Coating compositions, coated substrates, separators, secondary batteries, lithium-ion secondary batteries, and electrode materials

Abstract

[Problem] To provide a coating composition which enables coating having excellent high speed coatability and surface smoothness, when the coating composition is used in a coating liquid for: a coating material containing mainly a polymer; an ink; an adhesive; a positive electrode, a negative electrode or a separator of lithium ion battery; or the like. [Solution] This coating composition contains a filler, a binder, a thickening agent and a solvent, and is characterized in that the aspect ratio of the filler is 2 or more, the binder is at least one type selected from among a diene rubber and a (meth)acrylate polymer, the viscosity of the coating composition, as measured at a shear rate of 0.01 / s, is 1.0×106 Pa·s or less, and the thixotropy index (TI) is 1.1×106 or more. [thixotropy index (TI)] = [viscosity of coating composition measured at a shear rate of 0.01 / s] / [viscosity of coating composition measured at a shear rate of 10,000 / s].

Description

[Technical Field]

[0001] The present invention relates to a composition comprising a filler, a binder, and a thickener, and more particularly to a coating composition containing a polymer that can form a coated product with excellent high-speed coating properties and surface smoothness. [Background technology]

[0002] Coating and printing technologies using compositions are widely used in industrial fields from an environmental, safety, and efficiency perspective. Such printing technologies require the ability to dispense and apply the minimum necessary composition at high speed and with high precision, while also possessing high coating properties, resulting in a smooth coated surface.

[0003] However, the physical properties of compositions with excellent coating properties were not understood. For example, Patent Document 1 discloses that a battery separator coating solution with excellent dispersibility and ease of coating can be obtained by setting a suspension of fibrous cellulose diluted with deionized water to a specific TI (thixotropy index).

[0004] However, the TI (Timing Index) for compositions other than fibrous cellulose and deionized water is not disclosed. Furthermore, there is no description or suggestion regarding high-speed coating properties. Patent Document 2 discloses a coating liquid for metal ion secondary battery separators that can form a uniform coating film with excellent coating properties by setting the viscosity ratio at a predetermined shear rate to a specific level or higher.

[0005] However, Patent Document 2 describes a coating liquid in which the water-soluble component content is 5% by mass or less and the solid content is extremely high, and it does not necessarily suggest anything in terms of high-speed coating properties or surface smoothness. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2018 / 070473 [Patent Document 2] Patent No. 5829557 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] While many of the compositions exhibit good coating properties, the characteristics that contribute to high-speed coating and surface smoothness were not clear. [Means for solving the problem]

[0008] Under these circumstances, the inventors conducted diligent research and found that by using a composition in which the viscosity ratio at high and low shear rates is within a specific range, it is possible to form a coating film with excellent coating properties and surface smoothness, and that it can be fully used for the above-mentioned applications, thus completing the present invention.

[0009] In other words, the configuration of the present invention is as follows. [1] A coating composition comprising a filler, a binder, a thickener, and a solvent, The aspect ratio of the filler is 2 or more. The binder comprises at least one selected from diene rubber and (meth)acrylate polymers. The viscosity of the coating composition measured at a shear rate of 0.01 / s is 1.0 × 10⁻⁶ 6 It is less than or equal to Pa·s. The following thixotropy index (TI) is 1.1 × 10⁻⁶ 6 A coating composition characterized by the above; [Thixotropy Index (TI)] = [Viscosity of coating composition measured at a shear rate of 0.01 / s] / [Viscosity of coating composition measured at a shear rate of 10000 / s]. [2] The coating composition of [1], wherein the ratio of the filler to the thickener is 0.1 to 500 by mass (filler / thickener). [3] The coating composition of [1] or [2], wherein the thickening agent is poly-N-vinyl carboxylic acid amide. [4] The coating composition according to [1] to [3], wherein the thickener is poly-N-vinylacetamide. [5] The coating composition according to [1] or [2], wherein the thickener is polyvinylpyrrolidone. [6] The coating composition according to [1] to [5], which contains water as a solvent. [7] The coating composition according to [1] to [6], wherein the value of the thixotropy index (TI) is 1.1×10 7 or less. [8] The coating composition according to [1] to [7], wherein the aspect ratio of the filler is 100 or less. [9] A coated substrate comprising a coating film formed from the coating composition according to [1] to [8] and a substrate.

[10] A separator formed from the coated substrate according to [9].

[11] A secondary battery using the separator according to

[10] .

[12] A lithium-ion secondary battery using the separator according to

[10] .

[13] An electrode material comprising a coating film formed from the coating composition according to [1] to [8] provided on the surface of a substrate. [Advantages of the Invention]

[0010] The coating composition of the present invention can obtain a coating film with a smooth surface on the coating surface when coating the composition at high speed and with high precision. If such a technique is adopted for forming electrodes, separators, etc. of secondary batteries, particularly lithium-ion secondary batteries, the production efficiency of secondary batteries can be improved. [Embodiments for Carrying Out the Invention]

[0011] Hereinafter, embodiments for carrying out the present invention will be described. [Coating Composition] The coating composition of the present invention contains a filler, a binder, a thickener, and a solvent. The aspect ratio of the filler is 2 or more, the binder contains at least one selected from diene rubber and (meth)acrylate polymer, and the viscosity of the coating composition measured at a shear rate of 0.01 / s is 1.0×10 6 Pa·s or less.

[0012] The following thixotropy index (TI) is 1.1×10 6 or more, preferably 3.0×10 6 or more, and more preferably 1.0×10 7 or more. Also, the thixotropy index (TI) is preferably 1.1×10 8 or less, more preferably 5.0×10 7 or less. Such a predetermined thixotropy index (TI) can be adjusted by the above composition.

[0013] [Thixotropy index (TI)] = [Viscosity of the coating composition measured at a shear rate of 0.01 / s] / [Viscosity of the coating composition measured at a shear rate of 10000 / s]. In the thixotropy index (TI) of the present invention, it is the ratio of the viscosity at a high shear rate to the viscosity at a low shear rate. When the coating is performed at high speed and high precision due to this ratio being within a predetermined range, streaks or flow on the surface do not occur, and an extremely smooth coating film can be obtained. [Filler] As the filler, those made of inorganic substances are used. Preferred fillers include alumina, boehmite, talc, kaolin, calcium carbonate, calcium phosphate, amorphous silica, crystalline glass filler, titanium dioxide, silica-alumina composite oxide particles, barium sulfate, calcium fluoride, lithium fluoride, zeolite, molybdenum sulfide, mica, etc. Among these, alumina and boehmite are more preferred.

[0014] The shape of the filler is not particularly limited as long as the aspect ratio is 2 or more, and in addition to ellipsoidal, polyhedral, plate-like, scaly, columnar, and tubular shapes, it may also be fibrous. The aspect ratio of the filler is 2 or more, more preferably 5 or more, and even more preferably 10 or more. If the aspect ratio of the filler is 2 or more, the thixotropy index (TI) is achieved, and even when high-speed, high-precision coating is performed, an extremely smooth coating film can be obtained without the occurrence of streaks or flows on the surface. Furthermore, for example, when used as a separator, even if lithium dendrites grow, the crystal pathways become longer, which has the advantage of making it difficult for them to reach the separator base film. The aspect ratio of the filler is preferably 100 or less.

[0015] The major axis of the filler is preferably in the range of 0.1 to 1000 μm, and more preferably 1 to 500 μm. The minor diameter of the filler is preferably in the range of 0.01 to 100 μm, more preferably 0.1 to 10 μm. [Thickener] The thickener consists of an organic polymer. The binder described later is not included in the thickener. Preferred thickeners include polysaccharides such as poly-N-vinyl carboxylic acid amide, poly-N-vinylpyrrolidone, sodium salt of carboxymethylcellulose, polyacrylamide, polyvinyl alcohol, carrageenan, xanthan gum, guar gum, and pectin; cellulose polymers such as carboxymethylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, methylethylhydroxycellulose, methylcellulose, and hydroxypropylcellulose; and ammonium salts and alkali metal salts of these cellulose polymers.

[0016] Of these, poly-N-vinyl carboxylic acid amide or poly-N-vinylpyrrolidone is preferred, more preferably poly-N-vinyl carboxylic acid amide, and even more preferably poly-N-vinylacetamide. Using such a thickening agent allows the thixotropy index (TI) to be adjusted to a predetermined range, and a coated product with an excellent surface appearance can be obtained.

[0017] Specific examples of monomers that constitute poly-N-vinyl carboxylic acid amides include N-vinylformamide, N-vinylacetamide, N-vinylpropionamide, N-vinylbenzamide, N-vinyl-N-methylformamide, N-vinyl-N-ethylformamide, N-vinyl-N-methylacetamide, and N-vinyl-N-ethylacetamide.

[0018] These may be either homopolymers or copolymers. When copolymerizing, it is possible to copolymerize salts of itaconic acid, maleic acid, crotonic acid, (meth)acrylic acid, etc., but this is not particularly limited.

[0019] The N-vinylacetamide component in the poly-N-vinylcarboxylic acid amide is preferably 60 mol% or more. The viscosity of the thickening agent is preferably 30 mPa·s to 10,000 mPa·s in its natural state (without adjusting the solution concentration). A viscosity within this range is preferable as it facilitates coating. [binder] The binder is preferably at least one selected from diene rubber and (meth)acrylate polymer, and more preferably consists only of at least one selected from diene rubber and (meth)acrylate polymer. Examples of diene rubber include styrene-butadiene rubber, butyl rubber, butadiene rubber, isoprene rubber, acrylonitrile-butadiene rubber, ethylene-propylene-diene rubber, or modified versions thereof. The (meth)acrylate polymer refers to a polymer containing at least one of acrylate and methacrylate. The (meth)acrylate polymer may be copolymerized and contains 50 mol% or more of acrylate and methacrylate.

[0020] Other monomers included in the (meth)acrylate polymer are not particularly limited as long as they can copolymerize with (meth)acrylate. Of these, cross-linked acrylate emulsions are preferred. The acrylate emulsion may be a homopolymer or a copolymer. It may also be used as an emulsion or after solidification.

[0021] Furthermore, polyvinyl alcohol, poly(meth)acrylic acid, higher alcohol ethylene oxide adducts, and polypropylene glycol ethylene oxide adducts can also be used as binders. In the case of poly(meth)acrylic acid, the salt is not particularly limited, but a metal-free ammonium salt is preferred, for example, ammonium polyacrylate can be used. [solvent] The solvent is not particularly limited as long as it disperses or dissolves the above components without causing a reaction, but a volatile solvent is used considering drying properties. Specifically, water or a polar solvent that is compatible with water is used, but it is preferable that it contains 50% by mass or more of water, and it is more preferable that it is water alone. Ion-exchanged water is particularly preferred. Other solvents include alcohols such as methanol, ethanol, and isopropanol. [Dispersant] The coating composition of the present invention may optionally contain a dispersant. The dispersant is not particularly limited as long as it can disperse the filler, but dodecylbenzenesulfonic acid, sorbitol, and fatty acid esters of sorbitan are preferred. The salt is not particularly limited, but ammonium salts that do not contain metals are preferred. [Composition and preparation method of coating composition] The ratio of filler to thickener in the coating composition is preferably 0.1 to 500 by mass (filler / thickener), and more preferably 50 to 200. This ratio is preferable because it allows for easy application, good drying properties, and a coating layer with sufficient strength.

[0022] The mass of the filler in the coating composition is preferably in the range of 10 to 80% by mass, more preferably in the range of 20 to 50% by mass. Based on the solid content in the coating composition, the mass of the filler is preferably in the range of 50 to 99% by mass, more preferably in the range of 70 to 98% by mass. The binder is preferably included in the range of 0.1 to 20% by mass, more preferably in the range of 1 to 5% by mass, relative to the mass of the filler.

[0023] The mass of the binder (solids) in the coating composition is preferably in the range of 0.1 to 20% by mass, more preferably in the range of 1.0 to 5.0% by mass. Based on the solids in the coating composition, the mass of the binder (solids) is preferably in the range of 0.2 to 10% by mass, more preferably in the range of 0.5 to 5.0% by mass.

[0024] The mass of the thickener in the coating composition is preferably in the range of 0.01 to 20% by mass, more preferably in the range of 1.0 to 5.0% by mass. Based on the solid content in the coating composition, the mass of the thickener is preferably in the range of 0.2 to 10% by mass, more preferably in the range of 0.5 to 5% by mass.

[0025] The amount of dispersant in the coating composition is preferably in the range of 0.01 to 10% by mass, more preferably 0.1 to 5% by mass. Including it within this range allows for high dispersibility of the filler.

[0026] Typically, the amount of filler is preferably 0.1 to 1000 parts by mass, more preferably 1 to 200 parts by mass, per 100 parts by mass of a solvent such as water. Within this range, good fluidity of the coating composition is obtained, and the viscosity measured at a shear rate of 0.01 / s is 1.0 × 10⁻⁶. 6 A coating composition with a Pa·s or lower can be obtained.

[0027] The method of mixing each component of the coating composition is not particularly limited, but in order to achieve a more uniform mixture, it is preferable to dissolve or disperse the binder, thickener, etc. in the solvent before adding and mixing the filler. More preferably, it is preferable to add the filler sequentially while continuously stirring the solution in which the binder, thickener, etc. have been dissolved or dispersed, and then stir and mix to homogenize it. This makes it possible to achieve an ideal mixture. [Application] The coating composition of this embodiment can be used in various coating liquids such as paints, inks, adhesives, and positive electrodes, negative electrodes, and separators for lithium-ion batteries, depending on the type of filler that is incorporated.

[0028] The coating composition can be used as is as a coating liquid, but if necessary, its concentration and viscosity can be adjusted with a solvent or other appropriate means before use as a coating liquid. For example, a coating film is produced by applying the coating composition to the surface of a substrate and drying it. Alternatively, a coating film made of the coating composition can be provided on the surface of a substrate (referred to as a substrate with a coated film) to be used as an electrode material.

[0029] The coating composition of this embodiment comprises a filler, a binder, a thickener, a solvent, and a dispersant, and the aspect ratio of the filler is 2 or more, and it has a predetermined viscosity and TI, so even when the coating composition is applied at high speed and with high precision, a coating film with a smooth surface can be obtained on the coated surface.

[0030] The method of applying the coating composition to the substrate is not particularly limited, but in addition to spray coating, roll coating, bar coating, gravure coating, die coating, knife coating, inkjet coating, brush coating, and dipping, it is also possible to apply the coating continuously using a roll-to-roll pattern coating device.

[0031] Furthermore, the coating composition may also contain known materials added to the paint in addition to those mentioned above, such as surface modifiers, defoamers, leveling agents, pigments, dyes, and the like.

[0032] Films, nonwoven fabrics, porous materials, plate-like materials, etc., can be used as the base material without any particular restrictions. Examples of materials constituting the substrate include ethylene alone or copolymers with other α-olefins, homopolypropylene, copolymers of propylene and other olefins, polyethylene terephthalate, polyethylene naphthalate, polyamide ether ketone, polyimide, polyamide, polyphenylene sulfone, polyphenylene ether, polyethylene, polyether sulfone, polyether ether ketone, polybenzimidazole, polyetherimide, polyamideimide, poly(p-phenylene-2,6-benzobisoxazole), organic resin materials such as fluororesins and epoxy resins, metallic materials such as aluminum, copper, silver, and iron, and inorganic materials such as glass (silicon oxide), alumina, magnesia, aluminum nitride, aluminum carbide, silicon nitride, and barium titanate. The substrate may be used alone or in combination of two or more types. Of these, polyolefin is preferred as the substrate, more preferably at least one selected from polyethylene and polypropylene, and most preferably a three-layer laminate in the order of polypropylene / polyethylene / polypropylene. A porous substrate made of such materials can be used as a separator for secondary batteries, etc.

[0033] When the porous substrate is a polyolefin film, it is not particularly limited whether it is manufactured by a wet process or a dry process. Furthermore, in the case of a porous substrate consisting of a three-layer laminate, it is preferable that all three layers are manufactured by a dry process. Such a structure does not curl and has good heat resistance and mechanical strength.

[0034] The dry process refers to a dry process that does not use solvents during film manufacturing. Examples include melt molding of molten resin using a T-die or injection molding. The outer and inner layers may be manufactured using either the dry or wet process. The wet process involves forming a film using a resin with additives added and mixed, and then creating voids by solvent extraction of the additives.

[0035] The overall thickness of the substrate is appropriately selected based on the purpose, considering factors such as mechanical strength, performance, and miniaturization, and is preferably 7.0 μm or more, with an upper limit of 50 μm or less. A thickness within this range allows for high strength.

[0036] Furthermore, in the case of porous substrates, the air permeability measured in accordance with JIS P 8117:2009 is preferably 80 seconds / 100 ml or higher, with an upper limit of preferably 700 seconds / 100 ml or lower. Having air permeability within this range makes short circuits less likely and ion mobility high.

[0037] The porosity of the porous substrate is preferably 30% or more, and preferably 70% or less. With a porosity within this range, the mechanical strength is high, short circuits do not occur, and ion mobility can be high.

[0038] The maximum pore size of the porous substrate is preferably 0.05 μm or larger, and preferably 2 μm or smaller. Within this range, when used as a separator, ion mobility is high and resistance is low and large.

[0039] The thickness of the coating film is not particularly limited; any coating film with a thickness of 0.5 to 20 μm is acceptable, but it is not particularly restricted. There are no particular restrictions on the drying method of the coating film, and examples include spin drying, vacuum drying, hot air drying, and infrared drying. There are also no particular restrictions on the drying time.

[0040] When constructing a separator, it can be constructed by methods such as applying the coating composition to the surface of the substrate. When constructing electrodes, the battery electrodes can be constructed by mixing the coating composition with a positive electrode active material or a negative electrode active material and applying it to the surface of the substrate or the surface of the current collector; or by coating an electrode foil with a mixture of the coating composition with the positive electrode active material or the negative electrode active material or both; or by thinning the coating composition and inserting it into the surface of the current collector of the positive electrode or the negative electrode or both.

[0041] The components that make up a lithium-ion secondary battery can be broadly divided into positive electrode, negative electrode, separator, and electrolyte. The positive electrode and negative electrode each contain an active material that performs oxidation / reduction reactions by sending and receiving electrons. The positive electrode and negative electrode can be used in the form of a stacked electrode group with a battery separator in between, or a wound electrode group by further winding the stacked electrode group.

[0042] As for the positive electrode, there are no particular restrictions as long as it is a positive electrode that has been used in conventional lithium-ion secondary batteries. + It contains an active material capable of intercepting and releasing ions. As for the negative electrode, there are no particular restrictions as long as it is a negative electrode that has been used in conventional lithium-ion secondary batteries. + It contains an active material capable of intercepting and releasing ions.

[0043] The positive and negative electrodes can be used in the form of a stacked electrode group with a separator in between, or a wound electrode group by further winding these stacked electrodes. As the electrolyte, a solution of lithium salt dissolved in an organic solvent is used. The lithium salt is one that dissociates in the solvent. + There are no particular restrictions on the organic solvent, as long as it forms ions and does not cause side reactions such as decomposition within the voltage range used for the battery. The organic solvent is not particularly limited, as long as it dissolves the lithium salt and does not cause side reactions such as decomposition within the voltage range used for the battery.

[0044] Each component prepared using the coating composition of this embodiment is used as appropriate in each component of the battery. Lithium-ion batteries are used as power sources for various devices, including mobile phones, notebook computers and other portable devices, electric vehicles, hybrid vehicles, electric motorcycles, electric-assist bicycles, power tools, shavers, and many other applications that have been known for some time. [Examples]

[0045] The present invention will be described below with reference to examples, but the present invention is not limited in any way to these examples. [Materials used] · Filler Flake-like boehmite: Cerasure (manufactured by Kawai Lime Industry Co., Ltd.) Aspect ratio: 20-40, major axis 10 μm, minor axis 0.3 μm (average values) Flake-like alumina: Cerasure α (manufactured by Kawai Lime Industry Co., Ltd.) Aspect ratio: 20-40, major axis 13 μm, minor axis 0.4 μm (average values) ·binder Acrylate emulsion: Polyzol (registered trademark) LB-350 (manufactured by Showa Denko Corporation) SBR (Styrene-Butadiene Rubber Aqueous Dispersion): BM400B (Manufactured by Nippon Zeon Co., Ltd.) Ammonium polyacrylate: Aron® A-30SL (manufactured by Toagosei Co., Ltd.) • Thickening agent Poly-N-vinylacetamide PNVA(registered trademark)-1:GE191-043 (manufactured by Showa Denko Corporation), viscosity 5000 mPa·s, solids content 4% by mass Poly-N-vinylacetamide PNVA(registered trademark)-2:GE191-104 (manufactured by Showa Denko Corporation), viscosity in form 18000 mPa·s, solids content 10% by mass Poly-N-vinylacetamide PNVA(registered trademark)-3:GE191-107 (manufactured by Showa Denko Corporation), viscosity 50 mPa·s, solids content 10% by mass Carboxymethylcellulose CMC-Na:MAC350HC (manufactured by Nippon Paper Industries Co., Ltd.) Polyvinylpyrrolidone: PVP K-90 (manufactured by Tokyo Chemical Industry Co., Ltd.) • Dispersant Sodium dodecylbenzenesulfonate aqueous dispersion: Neoperex® G-65 (manufactured by Kao Corporation) [Examples 1-7, Comparative Examples 1-6] The specified amounts listed in Table 1 were measured into a 200 ml plastic container in the following order: deionized water, dispersant, binder, thickener, and inorganic filler. These were then placed into a rotary-orbiting kneader (Sinky ARE-250). The container was sealed tightly, and the mixture was prepared under the conditions of 60 seconds of mixing and 60 seconds of defoaming to obtain a uniform coating composition.

[0046] [Table 1] The following evaluations were performed on the obtained coating compositions. <Coating Test Method> A polypropylene sheet (1 mm thick) was fixed on the coating table of the coating machine, and 3.5 g of the obtained coating composition was applied to an area 15 cm wide and 30 cm long using a bar coater (Yoshimitsu Seiki Co., Ltd., width: 50 mm x thickness: 5 μm) on an automatic coating machine (Tester Sangyo Co., Ltd., Pi-1210) at a speed of 200 mm / second.

[0047] Subsequently, the coated polypropylene sheet was dried in a hot air dryer at a temperature of 40°C for 1 hour to obtain a coated sheet. <Heat resistance test method> From the coated sheet, the coated material was peeled off from a section with a consistent thickness (6-7 μm), and a rectangular piece (5 cm x 4 cm) was taken. The lengths of the four sides were then measured. These test pieces were then placed in a metal tray at a distance from each other to avoid interference.

[0048] The metal tray was placed in an air oven with an internal temperature of 150°C and left to stand for 15 minutes. After removing it, the dimensions of all four sides were measured. The measured test specimens were placed again in an air oven preheated to 200°C, left to stand for 15 minutes, and then removed. The dimensions of all four sides were then measured. [Measurement method] <rotational viscosity> Using a Brookfield DV2T viscometer with a SC4-28 spindle and a small sample adapter with a water jacket, 20g of the coating composition was placed in the sample holder, and the rotational viscosity (η) was measured at rotational speeds of 0.3 rpm and 100 rpm. 0.3 and η100 The ratio was determined by measuring the values.

[0049] Note that the shaded items in Examples 3, Comparative Examples 3 and 5 could not be calculated. "Over" indicates a value exceeding the measurement limit. <Solution viscosity> The coating compositions were evaluated using a B-type viscometer (Brookfield DV2T viscometer with SC4-28 spindle and water jacket with small sample adapter) at 23°C and 50 rpm.

[0050] Note that data was not measured in the blank spaces in Examples 3-7 and Comparative Example 6. <Shear viscosity, TI> The thixotropy index (TI) is calculated using the following formula.

[0051] Viscosity at a shear rate of TI = 0.01 / s (Pa·s) ÷ Viscosity at a shear rate of 10000 / s (Pa·s) Shear viscosity was measured using an Anton Parr rotational viscometer. Specifically, viscosity at 23°C was measured at a shear rate of 0.01 sec. -1 from 10000sec -1 The measurement was taken over 400 seconds, gradually increasing the speed, and continued for 10,000 seconds. -1 from 0.01 sec -1 The measurement was taken while gradually decreasing the shear rate over a period of 400 seconds. The measured values ​​obtained while decreasing the shear rate were defined as viscosity at each shear rate. <Coating film thickness> Using a Teclock PF-11J constant-pressure thickness gauge, measurements were taken at three points in accordance with JIS K 6400-1-2004: the center of the coated and dried film, and two points 10 cm above and below the center. The average was then calculated. <Appearance of the coated surface> The surface appearance of the coated sheet was evaluated according to the following criteria. ○: No voids were found on the coated surface. △: Up to 10 voids were observed on the coated surface. ×: More than 10 voids were observed on the coated surface. <Surface roughness> Using a Sartronic Duo surface roughness meter (manufactured by Taylor Hobson), the arithmetic mean roughness (Ra) of a coated sheet (15cm x 30cm) was measured at three points: the center and two points 10cm above and below the center, in accordance with JIS B0601-2013. The average was then calculated. The surface roughness ratio was obtained by dividing Ra by the coating film thickness. <Exfoliation Evaluation> A cellophane tape peel test was performed on the coated surface of the coated sheet using 15mm wide cellophane tape manufactured by Nichiban, and the adhesion between the coated material and the polypropylene sheet was evaluated in the following three stages. ○: The coated area did not peel off. △: The coating has peeled off slightly, but it is still usable. ×: The painted area peels off, making it unacceptable in practical use. <Heat resistance evaluation> A rectangular section of a certain thickness (6-7 μm) was taken from the coated sheet, and the lengths of its four sides were measured. The test pieces were then placed on a metal tray at intervals that would not interfere with each other.

[0052] The metal tray was placed in an air oven at an internal temperature of 150°C and left for 15 minutes. After removal, the dimensions of all four sides were measured. The measured test specimen was then placed again in an air oven adjusted to 200°C, left for 15 minutes, and then removed. The dimensions of all four sides were measured again. The following items were evaluated. ○: The shrinkage rate is 20% or less on all sides at 150℃ and 200℃. △: In the 150℃ and 200℃ tests, at least one edge exhibits a shrinkage rate of more than 20% but less than or equal to 30%, and the shrinkage rate of all edges is 30% or less. ×: In the 150℃ and 200℃ tests, some items exhibited a shrinkage rate exceeding 30% on either side. <Aspect Ratio> In accordance with JIS R1670-2006, the major axis and short side of 100 particles were measured using a microscope, averaged, and then calculated by dividing the average major axis by the average short side.

[0053] [Table 2] Table 2 shows that in the examples where TI was within a specific range, a coating film was formed that was free of surface irregularities, had high surface smoothness, and exhibited excellent peelability and heat resistance.

Claims

1. A coating composition comprising a filler, a binder, a thickener, and a solvent, The aspect ratio of the filler is 2 or more. The binder comprises at least one selected from diene rubber and (meth)acrylate polymers. The viscosity of the coating composition measured at a shear rate of 0.01 / s is 1.0 × 10⁻⁶. 6 It is less than or equal to Pa·s, The thixotropy index (TI) below (0.01 / 10000) is 1.1 × 10⁻⁶ 6 That's all. A coating composition characterized in that the thixotropy index (TI) (0.1 / 10000) is 8.052 × 10⁴ or greater. [Thixotropy Index (TI) (0.01 / 10000)] = [Viscosity of coating composition measured at a shear rate of 0.01 / s] / [Viscosity of coating composition measured at a shear rate of 10000 / s] [Thixotropy Index (TI) (0.1 / 10000)] = [Viscosity of coating composition measured at a shear rate of 0.1 / s] / [Viscosity of coating composition measured at a shear rate of 10000 / s]

2. The coating composition according to claim 1, wherein the ratio of the filler to the thickener is 0.1 to 500 by mass (filler / thickener).

3. The coating composition according to claim 1 or 2, wherein the thickening agent is poly-N-vinylcarboxylic acid amide.

4. The coating composition according to any one of claims 1 to 3, wherein the thickening agent is poly-N-vinylacetamide.

5. The coating composition according to claim 1 or 2, wherein the thickening agent is polyvinylpyrrolidone.

6. A coating composition according to any one of claims 1 to 5, comprising water as a solvent.

7. The thixotropy index (TI) (0.01 / 10000) value is 1.1 × 10 8 The coating composition according to any one of claims 1 to 6, which is as follows:

8. The coating composition according to any one of claims 1 to 7, wherein the aspect ratio of the filler is 100 or less.

9. The coating composition according to any one of claims 1 to 8, wherein the shape of the filler is flaky.

10. The coating composition according to any one of claims 1 to 9, wherein the binder further comprises ammonium polyacrylate.

11. A coated substrate comprising a coating film formed from the coating composition according to any one of claims 1 to 10 and the substrate.

12. A separator formed from a coated substrate according to claim 11.

13. A secondary battery using the separator described in claim 12.

14. A lithium-ion secondary battery using the separator described in claim 12.

15. An electrode material comprising a coating film formed from the coating composition according to any one of claims 1 to 10, provided on the surface of a substrate.

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