JP7161425B2 - Coating method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a novel method of forming a coating on an inorganic porous substrate.

Conventionally, silane-based compounds are used as the main component as a method of imparting water stopping performance and improving durability to inorganic porous substrates such as concrete and cement mortar, which have been used as the framework of buildings and civil engineering structures. A method of applying a solvent-based permeable water absorption inhibitor is widely used. In recent years, however, there has been an increasing demand for such materials to be water-based, in consideration of the surrounding environment and work hygiene.

As such a water-based material, for example, Patent Document 1 discloses a water-based primer containing a copolymer mainly composed of a cationic monomer, an alkoxysilane monomer, and an ethylenically unsaturated monomer. liquid is mentioned. This aqueous liquid undergoes a cross-linking reaction to form a water-blocking film, and by making it a resin liquid of high concentration and low viscosity, it is possible to improve substrate penetration, substrate reinforcement, and water resistance. is described.

JP-A-6-1680

However, in the process of impregnating the inorganic porous substrate with the aqueous liquid as in Patent Document 1, the aqueous liquid gels (hardens) on the surface layer of the substrate, and the inside of the substrate is sufficiently impregnated with the aqueous liquid component. In some cases, it was not possible to obtain a sufficient water stopping effect. In addition, the aqueous liquid component remaining on the surface of the base material without being impregnated may cause unevenness, which may adversely affect water stopping performance and aesthetics. Adhesion, durability, etc. cannot be obtained, and aesthetic appearance may be impaired. In addition, when a wetting agent, a penetrating agent, or the like is added to improve the impregnating property, the aqueous medium in the aqueous solution is easily impregnated into the base material, but the resin component forming the water stop coating is not sufficiently impregnated, resulting in the desired impregnation. performance could not be obtained.

The present invention has been made in view of such problems, and exhibits sufficient permeability and water stopping performance for inorganic porous substrates, and obtains a uniform finish with excellent aesthetics. An object of the present invention is to obtain a film forming method capable of

As a result of intensive studies on such problems, the present inventors have found that after applying an aqueous coating material containing a specific synthetic resin emulsion (A) and a water-soluble silane compound (B) in a specific weight ratio, The present invention was completed by discovering a method of forming a film by applying the material.

That is, the present invention has the following features.
1. A film forming method for forming a film on an inorganic porous substrate,
(I) containing a synthetic resin emulsion (A) and a water-soluble silane compound (B) on an inorganic porous substrate;
The synthetic resin emulsion (A) has an average particle size of 100 nm or less and a pH of 2 or more and 6 or less,
a step of applying an aqueous coating material containing 0.1 to 20 parts by weight of the water-soluble silane compound (B) to 100 parts by weight of the resin solid content of the synthetic resin emulsion (A);
(II) a step of applying a topcoat material after the aqueous coating material is dried;
A method of forming a film, comprising:
2. 1. The water-soluble silane compound (B) has a pH of less than 7 in a 1% by weight aqueous solution. The film forming method according to .
3. 1. The water-soluble silane compound (B) is an epoxy group-containing silane compound. or 2. The film forming method according to .

The method of forming a film of the present invention can exhibit sufficient permeability and water stopping performance on an inorganic porous substrate, and can provide a uniform finish with excellent aesthetics.

The film forming method of the present invention is a film forming method for forming a film on an inorganic porous substrate.
(Inorganic porous substrate)
Examples of the inorganic porous substrate of the present invention include those used for floor surfaces, floor materials, noncombustible boards, tunnel interior panels, exposed surfaces, etc. Examples include mortar, concrete, gypsum board, siding board, Examples include extruded boards, slate boards, fiber-mixed cement boards, calcium silicate boards, ALC boards, and the like.

The present invention provides such inorganic porous substrates with
(I) a step of applying a specific aqueous coating material containing a synthetic resin emulsion (A) and a water-soluble silane compound (B);
(II) a step of applying a topcoat material after the aqueous coating material is dried;
Especially in the above (I), when a specific aqueous coating material is applied, it has sufficient permeability, imparts water stopping performance to the inorganic porous substrate, and prevents unevenness etc. A finish excellent in aesthetics can be obtained without occurrence of scratches.

(Aqueous covering material)
The aqueous coating material in (I) above contains a synthetic resin emulsion (A) and a water-soluble silane compound (B).
As the synthetic resin emulsion (A) of the present invention,
(1) an average particle size of 100 nm or less (preferably 10 nm or more and 90 nm or less);
(2) pH is 2 or more and 6 or less (preferably 2.5 or more and 5 or less),
It is characterized by

When the average particle diameter of the resin particles of the synthetic resin emulsion (A) is within the range of (1) above, excellent permeability, reinforcement, and adhesion to the inorganic porous substrate can be exhibited. . As a result, excellent water stopping performance can be exhibited. On the other hand, if the average particle size of the resin particles exceeds the above range (1), sufficient waterproofing performance may not be obtained due to deterioration in permeability and reinforcing properties. In the present invention, the average particle size of resin particles is a value measured by a dynamic light scattering method. Specifically, it can be measured using a dynamic light scattering measurement device (“LB-550” manufactured by Horiba, Ltd.) or the like. (The measurement temperature is 25°C.)

Further, when the pH of the synthetic resin emulsion (A) is within the above range (2), excellent permeability, reinforcement and adhesion to the inorganic porous substrate can be exhibited. As a result, excellent water stopping performance can be exhibited. Although the mechanism of action is not clear, the surface of the inorganic porous substrate is alkaline except for a part, and it is thought that by forming a film in an alkaline environment, it can firmly adhere to the inorganic substrate. be done.

The synthetic resin emulsion (A) is not particularly limited, but is preferably an acrylic resin emulsion, more preferably an acrylic silicone resin emulsion. In this case, good adhesion to the inorganic porous substrate can be obtained.

Furthermore, the synthetic resin emulsion (A) of the present invention preferably contains a cationic acrylic resin emulsion that satisfies the above (1) and (2). As such a cationic acrylic resin emulsion, an aqueous dispersion of a polymer obtained by polymerizing a (meth)acrylic acid alkyl ester and a cationic monomer as essential components as constituent monomers is preferable.

The (meth)acrylic acid alkyl ester is the main component of the resin skeleton. In the present invention, alkyl acrylate and alkyl methacrylate are collectively referred to as alkyl (meth)acrylate. Moreover, a monomer is a general term for compounds having a polymerizable unsaturated double bond.

Specific examples of (meth)acrylic acid alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl ( meth)acrylate, n-amyl (meth)acrylate, isoamyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate Acrylate, octadecyl (meth)acrylate, cyclohexyl (meth)acrylate and the like. These can be used alone or in combination of two or more.

The cationic monomer is not particularly limited as long as it is a cationic monomer having an unsaturated double bond. etc. These can be used alone or in combination of two or more.

specifically,
Examples of cationic (meth)acrylamide-based monomers include (meth)acrylamides such as 3-acrylamidopropyltrimethylammonium chloride, 2-(meth)acrylamidoethyltrimethylammonium methosulfate, and 2-(meth)acrylamidoethyltrimethylammonium methosulfate. trialkylammonium salts;
(Meth) acrylamide-2-hydroxypropyltrimethylammonium chloride, 3-(meth)acrylamide-2-hydroxypropyltrimethylammonium methosulfate, 3-(meth)acrylamide-2-hydroxypropyltrimethylammonium chloride, etc. acrylamide hydroxyalkyltrialkylammonium salt;
Dialkylaminoalkyl (meth)acrylamide salts such as 2-dimethylaminoethyl (meth)acrylamide hydrochloride, 2-diethylaminopropyl (meth)acrylamide sulfate, 2-dimethylaminoethyl (meth)acrylamide hydrochloride;
Dialkylaminohydroxyalkyl (meth)acrylamide salts such as 3-dimethylamido-2-hydroxypropyl (meth)acrylamide hydrochloride and 3-diethylamino-2-hydroxypropyl (meth)acrylamide sulfate;
etc.

Examples of cationic maleic acid amide-based monomers include maleic acid (N,N-dimethylpropylenediamine monoamide) salts and the like. By including such a cationic monomer, it is possible to exhibit high adhesion to the inorganic porous substrate.

Furthermore, as the synthetic resin emulsion (A) of the present invention, a cationic acrylic silicone resin emulsion satisfying the above (1) and (2) is suitable. The cationic acrylic silicone resin emulsion is preferably an aqueous dispersion of a polymer obtained by polymerizing the (meth)acrylic acid alkyl ester, the cationic monomer, and the alkoxysilane monomer as essential components.

As the alkoxysilane monomer, those having a hydrolyzable alkoxy group together with a polymerizable double bond are preferred. Examples include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(β-methoxyethoxy)silane, and vinyltriacetoxysilane. , γ-(meth)acryloxypropyltrimethoxysilane, γ-(meth)acryloxypropyltriethoxysilane, vinyltrichlorosilane, γ-(meth)acryloxypropyltris(β-methoxyethoxy)silane, etc. can. These can be used alone or in combination of two or more.

In the present invention, aromatic monomers, vinyl ester-based monomers, acrylonitrile-based monomers, and the like may be added as components constituting the synthetic resin emulsion (A) in addition to the above monomers.
Examples of aromatic monomers include styrene, 2-methylstyrene, vinyltoluene, t-butylstyrene, chlorostyrene, vinylanisole, vinylnaphthalene, divinylbenzene, phenyl(meth)acrylate, and benzyl(meth)acrylate. .
Vinyl ester monomers include, for example, vinyl acetate, vinyl propionate, vinyl butyrate, and vinyl versatate.
Examples of acrylonitrile-based monomers include acrylonitrile and methacrylonitrile. These can be used singly or in combination of two or more.

The polymerization method of the synthetic resin emulsion (A) is not particularly limited, and for example, a polymerization initiator, a polymerization catalyst, a reducing agent, a surfactant, a pH adjuster, etc. can be used, and the polymerization is performed by a known method such as a batch method or an injection method. It is possible to The polymerization temperature at this time can also be appropriately selected.

The resin solid content of the synthetic resin emulsion (A) is preferably 1-50% by weight (more preferably 5-40% by weight). The synthetic resin emulsion (A) contains water as a medium, but can also contain a water-soluble solvent and the like. The minimum film-forming temperature and/or glass transition temperature of the synthetic resin emulsion (A) is preferably 5°C or lower (more preferably 0°C or lower). By adopting the component (A) having such a lowest film-forming temperature and/or glass transition temperature, it is possible to reduce the amount of the film-forming aid and the like used.

The water-based coating material of the present invention is characterized by containing a water-soluble silane compound (B) as an essential component. By containing the water-soluble silane compound (B), the permeability of the synthetic resin emulsion (A) is further increased, forming a coating inside the inorganic porous substrate and forming a uniform coating on the surface of the inorganic porous substrate. can be formed. For this reason, it is possible to exhibit even more excellent water stopping performance and to obtain a finish excellent in aesthetics. In particular, in a low-temperature environment, a sufficient coating can be formed to the inside of the inorganic porous substrate, and sufficient water stoppage can be obtained. Although the mechanism of action is not limited, in general, the viscosity of the aqueous coating material tends to increase in a low-temperature environment. less permeable. On the other hand, in the water-based coating material of the present invention, the viscosity of the water-based coating material is reduced by the action of the water-soluble silane compound (B). As a result, a sufficient coating can be formed inside the inorganic porous substrate. Due to the above action, sufficient permeability can be exhibited, and a coating can be formed inside the inorganic porous substrate, and a uniform coating can be formed on the surface of the inorganic porous substrate. In addition, the water-soluble silane compound in the present invention may be one that dissolves in water, preferably one that can be used to prepare a 1% by weight silane aqueous solution. When preparing this 1 wt % silane aqueous solution, the pH may be adjusted as necessary.

Examples of the water-soluble silane compound (B) include 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, Epoxy group-containing silane compounds such as sidoxypropylmethyldiethoxysilane and 3-glycidoxypropyltriethoxysilane; amino group-containing silane compounds such as 3-aminopropyltriethoxysilane and 3-aminopropyltriethoxysilane; (Meth)acryloxypropylmethyldimethoxysilane, 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropylmethyldiethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, etc. (meth) ) acrylic group-containing silane compounds; other examples include 3-mercaptopropyltrimethoxysilane, bis(triethoxysilylpropyl)tetrasulfide, and 3-isocyanatopropylethoxysilane. These can be used alone or in combination of two or more.

Further, the water-soluble silane compound (B) preferably has a pH of less than 7 (more preferably 1 or more and 6.5 or less, still more preferably 1.5 or more and 6 or less) as a 1 wt% silane aqueous solution. (That is, the solubility in water with a pH of less than 7 (more preferably 1 or more and 6.5 or less, more preferably 1.5 or more and 6 or less) is preferably at least 1 g/100 g or more.) In such a case, The stability of the water-based coating material can be enhanced (eg, gelation can be suppressed), and the effects of the present invention can be further enhanced. In the present invention, an epoxy group-containing silane compound is suitable as the water-soluble silane compound (B). The pH of the 1% by weight silane aqueous solution is the pH measured when the 1% by weight silane aqueous solution was prepared.

The water-soluble silane compound (B) is added in an amount of 0.1 to 20 parts by weight (preferably 0.3 to 15 parts by weight, more preferably 0.1 to 20 parts by weight) per 100 parts by weight of the resin solid content of the synthetic resin emulsion (A). 5 to 10 parts by weight). As a result, the water-based coating material has sufficient permeability to the inorganic porous substrate, and can form a uniformly finished coating film with excellent water stopping performance.

The aqueous coating material of the present invention preferably has a pH of 1.5 to 7 (more preferably 2 to 6.5). In addition, the heating residue is preferably 2 to 30% by weight (more preferably 5 to 20% by weight), and the viscosity measured by Iwata Cup NK-2 is 20 sec or less (more preferably 15 sec or less) (at a temperature of 23°C). be. In such a case, it is possible to impart sufficient permeability and water stopping performance to the inorganic porous substrate and obtain a uniform finish. The residual amount of the water-based coating material after heating is the value measured by the method of JIS K 5601-1-2, the heating temperature is 105° C., and the heating time is 60 minutes).

The method for producing the water-based coating material of the present invention is not particularly limited, and the synthetic resin emulsion (A) and the water-soluble silane compound (B) may be mixed by a conventional method, and stirring may be performed during mixing. The water-based coating material of the present invention preferably has a form in which the water-soluble silane compound (B) is dissolved in water, and the water-soluble silane compound (B) is mixed with the synthetic resin emulsion (A) in an unemulsified state. is preferred.

The aqueous coating material of the present invention preferably contains a film-forming aid (C). Thereby, it is possible to sufficiently exhibit the film formability inside the inorganic porous substrate. The film-forming aid (C) is preferably 10 parts by weight or less (more preferably 0.5 to 5 parts by weight) per 100 parts by weight of the resin solid content of the synthetic resin emulsion (A). Even when the mixed amount of the film-forming aid (C) is within the above range, the water-based coating material penetrates into the inorganic porous substrate to form a coating, so that the waterproof performance can be sufficiently exhibited. . In general, synthetic resin emulsions containing coalescents swell, increasing the viscosity of aqueous coatings. However, in the present invention, the action of the water-soluble silane compound (B) lowers the viscosity of the water-based coating material. can be fully demonstrated.

As the film-forming aid (C), any of water-insoluble, sparingly soluble, water-soluble, etc. can be used, and is not particularly limited. Examples include ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, and ethylene glycol monoethyl ether. Acetate, ethylene glycol diethyl ether, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monobutyl ether , 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, 2,2,4-trimethyl-1,3-pentanediol diisobutyrate, benzyl alcohol and the like. Propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monobutyl ether and the like are preferred. These can be used alone or in combination of two or more.

In addition to the above components, the water-based coating material of the present invention may optionally contain a coloring pigment, an extender pigment, an antirust pigment, a pH adjuster, a plasticizer, an antiseptic, an antifungal agent, an anti-algae agent, an antifoaming agent, A leveling agent, a pigment dispersant, an anti-settling agent, an anti-sagging agent, a matting agent, a catalyst, a cross-linking agent, a curing accelerator, an ultraviolet absorber, a light stabilizer, etc. are mixed within a range in which the effects of the present invention are not impaired. can do.

Various methods such as brush coating, roller coating, and spray coating can be employed for coating the water-based coating material. In the case of coating in a factory, it is also possible to use a roll coater, a flow coater, or the like, in addition to the above.

The coating amount of the aqueous coating material is preferably about 0.01 to 0.5 kg/m ² (more preferably 0.05 to 0.3 kg/m ² ). The number of times the water-based coating material is applied may be appropriately set depending on the state of the substrate, but is preferably 1 to 2 times. The drying time for the water-based coating material is preferably one hour or longer. The drying temperature is preferably 0° C. or higher and 50° C. or lower, more preferably 5° C. or higher and 40° C. or lower.

(Topcoat material)
The topcoat material in (II) above is not particularly limited as long as it is generally used for coating buildings and civil engineering structures. A film formed from the water-based coating material (I) can have excellent adhesion to a wide variety of topcoat materials. Usable topcoat materials include those containing a resin component and, if necessary, a color pigment.

Various resins can be used as the resin component. Examples of resin types include vinyl acetate resins, polyester resins, alkyd resins, vinyl chloride resins, epoxy resins, acrylic resins, urethane resins, acrylic silicon resins, fluorine resins, and composite resins thereof. Among these, one or more selected from acrylic resins, urethane resins, acrylic silicon resins, fluorine resins, and the like are suitable. Examples of forms of such resin components include water-soluble resins, water-dispersible resins (resin emulsions), solvent-soluble resins, solvent-free resins, non-aqueous-dispersible resins, powder resins, and the like. Among solvent-soluble resins and/or non-water-dispersible resins, so-called weakly solvent-type resins in which 50% by weight or more (preferably 60% by weight or more) of the total solvent is aliphatic hydrocarbon are also suitable. Examples of aliphatic hydrocarbons include n-hexane, n-pentane, n-octane, n-nonane, n-decane, n-undecane, n-dodecane, and aliphatic hydrocarbons such as terpine oil and mineral spirits. system solvents. Among these, water-soluble resins and/or water-dispersible resins are suitable in the present invention. Moreover, these resin components may have cross-linking reactivity. When a resin component having cross-linking reactivity is used, durability, water resistance, weather resistance, chemical resistance, adhesion, etc. of the film can be improved.

As the coloring pigment, for example, known inorganic coloring pigments, organic coloring pigments and the like can be used. By appropriately using one or more of these color pigments, the topcoat material can be set to have a desired hue. The mixing ratio of the color pigment is preferably 1 to 500 parts by weight, more preferably 5 to 200 parts by weight, still more preferably 10 to 100 parts by weight, per 100 parts by weight of the solid content of the resin component.

As the topcoat material of the present invention, those that form a transparent film can also be used, and in this case, while making use of the appearance of the inorganic porous substrate, it is possible to impart performance such as water stoppage, durability, and aesthetics. This is preferable because it can be done. One or two or more kinds of topcoat materials can be used. When two or more kinds of topcoat materials are used, it is also possible to use topcoat materials having different color tones to finish a multicolored appearance of two or more colors.

Such a topcoat material may contain various components other than the above components as long as the effects of the present invention are not significantly impaired. Examples of such components include thickeners, film-forming aids, leveling agents, wetting agents, plasticizers, antifreeze agents, pH adjusters, extender pigments, preservatives, antifungal agents, anti-algae agents, and antibacterial agents. agents, dispersants, antifoaming agents, adsorbents, fibers, cross-linking agents, ultraviolet absorbers, light stabilizers, antioxidants, catalysts, solvents, water and the like. The topcoat material of the present invention can be produced by uniformly mixing the various components described above by a conventional method.

A known coating tool can be used for coating the topcoat material. Examples of coating tools that can be used include sprays, rollers, and brushes.
The coating amount of the topcoat material may be appropriately set according to the surface shape of the substrate, the type of topcoat material, the type of coating equipment, etc., but is preferably 0.1 to 3 kg/m ² , more preferably 0.1 kg/m 2 . 15 to 2.5 kg/m ² . At the time of painting, the topcoat material can be diluted as needed.

Examples and comparative examples are shown below to further clarify the features of the present invention.

(Production of water-based coating materials 1 to 15)
According to the formulation shown in Table 1, components (A), (B), additives, and water were mixed in a conventional manner to obtain water-based coating materials 1-15.
In addition, the following were used as a raw material.
- (A1) acrylic resin emulsion (solid content: 40% by weight, average particle size: 70 nm, pH: 5.1)
- (A2) Cationic acrylic resin emulsion (solid content: 30% by weight, average particle size: 60 nm, pH: 3.7)
(A3) Cationic acrylic silicone resin emulsion (solid content: 30% by weight, average particle size: 40 nnm, pH: 3.5)
- (A4) acrylic resin emulsion (solid content: 40% by weight, average particle size: 125 nm, pH: 4.0)
- (A5) acrylic resin emulsion (solid content: 40% by weight, average particle size: 70 nm, pH: 8.7)
(B1) 3-glycidoxypropyltrimethoxysilane (active ingredient: 100% by weight, water solubility: pH 5.3 of a 1% by weight aqueous solution)
(B2) 3-glycidoxypropyltriethoxysilane (active ingredient: 100% by weight, water solubility: pH 4.0 of 1% by weight aqueous solution)
- (B3) 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane (active ingredient: 100% by weight, water solubility: pH 4.0 of a 1% by weight aqueous solution)
(B4) N-phenyl-3-aminopropyltrimethoxysilane (active ingredient: 100% by weight, water solubility: pH 4.0 of 1% by weight aqueous solution)
(B5) 3-aminopropyltrimethoxysilane (active ingredient: 100% by weight, water solubility: pH 10 of 1% by weight aqueous solution)
(B6) P-styryltrimethoxysilane (active ingredient: 100% by weight, water-insoluble)
(B7) Emulsion of propyltrimethoxysilane (active ingredient: 30% by weight, including surfactant)
・Additive 1: propylene glycol monobutyl ether ・Additive 2: antifoaming agent, thickener, etc.

(Examples I-1 to I-10, Comparative Examples I-1 to I-5)
Test samples [I] were prepared for the water-based coating materials 1 to 15, and the following evaluations were carried out. Results are shown in Table 1.
<Preparation of test sample [I]>
(I) An inorganic porous substrate (slate plate: L100×W100×T3 mm) was brush-coated with a water-based coating material at a coating amount of 0.1 kg/m ² and dried at room temperature (25° C.) for 24 hours.
(II) Next, a water-based topcoat material (acrylic silicone emulsion paint) was applied at a coating amount of 0.1 kg/m ² and dried for 24 hours under standard conditions. did.

<Permeability evaluation>
In the above step (I), the permeability of the aqueous coating material was visually evaluated. Evaluation criteria are as follows.
A: Good permeability.
B: Generally good permeability.
C: Slightly insufficient permeability.
D: Insufficient permeability.
<Aesthetic evaluation>
The state of the surface of the specimen [I] was visually evaluated for aesthetics (appearance). Evaluation criteria are as follows.
A: Even finish.
B: Partial unevenness occurs.
C: Defects such as cracks occurred in the film on the substrate surface.

<Water stopping evaluation>
The back surface of the test sample [I] was sealed with an epoxy resin and immersed in water for 24 hours to evaluate water permeability. Evaluation criteria are as follows.
A: No water permeation (no wet color).
B: Water partially permeates (partially wet color).
C: Water permeates the substrate (almost the entire surface becomes a wet color).
D: Water permeates the substrate (entire surface becomes wet).

(Examples II-1 to II-10)
For each of the water-based coating materials 1 to 10, the following specimen [II] was prepared and evaluated in the same manner. Results are shown in Table 2.
<Preparation of test sample [II]>
Specimen [II] was prepared in the same manner as for preparation of specimen [I], except that in step (I), after applying the water-based coating material, it was cured at a low temperature (5° C.) for 24 hours.

Claims (3)

A film forming method for forming a film on an inorganic porous substrate,
(I) containing a synthetic resin emulsion (A) and a water-soluble silane compound (B) on an inorganic porous substrate;
The synthetic resin emulsion (A) has an average particle size of 100 nm or less and a pH of 2 or more and 6 or less,
a step of applying an aqueous coating material containing 0.1 to 20 parts by weight of the water-soluble silane compound (B) to 100 parts by weight of the resin solid content of the synthetic resin emulsion (A);
(II) a step of applying a topcoat material after the aqueous coating material is dried;
A method of forming a film, comprising: 2. The method of forming a film according to claim 1, wherein the water-soluble silane compound (B) has a pH of less than 7 in a 1% by weight aqueous solution. 3. The film forming method according to claim 1, wherein the water-soluble silane compound (B) is an epoxy group-containing silane compound.