Abstract:
The present invention provides an organic solvent-free composition useful as an adhesive for bonding natural rubber compounds, synthetic rubber compounds and a combination of natural and synthetic rubber compounds.

Description:
This application is a continuation of application Ser. No. 08/470,915, filed Jun. 6, 1995, now abandoned, which is a division of 08/305,017 filed Sep. 13, 1994, allowed which is a continuation-in-part application of application Ser. No. 08/180,679, now U.S. Pat. No. 5,395,879. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention will now be described as embodied in several preferred embodiments. 
     Elastomers selected from the group consisting of natural rubber, styrene butadiene rubber, polybutadiene rubber, polychloroprene rubber, nitrile rubber, polyurethane rubber, butyl rubber and mixtures thereof, may be employed in the composition of the present invention. About 25.0 to 50.0% of elastomer by total weight of the composition is required for optimal adhesive properties. 
     The compositions of the present invention further comprise about 0.02 to 0.60 weight percent pH adjusters selected from the group consisting of potassium hydroxide, aqueous ammonia and mixtures thereof. 
     The compositions of the present invention also comprise about 0.10 to 1.8% surfactant/stabilizer selected from the group consisting of sodium lignosulfate, octylphenoxypolyethoxyethanol, polyoxyethylene sorbitrol fatty acid ester, sulfated fatty acid and mixtures thereof. 
     The compositions of the present invention are manufactured by mixing pH adjusters water with the elastomer emulsion, using mild agitation. The total water content is about 40 to 60 weight percent (by total weight of the composition). 
     Optionally, the compositions of the present invention may include up to about 10.0% carbon black selected from the group consisting of N-300 and N-200 series (designations used in the adhesive industry for carbon blacks) and mixtures thereof. 
     The compositions of the present invention may also optionally include up to about 0.75% zinc oxide. 
     The compositions of the present invention may also optionally include up to about 0.40% sulfur. 
     The compositions of the present invention may also optionally include up to about 0.20% accelerator selected from the group consisting of dibenzothiazyl disulfide, tetraethyl thiuram disulfide, tetramethyl thiuram disulfide, tetramethyl thiuram monosulfide, n-tert-butyl-2-benzothiazolesulfenamide, diphenyl guanidine and mixtures thereof, is a critical component of the compositions of the present invention. 
     The compositions of the present invention may also optionally include up to about 0.50% viscosity adjusters selected from the group consisting of hydroxyethyl cellulose, hydroxypropyl methylcellulose and mixtures thereof. 
     Lastly, the compositions of the present invention may also include up to about 23% resin emulsion selected from the group consisting of alkylphenol novolac, hydrogenated rosin and mixtures thereof. 
     Although the resulting aqueous adhesive may be used in tire applications, it is recommended that the aqueous adhesive made without carbon black be not used for tire applications. However, the aqueous adhesive made using carbon black may be advantageously applied to the bottom of an extruded tire tread and or to a carcass portion by spraying, dipping, brushing or flooding. After drying the adhesive, the tread is contacted with the carcass. The dried adhesive forms a thin layer between the tread and carcass portion of the tire. Further operations in the manufacture of the tire may be carried out in the usual manner. 
     The adhesive compositions of the present invention may also be used to bond tire tread ends to each other. However, in using the adhesives of the present invention in tire retreading, it has been found that both the surfaces to be bonded to each other have to be coated with the adhesive. It has also been determined that the adhesives of the present invention are capable of being used with a greater variety of rubbers than what is possible with the adhesives of parent application Ser. No. 08/180,679. Polyester fibers, yams, filaments, cords or fabric may be bonded to vulcanizable rubber compounds by means of the compositions of the present invention, in order to prepare radial, bias or belted-bias passenger tires, truck tires including the carcasses, belts, motorcycle and bicycle tires, off-the-road tires, transmission belts, V-belts, conveyor belts, hose, gaskets, rubbers tarpaulins and the like. 
     The invention will now be described as embodied in the following example compositions, wherein all percentages are by weight of the entire composition: 
     
         ______________________________________      #1    #2      #3      #4    #5______________________________________Water        44.53   54.67   46.39 54.59 48.95Natural Rubber        36.23   41.77   29.50 43.87 39.91Carbon Black 0.51    2.69    6.81  --    0.56Zinc Oxide   0.03    --      --    0.55  0.03Sulfur       0.02    --      --    0.37  0.02MBTS Accelerator        0.01    --      --    0.20  0.01Resin Emulsion        18.41   --      15.55 --    10.13Aqueous Ammonia        0.02    0.10    0.26  0.04  0.02Potassium Hydroxide        0.03    0.02    0.02  0.04  0.02Hydroxyethyl Cellulose        0.10    0.24    0.17  0.13  0.23Sodium Lignosulfate        0.11    0.51    1.30  0.21  0.12        100.0   100.0   100.0 100.0 100.0Strip Adhesion (ppi)*        94.0    96.0    120.0 92.0  91.0______________________________________ *ppi = pounds per inch (all showed rubber tear) 
    
     It has been discovered that carbon black is always required in tire retreading applications, as part of the solvent-free adhesive. Carbon black may be dispensed with in non-tire applications, but in such a non-tire application, an accelerator is always required. The accelerator speeds the adhesion of uncured rubber on cured rubber by curing the uncured rubber. 
     Thus it is apparent that there has been provided, in accordance with the invention, a composition useful as an adhesive for use with natural and synthetic rubbers, which composition fully satisfies the aspects and advantages set forth above. While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications and variations which fall within the spirit and broad scope of the appended claims.