|
Home
PET, the
abbreviation for Polyethylen-terephthalat, is fully recycable and may be
used for manufacturing new products in many industrial areas such as
packaging for detergents, cosmetics, high-quality carpets, foils, car
spare parts, pillow fillings for allergic persons and fabrics. Its
versatility in the many industries therefore makes it unreplacable.
Being a polymer, polyethylene terephthalate's molecules consist of long
chains of repeating units only containing the carbon (C), oxygen (O) and
hydrogen (H) organic elements.
PET was
first developed for use in synthetic fibres by British Calico Printers in
1941. The patent rights were then sold to DuPont and ICI who in turn sold
regional rights to many other companies.(1)
Although originally produced for fibres, PET began to be used for
packaging films in the mid 1960s and then, in the early 1970s, the
technique for blowing bi-axially oriented bottles was commercially
developed.
Bottles
now represent the most significant use of PET moulding resins.
Making
a PET bottle starts from the raw material: ethylene and paraxylene. These
two substances' derivatives (ethylene glycol and terephthalic acid) are
made to react to obtain the PET resin. The resin, in the shape of small
cylinders called pellets, is melt and injected into a mould to make a
preform. The preform, a sort of test tube shorter than what the bottle
will be but with thicker walls, is then blow-moulded. During the blow-moulding
phase, high-pressure air is blown into the preform allowing it to take the
exact shape of the mould it is set into. The final product is a
transparent, strong and lightweight bottle.
It is
the strength of the material that contibutes to make PET the success it
is. Indeed, carbonated soft drinks can generate pressure inside the bottle
reaching up to 6 bar. Such high pressure however, thanks to the alignment
of macromolecules (cristallisation) occurring both during the resin
spinning process and the blow-moulding process, is not capable of
deforming the bottle nor can it make the bottle explode.
Throughout
the years, the PET industry has increasingly taken on environmental
concerns, significantly decreasing the quantity of raw material needed for
the manufacture of bottles. Nowadays, a 1.5 liter PET container is
manufactured with just 35 grams of raw material!
Another
striking feature of PET on the environmental side is that it is fully
recyclable. It was in 1977 that the first PET bottle was recycled and was
turned into a bottle basecup. Soon however, the fiber industry discovered
the "new" material source and started using it for making
textiles, carpets and non-woven. Today, even though the "bottle to
bottle" recycling process is growing, the fiber market is still the
major outlet for recovered PET.
PET
containers form part of everyone's daily life: they contain water and soft
drinks but many other sorts of liquids as well, such as detergents or
soap.
The
main reasons lying behind the success of PET containers is that, thanks to
the molecular structure of the material set into a web, it is unbreakable.
What is more, PET packaging is lightweight, transparent and resealable.
Another
advantage of the material lies in its physical properties that allow for
great freedom in design.
(1)
Neumann, E H. Thermoplastic polyesters in Encyclopedia of Packaging
Technology, ed Bakker M. John Wiley, New York 1986
Up
The torque force, measured
in inch-pounds, required to screw a closure onto a container.
Applicator Cap
A closure designed to apply
the contents of the container.
Back-Off
A term used to denote
relaxation of forward thrust, i.e. loss of torque following application of
the closure. Back-off can be affected by top loading, compressibility and
resiliency of the closure liner, consistency of application torque, and
mechanical interaction of the closure and bottle.
Backing Liner
A compressible material,
usually pulp or foamed polyethylene, to which the facing liner is attached
or adhered. This compressible material compensates for any irregularities
on the sealing surface.
Band
That portion of the closure
that releases when the closure is removed from a bottle. The band is used
for tamper indication.
Bead
A depressed or raised circle
or ring around a container or closure.
Binding
Excess drag when the closure
is applied to the bottle. Binding is usually the result of interference.
Bottoming-Out
A condition where the bottom
skirt of the closure makes contact with the container (usually the
shoulder or transfer bead) before the land area of the container and the
closure (lined or linerless) create a seal.
Cavitation
The number of molding
stations within a mold.
Cavity
A mold component which forms
the exterior or external surface of the closure.
Cellulose Band
A band made of hydrated
cellulose film extruded in continuous tubing form. The cellulose tubing is
then processed and printed in this form and cut into individual bands of
predetermined lengths. The celon is allowed to air dry when it is applied
to the finish of the container. During the air-drying period, the
cellulose band shrinks to form a skin-tight film over the finish of the
bottle.
Center Gated Mold
A mold in which the cavity
is filled with resin through an orifice interconnecting the nozzle and the
center of the cavity area.
Child Resistant Closure
(Abbreviated “CR")
A closure requiring
dissimilar motions making removal by a child difficult. Child Resistant
closures are subject to current government regulations.
Chucks
A component of a capping
machine which holds the closure for application to the container.
Closure
Any structure or device
designed to close off the opening of a container and prevent loss of its
contents.
Closure Lining Machine
A high speed, specialized
machine using a punch’s die or specialized cutters to automatically cut
and insert liners into closures.
Closure Height
The overall height of the
closure proper. Closure height is measured from the closure top to the
open end of the closure. Closure height can be considered in terms of
“inside height or outside height".?
Closure Removal Torque
The amount of force
necessary to loosen, open, or remove a closure from a bottle.
Closure Skirt
The vertical wall of a
closure.
Closure Stripping Torque
The amount of force required
to cause the closure and/or bottle finish to distort and override the
matching closure-bottle threads.
Cocking
Mis-application of a closure
to a container. The closure’s appearance is uneven on the container or
it is pulled off to one side, due to an uneven downward pull of threads.
Cocking is normally caused by over torquing.
Compression Molding
A molding process whereby
thermoset plastic material is dropped into a cavity and formed under
pressure by a force. The process is primarily done on a rotary molding
machine.
Continuous Thread Closure
(Abbreviated “CT")
A non-interrupted spiral
design threaded closure. The main purpose of a CT closure is to mate with
corresponding bottle threads and provide sealing and re-sealing of the
container.
Core
A mold component which forms
the internal surface of the closure. The core also includes the threads.
Curl
A tubular structure formed
at the open end of a metal closure to provide a smooth, strong edge. The
curl facilitates automatic handling of the closure.
Cycle
The sequence of operations
in a process to complete one set of parts. The cycle is taken at a point
in the operation and ends when this point again starts.
Cycle Time
The time during which one
molding cycle is completed. Cycle time comprises injection of melt, cure,
recovery, part ejection, and clamping for next shot.
Deep Screw Cap
A cap having a deeper skirt
(more “H? and generally a heavier thread than the 400 finish series.
Dispensing Closure
A snap on or threaded
closure which allows for product dispensing, and usually resealing,
without removing the closure from the package.
Dome
A closure which has a
rounded top surface.
Dropper Cap
A closure that includes an
attached dropper and rubber bulb.
“E" Dimension
The smaller diameter of the
inside of the closure measured “thread to thread." The “E"dimension
corresponds to the “E" (outside wall) of the container. See the Cap
and Neck Finishes page for more information.
Facing Liner
The liner material attached
or adhered to the backing liner. The facing acts as a barrier to the
chemical reaction of the product.
Finish
The configuration of a
container top shaped to accommodate a closure.
Fitment
A plastic component that
snaps over the land area and functions as an orifice reducer or blocker.
Flash
Excessive undesirable
plastic materials on containers or closures formed along mold seams or
parting lines. Flash results from plastic flowing into the clearance
between mold components.
Flowed-in
A method of applying fluid
sealing compounds with a nozzle.
Friction cap
A closure held on by
friction upon application to the container, building up resistance to the
movement of the closure.
G-cap (G-450)
A 70 millimeter cap with a
deep screw threaded skirt (450).
Gasket
A liner applied between the
sealing surface of container lip and closure. A gasket provides the
ultimate seal.
Gate
An orifice through which the
molten resin enters the cavity. A gate is the small restricted opening
connecting the runner to the cavity.
GPI
Glass Packaging Institute
“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
“H?dimension is also the inside height of the closure, measured from the
bottom of the closure, in a line tangent to the threads of the closure,
terminating at the inside, top of the closure. The “H?dimension does not
include any liner (if used), or “linerless?seal, ribs, membranes, or any
other sealing element dimensions. See the Cap and Neck Finishes page for
more information.
“I" Dimension
The diameter of the opening
of the container measured from the inside wall to the inside wall. See the
Cap and Neck Finishes page for more information.
Induction Seal Liners
A specialized laminate
containing aluminum foil and a plastic heat sealable film which
hermetically seals a container through use of an “Induction Capsealing
Machine.?
Inner Seal
An additional seal of
moisture proof material applied to the top of container prior to or during
the application of the closure.
Interference
A condition where an
exterior diameter in the finish area of the bottle is larger than the
mating interior diameter of the closure.
Internal Threads
The threads on the interior
of the closure.
Interrupted Threads
Non-continuous threads on
the closure causing gaps. Interrupted threads are normally used in
beverage closures thread on (neck) finish of bottles in which the thread
has gaps or discontinuities. The gaps are at the parting line of the mold.
Injection Mold
A mold into which a
plasticated material is introduced from an exterior heating cylinder.
Injection Molding
A process by which a
plasticized material is forced into a mold.
Knurl
The indented or crimped
portion on the skirt at the top of the cap used for holding the liner in
the cap. The knurl is also used as a grip for removing the cap. The knurl
provides a non-skid surface during the threading operation.
“L" Dimension
The vertical distance from
the sealing surface to top part of neck bead, i.e., where the upper most
part of bead intersects the container neck.
Land
The lip of the container to
which the closure liner or land seal linerless feature compresses or
conforms to tolerance.
Land Seal
A sealing device which seals
by applying pressure to the top or land of the container finish.
Liner
A disk of paper, cork, foam,
plastic, etc., retained in a closure to provide a flexible barrier between
the closure and the sealing surface of the container.
Liner Well
The space provided in a
closure for a liner.
Linerless Closure
A thermoplastic closure
incorporating a molded-in sealing feature which, when applied to a
container with the appropriate finish, seals most liquids within the
container.
Lug Cap
A closure with raised
internal impressions that inter-mesh with identical threads on the finish
of container.
Matte Finish
A coating surface that
displays no gloss when observed at any angle. Matte finish is also
referred to as a “flat finish.?
Mechanical Breakaway Bands
A closure with a portion or
section of the skirt perforated or weakened in some manner so when the
closure is opened, the section is designed to break apart and either
remain on the container or attach to the closure to indicate the package
has been opened.
Metallizing
Applying a thin coating of
metal to a non-metallic surface. Metallizing can be done by chemical
deposition or by exposing the surface to a vaporized metal in a vacuum
chamber.
Modified Buttress Thread
Commonly referred to as
“M?style. The modified buttress thread was developed, with a 10 degree
pressure angle, to offer more closure-to-bottle thread contact.
Mold
The combination of mold
frame and tooling components needed to form a closure.
Mold Frame
The plates and components
required to direct plastic to the tools that form closures and remove the
closures from the mold.
Molding (compression)
A process of shaping or
forming material through the use of molds, heat, and pressure.
Molding (injection)
A process of shaping or
forming plastic objects from powder or granule form in a mold by cooling
the previously heated plastic.
Mouth
The open end of the cap
opposite the top.
Neck
The part of a container
where the shoulder cross section area decreases to form the finish.
Neck Rings
That part of the mold
equipment which forms the finish of the bottle.
Non-Threaded
Designates items which do
not require threading action when applied to glass or plastic containers.
Examples of non-threaded closures are snap caps, sifter fitments, pour-out
fitments, etc.
“O.D."
The abbreviation for Outside
Diameter.
Offset Neck
The vertical axis of the
neck finish is off center from the vertical axis of the container.
Orifice
An opening in a plug,
fitment, or dispensing cap through which the product is dispensed.
Overseal
An additional closure that
tamper-proofs the primary closure. The overseal is usually made of foil or
aluminum.
Phenolic
A type of thermoset plastic.
Pipette
The glass or plastic tube
portion of a medicinal dropper closure.
Pitch
The number of turns a thread
would circle a neck if the neck were extended one inch. Pitch is commonly
referred to as threads per inch. (T.P.I.)
Plastisol
A liquid mixture of resins
and plasticizers solidified by the application of heat.
Pour-out Finish
A bottle finish having
uniform undercut lips. The pour-out finish is designed to facilitate
pouring without dripping.
Removal Torque
The torque force, measured
in inch-pounds, required to unscrew a closure from a container.
“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.
Sealing Surface
The lip portion of the
finish which makes contact with the sealing gasket or liner and forms a
seal.
Shell
The hat shaped, preliminary
form of a metal closure prior to being threaded and knurled.
Shrink Factor
The change in dimension
which a closure undergoes after being molded. Shrinking is generally
caused by cooling and subsequent contraction of the plastic material.
Sifter Fitment
A plastic component of a
package designed to allow the shaking out of dry products, such as a table
salt shaker. The sifter fitment snaps over the glass bead with a metal or
a plastic cap applied over the fitment.
Skirt
The vertical wall of a
closure.
Snap Fit Closure
A closure held in place
through the use of beads or undercuts rather than threads.
SPI
Society of Plastics Industry
Spout Cap
A closure designed to
facilitate the pouring of the contents of the container.
Stacker Cap
A closure designed
specifically to nest with the bottom plate of a container to facilitate
the stacking of filled containers one on top of each other.
Stress Crack
An external or internal
crack in the plastic caused by tensile stress less than that of its
short-time mechanical strength. The development of such cracks is
frequently accelerated by the environment to which the plastic is exposed.
The stresses which cause cracking may be present internally or externally
or may be combinations of these stresses. The appearance of a network of
fine cracks is crazing.
Stripping Torque
The amount of application
torque that causes the threads of the closure to override the container
threads.
“T?Dimension
The major diameter of the
thread on a Continuous Thread. closure. See the Cap and Neck Finishes page
for more information.
T.P.I.
See Pitch.
Tamper Band
The tamper-evident feature
of the closure. The tamper band is usually connected to the closure skirt
by leaders or bridges.
Tamper Evident Breakaway
Band Closure
The section of the closure
skirt that is weakened or perforated in some manner. When the closure is
opened that section is designed to either remain on the container or stay
partially attached to the closure. The tamper evident breakaway band
closure is designed to reveal removal of the closure was attempted.
Tamper Evident Closure
A closure or liner system
incorporating a feature that visually indicates if the closure has been
removed or the product has been exposed. Removal of the closure or liner
system activates the indicating feature.
Tamper Evident Tear Band
A closure with a band,
usually with a tab for grasping, designed to be detached by the consumer.
The tamper evident tear band is designed to reveal removal of the closure
was attempted.
Thermoplastic
A plastic material that
repeatedly softens when heated and hardens when cooled.
Thermoset
A material that will undergo
or has undergone a chemical reaction by the action of heat, catalysts,
ultraviolet light, etc., leading to a relatively infusible and
cross-linked state. Typical of the plastics in the thermosetting family
are the epoxies, glytals, melamines, urea formaldehyde resins, and
phenolics. Thermosets are typically supplied in powder, granules, or
modules, and are normally processed by compression molding. Thermosets
cannot be remolded once processed.
Thread
Complimentary, helical
protrusions on the closure and the container.
Thread Profile
The cross section
configuration of a closure thread.
Thread Engagement
The actual contact made by
the closure and bottle finish thread. Thread engagement is usually
specified in number of turns.
Thread Start
The position at which the
full thread depth toward the open end of the closure first occurs.
Thread Turns
The measurement of thread
revolutions in a closure or on a container finish.
Tinplate
A thin sheet of steel with a
layer of tin used in manufacturing metal closures.
Tolerance
The permissible maximum
deviation from specified dimensions, quantities, or specifications. The
amount of variation allowed from the nominal dimension.
Tooling
The specific components in
contact with the plastic that form the closure.
Top Load
The amount of weight bearing
on the top of a package.
Torque
The rotational movement used
during application or removal of a continuous thread closure from a
container.
Torque Meter
A devise used to measure
application and removal torque. It is expressed in pound-force inches and
commonly referred to as “inch-pounds."
Unlined Closure
A closure without a liner
disk inserted, but designed to accept one.
Valve Cap
A closure that includes a
valve to regulate the flow of the product from the container.
Value Seal
A sealing devise which seals
on the inside of the neck finish of the container in the fashion of a
plug. A controlled inside finish diameter is required to accomplish a
seal.
|
