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Technical Insights on Coatings Science

NEW COALESCENT AID BREAK THROUGH PATENTED

Missouri S&T has been issued a European Patent (#1169397) for a new breakthrough technology to coalesce latex paint with zero added VOC. The technology involves mainly the use of glycol esters of unsaturated oils as coalescent aids. Oils such as sunflower, soybean, linseed, and/or any similar highly unsaturated drying oil, are potentially useful and can be converted to monoesters of ethylene, propylene, or other glycols. Initially, the additive acts as a plasticizing solvent. Subsequent air oxidation reduces its ability to plasticize the resin. Advantages include a slight reduction in resin use as well as a decrease in associative thickener level where used. Usage levels are similar to those used for conventional coalescent aids. This fundamental advance in coalescent technology has been shown to be very compatible with many commercial resins. This new fundamental advance in coalescent technology should allow the industry to further reduce VOC emissions from many architectural coatings. The new additive is being produced and marketed by Archer Daniels Midland, ADM, under the trade name Archer-RC.

UV CURE TECHNOLOGY

Two basic types of UV cure coatings are commonly practiced, radical and cationic cure. The former comprises the vast majority of the UV coatings used, approximately 92%. Radical cure coatings typically use acrylate esters as the reactive components, which are relatively low in cost. A nitrogen blanket can allow methacrylate esters that are less reactive but less irritating chemicals to also be employed.

Oxygen reaction with the growing radical on the polymer end reduces the conversion and average molecular weight when nitrogen is not used with methacrylates . Radical cure systems will cure in just seconds upon exposure to UV light. UV must penetrate to the substrate in order to obtain adhesion, thus the technology is limited mainly to thin film pigmented systems or clear coats. A rapid cure rate makes it ideal for many applications, such as inks or pre-finished floor coatings.

Cationic cure systems are more costly than radical cure due to the use of aliphatic epoxy resins and vinyl ethers though adding limited amounts polyol can help lower formulation cost. Cationic cure systems require significantly longer cure times, as long as 30 minutes after exposure to UV light via "dark reaction". This technology is better suited for thicker pigmented coatings since better through-cure of thick coatings can be obtained, especially if elevated temperatures are used due to the prominent dark reaction.

The UV cure market is growing at about a 15% annual rate, which makes it an attractive business to many coatings manufacturers. Improved UV generation technologies have been developed in recent years which allow reduced energy inputs and faster throughput of product.

Is there a topic you would like discussed? Contact us by e-mail at coatings@mst.edu.