Hot Tyre Marking FAQs

First, in the manufacture of all tyre rubber, an ingredient is used as an antioxidantantiozonant. This hemical functions as a preservative that allows the tyre to remain flexible, withstand the elements of the ozone and UV degradation and enjoy a long tread life. Chemicals such as diaryl-p-phenyenediamines and N-(1,3-dimethylbutyl)-N-‘-phenyl-p-phenylenediamine are commonly used. However, depending on the manufacturer, many derivatives of this type of chemical can also be used. The use of these chemicals is so common that the chemicals are referred to by codes such as 6PPD or IPPD, depending on the manufacturer. According to a recent conversation with a major tyre manufacturing engineer, the tyre manufacturers are fully aware of the problem of paw printing in the coating industry. Accordingly, many tyre manufacturers have selected the least detrimental (to flooring) chemical in the manufacture of tyres. However, many manufacturers are still using products such as the IPPD which is far more prone to discolor a coating than the 6PPD. Many chemical reasons exist that account for the paw printing, however, in layman terms, here is what information we have found.

Products such as the 6PPD are colorless when introduced into the tyre formulation and do not by itself cause the paw printing to occur. However, the moment that the 6PPD becomes oxidized, it only take a few parts per million of the 6PPD to create the typical paw print on a coating. To further compound this problem, a high aromatic greenish brown oil commonly used in the manufacture of tyres, continually leaches from the tyre and can contribute to the exudation of the 6PPD from the rubber. Unfortunately, the 6PPD can be easily oxidized. Once the material is oxidized, it turns to a purple/gray/black color depending on the severity of the oxidation. This color variance in conjunction with the actual concentration of the 6PPD accounts for the differing types of paw printing from slight deglossing to actual color changes. In addition, it is quite possible for atmospheric contaminants to cause sufficient oxidation to occur, resulting in a paw print. Surface contact in enough concentration results in surface paw printing.

Subsequently, the longer the tyre remains in contact with the area, the greater the chance that enough 6PPD will leach out of the tyre and into the coating itself. Given enough time in one location, not only will enough 6PPD migrate out of the tyre, but the constant exposure may result in the actual migration of the chemical into the coating creating a more pronounced and deeper stain.

Many other parameters play an important role in this phenomenon. These are mostly too technical to go into now. Sufficient to say that the problem is worse in synthetic rubber tyres.