Лако-красочные материалы — производство

Even before World War II, reclaim rubber was a popular material for many adhesive and sealant applications. At that time, virtually all rubber was natural rubber, which allowed material that had been de-vulcanized to be processed simultaneously with and to extend the new raw materials. Reclaim rubber has the advantage of already containing a selection of oils, fillers, resins, antioxidants, and antiozonants in the original formulation. When delivered in bale or sheeted form, the reclaim rubber will mix and process much the same as original forms of natural rubber. Since the war, however, and particularly since 1970, reclaim rubber has been losing ground in favor of other polymers. Several factors are contributing to this decline, the first of which is polymer purity. As mentioned, when all rubber was natural rubber, it was easy to find different grades of the same polymer for certain applications and use the reclaim in similar operations. The grades included belting regrind, tire regrind, even baby bottle nipple regrind, among others. Today, however, polymers of all different elastomeric bases enter the processing stream and it is extremely difficult, if not impossible, to separate different synthetic polymers in a blend. Coupled with this is the fact that different manufacturers will use different polymer blends for identical applications.

A second major factor contributing to the decline of reclaim rubber adhesives is the fact that factories processing cured rubber materials for reclaim emit strong odors, parti­cularly sulfurous odors. Many reclaim factories discontinued operations as air emissions rules and regulations became more stringent rather than try to contain the odors with different air control devices, which were both expensive to purchase and expensive to operate. A third major factor contributing to the decline of reclaim rubber is the fact that the highest usage of product made for adhesives and sealants was as a solvent-based product. After passage in 1990 of the Clean Air Act, solvent-based products started to decline in total volume for general industrial applications. This decline was accelerated by the difficulty in obtaining suitable reclaim rubber for specific formulations, since many adhesive formulations get ‘‘locked’’ into specific materials from specific sources. The final factor contributing to the decline in use of reclaim rubber adhesives is that most com­pounds today are black in color (except for baby bottle nipple regrind), whereas in the past a variety of colors were available.

Notwithstanding the factors just mentioned, reclaim rubber still remains a part of the elastomeric adhesive supply chain. Adhesives and sealants made from reclaim rubber are inexpensive, compared to a formulation prepared from new raw materials. Reclaim polymers are very compatible with other elastomers, and often improve overall properties when added to certain formulations. Reclaim elastomers can be processed and cured the same as new polymer, but because of the considerable processing used to produce reclaim rubber, when dispersed in solvents, often provide superior spray and substrate wetting properties. Also of value is that the typical reclaim rubber has improved heat resistance. Reclaim rubber is also very compatible with asphalt; blends of these materials are finding extensive use in construction applications. A new and growing application for reclaim polymers is as an ingredient in high performance polymer mixtures such as epoxies and acrylics. The addition of limited amounts of powdered reclaim rubber serves as a “tough­ening” polymer, providing a degree of elasticity, resilience, and compression strength to rigid polymers.

In addition to widespread use as a blend in asphalt/rubber sealants for roofing and other construction applications, reclaim rubber adhesives have been used as an insulation adhesive, as a pipe wrap adhesive, and as an ingredient in some pressure sensitive adhesives. Of interest is the fact that virtually every telephone installation in the United States before 1985 that required a cable splice used a reclaim rubber adhesive.