Лако-красочные материалы — производство

Phenolic resins are also extensively used in the binding of foundry molds. Both resol and novolak resins are used for this application. The sand is coated with the phenolic resin at a rate of 3 to 4%. The PF resin can be used both as an organic solvent solution and in powder form. Coating of the substrate can be done both at ambient or at higher tempera­ture. In higher-temperature coatings novolaks are the preferred resins and in this applica­tion, waterborne resins (75% resin) can also be used. Hexamethylenetetramine as well as wax are added. Hexamine is often added separately from the resin to avoid precuring.

Another equally important field of application of phenolic resins is in the binding of mineral fibers such as glassfiber and rock wool. These are used for thermal and acoustic insulation at densities in the range 2.5 to 70kg/m3. Both powder and liquid resins, gen­erally in water solution, are used for this purpose. Liquid resins are generally applied at about 10% concentration in water; the water evaporates, cooling the fiber and avoiding decomposition of the resins, and the resinated mat is then cured in a hot-air circulation oven at 175 to 200°C for 2 to 5 min.

Acid-setting (but not only) PF resins are extensively used in these fields, resins that cannot be used to bind wood or to impregnate paper for laminates due to the acid hydrolysis of the cellulose they would cause. However, even in the wood bonding field self-neutralizing acid-setting PF resins have been developed, although these are not used industrially. Self-neutralizing systems for the hardened glue line are based on special hardeners that allow rapid curing of the resin and equally quick return to neutrality of the hardened glue line on joint cooling. A good joint bonded with a rapidly self-neutraliz­ing PF resin shows high strength and high levels of adhesion and this system shows some promise in some applications of wood bonding [33].