Recycled micronized rubber formulation having improved abrasion resistance

Abstract

This invention is based upon the discovery that micronized solution styrene-butadiene rubber from postconsumer sources can be included in rubber formulations without severely compromising abrasion resistance. The micronized solution styrene-butadiene rubber utilized in the rubber formulations of this invention can be made by cryogenic grinding postconsumer rubber products using conventional procedures. For instance, it can be made by cryogenically grinding a tire tread containing a high level of solution styrene-butadiene rubber. The micronized solution styrene-butadiene rubber can then be blending into desired virgin rubbers and cured without significantly compromising the abrasion resistance of the rubber formulation. The rubber formulation of this invention is comprised of a natural or synthetic rubber and from 1 weight percent to 30 weight percent of a micronized rubber composition containing at least 10 weight percent solution styrene-butadiene rubber and having a particle size of 40 mesh to 200 mesh.

Claims

1. A rubber formulation which is particularly useful in rubber products or components of rubber products which are subject to abrasive forces, said rubber formulation comprising: at least one natural or synthetic rubber and from 1 weight percent to 30 weight percent of a micronized rubber composition having a particle size which is within the range of 40 mesh to 200 mesh, wherein the micronized rubber composition is comprised of at least 10 weight percent solution styrene-butadiene rubber.

2. The rubber formulation of claim 1 wherein the micronized rubber composition is present at a level which is within the range of 2 weight percent to 20 weight percent.

3. The rubber formulation of claim 1 wherein the micronized rubber composition is present at a level which is within the range of 3 weight percent to 15 weight percent.

4. The rubber formulation of claim 1 wherein the micronized rubber composition is present at a level which is within the range of 4 weight percent to 10 weight percent.

5. The rubber formulation of claim 1 wherein the micronized rubber composition has a particle size which is within the range of 60 mesh to 160 mesh.

6. The rubber formulation of claim 1 wherein the micronized rubber composition has a particle size which is within the range of 80 mesh to 120 mesh.

7. The rubber formulation of claim 1 wherein the micronized rubber composition is comprised of at least 20 weight percent of the solution styrene-butadiene rubber.

8. The rubber formulation of claim 1 wherein the micronized rubber composition is comprised of at least 30 weight percent of the solution styrene-butadiene rubber.

9. The rubber formulation of claim 1 wherein the micronized rubber composition is comprised of at least 40 weight percent of the solution styrene-butadiene rubber.

10. The rubber formulation of claim 1 wherein the micronized rubber composition is comprised of at least 50 weight percent of the solution styrene-butadiene rubber.

11. The rubber formulation of claim 1 wherein the micronized rubber composition is comprised of at least 60 weight percent of the solution styrene-butadiene rubber.

12. The rubber formulation of claim 1 wherein the micronized rubber composition is comprised of at least 70 weight percent of the solution styrene-butadiene rubber.

13. The rubber formulation of claim 1 which is comprised of 55 phr to 75 phr of solution styrene-butadiene rubber, 5 phr to 25 phr of high cis1,4-polybutadiene rubber, 5 phr to 25 phr of the micronized rubber composition.

14. The rubber formulation of claim 13 which is further comprised of 30 phr to 50 phr of reinforcing silica.

15. The rubber formulation of claim 14 which is further comprised of 3 phr to 12 phr of carbon black.

16. The rubber formulation of claim 5 which is comprised of 60 phr to 70 phr of solution styrene-butadiene rubber, 12 phr to 22 phr of high cis1,4-polybutadiene rubber, 12 phr to 22 phr of the micronized rubber composition.

17. The rubber formulation of claim 16 which is further comprised of 35 phr to 45 phr of reinforcing silica.

18. The rubber formulation of claim 17 which is further comprised of 4 phr to 8 phr of carbon black.

19. A tire which is comprised of a generally toroidal-shaped carcass with an outer circumferential tread, two spaced beads, at least one ply extending from bead to bead and sidewalls extending radially from and connecting said tread to said beads, wherein said tread is adapted to be ground-contacting, and wherein said tread is comprised of the rubber formulation as specified in claim 1.

20. A conveyor belt which is comprised of a carry cover layer, a reinforcement layer which is situated under the carry cover layer, and a pulley cover layer which is situated under the carry cover layer, wherein the carry cover layer is comprised of the rubber formulation as specified in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the abrasion loss of rubber formulation of this invention as compared to control formulations. This FIGURE shows that the rubber formulations of this invention provide excellent abrasion characteristics.

DETAILED DESCRIPTION OF THE INVENTION

(2) The rubber formulation of this invention includes at least one natural or synthetic rubber and micronized solution styrene-butadiene rubber (SSBR). The solution styrene-butadiene rubber utilized in accordance with this invention is synthesized by solution polymerization. In other words, the solution styrene-butadiene rubber is made by the copolymerization of 1,3-butadiene monomer and styrene monomer in a suitable organic solvent. The solution styrene-butadiene rubber utilized in the practice of this invention will typically contain from 20 weight percent to 30 weight percent bound styrene and from 70 weight percent to 80 weight percent bound butadiene. The solution styrene-butadiene rubber utilized in the practice of this invention will more typically contain from 22 weight percent to 25 weight percent bound styrene and from 75 weight percent to 78 weight percent bound butadiene. Such solution polymerizations can be initiated with an alkyl lithium compound, such as isobutyl lithium, with the monomers and resultant styrene-butadiene rubber being in a solution. Accordingly, the rubber is referred to as “solution styrene-butadiene rubber” because it is made via solution polymerization. This can be contrasted to emulsion styrene-butadiene rubber is in synthesized by emulsion polymerization.

(3) The natural or synthetic rubber into which the micronized styrene-butadiene rubber is blended can be virtually any desired kind of sulfur curable rubber. For instance, the rubber be natural rubber, synthetic polyisoprene rubber, high cis-1,4-polybutadiene rubber, medium vinyl polybutadiene rubber, high vinyl polybutadiene rubber, emulsion styrene-butadiene rubber, solution styrene-butadiene rubber, styrene-isoprene-butadiene rubber, styrene-isoprene rubber, butyl rubber, chlorobutyl rubber, bromobutyl rubber, polynorbornene rubber, ethylene-propylene rubber (EPR), ethylene-propylene-diene rubber (EPDM), nitrile rubber, carboxylated nitrile rubber, polychloroprene rubber (neoprene rubber), polysulfide rubbers, polyacrylic rubbers, silicon rubbers, chlorosulfonated polyethylene rubbers, and the like as well as various mixtures thereof.

(4) The micronized solution styrene-butadiene rubber employed in the formulations of this invention can be micronized utilizing virtually any technique which results in the SSBR having a small particle size which is typically between 40 mesh to 200 mesh. The micronized solution styrene-butadiene rubber utilized in the rubber formulations of this invention will more typically have a particle size of 60 mesh to 160 mesh. In some applications it may be advantageous to employ a micronized rubber powder having a particle size of 80 mesh to 120 mesh.

(5) The micronized solution styrene-butadiene rubber used in the rubber formulations of this invention can come from a wide variety of sources having a high content of solution styrene-butadiene rubber. For instance, it can be recovered from tire treads which include a high level of solution styrene-butadiene rubber. For example, the solution styrene-butadiene rubber can be recovered from vehicle tire treads in recapping procedures. More specifically, “rubber buffings” from tire treads containing high levels of solution styrene-butadiene rubber can be used in the practice of this invention. Such rubber buffings are comprised of rubber which has been buffed off of vehicle tire tread when preparing the old tire carcass for recapping. In the recapping procedure a new tread is applied to the old tire carcass and cured onto it to make the retreaded tire. In any case, such vehicle tire retread buffings which contain a high level are solution styrene-butadiene rubber and various other rubbers including natural rubber and various synthetic rubbers, such as synthetic polyisoprene rubber, polybutadiene rubber, and emulsion styrene-butadiene rubber, can be used.

(6) Accordingly, the micronized rubber powder utilized in accordance with this invention can be a blend of solution styrene-butadiene rubber with natural rubber, synthetic polyisoprene rubber, polybutadiene rubber, and emulsion styrene-butadiene rubber and a wide variety of other rubbers. In any case, the micronized solution styrene-butadiene rubber can consist solely of solution styrene-butadiene rubber or it can be a blend of the solution styrene-butadiene rubber with natural rubber, synthetic polyisoprene rubber, emulsion styrene-butadiene rubber, polybutadiene rubber and various mixtures thereof.

(7) In one specific embodiment of this invention the micronized solution styrene-butadiene rubber can be made utilizing the cryogenic grinding system described in U.S. Pat. No. 7,445,170 and an impact mill as described in U.S. Pat. No. 7,861,958. The teachings of U.S. Pat. No. 7,445,170 and U.S. Pat. No. 7,861,958 are incorporated herein for purposes of describing useful techniques and equipment which can be employed in making micronized solution styrene-butadiene rubber powder that can be employed in making renewed rubber compositions in accordance with this invention. Micronized rubber powder can also be made in many other ways other than described above, such as but not limited to a wet grinding process, ambient temperature grinding procedures, and other cryogenic processes. In any case the micronized solution styrene-butadiene rubber will contain at least 10 weight percent of the solution styrene-butadiene rubber polymer and from 10 weight percent to 90 weight percent additional rubbery polymers. The micronized solution styrene-butadiene rubber can contain at least 20 weight percent, at least 30 weight percent, at least 40 weight percent, at least 50 weight percent, at least 60 weight percent, or at least 70 weight percent solution styrene-butadiene rubber polymer with the balance of the polymer content of the micronized formulation being other rubbery polymers.

(8) The rubber formulation of this invention will include between 1 weight percent and 30 weight percent of the micronized rubber composition (including the solution styrene butadiene rubber) with the balance of the polymers being used in the formulation being desired virgin rubbers, such as natural rubber, polybutadiene rubber (high cis-1,4-polybutadiene rubber, medium vinyl polybutadiene rubber, low vinyl polybutadiene rubber), emulsion styrene-butadiene rubber, solution styrene-butadiene rubber, and the like. The rubber formulation of this invention will more frequently contain from 2 weight percent to 20 weight percent of the micronized rubber composition, and may contain from 3 weight percent to 15 weight percent of micronized rubber composition. For instance, the rubber formulation of this invention can contain from 4 weight percent to 10 weight percent of the micronized rubber composition with the balance of the rubber formulation being virgin rubbers.

(9) One rubber formulation of this invention which exhibits a particularly desirable combination of properties including excellent abrasion loss is comprised of 55 phr to 75 phr of virgin solution styrene-butadiene rubber, 5 phr to 25 phr of virgin high cis1,4-polybutadiene rubber, 5 phr to 25 phr of micronized rubber powder, 30 phr to 50 phr of reinforcing silica, and 3 phr to 12 phr of carbon black. Such a rubber formulation will preferably contain 60 phr to 70 phr of virgin solution styrene-butadiene rubber, 12 phr to 22 phr of virgin high cis1,4-polybutadiene rubber, 12 phr to 22 phr of micronized rubber powder, 35 phr to 45 phr of reinforcing silica, and 4 phr to 8 phr of carbon black.

(10) In one embodiment of this invention the micronized solution styrene-butadiene rubber is functionalized to attain an environmentally friendly, chemically functionalized, renewed rubber composition having a highly desirable combination of physical properties and which exhibits excellent processability. This functionalization is carried out (1) blending a micronized solution styrene-butadiene rubber powder with a processing aid and a functionalizing agent to produce a blended mixture; (2) processing the blended mixture under conditions of high shear and low temperature to produce a reacted mixture; (3) adding a stabilizer to the reacted mixture to produce the renewed rubber. The method for functionalization of the solution styrene-butadiene rubber is described in greater detail in U.S. Provisional Patent Application Ser. No. 61/986,696, filed on Apr. 30, 2014. The teachings of U.S. Provisional Patent Application Ser. No. 61/986,696 are incorporated by references herein for the purpose of disclosing a manner by which the solution styrene-butadiene rubber can be functionalized.

EXAMPLE 1

(11) Three model tread compounds were formulated to make a base material for comparison as micronized rubber powder to be used in a low rolling resistance model tread compound. Table 1 depicts a model tread compound for low rolling resistance applications using solution styrene butadiene rubber (SSBR) and polybutadiene (PBR). Table 2 illustrates a model natural rubber (NR) compound suitable for off the road applications, while Table 3 shows an economic tread compound using emulsion styrene butadiene rubber (ESBR) for replacement tire applications.

(12) TABLE-US-00001 TABLE 1 Model Low Rolling Resistance Tread Compound Recipe Control + Control + 10% 10% Standard SSBR/BR/Silica/Silane Compound Control MRP FMRP Units Description PHR PHR PHR SSBR solution styrene-butadiene rubber 103.13 103.13 103.13 (Tg = −30° C.) High Cis PBR high cis1,4-polybutadiene rubber 25.00 25.00 25.00 MRP micronized rubber powder 25.57 FMRP functional compound 25.57 Corsol 200 process oil 5.00 5.00 5.00 Aktiplast PP process aid - zinc salts of higher 2.00 2.00 2.00 molecular fatty acids N234 tread carbon black 10.00 10.00 10.00 Zeosil 1165MP silica 65.00 65.00 65.00 6PPD Antidegradant N-(1,3-Dimethylbutyl)-N′-phenyl- 2.00 2.00 2.00 p-phenylenediamine Antioxidant DQ polymerized 2,2,4-trimethyl-1,2- 0.50 0.50 0.50 (TMQ) dihydroquinoline Akrowax 5084 (Wax blend of microcrystalline wax and a 2.00 2.00 2.00 Blend) range of different melt-point paraffin waxes Si 266 Silane bis(triethoxysilylpropyl) 5.20 5.20 5.20 disulfide Zinc Oxide Dispersion cure activator 2.94 2.94 2.94 (85% ZnO) Stearic Acid activator 1.50 1.50 1.50 CBS N-cyclohexyl-2-benzothioazole 1.50 1.50 1.50 sulfenamide DPG diphenyl guanidine 1.70 1.70 1.70 Sulfur Dispersion cure agent 2.13 2.66 2.66 (80% Sulfur) Total PHR Finish 229.60 255.70 255.70 Batch

(13) TABLE-US-00002 TABLE 2 Model Natural Rubber Tread Compound Recipe Natural Rubber Tread Compound Control Units Description PHR Natural Rubber natural rubber 100.00 Clarimer L PD80 micronized rubber powder FMRP functional compound Corsol C200 process oil 5.00 N234 tread carbon black 50.00 6PPD Antidegradant N-(1,3-Dimethylbutyl)-N′-phenyl-p- 2.00 (PD-2) phenylenediamine TMQ Antidegradant polymerized 2,2,4-trimethyl-1,2- 1.50 dihydroquinoline Microcrystalline and blend of microcrystalline wax and a 1.50 Paraffin Wax Blend range of different melt-point paraffin waxes Zinc Oxide Dispersion cure activator 3.53 (85% ZnO) Stearic Acid activator 1.50 TBBS Accelerator N-tert-butyl-2 1.50 benzothiazolesulfenamide Sulfur Dispersion (80% cure agent 1.63 Sulfur) Total PHR Finish Batch 168.15

(14) TABLE-US-00003 TABLE 3 Model ESBR Tread Compound Recipe Emulsion SBR Tread Compound ESBR Tread Units Description PHR ESBR1500 (Non-oil Emulsion SBR (23.5% bound styrene, 52 52.00 extended) Mooney viscosity and cold polymerized) ESBR1763 (HV NAP Emulsion SBR (23.5% bound styrene, 27.27% 66.01 Oil Extended 27.27%) heavy naphthenic oil, 42 Mooney viscosity, and cold polymerized) PD80 micronized rubber powder FMRP functional compound Nytex 4700 Process process oil 6.00 Oil Struktol 40MS homogenizing agent - mixture of dark aromatic 1.00 hydrocarbon resins Alkyl Phenol phenolyic resin 3.00 Formaldehyde Novalak Tack Resin N234 tread carbon black 75.00 6PPD Antidegradant N-(1,3-Dimethylbutyl)-N′-phenyl-p- 2.00 (PD-2) phenylenediamine TMQ Antidegradant polymerized 2,2,4-trimethyl-1,2- 1.00 dihydroquinoline Microcrystalline and blend of microcrystalline wax and a range of 1.50 Paraffin Wax Blend different melt-point paraffin waxes Zinc Oxide Dispersion cure activator 3.53 (85% ZnO) Stearic Acid activator 2.00 TBBS Accelerator N-tert-butyl-2 benzothiazolesulfenamide 1.20 DPG Accelerator diphenyl guanidine 0.20 Sulfur Dispersion (80% cure agent 2.00 Sulfur) Total PHR Finish 216.44 Batch

(15) Each of the cured rubber plaques for the three model compounds were aged in an oven at 70° C. for four weeks. Once aged, each tread plaque was then cryogenically ground to create an 80 mesh type material for each of the starting materials.

(16) This ground material was then used as an additive for the low rolling model tread compound as outlined in Table 1 for comparison of abrasion characteristics. Each of the starting material micronized rubber powders was also functionalized to determine abrasion characteristics. Results of these trials are shown in FIG. 1.

(17) As can be seen from reviewing FIG. 1, the abrasion loss exhibited in Sample 4 wherein the micronized rubber was solution SBR was excellent with very low abrasion loss. In fact, the abrasion loss exhibited in Sample 4 as actually lower than that determined in the control where micronized rubber was not included in the rubber formulation. The abrasion loss determined in Sample 3 compared even more favorably to the increased levels of abrasion loss which were shown in Samples 2 and 3 which included micronized natural rubber and micronized ESBR, respectively.

(18) Samples 5 through 7 show that functionalization of the micronized rubber did not deteriorate abrasion loss characteristics in general. In fact, the samples which included functionalized micronized rubber powder (FNRP) exhibited lower abrasion loss than their unfunctionalized counterparts.

(19) While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention.