paperboard

Paperboard

Paperboard is (like paper) a 'vegetable-fibre web' formed from a water suspension. While there is no rigid differentiation between paper and paperboard, paperboard is generally thicker (usually over 0.25 mm or 10 points) than paper. According to ISO standards, paperboard is a paper with a basis weight (grammage) above 224 g/m², but there are exceptions.^[1] Paperboard can be single or multi-ply. Paperboard used for the manufacture of folding cartons and rigid set-up boxes is often called boxboard. Paperboards used for the manufacture of corrugated fiberboard are called containerboard. It can be easily cut and formed, is lightweight, and is strong used in packaging. Another enduse would be graphic printing, such as book and magazine covers or postcards. Sometimes it is referred to as cardboard, which is a generic, lay term used to refer to any heavy paper pulp based board.

History

In 1817, the first paperboard carton was produced in England. Folding carton first emerged around the 1860’s and was shipped flat to save space, ready to be set up by customers when they were required. 1879 saw the development of mechanical die cutting and creasing of blanks. In 1911 the first kraft sulphate mill was built in Florida and in 1915 the gable top milk carton was patented and in 1935 the first dairy plant was observed using them. Ovenable paperboard was introduced in 1974.^[2]

Production

Fibrous material is turned into pulp and bleached, to create one or more layers of board, which can be optionally coated for a better surface and/or improved visual appearance.

Raw materials

The above mentioned fibrous material can either come from fresh (virgin) sources (e.g. wood) or from recycled waste paper. Around 90% of virgin paper is made from wood pulp.^[3] Today paperboard packaging in general, and especially products from certified 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 recycled material.

• Hard wood: 0.05 inches (length) e.g. Birch which has short fibres. It is generally more difficult to work with however does provide higher strength. Although its fibres are not as long and strong as those in softwood, they make for a stiffer product. Hardwood fibres fill the sheet better and therefore make a smoother paper that is more opaque and better for printing.

• Soft wood: 0.13 inches (length) e.g. Pine and spruce which have typically long fibres.

• Recycled: Recycled material 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 and gets this from the added virgin fibres. Mixed waste paper is not usually de-inked for paperboard manufacture and hence the 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.^[4]

• Others: It is also possible to use the fibres of Straw, Hemp, Cotton, Flax

Pulping

Mainly two methods for extracting fibres from its source are used:

• Mechanical Pulping is a two stage process which results in a very high yield of wood fibres.

• Chemical Pulping uses chemical solutions to convert wood into pulp, yielding around 30% less than mechanical pulping.

Bleaching

Pulp used in the manufacture of paperboard can be 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 inks, bonding agents and other residue which causes a grey colouration. Although bleaching is not necessary for all end uses, it is vital for many graphical and packaging purposes. There are various different methods of 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 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 reduction using chemicals such as sodium bisulphite.^[4]

Plies

(1)single ply vs. (2)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. The benefits of multi ply paperboard are for example its higher creasing and folding performance.^[4]

Coating

In order to improve whiteness, smoothness and gloss of paperboard, one or more layers of coating is applied. Coatings are usually made up of:

• a pigment, which could be china clay, calcium carbonate or titanium dioxide,
• an adhesive or binder and water.

Additional components could be OBA (optical brightening agents).^[5]

Classifications

Based on the production process and the source of the pulp, different types of paperboard are produced. The common industry abbreviations are:

• FBB/GC/UC (Folding Box Board) is a virgin fibre board with a middle layer of mechanical (CTMP) pulp, which gives it a light yellow colour.

• SBB/SBS/SUS (Solid Bleached Board) is a virgin fibre board made purely from bleached chemical pulp, which is white throughout.

• SUB (Solid Unbleached Board) is a board made from unbleached chemical pulp (yellow) or recycled material (grey).

• WLC (White Lined Chipboard) is a board made from virgin and recycled material (grey).

Grades

The DIN Standard 19303 "Paperboard - Terms and grades" (Publication date : 2005-09) defines different grades of paperboard based on the surface treatment (first letter), the main furnish (second letter) and the colour (non-D grade) or bulk (D grade only) (numbering).

Example: GC1 would be a "pigment coated", "virgin mechanical pulp" board with a "white reverse side". Often the used paperboard type would be FBB, which was coated on both sides.

Common terms

Basis Weight (US): Is the weight of 500 sheets in pounds (mass).

Brightness: Brightness is a technical term that is defined as the amount of blue-white light that a paper reflects.^[6] This property is very subjective and individual to each buyer and end use as skin colour and food are better reproduced on ‘warm’ (yellow) whites and not blue whites.

Grammage: The grammage of the paperboard is assessed in accordance ISO 536.^[7] Grammage expresses weight per unit area and is measured in g/m².^[6]

PH: Surface pH is measured on a water extract and is on a scale of 0-14, 0 being acidic, 7 neutral and 14 alkaline.^[8]

Stiffness: Stiffness is one of the most important properties of paperboard as it affects the ability of cartons to run smoothly through the machine that erects, fills and closes them. Stiffness also gives strength and reduces the propensity of a carton to bulge under the weight of settling flowable contents such as cereals. Other factors which affect board stiffness include thickness, coatings, moisture content, grammage and density.^[6]

Smoothness: Smoothness is particularly important when being used for printing, the smoother the paperboard, the better the ink coverage. It is measured using air leak methods – the greater the rate of air leakage, at a specific air pressure, from under a cylindrical knife placed on the surface, the rougher the surface.^[6]

Caliper/Thickness: In the US caliper is usually expressed in thousandths of an inch (0.001”) or points, where a sheet of paperboard with a thickness of 0.024” would be 24 points. In Europe it is measured in g/m². Paperboard also tends to be referred to with thickness rather than weight.^[5]

Whiteness: It refers to the equal presence of all colours, because a truly white sheet will reflect all wavelengths of visible light equally.^[6]

Paperboard industry

The paperboard sector is mainly looked at in conjunction with the paper industry. The Paper & Paperboard market size (2007) had a value of 630.9 billion USD and a volume of 320.3 million metric tons .^[3] 40.1% of that market is European. About 50% of all produced paper is used for packaging, followed by printing and writing.^[3] The consumption of paper and paperboard seem to correlate with economic trends (GDP) ^[9] According to ProCarton, the consumption of paper and paperboard seem to correlate with economic trends (GDP)^[10] the sales of carton in Europe sum up to around 8 billion Euros worth. 5.4 million tonnes of cartonboard is consumes yearly by over 1,100 printers. Cartons make up one third of paper and board packaging and 15% of all packaging. A bit more than half (54%) of the European carton is produced using recovered fibre or waste paper.^[11]

The paper and paperboard industry is quite energy and capital intensive. A coated board line with 400kt/y will costs around 60 million Euros^[12] (about 85 million USD in 07/2009). Economies of scale apply, because of which a few large players often dominate the market place. E.g. in North America the top 5 producers have a market share of 85%.

See also

• Papermaking

References

Further reading

• Brody, A. L., and Marsh, K, S., "Encyclopedia of Packaging Technology", John Wiley & Sons, 1997, ISBN 0-471-06397-5
• Soroka, W, "Fundamentals of Packaging Technology", IoPP, 2002, ISBN 1-930268-25-4

External links

• TAPPI Technical Association of the Pulp and Paper Industry
• Paperboard Packaging A renewable, recyclable resource for innovation (Video)