JPH09255807A - Porous material of thermoplastic resin and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject porous material composed of a thermoplastic resin, especially a thermoplastic fluororesin, having mechanical properties essentially uniform in all directions and high mechanical strength and useful as a separation membrane, etc. SOLUTION: This porous material is a three-dimensional network structure material containing interconnected cells and composed of a non-fibrous fine bonding member formed by the coagulation and bonding of the particles of a thermoplastic resin A. The objective porous material can be produced by mixing the component A (preferably a tetrafluoroethylene-hexafluoropropylene copolymer, etc.) with (B) a resin soluble in an organic solvent (preferably a fluororesin soluble in an organic solvent), heat-treating the mixture at a temperature above the melting point of the component B and below the melting point of the component A and removing the component B by dissolving with an organic solvent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous body of a thermoplastic resin suitable for a separation membrane, a diaphragm, a dielectric material and a sensor material and a method for producing the same, and particularly to a porous body made of a thermoplastic fluororesin and its production. Regarding the method.

[0002]

2. Description of the Related Art Polytetrafluoroethylene, which is a typical fluororesin, is a resin having excellent heat resistance and chemical resistance, but it has a very high melt viscosity and is inferior in processability. It is difficult to manufacture the body. Therefore,
After being made porous by stretching or the like, it is used to process it into an arbitrary shape. Further, after directly molding a synthetic resin having heat resistance and chemical resistance such as a copolymer containing tetrafluoroethylene having thermoplasticity,
It is being made porous.

Further, polytetrafluoroethylene, or tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA),
Tetrafluoroethylene-hexafluoropropylene-
Perfluoroalkyl vinyl ether copolymer (EP
A), tetrafluoroethylene-ethylene copolymer (E
It is also carried out that a soluble salt such as salt is mixed with TFE), melt-kneaded, and then extrusion-molded, and then the salt is eluted to produce a porous body.

However, the melt viscosity of the fluororesin is large, and during extrusion molding, it is subjected to a very large shearing force, and the melted resin becomes a fiber. Moreover, if other substances are present, they will undergo even greater shearing force,
Fiberization progresses. Further, such a phenomenon also occurs when extrusion molding is performed after kneading a resin other than a fluororesin.

Further, an ethylene-tetrafluoroethylene copolymer, a solvent-soluble vinylidene fluoride polymer and an inorganic fine powder are melt-molded, and then the vinylidene fluoride polymer and the inorganic fine powder are extracted from the molded product. Japanese Patent Application Laid-Open No. 6-240042 discloses forming an ethylene-tetrafluoroethylene copolymer porous film by using this method, and by using this method, various shapes such as a tubular body can be produced by extrusion molding. can do.

However, in this method, since both the thermoplastic fluororesin and the solvent-soluble vinylidene fluoride resin are melt-molded in a molten state, the obtained molded product has directionality in the extrusion direction. The fibrous material was fused and the strength in the extrusion direction was obtained, but the strength in the other directions was small, and a porous body having open cells could not be obtained. As described above, according to the conventional method, it is difficult to obtain a porous body having an arbitrary shape having a three-dimensional open cell and a uniform strength distribution.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a porous body having open cells made of a thermoplastic resin, particularly a thermoplastic fluororesin, and a method for producing the porous body.

[0008]

The present invention provides a porous body made of a thermoplastic resin, which has open cells made of non-fibrous fine bonding members formed by agglomeration and bonding of particles of the thermoplastic resin. It is a porous body having a three-dimensional network structure, and in particular, the thermoplastic resin is a tetrafluoroethylene-hexafluoropropylene copolymer (FE
P), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether copolymer (EPA), tetrafluoroethylene-ethylene copolymer (ETFE), poly It is a porous body of a fluororesin made of a fluororesin selected from tetrafluoroethylene (PTFE), an amorphous fluororesin, and a fluorine-containing polyimide.

Further, in the method for producing a porous body made of a thermoplastic resin, a mixture of a resin soluble in an organic solvent and a thermoplastic resin is not less than the melting point of the resin soluble in an organic solvent and is a thermoplastic resin. After heat-molding at a temperature equal to or lower than the melting point, heat treatment is performed at a temperature equal to or higher than the melting point of the thermoplastic resin, and then a resin soluble in an organic solvent is eluted and removed by the organic solvent to produce a porous body of the thermoplastic resin.

Further, the thermoplastic resin is tetrafluoroethylene-hexafluoropropylene copolymer (FEP),
Tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether copolymer (EPA), tetrafluoroethylene-ethylene copolymer (ETFE), polytetrafluoroethylene (PTFE), amorphous fluororesin,
The method for producing a porous body of the thermoplastic resin is a fluororesin selected from fluorine-containing polyimide, wherein the resin soluble in an organic solvent is a fluororesin soluble in a solvent.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a resin soluble in an organic solvent and a thermoplastic resin are mixed to obtain a resin at a temperature not lower than the melting point of the resin soluble in the organic solvent and lower than the melting point of the thermoplastic resin. When the mixture was heat-molded, the resin soluble in the organic solvent was melted, but the thermoplastic resin having a high melting point was not melted, and the thermoplastic resin was filled in the melt of the resin soluble in the organic solvent. A molded body is obtained. Next, when heated to a temperature above the melting point of the thermoplastic resin, the resin soluble in the organic solvent and the thermoplastic resin do not mix at the melting point or above, so the thermoplastic resin is aggregated in the resin soluble in the organic solvent by melting. And then three-dimensionally combine.

As a result, in the melt of the resin soluble in the organic solvent, the non-fibrous fine bonding member has three-dimensionally continuous open cells due to aggregation and bonding of the thermoplastic resin particles. A mesh structure can be obtained. In the present invention, the term "non-fibrous finely-bonded member" refers to a member that is formed from the melt of the surface portion of the particles and that bonds the surrounding particles to each other. It differs from those bonded to each other at the surface portion, and also from those in which the particles are completely melted and joined by the fibrous material formed by the melt of the particles.

Therefore, the obtained porous body is not oriented in a specific direction such as an extrusion direction, has a three-dimensional network structure uniformly distributed, and has a mechanical strength in any direction. Also, a porous body having substantially uniform mechanical strength can be obtained.

The combination of an organic solvent-soluble resin and a thermoplastic resin that can be used in the present invention is selected from a thermoplastic resin having a melting point higher than the melting point of the organic solvent-soluble resin, and both resins can be used. Are selected from those that do not mix in the molten state.

Specifically, as the thermoplastic resin, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene- When a perfluoroalkyl vinyl ether copolymer (EPA), tetrafluoroethylene-ethylene copolymer (ETFE), polytetrafluoroethylene (PTFE), amorphous fluororesin, fluorine-containing polyimide, etc. are used,
NEOFLON VD which is a copolymer of tetrafluoroethylene and vinylidene fluoride as a resin soluble in an organic solvent
F (manufactured by Daikin), a copolymer THV (manufactured by 3M) with tetrafluoroethylene, vinylidene fluoride and hexafluoroprepylene can be used, and as the organic solvent used for elution of the resin, acetone and N-methylpyrrolidone (NMP) can be mentioned.

When polyethylene terephthalate (PET), polyphenylene sulfide (PPS), polycarbonate (PC), polyether ether ketone (PEEK), polyester type liquid crystal polymer (LCP) or the like is used as the thermoplastic resin, NEOFLON VDF (made by Daikin) which is a copolymer of tetrafluoroethylene and vinylidene fluoride as a resin soluble in an organic solvent, THV which is a copolymer of tetrafluoroethylene, vinylidene fluoride and hexafluoroprepylene
Polyvinylidene fluoride (manufactured by 3M) can be used. As an organic solvent used for elution of resin, polyvinylidene fluoride includes N-methylpyrrolidone (NM
P), dimethylformamide (DMF), dimethylsulfoxide (DMSO), and other resins include acetone and N-methylpyrrolidone (NMP).

Further, as the thermoplastic resin, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polyether ether ketone (PE
In the case of using EK), polycarbonate (PC), polysulfone (PSU) is used as a resin soluble in an organic solvent.
When polycarbonate is used, methylene chloride can be used as an organic solvent for elution, and when polysulfone (PSU) is used, ketones can be used.

Further, the thermoplastic resin of the present invention or the resin soluble in an organic solvent may be mixed in a powder state. However, it is used as a thermoplastic resin in an organic solvent solution of a fluororesin soluble in an organic solvent. It is possible to use any of those obtained by mixing the aqueous dispersion of the fluororesin to be used for gelation, and after stirring, the solid content is taken out and dried. As the aqueous dispersion of the fluororesin, one having an average particle diameter of 0.01 to 1 μm and a solid content of 1 to 60% by weight, which is obtained by emulsion polymerization, can be used.

The porosity can be easily adjusted by changing the mixing ratio of the resin soluble in the organic solvent and the thermoplastic resin. Further, in the formation of open cells and non-fibrous finely bonded members, a mixture of an organic solvent-soluble resin and a thermoplastic resin is equal to or higher than the melting point of the organic solvent-soluble resin and equal to or lower than the melting point of the thermoplastic resin. After heating and molding the resin mixture at the temperature of 1, the porosity or the diameter of the open pores can be adjusted by adjusting the heating time and the temperature when heating to a temperature equal to or higher than the melting point of the thermoplastic resin. .

Further, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl. When an aqueous dispersion of a fluororesin such as vinyl ether copolymer (EPA) or tetrafluoroethylene-ethylene copolymer (ETFE) is mixed with a fluororesin solution soluble in an organic solvent to cause gelation, The mixing amount of the dispersion is preferably 5 to 95%, more preferably 10 to 80% by volume ratio after drying. In this case, the concentration of the fluororesin solution soluble in the organic solvent is preferably 5 to 35% by weight, more preferably 10 to 25% by weight.
When these dispersions and a fluororesin solution soluble in an organic solvent are mixed, gelation occurs. After stirring, the solid content is taken out and dried to remove water. After this drying, heat molding is performed at a temperature not higher than the melting point of the fluororesin of the dispersion mixed and not lower than the melting point of the fluororesin soluble in the organic solvent.

A mixture of a resin soluble in an organic solvent and a thermoplastic resin is heat-molded at a temperature not lower than the melting point of the resin soluble in the organic solvent and not higher than the melting point of the thermoplastic resin. 1 below the decomposition temperature of the soluble resin and 5 ° C or more higher than the melting point of the thermoplastic resin
It is preferable to hold for 0 seconds to 1 minute.

As the heat molding, methods such as heat compression molding, extrusion molding and calender molding can be used, and it is possible to mold into any shape such as film, sheet or tube.

The thermoplastic resin porous material obtained by the present invention has continuous pores having a fine network structure. Further, since it is a porous body formed by bonding particles, the rate of dimensional change due to heat is lower than that of a porous body formed by stretching.
For example, a porous film of polytetrafluoroethylene which has been made porous by stretch cleavage shows a shrinkage due to heat of about 20% when heated to 200 ° C., but a tetrafluoroethylene-hexafluoropropylene copolymer (FEP) according to the present invention is used. The heat shrinkage of the porous body having a porosity of 70% when heated to 200 ° C. was about 1%.

The thermoplastic fluororesin porous material obtained by the present invention can be used as a separation membrane, a diaphragm, a battery separator, a dielectric material, and a sensor material. In addition, hydrophilicity can be imparted by including an inorganic substance such as silica or alumina in the porous body or coating the surface of the porous body with a hydrophilic resin such as an ion-exchange resin.

[0025]

The present invention will be described below with reference to examples. Example 1 118 g of an aqueous FEP dispersion (Mitsui DuPont Fluorochemicals, 120J, solids 57% by weight) having a particle diameter of 0.01 to 1 μm obtained by an emulsion polymerization method was added to a tetrafluoroethylene-vinylidene fluoride copolymer resin ( The mixture was mixed with 300 g of a 20 wt% acetone solution of Daikin Industries, Ltd. Neoflon VDF) to cause gelation. After stirring, the solid content was taken out by filtration, dried at 110 ° C. to remove water. The obtained agglomerate was pelletized at 240 ° C., and then formed into a sheet at 240 ° C. by an extruder to have a thickness of 10
After producing a sheet having a thickness of 0 μm to 1 mm, the sheet was heated to 300 ° C. while changing the heating time from 10 seconds to 1 minute depending on the thickness to produce sheets having different thicknesses. This sheet was immersed in acetone to completely dissolve and remove the tetrafluoroethylene-vinylidene fluoride copolymer resin. The obtained FEP
The porosity of the porous sheet is 50%, and the magnification is 500 with a scanning electron microscope (2500 CX manufactured by Hitachi, Ltd.).
A photograph of the surface observed with a magnification is shown in FIG. Uniform pores were obtained, and the maximum pore diameter was 1 μm. The cross section is 6
A photograph observed at 00 times is shown in FIG.

Example 2 Tetrafluoroethylene-ethylene copolymer (ETFE) powder having a particle size of 5 to 10 μm (Asahi Glass, Aflon CO
40 g of P, CA) tetrafluoroethylene-vinylidene fluoride copolymer resin (Daikin Industries, Neoflon VD
60 g of the powder of F) was kneaded and pelletized, and then coated with a metal wire at 230 ° C. by an extruder. After further heat treatment at 300 ° C., it was immersed in acetone and put therein, and the tetrafluoroethylene-vinylidene fluoride copolymer resin was completely dissolved and removed. The metal wire was pulled out to obtain a tetrafluoroethylene-ethylene copolymer porous tube. The obtained tetrafluoroethylene-ethylene copolymer porous tube has a porosity of 65%, and a photograph of the surface observed with a scanning electron microscope (2500CX manufactured by Hitachi, Ltd.) at a magnification of 500 is shown in FIG. Shown in. Maximum pore size is 3μ
m. A photograph of a cross section observed at 600 times is shown in FIG.

Comparative Example 1 PFA powder (Mitsui DuPont Fluorochemical MP-1
0 average particle size 20 μm) 40 g and tetrafluoroethylene-vinylidene fluoride copolymer (VDF) 60 g 34
The mixture was kneaded at 0 ° C to obtain pellets. Further, using a hot press, compression molding was performed at 340 ° C. to obtain a film having a thickness of 100 μm. After that, P was obtained after extracting VDF with acetone.
The porous body of FA was formed from a fibrous material oriented in the extrusion direction. Scanning electron microscope (manufactured by Hitachi Ltd. 25
00CX) shows a photograph of the surface observed at a magnification of 2000 times, and FIG. 3B shows a photograph of the cross section observed at a magnification of 300 times.

[0028]

Industrial Applicability According to the present invention, a mixture of a resin soluble in an organic solvent and a thermoplastic resin is heated at a temperature not lower than the melting point of the resin soluble in the organic solvent and not higher than the melting point of the thermoplastic resin to form a thermoplastic resin. Since the resin soluble in the organic solvent was eluted and removed after heating at a temperature above the melting point of the resin, the particles of the thermoplastic resin aggregated and formed a three-dimensional network structure. You can get the body.

[Brief description of drawings]

FIG. 1 is a scanning electron micrograph of a porous body of an example produced by the method of the present invention, (A) showing a surface and (B) showing a cross section.

FIG. 2 is a scanning electron micrograph of a porous body of another example produced by the method of the present invention, (A) showing the surface and (B) showing the cross section.

FIG. 3 is a scanning electron micrograph of a porous body produced by a conventional method.

Claims (4)

[Claims] 1. A porous body made of a thermoplastic resin, comprising a three-dimensional network structure having open cells made of non-fibrous finely bonded members formed by agglomeration and binding of particles of the thermoplastic resin. A porous body of plastic resin. 2. The thermoplastic resin is tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether. 2. A fluororesin selected from a copolymer (EPA), a tetrafluoroethylene-ethylene copolymer (ETFE), a polytetrafluoroethylene (PTFE), an amorphous fluororesin, and a fluorine-containing polyimide. Porous body of thermoplastic resin. 3. A method for producing a porous body made of a thermoplastic resin, wherein the mixture of the resin soluble in the organic solvent and the thermoplastic resin is higher than the melting point of the resin soluble in the organic solvent and A method for producing a porous body of a thermoplastic resin, characterized in that after thermoforming at a temperature below the melting point, a resin soluble in an organic solvent is eluted and removed by an organic solvent after heat treatment above the melting point of the thermoplastic resin. . 4. The thermoplastic resin is tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether. A fluororesin selected from a copolymer (EPA), a tetrafluoroethylene-ethylene copolymer (ETFE), a polytetrafluoroethylene (PTFE), an amorphous fluororesin, and a fluoropolyimide, and a resin soluble in an organic solvent is The method for producing a porous body of a thermoplastic resin according to claim 3, wherein the fluororesin is soluble in a solvent.