Лако-красочные материалы — производство

First made commercially available in Germany in 1936, this elastomer is officially known as acrylonitrile butadiene, and is usually the product of an emulsion polymer­ization process that combines the two monomers: acrylonitrile and butadiene. However, the polymer can also be made in a solution process, and with a variety of monomers. As a specialty polymer, and even though several commercial brands were available, Buna N (as it was first known) was little used until World War II, when the polymer’s unique oil and plasticizer resistance and high heat resistance became very important for transportation products. Nitrile rubber also exhibits excep­tional adhesion to metallic surfaces and is compatible with a wide range of additives and compounding ingredients.

Nitrile polymers used for the manufacture of adhesives generally contain 25% or more acrylonitrile, but in the base polymer the acrylonitrile content can vary from 15% to 50%. Increasing the acrylonitrile content improves the oil and plasticizer resistance and increases the polarity of the compound. However, higher levels of acrylonitrile also increase the hardness and modulus of the polymer, reducing the elasticity of the resulting polymer. Nitrile rubber can be produced by a ‘‘cold’’ (5°C) or ‘‘hot’’ (25-50°C) process, with most adhesive polymers produced by the hot process which induces more chain branching. Nitriles can be combined with other monomers in solution polymerization which increases functionality and improves compatibility with other reactive resins like acrylics, epoxies, and polyurethanes.

For many years following World War II, the primary use for nitrile rubber adhesives was as solvent dispersed compounds, often modified with phenolic resin to increase heat resistance and improve strength properties. Water-based nitrile adhesives have been grow­ing in recent years, but do not match the film strength of the solvent-based compounds. Liquid nitriles, particularly carboxy terminated types, have become a popular reactive resin for flexibilizing rigid polymer systems such as epoxies. Nitrile adhesive coated sur­faces can be heat or solvent reactivated within a specified time frame, or before cure occurs. Adhesives can be converted to reinforced or nonreinforced films, usually by casting a solvent-based solution onto release paper, for die cutting to part configuration. After part placement, adhesives can be reactivated and cured. [12] [13]

Good aging Generally requires the addition of antioxidants and ultraviolet (UV) absorbers if exposed for a long term to weathering, but the elastomer has good retention of properties in normal use.

Low building tack Even though used as a contact adhesive for many applications, the adhesive must be freshened with solvent before mating to assure good wet — out; otherwise high contact pressure or the addition of tackifying resins to the formula is required.

Curable Nitrile rubbers can be cured with sulfur or isocyanates, but some formula­tions exhibit improved properties on elevated temperature cycling, even with­out curatives. For consistent high performance, the polymer must be cured at elevated temperatures.

Chemical and moisture resistance Like most elastomers, there is a high degree of moisture resistance, and chemical resistance is excellent.

Good processing characteristics Adhesives can be supplied as contact bonding types—either in water — or solvent-based systems—hot-melt, pressure sensitive, or as reactive systems—either 100% solids content or solvent based.

Adhesion properties Exhibits strong bonds to most highly polar surfaces such as metals, but does not bond well to inert surfaces such as polyolefins.