JP6431688B2 - Coating material for separator, slurry, separator, and secondary battery - Google Patents

Description

  The present invention relates to a separator coating material, a slurry for forming a separator using the coating material, a separator manufactured using the slurry, and a secondary battery using the separator.

  In recent years, development of high-performance secondary batteries has been actively promoted in response to demands for electronic devices to be reduced in size and weight, multifunctional, and cordless. Examples of secondary batteries include nickel-cadmium secondary batteries (nickel batteries) obtained using cadmium, nickel-hydrogen secondary batteries (Ni-MH batteries) obtained using hydrogen storage alloys, and lithium compounds. Non-aqueous electrolyte secondary batteries (lithium ion batteries) that have been used.

  Such a secondary battery generally has a structure in which a separator is disposed between a positive electrode and a negative electrode in an electrolytic solution.

  The positive electrode and the negative electrode of the secondary battery are obtained by binding predetermined active material particles and desired additives to the surface of the metal current collector, respectively. In order to bind the active material particles to the current collector surface, a binder in which a polymer is dissolved or dispersed in an aqueous medium is used. Such an electrode binder has not only a binding property for binding the active material particles to the surface of the metal current collector, but also an electrolyte solution resistance for maintaining the binding property in the electrolyte solution. It is requested.

  Various binders have been reported as electrode binders (for example, Patent Documents 1 to 3).

  The separator of the secondary battery is a porous body that allows ions such as lithium ions to pass through during charging and discharging while preventing a short circuit between the positive electrode and the negative electrode. The secondary battery separator cuts off the current when the secondary battery's thermal runaway occurs due to overcharging, etc., as a high temperature safety function by melting the thermoplastic resin as the base material and closing the holes. The polyolefin porous substrate is widely used as a separator. In particular, there are many proposals for imparting heat resistance to separators. For example, a method for improving dimensional stability at high temperatures by adhering non-conductive particles having heat resistance to a porous substrate with a binder has been proposed. (Cited document 4). In order to adhere non-conductive particles to the surface of a porous substrate, a coating material in which a polymer is dissolved or dispersed in an aqueous medium is usually used. Such a coating material has required characteristics similar to those of an electrode binder, that is, an adhesive property for adhering non-conductive particles to the surface of a porous substrate, and an anti-resistance property for maintaining the adhesive property in an electrolyte solution. Not only the electrolyte properties but also the heat resistance to maintain the adhesion even during thermal runaway (the dimensional stability of the separator in a high temperature environment) and the permeability of the separator to allow ions to permeate in the electrolyte during charging and discharging. It is required to ensure temper.

  However, when a conventional electrode binder is used as a separator coating material, the following problems occur. The pores of the porous substrate were clogged, resulting in a decrease in air permeability and a decrease in secondary battery performance. Therefore, if the amount of the binder is reduced in order to ensure the air permeability of the separator, the adhesiveness between the nonconductive particles and between the nonconductive particles and the porous substrate is lowered, and the dimensional stability at high temperature is lowered and safety is increased. There was a problem. Therefore, when trying to ensure the desired adhesiveness, the air permeability decreased. When the air permeability decreased, the battery characteristics of the secondary battery deteriorated.

  Various coating materials have been reported as a coating material for a separator (Patent Document 5). However, the coating material has a predetermined separator air permeability and at the same time has excellent adhesiveness, and has good electrolytic solution resistance and heat resistance. Has not yet been developed.

JP-A-8-50894 WO2008 / 029502A1 JP2010-55972A JP2013-237203A JP2013-173283A

  The present invention is excellent in adhesion between non-conductive particles and between non-conductive particles and a porous substrate and air permeability of the resulting separator, and also has good resistance to electrolyte solution and heat resistance to heat generation. An object is to provide a coating material for a separator, a slurry for forming a separator using the coating material, a separator manufactured using the slurry, and a secondary battery using the separator.

  In the present specification, the adhesiveness regarding the separator means the adhesiveness from the viewpoint of achieving sufficient bonding between the nonconductive particles and between the nonconductive particles and the porous substrate while maintaining a predetermined air permeability. However, it should be used separately from the binding property relating to the electrode that does not require consideration of air permeability.

  In the present invention, a polyolefin resin containing 50 to 99 mass% of an unsaturated hydrocarbon component having 3 to 6 carbon atoms and 0.5 to 20 mass% of an unsaturated carboxylic acid component is dispersed in an aqueous medium together with a basic compound. The present invention relates to a coating material for a separator.

  The present invention also relates to a slurry for forming a separator containing the coating material and non-conductive particles.

  The present invention also relates to a separator having a porous layer formed by applying the slurry to at least one surface of a porous substrate.

  The present invention also relates to a secondary battery comprising the separator.

  The separator formed using the coating material for a separator according to the present invention is excellent in adhesiveness and air permeability between non-conductive particles and between non-conductive particles and a porous substrate at the same time, and is resistant to electrolyte. And heat resistance against heat generation are good.

[Coating material for separator]
The coating material for a separator according to the present invention is an aqueous dispersion in which a polyolefin resin is dispersed in an aqueous medium together with a basic compound.

  The polyolefin resin has 3 to 6 carbon atoms, preferably 3 to 4 carbon atoms, and most preferably 3 to 3 carbon atoms as a main monomer unit. It is necessary to contain 99% by mass, preferably 60 to 99% by mass, more preferably 70 to 99% by mass, and particularly preferably 73 to 95% by mass. When the content of the unsaturated hydrocarbon having 3 to 6 carbon atoms is less than 50% by mass, the adhesion between the nonconductive particles and between the nonconductive particles and the porous substrate may be lowered. On the other hand, if it exceeds 99% by mass, the content of the unsaturated carboxylic acid unit is relatively lowered, so that it may be difficult to make the resin water-based. When 50% or more of the unsaturated hydrocarbon components are unsaturated hydrocarbons having 2 carbon atoms, the heat resistance is lowered. If 50% or more of the unsaturated hydrocarbon components are unsaturated hydrocarbons having 7 or more carbon atoms, it becomes difficult to make the resin water-based.

  Specific examples of the unsaturated hydrocarbon component having 3 to 6 carbon atoms include propylene, 1-butene, isobutene, 1-pentene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-hexene and the like. Alkenes and dienes such as butadiene and isoprene. Two or more kinds of compounds may be contained as the unsaturated hydrocarbon component, and in that case, the total amount thereof may be within the above range. Among these, propylene or butene (especially from the viewpoints of ease of resin production, ease of aqueous formation, adhesion between non-conductive particles, adhesion between non-conductive particles and a porous substrate, etc.) 1-butene) is preferably included, and both may be used in combination. Butene includes 1-butene and isobutene. The total content of propylene and butene is preferably 50 to 99 mass% with respect to the total amount of the constituent components of the polyolefin resin.

  In addition to the unsaturated hydrocarbon component having 3 to 6 carbon atoms, the polyolefin resin preferably contains 1.5 to 45% by mass of ethylene with respect to the total amount of the constituent components of the polyolefin resin, It is more preferable to contain 0.5-30 mass%, and it is further more preferable to contain 0.5-25 mass%. By containing ethylene, the flexibility of the resin is increased, and as a result, not only the adhesiveness is improved, but also the aqueous solution is easily formed.

  The polyolefin resin preferably contains propylene or 1-butene as a main component as an unsaturated hydrocarbon component having 3 to 6 carbon atoms. Propylene or 1-butene as a main component means that propylene or 1-butene is contained in an amount of 50% by mass or more, preferably 70 to 100% by mass, based on the total amount of unsaturated hydrocarbon components having 3 to 6 carbon atoms. It means that. More preferably, the polyolefin resin contains propylene and ethylene, or contains propylene and 1-butene. The polyolefin resin may contain 1-butene and ethylene. In the case where the polyolefin resin contains either propylene or 1-butene and ethylene, a preferable constitution ratio is 50% of propylene or 1-butene when the total of propylene or 1-butene and ethylene is 100% by mass. -90 mass% and ethylene are 10-50 mass%.

  A particularly preferable constitution of the polyolefin resin is to contain two components of propylene and ethylene or three components of propylene, butene and ethylene. The preferable composition ratio in this case is more preferably 8 to 99% by mass of propylene, 0 to 90% by mass of butene, and 1 to 49% by mass of ethylene when the total of these two or three components is 100% by mass. The ratio is 50 to 99% by mass of propylene, 0 to 40% by mass of butene, and 1 to 40% by mass of ethylene.

  The polyolefin resin has an unsaturated carboxylic acid component as a monomer unit in the structure in an amount of 0.5 to 20% by mass based on the total amount of the constituent components of the polyolefin resin, from the viewpoint of its dispersibility and particle size at the time of dispersion. There is a need. The unsaturated carboxylic acid component is preferably 0.5 to 15% by mass, more preferably 0.5 to 12% by mass, further preferably 1 to 10% by mass, and 1 to 8% by mass. % Is particularly preferred. When the unsaturated carboxylic acid component is less than 0.5% by mass, it becomes difficult to make the polyolefin resin aqueous. On the other hand, when the amount exceeds 20% by mass, the particle size at the time of dispersion becomes small and the dispersibility is improved, so that the resin can be easily made water-based, but the electrolytic solution resistance is lowered and the heat resistance tends to be poor. is there.

  The unsaturated carboxylic acid component is an unsaturated carboxylic acid having at least one radical polymerizable bond (particularly a double bond) and at least one carboxyl group and anhydride thereof in one molecule. Specific examples thereof include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, aconitic acid, aconitic anhydride, fumaric acid, crotonic acid, citraconic acid, mesaconic acid, and allyl succinic acid. be able to. In addition, a compound having at least one carboxyl group or acid anhydride group in the molecule (in the monomer unit), such as a half ester or half amide of an unsaturated dicarboxylic acid, can also be exemplified. Two or more kinds of compounds may be contained as the unsaturated carboxylic acid component, and in that case, the total amount thereof may be within the above range). Of these, maleic anhydride, acrylic acid, and methacrylic acid are preferred, and maleic anhydride is more preferred from the viewpoint of ease of introduction into the polyolefin resin. The acid anhydride unit introduced into the polyolefin resin tends to take an acid anhydride structure in a dry state, and in an aqueous medium containing a basic compound, part or all of the acid anhydride units are opened to form a carboxylic acid or a salt thereof. Tend to be structure.

  The polyolefin resin contains (meth) acrylic acid ester in a proportion of 20% by mass or less with respect to the total amount of the constituent components of the polyolefin resin, from the viewpoint of facilitating aqueous formation and improving the adhesion to various materials. May be. Specific examples of (meth) acrylic acid esters include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, (meth) Examples include octyl acrylate, decyl (meth) acrylate, lauryl (meth) acrylate, octyl (meth) acrylate, dodecyl (meth) acrylate, stearyl (meth) acrylate, and the like.

  The polyolefin resin may contain 20% by mass or less of the following components in addition to the above components based on the total amount of the constituent components of the polyolefin resin. For example, alkenes and dienes having 7 or more carbon atoms such as 1-octene and norbornenes; maleate esters such as dimethyl maleate, diethyl maleate and dibutyl maleate; (meth) acrylic acid amides; methyl vinyl ether, Alkyl vinyl ethers such as ethyl vinyl ether; vinyl esters such as vinyl formate, vinyl acetate, vinyl propionate, vinyl pivalate, vinyl versatate; vinyl alcohol; 2-hydroxyethyl acrylate; glycidyl (meth) acrylate; (meth) Examples include acrylonitrile; styrene; substituted styrene; vinyl halides; halogenated vinylidenes; carbon monoxide; Mixtures of these can also be used.

  In the polyolefin resin, the copolymerization form of each component excluding the unsaturated carboxylic acid component is not particularly limited, and examples thereof include random copolymerization and block copolymerization. Of these, random copolymerization is preferred from the viewpoint of ease of polymerization.

  The unsaturated carboxylic acid component only needs to be copolymerized in the polyolefin resin, and specific examples of the copolymerization form include random copolymerization, block copolymerization, and graft copolymerization. In the case of graft copolymerization, for example, a method in which a polyolefin resin not containing an unsaturated carboxylic acid component and an unsaturated carboxylic acid are heated and melted to a temperature higher than the melting point of the polyolefin resin in the presence of a radical generator, An example is a method in which a resin is dissolved in an organic solvent and then reacted by heating and stirring in the presence of a radical generator. The former method is preferable because the operation is simple. Examples of the radical generator used for graft copolymerization include di-tert-butyl peroxide, dicumyl peroxide, tert-butyl hydroperoxide, tert-butyl cumyl peroxide, benzoyl peroxide, dilauryl peroxide, Examples thereof include organic peroxides such as cumene hydroperoxide, tert-butyl peroxybenzoate, ethyl ethyl ketone peroxide, and di-tert-butyl diperphthalate, and azonitriles such as azobisisobutyronitrile. These may be selected and used as appropriate based on the reaction temperature.

  The weight average molecular weight of the polyolefin resin is 20,000 or more from the viewpoint of further improving the adhesiveness between the nonconductive particles, the adhesiveness between the nonconductive particles and the porous base material, and the ease of making the resin aqueous. It is preferably 20,000 to 150,000, more preferably 30,000 to 120,000, particularly preferably 30,000 to 100,000, and 30,000. Most preferred is ~ 90,000. The weight average molecular weight of the resin can be determined using polystyrene resin as a standard using gel permeation chromatography (GPC).

  The melting point of the polyolefin resin is the viewpoint of further improving the adhesiveness between the nonconductive particles, the adhesiveness between the nonconductive particles and the porous substrate, the heat resistance as the porous substrate, and the ease of making the resin aqueous. Therefore, it is preferably 70 to 200 ° C, more preferably 80 to 180 ° C, still more preferably 90 to 175 ° C, and most preferably 100 to 170 ° C. The melting point of the resin can be determined by DSC (DSC-7 manufactured by Perkin Elmer).

  As the polyolefin resin, two or more kinds of polyolefin resins having different compositions, molecular weights and / or melting points may be contained. At this time, the ratio of the components of the entire two or more types of polyolefin resin may be in the above range. The ratio of the constituent components of each polyolefin resin is preferably in the above range.

  The following can be mentioned as polyolefin resin used for this invention. For example, “REXTAC” manufactured by Rexene in the United States, “Best Plast 408” and “Best Plast 708” manufactured by Huls in Germany, “Ubetak APAO” manufactured by Ube Lexen, etc. The polyolefin resin which introduce | transduced the unsaturated carboxylic acid component by these methods to these commercially available resin can be mentioned. Of the above-mentioned commercially available resins, it is preferable to use Bestplast 408 and Bestplast 708.

  The polyolefin resin used in the present invention may be crosslinked, and the adhesiveness can be further improved by the effect of crosslinking. As a method for crosslinking the polyolefin resin of the present invention in advance before being water-based, the above-mentioned polyolefin resin is further irradiated with an active energy ray such as an electron beam or radiation, or a crosslinking agent in a state where the resin is dissolved or melted. The method of making it react is mentioned. Examples of the crosslinking agent include a crosslinking agent having self-crosslinking properties, a crosslinking agent having a plurality of functional groups that react with carboxyl groups in the molecule, and a metal complex having a multivalent coordination site. More specifically, examples of the cross-linking agent include water-insoluble polyols, polyamines, and polythiols that are not usually used as surfactants. Furthermore, an isocyanate compound, a melamine compound, a urea compound, an epoxy compound, a carbodiimide compound, an oxazoline group-containing compound, a zirconium salt compound, and a silane coupling agent are exemplified.

  The separator coating material of the present invention is obtained by dispersing the above polyolefin resin in an aqueous medium together with a basic compound. The basic compound neutralizes part or all of the carboxyl groups in the polyolefin resin, preventing the aggregation between the fine particles due to the electric repulsive force between the generated carboxyl anions and imparting stability to the aqueous dispersion. Is done.

  The boiling point of the basic compound at normal pressure is preferably less than 250 ° C. from the viewpoint of water resistance, drying property and the like. In the present specification, “at normal pressure” means “at atmospheric pressure”. When the boiling point is 250 ° C. or higher, it is difficult to disperse the basic compound from the resin coating film by drying, and particularly the water resistance of the coating film at low temperature drying and adhesion to the substrate may deteriorate. is there. Specific examples of the basic compound are not particularly limited. For example, ammonia, triethylamine, N, N-dimethylethanolamine, isopropylamine, aminoethanol, dimethylaminoethanol, diethylaminoethanol, ethylamine, diethylamine, isobutylamine, dipropylamine, 3-ethoxypropylamine, 3-diethylaminopropylamine, sec-butylamine, propylamine, n-butylamine, 2-methoxyethylamine, 3-methoxypropylamine, 2,2-dimethoxyethylamine, monoethanolamine, morpholine, N-methylmorpholine, N-ethylmorpholine, pyrrole, pyridine, etc. Can be mentioned.

  The addition amount of the basic compound is preferably 0.5 to 3.0 times equivalent, more preferably 0.8 to 2.5 times equivalent to the carboxyl group in the polyolefin resin. It is particularly preferably 9 to 2.0 times equivalent. If the amount is less than 0.5 times equivalent, the addition effect of the basic compound is not recognized. If the amount exceeds 3.0 times equivalent, the drying time during the formation of the coating film becomes longer, or the stability of the aqueous dispersion deteriorates. There is a case.

  The addition amount of the basic compound in the separator coating material of the present invention is not particularly limited as long as the addition equivalent to the carboxyl group in the polyolefin resin is within the above range, but it is usually the total coating material amount. On the other hand, 0.01-5.0 mass% is preferable and 0.03-3.0 mass% is preferable.

  The method for dispersing the polyolefin resin in the aqueous medium is not particularly limited. For example, a method in which a polyolefin resin, a basic compound, and an aqueous medium are dispersed by heating and stirring in a sealed container under pressure can be used. The aqueous medium is a liquid containing water as a main component, and may contain the basic compound described above. The water-soluble organic solvent described later may also be contained in the aqueous medium in advance, or may be added to the container simultaneously with the aqueous medium.

  The degree of dispersion (volume average particle diameter (Dv) / number average particle diameter (Dn)) in the particle size distribution of the polyolefin resin dispersed in the coating material for separator of the present invention is sufficient to ensure the air permeability of the separator. From the viewpoint of achieving adhesion between nonconductive particles and between nonconductive particles and a porous substrate, 1 to 2.6 is preferable, more preferably 1 to 2.3, and most preferably 1 to 2.1. It is. By achieving such a degree of dispersion, the air permeability and adhesiveness of the separator measured in the examples, while ensuring an air permeability of 300 seconds / 100 ml or less, have an adhesiveness of 4.0 N / cm or more. Easy to achieve. More preferably, an adhesiveness of 4.8 N / cm or more can be easily achieved while ensuring an air permeability of 280 seconds / 100 ml or less. Most preferably, an adhesion of 5.1 N / cm or more can be easily achieved while ensuring an air permeability of 250 seconds / 100 ml or less. When the air permeability of the separator exceeds 300 seconds / 100 ml, the battery characteristics of the secondary battery deteriorate. The lower limit of the air permeability is preferably 210 seconds / 100 ml. The upper limit of the adhesiveness is usually 5.5 N / cm, preferably 6.0 N / cm.

As the dispersity (Dv / Dn) is closer to 1, the particles have a sharper particle size distribution.
The number average particle diameter (Dn) and the volume average particle diameter (Dv) of the polyolefin resin are measured by a dynamic light scattering method generally used for measuring the particle diameter of the fine particles.

  The degree of dispersion in the separator coating material of the present invention is determined by, for example, dispersing a polyolefin resin, a basic compound and an aqueous medium by heating and stirring in a closed container, and then actively dispersing the dispersion to room temperature in a water bath. This can be achieved by cooling.

  The number average particle diameter (Dn) is 0.5 μm or less from the viewpoint of achieving adhesion between the nonconductive particles and between the nonconductive particles and the porous substrate while ensuring the air permeability of the separator. Is preferably 0.3 μm or less, and more preferably 0.2 μm or less. From the same viewpoint, the volume average particle diameter of the polyolefin resin is preferably 1.0 μm or less, more preferably 0.7 μm or less, and particularly preferably 0.4 μm or less. The preferable lower limit of the number average particle size and the volume average particle size is usually 0.01 μm.

  From the viewpoint of handleability of the coating material, the solid content concentration in the coating material is preferably 1 to 50% by mass, more preferably 3 to 40% by mass, and more preferably 5 to 40% by mass. It is especially preferable that it is 30 mass%.

  In the production of the separator coating material of the present invention, it is preferable to add an organic solvent at the time of dispersion in order to promote dispersion of the polyolefin resin in an aqueous medium and reduce the dispersed particle size. The amount of the organic solvent to be used is preferably 50% by mass or less in the aqueous medium, more preferably 1 to 45% by mass, further preferably 2 to 40% by mass, and 3 to 35% by mass. It is particularly preferred that

  As the organic solvent, those having a solubility in water at 20 ° C. of 10 g / liter or more are preferable from the viewpoint of obtaining a good aqueous dispersion. Further preferable solubility is 20 g / liter or more, and particularly preferable solubility is 50 g / liter or more. The organic solvent preferably has a boiling point of less than 250 ° C, particularly preferably 50 ° C or more and less than 185 ° C, from the viewpoint of easy removal from the coating material or slurry. An organic solvent having a boiling point of 250 ° C. or higher is difficult to be scattered from the resin coating film by drying, and thus may deteriorate the adhesion between the materials.

  Specific examples of the organic solvent used include methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tert-butanol, n-amyl alcohol, isoamyl alcohol, sec-amyl alcohol, tert. Alcohols such as amyl alcohol, 1-ethyl-1-propanol, 2-methyl-1-butanol, n-hexanol and cyclohexanol; ketones such as methyl ethyl ketone, methyl isobutyl ketone, ethyl butyl ketone and cyclohexanone; tetrahydrofuran Ethers such as dioxane, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, sec-butyl acetate, 3-methoxybutyl acetate, propio Esters such as methyl acid, ethyl propionate, diethyl carbonate, dimethyl carbonate; and glycol derivatives such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol ethyl ether acetate, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, 3-methoxy-3-methyl-1-butanol, methoxybutanol, acetonitrile, dimethylformamide, dimethylacetamide, diacetone alcohol And ethyl acetoacetate; 1,2-dimethylglycerin; 1,3-dimethylglycerin; trimethylglycerin; and N-methylpyrrolidone. These organic solvents may be used in combination of two or more.

  Among the above organic solvents, ethanol, n-propanol, isopropanol, n-butanol, methyl ethyl ketone, cyclohexanone, tetrahydrofuran, dioxane, ethylene glycol monoethyl ether, ethylene glycol monopropyl are effective because they are highly effective in promoting aqueous formation of resins. Ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, and N-methylpyrrolidone are preferred. Among these, organic solvents having one hydroxyl group in the molecule are more preferable, and n-propanol, tetrahydrofuran, and ethylene glycol alkyl ethers are more preferable from the viewpoint that the resin can be made aqueous with a small amount of addition.

  When the above-mentioned organic solvent is used in the dispersion of the polyolefin resin, a part of the organic solvent is distilled out of the system by a solvent removal process generally called “stripping” after the dispersion. Can be reduced. By stripping, the content of the organic solvent in the coating material (aqueous dispersion) can be 10% by mass or less. If this is 5 mass% or less, it is environmentally preferable.

  In the coating material for separators of the present invention, it is preferable that the non-volatile aqueous agent is not substantially contained. “Substantially free of non-volatile water-based auxiliary” means that such an auxiliary is not used in the production of the secondary battery separator coating material, and the resulting secondary battery separator coating material results in this auxiliary agent. Means that it does not contain. Therefore, it is particularly preferable that the content of such an aqueous dispersion aid is zero, but within a range not impairing the effects of the present invention, the non-volatile component (solid content) in the coating material for the secondary battery separator. 3 mass% or less, preferably 1 mass% or less, and more preferably less than 0.5 mass% may be contained.

  The boiling point as used herein means the boiling point at normal pressure (atmospheric pressure). In addition, the hydration aid having no boiling point at normal pressure corresponds to the nonvolatile hydration aid referred to in the present invention. Here, “non-volatile” means that the boiling point is 250 ° C. or higher, and “aqueous auxiliary” means the purpose of promoting aqueous formation or stabilizing the aqueous dispersion in the production of an aqueous dispersion. Refers to drugs and compounds added in

  Examples of the nonvolatile aqueous auxiliary agent in the present invention include surfactants, compounds having a protective colloid action, modified waxes, acid-modified compounds having a high acid value, water-soluble polymers, polyols and the like.

  Examples of the surfactant include a cationic surfactant, an anionic surfactant, a nonionic (nonionic) surfactant, an amphoteric surfactant, a fluorosurfactant, and a reactive surfactant. In addition to those generally used for emulsion polymerization, emulsifiers are also included.

  Examples of the anionic surfactant include sulfate esters of higher alcohols; higher alkyl sulfonic acids and salts thereof; higher carboxylic acids such as oleic acid, stearic acid, and palmitic acid and salts thereof; alkylbenzene sulfonic acids and salts thereof; Examples thereof include oxyethylene alkyl sulfate salts; polyoxyethylene alkyl phenyl ether sulfate salts; vinyl sulfosuccinates and the like.

  Nonionic surfactants include polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyethylene glycol fatty acid ester, ethylene oxide propylene oxide block copolymer, polyoxyethylene fatty acid amide, ethylene oxide-propylene oxide copolymer, etc. And a compound having a polyoxyethylene structure. Moreover, sorbitan derivatives, such as polyoxyethylene sorbitan fatty acid ester, etc. are mentioned.

  Examples of amphoteric surfactants include lauryl betaine and lauryl dimethylamine oxide.

  Examples of reactive surfactants include alkylpropenylphenol polyethylene oxide adducts and their sulfate esters, allyl alkylphenol polyethylene oxide adducts and their sulfate esters, allyl dialkylphenol polyethylene oxide adducts and their sulfate esters, etc. And compounds having a reactive double bond.

  Compounds having protective colloid action, modified waxes, high acid value acid-modified compounds, water-soluble polymers include polyvinyl alcohol; carboxyl group-modified polyvinyl alcohol; carboxymethyl cellulose; hydroxyethyl cellulose; hydroxypropyl cellulose; modified starch; Polyacrylic acid and salts thereof; acid-modified polyolefin waxes and salts thereof having a weight average molecular weight of usually 5,000 or less, such as carboxyl group-containing polyethylene wax, carboxyl group-containing polypropylene wax, carboxyl group-containing polyethylene-propylene wax; Acrylic acid-maleic anhydride copolymer and salts thereof; styrene- (meth) acrylic acid copolymer, ethylene- (meth) acrylic acid copolymer, isobutylene-anhydrous Carboxyl group-containing polymer having an unsaturated carboxylic acid content of 20% by mass or more, such as an alternating carboxylic acid copolymer, (meth) acrylic acid- (meth) acrylic acid ester copolymer; and polyitaconic acid and salts thereof; Examples thereof include water-soluble acrylic copolymers having an amino group; gelatin; gum arabic; casein and the like compounds generally used as dispersion stabilizers for fine particles.

  Nonvolatile polyols include water-soluble diols, polyoxyalkylene diols, polyhydric alcohols, and the like. Specific examples include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butanediol, glycerin and the like.

  A resin dispersion can be added to the separator coating material of the present invention within a range that does not impair the effects of the present invention depending on the required performance. Examples of the resin dispersion include resins other than polyolefin resins (hereinafter referred to as “other resins”) and resin dispersions such as a crosslinking agent.

  The addition amount of the resin dispersion may be appropriately designed according to the purpose, but is preferably 0.1 to 300 parts by mass, and preferably 3 to 200 parts by mass with respect to 100 parts by mass of the polyolefin resin. More preferably, it is 5-100 mass parts. The amount of the resin dispersed in the resin dispersion is appropriately selected within the range of 0.1 to 300 parts by mass with respect to 100 parts by mass of the polyolefin resin in the coating material.

  The degree of dispersion and number average particle size in the particle size distribution of the resin dispersed in the resin dispersion are respectively the degree of dispersion and number in the particle size distribution of the polyolefin resin dispersed in the separator coating material of the present invention described above. It is preferably within the same range as the average particle size.

  Specific examples of other resins include polyvinyl alcohol, polyolefin resins other than the above-described polyolefin resins, polyvinyl acetate, polyvinyl chloride, acrylic resins, acrylic silicon resins, ethylene-vinyl acetate copolymers, vinyl acetate-acrylic copolymers. Copolymer, ethylene-aminoacrylamide copolymer, ethylene-aminoacrylate copolymer, polyvinylidene chloride, styrene-maleic acid resin, styrene-aminoalkylmaleimide copolymer, styrene-butadiene resin, styrene elastomer, butadiene resin, acrylonitrile -Butadiene resin, poly (meth) acrylonitrile resin, (meth) acrylamide resin, chlorinated polyethylene resin, chlorinated polypropylene resin, modified nylon resin, polyester resin, polyurethane resin, cell Over scan resins, phenol resins, silicone resins, epoxy resins, fluorine-containing resins, polyethylene imine, and the like UV-curable resin. These can be used alone or in admixture of two or more. When these resins are added, it is preferable to use a resin dispersion or aqueous solution.

  Various additives can be appropriately used for the separator coating material of the present invention in order to improve the adhesion. Examples of the additive include a crosslinking agent and a tackifier. You may use combining both.

  Examples of the crosslinking agent include a crosslinking agent having self-crosslinking properties, a crosslinking agent having a plurality of functional groups that react with carboxyl groups in the molecule, and a metal complex having a multivalent coordination site. Examples thereof include isocyanate compounds, melamine compounds, urea compounds, epoxy compounds, carbodiimide compounds, oxazoline group-containing compounds, zirconium salt compounds, and silane coupling agents. The addition amount of a crosslinking agent is suitably selected in the range of 0.01-100 mass parts with respect to 100 mass parts of polyolefin resin in a coating material.

  Various known tackifiers can be used. Examples thereof include rosins, rosin derivatives, and terpene resins. These 1 type can be used individually or in mixture of 2 or more types.

  Examples of rosins include raw material rosins such as gum rosin, wood rosin and tall oil rosin. Alternatively, a stabilized rosin or a polymerized rosin obtained by disproportionating or hydrogenating the raw material rosin can be used.

  Examples of rosin derivatives include rosin esters and rosin phenols. Among these, as the rosin ester, a rosin ester obtained by esterifying a rosin and a polyhydric alcohol, or a partial maleic obtained by partially fumarating or maleating a raw material rosin and then esterifying it. A partially maleated or partially fumarated disproportionated rosin obtained by partially fumarating or maleating the raw rosin, then disproportionating and then esterifying And polyhydric alcohol esters. The rosin phenols are those obtained by adding phenols to rosins and thermally polymerizing them, or subsequently esterifying them. The polyhydric alcohol used for esterification is not particularly limited, and may be diethylene glycol, glycerin, trimethylolpropane, trimethylolethane, 1,2,6-hexanetriol, 1,2,4-butanetriol, pentaerythritol, etc. Various known ones can be used.

  Examples of terpene resins include α-pinene resins and β-pinene resins; aromatic-modified terpene resins obtained by copolymerizing terpenes such as α-pinene and β-pinene and aromatic monomers such as styrene; These hydrides can be used.

  Among these tackifiers, rosin esters or terpene resins are preferable because the adhesion is improved. These tackifiers may be added to the separator coating material as an aqueous dispersion containing the tackifier, or may be added to the separator coating material after dissolving the tackifier. May be.

  When the tackifier is added, the amount is preferably 70 parts by mass or less with respect to 100 parts by mass of the polyolefin resin, and more preferably 1 to 50 parts by mass from the viewpoint of adhesiveness and air permeability. Preferably, it is 2-40 mass parts, More preferably, it is 3-30 mass parts.

  The separator coating material of the present invention can be irradiated with radiation for the purpose of improving adhesion by crosslinking.

  In this case, α-rays, β-rays (electron beams), γ-rays, X-rays, ultraviolet rays, and the like can be used as the radiation source used. Of these, β-rays, γ-rays and X-rays from cobalt 60 are preferred, and γ-rays and β-ray irradiation treatment using an electron accelerator are more preferred. One type of these radiations may be irradiated alone, or two or more types may be irradiated simultaneously, and one or more types of radiation may be irradiated after a certain period of time.

  When irradiating the aqueous dispersion with radiation, the aqueous dispersion placed in a container is placed near the radiation source. At this time, it is preferable to irradiate substantially uniformly by either changing the position of the radiation source or the container during irradiation or stirring the aqueous dispersion. Alternatively, in order to generate radicals, a part of the aqueous dispersion may be placed near the gamma ray source and irradiated, and then mixed with the remaining aqueous dispersion. Further, the aqueous dispersion may be irradiated with radiation while being pumped.

  Although the irradiation dose of a radiation is not specifically limited, 10-400 kGy is preferable, More preferably, it is 20-300 kGy, More preferably, it is 25-200 kGy. When the irradiation dose is less than 10 kGy, crosslinking is insufficient. On the other hand, if it exceeds 400 kGy, the crosslinking proceeds too much, the flexibility and mechanical properties are lowered, and cracks are likely to occur.

  Although there is no restriction | limiting in particular in the atmosphere at the time of irradiation of a radiation, The irradiation dose of a radiation can be made small, so that oxygen concentration is low. The atmosphere may be replaced with an inert gas such as nitrogen or argon.

  For the purpose of promoting crosslinking, the separator coating material may contain a known compound capable of generating active radical species by irradiation or a known compound that is crosslinked by radiation. For example, as the former, trade names: Irgacure 184, 907, etc., manufactured by Ciba Specialty Chemicals can be mentioned. Examples of the latter include Nippon Kasei Co., Ltd. trade names: Tyke triallyl isocyanurate (registered trademark in Japan), Tyke prepolymer (registered trademark in Japan), and the like. The preferable usage-amount of such a compound is 0.01-10 mass parts with respect to 100 mass parts of polyolefin resin.

  Crosslinking of the polyolefin resin after radiation irradiation can be confirmed by the presence or absence of an insoluble matter (gel) when the polyolefin resin is dissolved in a good solvent for the resin.

[Slurry for forming separator and separator]
When manufacturing a separator using the separator coating material of the present invention, first, a separator forming slurry is manufactured by mixing the separator coating material and non-conductive particles. And this separator is apply | coated to at least one surface of a porous base material, Preferably both surfaces are dried, and a separator is manufactured by shaping | molding using a roll press if desired. In addition, the separator can be produced by immersing the porous substrate in the slurry for forming the separator and then drying it.

The non-conductive particles are not particularly limited as long as they are particles having non-conductivity that can prevent a short circuit between the positive electrode and the negative electrode, and inorganic particles, organic particles, or a mixture thereof is used.
Specific examples of the inorganic particles include, for example, electrically insulating metal oxides, metal nitrides, metal carbides, and the like. Specifically, alumina (Al ₂ O ₃ ), magnesia (MgO), titania (TiO ₂ ), zirconia (ZrO ₂ ), silica (SiO ₂ ), silicon nitride (Si ₃ N ₄ ), aluminum nitride (AlN), Boron nitride (BN), titanium nitride (TiN), silicon carbide (SiC), boron carbide (B ₄ C), a combination of kaolinite and amorphous quartz can be suitably used. These inorganic particles may be used alone or in combination of two or more. Among these, silica, kaolinite, and alumina are preferable in consideration of heat resistance and adhesion when processed into a paint.
Specific examples of organic particles include, for example, ultrahigh molecular weight polyethylene, polystyrene, polymethyl methacrylate, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polytetrafluoroethylene, polyimide, Examples include polyetherimide, melamine, and benzoguanamine.

The number average particle diameter of the non-conductive particles is usually 0.1 to 10 μm, preferably 0.2 to 5 μm, and particularly preferably 0.5 to 4 μm.
As the number average particle diameter, a value measured by a method of analyzing a photograph obtained by an electron microscope with a particle diameter measuring instrument is used.

  In the slurry for forming the separator, the mixing ratio of the coating material for the separator and the non-conductive particles is determined from the viewpoint of further improving the gas permeability, heat resistance, and adhesion between the porous substrate and the non-conductive particles in the separator. Ratio in which the mass ratio of polyolefin resin to non-conductive particles in the coating material is 70/30 to 1/99, preferably 50/50 to 2/98, more preferably 40/60 to 2/98 It is preferable that

  In addition to the slurry for forming the separator, a leveling agent, an antifoaming agent, an anti-waxing agent, a pigment dispersant, an ultraviolet absorber, a catalyst, a photocatalyst, a UV curing agent, a wetting agent, a penetrating agent, a softening agent, Various agents such as thickeners, dispersants, water repellents, antistatic agents, anti-aging agents, vulcanization accelerators, pigments or dyes, carbon black, carbon nanotubes, glass fibers, oxirane ring-containing compounds, carboxymethyl cellulose, etc. It may be added. These may be used alone or in combination of two or more.

  The conditions and method for producing the slurry for forming the separator are not particularly limited. For example, the separator coating material, non-conductive particles, and other desired additives are mixed at room temperature or at an appropriately controlled temperature, and then mechanically mixed. Dispersion processing, ultrasonic dispersion processing, or the like can be applied. The non-conductive particles and other additives may be previously dispersed in a wetting agent and water and then mixed with the separator coating material.

  In order to improve the dispersibility of the slurry for forming the separator, a dispersion processing apparatus may be used. Examples of the dispersion processing apparatus that applies high shearing force to disperse by the shearing force between the slurry and the wall surface include a colloid mill, a roll mill, and a media mill represented by a ball mill and a sand mill. Further, a homogenizer type dispersion treatment device is exemplified as a dispersion treatment device that generates a jet flow in the slurry and disperses the slurry by a difference in slurry speed, that is, a liquid-liquid shearing between treatments. It is preferable to use this homogenizer type dispersion processing apparatus as the dispersion processing apparatus.

  In the production of the slurry for forming the separator, a small amount of a water-soluble polymer may be added as a wetting agent. Although there is no restriction | limiting in particular as a water-soluble polymer to be used, Cellulose derivatives, such as methylcellulose, carboxymethylcellulose, and hydroxymethylcellulose, are effective. These cellulose derivatives improve the wettability between each material of a nonelectroconductive particle and a porous base material. It is preferable that the compounding quantity is 0.01-3 mass parts with respect to 100 mass parts of total mass of polyolefin resin and nonelectroconductive particle, More preferably, it is 0.01-1 mass part, More preferably, it is 0.00. 01 to 0.5 parts by mass.

  The porous substrate is not particularly limited as long as it has a fine porous structure. Porous substrate strength, strength distribution profile, breaking strength, elongation, hardness, elongation retention under certain conditions, piercing elongation, breaking elongation, thermal shrinkage under certain conditions, certain ratio ( %) Shrinkage temperature, curvature, Young's modulus, tear strength, pore diameter, average pore diameter measured by silver press-in method, average fiber thickness, basis weight, fiber diameter, porosity, thickness, Thickness deviation, air permeability resistance, organic solvent permeability, organic solvent penetration rate, organic solvent penetration time change rate, solubility in organic solvent, swelling property in organic solvent, gel fraction, glass transition temperature, melt flow rate, Various properties such as intrinsic viscosity, molecular weight, molecular weight distribution, melting point, softening point, crystallinity, draw ratio, adhesive strength, dynamic friction coefficient, surface roughness, cushion ratio, loop stiffness, and combinations of various properties And its ratio, when processed under certain conditions Including retention of the various properties can be formed of the known. Furthermore, such various characteristics, combinations and ratios of various characteristics, retention ratio of various characteristics when processed under certain conditions, processing suitability to the separator, storage stability as a separator, stability, safety, Durability, adhesion, chemical resistance, flame resistance, heat resistance, shape retention, wrinkle suppression, breathability, electrolyte penetration, electrolyte resistance, shutdown, foreign matter resistance, piercing characteristics, separator Proper processing when incorporating into a secondary battery, storage stability, stability, safety, durability, chemical resistance, flame resistance, heat resistance, shape retention, shape retention of a secondary battery when made into a secondary battery May be appropriately designed in consideration of various performances such as performance, output characteristics, and battery characteristics.

  As a form of the porous base material for exhibiting the effects of the present invention more remarkably, a microporous film, a non-woven fabric, a woven / knitted fabric, a nanofiber fabric, paper, etc. are preferable, a microporous film and a non-woven fabric are more preferable, and microporous A film is particularly preferred. These may be used alone or in combination. Examples of the material for the porous substrate include polyolefin resins, polyester resins, polyamide resins, aramid resins, polyarylene sulfide resins, and cellulose resins. Of these, polyolefin resins are preferred, and polypropylene resins are preferred. A resin is more preferable. Here, “˜resin” means a resin composition containing “˜resin”, “˜resin” alone, “˜resin” copolymerized resin composition, and “˜resin” are blended. Resin compositions and the like.

  Examples of the microporous film made of a polyolefin-based resin include, for example, polyolefin first and second microporous layers described in International Publication WO10 / 104077, microporous film containing polypropylene described in JP2013-023673, and JP Polyolefin microporous membrane described in 2011-233542, polyolefin microporous membrane described in International Publication WO10 / 070930, polyolefin microporous membrane described in International Publication WO09 / 136648, JP2013-032505A Porous polyolefin film, porous resin film containing polyolefin resin described in JP 2012-229406 A, porous polypropylene film described in JP 2012-177106 A, and polio film described in JP 2012201390 A Fin-based porous film, porous polypropylene film described in JP2012-072380, polyolefin-based porous resin film described in JP2013-014103A, porous polypropylene film described in JP2012-007156A, No. 2011-171290, a porous polyolefin film containing a polypropylene resin described in JP 2011-168048 A, a polyolefin porous film described in International Publication No. WO 10/008003, and International Publication No. WO 07/046226 A microporous film mainly composed of the described polypropylene, a polyolefin porous film described in JP2013-026165A, and a polyolefin microporous film described in JP2011-065850A. It is possible to use a known exemplified things. Among them, a microporous film of polypropylene having an increased β crystal fraction obtained by using a β crystal method or a β crystal nucleating agent is preferable.

  Examples of the nonwoven fabric made of polyolefin resin include, for example, a polyolefin nonwoven fabric described in JP 2011-210701 A, a nonwoven fabric using polypropylene fibers described in JP 2011-070904 A, and a composite described in JP 2006-233691 A. It is possible to use known materials exemplified by non-woven fabrics in which the fusion component of high-strength polypropylene fibers is fused, non-woven fabrics described in International Publication WO 04/073094, and the like.

  Examples of the nonwoven fabric made of polyester resin include, for example, a wet nonwoven fabric described in JP2012-138235A, a nonwoven fabric containing polyester short fibers described in JP2010-238448A, and International Publication WO06 / 123811 It is possible to use known materials exemplified by non-woven fabric made of polyethylene terephthalate.

  Next, a method for laminating a porous layer by applying a coating for a secondary battery separator on at least one surface of a porous substrate will be described. The secondary battery separator paint of the present invention is applied to at least one surface of a porous substrate, and then a part or all of the aqueous medium in the applied secondary battery separator paint is dried to form a porous layer. can do.

  As a method for applying and drying the paint for the secondary battery separator, known methods such as gravure roll coating, reverse roll coating, wire bar coating, lip coating, air knife coating, curtain flow coating, spray coating, dip coating, brush coating After uniformly coating the surface of the porous substrate by the method, etc., setting it at around room temperature as necessary, and then subjecting it to drying treatment or heat treatment for drying, partially or all of the aqueous medium is dried to be uniform A simple coating film, that is, a porous layer can be formed in close contact with the surface of the porous substrate. Although a drying temperature is not specifically limited, it can dry favorably in the range of 50-120 degreeC, and the range of 60-100 degreeC is more preferable. In drying, it is preferable to dry all of the aqueous medium from the viewpoint of improving adhesion and heat resistance. Further, after drying, an aging treatment such as an aging treatment may be performed.

  In addition, the surface activation process may be previously performed on the application surface of the porous base material before application of the paint. Examples of the surface activation treatment include corona discharge treatment, flame plasma treatment, atmospheric pressure plasma treatment, low pressure plasma treatment, ozone treatment, electron beam irradiation treatment, ultraviolet irradiation treatment, chemical treatment, solvent treatment, anchor coat treatment, and primer treatment. Etc.

  The thickness of the porous layer in the present invention is preferably in the range of 0.5 to 10 μm, more preferably 1 to 9 μm, from the viewpoints of heat resistance, electrolyte permeability, permeability, and battery performance. It is preferably 2 to 8 μm, more preferably 3 to 7 μm.

  The secondary battery separator of the present invention can be obtained by laminating the porous layer on at least one surface of the porous substrate by the above method. In the secondary battery separator of the present invention, another functional layer other than the porous substrate and the porous layer may be provided on at least a part of the surface. As the functional layer, for example, a layer made of a known additive or stabilizer, an antistatic layer, an easy-adhesion layer, a sliding layer, a leveling layer, a flame retardant layer, a layer for improving compatibility with an electrolyte, an antioxidant layer , And a softening layer. The thickness of the functional layer may be determined in consideration of suitability as a packaging material and processability when laminated, and is not particularly limited.

  In the secondary battery separator of the present invention, strength, strength distribution profile, breaking strength, elongation, hardness, elongation retention under certain conditions, piercing elongation, breaking elongation, Young's modulus, tear strength, constant ratio ( %) Shrinkage temperature, curvature, pore diameter, average pore diameter measured by silver press-in method, average fiber thickness, basis weight, fiber diameter, porosity, thickness, thickness deviation, air permeability resistance , Organic solvent permeability, organic solvent penetration rate, rate of change of organic solvent penetration time, solubility in organic solvent, swelling in organic solvent, gel fraction, glass transition temperature (Tg), melt flow rate, intrinsic viscosity, Various characteristics such as molecular weight, molecular weight distribution, melting point, softening point, crystallinity, draw ratio, adhesive strength, dynamic friction coefficient, surface roughness, cushion ratio, loop stiffness, combinations of various characteristics and their proportions , Processing under certain conditions The retention rate of various characteristics during the operation, the combination of the various characteristics of the porous substrate and the various characteristics of the porous layer and the ratio thereof, etc. are the storage stability, stability, safety, durability, adhesion, Chemical properties, flame retardancy, heat resistance, shape retention, wrinkle suppression, breathability, electrolyte penetration, electrolyte resistance, shutdown, foreign matter resistance, piercing characteristics, when incorporating a separator into a secondary battery Suitable for processing, secondary battery storage stability, stability, safety, durability, chemical resistance, flame resistance, heat resistance, shape retention, shape retention, output characteristics, battery characteristics It is sufficient to design appropriately considering various performances such as.

The air permeability of the porous base material before applying the slurry is usually 150 to 700 seconds / 100 mL, preferably 150 to 500 seconds / 100 mL. Two or more different porous substrates or two or more of the same kind of porous substrates may be used in an overlapping manner. In that case, the air permeability of the porous substrate after the overlapping is within the above range. If it is.
In the present specification, the air permeability is represented by the time required to allow 100 mL of air to permeate. Specifically, a value measured by a method described later is used.

  The separator obtained in the present invention usually has an air permeability of 210 to 300 seconds / 100 mL, preferably 210 to 250 seconds / 100 mL.

[Secondary battery]
The separator formed using the separator-forming slurry of the present invention can be used in any secondary battery in which the separator is used for preventing a short circuit between electrodes in the electrolytic solution. Examples of the electrolyte include carbonates such as ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, propylene carbonate, and butylene carbonate; potassium hydroxide aqueous solution, sodium hydroxide and / or lithium hydroxide added to potassium hydroxide aqueous solution Alkaline aqueous solutions; lactones such as γ-butyrolactone; sulfolanes; nitriles such as acetonitrile; ionic liquids and the like. In the present invention, preferred electrolytes are carbonates.

  As a secondary battery that can use the separator formed using the separator-forming slurry of the present invention, for example, a nickel-cadmium secondary battery (nickel battery) obtained using cadmium, nickel obtained using a hydrogen storage alloy -A hydrogen secondary battery (Ni-MH battery), a non-aqueous electrolyte secondary battery (lithium ion battery) using a lithium compound, etc. are mentioned.

  Such a secondary battery is manufactured by enclosing the separator, the electrode, and the electrolyte prepared by the above-described method in a container according to a conventional method. At this time, well-known members can be used for the constituent members other than the separator, such as electrodes and electrolytic solutions.

  For example, as a constituent member other than a separator of a lithium ion battery, as an electrolytic solution, carbonates, preferably one kind of nonaqueous solvent such as propylene carbonate, ethylene carbonate, dimethyl carbonate, or a mixed solvent in which two or more kinds are mixed, A material to which a supporting electrolytic salt such as lithium hexafluorophosphate or lithium perchlorate is added is used. For the positive electrode, a paste prepared by adding a conductive material such as metal powder or carbon and a binder to an active material such as lithium cobaltate and kneading and preparing in the presence of N-methyl-2-pyrrolidone By applying to a current collector and drying, an active material such as lithium cobaltate and a conductive material are bound to each other by a binder, and this is further bound to a metal current collector. A negative electrode is made by adding a binder to a carbon material that is an active material, applying a paste kneaded and prepared in the presence of water or the like to a metal current collector with a doctor blade, and drying the paste to form a carbon material. It is bound to the current collector.

  Hereinafter, the present invention will be described in detail with reference to examples. However, this invention is not restrict | limited at all by the following Example.

  Various characteristics were measured or evaluated by the following methods.

(Measurement of volume average particle diameter and number average particle diameter of polyolefin resin particles)
The volume average particle diameter (Dv), the number average particle diameter (Dn), and the dispersity (Dv / Dn) are measured using a Nikkiso Co., Ltd. microtrack particle size distribution analyzer UPA150 (MODEL No. 9340, dynamic light scattering method). Asked. Here, the refractive index of the resin used for calculating the particle diameter was set to 1.50.
Most preferred dispersion degree A: 2.1 or less.
More preferable dispersity B: 2.3 or less;
Preferred dispersity C: 2.6 or less;

(Measurement of air permeability)
The air permeability of the secondary battery separator was measured by a method based on JIS P 8117. The measurement was performed using a digital type Oken air permeability tester (EG01 type) manufactured by Asahi Seiko Co., Ltd. The separator was set in the apparatus, and the time required for 100 ml of air to pass through was measured. Measurements were taken five times at different locations, and the average value was calculated. The higher the air permeability, the lower the battery internal resistance and the better the battery performance.
◎; 250 seconds / 100 ml or less;
○: 280 seconds / 100 ml or less;
Δ: 300 seconds / 100 ml or less (no problem in practical use);
X: 300 seconds / over 100 ml.

(Adhesiveness)
A measurement sample having a width of 2.5 cm and a length of 10 cm was cut out from the secondary battery separator, and the surface of the microporous film on which the paint was not applied was bonded to a steel plate having a sufficient thickness with a double-sided tape. Cellophane tape (Nichiban Co., Ltd., CT-18, 18 mm width) was applied to the coated porous layer side, and the stress when peeled at a rate of 50 mm / min in the direction of 180 ° from one side was measured. . The measurement was carried out three times for each sample, and the adhesive strength was evaluated with the average value as the peel strength.
A: 5.1 N / cm or more;
○: 4.8 N / cm or more;
Δ: 4.0 N / cm or more (no problem in practical use);
X: Less than 4.0 N / cm.

重量変化率：
◎；１４％以下；
○；１９％以下；
△；２４％以下（実用上問題なし）；
×；２４％超。
厚み変化率：
◎；５％以下；
○；１０％以下；
△；１５％以下（実用上問題なし）；
×；１５％超。 (Electrolytic solution resistance)
The aqueous polyolefin resin dispersion was dried at 80 ° C., 100 ° C., and 120 ° C. for 2 hours, respectively, to prepare a 500 mg dried sheet. Immerse the dried product in an electrolytic solution (ethylene carbonate / diethyl carbonate / methyl ethyl carbonate (1/1/1 weight ratio)), store at 60 ° C. for 2 weeks, remove from the electrolytic solution, and then gently wipe the electrolytic solution on the surface. The weight and thickness were measured, and the weight change rate and thickness change rate were calculated.

Weight change rate:
◎; 14% or less;
○: 19% or less;
Δ: 24% or less (no problem in practical use);
X: Over 24%.
Thickness change rate:
◎; 5% or less;
○: 10% or less;
Δ: 15% or less (no problem in practical use);
X: Over 15%.

(Heat resistance (135 ° C heat shrinkage))
The secondary battery separator was cut into a rectangular shape with a length of 150 mm and a width of 10 mm in the MD direction and the TD direction to obtain a test piece. A marked line was drawn on the test piece at intervals of 100 mm, and a heat treatment was performed by placing it in a hot air oven heated to 135 ° C. with a weight of 3.5 g suspended for 1 hour. After the heat treatment, the test piece was taken out and allowed to stand at room temperature for 24 hours, the distance between the marked lines was measured, the thermal shrinkage rate was calculated from the change in the distance between the marked lines before and after heating, and used as an index of dimensional stability. For each test piece, three samples were carried out in the MD direction and TD direction, and the average value was evaluated.
MD direction:
◎; 1.6% or less;
○: 2.6% or less;
Δ: 3.6% or less (no problem in practical use);
X: More than 3.6%.
TD direction:
◎; 2.3% or less;
○: 3.5% or less;
Δ: 4.7% or less (no problem in practical use);
X: More than 4.7%.

(Charge / discharge cycle test)
A secondary battery was manufactured and tested according to the following method.
Of-cathode prepared positive electrode active material in which LiCoO _2: 85 parts by mass of acetylene black as a conductive additive: 10 parts by weight PVDF and a binder: 5 parts by mass, N- methyl-2-pyrrolidone (NMP) A positive electrode mixture-containing paste was prepared by mixing uniformly as a solvent. This paste was intermittently applied to both sides of an aluminum foil having a thickness of 15 μm serving as a current collector so that the active material application length was 320 mm on the front surface and 250 mm on the back surface, dried, and then calendered to obtain a total thickness. The thickness of the positive electrode mixture layer was adjusted to 150 μm, and the positive electrode mixture layer was cut to a width of 43 mm to produce a positive electrode having a length of 340 mm and a width of 43 mm. Further, an aluminum tab was connected to the exposed portion of the aluminum foil of the positive electrode.

・ Production of negative electrode Graphite as negative electrode active material: 90 parts by mass, SBR as a binder: 2 parts by mass and carboxymethyl cellulose (CMC) as a viscosity modifier: 3 parts by mass with water added to be uniform Thus, a negative electrode mixture-containing paste was prepared. This negative electrode mixture-containing paste was intermittently applied on both sides of a 10 μm thick current collector made of copper foil so that the active material application length was 20 mm on the front surface and 260 mm on the back surface, dried, and then subjected to calendar treatment. The thickness of the negative electrode mixture layer was adjusted so that the total thickness was 142 μm, and the negative electrode mixture layer was cut to have a width of 45 mm to produce a negative electrode having a length of 330 mm and a width of 45 mm. Furthermore, the copper tab was connected to the exposed part of the copper foil of this negative electrode.

Battery assembly The positive electrode and the negative electrode obtained as described above were overlapped via the separator obtained in the present invention and wound into a spiral shape to obtain a wound electrode body. The wound electrode body is crushed into a flat shape, inserted into a rectangular battery case having a thickness of 4.2 mm and a width of 34 mm, and an electrolytic solution (a solvent in which ethylene carbonate and ethyl methyl carbonate are mixed at a volume ratio of 1: 2). Then, a solution in which LiPF ₆ was dissolved at a concentration of 1.2 mol / L) was injected, the opening of the battery case was sealed, and a lithium secondary battery was produced. In pre-charging (chemical conversion) after battery assembly, constant current charging up to 4.2 V at 150 mA and then constant voltage at 4.2 V so that the amount of electricity is 20% of the rated capacity of 750 mAh. Charging was performed for a total of 6 hours, and then a constant current discharge was performed up to 3 V at 150 mA.

-Test method The secondary battery is repeatedly subjected to 0.5C-2.5V constant current discharge in the thermostatic bath at 25 ° C after the above-described preliminary charging, 0.5C-4.0V constant current constant voltage charging. Thus, the cycle characteristics were evaluated. The initial capacity was set to 100%, the battery capacity after 500 cycles was determined, and the maintenance rate was calculated.
◎; 86% or more;
○; 83% or more;
Δ: 80% or more (no problem in practical use);
X: Less than 80%.

(High temperature storage stability)
After recharging the secondary battery for 5 cycles after charging and discharging at a constant current and a constant voltage of 0.5C-4.0V under the same conditions as the charge / discharge cycle test, the battery is placed in a thermostat at 50 ° C. Stored for 2 weeks. Then, the battery was taken out and 0.5 C-2.5 V constant current discharge was performed, and the discharge capacity retention rate after high temperature storage was calculated. In addition, the discharge capacity just before storing in a 50 degreeC thermostat was 100%.
◎; 75% or more;
○: 70% or more;
Δ: 65% or more (no problem in practical use);
X: Less than 65%.

(Content of unsaturated carboxylic acid unit)
The acid value of the polyolefin resin was measured according to JIS K5407, and the content of the unsaturated carboxylic acid unit was determined from the value.

(Structure of units other than unsaturated carboxylic acid units)
In orthodichlorobenzene (d ₄ ), 1H-NMR and 13C-NMR analysis (using an analyzer manufactured by Varian, 300 MHz) was performed at 120 ° C. for determination. In 13C-NMR analysis, measurement was performed using a gated decoupling method in consideration of quantitativeness.

(Weight average molecular weight of polyolefin resin)
The weight average molecular weight was determined using GPC analysis (HLC-8020 manufactured by Tosoh Corporation, and two KF-804L and one KF805L manufactured by SHODEX were connected to each other), tetrahydrofuran was used as the eluent, and the flow rate was 1 ml / min. It measured on 40 degreeC conditions. About 10 mg of resin was dissolved in 5.5 mL of tetrahydrofuran and filtered through a PTFE membrane filter as a measurement sample. The weight average molecular weight was determined from a calibration curve prepared with a polystyrene standard sample. When it was difficult to dissolve in tetrahydrofuran, it was dissolved in orthodichlorobenzene.

(Melting point of polyolefin resin)
Using DSC (DSC-7 manufactured by Perkin Elmer), the temperature was raised from −50 ° C. to 200 ° C. at a heating rate of 10 ° C./min, then rapidly cooled at 500 ° C./min and held at −50 ° C. for 5 minutes. did. Thereafter, the temperature was raised again from −50 ° C. to 200 ° C. at a heating rate of 10 ° C./min, and the melting point was measured.

(Solid content concentration of coating material)
An appropriate amount of the separator coating material was weighed, heated at 150 ° C. until the mass of the residue (solid content) reached a constant weight, and then weighed to determine the solid content concentration.

(Dry slurry coating amount)
The coating amount was determined from the weight of the porous substrate before and after the slurry application. The weight after application is the weight after complete drying.

(Manufacture of polyolefin resin “P-1”)
280 g of a propylene-ethylene copolymer (propylene / ethylene = 81.8 / 18.2% by mass, weight average molecular weight 85,000) was heated and melted in a four-necked flask under a nitrogen atmosphere. Thereafter, while maintaining the system temperature at 180 ° C., with stirring, 14.0 g of maleic anhydride as an unsaturated carboxylic acid and 6.0 g of di-t-butyl peroxide as a radical generator were each taken over 2 hours. Thereafter, the reaction was allowed to proceed for 1 hour. After completion of the reaction, the obtained reaction product was put into a large amount of acetone to precipitate a resin. This resin was further washed several times with acetone to remove unreacted maleic anhydride, and then dried under reduced pressure in a vacuum dryer to obtain polyolefin resin “P-1”.

(Manufacture of polyolefin resin “P-2”)
A polyolefin resin “P-2” was obtained in the same manner as the polyolefin resin “P-1” except that the amount of maleic anhydride was changed to 30 g.

(Manufacture of polyolefin resin “P-3”)
280 g of propylene-butene-ethylene terpolymer (manufactured by Huls Japan, Bestplast 708, propylene / butene / ethylene = 64.8 / 23.9 / 11.3 mass%) in a four-necked flask And heated and melted in a nitrogen atmosphere. Thereafter, while maintaining the system temperature at 170 ° C., 30.0 g of maleic anhydride as an unsaturated carboxylic acid and 6.0 g of dicumyl peroxide as a radical generator were respectively added over 1 hour with stirring. The reaction was carried out for 1 hour. After completion of the reaction, the obtained reaction product was put into a large amount of acetone to precipitate a resin. This resin was further washed several times with acetone to remove unreacted maleic anhydride and then dried under reduced pressure in a vacuum dryer to obtain a polyolefin resin “P-3”.

(Manufacture of polyolefin resin “P-4”)
In a four-necked flask, 280 g of propylene / 1-butene copolymer (mass ratio: propylene / 1-butene = 70/30) was heated and melted in a nitrogen atmosphere, and then the system temperature was maintained at 170 ° C. Under stirring, 25.0 g of maleic anhydride as an unsaturated carboxylic acid and 6.0 g of dicumyl peroxide as a radical generator were each added over 1 hour, and then reacted for 1 hour. After completion of the reaction, the obtained reaction product was put into a large amount of acetone to precipitate a resin. This resin was further washed several times with acetone to remove unreacted maleic anhydride and then dried under reduced pressure in a vacuum dryer to obtain polyolefin resin “P-4”.

(Manufacture of polyolefin resin “P-5”)
In a four-necked flask, 280 g of propylene / 1-butene copolymer (mass ratio: propylene / 1-butene = 46/54) was heated and melted in a nitrogen atmosphere, and the system temperature was maintained at 170 ° C. Under stirring, 45.0 g of maleic anhydride as an unsaturated carboxylic acid and 6.0 g of dicumyl peroxide as a radical generator were each added over 1 hour, and then reacted for 1 hour. After completion of the reaction, the obtained reaction product was put into a large amount of acetone to precipitate a resin. This resin was further washed several times with acetone to remove unreacted maleic anhydride and then dried under reduced pressure in a vacuum dryer to obtain a polyolefin resin “P-5”.

(Manufacture of polyolefin resin “P-6”)
A polyolefin resin “P-6” was obtained in the same manner as the polyolefin resin “P-1” except that the amount of maleic anhydride was changed to 5 g.

(Manufacture of coating material (aqueous dispersion) E-1 to E-6)
As the polyolefin resin, polyolefin resins “P-1” to “P-6” having the characteristics shown in Table 1 were used. 3. In a sealable pressure-resistant 1 liter glass vessel equipped with a heater equipped with a stirrer, 75 g of any of polyolefin resins “P-1” to “P-6”, 90 g of isopropyl alcohol (abbreviated as IPA), triethylamine When 5 g of distilled water and 130.5 g of distilled water were added and the stirring blade was rotated at a rotational speed of 300 rpm, the resin bottoms were not observed at the bottom of the container, and it was confirmed that they were in a floating state. Therefore, while maintaining this state, the heater was turned on and heated after 10 minutes. Then, the system temperature was kept at 140 to 145 ° C. and further stirred for 30 minutes. Thereafter, the glass container is placed in a water bath, cooled to room temperature (about 25 ° C.) with stirring at a rotational speed of 300 rpm, and then filtered under pressure through a 300-mesh stainless steel filter (wire diameter 0.035 mm, plain weave) 2 MPa) to obtain a milky white uniform coating material (aqueous dispersion).
As the polyolefin resins, coating materials (aqueous dispersions) “E-1” to “E-6” were obtained from the polyolefin resins “P-1” to “P-6” shown in Table 1, respectively. The solid content concentration was 25% by mass. Table 2 shows the volume average particle size, number average particle size, and degree of dispersion of the polyolefin resin in the coating material. An aqueous dispersion was not obtained from the polyolefin resin “P-6”, and the resin remained (see Comparative Example 2).

(Production of coating material E-7; use of non-volatile dispersion aid)
A polyolefin resin “P-1” having the characteristics shown in Table 1 was used as the polyolefin resin (A). In a sealable pressure-resistant 1 liter glass container equipped with a heater equipped with a stirrer, 75 g of “P-1”, 90 g of isopropanol, 15 g of emulsifier (New Pole PE-75, manufactured by Sanyo Chemical Co., Ltd.), 120 g of distilled water When stirring was performed at a rotation speed of the stirring blade of 300 rpm, it was confirmed that no precipitation of resin particles was observed at the bottom of the container, and the mixture was in a floating state. Therefore, while maintaining this state, the heater was turned on and heated after 10 minutes. Then, the system temperature was kept at 140 to 145 ° C. and further stirred for 30 minutes. Thereafter, the glass container is placed in a water bath, cooled to room temperature (about 25 ° C.) with stirring at a rotational speed of 300 rpm, and then filtered under pressure through a 300-mesh stainless steel filter (wire diameter 0.035 mm, plain weave) 2 MPa), and a milky white uniform coating material (aqueous dispersion) “E-7” was obtained. The solid content concentration was 25% by mass.

(Manufacture of microporous film)
93.0% by mass of homopolypropylene [MFR 15 g / 10 min (230 ° C., 2.16 Kg), density 0.9 g / cm 3], 6.5% by mass of ethylene-octene-1 copolymer [MFR 18 g / 10 min ( 190 ° C., 2.16 kg)], 0.3% by mass of N, N′-dicyclohexyl-2,6-naphthalenedicarboxamide, 0.2% by mass of antioxidant (IRGANOX 1010 manufactured by Ciba Specialty Chemicals) The mixture obtained by dry blending was fed to a twin-screw extruder and melt-kneaded at 290 ° C. to be pelletized. Next, this pellet was supplied to a single screw extruder and melt-extruded at 210 ° C., and after removing foreign matter with a 20 μm cut sintered filter, it was discharged from a T-die onto a cast drum whose surface temperature was controlled at 115 ° C., An unstretched sheet was obtained by casting the drum so as to be indirect for 12 seconds. Next, the film was preheated with a 115 ° C. ceramic roll and stretched 5 times in the MD direction of the film. After cooling, the end was then introduced into a tenter type stretching machine by holding the clip with a clip, and stretched 7 times at 145 ° C. in the TD direction. As it was, heat setting was performed at 150 ° C. for 5 seconds while relaxing 10% in the TD direction to obtain a microporous film having a thickness of 20 μm. The resulting microporous film had a 135 ° C. heat shrinkage in the MD direction of 5% and a 135 ° C. heat shrinkage in the TD direction of 18%. The air permeability was 210 seconds / 100 mL.

<Example 1>
7 g of coating material “E-1”, 8 g of silica particles having a number average particle size of 1.5 μm, 5 g of isopropanol, and 80 g of distilled water are mixed and stirred at room temperature to obtain a slurry (paint) for a secondary battery separator. Obtained.

  Wire slurry (# 12) is used so that the thickness of the porous layer after drying is 4 μm on one side of the microporous film (the side in contact with the drum during melt extrusion) of the obtained slurry for secondary battery separator Was applied by a bar coater method and dried at 100 ° C. for 1 minute to form a porous layer, thereby producing a secondary battery separator.

<Examples 2 to 4 and Comparative Examples 1 to 3>
Except having used the coating material shown in Table 2, the same operation as Example 1 was performed and the slurry for secondary battery separators and the secondary battery separator were obtained. In addition, "E-6" did not obtain a coating material, and no secondary battery separator slurry was obtained.

  Table 2 shows the evaluation results of the coating materials used in each Example / Comparative Example and the obtained separator and secondary battery.

  The secondary battery provided with the separator manufactured using the separator-forming slurry containing the coating material for a separator and the non-conductive particles of the present invention is not particularly limited in its use, but for example, an automobile, a portable electronic device, a backup Useful for applications such as power supplies.

Claims (8)

A polyolefin resin containing 50 to 99% by mass of an unsaturated hydrocarbon component having 3 to 6 carbon atoms and 0.5 to 20% by mass of an unsaturated carboxylic acid component (excluding those containing a nitrile group in the polyolefin resin ). A separator coating material characterized by being dispersed in an aqueous medium together with a basic compound.   The coating material according to claim 1, wherein the polyolefin resin has a number average particle size of 0.5 μm or less and a particle size distribution dispersity of 1 to 2.6.   The coating material according to claim 1, wherein the coating material is substantially free of a non-volatile water-based auxiliary.   The slurry for separator formation containing the coating material in any one of Claims 1-3, and a nonelectroconductive particle.   The slurry according to claim 4, wherein the mass ratio of the polyolefin resin and the nonconductive particles is 70/30 to 1/99.   The separator which has a porous layer formed by apply | coating the slurry of Claim 4 or 5 to the at least single side | surface of a porous base material.   The separator according to claim 6, wherein the material constituting the porous substrate is a polyolefin resin.   A secondary battery comprising the separator according to claim 6.