High Performance Protective Coatings - I

Excerpt: Till now we have learnt coatings for Marine Paints, from this issue we are starting new series of high performance protective coatings.

Till now we have learnt coatings for Marine Paints, from this issue we are starting new series of high performance protective coatings. In last issue we learnt high end epoxy coating which is also used in chemical industries. This issue starts with regular quality epoxy coating.

Tips to manufacture Epoxy Paints.
Epoxy Polymer or Resin comes in different grades like liquid
epoxy to solid epoxy.
Low molecular weight epoxies generally are:
180 - 200 EW are liquids
400 - 1000 EW are Semi Liquids (Viscous Material) and
2000 - 4000 EW are Solids Epoxy Ester

For Coating Application we mostly use 450EW Epoxy.

Now we have 50% Epoxy Resin Solution, why this solution is to be used.
• This solution is easy to handle as viscosity is less than 75%
Solution, which minimizes the loss during handling.
• In thinning stage, if by chance it gets added more than 75% solids than 50 % solids then the RM Cost of paint is also higher.
• Solvents like Xylene, Butanol or Toluene can be used to reduce the resin solids. Never use solvents like MTO, White Spirit or Kerosene to reduce the cost.
• Please check all Machinery, Pots, Stirrers, Filters and cans are free of Dust, Aliphatic Solvents, Oil and Grease.
• Selection of Pigments should be proper fading to UV lights should not be used. Pigments like TiO anatase gives more 2 chalking hence only use of TiO Rutile is suggested by the 2 author.
• Pigments reactive with chemicals should be avoided, such as Prussian Blue, Chromes and Rubine etc.
• Inert Extenders like Barites, China Clay, Talc can be used, but Calcite, Dolomite and Whiting should be avoided.
• Do not use any common additive like Nilset, CMG, Linseed Fatty Acids for grinding, very few additives are compatible with Epoxy Resin.
• Author suggests Soyalecethin as the best additive for Epoxy Paints, to avoid pin holes and orange peel.

Hardeners

There are two major types of hardeners viz., Polyamine and Polyamide. Comparison of both the hardeners is as follows:

Nowadays Polyamidoamine hardeners are also available which are used in surface tolerant epoxies.

Drawbacks of Epoxies

Epoxy amine unreacted amines swell the epoxy, which shows inferior or poor resistance to water as compared to alkyds / chlorinated rubbers.
• Orange peel / pin holes is a major problem, use 1 - 2% UF or add proper % of true solvent.
• Epoxy resin have very poor exterior durability - Heavy chalking is observed, yearly 15 - 20 microns loss of DFT due to chalking. Nowadays Silicone Epoxies are available which have very good UV resistance.

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High build epoxy / Single coat epoxy / high solids epoxy will reduce the cost of application, which is very important because rate of application is too high.

Take 450EW add 200 EW epoxy, means regular epoxy and liquid epoxy combination, this will give high solid low viscosity product. This may sometime result in sagging to avoid use rheological additive like Bentone Clay. As DFT is high it is better to add some extenders as a reinforcement to the film.

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