Epoxy polyamine finishes

In Chapter 12, we mentioned that the departure from the 100 per cent solids of the old oil paints, to the lower solids of modern finishes, was a consequence of the demand for paints with better performance. The paint industry s determination to provide the improved properties at higher solids was also mentioned. We have already seen in Chapter 14 how the epoxy/polyamine system meets these requirements. The finishes under discussion in this chapter are another approach to the problem. 

Some commercial durable antistatic finishes have been Hsted in Table 3 (98). Early patents suggest that amino resins (qv) can impart both antisHp and antistatic properties to nylon, acryUc, and polyester fabrics. CycHc polyurethanes, water-soluble amine salts cross-linked with styrene, and water-soluble amine salts of sulfonated polystyrene have been claimed to confer durable antistatic protection. Later patents included dibydroxyethyl sulfone [2580-77-0] hydroxyalkylated cellulose or starch, poly(vinyl alcohol) [9002-86-2] cross-linked with dimethylolethylene urea, chlorotria2ine derivatives, and epoxy-based products. Other patents claim the use of various acryUc polymers and copolymers. Essentially, durable antistats are polyelectrolytes, and the majority of usehil products involve variations of cross-linked polyamines containing polyethoxy segments (92,99—101). 

This reaction is an example of a two-pack epoxy finish where the n value of the epoxy resin is 8 to 12. Although giving a high degree of chemical resistance the reaction is sluggish so the common two-pack finishes are usually based on polyamines with epoxy resins having n values of 0 to 2. 

It has been pointed out that the simplest epoxy resins are liquids. Undiluted diepoxide 0 has a viscosity of 36-64 poises (3.6-6.4Pas) at 23 °C, but this viscosity can be lowered further by reactive diluents. The modified resin can have a viscosity as low as 5 poises (0.5Pas). The diluents have an epoxide functionality of only one, so they do not contribute to cross-linking, but they are chemically bound into the final cross-linked film. Since these liquid epoxies may be cured by liquid polyamines or polyamides, no further solvent is required for application. Thus the entire liquid paint can be converted to cross-linked solid without heating, so that it may be called solventless , or a 100% solids finish. 

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