Expanded rubber articles

Abstract

Expanded rubber articles and processes for making such, comprising: partially curing an expandable rubber formulation by heating it in a first mould cavity to form a moulded blank; releasing the moulded blank from the first mould cavity and allowing the moulded blank to expand to form an expanded moulded blank; and further curing and expanding the expanded moulded blank by heating it to form the expanded rubber article comprising an expanded rubber part, wherein the expanded moulded blank is heated in a second mould cavity. Optionally, the expanded moulded blank is contacted with a further rubber formulation and a substrate comprising a base material and an elastomer bonding layer in the second mould cavity to form an expanded rubber article additionally comprising a solid rubber part and a substrate.

Claims

1. A process for making an expanded rubber article, wherein the process comprises: a) a moulded blank formation step, in which an expandable rubber formulation, comprising an elastomeric material, a curing agent and an expansion agent, is heated in a first mould cavity to partially cure the expandable rubber formulation thereby forming a moulded blank, wherein the first mould cavity confines expansion of the expandable rubber formulation; b) a releasing step, in which the moulded blank is released from the first mould cavity, and in which the moulded blank expands to a volume larger than the volume of the first mould cavity thereby forming an expanded moulded blank; c) a stabilisation step, in which the expanded moulded blank is left to stabilise until the volume of the expanded moulded blank is substantially constant; and, d) a further curing step, in which the stabilised expanded moulded blank is heated to further cure and expand the expandable rubber formulation thereby forming the expanded rubber article; wherein the expanded moulded blank is heated in a second mould cavity in further curing step (d).

2. The process according to claim 1, wherein the elastomeric material comprises one or more rubber polymers selected from styrene butadiene rubber, butadiene rubber, natural rubber and ethylene propylene diene monomer rubber.

3. The process according to claim 1, wherein the expandable rubber formulation comprises ethylene propylene diene monomer rubber and, optionally, a peroxide cure system.

4. The process according to claim 1, wherein the expanded rubber article is cooled to a temperature of from 10 C. to 80 C. and then removed from the second mould cavity.

5. The process according to claim 1, wherein the expanded moulded blank is left to stabilise for a period of at least 24 hours.

6. The process according to claim 1, wherein the expanded moulded blank is contacted with an additional rubber formulation during the stabilisation step.

7. The process according to claim 1 additionally comprising: e) a surface preparation step, in which at least part of a surface of the expanded moulded blank is removed; wherein the surface preparation step (e) is carried out after the releasing step (b) and before the further curing step (d).

8. The process according to claim 1, wherein an insert is included in the first mould cavity, and wherein the insert defines a void in the moulded blank.

9. The process according to claim 8, wherein the insert is removed from the expanded moulded blank before the expanded moulded blank is heated in the further curing step.

10. The process according to claim 1, wherein a plurality of expanded moulded blanks are contacted with each other in the further curing step.

11. The process according to claim 1, wherein the expandable rubber formulation is contacted with an additional rubber formulation during the moulded blank formation step (a), the additional rubber formulation comprising an elastomeric material and a curing agent, wherein the additional rubber formulation is partially cured with the expandable rubber formulation during the moulded blank formation step (a) to provide a moulded blank comprising a partially cured and expanded rubber part bound to a partially cured additional rubber part, and wherein the rubber of the partially cured additional rubber part is a solid rubber.

12. The process of claim 7, wherein the process comprises an extrusion step in which the expandable rubber formulation and the additional rubber formulation are coextruded prior to the moulded blank formation step (a).

13. The process according to claim 1, wherein the expanded moulded blank is contacted with an additional rubber formulation during the further curing step (d), the additional rubber formulation comprising an elastomeric material and a curing agent, wherein the additional rubber formulation is at least partially cured during the further curing step (d) to provide an expanded rubber article comprising an additional rubber part bound to an expanded rubber part, and wherein the rubber of the additional rubber part is a solid rubber.

14. The process according to claim 11, wherein the elastomeric material of the additional rubber formulation is the same as the elastomeric material of the expandable rubber formulation.

15. The process according to claim 11, wherein a substrate is present in or forms part of the second mould cavity during the further curing step (d), and wherein at least part of the additional rubber formulation is contacted with the substrate during further curing step (d).

16. The process according to claim 15, wherein the substrate comprises a base material at least partially coated with an elastomer bonding agent, and wherein at least part of the additional rubber formulation is contacted with the elastomer bonding agent during the further curing step (d), the elastomeric bonding agent being at least partially cured during the further curing step (d) to form an elastomeric bonding layer adhered to at least part of the solid rubber part.

17. An expanded rubber article made by the process of claim 1, wherein the expanded rubber article is an expanded rubber product comprising: an expanded rubber part; a solid rubber part; and, a substrate comprising a base material at least partially coated with an elastomer bonding layer; wherein the expanded rubber part is bound to the substrate via the solid rubber part.

18. The product according to claim 17, wherein both the expanded rubber part and the solid rubber part comprise one or more rubber polymers selected from the list consisting of natural rubber, styrene butadiene rubber and butadiene rubber.

19. The product according to claim 17, wherein the expanded rubber part is bound to the substrate by means of cross-linking bonds between the expanded rubber part and the solid rubber part, and between the solid rubber part and the elastomer bonding layer.

20. The product according to claim 17, wherein the base material is a metal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings of which:

(2) FIG. 1 shows a depiction of the steps of a process according to a first embodiment of the invention.

(3) FIG. 2 shows a depiction of the steps of a process according to a second embodiment of the invention.

(4) FIG. 3 shows a depiction of the steps of a process according to a third embodiment of the invention.

(5) FIG. 4 is a schematic diagram of the bonding between the materials in the product prepared according to the second aspect of the invention.

(6) FIG. 5 shows a plan view of a clip for use with the moulded tyre of the fourth aspect of the invention.

(7) FIG. 6 shows a perspective view of the clip of FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

(8) FIG. 1 shows a first embodiment of a process for making an expanded rubber article 6 according to the first aspect of the invention

(9) To form an expanded rubber article comprising an open cell expanded rubber article, a cavity of a first mould 1 is partially filled with an expandable rubber formulation 2(a). During a moulded blank formation step (i)(a), the expandable rubber formulation 2(a) is heated to partially cure and expand it to form a moulded blank 3.

(10) To form an expanded rubber article comprising a closed cell expanded rubber article, a cavity of first mould 1 is substantially entirely filled with an expandable rubber formulation 2(b). During a moulded blank formation step (i)(b), the expandable rubber formulation 2(b) is heated to partially cure and expand it to form a moulded blank 3.

(11) The remaining steps of the process according to the first aspect of the invention are common to both the open and closed cell expanded rubber articles.

(12) In a releasing step (ii), the moulded blank 3 is released from the first mould 1 and expands further to form an expanded moulded blank 4.

(13) In step (iii) the expanded moulded blank 4 is transferred into a second mould 5.

(14) In a further curing step (iv), the expanded moulded blank 4 is further cured and expanded to form an expanded rubber article 6 in a cavity of the second mould 5.

(15) The expanded rubber article 6 is removed from the second mould 5 in step (v).

(16) FIG. 2 shows a second embodiment of a process for making an expanded rubber article 12 according to the first aspect of the invention.

(17) To form an expanded rubber article 12 comprising an closed cell expanded rubber part 11 and a solid rubber part 10, a cavity of a first mould 1 is substantially entirely filled with an expandable rubber formulation 2 and an additional solid rubber formulation 7. During a moulded blank formation step (i), the expandable rubber formulation 2 is heated to partially cure and expand it to form a moulded blank comprising partially cured and expanded rubber part 8 and partially cured solid rubber part 9.

(18) In releasing step (ii), the moulded blank is released from the first mould 1 and expanded further to form an expanded moulded blank 4.

(19) In step (iii), the expanded moulded blank 4 is transferred into a second mould 5.

(20) In further curing step (iv), the expanded moulded blank 4 is further cured and expanded to form an expanded moulded rubber article 12 comprising further cured and expanded rubber part 10 and further cured solid rubber part 11 in a cavity of second mould 5.

(21) The expanded rubber article 12 is removed from the second mould 5 in step (v).

(22) FIG. 3 shows a process according to the second aspect of the invention for making an expanded rubber product 17 of the third aspect of the invention.

(23) To form an expanded rubber article comprising an open cell expanded rubber article, a cavity of first mould 1 is partially filled with an expandable rubber formulation 2(a). During a moulded blank formation step (i)(a), the expandable rubber formulation 2(a) is heated to partially cure and expand it to form a moulded blank 3.

(24) To form an expanded rubber article comprising a closed cell expanded rubber article, a cavity of first mould 1 is substantially entirely filled with an expandable rubber formulation 2(b). During a moulded blank formulation step (i)(b), the expandable rubber formulation 2(b) is heated to partially cure and expand it to form a moulded blank 3.

(25) The remaining steps of the process according to the third aspect of the invention are common to both the open and closed cell expanded rubber articles.

(26) In a releasing step (ii), the moulded blank 3 is released from the first mould 1 and expands further to form an expanded moulded blank 4.

(27) In step (iii), the expanded moulded blank 4 is transferred into second mould 5 together with an additional rubber formulation 13. A substrate comprising a base material 15 and an elastomer bonding agent 14 and the second mould 5 together form a second mould cavity.

(28) In a further curing step (iv), the expanded moulded blank 4 is further cured and expanded to form an expanded rubber article 6 in the second mould cavity formed by the second mould 5 and the substrate. Also in the further curing step (iv), the additional rubber formulation 13 is at least partially cured to form a solid rubber part 16 bound to the expanded rubber article 6 and the elastomer bonding agent 14 of the substrate. The further curing step (iv) thus provides expanded rubber article 6 adhered to a substrate comprising base material 15 and elastomer bonding agent 14 via solid rubber part 16.

(29) An expanded rubber product 17, comprising the expanded rubber article 6, the solid rubber part 16 and the substrate comprising the base material 15 and the elastomer bonding agent 14, is removed from the second mould 5 in a removal step (v).

(30) FIG. 4 shows the bonding between materials in a product prepared according to the second aspect of the invention.

(31) Expanded rubber product 17 comprises an expanded rubber article 6 adhered to a substrate comprising a base material 15 and an elastomer bonding agent 14 via a solid rubber part 16. The expanded rubber article 6 is bound to solid rubber part 16 by means of crosslinking bonds 18 between rubber polymers in the expanded rubber article 6 and rubber polymers in the solid rubber part 16. The elastomer bonding agent 14 is bound to solid rubber part 16 by means of crosslinking bonds 19 between rubber polymers in the solid rubber part 16 and polymers in the elastomer bonding agent 14. The elastomer bonding agent 14 is bound to base material 15 by means of absorption 20 of elastomer bonding agent 14 onto the surface of base material 15.

(32) FIG. 5 shows a plan view of a clip 51 for use with the tyre of the fourth aspect of the invention. The clip 51 is in the shape of a flattened U, having two substantially parallel straight arms 52 extending perpendicularly from a straight crosspiece 53, the ends of the arms being pointed at their free ends 54 to permit convenient insertion of the arms 52 into the sidewall of a moulded tyre. In use, the pointed ends 54 of the clip 51 are forced into the sidewall of a tyre by applying a force against the crosspiece 53 until the arms 52 are fully embedded in the tyre. Once installed in the tyre, the clip can be used to push the tyre into pace inside a wheel rim, for example by applying force again to the crosspiece 53 to squash the tyre into the wheel rim, thereby giving an interference fit. Conveniently, the crosspiece 53 of the clip provides a hard surface that is less susceptible to damage when pushed against to force the tyre onto the wheel than, for example, the surface of the tyre itself.

(33) FIG. 6 shows a perspective view of the clip 51 of FIG. 5, the parts of the clip 51 being labelled with the same reference numerals used in FIG. 5. The clip 51 has a span s of around 17 mm, a height h of around 18 mm, a width w of around 3.5 mm and a material thickness t of around 1.5 mm. The clip 51 is made from metal (more particularly, stainless steel). Alternatively, the clip could be made from a plastic material, for example glass filled nylon.

EXAMPLES

(34) Embodiments of the invention will now be illustrated by means of the non-limiting examples.

Example 1

(35) The preparation of an expanded rubber product comprising an expanded rubber part bound to an aluminium metal part via a solid rubber part is described. The expanded rubber product is a wheel having a 390 mm diameter and a 140 mm width. The example shows how an expanded rubber part can be bonded to and shaped over an aluminium wheel hub.

(36) The skilled reader will appreciate that following mixing procedures are standard rubber industry mixing procedures that provide a good level of dispersion of ingredients. The mixed expandable rubber formulation and the mixed additional rubber formulation should be processed (cured) within 3 months of the mixing date.

(37) 1) Preparation of an Expandable Rubber Formulation

(38) An expandable rubber formulation was prepared using an elastomeric material comprising a blend of natural rubber (NR) & styrene butadiene rubber (SBR) rubber polymers. The components of the expandable rubber formulation are listed in Table 1.

(39) TABLE-US-00001 TABLE 1 Expandable Additional rubber rubber Material Material Type formulation formulation NR/SBR Rubber Polymer Elastomeric 100 100 Blend Material Carbon Black Filler 30 30 Synthetic Wax Process Aid 2 2 Clay Filler 7.5 7.5 Process Oil Processing Aid 20 20 Amine Anti-degradent Anti-degradent 1 1 Zinc Oxide Curing Agent 3 3 Stearic Acid Curing Agent 2 2 Sulphenamide Accelerator Curing Agent 1 1 Sulphur Crosslinking Curing Agent 2.5 2.5 Medium Blowing Agent Expansion 15 0 (Nitrogen releasing) Agent Total PHR 184 169

(40) The Polymers and Expansion Agents were first pre-blended on a 48 (1.22 m) two roll mill, then the bulk materials (Polymers/Expansion Agents, Process Aids, Fillers and anti-degradent) were internally mixed in a 45 litre Banbury mixer at 35 rotations per minute (RPM), with water cooled to 30 C. and the mixed formulation dumped at a temperature of 115 C. The Curing Agents were mixed in with the bulk materials on the two roll mill 24 hours later. The mixed expandable rubber formulation was sheeted off the two roll mill in a 10 mm thick sheet. The roll mills used a standard friction ratio and water cooling to 30 C.

(41) The shore hardness (Instron Shore A) of the skin of a tube formed from a section of the sheet of mixed expandable rubber formulation (45 mm inside diameter70 mm outside diameter50 mm wide) cured for 8 minutes at 150 C. was 35. Part of the skin was removed and the cut cellular surface of the tube was found to have a Shore hardness (Instron Shore A) of 25.

(42) 2) Preparation of an Additional Rubber Formulation

(43) An additional rubber formulation compatible with the expandable rubber formulation was also prepared. The components of the additional rubber formulation are listed in Table 1.

(44) The additional rubber formulation was mixed in one stage on an 18 (0.46 m) two roll mill, with the Polymers, Process Aids and Fillers added at the start of the mix cycle, and then the Curing Agents added 4 minutes into the 6 minute mixing cycle. The mixed additional rubber formulation was sheeted off the mill in a 2 mm thick sheet. The roll mills used a standard friction ratio and water cooling to 30 C.

(45) 3) Formation of the Expanded Moulded Blank

(46) A 10 mm thick sheet of mixed expandable rubber formulation from step (1) was cut to 100 mm width830 mm length and butt-joined to form a band. The band was compression moulded in a first mould (an aluminium compression mould) positioned between the pre-warmed platens of a hydraulic press for 22 minutes at 152 C. to form a moulded blank in the shape of a band. The moulded blank was released from the first mould and allowed to expand to form an expanded moulded blank in the form of a band having approximate dimensions of 1200 mm circumference150 mm width12.5 mm thick. To aid release from the mould, a mould release agent was used.

(47) The expanded moulded blank was left to cool for one hour at room temperature.

(48) 4) Preparation of the Substrate and Stabilisation of the Expanded Moulded Blank

(49) An aluminium wheel hub of 365 mm diameter140 mm width with 3 mm ventilation holes drilled through the base at 50 mm intervals was first abraded and then cleaned with a ketone cleaning solvent. A layer of elastomer bonding agent primer (EBAP) was applied to the abraded and cleaned surface by brush and then dried for 5 minutes at 50 C. in a fan assisted oven. A layer of elastomer bonding agent (EBA) was applied to the dried EBAP by brush and then dried for 5 minutes at 50 C. in a fan assisted oven. A 140 mm wide 1100 mm long section of a 2 mm thick sheet of mixed additional rubber formulation from step (2) was applied to the aluminium wheel hub over the dried EBA layer under finger pressure using a rotating jig. The outer surface of the additional rubber formulation was then solvent-wiped with the ketone cleaning solvent.

(50) The inner surface of the cooled expanded moulded blank from step (3) was solvent-wiped with the ketone cleaning solvent and then placed over the expandable rubber formulation applied to the aluminium wheel hub. The expanded moulded blank/additional rubber formulation/wheel hub assembly was then left for 24 hours, in which time the expanded moulded blank shrank and contracted around the wheel, increasing the pressure between the materials at the expanded moulded blank/additional rubber formulation and the additional rubber formulation/wheel hub interfaces.

(51) 5) Further Curing of the Expanded Moulded Blank

(52) The expanded moulded blank/additional rubber formulation/wheel hub assembly from step (4) was placed and clamped in a pre-warmed two part second mould (an aluminium tyre mould) and then heated for 40 minutes at 185 C. in an oven to form the expanded rubber product. The mould was removed from the oven and then left to cool at room temperature for 24 hours with the expanded rubber product still clamped inside. After cooling, the expanded rubber product was removed from the mould with the expanded rubber part having dimensions set to the mould profile.

Example 2

(53) The preparation of an expanded rubber product comprising two stainless steel plates bonded to an expanded rubber part via two solid rubber parts is described. The example shows how an expanded rubber part can be bonded to and sandwiched between two metal plates thereby providing vibration damping between the plates. In this example, the further curing step is performed using partially open tooling.

(54) The skilled reader will appreciate that the following mixing procedures are standard rubber industry mixing procedures that provide a good level of dispersion of ingredients. The mixed expandable rubber formulation and the mixed additional rubber formulation should be processed (cured) within 3 months of the mixing date.

(55) 1) Preparation of a Mixed Expandable Rubber Formulation

(56) An expandable rubber formulation with good damping properties i.e. relatively high hysteresis (or Tan Delta values as measured by a Dynamic Mechanical Analyser) was prepared comprising a blend of two polymers, one of which having relatively high hysteresis or tan Delta value (i.e. the blended compound has a tan Delta value of greater than 0.4 at 10 C., 10 Hz, 0.14% double strain amplitude (DSA) & shear mode). The components of the expandable rubber formulation are listed in Table 2.

(57) TABLE-US-00002 TABLE 2 Expandable Additional rubber rubber Material Material Type formulation formulation SBR/BIIR Rubber Elastomeric 100 0 Polymer Blend Material NR/SBR Rubber polymer Elastomeric 0 100 blend Material Carbon Black Filler 20 60 Synthetic Wax Process Aid 2 2 Clay Filler 0 7.5 Cross-linked Oil Process Aid 15 0 Process Oil Process Aid 0 20 Amine Anti-degradent Anti-degradent 1 1 Zinc Oxide Curing Agent 3 3 Stearic Acid Curing Agent 2 2 Sulphenamide Accelerator Curing Agent 1 1 Sulphur Crosslinking Curing Agent 2.5 2.5 Medium Blowing Agent Expansion 7.5 0 (Nitrogen releasing) Agent Total PHR 154 169

(58) The Polymers and the Expansion Agents were first pre-blended on a 48 (1.22 m) two roll mill, then the bulk materials (Polymers, Expansion Agents, Fillers, Process Aids and anti-degradent) were internally mixed in a 45 litre Banbury (at 35 RPM, with water cooled to 30 C. and the mixed formulation dumped at a temperature of 115 C.). The Curing Agents were mixed in with the bulk materials on a mill 24 hours later. The mixed expandable rubber formulation was sheeted off the mill in a sheet 10 mm thick. The rolls mills used a standard friction ratio and water cooling to 30 C.

(59) The shore hardness (Instron Shore A) of the skin of a tube formed from a section of the sheet of mixed expandable rubber formulation (45 mm inside diameter70 mm outside diameter50 mm wide) cured for 8 minutes at 150 C. was 25. Part of the skin was removed and the cut cellular surface of the tube was found to have a Shore hardness (Instron Shore A) of 15.

(60) 2) Preparation of a Mixed Additional Rubber Formulation

(61) An additional rubber formulation was formulated to be compatible with both the expandable rubber formulation and the application service requirements i.e. it was formulated to provide a relatively flexible solid rubber part when cured. The components of the additional rubber formulation are listed in Table 2. The polymer blend included in the additional rubber formulation lacked the high hysteresis/high tan Delta polymer.

(62) The additional rubber formulation was mixed in one stage on an 18 (0.46 m) two roll mill, with the Polymers, Process Aids and Fillers added at the start, and then the Curing Agents added 4 minutes into the 6 minute mixing cycle. The mixed additional rubber formulation was sheeted off the mill in a sheet 2 mm thick. The rolls mills used a standard friction ratio and water cooling to 30 C.

(63) The skilled reader will appreciate that the above mixing procedures are standard rubber industry mixing procedures that provide a good level of dispersion of ingredients.

(64) The expandable rubber formulation and the additional rubber formulation should be processed (cured) within 3 months of the mixing date.

(65) 3) Extrusion of the Mixed Expandable Rubber Formulation

(66) The mixed expandable rubber formulation from step (1) was extruded into tubes using a Barwell extruder. The extruded tube dimensions were 25 mm internal diameter50 mm outside diameter and had a weight of 58 g.

(67) 4) Calendaring of the Mixed Additional Rubber Formulation

(68) The mixed additional rubber formulation from step (2) was calendered to form sheets 0.5 mm thick300 mm wide to form sheets of calendared additional rubber formulation.

(69) 5) Formation of the Expanded Moulded Blank

(70) The extruded tubes of step (3) were pre-warmed in an air oven at 65 C. for 20 minutes. A hydraulic press having 600 mm square platens was pre-warmed to 150 C. for 4 hours together with a first mould (a multi cavity compression mould having cavities with 51 mm outside diameter25 mm inner diameterand 31 mm depth).

(71) The pre-warmed extruded tubes were inserted into the cavities of the first mould, and the first mould was pressed shut by the hydraulic press. The extruded tubes of mixed expandable rubber formulation were heated for 9 minutes at 150 C. to form moulded blanks. The moulded blanks were released and promptly removed from the first mould to allow them to expand to form expanded moulded blanks. Excess edge rubber was removed from the expanded moulded blanks (i.e. they were de-flashed). To aid release from the first mould a mould release agent was used. The expanded moulded blanks were around 5 times the size (by volume) of the cavities of the first mould, and weighed around 50 g.

(72) The expanded moulded blanks were allowed to shrink and stabilise for 72 hours on a work top at room temperature to form stabilised moulded blanks.

(73) 6) Preparing the Laminated Expanded Moulded Blanks

(74) The stabilised expanded moulded blanks from step (5) were mounted on a lathe and cut into 3 mm thick ring slices. Both planar sides of the 3 mm ring slices were laminated with portions of the 0.5 mm thick sheets calendered additional rubber formulation from step (4) to form laminated slices. A polyethylene liner was then applied to the outer, planar ends of the laminated slices. A polypropylene liner could have been used.

(75) The lined laminated slices were placed under pressure between metal plates having a load of at least 6 kg for 24 hours. The pressed laminated slices were then dye cut with a fly press having a metal punch to form the laminated expanded moulded blanks.

(76) 7) Further Curing of the Expandable Rubber Formulation

(77) A pair of stainless steel substrate plates 0.9 mm thick and having approximately the same shape as the laminated expanded moulded blanks of step (6) were provided for each dye cut laminated expanded moulded blank. The stainless steel substrate plates were abraded and degreased; then one side of each plate was partially coated with an EBAP by brush (although the partial coating could have been sprayed on) and left to air dry. A partial coating of an EBA was painted on over the EBAP coating (although this coating could also have been sprayed on) and left to air dry. As an alternative, both coatings could have been dried for 5 minutes at 50 C. in an oven. The coatings were applied only to the areas of the stainless steel substrate plates that were to be bonded to the laminate. Masking tape was used to prevent unwanted application of the coatings to other parts of the plates.

(78) The polyethylene liners were removed from the laminated expanded moulded blanks of step (6), and each laminated expanded moulded blank was placed between a pair of partially coated stainless steel substrate plates such that the outer additional rubber formulation layers of the laminated expanded moulded blanks were brought into contact with the parts of the stainless steel substrate plates coated with the EBAP and the EBA to form sandwich assemblies. The sandwich assemblies were then placed in open-sided restraining tools sized to hold a pair of stainless steel substrate plates against a die cut laminated slice. Each combined tool and sandwich assembly was heated in an oven for 20 minutes at 185 C. to further cure and expand the expandable rubber formulation to form an expanded rubber part, to at least partially cure the two layers of additional rubber formulation to form a pair of solid rubber parts, and to bond the expanded rubber part to the stainless steel substrate plates via the solid rubber parts to form the expanded rubber product.

(79) Following heating, the combined tool and expanded rubber products were removed from the oven, and the expanded rubber products were removed from the tools. The expanded rubber products were allowed to shrink and stabilise for 24 hours at room temperature. The stabilised expanded rubber products had overall thicknesses of 5.7 mm+/0.1 mm.

Example 3

(80) The preparation of an expanded rubber product comprising a hollow expanded rubber part bound to a solid rubber part is described. The expanded rubber product is a tyre having a 400 mm diameter and a 25 mm width. The example shows how an expanded rubber part having a cavity can be moulded, how an expanded rubber part can be bonded to a solid rubber part in the moulded blank formation step, and how two or more expanded moulded blanks can be bonded together during the further curing step. In this example, the moulded blank comprising an expanded rubber part and a solid rubber part is shaped into a tyre using a mould and wheel shaped insert during the further curing step.

(81) The skilled reader will appreciate that the following mixing procedures are standard rubber industry mixing procedures that provide a good level of dispersion of ingredients. The mixed expandable rubber formulation and the mixed additional rubber formulation should be processed (cured) within 3 months of the mixing date.

(82) 1) Preparation of an Expandable Rubber Formulation

(83) An expandable rubber formulation was prepared comprising a blend of two polymers. The expandable rubber formulation also comprised a carbon black, an inorganic filler, process aids, a wax, an anti-degradent, curing agents and a blowing agent The components of the expandable rubber formulation are listed in Table 3.

(84) TABLE-US-00003 TABLE 3 Expandable Additional rubber rubber Material Material Type formulation formulation NR/SBR/BR Rubber Elastomeric 100 100 Polymer Blend Material Carbon Black Filler 20 30 Clay Filler 20 20 Synthetic Wax Process aid 2 2 Process Oil Process aid 5 5 Amine Anti-degradent Anti-degradent 1 1 Zinc oxide Curing Agent 3 3 Stearic acid Curing Agent 2 2 Sulphenamide Accelerator Curing Agent 1 1 Sulphur Crosslinking Curing Agent 2.5 2.5 medium Blowing agent Expansion Agent 12 0 (Nitrogen releasing) Total PHR 168.5 166.5

(85) The Polymers and Expansion Agents were first pre-blended on a 48 (1.22 m) two roll mill, then the bulk materials (Polymers/Expansion Agents, Process Aids, Fillers and Anti-degradent) were internally mixed in a 45 litre Banbury (at 35 rotations per minute (RPM), with water cooled to 30 C. and the mixed formulation dumped at a temperature of 115 C.). The Curing Agents were mixed in with the bulk materials on a two roll mill 24 hours later. The mixed expandable rubber formulation was sheeted off the two roll mill in a sheet 8 mm thick. The roll mills used a standard friction ratio and water cooling to 30 C. Alternatively, to improve dimensional control, the material could be calendered out (using a three or four bowl calendar) into a sheet 8 mm thick600 mm wide wound onto a roll using a cardboard core with polyethylene liner.

(86) The shore hardness (Instron Shore A) of the skin of the expandable rubber tire core formed from a section of the sheet of mixed expandable rubber formulation (10 mm inside diameter20 mm outside diameter300 mm long) cured for 10 minutes at 150 C. was 55 shore.

(87) 2) Preparation of an Additional Rubber Formulation

(88) An additional solid rubber formulation (tread) compatible with the expandable rubber formulation (core) was also prepared. The components of the additional rubber formulation are listed in Table 3.

(89) The additional rubber formulation was mixed in one stage on an 18 (0.46 m) two roll mill, with the Polymers, Process Aids and Fillers added at the start of the mix cycle, and then the Curing Agents added 4 minutes into the 6 minute mixing cycle. The mixed additional rubber formulation was sheeted off the mill in a 2 mm thick sheet. The roll mills used a standard friction ratio and water cooling to 30 C.

(90) 3) Formation of the Expanded Moulded Blank (Tyre Core) Bonded to a Solid Rubber Formulation (Tyre Tread)

(91) The 8 mm thick sheet of mixed expandable rubber formulation from step (1) was cut to form a strip 60 mm wide300 mm long. The 2 mm thick sheet of additional solid rubber formulation was cut into a strip 32 mm wide and 300 long and laminated to the middle of the strip of expandable rubber formulation that had been previously cleaned or freshened using a solvent wipe. The reverse side of the laminated strip of expandable rubber formulation was wrapped around the middle of a 450 mm long steel mandrel having a 10 mm diameter. (Alternatively, an extruder having an appropriate die in the extruder head could be used to coextrude an equivalent tube of expandable rubber formulation and additional solid rubber formulation, and then a steel insert could be placed inside the extruded tube). The laminated tube blank and steel mandrel assembly was pre-warmed for 20 minutes at 70 C. and then placed in a first stage mould (an aluminium compression mould having a cavity 300 mm long and 20 mm in diameter, the mould comprising 10 mm diameter slots at each end of the cavity to accommodate the ends of the steel mandrel) The mould, laminated tube blank and steel mandrel assembly was then positioned between the pre-warmed platens of a hydraulic press and cured for 10 minutes at 150 C. to form a moulded blank in the shape of a tube having a tread bonded onto the upper surface. The moulded tube with bonded tread was released from the first mould and the steel insert removed, then the moulded tube with bonded tread was allowed to expand to form an expanded moulded blank comprising an expanded rubber part (tube) bonded to a solid rubber part (tread) having approximate dimensions of 20 mm diameter300 mm long and having a 10 mm (approx.) diameter internal cavity. To aid release from the mould a mould release agent was used. The expanded moulded blank was left to cool for one hour at room temperature. The resulting cooled expanded moulded blank comprised a tubular expanded rubber part having a circumference of approximately 63 mm, and a solid rubber part extending along the length of the tubular expanded rubber part and around approximately 32 mm of its circumference.

(92) 4) Preparation of the Tyre Blank for Further Curing Step

(93) The surface of the ends of five 20 mm diameter300 mm long tubular moulded blanks comprising an expanded rubber part (tube) and a solid rubber part (tread) were cut off, and the exposed end surfaces coated with an EBA. The coated ends were dried for 10 minutes at 50 C. (or air dried at room temperature for 1 hour) and then the moulded blanks tacked together inside a 400 mm diameter wheel-shaped aluminium mould insert. High temperature tape was used to tack the blanks in place around the insert.

(94) 5) Further Curing of the Expanded Moulded Blank

(95) The wheel-shaped insert of step 4, containing the five tacked together moulded blanks, was fitted into a pre-warmed two part second mould (an aluminium tyre mould), and the resulting assembly clamped together. The clamped assembly was heated for 40 minutes at 185 C. in an oven to form the expanded rubber product (tyre with tread). The clamped assembly was then removed from the oven and left to cool at room temperature for 24 hours (with the expanded rubber product still clamped inside). After cooling, the expanded rubber product was removed from the mould, and the high temperature tape was removed. The expanded rubber product had dimensions matching the mould profile, i.e. 400 mm diameter25 mm width35 mm depth (the expanded moulded blank expanded further in the second stage to be shaped by the profile of the wheel-shaped insert).

Example 4

(96) The preparation of an expanded rubber bound to a solid rubber material is described. More particularly, the preparation of a tyre based on a high modulus/low weight expandable rubber core and a solid rubber tread initially bonded together in the first moulding stage is described. The expanded rubber product is a tyre having a 630 mm diameter and a 35 mm width. The example shows how a rubber part can be bonded to a tread in the first moulding and curing stage and then shaped into a tyre using a mould and wheel-shaped insert during a further curing step.

(97) The following mixing procedures are standard rubber industry mixing procedures that provide a good level of dispersion of ingredients. The mixed expandable rubber formulation and the mixed additional rubber formulation should be processed (cured) within 3 months of the mixing date.

(98) 6) Preparation of an Expandable Rubber Formulation

(99) An expandable rubber formulation comprising a blend of two polymers was prepared. The expandable rubber formulation also comprised a carbon black, an inorganic filler, a process oil, a wax, an anti-degradent, curing agents and a blowing agent. The components of the expandable rubber formulation are listed in Table 4.

(100) TABLE-US-00004 TABLE 4 Expandable Additional rubber solid rubber Material Material Type formulation formulation Polymer 1 Polymer 70 70 Polymer 2 Polymer 30 30 Carbon Black Filler 45 30 Inorganic filler Filler 25 20 Wax Process aid 2 2 Process aid Process aid 10 5 Anti-degradent Anti-degradent 1 1 Metal oxide Curing Agent 3 3 Organic acid Curing Agent 2 2 Accelerator Curing Agent 1 1 Crosslinking medium Curing Agent 2 2 Blowing agent Agent Expansion 12 0 Total PHR 203 162

(101) The Polymers and Expansion Agents were first pre-blended on a 48 (1.22 m) two roll mill, then the bulk materials (Polymers/Expansion Agents, Process Aids, Fillers and anti-degradent) were internally mixed in a 45 litre Banbury (at 35 rotations per minute (RPM), with water cooled to 30 C. and the mixed formulation dumped at a temperature of 115 C.). The Curing Agents were mixed in with the bulk materials on a two-roll mill 24 hours later. The mixed expandable rubber formulation was sheeted off the two-roll mill in an 8 mm thick sheet. The roll mills used a standard friction ratio and water cooling to 30 C. Note: for improved dimensional control the material could also be calendered out (using a three or four bowl calendar) into 8 mm thick600 mm wide sheet wound onto a roll using a cardboard core with polyethylene liner.

(102) The shore hardness (Instron Shore A) of the skin of the expandable rubber tyre core formed from a section of the sheet of mixed expandable rubber formulation (10 mm inside diameter20 mm outside diameter300 mm long) cured for 10 minutes at 150 C. was 55 shore.

(103) 7) Preparation of an Additional Rubber Formulation

(104) An additional solid rubber formulation (tread) compatible with the expandable rubber formulation was also prepared. The components of the additional rubber formulation are listed in Table 4.

(105) The additional rubber formulation was mixed in one stage on an 18 (0.46 m) two roll mill, with the Polymers, Process Aids and Fillers added at the start of the mix cycle, and then the Curing Agents added 4 minutes into the 6 minute mixing cycle. The mixed additional rubber formulation was sheeted off the mill in a 2 mm thick sheet. The roll mills used a standard friction ratio and water-cooling to 30 C.

(106) 8) Formation of the Expanded Moulded Blank (Tyre Core) Bonded to a Solid Rubber Formulation (Tyre Tread)

(107) The expandable rubber formulation from step (1) was extruded into a cone shaped profile (32 mm30 mm) cut to 1850 mm length (1.35 kg approx.). The standard rubber extruder uses barrel, head and die temperatures from 60 C. to 80 C. at 180 cm per minute speed. Then the 2 mm thick solid rubber formulation was cut to 35 mm width and 1850 mm length and laminated to the middle of the 1850 mm long expandable rubber profile, (Note: the same profile could also be extruded with the solid rubber formulation coextruded onto the expandable rubber formulation). The pre-warmed (20 minutes at 70 C.) laminated blank was then compression moulded in a first stage mould (able to mould a single-piece ring). The butt-joined extruded blank was positioned between the pre-warmed platens of a hydraulic press and then cured for 10 minutes at 150 C. to form a moulded blank in the shape of a tyre. The moulded tyre with bonded tread was allowed to expand to form an expanded moulded blank with solid rubber bonded tread. To aid release from the mould a mould release agent was used. The expanded moulded blank was left to cool for one hour at room temperature.

(108) 9) Preparation of the Tire Blank for Further Curing Step

(109) The mould stage one blank tyre (1.2 kg approx.) was then installed onto a 26 inch bicycle wheel-shaped insert for the second vulcanisation step

(110) 10) Further Curing of the Expanded Moulded Blank

(111) The mould stage one blank tyre and wheel-shaped insert of step 9 was positioned in a pre-warmed further two-part curing mould having tread pattern and 16 ventilation holes incorporated into the sidewall portions of the curing mould, and then the assembly was clamped together. The clamped assembly was heated for 40 minutes at 185 C. in an oven to form the expanded rubber product (tyre with tread). The mould was removed from the oven and the expanded rubber product was removed from the mould and left to cool for 24 hours.

(112) Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein.

(113) Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.