WO1993020132A1

WO1993020132A1 - Recycling tyres

Info

Publication number: WO1993020132A1
Application number: PCT/CA1993/000142
Authority: WO
Inventors: Kenneth R. Nichols
Original assignee: Intervest, Inc.
Priority date: 1992-04-01
Filing date: 1993-04-01
Publication date: 1993-10-14
Also published as: AU3884593A; GB9207161D0

Abstract

Thermoplastic compounds are made from scrap rubber material such as used vehicle tyres. The rubber material is ground to a particle size smaller than 10 mesh and is substantially free of moisture, metal particles and fabric particles. The ground rubber material is blended into molten thermoplastic polymeric material, and the resulting blend is heated according to a predetermined time and temperature profile. Additives such as deodorants, disersing agents, colouring agents, etc. may also be added to the blend.

Description

TITLE OF INVENTION RECYCLING TYRES

FIELD OF INVENTION The present invention is directed to the recycling of scrap vulcanized rubber, particularly in tyres, by combining scrap rubber with polymeric material, particularly scrap polymeric material, to form a thermoplastic material, which is itself recyclable. BACKGROUND TO THE INVENTION

Vehicle tyres represent a considerable disposal problem and considerable effort has been made to find ways to recycle such tyres. The rubber in tyres is a vulcanized ther oset and hence resists efforts to mix it with other materials.

It has previously been suggested to recycle such materials by incorporating the same into compositions. Representative examples of this prior art comprise U.S. Patents Nos. 3,027,599, 4,028,288, 4,665,101 and 4,795,603. Many of these proposals are impractical or otherwise do not take into account the problem posed by attempting to combine incompatible materials.

Three major problems exist with respect to processing of scrap rubber and these are a problem of odor, a problem of colour and a processing problem. All three problems have inhibited large scale incorporation of tyre rubber into useful products. The present invention solves these problems.

SUMMARY OF THE INVENTION In the present invention, scrap rubber, particularly from vehicle tyres, is combined with polymeric materials to form a thermoplastic material. This result is achieved by combining the scrap rubber with the polymeric material in a particular way, as described herein. DETAILED DESCRIPTION OF THE INVENTION The invention is particularly concerned with recycling tyre crumb rubber, but the technique may be employed with other scrap rubber material. The scrap rubber first is sized to be less than about 10 mesh particle size, preferably about 10 to about 40 mesh particle size. Within this range, the smaller particle sizes permit larger quantities of the tyre crumb to be present in the thermoplastic material than the larger particle sizes.

The tyre crumb also contains moisture up to no more than about 2 wt%, preferably less than about 1 wt%. The tyre crumb is generally freed of steel preferably greater than about 98.5% free, more preferably greater than about 99% free. The crumb also is generally fabric free, preferably greater than about 95% free.

The grinding of the tyres to form the tyre crumb preferably is effected by grinding to the desired particle size in an ambient temperature operated mill which employs an ordered heat input, so that the temperature does not exceed about 230°F and subsequently is cooled down to about 120*F, so that the residual moisture content is below about 2 wt% and hence a separate drying operation is unnecessary. The polymeric material with which the tyre crumb is combined may be any convenient thermoplastic polymeric material, and may be a mixture of such materials. The thermoplastic polymeric material may be virgin polymeric material or, more preferably, scrap post-industrial thermoplastic polymeric material and scrap post-consumer thermoplastic polymeric material. Specific polymeric materials which may be utilized herein includes high density polyethylene, low density polyethylene, linear low density polyethylene, polypropylene homopolymer or copolymers and ethyl-vinyl acetate. The thermoplastic polymeric material generally comprises at least about 30 wt% of the combined product, with the balance comprising the rubber crumb and any other components, which may optionally be present. Generally, the thermoplastic product contains about 35 to about 65 wt% of rubber crumb.

The desired quantity of thermoplastic polymeric material is charged to an internal mixer having shear capabilities and which is capable of heating the thermoplastic material to above its melting point. The polymeric material is heated in the mixer to above its melting point to form a melt, generally within the temperature range of about 220" to about 450^βF.

To this melt is added minor components of the composition. One such component is a deodorant to mask odor of the tyre crumb as it is processed to form the novel blend of the invention with the polymeric material. In order to be effective in this regard, it is necessary that the deodorant possess stability over an elevated temperature range up to from about 350°F to about 600^βF, being the temperature range employed to form the blend and also that generally employed when the blend is incorporated, as a masterbatch, in end use compositions. The quantity of such deodorant which may be employed varies widely with the nature of the deodorant employed and the quantity of tyre crumb present in the composition. Generally, however, up to about 0.50 wt% of deodorant may be employed. A dispersing agent may be employed along with the deodorant to ensure rapid and uniform dispersion through the molten polymeric material so as to provide for effecting masking of the rubber. The quantity of dispersing agent employed generally is quite small and depends on the nature of the deodorant and the quantity used, preferably less than about 0.50 wt%. At least one coloring agent may be added which results in a coloured blend, which then may be used as a masterbatch to impart colour to an end-user product. Other additives which may be included are impact modifiers, process aids, polymer stabilizers as well as fillers. These materials may be incorporated in variable quantities to provide desirable properties to the product.

Following addition of such minor components and mixing to uniformly disperse the minor components in the melt, the tyre crumb then is added to the melt and blended in to form a uniform blend. Alternatively, the tyre crumb may be added at the same time as the minor components and dispersed in the melt at the same time. The blend is heated to a predetermined time and temperature profile, in order to attain a predictable and hence reproducible result, in terms of melt flow and density of product.

The predetermined time and temperature profile depends on the nature of the polymeric material chosen and the properties desired in the final product.

Once the desired predetermined time and temperature profile is complete, the mixing process is terminated and the resulting thermoplastic blend is removed from the mixer for further processing. Such processing may include conventional sheeting, forming, grinding and pelletizing operations.

The product that results from this procedure is a thermoplastic material of predictable properties containing a considerable proportion of tyre rubber crumb. The novel blend may be employed as such or may be provided in the form of a masterbatch to be combined with other thermoplastic or ther osetting materials to produce a wide variety of products, such as are conventionally formed by thermoplastic polymer processing procedures, such as injection molding. compression molding, blow molding and rotational molding, and extruding.

The novel blend is itself recyclable as are products incorporating the same, so that, once the tyre rubber crumb is incorporated into the novel blend, it becomes a recyclable material. Accordingly, the present invention provides a method of recycling tyres by combining tyre rubber crumb having specific properties with thermoplastic polymeric material to form a thermoplastic blend, which is itself recyclable.

EXAMPI-E A high density polyethylene having a melt index of 0.3 and a density of 0.950 was melted at about 330^βF and mixed with masking agent, modifier, stabilizer process aids, together with pigments. Vulcanized rubber crumb of 15 to 20 mesh particle size was mixed into the melt and the materials blended at a temperature of 350°F for 3 minutes.

Following blending the product- was cooled and recovered. The blend was tested as is and in a further 3:1 blend with high density polyethylene of density of 0.940 and melt index 0.4.

The following Table I gives the proportions of the components, while Table II gives the test results: TABLE I

Component Formula (wt)

HD Polyethylene 45.00

Rubber crumb 50.00

Impact modifier 5.00 Masking agent 0.50

Stabilized process aid 0.50

Pigment (white) 0.50

Pigment (blue) 0.60

Total 102.10 TABLE II

In summary of this disclosure, the present invention provides a novel recycling procedure for tyres and novel thermoplastic materials formed from the tyre rubber. Modifications are possible within the scope of this invention.

Claims

CLAIMS What we claim is:

1. A method of making a thermoplastic compound from scrap rubber material, comprising the steps of: a) heating a thermoplastic polymeric material to a temperature above its melting point so as to form a melt; b) adding the scrap rubber material to the melt, the scrap rubber material having a particle size smaller than about 10 mesh and being substantially free of moisture, metal particles and fabric particles; c) blending the scrap rubber material into the melt to form a uniform blend; and d) heating the uniform blend to a predetermined temperature for a predetermined time period such that the resulting thermoplastic compound has desired properties.

2. The method claimed in Claim 1, further comprising the steps of adding minor amounts of one or more additives to the melt and mixing the melt to disperse the additive in the melt.

3. The method claimed in Claim 2, wherein the one or more additives are added to the melt and are mixed in the melt before the step of adding the scrap rubber material to the melt.

4. The method claimed in Claim 2, wherein the additives are selected from the group consisting of a deodorant, a dispersing agent, a colouring agent, an impact modifier, a process aid, a polymer stabilizer and a filler.

SUBSTITUTE SHEET

5. The method claimed in Claim 4, wherein one of the additives is a deodorant capable of masking the odour of the scrap rubber material and possessing stability over a temperature range from about 350^βF to about 600"F.

6. The method claimed in Claim 5, wherein the deodorant comprises up to about 0.50 wt% of the thermoplastic compound.

7. The method claimed in Claim 5, wherein the additives include a dispersing agent for rapidly and uniformly dispersing the deodorant in the melt.

8. The method claimed in Claim 4, Claim 5, Claim 6 or Claim 7, wherein the additives include at least one colouring agent for imparting colour to the thermoplastic compound.

9. The method claimed in Claim 3, wherein the additives are selected from the group consisting of a deodorant, a dispersing agent, a colouring agent, an impact modifier, a process aid, a polymer stabilizer and a filler.

10. The method claimed in Claim 9, wherein one of the additives is a deodorant capable of masking the odour of the scrap rubber material and possessing stability over a temperature range from about 350^βF to about 600^βF.

11. The method claimed in Claim 10, wherein the deodorant comprises up to about 0.50 wt% of the thermoplastic compound.

12. The method claimed in Claim 10, wherein the additives also include a dispersing agent for rapidly and uniformly dispersing the deodorant in the melt.

13. The method claimed in Claim 9, Claim 10, Claim 11 or Claim 12, wherein the additives include at least one colouring agent for imparting colour to the thermoplastic compound.

14. The method claimed in Claim 1, wherein the particle size of the scrap rubber material is in the range between about 10 mesh to about 40 mesh.

15. The method claimed in Claim 1, wherein the scrap rubber material has less than about 2 wt% moisture.

16. The method claimed in Claim 15, wherein the scrap rubber material has less than about 1 wt% moisture.

17. The method claimed in Claim 1, wherein the scrap rubber material is greater than about 98.5 wt% free of metal particles.

18. The method claimed in Claim 17, wherein the scrap rubber material is greater than about 99 wt% free of metal particles.

19. The method claimed in Claim 1, wherein the scrap rubber material is greater than about 95 wt% free of fabric particles.

20. The method claimed in Claim 1, wherein the scrap rubber material has less than 1 wt% moisture, is greater than 99 wt% free of metal particles and is greater than 95 wt% free of fabric particles.

21. The method claimed in Claim 1, further comprising the step of grinding the scrap rubber material to a particle size smaller than about 10 mesh.

SUBSTITUTE SHE ET

22. The method claimed in Claim 21, wherein the grinding of the scrap rubber material is effected in a heated environment at a temperature less than about 230"F, and the scrap rubber material is subsequently cooled down to a temperature of about 120"F such that the resulting scrap rubber material is substantially free of moisture.

23. The method claimed in claim 22, wherein the scrap rubber material has less than about 2 wt % moisture.

24. The method claimed in Claim 1, wherein the thermoplastic polymeric material is a virgin polymeric material or a scrap polymeric material.

25. The method claimed in Claim 24, wherein the thermoplastic polymeric material is a scrap polymeric material.

26. The method claimed in Claim 1, Claim 24 or Claim 25, wherein the thermoplastic polymeric material comprises one or more materials selected from the group consisting of high density polyethylene, low density polyethylene, linear low density polyethylene, polypropylene homopolymer or copolymer and ethyl-vinyl acetate.

27. The method claimed in Claim 1, wherein the thermoplastic polymeric material is heated to a temperature in the range of about 220^βF to about 450^βF.

28. The method claimed in Claim 1, wherein the scrap rubber material comprises used vehicle tyres.

29. The method claimed in Claim 1, further comprising the step of processing the resulting thermoplastic compound to form an end-user product.

30. The method claimed in Claim 1, wherein the thermoplastic compound comprises at least about 30 wt% thermoplastic polymeric material and about 35 wt% to about 65 wt% scrap rubber material.

31. A method of making a thermoplastic compound from used vehicle tyres, comprising the steps of: a) heating a thermoplastic polymeric material to a temperature in the range of about 220°F to about 450"F so as to form a melt; b) adding minor amounts of one or more additives to the melt, the additives being selected from the group consisting of a deodorant, a dispersing agent, a colouring agent, an impact modifier, a process aid, a polymer stabilizer and a filler; c) mixing the melt to disperse the additives in the melt; d) adding the used vehicle tyres to the melt, the used vehicle tyres having a particle size in the range from about 10 mesh to about 40 mesh, having less than 1 wt% moisture, being greater than about 99 wt% free of metal particles and greater than about 95 wt% free of fabric particles; e) blending the used vehicle tyres into the melt to form a uniform blend; and f) heating the uniform blend to a predetermined temperature for a predetermined time period such that the resulting thermoplastic compound has desired properties.

32. The method claimed in Claim 31, further comprising the steps of grinding the used vehicle tyres in a heated environment at a temperature less than about 230"F, and subsequently cooling the used vehicle tyres to a temperature of about 120"F such that the used vehicle tyres has less than 1 wt% moisture.