JPH0546381B2 - - Google Patents

Description

[Detailed description of the invention]

Technical Field of the Invention The present invention relates to a composition based on polytetrafluoroethylene resin, and more specifically to a molding composition based on polytetrafluoroethylene resin that has excellent wear resistance and is less aggressive to mating parts. relating to things. 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. By the way, PTFE does not necessarily have good wear resistance and also 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 product has been improved, there is a problem in that 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 with less than 5% by weight of PPS added
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, when this molding composition contains glass fibers, it has the advantage that cracks do not occur during heating and baking, and the preforming pressure can be increased. Because of this, there was a problem in that the material exhibited aggressiveness toward the other member, causing friction with the other member. Furthermore, when the composition disclosed in Japanese Patent Publication No. 59-18420 contains graphite particles, since graphite particles with a large particle size are used, and the size of the graphite particles and the size of the PPS particles are different from each other. Since the relationship between the composition and the composition has not been specified, there still remains the problem that cracks occur when the composition is heated and fired. Therefore, the present inventors developed PTFE with added PPS.
In order to solve the problems associated with molding compositions based on They discovered that this was due to the gas generated from PPS during rapid heating and firing in this state, and further research revealed that if graphite particles with a specific particle size were placed on the surface of PPS particles, the gas generated from PPS particles could be generated. The present invention was completed based on the discovery that the gas that is present can be easily discharged from the system. 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 PTFE-based molding composition that does not cause cracks in the resulting molded product and allows for increased premolding pressure. Summary of the invention The molding composition based on polytetrafluoroethylene according to the present invention comprises 96-60% by weight of polytetrafluoroethylene powder and 2% polyphenylene sulfide powder having an average particle size of 10-30 μm.
-20% by weight and 2 to 20% by weight of graphite powder having an average particle size of 10 μm or less, and the average particle size of the graphite powder is 1/2 or less of the average particle size of polyphenylene sulfide powder. It is characterized by certain things. The PTFE-based molding composition according to the invention has, in addition to PTFE powder, a specific particle size.
Since it contains PPS powder and graphite powder, and the average particle size of the graphite powder is 1/2 or less of the average particle size of the PPS powder, a molded body is manufactured from this PTFE-based molding composition. At this time, the gas generated from the PPS can be easily led out of the molded product, so that cracks do not occur in the resulting molded product, and moreover, the preforming pressure of the molded product can be increased. Furthermore, the molded product obtained has excellent wear resistance, especially under water and high temperature conditions. DETAILED DESCRIPTION OF THE INVENTION The PTFE-based molding composition according to the present invention will be specifically described below. The PTFE-based molding composition according to the invention comprises 96-60% by weight of PTFE powder, 2-20% by weight of PPS powder with an average particle size of 10-30 μm and 10 μm of powder.
Graphite powder 2~ having an average particle size of m or less
20% by weight, and the average particle size of the graphite powder is 1/2 or less of the average particle size of the PPS powder. The PTFE powder preferably has a particle size of 10 to 40 μm, and both so-called molding powder and fine powder are used. Furthermore, the content of PTFE powder in the molding composition according to the present invention is 96 to 60% by weight;
If it exceeds 96% by weight, the wear resistance and mechanical strength of the molded product obtained will not be improved much, which is undesirable. On the other hand, if it is less than 60% by weight, the molded product obtained will have cracks or its mechanical strength will decrease. Therefore, it is undesirable. PPS powder has an average particle size of 10-30 μm. If the particle size of PPS exceeds 30μm, it will not mix uniformly with the PTFE powder, and the PTFE powder with this PPS added will
When heating and baking a molding composition based on
This is undesirable because a large amount of gas is suddenly generated from the PPS powder and cracks occur in the resulting molded product. PPS powder is contained in the molding composition in an amount of 2 to 20% by weight, but if it is less than 2% by weight, the abrasion resistance and mechanical strength of the resulting molded product will not be improved so much, which is not preferable; If it exceeds %, the resulting molded product may crack or swell, which is undesirable. The graphite powder has an average particle size of 10 μm or less, which is less than half the average particle size of PPS powder. If graphite powder is 10μ
If the average particle size exceeds m or exceeds 1/2 of the average particle size of the PPS powder, the gas generated from the PPS powder during heating and firing cannot be completely led out of the compact. For this reason, the gas generated from the PPS powder is trapped inside the compact,
Cracks occur in the resulting molded product. Graphite powder is included in the molding composition in an amount of 2 to 20% by weight, but less than 2% by weight, PPS
This is undesirable because the gas generated from the powder cannot be completely led out of the molded body.
If it exceeds % by weight, the proportion of the filler in the obtained molded product increases, which is undesirable because the mechanical strength deteriorates. By including graphite powder as described above in an amount of 2 to 20% by weight in a PTFE-based molding composition, the resulting molded product has excellent properties, especially in a moist atmosphere and at high temperatures. Shows wear resistance. For example, graphite powder like the one above
By including it in a molding composition consisting of PTFE powder and PPS powder in an amount of 10% by weight, the wear coefficient in water becomes approximately 1/10 of that when graphite powder is not included. . Furthermore, when comparing a molding composition containing graphite powder with the above-mentioned characteristic particle size and a molding composition containing graphite powder with an average particle size of 50 μm, the wear coefficient in water is lower than that of the specific particle size. 50μm if graphite powder is included
The amount is less than 1/2 that of the case containing graphite powder. Note that the PTFE-based molding composition according to the present invention may contain inorganic fillers such as glass fiber, molybdenum disulfide, and bronze powder, if necessary. In order to produce a molded article from the PTFE-based molding composition according to the present invention, PTFE
A molding composition based on PTFE may be compression molded according to a conventional method and then heated and fired at a temperature equal to or higher than the melting point of PTFE. At this time, there is no particular need to perform preheating as disclosed in Japanese Patent Application No. 60-245774 filed by the present applicant. Effects of the Invention The PTFE-based molding composition according to the present invention has a specific particle size in addition to PTFE powder.
Since it contains PPS powder and graphite powder, and the average particle size of the graphite powder is 1/2 or less of the average particle size of the PPS powder, a molded body is manufactured from this PTFE-based molding composition. At this time, the gas generated from PPS can be easily led out of the molded product, so that cracks do not occur in the resulting molded product, and moreover, the preforming pressure during molding can be increased. Furthermore, the molded product obtained has excellent wear resistance, especially under water and high temperature conditions. EXAMPLES The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples. Example 1 75 parts by weight of PTFE molding powder (7J manufactured by Mitsui Fluorochemical Co., Ltd.) with an average particle size of 30 μm,
15 parts by weight of PPS (P-4 manufactured by Philippe Petroleum International), which has been ground to an average particle size of 25 μm using a pulverizer, and 10 parts by weight of graphite powder with an average particle size of 6 μm are thoroughly homogenized in a dry process. A PTFE-based molding composition was prepared. The obtained molding composition was put into a mold and 300 kg/
A preform was produced by preforming at a pressure of cm ² . Next, this preformed body was heated and fired at 340° C., which is a temperature higher than the melting point of PTFE, to produce a PTFE-based molded body. The obtained molded body was immersed in water and weighed 6 kg/water.
A wear test was carried out by sliding against a mating member at 0.4 m/sec for 100 hours under a load of cm ² , and the wear coefficient was measured according to the table below. Wear coefficient = wear height [cm] / surface pressure [Kg/cm ² ] x sliding speed [
m/s] x time [hr] The wear height was calculated by dividing the weight loss of the compact before and after the test by the specific gravity to calculate the wear volume, and then dividing this wear volume by the contact area. The results are shown in Table 1. In addition, a wear test was carried out by sliding the obtained molded body against a mating member at 200°C and 300°C for 100 hours at a sliding speed of 0.5 m/sec under a load of 14 kg/cm ² .
The wear coefficient was measured. The results are shown in Table 2. It should be noted that this molded product was not found to have any aggressiveness towards the mating member. Example 2 85 parts by weight of PTFE molding powder (7J manufactured by Mitsui Fluorochemical Co., Ltd.) with an average particle size of 30 μm,
10 parts by weight of PPS (P-4 manufactured by Philips Petroleum International), which was ground to an average particle size of 25 μm using a pulverizer, and 5 parts by weight of graphite powder with an average particle size of 6 μm were thoroughly homogenized in a dry process. A PTFE-based molding composition was prepared. The obtained molding composition was put into a mold and 300 kg/
A preform was produced by preforming at a pressure of cm ² . Next, this preform was heated and fired at 340°C, which is a temperature higher than the melting point of PTFE, to produce a PTFE-based molded body. The obtained molded body was immersed in water for 6 hours.
Applying a load of Kg/cm ² and moving the mating member 100 m/sec at 0.4 m/sec.
A wear test was performed by sliding the test piece for a period of time, and the wear coefficient was measured according to the table below. Wear coefficient = wear height [cm] / surface pressure [Kg/cm ² ] x sliding speed [
m/s] x time [hr] The wear height was calculated by dividing the weight loss of the compact before and after the test by the specific gravity to calculate the wear volume, and then dividing this wear volume by the contact area. The results are shown in Table 1. In addition, a wear test was carried out by sliding the obtained molded body against a mating member at 200°C and 300°C for 100 hours at a sliding speed of 0.5 m/sec under a load of 14 kg/cm ² .
The wear coefficient was measured. The results are shown in Table 2. It should be noted that this molded product was not found to have any aggressiveness towards the mating member. Comparative Example 1 In Example 1, 85 parts by weight of PTFE molding powder and pulverized to an average particle size of 25 μm were used.
A PTFE-based molding composition was prepared by mixing with 15 parts by weight of PPS powder. The obtained molding composition was put into a mold and 300 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. Note that if no preheating treatment was performed at this time, cracks would occur in the resulting molded product. Using the molded body obtained as described above, the wear coefficients in water and under high temperature conditions were determined in the same manner as in Example 1, and are shown in Tables 1 and 2, respectively. It should be noted that this molded product was not found to have any aggressiveness towards the mating member. Comparative Example 2 Same as Example 1 except that graphite powder with an average particle size of 50 μm was used instead of graphite powder with an average particle size of 6 μm in Example 1, and a preheating treatment was added in the same manner as in Comparative Example 1. In the same manner, the wear coefficient was determined in water and under high temperature conditions. The results are shown in Tables 1 and 2. In this case as well, if the preheating treatment was not performed, cracks would occur in the molded product obtained. It should be noted that this molded product was not found to have any aggressiveness towards the mating member.

【table】

[Table] Tables 1 and 2 show that the PTFE-based molding composition of the present invention has excellent wear resistance, particularly under water and high temperature conditions.

Claims (1)

[Claims] 1 96-60% by weight of polytetrafluoroethylene powder, 2-20% by weight of polyphenylene sulfide powder with an average particle size of 10-30 μm, and 2-20% by weight of graphite powder with an average particle size of 10 μm or less %, and the average particle size of graphite powder is 1/ of the average particle size of polyphenylene sulfide powder.
A molding composition based on polytetrafluoroethylene, characterized in that the polytetrafluoroethylene-based molding composition has a polytetrafluoroethylene content of 2 or less.