JPS5955722A - Molding method of diaphragm made of fluorocarbon resin - Google Patents

Abstract

PURPOSE:To form a diaphragm having a uniform composition easily, by a method wherein a film is cut off from a molded unit obtained by pressing and molding mixture of powder of fluorocarbon resin and silicahydrate filled in a metallic die after mixing of each specific quantity of them. CONSTITUTION:Mixed powder is prepared by making dry method mixing, by a mixer, of 75-85wt% fluorocarbon resin, such as tetrafluoroethyline resin and hexafluoropropylene resin and 12-25wt% highly activated silicahydrate whose diameter of a primary particle is 10-20mmu and specific surface area is 200- 250cm<2>/g without applying a solvent. A diaphragm of high quality is obtained by cutting off a film from the molded unit obtained by heating and baking a molded mixed powder at a temperature of 330-380 deg.C after removal of the molded mixed powder obtained by pressing the molding the mixed powder filled within a metallic die by pressure of 150-300kg/cm<2>. As silicahydrate is dispersed evenly in the obtained diaphragm, electric resistance is low and stabilized performance can be maintained without having falling-off of the silicahydrate.

Description

[Detailed Description of the Invention] The invention relates to a method for producing a fluororesin diaphragm, and the fluororesin diaphragm has low stain resistance and low water permeability by incorporating hydrated silica fine powder. The present invention relates to a method for manufacturing.

The conventional method for producing a diaphragm is to mix fluororesin powder and fine silica powder together 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 the mixture is extruded and then heated and baked, but this manufacturing method has the disadvantage 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 dry mixed without using a solvent and then molded, but since the mixed powder is anhydrous, the powder becomes electrically charged during mixing. However, it was difficult to obtain a diaphragm with a uniform composition because it adhered to the wall of the mixer and granulated into lumps.

This invention solves the conventional drawbacks by dry mixing fluororesin powder and fine silica powder, molding the mixed powder under pressure, removing the mold, and then heating and baking to cut a film from the molded body. In particular, it provides a method for easily producing membranes of uniform composition.

In this invention, the fluororesin used is tetrafluoroethylene resin, hexafluoropropylene resin, etc., and the hydrated silica fine powder has a primary particle size of 10 to 2
0 micron IJ micron, specific surface area (BIT method) 200m
7g - 230mg of highly active silica is used.

The blended amount of fluororesin powder is 76-,! The amount of the hydrated silica fine powder to be blended is preferably 20 to 20% by weight. If the blended amount of hydrated silica fine powder is below /jwt% (the blended amount of fluororesin powder is lr!), the electrical resistance of the diaphragm will increase, and if the blended amount of hydrated silica fine powder is above cojwt% (If the amount of fluororesin powder is less than 7Jwt), it becomes difficult to mold the mixed powder, and the strength of the diaphragm also decreases.

The moisture content of the hydrated silica fine powder used in this invention is j-/J
% by weight is preferred, and moisture content! If the weight is less than 13% 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 shrink significantly and tend to crack when fired.

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.

Fill this mixed powder into a mold /, tθ ~ 300 k
Pressure molded at a pressure of g/l*2, 330-310 after demolding
A high-quality diaphragm can be obtained by cutting the membrane from a molded body obtained by heating and baking at a temperature of .degree.

Next, the present invention will be explained with reference to examples.

Example 1゜Tetrafluoroethylene resin powder
VH2.

The moisture content and weight s')tsl were dry mixed in a mixer, and this mixed powder was filled into a mold and the premolding pressure was set to 200.
Pressure molded with 4/cI112, inner diameter 7Qm.

A cylindrical molded body having an outer diameter of 2'lOwg was obtained. After heating and baking this, the thickness is 0. ．． 2111N, θ,, 2.1t III
The septum was cut. The performance of each diaphragm is shown in Table 1.

Table 1 Example 2 Tetrafluoroethylene resin powder/weight - and hydrated silica fine powder (N1psi'l LP manufactured by Nippon Silkani Industry).

Moisture content: 73 weight S
Pressure molded with "kq/ax", inner diameter 70KM.

A cylindrical molded body with an outer diameter of 2 mm and θ was obtained. After heating and baking this, the thickness is 0. ．． 211I, Q, 23m, Q, 3
The diaphragms of mg, Q, and Gu were cut. The performance of each diaphragm is shown in Table 2.

Table-2 Example 3゜Tetrafluoroethylene resin powder 7! Weight and water-containing silica fine powder (N1psil NS manufactured by Nippon Silikani Co., Ltd.).

Water content (Jwt%) and 200g/ax2 were dry mixed in a mixer, and this mixed powder was filled into a mold and press-molded at a pre-molding pressure of 300mm/ax2 to have an inner diameter of 70n.

A cylindrical molded body having an outer diameter of 2'lOW was obtained. After heating and baking this, a cod diaphragm having a thickness Q of 3 gm and θ was cut. The performance of each diaphragm is shown in Table 3.

Table 3 After fully equilibrating the diaphragm in a saline solution of jN, measurements are taken in a saline solution of jN at an AO of 1000 Hz and at a temperature of 1000 Hz.

Method for Measuring Water Permeation Amount The amount of distilled water permeating through a 20α2 membrane is measured under a pressure of water column/Om.

As described above, according to the present invention, since the fluororesin powder and the hydrated silica fine powder are dry-mixed, as soon as the powder is charged during mixing, uniformly dispersed and mixed powder can be obtained in a simple process. be able to. In addition, since the diaphragm is cut from the molded body after press-molding this mixed powder and then heating and firing, mass production of the diaphragm is easy.The obtained diaphragm has hydrated silica fine powder evenly dispersed, so it has a high electrical resistance. It has the advantage of having a small amount of water permeation, and since the hydrated silica fine powder is fused to the fluororesin, it does not fall off during use and maintains stable performance over a long period of time.

Patent applicant: NICHIAS Co., Ltd. 7 - 137-

Claims (2)

[Claims] (1) Fluororesin powder 7! ~trr weight and hydrated silica fine powder/J'~, 2! After dry mixing with the weight method,
This mixed powder is filled into a mold and weighs up to 300 kg/
A method for producing a fluororesin diaphragm, which comprises press molding at a pressure of cx2, demolding the mold, and then cutting the membrane from the resulting molded body. (2) The hydrated silica fine powder has a moisture content of j-
The fluororesin diaphragm according to claim 1, which is made of highly active silica having a specific surface area of 200m"7g-2J'Om"7g obtained by a wet method. manufacturing method.