Лако-красочные материалы — производство

One of the main uses of polyester resin is to function as the adhesive for glass-fiber lamination. The cross-linking reaction of unsaturated polyesters is exothermic; that is, it is accompanied by a rise in temperature. Indeed, one of the useful features of an inorganic adherend functioning also as a reinforcing agent in these resins is that the heat of reaction is dissipated efficiently, achieving better temperature control across the width of the lami­nate. Poor temperature control during curing often gives rise to one or several of the following defects: warpage, shrinkage, motley surface resulting from overcure, and blisters resulting from undercure [6].

Glass fibers are the preferred form of adherend for polyester resins since they provide the strongest laminates. The glass may be of various types: for example, electrical glass, a low-alkali borosilicate glass, or alkali glass with an alkali content of 10 to 15%. The low — alkali borosilicate glass gives laminates with the best weathering and electrical properties, but the alkali glass is cheaper. For good adhesion to be achieved between resin and glass it is necessary to remove any sizing (in the case of woven cloths) and then to apply a finish to the fibers. The function of a finish is to provide a bond between the inorganic glass and the organic resin. Today, the most important of these finishes are based on silane compounds. In a typical system vinyl trichlorosilane is hydrolyzed in the presence of glass fiber, and this condenses with hydroxyl groups on the surface of the glass [7].

The glass-fiber strands are converted into three basic forms: roving, filament yarn, and mat. These fibers have a high tensile strength and differ from natural fibers in that they have no inner cellular structure and therefore do not absorb moisture internally. They do absorb it on the surface, however, and can be wetted with organic liquids. The roving is in a twinelike form, prepared by twisting and collecting 60 simple yarns (12,240 filaments) on a spool. In this form glass is available for chopping into shorter fibers of varying lengths for use in preforming machines or for incorporation into molding compounds. The most common mat is obtained by cutting fibers into 5-cm lengths, collecting them by suction on a moving metal screen, applying a binder, baking, and collecting the bound mat in rolls. The 5-cm fiber length confers optimum properties in respect to manufacture, molding characteristics, and all-round strength properties [7].