RECYCLING OF VULCANIZED RUBBER PRODUCTS

Abstract

The invention relates to a process for recycling used rubber product, such as tires and/or other rubber products, containing the step of treating the rubber grind obtained by grinding the used rubber products, in the presence of a weak base and butadiene/styrene copolymer as well one or more additives to a shear stress of at least 15 to 25 MPa. The invention relates furthermore to re-vulcanizable re-rubber blend obtained by the process according to the invention and also to the tires and other rubber products obtained by vulcanizing thereof.

Claims

1-15. (canceled)

16. A process for the recycling of used vulcanized rubber products comprising the step of exposing the rubber grind obtained by processing the used vulcanized rubber containing products, in the presence of a weak base selected from the group consisting of alkaline earth metal hydroxides, and butadiene/styrene copolymer and one or more additives to a shear force of at least 15 to 25 MPa, wherein the weak base, the butadiene/styrene copolymer and the one or more additives are added to the rubber grind in the form of a mixture, wherein the amount of the weak base in the mixture is from 5 to 50 weight %, the amount of the butadiene/styrene copolymer is 2-40 weight %, and the amount of one or more additives is 10 to 70 weight %.

17. The process according to claim 16, wherein the weak base is selected from the group consisting of Ca(OH).sub.2, Mg(OH).sub.2 and mixtures thereof.

18. The process according to claim 16, wherein the butadiene/styrene copolymer is a butadiene/styrene copolymer containing 40 to 60 weight % of styrene.

19. The process according to claim 16, wherein the one or more additives are selected from the group consisting of bitumen, Na.sub.2CO.sub.3 and mixtures thereof.

20. The process according to claim 16, wherein the mixture of the weak base, the butadiene/styrene copolymer, and one or more additives is mixed with the rubber grind in a quantity of from 5 to 25 weight %, and the resultant mixture is exposed in an extruder to a shear force of at least 15 to 25 MPa.

21. The process according to claim 20, wherein a well-tightened extruder is used, wherein the extruder has a slot distance of 0.02 to 0.05 mm.

22. The process according to claim 20, wherein the mixture is passed through the same extruder several times, or passed through a series of several extruders sequentially coupled.

23. The process according to claim 20, wherein a cooled-heated extruder is used and the temperature of the mixture is adjusted to 60-80 C. by cooling or heating.

24. The process according to claim 16, further comprising the step of mixing one or more rubber industry additives with a mixture obtained after treating under the shearing force, and then vulcanizing said resulting mixture.

25. The process according to claim 16, comprising the steps of: used tires and/or other rubber products are cut and milled to a size of 2 to 4 mm for the production of a rubber grind, to the rubber grind weak base, a butadiene/styrene copolymer, and one or more additives are added, optionally in the form of a master blend, the resulting mixture is homogenized at 15 to 51 C. for 10 minutes to 2 hours to produce a homogenized mixture, the homogenized mixture is passed through an extruder at 50 C. to 150 C., the passage through the extruder is optionally repeated 2 times to 10 times, the re-rubber blend lead from the extruder is homogenized in a roll to produce a homogenized re-rubber blend, and to the homogenized re-rubber blend, optionally one or more rubber industry additives are added to produce are-vulcanizable re-rubber blend, the vulcanizable re-rubber blend is vulcanized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0026] The terms used in this specification are to be understood as follows:

[0027] processing of used vulcanized rubber containing (elastomeric) products means the management of used tires and/or other rubber products by grinding and subsequent firing or by use for secondary purposes;

[0028] recycling of used vulcanized rubber containing (elastomeric) products means the management of used tires and/or other rubber products by treatment with the process according to the invention, and then by re-vulcanization as a tire and/or by use as other rubber product;

[0029] tire means a product obtained by vulcanizing and shaping a rubber blend containing rubber and/or artificial rubber and one or more conventional additives using a method known to a person skilled in the art, said product being applicable as a rubber tire in the motor vehicle industry;

[0030] rubber product means a product obtained by vulcanizing and shaping a rubber blend containing rubber and/or artificial rubber and one or more conventional additives using a method known to a person skilled in the art, said product being applicable as a product other than a tire;

[0031] rubber blend means a mixture containing rubber and/or artificial rubber and one or more conventional additives;

[0032] re-rubber blend means a composition containing a rubber grind treated with the method according to the present invention and one or more conventional additives;

[0033] vulcanization means the curing of a rubber blend by conventional heat treatment;

[0034] re-vulcanization means the vulcanization of a blend of a re-rubber according to the invention;

[0035] base means an alkaline material suitable for the chemical decomposition of the cured structure obtained by vulcanization;

[0036] master blend means the composition of a weak base and butadiene/styrene copolymer and one or more additives;

[0037] shear force means the force present at shear stress, where the shear stress is a force acting in the plane of the cross section of a body, in this case the particle size of the rubber grind, which unit of measure is MPa.

[0038] Accordingly, the invention relates to a process for the recycling of used vulcanized rubber (elastomeric) containing products, wherein the rubber grind obtained by processing used vulcanized rubber containing (elastomeric) products, such as tires and/or other rubber products, in the presence of a weak base and butadiene/styrene copolymer and one or more additive material is exposed to a shear force of at least 15 to 25 MPa.

[0039] According to the present invention, the used tire is any tire that can be produced by curing and shaping a rubber blend containing rubber and/or artificial rubber and one or more conventional additives using a method known in the art, and which can be used as a tire in the automotive industry.

[0040] According to the invention, the used rubber product is any rubber product that can be produced by vulcanizing and shaping of a rubber blend containing a rubber and/or artificial rubber and one or more conventional additives by a method known to a person skilled in the art, and which can be used as a product other than a tire.

[0041] Used rubber products can be, for example, a rubber conveyor belt, an air spring, a tube compensator, a technical hose, a conveyor belt, a drive belt, an extruded mold, a rubber thread, a plate product, an extruded product, a rubber insulated cable and the like.

[0042] For processing the used tire and/or rubber product, the tire and/or rubber product is cut, for example, to a size of 1 to 10 cm, in particular 2 to 8 cm. The cut tire and/or rubber product is ground, to a size for example, 1 to 8 mm, in particular 2 to 4 mm. Grinding can be carried out with any grinding device, for example, crown gear grinding rod-grinding, beating cross grinding, jet grinding and knife-hummer grinding equipment. The knife-hummer grinding apparatus is preferably applicable.

[0043] The particle size obtained by grinding is checked by standard grading, for example by shaking sieve grading.

[0044] The resulting grind is physically separated from the eventual components built in that in the case of a tire may be such as metal cord, synthetic fabric and the like (EP2877329B1).

[0045] By use of said processing a rubber grind is obtained, which can be used as a starting material for the process of the present invention.

[0046] To the rubber grind a master blend comprising the weak base, butadiene/styrene copolymer, and one or more additive is added.

[0047] The weak base is usually selected from alkaline earth metal hydroxides, for example Ca(OH).sub.2, Mg(OH).sub.2 and their mixtures, especially Ca(OH).sub.2.

[0048] The amount of the base is generally 5 to 50 weight %, especially 20 to 50 weight % based on the weight of the master blend.

[0049] As butadiene/styrene copolymer a butadiene/styrene copolymer containing 40 to 80 weight %, in particular from 50 to 60 weight % of styrene may be used. By varying the styrene content, the Mooney's viscosity of the copolymer can be set within a wide range of limits. Preferably, a butadiene/styrene copolymer having Mooney's viscosity ranging from 40 to 80 Mooney degrees can be used. Measurement of Mooney viscosity can be accomplished using a Mooney shear disc viscometer, by a measurement method widely used in the rubber industry to determine the viscosity and apparent viscosity of the mixtures.

[0050] The amount of the butadiene/styrene copolymer generally ranges from 2 to 40 weight %, in particular from 10 to 30 weight % based on the weight of the master blend.

[0051] The master blend also contains various additives, for example, plasticizers, lubricants, and the like.

[0052] As plasticizer bitumen and an inorganic plasticizer, such as Na.sub.2CO.sub.3 and mixtures thereof can be used.

[0053] The applicable lubricants include various soaps, in particular Na-stearate, Ca-stearate, Zn-stearate, and mixtures thereof.

[0054] One or more of the above additives may be used. The amount of the additive is from 10 to 70 weight %, in particular 20 to 60% by weight, based on the weight of the master blend.

[0055] The amount of master blend is 5-25 weight %, especially 8-15 weight %, based on the rubber grind.

[0056] The rubber grind and the master blend is homogenized by stirring at a temperature of 15 C. to 50 C., in particular 25 C. to 30 C. and under normal pressure for 10 minutes to 3 hours, especially for 30 minutes to 2 hours.

[0057] The homogenized mixture is subjected to a shear force. The shear force applied exceeds the original tensile strength of the rubber. Accordingly, the applied shear force is at least 15 to 25 MPa, in particular at least 18 to 20 MPa, where the preferred value is 25 to 35 MPa.

[0058] The function of the shear force is to expose the rubber to a force exceeding its tensile strength, thereby physically removing the polymeric chains. The original tensile strength of the rubber is 15 to 25 MPa, in particular 18 to 20 MPa. Tensile strength can be determined, for example, according to DIN 53504 and ISO 37 standards.

[0059] The shear force treatment can be achieved by any known means, for example by means of an extruder, a knife mixer, a roller, and the like.

[0060] In one embodiment of the invention, the homogenized mixture is introduced into an extruder and the shear force is exerted by passing through the slots. In order to exert the appropriate shear force, well-tightened extruder is used, whereby the slot distance, that is the distance between the screw ridge and the wall of the extruder is 0.02 to 0.05 mm, in particular 0.03 to 0.04 mm. During the passage through the extruder, the mixture temperature rises to 50-100 C. The passage through the extruder is repeated 2 to 10 times. This can be accomplished by passing the mixture several times through the same extruder, or passing it through consecutive series of several extruders.

[0061] In another embodiment, a cooled-heated extruder is used and the temperature of the mixture is adjusted to 60-80 C. by cooling or heating.

[0062] The treatment with shear force will be performed until the formation of re-vulcanizable re-rubber blend (see below). To determine the endpoint of the treatment, a sample is obtained from the resulting mixture, it is vulcanized and checked for tensile strength of the mixture. In the case of tensile strength below the limit value, the mixture is returned to the extruder and the treatment with the shear force is repeated.

[0063] In one embodiment of the invention, after the shear force is applied, the treated mixture is homogenized again at 30 C. to 100 C., especially 50 C. to 80 C. for 10 to 60 minutes, especially 15 to 50 minutes. The repeated homogenization can be accomplished by passing between a pair of rolls or by mixing. For the passage between the pair of rolls, preferably a roller having a slot of 0.0520 mm, preferably 0.0815 mm, is used, wherein the difference between the roll speeds, i.e. the friction value is 1.05 to 3.5, preferably 1.5 to 3.2.

[0064] In another embodiment of the invention, the resulting mixture may optionally be filtered. This can be accomplished after applying the shear force and/or after the repeated homogenization. The filtration is carried out in the usual manner. According to one embodiment of the invention, the filtration is carried out using a metal mesh screen having a puncture of 0.5 to 1.5 mm, preferably 0.8 to 1.0 mm.

[0065] After the treatment with shear force, a re-rubber blend is obtained, which shows a great similarity in its physico-chemical properties to the properties of the conventional rubber blends. Accordingly, the re-rubber blend can be vulcanized in the conventional manner, and can be processed into tires or other rubber products. The physical properties of the thus obtained re-vulvanized rubber are the same as, or at least approximate to, the physical properties of the original vulcanizates. Examples of such physical properties include Shore hardness, which value is 58 to 63 Sh (for the original vulcanizates it is 65 to 70 Sh), where the measuring method is DIN 53505, ISO 48; the tensile strength, which value is 15 to 17 MPa (for original vulcanizates it is 18 to 20 MPa), where the measuring method DIN 53504, ISO 37; elongation at breakage, which value is 500 to 600% (for original vulcanizates it is 550 to 650%), where the measuring method DIN 53504, ISO 37.

[0066] Without wishing to be bound to a particular theory, it is assumed that the cross-linking structure formed by the original vulcanization disintegrates by the combined application of the base and the shear force. In particular, the long polymer chains break into shorter chains and the sulfur-sulfur bridges between the chains (SS) open. This can also be considered as the reversal of the vulcanization process, as a result of which, by the treatment according to the present invention, a blend physically and chemically similar to the original rubber blend prior to the vulcanization, so-called re-rubber blend can be obtained from the used tire and/or rubber product. The re-rubber blend can be used as a rubber industry starting material that is it can be converted into tires or other rubber products by conventional re-vulcanization.

[0067] The re-rubber blend contains the residues of the master blend and the residues of rubber additives introduced with the rubber grind. However, optionally the re-rubber blend may be mixed with various rubber additives, such as rubber industry additives conventional for rubber blends.

[0068] Examples of rubber industry additives include activators, plasticizers, sulfur and sulfur donors, soot, anti-aging agents, sunscreen agents, accelerators, and the like. Examples of activators include metal oxides, in particular zinc oxide. Examples of plasticizers include sodium carbonate. Examples of anti-aging inhibitors include antioxidants, phenolnaphthylamines, especially aldo alpha naphthylamine, phenyl alpha naphthylamine, phenyl beta naphthylamine; mono- and multicyclic phenols, especially 2,6-di-tert-butyl-4-methylphenol, styrenated phenols, 2,2-methylene bis(4-methyl-6-tert-butylphenol), 2,2-methylene bis(4-methyl-6-cyclohexylphenol); thiophenols, in particular 4,4thio bis(3-methyl-6-tert-butylphenol) and the like. Examples of sunscreen products include dialkyl or alkylaryl phenylenediamines such products branded as Protektor, Antilux or Okerin. Examples of accelerators include dithiocarbamates, xanthans, thiurams, benzothiazoles, benzothiazyl sulfonamides and dithioureas.

[0069] The amount of rubber industry additives is generally in the range of 2 to 6 weight %, especially 3 to 5 weight %.

[0070] In one embodiment, in the method according to the invention the following steps are taken: [0071] used tires and/or other rubber products are cut and milled to a size of 2 to 4 mm for the production of a rubber grind, [0072] to the rubber grind a master blend containing a weak base, butadiene/styrene copolymer, and one or more additives are added, [0073] the resulting mixture is homogenized at 15 to 51 C. for 10 minutes to 2 hours to produce a homogenized mixture, [0074] the homogenized mixture is passed through a well-tightened extruder at 50 C. to 100 C., [0075] the passage through the extruder is optionally repeated 2 times to 10 times, [0076] the re-rubber blend lead from the extruder is homogenized in a roll to produce a homogenized re-rubber blend, and [0077] to the homogenized re-rubber blend, optionally one or more rubber industry additives are added to produce a re-vulcanizable re-rubber blend.

[0078] The invention relates to a mixture of re-vulcanizable material composition comprising rubber and/or synthetic rubber and, optionally, one or more rubber industry additives, said material composition being obtainable by the process of the present invention.

[0079] The invention also relates to the use of the material composition according to the invention for the manufacture of a tire or other rubber product.

[0080] The re-vulcanization of the re-rubber blend is carried out using the conventional vulcanization process (Rubber Industry Manual, Volume I, Editor-in-Chief, Dr. Lszl Bartha, Taurus Omikk, Budapest, 5.8, p. 394 to 411).

[0081] For example, in order to re-vulcanize the re-rubber blend, the desired rubber industry additives are added to the re-rubber blend, the mixture is homogenized on a roll and vulcanised at a desired temperature in the vulcanization press. In order to determine the end point of vulcanization, a sample from the rubber product is taken, and the tensile strength of the product is checked.

[0082] By the re-vulcanization of the re-rubber blend, it is possible to produce tires and other rubber products, such as rubber conveyor belts, an air spring, a pipe compensator, a technical hose, a conveyor harness, a drive belt, an extruded mold, a rubber string, a plate product, an extruded product, rubber insulated cables and the like.

[0083] The invention also relates to a tire or other rubber product, which can be produced by vulcanizing the material composition according to the present invention.

[0084] The invention further relates to a method for producing a tire or other rubber product comprising the step of vulcanizing a material composition according to the invention.

[0085] The process according to the invention can be practiced in conventional equipment. Examples include containers, dispensers, grinders, shredders and/or granulators, mixers, extruders, delivery devices, and the like.

[0086] The device suitable for re-vulcanizing of the re-rubber blend is identical with the conventional vulcanizing apparatus. Such a device includes, for example, a hydraulic press tool equipped with heatable plates, which includes the vulcanization tool of the desired size.

[0087] The invention will be further illustrated by the following examples without limiting the scope of the present invention thereto.

EXAMPLE 1

Preparation of a Master Blend

[0088] To prepare a master blend necessary for 90 kg tire grind, 3 kg of Ca(OH).sub.2, 2 kg of bitumen, 2 kg of butadiene/styrene copolymer granules containing 60 weight % of styrene, and 3 kg of Na.sub.2CO.sub.3 is mixed, and the mixture is stirred at ambient temperature for 1 hour.

EXAMPLE 2

Preparation of Master Blend

[0089] To produce a master blend necessary for 90 kg tire grind, 0.5 kg of Mg(OH).sub.2, 5 kg of bitumen, 2.5 kg of butadiene/styrene copolymer granules containing 40 weight % of styrene and 2 kg of Na.sub.2CO.sub.3 is mixed, and the mixture is stirred at ambient temperature for 40 minutes.

EXAMPLE 3

Production and Re-Vulcanization of Re-Rubber Blend

[0090] The master blend and tire grind according to Example 1 was filled into a single screw extruder with a slot distance of 0.03 mm and dispersed for 40 minutes at 68 C., then passed through a friction grade 1.2 roller over a period of 30 minutes. The resultant rubber blend was blended to homogeneity with 1 weight % sulfur, 1 weight % mercaptobenzthiazole and 0.1 weight % soot, and vulcanized at 170 C. for 5 minutes at a pressure of 160 bar in a press oven apparatus.

EXAMPLE 4

Production and Re-Vulcanization of Re-Rubber Blend

[0091] The master blend and tire grind according to Example 2 was filled into a single screw extruder with a slot distance of 0.045 mm and dispersed for 30 minutes at 60 C. and passed through a friction grade 1.2 roller over a period of 30 minutes. The resulting re-rubber blend was vulcanized as described in Example 3.

EXAMPLE 5

Production and Re-Vulcanization of Re-Rubber Blend (Using an Extruder Other than Well-Tightened Extruder) (Comparative Example)

[0092] The mixture (master blend and rubber grind) as described in Example 4 was filled into a single-screw extruder (slot distance greater than 0.1 mm), dispersed for 30 minutes at 60 C., and passed through a 1.2 friction value roller over a period of 30 minutes. The resultant re-rubber blend was blended to homogeneity with 1 weight % sulfur, 1 weight % mercaptobenziazole and 0.1 weight % soot, and vulcanized at 170 C. for 5 minutes at a pressure of 160 bar in a press oven apparatus.

EXAMPLE 6

Production and Re-Vulcanization of Re-Rubber Blend (Using a Polymer Other than Butadiene/Styrene Copolymer) (Comparative Example)

[0093] In the same manner as in Example 1, a master blend was prepared and mixed with a rubber grind, except that polystyrene granules (rhenostyrol, manufacturer: Aikolon) were used instead of butadiene/styrene copolymer granules. With the resulting master blend a re-rubber blend was produced and it was re-extruded as described in Example 3.

EXAMPLE 7

The Technical Properties of the Re-Vulcanized Rubber According to Examples 3-6

[0094]

TABLE-US-00001 Physical property Example 3 Example 4 Example 5 Example 6 hardness (Sh ) 61.3 58.6 45-52 35-45 tensile strength (MPa) 16.3 15.2 1.5 1.2 elongation at 550 510 52 40 breakage (%)

[0095] From the data in the table, it can be seen that the technical properties of the re-vulcanized rubber in Examples 3 and 4 according to the invention correspond to the properties of the conventional rubber blends.

[0096] The exact measurement of the hardness of the test sample obtained in Comparative Example 5 is difficult due to the high permanent deformation of the vulcanizate. The measured value fluctuated from 45 (Sh) to 52 (Sh). The tensile strength decreased to 1.5 MPa. The elongation at break just reached 52%, which showed a high level of uncertainty.

[0097] With the test sample obtained in Comparative Example 6, a further deterioration of the physical-mechanical data was observed. The hardness further deteriorated as compared to Example 5 from 35 (Sh) to 45 (Sh). The tensile strength was only 1.2 MPa. The tensile elongation became irrelevantly low, showing a value below 40%.

[0098] The solution according to the present invention allows economical and environmentally friendly disposal of second-hand tires and/or other rubber products, and their recycling in the rubber industry. The present invention therefore significantly reduces the environmental impact of used tires and/or other rubber products, while simultaneously reducing the demand for fresh raw materials for the rubber industry.