JPH08217941A - Sliding member - Google Patents

Abstract

PURPOSE: To improve the sliding characteristics of a sliding member produced by using a polytetrafluoroethylene resin (PTFE) as the main material. CONSTITUTION: A polytetrafluoroethylene resin is compounded with flaky titanium dioxide particles as the filler. Pref., the particles have an average size mean value of the major axis (length) and the minor axis (breadth) in the plane direction] of 1-100μm, a thickness of 0.01-2μm, and an aspect ratio (length/ thickness) of 30 or higher. The amt. of the filler compounded is suitably about 2-40wt.%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of a sliding member made of a polytetrafluoroethylene resin composition.

[0002]

2. Description of the Related Art Polytetrafluoroethylene resin (tetrafluoroethylene resin, hereinafter referred to as "PTFE resin") is an engineering plastic that has excellent sliding properties as well as heat resistance, weather resistance, cold resistance and chemical resistance. Widely used as various sliding component materials (for example, dry bearings, bushes, ball seats, piston rings, sliding pads, ring seals, lip seals, etc.). Further, in order to improve its sliding characteristics, a proposal has been made on a resin composition in which PTFE resin is mixed with asbestos fiber, glass fiber, carbon fiber, metal fiber / powder, organic heat-resistant fiber, potassium titanate fiber, etc. as a filler. Have been made (JP-A-55-18430, JP-A-55-50052,
JP-A-58-167696, JP-A-59-54644, JP-A-60-250
054, JP-A-60-23625, JP-A-62-146944, etc.).

[0003]

Although various kinds of materials are used for the filler of the PTFE resin as described above, the use of asbestos fiber is being suppressed due to health problems such as carcinogenicity. Since glass fiber is extremely hard, the fact that the sliding member easily damages the mating member is a practical obstacle. The sliding member containing carbon fiber or metal fiber / powder is limited in its application to applications requiring insulation. Since the organic heat resistant fiber is supplied as chopped strands, a kneading step using an extruder, an injection molding machine or the like has to be adopted in order to uniformly mix it with the resin. The sliding member using the potassium titanate fiber has a problem that the resin is deteriorated due to the leaching of potassium ions in the fiber. In addition, recently, the applications and uses of sliding parts have been expanded and diversified, and the sliding conditions found in dry bearings have become more severe (higher speed, higher surface pressure, etc.). The present invention intends to provide an improved sliding member that overcomes the above-mentioned restrictions and drawbacks associated with conventional sliding members that use a filler material, and that can withstand the recently harsh operating environment. Is.

[0004]

The sliding member of the present invention is a sliding member formed by molding a resin composition in which a filler is mixed with a polytetrafluoroethylene resin, in which flaky titanium dioxide particles are used as the filler. It is characterized by being blended.

[0005]

The flaky titanium dioxide particles (TiO ₂ ) blended in the PTFE resin have very good dispersibility in the resin and, as a flaky shape effect, have a multi-layer orientation in the resin and slide. Greatly improves the wear resistance of members and is effective in improving strength and rigidity. Furthermore, the flaky titanium dioxide particles in the resin absorb and relieve internal stress associated with temperature rise and temperature drop on the sliding surface, and prevent peeling and crack damage on the surface of the sliding member. The low friction coefficient, which is a characteristic of the PTFE resin, is not impaired by blending the flaky titanium dioxide particles, and good sliding characteristics are maintained. Furthermore, the flaky titanium dioxide particles have no health hazard as pointed out with asbestos fibers, and do not significantly damage the mating material like glass fibers. In addition, the range of application for insulating applications is expanded as compared with the case of using conductive carbon fiber, metal fiber, powder, or the like. Since it has a particle morphology, the preparation of the resin composition, unlike the organic fiber (chopped strand), may employ a step of preparing a powder mixture with a mixer or the like, in addition to the kneading step with an extruder or the like. it can.
Of course, unlike the case of potassium titanate fiber, the concern of deterioration of the resin due to potassium is eliminated.

If the flaky titanium dioxide particles in the resin composition constituting the sliding member of the present invention are too large, the uniform dispersibility in the resin will decrease, while if they are too fine, flaky titanium dioxide particles will be produced. Reinforcing effect based on morphological characteristics (effect of improving wear resistance, strength, rigidity, etc.) is weakened. If the wall thickness is too thin, the thin piece shape is likely to be damaged in the step of mixing with the resin, and conversely, if it is too thick, the smoothness of the surface of the sliding member is impaired. From these points, the flaky titanium dioxide particles have an average size of 1 to 100 μm.
It is preferable that the thickness is 0.01 to 2 μm and the aspect ratio is 30 or more. [Here, "mean size" means
A value obtained by dividing the sum of the maximum diameter difference (length) and the shortest diameter difference (width) in the plane direction of flaky particles by 2, the aspect ratio means the ratio of "length / thickness". .

The blending ratio of the flaky titanium dioxide particles in the PTFE resin is preferably about 2% by weight or more in order to sufficiently bring out the blending effect. However, excessive mixing makes it difficult to mix and disperse uniformly,
It reduces the bond strength of the resin and promotes the tendency of cracks and cracks in the manufacturing process of the sliding member. Therefore, it is appropriate to set the upper limit to about 40% by weight.

As is well known, titanium dioxide is classified into rutile type and anatase type. In the temperature range over about 900 ° C., a phase change from anatase type to rutile type occurs, and in terms of high temperature stability. The rutile type is advantageous, but the anatase type is also stable up to about 900 ° C.
The function of the E resin as a reinforcing material is sufficiently ensured. Therefore, the flaky titanium dioxide particles used in the present invention may be either anatase type or rutile type, or a mixed phase of both.

The resin composition which is a raw material for molding the sliding member of the present invention is not different from the conventional one except that flaky titanium dioxide particles are used as a filler material. Flake-shaped titanium dioxide particles are used as silane coupling agents (aminosilane, vinylsilane, epoxysilane, methacryloxylan, mercaptoxylan) in order to improve dispersibility and binding to the resin prior to compounding with the resin. Etc.) or a titanate-based coupling agent (isopropyl triisostearoyl titanate, di (dioctyl pyrophosphate) ethylene titanate, etc.) is optionally applied. Further, an appropriate amount (for example, 2 to 10% by weight) of an appropriate additive (for example, a solid lubricant such as graphite or lead oxide) is blended with the flaky titanium dioxide particles, if necessary. The resin composition is prepared, for example, by adding a PTFE resin to a twin-screw extruder, kneading by adding flaky titanium dioxide (and additives such as a lubricant to be blended if necessary) to the molten resin, Extruding, water-cooling, cutting to produce a pellet, or PTFE
A method in which flaky titanium dioxide and other additives are added to the resin powder to prepare a uniform powder mixture with a mixer or the like can be applied.

The sliding member using the resin composition as a raw material can be manufactured by injection molding, extrusion molding or the like according to a conventional method, and in the case of the resin composition prepared as a powder mixture, a mold or the like is used. It is also possible to employ a process in which it is used for pressure molding, and then sintered under heating. In the latter case, the resin composition filled in the mold is subjected to an appropriate pressure at room temperature, for example, 10 to 30 MPa (about 100 to 300 Kg / c).
m ² ) after compression molding, the molded body is taken out of the mold and subjected to heat treatment in a sintering furnace at a temperature of about 350 to 400 ° C. for an appropriate time (for example, 1 to 4 Hr). can get. When the fired product is subjected to a compression molding process (for example, about 20 to 50 MPa, 2 to 10 minutes) using a mold or the like, the effects of high densification are abrasion resistance,
Strength and rigidity can be made higher.

[0011]

【Example】

[1] Preparation of Resin Composition and Manufacture of Sliding Member A resin composition is prepared by blending a powder of PTFE resin with a filler and uniformly mixing with a mixer. This is filled in a mold, compression-molded at room temperature with a pressure of 24.5 MPa (250 Kg / cm ² ), and then placed in a firing furnace. After achieving the baking treatment at a temperature of 380 ° C. (holding time 90 min), the product is taken out of the furnace, immediately put into a mold, and pressurized at 24.5 MPa (250 Kgf / cm ² ) and cooled. A test piece is obtained by machining this. Table 1 shows the composition of the test materials. No. 1 and 2
Is an invention example in which flaky titanium dioxide particles are mixed as a filler, No. 3 is a comparative example in which needle-shaped titanium dioxide particles are mixed, and No. 4 is an example in which no filler is mixed. PTFE resin: "Polyflon TFE" manufactured by Daikin Industries, Ltd.
Molding powder M-15 ". Flaky titanium dioxide particles: average size 25 μm [length (average) 40 μm, width (average) 10 μm], thickness (average) 0.5
μm, aspect ratio: 80. Needle-shaped titanium dioxide particles: diameter 0.2 to 0.5 μm, length 10 to 20 μm.

[0012]

[Table 1]

[2] Sliding characteristic test The friction coefficient μ was determined by a pin-on-disk friction and wear test.
And the specific wear rate (mm ³ / N · m) is measured. Specimen size: φ8 mm x 20 mm Counterpart material: S45C carbon steel (surface roughness 1.6S) Friction speed: 0.5 m / sec Friction distance: 4000 m Sliding surface pressure: 1-5 MPa

The results of the friction and wear test are shown in FIGS. 1 and 2 (FIG. 1: specific wear rate, FIG. 2: friction coefficient). The symbol in each figure shows the sample No. As shown in Fig. 1 (comparative material No. 4 in the upper left frame in the figure), invention examples No. 1 and No. 2 in which flaky titanium dioxide particles were mixed with PTFE resin
Has significantly higher wear resistance than No. 4, which is a single PTFE resin material, and its wear resistance is stably maintained even when the surface pressure increases. The test material No. 3 containing needle-shaped titanium dioxide particles also has higher wear resistance than the PTFE resin single material No. 4, but its wear resistance rapidly increases as the surface pressure increases. And the stability is lacking. Further, as shown in FIG. 2, the invention examples No. 1 and 2 are P
It has the same low friction coefficient as No. 4 which is a TFE resin single material, and its low friction coefficient is stable over a range of low surface pressure to high surface pressure.

[0015]

The sliding member of the present invention has a low friction coefficient and the like of the PTFE resin and a high degree of wear resistance due to the blending effect of the flaky titanium dioxide particles. Effective in improving the durability of the member against
Even in the use environment of high speed and high surface pressure such as dry bearing, it is possible to obtain effects such as smooth rotational movement.

[Brief description of drawings]

FIG. 1 is a graph showing the measurement results of specific wear rate-surface pressure.

FIG. 2 is a graph showing the measurement results of friction coefficient-surface pressure.

Claims (1)

[Claims] 1. A sliding member formed by molding a resin composition in which a filler is blended in a polytetrafluoroethylene resin, wherein flaky titanium dioxide particles are blended as a filler, and the wear resistance is characterized. Excellent sliding member.