Coatings of many types are used in
the manufacturing processes. Those coatings could be paint, adhesives, stains,
etc. Most of the coatings are high in solvent (VOC) content and are subject to heavy
environmental compliance regulation. This coatings glossary will get you up to speed
quickly and will help you with understanding the complexities of environmental compliance.
Glossary
of
Coatings and Their Constituents
- ACRYLIC
A resin resulting from the polymerization of derivatives of acrylic acids, including
esters of acrylic acid, methacrylic acid, acrylonitrile, and their copolymers. Acrylics
are also used in powder coatings in their thermoplastic form.
ACTIVE SOLVENT
A liquid which dissolves a binder.
ADDITIVES
Any substance added in small quantities to another substance, usually to improve
properties. Examples of additives include plasticizers, fungicides, and dryers.
ADHESIVE
A substance capable of holding materials together by surface attachment. Various
descriptive adjectives are used with the term adhesive to indicate certain
characteristics: physical (liquid adhesive, tape adhesive), chemical type (silicate
adhesive, resin adhesive), materials bonded (paper adhesive), and conditions of use
(hot-set adhesive).
AIR-DRIED COATINGS
Coatings which are not heated above 194 °F (90 °C) for coating or drying. In the South
Coast Air Quality Management District, curing also must be done below (rather than at or
below) 194 °F (90 °C) to qualify as air dried. Air-dried coatings also include
forced-air dried coatings.
ALIPHATIC SOLVENT
A solvent comprised primarily of straight chain hydrocarbons, including mineral spirits,
kerosene, and hexane. These solvents are characterized as volatile organic compounds.
ALKALI
Any substance that neutralizes acids. Alkalis are helpful in aqueous cleaning by
speeding soil removal and suspension. Alkali is synonymous with caustic.
ALKYD
A binder based on resins formed by the condensation of polyhydric alcohols with
polybasic acids. They may be regarded as complex polyesters (Thermoset)
AMINO RESINS
Resins used to crosslink polyesters, epoxies, acrylics, and alkyds to enhance their
durability.
AROMATIC SOLVENTS
Hydrocarbon solvents which contain an unsaturated ring of carbon atoms, including
benzene, naphthalene, anthracene, and their derivatives. Toluene (toluol) and xylene
(xylol) are commonly used aromatics. These solvents are characterized as volatile organic
compounds (VOCs).
AZEOTROPE
A liquid mixture that distills without change in composition and characterized by a
constant minimum or maximum boiling point which is lower or higher than any of the
components.
BAKED COATINGS
Coatings that are cured or dried at or above an oven air temperature of 194 °F (90
°C).
BARYTES
Colorless crystalline solids that are a form of barium sulfate (also called barite).
Barytes are used as an extender pigment in primers and coatings.
BENTONITE
A type of clay derived from volcanic ash and used as a paint pigment.
BINDER
The solid (non-volatile) material in a coating that binds the pigment and additive
particles together to form a film. In general, binders are resins.
BIOCIDE
A chemical agent capable of killing organisms responsible for microbial degradation.
Biocides are sometimes added to waterborne coatings.
BITUMINOUS COATING
An asphalt or tar compound used to provide a protective finish for a surface.
BLOCKED ISOCYANATES (BLOCKING AGENT)
Isocyanates, normally extremely reactive with water, can only be used in waterborne
coatings if they can be prevented from reacting before the water is baked out of the paint
film. This is done by capping or blocking the isocyanate group with a thermally
decomposable chemical. In a bake oven, the water evaporates, the chemical cap decomposes
and the isocyanate crosslinks the paint. Blocked isocyanates are often employed for E-coat
curing.
CARC
Chemical Agent Resistant Coatings. The polyurethane-based coatings are highly
crosslinked to resist chemical attack. CARC is often used on military equipment that might
become contaminated by nuclear, biological, or chemical substances.
CELLOSOLVE
The generic term for the solvent family of mono-alkyl ethers of ethylene glycol. For
example, a widely-used solvent is butyl cellosolve, which chemically is ethylene glycol
monobutyl ether.
CHLORINATED SOLVENTS
Powerful organic solvents that contain chlorine. Examples include 1,1,1-trichloroethane
and methylene chloride. These solvents are characterized as volatile organic compounds.
Their use is regulated and heavily restricted.
COATING
A liquid or mastic composition which is converted to a solid protective, decorative, or
functional adherent film after application as a thin layer. The South Coast Air Quality
Management District defines coatings as materials which are applied to a surface and which
form a continuous film in order to beautify and/or protect the surface.
COSOLVENTS
Water-miscible organic solvents. Waterborne paints frequently require cosolvents in
addition to water for easier manufacture and improved application properties.
CROSSLINKING
The setting up of chemical links between the molecular chains of a resin to form a
three-dimensional network polymer system. Crosslinking generally toughens and stiffens
coatings.
DILUENT
Liquids which increase the capacity of a solvent for the binder. Diluents cannot
dissolve the binder themselves, but rather are used to control viscosity, flash time, or
cost. While true solvents can be added in unlimited amounts to lower paint viscosity, it
may be more economical to lower viscosity with less-costly diluent solvents. When added to
a prepared paint, a diluent will lower the viscosity just as effectively as a true
solvent. However, if too much diluent is added, the resin will separate out of solution
and the paint becomes unusable.
DISPERSION COATING
A type of coating in which the binder molecules are present as colloidal particles and
spread uniformly throughout the formulation as a stable mixture.
DRIER
An additive which accelerates the drying of coatings.
EMULSION
A two-phase liquid system in which small droplets of one liquid (the internal phase) are
immiscible in, and are dispersed uniformly throughout, a second continuous liquid phase
(the external phase). This contrasts with a latex, which consists of solids dispersed in a
liquid.
EMULSION PAINT
A coating comprised of an emulsion of a resin binder in water.
ENAMELS
Topcoats which are characterized by their ability to form a smooth surface; originally
associated with a high gloss, but may also include a lower degree of gloss. Also a class
of substances having similar composition to glass with the addition of stannic oxide, or
other infusible substances to render the enamel opaque. Can be used to describe a coating
which forms a film through chemical union of its component molecules during cure and in
shop terminology can be used to describe paint which is no longer a lacquer. All paints,
powder or liquid, that form crosslinking chemical bonds during curing, are considered
enamels. The majority of industrial finishes fall into this category.
EPOXIES
Binders based on epoxy resins. Epoxy crosslinking is based on the reaction of the
epoxide groups with other materials such as amines, alcohols, phenols, carboxylic acids,
and unsaturated compounds. Also used as a thermoset powder coating.
EXEMPT COMPOUNDS
Hydrocarbon compounds excluded from the definition of volatile organic compound, as
defined by the U. S. Environmental Protection Service, on the basis that these compounds
have negligible contribution to tropospheric ozone formation. Acetone is an exempt
compound.
EXTENDER (PIGMENTS)
White powders used to give body to the coating.
FILM
One or more layers of coating covering an object or surface.
FLASH POINT
The lowest temperature of a liquid at which it gives off sufficient vapor to form an
ignitable mixture when mixed with air and brought into contact with an open flame or
spark.
FLASH-OFF TIME
The time required between application of successive wet-on-wet coatings or between
application and baking to allow the bulk of the solvents in the coating to rise slowly and
evaporate. In baked coatings the flash-off time helps to prevent solvent boil off and film
blistering.
FLAT COATINGS
Coatings which register gloss less than 15 on an 85-degree meter or less than 5 on a
60-degree meter. This definition is usually found in architectural coating rules.
FLOCCULATION
The formation of loose clusters of dispersed pigment particles in liquid coatings.
FREE RADICAL POLYMERIZATION
Reactive electrons that chemically bond to adjacent molecules and produce a cured paint
film. Certain organic compounds will form highly reactive electron configurations by the
action of UV light (or other activation sources). These reactive species are called free
radicals because, to an extent, 'free' electrons are available for bonding.
FUSION
The melting of a powder coating into a solid film.
HALOGENATED HYDROCARBONS (HALOGENATED SOLVENTS)
Formed by substituting one of the halogen elements (chlorine, bromine, or fluorine) into
a chemical compound to change both the physical and chemical natures of the compound.
HEAT-RESISTANT COATINGS
Designed to resist degradation upon continuous or intermittent exposures to a
predetermined elevated temperature. A San Diego Air Pollution Control District rule
stipulates that the coating must withstand temperatures of 400 °F during normal use as
determined by ASTM Method D-2485.
HIGH BOILERS
Solvents with a boiling point above 212 °F (Tail-end solvents). These solvents usually
evaporate during baking.
HIGH TEMPERATURE COATINGS
Coatings certified to withstand a temperature of 1,000 °F for 24 hours.
HIGH-SOLIDS
Solvent-borne coatings that contain greater than 50 % solids by volume or greater than
62 % (69 % for baked coatings) solids by weight.
HYDROCARBON SOLVENT
An organic compound consisting exclusively of the elements carbon and hydrogen. They are
principally deerived from petroleum and coal tar, and include aliphatic, aromatic, and
napthenic solvent.
HYDROXIDES
The chemical opposites of acids. Also known as caustics and alkalis. Examples are sodium
hydroxide and potassium hydroxide.
HYGROSCOPIC
Describes a substance that has the property of readily absorbing moisture from the air.
Hygroscopic materials, such as silica gel and calcium chloride, are used as dessicants.
Thinly spread deposits of hygroscopic materials can absorb enough water to completely
dissolve.
INHIBITOR
A chemical additive that retards undesired chemical reaction such as corrosion,
oxidation, drying, skinning, etc.
INITIATOR
A chemical added to help start a chemical reaction such as polymerization. Its action is
similar to that of a catalyst, except that it is usually consumed in the reaction.
INORGANIC POLYMERS
Substances whose principal structural features are made up of homopolar interlinkages
between multivalent elements other than carbon. This does not preclude the presence of
carbon-containing groups in the side branches, or in interlinkages between principal
structural members. Examples of such polymers are ethyl and butyl silicates, mica, clays,
and talc.
ISOCYANATE
A compound containing the functional group -N=C=O. Isocyanates are crosslinked with
hydroxyls to form polyurethanes.
KICK-OUT
The portion of binder that comes out of solution as small lumps.
LACQUER
Coating composition based on synthetic thermoplastic film-forming material dissolved in
organic solvent and dried primarily by solvent evaporation. Typical lacquers include those
based on nitrocellulose, other cellulose derivatives, vinyl resins, acrylic resins, etc.
LATENT SOLVENT
A liquid which cannot itself dissolve a binder but which increases the tolerance of the
coating for a diluent.
LATEX
Stable dispersion of polymeric solids in an aqueous medium.
NITROCELLULOSE
A binder (resin) based on polymer from cotton cellulose. Nitrocelluloses were primarily
used in lacquers and were widely used from the 1920s to the 50s on automobiles.
OIL BASE
Coatings which form films through crosslinking of unsaturated plant oil (drying oils) in
the presence of oxygen.
OXYGENATED SOLVENTS
Volatile organic compounds (VOCs) that contain oxygen in addition to carbon and
hydrogen. VOCs Include alcohols, esters, ketones, and ether-alcohols.
PHENOLIC RESINS
Resins comprised by condensation of phenols and aldehydes.
PIGMENT
Finely ground insoluble particles dispersed in coatings to influence properties such as
color, corrosion resistance, mechanical strength, hardness, durability, etc. Particles may
be natural or synthetic and also inorganic or organic.
POLYESTER
A polymer in which the monomer units are linked by the functional group -COO-. Polyester
has been used as thermoplastic powder coating, and as the following thermosetting powder
coatings: epoxy polyester hybrid powder, urethane polyester powder, and polyester TGIC
powder.
POLYETHYLENES
Thermoplastic resins composed of polymers of ethylene (CH2
CH2). Polyethylenes are normally translucent, tough, waxy
solids that are unaffected by water and a large range of chemicals. Frequently used in
powder coatings.
POLYMERS
A high-molecular-weight organic compound, natural or synthetic, with a structure that
can be represented by a repeated small unit, or mer.
POLYPROPYLENES
Tough, lightweight thermoplastic resins composed of polymers of propylene (CH2 CHCH2). They are commonly
used in powder coating.
POWDER COATINGS
Any coating applied as a dry (without solvent or other carrier), finely divided solid
which adheres to the substrate as a continuous film when melted and fused.
PRECURSOR
A chemical compound which is released into the atmosphere, undergoes a chemical change,
and leads to a new (secondary) pollutant. VOCs are precursors to ozone.
PRIMERS
Coatings that are designed for application to a surface to provide a firm bond between
the substrate and subsequent coatings.
REACTIVE DILUENT
A liquid which is a VOC during application and in which, through chemical reaction such
as polymerization, 20 % or more of the VOC becomes an integral part of the finished
coating.
RESIN
The polymer (plastic) component of a paint that cures to form a paint film. Also known
as binder or vehicle.
RETARDERS
Solvents added to a coating to slow down a chemical or physical change, such as the rate
of evaporation.
SEALERS
A liquid coat applied to porous substrates such as wood and plaster to prevent the
substrate from absorbing subsequent coatings.
SHELF LIFE
The length of time a coating may normally be stored without losing any chemical/physical
properties. Manufacturers typically specify the shelf life.
SILICONE RELEASE
A coating which contains silicone resins and intended to prevent food from sticking to
metal surfaces such as baking pans.
SILICONES
Resins consisting of silicon-oxygen linkages, unlike organic resins, which contain
carbon.
SOLUBILIZER
Compound that forms polar polymer ions when mixed with water-insoluble resins. Since
water is a polar solvent and resins are usually non-polar, the resins must be treated to
increase their polarity if they are to be used in waterborne paints.
SOLUTION PAINT
Resin molecules fully dissolved by solvents in the paint.
SOLVENCY
The degree to which a solvent holds a resin or other paint binder in solution.
SOLVENT
The liquid or blend of liquids used to dissolve or disperse the film-forming particles
and which evaporate during drying. A true solvent is a single liquid that can dissolve the
coating. Solvent is often used to describe terpenes, hydrocarbons, oxygenated, furans,
nitroparaffiins, and chlorinated solvents.
SOLVENT-BORNE
Coatings in which volatile organic compounds are the major solvent or dispersant.
SPECIFIC GRAVITY
Weight of a given volume of any substance compared with the weight of an equal volume of
water. Relative density.
STENCIL COATING
Ink or other coating that is rolled or brushed onto a template or stamp in order to add
identifying letters and/or numbers to metal parts and products.
SURFACE TENSION
The energy required to expand the surface of liquid by unit area. Liquids tend to reduce
their surface area due to unequal intermolecular attractive forces in this region. A low
degree of surface tension is preferred for liquid coatings to maximize adhesion and
minimize edge-pull and fish-eye effects.
SURFACER
Easily sanded coating used to fill surface irregularities.
TERPENE SOLVENTS
Terpene solvents are VOCs obtained from pine tress and are the oldest solvents used in
coatings. Includes turpentine, dipentene, and pine oil.
TGIC (Triglycidyl isocyanurate)
A complex chemical used to crosslink paint, especially polyester powders, to increase
exterior durability.
THERMOPLASTIC
Resin capable of being repeatedly softened by heat and hardened by cooling. These
materials, when heated, undergo a substantially physical rather than chemical change.
Thermoplastic resins can be completely dissolved with appropriate solvents.
THERMOSET
Resin that, when cured by application of heat or chemical means, changes into a
substantially infusible and insoluble material. Thermosetting resins will soften but will
not dissolve in any solvents.
THINNING
The process of adding volatile liquid to a coating to reduce its viscosity. This liquid
may be solvent, diluent, or mixtures of both. Also may be called reducing or "adding
make-up solvent."
THIXOTROPE
Substances that cause temporarily high paint viscosities by forming loosely-held,
three-dimensional particle networks within paint fluids. Agitation of the paint by
stirring, pumping, spraying, etc., quickly destroys the networks and viscosity drops
sharply. When agitation is halted, the networks reform rapidly and paint viscosity again
rises.
THIXOTROPY
The tendency for the viscosity of a liquid to be shear-rate dependent. When a liquid is
rapidly shaken, brushed, or otherwise mechanically disturbed the viscosity decreases
rapidly.
THROWING POWER
The ability of electro-deposited coatings to cover interior surfaces.
TOPCOAT
The final coating film or multiple layers of the same coating film applied to the
surface.
UNDERCOATERS
Coatings formulated and applied to substrates to provide a smooth surface for subsequent
coats.
URETHANES
Materials based on resins made by the condensation of organic isocyanates with compounds
or resins containing hydroxyl groups. Categories of polyurethane coatings include: single
component prereacted-urethane coatings; single component moisture-cured urethane coatings;
single component heat-cured urethane coatings; two-component catalyst-urethane coatings,
two-component polyurethane coatings; and one-component nonreactive lacquer-urethane
solution coatings.
VACUUM METALLIZING
Process in which surfaces are thinly coated by exposing them to metal vapor under
vacuum.
VARNISH
Clear or pigmented coatings formulated with various resins and designed to dry by
chemical reaction on exposure to air. These coatings are intended to provide a durable
transparent or translucent solid protective film.
VEHICLE
The liquid portion of a coating in which the pigment is dispersed; it is composed of
binder, solvent and diluent.
VINYL CHLORIDE POLYMERS
Polymers comprised by the polymerization of vinyl chloride or copolymerization of vinyl
chloride with other unsaturated compounds, the vinyl chloride being in greatest amount by
weight. Can be used in thermoplastic powder coatings.
VINYL RESINS
Resins which involve the unsaturated vinyl group (CH<font="-1"2
= CH-), including polyvinyl acetate, polyvinyl chloride, copolymers of these, the acrylic
and methacrylic resins, the polystyrene resins, etc.
VISCOSITY
The property of a fluid whereby it tends to resist relative motion within itself. A
thick liquid such as syrup has a high viscosity. Viscosity is often measured using an
efflux-type cup, which gives the time required for a given quantity of paint to flow
through a hole in the bottom of the metal cup at a given temperature (See Zahn Cup).
VOLATILE ORGANIC COMPOUND (VOC)
Any organic compound not specifically exempted by the U.S. EPA that participates in
atmospheric photochemical reactions. VOCs may be emitted during the application and/or
drying of coatings. In calculating the VOC content of the coating, exempt compounds and
water are excluded and are not considered to be part of the coating. Exempt compounds are
acetone, ethane, methane, carbon monoxide, carbon dioxide, carbonic acid, metallic
carbides, metallic carbonates, ammonium carbonate, methylene chloride, 1,1,1
trichloroethane (methyl chloroform), 1,1,2-trichlorolotrifluoroethane (CFC-113),
trichlorofluoromethane (CFC-11), dichlorodifluoromethane (CFC-12),
dichlorotetrafluoroethane (CFC-114), chloropentafluoroethane (CFC-115), trifluoromethane
(CFC-23), and chlorodifluoromethane (CFC-22). Many of these exempt compounds may
contribute to upper-atmosphere ozone destruction. Carbon dioxide is considered to be a
"greenhouse gas," which may contribute to global warming, and carbon monoxide is
a primary pollutant.
VOLATILITY
The tendency of a liquid to evaporate. Liquids with high boiling points have low
volatility and vice versa.
WATER-REDUCIBLE COATINGS
see WATERBORNE COATINGS.
WATERBORNE COATINGS
Coatings in which water is the major solvent or dispersant. Solvents or dispersants
include water-soluble polymers (water reducible), water-soluble colloidal dispersions, and
emulsions (including latex).
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