Glossary

A-stage An early stage in the reaction of certain thermosetting resins in which the material is fusible and still soluble in certain liquids. Sometimes referred to as Resol. (See also B-stage and C-stage.)

Abhesive A material that is adhesive resistant and applicable as a nonsticking surface coating; release agent.

Adhere, v To cause two surfaces to be held together by adhesion (q.v.). To be in a state of adherence.

Adherence The state in which two surfaces are held together by interfacial forces.

Adherend A body that is held to another body by an adhesive (a narrower term than substrate, q.v.).

Adhesion The state in which two surfaces are held together by interfacial forces which may consist of valence forces, or interlocking action, or both. (See also adhesion, mechanical and adhesion, specific.) The state in which two surfaces are held together by chemical, or physical forces, or both, with the aid of an adhesive. The attraction between substances which, when they are brought into contact, makes it necessary to do work to separate them.

Adhesion, mechanical Adhesion between surfaces in which the adhesive holds the parts together by interlocking action. (See also adhesion, specific.)

Adhesion, specific (sometimes called adhesion, molecular). Adhesion between surfaces which are held together by valence forces of the same type as those which give rise to cohesion. (See also adhesion, mechanical.)

Adhesive A substance capable of holding materials together by surface attachment. Adhesive is the general term and includes, among others, cement, glue, mucilage, and paste (q.v.). All of these terms are used interchangeably. Various descriptive adjectives are applied to the term to indicate characteristics such as physical form, chemical type, materials bonded, and conditions of use. A substance capable of bonding materials together by adhesion. Any material that causes one body to stick or adhere to another.

Adhesive, anaerobic An adhesive that cures spontaneously in the absence of oxygen and catalyzed by metallic ions. An adhesive that cures only in the absence of air after being confined between assembled parts. An example is dimethacrylate adhesive used for bonding assembly parts, locking screws and bolts, retaining gears and other shaft-mounted parts, and sealing threads and flanges.

Adhesive, assembly An adhesive that can be used for bonding parts together, such as in the manufacture of a boat, airplane, furniture. This term is commonly used in the wood industry to distinguish such adhesives, formerly called “joint glues,” from those used in making plywood, sometimes called “veneer glues.” It is applied to adhesives used in fabricating finished structures or goods, or subassemblies thereof, as differentiated from adhesives used in the production of sheet materials, such as plywood or laminates.

Adhesive, bonded (Note that the comma indicates bonded adhesive, not adhesive-bonded.) A solvent solution of resins, sometimes containing plasticizers, which dries at room temperature.

Adhesive, cold-setting An adhesive that sets at temperatures below 68°F (20°C).

Adhesive, contact An adhesive that is apparently dry to the touch and that will adhere to itself instantaneously upon contact; also called contact bond adhesive. An adhesive applied to both adherends and allowed to become dry, which develops a bond when the adherends are brought together without sustained pressure.

Adhesive, dispersion (or emulsion) A two-phase system with one phase (the adhesive material) in a liquid suspension.

Adhesive, encapsulated An adhesive in which the particles or droplets of one of the reactive components are enclosed in a protective film (microcapsules) to prevent cure until the film is destroyed by suitable means.

Adhesive, film An adhesive in film form, with or without a carrier, usually set by means of heat and pressure. The main advantage is uniformity of glueline thickness.

Adhesive, film-supported An adhesive material incorporating a carrier that remains in the bond when the adhesive is employed. The carrier support material is usually composed of organic and/or inorganic fibers which may be in woven form.

Adhesive, film-unsupported An adhesive material in film form without a carrier support.

Adhesive, foamed An adhesive, the apparent density of which has been decreased substantially by the presence of numerous gaseous cells dispersed throughout its mass.

Adhesive, foaming An adhesive designed to foam in situ, after application, in order to provide extensive gap-filling properties.

Adhesive, gap-filling An adhesive subject to low shrinkage in setting, employed as sealant.

Adhesive, heat-activated A dry adhesive that is rendered tacky or fluid by application of heat, or heat and pressure, to the assembly.

Adhesive, heat-sealing A thermoplastic film adhesive which is melted between the adherend surfaces by heat application to one or both of the adjacent adherend surfaces.

Adhesive, hot-melt An adhesive that is applied in a molten state and forms a bond on cooling to a solid state. A bonding agent which achieves a solid state and resultant strength by cooling, as contrasted with other adhesives which achieve the solid state through evaporation of solvents or chemical cure. A thermoplastic resin which functions as an adhesive when melted between substrate and cooled.

Adhesive, hot setting An adhesive that requires a temperature at or above 212°F (100°C) to set it.

Adhesive, intermediate temperature setting An adhesive that sets in the temperature range from 87°F to 211°F (31–99°C).

Adhesive, latex An emulsion of rubber or thermoplastic rubber in water.

Adhesive, multiple layer A film adhesive, usually supported with a different adhesive composition on each side, designed to bond dissimilar materials such as the core-to-face bond of a sandwich composite structure.

Adhesive, one-component An adhesive material incorporating a latent hardener or catalyst activated by heat. Usually refers to thermosetting materials, but also describes anaerobic, hot-melt adhesive, or those dependent on solvent loss for adherence. Thermosetting one-component adhesives require heat to cure.

Adhesive, pressure-sensitive A viscoelastic material which, in solvent-free form, remains permanently tacky at room temperature. Such material will adhere instantaneously and tenaciously to most solid surfaces with the application of very slight manual pressure. These adhesives are frequently used on tapes. An adhesive which, in the dry state, is aggressively and permanently tacky at room temperature and firmly adheres to a variety of dissimilar surfaces upon contact without the need for more than finger or hand pressure.

Adhesive, room temperature setting An adhesive that sets in the temperature range from 68°F to 86°F (20–30°C), in accordance with the limits for Standard Room Temperature specified in ASTM Methods D618.

Adhesive, separate application An adhesive consisting of two parts, one part being applied to one adherend and the other part to the other, the two then being brought together to form a joint. Acrylics are examples of this type.

Adhesive, solvent An adhesive having a volatile organic liquid as a vehicle. This term excludes water-based adhesives.

Adhesive, solvent-activated A dry adhesive or adherend that is rendered tacky just prior to use by application of a solvent.

Adhesive spread See spread.

Adhesive, structural A bonding agent used for transferring required loads between adherends exposed to service environments typical for the structure involved. An adhesive of proven reliability in engineering structural applications in which the bond can be stressed to a high proportion of its maximum failing load for long periods without failure. A material employed to form high-strength bonds in structural assemblies which perform load-bearing functions, and which may be used in extreme service conditions, e.g., high- and low-temperature exposure.

Adhesive, two-component An adhesive supplied in two parts which are mixed before application. Such adhesives usually cure at room temperature.

Adhesive, warm-setting A term that is sometimes used as a synonym for intermediate temperature-setting adhesive (q.v.).

Amylaceous, adj Pertaining to, or of, the nature of starch; starchy.

Anodize To coat a metal with a protective film by subjecting it to electrolytic action as in the anode of a cell.

Assembly (for adhesive) A group of materials or parts, including adhesive, which has been placed together for bonding, or which has been bonded together.

Autoclave A closed container which provides controlled heat and pressure conditions.

B-stage An intermediate stage in the reaction of certain thermosetting resins in which the material softens when heated to a rubbery state and swells when in contact with certain liquids, but may not entirely fuse or dissolve in some of the solvents which will dissolve resins in the A-stage. The resin in an uncured thermosetting adhesive is usually in this stage. Sometimes referred to as Resitol.

Backing The flexible supporting material for an adhesive. Pressure-sensitive adhesives are commonly backed with paper, plastic films, fabric, or metal foil; heat-curing thermosetting adhesives are often supported on glass cloth backing.

Bag molding (blanket molding) 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.

Bag, vacuum A flexible bag in which pressure may be applied to an assembly inside the bag by means of evacuation of the bag.

Binder A component of an adhesive composition that is primarily responsible for the adhesive forces which hold two bodies together.

Bite, n The penetration or dissolution of adherend surfaces by an adhesive.

Blister An elevation of the surface of an adherend, somewhat resembling in shape a blister on the human skin; its boundaries may be indefinitely outlined and it may have burst and become flattened. A blister may be caused by insufficient adhesive, inadequate curing time, temperature or pressure, or trapped air, water, or solvent vapor.

Blocked-curing agent A curing agent or hardener rendered unreactive, which can be reactivated as desired by physical or chemical means.

Blocking An undesired adhesion between touching layers of a material, such as occurs under moderate pressure during storage or use. An unintentional adherence between materials.

Blushing The condensation of atmospheric moisture at the bondline interface.

Body The consistency of an adhesive which is a function of viscosity, plasticity, and rheological factors.

Bond, n The union or joining of materials by adhesives. The attachment at the interface between an adhesive and an adherend.

Bond, v To unite or join materials by means of an adhesive.

Bondline See glue line.

Bond strength The unit load (force) supplied in 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 (the interface). The term adherence (q.v.) is frequently used in place of bond strength.

Bond, structural See structural bond.

C-stage The final stage in the reaction of certain thermosetting resins in which the material is relatively insoluble and infusible. Certain thermosetting resins in a fully cured adhesive layer are in this stage. Sometimes referred to as resite.

Catalyst A substance that markedly speeds up the cure of an adhesive when added in minor quantity compared to the amounts of the primary reactants. Material which promotes cross-linking in a polymer or accelerates drying.

Caul, n A sheet of material employed singly or in pairs in hot or cold pressing of assemblies being bonded. Cauls are used to protect either the faces of the assembly, or the press platens, or both against marring and staining to prevent sticking, to facilitate loading, to impart a desired surface tension or finish, or to provide uniform surface distribution. Cauls may be made of any suitable material, such as aluminum, stainless steel, hardboard, fiberboard, or plastic. The length and width dimensions are generally the same as those of the platen of the press where it is used.

Cement, n See adhesive and solvent cement. A synonym for adhesive; a mixture of water with finely powdered lime and clay which hardens and adheres to suitable aggregates to form concrete or mortar; an inorganic paste with adhesive properties.

Cement, v To bond with a cement.

Cohesion The state in which the particles of a single substance are held together by primary or secondary valence forces. In adhesives, cohesion is the state in which the particles of the adhesive or adherend are held together.

Cold pressing A bonding operation in which an assembly is subjected to pressure without the application of heat.

Collagen The protein derived from bone and skin used to prepare animal glue and gelatin.

Colophony The resin obtained from various species of pine trees.

Condensation A chemical reaction in which two or more molecules combine with the separation of water or some other simple compound. If a polymer is formed, the process is called polycondensation.

Consistency That property of a liquid adhesive by virtue of which it tends to resist deformation. Consistency is not a fundamental property, but is comprised of viscosity, plasticity, and other phenomena. The term is usually applied to materials whose deformations are not proportional to applied stresses.

Contact angle The angle between a substrate plane and the free surface of a liquid droplet at the line of contact with the substrate.

Contact bonding The deposition of cohesive materials on both adherend surfaces and their assembly under pressure.

Copolymer See polymer; polymerization.

Core The honeycomb structure used in sandwich panel construction; innermost portion of a multilayer adherend assembly.

Corrosion The chemical reaction between the adhesive or contaminant and the adherend surfaces, due to reactive components in the adhesive film, leading to deterioration of the bond strength.

Cottoning The formation of web-like filaments of adhesive between the applicator and the substrate surface.

Coverage The spreading power of an adhesive over the surface area of the adherend.

Crazing Fine cracks that may extend in a network on, under the surface of, or through a layer of adhesive.

Creep The dimensional change with time of a material under load, following initial instantaneous elastic or rapid deformation. Creep at room temperature is sometimes called cold flow.

Cross-linking (Crosslinking) The union of adjacent molecules of cured adhesive (often existing as long polymer chains) by catalytic or curing agents.

Cure, v To change the physical properties of an adhesive, usually thermosetting, by chemical reaction, which may be condensation, polymerization, vulcanization, or cross-linking. It is usually accomplished by the action of heat and catalyst, alone or in combination, with or without pressure.

Cure (curing) temperature The temperature to which an adhesive or an assembly is subjected to cure the adhesive.

Cure (curing) time The period of time necessary for an adhesive or an assembly to cure under specified conditions of temperature, pressure, or both.

Curing agent (hardener) A substance or mixture of substances added to an adhesive to promote or control the curing reaction. An agent which does not enter into the reaction is known as a catalytic hardener or catalyst. A reactive curing agent or hardener is generally used in much greater amounts than a catalyst, and actually enters into the reaction.

Degrease To remove oil and grease from adherend surfaces.

Delamination The separation of layers in a laminate because of failure of the adhesive, either in the adhesive itself, or at the interface between the adhesive and the adherend.

Dextrin A water-based product derived from the acidification and/or roasting of starch.

Dielectric curing The use of a high-frequency electric field through a joint to cure a synthetic thermosetting adhesive. A curing process for wood and other nonconductive joint materials. Curing results from the heat generated by the resonance of the molecules within the adhesive due to the imposed field.

Diluent An ingredient usually added to an adhesive to reduce the concentration of bonding materials. A liquid additive whose sole function is to reduce the concentration of solids and the viscosity of an adhesive composition. Also called thinner, which is deprecated by some workers.

Diluent, reactive A low-viscosity liquid added to a high-viscosity solvent-free thermosetting adhesive which reacts chemically with the adhesive during curing. The advantage of lowered viscosity is gained with minimum loss of other properties.

Doctor bar or blade A scraper mechanism that regulates the amount of adhesive on the spreader rolls or on the surface being coated. A mechanism (bar or blade) on application equipment for spreading a material evenly on the application rolls or on the surface being coated, thereby controlling its thickness.

Doctor roll A roller mechanism that revolves at a different surface speed, in a direction opposite to that of the spreader roll, resulting in a wiping action to control the amount of adhesive supplied to the spreader roll.

Double spread See spread.

Dry, v To change the physical state of an adhesive or an adherend by the loss of solvent constituents by evaporation, absorption, or both.

Elasticity, modulus of The ratio of stress to strain in elastically deformed material.

Elastomer A macromolecular material which, at room temperature, is capable of recovering substantially in size and shape after removal of deforming force.

Emulsion A stable dispersion of two or more immiscible liquids held in suspension by small percentages of substances called emulsifiers.

Extender A substance, generally having some adhesive action, added to an adhesive to reduce the amount of the primary binder required per unit area. Another function is to reduce costs. Such materials also improve void-filling properties and reduce crazing.

Failure, adherend Joint failure by cohesive failure of the adherend.

Failure, adhesive Rupture of an adhesive bond at the interface between the adhesive and the adherend. Rupture of an adhesive bond in which the separation appears visually to be at the adhesive/adherend interface.

Failure, cohesive Rupture of an adhesive bond in such a way that the separation appears to be within the adhesive. Rupture of an adhesive bond in which the separation appears visually to be in the adhesive or in the adherend.

Failure, contact The failure of an adhesive joint, as a result of incomplete contact during assembly, between adherend and adhesive surfaces or between adhesive surfaces.

Failure, wood The rupturing of wood fibers in strength tests on bonded specimens, usually expressed as the percentage of the total area involved which shows such failure. This is a form of adherend failure.

Fatigue A condition of stress from repeated flexing or impact force upon the adhesive–adherend interface; weakening of material caused by repetitive loading and unloading.

Faying surface The surface of an adherend which makes contact with another adherend.

Feathering The tapering of an adherend on one side to form a wedge section, as used in a scarf joint.

Filler A relatively nonadhesive substance added to an adhesive to improve its working properties, permanence, strength, or other qualities.

Filler sheet A sheet of deformable or resilient material that, when placed between the assembly to be bonded and the pressure applicator, or when distributed within a stack of assemblies, aids in providing uniform application of pressure over the area to be bonded.

Fillet That portion of an adhesive that fills the corner or angle formed where two adherends are joined. The term for junction of the outer skin and inner core in honeycomb assemblies.

Flow Movement of an adhesive during the bonding process before the adhesive is set. (See also cold flow under creep.)

Gel, n A semisolid system consisting of a network of solid aggregates in which liquid is held.

Gel, v To reach a gel condition or state.

Gelation Formation of a gel.

Glue, n Originally a hard gelatin obtained from hides, tendons, cartilage, bones, etc. of animals. Also, an adhesive prepared from this substance by heating with water. Through general use, the term is now synonymous with the term “adhesive.” The term is most commonly used for wood adhesives, however.

Glue line (bond line) The layer of adhesive which attaches two adherends. The interface between an adhesive and an adherend.

Green strength (grab) The ability of an adhesive to hold two surfaces together when first brought into contact and before the adhesive develops its ultimate bonding properties when fully cured.

Gum Any of a class of colloidal substances exuded by, or prepared from plants. Sticky when moist, they are composed of complex carbohydrates and organic acids which are soluble or swell in water.

Hardener A substance or mixture of substances added to an adhesive to promote or control the curing reaction by taking part in it by catalysis or cross-linking. The term is also used to designate a substance added to control the degree of hardness of the cured film.

Heat reactivation The use of heat to effect adhesive activity, e.g., hot-melt adhesive; completion of the curing process of a B-staged resin.

Heat seal The use of heat reactivation to prepare a joint with a thermoplastic material present, as a thin layer, on the adherends; bringing adherend surfaces to their melting point and bonding under pressure.

Heteropolymerization See polymerization.

Honeycomb core A sheet material, which may be metal, foamed into cells (usually hexagonal) and used for sandwich construction in structural assemblies, especially in aircraft construction.

Impact shock See strength, impact.

Inhibitor A substance that slows down a chemical reaction. Inhibitors are sometimes used in certain adhesives to prolong storage or working life.

Interface The contact area between adherend and adhesive surfaces.

Jig A form used to hold a bonded assembly until the adhesive has cured. A supporting frame for the production of laminate shapes under pressure.

Joint The location at which two adherends are held together with a layer of adhesive.

Joint, butt A joint made by bonding two surfaces that are perpendicular to the main surface of the adherends.

Joint, lap A joint made by placing one adherend partly over another and bonding together the portions of the adherends. Double lap joints involve the overlapping by opposing faces of one adherend.

Joint, scarf A joint made by cutting away similar segments of two adherends at an angle <45° to the major axis of two adherends and bonding the adherends with the cut areas fitted together to be coplanar.

Joint, starved A joint that has an insufficient amount of adhesive to produce a satisfactory bond. This condition may result from too thin a spread to fill the gap between the adherends, excessive penetration of the adhesive into the adherend (when porous), too short an assembly time, or the use of excessive pressure.

Laminate, n A product made by bonding together two or more layers of material or materials.

Laminate, v To unite layers of material with adhesive.

Laminate, cross, 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.

Laminate, parallel, n A laminate in which the grain of all layers of material are oriented approximately parallel to each other. A laminate in which all the layers of material are oriented approximately parallel with respect to the grain or strongest direction in tension.

Latex A stable dispersion of a polymeric material in an essentially aqueous medium.

Legging The drawing of filaments or strings when adhesive-bonded substrates are separated.

Mastic A high-viscosity, low-cost adhesive, either latex- or solvent-based, used in industrial applications, such as in applying wall boards and floor tiles. Mastics are applied by knife, trowel, or pressure guns and become immobile on loss of solvent or water.

Matrix The part of an adhesive which surrounds or engulfs embedded filler or reinforcing particles and filaments.

Modifier Any chemically inert ingredient added to an adhesive formulation that changes its properties.

Modulus See elasticity, modulus of and rigidity, modulus of.

Monomer A relatively simple compound that can react to form a polymer.

Mucilage An adhesive prepared from a gum and water. Also, in a more general sense, a liquid adhesive which has a low order of bonding strength. Mucilages are used in schools and offices for applications usually involving paper products.

Newtonian fluid A fluid in which the shearing rate is directly proportional to the applied torque.

Novalak A phenolic-aldehydic resin that, unless a source of methylene groups is added, remains permanently thermoplastic.

Open time See open assembly time under time, assembly.

Paste, n An adhesive composition having a characteristic plastic-type consistency, that is, a high order of yield value, such as that of an adhesive prepared by heating a mixture of starch and water and subsequently cooling the hydrolyzed product.

Penetration The passage of an adhesive into an adherend.

Permanence The resistance of an adhesive bond to deteriorating influences.

Photographing See telegraphing.

Pick-up roll A spreading device where the roll for picking up the adhesive runs in a reservoir of adhesive.

Plasticity A property of adhesives 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.

Plasticizer A material, such as a high-boiling point organic solvent, incorporated in an adhesive to increase its flexibility, workability, or distensibility. The addition of the plasticizer may cause a reduction in melt viscosity, lower the temperature of the second-order transition, or lower the elastic modulus of the solidified adhesive.

Polycondensation See condensation and polymer.

Polymer 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 (addition polymers) or polycondensation (condensation polymers). When two or more different monomers are involved, the product is a copolymer.

Polymerization A chemical reaction in which the molecules of a monomer are linked together to form large molecules whose molecular weight is a multiple of that in the original substance. When two or more different monomers are involved, the process is called copolymerization or heteropolymerization.

Porosity The ability of an adherend to absorb an adhesive.

Postcure, v To expose an adhesive assembly to an additional cure, following the initial cure, for the purpose of modifying specific properties.

Postvulcanization bonding Conventional adhesive bonding of previously vulcanized elastomeric adherends.

Pot life (working life) The period of time during which an adhesive or resin prepared for application after mixing with catalyst, solvent, or other compounding ingredients, remains usable. The effective working time for an adhesive after preparation; interval before the adhesive system becomes unusable through an increase in viscosity or curing.

Prebond treatment See surface preparation.

Pressure-sensitive adhesives (PSAs) Adhesive materials which bond to adherend surfaces at room temperature immediately as low pressure is applied. Adhesives which require only pressure application to effect permanent adhesion to an adherend.

Primer A coating applied to a surface of an adherend prior to the application of an adhesive to improve adhesion and/or durability of the bond.

Qualification test A series of tests conducted by the government procuring activity, or an agent thereof, to determine conformance of materials, or materials systems, to the requirements of a specification which normally results in a Qualified Products List (QPL) under the specification. Qualification under a specification generally requires conformance to all tests in the specification. It may, however, be limited to conformance to a specific type, or class, or both.

QPL See qualification test.

Release agent An adhesive material that prevents bond formation.

Release paper A sheet, serving as a protectant, or carrier, or both, for an adhesive film or mass that is easily removed from the film or mass prior to use.

Resin A solid, semisolid, or pseudosolid organic material that has an indefinite and often high molecular weight, exhibits a tendency to flow when subjected to stress, usually has a softening or melting range, and usually fractures conchoidally. A liquid resin is an organic polymeric liquid which, when converted to its final state for use, becomes a resin.

Resinoid Any of the class of thermosetting synthetic resins, either in their initial temporarily infusible state or in their final infusible state.

Resite An alternative term for C-stage (q.v.).

Resitol An alternative term for B-stage (q.v.).

Resol An alternative term for A-stage (q.v.).

Retrogradation A change of starch pastes from low to high consistency on aging.

Rosin A resin obtained as a residue in the distillation of crude turpentine from the sap of the pine tree (gum rosin), or from an extract of the stumps and other parts of the tree (wood rosin).

Sagging Run or flow-off of adhesive from an adherend surface due to application of excess or low-viscosity material.

Sandwich panel An assembly composed of metal skins (facings) bonded to both sides of a lightweight core.

Sealant A gap-filling material to prevent excessive absorption of adhesive, or penetration of liquid or gaseous substances.

Self-vulcanizing, adj Pertaining to an adhesive that undergoes vulcanization without the application of heat.

Service conditions The environmental conditions to which a bonded structure is exposed, e.g., heat, cold, humidity, radiation, vibration.

Set, v To convert an adhesive into a fixed or hardened state by chemical or physical action, such as condensation, polymerization, oxidation, vulcanization, gelation, hydration, or evaporation of volatile constituents. The term is most commonly used with thermoplastic adhesives, unless a chemical process, such as polymerization, is involved.

Shear, tensile The apparent stress applied to an adhesive in a lap joint.

Shelf life See storage life.

Shortness A qualitative term that describes an adhesive that does not string cotton, or otherwise form filaments or threads during application.

Shrinkage The volume reduction occurring during adhesive curing, sometimes expressed as a percentage volume or linear shrinkage; size reduction of adhesive layer due to solvent loss or catalytic reaction.

Single-spread See spread.

Sizing The process of applying a material on a surface in order to fill pores and thus reduce the absorption of the subsequently applied adhesive or coating, or to otherwise modify the surface properties of the substrate to improve the adhesion. Also, the material used for this purpose. The latter is sometimes called size.

Skinning The formation of a dry surface layer (skin) on an adhesive coating following too rapid evaporation of the solvent vehicle.

Slip The ability of an adhesive to accommodate adherend movement or repositioning after application to adherend surfaces.

Slippage The movement of adherends with respect to each other during the bonding process.

Slip sheet interliner A sheet or film used to cover an adhesive during handling; protective film for a film adhesive.

Softener A plasticizing additive to reduce adhesive embrittlement; component of elastomeric films to increase their flexibility.

Solids content The percentage by weight of the nonvolatile matter in an adhesive.

Solvent bonding See solvent welding.

Solvent cement An adhesive utilizing an organic solvent as the means of depositing the adhesive constituent. An adhesive which dissolves the plastics being joined, forming strong intermolecular bonds, then evaporating. An adhesive made by dissolving a plastic resin or compound in a suitable solvent or mixture of solvents. The solvent cement dissolves the surfaces (of the pipe and fittings) to form a bond between the mating surfaces, provided the proper cement is used for the particular materials and proper techniques are followed.

Solvent cement joint A joint made by using a solvent cement to unite the components.

Solvent cementing See solvent welding.

Solvent joint A joint made by using a solvent to unite the components.

Solvent reactivation The application of solvent to a dry adhesive layer to regenerate its wetting properties.

Solvent welding (solvent bonding or solvent cementing) The process of joining articles made of thermoplastic resins by applying a solvent capable of softening the surfaces to be joined, and pressing the softened surfaces together. Adhesion is attained by means of evaporation of the solvent, absorption of the solvent into adjacent material, and/or polymerization of the solvent cement. ABS, acrylics, cellulosics, polycarbonates, polystyrenes, and vinyls are plastics which may be joined in this way. The formation of a joint in which a self-bond between the polymeric components is promoted by the temporary presence of a solvent, in the absence of an extraneous adhesive.

Spread (adhesive spread) The quantity of adhesive per unit joint area applied to an adherend, usually expressed in points of adhesive per thousand square feet of joint area. (1) Single spread refers to the application of adhesive to only one adherend of a joint. (2) Double spread refers to application of adhesive to both adherends of a joint.

Squeeze-out Excess adhesive pressed out at the bondline due to pressure applied in the adherends.

Stabilizer An adhesive additive which prevents or minimizes change in properties, e.g., by adherend absorption, demulsification, or rapid chemical reaction.

Storage life The period of time during which a packaged adhesive can be stored under specified temperature conditions and remain suitable for use. Sometimes called shelf life. Refrigerated storage often extends storage life considerably.

Strength, cleavage The tensile load expressed as force per unit of width of bond required to cause cleavage separation of a test specimen of unit length.

Strength, dry The strength of an adhesive joint determined immediately after drying under specified conditions, or after a period of conditioning in the standard laboratory atmosphere.

Strength, fatigue The maximum load that a joint will sustain when subjected to repeated stress application after drying, or after a conditioning period under specified conditions.

Strength, impact Ability of an adhesive material to resist shock by a sudden physical blow directed against it. Impact shock is the transmission of stress to an adhesive interface by sudden vibration or jarring blow of the assembly, measured in work units per unit area.

Strength, longitudinal shear (lap-joint strength) The force necessary to rupture an adhesive joint by means of stress applied parallel to the plane of the bond.

Strength, peel The force per unit width necessary to bring an adhesive to the point of failure and/or to maintain a specified rate of failure by means of a stress applied in a peeling mode.

Strength, shear The resistance of an adhesive joint to shearing stresses; the force per unit area sheared, at failure.

Strength, tensile The resistance of an adhesive joint to tensile stress; the force per unit area under tension, at failure.

Strength, wet The strength of an adhesive joint determined immediately after removal from a liquid in which it has been immersed under specified conditions of time, temperature, and pressure. The term is commonly used to designate strength after immersion in water. In latex adhesives, the term is also used to describe the joint strength when the adherends are brought together with the adhesive still in the wet state.

Stringiness The property of an adhesive that results in the formation of filaments or threads when adhesive transfer surfaces are separated. Transfer surfaces include rolls, picker plates, stencils, etc. The complete breakoff of adhesive film when it is divided between transfer rollers, stencils, picker plates, etc.; uneven transfer of an adhesive to an adherend surface.

Structural adhesive See adhesive, structural.

Structural bond A bond that stresses the adherend to the yield point, thereby taking full advantage of the strength of the adherend. On the basis of this definition, a dextrin adhesive used with paper (e.g., postage stamps, envelopes) which causes failure of the paper, forms a structural bond. The stronger the adherend, the greater the demands placed on the adhesive. Thus, few adhesives qualify as “structural” for metals. A further requirement for a structural adhesive is that it should be able to stress the adherend to its yield point after exposure to its intended environment.

Substrate A material upon the surface of which an adhesive-containing substance is spread for any purpose, such as bonding or coating. A broader term than adherend (q.v).

Surface preparation (surface treatment) A physical or chemical preparation, or both, of an adherend to render it suitable for adhesive joining. The term prebond treatment is sometimes used, but is deprecated.

Syneresis The exudation by gels of small amounts of liquid on standing.

Tack 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.

Tack, aggressive See tack, dry.

Tack, dry, n The property of certain adhesives, particularly nonvulcanizing rubber adhesives, to adhere on contact to themselves at some stage in the evaporation of volatile constituents, even though they seem dry to the touch. Sometimes called aggressive tack. The self-adhesion property of certain adhesives which are touch-dry (a stage in the evaporation of volatile constituents).

Tack-dry (tacky-dry), adj The state of an adhesive which has lost sufficient volatiles (by evaporation or absorption into the adherend) to leave it in the required sticky (tacky) condition.

Tackifier An additive intended to improve the stickiness of a cast adhesive film; usually a constituent of rubber-based and synthetic resin adhesives.

Tack range (tack stage) 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.

Tacky-dry See tack-dry. Tape. A film form of adhesive which may be supported on carrier material.

Teeth The resultant surface irregularities or projections formed by the breaking of filaments or strings which may form when adhesive-bonded substrates are separated.

Telegraphing A condition in a laminate or other type of composite construction in which irregularities, imperfections, or patterns of an inner layer are visibly transmitted to the surface. Telegraphing is occasionally referred to as photographing. The visible transmission of faults, imperfections, and patterned striations occurring in an inner layer of a laminate structure.

Temperature, curing The temperature to which an adhesive or an assembly is subjected to cure the adhesive. The temperature attained by the adhesive in the process of curing, it (adhesive curing temperature) may differ from the temperature of the atmosphere surrounding the assembly (assembly curing temperature).

Temperature, drying The temperature to which an adhesive on an adherend, or in an assembly, or the assembly itself, is subjected to dry the adhesive. The temperature attained by the adhesive in the process of drying it (adhesive drying temperature) may differ from the temperature of the atmosphere surrounding the assembly (assembly drying temperature).

Temperature, maturing The temperature, for a given time and bonding procedure, which produces required characteristics in components bonded with ceramic adhesives.

Temperature, setting The temperature to which an adhesive or an assembly is subjected to set the adhesive. The temperature attained by the adhesive in the process of setting (adhesive setting temperature) may differ from the temperature of the atmosphere surrounding the assembly (assembly setting temperature).

Tests, destructive Tests involving the destruction of assemblies in order to evaluate the maximum performance of the adhesive bond.

Tests, nondestructive Inspection tests for the evaluation of bond quality without damaging the assembly, e.g., ultrasonics, visual inspection.

Thermoplastic, adj Capable of being repeatedly softened by heat and hardened by cooling.

Thermoplastic, n A material that will repeatedly soften when heated and harden when cooled.

Thermoset (thermosetting), adj Having the property of undergoing a chemical reaction by the action of heat, catalysis, ultraviolet light, etc., leading to a relatively infusible state.

Thermoset, n A material that has the property of undergoing, or has undergone a chemical reaction by the action of heat, catalysis, ultraviolet light, etc., leading to a relatively infusible state.

Thinner, n A volatile liquid added to an adhesive to modify the consistency or other properties. See diluent.

Thixotropic, adj A term applied to materials having the property of thixotropy (q.v.).

Thixotropy A property of adhesive systems of thinning upon isothermal agitation and thickening upon subsequent rest. A property of materials which display a reduction in viscosity when a shearing action is applied. Some adhesive systems become thinner in consistency on agitation and thicker again when left undisturbed.

Time, assembly The time interval between the spreading of the adhesive on the adherend and the application of pressure, or heat, or both, to the assembly. For assemblies involving multiple layers or parts, the assembly time begins with the spreading of the adhesive on the first adherend. Assembly time is the sum of the open and closed assembly times. Open assembly time is the time interval between the spreading of the adhesive on the adherend and the completion of assembly of the parts for bonding. During this period, the adhesive-coated surfaces are exposed to the air before being brought into contact. Closed assembly time is the time interval between completion of assembly of the parts for bonding and the application of pressure, or heat, or both, to cure or set the adhesive.

Time, curing The period of time during which an assembly is subjected to heat or pressure, or both, to cure the adhesive. Further cure may take place after removal of the assembly from the conditions of heat, or pressure, or both.

Time, drying The period of time during which an adhesive on an adherend or an assembly is allowed to dry with or without the application of heat, or pressure, or both.

Time, joint conditioning The time interval between the removal of the joint from the conditions of heat, pressure, or both, used to accomplish bonding and the attainment of approximately maximum bond strength. Sometimes called joint aging time.

Time, setting The period of time during which an assembly is subjected to heat, pressure, or both, to set the adhesive.

Vehicle The carrier medium (liquid) for an adhesive material which improves its ease of application to adherends; solvent component of an adhesive.

Viscosity The ratio of the shear stress existing between laminae of moving fluid and the rate of shear between these laminae. A fluid exhibits Newtonian behavior when the rate of shear is proportional to the shear stress. A fluid exhibits non-Newtonian behavior when an increase or decrease in the rate of shear is not accompanied by a proportional increase or decrease in the shear stress. A measure of the resistance to flow of a liquid. For Newtonian liquids, the shear rate is proportional to the shear stress between laminate of moving fluid; for non-Newtonian liquids it is not proportional.

Viscosity coefficient (coefficient of viscosity) The shearing stress tangentially applied that will induce a velocity gradient. A material has a viscosity coefficient of one poise when a shearing stress of one dyne per square centimeter produces a velocity gradient of 1 (cm/s)/cm.

Vulcanization A chemical reaction in which the physical properties of a rubber are changed in the direction of decreased plastic flow, less surface tackiness, and increased tensile strength by reacting it with sulfur or other suitable agents. The cross-linking of an adhesive material by means of heat or catalysis; the chemical reaction of rubber with sulfur or other agents to alter its physical properties, e.g., to cause less tackiness, reduced plastic flow, and increased tensile strength.

Vulcanize, v To subject to vulcanization (q.v).

Warp, n A significant variation from the original, true, or plane surface of a material. A distortion of an adherend surface.

Webbing Filaments or threads that may form when adhesive transfer surfaces are separated. Transfer surfaces may be rolls, picker plates, stencils, etc.

Weldbonding A process in which a joint is formed by spot welding through an uncured adhesive bondline or by flowing an adhesive into a spot-welded joint.

Wetting The process in which a liquid spontaneously adheres to and spreads on a solid surface. A surface is said to be completely wet by a liquid if the contact angle is zero, and incompletely wet if it is a finite angle. Surfaces are commonly regarded as unwettable if the angle exceeds 90°.

Wood veneer A thin sheet of wood, generally within the thickness range 0.01–0.25 in (0.3–6.3 mm) to be used in a laminate.

Working life See pot life.

Yield value The stress, either normal or shear, at which a marked increase in deformation occurs without an increase in load.