GB2044191A

GB2044191A - Improvements in or relating to tyres

Info

Publication number: GB2044191A
Application number: GB8006789A
Authority: GB
Original assignee: Dunlop Ltd
Current assignee: Dunlop Ltd
Priority date: 1979-03-16
Filing date: 1980-02-28
Publication date: 1980-10-15
Also published as: IT1209196B; IT8020677A0; GB2044191B

Abstract

An unpatterned (grooveless) porous tyre tread (16) and a pneumatic tyre (10) incorporating the porous tread, together with methods of manufacturing the tyre tread as a separate item and as an integral part of the tyre are described. The tyre tread (16) has numerous randomly orientated and randomly distributed interconnected passages extending from the surface substantially throughout the tread. These passages provide water drainage paths preventing build-up of water between the tyre tread and a wet road. The tyre tread (16) is preferably manufactured by bonding particulated elastomeric material with a binder mixture that forms a polymer upon curing. Whether formed separately or integrally with a tyre, the tread mould is unpatterned. <IMAGE>

Description

SPECIFICATION Improvements in or relating to tyres This invention relates to tyres, and more particularly to tyre treads and pneumatic tyres, and to the manufacture thereof.

Tyre treads may be moulded and cured integrally with a tyre carcass to form a complete tyre, or treads may be formed separately from the carcass for subsequent bonding thereto to form a complete tyre. A separately formed tread may take the form of a tread strip of a length at least equal to the circumference of the tyre into which it is to be incorporated, the ends of the tread strip being joined when the tread strip is located on the carcass during building of the tyre. Separately formed treads may be applied to new carcasses, or to the carcasses of used tyres from which the original tread has been removed.

Conventional tyre treads have a complex and precisely designed pattern of ribs and blocks to provide a network of surface grooves with the object of allowing a conventional tyre to operate on a wet paved surface without undue build-up of water between the tread and the paved surface. Such a build-up of water can seriously diminish the adhesion of the tyre to the paved surface and thus cause a dangerous reduction of braking and steering capabilities. These conventional tyretreads require intricate and expensive moulds to form the tread pattern.

The present invention proposes a novel form of tyre tread and a pneumatic tyre incorporating the novel tread (together with methods of manufacturing the tread and the tyre) which has an alternative approach to maintaining good adhesion on wet paved surface, and which obviates the requirement for intricately patterned moulds with consequent economic advantages.

According to a first aspect of the invention there is provided a tyre tread of elastomeric material formed to provide randomly distributed and randomly orientated interconnected passages extending from the tread surface substantially throughout the tread.

The void content of the tread (as hereinafter defined) may be in the range from 10% to 60%, and more preferably in the range from 25% to 40%. Said inter-connected passages constitute voids in the tread, and the total volume of said voids expressed as a fraction of the overall volume of the tread is, in this description, called the "void content" of the tread. The volume of elastomeric material between and defining the interconnected passages expressed as a fraction of the overall volume of the tread is, in this description, called the "solid content" of the tread. From the fore-going definitions, it will be seen that "void content" plus "solid content" equais the overall volume of the tread. Therefore if the void content is x%, then it follows that the solid content must be (100 - x)%.

In said tyre tread, the average cross-sectional area of the passages may be large or small relative to the cross-sectional area of adjacent tread material between and defining the passages. In the latter case (i.e.

relatively small passages), the tread may be termed a porous tread.

In said tyre tread, the void content may be substantially uniformly distributed throughout the tread.

Alternatively, the void content may vary between different regions of the tread substantially according to a predetermined void distribution pattern. As examples of void distribution patterns within the scope of the invention, the pattern may be such that the void content decreases or increases with increasing distance radially inwardly from the tread surface which will contact a road when the tread is part of a tyre; and alternatively or additionally the pattern may be such that the void content decreases or increases with increasing distance laterally inwardly from the lateral edges of the tread. Othervoid distribution patterns are possible within the scope of the invention.

The tyre tread may comprise numerous discrete regularly shaped or preferably irregularly shaped particles of an elastomeric material which is preferably of the type employed as tread stock in conventional tyres and which ma be material obtained from scrap tread stock. Said particles may have a substantially uniform size, or they may have at least two different sizes. The particles may have a volumetric size or sizes in the range from 6.5 x 10-5 ccto 1 sic., and more preferably in the range from 5 x 10-4 cc. to 4 x 10-2 cc.

The particles may have a hardness or a range of hardnesses in the range 30 to 85 Shore A. Particles of selected different sizes and/or hardnesses may be distributed within the tread substantially according to a predetermined particle distribution pattern.

Preferably said particles are mutually bonded into a cohesive mass. Said particles may be bonded by inter-particle fusion, and in the case where said particles are of uncured rubber, said interparticle fusion may comprise cross-linking the material of adjacent particles at their points of mutual contact. Alternatively, said particles may be mutually bonded into a cohesive mass by a binder matrix which may be a thermo-setting material, or composed of a binder material which solidifies upon curing to form the binder matrix with the particles thereby bound together. The binder material may be a thermo-setting resin, or a reaction mixture which forms a polymer upon being cured, and the polymer may be polyurethane, polyurea, polyamide, polybutadiene, or polypropylene.

Preferably the surface of the tread which will contact a paved surface when the tread is part of a tyre, is devoid of any regular pattern of blocks, ribs, slots or grooves.

According to a second aspect of the invention there is provided a pneumatic tyre comprising a carcass, and a tyre tread according to the first aspect of the invention. The tyre may be a radial tyre incorporating a tread-reinforcing breaker disposed between the carcass and the tread, or the tyre may be a cross-ply tyre, or the tyre may be a belted-bias type incorporating a tread-reinforcing breaker disposed between the carcass and the tread.

According to a third aspect of the invention there is provided a method of manufacturing a tyre tread according to the first aspect of the invention, comprising the steps of binding and shaping particulated elastomeric material to the required shape of the tread. Said particles may be bound by the step of interparticle fusion, and in the case where said particles are of uncured rubber, said fusion may comprise cross-linking the material of adjacent particles at their points of mutual contact. Alternatively said particles may be mutually bound by the step of forming a mixture of said particles with a binder material. The shaped mixture may be at least partly cured to form a cohesive mass.The shaping process may be performed by the step of extruding the mixture through a die whose orifice is shaped to the required cross-sectional shape of the tread, and the extruded tread may be cured immediately it leaves the die. The extruded tread may be severed into discrete lengths substantially equal to the circumference of a tyre into which the tread is to be incorporated. Alternatively, the shaping process may be performed by the step of placing the mixture in a mould having the shape and dimensions of a desired strip of tread, followed by the step of at least partly curing the mixture in said mould, and finally removing the tread strip from the mould. The mould may be annular such as to produce a tread band in the form of a jointless loop of tread.

The method of manufacturing the tyre tread may include the step of forming said particles by a particulation process which may be granulation of rubber sheet or block, which may be subjected to cryogenic freezing to facilitate granulation, or by rasping scrap tyre treads. When the material is particulated, it may be sieved to select particles of relatively uniform sizes from relatively non-uniformly sized particles produced by the particulation process.

According to a fourth aspect of the invention there is provided a method of manufacturing a tyre according to the second aspect of the invention, comprising the steps of forming the tyre tread by the method of the third aspect of the invention, applying the tyre tread to the tyre carcass, and consolidating the assembly of the tread and the carcass. The tread may be extruded onto the carcass, the assembly placed in a mould, heat and pressure applied to cure the assembly in the mould, and the tyre removed from the mould when the tyre is substantially completely cured.Alternatively, the carcass may be placed in a mould, a mixture of elastomeric particles and a binder material injected into the mould around the carcass, heat and pressure applied to cure the assembly in the mould, and the tyre removed from the mould when the tyre is substantially completely cured. As a further alternative, the tread may be preformed as a tread strip or a tread band, and the pre-formed tread bonded to the carcass. The bonding of the tread to the carcass may be performed by use of an adhesive. The tyre carcass and the tyre tread bonded thereto may be cured by being placed in an unpatterned mould followed by the application of heat and pressure.

In the manufacture of a tyre according to this fourth aspect of the present invention, the tyre carcass may initially be at least partly precured and additionally or alternatively the tyre tread may initially be substantially uncured. The tyre carcass may be the carcass of a used tyre from which the original tread has been removed.

The principles by which mineral particle sizes may be chosen to provide a given void content have been described in connection with "Delugrip" (Registered trade mark) road surface materials which comprise mineral particles of graded sizes embedded in an asphaltic binder. It is considered that the same principles are applicable to the manufacture of a tyre tread in accordance with the present invention. These principles have been detailed in the technical article entitled "The Rational Design of Aggregate Gradings for Dense Asphaltic Compositions" by G. Lees, published in "Proceedings of the Association of Asphalt Paving Technologists Conference", Kansas City, United States of America, February 1970. This article describes an approach to the control of void content with respect to the grading and physical properties of the particles.

The tyre treads and tyres of the present invention may be for any size and use of vehicle, for example motor-cycles, cars, light and heavy vans, trucks, buses, coaches, and aircraft.

Embodiments of the invention will now be described by way of examples, with reference to the accompanying drawings wherein: Figure 1 is a cross-section of a tyre in accordance with the invention, taken in a plane including the axis of the tyre; Figure 2 is a plan view to an enlarged scale, of a portion of the tread of the tyre of Figure 1, as viewed in the direction of the arrow II in Figure 1; Figures 3 and 4 are graphs of the braking performance at two different speeds on a wet test surface of two tyres in accordance with the invention, and of a standard tyre for comparison; and Figures 5and 6 are graphs of the cornering performance on a test surface at two different water depths, of the three tyres compared in Figures 3 and 4.

Referring first to Figure 1, this illustrates the cross-section of a tyre 10 in accordance with the invention, the section being taken in a plane including the rolling axis of the tyre 10. By way of example, the tyre 10 is a radial tyre having a reinforcing ply 12 of cords aligned substantially at 900 to the circumferential direction of the tyre, the ends of the ply 12 being turned-up around two bead cores 14. The tyre 10 also includes a tread 16 and a tread-reinforcing breaker 18 as is known in the tyre art. In a normal tyre, the tread 16 would be an intricately grooved layer of otherwise solid rubber moulded integral with the remainder of the tyre. However, in accordance with the invention, the tread 16 is formed as a porous layer of elastomeric material providing randomly interconnected and randomly orientated passages extending from the surface of the tread 16 substantially throughout the tread. (The tyre 10 could be other than a radial tyre, for example a cross-ply tyre, or a belted-bias tyre).

Some Examples of methods of forming the tread 16 and tyres incorporating such treads will now be given.

The tyre tread of the present invention may be incorporated into a tyre either by a retreading process (i.e.

bonded onto a used carcass) or as part of a tyre building process.

Example 1 One way to make a tyre according to the present invention is to: i) prepare a tread strip according to the present invention; ii) attach to the tread strip, by means of the binder used to create it, an uncured rubber-based undertread layer; iii) rasp a vulcanised tyre casing and coat it with a standard heat curable tread solution; iv) apply the tread strip/undertread to the solutioned casing and join the ends with the same tread solution; and v) cure the assembly in a plain tread mould, (i.e. a patternless mould).

Example 2 A tread strip was made by casting an intimate mixture of the following components into a wooden mould ofthe required dimensions: Parts Granulated whole tyre scrap consisting of vulcanised rubber particles of irregular shapes and assorted sizes up to 0.5 cc 500 Granulated whole tyre scrap consisting of vulcanised rubber particles of irregular shapes and graded to 10 B.S.

mesh (i.e. British Standard sieve number 10) 1000 Hydroxyl-tipped liquid polybutadiene of molecular weight 2800 (R45M ex. Arco) 360 Liquid form of methylele-bis-aniline diisocyanate containing higher functionality isocyanates (Suprasec DND ex l.C.I.) 140 Carbon black pigment dispersion 5 Stannous octoate 0.2 After 24 hours the mixture had cured to a non-tacky composite.

A tyre carcass was then prepared by rasping the tread from a car tyre, and the crown of the carcass was coated with a room-temperature curable adhesive composition of R45M (10 parts), Suprasec DND (4 parts) and stannous octoate (0.01 part). The tyre tread strip was then applied to the carcass and bandaged to the carcass with tape, the strip ends being joined by means ofthe same adhesive composition. An inner-tube was inflated within the carcass to help achieve intimate contact between the carcass and the tread strip. After 48 hours the bandage was removed and the inner-tube deflated, leaving a completed tyre.

Example 3 ruse ofalternative binder) An intimate mixture of the following components was cast into a mould of the required dimensions: Granulated vulcanised rubber, the particles being of generally uniform size having a mean diameter of 0.5 cm ant 65 Shore A hardness 100 pbw Adiprene L-167 (an isocyanate-functional polyurethane prepolymer ex Du Pont) 19 pbw Caytur 21 (a diamine curative ex Du Pont) 6 pbw Carbon black pigment dispersion 2 pbw The product, in the form of a tread strip, resulted after the mould had been heated to 120"C for one hour.

Example 4 (a further alternative binder) An intimate mixture of the following components was cast into a mould of the required dimensions: Granulated vulcanised rubber, as in Example 3 100 pbw Mixture A 14.6 pbw Liquidified form of diphenylmethane 4, 4'diisocyanate (Isonate 143L ex Upjohn) 10.2 pbw Carbon black pigment dispersion 2 pbw Stannous octoate 0.02 pbw Mixture A comprised: Ethylene oxide tipped, 2000 mw polypropylene glycol (Propylan D-2122 ex Lankro) 100 pbw Ethylene glycol 6.3 pbw Trimethylol propane 8.6 pbw The product, in the form of a tread strip, was obtained after the mould had been heated to 80"C for one hour.

Example 5 (Method of making a tyre with the tread of Example 3) A tread strip was prepared by the method of Example 3 using the same component materials.

A solution of a triisocyanate in methylene chloride (Desmodur Rex Bayer) was brushed into one side of the tread and allowed to dry. A solution of a zinc oxide containing compounded natural rubber in toluene was then brushed onto the triisocyanate treated surface and also allowed to dry. The tacky side of the tread was then attached around an uncured tyre carcass and the composite article placed in a plain-treaded tyre mould (i.e. an unpatterned mould). A rubber tube was inserted into the carcass and inflated to a pressure of 3.45 bar in order to make the uncured rubber conform to the internal dimensions of the mould and also to aid bonding of the tread to the carcass. The mould was then placed between the platens of a press and heated to 155"C for 60 minutes, after which the completed tyre was removed from the mould.

As an alternative to binding the particles together by a binder matrix, the particles may be fused together or the material of adjacent particles cross-linked at their points of contact, or the particles bonded by an adhesive or by being embedded in a thermosetting plastics material.

In order to provide comparative performance results, two tyres were made as described in Example 2, differing only in that the tread of one tyre was formed from coarse particles comprising 1500 parts by weight of granulated rubber of hardnesses 60-70 Shore A and a range of particle sizes up to 0.5 cc to provide a tyre hereafter called the "coarse tread" tyre, and the tread of the other tyre was formed from fine particles comprising 1000 parts by weight of granulated rubber of hardnesses 60-Shore A and average particle size graded to 10 B.S. mesh, to provide a tyre hereafter called the "fine tread" tyre. In both cases, the treads were bonded onto the carcass of a 155SR13 Dunlop SP 4tyre from which the original tread had been removed by buffing.A standard 155SR13 Dunlop SP 4 tyre with its original tread was employed in the tests to give equivalent results for a normally-treaded tyre with the same carcass structure. All three tyres were identically inflated to the normal pressure for a 155SR13 SP 4 tyre, i.e. 1.8 kg/cm2 ("SP 4" is a Registered Trade Mark).

Braking and cornering tests were carried out on an indoor drum-type testing machine, suitably instrumented for force measurement, and with facilities for supplying a controlled rate of water flow onto the drum's test surface in order to simulate a road covered with a predetermined depth of water.

Graphs of braking force coefficient against percentage slip for the coarse tread tyre, the fine tread tyre, and the standard tread SP 4tyre are shown in Figures 3 and 4, respectively for equiva lent vehicle speeds of 48 km/hour and 80 km/hour. In both cases, water flow rate was 7.5 litres/second, simulating a road flooded by rain to an approximate depth of 3 mm at 48 km/hour and 1 mm at 80 km/hour. Figure 3 indicates that both porous tread tyres have a maximum braking force coefficient approximately three times that of the standard-tread SP 4 at 48 km/hour in very wet conditions, with the coarse tread tyre performing somewhat better than the fine tread tyre.

Figure 4 shows that at 80/km/hour, both porous tread tyres perform approximately as well in braking as at 48 km/hour in the same water depth, but now approximately eight times better than the braking performance of the standard tread tyre.

Figures 3 and 4 show clearly that wet-road braking performance of tyres in accordance with the invention is substantially better than that of an otherwise identical tyre, but which has a conventionally patterned tread of surface grooves. The numerous randomly interconnected and randomly orientated passages in the tread of the present invention provide for a ready escape of water from between the road surface and the portion of the tread in contact therewith and into the bulk of the porous tread so preventing any excessive build-up of water in the contact patch which would otherwise reduce effective contact with the road and hence reduce braking performance.The water thus taken into the bulk of the tread can escape laterally through the edges of the tread and also radially out through the surface of the tread under centrifugal force as it leaves contact with the road upon continued rotation along the road.

Graphs of variations in available cornering force with variation in speed are shown in Figures 5 and 6 for the same three tyres whose braking performances were illustrated in Figures 3 and 4. In Figure 5, the water flow was 7.5 litre/second, while in Figure 6, the water flow was reduced to 1.0 litre/second. Both Figures 5 and 6 indicate that all three tyres had comparable cornering abilities at low speed (16km/hour and less), but that the porous tread tyres suffered little diminution with substantially increased speed (up to 100 km/hour) whereas the conventionally treaded tyre suffered a drastic loss of cornering ability at these increased speeds, more soon the wetter surface (Figure 5). In general, the wet road cornering ability of the fine tread tyre was marginally better than that of the coarse tread tyre.

Further comparative tests on the threee tyres compared in Figures 3-6 were undertaken to demonstrate noise generating properties of the respective treads. Generated sound pressure levels at speeds of 50 km/hour and 80 km/hour are tabulated below for the three tyres: Tyre 50 km/hour 80 km/hour Standard tread SP 4 82.5 dB(A) 88.0 dB(A) Fine tread tyre 76.0 dB(A) 85.0 dB(A) Coarse tread tyre 79.0 dB(A) 85.5 dB(A) Thus tyres in accordance with the invention are quieter in use than an equivalent conventionally-treaded tyre.

Tyres in accordance with the invention were also found to have improved grip on icy surfaces than equivalent conventionally-treaded tyres.

Thus the present invention provides tyre treads and tyres with such treads that have a markedly superior wet-grip capability and reduced noise generation, and moreover which obviate the requirement for the usual intricately patterned and highly expensive tread pattern-forming mould.

Claims

1. A tyre tread of elastomeric material formed to provide randomly distributed and randomly orientated interconnected passages extending from the tread surface substantially throughout the tread,

2. A tyre tread according to claim 1 wherein the void content of the tread (as hereinbefore defined), is in the range from 10% to 60%.

3. A tyre tread according to claim 2 wherein the void content of the tread (as hereinbefore defined), is in the range from 25% to 40%.

4. A tyre tread according to any one of claims 1, 2 or 3, wherein the average cross-sectional area of the passages is large relative to the cross-sectional area of adjacent tread material between and defining the passages.

5. A tyre tread according to any one of claims 1, 2 or 3, wherein the average cross-sectional area of the passages is small relative to the cross-sectional area of adjacent tread material between and defining the passages.

6. A tyre tread according to any one of claims 1 to 5 wherein the void content is substantially uniformly distributed throughout the volume of the tread.

7. A tyre tread according to any one of claims 1 to 5 wherein the void content varies between different regions of the tread substantially according to a predetermined void distribution pattern.

8. A tyre tread according to claim 7 wherein the void distribution pattern is such that the void content decreases with increasing distance radially inwardly from the tread surface, which will contact a road when the tread is part of a tyre.

9. A tyre tread according to claim 7 wherein the void distribution pattern is such that the void content increases with increasing distance radially inwardly from the tread surface which will contact a road when the tread is part of a tyre.

10. A tyre tread according to any one of claims 7, 8 or 9 wherein the void distribution pattern is such that the void content decreases with increasing distance laterally inwardly from the lateral edges of the tread.

11. A tyre tread according to any one of claims 7, 8 or 9 wherein the void distribution pattern is such that the void content increases with increasing distance laterally inwardly from the lateral edges of the tread.

12. A tyre tread according to any one of claims 1 to 11 wherein the tread comprises numerous discrete irregularly shaped particles of elastomeric material.

13. A tyre tread according to any one of claims 1 to 11 wherein the tread comprises numerous discrete regularly shaped particles of elastomeric material.

14. A tyre tread according to claim 12 or claim 13 wherein the elastomeric material is of the type employed as tread stock in conventional tyres.

15. A tyre tread according to any one of claims 12, 13 or 14 wherein the elastomeric material is material obtained from scrap tyres or scrap tread stock.

16. A tyre tread according to any one of claims 12 to 15 wherein said particles have a substantially uniform size.

17. A tyre tread according to any one of claims 12 to 15 wherein said particles have at least two different sizes.

18. A tyre tread according to any one of claims 12 to 17 wherein said particles have a volumetric size or sizes in the range from 6.5 x 10-5 cc to 15 cc.

19. A tyre tread according to claim 18 wherein said particles have a volumetric size or sizes in the range from 5 x 10-4 CC to 4 x 10-2 CC.

20. A tyre tread according to any one of claims 12 to 19 wherein said particles have a hardness or a range of hardnesses in the range 30 to 85 Shore A.

21. A tyre tread according to any one of claims 17 to 20 wherein particles of selected different sizes and/or hardnesses are distributed within the tread substantially according to a predetermined particle distribution pattern.

22. A tyre tread according to any of claims 12 to 21 wherein said particles are mutually bonded into a cohesive mass.

23. A tyre tread according to claim 22 wherein said particles are bonded by interparticle fusion.

24. A tyre tread according to claim 23 wherein said particles are of uncured rubber and said interparticle fusion comprises the cross-linking of the material of adjacent particles at their points of mutual contact.

25. A tyre tread according to claim 22 wherein said particles are mutually bonded into a cohesive mass by a binder matrix.

26. A tyre tread according to claim 25 wherein said binder matrix is a thermo-setting material.

27. A tyre tread according to claim 25 wherein the binder matrix is composed of a binder material which solidifies upon curing to form the binder matrix with the particles thereby bound together.

28. A tyre tread according to claim 27 wherein said binder material is a thermo-setting resin.

29. A tyre tread according to claim 27 wherein the binder material is a reaction mixture which forms a polymer upon being cured.

30. A tyre tread according to claim 29 wherein said polymer is comprised in the group of polyurethanes, polyureas, polyamides, polybutadienes and polypropylenes.

31. A tyre tread according to claim 29 or claim 30 wherein said reaction mixture comprises hydroxyl-tipped liquid polybutadiene, and liquid methylene-bis-aniline di-isocyanate.

32. A tyre tread according to claim 29 or claim 30 wherein said reaction mixture comprises an isocyanate-functional polyurethane prepolymer, and a diamine curative.

33. A tyre tread according to claim 29 or claim 30 wherein said reaction mixture comprises ethylene oxide tipped polypropylene glycol, ethylene glycol, trimethylol propane, and liquified diphenylmethane 4, 4'-di-isocyanate.

34. A tyre tread according to any one of claims 1 to 33 wherein the tread surface which will contact a paved surface when the tread is part of a tyre, is devoid of any regular pattern of blocks, ribs, slots or grooves.

35. A pneumatic tyre comprising a carcass, and a tyre tread according to any preceding claim.

36. A pneumatic tyre according to claim 35, in the form of a radial tyre, and incorporating a tread-reinforcing breaker disposed between said carcass and said tyre tread.

37. A pneumatic tyre according to claim 35 in the form of a cross-ply tyre.

38. A pneumatic tyre according to claim 35 in the form of a belted-bias tyre, and incorporating a tread-reinforcing breaker disposed between said carcass and said tyre tread.

39. A method of manufacturing a tyre tread according to any one of claims 1 to 34 comprising the steps of binding and shaping particulated elastomeric material to the required shape of the tread.

40. A method according to claim 39 wherein said particles are bound by the steps of inter-particle fusion.

41. A method according to claim 40 wherein said particles are of uncured rubber and said interparticle fusion comprises cross-linking the material of adjacent particles at their points of mutual contact.

42. A method according to claim 39 wherein said particles are mutually bound by the step of forming a mixture of said particles with a binder material.

43. A method according to claim 42, including the further step of at least partly curing the shaped mixture to form a cohesive mass.

44. A method according to claim 42 or claim 43 wherein the shaping process is performed by the step of extruding the mixture through a die whose orifice is shaped to the required cross-sectional shape of the tread.

45. A method according to claim 44 including the further step of at least partly curing the tread immediately it leaves the die.

46. A method according to claim 44 or claim 45 including the further step of severing the extruded tread into discrete lengths substantially equal to the circumference of tyres into which the tread lengths of tread are to be incorporated.

47. A method according to claim 42 wherein the shaping process is performed by the step of placing the mixture in a mould having the shape and dimensions of a desired strip of tread, followed by the steps of at least partly curing the mixture in said mould, and finally removing the tread strip from the mould.

48. A method according to claim 47 wherein the mould is annular whereby said steps produce a tread band in the form of a jointless loop of tread.

49. A method according to any one of claims 39 to 48 including the step of forming said particles by a particulation process comprising granulating sheet or block rubber.

50. A method according to claim 49 including the step of cryogenically freezing the rubber immediately prior to granulation, whereby to facilitate the granulation.

51. A method according to any one of claims 39 to 48 including the step of forming said particles by a particulation process comprising rasping scrap tyre treads.

52. A method according to any one of claims 49 to 51, including the further step of sieving said particles after the step of particulation such as to select particles of relatively uniform sizes from relatively non-uniformly sized particles produced by said particulation process.

53. A method of manufacturing a pneumatic tyre according to any one of claims 35 to 38, comprising the steps of forming the tyre tread according to any one of claims 39 to 52, applying the tyre tread to the tyre carcass, and consolidating the assembly of the tread and the carcass.

54. A method according to claim 53 wherein the steps of forming and applying the tyre tread to the tyre carcass are performed by extruding the tread onto the carcass, and the step of consolidating the assembly is performed by placing the assembly in a mould and then applying heat and pressure to cure the assembly in the mould, followed by the further step of removing the tyre from the mould when the tyre is substantially completely cured.

55. A method according to claim 53 wherein the steps of forming and applying the tyre tread to the tyre carcass are performed by placing the carcass in a mould, injecting a mixture of elastomeric particles and a binder material into the mould around the carcass, and the step of consolidation is performed by applying heat and pressure to cure the assembly of the carcass and the tread materials within the mould, followed by the further step of removing the tyre from the mould when the tyre is substantially completely cured.

56. A method according to claim 53 comprising the steps of preforming the tread as a tread strip or a tread band, and bonding the preformed tread onto the tyre carcass.

57. A method according to claim 56 wherein the tread is bonded onto the carcass by use of an adhesive.

58. A method according to claim 56 or claim 57, including the further step of curing the tyre carcass and the tyre tread bonded thereto in an unpatterned mould by the application of heat and pressure.

59. A method according to any one of claims 53 to 58 wherein the tyre carcass is initially at least partly precured.

60. A method according to any one of claims 53 to 59 wherein the tyre tread is initially substantially uncured.

61. A tyre tread substantially as hereinbefore described with reference to Example 2 or Example 3 or Example 4 or Figures 1 and 2 of the accompanying drawings.

62. A pneumatic tyre substantially as hereinbefore described with reference to Example 1 or Example 2 or Example 5 or Figures 1 and 2 of the accompanying drawings.

63. A method of manufacturing a tyre tread substantially as hereinbefore described with reference to Example 2 or Example 3 or Example 4 or Figures 1 and 2 of the accompanying drawings.

64. A method of manufacturing a pneumatic tyre substantially as herein before described with reference to Example 1 or Example 2 or Example 5 or Figures 1 and 2 of the accompanying drawings.