Patent GB-567838-A (GB)
Title: The production of semicarbazide-formaldehyde resins
IPC: C08G12/14
Filed: 1943-03-11
Abstract: Glass - clear, colourless, scratch - resistant resinous condensation products, which may be used to prepare coating and moulding compositions, are prepared by condensing semicarbazide or a salt thereof, e.g. the hydrochloride or sulphate, with formaldehyde or a substance such as paraformaldehyde or trioxane capable of yielding formaldehyde under the conditions of reaction, in aqueous solution at a pH of at least 5 and preferably of 7 to 9.  The condensation is preferably allowed to proceed with or without heat until a viscous solution is formed which may then be dehydrated, e.g. by distillation with or without the use of reduced pressure, or by exposing to the air with or without the application of heat.  To produce a solid moulded article, the mass after dehydration is ground, mixed with pigments, fillers or other colouring material, if desired, and moulded under heat and pressure to give an infusible product insoluble in water and organic solvents.  To prepare a coating composition, semicarbazide is added to the neutral or slightly alkaline formaldehyde solution and a water-soluble organic solvent, e.g. butanol, isobutanol, acetone is added before the condensation has proceeded to an insoluble stage.  Water is distilled off and the viscous solution may be used directly or combined with pigments, drying oils, driers, thinners as air-drying or baking coating compositions. Example (1) a mixture of semicarbazide and 37 per cent formaldehyde at a pH of 6 sets in 5 mins. to an opalescent gel after evolution of heat.  The gel is dehydrated by standing in the air for several days or storing under reduced pressure for several hours. Example (2) a solution of 20 parts semicarbazide and 80 parts of 37 per cent formaldehyde brought to pH 8 with NaOH is heated to boiling and 200 parts isobutanol added; an hour's boiling yields a viscous solution of the condensate in isobutanol. Paper is rendered more water resistant and mar resistant when dipped in this solution, drained and baked at 125 DEG  C. for 1 hr.  A film of the solution flowed on glass and baked at 125 DEG  C. for 1 hr. yields a glass-clear, hard, colourless coating.  Example (3) a composition prepared by mixing the solution prepared in example (2) with an isobutanol solution containing a quantity of a 55 per cent castor oil modified alkyd resin equal to the quantity of solid polymer present in the former solution, produces a hard flexible coating when flowed on glass and baked at 125 DEG  C. for 1 hr.  The solution prepared according to example (2) may be evaporated to dryness or treated with a non-solvent, e.g. excess water, to coagulate.  The partially condensed product with or without fillers and/or colouring materials, may be moulded by treating under pressure at temperatures preferably between 100-125 DEG  C. until dehydration is complete.  The resins of the invention may be dissolved in aqueous solutions of mineral acids and when HCl or HNO3 is used may be deposited therefrom by volatilisation.  Plasticizers, e.g. tricresyl phosphate, dibutyl phthalate, castor oil, abietic acid esters or a soluble alkyd resin may be incorporated with the condensate during or after condensation.