JPS6356891B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a fluororesin diaphragm, and relates to a method for manufacturing a fluororesin diaphragm that has low electrical resistance and low water permeability by blending fine hydrated silica powder. Conventionally, the method for producing this type of diaphragm is to mix fluororesin powder and fine silica powder with a solvent such as water or an organic solvent and an activator (dispersant) to form a paste, and then form this into a film. A wet method is used in which extrusion is followed by heating and baking, but this production method has the drawbacks that mixing is time-consuming and removal of the solvent and activator is time-consuming. A method has also been proposed in which fluororesin powder and anhydrous fine silica gel powder are mixed dry without using a solvent and then molded, but since the mixed powder is anhydrous, the powder becomes electrically charged during mixing. Since it adheres to the wall of the mixer and granulates into lumps, it is difficult to obtain a diaphragm with a uniform composition. This invention eliminates the conventional drawbacks and makes fluorine powder 75
-85% by weight, the moisture content at the time of mixing is 5-13% by weight, and the specific surface area obtained by the wet method is 200m ² /
After dry mixing with 15 to 25% by weight of hydrated silica fine powder, which is highly active silica with a weight of ~250 m ² /g, this mixed powder is filled into a mold and applied at a pressure of 150 to 300 Kg / cm ² . The present invention provides a method for easily manufacturing a diaphragm having a uniform composition by cutting the membrane from a molded body obtained by pressure molding, demolding, and heating and baking. In this invention, the fluororesin used is tetrafluoroethylene resin, hexafluoropropylene resin, etc., and the hydrated silica fine powder has a primary particle diameter of 10 to 20 millimicrons obtained by a wet method, and a specific surface area (BET Highly active silica having a particle diameter of 200 m ² /g ^{to 250 m 2} /g is used. The blending amount of fluororesin powder is 75 to 85
The amount by weight of the hydrated silica fine powder is preferably 15 to 25% by weight. When the amount of hydrated silica fine powder is 15% by weight or less (the amount of fluororesin powder is 85% or more), the electrical resistance of the diaphragm increases; If the blending amount is less than 75% by weight), it becomes difficult to mold the mixed powder, and the strength of the diaphragm also decreases. The water content of the hydrated silica fine powder used in this invention is preferably 5 to 13% by weight; if the water content is less than 5% by weight, the powder will be charged during mixing and uniform mixing will not be possible, and if it is more than 13% by weight, the molded product will not be able to be mixed uniformly. When firing, the molded product shrinks more and becomes more susceptible to cracking. When the above-mentioned hydrated silica fine powder and fluororesin powder are dry mixed in a mixer without using a solvent, the powder is not charged with electricity during mixing, and a mixed powder can be obtained that is very uniformly dispersed. This mixed powder is filled into a mold, pressure molded at a pressure of 150 to 300 kg/ ^cm2 , and after demolding, the membrane is cut from the molded body obtained by heating and baking at a temperature of 330 to 380°C. , a high quality diaphragm can be obtained. Next, the present invention will be explained with reference to examples. Example 1 85% by weight of tetrafluoroethylene resin powder and 15% by weight of hydrated silica fine powder (Nipsil VN3 manufactured by Nippon Silica Kogyo Co., Ltd., water content: 8% by weight) were dry mixed in a mixer,
This mixed powder is filled into a mold and the pre-molding pressure is 200.
Pressure molding was performed at Kg/cm ² to obtain a cylindrical molded body with an inner diameter of 70 mm and an outer diameter of 240 mm. After heating and baking this, the thickness is 0.2mm,
A diaphragm of 0.25 mm was cut. Table 1 shows the performance of each diaphragm.
It is as follows.

[Table] Example 2 Tetrafluoroethylene resin powder 81% by weight and hydrated silica fine powder (Nipsil LP manufactured by Nippon Silica Kogyo Co., Ltd., water content)
13% by weight) and 19% by weight are dry mixed in a mixer, this mixed powder is filled into a mold, and the pre-molding pressure is 250Kg/
A cylindrical molded body with an inner diameter of 70 mm and an outer diameter of 240 mm was obtained by pressure molding at cm ² . After heating and baking this, the thickness is 0.2mm,
Diaphragms of 0.25mm, 0.3mm, and 0.4mm were cut. The performance of each membrane is shown in Table 2.

[Table] Example 3 75% by weight of tetrafluoroethylene resin powder and 25% by weight of hydrated silica fine powder (Nipsil NS manufactured by Nippon Silica Kogyo Co., Ltd., water content: 5% by weight) were dry mixed in a mixer. Fill the mixed powder into the mold and pre-molding pressure 300
Pressure molding was performed at Kg/cm ² to obtain a cylindrical molded body with an inner diameter of 70 mm and an outer diameter of 240 mm. After heating and baking this, the thickness is 0.3mm,
A 0.4 mm diaphragm was cut. Table 3 shows the performance of each diaphragm.
It is as follows.

[Table] Method for measuring electrical resistance value After fully equilibrating the diaphragm with a 3N saline solution,
Measured in a 5N saline solution at 1000Hz AC at a temperature of 25℃. Method for measuring water permeation: Measure the amount of distilled water that permeates through a 20 cm ² membrane under the pressure of 1.0 m of water column. As described above, according to the present invention, since the fluororesin powder and the hydrated silica fine powder are dry mixed, the powder is not charged during mixing, and uniformly dispersed mixed powder can be obtained in a simple process. Can be done. In addition, since the diaphragm is cut from the molded body that is heated and fired after pressure-molding this mixed powder, it is easy to mass-produce the diaphragm.The resulting diaphragm has hydrated silica fine powder evenly dispersed, so it has a high electrical resistance. is small,
In addition, the amount of water permeation is small, and since the hydrated silica fine powder is fused to the fluororesin, it has the advantage that stable performance is maintained for a long period of time without falling off during use.

Claims (1)

[Claims] 1 Highly active silica with a water content of 5 to 13% by weight when mixed with fluororesin powder of 75 to 85% by weight, and a specific surface area of 200m ² /g to 250m ² /g obtained by a wet method. After dry mixing 15 to 25% by weight of hydrated silica fine powder, this mixed powder is filled into a mold.
A method for producing a fluororesin diaphragm, which is characterized in that the membrane is cut from a molded body obtained by pressure molding at a pressure of 150 to 300 Kg/cm ² , demolding the mold, and then heating and baking the molded body.