JP7777447B2 - Primer composition - Google Patents

Description

The present invention relates to a primer composition.

Traditionally, in residential construction, a primer is applied to the surface of an exterior wall material before the sealant is applied to the surface. Applying a primer to the surface of an exterior wall material, etc., improves adhesion between the adherend and the sealant, strengthening the surface, which may have weak surface strength.

Furthermore, primer compositions are not simply secondary materials for sealants; they are also expected to play a role in, for example, reducing the leaching of water, alkali, etc. from the adherend to the adhesive surface of the sealant, and reducing the migration of plasticizers, etc. from the adherend or sealant (see, for example, non-patent document 1).

However, after applying a sealant to a surface or other area to be treated, it may become necessary to repair the area due to deterioration of the sealant. In such cases, the existing sealant, i.e., the pre-applied sealant, is removed and a new sealant (post-applied sealant) is applied, but it may not be possible to completely remove the pre-applied sealant. In such cases, the post-applied sealant must be applied over the pre-applied sealant. Joining sealants requires good adhesion between the pre-applied and post-applied sealants. However, this adhesion often falls short of the desired target, and a primer is generally used for joining sealants.

However, even if a primer is used when joining sealants, there may be problems such as poor jointability between sealants or the inability to join sealants at all.

Therefore, a primer composition for jointing modified silicone sealants is known, which contains a) a polyisocyanate having an isocyanurate ring, b) an epoxy silane compound, c) one or more silane compounds selected from the group consisting of amino silane compounds having a structure represented by a specific formula, amino silane compounds having a structure represented by a specific formula, and ketimine silane compounds having a structure represented by a specific formula, and d) a film-forming resin, wherein b) the epoxy silane compound is a condensate of at least one epoxy silane represented by a specific formula, or a condensate of at least one epoxy silane represented by a specific formula and at least one alkoxy silane represented by a specific formula (see, for example, Patent Document 1).

Patent No. 4802448

Handbook of Construction Sealant Materials, Japan Sealant Industry Association, 2017, 19

However, the joint application primer composition described in Patent Document 1 merely achieves joint application properties through the use of aminosilane, and does not meet high standards for joint application properties (normal adhesion, water-resistant adhesion) for pre-applied sealants. Therefore, further improvements in these properties of joint application primer compositions are needed. Furthermore, primer compositions are also required to have properties that reduce the leaching of water, alkali, etc. from the interior of porous materials to the adhesive surface of the sealant, and reduce the migration of plasticizers, etc. from the adherend or sealant (hereinafter, in this specification, these properties will be referred to as "barrier properties").

Therefore, the object of the present invention is to provide a primer composition that has excellent barrier properties and also has excellent jointability when used with pre-applied sealants.

To achieve the above-mentioned objective, the present invention provides a primer composition containing (A) a film-forming component including at least one selected from the group consisting of a polyisocyanate compound having three or more isocyanate groups, polyester, polyester polyurethane, epoxy compound, and chlorinated polymer, and (B) an alkoxysilyl group-containing methyl methacrylate polymer having a weight-average molecular weight of less than 15,000.

It is also preferable that (B) above is an alkoxysilyl group-containing methyl methacrylate polymer containing an alkyl (meth)acrylate ester having an ester group having 8 or more carbon atoms.

The above primer composition may also further contain (C) an amino group-containing silane.

Furthermore, the above primer composition may also contain (D) a silane-based crosslinking agent.

The primer composition of the present invention can provide a primer composition that has excellent barrier properties and also has excellent jointability when used with pre-applied sealants.

<Numerical values and definitions of terms>
The definitions and meanings of terms used in this specification are as follows.

(Definition of room temperature)
In this specification, "room temperature (normal temperature)" refers to a temperature of 23°C.

(Terminology: solid at room temperature)
As used herein, the term "solid at room temperature" means that the substance (e.g., a given composition) is crystalline, partially crystalline, and/or glassy amorphous and has a softening point (as measured by ring and ball) or melting point greater than 23° C. The melting point is the maximum of the curve measured during a heating operation, e.g., by dynamic differential calorimetry (differential scanning calorimetry [DSC]), at which the material transitions from the solid state to the liquid state.

(Weight average molecular weight)
In this specification, the weight average molecular weight can be measured, for example, using a gel permeation chromatography (GPC) apparatus HLC-8220 (manufactured by Tosoh Corporation) under the following conditions using polystyrene as a standard substance.

Columns used: TSKgel SuperMultiporeHZ-M x 2, TSKguard column SuperMP(HZ)-M x 1, TSKgel SuperMultiporeHM-L x 1 Solvent: THF
Flow rate: 1.0ml/min
Measurement temperature: 40℃

(glass transition temperature)
The glass transition temperature (hereinafter sometimes referred to as "Tg") can be easily estimated from the type and amount of the monomer component using the Fox equation below.

1/Tg=W ₁ /Tg ₁ +W ₂ /Tg ₂ +...+W _n /Tg _n (Fox formula)

In the Fox equation, Tg is, for example, the glass transition temperature (K) of the acrylic resin, _W1 , _W2 , ..., _Wn are the weight fractions of each monomer, and _Tg1 , _Tg2 , ..., _Tgn are the glass transition temperatures of the homopolymers of each monomer. The glass transition temperatures of the homopolymers used in the Fox equation can be values described in literature, such as Mitsubishi Rayon Co., Ltd.'s Acrylic Ester Catalog (1997 edition) and Kyozo Kitaoka's "New Polymer Library 7: Introduction to Synthetic Resins for Paints," published by Polymer Publishing Co., Ltd., pp. 168-169.

<Summary of Primer Composition>
The present inventors have conducted extensive research to improve the various properties required of a primer composition. As a result, they have discovered that the properties of a primer can be maximized by adding a predetermined film-forming component whose non-volatile components are solid to the primer composition. That is, they have found that a primer composition having excellent barrier properties and seamless application can be obtained by using a predetermined film-forming component and a silyl group-containing polymer.

That is, the primer composition of the present invention is a composition containing (A) a film-forming component (hereinafter referred to as component (A)) and (B) an alkoxysilyl group-containing methyl methacrylate polymer (hereinafter referred to as component (B)). The primer composition of the present invention may also contain (C) an amino group-containing silane (hereinafter referred to as component (C)), (D) a silane-based crosslinking agent (hereinafter referred to as component (D)), and/or other additives.

<Details of Primer Composition>
The primer composition according to the present invention contains (A) a film-forming component containing at least one compound selected from a predetermined group of compounds, and (B) an alkoxysilyl group-containing methyl methacrylate polymer having a predetermined weight-average molecular weight. The primer composition according to the present invention can also be prepared by adding components (C), (D), and/or other additives to components (A) and (B). The primer composition according to the present invention has the property of being moisture-curable at room temperature.

<(A) Film-forming component>
The film-forming component (A) contained in the primer composition of the present invention is not particularly limited as long as it is a component capable of forming a film that becomes a primer layer. Specifically, component (A) is a compound containing a solid component that is solid at room temperature. Examples of component (A) include film-forming resins such as polyisocyanate compounds having three or more isocyanate groups, polyesters, polyester polyurethanes, chlorinated polymers, and/or epoxy compounds. Among these, from the viewpoints of superior chemical resistance, hot water resistance, and excellent adhesion development (specifically, initial adhesion), it is preferable to include at least one compound selected from the group consisting of polyisocyanate compounds having three or more isocyanate groups, polyesters, polyester polyurethanes, chlorinated polymers, and epoxy compounds. These compounds can be used alone or in combination of two or more types.

The amount of component (A) added to the primer composition (in terms of solids content) is preferably 1% or more, more preferably 2% or more, even more preferably 3% or more, and preferably 20% or less, more preferably 15% or less, and even more preferably 10% or less. If the amount added to the primer composition exceeds 20%, the viscosity during application may increase, reducing workability. If the amount added is less than 1%, the primer composition may penetrate the porous building material when applied to the porous building material, preventing it from exhibiting high film-forming properties. Note that this amount added represents a percentage when the total mass of the primer composition is taken as 100%.

[Polyisocyanate compound (A-1) having three or more isocyanate groups]
As component (A) of the primer composition of the present invention, a polyisocyanate compound (A-1) having three or more isocyanate groups (hereinafter referred to as component (A-1)) can be used from the viewpoints of exhibiting high film-forming properties, increasing film strength after application, and improving adhesion to poorly adhesive painted surfaces. Furthermore, the isocyanate groups harden to exhibit excellent adhesion to substrates (siding boards, etc.), and crosslinking of the isocyanate groups can improve hot water-resistant adhesion and heat-resistant adhesion to substrates.

Examples of polyisocyanate compounds having three or more isocyanate groups include addition reaction products of diisocyanate compounds, such as adducts using trimethylolpropane or glycol; isocyanurate-modified polyisocyanates of diisocyanates; allophanate-modified polyisocyanates; and biuret-modified polyisocyanates. These polyisocyanate compounds can be used alone or in combination of two or more.

Examples of diisocyanate compounds include aromatic polyisocyanates such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), and polymethylene polyphenylisocyanate (polymeric MDI), aliphatic polyisocyanates such as hexamethylene diisocyanate (HDI), and alicyclic polyisocyanates such as isophorone diisocyanate (IPDI).

Further examples of component (A-1) include polyisocyanate adducts obtained by reacting the above-mentioned polyisocyanate compounds (diisocyanate compounds) with compounds such as tris(phenylisocyanate)thiophosphate and trimethylolpropane (TMP), as well as adducts, biurets, and isocyanurates of polyisocyanate compounds. Hereinafter, such polyisocyanate compounds will be referred to as "isocyanate adducts." These can be used alone or in combination of two or more types.

Examples of such isocyanate adducts include an HDI-TMP adduct obtained by reacting HDI with TMP, an XDI-TMP adduct obtained by reacting XDI with TMP, a TDI-TMP adduct obtained by reacting TDI with TMP, a TMXDI-TMP adduct obtained by reacting TMXDI with TMP, an HXDI-TMP adduct obtained by reacting HXDI with TMP, an IPDI-TMP adduct obtained by reacting IPDI with TMP, a biuret of HDI, an isocyanurate of HDI, an isocyanurate of IPDI, and an isocyanurate of TDI. Of these, the TDI-TMP adduct and isocyanurate-modified adduct obtained by reacting TDI with TMP are preferred.

Preferred polyisocyanate compounds having an isocyanurate ring are isocyanurate-modified diisocyanate compounds obtained by trimerizing diisocyanate compounds. Examples of diisocyanate compounds include the aromatic polyisocyanates listed above. Among these, polyisocyanate compounds having an isocyanurate ring obtained by reacting a mixture of TDI and HDI are preferred, as they provide better initial adhesion and hot water-resistant adhesion to poorly adhesive coated surfaces, resulting in sufficient adhesion.

(A-1) Commercially available polyisocyanate compounds having three or more isocyanate groups include, for example, Takenate D-120N from Mitsui Chemicals, Inc., tris(phenylisocyanate)thiophosphate (Desmodur RFE) from Sumika Covestro Urethane Co., Ltd., a polyisocyanate compound having an isocyanurate ring obtained by reacting a mixture of HDI and TDI (Desmodur HL), and polymethylene polyphenylisocyanate (Sumidur 44V-10).

[Polyester (A-2)]
The primer composition according to the present invention may contain (A-2) polyester (hereinafter referred to as component (A-2)) as component (A). The polyester as component (A-2) is not particularly limited. Examples of the polyester main chain include polyesters obtained by reacting carboxylic acids, including aromatic dicarboxylic acids and aliphatic dicarboxylic acids having 6 to 12 carbon atoms, with polyol compounds; and polyesters obtained by ring-opening polymerization of lactones, such as polycaprolactone and polyvalerolactone.

The polyester's main chain contains an aromatic dicarboxylic acid and an aliphatic dicarboxylic acid with 6 to 12 carbon atoms as the carboxylic acid components used in the polyester skeleton, resulting in excellent chemical and hot water resistance, excellent adhesion to poorly adhesive coated panels (especially water-resistant adhesion), and sufficient adhesion even when used in low-temperature environments. The terminus of the polyester is not particularly limited. The polyester may be either linear or branched.

Examples of aromatic dicarboxylic acids that can be used in producing polyester include phthalic acid (e.g., orthophthalic acid, phthalic anhydride), isophthalic acid, and terephthalic acid. These may be used alone or in combination of two or more. Among these, terephthalic acid and/or isophthalic acid are preferred from the viewpoints of their excellent chemical and hot water resistance, excellent adhesion to poorly adhesive coated plates, and sufficient adhesion even when used in low-temperature environments.

Examples of aliphatic dicarboxylic acids having 6 to 12 carbon atoms that can be used in producing polyesters include adipic acid, azelaic acid, sebacic acid, and 1,12-dodecanedicarboxylic acid. These may be used alone or in combination of two or more. Of these, adipic acid and/or sebacic acid are preferred from the standpoints of superior chemical and hot water resistance, excellent adhesion to poorly adhesive coated plates, and sufficient adhesion even when used in low-temperature environments. Sebacic acid is more preferred from the standpoints of superior chemical and hot water resistance, and rapid adhesive development, resulting in sufficient adhesion even when used in low-temperature environments.

The molar ratio of aromatic dicarboxylic acid to aliphatic dicarboxylic acid (aromatic dicarboxylic acid/aliphatic dicarboxylic acid) is preferably 1/99 to 99/1, and more preferably 5/95 to 95/5, from the viewpoints of providing excellent chemical resistance, excellent hot water resistance, excellent adhesion to poorly adhesive coated boards, and sufficient adhesion even when used in low-temperature environments.

The polyol compounds that can be used in producing polyesters are not particularly limited as long as they contain two or more hydroxy groups. For example, polyol compounds commonly used in the production of polyester resins can be used. Preferred polyol compounds are compounds containing two hydroxy groups (i.e., diol compounds). Examples include low-molecular-weight polyols such as ethylene glycol, propylene glycol, glycerin, hexanetriol, and trimethylolpropane; polyether-based polyols such as polytetramethylene glycol, polyethylene glycol, polypropylene glycol, polyoxypropylene glycol, and polyoxybutylene glycol; polyolefin-based polyols such as polybutadiene polyol and polyisoprene polyol; adipate-based polyols; and lactone-based polyols. These may be used alone or in combination. Among these, ethylene glycol, propylene glycol, and neopentyl glycol are preferred due to their excellent adhesive properties.

The number average molecular weight of the polyester is preferably 3,000 or more, more preferably 15,000 or more, and preferably 70,000 or less, from the viewpoints of excellent chemical resistance, excellent adhesion to poorly adhesive coated panels, and sufficient adhesion even when used in low-temperature environments. Furthermore, from the viewpoint of excellent chemical resistance, excellent hot water resistance, the number average molecular weight of the polyester is preferably 15,000 or more, more preferably 15,000 or more and 70,000 or less. The number average molecular weight of the polyester is the molecular weight expressed in terms of polystyrene by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as a solvent.

There are no particular limitations on the method for producing the polyester. For example, conventional methods for producing polyesters can be used. Furthermore, multiple types of polyesters can be used alone or in combination of two or more.

[Polyester polyurethane (A-3)]
The primer composition according to the present invention may contain (A-3) polyester polyurethane (hereinafter referred to as component (A-3)) as component (A). There are no particular limitations on the (A-3) polyester polyurethane that can be used as the film-forming component in the primer composition of the present invention. For example, there may be mentioned compounds obtained by urethane-modifying the above polyesters having two or more hydroxy groups with a polyisocyanate compound (a difunctional or higher isocyanate compound). There are also no particular limitations on the main chain (polyester portion) of the polyester polyurethane. For example, there may be mentioned main chains similar to those of the above polyesters. Furthermore, the polyester polyurethane may be either linear or branched.

From the viewpoint of achieving superior chemical and hot water resistance, the number average molecular weight of the polyester polyurethane is preferably 10,000 or more, more preferably 15,000 or more, and preferably 100,000 or less, more preferably 70,000 or less. The number average molecular weight of the polyester polyurethane is the molecular weight expressed in terms of polystyrene by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as a solvent.

Here, an example of a method for urethane modification is to dissolve a polyester having two or more hydroxy groups in an organic solvent that does not react with the polyisocyanate compound, add the polyisocyanate compound, and if necessary, add a reaction catalyst such as an amine compound or an organometallic compound, and then heat.

In addition, examples of polyesters having two or more hydroxy groups that can be used to produce polyester polyurethane include the polyesters listed above. Two or more of these may be used in combination.

The polyisocyanate compound used in producing polyester polyurethane can be, for example, an alicyclic, aromatic, or aliphatic diisocyanate compound. That is, the diisocyanate compounds listed in the description of component (A-1) can be used.

In addition, tri- or higher functional isocyanate compounds such as adducts, isocyanurates, and biuret compounds can also be used as polyisocyanate compounds. Diisocyanate compounds are preferred as polyisocyanate compounds when producing polyester polyurethanes, as they are less likely to gel.

There are no particular restrictions on the method for producing polyester polyurethane. For example, conventionally known methods for producing polyester polyurethane can be used. Suitable commercially available polyester polyurethane products include Nipporan 3024 manufactured by Tosoh Corporation, and Pandex T-5205 and Pandex T-5210 manufactured by DIC Corporation. Multiple types of polyester polyurethane can be used alone or in combination.

[Epoxy compound (A-4)]
The primer composition according to the present invention may contain (A-4) an epoxy compound (hereinafter referred to as component (A-4)) as component (A). The epoxy compound reacts with (C) an amino group-containing silane to strengthen the network structure obtained after the primer composition is cured, thereby improving adhesion, water-resistant adhesion, and adhesion durability under high-temperature and high-humidity conditions. Furthermore, the strong network structure enhances barrier performance, preventing discoloration, deterioration, etc., of the sealant-bonded portion of the adherend and its surrounding area. In particular, the epoxy compound reacts with compounds having reactive groups to inhibit migration of the active compounds, thereby exhibiting excellent effectiveness in preventing discoloration, deterioration, etc., caused by compounds having reactive groups reactive to epoxy groups, such as amine compounds.

Epoxy compounds include aromatic, aliphatic, and alicyclic epoxy compounds that are solid at room temperature. Aromatic epoxy compounds include bisphenol A epoxy compounds, bisphenol F epoxy compounds, bisphenol AD epoxy compounds, bisphenol S epoxy compounds, naphthalene epoxy compounds, phenol novolac epoxy compounds, cresol novolac epoxy compounds, and multifunctional epoxy compounds.

Alicyclic epoxy compounds include hydrogenated aromatic epoxy compounds, cyclohexane-based, cyclohexyl methyl ester-based, cyclohexyl methyl ether-based, spiro-based, and tricyclodecane-based epoxy compounds. Specific examples include hydrogenated bisphenol A-type epoxy compounds; alicyclic epoxy compounds such as 3',4'-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate, 1,2:8,9-diepoxylimonene, 1,2-epoxy-4-vinylcyclohexane, and 1,2-epoxy-4-(2-oxiranyl)cyclohexane adduct of 2,2-bis(hydroxymethyl)-1-butanol (EHPE3150, manufactured by Daicel Corporation).

Among epoxy compounds, bisphenol A-type epoxy resins and alicyclic epoxy compounds that are solid at room temperature are preferred, as they can produce a primer that has excellent jointability when used with pre-applied sealants.

[Chlorinated polymer (A-5)]
The primer composition according to the present invention may contain (A-5) a chlorinated polymer (hereinafter referred to as component (A-5)) as component (A). The chlorinated polymer (A-5) is not particularly limited as long as it is a compound obtained by chlorinating natural rubber, synthetic rubber, polyolefin, or a modified product thereof (hereinafter, natural rubber, synthetic rubber, polyolefin, and a modified product thereof are also collectively referred to as "polymer").

As component (A-5), chlorinated natural rubber and chlorinated synthetic rubber are preferred from the viewpoint of providing superior adhesion of the resulting composition to difficult-to-adhere materials, and a primer with excellent jointability can be obtained, particularly when used with pre-applied sealants. Furthermore, the use of chlorinated polyisoprene is more preferred from the viewpoint of providing superior application workability for the resulting composition due to its low viscosity, and particularly superior adhesion of the resulting composition to difficult-to-adhere materials.

Examples of synthetic rubbers include polyisoprene, styrene-butadiene rubber (SBR), chloroprene rubber (CR), nitrile rubber (NBR), etc. Examples of polyolefins include polyethylene and polypropylene.

The weight-average molecular weight of component (A-5) is preferably 50,000 or more and 300,000 or less in terms of excellent adhesion to difficult-to-adhere materials. From the viewpoint of even better adhesion, the weight-average molecular weight of component (A-5) is more preferably 60,000 or more, even more preferably 70,000 or more, more preferably 280,000 or less, and even more preferably 260,000 or less.

From the viewpoint of excellent adhesiveness, the chlorine content of component (A-5) is preferably 40% by mass or more and 80% by mass or less. From the viewpoint of even better adhesiveness, the chlorine content of component (A-5) is more preferably 45% by mass or more, even more preferably 50% by mass or more, and even more preferably 80% by mass or less. The chlorine content of component (A-5) refers to the proportion of chlorine atoms in component (A-5).

<(B) Alkoxysilyl Group-Containing Methyl Methacrylate Polymer>
The alkoxysilyl group-containing methyl methacrylate polymer (B) is a (meth)acrylic ester polymer having an alkoxysilyl group and containing, as an essential monomer, methyl methacrylate, which is solid at room temperature. The alkoxysilyl group-containing methyl methacrylate polymer (B) according to the present invention is preferably a resin having a weight-average molecular weight of less than 15,000.

Component (B) allows the primer composition to exhibit excellent adhesion to the cured sealant (pre-applied sealant) and achieve good jointability. Furthermore, when component (B) is used in combination with component (C), described below, even better adhesion to the cured sealant (pre-applied sealant) and good jointability are achieved. Furthermore, the alkoxysilyl groups of component (B) and the alkoxysilyl groups of component (C), described below, harden, resulting in excellent adhesion to substrates (siding boards, etc.). Furthermore, crosslinking between the silyl groups of component (B) and component (C) improves hot water-resistant adhesion to substrates.

(alkoxysilyl group)
The alkoxysilyl group of component (B) has an alkoxy group bonded to a silicon atom and is capable of crosslinking by a silanol condensation reaction. Examples of the alkoxysilyl group include groups represented by the following general formula (1):

In general formula (1), ^R1 represents an alkyl group having 1 to 20 carbon atoms, a substituted alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, or an aralkyl group having 7 to 20 carbon atoms, and when there are two or more ^R1s , they may be the same or different. X represents an alkoxysilyl group, and when there are two or more Xs, they may be the same or different. a represents 0, 1, 2, or 3. In the alkoxysilyl group of general formula (1), it is preferable that a is 2 or 3. When a is 3, the curing rate is higher than when a is 2.

Specific examples of ^R1 include alkyl groups such as a methyl group and an ethyl group, substituted alkyl groups such as a methoxymethyl group, and cycloalkyl groups such as a cyclohexyl group. Of these, a methyl group is preferred, and from the viewpoint of increasing the curing rate, a substituted alkyl group in which the α-carbon is substituted with a polar group is preferred.

The alkoxysilyl group represented by X is not particularly limited and may be any conventionally known alkoxysilyl group. Among alkoxy groups, groups with fewer carbon atoms are more reactive, and the more carbon atoms there are, the lower the reactivity becomes, in the order methoxy group > ethoxy group > propoxy group. While the type can be selected depending on the purpose and application, methoxy groups and ethoxy groups are typically used. In the case of alkoxysilyl groups represented by general formula (1), a is preferably 2 or greater, taking curability into consideration.

Specific examples of the alkoxysilyl group include trialkoxysilyl groups (-Si(OR ² ) ₃ ) such as trimethoxysilyl group and triethoxysilyl group; and dialkoxysilyl groups (-SiR ¹ (OR ² ) ₂ ) such as methyldimethoxysilyl group and methyldiethoxysilyl group. Here, R ¹ is the same as above, and R ² is an alkyl group such as a methyl group or an ethyl group. As the alkoxysilyl group, trimethoxysilyl group and triethoxysilyl group are preferred from the viewpoint of high reactivity, and trimethoxysilyl group is more preferred. From the viewpoint of obtaining a flexible cured product, methyldimethoxysilyl group and methyldiethoxysilyl group are preferred.

Alkoxysilyl groups can be used alone or in combination of two or more. The alkoxysilyl groups can be present in the main chain, the side chain, or both.

The number (average value) of alkoxysilyl groups in component (B) per polymer molecule is preferably 0.3 or more, more preferably 0.5 or more, even more preferably 1 or more, and preferably 5 or less, more preferably 3 or less, and even more preferably 2.5 or less. If the number of alkoxysilyl groups contained in a molecule is less than 0.3, curability will be insufficient; if too many, the network structure will be too dense, resulting in poor mechanical properties.

(Method for introducing an alkoxysilyl group)
In preparing component (B), various known methods can be used to introduce alkoxysilyl groups into the (meth)acrylic acid ester polymer. For example, the following methods can be mentioned as examples of methods for introducing alkoxysilyl groups.

(1) An unsaturated compound having an alkoxysilyl group is copolymerized.
(2) Polymerization is carried out using an initiator or chain transfer agent having an alkoxysilyl group.
(3) A (meth)acrylic acid ester polymer having a functional group such as a hydroxyl group is reacted with a compound having an alkoxysilyl group and another functional group capable of reacting with the functional group, such as an epoxysilane.

Of these methods for introducing alkoxysilyl groups, (1) copolymerization of an unsaturated compound having an alkoxysilyl group is preferred from the perspective of ease of introduction of the alkoxysilyl group. A combination of methods (1) and (2) is also preferred. For example, a trimethoxysilyl group-containing (meth)acrylic polymer can be obtained as an alkoxysilyl group-containing methyl methacrylate polymer by using a synthesis method similar to Synthesis Example 4 of WO 2015-088021 using methyl methacrylate, ...

(Unsaturated Compound Having an Alkoxysilyl Group)
The unsaturated compound having an alkoxysilyl group used in copolymerization is preferably a (meth)acrylic acid alkyl ester or vinyl silane having an alkoxysilyl group. Examples of such compounds include 3-(meth)acryloxypropyl alkoxysilanes such as 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, and 3-(meth)acryloxypropyltriethoxysilane, and vinyl alkoxysilanes such as vinyltriethoxysilane. Among these, a (meth)acrylic acid alkyl ester having a substituted alkyl group in which the alkyl group having an alkoxysilyl group has 10 or less carbon atoms, preferably 3 or less carbon atoms, is preferred.

(Monomers other than the monomer having an alkoxysilyl group used in component (B))
Examples of other monomers, excluding the monomer having an alkoxysilyl group, used in the synthesis of the polymer of component (B) according to the present invention include methyl methacrylate random copolymers having a repeating unit represented by general formula (2) in which methyl methacrylate is an essential monomer component.

_-CH2C ( ^R3 )( ^COOR4 )- (2)

In the general formula (2), ^R3 represents a hydrogen atom or a methyl group, and ^R4 represents a hydrocarbon group which may have a substituent. Note that the (meth)acrylic acid ester refers to an acrylic acid ester and/or an alkyl methacrylic acid ester.

As the monomer having an alkoxysilyl group and the other monomer, excluding methyl methacrylate, used in the synthesis of the polymer of component (B) according to the present invention, alkyl (meth)acrylate esters are preferred, more preferably alkyl (meth)acrylate esters in which the alkyl group has 1 to 30 carbon atoms, and particularly preferably alkyl (meth)acrylate esters in which the alkyl group has 1 to 30 carbon atoms and has no substituent.

Examples of (meth)acrylic acid alkyl ester compounds include known compounds, such as methyl acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, and stearyl (meth)acrylate.

In addition, from the viewpoint of achieving excellent adhesion to the cured sealant (pre-applied sealant) and good jointability, (meth)acrylic acid alkyl esters with an ester group containing 8 or more carbon atoms, such as 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, and stearyl (meth)acrylate, are preferred. From the viewpoint of imparting flexibility to component (B), it is preferable to use (meth)acrylic acid alkyl esters with a glass transition temperature (Tg) of 0°C or less, such as n-butyl acrylate (Tg: -55°C), 2-ethylhexyl acrylate (Tg: -70°C), and lauryl acrylate (Tg: -3°C). Note that the glass transition temperature in this paragraph refers to the glass transition temperature of the homopolymer.

The hydrocarbon group, such as the alkyl group of the (meth)acrylic acid ester, may have a substituent such as a hydroxyl group, an alkoxy group, a halogen atom, or an epoxy group. Examples of such compounds include (meth)acrylic acid esters with a hydroxyl group, such as hydroxyethyl (meth)acrylate; (meth)acrylic acid esters with an alkoxy group, such as methoxyethyl (meth)acrylate; (meth)acrylic acid esters with an epoxy group, such as glycidyl (meth)acrylate; and (meth)acrylic acid esters with an amino group, such as diethylaminoethyl (meth)acrylate. It is also possible to use unsaturated compounds (macromonomers or macromers) with a polymer chain, such as acrylic acid esters with a polystyrene chain.

Furthermore, the alkoxysilyl group-containing methyl methacrylate polymer of component (B) may contain, in addition to repeating units derived from (meth)acrylic acid ester compounds, repeating units derived from compounds copolymerizable with these. Examples of compounds copolymerizable with (meth)acrylic acid ester compounds include acrylic acids such as (meth)acrylic acid; amide compounds such as (meth)acrylamide; vinyl ether compounds such as alkyl vinyl ether; and others such as acrylonitrile, styrene, α-methylstyrene, vinyl chloride, and vinyl acetate.

(Monomer usage ratio)
The amount of methyl methacrylate in the polymer of component (B) is less than 80% by weight, preferably 20% by weight or more, more preferably 30% by weight or more, and even more preferably 40% by weight or more. The proportion of the compound copolymerizable with the (meth)acrylic acid ester compound in the polymer of component (B) is preferably 20% by weight or less, more preferably 10% by weight or less, and even more preferably 5% by weight or less. However, when a macromonomer is used, the amount of the macromonomer in the polymer of component (B) is preferably 10% by weight or less, more preferably 5% by weight or less, and particularly preferably 3% by weight or less.

(glass transition temperature)
Component (B) has a glass transition temperature (Tg) of 0°C or higher and 120°C or lower. The glass transition temperature is preferably 0°C or higher, more preferably 20°C or higher, and even more preferably 40°C or higher. It is also preferably 120°C or lower, more preferably 100°C or lower, and even more preferably 80°C or lower. If the glass transition temperature is lower than 0°C, the adhesive strength immediately after adhesion tends to be poor. If the glass transition temperature exceeds 120°C, the viscosity increases, making it difficult to apply the primer to the adherend. The glass transition temperature can be easily estimated using the Fox equation described above.

The molecular weight of component (B) is preferably 1,000 or more, more preferably 2,000 or more, even more preferably 3,000 or more, and less than 15,000, more preferably 10,000 or less, and even more preferably 6,000 or less, in weight average molecular weight (molecular weight measured in terms of polystyrene by GPC). If the weight average molecular weight is less than 1,000, the initial adhesive strength after application will be low, and if it exceeds 20,000, the viscosity will be too high during application, reducing workability. It is also preferable that the polymer of component (B) be solid at room temperature or have a ring and ball softening point of 80°C or higher.

The amount of component (B) added to the primer composition is preferably 5% or more, more preferably 10% or more, even more preferably 20% or more, and preferably 60% or less, more preferably 50% or less, and even more preferably 40% or less. If the amount added exceeds 60%, the viscosity during application will be too high, reducing workability. If the amount added is less than 5%, good jointability will not be achieved. Note that this amount is expressed as a percentage when the total mass of the primer composition is taken as 100%.

(Polymerization method of component (B))
Radical polymerization can be used as the polymerization method for component (B). For example, conventional solution polymerization or bulk polymerization methods using thermal polymerization initiators such as benzoyl peroxide or azobisisobutyronitrile can be used. A method of polymerization using a photopolymerization initiator and irradiation with light or radiation can also be used. In radical copolymerization, a chain transfer agent such as lauryl mercaptan or 3-mercaptopropyltrimethoxysilane can be used to adjust the molecular weight. Radical polymerization methods using thermal polymerization initiators can also be used, and such methods can easily produce the polymer of component (B) according to the present invention. Other polymerization methods, such as living radical polymerization as described in JP-A-2000-086998, can also be used.

<(C) Amino Group-Containing Silane>
From the viewpoint of not only improving adhesion to the substrate (adhesive member) but also further improving adhesion to the cured sealant (pre-applied sealant) when used in combination with component (B) and achieving excellent jointability, the primer composition according to the present invention preferably further contains (C) an amino group-containing silane. Examples of the amino group of the (C) amino group-containing silane include monovalent functional groups formed by removing hydrogen from primary amines or secondary amines, and ketimine groups. Specifically, examples of the (C) amino group-containing silane according to the present invention include aminosilanes and ketimine silanes. Ketimine silanes are silane compounds that generate a specific amine upon reaction with moisture, and in the present invention, ketimine silanes are also included in component (C).

Examples of aminosilanes include mono-silylaminosilanes such as 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-(β-aminoethyl)-3-aminopropyltrimethoxysilane, N-(β-aminoethyl)-3-aminopropyltriethoxysilane, and N-(β-aminoethyl)-3-aminopropylmethyldiethoxysilane, and bis-silylaminosilanes such as bis-(trimethoxysilylpropyl)amine, bis-(triethoxysilylpropyl)amine, bis-(triethoxysilylpropyl)ethylenediamine, N-[2-(vinylbenzylamino)ethyl]-3-aminopropyltrimethoxysilane, and aminoethyl-aminopropyltrimethoxysilane.

Further examples of aminosilanes include aminosilane reactants such as the reaction product of the above aminosilane with an epoxy silane, the reaction product of an aminosilane with a silane having a (meth)acryloyloxy group, the reaction product of an aminosilane with an epoxy resin (bisphenol A diglycidyl ether, phenyl glycidyl ether, etc.), and the reaction product of an aminosilane with a polyacrylate; condensates obtained by partially condensing the above silanes (preferably aminosilane condensates obtained by partially condensing the above aminosilane, aminosilane reactant, and a mixture of the reactants); and modified derivatives of these.

Examples of ketimine-based silanes include N-(1,3-dimethylbutylidene)-3-(trimethoxysilyl)-1-propanamine, N-(1,3-dimethylbutylidene)-3-(triethoxysilyl)-1-propanamine, N-(1,3-dimethylbutylidene)-3-(methyldimethoxysilyl)-1-propanamine, and N-(1,3-dimethylbutylidene)-3-(methyldiethoxysilyl)-1-propanamine.

The amount of component (C) is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 1 part by mass or more, per 100 parts by mass of the total amount of components (A) and (B), and is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less. The amount of component (B) refers to the amount of solids in component (B) excluding the solvent component.

<(D) Silane-based crosslinking agent>
The primer composition according to the present invention may further contain (D) a silane-based crosslinking agent. Examples of (D) silane-based crosslinking agents include silane compounds having two or more alkoxysilyl groups, excluding component (C). (D) silane-based crosslinking agents strengthen the network structure obtained after the primer composition is cured, thereby improving adhesion, water-resistant adhesion, and adhesion durability under high-temperature, high-humidity conditions. (D) silane-based crosslinking agents can also improve the barrier properties of the primer composition by promoting crosslinking. Therefore, from the viewpoint of improving crosslink density, the number of alkoxysilyl groups in component (D) is preferably two or more, more preferably three or more.

Component (D) can be isocyanurate silane, carbasilatran, silane reactant, silane condensate, etc.

Examples of isocyanurate silanes include tris-(trimethoxysilylpropyl) isocyanurate, etc. Examples of carbasilatranes include the reaction product of 1.0 mol of 3-aminopropyltrimethoxysilane and 2.0 mol of 3-glycidoxypropyltrimethoxysilane described in Japanese Patent No. 3,831,481.

Examples of silane reactants and silane condensates (excluding compounds containing primary amino groups and secondary amino groups in this paragraph) include aminosilane reactants such as reactants of aminosilane and epoxy silane, reactants of aminosilane and isocyanate silane, reactants of aminosilane and silane having a (meth)acryloyloxy group, reactants of aminosilane and epoxy resin (bisphenol A diglycidyl ether, phenyl glycidyl ether, etc.), reactants of aminosilane and polyisocyanate, and reactants of aminosilane and polyacrylate; condensates obtained by partial condensation of the above silanes (preferably aminosilane condensates obtained by partial condensation of the above aminosilane, isocyanate silane, aminosilane reactant, and mixture of reactants); and modified derivatives thereof, such as amino-modified silyl polymers and silylated amino polymers.

When component (D) is used, the amount of (D) silane crosslinker is preferably 0.1 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 2 parts by mass or more, per 100 parts by mass of the total amount of components (A) and (B), and is preferably 60 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 15 parts by mass or less. The amount of component (B) refers to the amount of solids in component (B) excluding the solvent component.

<Other additives>
The primer composition of the present invention may contain other additives as needed, such as a methyl methacrylate polymer, a solvent, a condensation reaction-accelerating catalyst, a dehydrating agent, a silane adhesion promoter, a polyisocyanate compound (diisocyanate compound), a pigment, a dye, an antioxidant, an antistatic agent, and a flame retardant.

(Methyl methacrylate polymer)
As the methyl methacrylate polymer, a resin that is solid at room temperature and contains 80% by weight or more of methyl methacrylate and has a weight-average molecular weight Mw (apparent weight-average molecular weight converted into polymethyl methacrylate by GPC method) of 60,000 or more is preferred.

By ensuring that the proportion of methyl methacrylate in the resin is 80% by weight or more and the weight-average molecular weight is 60,000 or more, when the primer composition of the present invention is applied to a porous building material, the penetration of the primer composition into the porous building material can be further suppressed. As a result, the primer composition of the present invention can exhibit better film-forming properties, resulting in stronger film strength after application and superior adhesion.

Such resins include homopolymers of methyl methacrylate, or copolymers of methyl methacrylate with one or more copolymerizable monomers such as methyl acrylate, ethyl acrylate, butyl acrylate, acrylonitrile, acrylic acid, methacrylic acid, 2-hydroxyacrylate, maleic anhydride, styrene, or α-methylstyrene.

Copolymerizable monomers are preferably alkyl acrylates in which the alkyl group has 1 to 4 carbon atoms, such as methyl acrylate, ethyl acrylate, and n-butyl acrylate, and (meth)acrylic acid, with methyl acrylate, ethyl acrylate, and (meth)acrylic acid being more preferred, and methyl acrylate and (meth)acrylic acid being even more preferred. Copolymerization of methyl methacrylate with these monomers increases the solubility of the methyl methacrylate polymer in solvents and allows the viscosity of the primer composition of the present invention to be adjusted to an appropriate viscosity (thickening), making it less likely to penetrate porous building materials. As a result, the primer composition of the present invention can exhibit better film-forming properties, resulting in stronger film strength after application and superior adhesion.

Commercially available methyl methacrylate polymers include, for example, Delpowder (registered trademark) 80N, a copolymer with methyl acrylate (manufactured by Asahi Chemical Industry Co., Ltd.; polymethyl methacrylate, methyl methacrylate/methyl acrylate weight ratio of 97.5/2.5, weight average molecular weight of 100,000, reduced viscosity of 0.54 dL/g, glass transition temperature of 105°C), and Dianale (registered trademark) BR-84, a copolymer with (meth)acrylic acid (manufactured by Mitsubishi Rayon Co., Ltd.; polymethyl methacrylate, weight average molecular weight of 100,000, glass transition temperature of 105°C, acid value: 6.5 mg KOH/g).

The weight-average molecular weight (Mw) of the methyl methacrylate polymer is preferably 60,000 or more, more preferably 70,000 or more, even more preferably 80,000 or more, and particularly preferably 90,000 or more. Furthermore, the weight-average molecular weight (Mw) of the methyl methacrylate polymer is typically preferably 200,000 or less, more preferably 180,000 or less, even more preferably 160,000 or less, and particularly preferably 140,000 or less. A weight-average molecular weight (Mw) of the methyl methacrylate polymer of 60,000 or more can further improve the barrier properties, adhesion durability, and adhesion to porous surfaces of the primer composition. A weight-average molecular weight (Mw) of 200,000 or less can provide better adhesion durability, better workability, and better adhesion to porous surfaces of the primer composition.

The proportion of methyl methacrylate in the methyl methacrylate polymer is preferably 80% by weight or more, more preferably 90% by weight or more, and even more preferably 95% by weight or more. The glass transition temperature of the methyl methacrylate polymer is preferably 80°C or more, more preferably 90°C or more, and even more preferably 95°C or more, and is preferably 140°C or less, more preferably 120°C or less, and even more preferably 110°C or less.

The amount of methyl methacrylate polymer added to the primer composition is preferably 1% or more, more preferably 2% or more, even more preferably 3% or more, and preferably 20% or less, more preferably 15% or less, and even more preferably 10% or less. If the amount added to the primer composition exceeds 20%, the viscosity during application may increase, reducing workability. If the amount added is less than 1%, the primer composition may penetrate the porous building material when applied to the porous building material, preventing it from exhibiting high film-forming properties. Note that this amount added is expressed as a percentage when the total mass of the primer composition is taken as 100%.

(solvent)
Examples of the solvent include organic solvents such as aliphatic compounds (n-hexane, heptane, etc.), aromatic compounds (toluene, xylene, etc.), alcohols (methanol, ethanol, isopropyl alcohol, butanol, etc.), ketones (acetone, methyl ethyl ketone, etc.), esters (ethyl acetate, butyl acetate, etc.), ethers (tetrahydrofuran, butyl cellosolve, etc.), ligroin, etc. One or more of these solvents can be used, and an appropriate amount can be added to the primer composition according to the present invention.

Among these solvents, methyl ethyl ketone and ethyl acetate are preferred from the viewpoint of improving adhesion speed and workability. It is preferable to thoroughly dry or dehydrate the above solvents before use.

The solvent content of the primer composition of the present invention is preferably 40% to 90% by weight, and more preferably 50% to 80% by weight. A solvent content within this range ensures good application properties. The solvent content in the primer composition of the present invention can be varied as appropriate depending on the application and purpose of the composition.

(Condensation reaction accelerator)
As the catalyst for promoting the condensation reaction of the alkoxysilyl group, a wide variety of known curing catalysts can be used, and it is preferable to use, for example, a silanol condensation catalyst. Examples of the silanol condensation catalyst include metal catalysts, tin catalysts, and amine catalysts, and examples of the amine catalyst include organometallic compounds, amines (particularly tertiary amines), and salts of tertiary amines with carboxylic acids, etc.

Specific examples of organometallic compounds include divalent organotin compounds such as tin octoate; tetravalent organotin compounds such as dibutyltin dilaurate, dibutyltin diacetate, dioctyltin dilaurate, and reaction products of dibutyltin oxide with phthalic acid esters; chelate compounds of various metals such as dibutyltin bis(acetylacetonate), titanium tetrakis(acetylacetonate), aluminum tris(acetylacetonate), and acetylacetonate bismuth; and titanate esters such as tetrapropyl titanate.

Examples of amines include primary and secondary amines such as octylamine; polyamines; cyclic amines such as N-methylmorpholine and 1,8-diazabicyclo[5,4,0]-7-undecene (DBU); amine compounds and their carboxylate salts, such as aminophenol compounds such as 2,4,6-tris(dimethylaminomethyl)phenol; and reaction products of excess polyamines and epoxy compounds. These catalysts can be used alone or in combination of two or more.

Among these, tin-based catalysts and amine-based catalysts are preferred, with tin-based catalysts being particularly preferred, as they have high catalytic activity even in small amounts. Either tin-based catalysts or amine-based catalysts, or both, may be used. As tin-based catalysts, either divalent or tetravalent tin catalysts can be used alone, or both can be used in combination. As amine-based catalysts, tertiary amines are preferred.

When a condensation reaction-promoting catalyst is used, the amount of the condensation reaction-promoting catalyst is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and even more preferably 0.1 parts by mass or more, per 100 parts by mass of the total amount of components (A) and (B), and is preferably 10 parts by mass or less, more preferably 2 parts by mass or less, and even more preferably 1 part by mass or less.

(Dehydrating agent)
Examples of the dehydrating agent include silane compounds such as vinyltrimethoxysilane, dimethoxydiphenylsilane, methyltrimethoxysilane, phenyltrimethoxysilane, tetraethoxysilane, and tetramethoxysilane; and ester compounds such as methyl orthoformate and ethyl orthoformate. These dehydrating agents can be used alone or in combination of two or more. Note that, as the dehydrating agent, silane compounds are preferred, and dimethoxydiphenylsilane and phenyltrimethoxysilane are more preferred.

When a dehydrating agent is used, the amount of the dehydrating agent is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 1 part by mass or more, per 100 parts by mass of the total amount of component (A) and component (B); and is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less.

(Silane-based adhesion promoter)
Silane adhesion promoters can be added to the primer composition of the present invention because they are effective in improving adhesion to poorly adherent coated surfaces. Examples of silane adhesion promoters include epoxy silanes, acrylic silanes, mercapto silanes, urea silane coupling agents, and isocyanate silanes.

Examples of epoxy silanes include 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, and 3-glycidoxypropylmethyldiethoxysilane. Examples of acrylic silanes include 3-methacryloxypropyltrimethoxysilane. Examples of mercaptosilanes include 3-mercaptopropyltrimethoxysilane. Examples of urea silane coupling agents include 3-ureidopropyltrimethoxysilane and 3-ureidopropyltriethoxysilane. Examples of isocyanate silanes include 3-isocyanatepropyltriethoxysilane.

From the standpoint of adhesion, epoxy silanes, acrylic silane-based silanes, urea silane-based coupling agents, and isocyanate silanes are preferred, with epoxy silanes being more preferred.

When a silane-based adhesion promoter is used, the amount of the silane-based adhesion promoter is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 1 part by mass or more, per 100 parts by mass of the total amount of component (A) and component (B); and is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less.

(Polyisocyanate Compound (Diisocyanate Compound))
The primer composition according to the present invention may further contain a diisocyanate compound as a polyisocyanate compound. The diisocyanate compound is not particularly limited as long as it has two isocyanate groups in the molecule. Specific examples of the diisocyanate compound include the diisocyanate compounds listed in the description of component (A-1).

(Pigment)
The pigment may be either or both of an inorganic pigment and an organic pigment, such as titanium dioxide, zinc oxide, ultramarine, red iron oxide, lithopone, lead, cadmium, iron, cobalt, aluminum, hydrochloride, or sulfate, or an organic pigment such as an azo pigment or copper phthalocyanine pigment.

(dye)
As the dye, any known dye can be used, for example, a black dye, a yellow dye, a red dye, a blue dye, a brown dye, etc.

(anti-aging agent)
Examples of the antioxidant include hindered phenol compounds, hindered amine compounds, and benzotriazole compounds.

(Antistatic Agent)
Examples of the antistatic agent include hydrophilic compounds such as quaternary ammonium salts, polyglycols, and ethylene oxide derivatives.

(Flame retardant)
Examples of the flame retardant include chloroalkyl phosphate, dimethyl methyl phosphonate, bromine-phosphorus compounds, ammonium polyphosphate, neopentyl bromide polyether, and brominated polyether.

<Method for preparing primer composition>
The method for preparing the primer composition of the present invention is not particularly limited, but it can be prepared, for example, using a mixer capable of uniformly mixing liquids. For example, the primer composition can be prepared by weighing out predetermined amounts of the materials constituting the primer composition (component (A), component (B), component (C), component (D), and/or other additives) and mixing the weighed materials using a mixer with a single or double shaft, or a tank with a pulsator or the like at the bottom. In particular, it is preferable to use an apparatus equipped with a jacket and capable of variably adjusting the material temperature.

<Method of applying primer composition>
There are no particular limitations on the method for applying the primer composition of the present invention to an adherend, but the following application method is a preferred example. First, the primer composition of the present invention is applied evenly to the adherend surface at an application rate of 50 to 400 ml/ ^m² , for example, using a brush or paintbrush to lift the surface and drain the liquid so that it does not drip. 30 minutes to 8 hours after application, the sealant is applied. It is preferable to avoid application in rainy weather or in environments where water droplets or the like remain on the adherend surface, and application is preferably performed under conditions of 5°C to 35°C.

<Application>
The primer composition according to the present invention can be suitably used as a primer composition for construction, civil engineering, concrete, wood, metal, glass, plastic, etc., as a sealant, adhesive, etc. Furthermore, the primer composition according to the present invention has excellent jointability with cured sealants, and therefore can be suitably used particularly for sealants.

The primer composition of the present invention can also be suitably used as a primer for poorly adhesive coated members. Examples of poorly adhesive coated members for which the primer composition of the present invention can be used include acrylic electrodeposition coated members, fluorine baked coated members, and anodized coated members. The primer composition of the present invention can also be used for members other than poorly adhesive coated members.

<Effects of the embodiment>
The primer composition according to the present invention has high barrier properties, and therefore can inhibit the migration of plasticizers and the like from the adherend or sealant, and can exhibit high adhesive durability over a long period of time. The primer composition according to the present invention can also exhibit high adhesion to wet surfaces. Furthermore, the primer composition according to the present invention is also useful as a primer for joining pre-applied sealants.

The following examples are provided for more specific explanation. Please note that these examples are illustrative only and should not be construed as limiting.

(Synthesis Example 1: Alkoxysilyl Group-Containing Methacrylic Resin)
A (meth)acrylic polymer having a trimethoxysilyl group was synthesized as an alkoxysilyl group-containing methacrylic resin. Specifically, a (meth)acrylic polymer having a trimethoxysilyl group was obtained using 70.00 g of methyl methacrylate, 30.00 g of 2-ethylhexyl methacrylate, 12.00 g of 3-methacryloxypropyltrimethoxysilane, 0.10 g of titanocene dichloride as a metal catalyst, 8.60 g of 3-mercaptopropyltrimethoxysilane, and 20.00 g of a benzoquinone solution (95% THF solution) as a polymerization terminator, in accordance with the method of Synthesis Example 4 of WO2015-088021.

The ethyl acetate solution of the resulting reaction product was heated at 105°C to determine the solids content, which was 70.5%. Furthermore, the polystyrene-equivalent molecular weight of the resulting polymer measured by gel permeation chromatography (GPC) was found to be a weight average molecular weight (Mw) of 4,000 and a molecular weight distribution (Mw/Mn) of 2.4. Furthermore, ^1H -NMR measurement (measured using an NMR400 manufactured by Shimadzu Corporation in _CDCl3 solvent) confirmed that the polymer contained two trimethoxysilyl groups per molecule. Furthermore, the glass transition temperature was 61°C.

(Examples and Comparative Examples)
For each of Examples 1 to 8 and Comparative Examples 1 to 8, component (A), component (B), component (C), and other additives were mixed in the proportions shown in Table 1, and then stirred and mixed. This resulted in primer compositions according to the Examples and Comparative Examples. The primer compositions obtained in Examples 1 to 8 and Comparative Examples 1 to 8 were then subjected to the following evaluations. The results are shown in Table 1. In Table 1, the amount of each compounded substance is expressed in grams.

Details of the materials shown in Table 1 are as follows: The blending amount of component (B) in Table 1 includes the amount of the solvent.
(Component (A))
Desmodur HL (solid content 60%): mixed isocyanurate trimer of HDI and TDI (TDI:HDI = 3:2) (manufactured by Sumika Covestro Urethane Co., Ltd., isocyanate group concentration 10.5%, solid content 60% by mass, butyl acetate solution)
Takenate D-120N (solid content 75%): an adduct of bis(isocyanatomethyl)cyclohexane (hydrogenated XDI) and trimethylolpropane (TMP) (manufactured by Mitsui Chemicals, Inc., solid content 75% by weight, butyl acetate 25% by weight, isocyanate group content relative to the solution 11.0%)
Nipporan 3024: polyester-based polyurethane resin (manufactured by Tosoh Corporation, solid content 34% by mass, ethyl acetate solution, number average molecular weight: 38,000, weight average molecular weight: 130,000, softening temperature 45°C, Tg: -36°C)
EHPE3150: alicyclic epoxy resin (manufactured by Daicel Corporation, 1,2-epoxy-4-(2-oxiranyl)cyclohexane adduct of 2,2-bis(hydroxymethyl)-1-butanol)
Pergut S170: chlorinated polyisoprene (manufactured by Sumika Covestro Urethane Co., Ltd., molecular weight 220,000, chlorine content 64.5% or more)

(Component (C))
Ketimine coupling agent: N-(1,3-dimethylbutylidene)-3-(trimethoxysilyl)-1-propanamine, weight average molecular weight: 261

(catalyst)
U-360: manufactured by Nitto Kasei Co., Ltd., mercapto catalyst, dibutyltin isooctylthioglycolate

(Evaluation method: joint adhesion)
The joint adhesion was evaluated as follows. First, a sample of a modified silicone sealant (Cemedine's "POS Seal LM") was prepared as a pre-applied adherend by curing it for 7 days in a 23°C, 50% RH environment. Next, the primer composition according to Example 1 was applied to the surface of the cured sealant (adherend), and the sealant was left for 30 minutes in a 23°C, 50% RH environment. A bead of a modified silicone sealant (Cemedine's "POS Seal LM Ultra Weather Resistant") for joint application was then applied thereon to prepare a test specimen. This test specimen was cured for 3 days in a 23°C, 50% RH environment, and then cured for 4 days in a 50°C, 40% RH environment. A portion of the adhesive interface (i.e., a portion of the adhesive interface between the adherend and the modified silicone sealant) was cut with a knife, and the cut portion was peeled off by hand. The peeling state was then visually observed to evaluate the state of failure. The evaluation results are shown in the column "Joint adhesion: POS Seal LM" in Table 1. The evaluation criteria are as follows.

"◯": The pre-applied and/or post-applied sealant has undergone cohesive failure.
"X": Interfacial destruction occurred between the pre-applied sealant and the cured product of the primer composition.

In addition, joint adhesion was evaluated in the same manner as above, except that a sample of modified silicone sealant (Cemedine's "POS Seal LM Ultra Weather Resistant") cured for 7 days in a 23°C, 50% RH environment was prepared as the pre-applied adherend. The evaluation results are shown in the "Joint Adhesion: POS Seal LM Ultra Weather Resistant" column in Table 1. Furthermore, the other examples and comparative examples were evaluated in the same manner. The evaluation results are shown in Table 1.

(Evaluation method: Barrier properties)
The barrier properties were evaluated as follows. First, a repair paint (manufactured by KMEW) was applied to a slate board according to the coating specifications and allowed to dry for one day. Then, the primer composition according to Example 1 was applied to the coating in an amount of 20 mg/ ^cm² and allowed to dry for one hour. Then, diisononyl phthalate (DINP) was applied thereon in an amount of 10 mg/ ^cm² . This resulted in a test specimen. All steps were carried out in an environment of 23°C and 50% RH.

The resulting test specimens were then left in a 60°C environment for one day, after which the surface of the primer composition coated with DINP was scratched with a metal spatula to evaluate the softening of the paint. The evaluation criteria are as follows. The other examples and comparative examples were also evaluated in the same way. The evaluation results are shown in Table 1.

"○": No change "△": Some change is seen "×": Change is seen

As can be seen from Table 1, all of the primer compositions according to the examples were shown to have excellent both joint adhesion and barrier properties. Looking at the examples and comparative examples, it can be seen that the combination of component (A) and component (B) simultaneously exhibits both good joint adhesion and barrier properties.

The above describes embodiments and examples of the present invention, but the above-described embodiments and examples do not limit the invention as claimed. It should also be noted that not all combinations of features described in the embodiments and examples are necessarily essential to the means for solving the problems of the invention, and that various modifications are possible without departing from the technical concept of the present invention.

Claims (4)

A primer composition for adhesion of a sealant, comprising:
Component (A) consisting of at least one member selected from the group consisting of a polyisocyanate compound having three or more isocyanate groups , a polyester polyurethane, an epoxy compound, and a chlorinated polymer;
and component (B) which is an alkoxysilyl group-containing methyl methacrylate polymer having a weight average molecular weight of less than 15,000 and in which the amount of methyl methacrylate in the polymer is 20% by mass or more and less than 80% by mass,
the amount of component (A) added to the primer composition is 6.0 to 20% in terms of solid content,
The amount of component (B) added to the primer composition is 24.9 to 60% in terms of solid content. The primer composition according to claim 1, wherein (B) is an alkoxysilyl group-containing methyl methacrylate polymer containing an alkyl (meth)acrylate ester having an ester group having 8 or more carbon atoms. The primer composition according to claim 1 or 2, further comprising (C) an amino group-containing silane. The primer composition according to any one of claims 1 to 3, further comprising (D) a silane-based crosslinking agent.