| 摘要 |
Impregnation resins are prepared by condensation of melamine, aqueous formaldehyde and modifying agents at a pH between 8 and 10 and at a temperature between 80 and 100 DEG C. The condensation is continued until the water compatibility is from 1:1 to 1:1.5. The melamine:formaldehyde molar ratio is from 1:1.5 to 1:3.5. The modifying agents (modifiers) used are from 0.5 to 15% by weight of epsilon -caprolactam and thiourea, from 0.25 to 5% by weight of a hydrogensulphite (bisulphite), sulphite, difluorite, dithionite or sulphoxylate, calculated as the sodium salt, and optionally up to 6% by weight of at least one N,N-dialkylcarboxamide and of a polyhydric alcohol. The modifying agents can be added before, during or after the condensation. The percentage data are based on the total amount of melamine and formaldehyde. The reactivity, flexibility and shelf-life of the impregnation resins obtained meet high technical requirements.
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