Tack in Rubber

Abstract The expressions tack, tackiness, and stickiness have been in use since the beginning of the rubber industry. During the years their meaning has changed considerably. The first occasion where tackiness was mentioned was in the case of crude natural rubber. The surface of the rubber became tacky or sticky during storage. This phenomenon has been thoroughly discussed in the literature. As a general conclusion it was accepted that both oxidation and depolymerisation occurred. Three factors were reported to be the cause of these processes: light, traces of copper, and manganese. From our point of view we would call this effect stickiness, as we are only interested in the building tack of rubber. In the period when the only rubber was natural rubber and high loadings of highly active fillers were not generally used in compounds, building tack was no problem. Building tack was first mentioned in a publication by Griffith and Jones in 1928. They started their experiments by measuring tack in their search for methods to prevent cotton liners from sticking to unvulcanized rubber. One would have expected much work on the measurement and improvement of tack in Germany and Russia during the development of synthetic rubbers. However, this only proved to be the case in Russia. The first publication available was the translation of an article by Voyutskii and Margolina in 1957. From Voyutskii's work we were able to trace the first article in 1935 by Zhukov and Talmud, who studied the adhesive power of synthetic rubber. In the USA the first theoretical approach to the subject was by Josefowitz and Mark in 1942, who at that time did not realize the difference between stickiness and tack. This difference became clear when lack of tack became the big problem in the use of synthetic rubber. In many cases it was found that addition of resins and softeners gave a very sticky compound which had no building tack at all. The tack problem was first discussed at the ASTM symposium on the application of synthetic rubbers in 1944 by Juve who gave a definition of building tack. From that time, the problem has been studied regularly, especially from the practical side, to find ways and means to improve the building tack of synthetic rubbers.