Antistatic vehicle tire and method of manufacturing such a tire

Abstract

The invention relates to a vehicle tire comprising a tread portion and a package of reinforcement layers arranged underneath the tread portion. The tread portion comprises a tread base layer arranged underneath the tread layer, and at least one rubber member that extends in the radial direction of the tire from the ground contacting surface to the reinforcement package. The tread layer rubber composition has an electrical resistivity at room temperature of more than 108 ohm-cm, the tread base layer rubber composition of between 106 ohm-cm and 108 ohm-cm, the member rubber composition of less than 106 ohm-cm; and the rubber composition of at least one layer of the reinforcement package has a electrical resistivity at room temperature of less than 106 ohm-cm. The vehicle tire combines a low rolling resistance with improved conductivity to avoid build-up of static electricity.

Claims

1. A vehicle tire comprising: a tread portion and a package of rubberized reinforcement layers arranged radially inwards from the tread portion, the tread portion comprising a tread rubber layer that provides a ground contacting surface and is disposed in a radially outward part of the tire, and a tread base rubber layer arranged radially inwards from the tread layer, the tread portion further comprising at least one rubber member that extends in the radial direction of the tire from the ground contacting surface to at least one layer of the reinforcement package, the rubber composition of the tread rubber layer having an electrical resistivity at room temperature of more than 10.sup.8 ohm-cm; the rubber composition of the tread base rubber layer having an electrical resistivity at room temperature of between 10.sup.6 ohm-cm and 10.sup.8 ohm-cm; the rubber composition of the at least one rubber member having an electrical resistivity at room temperature of less than 10.sup.6 ohm-cm; and the rubber composition of the at least one layer of the reinforcement package having an electrical resistivity at room temperature of less than 10.sup.6 ohm-cm.

2. The vehicle tire according to claim 1, wherein the tread base layer rubber composition comprises 5-25 parts by weight on the total composition of carbon black having a nitrogen adsorption specific surface area (N.sub.2SA) according to ASTM D3037 above 60 m.sup.2/g and 10-35 parts by weight on the total composition of carbon black having a nitrogen adsorption specific surface area (N.sub.2SA) according to ASTM D3037 below 60 m.sup.2/g.

3. The vehicle tire according to claim 1, wherein the member rubber composition comprises 15-45 parts by weight on the total composition of carbon black having a nitrogen adsorption specific surface area (N.sub.2SA) according to ASTM D3037 above 60 m.sup.2/g.

4. The vehicle tire according to claim 1, the tread portion thereof further comprising rubber wing tips that are disposed at either side of the tire in the width direction thereof and extend in a circumferential direction of the tire, the rubber composition of the rubber wing tips having an electrical resistivity at room temperature of less than 10.sup.6 ohm-cm.

5. The vehicle tire according to claim 4, wherein the wing tip rubber composition comprises 20-50 parts by weight on the total composition of carbon black having a nitrogen adsorption specific surface area (N.sub.2SA) according to ASTM D3037 above 60 m.sup.2/g.

6. The vehicle tire according to claim 4, wherein the tread base rubber, wing tip rubber and/or reinforcement rubber compositions have a dibutyl phthalate absorption (DBP) according to ASTM 2414-90 of between 60-140 ml/100 g.

7. The vehicle tire according to claim 4, the wing tips being arranged in conductive contact with the tread base layer.

8. The vehicle tire according to claim 4, the wing tips being arranged in conductive contact with the at least one layer of the reinforcement package.

9. The vehicle tire according to claim 4, the wing tips being arranged in direct contact with the tread base layer.

10. The vehicle tire according to claim 4, the wing tips being arranged in direct contact with a sidewall layer.

11. The vehicle tire according to claim 10, the rubber composition of the sidewall layer and/or the at least one rubber member being the same as the rubber composition of the wing tips.

12. The vehicle tire according to claim 4, wherein the tread base rubber, wing tip rubber and/or reinforcement rubber compositions have a dibutyl phthalate absorption (DBP) according to ASTM 2414-90 of between 80-110 ml/100 g.

13. The vehicle tire according to claim 1, comprising an undertread rubber layer arranged radially inwards of the tread base layer, the rubber composition of the undertread rubber layer having an electrical resistivity at room temperature of more than 10.sup.6 ohm-cm.

14. The vehicle tire according to claim 13, the undertread layer rubber composition having an electrical resistivity at room temperature of more than 10.sup.8 ohm-cm.

15. The vehicle tire according to claim 1, each rubber member thereof extending in the circumferential direction of the tire over its total circumference.

16. The vehicle tire according to claim 1, the at least one rubber member is two rubber members arranged aside from each other in a central zone of the tire.

17. A method of manufacturing a vehicle tire according to claim 1, the method comprising: forming the tread portion by co-extruding the tread layer rubber composition, the tread base layer rubber composition and the member rubber composition to form a co-extrusion comprising three different rubber compositions; forming the tire with the co-extruded tread portion; and vulcanizing the tire.

18. The method of manufacturing a vehicle tire according to claim 4, the method comprising: forming the tread portion by co-extruding the tread layer rubber composition, the tread base layer rubber composition, the member rubber composition and the wing tip rubber composition to form a co-extrusion comprising four different rubber compositions; forming the tire with the co-extruded tread portion; and vulcanizing the tire.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The invention will now be further elucidated on the basis of the accompanying figures, without however being limited thereto. In the figures:

(2) FIG. 1 schematically shows a perspective exploded view of a cross-sectional part of a tire according to the prior art;

(3) FIG. 2 schematically shows a perspective view of a cross-sectional part of a tire according to an embodiment of the invention;

(4) FIG. 3 schematically shows a perspective view of a cross-sectional part of a tire according to another embodiment of the invention;

(5) FIG. 4 schematically shows a cross-section of the tread portion 20 of the tire of FIG. 1 after co-extrusion and before molding into shape; and

(6) FIG. 5 schematically shows a cross-section of the tread portion 20 of the tire of FIG. 2 after co-extrusion and before molding into shape.

DETAILED DESCRIPTION

(7) Referring to FIG. 1, tire 1 comprises a tread portion 20 that is composed of different parts as will be elucidated further below, and a sidewall portion 10 of a rubber polymer. The tread portion 20 comprises a tread layer 21 that is provided with longitudinal and transverse grooves 22 and provides a ground contacting surface 23 disposed in a radially outward part of the tread portion 20. The tread portion 20 further comprises a tread base layer 26 arranged underneath the tread layer 21, the tread base layer 26 being formulated to provide adequate adhesion to an underlying reinforcement package 12 (see also FIGS. 2 and 3) of several reinforcement layers. Reinforcement package 12 generally comprises one or more cap ply layers 6 (in FIG. 1 two cap ply layers (6a, 6b) are shown) which may be a nylon overhead, one or more belt or steel cord layers 7 (in FIG. 1 two belt layers (7a, 7b) are shown) and a carcass layer 13, provided underneath the belt layers 7. At the sides of the tread portion 20, wing tips 25 are provided disposed at either side of the tire in the width direction 5 thereof and extending in a circumferential direction 4 of tire 1. The carcass layer 13 is mechanically connected to the bead wire 14 and is provided with an inner liner 11 of a rubber that may differ from the rubber used in the sidewall 10.

(8) Referring to FIG. 2, a tire 1 according to an embodiment of the invention is shown. Tire 1 comprises a tread portion 20 that is composed of different parts as will be elucidated further below, and a sidewall portion 10 of a rubber polymer. The tread portion 20 comprises a tread layer 21 that is provided with longitudinal and transverse grooves 22 and provides a ground contacting surface 23 disposed in a radially outward part of the tread portion 20. The tread portion 20 further comprises a tread base layer 26 arranged underneath the tread layer 21, the tread base layer 26 being formulated to provide adequate adhesion to an underlying reinforcement package 12, which, as shown in FIG. 1 may comprise one or more cap ply layers 6, one or more belt or steel cord layers 7, and a carcass layer 13. At the sides of the tread portion 20, wing tips 25 are provided disposed at either side of the tire in the width direction 5 thereof and extending in a circumferential direction 4 of tire 1 in direct contact with the sidewall rubber 10. The carcass layer 13 is mechanically connected to the bead wire 14 and is provided with an inner liner 11. The tread portion 20 of the embodiment shown comprises a poorly conducting tread layer 21 whereas the wing tip 25 rubber composition has an electrical resistivity at room temperature of less than 10.sup.6 ohm-cm. In the embodiment shown, the tread portion 20 further comprises two rubber members (30a, 30b) that extend in the radial direction 3 of the tire from the ground contacting surface 23 to the reinforcement package 12.

(9) The tread layer 21 rubber composition has an electrical resistivity at room temperature of more than 10.sup.8 ohm-cm, and is therefore poorly conducting. The rubber composition used in the tread layer 21 of the present invention preferably comprises fillers containing silica for instance. Such compositions enhance the performance of the tire when driving on wet roads in particular and provide economical rolling resistance. The rubber compositions used in other parts of the tire may be synthetic rubbers or natural rubber and blends thereof. Non-limitative examples of synthetic rubbers include ethylene-propylene-diene copolymer rubber (EPDM), polyisoprene rubber (IR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), butyl rubber, and halogenated butyl rubber. Among these rubbers, SBR, such as SBR obtained by emulsion polymerization and SBR obtained by solution polymerization are preferably used.

(10) In accordance with the invention, the tread base layer 26 rubber composition has an electrical resistivity at room temperature of between 10.sup.6 ohm-cm and 10.sup.8 ohm-cm. The tread base layer 26 is this able to conduct some electrical charges (is moderately conducting) but is essentially formulated to improve rolling and handling behavior of the tire 1. The rubber composition of the members (30a, 30b) is chosen to have an electrical resistivity at room temperature of less than 10.sup.6 ohm-cm, while at least one layer rubber composition of the reinforcement package 12 has an electrical resistivity at room temperature of less than 10.sup.6 ohm-cm.

(11) Typical fillers used in the more conductive parts of the tire 1 comprise carbon black and/or ionic salts in amounts sufficient to obtain the electrical resistivity's mentioned above. Silane coupling agent may be used if desired, as well as other ingredients generally used in the rubber industry, such as zinc oxide, stearic acid, antioxidants, wax, and vulcanizing agents, within a range such the advantages of the present invention are not adversely affected. The conductive rubber compositions used in the tire for the wing tips 25 and/or the conductive rubbers members (30a, 30b) may be different or the same.

(12) According to another embodiment of the invention, a vehicle tire is provided wherein the tread base layer rubber composition comprises 5-25 parts by weight on the total composition of carbon black having a nitrogen adsorption specific surface area (N.sub.2SA) according to ASTM D3037 above 60 m.sup.2/g and 10-35 parts by weight on the total composition of carbon black having a nitrogen adsorption specific surface area (N.sub.2SA) according to ASTM D3037 below 60 m.sup.2/g.

(13) A typical member (30a, 30b) rubber composition comprises 25 parts by weight on the total composition of carbon black having a nitrogen adsorption specific surface area (N.sub.2SA) according to ASTM D3037 of 80 m.sup.2/g. A typical wing tip 25 rubber composition comprises 35 parts by weight on the total composition of carbon black having a nitrogen adsorption specific surface area (N.sub.2SA) according to ASTM D3037 of 60 m.sup.2/g. A typical tread base 26 rubber and/or reinforcement 12 rubber composition has a dibutyl phthalate absorption (DBP) according to ASTM 2414-90 of between 95 ml/100 g.

(14) In the embodiment shown, the wing tips 25 are arranged in conductive contact with the tread base layer 26. This is achieved by arranging the wing tips 25 in direct contact with the tread base layer 26, as shown in FIGS. 1 and 3. An alternative would be to provide a conductive layer (not shown) between the wing tips 25 and the moderately conducting layer 26. As also shown in the figures, the wing tips 25 are also arranged in conductive contact with the carcass layer 10, and this is achieved by arranging them in direct contact with the sidewall layers 10. This also means that the tread base layer 26 may not extend across the whole width of the tire tread portion 20. The present embodiment provides several conducting paths between the ground contacting surface 23 and the bead region 14, which is conductive per se. A first path is provided by the rubber members (30a, 30b) and the reinforcement package 12, whereas a second path is provided by the rubber members (30a, 30b), the tread base layer 26 and the wing tips 25. Providing several conducting paths allows to conduct more current but also improves the reliability of such conductance. If one path fails another path may still fulfill its function. It should be noted that the majority of the electrical current will flow through the rubber members (30a, 30b) directly to the reinforcement package 12 and to the bead region 14. A lesser amount of current will flow through the tread base layer 26 and wing tips 25 to the reinforcement package 12 and the bead region 14. This allows to optimize the properties of the tire 1 with respect to antistatic, rolling and handling behavior altogether.

(15) According to an embodiment of the method according to the invention, the tread layer 21, the tread base layer 26, the wing tips 25 and the rubber members (30a, 30b) are co-extruded using a triplex extrusion die in case the wing tip 25 rubber formulation is the same as the rubber formulation of the conductive members (30a, 30b). A cross-section of the produced co-extrusion 40 is shown in FIG. 4. The co-extrusion 40 may then be combined with other layers of the tire 1 such as a reinforcement layer 6, 7, 13, for instance by using a lamination drum.

(16) Referring to FIG. 4, another embodiment of a vehicle tire according to the invention is shown. The tire in this embodiment comprises a tread base layer 26 (the layer directly underneath the tread layer 21) and an undertread layer 24 arranged underneath the tread base layer 26. The undertread layer 24 rubber composition has an electrical resistivity at room temperature of more than 10.sup.7 ohm-cm. The undertread layer 24 is most conveniently co-extruded together with tread layer 21, tread base layer 26, and the conductive rubber members (30a, 30b).

(17) According to another embodiment of the method according to the invention, the tread layer 21, the tread base layer 26 and undertread layer 24, the wing tips 25 and the rubber members (30a, 30b) are co-extruded using a quadruplex extrusion die in case the wing tip 25 rubber formulation is the same as the rubber formulation of the conductive members (30a, 30b). A cross-section of the produced co-extrusion 40 is shown in FIG. 5. The co-extrusion 40 may then be combined with other layers of the tire 1 such as reinforcement layers 6, 7, 13, for instance by using a lamination drum.

(18) The thickness of the rubber layer as a continuous layer after the curing is 100 m-1 mm, preferably 200-800 m considering the durability up to the running end stage. When the thickness exceeds 1 mm, the rolling resistance of the tire is degraded and the occurrence of uneven wear is promoted as mentioned above and also the peeling phenomenon is apt to be caused due to the difference of modulus of elasticity to the tread rubber and it is difficult to stably maintain the low value of electric resistance in the tire up to the running end stage.

(19) Although the invention has been described herein by reference to specific embodiments thereof, it will be understood that such embodiments are illustrative only and are susceptible of modification and variation with departing from the inventive concepts disclosed. All such modifications and variations, therefore, are intended to be encompassed within the spirit and scope of the appended claims.