Processing methods, aminoplasts

Whatever the processing method, aminoplasts intended for use in modem industrial equipment should satisfy the most stringent requirements to stability of technological... 

The curves shown in Figs. 1-4 describe the particularly characteristic deformation processes of aminoplastics that are of importance for a correct choice of both the method and regimes of processing the material Under other prescribed... 

The principal processing methods of aminoplasts are pressing, pressure casting and extrusion. 

In Ref. [33] there is adiscussion of the method for calculating optimal temperature regimes and seasoning time in the processing of aminoplastics by taken account of the heating and hardening rates of the materials for different temperatures of preliminary heating (60 and 80 °C). 

The study of different methods of granulation of aminoplasts shows that the given process involves compaction of an homogeneous powdered product with subsequent sizing and forming of the compact product. 

The principal technological schemes of pressure casting as applied to articles from reactoplasts, as well as the analysis of the processes taking place in this method of treatment have been described in much detail in Ref [38], We would like to mention only certain specifics in the treatment of cast aminoplasts. To fill up the molding space with the aminoplast a pressure of KXF-200 MPa is necessary at the terminal stage of the filling-up of the molding space, the pressure should be reduced to 70 MPa to avoid overcompaction of the material [39]. 

At present the progress in the pressure casting method as applied to aminoplasts involves the automation of control for the casting process, as well as the elimination of the hardening of the composition melt in the distribution gates. 

The various components and raw materials of the resins can be determined using different chemical methods (Table 19). The content of total formaldehyde is accessible by hydrolysis of an aminoplastic resin this process, however, is not possible for PF resins. Urea can be determined in the easiest way from the resin nitrogen content. However, other possible... 

Adhesives of the aminoplastic (see Step polymerization) and phenol formaldehyde (see Phenolic adhesives single-stage resoles and Phenolic adhesives two-stage novolacs) types are most widely used. Although basically similar, an adhesive for plywood manufacture will require a different formulation to one for particle board, or medium-density fibre board (MDF) since methods of application and processing differ. Thus, in plywood, large sheets of veneer must be uniformly coated with adhesive, usually by a roller or curtain coater in particle board, chips or wafers must be coated with very fine adhesive droplets, while small bundles of wet fibres must be sprayed with adhesive in the manufacture of MDF. Hence, formulation and production of resins has become a mixture of art and science, with resin manufacturers able to produce resins tailored for use in a particular board-manufacturing plant, or with a particular species of timber. 

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