TECHNICAL FIELD

The present invention relates to a tyre retreading method.

BACKGROUND ART

Tyres with worn treads are normally otherwise perfectly good, which means disposing of them is both economically and ecologically unfeasible.

To solve the problem, it is now common practice to retread worn tyres, by fitting a new tread to the old casing.

Tyre retreading methods are mainly of two types : hot and cold.

Cold retreading comprises inserting a green-rubber connecting layer between the cleaned casing and a pre- cured tread, to ensure the old casing adheres properly to the new tread when the tyre is cold-cured.

Cleaning the casing also requires removing any extraneous material which gets into the tyre during use, and which may have damaged the belts underneath the tread. Removing this material normally also requires removing any damaged parts of the belts, and then scraping the portion involved.

The belts are normally made of steel or Kevlar, and serve to stabilize the casing where the tyre interacts with the road surface. Which means any poorly repaired belts could impair performance of the retreaded tyre.

The cleaned casing will have actual cavities in the areas normally occupied by the belts. And it is an object of the present invention to provide a solution to the presence of these cavities.

A common practice is to fill the cavities with the same mix used for the connecting layer connecting the casing to the new tread. Though successful in producing retreaded tyres, this solution has the drawback of forming, in the belt area, structurally discontinuous patches with mechanical characteristics that differ widely from those of the belts and do not guarantee the required performance.

A need is therefore felt for a tyre retreading method designed to eliminate the drawbacks of the known art .

DISCLOSURE OF INVENTION

According to the present invention, there is provided a tyre retreading method, wherein a new tread is applied to a worn-tyre casing; said method comprising a step of cleaning the casing, and a step of filling in holes in the casing with a filler material; said method being characterized in that said filler material comprises a thermosetting organic compound or a thermosetting polymer compound. In a preferred embodiment, the thermosetting organic compound or thermosetting polymer compound is in the group comprising epoxy, vinyl, amide and phenol compounds .

In a preferred embodiment, the filler material comprises a setting compound, preferably in the group comprising amino compound, amide compound, imino compound, and peroxide compound.

In a preferred embodiment, the filler material comprises 5 to 70 parts by weight of setting compound per 100 parts by weight of thermosetting organic compound or thermosetting polymer compound.

BRIEF DESCRIPTION OF THE DRAWINGS

A non-limiting embodiment of the present invention will be described by way of example with reference to the attached drawings, in which :

Figure 1 shows an impact resistance test result graph;

Figure 2 shows a dynamic rigidity test result graph.

BEST MODE FOR CARRYING OUT THE INVENTION EXAMPLES

A filler material was produced comprising 100 parts by weight of bisphenol A epoxy resin, 15 parts by weight of 4 , 4 ' -methylenebis-cyclohexanamine, and 5 parts by weight of natural-rubber latex. More specifically, the filler material was produced in a first step, in which the epoxy resin and latex were mixed; and a second step, in which the mix from the first step was mixed with the 4 , 4 ¹ -methylenebis- cyclohexanamine setting compound. The second step was conducted at low speed to prevent the setting compound from coagulating with the rubber latex.

The resulting filler material was heated to a cross-linking temperature ranging between 80 and 140°C, which appropriately overlaps with that to which retreaded tyres are heated to cure the connecting layer.

The filler material was tested for impact resistance and dynamic rigidity.

For comparison purposes, the same tests were carried out on a belt portion of a new casing (i.e. with all the belts intact) and on a connecting layer representing known filler material.

The impact resistance test was carried out using an MTS 831 machine, on which a 45° truncated-cone-shaped tip was compressed at a speed of 1 m/s.

As shown in the Figure 1 graph, unlike the connecting layer, the filler material according to the invention has more or less the same impact resistance as a new casing. In fact, the load required to penetrate the filler material according to the invention is only slightly less than that of the new casing, whereas that of the connecting layer is much lower.

The dynamic rigidity test was carried out using an MTS 831 machine, on which a 10 cm ² test piece was subjected to sinusoidal compression cycles with 10 Hz frequency, a rounded amplitude of 50N about the mean value, and a step-incremented applied-load range of 350 to 5000N.

The rectangle in the Figure 2 graph indicates the significant surface load range for normal tyre operation. Within this range, performance of the filler material according to the invention closely resembles that of the new casing, whereas the connecting layer is much less rigid.

The filler material according to the invention has also been found to adhere firmly to both the rubber and belt material.

The filler material according to the invention therefore has the advantage of filling the post-cleaning cavities in the casing with no mechanically discontinuous patches in the belt area, thus enhancing retreaded tyre performance, and so encouraging more widespread use of the retreading process, with all the economic and ecological advantages this affords.