KR20160143665A - Laminated porous film and production method therefor - Google Patents

Abstract

Heat-resistant laminated porous film which is not deteriorated in battery characteristics when used as a separator for a lithium secondary battery. The present invention relates to a laminated porous film having a porous layer comprising an imide polymer on one side or both sides of a porous layer made of polyolefin and having the following characteristics: 1) air permeability is JIS 10 seconds / 100 cc or more and 1000 seconds / 100 cc or less based on the standard P8117; 2) the alcoholic solvent does not remain in the porous layer made of the imide polymer; 3) The thickness of the porous layer made of the imide-based polymer is 1 μm or more and 20 μm or less.

Description

TECHNICAL FIELD [0001] The present invention relates to a laminated porous film,

The present invention relates to a laminated porous film and a method for producing the same. The laminated porous film can be suitably used as a separator for a power storage device, such as a separator for a lithium secondary battery.

BACKGROUND ART Lithium secondary batteries are widely used as batteries for use in electronic devices such as electric vehicles, personal computers, mobile phones and the like because of their high energy density.

When an internal short circuit or an external short circuit occurs due to a breakdown of the battery or the like, the lithium secondary battery may overheat due to a large current flow. Therefore, it is important to prevent the heat generation of the lithium secondary battery to a certain level or more, and to secure high safety. As a safety securing means, there has been widely put to practical use a method of providing a separator with a shutdown function for preventing the passage of ions between electrodes during heat generation to prevent heat generation.

As the separator having the shutdown function, for example, a porous film made of polyolefin is used. The separator made of this porous film can shut off the passage of ions because the polyolefin is melted and becomes non-porous at 110 to 160 캜 when the battery generates abnormal heat. However, the separator made of polyolefin tends to cause shrinkage or breakage at a high temperature, so that in some cases, the positive electrode and the negative electrode may be in direct contact with each other to cause a short circuit, and if abnormal heat generation due to short- .

As a method for solving such a problem, a porous layer made of a fluororesin such as polyvinylidene fluoride is laminated on one surface or both surfaces (hereinafter sometimes abbreviated as " surface ") of the porous film layer made of polyolefin A method of securing the shape stability at a high temperature has been proposed. Since the laminated separator has low heat resistance of the fluororesin itself constituting the heat resistant layer, the shape stability due to shrinkage at high temperature is not necessarily sufficient (for example, Patent Documents 1 and 2). Thus, a method of securing the shape stability at a high temperature by laminating a porous layer made of a heat-resistant resin such as polyimide or aramid on the porous film layer made of the polyolefin has been proposed.

As a method for forming the heat resistant porous layer, a solution containing a heat resistant resin (for example, an aramid resin) and a positive solvent thereof (for example, an amide solvent) or a poor solvent (for example, an alcohol solvent) A method has been proposed in which the surface of the film layer is coated and then dipped in a coagulating bath composed of a poor solvent of the heat resistant resin (for example, an alcohol solvent or water) to induce phase separation to make the film porous For example, Patent Documents 3 to 6).

However, in the laminated porous film obtained as described above, a slight amount of the alcohol-based solvent contained in the heat-resistant resin or the alcohol-based solvent used for causing phase separation remained in the heat-resistant porous layer formed. The proton of the hydroxyl group of the alcoholic solvent is chemically active. Therefore, when such a porous film is used in the above-mentioned lithium secondary battery separator and the like, a small amount of residual alcoholic solvent is eluted into the electrolyte of the lithium secondary battery and is usually used as LiPF ₆ used as an electrolyte Fluoroborate such as LiBF ₄ , fluorobisosalt such as LiAsF _6, and the like. That is, when these electrolytes are reacted with an alcohol-based solvent having an active proton, they decompose to generate hydrogen fluoride, which may deteriorate battery characteristics (for example, Patent Documents 7 and 8 and cited documents thereof). In addition, in the above-described production method, there is a problem from the viewpoint of environmental suitability because a large amount of a waste solution containing a good solvent and a poor solvent is generated from a coagulating bath used for phase separation.

Japanese Patent No. 4127989 Japanese Patent No. 4588286 Japanese Patent Laid-Open No. 2002-355938 Japanese Patent Application Laid-Open No. 2005-209570 Japanese Patent Application Laid-Open No. 2006-32246 Japanese Patent Application Laid-Open No. 2010-50024 Japanese Patent Laid-Open No. 2002-75440 Japanese Patent Application Laid-Open No. 2005-243458

Therefore, an object of the present invention is to provide a heat-resistant laminated porous film which, when used as a separator for a lithium secondary battery, does not deteriorate battery characteristics. Another object of the present invention is to provide a method for producing a laminated porous film having good environmental compatibility.

Means for Solving the Problems The present inventors have intensively studied in order to solve the above problems and found that a laminated film in which a porous layer made of an imide polymer is formed on the surface of a porous layer made of polyolefin is formed, And reached the present invention.

That is, the present invention has the following points.

≪ 1 > A laminated porous film having a porous layer made of imide-based polymer formed on the surface of a porous layer made of polyolefin, characterized by having the following characteristics:

1) The air permeability is 10 seconds / 100 cc or more and 1000 seconds / 100 cc or less as a gully value based on JIS P8117;

2) the alcoholic solvent does not remain in the porous layer made of the imide polymer;

3) The thickness of the porous layer made of the imide-based polymer is 1 μm or more and 20 μm or less.

&Lt; 2 > A separator for a lithium secondary battery, comprising the laminated porous film according to < 1 >.

&Lt; 3 > A coating film is formed by coating a surface of a porous layer made of polyolefin with a coating solution comprising an imide-based polymer, a mixed solvent containing an amide-based solvent and an ether-based solvent to form a coating film, Wherein a porous layer made of a polyolefin and a porous layer made of an imide polymer are laminated and integrated by forming a porous layer by causing phase separation in the coating film.

The laminated porous film of the present invention in which the porous layer made of the imide polymer having excellent heat resistance is laminated on the surface of the porous layer made of polyolefin has a good permeability and the porous layer made of imide- The film can be suitably used as a separator for a lithium secondary battery.

Further, according to the production process of the present invention, a laminated porous film can be obtained by a simple operation of removing the solvent by heating.

Hereinafter, the present invention will be described in detail.

In the laminated porous film of the present invention, a porous layer made of imide-based polymer is formed on the surface of the porous layer made of polyolefin. This laminated porous film is obtained by applying a coating liquid containing an imide-based polymer to the surface of a porous layer made of polyolefin (hereinafter sometimes abbreviated as &quot; S layer &quot;) to form a coating film, The solvent in the coating film is removed by heating to obtain a porous layer (hereinafter may be abbreviated as "P layer" hereinafter) comprising an imide polymer, which is laminated and integrated with the S layer.

The S layer is a porous film made of polyolefin having a structure having pores connected to the inside thereof and capable of allowing gas or liquid to permeate from one side to the other side, and is a base material of the laminated porous film of the present invention.

The proportion of the polyolefin component in the S layer is preferably 90% by volume or more, and more preferably 95% by volume or more. Examples of polyolefins include homopolymers or copolymers obtained by polymerizing olefins such as ethylene, propylene, 1-butene, 4-methyl-1-pentene and 1-hexene. Of these, polyethylene obtained by homopolymerizing ethylene is preferable, and high molecular weight polyethylene having a weight average molecular weight of 1 million or more is more preferable. Polypropylene obtained by homopolymerizing propylene is also preferable as the polyolefin.

The air permeability of the S layer is preferably set to 10 seconds / 100 cc or more and 500 seconds / 100 cc or less, preferably 100 seconds / 100 cc or more and 300 seconds / 100 cc or less, in terms of the gully value (JIS standard P8117). By setting the air permeability of the S layer in this manner, it is possible to ensure adequate air permeability as a separator for a lithium secondary battery when the P layers are laminated. The porosity of the S layer is preferably 20 to 80% by volume, more preferably 30 to 75% by volume from the viewpoint of securing the shutdown function while increasing the amount of electrolyte retained.

The pore size of the S layer is preferably not more than 3 mu m, more preferably not more than 1 mu m, from the viewpoint of obtaining sufficient air permeability when the laminated porous film is used as a separator for a lithium secondary battery and also preventing mixing of particles into the positive electrode and the negative electrode. desirable. The thickness of the S layer is preferably 8 to 50 mu m, more preferably 10 to 30 mu m, from the viewpoint of ensuring insulation by shutdown. Here, the thickness of the S layer is the thickness of the S layer as the material of the laminated porous film, and is measured based on JIS standard (K7130-1992).

The S layer is not particularly limited as far as the polyolefin is the main component, and may be a single layer structure composed of only one layer or a multi-layer structure composed of two or more layers. As the multilayer structure, for example, a structure in which a polyolefin layer made of another polyolefin is laminated on at least one surface of a polyolefin layer made of a certain polyolefin can be given. Among them, a structure (polypropylene layer / polyethylene layer / polypropylene layer) in which a polypropylene layer containing polypropylene as a main component is laminated on both sides of a polyethylene layer containing polyethylene as a main component is preferable.

As the porous film made of the polyolefin used for the S layer, a commercially available product can be used. Examples of commercially available products include porous polyethylene-made films of SK Corporation and Celgard, and polypropylene porous films of Celgard Corporation. These commercially available porous films have a shutdown function with a thickness of 9 to 25 mu m.

The imide polymer forming the P layer is a polymer having an imide bond in its main chain or a precursor thereof. Representative examples of the polymer having imide bond in the main chain include polyimide, polyamideimide, polyesterimide, and the like, but are not limited thereto.

Of the imide-based polymers, for example, polyimide or polyamideimide and mixtures thereof can be preferably used. As the polyimide, soluble polyimide (polyimide soluble in a solvent) can be preferably used. Of these imide-based polymers, aromatic polyimides and aromatic polyamideimides having excellent mechanical properties and heat resistance are preferable. The aromatic polyimide and aromatic polyamide imide may be thermoplastic or non-thermoplastic. The glass transition temperature of these imide-based polymers is preferably 200 ° C or higher, and more preferably 220 ° C or higher. By doing so, it is possible to ensure good heat resistance of the laminated porous film. Here, the glass transition temperature (Tg) can be confirmed by DSC (differential thermal analysis).

The laminated porous film of the present invention can be produced, for example, by the following method. That is, a mixed solvent comprising an amide type solvent (good solvent) for dissolving the imide polymer and an ether type solvent (poor solvent) not dissolving the imide type polymer solution is used when the imide type polymer solution is prepared using a solvent. Here, the positive solvent refers to a solvent which exhibits a solubility of 1% by mass or more at 25 占 폚 with respect to the imide-based polymer. Also, the poor solvent means a solvent having a solubility in an imide-based polymer of less than 1% by mass. A laminated porous film can be easily obtained by applying a solution prepared by dissolving an imide polymer in this mixed solvent (hereinafter sometimes abbreviated as &quot; imide-based coating solution &quot;) onto the surface of the S layer and drying.

The mixed solvent of the imide-based coating liquid may contain other solvent within the range not to impair the effect of the present invention.

By using such a mixed solvent, a coating film containing no alcoholic solvent can be obtained. Therefore, the alcoholic solvent does not remain in the porous layer obtained by drying the coating film.

When this imide based coating liquid is applied to the surface of the S layer and then the solvent in the coating film is removed by heating, phase separation occurs due to the action of an ether-based solvent (poor solvent) coexisting in the coating film, A porous film in which the P layer is laminated and integrated on the S layer can be obtained. Here, the temperature at which the solvent is removed by heating is preferably 100 to 150 占 폚. In drying, it is preferable to carry out drying in a non-wetted nitrogen gas or an air stream. By doing so, mixing of moisture into the coating film can be prevented. On the other hand, since the ether-based solvent does not contain chemically active proton, there is no problem even if a small amount of the ether-based solvent remains in the coated film after drying.

Examples of the amide solvent include N-methyl-2-pyrrolidone (NMP, boiling point: 202 ° C), N, N-dimethylformamide (boiling point: 153 ° C) Amide (DMAc, boiling point: 166 占 폚). These may be used alone, or two or more of them may be used in combination. Of these, NMP and DMAc are preferred.

The blending amount of the amide-based solvent is preferably 10% by mass or more, particularly preferably 10% to 70% by mass, more preferably 20% by mass to 40% by mass with respect to the total solvent amount from the viewpoint of dissolution of the imide polymer.

The ether-based solvent preferably has a boiling point higher than that of the amide-based solvent. The proportion thereof is preferably 5 ° C or higher, more preferably 20 ° C or higher, and still more preferably 50 ° C or higher. Specific examples thereof include diethylene glycol dimethyl ether (boiling point: 162 ° C), triethylene glycol dimethyl ether (TRGM, boiling point: 216 ° C), tetraethylene glycol dimethyl ether (TEGM, boiling point: 275 ° C) have. These may be used alone, or two or more of them may be used in combination. Of these, TEGM and TRGM are particularly preferable.

The blending amount of the ether-based solvent is preferably 30% by mass or more, particularly preferably 30% by mass to 90% by mass, more preferably 60% by mass to 80% by mass with respect to the total solvent amount from the viewpoint of air permeability.

Examples of the imide-based coating liquid include polyimide coatings such as U-imide varnish SP (polyimide varnish for porous formation) commercially available from UNITICA CO., LTD. And Uimide varnish IP (polyimide varnish for porous formation) Amide imide varnish) can be used.

The polyimide coating solution may be a commercially available product as described above. However, a solution prepared by dissolving a soluble polyimide powder obtained by mixing a raw material tetracarboxylic dianhydride component and a diamine component in approximately equimolar amounts and performing a polymerization reaction in the above mixed solvent Can also be used. This polymerization reaction is carried out by heating a polyamic acid (polyimide precursor) solution obtained by reacting a tetracarboxylic dianhydride component and a diamine component. At this time, it is preferable that water, which is a by-product when polyimide is produced from polyamic acid, is removed while being removed, for example, by azeotropy. For example, U.S. Patent No. 3422061, JP-A-58-49726, and the like can be referred to for details of a polymerization method of polyimide in which an imidization reaction is carried out while removing water.

The tetracarboxylic dianhydride component is preferably an aromatic tetracarboxylic acid dianhydride having an aromatic ring. Examples of the aromatic tetracarboxylic acid dianhydride component include pyromellitic acid, 3,3 ', 4,4'-biphenyltetracarboxylic acid (BPDA), 3,3', 4,4'-benzophenonetetracarboxylic acid, 3 , 3 ', 4,4'-diphenylsulfone tetracarboxylic acid, 3,3', 4,4'-diphenyl ether tetracarboxylic acid (ODPA), 2,3,3,4-benzophenonetetracarboxylic acid, 2,3 , 6,7-naphthalenetetracarboxylic acid, 1,4,5,7-naphthalenetetracarboxylic acid, 1,2,5,6-naphthalenetetracarboxylic acid, 3,3 ', 4,4'-diphenylmethane tetracarboxylic acid, (3,4-dicarboxyphenyl) propane, 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane, 3,4,9,10-tetracarboxyperylene, Bis [4- (3,4-dicarboxyphenoxy) phenyl] hexafluoropropane, 2,2-bis [4- (3,4-dicarboxyphenoxy) phenyl] propane and 2,2- Water is used. These may be used alone, or two or more of them may be used in combination. Of these, BPDA and ODPA are preferred.

The diamine component of the polyimide is preferably an aromatic diamine having an aromatic ring. Examples of the aromatic diamine component of the polyimide include p-phenylenediamine, m-phenylenediamine (MPD), 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl (DADE), 4,4'-diaminodiphenylmethane, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 2,2-bis [4- (Phenyl) propane (BAPP), 1,2-bis (anilino) ethane, diaminodiphenylsulfone, diaminobenzanilide, diaminobenzoate, diaminodiphenylsulfide, 2,2-bis bis (p-aminophenyl) hexafluoropropane, 1,5-diaminonaphthalene, diaminotoluene, diaminobenzotrifluoride, 1,4-bis aminophenoxy) benzene, 4,4'-bis (p-aminophenoxy) biphenyl, diaminoanthraquinone, 4,4'-bis - Bis (Anilino) Hexaflu (Anilino) pentafluorobutane, 1,5-bis (anilino) decafluoropentane, 1,7-bis (anilino) tetradecafluoroheptane, . These may be used alone, or two or more of them may be used in combination. Of these, DADE and BAPP are preferred.

The solid content concentration of the polyimide in the polyimide coating liquid is preferably from 1 to 50 mass%, more preferably from 5 to 25 mass%.

The polyimide contained in the polyimide coating liquid may be one in which the polyamic acid is partially imidized. The viscosity of the polyimide coating liquid at 30 캜 is preferably 1 to 150 Pa · s, more preferably 10 to 100 Pa · s.

In the present specification, a polyimide obtained by polymerization reaction of an aromatic tetracarboxylic acid dianhydride component and an aromatic diamine component as described above is referred to as &quot; aromatic polyimide &quot;.

As the polyamideimide coating solution, a commercially available product as described above may be used. However, the raw material tricarboxylic acid component (various tricarboxylic acids or anhydrides, acid chloride derivatives) and diamine components (various diamines or diisocyanate derivatives) Is mixed in approximately equimolar amounts, and a solution obtained by dissolving polyamideimide powder obtained by polymerization reaction in the above-mentioned mixed solvent may be used. As the polymerization method of the polyamideimide, an isocyanate method using anhydrous tricarboxylic acid and diisocyanate as raw materials, and an acid chloride method using anhydrous tricarboxylic acid chloride and diamine as raw materials can be used. However, The acid chloride method is preferably used to obtain the amideimide powder. For details of the polymerization method, reference can be made to Japanese Patent Publication No. 50-33120 (isocyanate method), Japanese Patent Publication No. 42-15637 (acid chloride method), and the like.

The tricarboxylic acid component is preferably an aromatic tricarboxylic acid having an aromatic ring. Examples of the aromatic tricarboxylic acid component include trimellitic acid chloride (TMC), trimellitic anhydride (TMA), hemimellitic acid chloride, and anhydrous hemimellitic acid. Among them, TMC and TMA are preferable. In addition, the aromatic tricarboxylic acid component may be partially substituted with a tetracarboxylic acid component such as pyromellitic acid, benzophenonetetracarboxylic acid, or biphenyltetracarboxylic acid.

The diamine component of the polyamideimide is preferably an aromatic diamine having an aromatic ring. Examples of the aromatic diamine component of the polyamideimide include m-phenylenediamine (MPD), p-phenylenediamine, 4,4'-diphenylmethane diamine, 4,4'-diamino Diphenyl ether (DADE), diphenylsulfone-4,4'-diamine, diphenyl-4,4'-diamine, o-tolidine, 2,4-tolylene diamine, 2,6- Diamine, xylylene diamine, naphthalene diamine, or diisocyanate derivatives thereof. These may be used alone, or two or more of them may be used in combination. Of these, DADE and MPD are preferred.

The solid content concentration of the polyamideimide in the polyamideimide coating liquid is preferably from 1 to 50 mass%, more preferably from 10 to 30 mass%.

The viscosity of the polyamideimide coating solution at 30 캜 is preferably from 1 to 150 Pa · s, more preferably from 5 to 100 Pa · s.

In the present specification, the polyamideimide obtained by polymerizing the above aromatic tricarboxylic acid component and aromatic diamine component is referred to as &quot; aromatic polyamideimide &quot;.

To the imide-based coating liquid, known additives such as various surfactants and organic silane coupling agents may be added, if necessary. If necessary, a polymer other than the imide-based polymer may be added to the imide-based coating liquid.

In order to form the coating film by applying the imide-based coating solution to the surface of the S layer, it is possible to employ a method of applying the coating solution continuously in a roll-to-roll manner or in a sheet form. As a coating device used at this time, for example, a die coater, a multilayer die coater, a gravure coater, a comma coater, a reverse roll coater, a doctor blade coater, a bar coater and the like can be used. As described above, by heating and removing the solvent in the obtained coating film, a P layer integrated with the S layer can be formed. Here, the application surface may be one side or both sides of the S layer.

The air permeability of the laminated porous film of the present invention is preferably 10 seconds / 100 cc or more and 1000 seconds / 100 cc or less, preferably 100 seconds / 100 cc or more and 600 seconds / 100 cc or less in terms of the gelling value (JIS standard P8117) More preferably 100 cc or more and 500 sec / 100 cc or less. By setting the air permeability in this way, it can be suitably used as a separator for a lithium secondary battery. That is, when the gull value is less than 10 sec / 100 ml, there is a case where the positive electrode is short-circuited by metal lithium deposited on the negative electrode in the lithium ion secondary battery. On the other hand, if the Gurley value exceeds 1000 seconds / 100 ml, the internal resistance of the battery becomes high, and high output density may not be obtained.

In the laminated porous film of the present invention, the alcohol-based solvent does not remain in the P layer. Here, &quot; no alcohol-based solvent remains &quot; means that no substantially alcohol-based solvent remains, and if the effect of the present invention is not impaired, the alcohol-based solvent may remain in a trace amount. Examples of the alcohol solvent include methanol, ethanol, propanol, isopropyl alcohol, 1-butanol, ethylene glycol, tripropylene glycol, glycerin and the like.

In the porous laminated film of the present invention, the thickness of the P layer is 1 mu m or more and 20 mu m or less, more preferably 1.5 mu m or more and 15 mu m or less, and more preferably 2 mu m or more and 10 mu m or less. By doing so, it is possible to secure the heat resistance of the porous film in which the P layer is laminated, while securing the good air permeability of the P layer. If the thickness of the P layer is too thin, the heat resistance of the porous film can not be ensured. On the other hand, if the thickness of the P layer is excessively large, air permeability can not be ensured. Here, the thickness of the P layer is a thickness calculated by subtracting the thickness of the S layer from the thickness of the laminated porous film, and the thickness of the laminated porous film is measured based on JIS standard (K7130-1992).

The porosity of the P layer is preferably 30 to 90% by volume, more preferably 40 to 80% by volume. By setting the porosity in this way, a laminated porous film having better mechanical properties and air permeability can be obtained. Here, the adjustment of the porosity can be performed by selecting the blending amount of the ether-based solvent, solvent removal conditions, and the like. On the other hand, the porosity of the P layer is a value calculated from the apparent density of the P layer and the true density (specific gravity) of the imide polymer constituting the P layer. Specifically, the porosity (volume%) is calculated by the following formula when the apparent density of the P layer is A (g / cm ³ ) and the true density of the imide polymer is B (g / cm ³ ).

Porosity (volume%) = 100-A x (100 / B)

The pore diameter of the P layer is preferably not more than 3 mu m, more preferably not more than 1 mu m, from the viewpoint of obtaining sufficient air permeability when the laminated porous film is used as a separator for a lithium secondary battery and preventing mixing of particles into the positive electrode and the negative electrode. desirable.

As described above, the obtained laminated porous film is excellent in air permeability and heat resistance, and the alcoholic solvent does not remain in the P layer, so that it can be suitably used as a separator for a lithium secondary battery. Further, according to the method for producing a laminated porous film of the present invention, a laminated porous film can be easily produced by a simple process without using a coagulating bath.

Example

Hereinafter, the present invention will be described more specifically based on examples, but the present invention is not limited to these examples.

[Example 1]

Celgard 2500 &quot; manufactured by Celgard was prepared as the porous film forming the S layer. This porous film was made of polypropylene and had a thickness of 25 占 퐉 and a gully value (JIS standard P8117) showing air permeability of 180 seconds / 100 cc. Next, &quot; U-imide varnish IP &quot; made by Unitika Co., Ltd. was prepared as an imide-based coating. As the solute, an aromatic polyamideimide having a Tg of 280 DEG C by DSC as a solute, a mixed solvent of NMP and TEGM was used as a solvent, and an alcoholic solvent was not included. The solid content concentration was 15 mass%. The coating solution was applied to one side of the porous film using a bar coater and dried in a nitrogen gas stream at 140 ° C in a wet state for 30 minutes to remove the solvent by heating so that the surface of the S layer had a thickness of 8 μm Of a laminated porous film (L-1) in which a P layer made of porous polyamideimide was integrated. The properties of the laminated porous film and the properties of the P layer are shown in Table 1.

[Example 2]

The laminated porous film (L-2) was obtained in the same manner as in Example 1, except that the thickness of the P-layer was 4 m. The properties of the laminated porous film and the properties of the P layer are shown in Table 1.

[Example 3]

The laminated porous film (L-3) was obtained in the same manner as in Example 1 except that the thickness of the P-layer was 15 m. The properties of the laminated porous film and the P layer were evaluated and the results are shown in Table 1.

[Example 4]

0.07 mol of DADE and 0.03 mol of MPD were added to a reaction vessel made of glass under a dry nitrogen gas atmosphere, 0.1 mol of NMP and 0.1 mol of triethylamine were added thereto, and the mixture was stirred to obtain an NMP solution having a solid concentration of 15% by mass. Thereafter, while keeping the solution at 10 캜 or lower, 0.1 mol of TMC in NMP (solid concentration: 20% by mass) was slowly added dropwise with stirring. After completion of dropwise addition, the solution was returned to room temperature and stirring was continued for 2 hours. The obtained solution was poured into a large amount of water to cause precipitation of the polyamideimide, followed by filtration and washing to obtain a yellow solid, which was then heated at 200 占 폚 for 12 hours for drying and imidization Polyamideimide powder (AP) was obtained. The Tg according to DSC of AP was 285 캜. Next, AP was dissolved in a mixed solvent of NMP and TEGM to obtain a polyamideimide coating solution (A-1) having a solid content concentration of 12 mass%. Here, the mixing ratio of NMP and TEGM was 70% by mass with respect to the mixed solvent mass. Using the coating solution (A-1), coating was carried out in the same manner as in Example 1 to obtain a laminated porous film (L-4) in which a P layer (having a thickness of 3 탆) of a porous polyamideimide was integrated on the surface of the S- . The properties of the laminated porous film and the properties of the P layer are shown in Table 1.

[Example 5]

A polyamideimide coating solution (A-2) having a solid concentration of 12 mass% was obtained in the same manner as in Example 4, except that the mixing ratio of NMP and TEGM was 80 mass% with respect to the mixed solvent mass. Using the coating solution (A-2), coating was carried out in the same manner as in Example 1 to obtain a laminated porous film (L-5) in which a P layer (thickness: 3 탆) of porous polyamideimide was integrated on the surface of the S- . The properties of the laminated porous film and the properties of the P layer are shown in Table 1.

[Example 6]

U Imide Varnish SP &quot; manufactured by UNITICA CO., LTD. Was prepared as an imide coating. As this solu- tion, an aromatic polyimide having a Tg of 225 ° C as measured by DSC was used. As a solvent, a mixed solvent of NMP and TEGM was used, and an alcohol-based solvent was not included. The solid content concentration was 15 mass%. The coating solution was applied to one surface of the porous film using a bar coater and dried in a nitrogen gas stream at 140 ° C for 30 minutes to remove the solvent by heating so that the surface of the S layer had a thickness of 4 μm (L-6) in which the P layer made of the porous polyimide was integrated. The properties of the laminated porous film and the properties of the P layer are shown in Table 1.

[Example 7]

0.04 mol of BPDA and 0.06 mol of ODPA were put into a reaction vessel made of glass under a dry nitrogen gas atmosphere and added with NMP to prepare a solution. Then, 0.1 mol of DADE was added to the NMP solution, and 0.04 mol of BPDA and 0.04 mol of ODPA The molar was slowly added and the mixture was reacted at 50 DEG C for 4 hours to obtain an NMP solution of polyamic acid (solid concentration: 15 mass%). Toluene was added to the polyamic acid solution to prepare a solution having a solid content concentration of 13 mass%. This solution was heated to 200 占 폚, and imidization reaction was carried out for 3 hours while separating the water coexisting with toluene along with the progress of the reaction. Thereafter, the polyimide solution obtained by removing toluene by distillation was poured into a large amount of water to induce precipitation of polyimide. The polyimide solution was filtered, washed, and crushed, and then heated at 120 ° C for 5 hours to obtain soluble polyimide powder (BP). The Tg of the powder BP by DSC was 231 캜. Next, the powder BP was dissolved in a mixed solvent of DMAc and TEGM to obtain a polyimide coating solution (B-1) having a solid content concentration of 12 mass%. Here, the mixing ratio of DMAc and TEGM was 70% by mass with respect to the mixed solvent mass. Using the coating solution (B-1), coating was carried out in the same manner as in Example 6 to obtain a laminated porous film (L-7) in which a P layer (thickness: 3 μm) made of porous polyimide was integrated on the surface of the S layer. The properties of the laminated porous film and the properties of the P layer are shown in Table 1.

[Example 8]

A coating solution (B-2) having a solid content concentration of 12 mass% was obtained in the same manner as in Example 4, except that the mixing ratio of DMAc and TEGM was changed to 60 mass% with respect to the mixed solvent mass. Using the coating solution (B-2), a multilayer porous film (L-8) in which a P layer made of porous polyimide having a thickness of 3 탆 was integrated was obtained on the surface of the S layer in the same manner as in Example 7. The properties of the laminated porous film and the properties of the P layer are shown in Table 1.

[Example 9]

A coating liquid (B-3) having a solid content concentration of 12 mass% was obtained in the same manner as in Example 7 except that TEGM was changed to TRGM. Using the coating solution (B-3), a multilayer porous film (L-9) in which a P layer made of porous polyimide having a thickness of 3 탆 was integrated on the surface of the S layer was obtained in the same manner as in Example 7. The properties of the laminated porous film and the properties of the P layer are shown in Table 1.

[Comparative Example 1]

The laminated porous film (M-1) was obtained in the same manner as in Example 1 except that the thickness of the P-layer was 25 m. The properties of the laminated porous film and the P layer were evaluated and the results are shown in Table 1.

[Comparative Example 2]

The polyamideimide powder (AP) used in Example 4 was dissolved in NMP to obtain a polyamideimide coating solution (A-3) having a solid content concentration of 12 mass%. Using the coating solution (A-3), coating was carried out in the same manner as in Example 1 to obtain a laminated porous film (M-2) in which a P layer (thickness: 3 탆) of polyamideimide was integrated on the surface of the S layer . The properties of the laminated porous film and the properties of the P layer are shown in Table 1.

[Comparative Example 3]

A polyamideimide coating solution (A-4) having a solid concentration of 12 mass% was obtained in the same manner as in Example 4, except that the mixing ratio of NMP and TEGM was changed to 25 mass% of the amount of TEGM relative to the mixed solvent mass. Using the coating solution (A-4), coating was carried out in the same manner as in Example 1 to obtain a laminated porous film (M-3) in which a P layer (having a thickness of 3 탆) of a porous polyamideimide was integrated on the surface of the S- &Lt; / RTI &gt; The properties of the laminated porous film and the properties of the P layer are shown in Table 1.

[Comparative Example 4]

The polyamideimide powder (AP) used in Example 4 was dissolved in a mixed solvent of NMP and tripropylene glycol (TPG) to obtain a polyamideimide coating solution (A-5) having a solid content concentration of 12 mass%. Here, the mixing ratio of NMP and TPG was 25 mass% with respect to the mixed solvent mass. A laminated porous film (M-4) in which a P layer (made of 3 m in thickness) of a porous polyamideimide was integrated on the surface of the S layer by applying the coating liquid A-5 in the same manner as in Example 1, . The properties of the laminated porous film and the properties of the P layer are shown in Table 1.

[Comparative Example 5]

A polyamideimide coating solution was prepared by dissolving the polyamideimide powder (AP) used in Example 4 in a mixed solvent of NMP and TPG to obtain a laminated porous film (M-5), but a uniform solution was obtained There was no. Here, the mixing ratio of NMP and TPG was 70 mass% with respect to the mixed solvent mass.

[Comparative Example 6]

The polyimide powder (BP) used in Example 7 was dissolved in a mixed solvent of DMAc and TPG to obtain a polyimide coating solution (B-4) having a solid concentration of 12 mass%. Here, the mixing ratio of DMAc and TPG was 25 mass% with respect to the mixed solvent mass. Using the coating solution (B-4), coating was carried out in the same manner as in Example 1 to obtain a laminated porous film (M-6) in which a P layer (thickness: 3 탆) made of polyimide was integrated on the surface of the S layer . The properties of the laminated porous film and the properties of the P layer are shown in Table 1.

[Comparative Example 7]

A polyimide coating liquid was prepared by dissolving the polyimide powder (BP) used in Example 7 in a mixed solvent of DMAc and TPG to obtain a laminated porous film (M-7), but a uniform solution could not be obtained. Here, the mixing ratio of DMAc and TPG was 70 mass% with respect to the mixed solvent mass.

As shown in the examples, the laminated porous film of the present invention in which the porous layer made of the imide-based polymer is formed on one side or both surfaces of the porous layer made of polyolefin is characterized in that the porous layer made of the imide polymer having excellent heat resistance is made of polyolefin The heat-resistant porous layer has a high porosity and a good air permeability, so that the laminated porous film laminated thereon is also excellent in air permeability. Further, the heat-resistant porous layer does not contain any alcohol-based solvent. Therefore, the laminated porous film of the present invention can be suitably used as a separator for a lithium secondary battery.

Further, according to the production method of the present invention, a laminated porous film can be obtained by a simple operation of removing the solvent by heating. Here, since the coagulating bath containing a poor solvent is not used, a waste liquid from the coagulating bath is not generated. Therefore, the environmental suitability is good.

The laminated porous film of the present invention is useful as, for example, a separator for a lithium secondary battery or a separator for a power storage device.

Claims (3)

A laminated porous film having a porous layer made of imide-based polymer formed on one side or both sides of a porous layer made of polyolefin, the laminated porous film having the following characteristics:
1) The air permeability is 10 seconds / 100 cc or more and 1000 seconds / 100 cc or less as a gully value based on JIS P8117;
2) the alcoholic solvent does not remain in the porous layer made of the imide polymer;
3) The thickness of the porous layer made of the imide-based polymer is 1 μm or more and 20 μm or less. A separator for a lithium secondary battery, comprising the laminated porous film according to claim 1. A coating liquid comprising a mixture of an imide-based polymer, an amide-based solvent and an ether-based solvent is applied to one surface or both surfaces of a porous layer made of polyolefin to form a coating film, and then the solvent in the coating film is heated A method for producing a laminated porous film according to claim 1, wherein a porous layer is formed by causing phase separation in a coating film so that a porous layer made of a polyolefin and a porous layer made of an imide polymer are laminated and integrated.