Patent GB-656470-A (GB)
Title: Improvements in or relating to the production of urea-formaldehyde resin
IPC: C08G12/42
Filed: 1948-01-13
Abstract: In the alkali catalyzed condensation of urea- and formaldehyde, the water in the reaction mixture is reduced in two stages in the first of which the quantity of water is reduced to not more than 20 per cent in presence of an acid not stronger than phosphoric acid and of a solvent alcohol boiling above 100 DEG  C. while in the second stage the distillation is continued in presence of a strong acid and at temperatures above 94 DEG  C. until a water-free syrup is obtained. The initial condensation is effected at 57-80 DEG  C. for a period of 2 hours in presence of a solvent for the condensate which is miscible with water, there being present at least 2 mols. formaldehyde per mol. urea and at least 1 part by weight of water per 1.2 parts formaldehyde.  Preferably 40-50 per cent of the formaldehyde is present as para-formaldehyde.  Solvents for the reaction are ethyl, methyl, propyl, isopropyl, butyl, isobutyl, secondary butyl, tertiary butyl alcohols and ether alcohols such as the monomethyl or ethyl or butyl ethers of ethylene glycol; ethyl lactate or methyl-3-hydroxy butyrate.  The formalin used is standardized at a pH of 8.25 and after adding sufficient alkali to do this, a further quantity of alkali is added to decompose the paraform.  The products obtained are compatible with oil-modified glyceryl-phthalate resins.  In examples: (1) 833 parts 40 per cent formaldehyde adjusted to pH 8.25 by NaOH is mixed with 222 parts paraform, 500 parts tertiary butanol and 4 parts 9.52 per cent NaOH, the mixture is heated to 74 DEG  C. under reflux and 485 parts urea then added, the temperature rising to 79 DEG  C. and being held at 65-68 DEG  C. for 4 hours; 2000 parts n-butanol are added and then 2.4 parts of the dihydrate of oxalic acid, the mixture being distilled until the temperature reaches 100 DEG  C.; 400 parts n-butanol are then added with 6.7 parts 4.9 per cent HCl in butanol and the distillation continued until the temperature rises to 125 DEG C., whereupon heating is discontinued and the solution diluted with 505 parts mixed xylenes, has a viscosity of U (Gardner-Holt); (2) by using a 9-inch distilling head a product having a viscosity of R was obtained.  In examples (3)-(15) by varying the conditions products having viscosities from D-Z were obtained.  These solutions blend with a sunflower seed oil-modified alkyd resin obtained by reacting 384 parts glycerine, 700 parts phthalic anhydride and 800 parts sunflower seed fatty acids at 205 DEG  C. in an inert atmosphere and then blowing the product with air at 205-260 DEG  C.  The mixture with addition of gamma-bromo-gamma-phenyl butyric acid as catalyst bakes in one hour at 175 DEG  F. to a hard tack-free resin.  The Specification as open to inspection under Sect. 91 gives fuller information as to the weak acids employed which are defined as acids having a dissociation constant in the range 0.0002.4 to 0.14 and tables are given of the weak and strong acids which may be employed and their dissociation constants.  Additional examples (examples 16-23, Cancelled) are given using formic, malic, salicylic, tartaric, maleic, phosphorus, and pyrophosphoric acids as the weak acids and p-toluene sulphonic acid, ZnCl2, alcoholic HCl, chloracetyl chloride as the strong acids.  This subject-matter does not appear in the Specification as accepted.