Glossary

English equivalent: blown film extrusion

A process in which plasticised polymer is formed into tubular film in an annular die and inflated with air to the required width. The film bubble is cooled and stabilised, then the film passes through the collapsing unit, haul-off and winder. Raw material selection, extruder output, blow-up ratio, cooling and haul-off speed affect the thickness and properties of the finished film.

English equivalent: film bubble

The inflated tubular film between the die and the collapsing unit. In this part of the line, the polymer is stretched and cooled, affecting its orientation and the film's properties. Changes in the bubble's shape, width or position can indicate process disturbances and lead to thickness variations.

English equivalent: tubular film

Film with a closed circumference, produced by the blown film process. After cooling and flattening, it can be wound as tubular film, formed with gussets or slit into centre-folded film or film webs. The product specification should distinguish between the lay-flat width, the thickness of the film itself and the gusset configuration.

English equivalent: lay-flat width

The width of flattened tubular film, measured across its direction of travel. For tubular film without gussets, it is approximately half the bubble circumference. This parameter defines the dimensions of the finished product and matters when setting the production width, slitting and converting the film.

English equivalent: annular die / blown film die

The line component that distributes the polymer melt and forms tubular film through an annular gap. Coextrusion dies combine material streams that form the individual film layers. Channel design, temperature, cleanliness and die condition affect flow uniformity and the thickness profile.

English equivalent: die gap

The distance between the surfaces forming the die's annular outlet. It affects melt flow conditions and the amount of stretching needed to achieve the target film thickness. Finished product thickness also depends on output, blow-up ratio and haul-off speed, so it does not directly correspond to the gap dimension.

English equivalent: air ring

A system directing airflow onto the outer surface of the film bubble near the die. It removes heat and contributes to bubble stabilisation. Airflow uniformity, air temperature, and the ring's setting and cleanliness are important for output and film thickness distribution.

English equivalent: Internal Bubble Cooling

A cooling system that exchanges air inside the film bubble. It supports heat removal and may enable increased line output while maintaining the required quality. Air supply and extraction must be coordinated with maintaining the specified bubble dimensions.

English equivalent: frost line / Frost Line Height

The visible boundary on the film bubble associated with polymer cooling and crystallisation. Its height above the die is abbreviated as FLH. The position and stability of this boundary help assess cooling and film formation conditions; they should be analysed in relation to the raw material, output and line settings.

English equivalent: Blow-Up Ratio

The ratio of the film bubble diameter to the annular die outlet diameter. It describes stretching in the transverse direction and is related to lay-flat width. BUR selection affects film orientation and mechanical properties; the appropriate value cannot be determined independently of the raw material, cooling and haul-off conditions.

English equivalent: haul-off

The unit that takes up the film and gives it a specified linear speed. On a blown film line, it works with the tubular film collapsing unit, while the nip rollers seal the bubble's enclosed space. Changing haul-off speed at constant output and width affects film thickness and stretching in the machine direction.

English equivalent: coextrusion

The simultaneous extrusion of several polymer streams combined into a single film structure. Individual layers may differ in composition and serve specific functions, such as sealability, strength or barrier properties. Product properties depend on the materials used, their compatibility and the layer ratios.

English equivalent: Machine Direction / Transverse Direction

MD is the direction in which the film travels on the line, and TD is the direction across it. Documentation may also use CD (Cross Direction) for the transverse direction. The distinction is needed when interpreting film strength, elongation, tear resistance and shrinkage, because results can differ between the two directions.

English equivalent: collapsing unit

A set of guides or rollers that gradually flattens the cooled film bubble before haul-off. Its adjustment affects film guiding, stress distribution and wrinkle formation. The unit's geometry is selected to suit the tubular film width, film type and line design.

English equivalent: winder

The unit that forms a roll of finished film. Control of tension, nip pressure and the winding process matters for roll hardness, end-face evenness and subsequent unwinding. Roll defects may result from winder settings as well as the film's thickness profile or surface properties.

English equivalent: Low Density Polyethylene

Low-density polyethylene, used to produce many types of blown film. Its branched structure affects processing properties, including melt behaviour during bubble formation. Individual grades differ in density, melt flow index and optical properties, among other characteristics, so selection must relate to the specific application.

English equivalent: Linear Low Density Polyethylene / metallocene LLDPE

LLDPE is linear low-density polyethylene. mLLDPE denotes grades produced using metallocene catalysts. These materials are used, among other purposes, to achieve the required film strength, puncture resistance and sealability; their proportion in the formulation also affects process operating requirements.

English equivalent: Medium Density Polyethylene / High Density Polyethylene

Medium-density and high-density polyethylene, respectively. Material density and structure affect stiffness, mechanical properties and film behaviour during cooling, among other factors. The polymer family name alone is insufficient to determine production conditions: the specific grade and its proportion in the formulation matter.

English equivalent: masterbatch

A concentrated mixture of pigments or functional additives in a polymer carrier. It is dosed into the raw material at a specified proportion to obtain the required film colour or properties. Selection takes account of carrier compatibility, active ingredient concentration, dispersion quality and the impact on the process and product application.

English equivalent: slip agent

An additive used to regulate friction on the film surface. It can facilitate film guiding, unwinding and operation on packaging machines. For migrating additives, the effect also depends on storage time and conditions, so the measured coefficient of friction should be related to sample age and the test method.

English equivalent: antiblock additive

An additive that reduces adhesion between contacting film surfaces, making it easier to open tubular film or unwind a roll. Selection takes account of effectiveness, optical properties and downstream processing requirements. Antiblock and slip additives perform different functions, although they may be used together in the same formulation.

English equivalent: regranulate

Recycled plastic reprocessed into pellet form. Its suitability for film production depends on factors including material origin, cleanliness, composition, filtration and previous processing history. When changing batches, it is important to check the consistency of properties and material behaviour on the line.

English equivalent: regrind

Material obtained by mechanically shredding plastic waste. Shredding alone does not include remelting and pelletising, so regrind must be distinguished from regranulate. The shape of the shredded pieces, bulk density and cleanliness affect conveying, dosing and the uniformity of extruder feeding.

English equivalent: Post-Consumer Recycled / Post-Industrial Recycled

Terms referring to the origin of recycled material. PCR comes from products after their use, while PIR comes from waste generated in industrial operations. When agreeing a formulation or declared recycled content, the waste source and classification rules used must be established; simply returning in-house trim to the process does not determine this classification.

English equivalent: gravimetric dosing

Feeding raw materials based on measurement of their mass. It allows control of formulation component ratios and, depending on the equipment, material consumption and output. Repeatability requires correct calibration and consideration of the properties of the material being dosed, particularly when working with lightweight trim or regrind.

English equivalent: edge trim

Narrow strips of film cut along its edges during width trimming or slitting. They are in-house production waste; depending on the line, they may be collected continuously and directed to reprocessing. Whether they can be returned to the formulation depends on composition, cleanliness and finished product requirements.

English equivalent: rheology

The field describing material flow and deformation. In film production, it covers viscosity, elasticity and melt behaviour under shear and extension, among other topics. It helps explain why two raw materials with similar MFR values may behave differently in the die and during bubble formation.

English equivalent: melt strength

The ability of a plasticised polymer to bear a load during stretching. It matters for bubble stability and the ability to operate the process at a given output and film thickness. It concerns material behaviour in the molten state, rather than the strength of finished film measured after cooling.

English equivalent: melt flow tester

An instrument for determining polymer flow rate indices such as MFR and MVR. Testing is conducted at a specified temperature and load according to the chosen method. The result helps compare raw material batches but does not replace assessment of material behaviour under actual extrusion conditions.

English equivalent: Melt Mass-Flow Rate / Melt Flow Index

The mass of polymer flowing through the melt flow tester die under specified conditions, expressed per 10 minutes in g/10 min. MFI is a commonly used term for this type of test. Results can be compared under matching measurement conditions; MFR alone does not describe melt strength or the full behaviour of the raw material in the process.

English equivalent: Melt Volume-Flow Rate

The volume of polymer flowing through the melt flow tester die under specified conditions, expressed per 10 minutes in cm³/10 min. The result should be reported with the test temperature and load. Converting MVR to MFR requires the melt density under the measurement conditions; room-temperature material density should not be substituted.

English equivalent: film thickness profile

The distribution of film thickness in a specified measurement direction, such as across the width or along the film's direction of travel. It reveals local deviations that the average value alone may not show. An uneven profile affects roll quality, raw material consumption and film behaviour during downstream processing.

English equivalent: film thickness / micrometre

Film thickness is usually expressed in micrometres: 1 µm = 0.001 mm, and 50 µm = 0.05 mm. When measuring flattened tubular film, it must be specified whether a single film layer or two superimposed sections are being measured. The result should be interpreted according to sample preparation and the chosen measurement method.

English equivalent: Coefficient of Friction

A quantity describing friction between the surfaces under test, such as film against film. A distinction is made between the static coefficient, associated with the start of movement, and the kinetic coefficient, measured during sliding. COF affects film handling and packaging; the result depends on the material, additives, surface condition and test conditions.

English equivalent: corona treatment

Treatment of the film surface with corona discharge to improve wettability and prepare it for printing, bonding or coating. Effectiveness depends on the polymer, treatment parameters, and storage time and conditions. The treatment level achieved must be assessed against the requirements of the specific downstream process.

English equivalent: heat sealability

The ability of a film to form the required bond under specified sealing conditions. It is assessed in relation to temperature, time, pressure and the properties of the sealant layer. Customers also need an appropriate operating window, seal strength and a process that can tolerate typical disturbances.

English equivalent: gels and inclusions

Local inhomogeneities visible in film that can impair its appearance and performance. They may be associated with incomplete plasticisation, material degradation or crosslinking, among other causes; inclusions may also originate from foreign contaminants. Identifying the cause requires assessment of the sample, raw material and process history, because a similar appearance does not always mean the same source of the problem.

English equivalent: sharkskin

A fine, repetitive surface irregularity that forms as the melt exits the die under certain flow conditions. It can reduce film smoothness and gloss. Diagnosis must distinguish it from other surface defects, and the analysis should consider the raw material, output, temperature and die outlet geometry.

English equivalent: film blocking

Unwanted adhesion between contacting film surfaces, making it difficult to open tubular film or unwind a roll. The phenomenon may depend on the formulation, film temperature, winding pressure and storage conditions. Analysis distinguishes the effects of antiblock and slip additives and checks process conditions.

English equivalent: telescoping

The axial shifting of successive film wraps, causing an uneven end face and a change in roll shape. It may become apparent during winding, storage or transport. Analysis considers tension, friction between surfaces, thickness profile and winding unit alignment, among other factors.

English equivalent: shrink film

Film designed to shrink when heated during packaging. Its behaviour is described by properties including shrinkage in the machine and transverse directions, shrink force and mechanical properties. Formulation and extrusion conditions must be selected in relation to the product being packaged and the operating conditions of the packaging equipment.

English equivalent: stretch hood film

Film used to make stretchable hoods that secure loads, usually on pallets. The hood is stretched and applied over the load, and stabilisation comes from the film's elastic properties, without heat shrinking. Key factors include holding force, permanent deformation, puncture resistance and compatibility with the packaging machine.

English equivalent: cast film

Film produced by extruding melt through a flat die and cooling it, usually on a chill roll. It is a distinct film-forming technology, with different cooling and material handling conditions from blown film. The term cast describes how the film is made; it is not a synonym for subsequent orientation.

English equivalent: film orientation

Controlled stretching of film under specified conditions, which aligns the polymer structure and changes product properties. Orientation may be in one or two directions. A distinction must be made between orientation arising during film formation and an additional, controlled orientation stage using dedicated equipment.

English equivalent: Machine Direction Orientation

Controlled stretching of film in its direction of travel, usually between sets of rollers operating at different speeds, at a suitably selected temperature. It changes film thickness and properties, including the relationship between behaviour in the machine and transverse directions. It can be a processing stage for film produced using various technologies.

English equivalent: biaxially oriented film

Film subjected to controlled stretching in two directions: machine and transverse. Orientation may take place sequentially or simultaneously, depending on the technology. Examples include BOPP for polypropylene and BOPET for polyethylene terephthalate; these names indicate both the material and biaxial orientation.