Editing Paperboard (section)

==Production==
{{See also|Paper machine}}
[[File:Takon kartonkitehdas Tammerkoski.jpg|thumb|upright=1.35|Metsä Board Tako paperboard factory near the [[Tammerkoski]] in [[Tampere]], [[Finland]]]]
Fibrous material is turned into [[Pulp (paper)|pulp]] and bleached to create one or more layers of board, which can be optionally coated for a better surface and/or improved appearance. Pulp board is produced on pulping machines that can handle higher grammage and several plies.

===Raw materials===
The above-mentioned fibrous material can either come from fresh (virgin) sources (e.g. wood) or from [[Paper recycling|recycled waste paper]]. Around 90% of virgin paper is made from [[timber|wood]] pulp.<ref name="ind">{{Citation 
|last=Datamonitor
|title=Global Paper and Paperboard - Industry Profile
|date=June 2008
|ref=0199-2406
}}</ref>
Today paperboard packaging in general, and especially products from [[ecolabel|certified]] [[sustainability|sustainable]] sources, are receiving new attention, as manufacturers dealing with environmental, health, and regulatory issues look to [[renewable resources]] to meet increasing demand. It is now mandatory in many countries for paper-based packaging to be manufactured wholly or partially from [[recycling|recycled]] material.
 
Raw materials include:

* '''[[Hardwood]]:''' C. {{convert|0.05|in|mm}} in length e.g. [[Birch]] which has short fibres. It is generally more difficult to work with; however, it does provide higher tensile strength, but lower tear and other strength properties. Although its fibres are not as long and strong as those in softwood, they make for a stiffer product defined by some stiffness tests. Hardwood fibres fill the sheet better and therefore make a smoother paper that is more opaque and better for printing. Hardwood makes an excellent corrugating medium.
*'''[[Softwood]]:''' C. {{convert|0.13|in|mm}} in length e.g. [[Pine]] and [[spruce]] which have typically long fibres and make superior paperboard in services where strength is important. Softwood makes excellent linerboard.
* '''[[Deinked pulp|Recycled]]:''' Used paper is collected and sorted and usually mixed with virgin fibres in order to make new material. This is necessary as the recycled fibre often loses strength when reused; the added virgin fibres enhance strength. Mixed waste paper is not usually [[Deinking|deinked]] (skipping the deinking stage) for paperboard manufacture and hence the [[pulping|pulp]] may contain traces of inks, adhesives, and other residues which together give it a grey colour. Products made of recycled board usually have a less predictable composition and poorer functional properties than virgin fibre-based boards.<ref name="igg">{{Cite journal
|last=Iggesund Paperboard AB
|title=Paperboard the Iggesund Way
|year=2008
|page=10
}}</ref> Health risks have been associated with using recycled material in direct food contact. Swiss studies have shown that recycled material can contain significant portions of mineral oil, which may migrate into packed foods.<ref>{{cite web
  |author=Federal Institute for Risk Assessment (Germany)
  |title=Migration of mineral oil from packaging materials to foodstuffs (BfR Opinion No. 008/2010 of 2009-12-09)
  |access-date=2010-04-21
  |url=http://www.bfr.bund.de/cm/230/migration_of_mineral_oil_from_packaging_materials_to_foodstuffs.pdf}}</ref> Mineral oil levels of up to 19.4&nbsp;mg/kg were found in rice packed in recycled board.<ref>{{cite web
  |author=Bundesinstitut für Risikobewertung
  |title=Übergänge von Mineralöl aus Verpackungsmaterialien auf Lebensmittel
  |access-date=2010-04-21
  |url=http://www.bfr.bund.de/cm/216/uebergaenge_von_mineraloel_aus_verpackungsmaterialien_auf_lebensmittel.pdf}}</ref>

* '''[[Tree-free paper|Others]]''': It is also possible to use the fibres of [[Bagasse|Sugarcane Bagasse]], [[Straw]], [[Hemp]], [[Cotton]], [[Flax]], [[Kenaf]], [[Abaca]] and other plant products

===Pulping===
{{Main|Pulp (paper)}}
Two principal methods for extracting fibres from their sources are:

* '''[[Chemical pulp]]ing''' uses chemical solutions to convert wood into pulp, yielding around 30% less than mechanical pulping; however, pulp made by the kraft process has superior strength
* '''[[Thermo mechanical pulp]]''' is a two-stage process which results in a very high yield of wood fibres at the expense of strength.

====Bleaching====
{{Main|Bleaching of wood pulp}}
Pulp used in the manufacture of paperboard can be [[bleaching of wood pulp|bleached]] to decrease colour and increase purity. Virgin fibre pulp is naturally brown in colour, because of the presence of [[lignin]]. Recycled paperboard may contain traces of [[ink]]s, [[Adhesive|bonding agents]] and other residue which colors it grey.
Although [[bleaching of wood pulp|bleaching]] is not necessary for all end-uses, it is vital for many graphical and packaging purposes. There are various methods of [[bleaching of wood pulp|bleaching]], which are used according to a number of factors for example, the degree of colour change required, chemicals chosen and method of treatment. There are three categories of [[bleaching of wood pulp|bleaching methods]]:

* Bleaching by '''delignification''' using [[chlorine gas]], which is a method that has been largely replaced by procedures which are gentler to the environment such as the use of oxygen as a replacement for the chlorine gas.	
* Bleaching by '''[[oxidation]]''' using chemicals such as [[chlorine dioxide]], [[hydrogen peroxide]] or [[sodium hypochlorite]].
* Bleaching by '''[[redox|reduction]]''' using chemicals such as [[sodium bisulphite]].<ref name="igg"/>

===Plies===
[[Image:Single vs multiply.svg|thumb|100px|(1)&nbsp;single-ply vs. (2)&nbsp;multi-ply]]Multi-ply paperboard generally has higher creasing and folding performance than single-ply as a result of layering different types of pulp into a single product. In cases where the same kind of pulp is being used in several layers, each separate layer is treated and shaped individually in order to create the highest possible quality.<ref name="igg"/>

===Coating===
In order to improve whiteness, smoothness and gloss of paperboard, one or more layers of [[Coating and printing processes|coating]] is applied. [[Coated paper]] is usually made up of:

* a [[pigment]], which could be [[china clay]], [[calcium carbonate]] or [[titanium dioxide]], usually a combination of two
* an adhesive or binder as [[styrene-butadiene]] emulsions or [[starch]]es and [[water]].

Additional components could be OBA ([[optical brightener|optical brightening agent]]s).<ref name="kir">{{Cite book
|last=Kirwan
|first=Mark J.
|title=Paper and paperboard packaging technology
|year=1998
|publisher=Blackwell Publishing
|location=London
|isbn=978-1-4051-6845-8
}}</ref>