Paper

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Sheet of paper
Paper is a thin, flat material produced by the compression of fibres. The fibres used are usually natural and based upon cellulose. The most common material is wood pulp from softwood trees such as pines, but other materials including cotton (flax) and hemp may be used.

Table of contents
1 Manufacture
2 Applications
3 History

Manufacture

The paper making process has four simple steps:

Preparation of the fibres:

The material to be used for making the paper needs to be made into a concentrated solution containing the fibres, called pulp. As many of these fibres are derived from natural sources, this requires many stages of separation and washing. Once the fibres have been extracted, they may also be bleached or dyed to alter the appearance of the final product.

Forming into sheets:

The pulp now needs to be formed into the desired shape. This can be achieved by a mould or by a continuous rolling process. A watermark may be impressed into the paper at this stage of the process.

In the case of the mould process, a quantity of the pulp is placed into a form, with a wire-mesh base (or other draining device), such that the fibres are left coated on the mesh, and excess water can drain away. At this time pressure may be applied to removed more water through a squeezing action. The paper may then be removed from the mould, wet or dry, and go on to further processing.

Modern, mass produced paper is made using a continuous rolling process. The mould gauze is replaced with a gauze conveyor belt, and the paper is passed through successive rollers that apply more and more pressure to remove the water.

Further additives:

Raw paper that contains only pressed and dried pulp is very absorbent (for example, blotting paper), and does not provide a good surface upon which to write or print. Thus, a huge variety of additives are employed to add desired properties to the paper. These are applied in a coating called the size.

Sizing agents are often polymers designed to provide a better printing surface. Starches are very commonly used, as is PVA, but there as many types of polymer employed as there are types of paper.

Sizing agents can also seek to improve the printing surface by smoothing it. The texture of raw paper is rough, and so to achieve greater smoothness, a sizing agent such as clay is used. Smooth, matt finish papers such as magazine paper (for the inside pages) are made in this way. The glossy effect (for example on the covers of fashion magazines) is achieved at the end of the printing process, by adding a clear layer (like varnish) over the printing, and so is not a property of the paper.

Other additives are employed to enhance various properties of the paper, the most common of which are optical brighteners.

Drying

The paper may actually be dried several times during its manufacture (dry paper is much stronger than wet, so it is best to keep the paper dry to prevent it breaking and stopping the production line).

Applications

In such cases making a copy that can not easily be distinguished from the original should be very difficult, to avoid abuse, see counterfeit.

official documents and private statements that are run through a computer are placed in individual letters by a "bursting machine".

History

A form of paper called papyrus, made from reedss, was made as early as 3000 BC in ancient Egypt, and then in ancient Greece and ancient Rome. The modern method of making paper from cotton rags was invented by Ts'ai Lun in AD 105. The Chinese technology was first exported to Japan in 610, where fibres (called bast) from the mulberry tree were used. From there the invention spread to India, where it was copied by the Arabs, who took it to Italy in about the 13th century.

Paper remained a luxury item through the centuries, until the advent of steam-driven paper making machines in the 19th century, which could make paper with wood fibres from wood pulp. Together with the invention of the practical fountain pen and the mass produced pencil of the same period, and in conjunction with the advent of the steam driven rotary printing press, wood based paper caused a major transformation of the 19th century economy and society in industrialized countries. Before this era a book or a newspaper was a rare luxury object and illiteracy was the norm for the majority of humanity. With the gradual introduction of cheap paper schoolbooks, fiction, non-fiction and newspapers became slowly available to nearly all the members of an industrial society. Cheap wood based paper also meant that keeping personal diaries or writing letters ceased to be reserved to a privileged few in those same societies. The office worker or the white-collar worker was slowly born of this transformation, which can be considered as a part of the industrial revolution and all of its phases.

See also: cardboard, ISO 216, paper sizes, paper mill, stationery.




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