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Papermaking - Background from Wikipedia

Posted on Tuesday, March 17, 2009 in Uncategorized

Papermaking has traditionally been traced to China about 105 AD, when Cai Lun, an official attached to the Imperial court during the Han Dynasty (202 BC-220 AD), created a sheet of paper using mulberry and other bast fibres along with fishnets, old rags, and hemp waste. However a recent archaeological discovery has been reported from near Dunhuang of paper with writing on it dating from 8 BC, while paper had been used in China for wrapping and padding since the 2nd century BC. Paper used as a writing medium became widespread by the 3rd century, and by the 6th century toilet paper was starting to be used in China as well. During the Tang Dynasty (618-907 AD) paper was folded and sewn into square bags to preserve the flavor of tea, while the later Song Dynasty (960-1279 AD) was the first government on Earth to issue paper-printed money (see banknote).

Modern papermaking began in the early 1800s in Europe with the development of the Fourdrinier machine, which produces a continuous roll of paper rather than individual sheets. These machines have become very large, up to 500 feet (~150 m) in length, producing a sheet 400 inches (~10 m) wide, and operating at speeds of over 60 mph (100 km/h).

Papermaking, regardless of the scale on which it is done, involves making a dilute suspension of fibers in water and allowing this suspension to drain through a screen so that a mat of randomly interwoven fibers is laid down. Water is removed from this mat of fibers by pressing and drying to make paper.

Manual preparation

Fibers are suspended in water to form a slurry in a large vat. The mold is a wire screen in a wooden frame (somewhat similar to an old window screen), which is used to scoop some of the slurry out of the vat. The slurry in the screen mold is sloshed around the mold until it forms a uniform thin coating. The fibers are allowed to settle and the water to drain. When the fibers have stabilized in place but are still damp, they are turned out onto a felt sheet which was generally made of an animal product such as wool or rabbit fur, and the screen mold immediately reused. Layers of paper and felt build up in a pile (called a ‘post’) then a weight is placed on top to press out excess water and keep the paper fibers flat and tight. The sheets are then removed from the post and hung or laid out to dry. A step-by-step procedure for making paper with readily available materials can be found online.

When the paper pages are dry, they are frequently run between rollers (calendered) to produce a harder writing surface. Papers may be sized with gelatin or similar to bind the fibres into the sheet. Papers can be made with different surfaces depending on their intended purpose. Paper intended for printing or writing with ink is fairly hard, while paper to be used for water color, for instance, is heavily sized, and can be fairly soft.

The wooden frame is called a “deckle”. The deckle leaves the edges of the paper slightly irregular and wavy, called “deckle edges”, one of the indications that the paper was made by hand. Deckle-edged paper is occasionally mechanically imitated today to create the impression of old-fashioned luxury. The impressions in paper caused by the wires in the screen that run sideways are called “laid lines” and the impressions made, usually from top to bottom, by the wires holding the sideways wires together are called “chain lines”. Watermarks are created by weaving a design into the wires in the mold. This is essentially true of Oriental molds made of other substances, such as bamboo. Hand-made paper generally folds and tears more evenly along the laid lines.

Laboratory-made paper

Hand-made paper is also prepared in laboratories studying papermaking and in paper mill quality labs. The “handsheets” made according to TAPPI Standard T 205 are circular sheets 15.9 cm (6.25 in) in diameter and are used to measure paper brightness, strength, degree of sizing and so on.

Industrial papermaking

A modern paper mill is divided into several sections, roughly corresponding to the processes involved in making hand-made paper. Pulp is refined and mixed in water with other additives to make a pulp slurry, the headbox distributes the slurry onto a moving, continuous screen, water drains from the slurry (by gravity or under vacuum), the wet paper sheet goes through presses and driers and is finally rolled into large rolls, often weighing several tons.

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