Coatings, epoxy functional resins

Since epoxy functional resins are widely available and contribute many desirable characteristics to coatings such as adhesion, toughness and abrasion resistance, it may be desirable to have UV-curable adhesives based on epoxy systems. In conventional UV-curable coatings, the... 

Figure 7. Paint adhesion loss in salt spray exposure (ASTM B117) as a function of ester content for chain-extended epoxy-amine and epoxy-ester resin based coatings. All coatings applied at 20-25 urn film thickness to SAE 1010 steel test panels, baked, scribed and exposed for 24 hours to salt spray conditions.

The commercially available phenoxy resin has Mw around 50,000 and little epoxy functionality. The phenoxy polymer is then classified as a polyol or a po-ly(hydroxy ether) [3]. Typical applications for the phenoxy resin are as hot-melt adhesives, coatings for beverage cans, and toughening agents for various epoxy resin formulations. The viscoelastic properties of phenoxy resins have been studied by Alegria et al. [11-15]. The phenoxy polymer can be used as a reference in the viscoelastic study of DGEBA oligomer. 

The polyester resin used in this study, MR 13006 (Aristech Corporation), was supplied as a 60-wt% solution in styrene monomer. The epoxy resin, a digly-cidyl ether of bisphenol A (Epon 828), was obtained from Shell Chemical Company. The reactive liquid rubber, an amino-terminated butadiene-acrylonitrile copolymer (ATBN 1300 x 16), was provided by the BFGoodrich Company. The resin was mixed with additional styrene monomer to maintain the ratio of reactive unsaturation in the polyester-to-styrene monomer at 1 to 3. We added 1.5 wt% of tert-butylperbenzoate initiator to the solution, which we then degassed under vacuum. The mixture was poured between vertical, Teflon-coated, aluminum plates and cured under atmospheric pressure at 100 °C. In the modified compositions, the rubber was first dissolved in the styrene monomer, and then all the other components were added and the solution cured as described. In all the compositions, the ratio of the amine functions with respect to the epoxy functions was kept at 1 to ensure complete cure of the epoxy. 

A large variety of hyperbranched polymers with acrylate, vinyl ether, allyl ether, or epoxy functions were studied as multifunctional cross-linkers in coatings and in thermosets, using thermal as well as UV curing methods Clearly, polyesters are most prominent in the field, with the Perstorp Boltom products leading in technical studies. The commercialized poly(esteramide)s from DSM, sold under the trade name Hybrane polyethylenimines from BASF AG, available under the trade name TupasoF and poly(urethane)s (PUs) and polyesters developed by BASF are examples for hyperbranched polymers suited for coatings and resin products. 

J. Samuelsson, P. SundeU and M. Johansson, Synthesis and polymerization of a radiation curable hyperbranched resin based on epoxy functional fatty acids , Prog Org Coat, 2004,50,193-8. 

Polystyrene—Glass coated with an epoxy resin along with an amino or epoxy functional silane. 

Epoxy resin cross-linked with an amine functional resin is also an important coating system used in high-performance applications. Catalysts used for such systems have been either acidic compounds bearing phenolic hydroxyl groups or a tertiary amine. One of the most commonly used catalysts for two-component epoxy systems is tris(dimethylamino)phenol (Figure 5.13). 

One-component baking types of coatings in which resins such as alkyd, polyester, hydroxyl functional acrylic or epoxy esters are cross-linked with amino resins are typically catalyzed by acid catalysts. Strong acid catalysts such as sulfonic acid and phos-... 

Epoxidized soybean oil does not form coatings at 185 C for several hours. Obviously, its epoxy groups do not polymerize under these conditions. Both triolein and vernonia oil form good coatings. These results show that vernonia oil drying is based on its unsaturated carbon-carbon double bonds and not on its epoxy functionality. This allows its application as a reactive diluent, not only in epoxy and epoxy-ester formulations, but in alkyd resins as well. 

The variations produced by the above reaction are almost unlimited. Practically, however, the range of resins offered by the manufacturers are restricted to those most commercially viable. Although each manufacturer will have their own commercial names or codes for their products, in order to differentiate between the variants possible, most coatings technologies generally refer to the Epikote series of epoxy resins when discussing resin types. A brief example of the resins and their epoxy functionality are listed in Table 2-6. 

Besides the above-mentioned coating systems, functional group terminated prepolymers based on acrylics, polyurethanes and alkyds can also be used as curing agents to obtain coating systems with tailor-made performance requirements. Recently, a few HS coatings formulations based on epoxy resins have been reported in the literature. " ... 

Solutions of PVC/ VA polymers can be blended with most acrylic resins to provide useful coatings, but with few other polymers. Carboxylated and epoxy-functional grades can be combined to provide heat-crosslinkable blends, at the expense of limited shelf stability. Hydroxyl-modihed grades have broader compatibility and may be blended with alkyd, urea, melamine, and epoxy resins, and with urethane pre-polymers. Such blends can be heat-crosshnked, resulting in tough, chemical-resistant hlms. Urethane blends are characterized by high mar and scratch resistance. 

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