Лако-красочные материалы — производство

William F. Harrington

Adhesive Information Services, Mishawaka, Indiana, U. S.A.

I. INTRODUCTION

At first, there was only natural rubber, a substance “discovered” by Christopher Columbus on his second voyage to the New World. Soft and tacky when solidified from the tree latex, it remained a curiosity for many years, eventually finding use as a ‘‘rubber,’’ as Joseph Priestley called it, since it would harden and rub-out pencil markings after it had aged some. The patent literature shows activity after 1791 when the first U. S. patent was issued for a mixture of rubber and solvent that was used to bond two layers of wool fabric together. In 1845, a patent was issued for an adhesive to be used in a self­adhering bandage that contained India Rubber, Gum of Southern Pine, Balsam of Peru, Ground Litharge, Extract of Capsicum Annum, and Turpentine. Just a few years earlier in 1839, Charles Goodyear discovered that the addition to natural rubber of sulfur and certain metallic oxides followed by heating changed the gummy rubber to a stretchable elastic material that, upon release of applied stress, would regain its original shape. Johnson and Johnson developed and patented a pressure sensitive adhesive that contained gum rubber and zinc oxide in 1899.

Also in 1899, Hermann Staudinger graduated from high school in Worms, Germany, continued his studies at several universities, eventually becoming a Professor of Organic Chemistry at the Institute of Chemistry of the Technische Hochschule in Karlsruhe, Germany. In the early 1920s, Professor Staudinger proposed a theory of macromolecular formation. Although his proposals were not immediately widely accepted, a number of researchers pursued certain aspects of his work. And with that research came the founda­tion of today’s synthetic rubber and plastics industries. By the 1930s, a whole host of new, high molecular weight polymers had been developed and were being refined into usable products. In the early to mid-1930s, there was little demand for these new polymers simply because the Southeast Asian natural rubber plantations, which had supplanted the origi­nal Brazilian forest collections, supplied all the necessary materials for most elastomeric applications at very low costs. By the late 1930s, that situation had changed, and rather dramatically. War on two continents increased the need for developing sustainable supplies of rubber materials to continue supplying the needs of industry, and eventually, the supplies of the war machines. Japan invaded and took control of Southeast Asia and, with it, the rubber plantations, which immediately threw the rest of the industrial world into disarray. Without natural rubber for tires, gaskets, belting, and hoses, and

the rubber-based adhesives used to make those products, modern civilization would have come quickly to a halt.

This situation was recognized immediately by the governments of both Germany and the United States, which embarked on the development of replacement supplies through the building of a synthetic rubber industry. In the United States, polychloroprene (Neoprene), styrene-butadiene rubber [General-purpose Rubber—Styrene (GRS), or Buna S], butyl, and acrylonitrile butadiene [General-purpose Rubber—Nitrile (GRN), or Buna N] were the primary polymers pursued for production. By the early 1940s, synthetic rubber production was underway, while the government instituted strict controls over existing supplies of natural rubber, both in solid bale form and latex, since there were some products that still required the use of natural rubber for manufacture. Even old tires, belting, hoses, molded goods, and other rubber fabricated materials were collected as the rubber reclaim industry grew out of the necessity to recover any usable elastomeric poly­mer. These controls were maintained in place by the U. S. government through the late 1940s and early 1950s, since the rubber plantations did not immediately recover full capacity and distribution immediately after the war. A limited supply of natural rubber allowed the synthetic rubber industry to grow in industrial markets and prosper into the 1950s, as new developments and continued high rates of production reinforced the stabil­ity of this new supply of polymers and kept production costs low.

However, despite all of this burgeoning growth of these new materials, natural rubber could not be replaced for all applications. Natural rubber has a molecular weight of approximately 1 million, solution grade styrene-butadiene rubber is typically only 100,000. Natural rubber does not have the natural chemical resistance of nitrile rubber, but can be compounded for many of the same properties, and is more often less expensive to use. While many synthetic elastomers have unique and special properties, natural rubber had the advantage, in the early years after the war especially, of nearly 150 years of experimentation, development, and production. As the century progressed into the 1960s and 1970s, however, Southeast Asia once again became embroiled in war and, even though the primary supplying countries of Malaysia and Indonesia were not directly involved, changes in supplies and distribution assisted the growth and acceptance of many synthetic polymers. As the synthetic rubber industry continued to grow, so did the products become more economical to use.