Glossary of Adhesives and Sealants

A

B

backing (n): In pressure-sensitive tapes, a relatively thin flexible supporting material to which an adhesive is applied. Pressure sensitive adhesives are commonly backed with paper, plastic films, fabric, or metal foil while heat curing thermosetting adhesives are often supported on glass cloth backing.
bag molding (n): A method of molding or bonding involving the application of fluid pressure, usually by means of air, steam, water, or vacuum, to a flexible cover which, sometimes in conjunction with the rigid die, completely encloses the material to be bonded. (ASTM D 907-06)
bedding (n): In building construction in glazing, a bead of sealant applied between a lite of glass or a panel and the stationary stop or sight bar of the sash or frame. It is usually the first bead to be applied when setting glass or panels. (ASTM C717-07a)
binder (n): In adhesive compounds , a component of an adhesive composition that is primarily responsible for its mechanical strength and adhesion. (ASTM D 907-06)
bleaching (n): An erroneous term used to denote a corrosion of the surface under a tape which has remained the original surface color while the surrounding surface area has discolored.
bleeding (n): Penetration through the tape of a coloring liquid (paint, etc.) onto the surface to which the tape is applied.
blister (n): An elevation of the surface of varied contour and dimensions, with a void beneath it. (ASTM D 907-06)
blocking (n): An undesired adhesion between touching layers of a material, such as occurs under moderate pressure during storage or use. (ASTM D 907-06)
bond breaker (n): In building construction, a material to prevent adhesion at a designated interface. (ASTM C717-07a)
bond durability (n): Test cycle, as described in ASTM C-920, for measuring the bond strength after repeated weather and extension cycling.
bond strength (n): The unit load applied to tension, compression, flexure, peel, impact, cleavage, or shear, required to break an adhesive assembly with failure occurring in or near the plane of the bond.
bond (n): The attachment between an adhesive and an adherend.
bond (v): To join adherends by means of an adhesive. (ASTM D 907-06)
bondline (n): The layer of adhesive which attaches two adherends. (ASTM D 907-06)

C

D

depolymerization (n): Separation of a complex molecule into simple molecules; also softening of a sealant by the same action.
dispersion (n): A two-phase system in which one phase is suspended in a liquid. (ASTM D 907-06)
double-coated (adj): In pressure sensitive tapes, the adhesive is applied on both sides of the backing, which serves principally as a car-rier for the adhesive.
dry (v): To change the physical state of an adhesive on an adherend or between adherends by the loss of solvent constituents by evaporation or absorption, or both. (ASTM D 907-06)
drying agent (n): A component of a sealant that accelerates the oxidation of oils or unsaturated polymers.
drying temperature (n): The temperature to which an adhesive or an assembly is subjected to dry the adhesive. (ASTM D 907-06)
drying time (n): The period of time during which an adhesive or an assembly is allowed to dry, with or without the application of heat or pressure, or both. (ASTM D 907-06)
durability (n): As related to adhesive joints, the endurance of joint strength relative to the required service conditions.
durometer (n): An instrument used to measure hardness or Shore A hardness; may also refer to the hardness rather than the instrument.

E

elasticity (n): The ability of a material to return to its original shape after removal of a load.
elastomer (n): A macromolecular material that can withstand large strains on short time scales without permanent plastic deformation. (ASTM D 907-06); a macromolecular material that returns rapidly to approximately its original dimensions and shape after substantial deformation by a weak force and release of the force (Note: Elastomers are divided into two major polymer systems C thermoset and thermoplastic) (ASTM C 717-07a)
elongation (stretch, ultimate elongation) (n): The distance a tape will stretch lengthwise before breaking, expressed as a percentage of original length. Elongation is not necessarily an indication of conformability.
emulsion (n): A heterogeneous system in which an immiscible liquid is distributed in fine drops in another liquid.
epoxy (n): A resin formed by combining epichlorohydrin and bisphenols; requires a curing agent for conversion to a plastic like solid; has outstanding adhesion and excellent chemical resistance.

F

fatigue failure (n): Failure of a material as a result of rapid cyclic deformation.
faying surface (n): The surface of an adherend which makes contact with another adherend.
fiber-reinforced plastic (FRP) (n): A plastic that contains fibers in various forms such as cloth, mat, strands, or chopped to enhance properties. (ASTM D 907-06)
filler (n): A solid material added to an adhesive to modify its strength, permanence, working properties, or other qualities, or to lower cost. (ASTM D 907-06)
film adhesive (n): An adhesive in film form, with or without a carrier, usually set by means of heat and/or pressure. The main advantage is uniformity of glue line thickness.
film (n): Uniform, homogenous, non-fibrous synthetic webs.
fisheyes (n): In pressure sensitive tapes, relatively small deformations (pock-marks) in the adhesive caused by the entrapment of air between layers in the roll. Note this is not an indication of a quality defect.
flaking (n): In pressure sensitive tapes, a condition sometimes occurring during the removal of masking tape, in which flakes or particles of paint break off of the tape backing.
flame resistance (n): Ability of a tape to withstand exposure to flame. Flame Resistant (fire retardant, self-extinguishing) materials will burn when exposed to flame, but will not continue to burn after the flame is removed. Compare to fireproof materials, which will not burn even when exposed to flame.
flexibility (n): Ability of a tape to be freely bent or flexed.
flow (n): Movement of an adhesive during the bonding process before the adhesive is set. (ASTM D 907-06)
foam (n): In pressure sensitive tape backing, a soft, cushiony material formed by creating bubbles in base materials, such as natural or synthetic rubbers, or other elastomeric materials.
foamed adhesive (n): An adhesive whose apparent density has been decreased by the presence of numerous gas-filled cells throughout its mass. (ASTM D 907-06)
freezing (n): In pressure sensitive tapes, a hardening of the adhesive after application, so that tape cannot be easily or cleanly removed.

G

gap-filling adhesive (n): An adhesive capable of forming and maintaining a bond between surfaces that are not close-fitting.
gapping (n): In pressure sensitive tapes, openings between layers of tape within a roll.
gasket (n): Any preformed, deformable device designed to be placed between two adjoining parts to provide a seal. (ASTM C 717-07a)
gel (n): A semisolid system consisting of a network of solid aggregates in which liquid is held. (ASTM D 907-06)
gelation (n): Formation of a gel. (ASTM D 907-06)
glass transition temperature (Tg) (n): The temperature at which an adhesive will become markedly less elastic and flexible.
gloss (n): In pressure sensitive tapes, an appearance characteristic of tape back-ings. Usually expressed by such terms as glossy, low gloss, matte, etc.

H

hardness (n): In building construction, the resistance to indentation as measured under specified conditions (ASTM C 717-07a); typically measured using a Durometer; on a Shore A Durometer scale, numbers range from 0 to 100 for rubber-like materials.
heat activated adhesive (n): A type of adhesive pre-applied to one or both adherends, that is rendered tacky by application of heat and forms a bond on cooling. (ASTM D 907-06)
heat resistance (n): The ability of a tape to with-stand exposure to specified temperatures after applica-tion to a surface. Clean removal after exposure may or may not be important depending on the intended func-tion of the tape and the type of adhesive.
holding power (shear adhesion) (n): The ability of a tape to resist the static forces applied in the same plane as the backing. Usually expressed in terms of time required for a given weight to cause a given amount of tape to come loose from a vertical panel.
hot-melt adhesive (n): A thermoplastic adhesive that is applied in a molten state and forms a bond upon cooling to a solid state. (ASTM D 907-06); a pressure sensitive adhesive applied to a tape backing in a molten form which then cools to form a conventional pressure sensitive.
hot-setting adhesive (n): A thermoplastic adhesive that is applied in a molten state and forms a bond upon cooling to a solid state. (ASTM D 907-06); a pressure sensitive adhesive applied to a tape backing in a molten form which then cools to form a conventional pressure sensitive.

I

J

joint conditioning time (n): The time interval between the removal of the joint from the conditions of heat or pressure, or both, used to accomplish bonding and the attainment of approximately maximum bond strength. (ASTM D 907-06)
joint (n)
adhesive joint (n): location at which two adherends are held together with a layer of adhesive.
finger joint (n): a joint formed by bonding two precut members shaped like fingers.
laminate joint (n): in wood bonding, a joint made by bonding layers of adherends face to face to form thicker stock.;
lap joint (n): a joint made by placing one adherend partly over another and bonding together the overlapped portions.;
scarf joint (n): a joint made by cutting away similar angular segments of two adherends and bonding the adherends with the cut areas fitted together.;
starved joint (n): a joint that has an insufficient amount of adhesive to produce a satisfactory bond.

L

label stock (n): Pressure sensitive materials, which are usually printed, frequently die-cut, furnished in roll or sheet form with a liner, and intended for use as labels.
laminate (n): Product made by bonding together two or more layers of material or materials.
cross laminate (n): a laminate in which some of the layers of material are oriented at right angles to the remaining layers with respect to the grain or strongest direction in tension.
parallel laminate (n): a laminate in which all the layers of material are oriented approximately parallel with respect to the grain or strongest direction in tension. (ASTM D 907-06)
laminate (v): To bond layers of material(s).
lamination (n): a. The process of preparing a laminate; b. any layer in a laminate. (ASTM D 907-06); c. in pressure sensitive tapes, a combination of two or more similar or dissimilar materials, which function as one backing.
lap joint (n): A joint made by placing one adherend partly over another and bonding together the overlapped portions. (ASTM D 907-06); a joint in which the component parts overlap so that the sealant or adhesive is placed into shear action.
lap sealant joint (n): In building construction, a joint where sealant is applied within the joint between approximately parallel substrates that are face-to-face. (ASTM C 717-07a)
latent strain (n): A discoloration in a surface to which tape has been applied, which does not become noticeable until sometime after removal, usually after the surface has been exposed to sunlight or heat.
latex (n): A stable dispersion of polymeric substance in an essentially aqueous medium. (ASTM D 907-06); a colloidal dispersion of a rubber (synthetic or natural) in water, which is the base for a sealant.

M

N

Newtonian behavior (n): The property of a liquid in which its viscosity is constant over a stated range of strain rates. (ASTM D 907-06)
non-Newtonian behavior (n): The property of a liquid in which its viscosity is not constant over a stated range of strain rates. (ASTM D 907-06)
nonvolatile content (n): The portion of a material that remains after volatile matter has been evaporated under specified ambient or accelerated conditions.
non-woven materials (n): Paper "tissues" or synthetic (e.g. rayon) non-woven fabrics.

O

oozing (n): In pressure sensitive tapes, a "squeezing out" of the adhesive from under the backing. When this occurs during the time in which the tape is in roll form, the edges of the roll become tacky.
opaqueness (n): In pressure sensitive tapes, the ability of a tape to prevent the transmission of light.

P

particle board (n): Same as hardboard, except that larger wood chips are used as the filler.
paste (n): An adhesive composition having a characteristic plastic-type consistency, that is, a high order of yield value, such as that prepared by heating a mixture of starch and water and subsequently cooling the hydrolyzed product. (ASTM D 907-06)
peel adhesion (n): The force per unit width, typically expressed in oz/in width (US), required to break the bond between a tape and a surface when peeled back usually at 180 degrees at a standard rate and condition.
peel strength (n): The average load per unit width of bondline required to separate progressively a flexible member from a rigid member or another flexible member.
peel test (n): A test of an adhesive or sealant using one rigid and one flexible substrate. The flexible material is folded back (usually 90 or 180 degrees) and the substrates are peeled apart. Strength is usually measured in pounds per inch of width (PLI).
penetration resistance (n): The ability of a tape to resist slow puncture under pressure.
penetration (n): The entering of an adhesive into an adherend. Discussion This property of a system is measured by the depth of penetration of the adhesive into the adherend. (ASTM D 907-06)
permanence (n): Resistance to appreciable changes in characteristics with time and environment. (ASTM D 907-06)
permanent set (n): The amount of deformation that remains in a sealant or adhesive after removal of a load.
phenolic resin (n): A thermosetting resin; usually formed by the reaction of phenol with formaldehyde.
physical cure (n): Cure by applied heat or evaporation. Physically curing adhesives are already present in their final chemical state upon application.
pinhole (n): In pressure sensitive tapes, a very small hole, which, may permit the passage of fight, moisture or electrical current.
plasticity (n): A property of a material that allows the material to be deformed continuously and permanently without rupture upon the application of a force that exceeds the yield value of the material. (ASTM D 907-06)
plasticizer (n): A substance of low or negligible volatility that lowers the softening range and increases workability, flexibility or extensibility of a polymer. (ASTM D 907-06)
plastisol (n): A physical mixture of resin (usually vinyl) compatible plasticizers and pigments. Mixture requires fusion at elevated temperatures in order to convert the plastisol to a homogeneous plastic material.
polyester (n): In pressure sensitive tapes, a strong film, usually transparent, having good resistance to moisture, solvents, oils, caustics, and many other chemicals.
polyethylene (n): A tough, stretchy film having very good low temperature characteristics.
polymer (n): A compound formed by the reaction of simple molecules having functional groups which permit their combination to proceed to higher molecular weights under suitable conditions. Polymers may be formed by polymerization (additional polymer) or polycondensation (condensation polymer). When two or more monomers are involved, the product is called a copolymer. (ASTM D 907-06)
polymerization (n): A chemical reaction in which the molecules of a monomer(s) are linked together in repeating units to form larger molecules. (ASTM D 907-06)
polypropylene (n): A new cousin of polyethylene, with generally similar properties, but stronger and hav-ing a higher temperature resistance.
pressure-sensitive adhesive (PSA) (n): A viscoelastic material which in solvent-free form remains tacky and will adhere instantaneously to most solid surfaces with the application of very slight pressure. (ASTM D 907-06). Pressure sensitive adhesives require no activation by water, solvent or heat in order to exert a strong adhesive holding force toward such materials as paper, plastic, glass, wood, cement and metals. They have a sufficiently cohesive holding and elastic nature so that, despite their aggressive tackiness, they can be handled with the fingers and removed from smooth surfaces without leaving a residue. primer (n): A coating applied to a surface, prior to the application of an adhesive, to improve the performance of the bond. (ASTM D 907-06)
priming (n): Applying a coating to improve the performance of the bond; in pressure sensitive tapes, coating the backing on the adhesive side with a thin layer of adhesive-like material, which serves as a bonding agent between the adhesive and the backing.

Q

qualification test (n): A series of tests conducted by the procuring activity, or an agent thereof, to determine conformance of materials, or materials system, to the requirements of a specification which normally results in a qualified products list under the specification.
quick stick (n): Also known as quick tack, finger tack, initial adhesion, wet grab -- the property of a pressure sensitive adhesive which allows it to adhere to a surface under very light pressure; it is determined by the ability of the adhesive to quickly wet the surface contacted.

R

reinforcement (n): In sealants, this is the increase in modulus, toughness, tensile strength, by the addition of selected fillers; in pressure sensitive tapes, material added to a tape to provide additional strength.
release agent (n): An adhesive material which prevents bond formation.
release coating (n): A coating applied to the backing on the side opposite the adhesive, which provides ease of unwind, and prevents delamination or tearing.
release liner (n): A web or sheet of material covering the adhesive side of a tape. It is removed prior to appli-cation. Most frequently found on double-coated tapes and label stocks.
release paper (n): A sheet, serving as a protectant or carrier, or both, for an adhesive film or mass, which is easily removed from the film or mass prior to use. (ASTM D 907-06)
removal (n): In pressure sensitive tapes, the act of pulling tape away from the surface to which it has been applied. resilience (n): A measure of energy stored and recovered during a loading cycle. It is expressed as a percentage. resin (n): Solid, semisolid, or liquid, usually organic material that has an indefinite molecular mass and, when solid, usually has a softening or melting range and exhibits a tendency to flow when subjected to stress. (ASTM D 907-06)
ridging (n): In pressure sensitive tapes, a mound-like swelling on the outer layers of a roll, lengthwise to the tape. Usually found on the more moisture sensitive materials, such as cellophane.
room-temperature-setting adhesive (n): An adhesive that sets in the temperature range from 20 to 30 °C (68 to 86 °F), in accordance with the limits for Standard Room Temperature specified in ASTM D618. (ASTM D 907-06)
rosin (n): A resin obtained as a residue in the distillation of crude turpentine from the sap of the pine tree (gum resin) or from an extract of the stumps and other parts of the tree (wood rosin). (ASTM D 907-06)

S

T

tack range (n): The period of time in which an adhesive will remain in the tacky-dry condition after application to an adherend, under specified conditions of temperature and humidity. (ASTM D 907-06)
tack (n): The property of an adhesive that enables it to form a bond of measurable strength immediately after adhesive and adherend are brought into contact under low pressure.
tackiness (n): The stickiness of the surface of a sealant or adhesive.
tear resistance (n): Ability of a tape to resist tearing, after a tear has been started by cutting or nicking the edge.
tear strength (n): The load required to tear apart a sealant specimen. ASTM test method D 624 expresses tear strength in pounds per inch of width.
tearing (n): Breaking or slivering of a tape during unwind.
tensile strength (n): In an adhesive joint, the maximum tensile stress that a material is capable of sustaining calculated from the maximum load applied perpendicular to the joint divided by the original cross-sectional area of the joint. (ASTM D 907-06); in pressure sensitive tapes, the force required to break a piece of tape by pulling on opposite ends of the piece.
thermoplastic (n, adj): Polymer or copolymer capable of being softened by heating and hardened by cooling. (ASTM D 907-06) Discussion a thermoplastic adhesive becomes softer as temperature increases, regardless of the number of heating cycles to which it is exposed.
thermoset (n, adj): Monomer, polymer or copolymer, which when cured, changes into a substantially infusible and insoluble product. (ASTM D 907-06) Discussion a thermosetting adhesive which sets up or hardens on first exposure to heat, and remains set regardless of subsequent temperature cycles.
thickness (n): Distance from one surface of either a tape, backing or adhesive to the other, usually expressed in mils or thousandths of an inch; usually measured under slight pressure with a special gauge or caliper.
thinner (n): A volatile liquid added to an adhesive to reduce the viscosity or other properties. (ASTM D 907-06)
transfer (n): In pressure sensitive tapes, normally refers to "adhesive transfer," but sometimes referring to any tape component which moves from its proper place to some other position during either unwind or removal.
transparency (n): The ability of a tape to allow trans-mission of light. A tape is rated as transparent if 10-point type can be easily read when the tape is applied directly over it.
two-component adhesive (n): An adhesive supplied in two parts which are mixed before application. Such adhesives usually cure at room temperature.

U

uniformity (n): The consistency of a single type of tape, either within a roll, or from roll to roll, or from lot to lot.
Unplasticized Vinyl (UPVC) (n): A tough durable plastic film, differing from PVC principally in that UPVC is not very stretchy.
urea-formaldehyde adhesive (n): a. an aqueous colloidal dispersion of urea-formaldehyde polymer which may contain modifiers and secondary binders to provide specific adhesive properties; b. a type of adhesive, based on a dry urea-formaldehyde polymer and water.

V

vacuum forming (n): A process in which an adherend is brought in intimate contact with a substrate to form an assembly by the evacuation of the surrounding air. (ASTM D 907-06)
vinyl (plasticized polyvinyl chloride, PVC) (n): A tough durable plastic film having excellent resis-tance to oils, chemicals and many solvents. It has excel-lent abrasion-resistance and can be colored. Its high stretch is due to the addition of a plasticizer.
viscosity coefficient (n): The shearing stress tangentially applied that will induce a velocity gradient. A material has a viscosity of one poise when a shearing stress of one dyne per square centimeter produces a velocity gradient of (1 cm/s)/cm. (See also viscosity.) (ASTM D 907-06)
viscosity (n): Of a liquid, the resistance to flow expressed as the ratio of the applied shear stress to the resulting rate of shearing strain. (See Newtonian behavior, non-Newtonian behavior, and thixotropy.) (Compare consistency.) (ASTM D 907-06)
void (n): In pressure sensitive tapes, a bare uncoated area on either the adhesive or release coated side of the tape.
vulcanization (n): An irreversible chemical change in which a rubber compound becomes less plastic with greater elasticity, strength, stability, and chemical resistance over a greater range of temperatures. (ASTM D 907-06)
vulcanize (v): To subject to vulcanization. (ASTM D 907-06)

W

warp (n): A significant variation from the original true, or plane surface. (ASTM D 907-06)
water absorption (n): The measure of the amount of water which will be soaked up by a tape and held.
water penetration rate (WPR) (n): In pressure sensitive tapes, the measure of a tape's ability to resist the passage of water through the tape itself expressed as g/100sq/in./24h.
water vapor transmission (WVT) (n): In pressure sensitive tapes, the weight of water vapor transmission through a tape measured in gram/hundred square inches/24 hours.
working life (n): The period of time during which an adhesive, after mixing with catalyst, solvent, or other compounding ingredients, remains suitable for use.(ASTM D 907-06)

Y

yield strain (n): The strain below which a material acts in an elastic manner, and above which it begins to exhibit permanent deformation or flow.
yield stress (n): The stress (either normal or shear) at which a marked increase in deformation occurs without an increase in load. (Synonym yield value) (ASTM D 907-06)

(This article is reproduced from Adhesives.org/Sealants.org.)