JP3046405B2 - Manufacturing method of porous body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel method for producing a porous material containing polytetrafluoroethylene (hereinafter referred to as PTFE) as an essential component.

[0002]

2. Description of the Related Art PTFE is excellent in various properties such as heat resistance, chemical resistance, sliding characteristics, and electrical insulation. And P
Since a porous body formed by molding TFE into a predetermined shape has the above-mentioned characteristics and also has gas permeability, it is being applied to a wide range of uses such as sealing materials, packings, cushioning materials, and filters.

[0003] As a method for producing such a porous PTFE body, for example, as disclosed in Japanese Patent Application Laid-Open No. Sho 61-66730, unfired PTFE is first heated at a temperature not lower than its melting point. And this fired PTF
A method is known in which E is pulverized into a powder, and then the fired powder is formed into a predetermined shape under a pressurized condition, and then heated again to a temperature equal to or higher than the melting point of PTFE.

[0004]

By the way, the porous PTFE obtained by the conventional method has a large creep deformation (cold flow) and is not suitable for use in a place where a large load or a large tightening force acts. There was a problem.

[0005]

The inventor of the present invention has conducted various studies to solve the above-mentioned problems of the prior art and found that PTFE
It has been found that a porous body having improved creep resistance can be obtained by using an unfired powder that has been granulated as a powder, mixing a filler with the unfired powder, molding the mixture, and then firing the mixture. It has been completed.

That is, the method for producing a porous body according to the present invention comprises:
The mixture of the granulated unfired PTFE powder and the filler is formed into a predetermined shape, and then heated to a temperature equal to or higher than the melting point of PTFE and fired.

In the present invention, unfired and granulated PTFE powder is used. "Granulation" means P
It means that a plurality of primary particles and / or secondary particles of TFE are aggregated, and the particle size is usually about 30 to 700 μm. Such granulated unfired PTFE powder,
M-31, M-32, M-3 from Daikin Industries, Ltd.
Third prize, 800 from Mitsui DuPont Fluorochemicals Co., Ltd.
-J, 820-J, etc. from Asahi Fluoropolymer Co., Ltd.
Since they are commercially available from Hoechst under the trade name of TF-1400 and the like, these can be obtained and used.

As the unfired powder of PTFE, what is generally called “molding powder” is also known, but when a non-granulated type “molding powder” is used in the method according to the present invention, A molded article having a porosity suitable for practical use cannot be obtained.

The filler used as a mixture with the above-mentioned PTFE powder can be used without any particular limitation as long as it is conventionally added for improving the creep resistance of the fluororesin. According to experiments performed by the inventor, it has been found that it is preferable to use “fibrous filler”.

As the fibrous filler, those having a diameter of about 5 to 50 μm and a length of about 5 to 5000 μm are preferable, and the value obtained by dividing the length by the diameter is about 20 to 200. Has been found to be preferable for improving creep resistance. Specific examples of these fibrous fillers include inorganic fibers such as carbon fibers, glass fibers and potassium titanate fibers, organic fibers such as aramid fibers, and whiskers such as silicon nitride and silicon carbide. The mixing ratio of the PTFE powder and the filler is determined by considering the moldability and the creep resistance of the obtained porous body.
It is preferable to use 5 to 50 parts by weight of filler based on 100 parts by weight of TFE powder.

In the present invention, first, a mixture of the granulated unfired PTFE powder and the filler is formed into a predetermined shape. The molding can be performed, for example, by filling the mixture in a mold and applying pressure. The pressure during molding is usually 10
g / cm ^{2 to} about 1000 kg / cm ² , preferably 1
The pressure is 0 to 300 kg / cm ² , and the pressing time is about 1 to 5 minutes. The molding under the pressurized condition is usually performed at room temperature.

After obtaining a molded article of a predetermined shape in this way,
This molded product is heated to a temperature equal to or higher than the melting point of PTFE and fired to obtain a porous body. The heating time is set depending on conditions such as the temperature and the size of the molded product.
5 hours.

The porosity and pore diameter of the porous body obtained by the method of the present invention are usually about 5 to 40.
%, And the pore diameter is about 5 to 50 μm. The porosity and pore diameter are mainly affected by the pressure during molding. For example, if other conditions are the same, the higher the pressure during molding, the lower the porosity and the smaller the pore diameter. Therefore, the porosity and pore diameter of the obtained porous body can be adjusted by appropriately setting the pressure during molding.

[0014]

The present invention is constructed as described above, and comprises a PTF
By a simple operation of forming a mixture in which a filler is blended with an unfired and granulated E powder as an E powder and firing the mixture, a porous body having excellent creep resistance can be obtained.

[0015]

The present invention will be described in more detail with reference to the following examples. The amounts of the materials used in Examples and Comparative Examples are all “parts by weight”.

Example 1 100 parts of granulated unfired PTFE powder (trade name: M-33, manufactured by Daikin Industries, Ltd.)
m, 20 parts of glass fiber having a length of 100 μm are added and mixed uniformly.

The mixture is filled in a cylindrical mold, and is pressed at room temperature (about 25 ° C.) at a pressure of 50 kg / cm ² for 5 minutes to form a column, and is taken out of the mold.

The molded body is heated at a temperature of 370 ° C. for 3 hours.
By heating and firing for a period of time, a porous body having a porosity of 18% and an average pore diameter of 17 μm was obtained.

The porosity was calculated by dividing the value obtained by subtracting the apparent specific gravity from the true specific gravity of the porous body by the true specific gravity, and multiplying the result by 100. The true specific gravity of the porous body is PTFE (fired).
And the weight average value of the true specific gravity of the glass fiber as the filler.

When the creep deformation rate of the porous body was measured, it was 4.9%. The creep deformation rate was determined by preparing a cylindrical sample having an outer diameter of 25.6 mm, an inner diameter of 20 mm, and a height of 20 mm, applying a load of 20 kg / cm ² to the sample at a temperature of 250 ° C. for 24 hours. The height before leaving (H ₁ ) and the height after leaving (H ₂ ) were measured, and H ₂ was subtracted from H ₁ to determine the height deformation (S), and this S was divided by H ₁ . The value was calculated by multiplying by 100.

Example 2 A diameter of 7 μm and a length of 200 parts per 100 parts of PTFE powder
The same operation as in Example 1 was carried out except that 50 parts of carbon fiber having a pore size of 33 μm and an average pore diameter of 41 μm were added.
Was obtained. Moreover, the creep deformation rate of this porous body was 7.3%.

Example 3 A diameter of 7 μm and a length of 500 were added to 100 parts of PTFE powder.
The same operation as in Example 1 was carried out except that 5 parts of aramid fiber (aromatic polyamide fiber) having a porosity of 6 μm was added.
%, And a porous body having an average pore diameter of 8 μm was obtained. The creep deformation rate of this porous body was 7.9%.

EXAMPLE 4 A diameter of 7 μm and a length of 50 μm were added to 100 parts of PTFE powder.
The same procedure as in Example 1 was carried out except that 20 parts of potassium titanate fiber of m was added, to obtain a porous body having a porosity of 15% and an average pore diameter of 20 μm. The creep deformation rate of this porous body was 4.3%.

Example 5 A diameter of 5 μm and a length of 50 μm were added to 100 parts of PTFE powder.
The operation was performed in the same manner as in Example 1 except that 20 parts of silicon carbide whiskers were added to obtain a porous body having a porosity of 13% and an average pore diameter of 15 μm. The creep deformation rate of this porous body was 4.0%.

Comparative Example 1 A porous body having a porosity of 4% and an average pore diameter of 3 μm was obtained in the same manner as in Example 1 except that no glass fiber was used. The creep deformation rate of this porous body was 11.5%.

Comparative Example 2 Non-granulated type unfired molding powder (trade name: M-1 manufactured by Daikin Industries, Ltd.) as PTFE powder
The procedure was the same as in Example 1, except that 2) was used. The obtained molded article was a non-porous body.

Comparative Example 3 The molding powder used in Comparative Example 2 was heated to a temperature of 370
Bake by heating at ℃ for 3 hours.

This calcined powder is put into a high-speed mixer and pulverized to obtain a powder that passes through a 100-mesh wire mesh.

This was filled in a cylindrical mold, pressed at room temperature at a pressure of 200 kg / cm ² for 5 minutes to form a column, taken out of the mold, and then heated at 370 ° C. for 3 hours to refire. As a result, a porous body having a porosity of 3% and an average pore diameter of 2 μm was obtained. The creep deformation rate of this porous body was 11.5%.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-49-57069 (JP, A) JP-A-4-279639 (JP, A) JP-A-57-146633 (JP, A) 105865 (JP, A) JP-B 46-10511 (JP, B1) JP-B 45-28644 (JP, B1) JP-T 1-502166 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) C08J 9/24 B29C 67/20

Claims (2)

(57) [Claims] 1. A mixture of a granulated unfired polytetrafluoroethylene powder and a filler is formed into a predetermined shape,
Next, a method for producing a porous body, comprising heating and firing at a temperature equal to or higher than the melting point of polytetrafluoroethylene. 2. The method for producing a porous body according to claim 1, wherein a fibrous filler is used as the filler.