WO2024181265A1 - Resin particles for creating pores in polyimide porous membrane, and method for producing same - Google Patents

Abstract

Provided are resin particles which are for creating pores in a polyimide porous membrane, and which are capable of suppressing an increase in slurry viscosity.　The present invention provides resin particles for creating pores in a polyimide porous membrane. The resin particles are formed of a (meth)acrylic resin. The proportion of (meth)acrylic monomer units in the (meth)acrylic resin is 60-100 mass%. The polarity on the surface of the resin particles is cationic.

Description

Resin particles for forming pores in polyimide porous membranes and method for producing the same

The present invention relates to resin particles for forming pores in polyimide porous membranes and a method for producing the same.

Polyimide porous membranes have higher heat resistance and porosity than polyolefin porous membranes, and are therefore used, for example, as separators for lithium-ion batteries.

In one example, a polyimide porous film can be obtained by coating a slurry made by mixing a polyamic acid solution with resin particles to form a coated sheet, drying the resulting coated sheet to form a dry sheet 5, and baking the dry sheet (see, for example, Patent Document 1). The baking imidizes the polyamic acid to form a polyimide film, and the burning of the resin particles forms numerous pores in the polyimide film, making the polyimide film porous.

WO2020/054416

Generally, when resin particles are added to a polyamic acid solution, the viscosity of the slurry becomes higher than the viscosity of the polyamic acid solution due to the effect of the resin particles. If the viscosity of the slurry becomes too high, the uniformity of the coating thickness tends to deteriorate, so a technology that suppresses the increase in viscosity of the slurry is desired.

The present invention was made in consideration of these circumstances, and provides resin particles for forming pores in polyimide porous membranes that can suppress an increase in the slurry viscosity.

According to the present invention, the following inventions are provided.
[1] Resin particles for forming pores in a polyimide porous membrane, the resin particles being composed of a (meth)acrylic resin, a ratio of (meth)acrylic monomer units in the (meth)acrylic resin being 60 to 100 mass %, and the polarity of the surface of the resin particles being cationic.
[2] The resin particles according to [1], wherein the emulsifier attached to the surface of the resin particles is a cationic emulsifier.
[3] The resin particles according to [1] or [2], wherein the polymer constituting the resin particles has a cationic group.
[4] The resin particle according to [3], wherein the cationic group of the polymer includes a cationic group derived from a cationic polymerization initiator.
[5] The resin particle according to [3] or [4], wherein the cationic group of the polymer includes a cationic group derived from a cationic group-containing monomer.
[6] A method for producing resin particles for forming pores in a polyimide porous membrane, the resin particles being composed of a (meth)acrylic resin, a ratio of (meth)acrylic monomer units in the (meth)acrylic resin being 60 to 100% by mass, the method including a polymerization step in which a monomer is polymerized in an aqueous medium to form the resin particles, and the polymerization is carried out under cationization conditions such that the polarity of the surfaces of the resin particles becomes cationic.
[7] The method according to [6], wherein the polymerization is carried out in the presence of a cationic emulsifier.
[8] The method according to [6] or [7], wherein the polymerization is carried out in the presence of a cationic polymerization initiator.
[9] The method according to any one of [6] to [8], wherein the monomer comprises a cationic group-containing monomer.

After extensive research, the inventors discovered that when the polarity of the resin particle surfaces is cationic, the increase in the viscosity of the slurry is suppressed, which led to the completion of the present invention.

FIG. 1A shows a dry sheet 5 formed by dispersing resin particles 1 in a polyamic acid film 5a, FIG. 1B shows a state in which the polyamic acid constituting the polyamic acid film 5a is imidized to form a polyimide film 2a, and FIG. 1C shows a state in which the resin particles 1 in the polyimide film 2a are burned away to form a large number of holes 2b in the polyimide film 2a, thereby forming a polyimide porous film 2. FIG. 2 is a cross-sectional view showing the configuration of a resin particle 1.

Below, an embodiment of the present invention will be described. The various features shown in the following embodiment can be combined with each other. Furthermore, each feature can be an independent invention. In this invention, "(meth)acrylic" is used to collectively refer to acrylic and methacrylic. Furthermore, "(meth)acrylate" is used to collectively refer to acrylate and methacrylate.

1. Structure of Resin Particle 1 A resin particle 1 according to one embodiment of the present invention will be described with reference to FIG. 1. The resin particle 1 according to this embodiment is used for forming holes in a polyimide porous film 2. As an example, as shown in FIG. 1A, the polyimide porous film 2 can be obtained by mixing a polyamic acid solution in which polyamic acid is dissolved in a solvent with resin particles 1, coating the resulting slurry to form a coated sheet, drying the resulting coated sheet to form a dry sheet 5, and baking the dry sheet 5. The dry sheet 5 is formed by dispersing the resin particles 1 in a polyamic acid film 5a.

The baking preferably includes baking at an imidization temperature and baking at a particle burnout temperature. The imidization temperature is the temperature at which the polyamic acid is imidized, and is, for example, 200 to 300°C. By baking at this temperature, as shown in FIG. 1B, the polyamic acid constituting the polyamic acid film 5a is imidized, and the polyamic acid film 5a becomes a polyimide film 2a. At this point, it is preferable that the resin particles 1 are not burned out. The imidization temperature is, for example, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, or 300°C, and may be within a range between any two of the values exemplified here.

The particle burnout temperature is the temperature at which the resin particles 1 are burned out, and is, for example, 310 to 400°C. By baking at this temperature, as shown in FIG. 1C, the resin particles 1 in the polyimide film 2a are burned out, and a large number of holes 2b are formed in the polyimide film 2a, forming a polyimide porous film 2. Specific examples of the particle burnout temperature are 310, 320, 330, 340, 350, 360, 370, 380, 390, and 400°C, and may be within a range between any two of the values exemplified here.

The resin particle 1 is composed of a (meth)acrylic resin. The (meth)acrylic resin is a polymer of monomers including a (meth)acrylic monomer, and contains a (meth)acrylic monomer unit. This monomer may contain only a (meth)acrylic monomer, or may contain other monomers other than a (meth)acrylic monomer. Examples of other monomers include monofunctional other monomers such as styrene monomers (styrene, methylstyrene, etc.) and polyfunctional other monomers such as divinylbenzene. The ratio of the (meth)acrylic monomer units in the (meth)acrylic resin is, for example, 60 to 100% by mass, and specifically, for example, 60, 65, 70, 75, 80, 85, 90, 95, 95, 96, 97, 98, 99, and 100% by mass, and may be within a range between any two of the numerical values exemplified here. The ratio of the other monomer units is obtained by subtracting the (meth)acrylic monomer units from 100% by mass.

(Meth)acrylic monomers include monofunctional (meth)acrylates and polyfunctional (meth)acrylates. Polyfunctional (meth)acrylates include difunctional, trifunctional, or tetrafunctional or higher (meth)acrylates.

The monofunctional (meth)acrylate is preferably a (meth)acrylic acid alkyl ester, and the (meth)acrylic acid alkyl ester preferably has an alkyl group having 1 to 12 carbon atoms, more preferably 1 to 8 carbon atoms.

Examples of (meth)acrylic acid alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, and dodecyl (meth)acrylate.

Examples of bifunctional (meth)acrylates include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyoxyethylene di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, etc.

Trifunctional (meth)acrylates include trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, propoxylated trimethylolpropane tri(meth)acrylate, tris(2-(meth)acryloxyethyl isocyanurate), etc.

Examples of tetrafunctional or higher (meth)acrylates include tetra(meth)acrylate compounds such as pentaerythritol tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, propoxylated pentaerythritol tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, ethoxylated dipentaerythritol tetra(meth)acrylate, propoxylated dipentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, ethoxylated ditrimethylolpropane tetra(meth)acrylate, and ethoxylated ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, etc.

The content of the polyfunctional monomer in the monomers constituting the (meth)acrylic resin is preferably 40% by mass or less. If it is more than this, the degree of cross-linking of the (meth)acrylic resin becomes too high. This content is, for example, 0 to 40% by mass, and specifically, for example, 0, 5, 10, 15, 20, 25, 30, 35, or 40% by mass, and may be in the range between any two of the numerical values exemplified here. The content (mass %) of the monofunctional monomer contained in the monomers constituting the (meth)acrylic resin can be calculated by 100% by mass - (content (mass %) of the polyfunctional monomer).

As shown in FIG. 2, the resin particle 1 preferably comprises a base particle 3 and a coating portion 4 that covers at least a portion of the surface of the base particle 3. Although the coating portion 4 is illustrated in FIG. 2 as covering the entire base particle 3, it may cover only a portion of the base particle 3. The proportion of the area of the surface area of the base particle 3 that is covered by the coating portion 4 is, for example, 20 to 100%, and more specifically, for example, 20, 30, 40, 50, 60, 70, 80, 90, or 100%, and may be in a range between any two of the numerical values exemplified here.

The base particle 3 is composed of a polymer of a first monomer, and the first monomer has a polyfunctional monomer content of 10 mass% or less. The coating portion 4 is composed of a polymer of a second monomer, and the second monomer has a polyfunctional monomer content of 65 mass% or more. With this configuration, the degree of cross-linking of the base particle 3 is low and the degree of cross-linking of the coating portion 4 is high. In other words, at least a portion of the surface of the base particle 3, which has a low degree of cross-linking, is coated with the coating portion 4, which has a high degree of cross-linking.

In general, the lower the degree of crosslinking of the resin particles 1, the higher the viscosity of the slurry containing the resin particles 1. In this embodiment, by covering at least a portion of the surface of the base particles 3 with the coating portion 4, it is possible to suppress an increase in the viscosity of the slurry while keeping the degree of crosslinking of the base particles 3 low. In general, the higher the degree of crosslinking of the resin particles 1, the greater the dimensional change of the polyimide porous film 2 during the baking process when forming the polyimide porous film 2. However, in this embodiment, the degree of crosslinking of the base particles 3 remains low, so that the dimensional change of the polyimide porous film 2 is suppressed. In this way, according to the present invention, it is possible to achieve both suppression of an increase in the viscosity of the slurry and suppression of a dimensional change of the polyimide porous film 2.

The content of the polyfunctional monomer in the first monomer is, for example, 0 to 10% by mass, specifically, for example, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10% by mass, and may be in the range between any two of the numerical values exemplified here. The content (mass %) of the monofunctional monomer contained in the first monomer can be calculated by 100% by mass - (content (mass %) of the polyfunctional monomer + content (mass %) of the other monomers).

The content of the polyfunctional monomer in the second monomer is, for example, 65 to 100% by mass, specifically, for example, 65, 70, 75, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100% by mass, and may be in the range between any two of the numerical values exemplified here. From the viewpoint of suppressing an increase in the slurry viscosity, the content of the polyfunctional (meth)acrylate in the second monomer is preferably 80% by mass or more, and more preferably 90% by mass or more. The content (mass%) of the monofunctional (meth)acrylate contained in the second monomer can be calculated by 100% by mass - (content (mass%) of the polyfunctional (meth)acrylate + content (mass%) of other monomers).

Examples of the monofunctional monomer in the first or second monomer include the above-mentioned monofunctional (meth)acrylate and styrene-based monomer. The monofunctional monomer preferably contains a monofunctional (meth)acrylate. From the viewpoint of easy particle formation, the monofunctional (meth)acrylate in the first or second monomer preferably contains methyl methacrylate. The content of the monofunctional (meth)acrylate in the first monomer is, for example, 60 to 100% by mass, specifically, for example, 60, 65, 70, 75, 80, 85, 90, 95, or 100% by mass, and may be within a range between any two of the numerical values exemplified here.

The polyfunctional monomer in the first monomer or the second monomer may be the above-mentioned polyfunctional (meth)acrylate or divinylbenzene. The polyfunctional monomer preferably contains a polyfunctional (meth)acrylate. The content of the polyfunctional (meth)acrylate in the polyfunctional monomer is, for example, 80 to 100% by mass, specifically, for example, 80, 85, 90, 95, or 100% by mass, and may be within a range between any two of the numerical values exemplified here.

The surface polarity of the resin particles 1 is cationic; in other words, the equivalent number of cationic groups present on the surface of the resin particles 1 is greater than the equivalent number of anionic groups. As shown in the examples described later, when the surface polarity of the resin particles 1 is cationic, the increase in viscosity of the slurry containing the resin particles 1 is suppressed compared to when the surface polarity is anionic.

The polarity of the surface of the resin particle 1 varies depending on the type of emulsifier, polymerization initiator, and monomer used in the polymerization of the resin particle 1. In one example, the polarity of the surface of the resin particle 1 can be made cationic by using at least one of a cationic emulsifier, a cationic polymerization initiator, and a monomer containing a cationic group in the polymerization process of the resin particle 1.

The cationic emulsifier adheres to the surface of the resin particle 1 and makes the polarity of the surface of the resin particle 1 cationic. Examples of cationic emulsifiers include quaternary ammonium salts such as lauryl trimethyl ammonium chloride, stearyl trimethyl ammonium chloride, cetyl trimethyl ammonium chloride, alkyl benzyl dimethyl ammonium chloride, dodecyl ammonium chloride, and dodecyl ammonium bromide; and alkyl amine salts such as lauryl amine acetate, coconut amine acetate, and stearyl amine acetate.

The cationic polymerization initiator and the cationic group-containing monomer introduce cationic groups into the polymer that constitutes the resin particle, thereby making the polarity of the surface of the resin particle 1 cationic. The polymerization of the resin particle 1 is carried out in an aqueous medium, and since cationic groups are highly hydrophilic, the polymerization proceeds while the cationic groups derived from the cationic polymerization initiator and the cationic groups derived from the cationic group-containing monomer are located at the site in contact with the aqueous medium. Therefore, the cationic groups derived from the cationic polymerization initiator and the cationic groups derived from the cationic group-containing monomer are located on the surface of the resin particle 1 even after the polymerization is completed, making the polarity of the surface of the resin particle 1 cationic.

A cationic polymerization initiator is a polymerization initiator that generates cations. Examples of cationic polymerization initiators include water-soluble azo polymerization initiators having an amidine group, such as 2,2'-azobis(2-methylpropionamidine) dihydrochloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., "V-50"), 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., "V-044"), Examples include 2,2'-azobis[2-(imidazolin-2-yl)propane]disulfate dihydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., "V-046B"), 2,2-azobis[N-(2-carboxyethyl)-2-methylpropionamidine]hydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., "VA-57"), and 2,2-azobis[2-(2-imidazolin-2-yl)propane] (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., "VA-061"), etc.

The cationic group-containing monomer is a monomer containing a cationic group, and is preferably a (meth)acrylic monomer having an ammonium group. The (meth)acrylic monomer having an ammonium group is preferably a quaternized product of a (meth)acrylic acid ester of an amino alcohol. Specific examples include quaternized products such as N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylate, N,N-diethylaminopropyl (meth)acrylate, N,N-dimethylaminobutyl (meth)acrylate, N,N-diethylaminobutyl (meth)acrylate, and N,N-dihydroxyethylaminoethyl (meth)acrylate, and a quaternized product of N,N-dimethylaminoethyl (meth)acrylate is particularly preferably used. Other cationic group-containing monomers include quaternized amino group-containing monomers such as vinylpyridine, methylvinylpyridine, N,N-dimethylaminostyrene, N,N-diethylaminostyrene, and N,N-dibutylaminostyrene.

The average particle diameter of the resin particles 1 is, for example, 0.01 to 10.0 μm, preferably 0.05 to 1.0 μm, and more preferably 0.1 to 0.5 μm. Specific examples of the average particle diameter are 0.01, 0.05, 0.1, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 1.0, 5.0, and 10.0 μm, and may be in a range between any two of the numerical values exemplified here. The average particle diameter can be measured by the method shown in the examples.

The average particle diameter of the base particles 3 is, for example, 0.01 to 10.0 μm, preferably 0.05 to 1.0 μm, and more preferably 0.1 to 0.5 μm. Specific examples of the average particle diameter are 0.01, 0.05, 0.1, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 1.0, 5.0, and 10.0 μm, and may be in a range between any two of the numerical values exemplified here. The average particle diameter can be measured by the method shown in the examples.

The particle size ratio defined by [average particle size of resin particles 1/average particle size of base particles 3] is, for example, 1.00 to 1.50, preferably 1.00 to 1.30, and even more preferably 1.001 to 1.30 from the viewpoint of suppressing dimensional changes. Theoretically, the particle size ratio is greater than 1, but may be 1.00 due to calculation errors caused by rounding. Specific examples of this particle size ratio are 1.00, 1.001, 1.005, 1.01, 1.02, 1.03, 1.04, 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45, and 1.50, and may be in the range between any two of the numerical values exemplified here.

The coefficient of variation (CV value) of the average particle size of the resin particles 1 is preferably 10% or less, and more preferably 5% or less. The coefficient of variation (CV value) is calculated by the following formula.
Coefficient of variation (CV value) = (standard deviation of particle size distribution of resin particles ÷ average particle size of resin particles) × 100

The average particle size and particle size distribution can be measured by the method shown in the Examples. If they are within the range, when a polyimide porous film is formed using the resin particles of the present invention, the mechanical strength of the porous polyimide film is further improved.

2. Method for Producing Resin Particles 1 The method for producing resin particles 1 according to one embodiment of the present invention includes a polymerization step.

In the polymerization process, the monomer is polymerized in an aqueous medium to form resin particles 1. This polymerization is performed under cationization conditions in which the polarity of the surface of the resin particles 1 becomes cationic. After the polymerization process, the resin particles 1 can be dried and crushed to make them into a powder state. The drying conditions are appropriately adjusted according to the capacity and capacity of the dryer used. General-purpose hot air drying, reduced pressure drying, vacuum drying, etc. can be appropriately selected. Crushing is preferably performed at 10 to 40°C, and the crushing pressure is preferably 0.1 to 0.5 MPa. The resin particles 1 may be classified as necessary to make the particle diameter, coefficient of variation, etc. within a predetermined range. For classification, either wet classification or dry classification can be used. For wet classification, for example, the polymerization liquid after polymerization can be passed through a metal mesh, and for dry classification, the particles after polymerization, further drying, and crushing can be classified using an appropriate classification device.

The polymerization step preferably includes a base particle formation step and a second monomer polymerization step. In the base particle formation step, a first monomer is polymerized in an aqueous medium to form base particles 3, and in the second monomer polymerization step, a second monomer is polymerized in an aqueous medium in the presence of base particles 3 to form resin particles 1. The first and second monomers are as described above.

Polymerization in an aqueous medium includes, for example, soap-free emulsion polymerization, emulsion polymerization, suspension polymerization, seed polymerization, etc.

Aqueous media that can be used in the above polymerization include water and mixtures of water and hydrophilic organic solvents. Examples of water include purified water (e.g., ion-exchanged water, distilled water), groundwater, and tap water. Examples of hydrophilic organic solvents include lower alcohols such as methanol, ethanol, and isopropanol; polyhydric alcohols such as ethylene glycol, propylene glycol, butanediol, diethylene glycol, and triethylene glycol; cellosolves such as methyl cellosolve and ethyl cellosolve; ketones such as acetone; ethers such as tetrahydrofuran; and esters such as methyl formate. The hydrophilic organic solvents may be used alone or in combination of two or more. The amount of hydrophilic organic solvent added is usually 10 parts by mass or less per 100 parts by mass of water.

In the above polymerization method, the polymerization temperature is usually 40 to 100°C, preferably 55 to 85°C, and the polymerization time is usually 1 to 24 hours, preferably 1 to 10 hours.

The polymerization is preferably carried out in the presence of a polymerization initiator and/or an emulsifier. The amount of the polymerization initiator used is preferably 0.1 to 10 parts by mass per 100 parts by mass of the monomer components. The amount of the emulsifier used is preferably 0.01 to 20 parts by mass per 100 parts by mass of the monomer components.

In one example, the above-mentioned cationization conditions can be achieved by using at least one of a cationic emulsifier, a cationic polymerization initiator, and a cationic group-containing monomer in the polymerization process of the resin particles 1. In other words, the above-mentioned cationization conditions can be achieved by performing polymerization in the presence of a cationic emulsifier and/or a cationic polymerization initiator, and/or by performing polymerization using a monomer that includes a cationic group-containing monomer.

The cationic emulsifier, cationic polymerization initiator, and cationic group-containing monomer are as explained in "1. Structure of resin particle 1", and by using these, the number of equivalents of cationic groups present on the surface of resin particle 1 can be increased, making the polarity of the surface of resin particle 1 cationic.

The above polymerization preferably does not use an anionic emulsifier, does not use an anionic polymerization initiator, and/or does not use an anionic group-containing monomer. This inhibits an increase in the number of equivalents of anionic groups present on the surface of the resin particle 1, making it easier for the polarity of the surface of the resin particle 1 to become cationic. When an anionic emulsifier, an anionic polymerization initiator, and/or an anionic group-containing monomer are used, it is preferable that the total number of equivalents is smaller than the total number of equivalents of the cationic emulsifier, cationic polymerization initiator, and cationic group-containing monomer. This makes it easier for the polarity of the surface of the resin particle 1 to become cationic.

1. Production of Resin Particles Resin particles of the Examples and Comparative Examples were produced according to the following methods. The meanings of the abbreviations and product details in the following explanation are as follows.

<Monomer>
MMA: methyl methacrylate EGDMA: ethylene glycol dimethacrylate MAA: methacrylic acid HEMA: hydroxyethyl methacrylate DQ-100: dimethylaminoethyl methacrylate quaternary product (manufactured by Kyoeisha Chemical Co., Ltd., "Light Ester DQ-100")

<Chain Transfer Agent>
n-OM: Chain transfer agent, n-octyl mercaptan

<Emulsifier>
Emulsifier A: Cationic emulsifier, lauryl trimethyl ammonium chloride Emulsifier B: Anionic emulsifier, sodium alkylbenzene sulfonate Emulsifier C: Anionic emulsifier, polyoxyethylene distyrenated methylphenyl ether sulfate

<Polymerization initiator>
V-50: cationic polymerization initiator, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product name "V-50", water-soluble azo polymerization initiator, 2,2'-azobis(2-methylpropionamidine) dihydrochloride APS: anionic polymerization initiator, ammonium persulfate Bw: polymerization initiator, benzoyl peroxide, manufactured by NOF Corporation, product name "Niper BW"
KPS: Anionic polymerization initiator, potassium persulfate

1-1. Production of Resin Particles The resin particles of Example 1 and Comparative Example 1 were produced by a method including a base particle formation step and a second monomer polymerization step.

The compositions of the compounds used in the base particle formation process and the second monomer polymerization process are summarized in Table 1. The units of composition are parts by mass.

Example 1
First, 90 parts by mass of MMA, 10 parts by mass of EGDMA, 213 parts by mass of ion-exchanged water, and 0.01 parts by mass of emulsifier A were charged into a reaction apparatus equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen inlet tube, and the temperature was raised to 68°C while introducing nitrogen gas. Next, 0.25 parts by mass of V-50 was added to start the polymerization reaction. After that, the mixture was kept at 68°C for 120 minutes, and then heated to 90°C for 60 minutes to obtain resin particles. Since the resin particles contain cationic functional groups derived from emulsifier A and V-50, the polarity of the surface of the resin particles is cationic.

<Comparative Example 1>
Resin particles were produced in the same manner as in Example 1, except for the following points.
As an emulsifier, 0.3 parts by mass of emulsifier B was used in place of 0.01 parts by mass of emulsifier A.
As a polymerization initiator, 0.3 parts by mass of APS was added in place of 0.25 parts by mass of V-50.
The resin particles contain anionic functional groups derived from emulsifier B and APS, and the polarity of the surfaces of the resin particles is anionic.

Example 2
Base particle formation process First, 92.1 parts by mass of MMA, 2.9 parts by mass of EGDMA, 213 parts by mass of ion-exchanged water, and 0.01 parts by mass of emulsifier A were charged into a reaction apparatus equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen inlet tube, and the temperature was raised to 68°C while introducing nitrogen gas. Next, 0.25 parts by mass of V-50 was added to start the polymerization reaction. After that, the mixture was kept at 68°C for 120 minutes to obtain base particles.

Second monomer polymerization step: After that, an emulsion of 5 parts by mass of EGDMA, 10 parts by mass of ion-exchanged water, and 0.05 parts by mass of emulsifier A was added dropwise for 10 minutes, and then the mixture was held for 30 minutes, and then heated to 90°C and held for 60 minutes to polymerize particles. After cooling the reaction liquid, the mixture was filtered through a 400 mesh filter, dried using a spray dryer, and crushed using a jet mill to obtain resin particles. Since the resin particles contain cationic functional groups derived from emulsifier A and V-50, the polarity of the surface of the resin particles is cationic.

<Comparative Example 2>
Resin particles were produced in the same manner as in Example 2, except for the following points.
As an emulsifier, emulsifier B was used instead of emulsifier A.
In the base particle forming step, 0.3 parts by mass of APS was added as a polymerization initiator instead of 0.25 parts by mass of V-50.

The resin particles contain anionic functional groups derived from emulsifier B and APS, making the surface of the resin particles anionic in polarity.

1-2. Production of resin particles by seed polymerization method Resin particles of Example 3 and Comparative Examples 3 to 5 were produced by seed polymerization method. In the seed polymerization method, resin particles were produced by a seed particle formation step and a seed polymerization step. The seed particle formation step was carried out under the same conditions in all Examples and Comparative Examples, and various resin particles having different types of functional groups exposed on the surface of the resulting resin particles were produced by changing the compound used in the seed polymerization step.

Table 2 shows the compositions of the compounds used in the seed polymerization process in Example 3 and Comparative Examples 3 to 5. The units of composition are parts by mass. The ratio of the components derived from the seed particles in the final resin particles is 3.7% by mass, so the composition of the resin particles is the composition shown in Table 2 plus 3.7% by mass of the seed particle composition.

Example 3
- Seed particle formation step First, 20 parts by mass of MMA, 394 parts by mass of ion-exchanged water, and 0.05 parts by mass of emulsifier A were charged into a reaction apparatus equipped with a stirrer, a reflux condenser, and a thermometer, and the temperature was raised to 70°C. Next, 1.0 part by mass of V-50 was added to start the polymerization reaction. Then, 5 minutes after the start of the reaction, 80 parts by mass of MMA and 2 parts by mass of n-OM were dropped over 30 minutes to form a seed emulsion containing seed particles.

- Seed polymerization step Next, 20.6 parts by mass of seed emulsion and an emulsified liquid (66.1 parts by mass of MMA, 30 parts by mass of EGDMA, 1.05 parts by mass of Bw, 200 parts by mass of tap water, 1 part by mass of emulsifier A, and 0.05 parts by mass of sodium nitrite) were charged into a reactor equipped with a stirrer, a reflux condenser, and a thermometer, and the temperature was raised to 50 ° C. and the mixture was allowed to swell for 30 minutes. Thereafter, 0.2 parts by mass of DQ-100 was added, and the mixture was heated to 70 ° C. to carry out a polymerization reaction. After cooling the reaction liquid, the mixture was filtered through a 400 mesh filter, dried with a spray dryer, and crushed with a jet mill to obtain resin particles. Since cationic functional groups derived from DQ-100 and emulsifier A are present on the surface of the resin particles, the polarity of the surface of the resin particles is cationic.

<Comparative Example 3>
In Comparative Example 2, resin particles were obtained by the same method as in Example 2, except that in the seed particle formation step, 0.01 parts by mass of ammonium lauryl sulfate was added instead of emulsifier A, 0.5 parts by mass of APS was added instead of V-50, 1 part by mass of MAA was added instead of DQ-100, and 0.99 parts by mass of emulsifier C was added instead of emulsifier A in the seed polymerization step. Since anionic functional groups derived from MAA and emulsifier C are present on the surface of the resin particles, the polarity of the surface of the resin particles is anionic.

<Comparative Example 4>
In Comparative Example 4, resin particles were obtained in the same manner as in Comparative Example 3, except that 1 part by mass of HEMA was added instead of MAA in the seed polymerization step. Since anionic functional groups derived from emulsifier C are present on the surfaces of the resin particles, the polarity of the surfaces of the resin particles is anionic.

<Comparative Example 5>
In Comparative Example 5, resin particles were obtained in the same manner as in Comparative Example 3, except that MAA was not added in the seed polymerization step and 0.5 parts by mass of KPS was additionally added as a polymerization initiator. Since anionic functional groups derived from KPS and emulsifier C are present on the surface of the resin particles, the polarity of the surface of the resin particles is anionic.

2. Measurement of particle size and slurry viscosity The particle size and slurry viscosity of the resin particles shown in Tables 1 and 2 were measured, and the average particle size, particle size ratio, and CV value were calculated. The results are shown in Table 3. When comparing Example 1 and Comparative Example 1, and Example 2 and Comparative Example 2, which have almost the same particle size and the same polymerization process, Examples 1 and 2, in which the polarity of the surface of the resin particles is cationic, had a lower slurry viscosity than Comparative Examples 1 and 2, in which the polarity of the surface of the resin particles is anionic. When comparing Example 3 and Comparative Examples 3 to 5, in which the particle size is almost the same, Example 3, in which the polarity of the surface of the resin particles is cationic, had a lower slurry viscosity than Comparative Examples 3 to 5, in which the polarity of the surface of the resin particles is anionic.

As shown in Tables 1 to 3, Examples 1 to 3, in which the polarity of the resin particle surface is cationic, had a lower slurry viscosity than Comparative Examples 1 to 5, in which the polarity of the resin particle surface is anionic.

Measurement of particle size From the image of the powdered base particles or resin particles taken by a scanning electron microscope at 20,000 times magnification, 200 particles of average size were selected, and the diameter of each particle was measured to obtain the particle size distribution. The average value of the particle diameter was taken as the average particle size, and the average particle size of the resin particles was divided by the average particle size of the base particles to calculate the particle size ratio. In addition, the CV value was calculated by dividing the standard deviation of the particle size distribution of the resin particles by the average particle size of the resin particles.

Measurement of Slurry Viscosity The slurry viscosity was measured according to the following measurement method 1. As the rotation/revolution type mixer, a Thinky Mixer ARE-310 (manufactured by THINKY Corporation) was used.

(Measurement Method 1)
First, 1.2 g of polyamic acid, 14 g of dimethylacetamide (DMAc), and 4.8 g of the resin particles are weighed out, and a rotation/revolution mixer is used to mix the mixture at 2000 rpm for 5 min and defoaming at 2200 rpm for 30 sec three times to obtain a slurry. Next, the slurry viscosity of the obtained slurry is measured with an E-type viscometer at 5 rpm and at a liquid temperature of 25° C. after 2 days have passed since the preparation of the slurry at 25° C.

1: Resin particles, 2: Polyimide porous film, 2a: Polyimide film, 2b: Holes, 3: Base particles, 4: Coating, 5: Drying sheet, 5a: Polyamic acid film

Claims (9)

A resin particle for forming pores in a polyimide porous membrane, comprising:
The resin particles are composed of a (meth)acrylic resin,
The proportion of the (meth)acrylic monomer unit in the (meth)acrylic resin is 60 to 100% by mass,
The resin particles have a surface having cationic polarity. The resin particle according to claim 1 ,
The emulsifier attached to the surface of the resin particles is a cationic emulsifier. The resin particle according to claim 1 ,
The resin particles, wherein the polymer constituting the resin particles has a cationic group. The resin particles according to claim 3,
The cationic group of the polymer includes a cationic group derived from a cationic polymerization initiator. The resin particles according to claim 3 or 4,
The cationic group of the polymer includes a cationic group derived from a cationic group-containing monomer. A method for producing resin particles for forming pores in a polyimide porous membrane, comprising the steps of:
The resin particles are composed of a (meth)acrylic resin,
The proportion of the (meth)acrylic monomer unit in the (meth)acrylic resin is 60 to 100% by mass,
The method comprises a polymerization step,
In the polymerization step, a monomer is polymerized in an aqueous medium to form the resin particles;
The polymerization is carried out under cationization conditions such that the polarity of the surface of the resin particles becomes cationic. 7. The method of claim 6,
The process wherein the polymerization is carried out in the presence of a cationic emulsifier. 7. The method of claim 6,
The process wherein the polymerization is carried out in the presence of a cationic polymerization initiator. The method according to any one of claims 6 to 8,
The method wherein the monomer comprises a cationic group-containing monomer.