Coating Glossary

Published by the Custom Coating Section of the Fluoropolymers Division

Published June 1997

Publication #: BPC 104

SPI Publication Number: BPC 104

NOTE TO USERS

Table of Contents

A/B

Abrasion --C A wearing, grinding, or rubbing away by friction.

Additive --C A substance added to a formulation in relatively small amounts to impart or improve desirable properties or suppress undesirable properties.

Alkaline wash --C Cleaning process that employs a high pH solution (caustic). A good choice for parts with little buildup of contaminants.

Aluminum oxide --C Hard particulate medium used in grit blasting to clean and roughen surfaces that are to be coated.

Anodizing --C Creating a hard oxide surface on aluminum parts via an electrolytic process. Unsealed anodized surfaces have a porosity that makes them excellent substrates for coatings.

ASTM --C American Society of Testing Materials

Average particle size --C The average diameter of powder particles as determined by various test methods.

Back Ionization --C -A condition occurring during electrostatic application of powder in which an excessive buildup of charged powder particles limits further powder from being deposited on the substrate. It may also be referred to as electrostatic rejection and/or repelling. (See Faraday Cage Effect.)

Binder --C Tough polymer that acts as an adhesive to join elements of matrix coatings.

Break-in --C Initial wear of mechanical components when large surface asperities can cause high friction and wear rates.

Breakout --C A violent or forceful break from a restraining condition.

Buffing/Burnishing --C Process of polishing cured coating to improve release and low friction.

Bulk density --C The mass per unit of volume in powder form, including the air trapped between particles.

Burn-off --C A method of removing a coating. Temperature is elevated above the degradation point of the coating and held there until the coating breaks down (See surface preparation).

C

Carrier --C The liquid portion of a coating (solvent or water) in which solids are dissolved or suspended.

Cloud-chamber technique --C The method of moving a charged or uncharged object through a charged or uncharged cloud of powder in an enclosed chamber.

Coefficient of friction --C A number expressing the amount of frictional effect usually expressed two ways: static or dynamic.

Cold flow --C Tendency of plastic materials to migrate slowly under heavy loads and/or over time.

Compatibility --C The capacity of different materials from different sources or of different compositions to be combined and applied so as to yield no visible or mechanically measurable differences in the cured film or application properties. Also, the ability of coating materials to withstand the elements of their environment.

Contact angle --C A means of quantifying the nonstick properties of a coating by measuring the ability of a liquid to wet its surface. Its an expression of the relationship between the surface tension of a liquid and the surface energy of the surface on which the liquid rests. For a droplet of liquid resting on a flat, level surface, the measurement is made by determining the angle in degrees) which is formed by extending a line from the intersection of the liquid and the plane to the outmost point of contact of the liquid--=s curvature. As surface energy decreases (as in a nonstick coating), the contact angle increases.

Conductor --C Material that can support flow of electrical current. Fluoropolymer coatings are normally insulators, but can be modified with certain fillers and pigments to make them conductive.

Corona gun --C A powder gun that uses corona charging.

Corona charge --C An electrostatic charge induced on powder particles by passing them through an electrostatic field generated by a high-voltage device.

Corrosion --C Process of metal decomposition (oxidation) in which metal ions are united with oxygen to form metal oxides. Fluoropolymer coatings provide excellent barriers against most corrosives.

Crosslinking --C Quality of thermosetting plastic resins in which polymer chains combine during curing process. In general, the greater the cross linking, the tougher and more chemically resistant the coating.

Cryogenic --C Temperatures less than -310EC ( -200EF).

Cure schedule --C The time/temperature relationship required to cure a coating.

Cure end point --C The point either during or following the cure schedule at which the coating film is determined to have developed specified properties.

Curing --C Process of bonding or fusing a coating to a substrate with heat and developing specified properties in the coating.

Cut-through resistance --C A coating film's resistance to penetration resulting from the combined application of sharp edges, heat and pressure.

D/E

Die casting --C Alloy casting process commonly used to produce high volumes of intricate parts. The process sometimes entraps small bubbles in the metal that can result in "blow holes" when the coating is cured.

Dielectric strength --C Ability of a coating to resist the passage of electric current.

Dip/spin --C Coating application technique in which small parts are placed in a basket that is lowered into a coating bath, then raised and spun to remove excess coating. An economical system for coating high volumes of small parts.

Dry blending --C A process for powder-coating manufacturing in which materials are blended without melting.

Dry (solid) lubricants --C Solid materials such as PTFE, Moly Disulfide (MoS₂) and graphite that have low coefficients of friction.

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

Elastomers --C Any of various elastic substances resembling rubber.

Electrostatic fluidized bed --C A deposition method of charging fluidized powder so that it is deposited onto a substrate (usually grounded).

Electrostatic spray --C A deposition method of spraying and charging a coating so that it is deposited on a substrate (usually grounded). A spray application process in which the coating and part to be coated are oppositely charged; process provides excellent "wrap" of coating around the part, even on sides opposite the spray gun. (See Corona Charge and Tribo Charging).

Engineering plastics --C Plastic resins that have high-performance properties such as high temperature stability, hot hardness, abrasion resistance and corrosion resistance.

Environmental regulations --C Federal, state or local laws, statutes or regulations of which their intent is to protect human health and the environment. Examples are the Clean Air Act (CAA), and the regulations which govern the storage, transportation and disposal of hazardous waste, the Resource Conservation and Recovery Act (RCRA).

Epoxy --C A flexible resin, usually thermosetting, made by polymerization of an epoxide and used chiefly in coatings and adhesives.

Extruder --C A device that raises a powder mixture to its melt temperature and --Asqueezes--@ this out in a flat --Aribbon.--@

ETFE (ethylene tetrafluoroethylene) --C A thermoplastic member of the fluoropolymer family. ETFE is noted for exceptional chemical resistance, toughness and abrasion resistance.

F/G/H

Faraday cage effect --C Repulsion of charged particles because of the part's concave shape. Charges build at the entry area, preventing penetration into the cavity.

FEP (fluorinated ethylene propylene) --C A thermoplastic member of the fluoropolymer family. FEP has excellent non stick and non wetting properties.

Fillers --C Pigments and other solids used to alter properties of coatings.

Film formation --C A continuous film formed due to heated polymer particles melting and coalescing or cross-linking.

Flash point --C The lowest temperature at which a solvent will generate sufficient vapors to ignite in the presence of flame.

Flashing --C A brief sub cure (at lower temperatures than the final cure) to drive off solvents or carriers prior to full cure. This helps prevent bubbling. See "Partial cure."

Fluidized Bed Coating --C A method of applying a coating to an article in which the article is immersed in a dense-phase fluidized bed (a fixed container in which powder is aerated) of powdered resin. Preheated objects may be coated by dipping directly into the fluidized powder. In an electrostatic fluidized bed coating the part is usually not heated but is charged and passed over a fluidized bed of power which has the opposite charged.

Flocking deposition --C A deposition method of applying powder by spray to a substrate heated above the melt point of the powder.

Fluoropolymers --C Family of engineering plastics containing fluorine, characterized by high thermal stability, almost universal chemical resistance and low friction.

Fretting --C Wear or corrosion phenomenon caused by vibration among tightly clamped or fastened surfaces.

Friction (dynamic) --C Resistance to continued motion between two surfaces; also known as sliding friction.

Friction (static) --C Resistance to initial motion between two surfaces.

Fusion --C The melting and flowing of heated polymer particles to form a continuous film.

Gel Time --C The interval required at a given temperature for a powder to be transformed from a dry solid to a gel.

Graphite --C A carbon-based dry lubricant that is preferred for high-temperature applications.

Grounding --C Being electrically connected to earth or a negative charge.

Hot hardness --C Ability of a coating to retain hardness and wear resistance at elevated temperatures. Usually a characteristic of coatings based on thermosetting resin binders.

HVLP (high volume, low pressure) --C A spray technique utilizing high pressure in combination with low air velocity to increase transfer efficiency and reduce air pollution.

Hybrid resin --C A combination of two or more common resins.

Hydrogen embrittlement --C Embrittlement of carbon steel caused by absorption of atomic hydrogen in plating, pickling or acid cleaning processes.

I/J/K/L

Intercoat adhesion --C A coating's ability to adhere to previously applied films, including primers.

Kesternich --C German scientist who developed the Kesternich Cabinet and test method used for acid rain simulation (DIN 50018).

KN --C Kilo-Newton (1 KN = 1,000 Newtons), a metric measure of force, equivalent to "pounds force" (LBF), (1 newton = 0.225 pounds of force).

LBF --C Pounds force, a measure of force, also expressed as "Kilo-Newtons" (KN).

Lower Explosive Limit (LEL) --C The lowest percentage at which organic particles suspended in air will ignite if a source of ignition is introduced. It is also referred to as minimum explosive concentration (MEC).

M/N/O

Matrix coating --C One in which some ingredients, such as the lubricant (PTFE), which is soft, are enveloped in others (the matrix, such as harder, more wear-resistant binders). Also referred to as --Aresin bonded coating.--@

Melt point --C The temperature at which a polymer particle will begin to melt and flow.

Micron --C As commonly used in the coating industry, is equivalent to 1/25th of a mil, i.e., 25 microns are equivalent to one mil of coating thickness, or one mil of coating thickness is equivalent to 25 microns.

Migration (of lubricant) --C Characteristic of any lubricant which is under pressure to move away from bearing area.

Mil --C One thousandth (0.001) of an inch (25.4 microns). Most common non-metric measurement of coating thickness.

Mill --C A device that breaks up the melt-mix extrusion into powder particles of a determined average particle size.

Moly, moly disulfide, molybdenum disulfide, MoS₂ --C Four names for the same naturally occurring substance that has good low-friction and high load-bearing properties.

Noise damping --C The absorption of sound vibrations. Fluoropolymer coatings form good noise damping surfaces.

Nonelectrostatic depositions --C Depositing powder onto a substrate that is heated above the melt point of the powder material. Two methods are flocking and fluidized bed.

Oleophobic --C Oil shedding .

P

Partial cure --C Process sometimes utilized when multiple layers of fluoropolymer coatings are to be applied. The first coat is incompletely cured. The second coat is applied and both are fully cured together. See "Flashing."

Pencil hardness --C A value determined by measuring the relative hardness of a coating based upon the ability of the coating to resist penetration and gouging by pencil lead of varying hardness. The order of pencils from softest to hardest is 4B, 3B, 2B, B, HB, F, H, 2H, 3H, 4H, 5H, 6H, 7H, and 8H. The hardness rating of the coating is equal to the first pencil which does not penetrate and gouge the coating.

PFA (perfluoroalkoxy) --C Thermoplastic member of fluoropolymer family of engineering plastics, one characterized by excellent release, low friction and toughness.

pH --C An expression of the degree of acidity or alkalinity of a substance. Neutrality is pH₇ --C acid solutions are less than 7 and alkaline solutions are greater than 7.

Phenolic --C A resin or plastic, usually thermosetting, made by condensation of a phenol with an aldehyde and used for molding, insulating, coatings and adhesives.

Phosphating --C Surface pretreatment used on ferrous or aluminum parts that provides a very thin crystalline film that enhances both corrosion resistance and adhesion.

Pigment --C Finely divided, insoluble colored substance used to impart color to a coating.

Plasma deposition technique --C A method of applying powder using compressed gas and melting the powder in a flame before the powder impinges on a surface.

Plate flow --C The distance a powder coating flows in the molten state prior to the gel. Also referred to as inclined-plate flow, glass-plate flow and pill flow.

Polymer fume fever --C An illness characterized by temporary flu-like symptoms caused by inhaling the products released during the decomposition of fluoropolymers.

Post cure --C A second cure at high temperature to enhance specific properties such as release and non- wetting.

Post forming --C Process of shaping parts after a coating has been applied and cured, a technique commonly used with stamped, blanked or spun parts.

Pourability --C The ability of a dry powder to flow uniformly or to be continuously poured from a container at a steady rate.

Powder metal --C Material formed by compressing particles and heating (sintering) to solidify and strengthen them.

Powder coatings --C Finely divided particles of organic polymers, pigments and additives.

Preheating --C Warming of parts prior to application of a coating, recommended when adhesion is critical and when parts are being coated in humid atmospheres. In some cases, this technique can be used to achieve higher-than-normal film builds.

Preloads (for fasteners) --C The "tightness" of a fastener, equal to the make-up energy applied minus the energy required to overcome friction at the fastener's bearing surfaces and threads.

Pressure spraying --C Coating technique similar to siphon spraying, except that the coating is delivered from a pressurized pot to the spray nozzle under positive pressure. Generally used for high-volume production.

Pretreatment --C Processes for cleaning and conditioning a substrate to be coated. Next to the choice of coating, this may be the most important factor in the use of high-performance coatings.

PTFE (polytetrafluoroethylene) --C A thermoplastic member of the fluoropolymer family of plastics. PTFE has the lowest coefficient of friction of any known solid and the highest operating temperatures of the fluoropolymers.

PV, limiting PV (LPV) factor --C Mathematical limit of a coating's load-carrying ability and wear resistance under bearing conditions.

PVDF (Polyvinylidene fluoride) --C High-molecular weight thermoplastic of vinylidene fluoride with excellent strength, wear resistance and creep resistance.

Q/R/S

Reclaim --C Collection and reuse of overspray powder.

Resistance (electrical) --C The opposition offered by a coating to the passage of an electric current through it.

Salt fog --C ASTM B-117 test procedure that simulates the corrosive environment caused by road salt and marine spray.

Sand blasting (also grit blasting) --C The process of surface cleaning and roughening that provides a mechanical "tooth" to aid coating adhesion. Media include aluminum oxide, even crushed walnut shells. The medium must be chosen to match the substrate and the foreign material on the substrate to be removed.

Sintering --C A process where the temperature of PTFE is raised to the point where PTFE particles soften and form a bond with each other.

Siphon spraying --C Most common technique for applying coatings, also known as "conventional air spray." The coating is drawn from a reservoir into an atomizing air nozzle and propelled toward the surface to be coated.

Surface preparation (Burn-off) --C The removal of a coating by elevating the temperature of the part(s) above the degradation point of the coating and holding it until the coating carbonizes

Static electricity --C Buildup of stationary electrical charge on a coating powder or a coated surface.

Stick-slip (chatter) --C Unstable sliding condition in which movement of one part over another starts and stops, caused by temporary overcoming of static friction.

Storage stability--The ability of a coating material to maintain uniform physical and chemical properties while in storage over an extended periods of time.

Substrate --C Any surface to be coated. This can include metals such as steel, cast iron, bronze, brass, aluminum, stainless steel, chromium and, with special precautions, nickel. Paper, most plastics, wood, leather, fabrics and glass can also be coated.

Surface appearance --C The smoothness gloss and presence or lack of surface defects in a coating.

Surface treatment --C Conditioning the substrate before coating through grit blast, phosphate, etc. May include the removal of a coating (See burnoff).

T/U/V

Tetrafluoroethylene (TFE) --C A monomer used as a chemical feedstock in the production of PTFE.

Thermoplastic --C Plastic resin that softens when reheated and hardens when cooled.

Thermoplastic resin --C A resin which will melt when heated and solidifies when cooled, and softens when reheated.

Thermosetting resin (Thermoset) --C A resin designed to undergo an irreversible chemical and physical change when undergoing a heat-cure schedule, i.e., A plastic resin that cross links during cure so that it does not soften when reheated.

Transfer efficiency --C The ratio of the amount of coating deposited on a substrate compared to the total amount directed at the part to be coated.

Transportability --C A powder coating's ability to be moved in the air steam through tubing and ducts.

Tribo gun --C A powder gun that uses tribo charging.

Tribo charging --C The process of creating a static electric charge on powder particles by action against a nonconductive material.

Upper Explosive Limit (UEL) --C The highest point at which organic particles suspended in air will ignite if a source of ignition is introduced.

Virgin powder --C Powder in its original package as shipped by the powdercoating manufacturer. "Nonvirgin" powder would be that which has been reclaimed in a powder-deposition process.

Volatile content --C The quantity, expressed as a percent weight of a coating, that is lost under specified conditions of temperature and time.

Volatility --C Characteristic of vaporizing. The rate of volatility varies among substances.

W/X/Y/Z

Wear --C Deterioration by friction (abrasion, spalling, cutting, fretting).

Weight solids --C Expressed as a percentage., it is the amount of a substance which remains relative to the total weight, after all volatile components of the substance have been evaporated. The determination is usually hastened by heating the substance in a controlled environment. The percentage weight solids may be determined by using this calculation:

Weight after heating ) weight before heating ' weight solids (percentage)

Wrap --C A characteristic of liquid and powder coatings in electrostatic application to adhere to areas of the substrate not in direct line of sight of the delivery--C system end point.

F inch --C One micro-inch, a millionth of an inch.

F --C One micron, a millionth of a meter. Also expressed as ,uM, or micrometer.

APPENDIX A TRADE NAME CROSS REFERENCES