COMPOSITION OF FLUOROPOLYMERS

Abstract: A wear-resistant solid fluoropolymer composition, e.g. of homo- and copolymers of tetrafluoroethylene (TFE), which has an extremely low coefficient of friction in dry sliding contact with metal, without the application of additional fluid lubricant, which composition comprises: a) a fluoropolymer, b) a poly(arylene sulphide) and c) another high aromatic polymer; and a process for preparing the foregoing solid fluoropolymer composition.

Description: COMPOSITION OF FLUOROPOLYMERS The present invention relates to a wear-resistant compos i t i on co pr i s i ng po I ymer i c fi l l ers and at I east one f I uoropo I ymer . It is we I l-known in the art that f I uoropo I ymers, such as homo- and copolymers of tetrafluoroethylene (TFE), have outstanding chemical and physical properties, in particular an extremely low coefficient of friction in dry sl iding contact with metal , which make them ideal components in situation w ich require operation with moving loaded contact, e.g. for shaft bearings or piston rings, under dry conditions, ie without the appl ication of additional fluid lubricant, and/or where the component is required to be as maintenance free as possible over its I ifetime under such dry conditions. Examples of these include appl ications in domestic or commercial machinery (including automotive and/or hydraul ic machinery). Such factors have lead to the rapid increase of the use of fluoropolymer compositions in such appl ications. However, the compositions known hitherto tend to suffer from a d i sadvantageous I y high wear rate. During dry si i d i ng contact with a smooth metal I ic surface such fluoropolymer compos itions form a fi lm on the metal surface, and it is this f i Im which dictates the interfacial tribological (frictional and wear) behaviour which i s observed . The fi lm takes a finite sl iding distance to equi l ibrate (known as the "break-in period"), and during break-in the friction and wear rate can each be orders of magnitude higher than at steady state. If the break-in period itself is considerable, the wear during the break-in period can form a significant part of the total . A reduction in the break-in period would clearl offer an advantage . It wi I I be seen from the foregoing that there is a need for a fluoropolymer composition which has in particular the comb i nat i on of a) an extremely low steady state coefficient of friction in dry si i d i ng contact with metals, together with b) a very short break-in period before -the steady state coefficient of friction and wear rate is achieved. Surprisingly, we have now found fluoropolymer compos i t i on compr i s i ng po I ymer i c fi l lers wh i ch comb i nes the above advantageous properties, and which make them ideal materials for the above mentioned special appl ications. Accordingly, the present invention provides a sol id fluoropolymer composition which comprises: a) a fluoropolymer, b) a poly(ar lene sulphide) (hereinafter a PS) and c) another high aromatic polymer (hereinafter an HAP). When used herein HAP means any polymer, at least 50 wt.%, preferably at least 65 wt.% and in particular 80 wt.% of which is made up of aromatic moieties. Together with a very short break— in period and low steady state coefficient of friction and wear rate, the present fluoropol mer composition has excel lent resistance to compression creep. Such materials typical ly comprise: a) a polymer main chain of aromatic diradicals, such as phenylene, in particular I ,4-pheny lene, b) I inked by functional groups, such as oxy , carbonyl , sulphonyl su I phony I oxy , amino and imino, and mixtures thereof . Suitable compositions of the present invention comprise up to 40 vol .% of PS, preferably up to 30 vo I . % , in particular 2 to 20 vol .% , and up to 30 vol .%, in particular 2 to 20 vol .%, and up to 30 vol .% of HAP, preferably up to 20 vo I . % , in particular 1 to 10 vol .%. (al l vol .% herein are relative to the total composition). SUB S TITUTESHEET Within the above ranges, the PS and HAP may suitably be present in a volume ratio in the range of from 5: 1 to 1 :2, e.g. 9:2 to 2:3, preferably 4: 1 to 1 : 1. The fluoropolymer content of the fluoropolymer composition of the present invention may be as low as 30 vol .%, e.g. as low as 50 vol .%, preferably 60 to 90 vo I . % , and in particular 70 to 97 vol .%. The exact proportions may of course be adjusted by routine trial to achieve the desired balance of frictional and wear properties for any given app I i cat i on . We have found that the proportions referred to in particular above combine an extremely low steady wear rate and low steady state coefficient of friction in dry siding contact, with a short break-in period. The fluoropolymer content of the composition may consist of one or more f I uoropo I ymers , often of one. This depends however on the desired properties of the composition. The or each fluoropol ymer wi l l typical ly compr ise repeat units derived from at least one f luoroolef in and, optional ly, at I east one olefinical ly unsaturated monomer wh i ch is not a f I uoroo I ef i n . Such f I uoropo I ymers may be prepared by conventional fluoropolymer dispersion or suspension polymerisation processes. Typical ly the fluoropolymer compr i ses a) 30-100 weight% (e.g. 50-100 weight%) of units derived from the f I uoroo I ef i n , and b) 0-70 weight% (e.g. 50-0 weight%) of other units (ie not derived from a f I uoroo I ef i n) . The f luoroolef in is broadly defined as an olefin having at least one fluorine atom substituent. Preferably the f luoroolef in is a perha I oo I ef i n in which al l the hydrogen atoms of the olefin are substituted with fluorine atoms and optional ly other halogen atoms. SUBSTITUTESHEET From the point of view of ease of production and resulting polymer properties f I uorooI ef i ns having 2 or 3 carbon atoms are preferable. Examples of such f I uoroo I ef ins include a) f I uoroeth I enes such as CF 2 =CF 2 , CH2 -CF2 ,CH2-CF2 , CH 2 =CHF, CCIF=CF 2 , CC I2 =CF 2 , CCIF=CCIF , CHF=CCI 2 . CH 2 =CCIF, and CCI 2 =CCIF; and b) f I uoropropy I enes such as CF3CF=CF 2 , CF3 CF=CHF , CFnCH=CF 2 , CFnCH=CH 2 , CF n CH=CH 2 , CF 3 CF=CHF, CHF 2 CH=CHF,and CF3 CH=CH 2 . Of the f I uoroethy I enes and f I uoropropy I enes l isted above tetrafluoroethylene (CF2 =CF2 ) ("TFE"), ch I orotr i f I uoroethy I ene (CCIF=CF 2 ) ("CTFE"), vinyl idene fluoride (CH 2 =CF2 ) ("VDF"), and hexaf I uoropropy I ene (CF2=CFCF3) ("HFP") are particularly preferred . Examples of non—f I uoroo I ef i ns as comonomers include, particularly, perf I uoro(a I ky I vinyl ethers) ("PAVE's") ^ Examples of such ethers include perf I uoro(prop I vinyl ether) ("PPVE"), and perf I uoro(a I y I dioxoles) such as perf luoro(2,2-dimethy I- 1 ,3-dioxole) ("PDD"). In principle the composition of the present invention may comprise any type of fluoropolymer; however, the advantages afforded by its use are more significant for non-melt processable f I uoropo I mers. These include polymers such as PTFE (homopo I ymer ) , or copolymers of TFE with monomers selected from other f I uoroethy I enes . Such compositions have to be produced by sintering granulates or coagulated dispersions. The invention may however also advantageously use me I t-processab I e types of f I uoropo I ymers , e - g • me I t- processable copolymers of TFE with monomers selected from: a) higher perf I uoro -olef ins of 3 to 10 carbon atoms (particularly HFP) and/or b) perf I uoroa I k I vinyl ethers of 3 to 10 carbons (part i cu I ar I y PPVE) . SUBSTITUTESHEET Copolymers of TFE/PPVE having 2 to 5 weight% PPVE (e.g. 2 to 4 weight% PPVE, typical ly 3 weight%) are also useful . The fluoropolymer may thus e.g. be PTFE, PTFE-HFP copolymer, polyCTFE, or a TFE—PAVE copolymer. Examples of such f I uoropo I ymers include, preferably, PTFE, in particular F I uon G163, G580, G108 or G190 (trade mark , 1C1 ) . The f I uoropo I ymer(s) in the composition precursor used to prepare the composition, e.g. by sintering or melting the fluoropolymer(s), wi l l conveniently be in granular or coagulated dispersion form, and depending on the type of the fluoropolymer(s), the compos i t i on wi l l compr ise an unsintered granulate or a particulate sinter of the f I uoropo I ymer (s) , and/or melted matrix. F I uoropo I ymer (s) , especial ly PTFE, with a mean particle size which is less than 60μ , e.g. 10 to 50μ , in particular 15 to 35μ wi I I be suitable. The arylene moiety in the PS is often pheny I ene , in particular 1 , 4-pheny I ene . The PS may be I inear or branched-cha i n and may be any PS, irrespective of the route by which it may have been prepared or processed. The main PS of interest in the compositions of the present invention is one based on po I y( 1 , 4-pheny I ene sulphide), whether I inear or branched-cha i n . Exam les of HAP's which may be used in the present compositions include poly(arylene etheretherketone) PEEK), poly(arylene etherketone) (PEK) and poly(arylene etherether ketone ketone) (PEEKK), and po \ y(ary I enepropy I ene- ar I eneetherether ketone) (PEDEK), and mixtures thereof. Examples of HAP's which may be used in the compositions of the present invention also include poly(arylene etherethersu I phone ) (PEES), poly(arylene ethersu I phone) (PES), po I y(ary I enepropy I eneary I ene etherether sulphone) (PEDES), and mixtures thereof. TITUTESHEET - ό - Examples of HAP's which may be used in the compositions of the present invention further include polyimide (PI), po I yami de imi de (PAI), po I ether i i de (PEI), po I y i i desu I phone (PIS), poly(arylene oxide) (PO), poly(arylene ketone), poly(arylene sulphone) (PS), poly(arylene sulphone) block copolymers, and po I ybenz imi dazo I e , and mixtures thereof. Mixtures of al I the foregoing classes of HAP's may be used . The arylene moiety in the foregoing HAP's is often phenylene, in particular 1 , 4-pheny I ene . The HAP may be I inear or branched-cha i n in the composition of the present invention. The HAP's of greatest interest among the foregoing HAP's are PI , PEEK and PEI , in particular those based on 1 , 4-pheny I ene . These HAP's may also be I inear or branched-cha i n . The PS and HAP wi I I typical ly be incorporated into the preparative precursor of the composition of the present invention as a particulate sol id. Each wi I I thus often be present in the composition as a particulate f i I ler in a sintered or melted matrix of f I uoropo I ymer (s) , depending on the physical properties of the latter. The PS and- HAP particles may range in mean size from 5 to 80μ , e.g. 10 to 60μ , in particular 20 to 50μ . The most suitable size, depending on the nature of the material and the desired properties of the composition, may be determined by routine trial . Most forms of the PS and most of the foregoing HAP's wi I I be present in the composition of the present invention in a form which has been heat treated. The mutual addition and initial blending is typical ly made at a temperature of usual ly 0 to 100 * C (e.g. 10 to 70*C, particularly 15 to 50 * C). SUBSTITUTESHEET The mixture is then held at a temperature (or varying temperature range) typical ly within the range 200 * C-400 * C. The temperature and time period and the order and timing of component additions for the thermal treatment is usual ly 5 specific to and critical for each component, and e.g. the temperature may vary outside the above range, and the time may vary from "zero time", ie no dwe I I at "on temperature", to 24 hours or more at the necessary temperature or temperature range, and/or other composition components added subsequently '0 to the heat treatment. In the case of the PS, for example, the procedure may involve dry blending the f I uoropo I ymer (s) and PS together, heat treating the blend for up to 24 hr . , fol lowed by remixing prior to blending with the HAP. 5 In certain cases, e.g. where the HAP is PI , al l the components may as an alternative be initial ly dry mixed and then heat treated together, fol lowed by comminution prior to fabr i cat i on . Blending may be carried out conventional ly, e.g. in a 0 Hensche I mixer, a tumble mixer or a Littleford blender, or through a hammer mi l l . Accordingly, the present invention provides a process for preparing the foregoing sol id fluoropolymer composition which comprises in any feasible order 5 a) dry blending the components as part i cu Iates , and b) optional ly, heat treating the po I ( 1 , 4—phenylene sulphide) and/or the high aromatic polymer, and then c) heating the blend to a temperature or varying temperature range sufficient to sintered or melted the 0 f I uoropo I mer (s) to form a matrix of f I uoropo I ymer (s) . In addition to conventional additives for such a fluoropolymer composition, such as pigments and processing aids, the composition may comprise additives known to confer a good steady state wear rate in dry si i d i ng contact. SUBSTITUTESHEET Examples include any of the fol lowing or any combination thereof, as up to 50 vol .% of the composition, e.g. up to 25 vol .%, preferably up to 10 vol .%: carbon such as carbon fibre and powder ,graph i tes (including e I ectrograph i t i sed carbon and flaky grap ite-, the latter e.g. having a size of less than 300 mesh and/or containing more than 95 wt.% fixed carbon, and coke flours; glass ibre and powder; metal powders, such as stainless steel , nickel and bronze powders; ceramic fibres and powders; metal cha I cogen i des , such as molybdenum disulphide and aluminium hydrox i de/hydrated aluminium oxide fibre and powder; calcium fluoride; and si I i ceous f i I lers, such as woI lastonite (calcium metas i l icate), aluminium si l icate and mica,. The present invention is now i I lustrated by reference to the fol lowing Example. ExampI e Al I the PTFE compositions prepared and evaluated and the i r components, are I i sted in Tab I e 1 be I ow. Al l were based on F I uon grade G163 (trade mark, ICI) PTFE, which in its unprocessed form is a granular powder with an average particle size of 25μ . The compositions were prepared by dry blending of the components as particulates in a Hensche I mixer. Each composition is heat treated after the initial blending for 8 to 24 hr . at 290 to 320 * C, and then reblended before subsequent conventional sintering into iscs of thickness 5 mm. The discs were then machined into square prisms of 5 mm side for frictional and wear evaluation. SUBSTITUTESHEET Compos i t i on 1 2 3 4 5 In Table 1 : the PS is Ryton P4 (trade mark, Phi l l ips Petroleum); The PI is polyamide Lenz i ng P84 (trade mark, Lenzing AG); and the PEEk used is Victrex 150P (trade mark, ICI), c.35μ. The frictional and wear tests were performed using an apparatus which is essential ly that described in Surface and Interface Analysis, 18, 1992, 303-305. This uses a pin on EN8 steel or LM24 aluminium under dry conditions at room temperature . The apparatus for such a test comprises a pivoted lever arm bearing the test specimen near one end. The specimen is biased into normal contact with the edge face of a rotating metal disc (here of EN8 steel by a constant load appl ied to the other end of the lever arm. Periodical ly the rotating disc is stopped, the specimen is removed, the mass loss of the specimen (due to wear at the contact surface with the disc) is determined. The test procedure is then resumed, optional ly unt i I the specimen is ful ly worn away . Prior to the present testing the steel counterfaces were re-finished to a roughness of 0.1μm Ra , and the specimens and counter faces were thoroughly degreased. The speed of rotation of the steel ring was set so as to achieve an interfacial sl iding speed of 1 m.s-1. a load of 1 mPa was app I i ed continuously during si iding. SUBSTITUTESHEET The specific wear rate was plotted as a function of ime, hence determining when a steady state. The friction coefficient μ was also determined during these tests. For each composition, four independent tests were carried out simultaneousl , to produce the mean values in Table 2 Table 2 Composition Steady state Friction Break-in Wear Rate Coefficient Period (m3. Nm- 1 μ Km x 10-16 ) 1 2.1 0.24 5 (error ± 15%) The compositions were found to have a short break-in period, which clearly offers the advantages set out hereinbefore over the related compositions known hitherto. SUBSTITUTE SHEET

Claims: C I a i ms 1. A so l id f I uoropo I ymer compos i t i on wh i ch compr i ses : a) a fluoropolymer, b) a poly(arylene sulphide) and c) another high aromatic polymer, at least 50 wt.% of which is made up of aromatic moieties. 2. A composition according to claim I wherein at least 80 wt.% of the high aromatic polymer is made up of aromatic mo i et i es . 3. A composition according to claim 1 wherein the high aromatic polymer comprises a) a I inear or branched polymer main chain of 1 ,4—pheny I ene aromat i c d i rad i ca I s , b) l inked by oxy, carbony 1 , su I phony I , su I phony I oxy , amino and imino, and mixtures thereof, and the poly(arylene sulphide) is a I inear or branched—cha i n po I y ( 1 , 4-pheny I ene sulphide). 4. A composition according to claim 3 which comprises 2 to 20 vol .% of l inear or branched-cha i n po I y ( 1 , 4-pheny I ene sulphide) , 1 to 10 vol .% of high aromatic polymer, and 70 to 97 vol .%. of f I uoropo I ymer (s ) relative to the total composition, and the po I y ( 1 , 4-pheny I ene sulphide) and the high aromatic polymer are present in a volume ratio in the range of from 4: 1 to 1 : 1. 5. A composition according to claim 1 wherein the poly(arylene sulphide ) and the high aromatic polymer are present in the composition as a particular fi l ler with particles of mean size from 20 to 50μ in a sintered or melted matrix of f I uoropo I ymer (s) . 6. A composition according to claim 5 wherein the f I uoropo I ymer (s ) is/are non-melt processable f I uoropo I ymer (s ) present as a sintered matrix of f I uoropo I ymer (s ) with a mean particle size which is 15 to 35μ . SUBSTITUTE SHEET 7. A composition according to claim 1 wherein the high aromatic polymer is a polyimide, po I yether imi de , or a poly(arylene etheretherketone) based on 1 ,4-pheny I ene , or a mixture thereof. 8. A composition according to claim 1 wherein the f I uoropoI ymer(s) is/are copolymer(s) of - at least one f luoroolef in which is a perha I oo I ef i n having 2 or 3 carbon atoms and, optional ly, at least one olefinical ly unsaturated monomer which is not a f I uoroo I ef in, having 3 to 10 carbon atoms, and which comprises a) 30-100 weight% (e.g. 50-100 weight%) of units derived from the perha I oo I ef i n and b) 0-70 weight% (e.g. 50-0 weight%) of the other units which are not a f I uoroo I ef i n) . 9. A composition according to claim 1 wherein up to 10 vo I .% of the compositions consists of an additive which is carbon; glass fibre or powder; metal powder; ceramic, fibres and powders; metal cha I cogeni de ; calcium fluoride; or a si l iceous fi l ler, or any comb i nat i on thereof . 10. A process for preparing a composition according to claim I which comprises in any feasible order a) dry blending the components as part i cu I ates , and b) optional ly, heat treating the po I y( 1 ,4-pheny I ene sulphide) and/or the high aromatic polymer, and then c) heating the blend to a temperature or varying temperature range sufficient to sintered or melted the f I uoropo I ymer (s) to form a matrix of f I uoropo I ymer (s) . SUBSTITUTE SHEET

Inventors: DAVIES MARK, HATTON PAUL MARTIN, DAVIES, MARK, HATTON, PAUL, MARTIN
Applicants: DAVIES MARK, HATTON PAUL MARTIN, ICI PLC, IMPERIAL CHEMICAL INDUSTRIES PLC
Application year: 1993
Main classification: C08L27
IPC codes: C08L27, C08L71, C08L79, C08L81, C08L87, C08L101