Coating material for secondary battery separators, secondary battery separator, method for manufacturing secondary battery separators, and secondary battery

Abstract

Provided is a coating material for a secondary battery separator, the coating material comprising water, a resin binder, an inorganic filler, and a surfactant. When the content percentage of the inorganic filler is 10 mass% in relation to the total amount of the coating material for a secondary battery separator, the coating material for a secondary battery separator satisfies the following equation. [SST - DST] / [SA when measuring SST - SA when measuring DST] ≤ -0.015　SA: Surface Age (ms)　SST: static surface tension (mN / m)　DST: dynamic surface tension (mN / m)

Description

Technical Field

[0001] The present invention relates to a coating material for a secondary battery separator, a secondary battery separator, a method for manufacturing a secondary battery separator, and a secondary battery.

Background Art

[0002] Conventionally, a separator for separating a positive electrode and a negative electrode and allowing ions in an electrolyte solution to pass therethrough has been provided in a secondary battery.

[0003] As such a separator, for example, a polyolefin porous membrane is known. Further, it is known to apply and dry a slurry containing a polymer on the surface of the separator to form a functional layer.

[0004] As the slurry applied to the separator, for example, the following separator slurry has been proposed. This separator slurry contains a thermoplastic polymer containing a particulate polymer and an acetylene-based surfactant, and contains the acetylene-based surfactant in a proportion of 0.001 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the thermoplastic polymer (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] On the other hand, the separator of a secondary battery is required to have air permeability in order to allow ions to pass therethrough. However, the functional layer formed by the above-described separator slurry has a problem of reducing the air permeability of the separator.

[0007] Furthermore, if the shape of the separator changes due to thermal contraction, a short circuit may occur between the positive and negative electrodes. Therefore, heat resistance is required for the functional layer.

[0008] The present invention provides a coating material for secondary battery separators that can be obtained with excellent heat resistance and air permeability, a secondary battery separator equipped with a coating film of the secondary battery separator coating material, a method for manufacturing the secondary battery separator, and a secondary battery equipped with the secondary battery separator. [Means for solving the problem]

[0009] The present invention [1] is a coating material for secondary battery separators comprising water, a resin binder, an inorganic filler, and a surfactant, wherein the coating material for secondary battery separators satisfies the following formula (1) when the content ratio of the inorganic filler is 10% by mass of the total amount of the coating material for secondary battery separators.

[0010] [SST-DST] / [SA during SST measurement-SA during DST measurement]≦-0.015(1) SA: Surface Age (ms) SST: Static surface tension (mN / m) measured by the bubble pressure method within the range of Surface Age 1003 ± 10 ms (25°C). DST: Dynamic surface tension (mN / m) measured by the bubble pressure method within the range of Surface Age 10.0 ± 0.5 ms (25℃).

[0011] The present invention [2] includes the coating material for secondary battery separators described in [1] above, wherein the dynamic surface tension is 65 mN / m or more when the content ratio of the inorganic filler is 10% by mass of the total amount of the coating material for secondary battery separators.

[0012] The present invention [3] includes the secondary battery separator coating material described in [1] or [2] above, wherein the static surface tension is 55 mN / m or less when the inorganic filler content is 10% by mass of the total amount of the secondary battery separator coating material.

[0013] The present invention [4] includes a coating material for secondary battery separators according to any one of the above [1] to [3], wherein the surfactant comprises an acetylene-based surfactant.

[0014] The present invention [5] includes a coating material for secondary battery separators according to any one of the above [1] to [4], wherein the HLB of the surfactant is 10 or more and 14 or less.

[0015] The present invention [6] includes a coating material for a secondary battery separator according to any one of the above [1] to [5], wherein the content ratio of the resin binder is 0.1 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the inorganic filler.

[0016] The present invention [7] includes a coating material for a secondary battery separator according to any one of the above [1] to [6], wherein the resin binder has repeating units derived from (meth)acrylamide and repeating units derived from a carboxyl group-containing vinyl monomer.

[0017] The present invention [8] includes a secondary battery separator comprising a porous membrane and a coating film of any one of the secondary battery separator coating materials described in [1] to [7] above, which is disposed on at least one side of the porous membrane.

[0018] The present invention [9] includes a method for manufacturing a secondary battery separator, comprising the steps of preparing a porous membrane and applying a coating material for secondary battery separators described in any one of the above [1] to [7] to at least one side of the porous membrane.

[0019] The present invention

[10] includes a secondary battery comprising a positive electrode, a negative electrode, and the secondary battery separator described in [8] disposed between the positive electrode and the negative electrode.

Effects of the Invention

[0020] The coating material for the secondary battery separator of the present invention contains water, a resin binder, an inorganic filler, and a surfactant. Also, the dynamic surface tension (DST), the static surface tension (SST), and the Surface Age (SA) at the time of their measurement satisfy a specific relational expression. Therefore, according to the coating material for the secondary battery separator of the present invention, a secondary battery separator excellent in heat resistance and air permeability can be obtained.

[0021] Since the secondary battery separator of the present invention includes a coating film of the above-described coating material for the secondary battery separator, it is excellent in heat resistance and air permeability.

[0022] According to the method for manufacturing the secondary battery separator of the present invention, a secondary battery separator excellent in heat resistance and air permeability can be efficiently manufactured.

[0023] [[ID=I8]] Since the secondary battery of the present invention includes the above-described secondary battery separator, it is excellent in heat resistance and air permeability, and as a result, it is excellent in durability and power generation efficiency.

Brief Description of the Drawings

[0024] [Figure 1] FIG. 1 is an explanatory diagram of [SST - DST] / [SA at the time of SST measurement - SA at the time of DST measurement].

Embodiments for Carrying Out the Invention

[0025] The coating material for the secondary battery separator of the present invention contains water, a resin binder, an inorganic filler, and a surfactant.

[0026] Examples of the resin binder include water-soluble polymers and water-insoluble polymers.

[0027] A water-soluble polymer is defined as a polymer in which, after dissolving 1 g of polymer in 100 ml of water by stirring for 24 hours and then filtering it through a 300-mesh wire mesh, the residual solid content is 0.1% or less.

[0028] Furthermore, a non-water-soluble polymer is defined as a polymer in which, after dissolving 1 g of polymer in 100 ml of water by stirring for 24 hours and then filtering it through a 300-mesh wire mesh, the residual solid content is 90% or more.

[0029] The water-soluble polymer is not particularly limited, but examples include water-soluble (meth)acrylic polymers. Examples of water-soluble (meth)acrylic polymers include polymers obtained by polymerizing water-soluble polymer raw materials (monomer compositions). (Meth)acrylic refers to acrylic and / or methacrylic.

[0030] The water-soluble polymer raw material contains, for example, (meth)acrylamide and a carboxyl group-containing vinyl monomer. Preferably, the water-soluble polymer raw material does not contain the alkyl (meth)acrylate described later, but contains (meth)acrylamide and a carboxyl group-containing vinyl monomer.

[0031] (Meth)acrylamide is acrylamide and / or methacrylamide. Methacrylamide is preferred as (meth)acrylamide. Acrylamide and methacrylamide can also be used in combination. From the viewpoint of heat resistance, methacrylamide alone is preferred as (meth)acrylamide.

[0032] In water-soluble polymer raw materials, the content of (meth)acrylamide is not particularly limited and is adjusted as appropriate within a range that provides excellent heat resistance and air permeability. More specifically, the content of (meth)acrylamide is, for example, 60 parts by mass or more, preferably 70 parts by mass or more, more preferably 75 parts by mass or more, and even more preferably 79 parts by mass or more, per 100 parts by mass of the total amount of water-soluble polymer raw materials. Alternatively, 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, per 100 parts by mass of the total amount of water-soluble polymer raw materials.

[0033] Carboxylate-containing vinyl monomers are copolymerizable with (meth)acrylamide and are copolymerizable monomers containing carboxylate groups.

[0034] Examples of carboxyl group-containing vinyl monomers include α,β-unsaturated carboxylic acids and their salts. Examples of α,β-unsaturated carboxylic acids include α,β-unsaturated monocarboxylic acids and α,β-unsaturated dicarboxylic acids. Examples of α,β-unsaturated monocarboxylic acids include (meth)acrylic acid and crotonic acid. Examples of α,β-unsaturated dicarboxylic acids include itaconic acid, maleic acid, fumaric acid, itaconic anhydride, maleic anhydride, and fumaric anhydride. Examples of salts include sodium salts, potassium salts, and ammonium salts. These can be used alone or in combination of two or more. From the viewpoint of heat resistance, α,β-unsaturated monocarboxylic acids are preferred as carboxyl group-containing vinyl monomers, more preferably (meth)acrylic acid, and particularly preferably methacrylic acid.

[0035] In water-soluble polymer raw materials, the content of carboxyl group-containing vinyl monomer is not particularly limited and can be adjusted as appropriate within a range that provides excellent heat resistance and air permeability. More specifically, the content of carboxyl group-containing vinyl monomer is, for example, 3 parts by mass or more, preferably 4 parts by mass or more, and more preferably 5 parts by mass or more, per 100 parts by mass of the total amount of water-soluble polymer raw materials. Alternatively, the content of carboxyl group-containing vinyl monomer is, for example, 40 parts by mass or less, preferably 30 parts by mass or less, more preferably 25 parts by mass or less, even more preferably 20 parts by mass or less, and particularly preferably 10 parts by mass or less, per 100 parts by mass of the total amount of water-soluble polymer raw materials.

[0036] Furthermore, the water-soluble polymer raw material may also contain copolymerizable monomers that can copolymerize with (meth)acrylamide and / or carboxyl group-containing vinyl monomers (hereinafter referred to as water-soluble copolymerizable monomers).

[0037] Examples of water-soluble copolymerizable monomers include alkyl (meth)acrylates, functional group-containing vinyl monomers (excluding carboxyl group-containing vinyl monomers), vinyl esters, aromatic vinyl monomers, N-substituted unsaturated carboxylic acid amides, heterocyclic vinyl compounds, vinylidene halides, α-olefins, dienes, and crosslinkable vinyl monomers.

[0038] Examples of alkyl (meth)acrylates include alkyl (meth)acrylates having an alkyl moiety with 1 to 12 carbon atoms. Note that (meth)acrylate refers to both acrylate and / or methacrylate. Examples of alkyl (meth)acrylates having an alkyl moiety with 1 to 12 carbon atoms include alkyl (meth)acrylates having an alkyl moiety with 1 to 4 carbon atoms and alkyl (meth)acrylates having an alkyl moiety with 5 to 12 carbon atoms. Examples of alkyl (meth)acrylates having an alkyl moiety with 1 to 4 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, and t-butyl (meth)acrylate. Examples of alkyl (meth)acrylates having an alkyl moiety with 5 to 12 carbon atoms include 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.

[0039] Examples of functional group-containing vinyl monomers (excluding carboxyl group-containing vinyl monomers) include hydroxyl group-containing vinyl monomers, amino group-containing vinyl monomers, glycidyl group-containing vinyl monomers, cyano group-containing vinyl monomers, sulfonic acid group-containing vinyl monomers and their salts, acetoacetoxy group-containing vinyl monomers, and phosphate group-containing compounds. Examples of hydroxyl group-containing vinyl monomers include 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate. Examples of amino group-containing vinyl monomers include 2-aminoethyl (meth)acrylate, 2-(N-methylamino)ethyl (meth)acrylate, and 2-(N,N-dimethylamino)ethyl (meth)acrylate. Examples of glycidyl group-containing vinyl monomers include glycidyl (meth)acrylate. Examples of cyano group-containing vinyl monomers include (meth)acrylonitrile. Examples of sulfonic acid group-containing vinyl monomers include allyl sulfonic acid, methallyl sulfonic acid, and acrylamide t-butyl sulfonic acid. Examples of salts include sodium salts, potassium salts, and ammonium salts. Specifically, examples include sodium allylsulfonate, sodium methallylsulfonate, and ammonium methallylsulfonate. An example of an acetoacetoxy group-containing vinyl monomer is acetoacetoxyethyl (meth)acrylate. An example of a phosphate group-containing compound is 2-methac Ri One example is leuloxyethyl acid phosphate.

[0040] Examples of vinyl esters include vinyl acetate and vinyl propionate. Examples of aromatic vinyl monomers include styrene and α -Examples include methylstyrene, p-methylstyrene, vinyltoluene, and chlorostyrene. Examples of N-substituted unsaturated carboxylic acid amides include N-methylol(meth)acrylamide. Examples of heterocyclic vinyl compounds include vinylpyrrolidone. Examples of vinylidene halogens include vinylidene chloride and vinylidene fluoride. Examples of α-olefins include ethylene and propylene. Examples of dienes include butadiene. Examples of crosslinkable vinyl monomers include vinyl monomers containing two or more vinyl groups. Examples of vinyl monomers containing two or more vinyl groups include methylenebis(meth)acrylamide, divinylbenzene, polyethylene glycol chain-containing di(meth)acrylate, trimethylolpropanetetraacrylate, and pentaerythritol Ri Thor triacrylate and pentaeris Ri One example is toll tetraacrylate.

[0041] These water-soluble copolymerizable monomers can be used individually or in combination of two or more types.

[0042] In water-soluble polymer raw materials, the content of water-soluble copolymerizable monomers is not particularly limited and is adjusted as appropriate within a range that provides excellent heat resistance and air permeability. More specifically, the content of water-soluble copolymerizable monomers is, for example, 0 parts by mass or more per 100 parts by mass of the total amount of water-soluble polymer raw materials. Alternatively, the content of water-soluble copolymerizable monomers is, for example, 40 parts by mass or less, preferably 20 parts by mass or less, per 100 parts by mass of the total amount of water-soluble polymer raw materials. Particularly preferably, the content of water-soluble copolymerizable monomers is 0 parts by mass per 100 parts by mass of the total amount of water-soluble polymer raw materials. In other words, the water-soluble polymer raw material is, particularly preferably, free of water-soluble copolymerizable monomers and consists of (meth)acrylamide and carboxyl group-containing vinyl monomers.

[0043] Then, a water-soluble polymer can be obtained by polymerizing the above-mentioned water-soluble polymer raw material by a known method. More specifically, for example, a water-soluble polymer raw material and a polymerization initiator are mixed with water, the water-soluble polymer raw material is polymerized, and then aged as necessary.

[0044] Polymerization initiators are not particularly limited, but examples include water-soluble initiators and oil-soluble initiators. Examples of water-soluble initiators include ammonium persulfate, potassium persulfate, hydrogen peroxide, and organic hydroperoxides. Examples of oil-soluble initiators include benzoyl peroxide and azobisisobutyronitrile. Known redox initiators can also be used as polymerization initiators. These can be used alone or in combination of two or more. Preferably, water-soluble initiators are used as polymerization initiators, and more preferably, ammonium persulfate.

[0045] The blending ratio of the polymerization initiator is, for example, 0.01 parts by mass or more, preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and even more preferably 0.25 parts by mass or more, per 100 parts by mass of the monomer composition. Alternatively, the blending ratio of the polymerization initiator is, for example, 3 parts by mass or less, preferably 2 parts by mass or less, and more preferably 1 part by mass or less, per 100 parts by mass of the monomer composition.

[0046] The polymerization conditions are set appropriately according to the purpose and application. For example, the pressure conditions are 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 more, preferably 1.5 hours or more. The polymerization time is, for example, 20 hours or less, preferably 10 hours or less.

[0047] Furthermore, the maturation conditions are set appropriately according to the purpose and application. For example, the maturation temperature may be, for example, 0°C or higher, preferably 10°C or higher. Alternatively, the maturation temperature may be, for example, 90°C or lower, preferably 80°C or lower.

[0048] Furthermore, in polymerization, known additives can be added in appropriate proportions to improve manufacturing stability. Examples of additives include pH adjusters, metal ion encapsulants, molecular weight regulators, chain transfer agents, and emulsifying stabilizers. The additives may be added to the monomer composition before polymerization, to the reaction solution during polymerization, or to the reaction solution after polymerization.

[0049] Furthermore, in the polymerization described above, a neutralizing agent is preferably added to adjust the pH. An example of a neutralizing agent is ammonia. The neutralizing agent is preferably added to the reaction solution after polymerization. The pH of the reaction solution after adding the neutralizing agent is, for example, 5 or higher, preferably 6 or higher. The pH of the reaction solution is, for example, 10 or lower.

[0050] This process yields a water-soluble polymer as a polymer of the water-soluble polymer raw material. More specifically, an aqueous solution of the water-soluble polymer is obtained by polymerizing the water-soluble polymer raw material in water.

[0051] The above water-soluble polymer has, for example, repeating units derived from (meth)acrylamide and repeating units derived from carboxyl group-containing vinyl monomer.

[0052] The content of repeating units derived from (meth)acrylamide in the water-soluble polymer is not particularly limited, but is the same as the content of (meth)acrylamide in the water-soluble polymer raw material. That is, the content of repeating units derived from (meth)acrylamide is, for example, 60% by mass or more, preferably 70% by mass or more, more preferably 75% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more, relative to the total amount of the water-soluble polymer. Alternatively, the content of repeating units 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, relative to the total amount of the water-soluble polymer.

[0053] Furthermore, the content of repeating units derived from carboxyl group-containing vinyl monomers in the water-soluble polymer is not particularly limited, but is the same as the content of carboxyl group-containing vinyl monomers in the water-soluble polymer raw material. That is, the content of repeating units derived from carboxyl group-containing vinyl monomers is, for example, 3% by mass or more, preferably 4% by mass or more, and more preferably 5% by mass or more, relative to the total amount of the water-soluble polymer. Also, the content of repeating units derived from carboxyl group-containing vinyl monomers is, for example, 40% by mass or less, preferably 30% by mass or less, more preferably 25% by mass or less, even more preferably 20% by mass or less, and particularly preferably 10% by mass or less, relative to the total amount of the water-soluble polymer.

[0054] Furthermore, the content of repeating units derived from water-soluble copolymerizable monomers in the water-soluble polymer is not particularly limited, but is the same as the content of water-soluble copolymerizable monomers in the water-soluble polymer raw material. That is, the content of repeating units derived from water-soluble copolymerizable monomers is, for example, 0% by mass or more with respect to the total amount of water-soluble polymer. Also, the content of repeating units derived from water-soluble copolymerizable monomers is, for example, 30% by mass or less, preferably 15% by mass or less, with respect to the total amount of water-soluble polymer. Particularly preferably, the content of repeating units derived from water-soluble copolymerizable monomers is 0% by mass with respect to the total amount of water-soluble polymer.

[0055] Furthermore, the weight-average molecular weight of the water-soluble polymer is, for example, 20,000 or more, preferably 30,000 or more, and more preferably 40,000 or more, from the viewpoint of obtaining excellent air permeability. Also, the weight-average molecular weight of the water-soluble polymer is, for example, 200,000 or less, preferably 180,000 or less, and more preferably 150,000 or less, from the viewpoint of obtaining excellent heat resistance. Note that the weight-average molecular weight is the polystyrene-equivalent molecular weight obtained by gel permeation chromatography.

[0056] Furthermore, from the viewpoint of obtaining excellent heat resistance, the glass transition temperature of the water-soluble polymer is, for example, 200°C or higher, preferably 210°C or higher, more preferably 220°C or higher, even more preferably 230°C or higher, and even more preferably 240°C or higher. Also, from the viewpoint of obtaining excellent heat resistance, the glass transition temperature of the water-soluble polymer is, for example, 400°C or lower, preferably 300°C or lower, and more preferably 280°C or lower. The glass transition temperature is calculated using the FOX formula (the same applies hereinafter).

[0057] Furthermore, in the aqueous solution of the water-soluble polymer, the content of the water-soluble polymer (solid content concentration) is, for example, 3% by mass or more, preferably 5% by mass or more, and more preferably 8% by mass or more. Also, the content of the water-soluble polymer (solid content concentration) is, for example, 50% by mass or less, preferably 30% by mass or less, and more preferably 20% by mass or less. The content of the water-soluble polymer (solid content concentration) can be adjusted as needed by adding or removing water. adjustment It will be done.

[0058] The non-water-soluble polymer is not particularly limited, but examples include non-water-soluble (meth)acrylic polymers. Examples of non-water-soluble (meth)acrylic polymers include polymers obtained by polymerizing non-water-soluble polymer raw materials (monomer compositions).

[0059] The water-insoluble polymer raw material contains, for example, an alkyl (meth)acrylate. Examples of alkyl (meth)acrylates include the alkyl (meth)acrylates mentioned above.

[0060] Furthermore, the non-water-soluble polymer raw material may contain copolymerizable monomers that can copolymerize with (meth)acrylate alkyl esters (hereinafter referred to as non-water-soluble copolymerizable monomers). Examples of non-water-soluble copolymerizable monomers include functional group-containing vinyl monomers. Examples of functional group-containing vinyl monomers include the carboxyl group-containing vinyl monomers, hydroxyl group-containing vinyl monomers, amino group-containing vinyl monomers, glycidyl group-containing vinyl monomers, cyano group-containing vinyl monomers, sulfonic acid group-containing vinyl monomers and their salts, and acetoacetoxy group-containing vinyl monomers and phosphate group-containing compounds. In addition, examples of non-water-soluble copolymerizable monomers include the vinyl esters, aromatic vinyl monomers, N-substituted unsaturated carboxylic acid amides, acrylamides and / or (meth)acrylamides, heterocyclic vinyl compounds, vinylidene halogenated compounds, α-olefins, dienes, and crosslinkable vinyl monomers.

[0061] Then, by polymerizing the above-mentioned water-insoluble polymer raw material using a known method, a water-insoluble polymer is obtained as a polymer of the water-insoluble polymer raw material. More specifically, a dispersion of the water-insoluble polymer is obtained by polymerizing the water-insoluble polymer raw material in water.

[0062] Non-water-soluble polymers are relatively hydrophobic compared to the water-soluble polymers mentioned above.

[0063] The glass transition temperature of the water-insoluble polymer is, for example, -30°C or higher, preferably -20°C or higher, preferably -15°C or higher, and also, for example, 80°C or lower, preferably 50°C or lower.

[0064] The resin binder can be used alone or in combination of two or more types. Preferably, the resin binder is a water-soluble polymer.

[0065] In other words, as a resin binder, the use of a water-soluble polymer alone is preferred. Alternatively, a combination of a water-soluble polymer and a non-water-soluble polymer can also be used as a resin binder.

[0066] When water-soluble polymers and water-insoluble polymers are used in combination, the water-soluble polymers and water-insoluble polymers may be manufactured separately and then mixed. Furthermore, the water-soluble polymers and water-insoluble polymers may form composite particles. That is, water-soluble polymer raw materials may be polymerized in the presence of a water-insoluble polymer to form core-shell particles. Similarly, water-insoluble polymer raw materials may be polymerized in the presence of a water-soluble polymer to form core-shell particles.

[0067] The proportion of resin binder is adjusted as a ratio to the total amount of solids in the coating material for secondary battery separators (hereinafter referred to as the coating material components for secondary battery separators). The coating material components for secondary battery separators (solids) refer to, for example, the total amount of solids of resin binder, inorganic filler, and surfactant.

[0068] The total amount of resin binder is, for example, 1 part by mass or more, preferably 1.5 parts by mass or more, per 100 parts by mass of the total amount of coating material components (solids) for secondary battery separators. Alternatively, the total amount of resin binder is, for example, 10 parts by mass or less, preferably 5 parts by mass or less, per 100 parts by mass of the total amount of coating material components (solids) for secondary battery separators.

[0069] Examples of inorganic fillers include oxides, nitrides, carbides, sulfates, hydroxides, silicates, and minerals. Examples of oxides include alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide. Examples of nitrides include silicon nitride, titanium nitride, and boron nitride. Examples of carbides include silicon carbide and calcium carbonate. Examples of sulfates include magnesium sulfate and aluminum sulfate. Examples of hydroxides include aluminum hydroxide and aluminum hydroxide oxide. Examples of silicates include calcium silicate, magnesium silicate, diatomaceous earth, silica sand, and glass. Examples of minerals include talc, kaolinite, decite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amethyst, bentonite, asbestos, and zeolite. Preferably, inorganic fillers include oxides and hydroxides, and more preferably, aluminum oxide and aluminum hydroxide oxide.

[0070] The inorganic filler (solid content) content is, for example, 90 parts by mass or more, preferably 94 parts by mass or more, per 100 parts by mass of the total amount of coating material components (solid content) for secondary battery separators. Alternatively, the inorganic filler (solid content) content is, for example, 99 parts by mass or less, preferably 98 parts by mass or less, per 100 parts by mass of the total amount of coating material components (solid content) for secondary battery separators.

[0071] Furthermore, the content of the resin binder is, for example, 0.01 parts by mass or more, preferably 0.1 parts by mass or more, and more preferably 1 part by mass or more, per 100 parts by mass of inorganic filler. Also, the content of the resin binder is, for example, 50 parts by mass or less, preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, per 100 parts by mass of inorganic filler. Excellent heat resistance and air permeability can be obtained if the content ratio of the resin binder and inorganic filler is within the above range.

[0072] Surfactants are added to adjust the relationship between the surface tension of the coating material for secondary battery separators and the surface age at the time of surface tension measurement to the range described below, as will be explained in more detail later.

[0073] In other words, as long as the relationship between the surface tension of the coating material for secondary battery separators and the surface age at the time of surface tension measurement can be adjusted to the range described later, the type of surfactant is not particularly limited.

[0074] More specifically, examples of surfactants include acetylene-based surfactants, polyether-based surfactants, and silicone-based surfactants.

[0075] Examples of acetylene-based surfactants include compounds in which ethylene oxide is added to the hydroxyl group of acetylene glycols (acetylene glycol EO adducts).

[0076] Examples of acetylene glycols include 2,5,8,11-tetramethyl-6-dodecine-5,8-diol, 5,8-dimethyl-6-dodecine-5,8-diol, 2,4,7,9-tetramethyl-5-decine-4,7-diol, 4,7-dimethyl-5-decine-4,7-diol, 2,3,6,7-tetramethyl-4-octyne-3,6-diol, 3,6-dimethyl-4-octyne-3,6-diol, and 2,5-dimethyl-3-hexyne-2,5-diol. These can be used individually or in combination of two or more. The number (total) of ethylene oxide added is not particularly limited, for example, 1 mole or more, preferably 2 moles or more. Also, the number (total) of ethylene oxide added is, for example, 40 moles or less, preferably 30 moles or less.

[0077] Acetylene-based surfactants are available commercially. Examples of commercially available acetylene-based surfactants include the Orphin D-10 series, Orphin E series, Orphin PD series, Orphin EXP series, Orphin WE series, Orphin SPC series, AF series, Orphin SK series, Orphin AK series, and Surfinol series (all manufactured by Nisshin Chemical Industry Co., Ltd.).

[0078] Examples of polyether-based surfactants include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyoxyethylene oleyl ether, polyoxyethylene stearyl ether, polyoxyethylene lauryl ether, polyoxyethylene dodecyl ether, polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, and polyoxyethylene / polyoxypropylene block copolymer. These can be used individually or in combination of two or more.

[0079] Polyether surfactants are available commercially. An example of a commercially available polyether surfactant is the Noptex ED series (manufactured by Sunopco).

[0080] Examples of silicone-based surfactants include dimethyl silicone, methylphenyl silicone, chlorophenyl silicone, alkyl-modified silicone, fluorine-modified silicone, amino-modified silicone, alcohol-modified silicone, phenol-modified silicone, carboxy-modified silicone, epoxy-modified silicone, fatty acid ester-modified silicone, and polyether-modified silicone. These can be used individually or in combination of two or more types.

[0081] Silicone-based surfactants are available commercially. Examples of commercially available silicone-based surfactants include the BYK series (manufactured by Bic Chemie Japan) and the polyether-modified silicone KF series (manufactured by Shin-Etsu Chemical Co., Ltd.).

[0082] Surfactants may be used alone or in combination of two or more types, as long as the relationship between the surface tension of the coating material for secondary battery separators and the surface age at the time of surface tension measurement can be adjusted to the range described below.

[0083] From the viewpoint of heat resistance and air permeability, acetylene-based surfactants are preferred as surfactants. The surfactant is more preferably an acetylene-based surfactant. Furthermore, as for the acetylene-based surfactant, only one type of acetylene-based surfactant may be used, or two or more types of acetylene-based surfactants may be used in combination.

[0084] The HLB of the surfactant is, for example, 9 or higher, preferably 10 or higher, from the viewpoint of heat resistance and air permeability. Alternatively, the HLB of the surfactant is, for example, 15 or lower, preferably 14 or lower, and more preferably 13 or lower, from the viewpoint of heat resistance and air permeability.

[0085] The surfactant (solid content) content is, for example, 0.005 parts by mass or more, preferably 0.01 parts by mass or more, per 100 parts by mass of the total amount of coating material components (solid content) for secondary battery separators. Alternatively, the surfactant (solid content) content is, for example, 1.0 part by mass or less, preferably 0.5 parts by mass or less, per 100 parts by mass of the total amount of coating material components (solid content) for secondary battery separators.

[0086] The coating material for secondary battery separators may further contain a dispersant. Examples of dispersants include ammonium polycarboxylate and sodium polycarboxylate. If the dispersant is ammonium polycarboxylate, the resin binder and inorganic filler can be uniformly dispersed, and a coating film of uniform thickness (described later) can be obtained.

[0087] The proportion 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) per 100 parts by mass (solid content) of the coating material component for secondary battery separators.

[0088] To obtain a coating material for secondary battery separators, first, an inorganic filler dispersion (slurry) is prepared by mixing an inorganic filler and a dispersant with water in the above proportions.

[0089] Next, the resin binder is added to the inorganic filler dispersion (slurry) in the above proportions and stirred. This yields a coating material for secondary battery separators.

[0090] The stirring method is not particularly limited, and known stirring devices can be used. Examples of stirring devices include ball mills, bead mills, planetary ball mills, vibrating ball mills, sand mills, colloid mills, attritors, roll mills, high-speed impeller dispersions, dispersers, homogenizers, high-speed impact mills, ultrasonic dispersions, and stirring blades.

[0091] The coating material for secondary battery separators can be obtained, for example, as a dispersion in water. The coating material for secondary battery separators may also contain known additives as needed. Examples of additives include hydrophilic resins, thickeners, wetting agents, defoaming agents, and pH-1200. adjustment Examples include agents. Additives can be used alone or in combination of two or more types.

[0092] The surface tension of such secondary battery separator coating materials is adjusted by the surfactant described above.

[0093] In other words, the dynamic surface tension of the coating material for secondary battery separators, the static surface tension of the coating material for secondary battery separators, and the surface life (Surface Age) at the time of measurement of these surface tensions have a predetermined relationship.

[0094] The dynamic and static surface tensions of the coating material for secondary battery separators are measured by the bubble pressure method, with the inorganic filler content adjusted to 10% by mass relative to the total amount of the coating material for secondary battery separators.

[0095] More specifically, dynamic surface tension is measured by the bubble pressure method at any value selected from the range of surface age (Surface Age) 10.0 ± 0.5 ms (25°C). In the following, dynamic surface tension may be abbreviated as DST, and surface age (Surface Age) may be abbreviated as SA.

[0096] When the inorganic filler content is 10% by mass relative to the total amount of the coating material for secondary battery separators, the dynamic surface tension (DST) of the coating material for secondary battery separators is relatively high, for example, 50 mN / m or more, preferably 60 mN / m or more, more preferably 65 mN / m or more, and even more preferably 70 mN / m or more.

[0097] Furthermore, when the inorganic filler content is 10% by mass relative to the total amount of coating material for secondary battery separators, the dynamic surface tension (DST) of the coating material for secondary battery separators is, for example, 100 mN / m or less.

[0098] Static surface tension is measured using the bubble pressure method at any value selected from the range of surface age (SST) 1003 ± 10 ms (25°C). Static surface tension is sometimes abbreviated as SST.

[0099] When the inorganic filler content is 10% by mass relative to the total amount of the coating material for secondary battery separators, the static surface tension (SST) of the coating material for secondary battery separators is relatively low, for example, 65 mN / m or less, preferably 60 mN / m or less, more preferably 55 mN / m or less, and even more preferably 52 mN / m or less.

[0100] Furthermore, when the inorganic filler content is 10% by mass relative to the total amount of coating material for secondary battery separators, the static surface tension (SST) of the coating material for secondary battery separators is, for example, 40 mN / m or more.

[0101] Furthermore, when the inorganic filler content is 10% by mass relative to the total amount of coating material for secondary battery separators, the SST, DST, and SA of the coating material for secondary battery separators satisfy the following formula (1).

[0102] [SST-DST] / [SA during SST measurement-SA during DST measurement]≦-0.015(1) SA: Surface Age (ms) SST: Static surface tension (mN / m) measured by the bubble pressure method within the range of Surface Age 1003 ± 10 ms (25°C). DST: Dynamic surface tension (mN / m) measured by the bubble pressure method within the range of Surface Age 10.0 ± 0.5 ms (25℃).

[0103] In other words, the slope of a graph (surface life-surface tension graph) with Surface Age (ms) on the horizontal axis and dynamic and static surface tension (mN / m) on the vertical axis is adjusted to a predetermined value or less by the surfactant mentioned above (see Figure 1).

[0104] The [SST-DST] / [SA during SST measurement-SA during DST measurement] shown in formula (1) above is, more specifically, -0.015 or less, preferably -0.017 or less, more preferably -0.019 or less, even more preferably -0.021 or less, and particularly preferably -0.023 or less.

[0105] If [SST-DST] / [SA during SST measurement-SA during DST measurement] is below the above upper limit, excellent heat resistance and air permeability can be obtained.

[0106] More specifically, by lowering the surface tension of the coating material for secondary battery separators using a surfactant, excellent coating stability can be obtained. However, lowering the surface tension of the coating material for secondary battery separators has the drawback that the coating material penetrates the porous membrane (described later), reducing its air permeability.

[0107] On the other hand, if the surface tension of the coating material for secondary battery separators is kept relatively high in order to suppress the penetration of the coating material, the stability of the coating film decreases, a homogeneous coating film cannot be obtained, and as a result, the heat resistance decreases.

[0108] In contrast to these, the coating material for secondary battery separators described above shows that the ratio of [SST-DST] / [SA during SST measurement-SA during DST measurement] is below the upper limit mentioned above.

[0109] Therefore, during and immediately after application of the coating material for secondary battery separators, the relatively high dynamic surface tension suppresses the penetration of the coating material into the porous membrane (described later). As a result, excellent air permeability is obtained.

[0110] Furthermore, after a predetermined time has elapsed since the application of the coating material for secondary battery separators, the relatively low static surface tension results in excellent coating stability and a relatively homogeneous coating. As a result, excellent heat resistance is obtained.

[0111] The lower limit of [SST-DST] / [SA during SST measurement-SA during DST measurement] is not particularly limited, but for example, it is -0.050 or higher, preferably -0.040 or higher.

[0112] The above-described coating material for secondary battery separators contains water, a resin binder, an inorganic filler, and a surfactant. Furthermore, the dynamic surface tension (DST), static surface tension (SST), and their surface age (SA) at the time of measurement satisfy a specific relationship. Therefore, using the above-described coating material for secondary battery separators, a secondary battery separator with excellent heat resistance and air permeability can be obtained.

[0113] Furthermore, this coating material for secondary battery separators can be suitably used as a coating material for secondary battery separators.

[0114] Secondary battery separators can be manufactured by known methods.

[0115] In this method, a porous membrane is first prepared. Examples of porous membranes include polyolefin porous membranes and aromatic polyamide porous membranes, with polyolefin porous membranes being preferred. Examples of polyolefins include polyethylene and polypropylene. The porous membrane may be surface-treated as needed. Examples of surface treatments include corona treatment and plasma treatment.

[0116] The thickness of the porous membrane is, for example, 1 μm or more, preferably 5 μm or more. Alternatively, the thickness of the porous membrane may be, for example, 40 μm or less, preferably 20 μm or less.

[0117] Next, in this method, the above-mentioned separator coating material is applied to at least one side of the porous film. Then, if necessary, the separator coating material is dried to obtain a coated film.

[0118] The coating method is not particularly limited, but examples include gravure coating, small-diameter gravure coating, reverse roll coating, transfer roll coating, kiss coating, dip coating, microgravure coating, knife coating, air doctor coating, blade coating, rod coating, squeeze coating, cast coating, die coating, screen printing, and spray coating.

[0119] As for the drying conditions, the drying temperature is, for example, 40°C or higher, and also, for example, 80°C or lower. The thickness of the coating film after drying is, for example, 1 μm or more, preferably 2 μm or more. Also, the thickness of the coating film after drying is, for example, 10 μm or less, preferably 8 μm or less.

[0120] This allows for the manufacture of a secondary battery separator comprising a porous membrane and a coating film of the aforementioned secondary battery separator coating material disposed on at least one side of the porous membrane.

[0121] In the above explanation, the coating film for secondary battery separators was placed on at least one side of the porous film, but it is also possible to place the above coating film on both sides of the porous film.

[0122] The above-mentioned secondary battery separator has a coating film of the above-mentioned secondary battery separator coating material, and therefore has excellent heat resistance and air permeability.

[0123] Furthermore, the above-described method for manufacturing secondary battery separators allows for the efficient production of secondary battery separators with excellent heat resistance and air permeability.

[0124] Furthermore, this secondary battery separator can be suitably used as a separator for secondary batteries.

[0125] The secondary battery comprises a positive electrode, a negative electrode, a secondary battery separator disposed between the positive and negative electrodes, and an electrolyte impregnated in the positive electrode, the negative electrode, and the secondary battery separator.

[0126] As the positive electrode, for example, a known electrode comprising a positive electrode current collector and a positive electrode active material laminated on the positive electrode current collector is used.

[0127] Examples of conductive materials for the positive electrode current collector include known conductive materials. Examples of conductive materials include aluminum, titanium, stainless steel, nickel, calcined carbon, conductive polymers, and conductive glass. These can be used individually or in combination of two or more types.

[0128] The positive electrode active material is not particularly limited, but examples include lithium-containing transition metal oxides, lithium-containing phosphates, and lithium-containing sulfates. These can be used individually or in combination of two or more.

[0129] As the negative electrode, for example, a known electrode comprising a negative electrode current collector and a negative electrode active material stacked on the negative electrode current collector can be used.

[0130] Examples of negative electrode current collectors include copper and nickel. These can be used individually or in combination of two or more types.

[0131] Examples of negative electrode active materials include graphite, soft carbon, and hard carbon. These can be used individually or in combination of two or more types.

[0132] If 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. Examples of carbonate compounds include ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC).

[0133] To manufacture a secondary battery, for example, a separator for the secondary battery is placed between the positive electrode and the negative electrode, these are then housed in a battery casing (cell), and an electrolyte is injected into the battery casing.

[0134] This makes it possible to obtain a rechargeable battery.

[0135] Because the above-mentioned secondary battery is equipped with the above-mentioned secondary battery separator, it has excellent heat resistance and air permeability, and as a result, excellent durability and power generation efficiency. [Examples]

[0136] In the following description, specific numerical values ​​such as mixing ratios (content), physical properties, and parameters may be replaced with the corresponding upper limits (values ​​defined as "less than or equal to" or "less than") or lower limits (values ​​defined as "greater than or equal to" or "greater than") of the mixing ratios (content), physical properties, and parameters described in the "Modes for Carrying Out the Invention" section above. Furthermore, unless otherwise specified in the following description, "parts" and "%" refer to mass.

[0137] Manufacturing Example 1 (Resin Binder) Stirring and reflux cooling vessel 300 parts by mass of distilled water were placed in a separable flask. Next, the flask was purged with nitrogen gas. Then, the distilled water was heated to 80°C. Next, 0.6 parts by mass of ammonium persulfate were added to the distilled water. mass A certain amount was added. Next, the monomer composition described below was continuously added to distilled water over 3 hours, and the mixture was held for another 3 hours to allow the reaction to proceed. After that, 5 parts by mass of 25% aqueous ammonia was added to the reaction solution to adjust the pH to 9.0. Then, an appropriate amount of water was added to adjust the solid content to 14.0%. This yielded an aqueous solution of resin binder.

[0138] Methacrylamide 95.0 parts by mass 5.0 parts by mass of methacrylic acid

[0139] Examples 1-4 and Comparative Examples 1-3 (Coating materials for secondary battery separators) 121.12 g of distilled water was mixed with 2.96 g of an aqueous solution of ammonium polycarboxylate (dispersant, manufactured by Sunopco, trade name SN5468) and stirred with a disperser (1000 rpm). Then, to the resulting mixture, boehmite (inorganic filler, aluminum hydroxide oxide, manufactured by Navaltec, trade name Apiral AOH60, average median diameter D) was added. 50 147.8 g of (0.9 μm) was added, and the mixture was stirred for 5 minutes, followed by further stirring in a homogenizer (5000 rpm) for 2 minutes. This yielded an inorganic filler dispersion (inorganic filler concentration 54% by mass).

[0140] 1.29 g of an aqueous solution of the resin binder from Production Example 1 (solid content concentration 14%) and 0.78 g of distilled water were stirred with a stirrer. Then, 13 g of the inorganic filler dispersion (solid content concentration 54%) and 0.032 g of surfactant were added to this mixture and stirred for 20 minutes.

[0141] Furthermore, the surfactants listed in Table 1 were used as surfactants in the mass proportions listed in Table 1.

[0142] Next, the resulting mixture was filtered through a 300-mesh filter (filtration particle size 48 μm). This yielded a coating material (coating liquid) for secondary battery separators.

[0143] Furthermore, the resin binder content in the coating solution was 8.5% by mass relative to the total amount of the coating solution. Also, the resin binder content was 2.49 parts by mass per 100 parts by mass of the total amount of coating material components (solids) for secondary battery separators.

[0144] Furthermore, in the coating liquid, the inorganic filler content was 46.5% by mass relative to the total amount of the coating material (coating liquid) for secondary battery separators. Also, the inorganic filler content was 97.5 parts by mass per 100 parts by mass of the total amount of the coating material components (solids) for secondary battery separators.

[0145] Furthermore, in the coating solution, the surfactant content was 0.21% by mass relative to the total amount of the coating material (coating solution) for secondary battery separators. Also, the surfactant content was 0.44 parts by mass per 100 parts by mass of the total amount of the coating material components (solids) for secondary battery separators.

[0146] Furthermore, in the coating solution, the content ratio of resin binder (solids) was 2.5 parts by mass and the content ratio of surfactant (solids) was 0.45 parts by mass per 100 parts by mass of inorganic filler.

[0147] Next, the above-mentioned secondary battery separator coating material (coating liquid) was applied to the surface of the polyolefin resin porous film using a wire bar. After coating, a 5 μm thick coating film was formed on the surface of the polyolefin resin porous film by drying at 50°C. This resulted in obtaining a secondary battery separator.

[0148] In addition, a separate coating solution for surface tension measurement was prepared from the above-mentioned coating solution. Specifically, distilled water was added to the above-mentioned coating solution to adjust the inorganic filler content to 10% by mass. This resulted in a coating solution for surface tension measurement (10% by mass inorganic filler).

[0149] In addition , tree The proportion of the lipid binder was 2.49 parts by mass per 100 parts by mass of the total amount of coating material components (solids) for secondary battery separators.

[0150] Furthermore, the inorganic filler content was 10% by mass relative to the total amount of coating liquid used for surface tension measurement. Additionally, the inorganic filler content was 97.5 parts by mass per 100 parts by mass of the total amount of coating material components (solids) for secondary battery separators.

[0151] Also , world The surfactant content was 0.44 parts by mass per 100 parts by mass of the total amount of coating material components (solids) for secondary battery separators.

[0152] Furthermore, in the coating solution for surface tension measurement, the content ratio of resin binder (solids) was 2.5 parts by mass and the content ratio of surfactant (solids) was 0.45 parts by mass per 100 parts by mass of inorganic filler.

[0153] Examples 5-8 and Comparative Examples 4-6 (Coating materials for secondary battery separators) As an inorganic filler, aluminum oxide (manufactured by Nippon Light Metal Co., Ltd., product name SMM22-B, average median diameter D) is used instead of boehmite. 50Except for using a 0.6 μm (0.6 μm) particle, a coating material (coating liquid) for secondary battery separators, a coating liquid for surface tension measurement, and a secondary battery separator were obtained using the same method as in Examples 1-4 and Comparative Examples 1-3.

[0154] Furthermore, the surfactants listed in Table 2 were used as surfactants in the mass proportions listed in Table 2.

[0155] <Surface tension> The dynamic and static surface tension of a coating solution (10% by mass inorganic filler) for surface tension measurement was measured at 25°C using a surface tension measuring device (Bubble Pressure Tensiometer BP-2, manufactured by Krus Corporation) by the bubble pressure method.

[0156] Tables 1 and 2 show the dynamic surface tension (DST, mN / m), its Surface Age (SA, ms) at the time of measurement, and the static surface tension (SST, mN / m), its Surface Age (SA, ms) at the time of measurement.

[0157] Furthermore, the values ​​of the following formulas were calculated based on the surface tension measurement results. The results are shown in Tables 1 and 2.

[0158] [SST-DST] / [SA during SST measurement - SA during DST measurement] SA: Surface Age (ms) SST: Static surface tension (mN / m) measured by the bubble pressure method within the range of Surface Age 1003 ± 10 ms (25°C). DST: Dynamic surface tension (mN / m) measured by the bubble pressure method within the range of Surface Age 10.0 ± 0.5 ms (25℃).

[0159] <Rating> (1) Heat resistance A secondary battery separator was cut into 5cm x 5cm pieces to serve as the test specimen. After leaving this specimen in an oven at 150°C for 1 hour, the length of each side was measured, and the thermal shrinkage rate was calculated. Furthermore, the heat resistance was evaluated based on the following criteria. The results are shown in Table 1. ◎: The thermal shrinkage rate was less than 10%. ○: The thermal shrinkage rate was 10% or more but less than 20%. △: The thermal shrinkage rate was between 20% and 40%. ×: The thermal shrinkage rate was 40% or more.

[0160] (2) Air permeability For secondary battery separators, the air permeability resistance was determined using an Ouken-type air permeability and smoothness tester manufactured by Asahi Seiko Co., Ltd., in accordance with JIS-P-8117 (2009). A lower air permeability resistance was considered to indicate superior ion permeability. Furthermore, the superiority of ion permeability was evaluated according to the following criteria. The results are shown in Table 1. ◎: The air permeability resistance was less than 190 s / 100 mL. ○: The air permeability resistance was between 190 s / 100 mL and 220 s / 100 mL. △: The air permeability resistance was between 220 s / 100 mL and 250 s / 100 mL. ×: The air permeability resistance was 250 s / 100 mL or higher.

[0161] [Table 1]

[0162] [Table 2]

[0163] The details of the abbreviations used in the table are as follows. Coating solution: Coating material for secondary battery separators (coating solution for surface tension measurement) EXP4123: Acetylene-based surfactant, trade name Orphine EXP4123, HLB 10-13, manufactured by Nisshin Chemical Industry Co., Ltd. E1010: Acetylene-based surfactant, trade name Orphine E1010, HLB 13-14, manufactured by Nisshin Chemical Industry Co., Ltd. E1020: Acetylene-based surfactant, trade name Orphine E1020, HLB 15-16, manufactured by Nisshin Chemical Industry Co., Ltd. BYK Dynwet800: Silicone-based surfactant, product name BYK Dynwet800, manufactured by BYK Chemie Japan.

[0164] The above invention is provided as an illustrative embodiment of the present invention, but this is merely illustrative and should not be interpreted restrictively. Modifications of the present invention that are obvious to those skilled in the art are included in the claims described below. [Industrial applicability]

[0165] The coating material for secondary battery separators, secondary battery separators, methods for manufacturing secondary battery separators, and secondary batteries of the present invention are suitably used in fields where heat resistance and air permeability are required for secondary batteries.

Claims

1. A coating material for secondary battery separators, comprising water, a resin binder, an inorganic filler, and a surfactant. When the inorganic filler content is diluted by adding distilled water to the total amount of the coating material for the secondary battery separator, The dynamic surface tension (DST), measured by the bubble pressure method within the range of Surface Age (SA) 10.0 ± 0.5 ms (25°C), is between 50 mN / m and 100 mN / m. The static surface tension (SST) measured by the bubble pressure method within the range of Surface Age (SA) 1003 ± 10 ms (25°C) is between 40 mN / m and 65 mN / m. A coating material for secondary battery separators, wherein the dynamic surface tension (DST), the static surface tension (SST), and the Surface Age (SA) satisfy the following formula (1). [SST - DST] / [SA during SST measurement - SA during DST measurement] ≤ -0.015 (1) SA: Surface Age (ms) SST: Static surface tension (mN / m) measured by the bubble pressure method within the range of Surface Age 1003 ± 10 ms (25°C). DST: Dynamic surface tension (mN / m) measured by the bubble pressure method within the range of Surface Age 10.0 ± 0.5 ms (25°C).

2. The coating material for secondary battery separators according to claim 1, wherein the dynamic surface tension is 65 mN / m or more when the content ratio of the inorganic filler is 10% by mass of the total amount of the coating material for secondary battery separators.

3. The coating material for secondary battery separators according to claim 1, wherein the static surface tension is 55 mN / m or less when the content ratio of the inorganic filler is 10% by mass relative to the total amount of the coating material for secondary battery separators.

4. The coating material for secondary battery separators according to claim 1, wherein the surfactant includes an acetylene-based surfactant.

5. The coating material for secondary battery separators according to Claim 1, wherein the HLB of the surfactant is 10 or more and 14 or less.

6. The coating material for secondary battery separators according to claim 1, wherein the content ratio of the resin binder is 0.1 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the inorganic filler.

7. The aforementioned resin binder, Repeating units derived from (meth)acrylamide, Repeating units derived from carboxyl group-containing vinyl monomers and A coating material for a secondary battery separator according to claim 1, having the following characteristics.

8. Porous membrane and A coating film of the secondary battery separator coating material according to claim 1, disposed on at least one side of the porous film, A secondary battery separator characterized by having the following features.

9. The process of preparing a porous membrane, and The process includes applying the secondary battery separator coating material described in claim 1 to at least one side of the porous membrane. A method for manufacturing a secondary battery separator, characterized by the following features.

10. A secondary battery comprising a positive electrode, a negative electrode, and a secondary battery separator according to claim 8 disposed between the positive electrode and the negative electrode.

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