, and more preferably contains at least one selected from the group consisting of diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, and carbodiimide-modified diphenylmethane diisocyanate.

[0048] The polyisocyanate curing agent (B) is preferably blended so that the molar ratio [NCO / OH] of the hydroxyl groups in the polyol base agent (A) to the isocyanato groups in the polyisocyanate curing agent (B) is 0.9 to 1.5, and more preferably [NCO / OH] is 1.0 to 1.3.

[0049] <Filler> The adhesive of the present invention may contain a known filler, such as an inorganic filler or an organic filler. 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 them, talc, zeolite, and silica are preferably used from the viewpoints of adhesion and foaming inhibition.

[0050] <Additives> The adhesive of the present invention 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. Such additives may be used alone or in combination of two or more.

[0051] Examples of the reaction accelerator include metal catalysts such as dibutyltin diacetate, dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin dimaleate, etc. The amount of the reaction accelerator is preferably 0.005 to 1% by mass based on the total mass of the polyol.

[0052] Examples of the silane coupling agent 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 the silane coupling agent added is preferably 0.05 to 10% by mass based on the total mass of the adhesive.

[0053] Examples of the leveling agent include polyether-modified polydimethylsiloxane, polyester-modified polydimethylsiloxane, aralkyl-modified polymethylalkylsiloxane, polyester-modified hydroxyl group-containing polydimethylsiloxane, polyetherester-modified hydroxyl group-containing polydimethylsiloxane, acrylic copolymers, methacrylic copolymers, polyether-modified polymethylalkylsiloxane, acrylic acid alkyl ester copolymers, methacrylic acid alkyl ester copolymers, and lecithin.

[0054] Examples of the defoaming agent include known ones such as silicone resin, silicone solution, copolymers of alkyl vinyl ether, alkyl acrylate, and alkyl methacrylate.

[0055] 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.

[0056] <Cured product> The cured product is obtained by curing the adhesive of the present invention, for example, by curing the adhesive of the present invention for 7 days in an environment of 23° C. and relative humidity of 50%, or by curing at 80° C. for 24 hours.

[0057] <Structure> The structure is characterized by having an adhesive layer between a first substrate and a second substrate, the adhesive layer being the above-mentioned cured product. The method for producing the structure is not particularly limited, and for example, the adhesive is applied to one surface of the first substrate, and then the second substrate is placed on the uncured adhesive surface, and a curing reaction is carried out at about 20 to 80°C to cure the adhesive, thereby obtaining the structure. The thickness of the adhesive layer after curing is preferably 0.1 μm to 300 mm.

[0058] <First base material, second base material> The adhesive of the present invention can be used for bonding between various kinds of substrates. Substrates that can be used as suitable first and second substrates include, for example, metals such as aluminum, thermoplastic polymers such as polyethylene, polypropylene, polyurethane, polyacrylate, polycarbonate and their copolymers, 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 the second substrate can be the same or different.

[0059] The adhesive of the present invention achieves both high adhesive strength and cohesive failure of the adhesive without the need for a primer when used on aluminum substrates, and structures using the adhesive are useful as structural members (panel parts, skeletal parts, suspension parts, etc.) for automobiles, building materials, ships, aircraft, and other transportation equipment. EXAMPLES

[0060] The present invention will be described in more detail below with reference to examples, but the following examples are not intended to limit the scope of the invention. In the examples, "parts" and "%" refer to "parts by mass" and "% by mass" unless otherwise specified.

[0061] <Average molecular weight (Mn)> The number average molecular weight (Mn) and mass average molecular weight (Mw) of the resin were determined by gel permeation chromatography (GPC) using standard polystyrene as the conversion value. The measurements were performed using a GPC-8020 (Tosoh Corporation) as the GPC device, tetrahydrofuran as the eluent, and three TSKgel SuperHM-M (Tosoh Corporation) columns connected in series under the conditions of a flow rate of 0.6 ml / min, an injection volume of 10 μl, and a column temperature of 40°C.

[0062] The abbreviations for compounds used in this specification are shown below. <Polyol> P-1000: Bifunctional polypropylene glycol, number average molecular weight 1,000, manufactured by ADEKA GI-2000: Polybutadiene polyol, number average molecular weight 2,000, manufactured by Nippon Soda Co., Ltd. · T5652; Bifunctional polycarbonate polyol, number average molecular weight 2000, product name "Duranol T5652", manufactured by Asahi Kasei Corporation · T5651; Bifunctional polycarbonate polyol, number average molecular weight 1000, product name "Duranol T5650E", manufactured by Asahi Kasei Corporation T5650E: Bifunctional polycarbonate polyol, number average molecular weight 500, product name "Duranol T5650E", manufactured by Asahi Kasei Corporation P-400: Bifunctional polypropylene glycol, number average molecular weight 400, manufactured by ADEKA P-2000: Bifunctional polypropylene glycol, number average molecular weight 2,000, manufactured by ADEKA T-400: Trifunctional polypropylene glycol, number average molecular weight 400, manufactured by Mitsui Chemicals ·TMP: Trimethylolpropane

[0063] <Polyisocyanate> ·TDI: Tolylene diisocyanate IPDI: Isophorone diisocyanate ·4,4'-MDI: 4,4'-diphenylmethane diisocyanate Liquid MDI: Millionate MN, manufactured by Tosoh Corporation Crude MDI: PM-200, manufactured by Wanhua Chemical

[0064] <Epoxy plasticizer> JP-100: Epoxidized polybutadiene, manufactured by Nippon Soda Co., Ltd. O-130P: Epoxidized soybean oil, manufactured by ADEKA

[0065] <Synthesis of polyol (C1-1) with 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 uniform stirring, the mixture was reacted for 5 hours at 110°C under a nitrogen atmosphere to obtain a urethane polyol (C1-1) having a number average molecular weight of 5,000.

[0066] (Polyol (C1-2)) In a reaction vessel, 100 parts of T5651 as a polyol and 30.5 parts of isophorone diisocyanate were charged, and after uniform stirring, the mixture was reacted at 90°C for 5 hours under a nitrogen atmosphere to obtain a urethane prepolymer. Next, the mixture was cooled to 80°C, 4.8 parts of ethanolamine were added, and the mixture was reacted at 75°C for 2 hours to obtain a polyurethane urea polyol (C1-2) having a number average molecular weight of 6,000.

[0067] (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 reacted at 110° C. for 5 hours under a nitrogen atmosphere, to obtain a urethane polyol (C1-3) having a number average molecular weight of 5,000.

[0068] (Polyol (C1-4)) In a reaction vessel, 100 parts of P-1000 as a polyol and 30.5 parts of isophorone diisocyanate were charged, and after uniform stirring, the mixture was reacted at 90°C for 5 hours 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 at 75°C for 2 hours to obtain a polyurethane urea polyol (C1-4) having a number average molecular weight of 6,500.

[0069] <Production of polyol base material> (Polyol base A1) To 20 parts of urethane polyol (C1-1), 80 parts of T5651, 5 parts of methylpentanediol, 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 agent A1.

[0070] (Polyol base A2-A22, A'1-A'3) Except for changing the compounding ratio of each component to that shown in Tables 1 and 2, the components were mixed in the same manner as for polyol base A1, to obtain polyol bases A2 to A22 and A'1 to A'3.

[0071] [Table 1]

[0072] [Table 2]

[0073] <Production of polyisocyanate curing agent> (Polyisocyanate hardener B1) In a reaction vessel, 12.5 parts of P-400, 12.6 parts of P-2000, and 1.7 parts of T-400 were charged and stirred uniformly, after which 31.2 parts of 4,4'-MDI was charged and reacted at 90°C for 3 hours under a nitrogen atmosphere to carry out a urethane reaction. After that, it was cooled to 50°C, and 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 a polyisocyanate curing agent (B1).

[0074] (Polyisocyanate hardener B2) In a reaction vessel, 7.6 parts of P-400 and 6.1 parts of TMP were charged and stirred uniformly, then 76.3 parts of liquid MDI were charged and reacted at 90°C for 3 hours under a nitrogen atmosphere to carry out a urethane reaction. After that, it 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 a polyisocyanate curing agent (B2).

[0075] (Polyisocyanate hardener B3) A reaction vessel was charged with 23.4 parts of P-400 and 46.6 parts of 4,4'-MDI, and reacted at 90°C for 3 hours under a nitrogen atmosphere to carry out a urethane reaction. After that, it 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 a polyisocyanate curing agent (B3).

[0076] (Polyisocyanate hardener B4) A reactor was charged with 23.4 parts of P-400 and 46.6 parts of 4,4'-MDI, and reacted for 3 hours at 90°C under a nitrogen atmosphere to carry out a urethane reaction. After that, it 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 a polyisocyanate curing agent (B4).

[0077] [Table 3]

[0078] <Preparation of adhesive> [Examples 1 to 26, Comparative Examples 1 to 3]

[0079] 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.

[0080] [Preparation of test pieces for measuring breaking strength and breaking elongation] The adhesive was filled into a 2 mm thick formwork, the surface was smoothed, and the material was cured under the following conditions. Test pieces were then punched out using a No. 3 dumbbell mold. Curing condition I: Cured for 7 days at 23°C and 50% relative humidity. Curing condition II: Curing for 24 hours at 80℃

[0081] [Breaking strength and elongation of cured coating film] Using the test pieces obtained above, a tensile test was carried out in a 25°C environment at a tensile speed of 500 mm / min in accordance with JIS K 6251 to measure the breaking strength (MPa) and breaking elongation (%). The results are shown in Tables 4 and 5.

[0082] <Adhesive evaluation> The adhesive thus obtained was subjected to the following evaluations, and the results are shown in Tables 4 and 5.

[0083] [Adhesion to aluminum substrate] The obtained adhesive compositions were 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, and then laminated to the same aluminum A5052 substrate and pressed to maintain a thickness of 0.3 mm. The substrate 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 a tensile speed of 10 mm / min under conditions of 25°C. (Evaluation Criteria) A: Shear adhesive strength is 20 MPa or more (very good) B: Shear adhesive strength is 10MPa or more and less than 20MPa (good) C: Shear adhesive strength is 3MPa or more and less than 10MPa (usable) D: Shear adhesive strength is less than 3MPa (not suitable for use)

[0084] [Cohesive failure] After the evaluation of the above [Adhesion to aluminum substrate], the test piece was visually inspected, and the proportion of the area of ​​the test piece where the adhesive had failed by cohesive failure and remained was evaluated as the cohesive failure rate. (Evaluation Criteria) A: Cohesive failure rate is 80% or more (very good) B: Cohesive failure rate is 60% or more and less than 80% (good) C: Cohesive failure rate is 40% or more and less than 60% (usable) D: Cohesive failure rate is less than 40% (unusable)

[0085] [Long-term resistance to moisture and heat] 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 rate (%) = (shear strength after storage / shear strength before storage) x 100 A: Shear strength retention is 75% or more (good) B: Shear strength retention is 50% or more but less than 75% (usable) C: Shear strength retention is less than 50% (unusable)

[0086] [Table 4]

[0087] [Table 5]

[0088] According to Tables 4 and 5, by combining a polyol base agent containing a polyol, a phosphoric acid compound, and a monoalcohol with a polyisocyanate curing agent, the phosphoric acid compound provides high adhesion to aluminum when the adhesive is used, and the monoalcohol creates a starting point for cohesive failure of the adhesive, thereby providing stable adhesive strength.

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) or (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: The 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 breaking strength (MPa) of the cured product obtained by curing the adhesive at 80° C. for 24 hours, measured in accordance with JIS K 6251

3. The adhesive according to claim 2, wherein a cured product obtained by curing the adhesive in an environment of 23°C and 50% relative humidity for 7 days, or a 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 claim 3 , wherein the monoalcohol (E) contains a monoalcohol having an aromatic ring.

5. The adhesive according to claim 3, which contains 1 to 50 mass% of the monoalcohol (E) relative to 100 mass% of the polyol (C).

6. The adhesive according to claim 3 , wherein the polyol (C) contains at least one of a polyether polyol and a polycarbonate polyol.

7. The adhesive according to claim 6 , 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.

8. The adhesive according to claim 7, wherein a mass ratio of the polyol (C1) to a total mass of the polyol (C1) and the polyol (C2) is 10 to 70 mass%.

9. A cured product obtained by curing the adhesive according to any one of claims 1 to 8.

10. A structure comprising an adhesive layer between a first substrate and a second substrate, the adhesive layer being the cured product according to claim 9.

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