Epoxy resins solvent-free coatings

Both types are based on low molecular epoxy resin. Solvent-free coatings, for instance epoxy and polyurethane, do not contain an active solvent unlike the conventional solvent-borne coatings (coatings in which a solvent is used to dissolve the binder). Solvent-free coatings offer... 

An epoxy resin formulation completely free of organic solvent was applied to carbon steel coupons using supercritical carbon dioxide (CO2) as the volatile solvent. Sleet coupons coated in this manner were compared to coupons coated with a standard military specification marine primer (MlL-P-24441) during exposure to aerated 0.5 nrl sodium chloride (NaCl). The solvent-free coating protected the steel from corrosion in this environment as well, if not better than, the solvent-based primer (Kendig et al., 1999). 

Compared to BPA, bisphenol F epoxy resins have lower viscosity, and their cross-linked films have higher and heat distortion temperatures along with better solvent and chemical resistance. Due to these excellent properties coupled with low viscosity, bisphenol F epoxy resins are popular in very high-solid and solvent-free coating systems. 

Thermosetting epoxy and polyurethane chemically-cured liquid resins can provide, among other characteristics, superior abrasion resistance coatings. Solvent-free formulation applied by hot spray techniques can achieve film thicknesses of up to 5 mm. 

Floor Coatings. Concrete floors are coated with low-solvent or solvent-free epoxy or acrylic resin materials that may be applied in any desired thickness. They are extremely resistant to abrasion, can be made slip resistant with sand, silicon carbide, or high-grade steel granulate, and are also resistant to mineral or vegetable oils and gasoline (used for warehouses and factory halls). 

In recent years, water-dispersed epoxy resins also have gained importance in a variety of applications. Water-soluble epoxy resins are prepared by the esterification of epoxy resin with drying oils/ fatty acids of drying oil, followed by the formation of either half esters of dicarboxylic epoxy esters, or maleinised epoxy esters through reaction with polybasic acid anhydrides. They become water soluble on neutralisation with dimethyl etha-nolamine (Fig. 7.4). The cationic polymerisation of emulsified epoxy resins by 1 % perchloric acid has also been reported. The polyols obtained were cross-linked with MF resin to produce waterborne coatings, which are free from co-solvent and show excellent solvent resistance at low bake temperatures. ... 

A plastisol may be regarded as an organosol in which the continuous phase is almost entirely liquid plasticizer (small amounts of solvent are used for viscosity adjustment). PVC plastisols are made from PVC powder, adipate and phthalate ester plasticizers and minor amounts of epoxy-type resin in solution to aid pigment dispersion and to help (with other additives) to keep the polymer stable to heat and oxidation. The resultant coating is nearly solvent-free and so can be applied in thick films (100-250 m) and stoved without disruption by escaping solvent. The plasticizer penetrates the particles, aiding sintering as the metal substrate reaches c. 200°C in 30-60 s. 

An approach to this problem is by the appropriate modification of acrylic primary dispersions to suit automotive coating requirements or solvent-free secondary dispersions of conventional resin types Hke epoxies, polyesters, polyurethanes. Today, the latest water-borne coatings are much more robust in terms of usage or appHca-tion friendhness and require significantly less heating or air-conditioning than two decades ago. They still require some additional dehydration or special kinds of flashes before going into ovens to help remove the water. 

Other. 2-Nitro-1-butanol is an excellent solvent for many polyamide resins, cellulose acetate butyrate, and ethylceUulose. It can be utilized in paint removers for epoxy-based coatings. 2-Hydroxymethyl-2-nitro-l,3-propanediol is usebil for control of odors in chemical toilets. Its slow release of formaldehyde ensures prolonged action to control odor, and there is no reodorant problem which sometimes is associated with the use of free formaldehyde. 2-Hydroxymethyl-2-nitro-l,3-propanediol solutions are effective preservative and embalming fluids. The slow Uberation of formaldehyde permits thorough penetration of the tissues before hardening. 

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