How Is a Sheet of Paper Made?
A sheet of paper consists of vegetable fibres of different sizes, twisted and intertwined with each other and finally squeezed together to make a sheet with a surface smooth enough to write or print on. Originally it was discovered that if a mixture of wood pulp and water was spread on a sieve, the water would drain away and leave a deposit which, when dry, could be peeled off as a sheet of paper. Although the Chinese had been using paper since A.D 105 it was not introduced into Europe until the 13th century.
The raw materials used for modern hand-made paper are cotton and linen rags. Such paper is very expensive to produce. Machine-made paper is processed in paper mills from esparto grass, wood and straw, and is much cheaper. The materials for both types of paper-making have to be put through the same basic procedure of repeated washing and bleaching to get rid of impurities.
Inside a paper making factory the pulp is fed to a paper machine where it is formed as a paper web and the water is removed from it by pressing and drying. Pressing the sheet removes the water by force; once the water is forced from the sheet, a special kind of felt, which is not to be confused with the traditional one, is used to collect the water; whereas when making paper by hand, a blotter sheet is used instead.
Drying involves using air or heat to remove water from the paper sheets. In the earliest days of paper making, this was done by hanging the sheets like laundry; in more modern times, various forms of heated drying mechanisms are used. On the paper machine, the most common is the steam-heated can dryer. These can reach temperatures above 200 °F (93 °C) and are used in long sequences of more than forty cans where the heat produced by these can easily dry the paper to less than six percent moisture.
The paper may then undergo sizing to alter its physical properties for use in various applications. Paper at this point is uncoated. Coated paper has a thin layer of material such as calcium carbonate or china clay applied to one or both sides in order to create a surface more suitable for high-resolution halftone screens. (Uncoated papers are rarely suitable for screens above 150 lpi.) Coated or uncoated papers may have their surfaces polished by calendaring. Coated papers are divided into matte, semi-matte or silk, and gloss. Gloss papers give the highest optical density in the printed image.
The paper is then fed onto reels if it is to be used on web printing presses, or cut into sheets for other printing processes or other purposes. The fibres in the paper basically run in the machine direction. Sheets are usually cut “long-grain”, i.e. with the grain parallel to the longer dimension of the sheet. Continuous form paper (or continuous stationery) is cut to width with holes punched at the edges, and folded into stacks.
The oldest known archaeological fragments of the immediate precursor to modern paper, date to the 2nd century BCE in China. The pulp papermaking process is ascribed to Cai Lun, a 2nd-century CE Han court eunuch. With paper as an effective substitute for silk in many applications, China could export silk in greater quantity, contributing to a Golden Age.
Its knowledge and uses spread from China through the Middle East to medieval Europe in the 13th century, where the first water powered paper mills were built. Because of paper’s introduction to the West through the city of Baghdad, it was first called bagdatikos. In the 19th century, industrial manufacture greatly lowered its cost, enabling mass exchange of information and contributing to significant cultural shifts. In 1844, the Canadian inventor Charles Fenerty and the German F. G. Keller independently developed processes for pulping wood fibres.
Before the industrialization of the paper production the most common fibre source was recycled fibres from used textiles, called rags. The rags were from hemp, linen and cotton. A process for removing printing inks from recycled paper was invented by German jurist Justus Claproth in 1774. Today this method is called deinking. It was not until the introduction of wood pulp in 1843 that paper production was not dependent on recycled materials from ragpickers.