JP7801883B2 - Composition for forming pores - Google Patents

Description

The present invention relates to a pore-forming composition.

Hollow particles and resin particles have traditionally been used as pore-forming agents in various matrices, such as porous ceramic molded bodies (see, for example, Patent Documents 1 and 2).

Japanese Patent Application Laid-Open No. 2004-292596 JP 2019-147870 A

In the case of hollow particles, due to their low particle strength, there was an issue that the particles would be crushed when mixed with various matrices, resulting in a decrease in porosity. In the case of resin particles, there was an issue that pores were difficult to form because they could not be sufficiently decomposed or removed even under high temperature and long-term conditions.

Therefore, the object of the present invention is to provide a pore-forming composition that easily forms pores and that also has high uniformity when the pores are formed.

The inventors conducted extensive research to achieve the above-mentioned objectives and came up with the present invention. Specifically, the pore-forming composition disclosed herein is a pore-forming composition containing alkali-soluble polymer particles and a resin, in which the absolute difference in contact angle between the polymer particles and the resin at 25°C is 10° to 55°.

The pore-forming composition disclosed herein can easily form pores, and exhibits uniform pore size and pore dispersibility. This makes it possible to apply the composition to a variety of fields, including fibers, ceramics, coatings, thermoplastic resins, thermosetting resins, and various films.

The present invention will be described in detail below. It should be noted that a combination of two or more of the individual preferred embodiments of the present invention described below is also a preferred embodiment of the present invention.
[Alkali-soluble polymer particles]
The alkali-soluble polymer particles (hereinafter sometimes referred to as pore-forming agents) of the present disclosure are polymer particles containing functional groups that have affinity for alkaline solutions. The functional groups that have affinity for alkaline solutions are functional groups that interact with alkaline solutions.

Functional groups that have affinity for alkaline solutions include, for example, hydroxyl groups, carboxylic acid groups, sulfonic acid groups, phosphate groups, groups having salt structures of these groups, epoxy groups, polyoxyethylene groups, etc.

The alkali-soluble polymer particles of the present disclosure may be any particles that can be dissolved in an alkaline solution.
An alkaline solution is a solution containing an alkaline compound and a solvent.

Examples of alkaline compounds include lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, diammonium hydrogen phosphate, dipotassium hydrogen phosphate, disodium hydrogen phosphate, lithium silicate, sodium silicate, potassium silicate, lithium carbonate, sodium carbonate, potassium carbonate, lithium borate, sodium borate, potassium borate, ammonia, trimethylamine, triethylamine, tributylamine, ethanolamine, diethanolamine, and triethanolamine.

Examples of solvents include water; alcohols such as methanol, ethanol, isopropyl alcohol, and hexanol; and ketones such as acetone and 2-butanone.

The alkaline solution is preferably an aqueous alkaline solution. Specific examples include an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, an aqueous calcium hydroxide solution, and an aqueous ammonia solution. An aqueous sodium hydroxide solution is more preferred.

The alkali-soluble polymer particles of the present disclosure are not particularly limited in terms of the temperature at which they can be dissolved in an alkaline solution, but they have high solubility not only at high temperatures such as 90°C, but also at temperatures such as 25°C.

The pH of the alkaline solution is preferably 7.5 to 14, more preferably 8.5 to 14, and even more preferably 9.0 to 14.

The pH of the alkaline dispersion containing the alkali-soluble polymer particles of the present disclosure and an alkaline solution is preferably 7.0 to 14, more preferably 7.2 to 13, and even more preferably 7.5 to 13.

The haze of an alkaline dispersion containing the alkali-soluble polymer particles of the present disclosure at a concentration of 5% by mass is preferably 10% or less, more preferably 5% or less, and even more preferably 3% or less. On the other hand, it is preferably 0.01% or more, more preferably 0.05% or more, and even more preferably 0.1% or more.

The total light transmittance of an alkaline dispersion containing the alkali-soluble polymer particles of the present disclosure at a concentration of 5% by mass is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more.

The volume average particle diameter of the alkali-soluble polymer particles of the present disclosure is preferably 10 nm or more, more preferably 50 nm or more, and even more preferably 100 nm or more. On the other hand, it is preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 1 μm or less. This tends to improve the uniformity of the pore diameter.

The volume average particle diameter of the alkali-soluble polymer particles disclosed herein can be measured, for example, by dynamic light scattering.

The contact angle of the alkali-soluble polymer particles of the present disclosure with water at 25°C is preferably 10° or more, more preferably 15° or more, and even more preferably 20° or more. On the other hand, it is preferably 110° or less, more preferably 100° or less, and even more preferably 95° or less.

<Structural Units Derived from Ethylenically Unsaturated Monomers>
The alkali-soluble polymer particles of the present disclosure have structural units derived from an ethylenically unsaturated monomer.

A structural unit derived from an ethylenically unsaturated monomer refers to a structural unit having the same structure as that formed by polymerization of the monomer, and is usually a structure in which at least one carbon-carbon unsaturated double bond contained in the monomer is replaced with a carbon-carbon single bond. Note that the structural unit derived from the monomer does not necessarily have to be a structural unit formed by actual polymerization of the monomer, and even a structural unit formed by a method other than polymerization of the monomer is included in the structural unit derived from the monomer, as long as it has the same structure as that formed by polymerization of the monomer. For example, in the case of acrylic acid, CH ₂ ═CH(—COOH), the structural unit derived from acrylic acid can be represented by —CH2-CH(—COOH)—.

Functional groups that have affinity for alkaline solutions include, for example, hydroxyl groups, carboxylic acid groups, sulfonic acid groups, phosphate groups, and groups having salt structures of these groups, epoxy groups, polyoxyethylene groups, etc.

The ethylenically unsaturated monomer of the present disclosure may have one or more functional groups that have affinity for alkaline solutions.

The alkali-soluble polymer particles of the present disclosure preferably contain structural units derived from the following general formula (1):

(In general formula (1), R ¹ represents an alkyl group having 1 to 4 carbon atoms, a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, or ammonium.)
The alkyl group having 1 to 4 carbon atoms represented by R ¹ is preferably an alkyl group having 1 to 2 carbon atoms, and more preferably an alkyl group having 1 carbon atom (methyl group).

The alkali metal atom represented by ^R1 is preferably lithium, sodium or potassium, more preferably sodium or potassium, and even more preferably sodium.

Examples of the alkaline earth metal atom represented by ^R1 include calcium and magnesium.

The ammonium represented by ^R1 is not limited to NH4 ⁺ , but is defined to include organic ammonium. Examples of organic ammonium include quaternary ammonium such as tetraalkylammonium such as tetramethylammonium and tetrabutylammonium; and ammonium (primary to tertiary ammonium) formed by protonating an amine. ^R1 is preferably an ammonium formed by protonating ammonia or an amine. Examples of the amine include trialkylamines (preferably tri- _C1-10 alkylamines) such as trimethylamine, triethylamine, and tributylamine; and hydroxyalkylamines (preferably di- or tri-(hydroxy- _C1-10 alkyl)amines) such as diethanolamine and triethanolamine, with hydroxyalkylamines being preferred.

The structural unit represented by the general formula (1) may be formed by a polymerization reaction of a monomer represented by the following general formula (2), but may also be formed by other methods. For example, a structural unit of an alkali metal, an alkaline earth metal, or an ammonium structural unit may be formed by polymerizing a monomer in which R ^{1 is} an alkyl group having 1 to 4 carbon atoms in the general formula (2) and hydrolyzing the polymer.

(In general formula (2), R ¹ represents an alkyl group having 1 to 4 carbon atoms, a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, or ammonium.)
In the general formula (2), R ¹ may be one type or two or more types. When ^{R 1} is two or more types, it may be formed by polymerizing two or more types of monomers represented by the general formula (2) above, or it may be formed by polymerizing a monomer represented by the general formula (2) above in which R ¹ is an alkyl group having 1 to 4 carbon atoms, and then partially hydrolyzing the ester group or hydrolyzing it with two or more types of basic substances.

It is preferable that the alkali-soluble polymer particles of the present disclosure are at least partially hydrolyzed.

The phrase "at least a portion of the alkali-soluble polymer particles of the present disclosure is hydrolyzed" means that the polymer is either a partial hydrolyzate, a complete hydrolyzate, or a hydrolysis-neutralized product thereof. For example, in the case of methyl acrylate, CH ₂ ═CH(—COO—CH ₃ ), the partial hydrolyzate contains both structural units derived from CH ₂ ═CH(—COO—CH ₃ ) and CH ₂ ═CH(—COO—H). The alkali-soluble polymer particles of the present disclosure preferably contain 40% by mass or more of the structural unit represented by general formula (1) above, based on the total amount of the alkali-soluble polymer particles, more preferably 50% by mass or more, even more preferably 60% by mass or more, even more preferably 70% by mass or more, particularly preferably 80% by mass or more, and most preferably 90% by mass or more. On the other hand, the amount is preferably 99.9% by mass or less, more preferably 99% by mass or less, even more preferably 97% by mass or less, and most preferably 95% by mass or less.

The alkali-soluble polymer particles of the present disclosure may have a multilayer structure, and may be, for example, core-shell particles composed of a core portion and a shell portion provided on the surface of the core portion.
When the alkali-labile polymer particles of the present disclosure have a multi-layer structure, the composition of the outermost layer is preferably within the above range.

By including the components in the above ranges, it is possible to adjust the pH, hydrophilicity, etc., so the pore-forming composition of the present disclosure can easily form pores, and the formed pores tend to be highly uniform.

<Structural units derived from other monomers>
The alkali-soluble polymer particles of the present disclosure may contain one or more structural units derived from monomers other than structural units derived from ethylenically unsaturated monomers (hereinafter also referred to as "structural units derived from other monomers").

Other monomers are not particularly limited and include (meth)acrylic monomers such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and lauryl (meth)acrylate; styrene-based monomers such as styrene, α-methylstyrene, p-methylstyrene, tert-butylstyrene, chlorostyrene, and vinyltoluene; (meth)acrylic acid, Carboxyl group-containing monomers such as leic acid, fumaric acid, crotonic acid, itaconic acid, and maleic anhydride; silane group-containing monomers such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(methoxyethoxy)silane, γ-(meth)acryloyloxypropyltrimethoxysilane, 2-styrylethyltrimethoxysilane, vinyltrichlorosilane, γ-(meth)acryloyloxypropylhydroxysilane, and γ-(meth)acryloyloxypropylmethylhydroxysilane; 2-hydroxyethyl(meth)acryloyloxypropylmethylhydroxysilane; Hydroxyl group-containing monomers such as acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; nitrogen atom-containing monomers such as (meth)acrylamide, N,N-dimethyl (meth)acrylamide, dimethylaminoethyl (meth)acrylamide, N-vinylpyrrolidone, and (meth)acrylonitrile; ethylene glycol methoxy (meth)acrylate, diethylene glycol methoxy (meth)acrylate, and the like. Examples include oxo group-containing monomers such as acrylate; fluorine atom-containing monomers such as trifluoroethyl (meth)acrylate, tetrafluoropropyl (meth)acrylate, and octafluoropentyl (meth)acrylate; epoxy group-containing monomers such as glycidyl (meth)acrylate; light-stabilizing monomers such as 2,2,6,6-tetramethylpiperidine-4-(meth)acrylate; ultraviolet absorbing monomers such as benzotriazole-based ultraviolet absorbing monomers and benzophenone-based ultraviolet absorbing monomers; and polyfunctional ethylenically unsaturated monomers.

The polyfunctional ethylenically unsaturated monomer is not particularly limited as long as it is a compound containing two or three or more ethylenic carbon-carbon double bonds, and examples thereof include compounds containing two or three or more ethylenic carbon-carbon double bonds of one or more types _selected from a CH _{2 ═CH- group, a CH 2 ═CH -} O- group, a CH ₂ ═CH _- CH ₂ -O- group, a CH _{2 ═C} (CH ₃ )-CH ₂ -O- group, a CH ₂ ═CH-CH ₂ -CH ₂ -O- group, a CH ₂ ═C(CH ₃ )-CH 2 -CH 2 -O- group, a CH ₂ ═CH-CO-O- group, a CH 2 ═C(CH 3 )-CO-O- group, and a CH 2 ═CH-CO-NH- group.

The polyfunctional ethylenically unsaturated monomer preferably has a molecular weight of 50 or more and 1,000 or less, and more preferably 100 or more and 400 or less.

There are no particular restrictions on the polyfunctional ethylenically unsaturated monomer, but from the standpoint of ease of handling during pore formation and the uniformity of the formed pores, it is preferable for the polyfunctional ethylenically unsaturated monomer to be one in which, for a number n (n is an integer of 2 or greater) of ethylenically unsaturated groups contained in one molecule of the polyfunctional ethylenically unsaturated monomer, n-1 or more are CH2=CH-CO-O- or CH2=CH-CO-NH- groups (hereinafter also referred to as a "hydrolyzable polyfunctional ethylenically unsaturated monomer").

Examples of polyfunctional ethylenically unsaturated monomers include polyfunctional acrylic esters and N,N'-methylenebisacrylamide.

Specific examples of polyfunctional acrylic esters include ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, 1,3-butanediol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, neopentyl glycol diacrylate, dipropylene glycol diacrylate, polypropylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, and acrylic-modified polydimethylsiloxane.

The alkali-soluble polymer particles of the present disclosure may contain one or more structural units derived from hydrolyzable polyfunctional ethylenically unsaturated monomers.

The alkali-soluble polymer particles of the present disclosure preferably contain structural units derived from hydrolyzable polyfunctional ethylenically unsaturated monomers in an amount of 0.01% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.5% by mass or more, even more preferably 2% by mass or more, and particularly preferably 5% by mass or more. On the other hand, the alkali-soluble polymer particles of the present disclosure preferably contain structural units derived from hydrolyzable polyfunctional ethylenically unsaturated monomers in an amount of 60% by mass or less, more preferably 50% by mass or less, even more preferably 40% by mass or less, even more preferably 20% by mass or less, and particularly preferably 10% by mass or less.

A structural unit derived from an other monomer refers to a structural unit in which at least one carbon-carbon double bond of the other monomer is replaced with a carbon-carbon single bond. For example, in the case of ethylene glycol diacrylate, CH ₂ ═CH—CO—O—CH ₂ CH ₂ O—CO—CH═CH ₂ , a structural unit derived from ethylene glycol diacrylate can be represented, for example, by —CH ₂ —CH—CO—O—CH ₂ CH ₂ O—CO—CH—CH ₂ —. A structural unit derived from an other monomer can be formed, for example, by radical polymerization of the other monomer. Note that the structural unit derived from the other monomer may have the same structure as the structure in which the carbon-carbon double bond of the other monomer is replaced with a carbon-carbon single bond, and is not limited to a structural unit formed by polymerization of the other monomer, and may be, for example, a structural unit formed by a reaction after polymerization.

The alkali-soluble polymer particles of the present disclosure preferably contain structural units derived from other monomers in an amount of 0.01% by mass or more, more preferably 0.1% by mass or more, even more preferably 1% by mass or more, even more preferably 2% by mass or more, and particularly preferably 5% by mass or more. On the other hand, the alkali-soluble polymer particles of the present disclosure preferably contain structural units derived from other monomers in an amount of 60% by mass or less, more preferably 40% by mass or less, even more preferably 20% by mass or less, even more preferably 15% by mass or less, and particularly preferably 10% by mass or less.

[Method for producing alkali-soluble polymer particles]
<Polymerization method>
The alkali-soluble polymer particles of the present disclosure can be obtained by polymerizing a monomer component containing, as an ethylenically unsaturated monomer, for example, a monomer represented by the above formula (2), and optionally other monomers, in an aqueous solvent, and then producing a partially or completely hydrolyzed polymer.

Polymerization methods include suspension polymerization, emulsion polymerization, and dispersion polymerization. Among these, emulsion polymerization, in which the above-mentioned raw material monomer components are dispersed in a reaction solvent in the presence of an emulsifier and a (radical) polymerization reaction is carried out, is preferred. Specifically, the method for producing the polymer of the present invention preferably includes emulsion polymerization, in which at least one monomer represented by formula (2) is dispersed in an aqueous solvent in the presence of an emulsifier and a polymerization reaction is carried out. Emulsion polymerization may be carried out in a single stage or in multiple stages.

One or more types of emulsifiers can be used, and they may be non-reactive surfactants or reactive surfactants having radically polymerizable groups in their structure.

Non-reactive surfactants include anionic and nonionic surfactants. Anionic surfactants include fatty acid salts, alkyl (aryl) sulfonates, alkyl sulfate ester salts, and polyoxyethylene alkyl (phenyl) ether sulfates. Nonionic surfactants include polyoxyethylene alkyl (phenyl) ethers, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene fatty acid esters, and polyoxyethylene polyoxypropylene block polymers.

Reactive surfactants include anionic and nonionic surfactants. Anionic reactive surfactants include, but are not limited to, ether sulfate reactive surfactants and phosphate ester reactive surfactants.

The amount of emulsifier is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and even more preferably 0.3 parts by mass or more, per 100 parts by mass of the total raw material monomer components; it is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, even more preferably 5 parts by mass or less, and particularly preferably 3 parts by mass or less.

In this disclosure, the aqueous solvent may be water alone or a mixture of water and a water-miscible organic solvent, with water alone being preferred. An aqueous solvent typically refers to a solvent with a water content of more than 50% by volume. Examples of water that can be used include ion-exchanged water (deionized water), distilled water, and pure water. Examples of water-miscible organic solvents that can be used include organic solvents that are uniformly miscible with water (such as lower alcohols). From the perspective of minimizing the amount of organic solvent remaining in the polymer, aqueous solvents containing 80% or more by volume of water are preferred, more preferably 90% or more by volume of water, even more preferably 95% or more by volume of water, and particularly preferably 99.5% or more by volume of water. Water-based solvents consisting essentially of water (water-based solvents containing 99.5% or more by volume of water) are particularly preferred, with water alone being most preferred.

When polymerizing the raw material monomer components, methods such as the use of a polymerization initiator, irradiation with ultraviolet or radiation, or application of heat are used. The use of a polymerization initiator is preferred, and from the standpoint of efficiently reacting the raw material monomer components and sufficiently reducing the amount of residual monomer, a polymerization initiator that combines an oxidizing agent and a reducing agent (redox polymerization initiator) is preferred.

<Hydrolysis method>
The alkali-soluble polymer particles of the present disclosure can be hydrolyzed by adding a basic aqueous solution such as an aqueous sodium hydroxide solution, an aqueous calcium hydroxide solution, an aqueous ammonia solution, or an aqueous cyclohexylamine solution.

The alkaline aqueous solution used for hydrolysis preferably has a pH of 7.0 or more and 14 or less. The concentration of the alkaline solution is preferably 0.1 wt % or more and 30 wt % or less. The amount of alkali used is preferably 0.01 mol or more and 200 mol or less relative to the total amount of structural units derived from the monomer. Furthermore, partial or complete neutralization can be performed by adding an appropriate amount of acid to the hydrolysis solution. By performing hydrolysis and neutralization, the group corresponding to R ¹ in formula ( ^{1) can be converted to a hydrogen atom, an alkali metal atom, an alkali metal atom, or ammonium. By adjusting the amount of acid or base used during polymerization, hydrolysis, and neutralization, or by adjusting the proportion of monomer units in which R 1} is a hydrogen atom, the pH and hydrophilicity of the polymer can be adjusted, thereby improving the operability during pore formation and the uniformity of the formed pores.

[Pore-forming composition of the present disclosure]
The pore-forming composition of the present disclosure contains the alkali-soluble polymer particles of the present disclosure. The content of the alkali-soluble polymer particles of the present disclosure in the pore-forming composition of the present disclosure is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more. On the other hand, it is preferably 80% by mass or less, more preferably 60% by mass or less, and even more preferably 40% by mass or less. By including the alkali-soluble polymer particles in the above range, pores tend to be easily formed.

The pore-forming composition of the present disclosure contains a resin. Resins include, but are not limited to, thermoplastic resins such as polyester resin, polyolefin resin, acrylic resin, polyamide resin, polyvinylidene chloride resin, ethylene-vinyl acetate resin, polyimide resin, polyethylene terephthalate resin, polysulfone resin, polyvinylidene fluoride resin, and PTFE; and thermosetting resins such as polylactic acid resin, polyhydroxybutyrate resin, polycaprolactone resin, polybutylene succinate resin, polybutylene adipate terephthalate resin, polybutylene succinate terephthalate resin, phenolic resin, urea resin, melamine resin, unsaturated polyester resin, diallyl phthalate resin, epoxy resin, epoxy acrylate resin, silicone resin, acrylic urethane resin, and urethane resin. The resin may be an emulsion resin dispersed in water. Examples of emulsion resins include acrylic emulsion resin. Specific examples include products manufactured by Nippon Shokubai Co., Ltd. under the trade name "U-Double." From the viewpoint of pore size uniformity, polyester resins and unsaturated polyester resins are preferred. Specific examples include Mitsubishi Chemical Corporation's (trade name: Nichigo Polyester), Toyobo Co., Ltd.'s (trade name: Vylonal), Takamatsu Oil & Fat Co., Ltd.'s (trade name: PES Resin), and Goo Chemical Industry Co., Ltd.'s (trade name: Plus Coat).

The contact angle of the resin of the present disclosure with water at 25°C is preferably 10° or greater, more preferably 15° or greater, and even more preferably 20° or greater. On the other hand, it is preferably 110° or less, more preferably 100° or less, and even more preferably 95° or less.

The pore-forming composition of the present disclosure preferably contains 20% by mass or more of the resin of the present disclosure, more preferably 40% by mass or more, and even more preferably 60% by mass or more. On the other hand, it preferably contains 99% by mass or less, more preferably 95% by mass or less, and even more preferably 90% by mass or less.

The pore-forming composition of the present disclosure may contain other components in addition to the alkali-soluble polymer particles and resin. These other components include solvents, dispersants, thickeners, film-forming aids, wetting agents, thickeners, pH adjusters, stabilizers, surfactants, adhesion promoters, fillers, antioxidants, antistatic agents, dyes, pigments, etc.

Examples of solvents include water; alcohols such as methanol, ethanol, isopropyl alcohol, and hexanol; ketones such as acetone and 2-butanone; acetates such as methyl acetate, ethyl acetate, and butyl acetate; and ethers such as tetrahydrofuran, diethyl ether, 1,2-dimethylethane, and diethylene glycol dimethyl ether.

In the pore-forming composition of the present disclosure, the absolute difference in contact angle between the alkali-soluble polymer particles and the resin at 25°C is preferably 10° or more, more preferably 15° or more, and even more preferably 20° or more. On the other hand, it is preferably 55° or less, more preferably 50° or less, and even more preferably 45° or less. This makes it easier to form pores, and the uniformity and dispersibility of the formed pores tend to be improved.

[Hole formation method of the present disclosure]
The pore-forming composition of the present disclosure can be added to various matrices such as fibers and then treated with, for example, alkali, to form pores in the matrix under mild conditions.

The method for adding the pore-forming composition of the present disclosure to various matrices is not limited, but examples include melt-mixing the pore-forming composition of the present disclosure with fibers, or applying a solvent containing the pore-forming composition of the present disclosure and fibers, followed by drying and removing the solvent.

The alkali treatment method (also referred to as the "alkali washing step") is not particularly limited. For example, it is preferably carried out by contacting an alkaline solution with a matrix containing the pore-forming composition of the present disclosure, but it may also be carried out by contacting an alkaline solution with a solvent containing the pore-forming composition of the present disclosure and fibers.

The alkali treatment step may be carried out at room temperature, under heating, or under cooling, but is preferably carried out at 40°C or below. The alkali treatment step may be carried out under normal pressure, under pressure, or under reduced pressure.

The alkaline component used in the alkaline treatment step may be an inorganic base or an organic base. For example, in the case of an aqueous alkaline solution, the pH is preferably 7.0 or more and 14 or less. The concentration of the alkaline solution is preferably 0.1% by weight or more and 30% by weight or less. The amount of alkali used is preferably 0.01 mol or more and 200 mol or less relative to the structural units derived from the ethylenically unsaturated monomer.

The pore formation method of the present disclosure preferably requires an alkaline washing step, but may also include optional steps such as a step of adding the polymer or the like of the present disclosure, a water washing step, or a solvent washing step.

[Uses of the pore-forming composition of the present disclosure]
The uses of the pore-forming composition used in the present invention are not limited, and since it can achieve uniformity in pore diameter and dispersibility of pores, it can be applied to various fields such as fibers, ceramics, coating films, various films, solid fuel cells, separators for secondary batteries, catalyst supports, heat insulating materials, and low-reflectivity materials.

The present invention will be explained in more detail below with reference to the following examples, but the present invention is not limited to these examples. Unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass."

<Volume average particle size>
The polymer dispersion was diluted with ion-exchanged water and measured using a light scattering particle size distribution analyzer ("Zetasizer Ultra" manufactured by Spectris) to determine the volume average particle diameter (nm) of the polymer by dynamic light scattering.

<Evaluation of alkali solubility>
To 10 parts by mass of the polymer aqueous dispersion, 3 parts by mass of a 10% by mass aqueous solution of sodium hydroxide was added, and ion-exchanged water was added so that the solid content of the polymer particles after mixing was 5% by mass, followed by thorough stirring with a stirrer tip. The total light transmittance (%) and haze (%) of the solution after stirring were measured using a haze meter ("NDH7000" manufactured by Nippon Denshoku Industries Co., Ltd.), and the alkali solubility was evaluated according to the following criteria. The values measured using ion-exchanged water alone were used as the blank (total light transmittance: 100%, haze: 0.0%) for calculation.
Good: Total light transmittance is 80% or more and haze is 10% or less. Poor: Total light transmittance is less than 80% or haze is higher than 10%.

<Contact angle of alkali-soluble particles>
The dried alkali-soluble particles were placed in a single layer on double-sided tape attached to a 25 mm x 75 mm glass slide, with no gaps between the particles. The excess particles were then removed with an air spray. This immobilized the alkali-soluble particles on the double-sided tape. The particles were confirmed to be immobilized without gaps using a microscope, and the sample was used for measurement. The sample measured approximately 20 mm in length and width. Using an automatic contact angle meter (Kyowa Interface Science Co., Ltd., "CA-X"), a 1 μL droplet of pure water was prepared at 25°C and placed on the sample. The contact angle was calculated using the θ/2 method. The contact angle measured 0.5 seconds after the sample was placed on the slide was recorded as the measured value. Five measurements were performed, and the average of the three measurements, excluding the maximum and minimum values, was used as the contact angle of the alkali-soluble particles.

<Resin contact angle>
A transparent polyethylene terephthalate film (hereinafter referred to as "PET film", manufactured by Toyobo Co., Ltd., Cosmoshine A4300, length: 297 mm, width: 210 mm, thickness: 0.100 mm) was coated with the resin using a bar coater so that the film thickness after coating was 50 μm, and the film was dried at 100 ° C. for 10 minutes in a constant temperature incubator (manufactured by Yamato Scientific Co., Ltd., "DNF400") to obtain a coating film. Using an automatic contact angle meter (manufactured by Kyowa Interface Science Co., Ltd., "CA-X"), a 1 μL droplet of pure water was prepared under conditions of 25 ° C. and allowed to adhere to the surface of the resulting coating film, and the contact angle was calculated using the θ/2 method. The contact angle value 30 seconds after application was taken as the measured value, and five measurements were performed. The average of the three points excluding the maximum and minimum values was taken as the contact angle of the resin.

<Evaluation of void formation>
(Optical property evaluation)
The haze (%) of the film-formed sample before and after the alkali treatment was evaluated using a haze meter ("NDH7000" manufactured by Nippon Denshoku Industries Co., Ltd.) The difference in haze value before and after the alkali treatment was calculated, and the presence or absence of voids was quantitatively evaluated according to the following criteria.
○: Haze value difference is 0.5% or more ×: Haze value difference is less than 0.5% (pore diameter evaluation)
A film-formed sample was cut out and attached to a sample stage with the surface on which the coating film was formed facing upward to prepare an evaluation sample. The film shape of the sample was observed using an electron microscope (JEOL Ltd., "JSM-7600FA"). The obtained microscopic images were visually evaluated qualitatively according to the following criteria.
3: Pores corresponding to the size of the alkali-soluble particles are present.
2: Pores smaller than the alkali-soluble particle size or deformed pores are present in some areas.
1: No voids corresponding to the alkali-soluble particle size are formed.
(Vacancy frequency evaluation)
The microscopic images obtained in the pore diameter evaluation were visually inspected to qualitatively evaluate the dispersibility of pores according to the following criteria.
2: There are many spherical voids.
1: Few spherical voids.
(comprehensive evaluation)
The judged values of the pore diameter evaluation and the pore frequency evaluation were summed up, and the pore formability of the film-formed sample was evaluated comprehensively according to the following criteria.
◎: Total judgement value is 4 or more. ○: Total judgement value is 3 or more.
×: The total judgement value is 2

[Synthesis of Polymer]
<Production Example A1>
Into a stainless steel reactor equipped with a stirrer, thermometer, and cooler, 832.0 parts by mass of deionized water and 0.96 parts by mass of anionic reactive surfactant ADEKA REASOAP SR-20 (active ingredient 100% by mass, manufactured by ADEKA Corporation) diluted with ion-exchanged water to 25.0% by mass of active ingredient (hereinafter referred to as "SR-20 (active ingredient 25.0% by mass)") were added, and the internal temperature was raised to 75°C and maintained at that temperature. Meanwhile, in a container separate from the reactor, 180.0 parts by mass of methyl 2-hydroxymethyl methacrylate (hereinafter referred to as "RHMA") and 20.0 parts by mass of triethylene glycol diacrylate (hereinafter referred to as "3EG-A") were mixed to prepare 200.0 parts by mass of a monomer composition.

After the atmosphere inside the reactor was purged with nitrogen gas, 40.0 parts by mass of the monomer composition, 21.0 parts by mass of hydrogen peroxide solution (hydrogen peroxide concentration: 1.28% by mass), and 21.0 parts by mass of an L-ascorbic acid aqueous solution (L-ascorbic acid concentration: 1.90% by mass) were added to the reactor to carry out an initial polymerization reaction. Next, the remaining 160.0 parts by mass of the monomer composition, 479.0 parts by mass of hydrogen peroxide solution (hydrogen peroxide concentration: 0.22% by mass), and 486.04 parts by mass of a mixture of 479.0 parts by mass of an L-ascorbic acid aqueous solution (L-ascorbic acid concentration: 0.33% by mass) and 7.04 parts by mass of SR-20 (active ingredient: 25.0% by mass) were uniformly added dropwise to the reactor over a period of 4 hours from different inlets. After the dropwise addition was completed, the internal temperature was raised to 85°C and maintained at that temperature for 2 hours for aging, after which the reaction solution was cooled to obtain a polymer aqueous dispersion (1a) in which polymer (1) was dispersed.

<Manufacture example A2>
A polymer aqueous dispersion (2a) in which the polymer (2) was dispersed was obtained in the same manner as in Production Example A1, except that the monomer composition described in Production Example A1 was changed from 180.0 parts by mass of RHMA and 20.0 parts by mass of 3EG-A to 170.0 parts by mass of RHMA, 20.0 parts by mass of 3EG-A, and 10.0 parts by mass of normal butyl acrylate (hereinafter referred to as "BA").

<Manufacture example A3>
In a stainless steel first reaction kettle equipped with a stirrer, thermometer, and cooler, 1,378 parts by mass of deionized water and 0.96 parts by mass of Adeka Reasoap SR-20 (active ingredient 10% by mass), an anionic reactive emulsifier mainly composed of an ether sulfate-type ammonium salt, were added, and the internal temperature was raised to 75°C and maintained at that temperature. Meanwhile, in a second reaction kettle different from the first reaction kettle, 120.0 parts by mass of RHMA and 30.0 parts by mass of 3EG-A were added to prepare 150 parts by mass of monomer composition A. Furthermore, in a third reaction kettle different from the first and second reaction kettle, 45.0 parts by mass of RHMA and 5.0 parts by mass of 3EG-A were mixed to prepare 50 parts by mass of monomer composition B.

Next, after purging the air inside the first reactor with nitrogen gas, 150 parts by weight of the monomer composition A, 20 parts by weight of hydrogen peroxide solution (concentration 3.35% by weight), and 20 parts by weight of an L-ascorbic acid aqueous solution (concentration 5.0% by weight) were added to the first reactor to carry out an initial polymerization reaction. Subsequently, 50 parts by weight of the monomer composition B, 100 parts by weight of hydrogen peroxide solution (concentration 0.83% by weight), 100 parts by weight of an L-ascorbic acid aqueous solution (concentration 1.25% by weight), and 100 parts by weight of a mixture of 7.04 parts by weight of SR-20 (active ingredient 10% by weight), 0.36 parts by weight of an ammonia aqueous solution (concentration 28% by weight), and 92.6% by weight of ion-exchanged water were uniformly added dropwise to the first reactor from different inlets over a period of 3 hours. After the dropwise addition was completed, the internal temperature of the first reaction vessel was maintained at 75°C and the mixture was aged at that temperature for 2 hours. The reaction solution was then cooled to obtain a polymer aqueous dispersion (3a) in which polymer (3) was dispersed.

<Manufacturing example A4>
A polymer aqueous dispersion (4a) in which the polymer (4) was dispersed was obtained in the same manner as in Production Example A3, except that the monomer composition B described in Production Example A3 was changed from 45.0 parts by mass of RHMA and 5.0 parts by mass of 3EG-A to 45.0 parts by mass of RHMA and 5.0 parts by mass of styrene (hereinafter referred to as "St").

[resin]
The following resins were used as the resin (C) to be blended with the alkali-soluble particles.
C-1: Nichigo Polyester WR-901, manufactured by Mitsubishi Chemical Corporation
C-2: U-DOUBLE EF-015, manufactured by Nippon Shokubai Co., Ltd.
C-3: Pluscoat Z-561, manufactured by Goo Chemical Industry Co., Ltd.

[Example 1]
(Preparation of Paint Composition)
Resin C-1 and polymer aqueous dispersion (1a) were mixed in a ratio of 100:20 in terms of solid content, and then thoroughly stirred with a stirrer tip to obtain a coating composition.
(Preparation of film-formed samples)
The coating composition was applied to a transparent polyethylene terephthalate film (hereinafter referred to as "PET film", manufactured by Toyobo Co., Ltd., Cosmoshine A4300, length: 297 mm, width: 210 mm, thickness: 0.100 mm) using a bar coater so that the film thickness after coating would be 50 μm, and the film was dried at 100°C for 10 minutes in a constant temperature incubator (manufactured by Yamato Scientific Co., Ltd., "DNF400") to obtain a PET film laminated with a coating film. The PET film was then immersed in a 1 wt% aqueous sodium hydroxide solution for 1 minute for alkali treatment to obtain a film-formed sample.

[Examples 2 to 9, Comparative Examples 1 and 2]
Film-forming samples were prepared in the same manner as in Example 1, except that the types of resin and polymer aqueous dispersion to be blended were changed to those shown in Table 1.

The results in Tables 1 and 2 demonstrate that a pore-forming composition can be provided that easily forms pores, has high pore size uniformity, and provides high pore dispersibility.

Claims (5)

A pore-forming composition comprising alkali-soluble polymer particles and a resin, wherein the alkali-soluble polymer particles have structural units derived from an ethylenically unsaturated monomer and have one or more functional groups selected from a hydroxyl group, a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, groups having a salt structure thereof, an epoxy group, and a polyoxyethylene group, and the absolute difference in contact angle with water between the polymer particles and the resin at 25°C is 10° to 55°. The pore-forming composition according to claim 1, wherein the volume average particle diameter of the alkali-soluble polymer particles is 10 nm to 10 μm. The pore-forming composition according to claim 1 or 2, wherein the alkali-soluble polymer particles have a haze of 0.01% to 10% in an alkaline dispersion containing 5% by mass of the polymer particles. The pore-forming composition according to any one of claims 1 to 3, wherein the alkali-soluble polymer particles are contained in an amount of 1% by mass to 80% by mass. 5. The pore-forming composition according to claim 1, wherein the alkali-soluble polymer particles contain a structural unit derived from the following general formula (1):
(In general formula (1), ^R1 represents an alkyl group having 1 to 4 carbon atoms, a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, or ammonium.)