JP2013133418A - Coating liquid, laminated porous film, and method for producing laminated porous film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator having high ion permeability and capable of controlling coming out of a powder, and to provide a coating liquid suitable for production thereof.SOLUTION: This coating liquid includes a filler, a medium and a binder resin. The binder resin comprises ≥90 wt.% of carboxymethyl cellulose (CMC) based on the total amount of the binder resin. The CMC is a mixture which meets a relationship of (CMC-A)/[(CMC-A)+(CMC-B)]=0.6 to 0.9 (weight ratio), wherein (CMC-A) represents CMC having a degree of etherification of 0.5 to 0.7, and (CMC-B) represents CMC having a degree of etherification of 1.1 to 1.5.

Description

  The present invention relates to a coating liquid used for producing a laminated porous film suitable as a separator for a non-aqueous electrolyte secondary battery, and a laminated porous film produced using the coating liquid.

  Non-aqueous electrolyte secondary batteries, particularly lithium ion secondary batteries, are widely used as batteries for personal computers, mobile phones, portable information terminals and the like because of their high energy density.

Non-aqueous electrolyte secondary batteries represented by these lithium secondary batteries are high in energy density, and when internal short circuit / external short circuit occurs due to damage of the battery or equipment using the battery, A large current flows and generates intense heat. Therefore, non-aqueous electrolyte secondary batteries are required to prevent heat generation beyond a certain level and ensure high safety.
As a means for ensuring such safety, a method of providing a shutdown function for preventing further heat generation by blocking the passage of ions between the positive and negative electrodes by a separator in the event of abnormal heat generation is common. As a method for imparting a shutdown function to the separator, a method in which a porous film made of a material that melts when abnormal heat is generated is used as the separator. That is, in the battery using the separator, the porous film melts and becomes non-porous when abnormal heat is generated, and the passage of ions can be blocked and further heat generation can be suppressed.

  As the separator having such a shutdown function, for example, a polyolefin porous film is used. The separator made of the porous film made of polyolefin suppresses further heat generation by blocking (shutdown) the passage of ions by melting and making non-porous at about 80 to 180 ° C. during abnormal heat generation of the battery. However, when the heat generation is severe, the separator made of the porous film may cause a short circuit due to direct contact between the positive electrode and the negative electrode due to shrinkage or film breakage. Thus, the separator made of a polyolefin porous film has insufficient shape stability and sometimes cannot suppress abnormal heat generation due to a short circuit.

As an improvement measure, some separators for non-aqueous electrolyte secondary batteries excellent in shape stability at high temperatures have been proposed. As one of the means, a laminate in which a heat-resistant layer containing fine particle filler and a porous film mainly composed of polyolefin as a substrate (hereinafter sometimes referred to as “substrate porous film”) are laminated. A separator for a nonaqueous electrolyte secondary battery made of a porous film has been proposed (see, for example, Patent Document 1). In such a separator, one of the problems is suppression of filler falling off from the surface of the laminated porous film, so-called “powder falling”.
When powder falls from the separator, problems such as the expected physical properties of the separator not appearing and the device being contaminated by the powder (filler) dropped when assembling the battery occur.

As a method for suppressing the above-mentioned filler falling off (powder falling), a method for modifying the surface of the filler (for example, refer to Patent Document 2), a method for characterizing the chemical structure of the binder resin and binding the filler (for example, Patent Document 3) and a method (for example, Patent Document 4) for controlling the average fiber diameter of the fiber fixing the filler and the particle diameter of the filler to a predetermined relationship have been proposed.
However, suppression of powder omission by these methods is not sufficient, and further improvement is required.

JP 2004-227972 A JP 2007-31151 A International Publication No. 2009/123168 Pamphlet JP 2006-331760 A

  An object of the present invention is to provide a separator having a high ion permeability and a more suppressed powder fall and a coating liquid suitable for the production thereof.

  As a result of intensive studies to solve the above problems, the present inventor has reached the present invention.

That is, the present invention relates to the following inventions.
<1>
A coating liquid containing a filler, a medium, and the following binder resin.
Binder resin: 90% by weight or more of the total amount of the binder resin is carboxymethyl cellulose (CMC), and the CMC has a degree of etherification = 0.5 to 0.7 (CMC-A) and a degree of etherification = 1.1. CMC (CMC-B) of ˜1.5 is a mixture satisfying the formula of (CMC−A) / [(CMC−A) + (CMC−B)] = 0.6 to 0.9 (weight ratio) is there.
<2>
The coating liquid as described in <1> containing 2-6 weight part of binder resins with respect to 100 weight part of said fillers.
<3>
The coating liquid according to <1> or <2>, wherein the filler is an inorganic filler.
<4>
The coating liquid according to <1>, <2>, or <3>, wherein the inorganic filler is alumina.
<5>
<1>-<4> The laminated porous film formed by laminating | stacking the component by which the medium was removed from the coating liquid in any one of <4> on the single side | surface or both surfaces of a base material porous film.
<6>
The laminated porous film according to <5>, wherein the substrate porous film is a porous film mainly composed of polyolefin.
<7>
<1> to <4> The coating liquid according to any one of <4> is applied to one or both sides of the substrate porous film, and then the medium is removed. A method for producing a laminated porous film comprising a material porous film.
<8>
The method for producing a laminated porous film according to <7>, wherein the substrate porous film is a porous film containing polyolefin as a main component.

  According to the present invention, there is provided a laminated porous film suitable as a separator for a non-aqueous electrolyte secondary battery that has a heat-resistant layer with suppressed powder fall and high shape-maintainability during heating and excellent ion permeability. can do.

The coating liquid of the present invention comprises a substrate porous film (hereinafter sometimes referred to as “A layer”) and a heat-resistant layer (hereinafter sometimes referred to as “B layer”) containing a filler and a binder resin. In the laminated porous film that is laminated, the laminated porous film that is suitably used for forming the B layer and prepared using the coating liquid is used as a separator, particularly as a separator for a non-aqueous secondary battery. Preferably used.
The heat-resistant layer (B layer) formed from the coating liquid of the present invention is formed by binding the filler contained in the coating liquid of the present invention with a binder resin, and the substrate porous film (A layer) is It has heat resistance at a non-porous temperature and imparts a shape maintaining function to the laminated porous film. The B layer is formed by applying the coating liquid according to the present invention to one or both sides of the A layer and then removing the solvent as a medium.
In addition, since the A layer has a property of melting and becoming nonporous when the temperature becomes high, when this is laminated with the B layer and used as a separator, it is melted and made nonporous in the event of abnormal heat generation. A shutdown function is added to the quality film. Details of the A layer will be described later.

Hereinafter, the coating liquid of the present invention will be described in detail.
The binder resin contained in the coating solution is 90% by weight or more of the total amount of the binder resin is carboxymethyl cellulose (CMC),
The CMC has a degree of etherification = 0.5 to 0.7 (hereinafter sometimes referred to as CMC-A) and a degree of etherification = 1.1 to 1.5 (hereinafter referred to as CMC-B). Sometimes)
(CMC-A) / [(CMC-A) + (CMC-B)] = 0.6 to 0.9 (weight ratio)
It is a mixture satisfying the following formula.

By using such a coating liquid of the present invention, a filler can be efficiently combined with a small amount of binder, and a B layer having high adhesion with the A layer can be formed, so that powder falling is suppressed, It is possible to provide a laminated porous film having a heat-resistant layer with high shape maintaining property during heating and excellent ion permeability, and the film is suitable as a separator for a non-aqueous electrolyte secondary battery.

  In addition, as long as it is a grade which does not impair the objective of this invention as needed, it may contain a small amount of other binder resins.

  In the present invention, the amount of the binder resin is preferably 2 to 6 parts by weight with respect to 100 parts by weight of the filler in the coating liquid, and hence the B layer formed from the coating liquid. If the amount is more than 6 parts by weight, the ion permeability may be insufficient. If the amount is less than 2 parts by weight, the amount of powder falling tends to increase.

As the filler in the present invention, an inorganic or organic filler generally called a filler can be used. Specifically, styrene, vinyl ketone, acrylonitrile, methyl methacrylate, ethyl methacrylate, glycidyl methacrylate, glycidyl acrylate, methyl acrylate, or a copolymer of two or more kinds; polytetrafluoroethylene, tetrafluoroethylene-6 Fluorine resin such as fluorinated propylene copolymer, tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride; melamine resin; urea resin; polyethylene; polypropylene; filler made of organic matter such as polymethacrylate, calcium carbonate, talc , Clay, kaolin, silica, hydrotalcite, diatomaceous earth, magnesium carbonate, barium carbonate, calcium sulfate, magnesium sulfate, barium sulfate, aluminum hydroxide, magnesium hydroxide, calcium oxide, acid Magnesium, titanium oxide, alumina, mica, zeolite, and a filler made of an inorganic substance such as glass. In addition, these fillers can be used individually or in mixture of 2 or more types.
Among these, from the viewpoint of heat resistance and chemical stability, the filler is preferably an inorganic filler, more preferably an inorganic oxide, and particularly preferably alumina.
Alumina has many crystal forms such as α-alumina, β-alumina, γ-alumina, and θ-alumina, and any of them can be suitably used. Of these, α-alumina is most preferred because it has particularly high thermal and chemical stability.
These filler materials can be used alone. Two or more materials can be mixed and used.

  Fillers can take various forms, such as spherical, oval, short, etc., and irregular shapes that do not have a specific shape, depending on the filler material manufacturing method and the dispersion conditions during preparation of the coating liquid. Any of these can be used.

  When the filler content is a heat-resistant layer, voids formed by contact between fillers are less likely to be clogged by other constituent materials such as a binder resin, and to maintain good ion permeability, When the total solid content in the coating liquid is 100%, it is preferably 60% by volume or more, and more preferably 70% by volume or more.

The solvent (dispersion medium) is not particularly limited as long as it is a solvent having a property of dissolving CMC and a property of dispersing filler, and it is not particularly limited as long as it is a single solvent or a mixed solvent. It is preferable in terms of environmental load and process, and more preferably a mixed solvent of water and an organic polar solvent from the viewpoint that the drying and removal rate is increased.
As the organic polar solvent to be used as a mixed solvent, an alcohol which is compatible with water at an arbitrary ratio and has an appropriate polarity is preferable, and among them, methanol, ethanol and isopropanol are used. The ratio of the water and the polar solvent is selected in consideration of the leveling property and the type of the binder resin to be used within the range in which the above contact angle range is achieved, and usually contains 50% by weight or more of water.

  Moreover, in this coating liquid, you may contain components other than a filler and binder resin in the range which does not impair the objective of this invention as needed. Examples of such components include a dispersant, a plasticizer, and a pH adjuster.

The method for obtaining the coating liquid by dispersing the filler or the binder resin is not particularly limited as long as it is a method necessary for obtaining a homogeneous coating liquid.
Examples thereof include a mechanical stirring method, an ultrasonic dispersion method, a high pressure dispersion method, and a media dispersion method.
The order of mixing is not limited as long as there is no particular problem such as the occurrence of precipitates, and a method of adding fillers, binder resins and other components to a solvent at once and mixing them, or a method of mixing after dispersing each in a solvent Either of these can be adopted.

<Substrate porous film (A layer)>
The A layer has a structure having pores connected to the inside thereof, and is configured so that gas or liquid can pass from one surface to the other surface.

Examples of the porous substrate film include polyolefin films, polyethylene terephthalate (PET), and nonwoven fabrics made of cellulose. Generally, the porous film melts and becomes nonporous (shutdown function) due to abnormal heat generation of the battery. In particular, a porous film containing a polyolefin as a main component (porous polyolefin film) is preferable.
When the A layer is a porous polyolefin film, the proportion of the polyolefin component is required to be 50% by volume or more of the entire A layer, preferably 90% by volume or more, and 95% by volume or more. More preferred.

  The polyolefin component of the porous polyolefin film preferably contains a high molecular weight component having a weight average molecular weight of 5 × 10 5 to 15 × 10 6. In the case where the A layer is a porous polyolefin film, it is preferable that a polyolefin component having a weight average molecular weight of 1,000,000 or more is included as the polyolefin component because the strength of the entire laminated porous film including the A layer and further the A layer is increased.

  Examples of the polyolefin include a high molecular weight homopolymer or copolymer obtained by polymerizing ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene and the like. Among these, high molecular weight polyethylene mainly having ethylene and having a weight average molecular weight of 1,000,000 or more is preferable.

  The pore size of the A layer is preferably 3 μm or less, and more preferably 1 μm or less in terms of ion permeability and prevention of particles entering the positive electrode and the negative electrode when used as a battery separator.

The air permeability of the A layer is usually in the range of 30 to 1000 seconds / 100 cc as a Gurley value, and preferably in the range of 50 to 500 seconds / 100 cc.
When the A layer has an air permeability in the above range, sufficient ion permeability can be obtained when used as a separator.

The film thickness of the A layer is appropriately determined in consideration of the film thickness of the heat-resistant layer of the laminated porous film.
In the case of forming the B layer by applying a coating solution on one or both sides of the A layer, the thickness of the A layer is preferably 4 to 40 μm, and more preferably 7 to 30 μm.

  The porosity of the A layer is preferably 20 to 80% by volume, more preferably 30 to 70% by volume. Within such a range, the ion permeability is excellent, and excellent characteristics are exhibited when used as a separator for a non-aqueous electrolyte secondary battery. If the porosity is less than 20% by volume, the amount of electrolyte retained may be small. If it exceeds 80% by volume, non-porous formation at the shutdown occurrence temperature becomes insufficient, that is, the current cannot be cut off during abnormal heat generation. There is a fear.

  As the basis weight of the A layer, the strength, film thickness, handling property and weight of the laminated porous film, and further, the weight energy density and volume energy density of the battery when used as a battery separator can be increased. Usually, it is 4-15 g / m <2>, and 5-12 g / m <2> is preferable.

The method for producing the A layer is not particularly limited. For example, as described in JP-A-7-29563, a plasticizer is added to a thermoplastic resin to form a film, and then the plasticizer is mixed with an appropriate solvent. As described in JP-A-7-304110, a film made of a thermoplastic resin produced by a known method is used, and a structurally weak amorphous portion of the film is selectively stretched. And a method of forming micropores. For example, when the A layer is formed from a polyolefin resin containing ultrahigh molecular weight polyethylene and a low molecular weight polyolefin having a weight average molecular weight of 10,000 or less, from the viewpoint of production cost, the following (1) to (4) A method through the steps is preferred.
Specifically, (1) 100 parts by weight of ultrahigh molecular weight polyethylene, 5 to 200 parts by weight of a low molecular weight polyolefin having a weight average molecular weight of 10,000 or less, and 100 to 400 parts by weight of an inorganic filler such as calcium carbonate are kneaded to polyolefin resin. Step (2) for obtaining a composition (2) Step for molding a sheet using the polyolefin resin composition (3) Step (4) for removing inorganic filler from the sheet obtained in step (2) (4) Step (3) The process of extending | stretching the obtained sheet | seat and obtaining A layer Moreover, the commercial item which has the said characteristic can be used for A layer.

The production method of the laminated porous film of the present invention is not particularly limited as long as it is a method capable of obtaining a porous film in which the above-described A layer and B layer are laminated,
A method of preparing a coating liquid containing an inorganic filler and a binder resin, and applying this directly onto the base porous film to remove the solvent (dispersion medium). Dipping the base porous film in the coating liquid And a method of removing the solvent (dispersion medium) after performing dip coding.
Among the methods for forming the B layer, the method of directly applying the coating liquid on the substrate porous film and removing the solvent (dispersion medium) is simple and the control of the coating amount is preferable.
In addition, in the case of laminating the B layer on both sides of the base porous film (A layer), a sequential laminating method of laminating the B layer on the other side after forming the B layer on one side, or the base porous film A simultaneous lamination method in which the B layer is simultaneously formed on both surfaces of the (A layer) is mentioned.

  The method for directly applying the coating liquid to the substrate porous film is not particularly limited as long as it can uniformly coat the substrate, and a conventionally known method can be adopted. For example, a capillary coating method, a spin coating method, a slit die coating method, a spray coating method, a roll coating method, a screen printing method, a flexographic printing method, a bar coater method, a gravure coater method, a die coater method, and the like can be employed. The thickness of the B layer to be formed can be controlled by adjusting the coating amount, the concentration of the binder resin in the coating liquid, and the ratio of the filler to the binder resin.

The coating liquid can be applied directly to the substrate porous film, but it is preferable to perform a hydrophilic treatment on the substrate porous film in advance. By hydrophilizing the substrate porous film, the coatability is further improved and a more uniform heat-resistant layer (B layer) can be obtained. This hydrophilization treatment is particularly effective when the concentration of water in the solvent is high.
Specific examples of the hydrophilic treatment method for the porous substrate film include chemical treatment with an acid or alkali, corona treatment, plasma treatment, and the like.
Here, in the corona treatment, in addition to being able to hydrophilize the substrate porous film in a relatively short time, modification of the polyolefin resin by corona discharge is limited only to the vicinity of the surface of the membrane, There is an advantage that high coatability can be secured without changing the properties.

The removal of the medium from the coating liquid applied on the substrate porous film is generally performed by drying, but is not limited thereto.
In addition, when a coating liquid is apply | coated on a base material porous film, the drying temperature of a medium is below the temperature which does not reduce the air permeability of a base material porous film, ie, the temperature which a shutdown produces.

The thickness of the B layer is usually from 0.1 μm to 10 μm, and preferably from 2 μm to 6 μm. If the B layer is too thick, the load characteristics of the battery may decrease when a non-aqueous electrolyte secondary battery is produced. There is a possibility that the separator may contract without being able to resist the thermal contraction of the film.
In addition, when B layer is formed in both surfaces of A layer, the thickness of said B layer points out the total thickness of both surfaces.

The B layer is formed as a porous film, and the pore diameter is preferably 3 μm or less, more preferably 1 μm or less, as the diameter of the sphere when the hole is approximated to a sphere. When the average pore diameter exceeds 3 μm, there is a possibility that problems such as short-circuiting easily occur when the carbon powder, which is the main component of the positive electrode or the negative electrode, or a small piece thereof falls off.
The porosity of the B layer is preferably 30 to 90% by volume, more preferably 40 to 85% by volume.

<Laminated porous film>
The thickness of the entire laminated porous film (A layer + B layer) of the present invention is usually 5 to 80 μm, preferably 5 to 50 μm, and particularly preferably 6 to 35 μm. When the thickness of the entire laminated porous film is less than 5 μm, the membrane is easily broken. On the other hand, if the thickness is too thick, the electric capacity of the battery tends to be small when used as a separator for a non-aqueous secondary battery.

  The porosity of the entire laminated porous film of the present invention is usually 30 to 85% by volume, preferably 35 to 80% by volume.

The air permeability of the laminated porous film of the present invention is preferably 50 to 2000 seconds / 100 cc in terms of Gurley value, and more preferably 50 to 1000 seconds / 100 cc.
By setting the air permeability to such a range, when a non-aqueous secondary battery is produced using the laminated porous film of the present invention as a separator, it exhibits sufficient ion permeability and has high load characteristics as a battery. can get.

  As the heating shape maintenance rate of the laminated porous film at a high temperature at which shutdown occurs, the smaller value in the MD direction or the TD direction is preferably 95% or more, and more preferably 97% or more. Here, the MD direction refers to the long direction during sheet forming, and the TD direction refers to the width direction during sheet forming. Note that the high temperature at which shutdown occurs is a temperature of 80 to 180 ° C., and usually about 130 to 150 ° C.

  In addition, in the laminated porous film of the present invention, for example, a porous film such as an adhesive film and a protective film other than the base material porous film (A layer) and the heat-resistant layer (B layer) is impaired. You may include in the range which is not.

The laminated porous film of the present invention is characterized by a small amount of powder falling off. Here, the amount of powder falling is small indicates that the peel strength (hereinafter sometimes referred to as peel strength) of the T-type peel test and the 180-degree peel test using a tape is high.
The T-type peel test is a method for evaluating the interfacial adhesive force between the A layer and the B layer, and the 180 degree peel test is a method for evaluating the adhesive force inside the B layer. In particular, when a laminated porous film is used as a separator for a non-aqueous electrolyte secondary battery, the filler is firmly adhered to the film because there are a step of cutting the film according to the shape of the battery and a step of transporting the roll. It is important that the amount of powder fall is small.

(1) Thickness measurement (unit: μm):
The thickness of the laminated porous film was measured with a high-precision digital length measuring machine manufactured by Mitutoyo Corporation.
(2) Weight per unit (unit: g / m2):
The laminated porous film was cut into a 10 cm long side and the weight W (g) was measured. The weight per unit area (g / m 2) = W / (0.1 × 0.1) was calculated. The basis weight of the heat resistant layer (B layer) was calculated by subtracting the basis weight of the base porous film (A layer) from the basis weight of the laminated porous film.
(3) Porosity:
The film was cut into a 10 cm long square, and weight: W (g) and thickness: D (cm) were measured. The weight of the material in the sample was calculated, the weight of each material: Wi (g) was divided by the true specific gravity, the volume of each material was calculated, and the porosity (volume%) was obtained from the following formula. The basis weight of each material was calculated from the amount and ratio used for film formation.
Porosity (volume%) = 100-[{(W1 / true specific gravity 1) + (W2 / true specific gravity 2) + .. + (Wn / true specific gravity n)} / (100 × D)] × 100
(4) Air permeability: Measured with a digital timer type Gurley type densometer manufactured by Toyo Seiki Seisakusho Co., Ltd. according to JIS P8117.
(5) T-type peel test In accordance with JIS standard K6854-3, a peeling rate was measured at 100 mm / min using a 3M Scotch clear tape as a peeling tape.
(6) 180 degree peel test Based on JIS standard K6854-2, the peeling rate was measured at 100 mm / min using the 3M company Scotch clear tape as a peeling tape.

<Substrate porous film (A layer)>
70% by weight of ultra high molecular weight polyethylene powder (340M, manufactured by Mitsui Chemicals), 30% by weight of polyethylene wax (FNP-0115, manufactured by Nippon Seiki Co., Ltd.) having a weight average molecular weight of 1000, and the ultra high molecular weight polyethylene and polyethylene wax Antioxidant (Irg1010, manufactured by Ciba Specialty Chemicals Co., Ltd.) 0.4% by weight, (P168, manufactured by Ciba Specialty Chemicals Co., Ltd.) 0.1% by weight, sodium stearate 1.3% by weight was added, and calcium carbonate having an average particle size of 0.1 μm (manufactured by Maruo Calcium Co., Ltd.) was added to 38% by volume with respect to the total volume. Thereafter, it was melt-kneaded with a biaxial kneader to obtain a polyolefin resin composition. The polyolefin resin composition was rolled with a pair of rolls having a surface temperature of 150 ° C. to produce a sheet. This sheet is immersed in an aqueous hydrochloric acid solution (hydrochloric acid 4 mol / L, nonionic surfactant 0.5% by weight) to remove calcium carbonate, and then stretched 6 times at 105 ° C. to make a polyethylene porous membrane A porous substrate film was obtained.
Film thickness: 17.7 μm
Basis weight: 6.8 g / m2
Air permeability: 83 seconds / 100cc

Example 1
(1) Production of coating solution The coating solution of Example 1 was prepared by the following procedure.
First, CMC (CMC-A) (Daiichi Kogyo Seiyaku Co., Ltd.) having a degree of etherification of 0.55 to 0.65 in a water-isopropyl alcohol (IPA) mixed solvent (water: IPA = 90: 10 (weight ratio)). Serogen 3H) and CMC having a degree of etherification of 1.15 to 1.45 (CMC-B) were dissolved at a weight ratio of (CMC-A) / (CMC-B) = 75/25 to give a CMC concentration of 0. A 70% by weight (vs. [CMC + solvent]) CMC solution was obtained.
Next, alumina (AKP-3000 manufactured by Sumitomo Chemical Co., Ltd.) was added so that the weight ratio was (CMC-A + CMC-B) / alumina = 3/100, and the mixture was stirred and mixed. Furthermore, a pressure of 60 MPa was applied to APV's gorin homogenizer (15MR-8TA type), and the mixture was passed through to disperse the filler. The operation of passing the liquid under pressure was carried out three times to prepare a coating liquid 1.
(2) Production and Evaluation of Laminated Porous Film B is a heat-resistant layer by applying and drying the above coating liquid 1 on a substrate porous film subjected to corona treatment at 50 W / (m 2 / min) with a bar coater. A layer was formed.
Table 2 shows the physical properties of the laminated porous film obtained by the above evaluation method.

Comparative Example 1
(1) Production of coating liquid A coating liquid 2 was obtained in the same manner as in the production of the (1) coating liquid in Example 1 except that CMC-A was used alone.
(2) Manufacture and Evaluation of Laminated Porous Film A laminated porous film was obtained in the same manner as in (2) Separation and evaluation of separator in Example 1, except that the coating liquid 2 was used as the coating liquid.
Table 2 shows the physical properties of the laminated porous film obtained by the above evaluation method.

Comparative Example 2
(1) Manufacture of coating liquid (CMC-A) / (CMC-B) = 50/50 Obtained.
(2) Production and Evaluation of Laminated Porous Film A laminated porous film was obtained in the same manner as in (2) Separation and evaluation of separator in Example 1, except that the coating liquid 3 was used as the coating liquid.
Table 2 shows the physical properties of the laminated porous film obtained by the above evaluation method.

Comparative Example 3
(1) Production of coating liquid (CMC-A) / (CMC-B) = 25/75 Except for setting to 25/75, the coating liquid 4 was prepared in the same manner as in (1) Production of the coating liquid. Obtained.
(2) Manufacture and Evaluation of Laminated Porous Film A laminated porous film was obtained in the same manner as in (2) Separation and evaluation of separator in Example 1, except that the coating liquid 4 was used as the coating liquid.
Table 2 shows the physical properties of the laminated porous film obtained by the above evaluation method.

Comparative Example 4
(1) Manufacture of coating liquid Coating liquid 5 was obtained in the same manner as in (1) Manufacturing of coating liquid in Example 1 except that CMC-B was used alone.
(2) Manufacture and Evaluation of Laminated Porous Film A laminated porous film was obtained in the same manner as in (2) Separation and evaluation of separator in Example 1 except that the coating liquid 5 was used as the coating liquid.
Table 2 shows the physical properties of the laminated porous film obtained by the above evaluation method.

Claims (8)

A coating liquid containing a filler, a medium, and the following binder resin.
Binder resin: 90% by weight or more of the total amount of binder resin is carboxymethyl cellulose (CMC),
The CMC has a degree of etherification = 0.5 to 0.7 (CMC-A) and a degree of etherification = 1.1 to 1.5 (CMC-B).
(CMC-A) / [(CMC-A) + (CMC-B)] = 0.6 to 0.9 (weight ratio)
It is a mixture satisfying the following formula.   The coating liquid according to claim 1, comprising 2 to 6 parts by weight of a binder resin with respect to 100 parts by weight of the filler.   The coating liquid according to claim 1, wherein the filler is an inorganic filler.   The coating liquid according to claim 1, wherein the inorganic filler is alumina.   The laminated porous film formed by laminating | stacking the component by which the medium was removed from the coating liquid in any one of Claims 1-4 on the single side | surface or both surfaces of a base material porous film.   The laminated porous film according to claim 5, wherein the substrate porous film is a porous film mainly composed of polyolefin.   After applying the coating liquid according to any one of claims 1 to 4 to one side or both sides of the substrate porous film, the medium is removed, and the layer containing the filler and the binder resin and the substrate porous For producing a laminated porous film comprising a porous film.   The method for producing a laminated porous film according to claim 7, wherein the substrate porous film is a porous film containing polyolefin as a main component.