Patent GB-587354-A (GB)
Title: Improvements in or relating to the manufacture of resinous condensation products
IPC: C08G12/32
Filed: 1944-04-19
Abstract: Hardened resins are prepared by initiating under heat condensation between aqueous formaldehyde or a polymer thereof and an aminotriazine containing not less than two amino groups, the whole of the aminotriazine being present as a previously formed salt of an inorganic or organic acid, and hardening the condensation product alone or with one or more inert materials by heat treatment or by ageing at ordinary temperatures.  The preferred aminotriazines are melamine, ammeline and melam.  The hardening of the resin is performed alone or in presence of inert materials such as fillers, fibres, webs, sheets, impregnable or coatable surfaces, colouring matter or plasticisers.  Water may be present in the initial condensation mixture in amount sufficient to result in a dilute solution of the condensate.  Such a solution is stable for some weeks, but evaporation of the water leaves a hardened resinous deposit.  Thermosetting resins may be precipitated from these solutions by addition of alkali.  By employing less water solutions are obtained which if not rapidly cooled and diluted gelatinise very readily to give masses which harden in air at ordinary temperature. Dry aminotriazine salt may be mixed with dry formaldehyde polymer to give a stable mixture which can be condensed together by heating, if desired with pressure or which may be dissolved with heat in water to yield solutions of the condensation products.  The solutions may be employed for addition to paper (see Group VIII), for impregnating wood, e.g. veneers, as adhesives, or by working up with fillers and, if desired, plasticisers and pigments to yield plastic masses which may be shaped and hardened at ordinary temperature or by baking. With limited amounts of water, the fillers and other ingredients may be added to the initial mixture of formaldehyde and aminotriazine salt, the mass shaped and hardened by heating. Solutions for use as adhesive may also contain fillers or thickening agents such as starch, dextrin or natural gum. Compositions may also include plasticisers and pigments. According to the examples: (1a) and (1b) melamine hydrochloride and formalin are condensed in water to yield a clear solution miscible in all proportions with water and stable for some weeks at room temperature.  (1c) Using more concentrated formalin a solution is obtained which sets on heating for a few minutes at 80 DEG  C., but which may be cooled and diluted with water before setting.  (2) A moderately viscous syrup is prepared from malamine hydrochloride and formalin.  It hardens to a transparent, infusible mass on standing for a few hours, dries to a water-insoluble transparent film, may be diluted with water with increase of stability and is suitable as a cold setting adhesive for wood.  (3) Melamine hydrochloride, formalin, wood flour and glycerol are kneaded together and compressed to a desired shape which hardens by heating in a suitable container at 100 DEG  C. Baking increases the hardness.  (4) In this example melamine sulphate is employed. (5) Melamine oxalate is used.  (6) Uses melamine formate.  (7) Uses melamine acetate.  (8) Melamine sulphite is employed.  (9) Finely-ground melamine hydrochloride is mixed with paraformaldehyde to give a potentially reaction dry powder which may be heated with water to yield a clear dilutable solution which gelatinises on heating and yields clear insoluble resins on drying.  The dry mixture may be dispersed in a starch paste adhesive prepared from Cassava flour and water.  The glue is suitable for plywood, e.g. by hot-pressing for 5-10 minutes at 90 DEG  C.  Specifications 455,008, 468,677, 480,316, 480,339, 562,715 and 14614/41 (as open to inspection under Sect. 91) are referred to.