JP2015103482A - Separator for power storage devices, power storage device, lithium ion secondary battery and copolymer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for power storage devices which is superior in adhesion with an electrode.SOLUTION: A separator for power storage devices comprises: a base material; and a layer formed on at least one part on at least one side of the base material and including a thermoplastic polymer. The thermoplastic polymer includes a copolymer having, as monomer units, 2-66 mass% of an ethylenic unsaturated monomer having a chain alkyl group with 8 or more carbon atoms, and 34-98 mass% of other monomers copolymerizable with the ethylenic unsaturated monomer having a chain alkyl group with 8 or more carbon atoms.

Description

  The present invention relates to a separator for an electricity storage device, an electricity storage device, a lithium ion secondary battery, and a copolymer.

  In recent years, development of nonaqueous electrolyte batteries centering on lithium ion batteries has been actively conducted. Usually, in a nonaqueous electrolyte battery, a microporous membrane (separator) is provided between positive and negative electrodes. Such a 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 micropores.

  In order to improve the cycle characteristics and safety of the nonaqueous electrolyte battery, improvement of the separator has been studied. In recent years, as portable devices become smaller and thinner, power storage devices such as lithium ion secondary batteries are also required to be smaller and thinner. On the other hand, in order to be able to carry for a long time, the capacity is increased by improving the volume energy density.

  Conventional separators have a characteristic that the battery reaction is quickly stopped if the separator is abnormally heated (fuse characteristics), preventing the dangerous situation where the cathode and anode materials react directly by maintaining the shape even at high temperatures. Performance related to safety such as performance (short characteristics) is required. In addition to these, recently, separators are also required to have improved adhesion to electrodes from the viewpoints of uniform charge / discharge current and suppression of lithium dendrite.

  By improving the close contact between the separator and the battery electrode, non-uniform charge / discharge current is less likely to occur, and lithium dendrite is less likely to precipitate, resulting in longer charge / discharge cycle life. Become.

  Under such circumstances, as an attempt to give the separator an adhesive property, for example, in Patent Document 1, a porous battery is provided for the purpose of providing a secondary battery excellent in discharge characteristics and safety (heat resistance). An adhesive-carrying porous film for a battery separator obtained by applying a reactive polymer on a membrane and drying it has been proposed. Similarly, Patent Document 2 proposes that an adhesive resin be present by applying a solution containing an adhesive resin to the surface of the polyolefin microporous membrane. In an electricity storage device such as a non-aqueous electrolyte battery, the active material of the positive electrode or the negative electrode repeatedly expands and contracts during charge and discharge, so that the adhesive has excellent adhesion with the electrode active material and at the same time in the electrolytic solution. Excellent cushioning is required.

JP 2007-59271 A JP 2011-54502 A

However, the separator using the adhesive-supporting porous film described in Patent Document 1 has a problem in that the adhesion between the reactive polymer and the porous film is not sufficient, and therefore, the adhesion with the electrode is not sufficient. . In addition, the microporous membranes described in Patent Documents 1 and 2 still have room for improvement from the viewpoint of handling property, adhesiveness, and lithium ion permeability when winding the battery.
This invention is made | formed in view of the said situation, and it aims at providing the separator for electrical storage devices which is excellent in adhesiveness with an electrode, an electrical storage device, a lithium ion secondary battery, and a copolymer.

  As a result of intensive studies to achieve the above-mentioned object, the present inventors have found that the above-mentioned problems can be solved if the separator for an electricity storage device has a specific polymer on at least a part of at least one side of the substrate. The present invention has been completed.

That is, the present invention is as follows.
[1] A separator for an electricity storage device comprising: a base material; and a layer containing a thermoplastic polymer formed on at least a part of at least one surface of the base material,
The thermoplastic polymer has at least 2 to 66% by mass of an ethylenically unsaturated monomer having a chain alkyl group having 8 or more carbon atoms and an ethylenically unsaturated monomer having a chain alkyl group having 8 or more carbon atoms. The separator for electrical storage devices containing the copolymer which has 34-98 mass% of other monomers copolymerizable with a monomer unit.
[2] The electricity storage device separator according to [1], wherein the ethylenically unsaturated monomer having a chain alkyl group having 8 or more carbon atoms is 2-ethylhexyl acrylate.
[3] The separator for an electricity storage device according to [1] or [2], wherein the other monomer includes an ethylenically unsaturated monomer having an amide group.
[4] The electricity storage device separator according to any one of [1] to [3], wherein the other monomer includes an ethylenically unsaturated monomer having a hydroxyl group.
[5] The electricity storage device separator according to any one of [1] to [4], wherein the other monomer includes a crosslinkable monomer.
[6] The separator for an electricity storage device according to any one of [1] to [5], wherein the other monomer includes an ethylenically unsaturated monomer having a cycloalkyl group.
[7] The electricity storage device separator according to any one of [1] to [6], wherein the other monomer includes an ethylenically unsaturated monomer having a carboxyl group.
[8] The separator for an electricity storage device according to [6], wherein the ethylenically unsaturated monomer having a cycloalkyl group is cyclohexyl acrylate or cyclohexyl methacrylate.
[9] The electricity storage according to any one of [1] to [8], wherein the degree of swelling of the copolymer with respect to a mixed solvent (mass ratio 2: 3) of ethylene carbonate and diethyl carbonate is 5.0 times or less. Device separator.
[10] The electricity storage device separator according to any one of [1] to [9], wherein the copolymer includes a copolymer produced by emulsion polymerization.
[11] The separator for an electricity storage device according to any one of [1] to [10], wherein the peel strength after pressing the aluminum foil at a temperature of 80 ° C. and a pressure of 10 MPa for 3 minutes is 5 N / m or more. .
[12] The electricity storage device separator according to any one of [1] to [11], wherein the layer containing the thermoplastic polymer is present in a dot shape on at least one surface of the base material.
[13] The separator for an electricity storage device according to any one of [1] to [12], wherein the base material is a polyolefin microporous film.
[14] An electricity storage device comprising the separator for an electricity storage device according to any one of [1] to [13].
[15] A lithium ion secondary battery comprising the electricity storage device separator according to any one of [1] to [13].
[16] Copolymerization with an ethylenically unsaturated monomer having a chain alkyl group having 8 or more carbon atoms, 2 to 66% by mass, and an ethylenically unsaturated monomer having a chain alkyl group having 8 or more carbon atoms Copolymer having 34 to 98% by mass of other possible monomers as monomer units.
[17] The copolymer according to [16], wherein the ethylenically unsaturated monomer having a chain alkyl group having 8 or more carbon atoms is 2-ethylhexyl acrylate.
[18] The copolymer according to [16] or [17], wherein the other monomer includes an ethylenically unsaturated monomer having an amide group.
[19] The copolymer according to any one of [16] to [18], wherein the other monomer includes an ethylenically unsaturated monomer having a hydroxyl group.
[20] The copolymer according to any one of [16] to [19], wherein the other monomer includes a crosslinkable monomer.
[21] The copolymer according to any one of [16] to [20], wherein the other monomer includes an ethylenically unsaturated monomer having a cycloalkyl group.
[22] The copolymer according to any one of [16] to [21], wherein the other monomer includes an ethylenically unsaturated monomer having a carboxyl group.
[23] The copolymer according to [21], wherein the ethylenically unsaturated monomer having a cycloalkyl group is cyclohexyl acrylate or cyclohexyl methacrylate.
[24] The copolymer according to any one of [16] to [23], wherein the degree of swelling of the copolymer with respect to a mixed solvent of ethylene carbonate and diethyl carbonate (mass ratio 2: 3) is 5.0 times or less. Polymer.
[25] The copolymer according to any one of [16] to [24], wherein the copolymer is a copolymer produced by emulsion polymerization.
[26]
The copolymer according to any one of [16] to [25], wherein the copolymer is used in an electricity storage device.
[27] The copolymer according to any one of [16] to [26], wherein the copolymer is used for a separator for an electricity storage device.
[28] An aqueous dispersion comprising water and the copolymer according to any one of [16] to [27] dispersed in the water.

  ADVANTAGE OF THE INVENTION According to this invention, the separator for electrical storage devices excellent in adhesiveness with an electrode, an electrical storage device, a lithium ion secondary battery, and a copolymer can be provided.

(A)-(E) are schematic diagrams which show the planar shape of the layer containing the thermoplastic polymer with which the separator of this invention is provided.

  Hereinafter, a mode for carrying out the present invention (hereinafter abbreviated as “this embodiment”) will be described in detail. The present invention is not limited to the following embodiment, and can be implemented with various modifications within the scope of the gist. In the present specification, “(meth) acryl” means “acryl” and “methacryl” corresponding thereto, “(meth) acrylate” means “acrylate” and “methacrylate” corresponding thereto, “(Meth) acryloyl” means “acryloyl” and its corresponding “methacryloyl”.

  The copolymer of this embodiment includes 2-66% by mass of an ethylenically unsaturated monomer (A) having a chain alkyl group having 8 or more carbon atoms and ethylene having the chain alkyl group having 8 or more carbon atoms. It is a copolymer having 34 to 98% by mass of another monomer (B) copolymerizable with the polymerizable unsaturated monomer as a monomer unit. The separator for an electricity storage device of this embodiment includes a base material and a layer containing a thermoplastic polymer (hereinafter referred to as “polymer layer”) formed on at least a part of at least one surface of the base material. The thermoplastic polymer is ethylenically unsaturated monomer (A) having a chain alkyl group having 8 or more carbon atoms (A) 2-66% by mass and ethylenic having the chain alkyl group having 8 or more carbon atoms It includes a copolymer having 34 to 98% by mass of another monomer (B) copolymerizable with an unsaturated monomer as a monomer unit. Here, the “ethylenically unsaturated monomer” means a monomer having one or more ethylenically unsaturated bonds in the molecule.

  The ethylenically unsaturated monomer (A) having a chain alkyl group having 8 or more carbon atoms is not particularly limited, but has a chain alkyl group having 8 or more carbon atoms and has an ethylenically unsaturated bond. One having one is mentioned. More specifically, the monomer (A) has 8 or more carbon atoms such as octyl (meth) acrylate having 8 carbon atoms, decyl (meth) acrylate having 10 carbon atoms, dodecyl (meth) acrylate having 12 carbon atoms, or the like. (Meth) acrylic acid ester monomers having a chain alkyl group and ester monomers in which the respective alkyl moieties are isomerized. Among these, 2-ethylhexyl (meth) acrylate classified into carbon number 8 is particularly preferable, and 2-ethylhexyl acrylate is more preferable from the viewpoint of polymerization stability at the time of producing the copolymer and lowering the Tg of the copolymer. preferable. These are used singly or in combination of two or more.

  The copolymer having the ethylenically unsaturated monomer (A) having a chain alkyl group having 8 or more carbon atoms as a monomer unit is prepared by using a monomer (A The other monomer (B) that can be copolymerized with ()) as a monomer unit. The other monomer (B) is a monomer different from the monomer (A). The other monomer (B) is not particularly limited, and examples thereof include an ethylenically unsaturated monomer (b1) having a carboxyl group, an ethylenically unsaturated monomer (b2) having an amide group, and a hydroxyl group. Ethylenically unsaturated monomer (b3), crosslinkable monomer (b4), ethylenically unsaturated monomer (b5) having a cycloalkyl group, ethylenically unsaturated monomer having a cyano group ( b6), an ethylenically unsaturated monomer (b7) having an aromatic group, other ethylenically unsaturated monomers (b8), and (meth) acrylic acid ester monomers (b9). Another monomer (B) is used individually by 1 type or in combination of 2 or more types. Further, the other monomer (B) may belong to two or more of the above monomers at the same time. That is, the other monomer (B) is an ethylenically unsaturated monomer having two or more groups selected from the group consisting of carboxyl group, amide group, hydroxyl group, cycloalkyl group, cyano group and aromatic group. A crosslinkable monomer having two or more groups selected from the group consisting of a carboxyl group, an amide group, a hydroxyl group, a cycloalkyl group, a cyano group and an aromatic group together with an ethylenically unsaturated bond It may be.

  Especially, it is preferable that another monomer (B) contains the ethylenically unsaturated monomer (b1) which has a carboxyl group from a viewpoint of the cushioning property improvement in a swelling state. Examples of the ethylenically unsaturated monomer (b1) having a carboxyl group include monocarboxylic acid monomers such as acrylic acid, methacrylic acid, itaconic acid half ester, maleic acid half ester, and fumaric acid half ester. And dicarboxylic acid monomers such as itaconic acid, fumaric acid and maleic acid. These are used singly or in combination of two or more. Among these, from the same viewpoint, acrylic acid, methacrylic acid and itaconic acid are preferable, and acrylic acid and methacrylic acid are more preferable.

  Further, from the viewpoint of improving the adhesion with the electrode (electrode active material), the other monomer (B) preferably contains an ethylenically unsaturated monomer (b2) having an amide group. The ethylenically unsaturated monomer (b2) having an amide group is not particularly limited, and examples thereof include acrylamide, methacrylamide, N, N-methylenebisacrylamide, diacetone acrylamide, diacetone methacrylamide, maleic amide and Maleimide is mentioned. These are used singly or in combination of two or more. Of these, acrylamide and methacrylamide are preferable. By using acrylamide and / or methacrylamide, the adhesion of the separator to the electrode (electrode active material) tends to be further improved.

  Further, from the viewpoint of improving the polymerization stability of the copolymer, the other monomer (B) preferably contains an ethylenically unsaturated monomer (b3) having a hydroxyl group. Examples of the ethylenically unsaturated monomer (b3) having a hydroxyl group include hydroxyl groups such as hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, polyethylene glycol acrylate and polyethylene glycol methacrylate (meta ) Acrylates. These are used singly or in combination of two or more. Of these, hydroxyethyl acrylate and hydroxyethyl methacrylate are preferred. By using hydroxyethyl acrylate and / or hydroxyethyl methacrylate, the polymerization stability of the copolymer tends to be improved.

  Further, from the viewpoint of making the insoluble content in the electrolytic solution to an appropriate amount, the other monomer (B) preferably contains a crosslinkable monomer (b4). The crosslinkable monomer (b4) is not particularly limited. For example, a monomer having two or more radical polymerizable double bonds, a functional group that gives a self-crosslinking structure during or after polymerization. The monomer which has. 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. Among these, polyfunctional (meth) acrylates are preferable from the viewpoint of better electrolytic solution resistance even in a small amount.

  The polyfunctional (meth) acrylate (b4) may be a bifunctional (meth) acrylate, a trifunctional (meth) acrylate, or a tetrafunctional (meth) acrylate. For example, polyoxyethylene diacrylate, polyoxyethylene diacrylate Methacrylate, polyoxypropylene diacrylate, polyoxypropylene dimethacrylate, neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, butanediol diacrylate, butanediol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol Examples include tetraacrylate and pentaerythritol tetramethacrylate. These are used singly or in combination of two or more. Of these, trimethylolpropane triacrylate and trimethylolpropane trimethacrylate are preferable from the same viewpoint as described above.

  Examples of the monomer having a functional group that gives a self-crosslinking structure during or after polymerization include, for example, an ethylenically unsaturated monomer having an epoxy group, an ethylenic monomer having a methylol group, and an ethylene having an alkoxymethyl group And an ethylenically unsaturated monomer having a hydrolyzable silyl group. These are used singly or in combination of two or more.

  Examples of the ethylenically unsaturated monomer having an epoxy group include glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, methyl glycidyl acrylate, and methyl glycidyl methacrylate. These are used singly or in combination of two or more. Of these, glycidyl methacrylate is preferred.

  Examples of the ethylenically unsaturated monomer having a methylol group include N-methylol acrylamide, N-methylol methacrylamide, dimethylol acrylamide, and dimethylol methacrylamide. These are used singly or in combination of two or more.

  Examples of the ethylenically unsaturated monomer having an alkoxymethyl group include N-methoxymethyl acrylamide, N-methoxymethyl methacrylamide, N-butoxymethyl acrylamide, and N-butoxymethyl methacrylamide. These are used singly or in combination of two or more.

  Examples of the ethylenically unsaturated monomer having a hydrolyzable silyl group include vinyl silane, γ-acryloxypropyltrimethoxysilane, γ-acryloxypropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, and γ. -Methacryloxypropyltriethoxysilane. These are used singly or in combination of two or more.

  Among the crosslinkable monomers (b4), polyfunctional (meth) acrylates are particularly preferable in that there is little variation in the degree of crosslinking.

  Further, from the viewpoint of improving the adhesion with the electrode, the other monomer (B) preferably contains an ethylenically unsaturated monomer (b5) having a cycloalkyl group. Although it does not specifically limit as an ethylenically unsaturated monomer (b5) which has a cycloalkyl group, What has a cycloalkyl group and one ethylenically unsaturated bond is mentioned. As the monomer (b5), more specifically, a (meth) acrylic acid ester having a cycloalkyl group such as cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, adamantyl (meth) acrylate, etc. The (meth) acrylic acid ester monomer which consists of a cycloalkyl group and a (meth) acryloyloxy group is more preferable. 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, an isopropyl group, and a tertiary butyl group. Among the monomers (b5), cyclohexyl (meth) acrylate is preferable from the viewpoint of good polymerization stability when preparing the copolymer. These are used singly or in combination of two or more.

Examples of the ethylenically unsaturated monomer (b6) having a cyano group include acrylonitrile and methacrylonitrile. Moreover, as an ethylenically unsaturated monomer (b7) which has an aromatic group, styrene, vinyl toluene, and alpha-methylstyrene are mentioned, for example. Of these, styrene is preferable. Other ethylenically unsaturated monomers (b8) include 1,3-butadiene, a monomer group having a conjugated double bond in the molecule, a monomer group having a vinyl group in the molecule, and the like. Can be mentioned.
Further, from the viewpoint of improving the oxidation resistance of the thermoplastic polymer containing the copolymer, the other monomer (B) preferably contains a (meth) acrylic acid ester monomer (b9). The (meth) acrylic acid ester monomer (b9) is a monomer different from the monomers (A) and (b1) to (b8). Examples of the (meth) acrylic acid ester monomer (b9) include (meth) acrylic acid esters having one ethylenically unsaturated bond and having a chain alkyl group having less than 8 carbon atoms, More specifically, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, (Meth) acrylate having an alkyl group such as n-hexyl (meth) acrylate (more preferably (meth) acrylate comprising an alkyl group and a (meth) acryloyloxy group). Further, (meth) acrylate having an aromatic ring such as benzyl (meth) acrylate and phenyl (meth) acrylate (more preferably (meth) acrylate composed of an aromatic ring and a (meth) acryloyloxy group) can be mentioned. Among these, a (meth) acrylic acid ester monomer comprising a chain alkyl group having 4 to 8 carbon atoms and a (meth) acryloyloxy group from the viewpoint of improving adhesion to an electrode (electrode active material). A (meth) acrylic acid ester monomer comprising an alkyl group having 6 to 8 carbon atoms and a (meth) acryloyloxy group is more preferable. More specifically, methyl methacrylate and butyl (meth) acrylate are preferable, and butyl (meth) acrylate and hexyl (meth) acrylate are more preferable. These (meth) acrylic acid ester monomers (b9) are used singly or in combination of two or more.

  The content of the ethylenically unsaturated monomer (A) having a chain alkyl group having 8 or more carbon atoms in the copolymer is 2 to 66% by mass with respect to 100% by mass of the copolymer. The lower limit is preferably 5% by mass, more preferably 10% by mass, still more preferably 12% by mass, and particularly preferably 15% by mass. When the content ratio of the ethylenically unsaturated monomer (A) having a chain alkyl group having 8 or more carbon atoms is within this range, the adhesion of the separator to the electrode (electrode active material) is improved. On the other hand, a more preferable upper limit is 60% by mass. When the content of the ethylenically unsaturated monomer (A) having a chain alkyl group having 8 or more carbon atoms is 60% by mass or less, the improvement of the polymerization stability at the time of preparing the copolymer and the copolymer The stiffness in the range of 0 ° C. to 80 ° C. does not decrease too much.

On the other hand, from the viewpoint of blocking resistance on the substrate and adhesion to the electrode in the presence of an electrolyte solvent inside the battery, in the design region of Tg = 40 ° C. or higher in the copolymer, the carbon number of 8 or higher. The content ratio of the ethylenically unsaturated monomer (A) having a chain alkyl group is preferably 3 to 20% by mass. More preferably, it is 5-19 mass%, More preferably, it is 10-19 mass%.
In addition, from the viewpoint of adhesiveness with the base material at the time of application on the base material, in the design region of Tg = 15 ° C. or lower in the copolymer, the chain alkyl having 8 or more carbon atoms in the copolymer is used. The content of the ethylenically unsaturated monomer (A) having a group is preferably 31 to 66% by mass.

  In other words, the content of the other monomer (B) in the copolymer is 98 to 34% by mass with respect to 100% by mass of the copolymer. The upper limit is preferably 95% by mass, more preferably 90% by mass, still more preferably 88% by mass, and particularly preferably 85% by mass. On the other hand, a more preferable lower limit is 40% by mass.

  Moreover, as a suitable containing form of the ethylenically unsaturated monomer (A) which has a C8 or more chain | strand alkyl group in the said copolymer, the single quantity below Tg = 0 degreeC in the said copolymer is used. 50% of the total monomer at 0 ° C. or lower when considering only the body (monomer having Tg = 0 ° C. or lower refers to a monomer that forms a homopolymer with Tg = 0 ° C. or lower). It is preferable to contain in the above ratio. More preferably, it is 60% or more, and further preferably 70% or more. When the proportion of the ethylenically unsaturated monomer (A) having a chain alkyl group having 8 or more carbon atoms contained in the monomer having Tg = 0 ° C. or less exceeds 50%, Adhesion is improved. Here, other than the ethylenically unsaturated monomer (A) having a chain alkyl group having 8 or more carbon atoms, monomers having a Tg = 0 ° C. or lower include alkyl acrylates such as ethyl acrylate, butyl acrylate, and hexyl acrylate. Compounds.

  Moreover, the content ratio of the total (meth) acrylic acid ester monomer in the copolymer is preferably 50 to 99.9% by mass, more preferably 60 to 99% with respect to 100% by mass of the copolymer. 9.9% by mass, more preferably 70-99.9% by mass, still more preferably 80-99.9% by mass. In this paragraph, the total (meth) acrylic acid ester monomer is an ethylenically unsaturated monomer (A) having a chain alkyl group having 8 or more carbon atoms, regardless of the structure of the substituent or the presence or absence of a functional group. And among the other monomers (B) copolymerizable with the monomer (A), all of the (meth) acrylic acid ester structure (refer to the preceding paragraph, ( It is different from the content of the (meth) acrylate monomer (b9)). When the content ratio of all (meth) acrylic acid ester monomers is within the above range, the oxidation resistance of the thermoplastic polymer becomes better when the separator is used in a non-aqueous electrolyte secondary battery.

  When the other monomer (B) contains an ethylenically unsaturated monomer (b1) having a carboxyl group, the content ratio of the ethylenically unsaturated monomer (b1) having a carboxyl group in the copolymer is: Preferably it is 0.1-5 mass% with respect to 100 mass% of copolymers. When the content ratio of the ethylenically unsaturated monomer (b1) having a carboxyl group is 0.1% by mass or more, the separator tends to improve cushioning properties in a swollen state, and is 5% by mass or less. The polymerization stability tends to be good.

  When the other monomer (B) contains an ethylenically unsaturated monomer (b2) having an amide group, the content ratio of the ethylenically unsaturated monomer (b2) having an amide group in the copolymer is: Preferably it is 0.1-10 mass% with respect to 100 mass% of copolymers, More preferably, it is 2-10 mass%. If the content of the ethylenically unsaturated monomer (b2) having an amide group is 0.1% by mass or more, the adhesion with the electrode (electrode active material) tends to be further improved, and 10% by mass or less. When it is, it exists in the tendency for the polymerization stability at the time of preparing a copolymer to improve more.

  When the other monomer (B) contains an ethylenically unsaturated monomer (b3) having a hydroxyl group, the content ratio of the ethylenically unsaturated monomer (b3) having a hydroxyl group in the copolymer is: Preferably it is 0.1-10 mass% with respect to 100 mass% of copolymers, More preferably, it is 1-10 mass%. When the content ratio of the ethylenically unsaturated monomer (b3) having a hydroxyl group is within the above range, the polymerization stability in preparing the copolymer tends to be further improved.

  When the other monomer (B) contains the crosslinkable monomer (b4), the content of the crosslinkable monomer (b4) in the copolymer is preferably 100% by mass of the copolymer. It is 0.01-10 mass%, More preferably, it is 0.1-5 mass%, More preferably, it is 0.1-3 mass%. When the content of the crosslinkable monomer (b4) is 0.01% by mass or more, the electrolytic solution resistance is further improved, and when it is 5% by mass or less, the deterioration of the cushioning property in the swollen state is further suppressed. Can do.

When the other monomer (B) contains an ethylenically unsaturated monomer (b5) having a cycloalkyl group, the content of the ethylenically unsaturated monomer (b5) having a cycloalkyl group in the copolymer The ratio is preferably 10 to 90% by mass and more preferably 30 to 90% by mass with respect to 100% by mass of the copolymer.
The glass transition temperature (hereinafter also referred to as “Tg”) of the copolymer is not particularly limited, but may be −40 to 80 ° C., preferably −35 to 80 ° C., more preferably − It is 30 degreeC-80 degreeC, More preferably, it is -30 degreeC-70 degreeC. By making Tg of a copolymer into the range of -40-80 degreeC, adhesiveness with the electrode (electrode active material) of a separator becomes still better. Moreover, adhesiveness with an electrode active material is made into a mixture of 5 to 40% by mass of a copolymer having a Tg of −40 ° C. to 15 ° C. and 60 to 95% by mass of a copolymer having a Tg of 40 to 80 ° C. While maintaining the above, handling properties such as powder-off and blocking resistance are improved.

  Here, the glass transition temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC). Specifically, it is 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.

  “Glass transition” refers to a change in calorific value associated with a change in the state of the polymer that is a test piece in DSC on the endothermic side. Such a change in heat quantity is observed as a step-like change shape in the DSC curve. The “step change” refers to a portion of the DSC curve until the curve moves away from the previous low-temperature base line to a new high-temperature base line. Note that a combination of a step change and a peak is also included in the step change.

  Further, the “inflection point” indicates a point at which the gradient of the DSC curve of the step-like change portion is maximized. Further, in the step-like change portion, when the upper side is the heat generation side, it can also be expressed as a point where the upward convex curve changes to the downward convex curve. “Peak” indicates a portion of the DSC curve from when the curve leaves the low-temperature side baseline until it returns to the same baseline again. “Baseline” refers to a DSC curve in a temperature region where no transition or reaction occurs in the test piece.

  In the separator of this embodiment, the swelling degree of the copolymer with respect to the mixed solvent of ethylene carbonate and diethyl carbonate (mass ratio 2: 3) is preferably 5.0 times or less, and 4.5 times or less. More preferably, it is 4.0 times or less, particularly preferably 3.5 times or less. When the degree of swelling is 5.0 times or less, the reliability of the electricity storage device can be further improved. 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 copolymer 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. A copolymer is obtained by polymerizing the monomer composition. In the polymerization, the composition of the monomer composition to be supplied is made constant throughout the entire polymerization process, or the morphological composition change of the particles of the resin dispersion to be produced is changed sequentially or continuously in the polymerization process. Various methods can be used as necessary, such as a method of giving When the copolymer is obtained by emulsion polymerization, for example, it may be in the form of an aqueous dispersion (latex) containing water and a particulate copolymer dispersed in the water.

  The surfactant is a compound having at least one or more hydrophilic groups and one or more lipophilic groups in one molecule. Examples of the surfactant include non-reactive alkyl sulfate, polyoxyethylene alkyl ether sulfate, alkyl benzene sulfonate, alkyl naphthalene sulfonate, alkyl sulfosuccinate, alkyl diphenyl ether disulfonate, naphthalene sulfone. Anionic interfaces such as acid formalin condensate, polyoxyethylene polycyclic phenyl ether sulfate, polyoxyethylene distyrenated phenyl ether sulfate, fatty acid salt, alkyl phosphate, polyoxyethylene alkylphenyl ether sulfate Activators and non-reactive polyoxyethylene alkyl ethers, polyoxyalkylene alkyl ethers, polyoxyethylene polycyclic phenyl ethers, polyoxyethylene disty Phenyl ether, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester, polyoxyethylene fatty acid ester, polyoxyethylene alkylamine, alkylalkanolamide, polyoxyethylene alkylphenyl ether, etc. Nonionic surfactants. In addition to these, a so-called reactive surfactant in which an ethylenic double bond is introduced into the chemical structural formula of a surfactant having a hydrophilic group and a lipophilic group may be used.

  Examples of the anionic surfactant in the reactive surfactant include an ethylenically unsaturated monomer having a sulfonic acid group, a sulfonate group or a sulfate ester group and a salt thereof, and a sulfonic acid group, or A compound having a group (ammonium sulfonate group or alkali metal sulfonate group) which is an ammonium salt or an alkali metal salt thereof is preferable. Specifically, for example, alkylallylsulfosuccinate (for example, Eleminol (trademark) JS-20 manufactured by Sanyo Chemical Co., Ltd., Latemuru (trademark; manufactured by Kao Corporation), S-120, S-180A, S- 180), polyoxyethylene alkylpropenyl phenyl ether sulfate ester salt (for example, Aqualon (trademark; the same shall apply hereinafter) HS-10 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), α- [1- [ (Allyloxy) methyl] -2- (nonylphenoxy) ethyl] -ω-polyoxyethylene sulfate ester salt (for example, ADEKA Corporation soap (trademark; the same shall apply hereinafter) SE-10N manufactured by ADEKA Corporation), ammonium. = Α-sulfonato-ω-1- (allyloxymethyl) alkyloxypolyoxyethylene (eg, Aquaron KH-10 manufactured by Ichi Kogyo Seiyaku Co., Ltd.), styrene sulfonate (for example, Spinomer (trademark) NaSS manufactured by Tosoh Organic Chemical Co., Ltd.), α- [2-[(allyloxy)- 1- (alkyloxymethyl) ethyl] -ω-polyoxyethylene sulfate ester salt (for example, Adeka Soap SR-10 manufactured by ADEKA Corporation), polyoxyethylene polyoxybutylene (3-methyl-3- Butenyl) ether sulfate (for example, LATEMUL PD-104 manufactured by Kao Corporation) may be mentioned.

  Examples of the nonionic surfactant in the reactive surfactant include α- [1-[(allyloxy) methyl] -2- (nonylphenoxy) ethyl] -ω-hydroxypolyoxyethylene (for example, Adeka Soap NE-20, NE-30, NE-40 manufactured by ADEKA Co., Ltd.), polyoxyethylene alkylpropenyl phenyl ether (for example, Aqualon RN-10, RN-20, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) RN-30 and RN-50), α- [2-[(allyloxy) -1- (alkyloxymethyl) ethyl] -ω-hydroxypolyoxyethylene (for example, Adeka Soap ER manufactured by ADEKA Corporation) -10)), polyoxyethylene polyoxybutylene (3-methyl-3-butenyl) A Le (for example, Kao Corp. LATEMUL PD-420.) And the like.

  Among the above-mentioned various surfactants, reactive surfactants are preferable, anionic reactive surfactants are more preferable, and reactive surfactants having a sulfonic acid group are more preferable. The surfactant is preferably used in an amount of 0.1 to 5 parts by mass with respect to 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. Examples of the water-soluble polymerization initiator include peroxodisulfates, peroxides, water-soluble azobis compounds, and peroxide-reducing agent redox systems. Examples of the peroxodisulfate include potassium peroxodisulfate (KPS), sodium peroxodisulfate (NPS), and ammonium peroxodisulfate (APS). Examples of the peroxide include hydrogen peroxide, t- Examples thereof include butyl hydroperoxide, t-butyl peroxymaleic acid, succinic acid peroxide, and benzoyl peroxide. Examples of water-soluble azobis compounds include 2,2-azobis (N-hydroxyethylisobutyramide), 2 And 2-azobis (2-amidinopropane) dichloride and 4,4-azobis (4-cyanopentanoic acid). Examples of the redox system of the peroxide-reducing agent include sodium peroxide and sodium peroxide. Sulfooxylate formaldehyde, sodium bisulfite, sodium thiosulfate Um, sodium hydroxymethanesulfinic acid, L- ascorbic acid, and its salts, cuprous salts, and include those that combine one or more reducing agents such as ferrous salts.

  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 is used individually by 1 type or in combination of 2 or more types.

  A monomer composition containing an ethylenically unsaturated monomer (A) having a chain alkyl group having 8 or more carbon atoms and another monomer (B) is emulsion-polymerized to obtain polymer particles. When forming a dispersion dispersed in a solvent (water), the solid content of the obtained dispersion is preferably 30% by mass to 70% by mass.

  The dispersion is preferably adjusted to have a pH 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 pH is more preferably adjusted with ammonia (water) or sodium hydroxide.

  The aqueous dispersion of this embodiment includes a copolymer obtained by copolymerizing the monomer composition containing the specific monomer as particles (copolymer particles) dispersed in water. In addition to water and the copolymer, the aqueous dispersion may contain a solvent such as methanol, ethanol, isopropyl alcohol, a dispersant, a lubricant, a thickener, a bactericide, and the like.

  The average particle size of the copolymer particles is preferably 100 to 250 nm, more preferably 120 to 250 nm, and still more preferably 130 to 250 nm. Setting the average particle size of the copolymer particles to 100 nm or more is preferable because the air permeability of a separator provided with a polymer layer and a base material described later supporting the layer can be maintained better. Moreover, it is preferable from the viewpoint of ensuring the dispersion stability of the aqueous dispersion that the average particle diameter of the copolymer particles is 250 nm or less. The average particle diameter of the copolymer particles can be measured according to the method described in the following examples.

  In addition, it can be confirmed by pyrolysis gas chromatography that the copolymer has an ethylenically unsaturated monomer (A) having a chain alkyl group having 8 or more carbon atoms as a monomer unit. More specifically, a homopolymer of an ethylenically unsaturated monomer (A) having a chain alkyl group having 8 or more carbon atoms is measured by pyrolysis gas chromatography, and the retention time of the pyrolyzate is determined in advance. decide. Next, when the copolymer is measured under the same conditions by pyrolysis gas chromatography and has a peak of pyrolysis product at the same retention time, a linear alkyl having 8 or more carbon atoms as the copolymer monomer unit is used. It can be presumed to have an ethylenically unsaturated monomer (A) having a group. Further, by using a homopolymer of an ethylenically unsaturated monomer (A) having a chain alkyl group having 8 or more carbon atoms as an internal standard, a chain having 8 or more carbon atoms in the copolymer monomer unit. It is also possible to determine the proportion of the ethylenically unsaturated monomer (A) having an alkyl group.

Since the separator of this embodiment has a polymer layer on at least a part of at least one surface of the base material, the electrode and the separator can be bonded through a hot pressing process. That is, the polymer layer can function as an adhesive layer.
The thermoplastic polymer preferably contains 60% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, and particularly preferably 98% by mass or more with respect to the total amount of the copolymer. In addition to the copolymer, the thermoplastic polymer may contain other components to the extent that the solution to the problem of the present invention is not impaired.

  The substrate used in the present embodiment may itself be one that has been conventionally used as a separator. The base material is preferably a porous film having a fine pore size, having no electron conductivity, ionic conductivity, high resistance to organic solvents. As such a porous membrane, for example, a polyolefin-based (for example, polyethylene, polypropylene, polybutene and polyvinyl chloride), and a microporous membrane containing a resin such as a mixture or copolymer thereof as a main component, polyethylene terephthalate, Microporous membrane containing resin such as polycycloolefin, polyethersulfone, polyamide, polyimide, polyimideamide, polyaramid, polycycloolefin, nylon, polytetrafluoroethylene, woven polyolefin fiber (woven fabric) ), Polyolefin fiber nonwoven fabric, paper, and aggregates of insulating substance particles. Among these, when a polymer layer is obtained through a coating process, the coating solution is excellent in coating property, the separator film thickness is made thinner, and the active material ratio in an electricity storage device such as a battery is increased to increase the volume per volume. From the viewpoint of increasing the capacity, a polyolefin microporous film containing a polyolefin-based resin as a main component is preferable. Here, “include as a main component” means to contain more than 50% by mass, preferably 75% by mass or more, more preferably 85% by mass or more, and further preferably 90% by mass or more. More preferably 95% by mass or more, particularly preferably 98% by mass or more, and may be 100% by mass.

  The thickness of a base material becomes like this. Preferably it is 0.5-40 micrometers, More preferably, it is 1-30 micrometers, More preferably, it is 1-10 micrometers. When the thickness of the base material is within this range, the resistance by the separator in the electricity storage device such as a battery becomes smaller, and when the polymer layer is obtained through the coating process, it is applied to the base material. Workability at the time is further improved.

  In the present embodiment, examples of the polyolefin-based resin used as the base material include homopolymers such as polyethylene and polypropylene, copolymers, and mixtures thereof. Examples of the polyethylene include low density, medium density, and high density polyethylene, and high density polyethylene is preferable from the viewpoint of piercing strength and mechanical strength. These polyethylenes may be used in combination of two or more for the purpose of imparting flexibility. The polymerization catalyst used in the production of these polyethylenes is not particularly limited, and examples thereof include Ziegler-Natta catalysts, Philips catalysts, and metallocene catalysts. From the viewpoint of achieving both high mechanical strength and high permeability, the viscosity average molecular weight of polyethylene is preferably 100,000 or more and 12 million or less, more preferably 200,000 or more and 3 million or less.

The viscosity average molecular weight (Mv) is calculated from the intrinsic viscosity [η] measured at a measurement temperature of 135 ° C. using decalin as a solvent based on ASTM-D4020 by the following formula.
Polyethylene: [η] = 6.77 × 10 ⁻⁴ Mv ^0.67 (Chiang formula)
Polypropylene: [η] = 1.10 × 10 ⁻⁴ Mv ^0.80

  Examples of polypropylene include homopolymers, random copolymers, and block copolymers, and one kind or a mixture of two or more kinds can be used. The polymerization catalyst is not particularly limited, and examples thereof include Ziegler-Natta catalysts and metallocene catalysts. Moreover, there is no restriction | limiting in particular also in the stereoregularity of a polypropylene, Any of isotactic, syndiotactic, and atactic may be sufficient. However, it is preferable to use isotactic polypropylene because it is inexpensive. Furthermore, an appropriate amount of polyolefins other than polyethylene and polypropylene, and additives such as antioxidants and nucleating agents may be added to the base material within the range not impairing the effects of the present invention.

  A method for producing a base material containing a polyolefin-based resin as a main component may be a known one. Examples of the manufacturing method include a dry manufacturing method and a wet manufacturing method. In the dry production method, for example, a film is first formed by melt extrusion of a polyolefin-based resin such as polypropylene or polyethylene. Thereafter, the film is annealed at a low temperature to grow a crystal domain, and in this state, the film is stretched to extend the amorphous region, thereby forming a microporous film as a substrate. In the wet manufacturing method, for example, first, a hydrocarbon solvent or other low molecular weight material and a polyolefin-based resin such as polypropylene or polyethylene are mixed, and then formed into a film shape. Next, the film in which the solvent and low-molecular material have gathered in the amorphous phase and have started to form the island phase is removed using another solvent that easily volatilizes the solvent and low-molecular material, so that A porous film is formed.

  The method for producing a nonwoven fabric or paper as a substrate may be a known one. The production method includes, for example, a chemical bond method in which a web is dipped in a binder and dried to bond fibers; a thermal bond method in which hot-melt fibers are mixed into the web and the fibers are partially melted to bond fibers. A needle punch method in which a needle having a stab is repeatedly stabbed into the web and mechanically entangled with the fiber; a high-pressure water flow is entangled between the fibers by jetting a high-pressure water stream from the nozzle through the net (screen).

  The base material used in the present embodiment may contain a filler (inorganic filler or organic filler) or a fiber compound for the purpose of controlling strength, hardness, and thermal shrinkage. In addition, when the base material is a laminate of non-conductive particles and a porous membrane layer containing a binder, the adhesion is improved, or the surface tension with the electrolyte is lowered to improve the liquid impregnation property. For this purpose, the substrate surface may be coated with a low molecular compound or a polymer compound in advance, or may be subjected to electromagnetic radiation treatment such as ultraviolet rays or plasma treatment such as corona discharge / plasma gas. In particular, it contains polar groups such as a carboxylic acid group, a hydroxyl group, and a sulfonic acid group from the viewpoint that the impregnation property of the electrolytic solution is high and the adhesion to the porous membrane layer containing the non-conductive particles and the binder is easily obtained. It is preferable to coat with a polymer compound.

  The base material used in the present embodiment may have a multilayer structure in which the above-mentioned base materials are stacked for the purpose of increasing the tear strength and the puncture strength. Specific examples include a laminate of a polyethylene microporous membrane and a polypropylene microporous membrane, and a laminate of a nonwoven fabric and a polyolefin microporous membrane.

  The air permeability of the substrate is not particularly limited, but is preferably 10 sec / 100 cc or more, more preferably 50 sec / 100 cc or more, preferably 1000 sec / 100 cc or less, more preferably 500 sec from the viewpoint of enhancing the performance of the electricity storage device. / 100 cc or less. The air permeability is preferably 10 sec / 100 cc or more from the viewpoint of further suppressing self-discharge of the electricity storage device. On the other hand, setting it to 1000 sec / 100 cc or less is preferable from the viewpoint of obtaining even better charge / discharge characteristics.

  Further, from the same viewpoint, the porosity of the base material is preferably 20% or more, more preferably 35% or more, preferably 90% or less, from the viewpoint of improving the mechanical strength while enhancing the performance of the electricity storage device. Preferably it is 80% or less. Setting the porosity to 20% or more is preferable from the viewpoint of securing excellent permeability of the separator. On the other hand, it is preferable to set it as 90% or less from a viewpoint of ensuring the outstanding puncture strength.

Further, the puncture strength of the substrate is preferably 200 g / 20 μm or more, more preferably 300 g / 20 μm or more, preferably 2000 g / 20 μm or less, from the viewpoint of improving reliability as a separator and suppressing thermal shrinkage. More preferably, it is 1000 g / 20 μm or less. It is preferable that the puncture strength is 200 g / 20 μm or more from the viewpoint of further suppressing film breakage due to the dropped active material or the like during battery winding. Moreover, it is also preferable from the viewpoint of further suppressing the fear of short-circuiting due to the expansion and contraction of the electrode accompanying charging and discharging. On the other hand, it is preferable to set it as 2000 g / 20 micrometers or less from a viewpoint which can further reduce the width | variety shrinkage by the orientation relaxation at the time of a heating.
These air permeability, porosity, and puncture strength are measured according to the methods described in Examples.

(Amount of polymer layer supported on substrate)
Loading amount to the substrate of the polymer layer in the present embodiment is preferably from 0.05 g / m ² or more 1.0 g / m ² or less in terms of solid content, more preferably 0.07 g / m ² or more 0.80 g / m ² Or less, more preferably 0.1 g / m ² or more and 0.70 g / m ² or less. To the carrying amount to the substrate of the layer with 0.05 g / m ² or more 1.0 g / m ² or less, the separator obtained, while further improving the adhesion between the polymer layer and the substrate, group It is preferable from the viewpoint of further suppressing the deterioration of the cycle characteristics (permeability) caused by closing the holes of the material.

  The amount of the polymer layer supported on the substrate can be adjusted, for example, by changing the concentration of the thermoplastic polymer or copolymer in the coating solution or the coating amount of the thermoplastic polymer solution. However, the method for adjusting the carrying amount is not limited to the above.

(Surface coverage)
In the present embodiment, the polymer layer is preferably present on the surface of the substrate with a surface coverage of 70% or less, more preferably 50% or less, and still more preferably with respect to the surface area per surface of the substrate. It is present on the surface of the substrate with a surface coverage of 45% or less, particularly preferably 40% or less. Moreover, it is preferable that a polymer layer exists on the surface of a base material with the surface coverage of 5% or more. It is preferable that the surface coverage of the polymer layer is 70% or less from the viewpoint of further suppressing clogging of the pores of the base material by the thermoplastic polymer (for example, the copolymer) and further improving the permeability of the separator. . On the other hand, setting the surface coverage to 5% or more is preferable from the viewpoint of further improving the adhesion to the electrode.

  The surface coverage of the polymer layer in the present embodiment is, for example, the thermoplastic polymer or copolymer concentration in the coating liquid applied to the substrate, the coating amount of the coating liquid, the coating method, and the coating in the separator manufacturing method described later. It can be adjusted by changing the conditions. However, the method for adjusting the surface coverage is not limited thereto. Moreover, the surface coverage of the polymer layer in this embodiment is measured according to the method as described in the following Example.

(Average thickness of polymer layer)
The average thickness of the polymer layer in the separator of the present embodiment is not particularly limited, but is preferably 2.0 μm or less, more preferably 1.0 μm or less, and further preferably 0.5 μm or less. Setting the average thickness of the polymer layer to 2.0 μm or less suppresses the decrease in permeability due to the polymer layer and also has an effect of adhering the polymer layers to each other or the polymer layer and the substrate when the separator is stored as a roll. From the standpoint of suppression. The average thickness of the polymer layer in the present embodiment is adjusted, for example, by changing the thermoplastic polymer or copolymer concentration in the coating liquid applied to the substrate, the coating amount of the coating liquid, the coating method, and the coating conditions. Can do. However, the adjustment method of the average thickness of a polymer layer is not limited to them.

(Presence form of polymer layer on substrate)
The presence form (pattern) on the base material of the polymer layer in the present embodiment is not particularly limited, and for example, the polymer layer may have a planar shape shown in black in FIG. That is, the polymer layer has, for example, a dot shape (for example, FIG. 1A), a lattice shape (for example, FIG. 1B), a linear shape (for example, FIG. 1C), a stripe shape (for example, FIG. 1 (D)), a tortoiseshell pattern (for example, (E) in FIG. 1), and the like may exist.

  In these, it is preferable that a polymer layer exists in the dot form on the at least single side | surface of a base material from a viewpoint of ensuring permeability | transmittance and a further improving uniform adhesiveness with an electrode. “Dot-like” indicates a state of a sea-island structure in which a polymer layer is present in an island shape on a substrate and a portion where the polymer layer is not present is a sea shape. Although the polymer layer may exist independently in the form of islands, a part of it may form a continuous surface, but the polymer layer is continuous in most parts, and most of the base material is polymer. It does not include the case where it is covered with a layer (when the sea of the sea-island structure is a polymer layer).

  When the polymer layer exists independently in an island shape, the distance between the island dots (the distance between the ends of the adjacent island dots) is 5 μm to 500 μm. It is preferable from the point of coexistence. The size of the dot (the longest diameter of one dot; the longest diameter) is not particularly limited, but is preferably 20 μm or more and 1000 μm or less on average, more preferably 30 μm or more and 800 μm or less, and further preferably 50 μm or more and 500 μm or less. is there. Setting the average major axis of the dots of the polymer layer to 20 μm or more and 1000 μm or less is preferable from the viewpoint of securing the adhesion to the electrode.

  The average major axis of the dots of the polymer layer can be adjusted, for example, by changing the copolymer or thermoplastic polymer concentration of the coating liquid, the coating amount of the coating liquid, the coating method, and the coating conditions. However, the method of adjusting the average major axis of the dots of the polymer layer is not limited to them.

The separator in this embodiment has a short temperature which is an index of heat resistance, preferably 150 ° C. or higher, and more preferably 160 ° C. or higher. Setting the short circuit temperature to 150 ° C. or higher is preferable from the viewpoint of the safety of the electricity storage device. The short temperature is measured by the method described in Japanese Patent No. 4733232.
Moreover, it is preferable that the separator in this embodiment is 50% or more of adhesiveness with the electrode measured by the method mentioned later.

(Method for manufacturing separator for thermoplastic polymer-carrying power storage device)
In the present embodiment, the method for supporting the thermoplastic polymer containing the copolymer on at least one surface (one surface) of the substrate is not particularly limited. For example, there is a method in which a coating liquid containing a thermoplastic polymer is applied to at least one surface of a substrate, and then a solvent or a dispersion medium of the coating liquid is removed as necessary.

  The solvent or dispersion medium contained in the coating solution is not particularly limited, but water is preferable. When the coating solution is applied to the substrate, if the coating solution gets into the substrate, the thermoplastic polymer containing the copolymer closes the surface and the inside of the pores of the substrate and the permeability is lowered. It becomes easy to do. In this regard, when water is used as the solvent or dispersion medium of the coating solution, it becomes difficult for the coating solution to enter the substrate, and the thermoplastic polymer including the copolymer is mainly present on the outer surface of the substrate. Since it becomes easy, the fall of permeability can be controlled more effectively, and is preferred. Examples of the solvent or dispersion medium that can be used in combination with water include ethanol and methanol.

  The method for applying the coating liquid to the substrate is not particularly limited as long as the required layer thickness and coating area can be realized. For example, a gravure coater method, a small diameter gravure coater method, a reverse roll coater method, a transfer roll Examples include a coater method, a kiss coater method, a dip coater method, a knife 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.

  In the present embodiment, it is preferable to perform a surface treatment on the surface of the base material prior to the application of the coating liquid because the coating liquid can be more easily applied and the adhesion between the base material and the thermoplastic polymer is improved. The surface treatment method is not particularly limited as long as the structure of the substrate (for example, the porous structure of the polyolefin microporous membrane) is not significantly impaired. For example, the corona discharge treatment method, the plasma treatment method, the mechanical surface roughening. Method, solvent treatment method, acid treatment method, and ultraviolet oxidation method.

  In the present embodiment, when the solvent is removed from the coating solution applied to the substrate, there is no particular limitation as long as it is a method that does not adversely affect the substrate. For example, when using a polyolefin microporous membrane as a substrate, a method of drying at a temperature below the melting point while fixing the substrate, a method of drying at a low temperature under reduced pressure, a copolymer immersed in a poor solvent for the copolymer And a method of extracting the solvent at the same time as coagulating.

  Further, when the copolymer contains copolymer particles and the substrate is a polyolefin microporous membrane, the glass transition is performed for the purpose of enhancing the adhesion between the copolymer particles and the polyolefin microporous membrane as the substrate. Copolymer particles having a temperature (Tg) of 15 ° C. or lower can be mixed and used. The copolymer particles having a Tg of 15 ° C. or less are preferably contained in an amount of 5 to 40% by mass with respect to the total amount of the copolymer particles. The degree of swelling of the copolymer having a Tg of 15 ° C. or lower is not particularly limited, but is preferably 5.0 times or less from the viewpoint of more effectively expressing the adhesiveness.

[Separator for electricity storage devices]
Although an electrical storage device provided with the electrical storage device separator of this embodiment is not specifically limited, For example, batteries, such as a nonaqueous electrolyte secondary battery, a capacitor, and a capacitor are mentioned. Among these, from the viewpoint of more effectively obtaining the benefits of the effects of the present invention, a battery is preferable, a non-aqueous electrolyte secondary battery is more preferable, and a lithium ion secondary battery is still more preferable. Since the separator for an electricity storage device of the present embodiment includes a polymer layer on a substrate, the separator has excellent handling properties when wound, adhesion with an electrode active material, and permeability.

  The separator of the present embodiment preferably has a peel strength with respect to the aluminum foil of 5 N / m or more, more preferably 10 N / m or more. This means that it is possible to easily confirm that the separator of this embodiment has adhesiveness without producing an electrode. The peel strength is measured as follows. That is, an aluminum foil used as a positive electrode current collector (manufactured by Fuji Paper Industries Co., Ltd., thickness: 20 μm) is cut out to 30 mm × 150 mm, and the surface of the polymer layer side in the separator of this embodiment is superimposed on the aluminum foil. After obtaining a laminate, the laminate is sandwiched between Teflon (registered trademark) sheets (manufactured by Nichias Corporation, Naflon (trademark) PTFE sheet TOMBO-No. 9000), and at a pressure of 80 ° C. and 10 MPa in the lamination direction. Pressurize for 3 minutes. In the sample thus obtained, the peel strength between the aluminum foil and the separator was measured at a tensile rate of 200 mm / min using an autograph AG-IS type (trademark) manufactured by Shimadzu Corporation according to JIS K6854-2. To do.

[Power storage device]
The electricity storage device of this embodiment includes an electricity storage device separator, and other configurations may be the same as those conventionally known. Although an electrical storage device is not specifically limited, For example, batteries, such as a non-aqueous electrolyte secondary battery, a capacitor, and a capacitor are mentioned. Among these, from the viewpoint of more effectively obtaining the benefits of the effects of the present invention, a battery is preferable, a non-aqueous electrolyte secondary battery is more preferable, and a lithium ion secondary battery is still more preferable. Hereinafter, a suitable aspect in the case where the electricity storage device is a non-aqueous electrolyte secondary battery will be described.

  The non-aqueous electrolyte secondary battery including the separator according to this embodiment includes a positive electrode, a negative electrode, and a non-aqueous electrolyte in addition to the separator. A positive electrode, a negative electrode, and a nonaqueous electrolyte solution are not specifically limited, A well-known thing can be used.

Examples of the positive electrode material (positive electrode active material) include lithium-containing composite oxides such as LiCoO ₂ , LiNiO ₂ , spinel type LiMnO ₄ , and olivine type LiFePO ₄ . Examples of the negative electrode material include carbon materials such as graphite, non-graphitizable carbonaceous, graphitizable carbonaceous, and composite carbon bodies; silicon, tin, metallic lithium, and various alloy materials. Each of the positive electrode and the negative electrode may include a current collector. Examples of the positive electrode current collector include an aluminum foil, and examples of the negative electrode current collector include a copper foil.

As the non-aqueous electrolyte, an electrolyte obtained by dissolving an electrolyte 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 .

The electricity storage device of this embodiment is manufactured as follows, for example. That is, the separator of this embodiment is produced as a vertically long separator having a width of 10 to 500 mm (preferably 80 to 500 mm) and a length of 200 to 4000 m (preferably 1000 to 4000 m). Next, the separator is stacked together with the positive electrode and the negative electrode in the order of positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator to obtain a laminate. Next, the laminate is wound into a cylindrical or flat spiral shape to obtain a wound body. And the electrical storage device is obtained by accommodating the said wound body in a battery can, and also inject | pouring electrolyte solution. In addition, the electricity storage device of this embodiment is obtained by laminating a positive electrode, a separator, a negative electrode, a separator, a positive electrode, or a negative electrode, a separator, a positive electrode, a separator, and a negative electrode in the order of a flat plate, It can also be manufactured through a process of housing and laminating and injecting an electrolytic solution therein.

  The various parameters described above are values measured according to the measurement methods in the examples described later unless otherwise specified.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to an Example. The measurement methods and evaluation methods for various physical properties used in the following synthesis examples, production examples, examples and comparative examples are as follows.

[Measuring method]
(1) Solid content About 1 g of the obtained aqueous dispersion of the copolymer was precisely weighed on an aluminum dish, and the mass of the aqueous dispersion weighed at this time was defined as (a) g. It was dried for 1 hour with a hot air dryer at 130 ° C., and the dry mass of the dried copolymer was (b) g. The solid content was calculated by the following formula.
Solid content = (b) / (a) × 100 [%]

(2) Average particle size of copolymer particles Using a light scattering method particle size measuring device (LEED & NORTHHRUP, trade name “MICROTRAC UPA150”), 50% particle size (nm) was measured to obtain an average particle size. .

(3) Weight of base material (polyolefin microporous film) A 10 cm × 10 cm square sample was cut from the base material, and mass was measured using an electronic balance AEL-200 (trade name) manufactured by Shimadzu Corporation. Is multiplied by the resulting mass 100 was calculated 1 m ² per layer of basis weight (g / m ²⁾ in.

(4) Porosity of Substrate (Polyolefin Microporous Membrane) A 10 cm × 10 cm square sample was cut from the substrate, its volume (cm ³ ) and mass (g) were determined, and the membrane density was 0.95 (g / cm ³ ) Calculated using the following formula.
Porosity = (1−mass / volume / 0.95) × 100

(5) Air Permeability of Substrate (Polyolefin Microporous Membrane) Air permeation resistance measured by Gurley type air permeability meter, G-B2 (trademark) manufactured by Toyo Seiki Co., Ltd. according to JIS P-8117 Was the air permeability.

(6) Puncture strength of substrate (polyolefin microporous membrane) Using a handy compression tester KES-G5 (trademark) manufactured by Kato Tech, the substrate was fixed with a sample holder having a diameter of 11.3 mm. Next, by performing 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 center of the fixed substrate. The puncture strength (g) was obtained as the maximum puncture load.

(7) Average pore size of substrate (polyolefin microporous membrane) It is known that the fluid inside the capillary follows the Knudsen flow when the fluid mean free path is larger than the capillary pore size, and the Poiseuille flow when it is small. Yes. Therefore, it was assumed that the air flow in the air permeability measurement of the base material follows the Knudsen flow, and the water flow in the base material permeability measurement follows the Poiseuille flow.

The average pore diameter d (μm) is the air permeation rate constant R _gas (m ³ / (m ² · sec · Pa)), the water permeation rate constant R _liq (m ³ / (m ² · sec · Pa)), From the air molecular velocity ν (m / sec), water viscosity η (Pa · sec), standard pressure P _s (= 101325 Pa), porosity ε (%), and film thickness L (μm), the following equation is used. Asked.
d = 2ν × (R _liq / R _gas ) × (16η / 3Ps) × 10 ⁶
Here, R _gas was calculated | required from the air permeability (second) using the following formula.
R _gas = 0.0001 / (air permeability × (6.424 × 10 ⁻⁴ ) × (0.01276 × 101325))
R _liq was determined from the water permeability (cm ³ / (cm ² · sec · Pa)) using the following formula.
R _liq = water permeability / 100

The water permeability was determined as follows. A base material previously immersed in ethanol is set in a stainless steel liquid-permeable cell having a diameter of 41 mm, and after the ethanol of the base material is washed with water, water is permeated through the base material with a differential pressure of about 50000 Pa, From the water permeability (cm ³ ) when 120 seconds passed, the water permeability per unit time, unit pressure, and unit area was calculated and used as the water permeability.

Ν is a gas constant R (= 8.314), an absolute temperature T (K), a circumference π, and an average molecular weight M of air (= 2.896 × 10 ⁻² kg / mol), using the following formula. Asked.
ν = ((8R × T) / (π × M)) ^1/2

(8) Average thickness of polymer layer The average thickness of the polymer layer was measured by observing the cross section of the separator using a scanning electron microscope (SEM) “Model S-4800, manufactured by HITACHI”. More specifically, the separator was cut out to about 1.5 mm × 2.0 mm and dyed with ruthenium. The stained sample and ethanol were placed in a gelatin capsule, frozen with liquid nitrogen, and then cleaved with a hammer. Next, the sample was subjected to osmium vapor deposition and observed at an acceleration voltage of 1.0 kV and 30000 times, and the average thickness of the polymer layer was calculated. The outermost surface area where the porous structure of the cross section of the substrate (polyolefin microporous film) was not visible in the SEM image was defined as the polymer layer area.

(9) Glass transition temperature of copolymer An appropriate amount of an aqueous dispersion (solid content = 38 to 42% by mass, pH = 9.0) containing a copolymer is placed in an aluminum dish and heated with a hot air dryer at 130 ° C. Dried for 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 measuring apparatus (manufactured by Shimadzu Corporation, model number: DSC6220). The measurement conditions were as follows.
(First stage temperature rise program)
Starting at 70 ° C., the temperature was increased at a rate of 15 ° C. per minute. After reaching 110 ° C., the temperature was maintained for 5 minutes.
(Second stage temperature drop program)
The temperature was lowered from 110 ° C. at a rate of 30 ° C. per minute. After reaching −100 ° C., the temperature was maintained for 4 minutes.
(Third-stage temperature rising program)
The temperature was raised from −100 ° C. to 130 ° C. at a rate of 15 ° C. per minute. DSC and DDSC data were acquired during the third stage of temperature increase.
The intersection of the straight line obtained by extending the base line in the obtained DSC curve to the high temperature side and the tangent at the inflection point was defined as the glass transition temperature (Tg).

(10) Swelling degree of copolymer with respect to electrolyte solution The aqueous dispersion containing the copolymer was allowed to stand in an oven at 130 ° C. for 1 hour and dried. The copolymer film obtained by drying was cut to 0.5 g. The cut sample is put in a 50 mL vial together with 10 g of a mixed solvent of ethylene carbonate: diethyl carbonate = 2: 3 (mass ratio), and the mixed solvent is infiltrated for 1 day. And the mass (Wa: g) was measured. Thereafter, the sample was allowed to stand in an oven at 150 ° C. for 1 hour, the mass was measured (Wb: g), and the degree of swelling of the copolymer with respect to the electrolytic solution was calculated from the following formula.
Swelling degree of copolymer to electrolyte (times) = (Wa−Wb) ÷ (Wb)

(11) Surface coverage of polymer layer The surface coverage of the polymer layer was measured using a scanning electron microscope (SEM) (model: S-4800, manufactured by HITACHI). The separator which is a sample was vapor-deposited on osmium, and observed under conditions of an acceleration voltage of 1.0 kV and 50 times, and the surface coverage was calculated from the following formula. In addition, the area | region where the porous structure of the base-material (polyolefin microporous film) surface is not visible on the SEM image was made into the polymer layer area | region.
Surface coverage of polymer layer (%) = Area of polymer layer ÷ (Area including pore portion of substrate + Area of polymer layer) × 100
The surface coverage in each sample was measured three times, and the arithmetic average value was obtained.

(12) Amount of polymer layer supported on base material For each of the base material (polyolefin microporous membrane) and the separator, the total mass of three samples cut into 10 cm x 10 cm was measured, and the polymer layer in the sample was calculated according to the following formula. The loading amount (solid content) of was measured.
Polymer layer loading (g / m ² ) = [(total mass of 3 separators) − (total mass of 3 substrates)] ÷ 3 × 100

[Evaluation method]
(13) Adhesiveness between separator and electrode The adhesiveness between the separator and the electrode was evaluated by the following procedure.
(Preparation of positive electrode)
92.2% by mass of lithium cobalt composite oxide (LiCoO ₂ ) as a positive electrode active material, 2.3% by mass of flake graphite and acetylene black as a conductive material, and 3.2% by mass of polyvinylidene fluoride (PVDF) as a binder A slurry was prepared by dispersing in N-methylpyrrolidone (NMP). This slurry was applied to one side of a 20 μm thick aluminum foil serving as a positive electrode current collector with a die coater, dried at 130 ° C. for 3 minutes, and then compression molded with a roll press. At this time, the active material coating amount of the positive electrode was 250 g / m ² , and the active material bulk density was 3.00 g / cm ³ .

(Preparation of negative electrode)
A slurry was prepared by dispersing 96.9% by mass of artificial graphite as a negative electrode active material, 1.4% by mass of ammonium salt of carboxymethyl cellulose and 1.7% by mass of an aqueous dispersion of styrene-butadiene copolymer as a binder in purified water. 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. At this time, the active material application amount of the negative electrode was set to 106 g / m ² , and the active material bulk density was set to 1.35 g / cm ³ .

(Adhesion test)
The electrode obtained by the above method was cut into a width of 20 mm and a length of 40 mm. An electrolytic solution (manufactured by Toyama Pharmaceutical Co., Ltd.) in which ethylene carbonate and diethyl carbonate are mixed at a ratio (volume ratio) of 2: 3 is dropped onto this electrode until it is immersed in the electrode active material. A separator (size: width 30 mm, length 50 mm) was overlaid so that the electrode covered the entire surface of the substrate or the separator. The obtained laminate was put in an aluminum zip bag and pressed at 80 ° C. and 10 MPa for 3 minutes. Thereafter, the laminate was removed from the bag, and the substrate or separator was peeled off from the electrode. At this time, adhesion evaluation was performed according to the following evaluation criteria from the ratio of the adhesion area of the electrode active material remaining on the base material or the separator (the area of one surface of the base material or the separator was 100%). In the adhesion test, when the inorganic filler was exposed on one side of the substrate or the separator, the laminate was prepared so that the surface on the side where the inorganic filler was not exposed was in contact with the electrode.
<Evaluation criteria>
The ratio of the adhesion area is 70% or more and 100% or less ... S
The ratio of the adhesion area is 50% or more and less than 70% ... A
The ratio of the adhesion area is 30% or more and less than 50%… B
The ratio of the adhesion area is 10% or more and less than 30%… C
Adhesion area ratio is 5% or more and less than 10%.
The ratio of the adhesion area is 0% or more and less than 5%… E

(14) Handling property of substrate and separator (blocking resistance)
A base material or a separator and a positive electrode current collector (aluminum foil manufactured by Fujishikushi Paper Co., Ltd., thickness: 20 μm) as an adherend are cut into 30 mm × 150 mm, and are stacked. (Trademark) sheet (Naflon (trademark) PTFE sheet TOMBO-No.9000 manufactured by NICHIAS Corporation). About each sample, the sample for a test was obtained by pressing in the lamination direction on condition of following 1) and 2).
1) 25 ° C., 5 MPa, 3 minutes 2) 40 ° C., 5 MPa, 3 minutes The peel strength between the base material or separator of each obtained test sample and the positive electrode current collector was measured by Autograph AG manufactured by Shimadzu Corporation. -Using IS type (trademark), measurement was performed at a tensile speed of 200 mm / min according to JIS K6854-2. Based on the peel strength value, the following evaluation criteria were used.
<Evaluation criteria>
Less than 6N / m
6N / m or more, less than 8N / m ・ ・ ・ △
8N / m or more ・ ・ ・ ×

(15) Simple adhesion test Aluminum foil (made by Fuji Paper Co., Ltd., thickness: 20 μm) as a substrate or separator and an adherend were cut into 30 mm × 150 mm, respectively, and laminated, and then the laminate was teflon ( (Registered trademark) sheet (Naflon (trademark) PTFE sheet TOMBO-No.9000 manufactured by NICHIAS Corporation). About each sample obtained in this way, the sample for a test was obtained by pressing in the lamination direction for 3 minutes on 80 degreeC and 10 Mpa conditions.
The peel strength between the base material or separator of each test sample obtained and the aluminum foil was measured using a Shimadzu Autograph AG-IS type (trademark) according to JIS K6854-2 with a tensile speed of 200 mm. Measured at / min. Based on the peel strength value, the following evaluation criteria were used.
<Evaluation criteria>
10N / m or more… ○
5N / m or more and less than 10N / m… △
Less than 5 N / m… ×

(16) Powder fall test Various aqueous dispersions were diluted with water so that the solid content was 30 parts by mass to prepare a coating liquid containing a thermoplastic polymer (solid content 30% by mass). Subsequently, the coating liquid was apply | coated to the single side | surface of each base material using the micro gravure coater. Then, the coating liquid after application | coating was dried at 60 degreeC, and water was removed. The degree to which the dry coating film of the copolymer formed when the coated surface after drying was rubbed with a finger was evaluated by the following evaluation criteria. The adhesion with the substrate was evaluated by a powder falling test.
No white powder falling off: ◎
Slightly white powder is generated: ○
White powder is generated but cannot be completely removed from the substrate side: △
White powder is generated and completely removed from the substrate side: ×

[Synthesis Example 1]
(Water dispersion 1)
In a reaction vessel equipped with a stirrer, reflux condenser, dropping 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 1.5 parts by mass were charged) (indicated as “KH1025” in the table). Next, the temperature inside the reaction vessel was raised to 80 ° C., and 7.5 parts by mass of a 2% aqueous solution of ammonium persulfate was added while maintaining the temperature at 80 ° C. 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 emulsion has 5 parts by mass of 2-ethylhexyl acrylate (indicated as “EHA” in the table) as a ethylenically unsaturated monomer (A) having a chain alkyl group having 8 or more carbon atoms, and a carboxyl group. As ethylenically unsaturated monomer (b1), 1 part by mass of methacrylic acid (in the table, indicated as “MAA”), 1 part by mass of acrylic acid (in the table, indicated as “AA”), an ethylenically unsaturated monomer having an amide group Acrylamide (in the table, indicated as “AM”) 3 parts by mass as the saturated monomer (b2), 2-hydroxyethyl methacrylate (in the table, “HEMA”) as the ethylenically unsaturated monomer (b3) having a hydroxyl group And 1 part by mass, trimethylolpropane triacrylate (A-TMPT, trade name, manufactured by Shin-Nakamura Chemical Co., Ltd. as a crosslinkable monomer (b4), “A-TMPT” in the table. Notation) 0.7 part by mass, glycidyl methacrylate (described in the table as “GMA”) 0.3 part by mass, γ-methacryloxypropyltrimethoxysilane (described in the table as “AcSi”) 0.3 part by mass As other (meth) acrylic acid ester monomers (b9), 68.7 parts by mass of methyl methacrylate (indicated as “MMA” in the table), 15 parts by mass of butyl methacrylate (indicated as BMA in the table), butyl acrylate (Indicated in the table as “BA”) 5 parts by mass, “Aqualon KH1025” (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as an emulsifier 4.5 parts by mass, 7.5% 2% aqueous solution of ammonium persulfate A mixture of 5 parts by mass 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 = 9.0 with an aqueous ammonium hydroxide solution (25% aqueous solution) to obtain an aqueous dispersion having a concentration of 40% (aqueous dispersion 1). About the copolymer in the obtained water dispersion 1, Tg, an average particle diameter, and the swelling degree with respect to electrolyte solution were measured with the said method. The obtained results are shown in Table 1.

[Synthesis Examples 2 to 22]
(Water dispersion 2-22)
Except having changed the kind and compounding ratio of a raw material as shown in Table 1-Table 3, it carried out similarly to the synthesis example 1, and obtained the water dispersions 2-22. In the table, "CHMA" is a cycloalkyl group. Means cyclohexyl methacrylate which is one of ethylenically unsaturated monomers (b5) having About the copolymer in the obtained water dispersions 2-22, the swelling degree with respect to Tg, a particle diameter, and electrolyte solution was measured with the said method. The obtained results are shown in Tables 1 to 3. In the table, the composition of raw materials is based on mass.

[Production Example 1]
(Manufacture of base material B1)
Mv is 700,000, 45 parts by mass of homopolymer high-density polyethylene, Mv is 300,000, homopolymer high-density polyethylene is 45 parts by mass, and Mv is 400,000. 10 parts by mass of a mixture of a homopolymer having 150,000 and polypropylene (mass ratio = 4: 3) 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, that is, 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. The sheet was stretched by a simultaneous biaxial stretching machine at a magnification of 7 × 6.4 and a temperature of 112 ° C., then immersed in methylene chloride, extracted by removing liquid paraffin and dried, and then a temperature of 130 by a tenter stretching machine. The film was stretched 2 times in the transverse direction at ° C. Thereafter, the stretched sheet was relaxed by about 10% in the width direction and subjected to heat treatment to obtain a base material B1 shown in Table 4.

  About the obtained base material B1, various physical properties were measured by the said method. Moreover, about the obtained base material B1, blocking resistance, adhesiveness, and the said simple adhesion test were done with the said method. Table 4 shows the obtained results.

[Production Example 2]
(Manufacture of base material B2)
Substrate B2 was obtained by the same operation as in Production Example 1 except that the stretching temperature and the relaxation rate were adjusted. The obtained base material B2 was evaluated and tested by the above method in the same manner as in Production Example 1. Table 4 shows the obtained results.

[Production Example 3]
(Manufacture of base material B3)
47.5 parts by mass of homopolymer high-density polyethylene having a viscosity average molecular weight of 700,000, 47.5 parts by mass of homopolymer high-density polyethylene having a viscosity average molecular weight of 250,000, and 5 parts by mass of homopolymer polypropylene having a viscosity average molecular weight of 400,000 Was dry blended using a tumbler blender. 1 part by mass of pentaerythrityl-tetrakis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] as an antioxidant is added to 99 parts by mass of the obtained polymer mixture, and again The mixture was obtained by dry blending using a tumbler blender. The obtained mixture was substituted with nitrogen and then fed to the twin-screw extruder with a feeder under a nitrogen atmosphere. Moreover, liquid paraffin was inject | poured into the extruder cylinder with the plunger pump.
The feeder and the pump were adjusted so that the liquid paraffin content ratio in the total mixture melt-kneaded and extruded was 67 mass% (resin composition concentration was 33 mass%).

  The melt-kneaded product was extruded and cast on a cooling roll through a T-die to obtain a sheet-like molded product. Then, base material B3 was obtained by operation similar to manufacture example 1 except having adjusted the extending | stretching temperature and the relaxation rate. About the obtained base material B3, it carried out similarly to manufacture example 1, evaluated various physical properties, blocking resistance, and adhesiveness, and performed the said simple adhesion test. Table 4 shows the obtained results.

[Production Example 4]
(Manufacture of base material B4)
25 parts by mass of ultra high molecular weight polyethylene having a viscosity average molecular weight of 2 million, 15 parts by mass of high density polyethylene having a viscosity average molecular weight of 700,000, 30 parts by mass of high density polyethylene having a viscosity average molecular weight of 250,000, and 120,000 in viscosity average molecular weight 30 parts by mass of copolymer polyethylene having a propylene unit content of 1 mol% was dry blended using a tumbler blender. 0.3 parts by mass of pentaerythrityl-tetrakis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] as an antioxidant was added to 99 parts by mass of the obtained polymer mixture. The mixture was obtained by dry blending again using a tumbler blender. The obtained mixture was substituted with nitrogen and then fed to the twin-screw extruder with a feeder under a nitrogen atmosphere. Liquid paraffin was injected into the extruder cylinder by a plunger pump.
The feeder and pump were adjusted so that the liquid paraffin content ratio in the total mixture melt-kneaded and extruded was 65 mass% (resin composition concentration was 35 mass%).

  The melt-kneaded product was extruded and cast on a cooling roll through a T-die to obtain a sheet-like molded product. Then, base material B4 was obtained by operation similar to manufacture example 1 except having adjusted the extending | stretching temperature and the relaxation rate. About the obtained base material B4, it carried out similarly to manufacture example 1, evaluated various physical properties, blocking resistance, and adhesiveness, and performed the said simple adhesion test. Table 4 shows the obtained results.

[Production Example 5]
(Manufacture of base material B5)
A base material B5 was obtained by the same operation as in Production Example 3, except that the stretching temperature and the relaxation rate were adjusted. About the obtained base material B5, it carried out similarly to the manufacture example 1, evaluated various physical properties, blocking resistance, and adhesiveness, and performed the said simple adhesion test. Table 4 shows the obtained results.

[Production Example 6]
(Manufacture of base material B6)
19.2 parts by weight of ultra high molecular weight polyethylene with a viscosity average molecular weight of 1 million, 12.8 parts by weight of high density polyethylene with a viscosity average molecular weight of 250,000, 48 parts by weight of dioctyl phthalate (DOP), and 20 parts by weight of fine silica After granulation, the mixture was melt-kneaded by a twin-screw extruder equipped with a T-die at the tip, extruded, rolled with rolls heated from both sides, and formed into a sheet having a thickness of 110 μm. DOP and fine silica were extracted and removed from the molded product to prepare a microporous membrane. Two microporous membranes were stacked and stretched 5 times in the MD direction at 120 ° C. and 2 times in TD at 120 ° C., and finally heat treated at 137 ° C. to obtain a base material B6. About the obtained base material B6, it carried out similarly to manufacture example 1, evaluated various physical properties, blocking resistance, and adhesiveness, and performed the said simple adhesion test. Table 4 shows the obtained results.

[Production Example 7]
(Manufacture of base material B7)
96.0 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 forming temperature 0 ° C. or less) 4.0 parts by mass, polycarboxylic An aqueous solution of ammonium acid (SN Dispersant 5468, manufactured by San Nopco) is uniformly dispersed in 100 parts by mass of water to prepare a coating solution, and a micro gravure coater is used on the surface of the polyolefin resin porous membrane B1. Applied. Water was removed by drying at 60 ° C., and a porous layer was formed with a thickness of 2 μm to obtain a base material B7. About obtained base material B7, it carried out similarly to manufacture example 1, evaluated blocking resistance and adhesiveness, and performed the said simple adhesion test. The results obtained are shown in Table 5.

[Production Example 8]
(Manufacture of base material B8)
A porous layer having a thickness of 4 μm was formed on one surface of the substrate B1 in the same manner as in Production Example 7 to obtain a substrate B8. About obtained base material B8, it carried out similarly to manufacture example 1, evaluated blocking resistance and adhesiveness, and performed the said simple adhesion test. The results obtained are shown in Table 5.

[Production Example 9]
(Manufacture of base material B9)
A porous layer having a thickness of 3 μm was formed on one surface of the base material B2 in the same manner as in Production Example 7 to obtain a base material B9. About obtained base material B9, it carried out similarly to manufacture example 1, evaluated blocking resistance and adhesiveness, and performed the said simple adhesion test. The results obtained are shown in Table 5.

[Production Example 10]
(Manufacture of base material B10)
A porous layer having a thickness of 7 μm was formed on one surface of the base material B5 in the same manner as in Production Example 7 to obtain a base material B10. About obtained base material B10, it carried out similarly to manufacture example 1, evaluated blocking resistance and adhesiveness, and performed the said simple adhesion test. The results obtained are shown in Table 5.

[Production Example 11]
(Manufacture of base material B11)
95.0 parts by mass of calcined kaolin (wet kaolin mainly composed of kaolinite (Al ₂ Si ₂ O ₅ (OH) ₄ ), calcined at high temperature, average particle size 1.8 μm), acrylic latex (solid content 180 parts by mass of water of 5.0 parts by mass with a concentration of 40%, an average particle size of 220 nm, a minimum film forming temperature of 0 ° C. or less, and 0.5 parts by mass of an aqueous ammonium polycarboxylate (SN Dispersant 5468 manufactured by San Nopco) A coating solution was prepared by uniformly dispersing the coating solution on the surface of the base material B3 and coated on the surface of the substrate B3 using a micro gravure coater. Water was removed by drying at 60 ° C., and a porous layer was formed with a thickness of 6 μm to obtain a base material B11. About obtained base material B11, it carried out similarly to manufacture example 1, evaluated blocking resistance and adhesiveness, and performed the said simple adhesion test. The results obtained are shown in Table 5.

[Production Example 12]
(Manufacture of base material B12)
Except that the stretching temperature and relaxation rate were adjusted, the same procedure as in Production Example 1 was followed, with a basis weight of 4.6 g / m ² , a film thickness of 7 μm, a porosity of 38%, an air permeability of 150 seconds, and a piercing A base material having a strength of 270 g and an average pore size of 0.070 μm was obtained. A porous layer having a thickness of 3 μm was formed on one surface of the base material in the same manner as in Production Example 7 to obtain base material B12. About obtained base material B12, it carried out similarly to manufacture example 1, evaluated blocking resistance and adhesiveness, and performed the said simple adhesion test. The results obtained are shown in Table 5.

  In addition to the above, a cellulose separator (model number “TF40” manufactured by Nippon Advanced Paper Co., Ltd.) was used as the base material B13. When the various physical properties of the base material B13 were measured in the same manner as in Production Example 1, the film thickness was 58 μm, the porosity was 76%, and the air permeability was 7 seconds. Moreover, as the base material B14, a Tencel thin film prepared by beating paper after tencel fiber (manufactured by Tencel Japan) was used. With respect to the base material B14, various physical properties were measured in the same manner as in Production Example 1. As a result, the film thickness was 89 μm, the porosity was 81%, and the air permeability was 2 seconds. Furthermore, as the base material B15, a polypropylene non-woven fabric (trade name “ELTAS” manufactured by Asahi Kasei Corporation) was used. When the various physical properties of the base material B15 were measured in the same manner as in Production Example 1, the film thickness was 98 μm, the porosity was 82%, and the air permeability was 0 seconds.

[Example 1]
The aqueous dispersion 4 was diluted with water so that the solid content was 30 parts by mass to prepare a coating liquid containing a thermoplastic polymer (solid content 30% by mass). Subsequently, the coating liquid was apply | coated to the single side | surface of base material B1 using the micro gravure coater. Then, the coating liquid after application | coating was dried at 60 degreeC, and water was removed. Furthermore, the coating solution was similarly applied to the other surface of the substrate B1, and dried again in the same manner as described above. In this way, the separator which formed the polymer layer on both surfaces of base material B1 was obtained. In this separator, the surface coverage of the polymer layer was 30%, and the average thickness of the polymer layer was 1 μm. Moreover, when confirmed with SEM, the polymer layer existed in the shape of a substantially circular dot on the surface of the base material B1.
About the obtained separator, the blocking resistance, powder fall-off property, adhesiveness, and the said simple adhesion test were done with the said method. The results obtained are shown in Table 6.

[Examples 2 to 40, Comparative Examples 1 to 8]
Except for changing the type and mixing ratio (% by mass) of the aqueous dispersion, the solid content (% by mass) in the coating solution, and the type of the substrate as shown in Tables 6 to 10, the same manner as in Example 1 was performed. A coating solution was prepared to produce a separator. Various physical properties and evaluation / test results of the obtained separator are shown in Tables 6 to 10.

  ADVANTAGE OF THE INVENTION According to this invention, the separator which is excellent also in the outstanding adhesiveness with an electrode (electrode active material) and also handling property can be provided. Therefore, the present invention is useful as a separator for an electricity storage device such as a battery such as a non-aqueous electrolyte secondary battery, a capacitor, and a capacitor, and has industrial applicability in these fields.

Claims (28)

A separator for an electricity storage device comprising: a base material; and a layer containing a thermoplastic polymer formed on at least a part of at least one surface of the base material,
The thermoplastic polymer is co-polymerized with 2 to 66% by mass of an ethylenically unsaturated monomer having a chain alkyl group having 8 or more carbon atoms and an ethylenically unsaturated monomer having a chain alkyl group having 8 or more carbon atoms. The separator for electrical storage devices containing the copolymer which has 34-98 mass% of other monomers which can superpose | polymerize as a monomer unit.   The separator for an electricity storage device according to claim 1, wherein the ethylenically unsaturated monomer having a chain alkyl group having 8 or more carbon atoms is 2-ethylhexyl acrylate.   The electrical storage device separator according to claim 1, wherein the other monomer includes an ethylenically unsaturated monomer having an amide group.   The electrical storage device separator according to any one of claims 1 to 3, wherein the other monomer includes an ethylenically unsaturated monomer having a hydroxyl group.   The electrical storage device separator according to any one of claims 1 to 4, wherein the other monomer includes a crosslinkable monomer.   The separator for an electricity storage device according to any one of claims 1 to 5, wherein the other monomer includes an ethylenically unsaturated monomer having a cycloalkyl group.   The electrical storage device separator according to any one of claims 1 to 6, wherein the other monomer includes an ethylenically unsaturated monomer having a carboxyl group.   The separator for an electricity storage device according to claim 6, wherein the ethylenically unsaturated monomer having a cycloalkyl group is cyclohexyl acrylate or cyclohexyl methacrylate.   The separator for an electricity storage device according to any one of claims 1 to 8, wherein the degree of swelling of the copolymer with respect to a mixed solvent of ethylene carbonate and diethyl carbonate (mass ratio 2: 3) is 5.0 times or less. .   The electricity storage device separator according to any one of claims 1 to 9, wherein the copolymer includes a copolymer produced by emulsion polymerization.   The separator for an electrical storage device according to any one of claims 1 to 10, wherein the peel strength after pressing the aluminum foil at a temperature of 80 ° C and a pressure of 10 MPa for 3 minutes is 5 N / m or more.   The electrical storage device separator according to any one of claims 1 to 11, wherein the layer containing the thermoplastic polymer is present in a dot shape on at least one surface of the base material.   The separator for an electricity storage device according to any one of claims 1 to 12, wherein the substrate is a polyolefin microporous membrane.   An electricity storage device comprising the separator for an electricity storage device according to any one of claims 1 to 13.   A lithium ion secondary battery provided with the separator for electrical storage devices of any one of Claims 1-13.   2 to 66% by mass of an ethylenically unsaturated monomer having a chain alkyl group having 8 or more carbon atoms and other monomers copolymerizable with the ethylenically unsaturated monomer having a chain alkyl group having 8 or more carbon atoms. A copolymer having 34 to 98% by mass of monomer as a monomer unit.   The copolymer according to claim 16, wherein the ethylenically unsaturated monomer having a chain alkyl group having 8 or more carbon atoms is 2-ethylhexyl acrylate.   The copolymer according to claim 16 or 17, wherein the other monomer includes an ethylenically unsaturated monomer having an amide group.   The copolymer according to any one of claims 16 to 18, wherein the other monomer includes an ethylenically unsaturated monomer having a hydroxyl group.   The copolymer according to any one of claims 16 to 19, wherein the other monomer includes a crosslinkable monomer.   The copolymer according to any one of claims 16 to 20, wherein the other monomer includes an ethylenically unsaturated monomer having a cycloalkyl group.   The copolymer according to any one of claims 16 to 21, wherein the other monomer includes an ethylenically unsaturated monomer having a carboxyl group.   The copolymer according to claim 21, wherein the ethylenically unsaturated monomer having a cycloalkyl group is cyclohexyl acrylate or cyclohexyl methacrylate.   The copolymer according to any one of claims 16 to 23, wherein the degree of swelling of the copolymer with respect to a mixed solvent of ethylene carbonate and diethyl carbonate (mass ratio 2: 3) is 5.0 times or less.   The copolymer according to any one of claims 16 to 24, wherein the copolymer is a copolymer produced by emulsion polymerization.   The copolymer according to any one of claims 16 to 25, wherein the copolymer is used in an electricity storage device.   The copolymer according to any one of claims 16 to 26, wherein the copolymer is used for a separator for an electricity storage device.   An aqueous dispersion comprising water and the copolymer according to any one of claims 16 to 27 dispersed in the water.

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