JPH0867796A - Tetrafluoroethylene resin composition - Google Patents

Abstract

PURPOSE: To obtain a tetrafluoroethylene resin compsn. which is excellent in abrasion resistance and does not damage the mating material in sliding even when the mating material is a soft metal such as aluminum. CONSTITUTION: This resin compsn. comprises 50-99vol.% tetrafluoroethylene resin and 1-50vol.% metal carbonate comprising lithium carbonate and/or sodium carbonate. This resin compsn. may further contain lithium phosphate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tetrafluoroethylene resin composition used as a sliding member for various devices.

[0002]

2. Description of the Related Art Generally, tetrafluoroethylene resin (hereinafter referred to as
(This is abbreviated as PTFE) not only has excellent heat resistance and chemical resistance, but also has a small coefficient of friction and self-lubricating properties. Therefore, materials for sliding parts such as bearings and gears, pipes, valves, etc. It has been widely used in various fields as so-called engineering plastics such as molded products.

However, since PTFE is not always satisfactory in wear resistance and is largely deformed (creep) under load, its use is limited under high load or high temperature.

In order to improve such a defect of abrasion resistance of PTFE, it has been attempted to add various fillers. Examples of the filler used in this case include glass fiber powder, glass beads and carbon. Fiber, graphite,
Examples thereof include inorganic fillers such as molybdenum disulfide, bronze, brass, lead oxide and molybdenum, and organic fillers such as aromatic polyester, polyimide, polyphenylene sulfide and aromatic polyamide.

Further, in order to improve the abrasion resistance of PTFE, a fluororesin composition obtained by adding a reinforcing agent such as glass fiber or carbon fiber to PTFE and a metal phosphate salt such as lithium phosphate or calcium phosphate is added to PTFE. JP-A-3-
It is disclosed in Japanese Patent No. 223397.

The fluororesin composition disclosed above exhibits relatively good wear resistance when stainless steel such as SUS304 is used as a sliding partner.

[0007]

However, in a composition obtained by adding a reinforcing agent and a metal phosphate to PTFE, the sliding partner material is an aluminum alloy softer than stainless steel (A50).
In the case of No. 56), the aluminum is damaged immediately after the start of sliding, and the aluminum abrasion powder thus generated attacks the sliding partner, resulting in a problem that the abrasion progresses remarkably.

Therefore, an object of the present invention is to solve the above-mentioned problems and to make a PTFE composition excellent in wear resistance, and also in sliding conditions against a soft metal such as aluminum. It is a composition that does not damage the mating material.

[0009]

In order to solve the above-mentioned problems, in the present invention, a tetrafluoroethylene resin is used as a main component, and lithium carbonate and sodium carbonate are added individually or in combination of both metal carbonates. It is a tetrafluoroethylene resin composition.

Further, the tetrafluoroethylene resin composition is obtained by adding 1 to 50% by volume of a metal carbonate of lithium carbonate or sodium carbonate alone or in combination thereof to 50 to 99% by volume of the tetrafluoroethylene resin. is there.

Alternatively, a tetrafluoroethylene resin composition is obtained by further adding lithium phosphate to the above tetrafluoroethylene resin composition.

The details will be described below. First, PTFE in the present invention is a polymer having tetrafluoroethylene as a repeating unit and having a molecular weight of 3,000,000 to 10,000,000. However, since this polymer has a high melt viscosity at a temperature of a melting point of 327 ° C or higher, compression molding is performed at the time of molding. Is possible, but
It is a resin that cannot be subjected to ordinary injection molding. Commercial PTFE
Examples thereof include Algoflon manufactured by Ikoku Montedison, Teflon manufactured by DuPont, Fluon manufactured by ICI, UK, and Polyflon manufactured by Daikin Industries.

Lithium carbonate, sodium carbonate or lithium phosphate used in the present invention is Li ₂ C, respectively.
It is a metal salt represented by O ₃ , Na ₂ CO ₃ , and Li ₃ PO ₄ . Powders and other forms of these can be obtained by the production method, but the appearance (shape) and the production method are not particularly limited.

When the above-mentioned metal salt is a powder, its average particle size is preferably 200 μm or less. This is because if the average particle size of the powder exceeds 200 μm, PTF
This is because cracks are likely to occur during the molding of the E composition, the moldability is poor, and the wear resistance of the molded body becomes unstable.

The compounding ratio of lithium carbonate, sodium carbonate or a mixture thereof or lithium phosphate as described above to PTFE is preferably 1 to 50% by volume with respect to 50 to 99% by volume of PTFE. This is because when the amount of the metal salt is less than 1% by volume, the intended effect of these additions on the friction and wear properties of the composition does not appear, and when it is more than 50% by volume, the moldability is significantly impaired, that is, the desired effect is not obtained. This is because it cannot be shaped into a shape, which is not preferable.

When the above-mentioned metal salt having water of crystallization is adopted, the water of crystallization is likely to evaporate during the molding (calcination) of the PTFE composition to cause cracks, but such a situation is avoided. In order to do so, the metal salt before mixing with PTFE should be heated at a baking temperature of PTFE (about 360 to 380).
The heat treatment may be performed in advance at a high temperature of (° C.) or higher.

As long as the effects of the present invention are not impaired,
Various fillers may be added to the PTFE composition. Examples of the filler include polyamideimide resin, polyetherimide resin, polyarylene sulfide resin, aromatic polyetherketone resin, polyarylene ether sulfone resin, phenol resin, aromatic polyester resin, polyimide resin, silicone resin, molten fluorine Including heat-resistant polymer materials such as resins, heat-resistant inorganic single fibers such as wollastonite, potassium titanate fibers, calcium sulfate fibers, composite fibers such as magnesium sulfate-based fibers, heat-resistant organic materials such as aromatic amide fibers Fibers, and also molybdenum disulfide, graphite, carbon, mica,
Examples thereof include inorganic powders for improving lubricity such as talc and molybdenum trioxide, and inorganic pigments for coloring such as iron oxide, cadmium sulfide, cadmium selenide, and carbon black.

When these raw materials are mixed and molded, the PT containing a filler, which has been widely used in the past, is used.
The molding may be performed under known FE molding conditions. As such a method, for example, dry mixing is performed with a mixer such as a tumbler mixer or a Henschel mixer, and the mixture is put in a mold, pre-formed by applying a pressure of 380 to 600 kg / cm ² , and then taken out from the mold. 3 compression molded products
A method of sintering at 70 ° C., a method of compression-molding batchwise while applying heat or a pressure, or a continuous molding method using a ram extruder can be adopted.

[0019]

The lithium carbonate, sodium carbonate, or a mixture of both used in combination, or lithium phosphate, which is added in the present invention, improves the wear resistance of PTFE and is a sliding mating material of a soft metal such as an aluminum alloy. A strong transition film is formed on the surface to protect the mating material from abrasion and damage.

[0020]

EXAMPLES The raw materials used in Examples and Comparative Examples are collectively shown below. The abbreviations or chemical symbols are shown in [], and the mixing ratios are all volume%.

(1) Tetrafluoroethylene resin [PTFE] manufactured by Mitsui DuPont Fluorochemicals: Teflon 7J (2) Lithium carbonate [Li ₂ CO ₃ ] manufactured by Wako Pure Chemical Industries, Ltd .:
Reagent (3) Sodium carbonate [Na ₂ CO ₃ ], Wako Pure Chemical Industries, Ltd .: Reagent (4) Lithium phosphate [Li ₃ PO ₄ ], Wako Pure Chemical Industries: Reagent (5) Potassium phosphate [K ₃ PO] ₄ ], manufactured by Wako Pure Chemical Industries:
Reagent (6) Sodium sulfate [Na ₂ SO ₄ ], Wako Pure Chemical Industries, Ltd .: Reagent (7) Potassium pyrophosphate [K ₄ P ₂ O ₇ ], Wako Pure Chemical Industries: Reagent (8) Calcium carbonate [CaCO ₃ ], Manufactured by Wako Pure Chemical Industries:
Reagent (9) sodium phosphate [Na ₃ PO _4], manufactured by Wako Pure Chemical Industries, Ltd.: Reagents (10) calcium phosphate [Ca ₃ (PO _{4) 2],} manufactured by Wako Pure Chemical Industries, Ltd.: Table 1 or Table reagents or raw materials After blending in the ratio shown in 2 and dry mixing, put this in a mold and 500 kg / cm ²
Pre-molding was carried out at a pressure of, and the compression molded product was baked at 370 ° C. From this molded body, a test piece having a predetermined shape and dimensions used in the test method described below was prepared, and its physical property values were measured. The results are also shown in Table 1 or Table 2.

Friction coefficient and wear coefficient Using a pin-on disk type friction and wear tester, sliding speed 8.3 m / min, load 700 gf, disk type mating material: aluminum alloy A5056 (surface roughness 3.2S), non-lubrication The friction coefficient of the pin type test piece (diameter 8 mm, radius of curvature of pin tip: R50) under the conditions was determined 1 minute after the start of the test and 120 minutes after the start of the test. In addition, the test machine
The wear coefficient (cm ³ / kgf · m) was calculated from the change in weight after and after the operation for 20 minutes and the specific gravity of the material.

The surface roughness of the sliding surface was measured after the test of the damage degree of the mating material, and it was not damaged at all (○ mark), and the surface roughness was damaged beyond 5S (×).
(Mark) was evaluated in two stages.

[0024]

[Table 1]

[0025]

[Table 2]

As is apparent from the test results of Tables 1 and 2, Comparative Examples 1, 3, 5, 6, 8 and 9 damage the aluminum alloy containing Mg as a sliding partner, and Comparative Examples 4 and In Nos. 7 and 10, the mating material was not damaged, but the wear coefficient was inferior.

In Comparative Examples 2, 11 and 12 using potassium phosphate as an additive, the friction and wear characteristics were good, but the exudation of the filler was observed on the surface of the test piece. This phenomenon is considered to be due to the high hygroscopicity of calcium phosphate, and this test piece could not maintain the sliding characteristics for a long period of time.

As described above, none of the comparative examples satisfied both the desired wear resistance and the mating material damage resistance.

On the other hand, in Examples 1 to 5 satisfying all the predetermined conditions, the aluminum alloy of the sliding partner was not damaged at all, the friction coefficient and wear coefficient before and after the test were stable and low, and the wear resistance was high. It exhibited excellent physical properties.

[0030]

As described above, according to the present invention, the tetrafluoroethylene resin is added with a metal carbonate of lithium carbonate, sodium carbonate, or a combination of both, or tetrafluoroethylene resin containing lithium phosphate. Since it is an ethylene resin composition, it has excellent abrasion resistance in addition to the original sliding properties of tetrafluoroethylene resin, and it does not damage even when a soft metal such as aluminum is used as the sliding partner material. Therefore, it can be said that this composition is most suitable as a material for sliding parts such as bearings.

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Claims (3)

[Claims] 1. A tetrafluoroethylene resin composition comprising a tetrafluoroethylene resin as a main component and metal carbonates of lithium carbonate and sodium carbonate, which are used alone or in combination thereof. 2. A tetrafluoroethylene resin of 50 to 99% by volume.
A tetrafluoroethylene resin composition obtained by adding 1 to 50% by volume of a metal carbonate of lithium carbonate or sodium carbonate, or a combination of both. 3. A tetrafluoroethylene resin composition obtained by further adding lithium phosphate to the tetrafluoroethylene resin composition according to claim 1 or 2.