SEALING ELEMENT AND/OR GUIDE RING MADE OF A COMPOSITION OF POLYTETRAFLUOROETHYLENE, PERFLUOROALKOXY POLYMER, AND FILLER

Abstract

The present invention relates to a sealing element and/or guide ring manufactured from a composition comprising: i) 50% to 98% by weight of polytetrafluoroethylene and/or modified PTFE, ii) 1% to 49% by weight of perfluoroalkoxy polymer and iii) 1% to 49% by weight of an inorganic filler selected from the group comprising charcoal, graphite, glass fibers, carbon fibers, molybdenum disulfide, metals such as copper, alloys such as bronze, ceramic particles such as aluminum oxide and any desired mixtures of two or more of the aforementioned substances.

Claims

1. A sealing element and/or guide ring manufactured from a composition comprising: i) 50% to 98% by weight of polytetrafluoroethylene and/or modified polytetrafluoroethylene, ii) 1% to 49% by weight of perfluoroalkoxy polymer and iii) 1% to 49% by weight of an inorganic filler selected from the group consisting of charcoal, graphite, glass fibers, carbon fibers, molybdenum disulfide, metals, alloys, ceramic particles and any mixtures of two or more of the aforementioned substances, wherein the chemically modified polytetrafluoroethylene optionally present is a polymer composed of tetrafluoroethylene monomer and less than 1% by weight of comonomer, and wherein the perfluoroalkoxy polymer is a copolymer of tetrafluoroethylene and perfluoroalkoxy comonomer containing more than 1% by weight of perfluoroalkoxy comonomer.

2. The sealing element and/or guide ring as claimed in claim 1, characterized in that the composition consists to an extent of 50% to 100% by weight, preferably to an extent of 65% to 100% by weight, more preferably to an extent of 75% to 100% by weight, even more preferably to an extent of 85% to 100% by weight and most preferably entirely of constituents i), ii) and iii), where the remainder to 100% by weight, if the sum total of constituents i), ii) and iii) is less than 100% by weight, is one or more polymers preferably selected from the group consisting of polyphenylene sulfides, polyphenylene sulfones, polyetheretherketones, polyimides and any desired mixtures of two or more of the aforementioned substances.

3. The sealing element and/or guide ring as claimed in claim 1 or 2, characterized in that the composition consists of: i) 50% to 93% by weight of polytetrafluoroethylene and/or chemically modified polytetrafluoroethylene, ii) 5% to 25% by weight of perfluoroalkoxy polymer and iii) 2% to 49% by weight of an inorganic filler selected from the group consisting of charcoal, graphite, glass fibers, carbon fibers, molybdenum disulfide, metals such as copper, alloys such as bronze, ceramic particles such as aluminum oxide and any desired mixtures of two or more of the aforementioned substances.

4. The sealing element and/or guide ring as claimed in claim 3, characterized in that the composition consists of: i) 55% to 93% by weight of polytetrafluoroethylene and/or chemically modified polytetrafluoroethylene, ii) 5% to 15% by weight of perfluoroalkoxy polymer and iii) 2% to 30% by weight of an inorganic filler selected from the group consisting of charcoal, graphite, glass fibers, carbon fibers, molybdenum disulfide, metals such as copper, alloys such as bronze, ceramic particles such as aluminum oxide and any desired mixtures of two or more of the aforementioned substances.

5. The sealing element and/or guide ring as claimed in at least one of the preceding claims, characterized in that the polytetrafluoroethylene and/or chemically modified polytetrafluoroethylene i) has a number-average molecular weight of 10.sup.6 g/mol or greater.

6. The sealing element and/or guide ring as claimed in at least one of the preceding claims, characterized in that the polytetrafluoroethylene and/or chemically modified polytetrafluoroethylene i) has an average particle size measured according to DIN ISO 13320 of 20 to 650 m and preferably of 20 to 50 m.

7. The sealing element and/or guide ring as claimed in at least one of the preceding claims, characterized in that the perfluoroalkoxy polymer ii) has the following general formula: ##STR00002## in which R is a C.sub.1-4-perfluoroalkyl radical and preferably a C.sub.1-3-perfluoroalkyl radical and m and n represent the number of repeating units, where n and m are preferably independently a number from 1 to 10000.

8. The sealing element and/or guide ring as claimed in at least one of the preceding claims, characterized in that the perfluoroalkoxy polymer ii) has a melt flow index measured according to DIN EN ISO1133 with 5 kg at 372 of 1 to 30 g/10 min and preferably a melt flow index of 2 to 20 g/10 min.

9. The sealing element and/or guide ring as claimed in at least one of the preceding claims, characterized in that the perfluoroalkoxy polymer ii) has an average particle size measured according to DIN ISO 13320 of 20 to 650 m and preferably of 20 to 50 m.

10. The sealing element and/or guide ring, wherein the composition comprises: i) 50% to 98% by weight of polytetrafluoroethylene and/or modified polytetrafluoroethylene, ii) 1% to 49% by weight of a thermoplastic perfluoropolymer other than polytetrafluoroethylene and iii) 1% to 49% by weight of an inorganic filler selected from the group consisting of charcoal, graphite, glass fibers, carbon fibers, molybdenum disulfide, metals such as copper, alloys such as bronze, ceramic particles such as aluminum oxide and any desired mixtures of two or more of the aforementioned substances.

11. The sealing element and/or guide ring as claimed in at least one of the preceding claims, characterized in that it is a piston ring or a packing ring.

12. A process for producing a sealing element and/or guide ring as claimed in at least one of the preceding claims, comprising the steps of: a) providing a composition having the features relating to the composition as claimed in at least one of claims 1 to 10, b) forming and sintering the composition provided in step a) into a raw blank, c) mechanically processing the raw blank provided in step b) into the sealing element.

13. The process as claimed in claim 12, characterized in that the forming and sintering in step b) is carried out i) by pressing the composition to form a green body and then sintering to form a raw blank, ii) by pressure sintering or iii) by extrusion into a green body and subsequent sintering into a raw blank.

14. A piston compressor comprising at least one sealing element and/or guide ring as claimed in at least one of claims 1 to 11.

Description

EXAMPLE 1

[0051] The following composition was produced by mixing:

70% by weight of DuPont Teflon PTFE 7A X,
5% by weight of PFA having a melt flow index of 10-17 g/10 min,
21% by weight of carbon powder having a particle size distribution of D.sub.90=40 m and a BET surface area of 10 m.sup.2/g and
4% by weight of graphite having a particle size distribution of D.sub.90=56 m and a BET surface area of 7 m.sup.2/g.

[0052] This composition was processed by mold-free sintering to give a hollow cylinder, by first compressing the composition at room temperature to give a hollow cylinder as green body having an inner diameter of 40 mm, having an outer diameter of 80 mm and having a height of 175 mm, before the green body thus obtained was sintered in an oven at a temperature of 375 C. to give a raw blank.

[0053] Subsequently, this raw blank was processed mechanically by material-removing processing to provide packing rings having an inner diameter of 50 mm, having an outer diameter of 74 mm and having a height of 4 mm.

[0054] The packing rings thus produced featured excellent pressure creep and cold flow properties.

EXAMPLE 2

[0055] Analogously to example 1, four different hollow cylinders were produced from a composition that comprised 0% by weight, 5% by weight, 10% by weight and 15% by weight of PFA, 21% by weight of carbon powder, 4% by weight of graphite and PTFE as the remainder to 100% by weight.

[0056] The deformation of these 4 shaped bodies was measured under a load of 13.8 MPa within 24 hours. The results are shown in FIG. 1 and show that even the addition of 5% by weight of PFA leads to a significant reduction in deformation under load, and an increase in the PFA content has a smaller effect thereon.