JP2019008882A - Slurry for pattern coating - Google Patents

Abstract

To provide a slurry for pattern coating which facilitates pattern coating of a desired shape on a polyolefin porous backing material used as the base material of a separator for power storage device.SOLUTION: A slurry for pattern coating on at least one side of a polyolefin porous backing material used as the base material of a separator for power storage device contains a thermoplastic polymer, and a disperse medium or solvent, and the maximum value of high shear viscosity is 5 cps or more for the shear rate of 50000 sor less.SELECTED DRAWING: None

Description

  The present invention relates to a slurry for pattern coating. More specifically, the present invention relates to a pattern coating slurry for pattern coating on at least one surface of a polyolefin porous substrate used as a substrate for a power storage device separator.

  In recent years, development of power storage devices such as non-aqueous electrolyte batteries has been actively conducted. Usually, an electrical storage device has a separator including a porous substrate between a positive electrode and a negative electrode. The separator has a function of preventing direct contact between the positive and negative electrodes and allowing ions to permeate through the electrolytic solution held in the porous substrate.

  Examples of the porous substrate include a polyolefin porous substrate. The polyolefin porous substrate is an electronic insulator, and is widely used as a separator for non-aqueous electrolyte batteries because of its ion permeability due to its porous structure. The polyolefin porous substrate shuts down the ionic conduction in the electrolyte and stops the progress of the electrochemical reaction when the nonaqueous electrolyte battery generates abnormal heat and closes the pores by heat melting. Also have.

  Attempts have been made to form a coating layer containing a thermoplastic polymer on the surface of such a porous polyolefin substrate to impart various performances, for example, adhesion to electrodes, to the electricity storage device. However, generally, the coating layer used for the separator can be a resistance for the electricity storage device. Therefore, when the coating area increases, the performance intended by the coating layer, for example, adhesion increases, but the resistance increases. On the other hand, when the adhesion area is small, an increase in resistance is suppressed, but performance due to the coating layer, for example, adhesiveness is lowered. Therefore, when designing the separator, it is necessary to design the product in consideration of the balance between the performance of the coating layer and the increase in resistance. For this purpose, it is important to be able to form a coating layer containing a thermoplastic polymer on the surface of a polyolefin porous substrate as desired, and a coating parimer capable of such pattern coating is required. ing.

  For example, in Patent Documents 1 to 3, a slurry containing a specific thermoplastic polymer is pattern-coated and dried on at least a part of at least one surface of a base material to form a coating layer, whereby an electrode and an electrode are formed. It describes that an electricity storage device separator having excellent adhesion is provided.

Japanese Patent Laid-Open No. 2006-122648 JP 2006-201367 A JP, 2006-207659, A

  However, in conventional slurries such as those described in Patent Documents 1 to 3, the pattern shape may change between coating and drying due to various factors described later, and the coating is applied according to the designed shape. It was difficult to form a work layer.

  Accordingly, one of the objects of the present invention is to provide a slurry for pattern coating that can be easily pattern-coated in a desired shape on a polyolefin porous substrate used as a substrate for an electricity storage device separator. That is.

As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by using a slurry having a viscosity of 5 cps or more in a low speed region (50000 s ⁻¹ or less) in high shear viscosity measurement. The present invention has been completed. That is, the present invention is as follows.
[1]
A pattern coating slurry for applying a pattern to at least one surface of a polyolefin porous substrate used as a substrate for a storage device separator,
The pattern coating slurry includes a thermoplastic polymer, a dispersion medium or a solvent,
The pattern coating slurry is a pattern coating slurry having a maximum value of high shear viscosity at a shear rate of 50000 s ⁻¹ or less of 5 cps or more.
[2]
Item 2. The pattern coating slurry according to Item 1, wherein the maximum value of the high shear viscosity is 5 cps or more and 10 cps or less.
[3]
3. The pattern coating slurry according to item 1 or 2, wherein the surface tension of the pattern coating slurry is 50 or more and 100 or less.
[4]
The viscosity of the pattern coating slurry when the solid content concentration is 30% by mass is 100 mPa · s or less, and when the solid content concentration is 50% by mass, the viscosity is 300 mPa · s or more. The slurry for pattern coating of any one of Claims 1.
[5]
The viscosity of the slurry for pattern coating is 100 mPa · s or less when the solid content concentration is 30% by mass, and the viscosity when the solid content concentration is 45% by mass is 150 mPa · s or more. The slurry for pattern coating of any one of Claims 1.
[6]
Item 1-5, in which the viscosity when the solid content concentration of the slurry for pattern coating is 30% by mass is 100 mPa · s or less, and the viscosity when the solid content concentration is 40% by mass is 150 mPa · s or more. The slurry for pattern coating of any one of Claims 1.
[7]
The viscosity of the pattern coating slurry when the solid content concentration is 30% by mass is 70 mPa · s or less, and when the solid content concentration is 40% by mass, the viscosity is 150 mPa · s or more. The slurry for pattern coating of any one of Claims 1.
[8]
The slurry for pattern coating of any one of the items 1-7 containing the said dispersion medium and the said dispersion medium contains water as a main component.
[9]
A copolymer in which the thermoplastic polymer has as a monomer unit at least one selected from the group consisting of (meth) acrylate monomers, conjugated diene monomers, and vinylidene fluoride monomers The separator for electrical storage devices which has pattern coating formed from the slurry for pattern coating of any one of the items 1-8 containing this.
[10]
The thermoplastic polymer contained in the coating slurry includes at least two thermoplastic polymers, and has at least two glass transition temperatures as a whole,
At least one of the glass transition temperatures is present in a region below 20 ° C.,
Item 10. The electrical storage device separator according to any one of Items 1 to 9, wherein at least one of the glass transition temperatures is present in a region of 20 ° C or higher.
[11]
Item 11. The power storage device separator according to any one of Items 1 to 10, wherein a degree of swelling of the thermoplastic polymer with respect to the electrolytic solution is 1 to 10 times.
[12]
The separator for electrical storage devices which has the pattern coating formed from the slurry for pattern coating of any one of the items 1-11 on the at least single side | surface of a polyolefin porous substrate.
[13]
Item 13. The electricity storage device separator according to Item 12, wherein the pattern coating is a dot pattern.
[14]
14. The electricity storage device separator according to item 12 or 13, wherein the dot has a diameter of 10 μm or more and 1000 μm or less, and an area occupation ratio of the dot is 5% or more and 80% or less.
[15]
A separator for an electricity storage device, comprising a polyolefin porous substrate, and a thermoplastic polymer coating layer covering at least a part of at least one surface of the polyolefin porous substrate,
A portion where the thermoplastic polymer coating layer is present on the polyolefin porous substrate and a portion where the thermoplastic polymer coating layer is not present are present in a sea-island shape,
The thermoplastic polymer contained in the thermoplastic polymer coating layer contains at least two thermoplastic polymers, and has at least two glass transition temperatures as a whole,
At least one of the glass transition temperatures is present in a region below 20 ° C.,
At least one of the glass transition temperatures exists in a region of 20 ° C. or higher.
Electric storage device separator.

  ADVANTAGE OF THE INVENTION According to this invention, the slurry for pattern coating which can be pattern-coated easily in a desired shape on the polyolefin porous substrate used as a base material of the separator for electrical storage devices can be provided.

  Having described exemplary embodiments and advantages of the present invention, other embodiments and other advantages of the present invention will become apparent from the following specification of the present application.

  Hereinafter, an embodiment of the present invention (hereinafter referred to as “this embodiment”) will be described in detail, but the present invention is not limited to this embodiment. In the present specification, the upper limit value and the lower limit value of each numerical range can be arbitrarily combined.

<Slurry for pattern coating>
The pattern coating slurry of the present embodiment is a pattern coating slurry for pattern coating on at least one surface of a polyolefin porous substrate used as a substrate for an electricity storage device separator. The pattern coating slurry includes a thermoplastic polymer and a dispersion medium or a solvent, and the pattern coating slurry has a maximum value of high shear viscosity at a shear rate of 50000 s ⁻¹ or less of 5 cps or more.

  The step of forming a coating layer of a predetermined pattern on the base material of the electricity storage device separator typically involves coating a slurry having a predetermined initial solid content on the polyolefin porous base material in a desired pattern, It involves gradually raising (ie, drying) the solid content to form a coating layer. With conventional slurries, the pattern shape may change between when the slurry is applied and when it is completely dried, making it difficult to form a coating layer according to the designed shape. . This is particularly a problem when it is desired to form a fine pattern having a structure on the order of several mm to several μm, for example. Although not limited to theory, and not limited to the following, the factors that cause the pattern shape to change include, for example: (1) that the coating slurry cannot be transferred to the desired shape when transferred to the substrate; and (2 It is conceivable that the slurry flows during the period from coating to drying, and the coating shape collapses.

<High shear viscosity>
On the other hand, the pattern coating slurry of the present embodiment contains a thermoplastic polymer, a dispersion medium or a solvent, and the maximum value of the high shear viscosity at a shear rate of 50000 s ⁻¹ or less is 5 cps or more. Easily transfer the coating slurry to the desired shape when transferring it to the base material, and it will be difficult for the slurry to flow between coating and drying. Can do. Therefore, the pattern coating slurry of this embodiment can easily form a pattern coating having a desired shape on the polyolefin porous substrate. This effect is particularly advantageous when it is desired to form a fine pattern having a structure of the order of several mm to several μm, for example.

  The theory is not yet clear, and it is not limited to the theory, but in general, since the separator production line is moving at high speed, external force such as acceleration due to the direction change of the line is applied to the slurry after coating. It is possible to join. Therefore, the inventors presume that the coating property, that is, the transfer property of the pattern coating slurry correlates with the viscosity at a somewhat higher share than the viscosity at a low share such as a B-type viscometer. In addition, it is difficult for the slurry to move from when the pattern coating slurry is transferred to drying, that is, the shape stability of the transferred pattern is higher than the high shear viscosity. The inventors estimate that it correlates with the rising profile.

The maximum value of the high shear viscosity at a shear rate of 50000 s ⁻¹ or less of the pattern coating slurry of this embodiment is 5 cps or more, preferably 7 cps or more. The maximum value of the high shear viscosity at a shear rate of 50000 s ⁻¹ or less is preferably 15 cps or less, more preferably 12 cps or less, and even more preferably 10 cps or less. The range of the maximum value of the high shear viscosity is preferably 5 cps or more and 15 cps or less, more preferably 7 cps or more and 12 cps or less. When the maximum value of the high shear viscosity at a shear rate of 50000 s ^-1 or less is 5 cps or more and 15 cps or less, it is easy to transfer the coating slurry to a desired shape, and the coating part is foamed during drying. Since it can be suppressed and the slurry is difficult to flow during the period from application to drying, pattern coating having a desired shape can be easily formed on the polyolefin porous substrate. .

<surface tension>
The surface tension of the pattern coating slurry of this embodiment is preferably 50 or more and 100 or less, more preferably 60 or more and 90 or less. If the surface tension of the slurry for pattern coating is 50 or more and 100 or less, the affinity for the polyolefin porous substrate is good, so it is easy to transfer the slurry to the desired shape when transferring the slurry for coating to the substrate. In addition, since the amount of the surfactant is not too large, the slurry is difficult to foam.

<Viscosity of slurry at each solid content concentration>
The relationship of the viscosity of the slurry with respect to the solid content concentration of the pattern coating slurry of the present embodiment is as follows.
When the solid content concentration of the pattern coating slurry is 30% by mass, the viscosity is preferably 5 mPa · s or more, more preferably 10 mPa · s or more, still more preferably 15 mPa · s or more, and 150 mPa · s or less. Preferably it is 100 mPa * s or less, More preferably, it is 50 mP * s or less.
When the solid content concentration of the pattern coating slurry is 40% by mass, the viscosity is preferably 30 mPa · s or more, more preferably 50 mPa · s or more, still more preferably 80 mPa · s or more, and 350 mPa · s or less. Preferably it is 250 mPa * s or less, More preferably, it is 180 mP * s or less.
When the solid content concentration of the pattern coating slurry is 45% by mass, the viscosity is preferably 70 mPa · s or more, more preferably 100 mPa · s or more, still more preferably 150 mPa · s or more, and 500 mPa · s or less. Preferably it is 400 mPa * s or less, More preferably, it is 250 mP * s or less.
When the solid content concentration of the pattern coating slurry is 50% by mass, the viscosity is preferably 100 mPa · s or more, more preferably 15 mPa · s or more, further preferably 200 mPa · s or more, and 700 mPa · s or less. Preferably it is 600 mPa * s or less, More preferably, it is 500 mP * s or less.
If the viscosity of the slurry with respect to the solid content concentration of the slurry for pattern coating is within the above range, foaming of the slurry during coating can be suppressed. It is possible to effectively prevent the slurry from flowing and the coating shape from collapsing until the slurry is dried.
The above values can be controlled by adjusting the monomer type, monomer addition amount, particle size, thickener type, thickener addition amount, and the like of the thermoplastic polymer in the slurry.

<Thermoplastic polymer>
Specific examples of the thermoplastic polymer contained in the pattern coating slurry include the following 1) to 4).
1) a conjugated diene polymer,
2) Acrylic polymer,
3) polyvinyl alcohol resin, and 4) fluorine-containing resin.
Among them, the above 1) conjugated diene polymer is preferable from the viewpoint of compatibility with the electrode, and 2) acrylic polymer and 4) fluorine-containing resin are preferable from the viewpoint of voltage resistance.
The slurry for pattern coating contains the thermoplastic polymer in an amount of preferably 5% by mass or more, more preferably 10% by mass or more, and still more preferably 15% by mass or more based on the total amount of the slurry. The pattern coating (also referred to as “thermoplastic polymer coating layer” in the present specification) obtained by drying the slurry for pattern coating is preferably 60% by mass or more, more preferably 90%, based on the total amount. The thermoplastic polymer is contained in an amount of at least mass%, more preferably at least 95 mass%, particularly preferably at least 98 mass%.
The slurry for pattern coating and the pattern coating may contain other components in addition to the above-mentioned thermoplastic polymer to such an extent that the solution of the problem of the present invention is not impaired.

The 1) conjugated diene polymer is a polymer containing a conjugated diene compound as a monomer unit. Examples of the conjugated diene compound include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, and substituted linear chains. Examples thereof include conjugated pentadienes, substituted and side chain conjugated hexadienes, and these may be used alone or in combination of two or more. Among these, 1,3-butadiene is particularly preferable.
Further, the conjugated diene polymer may contain a (meth) acrylic compound or other monomer described later as a monomer unit. Specifically, for example, styrene-butadiene copolymer and its hydride, acrylonitrile-butadiene copolymer and its hydride, acrylonitrile-butadiene-styrene copolymer and its hydride, and the like.

The 2) acrylic polymer is a polymer containing a (meth) acrylic compound as a monomer unit. The (meth) acrylic compound indicates at least one selected from the group consisting of (meth) acrylic acid and (meth) acrylic acid ester.
An example of such a compound is a compound represented by the following formula (P1).
_{^{CH 2 = CR Y1 -COO-R}} Y2 (P1)
In formula (P1), R ^Y1 represents a hydrogen atom or a methyl group, and R ^Y2 represents a hydrogen atom or a monovalent hydrocarbon group. When R ^Y2 is a monovalent hydrocarbon group, it may have a substituent and may have a hetero atom in the chain. Examples of the monovalent hydrocarbon group include a linear alkyl group, a cycloalkyl group, and an aryl group which may be linear or branched. Examples of the substituent include a hydroxyl group and a phenyl group, and examples of the hetero atom include a halogen atom and an oxygen atom. A (meth) acrylic compound is used alone or in combination of two or more.
Examples of such (meth) acrylic compounds include (meth) acrylic acid, chain alkyl (meth) acrylate, cycloalkyl (meth) acrylate, (meth) acrylate having a hydroxyl group, and phenyl group-containing (meth) acrylate. Can be mentioned.

More specifically, the chain alkyl group which is one kind of R ^Y2 is a chain alkyl group having 1 to 3 carbon atoms, which is a methyl group, an ethyl group, an n-propyl group, or an isopropyl group; Examples thereof include chain alkyl groups having 4 or more carbon atoms, such as a butyl group, an isobutyl group, a t-butyl group, an n-hexyl group, a 2-ethylhexyl group, and a lauryl group. Moreover, as an aryl group which is 1 type of ^RY2, a phenyl group is mentioned, for example.
Specific examples of the (meth) acrylic acid ester monomer having R ^Y2 include, for example, methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, t-butyl acrylate, and n-hexyl. Chain alkyl such as acrylate, 2-ethylhexyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate (Meth) acrylate having a group;
Examples include (meth) acrylates having an aromatic ring, such as phenyl (meth) acrylate and benzyl (meth) acrylate.

Among these, from the viewpoint of improving the adhesion to the electrode (electrode active material), a monomer having a chain alkyl group having 4 or more carbon atoms, more specifically, R ^Y2 has 4 carbon atoms. The (meth) acrylic acid ester monomer which is the above chain alkyl group is preferable. More specifically, at least one selected from the group consisting of butyl acrylate, butyl methacrylate, and 2-ethylhexyl acrylate is preferable. The upper limit of the number of carbon atoms in the chain alkyl group having 4 or more carbon atoms is not particularly limited, and may be 14, for example, but 7 is preferable. These (meth) acrylic acid ester monomers are used singly or in combination of two or more.

The (meth) acrylic acid ester monomer is a monomer having a cycloalkyl group as R ^Y2 instead of or in addition to the monomer having a chain alkyl group having 4 or more carbon atoms. It is also preferable to include. This also further improves the adhesion with the electrode.
More specifically, examples of such a monomer having a cycloalkyl group include cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, adamantyl (meth) acrylate, and the like. 4-8 are preferable, as for the number of the carbon atoms which comprise the alicyclic ring of a cycloalkyl group, 6 and 7 are more preferable, and 6 is especially preferable. Further, the cycloalkyl group may or may not have a substituent. Examples of the substituent include a methyl group and a t-butyl group. Among these, at least one selected from the group consisting of cyclohexyl acrylate and cyclohexyl methacrylate is preferable in terms of good polymerization stability when preparing an acrylic polymer. These are used singly or in combination of two or more.

Moreover, it is preferable that an acrylic polymer contains a crosslinkable monomer as a (meth) acrylic acid ester monomer instead of the above, or in addition, preferably in addition to the above. The crosslinkable monomer is not particularly limited. For example, a monomer having two or more radical polymerizable double bonds, a single monomer having a functional group that gives a self-crosslinking structure during or after polymerization. Examples include the body. These are used singly or in combination of two or more.
Examples of the monomer having two or more radical polymerizable double bonds include divinylbenzene and polyfunctional (meth) acrylate. The polyfunctional (meth) acrylate may be at least one selected from the group consisting of bifunctional (meth) acrylate, trifunctional (meth) acrylate, and tetrafunctional (meth) acrylate. Specifically, for example, polyoxyethylene diacrylate, polyoxyethylene dimethacrylate, polyoxypropylene diacrylate, polyoxypropylene dimethacrylate, neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, butanediol diacrylate, butanediol Examples include dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetraacrylate, and pentaerythritol tetramethacrylate. These are used singly or in combination of two or more. Especially, at least 1 sort (s) selected from the group which consists of a trimethylol propane triacrylate and a trimethylol propane trimethacrylate from a viewpoint similar to the above is preferable.

Examples of the monomer having a functional group that gives a self-crosslinking structure during or after polymerization include, for example, a monomer having an epoxy group, a monomer having a methylol group, a monomer having an alkoxymethyl group, and a hydrolyzable property. Examples thereof include a monomer having a silyl group. As the monomer having an epoxy group, an ethylenically unsaturated monomer having an alkoxymethyl group is preferable. Specifically, examples thereof include glycidyl (meth) acrylate, 2,3-epoxycyclohexyl (meth) acrylate, 3 , 4-epoxycyclohexyl (meth) acrylate, allyl glycidyl ether and the like.
Examples of the monomer having a methylol group include N-methylol acrylamide, N-methylol methacrylamide, dimethylol acrylamide, and dimethylol methacrylamide.
As the monomer having an alkoxymethyl group, an ethylenically unsaturated monomer having an alkoxymethyl group is preferable. Specific examples thereof include N-methoxymethylacrylamide, N-methoxymethylmethacrylamide, and N-butoxymethyl. Examples include acrylamide and N-butoxymethyl methacrylamide.
Examples of the monomer having a hydrolyzable silyl group include vinyl silane, γ-acryloxypropyltrimethoxysilane, γ-acryloxypropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, and γ-methacryloxypropyl. Examples include triethoxysilane.
These are used singly or in combination of two or more.

The acrylic polymer may further have other monomers as monomer units in order to improve various qualities and physical properties. Examples of such a monomer include a monomer having a carboxyl group (excluding (meth) acrylic acid), a monomer having an amide group, a monomer having a cyano group, and a hydroxyl group. For example, a monomer having an aromatic vinyl monomer, and an aromatic vinyl monomer.
Furthermore, various vinyl monomers having functional groups such as sulfonic acid groups and phosphoric acid groups, and vinyl acetate, vinyl propionate, vinyl versatate, vinyl pyrrolidone, methyl vinyl ketone, butadiene, ethylene, propylene, vinyl chloride Vinylidene chloride and the like can be used as necessary.
These are used singly or in combination of two or more. The other monomer may belong to two or more of the monomers at the same time.

Examples of the monomer having an amide group include (meth) acrylamide.
The monomer having a cyano group is preferably an ethylenically unsaturated monomer having a cyano group, and specific examples thereof include (meth) acrylonitrile.
As a monomer which has a hydroxyl group, 2-hydroxyethyl (meth) acrylate etc. are mentioned, for example.

  Examples of the aromatic vinyl monomer include styrene, vinyl toluene, α-methyl styrene, and the like. Styrene is preferred.

  The ratio of the (meth) acrylic compound as a monomer unit in the acrylic polymer is preferably 5 to 95% by mass with respect to 100% by mass of the acrylic polymer. The lower limit is more preferably 15% by mass, still more preferably 20% by mass, and particularly preferably 30% by mass. When the content ratio of the monomer unit is 5% by mass or more, it is preferable in terms of binding property to a substrate and oxidation resistance. On the other hand, a more preferred upper limit is 92% by mass, a still more preferred upper limit is 80% by mass, and a particularly preferred upper limit is 60% by mass. It is preferable for the content ratio of the monomer to be 95% by mass or less because the adhesion to the substrate is improved.

When the acrylic polymer has a chain alkyl (meth) acrylate or cycloalkyl (meth) acrylate as a monomer unit, the total content thereof is preferably 100% by mass of the acrylic polymer. 3 to 92% by mass, more preferably 10 to 90% by mass, still more preferably 15 to 75% by mass, and particularly preferably 25 to 55% by mass. The content of these monomers is preferably 3% by mass or more from the viewpoint of improving oxidation resistance, and the content of 92% by mass or less is preferable because the binding property to the substrate is improved.
When the acrylic polymer has (meth) acrylic acid as a monomer unit, the content is preferably 0.1 to 5% by mass with respect to 100% by mass of the acrylic polymer. When the content ratio of the monomer is 0.1% by mass or more, the separator tends to improve the cushioning property in the swollen state, and when it is 5% by mass or less, the polymerization stability tends to be good. is there.
When the acrylic polymer has a crosslinkable monomer as a monomer unit, the content of the crosslinkable monomer in the acrylic polymer is preferably 0. 0% with respect to 100% by mass of the acrylic polymer. It is 01-10 mass%, More preferably, it is 0.1-5 mass%, More preferably, it is 0.1-3 mass%. When the content ratio of the monomer is 0.01% by mass or more, the electrolytic solution resistance is further improved, and when it is 10% by mass or less, a decrease in cushioning property in the swollen state can be further suppressed.

  The acrylic polymer is obtained, for example, by a usual emulsion polymerization method. There is no restriction | limiting in particular regarding the method of emulsion polymerization, A conventionally well-known method can be used.

  For example, in a dispersion system containing the above-mentioned monomer, surfactant, radical polymerization initiator, and other additive components used as necessary in an aqueous medium as a basic composition component, each of the above monomers is included. An acrylic polymer is obtained by polymerizing the monomer composition. In the polymerization, a method of making the composition of the monomer composition to be supplied constant throughout the entire polymerization process, and changing the morphological composition of the particles of the resin dispersion produced by sequentially or continuously changing the polymerization process Various methods can be used as needed. When the acrylic polymer is obtained by emulsion polymerization, for example, it may be in the form of an aqueous dispersion (latex) containing water and a particulate acrylic polymer dispersed in the water.

Examples of the surfactant include anionic surfactants such as sodium dodecylbenzenesulfonate and sodium dodecylsulfate, nonionic surfactants such as polyoxyethylene nonylphenyl ether and sorbitan monolaurate, or octadecylamine acetate. Cationic surfactants can be used.
Various surfactants include non-reactive surfactants and reactive surfactants, and both can be used.
It is preferable to use 0.1 to 5 parts by mass of the surfactant based on 100 parts by mass of the monomer composition. Surfactant is used individually by 1 type or in combination of 2 or more types.

The radical polymerization initiator is one that initiates addition polymerization of monomers by radical decomposition with heat or a reducing substance, and any of inorganic initiators and organic initiators can be used. As the radical polymerization initiator, a water-soluble or oil-soluble polymerization initiator can be used.
The radical polymerization initiator is preferably used in an amount of 0.05 to 2 parts by mass with respect to 100 parts by mass of the monomer composition. A radical polymerization initiator can be used individually by 1 type or in combination of 2 or more types.

Examples of the 3) polyvinyl alcohol-based resin include polyvinyl alcohol and polyvinyl acetate.
Examples of the above 4) fluorine-containing resin include polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and ethylene-tetrafluoro. Ethylene copolymer, etc.
Each is listed.

The thermoplastic polymer may be in the form of particles. When the thermoplastic polymer particles are in the form of particles, the average particle size is preferably 0.01 μm to 5 μm, more preferably 0.05 μm to 3 μm, and still more preferably 0.1 μm to 1 μm. When the average particle size of the thermoplastic polymer is within the above range, it becomes easier to adjust the maximum value of the high shear viscosity at a shear rate of 50000 s ⁻¹ or less of the slurry for pattern coating to 5 cps or more.

  The average particle diameter of the thermoplastic polymer can be controlled by adjusting the polymerization time, polymerization temperature, raw material composition ratio, raw material charging order, pH, etc. of the thermoplastic polymer.

(Glass transition point and melting point of thermoplastic polymer)
The thermoplastic polymer preferably has a glass transition point (Tg) or melting point (Tm) of −50 ° C. or higher, more preferably −40 ° C. or higher, still more preferably −20 ° C. or higher, and preferably 150 ° C. or lower. A thermoplastic polymer that is preferably 120 ° C. or lower, more preferably 80 ° C. or lower is included. When the glass transition point or the melting point is within the above range, the thermoplastic polymer on the porous substrate is easily deformed during hot pressing, and the adhesion area to the electrode as the adherend increases. Thereby, the adhesion between the porous substrate and the thermoplastic layer or the adhesion between the separator and the electrode becomes better.

  The melting point and glass transition point are determined from the DSC curve obtained by differential scanning calorimetry (DSC). Specifically, the melting point is the intersection of the baseline in the DSC curve and the tangent of the slope of the melting endothermic peak, and the glass transition point is the straight line obtained by extending the baseline on the low temperature side to the high temperature side in the DSC curve, and the glass transition It is determined by the intersection with the tangent at the inflection point of the step-like change part.

  In the present specification, “glass transition” refers to DSC in which a change in the amount of heat accompanying a change in the state of the polymer occurs on the endothermic side. “Baseline” refers to a DSC curve in a temperature region where no transition or reaction occurs in the test piece. “Peak” refers to a portion of the DSC curve until the curve leaves the baseline and returns to the baseline. The “step change” indicates a portion of the DSC curve until the curve moves away from the previous baseline and moves to a new baseline. A step change includes a combination of a peak and a step change. The “inflection point” indicates a point at which the gradient of the DSC curve of the step-like change portion is maximized. In other words, the inflection point can also be expressed as a point where an upwardly convex curve changes to a downwardly convex curve in a step-like change portion.

The Tg of the thermoplastic polymer can be adjusted as appropriate by changing, for example, the type of monomer used in the production of the thermoplastic polymer and the blending ratio of each monomer. The Tg of the thermoplastic polymer is determined from the homopolymer Tg generally indicated for each monomer used in its production (eg, described in “A WILEY-INTERSCIENCE PUBLICATION”) and the blending ratio of the monomers. It can be estimated roughly. For example, thermoplastic polymers that incorporate a high proportion of monomers such as styrene, methyl methacrylate, and acrylonitrile that give a polymer with a Tg of about 100 ° C. have a high Tg. Further, for example, a thermoplastic polymer containing a high proportion of monomers such as butadiene giving a Tg polymer of about -80 ° C, n-butyl acrylate and 2-ethylhexyl acrylate giving a Tg polymer of about -50 ° C. Has a low Tg. The Tg of the thermoplastic polymer can be estimated by the FOX formula (Formula 1 below). As the glass transition point of the thermoplastic polymer, the one measured by the method using the DSC is employed.
1 / Tg = W ₁ / Tg ₁ + W ₂ / Tg ₂ +... + W _i / Tg _i +... W _n / Tg _n (1)
{Wherein Tg (K) represents the Tg of the copolymer, Tg _i (K) represents the Tg of the homopolymer of each monomer i, and W _i represents the mass fraction of each monomer}.

The gel fraction of the thermoplastic polymer is not particularly limited, but is preferably 80% by mass or more, more preferably 85% by mass from the viewpoint of suppressing dissolution in the electrolyte and maintaining the strength of the thermoplastic polymer inside the battery. % Or more, more preferably 90% by mass or more. Here, the gel fraction is determined by measuring the toluene insoluble matter.
The gel fraction can be adjusted by changing the monomer component to be polymerized, the charging ratio of each monomer, and the polymerization conditions.

The thermoplastic polymer preferably has swelling properties with respect to the electrolytic solution from the viewpoint of battery characteristics such as cycle characteristics. The dried thermoplastic polymer (or thermoplastic polymer dispersion) is infiltrated with the electrolyte for a predetermined time, and the weight of the thermoplastic polymer (A) after washing is set to Wa, and A is placed in an oven at 150 ° C. for 1 hour. When the mass after standing is defined as Wb, the degree of swelling of the thermoplastic polymer with respect to the electrolytic solution can be calculated by the following formula. The swelling degree is preferably 10 times or less, more preferably 6 times or less, still more preferably 5 times or less, still more preferably 4.5 times or less, and particularly preferably 4 times or less. Further, the degree of swelling is preferably 1 time or more, and more preferably 2 times or more.
Swelling degree of thermoplastic polymer to electrolyte (times) = (Wa−Wb) ÷ Wb
In addition, when a polymer layer contains 2 or more types of copolymers, a swelling degree is taken as the weighted average of the swelling degree of each copolymer.

  The swelling property of the thermoplastic polymer in the separator of the present embodiment with respect to the electrolytic solution is a mixed solvent composed of a mixed solvent (volume ratio 1: 2) with ethylene carbonate (EC): ethyl methyl carbonate (EMC) as a model of the electrolytic solution. Alternatively, it is preferable to measure using a mixed solvent (mass ratio 2: 3) of ethylene carbonate (EC) and diethyl carbonate (DEC).

  It is also preferable that the thermoplastic polymer contains at least two thermoplastic polymers and has at least two glass transition points as a whole. In this case, at least one of Tg of the thermoplastic polymer is preferably less than 20 ° C., more preferably 15 ° C. or less, and further preferably -50 ° C. or more and 15 ° C. or less. Thereby, it is excellent in the adhesiveness of a coating layer and a porous base material, As a result, since a separator is excellent in the adhesiveness with an electrode, the rigidity and cycling characteristics of an electrical storage device improve. In order to improve the adhesion between the thermoplastic polymer and the porous substrate, improve the handling properties of the separator, and / or suppress the powder falling of the thermoplastic layer, Tg present in the region below 20 ° C. More preferably, it exists only in the region of −50 ° C. or more and 15 ° C. or less.

  When the thermoplastic polymer has at least two glass transition points, it is preferable that at least one of Tg of the thermoplastic polymer is 20 ° C. or higher, more preferably 20 ° C. or higher and 150 ° C. or lower, and still more preferably. It exists in the region of 30 ° C. or higher and 120 ° C. or lower, more preferably 40 ° C. or higher and 80 ° C. or lower. When the glass transition temperature exists in the above range, the handling property of the separator becomes better. Furthermore, it is possible to further improve the adhesion between the electrode and the separator that are expressed by pressurization during battery production.

  A thermoplastic polymer having at least two glass transition points can be obtained, for example, by blending two or more thermoplastic polymers, using a thermoplastic polymer having a core-shell structure, or the like. In this specification, the “core-shell structure” means that the polymer has a form of a double structure of a central portion (core) and an outer shell portion (shell) covering the core, and the polymer composition of the core and the polymer composition of the shell. Refers to different polymers. By combining a high Tg polymer and a low Tg polymer in a polymer blend and core-shell structure, the glass transition point of the entire thermoplastic polymer can be controlled, and multiple functions can be imparted to the entire thermoplastic polymer. .

  In the case of a polymer blend, the stickiness resistance and the basic property can be reduced by blending two or more kinds of a polymer having a glass transition point in a region having a glass transition point of 20 ° C. or more and a polymer having a glass transition point in a region having a glass transition point of less than 20 ° C. Both adhesion to the material can be achieved. As a mixing ratio in the case of blending, a mass ratio of a polymer having a glass transition point of 20 ° C. or more and a polymer having a glass transition point of less than 20 ° C. is preferably 0.1: 99. .9 to 99.9: 0.1, more preferably 5:95 to 95: 5, still more preferably 50:50 to 95: 5, and still more preferably 60:40 to 90:10.

  In the case of the core-shell structure, the adhesiveness and compatibility with other materials (for example, a polyolefin porous substrate) can be adjusted by changing the type of polymer of the shell. By changing the polymer type of the core, for example, the adhesion of the polymer to the electrode after hot pressing can be adjusted. In the case of the core-shell structure, viscoelasticity can be controlled by combining a highly viscous polymer and a highly elastic polymer. In the case of a thermoplastic polymer having a core-shell structure, the glass transition point of the shell polymer is not limited, but is preferably 20 ° C. or higher and 150 ° C. or lower, more preferably 30 ° C. or higher and 120 ° C. or lower. The glass transition point of the core polymer is not limited, but is preferably less than 20 ° C, more preferably 15 ° C or less, and still more preferably -50 ° C or more and 15 ° C or less.

<Dispersion medium / solvent>
The slurry for pattern coating of this embodiment contains a thermoplastic polymer and its dispersion medium or solvent. In the present specification, “solvent” refers to a medium that can dissolve substantially all of the thermoplastic polymer, and “dispersion medium” refers to a medium that can disperse at least a portion of the thermoplastic polymer without dissolving it. Say. The dispersion medium is preferably a poor solvent for the thermoplastic polymer.

  Although it does not specifically limit as a solvent or a dispersion medium contained in the slurry for pattern coating, Water is preferable. When applying the pattern coating slurry to the base material, if the pattern coating slurry gets into the base material, the thermoplastic polymer is obtained by blocking the surface and the inside of the hole of the base material. The permeability of the separator tends to decrease. In this regard, when water is used as the solvent or dispersion medium for the pattern coating slurry, it becomes difficult for the pattern coating slurry to enter the substrate, and the thermoplastic polymer is mainly present on the outer surface of the substrate. It becomes easy to do. Therefore, it is preferable because a decrease in permeability of the obtained separator can be more effectively suppressed. Further, as this solvent or dispersion medium, only water may be used, or water and another solvent or dispersion medium compatible with water may be used in combination. Examples of the solvent or dispersion medium that can be used in combination with water include ethanol and methanol.

  When water is used as the medium, the pH is preferably adjusted in the range of 5 to 12 in order to maintain long-term dispersion stability. For pH adjustment, amines such as ammonia, sodium hydroxide, potassium hydroxide and dimethylaminoethanol are preferably used, and it is more preferable to adjust pH with ammonia (water) or sodium hydroxide.

<Other ingredients>
The pattern coating slurry of the present embodiment may be composed of a thermoplastic polymer and a dispersion medium or solvent, and may contain additives other than the thermoplastic polymer and the dispersion medium. Examples of the additive include a dispersant such as a surfactant, a thickener, and a pH adjuster. As the surfactant, for example, a low molecular weight dispersant, for example, a monomer ( _Cii ) having a plurality of ammonium salts or alkali metal salts of carboxylic acid, and a non-polymerizable compound having a plurality of ammonium salts or alkali metal salts of carboxylic acid ( Examples thereof include sodium alginate and sodium hyaluronate).

In order to adjust the maximum value of the high shear viscosity at a shear rate of 50000 s ⁻¹ or less of the slurry for pattern coating to 5 cps or more, a dispersant such as a surfactant, a thickener, a wetting agent, an antifoaming agent, an acid, Various additives such as a pH adjusting agent containing an alkali may be added. These additives are preferably those that can be removed upon solvent removal or plasticizer extraction. However, if they are electrochemically stable in the range of use of the lithium ion secondary battery and do not inhibit the battery reaction, May remain. Preferred additives preferably include a surfactant or a thickener, and further both.

Surfactants include anionic surfactants such as sodium dodecylbenzenesulfonate and sodium dodecylsulfate, nonionic surfactants such as polyoxyethylene nonylphenyl ether and sorbitan monolaurate, and cations such as octadecylamine acetate. Can be used.
When having an ion-dissociable acid group, for example, a carboxyl group, a sulfonic acid group, an amino acid group, and a maleic acid group, or when having an ion-dissociating acid base, for example, a carboxylate group, a sulfonate group, and maleic acid Those containing a plurality of bases and the like are preferred. Specifically, as the ion dissociable organic dispersant, polycarboxylate, polyacrylate, and polymethacrylate are more preferable. An ion dissociative organic dispersing agent may be used individually by 1 type, and may use 2 or more types together. By adjusting the type and addition amount of the surfactant, it becomes easier to make the surface tension 50 to 100.

Examples of the thickener include polyethylene glycols, polyethers, celluloses, polysaccharides, polyacrylamides, poly N-pyrrolidones, polyvinyl alcohols, modified polyacrylic acid, oxidized starch, phosphate starch, and modified starch. Etc. The blending ratio of the thickener is preferably 5% by mass or less, more preferably 3% by mass or less, based on the total amount of the slurry for pattern coating. The thickener is appropriately selected from the viewpoint of the viscosity of the slurry, pot life and particle size distribution. A thickener may be used alone or in combination of two or more. By adjusting the type and additives of the thickener, the maximum value of the high shear viscosity at a shear rate of 50000 s ⁻¹ or less of the pattern coating slurry can be 5 cps or more.

<< Method for producing slurry for pattern coating >>
The manufacturing method of the slurry for pattern coating of this embodiment is not limited. For example, a slurry for pattern coating can be produced by mixing components such as a thermoplastic polymer and a dispersion medium by any means and dispersing the components in the dispersion medium. The dispersion method is not limited, but for example, ball mill, bead mill, planetary ball mill, vibrating ball mill, sand mill, colloid mill, attritor, roll mill, high-speed impeller dispersion, disperser, homogenizer, high-speed impact mill, ultrasonic dispersion, stirring blade, etc. And mechanical stirring.

  It is preferable to synthesize a thermoplastic polymer by emulsion polymerization and use an emulsion obtained by emulsion polymerization as a slurry for pattern coating. The method and conditions for emulsion polymerization are not limited.

<< Separator for electricity storage device >>
The separator for an electricity storage device of this embodiment has a pattern coating formed from the slurry for pattern coating of this embodiment on at least one surface of the polyolefin porous substrate. In one embodiment, the separator for an electricity storage device may have a pattern coating on both surfaces of the polyolefin porous substrate. The pattern coating may be formed on one side or both sides of the substrate, or may be formed only on a part of one side or both sides so that the separator has high ion permeability.

<Pattern coating>
The shape of the pattern coating is not limited, and examples thereof include patterns such as a line shape, a diagonal line shape, a stripe shape, a dot shape, a lattice shape, a stripe shape, and a turtle shell shape. The pattern coating is preferably an oblique line pattern, a stripe pattern, and a dot pattern, more preferably a dot pattern. In this specification, “striped pattern” or “striped” means a pattern having a plurality of lines substantially parallel to the MD direction (machine direction) of a polyolefin substrate. In the specification of the present application, the “diagonal pattern” or “oblique pattern” means a pattern having a plurality of lines substantially parallel to a direction other than the MD direction of the polyolefin substrate. In the specification of the present application, “dot pattern” or “dot shape” means that a portion where a thermoplastic polymer is not present and a portion where a thermoplastic polymer is present are on a polyolefin porous substrate (sea: A portion where a thermoplastic polymer is not present, an island: a portion where a thermoplastic polymer is present.).

The pattern coating being a dot pattern provides one or more of the following advantages:
Since the separator can ensure the permeability of the separator due to the absence of the thermoplastic polymer, a high output battery can be obtained; and since the irregularities are formed on the surface of the substrate, the electrolyte can easily enter during the battery manufacturing process. Liquidity is good (that is, tact time in the battery manufacturing process is shortened).

  The dimension of the pattern coating is not limited, but preferably has a fine structure, for example, about several mm to several μm. For example, the pattern coating preferably has a structure of 2000 μm or less, more preferably 1000 μm or less, still more preferably 500 μm or less, and still more preferably 200 μm or less. In the specification of the present application, the pattern coating has, for example, “having a structure of 2000 μm or less”, for design of the pattern coating, at least a part of dimensions such as the width, length, interval, and radius of curvature of the pattern is 2000 μm. It means to control as follows. When the dimension of the pattern coating is within the above range, the advantage according to the present invention, that is, the pattern coating property becomes more remarkable.

  When the pattern coating is a dot pattern, the dot diameter is preferably 10 μm or more and 1000 μm or less, more preferably 50 μm or more and 800 μm or less, and further preferably 100 μm or more and 500 μm or less. The “dot diameter” means a diameter when the dot is circular, and means a shortest diameter passing through the center of gravity when the dot is not circular. The interval between dots is preferably 5 μm or more and 2000 μm or less, more preferably 10 μm or more and 1500 μm or less, still more preferably 25 μm or more and 1000 μm or less, and even more preferably 50 μm or more and 500 μm or less. The “interval between dots” means an interval between centers when the dots are circular, and means a distance between the centers of gravity when the dots are not circular.

  When the pattern coating is diagonal or striped, the line width is preferably 5 μm or more and 500 μm or less, more preferably 20 μm or more and 400 μm or less, still more preferably 35 μm or more and 300 μm or less, and even more preferably 50 μm or more and 200 μm or less. is there. The distance between the lines is preferably 5 μm or more and 2000 μm or less, more preferably 10 μm or more and 1500 μm or less, still more preferably 25 μm or more and 1000 μm or less, and even more preferably 50 μm or more and 500 μm or less.

  The area occupation ratio of the thermoplastic polymer on the polyolefin porous substrate is preferably 5% or more and less than 80%, more preferably 15% or more and 70% or less, and further preferably 20% or more and 60% or less. “Area occupancy” means the area ratio of the portion where the thermoplastic polymer is present to the total area of one side of the substrate when the pattern coating is disposed on one side of the polyolefin porous substrate. When pattern coating is arrange | positioned on both surfaces of the polyolefin porous base material, it means the area ratio of the part in which a thermoplastic polymer exists with respect to the total area of both surfaces of a base material.

  By adjusting to the area occupancy rate, the liquid injection property in the electrolytic solution injection process is improved. Furthermore, since the pores on the surface of the polyolefin porous substrate are maintained, the rate characteristics when used as a separator for an electricity storage device are excellent. The liquid injection property of the separator for an electricity storage device is an index indicating the ease with which the electrolytic solution enters during the battery manufacturing process. A higher liquid injection property is preferable because the tact time in the battery manufacturing process is shortened.

  The thickness of the pattern coating is preferably 0.01 μm or more, more preferably 0.1 μm or more, further preferably 6 μm or less, still more preferably 5 μm or less, and particularly preferably 4 μm or less. When the pattern coating is disposed on both sides of the porous substrate, the thickness of the thermoplastic layer means the thickness per side of the porous substrate. If the thickness of the pattern coating is 0.01 μm or more, it is easy to migrate the thermoplastic polymer to the surface of the thermoplastic layer when the separator is pressed. As a result, the thermoplastic layer functions as an adhesive layer and the separator. The adhesive strength with the electrode and the rigidity of the electricity storage device can be ensured. If the thickness of the thermoplastic layer is 6 μm or less, it is preferable because a decrease in the ion permeability of the separator can be suppressed.

<Polyolefin porous substrate>
The polyolefin porous substrate in the present invention will be described.
As the polyolefin porous substrate, a polyolefin microporous membrane having small electron conductivity, ionic conductivity, high resistance to an organic solvent, and a fine pore diameter is preferable.

  The polyolefin porous substrate is formed from a polyolefin resin composition in which the polyolefin resin occupies 50% by mass or more and 100% by mass or less of the resin component constituting the porous film from the viewpoint of improving the shutdown performance of the separator for the electricity storage device. A porous film is preferred. The proportion of the polyolefin resin in the polyolefin resin composition is more preferably 60% by mass or more and 100% by mass or less, and further preferably 70% by mass or more and 100% by mass or less.

The polyolefin resin contained in the polyolefin resin composition is not particularly limited. For example, α- selected from ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene and the like. Examples include homopolymers, copolymers, multistage polymers and the like obtained using olefins as monomers. These polyolefin resins may be used alone or in admixture of two or more.
Among these, from the viewpoint of the shutdown characteristics of the electricity storage device separator, the polyolefin resin is preferably polyethylene, polypropylene, a copolymer thereof, or a mixture thereof.
Specific examples of polyethylene include low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultra high molecular weight polyethylene, etc.
Specific examples of polypropylene include isotactic polypropylene, syndiotactic polypropylene, atactic polypropylene, etc.
Specific examples of the copolymer include an ethylene-propylene random copolymer and ethylene propylene rubber.

Among these, from the viewpoint of satisfying the required performance of the low melting point and high strength of the separator for an electricity storage device, it is preferable to use polyethylene, particularly high density polyethylene as the polyolefin resin. In the present invention, high density polyethylene means polyethylene having a density of 0.942 to 0.970 g / cm ³ . In the present invention, the density of polyethylene refers to a value measured according to the D) density gradient tube method described in JIS K7112 (1999).

  From the viewpoint of improving the heat resistance of the polyolefin porous substrate, it is preferable to use a mixture of polyethylene and polypropylene as the polyolefin resin. In this case, the ratio of polypropylene to the total polyolefin resin in the polyolefin resin composition is preferably 1 to 35% by mass, more preferably 3 to 20% by mass from the viewpoint of achieving both heat resistance and a good shutdown function. %, More preferably 4 to 10% by mass.

  Arbitrary additives can be contained in the polyolefin resin composition. Examples of additives include polymers other than polyolefin resins; inorganic fillers; phenol-based, phosphorus-based and sulfur-based antioxidants; metal soaps such as calcium stearate and zinc stearate; ultraviolet absorbers; light stabilizers An antistatic agent, an antifogging agent, a coloring pigment, and the like. The total addition amount of these additives is preferably 20 parts by mass or less with respect to 100 parts by mass of the polyolefin resin from the viewpoint of improving the shutdown performance, more preferably 10 parts by mass or less, and still more preferably 5 parts by mass. Or less.

The porous membrane has a porous structure in which a large number of very small pores are gathered to form a dense communication hole. Therefore, the porous membrane has excellent ion conductivity as well as good withstand voltage characteristics and high strength. It has the characteristics.
The polyolefin porous substrate may be a single layer film made of the above-described material or a laminated film.

  The film thickness of the polyolefin porous substrate is preferably from 0.1 μm to 100 μm, more preferably from 1 μm to 50 μm, still more preferably from 3 μm to 25 μm. From the viewpoint of mechanical strength, 0.1 μm or more is preferable, and from the viewpoint of increasing the capacity of the battery, 100 μm or less is preferable. The film thickness of the porous film can be adjusted by controlling the die lip interval, the draw ratio in the drawing step, and the like.

The average pore diameter of the polyolefin porous substrate is preferably 0.03 μm or more and 0.70 μm or less, more preferably 0.04 μm or more and 0.20 μm or less, still more preferably 0.05 μm or more and 0.10 μm or less, and particularly preferably 0.00. It is 06 μm or more and 0.09 μm or less. From the viewpoint of high ion conductivity and withstand voltage, 0.03 to 0.70 μm is preferable. The average pore diameter of the polyolefin porous substrate can be measured by the measurement method described later.
The average pore size is adjusted by controlling one or more selected from the composition ratio, the cooling rate of the extruded sheet, the stretching temperature, the stretching ratio, the heat setting temperature, the stretching ratio during heat setting, the relaxation rate during heat setting, and the like. can do.

The porosity of the polyolefin porous substrate is preferably 25% or more and 95% or less, more preferably 30% or more and 65% or less, and still more preferably 35% or more and 55% or less. 25% or more is preferable from the viewpoint of improving ion conductivity, and 95% or less is preferable from the viewpoint of withstand voltage characteristics. The porosity of the polyolefin porous substrate can be measured by the method described later.
The porosity of the polyolefin porous substrate is selected from the mixing ratio of the polyolefin resin composition and the plasticizer, the stretching temperature, the stretching ratio, the heat setting temperature, the stretching ratio during heat setting, the relaxation rate during heat setting, and the like. It can be adjusted by controlling one or more.

  The viscosity average molecular weight of the polyolefin porous substrate is preferably 30,000 or more and 12,000,000 or less, more preferably 50,000 or more and less than 2,000,000, still more preferably 100,000 or more and 1, Less than 1,000,000. A viscosity average molecular weight of 30,000 or more is preferred because the melt tension during melt molding increases, moldability is improved, and the strength tends to increase due to entanglement between polymers. On the other hand, a viscosity average molecular weight of 12,000,000 or less is preferable because uniform melt kneading is facilitated and the formability of the sheet, particularly thickness stability, tends to be excellent. When the viscosity average molecular weight is less than 1,000,000, it is preferable because the pores of the polyolefin porous substrate tend to be blocked when the temperature of the electricity storage device separator rises, and a good shutdown function tends to be obtained. The viscosity average molecular weight of the polyolefin porous substrate can be measured by the method described later.

<Physical properties of separators for electricity storage devices>
The separator for an electricity storage device of this embodiment has a pattern coating formed from the slurry for pattern coating of this embodiment on at least one surface of a polyolefin porous substrate, thereby ion permeability and adhesion to an electrode. Excellent in properties, blocking properties, and liquid injection properties.

(Ion permeability)
The ion permeability of the electricity storage device separator can be evaluated by the air permeability of the separator as described in the Examples section. The air permeability of the electricity storage device separator is preferably 10 to 10,000 seconds / 100 cc, more preferably 10 to 1,000 seconds / 100 cc, and further preferably 50 to 500 seconds / 100 cc. When the air permeability is within the above range, a large ion permeability is exhibited when the separator is applied to a lithium ion secondary battery.

(Film thickness)
The final film thickness of the separator is preferably 2 μm to 200 μm, more preferably 5 μm to 100 μm, and still more preferably 7 μm to 30 μm. If the film thickness is 2 μm or more, the mechanical strength tends to be sufficient. On the other hand, if it is 200 μm or less, the occupied volume of the separator is reduced, which tends to be advantageous in terms of increasing the capacity of the battery.

(Adhesiveness)
The adhesiveness of the electricity storage device separator can be evaluated by the peel strength between the separator and the electrode, as described in the Examples section. The separator for an electricity storage device is measured as a peel strength when the separator-containing layer containing the thermoplastic polymer is a positive electrode at a pressure of 1 MPa at 100 ° C. for 5 seconds (hereinafter also referred to as “heat peel strength”). Is done. As the peel strength of the separator, the value of the heat peel strength is preferably 2 mN / mm or more. A separator having a heat peel strength in the above range is preferable in terms of excellent adhesion between the electrode and the separator when applied to an electricity storage device described later. About the measuring method of said heat peeling strength, it describes concretely in the below-mentioned Example.

  Further, the separator in this embodiment is a 90 ° peel strength (hereinafter also referred to as “room temperature peel strength”) after two separators are stacked and pressed in the stacking direction at a temperature of 25 ° C. and a pressure of 5 MPa for 3 minutes. Is preferably 20 mN / mm or less, and more preferably 10 mN / mm or less. By satisfying this requirement, it is possible to obtain an effect that the separator is further excellent in blocking resistance and the handling property is further improved.

<< Method for producing separator for electricity storage device >>
The manufacturing method of the separator for the electricity storage device is:
Pattern coating slurry on at least one surface of the polyolefin porous substrate;
Drying the dispersion medium from the slurry for pattern coating,
The pattern coating slurry includes a thermoplastic polymer, a dispersion medium or a solvent,
The pattern coating slurry is preferably a method in which the maximum value of the high shear viscosity at a shear rate of 50000 s ⁻¹ or less is 5 cps or more.

<Method for producing polyolefin porous substrate>
There is no restriction | limiting in particular as a method of manufacturing a polyolefin porous base material, A well-known manufacturing method is employable. For example,
(1) A method in which a polyolefin resin composition and a pore-forming material are melt-kneaded and formed into a sheet, and then stretched as necessary, and then the pore-forming material is extracted to make it porous.
(2) A method in which a polyolefin resin composition is melt-kneaded and extruded at a high draw ratio, and then made porous by exfoliating the polyolefin crystal interface by heat treatment and stretching,
(3) A method in which a polyolefin resin composition and an inorganic filler are melt-kneaded and formed on a sheet, and thereafter the surface is made porous by peeling the interface between the polyolefin and the inorganic filler by stretching,
(4) After dissolving the polyolefin resin composition, it is immersed in a poor solvent for polyolefin to solidify the polyolefin, and at the same time remove the solvent to make it porous.
Etc.

  Hereinafter, as an example of a method for producing a polyolefin porous substrate, a method for extracting a pore-forming material after melt-kneading a polyolefin resin composition and a pore-forming material to form a sheet will be described.

  First, the polyolefin resin composition and the hole forming material are melt-kneaded. Examples of the melt-kneading method include, for example, polyolefin resin and other additives as required, while using a resin kneading apparatus such as an extruder, a kneader, a lab plast mill, a kneading roll, and a Banbury mixer while heating and melting the resin component. A method of introducing and kneading the pore-forming material at an arbitrary ratio is mentioned.

  Examples of the pore forming material include a plasticizer, an inorganic material, or a combination thereof.

Although it does not specifically limit as a plasticizer, It is preferable to use the non-volatile solvent which can form a uniform solution above melting | fusing point of polyolefin. Specific examples of such a non-volatile solvent include hydrocarbons such as liquid paraffin and paraffin wax; esters such as dioctyl phthalate and dibutyl phthalate; higher alcohols such as oleyl alcohol and stearyl alcohol. . In particular, liquid paraffin is preferable from the viewpoint of compatibility with multiple components and uniformity during stretching.
As a plasticizer mixing method, it is preferable that the polyolefin resin, other additives, and the plasticizer are pre-kneaded in advance at a predetermined ratio using a Henschel mixer or the like before being added to the resin kneading apparatus. is there. More preferably, in the pre-kneading, only a part of the plasticizer is added, and the remaining plasticizer is side-fed to the resin kneader while being appropriately heated and kneaded. By using such a kneading method, the dispersibility of the plasticizer is increased, and when the sheet-shaped molded body of the melt-kneaded product of the resin composition and the plasticizer is stretched in a later step, a high magnification is obtained without breaking the film. It will be possible to stretch the film.

  The ratio of the polyolefin resin composition and the plasticizer is not particularly limited as long as they can be uniformly melt-kneaded and formed into a sheet shape. For example, the mass fraction of the plasticizer in the composition comprising the polyolefin resin composition and the plasticizer is preferably 20 to 90 mass%, more preferably 30 to 80 mass%. When the mass fraction of the plasticizer is 90% by mass or less, the melt tension at the time of melt molding tends to be sufficient for improving moldability. On the other hand, when the mass fraction of the plasticizer is 20% by mass or more, even when the mixture of the polyolefin resin composition and the plasticizer is stretched at a high magnification, the polyolefin molecular chain is not broken, and the pore structure is uniform and fine. This is preferable because it is easy to form and the strength is easily increased.

  The inorganic material is not particularly limited. For example, oxide ceramics such as alumina, silica (silicon oxide), titania, zirconia, magnesia, ceria, yttria, zinc oxide, iron oxide; silicon nitride, titanium nitride, nitriding Nitride ceramics such as boron; silicon carbide, calcium carbonate, aluminum sulfate, aluminum hydroxide, potassium titanate, talc, kaolin clay, kaolinite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amicite, bentonite , Ceramics such as asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; and glass fibers. These may be used alone or in combination of two or more. Among these, silica, alumina, or titania is preferable from the viewpoint of electrochemical stability, and silica is particularly preferable from the viewpoint of easy extraction.

  The ratio between the polyolefin resin composition and the inorganic material is preferably 5% by mass or more, more preferably 10% by mass or more, based on the total mass, from the viewpoint of obtaining good separability. From the viewpoint of ensuring high strength of the polyolefin porous substrate, it is preferably 99% by mass or less, and more preferably 95% by mass or less, based on the total mass of the polyolefin resin composition and the inorganic material.

  Next, the melt-kneaded product is formed into a sheet shape. As a method for producing a sheet-like molded product, for example, a melt-kneaded product is extruded into a sheet shape via a T-die or the like, and brought into contact with a heat conductor to cool to a temperature sufficiently lower than the crystallization temperature of the resin component. And then solidify. Examples of the heat conductor used for cooling and solidifying include metals, water, air, and plasticizers. Among these, it is preferable to use a metal roll because of its high heat conduction efficiency. In addition, when the extruded kneaded product is brought into contact with a metal roll, sandwiching between the rolls further increases the efficiency of heat conduction, and the sheet is oriented to increase the film strength, and the surface smoothness of the sheet is also improved. Therefore, it is more preferable. The die lip interval when the melt-kneaded product is extruded from the T die into a sheet is preferably 200 μm or more and 3,000 μm or less, and more preferably 500 μm or more and 2,500 μm or less. When the die lip interval is 200 μm or more, the mess and the like are reduced, and there is little influence on the film quality such as streaks and defects, and the risk of film breakage and the like in the subsequent stretching process can be reduced. On the other hand, when the die lip interval is 3,000 μm or less, the cooling rate is fast and cooling unevenness can be prevented, and the thickness stability of the sheet can be maintained.

  Moreover, you may roll a sheet-like molded object. Rolling can be performed, for example, by a pressing method using a double belt press or the like. By performing rolling, the orientation of the surface layer portion can be particularly increased. The rolling surface magnification is preferably more than 1 and 3 or less, more preferably more than 1 and 2 or less. When the rolling ratio exceeds 1, the plane orientation increases and the film strength of the finally obtained porous film tends to increase. On the other hand, when the rolling ratio is 3 times or less, the orientation difference between the surface layer portion and the center is small, and a uniform porous structure tends to be formed in the thickness direction of the film.

Next, the pore-forming material can be removed from the sheet-like molded body to obtain a porous film. As a method for removing the hole forming material, for example, there may be mentioned a method of sufficiently drying after extracting the hole forming material by immersing the sheet-like molded body in an extraction solvent. The method for extracting the hole forming material may be either a batch type or a continuous type. In order to suppress the shrinkage of the porous film, it is preferable to constrain the end of the sheet-like molded body during a series of steps consisting of immersion and drying.
When removing the pore-forming material from the sheet-like molded body, the residual amount of the pore-forming material in the porous membrane is preferably less than 1% by mass with respect to the mass of the entire porous membrane.

The extraction solvent used for extracting the pore-forming material should be a poor solvent for the pore-forming material, a good solvent for the pore-forming material, and a boiling point lower than the melting point of the pore-forming material. Is preferred. As such an extraction solvent,
When a polyolefin resin is used as the pore-forming material, for example, hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane; hydrofluoroether, hydrofluorocarbon, etc. Non-chlorinated halogenated solvents; alcohols such as ethanol and isopropanol; ethers such as diethyl ether and tetrahydrofuran; ketones such as acetone and methyl ethyl ketone;
When an inorganic material is used as the pore-forming material, for example, an aqueous solution such as sodium hydroxide or potassium hydroxide is used.
Each can be used as an extraction solvent.

It is preferable to stretch the sheet-like molded body or porous film. Stretching may be performed before extracting the hole forming material from the sheet-shaped molded body, or may be performed on the porous film obtained by extracting the hole forming material from the sheet-shaped molded body. Further, it may be performed before and after extracting the hole forming material from the sheet-like molded body.
As the stretching treatment, either uniaxial stretching or biaxial stretching can be suitably used. From the viewpoint of improving the strength and the like of the obtained porous film, biaxial stretching is preferred. In particular, when the sheet-like molded body is stretched at a high magnification in the biaxial direction, the molecules are oriented in the plane direction, and the finally obtained porous film is difficult to tear and has high puncture strength. Examples of the stretching method include simultaneous biaxial stretching, sequential biaxial stretching, multistage stretching, and multiple stretching. Simultaneous biaxial stretching is preferable from the viewpoints of improvement of puncture strength, uniformity of stretching, and shutdown property. Further, from the viewpoint of controllability of plane orientation, successive biaxial stretching is preferable.

  The draw ratio is preferably in the range of 20 times to 100 times, and more preferably in the range of 25 times to 70 times, as the surface magnification. The stretching ratio in each axial direction is preferably in the range of 4 to 10 times in MD, 4 to 10 times in TD; 5 to 8 times in MD, 5 to 8 times in TD More preferably, it is the range. When the total area magnification is 20 times or more, there is a tendency that sufficient strength can be imparted to the obtained porous film. On the other hand, when the total area magnification is 100 times or less, film breakage in the stretching process is prevented and high productivity is achieved. Tends to be obtained.

  It is preferable to heat-treat the porous film for the purpose of heat setting from the viewpoint of suppressing shrinkage. Examples of the heat treatment method include one or more of a stretching operation for adjusting physical properties and a relaxation operation for reducing stretching stress. The relaxation operation may be performed after the stretching operation. These heat treatments can be performed using a tenter or a roll stretching machine.

The stretching operation may be performed by stretching at least 1.1 times, more preferably 1.2 times or more in one or more directions of the MD and TD of the membrane, to further increase the porosity with high strength and high porosity. It is preferable from the viewpoint of obtaining a film.
The relaxation rate in the relaxation operation (a value obtained by dividing the dimension of the film after the relaxation operation by the dimension of the film before the relaxation operation) is 1.0 or less in one or more directions of MD and TD of the film. Is preferably 0.97 or less, and more preferably 0.95 or less. The relaxation rate is preferably 0.5 or more from the viewpoint of film quality. The relaxation operation may be performed in both directions of MD and TD, or may be performed for only one of MD and TD.
The stretching and relaxation operations after this plasticizer extraction are preferably performed at TD. The temperature in the stretching and relaxation operation is preferably lower than the melting point of the polyolefin resin (hereinafter also referred to as “Tm”), and more preferably in the range of 1 ° C. to 25 ° C. lower than Tm. When the temperature in the stretching and relaxation operation is in the above range, it is preferable from the viewpoint of the balance between the reduction in thermal shrinkage and the porosity.

<< Porous layer containing inorganic filler and resin binder >>
The separator for an electricity storage device of this embodiment may include a porous layer containing an inorganic filler and a resin binder in addition to pattern coating formed on at least one surface of a polyolefin porous substrate. Hereinafter, the porous layer containing an inorganic filler and a resin binder will be described.

<Inorganic filler>
The inorganic filler used in the porous layer is not particularly limited, but is preferably one that has high heat resistance and electrical insulation and is electrochemically stable within the range of use of the lithium ion secondary battery.
As an inorganic filler, an aluminum compound, a magnesium compound, and another compound are mentioned, for example.
Examples of the aluminum compound include aluminum oxide, aluminum silicate, aluminum hydroxide, aluminum hydroxide oxide, sodium aluminate, aluminum sulfate, aluminum phosphate, and hydrotalcite.
Examples of the magnesium compound include magnesium sulfate and magnesium hydroxide.
Other compounds include, for example, oxide ceramics, nitride ceramics, clay minerals, silicon carbide, calcium carbonate, barium titanate, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, silica sand, glass Examples thereof include fibers. Examples of oxide ceramics include silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, iron oxide, and the like. Examples of nitride ceramics include silicon nitride, titanium nitride, and boron nitride. Examples of the clay mineral include talc, montmorillonite, sericite, mica, amicite, bentonite and the like.
These may be used alone or in combination.

  Among these, at least one selected from the group consisting of aluminum oxide, aluminum hydroxide oxide, and aluminum silicate is preferable from the viewpoint of electrochemical stability and heat resistance. Specific examples of aluminum oxide include alumina. Specific examples of the aluminum hydroxide oxide include boehmite. Specific examples of aluminum silicate include kaolinite, dickite, nacrite, halloysite, and pyrophyllite.

  As the aluminum oxide, alumina is more preferable from the viewpoint of electrochemical stability. By adopting particles mainly composed of alumina as the inorganic filler constituting the porous layer, it is possible to realize a very lightweight porous layer while maintaining high permeability. Furthermore, even when the porous layer thickness is thinner, thermal shrinkage of the porous film at a high temperature is suppressed, and excellent heat resistance tends to be exhibited. Alumina has many crystal forms such as α-alumina, β-alumina, γ-alumina, and θ-alumina, and any of them can be suitably used. Of these, α-alumina is most preferred because it is thermally and chemically stable.

  As the aluminum hydroxide oxide, boehmite is more preferable from the viewpoint of preventing internal short circuit due to generation of lithium dendrite. By adopting particles mainly composed of boehmite as the inorganic filler constituting the porous layer, a very lightweight porous layer can be realized while maintaining high permeability. Furthermore, even when the porous layer thickness is thinner, thermal shrinkage of the porous film at a high temperature is suppressed, and excellent heat resistance tends to be exhibited. Synthetic boehmite that can reduce ionic impurities that adversely affect the characteristics of the storage element is more preferable.

  Among aluminum silicates, kaolinite (hereinafter, also referred to as kaolin) mainly composed of kaolin mineral is preferable from the viewpoints of lightness and air permeability. Kaolin includes wet kaolin and calcined kaolin obtained by calcining it. Of these, calcined kaolin is particularly preferred from the viewpoint of electrochemical stability, since impurities are removed in addition to the release of crystal water during the calcining treatment. By adopting particles mainly composed of calcined kaolin as the inorganic filler constituting the porous layer, it is possible to realize a very lightweight porous layer while maintaining high permeability. Furthermore, even when the porous layer thickness is thinner, thermal shrinkage of the porous film at a high temperature is suppressed, and excellent heat resistance tends to be exhibited.

  The average particle size of the inorganic filler is preferably 0.1 μm or more and 10.0 μm or less, more preferably 0.2 μm or more and 5.0 μm or less, and further preferably 0.4 μm or more and 3.0 μm or less. preferable. Adjusting the average particle size of the inorganic filler to the above range is preferable from the viewpoint of increasing the air permeability and suppressing thermal shrinkage at high temperatures.

  The particle size distribution of the inorganic filler is preferably as follows. The minimum particle size is preferably 0.02 μm or more, more preferably 0.05 μm or more, and further preferably 0.1 μm or more. The maximum particle size is preferably 20 μm or less, more preferably 10 μm or less, and even more preferably 7 μm or less. The ratio of the maximum particle size / average particle size is preferably 50 or less, more preferably 30 or less, and still more preferably 20 or less. Adjusting the particle size distribution of the inorganic filler to the above range is preferable from the viewpoint of suppressing thermal shrinkage at high temperatures. The particle size distribution of the inorganic filler may further have one or more particle size peaks between the maximum particle size and the minimum particle size. As a method for adjusting the particle size distribution of the inorganic filler, for example, a method of pulverizing the inorganic filler using a ball mill, a bead mill, a jet mill or the like to adjust the particle size distribution to a desired particle size distribution, a blend after adjusting fillers having a plurality of particle size distributions And the like.

  Examples of the shape of the inorganic filler include a plate shape, a scale shape, a polyhedron, a needle shape, a columnar shape, a spherical shape, a spindle shape, and a lump shape. A plurality of inorganic fillers having the above shapes may be used in combination. Among these, from the viewpoint of improving permeability, one or more shapes selected from the group consisting of a plate shape, a scale shape, and a polyhedron are preferable.

  The proportion of the inorganic filler in the porous layer can be appropriately determined from the viewpoints of permeability and heat resistance. The proportion is preferably 50% by mass or more, more preferably 70% by mass or more, further preferably 80% by mass or more, particularly preferably 95% by mass or more, and most preferably 97% by mass or more. . The ratio is preferably less than 100% by mass, more preferably 99.99% by mass or less, still more preferably 99.9% by mass or less, and particularly preferably 99% by mass or less.

<Resin binder>
The resin binder is a resin that plays the role of binding the above-described inorganic fillers to each other. In addition to this, a resin that plays a role in binding the inorganic filler and the porous film to each other is preferable.
As the type of resin binder, a separator that is insoluble in the electrolyte of the lithium ion secondary battery when used as a separator and is electrochemically stable in the environment where the lithium ion secondary battery is used is used. Is preferred.

Specific examples of the resin binder include the following 1) to 7).
1) Polyolefin: For example, polyethylene, polypropylene, ethylene propylene rubber, and modified products thereof;
2) Conjugated diene polymer: for example, styrene-butadiene copolymer and its hydride, acrylonitrile-butadiene copolymer and its hydride, acrylonitrile-butadiene-styrene copolymer and its hydride, and the like;
3) Acrylic polymer: For example, methacrylic acid ester-acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer, etc .;
4) Polyvinyl alcohol resin: for example, polyvinyl alcohol, polyvinyl acetate;
5) Fluorine-containing resin: For example, polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer Coalescence etc .;
6) Cellulose derivatives: For example, ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose and the like;
7) A resin having a melting point and / or glass transition temperature of 180 ° C. or higher, or a polymer having no melting point but a decomposition temperature of 200 ° C. or higher: for example, polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, polyetherimide, polyamide Imido, polyamide, polyester, etc. In particular, from the viewpoint of durability, wholly aromatic polyamides, particularly polymetaphenylene isophthalamide, are preferred.
Among these, 2) conjugated diene polymer is preferable from the viewpoint of compatibility with the electrode, and 3) acrylic polymer and 5) fluorine-containing resin are selected from the group of empty from the viewpoint of voltage resistance. One or more of these are preferred.

The 2) conjugated diene polymer is a polymer containing a conjugated diene compound as a monomer unit.
Examples of the conjugated diene compound include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, and substituted linear chains. Examples include conjugated pentadienes, substituted and side chain conjugated hexadienes, and the like. These may be used alone or in combination of two or more. Among these, 1,3-butadiene is particularly preferable.

The 3) acrylic polymer is a polymer containing a (meth) acrylic compound as a monomer unit. The said (meth) acrylic-type compound shows at least 1 chosen from the group which consists of (meth) acrylic acid and (meth) acrylic acid ester.
Examples of (meth) acrylic acid used in the above 3) acrylic polymer include acrylic acid and methacrylic acid.
3) The (meth) acrylic acid ester used in the acrylic polymer is, for example, a (meth) acrylic acid alkyl ester such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, 2 -Ethylhexyl acrylate, 2-ethylhexyl amethacrylate, etc .;
And epoxy group-containing (meth) acrylic acid esters such as glycidyl acrylate and glycidyl methacrylate. These may be used alone or in combination of two or more. Among the above, at least one selected from the group consisting of acrylic acid and methacrylic acid is particularly preferable.

The above 2) conjugated diene polymer and 3) acrylic polymer are obtained by copolymerizing other monomers copolymerizable with a conjugated diene compound or a (meth) acrylic compound, respectively. Also good. Examples of other copolymerizable monomers used include unsaturated carboxylic acid alkyl esters, aromatic vinyl monomers, vinyl cyanide monomers, and unsaturated monomers containing a hydroxyalkyl group. , Unsaturated carboxylic acid amide monomer, crotonic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid and the like. These may be used alone or in combination of two or more. Among the above, an unsaturated carboxylic acid alkyl ester monomer is particularly preferable. Examples of the unsaturated carboxylic acid alkyl ester monomer include dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl itaconate, monomethyl fumarate, monoethyl fumarate and the like. These may be used alone or in combination of two or more.
The 2) conjugated diene polymer may be obtained by copolymerizing the (meth) acrylic compound as another monomer.

<Structure and forming method of porous layer>
The layer thickness of the porous layer is preferably 1 μm or more from the viewpoint of improving heat resistance and insulation, more preferably 1.0 μm or more, still more preferably 1.2 μm or more, particularly preferably 1.5 μm or more, Particularly preferably, it is 1.8 μm or more, and most preferably 2.0 μm or more. Further, from the viewpoint of increasing the capacity of the battery and improving the permeability, it is preferably 50 μm or less, more preferably 20 μm or less, still more preferably 10 μm or less, and particularly preferably 7 μm or less.

  The filling rate of the inorganic filler in the porous layer is preferably 95% by volume or less, more preferably 80% by volume or less, still more preferably 70% by volume or less, and particularly preferably 60% by volume or less from the viewpoint of lightness and high permeability. preferable. From the viewpoint of heat shrinkage suppression and dendrite suppression, the lower limit of the inorganic filler filling rate is preferably 20% by volume or more, more preferably 30% by volume or more, and still more preferably 40% by volume or more. The filling rate of the inorganic filler can be calculated from the layer thickness of the porous layer and the mass and specific gravity of the inorganic filler.

  The porous layer may be formed only on one side of the porous film or on both sides.

  Examples of the method for forming the porous layer include a method in which a porous layer is formed by applying a coating liquid containing an inorganic filler and a resin binder on at least one surface of a porous film mainly composed of a polyolefin resin. it can.

  The form of the resin binder in the coating solution may be an aqueous solution or dispersion dissolved or dispersed in water, or an organic medium solution or dispersion dissolved or dispersed in a general organic medium. However, a resin latex is preferred. “Resin latex” refers to a dispersion in which a resin is dispersed in a medium. When a resin latex is used as a binder, when a porous layer containing an inorganic filler and a binder is laminated on at least one surface of a polyolefin porous film, ion permeability is hardly lowered and a separator with high output characteristics is easily obtained. In addition, even when the temperature rises rapidly during abnormal heat generation, smooth shutdown characteristics are exhibited and high safety is easily obtained.

  The average particle diameter of the resin latex binder is preferably 50 to 1,000 nm, more preferably 60 to 500 nm, and still more preferably 80 to 250 nm. When the average particle size is 50 nm or more, when a porous layer containing an inorganic filler and a binder is laminated on at least one surface of the polyolefin porous film, it exhibits good binding properties, and when it is used as a separator, heat shrinkage is good. , Tend to be excellent in safety. When the average particle size is 1,000 nm or less, the ion permeability is hardly lowered and high output characteristics are easily obtained. In addition, even when the temperature rises rapidly during abnormal heat generation, smooth shutdown characteristics are exhibited and high safety is easily obtained. The average particle diameter can be controlled by adjusting a polymerization time, a polymerization temperature, a raw material composition ratio, a raw material charging order, a pH, a stirring speed, and the like when manufacturing the resin binder.

  As a medium for the coating liquid, a medium capable of uniformly or stably dispersing or dissolving the inorganic filler and the resin binder is preferable. Specific examples include N-methylpyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, water, ethanol, toluene, hot xylene, methylene chloride, hexane and the like.

  Various additives such as a surfactant, a thickener, a wetting agent, an antifoaming agent, a pH adjuster containing an acid or an alkali are added to the coating solution in order to improve dispersion stabilization and coating properties. An agent may be added. The total addition amount of these additives is 20 parts by mass or less as the amount of the active ingredient (the mass of the additive component dissolved when the additive is dissolved in the solvent) with respect to 100 parts by mass of the inorganic filler. Is preferable, more preferably 10 parts by mass or less, still more preferably 5 parts by mass or less.

  The method for dispersing or dissolving the inorganic filler and the resin binder in the medium of the coating liquid is not particularly limited as long as it is a method capable of realizing the dispersion characteristics of the coating liquid necessary for the coating process. Examples thereof include a ball mill, a bead mill, a planetary ball mill, a vibrating ball mill, a sand mill, a colloid mill, an attritor, a roll mill, a high-speed impeller dispersion, a disperser, a homogenizer, a high-speed impact mill, ultrasonic dispersion, and mechanical stirring using a stirring blade.

  The method for applying the coating liquid to the porous film is not particularly limited as long as it can achieve the required layer thickness and coating area. For example, gravure coater method, small diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air doctor coater method, blade coater method, rod coater method, squeeze coater method, cast Examples include a coater method, a die coater method, a screen printing method, and a spray coating method.

  Furthermore, it is preferable to apply a surface treatment to the surface of the porous film prior to the application of the coating liquid because the coating liquid can be easily applied and the adhesion between the inorganic filler-containing porous layer after coating and the porous film surface is improved. . The surface treatment method is not particularly limited as long as it does not significantly impair the porous structure of the porous membrane. Examples thereof include a corona discharge treatment method, a plasma discharge treatment method, a mechanical surface roughening method, a solvent treatment method, an acid treatment method, and an ultraviolet oxidation method.

  The method for removing the medium from the coating film after coating is not particularly limited as long as it does not adversely affect the porous film. For example, a method of drying at a temperature below its melting point while fixing the porous membrane, a method of drying under reduced pressure at a low temperature, extraction drying and the like can be mentioned. Further, a part of the solvent may be left within a range that does not significantly affect the battery characteristics. From the viewpoint of controlling the shrinkage stress in the MD direction of the porous film in which the porous film and the porous layer are laminated, it is preferable to appropriately adjust the drying temperature, the winding tension, and the like.

<Method of pattern coating>
The pattern coating method is not limited as long as a desired pattern and layer thickness can be realized. For example, gravure coater method, small diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife Examples include a coater method, an air doctor coater method, a blade coater method, a rod coater method, a squeeze coater method, a cast coater method, a die coater method, a screen printing method, and a spray coating method. The pattern coating method is preferably a gravure coater method because the degree of freedom of the thermoplastic polymer coating shape is high and a desired area ratio can be easily obtained.

  When the gravure coater method is used, pattern coating is performed using a gravure coater on which a desired pattern processing has been performed. As the shape of the pattern in the gravure coater, it can be a shape corresponding to the shape listed in the column “<Pattern Coating>”, preferably a pattern of dots, diagonal lines, or stripes, more preferably dots. It is a pattern. The depth of the pattern in the gravure coater is preferably 1 μm to 50 μm, more preferably 3 μm to 20 μm. If the depth is 1 μm or more, a sufficient amount of coating material in the cell can be secured, and coating defects can be reduced. If the depth is 50 μm or less, the slurry can easily enter the cell, and the coating property can be easily stabilized. By controlling the depth of the pattern in the gravure coater, the thickness of the coating pattern can be controlled. For the preferable diameter, width, distance, area occupancy, thickness and the like of each pattern, refer to the above-mentioned “<Pattern coating>” column.

  Prior to pattern coating, it is preferable to apply a surface treatment to the surface of the porous base material because the slurry can be easily applied and the adhesion between the base material and the pattern coating is improved. The surface treatment method is not limited as long as the porous structure of the substrate is not significantly impaired. For example, the corona discharge treatment method, the mechanical surface roughening method, the solvent treatment method, the acid treatment method, and the ultraviolet oxidation method. Etc.

<Drying method>
The method for drying the dispersion medium is not limited as long as the dispersion medium can be substantially removed from the pattern coating after coating to leave the pattern coating containing the thermoplastic polymer on the porous substrate. An allowable amount of dispersion medium may remain in the pattern coating after drying. Examples of the method of drying the dispersion medium include a method of drying at a temperature below the melting point while fixing the porous substrate, a method of drying under reduced pressure at a low temperature, and the like. From the viewpoint of controlling the shrinkage stress in the MD direction of the porous substrate (the machine direction of the porous substrate), it is preferable to adjust the drying temperature, the winding tension, and the like.

  From the viewpoint of pattern formability, the drying method is not particularly limited, but it is preferably within 20 seconds, more preferably within 15 seconds, after applying the slurry until reaching the solid content of the gel point. More preferably, it is within 10 seconds, and further within 5 seconds. After the gel point, the polyolefin microporous substrate is preferably dried under conditions that do not block the pores of the polyolefin microporous substrate.

<Power storage device>
The electricity storage device of this embodiment includes a positive electrode, a negative electrode, an electrolyte, and the electricity storage device separator of this embodiment. The electricity storage device typically includes an electrode laminate in which a positive electrode, a separator for an electricity storage device of the present embodiment, and a negative electrode are laminated in this order, or an electrode winding body obtained by winding an electrode laminate.

  Examples of the electricity storage device include, but are not limited to, a battery such as a nonaqueous electrolyte secondary battery, a capacitor, and a capacitor. From the viewpoint of more effectively obtaining the benefits of the effects of the present embodiment, the electricity storage device is preferably a battery, more preferably a non-aqueous electrolyte secondary battery, and even more preferably a lithium ion secondary battery. A preferred embodiment will be described below in the case where the electricity storage device is a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery.

  When manufacturing a lithium ion secondary battery using the separator for electrical storage devices of this embodiment, a positive electrode, a negative electrode, and electrolyte solution are not limited, Each can use a known material.

As the positive electrode, a positive electrode in which a positive electrode active material layer containing a positive electrode active material is formed on a positive electrode current collector can be suitably used. Examples of the positive electrode current collector include an aluminum foil. Examples of the positive electrode active material include lithium-containing composite oxides such as LiCoO ₂ , LiNiO ₂ , spinel type LiMnO ₄ , and olivine type LiFePO ₄ . The positive electrode active material layer may include a binder, a conductive material, and the like in addition to the positive electrode active material.

  As the negative electrode, a negative electrode in which a negative electrode active material layer containing a negative electrode active material is formed on a negative electrode current collector can be suitably used. Examples of the negative electrode current collector include copper foil. Examples of the negative electrode active material include carbon materials such as graphite, non-graphitizable carbonaceous, graphitizable carbonaceous, and composite carbon bodies; silicon, tin, metallic lithium, and various alloy materials.

As the electrolytic solution, a nonaqueous electrolytic solution can be used. The nonaqueous electrolytic solution is not limited, but an electrolytic solution in which an electrolyte is dissolved in an organic solvent can be used. Examples of the organic solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Examples of the electrolyte include lithium salts such as LiClO ₄ , LiBF ₄ , and LiPF ₆ .

  A method for producing a power storage device, preferably a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery, using the power storage device separator of the present embodiment will be exemplified below.

  The separator for an electricity storage device of this embodiment is produced as a separator having a vertically long shape having a width of 10 to 2000 mm, preferably 30 to 1500 mm, a length of 200 to 4,000 m, and preferably 1,000 to 4,000 m. The obtained separator was laminated in the order of positive electrode-separator-negative electrode-separator, or negative electrode-separator-positive electrode-separator, and wound into a circular or flat spiral shape to obtain an electrode winding body. An electricity storage device can be manufactured by placing the battery in a battery container and injecting an electrolytic solution.

  Alternatively, an electrode stack composed of the electricity storage device separator of the present embodiment, a positive electrode, and a negative electrode, or a folded electrode stack is placed in a battery container and injected with an electrolyte. Thus, an electricity storage device may be manufactured. The electrode laminate can be, for example, an electrode laminate that is laminated in the order of positive electrode-separator-negative electrode-separator-positive electrode or negative electrode-separator-positive electrode-separator-negative electrode. The battery container can be, for example, an aluminum film.

In any case, the method for producing the adhesive body is not particularly limited.For example, after the separator and the electrode are stacked, by performing at least one kind of processing of heating and pressing, Can be manufactured.
The heating and pressing can be performed in a state where the electrode and the separator are stacked. For example, at least one of heating and pressing can be performed by forming the above-described wound body or laminated body.
The heating and pressing may be performed before the electrode and the separator are accommodated in the exterior body, may be performed after the electrode and the separator are accommodated in the exterior body, respectively, and are performed both before and after being accommodated in the exterior body. May be.
When at least one of the heating and pressing is performed after the electrode and the separator are accommodated in the exterior body, it may be performed before injecting the electrolyte into the exterior body, or may be performed after the injection. Further, it may be performed both before and after injecting the electrolytic solution.
In particular, when a bag-shaped film is used as the exterior body, it is preferable to perform at least one of heating and pressing after accommodating the electrode and the separator in the exterior body and injecting an electrolytic solution. At this time, from the viewpoint of preventing the electrode and the separator from shifting, it is preferable to perform at least one of heating and pressing before accommodating them in the exterior body.

  The press temperature is preferably a temperature at which adhesiveness can be effectively expressed, for example, 20 ° C. or higher. The press temperature is preferably lower than the melting point of the polyolefin porous substrate, and more preferably 120 ° C. or less, from the viewpoint of suppressing clogging of the separator holes due to pressing or thermal shrinkage. The press pressure is preferably 20 MPa or less from the viewpoint of suppressing clogging of the separator holes. The press time may be 1 second or less when a roll press is used, and may be several hours when a surface press is used. By performing the above-described pressing method using the electricity storage device separator of the present embodiment, it is possible to effectively suppress the press back when the electrode winding body including the electrode and the separator is press-molded; or It is possible to prevent peeling and displacement after press-molding the electrode laminate including the electrode and the separator. Accordingly, it is possible to suppress the yield reduction in the battery assembly process and to shorten the production process time. Therefore, it is preferable to manufacture the electricity storage device using the manufacturing process including the pressing method.

  Since the electricity storage device of this embodiment has the separator for an electricity storage device of this embodiment that is excellent in ion permeability, adhesion to electrodes, and the like, it has excellent rate characteristics.

  Hereinafter, although an embodiment of the present invention is described concretely with an example and a comparative example, the present invention is not limited to these examples and a comparative example.

<< Measurement and evaluation method >>
<High shear viscosity>
Using a high shear rotational viscometer PM9002HV (manufactured by Mitsui Denki), the number of rotations was increased from 0 rpm to 12000 rpm at room temperature under the condition of 1200 rpm / sec.

<Contact angle>
The slurry was placed on the surface of Celgard C2500 and allowed to stand at 23 ° C. for 1 minute, and then measured using a CA-X150 contact angle meter manufactured by Kyowa Interface Science, Japan.

<Viscosity at each solid content concentration of slurry>
Using a B-type viscometer, the viscosity (mPa · s) of the coating solution at 25 ° C. was measured under the condition of a shear rate of 60 s-1.
The solid content concentration of each slurry was adjusted by gradually evaporating the solvent while stirring the slurry at 100 rpm on a 40 ° C. hot stirrer.

<Gel fraction of thermoplastic polymer (toluene insoluble content)>
A thermoplastic polymer coating solution (non-volatile content = 38 to 42%, pH = 9.0) is dropped on a Teflon (registered trademark) plate with a dropper (diameter 5 mm or less), and 30 ° C. with a hot air dryer at 130 ° C. Dried for minutes. After drying, about 0.5 g of the dried film was precisely weighed (a), taken into a 50 mL polyethylene container, poured into 30 mL of toluene, and shaken at room temperature for 3 hours. Thereafter, the content was filtered with 325 mesh, and the toluene insoluble matter remaining on the mesh was dried together with the mesh for 1 hour with a 130 ° C. hot air dryer. In addition, the 325 mesh used here measured the dry mass beforehand.
And after volatilizing toluene, the dry mass (b) of toluene insoluble matter was obtained by subtracting 325 mesh mass measured beforehand from the dry mass of toluene insoluble matter, and the total mass of 325 mesh. The gel fraction (toluene insoluble matter) was calculated using the following formula.
Gel fraction of thermoplastic polymer (toluene insoluble content) (%) = (b) / (a) × 100

<Swelling degree of thermoplastic polymer to electrolyte (times)>
The thermoplastic polymer or a solution in which the thermoplastic polymer is dispersed is allowed to stand in an oven at 130 ° C. for 1 hour, and then the dried thermoplastic polymer is cut out to 0.5 g and mixed at a predetermined component and mixing ratio. After putting it in a 50 mL vial together with 10 g of the solvent and infiltrating for a predetermined time, the sample was taken out, washed with the above mixed solvent, and the mass (Wa) was measured. Then, after leaving still in 150 degreeC oven for 1 hour, mass (Wb) was measured and the swelling degree with respect to the electrolyte solution of a thermoplastic polymer was measured from the following formula | equation.
Swelling degree of thermoplastic polymer with respect to electrolyte solution (times) = (Wa−Wb) / (Wb)
The components of the mixed solvent, the mixing ratio, and the permeation time were as follows.
Mixing ratio ethylene carbonate: ethyl methyl carbonate = 1: 2 (volume ratio)
Penetration time 3 hours

<Average particle size of thermoplastic polymer>
The average particle size of the thermoplastic polymer was measured using a particle size measuring device (Nikkiso Co., Ltd., Microtrac UPA150). The measurement conditions were loading index = 0.15 to 0.3 and measurement time 300 seconds. The numerical value (D50) of 50% particle diameter in the obtained data was described as the average particle diameter.

<Glass transition point (Tg) and melting point (Tm)>
The glass transition point and melting point of the thermoplastic polymer were determined from the DSC curve obtained by differential scanning calorimetry (DSC).
An appropriate amount of an aqueous dispersion (solid content = 38 to 42% by mass, pH = 9.0) containing a thermoplastic polymer was taken in an aluminum dish and dried in a hot air dryer at 130 ° C. for 30 minutes. About 17 mg of the dried film after drying was packed in an aluminum container for measurement, and a DSC curve and a DDSC curve in a nitrogen atmosphere were obtained with a DSC measurement apparatus (manufactured by Shimadzu Corporation, DSC 6220). The measurement conditions were as follows.
First stage temperature increase program: Start at 70 ° C., increase temperature at a rate of 15 ° C. per minute. Maintained for 5 minutes after reaching 110 ° C.
Second stage temperature drop program: temperature drop from 110 ° C. at a rate of 40 ° C. per minute. Maintained for 5 minutes after reaching -50 ° C.
Third stage temperature increase program: Temperature is increased from -50 ° C to 130 ° C at a rate of 15 ° C per minute. DSC and DDSC data are acquired at the third stage of temperature rise.
The melting point was determined by the intersection of the baseline in the DSC curve and the tangent of the slope of the melting endothermic peak. The glass transition point was determined by the intersection of a straight line obtained by extending the base line on the low temperature side in the DSC curve to the high temperature side and the tangent at the inflection point of the stepped change portion of the glass transition.

<Viscosity average molecular weight (Mv)>
For the thermoplastic polymer, the intrinsic viscosity [η] at 135 ° C. was determined in a decalin solvent in accordance with ASRM-D4020. Using this [η] value, the viscosity average molecular weight (Mv) of the thermoplastic polymer was calculated from the relationship of the following mathematical formula.
In the case of polyethylene: [η] = 0.00068 × Mv ^0.67
In the case of polypropylene: [η] = 1.10 × Mv ^0.80

<Film thickness>
Cut a 10cm x 10cm square sample from the polyolefin porous substrate, select 9 measurement points (3 points x 3 points) in a grid, and use a microthickness meter (Toyo Seiki Seisakusho Type KBM). The film thickness of each measurement location was measured at room temperature 23 ± 2 ° C. The average value of the nine measured values obtained was calculated as the film thickness of the substrate.

<Porosity>
A 10 cm × 10 cm square sample was cut from the polyolefin porous substrate, and its volume (cm ³ ) and mass (g) were determined. Using these values, the porosity was calculated according to the following formula, with the density of the substrate being 0.95 (g / cm ³ ):
Porosity (%) = (1−mass / volume / 0.95) × 100

<Air permeability>
The air permeability of the electricity storage device separator is the air resistance measured according to JIS P-8117, similarly to the air permeability of a general porous substrate. The air resistance is a time required for a specified volume of air to permeate per unit area and unit pressure difference, and is expressed in time (seconds) per 100 mL. The air permeability measured by a Gurley type air permeability meter G-B2 (trademark) manufactured by Toyo Seiki Co., Ltd. was defined as the air permeability (s ⁻¹ ).

<Puncture strength>
Using a handy compression tester KES-G5 (trademark) manufactured by Kato Tech, a polyolefin porous substrate was fixed with a sample holder having a diameter of 11.3 mm at the opening. Next, the center portion of the fixed polyolefin porous substrate is subjected to a piercing test in a 25 ° C. atmosphere at a piercing speed of 2 mm / sec using a needle having a radius of curvature of 0.5 mm at the tip, thereby maximizing the piercing. Puncture strength (g) was obtained as a load.

<Pattern formability>
The pattern formability (%) of the slurry for pattern coating to the polyolefin porous substrate is measured and evaluated using Celgard's model number “CG2500” (manufactured by Asahi Kasei Corporation) as the polyolefin porous substrate. The pattern formability is an index for evaluating the dimensional deviation between the pattern processed on the gravure coater and the pattern actually applied to the polyolefin porous substrate.
The pattern coating slurry to be measured was coated on CG 2500, and the pattern forming property was calculated using the following method. The average pattern area on the polyolefin porous substrate was observed with a scanning electron microscope (SEM) (manufactured by Hitachi, Ltd., S-4800). :
Pattern formability (times) = average pattern area on polyolefin porous substrate /
Average pattern area of gravure plate S: 0.7 to 2.0 times A: 0.6 to less than 0.7, more than 2.0 times to 3.0 times or less B: 0.4 to less than 0.6, Over 3.0 times and below 5.0 times C: Outside the range of 0.4 to 5.0 times

<Foamability>
The ease of foaming of each pattern coating slurry was evaluated according to JIS K3362: 2008 (8.5 foaming power and foam stability).
Height of foam generated when 200 mL of the obtained slurry for pattern coating (solid content concentration 30%) is collected and dropped from the height of 900 mm to the liquid surface over 30 seconds at room temperature. (Initial foaming height) was measured. Furthermore, the height of the foam after 5 minutes (the foaming height after 5 minutes) was measured. The measurement was carried out three times, and the average value was taken as the measurement value.

<Peel strength between separator and electrode>
Power storage device separator and positive electrode as an adherend (made by Enertech, positive electrode material: LiCoO ₂ , conductive auxiliary agent: acetylene black, binder: PVDF, LiCoO ₂ / acetylene black / PVDF (weight ratio) = 95/2 / 3, L / W: 36 mg / cm ² on both sides, density: 3.9 g / cc, thickness of Al current collector: 15 μm, thickness of positive electrode after pressing: 107 μm, respectively, with a width of 15 mm and a length of 60 mm Cut into a rectangular shape. These were laminated so that the thermoplastic polymer layer of the separator and the positive electrode active material faced to obtain a laminate. The obtained laminate was pressed under the following conditions.
Press pressure: 1 MPa
Temperature: 100 ° C
Pressing time: 5 seconds For the laminate after pressing, a force gauge ZP5N and MX2-500N (product name) manufactured by Imada Co., Ltd. are used to fix the electrode, grip the separator, and pull the separator, and the peeling speed is 50 mm. The peel strength was examined by performing a 90 ° peel test at / min. At this time, the average value of peel strength in a peel test for 40 mm in length performed under the above conditions was defined as peel strength.

<Binding with substrate>
A tape having a width of 12 mm and a length of 100 mm (manufactured by 3M) was applied to the thermoplastic polymer coating layer of the separator. The force when peeling the tape from the sample at a speed of 50 mm / min was measured using a 90 ° peel strength measuring device (product name: IP-5N, manufactured by IMADA). Based on the obtained measurement results, the adhesive strength was evaluated according to the following evaluation criteria.
○: 6 gf / mm or more ×: Less than 6 gf / mm

<Separator handling>
The coated surfaces of the electricity storage device separator were overlapped and pressed under conditions of a temperature of 30 ° C. and a pressure of 5 MPa for 3 minutes. Thereafter, the peel strength between the overlapping coated surfaces was measured at a tensile speed of 200 mm / min according to JIS K6854-2 using an autograph AG-IS type (trademark) manufactured by Shimadzu Corporation. The smaller the peel strength value (N / m), the better the handleability.

<Rate characteristics>
a. Production of positive electrode 90.4% by mass of nickel, manganese, cobalt composite oxide (NMC) (Ni: Mn: Co = 1: 1: 1 (element ratio), density 4.70 g / cm ³ ) as a positive electrode active material, 1.6% by mass of graphite powder (KS6) (density 2.26 g / cm ³ , number average particle diameter 6.5 μm) and acetylene black powder (AB) (density 1.95 g / cm ³ , number average) as conductive aids 3.8% by mass of particle diameter 48 nm) and polyvinylidene fluoride (PVDF) (density 1.75 g / cm ³ ) as a binder at a ratio of 4.2% by mass, and these are mixed with N-methylpyrrolidone (NMP). A slurry was prepared by dispersing in the slurry. This slurry was applied to one side of a 20 μm-thick aluminum foil serving as a positive electrode current collector using a die coater, dried at 130 ° C. for 3 minutes, and then subjected to compression molding using a roll press to obtain a positive electrode. Produced. The coating amount of the positive electrode active material at this time was 109 g / m ² .
b. Graphite powder A as prepared negative active material of the negative electrode (density 2.23 g / cm ^3, number average particle diameter 12.7 [mu] m) 87.6% by weight and graphite powder B (density 2.27 g / cm ^3, number average particle diameter 6.5 μm) is 9.7% by mass, and the ammonium salt of carboxymethyl cellulose as a binder is 1.4% by mass (in terms of solid content) (solid content concentration is 1.83% by mass aqueous solution) and the diene rubber latex is 1.7% by mass ( (Solid content conversion) (solid content concentration 40 mass% aqueous solution) was dispersed in purified water to prepare a slurry. This slurry was applied to one side of a 12 μm thick copper foil serving as a negative electrode current collector with a die coater, dried at 120 ° C. for 3 minutes, and then compression molded with a roll press to produce a negative electrode. The coating amount of the negative electrode active material at this time was 5.2 g / m ² .
c. Preparation of non-aqueous electrolyte solution By dissolving LiPF ₆ as a solute in a mixed solvent of ethylene carbonate: ethyl methyl carbonate = 1: 2 (volume ratio) to a concentration of 1.0 mol / L, a non-aqueous electrolyte solution was prepared. Prepared.
d. Battery assembly The separator for the electricity storage device obtained in each Example and Comparative Example was cut into a circle of 24 mmφ, and the positive electrode and the negative electrode were each cut into a circle of 16 mmφ. The negative electrode, the separator, and the positive electrode were stacked in this order so that the positive electrode and the active material surface of the negative electrode were opposed to each other, pressed, or heat pressed, and accommodated in a stainless steel container with a lid. The container and the lid were insulated, and the container was in contact with the negative electrode copper foil and the lid was in contact with the positive electrode aluminum foil. A battery was assembled by injecting 0.2 ml of the non-aqueous electrolyte into the container and sealing it.
e. Evaluation of rate characteristics d-2. After charging the simple battery assembled in step 3 at 25 ° C. to a battery voltage of 4.2 V at a current value of 3 mA (about 0.5 C), the current value starts to be reduced from 3 mA so as to maintain 4.2 V. The first charge after the battery was made was performed for a total of about 6 hours. Thereafter, the battery was discharged to a battery voltage of 3.0 V at a current value of 3 mA.
Next, after charging to a battery voltage of 4.2 V at a current value of 6 mA (about 1.0 C) at 25 ° C., the current value starts to be reduced from 6 mA so as to hold 4.2 V, so that a total of about 3 Charged for hours. Thereafter, the discharge capacity when discharging to a battery voltage of 3.0 V at a current value of 6 mA was defined as 1 C discharge capacity (mAh).
Next, after charging to a battery voltage of 4.2 V at a current value of 6 mA (about 1.0 C) at 25 ° C., the current value starts to be reduced from 6 mA so as to hold 4.2 V, so that a total of about 3 Charged for hours. Thereafter, the discharge capacity when discharging to a battery voltage of 3.0 V at a current value of 60 mA (about 10 C) was defined as 10 C discharge capacity (mAh).
And the ratio of 10 C discharge capacity with respect to 1 C discharge capacity was computed, and this value was made into the rate characteristic.
Rate characteristic (%) = (10C discharge capacity / 1C discharge capacity) × 100
Evaluation criteria

<< Synthesis of thermoplastic polymer particles >>
<Water dispersion a1>
In a reaction vessel equipped with a stirrer, reflux condenser, dripping tank and thermometer, 70.4 parts by mass of ion-exchanged water and “AQUALON KH1025” (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as an emulsifier In the table, indicated as “KH1025”. The same shall apply hereinafter.) 0.5 part by mass, “ADEKA rear soap SR1025” (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation, indicated as “SR1025” in the table, and so on) 0 And 5 parts by mass were charged. Next, the temperature inside the reaction vessel was raised to 80 ° C., and while maintaining the temperature at 80 ° C., a 2% aqueous solution of ammonium persulfate (indicated as “APS (aq) in the table, the same shall apply hereinafter)” 7.5. Part by mass was added to obtain an initial mixture. Five minutes after the completion of the addition of the ammonium persulfate aqueous solution, the emulsion was dropped from the dropping tank into the reaction vessel over 150 minutes.

The above emulsion is:
10 parts by mass of methoxypolyethyleneglycol methacrylate (denoted as PEGM in the table, the same shall apply hereinafter) as a monomer constituting the polyethylene glycol group-containing monomer unit (P);
As a monomer constituting the cycloalkyl group-containing monomer unit (A), cyclohexyl methacrylate (denoted as “CHMA” in the table, the same shall apply hereinafter) 30 parts by mass;
Methacrylic acid as a monomer constituting the carboxyl group-containing monomer unit (b1) (in the table, expressed as “MAA”; the same shall apply hereinafter) 1.0 part by mass;
Acrylic acid (in the table, indicated as “AA”, the same applies hereinafter) 1.0 part by mass;
Acrylamide as a monomer constituting the amide group-containing monomer unit (b2) (in the table, expressed as “AM”, the same shall apply hereinafter) 0.1 parts by mass;
2-hydroxyethyl methacrylate (expressed as “2HEMA” in the table, the same shall apply hereinafter) as a monomer constituting the hydroxyl group-containing monomer unit (b3);
Trimethylolpropane triacrylate (A-TMPT, trade name of Shin-Nakamura Chemical Co., Ltd., listed in the table as “A-TMPT” as a monomer constituting the crosslinkable monomer unit (b4). The same applies hereinafter) 0 .5 parts by mass;
As a monomer constituting the (meth) acrylic acid ester monomer unit (b5) other than the above, 1.0 part by mass of methyl methacrylate (in the table, expressed as “MMA”; the same shall apply hereinafter);
0.4 parts by mass of butyl methacrylate (denoted as “BMA” in the table, the same shall apply hereinafter);
1.0 part by mass of butyl acrylate (shown as “BA” in the table, the same shall apply hereinafter);
2-ethylhexyl acrylate (in the table, expressed as “2EHA”, the same shall apply hereinafter) 50.0 parts by mass;
As an emulsifier, 3 parts by mass of “AQUALON KH1025” (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), 3 parts by mass of “ADEKA rear soap SR1025” (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation) and p-styrene Sodium sulfonate (indicated in the table as “NaSS”, the same shall apply hereinafter) 0.05 parts by mass;
A mixture of 7.5 parts by mass of a 2% aqueous solution of ammonium persulfate; and 52 parts by mass of ion-exchanged water was prepared by mixing for 5 minutes with a homomixer.

  After completion of dropping of the emulsion, the temperature inside the reaction vessel was maintained at 80 ° C. for 90 minutes, and then cooled to room temperature. The obtained emulsion was adjusted to pH = 8.0 with a 25% aqueous ammonium hydroxide solution (indicated as “AW” in the table), and a small amount of water was added to obtain an aqueous dispersion having a solid content of 40%. (Aqueous dispersion a1). About the copolymer in the obtained water dispersion a1, the average particle diameter, the glass transition point, the shape after forming the thermoplastic layer, and the particle diameter after forming the thermoplastic layer were measured by the above methods. The obtained results are shown in Table 2.

<Water dispersion A1-A20>
Aqueous dispersions A1 to A20 were obtained in the same manner as the aqueous dispersion a1 except that the types and mixing ratios of the raw materials were changed as shown in Tables 2 and 3. About the copolymer of obtained water dispersion A1-A20 and a1, the particle diameter and the glass transition point (Tg) were measured by the said method. The obtained results are shown in Tables 2 and 3. In the table, the composition of raw materials is based on mass.

<< Manufacture of polyolefin porous substrate >>
<Base material B1>
45 parts by mass of a homopolymer high-density polyethylene having an Mv of 700,000,
45 parts by mass of a homopolymer high-density polyethylene having an Mv of 300,000,
5 parts by mass of a homopolymer polypropylene having an Mv of 400,000,
Was dry blended using a tumbler blender.
1 part by mass of tetrakis- [methylene- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate] methane as an antioxidant was added to 99 parts by mass of the obtained polyolefin mixture, and again a tumbler blender. Was used for dry blending to obtain a mixture.
The obtained mixture was supplied to the twin screw extruder by a feeder under a nitrogen atmosphere.
Further, liquid paraffin (kinematic viscosity at 37.78 ° C .: 7.59 × 10 ⁻⁵ m ² / s) was injected into the extruder cylinder by a plunger pump.
The operating conditions of the feeder and the pump were adjusted so that the ratio of liquid paraffin in the total mixture to be extruded was 65 parts by mass and the polymer concentration was 35 parts by mass.

Next, they are melt-kneaded while being heated to 230 ° C. in a twin-screw extruder, and the obtained melt-kneaded product is extruded through a T-die onto a cooling roll controlled at a surface temperature of 80 ° C. A sheet-like molded product was obtained by bringing into contact with a cooling roll and molding by cooling.
This sheet was stretched by a simultaneous biaxial stretching machine at a temperature of 112 ° C. and a magnification of 7 × 6.4. Thereafter, the stretched product was immersed in methylene chloride, and the liquid paraffin was extracted and dried, and then dried, and further stretched twice in the transverse direction at a temperature of 130 ° C. using a tenter stretching machine.
Thereafter, the stretched sheet was relaxed by about 10% in the width direction and heat-treated to obtain a polyolefin porous substrate B1. Table 1 shows the physical properties of the obtained substrate B1.

<Base material B2>
As the polyolefin porous substrate B2, Celgard's model number “CG2500” (manufactured by Asahi Kasei Co., Ltd.), which is a polypropylene single layer film, was prepared. Table 1 shows the base materials used.

<Base material B3>
97.0 parts by mass of aluminum hydroxide oxide (average particle size 1.0 μm), acrylic latex (solid content concentration 40%, average particle size 145 nm, minimum film formation temperature 0 ° C. or less) 3.0 parts by mass, and polycarboxylic acid A coating solution was prepared by uniformly dispersing 1.0 part by mass of an aqueous ammonium solution (SN Dispersant 5468, manufactured by San Nopco) in 100 parts by mass of water. Then, the coating liquid was apply | coated to the surface of polyolefin porous base material B2 using the gravure coater. Then, it dried at 60 degreeC and removed water. In this manner, a polyolefin porous substrate B3 was obtained by forming an aluminum hydroxide oxide layer (inorganic filler porous layer) with a thickness of 2 μm on the polyolefin porous substrate B2.

Example 1
The aqueous dispersion A1 described in Table 2 was adjusted to a solid content of 30% by mass by adding purified water to produce an organic binder-containing slurry. Next, as an additive to the slurry, an aqueous xanthan gum solution (manufactured by Sanki Co., Ltd., Kelzan M) prepared to a solid content concentration of 1.5% by mass is prepared, and the slurry is adjusted to 0.5% by mass relative to the amount of organic binder And stirred for 12 hours. The measurement results of the slurry are shown in Table 4.

<< Examples 2 and 3 >>
A slurry was prepared in the same manner as in Example 1 except that the amount of xanthan gum (manufactured by Sanki Co., Ltd., Kelzan M) was changed. The measurement results of the slurry are shown in Table 4.

<< Examples 4 and 5 >>
A slurry was prepared in the same manner as in Example 1 except that xanthan gum (manufactured by Sanki Co., Ltd., Kelzan M) was changed to CMC (manufactured by Daicel Corporation, carboxymethyl cellulose 2200) and the binder was changed as shown in Table 4. did. The measurement results of the slurry are shown in Table 4.

Example 6
Xanthan gum (manufactured by Miki Co., Ltd., Kelzan M) was changed to CMC (manufactured by Daicel Corporation, carboxymethyl cellulose 2200), and an alkylsulfonic acid surfactant (manufactured by Mitsui Cytec Co., Ltd., OT-75) was used as the surfactant. A slurry was prepared in the same manner as in Example 5 except that 0.1% by mass relative to the binder amount was added. The measurement results of the slurry are shown in Table 4.

Example 7
Except that the organic binder was changed to A4, and an alkyl sulfonic acid surfactant (manufactured by Mitsui Cytec Co., Ltd., OT-75) was added as a surfactant so as to be 0.1% by mass relative to the amount of the organic binder. A slurry was prepared in the same manner as in Example 1. The measurement results of the slurry are shown in Table 4.

Example 8
A slurry was prepared in the same manner as in Example 1 except that the organic binder was changed to A11 and the additive was not added. The measurement results of the slurry are shown in Table 4.

Example 9
A7 and A1 were mixed so that the amount of the organic binder was 80: 20% by mass, and then purified water was added so that the solid content concentration would be 30% by mass and stirred for 12 hours. A slurry was prepared in the same manner. The measurement results of the slurry are shown in Table 4.

Example 10
A10 and A1 were mixed so that the amount of the organic binder was 80: 20% by mass, and then purified water was added so that the solid content concentration was 30% by mass and stirred for 12 hours. A slurry was prepared in the same manner. The measurement results of the slurry are shown in Table 4.

<< Examples 11 to 13, Comparative Example 1 >>
A slurry was produced in the same manner as in Example 10 except that the slurry composition shown in Table 4 was used. The measurement results of the slurry are shown in Table 4.

<< Evaluation of separator: S1 >>
The prepared slurry C1 was applied in a pattern using a gravure roll in which a dot diameter of 800 μm and a depth of 5 μm was printed on one surface of the polyolefin microporous substrate B2 shown in Table 1, and the temperature was adjusted to 60 ° C. The separator S1 was obtained by drying and removing the water of the coating solution. The measurement results are shown in Table 5.

<< Evaluation of separator: S2 to S9 >>
The adjusted slurry and the base material to be coated were changed as shown in Table 5. Moreover, except having changed the gravure roll plate used so that a dot diameter and an area occupation rate might become Table 5, the separator was produced like S1.

  The slurry for pattern coating of the present invention can be used for pattern coating on at least one side of a polyolefin porous substrate used as a substrate for a separator for an electricity storage device. The obtained separator for an electricity storage device can be used for producing an electricity storage device, for example, a lithium ion battery.

Claims (15)

A pattern coating slurry for applying a pattern to at least one surface of a polyolefin porous substrate used as a substrate for a storage device separator,
The pattern coating slurry includes a thermoplastic polymer, a dispersion medium or a solvent,
The pattern coating slurry is a pattern coating slurry in which the maximum value of the high shear viscosity at a shear rate of 50000 s ⁻¹ or less is 5 cps or more.   The slurry for pattern coating of Claim 1 whose maximum value of the said high shear viscosity is 5 cps or more and 10 cps or less.   The pattern coating slurry according to claim 1 or 2, wherein the surface tension of the pattern coating slurry is 50 or more and 100 or less.   The viscosity when the solid content concentration of the slurry for pattern coating is 30% by mass is 100 mPa · s or less, and the viscosity when the solid content concentration is 50% by mass is 300 mPa · s or more. The slurry for pattern coating of any one of these.   The viscosity when the solid content concentration of the slurry for pattern coating is 30% by mass is 100 mPa · s or less, and the viscosity when the solid content concentration is 45% by mass is 150 mPa · s or more. The slurry for pattern coating of any one of these.   The viscosity when the solid content concentration of the slurry for pattern coating is 30% by mass is 100 mPa · s or less, and the viscosity when the solid content concentration is 40% by mass is 150 mPa · s or more. The slurry for pattern coating of any one of these.   The viscosity when the solid content concentration of the slurry for pattern coating is 30% by mass is 70 mPa · s or less, and the viscosity when the solid content concentration is 40% by mass is 150 mPa · s or more. The slurry for pattern coating of any one of these.   The slurry for pattern coating of any one of Claims 1-7 containing the said dispersion medium and the said dispersion medium contains water as a main component.   A copolymer in which the thermoplastic polymer has as a monomer unit at least one selected from the group consisting of a (meth) acrylic acid ester monomer, a conjugated diene monomer, and a vinylidene fluoride monomer The separator for electrical storage devices which has pattern coating formed from the slurry for pattern coating of any one of Claims 1-8 containing these. The thermoplastic polymer contained in the coating slurry contains at least two kinds of thermoplastic polymers, and has at least two glass transition temperatures as a whole,
At least one of the glass transition temperatures is present in a region below 20 ° C .;
The electrical storage device separator according to claim 1, wherein at least one of the glass transition temperatures is present in a region of 20 ° C. or higher.   The electrical storage device separator according to any one of claims 1 to 10, wherein a degree of swelling of the thermoplastic polymer with respect to the electrolytic solution is 1 to 10 times.   The separator for electrical storage devices which has the pattern coating formed from the slurry for pattern coating of any one of Claims 1-11 in the at least single side | surface of a polyolefin porous substrate.   The electricity storage device separator according to claim 12, wherein the pattern coating is a dot pattern.   14. The electricity storage device separator according to claim 12, wherein a diameter of the dots is 10 μm or more and 1000 μm or less, and an area occupation ratio of the dots is 5% or more and 80% or less. A separator for an electricity storage device, comprising a polyolefin porous substrate and a thermoplastic polymer coating layer covering at least a part of at least one surface of the polyolefin porous substrate,
A portion where the thermoplastic polymer coating layer is present on the polyolefin porous substrate and a portion where the thermoplastic polymer coating layer is not present are present in a sea-island shape,
The thermoplastic polymer contained in the thermoplastic polymer coating layer includes at least two thermoplastic polymers, and has at least two glass transition temperatures as a whole,
At least one of the glass transition temperatures is present in a region below 20 ° C .;
At least one of the glass transition temperatures exists in a region of 20 ° C. or higher.
Electric storage device separator.