Cross-linked acrylic polymer particles for the manufacture of separators

Abstract

To provide acrylic polymer particles that suppress swelling in a liquid medium used in production of a polyimide separator and can be thermally decomposed at a relatively low temperature, thereby obtaining a separator having good properties.SOLUTION: Crosslinked acrylic polymer particles according to the present invention for producing a separator comprise acrylic polymers which are crosslinked by a structure based on a crosslinking agent having (meth)acryloyl groups and allyl groups.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to crosslinked acrylic polymer particles for manufacturing separators.

Background Art

[0002] In recent years, lithium-ion secondary batteries have been widely used as power sources for electric vehicles and the like. The separator for a lithium-ion secondary battery used here is required to avoid puncture due to dendritic lithium growth that may occur when metallic lithium is used for the anode. Further, the separator for a lithium-ion secondary battery is required to satisfy various properties such as film thickness (thinness), mechanical strength, ionic conductivity (when containing an electrolytic solution), electrical insulation, electrolytic solution resistance, shutdown effect, liquid retention property with respect to the electrolytic solution, and wettability. As a separator satisfying such requirements, a separator made of polyimide having a three-dimensional regular array macropore (3DOM) structure excellent in mechanical strength has been proposed.

[0003] Patent Document 1 discloses a method for manufacturing a separator for a secondary battery, which is made of a porous resin film having pores with a three-dimensional cubic regular array structure and the pores being interconnected by communication holes.

[0004] This method includes a narrowly dispersed spherical fine particle dispersion slurry preparation step of uniformly dispersing narrowly dispersed spherical fine particles in a dispersion medium to prepare a fine particle dispersion slurry; a narrowly dispersed spherical fine particle dispersion film preparation step of drying the fine particle dispersion slurry to obtain a narrowly dispersed spherical fine particle dispersion film; a fine particle-resin film formation step of heat-treating the film to form a fine particle-resin film in which the fine particles are three-dimensionally regularly arrayed in a resin matrix; a porous resin film formation step of bringing the fine particle-resin film into contact with an inorganic acid, an organic acid, water, or an alkaline solution excluding hydrofluoric acid to dissolve and remove the fine particles, or heating the fine particle-resin film to remove the fine particles, and forming pores having a three-dimensional cubic regular array structure and being interconnected by communication holes in the resin matrix The dispersion medium comprises a precursor of the resin constituting the resin matrix, and the surface of the narrowly dispersed spherical fine particles is inert to the dispersion medium.

[0005] In Patent Document 2, A slurry is prepared by mixing polymer particles with a mixture of polyamic acid, ethylene glycol, and a nonionic surfactant in N,N-dimethylacetamide. Forming a film from the slurry, The film is heat-treated to convert the polyamic acid into polyimide through a thermal imidation reaction, and the polymer particles are removed by thermal decomposition to form a 3DOM structure in which multiple macropores of uniform shape and size are regularly arranged in the three-dimensional direction, thereby obtaining a polyimide separator having the 3DOM structure. A method for producing a polyimide separator is disclosed, characterized by containing the above polymer particles. Patent Document 2 states that the above polymer particles are thermally decomposable in a temperature range higher than 370°C and below the decomposition temperature of polyimide, and have a glass transition temperature lower than the glass transition temperature of polyimide, and that the above heat treatment is carried out in an inert gas atmosphere with an oxygen concentration of 10 vol% or less at a temperature higher than 370°C and below the decomposition temperature of polyimide. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2014 / 196656 [Patent Document 2] Japanese Patent Publication No. 2018-97915 [Overview of the project] [Problems that the invention aims to solve]

[0007] Obtaining a 3DOM structure by removing polymer particles through thermal decomposition is preferable from a safety standpoint. However, the polymer particles used here, such as polymethyl methacrylate particles, are soluble in the liquid medium used to dissolve polyamic acid. As a result, the particles swell in this liquid medium, and consequently, a stable 3DOM structure cannot be obtained.

[0008] Therefore, there is a need to provide acrylic polymer particles that can suppress swelling in the liquid medium used in the manufacture of polyimide separators, can be thermally decomposed at relatively low temperatures, and thereby yield separators with good properties. [Means for solving the problem]

[0009] The inventors, after diligent research, discovered that the above problems could be solved by the following means, and thus completed the present invention. That is, the present invention is as follows: <Aspect 1> Crosslinked acrylic polymer particles for the manufacture of a separator, The acrylic polymer is crosslinked with a crosslinking agent having (meth)acryloyl groups and allyl groups. Cross-linked acrylic polymer particles. <Aspect 2> The crosslinked acrylic polymer particles according to Aspect 1, wherein the crosslinking agent is an ester of (meth)acrylic acid and an allyl unsaturated alcohol. <Aspect 3> The crosslinked acrylic polymer particles according to aspect 1 or 2, wherein the content of the crosslinking agent-based structure is 20% by mass or less relative to the mass of the crosslinked acrylic polymer particles. <Aspect 4> Crosslinked acrylic polymer particles according to any one of aspects 1 to 3, wherein the 5% weight loss temperature in thermogravimetric analysis is less than 190°C. <Aspect 5> Crosslinked acrylic polymer particles according to any one of aspects 1 to 4, wherein the volume-average particle diameter measured by dynamic light scattering is 1.0 μm or less. <Aspect 6> The crosslinked acrylic polymer particles according to aspect 5, wherein the volume-average particle diameter is 50 nm to 500 nm. <Aspect 7> Crosslinked acrylic polymer particles according to any one of aspects 1 to 6, wherein the acrylic polymer is polymethyl methacrylate. <Aspect 8> Liquid medium, and Crosslinked acrylic polymer particles according to any one of embodiments 1 to 7, dispersed in the liquid medium. A dispersion of cross-linked acrylic polymer particles containing [the specified substance]. <Aspect 9> The dispersion according to aspect 8, wherein the liquid medium is an aprotic polar liquid medium. <Aspect 10> The dispersion according to aspect 8 or 9, further containing a polyamic acid. <Aspect 11> Applying the dispersion described in Aspect 10 to a substrate to be coated, and By heat-treating the coated dispersion, the polyamic acid is reacted to form a polyimide matrix, and the crosslinked acrylic polymer particles are eliminated to form interconnected pores. A method for manufacturing a porous separator, including the following. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide acrylic polymer particles that suppress swelling in the liquid medium used in the manufacture of polyimide separators and can be thermally decomposed at a relatively low temperature, thereby enabling the acquisition of separators with good properties. [Modes for carrying out the invention]

[0011] Cross-linked acrylic polymer particles The crosslinked acrylic polymer particles of the present invention for the manufacture of separators are Acrylic polymers are crosslinked with crosslinking agents having (meth)acryloyl groups and allyl groups.

[0012] Generally, when acrylic polymer particles are dispersed in a liquid medium used in the production of a separator made of polyamide, such as an aprotic polar liquid medium like N-methylpyrrolidone, or a mixed liquid medium containing these aprotic liquid media, they may dissolve or swell, and as a result, the variation in particle size may become large.

[0013] In contrast, the crosslinked acrylic polymer particles having the above configuration have appropriate chemical bonds formed. As a result, even when dispersed in the above liquid medium, swelling is suppressed, and as a result, a controlled porosity of the separator can be achieved. Further, the crosslinked acrylic polymer particles having the above configuration can be thermally decomposed at a relatively low temperature and the residue after heat treatment is reduced because appropriate strength chemical bonds are formed, thereby suppressing the deterioration of the separator characteristics due to the heat during decomposition.

[0014] In the present invention, the "5% weight loss temperature" means the temperature at which the mass decreases by 5% when a 20 mg sample is heated at a heating rate of 20 °C / min in nitrogen in thermogravimetric analysis (TGA). This 5% weight loss temperature may be 170 °C or higher, 175 °C or higher, 180 °C or higher, or 185 °C or higher. This analysis can be performed using, for example, Thermo plus EVO DSC8230 (Rigaku).

[0015] The volume average particle diameter of the crosslinked acrylic polymer particles is preferably 1.0 μm or less, 900 nm or less, 800 nm or less, 700 nm or less, 600 nm or less, 500 nm or less, or 450 nm or less from the viewpoint of favorably controlling the porosity of the separator. This average particle diameter may be 50 nm or more, 70 nm or more, 100 nm or more, 120 nm or more, 150 nm or more, 170 nm or more, 200 nm or more, 220 nm or more, 250 nm or more, 280 nm or more, or 300 nm or more. This average particle diameter means the value of the histogram average particle diameter (D50) based on the scattering intensity distribution measured by the dynamic light scattering method. The measurement by the dynamic light scattering method can be performed using, for example, DelsaMax CORE (Beckman Coulter).

[0016] Hereinafter, each component of the present invention will be described.

[0017] 〈Acrylic polymer〉 The acrylic polymer may be, for example, poly(meth)acrylic acid, polymethyl(meth)acrylate, polyethyl(meth)acrylate, polypropyl(meth)acrylate, polybutyl(meth)acrylate, polyisobutyl(meth)acrylate, polypentyl(meth)acrylate, polyhexyl(meth)acrylate, poly-2-ethylhexyl(meth)acrylate, etc.

[0018] [[ID=I3]] 〈Crosslinking agent〉 The crosslinking agent is a crosslinking agent having a (meth)acryloyl group and an allyl group. The crosslinking agent may have a (meth)acryloyl group and an allyl group at both ends.

[0019] The crosslinking of the crosslinked acrylic polymer particles is carried out by a crosslinking agent having a methacryloyl group and an allyl group. This makes it possible to lower the 5% weight loss temperature, satisfy the above volume average particle diameter, and further provide a crosslinking strength that is sufficiently appropriate to suppress the residue after swelling and heat treatment. As such a crosslinking agent, an ester of (meth)acrylic acid and an allyl unsaturated alcohol can be used.

[0020] In this specification, "(meth)acrylic acid" means acrylic acid or methacrylic acid.

[0021] In this specification, "allylic unsaturated alcohol" refers to an alcohol having an allyl group at its terminus. Examples of such allyllic unsaturated alcohols include 2-propen-1-ol (allyl alcohol), cis-2-buten-1-ol, trans-2-buten-1-ol, 3-buten-2-ol, etc. That is, the above ester may be an ester of methacrylic acid and allyl alcohol (allyl methacrylate).

[0022] From the viewpoint of suppressing the amount of residue after heat treatment, it is preferable that the content of the crosslinking agent-based structure be 20% by mass or less, 17% by mass or less, 15% by mass or less, or 13% by mass or less, relative to the mass of the crosslinked acrylic polymer particles. This content may be 1% by mass or more, 3% by mass or more, or 5% by mass or more, relative to the mass of the crosslinked acrylic polymer particles. This content can be estimated using the following formula, where the mass B of the crosslinking agent is the sum of the mass A of the acrylic polymer used for the production of the crosslinked acrylic polymer particles and the mass B of the crosslinking agent used for this production: B × 100 / (A + B)

[0023] Manufacturing method for cross-linked acrylic polymer particles The crosslinked acrylic polymer particles of the present invention can be produced, for example, by emulsion polymerization. Emulsion polymerization is a method comprising the steps of preparing an oil phase, preparing an aqueous phase, and mixing the oil phase and the aqueous phase to emulsify the components of the oil phase before polymerization.

[0024] The oil phase contains acrylic monomers and a crosslinking agent.

[0025] Examples of acrylic monomers that can be used include (meth)acrylic acid, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[0026] The above-mentioned crosslinking agents can be used as crosslinking agents.

[0027] From the viewpoint of ensuring that the content of the crosslinking agent-based structure is within the above range, it is preferable that the ratio of the mass of the crosslinking agent to the mass of the acrylic monomer used is 0.01 or more, 0.03 or more, or 0.05 or more, and 0.25 or less, 0.23 or less, 0.20 or less, 0.18 or less, 0.15 or less, or 0.13 or less.

[0028] The aqueous phase may contain water, a surfactant, and a polymerization initiator.

[0029] As for the water, ion-exchanged water, distilled water, etc., can be used.

[0030] The surfactant is not particularly limited, and cationic surfactants, anionic surfactants, and nonionic surfactants can be used.

[0031] Examples of cationic surfactants that can be used include ammonium salt-based surfactants such as tetramethylammonium chloride, and alkylamine salt-type surfactants such as monomethylamine hydrochloride.

[0032] Examples of anionic surfactants that can be used include carboxylic acid-type surfactants such as sodium octanoate and sulfonic acid-based surfactants such as sodium dialkyl sulfosuccinate.

[0033] Nonionic surfactants that can be used include, for example, ester-type surfactants such as glyceryl laurate, and ether-based surfactants such as polyoxyethylene alkyl ethers.

[0034] The process of emulsifying and further polymerizing the components of the oil phase can be carried out by adding the oil phase to the aqueous phase and emulsifying and mixing it while heating it to a predetermined temperature using a homogenizer or the like.

[0035] For example, ammonium persulfate can be used as a polymerization initiator.

[0036] Cross-linked acrylic polymer particle dispersion The crosslinked acrylic polymer particle dispersion of the present invention is Liquid medium, and Cross-linked acrylic polymer particles dispersed in a liquid medium It contains.

[0037] The crosslinked acrylic polymer particle dispersion of the present invention may further contain polyamic acid as a polyimide precursor.

[0038] (liquid medium) The liquid medium may be, for example, a liquid medium commonly used in the manufacture of polyimide separators. As the liquid medium, an aprotic polar liquid medium or a protic polar solvent can be used, and among these, the use of an aprotic polar liquid medium is preferred from the viewpoint of suppressing swelling.

[0039] Aprotic polar liquid media are generally solvents that do not contain acidic hydrogen. Examples of aprotic polar liquid media include N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone.

[0040] Protic polar liquid media are generally solvents containing acidic hydrogen. Examples of protic polar liquid media include phenolic liquid media, monohydric alcohol liquid media, and polyhydric alcohol liquid media.

[0041] As a phenolic liquid medium, for example, cresols can be used.

[0042] Examples of monohydric alcohol-based liquid media that can be used include ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butyl alcohol, 1-pentanol, isoamyl alcohol, sec-amyl alcohol, 3-pentanol, tert-amyl alcohol, n-hexanol, etc.

[0043] Examples of polyhydric alcohol-based liquid media that can be used include glycol-based liquid media such as propylene glycol, triethylene glycol, tetraethylene glycol, diglycerin, polyethylene glycol with a molecular weight of 600 or less, and glycerin.

[0044] (Cross-linked acrylic polymer particles) As cross-linked acrylic polymer particles, for example, the above-mentioned cross-linked acrylic polymer particles can be used.

[0045] From the viewpoint of good interoperability, the content of cross-linked acrylic polymer particles is preferably 20% by mass or more, 25% by mass or more, 30% by mass or more, or 35% by mass or more, based on the total mass of the cross-linked acrylic polymer particle dispersion. This content may be 70% by mass or less, 65% by mass or less, 60% by mass or less, 55% by mass or less, 50% by mass or less, or 45% by mass or less, based on the total mass of the cross-linked acrylic polymer particle dispersion.

[0046] (Polyamic acid) Polyamic acids are polymers of tetracarboxylic acids and diamines, and are precursors of polyimides obtained by equimolar polymerization of at least one tetracarboxylic acid and one diamine. Polyamic acids can be obtained by polymerizing the following tetracarboxylic acid acid anhydrides, particularly acid dianhydrides, with diamines.

[0047] The polyamic acid content is preferably 10% by mass or more, 15% by mass or more, 20% by mass or more, 25% by mass or more, or 30% by mass or more, based on the total mass of the cross-linked acrylic polymer particle dispersion, from the viewpoint of suppressing the porosity of the separator and, as a result, suppressing penetration by lithium. The content is preferably 40% by mass or less, 35% by mass or less, or 33% by mass or less, based on the total mass of the cross-linked acrylic polymer particle dispersion, from the viewpoint of creating good interconnected pores and, as a result, improving lithium ion permeability.

[0048] The polyamic acid content is preferably 100 parts by mass or more, 150 parts by mass or more, 170 parts by mass or more, 200 parts by mass or more, or 220 parts by mass or more per 100 parts by mass of crosslinked acrylic polymer particles in the crosslinked acrylic polymer particle dispersion, from the viewpoint of suppressing the porosity of the separator and, as a result, suppressing penetration by lithium. The content is preferably 500 parts by mass or less, 450 parts by mass or less, 400 parts by mass or less, 350 parts by mass or less, 300 parts by mass or less, 280 parts by mass or less, or 250 parts by mass or less per 100 parts by mass of crosslinked acrylic polymer particles in the crosslinked acrylic polymer particle dispersion, from the viewpoint of creating good interconnecting pores and, as a result, improving lithium ion permeability.

[0049] (Polyamic acid: tetracarboxylic acid) The tetracarboxylic acids that make up polyamic acids are ethylenetetracarboxylic acid, butanetetracarboxylic acid, cyclopentanetetracarboxylic acid, cyclohexanetetracarboxylic acid, 1,2,4,5-cyclohexanetetracarboxylic acid, 1,2,3,4-cyclohexanetetracarboxylic acid, pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid-1,2,4,5-), 1,1-bis(2,3-dicarboxyphenyl)ethane, bis(2,3-dicarboxyphenyl)methane, bis(3,4-dicarboxyphenyl)methane, 3,3',4,4'-biphenyltetracarboxylic acid, 2,2,6,6-biphenyltetracarboxylic acid, 2,2-bis(3,4-dicarboxyphenyl)propane, 2,2-bis(2,3-dicarboxyphenyl)propane, 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane, and 2,2-bis(2,3-di One or more of the following can be used: carboxyphenyl)-1,1,1,3,3,3-hexafluoropropane, bis(3,4-dicarboxyphenyl)sulfone, bis(3,4-dicarboxyphenyl) ether, bis(2,3-dicarboxyphenyl) ether, 3,3',4,4'-benzophenonetetracarboxylic acid, 2,2',3,3'-benzophenonetetracarboxylic acid, 4,4-(p-phenylenedioxy)diphthalic acid, 4,4-(m-phenylenedioxy)diphthalic acid, 1,2,5,6-naphthalenetetracarbone, 1,4,5,8-naphthalenetetracarboxylic acid, 2,3,6,7-naphthalenetetracarboxylic acid, 1,2,3,4-benzenetetracarboxylic acid, 3,4,9,10-perylenetetracarboxylic acid, 2,3,6,7-anthracenetetracarboxylic acid, 1,2,7,8-phenanthrenetetracarboxylic acid, 9,9-bisphthalate fluorene, etc.

[0050] (Polyamic acid: diamine) As the diamines constituting polyamic acid, fatty acid diamines, aromatic diamines, etc., can be used individually or in combination.

[0051] As the aliphatic diamine, those with approximately 2 to 15 carbon atoms can be preferably used, such as pentamethylenediamine, hexamethylenediamine, and heptamethylenediamine.

[0052] As aromatic diamines, diamino compounds having one or about 2 to 10 phenyl groups attached can be preferably used, such as phenylenediamine and its derivatives, diaminodiphenyl compounds and their derivatives, diaminotriphenyl compounds and their derivatives, diaminonaphthalene and its derivatives, aminophenylaminoindan and its derivatives, diaminotetraphenyl compounds and their derivatives, diaminohexaphenyl compounds and their derivatives, and cardo-type full orangeamine derivatives.

[0053] As the phenylenediamine, m-phenylenediamine, p-phenylenediamine, etc., can be used, and as the phenylenediamine derivative, a diamine to which an alkyl group such as a methyl group or an ethyl group is attached, such as 2,4-triphenylenediamine, can be used.

[0054] Diaminodiphenyl compounds are formed by the bonding of two aminophenyl groups to each other via other groups. These bonds include ether bonds, sulfonyl bonds, thioether bonds, alkylene or its derivative groups, imino bonds, azo bonds, phosphine oxide bonds, amide bonds, and ureylene bonds. Alkylene bonds typically have 1 to 6 carbon atoms, and their derivative groups are formed by the substitution of one or more hydrogen atoms in the alkylene group with halogen atoms or the like.

[0055] Examples of diaminodiphenyl compounds include 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl ketone, and 3,4'-diaminodiphenyl ketone. Examples include ton, 2,2-bis(p-aminophenyl)propane, 2,2'-bis(p-aminophenyl)hexafluoropropane, 4-methyl-2,4-bis(p-aminophenyl)-1-pentene, 4-methyl-2,4-bis(p-aminophenyl)-2-pentene, iminodianiline, 4-methyl-2,4-bis(p-aminophenyl)pentane, bis(p-aminophenyl)phosphine oxide, 4,4'-diaminoazobenzene, 4,4'-diaminodiphenylurea, 4,4'-diaminodiphenylamide, etc.

[0056] Diaminotriphenyl compounds consist of two aminophenyl groups and one phenylene group, each bonded via other groups, with the other groups being the same as those selected for diaminodiphenyl compounds.

[0057] Examples of diaminotriphenyl compounds include 1,3-bis(m-aminophenoxy)benzene, 1,3-bis(p-aminophenoxy)benzene, and 1,4-bis(p-aminophenoxy)benzene. Examples of diaminonaphthalenes include 1,5-diaminonaphthalene and 2,6-diaminonaphthalene. An example of aminophenylaminoindanes is 5 or 6-amino-1-(p-aminophenyl)-1,3,3-trimethylindanes.

[0058] Examples of diaminotetraphenyl compounds that can be used include 4,4'-bis(p-aminophenoxy)biphenyl, 2,2'-bis[p-(p'-aminophenoxy)phenyl]propane and 2,2'-bis[p-(p'-aminophenoxy)biphenyl]propane, and 2,2'-bis[p-(m-aminophenoxy)phenyl]benzophenone.

[0059] As a cardo-type fluorene derivative, 9,9-bisaniline fluorene can be used.

[0060] Furthermore, these aromatic diamines may be compounds in which the hydrogen atoms are substituted with at least one substituent selected from the group consisting of halogen atoms, methyl groups, methoxy groups, cyano groups, phenyl groups, and the like.

[0061] Method for manufacturing porous separators The present invention's method for manufacturing a porous separator is: The above crosslinked polymethyl methacrylate dispersion containing polyamic acid is applied to the substrate to be coated, and By heat-treating the coated dispersion, the polyamic acid is reacted to form a polyimide matrix, and the crosslinked acrylic polymer particles are eliminated to form interconnected pores. Includes.

[0062] The substrate to be coated can be any substrate that is inert to the dispersion and has a flat surface that allows the separator to be easily peeled off after drying. Examples include glass plates, polymer sheets such as polyethylene terephthalate, polypropylene, aramid, cellulose, and polytetrafluoroethylene, and metal sheets such as stainless steel.

[0063] The heat treatment temperature is not particularly limited as long as it is a temperature that can react the polyamic acid to form a polyimide matrix and eliminate the crosslinked acrylic polymer particles, for example, it may be 300°C or higher, 320°C or higher, 330°C or higher, 340°C or higher, or 345°C or higher, and may also be 500°C or lower, 480°C or lower, 450°C or lower, 400°C or lower, 380°C or lower, or 360°C or lower.

[0064] This heat treatment can be carried out in an atmospheric environment or in an inert atmosphere with a low oxygen concentration, such as a nitrogen atmosphere. When the heat treatment is carried out in an inert atmosphere, the oxygen concentration may be 10 vol% or less, 5 vol% or less, 4 vol% or less, 3 vol% or less, 2 vol% or less, or 1 vol% or less, and may also be 0 vol% or greater than 0 vol%. [Examples]

[0065] The present invention will be specifically described by examples and comparative examples, but the present invention is not limited thereto.

[0066] Preparation of polymethyl methacrylate particles <Example 1> A 2-liter flask was fitted with a stirrer, reflux condenser, thermometer, nitrogen gas inlet tube, and 1000 ml separatory funnel for monomer addition, and placed in a hot water bath. The following components were added to this flask to prepare an aqueous phase. The internal temperature of this aqueous phase was raised to 50°C while introducing nitrogen gas: Water: Distilled water 639.2 parts by mass Surfactant: Sodium dialkyl sulfosuccinate (referred to as "SDASS" in Table 1) 0.7 parts by mass Initiator: Ammonium persulfate (APS) 0.6 parts by mass

[0067] On the other hand, an oil phase was prepared by mixing 339.2 parts by mass of methyl methacrylate (MMA) as a monomer with 20 parts by mass of allyl methacrylate (AMA) as a crosslinking agent.

[0068] This oil phase was added to the aqueous phase, maintained at a temperature of approximately 50°C, through the separatory funnel under stirring for 3 hours to carry out emulsion polymerization. After further aging for 5 hours, polymerization was completed, yielding 1000 parts by mass of a particle dispersion.

[0069] <Examples 2-3 and Comparative Examples 1-6> Particles for Examples 2-3 and Comparative Examples 1-6 were prepared in the same manner as in Example 1, except that the manufacturing conditions were changed as shown in Table 1. In Table 1, "EMA" refers to ethyl methacrylate.

[0070] Furthermore, the crosslinking agents shown in Table 1 are as follows: Acrylic A: Viscoat #195, Osaka Organic Chemical Industry Co., Ltd. (1,4-butanediol diacrylate) Acrylic B: Viscoat #295, Osaka Organic Chemical Industry Co., Ltd. (Trimethylolpropane Triacrylate) TAIC: Triallyl isocyanurate

[0071] Evaluation as acrylic polymer particles <Measurement of physical properties> (Volume-average particle size) The volume-average particle size of the obtained particles was measured using dynamic light scattering with a DelsaMax CORE (Beckman Coulter).

[0072] (5% weight loss temperature) Using a thermogravimetric analyzer (Rigaku Corporation), 20 mg of the obtained particles were heated in nitrogen at a heating rate of 20°C / min, and the temperature was measured when the mass decreased by 5%.

[0073] <Dispersibility> 0.5 g of the obtained particles were added to 1.0 g of N-methylpyrrolidone (NMP) as a liquid medium, stirred, and observed visually. The evaluation criteria were as follows: A: The dispersion did not become gel-like, and the particles were well dispersed. B: The dispersion became gel-like.

[0074] <Residue rate> The evaluation criteria are as follows: A: The particle's 5% weight loss temperature is within the range of 190°C to 300°C. B: The particle's 5% weight loss temperature is below 190°C or above 300°C.

[0075] 《Separator fabrication and evaluation of residue rate》 A slurry was prepared by dissolving 7.0 g of polyamic acid in 13.3 g of N-methylpyrrolidone (NMP) as a liquid medium, and then mixing in 3.0 g of prepared acrylic polymer particles. The solid content concentration in the slurry was 43.0% by mass. This slurry was coated onto a glass substrate and heat-treated at 350°C for 2 hours in a nitrogen atmosphere containing 2 vol% oxygen to obtain a porous separator with interconnecting pores.

[0076] The residue rate was calculated using the following formula, based on the mass X of the reaction system after heat treatment, the theoretical mass Y of the polyimide obtained from the polyamic acid used, and the mass Z of the acrylic polymer particles used: {(XY)×100} / Z

[0077] Evaluation as a separator <exterior> The obtained separators were visually inspected. The evaluation criteria were as follows: A: A uniform separator was obtained. B: A uniform separator could not be obtained.

[0078] <Uniformity of the connecting holes> The uniformity of the communication holes in the fabricated separators was observed using an electron microscope S-3400N (Hitachi High-Technologies Corporation). The evaluation criteria were as follows: A: It had uniform communication holes. B: It did not have uniform communication holes.

[0079] Table 1 shows the configurations and evaluation results of the examples and comparative examples.

[0080] [Table 1]

[0081] Table 1 shows that the particles in the examples in which the acrylic polymer was crosslinked with a crosslinking agent having (meth)acryloyl and allyl groups exhibited good dispersibility and a low residue rate, while the separators obtained using these particles had good film-forming properties and appearance.

Claims

1. Crosslinked acrylic polymer particles for the manufacture of separators, The acrylic polymer is crosslinked with a crosslinking agent having (meth)acryloyl groups and allyl groups. The content of the crosslinking agent-based structure is 5% by mass or more and 20% by mass or less relative to the mass of the crosslinked acrylic polymer particles, and The 5% weight loss temperature in thermogravimetric analysis is less than 190°C. Cross-linked acrylic polymer particles.

2. The crosslinked acrylic polymer particles according to claim 1, wherein the crosslinking agent is an ester of (meth)acrylic acid and an allyl unsaturated alcohol.

3. The crosslinked acrylic polymer particles according to claim 1 or 2, wherein the volume-average particle diameter measured by dynamic light scattering is 1.0 μm or less.

4. The crosslinked acrylic polymer particles according to claim 3, wherein the volume-average particle diameter is 50 nm to 500 nm.

5. The crosslinked acrylic polymer particles according to any one of claims 1 to 4, wherein the acrylic polymer is polymethyl methacrylate.

6. liquid medium, Dispersed in the aforementioned liquid medium are crosslinked acrylic polymer particles, and Polyamic acid It contains, The aforementioned crosslinked acrylic polymer particles are formed by crosslinking the acrylic polymer with a crosslinking agent having (meth)acryloyl groups and allyl groups. Crosslinked acrylic polymer particle dispersion for the manufacture of separators.

7. The dispersion according to claim 6, wherein the liquid medium is an aprotic polar liquid medium.

8. Applying the dispersion according to claim 6 or 7 to a substrate to be coated, By heat-treating the coated dispersion, the polyamic acid is reacted to form a polyimide matrix, and the crosslinked acrylic polymer particles are eliminated to form interconnected pores. A method for manufacturing a porous separator, including the following.

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