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POWDER COATING, December 2016 11 Epoxy. A reactive group commonly pre- sent in resins (epoxy resins, GMA resins) or crosslinkers (triglycidyl isocya- nurate, or TGIC). Epoxy equivalent weight (EEW). The weight of the resin containing 1 gram equivalent of epoxide; also called weight per epoxide group (WPE) and epoxy molec- ular mass (EMM). Epoxy groups. Functional groups with the structure: O -C-C- Epoxy resin. A polymeric product charac- terized by possessing epoxy functional groups (three-member, cyclic ring with two carbon atoms and one oxygen atom) that are capable of reacting with other function- al groups such as carboxylic acids to form new chemical bonds. Equivalent weight. The weight of a polymer per functional group, for exam- ple, 450 grams per hydroxyl group. Ester. The compound formed by the elimination of water and the bonding of an alcohol and an organic acid. Esterification. A reaction that pro- duces ester linkage. F Flow agent. Substance added to a pow- der to increase flow characteristics dur- ing the curing process. Free radical. A highly reactive elec- tron-deficient molecule. Functionality. Ability of a compound to form covalent bonds; compounds may be mono-, di-, tri-, or polyfunctional; that is, one, two, three, or many functional groups may participate in a reaction. Fusion. See Sintering. G Gel time. Amount of time it takes for a resin to set (stop flowing) at a given temperature. Glass transition temperature. The tem- perature at which polymer molecules are able to move fairly freely even in the solid state. Rub ber is elastic because the mole - cules at room temperature are above their glass transition temperature and can be easily stretched out of position. Glycidyl methacrylate (GMA) acrylic. An acrylic resin that has an epoxy group for curing. Glycol. A chemical compound character- ized by having two hydroxyl (-OH) function- al groups bonded to the same molecule. Is also commonly re ferred to as a diol. Glycoluril. A chemical compound derived from urea-formaldehyde reaction prod- ucts. Reacts with hydroxyl functional polyesters at conventional cure oven tem- peratures. H Hardener. Curing agent; promoter; cata- lyst. Homopolymerize. A polymer made up of similar repeat units. Hybrid coating. A powder coating based on a blend of polyester and epoxy resins reacting during the cure cycle to yield the binder. Hydroxyalkylamides (HAA). Chem ical compounds that have a specific spacial arrangement of the hydroxyl functionality and amide chemical bonds that provides internal catalysis to the reaction of the hydroxyl with carboxylic acids. Hydroxyl. Reactive group commonly present in resins for urethane coatings, either polyester or acrylic. Hydroxyl equivalent weight. The weight of a resin that contains one equiv- alent of hydroxyl functionality. Hydroxyl functional acrylic. An acrylic resin that has hydroxyl functional groups for curing. Hydroxyl number. A measure of hydroxyl (-OH) functionality in a resin. Usually reported at milli grams potassium hydrox- ide per gram resin (mg KOH/g). I Isocyanate. Chemical functionality that reacts with hydroxyl functionality to yield a urethane chemical bond. M Maleic functional. A polymer contain- ing functional groups de rived from react- ed maleic acid or anhydride. Masterbatch. A plastic, rubber, or elas- tomer mixture in which there is a high additives concentration, such as plastic with color pigment; used to proportion additives accurately into large bulks of plastic, rubber, or elastomer. (Meth)acrylate ester. CH2:C(CH3) COOR Methacrylic acid ester in which R can be methyl, ethyl, iso butyl, or any other of many alkyl groups. Methanol-blocked melamine. A cross lin k - er for hydroxyl- or carboxylic-acid-contain - ing resins. The reactive sites are blocked with meth anol, which releases during cure. Moiety. A part, portion, or share. Molecular weight. A measure of the size or length of a polymer chain. Usually re - ported as an average mass unit. Higher molecular weights tend to lead to higher melt viscosity. Monomer. A primary molecule, or build- ing block, in a polymer product, such as ethylene (in polyethylene) and glycols (in polyesters). Multifunctional resins. See Up graded resins. N Novolac resin. Any of the thermoplastic phenol-formaldehyde resins made with an excess of phenol in the reaction; used in varnishes. O Oxime-blocked isocyanate. An isocy - anate crosslinker in which the reactive iso- cyanates are blocked by an oxime group. Oximes. A large family of chemical com- pounds; some can be used as a blocking agent for isocyanate. P Pendant groups. Part of the (meth) acrylic monomer that gives each mon omer its spe- cific set of prop erties. Phenolic resins. A particular group of film formers. Resins made from phenols and aldehydes. Photoinitiator. A compound that initiates a reaction after irradiation with intense light. Polyester. A polymer characterized by hav- ing multiple ester chemical links in its back- bone structure and formed by the reaction of glycols or polyols with di-, tri-, or polycarbox ylic acids at high temperatures. Polymer. A chemical compound charac- terized by having a large molecular mass and produced by chemically linking smaller mole cules together. Main compo- nent of the binder. Polyols. Resin—acrylic or poly ester— that contains hydroxyl functional reac- tive groups (alcohols). Q QUV. Accelerated weathering test in which painted panels are exposed to ultraviolet light. RAW MATERIALS GLOSSARY