JP7103760B2 - Pattern coating slurry - Google Patents

Description

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

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

Examples of the porous substrate include a polyolefin porous substrate. Although the polyolefin porous base material is an electronic insulator, it is widely used as a separator for a non-aqueous electrolyte battery because it exhibits ion permeability due to its porous structure. The polyolefin porous substrate has a shutdown function that, when a non-aqueous electrolyte battery generates abnormal heat, closes the pores by thermal melting, blocks ionic conduction in the electrolytic solution, and stops the progress of the electrochemical reaction. Also has.

Attempts have been made to form a coating layer containing a thermoplastic polymer on the surface of such a polyolefin porous substrate in a predetermined coating pattern to impart various performances to the power storage device while maintaining the transparency of the separator. It is done.

For example, in Patent Documents 1 to 3, a slurry containing a specific thermoplastic polymer is pattern-coated and dried to form a coating layer on at least a part of the substrate on at least one surface, thereby forming a coating layer with an electrode. It is described that a separator for a power storage device having excellent adhesion is provided.

JP-A-2016-122648 Japanese Unexamined Patent Publication No. 2016-201367 Japanese Unexamined Patent Publication No. 2016-2076559

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

Therefore, one of the objects of the present invention is to provide a pattern coating slurry that can be easily patterned into a desired shape on a polyolefin porous substrate used as a substrate for a separator for a power storage device. That is.

As a result of diligent studies to solve the above problems, the inventors of the present application have found that the above problems can be solved by using a slurry having a specific viscosity increase rate, and have completed the present invention. That is, the present invention is as follows.
[1]
A pattern coating slurry for pattern coating on at least one surface of a polyolefin porous substrate used as a substrate for a separator for a power storage device.
The pattern coating slurry contains a thermoplastic polymer and a dispersion medium.
While the dispersion medium is dried from the pattern coating slurry, the solid content region containing the initial solid content or more and less than 80% by mass includes a region in which the viscosity increase rate with respect to the increase in solid content is 10 mPa · s /% or more. Slurry for pattern coating.
[2]
The slurry for pattern coating according to item 1, wherein the sliding angle of the dynamic contact angle in the sliding method using the polyolefin porous substrate is 15 ° or more.
[3]
The pattern coating slurry according to item 1 or 2, wherein the dispersion medium contains water.
[4]
The pattern coating slurry according to any one of items 1 to 3, wherein the thermoplastic polymer contains a thermoplastic polymer having a glass transition point (Tg) or a melting point (Tm) of less than 20 ° C.
[5]
The pattern coating slurry according to any one of items 1 to 4, wherein the thermoplastic polymer contains a thermoplastic polymer having a glass transition point (Tg) or a melting point (Tm) of 20 ° C. or higher and 100 ° C. or lower.
[6]
Item 4. The pattern coating slurry according to any one of Items 1 to 5, wherein the pattern coating slurry has a viscosity of 100 mPa · s or less when the solid content concentration is 30% by mass.
[7]
Item 2. The pattern coating slurry according to any one of Items 1 to 5, wherein the pattern coating slurry has a viscosity of 70 mPa · s or less when the solid content concentration is 30% by mass.
[8]
A separator for a power storage device, which has a pattern coating formed from the pattern coating slurry according to any one of items 1 to 7 on at least one surface of the polyolefin porous substrate.
[9]
The separator for a power storage device according to item 8, wherein the pattern coating is a dot pattern.
[10]
The separator for a power storage device according to item 9, wherein the dot diameter is 5 μm or more and 500 μm or less, and the distance between the dots is 5 μm or more and 2000 μm or less.
[11]
The separator for a power storage device according to any one of Items 8 to 10, wherein the area occupancy of the thermoplastic polymer on the polyolefin microporous membrane is 20% or more and less than 80%.
[12]
A power storage device having a positive electrode, a negative electrode, an electrolyte, and a separator for a power storage device according to any one of items 8 to 11.

According to the present invention, it is possible to provide a pattern coating slurry that can be easily patterned into a desired shape on a polyolefin porous substrate used as a substrate for a separator for a power storage device.

Although exemplary embodiments and advantages of the present invention have been described, other embodiments and advantages of the present invention will become apparent from the following specification.

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

<< Slurry for pattern coating >>
The pattern coating slurry of the present embodiment is a pattern coating slurry for pattern coating on at least one surface of a polyolefin porous substrate used as a substrate for a separator for a power storage device. The pattern coating slurry contains a thermoplastic polymer and a dispersion medium, and the solid content increases in the solid content region of the initial solid content or more and less than 80% by mass while the dispersion medium is dried from the pattern coating slurry. Includes a region in which the rate of increase in viscosity with respect to 10 mPa · s /% or more.

The step of forming a coating layer of a predetermined pattern on the substrate of the separator for a power storage device typically comprises coating a slurry having a predetermined initial solid content on the porous polyolefin substrate in a desired pattern. It involves gradually increasing (ie, drying) the solid content to form a coating layer. With conventional slurries, the pattern shape may change between the time the slurry is applied and the time it is completely dried, making it difficult to form the coating layer according to the designed shape. .. This becomes a particular problem when it is desired to form a fine pattern having a structure on the order of several mm to several μm, for example. Factors that change the pattern shape, but not limited to theory, include: (1) foaming of the coated part when the dispersion medium is evaporated; and (2) between coating and drying. It is conceivable that the slurry will flow and the coating shape will collapse.

On the other hand, in the pattern coating slurry of the present embodiment, in the solid content region of the initial solid content or more and less than 80% by mass, the viscosity increase rate with respect to the increase of the solid content is 10 mPa · s /% or more (hereinafter, , Also referred to as "gelled region" in the present specification), (1) suppresses foaming of the coated portion in the region before the gelled region, and / or (2) after the gelled region. In this region, the coating pattern can be stabilized before the slurry flows, so that at least a part of the above factors can be eliminated. Therefore, the pattern coating slurry of the present embodiment can easily form a pattern coating of a desired shape on the polyolefin porous substrate. This effect is particularly advantageous when it is desired to form a fine pattern having a structure on the order of several mm to several μm, for example.

<Solid content and gelation area>
The lower limit of the viscosity increase rate in the gelled region may be 10 mPa · s /% or more, preferably 15 mPa · s /% or more, more preferably 20 mPa · s /% or more, still more preferably 25 mPa · s /% or more. , Even more preferably 30 mPa · s /% or more. The upper limit of the viscosity increase rate in the gelled region is preferably 1000 mPa · s /% or less, more preferably 750 mPa · s /% or less, still more preferably 500 mPa · s /% or less, still more preferably 300 mPa · s /% or less. Is. It is preferable that the upper limit of the viscosity increase rate in the gelled region is 1000 mPa · s /% or less because the paint agglomeration in the vicinity of the coated portion can be suppressed. The range of the viscosity increase rate in the gelled region is preferably 10 mPa · s /% or more and 1000 mPa · s /% or less, more preferably 20 mPa · s /% or more and 750 mPa · s /% or less, and further preferably 30 mPa · s /%. It is 500 mPa · s /% or less.

The gelled region may be present in the solid content region of the initial solid content or more and less than 80% by mass, preferably higher than the initial solid content and 5% by mass or more and 79% by mass or less, more preferably higher than the initial solid content and. In the solid content region of 10% by mass or more and 70% by mass or less, more preferably higher than the initial solid content and 13% by mass or more and 60% by mass or less, still more preferably higher than the initial solid content and 15% by mass or more and 50% by mass or less. exist. The presence of the gelled region in these ranges (1) suppresses foaming of the coated portion in the region before the gelled region, and (2) before the slurry flows in the region after the gelled region. The coating pattern can be stabilized.

The initial solid content of the pattern coating slurry of the present embodiment is not limited as long as a desired pattern can be coated on the base material of the separator for a power storage device and the shape can be maintained immediately after coating. The initial solid content of the pattern coating slurry is preferably 1% by mass or more and 60% by mass or less, more preferably 5% by mass or more and 55% by mass or less, still more preferably 10% by mass or more and 50% by mass or less, still more preferably. It is 15% by mass or more and 45% by mass or less. The viscosity of the pattern coating slurry when the solid content concentration is 30% by mass is preferably 100 mPa · s or less, and more preferably 70 mPa · s or less.

The gelled region of the pattern coating slurry is adjusted by the type, functional group, amount, particle size, etc. of the thermoplastic polymer, dispersion medium, and any other component, such as thickeners, and combinations thereof. can do.

<Sliding angle>
The pattern coating slurry of the present embodiment preferably has a sliding angle of 15 ° or more as a dynamic contact angle in a sliding method using a polyolefin porous substrate to which it should be coated. The substrate transported in the process of forming the pattern coating layer may typically experience coating, tilting, turning, and / or changes in transport speed, etc., while being transported. When the sliding angle is 15 ° or more, it is possible to more effectively prevent the shape of the coating pattern from changing and / or the position of the coating pattern from shifting due to these experiences.

The lower limit of the sliding angle may be 15 ° or more, preferably 25 ° or more, more preferably 35 ° or more, still more preferably 45 ° or more, still more preferably 55 ° or more. The upper limit of the sliding angle is not limited, but is preferably 90 ° or less, more preferably 85 ° or less, and further preferably 80 ° or less. The range of the sliding angle is preferably 25 ° or more and 90 ° or less, more preferably 35 ° or more and 85 ° or less, and further preferably 45 ° or more and 80 ° or less.

The gliding angle should be adjusted by the type, functional group, amount, particle size, etc. of the thermoplastic polymer, dispersion medium, and any other component, such as thickeners and surfactants, and combinations thereof. Can be done.

<Thermoplastic polymer>
Thermoplastic polymers include, but are not limited to, polyolefin resins such as polyethylene, polypropylene, and α-polyethylene; fluororesins such as polyvinylidene fluoride and polytetrafluoroethylene, and copolymers containing them; butadiene and isoprene. Diene-based polymers containing conjugated diene as a monomer unit, copolymers containing these, and hydrides thereof; acrylic polymers containing acrylic acid esters, methacrylic acid esters, etc. as monomer units, copolymers containing these, and the like. Hydrogenated products; rubbers such as ethylene propylene rubber, polyvinyl alcohol, and polyvinyl acetate; cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose; polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, polyetherimide, Examples thereof include resins having a melting point and / or a glass transition point of 180 ° C. or higher, such as polyamideimide, polyamide, and polyester, and mixtures thereof. At least one thermoplastic polymer selected from the group consisting of diene-based polymers, acrylic-based polymers, and fluorine-based polymers is preferable because of its excellent adhesion to electrodes, strength, and flexibility. The thermoplastic polymer may be used alone or in combination of two or more.

(Diene polymer)
Examples of the diene-based polymer include, but are not limited to, a polymer containing a conjugated diene having two conjugated double bonds such as butadiene and isoprene as a monomer unit. The conjugated diene monomer is not limited, for example, 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-phenyl-1,3-butadiene, 1,3-pentadiene, 2-. Examples thereof include methyl-1,3-pentadiene, 1,3-hexadiene, 4,5-diethyl-1,3-octadien, and 3-butyl-1,3-octadien. These monomers may be polymerized alone or copolymerized.

The proportion of the conjugated diene monomer unit in the diene polymer is not limited, but is, for example, 40% by mass or more, preferably 50% by mass or more, and more preferably 60% by mass or more in the total diene polymer.

The diene-based polymer may be a homopolymer of a conjugated diene monomer such as polybutadiene and polyisoprene, or may be a copolymer of a conjugated diene monomer and a copolymerizable monomer. Examples of the monomer copolymerizable with the conjugated diene monomer include the (meth) acrylate monomer described later and the following “other monomer”, and these may be used alone or in combination of two or more.

Examples of the "other monomer" include α, β-unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, and fumaric acid; styrene and chlorostyrene. , Vinyl toluene, t-butylstyrene, vinylbenzoic acid, methyl vinylbenzoate, vinylnaphthalene, chloromethylstyrene, hydroxymethylstyrene, α-methylstyrene, and styrene-based monomers such as divinylbenzene; olefins such as ethylene and propylene. Classes; Halogen atom-containing monomers such as vinyl chloride and vinylidene chloride; Vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate, and vinyl benzoate; Vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, and butyl biel ether; Vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, and isopropenyl vinyl ketone; heterocycle-containing vinyl compounds such as N-vinylpyrrolidone, vinylpyridine, and vinylimidazole; methyl acrylate, and methyl. Acrylic ester and / or methacrylic acid ester compounds such as methacrylate; hydroxyalkyl group-containing compounds such as β-hydroxyethyl acrylate and β-hydroxyethyl methacrylate; acrylamide, N-methylolacrylamide, and acrylamide-2-methylpropanesulfonic acid. And the like, amide-based monomers and the like can be mentioned. These other monomers may be used alone or in combination of two or more.

(Acrylic polymer)
The acrylic polymer is not limited, but is preferably a polymer containing a (meth) acrylate monomer as a monomer unit. In the specification of the present application, "(meth) acrylic acid" means "acrylic acid or methacrylic acid", and "(meth) acrylate" means "acrylate or methacrylate".

The (meth) acrylate monomer is not limited, for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, t-. Butyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, Alkyl (meth) acrylates such as lauryl (meth) acrylate, n-tetradecyl (meth) acrylate, and stearyl (meth) acrylate; hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate and the like. Hydroxy group-containing (meth) acrylate; amino group-containing (meth) acrylate such as aminoethyl (meth) acrylate; epoxy group-containing (meth) acrylate such as glycidyl (meth) acrylate can be mentioned. These monomers may be polymerized alone or copolymerized.

The ratio of the (meth) acrylate monomer unit is not limited, but is, for example, 40% by mass or more, preferably 50% by mass or more, and more preferably 60% by mass or more in the total acrylic polymer.

The acrylic polymer may be a homopolymer of a (meth) acrylate monomer or a copolymer of a (meth) acrylate monomer and a copolymerizable monomer. Examples of the monomer copolymerizable with the (meth) acrylate monomer include the conjugated diene monomer listed in the above item of diene polymer and "other monomers", and these may be used alone or in combination of two or more. You may.

(Fluorine polymer)
Examples of the fluoropolymer include, but are not limited to, a homopolymer of vinylidene fluoride monomer and a copolymer of a vinylidene fluoride monomer and a copolymerizable monomer. Fluorine-based polymers are preferred from the viewpoint of electrochemical stability.

The proportion of the vinylidene fluoride monomer unit is not limited, but is, for example, 40% by mass or more, preferably 50% by mass or more, and more preferably 60% by mass or more in the total fluorine-based polymer.

The monomer copolymerizable with the vinylidene fluoride monomer is not limited, for example, vinyl fluoride, tetrafluoroethylene, trifluorochloroethylene, hexafluoropropylene, hexafluoroisobutylene, perfluoroacrylic acid, perfluoromethacrylic acid, and the like. And fluorine-containing ethylenically unsaturated compounds such as fluoroalkyl esters of acrylic acid or methacrylic acid; fluorine-free ethylenically unsaturated compounds such as cyclohexyl vinyl ether and hydroxyethyl vinyl ether; fluorine-free diene such as butadiene, isoprene, and chloroprene. Examples include compounds.

Among the fluoropolymers, a homopolymer of vinylidene fluoride, a vinylidene fluoride / tetrafluoroethylene copolymer, a vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymer and the like are preferable. More preferred fluoropolymers are vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymers, the monomer composition of which is typically 30-90% by weight of vinylidene fluoride, 50-9% by weight of tetrafluoroethylene, and hexafluoro. 20 to 1% by mass of propylene. These fluorine-based polymers may be used alone or in combination of two or more.

As the monomer used in synthesizing the thermoplastic polymer, at least one monomer selected from the group consisting of a hydroxyl group, a carboxyl group, an amino group, a sulfonic acid group, an amide group, and a cyano group can also be used.

The monomer having a hydroxy group is not limited, and examples thereof include vinyl-based monomers such as pentenol.

Examples of the monomer having a carboxyl group include, but are not limited to, unsaturated carboxylic acids having an ethylenic double bond such as (meth) acrylic acid and itaconic acid; and vinyl-based monomers such as penthenic acid. ..

Examples of the monomer having an amino group include, but are not limited to, 2-aminoethyl methacrylate and the like.

The monomer having a sulfonic acid group is not limited, for example, vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth) Alice sulfonic acid, styrene sulfonic acid, (meth) acrylic acid-2-sulfonic acid ethyl, 2-acrylamide. Examples thereof include -2-methylpropanesulfonic acid and 3-allyloxy-2-hydroxypropanesulfonic acid.

Examples of the monomer having an amide group include, but are not limited to, acrylamide, methacrylamide, N-methylolacrylamide, and N-methylolmethacrylamide.

Examples of the monomer having a cyano group include, but are not limited to, acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-cyanoethyl acrylate and the like.

A preferred thermoplastic polymer for adjusting the pattern coating slurry to have a gelling region in the solid content region of the initial solid content or more and less than 80% by mass and / or a sliding angle of 15 ° or more is used. Although not particularly limited, for example, polyolefin resins such as polyethylene, polypropylene, and α-polyethylene; fluororesins containing polyvinylidene fluoride and polytetrafluoroethylene, and polymers containing these; conjugated diene such as butadiene and isoprene as a monomer unit. Diene-based polymers containing, and copolymers containing them, and hydrides thereof; acrylic polymers containing acrylic acid esters, methacrylic acid esters, etc. as monomer units, copolymers containing these, and hydrides thereof; ethylene propylene rubber, Rubbers such as polyvinyl alcohol and polyvinyl acetate; cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose; polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, and polyester. And so on. Further, as the monomer used when synthesizing the thermoplastic polymer, a monomer having a hydroxyl group, a sulfonic acid group, a carboxyl group, an amide group and a cyano group can also be used. Among these thermoplastic polymers, a diene polymer, an acrylic polymer, or a fluorine polymer is preferable because it is excellent in binding property to an electrode active material, strength, and flexibility.

The thermoplastic polymer is preferably in the form of particles. The average particle size of the thermoplastic polymer particles is preferably 0.01 μm or more and 5 μm or less, more preferably 0.05 μm or more and 3 μm or less, and further preferably 0.1 μm or more and 1 μm or less. When the average particle size of the thermoplastic polymer is within the above range, the pattern coating slurry has a gelling region in the solid content region of the initial solid content or more and less than 80% by mass, and / or the sliding angle is 15 ° or more. It becomes easier to adjust so that.

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

(Glass transition point and melting point of thermoplastic polymer)
The thermoplastic polymer preferably has a glass transition point (Tg) or a melting point (Tm) of 20 ° C. or higher and 100 ° C. or lower, more preferably 25 ° C. or higher and 90 ° C. or lower, more preferably 30 ° C. or higher and 80 ° C. or lower, and further preferably. It contains a thermoplastic polymer having a temperature of 35 ° C. or higher and 70 ° C. or lower. When the glass transition point or the melting point is within the above range, the thermoplastic polymer on the porous substrate is easily deformed during hot pressing, and the adhesion area to the electrode as an adherend increases. Thereby, the adhesiveness between the porous base material and the thermoplastic layer or the adhesiveness between the separator and the electrode becomes better.

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

In the present specification, the “glass transition” refers to a DSC in which a change in calorific value accompanying a change in the state of the polymer occurs on the endothermic side. “Baseline” refers to the DSC curve in the temperature range where no transition or reaction occurs on the test piece. The “peak” refers to the portion of the DSC curve from which the curve departs from the baseline until it returns to the baseline again. “Stepped change” refers to the portion of the DSC curve from the previous baseline to the transition to a new baseline. Staircase changes also include a combination of peaks and staircase changes. The "inflection point" indicates a point at which the gradient of the DSC curve of the stepped change portion is maximized. In other words, the inflection point can also be expressed as a point where the upwardly convex curve changes to the downwardly convex curve at the stepped change portion.

The Tg of the thermoplastic polymer can be appropriately adjusted by, for example, changing the type of the monomer used for producing the thermoplastic polymer and the compounding ratio of each monomer. The Tg of a thermoplastic polymer is determined from the Tg of the homopolymer generally shown for each monomer used in its production (eg, described in the "Polymer Handbook" (A WILEY-INTERSCIENCE PUBLICATION)) and the mixing ratio of the monomers. It can be roughly estimated. For example, a thermoplastic polymer containing a high proportion of monomers such as styrene, methylmethacrylate, and acrylonitrile that give a polymer of Tg at about 100 ° C. has a high Tg. Further, for example, a thermoplastic polymer containing a high ratio of monomers such as butadiene giving a polymer of Tg at about −80 ° C., n-butylacryllate giving a polymer of Tg at about −50 ° C., and 2-ethylhexylacryllate. Has a low Tg. The Tg of the thermoplastic polymer can be estimated by the formula of FOX (formula 1 below). As the glass transition point of the thermoplastic polymer, the one measured by the method using the DSC described above is adopted.
1 / Tg = W ₁ / Tg ₁ + W ₂ / Tg ₂ + ... + Wi _i / Tg _i + ... W _n / Tg _n (1)
{In the formula, Tg (K) indicates the Tg of the copolymer, Tgi (K) indicates the Tg of the homopolymer of each monomer _i , and _Wi indicates the mass fraction of each monomer}.

The thermoplastic polymer also preferably has at least two glass transition points. In this case, at least one of the Tg of the thermoplastic polymer is preferably less than 20 ° C., more preferably 15 ° C. or lower, still more preferably −50 ° C. or higher and 15 ° C. or lower. As a result, the adhesion between the coating layer and the porous substrate is excellent, and as a result, the separator is excellent in the adhesion to the electrode, so that the rigidity of the power storage device and the cycle characteristics are improved. Tg present in the region below 20 ° C. is used to improve the adhesion between the thermoplastic polymer and the porous substrate, improve the handleability of the separator, and / or suppress the powder falling off of the thermoplastic layer. It is even more preferable that it exists only in the region of −30 ° C. or higher and 15 ° C. or lower.

When the thermoplastic polymer has at least two glass transition points, at least one of the Tg of the thermoplastic polymer is preferably 20 ° C. or higher and 100 ° C. or lower, more preferably 30 ° C. or higher and 100 ° C. or lower, more preferably. It exists in the region of 40 ° C. or higher and 60 ° C. or lower. As a result, the thermoplastic layer has the handleability of the separator and the electrode and the separator because at least a part of the thermoplastic polymer maintains the state of particles when the separator is heated or pressurized for the production of the power storage device. Adhesion can be maintained.

The thermoplastic polymer having at least two glass transition points can be obtained, for example, by blending two or more kinds of thermoplastic polymers, using a thermoplastic polymer having a core-shell structure, and the like. As used herein, the term "core-shell structure" refers to a polymer having a dual structure consisting of a central portion (core) and an outer shell portion (shell) covering the core, and the polymer composition of the core and the polymer composition of the shell. Refers to a polymer different from. By combining a polymer having a high Tg and a polymer having a low Tg in a polymer blend and a core-shell structure, it is possible to control the glass transition point of the entire thermoplastic polymer and impart multiple functions to the entire thermoplastic polymer. ..

In the case of a polymer blend, by blending two or more types of a polymer having a glass transition point in a region of 20 ° C. or higher and a polymer having a glass transition point in a region of less than 20 ° C., stickiness resistance and basics can be obtained. It is possible to achieve both the applicability to the material. As for the mixing ratio in the case of blending, the mass ratio of the polymer having the glass transition point in the region of 20 ° C. or higher and the polymer having the glass transition point in the region of less than 20 ° C. is preferably 0.1:99. It is 9.9 to 99.9: 0.1, more preferably 5:95 to 95: 5, still more preferably 50:50 to 95: 5, and even more preferably 60:40 to 90:10.

In the case of the core-shell structure, the adhesiveness and compatibility with other materials (for example, polyolefin porous substrate, etc.) can be adjusted by changing the type of polymer of the shell. By changing the type of polymer in the core, for example, the adhesion of the polymer to the electrode after hot pressing can be adjusted. In the case of a core-shell structure, viscoelasticity can also be controlled by combining a highly viscous polymer and a highly elastic polymer. In the case of a thermoplastic polymer having a core-shell structure, the glass transition point of the polymer in the shell is not limited, but is preferably 20 ° C. or higher and 120 ° C. or lower, and more preferably 40 ° C. or higher and 100 ° C. or lower. The glass transition point of the polymer of the core is not limited, but is preferably less than 20 ° C., more preferably 15 ° C. or lower, still more preferably −30 ° C. or higher and 15 ° C. or lower.

<Dispersion medium>
The dispersion medium is preferably a poor solvent with respect to the thermoplastic polymer. Examples of the dispersion medium include, but are not limited to, N-methylpyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, water, ethanol, methanol, toluene, hot xylene, methylene chloride, hexane and the like.

The dispersion medium is preferably water or a mixed solvent of water and a water-soluble organic medium. Examples of the water-soluble organic medium include acetone, ethanol, methanol and the like. The dispersion medium preferably contains water, and more preferably water. When water is used as the dispersion medium of the slurry, the slurry is less likely to permeate into the porous polyolefin substrate, and the thermoplastic polymer is more likely to be present on the surface of the substrate, so that the pattern as designed is formed. This is preferable because it becomes easier and the decrease in permeability can be effectively suppressed.

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

Dispersant such as a surfactant in order to adjust the pattern coating slurry to have a gelling region in the solid content region of the initial solid content or more and less than 80% by mass and / or a sliding angle of 15 ° or more. , Thickeners, wetting agents, defoaming agents, pH adjusting agents containing acids and alkalis, and various other additives may be added. These additives are preferably those that can be removed at the time of solvent removal or plasticizer extraction, but are in the battery as long as they are electrochemically stable within the range of use of the lithium ion secondary battery and do not interfere with the battery reaction. May remain in. Preferred additives preferably include surfactants or thickeners, or both.

The surfactant is not particularly limited, and examples thereof include various anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants, and the like, among which anionic surfactants are used. Surfactants and nonionic surfactants are preferable.
Examples of the anionic surfactant include ion dissociable acid groups such as carboxyl groups, sulfonic acid groups, amino acid groups, and maleic acid groups, and ion dissociable organic dispersants such as polycarboxylates and polyacrylic acids. Those containing a plurality of salts, polymethacrylates and the like, or ion-dissociable acid bases such as carboxylic acid bases, sulfonic acid bases, maleic acid bases and the like are preferable. Specifically, alkylbenzene sulfonate, alkylphenyl sulfonate, alkylnaphthalene sulfonate, higher fatty acid salt, sulfate ester salt of higher fatty acid ester, sulfonate of higher fatty acid ester, sulfate ester salt of higher alcohol ether and sulfone. Examples thereof include acid salts, higher alkyl sulfosuccinates, polyoxyethylene alkyl ether carboxylates, polyoxyethylene alkyl ether sulfates, alkyl phosphates, polyoxyethylene alkyl ether phosphates and the like. Specific examples of these include dodecylbenzene sulfonate, isopropylnaphthalene sulfonate, monobutylphenylphenol monosulfonate, monobutylbiphenylsulfonate, dibutylphenylphenol disulfonate and the like.
Examples of the nonionic surfactant include polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, and glycerin fatty acid ester. , Polyoxyethylene glycerin fatty acid ester, polyglycerin fatty acid ester, sucrose fatty acid ester, polyoxyethylene alkylamine, polyoxyethylene fatty acid amide, fatty acid alkylolamide, alkylalkanolamide, acetylene glycol, polyoxyethylene adduct of acetylene glycol , Polyethylene glycol Polyethylene glycol block copolymer and the like. Among these, polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene dodecylphenyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, fatty acid. Alkyrolamide, acetylene glycol, polyoxyethylene adducts of acetylene glycol, polyethylene glycol, polypropylene glycol block copolymers are preferred.
Other surfactants include silicone surfactants such as polysiloxane oxyethylene adducts; fluorosurfactants such as perfluoroalkyl carboxylic acid salts, perfluoroalkyl sulfonates and oxyethylene perfluoroalkyl ethers. Biosurfactants such as spicrysporic acid, ramnolipide, lysolecithin and the like can also be used.
As the surfactant, one type may be used alone, or two or more types may be used in combination.

Further, if necessary, an antiseptic, a viscosity regulator, a pH regulator, a chelating agent, a plasticizer, an antioxidant, an ultraviolet absorber and the like can be added.

Thickeners include synthetic polymers such as, for example, polyethylene glycol, urethane-modified polyether, polyacrylic acid, polyvinyl alcohol, and vinylmethyl ether-maleic anhydride copolymer; carbomethoxycellulose, hydroxyethylcellulose, and hydroxypropyl. Cellulose derivatives such as cellulose; natural polysaccharides such as xanthan gum, dietangum, welan gum, gellan gum, guar gum, and carrageenan gum; and starches such as dextrin and pregelatinized starch. The thickener is appropriately selected from the viewpoint of the viscosity, pot life and particle size distribution of the slurry. Additives may be used alone or in combination of two or more.

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

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

<< Separator for power storage device >>
The separator for a power storage device of the present embodiment has a pattern coating formed from the pattern coating slurry of the present embodiment on at least one surface of the polyolefin porous base material. In one embodiment, the energy storage device separator may have pattern coatings on both sides of the polyolefin porous substrate in order to prevent the wound body from being pressed back after the separator is wound together with the electrodes. .. The pattern coating may be formed on one side or both sides of the base material, or may be formed on only a part of one side or both sides so that the separator has high ion permeability.

<Pattern coating>
The shape of the pattern coating is not limited, and examples thereof include patterns such as linear, diagonal, striped, dot-shaped, grid-like, striped, and hexagonal patterns. The pattern coating is preferably a diagonal line pattern, a stripe pattern, and a dot pattern, and more preferably a dot pattern. As used herein, the term "striped pattern" or "striped" means a pattern having a plurality of lines substantially parallel to the MD direction (mechanical direction) of the polyolefin substrate. In the present specification, the “diagonal line pattern” or “diagonal line pattern” means a pattern having a plurality of lines substantially parallel to a direction other than the MD direction of the polyolefin base material. In the specification of the present application, the "dot pattern" or "dot-like" means that a portion on the polyolefin porous substrate in which the thermoplastic polymer does not exist and a portion in which the thermoplastic polymer exists are sea-island-like (sea: The part where the thermoplastic polymer does not exist, the island: the part where the thermoplastic polymer exists.)

The dot pattern of the pattern coating provides one or more of the following advantages:
Since the dried thermoplastic polymer is swelled in the thickness direction of the base material, the adhesiveness to the electrode is improved;
High power batteries can be obtained because the permeability of the separator can be ensured by the part where the thermoplastic polymer is absent;
When the flow and / or storage form of the separator is reel-shaped, or when a plurality of separators for power storage devices are laminated, the number of contacts between the thermoplastic polymers existing on the overlapping separators is reduced. Blocking can be suppressed; and since irregularities are formed on the surface of the base material, the electrolytic solution easily penetrates in the battery manufacturing process and the liquid injection property is good (that is, the tact time in the battery manufacturing process is shortened). ).

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

When the pattern coating is a dot pattern, the diameter of the dots is preferably 5 μm or more and 500 μm or less, more preferably 20 μm or more and 400 μm or less, still more preferably 35 μm or more and 300 μm or less, still more preferably 50 μm or more and 200 μm or less. The "dot diameter" means the diameter when the dot is circular, and when it is not circular, it means the longest diameter passing through the center of gravity of the dot. The distance between the dots is preferably 5 μm or more and 2000 μm or less, more preferably 10 μm or more and 1500 μm or less, still more preferably 25 μm or more and 1000 μm or less, still more preferably 50 μm or more and 500 μm or less. The "distance between dots" means the distance between the centers when the dots are circular, and the distance between the centers of gravity when the dots are not circular. The area of one dot is preferably 1000 μm ² or more and 1000000 μm ² or less, more preferably 2500 μm ² or more and 250,000 μm ² or less, and further preferably 10000 μm ² or more and 90000 μm ² or less. When the size of the dot pattern is within the above range, the above-mentioned advantage due to the pattern coating being a dot pattern becomes more remarkable.

In one embodiment, the pattern coating is a dot pattern, the dot diameter is preferably 5 μm or more and 500 μm or less, and the dot spacing is preferably 5 μm or more and 2000 μm or less, and the dot diameter is 20 μm or more and 400 μm or less and the dots. It is more preferable that the distance between the dots is 10 μm or more and 1500 μm or less, and that the diameter of the dots is 35 μm or more and 300 μm or less and the distance between the dots is 25 μm or more and 1000 μm or less. When the size of the dot pattern is within the above range, the above-mentioned advantage due to the pattern coating being a dot pattern becomes more remarkable.

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

The area occupancy of the thermoplastic polymer on the polyolefin porous substrate is preferably 20% or more and less than 80%, more preferably 20% or more and 70% or less, and further preferably 20% or more and 60% or less. "Area occupancy" means the area ratio of the portion where the thermoplastic polymer is present to the total area of one side of the base material when the pattern coating is arranged on one side of the polyolefin porous base material. When the pattern coating is arranged on both sides of the polyolefin porous base material, it means the area ratio of the portion where the thermoplastic polymer is present to the total area of both sides of the base material.

By adjusting the area occupancy to the above level, the contact probability between the thermoplastic polymers when the separator is wound on the reel is suppressed, so that the blocking property is excellent, and the liquid injection property in the electrolytic solution injection process is good. Become. Furthermore, since the pores on the surface of the polyolefin microporous film are maintained, it is excellent in high-rate characteristics when used as a separator for a power storage device. Note that blocking generally refers to thermoplasticity existing on overlapping separators when the distribution and / or storage form of the separator is a reel shape, or when a plurality of separators for power storage devices are laminated. It means that the polymers are crimped to each other. The liquid injectability of the separator for a power storage device is an index showing the ease of penetration of the electrolytic solution in the battery manufacturing process. The higher the liquid injection property, the shorter the tact time in the battery manufacturing process, which is preferable.

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

<Polyolefin porous substrate>
The polyolefin porous base material may be any polyolefin porous base material containing a polyolefin resin as a main component, and is preferably a porous base material composed of a polyolefin resin. "Containing as a main component" means that a specific component or member is contained in an amount of more than 50% by mass. "Consists of" means that it is composed of a specific component or member, excluding unavoidable components and contamination.

From the viewpoint of the shutdown function of the separator, more than 50% by mass, preferably 75% by mass or more, more preferably 85% by mass or more, still more preferably 90% by mass or more, still more preferably 95% by mass or more of the polyolefin porous base material. Particularly preferably, the polyolefin resin accounts for 98% by mass or more.

Polyolefin resins include, but are not limited to, polyolefin resins used for general extrusion, injection, inflation, and blow molding, such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, And 1-octene and the like, homopolymers, copolymers, multistage polymers and the like. One type of polyolefin resin may be used alone, or two or more types may be used in combination.

As the polyolefin resin, polyethylene such as low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, and ultrahigh molecular weight polyethylene; polypropylene such as isotactic polypropylene and atactic polypropylene; ethylene-propylene random copolymer. , Ethylene-propylene block copolymers, polyethylene, and ethylene-propylene rubber are also mentioned.

As the polyethylene resin, high-density polyethylene is preferable because it has a low melting point and high strength. Two or more types of polyethylene may be used in combination to impart flexibility. Examples of the polymerization catalyst used for the polymerization of polyethylene include, but are not limited to, Ziegler-Natta-based catalysts, Philips-based catalysts, and metallocene-based catalysts.

In order to improve the heat resistance of the polyolefin porous base material, the polyolefin resin preferably contains polypropylene and a polyolefin resin other than polypropylene. The three-dimensional structure of polypropylene is not limited, and may be any of isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene. The ratio of polypropylene to the total mass of the polyolefin resin in the polyolefin resin composition is not limited, but is preferably 1 to 35% by mass, more preferably 3 to 20% by mass, from the viewpoint of achieving both heat resistance and a good shutdown function. %, More preferably 4 to 10% by mass. Examples of the polymerization catalyst used for the polymerization of polypropylene include, but are not limited to, Ziegler-Natta-based catalysts and metallocene-based catalysts.

Polyolefin resins other than polypropylene include, but are not limited to, homopolymers and copolymers of olefin hydrocarbons such as ethylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene. Be done. Specifically, examples of the polyolefin resin other than polypropylene include polyethylene, polybutene, ethylene-propylene random copolymer and the like.

From the viewpoint of the shutdown function of the porous polyolefin substrate, it is preferable to use polyethylene such as low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, and ultra high molecular weight polyethylene as the polyolefin resin other than polypropylene. .. Among these, from the viewpoint of strength, it is more preferable to use polyethylene having a density of 0.93 g / cm ³ or more measured according to JIS K7112.

The viscosity average molecular weight (Mv) of the polyolefin resin is not limited, but is preferably 30,000 or more and 120,000 or less, more preferably 50,000 or more and less than 2,000,000, and further preferably 100,000 or more and 1 It is less than one million. When the viscosity average molecular weight of the polyolefin resin is 30,000 or more, the melt tension at the time of melt-molding the base material is large, the moldability is improved, and a high-strength base material tends to be obtained by entanglement of the polymers. It is preferable because it is located in. When the viscosity average molecular weight is 12,000,000 or less, melt-kneading can be performed more uniformly, and the formability of the sheet, particularly the thickness stability tends to be excellent, which is preferable. When the viscosity average molecular weight is less than 1,000,000, the pores of the base material are easily closed when the temperature rises, and a good shutdown function tends to be obtained, which is preferable.

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

As a result of using a polyolefin having a viscosity average molecular weight of less than 1,000,000 alone, it is a mixture of a polyolefin having a viscosity average molecular weight of about 2,000,000 and a polyolefin having a viscosity average molecular weight of about 270,000. , A mixture having a viscosity average molecular weight of less than 1,000,000 as a whole may be used.

The polyolefin porous substrate may contain any additive. Additives include, but are not limited to, polymers other than polyolefins, inorganic particles, antioxidants, metal soaps, UV absorbers, light stabilizers, antistatic agents, antifogging agents, color pigments and the like. .. Examples of the antioxidant include phenol-based, phosphorus-based, and sulfur-based antioxidants. Examples of metal soaps include metal soaps such as calcium stearate and zinc stearate. The total content of any additive is preferably 0.001% by mass or more and 20 parts by mass or less, more preferably 10 parts by mass or less, still more preferably 5 parts by mass or less, based on 100 parts by mass of the polyolefin porous base. Is.

The porosity of the polyolefin porous substrate is preferably 20% or more, more preferably 35% or more, preferably 90% or less, and more preferably 80% or less. When the porosity is 20% or more, a separator having high ion permeability can be obtained. When the porosity is 90% or less, a separator having high puncture strength can be obtained.

The porosity of the polyolefin porous substrate is determined from, for example, the volume (cm ³ ), mass (g), and film density (g / cm ³ ) of the substrate.
Porosity = (volume-mass / membrane density) / volume x 100
Can be obtained by. For example, in the case of a polyolefin porous substrate composed of polyethylene, the porosity can be calculated assuming that the film density is 0.95 (g / cm ³ ). The porosity can be adjusted by changing the draw ratio of the polyolefin porous base material.

The air permeability of the polyolefin porous substrate is not limited, but is preferably 10 seconds / 100 cc or more, more preferably 50 seconds / 100 cc or more, preferably 1,000 seconds / 100 cc or less, and more preferably 500 seconds / It is 100 cc or less. When the air permeability is 10 seconds / 100 cc or more, self-discharge of the power storage device is suppressed, which is preferable. When the air permeability is 1,000 seconds / 100 cc or less, good charge / discharge characteristics can be obtained, which is preferable. In the present specification, the air permeability is the air permeability resistance measured according to JIS P-8117. The air permeability can be adjusted by changing the stretching temperature and / or the stretching ratio of the porous substrate.

The average pore size of the polyolefin porous substrate is preferably 0.15 μm or less, more preferably 0.1 μm or less, and preferably 0.01 μm or more. When the average pore diameter is 0.15 μm or less, the self-discharge of the power storage device is suppressed and the capacity decrease is suppressed, which is preferable. The average pore size can be adjusted by changing the draw ratio or the like when producing the porous polyolefin substrate.

The puncture strength of the polyolefin porous substrate is not limited, but is preferably 200 g / 20 μm or more, more preferably 300 g / 20 μm or more, preferably 2,000 g / 20 μm or less, and more preferably 1,000 g / 20 μm or less. be. When the puncture strength is 200 g / 20 μm or more, the film rupture due to the active material or the like that has fallen off during battery winding is suppressed, and the short circuit due to the expansion and contraction of the electrode due to charging / discharging is suppressed, which is preferable. When the puncture strength is 2,000 g / 20 μm or less, the width shrinkage due to the relaxation of orientation during heating is reduced, which is preferable. The puncture strength can be adjusted by adjusting the stretching ratio and / or the stretching temperature of the porous polyolefin substrate.

The film thickness of the polyolefin porous substrate is not limited, but is preferably 2 μm or more, more preferably 5 μm or more, preferably 100 μm or less, more preferably 60 μm or less, and further preferably 50 μm or less. When the film thickness is 2 μm or more, the mechanical strength is improved, which is preferable. When the film thickness is 100 μm or less, the occupied volume of the separator in the battery tends to decrease, which tends to contribute to increasing the capacity of the battery, which is preferable.

The polyolefin porous substrate has an average pore diameter of 0.15 μm or less and a film thickness from the viewpoint of suppressing self-discharge of the power storage device, reducing the occupied volume of the separator in the battery, and increasing the capacity of the battery. It is more preferable that the polyolefin microporous film has a thickness of 100 μm or less.

<Physical characteristics of separator for power storage device>
The separator for a power storage device of the present embodiment has a pattern coating formed from the pattern coating slurry of the present embodiment on at least one surface of a porous polyolefin base material, whereby ion permeability and adhesion to an electrode are provided. It has excellent properties, blocking properties, and liquid injection properties.

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

(Adhesiveness)
The adhesiveness of the separator for a power storage device can be evaluated by the peel strength between the separator and the electrode, as described in the column of Examples. The separator for a power storage device preferably has a peel strength of 5 N / m or more when it is superposed on an electrode and pressed under the conditions of a press temperature of 100 ° C., a press pressure of 1.0 MPa, and a press time of 5 seconds. When the peel strength measured under the above conditions is 5 N / m or more, it means that the adhesiveness between the separator and the electrode is good. By setting the peel strength within this range, sufficient adhesiveness between the separator and the electrode can be ensured, and peeling between the separator and the electrode due to expansion and contraction of the electrode due to charging and discharging and an increase in battery thickness can be suppressed. .. As a result, uniform lithium ion transfer is possible, generation of lithium dendrite is suppressed, and good cycle characteristics are achieved.

The electrode used for measuring the peel strength may be either a positive electrode or a negative electrode, but a positive electrode is preferable in order to appropriately grasp the adhesiveness of the separator for a power storage device. A positive electrode for a lithium ion secondary battery in which a positive electrode active material layer containing a positive electrode active material is formed on a positive electrode current collector is stacked so that the positive electrode active material layer and the pattern coating layer forming surface of the separator face each other. In addition, it is appropriate to measure the peel strength after pressing under the above conditions.

<< Manufacturing method of separator for power storage device >>
How to manufacture separators for power storage devices:
Pattern coating of a pattern coating slurry on at least one side of a polyolefin porous substrate;
Including drying the dispersion medium from the pattern coating slurry,
The pattern coating slurry contains a thermoplastic polymer and a dispersion medium.
The pattern coating slurry is a method in which the viscosity increase rate with respect to the increase in solid content is 10 mPa · s /% or more in the solid content region of the initial solid content or more and less than 80% by mass in the drying process. Is preferable.

<Manufacturing method of polyolefin porous base material>
The method for producing the polyolefin porous base material in the present embodiment is not particularly limited, and a known production method can be adopted. For example, a method in which a polyolefin resin composition and a plasticizer are melt-kneaded to form a sheet, stretched in some cases, and then made porous by extracting the plasticizer (wet method), or a polyolefin resin composition is melt-kneaded. After extruding with a high draw ratio, the polyolefin crystal interface is peeled off by heat treatment and stretching to make it porous (dry method). After melt-kneading the polyolefin resin composition and the inorganic filler and molding them on a sheet. , A method of making the polyolefin porous by peeling the interface between the polyolefin and the inorganic filler by stretching. After dissolving the polyolefin resin composition, it is immersed in a poor solvent for the polyolefin to solidify the polyolefin and at the same time remove the solvent to make it porous. There is a method of making it. In general, it is difficult to apply a good pattern to a polyolefin porous substrate produced by the dry method due to the influence of the surface condition, but even a polyolefin substrate produced by the dry method by using the slurry of the present invention can be used. Good pattern coating is possible.

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

When the gravure coater method is used, pattern coating is performed using a gravure coater that has been subjected to desired pattern processing. The shape of the pattern in the gravure coater can be a shape corresponding to the shape listed in the above "<Pattern coating>" column, and is preferably a dot, diagonal line, or stripe pattern. For the preferable diameter, width, distance, area, etc. of each pattern, refer to the above "<Pattern coating>" column.

It is preferable to apply a surface treatment to the surface of the porous base material prior to the pattern coating because the slurry can be easily applied and the adhesiveness between the base material and the pattern coating is improved. The surface treatment method is not limited as long as it does not significantly impair the porous structure of the base material, and is, for example, a corona discharge treatment method, a mechanical roughening method, a solvent treatment method, an acid treatment method, and an ultraviolet oxidation method. And so on.

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

From the viewpoint of pattern formation, the drying method is not particularly limited, but the time from application of the slurry to reaching the solid content of the gelled region is preferably within 20 seconds, more preferably within 15 seconds. More preferably, it is within 10 seconds, and further preferably within 5 seconds. After the gelation region, it is preferable to dry the polyolefin microporous base material under conditions that do not block the pores.

《Power storage device》
The power storage device of the present embodiment includes a positive electrode, a negative electrode, an electrolyte, and a separator for the power storage device of the present embodiment. The power storage device typically has an electrode laminate in which a positive electrode, a separator for a power storage device of the present embodiment, and a negative electrode are laminated in this order, or an electrode wound body in which the electrode laminate is wound.

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

When a lithium ion secondary battery is manufactured using the separator for a power storage device of the present embodiment, the positive electrode, the negative electrode, and the electrolytic solution are not limited, and known materials can be used for each.

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

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

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

A method of manufacturing a power storage device, preferably a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery, using the separator for a power storage device of the present embodiment is illustrated below.

The separator for a power storage device of the present embodiment is manufactured as a separator having a vertically elongated shape having a width of 10 to 500 mm (preferably 80 to 500 mm) and a length of 200 to 4,000 m (preferably 1,000 to 4,000 m). The obtained separators are laminated in the order of positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator, and wound in a circular or flat spiral shape to obtain an electrode wound body, and the electrode wound body is formed. A power storage device can be manufactured by putting it in a battery container and injecting an electrolytic solution.

Alternatively, the separator for the power storage device of the present embodiment, the electrode laminate composed of the positive electrode and the negative electrode, or the folded electrode laminate is placed in a battery container, and the electrolytic solution is injected. May produce a power storage device. The electrode laminate can be, for example, an electrode laminate in which a positive electrode-separator-negative electrode-separator-positive electrode or a negative electrode-separator-positive electrode-separator-negative electrode is laminated in the order of a flat plate. The battery container can be, for example, a film made of aluminum.

In either case, pressing can be performed on the electrode laminate or the electrode wound body. Specifically, a method of superimposing the separator for the power storage device, the positive electrode, and the negative electrode of the present embodiment so that the pattern coating layer of the separator and the active material layer of the electrode face each other and pressing the sheet can be mentioned.

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

It is also possible to perform hot pressing after injecting the electrolytic solution into the electrode laminate or the electrode winding body. In that case, the press temperature is preferably a temperature at which adhesiveness can be effectively exhibited, for example, 20 ° C. or higher. The temperature is preferably 120 ° C. or lower from the viewpoint of suppressing clogging or heat shrinkage of the separator holes due to hot pressing. The press pressure is preferably 20 MPa or less from the viewpoint of suppressing clogging of the separator holes. The press time is preferably 2 hours or less from the viewpoint of productivity.

Since the power storage device of the present embodiment has the separator for the power storage device of the present embodiment, which is excellent in ion permeability, adhesion to electrodes, etc., it is excellent in high rate characteristics.

Hereinafter, embodiments of the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples and Comparative Examples.

<< Measurement and evaluation method >>
<Solid content>
Approximately 1 g of the pattern coating slurry was precisely weighed on an aluminum plate, and the mass of the sample weighed at this time was defined as a (g). This was dried in a hot air dryer at 130 ° C. for 1 hour, and the dry mass of the sample after drying was defined as b (g). The solid content of the pattern coating slurry was calculated by the following formula.
Solid content = (b / a) x 100 (%)

<Gelation area>
The dispersion medium of the pattern coating slurry was dried from the initial solid content to a solid content of less than 80% by mass, and the viscosity of the slurry was measured each time the solid content increased by Δ5%. The viscosity increase rate (mPa · s /%) was calculated from the viscosity increase for each solid content Δ5%. The viscosity of the slurry was measured using a B-type viscometer (TVB10 type viscometer manufactured by Toki Sangyo Co., Ltd.) under the condition of a rotation speed of 60 rpm.

<Sliding angle>
For the sliding angle of the pattern coating slurry, a contact angle meter (manufactured by Kyowa Interface Science Co., Ltd., DMs-401) and a dynamic sliding method kit (manufactured by Kyowa Interface Science Co., Ltd., SA-Co1 / SA-Cs1) are used. Was measured. The liquid volume of the pattern coating slurry was 10 μL. The angle at which the amount of movement of the droplet exceeded 10 mm was defined as the sliding angle. The sliding angle is measured using a substrate on which the pattern coating slurry to be measured is scheduled to be coated.

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

<Glass transition point (Tg) and melting point (Tm)>
The glass transition point and melting point of the thermoplastic polymer were determined from the DSC curve obtained by differential scanning calorimetry (DSC).
An appropriate amount of an aqueous dispersion containing a thermoplastic polymer (solid content = 38 to 42% by mass, pH = 9.0) was placed in an aluminum dish and dried in a hot air dryer at 130 ° C. for 30 minutes. Approximately 17 mg of the dried film after drying was packed in an aluminum container for measurement, and a DSC curve and a DDSC curve under a nitrogen atmosphere were obtained with a DSC measuring device (manufactured by Shimadzu Corporation, DSC6220). The measurement conditions were as follows.
1st stage temperature rise program: Start at 70 ° C and raise the temperature at a rate of 15 ° C per minute. Maintained for 5 minutes after reaching 110 ° C.
Second stage temperature lowering program: The temperature is lowered from 110 ° C to 40 ° C per minute. Maintain for 5 minutes after reaching -50 ° C.
Third stage temperature rise program: The temperature is raised from -50 ° C to 130 ° C at a rate of 15 ° C per minute. Data of DSC and DDSC are acquired at the time of this third stage temperature rise.
The melting point was determined by the intersection of the baseline on the DSC curve and the tangent to the slope of the endothermic peak of melting. The glass transition point was determined by the intersection of a straight line extending the baseline on the low temperature side of the DSC curve to the high temperature side and a tangent line at the inflection of the stepwise change portion of the glass transition.

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

<Film thickness>
A 10 cm x 10 cm square sample is cut from a porous polyolefin substrate, 9 measurement points (3 points x 3 points) are selected in a grid pattern, and a microthickening instrument (Toyo Seiki Seisakusho Co., Ltd. type KBM) is used. , The film thickness of each measurement point was measured at room temperature 23 ± 2 ° C. The average value of the obtained nine measured values was calculated as the film thickness of the base material.

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

<Pattern formation>
The pattern formability (%) of the slurry for pattern coating on the polyolefin porous substrate is the dimensional difference between the pattern processed on the gravure coater and the pattern actually coated on the polyolefin porous substrate. It is an index for evaluating.
The pattern formation property was calculated using the following method. The average pattern area on the porous polyolefin substrate was observed with a scanning electron microscope (SEM) (manufactured by Hitachi, Ltd., S-4800).
Pattern formation (times) = average pattern area on polyolefin porous substrate /
The average pattern area pattern formability of the gravure plate was evaluated according to the following criteria.
S: 0.7 or more and 2.0 times or less A: 0.6 or more and less than 0.7, or 2.0 times or more and 3.0 times or less B: 0.4 or more and less than 0.6 or 3.0 times or more 5.0 times or less C: Less than 0.4 or more than 5.0 times

<Increased air permeability>
The air permeability of the separator for a power storage device is the air permeation resistance measured in accordance with JIS P-8117, similarly to the air permeability of a general porous substrate. The air permeation resistance is the time required for a specified volume of air to permeate per unit area and unit pressure difference, and is expressed in time (seconds) per 100 mL. The air permeability resistance measured by the Garley type air permeability meter GB2 (trademark) manufactured by Toyo Seiki Co., Ltd. was defined as the air permeability (s ^-1 ).
Next, the increase in air permeability (s ^-1 ) was calculated by subtracting the registration of the separator after pattern coating from the air permeability of the polyolefin microporous substrate.
The increase in air permeability was evaluated according to the following criteria.
S: 10s ^-1 or less A: 10s ^-1 or more and less than 20s ^-1 B: 20s ^-1 or more and less than 30s ^-1 C: 30s ^-1 or more

<Peeling strength>
Separator for power storage device and positive electrode as adherend (manufactured by enertech, positive electrode material: LiCoO ₂ , conductive aid: acetylene black, binder: PVDF, LiCoO ₂ / acetylene black / PVDF (weight ratio) = 95/2 / 3, L / W: 36 mg / cm ² on both sides, density: 3.9 g / cc, thickness of Al current collector: 15 μm, thickness of positive electrode after pressing: 107 μm), with a width of 15 mm and a length of 60 mm, respectively. It was cut into a rectangular shape. The thermoplastic polymer layer of the separator and the positive electrode active material were superposed so as to face each other to obtain a laminate. The obtained laminate was pressed under the following conditions.
Press pressure: 1 MPa
Temperature: 100 ° C
Pressing time: 5 seconds For the laminated body after pressing, the electrode is fixed using the force gauge ZP5N and MX2-500N (product name) manufactured by Imada Co., Ltd., and the peeling speed is 50 mm by the method of grasping and pulling the separator. A 90 ° peel test was performed at / min to check the peel strength. At this time, the average value of the peel strength in the peel test for a length of 40 mm performed under the above conditions was taken as the peel strength. The adhesiveness with the electrode was evaluated according to the following criteria.
Evaluation Criteria S: 15 N / m or more A: 10 N / m or more and less than 15 N / m B: 5 N / m or more and less than 10 N / m C: Less than 5 N / m

<Blocking property>
The coated surfaces of the separator for the power storage device were overlapped with each other, and the press was performed for 3 minutes under the conditions of a temperature of 30 ° C. and a pressure of 5 MPa. Then, the peel strength between the overlapping coated surfaces was measured using an Autograph AG-IS type (trademark) manufactured by Shimadzu Corporation at a tensile speed of 200 mm / min according to JIS K6854-2. Based on the value of peel strength, the blocking property was evaluated according to the following evaluation criteria.
Evaluation Criteria A (Good): Less than 5N / m B (Allowable): 5N / m or more and less than 10N / C (Evil): 10N / m or more and less than 20N / D (Defective): 20N / m or more

<Liquidability>
a. Preparation of positive electrode Nickel, manganese, cobalt composite oxide (NMC) (Ni: Mn: Co = 1: 1: 1 (element ratio), density 4.70 g / cm ³ ) was 90.4% by mass as the positive electrode active material. As a conductive auxiliary material, 1.6% by mass of graphite powder (KS6) (density 2.26 g / cm ³ , number average particle diameter 6.5 μm) and acetylene black powder (AB) (density 1.95 g / cm ³ , number average) Particle size 48 nm) was mixed at a ratio of 3.8% by mass, and polyvinylidene fluoride (PVDF) (density 1.75 g / cm ³ ) as a binder was mixed at a ratio of 4.2% by mass, and these were mixed with N-methylpyrrolidone (NMP). A slurry was prepared by dispersing the particles in the mixture. This slurry is applied to one side of a 20 μm-thick aluminum foil serving as a positive electrode current collector using a die coater, dried at 130 ° C. for 3 minutes, and then compression-molded using a roll press to obtain a positive electrode. Made. The amount of the positive electrode active material applied at this time was 109 g / m ² .
b. Preparation of negative electrode As the negative electrode active material, graphite powder A (density 2.23 g / cm ³ , number average particle diameter 12.7 μm) was 87.6% by mass and graphite powder B (density 2.27 g / cm ³ , number average particle diameter). 6.5 μm) was 9.7% by mass, and 1.4% by mass (solid content equivalent) of ammonium salt of carboxymethyl cellulose (solid content concentration 1.83% by mass aqueous solution) and 1.7% by mass of diene rubber-based latex as a binder. A slurry was prepared by dispersing (in terms of solid content) (an aqueous solution having a solid content concentration of 40% by mass) in purified water. This slurry was applied to one side of a copper foil having a thickness of 12 μm to be a negative electrode current collector with a die coater, dried at 120 ° C. for 3 minutes, and then compression-molded with a roll press to prepare a negative electrode. The amount of the negative electrode active material applied at this time was 5.2 g / m ² .
c. Preparation of non-aqueous electrolyte solution A non-aqueous electrolyte solution is prepared by dissolving LiPF ₆ as a solute in a mixed solvent of ethylene carbonate: ethyl methyl carbonate = 1: 2 (volume ratio) so as to have a concentration of 1.0 mol / L. Prepared.
d-1. Battery assembly The separators for power storage devices obtained in each of the examples and comparative examples were cut out into circles of 50 mmφ, and the positive electrode and the negative electrode were each cut into a circle of 40 mmφ. The negative electrode, the separator, and the positive electrode were stacked in this order so that the positive electrode and the active material surface of the negative electrode faced each other, pressed or heat-pressed, and housed in a stainless metal container with a lid. The container and the lid were insulated, and the container was in contact with the copper foil of the negative electrode and the lid was in contact with the aluminum foil of the positive electrode. 0.5 ml of the non-aqueous electrolytic solution was injected into the container along the side surface of the container and sealed, and then connected to an impedance analyzer and the resistance was measured to confirm the liquid injection property.
The liquid injection property was evaluated by the time required for the resistance value to become Ω or less.
Evaluation Criteria S (Good): Less than 200 seconds A (Allowable): 200 seconds or more and less than 400 seconds B (Evil): 400 seconds or more and less than 600 seconds C (Bad): 600 seconds or more

<High rate characteristics>
d-2. Battery assembly The separators for power storage devices obtained in each Example and Comparative Example were cut out into a circle of 24 mmφ, and the positive electrode and the negative electrode were each cut into a circle of 16 mmφ. The negative electrode, the separator, and the positive electrode were stacked in this order so that the positive electrode and the active material surface of the negative electrode faced each other, pressed or heat-pressed, and housed in a stainless metal container with a lid. The container and the lid were insulated, and the container was in contact with the copper foil of the negative electrode and the lid was in contact with the aluminum foil of the positive electrode. A battery was assembled by injecting 0.2 ml of the non-aqueous electrolytic solution into this container and sealing the container.
e. Evaluation of rate characteristics d-2. After charging the simple battery assembled in step 1 at 25 ° C. with a current value of 3 mA (about 0.5 C) to a battery voltage of 4.2 V, the current value is started to be throttled from 3 mA so as to maintain 4.2 V. The first charge after the battery was made was carried out for a total of about 6 hours. After that, the battery was discharged to a battery voltage of 3.0 V at a current value of 3 mA.
Next, at 25 ° C., the battery is charged to a battery voltage of 4.2 V with a current value of 6 mA (about 1.0 C), and then the current value is started to be throttled from 6 mA so as to maintain 4.2 V, for a total of about 3 Charged for hours. After that, the discharge capacity when discharged to a battery voltage of 3.0 V at a current value of 6 mA was defined as 1 C discharge capacity (mAh).
Next, at 25 ° C., the battery is charged to a battery voltage of 4.2 V with a current value of 6 mA (about 1.0 C), and then the current value is started to be throttled from 6 mA so as to maintain 4.2 V, for a total of about 3 Charged for hours. After that, the discharge capacity when discharged to a battery voltage of 3.0 V at a current value of 90 mA (about 15 C) was defined as 15 C discharge capacity (mAh).
Then, the ratio of the 15C discharge capacity to the 1C discharge capacity was calculated, and this value was used as the rate characteristic.
High rate characteristic (%) = (15C discharge capacity / 1C discharge capacity) x 100
Evaluation criteria S: 60% or more A: 50% or more and less than 60% B: 40% or more and less than 50% C: 30% or more and less than 40% D: less than 30%

<< Synthesis of thermoplastic polymer particles >>
<Water dispersion a1>
In a reaction vessel equipped with a stirrer, a reflux condenser, a dropping tank and a thermometer, 70.4 parts by mass of ion-exchanged water and "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) as an emulsifier, Notated as "KH1025" in the table. The same shall apply hereinafter.) 0.5 parts by mass and "Adecaria soap SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Co., Ltd., expressed as "SR1025" in the table. The same shall apply hereinafter) 0 .5 parts by mass was charged. Next, the temperature inside the reaction vessel was raised to 80 ° C., and while maintaining the temperature of 80 ° C., a 2% aqueous solution of ammonium persulfate (indicated as “APS (aq)” in the table; the same applies hereinafter) was added to 7.5. The mixture was added by mass to obtain an initial mixture. Five minutes after the addition of the ammonium persulfate aqueous solution was completed, the emulsion was added dropwise from the dropping tank to the reaction vessel over 150 minutes.

The above emulsion is:
10 parts by mass of methoxypolyethylene glycol methacrylate (denoted as PEGM in the table; the same applies hereinafter) as a monomer constituting the polyethylene glycol group-containing monomer unit (P);
As the monomer constituting the cycloalkyl group-containing monomer unit (A), cyclohexyl methacrylate (indicated as "CHMA" in the table; the same applies hereinafter) 30 parts by mass;
1.0 part by mass of methacrylic acid (denoted as "MAA" in the table; the same applies hereinafter) as a monomer constituting the carboxyl group-containing monomer unit (b1);
Acrylic acid (denoted as "AA" in the table. The same shall apply hereinafter) 1.0 part by mass;
Acrylamide (denoted as "AM" in the table; the same applies hereinafter) as a monomer constituting the amide group-containing monomer unit (b2) 0.1 part by mass;
2-Hydroxyethyl methacrylate (denoted as "2HEMA" in the table; the same applies hereinafter) as a monomer constituting the hydroxyl group-containing monomer unit (b3) 5 parts by mass;
Trimethylolpropane triacrylate (A-TMPT, trade name manufactured by Shin-Nakamura Chemical Industry Co., Ltd., referred to as "A-TMPT" in the table. The same shall apply hereinafter) 0 as a monomer constituting the crosslinkable monomer unit (b4). .5 parts by mass;
Methyl methacrylate (denoted as "MMA" in the table; the same applies hereinafter) 1.0 part by mass as a monomer constituting the (meth) acrylic acid ester monomer unit (b5) other than the above;
Butyl methacrylate (indicated as "BMA" in the table. The same shall apply hereinafter) 0.4 parts by mass;
Butyl acrylate (denoted as "BA" in the table. The same shall apply hereinafter) 1.0 part by mass;
2-Ethylhexyl acrylate (denoted as "2EHA" in the table. The same shall apply hereinafter) 50.0 parts by mass;
As emulsifiers, 3 parts by mass of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), 3 parts by mass of "Adecaria Soap SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation) and p-styrene. Sodium sulfonate (denoted as "NaSS" in the table. The same shall apply hereinafter) 0.05 parts by mass;
A mixture of 7.5 parts by mass of a 2% aqueous solution of ammonium persulfate; and 52 parts by mass of ion-exchanged water was prepared by mixing with a homomixer for 5 minutes.

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

<Aqueous dispersions A1 to A9>
The initial mixture shown in Tables 2 and 3 was changed to the same blending ratio as the aqueous dispersion a1, and the other emulsions were changed to the blending ratios shown in Tables 2 and 3, and the same synthesis as a1 was performed to carry out the same synthesis as A1 to A9. Each seed polymer aqueous dispersion (40% solid content) was obtained. The aqueous dispersions A1 to A9 were obtained by synthesizing in the same manner as the aqueous dispersion a1 except that the initial mixture and the emulsion were subsequently changed as shown in Tables 2 and 3. For the obtained copolymers of the aqueous dispersions A1 to A9 and a1, the particle size and the glass transition point (Tg) were measured by the above method. The results obtained are shown in Tables 2 and 3. In the table, the composition of raw materials is based on mass.

<< Production of Polyolefin Porous Base Material (Wet Method) >>
<Base material B1>
Homopolymer high-density polyethylene with Mv of 700,000 was added to 45 parts by mass.
Homopolymer high-density polyethylene with Mv of 300,000 was added to 45 parts by mass.
5 parts by mass of polypropylene of homopolymer having Mv of 400,000 and
Was dry-blended using a tumbler blender.
To 99 parts by mass of the obtained polyolefin mixture, 1 part by mass of tetrakis- [methylene- (3', 5'-di-t-butyl-4'-hydroxyphenyl) propionate] methane was added as an antioxidant, and the tumbler blender was used again. The mixture was obtained by dry blending using.
The resulting mixture was fed to a twin-screw extruder in a nitrogen atmosphere by a feeder.
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 pump were adjusted so that the proportion of liquid paraffin in the total mixture extruded was 65 parts by mass and the polymer concentration was 35 parts by mass.

Next, they are melt-kneaded while being heated to 230 ° C. in a twin-screw extruder, and the obtained melt-kneaded product is extruded through a T-die onto a cooling roll whose surface temperature is controlled to 80 ° C., and the extruded product is extruded. A sheet-shaped molded product was obtained by contacting with a cooling roll and molding (casting) to cool and solidify.
This sheet was stretched at a temperature of 112 ° C. at a magnification of 7 × 6.4 times by a simultaneous biaxial stretching machine. Then, the stretched product was immersed in methylene chloride to extract and remove liquid paraffin, dried, and further stretched twice in the transverse direction at a temperature of 130 ° C. using a tenter stretching machine.
Then, this stretched sheet was relaxed by about 10% in the width direction and heat-treated to obtain a polyolefin porous base material B1. Table 1 shows the physical characteristics of the obtained base material B1.

<Base material B2>
The following materials:
SiO ₂ "DM10C" (trademark, manufactured by Tokuyama Corporation),
High-density polyethylene with a viscosity average molecular weight of 700,000,
High-density polyethylene with a viscosity average molecular weight of 250,000,
Homopolypropylene with a viscosity average molecular weight of 400,000,
Liquid paraffin as a plasticizer, and pentaerythrityl-tetrakis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate as an antioxidant]
Was premixed with a super mixer to prepare a first raw material.

The following ingredients:
High-density polyethylene with an average viscosity molecular weight of 700,000, high-density polyethylene with an average viscosity molecular weight of 250,000,
Homopolypropylene with a viscosity average molecular weight of 400,000,
Liquid paraffin as a plasticizer, and pentaerythrityl-tetrakis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate as an antioxidant]
Was premixed with a super mixer to prepare a second raw material.

The first and second raw materials were supplied to two twin-screw same-direction screw extruder feed ports by a feeder. At this time, the liquid paraffin was side-fed to the twin-screw extruder cylinder together with each raw material so that the amount ratio of the plasticizer (liquid paraffin) in the total mixture extruded by melting and kneading was 60% by mass.

Subsequently, the melt-kneaded product is extruded between a pair of rolls via a gear pump, a conduit, and a T-die capable of co-extruding two or three layers, respectively, and the first layer made of the first raw material is used as the surface layer. A sheet-like composition (first layer-second layer-first layer) having a second layer made of a second raw material as an intermediate layer was obtained. After that, the polyolefin porous base material B2 was obtained by performing the same operation as in the production example of the polyolefin porous base material B1 except that the stretching temperature and the relaxation rate were adjusted.

<Base material B3>
As the polyolefin porous base material B3, a polypropylene single-layer film, Cellguard model number "CG2500" (dry-type polyolefin base material manufactured by Asahi Kasei Corporation) was prepared. The base materials used are shown in Table 1.

<Base material B4>
Aluminum hydroxide (average particle size 1.0 μm) 97.0 parts by mass, acrylic latex (solid content concentration 40%, average particle size 145 nm, minimum film formation temperature 0 ° C. or less) 3.0 parts by mass, and polycarboxylic acid A coating solution was prepared by uniformly dispersing 1.0 part by mass of an aqueous ammonium ammonium solution (SN Dispersant 5468 manufactured by Sannopco) in 100 parts by mass of water. Subsequently, the coating liquid was applied to the surface of the polyolefin porous base material B3 using a gravure coater. Then, it was dried at 60 ° C. to remove water. In this way, the polyolefin porous base material B4 was obtained by forming the aluminum hydroxide oxide layer (porous layer of the inorganic filler) on the polyolefin porous base material B3 with a thickness of 2 μm.

<< Example 1 >>
The aqueous dispersions A3 and a1 shown in Table 2 are mixed so that the solid content weight ratio is A3: a1 = 80: 20, and purified water is added to prepare an organic binder-containing slurry having a solid content of 25% by mass. did. Next, as an additive to the slurry, an aqueous solution of xanthan gum (manufactured by Sansho Co., Ltd., Kelzan M) prepared to have a solid content concentration of 1.5% by mass, and an alkylsulfonic acid-based surfactant (manufactured by Mitsui Cytec Co., Ltd., OT-75). Was added in a small amount and stirred for 5 minutes, and the solid content having a viscosity increase rate of 10 mPa /% or more and the sliding angle were measured. By repeating the adjustment of the added material, a slurry for pattern coating having a viscosity increase rate of 10 mPa /% or more, a solid content of 35% by mass, and a sliding angle of 60 ° was obtained.

The prepared paint was applied in a pattern on one side surface of the polyolefin microporous substrate B3 shown in Table 1 using a gravure roll having a dot diameter of 200 μm and a depth of 5 μm engraved in a dot shape, and at 60 ° C. Separator S1 was obtained by drying and removing water from the coating liquid. The diameter of the dots formed on the separator was 250 μm, and the distance between the dots was 300 μm.

<< Examples 2 and 3 >>
In Example 2, pattern coating was performed in the same manner as in Example 1 except that a gravure roll engraved with a diagonal line width of 200 μm and a depth of 5 μm was used, and the transfer line to the polyolefin substrate after coating was transferred. The width was 280 μm and the line spacing was 200 μm. In Example 3, pattern coating was performed in the same manner as in Example 1 except that a striped gravure roll having a width of 200 μm and a depth of 5 μm was used, and the transfer to the polyolefin substrate after coating was performed. The width of the lines was 280 μm, and the spacing between the lines was 200 μm.

<< Examples 4 to 20 and Comparative Examples 1 to 4 >>
Pattern coating was performed in the same manner as in Examples 1 to 3 except that the polyolefin microporous substrate, the aqueous dispersion, and the adjusted slurry shown in Tables 1 to 3 were used, and respective separators were obtained. Regarding the coating on the base material 4 in Example 19 and Comparative Example 4, the pattern coating was performed not on the layer of aluminum hydroxide oxide but on the polyolefin surface.

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

Claims (12)

A pattern coating slurry for pattern coating on at least one surface of a polyolefin porous substrate used as a substrate for a separator for a power storage device.
The pattern coating slurry contains a thermoplastic polymer and a dispersion medium.
While the dispersion medium is dried from the pattern coating slurry, the solid content region containing the initial solid content or more and less than 80% by mass includes a region in which the viscosity increase rate with respect to the increase in solid content is 10 mPa · s /% or more. Slurry for pattern coating. The slurry for pattern coating according to claim 1, wherein the sliding angle of the dynamic contact angle in the sliding method using the polyolefin porous substrate is 15 ° or more. The slurry for pattern coating according to claim 1 or 2, wherein the dispersion medium contains water. The pattern coating slurry according to any one of claims 1 to 3, wherein the thermoplastic polymer contains a thermoplastic polymer having a glass transition point (Tg) of less than 20 ° C. The pattern coating slurry according to any one of claims 1 to 4, wherein the thermoplastic polymer contains a thermoplastic polymer having a glass transition point (Tg) of 20 ° C. or higher and 100 ° C. or lower. The pattern coating slurry according to any one of claims 1 to 4, wherein the thermoplastic polymer contains a thermoplastic polymer having a melting point (Tg) of 35 ° C. or higher and 100 ° C. or lower. The pattern coating slurry according to any one of claims 1 to 6, wherein the pattern coating slurry has a viscosity of 100 mPa · s or less when the solid content concentration is 30% by mass. A separator for a power storage device, which has a pattern coating formed from the pattern coating slurry according to any one of claims 1 to 7 on at least one surface of the polyolefin porous substrate. The separator for a power storage device according to claim 8, wherein the pattern coating is a dot pattern. The separator for a power storage device according to claim 9, wherein the dot diameter is 5 μm or more and 500 μm or less, and the distance between the dots is 5 μm or more and 2000 μm or less. The separator for a power storage device according to any one of claims 8 to 10, wherein the area occupancy of the thermoplastic polymer on the polyolefin porous substrate is 20% or more and less than 80%. A power storage device having a positive electrode, a negative electrode, an electrolyte, and a separator for a power storage device according to any one of claims 8 to 11.