JPS60104319A - Polytetrafluoroethylene porous material and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a porous PTF molding of a porosity of 40% or more with a pore diameter of 0.1mum or less by using PTFE fine powder of an extremely high number average molecular weight. CONSTITUTION:PTFE fine powder of a molecular weight of ten million or more is mixted with a liquid lubricant, and the mixture is extruded or molded by rolling or a combination of extrusion and rolling. The unbaked molding is stretched to at least one direction with a stretching ratio of 200% or more in order to obtain a molding of a pore diameter of 0.2mum or less. To stabilize and strengthen the porous structure of such a porous molding of 0.2mum or less fine pore diameters, the molding is preferably heated and baked at about 327 deg.C under a condition that thermal shrinkage is prevented afterwards.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to polytetrafluoroethylene (hereinafter referred to as PTIE).
The present invention relates to a porous body made of a porous material (hereinafter referred to as "porous body") and a method for manufacturing the same.

(Prior art and its O1 problem) PTF E is a plastic with excellent heat resistance and chemical resistance, and this porous material is used as a filter for precision filtration of corrosive substances, a diaphragm for electrolysis, and for its water repellency. Recently, it has come to be used in a wide range of applications, such as various breathing valves.

Conventionally, the method for manufacturing such a PTF E porous body is to stretch an unfired PTF E molded body i at a temperature below the melting point of PTFE to make it porous, and then to make the PTF E porous body.
A method of firing by heating to a temperature higher than the crystal melting point of is known.

Although this method has the advantage of obtaining relatively high porosity, the lower limit of the pore size is approximately 0.2 μm;
It has been difficult to obtain porous bodies with smaller pore sizes.

As a result of various studies in order to obtain a porous PTFE material with an even smaller pore diameter, the inventors of the present invention found that the PTFE fine powder used as a raw material had an extremely high number average molecular weight (hereinafter abbreviated as molecular weight). We have discovered that it is possible to make the pores smaller.

(Contents of the Invention) The feature of the present invention is that a fine powder having a molecular weight of 10 million or more is used as a raw material. By using such fine powder, the pore size can be reduced to 0.1
We succeeded in obtaining a PTFE porous body with a porosity of 4096 or more and a porosity of 4096 or less.

The present invention can be applied to films, tubes, rods, yarns, etc. as porous bodies.

It has also been found that the use of such raw materials not only reduces the pore diameter but also increases the tensile strength.

In the present invention, molecular weight refers to PTFE as ASTM-D-
1457-56T, the following equation holds true:

SSG == -0,05791ogMn+2.611
3 Here, SSG represents the above-mentioned specific gravity, and Mn represents the molecular weight.

Next, details of the present invention will be explained.

The first step for obtaining a porous body by the method of the present invention is to use P with a molecular weight of 100.11 million or more, which is a feature of the present invention.
This is a process of mixing TFE fine powder and liquid lubricant. This lubricant may be a conventionally known lubricant; for example, hydrocarbons such as solvent naphtha, aromatic hydrocarbons such as toluene, etc. are used, and the amount thereof is 1% relative to PTFE.
5 to 50% by weight is suitable. Further, a filler such as a pigment for coloring can be added if necessary.

This mixture is then shaped by a process involving extrusion or rolling or a combination of both. For example, rods, tubes, strips, sheets, etc. can be formed using a ram extruder, and sheets and films can also be formed by rolling.

Moreover, these can also be compression molded before extrusion or rolling.

The green molded article containing the lubricant thus obtained is then stretched in at least one direction. This stretching can be carried out with the lubricant present or after its removal by evaporation, extraction, etc.

Taking film stretching as an example, this stretching process is carried out by changing the rotational speed of two rolls, but in order to obtain a pore size of 0.2 μm or less, which is the objective of the present invention, the stretching rate must be adjusted. It is preferable that it is 200% or more.

Although a porous body with a minute pore size of 0.2 μm or less can be obtained by such a method, it is possible to further stabilize and stabilize this porous structure.
To make it stronger, it will be heated to about 327mm in a heat shrinkage prevention state.
It is preferable to heat and bake at a temperature of .degree. C. or higher.

Here, the state of preventing heat shrinkage includes not only a state where shrinkage is completely prevented but also a state where some shrinkage is allowed.

(Example 1) 200 g of petroleum fraction (boiling point 150-250'') was added to 1000 g of PTFE fine powder with a number average molecular weight of 20 million, mixed, preformed, and then extruded under an extrusion pressure of 5
A plate-shaped molded product having a medium size of 3QQm and a thickness of 15su was obtained under a pressure of .degree.Ky/an''.

This material was passed through a calender roll in a direction perpendicular to the extrusion direction to obtain an unfired film with a thickness of 0.3 mm.

Next, this film was immersed in trichlene for 3 hours to remove the oil.

Furthermore, this unfired film was then stretched using a roll. At this time, the roll temperature was 300''C, the roll interval was 1 crystal, the stretching ratio was 600%, and the supply side roll speed was 6 m 7 minutes.

Next, this stretched film was brought into close contact with a mirror-finished stainless steel plate and heat-treated at 380°C for 20 minutes to sinter it.

The average pore diameter of this film was measured by mercury porosimetry and was found to be 0.05 μm. Moreover, the porosity was 50%.

(Comparative Example 1) Petroleum distillate (boiling point 150~
A sintered film was produced in the same manner as in Example 1 by adding 200 g of 250'C).

The average pore size of this film is 0.30 μm, and the porosity is 55
%Met.

Claims (1)

Scope of Claims: (1) A polytetrafluoroethylene porous material comprising polytetrafluoroethylene having a number average molecular weight of 10 million or more and having an average pore diameter of 0.2 μm or less. (2. A method for producing a porous body according to claim 1, comprising extruding and/or After forming by a method including rolling, the formed object is stretched in at least one direction at a temperature of about 327°C or less, with or without removing the liquid lubricant, and then, if necessary, heat-shrinked. Approximately 32 in prevention state
A method for producing a polytetrafluoroethylene porous body, which comprises firing at a temperature of 7°C or higher. (3) The method for producing a porous polytetrafluoroethylene material according to claim 2, wherein the stretching ratio is 200% or more.