GB2185697A - Multi-layer composite material - Google Patents

Abstract

The material is substantially improved in respect of mechanical and thermal load-carrying capacity and is distinguished by having a high level of resistance to wear, good resistance to corrosion and a low coefficient of friction. It has a cover layer forming the friction or sliding layer, with a matrix of thermoplastically workable plastics material, which can carry a high thermal loading, of thermoplastic amorphous polyetherimide into which are incorporated active filler materials with good sliding or friction properties. In addition the polyetherimide of the matrix may be stabilised by sterically hindered phenol derivatives as anti-oxidising and heat stabiliser agents or also by metallic inactivating agents, for example lead. In particular polyetherimide of the following structure is suggested. <IMAGE>

Description

SPECIFICATION Multi-layer composite material The invention relates two a multi-layer composite material, in particularforthe production of friction and sliding elements, which has a cover layer forming the friction or sliding layer, with a matrix ofthermoplastic- allyworkable plastics material which can carry a high thermal loading.

Composite plain bearings are known in which a layer provided with depressions or perforations and consisting of a polyimide is applied to a support body of steel by means of an acrylic epoxy adhesive, wherein the depressions or perforations in the polyimide are filled with a mixture of solid lubricant and a bearing metal, as disclosed in DE-OS 20 00 632. However those known composite plain bearings with polyimide plastics materials suffer from serious disadvantages, in particular because, in the event of a high level of mechanical and/orthermal loading, the bond between the steel backing member and the plastics material is so damaged thatthe material drops out during operation of the plain bearings.

DE-OS 2206400 discloses a composite material and a process for the production thereof, wherein the friction or sliding layer includes polyimide resins and/or polyimide lacquer constituents which inter alia may also comprise polyesterimides and polyamidimides.

Also known are layered composite materials in which the sliding layer comprises a fluorine polymer such asforexample polytetrafluoroethylene and additives such as lead or molybdenum sulphide (E. Hodes in Maschinenmarkt, issue 79, October 1973). Plain bearings made of such layered composite materials suffer from the disadvantage that the plastics materials used therein have a tendency to flow under a mechanical loading ("cold flow") and the sliding layer is broken up when the component is subjected to a vibration loading and is torn out of the porous sintered structurewhich is sintered on the steel backing member.

Also known are multi-layer plain bearings in which the porous sintered structure comprising CuSn10 carries a sliding layer consisting of of a mixture of polyvinylidenefluoridewith polytetrafluoroethylene and lead (DE-PS 2908081). The continuous-usetemperature of such known multi-layer plain bearings is about 120 0C but is considerably low for most uses.

A multi-layer dry plain bearing with a structure consisting of steel/porous sintered layer with a filling and a sliding layer of polyether-etherketone and C-fibres is disclosed in DE-OS 3221 785. Such a multi-layer dry plain bearing has a substantially higher continuous-usetemperature (200 "C)than that which has a sliding layer consisting of polyvinylidene fluoride, PTFE and lead. However, the multi-layer dry plain bearing disclosed in DE-OS 3221 785 suffers from a relatively high coefficient offriction, in particular when used in shock absorbers.

In comparison therewith, the problem of the present invention is that of providing a multi-layercomposite material with an improved sliding layerwhich can carrya high mechanical and thermal loading and which is also distinguished by a high level of resistance to wear, good resistance to corrosion and a low coefficient of friction.

In accordance with the invention, that problem is solved in that the matrix ofthe cover layer is formed from thermoplastic amorphopus polyetherimide and contains one or more active filling materials having good sliding or friction properties, from the group comprising carbon fibres, PTFE particles, graphite, molybdenum sulphide, boron nitride and the like, in amounts of between 8 and 20 % byvolume.

In spite of the imide groups contained in its molecularchains,th poiyetherimidewhich is to be used in accordance with the invention forforming the matrix of the cover layer forming the sliding layer is athermoplastic material which however is amorphous. Although generally, ofthermoplastic material, primarily those with a partly crystalline structure are suitable as plain bearing materials, in accordance with the invention the addition of active filler materials,that is to sayfilier materisl which has good sliding or friction properties provides surprisingly in the present case a sliding material for dry running, which is suitable in particularfor highertemperatures.That may be explained asfollows: In the case of a dry sliding or friction laoding, a friction force acts along the path of sliding movement whereby frictional work is performed and energy is transmitted into the surfaces of the members in sliding contact, primarily in the form of heat. The energy concentration which occurs in micro-contact regions results in localiy high temperatures (referred to as hot spots) which can result in integral heating of the sliding surfaces. The energy introduced which is predominantly converted into heat can activate for example physical and chemical reactions in the co-operating sliding members, which can result in fusing-on phenomena, and changes in structure and phase. Such events can initiate plastic deformation phenomena when a load is applied and can promote wear.All those disadvantageous characteristics have been surprisingly found to be overcome when using thermoplastic amorphous polyetherimide forforming the matrix of the cover layer or sliding layer.

In accordance with the invention, a further improvement may be achieved in that added to the polyetherimide ofthe matrix is one or more antioxidising and heat stabilising agents from the group comprising sterically hindered phenol derivatives, arylphosphonides, organic phosphonides, and thioesters individually or in a mixture, in amounts of between about 0.5to 2 by volume. 1 ,6-hexanediolbis-3-(3,5-di-tertiary butyl- 4-hydroxyphenyl)-propionate ortriethylene-glycol-bis-3-(tertiary butyl-4-hydroxy-5-methyl phenyl)propionate or pentaerythritol-tetrakis-3-(3,5-ditertiary butyl-4-hydroxyphenyl)-propionatei may be part icularlyconsidered as anti-oxidising and heatstabiliseragents.

For many purposes, in addition to or instead ofthe sterically hindered phenol derivatives, it is possibleto add to the polyester in the matrix, metallic inactivating agent, in particular lead, such as lead particles, of a size of < 40 m or also I ead compounds of inorganic or organic nature, for example lead soaps, as deactivating agent in amounts of between 1 and 5% by volume.In a preferred embodiment of the invention the matrix ofthe cover layer is formed from polyetherimide having the following structure:

The active filler materials which are included into the matrix of the cover layer may preferably be one or more active filler materials from the group comprising carbon fibres, PTFE-particles, and graphite, in amounts of between 8 and 20% by volume with respect to the volume of the cover layer.

For particularly good bonding ofthe cover layer to the backing layer, the polyetherimide matrix may be anchored in a sintered structure which is applied to the backing layer, in particular a steel layer, and comprising bearing material having at least emergency antiseizure properties, preferably CuSn1 0.

A process according to the invention is particularly suitable for the production of the multi-layer composite material according to the invention, wherein a powder mix comprising the matrix-forming polyetherimide and the active filler materials which are to be included in the friction or sliding layer, and optionallyantioxidising and heat stabiliser agent, are continuously put on to a strip-like roughened backing layer and uniformly distributed overthe width ofthe strip, wherein the resulting layer of powder mix is heated in a continuous furnace by infra-red radiation until the polyetherimide fuses togetherto form the matrix and is fused on to the surface of the backing layer, wherein thefriction or sliding layerformed with thefusing together of the matrix, while in the condition of still being heated, is pressed with a compacting effect into the roughening of the backing layer, and wherein the strip-like composite material formed in that way is cooled down.

That process may be advantageously carried out in a simple manner and continuously in a through-flow mode and thus economically, and may be reliably controlled.

Ifthe polyetherimide of the matrix is additionally to be stabilised with anti-oxidising and heatstabiliser agentfrom the group comprising sterically hindered phenol derivatives,the process according tothe invention may be carried out in such a fashion thatthe matrix-forming polyetherimide and the activefillermat- erials corresponding to the respectively desired composition of the friction or sliding layer is intensively mixed in finely divided form and in suitable amounts into a solution of anti-oxidising and heat-stabiliser agent, forming a pasty material, that the resulting pasty material is continuously applied to a strip-shaped roughened backing layer and pressed into the roughening of the backing layer,thatthe backing layer strip when coated in that way is heated in a continuous furnace from the coated side with infra-red radiation until the polyetherimide fuses together to form the matrix and is fused into the roughening of the backing layer, and that the friction or sliding layer formed in that way is compacted under pressure, preferably by rolling, and that finally the composite material is then cooled down.

The polyetherimide which is to be used in both forms of the process, forforming the matrix, may preferably have a particle size of < 160 Fm.

Embodiments of the invention are, by way of example, described in greater detail hereinafterwith reference to the accompanying diagrammatic drawings in which: Figure lisa diagrammatic view showing the overall procedure of the process for producing the multi-layer composite material according to the invention; Figure 2 is a block diagram in respect of the coefficient of sliding friction, for comparison between the multi-layer composite material according to the invention and comparable multi-layer composite materials known hitherto as high-grade materials; Figure3is a representation in the form of a graph of the temperature as measured on a test stand under loading in respect of samples, on known multi-layer composite materials in comparison with the multi-layer composite material according to the invention; and Figure4 is a view in section through the layered composite material according to the invention, with a magnification of about 100:1.

The sectional view shown in Figure 4through the multi-layer composite material 10 showsthe backing layer 11 of steel, which is copper-plated with a thin layer 14 on its surface 13 which carries the friction or sliding layer 12. A rough base 15 of spheroidal bronze is sintered as a porous sintered structure on to the thin copper-plating layer 14. The actual friction or sliding layer which has a matrix 16 of polyetherimide is fused overthat base 15. In that connection the matrix 16 is fused into the spaces or cavities in the sintered structure 15. Short graphite fibres 17 are incorporated into the matrix 16. In addition, particles of graphite 18 and PTFE-particles 19 are also incorporated into the matrix 16.It is also possible for other active filler materials, that is to say substances which enhance the sliding properties,to be incorporated into the matrix 16,for example glass powder, synthetic mica, molybdenum sulphide and the like.

With a structure of the multi-layer composite material substantially in accordance with the example shown in Figure 4 and when using the compositions set out hereinafter in the form of a table, no drop-out phen omena occurred with loading tests under high temperatures ( > 150 0Cto 200 "C) and high loadings (27 N/ mm2).

Following Tables 1 and 2 show some samples of compositions which could be satisfactorily processed in the production of multi-layer composite material. In that connection, polyetherimide in accordance with the following formula was used:

Table 1 Composition No.

1 85.21 Polyetherimideaccordingtoformula 4.77 Lead 10.02 PTFE 2 77.72 Polyetherimide according toformula 8.71 Lead 11.29 C-fibres 2.28 PTFE 3 87.55 Polyetherimide according to formula 2.57 PTFE 8.89 C-fibres 0.70 Graphite 4 81.87 Polyetherimide according toformula 6.73 PTFE 10.70 C-fibres 0.70 Graphite The following were taken for the usefsterically hindered phenol derivatives as anti-oxidising and heat stabiliser agents:: Triethyleneg lycol-bis-3-(3-tertia ry butyl-4-hyd roxy-5-methyl-phenyl)-propionate - hereinafter referred to as sterically hindered phenol derivative No. 1; 1 ,6-hexanediolbis-3-(3,5-di-tertiary butyl-4-hydroxyphenyl)-propionate - hereinafter referred to as sterically hindered phenol derivative No.2; Pentaeryth ritol-tetrakis-3-(3,5-di-tertiary butyl-4-hydroxyphenyl)-propionate - hereinafter referred to as sterically hindered phenol derivative No.3.

Table 2: Composition No.

1 86.85 Polyetherimide according toformula 2.57 Lead 8.89 C-fibres 0.99 Graphite 0.70 Sterically hindered phenol derivative No.1 2 80.67 Polyetherimide according to formula 6.73 PTFE 10.70 C-fibres 0.70 Graphite 1.20 Sterically hindered phenol derivative No.2 When using such compositions it is possible to produce multi-layer composite material which is suitable forthe production of plain bearings.The manufacturing procedureforproducing such mutli-layercomposite material is as follows, as shown in the diagrammatic view in Figure 1, in one alternative form of the process: The strip with a porous sintered structure, comprising bearing alloy having emergency antiseizure prop- erties, in particular CuSn1 0, passes from a feed roll 1 through a straightening machine 2to a powderapplica- tor device 3 which essentially comprises a strip edge guide means and a stripper4 of preferably solid PTFE.

The stripper4 distributes the powder mixture which is applied behind itto the steel strip provided with the sintered structure, and sets the desired thickness of the layer of powder mixture. From there the composite strip when coated in that way passes through a furnace which is heated with infra-red radiant heaters, for fusing the matrix plastics on to the strip. Arranged downstream of the furnace region is a pair of rollers 6 which workthe plastics mix into the porous sintered structure and set the desired final thickness ofthe sliding layer. Arranged following the pair of rollers 6 are a cooling device 7 and a wind-on device 8.For another alternative form of the process in which pasty mixtures are to be applied, an applicator roller device is used instead of the powder applicator device 3 and the stripper 4. By means of the roller when set to the correct dimension, the pasty mix isworked into the porous sintered structure, for example atin-bronze structure, in such a way as to produce a sliding layer which covers over the sintered structure, of 80 ijm. The composite strip when coated in that way is then passed through the furnace in order to expel the solvent (for example acetone) and to fuse the polyetherimide on to the strip. The strip is then finally compacted by means of a pair of rollers two a thickness of 50 Fm in respect ofthe sliding layer.

Plain bearings may be produced in known mannerfrom the multi-layer composite material produced using one or other of the alternative forms of the process.

In a preferred manner of carrying the process into effect, the powder mixes used, of Tables 1 and 2, are produced in accordance with the following four Examples.

Example 1: Polyetherimide in accordance with the above-indicated formula, lead, C-fibres and PTFE in accordance with composition No.2 in Table 1 were mixed in a high-speed mixer and processed at 410 "C in a normal screw extruderwith an a/D-ratio of 20:1 to form extrudates which were granulated. The granular material was then ground up to form powder, with the assistance of nitrogen, and then processed, as described above, on a steel/sintered bronze strip coating installation.

Example2: Polyetherimide in accordance with theabove-indicated formula, lead and PTFE in accordance with composition No. 1 in Table 1 were mixed as described in Example 1 and processed by means of an extruderto form a foil of 100 Fm in thickness. The foil was firstly wound up and then, coming from a feed roll,worked into a steel/sintered bronze strip, using pressure and temperature, in such a way as to produce a sliding layer of 60 Cm, which covers over the sintered structure.

Example 3: Polyetherimide in accordance with the above-indicatedformula, PTFE, C-fibres, graphite and sterically hindered phenol derivative No. 2 as referred to above were extruded after intimate dry mixing to form ex trudateswhich were then granulated and ground up. The powder obtained was processed in the strip coating installation, as described in Example 1. The additional use of metal deactivators, in addition to the antioxidising agent, was not found to be necessary here.

Example 4: Polyetherimide in accordance with the above-indicated formula, PTFE, C-fibres and graphite were introduced into a solution ofsterically hindered phenol derivative No. 2 as referred to above, in such a way asto produce a pasty material. The pasty material was applied to the steel/tin bronze composite strip, on the strip coating installation shown in Figure 1, upstream of the coating roller.

Tests with samples of multi-layer composite material produced by the above-indicated process were carried out on a stylus-disctrobometer in comparison with samples of multi-layercomposite materials known hitherto as high-grade materials. The test results are as follows: Listofmaterials:: Material Structure ofthe Pore filling material No. substrate andplasticssllding layer 1 Steel/porous PTFEwith MoS2 sintered structure of CuSn10 2 Steel/porous PTFE with Pb sintered structure ofCuSnlO 3 Steel/porous Polyetheretherketone sintered structure with carbon fibre and ofCuSnlO graphite 4 Steel/porous Polyvinylidene sinteredstructure fluoridewith PTFE ofCuSnlO and lead 5 Steel/porous Polyetherimide with sintered structure carbon fibre, of CuSn 10 graphite and PTFE, stabilised with sterically hindered phenol derivative No.3 as referred to above The test results shown by the views in Figures 2 and 3 show that material No. 5 is superior to the materials known hitherto as high-grade materials, both in respect of the coefficient of sliding friction IL and thetemperature as measured at the backofthetest-piece, overthe test time. In that connection is should additionally be noted that material No. 3 has in practice been objected to as suffering from an excessively high coefficient of friction for many uses. Material No.4 suffers from the deficiency of excessively low resitance to heat.

Instead ofthe sterically hindered phenol derivatives referred to in the foregoing Examples for the poly- etherimide as anti-oxidising and heat stabiliseragent, itis also possible to use lead stabilisers in amounts of between about 1 % to 5 by volume with respect to the polyetherimide.Inorganic lead compounds, in particular lead salts such as white lead, basic lead carbonate,tribasic lead sulphate,tetrabasic lead sulphate, dibasic lead phosphite and lead silicate, may be used as such lead stabiiisers. It is also possible preferablyto use organic lead compounds, in particular lead soaps, as lead stabilisers, for example dibasic lead stearate, neutral lead stearate, dibasic lead phthalate,tribasic lead maleate and lead salicylate. Suitable combinations of such deactivator and heatstabiliser agents based on lead stabilisers,which agents are to be added to the polyetherimide, may also be added in the form of lead coprecipitates in an amount of between 2 and 5%by volume with respectto the volume of the matrix-forming polyetherimide.

Claims (20)

1. A multi-layer composite material, in particularforthe production of friction and sliding elements, which has a cover layer forming the friction or sliding layer, with a matrix ofthermoplasticallyworkable plastics material which can carry a high thermal loading, wherein the matrix of the cover layer is formed from thermoplastic amorphous polyetherimide and contains one or more active fillers having good sliding or friction properties, in amounts of between 8 and 20 % byvolume, as inclusions.

2. A material according to Claim 1 wherein the active fillers are selected from the group comprising carbon fibres, PTFE particles, graphite, molybdenum sulphide and boron nitride.

3. A material according to Claim 1 or 2 wherein added to the polyetherimide of the matrix is one or more anti-oxidising and heatstabilising agents in amounts of between substantially 0.5 and 2 by volume.

4. A matrix according to Claim 3 wherein the anti-oxidising and heat stabilising agents are selected from the group comprising sterically hindered phenol derivatives arylphosphonides, organic phosphonides, and thioesters individually or in a mixture.

5. A material according to Claim 3 or 4 wherein 1 ,6-hexanediolbis-3-(3,5-di-tertiary butyI-4- hydroxyphenyl)-propionate or pentaerythritol-tetrakis-3-(3,5-di-tertiary butyl-4-hydroxyphenyl )- propionatel ortriethyleneglycol-bis-3-(tertiary butyl-4-hydroxy-5-methylphenyl)-propionate is provided as the anti-oxidising and heat stabliser agent.

6. A material according to Claim 1 wherein metallic inactivating agent is added in amounts of between substantially 5 and 10 by volume, to the polyetherimide of the matrix.

7. A matrix according to Claim 6 wherein the metallic activating agent is lead.

8. A matrix according to Claim 7 wherein the lead is in particles of a size < 40pWm.

9. A material according to Claim 1 wherein one or more inorganic lead salts and/or lead soaps are added as deactivation agents in amounts of between substantially 1 and 5% by volume to the polyetherimide ofthe matrix.

10. A matrix according to Claim 9 wherein the lead soap is a lead stearate.

11. A material according to any one of Claims 1 to 10 wherein the matrix of the cover layer is of polyetherimide having the following structure:

12. A material according to any one of Claims 1 to 11 wherein the polyetherimide matrix is anchored in a sintered structure which is applied to the backing layer, the sintered structure comprising bearing material which has at least emergency anti-seizure properties.

13. A matrix according to Claim 12 wherein the backing layer is of steel.

14. A matrix according to Claim 12 or 13 wherein the bearing material having at least emergency anti- seizure properties is CuSn10.

15. A process for the production of multi-layer composite material according to Claim 1 wherein a powder mix comprising the matrix-forming polyetherimide and the active filler materials which are to be included in the friction or sliding layer, and optionally anti-oxidising and heat-stabiliser agent, are continuously put on to a strip-like roughened backing layer and uniformly distributed over the width of the strip, wherein the resulting layer of powder mix is heated in a continuous furnace by infra-red radiation until the polyetherimide fusestogetherto form the matrix and is fused on to the surface of the backing layer, wherein the friction or sliding layer formed with the fusing together of the material while still being processable, is pressed with a compacting effect into the roughening ofthe backing layer, and wherein the strip-like composite material formed in thatway is cooled down.

16. A process for the production of multi-layer composite material according to Claim 2 wherein the matrix-forming polyetherimide and the active filler materials corresponding to the desired composition of the friction or sliding layer is intensively mixed in finely divided form and in suitable amounts into a solution of anti-oxidising and heat-stabiliser agent, forming a pasty material, wherein the resulting pasty material is continuouslyappliedto a strip-shaped roughened backing layer and pressed into the roughening ofthe backing layer, wherein the backing layer strip when coated in that way is heated in a continuous furnace from the coated side with infra-red radiation until the polyetherimide fuses together to form the matrix and is fused into the roughening of the backing layer, wherein the friction or sliding layerformed in that way is compacted under pressure, and the composite material is then cooled down.

17. A process according to Claim 16 wherein the compaction is performed by rolling.

18. A process according to Claim 15 or 16 wherein the polyetherimide used for forming the matrix has a particle size of < 160clam.

19. A multi-layer composite material according to Claiml substantially as herein described.

20. A process according to Claim 15 or 16 substantially as herein described.