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of Terms
Alloy
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.
Annealing
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.
Bakelite
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.
Banbury
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.
Bleed
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.
Blister
A raised area on the surface of a molding caused by the pressure of gases
inside it on its incompletely hardened surface.
Bloom
A visible exudation of efflorescence on the surface of a material.
Blueing
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.
Boss
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.
Butadiene
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.
Calender
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.
Cast
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.
Cavity
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.
Celluloid
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.
Cellulose
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.
Chalking
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.
Clearance
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.
Conveyor
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.
Crazing
Fine cracks which may extend in a network on or under the surface or
through a layer of a plastic material.
Creep
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.
Cross-Linking
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.
Crystallinity
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.
Cycle
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.
Degradation
A deleterious change in the chemical structure of a plastic.
Delamination
The separation of the layers in a laminate caused by the failure of the
adhesive.
Density
Weight per unit volume of a substance, expressed in grams per cubic centimeter,
pounds per cubic foot, etc.
Desiccant
Substance which can be used for drying purposes because of its affinity
for water.
Destaticization
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.
Discoloration
Any change from the original color, often caused by overheating, light
exposure, irradiation, or chemical attack.
Draft
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.
Dyes
Synthetic or natural organic chemicals that are soluble in most common
solvents. Characterized by good transparency, high tinctorial strength,
and low specific gravity.
Elastomer
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.
Elongation
The fractional increase in length of a material stressed in tension.
Embossing
Techniques used to create depressions of a specific pattern in plastics
film and sheeting.
Encapsulating
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.
Extender
A substance generally having some adhesive action, added to a plastic
composition to reduce the amount of the primary resin required per
unit area.
Extrudate
The product or material delivered by an extruder, such as film, pipe,
the coating on wire, etc.
Extrusion
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.
Fabricate
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.
Female
In molding practice, the indented half of a hold designed to receive
the male half.
Film
An optional term for sheeting having a nominal thickness not greater
than 0.010 inch.
Finish
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.
Flake
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.
Flammability
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.
Flock
Short fibers of cotton, etc., used as fillers for molding materials.
Flocking
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.
Gate
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.
Gel
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.
Gloss
The shine or luster of the surface of a material.
Haze
The degree of cloudiness in a plastics material.
Heat-Deflection Temperature
The temperature at which a standard test bar (ASTM D648) deflects 0.010
in. under a stated load of either 66 or 264 p.s.i.
Heat-Sealing
A method of joining plastic films by simultaneous application of heat
and pressure to areas in contact. Heat may be supplied conductively
or dielectrically.
Homopolymer
A polymer, consisting of (neglecting the ends, branch junctions, and
other minor irregularities) a single type of repeating unit.
Hopper
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.
Hydraulic
A system in which energy is transferred from one place to another by
means of compression and flow of a fluid.
Hygroscopic
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.
Inhibitor
A substance that slows down chemical reaction. Inhibitors are sometimes
used in certain types of monomers and resins to prolong storage life.
Insert
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.
Instron
An instrument utilized to determine the tensile and compressive properties
of material.
Interlock
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.
Jig
Tool for holding component parts of an assembly during the manufacturing
process, or for holding other tools. Also called a Fixture.
Kirksite
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.
Laminate
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.
Lay-Up
(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.!
Lip
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.
Masterbatch
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 inch orifice when subjected to 2160 gms. Force in 10 minutes
at 190 degrees 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.
Mold
(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.
Monomer
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.
Nylon
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.
Olefins
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.
Opaque
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.
Orange-Peel
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.
Orientation
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.
Pellet
A small ball or spherical shape.
Pelletizing
A process of producing pellets.
Permeability
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.
Pigment
Any colorant, usually an insoluble powdered substance used to produce
a desired color or hue.
Pinhole
A very small hole in the extruded resin coating.
Pit
An imperfection, a small crater in the surface of the plastic, with its
width of approximately the same order of magnitude as its depth.
Plastic
(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.
Plasticize
To soften a material and make it plastic or moldable, either by means
of a plasticizer or the application of heat.
Plasticizer
Chemical agent added to plastic compositions to make then softer and
more flexible.
Platens
The mounting plates of a press to which the entire mold assembly is bolted.
Pleat
A thermoforming defect where plastic gathers around a prominent part
feature.
Plug-And-Ring
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.
Polyester
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.
Polyethylene
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.
Polymer
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.
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
of the original substance. When two or more monomers are involved,
the process is called copolymeriztion or heteropolymerization.
Polyolefin
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.
Polypropylene
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.
Polystyrene
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.
Postforming
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.
Preheating
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.
Preprinting
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.
Purging
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.
Regrind
See Reworked Plastics
Reprocessed Plastic
A thermoplastic prepared from scrap industrial plastic by other than
the original processor.
Resin
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.
Rib
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.
Rubber
An elastomer capable of rapid elastic recovery after being stretched
to at least twice its length at temperatures from 0 to 150 degrees
F, at any humidity. Specifically, Hevea or natural rubber, the standard
of comparison for elastomers.
Sag
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.
Sample
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.
Scrap
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.
Segregation
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.
Shrinkage
Contraction of a part upon cooling.
Shrink Fixture
See Cooling Fixture.
Silicone
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 degrees 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.
Sweating
Exudation of small drops of liquid, usually a plasticizer or softener,
on the surface of a plastic part.
Tensile Strength
The pulling stress, in psi, 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., degree C.
Thermal Stress Cracking (TSC)
Crazing and cracking of some thermpolastic resins which results from
over- exposure to elevated temperatures.
Thermoforming
Any process of forming thermoplastic sheet which consists of heating
the sheet and pulling it down onto a mold surface.
Tolerance
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.
Ultraviolet
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.
Undercut
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.
Voids
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.
Volatiles
The portion of a substance that is readily vaporized.
Warpage
Dimensional distortion in a plastic object after molding.
Web
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.
Wrinkle
An imperfection in reinforced plastics that has the appearance of a wave
molded into one or more piles of fabric or other reinforcing material.
