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Aspects of self stratifying coatings

Benjamin, S. (1994). Aspects of self stratifying coatings. (Unpublished Doctoral thesis, City, University of London)

Abstract

Liquid unpigmented coatings can be prepared which spontaneously stratify after application to a metallic substrate.

Stratification can be seen to be dependent upon the solubility of pairs of polymers in common solvents; the occurrence of phase separation and subsequent layer formation.

The solubility of commercial resin pairs in common solvents has been studied using the three - dimensional solubility parameter of Hansen. Attempts have been made to extend the use of solubility parameters to the prediction of phase behaviour. However, no clear correlation of stratification with Hansen solubility parameter data has been established. Experimental phase diagrams have been constructed to provide information on phase behaviour.

After the occurrence of phase separation, stratification has been observed to be a surface energy driven process. Stratification has been predicted from surface energy data of resin / solvent solutions with some success.

Experimental stratifying coatings have been characterised using elemental analysis and infra red spectroscopy. Epoxy / acrylic and epoxy / fluorinated- polyether systems can be observed to stratify experimentally. It has been shown that stratification of these systems is improved by curing the epoxy component with a proprietary polyoxypropyleneamine curing agent. The most favourable conditions are a resin ratio of 1:1 and a dry film thickness of at least 100 microns.

Extension to systems containing a protective pigment in the layer at the substrate interface has shown success. Addition of a second pigment proved more difficult. Some success was achieved using a silane coated titanium dioxide pigment which could be located in the fluorinated polyether resin. However, this was an isolated case.

It has been shown that the coatings produced perform at least as well as their two-coat counterparts when subjected to standard paint testing methods.

Publication Type: Thesis (Doctoral)
Subjects: Q Science > QD Chemistry
Departments: School of Science & Technology
School of Science & Technology > School of Science & Technology Doctoral Theses
Doctoral Theses
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