PROCESS FOR THE PRODUCTION OF RUBBER PRODUCTS

Abstract: A process for the production of rubber products comprises forming a moulding material from a first and second ingredient. The first ingredient comprises powdered rubber and the second ingredient comprises sulphur. The moulding material is compressed in a mould to form the rubber product. The moulding material may be compressed in the mould to a pressure of up to 6.8 tons per square inch and the temperature of the moulding may be elevated to be about 100 DEG C during compression.

Description: 1 Process for the Production of Rubber Products This invention relates to a process for the production of rubber products. In the tyre remould industry, a considerable amount of rubber is produced as a waste product. Although this waste product has some industrial use, it requires expensive bonding agents. According to one aspect of this invention there is provided a process for the production of a rubber product, the process comprising forming a moulding material from a first ingredient comprising powdered rubber and a second ingredient comprising sulphur, and compressing the moulding material in a mould to form said rubber product. The moulding material may be compressed in said mould to a pressure of up to substantially 6.8 tons force per square inch. The moulding material is desirably compressed to a pressure in the range of substantially 32 pounds force per square inch (psi) to substantially 6.8 tons per square inch, preferably substantially 129psi to substantially 6.8 tons per square inch, more preferably substantially 129psi to substantially 1270psi, and in one embodiment is compressed to an initial pressure in the range of substantially 380psi to substantially 1270psi. In some embodiments the pressure of the moulding may increase during the moulding stage. The temperature of the moulding material may be elevated during compression. Desirably, the temperature of the moulding material is elevated to be above 100°C, desirably in the range of substantially 100°C to substantially 170°C during compression. Preferably the temperature is elevated to be in the range of substantially 120°C to substantially 170°C , more preferably substantially 140°C to substantially 170°C . The temperature of the moulding material may be elevated to be in the range of substantially 160°C to substantially 170°C during compression. The moulding material may be compressed for over 10 minutes to allow the moulding material to cure. Desirably, the moulding material is compressed for a period of time of between substantially 10 minutes to substantially 2 hours or substantially 3 hours. Preferably, the moulding material is compressed for a period of time of between 10 minutes and substantially 60 minutes. More preferably the moulding material is compressed for a period of time of between substantially 20 minutes and substantially 60 minutes. In one embodiment, the moulding material may be compressed for a period of time of between substantially 40 minutes and substantially 60 minutes. The amount of sulphur in the moulding material may be in the range of substantially 0.5% w/w to substantially 25% w/w with respect to the weight of the first ingredient, preferably in the range of substantially 0.5% to substantially 10% w/w, more preferably in the range of substantially 0.5% w/w to substantially 5% w/w. In particular embodiments, the amount of sulphur in the moulding material is substantially 0.5% w/w, substantially 1% w/w, or substantially 5% w/w. Preferably, the sulphur is in a powder form. Thus sulphur powder may have a size of substantially 300 mesh or finer. The sulphur and rubber are preferably thoroughly mixed to form a substantially uniform mixture. The powdered rubber may have a particle size in the range of substantially 16 mesh to substantially 300 mesh, preferably in the range of substantially 16 mesh to substantially 50 mesh, more preferably substantially 40 mesh. The first ingredient may comprise up to 100% powdered rubber, or may include other matter, for example fibrous matter. The second ingredient may comprise powdered sulphur in a carrier, which may be a mineral oil. In one embodiment, the second ingredient is a 300 mesh sulphur/mineral oil mix. An example of such a mix is manufactured by Hays Chemicals under the designation UNI350 5MI/226/S/97 GB/246S. The process may involve a pre-compacting step before applying said compression step above. The pre-compacting step may involve applying a pressure of the range of above substantially 64psi, desirably above substantially 129psi. Preferably, the pre-compacting step is carried out at a pressure in the range of substantially 64psi to substantially 1935psi, more preferably in the range of substantially 129psi to substantially 1905psi. In one embodiment, the pre-compacting step is carried out at a pressure of substantially 1905psi or substantially 1935psi. Embodiments of the invention will now be described by way of example only, with reference to the accompanying drawing which shows schematically a tool in the form of a mould for forming the rubber product. A first ingredient, comprising a 40 mesh powdered rubber formed, for example, as a waste product (known as rubber dust) from the production of tyre remoulds is graded and mixed with a second ingredient or mixture, comprising a 300 mesh sulphur/mineral oil mix to form a moulding material. The amount of the second ingredient in the moulding material is selected to provide an amount of sulphur of 1% w/w with respect to the weight of the first ingredient. The moulding material is then thoroughly mixed, by any means known in the art, and then added to a mould. The material is compressed in the mould up to a pressure of substantially 400 psi, and heated to a temperature in the range of 130°C to 160°C. The pressure and heat are applied to the moulding material for a period of about 40 minutes, during which time, the moulding material cures to form a cohesive solid moulding. The process described in the above embodiment has the advantage that 4 it allows cohesive mouldings to be produced from rubber dust, which possess sufficient mechanical stability to be able to be used in many areas where ordinary rubber could be used. Various modifications can be made without departing from the scope of the invention. For example, the first ingredient may comprise a mix of powdered rubber and a powdered fibrous material. Further examples are described below using various different parameters of composition, pressure, temperature and time. Rubber Dust/Sulphur Mixtures The following rubber dust/sulphur mixes were used: Mix Reference % Added Sulphur (by weight) TF1 0.5% TF2 1.0% TF3 5.0% TF4 10.0% TF5 25.0% Mixing Procedures The mixing equipment used to prepare each mixture comprised an electric Hobart food type mixer fitted with an open whisk and 5 litre mixing basin. Each mix was prepared by weighing out 500g of rubber dust and then adding the appropriate amount of sulphur to it. The sulphur was sieved prior to its addition, using a 300 mesh sieve, in order to remove any lumps. The mixture was then loaded in to the mixing chamber, the whisk raised and the mixer set to a speed of 270 rpm, and allowed to mix for a period of 20 minutes. The mixed batch was regarded to be satisfactory if it had uniform colour and was free from undispersed lumps. The mixed material was then placed into a clean polythene bag and labelled prior to moulding. Tooling The tooling used for moulding of plaques is a mould 10 which comprises a bottom plate 12 with a cavity 14. In the example described, the cavity has a size of 119.4 mm diameter x 30.5 mm depth. The mould 10 also includes a top plate in the form of a piston 16. In the example described, the piston has a diameter of 119 mm and depth of 18.3 mm, which gave a final cavity size of 119.4 mm diameter x 12.2 mm height. Tnitial Moulding Trials Prior to carrying out any moulding work, it was first necessary to determine the quantity of dust mixture required to fill the mould 10 and also whether, and how much, the material needed to be compacted under pressure before applying the final moulding pressure. A number of experimental mouldings established that 195g appeared to be the optimum quantity of dust mixture 18 to fill the cavity 14 and form a complete moulding. A series of mouldings were then carried out using this quantity of mixture, at pre-compaction pressures ranging from 1905 lb/sq in. down to 64 lb/sq in. and moulding conditions set at 40 minutes at 160°C, with final moulding pressure set at 129 lb/sq in. in each case. The mouldings were checked for hardness and sectioned to check the level of compaction. These trials established that it appeared beneficial to pre-compact the mixture in the cavity before the final moulding pressure was applied, in order to ensure the material becomes fully compacted. Pre-compacting the mixture at a pressure of 129 lb/sq in. and above, was found to be desirable in order to produce a fully formed moulding with satisfactory properties. The remaining moulding trials it was decided to use a pre-compaction pressure of 1905 lb/sq in. Moulding of Plaques The general moulding procedure for preparation of moulded products or plaques is as follows: Prior to each moulding a nominal weight of 195g of the particular mixture is weighed into a clean aluminium container. The mould 10 is preheated up to the required moulding temperature in an electrically heated hydraulic press (not shown). The mould 10 is then taken from the press and the piston 16 removed. The cavity 14 is then completely filled with the moulding material or mixture 18, the piston 16 repositioned, and pressed down by hand. The piston 16 is removed and refilled with mixture and the piston 16 replaced. Then the mould 10 is placed in the press and the platens closed just enough to compact the mixture 18 further into the cavity 14. The mould 10 is again removed from the press, the piston 16 removed and the remainder of the mixture 18 placed into the cavity 14. The mould 10 is reassembled, placed back into the press and subjected to an initial moulding pressure of approximately 1935 lb/sq in. to compact the mixture 18. The pressure is then immediately reduced to the requisite moulding pressure for the stated cure time. The arrow P represents the application of pressure to the mixture 18 via the piston 16. On completion of the cure cycle, the mould 10 is removed from the press and the piston 16 removed. The moulded product or plaque is removed from the cavity 14 and allowed to cool to room temperature. Stage 1: Determination of moulding compression The moulding pressure used to form the moulded plaques was calculated from the following formula.: Moulding Pressure = Line Pressure x Area of Ram Cavity Area Moulding of plaques from each of the five formulations were carried out at moulding pressures ranging from 6.8 Tons per square inch to below 129 lb per square inch. The cure conditions for these initial trials were maintained at 40 minutes at 160°C throughout. The results of these initial moulding trials are listed in Table 1. TABLE 1 : MOULDING TRIALS WITH RUBBER DUST/SULPHUR MIXES STAGE 2: Evaluation of pressure required to form a complete moulding SAMPLE PRESSURE TEMP TIME HARDNESS COMMENT REF TF1 6.8 Tons/sq in 160 40' 68A Fully formed TF2 160 40' 71-75A TF3 160 40' 85A TF4 160 40' 95A V. brittle 8 TF5 160 40' 100A V. brittle TF1 3.4Tons/sq in 160 40' 65-70A Fully formed TF2 a 160 40' 70- 74 A TF3 u 160 40' 80-85A TF4 160 40' 95A V. brittle TF5 160 40' 100A V. brittle TF1 0.567Tons/sq in 160 40' 65-70-A Fully formed TF2 (127001bs/sq in) 160 40' 68-70A TF3 160 40' 80-85A TF4 160 40' 90-95A Brittle TF5 160 40' 100A+ Sample cracked around edge. TFO* 160 40' 60-65A Splits in moulding TF5 5161b/sq in 160 40' 100A Bloomed/brittle TF2 387to9001b/sq in** 160 40' 70-75A Fully formed TF2 258to6451b/sq in** 160 40' 70-72A TF1 129to4191b/sq in** 160 40' 68-70A TF3 129to2901b/sq in** 160 40' 80-85A TF3 32to641b/sq in** 160 40' 80IRHD "*•** (ATF3) TF1 Press closed but not 160 40' Part compacted but pressure not fully formed. V spongy. TF1 64.51b/sq in(ATFl) 160 40' 69 IRHD Fully formed *** TF2 32 lb/sq in(ATF2) 160 40' 72IRHD Fully formed *** TF4 321b/sq in 160 40' 90/95 A Formed/Bloomed TF5 <32Ib/sq in 160 40' 95+A Formed/ Slight Bloom 9 TF2 129to5161b/sq in** 160 40' 67-70A Fully formed * TFO represents the compacted rubber dust containing no additional sulphur. ** Due to expansion on curing, a range of moulding pressure is quoted. *** Slit to examine consistency. It was possible to form a complete moulding with all five of the formulations with moulding pressures between 6.8 Tons/sq in and approximately 321b/sq in. Formulations containing 0.5%, 1.0% and 5.00% added sulphur were found to form complete mouldings which were flexible. Formulations containing 10.0% and 25.0% added sulphur were found to be very stiff and brittle. These materials were very similar to ebonite rubber in nature. Stage 2: Evaluation of limits for Moulding timp and temperature This stage of the work involved an evaluation of the limits fro moulding time and temperature on the dust/sulphur mixture containing 1% added sulphur (TF2). Moulding Moulding in each case was carried out as detailed above and the samples were then assessed for completeness of moulding and apparent hardness. Each moulding was then sectioned, using a SAS slitting machine, and the quality of the internal surface finish was visually assessed to determine the degree of dispersion and compaction. Moulding trails were then carried out to cover a range of "low", medium" and "high" pressures, at a variety of moulding times and temperatures. In the initial phase of stage 2, the moulding pressure was set at 1291b/sq in. (Low pressure) and mouldings were carried out at the cure times and cure 10 temperatures as follows: Trial No. Cure Time(--nins) Cure Temp (°C) 1 20 160 2 10 160 3 60 160 4 40 140 5 40 130 6 40 160 7 40 120 8 20 130 9 40 100 13 20 100 19 40 170 20 20 170 In the second phase of Stage 2, the following samples were moulded at a pressure of 6451b/sq in, (Medium pressure) at the time and temperatures indicated below. Trial No. Cure Tme(mins) Cure 10 40 120 11 20 130 12 40 100 14 20 100 21 40 170 22 40 140 In the third phase of Stage 2, the following samples were moulded at a pressure of 1270 lb/sq in, (High pressure) at the times and temperatures indicated below: 11 Trial No. Cure Time(mins) Cure Temp (°C 15 20 160 16 40 140 17 40 120 18 20 100 The results of phases 1 to 3 of stage 2 are shown in Table 2. TABLE 2 STAGE 2: Evaluation of Cure Time and Cure Temperature on formulation TF2 (1% added sulphur mixture) Test Mould Press Cure Time Cure Temp Hardness Comment (lb/sq in) (mins) (°C) (IRHD) 19 129 40 170 73 Smooth slit surface 20 129 20 170 72 Smooth slit surface 1 129 20 160 74 Smooth slit surface 2 129 10 160 70 Slit surface broken up 3 129 60 160 73 Smooth slit surface 6 129 40 160 72 4 129 40 140 73 5 129 40 130 68 8 129 20 130 67 Rougher/pitted surface 7 129 40 120 66 9 129 40 100 62 13 129 20 100 57 21 645 40 170 73 Smooth slit surface 22 645 40 140 74 II 11 11 645 20 130 69 Slit surface bitty & broken up 10 645 40 120 70 Rougher/pitted surface 12 12 645 40 100 65 Rougher/pitted surface 14 645 20 100 60 11 II II 15 1270 20 160 73 Slightly pitted 16 1270 40 140 73 II II 17 1270 40 120 68 Surface broken up 18 1270 20 100 58 Rougher/pitted surface Physical Testing In order to assess the basic physical properties of samples moulded under a range of curing times and temperatures, selected samples underwent tensile tests and compression set tests, in accordance with the methods detailed below. The tests also included samples prepared from different dust/sulphur mixtures which were moulded at very low pressure. Hardness Determination The hardness of each material was determined in general accordance with BS903 Part A26 Normal Hardness Method: 1995. Each material was placed into a Wallace Normal hardness apparatus calibrated to the requirements of the specification, five hardness readings were taken on the moulded surface, and the median calculated. Tests were carried out on the disks as supplied and hence the results are quoted as apparent hardness. Tensile Properties: For each of the materials supplied five type 2 dumb-bells conforming to the requirements of BS903 Part A2 1995 were prepared. The test pieces were dimensioned before being placed in turn into a Nene universal tensile tester set at a speed of 500mm/.min and the elongation at break being recorded by use of a Wallace optical extensometer. From the graphs obtained the maximum tensile 13 strength, modulus values and elongation at break were recorded. Compression Set: Three type B test pieces were rotary cut from each moulded plaque. These were dimensioned before being placed into lubricated compression plates and compressed by 25% of their original thickness. They were then placed into an oven set at 70 + 2°C for a period of 24 hours after which time they were removed from the oven and released from the compression plates. They were then allowed to recover at 23 ± 2°C for 30 mins before being dimensioned at the percentage set calculated in accordance with BS 903 Part A6: 1992. Ambient temperature was maintained at 23°C + 2°C and all equipment used was calibrated to the accuracy required in the appropriate standard. The physical properties achieved are shown in Table 3. Table 3 Property /Parameter Sample (Trial No) ATF1 ATF2 ATF3 19 1 4 7 13 10 14 16 O Mould Press (lb/sq in) 63 32 32 129 129 129 129 129 129 129 645 645 1270 Cure Temp (°C) 160 160 160 170 160 160 160 140 120 100 120 100 140 z- Cure Time (mins) 40 40 40 40 60 40 20 40 40 20 40 20 40 V Apparent Hardness H H (IRHD) 69 72 80 73 73 72 74 73 66 57 70 60 73 H Tensile Strength (Mpa) 3.55 5.82 5.6 7.7 6.9 5.5 7.03 6.87 2.12 0.82 2.93 0.89 6.4 -*- t-β 50% Modulus (Mpa) 1.4 1.6 3.3 1.6 1.6 1.5 1.77 1.77 1.28 - 1.3 0.89 1.6 100% Modulus (Mpa) 2.4 3.2 - 2.9 3.1 2.9 3.25 3.22 1.98 - 2.3 - 3.1 H 150% Modulus (Mpa) 3.7 5.3 - 5.0 5.2 4.7 5.45 5.24 - - - - 5.2 CjU Elongation at Break (%) 150 160 75 205 180 170 180 190 115 50 135 50 180 Compression Set (%) 26.4 22.5 19.4 21.0 21.7 29.4 32.6 39.4 42.5 47.7 47.1 48.6 33.3 (24 Hrs @ 70°C) ATF1 = Mixture containing 0.5% added sulphur ATF2 = Mixture containing 1.0% added sulphur ATF3 = Mixture containing 5.0% added sulphur n H CO © © 00 v© 14 The above description of experimental trials is intended to be by way of example only. The skilled person will immediately appreciate that the process can be used in a larger industrial moulding plant by a simple scaling up of the amounts of the ingredients in the mixture. Proportions, temperatures, pressures and other parameters specified in the appended claims will remain substantially the same. Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims: 15 CLAIMS 1. A process for the production of a rubber product, the process comprising forming a moulding material from a first ingredient comprising powdered rubber and a second ingredient comprising sulphur and compressing the moulding material in a mould to form said rubber product. 2. A process according to claim 1 wherein the moulding material is compressed in said mould to a pressure of up to substantially 6.8 tons per square inch. 3. A process according to claim 1 wherein the moulding material is compressed in said mould to a pressure in the range of substantially 2psi to substantially 6.8 tons per square inch. 4. A process according to claim 1 wherein the moulding material is compressed in said mould to a pressure in the range of substantially 129psi to substantially 6.8 tons per square inch. 5. A process according to claim 1 wherein the moulding material is compressed in said mould to a pressure in the range substantially 129psi to substantially 1270psi. 6. A process according to claim 1 wherein the moulding material is compressed in said mould to a pressure in the range of substantially 380psi to substantially 1270psi. 7. A process according to any preceding claim wherein the temperature of the moulding material is elevated during compression. 8. A process according to claim 7 wherein the temperature of the moulding material is elevated to be above 100°C during compression. 16 9. A process according to claim 7 wherein the temperature of the moulding material is elevated to be in the range of substantially 100°C to substantially 170°C during compression. 10. A process according to claim 7 wherein the temperature of the moulding material is elevated to be in the range of substantially 120°C to substantially 170°C during compression. 11. A process according to claim 7 wherein the temperature of the moulding material is elevated to be in the range of substantially 140°C to substantially 170°C during compression. 12. A process according to claim 7 wherein the temperature of the moulding material is elevated to be in the range of substantially 160°C to substantially 170°C during compression. 13. A process according to any preceding claim wherein the moulding material is compressed for at least substantially 10 minutes during moulding. 14. A process according to claim 13 wherein the moulding material is compressed for up to substantially 60 minutes. 15. A process according to claim 13 wherein the moulding material is compressed for a period of time of between substantially 10 minutes and substantially 60 minutes. 16. A process according to claim 13 wherein the moulding material is compressed for a period of time of between substantially 20 minutes and substantially 60 minutes. 17. A process according to claim 13 wherein the moulding material is compressed for a period of time of between substantially 40 minutes and substantially 60 minutes. 17 18. A process according to any preceding claim wherein the amount of sulphur in the moulding material is in the range of substantially 0.5% w/w to substantially 2.5% w/w with respect to the weight of the first ingredient. 19. A process according to any of claims 1 to 17 wherein the amount of sulphur in the moulding material is in the range of substantially 0.5% to substantially 10% w/w with respect to the weight of the first ingredient. 20. A process according to any of claims 1 to 17 wherein the amount of sulphur in the moulding material is in the range of substantially 0.5% w/w to substantially 5% w/w with respect to the weight of the first ingredient. 21. A process according to any of claims 1 to 17 wherein the amount of sulphur in the moulding material is substantially 0.5% w/w, substantially 1% w/w, or substantially 5% w/w with respect to the weight of the first ingredient. 22. A process according to any of claims 2 to 6 which includes a pre- compacting step prior to the step of compressing the moulding material. 23. A process according to claim 22 wherein the pre-compacting step involves applying a pressure of above substantially 64psi. 24. A process according to claim 22 wherein the pre-compacting step involves applying a pressure in the range of substantially 64psi to substantially 1935psi. 25. A process according to claim 22 wherein the pre-compacting step involves applying a pressure in the range of substantially 129psi to substantially 1905 psi. 26. A process according to claim 22 wherein the pre-compacting step involves applying a pressure of substantially 1905psi or substantially 1935psi. 18 27. A process according to any preceding claim wherein the sulphur is in a powder form, the sulphur and rubber being thoroughly mixed to form a substantially uniform mixture. 28. A process according to any preceding claim wherein the second ingredient comprises a powdered sulphur having a particle size in the range of substantially 300 mesh or finer. 29. A process according to any preceding claim wherein the first ingredient comprises a powdered rubber having a particle size in the range of substantially 16 mesh to substantially 300 mesh. 30. A process according to claim 29 wherein the first ingredient comprises a powdered rubber having a particle size in the range of substantially 16 mesh to substantially 50 mesh. 31. A process according to claim 29 wherein the first ingredient comprises a powdered rubber having a particle size of substantially 40 mesh. 32. A process according to any preceding claim wherein the first ingredient comprises up to 100% powdered rubber. 33. A process according to claim 32 wherein the first ingredient comprises powdered rubber and a fibrous material. 34. A process according to any preceding claim wherein the second ingredient comprises powdered sulphur in a carrier. 35. A process according to claim 32 wherein the carrier is a mineral oil.

Inventors: BLOOD PHILLIP, FARMER ANTHONY LEWIS, BLOOD, PHILLIP, FARMER, ANTHONY, LEWIS
Applicants: BLOOD PHILLIP, FARMER ANTHONY LEWIS, BLOOD, PHILLIP, FARMER, ANTHONY, LEWIS
Application year: 1999
Main classification: B29C43
IPC codes: B29C43