Лако-красочные материалы — производство

Building on technologies first developed in Germany in the early 1930s, Robert M. Thomas and William J. Sparks, both employees of Standard Oil (now ExxonMobil Chemical), patented a new synthetic rubber in 1937. Butyl rubber is characterized by a very saturated linear polymer chain, leaving little space between molecules for transmis­sion of air, vapors, moisture, or water. As such, butyl rubber was successfully used during World War II as a substitute for natural rubber in the manufacture of tire inner tubes and curing bladders.

Butyl rubber is a polymerization product of reacting isobutylene with a portion of an isoprene molecule, thus providing a controlled degree of unsaturation in the resulting polymer chain. The lower the percentage of unsaturation, the more thermoplastic the polymer is; the higher the unsaturation, the more opportunity for crosslinking the polymer into an elastic thermoset. (Unsaturation is a term used to describe the density of carbon — carbon double bonds, i. e., reactive sites.) The level of unsaturation can be polymerized into the base polymer for specific properties. For some applications, the polymer can be halogenated to increase molecular polarity and functionality, increasing the ability of the polymer to bond to polar surfaces or provide for curing by alternative mechanisms. In addition, partially or pre-crosslinked grades of butyl rubber are available which exhibit higher modulus than base grades. Butyl rubber can be blended with many other elastomers and polymers to modify its basic properties, or the properties of the other elastomer formulation, and the polymer is compatible with many kinds of fillers and additives.

Early adhesive uses of butyl rubber generally consisted of solvent-based dispersions, or tape and ‘‘rope’’ extrusion of formulated solid rubber. Extensive use was made of butyl rubber’s inherent tackiness in highly saturated grades of the polymer to make pressure sensitive tapes and precoated films. The polymers are also extensively used as major components of hot-melt adhesives, solid rubber sealing tapes, and caulking grades of sealants and mastics, of which most were high solids content solvent-based formulations. [10]

High initial tack Even without tackifying resin, the inherent tack of certain grades provides for excellent contact bond and pressure sensitive adhesives.

Good chemical resistance While not as good as polychloroprene-based products, butyl polymers have resistance to vegetable and animal oils, and many other chemicals. Most solvent and petroleum products will cause swelling, even in cured products.

Wide substrate range Even though the base polymers are of relatively low polarity, the inherent tackiness and linear molecules make them bond to most surfaces. Some compounds are suitable for bonding to polyolefins and other highly unsaturated polymers. However, bond strength for most pressure sensitive applications tends to be quite low, leading to creep under sustained stress. Even crosslinked polymers are often limited to low strength applications.

High flexibility and impact resistance Low levels of crosslinking and subsequent chain entanglements provide for stretching and stress absorption.

Variable heat resistance A wide range of heat resistance is available, usually depen­dent on the degree of unsaturation in the base polymer and the type of cure mechanism used, if any.

Superior aging performance With few sites for oxidation to take place, butyl rubber compounds are typically very resistant to ambient aging, which accounts for its high volume use in sealant compounds.

Wide range of choices Because butyl rubber comes in so many grades and polymer variations, many kinds of compounds can be formulated. Different curing mechanisms can be used, high levels of fillers can be used, and products can range from very soft to hard. [11]