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Pulp is the basic material for the manufacturing of paper and can be obtained from differing materials: from wood and related types of cellulose such as, for instance, sugarcane bagasse or straw, plant fibres from hemp or linen, cloth (rags), or paper (recycling).
The cloth is sieved, washed and left to ferment over a period of several weeks. The rags are then cut and frayed in special mills. |
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The wood is separated from the bark and chaffed, the wood chips are then pulverised in presses or in grinders with the addition of water. The particles are finally filtered and cleaned in several successive baths in order to achieve a homogenous fibre pulp.
The pulps of today are generally a mixture of wood fibres and paper, to which a binding agent is added for the better formation of the sheets. |
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Modern paper production is completed with the help of gigantic machines which can be over 100 meters long and up to 10 meters wide: The paper webs are produced at speeds of up to 1,800 m/min. A paper machine is an expensive investment, with a new machine frequently costing around a million Euros. |
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Process for a Fourdrinier machine
As soon as it reaches the machine, the pulp is dissolved in water (at a ratio of 5% pulp to 95% water). The pulp which has been prepared in this way then reaches a tank at the beginning of the paper machine, the reservoir tank. This breaks open the fibres uniformly and provides the paper pulp which runs through the paper machine with its shape.
The mixture must then be drained in order to structure the sheet. The first phase of the so-called wet section is the continuously rotating screen where the water content of the fibre pulp is reduced from 95% to 80% (moving screen). The dripping water which contains any fibres which have escaped the screening is recycled.
The sheet, which is still wet, is then fed through a succession of pressure rollers which are equipped with absorbent felts (wet press section). At the end of this section, the sheet has lost some of its weight and has a water content of just 60% | |
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The final phase, during which the paper attains its final water content of 5%, is the drying section. This consists of a sequence of several drying cylinders which are arranged on top of each other in double format and which are heated with steam.
Their temperature reaches up to 120°C as a result of which the moisture evaporates. The temperature gradually decreases from one cylinder to the next.
The paper manufacturing process ends with the production of a 'mother roll web' which is cut into the necessary size for the winder. The rolls of paper can then be used immediately for printing on the revolving printing press, or cut into sheets of differing size and format.
The most common paper machine today is the long screen machine, which in French is named after its inventor, Fourdrinier. The formation of the paper sheets occurs through the drip drying of the fibre layer on a plastic gauze.
This gauze is placed over rollers which continually rotate. The long screen machines are very long and function on the basis of continual operation. |
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Process for a cylinder-mould-machine.
This is a machine with a long tradition which is now used increasingly infrequently and is only used for special papers and high security papers.
With this machine, the sheet of paper is manufactured using a large rotating cylinder. This immerses in a vat which is filled with the liquid paper pulp so that during the rotation, the fibres adhere to the cylinder when it emerges from the paper pulp. A rotating felt removes the fibre carpet from the cylinder from which the final product, the sheet of paper is made. Finally, this sheet runs through the press section and then the drying cylinders.
This manufacturing method is slower and is used for high quality paper which also explains the higher price of such paper.
This method also achieves excellent paper attributes, however: 100% cotton (water and ink resistant, robust handling), homogenous transparency, consistent fibre distribution, the watermark can be extremely sophisticated, the grain is very discreet and it naturally leads to irregular edges, or so-called deckle edges. |
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