Formaldehyde-based cross-linkers

Phenolic resins were among the first synthetic resins explored by the coating industry, initially used to modify properties of oil-based varnishes as a replacement for some natural hard resins. They are essentially solvent-soluble phenol-formaldehyde condensates with reactive methyllol groups. They are widely used as cross-linkers for thermosetting baking finishes, yielding films with excellent solvent and corrosion resistance properties coupled with favorable mechanical properties. 

Based on the type of amino compound, the aminoplasts used in coatings are classified as four main types urea formaldehyde (UF), melamine formaldehyde (MF), benzoguanamine formaldehyde (BF) and glycouril formaldehyde (GF) resins. The majority of commercially used amino cross-linkers are MFs and UFs, with others used only for specialty applications. These resins vary in their characteristics as summarized below ... 

It should be noted that despite their widespread acceptance in the coating industry as a cross-linker of choice for many high performance coatings, aminoplast cross-linkers face many challenges. In the most developed countries, the trend is away from formaidehyde-based polymers due to the highly toxic nature of formaldehyde. 

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