Plastic Antifriction Material

Abstract

A plastic antifriction material containing a polyimide resin, powdered solid lubricants as fillers, and also polyarylates or aromatic polyamides.

Description

This invention relates to plastic antifriction materials intended for the fabrication of elements of dry-friction assemblies, such as bearing cages, sliding bearing bushings, and geared transmission components.

Plastic antifriction materials derived from polyimide plastics filled with solid lubricants, e.g., graphite or molybdenum disulfide are known.

When used in dry friction assemblies, this known antifriction material exhibits a marked increase of its friction coefficient with the increase of the working temperatures up to 70.degree.- 120.degree. C., which precludes the employment of the material under the aforesaid conditions, despite its good mechanical characteristics.

It is an object of the present invention to eliminate the aforementioned disadvantage.

It is a further and more specific object of the present invention to provide an antifriction material noted for its stable coefficient of friction over a wide temperature range.

This object is accomplished by the provision of a plastic antifriction material derived from a polyimide resin filled with powdered solid lubricants and also containing, according to the invention, polyarylates or aromatic polyamides.

Under dry friction conditions when polymer molecules are subjected to both thermal effects and mechanical cracking, rigid-chain polymers, such as polyarylates or aromatic polyamides, exhibit superior performance characteristics due to their less pronounced authohesion properties.

The incorporation of rigid-chain polyarylates or aromatic polyamides into a polyimide resin-based antifriction material exerts a stabilizing effect on the coefficient of friction over a wide temperature range.

It is expedient to employ an antifriction material of the following composition, percent by weight: polyimide, 4-78; filler (solid lubricants), 2-95, and polyarylates or aromatic polyamides, 1-20.

In order to enhance the thermal and electrical conductivity of the present antifriction material, to improve its moldability and also to raise its hardness and wear resistance, it is good practice to additionally incorporate thereinto metal powders as fillers.

In the latter case, the antifriction material should preferably be of the following composition, percent by weight: polyimide, 4-78; solid lubricants, 2-75; polyarylates or aromatic polyamides, 1-20, and metal powders, 20-40.

The antifriction material, according to the present invention, is prepared as follows.

Polycondensation of an aromatic diamine with an aromatic tetracarboxylic acid dianhydride yields a polyamido carboxylic acid, which, on being subjected to polycyclization gives a polyimide.

The polyimide obtained in the form of a fused mass is thoroughly ground to prepare a homogeneous powder which is then mixed in a vibrating mill with powdered polyarylate or aromatic polyamide and powdered filler (solid lubricant, e.g., molybdenum disulfide or graphite). The polyarylate or aromatic polyamide used as a component of the antifriction material should have a softening or melting point that lies close to the temperature at which the polyimide is being processed.

The polyarylates employed as an antifriction material component are prepared from aromatic dicarboxylic acid chlorides and bisphenols in a high-boiling solvent by the equilibrium high-temperature polycondensation method. The polyarylates thus obtained are precipitated with an excess of solvent, filtered off and dried to constant weight.

To prepare the aromatic polyamides used as an antifriction material component, aromatic diamines and aromatic dicarboxylic acid chlorides in a tetrahydrofuran-water-soda medium are subjected to low-temperature polycondensation, followed by filtering off and drying the resultant polymers.

In order to prepare an antifriction material noted for its enhanced thermal and electrical conductivity, metal powders, e.g., powdered copper or silver, are incorporated into the blend of the aforesaid components at the mixing step.

The resultant moulding composition which consists of a finely divided homogeneous powder is subjected to high-temperature moulding.

The above procedure yields an antifriction material exhibiting high mechanical strength, good workability, a stable coefficient of friction over a wide temperature range, and superior wear resistance.

For a better understanding of the present invention, given hereinbelow are the following examples of preparing the antifriction material.

EXAMPLE 1

Dianhydride of diphenyl oxide-3,3',4,4' -tetracarboxylic acid and diaminodiphenyl ether taken in a molar ratio of 1:1 are subjected to polycondensation in dimethylformamide at a temperature of 10.degree.- 25.degree. C. for a period of 4 hours, with continuous stirring. The resultant polyamidoacid is precipitated with a benzene-acetone mixture taken in a five-fold excess and dried in a vacuum cabinet at 80.degree. C. for 2 hours. The dry polyamido acid thus obtained is then polycyclized in vacuo (1 mm. Hg) at a temperature of 100.degree. C. for 2 hours, at 200.degree. C. for 3 hours, and at 300.degree. C. for 1.5 hours.

Polycyclization yields a polyimide having the following structural formula ##SPC1##

The polyimide is triturated to obtain a homogeneous powder.

35.7 g. of the powdered polyimide, 450 g. of powdered molybdenum disulfide (particle size, 1-2 .mu.), and 12.5 g. of powdered polyarylate of the following structural formula ##SPC2##

are mixed in a vibrating mill for 2 minutes until a homogeneous mass is obtained.

The polyarylate having the aforespecified structure is prepared from terephthaloyl chloride and phenolphthalein by the high-temperature polycondensation technique. The process is conducted at a temperature of 220.degree. C. for a period of 12 hours and comprises stirring, in a stream of argon, a mixture of equimolar amounts of the starting compounds dissolved in Sovol (chlorinated biphenyl).

The resultant polyarylate is dissolved in chloroform to obtain a 5 percent solution and thereafter precipitated with a five-fold excess of methyl alcohol, filtered off and dried at a temperature of 120.degree. C. for 6 hours.

The components are mixed in a vibrating mill to give a moulding composition, which is thereafter moulded at a temperature of 390.degree.-410.degree. C. and a specific pressure of 1,000 to 1,200 kg./cm..sup.2.

The antifriction material prepared as disclosed hereinbefore exhibits the following physical and mechanical characteristics:

Brinell hardness, kg./mm..sup.2 20 Impact strength, kg./cm./cm..sup.2 3 Intensity of linear wear 1.times.10.sup.-.sup. 9 Coefficient of friction 0.12 Maximum working temperature, .degree.C. 240

example 2 ##SPC3##

derived from diphenyl oxide 3,3',4,4' -tetracarboxylic acid dianhydride and m-phenylene diamine, and a polyarylate of the general formula ##SPC4##

derived from terephthaloyl dichloride and dihydroxydiphenylfluorene are prepared as disclosed in example 1.

37.5 g. of the powdered polyimide, 12.5 g. of the powdered polyarylate and 450 g. of powdered molybdenum disulfide (particle size, 1-2.mu.) are mixed in a vibrating mill for a period of 2 minutes to obtain a homogeneous mass.

The moulding composition thus prepared is subjected to moulding at a temperature of 490.degree.-500.degree. C. and a specific pressure of 1,000 to 1,200 kg./cm..sup.2

The antifriction material exhibits the following physical and mechanical characteristics:

Brinell hardness, kg./mm..sup.2 21 Impact strength, kg.cm./cm..sup.2 2 Intensity of linear wear 1.3.times.10.sup.-.sup. 9 Coefficient of linear wear 0.12 Maximum working temperature, .degree.C. 260

example 3

fifty grams of powdered a polyimide prepared as disclosed in example 1 is mixed in a vibrating mill with 420 g. of graphite powder and 20 g. of polymetaphenylene isophthalamide of the structural formula ##SPC5##

The aforesaid polyamide is prepared from metaphenylene diamine and isophthaloyl dichloride by low-temperature polycondensation in a tetrahydrofuran-water-soda medium, the starting compounds being taken in molar ratio of 1:1. The resultant polymer is separated by filtration and dried in a vacuum cabinet at 100.degree. C. for a period of 6 hours.

The moulding composition prepared by mixing the aforesaid components in a vibrating mill is moulded at a temperature of 390.degree.- 410.degree. C. and under a specific pressure of 1,000-1,200 kg./cm..sup.2

The antifriction material exhibits the following physical and mechanical properties:

Intensity of linear wear 0.9.times.10.sup.-.sup. 9 Coefficient of friction 0.1 Maximum working temperature, .degree.C. 250

example 4

37.5 g. of powdered polyimide prepared as disclosed in example 2 is mixed in a vibrating mill for a period of 2 minutes with 450 g. of graphite powder and 12.5 g. of polyamide having the structural formula ##SPC6##

the polyamide being synthesized from anilinephthalein and isophthalic acid by the method disclosed in example 3.

The moulding powder thus obtained is moulded at a temperature of 490.degree.-500.degree. C. and under a specific pressure of 1,000 to 1,200 kg./cm..sup.2

The antifriction material exhibits the following physical and mechanical characteristics:

Intensity of linear wear 0.9.times.10.sup.-.sup. 9 Coefficient of friction 0.1 Maximum working temperature, .degree.C. 270

example 5

37.5 g. of powdered polyimide and 12.5 g. of polyarylate prepared as disclosed in example 1, 325 g. of molybdenum disulfide powder (particle size, 1-2 .mu.), and 125 g. of copper powder are blended in a vibrating mill for a period of 2 minutes.

The moulding composition thus obtained is moulded at a temperature of 390.degree.-410.degree. C. and under specific pressure of 1,000 to 1,200 kg./cm..sup.2

The antifriction material exhibits the following physical and mechanical characteristics:

Brinell hardness, kg./mm..sup.2 24 Impact strength, kg.cm./cm..sup.2 2.5 Coefficient of friction 0.1 Maximum working temperature, .degree.C. 250

Example 6

37.5 g. of powdered polyimide prepared as disclosed in example 1, 12.5 g. of polyamide prepared by the procedure of example 3, 325 g. of molybdenum disulfide powder (particle size, 1-2 .mu.), and 125 g. of silver powder are mixed in a vibrating mill for a period of 2 minutes.

The moulding composition thus obtained is subjected to compression moulding at a temperature of 390.degree.-410.degree. C. and under specific pressure of 1,000 to 1,200 kg./cm..sup.2

The antifriction material exhibits the following physical and mechanical characteristics:

Brinell hardness, kg./mm..sup.2 22 Intensity of linear wear 0.7.times.10.sup.-.sup. 9 Maximum working temperature, .degree.C. 250

although the present invention has been described with reference to the preferred embodiment thereof, it will be readily understood by those skilled in the art that various changes and modifications can be practised without departing from the spirit and scope of the invention as disclosed in the description and appended claims.

Claims

We claim:

1. An antifriction material having a stable coefficient of friction over a wide temperature range comprising

1. 4 to 78 percent by weight of one or more aromatic polyimide resins prepared by polycondensation of an aromatic diamine with an aromatic tetracarboxylic acid dianhydride to yield a polyamido carboxylic acid which after being subjected to polycyclization gives a polyimide,

2. 2 to 75 percent by weight of one or more solid inorganic lubricants, and

3. 1 to 20 percent by weight of one or more rigid-chain polymers selected from the group consisting of (a) polyarylates prepared by polycondensation of aromatic dicarboxylic acid chlorides and bisphenols and (b) aromatic polyamides prepared by polycondensation of aromatic diamines and aromatic dicarboxylic acids or their chlorides.

2. An antifriction material as in claim 1 which further comprises a powdered metal filler.

3. An antifriction material as in claim 2 which comprises 4 to 78 percent of polyimide resin, 2 to 78 percent by weight of solid lubricants, 20 to 40 percent by weight of powdered metal filler, and 1 to 20 percent by weight of the polyarylate or aromatic polyamide polymer.

4. An antifriction material as in claim 1 wherein the polyimide is prepared from diphenyl oxide 3,3', 4, 4' -tetracarboxylic dianhydride and a diamine selected from the group consisting of 4,4'-diaminodiphenyl ether and m-phenylenediamine.

5. An antifriction material as in claim 1 wherein the polyarylate is prepared from terephthaloyl chloride and a bisphenol selected from the group consisting of phenolphthalein and dihydroxydiphenyl fluorene.

6. An antifriction material as in claim 1 wherein the polyamide is prepared from isophthaloyl dichloride and an amine selected from the group consisting of m-phenylenediamine and anilinephthalein.

7. An antifriction material as in claim 1 wherein the solid lubricant is selected from the group consisting of molybdenum disulfide and graphite.

8. An antifriction material as in claim 2 wherein the metal is copper or silver.