Primer composition, coating film obtained therefrom, exterior material for secondary battery containing said coating film, and secondary battery

Abstract

The present invention provides a primer composition that provides an exterior material for secondary batteries that does not experience a decrease in adhesive strength even in high-temperature environments and has excellent electrolyte resistance, a coating film obtained therefrom, an exterior material for secondary batteries containing the coating film, and a secondary battery. [Solution] A primer composition comprising: 100 parts by mass of an acid-modified polypropylene resin aqueous dispersion (A); 0.5 to 3.0 parts by mass of a modified polyvinyl alcohol having a carbonyl group (B); 1.0 to 5.0 parts by mass of adipic acid dihydrazide (C); 5.0 to 10.0 parts by mass of an oxazoline compound (D); and water, wherein the aqueous dispersion (A) has a melting point of 143 to 148°C measured in accordance with JIS K 7121 under a nitrogen stream at a heating rate of 10°C / min, and an acid value of 20 to 30 mgKOH / g measured in accordance with JIS K 2501; and the modified polyvinyl alcohol (B) has a degree of saponification of 98 to 99 mol% measured in accordance with JIS K 6726.

Description

Technical Field

[0001] The present invention relates to a primer composition, a coating film obtained therefrom, an exterior material for a secondary battery including the coating film, and a secondary battery.

Background Art

[0002] As a driving power source for portable electronic devices such as mobile phones and notebook computers; a driving power source for electric vehicles, hybrid vehicles, etc.; a stationary storage battery used as a backup power source during power outages in houses, commercial facilities, hospitals, factories, etc.; etc., laminated lithium ion batteries are widely adopted. With the expansion of the applicable uses of lithium ion batteries, the batteries are required to have long-term functional maintenance in electric vehicle and stationary battery applications, resistance to temperature rise during charge and discharge and temperature rise of the use environment due to high functionality (high capacity and high output), etc. In order to meet such requirements, the exterior material for a lithium ion battery is required to have high adhesive strength between layers, and to maintain excellent electrolyte resistance without a decrease in adhesive strength in a high temperature environment.

[0003] The exterior material usually has a structure in which a base material layer, a barrier layer made of aluminum foil or the like, an adhesive layer, and a sealant layer are laminated in this order. To increase the heat resistance of the exterior material, it is important to increase the adhesive strength between layers. In particular, various studies have been made on the improvement of the adhesive layer. For example, Patent Document 1 discloses an exterior body for a battery in which a base material layer, a barrier layer, an adhesive layer, and a sealant layer are laminated in this order, wherein the adhesive layer contains a specific acid-modified polypropylene resin and a crosslinking agent containing at least one of an oxazoline compound and an epoxy compound in a specific ratio, and the sealant layer is made of a polypropylene resin, and the exterior material is shown to be excellent in electrolyte resistance and liquid leakage resistance.

[0004] Patent Document 2 discloses an adhesive composition comprising a crystalline modified olefin polymer and a crosslinking agent comprising an epoxy compound and / or an oxazoline compound, wherein the modified olefin polymer is modified by a monomer having an acid anhydride group, and the ring-opening rate of the ring structure derived from the acid anhydride group is 50% to 90%, and the composition is shown to have excellent adhesion, pot life and heat resistance during low-temperature lamination. Patent Document 3 discloses an adhesive composition containing a modified polyolefin (A), polycarbodiimide (B), and an organic solvent (C) having a specific acid value, and the composition is shown to have good pot life and excellent adhesion to both polyolefin resin substrates and metal substrates.

[0005] Furthermore, Patent Document 4 discloses a coating composition comprising an acid-modified polyolefin resin, at least one of polyvinyl alcohol and ethylene-vinyl alcohol copolymer, a hydrazide compound, a basic compound, and an aqueous medium in predetermined proportions, and shows that a coating film with excellent adhesion to various substrates, water resistance at high temperatures, and chemical resistance can be obtained. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2012-216364 [Patent Document 2] Japanese Patent Publication No. 2023-180312 [Patent Document 3] International Publication No. 2015 / 033703 [Patent Document 4] Japanese Patent Publication No. 2016-194078 [Overview of the project] [Problems that the invention aims to solve]

[0007] The compositions disclosed in Patent Documents 2 and 3 mainly consist of organic solvent solutions of modified polyolefins. However, in order to make the modified polyolefins soluble in the solvent, it is necessary to lower the crystallinity of the modified polyolefins. Even when crosslinking agents are added to these compositions, the heat resistance of the resulting coating films is insufficient. The adhesive layer disclosed in Patent Document 1 is an aqueous dispersion of acid-modified polypropylene resin blended with an oxazoline compound or epoxy compound as a crosslinking agent. The coating composition disclosed in Patent Document 4 is an aqueous dispersion of acid-modified polyolefin resin blended with polyvinyl alcohol and a hydrazide compound. Exterior materials using coating films obtained from the adhesive layer of Patent Document 1 and the composition of Patent Document 4 exhibit a certain level of adhesive strength and electrolyte resistance in high-temperature environments, but further improvement of these properties is desired.

[0008] The present invention aims to provide a primer composition that provides an exterior material for secondary batteries that does not experience a decrease in adhesive strength even in high-temperature environments and has excellent electrolyte resistance, a coating film obtained therefrom, an exterior material for secondary batteries containing the coating film, and a secondary battery. [Means for solving the problem]

[0009] The present inventors have diligently studied methods to suppress the decrease in adhesive strength, particularly the decrease in adhesive strength between the metal foil layer and the sealant layer, in high-temperature environments for exterior materials for secondary batteries, and to improve electrolyte resistance. As a result, they have found that the problems of the present invention can be solved by using a primer composition in which a specific resin, crosslinking agent, etc., are blended in a specific proportion in a specific acid-modified polypropylene resin aqueous dispersion for bonding the metal foil layer and the sealant layer, leading to the present invention.

[0010] The present invention relates to the following [1] to

[10] . [1] A primer composition comprising: 100 parts by mass of an acid-modified polypropylene resin aqueous dispersion (A); 0.5 to 3.0 parts by mass of a modified polyvinyl alcohol having a carbonyl group (B); 1.0 to 5.0 parts by mass of adipic acid dihydrazide (C); 5.0 to 10.0 parts by mass of an oxazoline compound (D); and water, wherein the aqueous dispersion (A) has a melting point of 143 to 148°C measured in accordance with JIS K 7121 under a nitrogen stream at a heating rate of 10°C / min, and an acid value of 20 to 30 mgKOH / g measured in accordance with JIS K 2501; and the modified polyvinyl alcohol (B) has a degree of saponification of 98 to 99 mol% measured in accordance with JIS K 6726. [2] The primer composition according to [1], wherein component (A) is an aqueous dispersion of polypropylene resin modified with maleic anhydride. [3] The primer composition according to [1] or [2], wherein component (B) is a polyvinyl alcohol containing diacetone acrylamide units. [4] A primer composition according to any one of [1] to [3], wherein the amount of oxazoline group of component (D) is 5 to 10 mmol / g. [5] A primer composition according to any one of [1] to [4], wherein the content ratio of component (C) to component (B) is 0.3 to 5 by mass. [6] A primer composition according to claim 1 or 2, comprising a first agent and a second agent, A primer composition comprising: a first agent containing components (A) to (C) and water, but not component (D); and a second agent containing component (D) and water, but not components (A) to (C). [7] A primer composition according to any one of [1] to [6] for use in the manufacture of exterior materials for secondary batteries. A coating film obtained by drying any one of the primer compositions described in [8], [1], to [7]. [9] An exterior material for a secondary battery comprising a base layer, an adhesive layer, a metal foil layer, a primer layer, and a sealant layer laminated in this order, wherein the primer layer is the coating film described in [8]. A secondary battery comprising the casing material for secondary batteries described in

[10] [9] and a power generation element. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a primer composition that provides an exterior material for secondary batteries that does not experience a decrease in adhesive strength even in high-temperature environments and has excellent electrolyte resistance, a coating film obtained therefrom, an exterior material for secondary batteries containing the coating film, and a secondary battery. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 shows an example of a laminate-type battery or capacitor according to the present invention. [Figure 2] Figure 2 shows an example of the layer structure of the exterior material according to the present invention. [Modes for carrying out the invention]

[0013] The primer composition of the present invention comprises 100 parts by mass of an acid-modified polypropylene resin aqueous dispersion (A); 0.5 to 3.0 parts by mass of a modified polyvinyl alcohol having a carbonyl group (B); 1.0 to 5.0 parts by mass of adipic acid dihydrazide (C); 5.0 to 10.0 parts by mass of an oxazoline compound (D); and water. The aqueous dispersion (A) has a melting point of 143 to 148°C, measured in accordance with JIS K 7121 under a nitrogen stream at a heating rate of 10°C / min, and an acid value of 20 to 30 mgKOH / g, measured in accordance with JIS K 2501; and the modified polyvinyl alcohol (B) has a degree of saponification of 98 to 99 mol%, measured in accordance with JIS K 6726. The primer composition utilizes two crosslinking systems, components (A) and (D), and components (B) and (C), which further improve the heat resistance of the resulting coating. By using the primer composition as a primer layer for secondary battery casing materials, particularly as a primer layer for bonding the metal foil layer and the sealant layer, it is possible to create a secondary battery casing material that exhibits excellent electrolyte resistance without a decrease in adhesive strength, even in high-temperature environments.

[0014] <Primer composition> The primer composition contains 100 parts by mass of an aqueous dispersion (A) of an acid-modified polypropylene resin; 0.5 to 3.0 parts by mass of a modified polyvinyl alcohol (B) having a carbonyl group; 1.0 to 5.0 parts by mass of adipic acid dihydrazide (C); 5.0 to 10.0 parts by mass of an oxazoline compound (D); and water. Hereinafter, each component will be described in detail.

[0015] [Aqueous dispersion (A) of acid-modified polypropylene resin] The primer composition contains an aqueous dispersion (A) of an acid-modified polypropylene resin as a main component. When an organic solvent solution of an acid-modified polypropylene resin is used as the main component of the primer composition, in order to make the acid-modified polypropylene resin soluble in the solvent, it is necessary to lower the crystallinity of the resin. Even when a crosslinking agent is added, there is a limit to improving the heat resistance of the obtained coating film. By using the aqueous dispersion (A) of an acid-modified polypropylene resin as the main component of the primer composition, the melting point of the resin can be raised, and in combination with the components (B) to (D) shown below, it becomes possible to improve the heat resistance of the obtained coating film. Component (A) may be used alone or in combination of two or more.

[0016] Examples of the acid-modified polypropylene resin include polypropylene-based resins graft-modified with unsaturated carboxylic acids, unsaturated carboxylic acid anhydrides, etc.; copolymers of propylene and acrylic acid, methacrylic acid, etc.; metal-crosslinked polypropylene-based resins, etc. The polypropylene resin before acid modification may be a copolymer of propylene and ethylene or an α-olefin having 4 or more carbon atoms. Examples of the α-olefin having 4 or more carbon atoms include isobutylene, 2-butene, 1-butene, 1-pentene, 1-hexene, etc. In such a copolymer, the content of the polymerization unit derived from propylene is 50% by mass or more, preferably 50 to 95% by mass, and more preferably 70 to 95% by mass. When the content of the polymerization unit derived from propylene is 70 to 95% by mass, good heat resistance and adhesiveness can be exhibited.

[0017] Regarding component (A), the melting point measured in accordance with JIS K 7121 under a nitrogen atmosphere at a heating rate of 10°C / min is 143-148°C. By setting the melting point of the aqueous dispersion (A) within the above range, the heat-resistant coating obtained from the primer composition can be made highly heat-resistant.

[0018] The acid value of component (A), measured in accordance with JIS K 2501, is 20-30 mgKOH / g. By setting the acid value of the aqueous dispersion (A) within the above range, the adhesion between the coating film obtained from the primer composition and the acid-resistant treatment layer (metal foil chemical conversion treatment layer) can be improved.

[0019] Component (A), when used as an exterior material for secondary batteries, preferably contains 0.1 to 10% by mass of acid component, more preferably 0.3 to 10% by mass, and even more preferably 1 to 9% by mass, from the viewpoint of adjusting the adhesive strength between the resulting primer layer, acid-resistant treatment layer, and sealant layer, as well as electrolyte resistance. If the acid component content is less than 0.1% by mass, it tends to be difficult to stably produce the aqueous dispersion (A), and sufficient adhesion between the primer layer and the acid-resistant treatment layer may not be obtained. Furthermore, if the acid component content exceeds 10% by mass, the adhesive strength between the primer layer and the sealant layer and the electrolyte resistance tend to decrease when used as an exterior material for secondary batteries.

[0020] Examples of acid-modified components include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid, fumaric acid, crotonic acid, as well as half-esters and half-amides of unsaturated dicarboxylic acids. The form of introduction of the acid-modified component is not limited and includes, for example, random copolymerization, block copolymerization, graft copolymerization (graft modification), and copolymerization by thermal reduction. From the viewpoint of adhesion and heat resistance, component (A) is preferably an aqueous dispersion of polypropylene resin modified with maleic anhydride.

[0021] From the viewpoint of dispersion stability and adhesive strength and electrolyte resistance in high-temperature environments when used as an exterior material for secondary batteries, the weight-average molecular weight of component (A) is preferably 1,000 to 100,000, more preferably 5,000 to 80,000, even more preferably 10,000 to 50,000, and particularly preferably 20,000 to 40,000. The weight-average molecular weight of component (A) can be determined by a gel permeation chromatography (GPC) apparatus.

[0022] The method for dispersing the acid-modified polypropylene resin in an aqueous medium is not particularly limited, but for example, by placing predetermined amounts of acid-modified polypropylene resin and water in a sealed container equipped with a stirrer, and heating and stirring in the presence of a basic compound and, if necessary, an organic solvent, the acid-modified polypropylene resin can be stably dispersed in an aqueous medium. Any basic compound that can neutralize the carboxyl group is acceptable. Examples of basic compounds include metal hydroxides such as LiOH, KOH, and NaOH; and organic amine compounds such as ammonia, triethylamine, and alkanolamine. From the viewpoint of the water resistance of the coating film, volatile organic amine compounds are preferred.

[0023] Component (A) is commercially available, and examples include Arrowbase® YA-6010 (melting point: 145°C, acid value: 20-30 mgKOH / g, solid content concentration: 25% by mass, pH: 8-11) manufactured by Unitika Ltd.

[0024] [Modified polyvinyl alcohol having a carbonyl group (B)] The primer composition contains 0.5 to 3.0 parts by mass of modified polyvinyl alcohol (B) having a carbonyl group, per 100 parts by mass of an aqueous dispersion of acid-modified polypropylene resin (A). Component (B) is a component that improves the heat resistance of the resulting coating film by crosslinking it with adipic acid dihydrazide (C). By setting the content of component (B) within the above range, compatibility with component (A) can be maintained while appropriately crosslinking with component (C), thereby improving the adhesion between the resulting coating film and the acid-resistant treatment layer, and further improving the heat resistance. Component (B) may be used alone or in combination of two or more types.

[0025] Component (B) can be produced by copolymerizing a fatty acid vinyl ester monomer and a carbonyl group-containing monomer, followed by completely or partially saponifying the resulting polymer. Examples of fatty acid vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl pivalate, and vinyl versatate, with vinyl acetate being preferred. As for the saponification method, alkaline saponification and acid saponification methods can be employed. Among these, the method of alcohol decomposition using an alkaline solution in methanol is preferred.

[0026] Component (B) has a saponification degree of 98-99 mol% as measured in accordance with JIS K 6726. By setting the saponification degree of modified polyvinyl alcohol (B) within the above range, the resulting coating film can be made tougher.

[0027] From the viewpoint of crosslinking with component (C), component (B) is preferably a polyvinyl alcohol containing diacetone acrylamide units.

[0028] Diacetone acrylamide units can be introduced by known methods, such as saponifying a polymer obtained by copolymerizing a fatty acid vinyl ester with diacetone acrylamide. The content of diacetone acrylamide units is preferably 0.1 to 15 mol%, and more preferably 0.5 to 10 mol%. If the content of diacetone acrylamide is less than 0.1 mol%, the heat resistance of the resulting coating film tends to be insufficient. If the content exceeds 15 mol%, the crosslinking reaction becomes saturated, and the water solubility decreases, making it difficult to work with. Polyvinyl alcohol containing diacetone acrylamide units is commercially available; for example, D Polymer manufactured by Nippon Vinegar & Polyvinyl Alcohol Co., Ltd. is one such example.

[0029] The average degree of polymerization of component (B) is not particularly limited, but is preferably between 100 and 2,000.

[0030] Furthermore, within the limits that do not impair the effects of the present invention, component (B) may be copolymerized with monomers other than the fatty vinyl ester monomer and the carbonyl group-containing monomer. Other monomers include unsaturated monocarboxylic acids such as crotonic acid, acrylic acid, and methacrylic acid, and their esters, salts, anhydrides, amides, and nitriles; unsaturated dicarboxylic acids such as maleic acid, itaconic acid, and fumaric acid, and their salts; α-olefins having 2 to 30 carbon atoms; alkyl vinyl ethers; vinylpyrrolidones, etc.

[0031] Component (B) can be prepared as an aqueous solution by known methods.

[0032] [Dihydrazide adipic acid (C)] The primer composition contains 1.0 to 5.0 parts by mass of adipic acid dihydrazide (C) per 100 parts by mass of an acid-modified polypropylene resin aqueous dispersion (A). Component (C) is a component that improves the heat resistance of the resulting coating film by crosslinking with component (B). By setting the content of component (C) within the above range, good adhesion between the resulting coating film and the acid-resistant treatment layer, as well as good heat resistance of the coating film, can be achieved.

[0033] The ratio of component (C) to component (B) is preferably 0.3 to 5 by mass, and more preferably 0.3 to 1.0. By setting the ratio of component (C) to component (B) within the above range, the resulting coating film can be made highly heat resistant.

[0034] Component (C) can be prepared as an aqueous solution by known methods.

[0035] [Oxazoline compound (D)] The primer composition contains 5.0 to 10.0 parts by mass of an oxazoline compound (D) per 100 parts by mass of an acid-modified polypropylene resin aqueous dispersion (A). Component (D) is a component that improves the heat resistance of the resulting coating film by crosslinking with the acidic groups of component (A). By setting the content of component (D) within the above range, the resulting coating film can be made highly heat resistant. Preferably, the content of component (D) is 5.0 to 8.0 parts by mass per 100 parts by mass of component (A). Component (D) may be used alone or in combination of two or more types.

[0036] The amount of oxazoline groups in component (D) is preferably 5 to 10 mmol / g. The number-average molecular weight of component (D) is preferably 30,000 to 50,000.

[0037] Component (D) is commercially available, for example, the Epocross (registered trademark) series manufactured by Nippon Shokubai Co., Ltd. Specifically, this includes water-soluble types such as "WS-300," "WS-500," and "WS-700," and emulsion types such as "K-1010E," "K-1020E," "K-1030E," "K-2010E," "K-2020E," and "K-2030E."

[0038] [water] The primer composition contains water as a medium for dispersing an acid-modified polypropylene resin aqueous dispersion (A). The primer composition may also contain a water-soluble organic solvent as a medium. Examples of water-soluble organic solvents include methanol, ethanol, n-propanol, isopropanol, n-butanol, methyl ethyl ketone, tetrahydrofuran, dioxane, acetone, ethylene glycol monoethyl ether, and ethylene glycol monobutyl ether.

[0039] [Other ingredients] The primer composition may also contain resins other than components (A) and (B), crosslinking agents other than components (C) and (D), leveling agents, wetting agents, defoaming agents, pigments, dyes, dispersants, etc., to the extent that it does not impair the effects of the present invention. The content ratio of other components to 100 parts by mass of the acid-modified polypropylene resin aqueous dispersion (A) is preferably 10.0 parts by mass or less, and more preferably 5.0 parts by mass or less.

[0040] <Preferred Forms of Composition> The primer composition may be a one-component composition containing all of components (A) to (D); or, considering the storage stability of the composition, it may be a two-component composition containing components (A) to (C) and component (D) in separate containers. In the case of a two-component composition, it is preferable that the first component contains components (A) to (C) and water, but does not contain component (D); and the second component contains component (D) and water, but does not contain components (A) to (C). In the case of a two-component composition, the first and second components are mixed at the time of use to prepare the primer composition.

[0041] <Method for preparing a primer composition> A one-component primer composition can be manufactured by dissolving or dispersing components (A) to (D), and other components as needed, in an aqueous medium to form a liquid, and then mixing each liquid in a predetermined proportion. In a two-component primer composition, the first and second components are prepared separately. The first component can be prepared by dissolving or dispersing components (A) to (C), and other components as needed, in an aqueous medium to form a liquid, and then mixing the liquids in a predetermined ratio. The second component can be prepared by dissolving or dispersing component (D), and other components as needed, in an aqueous medium to form a liquid, and then mixing the liquids in a predetermined ratio.

[0042] From the viewpoint of ease of handling, the solid content concentration of the primer composition is preferably 5 to 25% by mass, and more preferably 10 to 22% by mass. The same applies to the solid content concentrations of the first and second components in a two-component primer composition.

[0043] From the viewpoint of ease of handling, the primer composition preferably conforms to JIS Z 8803 and has a viscosity of 1 to 100 mPa·s, and more preferably 10 to 60 mPa·s, as measured at 25°C. The viscosity of the first and second components in a two-component primer composition is also similar.

[0044] <Uses of primer compositions> The coating film obtained by drying the primer composition has good adhesion to various substrates and excellent heat resistance because it uses two cross-linking systems, components (A) and (D) and components (B) and (C). In particular, the primer composition can be suitably used in the manufacture of casing materials for secondary batteries, especially those used in high-temperature environments. By using the primer composition as a primer layer for secondary battery casing materials, especially as a primer layer that bonds the metal foil layer and the sealant layer, it is possible to produce secondary battery casing materials that do not experience a decrease in adhesive strength even in high-temperature environments and have excellent electrolyte resistance.

[0045] <coating film> One aspect of the present invention is a coating film obtained by drying a primer composition. The primer composition can be applied to various substrates by known methods. The substrate is not particularly limited and can include, for example, plastic molded articles, thermoplastic resin films, fibers, nonwoven fabrics, glass, metals, metal foils, paper, etc. However, a substrate is preferably used in which the particles of component (A) can withstand the drying heating conditions of 160°C to 180°C for 2 to 5 minutes required for film formation.

[0046] After applying the primer composition to the substrate, the solvent contained in the composition is dried to form coating particles of component (A), and a primer coating film can be obtained by heating it above the melting point of component (A). During the drying process, components (A) and (D) and components (B) and (C) undergo crosslinking reactions, respectively, resulting in a highly heat-resistant coating film. The drying method and drying conditions are not particularly limited and can be set appropriately according to the thickness of the coating film, etc. In order to efficiently dry the applied primer composition and promote film formation, the drying temperature is preferably 160 to 200°C, and more preferably 180 to 200°C.

[0047] The thickness of the coating film after drying is preferably 0.1 to 10 μm, more preferably 1.0 to 8.0 μm, and even more preferably 3.0 to 5.0 μm. By setting the thickness of the coating film within the above range, when the primer composition is used as a primer layer to bond the metal foil layer and the sealant layer in the secondary battery casing material, high adhesive strength can be obtained, and even in high-temperature environments, there is no decrease in adhesive strength, resulting in a secondary battery casing material with excellent electrolyte resistance.

[0048] <Exterior material for secondary batteries> Another aspect of the present invention is an exterior material for a secondary battery comprising a base layer, an adhesive layer, a metal foil layer, a primer layer, and a sealant layer laminated in this order, wherein the primer layer is a coating film obtained by drying a primer composition.

[0049] Figure 1 shows an example of a laminate-type battery or capacitor according to the present invention. The laminate-type battery or capacitor is constructed by sealing a laminated electrode group, in which a positive electrode plate and a negative electrode plate are laminated with a separator in between, and an electrolyte (neither of which is shown) in an outer casing material 3. The tab leads 9 connected to the positive electrode plate and the tab leads 10 connected to the negative electrode plate are sealed in the sealant layer of the outer casing material 3 via a tab lead sealing film 2, and then removed. One end of the lead conductor 1 in the vertical direction is exposed to the outside from the outer casing material 3 and serves as a connection terminal to an external device, etc., while the other end is connected to the electrode plate leads of the battery within the outer casing material 3. The vertical direction of the lead conductor refers to the direction in which the lead conductor is exposed to the outside from the outer casing material in order to serve as a connection terminal to an external device, etc.

[0050] The exterior material 3 serves as the outer casing for a laminate-type battery or capacitor. The exterior material is constructed by laminating at least a base layer, an adhesive layer, a metal foil layer, a primer layer, and a sealant layer in this order. Figure 2 shows an example of the layer structure of the exterior material according to the present invention. In the exterior material of Figure 2, an acid-resistant treatment layer 13 is provided on both sides of the metal foil layer 14, and the exterior material is constructed by laminating a base layer 11, an adhesive layer 12, an acid-resistant treatment layer 13, a metal foil layer 14, an acid-resistant treatment layer 13, a primer layer 15, and a sealant layer 16 in this order. The exterior material 3 is sealed into a bag shape by, for example, two rectangular sheets of exterior material, by heat-sealing the surrounding sealant layers together. The tab leads 9 and 10 are heat-sealed to the sealant layer of the exterior material 3 via the tab lead sealing film 2, thereby sealing the tab leads 9 and 10 to the exterior material 3.

[0051] The base layer 11 is a layer that imparts mechanical strength to the exterior material. As the base layer, a biaxially oriented polyamide film, a biaxially oriented polyester film, or a laminate thereof can be used. The thickness of the base layer 11 is preferably 10 to 35 μm, and more preferably 10 to 25 μm.

[0052] The metal foil layer 14 is a layer that prevents water vapor and other substances from entering the interior, which is sealed by the outer packaging material 3, from the outside. As the metal foil layer 14, metal foil such as aluminum, nickel, or stainless steel can be used, but aluminum foil is preferred from the viewpoint of lightness, thermal conductivity, and processability. The thickness of the metal foil layer 14 is preferably 10 to 100 μm, and more preferably 20 to 60 μm.

[0053] In lithium-ion batteries, the electrolyte solution contains lithium salts such as LiPF6 and LiBF4. These salts react with moisture that enters from the outside, generating hydrofluoric acid, which can corrode the aluminum foil layer. To prevent such corrosion of the metal foil layer 14 by hydrofluoric acid and to improve the adhesion between the substrate layer 11 and the metal foil layer 14, and between the metal foil layer 14 and the primer layer 15, it is preferable to provide an acid-resistant treatment layer 13 on at least one side of the metal foil layer 14, and more preferable to provide the acid-resistant treatment layer 13 on both sides of the metal foil layer 14. The acid-resistant treatment layer 13 can be provided, for example, by trivalent chromate conversion treatment. The thickness of the acid-resistant treatment layer 13 is preferably 0.1 to 1.0 μm, and more preferably 0.2 to 0.5 μm.

[0054] The adhesive layer 12 is a layer for bonding the base layer 11 to the metal foil layer 14, or the base layer 11 to the acid-resistant treatment layer 13. A polyurethane resin or the like can be used as the adhesive layer. The thickness of the adhesive layer is preferably 1.0 to 10.0 μm, and more preferably 3.0 to 5.0 μm.

[0055] The primer layer 15 is a layer for bonding the metal foil layer 14 to the sealant layer 16, or the acid-resistant treatment layer 13 to the sealant layer 16. The primer layer 15 can be formed by applying, drying, and film-forming a primer composition on one of the layers of the metal foil layer 14, the acid-resistant treatment layer 13, and the sealant layer 16. From the viewpoint of adhesion, it is preferable to form the primer layer 15 by applying, drying, and film-forming a primer composition on the metal foil layer 14 or the acid-resistant treatment layer 13. The thickness of the primer layer is preferably 0.1 to 10.0 μm, and more preferably 3.0 to 5.0 μm.

[0056] The sealant layer 16 adheres to the primer layer 15 and also adheres the surfaces opposite to the surface adhering to the primer layer 15 (hereinafter also referred to as the heat seal layer) to create a sealed bag-like structure. The sealant layer 16 may be a single-layer film or a laminated film of two or more layers.

[0057] From the viewpoint of adhesion to the primer layer 15 and adhesive strength and electrolyte resistance in high-temperature environments, the adhesive surface of the sealant layer 16 to the primer layer 15 is preferably made of acid-modified polypropylene resin or a random copolymer of propylene and ethylene or α-olefin having 4 or more carbon atoms; preferably made of acid-modified polypropylene resin or a random copolymer of propylene and ethylene and / or 1-butene; and more preferably made of acid-modified polypropylene resin.

[0058] From the viewpoint of adhesion between heat seal layers and electrolyte resistance in high-temperature environments, the heat seal layer is preferably a random copolymer of propylene and ethylene or an α-olefin having 4 or more carbon atoms, and more preferably a random copolymer of propylene and ethylene and / or 1-butene.

[0059] From the viewpoint of improving heat resistance while maintaining adhesion to the primer layer 15 and adhesion between the heat seal layers, the sealant layer 16 preferably has an intermediate layer made of a high melting point resin. That is, the sealant layer 16 preferably consists of at least three layers, in which an adhesion layer to the primer layer 15, an intermediate layer, and a heat seal layer are sequentially laminated. The intermediate layer preferably conforms to JIS K 7121, has a melting point of 150 to 165°C measured in a nitrogen stream at a heating rate of 10°C / min, and is preferably selected from the group consisting of block copolymers of propylene and ethylene and propylene homopolymers.

[0060] The total thickness of the sealant layer 16 is preferably 21 to 100 μm, and more preferably 32 to 80 μm. When the sealant layer 16 is composed of three layers, consisting of an adhesive layer with the primer layer 15, an intermediate layer, and a heat-seal layer, the thickness of the adhesive layer with the primer layer 15 is preferably 1.0 to 30 μm, and more preferably 2.0 to 20 μm. The thickness of the intermediate layer is preferably 10 to 50 μm, and more preferably 20 to 40 μm. The thickness of the heat-seal layer is preferably 10 to 40 μm, and more preferably 10 to 30 μm.

[0061] <Manufacturing method for exterior materials for secondary batteries> The method for manufacturing the exterior material for secondary batteries is not particularly limited, but examples include a method that includes: step 1 providing an acid-resistant treatment layer 13 on one or both sides of a metal foil layer 14; step 2 applying, drying, and forming a primer composition on the acid-resistant treatment layer 13 obtained in step 1 to form a primer layer 15; step 3 placing a separately prepared sealant layer 16 and the primer layer 15 obtained in step 2 opposite each other and heat-bonding them using a hot roll or the like; and step 4 laminating a base layer 11 via an adhesive layer 12 provided by a dry lamination method or the like on the side of the resulting laminate opposite to the sealant layer 16 (the metal foil layer 14 or the other acid-resistant treatment layer 13 provided on the metal foil layer 14). The conditions for the heated rolls in step 3 are not particularly limited, but from the viewpoint of increasing the adhesive strength between the primer layer 15 and the sealant layer 16, the temperature of the roll in contact with the metal foil layer 14 or the other acid-resistant treatment layer 13 provided on the metal foil layer 14 is preferably 160 to 250°C, and more preferably 200 to 250°C. Furthermore, the temperature of the roll in contact with the sealant layer 16 is preferably 60 to 100°C, and more preferably 80 to 100°C.

[0062] <Secondary battery> A further aspect of the present invention is a secondary battery comprising an outer casing for a secondary battery and a power generation element. Examples of the power generation element include a positive electrode consisting of a positive electrode active material and a current collector, a separator, a negative electrode consisting of a negative electrode active material and a current collector, an electrolyte, and tab leads connected to the positive and negative electrodes and exposed to the outside of the outer casing. [Examples]

[0063] The present invention will be described in further detail below based on examples and comparative examples.

[0064] [Method for evaluating raw materials] The evaluation methods for the raw materials used in the examples and comparative examples are as follows.

[0065] 1.DSC measurement For the dried samples of the acid-modified polypropylene resin constituting the primer layer composition and the resin constituting the sealant layer, the melting point was defined as the temperature of the endothermic peak when the samples were heated from -50°C to 200°C in a nitrogen stream at a rate of 10°C / min using a differential scanning calorimeter (DSC) in accordance with JIS K 7121.

[0066] 2. Acid value The acid value of dried samples of the acid-modified polypropylene resin constituting the primer layer composition was measured in accordance with JIS K 2501.

[0067] 3. Degree of saponification For modified polyvinyl alcohol (B) containing carbonyl groups, the degree of saponification was measured in accordance with JIS K 6726.

[0068] [Raw materials used] The raw materials used in the examples and comparative examples are as follows:

[0069] 1. Acid-modified polypropylene resin Maleic anhydride-modified polypropylene aqueous dispersion (A) (manufactured by Unitika Ltd., Arrowbase® YA-6010, melting point: 145°C, acid value: 20-30 mgKOH / g, solid content concentration: 25% by mass, pH: 8-11 (physical properties are catalog values)) Maleic anhydride-modified polypropylene solution (manufactured by Toyobo MC Co., Ltd., Hardlen® PMA-TH, melting point: 95°C, acid content: 1.1% by mass, solvent: mixed solvent of 90% by mass cyclohexane and 10% by mass 2-butanone, solids concentration: 14% by mass (physical properties are catalog values))

[0070] 2. Modified polyvinyl alcohol having a carbonyl group (B) Diacetone acrylamide-modified polyvinyl alcohol (B) (manufactured by Nippon Vivaceum Co., Ltd., DF-17, degree of saponification: 98-99 mol% (catalog value)) A 10% by mass aqueous solution of diacetone acrylamide-modified polyvinyl alcohol (B) was prepared and used in the preparation of the primer composition.

[0071] 3. Dihydrazide adipic acid (C) Dihydrazide adipic acid (ADH) (manufactured by Otsuka Chemical Co., Ltd.) A 10% by mass aqueous solution of adipic acid dihydrazide (C) was prepared and used in the preparation of the primer composition.

[0072] 4. Crosslinking agent Oxazoline group-containing polymer (D) (manufactured by Nippon Shokubai Co., Ltd., Epocross® WS-300 (aqueous solution), solid content concentration: 10% by mass, pH: 7-10, oxazoline group: 7.7 mmol / g (physical properties are catalog values)) Carbodiimide group-containing polymer (manufactured by Nisshinbo Chemical Co., Ltd., Carbodilite® (registered trademark) (aqueous solution), solid content concentration: 40% by mass, pH: 8-11 (physical properties are catalog values)) Isocyanate group-containing polymer (manufactured by Asahi Kasei Corporation, Duranate® TPA-100, solids content: 100% by mass, NCO%: 23.1% by mass (physical properties are catalog values)) Epoxy group-containing polymer (manufactured by Toyobo Co., Ltd., Hardlen® LAE-004 (MEK solution), solids content concentration: 61-65% by mass (physical properties are catalog values))

[0073] 5. Raw materials for the sealant layer (a-1) Maleic anhydride-modified polypropylene (manufactured by Mitsui Chemicals, Inc., EX005, melting point: 155℃, MFR: 7.0g / 10min (physical properties are catalog values)) (b-1) Propylene-ethylene block copolymer (manufactured by Sun Allomer Co., Ltd., Sun Allomer® PC480A, melting point: 160℃, MFR: 2.0g / 10min (physical properties are catalog values)) (r-1) Propylene-based random copolymer (manufactured by Sun Allomer Co., Ltd., Sun Allomer® PC630S, melting point 142℃, MFR 7.5g / 10min (physical properties are catalog values))

[0074] Example 1 Based on solid content, 5.0 parts by mass of oxazoline group-containing polymer (D), 1.0 part by mass of diacetone acrylamide-modified polyvinyl alcohol (B), and 1.0 part by mass of adipic acid dihydrazide (C) were sequentially added to 100.0 parts by mass of maleic anhydride-modified polypropylene aqueous dispersion (A) as crosslinking agents, and the mixture was stirred for 10 minutes to obtain the primer composition of Example 1 with a solid content concentration of 21.0% by mass.

[0075] Example 2 A primer composition for Example 2 with a solid content of 21.1% by mass was obtained in the same manner as in Example 1, except that the amount of diacetone acrylamide-modified polyvinyl alcohol (B) was changed to 0.5 parts by mass.

[0076] Example 3 A primer composition for Example 3 with a solid content of 20.8% by mass was obtained in the same manner as in Example 1, except that the amount of diacetone acrylamide-modified polyvinyl alcohol (B) was changed to 2.0 parts by mass.

[0077] Example 4 A primer composition for Example 4 with a solid content of 20.6% by mass was obtained in the same manner as in Example 1, except that the amount of diacetone acrylamide-modified polyvinyl alcohol (B) was changed to 3.0 parts by mass.

[0078] Example 5 A primer composition for Example 5 with a solid content concentration of 20.2% by mass was obtained in the same manner as in Example 1, except that the amount of adipic acid dihydrazide (C) was changed to 5.0 parts by mass.

[0079] Example 6 A primer composition for Example 6 with a solid content of 20.0% by mass was obtained in the same manner as in Example 1, except that the amount of oxazoline group-containing polymer (D) was changed to 10.0 parts by mass.

[0080] Comparative Example 1 Using 100.0 parts by mass of the maleic anhydride-modified polypropylene aqueous dispersion (A) as is, a primer composition of Comparative Example 1 with a solid content concentration of 25.0% by mass was obtained.

[0081] Comparative Example 2 A primer composition for Comparative Example 2 with a solid content of 21.4% by mass was obtained in the same manner as in Example 1, except that diacetone acrylamide-modified polyvinyl alcohol (B) and adipic acid dihydrazide (C) were not included.

[0082] Comparative Example 3 A primer composition for Comparative Example 3 with a solid content of 22.2% by mass was obtained in the same manner as in Example 1, except that the oxazoline group-containing polymer (D) was not included.

[0083] Comparative Example 4 A primer composition for Comparative Example 4 with a solid content of 21.2% by mass was obtained in the same manner as in Example 5, except that the oxazoline group-containing polymer (D) was not included.

[0084] Comparative Example 5 A primer composition for Comparative Example 5 with a solid content of 22.6% by mass was obtained in the same manner as in Example 1, except that 5.0 parts by mass of a carbodiimide group-containing polymer was added instead of the oxazoline group-containing polymer (D).

[0085] Comparative Example 6 A primer composition for Comparative Example 6 with a solid content of 23.1% by mass was obtained in the same manner as in Example 1, except that 10.0 parts by mass of a carbodiimide group-containing polymer was added instead of the oxazoline group-containing polymer (D).

[0086] Comparative Example 7 A primer composition for Comparative Example 7 with a solid content concentration of 20.4% by mass was obtained in the same manner as in Example 1, except that the amount of diacetone acrylamide-modified polyvinyl alcohol (B) was changed to 4.0 parts by mass.

[0087] Comparative Example 8 Based on solid content, 32.0 parts by mass of an isocyanate group-containing polymer was added to 100.0 parts by mass of a maleic anhydride-modified polypropylene solution as a crosslinking agent, and this mixture was stirred and mixed for 10 minutes to obtain the primer composition of Comparative Example 8 with a solid content concentration of 17.7% by mass.

[0088] Comparative Example 9 Based on solid content, 12.1 parts by mass of epoxy group-containing polymer was added to 100.0 parts by mass of maleic anhydride-modified polypropylene solution as a crosslinking agent, and this mixture was stirred and mixed for 10 minutes to obtain the primer composition of Comparative Example 9 with a solid content concentration of 14.8% by mass.

[0089] [Method for evaluating primer compositions] The evaluation methods for the primer compositions of the examples and comparative examples are as follows.

[0090] 1. Stability of the primer layer composition The viscosity of the primer layer compositions immediately after preparation and after storage for one day at 25°C and 40°C was measured at 25°C using a TV-200EH viscometer manufactured by Toki Sangyo Co., Ltd., in accordance with JIS Z 8803. For compositions immediately after preparation and those stored at 40°C, the viscosity was measured after adjusting the liquid temperature to 25°C. Table 1 shows the formulation and viscosity measurement results for the primer compositions of Examples 1-6 and Comparative Examples 1-9. The compositions of Comparative Examples 8 and 9 gelled after being stored at 25°C and 40°C for one day, respectively, so viscosity measurement was not possible.

[0091] [Table 1]

[0092] 2. Adhesion Strength 1 (Composition: Primer layer coated foil / Single layer film / Primer layer coated foil) 1) Preparation of maleic anhydride-modified polypropylene single-layer film Using a single-layer T-die extrusion machine, (a-1) maleic anhydride-modified polypropylene was melt-extruded to form a single-layer film with a thickness of 25 μm and a width of 350 mm. A sample measuring 80 mm in length and 70 mm in width was cut from the resulting single-layer film and used for measuring the adhesive strength 1. 2) Preparation of primer-coated foil On one side of an 80mm long x 70mm wide x 0.04mm thick aluminum foil (A1N30, manufactured by UACJ Corporation) that had been treated with trivalent chromate on both sides, the primer compositions of the examples and comparative examples were applied using a bar coater (OSP-22, manufactured by OSG System Products Co., Ltd.). This was then dried in an oven set to 180°C for 2 minutes to form a film, obtaining aluminum foil with a primer layer having a thickness of 5 μm. For Comparative Examples 8 and 9, one side of the aluminum foil was coated using a bar coater (OSG System Products Co., Ltd., OPS-42), dried in an oven set to 80°C for 2 minutes, and the solvent was evaporated to obtain aluminum foil having a primer layer with a thickness of 5 μm. 3) Preparation of adhesion test specimens Under a 120°C environment, the single-layer film obtained in 1) stretches under tensile stress, making it impossible to measure the adhesive strength using the adhesion test specimen between the primer-coated foil and the single-layer film. Therefore, an adhesion test specimen consisting of primer-coated foil / single-layer film / primer-coated foil was prepared and used to measure the adhesive strength under 25°C and 120°C environments. Using two primer-coated foils prepared in (2), a single-layer film sample prepared in (1) was sandwiched between them so that each primer layer was in contact with the single-layer film. This was then sandwiched between two heat-sealing bars heated to 180°C, with an 80 μm thick glass cloth-impregnated heat-resistant sheet in between, and bonded under conditions of 0.5 MPa and 5 seconds to prepare an adhesion test specimen. 4) Measurement of T-type peel adhesion strength under 25°C and 120°C conditions The prepared adhesive test specimens were stored at 80°C for 18 hours. Subsequently, at 25°C and 120°C, in accordance with JIS K 6854-3, one coated foil was fixed to one jig and the remaining coated foil to the other jig, and a T-shaped peel test was performed at a tensile speed of 100 mm / min. The average value of the central portion, excluding the 10% before and after the peel test data, was defined as the adhesive strength. For the adhesive test specimens at 25°C, the measurement was performed after leaving them in that environment for 4 hours. The measurement was repeated 5 times for each specimen, and the average value was defined as the adhesive strength of that specimen. At 25°C, an adhesive strength of 14 N / 15 mm or higher was considered to indicate excellent adhesion. At 120°C, an adhesive strength of 5.0 N / 15 mm or higher was considered to indicate excellent adhesion in high-temperature environments.

[0093] Table 2 shows the measurement results for adhesive strength 1 for the primer compositions of Examples 1-6 and Comparative Examples 3-6, 8, and 9.

[0094] [Table 2]

[0095] 3. Adhesion strength 2 (Primer layer coated foil / sealant film composition) 1) Preparation of sealant film Using a 3-layer T-die co-extrusion molding machine, a 3-layer sealant film with a total thickness of 80 μm was produced by sequentially co-extruding (a-1) maleic anhydride-modified polypropylene 16 μm as the adhesive layer to the primer layer coated foil, (b-1) propylene-ethylene block copolymer 48 μm as the intermediate layer, and (r-1) propylene-based random copolymer 16 μm as the heat seal layer. 2) Preparation of adhesion test specimens A primer-coated foil having a 5 μm thick primer layer was obtained using the same method as in 2) above. The coated foil was placed on top and the sealant film on the bottom, and the primer layer of the coated foil and the adhesive layer of the sealant film to the coated foil were placed opposite each other. This was then sandwiched between an upper heat seal bar heated to 180°C and a lower heat seal bar heated to 60°C, with an 80 μm thick glass cloth impregnated heat-resistant sheet in between, and bonded under conditions of 0.5 MPa and 5 seconds to prepare an adhesion test specimen. 3) Measurement of T-type peel adhesion strength in a 25°C environment The prepared adhesive test specimens were stored at 80°C for 18 hours, then left at 25°C for 4 hours. In accordance with JIS K 6854-3, the coated foil was fixed to one jig and the sealant film to the other jig, and a T-shaped peel test was performed at a tensile speed of 100 mm / min. The average value of the central portion, excluding the 10% before and after the peel test data, was defined as the adhesive strength. The measurement was repeated 5 times for each test specimen, and the average value was defined as the adhesive strength of that specimen. An adhesive strength of 14 N / 15 mm or higher was considered to indicate excellent adhesion.

[0096] Table 3 shows the measurement results for adhesive strength 2 for the primer compositions of Examples 1-6 and Comparative Examples 1-6.

[0097] [Table 3]

[0098] 4. Adhesion strength after immersion in electrolyte solution Adhesion test specimens were prepared in the same manner as described in 3.2) above, stored at 80°C for 18 hours, and then left at 25°C for 4 hours. The obtained adhesion test specimens were immersed in a 1 mol / L LiPF6 electrolyte solution in ethylene carbonate:diethyl carbonate:dimethyl carbonate = 1:1:1 with 1,000 ppm of distilled water added, and left in an 85°C constant temperature bath for 3 days and 7 days. After being removed from the constant temperature bath, the adhesion test specimens were washed with dimethyl carbonate solution, then rinsed with water and dried. Adhesion test specimens immersed in electrolyte solution were stored for 24 hours at 25°C. Under the same conditions, in accordance with JIS K 6854-3, the coated foil was fixed to one jig and the sealant film to the other jig, and a T-shaped peel test was performed at a tensile speed of 100 mm / min. The average value of the central portion, excluding the 10% before and after the peel test data, was defined as the adhesive strength. The measurement was repeated 5 times for each test specimen, and the average value was defined as the adhesive strength of that specimen. If the adhesive strength of the adhesion test specimen after 7 days of storage in an 85°C constant temperature bath was 80% or more of the initial value and 12N / 15mm or more, it was determined that the electrolyte resistance was excellent. If the adhesive strength of the adhesion test specimen after 7 days of storage in an 85°C constant temperature bath was 70% or more of the initial value and 12N / 15mm or more, it was determined that the electrolyte resistance was practically acceptable.

[0099] Table 4 shows the results of measuring the adhesive strength after immersion in the electrolyte for the primer compositions of Examples 1-6 and Comparative Examples 2 and 4-6.

[0100] [Table 4]

[0101] As shown in Tables 1-4, the primer compositions of Examples 1-6 exhibit excellent storage stability, and the laminates obtained by using the coating film from these compositions to bond trivalent chromate-treated aluminum foil and sealant film show no decrease in adhesive strength even in high-temperature environments, demonstrating excellent resistance to electrolytes.

[0102] Comparative Example 1, which used only the aqueous dispersion of maleic anhydride-modified polypropylene (A), and Comparative Example 2, which was a mixture of the aqueous dispersion (A) and an oxazoline group-containing polymer (D), exhibited significantly inferior adhesive strength at 25°C. Comparative Examples 3 and 4, consisting of the three components of the aqueous dispersion (A), diacetone acrylamide-modified polyvinyl alcohol (B), and adipic acid dihydrazide (C), exhibited poor adhesion at 120°C. Comparative Examples 5 and 6, which used a carbodiimide group-containing polymer instead of the oxazoline group-containing polymer (D), exhibited poor electrolyte resistance at 85°C. Comparative Example 7, in which the amount of diacetone acrylamide-modified polyvinyl alcohol (B) was 4.0 parts by mass per 100 parts by mass of the aqueous dispersion (A), showed thickening of the composition over time, resulting in unstable coating amounts during application and poor coating stability. Comparative Examples 8 and 9, which were prepared by blending an isocyanate group-containing polymer and an epoxy group-containing polymer, respectively, into a maleic anhydride-modified polypropylene solution, exhibited poor storage stability and poor adhesion at 120°C, which was attributed to the low melting point of the maleic anhydride-modified polypropylene used. [Industrial applicability]

[0103] The primer composition of the present invention can be suitably used in the manufacture of exterior materials for secondary batteries used in high-temperature environments. [Explanation of symbols]

[0104] 1 Lead conductor 2. Film for sealing tab leads 3. Exterior materials 9. Tab lead on the positive terminal side 10. Tab lead on the negative electrode side 11 Base material layer 12 Adhesive layer 13 Acid-resistant layer 14 Metal foil layer 15. Primer layer 16. Sealant layer

Claims

1. Acid-modified polypropylene resin aqueous dispersion (A) 100 parts by mass, 0.5 to 3.0 parts by mass of modified polyvinyl alcohol (B) having a carbonyl group, Dihydrazide adipic acid (C) 1.0 to 5.0 parts by mass, 5.0 to 10.0 parts by mass of oxazoline compound (D), and water A primer composition comprising, The aqueous dispersion (A) has a melting point of 143 to 148°C, measured in accordance with JIS K 7121 under a nitrogen atmosphere at a heating rate of 10°C / min, and an acid value of 20 to 30 mgKOH / g, measured in accordance with JIS K 2501. The modified polyvinyl alcohol (B) is a primer composition having a degree of saponification of 98 to 99 mol%, as measured in accordance with JIS K 6726.

2. The primer composition according to claim 1, wherein component (A) is an aqueous dispersion of polypropylene resin modified with maleic anhydride.

3. The primer composition according to claim 1 or 2, wherein component (B) is polyvinyl alcohol containing diacetone acrylamide units.

4. The primer composition according to claim 1 or 2, wherein the amount of oxazoline groups in component (D) is 5 to 10 mmol / g.

5. The primer composition according to claim 1 or 2, wherein the content ratio of component (C) to component (B) is 0.3 to 5 by mass.

6. A primer composition according to claim 1 or 2, comprising a first agent and a second agent, A primer composition comprising: a first agent containing components (A) to (C) and water, but not component (D); and a second agent containing component (D) and water, but not components (A) to (C).

7. A primer composition according to claim 1 or 2 for use in the manufacture of outer casing material for secondary batteries.

8. A coating film obtained by drying the primer composition according to claim 1 or 2.

9. An exterior material for a secondary battery comprising a base layer, an adhesive layer, a metal foil layer, a primer layer, and a sealant layer laminated in this order, wherein the primer layer is the coating film described in claim 8.

10. A secondary battery comprising the exterior material for a secondary battery described in claim 9 and a power generation element.

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