Abstract:
A cut resistant pneumatic tire is provided. The tire has embedded in its sidewalls and/or tread, short lengths of adhesive coated monofilament nylon fibers. Adhesion between the rubber of the tire and the adhesive coated fibers provides a stiffer, more cut resistant composition.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to cut resistant pneumatic tires, especially off-the-road tires and heavy duty off-the-road tires. 
     Heavy duty off-the-road tires, because of the nature of their use, are exposed to cutting and delamination caused by sharp rocks and uneven terrain. In the prior art, this problem was sometimes addressed by including wire fragments embedded in the rubber of the tread and sidewalls of such tires. Although shredded wire works well to prevent cut growth, it may be relatively expensive (brass coated wire works best), and is very difficult to handle and process into rubber. Wire tends to jam the processing equipment and causes accelerated wear of the processing equipment. 
     It is an object of the present invention to provide a cut resistant tire having at least as good cut resistance properties as wire reinforced tires, which are easier to process and to build than wire reinforced tires. 
     Other objects of the invention will be apparent from the following specification and claims. 
     SUMMARY OF THE INVENTION 
     A cut resistant pneumatic tire is provided which comprises at least a pair of beads, carcass plies comprising parallel cord reinforcement wrapped around the beads, a tread disposed over the carcass plies in a crown area of the tire, and sidewalls disposed over the carcass plies between the tread and the beads. The tread and/or the sidewalls or both has disposed therein about 1-20 phr adhesive coated chopped monofilament, nylon fibers. The nylon fibers used have an oblong cross section 0.51 cm (0.20 inch) 0.127 cm (0.050 inch) inches wide, about 0.017 inches thick and about to 1.27 inches long. In the preferred embodiment, the adhesive causes the nylon fibers to bond to the rubber of the tire. The nylon monofilament used, prior to processing into fiber, has a tenacity of at least 6 g/denier, an initial modulus of at least 30 g/denier and a shrinkage of not greater than 5%. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a heavy duty off-the-road tire having adhesive coated monofilament nylon fibers dispersed in the tread and sidewalls. 
     FIG. 2 illustrates oblong monofilament fibers used in the invention. 
     FIG. 3 illustrates a cross section of a heavy duty off-the-road tire having nylon fibers dispersed in the tread, sidewalls and tread base. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference now to FIGS. 1 and 3, a heavy duty, off-the-road tire 10 of the invention is illustrated. The tire comprises beads 12, carcass plies 14 wrapped around beads 12, tread base 16 disposed over carcass plies 14 in a crown area of tire 10, tread 18 disposed over tread base 16 and sidewall 20, disposed between the tread and beads 12. 
     As used herein, when used in a general sense, the term tread includes the tread 18 and tread base 16. 
     In the illustrated embodiment, fibers 22 are dispersed in the tread 18, tread base 16 and sidewall 20. Those skilled in the art will recognize that, for a given purpose, a tire may be constructed according to the invention having fiber in any one portion, or a combination of two or more of the illustrated portions of the tire. 
     When employed in tread 18 and sidewall 20, the fibers 22 improve the cut resistance of the tire, and when used in tread base 16, the fibers help prevent delamination of the tire. 
     It is believed that monofilament fibers demonstrate improved strength over flock fibers or multi-filament fibers because of their integrity, i.e. the fibers will not break up into component parts during processing. It is believed that any high strength or high modulus monofilament fiber, e.g. aramid, polyester, or nylon can be used in the invention. 
     The fibers used in the invention (illustrated in FIG. 2) are prepared by E. I DuPont Nemours Inc, Wilmington, Delaware by coating an oblong nylon monofilament (Hyten™, available from DuPont) with an adhesive and chopping the adhesive coated monofilament into short pieces. The fibers of the invention have a length of about (0.254 cm) to 1.27 cm (0.5 cm), preferably 0.508 cm (0.2 cm) to 0.889 cm (0.35 in.), a thickness of about 0.013 cm (0.005 cm) to 0.043 cm (0.017 cm) preferably 0.025 cm (0.01 in.) to 0.036 cm (0.014 in), and a width of 0.051 cm (0.020 in) to 0.127 cm. (0.050 in.), preferably 0.076 cm (0.03 in.) to 0.102 cm (0.04 in.). Prior to processing, the monofilament has a tenacity of at least 6 g/denier, an initial modulus of at least 30 g/denier and a shrinkage of not greater than 5%. 
     The fibers are coated with adhesive using conventional processing using a single end dip coating and a multi-end (15 to 20 or more ends) chopping process to obtain fiber having the desired length. In the illustrated embodiment, the monofilament used was about 2000 denier and had a tenacity of about 9 g/denier, an initial modulus of about 50 g/denier, an elongation at break of at least 18% and a shrinkage of not greater than 4%. 
     As is known in the art, RFL (resorcinol, formaldehyde, latex) adhesives provide a means for bonding substances to rubber that do not generally bond well to rubber. 
     It was theorized according to the present invention that improving the bond between fibers and rubber using an RFL coating on the fibers would improve the stiffness, tear resistance, stone penetration and other properties of the rubber composition. 
     The RFL solution used for coating the fibers comprised, in general, water, formaldehyde, latex, resorcinol, sodium hydroxide, ammonium hydroxide and RF resin. 
     The RFL coated fibers were processed into rubber using a Banbury mixer, made by Ferrell Corp, and the consistency and appearance of the fiber loaded rubber was similar to that observed for rubber which is loaded with shredded wire. 
     When loaded with 1-20 phr fibers, preferably 1-5 phr, it was found that rubber compounds incorporating the adhesive coated fibers demonstrated remarkably improved tear resistance as compared to a control compound prepared without the use of fibers. 
     Tires of the invention are made as is conventional in the art except that the rubber used to make the tread, tread base, and/or sidewalls is loaded with the adhesive coated fibers described herein instead of shredded wire. It is believed that because of the adhesive coating there is a substantial interaction between the fiber and rubber which is responsible for the improved properties described in the following examples. 
     Rubber compounds containing adhesive coated chopped monofilament fibers and used in the tire of the invention demonstrated a 300% modulus of about 4-9 MPa, a tensile strength of 5-25 MPa, an elongation of 250-750%, a 100° C. rebound of 30-64, preferably 58-64, and a 100° C. hardness of 48-56. The invention is illustrated further with reference to the following examples. 
     EXAMPLE 1 
     Industrial Dip Solutions 
     This example illustrates standard RFL dip solutions used by DuPont on synthetic fibers. It is believed that the first formulation provided below was used for the RFL coating on the fibers described herein. 
     In the following formulations, the first number illustrated represents the strength of the composition used in percentage by weight in water, and the second number illustrates the amount of the composition (by weight %) used in the RFL dip formulation. 
     
         ______________________________________Formaldehyde Dip Solutions______________________________________1.      Formaldehyde 37% (2%)   *Gen-Tac 41% (42%)   Resorcinol Flakes (2%)   Sodium Hydroxide 1.67% (3%)   Ammonium Hydroxide 28-30% (2%)   H.sub.2 O 49%2.      Formaldehyde 37% (8%)   Gen-Tac 41% (48%)   Resorcinol Flakes (15%)   H.sub.2 O 29%3.      Formaldehyde 37% (2%)   Gen-Tac 41% (33%)   **PEXWL Additive 20% (18%)   Resorcinol Flakes (2%)   Sodium Hydroxide 2.86% (7%)   H.sub.2 O 38%4.      Formaldehyde 37% (2%)   Gen-Tac 41% (45%)   ***Penacolite R2170 75% (4%)   Ammonium Hydroxide 28-30% (1%)   ****Vulcan 3 (HAF Carbon Black) 25% (11%)   H.sub.2 O 39%5.      Formaldehyde 37% (2%)   Gen-Tac 41% (5%)   Penacolite R2170 75% (4%)   Ammonium   Hydroxide 28-30% 1%   H.sub.2 O 43%______________________________________ *Gen-Tac is the tradename for SBR latex solution which is available from General Tire. **PEXWL is a DuPont code name. ***Penacolite R 2170 is an RF resin equivalent to Penasic, available from Goodyear ****Vulcan 3 is a carbon black available from Cabot Corp. 
    
     EXAMPLE 2 
     This example illustrates physical properties observed in sidewall rubber compound when loaded with various amounts of adhesive coated fibers. The adhesive coated fibers used in the compound comprised oblong monofilament nylon (Hyten) approximately 0.089 cm (0.035 in.) wide, 0.028 cm (0.011 in.) thick and 0.635 cm (0.25 in.) long. The fibers had been coated with the RFL adhesive described in Example 1. It is believed that the first formula described in the example was used. 
     In the formulation described, Nolo is natural rubber, Nadenic is synthetic polybutadiene rubber and 399 is carbon black 399. In addition to the ingredients listed, each compound contained 0.5-1.0 phr vulcanizing agents and 0.5 to 1.5 phr resorcinol resin curing agents, 4-5 phr oils, 1-2 phr accelerators and 2-3 phr antioxidants. Compound 253 is used as the control. 
     In the ATS aging test, samples of the rubber composition were tested after vulcanization, and again after 14 days in an oven at 70° C. 
     
         ______________________________________SUBJ: DIPPED CHOPPED HYTEN LABEVALUATION OTR TIRE CMPDSCompound No.       253      254    255    256  257______________________________________Nolo (phr)  50       50     50     50   50Nadenic     50       50     50     50   50(phr)399         45       45     45     42.5 42.5(Chopped    --        2      4     4    2Hyten (phr)______________________________________ATS     Reg/Aged140/135 253      254      255    256    257______________________________________300% Mod   5.5/8.0  5.0/7.8  5.0/7.6                            4.5/   5.0/Ten     19.6/18.8            8.2/8.0  7.2/7.8                            6.5/5.8                                   9.0/6.4Elong   670/575  400/325  375/310                            370/275                                   450/295Reb @   60/60    61.5/60.0                     61/60  62/60  62/61100CHard @  52/54    50.5/53  52/53.5                            50/53  51/52100CSp Gr   1.097    1.094    1.096  1.088  1.090Zwick Reb   56.4     56.8     56.4   57.6   58.2AgedDispersion   68       68       50     50     50*Bdgstne   576      578      575    563    580Pent______________________________________ 
    
     Rheometer data, not shown, has demonstrated that the cure rate of the fiber loaded compound is not changed as compared to the control. 
     In the Hot Flex test, a strip sample of rubber is penetrated with a pin, subjected to mechanical flexing for a set period of time, and the size of any crack propagating from the pin hole is measured. 
     
         ______________________________________PD100C   253       254    255     256  257______________________________________ Hot PGFlex     Reg/Aged5&#39;       1/1       1/1    1/1     1/1  1/1 30      1/1       1/2    1/1     1/1  1/1120      1/3       3/4    2/1     2/8  1/2180      2/7       3/4    2/1     2/8  2/2240      3/8       4/4    3/1     3/8  3/2______________________________________ 
    
     In the Instron tear test, a sample of rubber is cut and then stretched to break. 
     The force at break in Newtons (N) is measured. 
     
         __________________________________________________________________________Reg/Aged__________________________________________________________________________**Inst TearIntgAvg  2075/2050        3124/2056              3661/1777                    2954/1913                          2478/1846PkAvg  293/314        367/338              364/329                    346/330                          327/314***Din AbrVol LossWt Loss  74    77    76    79    81__________________________________________________________________________ 
    
     In the Stebler adhesion test, two or more strips of rubber are laminated and the force needed to separate them is measured. In this test, the adhesion of the sidewall rubber was measured when a strip of the rubber was laminated with itself (the same rubber composition), as well as with conventional base rubber, bias ply rubber, and radial ply rubber. The subscript numbers are a subjective indication of the roughness of the rubber surface of the lamination, 1 being the best and 4 being relatively smooth. A rough surface indicates tearing between the laminate layers which suggests a higher adhesion between the layers than rubber strength in the layers. 
     
         ______________________________________****StebAdh     253      254      255    256    257______________________________________self    144/177  142/167  145/178                            150/177                                   148/166Base    94/115.sub.2            94/118.sub.2                     97/117 85/102.sub.2                                   93/113.sub.2Bias    85/104.sub.2-3            77/92.sub.2-3                     78/97.sub.2                            75/90.sub.2                                   85/102.sub.2Radial  53/62.sub.3            52/63.sub.2-3                     50/65.sub.2-3                            58/64.sub.3                                   59/70.sub.2-3______________________________________Steb Adh   Aged 14 days oven @ 70° C.______________________________________self    95/115.sub.1            107/133  101/119                            92/107 101/121Base    65/78.sub.2            62/--.sub.2                     67/78  60/71.sub.2                                   55/67.sub.2-3Bias    63/74.sub.2-3            63.sub.2-3                     61/71.sub.2-3                            58/71.sub.2-3                                   60/70.sub.2-3Radial  30/--.sub.4-5            23/--.sub.4-5                     29/41.sub.4                            25/--.sub.4                                   21/--.sub.4-5______________________________________ *Bridgestone Penetration Test **Instron Tear Test ***Din Abrasion Test ****Stebler Adhesion Test 
    
     Tests for the sidewall rubber demonstrate improved tear and flexing resistance properties when the fiber is loaded with adhesive coated fibers. Other demonstrated properties were at least as good as the control. Compound 255 demonstrated the best overall results. Similar tests were run on tread compounds (base and cap) as illustrated below. The compounds described below, in addition to the ingredients described, contained 0.5-1.0 phr vulcanizing agents, 4-5 phr oils, 1-2 phr accelerators, and 2-3 phr antioxidants. 
     
         __________________________________________________________________________SUBJECT: DIPPED CHOPPED HYTEN LAB EVALUATION OTR TREAD CMPDS   1. Base Compound       2. *Cap Compound   792                    796   Control        793     794  795  Control                               797      798  799__________________________________________________________________________Nolo (phr)   100  100     100  100  100  100      100  100CB 599 (phr)   30   30      30   27.5 --   --       --   --CB 405 (phr)   --   --      --   --   45   45       45   42.5Hysil   20   20      20   18.5 15   15       15   12.5571 (phr)(Chopped   --   2       4    4    --   2        4    4HytenATS 140/135   UTS/ATS Results aged 14 days oven @ 70° C.300% Mod   9.2/13.6        9.1/--  9.5/--                     --/--                          9.0/13.2                               9.0/--   9.5/--                                             8.0/--Ten     26.2/20.5        10.8/11.6                10.5/8.9                     8/9.0                          22.8/16.2                               10.5/9.4 10.2/8.2                                             9.0/8.4Elong   600/451        335/290 300/245                     280/247                          580/394                               330/257  320/222                                             320/250Reb @ 100° C.   68   68.5    69.3 72.2 55.5 57       56   60.2Aged    70   71      71   70   55   55       55   57Hard @  100° C.   55   55      55   54   55   54       56   54.7Sp Gr   1.117        1.123   1.119                     1.109                          1.137                               1.138    1.138                                             1.126Zwick Reb   Aged Results 14 days oven @ 70° C.   69.2 66.2    66.4 69.4 50.2 49.6     49.0 51.2Dispersion   80   60      60   60   75   55       60   55Bdgstne Pent   543  529     533  542  478  481      475  480__________________________________________________________________________                    795                     799                    4 phr                   4 phr  792   793   794   lo blk                          796   797   798   lo blkPD100C Control        2 phr 4 phr HISIL Control                                2 phr 4 phr HISIL__________________________________________________________________________Hot PG Flex  Reg Aged5&#39;     2/3   2/2   2/3   3/3   2/2   2/1   2/2   3/230     2/9   2/8   2/9   8/20  2/5   2/1   2/5   3/360     3/17  2/14  4/13  13/36 2/7   2/1   2/6   3/3120    5/28  3/17  11/22 24/0  2/8   2/2   2/6   6/3180    11/39 4/20  14/28 30/-- 2/8   2/2   2/26  6/5240    15/-- 4/26  16/32 37/-- 2/8   2/2   2/28  7/6Inst Tear  Reg AgedIntg Avg  1665/1457        1573/1594              1508/1319                    1551/1403                          1924/1782                                1978/1776                                      1542/1572                                            2205/2198Pk Avg 315/324        335/353              327/336                    342/328                          382/420                                394/366                                      374/380                                            415/434Din AbrVol Loss  147   144   137   134   178   181   169   165Wt Loss  --    149   143   137   186   187   176   169Steb Adhself   130/157.sub.1        141/165.sub.1              129/158.sub.1                    94/109.sub.1                          238/285.sub.1                                247/293.sub.1                                      240/298.sub.1                                            231/279.sub.1TA076  116/144.sub.1        134/161.sub.1              122/144.sub.1                    114/137.sub.1                          102/119.sub.1                                103/118.sub.1                                      121/143.sub.1                                            114/132.sub.1GB018  110/134.sub.1        115/136.sub.1              96/114.sub.1                    101/120.sub.1                          95/113.sub.1                                89/105.sub.1                                      96/116.sub.1                                            87/108.sub.1GB135  83/101.sub.1        89/106.sub.1              68/79.sub.1-2                    83/96.sub.1                          123/146.sub.1                                124/145.sub.1                                      123/133.sub.1                                            128/150.sub.1TA334  53/63.sub.2        61/72.sub.2              61/73.sub.2                    62/72.sub.2                          52/62.sub.2                                55/65.sub.2                                      53/64.sub.2                                            58/69.sub.2Steb Adh  Aged 14 days oven @ 70° C.self   89/98.sub.1        119/151              91/105                    78/97 163/188                                158/159                                      148/178                                            160/198TA076  95/111.sub.1        84/99 92/111                    79/93 58/64.sub.2                                69/80.sub.2                                      58/67.sub. 2                                            58/60.sub.3GB018  66/79.sub.2        61/74 69/85 68/82 32/40.sub.3                                45/55.sub.2-3                                      45/55.sub.2-3                                            39/52.sub.3GB135  55/64.sub.1-2        61/76.sub.1-2              40/56.sub.2                    57/70.sub.2                          51/59.sub.2                                38/53.sub.3                                      50/62.sub.2-3                                            57/70.sub.2TA334  35/42.sub.3-4        37/44.sub.3-4              39/48.sub.3                    37/43.sub.3-4                          20/25.sub.4                                22/29.sub.4                                      14/21.sub.4                                            18/24.sub.4__________________________________________________________________________ 
    
     From the above data it can be again concluded that the fiber loaded compounds demonstrate superior tear resistance, adhesion and rebound properties. 
     The base compound 794 and cap compound 799 were shown to have the best overall properties. 
     While specific embodiments of the invention have been illustrated and described, it will be recognized by those skilled in the art that the invention can be variously modified and practiced without departing from the spirit of the invention. The invention is limited only by the following claims.