JPH0437772B2 - - Google Patents

Description

[Detailed description of the invention]

Technical Field of the Invention The present invention relates to a method for producing a molded article based on polytetrafluoroethylene resin, and more specifically, the present invention relates to a method for manufacturing a molded article based on polytetrafluoroethylene resin, which has excellent wear resistance and is less aggressive to mating members. The present invention relates to a method for manufacturing a molded object. Technical background of the invention and its problems Polytetrafluoroethylene resin (PTFE)
) has excellent heat resistance and chemical resistance, as well as low coefficient of friction and self-lubricating properties, so it is widely used as molded products such as sliding materials, pipes, valves, and pots. ing. However, PTFE does not necessarily have good wear resistance and does not have sufficient compressive strength.
Various fillers have been added to PTFE to improve its wear resistance and mechanical strength.
Inorganic fillers such as glass fiber, carbon fiber, graphite, molybdenum disulfide, and bronze powder are known as fillers added to such PTFE. However, PTFE to which inorganic fillers such as glass fibers are added, as mentioned above, is
Although the wear resistance of the PTFE molded product itself is improved, if the mating member that comes into contact with the PTFE molded product is soft, the mating member will wear out. In order to solve these problems, we developed polyphenylene sulfide (hereinafter referred to as "polyphenylene sulfide"), a heat-resistant polymer.
It has been proposed that PPS (sometimes abbreviated as PPS) be added to PTFE, and this PPS is added.
PTFE molded products have the excellent advantage of not causing wear on the mating member even if the mating member is soft. However, PTFE containing 5% by weight or more of PPS
When manufacturing a molded object using a molding composition based on , the molding composition is put into a mold and compressed to preform, and the obtained preform is taken out from the mold and heated. When a free baking method was adopted, there was a serious problem in that cracks occurred in the molded product during heating. Also the above
When preforming a PTFE-based molding composition, if the preforming pressure is 300 Kgf/cm ² or more,
There was a problem in that the preforming pressure could not be increased because cracks would occur in the resulting molded product. If a molded article is produced without increasing the preforming pressure, a dense molded article with excellent mechanical strength cannot be obtained. Such PPS was added as a filler
In order to solve the problems associated with PTFE-based molding compositions, Japanese Patent Publication No. 59-18420
Characterized by adding 10 to 30% by weight of graphite or glass fiber in addition to PPS to PTFE
Molding compositions based on PTFE are disclosed. However, although this molding composition has the advantage that cracks do not occur during heating and firing and the preforming pressure can be increased, since the composition contains graphite or glass fiber, it There was a problem in that the aggressiveness towards the parts appeared and the mating parts were worn out. Therefore, the present inventors developed PTFE with added PPS.
In order to solve the problems associated with molding compositions based on Moreover,
The present invention was completed by discovering that this is due to the gas generated from PPS because the PPS particles are heated and fired rapidly without being uniformly dispersed in the PTFE particles. Purpose of the Invention The present invention aims to solve the problems associated with the prior art as described above, and is aimed at solving the problems associated with the prior art as described above. The object of the present invention is to provide a method for producing a molded body from a PTFE-based molding composition, which allows the preforming pressure to be increased without causing cracks in the resulting molded body. . Summary of the Invention The method for producing a molded article based on polytetrafluoroethylene according to the present invention comprises 95 to 80% by weight of polytetrafluoroethylene powder and 5 to 80% by weight of polyphenylene sulfide powder having a particle size of 80 μm or less.
20% by weight (however, the total of the above polytetrafluoroethylene powder and the above polyphenylene sulfide powder is 100% by weight), and
The obtained mixture is pressurized to 300 to 700 Kgf/cm ² and preformed, and then the preform is preheated at a temperature above the melting point of polyphenylene sulfide and below the melting point of polytetrafluoroethylene, and then It is characterized by heating and firing at a temperature higher than the melting point of tetrafluoroethylene. According to the present invention, after uniformly mixing PTFE powder with PPS powder having a specific particle size, the mixture is heated and maintained at a temperature above the melting point of PPS but below the melting point of PTFE, and then heated to a temperature above the melting point of PTFE. do
Since we manufacture molded bodies based on PTFE, there is no sudden gas generation from PPS, and therefore no cracks occur in the resulting molded bodies, and the preforming pressure can be increased, making it dense and dense. A PTFE-based molded body with mechanical strength is obtained. DETAILED DESCRIPTION OF THE INVENTION The method for producing a molded article based on PTFE according to the present invention will be specifically described below. In the present invention, first, a PTFE-based molding composition is prepared by uniformly mixing PTFE powder and PPS powder. The PTFE powder is used in the molding composition in an amount of 95-80% by weight and the PPS powder in an amount of 5-20% by weight. (However, the total of the above polytetrafluoroethylene (PTFE) powder and the above polyphenylene sulfide (PPS) powder is 100%
Weight%. The PTFE powder preferably has a particle size of 10 to 40 μm, and both so-called molding powder and fine powder are used. PPS powder is 80μm or less, preferably 20-30μm
It has a particle size of If the particle size of PPS exceeds 80 μm, it will not mix uniformly with the PTFE powder, and gas will be rapidly generated from the PPS powder when heating and baking a PTFE-based molding composition to which PPS has been added. This is not preferred because cracks occur in the molded product obtained. It is also possible to add an inorganic filler to the PTFE-based molding composition according to the present invention in an amount that does not promote wear of the mating member. Examples of such inorganic fillers include glass fiber, graphite, molybdenum disulfide, bronze powder, and carbon fiber. For example, when graphite is used as an inorganic filler, it can be used in an amount of up to 10% by weight in a molding composition, and in this case, the resulting molded product has almost no aggressiveness against the mating material. do not have. The PTFE-based molding composition obtained in this way is put into a mold etc. and weighs 300 to 700 kg.
Preforming is performed by applying pressure to f/cm ² to form a preform. When pressurizing this molding composition to preform, the particle size of the PPS powder is set to 80 μm or less, preferably 20 μm or less.
If the thickness is not ~30μm, the preforming pressure should be 300~700Kg.
f/cm ² is not possible. If the preforming pressure
If it is not 300 Kgf/cm ² or more, it will not be possible to obtain a dense preform, and therefore it will not be possible to obtain a compact and excellent mechanical strength. Next, the preform obtained as above,
Heat and maintain at a temperature above the melting point of PPS but below the melting point of PTFE. Note that the melting point of PPS is about 285°C, and the melting point of PTFE is about 327°C. It is desirable that the preform be maintained at a temperature within the above range for at least 10 minutes, preferably 30 minutes or more. Such preheating of the preform may be performed after the preform is removed from the mold, or may be performed while the preform is housed in the mold. The preform is heated above the melting point of PPS and is made of PTFE.
By heating and maintaining the temperature below the melting point of
This prevents the sudden evolution of gas from the PPS when the preform is heated to a temperature above the melting point of PTFE, and thus prevents the formation of cracks in the resulting PTFE-based molded body. Ru.
In addition, when the preform is heated and held in the above temperature range, the gas generated from PPS is gradually released from the preform, so the preforming pressure applied to the molding composition when forming the preform is reduced. can be increased. Next, after subjecting the preform to a preheating treatment as described above, the preform is heated to a temperature equal to or higher than the melting point of PTFE, thereby obtaining a PTFE-based molded body. When heating the preform to a temperature equal to or higher than the melting point of PTFE, the preform may be taken out of the mold and heated, or the preform may be heated while being housed in the mold. Effects of the Invention As described above, since the PTFE-based molded product obtained by the present invention contains PPS, the molded product itself has excellent wear resistance and does not wear out the mating member. In addition, cracks do not occur in the molded product, and since the preforming pressure can be increased during production of the preform, a molded product that is dense and has excellent mechanical strength can be obtained. However, the present invention is not limited to these examples. Example 1 85 parts by weight (85
% by weight) and 15 parts by weight (i.e. 15% by weight of PPS (P-4 manufactured by Philips Petroleum International) pulverized to an average particle size of 20 μm in a pulverizer (i.e. 15% by weight, however, the difference between PTFE powder and PPS powder the total
100% by weight. ) were thoroughly and uniformly mixed in a dry process to prepare a PTFE-based molding composition. The obtained molding composition was put into a mold and 600 kg/
A preform was produced by preforming at a pressure of cm ² . Next, this preform is taken out from the mold,
It was preheated by holding it at 300°C for 30 minutes, which is a temperature above the melting point of PPS and below the melting point of PTFE. Next, the preformed body subjected to the preheating treatment was heated and fired at 340°C, which is a temperature higher than the melting point of PTFE. The true specific gravity [g/cm ³ ] of the obtained molded body, the wear of the molded body itself, and the wear of the mating member were measured, and the results are shown in Table 1. Note that the wear of the molded body itself and the wear of the mating member were measured as follows. As for the wear of the compact itself, the wear volume was calculated by dividing the weight loss before and after the test by the specific gravity, and the wear height was calculated from the contact area to calculate the wear count. Wear count = wear height [cm] / surface pressure [Kg/cm ² ] x sliding speed [
m/S] x time [hr] Wear of the mating member was calculated by dividing the weight loss before and after the test by the sliding distance [Km]. Example 2 75 parts by weight (83
(% by weight) and 15 parts by weight (i.e. 17% by weight of PPS (manufactured by Philips Petroleum International P-4) crushed to an average particle size of 20 μm in a crusher (i.e. 17% by weight, however, the total of PTFE powder and PPS powder) of
100% by weight. ) and 10 parts by weight of graphite (CB manufactured by Nippon Graphite Co., Ltd.) having an average particle size of 40 μm were thoroughly and uniformly mixed in a dry process to prepare a PTFE-based molding composition. A molded body was produced from the obtained molding composition in the same manner as in Example 1, and the true specific gravity of the molded body, the wear of the molded body itself, and the wear of the mating member were measured, and the results are shown in Table 1. Example 3 A molded body was produced in the same manner as in Example 1, except that the obtained molding composition was put into a mold and preformed at a pressure of 300 kg/cm ² to produce a preformed body. was manufactured. The true specific gravity of the obtained molded body, the wear of the molded body itself, and the wear of the mating member were measured, and the results are shown in Table 1. Example 4 Molding was carried out in the same manner as in Example 1, except that in Example 2, the obtained molded body composition was put into a mold and preformed at a pressure of 300 kg/cm ² to produce a preformed body. manufactured the body. The true specific gravity of the obtained molded body, the wear of the molded body itself, and the wear of the mating member were measured, and the results are shown in Table 1. Comparative Example 1 Example 1 except that 15 parts by weight of glass fiber was used instead of PPS as a filler.
A PTFE-based molded body was produced in the same manner as described above. The true specific gravity of the obtained molded body, the wear of the molded body itself, and the wear of the mating member were measured, and the results are shown in Table 1.

[Table] From Table 1, it can be seen that the PTFE-based molded body obtained according to the present invention has low wear on the molded body itself and also has low aggressiveness toward the mating member. Comparative Example 2 The preform obtained in Example 1 was
Immediately without preheating at a temperature of 340℃
A molded body was produced in the same manner as in Example 1, except that the preformed body was heated and fired at a temperature of . The resulting molded product was found to have cracks and had low mechanical strength. Comparative Example 3 A molded article was produced in the same manner as in Example 1, except that PPS that had not been subjected to pulverization treatment and had an average particle diameter of 80 μm was used. The resulting molded product was found to have some cracks, albeit slightly.

Claims (1)

[Scope of Claims] 1 95 to 80% by weight of polytetrafluoroethylene powder and 5 to 20% by weight of polyphenylene sulfide powder having an average particle size of 80 μm or less (provided that the polytetrafluoroethylene powder and the polyphenylene sulfide powder have an average particle size of 80 μm or less) rensulfide powder (total of 100% by weight) and the resulting mixture was
After preforming under pressure of ~700Kgf/ ^cm2 , the preform is preheated at a temperature above the melting point of polyphenylene sulfide but below the melting point of polytetrafluoroethylene, and then heated to a temperature above the melting point of polytetrafluoroethylene. 1. A method for producing a molded article based on polytetrafluoroethylene, which comprises heating and firing at a temperature of . 2 The preform is heated at a temperature of 290 to 310°C at least
The method according to claim 1, wherein the method is preheated for 10 minutes or more. 3. The method according to claim 1, wherein the polyphenylene sulfide powder has an average particle size of 20 to 30 μm.