WITH LOW ELECTRICAL RESISTANCE

DESCRIPTION

The present invention relates to a method for the manufacture of a pneumatic tyre with high electrical conductivity.

Some types of pneumatic tyres, such as those for passenger cars, are affected by the problem relating to low electrical conductivity and, therefore, to the difficulty with which the electrostatic charges, which inevitably form on the bodies of such cars, can be discharged to the ground by means of the passage of electric charges, firstly from the vehicle to the pneumatic tyre through the rim and, subsequently, from the pneumatic tyre to the ground. This problem is mainly due to replacement of the carbon black within the tread for vehicles with silica. In fact, as is known to a person skilled in the art, the use of silica as a substitution for carbon black, if on the one hand makes it possible to obtain significant advantages both with regard to rolling resistance and wet grip, on the other hand implies the disadvantage, which increases with increased silica content, of determining an increase in the electrical resistivity of the compounds themselves.

A solution adopted in order to solve the above problem regards the insertion within the tread bands of one or more conductor elements, some of which define a portion of the rolling surface of the tread connected to the conductive components arranged within the pneumatic tyre. The presence of such conductor elements implies a series of disadvantages that are due both to possible irregular wear of the tread as a whole, and to a particular complexity of preparation of the tread that can, furthermore, impose the use of production means that are different from those that are normally employed.

For a more complete understanding of the problems mentioned above, it should be pointed out that, in order to further improve the rolling resistance, also within the compounds of the inner portions of the pneumatic tyre, the carbon black can be replaced with silica. This necessarily results in a decrease in conductivity also of the inner portions and, consequently, the passage of the electric charges within the pneumatic tyre will be further disadvantaged .

The inventors of the present invention have found a solution that guarantees the discharge to earth of the electrostatic charges formed on the car body, independently of the electrical conductivity of the various portions of the pneumatic tyre or of the degree of wear of the relative tread portion. In this way it will be possible to manufacture a pneumatic tyre characterized by a low rolling resistance, without this leading to problems caused by a failure to discharge the electrostatic charges to earth.

The object of the present invention is a method for the manufacture of pneumatic tyres; said method being characterized in that it comprises a surface deposition step, wherein on an outer surface of a finished pneumatic tyre a conductive material is deposited in vapor form, up until the formation of a conductive layer.

Preferably, the conductive layer covers the entire outer surface of said pneumatic tyre.

Preferably, the conductive layer has a thickness of between 2 nm and 1 pm.

The term "finished pneumatic tyre" refers to a pneumatic tyre that has already been subjected to the vulcanization process.

Preferably, said surface deposition step is performed by means of sputtering techniques or else carbon evaporation or vapor deposition.

Preferably, said conductive material is selected from graphite, aluminum, copper or alloys thereof. A further object of the present invention is a pneumatic tyre manufactured according to the present invention .

For a better understanding of the present invention, the following example is given for illustrative and non limiting purpose.

EXAMPLES

A deposition was made on an outer surface of a pneumatic tyre and by means of a sputtering technique. In particular, the outer surface of the pneumatic tyre was used as a deposition surface in a Chemical Vapor Deposition process wherein the target material used was graphite. The deposition process was performed under vacuum at a pressure of less than 0.1 Pa.

By means of the deposition process described above, a 0.1 pm layer of graphite was deposited over the entire outer surface of the pneumatic tyre. In this regard it should be specified that the graphite layer was also deposited upon the outer surface portions of the pneumatic tyre between the tread pattern blocks .

After the formation of the graphite layer, the pneumatic tyre was subjected to a measurement of the electrical resistance between the rim and a central portion of the central tread portion in accordance with the international standard ASTM F 1971-05. This measurement provided an electrical resistance value of 30 MOhm.

The same measurement, carried out under the same operating conditions, was performed on the same type of pneumatic tyre, which however was not subjected to the surface deposition step and was, therefore, devoid of the graphite layer. The measurement provided an electrical resistance value greater than 100 MOhm.

From the experimental tests described above it is clear how the method of the present invention is able to guarantee the production of a pneumatic tyre comprising an outer surface characterized by a low electrical resistance. In this way the discharge to earth of the electrostatic charges formed on the car body is ensured. With the pneumatic tyre of the present invention, the discharge of the electrostatic charges takes place entirely on the outer surface of the pneumatic tyre, from the metal rim to the road surface. In this way it will be possible to manufacture a pneumatic tyre with low rolling resistance guaranteeing, at the same time, the correct discharge of the electrostatic charges formed on the car.

Furthermore, the sputtering technique guarantees the implementation of the layer of the conductive material also within the recesses of the tread pattern. In this way, even when part of the tread is consumed, the presence of the layer of conductive material within the recesses will equally guarantee the conductivity needed in order to discharge the electrostatic charges to earth.