Raw materials for coating materials for secondary battery separators, coating materials for secondary battery separators, secondary battery separators, and secondary batteries

Abstract

This raw material for a secondary battery separator coating material contains: a resin which is a reaction product of a polyvinyl alcohol and a modified methylolmelamine condensation resin having an acidic group; or a polyvinyl alcohol and a modified methylolmelamine condensation resin having an acidic group.

Description

Technical Field

[0001] The present invention relates to a coating material raw material for a secondary battery separator, a coating material for a secondary battery separator, a secondary battery separator, and a secondary battery. Specifically, it relates to a coating material raw material for a secondary battery separator, a coating material for a secondary battery separator containing the coating material raw material for a secondary battery separator, a secondary battery separator provided with a coating film of the coating material for a secondary battery separator, and a secondary battery provided with the secondary battery separator.

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

[0003] As such a separator, for example, a polyolefin porous membrane is known.

[0004] On the other hand, a coating layer may be provided on the surface of the separator to impart various physical properties. Such a coating layer is formed, for example, by applying a coating material for a secondary battery separator to the surface of the separator and drying it.

[0005] As such a coating material for a secondary battery separator, for example, a coating material raw material for a secondary battery separator containing a water-soluble polymer obtained by polymerizing a water-soluble polymer raw material containing methacrylamide and methacrylic acid, and an inorganic filler have been proposed (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] On the other hand, thermal shrinkage can change the shape of the separator, potentially causing a short circuit between the positive and negative electrodes. Therefore, the coating layer must be heat-resistant.

[0008] The present invention aims to provide a raw material for a secondary battery separator coating material that is excellent in heat resistance and ion permeability, a coating material for a secondary battery separator containing the raw material for the secondary battery separator coating material, a secondary battery separator having a coating film of the secondary battery separator coating material, and a secondary battery having the secondary battery separator. [Means for solving the problem]

[0009] The present invention [1] is a coating material raw material for secondary battery separators, comprising a resin which is a reaction product of a modified methylolmelamine condensation resin having an acidic group and polyvinyl alcohol, or comprising the modified methylolmelamine condensation resin having an acidic group and the polyvinyl alcohol.

[0010] The present invention [2] includes the resin, wherein the acidic group is a sulfonic acid group, and comprises the raw material for a coating material for a secondary battery separator as described in [1] above.

[0011] The present invention [3] includes the raw material for a secondary battery separator coating material described in [1] above, comprising the modified methylolmelamine condensation resin having the acidic group and the polyvinyl alcohol, wherein the content ratio of the polyvinyl alcohol is 5 parts by mass or more and less than 50 parts by mass per 100 parts by mass of the modified methylolmelamine condensation resin.

[0012] The present invention [4] includes a coating material for secondary battery separators, comprising the raw material for a coating material for secondary battery separators described in any one of the above [1] to [3], and inorganic particles.

[0013] The present invention [5] includes a secondary battery separator comprising a porous membrane and a coating film of the secondary battery separator coating material described in [4] above, which is disposed on at least one side of the porous membrane.

[0014] The present invention [6] includes a secondary battery comprising a positive electrode, a negative electrode, and a secondary battery separator as described in [5] above, disposed between the positive electrode and the negative electrode. [Effects of the Invention]

[0015] The raw material for the coating material of the secondary battery separator of the present invention contains a resin which is a reaction product of a modified methylolmelamine condensation resin having acidic groups and polyvinyl alcohol, or contains a modified methylolmelamine condensation resin having acidic groups and polyvinyl alcohol. Therefore, it has excellent heat resistance and ion permeability.

[0016] The coating material for secondary battery separators of the present invention contains the raw materials for the coating material for secondary battery separators of the present invention. Therefore, it has excellent heat resistance and ion permeability.

[0017] The secondary battery separator of the present invention comprises a coating film of the coating material for secondary battery separators of the present invention. Therefore, it exhibits excellent heat resistance and ion permeability.

[0018] The secondary battery of the present invention is equipped with the secondary battery separator of the present invention. Therefore, it has excellent heat resistance and ion permeability. [Modes for carrying out the invention]

[0019] The raw material for the coating material for secondary battery separators contains a resin which is a reaction product of a modified methylolmelamine condensate resin having acidic groups and polyvinyl alcohol, or contains a modified methylolmelamine condensate resin having acidic groups and polyvinyl alcohol. The first invention, in which the raw material for the coating material for secondary battery separators contains a resin which is a reaction product of a modified methylolmelamine condensate resin having acidic groups and polyvinyl alcohol, and the second invention, in which the raw material for the coating material for secondary battery separators contains a modified methylolmelamine condensate resin having acidic groups and polyvinyl alcohol, will be described in detail below.

[0020] 1. Raw materials for coating materials used in secondary battery separators <<First Invention>> The coating material raw material for a secondary battery separator contains a resin that is a reaction product of a modified methylol melamine condensation resin having an acidic group and polyvinyl alcohol.

[0021] The resin is a reaction product of a modified methylol melamine condensation resin having an acidic group and polyvinyl alcohol.

[0022] <Modified methylol melamine condensation resin having an acidic group> The modified methylol melamine condensation resin having an acidic group (hereinafter sometimes referred to as the modified methylol melamine condensation resin) is a condensation polymer of modified methylol melamine.

[0023] Modified methylol melamine is a reaction product of methylol melamine and an acid component.

[0024] [Methylol melamine] Methylol melamine is a reaction product of melamine and formaldehyde or paraformaldehyde. When paraformaldehyde is used, paraformaldehyde is hydrolyzed to formaldehyde and then reacted with melamine.

[0025] To react melamine and formaldehyde, water, melamine, and formaldehyde are mixed and heated.

[0026] The blending amount of formaldehyde with respect to 1 mol of melamine, although described in detail later, is, from the viewpoint of increasing the molecular weight, for example, 3.0 or more, preferably more than 3.0, more preferably 3.2 or more, still more preferably 3.3 or more, and also, for example, 5.0 or less, preferably 4.0 or less.

[0027] As the heating conditions, the heating temperature is, for example, 40°C or higher, preferably 50°C or higher, and also, for example, 90°C or lower, preferably 80°C or lower. Also, the heating time is, for example, 0.5 hours or more, preferably 2 hours or more, and also, for example, 6 hours or less.

[0028] Furthermore, in the above reaction, the pH is 3.0 or higher, preferably 4.0 or higher, more preferably 8.0 or higher, even more preferably 9.0 or higher, particularly preferably 10.0 or higher, and for example, 13.0 or lower, preferably 12.0 or lower, and more preferably 11.8 or lower. The pH can be adjusted by adding an alkali (for example, sodium hydroxide).

[0029] This causes melamine (general formula (1-1) below) and formaldehyde (general formula (1-2) below) to react, yielding methylolmelamine (general formula (1-3) below). [ka]

[0030] Preferably, methylolmelamine (general formula (1-3) above) is trimethylolmelamine, in which 3 of the 6 hydrogens in the amino group of melamine are modified into methylol groups, or methylolmelamine is tetramethylolmelamine, in which 4 of the 6 hydrogens in the amino group of melamine are modified into methylol groups.

[0031] [Modified methylol melamine] As described above, modified methylolmelamine is a reaction product of methylolmelamine and an acidic component.

[0032] The acidic component is a component that can react with the methylol group of methylolmelamine. Furthermore, the acidic component is a component that introduces an acidic group into methylolmelamine by reacting with the methylol group of methylolmelamine.

[0033] Examples of acidic components include carboxylic acids, phosphoric acid, and sulfurous acid.

[0034] Examples of carboxylic acids include maleic acid, succinic acid, phthalic acid, formylbenzoic acid, aminobenzoic acid, acrylic acid, methacrylic acid, and amino acids (e.g., glycine). Carboxylic acids also include their salts and anhydrides. Examples of carboxylic acid salts include sodium maleate and sodium succinate. Examples of carboxylic acid anhydrides include maleic anhydride, succinic anhydride, and phthalic anhydride.

[0035] Examples of phosphoric acid include phosphonobenzoic acid and aminophenylphosphonic acid. Furthermore, phosphoric acid includes its salts. An example of a phosphoric acid salt is sodium phosphonobenzoate.

[0036] Examples of sulfurous acids include sulfobenzoic acid, formylbenzenesulfonic acid, sulfanilic acid, pyrosulfite, and sulfurous acid. Sulfurous acids also include their salts. Examples of sulfurous acid salts include sodium bisulfite, sodium sulfite, and sodium pyrosulfite. Preferably, sulfurous acids include sodium bisulfite, sulfanilic acid, and sodium pyrosulfite. More preferably, sulfurous acids include sodium bisulfite.

[0037] Preferably, sulfurous acid is used as the acid component.

[0038] Acidic components can be used alone or in combination of two or more types.

[0039] Modified methylolmelamine is obtained by reacting methylolmelamine with an acidic component.

[0040] To react methylolmelamine with an acid component, mix water, methylolmelamine, and the acid component, then heat the mixture.

[0041] The amount of acid component added is, for example, 0.44 moles or more, preferably 0.50 moles or more, more preferably 0.60 moles or more, even more preferably 0.70 moles or more, or, for example, 1.00 mole or less, preferably 0.90 moles or less, and more preferably 0.80 moles or less, per mole of methylolmelamine.

[0042] The heating conditions include a heating temperature of, for example, 50°C or higher, preferably 70°C or higher, and also, for example, 100°C or lower, preferably 90°C or lower. The heating time is, for example, 0.5 hours or more, preferably 1 hour or more, and also, for example, 6 hours or less.

[0043] This causes methylolmelamine to react with the acid component, yielding modified methylolmelamine. More specifically, one of the methylol groups in methylolmelamine can be modified by the acid component into an acidic group derived from the acid component.

[0044] In other words, modified methylolmelamine has acidic groups derived from the acid component. Specifically, when the acid component is a carboxylic acid, modified methylolmelamine has a carboxyl group as its acidic group. When the acid component is phosphoric acid, modified methylolmelamine has a phosphoric acid group as its acidic group. When the acid component is sulfite, modified methylolmelamine has a sulfonic acid group as its acidic group. A sulfonic acid group is a preferred example of an acidic group.

[0045] More specifically, when the acid component is sodium bisulfite, methylolmelamine (general formula (1-3) below) reacts with sodium bisulfite (general formula (2-1) below) to obtain modified methylolmelamine (general formula (2-2) below). The modified methylolmelamine represented by general formula (2-2) below has a sulfonic acid group as its acidic group. [ka]

[0046] As the modified methylolmelamine, a modified methylolmelamine represented by the above general formula (2-2) is preferred.

[0047] As described above, modified methylolmelamine condensation resin is a condensation polymer of modified methylolmelamine (modified methylolmelamine having acidic groups). The method for producing modified methylolmelamine condensation resin will be described later.

[0048] <Polyvinyl alcohol> Polyvinyl alcohol is an ingredient that imparts wettability and improves adhesion when this resin is used as a raw material for coating materials for secondary battery separators.

[0049] Examples of polyvinyl alcohol include unmodified polyvinyl alcohol and modified polyvinyl alcohol.

[0050] Examples of modified polyvinyl alcohols include anionic group-modified polyvinyl alcohol (e.g., carboxyl group-modified polyvinyl alcohol, sulfo group-modified polyvinyl alcohol) and hydrophobic group-modified polyvinyl alcohol. Preferably, anionic group-modified polyvinyl alcohol is used as the modified polyvinyl alcohol. More preferably, carboxyl group-modified polyvinyl alcohol is used as the modified polyvinyl alcohol.

[0051] Preferably, modified polyvinyl alcohol is used as the polyvinyl alcohol.

[0052] Polyvinyl alcohol transformation The molarity is, for example, 70 mol% or more, preferably 85 mol% or more, more preferably 90 mol% or more, even more preferably 95 mol% or more, and also, for example, 100 mol% or less, preferably 99 mol% or less.

[0053] Polyvinyl alcohol can be used alone or in combination with two or more other types.

[0054] Furthermore, polyvinyl alcohol can also be prepared as an aqueous solution of polyvinyl alcohol. In the aqueous solution of polyvinyl alcohol, the solid content concentration of polyvinyl alcohol is, for example, 5% by mass or more, and for example, 50% by mass or less.

[0055] <Method for manufacturing resin> The resin is obtained by reacting a modified methylolmelamine condensation resin with polyvinyl alcohol.

[0056] More specifically, the resin is obtained by producing a modified methylolmelamine condensation resin by dehydrating and condensing modified methylolmelamine, and then reacting this modified methylolmelamine condensation resin with polyvinyl alcohol. In other words, such a resin is distinguished from a resin obtained by first obtaining a modified methylolmelamine condensation resin by dehydrating and condensing modified methylolmelamine, and then reacting it with vinyl alcohol.

[0057] Specifically, first, modified methylolmelamine and polyvinyl alcohol are mixed with water. Next, the modified methylolmelamine is dehydrated and condensed, and the modified methylolmelamine condensation resin obtained by dehydration condensation is reacted with polyvinyl alcohol.

[0058] In the above dehydration condensation, two methylol groups in modified methylolmelamine undergo dehydration condensation to obtain a modified methylolmelamine condensed resin.

[0059] Furthermore, modified methylol melamine condensation resin and polyvinyl alcohol ofIn the reaction, the methylol groups of the modified methylolmelamine condensation resin react with the hydroxyl groups of polyvinyl alcohol. The reaction between methylol and hydroxyl groups is described, for example, in the Journal of Cleaner Production Volume 255, 10 May 2020, 120062, 'Efficient removal of Congo red dye from aqueous solution by adsorbent films of polyvinyl alcohol / melamine-formaldehyde composite and bactericidal effects'.

[0060] Furthermore, in this reaction, for example, an acid (e.g., sulfuric acid) is added, and the mixture is heated in water at a pH of 5 or higher but less than 8.

[0061] The heating conditions include a heating temperature of, for example, 50°C or higher, preferably 60°C or higher, and for example, 90°C or lower, preferably 80°C or lower. The heating time is, for example, 1 hour or more, preferably 2 hours or more, and for example, 6 hours or less.

[0062] The proportion of modified methylolmelamine is, for example, 70 parts by mass or more, preferably 80 parts by mass or more, more preferably 85 parts by mass or more, and also, for example, 99 parts by mass or less, preferably 95 parts by mass or less, based on 100 parts by mass of the total amount of modified methylolmelamine and polyvinyl alcohol.

[0063] Furthermore, the proportion of polyvinyl alcohol is, for example, 1 part by mass or more, preferably 5 parts by mass or more, and for example, 30 parts by mass or less, preferably 20 parts by mass or less, and more preferably 15 parts by mass or less, based on 100 parts by mass of the total amount of modified methylolmelamine and polyvinyl alcohol.

[0064] As described above, the modified methylolmelamine condensation resin reacts with polyvinyl alcohol to obtain a resin (an aqueous solution of the resin).

[0065] The reaction from melamine to resin described above can be carried out continuously or in stages.

[0066] In the aqueous solution of the resin, the solid content concentration of the modified methylolmelamine condensed resin is, for example, 10% by mass or more, preferably 15% by mass or more, and for example, 40% by mass or less.

[0067] Such resins have the same acidic groups as modified methylolmelamine.

[0068] In the above explanation, methylolmelamine is reacted with an acid component to obtain modified methylolmelamine, and then modified methylolmelamine condensation resin is obtained by dehydration condensation of the modified methylolmelamine. However, depending on the amount of acid component added, not all of the methylolmelamine may react with the acid component, and some methylolmelamine may remain. In such cases, the three methylol groups in the methylolmelamine and the two methylol groups in the modified methylolmelamine condense together.

[0069] The resin is a reaction product of a modified methylolmelamine condensation resin containing acidic groups and polyvinyl alcohol. Therefore, it exhibits excellent heat resistance, ion permeability, and storage stability.

[0070] Furthermore, the raw material for the coating material of the secondary battery separator includes the above-mentioned resin (an aqueous solution of the above-mentioned resin).

[0071] Furthermore, the raw materials for the coating material of secondary battery separators may include, as needed, wetting agents, dispersants, hydrophilic resins, humectants, defoamers, and pH adjusters. Adjustment Additives such as chemicals can be blended in appropriate proportions. In other words, the raw material for the coating material of secondary battery separators may contain additives as needed. The additives can be blended during and / or after the manufacture of the resin described above.

[0072] On the other hand, this coating material raw material for secondary battery separators contains a resin obtained using polyvinyl alcohol, and therefore has excellent wettability. For this reason, the coating material raw material for secondary battery separators has excellent wettability even without containing a wetting agent. In other words, the coating material raw material for secondary battery separators preferably contains the above-mentioned resin and does not contain a wetting agent.

[0073] In the raw material for coating material for secondary battery separators, the solid content concentration of the above resin is, for example, 10% by mass or more, preferably 15% by mass or more, and for example, 40% by mass or less.

[0074] The raw material for the coating material used in secondary battery separators contains the above-mentioned resin. Therefore, it exhibits excellent heat resistance, ion permeability, and storage stability.

[0075] <<Second Invention>> The raw material for the coating material of secondary battery separators contains a modified methylolmelamine condensation resin having acidic groups and polyvinyl alcohol.

[0076] <Modified methylol melamine condensation resin containing acidic groups> The modified methylolmelamine condensation resin having an acidic group is the same as the modified methylolmelamine condensation resin having an acidic group in the first invention. In other words, the modified methylolmelamine condensation resin having an acidic group is a condensation polymer of modified methylolmelamine. Modified methylolmelamine is a reaction product of methylolmelamine and an acidic component.

[0077] Methylolmelamine is a reaction product of melamine and formaldehyde.

[0078] The amount of formaldehyde added per mole of melamine is, for example, 2.4 moles or more, preferably 2.6 moles or more, more preferably 2.8 moles or more, even more preferably 2.9 moles or more, or, for example, 5.0 moles or less, preferably 4.0 moles or less, more preferably 3.3 moles or less, even more preferably 3.1 moles or less.

[0079] If the amount of formaldehyde added to 1 mole of melamine is above the lower limit and below the upper limit, almost all of the three amino groups in melamine can be converted into methylol groups.

[0080] Also, melamine and formaldehyde and of In the reaction, the heating temperature, heating time, and pH are the same as in the first invention.

[0081] Preferably, methylolmelamine is trimethylolmelamine, in which all three amino groups in melamine are modified into methylol groups.

[0082] Furthermore, as mentioned above, modified methylolmelamine is a reaction product of methylolmelamine and an acidic component.

[0083] Examples of acidic components include those listed in the first invention. Preferably, sulfurous acid is used as the acidic component.

[0084] Acidic components can be used alone or in combination of two or more types.

[0085] And, similar to the first invention, modified methylolmelamine is obtained by reacting methylolmelamine with an acid component. Specifically, to react methylolmelamine with an acid component, water, methylolmelamine, and the acid component are mixed and heated.

[0086] The amount of acid component added is, for example, 0.10 moles or more, preferably 0.15 moles or more, more preferably 0.30 moles or more, even more preferably 0.40 moles or more, particularly preferably 0.43 moles or more, and, for example, less than 0.70 moles, preferably 0.65 moles or less, more preferably 0.60 moles or less, and even more preferably 0.50 moles or less, per mole of methylolmelamine.

[0087] The heating conditions are the same as those of the first invention.

[0088] This causes methylolmelamine to react with the acid component, yielding modified methylolmelamine. More specifically, one of the methylol groups in methylolmelamine can be modified by the acid component into an acidic group derived from the acid component. A sulfonic acid is a preferred example of the acidic group.

[0089] As described above, the modified methylolmelamine condensation resin having acidic groups is a condensation polymer of modified methylolmelamine (modified methylolmelamine having acidic groups).

[0090] To perform condensation polymerization of modified methylolmelamine, for example, the pH is adjusted by adding an acid (for example, sulfuric acid) to a pH of 5 or higher and less than 8, and the modified methylolmelamine is heated in water.

[0091] The heating conditions include a heating temperature of, for example, 50°C or higher, preferably 60°C or higher, and for example, 90°C or lower, preferably 80°C or lower. The heating time is, for example, 1 hour or more, preferably 2 hours or more, and for example, 6 hours or less.

[0092] Subsequently, an alkali (for example, sodium hydroxide) is added to adjust the pH to, for example, between 11 and 13, thereby stopping the condensation polymerization reaction.

[0093] As a result, the two methylol groups in the modified methylolmelamine undergo dehydration condensation to obtain a modified methylolmelamine condensation resin (an aqueous dispersion of the modified methylolmelamine condensation resin).

[0094] The reaction from melamine to modified methylolmelamine condensation resin described above can be carried out continuously or in stages.

[0095] In the aqueous dispersion of the modified methylolmelamine condensed resin, the solid content concentration of the modified methylolmelamine condensed resin is, for example, 10% by mass or more, preferably 15% by mass or more, and for example, 40% by mass or less.

[0096] Such modified methylolmelamine condensed resins have the same acidic groups as modified methylolmelamine.

[0097] The content of the modified methylolmelamine condensation resin is, for example, 60 parts by mass or more, preferably 70 parts by mass or more, more preferably 80 parts by mass or more, and also, for example, 98 parts by mass or less, preferably 90 parts by mass or less, based on 100 parts by mass of the total amount of the modified methylolmelamine condensation resin and polyvinyl alcohol.

[0098] In the above explanation, methylolmelamine is reacted with an acid component to obtain modified methylolmelamine, and then modified methylolmelamine condensation resin is obtained by dehydration condensation of the modified methylolmelamine. However, depending on the amount of acid component added, not all of the methylolmelamine may react with the acid component, and some methylolmelamine may remain. In such cases, the three methylol groups in the methylolmelamine and the two methylol groups in the modified methylolmelamine condense together.

[0099] <Polyvinyl alcohol> Examples of polyvinyl alcohol include the polyvinyl alcohol mentioned in the first invention. Preferably, anionic group-modified polyvinyl alcohol is used as the polyvinyl alcohol. More preferably, carboxyl group-modified polyvinyl alcohol is used as the modified polyvinyl alcohol.

[0100] Polyvinyl alcohol transformation The degree is the Ken mentioned in the first invention. transformation It is similar to degrees.

[0101] Polyvinyl alcohol can be used alone or in combination with two or more other types.

[0102] The polyvinyl alcohol content is, for example, 3 parts by mass or more, preferably 5 parts by mass or more, more preferably 6 parts by mass or more, even more preferably 10 parts by mass or more, per 100 parts by mass of modified methylolmelamine condensed resin. Also, for example, 60 parts by mass or less, preferably less than 50 parts by mass, 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, from the viewpoint of improving heat resistance and ion permeability.

[0103] Furthermore, the polyvinyl alcohol content is, for example, 2 parts by mass or more, preferably 10 parts by mass or more from the viewpoint of improving heat resistance, and, for example, 40 parts by mass or less, preferably 30 parts by mass or less, and more preferably 20 parts by mass or less, from the viewpoint of improving heat resistance and ion permeability, based on 100 parts by mass of the total amount of modified methylolmelamine condensed resin and polyvinyl alcohol.

[0104] Furthermore, polyvinyl alcohol can also be prepared as an aqueous solution of polyvinyl alcohol. In the aqueous solution of polyvinyl alcohol, the solid content concentration of polyvinyl alcohol is, for example, 5% by mass or more, and for example, 50% by mass or less.

[0105] <Preparation of raw materials for coating materials used in secondary battery separators> The raw materials for the coating material used in secondary battery separators are prepared by separately packaging a modified methylolmelamine condensate resin (an aqueous dispersion of the modified methylolmelamine condensate resin) containing acidic groups and polyvinyl alcohol. These are then blended together at the time of use.

[0106] Furthermore, the raw materials for the coating material of secondary battery separators may include, as needed, wetting agents, dispersants, hydrophilic resins, humectants, defoamers, and pH adjusters. Adjustment Additives such as chemical agents can be blended in appropriate proportions. In other words, the raw material for the coating material of secondary battery separators may contain additives as needed. The additives can be blended with modified methylolmelamine condensation resin and / or polyvinyl alcohol having acidic groups.

[0107] On the other hand, this coating material raw material for secondary battery separators contains a modified methylolmelamine condensation resin having acidic groups and polyvinyl alcohol, and therefore has excellent wettability. For this reason, the coating material raw material for secondary battery separators has excellent wettability even without containing a wetting agent. In other words, the coating material raw material for secondary battery separators preferably contains a modified methylolmelamine condensation resin having acidic groups and polyvinyl alcohol, and does not contain a wetting agent.

[0108] The raw material for the coating material used in secondary battery separators contains a modified methylolmelamine condensation resin with acidic groups and polyvinyl alcohol, resulting in excellent heat resistance and ion permeability.

[0109] Furthermore, these raw materials for coating materials for secondary battery separators (first and second inventions) can be suitably used, in particular, as raw materials for coating materials for secondary battery separators.

[0110] The following describes in detail the coating material for secondary battery separators obtained using this raw material for secondary battery separator coatings.

[0111] 2. Coating material for secondary battery separators The coating material for secondary battery separators includes the above-mentioned raw materials for secondary battery separator coating materials and inorganic particles.

[0112] Examples of inorganic particles include oxides, nitrides, carbides, sulfates, hydroxides, and potassium titanate. 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 talc, kaolinite, decite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amethyst, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, silica sand, and glass.

[0113] Preferably, the inorganic particles are hydroxides. More preferably, the inorganic particles are aluminum hydroxide oxide.

[0114] The average median diameter D50 of the inorganic particles is, for example, 0.1 μm or more, preferably 0.5 μm or more, and for example, 5 μm or less, preferably 1 μm or less.

[0115] Inorganic particles can be used alone or in combination of two or more types.

[0116] The proportion of inorganic particles will be discussed later.

[0117] To manufacture the coating material for secondary battery separators, first, an aqueous dispersion of inorganic particles is prepared by mixing inorganic particles and, if necessary, a dispersant with water. If a dispersant is included, the coating material for secondary battery separators will contain the dispersant.

[0118] Examples of dispersants include ammonium polycarboxylate and sodium polycarboxylate. Ammonium polycarboxylate is preferred as the dispersant.

[0119] The proportion of the dispersant (solid content) is, for example, 0.1 parts by mass or more, preferably 0.5 parts by mass or more, and for example, 10 parts by mass or less, preferably 3 parts by mass or less, per 100 parts by mass of inorganic particles.

[0120] Dispersants can be used alone or in combination of two or more types.

[0121] Next, the aqueous dispersion of inorganic particles is mixed with the raw material for the coating material for secondary battery separators (aqueous dispersion of the raw material for the coating material for secondary battery separators) and stirred.

[0122] The stirring method is not particularly limited and includes, for example, ball mills, bead mills, planetary ball mills, vibrating ball mills, sand mills, colloid mills, attritors, roll mills, high-speed impeller dispersion, stirrers, dispersers, homogenizers, high-speed impact mills, ultrasonic dispersion, and stirring blades.

[0123] Furthermore, the coating material for secondary battery separators may contain the above-mentioned additives in appropriate proportions as needed. In other words, the coating material for secondary battery separators may contain the above-mentioned additives as needed. Preferably, the coating material for secondary battery separators does not contain wetting agents.

[0124] These additives can be used individually or in combination of two or more types.

[0125] This yields a coating material for secondary battery separators. Furthermore, such a coating material for secondary battery separators can be obtained as an aqueous dispersion in water.

[0126] The solid content concentration of the aqueous dispersion of the coating material for secondary battery separators is, for example, 10% by mass or more, preferably 20% by mass or more, more preferably 30% by mass or more, and also, for example, 50% by mass or less.

[0127] Furthermore, in the coating material (solids) for secondary battery separators, the content of the raw material (solids) for the coating material for secondary battery separators is, for example, 3.0 parts by mass or more, preferably 4.2 parts by mass or more, and 10.0 parts by mass or less, preferably 7.0 parts by mass or less, and more preferably 6.0 parts by mass or less, based on 100 parts by mass of the total amount of the raw material (solids) for the coating material for secondary battery separators and inorganic particles. Furthermore, the content of inorganic particles is, for example, 90.0 parts by mass or more, preferably 93.0 parts by mass or more, more preferably 94.0 parts by mass or more, and for example, 97.0 parts by mass or less, and preferably 95.8 parts by mass or less, based on 100 parts by mass of the total amount of the raw material (solids) for the coating material for secondary battery separators and inorganic particles.

[0128] Furthermore, in the coating material (solid content) for secondary battery separators, the content of the raw material (solid content) for the coating material (solid content) for secondary battery separators is, for example, 3.0 parts by mass or more, preferably 4.0 parts by mass or more, more preferably 4.4 parts by mass or more, or, for example, 10.0 parts by mass or less, preferably 7.0 parts by mass or less, more preferably 6.0 parts by mass or less, and even more preferably 5.0 parts by mass or less, per 100 parts by mass of the total amount of inorganic particles.

[0129] The coating material for secondary battery separators contains raw materials for secondary battery separator coatings. Therefore, secondary battery separators equipped with a coating film obtained using this coating material have excellent heat resistance and ion permeability.

[0130] The secondary battery separator obtained using this secondary battery separator coating material will be described in detail below.

[0131] 3. Secondary battery separator The secondary battery separator comprises a porous membrane and a coating film of a secondary battery separator coating material disposed on at least one side of the porous membrane.

[0132] [Porous membrane] Examples of porous membranes include polyolefin porous membranes and aromatic polyamide porous membranes. Examples of polyolefin porous membranes include polyethylene porous membranes and polypropylene porous membranes. Preferably, a polyolefin porous membrane is used as the porous membrane.

[0133] The thickness of the porous film is, for example, 1 μm or more, preferably 5 μm or more, and for example, 40 μm or less, preferably 20 μm or less.

[0134] [Coating film] The coating provides heat resistance to the porous film. The coating consists of a coating material for secondary battery separators.

[0135] The thickness of the coating film is, for example, 1 μm or more, and for example, 10 μm or less, preferably 8 μm or less.

[0136] [Manufacturing method for secondary battery separators] A method for manufacturing a secondary battery separator comprises a first step of preparing a porous membrane, and a second step of applying a separator coating material to at least one side of the porous membrane.

[0137] (1st step) In the first step, a porous membrane is prepared.

[0138] (2nd process) In the second step, a coating material for secondary battery separators is applied to at least one side of the porous film, and then dried as necessary. This obtains a coated film.

[0139] To apply a coating material for secondary battery separators to at least one side of a porous film, first, if necessary, a surface treatment is applied to one side of the porous film to form a surface treatment layer. In other words, in such a case, the secondary battery separator comprises a porous film, a surface treatment layer, and a coating film of the secondary battery separator coating material.

[0140] Examples of surface treatments include corona discharge treatment, glow discharge treatment, plasma treatment, and ozone treatment. In this manufacturing method, surface treatment is preferably omitted from the viewpoint of improving ion permeability. In other words, the secondary battery separator preferably does not have a surface treatment layer.

[0141] Furthermore, there are no particular limitations on the coating method for applying the coating material for secondary battery separators. Examples include the wire bar method, gravure coater method, small-diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, microgravure coating 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. Preferably, the wire bar method is used as the coating method.

[0142] The drying temperature is, for example, 40°C or higher, and for example, 80°C or lower.

[0143] 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.

[0144] 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.

[0145] This secondary battery separator is equipped with a coating film of the secondary battery separator coating material described above. Therefore, the secondary battery separator has excellent heat resistance and ion permeability. For this reason, this secondary battery separator can be suitably used in the manufacture of secondary batteries.

[0146] 4. Secondary battery 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.

[0147] 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.

[0148] Examples of current collectors for the positive electrode include conductive materials such as aluminum, titanium, stainless steel, nickel, calcined carbon, conductive polymers, and conductive glass.

[0149] The positive electrode active material is not particularly limited, but known positive electrode active materials include lithium-containing transition metal oxides, lithium-containing phosphates, and lithium-containing sulfates.

[0150] These positive electrode active materials can be used individually or in combination of two or more types.

[0151] 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.

[0152] Examples of current collectors for the negative electrode include conductive materials such as copper and nickel.

[0153] The negative electrode active material is not particularly limited, but carbon active materials are examples. Examples of carbon active materials include graphite, soft carbon, and hard carbon.

[0154] These negative electrode active materials can be used individually or in combination of two or more types.

[0155] When lithium-ion batteries are used as the electrolyte and secondary battery, examples include solutions in which lithium salts are dissolved in carbonate compounds such as ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC).

[0156] To manufacture a rechargeable battery, for example, a separator for the rechargeable battery is placed between the positive and negative electrodes, these are then housed in a battery casing (cell), and an electrolyte is injected into the battery casing. This allows a rechargeable battery to be obtained.

[0157] The above-mentioned secondary battery is equipped with the above-mentioned secondary battery separator. Therefore, it has excellent heat resistance and ion permeability.

[0158] <Effects and Effects> In the first invention, the raw material for the coating material of the secondary battery separator includes a resin which is a reaction product of a modified methylolmelamine condensation resin having acidic groups and polyvinyl alcohol. Therefore, it has excellent heat resistance and ion permeability.

[0159] More specifically, the resin is obtained using a modified methylolmelamine condensation resin that has acidic groups with excellent heat resistance. Therefore, it has excellent heat resistance.

[0160] Furthermore, since the resin is obtained using polyvinyl alcohol, it has excellent wettability. Therefore, a uniform coating film can be formed. This improves heat resistance and ion permeability.

[0161] Furthermore, because the resin has excellent wettability, for example, when applying a coating material raw material for secondary battery separators containing this resin to the surface of a porous film, the coating film can be formed without applying a surface treatment (e.g., corona discharge treatment) to the surface of the porous film.

[0162] When a surface treatment is applied to the surface of a porous membrane, the interaction between the coating material raw material for secondary battery separators and the porous membrane becomes stronger, and some of the coating material raw material may penetrate into the pores of the porous membrane. This can lead to a decrease in ion permeability.

[0163] On the other hand, with this coating material raw material for secondary battery separators, a coating film can be formed on the surface of the porous membrane without surface treatment, thus preventing some of the coating material raw material from entering the pores of the porous membrane. Therefore, ion permeability can be further improved.

[0164] Furthermore, this resin also exhibits excellent storage stability.

[0165] More specifically, from the viewpoint of improving wettability, it is also considered to first condense and polymerize modified methylolmelamine to obtain a modified methylolmelamine condensation resin having acidic groups, and then add polyvinyl alcohol to this modified methylolmelamine condensation resin. In other words, in such cases, polyvinyl alcohol is added later.

[0166] However, in such cases, if the mixture is stored for a certain period after the addition of polyvinyl alcohol, gelation occurs due to the interaction between the hydroxyl groups of the polyvinyl alcohol and the methylol groups of the modified methylolmelamine resin.

[0167] On the other hand, this resin is obtained by dehydrating and condensing modified methylolmelamine, and then reacting the modified methylolmelamine condensed resin having acidic groups obtained by the dehydration condensation with polyvinyl alcohol beforehand. In other words, in such cases, polyvinyl alcohol is added in advance.

[0168] The gelation described above can be suppressed by reacting the modified methylolmelamine condensation resin with polyvinyl alcohol in advance. Although the reason is not entirely clear, it is presumed that by reacting the modified methylolmelamine resin with polyvinyl alcohol in advance, the hydroxyl groups of the polyvinyl alcohol are consumed in the reaction, thus reducing the amount of hydroxyl groups in the polyvinyl alcohol during storage, and as a result, storage stability can be improved.

[0169] In the second invention, the raw material for the coating material of the secondary battery separator contains a modified methylolmelamine condensation resin having acidic groups and polyvinyl alcohol. Therefore, it has excellent heat resistance and ion permeability.

[0170] For more details, the coating material raw material for secondary battery separators contains a modified methylolmelamine condensation resin that has acidic groups with excellent heat resistance. Therefore, it has excellent heat resistance.

[0171] Furthermore, the coating material raw material for secondary battery separators contains polyvinyl alcohol, resulting in excellent wettability. Therefore, a uniform coating film can be formed. This, in turn, improves heat resistance and ion permeability.

[0172] Furthermore, because the raw material for the coating material for secondary battery separators has excellent wettability, a coating film can be formed on the surface of the porous film without the need for surface treatment (e.g., corona discharge treatment).

[0173] When a surface treatment is applied to the surface of a porous membrane, the interaction between the coating material raw material for secondary battery separators and the porous membrane becomes stronger, and some of the coating material raw material may penetrate into the pores of the porous membrane. This can lead to a decrease in ion permeability.

[0174] On the other hand, with this coating material raw material for secondary battery separators, a coating film can be formed on the surface of the porous membrane without surface treatment, thus preventing some of the coating material raw material from entering the pores of the porous membrane. Therefore, ion permeability can be further improved.

[0175] The coating material for secondary battery separators contains the above-mentioned raw materials for secondary battery separator coatings. Therefore, it has excellent heat resistance and ion permeability.

[0176] The secondary battery separator is equipped with a coating film of the above-mentioned secondary battery separator coating material. Therefore, it has excellent heat resistance and ion permeability.

[0177] The secondary battery is equipped with the secondary battery separator described above. Therefore, it has excellent heat resistance and ion permeability. [Examples]

[0178] 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.

[0179] <Details of ingredients> The trade names and abbreviations of the components used in each example and each comparative example will be described in detail below. AF17: Carboxylate-modified polyvinyl alcohol, ken transformation Concentration exceeding 96 mol%, manufactured by Nippon Vinegar Bi-Poval Co., Ltd. Gosenex CKS-50: Sulfo-modified polyvinyl alcohol, ken transformation 99 mol%, manufactured by Mitsubishi Chemical Corporation. Gosenex WO-320: Hydrophilic modified polyvinyl alcohol, ken transformation 98.5 mol%, manufactured by Mitsubishi Chemical Corporation. Kurarepoval 5-98: Unmodified polyvinyl alcohol, ken transformation 98 mol% to 99 mol%, manufactured by Kuraray Co., Ltd. Kurarepoval 60-98: Unmodified polyvinyl alcohol, ken transformation98 mol% to 99 mol%, manufactured by Kuraray Co., Ltd. Kurarepoval 44-88: Unmodified polyvinyl alcohol, ken transformation Concentration: 87 mol% to 89 mol%, manufactured by Kuraray Co., Ltd. Kurarepoval 5-74: Unmodified polyvinyl alcohol, ken transformation 72.5-74.5 mol%, manufactured by Kuraray Co., Ltd. Wetting agent: Acetylene-based surfactant, Olphine E1010, manufactured by Nisshin Chemical Industry Co., Ltd. Ammonium polycarboxylate: Dispersant, aqueous solution of ammonium polycarboxylate, trade name SN5468, manufactured by Sunopco Corporation.

[0180] <<First Invention>> <Preparation of an aqueous solution of polyvinyl alcohol> In a separable flask equipped with a stirrer, 100 parts by mass of water were charged, and while stirring, 10 parts by mass of each polyvinyl alcohol (AF17, Gosenex CKS-50, Gosenex WO-320, and Kurarepoval 5-98) were gradually added, and the temperature was raised to 95°C and maintained for 5 hours. After confirming that the polyvinyl alcohol was completely dissolved, it was cooled, and an appropriate amount of water was added to prepare a 10% aqueous solution of polyvinyl alcohol for each polyvinyl alcohol.

[0181] <Resin manufacturing> Manufacturing Example 1 33.0 parts by mass of water and 114.8 parts by mass of 37% formaldehyde are mixed using a stirrer, thermometer, and reflux meter. With tube tree of The mixture was placed in a four-necked flask and stirred. Then, 51 parts of melamine were added while stirring. Next, the temperature was raised to 60°C, the pH was adjusted to 11.0 with a 40% sodium hydroxide aqueous solution, and the reaction was continued at 67°C for 2 hours, followed by cooling to 50°C. This yielded methylolmelamine.

[0182] Next, 32 parts by mass of sodium bisulfite was added, the pH was adjusted to 11.5 with a 40% sodium hydroxide aqueous solution, and the reaction was carried out at 80°C for 4 hours. This yielded modified methylolmelamine. Then, 150 parts by mass of a 10% aqueous solution of AF17 and 342 parts by mass of water were added, the pH was adjusted to 6.6 with 40% sulfuric acid, and the reaction was carried out at 72°C for 8 hours. After that, the pH was adjusted to 12.0 with a 25% sodium hydroxide aqueous solution to stop the reaction. After that, an appropriate amount of water was added. This yielded a resin (aqueous solution of the resin) (solid content concentration 16% by mass).

[0183] Manufacturing Examples 2-4 A resin (aqueous solution of resin) (solid content concentration 16% by mass) was obtained using the same procedure as in Manufacturing Example 1. However, the formulation of each component was changed according to Table 1. The values ​​listed in Table 1 are parts by mass (solid content).

[0184] Comparative Manufacturing Example 1 200.0 parts by mass of distilled water were charged into a separable flask equipped with a stirrer and reflux condenser, and after purging with nitrogen gas, the temperature was raised to 80°C. Next, 0.6 parts by mass of ammonium persulfate was added, followed by the continuous addition of the monomer composition described below over 3 hours, and the mixture was held for another 3 hours to complete the polymerization. The pH was adjusted to 9.0 by adding aqueous ammonia, and then an appropriate amount of water was added to obtain an aqueous solution of a water-soluble polymer with a solid content of 16.0%. {Monomer composition} Methacrylamide 95.0 parts by mass 5.0 parts by mass of methacrylic acid 25% aqueous ammonia, 5.0 parts by mass Distilled water 300.0 parts by mass

[0185] Reference manufacturing example 1 692.0 parts by mass of water and 277.8 parts by mass of 37% formaldehyde are mixed using a stirrer, thermometer, and reflux system. With tube tree ofThe mixture was placed in a four-necked flask and stirred. Then, 144.0 parts of melamine were added under stirring. The temperature was raised to 60°C, the pH was adjusted to 11.0 with a 25% sodium hydroxide aqueous solution, and the reaction was continued at 75°C for 3 hours, after which it was cooled to 60°C. This yielded methylolmelamine.

[0186] Next, 50.9 parts by mass of sodium bisulfite was added as the acid component, and the mixture was reacted at 80°C for 2 hours. This yielded modified methylolmelamine.

[0187] Next, after cooling to below 40°C, water was added to adjust the solid content concentration to 20% by mass. Further, the pH was adjusted to 6.8 with 40% sulfuric acid, and condensation was carried out at 70°C for 3 hours. After that, the pH was adjusted to 12.0 with a 25% sodium hydroxide aqueous solution to stop the reaction. Then, an appropriate amount of water was added to obtain a resin (aqueous solution of the resin) (solid content concentration 18% by mass).

[0188] <Manufacturing of raw materials for coating materials for secondary battery separators, coating materials for secondary battery separators, and secondary battery separators> Example 1 (Manufacturing of raw materials for coating materials used in secondary battery separators) The resin from Manufacturing Example 1 was used as a raw material for coating material for secondary battery separators.

[0189] (Manufacturing of coating materials for secondary battery separators) According to the formulation described in Table 2, a dispersant was added to 123 parts by mass of water. Then, while stirring with a disperser (1000 rpm), 100 parts by mass of boehmite (aluminum hydroxide oxide, manufactured by Navaltec, trade name "Apiral AOH60", average median diameter D50: 0.9 μm) was gradually added as inorganic particles. After the addition, the mixture was further stirred with a homogenizer (5000 rpm). This yielded an aqueous dispersion of inorganic particles (solid content of inorganic particles 45% by mass).

[0190] Next, a raw material for a secondary battery separator coating was added to an aqueous dispersion of inorganic particles, and water was added as needed and the mixture was stirred.

[0191] Subsequently, this was filtered through a 300-mesh filter (filtration particle size 48 μm). This produced a coating material for secondary battery separators (a dispersion of the coating material for secondary battery separators). The solid content concentration of the dispersion of the coating material for secondary battery separators was 40% by mass.

[0192] (Manufacturing of secondary battery separators) [1st step] As a porous membrane, a polyolefin porous membrane (without surface treatment (corona treatment)) was prepared.

[0193] [Second process] Using a wire bar, the above-mentioned coating material for secondary battery separators (a dispersion of the coating material for secondary battery separators) was applied to one side of a polyolefin porous membrane, and then dried at 50°C. This formed coated films of the coating material for secondary battery separators (4 μm and 2 μm thick) on one side of the polyolefin porous membrane. A secondary battery separator was then manufactured.

[0194] Examples 2 to 4, Comparative Example 1, and Reference Example 1 A coating material raw material for secondary battery separators, a coating material for secondary battery separators, and a secondary battery separator were obtained based on the same procedure as in Example 1. However, the formulation of each component was changed according to Table 2. The values ​​listed in Table 2 are parts by mass (solid content). In Comparative Example 1, a coating material for secondary battery separators was produced by blending an aqueous solution of the water-soluble polymer of Manufacturing Comparative Example 1, which is a coating material raw material for secondary battery separators, with E1010. In Reference Example 1, a coating material for secondary battery separators was produced by blending the resin of Manufacturing Reference Example 1, which is a coating material raw material for secondary battery separators, with an aqueous solution (10%) of AF.

[0195] <Rating> [Heat resistance] The secondary battery separators for each example, comparative example, and reference example were cut into 5cm x 5cm pieces to serve as test specimens. These test specimens were left in an oven at 150°C for 1 hour. The length of each side of the test specimen was measured before and after the period of time. The shrinkage rate was calculated from the lengths of each side before and after shrinkage using the following formula (1). The results are shown in Table 2. Shrinkage rate (%) = {Average length of one side before shrinkage (cm) - Average length of one side after shrinkage (cm)} / Average length of one side before shrinkage (cm) × 100 (1)

[0196] [Ion permeability] For each example, comparative example, and reference example of secondary battery separators, the air permeability resistance was determined using an Ogane-type air permeability and smoothness tester manufactured by Asahi Seiko Co., Ltd., in accordance with JIS-P-8117. The decrease in air permeability relative to the air permeability of the porous membrane itself was defined as Δ air permeability. Specifically, Δ air permeability was calculated based on the following formula (2). A smaller Δ air permeability was considered to indicate superior ion permeability. The results are shown in Table 2. ΔAir permeability = Measured air permeability - 180 (Air permeability of the porous membrane itself) (2)

[0197] [Storage stability] The change in viscosity of the resins from each manufacturing example and each reference manufacturing example, as well as the aqueous solution of the water-soluble polymer from Comparative Example 1, was measured after storage at 40°C for one month. Viscosity was measured using a VISCOMETER manufactured by Toki Sangyo Co., Ltd. at 60 rpm and 25°C. The change in viscosity was calculated based on the following formula (3). The results are shown in Table 2. Viscosity change = (Viscosity after 1 month of storage at 40°C - Viscosity immediately after polymerization) / Viscosity immediately after polymerization (3)

[0198] <Consideration> Examples 1 to 4, which use a resin that is a reaction product of a modified methylolmelamine condensation resin having an acidic group and polyvinyl alcohol, show superior heat resistance compared to Comparative Example 1, which uses an acrylic water-soluble polymer.

[0199] Examples 1 to 4, in which polyvinyl alcohol is added beforehand, show superior storage stability compared to Reference Example 1, in which polyvinyl alcohol is added later.

[0200] <<Second Invention>> <Manufacturing of modified methylol melamine condensation resin containing acidic groups> Manufacturing Example 5 692.0 parts by mass of water and 277.8 parts by mass (3.43 moles) of 37% formaldehyde were placed in a four-necked flask equipped with a stirrer, thermometer, and reflux tubing, and stirred. Then, 144.0 parts by mass (1.14 moles) of melamine were added under stirring. The mixture was heated to 60°C, the pH was adjusted to 11.0 with a 25% sodium hydroxide aqueous solution, and the reaction was continued at 75°C for 3 hours before cooling to 60°C. This yielded methylolmelamine.

[0201] Next, 50.9 parts by mass (0.489 moles) of sodium bisulfite was added as the acid component, and the mixture was reacted at 80°C for 2 hours. This yielded modified methylolmelamine.

[0202] Next, after cooling to below 40°C, water was added to adjust the solid content concentration to 20% by mass. Furthermore, the pH was adjusted to 6.8 with 40% sulfuric acid, and condensation was carried out at 70°C for 3 hours. After that, the pH was adjusted to 12.0 with a 25% sodium hydroxide aqueous solution to stop the reaction. This yielded a modified methylolmelamine condensation resin (aqueous dispersion of modified methylolmelamine condensation resin). Next, an appropriate amount of water was added to adjust the solid content concentration of the aqueous dispersion of modified methylolmelamine condensation resin to 18% by mass.

[0203] Manufacturing Example 6 692.0 parts by mass of water and 259.3 parts by mass (3.20 moles) of 37% formaldehyde were placed in a four-necked flask equipped with a stirrer, thermometer, and reflux tubing, and stirred and mixed. Then, 144.0 parts by mass (1.14 moles) of melamine were added under stirring. The mixture was heated to 60°C, the pH was adjusted to 11.0 with a 25% sodium hydroxide aqueous solution, and the reaction was continued at 75°C for 3 hours, after which it was cooled to 60°C. This yielded methylolmelamine.

[0204] Next, 33.9 parts by mass (0.426 moles) of sodium bisulfite was added as the acid component, and the mixture was reacted at 80°C for 2 hours. This yielded modified methylolmelamine.

[0205] Next, after cooling to below 40°C, water was added to adjust the solid content concentration to 20% by mass. Furthermore, the pH was adjusted to 6.8 with 40% sulfuric acid, and condensation was carried out at 70°C for 3 hours. After that, the pH was adjusted to 12.0 with a 25% sodium hydroxide aqueous solution to stop the reaction. This yielded a modified methylolmelamine condensation resin (aqueous dispersion of modified methylolmelamine condensation resin). Next, an appropriate amount of water was added to adjust the solid content concentration of the aqueous dispersion of modified methylolmelamine condensation resin to 18% by mass.

[0206] <Manufacturing of acrylic water-soluble polymers> Manufacturing example 7 200.0 parts by mass of distilled water were charged into a separable flask equipped with a stirrer and reflux condenser, and after purging with nitrogen gas, the temperature was raised to 80°C. Next, 0.6 parts by mass of ammonium persulfate was added, followed by the continuous addition of the monomer composition described below over 3 hours, and the mixture was held for another 3 hours to complete the polymerization. The pH was adjusted to 9.0 by adding aqueous ammonia, and then an appropriate amount of water was added to obtain an aqueous solution of a water-soluble polymer with a solid content of 20.0%. {Monomer composition} Methacrylamide 95.0 parts by mass 5.0 parts by mass of methacrylic acid 25% aqueous ammonia, 5.0 parts by mass Distilled water 300.0 parts by mass

[0207] <Preparation of polyvinyl alcohol> Each polyvinyl alcohol (Kurarepoval 60-98, AF17, Kurarepoval 44-88, Kurarepoval 5-74) was prepared as follows. Specifically, 100 parts by mass of water were placed in a separable flask equipped with a stirrer, and 10 parts by mass of polyvinyl alcohol were gradually added while stirring. The temperature was then raised to 95°C and maintained for 3 hours. After confirming that the polyvinyl alcohol was completely dissolved, it was cooled, and an appropriate amount of water was added to prepare a 10% aqueous solution of polyvinyl alcohol.

[0208] <Manufacturing of raw materials for coating materials for secondary battery separators, coating materials for secondary battery separators, and secondary battery separators> Examples 5 to 11, and Comparative Examples 2 to 4 (Manufacturing of raw materials for coating materials used in secondary battery separators) According to the formulations described in Table 3, a modified methylolmelamine condensation resin having acidic groups and polyvinyl alcohol were prepared separately. This produced a raw material for a coating material for secondary battery separators. In Comparative Example 4, an acrylic water-soluble polymer was used instead of the modified methylolmelamine condensation resin having acidic groups. The values ​​listed in Table 3 represent the solid content.

[0209] (Manufacturing of coating materials for secondary battery separators) According to the formulation described in Table 3, a dispersant was added to 123 parts by mass of water. Then, while stirring with a disperser (1000 rpm), 100 parts by mass of boehmite (aluminum hydroxide oxide, manufactured by Navaltec, trade name "Apiral AOH60", average median diameter D50: 0.9 μm) was gradually added as inorganic particles. After the addition, the mixture was further stirred with a homogenizer (5000 rpm). This yielded an aqueous dispersion of inorganic particles (solid content of inorganic particles 45% by mass).

[0210] Next, a raw material for a secondary battery separator coating was added to an aqueous dispersion of inorganic particles (specifically, a modified methylolmelamine condensation resin (or acrylic water-soluble polymer) having acidic groups, which had been prepared separately, was mixed with polyvinyl alcohol), water was added as needed, and the mixture was stirred.

[0211] Subsequently, this was filtered through a 300-mesh filter (filtration particle size 48 μm). This produced a coating material for secondary battery separators (a dispersion of the coating material for secondary battery separators). The solid content concentration of the dispersion of the coating material for secondary battery separators was 40% by mass.

[0212] (Manufacturing of secondary battery separators) [1st step] As a porous membrane, a polyolefin porous membrane (without surface treatment (corona treatment)) was prepared.

[0213] [Second process] Using a wire bar, the above-mentioned coating material for secondary battery separators (a dispersion of the coating material for secondary battery separators) was applied to one side of a polyolefin porous membrane, and then dried at 50°C. This formed a coating film (4 μm thick) of the coating material for secondary battery separators on one side of the polyolefin porous membrane. A secondary battery separator was then manufactured.

[0214] <Rating> [Heat resistance] Similar to the first invention, heat resistance was evaluated. The results are shown in Table 3.

[0215] [Ion permeability] Similar to the first invention, ion permeability was evaluated. The results are shown in Table 3.

[0216] <Consideration> Examples 5 to 11, which include a modified methylolmelamine condensation resin having an acidic group and polyvinyl alcohol, are found to have superior heat resistance and excellent ion permeability compared to Comparative Example 2, which does not contain polyvinyl alcohol, and Comparative Examples 3 and 4, which do not contain a modified methylolmelamine condensation resin having an acidic group.

[0217] [Table 1]

[0218] [Table 2]

[0219] [Table 3]

[0220] 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 below.

[0221] The raw material for coating material for secondary battery separators, the coating material for secondary battery separators, and the secondary battery separator of the present invention are suitably used in the manufacture of secondary batteries.

Claims

1. It contains a resin which is a reaction product of a modified methylolmelamine condensation resin having an acidic group and polyvinyl alcohol, or A raw material for a coating material for a secondary battery separator, comprising the modified methylolmelamine condensation resin having the acidic group and the polyvinyl alcohol.

2. The aforementioned resin is included, The raw material for a coating material for a secondary battery separator according to claim 1, wherein the acidic group is a sulfonic acid group.

3. It does not contain a resin which is a reaction product of the modified methylolmelamine condensation resin having the acidic group and polyvinyl alcohol, but contains the modified methylolmelamine condensation resin having the acidic group and the polyvinyl alcohol, The raw material for a coating material for a secondary battery separator according to claim 1, wherein the content of the polyvinyl alcohol is 5 parts by mass or more and less than 50 parts by mass per 100 parts by mass of the modified methylolmelamine condensate resin.

4. A coating material for a secondary battery separator, comprising the coating material raw material for a secondary battery separator described in claim 1 and inorganic particles.

5. Porous membrane and The coating film of the secondary battery separator coating material according to claim 4, which is disposed on at least one side of the porous film, A secondary battery separator equipped with the following features.

6. A secondary battery comprising a positive electrode, a negative electrode, and a secondary battery separator according to claim 5 disposed between the positive electrode and the negative electrode.

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