Лако-красочные материалы — производство

At one time, this polymer was one of the most commonly used adhesive types made from a rubber, taking over from natural rubber in the 1950s and 1960s. The primary reason for this high usage was a direct result of the rubber’s chemical nature. Structurally, polychlor — oprene is similar to natural rubber, and in fact was originally described as synthetic natural rubber. The difference between the two is that in the repeat monomer unit that becomes the long chain polymer, polychloroprene has a chlorine atom positioned in one of the positions where natural rubber has a hydrogen atom. This chlorine atom provides the advantage of higher polarity for the polymer molecule, which is a great aid in developing adhesion to a diverse group of surfaces.

Polychloroprene was developed almost by accident. Experimenting with a copper chloride catalyst and acetylene gas in the 1920s, one of the trials by Father Julius Nieuwland of the University of Notre Dame yielded a black tarry substance. Eventually, Dr. Nieuwland was able to synthesize a divinylacetylene polymer and reported his results in a paper. Later, working with DuPont scientists after contact was established following the paper’s publication, the reaction conditions were controlled and treatment with hydrochloric acid yielded a chloroprene monomer. Polymerization of that monomer produced a rubberlike polymer that was eventually commercialized as DuPrene, later renamed Neoprene. This new polymer exhibited many of the characteristics of natural rubber in processing, and a number of superior properties in use. Higher chemical resis­tance, better aging, and improved temperature resistance were just a few properties that were promising. However, since polychloroprene was a manufactured product, it was not competitive with an agricultural product in the 1930s. In addition, for most adhesive applications, higher cost aromatic solvents were required, in part, for dissolution as com­pared to aliphatic solvents typically used for natural rubber. And in many applications, higher solids contents were required to achieve certain viscosities as compared to natural rubber compounds, which also increased overall cost. During World War II, however, there was high demand for a rubber that matched many of the properties of natural rubber. After the war, polychloroprene retained its popularity because of its exceptional performance in contact bond applications.

Polychloroprene comes in two varieties for manufacturing adhesives: solid rubber, and emulsion or latex. Solid rubber was the preferred form for most of the second half of the twentieth century since it was available in a number of grades, all of which could be intermingled for specific characteristics, and could easily be converted into a solvent-based cement. Most solvents were inexpensive before the oil crisis of the late 1970s, which provided for inexpensive adhesives. Drying times could be controlled with mixtures of solvents, which also allowed for quick process times compared to other adhesive systems. Combination with phenolic resins and metallic oxides yielded improved characteristics that made the compound suitable for myriad applications. However, owing to increasingly stringent environmental laws and regulations, solvent-based polychloroprene adhesives have been losing favor in some applications, even though processing and end use perfor­mance are usually superior to that of most water-based polychloroprene systems.