Acrylic-melamine coatings

Figure 2. Infrared spectra of acrylic-melamine coating. Spectrum A denotes cured coating B denotes coating exposed to condensing humidity and C denotes coating exposed in QUV weathering chamber. (Reproduced with permission from ref. 12. Copyright 1984 John Wiley.)...

Electron Spin Resonance Determination of Nitroxide Kinetics in Acrylic/ Melamine Coatings... 

Figure 6. Nitroxide concentration versus exposure time in acrylic/melamine coatings A-Jl Coatings were doped with 1J by weight HALS-A and exposed in the modified weather chamber at a dewpoint of 25 C.

The concentration of NO in PO and acrylate/melamine coatings grows from the beginning of the photo-oxidation, reaches a maximum and then drops to a very low steady-state level [15,125,130,147]. The equilibrium concentration of NO varies markedly according to the nature of the polymer matrix, its thermal history and the parent HAS. A steady-state value of about 10-4 moll-1 nitroxides was reported in photo-oxidized PO. 

It is the purpose of this paper to further characterize the changes in crosslink structure that occur on weathering. In particular, a detailed study of the dependence of the rate of methoxy disappearance on humidity and light intensity is presented which verifies the photoenhancement of hydrolysis. The effect of changes in the composition of the acrylic/melamine coating and the effect of common photostabilizers on the rate of photohydrolysis has been determined. Finally, possible mechanisms for photoenhanced hydrolysis are discussed. 

Materials. The acrylic melamine coatings used in this study are described in the preceeding paper (4). Formulations used in the gloss loss measurements contained 23% by weight of Ti02. The synthesis of the nitroxide dopant used in these studies (1.) has been previously described (24). 

Figure 10. Rate of gloss loss versus the square root of the coating photoinitiation rate determined from the nitroxide doping experiments for the acrylic melamine coatings.

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