Studies on the properties of #beta#-ketoester modified hydroxylated polyesters based high solids polyurethane coatings

摘要

Two Pack High Solids Polyurethane Coatings (HSCs) are becoming more and more accepted as an alternative to conventional systems in various segments of the industrial coatings market not only because of their environmental effect, but also for their technical performance. As regulations become more restrictive, the efforts have been shifted towards the increase of application solids of HSCs or solventless coatings. The increase of application solids can be effected either by reducing the molecular weight of the oligomers or by reduction in viscosity of the oligomer. Hydroxylated Polyesters (HPs) is one of the important oligomeric precursors for the development of two pack polyurethane HSCs and the wide array of monomers available for its synthesis give enough scope for researchers to design oligomers of their choice. In this paper, two approaches have been adopted for the reduction of viscosity or to increase the application solids. The first is to replace main diol moiety NPG in a most widely used HP formulation based on adipic acid, isopthalic acid, trimethylol propane and neopentyl glycol (NPG) with 1,4 cyclohexane dimethanol and 1,3 propane diol, while the second is to introduce #beta#-ketoester moiety in different percentages to the resultant three HPs backbone. The oligomers were characterised by gel permeation chromatography and differential scanning calorimetry. The influence of diol structures, percent #beta#-ketoester incorporation and temperature of HPs has been studied. The results indicate that the replacements of diols and B-ketoester incorporation helps in significant reduction of viscosity of HPs. The potentialities of these HPs in coating formulation have been studied by developing two pack clear coats with diphenylmethane diisocyanate. The performance of these coatings were evaluated by determining their tensile properties, dynamic mechanical properties, corrosion resistance properties, adhesion and other coating properties such as flexibility, impact, abrasion, etc. The crosslink density (XLD) was calculated by using dynamic mechanical thermal analyser (DMTA) data. An attempt has been made to correlate both the quantitative and qualitative results so that it can give some insight into the intelligent design of coating systems for long term performance. The results indicate that the #beta#-ketoester incorporation in HPs backbone not only helps in achieving higher application solids but also improved coating properties, depending upon the extent of incorporation.