SEALING ELEMENT AND METHOD OF MANUFACTURE OF A SEALING ELEMENT

Abstract

Disclosed is a sealing element and a method of manufacture. The sealing element has a sealing surface for providing a seal against a contact surface. A sintered PTFE film is coupled to the elastomeric body, and defines the sealing surface, which is of particular suitability for a dynamic seal. The sealing film comprises a lubricious particulate material.

Claims

1. A sealing element having a sealing surface for providing a seal against a contact surface, the sealing element comprising: an elastomeric body comprising an elastomeric material; and a sintered polytetrafluoroethylene (PTFE) film coupled to the elastomeric body, and defining the sealing surface; the film having a thickness between around 25 microns and 200 microns, and the film comprising between around 5 wt % and 40 wt % of a lubricious particulate material.

2. The sealing element of claim 1, wherein the sintered PTFE film comprises a skived PTFE film, a cast PTFE film, an extruded PTFE film or an expanded PTFE (ePTFE) film.

3. (canceled)

4. The sealing element of claim 2, wherein the sintered PTFE film is a biaxially expanded ePTFE film.

5. (canceled)

6. The sealing element of claim 1, wherein the sintered PTFE film comprises an expanded PTFE film, and wherein the sintered ePTFE film comprises a penetrated region adjacent to the elastomeric body in which elastomeric material is present in pores of the sintered ePTFE film and an unpenetrated region adjacent to the sealing surface.

7. The sealing element of claim 1, wherein the sealing element comprises a multilayer laminate, the multilayer laminate comprising the sintered PTFE film defining the sealing surface and at least one intermediate layer.

8. The sealing element of claim 7, wherein the multilayer laminate comprises the sintered PTFE layer defining the sealing surface and at least one intermediate PTFE layer.

9. The sealing element of claim 8, wherein the multilayer laminate comprises a porous PTFE intermediate layer adjacent to the elastomeric body.

10. (canceled)

11. (canceled)

12. The sealing element of claim 7, wherein the multilayer laminate comprises at least one intermediate thermoplastic layer.

13. The sealing element of claim 7, wherein the thickness of the sintered PTFE film defining the sealing surface and each intermediate film layer together are between around 30 and 250 microns.

14. (canceled)

15. The sealing element of claim 1, wherein the sintered PTFE film comprises an expanded PTFE film, and wherein the sintered ePTFE film defining the sealing surface is at least partially densified.

16. (canceled)

17. The sealing element of claim 1, wherein the elastomeric body comprises one or more elastomeric materials selected from; natural rubbers (polyisoprenes), butadienes, ethylene propylenes (EPR, or EPM), ethylene propylene dienes (EPDR, or EPDM), styrene-butadienes (SBR), isobutenes, urethanes, acrylics or nitriles (acrylonitrile-butadienes, i.e., ABR), halogenated nitriles, chloroelastomers such as chloroprenes, perfluoroelastomers, fluoroelastomers, silicones, fluorosilicones, epichlorohydrin rubbers, polyether block amides (PEBA), chlorosulfonated polyethylenes (CSM), ethylene-vinyl acetates (EVA).

18. (canceled)

19. The sealing element of claim 1, wherein the lubricious particulate material is provided in the form of a powder or in microfibrous form, or wherein the lubricious particulate material comprises micro-particles, or nano-particles.

20. (canceled)

21. The sealing element of claim 1, wherein the lubricious particulate material comprises or consists of a carbon-based component.

22. The sealing element of claim 21, wherein the lubricious particulate material consists essentially of graphite.

23. (canceled)

24. (canceled)

25. (canceled)

26. (canceled)

27. The sealing element of claim 21, wherein the ratio of the Carbon (C):Fluorine (F) ratio (C:F) as measured normal to the sealing surface of the sintered PTFE film to the C:F ratio as measured normal to the thickness of the sintered PTFE film is less than or equal to 0.8; less than or equal to 0.7; less than or equal to 0.6.

28. (canceled)

29. A sintered ePTFE film for use in the manufacture of a sealing element, the ePTFE film comprising between around 5 wt % and 40 wt % of a lubricious particulate material and having a thickness between around 25 microns and 700 microns, the ePTFE film being uniaxially or biaxially expanded.

30. The ePTFE film of claim 29, wherein the ePTFE film is biaxially expanded.

31. The ePTFE film of claim 29, wherein the lubricious particulate material consists essentially of graphite; or a mixture of graphite and one or more particulate carbon-based components.

32. (canceled)

33. (canceled)

34. (canceled)

35. A method of manufacturing a sealing element having an elastomeric body and a sealing surface for providing a seal against a contact surface, the method comprising: providing a sintered PTFE film, the sintered PTFE film comprising between around 5 wt % and 40 wt % of a lubricious particulate material; or a multilayer laminate comprising the sintered PTFE film and at least one further film layer; placing the sintered PTFE film or multilayer laminate over at least a part of a surface of a mould cavity; and introducing an elastomeric material into the mould cavity to overmould the sintered PTFE film or multilayer laminate and form a sealing element, wherein the sintered PTFE film or multilayer laminate is coupled to the elastomeric body, has a thickness of between around 25 and 200 microns and wherein the sintered PTFE film defines the sealing surface.

36. (canceled)

37. (canceled)

39. The method of claim 35, wherein the sintered PTFE film or multilayer laminate is gas permeable.

40. (canceled)

41. (canceled)

42. (canceled)

Description

DESCRIPTION OF THE DRAWINGS

[0170] Non-limiting example embodiments are described in greater detail below with reference to the figures, in which:

[0171] FIG. 1 shows an exploded view of wear test and coefficient of friction test apparatus.

[0172] FIGS. 2 and 3 the mould used to conduct mouldability testing.

[0173] FIG. 4 shows the mould used to prepare test sealing elements.

[0174] FIG. 5 shows a plot of wear vs time for examples 1-11.

[0175] FIG. 6 shows a plot of coefficient of friction vs time for examples 1-11.

[0176] FIG. 7 shows (a) an SEM image and (b) an EDS image of a portion of the sealing surface of the moulded article of example 1 (viewed from above) and; (c) an SEM image and (b) an EDS image of a cross section taken through the moulded article of example 1 (viewed from normal to the sealing surface).

[0177] FIG. 8 shows (a) an SEM image and (b) an EDS image of a portion of the sealing surface of the moulded article of example 2 (viewed from above) and; (c) an SEM image and (b) an EDS image of a cross section taken through the moulded article of example 2 (viewed from normal to the sealing surface).

[0178] FIG. 9 shows (a) an SEM image and (b) an EDS image of a portion of the sealing surface of the moulded article of example 3 (viewed from above) and; (c) an SEM image and (b) an EDS image of a cross section taken through the moulded article of example 3 (viewed from normal to the sealing surface).

[0179] FIG. 10 shows (a) an SEM image and (b) an EDS image of a portion of the sealing surface of the moulded article of example 6 (viewed from above) and; (c) an SEM image and (b) an EDS image of a cross section taken through the moulded article of example 6 (viewed from normal to the sealing surface).

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0180] A series of test and comparative examples of moulded articles the same general construction test sealing elements were prepared using a compression moulding process, from a range of elastomeric materials and films, detailed below. The moulded articles were of materials suitable for the manufacture of sealing elements, but of a shape and configuration adapted for the testing procedures described below.

[0181] The mould used for preparing the examples is shown in FIG. 4. The mould included a mould base 29 having a cavity 31 defining a mould surface. The mould cavity had dimensions of approximately 75 mm×75 mm×3 mm deep with a 45 degree chamfer around the perimeter thereof.

[0182] The mould base was placed on the lower platen of the hydraulic press (not shown) and centred on the platen. Pins 31 surround the cavity and correspond to apertures 34 in a mould top 27, to assist in holding the film 100 in position when placed over the mould base 29.

[0183] Film samples 100 were cut to size and provided with holes corresponding to the pins 31 in the mould base 29.

[0184] A block of uncured elastomeric material 102 was placed on top of the test film sample and centred in the mould over the mould cavity 31. The mould top 27 was placed on the mould base 29 using the pins 31 for alignment.

[0185] The mould base 29 and top 27 were pre-heated prior to placement of the film 100 and elastomeric material 102.

[0186] The elastomeric material 102 was then compression moulded to the film 100 using the hydraulic press (not shown) and cured in the mould 29. A press load of 146.4 kN (40,000 pounds) was used for each example. The press load was released after the end of the prescribed curing time. The mould and moulded part were removed from the press after the press load was released. The moulded part was removed from the mould immediately.

[0187] The excess film and elastomer was trimmed away from the perimeter of the moulded parts.

[0188] The uncured elastomer compounds used to prepare the examples were an FKM elastomer (Viton™ A), hydrogenated nitrile butadiene rubber (HNBR), and ethylene propylene diene monomer rubber (EPDM).

[0189] The FKM (Viton™ A) elastomer, compound number EE96070A, is commercially available from Eagle Elastomer, Inc. of Cuyahoga Falls, Ohio, USA. The EE96070A compound has a Shore A durometer of 75 when cured and post cured.

[0190] The HNBR rubber compound, compound number HNBR71 B, is commercially available from J. J. Short Associates, Inc. of Macedon, N.Y., USA. The HNBR rubber has a Shore A durometer of 70.

[0191] The EPDM rubber, compound number EP70PEROX, is commercially available from J. J. Short Associates, Inc. of Macedon, N.Y., USA. The EPDM rubber has a Shore A durometer of 70.

[0192] The curing temperature and curing time for the FKM Viton™ A compound was 188° C. and 4 minutes, respectively. The molded examples made with the FKM Viton A elastomer were post cured in a preheated convective oven at 200° C. for 6 hours. The curing temperature and curing time for the EPDM compound was 160° C. and 20 minutes, respectively. The curing temperature and curing time for the hydrogenated nitrile butadiene rubber (HNBR) was 160° C. and 20 minutes, respectively.

[0193] The sintered PTFE films as used in the examples are manufactured as follows:

1. Sintered ePTFE Film with 24 wt % Lubricious Particulate Material

[0194] A PTFE aqueous dispersion containing approximately 22% by weight solids, the majority of which are PTFE particles having a particle size in a range from about 0.05 μm to about 5 μm was used to produce a 24% by weight graphite filled PTFE mixture. PTFE aqueous dispersion can be purchased from the Chemours Company.

[0195] The graphite used in this example was a high synthetic graphite 99% plus carbon Grade #TC305 which was purchased from Asbury Carbons and has a medium particle size between 6.5 and 19 μm.

[0196] 1.6 kg of the aforementioned graphite was slurried into 27 kg (60 lb) of de-ionized water. The slurry was then coagulated with 5.17 kg of PTFE dispersion for a mix time of 3 minutes. The resulting coagulum was then dried at 1650° C. for 24 hours. The dried coagulum was then frozen at −30° C. for two hours, and then screened through a 6 mm opening screen to help turn the coagulum into a powder form. The powder was then lubricated with mineral spirits at a ratio of 0.22 kg of lubricant to 1 kg of powder by weight.

[0197] The lubricated powder was tumbled and the material was once again refrozen at −30° C. for 24 hours, and again re-screened through the 6 mm screen to break up any large lumps of the lubricated graphite/PTFE mixture. The resulting lubricated powder was then allowed to dwell at ambient room conditions for 24 hours.

[0198] The material was then poured into a preform to make a 10 cm diameter pellet and dwelled in a 49° C. oven for 24 hours prior to being extruded into a tape form. A double cavity die with a thickness of 660 μm was used to create an extrudate tape that was roughly 15 cm wide. The extrudate was then calendered through precision rollers to a thickness of 440 μm. The lubricant was then removed using an air floatation dryer with a set point temperature of 2100° C. at a 1:1 ratio.

[0199] The tape was then expanded in the longitudinal direction on a MDO drum expander at drum set point temperatures of 270° C. at a ratio of 2.0:1 and an approximate stretch rate of 30%/s.

[0200] The roughly 13 cm wide tape was then cut into roughly 38 cm lengths and placed into a biaxial expanding heated pantograph. This pantograph has the ability to grab and hold all edges of the tape and after some period of heat up time for the sample, the pantograph has the ability to apply a stretch ratio to one or both directions at the same or different stretch rates.

[0201] A temperature of 320° C., and a dwell time of 30 seconds prior to the expansion, was used. An additional expansion ratio of 1.25:1 in the machine direction was followed immediately by a 4:1 expansion ratio in the transverse direction; both at the same stretch rate of 35%/s.

[0202] The membrane was restrained on a frame and removed while the clamshell oven was then heated up to a temperature of 380° C. Once the oven settled at the 380° C. temperature, the membrane was transferred back to the pantograph frame for 1:1 restraining purposes and the membrane then received 90 seconds of oven dwell time to “amorphously lock” or “sinter” the sample before removing the oven and the membrane sample from the pantograph frame.

[0203] The resulting membrane was about 0.25 mm (10 mils) thick with a bulk density of 0.40 gcm.sup.−3.

[0204] The resulting Tensile Strength was 7.85 M Pa in the longitudinal direction and 7.28 M Pa. in the transverse direction providing a near balanced strength membrane.

2. Sintered ePTFE Film with 12 wt % Lubricious Particulate Material

[0205] A PTFE aqueous dispersion containing approximately 22% by weight solids, the majority of which are PTFE particles having a particle size in a range from about 0.05 μm to about 5 μm was used to produce a 12% by weight graphite filled PTFE mixture. PTFE aqueous dispersion can be purchased from the Chemours Company. The graphite used in this example was a high synthetic graphite 99% plus carbon Grade #TC305 which was purchased from Asbury Carbons and has a medium particle size between 6.5 and 19 μm.

[0206] 0.82 kg (1.8 lb) of the aforementioned graphite was slurried into 27 kg (60 lb) of de-ionized water. The slurry was then coagulated with 6 kg (13.2 lb) of PTFE dispersion for a mix time of 6 minutes. The resulting coagulum was then dried at 165° C. for 24 hours. The dried coagulum was then frozen at −30° C. for two hours, and then screened through a 0.635 cm (¼″) opening screen to help turn the coagulum into a powder form.

[0207] The powder was then lubricated with mineral spirits at a ratio of 0.22 kg of lubricant to 1 kg of powder by weight. The lubricated powder was tumbled and the material was once again refrozen at −30° C. for 24 hours, and again re-screened through the 0.635 cm screen to break up any large lumps of the lubricated graphite/PTFE mixture. The resulting lubricated powder was then allowed to dwell at ambient room conditions for 24 hours.

[0208] The material was then poured into a preform to make a 10 cm (4″) diameter pellet and dwelled in a 49° C. oven for 24 hours prior to being extruded into a tape form. A double cavity die with a thickness of 0.66 cm (26 mils) was used to create an extrudate tape that was roughly 15 cm (6 inches) wide.

[0209] The extrudate was then calendered through precision rollers to a thickness of 0.444 mm (17.5 mils) thick. The lubricant was then removed using an air floatation dryer with a set point temperature of 210° C. at a 1:1 ratio. The tape was then expanded in the longitudinal direction on a MDO drum expander at drum set point temperatures of 270° C. at a ratio of 2.0:1 and an approximate stretch rate of 30%/s

[0210] The roughly 13 cm wide tape was then cut into roughly 38 cm lengths and placed into a biaxial expanding heated pantograph. This pantograph has the ability to grab and hold all edges of the tape and after some period of heat up time for the sample, the pantograph has the ability to apply a stretch ratio to one or both directions at the same or different stretch rates.

[0211] A temperature of 320° C. and a dwell time of 30 seconds prior to the expansion, was used. An additional expansion ratio of 1.25:1 in the machine direction was followed immediately by a 4:1 expansion ratio in the transverse direction; both at the same stretch rate of 35%/s.

[0212] The membrane was restrained on a frame and removed while the clamshell oven was then heated up to a temperature of 380° C. Once the oven settled at the 380° C. temperature, the membrane was transferred back to the pantograph frame for 1:1 restraining purposes and the membrane then received 90 seconds of oven dwell time to “amorphously lock” or “sinter” the sample before removing the oven and the membrane sample from the pantograph frame.

[0213] The resulting membrane was about 0.25 mm (10 mils) thick with a bulk density of 0.42 gcm.sup.−3.

[0214] The resulting Tensile Strength was 8.51 M Pa in the longitudinal direction and 9.42 M Pa. in the transverse direction providing a near balanced strength membrane.

3. Sintered ePTFE Film with 6 wt % Lubricious Particulate Material

[0215] A PTFE aqueous dispersion containing approximately 22% by weight solids, the majority of which are PTFE particles having a particle size in a range from about 0.05 μm to about 5 μm was used to produce a 6% by weight graphite filled PTFE mixture. PTFE aqueous dispersion can be purchased from the Chemours Company. The graphite used in this example was a high synthetic graphite 99% plus carbon Grade # TC305 which was purchased from Asbury Carbons and has a medium particle size between 6.5 and 19 μm.

[0216] 0.41 kg (0.9 lb) of the aforementioned graphite was slurried into 27 kg (60 lb) of de-ionized water. The slurry was then coagulated with 6.35 kg (14 lb) of PTFE dispersion for a mix time of 10 minutes. The resulting coagulum was then dried at 165° C. for 24 hours. The dried coagulum was then frozen at −30° C. for two hours, and then screened through a 0.635 cm (¼″) opening screen to help turn the coagulum into a powder form.

[0217] The powder was then lubricated with mineral spirits at a ratio of 0.22 kg of lubricant to 1 kg of powder by weight. The lubricated powder was tumbled and the material was once again refrozen at −30° C. for 24 hours, and again re-screened through the 0.635 cm screen to break up any large lumps of the lubricated graphite/PTFE mixture. The resulting lubricated powder was then allowed to dwell at ambient room conditions for 24 hours.

[0218] The material was then poured into a preform to make a 10 cm (4″) diameter pellet and dwelled in a 49° C. oven for 24 hours prior to being extruded into a tape form. A double cavity die with a thickness of 0.66 cm (26 mils) was used to create an extrudate tape that was roughly 15 cm (6 inches wide).

[0219] The extrudate was then calendered through precision rollers to a thickness of 0.444 mm (17.5 mils) thick. The lubricant was then removed using an air floatation dryer with a set point temperature of 210° C. at a 1:1 ratio. The tape was then expanded in the longitudinal direction on a MDO drum expander at drum set point temperatures of 270° C. at a ratio of 2.0:1 and an approximate stretch rate of 30%/s.

[0220] The roughly 13 cm wide tape was then cut into roughly 38 cm lengths and placed into a biaxial expanding heated pantograph. This pantograph has the ability to grab and hold all edges of the tape and after some period of heat up time for the sample, the pantograph has the ability to apply a stretch ratio to one or both directions at the same or different stretch rates.

[0221] A temperature of 320° C., and a dwell time of 30 seconds prior to the expansion, was used. An additional expansion ratio of 1.25:1 in the machine direction was followed immediately by a 4:1 expansion ratio in the transverse direction; both at the same stretch rate of 35%/s.

[0222] The membrane was restrained on a frame and removed while the clamshell oven was then heated up to a temperature of 380° C. Once the oven settled at the 380° C. temperature, the membrane was transferred back to the pantograph frame for 1:1 restraining purposes and the membrane then received 90 seconds of oven dwell time to “amorphously lock” or “sinter” the sample before removing the oven and the membrane sample from the pantograph frame.

[0223] The resulting membrane was about 0.25 mm (10 mils) thick with a bulk density of 0.41 gcm.sup.−3. The resulting Tensile Strength was 8.71 MPa in the longitudinal direction and 10.38 MPa. in the transverse direction providing a near balanced strength membrane.

4. Sintered PTFE Film with 25% Lubricious Particulate Material

[0224] A 0.13 mm thick skived PTFE film with 25% graphite filler that had been etched on side with a sodium ammonia etchant. The graphite filled etched skived PTFE film is commercially available from Enflo LLC of Bristol, Conn., USA.

5. Porous “POREX” PTFE Membrane

[0225] The Porex PM6M membrane is commercially available from Interstate Specialty Products of Sutton, Mass., USA. The Porex PM6M porous PTFE membrane had a thickness of 0.1 mm (0.004″) and a pore size of 5 microns (properties available on the supplier's website).

6. Natural Skived PTFE Film

[0226] The etched skived PTFE film is commercially available from Enflo LLC of Bristol, Conn., USA.

[0227] Table 1 summarizes the properties of the film materials as described above

TABLE-US-00001 TABLE 1 Elongation Maximum at Maximum Maximum Elongation Thickness Mass/Area Density Load Load Stress at Break Material (μm) (g/mt.sup.2) (g/cc) Direction (N) (%) (MPa) (%) Porex PM6M 104.1 147.1 1.413 MD 24.47 87.8 9.14 87.8 TD 26.24 81.1 9.96 81.1 Natural Skived PTFE 101.3 218 2.15 MD 96.97 348.9 37.72 348.9 TD 70.73 206.4 27.42 206.4 25% Graphite Filled Skived PTFE 150.4 271.1 1.806 MD 35.59 11.6 9.36 11.6 TD 20.46 4.4 5.32 6.6 5% Graphite filled ePTFE Membrane 320.0 145 0.453 MD 68.50 113 8.71 121.9 TD 87.63 94 10.38 101.1 12% Graphite filled ePTFE Membrane 269.2 112 0.416 MD 58.72 94 8.51 107.5 TD 64.05 86 9.42 88.3 24% Graphite filled ePTFE Membrane 243.8 99 0.407 MD 45.37 76 7.85 80.6 TD 48.04 61 7.28 63.6 (MD = machine direction; TD = transverse direction)

EXAMPLE 1 (6% GRAPHITE EPTFE/VITON)

[0228] A moulded article was prepared as described above with reference to FIG. 4, using 51 grams of the FKM Viton™ A elastomer compound and the 6% graphite filled ePTFE film. At the end of the 24 hour wear test (test protocol described below) the depth of the wear groove in the film layer was 51.6 microns. The coefficient of friction at the end of the wear test was 0.185.

EXAMPLE 2 (12% GRAPHITE EPTFE/VITON)

[0229] A moulded article was prepared using 49 grams of the FKM Viton™ A elastomer compound and the 12% graphite filled ePTFE film. At the end of the 24 hour wear test the depth of the wear groove in the film layer was 41.9 microns. The coefficient of friction at the end of the wear test was 0.181.

EXAMPLE 3 (24% GRAPHITE EPTFE/VITON)

[0230] A moulded article was prepared using 51 grams of the FKM Viton™ A elastomer compound and the 24% graphite filled ePTFE film. At the end of the 24 hour wear test the depth of the wear groove in the film layer was 32.5 microns. The coefficient of friction at the end of the wear test was 0.185.

EXAMPLE 4 (6% GRAPHITE EPTFE/HNBR)

[0231] A moulded article was prepared using 26 grams of the HNBR compound and the 6% graphite filled ePTFE film. At the end of the 24 hour wear test the depth of the wear groove in the film layer was 71.2 microns. The coefficient of friction at the end of the wear test was 0.268.

EXAMPLE 5 (12% GRAPHITE EPTFE/HNBR)

[0232] A moulded article was prepared using 26 grams of the HNBR compound and the 12% graphite filled ePTFE film. At the end of the 24 hour wear test the depth of the wear groove in the film layer was 57.2 microns. The coefficient of friction at the end of the wear test was 0.220.

EXAMPLE 6 (6% GRAPHITE EPTFE/HNBR)

[0233] A moulded article was prepared using 22 grams of the HNBR compound and the 24% graphite filled ePTFE film. At the end of the 24 hour wear test the depth of the wear groove in the film layer was 52.8 microns. The coefficient of friction at the end of the wear test was 0.213.

EXAMPLE 7 (24% GRAPHITE EPTFE/EPDM)

[0234] A moulded article was prepared using 25 grams of the HNBR compound and the 24% graphite filled ePTFE film. At the end of the 24 hour wear test the depth of the wear groove in the film layer was 63.2 microns. The coefficient of friction at the end of the wear test was 0.324.

COMPARATIVE EXAMPLE 8 (POREX/VITON)

[0235] A moulded article was prepared using 49 grams of the FKM compound and Porex PM6M porous PTFE membrane. At the end of the 24 hour wear test the depth of the wear groove in the film layer was 87.9 microns. The coefficient of friction at the end of the wear test was 0.342.

COMPARATIVE EXAMPLE 9 (4 MIL NATURAL SKIVED PTFE/EPDM)

[0236] A moulded article was prepared using 27 grams of the EPDM compound and a 0.1 mm thick natural skived PTFE film that had been chemically etched on one side with sodium ammonia etchant. At the end of the 24 hour wear test the depth of the wear groove in the film layer was 244.1 microns. The coefficient of friction at the end of the wear test was 1.231. The skived PTFE film had been completely worn through during the 24 hours.

EXAMPLE 10 (25% GRAPHITE FILLED SKIVED PTFE/EPDM)

[0237] A moulded article was prepared using 32 grams of the EPDM compound and a 0.13 mm thick skived PTFE film with 25% graphite filler that had been etched on side with a sodium ammonia etchant. At the end of the 24 hour wear test the depth of the wear groove in the film layer was 39.6 microns. The coefficient of friction at the end of the wear test was 0.166.

[0238] The examples and comparative examples are summarized in Table 2:

TABLE-US-00002 TABLE 2 Description (film/Elastomeric body) Example 1 6 wt % graphite ePTFE/Viton Example 2 12 wt % graphite ePTFE/Viton Example 3 24 wt % graphite ePTFE/Viton Example 4 6 wt % graphite ePTFE/HNBR Example 5 12 wt % graphite ePTFE/HNBR Example 6 24 wt % graphite ePTFE/HNBR Example 7 24 wt % graphite ePTFE/EPDM Comparative Porex/Viton Example 8 Comparative Natural skived PTFE/EPDM Example 9 Example 10 25 wt % graphite skived PTFE/EPDM

Physical Properties of the PTFE Film and Comparative Films

Tensile Strength Method

[0239] ASTM D638-14 Standard Test Method for Tensile Properties of Plastics was used.

[0240] Tensile strength (TS) measurements were taken using 1″×6″ (2.54×15.2 cm) samples stamped out of each film. The test equipment by the company Instron, USA is set up to have a 2″ (2.54 cm) gap allowing roughly 2 inches (2.54 cm) to be gripped and held in each clamp. A cross head speed of 20 inches per minute (51 cm/minute) was used. The maximum load obtained during the tensile pull and was used to calculate MTS using the following formulae (1a to 1c):

[00001]$\begin{array}{cc}\mathrm{TS}\left(\mathrm{psi}\right)=\frac{\mathrm{Load}\left(\mathrm{lb}.-f\right)\times \mathrm{PTFE}\mathrm{full}\mathrm{density}-\left(2.18{\text{g/cm}}^3\right)}{\mathrm{Thickness}\left(\mathrm{in}.\right)\times \mathrm{width}\left(\mathrm{in}.\right)\times \mathrm{sample}\mathrm{density}\left(\text{g/c}{m}^3\right)}& \left(1a\right)\\ \mathrm{TS}\left(\mathrm{kg}-\mathrm{forc}\text{e/c}{m}^2\right)=\frac{\mathrm{Load}\left(\mathrm{kg}.-\mathrm{force}\right)\times \mathrm{PTFE}\mathrm{full}\mathrm{density}-\left(2.18\text{g/c}{m}^3\right)}{\mathrm{Thicknesses}\left(\mathrm{cm}\right)\times \mathrm{width}\text{(cm})\times \mathrm{sample}\mathrm{density}\left(\text{g/c}{m}^3\right)}& \left(1b\right)\\ \mathrm{TS}\left(\mathrm{MPa}\right)=10.197\times \mathrm{TS}\left(k\text{g/c}{m}^2\right)& \left(1c\right)\end{array}$

Thickness (μm)

[0241] The thickness of the PTFE films was measured using a desk mounted Heidenhain thickness gauge model SGMT 60M.

Mass/Area (g/m.SUP.2.)

[0242] The mass/area weights of the films were determined using a Toledo Mettler scale model AG 204.

Density (g(cc)

[0243] The density is calculated using the 1″×6″ (2.54×15 cm) samples for the tensile tests. The samples are weighed and the thickness is measured. The density is calculated by dividing the mass (g) by the volume of the sample (cm.sup.3).

Elongation at Break (%)

[0244] Elongation-to break was calculated in accordance with ASTM D638-14, section 11.3.1.2; by reading the extension (change in gauge length) at the point of rupture. The gauge length at the point of rupture was divided by the original gage length and multiplied by 100.

Elongation (%)=Lf−Li/Li×100

[0245] where Li=is the initial gap between the clamps and Lf=The final full distance pulled until breakage including the gap distance

Mouldability

[0246] Mouldability tests were conducted using a platen press and the mould shown in FIG. 2, which comprises a heated mould top 17 and mould base 19. A cross sectional view of region X through the mould base 19 is also shown. The mould 19 has an annular channel 21, defining a mould cavity having the following dimensions: [0247] Inner Diameter=25.4 mm (1.0″) [0248] Outer Diameter=34.93 mm (1.38″) [0249] Depth=7.16 mm (0.282″) with a radius of 4.78 mm in the bottom of the cavity

[0250] The mould top 17 was heated to 160° C. (320° F.). The mould base 19 was preheated before each test. The film samples were cut to approximately 114 mm in length and width. A hole pattern was cut in the film samples 22 to secure the film with the dowel pins 23 in the mould 19, as shown in FIG. 3. The hole pattern had a hole diameter of 7.94 mm (0.313 inches) on a circular centre line of 76.2 mm (3 inches) in diameter. A disk of uncured elastomeric material 24, EPDM rubber, with a thickness of about 3 mm was cut with a hole punch with a diameter of 38.1 mm.

[0251] The cut film sample was placed over the mould base 19 (passing the pins 23 through the holes in the film 22). The EPDM disk was placed on top of the test film sample and centred in the mould over the mould cavity. The mould top was placed on the mould base using the dowel pins to align the mould top with the mould base. The mould was placed on the lower platen of the hydraulic press and centred on the platen.

[0252] A press load of 89 kN (20,000 lb) was applied to the platens and held for a dwell time of 20 minutes to cure the EPDM rubber. At the end of the dwell time the press load was released and the mould was removed from the press. The mould top was removed and the moulded part was removed from the mould cavity. The moulded part was visually inspected for any tearing in the film. A pass/fail criteria was used in the evaluation. Samples that had no tearing in the film over the moulded surface (area of the mould cavity) were considered passing.

[0253] Mouldability test results are set out in Table 3.

TABLE-US-00003 TABLE 3 Film Pass/Fail 24 wt % graphite ePTFE Pass 12 wt % graphite ePTFE Pass Natural skived PTFE Pass 25 wt % graphite skived PTFE Fail

[0254] The PTFE film has sufficient “mouldability” (i.e. the ability to form a connection with the elastomeric body) without tearing or blistering.

Wear Rate Testing and Coefficient of Friction—ASTM D3702-94 (Reapproved 2014)

[0255] (ASTM D 3702; Test Method for Wear Rate and Coefficient of Friction of Materials in Self-Lubricated Rubbing Contact using a Thrust Washer Testing Machine, American Society Testing & Materials, USA, 1978-1994, which is incorporated herein by reference).

[0256] The wear resistance and coefficient of friction properties of the moulded examples were measured using an automated tribometer (LRI-1a Automated Tribometer, Lewis Research Inc., Lewes, Del., USA) and following the test procedures defined in the ASTM D3702-94 (2014) test method with noted exceptions.

[0257] The test set up for the wear tests can be seen in FIG. 1. A test sample 1 was placed on a test sample platform 3 and retained by a hold-down ring 5 bolted to the platform through the test sample, with dimensions of 71.5 mm by 36.5 mm (rectangular plates). A steel thrust bearing 7 is coupled to annular holder 9. The holder 9 is coupled to a rotary spindle 11, by drive pins 13, which slot into corresponding apertures 15 in the holder 9.

[0258] A 1018 steel ASTM D3702 thrust bearing 7 was used to wear against the PTFE film layer in the test samples. The pressure applied to the test samples was 345 kPa (50 psi) and the rotational speed of the thrust bearing was 34 rpm (10 fpm). The test duration was 24 hours. No break-in interval was used prior to determining the wear in the samples. The tests were performed under dry conditions. The wear groove depth and the coefficient of friction (CoF) were measured continuously throughout the tests. The overall wear rate was calculated by the following equation:

[0259] Overall wear rate (μm/hr)=wear groove depth at the end of the test (μm)/test duration (hr) Wear test and coefficient of friction test results are summarised in Table 4. Plots vs. time of these data are in FIGS. 5 and 6.

[0260] The stiffness of the elastomeric body has been found to have an effect on the wear performance and coefficient of friction (e.g. examples 1-3 as compared to examples 4-6). The Viton had the highest durometer at around 75 while the HNBR and EPDM had a durometer of 70.

TABLE-US-00004 TABLE 4 Depth of the Overall Wear Groove CoF Wear Rate after 24 hr after (μm/hr) (μm) 24 hrs Example 1 3.581E−02 51.6 0.185 Example 2 2.911E−02 41.9 0.181 Example 3 2.258E−02 32.5 0.185 Example 4 4.940E−02 71.1 0.268 Example 5 3.970E−02 57.2 0.22 Example 6 3.669E−02 52.8 0.213 Example 7 4.393E−02 63.2 0.324 Comparative 6.104E−02 87.9 0.342 Example 8 Comparative 1.695E−01 244.1 1.231 Example 9 Example 10 2.752E−02 39.6 0.166

[0261] The relationship between sealing film thickness and elastomer body stiffness is also a factor in wear resistance and CoF performance. The ePTFE sealing films became partially densified during compression moulding, reducing the film thickness from around 250-300 μm to around 75-100 μm in the final test sealing elements. This compares to a skived PTFE film thickness of ca. 150 μm.

SEM/EDS Method

[0262] Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were used to analyze the distribution of the graphite particles in the ePTFE film in the inventive examples. A Hitachi High-Resolution scanning electron microscope with EDS detector, ModelSU8230, was used. An accelerating voltage of 2 to 5 kV was used for imaging and 10 kV was used for EDS analysis. A working distance of at least 15 mm between the detector and the sample was required for the EDS detector. Samples were prepared by slicing a section from the molded samples with a carbon steel blade to have a cross sectional view of the elastomeric body and the PTFE film. Samples were also prepared having a top down view of the top surface of the PTFE film in the molded samples. The samples were mounted to an SEM sample stub using a carbon adhesive tape. The samples were coated with approximately 2.5 nm of platinum to reduce charging.

[0263] The thickness of the PTFE film was measured in the SEM images at multiple locations.

[0264] The results are summarized in table 5.

[0265] EDS was used to identify the lubricious particles (graphite) in the PTFE film of the inventive examples and to calculate the amount of graphite by measuring the amount of carbon and fluorine on an atomic percentage basis. A 500× magnification was used for the EDS scans. EDS scans were performed on the top surface of the PTFE film and through the thickness of the PTFE film.

[0266] A carbon to fluorine ratio (C: F) was calculated from the measured percentages of carbon aid fluorine atoms. Pure PTFE has a carbon to fluorine ratio of 1:2, or 0.5, since there is one carbon atom for every two fluorine atoms in PTFE.

[0267] The amount of graphite in the EDS scan area can be estimated from the following equation:

% graphite=(0.67×C:F−0.33)/(0.67+0.67×C:F)×100% [0268] Where C:F is the carbon to fluorine ratio from the EDS analysis

[0269] Results of the EDS analysis are summarized in table 6 and 7.

[0270] TABLE 5 summarizes the thickness measurement based on the SEM images shown in FIGS. 7 to 10.

TABLE-US-00005 TABLE 5 Thickness Measurements from SEM Comparative Comparative Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 Example 10 43 64 45 65 44 56 68 79 96 140 43 61 60 41 40 68 59 68 98 140 39 74 53 70 39 63 55 78 95 130 46 64 53 53 38 49 57 84 97 140 52 80 53 59 38 55 53 81 98 140 51 66 60 49 39 51 68 83 97 140 43 94 70 62 39 80 66 80 96 130 44 67 54 63 48 83 98 78 96 130 47 73 60 57 44 94 88 79 93 140 45 52 48 62 38 88 86 77 96 140 46 59 68 60 30 88 97 78 97 140 42 62 67 53 36 64 81 80 95 140 53 46 49 57 55 55 55 48 51 51 53 56 Average (μm) 47 65 57 58 39 67 73 79 96 138 STD 4.7 12.3 7.5 7.8 4.5 15.8 16.3 3.98 1.4 4.5 Max 55 94 70 70 48 94 98 84 98 140 Min 39 46 45 41 30 48 53 68 93 130

[0271] Table 6 lists the C:F ratios and percent graphite from the EDS analysis as measured in the cross sections, examples of which are shown in FIG. 7-10.

TABLE-US-00006 TABLE 6 Atomic % % Graphite Graphite Carbon Flourine C:F Ratio (atomic %) wt % Example 1 36.08 63.92 0.56 4.32 3.15 43.17 56.41 0.77 15.68 11.84 Average: 39.63 60.17 0.67 10.00 7.50 Example 2 51.07 48.1 0.94 23.07 18.14 49.09 50.26 1.00 25.37 19.73 48.77 50.57 0.96 23.85 18.52 Average: 49.64 49.64 0.97 24.10 18.80 Example 3 53.37 46.63 1.14 30.26 23.80 51.68 47.91 1.08 28.24 22.16 52.29 47.35 1.1 28.93 22.74 Average: 52.45 47.30 1.11 29.14 22.90 Example 6 53.37 46.63 1.14 30.26 23.80 56.48 42.89 1.32 35.67 28.69 54.36 49.71 1.22 32.77 24.64 Average: 54.74 46.41 1.23 32.90 25.71 Example 10 53.37 46.63 1.14 30.26 23.80 62.88 35.67 1.76 45.92 38.50 63.32 35.33 1.79 46.50 39.01 Average: 59.86 39.21 1.56 40.89 33.77

[0272] Table 7 lists the C:F ratios and percent graphite from the EDS analysis as measured in the top surface, examples of which are shown in FIG. 7-10. Table 8 shows a summary of the D:F ratios set out in tables 6 and 7, together with a ratio of top:cross section C:F ratios.

TABLE-US-00007 TABLE 7 Atomic % % Graphite Graphite Carbon Fluorine C:F Ratio (Atomic %) wt % Example 1 35.08 64.92 0.54 3.08 2.24 34.65 65.35 0.53 2.45 1.77 Average: 34.87 65.14 0.54 2.77 2.01 Example 2 36.07 63.52 0.56 4.32 3.17 35.61 63.86 0.56 4.32 3.17 Average: 35.84 63.69 0.56 4.32 3.17 Example 3 40.24 59.76 0.67 10.63 7.89 39.9 59.73 0.67 10.63 7.91 Average: 40.07 59.75 0.67 10.63 7.90 Example 6 39.79 59.49 0.67 10.63 7.94 40.81 58.54 0.67 10.63 7.97 Average: 40.30 59.02 0.67 10.63 7.95 Example 10 80.83 12.06 6.70 80.62 80.70 81.37 12.59 6.46 79.99 78.98 86.52 7.33 11.80 88.34 90.04 Average: 82.91 10.66 8.32 82.98 83.24

[0273] The equation for calculating the wt % of graphite based on the atomic % is:

Wt % graphite=[Atomic % Graphite*12.011]/[(Atomic % Carbon*12.011)+(Atomic % Fluorine*18.998)]

TABLE-US-00008 TABLE 8 Top Surface Bottom Surface Top Surface: C:F Ratio C:F Ratio Bottom Surface Example 1 0.54 0.67 0.80 Example 2 0.56 0.97 0.58 Example 3 0.67 1.11 0.61 Example 6 0.67 1.23 0.55 Example 10 8.32 1.56 5.32

[0274] The inventors surprisingly found through the EDS analysis that there was less graphite visible on the top surface of the of the PTFE film than throughout the thickness of the film in the samples made with graphite filled expanded PTFE film. This means that the examples made with the graphite filled expanded PTFE have a PTFE rich top surface.

Thermogravimetric Analysis

[0275] Thermogravimetric Analysis is a method which can be used to determine the weight percentage of the lubricious particulate material in the PTFE film using a thermogravimetric analyzer. In the TGA method, a sample of the PTFE film ranging in weight of 2.5 to 5 mg is heated at a uniform rate under a nitrogen atmosphere. The nitrogen, or other inert gas, atmosphere is used to prevent oxidation of the particulate material. The thermogravimetric analyzer records the change in weight of the sample over time or temperature. The PTFE component in the film thermally degrades through a temperature range of 450° C. to 625° C. Above 625° C. the PTFE component has fully decomposed. The residual weight of the sample after the PTFE component has decomposed can be attributed to the lubricious particulate material. For example, where the lubricious particulate material in the PTFE film is graphite, graphite is thermally stable above 700° C., therefore the residual weight of the film sample in the TGA curve at 700° C. can be attributed to the graphite content in the film. For materials that thermally decompose at temperatures below that of PTFE, the changes in weight in the TGA curve can be used to determine the amount of particulate material in the PTFE film, as well.

Initial Porosity and Final Porosity Calculations

[0276] The theoretical maximum density of each of the graphite filled ePTFE films was calculated from the following equation:

Density=% graphite×graphite density+% PTFE×PTFE density

[0277] The density of the graphite powder was provided by the supplier and had a value of 2.7 g/cm.sup.3.

[0278] The density of PTFE used in the calculation was 2.25 g/cm.sup.3.

[0279] The film density from Table 1 was used to estimate the initial porosity in the graphite filled ePTFE membranes using the following equation:

% Porosity=film density/Theoretical maximum density×100

[0280] The results of the initial porosity estimations are shown in Table 9.

TABLE-US-00009 TABLE 9 Theoretical Density of Film Initial Graphite filled PTFE Density Porosity Content (%) (g/cm.sup.3) (g/cm.sup.3) (%)  6% 2.277 0.453 80% 12% 2.304 0.416 82% 24% 2.358 0.407 83%

[0281] The residual porosity in the compressed ePTFE films in the inventive examples was calculated from the following equation:

% Residual porosity=Initial Porosity(%)×[Compressed Film Thickness/Initial Film Thickness]

[0282] The results are shown in the Table 10.

TABLE-US-00010 TABLE 10 Initial Film Initial Compressed Final Thickness Porosity Film Thickness Porosity | (μm) (%) (μm) (%) Example 1 320.0 80% 46.7 12% Example 2 260.2 82% 65 20% Example 3 243.8 82% 57 19% Example 4 320.0 80% 58 15% Example 5 269.2 82% 39 12% Example 6 243.8 82% 67 22% Example 7 243.8 82% 73 25%

[0283] Referring now to the EDS images in FIGS. 7(b) and 7(d), the red (in the original images) spots indicate the presence of a graphite particle. Selections of the larger of the particles visible are highlighted by the arrows in the figures.

[0284] The C:F ratio values of table 6 are based upon the portion of the image within box A.

[0285] Referring now to the cross sectional SEM image in FIG. 7(c), the material of the elastomeric body 200 and of the sintered PTFE film 202 can be seen. The film 202 has a sealing surface 204 and is coupled to the elastomeric body 200 at a boundary 206 (a portion of which is highlighted by the dotted line), wherein elastomer penetrates the pores of the ePTFE film 202. The penetrated region at the boundary is less than 5 microns thick and not visible in the scale of the SEM images shown.

[0286] Some variation in the overall thickness of the sintered PTFE film 202 defining the sealing layer 204 can be seen in the image to vary (thicknesses 208a, b and c), which is even more pronounced in relation to other samples (see FIGS. 8(c) and 10(c) in particular), and such variations vary with moulding conditions (elastomer viscosity, pressure and the like).

[0287] The corresponding features observable in FIGS. 7(a)-(d) can also be seen in FIGS. 8-10.