Benzoguanamine formaldehyde condensations

The can and coil coatings, generally, are cross-linked with phenol, melamine, or urea-formaldehyde condensation products at elevated temperatures (150-200°C) with acid catalysts. Normal epoxy-amino resin weight ratios are epoxy-urea, 70 30 epoxy-benzoguanamine, 70 30 epoxy-melamine, 80 20, and 90 10. Increasing cross-linker levels give improved thermal and chemical resistance at the sacrifice of coating flexibility and adhesion. 

Amino polymers are derived from various amines and formaldehyde. Example amines used for these polymers are urea, benzoguanamine, melamine, and aniline, with the most common forms being urea and melamine resins. The formation of amino resins is complex, because the addition and condensation products of the amine and formaldehyde take multiple pathways involving by-products and side reactions. There is no general formula for a urea-based resins. The early reaction products are similar to those formed in phenolic resins or polyurethanes, but these early reaction products react further to form the final high polymer. Only the final reaction products will be considered in this section. 

Benzoguanamine closely resembles melamine in that reaction with formaldehyde gives methylol derivatives and then resinous condensates. Butylated... 

To a resin flask equipped with a mechanical stirrer and condenser is added 26.3 gm (10.14 moles) of benzoguanamine, 3.7 gm (0.026 mole) of hexamine, and 79 gm (0.98 mole) of formaldehyde. The mixture is heated to 80 -85 C and the pH adjusted with ammonium hydroxide. Then a solution containing 740 gm of 37% (9.0 moles) formaldehyde and 370 gm (6.2 moles) of urea is added and the mixture stirred and heated for 40 min at 75 -80°C and pH 7.5-8.0. The resulting reaction mixture is treated with 0.4 gm of ammonium chloride at 60°C, and 250 gm of wood pulp is added. The mixture is agitated 20 min, dried, and pulverized to give a molding powder. 

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