Viscoelastic properties and coating performance of water‐soluble acrylic copolymers crosslinked with melamine resin

Acrylic copolymers with different amounts of carboxyl and hydroxyl groups for obtaining practical performance of melamine‐cured acrylic coatings was investigated. Property testing results indicated that glass transition temperature ( T g ) and shear modulus increased, and molecular weight between crosslinks ( M c ) decreased with the increase of hydroxyl and carboxyl number in the acrylic copolymers. The degree of crosslinks influenced the resistance to solvent and chemicals at a lower baking temperature. Compared with acrylic acid, itaconic acid as a carboxyl monomer was more effective in inducing a lower baking schedule. The water‐soluble acrylic copolymer, which is neutralized with triethylamine, consists of 20 wt % methylmethacrylate, 55 wt % buthylacrylate, 15 wt % hydroxyethyl methacrylate, and 10 wt % itaconic acid. The copolymer showed higher crosslinks when cured with methoxymethyl melamine formaldehyde resin under a relatively lower baking schedule at 135°C for 30 min. It also has excellent solvent and chemical resistance. This coating film has a T g value of 39°C, modulus of 2 × 10 8 dyne/cm 2 in the rubbery state, and M c value of 464. Also the acrylic copolymer films with M c < 900 have good properties for solvent, acid, and alkali resistance. © 1995 John Wiley & Sons, Inc.