Raw material for coating material for secondary battery separator, coating material for secondary battery separator, secondary battery separator, manufacturing method for secondary battery separator, and secondary battery

Abstract

This coating starting material for a secondary battery separator contains a conjugated polymer of: a water-soluble polymer having an SP value of 13.0 (cal / cm3)1 / 2 or higher; and a water-insoluble polymer having an SP value less than 13.0(cal / cm3)1 / 2. The water-soluble polymer contains a first reactive functional group. The water-insoluble polymer contains a second reactive functional group capable of chemically bonding to the first reactive functional group. At least part of the first reactive functional group and at least part of the second reactive functional group are chemically bonded to one another in said conjugated polymer.

Description

[Technical field]

[0001] The present invention relates to a raw material for a coating material for a secondary battery separator, a coating material for a secondary battery separator, a secondary battery separator, a method for producing a secondary battery separator, and a secondary battery. [Background technology]

[0002] Conventionally, a separator is provided in a secondary battery to separate the positive electrode from the negative electrode and to allow ions in the electrolyte to pass through.

[0003] As such a separator, for example, a polyolefin porous film is known, and it is also known to provide various functional layers on the surface of the separator.

[0004] As a functional layer formed on a separator, for example, a functional layer obtained by applying a functional layer composition containing alumina and a resin to a polyethylene separator substrate and drying it is known. As a functional layer composition, a mixture of a water-soluble polymer obtained by polymerizing acrylamide, methacrylic acid, and dimethylacrylamide, a particulate polymer obtained by polymerizing n-butyl acrylate, methacrylic acid, acrylonitrile, N-methylolacrylamide, and allyl glycidyl ether, alumina, a dispersant, and a surfactant has been proposed (for example, see Patent Document 1 (Example 1)). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2017 / 026095 Summary of the Invention [Problem to be solved by the invention]

[0006] On the other hand, if the shape of the separator changes due to heat shrinkage, there is a possibility of a short circuit between the positive electrode and the negative electrode. Therefore, the functional layer is required to have heat resistance. However, the functional layer has a problem that its heat resistance is insufficient.

[0007] In addition, the separator of a secondary battery needs to pass ions in order to generate electricity, and therefore the functional layer needs to be air permeable. However, the functional layer has a drawback in that it reduces the air permeability of the separator.

[0008] Furthermore, the functional layer is required to have improved adhesion to the separator, but the above-mentioned functional layer has a problem in that it does not have sufficient adhesion to the separator.

[0009] In addition, from the viewpoint of productivity of the functional layer, the composition for the functional layer is required to have storage stability, uniform dispersibility, and low viscosity.

[0010] The present invention relates to a coating material raw material for secondary battery separators, which can provide secondary battery separators that have excellent heat resistance, air permeability, and adhesion, and which are also excellent in storage stability, uniform dispersion, and low viscosity; a coating material for secondary battery separators that contains the coating material raw material for secondary battery separators; a secondary battery separator that has a coating film of the coating material for secondary battery separators; a manufacturing method for the secondary battery separator; and a secondary battery that has the secondary battery separator. [Means for solving the problem]

[0011] The present invention [1] has an SP value of 13.0 (cal / cm 3 ) 1 / 2 The above water-soluble polymer and SP value 13.0 (cal / cm 3 ) 1 / 2the water-soluble polymer comprises a composite polymer with a water-insoluble polymer of less than 1000 nm, the water-soluble polymer comprises a first reactive functional group, the water-insoluble polymer comprises a second reactive functional group capable of chemically bonding to the first reactive functional group, and in the composite polymer, at least a portion of the first reactive functional group and at least a portion of the second reactive functional group are chemically bonded to each other.

[0012] The present invention [2] includes the coating material raw material for secondary battery separators described in the above [1], in which the first reactive functional group of the water-soluble polymer includes a carboxy group, and the second reactive functional group of the water-insoluble polymer includes a glycidyl group.

[0013] The present invention [3] includes the coating material raw material for secondary battery separators according to the above [1] or [2], wherein the water-soluble polymer has a repeating unit derived from a (meth)acrylamide and a repeating unit derived from a carboxyl group-containing vinyl monomer, and the water-insoluble polymer has a repeating unit derived from a (meth)acrylic acid alkyl ester and a repeating unit derived from a glycidyl group-containing vinyl monomer.

[0014] The present invention [4] includes the coating material raw material for secondary battery separator according to any one of the above [1] to [3], wherein the water-soluble polymer is 50 parts by mass or more and 99 parts by mass or less, and the water-insoluble polymer is 1 part by mass or more and 50 parts by mass or less, relative to 100 parts by mass of the total amount of the water-soluble polymer and the water-insoluble polymer.

[0015] The present invention [5] includes the raw material for a coating material for a secondary battery separator according to any one of the above [1] to [4], wherein the water-soluble polymer has a weight average molecular weight of 10,000 or more and 200,000 or less.

[0016] The present invention [6] includes the raw material for a coating material for a secondary battery separator according to any one of the above [1] to [5], wherein the water-soluble polymer has a glass transition temperature of 150°C or more and 240°C or less.

[0017] The present invention [7] includes the raw material for a coating material for a secondary battery separator according to any one of the above [1] to [6], wherein the water-insoluble polymer has a glass transition temperature of −40° C. or more and 50° C. or less.

[0018] The present invention [8] includes a coating material for a secondary battery separator, which includes the coating material raw material for a secondary battery separator according to any one of the above [1] to [7].

[0019] The present invention [9] further includes the coating material for a secondary battery separator according to the above [8], which contains an inorganic filler and a dispersant.

[0020] The present invention

[10] includes a secondary battery separator comprising a porous membrane and a coating film of the coating material for secondary battery separator according to [8] or [9] above, which is disposed on at least one side of the porous membrane.

[0021] The present invention

[11] includes a method for producing a secondary battery separator, comprising the steps of: preparing a porous membrane; and applying the coating material for a secondary battery separator according to the above [8] or [9] to at least one side of the porous membrane.

[0022] The present invention

[12] includes a secondary battery comprising a positive electrode, a negative electrode, and the secondary battery separator described in the above

[10] disposed between the positive electrode and the negative electrode. Effect of the Invention

[0023] The coating material raw material for secondary battery separators of the present invention comprises a composite polymer of a water-soluble polymer and a water-insoluble polymer, the water-soluble polymer comprises a first reactive functional group, the water-insoluble polymer comprises a second reactive functional group capable of chemically bonding to the first reactive functional group, and in the composite polymer, at least a portion of the first reactive functional group and at least a portion of the second reactive functional group are chemically bonded to each other.

[0024] Therefore, the coating material raw material for secondary battery separators of the present invention has excellent storage stability, uniform dispersion, and low viscosity. Furthermore, the coating material raw material for secondary battery separators of the present invention can provide secondary battery separators with excellent heat resistance, air permeability, and adhesion.

[0025] Since the coating material for secondary battery separators of the present invention contains the above-mentioned raw materials for the coating material for secondary battery separators, it is possible to improve the productivity of secondary battery separators. Furthermore, the coating material for secondary battery separators of the present invention can provide secondary battery separators having excellent heat resistance, air permeability, and adhesion.

[0026] The secondary battery separator of the present invention has a coating film of the above-mentioned coating material for secondary battery separators, and therefore has excellent productivity, heat resistance, air permeability and adhesion.

[0027] According to the method for producing a secondary battery separator of the present invention, a secondary battery separator excellent in heat resistance, air permeability and adhesion can be produced efficiently.

[0028] The secondary battery of the present invention is excellent in productivity, heat resistance, air permeability and adhesion because it includes the above-mentioned secondary battery separator. As a result, the secondary battery of the present invention is excellent in productivity, heat resistance, air permeability and adhesion. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] The coating material raw material for secondary battery separators of the present invention includes a composite polymer of a water-soluble polymer and a water-insoluble polymer. The composite polymer includes a water-soluble polymer and a water-insoluble polymer, and the water-soluble polymer and the water-insoluble polymer are chemically bonded to each other. That is, the composite polymer is formed by chemically bonding the water-soluble polymer and the water-insoluble polymer.

[0030] The water-soluble polymer is a polymer that improves the solubility in water of the raw material of the coating material for the secondary battery separator. The water-soluble polymer is relatively hydrophilic, and the SP value (solubility parameter) of the water-soluble polymer is 13.0 (cal / cm 3) 1 / 2 That's all.

[0031] The SP value can be calculated using the calculation software CHEOPS (version 4.0) from Million Zillion Software, Inc. The calculation method used in the calculation software is described in Computational Materials Science of Polymers (AAAskadskii, Cambridge Intl Science Pub (2005 / 12 / 30)) Chapter XII (hereinafter the same).

[0032] More specifically, the SP value (solubility parameter) of the water-soluble polymer is 13.0 (cal / cm 3 ) 1 / 2 More preferably, 13.2 (cal / cm 3 ) 1 / 2 More preferably, 13.4 (cal / cm 3 ) 1 / 2 The SP value (solubility parameter) of the water-soluble polymer is, for example, 20.0 (cal / cm 3 ) 1 / 2 Preferably, 18.0 (cal / cm 3 ) 1 / 2 Less than or equal to 16.0 (cal / cm 3 ) 1 / 2 The following is the result.

[0033] The water-soluble polymer contains a first reactive functional group. The first reactive functional group is a functional group for chemically bonding to a second reactive functional group (described later) of a water-insoluble polymer (described later). Examples of the first reactive functional group include a carboxy group, a hydroxyl group, a glycidyl group, an isocyanate group, and a phosphate group. From the viewpoint of ease of production of the composite polymer, a carboxy group is preferably used as the first reactive functional group.

[0034] The water-soluble polymer is obtained by polymerizing a water-soluble polymer raw material (monomer composition) by a known method. The water-soluble polymer raw material is appropriately selected so that the SP value of the water-soluble polymer falls within the above range and the first reactive functional group is contained in the water-soluble polymer.

[0035] More specifically, the water-soluble polymer raw material contains, for example, (meth)acrylamide and a first reactive functional group-containing monomer. Note that, (meth)acryl refers to acrylic and / or methacrylic (hereinafter the same).

[0036] If the water-soluble polymer raw material contains (meth)acrylamide, the water-soluble polymer has a repeating unit derived from (meth)acrylamide, and therefore the water solubility (SP value) can be well adjusted.

[0037] The (meth)acrylamides include acrylamide and methacrylamide, and preferably methacrylamide.

[0038] The first reactive functional group-containing monomer is a monomer containing the above-mentioned first reactive functional group and an ethylenic double bond. Examples of the first reactive functional group-containing monomer include a carboxyl group-containing vinyl monomer, a hydroxyl group-containing vinyl monomer, a glycidyl group-containing vinyl monomer, an isocyanate group-containing vinyl monomer, and a phosphoric acid group-containing vinyl monomer.

[0039] Examples of the carboxyl group-containing vinyl monomer include monocarboxylic acid, dicarboxylic acid, and their salts. Examples of the monocarboxylic acid include (meth)acrylic acid. Examples of the dicarboxylic acid include itaconic acid, maleic acid, fumaric acid, itaconic anhydride, maleic anhydride, and fumaric anhydride. These can be used alone or in combination of two or more.

[0040] Examples of hydroxyl group-containing vinyl monomers include hydroxymethyl(meth)acrylate, 2-hydroxyethyl(meth)acrylate, 3-hydroxypropyl(meth)acrylate, 1-methyl-2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate, and 4-hydroxybutyl(meth)acrylate.

[0041] Examples of glycidyl group-containing vinyl monomers include glycidyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate glycidyl ether, and allyl glycidyl ether.

[0042] Examples of isocyanate group-containing vinyl monomers include isocyanatomethyl (meth)acrylate, 2-isocyanatoethyl (meth)acrylate, 3-isocyanatopropyl (meth)acrylate, 1-methyl-2-isocyanatoethyl (meth)acrylate, 2-isocyanatopropyl (meth)acrylate, and 4-isocyanatobutyl (meth)acrylate.

[0043] Examples of the phosphoric acid group-containing vinyl monomer include acid phosphooxyethyl (meth)acrylate and mono(2-hydroxyethyl (meth)acrylate) phosphate.

[0044] These first reactive functional group-containing monomers can be used alone or in combination of two or more. When two or more types of first reactive functional group-containing monomers are used in combination, the type of the first reactive functional group-containing monomer is appropriately selected so that the first reactive functional groups are not bonded to each other.

[0045] As the first reactive functional group-containing monomer, a carboxyl group-containing vinyl monomer is preferably used. If the water-soluble polymer raw material contains a carboxyl group-containing vinyl monomer, the water-soluble polymer has a repeating unit derived from the carboxyl group-containing vinyl monomer, and therefore has excellent water solubility.

[0046] The water-soluble polymer raw material may contain a copolymerizable monomer (hereinafter referred to as a first copolymerizable monomer) as an optional component. Examples of the first copolymerizable monomer include a monomer copolymerizable with (meth)acrylamide and / or a first reactive functional group-containing monomer.

[0047] Examples of the first copolymerizable monomer include (meth)acrylic acid alkyl esters. Examples of (meth)acrylic acid alkyl esters include alkyl (meth)acrylates having an alkyl portion with 1 to 20 carbon atoms. Examples of such alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, n-amyl (meth)acrylate, isoamyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, and octadecyl (meth)acrylate. These can be used alone or in combination of two or more.

[0048] Examples of the first copolymerizable monomer include a tertiary amino group-containing vinyl monomer, a quaternary ammonium group-containing vinyl monomer, a cyano group-containing vinyl monomer, a sulfonic acid group-containing vinyl monomer, and an acetoacetoxy group-containing vinyl monomer.

[0049] Examples of the tertiary amino group-containing vinyl monomer include N,N-dialkylaminoalkyl(meth)acrylate and N,N-dialkylaminoalkyl(meth)acrylamide. Examples of the N,N-dialkylaminoalkyl(meth)acrylate include N,N-dimethylaminoethyl(meth)acrylate, N,N-diethylaminoethyl(meth)acrylate, N,N-dimethylaminopropyl(meth)acrylate, N,N-di-t-butylaminoethyl(meth)acrylate, and N,N-dimethylaminobutyl(meth)acrylate. Examples of the N,N-dialkylaminoalkyl(meth)acrylamide include N,N-dimethylaminoethyl(meth)acrylamide, N,N-diethylaminoethyl(meth)acrylamide, and N,N-dimethylaminopropyl(meth)acrylamide.

[0050] Examples of the quaternary ammonium group-containing vinyl monomer include quaternized products obtained by reacting the above-mentioned tertiary amino group-containing monomer with a quaternizing agent. Examples of the quaternizing agent include epihalohydrin, benzyl halide, and alkyl halide.

[0051] An example of the cyano group-containing vinyl monomer is (meth)acrylonitrile.

[0052] Examples of the sulfonic acid group-containing vinyl monomer include allyl sulfonic acid, methallyl sulfonic acid, and acrylamido t-butyl sulfonic acid. Examples of the sulfonic acid group-containing vinyl monomer include salts. Examples of the salts include sodium salts, potassium salts, and ammonium salts. More specifically, examples of the salts of the sulfonic acid group-containing monomer include sodium allyl sulfonate, sodium methallyl sulfonate, and ammonium methallyl sulfonate.

[0053] An example of an acetoacetoxy group-containing vinyl monomer is acetoacetoxyethyl (meth)acrylate.

[0054] Further, examples of the first copolymerizable monomer include vinyl esters, aromatic vinyl monomers, unsaturated carboxylic acid amides (excluding (meth)acrylamide), heterocyclic vinyl compounds, vinylidene halides, α-olefins, dienes, and crosslinkable vinyl monomers. Examples of the vinyl esters include vinyl acetate and vinyl propionate. Examples of the aromatic vinyl monomers include styrene, α - Examples of the unsaturated carboxylic acid amide include, for example, N-methylol (meth)acrylamide. Examples of the heterocyclic vinyl compound include, for example, vinylpyrrolidone. Examples of the vinylidene halide compound include, for example, vinylidene chloride and vinylidene fluoride. Examples of the α-olefins include, for example, ethylene and propylene. Examples of the dienes include, for example, butadiene. Examples of the crosslinkable vinyl monomer include, for example, methylene bis (meth) acrylamide, divinylbenzene, polyethylene glycol chain-containing di (meth) acrylate, trimethylol propane tetraacrylate, pentaerythritol, tetra ... R Thorium triacrylate and pentaerythritol R Examples include toltetraacrylate.

[0055] These first copolymerizable monomers can be used alone or in combination of two or more kinds. As the first copolymerizable monomer, from the viewpoints of heat resistance and air permeability, a tertiary amino group-containing vinyl monomer is preferably used.

[0056] In addition, a first reactive functional group-containing monomer containing a type of first reactive functional group that cannot react with a second reactive functional group described later (or can react but hardly reacts in terms of reaction rate, etc.) due to a combination of the first reactive functional group and the second reactive functional group is classified as a first copolymerizable monomer. From the viewpoint of adjusting the degree of water solubility (SP value), a preferred example of the first copolymerizable monomer is a hydroxyl group-containing vinyl monomer as described above as the first reactive group-containing monomer.

[0057] Also, preferably, the first copolymerizable monomer does not contain a (meth)acrylic acid alkyl ester. That is, the water-soluble polymer raw material preferably does not contain a (meth)acrylic acid alkyl ester. More specifically, a monomer composition that does not contain a (meth)acrylic acid alkyl ester is preferably a water-soluble polymer raw material, and is differentiated from a water-insoluble polymer raw material described below.

[0058] In the water-soluble polymer raw material, the ratio of each monomer is appropriately selected so that the SP value of the water-soluble polymer falls within the above range and the water-soluble polymer contains the above first reactive functional group.

[0059] For example, the water-soluble polymeric raw material consists of (meth)acrylamide and a first reactive functional group-containing monomer, or consists of (meth)acrylamide, a first reactive functional group-containing monomer and a first copolymerizable monomer.

[0060] The water-soluble polymer raw material preferably consists of (meth)acrylamide and a carboxy group-containing vinyl monomer, or consists of (meth)acrylamide, a carboxy group-containing vinyl monomer and a first copolymerizable monomer.

[0061] From the viewpoint of obtaining excellent heat resistance, the content of (meth)acrylamide is, for example, 40 parts by mass or more, preferably 50 parts by mass or more, more preferably 60 parts by mass or more, and even more preferably 70 parts by mass or more, relative to 100 parts by mass of the total amount of the water-soluble polymer raw material. Also, from the viewpoint of obtaining excellent heat resistance, the content of (meth)acrylamide is, for example, 97 parts by mass or less, preferably 96 parts by mass or less, and more preferably 95 parts by mass or less, relative to 100 parts by mass of the total amount of the water-soluble polymer raw material.

[0062] The content of the first reactive functional group-containing monomer is, for example, 3 parts by mass or more, preferably 8 parts by mass or more, more preferably 10 parts by mass or more, relative to 100 parts by mass of the total amount of the water-soluble polymer raw material. The content of the first reactive functional group-containing monomer is, for example, 60 parts by mass or less, preferably 40 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less, relative to 100 parts by mass of the total amount of the water-soluble polymer raw material.

[0063] In addition, in the water-soluble polymer raw material, the content ratio of the first copolymerizable monomer is, for example, 40 parts by mass or less, preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and for example, 0 parts by mass or more, per 100 parts by mass of the total amount of the water-soluble polymer raw material.

[0064] The water-soluble polymer is obtained by polymerizing the water-soluble polymer raw material described above by the method described below. The content of the repeating units derived from each monomer in the water-soluble polymer is the same as the content of each monomer in the water-soluble polymer raw material.

[0065] That is, the content of the repeating unit derived from (meth)acrylamide is, for example, 40% by mass or more, preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, based on the total amount of the water-soluble polymer, from the viewpoint of obtaining excellent heat resistance. Also, the content of the repeating unit derived from (meth)acrylamide is, for example, 97% by mass or less, preferably 96% by mass or less, and more preferably 95% by mass or less, based on the total amount of the water-soluble polymer, from the viewpoint of obtaining excellent heat resistance.

[0066] The content of the repeating unit derived from the first reactive functional group-containing monomer is, for example, 3% by mass or more, preferably 8% by mass or more, more preferably 10% by mass or more, based on the total amount of the water-soluble polymer. The content of the repeating unit derived from the first reactive functional group-containing monomer is, for example, 60% by mass or less, preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less, based on the total amount of the water-soluble polymer.

[0067] In addition, the content of the repeating unit derived from the first copolymerizable monomer is, for example, 40 mass% or less, preferably 20 mass% or less, more preferably 15 mass% or less, and for example, 0 mass% or more, relative to the total amount of the water-soluble polymer.

[0068] The weight average molecular weight of the water-soluble polymer (weight average molecular weight in terms of standard polyethylene glycol / polyethylene oxide measured by GPC method) is, from the viewpoints of heat resistance and air permeability, for example, 5,000 or more, preferably 10,000 or more, more preferably 30,000 or more, and even more preferably 50,000 or more. Also, from the viewpoint of low viscosity, the weight average molecular weight of the water-soluble polymer (weight average molecular weight in terms of standard polyethylene glycol / polyethylene oxide measured by GPC method) is, for example, 500,000 or less, preferably 200,000 or less, more preferably 150,000 or less, even more preferably 100,000 or less, and particularly preferably 80,000 or less.

[0069] When the weight-average molecular weight of the water-soluble polymer is within the above range, it is possible to particularly improve the storage stability, uniform dispersibility, and low viscosity. The weight-average molecular weight is measured according to the method described in the Examples below.

[0070] From the viewpoints of heat resistance and air permeability, the glass transition temperature of the water-soluble polymer is, for example, 100° C. or higher, preferably 150° C. or higher, more preferably 200° C. or higher, and even more preferably 210° C. or higher. From the viewpoint of flexibility of the coating layer formed by applying the coating material for secondary battery separators, the glass transition temperature of the water-soluble polymer is, for example, 300° C. or lower, preferably 240° C. or lower, more preferably 230° C. or lower, and even more preferably 220° C. or lower.

[0071] If the glass transition temperature of the water-soluble polymer is within the above range, a secondary battery separator having excellent heat resistance, air permeability, and adhesion can be obtained, and further, the storage stability, uniform dispersion, and low viscosity can be improved. The glass transition temperature is calculated by the FOX formula (hereinafter the same).

[0072] The specific gravity of the water-soluble polymer is, for example, 1.02 or more, preferably 1.05 or more.The specific gravity of the water-soluble polymer is, for example, 1.20 or less, preferably 1.15 or less.

[0073] The water-insoluble polymer is a polymer that improves the adhesion of the raw material of the coating material for the secondary battery separator. The water-insoluble polymer is relatively hydrophobic, and the SP value (solubility parameter) of the water-insoluble polymer is 13.0 (cal / cm 3 ) 1 / 2 is less than.

[0074] More specifically, the SP value (solubility parameter) of the water-insoluble polymer is 13.0 (cal / cm 3 ) 1 / 2 Less than 12.5 (cal / cm 3 ) 1 / 2 Less than or equal to 12.0 (cal / cm 3 ) 1 / 2More preferably, 11.0 (cal / cm 3 ) 1 / 2 The SP value (solubility parameter) of the water-insoluble polymer is, for example, 7.0 (cal / cm 3 ) 1 / 2 More preferably, 8.0 (cal / cm 3 ) 1 / 2 More preferably, 9.0 (cal / cm 3 ) 1 / 2 That's all.

[0075] The water-insoluble polymer contains a second reactive functional group. The second reactive functional group is a functional group for chemically bonding to the first reactive functional group of the water-soluble polymer. Examples of the second reactive functional group include a carboxyl group, a hydroxyl group, a glycidyl group, an isocyanate group, and a phosphate group. The second reactive functional group is appropriately selected depending on the type of the first reactive functional group.

[0076] More specifically, for example, when the first reactive functional group contains a carboxy group, for example, a glycidyl group capable of bonding to a carboxyl group is selected as the second reactive functional group. Also, for example, when the first reactive functional group includes a hydroxyl group, the second reactive functional group is selected to be, for example, an isocyanate group capable of bonding to a hydroxyl group. Also, for example, when the first reactive functional group includes a glycidyl group, the second reactive functional group is selected to be, for example, a carboxyl group and / or a phosphate group capable of bonding to a glycidyl group. Also, for example, when the first reactive functional group includes an isocyanate group, the second reactive functional group is selected to be, for example, a hydroxyl group capable of bonding to an isocyanate group. Also, for example, when the first reactive functional group includes a phosphate group, case As the second reactive functional group, a glycidyl group capable of bonding to a phosphate group is selected. From the viewpoint of ease of production of the composite polymer, the second reactive functional group is preferably a glycidyl group.

[0077] The water-insoluble polymer is obtained by polymerizing a water-insoluble polymer raw material (monomer composition) by a known method. The water-soluble polymer raw material is appropriately selected so that the SP value of the water-insoluble polymer falls within the above range and the second reactive functional group is contained in the water-insoluble polymer.

[0078] More specifically, the water-insoluble polymer raw material (monomer composition) contains, for example, a (meth)acrylic acid alkyl ester and a second reactive functional group-containing monomer.

[0079] If the water-insoluble polymer raw material contains an alkyl (meth)acrylate, the water-insoluble polymer has repeating units derived from the alkyl (meth)acrylate, and therefore the water-insolubility (SP value) can be well adjusted.

[0080] Examples of the (meth)acrylic acid alkyl ester include the above-mentioned (meth)acrylic acid alkyl esters, and more specifically, alkyl (meth)acrylates having an alkyl moiety with 1 to 20 carbon atoms. These can be used alone or in combination of two or more kinds. As the (meth)acrylic acid alkyl ester, preferred examples include alkyl (meth)acrylates having an alkyl moiety with 1 to 4 carbon atoms, and more preferred examples include n-butyl (meth)acrylate.

[0081] The second reactive functional group-containing monomer is a monomer containing the above-mentioned second reactive functional group and an ethylenic double bond. Examples of the second reactive functional group-containing monomer include the above-mentioned carboxyl group-containing vinyl monomer, the above-mentioned hydroxyl group-containing vinyl monomer, the above-mentioned glycidyl group-containing vinyl monomer, the above-mentioned isocyanate group-containing vinyl monomer, and the above-mentioned phosphoric acid group-containing vinyl monomer.

[0082] These second reactive functional group-containing monomers can be used alone or in combination of two or more. When two or more types of second reactive functional group-containing monomers are used in combination, the type of second reactive functional group-containing monomer is appropriately selected so that the second reactive functional groups are not bonded to each other.

[0083] The second reactive functional group-containing monomer is appropriately selected depending on the type of the first reactive functional group-containing monomer, that is, the first reactive functional group and the second reactive functional group are appropriately selected so as to have the above-mentioned combination.

[0084] More specifically, for example, when the first reactive functional group-containing monomer contains a carboxyl group-containing vinyl monomer, the second reactive functional group is selected as a glycidyl group-containing vinyl monomer. Also, for example, when the first reactive functional group-containing monomer contains a hydroxyl group-containing vinyl monomer, the second reactive functional group is selected as an isocyanate group-containing vinyl monomer. Also, for example, when the first reactive functional group-containing monomer contains a glycidyl group-containing vinyl monomer, the second reactive functional group is selected as a carboxyl group-containing vinyl monomer and / or a phosphoric acid group-containing vinyl monomer. For example, when the first reactive functional group-containing monomer contains an isocyanate group-containing vinyl monomer, the second reactive functional group-containing monomer is selected to be a hydroxyl group-containing vinyl monomer. case As the second reactive functional group-containing monomer, a glycidyl group-containing vinyl monomer is selected.

[0085] As the second reactive functional group-containing monomer, a glycidyl group-containing vinyl monomer is preferably used. If the water-insoluble polymer raw material contains a glycidyl group-containing vinyl monomer, the water-insoluble polymer has a repeating unit derived from the glycidyl group-containing vinyl monomer, and therefore the production sex Composite polymers are often obtained.

[0086] The water-insoluble polymer raw material may also contain a copolymerizable monomer (hereinafter referred to as a second copolymerizable monomer) as an optional component. Examples of the second copolymerizable monomer include a monomer copolymerizable with the (meth)acrylic acid alkyl ester and / or the second reactive functional group-containing monomer.

[0087] Examples of the second copolymerizable monomer include the above-mentioned tertiary amino group-containing vinyl monomer, the above-mentioned quaternary ammonium group-containing vinyl monomer, the above-mentioned cyano group-containing vinyl monomer, the above-mentioned sulfonic acid group-containing vinyl monomer, the above-mentioned acetoacetoxy group-containing vinyl monomer, the above-mentioned vinyl esters, the above-mentioned aromatic vinyl monomer, the above-mentioned unsaturated carboxylic acid amide (including (meth)acrylamide), the above-mentioned heterocyclic vinyl compound, the above-mentioned vinylidene halide compound, the above-mentioned α-olefins, the above-mentioned dienes, and the above-mentioned crosslinkable vinyl monomer.

[0088] These second copolymerizable monomers can be used alone or in combination of two or more kinds. From the viewpoint of adhesion, preferred as the second copolymerizable monomer are aromatic vinyl monomers.

[0089] In addition, the above-mentioned first reactive functional group can be obtained by combining the first reactive functional group and the second reactive functional group. Response A second reactive functional group-containing monomer containing a type of second reactive functional group that cannot react with the reactive functional group (or that can react but hardly reacts in terms of reaction rate, etc.) is classified as a second copolymerizable monomer. From the viewpoint of adjusting the degree of water insolubility (SP value), preferred examples of the second copolymerizable monomer include the carboxyl group-containing vinyl monomer and the hydroxyl group-containing vinyl monomer described above as the second reactive group-containing monomer.

[0090] In addition, the water-insoluble polymer raw material preferably does not substantially contain a cyano group-containing vinyl monomer (specifically, (meth)acrylonitrile). Substantially not containing a cyano group-containing vinyl monomer means that the cyano group-containing vinyl monomer is, for example, 2.0 mass % or less, preferably 1.0 mass % or less, based on the water-insoluble polymer raw material. When a cyano group-containing vinyl monomer is blended, the electrolyte resistance of the coating material for secondary battery separator (described later) may decrease, so the water-insoluble polymer raw material preferably does not contain a cyano group-containing vinyl monomer.

[0091] In the water-insoluble polymer raw material, the ratio of each monomer is appropriately selected so that the SP value of the water-insoluble polymer falls within the above range and the water-insoluble polymer contains the above-mentioned second reactive functional group.

[0092] For example, the water-insoluble polymeric material consists of a (meth)acrylic acid alkyl ester and a second reactive functional group-containing monomer, or consists of a (meth)acrylic acid alkyl ester, a second reactive functional group-containing monomer and a second copolymerizable monomer.

[0093] The water-insoluble polymer raw material preferably consists of a (meth)acrylic acid alkyl ester and a glycidyl group-containing vinyl monomer, or consists of a (meth)acrylic acid alkyl ester, a glycidyl group-containing vinyl monomer and a second copolymerizable monomer.

[0094] For example, the content of the (meth)acrylic acid alkyl ester is, for example, 20 parts by mass or more, preferably 30 parts by mass or more, relative to 100 parts by mass of the water-insoluble polymer raw material, from the viewpoint of obtaining excellent adhesion. Also, the content of the (meth)acrylic acid alkyl ester is, for example, 99 parts by mass or less, preferably 90 parts by mass or less, more preferably 80 parts by mass or less, and even more preferably 70 parts by mass or less, relative to 100 parts by mass of the water-insoluble polymer raw material, from the viewpoint of obtaining excellent adhesion.

[0095] The content (total amount) of the second reactive functional group-containing monomer is, for example, 1 part by mass or more, preferably 2 parts by mass or more, more preferably 3 parts by mass or more, and even more preferably 4 parts by mass or more, relative to 100 parts by mass of the water-insoluble polymer raw material. The content (total amount) of the second reactive functional group-containing monomer is, for example, 30 parts by mass or less, preferably 20 parts by mass or less, and more preferably 10 parts by mass or less, relative to 100 parts by mass of the water-insoluble polymer raw material.

[0096] In addition, the content of the second copolymerizable monomer in the water-insoluble polymer raw material is, for example, 0 parts by mass or more, preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more, relative to 100 parts by mass of the total amount of the water-insoluble polymer raw material. In addition, the content of the second copolymerizable monomer in the water-insoluble polymer raw material is, for example, 80 parts by mass or less, preferably 70 parts by mass or less, relative to 100 parts by mass of the total amount of the water-insoluble polymer raw material.

[0097] The water-insoluble polymer is obtained by polymerizing the water-insoluble polymer raw material described above by the method described below. The content of the repeating units derived from each monomer in the water-insoluble polymer is the same as the content of each monomer in the water-insoluble polymer raw material.

[0098] That is, the content of the repeating unit derived from the (meth)acrylic acid alkyl ester is, for example, 20% by mass or more, preferably 40% by mass or more, based on the total amount of the water-insoluble polymer, from the viewpoint of obtaining excellent adhesion. Also, the content of the repeating unit derived from the (meth)acrylic acid alkyl ester is, for example, 99% by mass or less, preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less, based on the total amount of the water-insoluble polymer.

[0099] The content of the repeating unit derived from the second reactive functional group-containing monomer is, for example, 1 mass% or more, preferably 2 mass% or more, more preferably 3 mass% or more, and even more preferably 4 mass% or more, based on the total amount of the water-insoluble polymer. The content of the repeating unit derived from the second reactive functional group-containing monomer is, for example, 30 mass% or less, preferably 20 mass% or less, and more preferably 10 mass% or less, based on the total amount of the water-insoluble polymer.

[0100] In addition, the content of the repeating unit derived from the first copolymerizable monomer is, for example, 0 mass% or more, preferably 10 mass% or more, more preferably 20 mass% or more, and even more preferably 30 mass% or more, and for example, 70 mass% or less, relative to the total amount of the water-insoluble polymer.

[0101] The content of the repeating unit derived from the second copolymerizable monomer is, for example, 0% by mass or more, preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, based on the total amount of the water-insoluble polymer. The content of the repeating unit derived from the second copolymerizable monomer is, for example, 80% by mass or less, preferably 70% by mass or less, based on the total amount of the water-insoluble polymer.

[0102] From the viewpoints of air permeability and adhesiveness, the water-insoluble polymer has a glass transition temperature of, for example, −60° C. or higher, preferably −40° C. or higher, more preferably −20° C. or higher, and even more preferably 0° C. or higher. From the viewpoints of low viscosity and adhesiveness, the water-insoluble polymer has a glass transition temperature of, for example, 70° C. or lower, preferably 50° C. or lower, more preferably 30° C. or lower, and even more preferably 10° C. or lower.

[0103] When the water-insoluble polymer has a glass transition temperature within the above range, a secondary battery separator having excellent heat resistance, air permeability, and adhesion can be obtained, and further, improved storage stability, uniform dispersion, and low viscosity can be achieved.

[0104] The water-insoluble polymer has a specific gravity of, for example, 0.85 or more, preferably 0.89 or more, and for example, 0.98 or less, preferably 0.95 or less.

[0105] The difference between the specific gravity of the water-soluble polymer and the specific gravity of the water-insoluble polymer is, for example, 0.04 or more, preferably 0.10 or more, and the difference between the specific gravity of the water-soluble polymer and the specific gravity of the water-insoluble polymer is, for example, 0.35 or less, preferably 0.25 or less.

[0106] Next, a method for producing the composite polymer and the raw material for the coating material for secondary battery separator will be described.

[0107] Specifically, the methods for producing the composite polymer and the raw material for the coating material for the secondary battery separator include, for example, the first method and the second method. In the first method, for example, a water-soluble polymer raw material is polymerized to obtain a water-soluble polymer, and then a water-insoluble polymer raw material is polymerized in the presence of the water-soluble polymer. In the second method, first, a water-insoluble polymer raw material is polymerized to obtain a water-insoluble polymer, and then the water-soluble polymer raw material is polymerized in the presence of the water-insoluble polymer. The first method is preferable.

[0108] The first method includes a step (first step) of obtaining a water-soluble polymer by polymerizing a water-soluble polymer raw material, and a step (second step) of obtaining a water-soluble polymer by polymerizing a water-insoluble polymer raw material in the presence of the water-soluble polymer, and chemically bonding at least a portion of the first reactive functional groups to at least a portion of the second reactive functional groups.

[0109] More specifically, in the first step, the water-soluble polymer raw material is polymerized to obtain a water-soluble polymer. In the synthesis of the water-soluble polymer, a known polymerization initiator is mixed with water, and the water-soluble polymer raw material is dropped into the water to polymerize the water-soluble polymer raw material. In addition, in the polymerization of the water-soluble polymer, a known emulsifier (surfactant) can be mixed as necessary from the viewpoint of improving the production stability.

[0110] The polymerization conditions are appropriately set according to the type of water-soluble polymer raw material. For example, under normal pressure, the polymerization temperature is, for example, 30° C. or higher, preferably 50° C. or higher. The polymerization temperature is, for example, 95° C. or lower, preferably 85° C. or lower. The polymerization time is, for example, 1 hour or higher, preferably 2 hours or higher. The polymerization time is, for example, 30 hours or lower, preferably 20 hours or lower.

[0111] In the polymerization of the water-insoluble polymer, from the viewpoint of improving the production stability, for example, known additives can be blended in an appropriate ratio. Examples of the additives include a pH adjuster, a metal ion sequestering agent, and a molecular weight regulator (chain transfer agent).

[0112] This causes the water-soluble polymer raw material to be polymerized to obtain a water-soluble polymer. The water-soluble polymer has a repeating unit derived from the monomer containing the first reactive functional group. That is, the water-soluble polymer contains the first reactive functional group in the molecule.

[0113] The water-soluble polymer is obtained as an aqueous solution in which the polymer is dissolved in water. The solid content of the aqueous solution is appropriately set depending on the purpose and application.

[0114] In the second step, the water-insoluble polymer raw material is polymerized in the presence of the water-soluble polymer. More specifically, the water-insoluble polymer raw material is emulsified in water, and the emulsion is added to the aqueous solution of the water-soluble polymer to polymerize the water-insoluble polymer raw material.

[0115] The polymerization conditions are appropriately set according to the type of water-insoluble polymer raw material. For example, under normal pressure, the polymerization temperature is, for example, 30° C. or higher, preferably 50° C. or higher. The polymerization temperature is, for example, 95° C. or lower, preferably 85° C. or lower. The polymerization time is, for example, 0.5 hours or higher, preferably 1.5 hours or higher. The polymerization time is, for example, 20 hours or lower, preferably 10 hours or lower.

[0116] This causes the water-insoluble polymer raw material to be polymerized to obtain a water-insoluble polymer. The water-insoluble polymer has a repeating unit derived from the second reactive functional group-containing monomer. That is, the water-insoluble polymer contains the second reactive functional group in the molecule.

[0117] In this method, as the water-insoluble polymer is produced, at least a portion of the second reactive functional groups in the water-insoluble polymer chemically bonds with at least a portion of the first reactive functional groups in the water-soluble polymer.

[0118] More specifically, for example, when the first reactive functional group includes a carboxy group, the carboxy group is chemically bonded to a glycidyl group as a second reactive functional group. Also, for example, when the first reactive functional group includes a hydroxyl group, the hydroxyl group is chemically bonded to an isocyanate group as a second reactive functional group. Also, for example, when the first reactive functional group includes a glycidyl group, the glycidyl group is chemically bonded to a carboxyl group and / or a phosphate group as a second reactive functional group. Also, for example, when the first reactive functional group includes an isocyanate group, the isocyanate group is chemically bonded to a hydroxyl group as a second reactive functional group. Also, for example, when the first reactive functional group includes a phosphate group, the glycidyl group is chemically bonded to a carboxyl group and / or a phosphate group as a second reactive functional group. case The phosphate group is chemically bonded to a glycidyl group as a second reactive functional group.

[0119] The reaction conditions are appropriately set depending on the type of the first reactive functional group and the type of the second reactive functional group. The reaction of the first reactive functional group and the second reactive functional group usually proceeds simultaneously with the synthesis of the water-insoluble polymer in the second step.

[0120] As a result, the water-soluble polymer and the water-insoluble polymer can be chemically bonded to obtain a composite polymer of the water-soluble polymer and the water-insoluble polymer, thereby obtaining a dispersion containing the composite polymer (a raw material for a coating material for a secondary battery separator).

[0121] In this dispersion, the content of the raw material of the coating material for a secondary battery separator (solid content concentration of the dispersion) is, for example, 5 mass % or more and, for example, 50 mass % or less.

[0122] In such a coating material raw material for secondary battery separator, the ratio of the mass of the water-soluble polymer to the mass of the water-insoluble polymer is appropriately set according to the purpose and use. For example, the water-soluble polymer is, for example, 40 parts by mass or more, preferably 50 parts by mass or more, more preferably 60 parts by mass or more, even more preferably 70 parts by mass or more, and particularly preferably 80 parts by mass or more, based on 100 parts by mass of the total amount of the water-soluble polymer and the water-insoluble polymer, from the viewpoint of heat resistance. Also, the water-soluble polymer is, for example, 99.9 parts by mass or less, preferably 99 parts by mass or less, more preferably 97 parts by mass or less, and even more preferably 95 parts by mass or less, based on 100 parts by mass of the total amount of the water-soluble polymer and the water-insoluble polymer, from the viewpoint of air permeability and adhesion.

[0123] In addition, from the viewpoints of air permeability and adhesion, the amount of the water-insoluble polymer is, for example, 0.1 part by mass or more, preferably 1 part by mass or more, more preferably 3 parts by mass or more, and more preferably 5 parts by mass or more, based on 100 parts by mass of the total amount of the water-soluble polymer and the water-insoluble polymer. In addition, from the viewpoint of heat resistance, the amount of the water-insoluble polymer is, for example, 60 parts by mass or less, preferably 50 parts by mass or less, more preferably 40 parts by mass or less, even more preferably 30 parts by mass or less, and particularly preferably 20 parts by mass or less, based on 100 parts by mass of the total amount of the water-soluble polymer and the water-insoluble polymer.

[0124] The mass of the water-insoluble polymer and the mass of the water-soluble polymer can be calculated from the amounts of the water-insoluble polymer raw material and the water-soluble polymer raw material charged. That is, the mass of the water-soluble polymer means the mass of the water-soluble polymer raw material, and the mass of the water-insoluble polymer means the mass of the water-insoluble polymer raw material.

[0125] The coating material raw material for secondary battery separators of the present invention includes a composite polymer of a water-soluble polymer and a water-insoluble polymer, the water-soluble polymer includes a first reactive functional group, the water-insoluble polymer includes a second reactive functional group capable of chemically bonding to the first reactive functional group, and in the composite polymer, at least a portion of the first reactive functional group and at least a portion of the second reactive functional group are chemically bonded to each other.

[0126] Therefore, the above-mentioned coating material raw material for secondary battery separators has excellent storage stability, uniform dispersion, and low viscosity. Furthermore, the above-mentioned coating material raw material for secondary battery separators can provide secondary battery separators with excellent heat resistance, air permeability, and adhesion.

[0127] In particular, when the water-soluble polymer and the water-insoluble polymer are simply mixed without forming a composite polymer, separation occurs due to the difference in specific gravity between the water-soluble polymer and the water-insoluble polymer. In order to suppress separation, it has been considered to prepare the water-soluble polymer and the water-insoluble polymer separately and mix them when used, but this operation is complicated and the mixture has poor uniform dispersion.

[0128] In contrast, in the above-mentioned coating material raw material for secondary battery separators, the water-soluble polymer and the water-insoluble polymer are chemically bonded to form a composite polymer, which can suppress separation due to the difference in specific gravity and provide excellent storage stability. Furthermore, since the water-soluble polymer and the water-insoluble polymer are chemically bonded to form a composite polymer, a mixing process is not required during use, and the raw material is excellent in workability and uniform dispersion.

[0129] Furthermore, when the water-soluble polymer and the water-insoluble polymer are not chemically bonded to each other and do not form a composite polymer, the interaction between the water-soluble polymers is large, which causes an increase in viscosity.

[0130] In contrast, in the above-mentioned raw material for the coating material for secondary battery separator, the water-soluble polymer and the water-insoluble polymer are chemically bonded to each other to form a composite polymer, so that the water-soluble polymer is fixed to the water-insoluble polymer, and therefore the interaction between the water-soluble polymers is suppressed, and as a result, the increase in viscosity is suppressed, and an excellent low viscosity is obtained.

[0131] The coating material for a secondary battery separator of the present invention contains the above-mentioned raw material for the coating material for a secondary battery separator, and, if necessary, an inorganic filler and a dispersant.

[0132] The blending ratio of the coating material raw materials for secondary battery separators is the total amount of the coating material raw materials for secondary battery separators, the inorganic filler, and the dispersant (hereinafter referred to as the coating material components for secondary battery separators).

[0133] For example, the amount is 0.1 parts by mass or more (solid content) and, for example, 10 parts by mass or less (solid content) relative to 100 parts by mass (solid content).

[0134] Inorganic fillers include, for example, oxides, nitrides, carbides, sulfates, hydroxides, silicates, and minerals. Oxides include, for example, alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide. Nitrides include, for example, silicon nitride, titanium nitride, and boron nitride. Carbides include, for example, silicon carbide and calcium carbonate. Sulfates include, for example, magnesium sulfate and aluminum sulfate. Hydroxides include, for example, aluminum hydroxide and aluminum oxide hydroxide. Silicates include, for example, calcium silicate, magnesium silicate, diatomaceous earth, silica sand, and glass. Minerals include, for example, talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, and zeolite. Inorganic fillers preferably include oxides and hydroxides, more preferably aluminum oxide and aluminum oxide hydroxide.

[0135] The mixing ratio of the inorganic filler is, for example, 50 parts by mass or more (solid content) and, for example, 99.7 parts by mass or less (solid content) per 100 parts by mass (solid content) of the coating material components for secondary battery separators.

[0136] Examples of the dispersant include ammonium polycarboxylate and sodium polycarboxylate. When the dispersant is ammonium polycarboxylate, the above-mentioned raw material of the coating material for the secondary battery separator and the inorganic filler can be uniformly dispersed, and a coating film (described later) with a uniform thickness can be obtained.

[0137] The mixing ratio of the dispersant is, for example, 0.1 parts by mass or more (solid content) and, for example, 5 parts by mass or less (solid content) with respect to 100 parts by mass (solid content) of the coating material components for a secondary battery separator.

[0138] To obtain the coating material for a secondary battery separator, first, the inorganic filler and the dispersant are mixed in the above-mentioned ratio with water to prepare an inorganic filler dispersion.

[0139] Next, the raw material for the coating material for secondary battery separators (or the dispersion liquid containing the raw material for the coating material for secondary battery separators) is mixed into the inorganic filler dispersion liquid in the above ratio and stirred, thereby obtaining the coating material for secondary battery separators.

[0140] The stirring method is not particularly limited, and a known stirring device can be used, such as a ball mill, a bead mill, a planetary ball mill, a vibration ball mill, a sand mill, a colloid mill, an attritor, a roll mill, a high-speed impeller dispersion, a disperser, a homogenizer, a high-speed impact mill, an ultrasonic dispersion, and a stirring blade.

[0141] The coating material for the secondary battery separator is obtained, for example, as a dispersion liquid dispersed in water. The coating material for the secondary battery separator may contain known additives as necessary. Examples of the additives include hydrophilic resins, thickeners, wetting agents, antifoaming agents, and pH adjusting agents. adjustment The additives can be used alone or in combination of two or more kinds.

[0142] The above-mentioned coating material for secondary battery separators contains the above-mentioned raw material for coating material for secondary battery separators, so that it is possible to improve the productivity of secondary battery separators. Furthermore, the above-mentioned coating material for secondary battery separators can provide secondary battery separators with excellent heat resistance, air permeability, and adhesion.

[0143] This coating material for secondary battery separators can be suitably used as a coating material for secondary battery separators.

[0144] The secondary battery separator of the present invention can be produced by a known method.

[0145] In this method, first, a porous membrane is prepared. For example, the porous membrane may be a polyolefin porous membrane or an aromatic polyamide porous membrane, and preferably a polyolefin porous membrane. For example, the polyolefin may be polyethylene or polypropylene. If necessary, the porous membrane may be surface-treated. For example, the surface treatment may be corona treatment or plasma treatment.

[0146] The thickness of the porous membrane is, for example, 1 μm or more, or preferably 5 μm or more.The thickness of the porous membrane is, for example, 40 μm or less, or preferably 20 μm or less.

[0147] Next, in this method, the separator coating material is applied to at least one side of the porous membrane, and then, if necessary, the separator coating material is dried to obtain a coating film.

[0148] The coating method is not particularly limited, and examples thereof include gravure coater method, small diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, microgravure coat method, knife coater method, air doctor coater method, blade coater method, rod coater method, squeeze coater method, cast coater method, die coater method, screen printing method, and spray coating method.

[0149] As for the drying conditions, the drying temperature is, for example, 40° C. or more, and, for example, 80° C. or less. The thickness of the coating film after drying is, for example, 1 μm or more, preferably 2 μm or more. The thickness of the coating film after drying is, for example, 10 μm or less, preferably 8 μm or less.

[0150] In this way, a secondary battery separator is manufactured, which includes a porous membrane and a coating film of the above-mentioned coating material for secondary battery separators that is disposed on at least one surface of the porous membrane.

[0151] In the above description, the coating film of the coating material for a secondary battery separator is disposed on at least one side of the porous membrane, but the above coating film may be disposed on both sides of the porous membrane.

[0152] The secondary battery separator has a coating film of the coating material for secondary battery separators, and is therefore excellent in productivity, heat resistance, air permeability and adhesion.

[0153] Moreover, according to the above-mentioned method for producing a secondary battery separator, a secondary battery separator having excellent heat resistance, air permeability and adhesion can be efficiently produced.

[0154] This secondary battery separator can be suitably used as a separator for a secondary battery.

[0155] The secondary battery of the present invention comprises a positive electrode, a negative electrode, the above-mentioned secondary battery separator disposed between the positive electrode and the negative electrode, and an electrolyte impregnated in the positive electrode, the negative electrode, and the above-mentioned secondary battery separator.

[0156] As the positive electrode, for example, a known electrode including a positive electrode current collector and a positive electrode active material laminated on the positive electrode current collector is used.

[0157] The positive electrode current collector may be made of a known conductive material. Examples of the conductive material include aluminum, titanium, stainless steel, nickel, baked carbon, conductive polymers, and conductive glass. These may be used alone or in combination of two or more kinds.

[0158] The positive electrode active material is not particularly limited, but examples thereof include lithium-containing transition metal oxides, lithium-containing phosphates, and lithium-containing sulfates. These may be used alone or in combination of two or more kinds.

[0159] As the negative electrode, for example, a known electrode including a negative electrode current collector and a negative electrode active material laminated on the negative electrode current collector is used.

[0160] Examples of the negative electrode current collector include copper and nickel, which can be used alone or in combination of two or more kinds.

[0161] Examples of the negative electrode active material include graphite, soft carbon, and hard carbon. These can be used alone or in combination of two or more kinds.

[0162] When the secondary battery is a lithium ion battery, the electrolyte may be, for example, a solution in which a lithium salt is dissolved in a carbonate compound, such as ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC).

[0163] To manufacture a secondary battery, for example, a separator for the secondary battery is sandwiched between a positive electrode and a negative electrode, and these are housed in a battery casing (cell), and an electrolyte is injected into the battery casing.

[0164] In this way, a secondary battery can be obtained.

[0165] The secondary battery includes the secondary battery separator, and therefore has excellent productivity, heat resistance, air permeability, and adhesion. As a result, the secondary battery has excellent productivity, heat resistance, air permeability, and adhesion. EXAMPLES

[0166] Specific numerical values ​​of the blending ratio (content ratio), physical property values, parameters, etc. used in the following description can be replaced with the upper limit values ​​(numerical values ​​defined as "not more than" or "less than") or lower limit values ​​(numerical values ​​defined as "not less than" or "exceeding") of the corresponding blending ratio (content ratio), physical property values, parameters, etc. described in the above "Form for carrying out the invention." In addition, unless otherwise specified in the following description, "parts" and "%" are based on mass.

[0167] 1. Preparation of coating material raw material for secondary battery separator Examples 1 to 23 and Comparative Examples 1 to 6 Mixer, reflux cooling vessel Into a separable flask equipped with a separator, 600 parts of distilled water and 1 part of sodium lauryl sulfate (surfactant) were charged and heated to 70° C. Next, potassium persulfate (KPS, polymerization initiator) was added to the separable flask according to the descriptions in Tables 1 to 4.

[0168] 100 parts of the water-soluble polymer raw material prepared according to the descriptions in Tables 1 to 4 was dissolved in 300 parts of distilled water. The solution was then continuously added to the above-mentioned separable flask, which had been purged with nitrogen gas, at 75°C over 180 minutes. Thereafter, the water-soluble polymer raw material was stirred at 75°C for 4 hours to complete the polymerization. This resulted in an aqueous solution of a water-soluble polymer having a carboxy group (first reactive functional group).

[0169] Next, the water-insoluble polymer raw material prepared according to the description in Tables 1 to 4 was emulsified with soapy water. Next, the emulsion was added to the above-mentioned aqueous solution of the water-soluble polymer all at once. The mixture was stirred at 75°C for 4 hours while stirring to complete the polymerization. As a result, a water-insoluble polymer having a glycidyl group (second reactive functional group) was obtained. In addition, the carboxy group of the water-soluble polymer was reacted with the glycidyl group of the water-insoluble polymer to obtain a composite polymer in which the water-soluble polymer and the water-insoluble polymer were chemically bonded. Note that the water-insoluble polymers of Comparative Examples 1 to 6 did not have a glycidyl group (second reactive functional group), and the water-soluble polymer did not react with the water-insoluble polymer. Therefore, in Comparative Examples 1 to 6, a composite polymer was not obtained, and a mixed polymer of the water-soluble polymer and the water-insoluble polymer was obtained.

[0170] In this way, a separator coating material raw material was obtained as a composite polymer dispersion or a mixed polymer dispersion (hereinafter, polymer dispersion). The solid content of the dispersion was 10.0% by mass.

[0171] In addition, the glass transition temperatures (Tg, units: ° C.) of the water-insoluble polymer and the water-soluble polymer were calculated by the following FOX formula.

[0172] 1 / Tg=W1 / Tg1+W2 / Tg2+···+W n / Tg n (1) [In the formula, Tg is the glass transition temperature of the copolymer (unit: K), Tg i (i=1, 2, . . . n) is the glass transition temperature (unit: K) when monomer i forms a homopolymer, W i (i = 1, 2, ..., n) represents the mass fraction of monomer i in all monomers.]

[0173] In addition, the solubility parameters (SP value, unit: : (cal / cm 3 ) 1 / 2 ) was calculated using the calculation software CHEOPS (version 4.0) from Million Zillion Software. The calculation method used was the method described in Computational Materials Science of Polymers (AAAskadskii, Cambridge Intl Science Pub (2005 / 12 / 30)) Chapter XII.

[0174] The weight average molecular weight of the water-soluble polymer was measured by the following method and conditions. That is, when the polymerization of the water-soluble polymer was completed, the water-soluble polymer was sampled. Next, the weight average molecular weight (Mw) of the sample was determined using a GPC device (device name: P KP-22, Flom Co., Ltd.). The measurement conditions are as follows. The weight average molecular weight is a molecular weight calculated in terms of standard polyethylene glycol / polyethylene oxide.

[0175] Sample concentration: 0.1(w / v)% Sample injection volume: 100μL Eluent: 0.2M NaNO3 / acrylonitrile (AN) = 90 / 10 ·Flow rate: 1.0ml / min ·Measurement temperature: 40℃ Column: ShodexohPAK SB-806M HQ x 2

[0176] Comparative Example 7 A dispersion liquid was obtained as a raw material for a separator coating material in accordance with Example 1 of International Publication WO2017 / 026095.

[0177] That is, the water-soluble polymer raw material was charged into a four-neck flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube according to the description in Tables 1 to 4, and oxygen in the reaction system was removed with nitrogen gas. Next, 7 parts of a 5% aqueous ammonium persulfate solution and 3 parts of a 5% aqueous sodium hydrogen sulfite solution were added to the flask as polymerization initiators under stirring, and the temperature was raised from room temperature to 80°C and kept at that temperature for 3 hours to polymerize the water-soluble polymer raw material. Then, 162 parts of ion-exchanged water was added to obtain an aqueous solution of the water-soluble polymer.

[0178] Separately, 70 parts of ion-exchanged water, 0.15 parts of sodium lauryl sulfate as an emulsifier, and 0.5 parts of ammonium peroxodisulfate as a polymerization initiator were fed to a reactor equipped with a stirrer, the gas phase was replaced with nitrogen gas, and the temperature was raised to 60°C. Thereafter, in accordance with the description in Tables 1 to 4, the water-insoluble polymer raw material was continuously added to the reactor, polymerization was carried out at 60°C during the addition, and after the addition was completed, the reaction was terminated after stirring at 70°C for 3 hours. As a result, a dispersion of a water-insoluble polymer was obtained.

[0179] The obtained water-soluble polymer dispersion and the water-insoluble polymer dispersion were mixed to obtain a mixed polymer dispersion (polymer dispersion) as a separator coating material raw material. The mixing ratio was 1 part by mass of the water-soluble polymer and 2 parts by mass of the particulate polymer.

[0180] Comparative Example 8 Mixer, reflux cooling vessel Into a separable flask equipped with a separator, 600 parts of distilled water and 1 part of sodium lauryl sulfate (surfactant) were charged and heated to 70° C. Next, potassium persulfate (KPS, polymerization initiator) was added to the separable flask according to the description in Table 5.

[0181] 100 parts of the high SP value polymer raw material prepared according to the description in Table 5 was added to 300 parts of distilled water. In addition, 2 parts of sodium lauryl sulfate (surfactant) were added as an emulsifier. Next, the emulsion was continuously added to the above-mentioned separable flask substituted with nitrogen gas at 75°C over 180 minutes. Thereafter, the emulsion was stirred at 75°C for 2 hours to complete the polymerization. As a result, an aqueous dispersion of a high SP value polymer having a carboxy group (first reactive functional group) was obtained.

[0182] Next, the low SP value polymer raw material prepared according to the description in Table 5 was emulsified with 1 part of sodium lauryl sulfate (surfactant). Then, the emulsion was added all at once to the aqueous dispersion of the high SP value polymer. The mixture was stirred at 75°C for 4 hours while stirring to complete the polymerization. This resulted in a low SP value polymer having a glycidyl group (second reactive functional group). At the same time, a core-shell aqueous dispersion in which the high SP value polymer and the low SP value polymer were bonded via the glycidyl group and the carboxy group was also obtained.

[0183] Comparative Example 9 A dispersion liquid was obtained as a raw material for a separator coating material in accordance with Example 1 of International Publication WO2010 / 134501.

[0184] That is, 230 parts of toluene, 50 parts of n-butyl acrylate, 50 parts of styrene oligomer, and 1 part of t-butylperoxy-2-ethylhexanate (polymerization initiator) were placed in an autoclave equipped with a stirrer and thoroughly stirred. The styrene oligomer was a one-terminated methacryloylated polystyrene oligomer (manufactured by Toa Gosei Chemical Industry Co., Ltd., product name AS-6, SP value 9.9 (cal / cm 3 ) 1 / 2 ) was.

[0185] The autoclave was then heated to 90°C to polymerize the above components. This resulted in a solution of a polymer (hereinafter referred to as a graft polymer). The main chain of the graft polymer was composed of n-butyl acrylate (a component that exhibits swelling properties in the electrolyte). The side chain of the graft polymer was composed of styrene (a component that does not exhibit swelling properties in the electrolyte).

[0186] The polymerization conversion rate was calculated from the solid concentration of the solution. The polymerization addition rate was about 98%. The weight average molecular weight of the graft polymer was about 50,000. The glass transition temperature of the graft polymer was 25°C.

[0187] 2. Manufacture of coating material for secondary battery separator and secondary battery separator Using the raw materials for the coating material for secondary battery separators of each of the Examples and Comparative Examples, coating materials for secondary battery separators were prepared, and secondary battery separators were obtained.

[0188] That is, 100 parts by mass of aluminum hydroxide oxide (manufactured by Taimei Chemical Industry Co., Ltd., boehmite Grade C06, particle size: 0.7 μm) as a pigment, and 3.0 parts by mass (solid content equivalent) of an aqueous solution of ammonium polycarboxylate (manufactured by San Nopco Ltd., SN Dispersant 5468) as a dispersant were uniformly dispersed in 110 parts by mass of water to obtain a pigment dispersion. Next, a polymer dispersion (a raw material for a coating material for a secondary battery separator) was added to this pigment dispersion so that the solid content was 5 parts by mass, and water was further added to adjust the solid content to 40% by mass, and the mixture was stirred for 15 minutes to prepare a coating material for a secondary battery separator.

[0189] On the other hand, the surface of the polyolefin resin porous membrane was subjected to a corona treatment. More specifically, the polyolefin resin porous membrane was SW509C+ (film thickness 9.6 μm, porosity 40.6%, air permeability 158 g / 100 ml, surface density 5.5 g / m 2A polyolefin resin porous film was prepared (Changzhou Xingyuan New Energy Materials Co., Ltd.). Next, the surface of the polyolefin resin porous film was cut to A4 size, and then the surface of the polyolefin resin porous film was corona-treated using a switchback automatic traveling corona surface treatment device (Wedge Co., Ltd.) under the conditions of output of 0.15 kW, conveying speed of 3.0 m / s × 2 times, and corona discharge distance of 9 mm.

[0190] Next, the above-mentioned coating material for secondary battery separator was applied to the surface of the corona-treated polyolefin resin porous membrane using a wire bar. After application, the coating material was dried at 50° C. to form a 5 μm coating film on the surface of the polyolefin resin porous membrane.

[0191] In this way, a secondary battery separator was produced.

[0192] 3. Evaluation (1) Heat resistance The secondary battery separator was cut into a size of 5 cm x 5 cm to prepare a test piece. After leaving the test piece in an oven at 150°C for 1 hour, the length of each side was measured and the thermal shrinkage rate was calculated. The heat resistance was evaluated according to the following criteria.

[0193] ⊚: The heat shrinkage rate was less than 15%. ◯: The heat shrinkage rate was 15% or more and less than 25%. △: The heat shrinkage rate was 25% or more and less than 65%. △△: The heat shrinkage rate was 65% or more and less than 80%. ×: The heat shrinkage rate was 80% or more.

[0194] (2) Air permeability The secondary battery separator was measured for air permeability resistance according to JIS-P-8117 using an Oken type air permeability smoothness tester manufactured by Asahi Seiko Co., Ltd. The smaller the air permeability resistance, the better the ion permeability was evaluated. In addition, the ion permeability was evaluated according to the following criteria.

[0195] ◎: Air resistance was less than 180s / 100mL. ○: Air resistance was 180s / 100mL or more and less than 220s / 100mL. △: Air resistance was 220 s / 100 mL or more and less than 300 s / 100 mL. ×: Air resistance was 300 s / 100 mL or more.

[0196] (3) Adhesion The secondary battery separator was cut into a size of 5 cm x 10 cm to prepare a test piece. Cellophane adhesive tape was attached to the coating film of the coating material for secondary battery separators in a manner conforming to JIS Z1522, and a 180° peel test was carried out. The cellophane adhesive tape was pulled at a speed of 10 mm / min. The measurement was carried out three times, and the average value was calculated. In addition, the adhesion was evaluated according to the following criteria.

[0197] ⊚: The average adhesive strength was 70 N / m or more. ◯: The average adhesive strength was 50 N / m or more and less than 70 N / m. △: The average adhesive strength was 20 N / m or more and less than 50 N / m. △△: Average adhesive strength is 1 N / m or more but less than 20N / m. ×: The average adhesive strength was less than 1 N / m.

[0198] (4) Storage stability The storage stability of the raw material for coating material for secondary battery separators was evaluated by the following method. That is, 1 L of the polymer dispersion (raw material for coating material for secondary battery separators) was stored in a thermostatic chamber at 40°C. After six months, the viscosity change and pH change of the composite polymer dispersion were measured. Furthermore, the appearance change (layer separation and color) of the composite polymer dispersion was visually observed. Then, the viscosity change, pH change, and appearance change were each evaluated on a scale of 1 to 4, and the storage stability was evaluated based on the lowest score. The evaluation criteria are as follows.

[0199] Viscosity change 4 points: 0% or more and 5% or less 3 points: more than 5% but less than 10% 2 points: more than 10% but less than 30% 1 point: over 30%

[0200] pH change 4 points: 0 or more and 0.5 or less 3 points: over 0.5 but under 1.0 2 points: over 1.0 but under 2.0 1 point: over 2.0

[0201] Appearance changes 4 points: No change in appearance. 3 points: slight change in appearance. 2 points: Appearance changed. 1 point: Significant change in appearance.

[0202] Overall rating (storage stability) ◎: The lowest score in the evaluation of viscosity change, pH change and appearance change is 4 points. ○: The lowest score in the evaluation of viscosity change, pH change and appearance change was 3 points. △: The lowest score in the evaluation of viscosity change, pH change and appearance change was 2 points. ×: The lowest score in the evaluation of viscosity change, pH change and appearance change is 1 point.

[0203] (5) Uniform dispersibility The uniform dispersion of the raw material of the coating material for secondary battery separator was evaluated by the following method. That is, the zeta potential of the coating material for secondary battery separator was measured 10 times with a concentrated cell of a zeta potential measuring device (ELSZ-2000 manufactured by Otsuka Electronics Co., Ltd.). The uniform dispersion was evaluated according to the following criteria.

[0204] ◎: The difference between the maximum and minimum zeta potential values ​​out of 10 measurements is less than 5% of the average value of the 10 measurements. ○: The difference between the maximum and minimum values ​​of the zeta potential out of 10 measurements is 5% or more but less than 10% of the average value of the 10 measurements. △: The difference between the maximum and minimum values ​​of zeta potential out of 10 measurements is 10% or more but less than 15% of the average value of the 10 measurements. ×: The difference between the maximum and minimum values ​​of the zeta potential among 10 measurements is 15% or more of the average value of the 10 measurements.

[0205] (6)Low viscosity The low viscosity of the raw material of the coating material for secondary battery separator was evaluated by the following method. That is, the solid content concentration of the polymer dispersion was adjusted to 10 mass %, and the viscosity of the dispersion at 25°C was measured with a BM type viscometer. The evaluation criteria are as follows.

[0206] ◎: Less than 1000 mPa s ○: 1000 mPa s or more and less than 2000 mPa s △: 2000mPa·s or more and less than 6000mPa·s ×:6000mPa·s or more

[0207] [Table 1]

[0208] [Table 2]

[0209] [Table 3]

[0210] [Table 4]

[0211] [Table 5]

[0212] In the table, the formulation (parts by mass) of the water-soluble polymer raw material indicates the amount of raw material component (monomer) blended relative to 100 parts by mass of the water-soluble polymer. Also, the formulation (parts by mass) of the water-insoluble polymer raw material indicates the amount of raw material component (monomer) blended relative to 100 parts by mass of the water-insoluble polymer. Also, the ratio of the water-soluble polymer to the water-insoluble polymer follows the "water-insoluble polymer / water-soluble polymer (mass ratio)" in the table.

[0213] In addition, the compounding recipe (parts by mass) for the high SP value polymer raw material in the table indicates the amount of raw material component (monomer) mixed for 100 parts by mass of the high SP value polymer. In addition, the compounding recipe (parts by mass) for the low SP value polymer raw material indicates the amount of raw material component (monomer) mixed for 100 parts by mass of the low SP value polymer. In addition, the ratio of the high SP value polymer to the low SP value polymer follows the "high SP value polymer / low SP value polymer (mass ratio)" in the table.

[0214] Details of the abbreviations in the table are given below. Mam: methacrylamide AM: Acrylamide Mac: Methacrylic acid Ac: acrylic acid HEMA: 2-hydroxyethyl methacrylate DMAEMA: N,N-Dimethylaminoethyl methacrylate DMAM: Dimethylacrylamide St: styrene MMA: Methyl methacrylate BA: n-butyl acrylate 2EHA:2 - Ethylhexyl acrylate GMA: glycidyl methacrylate AN: Acrylonitrile N-MAM: N-methylolacrylamide AGE: Allyl glycidyl ether KPS: Potassium persulfate Tg: Glass transition temperature, unit: °C SP value: solubility parameter, unit: (cal / cm 3 ) 1 / 2

[0215] The above invention is provided as an exemplary embodiment of the present invention, but this is merely an example and should not be interpreted as being limited. Modifications of the present invention that are obvious to those skilled in the art are included in the scope of the following claims. [Industrial Applicability]

[0216] The raw material for a coating material for a secondary battery separator, the coating material for a secondary battery separator, the secondary battery separator, the method for producing a secondary battery separator, and the secondary battery of the present invention are suitably used in the field of secondary batteries.

Claims

1. SP value 13.0 (cal / cm ３ ) １／２ The water-soluble polymers described above, SP value 13.0 (cal / cm ３ ) １／２ comprising a polymer conjugated with a water insoluble polymer of less than the water-soluble polymer comprises a first reactive functional group; the water insoluble polymer comprises a second reactive functional group capable of chemically bonding to the first reactive functional group; In the composite polymer, At least a portion of the first reactive functional groups; A coating material raw material for a secondary battery separator, which is chemically bonded to at least a portion of the second reactive functional groups.

2. the first reactive functional group of the water-soluble polymer comprises a carboxy group; The coating material raw material for a secondary battery separator according to claim 1 , wherein the second reactive functional group of the water-insoluble polymer includes a glycidyl group.

3. The water-soluble polymer is A repeating unit derived from (meth)acrylamide; and a repeating unit derived from a carboxy group-containing vinyl monomer, The water-insoluble polymer is A repeating unit derived from an alkyl (meth)acrylate ester; 2. The coating material raw material for a secondary battery separator according to claim 1, further comprising a repeating unit derived from a glycidyl group-containing vinyl monomer.

4. For 100 parts by mass of the total amount of the water-soluble polymer and the water-insoluble polymer, The water-soluble polymer is 50 parts by mass or more and 99 parts by mass or less, The coating material raw material for a secondary battery separator according to claim 1 , wherein the water-insoluble polymer is from 1 part by mass to 50 parts by mass.

5. 2. The coating material raw material for a secondary battery separator according to claim 1, wherein the water-soluble polymer has a weight average molecular weight of 10,000 or more and 200,000 or less.

6. 2. The coating material raw material for a secondary battery separator according to claim 1, wherein the water-soluble polymer has a glass transition temperature of 150° C. or more and 240° C. or less.

7. 2. The coating material raw material for secondary battery separator according to claim 1, wherein the water-insoluble polymer has a glass transition temperature of -40°C or more and 50°C or less.

8. A coating material for a secondary battery separator, comprising the raw material for the coating material for a secondary battery separator according to claim 1.

9. Further, the composition contains an inorganic filler and a dispersant. The coating material for a secondary battery separator according to claim 8 .

10. A porous membrane; A coating film of the coating material for a secondary battery separator according to claim 8 arranged on at least one surface of the porous film; A secondary battery separator comprising:

11. Providing a porous membrane; and A step of applying the coating material for a secondary battery separator according to claim 8 to at least one surface of the porous membrane is provided. A method for producing a secondary battery separator, comprising:

12. A secondary battery comprising: a positive electrode; a negative electrode; and the secondary battery separator according to claim 10 disposed between the positive electrode and the negative electrode.

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