Paper and Its Uses/Chapter 6
CHAPTER VI
MANUFACTURE OF BOARDS
The manufacture of boards is varied, ranging from Bristol boards to millboards, and including ivory boards, pasteboards, triplex boards, strawboards, and pulp boards.
For pulp boards the description of papermaking will serve in its entirety, as the boards are made on the Fourdrinier, being engine-sized, reeled at the end of the machine, well rolled later, cut into sheets, sometimes plate-glazed after this, and then sorted and packed. There is one point of variation only, and that is in speed. As there is much more "stuff" let down to the wire, a greater thickness of material for the water to drain from demands more time, and so the output is relatively slower than when paper is being made.
For ivory boards, two or more sheets of fine paper made on a Fourdrinier, or else on a cylinder machine, are brought together at the couch rolls, and the sheets are pressed and rolled together without the use of paste.
Cylinder machines are invariably used for duplex, triplex, and boards of several layers other than paste boards and those already described. Instead of a travelling wire, a wire-covered cylinder is the means of forming the film of pulp. The cylinder revolves in a vat of pulp, takes up a thin layer of the fibre, and, pressing against a travelling felt, leaves its film of paper, and as there are several cylinders, each in its own vat, producing paper in the same way, the several webs are brought together, rolled, dried, and reeled. In the case of a duplex board the pulp may be the same colour, or of two different shades. In triplex boards, the outsides are frequently thin and different in colour, compared with the middle sheet. Cylinder machines with as many as seven vats are in use, and forty to fifty drying cylinders are necessary to complete the extraction of the water.
Pasteboards are made up from middles and pastings. These are obtained from mills making specialities of these lines, the middles very often consisting of a moderately thick paper of poor quality, but the outsides are of fairly fine paper. The papers are not glazed, but after pasting together the web is thoroughly rolled and the surface obtained by subsequent calendering. Bristol boards are made from the finest materials, all-rag, tub-sized papers, the same paper throughout pasted, pressed and surfaced by hot-pressing. Other boards supplied under this title are made of good drawing paper for outsides, and cartridge for middles. The best boards are made by hand, and take considerable time and care in manufacture.
Millboards, the thicker kinds of box boards, slate boards, leather boards, portmanteau boards, and carriage panels are made on a special board machine. For leather boards a large percentage of pulped leather is sometimes employed. For the other kinds a large variety of materials finds its way to the machine, but it is waste in the form of flax, ropes, coarse rags for the best qualities, and for the lower grades waste papers of all kinds. The stronger materials are boiled and beaten, bleaching being unnecessary. Waste papers are simply steamed and pulped. All materials are strained, diluted with water, and forwarded to the vat or stuff-chest of the machine. The board machine is comparatively short, consisting of a cylinder which lifts the film of pulp, delivers it to the endless felt, and a cylinder at the other end of the machine receives the web, which continues to roll round until the desired thickness is attained, when the wet board is dexterously slit by the attendant and taken off to the pile. Here the boards are alternated with sheets of felt or canvas, and the water is pressed out. The boards are hung up singly to dry in a heated chamber, and are afterwards damped slightly, rolled heavily, and cut to size.