JPH0135031B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a thermosetting adhesive and an adhesion method, and more particularly to a thermosetting adhesive with excellent heat resistance. Conventionally, various adhesives have been used in many laminated materials and composite materials. In addition, so-called polyisocyanate adhesives, such as mixtures of urethane polymers or polyisocyanates and active hydrogen atom-containing compounds, have strong adhesive strength, excellent water resistance and chemical resistance, and depending on the composition, elasticity and flexibility. It has many characteristics such as being suitable for bonding parts that are bent or deflected.
Textile materials, natural and synthetic rubber, plastics,
It is used to bond various materials such as metal and glass. In recent years, plastics have been used as industrial materials, building materials,
It has come to be widely used in packaging materials, etc., and there is a growing demand for adhesives that can be used to bond plastics and have heat resistance, especially in automotive materials. However, conventional polyisocyanate-based adhesives have poor heat resistance, and other rubber-based, epoxy-based, and other various adhesives also do not have sufficient heat resistance. The present inventors have developed an active hydrogen-containing polyfunctional compound (A) containing a specific polymeric polyol as an essential component, and a polyisocyanate compound (B ), the inventors have discovered that the above object can be achieved by using a thermosetting adhesive comprising a trimerization catalyst (C), and have arrived at the present invention. That is, the present invention provides a polymer polyol with an average molecular weight of 1,000 to 10,000, which is composed of a polymer polyol with a molecular weight of 2,000 to 10,000 selected from polymer polyols, OH-containing vinyl polymers, and OH-terminated urethane prepolymers, and if necessary, other polymer polyols and/or crosslinking agents.
10,000 active hydrogen-containing polyfunctional compound (A), a polyisocyanate compound (B) that does not have a large excess of isocyanurate rings with respect to the active hydrogen-containing group of (A), a trimerization catalyst (C), and, if necessary, an organic solvent. Isocyanurate ring-forming thermosetting adhesive (first invention)
and an adhesion method (second invention) characterized in that the adhesive is present between substrates and cured by heating. Active hydrogen-containing polyfunctional compound used in the present invention
(A) contains two or more active hydrogen-containing groups (hydroxyl group, carboxyl group, amino group, mercapto group, etc.) at the end or in the molecular chain, and contains a polymeric polyol as at least a part of the polymer polyol. One containing at least one polymeric polyol selected from the group consisting of a polymer polyol, an OH group-containing vinyl polymer, and an OH group-terminated urethane prepolymer is used. Examples of polymer polyols include polymer polyols prepared from polyether polyols and/or polyester polyols and/or polyether ester polyols and optionally crosslinking agents and ethylenically unsaturated monomers. Polyether polyols used in the production of polymer polyols include compounds with structures in which alkylene oxide is added to polyfunctional compounds containing active hydrogen atoms, such as polyhydric alcohols, polyphenols, ammonia, amines, and polycarboxylic acids. It will be done. The polyhydric alcohols include dihydric alcohols such as ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, and neopentyl glycol, and glycerin, trimethylolpropane, pentaerythritol, sorbitol, Trivalent or higher polyhydric alcohols such as sucrose; examples of polyhydric phenols include pyrogallol,
In addition to polyhydric phenols such as hydroquinone, bisphenols such as bisphenol A; examples of amines include monoamines such as butylamine, ethylenediamine, trimethylenediamine,
aliphatic polyamines such as diethylenetriamine,
Alicyclic polyamines such as cyclohexylene diamine, dicyclohexylmethane diamine, isophorone diamine, aromatic polyamines such as phenylene diamine, tolylene diamine, xylylene diamine, diphenylmethane diamine, polyphenylmethane polyamine, piperazine, aminoethyl piperazine, etc. heterocyclic polyamines and alkanolamines such as monoethanolamine, diethanolamine, and triethanolamine; and polycarboxylic acids such as aliphatic polycarboxylic acids such as succinic acid and adipic acid, phthalic acid, terephthalic acid, and trimellitic acid; Examples include aromatic polycarboxylic acids. Two or more kinds of the above-mentioned active hydrogen atom-containing compounds can also be used. Examples of the alkylene oxide added to the active hydrogen atom-containing compound include ethylene oxide (hereinafter abbreviated as EO), propylene oxide (hereinafter abbreviated as PO),
Examples include butylene oxide, tetrahydrofuran, styrene oxide, and epichlorohydrin. The alkylene oxides may be used alone or in combination of two or more, and in the latter case, block addition, random addition, or a mixture of both may be used. Among these alkylene oxides, PO and/or EO are preferred, but it is also preferable to use these together with a small amount of other alkylene oxides (butylene oxide, tetrahydrofuran, styrene oxide, etc.) depending on the required function. Polyester polyols and polyether ester polyols used in the production of polymer polyols include, for example, condensed polyester polyols obtained by reacting polyols with dicarboxylic acids (or dicarboxylic acid anhydrides and alkylene oxides), and ring-opened lactones. Examples include polyester polyols obtained by polymerization. Examples of the above-mentioned polyols include low-molecular polyols, such as diols such as ethylene glycol, propylene glycol, 1,6 hexanediol, diethylene glycol, neopentyl glycol, bis(hydroxymethyl)cyclohexane, and bis(hydroxyethyl)benzene; trimethylolpropane, glycerin, etc. ; polyether polyols (such as polyalkylene glycols) and mixtures thereof. Examples of dicarboxylic acids include succinic acid, glutamic acid, adipic acid, sebacic acid, maleic acid, fumaric acid, phthalic acid, terephthalic acid, dimer acid, and mixtures thereof. Furthermore, polyether ester polyols obtained by reacting polyoxyalkylene polyols with polycarboxylic acid anhydrides and cyclic ether compounds as described in Japanese Patent Publication No. 48-10078 can also be used. Combined use of polyether polyol and polyester polyol or polyether ester polyol (for example, in a weight ratio of 5:95 to 95:
5) can also be used for the production of polymer polyols. Examples of ethylenically unsaturated monomers used in the production of polymer polyols include the following. (a) Acrylic acid, methacrylic acid, and their derivatives: acrylonitrile, methacrylonitrile, acrylic acid, methacrylic acid and their salts, methyl acrylate, methyl methacrylate, dimethylaminoethyl methacrylate, acrylamide, methacrylamide, etc. (b) Aromatic vinyl monomers: styrene, α-methylstyrene, etc. (c) Olefinic hydrocarbon monomers: ethylene, propylene, butadiene, isobutylene, isoprene, 1,4-pentadiene, etc. (d) Vinyl ester monomer: vinyl acetate, etc. (e) Vinyl halide monomers: vinyl chloride, vinylidene chloride, etc. (f) Vinyl ether monomers: vinyl methyl ether, etc. Among these, preferred are acrylonitrile, methyl methacrylate, styrene, and butadiene. Particularly preferred is acrylonitrile, a combination of acrylonitrile and styrene (styrene:acrylonitrile weight ratio 0:100 to 60:40)
It is. Although the proportions of polyol and monomer used in polymer polyols can vary over a wide range,
Usually, the amount of the ethylenically unsaturated monomer (or polymer) is 2 to 70 parts by weight, preferably 5 to 40 parts by weight, per 100 parts by weight of the polyol. As a polymer polyol, Japanese Patent Publication No. 41-3473,
Special Publication No. 39-24737, Special Publication No. 54-19433, Japanese Patent Publication No. 1983-1943
Examples include those described in No. 56-26924. Examples of the polyester polyol and polyether ester polyol used as at least a part of (A) in the adhesive of the present invention include those mentioned above (described in the section on production of polymer polyol). Examples of OH-containing vinyl polymers include acrylic polyols, such as JP-A-49-98499, JP-A-Sho.
Examples include hydroxyalkyl (meth)acrylate (co)polymer and vinyl acetate (co)polymer hydrolyzate described in No. 65767. The OH-terminated urethane prepolymer is obtained by reacting a polymeric polyol with an insufficient amount of an organic polyisocyanate. As the polymer polyol used in the production of the above prepolymer, polyether polyol, polyester polyol, polyether ester polyol, and/or OH-containing vinyl polymer can be used. and those mentioned in the section of OH-containing vinyl polymers).
As the organic polyisocyanate, those described in (B) below (particularly MDI, TDI, etc.) can be used. At least a portion (for example, 5% by weight or more, preferably 10 to 90% by weight) of the polymer polyol is a polymer polyol, an OH-containing vinyl polymer, an OH
By using a polymer polyol selected from the group consisting of terminal urethane prepolymers, adhesiveness, heat resistance, film formability, and durability can be improved. Heat resistance and adhesion can be improved by using a polymer polyol as at least a part. By using an OH-containing vinyl polymer or an OH-terminated urethane prepolymer, film formability and durability can be improved. By using two or more of these polymer polyols in combination, both effects can be obtained. In the present invention, in addition to the above-mentioned polymer polyol, other polymer polyols (for example, polyether polyol) can be used in combination, if necessary. As the polyether polyol, those mentioned above (described in the section of polymer polyol production) can be used. The weight ratio of the above polymer polyol and other polymer polyol (polyether polyol) can be varied, for example, from 100:0 to 5:95.
Preferably, the ratio can be 95:5 to 10:90.
By using polyether polyol together,
Reduces viscosity, improves workability and permeability. The molecular weight of the polymer polyol is usually 300 to 10,000, preferably 500 to 8,000, and more preferably 2,000 to 7,000.
It is. If it is less than 300, the reaction with isocyanate increases, which is disadvantageous in extending pot life. Furthermore, polymer polyols having a molecular weight of more than 10,000 tend to produce by-products during production, are not common, and have high viscosity, which is disadvantageous in terms of work. OH− value is usually
400-15 preferably 200-20 more preferably 130
~25. The number of functional groups is usually 2 to 4, preferably 2
~3. Examples of the crosslinking agent that may be used as necessary in the present invention include active hydrogen-containing low-molecular polyfunctional compounds having a molecular weight of 30 to 300, such as polyols, polyamines, and amino alcohols. Examples of low-molecular polyols include polyhydric alcohols (mentioned as raw materials for polyether polyols in the section on the production of polymer polyols); and active hydrogens such as polyhydric alcohols, polyhydric phenols, ammonia, amines, and polycarboxylic acids. Examples include alkylene oxide low molar adducts of atom-containing polyfunctional compounds. Preferred low molecular polyols are:
ethylene glycol, 1,4-butanediol,
Trimethylolpropane, glycerin and their alkylene oxides (PO and/or
EO) is an adduct. Examples of polyamines include aliphatic, alicyclic,
Examples include aromatic and heterocyclic polyamines. Examples of amino alcohols include ethanolamine and propanolamine. The amount of the crosslinking agent used can be varied depending on the purpose and required performance, but is generally 30% or less (based on the total weight of the polymer polyol and the crosslinking agent, the same applies hereinafter), and particularly preferably 10% or less. If the amount of crosslinking agent exceeds the above range, the adhesive layer will become brittle. The average molecular weight of the active hydrogen-containing polyfunctional compound (A) (high molecular polyol and optionally crosslinking agent) is 1000~
It is 10000. The average number of functional groups is usually 2 to 4, preferably 2 to 3. The overall viscosity of (A) is usually 100 cps (25℃) ~ 1 million
cps (25℃) preferably 500cps (25℃) ~ 100,000cps
(25℃). The polyisocyanate compound (B) having no isocyanurate ring used in the present invention includes:
Those conventionally used in polyurethane production can be used, including urethane polymers obtained by reacting organic polyisocyanates and polyols with excess organic polyisocyanates. Examples of organic polyisocyanates include aliphatic polyisocyanates (hexamethylene diisocyanate, lysine diisocyanate, etc.), alicyclic polyisocyanates (hydrogenated diphenylmethane diisocyanate, isophorone diisocyanate, hydrogenated tolylene diisocyanate, etc.), aromatic polyisocyanates [trisine diisocyanate, etc.] diisocyanate (TDI),
diphenylmethane diisocyanate (MDI),
naphthylene diisocyanate, xylylene diisocyanate, etc.] and mixtures thereof. Preferred among these are aromatic diisocyanates, and particularly preferred are:
TDI and MDI. These polyisocyanates are crude polyisocyanates, e.g.
TDI, crude MDI [crude diaminodiphenylmethane {condensation product of formaltehyde and an aromatic amine or a mixture thereof: a mixture of diaminodiphenylmethane and a small amount (e.g. 5 to 20% by weight) of a trifunctional or higher functional polyamine} phosgenates: polyallyl polyisocyanate (PAPI)] or modified polyisocyanates such as liquefied MDI (carbodiimide modification, trihydrocarbyl phosphate modification, etc.). Examples of polyols used in the production of the urethane prepolymer include glycols such as ethylene glycol, propylene glycol, diethylene glycol, and dipropylene glycol; triols such as trimethylolpropane and glycerin; high-functional polyols such as pentaerythritol and sorbitol; alkylene oxide (EO and/or
PO) adducts. The above polyol preferably has an equivalent weight of 30 to 500, particularly 30 to 200. Among these, preferred ones have a functional group number of 2 to 3.
belongs to. The free isocyanate group content of the above modified polyisocyanate and prepolymer is:
It is usually 10 to 35%, preferably 15 to 32%, particularly preferably 20 to 30%. Two or more kinds of the polyisocyanate compounds (B) can be used in combination (eg, a modified polyisocyanate and a prepolymer are used together). The viscosity (25°C) of (B) is usually 500 to 20,000 cps, preferably 300 to 1000 cps. In the present invention, it is necessary that the polyisocyanate compound does not have an isocyanurate ring,
Those having an isocyanurate ring have a high viscosity, are unstable, tend to change in viscosity, and cannot obtain uniform adhesion. In producing the thermosetting adhesive in the present invention, the isocyanate index is usually 200 to 5,000, preferably 500 to 3,000, and more preferably 1,100 to 2,000. If the isocyanate index is lower than the above range, the heat resistance will be insufficient, and if it is higher, it will become brittle. (A) and (B)
The weight ratio is usually 100/20 to 100/500, preferably
It is 100/50 to 100/300. As the trimerization catalyst used in the present invention, known ones can be used. Examples of such catalysts include "Polyurethanes, Chemistry and Technology" by JR Saunders, Parts 1.94-97.
Page (Interscience Publishers
1964) or "Journal of Cellular Plastics" Vol. 1, Na. 1, pages 85-90 can be used, but are not limited thereto. Some specific examples of trimerization catalysts include (a) alkali metal salts of various carboxylic acids (alkali metal salts of aliphatic monocarboxylic acids such as acetic acid, propionic acid, butyric acid, octanoic acid, oleic acid, stearic acid, etc.); Alkali metal salts of aliphatic dicarboxylic acids such as malonic acid, maleic acid, and fumaric acid; aromatic carboxylic acids such as benzoic acid, cinnamic acid, phthalic acid, β-naphthalic acid, etc.; alkali metal salts of segmented ring carboxylic acids). (b) Strong organic bases [e.g. 2,4,6-tris(dimethylaminomethyl)phenol, N,N',N''-tris(dimethylaminopropyl)-sym-hexahydrotriazine, benzylmethylammonium hydroxide, benzyl trimethylammonium methoxide, sodium methoxide, 1,8-diazabicyclo(5,4,0)undecene-7, etc.], (c) metal salt of naphthenic acid, (d) merging catalyst (triethylenediamine and aldehydes, triethylenediamine and epoxy compounds). (e) Alkali metal salts of weakly acidic substances other than carboxylic acids (e.g. benzenesulfinic acid, potassium salt of P-nitrophenol, etc.). (f) Organic acid salts of strong organic bases (e.g. , 8-diazabicyclo(5,4,0)undecene-7 fatty acid salt, etc.).In addition, two or more types may be used in combination, and a co-catalyst may be used as necessary. Among these, preferred are tertiary amines or salts thereof, and salts of strong bases, and catalysts with temperature-sensitive catalytic activity are particularly preferred.Specifically, neutralized salts of strong bases such as 1,8
-diazabicyclo(5,4,0)undecene-7
Organic acid salts (phenol salts, fatty acid salts, etc.) are preferred. The amount of catalyst used is usually 0.1 to 10 parts per 100 parts of (B).
part, preferably 1 to 5 parts. The organic solvent used as necessary in the present invention can be arbitrarily selected depending on the purpose. Examples of solvents include ketones such as acetone and methyl ethyl ketone; hydrocarbons such as toluene; ethers such as tetrahydrofuran and dioxane; amides such as N,N-dimethylformaldehyde; nitriles such as acetonitrile; esters such as ethyl acetate; Halogenated hydrocarbons such as methylene chloride; and mixed solvents thereof can be used. In terms of volatilization rate, compounds with relatively low boiling points, such as acetone and toluene, are preferred. The amount of solvent used can be varied, but in general, the solid content of the adhesive is usually 15 to 100%, preferably 30%.
~70% is used. If the solid content is high, it is good for brush coating, but it is disadvantageous for spraying, and if the solid content is low, it takes time for the solvent to volatilize, which is not preferable. Various additives can be used in the adhesives of the invention. For example, antioxidants (e.g. 2,6-
di-tert-butyl-4-methylphenol, 2,
5-di-tert-butylhydroquinone, etc.), ultraviolet absorbers (such as Tinuvin P, Irganox
1010), hydrolysis inhibitors (e.g. 3,3'-
diisopropyl-4,4'-biphenylenecarbodiimide, etc.), a fungicide (for example, 8-hydroxyquinoline, etc.), etc. may be added in an amount of about 5% or less based on the solid content. Also, Special Publication No. 48-171,
It is also possible to mix in tackifying resins, softeners, flame retardants, natural or synthetic resins, organic pigments, inorganic pigments, or fiber materials as described in Japanese Patent Publication No. 34-2145. In order to improve the adhesion to metals, epoxy resins and silane coupling agents, such as those described in Japanese Patent Publication No. 51-18979 and US Pat. Nos. 3,309,261 and 3,391,054, may be added. The adhesive according to the present invention is preferably applied in a one-component form by premixing (A), (B), (C) and, if necessary, an organic solvent and other additives.
An adhesive can also be formed from (B), (C) and, if necessary, an organic solvent and other additives. For example, a two-component type [component containing (A) and (B) and component (C), or
Components containing (A) and (C) and component (B), etc.) are simultaneously applied to the surface to be adhered, and two
An example is a method of applying one component of the liquid to the other and bonding the other component under pressure. When bonding using the adhesive of the present invention, all commonly known methods can be employed. For example, applying the adhesive to the adhesive surface by spraying or brushing; adhering the adhesive by gluing, dipping, etc., volatilizing the solvent if necessary, then aligning the adhesive surfaces and heating under pressure if necessary. A common method is to cure the adhesive. The curing temperature is usually 50°C or higher, preferably 60 to 100°C. The curing time is usually 1 minute to 1 hour, preferably 5 minutes or less. The adhesive of the present invention exhibits extremely excellent adhesion, especially when adhering plastics and sheets, whereas conventional isocyanate adhesives exhibit poor adhesion at high temperatures. It exhibits high adhesive strength not found in known adhesives. Moreover, unlike conventional isocyanate-based adhesives, which have a longer pot life and a longer curing time, polyisocyanurate cures rapidly, increasing the pot life at room temperature and shortening the heat curing time. It has excellent features that allow it to In addition, isocyanate-based adhesives that have isocyanurate rings in advance have disadvantages in handling isocyanate and higher costs than adhesives that form isocyanurate rings on the substrate according to the present invention, and also have poor heat resistance. It is disadvantageous in The adhesive according to the present invention can be used in a wide variety of applications for bonding various materials. For example, wood, paper, fiber materials, natural and synthetic rubber, hard or soft plastics (e.g. AS resin, ABS resin, modified polyphenylene oxide resin, nylon, vinyl chloride, polyester, etc.) can be coated, sprayed, impregnated, etc. ) Urethane foam, plastic foam sheet (e.g. foamed vinyl chloride sheet, etc.)
Various laminated materials and composite materials can be provided by bonding leather, metal, glass, ceramics, stone, concrete, etc. of the same type or different types. The adhesive according to the invention can optionally also be used as a primer. For example, after coating an iron plate with adhesive, use foamed urethane, sealant, etc.
Paint etc. can be applied. Applications of the adhesive according to the present invention include adhesion of plastics and sheets, glass laminates, pretreatment of reinforced plastic substrates, lamination of reinforced plastics, production of heat-resistant fabrics, binder for abrasive materials, adhesion of plywood, and heat-resistant sealed packaging. etc. can be mentioned. The present invention will be explained below with reference to examples, but the present invention is not limited thereto (parts shown in the examples represent parts by weight). Example 1 100 g of polymer polyol and 3 g of catalyst are mixed in 160 g of acetone. Then isocyanate
An adhesive composition was prepared by mixing 150 g of I. The isocyanate index at this time was 2070. Adhesive is sprayed to a thickness of 30 m onto the AS resin substrate. After drying the solvent and pressurizing the foamed PVC sheet, pressurize the atmospheric temperature to 90℃ 1
The adhesive was cured at Kg/cm ² for 5 minutes. As a comparative example, use the urethane adhesive Bostik 7662.
(manufactured by Bostik Japan) was carried out in the same manner. Polymer polyols PO and EO in glycerin
It is a polymer polyol made from polyether with a molecular weight of 5,000 and acrylonitrile and has an OH monovalent value of 28. The catalyst was U-CAT SA No. 1 (manufactured by Sun Abbott). The isocyanate was carbodiimide-modified diphenylmethane isocyanate with an NCO% of 29%. Adhesive strength at 20℃, 80℃, 120℃ (180° peel)
The results of the measurements are shown in Table 1.

[Table] Example 2 In the same manner as in Example 1, polymer polyol,
Alternatively, using a combination system of this and polyether polyol 2, polyester polyol 3, or crosslinking agent 1, using a catalyst, isocyanate, and isocyanate 2, and changing the isocyanate index, polymer polyol, and isocyanate, the same conditions (90
The AS resin and the foamed vinyl chloride sheet were bonded together at 20°C (180° peeling). Polyether polyol 2 is a polyether with a molecular weight of 3000 that is made by adding PO to glycerin.
OH monovalent is 56. Polyester polyol 3 is a polyester made from ethylene glycol, 1,4-butanediol, and adipic acid, and has an OH monovalent value of 45. Crosslinker 1 is 1,4-butanediol. Isocyanate 2 is a prepolymer of diphenylmethane diisocyanate and triethylene glycol and has an NCO% of 24%. The results are shown in Table 2.

【table】

[Table] Example 3 In the same manner as in Example 1, using a polymer polyol, catalyst, toluene, and isocyanate, the adherend was changed and bonding was carried out under the same curing conditions (90° C. x 5 minutes). The results are shown in Table 3.

[Table] Example 4 In the same manner as in Example 1, an OH-containing vinyl polymer (Hytaloid 3003 manufactured by Hitachi Chemical Co., Ltd., OH value 30),
Adhesion was carried out using catalysts, acetone and isocyanates.

【table】

[Table] Example 5 Bonding was carried out in the same manner as in Example 1 using an OH-containing urethane prepolymer, catalyst, acetone, and isocyanate. OH-terminated urethane prepolymer is toluene
3100g, 5000g of ethylene butylene adipate (molecular weight 2500) and 174g of tolylene diisocyanate were reacted in 2070g of methyl ethyl ketone.
The pure OH value was 21.4.

【table】

[Table] * There was cohesive failure of the foamed PVC layer.

Claims (1)

[Claims] 1. Polymer polyol, OH-containing vinyl polymer,
Active hydrogen-containing polyfunctional compound (A) with an average molecular weight of 1000 to 10,000, consisting of a polymer polyol with a molecular weight of 2,000 to 10,000 selected from an OH-terminated urethane prepolymer, and optionally other polymer polyols and/or a crosslinking agent. ) A polyisocyanate compound (B) that does not have a large excess of isocyanurate rings with respect to the active hydrogen-containing group, a trimerization catalyst (C), and if necessary,
An isocyanurate ring-forming thermosetting adhesive made from an organic solvent. 2. The adhesive according to claim 1, wherein (B) is used in an amount such that the isocyanate index is 200 to 5,000. 3. The adhesive according to any one of claims 1 to 2, wherein the weight ratio of the polymer polyol to the other polymer polyol is 100:0 to 5:95. 4 Other polymer polyols have a molecular weight of 2000 to 10000
The adhesive according to any one of claims 1 to 3, which is a polyether polyol. 5. The adhesive according to any one of claims 1 to 4, wherein the crosslinking agent is a polyol, polyamine, and/or amino alcohol having a molecular weight of 30 to 300. 6. The adhesive according to any one of claims 1 to 5, wherein (B) is an organic polyisocyanate or a urethane prepolymer obtained by reacting a polyol with an excess of an organic polyisocyanate. 7. The adhesive according to claim 1, wherein (C) is a trimerization catalyst having temperature-sensitive catalytic activity. 8 Between the substrates, a polymer polyol with an average molecular weight of 1000, consisting of a polymer polyol with a molecular weight of 2000 to 10000 selected from polymer polyols, OH-containing vinyl polymers, and OH-terminated urethane prepolymers, and other polymer polyols and/or crosslinking agents as necessary. ~10,000 active hydrogen-containing polyfunctional compound (A), a polyisocyanate compound (B) that does not have a large excess of isocyanurate rings with respect to the active hydrogen-containing group of (A), a trimerization catalyst (C), and, if necessary, an organic An adhesion method characterized by curing by heating in the presence of an isocyanurate ring-forming thermosetting adhesive made of a solvent. 9. The bonding method according to claim 8, wherein the thermosetting adhesive is heated and cured at a temperature of 50° C. or higher. 10. The bonding method according to claim 8 or 9, wherein the thermosetting adhesive is interposed between a hard plastic and a soft plastic sheet and cured by heating.