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| Basic Idea Paper is a flat material normally made from compressed, interlocked and adhered fibers. The word derives from the Egyptian "Papyrus". In recent years the fibre is typically:
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Papyrus reids had a rather limited habitat in the Nile delta and seem to have been driven near extinction by overuse.
A process for making paper seems to have been discovered in China perhaps around 100 BCE. It's importance was recognised because it was kept secret - information is power. The idea nevertheless passed to Korea, and to Japan. Paper was apparently being made in Moorish Andalusia in the 11th century. Later it spread to Italy (around the 14th century CE). Paper is a key to the industrial revolution because without it mass printing and literacy would have been impossible.
The parchments and other materials used as paper in Europe before the 14th century were typically animal skins. Vellum (from the Latin "vitulus" =calf) was originally pig, sheep or calf skin soaked in lime and dried under tension. Old parchment is basically collagen. Modern vellum is usually a cotton based paper although traditional skin product is of interest to artists.
For many years paper was made from rag fibre. Clothing was relatively expensive and people were not anxious to discard it in the 16th century so paper was expensive. The main source of paper came to be linen fibre specially grown for the job.
Cloth and field-grown fibers can still be used as the basis for paper and there is considerable interest in using hemp, although the last British mill that could handle it closed a couple of years ago. There is some suggestion that the field crops give a better yield of paper for less energy and emissions than using wood pulp.
During the 19th century inventors perfected ways to make paper from softwood trees. Only about 1% of paper is currently made from anything other than wood pulp.
Paper making from rag, linen and recycled paper can be done by hand. Highly consistent paper at a low price requires:
- a low cost feedstock - most paper is now made from timber.
- a considerable chain of processes that tends to be the work of large factories.
Fourdriner machines invented at the start of the nineteenth century are the continuous process that actually makes paper from pulp. Any pulp can be used providing there are enough long cellulose fibres..
The basic process is to turn fibrous vegetable matter into a fine pulp mainly of cellulose. The fibres are usually derived from trees and most pulp is made by the Kraft process.
The trees used for paper making are mainly softwoods from temperate forests - spruce and larch. Birch and eucalyptus can be used as well.
Trees are generally grown to about 15 metres tall and 150 -200 mm diameter. They are harvested in lengths of about one or two metres, which can be lifted by man or machine.
The biggest single source of paper-making timber is the Southeastern US which is the largest pulp producing region in the world, clearing 1.2 million acres of forest per year. 
Production is changing, however, with more investment going to Central Europe, Latin America and Asia. (Econ 200506 p76)
Logs are placed in a debarking drum which rotates carrying the logs around so that they rub and lose all bark. Bark has some market as a peat substitute and for bio-degradeable paving and garden coverings. One of the main uses is fuel for paper mills.
Chippers take the bare logs and break them into fairly regular lumps which are the feedstock for the pulp process.
Pulp Making.
Paper is basically cellulose fibers. The fibers of a tree have to be broken down and usually the non -cellulose lignin (resinous) part of the wood is separated out. Overall about a third to half of a tree is actually used for paper.
Pulping and separation uses a succession of mechanical, steam and chemical processes. Worldwide, paper making is thought to be the fifth largest industrial consumer of energy, using 4% of total production. A paper mill can therefore be a bad neighbour wasting lots of energy and creating lots of effluent. The processes could be made efficient, waste bark powered and with little or no net waste emission. (CO2 releases can be balanced by new growth of trees)
Groundwood ( GW) is wood crushed with grinders and soaked - it tends to be used in newsprint and paperboards.
Thermomechanical Pulp (TMP) is crushed in a refiner with steam at high pressure.
The lignin which strengthens timber remains in GW and TMP. For finer paper it is usually removed - it rapidly turns yellow or brown so it can only be retained in papers where this would not matter (like packaging, wrapping and newspaper ). Lignin removal is done in digesters - which are a major consumer of energy and / or chemicals in the paper making process. However liginin separated from pulp is quite widely used in other processes.
To remove the lignin, chips pass to a digester where they are cooked to soften them. Digesters can be:
Sulphite or acid process - cooked with calcium acid sulphite
Sulphate or alkaline process - also known as the kraft process.
Biological - using fungi that can rapidly break down lignin but leave cellulose intact - so far this is experimental.
The kraft chemical pulping process removes lignin as sulphates. The process was developed by Carl Dahl in 1884. Most of the pulp used for office papers is treated using the kraft process - it is used for about 80% of the production volume of paper.
Coarse pulp, sodium hydroxide and sodium sulphide are fed into heated pressure vessels called digesters. The lignin breaks down and can be run off from the cellulose component of the wood.
Black liquor is the liquid waste containing the sulphated waste lignin half of the wood. Black liquor can just be a waste, in which case it will destroy any river it is dumped in. Luckily black liquor does have several potential uses. It can be concentrated by evaporation and burned to generate steam for the mill process. The inorganic material can then be recovered to regenerate the sodium hyroxide and sodium sulphide for the pulping process. During evaporation the black liquor separates out and a "soap" floats to the surface which can be acidified to produce tall oil - a source of resins and fatty acids.
The lignosulphonate materials also have several uses - dispersants in cement, deflocculants in drilling muds, water treatment materials and textile dyes, raw materials for ethanol and even vanilin flavourings.
The cellulose produced by the kraft process is strong (kraft is German for stong) but rougher and more difficult to bleach than material produced by the sulfite process.
Refiners break down the softened chips. The chips are fed from the digester under pressure between rotating steel plates which rip them into fibres. Fibrils on the longer fibers partially detach and bloom outward forming a shape that will tend to lock together with it's neighbours.
The Masonite process breaks fibers down largely using steam.
Defibrators break pulp into fibers using steam and grinding surfaces. The grinding surfaces are disks with radial grooves to provide the grinding surface. One disk is static and the other rotates at upwards of 1000 RPM. Wood chips are fed into the centre and centifugal forces push them to the circumference where the fibers can be gathered. The whole apparatus is heated by steam to soften the wood. The process was invented by Arne Asplund and became the main product of Defibrator AB. The trademark is now owned by Metso which is an engineering concern involved in paper and mineral work.
At this point the fibres are brown, which wouldn't contrast with print very well.
The sulphite process uses calcium hypochlorite as a bleach
The sulphate process tends to use chlorine dioxide
A further wash with sodium hydroxide removes remaining impurities. The bleaching and washing process are repeated until the pulp reaches the required brightness. Brightness is specially important for colour print - if the paper isn't white and bright the colour space available will be low.
Brightness is important for printing papers so manufacturers can't ignore it. On the other hand chlorine bleaches are an environmental concern so the pulp industry is switching to alternatives such as oxygen, ozone and hydrogen peroxide.
Pulp mills are rarely small scale investments. "The Economist" says "building even a modest one from scratch can cost $1 billion" and that "the biggest projects, designed to produce over 200,000 tonnes of pulp a year, generally seek funds from overseas." (Econ 200506 p76)
Pulp can be fed directly into the next stage of paper making. Alternatively it can be shipped in a tanker or as dried sheets.
Paper making begins with creating the right consistency of pulp slurry from virgin pulp, broke (waste paper), sizing, fillers and colourings. For instance, calcium carbonate (limestone) or kaolin (china clay) are added to give a paper that will polish well. This might pass into a further efiner where they are mixed and brushed to provide the consistency required in the remainder of the process.
Pulp mixture is diluted with water to form a thin slurry. The thin slurry is caught in a flat fine mesh screen. Water drains through the screen whilst the cellulose forms a web on the surface. Patterns in the mesh may be used to form a watermark in the web although this might also be applied at the drying stage by an embossed "dandy roller".
Placing the paper on the mesh can be done by hand or by machine. Mold papers are often made by hand with individual surrounds at the page size and a fine wire-mesh base being used. Handmade papers are popular with artists and graphic designers and some of them will pass through a laser printer succesfully - although anything with much texture may displace the toner and be rather spoiled by pressure in the fuser. Inkjet paper generally has to be fairly flat - texture might brush the head and cause streaking.
Handmade paper nicely printed may help give value to a certificate or gift - and could give special impact to a business presentation.
Fourdrinier Process.
The majority of paper is made by a Fourdinier machine.
The Fourdrinier machine is one of those inventions whose origins cause quarrels due to several claimants and national pride. One of the earliest machines was built for the Fourdrinier brothers who had a stationery shop in London circa 1801. Aquaintances from revolutionary France brought the idea which originated with Nicholas Louis Robert of Essones. The Fourdriniers invested in a mill at Frogmore, Hertfordshire and later in their own mill nearby at Two Waters and then at St Neots. The Fourdrinier machine is one of the earliest continual processes.
The headbox is the start of the Fourdrinier machine. It is usually mounted above a moving conveyor of wire mesh so that the slurry from the headbox is carried away in a thin layer on the conveyor. A blade called the slice determines the thickness of the material, which will become its weight per square metre.
The fourdrinier table vibrates the material on its conveyor. Vibration causes the fibres to interlock and form a web, and some of the water squeezes out. Suction boxes below the table assist the removal of water. The material now has some structural integrity and the wire mesh conveyor can rotate back under the table leaving the web to carry on.
The press section removes more water using a series of rollers forming nips. The water can be carried away in troughs, using a felt conveyor or through vaccum pumps working through porous rollers. A succession of ollers flaten and smooth the sheet giving it an even thickness..
Drying is done by steam heated rollers. Sizing agents may be added to change the surface characteristic of the web of paper - these can include starch and glue to reduce surface fuzzines and resin to give water resistance. Moisture content is reduced to about 6%. If moisture levels were pushed lower than this the hygroscopic nature of paper would become more evident and it might tend to pick up water from the atmosphere, changing its weight and size.
The calender is a series of rollers which further smooth the paper. Pressure of the rollers forces any proud material down and gives a plain machine finish or a polished supercalendered finish. Calender rollers are typically in several successive pairs with one being cast iron and the other having a relatively soft cover of polymer, compressed cotton or paper. The paired rollers give a wider nip with more even pressure
Finish needs to match the intended printing task.
Newspaper is cheap and absorbent for high speed printing. Although colour is common in today's newsprint it is typically at low resolution (less than 100dpi) and occupies small spaces on one side of the page so the paper doesn't saturate. The paper doesn't even have to be very white.
Magazine paper is much smoother to suit the halftone print process. The smaller the individual rosettes that can be resolved the better the page will look - with 300 dpi being typical.
Catalogues and full colour books will have even higher gloss to support a better halftone. This may be improved still further by a coating.
Copy paper formulations have changed a bit in recent years. The original requirement was for a smooth precisely cut paper with the right electrostatic properties for photocopying machines. Now the paper also has a smooth but absorbently sized surface to accomodate the likelihood of inkjet printing. Inkjet photography may use a special paper that is both absorbent and given a highly polished glossy finish which is not so suited to laser printing (the sizing breaks away).
The web of paper is finally wound onto a roll for storage and shipping - or for final cutting.
Variations.
Naturally there are variations on a process whose origins stretch back over 200 years. For instance a drum might lift pulp slurry out of a vat then pass it on, rather than the head-box arrangement. Heated rollers and evaporation would have been favoured at one time, now controlled pressure and vaccuum rollers might be more energy efficient.
Web Paper.
The paper web is a finished product only for newsprint and high speed presses. The rolls involved need a crane to lift them and a lorry to shift them.
Paper can undergo additional finishing processes - for instance being passed through an off-line calender. Plater finished paper is cut then compressed between copper or zinc plates.
Cutting is one of the main stages in creating the products people are familiar with.
Paper can also be
cut then rolled - fax, POS and plotter paper
cut then fanfolded - traditional green-lined 14" computer paper
fanfolded as multipart with carbon paper or carbonless copy paper.
Although a lot of paper is used in print the material is used in
cardboard boxes - commonly the outer protection for almost all durable goods
packaging - groceries used to be packed in brown paper bags and there is renewed appreciation of the benefits of easily recycled materials For instance pulp pallettes and mouldings are used to secure electronic goods and cartridges for shipment
hygeine applications (toilet roll, paper towells, sanitary pads, bandages). 
Environment and Recycled Fibre.
Paper is sometimes regarded as an environmental villain, demolishing forests and polluting rivers.
Paper making companies including some of the best known do still seem to be clear cutting old growth forests including those that are home to endangered wildlife. Fortunes are still made by illegal logging. Even where trees are specially planted, forestry for paper has tended towards monoculture - plantations of spruce trees in Europe. In the southeast US the loblolly pine tends to be the lumber and pulp tree. Problems with "tree farms" or plantation are that they tend :
| to support only 10% of the plant and animal species of natural forest |
| to use a lot of herbicide and chemical fertiliser - partly because they are not biodiverse, and these artificial inputs contribute to ground and surface water pollution. |
Monoculture and clear cutting still have their adherents. Organisations like the UK's Forestry Commission have found more sustainable practices work well. 
About half of a tree is unwanted lignin and separating this out can use a large input of sulphurous chemical. Whitening the pulp often uses chlorine. With sulphur and chlorine as major inputs pulp mills have often been serious polluters. With a bit of care paper making could conceivably be environmentally neutral, forests recovering carbon from the atmosphere as raw material and fuel. Factories recycling their own waste.
Globally the paper and packing industries don't come close to environmental neutrality. Paper consumption seems to be rising at least as quickly as ecycling so that there has been no net reduction in virgin pulp use in most markets.
The Centre for International Forestry Research, based in Indonesia, eports on logging worldwide. In he latest report Machteld Spek, a financial analyst, is concerned that disregarding sustainability exposes investors to financial risk - multi-billion dollar projects have been going ahead without secure, legal supplies of wood for pulp. (Econ 200506 p76). Big banks do seem to be tightening up on their lending policies so perhaps the paper making environmental footprint might diminish.
In Britain the recycled part of paper has risen to 60% and a piece of office paper kept clean can go through the recycling process seven times. However raising the percentage recycled is getting increasingly difficult. Some paper uses like food wrapping don't suit recycling (although they may still be the least bad option). Some paper is contaminated and can't be used. Some people are simply resistant to the message.
Recycled paper has already had lignin removed so this energy intensive stage is not needed. On the other hand recycling often means moving paper hundreds of kilometres to a paper mill. If there are not paper mills within egions the savings from recycling may be less certain.
Most "recycled" office papers are partly made from "broke" and partly virgin pulp. The virgin pulp provides the long fibres that provides strength to the paper. Paper can be made entirely (or largely) from recycled material but the costs rise about 30%. The shorter fibers from recycling can be used in hygeine products - after which they aren't suited to recycling (except as manure).
Recycling is also important because it stops paper going to landfill. Incineration turns paper largely to steam and C02 (with a few more noxious substances) which returns the materials to their original form. Landfill turns paper to methane - a more potent greenhouse gas.
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Paper is usually made in big rolls - but mostly cut to size before it is used.
International paper sizes are set by ISO 216. The sizes range from A0 upwards although by A8 the page is about the size of a credit card. Each size is made by successively folding a piece of A0 paper which has a surface area 1 metre square. The most widely used size is A4.
The ISO 216 sizes are all based on a single aspect ratio which is based on the square root of two or the proportions 1:1.4142. Georg Lichtenberg conceived the idea of basing paper on this ratio in 1786. Dr Walter Porstmann turned the idea into a system of practical paper sizes in the early 20th Century and it was adopted in Germany as DIN 476 in 1922.
The idea makes:
- Printing presses match standard paper rather well and generally cuts waste in the printing process. An A0 machine can print everything, A1 most things. An A3 printer can also handle A4 and so forth.
- Scaling documents easy - so an A3 diagram can be reduced to an exact fit on A4 and A4 text enlarged to a poster on A3.
The idea is so neat that it has been widely adopted - the only exceptions being the US and Canada. The US (and the English speaking world generally) has a long- standing difficulty with metric measurements, on which the ISO scheme is based. Mexico and the Phillipines have officially adopted the system but the dominance of US paper makers means US standard paper is cheaper. Of course the dominance of the US in computer standards means that many computer devices - including printers - are usually described in inches.
The A series paper sizes look superficially as though they were concocted using random numbers but remember that area changes whilst aspect ratio is preserved:- A0 is 1 square metre, A1 half a metre and so forth. This is really handy in printing where the cost of printing so many booklets and catalogues can be estimated by taking its page size to the nearest A series multiple. A4 documents are most economically printed in multiples of 16 pages because offset litho presses typically take A0 sheet.
A0 is a sheet 1189 x 841 mm (almost exactly 1m2). Folded in two across the longer dimension this gives a sheet 841 x 594 mm with the same aspect atio. After 4 folds the paper makes 16 sheets of A4 at 297 x 210 mm.
The A series is quite flexible but there are times when it doesn't give quite enough range. For instance an A4 envelope would be too small for A4 and an A3 envelope far too big. ISO also approves the B series for use in "exceptional circumstances" and the C series ISO 269 which is intermediate between the two. A4 fits a C4 envelope and a C4 envelope fits inside a B4 Envelope. The only common use of the B series is for envelopes.
| A | B | C | |
| 0 | 841 x 1189 | 1000 x 1414 | 917 x 1297 |
| 1 | 594 x 841 | 707 x 1000 | 648 x 917 |
| 2 | 420 x 594 | 500 x 707 | 458 x 648 |
| 3 | 297 x 420 | 353 x 500 | 324 x 458 |
| 4 | 210 x 297 | 250 x 353 | 229 x 324 |
| 5 | 148 x 210 | 176 x 250 | 162 x 229 |
| 6 | 105 x 148 | 125 x 176 | 114 x 162 |
| 7 | 74 x 105 | 88 x 125 | 81 x 114 |
| 8 | 52 x 74 | 62 x 88 | 57 x 81 |
| 9 | 37 x 52 | 44 x 62 | 40 x 57 |
| 10 | 26 x 37 | 31 x 44 | 28 x 40 |
| Aspect ratio is √2 or 1.4142 |
DIN 476 allows the street poster sized 4A0 at 1682 x 2378 mm and 2A0 1189 x 1682 mm. There are a few industrial plotter-printers that can deal with paper at this size.
Tolerances are:
+/- 1.5mm for dimensions to 150mm
+/- 2.0mm for dimensions 150 to 600mm
+/- 3.0mm for dimensions above 600mm
This allows for papers natural tendency to change dimension with water content, and for a certain amount of folding and guillotining.
US Paper Sizes
The ISO paper sizes have never caught on in the US. Printers are made for global markets but the biggest presence in the printer industry is HP and they are US based. A lot of the information online naturally uses US standards so we need a cross reference.The American National Standards Institute (ANSI) defined a set of regular paper sizes based on the de-facto letter size. (NSI / ASME Y14.1 of 1996).
| ISO A equiv | ANSI Name | in x in | mm x mm | Ratio |
| A4 | ANSI A Letter | 8½ x 11 | 216 x 279 | 1.2941 |
| A3 | ANSI B Ledger | 17 x 11 | 432 x 279 | 1.5455 |
| A3 | ANSI B Tabloid | 11 17 | 279 x 432 | 1.5455 |
| A2 | ANSI C | 17 x 22 | 432 x 559 | 1.2941 |
| A1 | ANSI D | 22 x 34 | 559 x 864 | 1.5455 |
| A0 | ANSI E | 34 x 44 | 864 x 1118 | 1.2941 |
Legal size is also common in the US, it measures 216 x 356 mm or 8.5 x 14 inches.
The problem with the ANSI sizes is that not everyone uses them. In particular there are a set of paper sizes used for architecture. These paper sizes have the merit of aspect ratios being small numbers. Wide bodied printers (plotters) are commonly made in C, D and E sizes.
| Approx ISO equiv | Architecture Name | in x in | mm x mm | Ratio |
| c A4 | Arch A | 9 x 12 | 229 x 305 | 3:4 |
| c A3 | Arch B | 12 x 18 | 305 x 457 | 2:3 |
| c A2 | Arch C | 18 x 24 | 457 x 610 | 3:4 |
| c A1 | Arch D | 24 x 36 | 610 x 914 | 2:3 |
| c A0 | Arch E | 36 x 48 | 914 x 1219 | 3:4 |
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Paper thickness is generally expressed as "grammage". There is usually a close relationship between thickness, density and paper properties like strength because weight reflects the amount of cellulose involved. Grammage is defined in ISO 536.
The grammage refers to a one square meter page so an A0 sheet of 80 gram per square meter paper will indeed weigh 80 gramms. An A4 sheet weighs 80/16=5 grammes.
The US uses paper desnity measured in pounds for a ream of 500 sheets, however the ream weight is measured before it is cut - so the actual weight of a ream may be different from the paper delivered.
Quantity.
A stack of 500 sheets of paper is a ream. Paper is usually packed in boxes of 5 reams.