The reaction of polycondensation

The polycondensation reaction is carried out in two phases. Formalin is loaded into the reactor and the meshka drive is included. The acid number of formalins is brought to pH = 7.5-8 by the addition of a 40% solution of caustic toata, then 75% of the urea is loaded from the total amount provided by the recipe, steam is supplied to the steam shirt and the mixture is heated to 50-55 °.  Further heating to 80 ° occurs within 25-50 minutes. Due to the exothermia of the reaction. At this temperature, the mixture is kept for an hour, and then the rest of the urea is introduced into the reactor, which causes a decrease in temperature.

It is raised again to 80 ° and supported for 30 minutes., In this case, the pH of the condensed mass should be 6.5. After the specified time, the pH of the medium is reduced to 6 by the addition of a saturated NH4C1 solution, after which the condensation is continued at 80 ° for another hour before the improving, which is characterized by clouding of the mass, and cooled the mass up to 70 °. This is where the M-48 resin process ends.

To obtain the resin of the M-60 brand, the M-48 resin is subjected to a vacuum dry up to 60%concentration at a temperature of 60-55 ° and a residual pressure of 60-100 mm. RT. Art. The resulting tar is cooled up to 20-25 ° for 30-45 minutes. and drained in storage containers.

The viscosity of the vacuum resin according to the viscometer of the BI-4 to 180 seconds. With the addition of 1% chloride of ammonium, the resin is desirable for 50-65 seconds. Adhesive vitality 7-10 hours. The shelf life of the resin M-60 at 20 ° 2-3 months.   When stored, these resins are delapped, and therefore before use they must be thoroughly mixed.

Carbamide resins have very different vitality. This can be noted even in different parties of the same brand of resin. The first months, the viscosity grows slowly, then the process begins to accelerate and in a relatively short time there is a sharp increase in viscosity and gelatinization.

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