Synthetic resins intended for use as binders must meet certain technological requirements. Compliance with these requirements ensures the convenience of applying binders, high qualities of the manufactured plates and an acceptable cost.
1. Binders should be made of incomparable raw materials. Typically, in the production of wood-bruise, 6-10% of the binders are added to crushed wood (in terms of a dry product). Therefore, at the planned growth rate of the production of chips in 1965. It will take about 180 thousand. T resins per year (in terms of anhydrous product).
2. Binders should be cheap. According to projects for the shops under construction in the USSR, at a price of resin 400 rubles. per 1 ton, the share of binders in the total value of the plates is about 45%. Naturally, a decrease in the value of the binders will lead to a noticeable reduction in the value of the plates.
3. It is necessary that the binders are enough, firmly connect the particles of wood among themselves and provide the strength of the plate specified by technical conditions.
4. Plates must have sufficient water resistance. Typically, water absorption of plates without hydrophobizing additives when immersed in water for 24 hours. and a temperature of 20 ° is 60-80% of the weight of the plate, and swelling is 15-25%. In this case, the plate, of course, should maintain its integrity.
5. The normal concentration of the working solution of the binder is considered to be 50%- with this concentration, the resin should be freely sprayed with compressed air at a pressure of 3-4 ati. The binders with the viscosity of the working solution within 70-350 centipuas are well sprayed. Since the resin is usually added in the resin, and in addition, often paraffin emulsion, the concentration of the resin should be at least 60%. The use of working solutions with a concentration of less than 50% leads to excess humidity of the pressed mixture, which causes strata of the plates during pressing or reducing the productivity of the press.
6. Resins should maintain their viability for at least several months at least at room temperature, since otherwise they are transported, storage and use will be difficult.
7. The binder should quickly harden at an elevated temperature. Typically, hardeners are added to the binding (urea resins), accelerating the hardening of the glue in the process of hot pressing. By changing the contents of the hardener, it is possible to regulate the rate of resin hardening within the known limits, adapting it to the technological conditions of production.
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