Adhesive composition, separator, non-aqueous secondary battery, and method for producing adhesive composition

Abstract

An object of the present invention is to achieve both blocking resistance and powder shedding resistance while preventing a decrease in lithium ion permeability. [Solution] The polymer particles have a core-shell structure, and the shell portion of the polymer particle contains an acid group-containing monomer as a constituent unit. The dispersant is contained in an amount of 2 to 18 parts by mass per 100 parts by mass of the monomer constituting the polymer particle. The proportion of the core portion in a total of 100% by mass of the core portion and shell portion of the polymer particle is 30 to 80% by mass. The polymer particles have an average particle diameter D50 of 300 to 1500 nm, where the average particle diameter D50 is the particle diameter at a cumulative 50% in a volume-based particle size distribution measured by a laser diffraction / scattering method. The monomer constituting the polymer particle is a (meth)acrylic acid alkyl ester monomer or a mixture of a (meth)acrylic acid alkyl ester monomer and an aromatic vinyl monomer.

Description

[Technical Field]

[0001] The present invention relates to an adhesive composition, a separator, a non-aqueous secondary battery, and a method for producing the adhesive composition. [Background technology]

[0002] In the manufacturing process of non-aqueous secondary batteries (e.g., lithium-ion secondary batteries), an adhesive is sometimes applied to both sides of the separator to improve adhesion between the separator, which is a lithium-ion permeable membrane, and the electrodes. The adhesive-coated separator is then dried and rolled up for storage. The rolled-up pressure can cause the adhesive layers to be pressed together, resulting in peeling of the adhesive layers (hereinafter also referred to as "blocking"). To prevent blocking, measures such as designing a high Tg (glass transition temperature) for the adhesive layer or crosslinking can be used. However, these measures can lead to the problem of the adhesive layer detaching from the separator (hereinafter also referred to as "powdering") due to a decrease in film-forming properties.

[0003] Therefore, in order to prevent powder falling off, binders such as fluorine-based polymers such as polyvinylidene fluoride (PVdF), styrene-butadiene copolymers (SBR), butadiene-acrylonitrile copolymers (NBR), and (meth)acrylic acid ester copolymers have conventionally been added to adhesives (Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2010 / 024328 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-154108 [Patent Document 3] International Publication No. 2019 / 131347 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in Patent Documents 1 to 3, if the phase dispersion between the adhesive and the binder is insufficient, the powder shedding suppression effect cannot be obtained due to phase separation, and powder shedding may occur. When the amount of binder added increases, the lithium ion permeability decreases, which further causes blocking.

[0006] Therefore, an object of the present invention is to provide an adhesive composition that prevents a decrease in lithium ion permeability while achieving both blocking resistance and powder shedding resistance. [Means for solving the problem]

[0007] In order to achieve the object of the present invention, an adhesive composition according to one embodiment comprises the following: polymer particles and a dispersant, the polymer particles having a core-shell structure, the shell portion of the polymer particles containing an acid group-containing monomer as a structural unit, the dispersant being contained in an amount of 2 to 18 parts by mass per 100 parts by mass of the monomers constituting the polymer particles, the proportion of the core portion in a total of 100% by mass of the core portion and shell portion of the polymer particles being 30 to 80% by mass, the polymer particles having an average particle diameter D50 of 300 to 1500 nm, the average particle diameter D50 being the particle diameter at a cumulative 50% in a volume-based particle size distribution measured by a laser diffraction / scattering method, and the monomer constituting the polymer particles being a (meth)acrylic acid alkyl ester monomer or a mixture of a (meth)acrylic acid alkyl ester monomer and an aromatic vinyl monomer. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide an adhesive composition that prevents a decrease in lithium ion permeability while achieving both blocking resistance and powder shedding resistance. DETAILED DESCRIPTION OF THE INVENTION

[0009] The following describes the embodiments in detail. Note that the following embodiments do not limit the scope of the invention as claimed, and not all combinations of features described in the embodiments are necessarily essential to the invention. Two or more features among the multiple features described in the embodiments may be combined in any desired manner.

[0010] In this specification, the expression "A to B" representing a range of numerical values ​​is synonymous with "A or more" and "B or less," and includes the lower limit A and the upper limit B.

[0011] <Adhesive composition> In one embodiment, the adhesive composition comprises at least polymer particles and a dispersant. The adhesive composition may optionally further comprise a dispersion medium such as water. When the adhesive composition comprises a dispersion medium, the adhesive composition takes the form of a slurry.

[0012] In one embodiment, the adhesive composition does not contain a binder. Here, as explained at the beginning of this specification, the binder refers to a fluoropolymer such as polyvinylidene fluoride (PVdF), a styrene-butadiene copolymer (SBR), a butadiene-acrylonitrile copolymer (NBR), a (meth)acrylic acid ester copolymer, or the like. It should be noted that the (meth)acrylic acid ester copolymer is a different substance from the polymer particles (polymer particles A to C) explained in this specification. Because the adhesive composition in this specification does not contain a binder that has been conventionally used, it can achieve both blocking resistance and powder shedding resistance.

[0013] <Polymer particles> In this specification, the term "polymer particles" refers to resin particles formed by polymerizing a monomer component containing at least a (meth)acrylic acid ester as a polymerizable monomer, and has at least a structural unit derived from a (meth)acrylic acid ester.

[0014] In this specification, the term "(meth)acrylic" is intended to include both the terms "acrylic" and "methacrylic." Similarly, the term "(meth)acrylate" is intended to include both the terms "acrylate" and "methacrylate."

[0015] The (meth)acrylic resin particles (polymer particles) may be polymer (homopolymer) particles obtained by polymerizing one type of polymerizable monomer ((meth)acrylic acid ester), or may be copolymer particles obtained by copolymerizing two or more types of polymerizable monomers including a (meth)acrylic acid ester. The polymer particles are preferably copolymer particles.

[0016] In this specification, "polymer particles" refers to at least one of polymer particles A, polymer particles B, and polymer particles C. Here, polymer particles C are polymer particles containing polymer particles A and polymer particles B in an arbitrary mixing ratio. In one embodiment, when the polymer particles are polymer particles C containing polymer particles A and polymer particles B, the mixing ratio of polymer particles A to polymer particles B is 1 / 99 to 99 / 1.

[0017] (core-shell structure) The polymer particles A and B have a core-shell structure including a core portion and a shell portion. When the polymer particles A and B have a core-shell structure, both blocking resistance and powder shedding resistance can be achieved. On the other hand, when the polymer particles A and B have a non-core-shell structure (i.e., only a core portion), blocking resistance decreases.

[0018] In one embodiment, the polymer particles (polymer particles A or polymer particles B) may have a protective colloid layer of a dispersant oriented around the polymer particles. The presence of a protective colloid layer around the polymer particles can improve the dispersibility of the polymer particles in an aqueous medium. Thus, the provision of a protective colloid layer on the polymer particles exhibits a significant effect of achieving both blocking resistance and powder shedding resistance.

[0019] The core portion of polymer particle A and polymer particle B contains at least one of a (meth)acrylic acid alkyl ester monomer, a hydroxyl group-containing monomer, an acid group-containing monomer, a crosslinkable monomer, and an aromatic vinyl monomer as a constituent unit.

[0020] The shell portions of polymer particles A and polymer particles B contain at least one of a (meth)acrylic acid alkyl ester monomer, a hydroxyl group-containing monomer, an acid group-containing monomer, a crosslinkable monomer, and an aromatic vinyl monomer as a constituent unit.

[0021] In one embodiment, the shell portions of polymer particles A and polymer particles B contain an acid group-containing monomer as a structural unit. This improves the storage stability of the adhesive composition. On the other hand, if the shell portions of polymer particles A and polymer particles B do not contain an acid group-containing monomer as a structural unit, the storage stability of the adhesive composition decreases.

[0022] In one embodiment, the core portion of the polymer particle (polymer particle A or polymer particle B) contains a (meth)acrylic acid alkyl ester monomer as a constituent unit, and the shell portion of the polymer particle (polymer particle A or polymer particle B) further contains a (meth)acrylic acid alkyl ester monomer as a constituent unit.

[0023] In one embodiment, the core portion of the polymer particle (polymer particle A or polymer particle B) further contains an aromatic vinyl monomer as a constituent unit.

[0024] In one embodiment, the (meth)acrylic acid alkyl ester monomer constituting the core portion of the polymer particle (polymer particle A or polymer particle B) includes methyl methacrylate.

[0025] ((Meth)acrylic acid ester) Examples of (meth)acrylic acid esters include (meth)acrylic acid alkyl ester monomers, hydroxyl group-containing monomers, (meth)acrylic acid alkoxyalkyl esters, (meth)acrylic acid aralkyl esters, (meth)acrylic acid aryl esters, and other (meth)acrylic acid esters. One or more of these (meth)acrylic acid esters can be used. Among these, it is preferable that the monomer component constituting the (meth)acrylic resin particles (polymer particles) contains at least a (meth)acrylic acid alkyl ester monomer.

[0026] ((Meth)acrylic acid alkyl ester monomer) Examples of the (meth)acrylic acid alkyl ester monomer include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, sec-butyl (meth)acrylate, n-amyl (meth)acrylate, isoamyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, and isopropyl (meth)acrylate. Examples of suitable alkyl (meth)acrylates include alkyl (meth)acrylates having a linear or branched alkyl group, such as decyl (meth)acrylate, n-undecyl (meth)acrylate, n-dodecyl (meth)acrylate, n-tridecyl (meth)acrylate, n-tetradecyl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, and behenyl (meth)acrylate; and alicyclic alkyl (meth)acrylates, such as cyclohexyl (meth)acrylate, 4-tert-butylcyclohexyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, and dicyclopentenyl (meth)acrylate. One or more of these alkyl (meth)acrylates may be used. Among these, alkyl (meth)acrylate monomers having a linear or branched alkyl group with 1 to 18 carbon atoms (more preferably 1 to 12 carbon atoms) are preferred. In one embodiment, the (meth)acrylic acid alkyl ester monomer constituting the polymer particles A or the polymer particles B is a (meth)acrylic acid alkyl ester monomer having a linear or branched alkyl group having 1 to 18 carbon atoms (more preferably 1 to 12 carbon atoms), and preferably includes at least one of butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, and isobornyl methacrylate.The content of all (meth)acrylic acid alkyl ester monomers constituting polymer particles A or polymer particles B is 49.1 to 100.0 parts by mass, preferably 50.0 to 100.0 parts by mass, and more preferably 52.0 to 100.0 parts by mass. Note that the content of all (meth)acrylic acid alkyl ester monomers constituting polymer particles A or polymer particles B includes the content of (meth)acrylic acid alkyl ester monomers constituting the core portion and the content of (meth)acrylic acid alkyl ester monomers constituting the shell portion.

[0027] (Hydroxyl group-containing monomer) Examples of hydroxyl group-containing monomers include (meth)acrylic acid hydroxyalkyl esters such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate. One or more of these may be used. Among these, 2-hydroxyethyl (meth)acrylate is preferred. In one embodiment, the hydroxyl group-containing monomer constituting polymer particles A or polymer particles B is a (meth)acrylic acid hydroxyalkyl ester, preferably 2-hydroxyethyl methacrylate. The content of all hydroxyl group-containing monomers constituting polymer particles A or polymer particles B is 0.0 to 1.5 parts by mass, preferably 0.0 to 1.4 parts by mass, and more preferably 0.0 to 1.3 parts by mass. Note that the content of all hydroxyl group-containing monomers constituting polymer particles A or polymer particles B includes the content of hydroxyl group-containing monomers constituting the core portion and the content of hydroxyl group-containing monomers constituting the shell portion.

[0028] ((Meth)acrylic acid alkoxyalkyl ester) Examples of (meth)acrylic acid alkoxyalkyl esters include 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-butoxyethyl (meth)acrylate, ethoxyethoxyethyl (meth)acrylate, and 2-phenoxyethyl (meth)acrylate, and one or more of these can be used.

[0029] ((Meth)acrylic acid aralkyl ester) Examples of (meth)acrylic acid aralkyl esters include benzyl (meth)acrylate, 2-phenylethyl (meth)acrylate, methylbenzyl (meth)acrylate, and naphthylmethyl (meth)acrylate, and one or more of these can be used.

[0030] (Other (meth)acrylic acid esters) Other (meth)acrylic acid esters include, for example, polyalkylene glycol (meth)acrylates such as polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, and methoxypolyethylene glycol mono(meth)acrylate; (meth)acrylic acid alkyl esters having a halogen atom such as 2-chloroethyl (meth)acrylate, trifluoroethyl (meth)acrylate, 2-(perfluorobutyl)ethyl (meth)acrylate, and perfluorooctylethyl (meth)acrylate; (meth)acrylic acid esters having an amino group such as 2-(dimethylamino)ethyl (meth)acrylate, 2-(diethylamino)ethyl (meth)acrylate, and 3-(dimethylamino)propyl (meth)acrylate; (meth)acrylic acid esters having a carboxy group such as carboxyethyl (meth)acrylate and carboxypentyl (meth)acrylate; Examples of suitable acrylates include (meth)acrylic acid esters and derivatives thereof having an epoxy group, such as glycidyl (meth)acrylate, glycerin mono(meth)acrylate, 2-methylglycidyl (meth)acrylate, and 3,4-epoxycyclohexylmethyl (meth)acrylate; (meth)acrylates having a sulfonic acid group, such as 2-sulfoethyl (meth)acrylate and 3-sulfopropyl (meth)acrylate; (meth)acrylates having a phosphoric acid group, such as 2-(phosphonooxy)ethyl (meth)acrylate; (meth)acrylates having an isocyanate group, such as 2-isocyanatoethyl (meth)acrylate; (meth)acrylates having a heterocyclic ring, such as tetrahydrofurfuryl (meth)acrylate; and alkyl- or allyl-terminated polyalkylene glycol mono(meth)acrylates, such as methoxypolyethylene glycol (meth)acrylate and phenoxypolyethylene glycol (meth)acrylate. These may be used alone or in combination.

[0031] The (meth)acrylic resin particles (polymer particles) may be resin particles obtained by polymerizing a monomer component containing the above-mentioned (meth)acrylic acid ester and another polymerizable monomer copolymerizable with the (meth)acrylic acid ester. In this case, the (meth)acrylic resin particles may have a structural unit derived from the (meth)acrylic acid ester and a structural unit derived from the other polymerizable monomer copolymerizable with the (meth)acrylic acid ester.

[0032] (Other polymerizable monomers) The other polymerizable monomer is preferably an acid group-containing monomer, and the (meth)acrylic resin particles (polymer particles) preferably contain structural units derived from the acid group-containing monomer. In this specification, the acid group-containing monomer includes unsaturated carboxylic acids, as well as their anhydrides and monoesters. In one embodiment, the acid group-containing monomer is an unsaturated carboxylic acid.

[0033] (Acid group-containing monomer) Examples of the acid group-containing monomer include unsaturated carboxylic acids such as (meth)acrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, and citraconic acid; anhydrides of unsaturated carboxylic acids such as maleic anhydride and itaconic anhydride; and monoesters of unsaturated carboxylic acids such as monomethyl maleate, monobutyl maleate, monomethyl itaconic acid, and monobutyl itaconic acid. It is more preferable to use one or more of these acid group-containing monomers. Among these, (meth)acrylic acid is even more preferable. In one embodiment, the acid group-containing monomer constituting polymer particles A or polymer particles B is an unsaturated carboxylic acid, preferably (meth)acrylic acid. The content of all acid group-containing monomers constituting polymer particles A or polymer particles B is 0.1 to 2.5 parts by mass, preferably 0.15 to 2.4 parts by mass, and more preferably 0.2 to 2.3 parts by mass. It should be noted that the content of all acid group-containing monomers constituting polymer particles A or polymer particles B includes the content of acid group-containing monomers constituting the core portion and the content of acid group-containing monomers constituting the shell portion.

[0034] (Polymerizable monomers other than acid group-containing monomers) Examples of polymerizable monomers other than the acid group-containing monomer include unsaturated monomers having a nitrogen atom, aromatic vinyl monomers, etc. Among these, aromatic vinyl monomers are preferred, and the (meth)acrylic resin particles preferably contain structural units derived from aromatic vinyl monomers.

[0035] (Unsaturated monomers containing nitrogen atoms) Examples of unsaturated monomers having a nitrogen atom include unsaturated monomers having a cyano group such as acrylonitrile and methacrylonitrile; (meth)acrylamide, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-methylol(meth)acrylamide, N-butoxymethyl(meth)acrylamide, N-[2-dimethylaminoethyl](meth)acrylamide, N-[3 Examples of suitable monomers include acrylamide monomers such as N-dimethylaminopropyl (meth)acrylamide, diacetone acrylamide, 4-acryloylmorpholine, and 4-methacryloylmorpholine; acetamide monomers having a vinyl group such as N-vinylacetamide and N-vinyl-N-methylacetamide; and nitrogen-containing heterocyclic compounds having a vinyl group such as N-vinyl-2-pyrrolidone, 4-vinylpyridine, 1-vinylimidazole, 2-vinyl-2-oxazoline, and 2-isopropenyl-2-oxazoline. These may be used alone or in combination.

[0036] (aromatic vinyl monomer) Examples of aromatic vinyl monomers include styrene-based monomers such as styrene, α-methylstyrene, o-, m-, and p-methylstyrene, o-, m-, and p-ethylstyrene, 4-tert-butylstyrene, o-, m-, and p-hydroxystyrene, o-, m-, and p-methoxystyrene, o-, m-, and p-ethoxystyrene, o-, m-, and p-chlorostyrene, o-, m-, and p-bromostyrene, o-, m-, and p-fluorostyrene, and o-, m-, and p-chloromethylstyrene. One or more of these may be used. Among these, styrene is preferred. In one embodiment, the aromatic vinyl monomer constituting polymer particles A or polymer particles B is a styrene-based monomer, preferably styrene. The content of all aromatic vinyl monomers constituting polymer particles A or polymer particles B is 0.0 to 51.0 parts by mass, preferably 0.0 to 50.0 parts by mass, and more preferably 0.0 to 49.0 parts by mass. It should be noted that the content of all aromatic vinyl monomers constituting polymer particles A or polymer particles B includes the content of aromatic vinyl monomers constituting the core portion and the content of aromatic vinyl monomers constituting the shell portion.

[0037] As the other polymerizable monomer, in addition to the above-mentioned acid group-containing monomer, unsaturated monomer having a nitrogen atom, and aromatic vinyl monomer, it is also possible to use, for example, vinyl-based monomers, unsaturated alcohols, vinyl ether-based monomers, vinyl ester-based monomers, unsaturated monomers having an epoxy group, and unsaturated monomers having a sulfonic acid group.

[0038] Examples of vinyl monomers include vinyl chloride and vinyl fluoride.

[0039] Examples of unsaturated alcohols include vinyl alcohol and allyl alcohol.

[0040] Examples of vinyl ether monomers include methyl vinyl ether, ethyl vinyl ether, isobutyl vinyl ether, phenyl vinyl ether, 2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether, and diethylene glycol monovinyl ether.

[0041] Examples of vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl caprylate, vinyl laurate, vinyl stearate, and vinyl versatate.

[0042] Examples of the unsaturated monomer having an epoxy group include allyl glycidyl ether.

[0043] Examples of unsaturated monomers having a sulfonic acid group include vinyl sulfonic acid, styrene sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, and 2-(meth)acrylamide-2-methylpropane sulfonic acid, and one or more of these can be used.

[0044] (Crosslinking monomer) Furthermore, a crosslinkable monomer that can function as a crosslinking agent can also be used as the monomer component constituting the polymer particles. A monomer having two or more polymerizable unsaturated bonds can be used as the crosslinkable monomer. Examples of the crosslinkable monomer include 2-hydroxy-3-acryloyloxypropyl(meth)acrylate, ethylene glycol di(meth)acrylate, 1,3-butanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, and the like. Examples of the acrylate include difunctional (meth)acrylates such as tri(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, and glycerin di(meth)acrylate; polyfunctional (meth)acrylates such as pentaerythritol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetraacrylate, and dipentaerythritol hexaacrylate; allyl (meth)acrylate; divinylbenzene; and diallyl phthalate. One or more of these can be used.

[0045] Examples of the crosslinkable monomer include silane coupling agents such as 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, and 3-acryloxypropyltrimethoxysilane. One or more of these may be used. In one embodiment, the crosslinkable monomer constituting the polymer particles A or B is a bifunctional (meth)acrylate, preferably ethylene glycol dimethacrylate. The content of all crosslinkable monomers constituting the polymer particles A or B is 0.0 to 2.0 parts by mass, preferably 0.0 to 1.5 parts by mass, and more preferably 0.0 to 1.2 parts by mass. It should be noted that the content of all crosslinkable monomers constituting the polymer particles A or B includes the content of crosslinkable monomers constituting the core portion and the content of crosslinkable monomers constituting the shell portion.

[0046] (Core ratio) The ratio of the core portion of the polymer particles (polymer particles A or polymer particles B) to the total of the core portion and shell portion (100% by mass) is 30 to 80% by mass. When the ratio of the core portion is within the above range, a decrease in adhesiveness can be prevented. On the other hand, when the ratio of the core portion is outside the above range, adhesiveness decreases.

[0047] (Physical Properties) The physical properties of the polymer particles (polymer particles A or polymer particles B) will be described below.

[0048] (Average particle size D50) The average particle diameter D50 of the polymer particles (polymer particles A or polymer particles B) is preferably 300 to 1500 nm, more preferably 330 to 1480 nm. Here, the average particle diameter D50 is the particle diameter at a cumulative 50% in the volume-based particle size distribution measured by a laser diffraction / scattering method. When the average particle diameter D50 is within the above range, a decrease in adhesiveness and lithium ion permeability can be prevented. On the other hand, when the average particle diameter D50 is less than 300 nm, lithium ion permeability decreases. Furthermore, when the average particle diameter D50 exceeds 1500 nm, adhesiveness decreases.

[0049] (glass transition temperature) The polymer particles contain at least one of polymer particles A and polymer particles B. The polymer particles may be polymer particles C containing polymer particles A and polymer particles B in any ratio. Here, the glass transition temperature of the core portion of polymer particle A is 30 to 90°C. The glass transition temperature of the shell portion of polymer particle A is 30 to 130°C. The glass transition temperature of the core portion of polymer particle B is 30 to 90°C. The glass transition temperature of the shell portion of polymer particle B is -70 to 20°C. The above-mentioned various glass transition temperatures are glass transition temperatures determined by differential scanning calorimetry (DSC). Detailed conditions for differential scanning calorimetry (DSC) are shown below.

[0050] An appropriate amount of the aqueous dispersion containing polymer particles was placed on a release paper and allowed to stand at room temperature for 24 hours to obtain a dried aqueous dispersion. 10 mg of this dried sample was used as a measurement sample and measured using a differential scanning calorimeter (Rigaku Corporation, "DSC8231") in a nitrogen atmosphere at a temperature range of -100 to 200°C and a heating rate of 20°C / min to obtain a DSC curve and a DDSC curve. The glass transition temperature of the obtained DSC curve was determined using the method described in JIS-K7121. Specifically, the glass transition temperature (Tg) was determined as the intersection of a line equidistant in the vertical direction from a line extending the low-temperature and high-temperature baselines with the curve representing the stepwise change in the glass transition.

[0051] <Dispersant> The dispersant is a substance intended to prevent reagglomeration and sedimentation of polymer particles (polymer particles A or polymer particles B) in an aqueous medium. The dispersant can function as a protective colloid layer oriented around the polymer particles (polymer particles A or polymer particles B). This can impart blocking resistance and powder shedding resistance to the adhesive layer. In one embodiment, the dispersant is a water-soluble polymer. Water-soluble polymers include natural polymers, semi-synthetic polymers, and synthetic polymers, and one or more of these can be used. In one embodiment, the dispersant includes at least one of a semi-synthetic polymer and a synthetic polymer. The dispersant preferably includes at least one of a cellulose-based semi-synthetic polymer and an acrylic acid-based water-soluble polymer.

[0052] Examples of natural polymers include starch (corn starch, etc.), sugars (mannan, pectin, etc.), seaweed (agar, alginic acid, etc.), plant mucilages (various gums), microbial mucilages (dextran, pullulan, etc.), and proteins (glue, gelatin, etc.). One or more of these may be used.

[0053] Semi-synthetic polymers include, for example, cellulose-based polymers (carboxymethylcellulose or its salts (such as sodium carboxymethylcellulose), hydroxyethylcellulose, etc.) and starch-based polymers (oxidized starch, modified starch, etc.). Of these, cellulose-based polymers are preferred, and sodium carboxymethylcellulose is more preferred, but the present invention is not limited to these. One or more of these may be used.

[0054] The synthetic polymer is preferably an acrylic acid-based water-soluble polymer. In one embodiment, the dispersant is an acrylic acid-based water-soluble polymer. Examples of the acrylic acid-based water-soluble polymer include sodium polyacrylate, polyacrylamide, polyvinyl alcohol, polyethyleneimine, polyethylene oxide, and polyvinylpyrrolidone. One or more of these may be used. Among these, polyvinyl alcohol and polyvinylpyrrolidone are preferred, but the dispersant is not particularly limited as long as it can exhibit the function of a protective colloid layer.

[0055] (Polyvinyl alcohol) In one embodiment, the dispersant is polyvinyl alcohol. Polyvinyl alcohol (hereinafter also referred to as PVA) is a water-soluble polymer with good film-forming properties. A film formed from polyvinyl alcohol can impart excellent adhesion and solvent resistance, as well as blocking resistance and resistance to powder shedding (the property of suppressing powder shedding from the separator), to the adhesive layer of the present invention. Polyvinyl alcohol has two types of functional groups, hydrophilic and hydrophobic groups. Therefore, polyvinyl alcohol has surface-active properties and can function as a protective colloid in the emulsification and suspension polymerization reaction of monomers.

[0056] (Saponification degree) The saponification degree of polyvinyl alcohol can be adjusted by the degree to which acetate groups in the structure are converted to hydroxyl groups in the process of saponifying the polyvinyl acetate resin. The saponification degree of polyvinyl alcohol is measured in accordance with JIS K 6726-1994. Generally, the saponification degree of polyvinyl alcohol is 60 to 100 mol %. In one embodiment, fully saponified, intermediately saponified, or partially saponified polyvinyl alcohol can be used as the emulsion protective layer for polymer particles (polymer particles A or polymer particles B). In one embodiment, the saponification degree of polyvinyl alcohol is preferably 70 to 99 mol %, and more preferably 80 to 90 mol %. By using polyvinyl alcohol with a saponification degree of 70 to 99 mol %, the protective colloidal effect of polyvinyl alcohol can be fully achieved, thereby improving the dispersion stability of the polymer particles. On the other hand, when polyvinyl alcohol with a saponification degree of less than 70 mol % is used, the protective colloidal properties are reduced, resulting in reduced powder shedding resistance.

[0057] (Blend amount) In one embodiment, the adhesive composition preferably contains 2 to 18 parts by mass, more preferably 5 to 10 parts by mass, of a dispersant relative to 100 parts by mass of all monomers (composing polymer particles A or B) used in emulsion polymerization, from the viewpoint of achieving both blocking resistance and dusting resistance while preventing a decrease in lithium ion permeability. Here, all monomers constituting polymer particles A or B are (meth)acrylic acid alkyl ester monomers or a mixture of (meth)acrylic acid alkyl ester monomers and aromatic vinyl monomers. More specifically, "100 parts by mass of all monomers" refers to 100 parts by mass of (meth)acrylic acid alkyl ester monomers or 100 parts by mass of a mixture of (meth)acrylic acid alkyl ester monomers and aromatic vinyl monomers. Furthermore, if the amount of dispersant is less than 2 parts by mass, the adhesive layer will have insufficient dusting resistance. Furthermore, if the blending amount of the dispersant exceeds 18 parts by mass, the average particle size D50 of the polymer particles (polymer particles A or polymer particles B) becomes small, resulting in a decrease in lithium ion permeability.

[0058] (Degree of polymerization) In one embodiment, the degree of polymerization of the polyvinyl alcohol that functions as the emulsified protective layer for the polymer particles (polymer particles A or polymer particles B) is preferably 300 to 4500, more preferably 500 to 2500. When the degree of polymerization of the polyvinyl alcohol is 500 or more, both resistance to powder shedding and blocking resistance can be achieved. On the other hand, when the degree of polymerization of the polyvinyl alcohol exceeds 4500, the adhesiveness decreases. Thus, when the degree of polymerization of the polyvinyl alcohol is in the above numerical range (300 to 4500), the viscosity of the emulsion does not become excessively high, and can be controlled to a practical viscosity.

[0059] The polyvinyl alcohol may be unmodified polyvinyl alcohol in which no functional groups other than hydroxyl groups and acetate groups have been introduced, or may be modified polyvinyl alcohol in which functional groups other than hydroxyl groups and acetate groups have been introduced. The adhesive composition of the present embodiment contains at least one of unmodified polyvinyl alcohol and modified polyvinyl alcohol.

[0060] Examples of modified polyvinyl alcohols include ethylene-modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, and carboxylic acid-modified polyvinyl alcohol. Ethylene-modified polyvinyl alcohol is a fully or partially saponified copolymer containing ethylene-derived structural units and vinyl acetate-derived structural units. Acetoacetyl-modified polyvinyl alcohol is a compound obtained by reacting diketene with the hydroxy group of a fully or partially saponified polymer containing vinyl acetate-derived structural units to introduce an acetoacetyl group. Sulfonic acid-modified polyvinyl alcohol is a fully or partially saponified copolymer containing vinyl acetate-derived structural units and ethylenically unsaturated sulfonic acid-derived structural units such as vinyl sulfonic acid and acrylamidomethylpropanesulfonic acid. Carboxylic acid-modified polyvinyl alcohol is a fully or partially saponified copolymer containing vinyl acetate-derived structural units and ethylenically unsaturated carboxylic acid-derived structural units such as (meth)acrylic acid and itaconic acid.

[0061] In one embodiment, the adhesive composition preferably contains a dispersant (e.g., polyvinyl alcohol) in the pre-emulsion form of the core and shell portions of the polymer particles (polymer particles A or polymer particles B). However, polyvinyl alcohol may be used in the pre-emulsion emulsification of either the core or shell portion. By using polyvinyl alcohol in the pre-emulsification of either the core or shell portion, the polyvinyl alcohol is oriented in the emulsion protective layer of the polymer particles (polymer particles A or polymer particles B), forming a protective colloid layer through emulsification and contributing to the dispersion of the polymer particles (polymer particles A or polymer particles B). The greatest feature of the present invention is that polymer particles (polymer particles A or polymer particles B) are emulsified and dispersed in polyvinyl alcohol to form polymer particles covered with a particle protective layer. This makes it possible to form polymer particles (polymer particles A or polymer particles B) that are resistant to blocking and powder shedding without adding a binder after emulsion polymerization is complete. The polyvinyl alcohol may function as a protective colloid layer for the polymer particles (polymer particles A or polymer particles B), or may be dissolved in the aqueous medium.

[0062] <Surfactant> Examples of surfactants that can be used include anionic surfactants such as sodium dodecylbenzenesulfonate and sodium dodecyl sulfate, nonionic surfactants such as polyoxyethylene nonylphenyl ether and sorbitan monolaurate, and cationic surfactants such as octadecylamine acetate. In one embodiment, the surfactant is an anionic surfactant, preferably sodium dodecylbenzenesulfonate. In one embodiment, the content of the surfactant is 0.0 to 2.0 parts by mass, preferably 0.0 to 1.5 parts by mass, and more preferably 0.0 to 1.0 parts by mass, relative to 100 parts by mass of the total of the (meth)acrylic acid alkyl ester and aromatic vinyl monomer constituting the polymer particles A or polymer particles B.

[0063] <Polymerization initiator> The polymerization initiator is not particularly limited, and any known polymerization initiator can be used. For example, polymerization initiators generally used in radical polymerization, such as those listed below, can be used appropriately.

[0064] Examples of the polymerization initiator include persulfates such as potassium persulfate, sodium persulfate, and ammonium persulfate; oils such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), and 2-phenylazo-4-methoxy-2,4-dimethylvaleronitrile; Soluble azo compounds; 2,2'-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamide}, 2,2'-azobis{2-methyl-N-[2-(1-hydroxyethyl)]propionamide}, 2,2'-azobis{2-methyl-N-[2-(1-hydroxybutyl)]propionamide}, 2,2'-azobis[2-(5-methyl-2-imidazolin-2-yl) propane] and its salts, 2,2'-azobis[2-(2-imidazolin-2-yl)propane] and its salts, 2,2'-azobis[2-(3,4,5,6-tetrahydropyrimidin-2-yl)propane] and its salts, 2,2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane} and its salts, 2,2'-azobis(2-methylpropionamidine) and its salts, Examples of the water-soluble azo compounds include 2,2'-azobis(2-methylpropynamidine) and its salts, 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine] and its salts, and organic peroxides such as benzoyl peroxide, cumene hydroperoxide, t-butyl hydroperoxide, t-butylperoxy-2-ethylhexanoate, and t-butylperoxyisobutyrate. These may be used alone or in combination of two or more.

[0065] <Other additives> Other additives that may be contained in the adhesive composition are not particularly limited, and examples thereof include known additives. Examples of known additives include non-conductive particles, surface tension modifiers, viscosity modifiers, reinforcing materials, electrolyte additives, etc. Note that these components may be used alone or in combination of two or more types in any ratio.

[0066] <Method of manufacturing adhesive composition> In one embodiment, a method for producing an adhesive composition containing polymer particles having a core-shell structure includes the steps of: polymerizing a pre-emulsion containing a (meth)acrylic acid alkyl ester monomer to form a core portion; and polymerizing a pre-emulsion containing the (meth)acrylic acid alkyl ester monomer and an acid group-containing monomer to form a shell portion on the outer surface of the core portion. The core portion-forming step and / or the shell portion-forming step are carried out in the presence of a dispersant. The adhesive composition contains 2 to 18 parts by mass of a dispersant per 100 parts by mass of the monomers constituting the polymer particles. By using a dispersant amount within the above range, both blocking resistance and powder shedding resistance can be achieved while preventing a decrease in lithium ion permeability. On the other hand, if the dispersant amount is less than 2 parts by mass, the powder shedding resistance of the adhesive layer decreases. Furthermore, if the dispersant amount exceeds 18 parts by mass, the average particle diameter D50 of the polymer particles (polymer particles A or polymer particles B) decreases, resulting in a decrease in lithium ion permeability. In one embodiment, the dispersing agent is at least one of a cellulose-based semi-synthetic polymer and an acrylic acid-based water-soluble polymer, such as at least one of polyvinyl alcohol, carboxymethyl cellulose or a salt thereof (sodium carboxymethyl cellulose), and polyvinylpyrrolidone.

[0067] The polymer particles (polymer particles A or polymer particles B) are prepared by stepwise polymerization of a core monomer and a shell monomer, varying the ratio of these monomers over time. Specifically, the polymer particles (polymer particles A or polymer particles B) are prepared by a continuous multi-stage emulsion polymerization method or multi-stage suspension polymerization method in which a polymer (core) obtained in an earlier step (a step for forming the core) is sequentially coated with a polymer (shell) in a later step (a step for forming the shell). The dispersant may be present in at least one of the earlier and later steps. As described above, the dispersant functions as a protective colloid layer for the core-shell structured polymer particles (polymer particles A or polymer particles B) and can improve the dispersion stability of the polymer particles.

[0068] <Applications of adhesive composition> In one embodiment, the adhesive composition is an adhesive composition for bonding between battery components of a non-aqueous secondary battery, where the battery components refer to, for example, between a separator and a negative electrode or between a separator and a positive electrode.

[0069] <Separator for non-aqueous secondary batteries> In one embodiment, a separator for a non-aqueous secondary battery includes a substrate and an adhesive layer formed on at least one surface of the substrate and made of the adhesive composition described above. The separator may further include components other than the adhesive layer on the substrate. The separator is a battery component that separates the positive electrode and the negative electrode in a non-aqueous secondary battery to prevent short circuits between the positive electrode and the negative electrode.

[0070] (base material) Examples of the substrate include a substrate containing an organic material. The substrate containing an organic material is a porous member made of an organic material. Examples of the substrate containing an organic material include a microporous film or nonwoven fabric containing a polyolefin resin such as polyethylene or polypropylene, or an aromatic polyamide resin. From the viewpoint of excellent strength, the substrate is preferably a microporous film or nonwoven fabric made of polyethylene. The thickness of the substrate is not particularly limited, but is preferably 5 to 30 μm, more preferably 5 to 20 μm, and even more preferably 5 to 18 μm. The substrate may further include an inorganic filler layer.

[0071] Inorganic fillers are electrochemically stable materials in the environment in which nonaqueous secondary batteries are used. Examples of inorganic fillers include oxide particles such as aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, BaTiO3, ZrO, and alumina-silica composite oxide; nitride particles such as aluminum nitride and boron nitride; covalently bonded crystalline particles such as silicon and diamond; sparingly soluble ionic crystalline particles such as barium sulfate, calcium fluoride, and barium fluoride; and clay particles such as talc and montmorillonite. These particles may be subjected to element substitution, surface treatment, solid solution formation, etc. as needed, and may be used alone or in combination of two or more types. Among these, oxide particles are preferred from the viewpoints of stability in the electrolyte and potential stability.

[0072] (Application method) The following methods (1) to (3) can be mentioned as methods for forming an adhesive layer on the above-mentioned substrate. (1) A method in which an adhesive composition is applied to the surface of a substrate and then dried; (2) a method of immersing a substrate in an adhesive composition and then drying the same; and (3) A method in which an adhesive composition is applied to a release substrate, dried to produce an adhesive layer, and the resulting adhesive layer is transferred to the surface of the substrate. Among these, method (1) is preferred because it is easy to control the thickness of the adhesive layer.

[0073] More specifically, method (1) includes a step of applying an adhesive composition onto a substrate (application step), and a step of forming an adhesive layer by drying the adhesive composition applied onto the substrate (adhesive layer formation step). Note that the adhesive layer may be formed on only one side of the substrate or on both sides of the substrate, depending on the structure of the nonaqueous secondary battery to be manufactured.

[0074] (Coating process) In the coating step, examples of the method for coating the adhesive composition onto the substrate include the doctor blade method, reverse roll method, direct roll method, gravure method, extrusion method, and brush coating method.

[0075] (Adhesive layer formation process) In the adhesive layer forming step, methods for drying the adhesive composition on the substrate include, for example, drying with warm air, hot air, or low-humidity air, vacuum drying, and drying by irradiation with infrared rays or electron beams, etc. The drying conditions are not particularly limited, but the drying temperature is preferably 30 to 150°C.

[0076] <Non-aqueous secondary battery> In one embodiment, the nonaqueous secondary battery includes a separator having an adhesive layer made of an adhesive composition provided on at least one surface thereof.

[0077] An example of a non-aqueous secondary battery is a lithium ion secondary battery. A lithium ion secondary battery is a battery that has characteristics such as being small, lightweight, and having a high energy density, and is capable of repeated charging and discharging. With such excellent characteristics, a lithium ion battery is used in a wide range of applications. A non-aqueous secondary battery can include the above-mentioned separator, battery components (positive electrode, negative electrode), and electrolyte.

[0078] <Method of manufacturing adhesive composition> The definitions of the abbreviations in Tables 1 to 6 are as follows: ST: styrene BA: n-butyl acrylate 2EHA: 2-ethylhexyl acrylate MMA: Methyl methacrylate 2HEMA: 2-hydroxyethyl methacrylate MAAC: methacrylic acid EDMA: Ethylene glycol dimethacrylate IB-X: Isobornyl methacrylate Powder shedding resistance: See test 1 below Blocking resistance: See test 2 below Adhesion: See test 3 below Lithium ion permeability: See test 4 below

[0079] (Brief explanation of the table) Table 1 shows the raw material formulations of the adhesive compositions of Examples 1 to 13 and the test results. Table 2 shows the raw material formulations of the adhesive compositions of Comparative Examples 1 to 6 and the test results. Table 3 shows the raw material formulations of the adhesive compositions of Examples 14 to 26 and the test results. Table 4 shows the raw material formulations of the adhesive compositions of Comparative Examples 7 to 12 and the test results. Table 5 shows the raw material formulations of the adhesive compositions of Examples 27 to 38 and the test results. Table 6 shows the raw material formulations of the adhesive compositions of Comparative Examples 13 to 18 and the test results.

[0080] [Table 1]

[0081] [Table 2]

[0082] [Table 3]

[0083] [Table 4]

[0084] [Table 5]

[0085] [Table 6]

[0086] <Example 1: Method for producing polymer particles A> First, the method for producing the core portion of polymer particle A will be described with reference to the raw material composition in Table 1. An emulsification vessel was charged with 65.0 parts of ion-exchanged water, 33.6 parts of styrene (ST), 14.7 parts of 2-ethylhexyl acrylate (2-EHA), 21.7 parts of methyl methacrylate (MMA), 0.7 parts of 2-hydroxyethyl methacrylate (2-HEMA) as a hydroxyl group-containing monomer, 14.0 parts of a 10% aqueous polyvinyl alcohol solution (trade name: J-POVAL JP-05, manufactured by Nippon Acetic Acid & Poval Co., Ltd.) as a dispersant, 0.14 parts of sodium dodecylbenzenesulfonate as a surfactant, and 1.7 parts of a 5% aqueous potassium persulfate solution as a polymerization initiator, and the mixture was stirred to obtain a monomer emulsion for the core portion containing the dispersant (polyvinyl alcohol).

[0087] Next, 112.9 parts of ion-exchanged water was charged into a reactor equipped with a stirrer, reflux condenser, thermometer, dropping device, and nitrogen gas inlet tube, and the internal temperature was raised to 80°C while stirring. 4.4 parts of a 5% aqueous potassium persulfate solution was added, and the core monomer emulsion was added dropwise at the same temperature while carrying out a polymerization reaction for 2 hours. 30 minutes after the end of the dropwise addition of the core monomer emulsion, an emulsified mixture for the shell part was prepared.

[0088] The method for producing the shell portion of polymer particle A will be described with reference to the raw material composition in Table 1. 29.5 parts of ion-exchanged water, 30.0 parts of MMA and 0.3 parts of 2-HEMA as raw monomer materials, 1.5 parts of methacrylic acid (MAAC) as an acid group-containing monomer, 6.0 parts of a 10% aqueous solution of polyvinyl alcohol (trade name: J-POVAL JP-05, manufactured by Nippon Acetic Acid & Poval Co., Ltd.) as a dispersant, 0.06 parts of sodium dodecylbenzenesulfonate as a surfactant, and 0.7 parts of a 5% aqueous solution of potassium persulfate as a polymerization initiator were placed in an emulsification vessel and stirred to obtain a monomer emulsion for the shell portion containing the dispersant (polyvinyl alcohol).

[0089] Sixty minutes after the core portion was added dropwise, the shell portion monomer emulsion was added dropwise while the polymerization reaction continued for one hour. After the shell portion monomer emulsion was added dropwise, the internal temperature was maintained at 80°C and the post-reaction was continued for another two hours, after which the internal temperature was cooled to room temperature. To ensure emulsion particle stability, 0.8 parts of 25% aqueous ammonia was added to adjust the emulsion pH to 8-9 or higher, yielding polymer particles A1 containing the dispersant (polyvinyl alcohol) specified in the present invention. The various properties of the resulting polymer particles A1 were pH 8.5, viscosity 35 mPa·s / 25°C, and solids content 30.0%.

[0090] <Examples 2 to 26 and Comparative Examples 1 to 12: Methods for producing polymer particles A and polymer particles B> Polymer particles A or polymer particles B were produced by the same production method as in Example 1, except that the monomers constituting the monomer emulsion mixture used in Example 1 were changed to the monomers shown in Examples 2 to 26 and Comparative Examples 1 to 12 in Tables 1 to 4, respectively. As a result, polymer particles A2 to 19 containing dispersants and polymer particles B1 to 19 were produced. 19 obtained.

[0091] <Examples 27 to 38 and Comparative Examples 13 to 18: Method for producing polymer particles C> Polymer particles A and polymer particles B produced in any of Examples 1 to 26 (or Comparative Examples 1 to 12) were blended in the blending amounts shown in Tables 5 and 6 by emulsion weight to obtain polymer particles C1 to 18 containing a dispersant.

[0092] <Test Method> The adhesive compositions (hereinafter also referred to as adhesives) of Examples 1 to 38 and Comparative Examples 1 to 18 were used to carry out the following Tests 1 to 4.

[0093] (Test 1: Evaluation of powder shedding resistance) A bar coater was used to apply adhesive at a rate of 1.0 g / m onto a single-layer polyethylene separator (SC12-S3, manufactured by GELLEC). 2 The adhesive was applied so that the surface was dry, and then dried at 40°C. After drying, the adhesive was rubbed with a finger for a distance of 20 cm or more while applying a load of 200±50 g, and the amount of adhesive that came off from the separator was used to evaluate the resistance to powder shedding according to the following criteria. A (Good): Less than 25% adhesive detachment observed visually B (normal): Adhesive detachment is visually observed at 25-50% C (poor): Adhesive detachment is visually observed at 51% or more.

[0094] (Test 2: Evaluation of blocking resistance) The adhesive was applied at a rate of 1.0 g / m using a bar coater onto a separator (SC18-D6, manufactured by GELLEC) with an inorganic filler layer. 2 The adhesive was applied to the adhesive-coated surfaces so that they were dry, and then dried at 40°C. The adhesive-coated surfaces were placed together and thermocompressed at 60°C and 6 MPa for 30 seconds. The thermocompressed samples were then cut into 25 mm widths and the 180° peel strength was measured using a peel tester at a speed of 300 mm / min. Blocking resistance was evaluated according to the following criteria. A (Good): Peel strength is less than 5.0 N / m B (normal): Peel strength is 5.0 to 10.0 N / m C (poor): Peel strength is 10.1N or more

[0095] (Test 3: Evaluation of Adhesion) The adhesive was applied at a rate of 1.0 g / m using a bar coater onto a separator (SC18-D6, manufactured by GELLEC) with an inorganic filler layer. 2The adhesive was applied to the adhesive-coated surface and dried at 40°C. The adhesive-coated surface was then mated with the surface of a negative electrode sheet prepared in-house, and thermocompression bonded at 60°C and 6 MPa for 30 seconds. The thermocompression-bonded sample was cut into 25 mm wide pieces, and the 180° peel strength was measured at a speed of 300 mm / min using a peel tester. Adhesion was evaluated according to the following criteria. A (Good): Peel strength is 10.1 N / m or more B (normal): Peel strength is 5.0 to 10.0 N / m C (poor): Peel strength less than 5.0N

[0096] (Test 4: Evaluation of lithium ion permeability) The adhesive was applied at a rate of 1.0 g / m using a bar coater onto a separator (SC18-D6, manufactured by GELLEC) with an inorganic filler layer. 2 The coating was applied so that the coating became dry, and then dried at 40°C. The air permeability increase rate was calculated from the Gurley value (seconds / 100 ml) measured using a Gurley tester, and the lithium ion permeability was evaluated according to the following evaluation criteria. A (Good): Air permeability increase rate is less than 25% B (normal): Air permeability increase rate is 25-50% C (bad): Air permeability increase rate 51% or more

[0097] <Test Results> With reference to Tables 1 to 6, the test results of Examples 1 to 38 and Comparative Examples 1 to 18 will be explained.

[0098] As shown by the results of Tests 1 to 4, Examples 1 to 38 were excellent in all of powder-fall resistance, blocking resistance, adhesion, and lithium ion permeability in a balanced manner. On the other hand, Comparative Examples 1 to 18 were not excellent in all of powder-fall resistance, blocking resistance, adhesion, and lithium ion permeability in a balanced manner. The reason why at least one of the performances of Comparative Examples 1 to 18 was deteriorated will be explained below. Hereinafter, polyvinyl alcohol will be referred to as PVA.

[0099] In Comparative Example 1, the content of the dispersant was less than the lower limit specified in this specification, and therefore the resistance to powder falling off was reduced.

[0100] In Comparative Example 2, the content of the dispersant exceeded the upper limit specified in this specification, and the average particle diameter D50 was less than the lower limit specified in this specification, so that the lithium ion permeability decreased.

[0101] In Comparative Example 3, the average particle diameter D50 of the polymer particles A exceeded the upper limit specified in this specification, and therefore the adhesiveness was reduced.

[0102] In Comparative Example 4, the degree of saponification of the PVA, which is an example of a dispersant, was less than the lower limit specified in this specification, and therefore the protective colloid properties were reduced, resulting in reduced resistance to powder falling.

[0103] In Comparative Example 5, the shell portion of the polymer particles A did not contain an acid group-containing monomer, and therefore the storage stability was deteriorated, and Tests 1 to 4 could not be carried out.

[0104] In Comparative Example 6, the polymer particles A did not have a core-shell structure, and therefore the blocking resistance was reduced. Note that the polymer particles A of Comparative Example 6 did not have a shell portion, but only a core portion.

[0105] In Comparative Example 7, the content of the dispersant was less than the lower limit specified in this specification, and therefore the blocking resistance was reduced.

[0106] In Comparative Example 8, the content of the dispersant exceeded the upper limit specified in this specification, and the average particle diameter D50 of the polymer particles B was less than the lower limit specified in this specification, so the lithium ion permeability decreased.

[0107] In Comparative Example 9, the proportion (mass %) of the core portion of the polymer particles B exceeded the upper limit specified in this specification, and therefore the adhesiveness decreased.

[0108] In Comparative Example 10, the average particle diameter D50 of the polymer particles B exceeded the upper limit specified in this specification, and therefore the adhesiveness was reduced.

[0109] In Comparative Example 11, the degree of saponification of the PVA, which is an example of a dispersant, was less than the lower limit specified in this specification, and therefore the protective colloid properties were reduced, resulting in reduced resistance to powder falling.

[0110] In Comparative Example 12, the shell portion of the polymer particles B did not contain an acid group-containing monomer, and therefore the storage stability was deteriorated, and Tests 1 to 4 could not be carried out.

[0111] In Comparative Examples 13 to 18, polymer particles C contained polymer particles A or polymer particles B, which had reduced performance in at least one of all evaluation items, and therefore at least one performance was reduced or tests 1 to 4 could not be performed.

[0112] As described above, the present invention has the remarkable effect of providing an adhesive composition that prevents a decrease in lithium ion permeability while simultaneously achieving both blocking resistance and powder shedding resistance. The present invention also has excellent adhesion.

[0113] Furthermore, the present invention can provide an adhesive composition that does not use polyvinylidene fluoride (PVdF), a type of persistent PFAS (perfluoroalkyl and polyfluoroalkyl compounds), making it possible to contribute to Goal 12 of the United Nations-led Sustainable Development Goals (SDGs), which is "Responsible Consumption and Production."

[0114] The invention is not limited to the above-described embodiment, and various modifications and variations are possible within the scope of the gist of the invention.

Claims

1. polymer particles; a dispersant; Contains no binder, The polymer particles have a core-shell structure, the shell portion of the polymer particle contains an acid group-containing monomer as a constituent unit, The dispersant is contained in an amount of 2 to 18 parts by mass relative to 100 parts by mass of the monomer constituting the polymer particles, the proportion of the core portion of the polymer particle in the total of the core portion and the shell portion is 30 to 80% by mass, the average particle diameter D50 of the polymer particles is 300 to 1500 nm; Here, the average particle diameter D50 is a particle diameter at a cumulative 50% in a volume-based particle size distribution measured by a laser diffraction / scattering method, the monomer constituting the polymer particles is a (meth)acrylic acid alkyl ester monomer or a mixture of a (meth)acrylic acid alkyl ester monomer and an aromatic vinyl monomer; the polymer particles are provided with a protective colloid layer of the dispersant oriented around the polymer particles; Adhesive composition.

2. the core portion of the polymer particle contains a (meth)acrylic acid alkyl ester monomer as a constituent unit, the shell portion of the polymer particle further contains a (meth)acrylic acid alkyl ester monomer as a constituent unit; The adhesive composition of claim 1 .

3. the dispersant is polyvinyl alcohol; The saponification degree of the polyvinyl alcohol is 70 to 99 mol %; Here, the saponification degree of the polyvinyl alcohol is measured in accordance with JIS K 6726-1994. The adhesive composition of claim 1 .

4. the dispersant is polyvinyl alcohol; The degree of polymerization of the polyvinyl alcohol is 300 to 4500. The adhesive composition of claim 1 .

5. The dispersant is a water-soluble polymer. The adhesive composition of claim 1 .

6. The dispersant includes at least one of a semi-synthetic polymer and a synthetic polymer. The adhesive composition of claim 1 .

7. The dispersant contains at least one of a cellulose-based semi-synthetic polymer and an acrylic acid-based water-soluble polymer. The adhesive composition of claim 1 .

8. the polymer particles include at least one of polymer particles A and polymer particles B, The glass transition temperature of the core portion of the polymer particle A is 30 to 90°C, The glass transition temperature of the shell portion of the polymer particles A is 30 to 130°C, and / or The glass transition temperature of the core portion of the polymer particle B is 30 to 90°C, The glass transition temperature of the shell portion of the polymer particles B is −70 to 20° C. Here, the glass transition temperature is a glass transition temperature determined based on differential scanning calorimetry (DSC). The adhesive composition of claim 1 .

9. When the polymer particles are polymer particles C containing the polymer particles A and the polymer particles B, the mixing ratio of the polymer particles A to the polymer particles B is 1 / 99 to 99 / 1. The adhesive composition of claim 8.

10. the core portion of the polymer particle further contains an aromatic vinyl monomer as a constituent unit; The adhesive composition of claim 2.

11. the (meth)acrylic acid alkyl ester monomer constituting the core portion of the polymer particle includes methyl methacrylate; The adhesive composition of claim 2.

12. The acid group-containing monomer is an unsaturated carboxylic acid. The adhesive composition of claim 1 .

13. For bonding between battery components of non-aqueous secondary batteries, The adhesive composition of claim 1 .

14. A substrate; an adhesive layer formed on at least one surface of the substrate and comprising the adhesive composition according to any one of claims 1 to 13; Separator.

15. A substrate; an adhesive layer formed on at least one surface of the substrate and comprising the adhesive composition according to any one of claims 1 to 13; Non-aqueous secondary battery.

16. A method for producing an adhesive composition containing polymer particles having a core-shell structure, comprising: a step of polymerizing a pre-emulsion containing a (meth)acrylic acid alkyl ester monomer to form a core portion; and a step of polymerizing a pre-emulsion containing a (meth)acrylic acid alkyl ester monomer and an acid group-containing monomer to form a shell portion on the outer surface of the core portion, the step of forming the core portion and / or the step of forming the shell portion are carried out in the presence of a dispersant, The adhesive composition does not contain a binder, the adhesive composition contains 2 to 18 parts by mass of the dispersant per 100 parts by mass of the monomer constituting the polymer particles, the monomer constituting the polymer particles is the (meth)acrylic acid alkyl ester monomer or a mixture of the (meth)acrylic acid alkyl ester monomer and an aromatic vinyl monomer; the polymer particles are provided with a protective colloid layer of the dispersant oriented around the polymer particles; A method for producing an adhesive composition.

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