KR20170041690A - Method for producing film and method for storing application liquid - Google Patents

Abstract

Provided are a method for producing a film and a method for storing a coating liquid, which can obtain a film in which defects due to coating unevenness do not occur in the film, and when the coating film is made into a porous film, a film having sufficient air permeability is maintained. The method for producing the film and the method for storing the coating liquid are such that the coating liquid comprising the aromatic polymer, the inorganic particles and the solvent is stirred at a peripheral speed of the stirring member of 0.05 m / sec to 2.0 m / sec.

Description

TECHNICAL FIELD [0001] The present invention relates to a method for producing a film,

The present invention relates to a method for producing a film and a method for storing a coating liquid.

BACKGROUND ART Non-aqueous electrolyte secondary batteries such as lithium secondary batteries are currently widely used as batteries for use in devices such as personal computers, cellular phones, and portable information terminals.

These nonaqueous electrolyte secondary batteries typified by lithium secondary batteries have high energy density. Therefore, when an internal short circuit or an external short-circuit occurs due to breakage of the battery or breakage of the device using the battery, a large current flows and the non-aqueous electrolyte secondary battery may generate heat. For this reason, it is required to secure high safety by preventing heat generation at a certain level or more in the nonaqueous electrolyte secondary battery.

As a method of securing the safety of the nonaqueous electrolyte secondary battery, a method of imparting a shutdown function to the nonaqueous electrolyte secondary battery is generally used. The shutdown function is a function to prevent the passage of ions between the positive electrode and the negative electrode by the separator when abnormal heat is generated in the non-aqueous electrolyte secondary battery, thereby preventing additional heat generation. In short, as a method of securing the safety of the nonaqueous electrolyte secondary battery, for example, when an abnormal current flows in the separator disposed between the positive electrode and the negative electrode in the battery due to an internal short circuit between the positive electrode and the negative electrode, A method of shutting off an electric current to block the flow of an excessive current in the battery and thereby giving a function of suppressing additional heat generation is generally applied. Here, when the use temperature of the non-aqueous electrolyte secondary battery exceeds the normal use temperature, the shutdown is performed by melting the separator by heat generated and consequently closing the pores formed in the separator. In addition, it is preferable that after the shutdown, the separator maintains the shutdown state without being destroyed by heat even when the battery temperature reaches a certain high temperature.

As the separator, a porous film mainly composed of polyolefin which is melted at, for example, about 80 to 180 DEG C when abnormal heat generation occurs is generally used. However, since the separator made of the porous film has insufficient shape stability at high temperature, the separator shrinks or rupture occurs in the separator while the shutdown function is being performed. As a result, even if the shutdown function is executed, there is a possibility that the positive electrode and the negative electrode come into direct contact with each other and cause an internal short circuit. That is, there is a possibility that the separator made of the porous film can not sufficiently suppress the abnormal heat generation due to the internal short circuit. Therefore, a separator capable of ensuring higher safety is required.

Thus, a method of imparting shape stability at a high temperature to a separator by laminating a heat-resistant porous layer made of a material having heat resistance to the porous film has been studied. As such a heat-resistant porous layer, for example, it has been proposed to use a wholly aromatic polyamide porous membrane (see, for example, Patent Documents 1 and 2). The wholly aromatic polyamide porous membrane may be obtained by, for example, forming a particulate membrane from a particulate-dispersed wholly aromatic polyamide solution comprising a wholly aromatic polyamide, an inert microparticle or a metal oxide microparticle, and a solvent, And dissolving away the fine particles.

Japanese Unexamined Patent Publication No. 2000-191823 (published on July 11, 2000) Japanese Unexamined Patent Publication No. 2001-98106 (published on April 10, 2001)

However, heretofore, in the method of forming the heat resistant porous layer by using the solution of the material constituting the heat resistant porous layer such as the wholly aromatic polyamide as the coating liquid, the obtained heat resistant porous layer may have unevenness in surface coverage, There may or may not be. Therefore, the performance of the heat-resistant porous layer was not sufficient.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method of producing a film which does not cause defects attributable to nonuniform coating on the film and maintains a sufficient air permeability when formed into a porous film, And to provide a storage method.

In order to solve the above problems, a method for producing a film according to the present invention is a method of stirring a coating liquid comprising a composition containing an aromatic polymer, inorganic particles and a solvent at a peripheral speed of 0.05 m / sec to 2.0 m / And a coating step of applying the coating liquid mixed in the stirring step to at least one side of the base material.

In the method for producing a film according to the present invention, it is preferable that the inorganic particles have an average particle size of 0.005 mu m to 2.5 mu m.

In the method for producing a film according to the present invention, it is preferable that the viscosity of the coating liquid mixed in the stirring step is 0.5 Pa · s to 20 Pa · s.

In the method for producing a film according to the present invention, it is preferable that the coating liquid contains inorganic particles having a specific surface area of 0.5 m 2 / g to 10 m 2 / g.

In order to solve the above problems, a method of storing a coating liquid according to the present invention is a method of storing a coating liquid comprising a composition containing an aromatic polymer, inorganic particles and a solvent at a peripheral speed of 0.05 m / sec to 2.0 m / sec And stirring the mixture.

As described above, the method for producing a film according to the present invention is a method of stirring a coating liquid comprising a composition containing an aromatic polymer, inorganic particles and a solvent at a peripheral speed of 0.05 m / sec to 2.0 m / sec of a stirring member And a coating step of applying the coating liquid mixed in the stirring step to at least one side of the base material. Therefore, it is possible to avoid the occurrence of defects caused by uneven coating on the obtained film. In addition, an effect that a film having sufficient air permeability can be produced is obtained.

The method of storing a coating liquid according to the present invention is a method of stirring a coating liquid comprising a composition containing an aromatic polymer, inorganic particles and a solvent at a peripheral speed of 0.05 m / sec to 2.0 m / sec of a stirring member, As shown in FIG. Therefore, it is possible to avoid the occurrence of defects attributable to coating nonuniformity in the film obtained from the coating liquid after storage. In addition, an effect that a film having sufficient air permeability can be produced is obtained.

Hereinafter, embodiments of the present invention will be described in detail. Unless otherwise specified in the present specification, "A to B" indicating numerical ranges means "A or more and B or less".

I. Manufacturing Method of Film

The inventors of the present invention have conducted intensive studies in view of the above problems and found that when a heat resistant porous layer is formed by using a solution of a material constituting a heat resistant porous layer as a coating liquid, By studying, we have found that the above problems can be solved.

That is, in many cases, a filler is added to a solution of an aromatic polymer as a material constituting the heat resistant porous layer. The inventors of the present invention have found that, when an inorganic particle is added as a filler, after preparing a coating liquid comprising a composition comprising an aromatic polymer, an inorganic particle and a solvent, the coating liquid is further added at a peripheral speed of 0.05 m / sec to 2.0 m / Lt; / RTI > The inventors of the present invention have thus found that a defect caused by nonuniform coating is not generated in the heat resistant porous layer obtained by applying the coating liquid after the stirring to the base material and that the sufficient air permeability is maintained.

That is, the method for producing a film according to the present invention comprises a stirring step of stirring a coating liquid comprising a composition containing an aromatic polymer, inorganic particles and a solvent at a peripheral speed of 0.05 m / sec to 2.0 m / sec of a stirring member, And a coating step of applying the coating liquid mixed in the stirring step to at least one side of the substrate.

I-1. Stirring process

In the present invention, in the stirring step, a coating liquid comprising a composition containing an aromatic polymer, inorganic particles and a solvent is stirred at a peripheral speed of 0.05 m / sec to 2.0 m / sec of a stirring member.

(Aromatic polymer)

The aromatic polymer used in the present invention is more preferably a nitrogen-containing aromatic polymer, and examples thereof include aromatic polyamides, aromatic polyimides, and aromatic polyamideimides. They are excellent in heat resistance and can be suitably used for a heat-resistant porous layer constituting a separator, particularly in the field of production of a nonaqueous electrolyte secondary battery. In this case, the nitrogen-containing aromatic polymer is more preferably an aromatic polyamide.

Specific examples of the aromatic polyamide include poly (paraphenylene terephthalamide), poly (metaphenylene isophthalamide), poly (parabenzamide), poly (methabenzamide), poly 4,4'-biphenylene dicarboxylic acid amide), poly (paraphenylene-4,4'-biphenylene dicarboxylic acid amide), poly (metaphenylene-4,4'-biphenylene dicarboxylic acid Amide), poly (paraphenylene-2,6-naphthalene dicarboxylic acid amide), poly (metaphenylene-2,6-naphthalene dicarboxylic acid amide), poly (2-chloroparaffene terephthalamide) , Paraphenylene terephthalamide / 2,6-dichloro-paraphenylene terephthalamide copolymer, and metaphenylene terephthalamide / 2,6-dichloropara phenylene terephthalamide copolymer. Of these, the aromatic polyamide is more preferably a para-aromatic polyamide because it has high heat resistance and tends to be porous. The aromatic polyamide may be a mixture of two or more of the aromatic polyamides exemplified above.

As the aromatic polyimide, a wholly aromatic polyimide prepared by condensation polymerization of an aromatic dianhydride and an aromatic diamine is more preferable. Specific examples of the aromatic acid dianhydride include pyromellitic dianhydride, 3,3 ', 4,4'-diphenylsulfone tetracarboxylic acid dianhydride, 3,3', 4,4'-benzophenonetetra Carboxylic acid dianhydride, 2,2'-bis (3,4-dicarboxyphenyl) hexafluoropropane, and 3,3 ', 4,4'-biphenyltetracarboxylic acid dianhydride. . Specific examples of the aromatic diamine include oxydianiline, paraphenylenediamine, benzophenonediamine, 3,3'-methylenedianiline, 3,3'-diaminobenzophenone, 3,3'-diaminodiphenyl Sulfone, and 1,5'-naphthalenediamine. As the aromatic polyimide, a polyimide soluble in a solvent may be more preferably used. Examples of such a polyimide include polyimide prepared by polycondensation of 3,3 ', 4,4'-diphenylsulfone tetracarboxylic acid dianhydride and aromatic diamine.

Examples of the aromatic polyamide imide include those obtained by polycondensing an aromatic dicarboxylic acid and an aromatic diisocyanate, and polycondensation products obtained by using an aromatic dianhydride and an aromatic diisocyanate. Specific examples of the aromatic dicarboxylic acid include isophthalic acid and terephthalic acid. Specific examples of the aromatic acid dianhydride include trimellitic anhydride and the like. Specific examples of the aromatic diisocyanate include 4,4'-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, orthotrimethylene diisocyanate, and m-xylene diisocyanate. .

The weight average molecular weight of the aromatic polymer is not particularly limited but is usually 5,000 or more, more preferably 8,000 or more, and usually 1,000,000 or less, and more preferably 500,000 or less.

(Inorganic particles)

As the inorganic particles, for example, particles made of an inorganic material such as a metal oxide, a metal nitride, a metal carbide, a metal hydroxide, a carbonate, and a sulfate can be preferably used. Of these, particles made of an inorganic material having low conductivity can be more preferably used as the inorganic particles. More specific examples of the inorganic particles include particles of, for example, alumina, silica, titanium dioxide, barium sulfate, zirconium oxide, calcium carbonate, and barium titanate. The inorganic particles may be used singly or in combination of two or more. By using the inorganic particles in the coating liquid, it becomes possible to precisely control the voids (porosity and pore size, etc.) in the resulting film. Among these inorganic particles, alumina is more preferably used alone or in combination with other inorganic particles in terms of chemical stability.

The average particle size of the inorganic particles is preferably 0.005 占 퐉 or more, more preferably 0.01 占 퐉 or more, and even more preferably 0.1 占 퐉 or more. The average particle size of the inorganic particles is preferably 2.5 占 퐉 or less, more preferably 2.0 占 퐉 or less, and even more preferably 1.5 占 퐉 or less.

Here, the average particle diameter of the inorganic particles refers to the average particle diameter (D ₅₀ ) of all the inorganic particles contained in the coating liquid supplied to the stirring step, and is a value measured by the method described in the examples. In order to enable precise control of the pores (porosity, pore size, etc.) in the resulting film, the average particle size of the inorganic particles is preferably 0.005 탆 or more. In addition, in order for the obtained film to be untreated and to have a smooth coated surface, it is preferable that the average particle diameter of the inorganic particles is 2.5 m or less.

The specific surface area of the inorganic particles is preferably 0.5 m 2 / g or more, more preferably 1 m 2 / g or more, and still more preferably 2 m 2 / g or more. The specific surface area of the inorganic particles is preferably 200 m 2 / g or less, more preferably 150 m 2 / g or less, and even more preferably 120 m 2 / g or less.

Here, the specific surface area of the inorganic particles refers to a value obtained by measurement by the BET method.

The coating liquid preferably contains inorganic particles having a specific surface area of 0.5 m 2 / g to 10 m 2 / g, more preferably inorganic particles having a specific surface area of 2 m 2 / g to 8 m 2 / g do. By including the inorganic particles having a specific surface area of 0.5 m 2 / g to 10 m 2 / g, precise control of the voids (porosity, pore size, etc.) in the resulting film becomes easier.

The proportion of the inorganic particles having a specific surface area of 0.5 m 2 / g to 10 m 2 / g contained in the coating liquid is preferably 10% by weight or more based on all the inorganic particles contained in the coating liquid, More preferably not less than 20% by weight, more preferably not less than 40% by weight, further preferably not more than 90% by weight, more preferably not more than 80% by weight, still more preferably not more than 60% by weight.

The shape of the inorganic particles is not particularly limited. Examples of the shape include a substantially spherical shape, a plate shape, a columnar shape, a needle shape, a whisker shape, and a fibrous shape. Among these, the shape of the inorganic particles is preferably spherical in view of easy formation of uniform holes.

Examples of the substantially spherical particles include particles having an aspect ratio (particle diameter / particle diameter) of not less than 1 and not more than 1.5. The aspect ratio of the particles can be measured by an electron microscope.

The amount of the inorganic particles to be used is preferably 1% by weight or more, more preferably 10% by weight or more, and even more preferably 100% by weight or more based on the weight of the aromatic polymer. The amount of the inorganic particles to be used is preferably 1500 wt% or less, more preferably 1000 wt% or less, and further preferably 500 wt% or less of the weight of the aromatic polymer. When the obtained film is used in a separator for a nonaqueous electrolyte secondary battery, the amount of the inorganic particles used is preferably 1% by weight or more based on the weight of the aromatic polymer, in order to sufficiently promote ion permeability and cell characteristics. When the amount of the inorganic particles used is 1500 wt% or less of the weight of the aromatic polymer, when the resulting film is used in a separator for a non-aqueous electrolyte secondary battery, the separator does not fall off, Do.

(menstruum)

The solvent is not particularly limited as long as it is a solvent capable of dissolving the aromatic polymer, and examples thereof include organic solvents. Among them, as the solvent, a polar organic solvent can be more preferably used from the viewpoint of solubility in an aromatic polymer.

The polar organic solvent includes, for example, a polar amide solvent, a polar urea solvent, and the like. More specifically, examples of the polar organic solvent include N, N'-dimethylformamide, N, N'-dimethylacetamide, N-methyl 2-pyrrolidone, tetramethylurea, dimethylsulfoxide, o-chlorophenol and the like. For example, when an aromatic polyamide is used as the aromatic polymer, it is preferable to use N, N'-dimethylformamide, N, N'-dimethylacetamide, N-methyl 2- pyrrolidone or tetramethylurea It is more preferable to use it.

The amount of the solvent, that is, the total concentration of the aromatic polymer and the inorganic particles in the coating liquid is preferably 1% by weight or more, more preferably 2% by weight or more, and more preferably 4% More preferable. The amount of the solvent used, that is, the total concentration of the aromatic polymer and the inorganic particles in the coating liquid is preferably 50 wt% or less, more preferably 40 wt% or less, and 30 wt% or less More preferable. In order to efficiently form a coating film, it is preferable that the total concentration of the aromatic polymer and the inorganic particles in the coating liquid is 1 wt% or more. In order to obtain a coating liquid having sufficient fluidity, it is preferable that the total concentration of the aromatic polymer and the inorganic particles in the coating liquid is 50% by weight or less.

(Other components)

In the present step, the coating liquid comprising the aromatic polymer, the inorganic particles, and the composition containing the solvent may be stirred. However, the composition may contain the aromatic polymer, the inorganic particles, and other components in addition to the solvent.

Examples of the other components include antioxidants, lubricants, anti-blocking agents, flame retardants and the like. The amount of the other components to be used may be within a range that does not impair the effect of the present invention.

(Production method of coating liquid)

The coating liquid can be obtained by blending the aromatic polymer, the inorganic particles, the solvent and, if necessary, the other components. Alternatively, the coating liquid may be obtained by appropriately adding the inorganic particles, the solvent and, if necessary, other components to the reaction mixture in which the aromatic polymer is synthesized.

(Stirring condition)

In this step, the coating liquid is stirred at a peripheral speed of 0.05 m / sec to 2.0 m / sec of the stirring member while maintaining the coating liquid at 40 ° C or lower.

The temperature at the time of stirring is more preferably 35 DEG C or lower, and further preferably 30 DEG C or lower. In order to suppress the Brownian motion of the inorganic particles and suppress the aggregation of the inorganic particles, the stirring temperature is preferably kept at 40 캜 or lower. The lower limit of the temperature at the time of stirring may be a temperature at which the solvent is liquid, and is preferably -20 ° C or higher.

The peripheral velocity of the stirring member at the time of stirring may be 0.05 m / sec or more, more preferably 0.1 m / sec or more. In addition, the peripheral velocity of the stirring member at the time of stirring may be 2.0 m / sec or less, more preferably 1.8 m / sec or less, and further preferably 1.5 m / sec or less. In order that the Brownian motion of the inorganic particles in the coating liquid is suppressed and the agglomeration of the inorganic particles is suppressed, it is preferable that the above-mentioned main speed is 0.05 m / sec or more. On the other hand, in order that the increase in the collision frequency of the inorganic particles by the shearing force is suppressed and the aggregation of the inorganic particles is suppressed, the peripheral velocity is preferably 2.0 m / sec or less. When aggregation of the inorganic particles proceeds, defects due to uneven application tend to occur in the film obtained from the coating liquid containing the aggregated inorganic particles.

In the present invention, the main circumference of the stirring member means a value represented by the following formula. In the following equation,? Represents a circumferential rate (= 3.14). When the stirring member is a stirring blade, the diameter of the following stirring member means a blade diameter. The diameter of the blade is twice the length of the blade to the tip of the blade.

(M / sec) = diameter of stirring member (m) 占 π × number of rotations (times / sec)

In the present step, the shape of the agitating member is not particularly limited, and it is considered that the effect of the present invention is obtained when the main component of the agitating member is within the above range. The stirring member is more preferably a stirring blade, and examples thereof include propeller blades, turbine blades, paddle blades, anchor blades, and full zone blades. The wing number of the stirring wing is not particularly limited, and is, for example, 2 to 10 wings. Further, a plurality of agitating members may be provided in the axial direction of the agitating shaft, or one agitating member may be provided.

Further, the size of the agitating member, more preferably the size of the agitating blade is not particularly limited, and the size according to the agitating tank can be selected. The size of the stirring blade is preferably 0.4 or more, more preferably 0.5 or more, and still more preferably 0.6 or more. The diameter of the dimple / landscaping is preferably 0.95 or less, more preferably 0.9 or less, and still more preferably 0.85 or less. Here, the landscape means the inside diameter of the stirring tank.

The blade sectional area / cross sectional area is preferably 0.005 or more, more preferably 0.010 or more, and further preferably 0.015 or more. The blade sectional area / cross sectional area is preferably 0.5 or less, more preferably 0.4 or less, and further preferably 0.3 or less. Here, the rough cross sectional area refers to the cross sectional area of the coating liquid in the stirring tank, and the blade cross sectional area refers to a value obtained by multiplying the square of the length from the wing post to the tip of the blade multiplied by the circumferential ratio.

The depth from the application liquid surface to the top of the stirring vane / depth of the coating liquid in the stirring tank is preferably 0.01 or more, more preferably 0.02 or more, and further preferably 0.04 or more. The depth from the coating liquid surface to the top of the stirring vane / depth of the coating liquid in the stirring tank is preferably 0.2 or less, more preferably 0.15 or less, and further preferably 0.10 or less.

The depth of the coating liquid in the height from the bottom of the stirring tank to the bottom of the stirring wing / stirring tank is preferably 0.01 or more, more preferably 0.02 or more, and further preferably 0.03 or more. The depth of the coating liquid in the height from the bottom of the stirring tank to the lower end of the stirring wing / stirring tank is preferably 0.7 or less, more preferably 0.5 or less, still more preferably 0.3 or less.

The stirring time in the present step is preferably 1 hour or more, more preferably 4 hours or more, and even more preferably 10 hours or more. The stirring time is preferably 100 hours or less, and more preferably 50 hours or less. In order for the appearance of the film obtained from the coating liquid mixed by the stirring step and the degree of air permeability when the coating film is made into a porous film, the stirring time is preferably within the above range.

In this step, it is preferable that the total stirring time is within the above range, but it may be continuously stirred for the above stirring time, or may be intermittently stirred so that the total stirring time falls within the above range.

In the case of intermittently stirring, the stirring time is preferably 1 hour or more, and more preferably 2 hours or more. The stirring time is preferably 10 hours or less, more preferably 7 hours or less. It is preferable that the time interval from the end of the stirring at any time to the start of the stirring at the time of intermittent stirring is 1 hour or more, more preferably 3 hours or more, and even more preferably 5 hours or more. It is preferable that the time interval between the completion of the stirring of one time and the start of the stirring of the next time is within 50 hours, more preferably within 40 hours, and further preferably within 30 hours. In addition, in the case of intermittent stirring, the number of stirring times is preferably two times or more. The number of times of stirring is preferably 20 or less, more preferably 10 or less, and particularly preferably 5 or less. Here, it is preferable that the time interval from the end of the stirring of one time to the start of the stirring of the next time is the time interval shown above. However, in order to further improve the appearance of the film obtained from the coating liquid mixed by the stirring process and the degree of air permeability when the coating film is made into a porous film, the time interval from the end of the first stirring to the start of the second stirring Is set to be shorter than the time interval from the end of the second or subsequent stirring to the start of stirring of the next stirring. In this case, the time interval from the end of the first stirring to the start of the second stirring is preferably 1 hour or more, more preferably 2 hours or more, and further preferably 3 hours or more. The time interval from the end of the first stirring to the start of the second stirring is preferably 20 hours or less, more preferably 15 hours or less, and even more preferably 10 hours or less. The time interval from the end of the second or subsequent stirring to the start of the stirring of the next stirring is as described above.

The agitation of the coating liquid in the stirring step is preferably started within 20 hours after preparation of the coating liquid, and more preferably within 2 to 15 hours after preparation of the coating liquid. In order to suppress agglomeration of the inorganic particles and further improve the appearance of the film obtained from the coating liquid mixed by the stirring step and the degree of air permeability when the coating film is made into a porous film, It is preferable to start within 20 hours after the preparation of the liquid.

The viscosity of the coating liquid mixed in the stirring step is not limited to this. However, from the viewpoint of suppressing the settling of the inorganic particles and further improving the coating property, the viscosity of the coating liquid is preferably 0.5 Pa · s to 20 Pa · s. By making the coating property better, the application speed of the coating liquid can be increased, and the occurrence of defects in the resulting porous film can be further suppressed. The viscosity of the coating liquid mixed in the stirring step is preferably 0.5 Pa s or more, more preferably 1 Pa s or more, and still more preferably 1.5 Pa s or more. The viscosity of the coating liquid mixed in the stirring step is preferably 20 Pa · s or less, more preferably 18 Pa · s or less, and further preferably 15 Pa · s or less. In the present invention, the viscosity refers to a value measured by the method described in the examples.

The average particle diameter of the inorganic particles in the coating liquid mixed in the stirring step is preferably 0.005 탆 or more, more preferably 0.01 탆 or more, and even more preferably 0.1 탆 or more. The average particle size of the inorganic particles is preferably 2.5 占 퐉 or less, more preferably 2.0 占 퐉 or less, and even more preferably 1.5 占 퐉 or less.

Here, the average particle size of the inorganic particles means the average particle size (D ₅₀ ) of all the inorganic particles contained in the coating liquid mixed in the stirring step, and refers to a value measured by the method described in the examples. In order to enable precise control of the pores (porosity, pore size, etc.) in the resulting film, the average particle size of the inorganic particles is preferably 0.005 탆 or more. In addition, in order for the obtained film to be untreated and to have a smooth coated surface, it is preferable that the average particle diameter of the inorganic particles is 2.5 m or less.

According to the present invention, the average particle size of the inorganic particles in the coating liquid mixed in the stirring step is preferably 50% to 200% of the average particle size of the inorganic particles in the coating liquid before being mixed in the stirring step, , More preferably 70% to 150%, further preferably 80% to 120%, particularly preferably 90% to 110%. On the other hand, when the prepared coating liquid is not subjected to the stirring treatment of the present step, the average particle size of the inorganic particles in the coating liquid becomes larger than the above range. It was also confirmed that once the average particle size of the inorganic particles exceeds the above range, the average particle size of the inorganic particles can not be reduced even when redispersed immediately before the application. By storing the prepared coating liquid in the above-described manner, aggregation of the inorganic particles is suppressed, and the appearance of the film obtained from the coating liquid mixed by the stirring step and the degree of permeability when the coated film is made into a porous film are further improved I think it can be done.

In addition, since the coating liquid mixed in the stirring step is excellent in storage stability, it can be preferably used also in the case where the coating liquid is supplied to the coating step after the day of the stirring step. From the viewpoint of storage stability, it is preferable that the period from the stirring to the use in the coating step is 2 days or less.

I-2. Coating process

In this step, the coating liquid mixed in the stirring step is applied to at least one side of the substrate.

For example, in this step, the coating liquid is applied to a substrate such as a base film, a steel belt, a roll, and a drum, and a coating film is obtained. As the base film, for example, polyethylene terephthalate, paper subjected to release treatment and the like can be given. The thickness of the base film may be appropriately selected depending on the application of the obtained film. For example, when the above-mentioned coating liquid is applied to at least one side of the base film and then peeled and used, the thickness of the base film is usually 50 to 200 mu m. The coating liquid may be applied on a steel belt having a mirror-finished corrosion resistance, or the coating liquid may be coated on a roll having a mirror-finished finish or on a drum. Examples of the application method of the coating liquid include a coating method such as a knife, a blade, a bar, a gravure, and a die. Among them, the application method of the coating liquid is preferably a coating method using a bar, a knife, or the like, because it is simple. The coating liquid may be applied two or more times.

Alternatively, the coating liquid may be applied to the porous substrate. The porous substrate may be in the form of a nonwoven fabric, a woven fabric, a woven fabric, a sheet or the like, but is not limited thereto.

The above-mentioned coating liquid may be applied to a substrate such as a base film, a steel belt, a roll, and a drum, and then the porous film may be contacted with the porous substrate. Alternatively, the porous substrate may be fixed to a substrate such as a base film, a steel belt, a roll, and a drum, and the coating liquid may be applied to the porous substrate.

The porous substrate may be made of any material capable of impregnating liquid, for example, a thermoplastic resin. In the present invention, when the laminated film obtained by applying the coating liquid to a porous substrate is used as a separator for a nonaqueous electrolyte secondary battery, the porous substrate is preferably a thermoplastic resin in order to impart a shutdown function to the separator . It is more preferable that such a thermoplastic resin is a thermoplastic resin that is softened at 80 to 180 占 폚 to occlude porous pores and does not dissolve in an electrolytic solution. Specific examples of the thermoplastic resin include polyolefins such as polyethylene, polypropylene, polybutene, and ethylene-propylene copolymer; And thermoplastic polyurethanes. From the viewpoint of softening at a lower temperature to cause shutdown, it is more preferable that the thermoplastic resin contains polyethylene. Specific examples of the polyethylene include low density polyethylene, high density polyethylene, polyethylene such as linear polyethylene, and ultra high molecular weight polyethylene having a molecular weight of 1,000,000 or more. In order to further increase the piercing strength of the porous substrate, it is preferable that the thermoplastic resin contains at least ultra high molecular weight polyethylene. In addition, the thermoplastic resin preferably contains a wax composed of a polyolefin having a low molecular weight (weight average molecular weight of 10,000 or less).

When the laminated film obtained by applying the coating liquid to the porous substrate is used as a separator for a nonaqueous electrolyte secondary battery, the thickness of the porous substrate is preferably 3 m or more, and more preferably 5 m or more. The thickness of the porous substrate is preferably 40 占 퐉 or less, and more preferably 30 占 퐉 or less. When the thickness of the substrate is 3 m or more, it can be preferably used as a shutdown layer of the separator. Further, when the thickness of the substrate is 40 m or less, a high electric capacity can be achieved.

When the laminated film obtained by applying the above coating liquid to the porous substrate is used as a separator for a non-aqueous electrolyte secondary battery, the permeability by the Gurley method of the above substrate is preferably 10 seconds / 100 cc or more, Is 30 seconds / 100 cc or more, and more preferably 50 seconds / 100 cc or more. The permeability of the base material according to the gelling method is preferably 300 seconds / 100 cc or less, and more preferably 250 seconds / 100 cc or less. In order to preferably maintain the electrolytic solution, it is preferable that the air permeability of the substrate is 300 sec / 100 cc or less. In order to secure the strength of the separator, the permeability of the substrate is preferably 10 seconds / 100 cc or more. Here, the term "specular shade" refers to a value measured by the method described in the embodiment.

When the laminated film obtained by applying the coating liquid to the porous substrate is used as a separator for a nonaqueous electrolyte secondary battery, the apparent weight of the substrate is preferably 2 g / m 2 or more, more preferably 2.5 g / m < 2 > or more, and more preferably 3 g / m < 2 > The apparent weight of the substrate is preferably 20 g / m 2 or less, more preferably 18 g / m 2 or less, and further preferably 15 g / m 2 or less. In order for the mechanical strength to be sufficiently high, the apparent weight of the substrate is preferably 2 g / m 2 or more. Further, in order for the battery to be lightweight, the apparent weight of the substrate is preferably 20 g / m 2 or less. Here, the apparent weight refers to a value calculated by the method described in the embodiment.

In this step, the coating liquid mixed in the stirring step may be applied to at least one side of the substrate. Therefore, depending on the application of the coating film, the coating liquid may be applied to one side of the substrate or both sides thereof.

The thickness of the coating film obtained in this step is not particularly limited, but it is in the range of 5 탆 to 500 탆.

I-3. Other processes

The method for producing a film according to the present invention may include at least the stirring step and the coating step. However, the method for producing a film according to the present invention may further comprise: an aromatic polymer synthesis step of producing the aromatic polymer, a coating liquid preparation step of preparing the coating liquid, and a step of forming a porous film from the coating film obtained in the coating step And at least one step selected in the porous film forming step.

(Aromatic Polymer Synthesis Process)

The aromatic polymer synthesizing step is a step of producing the aromatic polymer. In the present invention, the production method of the aromatic polymer is not particularly limited, and conventionally known methods can be appropriately used.

For example, when the aromatic polymer is an aromatic polyamide, the aromatic diamine and the compound having a hydrolyzable reactive group which forms a structure represented by -C (= O) NH- by reacting with an amino group are dissolved in an organic solvent , To thereby produce the aromatic polymer.

Examples of the aromatic diamine include oxydianiline, paraphenylenediamine, metaphenylenediamine, benzophenonediamine, 3,3'-methylenedianiline, 3,3'-diaminobenzophenone, and 3, 3'-diaminodiphenylsulfone, 1,5'-naphthalenediamine, and the like. Among them, the aromatic diamine is more preferably para-phenylenediamine. These aromatic diamines may be used singly or in combination of two or more.

Examples of the compound having a hydrolyzable reactive group (hereinafter referred to as a reactive group-containing compound) that forms a structure represented by -C (= O) NH- by reacting with the amino group include a compound having an aromatic acyl group. Specifically, examples of the reactive group-containing compound include a di (meth) acrylate which forms a urea bond (-NH-C (= O) NH-) by reacting with an aromatic acid dianhydride, an aromatic acid dihalide, Isocyanate.

Specific examples of the aromatic acid dianhydride include pyromellitic acid dianhydride, 3,3 ', 4,4'-diphenylsulfone tetracarboxylic acid dianhydride, 3,3', 4,4 -Benzophenone tetracarboxylic acid dianhydride, 2,2'-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride, and 3,3 ', 4,4'-biphenyltetracarboxylic acid 2-anhydride and the like.

The aromatic acid dihalide is more preferably an aromatic acid dichloride. Examples of the aromatic acid dichloride include phthalic acid dichloride, terephthalic acid dichloride, pyromellitic acid dichloride, 3,3 ', 4,4'-diphenylsulfone tetracarboxylic acid dichloride, 3,3' 4,4'-benzophenonetetracarboxylic acid dichloride, 2,2'-bis (3,4-dicarboxyphenyl) hexafluoropropane dichloride, 3,3 ', 4,4'-biphenyltetracarboxyl 1,2-phenylene dicarboxylic acid dichloride, 1,3-phenylene dicarboxylic acid dichloride, 1,4-phenylene dicarboxylic acid dichloride, 1,2-naphthylene dicarboxylic acid dichloride , 1,3-naphthylene dicarboxylic acid dichloride, 1,4-naphthylene dicarboxylic acid dichloride, 1,5-naphthylene dicarboxylic acid dichloride, 1,6-naphthylene dicarboxylic acid dichloride, 1 , 7-naphthylene dicarboxylic acid dichloride, 1,8-naphthylene dicarboxylic acid dichloride, 2,3-naphthylene dicarboxyl Naphthylene dicarboxylic acid dichloride, 3,3'-biphenylene dicarboxylic acid dichloride, 3,3'-benzophenone dicarboxylic acid dichloride, and 3,3'-diphenyl Sulfone dicarboxylic acid dichloride, and the like.

As the diisocyanate, an aromatic diisocyanate is more preferable. Examples of the aromatic diisocyanate include 1,2-phenylene diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 1,2-naphthylene diisocyanate, 1,3-naphthyl Naphthylene diisocyanate, 1,6-naphthylene diisocyanate, 1,7-naphthylene diisocyanate, 1,8-naphthylene diisocyanate, 1,2-naphthylene diisocyanate, Naphthylene diisocyanate, 3,3'-biphenylene diisocyanate, 3,3'-benzophenone diisocyanate, and 3,3'-diphenylsulfone diisocyanate, and the like. .

Among the above-exemplified compounds, the reactive group-containing compound is more preferably an aromatic acid 2 halide, more preferably terephthalic acid dichloride. These reactive group-containing compounds may be used alone or in combination of two or more.

The aromatic polymer is obtained, for example, by reacting (polymerizing) the aromatic diamine and the reactive group-containing compound in an organic solvent in which a chloride of an alkali metal or an alkaline earth metal is dissolved at a reaction temperature of -20 ° C to 50 ° C have. The molar ratio of the aromatic diamine and the reactive group-containing compound (aromatic diamine / reactive group-containing compound) is preferably 1.0 to 1.1. The concentration of the chloride dissolved in the organic solvent is preferably 2 wt% to 10 wt%.

Examples of the chloride include chlorides of alkali metals such as sodium chloride and potassium chloride, and chlorides of alkaline earth metals such as magnesium chloride and calcium chloride. Of these, calcium chloride is more preferable. These chlorides may be used alone or in combination of two or more.

By adjusting the molar ratio of the aromatic diamine to the reactive group-containing compound (aromatic diamine / reactive group-containing compound) within the above range and further adjusting the reaction temperature within the above range, the concentration of the chloride dissolved in the organic solvent By adjusting to the above-mentioned range, an aromatic polymer having a degree of polymerization sufficient for forming the heat resistant porous layer can be obtained.

Examples of the organic solvent include aprotic polar solvents. Specific examples of the aprotic polar solvent include lower alcohols such as methyl alcohol, ethyl alcohol and isopropyl alcohol, aliphatic alcohols such as hexane, acetone, toluene, xylene, N-methyl- , N, N-dimethylacetamide, and N, N-dimethylformamide. Among them, the aprotic polar solvent is more preferably N-methyl-2-pyrrolidone. These organic solvents may be used alone or in combination of two or more.

The amount of the organic solvent to be added to the total amount of the aromatic diamine and the reactive group-containing compound is such that the total concentration (concentration of the starting material) of the aromatic diamine and the reactive group-containing compound at the start of the reaction in the organic solvent is 1 wt% By weight.

(Coating liquid preparation step)

The coating liquid preparing step is a step of preparing a coating liquid containing the aromatic polymer, the inorganic particles, the solvent and, if necessary, the other components.

In the present step, the aromatic polymer, the inorganic particles, the solvent and, if necessary, the other components are blended, mixed and dispersed. Alternatively, in the present step, the inorganic particles, the solvent and, if necessary, other components are added to the reaction mixture in which the aromatic polymer is synthesized.

The coating liquid in which the inorganic particles are dispersed may be filtered using a filter such as a wire mesh to remove the polymer gel and the coarse inorganic particles.

(Porous film forming step)

The porous film forming step is a step of forming a porous film from the coating film obtained in the coating step and includes, for example, the following steps (1a) and (2a) in this order.

(1a) A step of precipitating an aromatic polymer in the coating film to obtain an precipitated film.

(2a) a step of removing the solvent in the deposited film to obtain a porous film.

In step (1a), the aromatic polymer in the coating film obtained in the coating step is precipitated to obtain a precipitated film. Here, the precipitation can be carried out, for example, by placing a coating film in an atmosphere whose humidity is controlled at a temperature of 20 占 폚 or more to deposit an aromatic polymer, and immersing the coating film in the coagulating solution to obtain a precipitation film. Alternatively, the coating film may be immersed in the coagulating solution, and the precipitation and coagulation of the aromatic polymer may be performed at the same time to obtain a precipitated film. Further, in order to uniformly and quickly carry out precipitation, a poor solvent such as water may be added to the coating liquid in advance. As the coagulating solution, an aqueous solution or an alcohol-based solution may be used.

In the step (1a), by evaporating part or all of the solvent in the coating film, the nitrogen-containing aromatic polymer can be precipitated to obtain an precipitated film. In this case, a semi-dried or dried precipitated film is obtained.

In the step (2a), the solvent is removed from the precipitation film to obtain a porous film. The solvent may be removed by evaporating part or all of the solvent, or may be washed and removed with a solvent capable of dissolving the solvent in the coating liquid such as water, an aqueous solution or an alcohol-based solution. In the case of using water for removal, it is preferable to use ion-exchanged water in order to suppress incorporation of metal ions. It is also preferable that the solvent in the coating liquid is washed in an aqueous solution containing a certain concentration and then further washed with water. The dissolution aid may be washed and removed with water, an aqueous solution, an alcohol-based solution, or the like. In the case of using water for removal, it is preferable to use ion-exchanged water in order to suppress incorporation of metal ions.

In the step (2a), the obtained porous film may be dried by heating, drying, air drying or the like if necessary.

In the step (2a), the porous film may be peeled from the base material. Alternatively, a laminated film having a porous film formed on a substrate may be obtained without peeling the porous film from the substrate.

Since the porous film obtained in the present invention contains an aromatic polymer, it is a film having almost no deterioration in strength up to about 200 캜, maintaining its shape up to about 300 캜, and having excellent heat resistance. Therefore, the porous film obtained in the present invention can be used particularly preferably for a separator for a nonaqueous electrolyte secondary battery, and can be sufficiently used for a water-based electrolyte secondary battery, a nonaqueous electrolyte primary battery, and a separator for a capacitor.

When the porous film is used as a heat-resistant porous layer in a separator such as a battery, it is preferable to form a laminated film having the porous film formed on a porous substrate that can be used as a shutdown layer. Thus, the laminated film can be directly used as a battery separator comprising a shutdown layer and a heat resistant porous layer. Alternatively, the separator for a battery comprising the shutdown layer and the heat resistant porous layer can be manufactured by joining the porous film obtained by peeling from the base material to the shutdown layer by an adhesive, heat melting or the like.

When the laminated film obtained in the present invention is used as a separator for a battery, it is preferable that the separator for a battery has an air permeability of 20 sec / 100 cc or more, preferably 50 Sec / 100 cc or more. The permeability by the Gulley method is preferably 2000 sec / 100 cc or less, more preferably 300 sec / 100 cc or less, and further preferably 200 sec / 100 cc or less. The apparent weight of the separator is preferably 3 g / m 2 or more. The apparent weight of the separator is preferably 100 g / m 2 or less, more preferably 50 g / m 2 or less, and still more preferably 30 g / m 2 or less. The thickness of the separator is preferably as thin as possible so long as the effect on safety as a separator is maintained in that the volume energy density of the battery or the like is increased and the internal resistance is reduced. Therefore, the upper limit of the thickness of the separator is preferably 200 占 퐉 or less, more preferably 40 占 퐉 or less, and still more preferably 30 占 퐉 or less. The lower limit of the thickness of the separator is preferably 5 占 퐉 or more.

In the method for producing a film of the present invention, the laminated film obtained by applying the coating liquid to at least one side of the porous substrate is preferably such that the increase in air permeability due to lamination is less than the apparent weight of the laminated film It is preferably not more than 35 seconds / 100 cc per 1 g / m < 2 > of the weight increase, more preferably not more than 30 seconds / 100 cc.

II. How to store coating liquid

In the method for producing a film according to the present invention, after the coating liquid is prepared, the coating liquid is mixed by the stirring step. It is also possible to obtain a film obtained from the coating liquid mixed by the stirring step without causing defects attributable to nonuniform coating and maintaining a sufficient degree of air permeability when the coating film is made into a porous film.

The constitution of mixing the coating liquid by the stirring step may be referred to as a method of storing the coating liquid. Therefore, the present invention also includes a method of storing the coating liquid.

That is, a method of preserving a coating liquid according to the present invention is a method of preserving a coating liquid comprising stirring the coating liquid comprising the aromatic polymer, the inorganic particles, and the solvent at a peripheral speed of the stirring member of 0.05 m / sec to 2.0 m / sec will be.

Here, the specific storage method such as the coating liquid and the stirring conditions is the same as described in the above "stirring step".

The present invention is not limited to the above-described embodiments, but various modifications may be made within the scope of the claims, and embodiments obtained by appropriately combining the technical means disclosed in the different embodiments may be also included in the technical scope of the present invention . Further, by combining the technical means disclosed in each embodiment, a new technical characteristic can be formed.

Example

Hereinafter, the present invention will be described in more detail by way of examples and comparative examples, but the present invention is not limited to the examples. Hereinafter, for convenience, " liter " is simply referred to as " l ".

Measurement methods and evaluation methods in the examples and comparative examples are shown below. Unless otherwise stated, the following measurement method and evaluation method were carried out under the conditions of a temperature of 25 캜 and a humidity of 50 RH%.

(a) Appearance of coating liquid

The appearance of the coating liquid was visually confirmed.

(b) Average particle size (D ₅₀ )

0.2 g of the coating liquid supplied to the stirring step and the coating liquid (after storage) after the stirring step was diluted with a solvent used in the coating liquid so that the total amount became 50 g to obtain a diluted liquid. 10 ml of the solvent and 2 ml of the dilution were added to the measurement cell and the average particle size (D ₅₀ ) was measured using a laser diffraction particle size distribution meter (SALD-2200 manufactured by Shimadzu Corporation).

(c) Viscosity of the coating liquid

The coating liquid was measured with an M3 rotor at 12 rpm and 24 DEG C using a B-type viscometer (VISCOMETER TVB-10, manufactured by TOKI SANGYO CO., LTD.).

(d) Appearance of coated surface

The coated surface was visually observed.

(e) Measurement of air permeability by gully method

The air permeability of the porous film, the laminated film, and the porous substrate was measured by a Juli type densometer manufactured by Toyo Precision Machinery Co., Ltd. based on JIS P8117.

(f) Apparent weight

A sample of the porous film, the laminated film, and the porous substrate was cut into a square having a length of 8 cm on one side, and the weight (g) was measured. The apparent weight was calculated by the following formula.

Apparent weight (g / m 2) = Weight (g) / (0.08 (m) x 0.08 (m))

[Preparation Example 1: Preparation of aromatic polymer]

As the aromatic polymer, poly (paraphenylene terephthalamide) (hereinafter abbreviated as PPTA) was prepared by the following method.

A 3 L separable flask having a stirrer, a thermometer, a nitrogen inlet tube and a powder stirrer was used. After sufficiently drying the inside of the flask, 2200 g of N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) was placed in the flask, 158.37 g of calcium chloride (used for vacuum drying at 200 DEG C for 2 hours) And the temperature was raised to 100 DEG C to completely dissolve the calcium chloride. Thereafter, the temperature of the obtained solution was returned to room temperature (25 캜).

Subsequently, 70.136 g of paraphenylenediamine (hereinafter abbreviated as PPD) was added to this solution and completely dissolved. 128.05 g of terephthalic acid dichloride (hereinafter abbreviated as TPC) was added with stirring while maintaining the temperature of the solution at 20 占 占 폚. The TPC was added in three portions at intervals of about 10 minutes. After completion of the addition of TPC, the reaction of PPD and TPC was aged for 1 hour with stirring while maintaining the temperature of the solution at 20 占 占 폚. As a result, a PPTA solution was obtained. The obtained PPTA exhibited optical anisotropy. When the weight of the aromatic polymer, the calcium chloride and the solvent in the obtained PPTA solution was taken as 100, the weight of the aromatic polymer was 6.0.

[Example 1]

(Preparation of Coating Solution)

The PPTA solution obtained in Production Example 1 was weighed in a weight of 100 g into a 500 ml separable flask having a stirrer, a thermometer, a nitrogen inlet tube and a liquid feedstock. 300 g of NMP and 6 g of alumina filler A (alumina C manufactured by Nippon Aerosil Co., average particle diameter 0.013 占 퐉, specific surface area 100 m2 / g) and 6 g of alumina filler B ( Manufactured by Sumitomo Chemical Co., Ltd., AA03, average particle diameter 0.3 mu m, specific surface area 5.0 m < 2 > / g). The composition after the addition was stirred for 10 minutes and filtered through a wire mesh of 1000 mesh to obtain a coating liquid 1. The average particle size (D ₅₀ ) of the inorganic particles of the coating liquid 1 was 0.76 μm and the viscosity of the coating liquid 1 was 3.2 Pa · s.

(2. Storage of Coating Solution)

The coating liquid 1 was weighed in an amount of 300 g to a separable flask equipped with a 0.5 L estrogen cock in 10 minutes from the end of the stirring. Thereafter, the entire separable flask was immersed in a thermostatic chamber set at 20 DEG C, and stored for 72 hours at the end of the stirring. During the storage period, the coating liquid 1 was intermittently stirred three times in total at a peripheral speed of 0.5 m / s using a full zone blade having a blade diameter of 0.65. Specifically, the coating liquid 1 was stirred for 4 hours (4 hours × 3 times = 12 hours in total) for 6 hours, 30 hours, and 54 hours from the end of the stirring, respectively. The depth of the coating liquid in the mixing tank from the surface of the coating liquid to the top of the stirring blade / depth of the coating liquid in the stirring tank was 0.08, and the height from the bottom of the stirring tank to the bottom of the stirring blade / depth of the coating liquid in the stirring tank 0.03.

The coating liquid 1 after 72 hours of storage was a uniform liquid in which the inorganic particles were not precipitated. The coating liquid 1 after 72 hours of storage was taken out from the mouth of the separable flask, and the average particle diameter and the viscosity thereof were measured. The average particle size (D ₅₀ ) of the inorganic particles of the coating liquid 1 was 0.78 μm and the viscosity of the coating liquid 1 was 3.0 Pa · s.

(3. Production of porous film)

The coating liquid 1 taken out from the mouth of the separable flask within 1 hour after 72 hours of storage was coated on the PET film with a bar coater PI-1210 manufactured by Tester Industry Co., Ltd., To form a coating film on the PET film. Thereafter, the formed coating film was left in air at 50 DEG C and a relative humidity of 70% for 1 minute to precipitate an aromatic polymer. The coating film on which the aromatic polymer was precipitated was immersed in the ion exchange water tank together with the base material, and the coating film was peeled from the PET film while immersed in the ion exchange water bath, and the ion exchange water was passed through the peeled coating film to remove calcium chloride and the solvent. Thereafter, the coating film from which the calcium chloride and the solvent were removed was dried in an oven at 120 DEG C for 60 minutes to obtain a porous film.

The coating film coated with the coating liquid 1 after being stored in the PET film for 72 hours was not uniform in coating. In addition, defects on the stripe caused by uneven application were not observed in the obtained porous film.

(4. Production of laminated film)

As the substrate, a porous substrate made of polyethylene was used. The porous substrate had a thickness of 25 占 퐉, an air permeability of 85 seconds / 100 cc, and an apparent weight of 12 g / m2. The porous substrate was fixed on a PET film having a thickness of 100 占 퐉. Thereafter, the coating liquid 1 taken out from the mouth of the separable flask was coated on the porous substrate by a bar coater PI-1210 manufactured by Tester Industries Co., Ltd. for one hour after the storage for 72 hours without agitation, To form a coating film. Thereafter, the formed coating film was left in air at 50 DEG C and a relative humidity of 70% for 1 minute to precipitate an aromatic polymer. The porous substrate on which the coating film was formed was peeled from the PET film while the coating film on which the aromatic polymer was precipitated was immersed in the ion-exchange water bath together with the base material and the PET film and immersed, and the porous substrate on which the peeled coating film was formed, , And the calcium chloride and the solvent were removed. Thereafter, the porous substrate on which the coating film was formed, from which calcium chloride and the solvent had been removed, was dried in an oven at 70 캜 for 10 minutes to obtain a laminated film.

The apparent weight of the obtained laminated film was 15 g / m 2, and the air permeability was 165 sec / 100 cc. The laminated film had an increase in apparent weight of 3 g / m 2, an increase in air permeability of 80 seconds / 100 cc, and an increase in air permeability per 1 g / m 2 of apparent weight as compared with the porous substrate before lamination was 27 seconds / 100 Respectively.

The coating film on which the coating liquid 1 was applied after being stored for 72 hours on the porous substrate was not uniform in coating. Also, in the obtained laminated film, defects on the stripe caused by uneven application were not observed.

[Example 2]

(Preparation of Coating Solution)

A coating liquid 2 was prepared in the same manner as in Example 1 (1. Preparation of coating liquid). The average particle diameter (D ₅₀ ) of the inorganic particles of the coating liquid 2 was 0.75 μm, and the viscosity of the coating liquid 2 was 3.3 Pa · s.

(2. Storage of Coating Solution)

The coating liquid 2 was stored in the same manner as in Example 1 (2. Storage of coating liquid) except that the stirring was performed at a peripheral speed of 1.0 m / s. The coating liquid 2 after 72 hours of storage was a uniform liquid in which the inorganic particles were not precipitated. After 72 hours of storage, the coating liquid 2 was taken out from the mouth of the separable flask, and the average particle diameter and the viscosity thereof were measured. The average particle size (D ₅₀ ) of the inorganic particles of the coating liquid 2 was 0.72 μm and the viscosity of the coating liquid 2 was 2.9 Pa · s.

(3. Production of laminated film)

A laminated film was obtained in the same manner as in Example 1 (4. Production of laminated film). In the same manner as in Example 1, the coating liquid 2 taken out from the mouth of the separable flask after storage on the porous substrate was applied as it was without stirring.

The apparent weight of the obtained laminated film was 16 g / m 2, and the air permeability was 175 sec / 100 cc. The laminated film had an increase in apparent weight of 4 g / m 2, an increase in air permeability of 90 seconds / 100 cc, and an increase in permeability per 1 g / m 2 of apparent weight, compared with that of the porous substrate before lamination, Respectively.

The coated film on which the coating liquid 2 was applied after being stored for 72 hours on the porous substrate was not observed to be uneven in coating. Also, in the obtained laminated film, defects on the stripe caused by uneven application were not observed.

[Comparative Example 1]

(Preparation of Coating Solution)

A coating liquid 3 was prepared in the same manner as in Example 1 (1. Preparation of coating liquid). The average particle size (D ₅₀ ) of the inorganic particles of the coating liquid 3 was 0.77 μm and the viscosity of the coating liquid 3 was 3.5 Pa · s.

(2. Storage of Coating Solution)

During the storage period, the coating liquid 3 was stored in the same manner as in Example 1 (2. Storage of coating liquid) except that the coating liquid 3 was stirred at a peripheral speed of 2.5 m / s for 4 hours.

In the coating liquid 3 after 72 hours of storage, the settling of the inorganic particles was observed. After keeping for 72 hours, the coating liquid 3 was taken out from the mouth of the separable flask, and the average particle diameter and the viscosity thereof were measured. The average particle size (D ₅₀ ) of the inorganic particles of the coating liquid 3 was 3.54 탆, which was larger than before storage.

(3. Production of porous film)

A porous film was obtained in the same manner as in Example 1 (3. Production of porous film). In the same manner as in Example 1, the coating liquid 3 taken out from the mouth of the separable flask after storage on a PET film was applied as it was without stirring.

Coating unevenness was observed in the coating film coated with the coating liquid 3 after the PET film was stored for 72 hours. Also, in the obtained porous film, defects on the stripe caused by nonuniform coating were confirmed at the point where the film surface reached.

(4. Production of laminated film)

A laminated film was obtained in the same manner as in Example 1 (4. Production of laminated film). Further, in the same manner as in Example 1, the coating liquid 3 taken out from the mouth of the separable flask after storage on the porous substrate was applied as it was without stirring.

The obtained laminated film had an apparent weight of 16 g / m 2 and an air permeability of 230 sec / 100 cc. The laminated film had an apparent weight of 4 g / m < 2 >, an increase in air permeability of 145 sec / 100 cc and an air permeability of 38 sec / 100 cc per 1 g / m 2 of the apparent weight .

Coating unevenness was observed in the coating film on which the coating liquid 3 was applied after being stored for 72 hours on the porous substrate. Also, in the obtained porous film, defects on the stripe caused by nonuniform coating were confirmed at the point where the film surface reached.

[Comparative Example 2]

(Preparation of Coating Solution)

A coating liquid 4 was prepared in the same manner as in Example 1 (1. Preparation of coating liquid). The average particle size (D ₅₀ ) of the inorganic particles of the coating liquid 4 was 0.75 μm, and the viscosity of the coating liquid 4 was 3.3 Pa · s.

(2. Storage of Coating Solution)

The coating liquid 4 was weighed in an amount of 300 g in a 0.5 L separable flask 10 minutes after the end of the stirring as a starting point. Thereafter, the entire separable flask was stored in a thermostatic chamber set at 20 DEG C for one week. During the storage period, the coating liquid 4 was left stationary without stirring.

In the coating liquid 4 after storage, the settling of the inorganic particles was observed. The coating liquid 4 after storage was taken out from the mouth of the separable flask, and the average particle diameter and the viscosity thereof were measured. The average particle diameter (D ₅₀ ) of the inorganic particles of the coating liquid 4 was 2.84 탆, which was larger than that before storage.

(3. Production of porous film)

A porous film was obtained in the same manner as in Example 1 (3. Production of porous film). In the same manner as in Example 1, the coating liquid 4 taken out from the mouth of the separable flask after storage on a PET film was applied as it was without stirring.

The coating film on which the coating liquid 4 after the storage on the PET film was applied was found to have nonuniform coating. Also, in the obtained porous film, defects on the stripe caused by nonuniform coating were confirmed at the point where the film surface reached.

Industrial availability

The method for producing a film and the method for storing a coating liquid according to the present invention can be widely used in the field of manufacturing a nonaqueous electrolyte secondary battery which can secure high safety, for example.

Claims (5)

A stirring step of stirring a coating liquid comprising a composition containing an aromatic polymer, inorganic particles and a solvent at a peripheral speed of 0.05 m / sec to 2.0 m / sec of a stirring member,
And a coating step of applying the coating liquid mixed in the stirring step to at least one side of the base material. The method according to claim 1,
Wherein the inorganic particles have an average particle diameter of from 0.05 mu m to 2.5 mu m. 3. The method according to claim 1 or 2,
Wherein the viscosity of the coating liquid mixed in the stirring step is from 0.5 Pa s to 20 Pa s. 4. The method according to any one of claims 1 to 3,
Wherein the coating liquid contains inorganic particles having a specific surface area of 0.5 m 2 / g to 10 m 2 / g. Wherein the coating liquid containing the aromatic polymer, the inorganic particles and the solvent is stirred at a peripheral speed of the stirring member of 0.05 m / sec to 2.0 m / sec.