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Glossary of Terms

Powder Coating Terms & Definitions

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Abrasive - Coarse material used in abrasive blast cleaning, such as sand, grit, steel shot, or glass or plastic beads.

Acrylic - A powder coating with a significant content of a polymer containing short chain esters of various acrylic monomers.

Acrylic Resin - A clear resin derived from polymerized esters of various acrylic monomers. Acrylics are widely used as automotive and appliance topcoats and in other applications where resistance to chalking with exposure to sunlight is important. Physical properties can be controlled in part by choice of alcohol to make the ester.

Additives - Chemicals added to a powder coating to improve some property of a resin system such as flow control, gloss control, and texturing additives.

Adhesion - Bonding strength. Molecular attraction to the surface to which a substance is applied. A condition where one material is attached to another by means of surface attraction. Adhesion is affected by the condition of the surface to be coated, by closeness of contact, and molecular forces. The surface being coated should allow a certain amount of penetration, be chemically clean, be hard, not too smooth, and non-porous, to achieve good adhesion.

Agglomerate - A clump of powder particles bound loosely together into clusters containing entrapped air.

Air Cap/Nozzle - Perforated housing (at the head of a spray gun or nozzle) which directs compressed air against a coating material to form and shape it into an atomized cloud.

Air Velocity - Measurement of air speed, typically in feet per minute.

Air Volume - Measurement of air volume in cubic feet per minute.

Alkali - Caustic. Inorganic substances that share the characteristic of being strongly basic (high pH). (Example: Sodium hydroxide or caustic soda, lye, etc.)

Ambient - Usual or surrounding environmental conditions.

Anchor Pattern - Profile of a surface. Usually refers to surface profile after blasting.

Application - Process of applying a coating to a substrate.

Aqueous - A water-based material.

Arcing - A discharge of built-up electrical charge, often in the form of a spark, to a point of lower charge, usually ground.

ASTM - The American Society for Testing Materials, the source for voluntary consensus standards for materials, products, systems, and services.

B-staging - A process describing a powder coating material that has partially reacted or cured during manufacturing or storage.

Back Ionization - A condition which may occur during electrostatic application of powder where an excessive build-up of charged powder particles limits further powder to be deposited on the substrate and can reverse the electrical charge of the surface layer of powder particles. May also be referred to as Electrostatic Rejection and/or Repelling

Blast Cleaning - Removal of surface contaminate from a part by use of an air- or mechanically-propelled abrasive.

Blistering - Bubbles formed under a cured powder film, usually caused by the expansion of trapped air, moisture, or corrosion, either in a coating or in the substrate.

Blacked Isocyanate - A curing agent for hydroxyl-containing resins. Releases the blocked agent upon reaching an elevated temperature.

Bonding - Adhesion or secure joining of coating-to-coating or coating-to-substrate.

BTU - British Thermal Unit, the quantity of heat required to raise the temperature of 1 pound of water, 1 degree F, at a surrounding temperature of 39.2 degrees F.

BTUH - BTU's times hours.

Cartridge Booth
 - A type of powder booth that incorporates a cartridge filter system for powder overspray recovery.

Cartridge Collector - A self-contained unit with a cartridge filter housing or box for recovery of oversprayed powder that is used with a powder booth.

Catalyst - A special chemical that promotes the curing reaction.

Cleaner - Detergent, alkali, acid, solvent, or other cleaning material, often water- or steam-borne, used to clean and degrease parts prior to application of powder.

Clear Coat - An unpigmented powder coating applied over a color or base metal such as brass.

Coalescent Filter - A filter used in the compressed air line to fuse and trap liquid particles in the air stream.

Color Chip - Small piece of paper, celluloid, or other material, coated with finishing material and used as a color finish sample.

Compliance Coating - Coating which meets EPA defined standards for air, water, and waste disposal regulations.

Conversion Coating - Inorganic (zinc/iron phosphate) pretreatment for metal substrates that prepares the surface for powder coating.

Corona - A glowing, bluish or reddish area created by a discharge of electricity.

Corona Charging - The process of inducing a static electric charge on powder particles by passing the powder through an electrostatic field generated by a high voltage device.

Corrosion - Decomposition or reaction of metal with oxygen, water, or other chemicals, when exposed to a particular environment.

Counterflow - Transporting overflowed solution from one washer stage to another for reuse.

Cratering - Small round depressions on a paint film.

Creepage - Corrosion under a scribe line or edge after salt spray or other testing.

Cross Contamination - A condition when two or more powders are mixed by accident, usually resulting in a reduction in quality.

Cubic Feet Per Minute - Volume movement of a fluid. A measure used to size powder systems based on captive air. If not otherwise defined, the conditions are presumed to be air at a temperature of 68 degrees F, a pressure of 14.70 pounds per cubic foot. In gas industries, the temperature of standard air is usually given at 60 degrees F.

Cure - For thermoset powders, the polymerization of the resins and crosslinkers in the binder system to the desired molecular weight and physical properties of the coating, converting from a dry state to a solid continuous film.

Cyclone - A cylindrical device that separates powder particles from the air stream by centrifugally spinning the particles around its perimeter to the bottom for recovery. Some of the finer particles pass through the cyclone to a collector.

Decorative Coating
 - A coating designed primarily for cosmetic appearance and secondarily for protection. Decorative coatings are usually thin films (>5 mils).

Deflector - Conical shaped disc attached to the end of a powder gun to evenly distribute powder in a 360 degree pattern. Used to shape or direct the powder pattern.

Deionized Water - Water containing no ions other than hydrogen and hydroxyl ions. Usually produced through the use of ion exchange resins and used for rinsing parts after a seal rinse in a spray washer.

Delamination - Separation between two layers of coating or the coating and the substrate.

Delivery - The process of moving the coating powder through the application equipment to the end product. 

Discoloration - Color change.

DOI - Distinctness of Image. A test used to describe the surface reflectance of a paint film. A mirror would have very high DOI, but a low gloss texture would have no DOI.

Down-draft Booth - A powder booth in which the extraction opening is at the bottom of the booth.

Drag-out - Process of solution entrapment being pulled with the product typically out of a washer zone or coating enclosure.

Dry Film Thickness - Depth of applied coating powder before curing.

Edge Coverage - A coating powder's ability to flow over, build, and adhere to sharp corners, angles and edges.

Electrode - A metal filament within or at the end of a powder gun, used to create air ions as high voltage is applied. Powder is charged by the attachment of air ions.

Electrostatic Spray Technique - A deposition method of spraying and charging powder so that it is deposited on a grounded substrate.

Environmental Protection Agency (EPA) - Agency of the U.S. Government whose purpose is to regulate and control those agents affecting the environment.

Epoxy - A type of coating powder manufactured with epoxy resin, and generally having high mechanical strength and corrosion resistance but limited gloss and color retention when exposed to sunlight.

Etching - Surface preparation of metal by chemical process. Removal of a layer of the base metal.

Extruder - Device used to melt-mix plastics and/or coating powders. An extruder utilizes heat and mechanical kneading to achieve a homogeneous mixture.