Before giving actual formulations I would like to give some basic principles for formulations.
Stoving can be defined as a process in which the curing film is acheived with the help of Elevated Temperature and cross link polymer with the help of Amino Resin.
The product to be finished is governed by the size and the form of the finishing equipment particularly the baking oven. The basics of formulations for all baked enamels is the Alkyd-amine system but for relatively inexpensive general type of baked enamel, either the rosinated Alkyd linseed oil or DCO alkyds are selected.
The use of Butanol is the most overlooked point in the Alkyd-Amine series. Many complaints of gelation or incompatibility can be traced to the failure of non-addition of this alcohol in the solvent combination. The amount used depends on the melamine selected and on the solvent combination in the Amine resin solution itself. In general, for the urea resins requirements for butanol may not be as critical as for the melamine resins, and in many instances. The butanol in the original solution will be sufficient but this should be evaluated before. Benzoic acid is added as a reaction terminator/stopper which prevents further polymerization, increases stability and add to shelf life. Add only 0.1 kg Benzoic acid in 0.9 kg Butanol and use 1% of batch size is recommended. 1st quality stoving finish is a combination of coconut oil modified Alkyd Short DCO and Amine resin. (Urea or Melamine). The inexpensive alkyd resins are more preferred as they allow the addition of quantities of inexpensive solvents without a decided decrease in viscosity and hence called as “High Drink” resins.
Thousands of applications still rate the merit of an enamel by the body or viscosity besides DCO resins have good adhesion and show good flexibility also.
They surely have some drawbacks such as little yellowing, wrinkling, so it is advised to use it in combination with modified coconut oil and Amine resins.
Coconut oil alkyds are not film formers and don’t have adhesion property but impart extreme flexibility to the film so that there will be no cracking after the post forming operations.
Here I would I like to share my experience.
Once my client used 10% additional melamine to stoving clear to get hardness but he was not getting film cured and also material gelled within a week, then I asked him about BUTANOL % , and he replied as there was no stock, he had added melamine, this shows that for cross linking Alkyd-Amino Butylated atmosphere is MUST.
Then only cross-linking can take place.