Medical Device Coatings Glossary

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A

Abrasion: A wearing, grinding, or rubbing away caused by friction.

Additives: Materials added to a coating to enhance certain properties.

Adhesion: The bond strength of a coating to the substrate whether metallic, nonmetallic, plastic or rubber.

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

Aluminum oxide: Hard particulate medium used in grit blasting to clean rough surfaces that are to be coated.

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

ASTM: American Society of Testing and Materials.

Average particle size: The average diameter of particles as determined by various test methods.

B

Binder: Tough polymer that acts as adhesive to join elements of matrix coatings.

Break-in: The initial wear period of a mechanical component that has a higher frictional value and wear, that leads to the burnishing, or leveling out, of the coating. Resulting in a lower frictional value.

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

Burn-off: The pre-baking of a part at 10-25 F above the final cure temperature of the selected coating. This burn-off ensures that all oils and contaminates have been removed from the substrate.

C

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

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

Conductor: Material that can support flow of electrical current. Coatings are normally insulators but can be modified with certain fillers and pigments.

Contact angle: A means of quantifying the non-stick properties of a coating by measuring the ability of a liquid to wet its surface.

Corrosion: 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: Quality of thermosetting plastic resins in which polymer chains combine during curing process. In general, the greater the crosslinking, the tougher and more chemically resistant the coating.

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

Cure schedule: The time/temperature relationship required to completely set or sinter a material. Various materials have their own optimal cure schedule that must be followed to avoid contamination and improve performance for specific applications. When following the specifics of a given cure schedule, it is imperative to adhere to the same controlled conditions in order to achieve specific properties along with consistent results.

Cure Test: A solvent rub test using MEK or other solvents, to test the coating for completeness of cure base and no attack of the solvent on the cured coating, after a specific amount of rubs with a Q-tip.

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

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

Cryogenic: Temperatures less than -130ºC/-200ºF: Bonded dry film lubricants continue to perform at these temperatures.

D

Defelsko: Coating thickness gauge that can measure coatings on metallic and non-metallic substrates.

Dielectric strength: Ability of a coating to resist the passage of electrical current.

Dip/spin: 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 (solid) Lubricants: Solid materials such as PTFE, Moly Disulfide (MoS2 ) and graphite that have low coefficients of friction.

E

Elastomers: Any various elastic substances resembling rubber.

Electrostatic spray: 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.

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

Epoxy: A flexible resin, usually thermosetting, made by the polymerizing of an epoxide and used chiefly in coatings and adhesives.

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

F

FEP (fluorinated ethylene propylene): A thermoplastic member of the fluoropolymer family: FEP has the best non-stick and non-wetting properties of these materials.

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

Final cure: The final time and temperature required to complete the final cure, sintering, melt flow or cross linking of a coating.

Flashing: A brief subcure (at lower temperatures than the final cure) to drive off solvents/carriers prior to full cure. This helps prevent bubbling.

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

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

Fretting: Wear phenomenon caused by vibration among tightly clamped or fastened surfaces.

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

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

G

Gainsharing: Incentive program aimed at improving production, quality, and attendance through financial sharing with employees.

Graphite: Carbon-based dry lubricant that is preferred for high temperature applications.

H

Holiday check: A DC electrical test using a wet sponge apparatus that detects pinholes or porosity in a coating. The DC voltage of the apparatus is variable to allow for detection of pinholes at different levels without the destruction of the coating.

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

Hydrophilic: A coating that has a strong affinity for water and when wetted, its properties become extremely non-stick and slippery.

I

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

J

Job Boss: A Software package developed for job shop companies that is used to track product processing costs, including labor and material. It also includes quoting functions, material management, scheduling and shop floor control. It has the capability of producing reports for final product cost review and JIT delivery performance.

K

L

lbf: Pounds force. A measure of force, also expressed as “Kilo-Newtons” (KN).

M

Matrix coating: Coating in which some ingredients, such as the lubricant (PTFE), which is soft, is enveloped in others (the matrix, such as harder, more wear-resistant binders).

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

Microinch (µ inch): A millionth of an inch.

Micrometer: A device for measuring very small measurements. Unit of length equal to one thousandth of a millimeter (10 to the -3 e) or one millionth of a meter (10 to the -6 e).

Micron(µ): One micron, one millionth of a meter (.001mm). Also expressed as µm or micrometer. 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): Characteristic of any fluid lubricant to move away from bearing area.

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

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

N

Noise damping: The absorption of sound vibrations. Xylan® coatings form good noise damping surfaces.

O

Oleophobic: Repels Oil. Oil does not wet out on the surface of coating but beads up on it.

Orange Peel: The varying degrees surface roughness or finish similar to that of an orange.

P

Partial cure: 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.

PFA (perfluoroalkoxy): The thermoplastic member of fluoropolymer family of engineering plastics, one characterized by excellent release and low friction.

Pencil hardness: 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 when tested from softest to hardest.

pH: An expression of the degree of acidity or alkalinity of a substance expressed as a number from 0 to 14. Neutrality is pH7. Acid solutions are less than 7 and alkaline solutions are greater than 7.

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

Phosphating: Surface pretreatment used on ferrous parts that provide a very thin crystalline film that enhances both corrosion resistance and adhesion.

Pinhole: A pin hole in a coating, as if made by a pin, that allows potential exposure or a leak path to the substrate beneath the coating.

Polyamide-Imide (PAI): A high strength plastic with the highest strength and stiffness of any thermoplastic up to 275°C (525°F). It has outstanding resistance to wear, creep, and chemicals-including strong acids and most organics-and is ideally suited for severe service environments.

Polyarylsulfone (PAS): A thermally-stable thermoplastic resin consisting mainly of phenyl and biphenyl groups linked by ether and sulfone groups (3M Company). The material is resistant to high and low temperatures and has good impact, chemical and solvent resistant and electrical insulating properties.

Polyethersulfones (PES): Highly resilient thermoplastic plastics. Materials made of polyethersulfones are transparent or slightly transparent (high light transmission and refractive index), resistant to hydrolysis, and provide excellent chemical resistance to mineral lubricants, aliphatic hydrocarbons, acids and alkalis. The thermoplastic polyethersulfone has a melting range or glass transition temperature of approximately 220°C and can be processed to form a finished product with up to 30% inorganic fillers, fiberglass or carbon fibers in an extrusion (extruded profiles) or injection molding process. Due to their optimum electrical insulating properties, polyethersulfones have applications in the electronics and automobile industries. Polyethersulfones are also used in the medical sector, the food sector (membrane technology), as well as in aircraft cabins.

Polymer fume fever: 24-hour flu-like symptoms (with no long-term effects) cause by inhaling the gasses released during the decomposition of fluoropolymers.

Porosity: Pinholes or minute pores in a coating that allow potential exposure or leak path in the coating to the substrate, one reason for the failure of chemical, electrical or corrosion resistant coating. Can be detected with a spark check test or holiday checker.

Postcure: A second cure at high temperature to enhance specific properties such as release and nonwetting.

Postforming: Process of shaping parts after a coating has been applied and cured, a technique commonly used with stamped, blanked or spun parts.

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

Preheating: Warming of parts prior to application of 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.

Pressure spraying: 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: 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): A thermoplastic member of the fluoropolymer family of plastics. PTFE has the lowest coefficient of friction of any known solid and the highest temperature resistance of the fluoropolymers.

PVDF (Polyvinylidene fluoride): High-molecular weight thermoplastic of vinylidene fluoride with greater strength, wear resistance and creep resistance than FEP, PFA or PTFE.

Q

R

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

S

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

Sand blasting (also grit blasting): Surface cleaning and roughing process that provides a mechanical “tooth” to aid the coating adhesion. Media include aluminum oxide, even crushed walnut shells. The medium must be chosen to match the substrate and foreign material on the substrate to be removed.

Siphon spraying: Most common technique for applying coatings, also known as “conventional”. Coating is drawn from a reservoir into an atomizing air nozzle and propelled toward the surface to be coated.

Spark check: A DC electrical test that can be used detect pinholes or porosity in a coating. The DC voltage is variable to allow for different levels of testing. The testing voltage is anywhere from 50 to 5000 VDC, depending on the coating and the application or specification requirements.

Static electricity: Buildup of stationary electrical charge on a coated surface.

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

Substrate: 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: The smoothness, gloss and presence, or lack of surface defects in a coating.

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

T

Thermoplastic: Plastic resin that softens when reheated.

Thermoset: Plastic resin that crosslinks during cure so that it does not soften when reheated.

Transfer efficiency: The amount (percentage) of a coating that actually reaches and stays on the part being coated. Some coating methods give far higher transfer efficiency than others.

Tape Test: An ASTM method D3359-02 for measuring the adhesion of a coating to a substrate using a specific tape and technique.

U

V

W

Wear: Deterioration by friction (abrasion, spalling, cutting and fretting).

Weight solids: 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.

X

Y

Z