Terms and concepts

The property of being directionally dependent. For paperboard this usually refers to the difference in strength- and stiffness properties depending on for which sheet direction (MD or CD) they are assessed.

A broad term which usually describes matter that can be broken down either through an aerobic (composting) process or an anaerobic (digestion) process into its organic parts. Inorganic materials, either alone or in compounds with organic materials, will not biodegrade. The term “biodegradable” is not very well defined with regard to the expected quality of the degraded matter, nor is any specific time frame required. This means that many organic products can claim to be biodegradable because in a broad sense they will eventually degrade over time in a variety of ambient environments.

Biogenic energy
Energy which is fuelled by constituents derived from the life processes of either plants or other living organisms.

A renewable energy source derived from living materials
in contrast to one derived from geological processes. Usually the term describes wood-, plant- and waste residues used in incineration as a replacement for fossil fuel. Biomass is also used in biochemical energy plants such as anaerobic digestion plants.

Blank (carton)   
A die-cut specimen of a carton or box which has not yet been glued, erected and filled.

Also referred to as “mill broke”. During the manufacturing process, waste paper or paperboard is recovered and repulped for reuse in new paperboard. This waste paper or board is called “broke”. A sort of in-house recycled fibre, broke can contain coating particles, dye and fillers.

Carbon dioxide   
The chemical compound CO2, which naturally occurs in the atmosphere. In a natural process called photosynthesis, carbon dioxide is absorbed by plants, algae and bacteria and transformed into carbohydrates (energy) and oxygen with the help of sunlight and water. Carbon dioxide is a greenhouse gas. The combustion of fossil fuels, e.g. oil and natural gas, releases the fossil carbon dioxide stored in the fuel. The composting or combustion of biomass also releases carbon dioxide. However, in the latter case, almost the same amount of carbon dioxide as that released is absorbed by photosynthesis during the growth of the equivalent amount of biomass.

A term describing matter which will biodegrade in a composting process (aerobic degradation). All compostable products are biodegradable by default but the opposite is not necessarily true. “Compostable” often refers to the standards defining expected performance in an industrial composting facility, such as the American standard ASTM 6400 and EN 13432. The standards define within which time frame the products should degrade to a certain fragment size and quality, and also place clear limits on the ecotoxicity and heavy metal content of the final compost.

Continuous cooking process   
The chemical pulping process which feeds a continuous stream of chipped wood through a digester. The fibres are detached from each other by dissolving the lignin in a liquor consisting of a solution of caustic soda and sodium sulphide. The chips travel vertically through the digesting tower while gradually being dissolved. At the bottom of the tower the fibres are pumped to subsequent bleaching steps and then further to the board machine. The opposite way to perform chemical pulping is the batch process, in which large batches are cooked in a container and then ejected before a new batch is loaded.

The process of separating wood fibres from each other. The two main processes are mechanical or chemical defibration (pulping).

The process of removing printing ink and other impurities when preparing recycled fibre from printed waste paper for a new papermaking process. The most common technique is to add caustic soda to the pulp in the pulping process and then remove the freed ink and other smaller particles by the flotation technique, whereby the small ink particles and impurities attach themselves to air bubbles induced into the low consistency stock. The term DIP (de-inked pulp) is commonly used. Other important steps in recycled pulp production are high consistency cleaning and screening in multiple steps.

Dot gain   
The phenomena in printing whereby halftone dots in screened images appear or become larger than intended on the finished printed surface compared to the original screened image. Also known as Tone Value Increase (TVI).

Pigments such as clay or titanium dioxide added to the pulp to improve the opacity of thin papers.

Smaller fragments of fibres which have come loose in the chipping and defibration process. Fines from chemical pulping and mechanical pulping have very different characteristics.

Grain direction   
The grain direction of a paperboard sheet is the same as the dominant fibre direction. This is parallel to the machine direction (MD) in the paperboard-making process.

Halo (flexo printing)   
The halo effect in flexographic printing describes the increased ink amount around the perimeter of the printed image. This is a result of ink being pressed out over the edge of the raised printing form when the form is pressed against the substrate.

I-beam principle   
An I-beam is a construction element, (usually a steel beam) which has been designed to resist a large load and is strong compared to how much of its mass bears the load. The cross section of such a beam resembles the capital letter "I". An I-beam has wide horizontal flanges to absorb tensile- and compression forces and a vertical web, or waist, to resist shear forces. Stress from the bending force will be highest furthest from the neutral length axis, that is, at the flanges. By concentrating the bulk of stress-absorbing material at this point it is possible to minimise the need for material closer to the neutral axis. In paperboard making this is done by using strong and dense chemical pulp in outer layers as "flanges" and weaker, bulkier pulp (either mechanical or recycled) in between the layers making up the "web".

Ink density   
A unit describing the amount of ink being transferred from the printing press to the surface of the paper or paperboard. Ink density is an optical unit with a logarithmic scale. When measuring density, the amount of light absorbed by the ink within a defined area is evaluated against a reference value from either a standard reflecting calibration tile or unprinted paper of the same sort. The different colours – cyan, magenta and yellow – can be measured using red, green and blue filters in the densitometer. Density can also be calculated using reflective data from a spectrophotometer.

Ink trap   
The measurable property describing the amount of ink transferred onto a previously printed ink film. The amount of ink transferred onto another ink is measured with a densitometer. The value is compared to the density the ink would have if printed onto plain paper. The ink trap amount is described in percent. Ink trapping characteristics are governed by the setting speed of the first ink to be laid down. This setting speed influences the tack build-up in the first ink. When the first ink film has high tack (i.e. resistance to ink splitting), the second ink to be laid down on top of the first one will transfer more easily, and the main ink split when exiting the printing nip will thus occur in the second ink film. Tack development can be influenced by both the ink manufacturer and the coating characteristics of the paper or paperboard.

Integrated process   
An integrated mill has both pulp production and paperboard manufacturing at the same site and often in a continuous pulping process. The level of integration can be elevated by integrating other processes, such as a sawmill, and bioenergy solutions.

The term can have two different meanings. “Makeready time” or “makeready procedures” refer to all the preparation steps required to set up and adjust a paper converting machine, printing press or finishing equipment. In a different context, “the makeready” refers to the counter die used in the die-cutting operation.

Market pulp   
Market pulp refers to pulp sold on the pulp market in bale or sheet form by pulp producers to paper, paperboard mills or other fibre-forming industries, such as those making formed trays, etc.

Migration in the context of food packaging describes the extent to which foreign substances transfer to the packed food from the surrounding materials. The sources of such foreign substances can be packaging materials, inks, glue or other added materials. Different types of food vary in their susceptibility to migration, depending mainly on their moisture- and fat content. Substances with a molecular mass over 1,000 Dalton or molecule chains larger than 24 carbon atoms are unlikely to migrate from a material over to food.

Mono material   
A packaging material which consists mainly of one type of material, such as paper, aluminium, tin or glass. The term is used in the context of licence fees for various European collection, sorting and recycling systems. The fees for mono materials are considerably lower (up to five-fold/kg) than for composite materials. The threshold for being considered as a mono material varies slightly, but the most stringent level is used by the German Duales System Deutschland GmbH (DSD). This states that the packaging must consist of a minimum of 95% of one of the main packaging materials. This rules out some plastic coated paperboard, in which typically 15-20 g/m2 of plastic (PE/PET/PP) is extrusion coated onto a paperboard with a grammage of between 240 to 300 g/m2. However, liquid packaging board (LPB) has received special dispensation and has its own licence threshold, which is lower than that for normal composites.

Multi-layer or multi-ply paperboard is a board constructed from more than one fibre layer. The layers are pressed together in a wet state directly in the board machine. The different layers can consist of different types of pulp and have different ratios between their long and short fibres.

Pulping describes the process of converting the chipped logs to individual, separated fibres, i.e.  defibration.

Refining occurs at two stages of the paperboard-making process. In mechanical pulp production, the wood chips are fed into a refiner to be ground to separate the fibres from each other. The process can be aided by steam or chemicals to promote defibration.

The second stage of refining occurs during stock preparation just before the board machine. A series of low consistency refiners beat the fibres gently to enlarge the fibre contact area, which in turn increases the stock’s bonding abilities and sheet-forming ability but lowers its bulk.

Register describes the degree of precision with which subsequent printing and converting steps can align with each other relative to the design. The term “misregister” is used when this alignment varies throughout one batch or run. Misregister can occur for many reasons, such as vibrations in machines, or poor hygro-stability or flatness in the paperboard sheet.

Renewable resource   
A renewable resource is one which naturally regenerates itself within a reasonable period of time. These resources are part of our normal ecosystem. The term is often used in discussions about renewable energy.

Safety (product)   
“Safety” in this context refers to the suitability of the paperboard for its intended use, with particular reference to meeting food safety regulations when the food is in direct contact with the paperboard surface.

Secondary packaging   
Secondary packaging is used to contain a number of grouped unit packages (primary packages) merely in order to display the unit packages until their purchase or to simplify shelf replenishment. Secondary packaging can always be removed without changing the characteristics and function of the unit packages. Secondary packaging is often made of paperboard or corrugated board. When secondary packaging plays a significant promotional role, it is often referred to as display outers.

Slit and chop   
These terms refer to the two main cutting directions when sheeting a paperboard web from a reel. The cut made in the unwinding direction (which is also the machine direction) is called the slit. The cut made across the web perpendicular to the machine direction at certain intervals is called the chop. The slit is thus always parallel to the fibre direction and the chop perpendicular to the fibre direction.

The stock is the final stage of the pulp before it is pumped onto the wire mesh to form the sheet. In contrast to pulp, which is normally a single type of fibre produced by one defibration process, stock can consist of a blend of different fibres (this composition is called “the furnish”) plus additives as colouring additives and retention chemicals to retain fines in the paperboard structure, thus promoting strength. The fibres may also at this stage have been refined.

Swarf refers to the shavings or chips from the edges of a material which has been exposed to mechanical converting operations such as die-cutting or punching. This occurs mainly with paperboards which have been coated with metallised film or foil, but can also occur with very hard coatings such as UV varnishes.

Transport packaging   
Also called tertiary packaging, transport packaging facilitates the safe and efficient transportation of grouped sales units with or without secondary packaging. The dominant material is corrugated board, although it is possible to replace corrugated transport packaging with stiffer secondary packaging plus shrink wrap or stretch film on a pallet load.

Unit package   
This is also known as primary packaging or sales packaging. A unit package contains one sales unit at the point of purchase by the consumer. Unit packaging is made of a variety of materials such as paperboard, glass, plastic, tin or aluminium.

Virgin fibre   
Also called primary wood fibre, virgin fibre is the fresh fibre produced from harvested forests as opposed to recycled fibre.

Wet end   
The wet end refers to the wire section of the board machine where the stock is pumped onto a mesh to form the fibre network. The wet end stops where the press section starts. At the wet end, the water content of the stock is reduced from approximately 98% to 80% by means of drainage.

The term “yield’ describes how much pulp can be produced from a defined amount of timber. The yield from mechanical pulping is typically 85 to 95%, while from chemical pulping it is about 45%. The lower yield from chemical pulping is due to the delignification process that removes the lignin in the pulp. The lignin is then used as a biofuel in the process of recovering the cooking chemicals


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