WO2026009962A1 - Primer composiiton and adhesion method - Google Patents

Abstract

A primer composition for a porous substrate, said primer composition: containing (A) a (meth)acrylic copolymer having an alkoxysilyl group, (B) an adhesion improver comprising a reaction mixture of (B1) and/or (B2), (B1) being a reaction mixture of a polyfunctional isocyanate compound and a mercapto alkylsilane compound and (B2) being a reaction mixture of a polyfunctional epoxy compound and an aminoalkylsilane compound, and (C) an organic solvent; and exhibiting good adhesion properties even after a processing (application and curing) site has been immersed in water.

Description

Primer composition and adhesion method

The present invention relates to a primer composition for porous substrates, and in particular to a primer composition that 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 that maintains good adhesion even after immersion in water, as well as a method for bonding a silicone resin to a porous substrate using the primer composition.

Cured products of silicone rubber compositions (silicone rubber cured products) selected from room-temperature condensation-curing silicone compositions and addition-curing silicone compositions are used in a wide range of fields (such as sealants for building materials and adhesives in the electrical and electronic fields) due to their excellent heat resistance, cold resistance, weather resistance, electrical insulation, and safety, and are often used as components combined with various substrates. Generally, in order to adhere cured products of these silicone rubber compositions to various substrates, a primer composition is applied to the substrate (adherend) beforehand.

Known primers include carbon functional silanes, such as aminoalkylsilanes, which have functional groups that can react with one of the components of silicone rubber compositions. However, these have the drawback of reducing adhesive strength and, in some cases, causing peeling if moisture is present in the application area. In particular, when the adherend is a porous material, the large number of voids present means that the material may contain moisture. This means that the primer layer (coated surface) is susceptible to moisture not only from the outer surface but also from the material itself, reducing adhesion and making it susceptible to peeling. Furthermore, when outdoor use is anticipated, even if the material is sufficiently dry at the time of application, it may still be affected by rainwater, so high water resistance is required.

With regard to wood, among other porous materials, there are currently high hopes for its use in light of the recent push for carbon neutrality. However, there are few examples of room-temperature condensation-curing silicone compositions and addition-curing silicone compositions being used on wood as an adherend. In addition, because wood itself contains moisture and resin, it is difficult to achieve adhesive properties with these compositions. Furthermore, it is extremely difficult to maintain sufficient adhesiveness even after the applied (coated and cured) area has been immersed (submerged) in water.

In this regard, Japanese Patent Application Laid-Open 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.

Furthermore, Japanese Patent Application Laid-Open No. 48-75633 (Patent Document 2) describes how reacting aminoalkylalkoxysilane and epoxyalkylalkoxysilane under specified conditions to form an adhesion promoter maintains adhesive strength even after the applied (applied and cured) area is immersed in water.

However, Patent Document 1 assumes that concrete, which can be affected by alkalinity, is used as the substrate, while Patent Document 2 evaluates glass or aluminum as the substrate; neither document evaluates the adhesive properties, particularly water-resistant adhesive properties, of porous materials as the substrate.

Japanese Patent Application Publication No. 11-209682 Japanese Patent Application Publication No. 48-75633

The present invention has been developed in light of the above circumstances, and aims to provide a primer composition for porous substrates, particularly wood, that maintains good adhesion even after the applied (applied and cured) area is immersed in water, as well as a method for bonding silicone resin to a porous substrate.

As a result of intensive research conducted by the inventors to solve the above-mentioned problems, they discovered that adding a reaction mixture of a polyfunctional isocyanate compound and a mercaptoalkylsilane and/or a reaction mixture of a polyfunctional epoxy monomer and an aminoalkylsilane is effective in improving the adhesion, particularly water-resistant adhesion, of a primer composition for porous substrates at the application (coating and curing) point. They also discovered that combining a hydrolyzable organosilane compound with an acrylic copolymer containing alkoxysilyl groups is extremely effective, leading to the completion of the present invention.

That is, the present invention provides the following primer composition and adhesion method.
[1]
(A) a (meth)acrylic copolymer having an alkoxysilyl group;
(B) an adhesion improver comprising a reaction mixture of the following components (B1) and/or (B2);
A primer composition for porous substrates, comprising: (B1) a reaction mixture of a polyfunctional isocyanate compound and a mercaptoalkylsilane compound; (B2) a reaction mixture of a polyfunctional epoxy compound and an aminoalkylsilane compound; and (C) an organic solvent.
[2]
The primer composition according to [1], wherein the component (B1) is a reaction mixture of a hydrolyzable organosilane compound having no amino group or no mercapto group and/or a partial hydrolysis condensate thereof.
[3]
The primer composition according to [1] or [2], wherein the component (B2) is a reaction mixture of a hydrolyzable organosilane compound having no amino group or no mercapto group and/or a partial hydrolysis condensate thereof.
[4]
The primer composition according to any one of [1] to [3], wherein the component (B2) contains an epoxy prepolymer represented by the following average composition formula (1):
(In formula (1), X independently represents 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 independently represents an alkylene group having 3 to 12 carbon atoms or an arylene group having 6 to 10 carbon atoms; R ² and R ³ independently represent 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 independently represents 1 or 2; m independently represents a number from 0 to 3; and n represents a number from 0 to 50.)
[5]
The primer composition according to any one of [1] to [4], wherein the component (B2) 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, 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), ^R2 and ^R3 each independently represent 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.)
[6]
The primer composition according to [5], wherein the aminoalkylsilane compound is γ-aminopropyltrimethoxysilane or γ-aminopropyltriethoxysilane.
[7]
The primer composition according to any one of [1] to [6], further comprising (D) a hydrolyzable organosilane compound and/or a partial hydrolysis condensate thereof.
[8]
The primer composition according to any one of [1] to [7], wherein the (meth)acrylic copolymer of the component (A) is a copolymer of a (meth)acrylic acid ester monomer having an alkoxysilyl group and a (meth)acrylic acid ester monomer not having an alkoxysilyl group.
[9]
The primer composition according to [8], wherein the content of the (meth)acrylic acid ester monomer having an alkoxysilyl group in the entire monomer components of the component (A) is 1 to 30 mass %.
[10]
The primer composition according to any one of [1] to [9], wherein the component (C) is any one or a mixture of two or more selected from aromatic hydrocarbon solvents, alcohol solvents, ketone solvents, ether solvents, ester solvents, and paraffin solvents.
[11]
The primer composition according to any one of [1] to [10], wherein the component (C) 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.
[12]
The primer composition according to any one of [1] to [11], which is used for bonding 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.
[13]
The primer composition according to any one of [1] to [12], which is for improving water-resistant adhesion.
[14]
The primer composition according to any one of [1] to [13], wherein the porous substrate is made of wood.
[15]
A method for adhering a silicone resin to a porous substrate, comprising the steps of: applying the primer composition according to any one of [1] to [14] 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 a cured silicone rubber.
[16]
The adhesion method according to [15], which improves the water-resistant adhesion between the silicone resin and the porous substrate.

The primer composition of the present invention is applied to the surface of a porous substrate to form a primer layer, which allows the formed on top of it to adhere well to the porous substrate, such as a cured product (cured silicone rubber product) of a silicone rubber composition selected from a room-temperature condensation-curable silicone composition and an addition-curable silicone composition, and in particular a cured product layer of a room-temperature condensation-curable silicone rubber composition, and maintains good adhesion even after immersion in water.

The present invention will be described in detail below, but the present invention 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.

[Primer composition]
The primer composition of the present invention comprises:
(A) a (meth)acrylic copolymer having an alkoxysilyl group;
(B) an adhesion improver comprising a reaction mixture of the following components (B1) and/or (B2);
The composition is for use on a porous substrate, and contains (B1) a reaction mixture of a polyfunctional isocyanate compound and a mercaptoalkylsilane compound, (B2) a reaction mixture of a polyfunctional epoxy compound and an aminoalkylsilane compound, and (C) an organic solvent.

-Component (A)-
Component (A) is a (meth)acrylic copolymer having an alkoxysilyl group, and in particular, an acrylic copolymer obtained by copolymerizing a monomer component containing a (meth)acrylic acid ester having an alkoxysilyl group and a (meth)acrylic acid ester not having an alkoxysilyl group, and has the function of forming a film on an adherend.

The acrylic copolymer that constitutes component (A) is obtained by copolymerizing monomer components including at least one type of (meth)acrylic acid ester that has an alkoxysilyl group in its molecule (hereinafter referred to as alkoxysilyl group-containing component (A1)) and at least one type of (meth)acrylic acid ester that does not have an alkoxysilyl group in its molecule (hereinafter referred to as alkoxysilyl group-free component (A2)).

The polymerization method for copolymerizing the above-mentioned monomer components is not particularly limited, but examples include radical polymerization, cationic polymerization, and anionic polymerization. Among these, random radical polymerization using an organic peroxide or organic azo compound as an initiator is an effective and simple method.

This alkoxysilyl group-containing component (A1) is a monomer component containing at least one (meth)acrylic acid ester having an alkoxysilyl group in the molecule. In this monomer, the (meth)acrylic acid ester having an alkoxysilyl group can be used alone or in combination of two or more. Furthermore, the (meth)acrylic acid ester having an alkoxysilyl group has at least one, and preferably two or three, alkoxysilyl groups in one molecule.

Here, examples of (meth)acrylic acid esters having an alkoxysilyl group in the molecule include 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, and 3-(meth)acryloxypropylmethyldiethoxysilane. Of these, 3-(meth)acryloxypropyltrimethoxysilane is particularly preferred.

The content of this alkoxysilyl group-containing component (A1) is 1 to 30% by mass, and preferably 1 to 20% by mass, where the total mass of the monomer components used to obtain component (A) (the sum of components (A1) and (A2)) is taken as 100% by mass. If the content of component (A1) is less than 1% by mass or more than 30% by mass of the total monomer components used to obtain component (A), adhesion to the adherend may be impaired.

This alkoxysilyl group-free component (A2) is a monomer component containing at least one (meth)acrylic acid ester that does not have an alkoxysilyl group in the molecule. In this monomer, one or more alkoxysilyl group-free (meth)acrylic acid esters can be used in combination.

Furthermore, examples of (meth)acrylic acid esters that do not have an alkoxysilyl group include acrylic acid esters and methacrylic acid esters such as methyl acrylate, ethyl acrylate, n-butyl acrylate, tert-butyl acrylate, isobutyl acrylate, isopentyl acrylate, n-hexyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, and isobornyl acrylate, and methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate, isobutyl methacrylate, isopentyl methacrylate, n-hexyl methacrylate, isooctyl methacrylate, 2-ethylhexyl methacrylate, n-octyl methacrylate, and isobornyl methacrylate. The (meth)acrylic acid ester not containing an alkoxysilyl group is preferably an aliphatic hydrocarbon ester of (meth)acrylic acid, more preferably an alkyl (meth)acrylic acid ester having an alkyl group containing 1 to 20 carbon atoms, and even more preferably an alkyl (meth)acrylic acid ester having an alkyl group containing 1 to 10 carbon atoms. Of these, particularly preferred are methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, and tert-butyl (meth)acrylate.

The content of this alkoxysilyl group-free component (A2) is 70 to 99 mass%, and preferably 80 to 99 mass%, when the mass of all the monomer components used to obtain component (A) (the sum of components (A1) and (A2)) is taken as 100 mass%. If the content of component (A2) is less than 70 mass% or more than 99 mass% of the total monomers used to obtain component (A), adhesion to the adherend may be impaired.

The amount of component (A) blended is 2 to 100 parts by mass, and preferably 5 to 50 parts by mass, per 10 parts by mass of component (B), described below. If the amount of component (A) blended is too small, adhesion may be impaired, while if it is too large, uneven coating may occur when applied to the adherend.

-(B) Component-
Component (B) is an adhesion improver consisting of a reaction mixture of the following components (B1) and/or (B2):
(B1) A reaction mixture of a polyfunctional isocyanate compound and a mercaptoalkylsilane compound. (B2) A reaction mixture of a polyfunctional epoxy compound and an aminoalkylsilane compound.

((B1) component)
The reaction mixture of the polyfunctional isocyanate compound and mercaptoalkylsilane compound of component (B1) is an adduct of the polyfunctional isocyanate compound (a monomer and/or a polymer thereof having two or more isocyanate groups in the molecule) and a mercaptoalkylsilane compound (a hydrolyzable mercaptoalkylsilane and/or a hydrolyzed condensation polymer thereof) (i.e., an addition reaction product in which a mercapto group in the mercaptoalkylsilane compound is added to an isocyanate group in the polyfunctional isocyanate compound), and functions as a film-forming component and an adhesive component.

Examples of polyfunctional isocyanate compounds include aliphatic isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, naphthalene diisocyanate, dimer acid diisocyanate, and lysine diisocyanate methyl ester; isocyanurate silanes such as tris(trimethoxysilyl)isocyanurate; and polymers or partial hydrolysates of isocyanate group-containing silane compounds such as isocyanate group-containing mercaptosilanes, gamma-isocyanate propyl trimethoxysilane, gamma-isocyanate propyl triethoxysilane, gamma-isocyanate propyl methyl diethoxysilane, and gamma-isocyanate propyl methyl dimethoxysilane. These may be used alone or in combination of two or more.

Examples of mercaptoalkylsilane compounds include hydrolyzable organosilane compounds (silane coupling agents) that contain a mercapto group and two or three hydrolyzable groups, such as alkoxy groups, bonded to silicon atoms in the molecule, such as mercapto-containing silanes such as gamma-mercaptopropyltrimethoxysilane, gamma-mercaptopropyltriethoxysilane, gamma-mercaptopropylmethyldimethoxysilane, and gamma-mercaptopropylmethyldiethoxysilane, and/or their hydrolyzed condensation polymers. Excellent film-forming ability is observed when the molecule contains three or more hydrolyzable groups, and trialkoxymercaptoalkylsilanes such as gamma-mercaptopropyltrimethoxysilane and gamma-mercaptopropyltriethoxysilane are preferred. These silane coupling agents may be used alone or in combination of two or more.

For the addition reaction between a polyfunctional isocyanate compound and a mercaptoalkylsilane compound, the amount of mercapto groups in the mercaptoalkylsilane compound is preferably 0.01 to 100 moles, and more preferably 0.1 to 10 moles, per mole of isocyanate groups in the polyfunctional isocyanate compound.

There are no particular limitations on the method for synthesizing the reaction mixture of a polyfunctional isocyanate compound and a mercaptoalkylsilane compound. For example, if the mercaptoalkylsilane compound is hydrolyzable, the polyfunctional isocyanate compound and the mercaptoalkylsilane compound can be mixed for 30 minutes to 12 hours at room temperature (23±15°C) in an atmosphere protected from moisture. At this time, an organic solvent such as toluene or ethyl acetate, which will become component (C) described below, can be used, and a reaction catalyst (catalytic amount) such as tin 2-ethylhexanoate can also be added.

Examples of such reaction catalysts include non-metallic organic catalysts and metallic catalysts.

Known non-metallic organic catalysts can be used, including, but not limited to, phosphazene-containing compounds such as N,N,N',N',N'',N''-hexamethyl-N'''-(trimethylsilylmethyl)-phosphorimidic triamide; amine compounds or salts thereof such as n-octylamine, hexylamine, dodecylamine phosphate, and tetramethylguanidine; quaternary ammonium salts such as benzyltriethylammonium acetate; dialkylhydroxylamines such as dimethylhydroxylamine and diethylhydroxylamine; tetramethylguanidylpropyltrimethoxysilane, tetramethylguanidylpropylmethyldimethoxysilane, and tetramethylguanidylpropyltris(trimethylsiloxy)silane. Furthermore, the non-metallic organic catalysts may be used alone or in combination of two or more.

Known metal catalysts can be used, for example, organotin compounds such as tin 2-ethylhexanoate (tin octoate), dibutyltin diacetate, dibutyltin dilaurate, dibutyltin dioctoate, dioctyltin dineodecanoate, and di-n-butyl-dimethoxytin; titanate esters or titanium chelate compounds such as tetraisopropoxytitanium, tetra-n-butoxytitanium, tetrakis(2-ethylhexoxy)titanium, dipropoxybis(acetylacetonato)titanium, and titanium isopropoxyoctylene glycol; zinc naphthenate, zinc stearate, and zinc-2-ethyloctanoate. Examples of suitable metal catalysts include, but are not limited to, aluminum alcoholate compounds such as aluminum citrate, iron 2-ethylhexoate, cobalt 2-ethylhexoate, manganese 2-ethylhexoate, cobalt naphthenate, aluminum isopropylate, and aluminum secondary butylate; aluminum chelate compounds such as aluminum alkyl acetate diisopropylate and aluminum bisethylacetoacetate monoacetylacetonate; and organic bismuth compounds such as bismuth(III) neodecanoate, bismuth(III) 2-ethylhexanoate, bismuth(III) citrate, and bismuth octoate. Furthermore, metal catalysts may be used alone or in combination of two or more.

The amount of the reaction catalyst is preferably 0.001 to 10% by mass, and more preferably 0.01 to 1% by mass, of the total amount of component (B1) (excluding any organic solvent added during the synthesis). Within this range, the reaction of component (B1) can be promoted without affecting adhesion.

((B2) component)
The reaction mixture of the polyfunctional epoxy compound and aminoalkylsilane compound of component (B2) 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 to (a part of) an epoxy group in the polyfunctional epoxy compound), and functions as a film-forming component and an adhesive component.

A polyfunctional epoxy compound is a polyfunctional monomer that has two or more epoxy groups in its molecule and does not contain any reactive functional groups other than epoxy groups. It preferably contains two glycidyl ether groups and/or alicyclic epoxy groups, and more preferably is an aliphatic epoxy compound containing two glycidyl ether groups.

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. Bisphenol A diglycidyl ether is preferred from the standpoints of cost and solubility in solvents. These compounds may be used alone or in combination of two or more.

Aminoalkylsilane compounds include, for example, hydrolyzable organosilane compounds (silane coupling agents) containing 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, such as γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, 3-2-(aminoethylamino)propyltrimethoxysilane, and 3-2-(aminoethylamino)propyltriethoxysilane, and/or their hydrolyzed condensation polymers (organosiloxane oligomers containing 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). Excellent film-forming and adhesive properties are observed when primary amino groups and methoxy groups are present, and γ-aminopropyltrimethoxysilane, 3-2-(aminoethylamino)propyltrimethoxysilane, etc. are preferred. These compounds may be used alone or in combination of two or more.

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

There are no particular limitations on the method for synthesizing the reaction mixture of a polyfunctional epoxy compound and an aminoalkylsilane compound. For example, if 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-protected environment.

Component (B) may be a reaction mixture of a polyfunctional isocyanate compound and a mercaptoalkylsilane compound (component (B1)), or a reaction mixture of a polyfunctional epoxy compound and an aminoalkylsilane compound (component (B2)). These may be used alone or in combination of two or more. When components (B1) and (B2) are used in combination, the mass ratio of components (B1) to (B2) is preferably 100:1 to 1:100, and more preferably 50:1 to 1:50.

As component (B), the reaction mixture of component (B1) of a polyfunctional isocyanate compound and a mercaptoalkylsilane compound may further be a reaction mixture with a hydrolyzable organosilane compound that does not have an amino group or a mercapto group and/or a partial hydrolyzed condensate thereof. Furthermore, the reaction mixture of component (B2) of a polyfunctional epoxy compound and an aminoalkylsilane compound may further be a reaction mixture with a hydrolyzable organosilane compound that does not have an amino group or a mercapto group and/or a partial hydrolyzed condensate thereof.

Examples of hydrolyzable organosilane compounds that do not have amino groups or mercapto groups 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.

When added, the content of the hydrolyzable organosilane compound and/or its partial hydrolysis condensate in component (B) that does not have an amino group or a mercapto group is preferably 1 to 50 mass% of component (B1) or (B2), and more preferably 5 to 40 mass%. Keeping it within this range can improve the storage stability of the composition.

The following further describes the epoxy prepolymer contained in the (B2) component, which is a reaction mixture of a polyfunctional epoxy compound and an aminoalkylsilane compound with a hydrolyzable organosilane compound that does not have an amino group and/or a partial hydrolyzed condensate thereof. In the present invention, the (B2) component, which is a reaction mixture of a polyfunctional epoxy compound and an aminoalkylsilane compound with a hydrolyzable organosilane compound that does not have an amino group and/or a partial hydrolyzed condensate thereof, contains the epoxy prepolymer described below as the main component. "Containing the epoxy prepolymer as the main component" as used here 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.

[Epoxy prepolymer]
The epoxy prepolymer contained in the reaction mixture of component (B2), 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 hydrolysis condensate thereof, is represented by the following average composition formula (1):
(In formula (1), X independently represents 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 independently represents an alkylene group having 3 to 12 carbon atoms or an arylene group having 6 to 10 carbon atoms; R ² and R ³ independently represent 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 independently represents 1 or 2; m independently represents a number from 0 to 3; and n represents a number from 0 to 50.)

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 divalent hydrocarbon groups include linear or branched alkylene groups having 1 to 20 carbon atoms, and cyclic divalent hydrocarbon groups having 3 to 31 carbon atoms (monocyclic divalent hydrocarbon groups or polycyclic divalent hydrocarbon groups). X may contain one or more of these groups, and may also contain an oxygen atom, a nitrogen atom, or a sulfur atom.

X has 1 to 31 carbon atoms, 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, and more preferably contains a phenylene group. It is particularly preferred that X is a divalent hydrocarbon group having 1 to 20 carbon atoms, which may contain oxygen atoms and/or sulfur atoms, 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.

Specific examples of X include those represented by the following formulas (5a) to (5g). Note that the dashed lines in the formulas indicate bonds. In particular, formula (5d) below is preferred from the standpoints of cost and solubility in solvents used in primer preparation.

R ¹ is 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.

^R2 and ^R3 are 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, and 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 groups; and cycloalkyl groups such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, and isobornyl groups. Specific examples of aryl groups having 6 to 10 carbon atoms include phenyl, tolyl, xylyl, α-naphthyl, and β-naphthyl groups. Some or all of the hydrogen atoms of these groups may be substituted with an alkyl group, an aryl group, a halogen atom such as F, Cl, or Br, a cyano group, or the like. Among these, ^R2 and ^R3 are preferably a methyl group, an ethyl group, a vinyl group, or a phenyl group, and from the standpoints of reactivity and cost, a methyl group or a vinyl group is more preferred.

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.

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 or mercapto groups represented by the general formula (4).

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, for example, as the polystyrene-equivalent weight-average molecular weight by gel permeation chromatography (GPC) analysis using tetrahydrofuran as the developing solvent.

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

[Method of manufacturing epoxy prepolymer]
The above-mentioned method for producing an epoxy prepolymer is characterized by mixing and reacting (B2a) a bifunctional epoxy compound (diglycidyl compound) represented by the following general formula (2), (B2b) an aminoalkylsilane compound represented by the following general formula (3), and (B2c) a hydrolyzable organosilane compound (alkylalkoxysilane) having no amino group or mercapto group represented by the following general formula (4):

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

(In formula (3), R ¹ , R ² , R ³ and m are the same as R ¹ , R ² , R ³ and m in average composition formula (1), respectively.)

(In formula (4), R ² and R ³ are the same as R ² and R ³ in average composition formula (1), respectively, and l′ is 2 or 3.)

Examples of the diglycidyl compound represented by formula (2) of component (B2a) include 1,2-cyclohexanedicarboxylate diglycidyl, neopentyl glycol diglycidyl, bisphenol A diglycidyl, bisphenol F diglycidyl, bisphenol AF diglycidyl, and 2,2-bis(4-glycidyloxyphenyl)propane. Bisphenol A diglycidyl is preferred from the standpoints of cost and solubility in solvents. Furthermore, hydrolyzed condensation polymers (organosiloxane oligomers having two glycidyl groups per molecule) of hydrolyzable glycidyl compounds such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropyldimethoxysilane, and 3-glycidoxypropyldiethoxysilane may also be used as component (B2a).

The aminoalkylsilane compound represented by formula (3) of component (B2b) above includes, for example, (hydrolyzable) organosilane compounds (silane coupling agents) such as γ-aminopropyltrimethoxysilane and γ-aminopropyltriethoxysilane, each of which has 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. γ-aminopropyltrimethoxysilane is particularly preferred, as it exhibits excellent film-forming and adhesive properties when it contains a methoxy group. It is also possible to use 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) as component (B2b).

Examples of the alkylalkoxysilane represented by formula (4) of component (B2c) include methyltrimethoxysilane, octyltrimethoxysilane, dimethyldimethoxysilane, vinyltrimethoxysilane, phenyltrimethoxysilane, and methyltriethoxysilane, with methyltrimethoxysilane or vinyltrimethoxysilane being preferred from the standpoints of cost and reactivity.

The amount of component (B2b) added is preferably 0.1 to 1.0 moles, and more preferably 0.1 to 0.6 moles, per mole of (B2a) the polyfunctional epoxy compound (diglycidyl compound) represented by general formula (2).

The amount of component (B2c) added is preferably 1.0 to 10.0 moles, and more preferably 1.0 to 5.0 moles, per mole of (B2a) the polyfunctional epoxy compound (diglycidyl compound) represented by general formula (2).

In the method for producing an epoxy prepolymer, the temperature at which (B2a) the diglycidyl compound represented by the general formula (2), (B2b) the aminoalkylsilane represented by the general formula (3), and (B2c) the alkylalkoxysilane represented by the general formula (4) are mixed and reacted is 10 to 90°C, preferably 20 to 70°C. Temperatures outside this range may result in a significant decrease in reaction or a significant increase in viscosity, making it difficult to recover the reaction product. The reaction time for mixing and reacting is preferably 2 hours to 5 days, and more preferably 8 hours to 3 days.

The method for producing the epoxy prepolymer produces a reaction mixture (epoxy prepolymer containing side chain alkoxysilanes) that is liquid at room temperature (23°C ± 15°C) or that is soluble in the organic solvents (C) used in the present invention, such as aromatic hydrocarbon solvents, alcohol solvents, ketone solvents, ether solvents, ester solvents, and paraffin solvents.

The blending amount of component (B) is preferably 1 to 70 mass% of the total mass of components (A), (B), and (C), and more preferably 5 to 50 mass%. Within this range, it can exhibit good adhesion as a primer layer provided between the porous substrate and the silicone resin layer.

-(C) Component-
The organic solvent of component (C) may be any solvent that dissolves the components of the primer composition in any desired proportion and is volatile at the same time. 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-circuit 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.

Specific examples of component (C) 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. These can be used alone or in combination with two or more solvents. Of these, aromatic hydrocarbon solvents, paraffin solvents, and ester solvents are preferred, with toluene, hexane, ethyl acetate, butyl acetate, and isobutyl acetate being particularly preferred.

By incorporating component (C), it is possible to adjust the workability of the primer composition during application and drying. There are no particular restrictions on the amount of component (C) incorporated, but it is usually 5 to 1,000 parts by mass, and preferably 5 to 100 parts by mass, per 10 parts by mass of component (B). This range ensures a uniform coating of the primer composition when it is formed, and reduces unevenness on the coating surface. Note that when components (A), (B), etc. are added as a solution, the amount of component (C) incorporated refers to the total amount in the composition, including the solvent in the solution.

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

The hydrolyzable organosilane compound and/or its partial hydrolysis condensate in component (D) may be the same as the hydrolyzable organosilane compound and/or its partial hydrolysis condensate in component (B) that does not have an amino group or a mercapto group, 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, dimethyl Examples include alkoxysilanes such as dimethoxysilane, 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.

The amount of component (D) to be blended is not particularly limited, but is 0.01 to 100 parts by mass, and preferably 0.1 to 10 parts by mass, per 10 parts by mass of component (B).Within this range, there is no effect on the preparation and good storage stability can be achieved.
In addition, when a hydrolyzable organosilane compound and/or its partial hydrolysis condensate that does not have an amino group or a mercapto group is added to the components (B1) and (B2), the component (D) does not need to be added.

-Other additives-
In addition to the above-described components (A) to (D), the primer composition of the present invention may further contain at least one known additive selected from pigments, dyes, antioxidants, antioxidants, adhesion promoters, antistatic agents, and flame retardants such as antimony oxide and chlorinated paraffins, within the range that does not impair the object of the present invention.Furthermore, mildew inhibitors, antibacterial agents, etc. may also be added within the range that does not impair the object of the present invention.

The primer composition of the present invention is preferably used for bonding a cured product of a room-temperature condensation-curing silicone rubber composition or an addition-curing silicone rubber composition to a porous substrate. In other words, it can be suitably used to improve adhesion between a porous substrate and a silicone resin composed of a room-temperature condensation-curing silicone rubber composition or a cured product of an addition-curing silicone rubber composition (cured silicone rubber product). It 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, and cured cement), but wood is preferred, and examples of wood materials include cypress, cedar, and pine. The porous substrate may also be treated as desired to improve the durability, weather resistance, and design of the substrate.

[Method for bonding silicone resin to porous substrate]
The method of the present invention for bonding a silicone resin (cured silicone rubber layer) to a porous substrate 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.

As a method for bonding the silicone resin (cured silicone rubber layer) of the present invention to a porous substrate, for example, the primer composition of the present invention may be applied to the surface of the porous substrate (by applying (spraying) with a brush or nonwoven fabric, and then air-drying (curing) at room temperature (23°C ± 15°C) for 30 minutes to 12 hours, preferably 30 minutes to 2 hours (also known as primer treatment)), forming a primer layer. Then, a silicone rubber composition selected from a room-temperature condensation-curable silicone rubber composition and an addition-curable 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., by applying a room-temperature condensation-curable silicone rubber composition and curing the composition at room temperature (23°C ± 15°C), or by applying an addition-curable silicone rubber composition and curing the composition at room temperature (23°C ± 15°C) or by heating (50 to 100°C)), thereby forming a silicone resin consisting of cured silicone rubber, thereby bonding the silicone resin to the porous substrate.

According to the present invention, the surface of a porous substrate such as wood is primed with the primer composition of the present invention, 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. This coating is then cured, allowing the applied (cured) area to exhibit good adhesion even after immersion in water, thereby improving the water-resistant adhesion between the silicone resin and the porous substrate.

The present invention will be explained in detail below using 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." Also, room temperature refers to 23°C.

[Synthesis Example 1: 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.

[Synthesis Example 2: Preparation of Acrylic Polymer 2]
An acrylic polymer solution 2 was obtained in the same manner as in Synthesis Example 1, except that 1.8 parts by mass of 3-methacryloxypropyltrimethoxysilane was not used.

Synthesis Example 3: Preparation of reaction mixture 1 of polyfunctional isocyanate compound and mercaptoalkylsilane
To 53 parts by mass of ethyl acetate, 18 parts by mass of N3200XPM (aliphatic polyisocyanate solution (containing 73% by mass of aliphatic polyisocyanate); manufactured by Godo Chemical Co., Ltd.), 30 parts by mass (0.15 mol) of γ-mercaptopropyltrimethoxysilane, and 0.1 parts by mass of tin 2-ethylhexanoate were added, and the mixture was stirred at room temperature for 40 minutes while blocking moisture, to obtain reaction mixture 1.

Synthesis Example 4: Preparation of reaction mixture 2 of polyfunctional isocyanate compound and mercaptoalkylsilane
To 28 parts by mass of toluene, 17 parts by mass (0.10 mol) of tolylene diisocyanate, 39 parts by mass (0.20 mol) of γ-mercaptopropyltrimethoxysilane, and 0.2 parts by mass of tin 2-ethylhexanoate were added, and the mixture was stirred at room temperature for 1 hour in a moisture-blocking environment, thereby obtaining reaction mixture 2.

Synthesis Example 5: Preparation of reaction mixture 1 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 using a reflux condenser under moisture-blocking conditions, and stirred at 60°C for 8 hours to obtain reaction mixture 3.

Synthesis Example 6: Preparation of reaction mixture 2 of polyfunctional epoxy compound and aminoalkylsilane
To 34 parts by mass (0.10 mol) of 2,2-bis(4-glycidyloxyphenyl)propane, 12 parts by mass (0.05 mol) of N-[3-(trimethoxysilyl)propyl]butan-1-amine and 7.5 parts by mass (0.06 mol) of methyltrimethoxysilane were added, and the mixture was stirred at 60°C for 8 hours under reflux using a reflux hood while being protected from moisture, to obtain reaction mixture 4.

[Example 1]
To 27 parts by mass of [acrylic copolymer solution 1] obtained in Synthesis Example 1, 18 parts by mass of [reaction mixture 1] obtained in Synthesis Example 3, 27 parts by mass of toluene, 7.2 parts by mass of γ-mercaptopropyltrimethoxysilane as an adhesion promoter, and 23 parts by mass of Dismodur HL (a solution of a compound (isocyanurate) formed by an addition reaction of triresin isocyanate (TDI) and hexamethylene diisocyanate (HDI); manufactured by Covestro), were added, and the mixture was mixed uniformly at room temperature for 1 hour in a moisture-protected environment, to obtain Composition 1.
The obtained composition 1 was applied uniformly with a brush to the main surface of a porous substrate, a wooden board (cypress) (dimensions (length × width × length): 50 mm × 50 mm × 25 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 dealcoholization-type (room temperature condensation curing type) 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 wooden board that had been coated with composition 1, to prepare a test piece for evaluating adhesion.

[Example 2]
To 10 parts by mass of [acrylic copolymer solution 1] obtained in Synthesis Example 1, 18 parts by mass of [reaction mixture 2] obtained in Synthesis Example 4 and 6.0 parts by mass of toluene were added, and the mixture was mixed uniformly at room temperature for 30 minutes in a moisture-protected environment to obtain composition 2.
Using the obtained composition 2, a test piece for evaluating adhesiveness was prepared in the same manner as in Example 1.

[Example 3]
To 15 parts by mass of [acrylic copolymer solution 1] obtained in Synthesis Example 1, 18 parts by mass of [reaction mixture 3] obtained in Synthesis Example 5 and 18 parts by mass of toluene were added, and the mixture was mixed uniformly at room temperature for 30 minutes under moisture protection, to obtain composition 3.
Using the obtained composition 3, a test piece for evaluating adhesiveness was prepared in the same manner as in Example 1.

[Example 4]
To 15 parts by mass of [acrylic copolymer solution 1] obtained in Synthesis Example 1, 18 parts by mass of [reaction mixture 4] obtained in Synthesis Example 6 and 18 parts by mass of toluene were added, and the mixture was mixed uniformly at room temperature for 30 minutes under moisture protection, to obtain composition 4.
Using the obtained composition 4, a test piece for evaluating adhesiveness was prepared in the same manner as in Example 1.

[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).

[Comparative Example 2]
Composition 5 was obtained in the same manner as in Example 1, except that 27 parts by mass of [acrylic copolymer solution 1], 7.2 parts by mass of γ-mercaptopropyltrimethoxysilane, and 23 parts by mass of Dismodur HL were not used, that is, 18 parts by mass of [reaction mixture 1] and 27 parts by mass of toluene were added, and the mixture was mixed uniformly at room temperature for 1 hour in a moisture-protected environment.
Using the obtained composition 5, a test piece for evaluating adhesiveness was prepared in the same manner as in Example 1.

[Comparative Example 3]
Composition 6 was obtained in the same manner as in Example 2, except that 10 parts by mass of [acrylic copolymer solution 1] was not added.
Using the obtained composition 6, a test piece for evaluating adhesiveness was prepared in the same manner as in Example 1.

[Comparative Example 4]
Composition 7 was obtained in the same manner as in Example 3, except that 15 parts by mass of [acrylic copolymer solution 1] was not added.
Using the obtained composition 7, a test piece for evaluating adhesiveness was prepared in the same manner as in Example 1.

[Comparative Example 5]
Composition 8 was obtained in the same manner as in Example 2, except that 10 parts by mass of [Acrylic Polymer Solution 2] obtained in Synthesis Example 2 was added instead of 10 parts by mass of [Acrylic Copolymer Solution 1].
Using the obtained composition 8, a test piece for evaluating adhesiveness was prepared in the same manner as in Example 1.

[Evaluation of Adhesion]
Using the test pieces for evaluating adhesiveness prepared in Examples 1 to 4 and Comparative Examples 1 to 5, the adhesiveness to wood (cypress) was evaluated by the following method.

[Initial adhesion]
The test pieces for evaluating adhesion were aged for 7 days under conditions of a temperature of 23°C and a humidity of 50% RH, and then the bead-shaped cured silicone rubber of the silicone sealant was cut with a knife and the cut portion was peeled off by hand (the bead-shaped cured silicone rubber was pinched with the fingers and pulled in the direction of peeling away from the wood), and the state of peeling was observed to evaluate the state of the adhesive interface between the wood (adherend including the primer layer) and the bead-shaped cured silicone rubber.
The evaluation was based on the following criteria: if the area of the primer layer that had cohesively failed on the peeled surface of the bead-shaped cured silicone rubber (sealant) was 90% or more, it was given a "good"; if it was 50% or more but less than 90%, it was given a "fair"; and if it was less than 50%, it was given an "unsatisfactory" rating. The test results for initial adhesion when each primer composition was used are shown in Table 1.

[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 hot 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.

The results in Table 1 show that Examples 1 to 4 not only exhibited good initial adhesion, but also good adhesion after immersion in water (water-resistant adhesion). On the other hand, while Comparative Examples 1 to 5 exhibited good initial adhesion, Comparative Example 4 was rated "△" for water-resistant adhesion, and Comparative Examples 1, 2, 3, and 5 were rated "X."

[Synthesis Example 7: Synthesis of epoxy prepolymer 1]
A 500 ml separable flask equipped with a stirrer, a reflux condenser, and a thermometer was charged with 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, 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):

The weight average molecular weight of the obtained epoxy prepolymer was confirmed to be 2,808 by GPC measurement.
In the examples, the weight average molecular weight is a value obtained by GPC (gel permeation chromatography) analysis using polystyrene as a standard substance under the following conditions.
[Measurement conditions]
Developing solvent: tetrahydrofuran (THF)
・Flow rate: 0.35ml/min
Column: Multipore HZ-H x 4 (Tosoh Corporation)
Column temperature: 40°C
Sample injection volume: 10 μL (THF solution with a concentration of 0.2% by mass)

[Synthesis Example 8: 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, 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). GPC measurement confirmed that the weight-average molecular weight of the obtained epoxy prepolymer was 2,020.

[Synthesis Example 9: Preparation of epoxy prepolymer 3]
A 500 ml separable flask equipped with a stirrer, reflux condenser, and 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, 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). GPC measurement confirmed that the weight-average molecular weight of the obtained epoxy prepolymer was 2,090.

[Example 5]
40 parts by mass of [acrylic copolymer solution 1] obtained in Synthesis Example 1, 30 parts by mass of [epoxy prepolymer 1] obtained in Synthesis Example 7, and 30 parts by mass of toluene were mixed uniformly at room temperature for 1 hour under moisture protection to obtain Composition 9.
The obtained composition 9 was applied uniformly with a brush to the main surface of a porous substrate, a wooden plate (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 dealcoholization-type (room temperature condensation curing type) 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 wooden piece to which composition 9 had been applied, to prepare a test piece for evaluating adhesion.

[Example 6]
A test piece for evaluating adhesiveness was prepared in the same manner as in Example 5, except that epoxy prepolymer 2 was used instead of epoxy prepolymer 1.

[Example 7]
A test piece for evaluating adhesiveness was prepared in the same manner as in Example 5, except that Epoxy Prepolymer 3 was used instead of Epoxy Prepolymer 1.

[Comparative Example 6]
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).

[Evaluation of Adhesion]
Using the test pieces for evaluating adhesiveness prepared in Examples 5 to 7 and Comparative Example 6, the adhesiveness to wood (cypress) was evaluated by the following method.

[Initial adhesion]
The test pieces for evaluating adhesion were aged for 7 days under conditions of a temperature of 23°C and a humidity of 50% RH, and then the bead-shaped cured silicone rubber of the silicone sealant was cut with a knife and the cut portion was peeled off by hand (the bead-shaped cured silicone rubber was pinched with the fingers and pulled in the direction of peeling away from the wood), and the state of peeling was observed to evaluate the state of the adhesive interface between the wood (adherend including the primer layer) and the bead-shaped cured silicone rubber.
The evaluation was based on the following criteria: if the proportion of the area of cohesive failure on the peeled surface of the bead-shaped cured silicone rubber (sealant) was 80% or more, it was given a "Good", if it was 50% or more but less than 80%, it was given a "Fair", and if it was less than 50%, it was given an "Poor". The test results for initial adhesion when each primer composition was used are shown in Table 2.

[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, and after thorough drying, they were 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 2.

The results in Table 2 show that Examples 5 to 7 not only exhibited good initial adhesion, but also good adhesion (water-resistant adhesion) after immersion in water.

Claims (16)

(A) a (meth)acrylic copolymer having an alkoxysilyl group;
(B) an adhesion improver comprising a reaction mixture of the following components (B1) and/or (B2);
A primer composition for porous substrates, comprising: (B1) a reaction mixture of a polyfunctional isocyanate compound and a mercaptoalkylsilane compound; (B2) a reaction mixture of a polyfunctional epoxy compound and an aminoalkylsilane compound; and (C) an organic solvent. The primer composition according to claim 1, wherein the component (B1) is further a reaction mixture with a hydrolyzable organosilane compound that does not have an amino group or a mercapto group and/or a partial hydrolysis condensate thereof. The primer composition according to claim 1, wherein the component (B2) is further a reaction mixture with a hydrolyzable organosilane compound that does not have an amino group or a mercapto group and/or a partial hydrolysis condensate thereof. 2. The primer composition according to claim 1, wherein the component (B2) comprises an epoxy prepolymer represented by the following average composition formula (1):
(In formula (1), X independently represents 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 independently represents an alkylene group having 3 to 12 carbon atoms or an arylene group having 6 to 10 carbon atoms; R ² and R ³ independently represent 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 independently represents 1 or 2; m independently represents a number from 0 to 3; and n represents a number from 0 to 50.) 2. The primer composition according to claim 1, wherein the component (B2) comprises a reaction product of a polyfunctional epoxy compound represented by the following general formula (2), an aminoalkylsilane compound represented by the following general formula (3), and a hydrolyzable organosilane compound having no amino group or mercapto group represented by the following 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, 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), ^R2 and ^R3 each independently represent 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.) The primer composition according to claim 5, wherein the aminoalkylsilane compound is γ-aminopropyltrimethoxysilane or γ-aminopropyltriethoxysilane. The primer composition according to claim 1, further comprising (D) a hydrolyzable organosilane compound and/or a partial hydrolysis condensate thereof. The primer composition according to claim 1, wherein the (meth)acrylic copolymer of component (A) is a copolymer of a (meth)acrylic acid ester monomer having an alkoxysilyl group and a (meth)acrylic acid ester monomer not having an alkoxysilyl group. The primer composition according to claim 8, wherein the content of the (meth)acrylic acid ester monomer having an alkoxysilyl group in the total monomer components of component (A) is 1 to 30 mass%. The primer composition according to claim 1, wherein component (C) is 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. The primer composition according to claim 1, wherein component (C) 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. The primer composition according to claim 1, which is used to bond a cured product of a room-temperature condensation-curing silicone rubber composition or an addition-curing silicone rubber composition to a porous substrate. The primer composition according to claim 1, which is used to improve water-resistant adhesion. The primer composition according to claim 1, wherein the porous substrate is made of wood. A method for bonding a silicone resin to a porous substrate, comprising the steps of: applying the primer composition described in any one of claims 1 to 14 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. The bonding method described in claim 15, which improves the water-resistant adhesion between the silicone resin and the porous substrate.