Energy-saving crosslinking agent for low-temperature baking varnish
A technology of bridging agent and baking paint, applied in the field of bridging agent for low-temperature baking paint and its preparation, can solve the problems of long drying time, high baking temperature, waste of energy use and the like
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[0095] Preparation method of bridging agent for baking varnish
[0096] The present invention improves the polymerization process and provides a novel preparation method of a bridging agent for baking varnish, comprising steps
[0097] (a) paraformaldehyde and melamine carry out carboxymethylation reaction in short chain alcohol;
[0098] (b) adding the first acid to adjust to acidity;
[0099] (c) dehydration carries out etherification reaction;
[0100] (d) adding the second acid, mixing uniformly to obtain the bridging agent for baking varnish,
[0101] Wherein, the short-chain alcohol is n-butanol, isobutanol or a mixture thereof.
[0102] In another preferred example, the mass ratio of the melamine: the paraformaldehyde: the short-chain alcohol is 126:81-260:222-888; preferably, the melamine: the paraformaldehyde: The mass ratio of the short chain alcohol is 126:(100-230):(300-700).
[0103] In another preferred example, the molar ratio of the melamine: the paraforma...
Embodiment 1
[0168] 1.1 Preparation of bridging agent
[0169] Put 600 kg of isobutanol into a polymerization kettle with stirring and reflux condenser, and adjust the solution to pH=8.0 with lye under stirring.
[0170] Add 154kg of paraformaldehyde and heat to reflux until the solution is clear and transparent, then cool down to below 60°C.
[0171] Add 130 kg of melamine, heat up to reflux; add 5 kg of formic acid (the first acid) when it is completely clear, adjust the pH of the solution to be less than 7, start the dehydration etherification reaction, and add 35 kg of benzenesulfonic acid (the second acid) solution, mix well Obtain bridging agent afterward, gross weight is 924kg, filter packing.
[0172] 1.2 Preparation of coating composition
[0173] The amino resin bridging agent prepared in Example 1.1, the existing amino resin (isobutyl etherified amino resin synthesized by adding acid in one step, as a comparison) are mixed with alkyd resin respectively to form a coating compos...
Embodiment 2
[0193] 2.1 Preparation of bridging agent
[0194] Put 510 kg of n-butanol into a polymerization kettle with stirring and reflux condenser, and adjust the solution to pH=7.3 with lye under stirring.
[0195] Add 200kg of paraformaldehyde and heat to reflux until the solution is clear and transparent, then cool down to below 60°C.
[0196] Add 130 kg of melamine, heat up to reflux; add 8 kg of acetic acid (the first acid) when it is completely clarified, adjust the pH value of the solution to be less than 7, and start the dehydration etherification reaction until the end of dehydration.
[0197] Add 10 kg of p-toluenesulfonic acid (second acid) solution, and the reaction is completed to obtain a bridging agent with a total weight of 858 kg, which is filtered and packaged.
[0198] 2.2 Preparation of coating composition
[0199] The amino resin bridging agent prepared in Example 2.1, the existing amino resin (isobutyl etherified amino resin synthesized by adding acid in one ste...
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