THERMOPLASTIC RUBBER OBTENTION METHOD

Abstract: A method is disclosed for obtaining a thermoplastic rubber, from raw materials which comprehend used rubber artifacts, like tires and other rubber products, devulcanized by means of physical, chemical, or physico-chemical process, transformed into a uniform and regular batch, which is blended to a thermoplastic, thus obtaining a thermoplastic rubber for diversified industrial applications.

Description: THERMOPLASTIC RUBBER OBlENTlON METHOD The present invention is related to new method for obtaining a thermoplastic rubber, using as main products the devulcanized rubber or rubbers of Little vulcanizing, along with a thermoplastic. The thermoplastic rubber is already known, since the last century, under the names of gutta-percha, balata ou chicle. It is a form of IRANS 1 - 4 poiyisoprene, obtained fro the latex of one sapotacea. differing of the natural rubber, wich is the form of CIS 1 - 4 poiyisoprene. The gutta-percha is a hard, low elongation, low water permeabili y and high dieletric resistance product. It has e n used for many y<_ar . in the coating of eletric cables, namely submarine cables, golf balls, heat-sealing adhesive- . chewing gums, varnishes, etc, along with a various applications in dental treatment. With the devellopment or the synthetic polymers, appeared the rRANS-polyisoprene and the TRANS-polybutadiene with characteristics approachi g those of the natural polymers. They can be vulcanized, resulting in a product more or less crystall ne wich keeps the deformation at ambient temperature, being recoverable by heating. They are reinforced with carbon black, acquiring exeLent abrasion resistance, thus being applied in heels, soles, pavements, gaskets, sponges, golf balls, battery cases, etc. New kinds of polymers were also develloped, now no more in the TRANS 1 - 4 form, like the by-pr-oducts of the POLYUKL"IHA LS, POLYt. l I-KG, CI 11.ENICC a d OLEFINICS. Iho most used are the STIRENIC thermoplastic rubbers, followed by the OLEFINICS and POLYESTERS. The polyur eLhanes, due to their high cost, are used only in very rare and specific cases. The main use of thermoplastic rubbers is in the manufacture of heels and soles, gaining back large slice of the market that haε been absorbed by _..«_ poJyvi yl chloride ( V ) . As is of general knowledge. the processing of plastic: i . much more economic than the processing 01 " the. conventional rubber, since it is not neices-. at y to vulcanize, the plastic and the process burrs may _e uι;ed anew, with Lhe same characteristics of the original product. The rubber in its natural state is composed of different products, wich are blended, homogenized, allowed to rest for 24 hours, pre-molded. vulcanized and, finally, burred. The burrs and vulcanization left-overs Ara not ready re-usable, and they have to be reclaimed. The vulcanization transforms the rubber blend from a plastic state into an elastic state, and it does not return to the plastic state, as ' is the case of plastics, by means of mere heating. Only in rare cases, when the thermoplastic is cured. its burrs cannot be re-used by mere heatinq. It is necessary to uncure them, a process akin to devulcanization. Thus. the main application of the. thermoplastic rubber, after blending, is to be processed, without the need to vulcanize it, and left-overs and the burrs may return to the initial procesε. Although there are many kinds o1 thermoplastic rubbers Mis¬ applications in industry. the price factor keeps some restriction'-" to thc.ii use. πhinlJy because ol the difficulti s that thermoplastics show on beinu biendeo with pigments that, would manLain or enhance the characteris ics. The inventor develloped a simple method tor the manufacturing of thermoplastic rubber wich fulfills not only the product quality requirement, but also the econo ic one, that is, producing it from a pientyful and problematic raw material, wich is the already vulcanized rubber artifact, like tires, leftovers or surplus of pre-vulcanized moldings, transforming it, blended with thermoplastics, in a Kind of thermoplastic rubber with- characteristics adequated tor being used in a rubber artifact. The al ready vulcanized rubber artifact undergoes a devulcanization process, physical, chemical or physico-chemical, being transformed into a regular and uniform batch, known as Regenerated Rubber. Reclaimed Rubber, Devulcanized Rubber or Devulcanized Rubber "Master atoh" . This devulcanized rubber is heated to the plastic melting point and blended with it. The batch thus obtained iε homogenized, its crosslinking degree is adjusted with vulcanizer agent, and thereafter cut into little pieces by a pelletization process. In thiε way it can be reprocessed as a normal thermoplastic. The present method can be carried out in two different ways: 1) putting all products into the mill at the same time, or; _.) putting them separeteiy. None of both forms alters substantially the end product, the choice depending only of the criteria and faccilities of the operator. As seen before, the process iε comprehended of a blending of devulcanized rubber with a thermoplastic, wich can be a poiyparaffine or a polyvinyl chloi ide, or any oth_r thermoplastic, adding or not other products, wich are selected as a function of the fin__ application characteristics, aε. Tor example. resins, vulcanizerε. oils, accelerators, retarders, pigments, dyers, dispersants. etc. Dϋterent compositions were prepeared: EXAMPLE 81: About 200 g of polypropylene were put into an open blender, heated to about 180°C. The temperature was adjusted in a way that the polypropylene waε totaly molten and adhering to the roll. About 200 g of devulcanized tire rubber, previously neated and laminated with dispersant product, were added little by little. After all rubber was added .to the batch, it was homogenized, cut into strips and pelletized. The product, after resting for 24 hours, was injected into a test mold and its characteristics were determined: DENSITY 1.013 g/cm 3 HARDNESS 85 Shore A TEAR STRENGHT 110 kg/cm 2 ELONGATION .-. 300 _; WEAR 400 cm 3 FLEXION > 5,000 N EXAMPLE #2: Into a manganese steel ball mill were put 200 g of pure rubber, already vulcanized, 1,200 g of toluene and 200 g of high density polyethylene. The batch was allowed to swell for 24 hours and thereafter the grinding started. After 48 hours it was removed from the mill and dryed. The product was put into a roll blender previously heaten to 180°C, melting point of the high density polyethylene, and integrally blended, i hereafter is wa homogenized with dispersant. aαent and the crossiinkig degree was adjusted with a curing aαent. The product, after resting for 24 hours was injected into a test mold and i s characteristics were determined: DENSITY 0.92 α/cm 3 HARDNESS t>0 Shore A TEAR STRENGHT 98 kg/cm 2 ELONGATION '.. 400 . WEAR 580 cm 3 FLEXION > 2.000 N EXAMPLE __: In an open blender were added 200 g of pre-vulcanized rubber and 2 g of bezoic acid, and the batch was homogenized. The product was cut into little pieces and put into a manganese steel ball mill, along with 1,200 g of trichioroethylene and 200 g of PVC. The batch was allowed to swell for 12 hours and thereafter the grinding started. After 48 hours the batch was removed from the ball mill and dryed. The product was put into a cilinder blender, pre-heated to the melting point of PVC, homgenized with a dispersant agent, had its crosslinking αegree adjusted and was cut into stripes. The product was thereafter pelletized and allowed to rest for 24 hours. Following this it was injected into a test mold and its characteristics were determined: DENSITY 1.030 g/cm 3 HARDNESS 61 Shore A 1 EAR STRENGHT 121.5 kg/cm 2 ELONGATION 432 % WEAR , 422 crrr FLEXION > 3,000 N

Claims: CLAI MS 1. A thermoplastic rubber obtention method usinci raw materiaLs that comprehend used rubber art facts, like tires and other devulcanized rubber products, characterized in that this rubber, devulcanized by meansa of a physical, chemical, or physico- chemical procesε, transformed into an uniform an regular batch, iε blended with a thermoplastic, thus obtaining a thermoplastic rubber for industrial applications. 2. A method, according to claim 1, characterized in that the thermoplastic rubber has its crosslinking degree adjusted, if necessary. 3. A method, according to claim 1, characterized in that the reclaimed rubber is heated to the melting point of the plastic and thereafter is homogenized and corrected with dispersant agent, resins, pigments, etc. and, afterwards, pelletized. 4. A method, according to claim 1, characterized in that the blending is made of 5 to 95 _■ in weight of devulcanized rubber, in relation to the ammount of thermoplastic.

Inventors: OLIVEIRA DA CUNHA LIMA LUIZ CA, OLIVEIRA DA CUNHA LIMA, LUIZ, CARLOS
Applicants: OLIVEIRA DA CUNHA LIMA LUIZ CA, OLIVEIRA DA CUNHA LIMA, LUIZ, CARLOS
Application year: 1991
Main classification: C08L17
IPC codes: C08L17