JPH07110906B2 - Water-dispersed composition for forming porous film, porous film, and method for forming porous film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a composition for forming a porous film and a porous film-forming composition for forming a porous film excellent in moisture permeability and absorbability by coating and drying on a substrate. And a method for forming a porous film.

[Prior Art] Since a synthetic resin can form a uniform and continuous film when applied on a substrate as a solvent solution, an aqueous solution or an aqueous emulsion, that is, an aqueous emulsion, a binder for paints, adhesives, papers, etc. It is used in a wide range of applications such as processing binders and fiber treatment agents.

The film thus obtained was a uniform, continuous film having a high airtightness.

In recent years, these applications have been diversified, so that not only a film having high airtightness but also a film having high moisture permeability and high absorbency has been demanded. For example, a paint is required to have a coating film that can pass moisture instead of stopping moisture. This is because not only the appearance of the coating film, but also higher performance such as dew condensation prevention and humidity control effect is required.

In addition, in the case of adhering or coating a porous substrate such as paper, fiber or a porous film, in order to not lose the characteristics of the porous substrate, a porous adhesive layer or a porous coating layer is used. Had to be formed.

Many synthetic resin binders for forming a film having high moisture permeability and high absorbency have been studied and proposed, but sufficient synthetic resin binders have not been obtained yet. If fine pores can be formed in the film, a film with very high moisture permeability and absorbency should be obtained, so a porous film was investigated.

Conventionally, as a method for forming a porous film, for example, JP-A-61
As disclosed in Japanese Patent Publication No. 79620, for example, a polyolefin such as polynoethylene is made into a sheet form by containing 30% by weight or more of an inorganic filler containing at least one alkaline earth metal oxide such as calcium carbonate. A porous film is formed by stretching at least uniaxially.

Also, as disclosed in Japanese Patent Publication No. 61-17852,
In the presence of a water-soluble or hydrophilic polymer, a vinyl monomer that gives a hydrophobic polymer is emulsion-polymerized, and a film is formed using the aqueous emulsion, and then the hydrophobic component is solvent-extracted to form a porous film. Is made.

However, since all of these porous coatings require secondary processing such as stretching or extraction after forming the coating, coating and drying such as a porous coating layer or a porous adhesive layer is required. It was not possible to use it only for the purpose.

[Problems to be Solved by the Invention] A composition for forming a porous film, a porous film, and a porous film which form a porous film by coating a substrate and then drying the film without impairing the properties of the film. It is to provide a forming method.

[Means for Solving the Problems] That is, the present inventors have studied an aqueous composition that quantitatively produces pores in the process of forming a film, and in particular, a composition obtained by blending a synthetic resin emulsion and colloidal silica. The present invention has been completed as a result of intensive studies, paying attention to the fact that a film obtained from a product has a large water permeability.

BEST MODE FOR CARRYING OUT THE INVENTION 1. A porous film forming composition comprising a film forming aqueous emulsion composed of synthetic resin particles having a particle size of 0.03 to 10 μm and water and colloidal silica, wherein the film forming aqueous emulsion is α, β-ethylenic An emulsion obtained by emulsion-polymerizing an unsaturated monomer and acrylic silane or vinyl silane, and the particle size of colloidal silica is 1/3 or less of the particle size of synthetic resin particles, and the compounding amount of the colloidal silica is synthetic. A porous film-forming water-dispersed composition, which is 0.5 to 30 times the weight of completely covering the resin particles.

2. The water-dispersible composition for forming a porous film according to claim 1, wherein the acrylic silane or vinyl silane is a silane compound having a methoxy group and / or an acetoxy group.

3. A film-forming aqueous emulsion reacts with the functional group in an emulsion obtained by emulsion polymerization of an α, β-ethylenically unsaturated monomer and an α, β-ethylenically unsaturated monomer having a functional group. The water-dispersible composition for forming a porous film according to claim 1 or 2, which is an emulsion in which a silane group is introduced into a synthetic resin which is emulsified by reacting a silane compound having a property of reacting.

4. The aqueous dispersion composition for forming a porous film according to any one of claims 1 to 3, wherein the film-forming aqueous emulsion is an emulsion obtained by emulsion polymerization using a polymerizable emulsifier.

5. Voids formed by coating the substrate with the water-dispersible composition for forming a porous film according to any one of claims 1 to 4 and drying the film to form a surface having colloidal silica. A porous film composed of synthetic resin particles covered with colloidal silica arranged in the film.

6. The porous coating film according to claim 5, wherein the pores formed on the surface of the coating film with colloidal silica are communicating pores.

7. The pores formed on the surface of the coating with colloidal silica are independent pores and communicating pores.
The porous film described in.

8. The water-dispersible composition for forming a porous film according to claim 1 is applied to the surface of a protected substrate and dried at a temperature not lower than the minimum film forming temperature, and the surface is made of colloidal silica. A method for forming a porous film having formed pores.

Although the theoretical elucidation of the process by which the porous film-forming composition of the present invention is formed on the substrate only by coating and drying is not always sufficient, the porosity of the present invention Features of the composition for forming a high quality film: 1. It comprises a film forming aqueous emulsion composed of synthetic resin particles containing a silane group and water, and colloidal silica.

2. The particle size of colloidal silica is 1/3 or less of the particle size of synthetic resin.

3. The amount of colodyl silica blended is the amount that covers the synthetic resin.
0.5 to 30 times, preferably 1 to 20 times.

Can be given.

Further, the pores of the porous film of the present invention are characterized by: 1. If the particle size of the synthetic resin particles used is large, the pores are large, and if the particle size is small, the pores are small.

2. The pores are surrounded by particles of colloidal silica.

Based on the above, the present inventors consider as follows.

Since the synthetic resin particles have a silane group, the surface of the synthetic resin particles is coated with colloidal silica, and the synthetic resin particles coated with the colloidal silica are fused to form a film during the drying process. The colloidal silica partially inhibits the fusion, and pores surrounded by the colloidal silica are generated to form a porous film.

Further, in the process in which moisture remaining inside is released to the outside of the film through the formed pores on the surface of the film, voids are also formed inside and a communication hole is formed.

An electron micrograph of the porous film obtained according to the present invention is attached.

As is clear from the electron micrograph, the porous film obtained by the present invention is produced by applying the aqueous composition of the present invention to a substrate and drying, and is present in the film containing the filler or in the film. It is completely different from the porous film formed by elution of soluble resin particles or the like, that is, by the post-treatment of the film.

The pores of the porous film of the present invention are controlled by the synthetic resin particle size, and the synthetic resin particle size is 0.03 μm to 10 μm.
If it is large, large pores are obtained, and if it is small, small pores are obtained. In order to obtain uniform pores, it is preferable that the synthetic resin particles have a substantially uniform particle diameter, and in the case of two or more kinds having extremely different particle diameters, the pore size will also be non-uniform.

It is necessary that the synthetic resin particles contain a silane group,
The silane group provides sufficient bonding between the synthetic resin particles and the colloidal silica particles, but synthetic resin particles containing no silane group are not preferable because such effects cannot be obtained.

The particle size of colloidal silica needs to be 1/3 or less of that of synthetic resin particles, and a porous film cannot be obtained even if colloidal silica having a particle size exceeding 1/3 is used. In addition, the amount of colloidal silica blended is 0.
It is 5 to 30 times, preferably 1 to 20 times.

The amount of colloidal silica that covers the synthetic resin particles depends on the particle size of the synthetic resin particles and the particle size of the colloidal silica, and is a multiple that indicates how many times the amount of colloidal silica used is the amount that covers the synthetic resin particles. Is calculated by the following formula.

N = W (si / p) / W (si) N; multiple of the amount of coating synthetic resin particles W _{(si / p)} ; amount of colloidal silica used per 1 part by weight of resin W _(si) ; 1 part by weight of resin the amount of colloidal silica necessary to coat the _{W (si) = W si /} W p W si; weight of colloidal silica cover one resin particles W _p; weight of one resin particle W _si = 1/6・ Π ² · D _p ² · D _si · ρ _si W _p = _1/6 · π · D _p ³ · ρ _p π; Circularity D _p ; Particle diameter of synthetic resin particle D _si ; Colloidal silica particle Diameter ρ _si ; Specific gravity of colloidal silica ρ _p ; Specific gravity of synthetic resin If the multiple of the amount of coating synthetic resin particles is less than 0.5 or more than 30, voids cannot be obtained or uniform voids can be obtained. I can't.

The film-forming aqueous emulsion composed of silane group-containing synthetic resin particles and water used in the present invention is not particularly limited, but is an aqueous emulsion obtained by emulsion polymerization of α, β-ethylenically unsaturated monomers. Is preferable from the viewpoint of particle size. As a method for introducing a silane group, an α, β-ethylenically unsaturated monomer and an acrylic silane or a vinylsilane are emulsion-polymerized, or an α, β-ethylenically unsaturated monomer and a α, β having a functional group are used. A preferred method is to react an emulsion obtained by emulsion polymerization of an ethylenically unsaturated monomer with a silane compound having reactivity with the functional group.

Examples of the α, β ethylenically unsaturated monomer used in the present invention include acrylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and lauryl acrylate; methyl methacrylate, Ethyl methacrylate, butyl methacrylate,
Suitable are methacrylic acid esters such as isobutyl methacrylate, 2-ethylhexyl methacrylate, and lauryl methacrylate; acrylonitrile, methacrylonitrile; styrene, methylstyrene, and chlorostyrene. Of these, it is particularly preferable to combine a monomer having a high glass transition temperature and a monomer having a low glass transition temperature.

Particularly, methacrylic acid ester-based monomers are mainly used. Further, a styrene-acrylic monomer which is rich in styrene is also preferably used.

Examples of the monomer to be copolymerized with the above-mentioned monomer include methyl crotonate, ethyl crotonate, dibutyl maleate, diethyl fumarate, and the like, acrylic acid esters, unsaturated carboxylic acid esters other than methacrylic acid esters. Or unsaturated polycarboxylic acid esters; branched at the α-position such as vinyl acetate, vinyl dipropionate, vinyl laurate, vinyl stearate, vinyl bivalate and Veova (registered trademark of Shell Chemical Co.) One or more vinyl esters such as vinyl ester of saturated carboxylic acid; vinyl chloride, vinylidene chloride; ethylene and the like.

Further, the α, β ethylenically unsaturated monomer may be used in combination with an α, β ethylenically unsaturated monomer having a functional group in an amount of 30% by weight or less.

Examples of the α, β eletic unsaturated monomer having a functional group include acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, maleic anhydride, maleic acid monoester, fumaric acid monoester, etc. Unsaturated carboxylic acids or unsaturated polyvalent carboxylic acid derivatives; unsaturated carboxylic acid amides such as acrylamide and methacrylamide; N-methylol unsaturated carboxylic acid amides such as N-methylol acrylamide and N-methylol methacrylamide; Unsaturated glycidyl compounds such as glycidyl acrylate and glycidyl methacrylate; alkylol unsaturated compounds such as hydroxyethyl acrylate, hydroxypropyl methacrylate and hydroxy vinyl ether; diallyl phthalate, divinylbenzene or diallyl Object compound is one or more of such.

Acrylic silanes or vinyl silanes used in the present invention are preferably those of the field of water addition, such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (2-methoxy-ethoxy) silane, vinyltriacetoxysilane, γ. -Methacrylooxypropyltrimethoxysilane, vinyltrichlorosilane,
γ-methacrylooxypropyltris (methoxy-ethoxy) silane, etc., but γ from the viewpoint of non-polymerizability
Most preferred are methacrylooxypropyltrimethoxysilane and vinyltrimethoxysilane.

The proportion of the monomer used is α, β ethylenically unsaturated monomer 9
Acrylic silane or vinyl silane 0.5 to 15 parts by weight is suitable for 9.5 to 85 parts by weight. Preferably α, β
The amount of the acrylic silane or vinyl silane is 2.0 to 10 parts by weight based on 98.0 to 90 parts by weight of the ethylenically unsaturated monomer.

In order to produce a film-forming aqueous emulsion using acrylic silane or vinyl silane in the present invention, the aforementioned α, β-ethylenically unsaturated monomer and acrylic silane or vinyl silane are used in the presence of an emulsifier with a polymerization catalyst. Obtained by emulsion polymerization.

As a polymerization method, a monomer charging method may be a batch method or a continuous feeding method. Alternatively, a method may be used in which a part is first polymerized and the rest is continuously fed.

The monomer continuously fed may be as it is, but a method of feeding it as a monomer emulsion using water and an emulsifier is very suitable. Further, high temperature polymerization or redox polymerization may be used.

Especially when water resistance is required for the porous film, a polymerizable emulsifier is preferably used as the emulsifier. (1) Alkylallyl sulfone succinate alkali salt (In the formula, R ¹ is an alkyl group having 8 to 20 carbon atoms.) (2) Sodium (glycerin n-alkenylsuccinoylglycerin) borate (In the formula, R ² is an alkyl group having 12 to 20 carbon atoms) (3) Alkali salt of sulfopropyl maleic acid monoalkyl ester (In the formula, R ³ is an alkyl group having 8 to 20 carbon atoms.) (4) Polyoxyethylene alkyl ester of acrylic acid or methacrylic acid (In the formula, R ⁴ is H or CH, R ⁵ is an alkyl group having 8 to 20 carbon atoms, and n is an integer of 1 to 20) and the like.

The amount of polymerizable emulsifier used is 100 parts by weight of all monomers.
0.5 to 10 parts by weight is suitable, and preferably 1 to 5 parts by weight.

A film-forming aqueous emulsion obtained by reacting a silane compound with an emulsion obtained by emulsion polymerization to introduce a silane group,
Emulsification by using an α, β-ethylenically unsaturated monomer having a functional group in place of acrylic silane or vinyl silane in the method of emulsion polymerizing an α, β-ethylenically unsaturated monomer and acrylic silane or vinyl silane. It is produced by adding a silane compound to an emulsion obtained by polymerization and reacting it.

Aminosilane and / or epoxysilane is used as the silane compound.

As aminosilane, N- (2-aminoethyl) 3-aminopropylmethyldimethoxysilane, N- (2-aminoethyl) 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-phenyl-3-amino Propyltrimethoxysilane is preferred.

Aminosilane is particularly effective for aqueous copolymer emulsions having glycidyl groups or carboxyl groups introduced.

Epoxy silanes include 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 2- (3,
4 Epoxycyclohexyl) ethyltrimethoxysilane is preferred.

Epoxysilanes are particularly effective for aqueous copolymer emulsions having amino groups or carboxyl groups introduced.

As the synthetic resin particles containing a silane group in the present invention, the presence of more silane groups near the surface (outside) of the copolymer particles is more reactive to colloidal silica than the silane groups are uniformly present in the synthetic resin. Is larger, which is preferable. Therefore, an emulsion obtained by emulsion polymerization of an α, β-ethylenically unsaturated monomer and an α, β-ethylenically unsaturated monomer having a functional group is reacted with a silane compound having reactivity with the functional group. An emulsion in which a silane group is introduced into a synthetic resin which has been emulsified to form a silane group is particularly preferable.

As the colloidal silica used in the present invention,
Ultrafine particle silica sol dispersed in water in a colloidal form, or ultrafine particle powder silica, and the particle size of each primary particle must be 1/3 or less of the particle size of the synthetic resin particles containing a silane group used in the present invention. But it is especially preferred
It is 0.01 μm or less.

The aqueous composition for forming a porous film of the present invention can form a porous film excellent in moisture permeability and absorbability by coating and drying the substrate, and the substrate is not particularly limited.

Drying after coating may be natural drying or artificially heating and drying. The drying temperature is preferably at least the minimum film forming temperature of the copolymer.

The thickness of the coating depends on the intended use of the porous coating,
There is no particular limitation. A relatively thick coating is required when using a paint coating made of a porous coating, for example, about 0.1 to 0.5 mm, and a relatively thin coating is sufficient for the printing ink receiving layer of a synthetic resin film made of a porous coating. It is about 5 μm.

Further, in the composition for forming a porous film of the present invention, a colorant, a thickener, an antiseptic, an anticorrosive, a fluorescent agent, an aromatic, a deodorant, etc. may be appropriately added so long as they do not impair the air permeability. It can be blended.

[Examples] Next, the present invention will be described with reference to Examples and Comparative Examples.

Example 1 Emulsion polymerization of a mixed monomer consisting of 70 parts by weight of butyl acrylate and 30 parts by weight of methyl methacrylate was dropped into an aqueous solution of 2 parts by weight of sodium alkylphenyl ether sulfonate in 107 parts by weight of water, From the time when the remaining amount of the mixed monomer became 1/5, 5 parts by weight of γ-metachlorooxypropyltrimethoxysilane was added dropwise and emulsion polymerization was performed.
A film-forming aqueous emulsion composed of synthetic resin particles containing a silane group and water was obtained.

The film-forming aqueous emulsion has a solid content concentration of 50% by weight,
The resin particle size was 0.6 μm.

Film formation A composition for forming a porous film is prepared by adding 24 parts by weight (solid content) of a colloidal silica aqueous solution having a solid content concentration of 40% by weight and a particle diameter of 0.05 μm (solid content) to 76 parts by weight (solid content) of an aqueous emulsion. I got a thing.

The particle size ratio of the composition for forming a porous film was 1/12, the particle size of synthetic resin particles was 0.6 μm, and the compounding amount of colloidal silica was 1 time the amount of coating synthetic resin particles.

First, an electron micrograph of the porous film obtained in Example 1 is shown.
Shown in the figure. According to the present invention, such extremely uniform pores are obtained.

Example 2 An aqueous solution obtained by dissolving 3 parts by weight of a sodium salt of alkylallyl sulfosuccinate in 109 parts by weight of a mixed monomer consisting of 70 parts by weight of butyl acrylate, 30 parts by weight of methyl methacrylate and 1 part by weight of acrylic acid. During the emulsion polymerization,
From the time when the remaining amount of the mixed monomer became 1/5, 5 parts by weight of γ-methacrylooxypropyltrimethoxysilane was also added dropwise to carry out emulsion polymerization, and composed of synthetic resin particles containing a silane group and water. A film-forming aqueous emulsion was obtained.

The film-forming aqueous emulsion has a solid content concentration of 50% by weight,
The resin particle size was 0.08 μm.

Film-forming composition: 87 parts by weight (solid content) of aqueous emulsion, 13 parts by weight (solid content) of colloidal silica aqueous solution having a solid content concentration of 40% by weight and a particle size of 0.003 μm (solid content), and stirred uniformly to form a porous film-forming composition. I got a thing.

The particle size ratio of the composition for forming a porous film was 1/26, the particle size of synthetic resin particles was 0.6 μm, and the compounding amount of colloidal silica was 1 time the amount of coating synthetic resin particles.

The second is an electron micrograph of the porous film obtained in Example 2.
Shown in the figure. According to the present invention, extremely uniform pores having a diameter of 0.03 μm can be obtained.

Example 3 Dropwise emulsion polymerization of a mixed monomer consisting of 50 parts by weight of styrene and 50 parts by weight of 2-ethylhexyl acrylate in an aqueous solution in which 1 part by weight of sodium salt of alkylallyl sulfosuccinate is dissolved in 103 parts by weight of water. Then, from the time when the remaining amount of the mixed monomer became 1/5, 2 parts by weight of vinyltrimethoxysilane was added dropwise and emulsion polymerization was performed to form a film composed of synthetic resin particles containing a silane group and water. A formed aqueous emulsion was obtained.

The film-forming aqueous emulsion has a solid content concentration of 50% by weight,
The resin particle size was 1.0 μm.

Film forming composition 50 parts by weight (solid content) of solid content concentration of 40% by weight, and 50 parts by weight of solid solution of colloidal silica having a particle diameter of 0.025 μm (solid content) are added and stirred uniformly to form a porous film forming composition. I got a thing.

The particle size ratio of the composition for forming a porous film was 1/40, the particle size of synthetic resin particles was 0.6 μm, and the compounding amount of colloidal silica was 10 times the amount of coating synthetic resin particles.

The third is an electron micrograph of the porous film obtained in Example 3.
Shown in the figure. According to the present invention, extremely uniform large pores having a diameter of 0.3 μm can be obtained.

Example 4 An aqueous solution obtained by dissolving 1 part by weight of sodium alkylphenyl ether sulfonate in 107 parts by weight of water, a mixed monomer consisting of 80 parts by weight of ethyl acrylate, 20 parts by weight of methyl methacrylate, and 3 parts by weight of dimethylaminoethyl methacrylate. Into it, emulsion polymerization was added dropwise to obtain an aqueous dispersion, and further 2-
3 parts by weight of (3,4 epoxycyclohexane) ethyltrimethoxysilane was added and mixed to obtain a film-forming aqueous emulsion composed of synthetic resin particles containing a silane group and water.

The film-forming aqueous emulsion has a solid content concentration of 50% by weight,
The resin particle size was 1.0 μm.

Film-forming A composition for forming a porous film is prepared by adding 24 parts by weight (solid content) of a colloidal silica aqueous solution having a solid content concentration of 40% by weight and a particle size of 0.08 μm (solid content) to 76 parts by weight (solid content) of an aqueous emulsion. I got a thing.

The particle size ratio of the composition for forming a porous film was 1/13, the particle size of the synthetic resin particles was 0.6 μm, and the compounding amount of colloidal silica was 1 time the amount of coating the synthetic resin particles.

Example 5 An aqueous solution prepared by dissolving 3 parts by weight of a sodium salt of alkylallyl sulfosuccinate in 108 parts by weight of a mixed monomer composed of 80 parts by weight of ethyl acrylate, 20 parts by weight of methyl methacrylate and 2 parts by weight of glycidyl methacrylate. Into the mixture, emulsion polymerization was performed dropwise to obtain an aqueous dispersion, and 3 parts by weight of N- (2-aminoethyl) 3-aminopropylmethyl-dimethoxysilane was further added and mixed to obtain synthetic resin particles containing a silane group. A film-forming aqueous emulsion composed of water was obtained.

The film-forming aqueous emulsion has a solid content concentration of 50% by weight,
The resin particle size was 0.08 μm.

Film-forming composition 40 parts by weight (solid content) of solid content concentration of 40% by weight, 60 parts by weight of solid solution of colloidal silica having a particle size of 0.003 μm (solid content) and uniformly stirred to form a porous film-forming composition. I got a thing.

The particle size ratio of the composition for forming a porous film was 1/26, the particle size of synthetic resin particles was 0.6 μm, and the compounding amount of colloidal silica was 10 times the amount of coating synthetic resin particles.

Example 6 An aqueous solution prepared by dissolving 2 parts by weight of sodium salt of alkylallyl sulfosuccinate in 109 parts by weight of a mixed monomer comprising 50 parts by weight of styrene, 50 parts by weight of 2-ethylhexyl acrylate and 2 parts by weight of acrylic acid. Into the mixture, emulsion polymerization was performed dropwise to obtain an aqueous dispersion, and 5 parts by weight of 3-glycidoxypropyltrimethoxysilane was further added and mixed to form a film composed of synthetic resin particles containing a silane group and water. An aqueous emulsion was obtained.

The film-forming aqueous emulsion has a solid content concentration of 50% by weight,
The resin particle size was 0.6 μm.

Film-forming composition: 71 parts by weight (solid content) of aqueous emulsion, 29 parts by weight (solid content) of colloidal silica aqueous solution having a solid content concentration of 40% by weight and a particle size of 0.003 μm, and stirred uniformly to form a porous film-forming composition. I got a thing.

The particle size ratio of the composition for forming a porous film was 1/200, the particle size of the synthetic resin particles was 0.6 μm, and the compounding amount of colloidal silica was 20 times the amount of coating the synthetic resin particles.

Comparative Example 1 A film-forming aqueous emulsion (containing no colloidal silica aqueous solution) composed of the silane group-containing synthetic resin particles obtained in Example 1 and water.

Comparative Example 2 The colloidal silica aqueous solution used in Example 1.

Comparative Example 3 30 parts by weight (solid content) of a film-forming aqueous emulsion composed of the synthetic resin particles containing a silane group and water obtained in Example 2 were added to 70 parts by weight of the aqueous colloidal silica solution used in Example 1 (solid content). Minutes) and uniformly stirred.

The particle size of colloidal silica is 1/1 of the particle size of synthetic resin particles.
It is 6 and exceeds 1/3.

An electron micrograph of the film obtained in Comparative Example 3 is shown in FIG. As is apparent from the comparative examples, it is understood that only the film having no pores is formed in the absence of the constituent features of the present invention.

Comparative Example 4 A composition in which 0.2 parts by weight (solid content) of the colloidal silica aqueous solution used in Example 2 was added to 99.8 parts by weight (solid content) of the film-forming aqueous emulsion obtained in Example 6 and uniformly stirred.

This is the case where the amount of the colloidal silica particles theoretically covers the synthetic resin particles is 1/10.

(Test method) Presence or absence of pores: The aqueous compositions obtained in Examples and Comparative Examples were
A polyethylene film having a thickness of 100 μm is coated with a No. 20 bar coater and dried at 50 ° C. for 5 minutes to form a test film.

The film showed exactly the same performance as that when dried at room temperature for 24 hours.

Scanning electron microscope (JE JS
M25S-III).

◯: Voids with a diameter of approximately 0.05 to 0.2 μm communicate with each other.

X: No holes at all.

Water resistance of film: The test film obtained above was immersed in room temperature water for 24 hours, and examined for blisters, whitening and peeling.

○: No abnormality.

Δ: Whitening occurs.

X: Whitening, blistering, and peeling.

Water permeability of film: The aqueous compositions obtained in Examples and Comparative Examples were applied to Kent paper so as to have a solid content of 20 g / m ² , and at 70 ° C.
It was dried for 10 minutes and left at room temperature for 24 hours to form a film.

The funnel was fixed in reverse on the film, the periphery was sealed, the funnel was filled with water, and the amount of water permeated for 120 seconds was measured to determine the water permeation amount (g / m ² ).

○: 8 g / m ² or more ×: less than 8 g / m ² The manufacturing specifications and coating performances of Examples and Comparative Examples are shown in Table 1 and Table 2.
It is summarized in the table.

(Effect) The composition for forming a porous film of the present invention comprises a film-forming aqueous emulsion composed of silane group-containing synthetic resin particles having a particle size of 0.03 μ to 10 μ and water, and a particle size of the synthetic resin particles of 1 / 3
The colloidal silica is the following, and the compounding amount of the colloidal silica is 0.5 to 30 of the amount for coating the synthetic resin particles.
Since it is a mixture with double the adhesive strength to silica, when it is applied to a substrate and dried, its surface is coated with colloidal silica due to the silane groups of the synthetic resin particles, and the synthetic resin particles coated with colloidal silica dries. Although it forms a film by fusion in the course of the process, the fusion is partially inhibited by colloidal silica on the surface of the synthetic resin particles, pores surrounded by colloidal silica are generated according to the particle size of the synthetic resin particles, Part or all of them become communication holes, forming a film with extremely excellent air permeability. Moreover,
Since the film is formed except for the holes, the properties such as adhesion, flexibility, elasticity, and toughness of the synthetic resin are not impaired.

Further, since the porous film obtained in the present invention has excellent performance, it is formed on the back surface of a synthetic resin film or paper,
As an ink receiving layer, it is possible to improve the acceptability of printing ink.

By using it as a binder for paints, a coating film with excellent breathability can be obtained.

In addition, a top coat with excellent breathability can be obtained by applying it as it is.

An antifogging layer and a dew condensation preventing layer can be formed.

By coating with fertilizers or chemicals, sustained release can be imparted to the contained water-soluble compound.

[Brief description of drawings]

FIG. 1 is an electron micrograph showing the crystal structure of the porous film obtained in Example 1. FIG. 2 is an electron micrograph showing the crystal structure of the porous film obtained in Example 2. FIG. 3 is an electron micrograph showing the crystal structure of the porous film obtained in Example 3. FIG. 4 is an electron micrograph showing the crystal structure of the film obtained in Comparative Example 3.

Claims (8)

[Claims] 1. A porous film-forming composition comprising a film-forming aqueous emulsion composed of synthetic resin particles having a particle size of 0.03 to 10 μm and water and colloidal silica, wherein the film-forming aqueous emulsion is an α, β-ethylenic An emulsion obtained by emulsion-polymerizing a saturated monomer and acrylic silane or vinyl silane, the particle size of colloidal silica is 1/3 or less of the particle size of the synthetic resin particles, and the amount of the colloidal silica compounded is a synthetic resin. 0.5-30 by weight to completely cover the particles
A water-dispersible composition for forming a porous film, characterized in that it is doubled. 2. The water-dispersible composition for forming a porous film according to claim 1, wherein the acrylic silane or vinyl silane is a silane compound having a methoxy group and / or an acetoxy group. 3. A film-forming aqueous emulsion, wherein an α, β-ethylenically unsaturated monomer and an α, β-ethylenically unsaturated monomer having a functional group are emulsion-polymerized to obtain an emulsion having the functional group. The water-dispersible composition for forming a porous film according to claim 1 or 2, which is an emulsion in which a silane group is introduced into a synthetic resin which is emulsified by reacting a silane compound having reactivity with a group. 4. The aqueous dispersion composition for forming a porous film according to any one of claims 1 to 3, wherein the film-forming aqueous emulsion is an emulsion obtained by emulsion polymerization using a polymerizable emulsifier. . 5. A water-dispersible composition for forming a porous film according to any one of claims 1 to 4 is applied to a substrate and dried to form a film, and the surface is formed of colloidal silica. A porous film made of synthetic resin particles covered with colloidal silica having pores arranged in the film. 6. The porous coating according to claim 5, wherein the pores formed on the surface of the coating with colloidal silica are communicating pores. 7. The pores formed on the surface of the coating with colloidal silica are independent pores and communicating pores.
Or the porous film described in 6. 8. A surface characterized by applying the water-dispersible composition for forming a porous film according to claim 1 to a surface of a substrate to be protected and drying at a temperature not lower than a minimum film forming temperature. A method for forming a porous film having pores formed of colloidal silica.