by Gautam Shah ➔
Paper forming means forming or casting a sheet of paper from the pulp over a surface that will allow removal of water. The pulp nominally is 1 Lt of water and 1 to 10 grams of solid matter. For draining off the water a bed of wire mesh, deckle, fabric, etc. are used. The quality of pulp and the forming process determine the basic nature of paper. Later processes of conversion further modify the surface qualities.
The differences between various grades and types of paper are determined by:
1. Type of fibre or pulp
2. Degree of beating or refining of the pulp
3. Addition of various materials to the stock
4. Sheet formation method, basis weight or substance per unit area
5. Physical or chemical treatments after paper formation.
Paper is produced by three basic processes:
a. Hand made or traditional way
b. Mould made or semi-industrial way
c. Machine made or fully industrialized way
HAND MADE PAPERS
The basic process of making paper has not changed in more than 2,000 years. It involves two stages, the pulp forming and the formation of felted sheets. The pulp suspension is spread on a porous surface, to drain out the excess water. The pulp forming process may be partly mechanical or chemical but sheet formation is a hand operation.
In making paper pulp by hand, an appropriate mix of raw materials is placed in a vat or trough and is pounded with a heavy pestle or hammer to separate the fibres. During this phase the material is washed with running water to remove impurities. When the fibres are sufficiently broken up, they are kept in water suspension. At this stage the pulp, called half stuff, is ready for the actual process of paper making.
Paper is formed over a mould, a reinforced sheet of metal mesh having either a square mesh pattern, called a wove-pattern, or a pattern of more widely spaced longitudinal wires held together with smaller transverse wires, called a laid pattern. The mould pattern imprints itself on the finished sheet of paper. Handmade papers that are not given special finishes are identified as wove or laid papers, depending on the style of mould that is used in their making.
There are TWO processes for manufacturing hand made papers.
1. A framed wire mesh -mould, called a deckle is dipped into a steam heated pulp tub. When the frame is removed from the vat, the surface of the mould is coated with a thin film of fibre-water mixture. It is given a shake to orient the deposition of fibres in all directions. It also causes the individual fibres to interlock with those adjacent ones, giving strength to the sheet and allow drainage of much of the water from the mixture through the mould mesh. The frame along with the deposited mass is allowed to settle until the paper is sufficiently cohesive to permit its removal from the deckle. The paper is then transferred onto a felt blanket. Several layers of blankets are pressed together to remove the excess water. The sheets are then separated and allowed to dry in a natural or forced air ventilation system.
2. In the second process, the wire mesh frame is nearly similar. But instead of dipping the frame in the pulp tub, the pulp is allowed to float in horizontally, or is poured over a submerged mesh. The pulp is levelled with jerks. The entire frame is placed in a shaded area to drain and dry. Pressing if any occurs much later and often without interleaving of felt blankets.
A major structural feature of a paper web is the lack of uniformity in weight per unit area. Minimizing these variations involves skill. Dilute suspension of fibres (1 to 10 grams of dry solids per litre) in water is allowed to drain through a net (woven polyester fabric) to leave behind a coherent layer 6 to 18 mm deep and several metres wide are formed. A visible change occurs in the appearance of the stock, as it reaches a concentration of 20 g, dry solids per 1 litre, its surface ceases to be mobile, loses the liquid sheen and becomes matt. At this stage natural drainage stops, further forming is done by vacuum removal of water and pressing by a roller.
The sheets of paper are separated from the felts, stacked, and pressed. The process of pressing the stack of paper is repeated several times, and each time, and the stack is built up with the individual sheets in different orientations relative to one another. This procedure improves the surface of the finished paper and is called exchanging. The final stage in paper making is drying. The paper is hung, in groups of four or five sheets, over ropes in a special drying room until its moisture has almost completely evaporated.
Hand made papers are produced in small quantities, with local raw materials (often rare or scarce), and techniques (traditional, proprietary, rudimentary). Even where machine or chemical pulps are used, the unique style of forming gives a special flavour.
All hand made papers are unique in quality, texture and colour. Batch to batch acute variations gives a variegated character. Hand made papers have deckled edge on all the four sides, lesser thickness over the border regions, and multidirectional nonuniform grain structure. Hand made papers are less compact or dense. Hand made papers are naturally fluffy and absorbent unless heavily sized and severely calendered. Handmade paper is a reflection of its maker’s personality.
Hand made Papers are widely used for craft and decorative purposes. For writing or printing, however, it needs additional treatments following drying to make it less absorbent. The treatment consists of sizing the paper. Rough-textured papers are pressed lightly for a comparatively short period, and smooth-surfaced papers are pressed heavily for comparatively long periods.
Museum of Handmade Paper (Museo della Carta) View of Piazza del Duomo.
The Museum of Handmade Paper, located in Mill Valley in the northern part of the modern town, celebrates the long-established paper making tradition in Amalfi. The town was one of the first centres of paper making in Europe, the skill having been acquired by the Amalfitans from the Arabs. The museum is housed in an ancient paper mill which was once owned by the Milano family, a family famous in Amalfi for its involvement in the production and manufacture of paper. In 1969 the building was converted into a museum as a result of the will of Nicholas Milano, the mill’s then owner. The museum contains the machinery and equipment (restored and fully functional) that was once used to manufacture paper by hand.
MOULD MADE PAPER
Mould made papers are also produced on machines that are fairly automatized. The basic paper formation technique is like any hand made paper, but these are continuous one. A rotating mesh drum with part of the surface submerged in a pulp tub, draws in the pulp due to a partial vacuum. The drum continuously transfers the mass on the other side to felt-covered rollers which press the mass to drain out the excess water. The process is not only fast and continuous but provides a uniform output. Mould made papers have grain orientation along the length. Only two edges of a mould made paper are deckled. Mould made papers are fairly smooth, compact, of even thickness and uniform quality. Straw board sheets, rag papers, card papers, card boards, carton box papers, ledger paper, art work, graphics and lithography papers etc. are produced by this process. Most mould papers have one face with mesh impression while the other, face is comparatively smoother.
Machine paper making is more complex, but basic processes are similar to hand-papermaking. Nominally paper machines can be divided into two main types: Cylinder machines and Fourdrinier’s machines.
Machine-made papers are produced in very large scale plants. Paper output is of very uniform quality, colour and thickness. Production of very wide (6 mts) and in large continuous lengths is possible. For the cheapest grades of paper, such as newsprint, ground-wood pulp alone is used. For better grades, chemical wood pulp, or a mixture of pulp and rag fibres, are employed. For the finest papers, such as the highest grades of writing papers, rag fibre alone is used.
Additives like colouring matter, sizing material such as rosin or glue, and fillers such as sulphate of lime or kaolin, which give added weight and body to the finished paper, are mixed into the pulp.
The face touching the wire mesh shows impression of wire compared to even face of the top side. In twin wire mesh processes two thin sheets are cast and their wire faces are joined together (usually without gums or sizing materials) to achieve both side smooth paper. Such sheets, because of natural lamination and disorientation of fibres show high strength, stability and tear resistance, as in currency notes.
The dandy roll is a light unit lightly upon the wire and the surface of the sheet. Its function is to flatten the top surface of the sheet and improve the finish. Dandy rolls help create woven. laid and imprints names, insignia, or designs called watermarks. Paper watermarks have served to identify the makers of fine papers since the early day. A watermark is actually a thinner part of the sheet and is visible because of greater transmission of light.