Abstract:
Old, spent or worn tires are recycled by removing non-rubber components such as belts, beads, and fabric, and grinding the remaining cured rubber into fine sized particles. The ground particles generally replace equivalent amounts of rubber and additives in various tire formulated components such as tire treads. Good physical properties of the end product are retained.

Description:
FIELD OF INVENTION 
     The present invention relates to fine sized ground tire rubber which is substituted as a partial rubber source for a specific tire component such as a tire tread. 
     BACKGROUND OF THE INVENTION 
     Heretofore, large particle size ground rubber (10 to 40 U.S. Standard Mesh) has been utilized for many years in various tire components, but with significant losses of physical properties. Ground tire rubber has also been utilized in asphalt. 
     SUMMARY OF INVENTION 
     Old, spent, worn, etc. Times with the fabric and metal removed therefrom are shredded. The remaining rubber is ground into fine sized particles of about 90 U.S. Standard Mesh or smaller. The particles, which are cured, are recycled by substituting the same for generally an equivalent removed amount of rubber and additives for a specific tire component. 
     DETAILED DESCRIPTION 
     As a replacement source of rubber, scrap, old, or worn tires are shredded and the non-rubber components thereof, such as tire belts, tire beads and fabric ply, are removed. The tires can be from passenger vehicles, buses, preferably trucks, and the like and can be of a bias ply construction or preferably of a radial ply construction. The major rubber components of such tires are generally natural rubber, synthetic isoprene, polybutadiene, styrene-butadiene rubber, halobutyl rubber, and the like. Such cured rubber which contains various additives therein is ground into fine sized particles and recycled by replacing generally an equivalent amount of a rubber otherwise used in the formulation of a tire component rubber. The above tires, of course, contain conventional or suitable amounts of typical additives known to the art such as one or more types of carbon black; curing aids such as sulfur or sulfur containing compounds; various accelerators, such as amines, disulfides, guanidines, thioureas, thiazoles, thiurarris, sulfenamides, dithiocarbamates, and the like. Other additives include silica; silica coupling agents; various oils such as aromatic, naphthenic, or paraffinic; various antioxidants and antiozonants such as various phenylenediamines; various aliphatic acids such as stearic acid; zinc oxide; various waxes such as micro crystalline waxes; various peptizers; and the like. Various fillers can also be utilized such as clay, for example kaolin clay, and the like. 
     An important aspect of the present invention is that the shredded tire rubber containing various additives therein is ground into fine size particles such as 90 mesh or smaller, desirably 120 or smaller, and preferably 200 U.S. Standard Mesh or smaller. Any rubber grinding method or process can be utilized so long as the rubber is not scorched, degraded, or otherwise damaged during grinding thereof. A particularly preferred method of grinding the rubber is in the presence of water, which keeps the rubber temperature low, as well as extinguishes any possibility of a fire. A more detailed description of such a preferred grinding method is set forth in U.S. Pat. Nos. 4,374,573; 4,714,201; 5,238,194; and 5,411,215, which are hereby fully incorporated by reference. Another method is cryogenically grinding the tire rubber. When cured rubber is recycled according to any of the above methods, and analyzed for chemical composition, a small portion (e.g. about 10%) is ash. 
     Cured, ground rubber is generally utilized in a slightly larger amount to replace, substitute, or compensate for a partial amount of uncured rubber-additive tire formulation. That is, if a specific tire component formulation, contains a total of 100 parts by weight of uncured rubber, and it is desired to add, for example, 30 parts by weight of ground rubber, a slightly smaller amount by weight, for example, about 27 parts by weight of the uncured tire formulation is deleted. Of the 27 parts deleted, 15 parts are rubber, 9 parts are filler (e.g. Carbon Black, Silica), and 3 parts are softener (e.g. oil). In other words, while the preferred amount of rubber and additives replaced, compensated or substituted is about 90% by weight of the recycled rubber added, the actual added recycled amount can generally range from about 40% to about 150%, desirably from about 60% to about 125%, and more desirably from about 80% to about 100%. Although different tire sources or a specific component of a tire will yield different amounts of basically three groups of compounds, that is rubber, fillers such as carbon black, silica, etc. and softeners such as oils, stearic acid, waxes, and the like, the amount of the replacement fine sized ground rubber cured particles containing additives therein is generally within the above noted ranges. 
     The actual amount of the recycled ground tire rubber particles utilized in any tire component rubber-additive formulation is generally up to or from about 2 to about 50 parts by weight, desirably from about 5 to about 30 parts by weight, and preferably from about 7 to about 15 or 20 parts by weight for every 100 total parts by weight of the specific tire component rubber-additive formulation including the ground rubber-additive particles. While generally the ground tire rubber particles can be utilized in formulating any component of a tire, desired tire components include the side wall, the innerliner, the bead filler, with the tire tread being especially preferred. 
     The tire component formulation can contain conventional or typical amounts of conventional or typical rubbers and such formulations are generally known to the art. While the type and amounts of rubbers and additives can vary from component to component, they all generally comprise various rubbers such as natural rubber, synthetic isoprene, styrene-butadiene rubber, polybutyldiene, halobutyl rubber, and the like. Such rubbers also include emulsion rubbers such as ESBR 1502, 1712, 1721, and the like, as well as solution SBR such as the various Duradene rubbers made by the Bridgestone/Firestone, Inc. Various carbon blacks can be utilized such as the N 100, N 200, or N 300 series. Various types of oil can be utilized such as aromatic, naphthenic, paraffinic, and the like. Various antiozonates can be utilized, as well as various antioxidants such as 6 PPD, 1 PPD, and the like, along with various waxes such as microcrystalline waxes. Still other additives include various aliphatic acids such as stearic acids; zinc oxide; various peptizers, and the like. Curing aids include sulfur or sulfur containing compounds and various accelerators include amines, disulfides, guanidines, thioureas, thiazoles, thiurams, sulfenamides, dithiocarbamates, and the like with specific examples including TBBS (N-Tert-Butyl-Benzothiazolesulfenamide), CBS (Cyclohexyl Benzothiazolesulfenamide), DPG (Diphenylguanidine), and TMTD (Tetramethylthiuram Disulfide). Silica as well as silica coupling agents can also be utilized as well as various fillers such as clay. 
     The ground cured tire rubber particles can be blended or mixed with a tire component rubber additive or formulation by any conventional or common method. Suitable mixing methods include blending in a Banbury, blending on a two-roll mill, and the like. Once the above noted ground rubber and conventional rubber-additive formulation have been blended to form a tire component composition, they can be assembled into a specific tire component in accordance with conventional techniques, methods, and the like well known to the art and to the literature. Thus, the blended rubber composite can be applied to a tire carcass in the form of a sheet to eventually form a tire tread, placed in a tire curing mold and cured in a conventional manner at typical times and temperatures. 
    
    
     The present invention will be better understood by reference to the following examples, which serve to illustrate but not to limit the invention. 
     The formulations set forth in Tables I through VI containing 200 mesh ground rubber or a mesh size as otherwise indicated were generally prepared in the following manner. A master batch was made by adding all of the polymers or rubber, fillers such as carbon black, ground rubber particles, oil, optionally silica, zinc oxide, and stearic acid to a Banbury. These ingredients were mixed from about 1.5 to about 2.5 minutes and dropped at a temperature of from about 270° F. to about 350° F. The stock was aged for a minimum of four (4) hours before the next or final stage. An optional re-mill can be utilized. 
     In the final stage, all the antioxidants, accelerators, sulfur, and the master batch were added to a Banbury. The mix time was approximately from about 60 to 80 seconds and dropped at a temperature of from about 190° F. to about 220° F. 
     Various formulations for a tire tread are set forth in Tables I through V, wherein the amounts listed are parts by weight were prepared in the above manner and tested. 
     
       
         
               
               
               
               
             
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE I 
               
               
                   
                   
               
             
             
               
                   
                   
                 Control 
                 Ex. I 
               
               
                   
                   
               
               
                   
                 Solution SBR 
                 80.00 
                 67.50 
               
               
                   
                 Natural Rubber 
                 20.00 
                 17.50 
               
               
                   
                 Ground Rubber 
                 0.00 
                 30.00 
               
               
                   
                 Carbon Black 
                 65.00 
                 56.00 
               
               
                   
                 Oil 
                 6.75 
                 3.75 
               
               
                   
                 Antioxidants 
                 2.00 
                 2.00 
               
               
                   
                 Zinc Oxide 
                 2.00 
                 2.00 
               
               
                   
                 Stearic Acid 
                 2.00 
                 2.00 
               
               
                   
                 Accelerators 
                 1.40 
                 1.40 
               
               
                   
                 Sulfur 
                 1.70 
                 1.70 
               
               
                   
                   
               
             
          
           
               
                 Physical Properties 
               
               
                   
               
             
          
           
               
                   
                 Stress/Strain 
                 M 100% RT (MPa) 
                 2.07 
                 2.13 
               
               
                   
                   
                 Tensile RT (MPa) 
                 21.15 
                 20.65 
               
               
                   
                   
                 Elongation % 
                 390.50 
                 399.00 
               
               
                   
                 Ring Tear 
                 100° C. PSI 
                 322.00 
                 333.00 
               
               
                   
                 Zwick Rebound 
                 RT 
                 38.00 
                 38.60 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE II 
               
               
                   
                   
               
             
             
               
                   
                   
                 Control 
                 Ex. 2 
                 Ex. 3 
                 Ex. 4 
               
               
                   
                   
               
               
                   
                 Emulsion SBR 
                 36.36 
                 34.96 
                 33.56 
                 32.20 
               
               
                   
                 Solution SBR 
                 43.64 
                 41.96 
                 40.28 
                 38.60 
               
               
                   
                 Natural Rubber 
                 20.00 
                 19.23 
                 18.46 
                 17.69 
               
               
                   
                 Ground Rubber 
                 0.00 
                 10.00 
                 20.00 
                 30.00 
               
               
                   
                 Carbon Black 
                 42.50 
                 39.50 
                 36.50 
                 33.50 
               
               
                   
                 Silica 
                 15.00 
                 15.00 
                 15.00 
                 15.00 
               
               
                   
                 Oil 
                 8.00 
                 7.00 
                 6.00 
                 5.00 
               
               
                   
                 Antioxidants 
                 3.00 
                 3.00 
                 3.00 
                 3.00 
               
               
                   
                 Zinc Oxide 
                 2.00 
                 2.00 
                 2.00 
                 2.00 
               
               
                   
                 Stearic Acid 
                 1.00 
                 1.00 
                 1.00 
                 1.00 
               
               
                   
                 Accelerators 
                 2.50 
                 2.50 
                 2.50 
                 2.50 
               
               
                   
                 Sulfur 
                 2.00 
                 2.00 
                 2.00 
                 2.00 
               
               
                   
                   
               
             
          
           
               
                 Physical Properties 
               
               
                   
               
             
          
           
               
                 Stress/Strain 
                 M 100% RT (MPa) 
                 3.31 
                 3.20 
                 3.24 
                 3.14 
               
               
                   
                 Tensile RT (MPa) 
                 18.65 
                 17.99 
                 20.88 
                 19.86 
               
               
                   
                 Elongation % 
                 402.60 
                 385.80 
                 442.80 
                 426.90 
               
               
                 Ring Tear 
                 100° C. PSI 
                 395.40 
                 364.10 
                 328.70 
                 335.90 
               
               
                 Zwick 
                 RT 
                 31.50 
                 32.00 
                 33.10 
                 32.80 
               
               
                 Rebound 
               
               
                   
               
             
          
         
       
     
     
       
         
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE III 
               
               
                   
                   
               
             
             
               
                   
                   
                 Control 
                 Ex. 8 
                 Ex. 9 
                 Ex. 10 
               
               
                   
                   
               
               
                   
                 Solution SBR 
                 77.05 
                 73.55 
                 70.05 
                 66.55 
               
               
                   
                 Butadiene Rubber 
                 33.00 
                 31.50 
                 30.00 
                 28.50 
               
               
                   
                 Ground Rubber 
                 0.00 
                 10.00 
                 20.00 
                 30.00 
               
               
                   
                 Carbon Black 
                 36.00 
                 33.00 
                 30.00 
                 27.00 
               
               
                   
                 Silica 
                 35.00 
                 35.00 
                 35.00 
                 35.00 
               
               
                   
                 Oil 
                 31.20 
                 30.20 
                 29.20 
                 28.20 
               
               
                   
                 Antioxidants 
                 2.45 
                 2.45 
                 2.45 
                 2.45 
               
               
                   
                 Zinc Oxide 
                 1.70 
                 1.70 
                 1.70 
                 1.70 
               
               
                   
                 Stearic Acid 
                 1.00 
                 1.00 
                 1.00 
                 1.00 
               
               
                   
                 Accelerators 
                 2.40 
                 2.40 
                 2.40 
                 2.40 
               
               
                   
                 Sulfur 
                 2.00 
                 2.00 
                 2.00 
                 2.00 
               
               
                   
                   
               
             
          
           
               
                 Physical Properties 
               
               
                   
               
             
          
           
               
                 Stress/Strain 
                 M 100% RT (MPa) 
                 1.37 
                 1.42 
                 1.44 
                 1.45 
               
               
                   
                 Tensile RT (MPa) 
                 16.22 
                 16.54 
                 16.49 
                 16.45 
               
               
                   
                 Elongation % 
                 507.00 
                 600.80 
                 593.30 
                 586.80 
               
               
                 Ring Tear 
                 100° C. PSI 
                 323.00 
                 302.00 
                 316.00 
                 289.00 
               
               
                 Zwick 
                 RT 
                 39.20 
                 38.80 
                 38.90 
                 39.00 
               
               
                 Rebound 
               
               
                   
               
             
          
         
       
     
     
       
         
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE IV 
               
               
                   
               
             
             
               
                   
                 Control 
                 Ex. 11 
                 Ex. 12 
                 Ex. 13 
                 Ex. 14 
                 Ex. 15 
               
               
                   
               
               
                 Solution SBR 
                 50.00 
                 47.72 
                 45.43 
                 43.15 
                 40.86 
                 38.58 
               
               
                 Solution SBR 
                 34.40 
                 32.83 
                 31.26 
                 29.69 
                 28.12 
                 26.55 
               
               
                 Natural Rubber 
                 25.00 
                 23.86 
                 22.71 
                 21.57 
                 20.42 
                 19.28 
               
               
                 Ground Rubber 
                 0.00 
                 10.00 
                 20.00 
                 30.00 
                 40.00 
                 50.00 
               
               
                 Carbon Black 
                 32.50 
                 29.50 
                 26.50 
                 23.50 
                 20.50 
                 17.50 
               
               
                 Silica 
                 36.00 
                 36.00 
                 36.00 
                 36.00 
                 36.00 
                 36.00 
               
               
                 Oil 
                 13.00 
                 12.00 
                 11.00 
                 10.00 
                 9.00 
                 8.00 
               
               
                 Antioxidants 
                 2.00 
                 2.00 
                 2.00 
                 2.00 
                 2.00 
                 2.00 
               
               
                 Zinc Oxide 
                 3.00 
                 3.00 
                 3.00 
                 3.00 
                 3.00 
                 3.00 
               
               
                 Stearic Acid 
                 1.50 
                 1.50 
                 1.50 
                 1.50 
                 1.50 
                 1.50 
               
               
                 Accelerators 
                 2.10 
                 2.10 
                 2.10 
                 2.10 
                 2.10 
                 2.10 
               
               
                 Sulfur 
                 1.70 
                 1.70 
                 1.70 
                 1.70 
                 1.70 
                 1.70 
               
               
                   
               
             
          
           
               
                 Physical Properties 
               
               
                   
               
             
          
           
               
                 Stress/Strain 
                   
                   
                   
                   
                   
                   
               
               
                 M 100% RT 
                 2.03 
                 2.02 
                 1.98 
                 1.94 
                 1.90 
                 1.90 
               
               
                 (MPa) 
               
               
                 Tensile RT 
                 18.48 
                 18.18 
                 17.34 
                 18.17 
                 17.41 
                 18.28 
               
               
                 (MPa) 
               
               
                 Elongation % 
                 438.60 
                 446.70 
                 434.10 
                 461.00 
                 449.90 
                 497.70 
               
               
                 Ring Tear 
               
               
                 100° C. PSI 
                 286.00 
                 254.00 
                 249.60 
                 279.80 
                 268.70 
                 238.60 
               
               
                 Zwick 
               
               
                 Rebound 
               
               
                 RT 
                 41.20 
                 41.90 
                 42.10 
                 43.00 
                 43.30 
                 43.80 
               
               
                   
               
             
          
         
       
     
     As apparent from the data in all of the above four tables, retention of physical properties using the finely ground reclaimed tire rubber was quite good. In fact, in many instances, physical properties were actually improved. 
     
       
         
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
           
               
                 TABLE V 
               
               
                   
               
             
             
               
                   
                   
                   
                   
                 Control 
                 Control 
               
               
                   
                 Control 
                 Ex. 11 
                 Ex. 12 
                 2 
                 3 
               
               
                   
               
               
                 Solution SBR 
                 80.00 
                 67.46 
                 67.46 
                 67.46 
                 67.46 
               
               
                 Natural Rubber 
                 20.00 
                 17.54 
                 17.54 
                 17.54 
                 17.54 
               
               
                 200 Mesh Ground 
                 — 
                 30.00 
                 — 
                 — 
                 — 
               
               
                 Rubber 
               
               
                 120 Mesh Ground 
                 — 
                 — 
                 30.00 
                 — 
                 — 
               
               
                 Rubber 
               
               
                 80 Mesh Ground Rubber 
                 — 
                 — 
                 — 
                 30.00 
                 — 
               
               
                 60 Mesh Ground Rubber 
                 — 
                 — 
                 — 
                 — 
                 30.00 
               
               
                 Carbon Black 
                 65.00 
                 56.00 
                 56.00 
                 56.00 
                 56.00 
               
               
                 Oil 
                 6.75 
                 3.75 
                 3.75 
                 3.75 
                 3.75 
               
               
                 Antioxidants 
                 2.00 
                 2.00 
                 2.00 
                 2.00 
                 2.00 
               
               
                 Zinc Oxide 
                 2.00 
                 2.00 
                 2.00 
                 2.00 
                 2.00 
               
               
                 Stearic Acid 
                 2.00 
                 2.00 
                 2.00 
                 2.00 
                 2.00 
               
               
                 Accelerators 
                 1.40 
                 1.40 
                 1.40 
                 1.40 
                 1.40 
               
               
                 Sulfur 
                 1.70 
                 1.70 
                 1.70 
                 1.70 
                 1.70 
               
               
                   
               
             
          
           
               
                 Physical Properties 
               
               
                   
               
             
          
           
               
                 Stress/Strain 
                   
                   
                   
                   
                   
               
               
                 M 100% RT (MPa) 
                 2.10 
                 2.13 
                 2.03 
                 2.03 
                 2.07 
               
               
                 Tensile RT (MPa) 
                 21.15 
                 19.50 
                 20.53 
                 20.72 
                 19.44 
               
               
                 Elongation % 
                 532.40 
                 509.60 
                 525.40 
                 478.30 
                 483.40 
               
               
                 Ring Tear 
               
               
                 100° C. PSI 
                 364.40 
                 374.50 
                 333.40 
                 281.70 
                 282.20 
               
               
                 Zwick 
               
               
                 Rebound 
               
               
                 RT 
                 38.00 
                 38.00 
                 38.30 
                 36.40 
                 34.00 
               
               
                   
               
             
          
         
       
     
     As apparent from Table V, large size ground rubber particles (Control 2 and 3) had poor physical properties such as ring tear and rebound whereas Examples 11 and 12 containing 200 Mesh and 120 Mesh ground rubber respectively had good properties. 
     While in accordance with the patent statutes, the best mode and preferred embodiment have been set forth, the scope of the invention is not limited thereto, but rather by the scope of the attached claims.