Coatings, amino resins

Liquid coating resins are prepared by reacting methanol or butanol with the initial hydroxyme-thylureas. Ether exchange reactions between the amino resin and the reactive sites on the polymer produce a cross-linked film. 

Catalysts. The alkanolamines continue to find use as blocked catalysts for textile resins, coatings resins, adhesives, etc. Of particular utifity in curing durable-press textiles is AMP-HCl. Other salts, such as those of the benzoin tosylate or A-toluenesulfonic acid, find utifity in melamine- or urea-based coatings (18) (see Amino resins and plastics). 

Synthetic Applications. Oxazolines, which ate synthesized as indicated above, have been utilized in many different appHcations (25). When used in resin formulations, AMP, AEPD, and TRIS AMINO can incorporate the oxazoline stmeture into the polymer stmeture (26). Because they ate polyols, both AEPD and TRIS AMINO can be used in polyester resin modification. Oxazoline alkyd films ate characterized by improved performance, particularly salt-spray resistance and gloss (see Alkyd resins Coatings, special purpose, high performance). 

Nitrocellulose based lacquers often contain short or medium oil alkyds to improve flexibiUty and adhesion. The most commonly used are short oil non drying alkyds. Amino resins or urethane resins with residual isocyanate functional groups may be added to cross-link the coating film for improved solvent and chemical resistance. The principal appHcations are furniture coatings, top lacquer for printed paper, and automotive refinishing primers. 

Amino resins are also often used for the cure of other resins such as alkyds and reactive acryUc polymers. These polymer systems may contain 5—50% of the amino resin and are commonly used in the flexible backings found on carpets and draperies, as well as in protective surface coatings, particularly the durable baked enamels of appHances, automobiles, etc. 

The future for amino resins and plastics seems secure because they can provide quaHties that are not easily obtained in other ways. New developments will probably be in the areas of more highly specialized materials for treating textiles, paper, etc, and for use with other resins in the formulation of surface coatings, where a small amount of an amino resin can significantly increase the value of a more basic material. Additionally, since amino resins contain a large proportion of nitrogen, a widely abundant element, they may be in a better position to compete with other plastics as raw materials based on carbon compounds become more costly. 

Paraformaldehyde [30525-89-4] is a mixture of polyoxymethylene glycols, H0(CH20) H, with n from 8 to as much as 100. It is commercially available as a powder (95%) and as flake (91%). The remainder is a mixture of water and methanol. Paraformaldehyde is an unstable polymer that easily regenerates formaldehyde in solution. Under alkaline conditions, the chains depolymerize from the ends, whereas in acid solution the chains are randomly cleaved (17). Paraformaldehyde is often used when the presence of a large amount of water should be avoided as in the preparation of alkylated amino resins for coatings. Formaldehyde may also exist in the form of the cycHc trimer trioxane [110-88-3]. This is a fairly stable compound that does not easily release formaldehyde, hence it is not used as a source of formaldehyde for making amino resins. 

Cured amino resins are far too brittle to be used alone as surface coatings for metal or wood substrates, but in combination with other film formers (alkyds, polyesters, acryUcs, epoxies) a wide range of acceptable performance properties can be achieved. These combination binder coating formulations cure rapidly at slightly elevated temperatures, making them well suited for industrial baking appHcations. The amino resin content in the formulation is typically in the range of 10—50% of the total binder soHds. 

Amino resins are used by the paper industry in large volume for a variety of apphcations. The resins are divided into two classes according to the mode of appHcation. Resins added to the fiber slurry before the sheet is formed are called wet-end additives and are used to improve wet and dry strength and stiffness. Resins appHed to the surface of formed paper or board, almost invariably together with other additives, are used to improve the water resistance of coatings, the sag resistance in ceiling tiles, and the scuff resistance in cartons and labels. 

Other amino resins besides MF resins are used to a lesser degree in coatings. Urea—formaldehyde resins are used in some coatings for wood furniture because these resins cross-link at lower temperatures than MF resins and the higher water resistance and exterior durabiUty that can be obtained using MF resins are not needed. Ethers of formaldehyde derivatives of 6-phenyl-l,3,5-triazine-2,4-diamine [91-76-9] (benzoguanamine resins) give... 

Coating materials may be based on short or medium-oil alkyds (e.g. primers for door and window frames) nitrocellulose or thermoplastic acrylics (e.g. lacquers for paper or furniture finishes) amino resin-alkyd coatings, with or without nitrocellulose inclusions, but with a strong acid catalyst to promote low temperature cure (furniture finishes) two-pack polyurethanes (furniture, flat boards) unsaturated polyester resins in styrene with free-radical cure initiated by peroxides (furniture) or unsaturated acrylic oligomers and monomers cured by u.v. radiation or electron beams (coatings for record sleeves paperback covers, knock-down furniture or flush interior doors). 

Aminoquinolines, 21 185, 199 Amino resins, 16 409. See also Amino resins and plastics coating resins, 7 96-98 formaldehyde in, 12 121 Amino resins and plastics, 2 618-652 chemistry of resin formation,... 

Extensive use of these resins is found in textile and paper-treating and surface coatings. Many types of clothing also can be given a permanent press by an amino resin treatment. Amino resins can be molded and are used for radio cabinets, buttons, switch plate covers, dishware, and Formica. 

The Food and Drug Administration (1999) permits the use of triethanolamine as a component of adhesives in food packaging as an indirect food additive, as a component of the uncoated or coated food contact surface of paper and paper board for use with dry solid foods with no free fat or oil on the surface, and to adjust pH during the manufacture of amino resins permitted for use as components of paper and paper board in the United States. 

Amino resms are probably the mos important modifiers for alkyd resins. Many industrial baking enamels, such as those for appliances, coil coatings, and automotive finishes (especially refinishing enamels), are based on alkyd-amino resin blends. Some of the so-called catalyzed lacquers for finishing wood substrate require very low bake or no bake at all. 

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