Лако-красочные материалы — производство

A basic formulation capable of giving more than adequate results is presented here so that a starter in the field can get aquainted with these types of adhesives. The procedure for the preparation of this resin can be modified in many ways by varying catalysts, concentra­tion, molar ratios, and condensation conditions.

Phenol, 110 parts by mass + 22 parts water First formalin 37% solution, 49 parts by mass H2SO4 10% solution, 22 parts by mass First NaOH 40% solution, 4.5 parts by mass

Second NaOH 40% solution, 9.25 parts by mass

Second formalin 37% solution, 90 to 93 parts by mass

Methanol or methylated spirits, 30 parts by mass (at start of reaction)

Resorcinol, 71 parts by mass

Tannin extract, 19 parts by mass (only as a thickener: another thickener can also be used as soon as it is not excessively sensitive to water attack).

Phenol, water, methanol, and the first amount of formalin solution are charged in the reaction vessel and heated mildly until the phenol is dissolved. H2SO4 is added and the temperature increased to reflux under continuous mechanical stirring. The mixture is refluxed for 3.5 to 4h (generally ± 4h) under continuous mechanical stirring. It is cooled to 50 to 60°C and the following is added: the two amounts of NaOH 40% solution (slowly) and the second amount of formalin solution while maintaining the mix under continuous mechanical stirring. The mixture is then refluxed for 4.5 to 4.75 h and then the resorcinol added. The mixture is refluxed for a further 30 to 50 min. Spray-dried mimosa tannin extract is added immediately before or during cooling to adjust the viscosity to the wanted level; the pH must be adjusted to 8.5 to 9.5 according to the pot life required. The reaction must be carried out under continuous mechanical stirring throughout the whole reaction period. The hardener is a 50: 50 mixture of paraformaldehyde 96% (usually a fast grade) fine powder and 180- to 200-mesh softwood flour (60 : 40 mass proportion) which is added to the liquid resin generally in the proportions by mass of liquid resin: powder hardener = 100: 20 to 100: 25.