| 摘要 |
A stable, aqueous solution of a melamine-urea-formaldehyde reaction product equivalent, for resin forming purposes, to an aqueous solution of formaldehyde, melamine and urea, is obtained by (A) incorporating with an aqueous formaldehyde solution containing 30 to 50% by weight formaldehyde, at a temperature below 80 DEG C., melamine and urea in amounts such that the resulting mixture contains 2.5 to 5.0 mols. of formaldehyde for each mol. of amino group in the melamine and urea, and 0.5-2.5 mols. of melamine for each mol. of urea, (B) if necessary adjusting the pH of the mixture to within the range 4.5 to 6.0, (C) heating the mixture to 60 DEG to 80 DEG C., and then (D) distilling water from the mixture until the liquid residue contains 60 to 90% of all the components other than water. The pH of the aqueous formaldehyde may be adjusted before adding the urea and melamine, so that the pH of the mixture is 4.5 to 6.0. The water may be removed by "flash" evaporation. The products are stable liquids which may be used to prepare resins with additional urea and melamine. Examples are given. |
