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10 POWDER COATING, December 2017 A Acid. A species that reacts in liquid water to generate hydrogen ions. See Acid groups. Acid equivalent weight. The weight of resin that contains one equivalent of carboxylic acid functionality. Acid functional acrylic. An acrylic resin that has carboxylic acid functional groups for curing. Acid groups. Also, carboxylic acid, organ- ic acid that possesses one or more carboxyl groups. The simplest member of the series is formic acid HCOOH. See Acid. Acid number. A measure of acidity, typically resulting from carboxylic acid functional groups on the polyester. Usually reported as milligrams potassi- um hydroxide per gram resin (mg KOH/g). Adduct. (1) A chemical compound that forms from chemical addition of two species, for example, reaction of butadi- ene with styrene forms an adduct, 4- phenyl-1-cyclo hexene; (2) the complex compound formed by association of an inclusion complex. Aliphatic esters. Nonaromaticity-con- taining esters (see Aromatic monomers) typically used to produce improved exteri- or-durable polyester resins. Allyl. Compounds whose functional groups are based on CH 2 = CRH- where R may be a hydrogen or other alkyl group. Amines. Any group of organic com- pounds of nitrogen—used as a curing agent when combined with epoxy resin— contains the NH 2 group. Anhydride. A reactive chemical com- pound that combines with water to yield two acid functional groups or with hydroxyls to yield an acid and an ester chemical link. Aromatic monomers. Monomers used to make relatively inexpensive poly - esters. The composition is such (aro- maticity) that the polyester derived from it has only limited ex terior durability. B Backbone chain. Base chemical used to polymerize a chemical compound or resin. Examples of epoxy resins are epichlorohydrin and bisphenol-A. Benzoin. An additive used in some pow - der coating formulations as a degassing agent. Air or other gases expelled dur- ing cure from the substrate or the pow- der coating can become trapped below the surface of the finish, causing blis- ters, bubbles, or small holes—such as microcraters or pinholes. Benzoin pre- vents these film defects and promotes flow and leveling of the powder finish. Binder. The powder coating component that binds to the pigments and fillers and provides adhesion to the substrate. Bisphenol A. Aromaticity-containing monomer (see Aromatic mono mers) typically used in epoxy resins for pow- der and other coatings. Blocked isocyanate curative. A group of urethane curing agents with iso- cyanate groups bonded (block ed) to a blocking agent (most often E-capro- lactam, see next page) to render them chemically inert at ambient tempera- tures. At elevated temperatures, gener- ally more than 250°F (121°C), the cura- tive deblocks and the resulting iso- cyanate groups react with the hydroxyl groups of the resin or resins. Blocking. The tendency of some pow- der coating resins to agglomerate or stick together during storage; also called sintering or fusing. C Carboxyl group. -COOH The function- al group of carboxylic acid. Also known as carboxy group. Carboxylic acid. The -COOH chemical unit. It provides acidity, reacts with hydroxyls to make esters, and is com- monly used as the polyester resin func- tional group that reacts with epoxide resins and TGIC during coating cure conditions to yield durable coatings. Cation. Specifically, for cationic poly- merization is a process in which the active end of the growing polymer molecule is a positive ion. Cresol. One of three poisonous, color- less isomeric methyl phenols, o-cresol, m-cresol, p-cresol; used in the produc- tion of phenolic resins, tricresyl phos- phate, disinfectants, and solvents. Crosslink. A generic term for chemical bonds that link polymer chains to each other, or the process of linking polymer chains to each other. Provides enhanced solvent resistance and durability. Often synonymous with curing. D Dicyandiamide. A typical representa- tive among the aliphatic solid amines used as curing agents in the production of epoxy powder coatings. Dodecanedioic acid (DDA). Cross - linker for glycidyl methacrylate (GMA) acrylic resins. It contains two carboxylic acid groups, enabling it to react, or cure, with the epoxy group of the GMA resin. Dry blending. Two final powder coat- ings are mixed together rather than extruded together. E E-caprolactam, or E-cap. A widely used blocking agent for isocyanate cura- tives. During cure, up to 80 percent of the E-cap evaporates from the powder finish. The rest is re tained in the film. E-cap is biodegradable. E-caprolactam-blocked iso pher one diisocyanate (IPDI). One of the wide- ly used crosslinkers for urethane pow- der coatings (see E-caprolactam and Blocked isocyanate curative). EMMAQUA. Accelerated exterior- durable test method in which natural sunlight amplified by mirrors is directed to painted panels. Epoxide. A reactive group in which an oxygen atom is joined to each of two car- bon atoms that are already bonded. Glossary of Raw Materials Terms