Stretch wrap or stretch film is a highly stretchable
plastic film
Plastic film is a thin continuous polymeric material. Thicker plastic material is often called a "sheet". These thin plastic membranes are used to separate areas or volumes, to hold items, to act as barriers, or as printable surfaces.
Plas ...
that is wrapped around items. The elastic recovery keeps the items tightly bound. In contrast,
shrink wrap
Shrink may refer to:
Common meanings
*Miniaturization
*Shrink, a slang term for:
** a psychiatrist
** a psychoanalyst
** a psychologist
Arts, entertainment, and media
* ''Shrink'' (album), album by German indie rock/electronica group The Notwist
...
is applied loosely around an item and shrinks tightly with heat. While it is visually similar to
plastic food wrap, it is not usually made of material rated as safe for
food contact.
It is frequently used to secure pallet loads to one another but also may be used for bundling smaller items. Types of stretch film include bundling stretch film, hand stretch film, extended core stretch film, machine stretch film and static dissipative film.
Materials
The most common stretch wrap material is
linear low-density polyethylene
Linear low-density polyethylene (LLDPE) is a substantially linear polymer (polyethylene), with significant numbers of short branches, commonly made by copolymerization of ethylene with longer-chain olefins. Linear low-density polyethylene differs s ...
(LLDPE), which is produced by
copolymerization
In polymer chemistry, a copolymer is a polymer derived from more than one species of monomer. The polymerization of monomers into copolymers is called copolymerization. Copolymers obtained from the copolymerization of two monomer species are some ...
of
ethylene
Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds).
Ethylene i ...
with
alpha-olefin
In organic chemistry, alpha-olefins (or α-olefins) are a family of organic compounds which are alkenes (also known as olefins) with a chemical formula , distinguished by having a double bond at the primary or alpha (α) position.''Petrochemical ...
s, the most common of which are
butene
Butene, also known as butylene, is an alkene with the formula . The word ''butene'' may refer to any of the individual compounds. They are colourless gases that are present in crude oil as a minor constituent in quantities that are too small for ...
,
hexene
In organic chemistry, hexene is a hydrocarbon with the chemical formula . The prefix "hex" is derived from the fact that there are 6 carbon atoms in the molecule, while the "-ene" suffix denotes that there is an alkene present—two carbon atom ...
and
octene
Octene is an alkene with the formula . Several isomers of octene are known, depending on the position and the geometry of the double bond in the carbon chain.
The simplest isomer is 1-octene, an alpha-olefin used primarily as a co-monomer in pr ...
. The use of higher alpha-olefins (hexene or octene) gives rise to enhanced stretch film characteristics, particularly in respect of elongation at break and
puncture resistance
Puncture resistance denotes the relative ability of a material or object to inhibit the intrusion of a foreign object. This is defined by a test method, regulation, or technical specification. It can be measured in several ways ranging from a s ...
. Other types of
polyethylene
Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging ( plastic bags, plastic films, geomembranes and containers including bo ...
and
PVC can also be used. Many films have about 500% stretch at break but are only stretched to about 100 – 300% in use. Once stretched, the elastic recovery is used to keep the load tight.
There are two methods of producing stretch wrap:
*Blown: the resin is melted and extruded through an annular die, it is air-cooled. This is a slower process but provides for higher cling quality. Blown film is not a consistent extrusion process, leading to inconsistencies across the film web. The cost of production is also higher due to the quantity that can be produced per hour.
*Cast: the film is extruded through a slot die, then passed over cooling rollers. This makes the cooling process quick. Cast films are more consistent and have better performance characteristics. The cling quality is not as good as blown but more can be produced in an hour with lower costs.
Other properties such as break strength, cling, clarity, tear resistance,
static discharge
Electrostatic discharge (ESD) is a sudden and momentary flow of electric current between two electrically charged objects caused by contact, an electrical short or dielectric breakdown. A buildup of static electricity can be caused by tribochargin ...
, etc. are also important.
Functions
In
pallet
A pallet (also called a skid) is a flat transport structure, which supports goods in a stable fashion while being lifted by a forklift, a pallet jack, a front loader, a jacking device, or an erect crane. A pallet is the structural foundat ...
unitizing, stretch wrap can have several functions:
* improved stability of products or packages, forming a
unit load
The term unit load refers to the size of an assemblage into which a number of individual items are combined for ease of storage and handling, for example a pallet load represents a unit load which can be moved easily with a pallet jack or forkli ...
* more efficient handling and storage of unit loads
* some degree of dust and moisture protection
* some degree of
tamper resistance
Tamperproofing, conceptually, is a methodology used to hinder, deter or detect unauthorised access to a device or circumvention of a security system. Since any device or system can be foiled by a person with sufficient knowledge, equipment, and ti ...
and resistance to
package pilferage
Package pilferage is the theft of part of the contents of a package. It may also include theft of the contents but leaving the package, perhaps resealed with bogus contents. Small packages can be pilfered from a larger package such as a shippin ...
* some degree of sun protection (UV stretch wraps)
Making sure boxes stay on the pallet and properly aligned is an important consideration in warehouse distribution, especially as the demands for increased throughput continues to rise.
Applications
Categories and sub-categories of stretch wrappers:
''Manual'' (or ''Hand'') ''Wrappers:''
* ''
Extended core:'' An extension of the film's core serves as a handle for wrapping; this type of wrapper offers little stretch control and is hard on hands.
* ''
Mechanical brake:'' A simple structure supports a film roll and a mechanical brake system provides resistance creating stretch of the film.
* ''Pole wrappers:'' Similar to the ''mechanical brake'' system, but the roll and brake are at the end of an extended pole, creating an ergonomic design which eliminates the need to bend to wrap the bottoms of loads and strain to reach the tops of loads.
*''Prestretch hand wrappers.'' One-hand-operated wrapping tool with a mechanical pre stretch achieved by 2 guiding rollers for the stretch film with different speeds.
''Semi-Automatic Wrappers:''
* ''
Turntable wrappers:'' The load to be wrapped sits on a turntable which spins the load relative to the film roll, which is housed in a carriage which can move up and down a fixed "mast". Stretch is achieved by rotating the load at a faster rate than the film is fed.
* ''
Orbital wrappers:'' The film is housed in a carriage on a vertical ring, the load is fed horizontally through the eye of the rotating ring, applying film to the load. A variation of an orbital stretch wrapper is a horizontal ring system, in which the load remains still while a horizontal ring is rotated around the load and moves up and down vertically relative to the load, similar to a rotary arm stretch wrapper.
* ''Rotary arm wrappers:'' In this system, the load remains still while a rotating arm turns around it wrapping the load. This system is used for light loads or for speeds which would otherwise cause the load to topple due to high rotation speeds.
''Automatic Wrappers:''
Automatic wrappers are generally a variant of a semi-automatic system. Automatic wrappers include a conveyor system to automatically load the wrapping machine and automatic systems to apply, seal, and cut the film.
* ''
Turntable wrappers:'' The load to be wrapped sits on a turntable which spins the load relative to the film roll, which is housed in a carriage which can move up and down a fixed "mast". Stretch is achieved by rotating the load at a faster rate than the film is fed.
* ''Rotary arm wrappers:'' In this system, the load remains still while a rotating arm turns around it wrapping the load. This system is used for light loads or for speeds which would otherwise cause the load to topple due to high rotation speeds.
* ''Rotary ring wrappers:'' The film is housed in a carriage on a horizontal ring in which the load remains static while the horizontal ring is rotating around the load and moves up and down vertically relative to the load, similar to a rotary arm stretch wrapper. The rotary ring technology is really a more balanced system with less wear and maintenance than the other available wrapping technologies. These wrappers are capable to reach the highest production capacities (up to 160 pallets/hour).
See also
*
Packaging and labeling
Packaging is the science, art and technology of enclosing or protecting products for distribution, storage, sale, and use. Packaging also refers to the process of designing, evaluating, and producing packages. Packaging can be described as a co ...
*
Palletizer
A palletizer or palletiser is a machine which provides automatic means for stacking cases of goods or products onto a pallet.
Manually placing boxes on pallets can be time consuming and expensive; it can also put unusual stress on workers. The f ...
*
Plastic recycling
Plastic recycling is the reprocessing of plastic waste into new products. When performed correctly, this can reduce dependence on landfill, conserve resources and protect the environment from plastic pollution and greenhouse gas emissions.
A ...
*
Plastic wrap
Plastic wrap, cling film, Saran wrap, cling wrap, Glad wrap or food wrap is a thin plastic film typically used for sealing food items in containers to keep them fresh over a longer period of time. Plastic wrap, typically sold on rolls in boxes ...
*
Slip sheet
Slip sheets are thin, pallet-sized sheets made of plastic, heavy laminated kraft paperboard, or corrugated fiberboard and are used in commercial shipping, replacing traditional wooden pallets. The unit load is usually stretch wrapped or shrink ...
*
Semiembossed film {{unreferenced, date=July 2013
Semiembossed film is used as a liner to the calendared rubber to retain the properties of rubber and also to prevent dust and other foreign matters from sticking to the rubber while calendaring and during storage. It ...
References
Further reading
*
ASTM International
ASTM International, formerly known as American Society for Testing and Materials, is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, an ...
D4649 Guide for Selection and Use of Stretch Wrap Films
* Yam, K. L., "Encyclopedia of Packaging Technology", John Wiley & Sons, 2009,
{{packaging
Packaging
Plastics applications