Лако-красочные материалы — производство

The use of adhesives in building construction imposed exacting requirements upon quality and application techniques [92] — [98]. In addition to durability and resistance to mechanical stress, temperature and weather resistance are prime requirements. In prefabricated construction, the use of adhesives was an important requirement for efficient assembly techniques.

Adhesives as Additives for Hydraulic Compositions. Synthetic resin dispersions and redispersible synthetic resin powders that are added to cement-containing concrete mixes and mortars must be resistant to alkali and dilutable with water. Redispersible powders are added to cement-based adhesives in factory made mortars, while synthetic resin dispersions are mixed with the powder compound on the building site just before the adhesive is applied. The products that have been specifically developed for this purpose include, in particular, copolymers of vinyl acetate in combination with other esters or with ethylene and terpolymers of vinyl acetate, vinyl chloride, and vinyl laurate and also copolymers based on acrylates, methyl methacrylates and styrene, as well as styrene-butadiene. The additives modify the properties of the concrete. For example, they considerably improve the adherence of new concrete to old concrete. In addition, resistance to dynamic stress is considerably increased. The addition of anionic melamine resins is recommended also for establishing certain rheological properties. Adhesives based on cellulose ethers are added to cement-based systems and gypsum plasters to improve adhesion to the substrate and, by virtue of their hydrophilic character, retain water, thereby preventing mortars and plasters from drying out and improving their strength. Starch and starch ethers are used to modify the adhesion of cement mortars to mineral substrates.

Prefabricated Construction. Sandwich elements are widely used in prefabricated construction. In this case, bonding must meet stringent requirements with regard to stability and durability, especially in the case of exterior wall elements. Deflections attributable to differential temperature or moisture-induced expansion or contraction can amount to as much as 5 % of the length. The adhesive layer must be permeable to water vapor or act as a water barrier, depending on the structure and function of a given element. The adhesives used are two-component reactive resins, based mainly on epoxy resins, but polyurethane resins are used as well, as are elastomer-based contact adhesives that are applied on both sides.

With building components based on synthetic resin concrete (polymer concrete), the cement may be replaced partly or completely by organic binders, such as со — or terpolymeric vinyl acetates, acrylates or epoxy resins. Such systems are described as
polymer cement (PC) if the cement as binder has been totally replaced with organic binders, and as polymer cement concrete (PCC) if the cement binder has been partly replaced by organic binders. These systems are mainly used to reface concrete surfaces.

Low-viscosity reactive resins are used to seal cracks in concrete constructions. These epoxy and polyurethane resins show excellent creepability and bond strength to con­crete.

Assembly Adhesives. In carcass work, cement mortar is still widely used as a binder for mineral components. The disadvantages of cement mortar include its long curing time, its poor adhesion to old concrete, and its poor resistance to dynamic stress. For these reasons, adhesive mortars have been developed. They are mixtures of liquid, curable synthetic resins, such as epoxy resins or unsaturated polyester resins, blended with mineral additives, generally quartz, and the corresponding hardeners. They establish an excellent bond with hardened concrete, stone, metals, and certain plastics, and are used for applications involving particularly severe stress, for example, for cementing rail supports onto concrete sleepers, for fixing dowels and anchor bolts in concrete, for steel reinforcements, and for the permanent bonding of high-grade concrete elements.

For applications such as swimming pools and water-purification tanks, for which chemical resistance is required, or where resistance to dynamic stress is needed, special epoxy resins are used. Blends of a waterborne synthetic emulsion with a cement compound are suitable for applications with lower requirements. In some cases, e. g. sewage-treatment plants, elastomer-modified bitumen mortars are still used.

Another important application of reactive resins is the production of resin-bonded screeds that, by virtue of their high mechanical and chemical stability, are used, for example, for industrial floors. One particular problem is the bonding of old concrete to new concrete, where peeling occurs because of the shrinkage of the new concrete layer. By applying intermediate layers of a suitable epoxy resin mortar, it is possible to establish permanent bonds with strengths greater than that of the concrete.