Abstract:
A process for reclaiming cured or semi-cured rubber, by subjecting a mass of rubber to be reclaimed to a solvent effective to swell said mass, passing the formed swollen mass of rubber through restriction means having small openings, such as a perforated plate, deleterious or devulcanizing substances being comprised in at least one of said restriction means and said swollen mass of rubber.

Description:
This is a continuation of application Ser. No. 08/185,546, filed on Jan. 21, 1994 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a process for reclaiming cured or semi-cured rubber and to rubber reclaimed by said process. 
     It is important in industry to reduce costs, increase efficiency, use less expensive raw materials and add value to by-products. The trend in the rubber reclaiming industry is to find methods which produce a useful formulation at a lower cost and with a better quality. Certainly, as close as these methods come to the composition of origin the better such reclaiming will be deemed. 
     2. Description of the Related Art 
     Brazilian patent specification PI 8500981 discloses a process for regenerating vulcanized rubber using the combined action of a solvent which swells the rubber and a material which is deleterious or devulcanizing. Deleterious materials described include copper, manganese, iron, chrome, nickel and cobalt, and their alloys and derivatives. These metals may be a part of the milling material. Devulcanizing agents disclosed include derivatives of guanidine, hydrazine and phenylamine. It describes the employment of mills in which the deleterious action of certain chemical materials are applied at the same time in which the particles are reduced. This process resulted in obtaining a better quality reclaim at a lower cost than the one achieved out of the same composition but reclaimed by the conventional process, in which heating is applied as a reclaiming means (in a digestor or autoclave), along with mechanical refining. 
     The process of Brazilian PI 8500891 requires a long milling time, typically 8-10 hours. 
     GB 1334718 discloses a process for pulverizing rubber, which includes subjecting the fragments of this material to a temperature of less than -40° C., by means of cryogenic agents, to facilitate the separation of the rubber from the remaining constituents of the compositions, including the metallic components. After the separation has been made, there is a conventional pulverization process, such as the use of a hammer or other mill. Although the separation of the constituents is thus facilitated, this process has the inconvenience of operating at excessively low temperatures and using a great deal of liquid nitrogen. 
     In U.S. Pat. No. 2,088,920, a process is described for regenerating rubber, using derivatives of guanidine, which have devulcanizing proteins. For an adequate mixture to be made as between the devulcanizer and the rubber, the latter should be freely divided. However, in this patent, there is no description of the specific pulverization process which should be used. 
     In U.S. Pat. No. 4,156,508, a mechanical process is described, using pressure and high temperatures and passing through a refiner to reduce and regenerate the particles of vulcanized rubber, giving a regenerated product with a Shore hardness of between 50 and 62. 
     BR 7606727 describes a process for the recovery and re-use of elastomeric vulcanized material, which involves raising the temperature on the surface of the material to between 2000° and 3000° C. for a brief period of from 1 to 10 seconds. 
     GB 505156 describes a method for pulverizing remains of vulcanized rubber, such objective being achieved by a continuous process, which basically involves the following steps: 
     (1) impregnation of the material to be pulverized, with an intumescent agent; and 
     (2) submitting the material to the mechanical action of a mill so as to reduce the residue to a fine powder and separate the other constituents of the composition from the rubber. 
     In accordance with this patent, any adequate intumescing agents may be used, preferably non-inflammable, chlorated organic solvents. 
     German 2 815 122 employs swelling to weaken the rubber and thus make easier the removal of fibers and wires that reinforce the rubber articles. The process, however, does not reclaim the rubber; it only reduces particles size to between 0.3 to 0.8 millimeters. The use of the rubber obtained thereby is limited to loading other compositions. 
     SUMMARY OF THE INVENTION 
     The present invention pertains to a process of total reclaim of cured or semi-cured rubber, much faster than the process of Brazilian Patent specification PI 8500981. The process of the present invention comprises forming a swollen mass of rubber by subjecting a mass of rubber to be reclaimed to a solvent effective to swell said rubber to be reclaimed, passing the swollen mass of rubber through restriction means having small openings, with deleterious or devulcanizing substances being comprised in at least one of said restriction means and said swollen mass of rubber. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic illustration of the process of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the process of the present invention, rubber is passed through restricted openings under pressure and is reduced in size, at the same time in which it contacts deleterious elements. Following its decompression to a lower pressure it suffers a second break by the produced flash, induced by the solvent which swells the rubber particle. If this operation is repeated with more restricted (smaller) openings each repetition, the reclaim becomes better each repetition, more homogeneous and with characteristics closer to the original rubber composition. 
     The employment of rubber devulcanizing agents and activators of deleterious elements modify the characteristics of the reclaim and speed their actions. Therefore, one applies deleterious or devulcanizing substances. Preferably the deleterious substances are copper, manganese, cobalt, or their alloys or compounds such as salts, e.g. chlorides, acetates, sulphates. Preferably the devulcanzing agents are guanidines and their derivatives such as diphenylguanidine, hydrazines and their derivatives such as phenyl hydrazine, phenyl mines, such as aniline, etc. Other devulcanizing agents often used are the derivatives of fatty acids, mixtures of organo-metallic complexes, halogenated derivatives such as pentachlorothiobenzene, benzoic acid, phthalic anhydride, etc. In this same operation sequence, where the rubber formulation is swollen and broken through restrictions, other products can be added such as plasticizers, resins, loads (fillers), antioxidants, accelerators, curing agents, etc. The product thus obtained in paste or thick oil form is dried in an appropriate drier, the solvent being recovered and capable of being recycled. 
     Solvents which can be used to cause swelling of cured rubber are: 
     ETHERS: ethyl ether, isopropyl ether, butyl ether, hexyl ether, dichlorethyl ether, triglycol dicloride, ethylene oxide, propylene oxide, vinyl ethyl ether, vinyl isopropyl ether. 
     ESTERS: ethyl acetate, isopropyl acetate, butyl acetate, methyl amyl acetate, 2-ethylbutyl acetate, 2-ethylhexyl acetate, methyl acetoacetate, ethyl acetoacetate, amyl acetate. 
     KETONES: acetone, methyl ethylketone, methyl amyl ketone, diacetone alcohol, diisobutyl ketone, acetyl acetone. 
     AMINES: phenyl amine, diphenyl amine, butyl amine, dibutyl amine. 
     CHLORIDES: ethylene dichloride, propylene dicloride, carbon tetrachloride, chloroform, trichlorethane, butyl chloride, vinyl chloride, perchlorethylene. 
     HYDROCARBONS: benzene, toluene, xyilene, rubber solvent, aromatic oil, naphtenic oil, paraffinic oil. 
     PINE DERIVATIVES: pine oil, pine tar 
     It is preferred that the deleterious substances should be provided by being comprised in the restriction means, for example, by use of a perforated plate made or iron-manganese, brass and alloys with copper, manganese or cobalt, or by use of a screen or metallic sponge made of, e.g. copper. This avoids an economic loss from adding agents which are difficult or impossible to recover. 
     In accordance with the present invention, the step of passing through restriction means can often be done in as little time as 5 seconds to 4 minutes, which contrasts with the 8 to 10 hours typical of the prior art milling. 
     The restriction means preferably is metallic and may be one or more of perforated plates or plaques, screens, sponges or porous plaques. 
     The rubber to be reclaimed is any type of vulcanized, semi-vulcanized, cured or semi-cured rubber compositions. In the process of the invention, the swollen rubber mass may be heated or at ambient temperature and may be at a pressure lower or higher than atmospheric. The amounts of deleterious or devulcanizing substances, and the temperatures and pressures used are variable, depending on the rubber composition to be reclaimed. Normally, ambient temperature is used, with enough pressure to force the rubber composition through the restriction means. 
     The process has the following stages as may be seen in FIG. 1 Cured rubber  A! is swollen with an appropriate solvent  B! in tank  1!. Then it is forced through very fine restriction means such as an iron-manganese plate with bores or openings  2! of 3 millimeters in diameter, with the use of an injector (comprising a piston)  3!. The swollen rubber reduced to small pieces is kept in a tank  4! where other products may be added to form the desired composition, such a plasticizer  C!, resins  D!, fillers  E!, antioxidants  F!, accelerators  G!, curing agents  H!, etc. Thereafter, the composition is passed through other injectors  5!,  6!, each one with plates having smaller diameters bores or openings  7!,  8!, until obtaining the desired size. Such size of the grain or dust of solvent swollen rubber is conditional to the desired degree of reclaim. The thinner it becomes a higher degree of reclaim is achieved A. A following stage is to submit the composition to a dryer  9!, where the dry rubber is recovered  I! (being named &#34;Relastomer&#34;), and the solvent is recovered  K!, and is recycled to the process. 
     Except for indicated comparative examples, the examples of the present invention used a perforated iron-manganese plate as described above for the restriction means. The formulations are given in parts by weight. 
     EXAMPLES 
     Example #1 
     It was prepared with the following natural rubber formulations: 
     
         ______________________________________Natural rubber           100.00Zinc oxide               5.00Stearic acid             2.00Carbon Black N-330       45.00BLE antioxidant (Reaction of                    1.00diphenylamine with acetone)Plasticizer (Aromatic oil)                    4.00Accelerator (Sulfenamide)                    0.60Sulphur                  2.50TOTAL                    160.10CHARACTERISTICSVulcanizing   30 min.        145 C.Tensile strength         kg/cm2         285300% Modulus  kg/cm2         115Elongation at break         %              500Hardness      Shore A         65RECLAIMEDSample 1:     Reclaim NR pureSample 2:     Reclaim NR pure                        100.00         Accelerator    0.30         (Sulfenamide)         Sulphur        1.25TOTAL                        101.55______________________________________CHARACTERISTICSVulcanizing  30 min.            at 145 C.                  Sample 1 Sample 2______________________________________Tensile strength        kg/cm2    150      190300% Modulus kg/cm2     95      105Elongation at break        %         480      400Hardness     Shore A    65       67______________________________________ 
    
     Example #2 
     It was prepared with the following acrylonitrile-butadiene NBR rubber formulation: 
     
         ______________________________________Hycar ® 1042 B. F. Goodrich ®                    100.00(Acrylonitrile-butadiene rubber)Zinc oxide               5.00Stearic acid             1.50Carbon black N-550       30.00Carbon black N-762       40.00Plasticizer (Tricresyl phosphate)                    7.00Plasticizer (Epoxidised castor-oil)                    8.00Accelerator (Tetramethylthiuram disulfide)                    0.60Sulphur                  1.00TOTAL                    193.10CHARACTERISTICSVulcanizing   30 min.        at 155 C.Tensile strength         kg/cm2         160300% Modulus  kg/cm2         150Elongation at break         %              330Hardness      Shore A         62RECLAIMEDSample 1:     Reclaim NBR pureSample 2:     Reclaim NBR pure                        193.00         Accelerator    0.30         (Tetramethylthiuram         disulfide)         Sulphur        0.50TOTAL                        193.80______________________________________CHARACTERISTICSVulcanizing  30 min.            at 155 C.                  Sample 1 Sample 2______________________________________Tensile strength        kg/cm2    80       110300% Modulus kg/cm2    60       --Elongation at break        %         300      260Hardness     Shore A   62        65______________________________________ 
    
     Example #3 
     It was prepared with the following polychloroprene CR rubber formulation: 
     
         ______________________________________Neoprene ® W Dupont ®&#39;s (Polychloroprene)                    100.00Zinc oxide               5.00Magnesium oxide          4.0Stearic acid             1.0Carbon black N-110       30.00Plasticizer (Naphtenic oil)                    4.00Coumarone-indene resin   4.00Vaseline                 2.0Antioxidant (Polymerized trimethylquinoline)                    2.0Accelerator (Tetramethylthiuram disulfide)                    0.60Accelerator (Diphenylguanidine)                    0.60Sulphur                  1.00TOTAL                    154.20CHARACTERISTICSVulcanizing   30 min.        at 155C.Tensile strength         kg/cm2         255300% Modulus  kg/cm2         110Elongation at break         %              520Hardness      Shore A        66RECLAIMEDSample 1:     Reclaim CR pureSample 2:     Reclaim CR     154.00         Accelerator    0.30         (Tetramethylthiuram         disulfide)         Accelerator    0.30         (Diphenylguanidine)         Sulphur        0.50TOTAL                        155.10______________________________________CHARACTERISTICSVulcanizing  30 min.            at 155C.                  Sample 1 Sample 2______________________________________Tensile strength        kg/cm2    150      200300% Modulus kg/cm2     80      140Elongation at break        %         500      410Hardness     Shore A    66       68______________________________________ 
    
     Example #4 
     It was prepared with the following styrene butadiene rubber SBR rubber formulation: 
     
         ______________________________________SBR 1502 (styrene butadiene rubber)                    100.00Zinc oxide               4.00Carbon black N-672       25.00Antioxidant (Polymerized trimethylquinoline)                    1.00Accelerator (Sulfenamide)                    1.80Accelerator (Tetramethylthiuram disulfide)                    1.30Accelerator (Tetraethylthiuram disulfide)                    1.30TOTAL                    134.40CHARACTERISTICSVulcanizing  20 min.          at 155C.Tensile strength        kg/cm2           155300% Modulus kg/cm2            39Elongation at break        %                700Hardness     Shore A           49RECLAIMEDSample 1:    Reclaim SBR pureSample 2:    Reclaim SBR      134.40        Accelerator      0.90        (Sulfenamide)        Accelerator      0.60        (Tetramethylthiuram        disulfide)        Accelerator      0.60        (Tetraethylthiuram        disulfide)TOTAL                         136.50______________________________________CHARACTERISTICSVulcanizing  20 min.            at 155C.                  Sample 1 Sample 2______________________________________Tensile strength        kg/cm2    65       105300% Modulus kg/cm2    15        65Elongation at break        %         650      570Hardness     Shore A   49        52______________________________________ 
    
     Example #5 
     It was prepared with the following isobutylene-isoprene copolymer IIR rubber formulation: 
     
         ______________________________________Exxon ® Butyl 268 ® (Isobutylene-                    100.00isoprene copolymer)Zinc oxide               5.00Carbon black N-550       25.00Carbon black N-762       25.00Plasticizer (Paraffinic oil)                    10.00Accelerator (Tetramethylthiuram disulfide)                    1.00Accelerator (Tetraethylthiuram disulfide)                    0.50Sulphur                  2.00TOTAL                    168.50CHARACTERISTICSVulcanizing  20 min.          152C.Tensile strength        kg/cm2           110.00300% Modulus kg/cm2           55.00Elongation at break        %                400.00Hardness     Shore A          52.00RECLAIMEDSample 1:    Reclaim IIR pureSample 2:    Reclaim IIR      168.50        Accelerator      0.50        (Tetramethylthiuram        disulfide)        Accelerator      0.25        (Mercaptobenzothiazole)        Sulphur          1.00TOTAL                         170.25______________________________________CHARACTERISTICSVulcanizing  20 min.            at 152C.                  Sample 1 Sample 2______________________________________Tensile strength        kg/cm2    50       78300% Modulus kg/cm2    20       52Elongation at break        %         360      310Hardness     Shore A   52       54______________________________________ 
    
     Example #6 
     It was prepared with the following polybutadiene rubber (BR) rubber formulation: 
     
         ______________________________________BR-55 Coperbo ® (Polybutadiene rubber)                    100.00Stearic acid             2.00Zinc oxide               5.00Accelerator (Sulfenamide)                    1.25Accelerator (Tetramethylthiuram disulfide)                    0.15Sulphur                  10.00TOTAL                    118.40CHARACTERISTICSVulcanizing  10 min.         at 150C.Hardness     Shore A         66Resilience   %               92RECLAIMEDSample 1:    Reclaim BR pureSample 2:    Reclaim BR      118.40        Sulfenamide     0.60        Accelerator     0.10        (Tetramethylthiuram        disulfide)        Sulphur         2.00TOTAL                        121.10______________________________________CHARACTERISTICSVulcanizing  10 min.            at 150C.                  Sample 1 Sample 2______________________________________Hardness     Shore A   66       68Resilience   %         70       85______________________________________ 
    
     Example #7 
     It was prepared with the following chlorosulfonated polyethylene CSM rubber formulation: 
     
         ______________________________________HYPALON-40 ® Dupont ®&#39;s                    100.00(Chlorosulfonated polyethylene)Litharge                 20.00Magnesium carbonate      20.00Carbon black N-762       50.00Plasticizer (Aromatic oil)                    10.00Accelerator (Mercaptobenzothiazole)                     0.50Accelerator Dupont ®&#39;s                     2.00(Thiuram hexasulphide)TOTAL                    202.50CHARACTERISTICSVulcanizing  30 min.          at 155C.Tensile strength        kg/cm2           225Elongation at break        %                200Hardness     Shore A          73RECLAIMEDSample 1:    Reclaim CMS pureSample 2:    Reclaim CMS      202.50        Accelerator      0.25        (Mercaptobenzothiazole)        Accelerator Dupont ®&#39;s                         1.00        (Thiuram hexasulphide)TOTAL                         203.75______________________________________CHARACTERISTICSVulcanizing  30 min.            at 155C.                  Sample 1 Sample 2______________________________________Tensile strength        kg/cm2    140      180Elongation at break        %         120      100Hardness     Shore A    73       76______________________________________ 
    
     Example #8 
     It was prepared with the following fluorelastomer (FMK) rubber formulation: 
     
         ______________________________________VITON B ® Dupont ®&#39;s (Fluorelastomer)                    100.00Litharge                 15.00Carbon black N-991       30.00Vulcanizer (Hexanediamine - Dupont ®&#39;s)                     3.00TOTAL                    148.00CHARACTERISTICSVulcanizing  20 min.          at 177C.Heating      24 hours         260C.Tensile strength        kg/cm2           155Elongation at break        %                200Hardness     Shore A          78RECLAIMEDSample 1:    Reclaim FMK pureSample 2:    Reclaim FMK      148.00        Vulcanizer (Hexane-                         1.5        diamine - Dupont ®&#39;s)TOTAL                         149.5______________________________________CHARACTERISTICSVulcanizing  20 min.            at 177C.                  Sample 1 Sample 2______________________________________Tensile strength        kg/cm2    80       110Elongation at break        %         160      140Hardness     Shore A   78        82______________________________________ 
    
     Example #9 
     It was prepared with the following propylene-diene terpolymer EPDM rubber formulation: 
     
         ______________________________________NITRIFLEX ® N-762 (Propylene-diene terpolymer)                    100.00Zinc oxide               5.00Stearic acid             2.00Carbon black N-660       80.00Plasticizer (Paraffinic oil)                    10.00Accelerator (Mercaptobenzothiazole disulphide)                    1.50Accelerator (Tetramethylthiuram disulfide)                    0.80Accelerator (Zinc carbamate)                    0.80Sulphur                  2.00TOTAL                    202.10CHARACTERISTICSVulcanizing  25 min.          at 170C.Tensile strength        kg/cm2           160.00300% Modulus kg/cm2           80.00Elongation at break        %                350.00Hardness     Shore A          73.00RECLAIMEDSample 1:    Reclaim EPDM pureSample 2:    Reclaim EPDM     232.90        Accelerator      0.70        (Mercaptobenzothiazole        disulphide)        Accelerator      0.40        (Tetramethylthiuram        disulfide)        Accelerator      0.40        (Zinc carbamate)        Sulphur          1.00TOTAL                         235.40______________________________________CHARACTERISTICSVulcanizing  25 min.            at 170C.                  Sample 1 Sample 2______________________________________Tensile strength        kg/cm2    60.00    100.00300% Modulus kg/cm2    35.00     60.00Elongation at break        %         340.00   300.00Hardness     Shore A   73.00     76.00______________________________________ 
    
     A basic composition was prepared as starting point for a comparison among the reclaim processes: 
     1. Basic composition; 
     2. Reclaim A--reclaim under a slurry mean for reducing particles by means of milling, Patent  PI! BR-8500981; 
     3. Reclaim--using autoclave and refiner under a dry process; 
     4. Reclaim B--reclaim under a slurry mean for reducing particles by means of their passing through restrictions, as described in this Patent. 
     
         ______________________________________1. Basic composition;______________________________________SBR-1712 (Styrene butadiene rubber)                 100.00Carbon Black N-220    27.50Carbon Black N-336    20.00Plasticizer (Aromatic oil)                 4.00Coumarone-indene resin                 5.00Antioxidant (Polymerized trimethylquinoline)                 1.50Zinc oxide            5.00Stearic acid          1.00Accelerator (Sulfenamide)                 1.50Accelerator (Diphenylguanidine)                 0.50Sulphur               1.50TOTAL                 167.50CHARACTERISTICSVulcanizing    45 min  at 150C.Tensile strength          kg/cm2  139.30300% Modulus   kg/cm2   62.10Elongation at break          %       540.00Hardness       Shore A  58.00Abrasion       mm3      0.26______________________________________2. Reclaim A______________________________________SBR-1712 (Styrene butadiene rubber)                 100.00Reclaim A             63.20Carbon black N-336    23.10Carbon black N-220    32.00Zinc oxide            7.10Stearic acid          1.40Plasticizer (Aromatic oil)                 5.70Coumarone-indene resin                 7.10Antioxidant (Polymerized trimethylquinoline)                 2.20Accelerator (Sulfenamide)                 2.20Accelerator (Diphenylguanidine)                 0.70Sulphur               2.20TOTAL                 246.90CHARACTERISTICSVulcanizing    45 min  at 150C.Tensile strength          kg/cm2  136.80300% Modulus   kg/cm2   60.60Elongation at break          %       500.00Hardness       Shore A  58.00Abrasion       mm3      0.29______________________________________3. Reclaim - Usual Commercial Process______________________________________SBR-1712 (Styrene butadiene rubber)                 100.00Reclaimed rubber      63.20Carbon black N-336    23.10Carbon black N-220    32.00Zinc oxide            7.10Stearic acid          1.40Plasticizer (Aromatic oil)                 5.70Coumarone-indene resin                 7.10Accelerator (Sulfenamide)                 2.20Sulphur               2.20TOTAL                 244.00CHARACTERISTICSVulcanizing    45 min  at 150C.Tensile strength          kg/cm2  118.40300% Modulus   kg/cm2   54.20Elongation at break          %       520.00Hardness       Shore A  58.00Wear           mm3      0.34______________________________________4. Reclaim B - A New Process______________________________________SBR-1712 (Styrene butadiene rubber)                 100.00Reclaim B             63.00Carbon black N-336    23.10Carbon black N-220    32.00Zinc oxide            7.10Stearic acid          1.40Plasticizer (Aromatic oil)                 5.70Coumarone-indene resin                 7.10Antioxidant (Polymerized trimethylquinoline)                 2.20Accelerator (Sulfenamide)                 2.20Accelerator (Diphenylguanidine)                 0.70Sulphur               2.20TOTAL                 246.70CHARACTERISTICSVulcanizing    45 min  at 150C.Tensile strength          kg/cm2  135.00300% Modulus   kg/cm2   62.00Elongation at break          %       450.00Hardness       Shore A  58.00Abrasion       mm3      0.30______________________________________