ELASTIC ARTICLE MANUFACTURE

Abstract: There is provided a process in which a vulcanised natural or synthetic rubber, containing less than 30 % by weight of filler material, is compounded in a rubber mill with between 5 and 30 by weight of unvulcanised, natural or synthetic rubber material including vulcanising agents, and is broken down (by repeatedly passing it through a narrow slit) until the maximum particle size is less than 5 mm. The broken down material can then be molded to form particles such as fatigue prevention mats for offices and factories, mats for the home and mats for use in horse boxes or cow barns. It is also possible to produce solid tyres for fork lift truck wheels, solid tyres for wheel barrows and tyres for small wheels or trolleys using the process of the present invention.

Description: ELASTIC ARTICLE MANUFACTURE Background to the Invention Elastic threads, tapes and rings that are used particularly in garments such as underwear, swimwear and nappies are typically made from material of high elasticity and low plasticity such as natural or synthetic rubber or thermoplastic elastomer. These materials include vulcanised natural rubber, synthetic polyisoprene, synthetic nitrile polymers, ethylene, propylene diene rubber (EPDM) based polymers, and polybutadiene polymer. Such elastic materials are typically white or at least light in colour, have talc on their surface and include only a small quantity, typically less than 30% by weight of filler. Inevitably during the production and conversion process of such materials, scrap material is produced. In general, scrap material produced during production and before vulcanisation can be recycled particularly where it is combined with more than 80% of virgin stock. However, after the rubber is vulcanised, unless the scrap material is in pieces that are sufficiently large for it to be used for other purposes, it is simply discarded and ends up in land-fill sites. Considerable work and activity has taken place to produce technology that can attempt to recover material from vehicle tyres. Tyres contain considerable quantities of metal and textile reinforcement and are also made from very different material than is used for elastic tapes and threads. Typically, the rubber material is heavily filled with more than 50% of carbon black and oil. The technology that has been developed to recover material rom tyres can produce vulcanised rubber crumb and a form of de-vulcanised reclaim which can be used as an additive in tyre- manufacture. Summary of the Invention According to the present invention there is provided a process in which a vulcanised, natural or synthetic rubber containing less than 30% by weight of filler material is compounded in a rubber mill with between 5 and 30% by weight of unvulcanised natural or synthetic rubber material including vulcanising agents and is broken down at least until the maximum particle size is less than 5 mm. Preferably, the rubber contains less than 25% by weight of filler material. Typically, the material resulting from the compounding in a mill is then put under pressure and heated in a mould to produce a vulcanised moulded article. When the compounded material is heated under pressure in a mould the unvulcanised natural or synthetic rubber including vulcanising agents acts as a binding agent and forms strong adhesive bonds with the broken down scrap, previously vulcanised, material as well as itself becoming vulcanised. Typically, the compounded material is heated to a temperature of between 120°C and 200°C in the mould to produce the vulcanised moulded article. Moulded articles such as fatigue prevention mats for offices and factories, mats for the home and mats for use in horse boxes or cow barns can be produced as can solid tyres for fork lift truck wheels, solid tyres for wheel barrows or tyres for small wheels or trolleys. As an alternative to moulding the compounded material, if it is compounded until the maximum particle size for the pre-vulcanised scrap rubber material is less than 0.4 mm it is possible to add such a compounded material back into virgin stock provided that the total content of the pre- vulcanised material is less than 10 to 20% by weight of the virgin stock to produce low-gauge rubber sheeting which can then be converted into elastic tapes, threads and rings. Depending upon the final product to be produced, the size to which the vulcanised material is broken down in the mill can vary depending upon the time on the mill, the temperature at which the milling is carried out and the gap between the mill rolls. In general, the longer the milling process the more finely the pre-vulcanised scrap material is ground and the smoother and more homogeneous the final moulded article. Increasing the milling time naturally reduces the throughput of the process and leads to greater cost so that, inevitably a compromise is reached depending upon the intended use of the material . The scrap vulcanised material can be mixed with unvulcanised rubber of the same properties, i.e. unvulcanised rubber which, after vulcanisation will produce the same modulus, tensile elongation, etc., as the scrap vulcanised material. However, it is also possible to compound the scrap vulcanised material with unvulcanised rubber having properties which are lower or higher in, for example, modulus tensile and elongation to give products with a range of properties. A typical temperature for the material during its compounding in the mill is between 20 and 75°C and, by compounding the rubber at this temperature it does not give rise to undesirable odours which can arise from high temperature grinding or de-vulcanisation processes. Typically, the mill roll gap is between 0 and 1 mm and preferably the amount of unvulcanised rubber material that is added in the compounding stage is 15 or 20% or between 10 and 20% by weight. The generally white or light coloured scrap material also leads to the finished product being able to be white or light coloured or, by adding dye during the compounding stage being able to be produced in a range of attractive colours. It is also possible to add a blowing agent during the compounding stage to be able to obtain foamed or sponge rubber products. Brief Description of the Drawing Fig. 1 is a schematic illustration of an example of a process according to the present invention. Detailed Description Figure 1 is a schematic representation showing the process steps according to one example of the present invention, in particular it shows an example of a scaled-up version of the process . Initially the constituent parts to be blended must be weighed, in order to ensure the correct composition is obtained. A wide range of blends are possible using the present invention. To keep costs down a high percentage of scrap (85%) and a low percentage of other additives is desirable. In this example, for approximately 25kg of final product, the weights of each component are as follows, scrap rubber at 21.25 kg (83%), unvulcanised rubber mix 3.75 kg (14.6%) and sulphur powder 0.6 kg (2.4%), giving a total of 25.6 kg. These components are mixed and undergo a pre-grind or shredding process in a shredding mill 1. The shredded material is then transferred to and held in a storage bin 2. Batches of the shredded material are fed to a grinding mill as required. The grinding mill includes a pair of mill rolls 4 and a hopper 3 positioned over the mill rolls to control the feed of the shredded material . The mill rolls are 84 inches (2.13m) wide, smooth rolls and are mounted so as to have a mill nip setting of 0.7mm ± 0.1mm. The mill friction ratio is set to between 1.4 and 1.0. Batches of the shredded material are fed between the mill rolls. Each batch is approximately 25 kg because each batch has to be manually lifted after it passes through the nip, as will be explained later on. Each pass through the nip takes 15 seconds . After the shredded material is passed through the mill nip it falls onto a conveyor 5 which conveys the shredded material to a bucket 6. Once the entire batch has been transferred to the bucket it is lifted to a bucket emptying position where it releases the shredded material back into the hopper 3 so that it can pass through the mill rolls again. Each batch of material is passed through the mill nip 15 times in order to give adequate blending and size reduction. After the 15 passes the material temperature reaches 70°C ± 5°C. After the final pass the material is spread in a layer about 2 cm thick and is left to cool to room temperature, which takes about 30 minutes. After cooling, the material is packed in plastic bags in 5 to 10 kg quantities and can be stored or shipped in this form to a moulding station. Typically moulding is conducted at a pressure of 3,500 psi (2.5 x 10.7 Pa) at a temperature of 140°C. Typically the moulding time is 20 to 25 minutes. In the table below the properties of a couple of samples made according to the process of present invention are given. Sample A was made using the mixture described above, 83% vulcanised scrap, 14.6% unvulcanised mixed rubber compound and 2.4% sulfur powder. Sample B was made using 85% vulcanised scrap and 15% unvulcanised mixed rubber compound. Both mixtures were moulded in a laboratory at a temperature of 143°C, under a pressure of 3,500psi, for 40 minutes. Clearly, Sample B with a higher proportion of unvulcanised mixed rubber compound is softer and has a lower modulus than Sample A but has a higher breaking point .

Claims: CLAIMS 1. A process in which vulcanised, natural or synthetic rubber containing less than 30% by weight of filler material is compounded in a rubber mill with between 5 and 30% by weight of unvulcanised natural or synthetic rubber material including vulcanising agents and is broken down at least until the maximum particle size is less than 5 mm. 2. A process according to claim 1, in which the rubber contains less than 25% by weight of filler material. 3. A process according to claim 1 or 2 , in which the material resulting from the compounding in a mill is then put under pressure and heated in a mould to produce a vulcanised moulded article. 4. A process according to claim 3, in which the material is heated to a temperature between 120 and 200°C in the mould. 5. A process according to claim 3 or 4, in which the moulded articles are fatigue prevention mats for offices and factories, mats for the home, mats for use in horse boxes or cow barns, solid tyres for fork lift truck wheels, solid tyres for wheel barrows or tyres for small wheels or trolleys . 6. A process according to claim 1 or 2 , in which the compounded material is compounded until the maximum particle size for the pre-vulcanised rubber material is less than 0.4 mm and then such compounded material is added into virgin stock provided that the total content of the pre-vulcanised material is less than 10 to 20% by weight of the virgin stock. 7. A process according to claim 6, in which the material is used to produce low-gauge rubber sheeting for conversion into elastic tapes, threads and rings. 8. A process according to any one of the preceding claims, in which the temperature of the material during its compounding in the mill is between 20 and 75°C. 9. A process according to any one of the preceding claims, in which the mill roll gap is between 0 and 1 mm. 10. A process according to any one of the preceding claims, in which the amount of unvulcanised rubber material that is added in the compounding stage is between 10 and 20% by weight. 11. A process according to any one of the preceding claims, in which a dye is added during the compounding stage . 12. A process according to any one of the preceding claims, in which a blowing agent is added during the compounding stage .

Inventors: FLYNN EDWARD, FLYNN, EDWARD
Applicants: FLYNN EDWARD, INNOVATIVE ELASTICS LTD, FLYNN, EDWARD, INNOVATIVE ELASTICS LIMITED
Application year: 2001
Main classification: B29B
IPC codes: B29B17, C08L19, C08L21