Thermoforming Glossary


Composite material made by blending polymers or copolymers with other polymers or elastomers under selected conditions. Kydex is a widely known example of an Acrylic/PVC alloy.


A process of holding a material at a temperature near, but below, its melting point. The objective of annealing is to permit stress relaxation without distortion of shape. It is often used on injection molded articles to relieve stresses set up by flow in the mold.

Antistatic Agents

Methods of minimizing static electricity in plastic materials. Such agents are of two basic types: (1) metallic devices which come in contact with the plastics and conduct the static to earth. Such devices give complete neutralization at the time, but because they do not modify the surface of the material it can become prone to further static during subsequent handling; (2) chemical additives which, mixed with the compound during processing, give a reasonable degree of protection to the finished products.


The proprietary name for phenolic and other plastics materials produced by Bakelite Limited, but often used indiscriminately to describe any phenolic molding material or molding. The name is derived from that of Dr. Leo Hendrik Baekeland (1863-1944), a Belgian who, through his work on the synthesis of phenolic resins and their commercial development in the early 1900's, is generally considered to be the "father" of the plastics industry.


An apparatus for compounding materials composed of a pair of contra-rotating rotors which masticate the materials to form a homogeneous blend. This is an internal type mixer which produces excellent mixing.

Beta Gage

A gage consisting of two facing elements, a B-ray-emitting source and a B-ray detector. When a sheet material is passed between the elements, some of the B-rays are absorbed, the percent absorbed being a measure of the areal density or thickness of the sheet.


To give up color when in contact with water or a solvent: undesired movement of certain materials in a plastic (e.g. plasticizers in vinyl) to the surface of the finished article or into an adjacent material. Also called Migration.


A raised area on the surface of a molding caused by the pressure of gases inside it on its incompletely hardened surface.


A visible exudation of efflorescence on the surface of a material.


A mold blemish in the form of a blue oxide film which occurs on the polished surface of a mold as a result of the use of abnormally high mold temperatures.


Protuberance on a plastic part designed to add strength, to facilitate alignment during assembly, to provide for fastenings, etc.

Bottom Plate

Part of the mold which contains the heel radius and the push-up.

Breaker Plate

A perforated plate at the rear end of an extruder head. It often supports the screens that prevent foreign particles from entering the die.


A gas, insoluble in water but soluble in alcohol and ether, obtained from the cracking of petroleum, from coal tar benzene or from acetylene produced from coke and lime. It is widely used in the formulation of copolymers with styrene, acrylonitrile, vinyl chloride and other monomeric substances, where it imparts flexibility to the subsequent moldings.

Butadiene Styrene Plastics

A synthetic resin derived from the copolymerization of butadiene gas and styrene liquids.


To prepare sheets of material by pressure between two or more counter-rotating rolls (also used in reference to the machine used to perform this operation).

Carbon Black

A black pigment produced by the incomplete burning of natural gas or oil. It is widely used as a filler, particularly in the rubber industry. Because it possesses useful ultraviolet protective properties, it is also much used in polyethylene compounds intended for such applications as cold water piping and black agricultural sheet.


To form a "plastic" object by pouring a fluid monomer-polymer solution into an open mold where it finishes polymerizing. Forming plastic film and sheet by pouring the liquid resin onto a moving belt or by precipitation in a chemical bath.

Cast Film

A film made by depositing a layer of plastic, either molten, in solution, or in a dispersion, onto a surface, solidifying and removing the film from the surface.


Depression in a mold made by casting, machining, hobbing, or a combination of these methods: depending on number of such depressions, molds are designates as single-cavity or multi-cavity.


A thermoplastic material made by the intimate blending of cellulose nitrate with camphor. Alcohol is normally employed as a volatile solvent to assist plasticization, and is subsequently removed.


A natural high polymeric carbonhydrate found in most plants; the main constituent of dried woods, jute, flax, hemp, ramie, etc. Cotton is almost pure cellulose.

Cellulose Acetate

An acetic acid ester of cellulose. It is obtained by the action, under rigidly controlled conditions, of acetic acid and acetic anhydride on purified cellulose usually obtained from cotton linters. All three available hydroxyl groups in each glucose unit of the cellulose can be acetylated but in the material normally used for plastics it is usual to acetylate fully and then to lower the acetyl value by partial hydrolysis. When compounded with suitable plasticizers it gives a tough thermoplastic material.

Cellulose Acetate Butyrate

An ester of cellulose made by the action of a mixture of acetic and butyric acids and their anhydrides on purified cellulose. It is used in the manufacture of plastics which are similar in general properties to cellulose acetate but are tougher and have better moisture resistance and dimensional stability.


A powdery residue on the surface of a material often resulting from degradation.

Chill Roll

A cored roll, usually temperature controlled with circulating water, which cools the web before winding. For chill roll (cast) film, the surface of the roll is highly polished. In extrusion coating, either a polished or a matte surface may be used depending on the surface desired on the finished coating.

Chill Roll Extrusion

The extruded film is cooled while being drawn around two or more highly polished chill rolls cored for water cooling for exact temperature control.

Chlorinated Polyether

The polymer is obtained from pentaerythritol by preparing a chlorinated oxetane and polymerizing it to a polyether by means of opening the ring structure.

Chromium Plating

An electrolytic process that deposits a hard film of chromium metal onto working surfaces of other metals where resistance to corrosion, abrasion, and/or erosion is needed.

Chlorinated Polyvinyl Chloride Plastics

Plastics based on chlorinated polyvinyl chloride in which the chlorinated polyvinyl chloride is in the greatest amount by weight.

Clamping Plate

A plate fitted to a mold and used to fasten the mold to a molding machine.


A controlled distance by which one part of an object is kept separated from another part.

Coefficient of Expansion

The fractional change in length (sometimes volume, specified) of a material for a unit change in temperature. Values for plastics range from 0.01 to 0.2 mils/in., degree C.

Compression Ratio

In an extruder screw, the ratio of volume available in the first flight at the hopper to the last flight at the end of the screw.


A mechanical device to transport material from one point to another, often continuously.

Cooling Fixture

Block of metal or wood holding the shape of a molded piece which is used to maintain the proper shape or dimensional accuracy of a molding after it is removed from the mold, until it is cool enough to retain its shape without further appreciable distortion. Also known as Shrink Fixture.


Fine cracks which may extend in a network on or under the surface or through a layer of a plastic material.


The dimensional change with time of a material under load, following the initial instantaneous elastic deformation. Creep at room temperature is sometimes called Cold Flow.

Cross Laminate

A laminate in which some of the layers of material are oriented approximately at right angles to the remaining layers with respect to the grain or strongest direction in tension.


Applied to polymer molecules, the setting-up of chemical links between the molecular chains. When extensive, as in most thermosetting resins, cross-linking makes one infusible super-molecule of all the chains.


A state of molecular structure in some resins which denotes uniformity and compactness of the molecular chains forming the polymer. Normally can be attributed to the formation of solid crystals having a definite geometric form.


The complete repeating sequence of operations in a process or part of a process. In molding, the cycle time is the period, or elapsed time, between a certain point in one cycle and the same point in the next.

Daylight Opening

Clearance between two platens of a press in the open position.

Decorative Sheet

A laminated plastics sheet used for decorative purposes in which the color and/or surface pattern is an integral part of the sheet.


A deleterious change in the chemical structure of a plastic.


The separation of the layers in a laminate caused by the failure of the adhesive.


Weight per unit volume of a substance, expressed in grams per cubic centimeter, pounds per cubic foot, etc.


Substance which can be used for drying purposes because of its affinity for water.


Treating plastics materials to minimize their accumulation of static electricity and consequently, the amount of dust picked up by the plastics because of such charges.

Die Blades

Deformable members attached to a die body which determine the slot opening and which are adjusted to produce uniform thickness across the film or sheet produced.

Die Cutting

Blanking. Cutting shapes from sheet stock by striking it sharply with a shaped knife edge known as a steel-rule die. Clicking and Dinking are other names for die cutting of this kind.

Die Gap

The distance between the metal faces forming the die opening.

Dielectric Strength

The electric voltage gradient at which an insulating material is broken down or "arced through", in volts per mil of thickness.

Die Lines

Vertical marks on the parison caused by damage of die parts or contamination.


Any change from the original color, often caused by overheating, light exposure, irradiation, or chemical attack.


The degree of taper of a side wall or the angle of clearance designed to facilitate removal of parts from a mold.

Drape Forming

Method of forming thermoplastic sheet in which the sheet is clamped into a movable frame, heated, and draped over high points of a male mold. Vacuum is then pulled to complete the forming operation.

Draw Down Ratio

The ratio of the thickness of the die opening to the final thickness of the product.

Dry Coloring

Method commonly used by fabricators for coloring plastics by tumble blending uncolored particles of the plastic material with selected dyes and pigments.


Synthetic or natural organic chemicals that are soluble in most common solvents. Characterized by good transparency, high tinctorial strength, and low specific gravity.


A material which at room temperature stretches under low stress to at least twice its length and snaps back to the original length upon release of stress. See also Rubber.

Electroformed Molds

A mold made by electroplating metal on the reverse pattern of the cavity. Molten steel may be then sprayed on the back of the mold to increase its strength.


The fractional increase in length of a material stressed in tension.


Techniques used to create depressions of a specific pattern in plastics film and sheeting.


Enclosing an article (usually an electronic component or the like) in a closed envelope of plastic, by immersing the object in a casting resin and allowing the resin to polymerize or, if hot, to cool.

Environmental Stress Cracking

The susceptibility of a thermoplastic article to crack or craze under the influence of certain chemicals and stress.

Ethylene Plastics

Plastics based on polymers of ethylene or copolymers of ethylene with other monomers, the ethylene being in greatest amount by mass.


A substance generally having some adhesive action, added to a plastic composition to reduce the amount of the primary resin required per unit area.


The product or material delivered by an extruder, such as film, pipe, the coating on wire, etc.


The compacting of a plastic material and the forcing of it through an orifice in more or less continuous fashion.

Extrusion Coating

The resin is coated on a substrate by extruding a thin film of molten resin and pressing it onto or into the substrates, or both, without the use of an adhesive.


To work a material in a finished form by machining, forming, or other operation or to make flexible film or sheeting into end products by sewing, cutting, sealing, or other operation.


In molding practice, the indented half of a hold designed to receive the male half.


An optional term for sheeting having a nominal thickness not greater than 0.010".


The plastic forming the opening of a container shaped to accommodate a specific closure. Also, the ultimate surface structure of an article.

First Article

An initial part, off production tooling, representative of production quality.

Fish Eye

A fault in transparent or translucent plastics materials, such as film or sheet, appearing as a small globular mass and caused by incomplete blending of the mass with surrounding material.


Used to denote the dry, unplasticized base of cellulosic plastics.

Flame Retardant Resin

A resin which is compounded with certain chemicals to reduce or eliminate its tendency to burn. For polyethylene and similar resins, chemicals such as antimony trioxide and chlorinated paraffins are useful.

Flame Treating

A method of rendering inert thermoplastic objects receptive to inks, lacquers, paints, adhesives, etc., in which the object is bathed in an open flame to promote oxidation of the surface of the article.


Measure of the extent to which a material will support combustion.

Flexural Modulus

A measure of the strain imposed in the outermost fibers of a bent specimen.

Flexural Strength

The strength of a material in bending, expressed as the tensile stress of the outermost fibers of a bent test sample at the instant of failure. With plastics this value is usually higher than the straight tensile strength.


Short fibers of cotton, etc., used as fillers for molding materials.


A method of coating by spraying finely dispersed powders or fibers.

Fluorescent Pigments

By absorbing unwanted wave-lengths of light and converting them into light of desired wave-lengths, these colors seem to possess an actual glow of their own.

Foaming Agents

Chemicals added to plastics and rubbers that generate inert gasses on heating, causing the resin to assume a cellular structure.

Foil Decorating

Molding paper, textile, or plastic foils printed with compatible inks directly into a plastic part so that the foil is visible below the surface of the part as integral decoration.

Friction Coefficient

A number expressing the amount of frictional effect.


In injection and transfer molding, the orifice through which the melt enters the cavity. Sometimes the gate has the same cross-section as the runner leading to it; often, it is severely restricted.


In polyethylene, a small amorphous resin particle which differs from its surroundings by being of higher molecular weight and/or crosslinked, so that its processing characteristics differ from the surrounding resin to such a degree that it is not easily dispersed in the surrounding resin. A gel is readily discernible in thin films.


The shine or luster of the surface of a material.


The degree of cloudiness in a plastics material.

Heat-Deflection Temperature

The temperature at which a standard test bar (ASTM D648) deflects 0.010" under a stated load of either 66 or 264 p.s.i.


A method of joining plastic films by simultaneous application of heat and pressure to areas in contact. Heat may be supplied conductively or dielectrically.


A polymer, consisting of (neglecting the ends, branch junctions, and other minor irregularities) a single type of repeating unit.


Conical feed reservoir into which molding powder is loaded and from which it falls into a molding machine or extruder, sometimes through a metering device.

Hopper Dryer

A combination feeding and drying device for extrusion and injection molding of thermoplastics. Hot air flows upward through the hopper containing the feed pellets.

Hot Gas Welding

A technique of joining themooplastic materials (usually sheet) whereby the materials are softened by a jet of hot air from a welding torch, and joined together at the softened points. Generally a thin rod of the same material is used to fill and consolidate the gap.

Hot Stamping

Engraving operation for marking plastics in which roll leaf is stamped with heated metal dies onto the face of the plastics. Ink compounds can also be used. By means of felt rolls, ink is applied to type and by means of heat and pressure, type is impressed into the material, leaving the marking compound in the indentation.


A system in which energy is transferred from one place to another by means of compression and flow of a fluid.


Characteristic of some plastics allowing them to take on moisture (polystyrene, ABS, Acrylics, and Polycarbonate are examples). Hygroscopic materials generally require pre-drying prior to forming.

Impact Bar (Specimen)

A test specimen of specified dimensions which is utilized to determine the relative resistance of a plastic to fracture by shock.

Impact Resistance

Relative susceptibility of plastics to fracture by shock, e.g., as indicated by the energy expended by a standard pendulum type impact machine in breaking a standard specimen in one blow.

Impact Strength

(1) The ability of a material to withstand shock loading. (2) The work done in fracturing, under shock loading, a specified test specimen in a specified manner.


A substance that slows down chemical reaction. Inhibitors are sometimes used in certain types of monomers and resins to prolong storage life.


An integral part of a plastics molding consisting of metal or other material which may be molded into position or may be pressed into the molding after the molding is competed.


An instrument utilized to determine the tensile and compressive properties of material.


A safety device designed to insure that a piece of apparatus will not operate until certain precautions have been taken.

IZOD Impact Test

A test designed to determine the resistance of a plastics material to a shock loading. It involves the notching of a specimen, which is then placed in the jaws of the machine and struck with a weighted pendulum. See also Impact Strength.


Tool for holding component parts of an assembly during the manufacturing process, or for holding other tools. Also called a Fixture.


An alloy of aluminum and zinc used for the construction of molds; it imparts a high degree of heat conductivity to the mold.

Kriss-Roll Coating

This roll arrangement carries a metered film of coating to the web; at the line of web contact it is split with part remaining on the roll, the remainder of the coating adhering to the web.

Kraft Paper

Paper made from sulfate wood pulp.


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

Laminated Plastics (Synthetic Resin-Bonded Laminate)

A plastics material consisting of superimposed layers of a synthetic resin impregnated or coated filler which have been bonded together, usually by means of heat and pressure, to form a single piece.


(n) As used in reinforced plastics, the reinforcing material placed in position in the mold; also the resin-impregnated reinforcement. (v) The process of placing the reinforcing material in position in the mold.

Linear Molecule

A long chain molecule as contrasted to one having many side chains or branches.


The extreme outer edge of the top of a container intended to facilitate pouring.

Low Pressure Laminates

In general, laminates molded and cured in the range of pressures from 400 p.s.i. down to and including pressures obtained by the mere contact of the piles.

Mark Off

In thermoforming, the build-up of material where plastic is formed over sharp corners. Can be reduced by pre-stretching material prior to forming.


A plastics compound which includes a high concentration of an additive or additives. Master batches are designed for use in appropriate quantities with the basic resin or mix so that the correct end concentration is achieved. For example, color masterbatches for a variety of plastics are extensively used as they provide a clean and convenient method of obtaining accurate color shades.

Melt Flow

The flow rate obtained from extrusion of a molten resin through a die of specified length and diameter under prescribed conditions of time, temperature and load as set forth in ASTM D1238.

Melt Fracture

An instability in the melt flow through a die starting at the entry to the die. It leads to surface irregularities on the finished article like a regular helix or irregularly spaced ripples.

Melt Index

The amount, in grams, of a thermoplastic resin which can be forced through a 0.0825" orifice when subjected to 2160 gms. Force in 10 minutes at 190°C.

Melting Point

The temperature at which solid and liquid forms of a substance are in equilibrium. In common usage the melting point is taken as the temperature at which the liquid first forms in small samples as its temperature is increased gradually.

Melt Instability

An instability in the melt flow through a die starting at the land of the die. It leads to the same surface irregularities on the finished part as melt fracture.

Melt Strength

The strength of the plastic while in the molten state.

Melt Temperature

The temperature of the molten plastic just prior to entering the mold or extrusion die.

Modulus of Elasticity

The ratio of stress to strain in a material that is elastically deformed.

Moisture Vapor Transmission

The rate at which water vapor permeates through a plastic film or wall at a specified temperature and relative humidity.


(v) To shape plastic parts or finished articles by heat and pressure. (n) The cavity or matrix into or onto which the plastic composition is placed and from which it takes its form.

Molding Shrinkage

(Mold Shrinkage, Shrinkage, Contraction). The difference in dimensions, expressed in inches per inch, between a molding and the mold cavity in which it was molded, both the mold and the molding being at normal room temperature when measured.

Mold Release

See Parting Agent.


A relatively simple compound which can react to form a polymer, See also Polymer.

Multi-Cavity Mold

A mold with two or more mold impressions, i.e., a mold which produces more than one molding per forming cycle.

NC (Numerical Control) Trim

Computerized trimming process utilizing three and five axis routers for secondary trim operations.

Notch Sensitivity

The extent to which the sensitivity of a material to fracture is increased by the presence of a surface in homogeneity such as a notch, a sudden change in section, a crack, or a scratch. Low notch sensitivity is usually associated with ductile materials, and high notch sensitivity with brittle materials.


the generic name for all synthetic fiber forming polyamides; they can be formed into monofilaments and yarns characterized by great toughness, strength and elasticity, high melting point, and good resistance to water and chemicals. the material is widely used for bristles in industrial and domestic brushes, and for many textile applications; it is also used in injection molding gears, bearings, combs, etc.


A group of unsaturated hydrocarbons, named after the corresponding paraffins by addition of the "ene" or "ylene" to the stem. Examples are ethylene and propylene.


Descriptive of a material or substance which will not transmit light. Opposite of transparent. Materials which are neither opaque nor transparent are sometimes described as semi-opaque, but are more properly classified as translucent.


Unintentionally rough surfaces, sometimes associated with improperly painted parts.

Organic Pigments

Characterized by good brightness and brilliance. They are divided into toners and lakes. Toners, in turn, are divided into insoluble organic toners and lake toners. The insoluble organic toners are usually free from salt-forming groups. Lake toners are practically pure, water-insoluble heavy metal salts of dyes without the fillers or substrates of ordinary lakes. Lakes, which are not as strong as lake toners, are water-insoluble heavy metal salts or other dye complexes precipitated upon or admixed with a base or filler.


The alignment of the crystalline structure in polymeric materials so as to produce a highly uniform structure. Can be accomplished by cold drawing or stretching during fabrication.

Overlay Sheet (Surfacing Mat)

A nonwoven fibrous mat (either in glass, synthetic fiber, etc.) used as the top layer in a cloth or mat layup to provide a smoother finish or minimize the appearance of the fibrous pattern.

Parting Agent

A lubricant, often wax, used to coat a mold cavity to prevent the molded piece from sticking to it, and thus to facilitate its removal from the mold. Also called Release Agent.

Pearlescent Pigments

A class of pigments consisting of particles that are essentially transparent crystals of a high refractive index. The optical effect is one of partial reflection from the two sides of each flake. When reflections from parallel plates reinforce each other, the result is a silvery luster. Effects possible range from brilliant highlighting to moderate enhancement of the normal surface gloss.


A small ball or spherical shape.


A process of producing pellets.


The passage or diffusion of a gas, vapor, liquid, or solid through a barrier without physically or chemically affecting it. Also the rate of such passage.


Any colorant, usually an insoluble powdered substance used to produce a desired color or hue.


A very small hole in the extruded resin coating.


An imperfection, a small crater in the surface of the plastic, with its width of approximately the same order of magnitude as its depth.


(n) One of many high-polymeric substances, including both natural and synthetic products, but excluding the rubbers. At some stage in its manufacture every plastic is capable of flowing, under heat and pressure if necessary, into the desired final shape. (v) Made of plastic; capable of flow under pressure or tensile stress.

Plastic Memory

A phenomenon of plastics to return to its original molded form. Different plastics possess varying degrees of this characteristic.

Plastics Tooling

Tools, e.g., dies, jigs, molds, fixtures, etc., for the molding, forming, casting or laminating of plastics materials.


To soften a material and make it plastic or moldable, either by means of a plasticizer or the application of heat.


Chemical agent added to plastic compositions to make then softer and more flexible.


The mounting plates of a press to which the entire mold assembly is bolted.


A thermoforming defect where plastic gathers around a prominent part feature.


Method of sheet forming in which a plug, functioning as a male mold, is forced into a heated plastic sheet held in place by a clamping ring.

Plug Forming

A thermoforming process in which a plug or male mold is used to partially preform the part before forming is completed using vacuum or pressure.

Pock Marks

Irregular indentations on the surface of a pressure formed part caused by insufficient contact of the plastic with the mold surface. They are due to low pressure, air gas entrapment, or moisture on the mold surface.

Polishing Roll

A roll or series of rolls, which have a highly polished chrome plated surface, that are utilized to produce a smooth surface on sheet as it is extruded.

Polycarbonate Resins

Polymers derived from the direct reaction between aromatic and aliphatic dihydroxy compounds with phosgene or by the ester exchange reaction with appropriate phosgene-derived precursors.


A resin formed by the reaction between a dibasic acid and a dihydroxy alcohol, both organic. Modification with multi-functional acids and/or bases and some unsaturated reactants permit cross-linking to thermosetting resins. Polyesters modified with fatty acids are called Alkyds.


A thermoplastic material composed by polymers of ethylene. It is normally a translucent, tough, waxy solid which is unaffected by water and by a large range of chemicals.


A high-molecular-weight organic compound, natural or synthetic, whose structure can be represented by a repeated small unit, the mer; e.g. polyethylene, rubber, cellulose. Synthetic polymers are formed by addition or condensation polymerization of monomers. If two or more monomers are involved, a copolymer is obtained. Some polymers are elastomers, some plastics.


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 of the original substance. When two or more monomers are involved, the process is called copolymeriztion or heteropolymerization.


A polymer prepared by the polymerization of an Olefin as the sole monomer.

Polyolefin Plastics

Plastics based on polymer made with an Olefin as essentially the sole Monomer.


A tough, lightweight rigid plastic made by the polymerization of high-purity propylene gas in the presence of an organometallic catalyst at relatively low pressures and temperatures.


A water-white thermoplastic produced by the polymerization of styrene (ethyl benzene). The electrical insulating properties of polystyrene are outstanding, and the material is relatively unaffected by moisture.

Polyvinyl Acetal

A member of the family of vinyl plastics, polyvinyl acetal is the general name for resins produced from a condensation of polyvinyl alcohol with a aldehyde. There are three main groups: polyvinyl acetal itself; polyvinyl butyral, and polyvinyl formal. Polyvinyl acetal resins are thermoplastics which can be processed by casting, extruding, molding and coating, but their main uses are in adhesives, lacquers, coatings and films.

Polyvinyl Acetate

A thermoplastic material composed of polymers of vinyl acetate in the form of a colorless solid. It is obtainable in the form of granules, solutions, latices, and pastes, and is used extensively in adhesives, for paper and fabric coatings, and in bases for inks and lacquers.

Polyvinyl chloride (PVC)

A thermoplastic material composed of polymers of vinyl chloride; a colorless solid with outstanding resistance to water, alcohols, and concentrated acids and alkalies. It is obtainable in the form of granules, solutions, latices, and pastes. Compounded with plasticizers it yields a flexible material superior to rubber in aging properties. It is widely used for cable and wire coverings in chemical plants, and in the manufacture of protective garments.

Polyvinyl Chloride Acetate

A thermoplastic material composed of copolymers of vinyl chloride and vinyl acetate; a colorless solid with good resistance to water, and concentrated acids and alkalies. It is obtainable in the form of granules, solutions, and emulsions. Compounded with plasticizers it yields a flexible material superior to rubber in aging properties. It is widely used for cable and wire coverings, in chemical plants, and in protective garments.


The forming, bending, or shaping of fully cured, C-stage thermoset laminates that have been heated to make them flexible. On cooling the formed laminate retains the contours and shape of the mold over which it has been formed.


The heating of a compound prior to molding or casting in order to facilitate the operation or to reduce the molding cycle.

Preheat Roll

In extrusion coating, a heated roll installed between the pressure roll and the unwind roll whose purpose is to heat the substrate before it is coated.


In sheet thermoforming, the distorted printing of sheets before they are formed. During forming the print assumes its proper proportions.

Pre-Production Sample

Hand-trimmed sample of a thermoformed part, submitted to the customer for approval prior to the creation of production fixturing and programming.

Press Polish

A finish for sheet stock produced by contact, under heat and pressure, with a very smooth metal which gives the plastic a high sheen.

Pressure Forming

A thermoforming process wherein pressure is used to push the sheet to be formed against the mold surface as opposed to using a vacuum to suck the sheet flat against the mold.

Pressure Roll

In extrusion coating, the roll with which the chill roll applies pressure to the substrate and the molten extruded web.

Prototype Mold

A simplified mold construction often made from wood (in thermoforming), used to obtain information for the final mold/part design.


Cleaning one color or type of material from the extruder by forcing it out with the new color or material to be used in subsequent production.

Quench Tank Extrusion

The extruded film is cooled in a quench-water bath.

Recycled Plastic

A plastic prepared from used articles which have been cleaned and reground.

Reformulated Plastic

Recycled plastic that has been upgraded to alter or improve performance capability or to change characteristics through use of plasticizers, fillers, stabilizers, pigments, etc.


See Reworked Plastics

Reprocessed Plastic

A thermoplastic prepared from scrap industrial plastic by other than the original processor.


Any of a class of solid or semi-solid organic products of natural or synthetic origin, generally of high molecular weight with no definite melting point. Most resins are polymers.

Reworked Plastic

A thermoplastic from a processor's own production that has been reground or pelletized after having been previously processed by molding, extrusion, etc.


A reinforcing member of a fabricated or molded part.

Rigid PVC

Polyvinyl chloride or polyvinyl chloride/acetate copolymer characterized by a relatively high degree of hardness; it may be formulated with or without a small percentage of plasticizer.

Rockwell Hardness

A common method of testing a plastics material for resistance to indentation in which a diamond or steel ball, under pressure, is used to pierce the test specimen. The load used is expressed in kilograms and a 10-kilogram weight is first applied and the degree of penetration noted. The so-called major load (60 to 150 kilograms) is next applied and a second reading obtained. The hardness is then calculated as the difference between the two loads and expressed with nine different prefix letters to denote the type of penetrator used and the weight applied as the major load.


An elastomer capable of rapid elastic recovery after being stretched to at least twice its length at temperatures from 0 to 150°F, at any humidity. Specifically, Hevea or natural rubber, the standard of comparison for elastomers.


The flow of a molten sheet in a thermoforming operation. Heated plastic sheet will sag prior to forming. The sag distance is often measured by electric eye, and is a good indication of the material's readiness to form.


A small part or portion of a material or product intended to be representative of the whole.

Sandwich Heating

A method of heating a thermoplastic sheet prior to forming which consists of heating both sides of the sheet simultaneously.

Saran Plastic

See Vinylidene Chloride Plastics.


Any product of a molding operation that is not part of the primary product. In thermoforming this is generally trip scrap, and it can be reground and reused.


A close succession of parallel, relatively narrow and sharply defined, wavy lines of color on the surface of a plastic which differ in shade from surrounding areas, and create the impression that the components have separated.

Sheer Strength

(a) the ability of a material to withstand shear stress. (b) the stress at which a material fails in shear.

Sheet (Thermoplastic)

A flat section of a thermoplastic resin with the length considerably greater than the width and 10 mils or greater in thickness.

Sheeter Lines

Parallel scratches or projecting ridges distributed over a considerable area of a plastic sheet.

Sheet Train

The entire assembly necessary to produce sheet which includes extruder, die, polish rolls, conveyor, draw rolls, cutter, and stacker.

Shore Hardness

A method of determining the hardness of a plastic material using a scelroscope. This device consists of a small conical hammer fitted with a diamond point and acting in a glass tube. The hammer is made to strike the material under test and the degree of rebound is noted on a graduated scale. Generally, the harder the material the greater will be the rebound.


Contraction of a part upon cooling.

Shrink Fixture

See Cooling Fixture.


One of the family of polymeric materials in which the recurring chemical group contains silicon and oxygen atoms as links in the main chain. At present these compounds are derived from silica (sand) and methyl chloride. The various forms obtainable are characterized by their resistance to heat. Silicones are used in the following applications: (a) Greases for lubrication, (b) Rubber-like sheating for gaskets, etc. (c) heat-stable fluids and compounds for waterproofing, insulation, etc. (d) Thermosetting insulating varnishes and resins for both coating and laminating.

Slip Additive

A modifier that acts as an internal lubricant which exudes to the surface of the plastic during and immediately after processing. In other words, a non-visible coating blooms to the surface to provide the necessary lubricity to reduce coefficient of friction and thereby improve slip characteristics.

Slip Forming

Sheet forming technique in which some of the plastic sheet material is allowed to slip through the mechanically operated clamping rings during a stretch-forming operation.

Slump Forming

Heat forming of sheet plastic over a mold without the aid of clamping frames or vacuum.

Snap-Back Forming

Sheet forming technique in which an extended heated plastic sheet is allowed to contract over a make from shaped to the desired contours.

Specific Gravity

The density (mass per unit volume) of any material divided by that of water at a standard temperature, usually 4°C. since water's density is nearly 1.00 g./cc., density in g./cc. And specific gravity are numerically nearly equal.

Sprayed Metal Molds

Mold made by spraying molten metal onto a master until a shell of predetermined thickness is achieved. Shell is then removed and backed up with suitable material. Often used in production of high-detail female pressure forming molds.

Stress Crack

An external or internal crack in a plastic caused by tensile stresses less than its short-time mechanical strength.

Stretch Forming

A plastic sheet forming technique in which the heated thermoplastic sheet is stretched over a mold and subsequently cooled.

Surface Treating

Any method of treating a polyolefin so as to alter the surface and render it receptive to inks, paints, lacquers and adhesives such as chemical, flame, and electronic treating.


Exudation of small drops of liquid, usually a plasticizer or softener, on the surface of a plastic part.

Tensile Strength

The pulling stress, in p.s.i., required to break a given specimen. Area used in computing strength is usually the original, rather than the necked-down area.

Thermal Expansion (coefficient of)

The fractional change in length (sometimes volume, specified) of a material for a unit change in temperature. Values for plastics range from 0.01 to 0.2 mils/in., °C.

Thermal Stress Cracking (TSC)

Crazing and cracking of some thermpolastic resins which results from over- exposure to elevated temperatures.


Any process of forming thermoplastic sheet which consists of heating the sheet and pulling it down onto a mold surface.


A specified allowance for deviations in weighing, measuring, etc., or for deviations from the standard dimensions or weight. Often used in reference to dimensions on a print.


Zone of invisible radiations beyond the violet end of the spectrum of visible radiations. Since UV wavelengths are shorter than the visible, their photons have more energy, enough to initiate some chemical reactions and to degrade most plastics.


Having a protuberance or indentation that impedes withdrawal from a mold.

UV Stabilizer (Ultraviolet)

Any chemical compound which, when admixed with a thermoplastic resin, selectively absorbs UV rays.

Vacuum Forming

Method of sheet forming in which the plastic sheet is clamped in a stationary frame, heated, and drawn down by a vacuum into a mold. In a loose sense, it is sometimes used to refer to all sheet forming techniques, including Drape Forming.

Vinyl Chloride Plastics

Plastics based on polymers of vinyl chloride or copolymers of vinyl chloride with other monomers, the vinyl chloride being in greatest amount by mass.

Vinylidene Chloride Plastics

Plastics based on polymer resins made by the polymerization of vinylidene chloride or compoymerization of vinylidene chloride with other unsaturated compounds, the vinylidene chloride being in the greatest amount by weight.

Virgin Material

A plastic material in the form of pellets, granules, powder, flock, or liquid that has not been subjected to use or processing other than that required for its initial manufacture.


In a solid plastic, an unfilled space of such size that it scatters radiant energy such as light. A cavity unintentionally formed in a cellular material and substantially larger than the characteristics of individual cells.


The portion of a substance that is readily vaporized.


Dimensional distortion in a plastic object after molding.


A thin sheet in process in a machine. The molten web is that which issues from the die. The substrate web is the substrate being coated.

Wood Model

A model of part made in wood to assist in the design of a production part.


An imperfection in reinforced plastics that has the appearance of a wave molded into one or more piles of fabric or other reinforcing material.