Лако-красочные материалы — производство

The major application area for all pressure-sensitive adhesives is in tapes. Self-stick labels provide a second large area, while a range of miscellaneous applications make up the balance of pressure-sensitive adhesive use.

A. Tapes

Tapes may be classified according to application areas, such as electrical, packaging, or medical, or in terms of the type of tape, usually defined by the backing, which may be paper, fiber, film, foil, or foam. Figures drawn from various tables produced by the Fredonia Group Inc. and published in Adhesives Age in June 1991 and the Frost and Sullivan Report, ‘‘The USA Market for Pressure Sensitive Adhesives,’’ in Adhesives Age in August 1991 showed that of a total U. S. pressure-sensitive adhesives market in 1989 of $4.9 billion, $2.6 billion was for sales of pressure-sensitive tapes. Table 6 illustrates the relative importance of the various backings and application areas.

An apparently simple tape may comprise a number of elements, including a release coating, the backing, a primer, and the adhesive layer. The release coating ensures that the adhesive layer does not transfer partially or completely to the back of the tape from the coated side. With certain types of backing a release layer may not be necessary, and in some instances a separate release film may be necessary. The release coating should allow the tape to unwind easily but not spontaneously. The need for priming also depends on the nature of the backing and may take the form of an applied coating or layer, a chemical treatment such as corona treatment, or a physical treatment such as exposure to heat. Priming may sometimes be necessary to inhibit movement of plasticizer from backing to adhesive layer, or vice versa, but the usual purpose of priming is to obtain adequate adhesion to the substrate. The earlier backings used were cloth, mainly for first-aid dressing. Cloth backings allow the skin to breathe and offer good flexibility and tensile strength while permitting easy tear. Generally, no priming or release coating is needed. Fabrics used include cotton, nylon, and polyester. Paper backing is the cheapest type of backing available. Saturated paper backings have better physical properties than unsaturated paper, particularly for tensile and tear strengths, water resistance and perme­ability, and generally do not require release backings, while unsaturated papers usually require some aid to release. Saturated papers are predominant for general-purpose creped masking tapes.

Plastic films comprise more than 60% of all tape backings. Originally based on cellophane, a wide range of plastics is now available for various applications. Polyester, unplasticized poly(vinyl chloride) (PVC), and biaxially oriented polypropylene (BOPP) are used for packaging tapes, while PVC is still preferred for electrically insulating tapes. Cellulose acetate is used for ‘‘invisible’’ tapes, and poly(tetrafluoroethylene) (PTFE), par­ticularly in conjunction with silicon-based pressure-sensitive adhesives, is used where resistance to elevated temperatures, chemical inertness, or low friction are the main requirements. Plastic films are impermeable, thin, uniform, and smooth and are generally inert with good dielectric properties. Reinforced with glass fibers or rayon embedded in the tape to distribute the load over greater areas, they are suitable for heavy-duty packaging applications.

Other backings used include foams, typically PVC or polyurethane, rubber, and metal foils. Foams are used for sealing and gasketing or thermal or acoustic insulation. They work particularly well on uneven surfaces. Adhesive may be applied to both surfaces, allowing their use as assembly adhesives. A double-sided, release-coated interlayer is necessary for double-sided tapes. With foams, care must be taken to select an adhesive that does not cause the foam to collapse, either through solvent action or as a result of excessive heat. Rubber backings are used where flexibility is a primary requirement, although they also offer excellent electrical insulation. Aluminum foils are used mainly in the construction industry, to act as a moisture seal, to reflect heat or for insulation, or to offer a controlled leakage path for static electricity. Lead foils are occasionally used to screen harmful radiation.

Pressure-sensitive adhesives may also be coated directly onto release paper in order to produce transfer tapes, in which, as the name implies, the adhesive film will transfer from the release coating onto a substrate with which it is brought into contact. This permits exact placement of accurately controlled quantities of adhesive. Great care must be exercised in the choice of release paper to ensure successful application.

Packaging tapes represent the largest end use. Packaging, which includes closing of cartons, sealing containers, bundling, and protection of surfaces is based primarily on paper or plastic film backings, but other types may be used as well. Film-backed paper is replacing saturated paper for packaging applications, especially for masking and protection, while reinforced tapes are used for strapping large containers or bundling articles.

Hospital tapes and first-aid dressings still constitute an important area for pressure- sensitive tapes. Because of their ability to breathe, cloth tapes are still widely used, but other backings are now making their appearance for special applications, including invisible dressings and rigid or elastic support tapes. Choice of ingredients for adhesives is controlled by the need to produce a system that will not irritate the skin or inhibit healing.

In addition, it must not lose adhesion as a result of perspiration, but must permit easy and clean removal. Traditional adhesives were based on natural rubber and zinc oxide, but water-based acrylic systems now dominate.

Office and graphic art applications require a diversity of tapes and backings. Block — out tapes are often multilayer constructions incorporating colored films. Printed films are used for graphics displays, while clear protective sheets may be used to protect printed graphics against smudging or erasure. Dye-cut lettering is available. A variety of clear-film backings is used for temporary fixing tapes.

Electrical tapes or insulating tapes require adhesives that will not corrode wiring, joints, or components. They should resist deterioration resulting from age and exposure to heat. Occasionally, chemical resistance may also be required. PVC is still the most widely used backing, but other films, especially polyester, are increasing in use. Rubber — or elastomer-based adhesives are suitable for service up to 130°C, acrylics to 155°C, while silicones, preferably on PTFE, can be used up to 180°C.

Other applications include thermal and acoustic insulation and tinted films for glass in the construction industry, wood-grained or other decorative vinyls for the automotive and furniture industries, double-sided tapes for mounting or splicing, and foams for gaskets and seals in the appliance industry.