For some years, the tyre industry has been producing tyres with coloured portions for various, not least of all aesthetic, reasons.
The methods used to date are based on using a rubber compound coloured with appropriate pigments.
More specifically, the most commonly used methods substantially comprise using three layers a first cushion layer contacting the inner layers of the tyre; a coloured second layer made from the coloured compound; and a third outer cover layer, which is removed prior to sale.
This method is not always successful in preventing deterioration of the coloured portion, particularly by chemical agents migrating from the inner layers of the tyre to the coloured outer compound. A common practice to slow down deterioration is to increase the thickness of the coloured layer, though this has inevitable drawbacks in terms of heat generation and, therefore, rolling resistance.
The Applicant has devised a method of producing coloured tyre portions, whereby a polymer barrier layer obtained from an aqueous dispersion is deposited on the part of the tyre for colouring, as described in Patent Applications TO2009A000964 and TO2010A000850, which are included herein by way of reference.
The above method has the major advantage of producing coloured tyre portions of durable colour, and with no impairment in rolling resistance.
On the other hand, it has the drawback of the dispersion taking a long time to dry to form the barrier layer.