Plastic Glossary

Aesthetics – The sum total of the visual response to the beauty of an object. Elements of aesthetics may include: color, shape or particular features of the object.

Aging – The physical and/or chemical change of a material with respect to time, under defined environmental conditions, leading to improvement or deterioration of properties.

Amber – A chromatic (brown) color of glass or plastic containers. It is used principally to protect the contents of the container from exposure to light.

Antioxidant – A chemical substance added to a plastic resin to minimize or prevent the effects of oxygen attack on the plastic, e.g., yellowing or degradation. Chemical attacks by oxygen can render a plastic brittle or cause it to lose desired mechanical properties.

Antistatic Agent – A chemical substance applied to the surface of a plastic article or incorporated in the plastic from which the article is made. The antistatic agent renders the surface of the plastic article less susceptible to the accumulation of electrostatic charges which attract and hold fine dirt or dust on the surface of the plastic article.

Barrier Resins – A group of resins specially formulated to resist the transmission of oxygen, water, solvents, essential oils, etc.

Blow Molding – A method of fabrication in which a warm plastic parison (hollow tube) is placed between the two halves of a mold (cavity) and, by using air pressure, the parison is forced to assume the shape of the cavity. The air pressure is introduced through the inside of the parison. The air pressure forces the plastic against the surface of the mold that defines the shape of the container.

Buttress Thread – A design of thread profile (cross section) which takes the form of a truncated triangle or slight modification of that form. It is usually positioned so the right angle is at the bottom of the thread cross section and adjacent to the neck of the bottle finish. The horizontal leg of the right triangle is the bearing surface for a matching cap thread. It is designed to withstand maximum force in one direction only.

Capacity – (1) The amount of space provided inside a container for a given amount of product. (2) The total amount of volume inside the container. The latter is more correctly called the overflow capacity.

Clarity – Freedom of haze or cloudiness in a plastic material.

Closure – A devise used to seal off the opening of the bottle to prevent the loss of its contents.

Color Concentrate – A measured amount of dye or pigment incorporated into a predetermined amount of plastic. This pigmented or colored plastic is then mixed into larger quantities of plastic material used for molding. The “concentrate” is added to the bulk of plastic in measured quantity in order to produce a precise, predetermined color of the molded bottles.

Continuous Thread – An uninterrupted protruding helix on the neck of a container used to hold a screw-type closure.

Copolymer – A material whose chemical structure is made of long chains of two differently structured chemical units (Monomers) which repeat a more or less regular pattern in the chain.

Deflashing – Any technique or method removing excess unwanted material from a molded article. Specifically, the excess material is removed from places on the article where parting lines of the mold that formed the article may have caused the excess material to be formed.

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

Drop Test – Any test method in which the article being tested is dropped in a specified manner for a specified number of times or until the article fails from impact.

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

“E” Dimension – The outside diameter of neck on a threaded bottle neck (finish). The diameter of the neck (finish) is measured across the root of the threads.

Environmental Stress Cracking (ESC) – The susceptibility of a thermoplastic article to cracking under the influence of certain chemicals and stress.

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

Fill Point – The level to which a container must be filled to furnish a designated quantity of the contents.

Finish – The plastic forming the opening of a container and shaped to accommodate a specific closure.

Fitment – A device used as part of a closure assembly to accomplish a certain purpose such as, dropper, sprinkler, powder shakers, etc.

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

Flash – The extra plastic attached to a molding along the parting line. The flash must be removed before the parts can be considered literally finished.

Fluorination – Is an extra process in which a thermoplastic article (container or closure) is exposed to fluorine gas. The fluorine substitutes with some hydrogen atoms in the polymer chain creating a barrier and surface enhancement. Benefits include improved barrier properties and reduced solvent absorption and permeation.

“H” Dimension – The height of the bottle finish measured from the sealing surface, in a line parallel to the axis of the finish and tangent to the threads on the finish, down to a point where the line intersects the body (shoulder) of the container. The inside height of the closure measured from the bottom of the closure, in a line tangent to the threads of the closure and terminating at the inside, top of closure.

HDPE – An abbreviation for High Density Polyethylene.

Head Space – The space between the fill level of a container and the sealing surface.

Heel – The part of a bottle between the bottom bearing surface and the side wall.

Hygroscopic – Tending to absorb moisture.

“I” Dimension – A specified minimum diameter inside the bottle neck. A minimum diameter is specified to allow sufficient clearance for filling tubes to enter the bottle neck easily.

“I.D.” – An abbreviation for Inside Diameter.

Impact Resistance – Relative susceptibility of plastics to fracture by shock. Impact resistance is indicated by the energy expended by a standard pendulum type impact machine in breaking a standard specimen in one blow.

Injection Blow Molding – A blow molding process in which the parison to be blown is formed by injection molding.

Injection Molding – A molding procedure whereby a heat-softened plastic material is forced from a cylinder into a relatively cool cavity giving the article the desired shape.

Injection Molds – A mold into which a plasticated material is introduced from an exterior heating cylinder.

“L” Dimension – The vertical distance from the sealing surface to the top part of neck bead, i.e., where the uppermost part of the bead intersects the container neck.

“L” Style Thread – A type of thread contour (cross-section) roughly trapezoidal in outline. The outermost part is radiussed a “general purpose” thread contour designed for use with metal or plastic closures.

Light Resistance – The ability of a plastic material to withstand exposure to light, usually sunlight or the ultraviolet part of the light spectrum, without change of color or loss of physical and/or chemical properties.

Lug – (1) A type of thread configuration designed so the thread segments are disposed equidistantly around a bottle neck (finish). The closure has matching portions that engage each of the thread segments (2) A small indentation or raised portion on the surface of a container. The lug provides a means of indexing the container for operations such as multi-color decoration or labeling.

Mil – A unit of measurement equal to .001 inch.

Minimum Wall – A term designating the minimum thickness of the wall of a bottle.

Moisture Vapor Transmission Rate (MVTR) – The rate at which water vapor permeates through a plastic film or bottle wall at a specified temperature and at relative humidity.

Mold – The cavity or matrix into which the plastic composition is placed and from which it takes its form.

Mold Seam – A vertical line formed at the point of contact of the mold halves. The prominence of the line depends on the accuracy with which the mating mold halves are matched.

Multi-layer bottle - A bottle that is co-extruded with two or more layers to contain oxygen sensitive foods or industrial chemicals.

Narrow Mouth – A finish of a plastic container in which the diameter is small relative to the diameter of the body.

Neck – The part of a container where the shoulder cross section area decreases to form the finish.

Offset Printing – A printing technique in which ink is transferred from a reservoir to a printing plate. For the ink printing plate, the image is printed on a cylindrical rubber roll (blanket) and then to the object to be printed.

Opaque – A term describing a material or substance which will not transmit light.

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

Overflow Capacity – The capacity of a container to the top of the finish or to the point of overflow.

Paneling – Distortion, side wall collapse of a container occurring during aging or storage. Paneling is caused by the development of a reduced pressure inside the bottle.

Parting Line – A mark on a molding or casting where the halves of mold meet in closing.

Permeability – (1) The passage or diffusion of a gas, vapor, liquid, or solid through a barrier without physically or chemically affecting it. (2) The rate of such passage.

PET (Polyethylene Terephthalate) – Known as thermoplastic polyester. PET has the unusual ability to exist in either an amorphous or highly crystalline state. The crystalline state is necessary for extruding the material. The amorphous state permits it to be oriented.

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

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

Polypropylene – A tough, light-weight 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 (vinyl benzene).

Polyvinyl Chloride (PVC) – A thermoplstic material composed of polymers of vinyl chloride. PVC is a colorless solid with outstanding resistance to water, alcohols, and concentrated acids and alkalies

Pour-Out Finish – A container finish having uniform undercut lips as a sealing surface. The pour-out finish is designed to facilitate pouring without dripping.

Preform – Used in the blow molding processes. A heat-softened polymer is formed into a shape similar to a thick test tube with neck threads. This tube is subsequently inflated while inside a blow mold to create the shape of the desired article.

Programming – The extrusion of a parison which differs in thickness in the length direction in order to equalize wall thickness of the blown container. It can be done with a pneumatic or hydraulic device which activates the mandrel shaft and adjusts the mandrel position during parison extrusion (parison programmer, controller, or variator). It can also be done by varying extrusion speed on accumulator-type blow molding machines.

Push-Up – The recessed area on the bottom of a bottle designed to allow an even bearing surface on the outside edge to prevent the bottle from rocking.

“S” Dimension – Locates the position of the bottle thread with respect to the sealing surface. The “S” dimension is the vertical distance from the sealing surface to the intersection of the finish wall and the top part of the first part of bottle thread where full depth contour exists.

Screen Printing (ACL) – A printing technique involving the passage of printing medium, such as ink, through a web or fabric, which has been stretched on a frame, to which a refined form of stencil has been applied. The stencil openings determine the form and dimensions of the imprint thus produced.

Sealing Surface – The lip portion of the finish that makes contact with the sealing gasket or liner to form a seal.

Shrinkage – The change in dimension (decrease) a molded article undergoes after being molded. Shrinkage is caused by cooling and subsequent contraction of the plastic material.

Surface Treating – Any method of treating a plastic to alter the surface and render it receptive to inks, paints, lacquers and adhesives. Examples of surface treating are chemical, flame, or electronic treating.

“T” Dimension – The outside diameter of the thread helix on a bottle finish.

Thermoplastic – (a) Capable of being repeatedly softened by heat and hardened by cooling. (b.) A material that will repeatedly soften when heated and harden when cooled. Typical of the thermoplastics family are the styrene polymers and copolymers, acrylics, cellulosics, polyethylenes, vinyls, nylons, and the various fluorocarbon materials.

Top Load – The amount of weight bearing on the top of a container. The term is sometimes used to indicate the maximum load the container will bear without becoming distorted.