The Manufacture of Paper / With Illustrations, and a Bibliography of Works Relating to Cellulose and Paper-Making

by R. W. Sindall

The beater is first partially filled with water, and the drained half-stuff added gradually until the “furnish,” a convenient term applied to the contents of the engine, has the proper consistency, which varies according to the nature and quality of paper required.

The mass is circulated steadily round the engine by the action of the beater roll, which is lowered from time to time until the distance between the knives on the roll and those on the bed-plate has been set to the desired adjustment. This lowering of the roll and its proper adjustment call for the greatest care.

Influence of the Beating.—The importance of this operation can easily be judged from one or two specific examples. In the case of rag papers the two extremes of variation are represented by the ordinary blotting paper on the one hand and a hard strong writing paper known as a loan on the other. Now the great difference in these papers may be traced to the careful selection of the rag and the treatment in the beater as the two primary causes of the final results.

For blotting papers it is essential that the rags should be old and tender. In the beating operation subsequent to the usual boiling and bleaching processes the half-stuff is beaten quickly with sharp knives, the roll being lowered soon after the engine is filled, so that the beating is finished in about one to one and a half hours.

For the strong writing paper new strong rags are selected. In the beating process the knives used are dull, the roll is lowered slowly and cautiously, and the beating goes on for eight to ten hours.

The effect of such difference in treatment is easily seen by examination of the fibres of the papers under the microscope. In the first case the fibres appear short with clean cut ends, the shape little distorted, the structure well defined, bearing a strong resemblance to the unbeaten material. In the case of the well-beaten paper the ends of the individual fibres appear to be drawn or frayed out, the fibres do not possess the sharp well-defined outline characteristic of blotting paper; they are partly split up into fibrillæ which lie together in a confused mass.

In the blotting paper these effects are produced because the knives being sharp cut up the material quickly, and in the writing paper because the dull “tackle” tends to draw out the fibres and tear them up lengthwise.

The practical result is a spongy, soft, and bulky blotting and a hard, strong, heavy writing paper. Of course the great difference between a blotting and a writing paper is not all due to this one operation, but is obtained by a series of operations, of which one of the most important is, however, the beating.

Colouring the Paper.—The pulp is brought to any desired tint by the addition of mineral pigments or aniline dyes to the contents of the engine. The latter soluble dyes, however, are seldom used for high-class rag papers. Prussian blue, ultramarine, and smalts are chiefly used for this purpose, giving toned blue, azure, and blue laid papers.