Question mark in a bubble depicting Poly Postal Packaging, manufacturers of mailing bags glossary of terms

An additive which inhibits the growth of certain bacteria. Various types are available - the most common containing trychlosan depending on the type of bacteria targeted.

Anti-block An additive in the polymer to avoid the film sticking together and becoming blocked during extrusion. This Anti-block is usually added by the polymer manufacturer so that the film grade we buy is ready mixed. (see ‘Blocking’ below).

An additive which reduces the static electricity present in most finished plastic goods (caused by friction generated during processing). This 'static' is most apparent in very thin films - particularly HDPE.

Barrier Film:
A term to describe film that is a good barrier to gases, aromas and flavours - typically, high barrier materials are going to be oxygen barrier materials, of which the most common are EVOH and nylon resins used in conjunction with polyethylene. To create the specific barrier required either co-extrusion, lamination or coating is used.

A material which will degrade through microbial action - generally in the earth or in landfill sites. There is considerable discussion, indeed controversy, as to the definition of this term. Various additives are available to accelerate this process under certain conditions.

A stack (or block) or bags or carriers (normally 50 or 100) attached to a header strip by a perforated line enabling them to be torn off one at a time. The header strip is normally punched with 2 holes, so that the block can be placed on hooks for convenience.

Blocked Film:
When extruded film is impossible to open - this can be due to a number of factors such as not allowing the film to cool sufficiently, having the nip rollers too tight on the extruder, over treating of the film or using unsuitable polymer.

A condition affecting mainly LDPE and LLDPE bags, where 2 layers of film stick to each other, making the bag difficult (or in extreme cases, impossible) to open. Bags in this state are 'blocked’.

Blow Ratio:
The degree to which the polythene bubble is blown - expressed as a ratio of the diameter of the bubble to the diameter of the extruder die. The greater the blow up ratio, the stronger the film will be as the polymer chains in the film become stretched and intertwined. A typical ratio will be 3:1.

Centre Fold Sheet(ing) [CFS]:
The same as 'lay flat tubing' but with a slit on 1 edge.

Coex (Co-extrusion):
The extrusion of two or more layers of polythene film at the same time which are then layered together to produce a film which has far better benefits in strength, puncture resistance and tear resistance.  This type of film is commonly used and enables different colours to be layered with each other.

A material which will fully degrade in the specific conditions of a compost heap with the presence of certain defined chemicals and/or microbes.

Corona Discharge Treatment:
The film is passed through a device which changes the surface resistivity of the film (effectively scuffing the film electrically), so that ink, adhesives etc. can be applied to the film more easily.

Double Wound Sheeting (DWS):
A double layer of film wound on to a reel - made by slitting layflat tubing on both edges and winding on to 1 reel.

Defence Standard 93-19/1:
Established by the MoD in 1976 as they felt there was no other acceptable national standard available at the time in relation to polythene film. Still used as a benchmark and Polybags' tolerances are in accordance with this standard.
Die Line:
A line of weakness (seam) in the film caused by a piece of contamination caught in the die. Often difficult to spot, the film will tear easily along this seam under any pressure.

the edges of single wound or double wound sheet film are slit by fixed blades so that the width of the film is accurate to 2mm. This is more expensive than standard film because of the wasted trim and should only be specified when accurate width is essential.

Electro-conductive polymer:
Polymer with a high carbon content to allow the dissipation of static electric. Due to the carbon it is a black polymer but can be extruded like any low density polythene film.

A series of small indentations in the film give a cosmetic effect.

End (Bottom) Weld:
A bag with the seal at the base of the bag, separated from the end of the bag by a small skirt as the sealing and cutting are separate processes. Bag length is measured from top to bottom of the bag INCLUDING the skirt which is typically up to 1cm.
A specific sized pallet somewhat smaller than the traditional pallet. A europallet measures 800mm x 1200mm and some customers insist on it for pallet deliveries. We have a stock of both euro and standard pallets.
A hole in a bag for hanging it on a hook - the shape is a punched hole with a horizontal slot either side.

Added to polythene film to improve puncture resistance, sealability and surface strength.

Flexographic print:
A print process where ink is coated onto a raised printing plate (usually rubber or plastic) which is then rolled against the film to produce the printed image. The most common form of print for short run print. As opposed to 'Gravure' printing.
To describe when the layflat on a core is rolled right up to the edge of the core so that there is no ‘lip'.

Flame Retardant:
An additive which reduces the flammability of a material.

In plastics, this is an additive to give the material a scent (e.g. lemon) which is incorporated into the material itself during processing, rather than being applied to the outer surfaces after processing.

Imperial equivalent of micron, 1/1000th of an inch (0.001"), thus 1 micron = 4 gauge etc (approx.).

Gravure print:
A print process where ink is smeared onto an engraved metal roller which is then passed against the polythene film to produce the printed image. A high quality but relatively expensive print process. As opposed to 'Flexographic' printing.
A fold in the side or bottom of the bag so that the closed width is less than the open width. A side gusset is produced in extrusion using gusset boards that push in at the side of the bubble on the cooling tower.

Gusseted layflat tubing (GLFT):
Layflat tubing with the edges tucked in.

High Slip:
An additive which makes film more slippery (desirable in some applications, undesirable in others).

J Fold Sheeting (JFS):
Similar to centre fold sheeting, but slit at a point not on the edge - mainly used for making side weld bags with a lip.

When two separate films are physically joined together by use of an adhesive (laminate) to combine the best physical properties of both of the films.

Layflat Tubing (LFT):
A tube of material which is squashed flat and wound on to a reel.

Linear (LLDPE):
A polymer similar to low density polymer (LDPE).
Light Proof:
The same as opaque - i.e. no light should pass through. The term light proof is often used to emphasise the importance e.g. the bag is going to be used in a film processing room.
Low Slip:
Used to describe polymer that has not had slip additive added - often used for large sacks that are to be stacked and must not slide. We buy in ready formulated low slip

A fairly new member of the polythene family - excellent clarity and strength, but difficult to extrude and process.

Master batch:
A colour producing additive that is added in varying quantities depending on whether a tint or opaque colour is required - usually between 1% and 5%.
Maxi grip bags:
A Self Seal bag with a double grip seal to make it more secure than a standard grip seal bag.

A linear measurement, 1/1000 of 1mm (0.001mm).

A series of tiny holes in the film, making it pervious to air and other gases.

The extrusion of one single layer of polythene film.  This type of film is commonly used in the manufacture of clear films/polybags and some dark coloured mailing bags like grey mailing bags for example.  Any polythene films which are extruded as a mono film and in a light colour, like, white, yellow etc will always be see through.

Coloured film where you can not see sunlight through the film.
Pallet Wrap:
Simply stretchwrap that is used to bind a pallet together - normally comes in large rolls.

A material which will degrade in sunlight. All polyethylenes eventually degrade in this way and photodegradable additives considerably accelerate this process.

Printed Warning Notice (PWN):
Normally in red or black ink, a simple printed warning about the danger of suffocation with polythene bags.
Random Repeat Print:
Where a print is not kept in register and so the print will not be kept at the same position on each bag during conversion. The repeat length depends on the circumference of the print cylinder and the number of print plates in use.

A processed plastic which has been used for its intended purpose and subsequently reworked.

Registered Repeat:
Print which is kept in register to enable print to be kept in the same position on each bag. This is enabled by having a register mark produced when printing (the printed image itself can be used if it has a clear starting point) This register mark is then picked up by a 'magic eye' (photoelectric cell) on the bag maker. Registered print can therefore only be converted one-up.
Regran / Recycled Material Regran:
Short for regranulated and refers to the pellets that are produced from reprocessed scrap film. Regran film is of a lower quality than virgin and should not normally be run in less than 150gauge thickness.

A processed plastic which has not been used (e.g. factory waste) and subsequently reworked.

Sack grade:
A term to describe a type of polymer with a different melt flow index, suitable for sack making.
Self Seal:
(Also called gripper / grippa / minigrip) bags Sideweld bags with a ridge of polythene near the top that clicks together to seal the bag. This seal can be clicked open or shut. Self seal bags are primarily made abroad and imported. Please do not confuse with top tac bags.
Sheeting Layflat:
Tubing that has been cut on either one side (for centre fold sheeting) or both sides (for double wound sheeting). If the sheeting is separated and collected on two separate take-offs, single wound sheeting can be produced.
Shielding bag:
A specific bag to shield the contents from electromagnetic radiation. A metallised bag is a form of shielding bag.
Shrink film:
Film that shrinks on application of heat (e.g. a heat gun or tunnel). Useful for securely wrapping goods and to prevent tampering of goods. Whilst all film shrinks, the phrase shrinkfilm is used to describe film that shrinks in a known way. This depends on the film characteristics and the manner in which it is extruded. Low slip LDPE is one of a number of typical shrink films along with PVC and PP.
Side Weld:
A bag where the sides of the bag is created using a heated knife. It is weaker than an end weld bag but cheaper to produce and has no skirt. (You can produce a side skirt weld bag if required with conventional end weld seals but at the side).

Single Wound Sheeting (SWS):
A single layer of film wound on to a reel - made by slitting layflat tubing on both edges and winding on to 2 reels.

A bag that is open both ends rather than sealed at one. In order to produce sleeves the heat sealer is deactivated on the end weld bag maker leaving just the cutting mechanism.
Slip Slip:
Is defined as the inverse of the dynamic coefficient of friction. It is an additive added by the manufacturer to allow polythene to be converted easily (less friction with rollers) and for bags to open easily. Different formulations of LDPE have varying amounts of slip and so are termed either low or high slip. Normal slip is between 1.7 and 3.0.
Standard pallet:
A standard pallet measures approximately 1000mm x 14000mm although there are some variations in size. Recently some companies have standardised racking to take europallets which are slightly smaller.
Stretch wrap:
A complex material, normally PVC or polyolefin based with plasticising agents added, designed to conform to whatever shape comes to hand.
Tensile Strength:
Reflects the maximum load the film is capable of supporting.
Tint colour film - where only a very little masterbatch is added (usually about 1%) to give a tint of colour, the film remaining see through (translucent).
Top Tac bags (or mailing bags:
A bag which has had an adhesive strip attatched to the top of the bag (usually on a lip). The strip consists of adhesive coated on a non sticksilicone tape which is removed to allow the bag to seal. Depending on the adhesive properties, permanent or resealable bags can be produced.

see corona discharge treatment above.

UV Stabliser:
An additive which reduces the tendency of plastic materials to photo-degrade as a result of ultraviolet rays (i.e. sunlight).

Virgin Material:
A term used to describe polymer direct from the manufacturer rather than reprocessed material. As such, we can guarantee it is non-contaminated and can be used for food grade applications.
Water soluble bag:
A bag that dissolves after contact with water - useful in certain hygiene disposal applications. The polymer is formulated with alcohol to create the breakdown of the material on contact with the water. The bag can either be soluble in cold or hot water.
Wicketted Bags:
Bags that have been bundled together by means of a small metal hanger that is put through 2 punched holes near the top of the bag - often used in retail applications or on-line packing machines for easy handling of the bags.

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