JPS5918420B2 - Polytetrafluoroethylene molding composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses 90 to 50% by weight of polytetrafluoroethylene.
, a polytetrafluoroethylene molding composition comprising 5 to 20% by weight of polyphenylene sulfide and 10 to 30% by weight of graphite or glass fiber powder.

Polytetrafluoroethylene (hereinafter abbreviated as PTFE)
Because it has a low coefficient of friction and self-lubricating properties, it is widely used as bearing materials, pipes, valves, cocks, and other molded products.

However, the abrasion resistance is not necessarily good and the compressive strength is low, so various fillers have been added to it for a long time to improve its mechanical properties, abrasion resistance, etc.

Generally, inorganic fillers such as glass fiber powder, carbon fiber, asbestos, graphite, molybdenum disulfide, and bronze powder are mixed as such fillers, but these inorganic fillers often have problems when the mating material is soft. It can wear them out. Recently, attempts have been made to improve mechanical strength by blending PTFE with heat-resistant polymers such as aromatic polyester or polyimide instead of these inorganic fillers, but all of these heat-resistant polymers are expensive. Therefore, they cannot avoid economic disadvantage. When polyphenylene sulfide (hereinafter abbreviated as PPS), which is a relatively inexpensive heat-resistant polymer, is blended with PTFE,
Although it is economically advantageous, it causes various difficulties in molding.

That is, if PPS is added to the extent that the mechanical properties of PTFE can be improved, for example, 10% by weight or more, the free baking method will generate cracks during firing, making it necessary to use the hot coining method, resulting in poor productivity.

Furthermore, when PPS is blended, cracks tend to occur unless the preforming pressure is very low. The present inventors have conducted various studies to develop PPS-filled PTFE with excellent moldability by using PPS, an inexpensive heat-resistant polymer, as a filler. It has been found that a PTFE composition that can be subjected to a free baking method can be obtained by using the above in combination.

That is, in the present invention, the pps added to PTFE is 5
~20% by weight, and below 5% by weight, PTF
If the amount exceeds 20% by weight, cracks will occur without improving the mechanical properties of E. Also, PPS is 2700C
The generation of diglac is reduced by heat treatment for 5 hours or more. In the present invention, the amount of graphite or glass fiber powder used as an inorganic filler in combination with PPS is 10 to 10%.
It is blended in a range of 30% by weight.

If it is less than 10% by weight, cracks cannot be prevented;
This is because tensile strength, elongation, etc. decrease when the amount exceeds % by weight.

It should be noted that various other inorganic and polymeric fillers may be added to the composition of the present invention as long as the blending ratios of the above compositions are not changed. Example 1 70 parts of PTFE molding powder (Polyflon M-12 manufactured by Daikin Industries, Ltd. KK) (the weights are the same below), 10 parts of polyphenylene sulfide (Ryton P-4 manufactured by Philips Petroleum International), and A composition of the present invention was compression molded by mixing 20 parts of graphite (CP manufactured by Nippon Graphite KK) in a conventional dry method.

The results were as shown in Table 1, and a dense molded product was obtained that did not generate cracks even at 500 kg/d and did not allow gas to pass through. Examples 2 to 5 Example 1 with different blending ratios of PPS and graphite
A composition produced according to the method was compression molded.

The results are as shown in Table 1, and both are 500kg/
A dense molded product that does not allow gas to pass through was obtained, which could be molded at Clit or higher. Example 6 Compression molding was performed according to Example 1, using glass fiber powder instead of graphite.

As shown in Table 1, the results were similar to those obtained when graphite was used. Comparative Example 1 A composition in which 90 parts of PTFE was mixed with 30 parts of PPSLO
At 0k9/CliL, a crack occurred and the weight was 150kg/
d can be molded, but the compressive strength is not as high as that of soil.

Comparative Example 2 The mixed composition of 80 parts of PTFE and 2 parts of PPS was the same as in Comparative Example 1, and the molded article at 150 k9/d slightly permeated gas.

Comparative Examples 3 and 4 Cracks occur when a composition containing molybdenum disulfide instead of graphite is molded at 500 kg/Cld.

Comparative Example 5 When glass fiber powder is blended with PTFE without blending PPS, it can be molded at 500 kg/CTit, but the compressive strength is slightly inferior to the case where PPS is blended.

Claims (1)

[Claims] 1 A polytetrafluoroethylene molding composition comprising a mixture of 90 to 50% by weight of polytetrafluoroethylene, 5 to 20% by weight of polyphenylene sulfide, and 10 to 30% by weight of graphite or glass fiber powder.