Abstract:
A process for producing cured rubber is disclosed wherein the process comprises:
       A) mixing rubber, carbon black, and azodicarbonamide without other curative ingredients;   B) adding the remaining curative ingredients in one or more subsequent mixing steps; and then   C) curing the rubber;
 
whereby a cured rubber having improved hysteresis is obtained.
       
 
     The cured rubber thus obtained is particularly useful in tires and tire treads.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is directed to a process for promoting the interaction between carbon black and rubber. More particularly, the present invention is directed to the use of azocarbonamide as a promoter of the interaction between carbon black and rubber. 
     2. Description of Related Art 
     Fillers, such as carbon black, are added to elastomeric compounds for a variety of reasons. They act as a low cost diluent and as reinforcing agents, giving higher-modulus, higher strength and greater wear resistance. The interaction between filler and an elastomer matrix is also very important to the enhancement of desirable properties such as hysteresis, and wear resistance. It is believed that when the interaction between the carbon black filler and the polymer matrix is increased, dynamic properties are improved. This is generally evidenced by lower hysteresis at elevated temperatures that would result in lower rolling resistance when the rubber is used to make automobile tires. Increased interaction between the polymer and filler can also result in cured rubber with lower heat build-up. 
     Interaction of rubber to the filler also results in changes in other properties. When rubber and carbon black interact, the amount of bound rubber increases. This is due to some of the polymer being strongly bonded to the surface of the carbon black. This is demonstrated by dissolving the uncured rubber in a good solvent, leaving the carbon black and bound polymer as a gel. In the absence of interaction, this quantity of gel will be minimal, and when interaction increases the amount of gel will increase. The increase in the amount of bound rubber gel in the uncured compound may be taken as evidence of increased interaction between the filler and polymer. 
     In the absence of interaction between filler and its elastomeric matrix, the filler forms a loosely bonded network within the matrix, which remains after curing. When the dynamic storage modulus, designated G′, is measured in the cured rubber sample, the filler network acts to increase the modulus at low strain. As the applied strain on the rubber sample is increased, the bonds that form this filler network are broken, and it no longer contributes to the modulus. Thus, in the presence of small or low interaction between filler and the elastomer matrix, the dynamic storage modulus, G′, will diminish as the applied strain is increased. This is known as the Payne Effect. As the filler to polymer matrix interaction increases, the filler-filler network should be decreased in the final cured elastomer. Thus when applied strain is increased as the dynamic measurement is made, the storage modulus, G′, does not decrease as rapidly with an increase in the strain. The diminution of the Payne Effect is also taken as evidence that increased filler-polymer interaction has taken place. Another way to measure this is by the % G′ Retained, which is simply the ratio of high strain/low strain, where higher is better. 
     Similarly, when the modulus of a cured sample is measured in simple extension, the modulus will increase as the strain increases. When a sample that has increased filler interaction to the matrix is compared to a control, the ratio of the modulus at high strain to the modulus at low strain will be higher. Thus, an increase in the ratio of the modulus at 300% extension to the modulus at 5% extension, (M 300 /M 5 ), may be taken as evidence that additional interaction has taken place. 
     In the past some other chemicals have been added to rubber to improve the interaction of carbon black with the rubber matrix. N-Methyl-N,4-dinitrosoaniline was used commercially 1 , but was discontinued due to concerns about toxicity. (See, Leeper et al.,  Rubber World , 135:413–28, (1956); Walker et al.,  Rubber Age , 90:925–31(1962)). N,N′-bis (2-methyl-2-nitropropyl)-1,6-diaminohexane has been reported to be useful and is being sold as Sumifine 1162. (See, Yamaguchi et al.,  Rubber World , 199:30–38(1989)). Several other materials have been proposed as being useful, but so far have not attained any commercial sigificance. Benzofurazan oxide has been suggested, but it evolves a strong undesirable odor during processing. (See, D. F. Graves,  Rubber Chem. TechnoL , 66:61–72, (1993); and U.S. Pat. Nos. 4,751,271; 4,975,497; and 5,001,171). Para-amino-benzenesulfonyl azide has also been suggested as a carbon black promoter, but so far it is not available commercially. (See, Gonzalez et al.,  Rubber Chem. Technol . 69:266–72 (1996). Benzimidazolinones, hydroxybenzimidazole oxides and related materials have also been reported to be effective. (See, U.S. Pat. Nos. 4,761,446 and 4,762,870). 
     Azodicarbonamide has been known to the rubber industry for some time. It is normally used as a chemical foaming agent for rubber and plastics, in order to obtain foamed rubber or plastic goods. In the manufacture of foamed rubber, azodicarbonamide is mixed with the uncured rubber polymer, along with curatives, antidegradants, and other auxiliary additives. The rubber is then heated to decompose the azodicarbonamide to gaseous products and initiate the curing reactions in such a way that the gases are trapped in the cured rubber as bubbles to provide a cured foamed rubber product. 
     Bridgestone Corporation has disclosed the use of blowing agents in tread compounds to make a tread with closed cells that gives better traction on ice and snow. The specific invention disclosed is a foamed tread with cells of a specified size and density. When azodicarbonamide was used in their examples, they added activators to bring the decomposition point down to the normal curing range. 
     U.S. Pat. No. 4,255,536 discloses a copolymer of a conjugated diene/monovinylarene modified by reaction with a dihydrocarbyl azodicarboxylate. 
     U.S. Pat. No. 5,109,902 discloses a pneumatic tire comprising a toroidal carcass, a belt composed of at least two rubberized cord layers arranged radially outside the carcass, and a tread surrounding the periphery of the belt. The tread rubber comprises a base rubber made of a foamed rubber, and a cap rubber made of a non-foam rubber. The cap rubber is arranged radially outside the base rubber. 
     U.S. Pat. Nos. 5,147,477 and 5,351,734 disclose a pneumatic tire which comprises a case and a tread which covers a crown portion of the case. The tread includes a foamed rubber which has a volume not less than 10% of that of the entire of the tread, and the foamed rubber is formed of a rubber composition which contains rubber components each having a glass transition point not higher than −60° C. 
     U.S. Pat. No. 5,571,350 discloses a pneumatic tire for all seasons comprising a tread provided with a foamed rubber containing a given amount of a particular resin such as crystalline syndiotactic 1,2-polybutadiene having specified hardness and average particle size, and having specified expansion ratio, average expanded cell size and storage modulus (E′) at −20° C. of a given range, and said to exhibit satisfactory braking and traction performances at not only dry-on-ice state but also wet-on-ice state while sufficiently holding the steering stability, durability and low fuel consumption in summer season. 
     U.S. Pat. No. 5,753,365 discloses a rubber composition including a rubber component and particulates of a crystalline syndiotactic-1,2-polybutadiene resin dispersed therein. The particulates have an average particle diameter of 1 to 500 μm, and the melting point of the crystalline syndiotactic-1,2-polybutadiene resin is not less than 110° C. The compounding ratio of the resin is 5 to 60 parts by weight relative to 100 parts by weight of the rubber component. The rubber composition is said to be useful for tires, other rubber articles, etc. With respect to tires in particular, a pneumatic tire includes a rubber composition used for a tread, wherein the rubber composition includes a rubber component and particulates of crystalline syndiotactic-1,2-polybutadiene resin. The matrix portion of the tread rubber other than the above particulates is preferably a foamed rubber. 
     U.S. Pat. No. 5,776,991 discloses a foamed rubber composition for pneumatic tires comprising at least one diene polymer as a rubber ingredient and includes closed cells in a matrix rubber, each of these cells being covered with a coat layer made from a given amount of a resin or resin composite having a JIS-C hardness of not less than 75, a particle size of 10–200 μm and a reacted conjugate diene unit content of not less than 10% by weight. In the production of the foamed rubber composition, the melting point or glass transition point of the resin or resin composite is restricted to at least 5° C. lower than the vulcanizing temperature. 
     U.S. Pat. No. 5,788,786 discloses a pneumatic tire in which a foamed rubber layer having closed cells is provided at a surface of a tire tread which substantially contacts at least a road surface, wherein the foamed rubber layer has closed cells whose average diameter is about 1 m to about 120 m and has an expansion ratio of about 1% to about 100%, a solid-phase rubber portion of the foamed rubber layer has a rubber composition in which at least both of a diene-type rubber and silica are mixed, and an amount of the silica is about 10 to about 80 parts by weight based on 100 parts by weight of the diene-type rubber. The pneumatic tire is said to exhibit excellent traction and braking abilities and controllability on snowy, icy and wet road surfaces. 
     U.S. Pat. No. 5,798,009 discloses a foamed rubber composition for tire comprising a particular amount of particles having specified hardness and average particle size and containing aluminum-bonded hydroxy group and/or silicon-bonded hydroxy group at its surface, and a particular amount of at least one specified silane coupling agent, and is said to develop excellent performances on ice. Further, pneumatic tires contain the foamed rubber composition as a tread rubber. 
     SUMMARY OF THE INVENTION 
     It has now been found that azodicarbonamide can promote interaction between the rubber polymer and carbon black in unsaturated rubber compounds. As a result of the interaction, the dynamic properties of the rubber, such as the reduction of hysteresis, are improved. 
     More particularly, the present invention is directed to a process for producing cured rubber with improved hysteresis comprising mixing rubber, carbon black, and azodicarbonamide without other curative ingredients, then adding the remaining curative ingredients in subsequent mixing steps and curing the rubber. 
     In another embodiment, the present invention is directed to an article of manufacture comprising a cured rubber produced by a process comprising:
         A) mixing rubber, carbon black, and azodicarbonamide without other curative ingredients;   B) adding the remaining curative ingredients in one or more subsequent mixing steps; and then   C) curing the rubber.       

     It is preferred that the article be a tire or a tire tread. Where the azodicarbonamide is used in a tire tread, it is preferably employed at a concentration of 0.1 to 20 phr in the tread compound. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As noted above, azodicarbonamide promotes an interaction between the rubber polymer and carbon black in unsaturated rubber compounds, and, as a result of the interaction, the dynamic properties of the rubber are improved. 
     The interaction can be brought about by mixing the azodicarbonamide with the rubber and carbon black in the first step of the rubber production process, at an elevated temperature. Alternatively, the rubber and carbon black can be mixed in a first step and the azodicarbonamide added in a second step. Other compounding ingredients, such as extending oil, or wax may be present during this mixing step, but the presence of vulcanizing agents or other curatives must be avoided. In particular, chemicals known to activate the decomposition of azodicarbonamide must not be added during the same mixing step with the azodicarbonamide. Zinc oxide and other zinc compounds, which are normally added to complement the vulcanization system should not be added in the same mix step with azodicarbonamide, as they are known to activate its decomposition. They may, however, be added in a subsequent lower temperature mixing step. 
     As also mentioned above, in the manufacture of foamed rubber as known in the art, azodicarbonamide is mixed with the uncured rubber polymer, along with curatives, antidegradants, and other auxiliary additives. The rubber is then heated to decompose the azodicarbonamide to gaseous products and initiate the curing reactions in such a way that the gases are trapped in the cured rubber as bubbles to provide a cured foamed rubber product. 
     In light of this usual function for azodicarbonamide, it was surprising to find that by employing certain mixing procedures, it could be used to promote an interaction between the rubber polymer and carbon black filler in the cured rubber compound, without the formation of bubbles or cellular structure. 
     In order to realize the benefits of azodicarbonamide as a promoter for the interaction of carbon black with rubber, the azodicarbonamide must either be added to the rubber in the same mixing step as the carbon black or added in a second step to the rubber/carbon black mixture prior to the addition of vulcanizing agents or other curatives. If the azodicarbonamide is added in a later step, the improvement in dynamic properties will not be obtained, or will be distinctly reduced. Also, the full extent of the desired improvement will not be realized if the azodicarbonamide is mixed with the rubber in a mixing step prior to the incorporation of the carbon black filler. 
     It is also necessary to attain a certain minimal temperature, about 320° F. (160° C.), during the mixing of the rubber, carbon black, and azodicarbonamide. To obtain the best results, this temperature should be maintained while mixing for at least three minutes. An improvement in dynamic properties can be realized by simply allowing the batch to reach this temperature, but the greatest benefit will result if the batch is mixed at the high temperature for at least three minutes. 
     Once mixed, the rubber compound may placed in a mold and cured by heating in the normal manner for rubber goods. The curing process is not accompanied by the formation of gas bubbles or cells in the final product. This was confirmed by examination under magnification and by the measurement of the density of the final cured rubber. Also, the density of the cured rubber containing azodicarbonamide mixed according to the method of this invention was not substantially lower than that obtained from a similar recipe containing no azodicarbonamide. This indicated that there were no voids or bubbles present in the final cured rubber. 
     The azodicarbonamide may be used to improve the dynamic properties of many different kinds of rubber. The rubber may be a single polymer, or a blend of different polymers. Examples of the different polymers that may be used are: emulsion polymerized styrene-butadiene rubber, solution polymerized styrene-butadiene rubber, polybutadiene, natural rubber, polyisobutylene, and polyisoprene. The invention has been particularly tested with solution polymerized styrene-butadiene rubber with medium to high vinyl groups. It is preferred that the azodicarbonamide be employed at a concentration of from about 0.1 to about 20 phr in the rubber polymer, more preferably at a concentration of from about 0.1 to about 10 phr. 
     The carbon blacks suited for use with the azodicarbonamide are those normally used in elastomeric compounds. These are carbon blacks with Nitrogen Surface Areas of 10–250 10 3  m 2 /kg, as determined by ASTM D4820. The structure or DBPA Number of the black should measure from 10–250×10 −5  m 3 /kg by ASTM D2414. It is preferred that the carbon black be employed at a concentration of from about 30 to about 150 parts per hundred of rubber. 
     EXAMPLES 
     Formulations and Materials: 
     The raw materials used in the following examples are all obtained from commercial sources. 
     The SBR used is Solflex 1216, solution polymerized styrene-butadiene rubber produced by Goodyear Polymers. The styrene content is 12%, the vinyl content is 46% and the T g  is −45° C. 
     The BR used is Budene 1207, polybutadiene rubber produced by Goodyear. 
     The carbon blacks used were produced by Engineered Carbons Inc. 
     The oil used is Sundex 8125, aromatic processing oil produced by Sun Oil. 
     The azodicarbonamide used was Celogen® AZ 130, produced by the Uniroyal Chemical Co. 
     Zinc Oxide, produced by the Zinc Corporation of America. 
     Stearic acid, produced by Monson Chemical. 
     The 6PPD used is Flexzone 7P, a trademark of the Uniroyal Chemical Company for N-(1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine. 
     The wax is Bowax 615, microcrystalline wax produced by IGI Boler Inc. 
     The TBBS is Delac NS, a trademark of the Uniroyal Chemical Company for N-tert-butyl-2-benzothiazolylsulfenamide, (TBBS). 
     Sulfur 21-10 is produced by Georgia Gulf 
     A general mixing procedure is given below: 
     First Pass: 
     The rubber, carbon black, azodicarbonamide, and processing oil are charged to a laboratory internal mixer and mixed for 1.5 minutes. Alternatively, the rubber and carbon black could be mixed prior to the addition of the azodicarbonamide. The ram is raised and a sweep performed. The ram is lowered and mixing continued until a designated temperature is reached. The materials are then mixed for a predetermined time at the designated temperature and then discharged as a first masterbatch. 
     Second Pass: 
     The first masterbatch, mixed in the first pass, is charged to the mixer. Stearic acid, zinc oxide, antiozonant, and wax are added. These ingredients are added in a second pass to avoid possible interference with the promoting process. The materials are mixed for one minute, then the ram is raised and a sweep performed. The ram is lowered and mixing continued until the batch reaches an internal temperature of 138° C., or for a maximum of 5 minutes, thereby producing a second masterbatch. 
     Third Pass: 
     The second masterbatch, produced in the second pass, is charged to the mixer. The curatives, sulfur, and accelerators, are added. The materials are mixed for one minute, then the ram is raised and a sweep performed. The ram is lowered and mixing continued until the batch reaches an internal temperature of 104° C. 
     Materials for the examples were mixed in a Farrel BR1600 internal mixer, with a volume of 1.6 liters. The curing properties were determined on a Model ODR 2000 oscillating disc rheometer. The dynamic properties were determined at 60° C. and 10 Hz over a strain range of 0.2 to 14% single strain amplitude using a Model RPA 2000 Rubber Process Analyzer. 
     Standard ASTM test methods were used for measurement of Mooney viscosity (D3346-90), ODR cure characteristics (D2084-92), stress-strain (D412-92), and Shore A hardness (D2240-91). 
     The advantages and the important features of the present invention will be more apparent from the following examples. 
     Example 1 
     This example demonstrates the use of azodicarbonamide in reducing hysteresis and the benefit of mixing it with rubber and carbon black in a separate mixing step. A comparison of compounds B and D demonstrates that the greatest reduction in hysteresis is obtained when the azo compound is added along with the carbon black and that adding the carbon in a separate step after the incorporation of the azo compound not only produces less reduction in hysteresis, but also reduces scorch safety. A comparison of compounds B and C shows that the presence of other compounding ingredients in the same mixing step along with the carbon and the azo compound produces a final rubber vulcanizate with higher hysteresis than that produced when the rubber, carbon, and azo compound are mixed without other compounding ingredients. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
               
             
               
               
               
               
               
             
               
             
               
               
               
               
               
             
               
             
               
               
               
               
               
             
               
             
               
               
               
               
               
             
               
             
               
               
               
               
               
             
           
               
                   
               
               
                   
                 A 
                 B 
                 C 
                 D 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 SBR 
                 75.00 
                 75.00 
                 75.00 
                 75.00 
               
               
                 BR 
                 25.00 
                 25.00 
                 25.00 
                 25.00 
               
               
                 N234 Carbon Black 
                 72.00 
                 72.00 
                 72.00 
                 0.00 
               
               
                 Oil 
                 32.50 
                 32.50 
                 32.50 
                 0.00 
               
               
                 Azodicarbonamide 
                 0.00 
                 3.00 
                 3.00 
                 3.00 
               
               
                 Zinc Oxide 
                 0.00 
                 0.00 
                 2.50 
                 0.00 
               
               
                 Stearic Acid 
                 0.00 
                 0.00 
                 1.00 
                 0.00 
               
               
                 6PPD 
                 0.00 
                 0.00 
                 2.00 
                 0.00 
               
               
                 Wax 
                 0.00 
                 0.00 
                 1.50 
                 0.00 
               
               
                 TOTAL MB-1 
                 204.50 
                 207.50 
                 214.50 
                 103.00 
               
               
                   
               
             
          
           
               
                 Mixing Note: MB-A Bring temperature up to 320 F. and discharge 
               
               
                 MB B-D Bring temperature up to 320 F., hold 5 min. and discharge. 
               
             
          
           
               
                 MB-1 
                 204.50 
                 207.50 
                   
                 103.00 
               
               
                 N234 Carbon Black 
                 0.00 
                 0.00 
                   
                 72.0 
               
               
                 Oil 
                 0.00 
                 0.00 
                   
                 32.5 
               
               
                 Zinc Oxide 
                 2.50 
                 2.50 
                   
                 2.50 
               
               
                 Stearic Acid 
                 1.00 
                 1.00 
                   
                 1.00 
               
               
                 6PPD 
                 2.00 
                 2.00 
                   
                 2.00 
               
               
                 Wax 
                 1.50 
                 1.50 
                   
                 1.50 
               
               
                 TOTAL MB-2 
                 211.5 
                 214.5 
                   
                 214.5 
               
               
                   
               
             
          
           
               
                 Mixing Note: A - B Bring temperature up to 280 F. and discharge. 
               
               
                 D - Bring temperature up to 300 F. and discharge. 
               
             
          
           
               
                 MB-2 
                 211.50 
                 214.50 
                 0.00 
                 214.50 
               
               
                 MB-1 
                 0.00 
                 0.00 
                 214.50 
                 0.00 
               
               
                 TBBS 
                 1.50 
                 1.50 
                 1.50 
                 1.50 
               
               
                 Sulfur 21-10 
                 2.00 
                 2.00 
                 2.00 
                 2.00 
               
               
                 TOTAL 
                 215.00 
                 218.00 
                 218.00 
                 218.00 
               
               
                   
               
             
          
           
               
                 Mixing Note: Bring temperature up to 220 F. and discharge. 
               
             
          
           
               
                 Rheometer - 
                   
                   
                   
                   
               
               
                 ODR 2000 @ 160 C. 
               
               
                 ML, Nm 
                 0.91 
                 1.1 
                 1.0 
                 0.95 
               
               
                 MH, Nm 
                 4.33 
                 4.80 
                 4.6 
                 4.78 
               
               
                 ts2, Minutes 
                 4.9 
                 5.7 
                 5.4 
                 3.6 
               
               
                 t50, Minutes 
                 7.7 
                 13.1 
                 11.8 
                 11.9 
               
               
                 t90, Minutes 
                 11.2 
                 19.1 
                 16.9 
                 17.9 
               
               
                 Mooney Scorch 
               
               
                 MS @ 135 C. 
               
               
                 t3, Minutes 
                 14′ 
                 23′ 
                 18′ 
                 9′ 
               
               
                 Mooney Viscosity 
                 76 
                 79 
                 79 
                 78 
               
               
                 ML 1′ + 4′ @ 100 C. 
               
               
                 Stress/Strain 
               
               
                 Cure Time @ 160 C., 
                 15 
                 25 
                 25 
                 25 
               
               
                 Min. 
               
               
                 100% Modulus, MPa 
                 2.4 
                 3.6 
                 3.7 
                 3.7 
               
               
                 300% Modulus, MPa 
                 11.2 
                   
                 17.1 
                 16.2 
               
               
                 Tensile, MPa 
                 18.8 
                 16.8 
                 17.6 
                 18.7 
               
               
                 % Elongation 
                 460 
                 280 
                 300 
                 330 
               
               
                 Hardness, Shore A 
                 64 
                 65 
                 67 
                 67 
               
             
          
           
               
                 Tan Delta 
               
             
          
           
               
                 RPA 2000 @ 60 C., 
                   
                   
                   
                   
               
               
                 10 Hz 
               
               
                 % Strain 
               
               
                  0.7 
                 0.154 
                 0.112 
                 0.127 
                 0.134 
               
               
                  1 
                 0.177 
                 0.141 
                 0.148 
                 0.163 
               
               
                  2 
                 0.242 
                 0.177 
                 0.199 
                 0.219 
               
               
                  5 
                 0.276 
                 0.211 
                 0.226 
                 0.250 
               
               
                  7 
                 0.281 
                 0.208 
                 0.224 
                 0.249 
               
               
                 14 
                 0.267 
                 0.199 
                 0.216 
                 0.237 
               
             
          
           
               
                 G′kPa 
               
             
          
           
               
                 % Strain 
                   
                   
                   
                   
               
               
                  0.7 
                 6105 
                 4705 
                 5463 
                 7360 
               
               
                  1 
                 5447 
                 4321 
                 4924 
                 6530 
               
               
                  2 
                 3967 
                 3464 
                 3766 
                 4895 
               
               
                  5 
                 2543 
                 2526 
                 2683 
                 3209 
               
               
                  7 
                 2214 
                 2279 
                 2381 
                 2802 
               
               
                 14 
                 1659 
                 1839 
                 1864 
                 2093 
               
               
                   
               
             
          
         
       
     
     Example 2 
     This example demonstrates that the rubber, carbon black, and azo compound should be mixed at least three minutes to obtain the full benefit of the addition of the azo compound. Although the compounds may be mixed for longer times, there is no benefit to be gained. 
     
       
         
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                   
               
               
                   
                 A 
                 B 
                 C 
                 D 
                 E 
                 F 
                 G 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 SBR 
                 75.00 
                 75.00 
                 75.00 
                 75.00 
                 75.00 
                 75.00 
                 75.00 
               
               
                 BR 
                 25.00 
                 25.00 
                 25.00 
                 25.00 
                 25.00 
                 25.00 
                 25.00 
               
               
                 N234 Carbon 
                 72.00 
                 72.00 
                 72.00 
                 72.00 
                 72.00 
                 72.00 
                 72.00 
               
               
                 Black 
               
               
                 Oil 
                 32.50 
                 32.50 
                 32.50 
                 32.50 
                 32.50 
                 32.50 
                 32.50 
               
               
                 Azodicarbonamide 
                 0.00 
                 3.00 
                 3.00 
                 3.00 
                 3.00 
                 3.00 
                 3.00 
               
               
                 TOTAL 
                 204.50 
                 207.50 
                 207.50 
                 207.50 
                 207.50 
                 207.50 
                 207.50 
               
               
                   
               
               
                 Mixing: 
               
               
                 A - Bring temperature up to 320 F. and discharge. 
               
               
                 B - Bring temperature up to 320 F., hold 5 min. and discharge. 
               
               
                 C - Bring temperature up to 320 F., hold 4 min. and discharge. 
               
               
                 D - Bring temperature up to 320 F., hold 3 min. and discharge. 
               
               
                 E - Bring temperature up to 320 F., hold 2 min. and discharge. 
               
               
                 F - Bring temperature up to 320 F., hold 1 min. and discharge. 
               
               
                 G - Bring temperature up to 320 F., and discharge. 
               
             
          
         
       
     
     
       
         
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
               
               
             
           
               
                   
               
               
                   
                 A 
                 B 
                 C 
                 D 
                 E 
                 F 
                 G 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 MB-1 
                 204.50 
                 207.50 
                 207.50 
                 207.50 
                 207.50 
                 207.50 
                 207.50 
               
               
                 Zinc Oxide 
                 2.50 
                 2.50 
                 2.50 
                 2.50 
                 2.50 
                 2.50 
                 2.50 
               
               
                 Stearic Acid 
                 1.00 
                 1.00 
                 1.00 
                 1.00 
                 1.00 
                 1.00 
                 1.00 
               
               
                 6PPD 
                 2.00 
                 2.00 
                 2.00 
                 2.00 
                 2.00 
                 2.00 
                 2.00 
               
               
                 Wax 
                 1.50 
                 1.50 
                 1.50 
                 1.50 
                 1.50 
                 1.50 
                 1.50 
               
               
                 TOTAL 
                 211.50 
                 214.50 
                 214.50 
                 214.50 
                 214.50 
                 214.50 
                 214.50 
               
               
                 MB-2 
                 211.50 
                 214.50 
                 214.50 
                 214.50 
                 214.50 
                 214.50 
                 214.50 
               
               
                 TBBS 
                 1.50 
                 1.50 
                 1.50 
                 1.50 
                 1.50 
                 1.50 
                 1.50 
               
               
                 Sulfur 21-10 
                 2.00 
                 2.00 
                 2.00 
                 2.00 
                 2.00 
                 2.00 
                 2.00 
               
               
                 TOTAL 
                 215.00 
                 218.00 
                 218.00 
                 218.00 
                 218.00 
                 218.00 
                 218.00 
               
               
                   
               
               
                 Mix Time 
                 0 min. 
                 5 min. 
                 4 min. 
                 3 min. 
                 2 min. 
                 1 min. 
                 0 min. 
               
               
                 Rheometer-MDR 
               
               
                 2000 @ 160 C. 
               
               
                 ML, Nm 
                 0.35 
                 0.31 
                 0.30 
                 0.32 
                 0.32 
                 0.30 
                 0.32 
               
               
                 MH, Nm 
                 2.1 
                 2.3 
                 2.3 
                 2.4 
                 2.4 
                 2.4 
                 2.4 
               
               
                 ts2 
                 5.1 
                 6.5 
                 5.7 
                 5.3 
                 5.0 
                 5.2 
                 5.1 
               
               
                 t50 
                 7.1 
                 12.4 
                 12.2 
                 12.4 
                 12.2 
                 12.4 
                 12.3 
               
               
                 t90 
                 10.2 
                 17.8 
                 18.4 
                 18.3 
                 18.1 
                 18.4 
                 18.3 
               
               
                 Stress/Strain 
               
               
                 Cure times @ 160 C. 
                 15′ 
                 25′ 
                 25′ 
                 25′ 
                 25′ 
                 25′ 
                 25′ 
               
               
                 100% Mod. MPa 
                 2.5 
                 3.6 
                 3.6 
                 3.5 
                 3.6 
                 3.8 
                 3.5 
               
               
                 300% Mod. MPa 
                 12.1 
                   
                   
                   
                   
                 18.1 
                 17.2 
               
               
                 Tensile MPa 
                 20.8 
                 16.5 
                 16.3 
                 16.8 
                 17.0 
                 18.8 
                 18.5 
               
               
                 % Elongation 
                 460 
                 260 
                 280 
                 280 
                 290 
                 310 
                 310 
               
               
                 Hardness Shore A 
                 65 
                 65 
                 66 
                 65 
                 67 
                 68 
                 68 
               
               
                 Mooney Viscosity 
                 87 
                 78 
                 80 
                 80 
                 80 
                 78 
                 81 
               
               
                 ML 1′ + 4′ @ 100 C. 
               
               
                 Mooney Scorch MS @ 
               
               
                 135 C. 
               
               
                 t3 
                 20′ 
                 25′ 
                 25′ 
                 24′ 
                 22′ 
                 22′ 
                 19′ 
               
             
          
           
               
                 TAN D 
               
             
          
           
               
                 RPA 2000 @ 60 C., 
                   
                   
                   
                   
                   
                   
                   
               
               
                 10 Hz 
               
               
                 % Strain 
               
               
                  0.7 
                 0.139 
                 0.104 
                 0.103 
                 0.104 
                 0.104 
                 0.103 
                 0.105 
               
               
                  1 
                 0.160 
                 0.129 
                 0.119 
                 0.126 
                 0.129 
                 0.129 
                 0.134 
               
               
                  2 
                 0.221 
                 0.174 
                 0.169 
                 0.173 
                 0.182 
                 0.192 
                 0.188 
               
               
                  5 
                 0.268 
                 0.211 
                 0.213 
                 0.213 
                 0.220 
                 0.228 
                 0.236 
               
               
                  7 
                 0.261 
                 0.207 
                 0.204 
                 0.208 
                 0.217 
                 0.223 
                 0.235 
               
               
                 14 
                 0.247 
                 0.197 
                 0.191 
                 0.196 
                 0.204 
                 0.208 
                 0.219 
               
             
          
           
               
                 G′kPa 
               
             
          
           
               
                 % Strain 
                   
                   
                   
                   
                   
                   
                   
               
               
                  0.7 
                 5960 
                 4613 
                 4667 
                 5019 
                 5463 
                 5929 
                 6327 
               
               
                  1 
                 5405 
                 4290 
                 4328 
                 4525 
                 5049 
                 5323 
                 5722 
               
               
                  2 
                 4003 
                 3451 
                 3476 
                 3642 
                 3902 
                 4066 
                 4440 
               
               
                  5 
                 2529 
                 2435 
                 2396 
                 2582 
                 2722 
                 2801 
                 2902 
               
               
                  7 
                 2244 
                 2215 
                 2235 
                 2311 
                 2405 
                 2494 
                 2555 
               
               
                 14 
                 1768 
                 1789 
                 1841 
                 1882 
                 1946 
                 1990 
                 2050 
               
               
                   
               
             
          
         
       
     
     In view of the many changes and modifications that can be made without departing from principles underlying the invention, reference should be made to the appended claims for an understanding of the scope of the protection to be afforded the invention.