JP2015230796A - Separator coating material, slurry for separator formation, separator, and secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator coating material which is superior in the adhesiveness between non-conductive particles and between a non-conductive particle and a porous base material, and the separator air permeability, and satisfactory in electrolyte resistance against electrolyte and heat resistance, and others.SOLUTION: A separator coating material comprises: an aqueous medium; and a polyolefin resin dispersed in the aqueous medium. The polyolefin resin includes an olefin component and an unsaturated carboxylic acid component as copolymer components. The olefin component includes propylene (A), and an olefin (B) other than the propylene. The mass ratio (A/B) of the propylene (A) to the olefin (B) other than the propylene is 60/40 to 95/5. The content of the unsaturated carboxylic acid component as a copolymer component is 0.5-15 pts.mass to a total of 100 pts.mass of the propylene (A) and the olefin (B) other than the propylene.

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 for a separator that is excellent in adhesion between non-conductive particles and between non-conductive particles and a porous substrate and the air permeability of the separator obtained, and has good resistance to electrolyte and heat resistance to the electrolyte. An object is to provide a 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.

  As a result of intensive studies to solve the above problems, the present inventors have used a polyolefin resin having a composition containing a specific amount of a specific component, and a coating material for a separator which is dispersed in an aqueous medium. As a result, the inventors have found that the above problems can be solved, and have reached the present invention.

That is, the gist of the present invention is as follows.
(1) A separator coating material in which a polyolefin resin is dispersed in an aqueous medium, wherein the polyolefin resin contains an olefin component and an unsaturated carboxylic acid component as a copolymer component, and the olefin component is propylene ( A) and an olefin (B) other than propylene, the mass ratio (A / B) of propylene (A) and olefin (B) other than propylene is 60/40 to 95/5, The content of the unsaturated carboxylic acid component as a copolymer component is 0.5 to 15 parts by mass with respect to 100 parts by mass in total of propylene (A) and olefins other than propylene (B). Coating material for separator.
(2) The coating material for a separator according to (1), wherein the amount of the unsaturated carboxylic acid monomer in the dry residue is 10,000 ppm or less.
(3) The coating material for a separator as described in (1) or (2), which does not substantially contain a non-volatile aqueous agent.
(4) The separator coating material according to any one of (1) to (3), wherein the olefin (B) other than propylene is butene.
(5) The separator coating material according to any one of (1) to (4), wherein the degree of dispersion in the particle size distribution of the polyolefin resin is 1 to 2.6.
(6) A separator-forming slurry comprising the separator coating material according to any one of (1) to (5) and non-conductive particles.
(7) The slurry for separator formation as described in (6) whose containing mass ratio of the coating material for separators and a nonelectroconductive particle is 70 / 30-1 / 99.
(8) A separator having a porous layer formed by applying the separator-forming slurry described in (6) or (7) on at least one surface of a porous substrate.
(9) The separator according to (8), wherein the material constituting the porous substrate is a polyolefin resin.
(10) A secondary battery comprising the separator according to (8) or (9).

  Since the separator coating material of the present invention is a polyolefin resin containing a specific amount of a specific component dispersed in an aqueous medium, the separator formed using the separator coating material of the present invention is non-conductive. It is excellent in adhesion between the particles and between the non-conductive particles and the porous substrate and air permeability at the same time, and has good resistance to electrolyte solution and heat resistance to heat generation.

[Coating material for separator]
The separator coating material of the present invention is obtained by dispersing a polyolefin resin in an aqueous medium.

<Polyolefin resin>
First, the polyolefin resin will be described.
The polyolefin resin in the present invention contains an olefin component and an unsaturated carboxylic acid component as a copolymer component, and the olefin component contains propylene (A) and an olefin (B) other than propylene.
In the present invention, the mass ratio (A / B) between propylene (A) and olefins other than propylene (A / B) is a viewpoint of reducing the dispersed particle diameter of the polyolefin resin, and non-conductive particles and non-conductive particles. -From a viewpoint of improving the adhesiveness between porous base materials, it is required that it is 60 / 40-95 / 5, and it is preferable that it is 60 / 40-80 / 20. When the proportion of propylene (A) is less than the above proportion, the particle diameter after dispersion of the polyolefin resin becomes large and the gas permeability is poor. Further, the non-conductive particles and the adhesion between the non-conductive particles and the porous substrate are lowered, and the resistance to the electrolytic solution with respect to the electrolytic solution is inferior.
On the other hand, when the proportion of propylene (A) is larger than the above proportion, the particle diameter after dispersion of the polyolefin resin becomes large and the air permeability is poor. Furthermore, the adhesiveness between the conductive particles and between the nonconductive particles and the porous substrate is lowered.

  Examples of the olefin (B) other than propylene include ethylene, 1-butene, isobutene, 1-pentene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-hexene, 1-octene and norbornenes. Examples include alkenes and dienes such as butadiene and isoprene. Among them, the ease of production of polyolefin resin, the ease of making it water-soluble, the adhesiveness to various materials, especially the non-conductive particles and the non-conductive particles and the adhesion between the porous substrate and the blocking property, etc. Therefore, it is preferable that it is butene (1-butene, isobutene, etc.).

  In addition, ethylene as an olefin (B) other than propylene has a content in the olefin component of preferably 10% by mass or less, more preferably 5% by mass, and an olefin other than propylene (B). More preferably, it does not contain ethylene. Generally, when the polyolefin resin contains ethylene, it is known that a crosslinking reaction occurs competitively when an unsaturated carboxylic acid component is copolymerized by a method as described later. When the crosslinking reaction proceeds, the polyolefin resin obtained by acid modification may have a high molecular weight, and the operability of acid modification may be reduced. Further, the particle diameter of the polyolefin resin in the aqueous medium may increase, and further, depending on the ethylene content, it may be difficult to disperse the polyolefin resin in water. Therefore, the olefin component of the polyolefin resin in the present invention is preferably composed of other than ethylene.

  In the polyolefin resin, the copolymerization form of each component is not limited, and examples thereof include random copolymerization, block copolymerization, and graft copolymerization. From the viewpoint of ease of polymerization, random copolymerization is preferable. . Moreover, you may mix and use multiple types of polyolefin resin as needed.

  The polyolefin resin in this invention is resin which contains the said olefin component and unsaturated carboxylic acid component as a copolymerization component. From the viewpoint of dispersibility in an aqueous medium, the content of the unsaturated carboxylic acid component as a copolymerization component is 100 parts by mass (A + B) in total of propylene (A) and olefin (B) other than propylene. It is necessary to be 0.5 to 15 parts by mass, preferably 0.5 to 10 parts by mass, more preferably 0.5 to 8 parts by mass, and 1 to 7 parts by mass. Is more preferable, and it is most preferable that it is 1.5-7 mass parts. When the content of the unsaturated carboxylic acid component is less than 0.5 parts by mass, it becomes difficult to make the polyolefin resin aqueous. On the other hand, if the content of the unsaturated carboxylic acid component exceeds 15 parts by mass, it becomes easy to make the resin water-based. Getting worse. Moreover, since the resin molecular weight after the modification treatment tends to be low, the heat resistance and the like are poor.

As unsaturated carboxylic acid components, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, aconitic acid, aconitic anhydride, fumaric acid, crotonic acid, citraconic acid, mesaconic acid, allyl succinic acid, etc. In addition, compounds having at least one carboxyl group or acid anhydride group in the molecule (in the monomer unit), such as unsaturated dicarboxylic acid half esters and half amides, can also be used. Among these, maleic anhydride, acrylic acid, and methacrylic acid are preferred in terms of ease of introduction into a polyolefin resin containing propylene (A) and an olefin (B) other than propylene (hereinafter referred to as an unmodified polyolefin resin). Is preferred, and maleic anhydride is more preferred.
Accordingly, in the present invention, as described above, butene is suitable as the olefin (B) other than propylene, and therefore, it is preferable to use a propylene / butene / maleic anhydride terpolymer as the polyolefin resin.

The unsaturated carboxylic acid component may be copolymerized in the polyolefin resin, and its form is not limited. Examples thereof include random copolymerization, block copolymerization, and graft copolymerization.
In addition, the acid anhydride component introduced into the polyolefin resin tends to take an acid anhydride structure in a dry state, and a part or all of the ring is opened in an aqueous medium containing a basic compound described later, and the carboxylic acid or It tends to be its salt.

The method for introducing the unsaturated carboxylic acid component into the unmodified polyolefin resin is not particularly limited. For example, in the presence of a radical generator, the unmodified polyolefin resin and the unsaturated carboxylic acid component are heated above the melting point of the unmodified polyolefin resin. A method of melting and reacting, or a method in which an unmodified polyolefin resin and an unsaturated carboxylic acid component are dissolved in an organic solvent and then heated and stirred in the presence of a radical generator to react with the unmodified polyolefin resin. The method of graft-copolymerizing an unsaturated carboxylic acid component is mentioned.
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 azo compounds such as azobisisobutyronitrile. These may be appropriately selected and used depending on the reaction temperature.

The polyolefin resin in the present invention may contain other components other than those described above as necessary. Other components include (meth) acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate, and butyl (meth) acrylate, maleic acid such as dimethyl maleate, diethyl maleate, and dibutyl maleate. Acid esters, (meth) acrylic amides, alkyl vinyl ethers such as methyl vinyl ether and ethyl vinyl ether, vinyl esters such as vinyl formate, vinyl acetate, vinyl propionate, vinyl pivalate, vinyl versatate and vinyl esters Vinyl alcohol, 2-hydroxyethyl acrylate, glycidyl (meth) acrylate, (meth) acrylonitrile, styrene, substituted styrene, vinyl halides, vinylidene halides, carbon monoxide, Diacid Sulfur and the like, may be a mixture thereof.
In general, the content of these other components is preferably 10% by mass or less of the polyolefin resin.

  In the present invention, a commercially available polyolefin resin may be used. For example, Tough Selenium series manufactured by Sumitomo Chemical Co., Ltd., Tuffmer series manufactured by Mitsui Chemicals, APAO series (amorphous polyalphaolefin) manufactured by REXtac, Ricosen PP series manufactured by Clariant, and Evonik Degussa Best plast. Further, as the polyolefin resin, a commercially available unmodified polyolefin resin obtained by introducing an unsaturated carboxylic acid component by a known method may be used.

As described later, the separator coating material of the present invention preferably has an unsaturated carboxylic acid monomer amount in the dry residue of 10,000 ppm or less.
According to the present inventors, the amount of unsaturated carboxylic acid monomer in the dry residue of the aqueous dispersion containing only the polyolefin resin as a solid component coincides with the amount of unsaturated carboxylic acid monomer measured with the polyolefin resin raw material before the aqueousization. It has been confirmed that
Therefore, as the polyolefin resin constituting the separator coating material of the present invention, it is preferable to use one having an unsaturated carboxylic acid monomer amount of 10,000 ppm or less. In the polyolefin resin, the unsaturated carboxylic acid monomer amount is 5, Is more preferably 1,000 ppm or less, still more preferably 1,000 ppm or less, particularly preferably 500 ppm or less, and most preferably 100 ppm or less.

Usually, when an unsaturated carboxylic acid component is introduced into an unmodified polyolefin resin by the method described later, an unreacted unsaturated carboxylic acid monomer remains in the polyolefin resin. Moreover, if there is much content of the unsaturated carboxylic acid component as a copolymerization component in polyolefin resin, it exists in the tendency for many unreacted unsaturated carboxylic acid monomers to remain | survive.
When an aqueous dispersion is continuously produced using a polyolefin resin having an unsaturated carboxylic acid monomer content exceeding 10,000 ppm, the volume average particle diameter of the resin in the aqueous dispersion increases as the number of production increases, and the aqueous dispersion The viscosity of the dispersion may increase. In addition, a coating material for a separator in which a polyolefin resin having an unsaturated carboxylic acid monomer amount exceeding 10,000 ppm is dispersed in an aqueous medium includes non-conductive particles and adhesion between non-conductive particles and a porous substrate. It tends to be inferior in electrolytic solution resistance to the electrolytic solution.

  The method for reducing the amount of the unsaturated carboxylic acid monomer in the polyolefin resin is not particularly limited. For example, a method for distilling the polyolefin resin under reduced pressure, a method for separating the polyolefin resin by dissolving it in a solvent and reprecipitation, a powder And a method of washing the pelletized polyolefin resin in water or an organic solvent, a method of reducing by a Soxhlet extraction method, and the like. Among them, from the viewpoints of operability and reduction efficiency, a method of distilling from a polyolefin resin under reduced pressure, a method of separating a polyolefin resin by dissolving it in a solvent and reprecipitation, a polyolefin resin made into a powder or pellet form with water or an organic solvent The method of washing in is preferred.

  As a method for quantifying the amount of the unsaturated carboxylic acid monomer in the polyolefin resin, a known method can be used. As an example, an unsaturated carboxylic acid monomer can be extracted from a resin with an extraction solvent such as water, acetone, MEK, methanol, ethanol, etc., and quantified using liquid chromatography, gas chromatography, or the like. Moreover, when quantifying the acid anhydride of an unsaturated carboxylic acid monomer, you may quantify as a corresponding unsaturated carboxylic acid monomer by hydrolyzing.

  The polyolefin resin in the present invention preferably has a weight average molecular weight of 5,000 to 200,000, more preferably 10,000 to 150,000, and more preferably 20,000 to 120,000. More preferably, it is particularly preferably 30,000 to 100,000, and most preferably 35,000 to 80,000. When the weight average molecular weight of the polyolefin resin is less than 5,000, the adhesion to the substrate tends to be lowered, or the obtained substrate tends to be hard and lack flexibility, while the weight average molecular weight is 200,000. If it exceeds 1, the aqueous resin tends to be difficult. In addition, the weight average molecular weight of resin can be calculated | required on the basis of polystyrene resin using a gel permeation chromatography (GPC).

<Aqueous medium>
The separator coating material of the present invention is obtained by dispersing the above polyolefin resin in an aqueous medium. The aqueous medium in the present invention is a liquid containing water as a main component, and contains a basic compound described later. Preferably, it may further contain an organic solvent.

  By containing a basic compound, some or all of the carboxyl groups in the polyolefin resin are neutralized, and aggregation between the fine particles is prevented by the electric repulsion between the generated carboxyl anions. Is provided with stability.

  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 effect of adding a basic compound is not recognized. If the amount exceeds 3.0 times equivalent, the drying time at the time of forming the coating film becomes longer, or the stability of the coating material for the separator deteriorates. Sometimes.

  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.

  In the present invention, an organic solvent may be added at the time of aqueous formation in order to promote the aqueous formation of the polyolefin resin and reduce the dispersed particle size. As content of an organic solvent, 50 mass% or less is preferable with respect to the whole aqueous medium, It is more preferable that it is 1-45 mass%, 2-40 mass% is further more preferable, 3-35 mass% is especially preferable. When the content of the organic solvent exceeds 50% by mass, it cannot be regarded as an aqueous medium substantially and does not deviate from one of the objects of the present invention (environmental protection). Body stability may be reduced.

The organic solvent preferably has a solubility in water at 20 ° C. of 10 g / L or more, more preferably 20 g / L or more, and more preferably 50 g / L or more from the viewpoint of obtaining a coating material with good dispersion stability. More preferred.
As the organic solvent, those having a boiling point of 150 ° C. or less are preferable from the viewpoint of easy removal from the coating material or slurry and from the viewpoint of efficient removal from the coating film in the process of film formation. Organic solvents with boiling points exceeding 150 ° C tend to be difficult to scatter from coating materials and slurry coatings by drying, especially the water resistance of coatings at low temperature drying and adhesion to substrates are reduced. There are things to do.

  Preferred organic solvents include, for example, methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tert-butanol, n-amyl alcohol, isoamyl alcohol, sec-amyl alcohol, tert-amyl alcohol. , Alcohols such as 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, ethers such as tetrahydrofuran and dioxane , Ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, sec-butyl acetate, 3-methoxybutyl acetate, methyl propionate , Esters such as ethyl propionate, diethyl carbonate, dimethyl carbonate, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, glycol derivatives such as 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, ethyl acetoacetate, 1,2 -Dimethyl glycerol, 1, 3- dimethyl glycerol, a trimethyl glycerol, etc. are mentioned.

Among them, since it is effective for promoting the aqueousization of polyolefin resin, ethanol, n-propanol, isopropanol, n-butanol, methyl ethyl ketone, cyclohexanone, tetrahydrofuran, dioxane, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol Monobutyl ether and diethylene glycol monomethyl ether are preferred.
In the present invention, a mixture of these organic solvents may be used.

  Furthermore, as an organic solvent that is effective in promoting the aqueousization of polyolefin resin, an organic solvent other than the above may be added, and the solubility in water at 20 ° C. is less than 10 g / L, for the same reason as above, An organic solvent having a boiling point of 150 ° C. or lower is preferable. Examples of such organic solvents include olefin solvents such as n-pentane, n-hexane, n-heptane, cycloheptane, cyclohexane and petroleum ether, aromatic solvents such as benzene, toluene and xylene, and carbon tetrachloride. 1,2-dichloroethane, 1,1-dichloroethylene, trichloroethylene, 1,1,1-trichloroethane, and halogen solvents such as chloroform. The amount of these organic solvents added is preferably 15% by mass or less in the aqueous medium, more preferably 10% by mass or less, and further preferably 5% by mass or less. When the addition amount exceeds 15% by mass, gelation or the like may be caused.

<Coating material for separator>
The particle diameter of the polyolefin resin particles in the separator coating material of the present invention is from the viewpoint of achieving adhesion between the non-conductive particles and between the non-conductive particles and the porous substrate while ensuring the air permeability of the separator. The number average particle diameter (Dn) is preferably 0.5 μm or less, more preferably 0.3 μm or less, and particularly preferably 0.2 μm or less.
Further, from the same viewpoint, the volume average particle diameter (Dv) of the polyolefin resin particles in the separator coating material of the present invention is preferably 1.0 μm or less, more preferably 0.7 μm or less, It is especially preferable that it is 0.4 micrometer or less. The preferable lower limit of the number average particle size and the volume average particle size is usually 0.01 μm.

  The degree of dispersion (volume average particle size (Dv) / number average particle size (Dn)) in the particle size distribution of the polyolefin resin dispersed in the separator coating material 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 separators measured in the examples have an air permeability of not less than 300 seconds / 100 ml and an adhesiveness of not less than 3.0 N / cm. Easy to achieve. More preferably, an adhesiveness of 3.8 N / cm or more can be easily achieved while ensuring an air permeability of 280 seconds / 100 ml or less. Most preferably, an adhesiveness of 4.1 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.

As the degree of dispersion (Dv / Dn) in the particle size distribution 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 dispersity in the separator coating material of the present invention is determined by, for example, dispersing the polyolefin resin and the aqueous medium by heating and stirring in a sealed container and then actively cooling the dispersion to room temperature in a water bath. Can be achieved.

  The separator coating material of the present invention preferably contains substantially no non-volatile aqueous agent. Although the present invention does not exclude the use of non-volatile aqueous additives, the polyolefin resin can be finely and stably incorporated into an aqueous medium by using the production method described below without using an aqueous additive. Can be dispersed.

  As used herein, the term “aqueous auxiliary” refers to a drug or compound added for the purpose of promoting aqueous formation or stabilizing an aqueous dispersion in the production of the separator coating material of the present invention. “Performance” refers to having no boiling point at normal pressure or having a high boiling point (eg, 300 ° C. or higher) at normal pressure.

  “Substantially free of non-volatile aqueous additive” means that such an auxiliary is not used during production (when the aqueous resin is made), and the resulting dispersion does not contain this auxiliary as a result. means. Therefore, it is particularly preferable that the content of such an aqueous auxiliary agent is zero, but within a range not impairing the effects of the present invention, it is 5% by mass or less, preferably 2% by mass or less, and further, Preferably, it may be contained less than about 0.5% by mass.

  Examples of the non-volatile auxiliary agent used in the present invention include an emulsifier described later, a compound having a protective colloid action, a modified wax, an acid-modified compound having a high acid value, and a water-soluble polymer.

  Examples of the emulsifier include a cationic emulsifier, an anionic emulsifier, a nonionic emulsifier, and an amphoteric emulsifier. In addition to those generally used for emulsion polymerization, surfactants are also included. For example, anionic emulsifiers include higher alcohol sulfates, higher alkyl sulfonates, higher carboxylates, alkyl benzene sulfonates, polyoxyethylene alkyl sulfate salts, polyoxyethylene alkyl phenyl ether sulfate salts, vinyl sulfosuccinates. Nonionic emulsifiers 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. Compounds having a polyoxyethylene structure such as copolymers and sorbitan derivatives such as polyoxyethylene sorbitan fatty acid esters And examples of the amphoteric emulsifiers, lauryl betaine, lauryl dimethyl amine oxide, and the like.

  Compounds having protective colloid action, modified waxes, acid-modified compounds with high acid value, water-soluble polymers include polyvinyl alcohol, carboxyl group-modified polyvinyl alcohol, carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, modified starch, polyvinylpyrrolidone Polyacrylic acid and salts thereof, carboxyl group-containing polyethylene wax, carboxyl group-containing polypropylene wax, carboxyl group-containing polyethylene-propylene wax, and other acid-modified polyolefin waxes having a number average molecular weight of usually 5000 or less and salts thereof, acrylic acid-anhydride Maleic acid copolymer and salt thereof, styrene- (meth) acrylic acid copolymer, ethylene- (meth) acrylic acid copolymer, isobutylene-maleic anhydride A carboxyl group-containing polymer having an unsaturated carboxylic acid content of 10% by mass or more, such as an acid alternating copolymer, a (meth) acrylic acid- (meth) acrylic acid ester copolymer, and a salt thereof, polyitaconic acid and a salt thereof, amino Examples thereof include water-soluble acrylic copolymers having a group, gelatin, gum arabic, and casein, and compounds generally used as fine particle dispersion stabilizers.

  The separator coating material of the present invention requires that the amount of unsaturated carboxylic acid monomer in the dry residue be 10,000 ppm or less, more preferably 5,000 ppm or less, and 1,000 ppm or less. More preferably, it is particularly preferably 500 ppm or less, and most preferably 100 ppm or less. When the additive mentioned later is included, a dry residue points out the dry residue in the coating material for separators after additive addition.

  As described above, the unsaturated carboxylic acid monomer remains in the polyolefin resin. Moreover, an unsaturated carboxylic acid monomer may remain in components other than the polyolefin resin. When the amount of the unsaturated carboxylic acid monomer contained in the dry residue of the separator coating material exceeds 10,000 ppm, the adhesion between the non-conductive particles and between the non-conductive particles and the porous substrate, and the anti-electrolysis property against the electrolytic solution It tends to be inferior in liquidity. In other words, in the case of a secondary battery that is used for a long time in the electrolyte, the coating material swells, resulting in a decrease in separator air permeability or a decrease in adhesion, resulting in non-conductive particles falling off. As a result, battery characteristics are deteriorated.

  The method for quantifying the amount of the unsaturated carboxylic acid monomer in the dry residue of the separator coating material is not particularly limited. For example, a dry residue obtained by removing the liquid medium from the coating material is prepared, and the unsaturated carboxylic acid in the polyolefin resin is prepared. It can be quantified by the same method as the method for quantifying the acid monomer.

<Method for producing separator coating material>
Next, an example of the manufacturing method of the separator coating material will be described.
The method for obtaining the coating material for a separator of the present invention comprises heating and stirring each of the components described above, that is, a polyolefin resin, an aqueous medium, an organic solvent, a basic compound, and the like in a sealable container. This method is most preferable.

  As a container, the apparatus used as a solid / liquid stirring apparatus or an emulsifier can be used, It is preferable to use the apparatus which can pressurize 0.1 Mpa or more. The stirring method and the rotation speed of stirring are not particularly limited, but may be stirring at a low speed such that the polyolefin resin is in a floating state in an aqueous medium. Therefore, high-speed stirring (for example, 1000 rpm or more) is not essential, and an aqueous dispersion can be produced with a simple apparatus.

  For example, raw materials such as a polyolefin resin and an aqueous medium are charged into the apparatus, and the mixture is preferably stirred and mixed at a temperature of 40 ° C. or lower. Next, stirring is continued until coarse particles disappear, preferably while maintaining the temperature in the tank at 80 to 240 ° C, preferably 100 to 220 ° C, more preferably 110 to 200 ° C, particularly preferably 110 to 190 ° C. (For example, 5 to 300 minutes).

  In this method, a basic compound, an organic solvent, and water may be added as appropriate, and the ratio at that time may be appropriately determined according to the desired solid content concentration, particle size, degree of dispersion, and the like. The method of adding a basic compound, an organic solvent, or water is not particularly limited, and there are a method of adding under pressure using a gear pump, a method of lowering the temperature in the system, and then opening and adding. The total amount of the basic compound, organic solvent or water to be added is preferably adjusted so that the solid content concentration after mixing is 1 to 50% by mass, more preferably 2 to 45% by mass, An amount of 3 to 40% by mass is particularly preferred.

Moreover, after additional mixing, it heats again to the temperature of 80-240 degreeC, and stirs. Thus, the weight average particle diameter of polyolefin resin can be made small by adding what comprises an aqueous medium, and heating and stirring again. Thus, it is preferable to make the resin aqueous by a two-stage process in order to adjust the dispersity of the particle size distribution within a preferable range.
In addition, the method of adding the basic compound, the organic solvent, and water is not particularly limited, but the method of adding the product under pressure using a gear pump or the like, the method of adding the product after the system temperature is once lowered to normal pressure, etc. There is.
What is necessary is just to determine suitably the ratio of the basic compound to mix | blend, the organic solvent, and water according to the solid content density | concentration, particle diameter, dispersion degree, etc. which are desired. In addition, the total amount of the basic compound, organic solvent, and water is preferably adjusted so that the solid content concentration after blending is 1 to 50% by mass, more preferably 2 to 45% by mass. An amount of 40% by weight is particularly preferred.

  When the above organic solvent is used during the production of the separator coating material, after making the resin aqueous, a part thereof is distilled out of the system by a solvent removal process generally referred to as “stripping”. The content of may be reduced. By stripping, the content of the organic solvent in the separator coating material can be 10% by mass or less, more preferably 5% by mass or less, and more preferably 1% by mass or less. In the stripping process, it is possible to distill off substantially all of the organic solvent used to make the aqueous solution, but it is necessary to increase the degree of vacuum of the equipment and lengthen the operation time. In consideration, the lower limit of the organic solvent content is preferably about 0.01% by mass.

Examples of the stripping method include a method in which the aqueous dispersion is heated with stirring at normal pressure or reduced pressure to distill off the organic solvent. In addition, since the solid content concentration is increased by distilling off the aqueous medium, for example, when the viscosity increases and the workability decreases, water is added to the aqueous dispersion in advance. Also good.
The solid content concentration of the aqueous dispersion can be adjusted by, for example, a method of distilling the aqueous medium or a method of diluting with water.

  By employing the above production method, it becomes possible to prepare a coating material for a separator that is a uniform liquid aqueous dispersion in which a polyolefin resin is efficiently dispersed or dissolved in an aqueous medium. Here, the uniform liquid state means that a portion where the solid content concentration is locally different from other portions such as precipitation, phase separation or skinning is not found in the coating material for the separator. That means.

<Additives>
In order to further improve the performance according to the purpose, other polymers, tackifiers, inorganic particles, crosslinking agents, pigments, dyes, and the like can be added to the separator coating material of the present invention.

  Other polymers and tackifiers added to the separator coating material of the present invention are not particularly limited. For example, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyvinyl chloride, polyvinylidene chloride, ethylene- (meth) acrylic acid copolymer, ethylene- (meth) acrylic acid ester-maleic anhydride copolymer, styrene -Maleic acid resin, styrene-butadiene resin, butadiene resin, acrylonitrile-butadiene resin, polyurethane resin, poly (meth) acrylonitrile resin, (meth) acrylamide resin, chlorinated polyethylene resin, chlorinated polypropylene resin, polyester resin, modified nylon resin , Urethane resins, rosin and other tackifying resins, phenol resins, silicone resins, epoxy resins and the like, and a plurality of them may be mixed and used as necessary. In addition, although these polymers may be used in the solid state, it is preferable to use those processed into an aqueous dispersion from the viewpoint of maintaining the stability of the aqueous dispersion. Among these, it is preferable to add a polyurethane resin from the viewpoints of adhesion to a substrate, chemical resistance, and heat resistance.

As the polyurethane resin, a polymer containing a urethane bond in the main chain can be used. For example, a polymer obtained by a reaction between a polyol compound and a polyisocyanate compound can be used.
The polyol component constituting the polyurethane resin is not particularly limited. For example, water, ethylene glycol, diethylene glycol, triethylene glycol, 1,3-butanediol, 1,4-butanediol, 1,2-propanediol, 1 , 3-propanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, methyl-1,5-pentanediol, 1,8-octanediol, 2-ethyl-1,3-hexane Low molecular weight glycols such as diol, diethylene glycol, triethylene glycol, and dipropylene glycol; low molecular weight polyols such as trimethylolpropane, glycerin, and pentaerythritol; and polyols having ethylene oxide and propylene oxide units. Le compounds, polyether diols, high molecular weight diols such as polyester diols, bisphenols such as bisphenol A, bisphenol F, dimer diol, and the like to the carboxyl group of the dimer acid was converted to hydroxyl groups.

  Moreover, as a polyisocyanate component which comprises a polyurethane resin, the 1 type, or 2 or more types of mixture of well-known diisocyanate which belongs to aromatic, aliphatic, or alicyclic can be used. Specific examples of diisocyanates include tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 1,3-phenylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, 1,5-naphthalene diisocyanate, isophorone diisocyanate, dimethyl diisocyanate, lysine diisocyanate. , Hydrogenated 4,4′-diphenylmethane diisocyanate, hydrogenated tolylene diisocyanate, dimerized isocyanate obtained by converting a carboxyl group of dimer acid into an isocyanate group, and adducts, biurets, and isocyanurates thereof. As the diisocyanates, trifunctional or higher functional polyisocyanates such as triphenylmethane triisocyanate and polymethylene polyphenyl isocyanate may be used.

  In this invention, a commercially available thing can be used as a water-based polyurethane resin suitable for adding to the coating material for separators. Examples of commercially available water-based polyurethane resins include Takelac series (W-615, W-6010, W-511, etc.) manufactured by Mitsui Chemicals, Adekabon titer series (HUX-232, HUX-320, HUX- manufactured by Adeka). 380, HUX-401, etc.), Daiichi Kogyo Seiyaku Co., Ltd. Superflex series (500, 550, 610, 650, etc.), Dainippon Ink & Chemicals Hydran series (HW-311, HW-350, HW- 150) and the like.

  Inorganic particles added to the separator coating material of the present invention include metal oxides such as magnesium oxide, zinc oxide and tin oxide, inorganic particles such as calcium carbonate and silica, vermiculite, montmorillonite, hectorite, hydrotalcite, Examples thereof include layered inorganic compounds such as synthetic mica. The average particle diameter of these inorganic particles is preferably 0.005 to 10 μm and more preferably 0.005 to 5 μm from the viewpoint of the stability of the aqueous dispersion. A plurality of inorganic particles may be mixed and used. Zinc oxide can be used for ultraviolet shielding, and tin oxide can be used for antistatic purposes.

As a crosslinking agent to be added to the separator coating material of the present invention, a crosslinking agent having a self-crosslinking property, a compound having a plurality of functional groups that react with an unsaturated carboxylic acid component in the molecule, and a metal having a polyvalent coordination site Etc. can be used.
Specific examples include oxazoline group-containing compounds, carbodiimide group-containing compounds, isocyanate group-containing compounds, epoxy group-containing compounds, melamine compounds, urea compounds, zirconium salt compounds, silane coupling agents, and the like. You may mix and use things. Among these, from the viewpoint of ease of handling, it is preferable to add an oxazoline group-containing compound, a carbodiimide group-containing compound, an isocyanate group-containing compound, or an epoxy group-containing compound.

The oxazoline group-containing compound is not particularly limited as long as it has at least two oxazoline groups in the molecule. For example, 2,2′-bis (2-oxazoline), 2,2 It has an oxazoline group such as' -ethylene-bis (4,4'-dimethyl-2-oxazoline), 2,2'-p-phenylene-bis (2-oxazoline), bis (2-oxazolinylcyclohexane) sulfide, etc. Examples thereof include compounds and oxazoline group-containing polymers. These 1 type (s) or 2 or more types can be used. Among these, an oxazoline group-containing polymer is preferable because it is easy to handle.
The oxazoline group-containing polymer is generally obtained by polymerizing an addition polymerizable oxazoline such as 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline. The oxazoline group-containing polymer may be copolymerized with other monomers as necessary. The polymerization method of the oxazoline group-containing polymer is not particularly limited, and a known polymerization method can be employed.

  Examples of commercially available oxazoline group-containing polymers include EPOCROSS series manufactured by Nippon Shokubai Co., Ltd., for example, water-soluble type “WS-500”, “WS-700”; emulsion type “K-1010E”, “ K-1020E "," K-1030E "," K-2010E "," K-2020E "," K-2030E "and the like.

  The compound containing a carbodiimide group is not particularly limited as long as it has at least two carbodiimide groups in the molecule. For example, compounds having a carbodiimide group such as p-phenylene-bis (2,6-xylylcarbodiimide), tetramethylene-bis (t-butylcarbodiimide), cyclohexane-1,4-bis (methylene-t-butylcarbodiimide) And polycarbodiimide which is a polymer having a carbodiimide group. These 1 type (s) or 2 or more types can be used. Among these, polycarbodiimide is preferable from the viewpoint of easy handling.

  The production method of polycarbodiimide is not particularly limited, and can be produced, for example, by a condensation reaction involving decarbonization of an isocyanate compound. The isocyanate compound is not limited, and any of aliphatic isocyanate, alicyclic isocyanate, and aromatic isocyanate may be used. The isocyanate compound may be copolymerized with a polyfunctional liquid rubber, polyalkylene diol or the like, if necessary. As a commercially available product of polycarbodiimide, there is a carbodilite series manufactured by Nisshinbo. Specific products include, for example, water-soluble type “SV-02”, “V-02”, “V-02-L2”, “V-04”; emulsion type “E-01”, “E -02 "; organic solution type" V-01 "," V-03 "," V-07 "," V-09 "; solvent-free type" V-05 "and the like.

  The compound containing an isocyanate group is not particularly limited as long as it has at least two isocyanate groups in the molecule. For example, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, diphenylmethane 2,4′- or 4,4′-diisocyanate, polymethylene polyphenyl diisocyanate, tolidine diisocyanate, 1,4-diisocyanatobutane, Hexamethylene diisocyanate, 1,5-diisocyanato-2,2-dimethylpentane, 2,2,4- or 2,4,4-trimethyl-1,6-diisocyanatohexane, 1,10-diisocyanatodecane, 1,3- or 1,4-diisocyanatocyclohexane, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-cyclohexane, 4,4'-diisocyanatodicyclohexylmethane, hexahydrotoluene 2, 4- or 2,6-diisocyanate, perhydro-2,4'- or 4,4'-diphenylmeta Polyisocyanate compounds such as diisocyanate, naphthalene 1,5-diisocyanate, xylylene diisocyanate, 1,3-bis (isocyanatomethyl) cyclohexane, tetramethyl xylylene diisocyanate, or modified products thereof. Here, the modified product is obtained by modifying the diisocyanate of the polyfunctional isocyanate compound by a known method, for example, allophanate group, burette group, carbodiimide group, uretonimine group, uretdione group, Examples thereof include a polyfunctional isocyanate compound having an isocyanurate group and the like, and an adduct type polyfunctional isocyanate compound modified with a polyfunctional alcohol such as trimethylolpropane. In addition, the said isocyanate group containing compound may contain monoisocyanate in 20 mass% or less. Moreover, these 1 type (s) or 2 or more types can be used.

  The compound containing an isocyanate group can be usually obtained by reacting a polyfunctional isocyanate compound with a monovalent or polyvalent nonionic polyalkylene ether alcohol. Commercially available products of such water-based polyfunctional isocyanate compounds include: Bayhydur 3100, Bihydur VPLS2150 / 1, SBU Isocyanate L801, Desmodur N3400, Desmodur VPLS2102, Desmodur manufactured by Sumitomo Bayer Urethane Co., Ltd. VPLS2025 / 1, SBU isocyanate 0772, Desmodur DN, Takenate WD720, Takenate WD725, Takenate WD730, Duranate WB40-100, Duranate WB40-80D, Duranate WX-1741, BASF, manufactured by Asahi Kasei Corporation There are Basonat HW-100, Basonat LR-9056, etc. manufactured by the company.

  The epoxy compound is not particularly limited as long as it has at least two epoxy groups in the molecule. For example, bisphenol A diglycidyl ether, bisphenol A β-dimethyl glycidyl ether, bisphenol F diglycidyl ether, tetrahydroxyphenylmethane tetraglycidyl ether, resorcinol diglycidyl ether, brominated bisphenol A diglycidyl ether, chlorinated bisphenol A diglycidyl ether, Glycidyl ether types such as hydrogenated bisphenol A diglycidyl ether, diglycidyl ether of bisphenol A alkylene oxide adduct, novolac glycidyl ether, polyalkylene glycol diglycidyl ether, glycerin triglycidyl ether, pentaerythritol diglycidyl ether, epoxy urethane resin; p-Oxybenzoic acid glycidyl ether Glycidyl ether / ester type such as terephthalic acid; glycidyl ester type such as phthalic acid diglycidyl ester, tetrahydrophthalic acid diglycidyl ester, hexahydrophthalic acid diglycidyl ester, acrylic acid diglycidyl ester, dimer acid diglycidyl ester; , Glycidylamine types such as tetraglycidyldiaminodiphenylmethane, triglycidylisocyanurate, triglycidylaminophenol; linear aliphatic epoxy resins such as epoxidized polybutadiene and epoxidized soybean oil; 3,4-epoxy-6methylcyclohexylmethyl-3 , 4-Epoxy-6methylcyclohexanecarboxylate, 3,4-epoxycyclohexylmethyl (3,4-epoxycyclohexane) carboxylate, bis (3 , 4-epoxy-6methylcyclohexylmethyl) adipate, vinylcyclohexene diepoxide, dicyclopentadiene oxide, bis (2,3-epoxycyclopentyl) ether, limonene dioxide, and the like. These 1 type (s) or 2 or more types can be used.

  Examples of commercially available epoxy compounds include water-based compounds suitable for the present invention, such as Denasel series (EM-150, EM-101, etc.) manufactured by Nagase Chemtech, Adeka Resin series manufactured by Asahi Denka Kogyo Co., Ltd. Adeka Resins EM-0517, EM-0526, EM-11-50B, and EM-051R manufactured by Asahi Denka Co., Ltd., which are polyfunctional epoxy resin emulsions, are preferable from the viewpoint of improving UV ink adhesion and scratch resistance.

  The addition amount of the cross-linking agent is preferably 0.01 to 80 parts by mass, and 0.1 to 50 parts by mass with respect to 100 parts by mass of the polyolefin resin, from the viewpoint of improving adhesiveness and electrolytic solution resistance. It is more preferable that the amount is 0.5 to 30 parts by mass. When the addition amount of the cross-linking agent is less than 0.01 parts by mass, the adhesiveness and the electrolytic solution resistance may not be sufficiently improved, and when it exceeds 80 parts by mass, the workability and the like may be deteriorated.

<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 (Al2O3), magnesia (MgO), titania (TiO2), zirconia (ZrO2), silica (SiO2), silicon nitride (Si3N4), aluminum nitride (AlN), boron nitride (BN), titanium nitride (BN) TiN), silicon carbide (SiC), boron carbide (B4C), 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 the slurry for forming the separator, an organic solvent may be added to the slurry in order to disperse the non-conductive particles and the coating material uniformly and stably and to improve the wettability of the slurry to the porous substrate. The organic solvent is preferably a solvent that can be removed from the porous substrate after slurry coating. For example, N-methylpyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, toluene, xylene, hexane, Mention may be made of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol and the like.
Moreover, in order to further improve the coating property of the slurry to the porous substrate, various kinds of surfactants and other dispersants, thickeners, wetting agents, antifoaming agents, pH adjusting agents including acids and alkalis, etc. Additives may be added.

  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 of laminating a porous layer by applying a slurry for forming a separator on at least one surface of a porous substrate will be described. The separator-forming slurry of the present invention can form a porous layer by applying to at least one side of a porous substrate and then drying a part or all of the aqueous medium in the applied separator-forming slurry. .

  As a method for applying and drying the slurry for forming the 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, etc. After coating uniformly on the surface of the porous substrate and setting it at around room temperature as necessary, a part or all of the aqueous medium is dried by subjecting it to a drying treatment or a heat treatment for drying. A 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 separator of the present invention can be obtained by laminating a porous layer on at least one surface of the porous substrate by the above method. In the 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 thereof. 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 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 (%) Shrinking temperature when shrinking, curvature, pore diameter, average pore diameter measured by silver intrusion method, average fiber thickness, basis weight, fiber diameter, porosity, thickness, thickness deviation, air 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, molecular weight, molecular weight Various characteristics such as distribution, melting point, softening point, crystallinity, draw ratio, adhesive strength, dynamic / static friction coefficient, surface roughness, cushion ratio, loop stiffness, combinations of various characteristics and their ratios, constant conditions When processing with The retention rate of seed characteristics, the combination of various characteristics of the porous substrate and the various characteristics of the porous layer, and their proportions, etc. are storage stability, stability, safety, durability, adhesiveness, chemical resistance, Flame resistance, heat resistance, shape retention, wrinkle suppression, breathability, electrolyte penetration, electrolyte resistance, shutdown, foreign matter resistance, piercing characteristics, processing suitability when incorporating a separator into a secondary battery, Rechargeable battery storage stability, stability, safety, durability, chemical resistance, flame resistance, heat resistance, shape retention, shape retention, output characteristics, battery characteristics, etc. What is necessary is just to design suitably in consideration of performance.

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 of the present invention has an air permeability of usually 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.

EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.
Various characteristics were measured or evaluated by the following methods.

1. Polyolefin resin (1) Content of unsaturated carboxylic acid component The content of unsaturated carboxylic acid component relative to the total of propylene (A) and olefins other than propylene (B) is determined by infrared absorption spectrum analysis (Perkin Elmer System-2000). It was determined by a Fourier transform infrared spectrophotometer, resolution 4 cm ⁻¹ ).
(2) Structure of resin other than unsaturated carboxylic acid component The mass ratio of propylene (A) and olefin (B) other than propylene was 1H-NMR at 120 ° C. in orthodichlorobenzene (d ₄ ), ¹³ C-NMR analysis (manufactured by Varian, 300 MHz) was performed. ^{In 13} C-NMR analysis, measurement was performed based on a gated decoupling method in consideration of quantitativeness.
(3) Weight average molecular weight The weight average molecular weight was measured using GPC analysis (HLC-8020 manufactured by Tosoh Corporation, and two KF-804L and one KF805L manufactured by SHODEX were connected to each other) and tetrahydrofuran was used as an eluent. The measurement was performed under conditions of a flow rate of 1 ml / min and 40 ° C. 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.
(4) Unsaturated carboxylic acid monomer amount About 0.05 g of polyolefin resin pellets freeze-pulverized and pulverized were precisely weighed and extracted with 20 ml of methanol as an extraction solvent at room temperature by continuous inversion and mixing for 21 hours. The filtrate obtained by filtering this extract with a disk filter (pore size: 0.45 μm) was subjected to high performance liquid chromatography (HP1100, manufactured by Hewlett Packard, column is Puresil 5 μm C18 120Å φ4.6 mm × 250 mm (40 ° C.) manufactured by Waters). Quantified.
When the amount of the unsaturated carboxylic acid monomer was less than 1000 ppm, the amount of polyolefin resin pellets was changed to 0.5 g, and the amount was similarly determined.
A calibration curve was prepared using a standard sample of an unsaturated carboxylic acid monomer component with a known concentration.

2. Coating Material for Separator (1) Number average particle size, weight average particle size, and degree of dispersion of polyolefin resin particles Volume average particle size (Dv), number average, using a Nitraso Wave Co., Ltd. Nanotrac Wave-UZ152 particle size distribution analyzer The particle diameter (Dn) and dispersity (Dv / Dn) were determined. Here, the refractive index of the resin used for calculating the particle diameter was set to 1.50.
The degree of dispersion was calculated based on the following formula.
Dispersity = Volume average particle diameter (Dv) / Number average particle diameter (Dn)
(2) Unsaturated carboxylic acid monomer amount About 0.05 g of fine powder obtained by freeze-pulverizing the dry residue obtained by drying the separator coating material is precisely weighed, and 20 ml of methanol is used as the extraction solvent. Extraction was performed for 21 hours at room temperature by inversion mixing. The filtrate obtained by filtering this extract with a disk filter (pore size: 0.45 μm) was subjected to high performance liquid chromatography (HP1100, manufactured by Hewlett Packard, column is Puresil 5 μm C18 120Å φ4.6 mm × 250 mm (40 ° C.) manufactured by Waters). Quantified.
When the amount of unsaturated carboxylic acid monomer was less than 1000 ppm, the amount of the dry residue was changed to 0.5 g, and the amount was similarly determined.
A calibration curve was prepared using a standard sample of an unsaturated carboxylic acid monomer component with a known concentration.

3. Secondary battery separator (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: 4.0 N / cm or more;
○: 3.8 N / cm or more;
Δ: 3.0 N / cm or more (no problem in practical use);
X: Less than 3.0 N / cm.

(Electrolytic solution resistance 1)
The separator coating material was dried at 80 ° C., 100 ° C., and 120 ° C. for 2 hours each 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 [%] = ((weight after immersion in electrolytic solution [g] −weight before immersion in electrolytic solution [g]) / weight before immersion in electrolytic solution [g]) × 100
◎; 15% or less;
○: 20% or less;
Δ: 25% or less (no problem in practical use);
X: Over 25%.
Thickness change rate [%] = ((Thickness after immersion in electrolytic solution [μm] −Thickness before immersion in electrolytic solution [μm]) / Thickness before immersion in electrolytic solution [μm]) × 100
◎; 5% or less;
○: 10% or less;
Δ: 15% or less (no problem in practical use);
X: Over 15%.

(Electrolytic solution resistance 2)
A sample similar to the measurement sample used in the adhesion test was immersed in an electrolytic solution (ethylene carbonate / diethyl carbonate / methyl ethyl carbonate (1/1/1 weight ratio)) and stored at 60 ° C. for 2 weeks. After taking out, the electrolyte solution on the surface was lightly wiped and the adhesion test was conducted. As in the following equation, the adhesive change rate before and after immersion was determined.
Adhesion change rate [%]: ((peel strength before immersion [N / cm] −peel strength after immersion [N / cm]) / peel strength before immersion [N / cm]) × 100

(Heat resistance (105 ° 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 105 ° C. with a 3.5 g weight 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%.

4). Secondary battery (charge / discharge cycle test)
A secondary battery was manufactured and tested according to the following method.
-Preparation of positive electrode LiCoO2 as positive electrode active material: 85 parts by mass, acetylene black as a conductive auxiliary agent: 10 parts by mass, PVDF as a binder: 5 parts by mass, N-methyl-2-pyrrolidone (NMP) as solvent Were mixed in a uniform manner to prepare a positive electrode mixture-containing paste. 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 are overlapped via secondary battery separators obtained in Examples and Comparative Examples described later, and wound into a spiral shape to form a wound electrode body. It was. 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). A solution in which LiPF6 was dissolved at a concentration of 1.2 mol / L) was injected, and the opening of the battery case was sealed to produce a lithium secondary battery. 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 obtained secondary battery was charged in a constant temperature bath at 25 ° C., after the above-described preliminary charging, 0.5 C-4.0 V constant current constant voltage charging, and then 0.5 C-2.5 V constant current discharging. The cycle characteristics were evaluated by repeating the above. The initial capacity was set to 100%, the battery capacity after 500 cycles was determined, and the maintenance rate was calculated.
◎; 95% or more;
○: 90% or more;
Δ: 85% or more (no problem in practical use);
X: Less than 85%.

(High temperature storage stability)
After the above-described preliminary charging, the obtained secondary battery was repeatedly charged and discharged at a constant current and a constant voltage of 0.5 C to 4.0 V for 5 cycles under the same conditions as the charge and discharge cycle test, and then a thermostat at 50 ° C The battery was put in and 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%.

(Manufacture of polyolefin resin)
Production Example 1: Polyolefin resin P-1
280 g of propylene-butene copolymer (mass ratio: propylene / 1-butene = 80/20) was dissolved in 470 g of xylene under a nitrogen atmosphere in a four-necked flask, and the system temperature was kept at 140 ° C. Under stirring, 40.0 g of maleic anhydride as an unsaturated carboxylic acid and 28.0 g of dicumyl peroxide as a radical generator were added over 2 hours, respectively, and then reacted for 6 hours. After completion of the reaction, the obtained reaction product was put into a large amount of acetone to precipitate a resin.
The precipitated resin was washed once with an acetone solution of triethylamine (mass ratio: triethylamine / acetone = 1/4), and then washed with acetone to remove unreacted maleic anhydride, and then a vacuum dryer. Then, it was dried under reduced pressure to obtain polyolefin resin P-1. The properties of the obtained resin are shown in Table 1.

Production Example 2: Polyolefin resin P-2
A polyolefin resin P-2 was obtained in the same manner as in Production Example 1 except that a propylene-butene copolymer having a mass ratio of propylene / 1-butene = 65/35 was used.

Production Example 3: Polyolefin resin P-3
In Production Example 1, the same procedure was followed except that a propylene-ethylene copolymer (mass ratio: propylene / ethylene = 92/8) was used in place of the propylene-butene copolymer, and the polyolefin resin P- 3 was obtained.

Production Example 4: Polyolefin resin P-4
The same operation as in Production Example 1 except that a propylene-butene-ethylene copolymer (mass ratio: propylene / 1-butene / ethylene = 65/24/11) was used instead of the propylene-butene copolymer. To obtain a polyolefin resin P-4.

Production Example 5: Polyolefin resin P-5
In Production Example 1, a polyolefin resin P-5 was obtained in the same manner as described above except that the washing step with acetone was omitted.

Production Example 6: Polyolefin resin P-6
A polyolefin resin P-6 was obtained in the same manner as in Production Example 1 except that the acetone solution of triethylamine was changed to acetone.

Production Example 7: Polyolefin resin P-7
In Production Example 1, the amount of maleic anhydride added was changed to 70.0 g instead of 40.0 g, the amount of dicumyl peroxide added was changed to 33.0 g instead of 28.0 g, and washing step with an acetone solution of triethylamine A polyolefin resin P-7 was obtained in the same manner as described above except that was omitted.

Production Example 8: Polyolefin resin P-8
In Production Example 7, a polyolefin resin P-8 was obtained in the same manner as described above except that the washing step with acetone was omitted.

Production Example 9: Polyolefin resin P-9
The same operation as in Production Example 1 was carried out except that the amount of maleic anhydride added was changed to 24.0 g instead of 40.0 g, and the amount of dicumyl peroxide added was changed to 18.5 g instead of 28.0 g. Thus, a polyolefin resin P-9 was obtained.

Production Example 10: Polyolefin resin P-10
In Production Example 3, the same procedure was performed except that the amount of maleic anhydride added was changed to 46.0 g to 56.0 g, and the washing step with acetone solution of triethylamine and the washing step with acetone were omitted. A polyolefin resin P-10 was obtained.

Production Example 11: Polyolefin resin P-11
In Production Example 1, the amount of maleic anhydride added was changed to 70.0 g instead of 40.0 g, the amount of dicumyl peroxide added was changed to 20.0 g instead of 28.0 g, and the washing step with an acetone solution of triethylamine A polyolefin resin P-11 was obtained in the same manner as described above except that the washing step with acetone was omitted.

Production Example 12: Polyolefin resin P-12
In Production Example 3, the amount of maleic anhydride added was changed to 70.0 g instead of 40.0 g, the amount of dicumyl peroxide added was changed to 20.0 g instead of 28.0 g, and the washing step with triethylamine in acetone solution A polyolefin resin P-12 was obtained in the same manner as above except that the washing step with acetone was omitted.

Production Example 13: Polyolefin resin P-13
A polyolefin resin P-13 was obtained in the same manner as in Production Example 1, except that a propylene-butene copolymer having a mass ratio of propylene / 1-butene = 97/3 was used.

Production Example 14: Polyolefin resin P-14
A polyolefin resin P-14 was obtained in the same manner as in Production Example 1 except that a propylene-butene copolymer having a mass ratio of propylene / 1-butene = 50/50 was used.

Production Example 15: Polyolefin resin P-15
The same method as in Production Example 1 was carried out except that the amount of maleic anhydride added was changed to 2.0 g instead of 40.0 g, and the amount of dicumyl peroxide added was changed to 1.4 g instead of 28.0 g. Thus, a polyolefin resin P-15 was obtained.

Production Example 16: Polyolefin resin P-16
In the same manner as in Production Example 1, a polyolefin resin P-1 was obtained. A polyolefin resin was obtained in the same manner as in Example 1 except that this polyolefin resin P-1 was used instead of the propylene-butene copolymer in Production Example 1 (this polyolefin resin is referred to as P-2). Further, a polyolefin resin was obtained in the same manner as in Example 1 except that this polyolefin resin P-2 was used instead of the propylene-butene copolymer in Production Example 1 (this polyolefin resin is designated as P-3). ). Furthermore, a polyolefin resin P-16 was obtained in the same manner as in Example 1 except that this polyolefin resin P-3 was used in Production Example 1 instead of the propylene-butene copolymer.

Table 1 shows the properties of the polyolefin resins obtained in Production Examples 1 to 16.

(Manufacture of microporous film for secondary battery separator)
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
Using a stirrer equipped with a 1 L glass container that can be sealed with a heater, 60.0 g of polyolefin resin P-1, 99.0 g of tetrahydrofuran, 11.6 g of DMEA, and 159.4 g of distilled water were added to glass. When charged in the container and stirred at a rotational speed of the stirring blade of 300 rpm, no resin precipitation was observed at the bottom of the container, confirming that it 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 maintained at 130 ° C. and further stirred for 60 minutes.
Then, after cooling to room temperature (about 25 ° C.) while stirring at an air-cooling speed of 300 rpm, 250 g of the aqueous dispersion and 120 g of distilled water were charged into a 0.5 L two-necked round bottom flask, A Liebig condenser was installed and the flask was heated in an oil bath to distill off the aqueous medium. When about 120 g of the aqueous medium was distilled off, heating was terminated and the mixture was cooled to room temperature. After cooling, the liquid component in the flask was pressure filtered (air pressure 0.2 MPa) with a 300 mesh stainless steel filter (wire diameter 0.035 mm, plain weave) to give a milky white uniform polyolefin resin aqueous dispersion (separator coating material) ) E-1 was obtained. At this time, almost no resin remained on the filter.
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 were mixed and stirred at room temperature to obtain a slurry for forming a separator.
A wire bar (# 12) is used on one side of one microporous film (the side in contact with the drum during melt extrusion) so that the thickness of the porous layer after drying is 4 μm. Then, it 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.

Example 2
60.0 g polyolefin resin P-1, 45.0 g ethylene glycol-n-butyl ether, 8.0 g DMEA and 137.0 g When distilled water was charged into a glass container and stirred at a rotation speed of 300 rpm, no resin precipitation was observed at the bottom of the container, confirming that it 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 160 ° C. and further stirred for 60 minutes.
Thereafter, it was cooled by air cooling until the internal temperature reached 80 ° C., opened, and 45.0 g of tetrahydrofuran, 5.0 g of DMEA and 30.0 g of distilled water were added. Thereafter, the mixture was sealed, and the stirring speed was 300 rpm, the system temperature was kept at 140 ° C., and the mixture was further stirred for 60 minutes.
Then, after cooling to room temperature (about 25 ° C.) while stirring with air rotation at 300 rpm, pressure filtration (air pressure 0.2 MPa) is performed with a 300 mesh stainless steel filter (wire diameter 0.035 mm, plain weave). A slightly cloudy dispersion was obtained. At this time, almost no resin remained on the filter.
250 g of the obtained dispersion and 120 g of distilled water were charged into a 0.5 L two-necked round bottom flask, a mechanical stirrer and a Liebig condenser were installed, the flask was heated in an oil bath, and the aqueous medium was retained. Left. When about 120 g of the aqueous medium was distilled off, heating was terminated and the mixture was cooled to room temperature. After cooling, the liquid component in the flask was pressure filtered (air pressure 0.2 MPa) with a 300 mesh stainless steel filter (wire diameter 0.035 mm, plain weave) to obtain a milky white uniform aqueous dispersion (separator coating material) E -2 was obtained.
A secondary battery separator was obtained in the same manner as in Example 1 except that the coating material “E-2” was used.

Examples 3-4, 6-11
Instead of the polyolefin resin P-1, P-2 is used in Example 3, P-3 is used in Example 4, P-5 is used in Example 6, P-6 is used in Example 7, P is used in Example 8. The dispersion was obtained in the same manner as in Example 2, except that P-7 was used in Example 9, P-8 was used in Example 9, P-9 was used in Example 10, and P-10 was used in Example 11. .
250 g of the obtained dispersion and 120 g of distilled water were charged into a 0.5 L two-necked round bottom flask, a mechanical stirrer and a Liebig condenser were installed, the flask was heated in an oil bath, and the aqueous medium was retained. Left. When about 120 g of the aqueous medium was distilled off, heating was terminated and the mixture was cooled to room temperature. After cooling, the liquid component in the flask was pressure filtered (air pressure 0.2 MPa) with a 300 mesh stainless steel filter (wire diameter 0.035 mm, plain weave) to obtain a milky white uniform aqueous dispersion (separator coating material) E -3, E-4, E-6, E-7, E-8, E-9, E-10, E-11 were obtained. In Examples 8, 9, and 11, the amount of DMEA was 12.0 g.
Furthermore, it carried out like Example 1 except having used each obtained coating material, and obtained the separator for secondary batteries, respectively.

Example 5
In Example 1, an aqueous dispersion (separator coating material) E was prepared in the same manner as in Example 1 except that P-4 was used instead of the polyolefin resin P-1 and the amount of DMEA was changed to 12.0 g. -5 was obtained.
Furthermore, it carried out like Example 1 except having used obtained coating material "E-5", and obtained the separator for secondary batteries.

Example 12
Separator coating material “E-1” and an aqueous polyurethane resin dispersion (Takelac W-6010, manufactured by Mitsui Chemicals, Ltd.) with respect to 100 parts by mass of olefin resin solids, the amount of polyurethane resin solids is 50 parts by mass. Thus, a separator coating material E-12 was obtained.
Further, a secondary battery separator was obtained in the same manner as in Example 1 except that the obtained coating material “E-12” was used.

Examples 13-15
The same operation as in Example 12 except that E-2 was used in Example 13, E-3 was used in Example 14, and E-4 was used in Example 15 instead of the separator coating material “E-1”. And separator coating materials E-13 to E-15 were obtained. In Example 14, the amount of solid content of polyurethane resin was 30 parts by mass.
Furthermore, it carried out like Example 1 except having used each obtained coating material, and obtained the separator for secondary batteries.

Example 16
Separator coating material “E-1”, an aqueous solution of an oxazoline group-containing compound (WS-700 solid content concentration: 25% by mass, manufactured by Nippon Shokubai Co., Ltd.) and an aqueous polyurethane resin dispersion are added to 100 parts by mass of the olefin resin solid content. The mixture was mixed so that the solid content of the oxazoline group-containing compound was 10 parts by mass and the solid content of the polyurethane resin was 50 parts by mass to obtain a coating material E-16 for a separator.
Furthermore, it carried out similarly to Example 1 except having used obtained coating material "E-16", and obtained the separator for secondary batteries.

Example 17
A separator coating material E-17 was obtained in the same manner as in Example 16 except that the separator coating material E-2 was used instead of the separator coating material “E-1”.
Further, a secondary battery separator was obtained in the same manner as in Example 1 except that the obtained coating material “E-17” was used.

Examples 18-19
In place of the polyolefin resin P-1, the same operation as in Example 2 was performed except that P-11 was used in Example 18 and P-12 was used in Example 19, and the separator coating material E-18, E-19 was obtained. In Example 18, the amount of DMEA was 12.0 g.
Furthermore, it carried out like Example 1 except having used each obtained coating material, and obtained the separator for secondary batteries.

Example 20
In Example 2, Neugen EA-190D (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., a nonionic surfactant), which is a non-volatile aqueous agent, was added so as to be 3% by mass with respect to the polyolefin resin. The same operation as in Example 2 was performed to obtain an aqueous dispersion (coating material) E-20.

Comparative Examples 1-3
In place of the polyolefin resin P-1, the same operation as in Example 2 was performed except that P-13 was used in Comparative Example 1, P-14 was used in Comparative Example 2, and P-16 was used in Comparative Example 3. The separator coating materials E-21 to E-23 were obtained.
Furthermore, it carried out like Example 1 except having used each obtained coating material, and obtained the separator for secondary batteries.

Comparative Example 4
Except that P-15 was used instead of the polyolefin resin P-1, the same operation as in Example 2 was performed, and a large amount of resin was confirmed on the filter. Since the polyolefin resin P-15 did not substantially disperse, an aqueous dispersion (a coating material for a separator) could not be obtained.

Evaluation of the secondary battery obtained using Examples 1-20, the coating material for separators obtained in Comparative Examples 1-3, the separator for secondary batteries obtained using the coating material, and the separator for secondary batteries The results are shown in Table 2.

As shown in Table 2, the separator coating materials of the present invention obtained in Examples 1 to 20 are excellent in separator permeability, non-conductive particles, and non-conductive particles-porous substrate. In addition, since the resistance to electrolytic solution is good, the change in weight and thickness is small, and the change in adhesiveness after immersion in the electrolyte is also stable, so it has excellent secondary battery cycle characteristics and high-temperature stability. The characteristic was shown.
Especially, in the case of the coating material for separators which added the oxazoline group containing compound crosslinking agent and the polyurethane resin (Examples 12-17), adhesiveness improved further and the battery cycle characteristic improved.

On the other hand, the separator coating materials obtained in Comparative Examples 1 and 2 have a mass ratio (A / B) of propylene (A) constituting the polyolefin resin and olefin (B) other than propylene defined in the present invention. Therefore, the dispersity of the aqueous dispersion was lowered, the separator air permeability was lowered, and the battery characteristics were inferior. Comparative Example 1 had low initial adhesiveness and low battery characteristics, and Comparative Example 2 had poor electrolytic solution resistance, a large volume change after immersion, and low battery characteristics such as storage stability.
The separator coating material obtained in Comparative Example 3 has too much content of unsaturated carboxylic acid component constituting the polyolefin resin, so there is no problem in air permeability and adhesiveness. The change was great, and the adhesiveness was greatly reduced. Moreover, since the molecular weight is low, the heat resistance is also inferior, and as a result, the battery characteristics showed low values of cycle characteristics and high-temperature storage stability.

Claims (10)

A coating material for a separator in which a polyolefin resin is dispersed in an aqueous medium, the polyolefin resin containing an olefin component and an unsaturated carboxylic acid component as a copolymer component, and the olefin component comprising propylene (A) and And olefin (B) other than propylene, the mass ratio (A / B) of propylene (A) and olefin (B) other than propylene is 60/40 to 95/5, and propylene (A ) And 100 parts by mass of the olefin other than propylene (B), the content of the unsaturated carboxylic acid component as the copolymer component is 0.5 to 15 parts by mass. Coating material. 2. The coating material for a separator according to claim 1, wherein the amount of the unsaturated carboxylic acid monomer in the dry residue is 10,000 ppm or less. The separator coating material according to claim 1, wherein the coating material for a separator according to claim 1 or 2 is substantially free of a non-volatile water-based auxiliary. The separator coating material according to any one of claims 1 to 3, wherein the olefin (B) other than propylene is butene. The coating material for a separator according to any one of claims 1 to 4, wherein the degree of dispersion in the particle size distribution of the polyolefin resin is 1 to 2.6. The separator formation slurry containing the coating material for separators in any one of Claims 1-5, and a nonelectroconductive particle. The slurry for forming a separator according to claim 6, wherein the mass ratio of the separator coating material and the non-conductive particles is 70/30 to 1/99. The separator which has a porous layer formed by apply | coating the slurry for separator formation of Claim 6 or 7 to the at least single side | surface of a porous base material. The separator according to claim 8, wherein the material constituting the porous substrate is a polyolefin resin. A secondary battery comprising the separator according to claim 8.