Primer composition, adhesion method, and epoxy prepolymer

Abstract

A primer composition for a porous substrate, said primer composition: containing (A) an adhesion improver comprising a reaction mixture of a polyfunctional epoxy compound and an aminoalkylsilane compound, and (B) an organic solvent; not containing a (meth)acrylic copolymer; exhibiting superior application properties; not compromising the external appearance of the substrate even after processing; and exhibiting good adhesion properties even after a processing (application and curing) site has been immersed in water.

Description

Primer composition, adhesion method, and epoxy prepolymer

[0001] The present invention relates to a primer composition for porous substrates, and in particular to a primer composition that has excellent workability, bonds a silicone resin such as a room-temperature condensation-curing silicone rubber composition or a cured product (cured silicone rubber product) of an addition-curing silicone rubber composition to a porous substrate, and exhibits good adhesion even after immersion in water; a method for bonding a silicone resin to a porous substrate using the primer composition; and an epoxy prepolymer.

[0002] Cured products of silicone rubber compositions (silicone rubber cured products) selected from room-temperature condensation-curable silicone compositions and addition-curable silicone compositions are used in many fields (such as sealing materials for building materials and adhesives in the electrical and electronic fields) due to their excellent heat resistance, cold resistance, weather resistance, electrical insulation, safety, etc., and are often used as parts combined with various substrates. Generally, in order to adhere cured products of these silicone rubber compositions to various substrates, a method is adopted in which a primer composition is applied to the substrate (adherend) in advance.

[0003] Known primers include carbon functional silanes, such as aminoalkylsilanes, which have functional groups that can react with one component of a silicone rubber composition. However, these primers have the drawback of reducing adhesive strength and, in some cases, causing peeling when moisture is present at the application site. In particular, when the substrate is a porous material, the presence of numerous voids can lead to moisture in the material. This can cause the primer layer (coated surface) to be affected by moisture not only from the outer surface but also from the material itself, resulting in reduced adhesion and prone to peeling. Furthermore, when outdoor use is anticipated, even if the material is sufficiently dry at the time of application, it may be affected by rainwater, requiring high water resistance. Additionally, in areas where design is important, there is concern about changes in appearance due to application, necessitating the development of a primer that does not impair the appearance.

[0004] Among porous materials, wood in particular is seeing increased use in recent years due to the promotion of carbon neutrality. However, there are few examples of the use of room-temperature condensation-curing silicone compositions and addition-curing silicone compositions on wood as an adherend. In addition, because wood itself contains moisture and resin, it is difficult to achieve adhesive properties from these compositions. Furthermore, it is extremely difficult to maintain sufficient adhesive properties even after the applied (applied and cured) area has been immersed in water (submerged).

[0005] In this regard, Japanese Patent Laid-Open Publication No. 11-209682 (Patent Document 1) describes a composition made of an acrylic copolymer that exhibits high adhesive strength even when immersed in an alkaline aqueous solution.

[0006] Furthermore, Japanese Patent Laid-Open Publication No. 48-75633 (Patent Document 2) describes that by reacting an aminoalkylalkoxysilane with an epoxyalkylalkoxysilane under specified conditions to form an adhesion promoter, the applied (applied and cured) area maintains its adhesive strength even after immersion in water.

[0007] However, the acrylic copolymer constituting the composition in Patent Document 1 has a high viscosity, and the glossiness of the acrylic resin appears at the applied portion, which may impair the appearance of the substrate when the substrate is a porous material, etc. Furthermore, Patent Document 1 assumes that the substrate is concrete, which may be affected by alkalinity, while Patent Document 2 evaluates glass or aluminum as the substrate, and neither evaluates the adhesion, particularly water-resistant adhesion, of porous materials as the substrate.

[0008] JP-A-11-209682 JP-A-48-75633

[0009] The present invention has been made in view of the above circumstances, and aims to provide a primer composition for porous substrates, particularly wood, which has excellent application workability, does not impair the appearance of the substrate even after application (i.e., after treatment with the primer composition), and exhibits good adhesion even after the applied (applied and cured) area is immersed in water; a method for bonding a silicone resin to a porous substrate; and an epoxy prepolymer.

[0010] As a result of intensive research into solving the above-mentioned problems, the present inventors have discovered that adding a reaction mixture of a polyfunctional epoxy monomer and an aminoalkylsilane is effective in improving the adhesion, particularly the water-resistant adhesion, of a primer composition for porous substrates at the application (coating and curing) point, and have thus completed the present invention.

[0011] That is, the present invention provides the following primer composition, adhesion method, and epoxy prepolymer. [1] A primer composition for porous substrates, comprising: (A) an adhesion improver consisting of a reaction mixture of a polyfunctional epoxy compound and an aminoalkylsilane compound; and (B) an organic solvent, and characterized by not containing a (meth)acrylic copolymer. [2] The primer composition according to [1], wherein the component (A) is further a reaction mixture of a hydrolyzable organosilane compound not having an amino group and / or a partial hydrolyzed condensate thereof. [3] The primer composition according to [1] or [2], wherein the component (A) comprises an epoxy prepolymer represented by the following average composition formula (1): (In formula (1), X is independently a divalent hydrocarbon group having 1 to 31 carbon atoms which may contain an oxygen atom, a nitrogen atom, or a sulfur atom; R 1 are independently an alkylene group having 3 to 12 carbon atoms or an arylene group having 6 to 10 carbon atoms, and R 2 and R 3 are each independently an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms or an unsubstituted or substituted aryl group having 6 to 10 carbon atoms, l is independently 1 or 2, m is independently a number from 0 to 3, and n is a number from 0 to 50.) [4] The primer composition according to any one of [1] to [3], wherein the component (A) comprises a reaction product of a polyfunctional epoxy compound represented by the following general formula (2), an aminoalkylsilane compound represented by the general formula (3), and a hydrolyzable organosilane compound having no amino group or mercapto group represented by the general formula (4): (In formula (2), X represents a divalent hydrocarbon group having 1 to 31 carbon atoms and optionally containing an oxygen atom, a nitrogen atom, or a sulfur atom, and having at least one of an alkylene group which may have a branched structure, a monocyclic structure, and a polycyclic structure.) (In formula (3), R1 is an alkylene group having 3 to 12 carbon atoms or an arylene group having 6 to 10 carbon atoms, and R 2 and R 3 are each independently an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms or an unsubstituted or substituted aryl group having 6 to 10 carbon atoms, and m is a number from 0 to 3. (In formula (4), R 2 and R 3 are each independently an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms or an unsubstituted or substituted aryl group having 6 to 10 carbon atoms, and l' is 2 or 3.) [5] The primer composition according to any one of [1] to [4], further containing (C) a hydrolyzable organosilane compound and / or a partial hydrolysis condensate thereof. [6] The primer composition according to any one of [1] to [5], wherein component (B) is any one or a mixture of two or more solvents selected from aromatic hydrocarbon solvents, alcohol solvents, ketone solvents, ether solvents, ester solvents, and paraffin solvents. [7] The primer composition according to any one of [1] to [6], wherein component (B) has a flash point of -40°C or higher, a boiling point of 41°C or higher, and an ignition point of 101°C or higher. [8] The primer composition according to any one of [1] to [7], which is used for bonding a cured product of a room-temperature condensation-curable silicone rubber composition or an addition-curable silicone rubber composition to a porous substrate. [9] The primer composition according to any one of [1] to [8], which is used to improve water-resistant adhesion.

[10] The primer composition according to any one of [1] to [9], wherein the porous substrate is made of wood.

[11] A method for bonding a silicone resin to a porous substrate, comprising the steps of: applying the primer composition according to any one of [1] to

[10] to the surface of the porous substrate to form a primer layer; and then applying and curing a room-temperature condensation-curable silicone rubber composition or an addition-curable silicone rubber composition to the surface of the primer layer to form a silicone resin layer made of a cured silicone rubber.

[12] The bonding method according to

[11] , which improves water-resistant adhesion between a silicone resin and a porous substrate.

[13] An epoxy prepolymer represented by the following average composition formula (1): (In formula (1), X is independently a divalent hydrocarbon group having 1 to 31 carbon atoms which may contain an oxygen atom, a nitrogen atom, or a sulfur atom; R 1 are independently an alkylene group having 3 to 12 carbon atoms or an arylene group having 6 to 10 carbon atoms, and R 2 and R 3 are each independently an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms or an unsubstituted or substituted aryl group having 6 to 10 carbon atoms, l is independently 1 or 2, m is independently a number from 0 to 3, and n is a number from 0 to 50.)

[14] The epoxy prepolymer according to

[13] , which is a reaction product of a polyfunctional epoxy compound represented by the following general formula (2), an aminoalkylsilane compound represented by the general formula (3), and a hydrolyzable organosilane compound having no amino group or mercapto group represented by the general formula (4): (In formula (2), X represents a divalent hydrocarbon group having 1 to 31 carbon atoms and optionally containing an oxygen atom, a nitrogen atom, or a sulfur atom, and having at least one of an alkylene group which may have a branched structure, a monocyclic structure, and a polycyclic structure.) (In formula (3), R 1 is an alkylene group having 3 to 12 carbon atoms or an arylene group having 6 to 10 carbon atoms, and R 2 and R 3 are each independently an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms or an unsubstituted or substituted aryl group having 6 to 10 carbon atoms, and m is a number from 0 to 3. (In formula (4), R 2 and R 3are each independently an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms or an unsubstituted or substituted aryl group having 6 to 10 carbon atoms, and l' is 2 or 3.)

[15] The epoxy prepolymer according to

[14] , wherein the aminoalkylsilane compound is γ-aminopropyltrimethoxysilane or γ-aminopropyltriethoxysilane.

[16] The epoxy prepolymer according to any one of

[13] to

[15] , which is used as a primer for a porous substrate.

[17] The epoxy prepolymer according to

[16] , which improves adhesion between a cured product of a room-temperature condensation-curable silicone rubber composition or an addition-curable silicone rubber composition and a porous substrate.

[18] The epoxy prepolymer according to

[16] or

[17] , wherein the porous substrate is made of wood.

[0012] The primer composition of the present invention has excellent application workability, and when applied to the surface of a porous substrate to form a primer layer, the appearance of the porous substrate is not impaired. Furthermore, a silicone resin layer such as a cured product (silicone rubber cured product) of a silicone rubber composition selected from a room-temperature condensation-curable silicone composition and an addition-curable silicone composition, formed on the primer layer, can be well adhered to the porous substrate, and good adhesion can be maintained even after immersion in water.

[0013] The present invention will be described in detail below, but is not limited thereto. In the present invention, "(meth)acrylic copolymer" refers to either or both of an acrylic copolymer and a methacrylic copolymer, "acrylic copolymer" refers to a copolymer having an acrylic (also called acryloyl) group, and "methacrylic copolymer" refers to a copolymer having a methacrylic (also called methacryloyl) group. "(Meth)acrylic acid ester" refers to either or both of an acrylic acid ester and a methacrylic acid ester.

[0014] [Primer Composition] The primer composition of the present invention is for use on porous substrates, and is characterized by containing (A) an adhesion improver comprising a reaction mixture of a polyfunctional epoxy compound and an aminoalkylsilane compound, and (B) an organic solvent, and not containing a (meth)acrylic copolymer.

[0015] - Component (A) - Component (A) is an adhesion improver comprising a reaction mixture of a polyfunctional epoxy compound and an aminoalkylsilane compound.

[0016] The reaction mixture of a polyfunctional epoxy compound and an aminoalkylsilane compound is an adduct of a polyfunctional epoxy compound (a monomer and / or a polymer thereof having two or more epoxy groups in the molecule) and an aminoalkylsilane compound (a hydrolyzable aminoalkylsilane and / or a hydrolyzed condensation polymer thereof) (i.e., an addition reaction product in which an amino group in the aminoalkylsilane compound is addition-reacted with (a part of) an epoxy group in the polyfunctional epoxy compound), and functions as a film-forming component and an adhesive component.

[0017] The polyfunctional epoxy compound is a polyfunctional monomer having two or more epoxy groups in the molecule and containing no reactive functional groups other than the epoxy group, and is preferably one containing two glycidyl ether groups and / or alicyclic epoxy groups, and more preferably an aliphatic epoxy compound containing two glycidyl ether groups.

[0018] Examples of polyfunctional epoxy compounds include 1,2-cyclohexanedicarboxylate diglycidyl, neopentyl glycol diglycidyl ether, bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, and bisphenol AF diglycidyl ether. Other examples include polymers or partial hydrolysates of epoxy group-containing silane compounds such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropyldimethoxysilane, and 3-glycidoxypropyldiethoxysilane. From the viewpoints of cost and solubility in solvents, bisphenol A diglycidyl ether is preferred. These compounds may be used alone or in combination of two or more.

[0019] Examples of aminoalkylsilane compounds include hydrolyzable organosilane compounds (silane coupling agents) having an alkyl group substituted with a primary amino group and / or a secondary amino group in the molecule and two or three hydrolyzable groups such as alkoxy groups bonded to silicon atoms in the molecule, such as γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, 3-2-(aminoethylamino)propyltrimethoxysilane, and 3-2-(aminoethylamino)propyltriethoxysilane, and / or hydrolyzed condensation polymers thereof (organosiloxane oligomers having an alkyl group substituted with a primary amino group and / or a secondary amino group in the molecule and residual hydrolyzable groups such as alkoxy groups). In particular, compounds having a primary amino group and a methoxy group exhibit excellent film-forming ability and adhesive properties, and γ-aminopropyltrimethoxysilane, 3-2-(aminoethylamino)propyltrimethoxysilane, etc. are preferred. These compounds may be used alone or in combination of two or more.

[0020] For the addition reaction of a polyfunctional epoxy compound and an aminoalkylsilane compound, the amount of the aminoalkylsilane compound is preferably 0.01 to 100 moles, more preferably 0.1 to 10 moles, of amino groups per mole of epoxy groups of the polyfunctional epoxy compound.

[0021] The method for synthesizing the reaction mixture of the polyfunctional epoxy compound and the aminoalkylsilane compound is not particularly limited. For example, when the aminoalkylsilane compound is hydrolyzable, the polyfunctional epoxy compound and the aminoalkylsilane compound may be mixed for 4 to 12 hours at a temperature of 40 to 90°C in a moisture-blocked state.

[0022] As the component (A), a reaction mixture of a polyfunctional epoxy compound and an aminoalkylsilane compound may be used alone or in combination of two or more.

[0023] The reaction mixture of the polyfunctional epoxy compound and aminoalkylsilane compound of component (A) may further be a reaction mixture with a hydrolyzable organosilane compound having no amino group and / or a partial hydrolyzed condensate thereof.

[0024] Examples of hydrolyzable organosilane compounds that do not have an amino group include ketoxime group-containing silanes such as methyltris(methylethylketoxime)silane, vinyltris(methylethylketoxime)silane, phenyltris(methylethylketoxime)silane, and methyltris(dimethylketoxime)silane; alkoxysilanes such as methyltrimethoxysilane, octyltrimethoxysilane, dimethyldimethoxysilane, vinyltrimethoxysilane, phenyltrimethoxysilane, methyltriethoxysilane, and 2-ethylhexyl α-(dimethoxymethylsilyl)propionate; isopropenoxy group-containing silanes such as methyltriisopropenoxysilane, ethyltriisopropenoxysilane, vinyltriisopropenoxysilane, and phenyltriisopropenoxysilane; acetoxysilanes such as methyltriacetoxysilane, ethyltriacetoxysilane, and vinyltriacetoxysilane; and partial hydrolysis condensates of these silanes. These may be used alone or in combination of two or more.

[0025] When added, the content of the hydrolyzable organosilane compound having no amino group and / or its partial hydrolysis condensate in component (A) is preferably 1 to 50 mass %, and more preferably 5 to 40 mass %. By keeping the content within this range, the storage stability of the composition can be improved.

[0026] The epoxy prepolymer contained in the component (A), which is a reaction mixture of a polyfunctional epoxy compound and an aminoalkylsilane compound, further contains a hydrolyzable organosilane compound not having an amino group and / or a partial hydrolyzed condensate thereof, is further described below. In the present invention, the component (A), which is a reaction mixture of a polyfunctional epoxy compound and an aminoalkylsilane compound, further contains a hydrolyzable organosilane compound not having an amino group and / or a partial hydrolyzed condensate thereof, contains the epoxy prepolymer described below as a main component. "Containing the epoxy prepolymer as a main component" as used herein means that the reaction mixture contains 50% by mass or more of the epoxy prepolymer, preferably 70% by mass or more, and more preferably 90% by mass or more of the epoxy prepolymer.

[0027] [Epoxy Prepolymer] The epoxy prepolymer contained in the reaction mixture of component (A), which is a reaction mixture of a polyfunctional epoxy compound and an aminoalkylsilane compound, further contains a hydrolyzable organosilane compound having no amino group and / or a partial hydrolyzed condensate thereof, is represented by the following average composition formula (1): (In formula (1), X is independently a divalent hydrocarbon group having 1 to 31 carbon atoms which may contain an oxygen atom, a nitrogen atom, or a sulfur atom; R 1 are independently an alkylene group having 3 to 12 carbon atoms or an arylene group having 6 to 10 carbon atoms, and R 2 and R 3 are each independently an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms or an unsubstituted or substituted aryl group having 6 to 10 carbon atoms, l is independently 1 or 2, m is independently a number from 0 to 3, and n is a number from 0 to 50.

[0028] In formula (1), X is independently a divalent hydrocarbon group having 1 to 31 carbon atoms which may contain an oxygen atom, a nitrogen atom, or a sulfur atom. Examples of the divalent hydrocarbon group include a linear or branched alkylene group having 1 to 20 carbon atoms and a cyclic divalent hydrocarbon group having 3 to 31 carbon atoms (a monocyclic divalent hydrocarbon group or a polycyclic divalent hydrocarbon group). X may contain one or more of these groups and may contain an oxygen atom, a nitrogen atom, or a sulfur atom.

[0029] The number of carbon atoms in X is 1 to 31, preferably 1 to 20. Examples of linear alkylene groups include methylene, ethylene, n-propylene (trimethylene), n-butylene (tetramethylene), and n-hexylene (hexamethylene). Examples of branched alkylene groups include isobutylene, sec-butylene, isopentylene, isohexylene, isooctylene, and 2-ethylhexylene. Examples of monocyclic divalent hydrocarbon groups include 1,2- and 1,3-cyclopentylene and 1,4-cyclohexylene. Examples of polycyclic divalent hydrocarbon groups include 1,3-, 1,4-, and 1,5-naphthylene and anthrylene. Examples of structures containing oxygen, nitrogen, or sulfur atoms include carbonyl groups, ether bonds, and amino groups. X preferably contains an arylene group, more preferably a phenylene group. X is particularly preferably a divalent hydrocarbon group having 1 to 20 carbon atoms, which may contain an oxygen atom and / or a sulfur atom, and which has an oxygen atom at each of its two ends, and which forms an ether bond (C-O-C bond) between each of the adjacent carbon atoms to which X is bonded.

[0030] Specific examples of X include those represented by the following formulas (5a) to (5g). The dashed lines in the formulas indicate bonds. In particular, the following formula (5d) is preferred from the standpoints of cost and solubility in a solvent during primer preparation.

[0031]

[0032] R 1are independently an alkylene group having 3 to 12 carbon atoms or an arylene group having 6 to 10 carbon atoms, and examples thereof include alkylene groups such as an n-propylene (trimethylene) group, an isopropylene (methylethylene) group, a butylene (tetramethylene) group, an isobutylene (methyltrimethylene) group, a tert-butylene (dimethylethylene) group, a pentamethylene group, a hexylene (hexamethylene) group, a heptamethylene group, an octamethylene group, a nonamethylene group, a decamethylene group, and a dodecamethylene group; cycloalkylene groups such as a 1,3- or 1,2-cyclopentylene group or a 1,4-cyclohexylene group; and arylene groups such as a phenylene group, a tolylene group, a xylylene group, and an α- or β-naphthylene group. Among these, alkylene groups such as propylene (trimethylene) group and hexylene (hexamethylene) group are preferred, with propylene (trimethylene) group being particularly preferred.

[0033] R 2 and R 3 are each independently an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms or an unsubstituted or substituted aryl group having 6 to 10 carbon atoms. The alkyl group having 1 to 10 carbon atoms may be linear, cyclic, or branched. Specific examples thereof include linear or branched alkyl groups such as methyl, ethyl, n-propyl, i-propyl, n-butyl, s-butyl, t-butyl, n-pentyl, neopentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, and n-decyl; and cycloalkyl groups such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, and isobornyl. Specific examples of aryl groups having 6 to 10 carbon atoms include phenyl, tolyl, xylyl, α-naphthyl, and β-naphthyl. Some or all of the hydrogen atoms in these groups may be substituted with alkyl groups, aryl groups, halogen atoms such as F, Cl, and Br, or cyano groups. Among these, R 2 and R 3 As the alkyl group, a methyl group, an ethyl group, a vinyl group, or a phenyl group is preferred, and in terms of reactivity and cost, a methyl group or a vinyl group is more preferred.

[0034] n is a number from 0 to 50, preferably a number from 0 to 20, and particularly preferably a number from 0 to 5. m is a number from 0 to 3, and particularly preferably 3, and l is 1 or 2, and particularly preferably 2.

[0035] The epoxy prepolymer is preferably a reaction product of a bifunctional epoxy compound (diglycidyl compound) represented by the general formula (2) described below, an aminoalkylsilane compound represented by the general formula (3), and a hydrolyzable organosilane compound (alkylalkoxysilane) having no amino group or mercapto group represented by the general formula (4).

[0036] The weight-average molecular weight of the epoxy prepolymer is preferably 500 to 100,000, and more preferably 1,000 to 5,000. The weight-average molecular weight of the epoxy prepolymer can be determined as a polystyrene-equivalent weight-average molecular weight by gel permeation chromatography (GPC) analysis using, for example, tetrahydrofuran as a developing solvent.

[0037] Examples of preferred epoxy prepolymers include the following: wherein Me represents a methyl group.

[0038] [Method for Producing Epoxy Prepolymer] The method for producing the above-mentioned epoxy prepolymer is characterized by mixing and reacting (A1) a bifunctional epoxy compound (diglycidyl compound) represented by the following general formula (2), (A2) an aminoalkylsilane compound represented by the following general formula (3), and (A3) a hydrolyzable organosilane compound (alkylalkoxysilane) having no amino group or mercapto group represented by the following general formula (4):

[0039] (In formula (2), X is the same as X in average composition formula (1).)

[0040] (In formula (3), R 1 , R 2 , R 3 and m are R in the average composition formula (1), 1 , R 2 , R3 and m.)

[0041] (In formula (4), R 2 , R 3 are R in the average composition formula (1), 2 , R 3 and l' is 2 or 3.

[0042] Examples of the diglycidyl compound represented by formula (2) of component (A1) include 1,2-cyclohexanedicarboxylate diglycidyl, neopentyl glycol diglycidyl, bisphenol A diglycidyl, bisphenol F diglycidyl, bisphenol AF diglycidyl, and 2,2-bis(4-glycidyloxyphenyl)propane. From the standpoints of cost and solubility in solvents, bisphenol A diglycidyl is preferred. Furthermore, hydrolysis condensation polymers (organosiloxane oligomers having two glycidyl groups in the molecule) of hydrolyzable glycidyl compounds such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropyldimethoxysilane, and 3-glycidoxypropyldiethoxysilane may also be used as component (A1).

[0043] Examples of the aminoalkylsilane compound represented by formula (3) of component (A2) include (hydrolyzable) organosilane compounds (silane coupling agents) having an alkyl group substituted with a primary amino group in the molecule and 0 to 3 hydrolyzable groups such as alkoxy groups bonded to silicon atoms in the molecule, such as γ-aminopropyltrimethoxysilane and γ-aminopropyltriethoxysilane. γ-Aminopropyltrimethoxysilane is particularly preferred, as it exhibits excellent film-forming and adhesive properties when it contains a methoxy group. Alternatively, a hydrolyzed condensation polymer of the aminoalkylsilane compound represented by formula (3) (an organosiloxane oligomer having an alkyl group substituted with a primary amino group in the molecule and residual hydrolyzable groups such as alkoxy groups) may be used as component (A2).

[0044] Examples of the alkylalkoxysilane represented by formula (4) of the component (A3) include methyltrimethoxysilane, octyltrimethoxysilane, dimethyldimethoxysilane, vinyltrimethoxysilane, phenyltrimethoxysilane, and methyltriethoxysilane. From the standpoints of cost and reactivity, methyltrimethoxysilane or vinyltrimethoxysilane is preferred.

[0045] The amount of component (A2) added is preferably 0.1 to 1.0 mol, and more preferably 0.1 to 0.6 mol, per 1 mol of the polyfunctional epoxy compound (diglycidyl compound) represented by general formula (2) (A1).

[0046] The amount of component (A3) added is preferably 1.0 to 10.0 moles, and more preferably 1.0 to 5.0 moles, per mole of the polyfunctional epoxy compound (diglycidyl compound) represented by general formula (2) (A1).

[0047] In the method for producing an epoxy prepolymer, the temperature at which (A1) the diglycidyl compound represented by the general formula (2), (A2) the aminoalkylsilane represented by the general formula (3), and (A3) the alkylalkoxysilane represented by the general formula (4) are mixed and reacted is 10 to 90°C, preferably 20 to 70°C. If the temperature is outside this range, the reaction may be significantly slowed or the viscosity may increase significantly, making it difficult to recover the reaction product. The reaction time for mixing and reacting is preferably 2 hours to 5 days, more preferably 8 hours to 3 days.

[0048] According to the method for producing the epoxy prepolymer, a reaction product (side-chain alkoxysilane-containing epoxy prepolymer) can be obtained that is liquid at room temperature (23°C ± 15°C) or soluble in the organic solvent (B) used in the present invention, namely, aromatic hydrocarbon solvents, alcohol solvents, ketone solvents, ether solvents, ester solvents, and paraffin solvents.

[0049] The above-mentioned epoxy prepolymer is suitable as a primer for porous substrates, and is particularly suitable for improving the adhesion between a cured product of a room-temperature condensation-curable silicone rubber composition or an addition-curable silicone rubber composition and a porous substrate.

[0050] - Component (B) - The organic solvent for component (B) may be any organic solvent capable of dissolving the components in the primer composition in any desired proportion and having volatility, and from the standpoint of ease of handling, it is preferable for the organic solvent to have a flash point of -40°C or higher, a boiling point of 41°C or higher, and an ignition point of 101°C or higher, and more preferably a flash point of -30°C or higher, a boiling point of 60°C or higher, and an ignition point of 200°C or higher. The flash point referred to here is a value measured by the rapid equilibrium closed-loop method described in JIS-K2265-2:2007, the boiling point is a value at 1 atmosphere (1013 hPa), and the ignition point is the lower limit of the temperature at which the organic solvent instantly ignites when dropped into a container heated to a constant temperature.

[0051] Specific examples of component (B) include aromatic hydrocarbon solvents such as benzene, toluene, and xylene; alcohol solvents such as methanol, ethanol, isopropyl alcohol, and ethylene glycol monomethyl; ketone solvents such as acetone and methyl ethyl ketone; ether solvents such as tetrahydrofuran and dioxane; ester solvents such as ligroin, ethyl acetate, butyl acetate, and isobutyl acetate; and paraffin solvents such as hexane and cyclohexane, which can be used alone or as a mixed solvent of two or more. Among these, aromatic hydrocarbon solvents, paraffin solvents, and ester solvents are preferred, and toluene, hexane, ethyl acetate, butyl acetate, and isobutyl acetate are particularly preferred.

[0052] The incorporation of component (B) allows adjustment of the workability of the primer composition during application and drying. The amount of component (B) is not particularly limited, but is 5 to 1,000 parts by mass, preferably 5 to 100 parts by mass, per 10 parts by mass of component (A). Within this range, a uniform coating film of the primer composition can be formed, and unevenness on the coating film surface can be suppressed. When component (A) and other components are added as a solution, the amount of component (B) refers to the total amount in the composition, including the solvent in the solution.

[0053] —Component (C)— The primer composition of the present invention may further contain, as an optional component (C), a hydrolyzable organosilane compound and / or a partial hydrolyzed condensate thereof, for the purpose of improving the storage stability of the composition.

[0054] The hydrolyzable organosilane compound and / or partial hydrolysis condensate thereof of component (C) may be the same as the hydrolyzable organosilane compound and / or partial hydrolysis condensate thereof not having an amino group in component (A), and examples thereof include ketoxime group-containing silanes such as methyltris(methylethylketoxime)silane, vinyltris(methylethylketoxime)silane, phenyltris(methylethylketoxime)silane, and methyltris(dimethylketoxime)silane; methyltrimethoxysilane, octyltrimethoxysilane, dimethyldimethoxysilane, and the like. Examples of the silane include alkoxysilanes such as silane, vinyltrimethoxysilane, phenyltrimethoxysilane, methyltriethoxysilane, and 2-ethylhexyl α-(dimethoxymethylsilyl)propionate; isopropenoxy group-containing silanes such as methyltriisopropenoxysilane, ethyltriisopropenoxysilane, vinyltriisopropenoxysilane, and phenyltriisopropenoxysilane; acetoxysilanes such as methyltriacetoxysilane, ethyltriacetoxysilane, and vinyltriacetoxysilane; and partial hydrolysis condensates of these silanes. These may be used alone or in combination of two or more.

[0055] The amount of component (C) to be added is not particularly limited, but if it is added, it is 0.01 to 100 parts by mass, preferably 0.1 to 10 parts by mass, per 10 parts by mass of component (A). Within this range, there is no effect on adhesiveness, and good shelf life can be achieved. Note that when a hydrolyzable organosilane compound without an amino group and / or its partial hydrolysis condensate is added to component (A), component (C) does not need to be added.

[0056] -Other Additives- In addition to the above-described components (A) to (C), the primer composition of the present invention may further contain at least one known additive selected from the group consisting of pigments, dyes, antioxidants, antioxidants, adhesion promoters, antistatic agents, and flame retardants such as antimony oxide and chlorinated paraffins, within the scope of the present invention. Furthermore, mildew inhibitors, antibacterial agents, etc. may also be added within the scope of the present invention.

[0057] The viscosity of the primer composition of the present invention at 23°C is 30 mm 2 / s or less, and 1.0 to 20 mm 2 The viscosity of the primer composition can be measured with a capillary viscometer (Cannon-Fenske viscometer).

[0058] The primer composition of the present invention is preferably used for bonding a cured product of a room-temperature condensation-curable silicone rubber composition or an addition-curable silicone rubber composition to a porous substrate. That is, it can be suitably used to improve the adhesion between a porous substrate and a silicone resin consisting of a cured product (silicone rubber cured product) of a room-temperature condensation-curable silicone rubber composition or an addition-curable silicone rubber composition, and is particularly suitable for improving adhesion (water-resistant adhesion) when the application site is submerged (submerged). In the present invention, examples of porous substrates include wood, synthetic wood, and cured products of hydraulic compositions (cured mortar, cured concrete, cured cement), but wood is preferred, and examples of wood materials include cypress, cedar, and pine. Furthermore, the porous substrate may be treated as desired to improve the durability, weather resistance, and design of the substrate.

[0059] [Method for bonding silicone resin to porous substrate] The method for bonding a silicone resin (cured silicone rubber layer) to a porous substrate according to the present invention is characterized by comprising the steps of: applying the primer composition of the present invention described above to the surface of a porous substrate to form a primer layer; and then applying and curing a room-temperature condensation-curable silicone rubber composition or an addition-curable silicone rubber composition to the surface of the primer layer to form a silicone resin layer made of cured silicone rubber.

[0060] As a method for adhering the silicone resin of the present invention (cured silicone rubber layer) to a porous substrate, for example, the primer composition of the present invention may be applied to the surface of the porous substrate (coating with a brush or nonwoven fabric, followed by air drying (curing) at room temperature (23°C ± 15°C) for 30 minutes to 12 hours, preferably 30 minutes to 2 hours (also referred to as primer treatment)) to form a primer layer, and then a silicone rubber composition selected from a room temperature condensation curing silicone rubber composition and an addition curing silicone rubber composition is applied to the outer surface of the primer layer to form the silicone rubber composition layer, and the silicone rubber composition layer is cured (i.e., a room temperature condensation curing silicone rubber composition is applied and the composition is cured at room temperature (23°C ± 15°C), or an addition curing silicone rubber composition is applied and the composition is cured at room temperature (23°C ± 15°C) or by heating (50 to 100°C)), thereby forming a silicone resin consisting of the cured silicone rubber, thereby adhering the silicone resin to the porous substrate.

[0061] According to the present invention, after the primer treatment of the surface of porous substrate such as wood with the primer composition of the present invention, a silicone rubber composition selected from room temperature condensation curing silicone rubber composition and addition curing silicone rubber composition is applied, and this coating film is cured, so that this applied (coated and cured) part shows good adhesion even after immersion in water, and in particular improves the water-resistant adhesion between silicone resin and porous substrate.In addition, because the primer composition of the present invention does not contain (meth)acrylic copolymer, even after primer treatment, the appearance of substrate, especially porous substrate such as wood, is not impaired.

[0062] The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples. Note that the number of moles in the following examples is when "parts by mass" is "g." Room temperature refers to 23°C.

[0063] Synthesis Example 1 Preparation 1 of Reaction Mixture of Polyfunctional Epoxy Compound and Aminoalkylsilane To 51 parts by mass (0.15 mol) of 2,2-bis(4-glycidyloxyphenyl)propane, 9.0 parts by mass (0.05 mol) of γ-aminopropyltrimethoxysilane and 27 parts by mass (0.20 mol) of methyltrimethoxysilane were added, and the mixture was refluxed in a reflux condenser under moisture-blocking conditions, and stirred at 60° C. for 8 hours to obtain Reaction Mixture 1.

[0064] Synthesis Example 2: Preparation 2 of reaction mixture of polyfunctional epoxy compound and aminoalkylsilane A reaction mixture 2 was obtained in the same manner as in Synthesis Example 1, except that 38 parts by mass of vinyltrimethoxysilane was used instead of 27 parts by mass of methyltrimethoxysilane.

[0065] Synthesis Example 3: Preparation of Acrylic Copolymer 1 To 47 parts by mass of ethyl acetate, 34 parts by mass of methyl methacrylate and 1.8 parts by mass of 3-methacryloxypropyltrimethoxysilane were added, mixed under nitrogen aeration, and heated to a temperature of 80°C. Next, 0.1 parts by mass of 2,2'-azobis(2-methylbutyronitrile) was added and mixed to dissolve. The mixture was further aged at 80°C for 3 hours and then cooled to 40°C or below. After cooling, 0.02 parts by mass of 4-methoxyphenol was added to stop the reaction, and a colorless, transparent acrylic copolymer solution 1 was obtained.

[0066] Example 1 18 parts by mass of toluene was added to 18 parts by mass of [Reaction Mixture 1] obtained in Synthesis Example 1, and the mixture was mixed uniformly at room temperature for 1 hour under moisture-shielded conditions to obtain Composition 1. The obtained Composition 1 was applied with a brush to the main surface of a porous substrate, a plank of wood (Japanese cypress) (main surface dimensions: 120 mm × 120 mm), and left to stand for 30 minutes under conditions of a temperature of 23°C and a humidity of 50% RH to form a primer layer. After that, a dealcohol-curing (room-temperature condensation-curing) two-component silicone sealant (SEALANT-FC-295SG: manufactured by Shin-Etsu Chemical Co., Ltd.) was applied in the form of a bead (diameter 10 mm, length 50 mm) to the surface (on the primer layer) of the wood to which Composition 1 had been applied, to obtain a test piece for evaluating adhesion.

[0067] [Example 2] Composition 2 was obtained in the same manner as in Example 1, except that 18 parts by mass of isobutyl acetate was used instead of 18 parts by mass of toluene. Using the obtained composition 2, a test piece for evaluating adhesion was prepared in the same manner as in Example 1.

[0068] Example 3 18 parts by mass of toluene was added to 18 parts by mass of [Reaction Mixture 2] obtained in Synthesis Example 2, and the mixture was mixed uniformly at room temperature for 1 hour under moisture protection to obtain Composition 3. Using the obtained Composition 3, a test piece for evaluating adhesion was prepared in the same manner as in Example 1.

[0069] [Example 4] Composition 4 was obtained in the same manner as in Example 3, except that 18 parts by mass of isobutyl acetate was used instead of 18 parts by mass of toluene. Using the obtained composition 4, a test piece for evaluating adhesion was prepared in the same manner as in Example 1.

[0070] Comparative Example 1 Test pieces for evaluating adhesion were prepared in the same manner as in Example 1, except that no primer composition was used (i.e., the two-component silicone sealant was applied directly to the wood without forming a primer layer).

[0071] [Comparative Example 2] Composition 5 was obtained in the same manner as in Example 1, except that 18 parts by mass of toluene was not added. An attempt was made to prepare a test piece for evaluating adhesion using the obtained composition 5 in the same manner as in Example 1, but the viscosity of the composition was extremely high, making it difficult to apply the composition uniformly to the surface of the substrate, and therefore preparation of the test piece was discontinued.

[0072] [Comparative Example 3] Composition 6 was obtained in the same manner as in Example 3, except that 18 parts by mass of toluene was not added. An attempt was made to prepare a test piece for evaluating adhesion using the obtained composition 5 in the same manner as in Example 1, but the viscosity of the composition was extremely high, making it difficult to apply the composition uniformly to the surface of the substrate, and therefore preparation of the test piece was discontinued.

[0073] [Comparative Example 4] Composition 7 was obtained in the same manner as in Example 1, except that 15 parts by mass of [Acrylic Copolymer Solution 1] was added. Using the obtained composition 7, a test piece for evaluating adhesion was prepared in the same manner as in Example 1.

[0074] [Evaluation of Adhesion] Using the test pieces for evaluating adhesion prepared in Examples 1 to 4 and Comparative Examples 1 to 4, the adhesion to wood (cypress) was evaluated by the following method.

[0075] [Physical Property Evaluation Test] [Initial Adhesion] The test pieces for adhesiveness evaluation were aged for 7 days under conditions of 23°C and 50% RH, after which the bead-shaped silicone rubber cured product of the silicone sealant was cut with a knife and the cut portion was manually peeled off (the bead-shaped silicone rubber cured product was pinched with fingers and pulled in the direction of peeling from the wood), and the peeling state was observed to evaluate the state of the adhesive interface between the wood (adherend including the primer layer) and the bead-shaped silicone rubber cured product. The evaluation was carried out as follows: if the area ratio of the primer layer that had cohesively failed on the peeled surface of the bead-shaped silicone rubber cured product (sealant) was 90% or more, it was rated as "Good", if it was 50% or more but less than 90%, it was rated as "Average", and if it was less than 50%, it was rated as "Poor". The initial adhesion test results for each primer composition are shown in Table 1.

[0076] [Water-resistant adhesion] After aging for 7 days under conditions of a temperature of 23°C and a humidity of 50% RH, the specimens were further immersed in warm water at 50°C for 7 days, dried for 1 to 3 hours, and then evaluated in the same manner as in the test for initial adhesion. The test results for water-resistant adhesion when each primer composition was used are shown in Table 1.

[0077]

[0078] From the results in Table 1, Examples 1 to 4 and Comparative Example 4 showed good adhesion not only in the initial stage but also after immersion in water (water-resistant adhesion). On the other hand, Comparative Example 1 was evaluated as "×" for water-resistant adhesion.

[0079] The viscosity of each composition prepared in Examples 1 and 3 and Comparative Example 4 immediately after preparation was measured at room temperature (23°C) using a capillary viscometer (Cannon-Fenske viscometer, manufactured by Shibata Scientific Products Co., Ltd.). The appearance of the wood surface after the primer layer was formed was also visually evaluated for gloss. The viscosity and evaluation results of each primer composition are shown in Table 2.

[0080]

[0081] The results in Table 2 show that Comparative Example 4 has a significantly higher viscosity than Examples 1 and 3, and there is a concern that compositions containing acrylic polymers may impair coating workability. Furthermore, in Examples 1 and 3, the appearance of the wood after primer layer formation did not exhibit the gloss that would be attributed to a cured acrylic film, and the appearance of the substrate was not impaired. On the other hand, in Comparative Example 4, the gloss characteristic of a cured acrylic film was observed after primer layer formation. With compositions containing acrylic polymers, the gloss characteristic of a cured acrylic film may impair the appearance of the substrate after coating.

[0082] Synthesis Example 4 Synthesis of Epoxy Prepolymer 1 Into a 500 ml separable flask equipped with a stirrer, a reflux condenser, and a thermometer, 68.08 g (0.2 mol) of bisphenol A diglycidyl ether, 17.93 g (0.1 mol) of γ-aminopropyltrimethoxysilane, and 29.65 g (0.2 mol) of vinyltrimethoxysilane were placed, heated to 60° C., and stirred for 3 days to obtain a colorless, transparent liquid (epoxy prepolymer 1) composed of a compound represented by the following formula (11).

[0083] The weight-average molecular weight of the obtained epoxy prepolymer was confirmed to be 2808 by GPC measurement. In this example, the weight-average molecular weight is a value analyzed by GPC (gel permeation chromatography) using polystyrene as a standard substance under the following conditions. [Measurement conditions] Developing solvent: tetrahydrofuran (THF) Flow rate: 0.35 ml / min Column: Multipore HZ-H x 4 (manufactured by Tosoh Corporation) Column temperature: 40°C Sample injection volume: 10 μL (THF solution with a concentration of 0.2% by mass)

[0084] Synthesis Example 5: Synthesis of epoxy prepolymer 2 A 500 ml separable flask equipped with a stirrer, reflux condenser, and thermometer was charged with 43.26 g (0.2 mol) of neopentyl glycol diglycidyl ether, 17.93 g (0.1 mol) of γ-aminopropyltrimethoxysilane, and 29.65 g (0.2 mol) of vinyltrimethoxysilane, and the mixture was heated to 60° C. and stirred for 3 days to obtain a colorless, transparent liquid (epoxy prepolymer 2) composed of a compound represented by the following formula (12). The weight-average molecular weight of the obtained epoxy prepolymer was confirmed to be 2020 by GPC measurement.

[0085] Synthesis Example 6: Synthesis of Epoxy Prepolymer 3 A 500 ml separable flask equipped with a stirrer, a reflux condenser, and a thermometer was charged with 34.84 g (0.2 mol) of ethylene glycol diglycidyl ether, 17.93 g (0.1 mol) of γ-aminopropyltrimethoxysilane, and 29.65 g (0.2 mol) of vinyltrimethoxysilane, and the mixture was heated to 60° C. and stirred for 3 days to obtain a colorless, transparent liquid (epoxy prepolymer 3) composed of a compound represented by the following formula (13): The weight-average molecular weight of the obtained epoxy prepolymer was confirmed to be 2,090 by GPC measurement.

[0086] [Example 5] 18 parts by mass of [epoxy prepolymer 1] obtained in Synthesis Example 4 was added to 18 parts by mass of toluene, and the mixture was mixed uniformly at room temperature for 1 hour under moisture-shielded conditions to obtain Composition 8. The obtained Composition 8 was used as a primer and applied with a brush to the main surface of a porous substrate, a plank of wood (cypress) (main surface dimensions: 120 mm x 120 mm), and left to stand for 30 minutes under conditions of a temperature of 23 ° C and a humidity of 50% RH to form a primer layer. After that, a dealcohol-type (room temperature condensation curing type) two-component silicone sealant (SEALANT-FC-295SG: manufactured by Shin-Etsu Chemical Co., Ltd.) was applied in a bead shape (diameter 10 mm, length 50 mm) to the primer-coated surface (on the primer layer) of the wood to obtain a test piece for adhesiveness evaluation. The appearance of the wood surface after the primer layer was formed was visually evaluated for gloss.

[0087] [Example 6] Test pieces for adhesiveness evaluation were prepared in the same manner as in Example 5, except that epoxy prepolymer 2 was used instead of epoxy prepolymer 1. The appearance of the wood surface after the primer layer was formed was visually evaluated for gloss.

[0088] [Example 7] Test pieces for evaluating adhesion were prepared in the same manner as in Example 5, except that epoxy prepolymer 3 was used instead of epoxy prepolymer 1. The appearance of the wood surface after the primer layer was formed was visually evaluated for gloss.

[0089] Comparative Example 5 Test pieces for evaluating adhesion were prepared in the same manner as in Example 5, except that no primer composition was used (i.e., the two-component silicone sealant was applied directly to the wood without forming a primer layer).

[0090] [Evaluation of Adhesion] Using the test pieces for adhesiveness evaluation prepared in Examples 5 to 7 and Comparative Example 5, the adhesiveness to wood (cypress) was evaluated by the following method.

[0091] [Initial Adhesion] The test pieces for adhesiveness evaluation were aged for 7 days under conditions of 23°C and 50% RH, after which the bead-shaped silicone rubber cured product of the silicone sealant was cut with a knife and the cut portion was manually peeled off (the bead-shaped silicone rubber cured product was pinched with fingers and pulled in the direction of peeling from the wood), and the peeling state was observed to evaluate the state of the adhesive interface between the wood (adherend including the primer layer) and the bead-shaped silicone rubber cured product. The evaluation was based on the following criteria: "Good" indicates that the percentage of the area of ​​cohesive failure on the peeled surface of the bead-shaped silicone rubber cured product (sealant) was 80% or more; "Fair" indicates that the percentage was 50% or more but less than 80%; and "Poor" indicates that the percentage was less than 50%. The initial adhesion test results for each primer composition are shown in Table 3.

[0092] [Water-resistant adhesion] After aging for 7 days under conditions of a temperature of 23°C and a humidity of 50% RH, the specimens were further immersed in water at 50°C for 7 days, thoroughly dried, and then evaluated in the same manner as in the test for initial adhesion. The test results for water-resistant adhesion when each primer composition was used are shown in Table 3.

[0093]

[0094] From the results in Table 3, Examples 5 to 7 showed not only good initial adhesion but also good adhesion after immersion in water (water-resistant adhesion).

Claims

1. A primer composition for porous substrates, comprising: (A) an adhesion promoter consisting of a reaction mixture of a polyfunctional epoxy compound and an aminoalkylsilane compound; and (B) an organic solvent, and not containing a (meth)acrylic copolymer.

2. The primer composition according to claim 1, wherein the component (A) is a reaction mixture of a hydrolyzable organosilane compound having no amino group and / or a partial hydrolysis condensate thereof.

3. The primer composition according to claim 1, wherein the component (A) comprises an epoxy prepolymer represented by the following average composition formula (1): (In formula (1), X is independently a divalent hydrocarbon group having 1 to 31 carbon atoms which may contain an oxygen atom, a nitrogen atom, or a sulfur atom; R 1 are independently an alkylene group having 3 to 12 carbon atoms or an arylene group having 6 to 10 carbon atoms, and R 2 and R 3 are each independently an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms or an unsubstituted or substituted aryl group having 6 to 10 carbon atoms, l is independently 1 or 2, m is independently a number from 0 to 3, and n is a number from 0 to 50.

4. The primer composition according to claim 1, wherein the component (A) comprises a reaction product of a polyfunctional epoxy compound represented by the following general formula (2), an aminoalkylsilane compound represented by the general formula (3), and a hydrolyzable organosilane compound having no amino group or mercapto group represented by the general formula (4): (In formula (2), X represents a divalent hydrocarbon group having 1 to 31 carbon atoms and optionally containing an oxygen atom, a nitrogen atom, or a sulfur atom, and having at least one of an alkylene group which may have a branched structure, a monocyclic structure, and a polycyclic structure.) (In formula (3), R 1 is an alkylene group having 3 to 12 carbon atoms or an arylene group having 6 to 10 carbon atoms, and R 2 and R 3 are each independently an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms or an unsubstituted or substituted aryl group having 6 to 10 carbon atoms, and m is a number from 0 to 3. (In formula (4), R 2 and R 3 are each independently an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms or an unsubstituted or substituted aryl group having 6 to 10 carbon atoms, and l' is 2 or 3.

5. The primer composition according to claim 1, further comprising (C) a hydrolyzable organosilane compound and / or a partial hydrolysis condensate thereof.

6. The primer composition according to claim 1, wherein the component (B) is any one or a mixture of two or more solvents selected from aromatic hydrocarbon solvents, alcohol solvents, ketone solvents, ether solvents, ester solvents and paraffin solvents.

7. The primer composition according to claim 1, wherein component (B) has a flash point of -40°C or higher, a boiling point of 41°C or higher, and an ignition point of 101°C or higher.

8. The primer composition according to claim 1, which is used to bond a cured product of a room temperature condensation curing type silicone rubber composition or an addition curing type silicone rubber composition to a porous substrate.

9. The primer composition according to claim 1, which is used to improve water-resistant adhesion.

10. The primer composition of claim 1, wherein the porous substrate is made of wood.

11. A method for adhering a silicone resin to a porous substrate, comprising the steps of: applying a primer composition according to any one of claims 1 to 10 to the surface of a porous substrate to form a primer layer; and then applying and curing a room-temperature condensation-curing silicone rubber composition or an addition-curing silicone rubber composition to the surface of the primer layer to form a silicone resin layer made of a cured silicone rubber.

12. The bonding method according to claim 11, which improves the water-resistant adhesion between a silicone resin and a porous substrate.

13. An epoxy prepolymer represented by the following average composition formula (1): (In formula (1), X is independently a divalent hydrocarbon group having 1 to 31 carbon atoms which may contain an oxygen atom, a nitrogen atom, or a sulfur atom; R 1 are independently an alkylene group having 3 to 12 carbon atoms or an arylene group having 6 to 10 carbon atoms, and R 2 and R 3 are each independently an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms or an unsubstituted or substituted aryl group having 6 to 10 carbon atoms, l is independently 1 or 2, m is independently a number from 0 to 3, and n is a number from 0 to 50.

14. The epoxy prepolymer according to claim 13, which is a reaction product of a polyfunctional epoxy compound represented by the following general formula (2), an aminoalkylsilane compound represented by the general formula (3), and a hydrolyzable organosilane compound having no amino group or mercapto group represented by the general formula (4). (In formula (2), X represents a divalent hydrocarbon group having 1 to 31 carbon atoms and optionally containing an oxygen atom, a nitrogen atom, or a sulfur atom, and having at least one of an alkylene group which may have a branched structure, a monocyclic structure, and a polycyclic structure.) (In formula (3), R 1 is an alkylene group having 3 to 12 carbon atoms or an arylene group having 6 to 10 carbon atoms, and R 2 and R 3 are each independently an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms or an unsubstituted or substituted aryl group having 6 to 10 carbon atoms, and m is a number from 0 to 3. (In formula (4), R 2 and R 3 are each independently an unsubstituted or substituted alkyl group having 1 to 10 carbon atoms or an unsubstituted or substituted aryl group having 6 to 10 carbon atoms, and l' is 2 or 3.

15. The epoxy prepolymer of claim 14, wherein the aminoalkylsilane compound is γ-aminopropyltrimethoxysilane or γ-aminopropyltriethoxysilane.

16. The epoxy prepolymer of claim 13, which is used as a primer for porous substrates.

17. The epoxy prepolymer according to claim 16, which improves the adhesion between a cured product of a room temperature condensation curing type silicone rubber composition or an addition curing type silicone rubber composition and a porous substrate.

18. The epoxy prepolymer of claim 16, wherein the porous substrate is made of wood.

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