Powder Coating Glossary of Terms

This Glossary of Terms for Powder Coating has been reproduced from that published by our parters at Interpon Powder Coatings (Akzo Nobel). If you read a term that you don’t understand on our site or posts in the context of powder coating, please refer to the meanings of the terms below.

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Acrylic - A powder coating material with a high content of a polymer consisting of short chain esters of several acrylic monomers.

Additive - A material added to a powder coating material to improve one or more properties.

Adhesion - The firm attachment of a coating to a substrate or another coating.

Air, compressed - Air at any pressure higher than the atmospheric pressure.

Alkaline - An environment that has the characteristic of being strongly basic (high pH).

Ambient Temperature - The usual, or surrounding, environmental conditions.

Anti-oxidant - A compound added to powder coating materials to slow down the oxidation.

Application - The process of applying a powder coating material onto a substrates surface.

ASTM - American Society for Testing Materials, being the institute that controls standards for materials, systems and services.

Atlas (Xenon Arc) Weather-Ometer (ASTM G 26, Method A) - An accelerated test which simulates the effects of weathering through the use of a filtered zenon arc light source.

Back Ionization - An excessive build-up of charged powder particles during electrostatic application which limits the ability of additional powder to be deposited onto the substrate; can neutralize the electrical charge of subsequently sprayed powder particles.

Binder - The polymer(s) as the main component of the powder that will polymerize later and binds the other components into the solid powder coating film.

Blistering - The effect, usually at the scribe, of blisters formed under a cured powder film.

Blooming - A haze on the surface of a coating which can be easily removed.

Bonding - The firmly joining together of a powder coating film to the substrate or of two coating films.

Brightness - The degree to which a surface reflects light (see Gloss).

Bulk density - Mass per unit of volume including the air filled voids in the bulk material.

Caking - Agglomeration of individual powder particles or sticking of powder to walls or components of equipment.

Cartridge filter - A filter construction containing one or more cartridges that function as a filtering element.

Catalyst - A material that accelerates the crosslinking, hardening or curing reaction of a mixture of polymers or polymers.

Chalking - Degradation of a coating due to UV exposure, which results in loss of colour and gloss.

Checking - Checking is the formation of breaks in the surface of a powder coating which are sufficiently fine as to not render the underlying metal visible.

Chemical Pre-treatment - Modification to a substrate surface by chemical treatment with chromate ions, chromate/phosphate ions, phosphate ions or other proven methods.

Chromating - Preparation process for metal substrates, in the form of a conversion coating using chromium, and forming an inert chromate coating film, prior to the application of powder coating material.

Classifier - An equipment to separate particles from another fluid, much like a cyclone, whereby the separation cut is adjustable, within a range, with an additional device.

Clean Air Act - Act which empowers the EPA to improve the quality of air through enforcement of the developed pollution standards.

Clear coat - A non-pigmented coating applied on a base metal such as aluminium or over a previously applied pigmented coating.

Coating powder - Powder material being a mixture of polymer, pigment, filler and additives, for application on substrates with the objective to form a coating film thereafter. See also powder coating material.

Compatibility - The capacity of coating powders from either different sources or of different compositions when combined and applied which yield no visible or mechanically measurable differences in the cured film or application properties.

Composition - The parts of a mixture, formulation or recipe, usually expressed as percentages.

Contamination - Any foreign material, such as soil, dirt or unwanted chemicals, that deteriorate the quality of the coating film.

Contrast Ratio - A value related to the hiding power of a coating which must be reported at a specific film thickness; the ratio of the reflectance of a coating is measured over black and white backgrounds at the same film thickness; the results are measured as a numerical value – in general, a 0.98 contrast ratio is visually opaque; directly related to product pigmentation; minimum film thickness with full coverage of the substrate is critical (see also Hiding Power or Opacity).

Conversion coating - Preparation process for metal substrates, with the help of iron, chromium or zinc, prior to powder coating application.

Conveyor - A chain mechanism that transports the parts to be coated, in a hanging position, through all steps of the application process.

Corona Charging - The induction of powder particles exposed to an electrostatic field generated by a high voltage device.

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

Coverage (calculated) - Determines the m2/kg adjusted accordingly for application film thicknesses.

Cracking - The arising of crevices or cuts in the surface of a coating film by chemical or mechanical influences.

Cratering - The appearance of tiny pitts (like mini craters) visible to the trained eye without enlargement at the surface of a powder coating film, usually due to some form of incompatibility.

Cross contamination - The deterioration of a coating film occurring when powders are used in mixed form when they are not compatible.

Cross hatch - A testing method to investigate the adhesion properties of a coating film.

Crosslinking - The multi-directional linking together of polymer molecules through chemical reactions, stimulated by a curing agent.

Cure Schedule - The time at temperature necessary for a coating to develop specific properties.

Curing - The hardening or cross-linking process.

Curing agent - A crosslinker or hardener that stimulates the curing of a binder system.

Curing oven - An oven in which the powder coated parts are exposed at the required temperature so that the cross-linking reaction can take place for a pre-determined time.

Cyclone - A cylindrical type of equipment for separating particles from another fluid applying centrifugal forces.

De-ionized water - Water which has been treated such that it does not contain water foreign ions.

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

Dielectric Strength - Property of an insulating material where electrical breakdown occurs under specific conditions of test, expressed in volts per mil.

Disbondment (see also Blistering) - The effect, usually at the scribe, of blisters formed under a cured powder film.

Dispersion - A suspension or mixture of particles in another fluidum.

Distinctness of Image (DOI) - The sharpness of an image reflected by a coating’s surface.

Dry Crosshatch Adhesion (ISO 2409) - Determines the relative adhesion of a coating to the substrate.

DSC - A Differential Scanning Calorimeter can measure several thermodynamic properties of chemicals.

Dust - Particular matter which is, or has been, airborn with a particle size below 75 micron.

Dust explosion - The confined rapid combustion of dust particles which are airborn causing strong expansion effects.

Dwell Time - The length of time a part is in an oven.

Edge Coverage - The ability of a coating in its cured state to flow, build, and adhere to sharp corners, angles and edges.

Electrostatic charging - The process of transferring a static electric charge on powder particles.

Electrostatic Spray (Corona) Method - The induction of powder particles exposed to an electrostatic field generated by a high voltage device.

Emmaqua - Weathering test performed in Arizona where panels placed in a special apparatus are exposed to a brief water spray and magnified sunlight; ambient humidity is fairly low.

EPA - The Environmental Protection Agency is a USA Government Institute which regulates and controls organizations influencing the environment.

Epoxy resin - A thermosetting polymer, produced on the basis of epichloro-hydrin, which can be further polymerized by the addition of a hardener.

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

Extender - A type of pigment which also transmits special properties to a powder coating material.

Extrudate - The resulting product coming out of an extruder, be it in the initial molten form or the solidified state thereafter.

Extruder - A machine that mixes solid particles by using mechanical kneading and the subsequent heat-development until a molten fluidum is created of a homogeneous composition.

Faraday Cage Effect - The lack of penetration of powder particles into cavities or recessed areas of a substrate due to its configuration.

Fat edge - Thicker than usual coating film to be found along edges of a flat substrate.

Ferrous - Metal containing an amount of iron.

Field lines - Imaginable lines of force in an energy field (e.g. electrostatic).

Filiform - Corrosion or creep resembling a thread-like formation.

Filler - Inorganic inert material; also extender or certain pigments.

Film thickness - Height of a cured coating film measured in microns.

Fines - Small powder particles, usually less than 10 microns.

Flash off - The process-step in liquid coating application of allowing the solvent to evaporate prior to curing.

Flash rust - A molecular film of rust appearing on a steel surface within minutes after pre-treatment.

Flexibility (Mandrel bend test, ISO 1519) -  Measures a coatings’ bend capability over a given shape.

Flop - A characteristic of metallic coatings to change color when viewed at different angles.

Flow - Measure of self-levelling; the nature of a coating which allows it to level or spread into a smooth film of uniform thickness before hardening.

Fluidity - The degree to which powder coating material can be brought to fluidization.

Fluidized bed - Container in which powder is kept suspended in air continuously.

Galvanized steel - Steel coated with a thin layer of zinc.

Gel Time - The interval of time at a given temperature required for a material to be transformed from a dry solid, through a liquid state, to a gel-like condition; measured in seconds at a given temperature.

Glass Plate Flow/Hot Plate Melt Flow (HPMF)/Incline Plate Flow - A measurement on an inclined surface when powder is in a molten state; usually measured in millimetres at a given temperature and angle.

Gloss (ISO 2813) - Surface reflection of directed light, measured in units; the most common angle of measurement is 60°; a 20° angle should also be considered for certain full gloss formulations and an 85° angle for low gloss products.

Grounding - The principle of bringing the electrical potential in equilibrium with a neutral mass.

Hardener - See curing agent.

Hardness - The ability of a cured powder coating film to withstand the penetration of a standardized object.

Hazardous - A condition of contact or case of presence in which a risky, dangerous or less healthy or toxic situation is created.

Hiding Power - The extent to which a powder coating masks the color and pattern of the surface to which it is applied at a given film thickness (see also Contrast Ratio or Opacity).

Holiday - A localizedcoatingdefect,characterizedbyaveryloworzerocoatingthickness.

Humidity Resistance (DIN 50017) - Measures a coating’s ability to withstand exposure to 100% relative humidity at various temperatures.

Hybrid - A polyester or acrylic powder coating material which has been epoxy-modified.

Hygroscopic - The tendency of a substance to attract or absorb moisture from the air.

Impact Fusion - The tendency of powder particles to fuse with other particles at points of impact in the application equipment during the application process.

Impact Resistance (ASTM D 2794, Direct/Reverse) - Measures a coating’s ability to withstand a force; expressed in Nm; results can be affected by type of substrate, film thickness, or diameter of indenter.

Incompatibility - The impossibility of powders to be used and applied in a mixture of any composition, without any visible or mechanically measurable differences of the resulting powder coating film when compared to the virgin materials.
Infrared (IR) Cure - A method of curing powder which utilizes direct exposure to light energy in the IR region of the light spectrum.

Infrared radiation - Energy in the infra-red region of the electromagnetic spectrum just above the visible light range.

Inhibitor - An additive used to delay or neutralize a chemical reaction.

Inorganic - The sort of materials not containing carbon compounds such as metals and its derivatives.

Intercoat Adhesion - The ability of a coating to adhere to previously applied films.

Karl Fisher test - Chemical testing method to determine the moisture content of powdery materials.

LEL - The Lower Explosive Limit is the lowest concentration of organic powder suspended in air which can be brought to explosion when ignited by a standardized energy source.

Levelling - A powder’s ability to flow into a smooth, uniform thickness (free from defects).

Mandrel bend test - A mechanical method for testing the flexibility of a coating film applied on a standardized sample plate.

Mar Resistance - A coating’s ability to withstand contact without blemishing.

Metal Temperature - The temperature of a part at any time during the cure cycle; varies based upon mass of part and dwell time.

Metamerism - A definition applicable to a coating film when its color appears different when viewed in light of varying wavelengths.

Micron - Standard unit of measuring a coating film thickness. (1/1000 of 1mm).

Micronizing - Grinding powder to the range of microns.

Mil – Standard unit of measuring film thickness in USA (1/1000 of an inch) equivalent to 25.4 mirons.

Monomer - A molecule that has the ability to chemically react with another monomer by forming a long chain of identical sections, the polymer.

MSDS - A Material Safety Data Sheet provides the hazardous components, other safety and health hazards, protection equipment and first-aid procedures.

NFPA - The National Fire Protection Association is a USA organization that indicates the health, reactivity and flammability hazards of chemicals.

Non ferrous - A material containing no iron.

OEL - The Occupational Exposure Limit relates to the exposure limit by inhalation and refers to the concentration of hazardous materials in the atmospheric air.

Opacity - The ability to hide the underlying substrate at a given film thickness (see also Contrast Ratio or Hiding Power).

Orange Peel - A surface appearance which has an irregular appearance similar to the skin of an orange and is generally caused by restricted the limited flowing ability of the powder coating material.

Organic - The sort of materials containing carbon compounds such as many polymers, certain pigments and additives, etc.

OSHA - The Occupational Safety and Health Administration is a USA organization for the control of safety and health issues.

Out-Gassing - Air or gas that escapes from the sub-surface beneath or within the coating and causes blisters, bubbles, or small holes; frequently occurs with zinc or aluminium castings or galvanized steel.

Over-bake - The application of heat using more time and/or temperature than is required for cure which often causes the coating to become too brittle; color and gloss may be adversely affected.

Over-curing - The application of higher than recommended curing–values (temperature, time or both).

Overspray - Material not deposited on the part or rack; it may be recovered with the appropriate equipment.

Particle Size Distribution (PSD) - The overall range of particles (from coarse to fine) resulting from the grinding process; measured in microns; varies with product.

Passivation - Chemical treatment of a metallic surface with the objective to make it less reactive.

Pencil Hardness (ASTM D3363-74) - Relative rating of a coating’s ability to resist scratching; measured as mar and/or gouge.

Penetration - Ability of particles to penetrate towards and onto the surfaces of Faraday cage like areas such as cavities and recesses.

Phosphating Preparation - Process for metal substrates, in the form of a conversion coating using iron (chromium) or zinc, and forming an inert phosphate coating film, prior to the application of powder coating material.

Pickling - A cleaning step of hot rolled steel plate, usually carried out in the steel mill, to remove the milling scale before the metal is oiled to protect it from corroding.

Pinhole - The appearance of tiny holes (like from a needle) visible to the eye without enlargement at the surface of a powder coating film, usually due to the insufficient ability of gasses to escape from the molten film during curing.

Plate flow - A test to measure the ability to flow during the curing of a powder during which a compressed pile of powder is placed on an inclined plate that is subjected to a preset temperature.

Polyester - A thermosetting polymer, saturated carboxyl or hydroxyl terminated, which can be further polymerized by the addition of a hardener.

Polymer - A long molecule that has been formed out of a large series of monomers by a chemical reaction.

Polymerization - The reaction in which a large molecule (polymer) is formed by chemically binding identical sections (monomers) to a long chain. Curing reaction.

Post-formability - The ability of a cured coating to withstand severe bending without the appearance of cracks.

Potable - Suitable for drinking.

Powder coating - The application of powder coating material on substrates in order to form a coating film thereafter.

Powder coating material - The ultimate dry solid compound including all necessary ingredients, ground to powder and ready to be applied as a coating material on a given substrate.

Powder pump - A lifting and moving device that applies air for transporting either powder from one container to another or towards an operating device.

Pre-mixing - The mixing and size reduction of all necessary raw materials for the production of powder coating material prior to feeding them to the extruding step.

Pre-treatment - The preparation of a part prior to the application of a coating powder in order to improve adhesion and corrosion resistance.

Primer - A coating applied to a surface to improve adhesion of a topcoat and/or improve corrosion resistance.

QUV - Accelerated weathering test performed at elevated temperatures in which coated panels are exposed to regular cycles of intense UV light alternated with dark cycles where water is allowed to condense on the panels.

Radiation curing - The application of energy-rays of a particular range of the electromagnetic spectrum for curing of a coating layer.

Reclaim - Any material not deposited onto parts; usually mixed with virgin material for future applications.

Recoatability - A cured coating’s ability to accept another coat.

Recovery - The entire process step of the powder application process in which the non-deposited powder is reclaimed, recycled and added to the virgin powder for re-use.

Recycling - The action in the powder recovery step of the powder application process by which the reclaimed powder is fed back.

Reflectance - The percent of light reflected at a given wavelength; the illuminant, degree of observer and the wavelength must be specified; color (not gloss) dependent – whites will have the highest values.

Reflectivity - The reflectance of a coating at a film thickness such that any further increase in thickness will not affect the amount of light reflected.

Resin - A polymeric, organic material, be it  from a natural or a synthetic source, which can be further cross-linked or polymerized by the addition of a hardener.

Respirator - Safety breathing face-mask.

Rework - A correction procedure to correct shortcomings on a powder coated article.

Salt spray test, acetic (ISO 9227) - The degree of corrosion determined at the scribe based upon a prescribed time period; should be tested with a control.

Scale – Rust layer on steel originating from the hot roll steel-milling process.

Seal rinse - A step in the pre-treatment process where the metal surface is passivated to prevent corrosion prior to the powder coating of substrates.

Service Temperature (continuous or intermittent) - The temperature which a finish is able to withstand for an extended period of time or number of cycles without degradation.

Shelf Life - The period of time a coating retains its application and appearance properties if stored according to the manufacturer’s recommended conditions.

Sieve - A screening mechanism applying a wire mesh to separate a certain portion out of too coarse or contaminated material.

Significant Surface - The part of the article covered or to be covered by the coating and for which the coating is essential for serviceability and/or appearance.

Softening point - The temperature at which a polymer or a powder coating material first starts to melt.

Soil - Any foreign material that adheres to a substrates surface prior to the pre-treatment.

Solvent - A liquid of one or more components often applied in the liquid paint industry to dissolve paints.

South Florida Exposure (ISO 2810) - Exposure to typical heat, humidity and sunlight conditions at southern latitudes; measurements are generally the change in gloss and/or colour (Delta E).

Specific Gravity - The density of a formulation relative to water.

Spray booth - A special cabin in which powder coating material is sprayed, manually or automatically, onto substrates under strictly controlled conditions.

Stripping - The procedure to remove a coating film from a substrate in order to be recoated.

Substrate - The article or product to be powder coated.

Surfactant - Chemical additive to control the surface tension of a material.

Taber Abrasion - Resistance to wear.

Temperature Stability - Appearance and adhesion after a period of time at a prescribed temperature and film build.

TGIC - Triglycidyl Isocyanurate is a curing agent for carboxyl terminated polymers.

Thermoplastic - A powder coating which will repeatedly melt when subjected to heat and solidify when cooled.

Thermoset - A powder coating which, when subjected to heat, undergoes an irreversible chemical reaction during the cure cycle.

TLV - The Threshold Limit Value is the concentration of chemicals in air to which persons may be daily exposed without harm.

Touch-up - The repair of small damages on a coating film or the paint to be used for that purpose.

Toxic - Poisonous.

Transfer Efficiency - The amount of powder attracted to the part compared to the amount of powder sprayed; measured as a percentage.

Triboelectric Spray Method - Powder particles receive an electric charge through the use of frictional contact with a nonconductive material.

UEL - The Upper Explosive Limit is that concentration of organic powder suspended in air above which the mixture will not explode if ignited by a standardized energy source.

Ultra violet stabilizer - A chemical additive that absorbs part of the UV radiation in the sunlight.

Ultraviolet Radiation (UV) - Light energy from the UV region of the light spectrum which can break certain chemical bonds and contribute to the fading and wear of coatings.

Undercured - The application of an insufficient curing temperature, time or both.

Urethane - A thermosetting hydroxyl functional polymer, usually reacted with an isocyanic curing agent.

Venturi - A special shaped restriction in a powder pump body.

Vibratory box feeder - A moving device that applies vibration for transporting powder from a box container to another hopper.

Virgin Material - Powder which has not been mixed with reclaim material.

Virgin Powder - Fresh powder coating material directly from the supplier not containing any reclaim.

Volatile Organic Compounds (VOC’s) – Carbon based compounds which can undergo an atmospheric photochemical reaction, contributing to air pollution and causing ozone depletion.

Washer zone - The immersion or recirculating spray cleaning step of the pre-treatment system.

Water Resistance - A coating’s ability to withstand immersion in water at prescribed temperatures for specified time periods.

Weatherability - Degradation caused by humidity, temperature, and exposure to sunlight.

Weld splatter - Contaminations left behind on a metal surface after welding such as slag or beads.

Wrap - A characteristic of coating powders during electrostatic application to seek out and adhere to areas of the substrate not in the direct line of sight of the delivery system end point.

Yellowing - Development of a yellow color or cast of a coating due to aging or cure variables; more evident in light colored formulations.

Please see the original source for this Glossary of Terms on the Interpon website.