Antistatic tire

Abstract: An antistatic tire (1) and relative production method, whereby a portion (17; 24; 27) of a tread (4) made of an electrically insulating mix is hollowed out and filled with a cement (C) in the form of a carbon black mix in a volatile liquid; the carbon black mix being left inside the hollow portion (17; 24; 27) when the volatile liquid evaporates, and defining inside the tread (4) at least one conducting body (18; 25; 29) communicating with a rolling surface (8) of the tire (1).

Description: The present invention relates to an antistatic tire. More specifically, the present invention relates to an antistatic tire of the type comprising electric current conductors on the tread, for grounding the static electricity of a vehicle. Antistatic tires are disclosed in several prior documents including EP-A-705722, GB 544757 and EP-A-787604. In particular, from EP-A-705722 as the dosest prior art, antistatic tires are known wherein the tread, shoulders and sidewalls are covered with a thin conductive layer of a conducting mix, which is applied uniformly on the tread blocks and in the grooves between the blocks to form an electrical bridge between the sidewalls, shoulders and tread. The above solution involves several drawbacks, due to rapid in-service wear of the conductive layer portion covering the blocks, and crumbling of the conductive layer portion covering the grooves, as a result of the fatigue stress to which the tread is subjected in use. Crumbling of the conductive layer is especially marked in the groove region, where the effects of fatigue stress concentrate. As a result, the original continuous conducting layer of the tire is soon interrupted at various points and no longer capable of grounding the electric charges. It is an object of the present invention to provide a straightforward, low-cost method of producing antistatic tires capable of maintaining lifelong electrical conductivity. According to the present invention, there is provided a method of producing an antistatic tire as claimed in Claim 1. The present invention also relates to an antistatic tire formed using the above method. According to the present invention, there is provided an antistatic tire as claimed in Claim 5. The present invention will be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a schematic cross section, with parts removed for clarity, of a preferred embodiment of the tire according to the present invention; Figure 2 shows a plan view of a portion of the Figure 1 tire; Figure 3 shows a view in perspective of the tire portion in Figure 2; and Figure 4 shows a section along line IV-IV in Figure 3. Number 1 in Figure 1 indicates an antistatic tire having an axis of rotation 2 and a plane of symmetry 3 perpendicular to axis 2. Tire 1 comprises a tread 4 in the form of a cylindrical shell extending about axis 2 and having two symmetrical halves on either side of plane 3; tread 4 comprises a central portion 5, and two annular shoulders 6 located on either side of plane 3 to define the opposite lateral ends of tread 4; and shoulders 6 are formed from a rubber mix having an electrical resistivity of less than 10 9 ohms x cm and substantially equal to the electrical resistivity of the mix on sidewalls 7 of tire 1. With reference to Figures 2, 3 and 4, tread 4 is defined externally by a rolling surface 8, which is defined by the outer surfaces of shoulders 6, and by the outer surfaces of a number of blocks 9 and annular beads 10 defined on central portion 5 by a number of grooves 11 substantially crosswise to plane 3, and by circumferential annular-grooves 12. Tread 4 also comprises a network or matrix of slits comprising a number of slits 13 and 14, which extend to a given depth, preferably of at least a millimeter, through rolling surface 8 and the surface of grooves 11 and 12. Each slit 13, 14 is defined by two facing walls 15 and 16, which define part of a hollow portion or region 17 extending along the whole of tread 4. Hollow region 17 houses an electrically conducting matrix 18 made from a carbon black mix having an electrical resistivity of less than 10 9 ohms x cm to form an electrical bridge between the tread and sidewalls 7 of tire 1, which, as stated, are made from an electrically conducting mix. Matrix 18 is formed from a cement "C" comprising the aforementioned mix, which is of known type and provides for bonding the facing walls 15 and 16 of slits 13 and 14. The electrically conducting matrix 18 is formed by means of a series of operations comprising the steps of knurling rolling surface 8 and grooves 11 and 12 of tread 4 to form the matrix of slits 13 and 14; stressing tread 4 to separate the facing walls 15 and 16 of slits 13 and 14 and define hollow region 17; and pouring inside hollow region 17 a cement "C" comprising said carbon black mix in a volatile liquid solution, which, when evaporated, leaves the mix inside hollow region 17. In use, whereas the part of matrix 18 extending along at least part of rolling surface 8 is worn off, the part of matrix 18 extending along grooves 11 and 12 remains substantially intact, and is capable of ensuring life-long conductivity of tire 1.

Claims: A method of producing an antistatic tire, the tire (1) comprising two electrically conducting sidewalls (7); a tread (4) made of at least one electrically insulating mix, said tread (4) comprising two lateral electrically conducting shoulders (6) and being defined externally by a rolling surface (8); and a number of surface transverse and circumferential grooves (11, 12) crossing each other to define a groove pattern on the tread (4); and the method being characterized by comprising the steps of forming in the tread (4) a matrix of superficial transverse and circumferential slits (13, 14) crossing each other, the slit matrix extending over the rolling surface (8) and inside said grooves (11, 12); pouring into said superficial slits (13, 14) a cement (C) comprising a carbon black mix in a volatile liquid; and evaporating the volatile liquid to leave said carbon black mix inside said slits (13, 14) to define, superficially inside the tread (4), at least one electrically conducting matrix (18) communicating with said rolling surface (8) and said shoulders (6). A method as claimed in Claim 1, wherein said superficial slits (13, 14) are at least 1 mm deep. A method as claimed in Claim 1 or 2, wherein said matrix of slits (13, 14) is formed by knurling. A method as claimed in any of the preceding Claims, and further comprising the step of stressing the tread (4) to open said slits (13, 14) before pouring said cement (C). An antistatic tire comprising two electrically conducting sidewalls (7); a tread (4) made of at least one electrically insulating mix, said tread (4) comprising two lateral electrically conducting shoulders (6) and being defined externally by a rolling surface (8); and a number of surface transverse and circumferential grooves (11, 12) crossing each other to define a groove pattern on the tread (4); characterized by further comprising a matrix of superficial transverse and circumferential slits (13, 14) crossing each other, the slit matrix extending in the tread (4) over the rolling surface (8) and inside said grooves (11, 12); and at least one electrically conductive matrix (18) occupying said slit matrix and made of a cement (C) comprising a carbon black mix; said electrically conductive matrix (18) communicating with said rolling surface (8) and said shoulders (6)and having been formed by pouring into said slit matrix said carbon black mix in a volatile liquid, and by evaporating the volatile liquid to leave said carbon black mix inside said slits (13, 14). A tire as claimed in Claim 5, wherein said superficial slits (13, 14) are at least 1 mm deep.

Inventors: DUCCI STEFANO, KONDO YOCHIRO, SILICANI JOSE, STRAFFI PAOLO, DUCCI, STEFANO, KONDO, YOCHIRO, SILICANI, JOSE, STRAFFI, PAOLO, Silicani, José
Applicants: BRIDGESTONE CORP, BRIDGESTONE CORPORATION
Application year: 1998
Main classification: B60C19
IPC codes: B29D30, B60C11, B60C19, B29K21