JP2018065902A - Porous composite film, and production method of porous composite film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous composite film excellent in heat resistance, mechanical properties, dimensional stability, and gas permeability, and a production method thereof.SOLUTION: <1> A porous composite film is composed of a fluorine-containing polymer and a nonthermoplastic PI, wherein the nonthermoplastic PI is 15-30 mass% relative to the porous composite film. The porous composite film has a Gurley value based on JIS P-8117 of 3,000 seconds or less. <2> A production method of the porous composite film includes a step for impregnating a porous fluorine-containing polymer film with a nonthermoplastic PI precursor solution containing an amide-based solvent and an ether-based solvent followed by drying and thermal hardening.SELECTED DRAWING: None

Description

The present invention relates to a porous composite film and a method for producing the same.

Among the fluorine-containing polymers, a porous film made of polytetrafluoroethylene (PTFE) is an electronic material, an optical material, a separator for a lithium secondary battery, a filter, using its excellent heat resistance and high porosity. It is used in the fields of industrial materials such as separation membranes, wire coatings, medical materials, liquid filters, gas filters and the like. As a method for producing a porous PTFE film, a method utilizing porous formation by stretching has been widely put into practical use. The porous PTFE film obtained by this method is excellent in mechanical strength but poor in dimensional stability at high temperatures. As a method for improving the dimensional stability, Patent Documents 1 and 2 disclose that a porous PTFE film is impregnated with a heat-resistant polymer solution such as polyimide (PI) or polyurethane, and dried to obtain a part of the surface of the PTFE cell. Alternatively, a method of forming a composite by covering the whole with a heat-resistant polymer has been proposed.

US Published Patent No. 20160075914 US Published Patent No. 20160075915

However, even with the porous composite film disclosed in the above document, the dimensional change rate when exposed to a high temperature, for example, about 300 ° C., exceeds 1%, and the dimensional stability is not sufficient.

Accordingly, the present invention solves the above-described problems, and provides a heat-resistant porous composite film having good air permeability and excellent dimensional stability at a high temperature of 300 ° C. or higher, and a method for producing the same. With the goal.

The inventors of the present invention have found that the above-mentioned problems can be solved by specifying the air permeability of the porous composite film after specifying the configuration of the porous composite film, and have completed the present invention. It was.

The present invention has the following objects.
<1> A porous composite film comprising a fluorine-containing polymer and a non-thermoplastic PI, wherein the non-thermoplastic PI content is 15 to 30% by mass relative to the mass of the porous composite film, and JIS P-8117 A porous composite film characterized in that the Gurley value based on the above is 3000 seconds or less.
<2> The porous composite film according to claim 1, further comprising a step of impregnating a porous fluorine-containing polymer film with a non-thermoplastic PI precursor solution containing an amide solvent and an ether solvent, followed by drying and thermosetting. Manufacturing method.

Since the porous composite film of the present invention has excellent dimensional stability at high temperatures and high air permeability, it is an industrial material such as an electronic material, an optical material, a separator for a lithium secondary battery, a filter, a separation membrane, and a wire coating. It can be suitably used in the fields of medical materials, liquid filters, gas filters and the like.

The porous composite film of the present invention comprises a fluorine-containing polymer and a non-thermoplastic PI, and a part of pores in the porous fluorine-containing polymer film is filled with the non-thermoplastic PI. The porous fluorine-containing polymer film used here is PTFE, polyvinylidene fluoride (PVDF), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), It is made of a fluorine-containing polymer such as ethylene-tetrafluoroethylene copolymer (ETFE) or polychlorotrifluoroethylene (PCTFE), and is preferably made of PTFE from the viewpoint of chemical resistance and heat resistance. The porous PTFE film is produced from a PTFE resin by a stretching method or a wet papermaking method, and a commercially available product can be used. Specific examples of commercially available products include “Poreflon” manufactured by Sumitomo Electric Fine Chemical Co., “TEMISH” manufactured by Nitto Denko Corporation, “Goa Microfiltration Media” manufactured by Gore Japan, and “Tomy Filec” manufactured by Yodogawa Paper Co., Ltd. be able to. These porous PTFE films are preferably subjected to a known surface treatment such as a silane coupling agent treatment, a plasma treatment, a hydrophilization treatment with a surfactant or the like in order to improve the adhesion to PI.

It is preferable to use a porous fluorine-containing polymer film having a thickness of 10 to 200 μm, an average pore diameter of 0.05 to 5 μm, and an air permeability of 1 to 200 seconds as a Gurley value based on JIS P-8117. These porous fluorine-containing polymer films are preferably subjected to a known surface treatment such as silane coupling agent treatment or plasma treatment in order to improve adhesion to PI.

The non-thermoplastic PI constituting the porous composite film is a heat-resistant polymer having an imide ring and refers to PI that does not exhibit thermoformability such as injection molding or extrusion molding at a temperature of less than 350 ° C. The non-thermoplastic PI usually does not show a glass transition temperature by DSC, but even when it shows a glass transition temperature, it is 250 ° C. or higher. By filling the non-thermoplastic PI with 15 to 30% by mass, preferably 16 to 25% by mass, based on the mass of the porous composite film, good air permeability and high temperature are obtained. It can be set as the porous composite film which ensured dimensional stability simultaneously. Here, the air permeability of the porous composite film is 3000 seconds or less, preferably 1000 seconds or less, and more preferably 500 seconds or less as a Gurley value based on JIS P-8117. The lower limit of the Gurley value is not limited, but is usually 10 seconds or longer, preferably 50 seconds or longer, and more preferably 100 seconds or longer.

The porous composite film of the present invention is, for example, impregnated in a porous fluorine-containing polymer film with a polyamic acid (hereinafter sometimes abbreviated as “PAA”) which is a precursor of non-thermoplastic PI, and then dried. It can be obtained by thermosetting. By doing in this way, a part or all of the fluorine-containing polymer cell surface which comprises a porous fluorine-containing polymer film can be coat | covered with non-thermoplastic PI. The non-thermoplastic PI may be porous or non-porous, but is preferably non-porous from the viewpoint of improving dimensional stability.

PAA is a reaction product of approximately equimolar tetracarboxylic dianhydride (TA) and diamine (DA).

Specific examples of TA include pyromellitic dianhydride (PMDA), 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA), 2,3,3 ′, 4′-biphenyltetra. Carboxylic dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride, 4,4′-oxydiphthalic anhydride, and 3,3 ′, 4,4′-diphenylsulfone tetracarboxylic acid A dianhydride etc. are mentioned. These may be used alone or in combination of two or more. Of these, PMDA and BPDA are preferable.

Specific examples of DA include 4,4′-diaminodiphenyl ether (DADE), 2,2-bis [4- (4-aminophenoxy) phenyl] propane (BAPP), p-phenylenediamine (PDA), m-phenylene. Diamine, 2,4-diaminotoluene, 4,4′-diaminobiphenyl, 4,4′-diamino-2,2′-bis (trifluoromethyl) biphenyl, 3,3′-diaminodiphenylsulfone, 4,4 ′ -Diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenylmethane 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 1,3-bis (3 Aminophenoxy) benzene, 4,4′-bis (4-aminophenoxy) biphenyl, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] sulfone, and the like. . These may be used alone or in combination of two or more. Of these, DADE, BAPP, and PDA are preferable.

As a solvent for the PAA solution, it is preferable to use a mixed solvent obtained by mixing a good solvent that dissolves PAA as a solute and a solvent that becomes a poor solvent for PAA. Here, the good solvent refers to a solvent having a solubility in PAA of 1% by mass or more at 25 ° C., and the poor solvent refers to a solvent having a solubility in PAA of less than 1% by mass at 25 ° C.

As the good solvent, an amide solvent having good solubility in PAA is preferably used. Examples of the amide solvent include N-methyl-2-pyrrolidone (NMP), N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc) and the like. These may be used alone or in combination of two or more.

As the poor solvent, an ether solvent having better permeability to the porous fluorine-containing polymer film is preferably used than a ketone solvent such as MEK. Examples of the ether solvent include tetrahydrofuran (THF), dimethoxyethane (DME), dioxane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and the like. These may be used alone or in combination of two or more. Of these, THF and DME are preferable. By using these ether solvents, good impregnation of the PAA solution into the porous fluorine-containing polymer film can be obtained, and a uniform porous composite film can be obtained.

As a compounding quantity of the poor solvent in a mixed solvent, it is preferable to set it as 50-95 mass% with respect to mixed solvent mass, and it is more preferable to set it as 60-90 mass%. By doing in this way, the favorable impregnation property with respect to the porous fluorine-containing polymer film of a PAA solution is securable.

The PAA solution can be obtained, for example, by reacting substantially equimolar TA and DA at a temperature of 100 ° C. or lower in the mixed solvent. The PAA solution is obtained by polymerization reaction in a good solvent to obtain a solution, and then a poor solvent is added thereto, or a suspension is obtained by polymerization reaction in the poor solvent and then a good solvent is added thereto. Can also be obtained.

The concentration of PAA in the PAA solution is preferably 3 to 30% by mass, and more preferably 5 to 15% by mass.

The viscosity of the PAA solution at 30 ° C. is preferably in the range of 0.01 to 100 Pa · s, more preferably 0.1 to 50 Pa · s.

You may add well-known additives, such as various surfactants and a silane coupling agent, to a PAA solution in the range which does not impair the effect of this invention as needed. Moreover, you may add other polymers other than PAA to PAA solution in the range which does not impair the effect of this invention as needed.

The porous composite film can be obtained, for example, by impregnating a porous fluorine-containing polymer film with a PAA solution, drying it at 100 to 170 ° C., and then performing a heat treatment at 200 to 350 ° C. in a nitrogen gas atmosphere. it can.

The impregnation of the porous fluorine-containing polymer film with the PI solution can be performed by applying or dipping the PI solution on the surface of the porous fluorine-containing polymer film. As the coating machine, a die coater, a lip coater, a gravure coater, a bar coater, a doctor blade coater, a comma coater, a reverse roll coater, a bar reverse roll coater or the like can be used. Moreover, when using an immersion method, what is necessary is just to remove the excess PI solution adhering to the surface using a roll press, a mangle, etc. after immersing a porous fluorine-containing polymer film in PI solution.

Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to the examples.

<Example 1>
In a glass reaction vessel, under a nitrogen atmosphere, DADE: 0.96 mol, a mixed solvent composed of DMAc and DME (the mixing ratio of DMAc / DME was set to 20/80 by mass) was stirred, and DADE was stirred. Dissolved. While gradually cooling this solution to 30 ° C. or less with a jacket, PMDA: 1.00 mol was gradually added, followed by polymerization at 50 ° C. for 5 hours to obtain a PAA solution having a solid content concentration of 6% by mass. This solution was applied to and impregnated on the surface of a plasma-treated PTFE film (“PORFLON” manufactured by Sumitomo Electric Fine Polymer Co., Ltd., thickness: 30 μm Gurley value: 23 seconds). Thereafter, the periphery of the film is fixed with a metal frame, dried at 130 ° C. for 10 minutes and at 150 ° C. for 20 minutes, treated at 300 ° C. for 60 minutes in a nitrogen gas atmosphere, and thermally cured to form PAA. Was converted to non-thermoplastic PI to obtain a porous composite film (C-1). The non-thermoplastic PI content of C-1 was 16.8% by mass relative to C-1 mass. It was 260 seconds when the Gurley value of C-1 was measured based on JIS P-8117. Further, when C-1 was cut into 5 cm squares and placed on a hot plate at 300 ° C. for 30 seconds to measure the dimensional change rate (average value of contraction rate in the vertical and horizontal directions), it was 1% or less. there were.

<Example 2>
“PMDA: 1.00 mol” was changed to “BPDA: 1.00 mol” and “DADE: 0.96 mol” was changed to “a mixture of DADE: 0.20 mol and PDA: 0.76 mol”. It carried out similarly to Example 1 and obtained the porous composite film (C-2) whose non-thermoplastic PI content is 21.5 mass%. When the C-2 galley value and the dimensional change rate at 300 ° C. were measured in the same manner as in Example 1, the galley value was 570 seconds, and the dimensional change rate was 1% or less.

<Comparative Example 1>
A porous composite film (R-1) was obtained in the same manner as in Example 1 except that the non-thermoplastic PI content was 13.5% by mass. In the same manner as in Example 1, when the R-1 galley value and the dimensional change rate at 300 ° C. were measured, the galley value was 210 seconds, but the dimensional change rate was 1%. It was over.

<Comparative example 2>
A porous composite film (R-2) was obtained in the same manner as in Example 1 except that the non-thermoplastic PI content was 11.6% by mass. In the same manner as in Example 1, when the galley value of R-2 and the dimensional change rate at 300 ° C. were measured, the galley value was 150 seconds, but the dimensional change rate was 1%. It was over.

<Comparative Example 3>
A porous composite film (R-3) was obtained in the same manner as in Example 1 except that the non-thermoplastic PI content was 33.5% by mass. In the same manner as in Example 1, when the G-3 value of R-3 and the dimensional change rate at 300 ° C. were measured, the dimensional change rate was 1% or less, but the Gurley value exceeded 3000 seconds. It was.

As shown in the examples, the porous composite film of the present invention in which the content of non-thermoplastic PI is in a predetermined range has good dimensional stability in addition to excellent heat resistance and good air permeability. I know that.

The porous composite film of the present invention is used in fields such as electronic materials, optical materials, lithium secondary battery separators, filters, separation membranes, electric wire coatings and other industrial materials, medical materials, liquid filters, gas filters, etc. Can be suitably used.

Claims (2)

A porous composite film comprising a fluorine-containing polymer and a non-thermoplastic polyimide, wherein the non-thermoplastic polyimide content is 15 to 30% by mass with respect to the mass of the porous composite film, and a galley based on JIS P-8117. A porous composite film having a value of 3000 seconds or less. The method for producing a porous composite film according to claim 1, further comprising a step of impregnating the porous fluorine-containing film with a non-thermoplastic polyimide precursor solution containing an amide solvent and an ether solvent, followed by drying and thermosetting.