M.G. Caps.-A large number of thin papers used by the bakery and confectionery trades, the drapery and dry-goods trades are generally known as M.G. papers. These two letters signify that the papers are machine-glazed, and usually on one side only. The majority of the papers are manufactured from hard sulphite wood pulp, possessing great strength, the colour being of secondary importance. The preliminary operations in the manufacture of the paper are of the usual order, but the paper-machine is of peculiar construction, being known as the single-cylinder, or Yankee machine.

The wet end of the machine resembles the ordinary Fourdrinier in having the usual strainers, endless wire, and couch-rolls. The wet web of paper is transferred from the couch-roll on to an endless felt, which carries the paper over one large drying-cylinder, 10 to 12 feet in diameter, which is placed on a tall framework over the wet end of the machine. The outside of the cylinder is well

polished, so that the surface of the paper which comes into immediate contact with it becomes highly glazed. This machine is specially adapted for such thin papers as M.G. Caps, biscuit papers, tissues, and the like.

Single Cylinder Paper-machine. The pulp flows from a stuff-chest through the strainer a into the distributing box b, and on to the endless wire c. The excess water is removed by the usual suction-boxes dd, and the wet sheet of paper then passes through the couch-rolls ee, over the guide-rolls ff, round the drying cylinder g, and is finally reeled up at h. The felt carrying the wet paper from the couch-rolls to the drying-cylinder passes through a washingtrough k, which removes dirt and small fibre. (Fig. 67.)

Millboard. The manufacture of boards for boxes is a simple operation carried out by means of the board machine, which is practically identical with the wet-press machine used in making sheets of mechanical pulp.

The raw material used consists of old waste papers mixed occasionally with boiled gunny. The papers are soaked in hot water, broken up, mixed with any other material selected, and beaten for a short time to ensure thorough

F

incorporation, after which the mixture diluted with the required quantity of water is discharged into stuff-chests.

The pulp flows from the stuff-chest into the reservoir A of the board machine, in which revolves a large hollow wire-covered cylindrical drum B. The water with which the pulp is mixed passes through the wire into the interior of the drum, and flows away by means of an overflow pipe fixed at the centre of the drum (not shown in the drawing) on the outside of the reservoir. The pulp adheres to the outer surface of the drum and comes into contact, as the drum revolves, with an endless felt passing round the roll C. The wet sheet adheres

to the felt, and is carried by it over the guide-roll D, and between the couch-rolls E F. The sheet of pulp winds itself continuously round the upper roll E, while the felt passes round the lower roll F under the machine, between the guide-rolls G, back to the roll C. (Fig. 68.)

The thin sheet being wound continuously on the couch-roll E, is gradually formed into one thick sheet. The thickness of the board is determined by the number of revolutions made by the roll E. A bell is attached to the frame of the machine near the shaft of the roll E, and as soon as the sheet is the required

Fig. 69. Diagram to illustrate method of slitting thick pulp boards on the
Board Machine.

thickness the bell rings, and the men in attendance at once remove the sheet without stopping the machine, an operation which is easily effected.

The machine shown in Fig. 68 is constructed to make a sheet of given width, determined by the width of the couch-roll E, and of given length, determined by the diameter of the roll E. Thus a couch-roll 72 inches long and 14 inches diameter will give a sheet 72 inches by 44 inches.

If the distance between the couch-rolls and the reservoir is increased, an additional appliance may be used by means of which the full width of 72 inches can be automatically cut up into two or more smaller sizes. This consists, as shown in Fig. 69, of a small circular disc K fixed on a shaft M stretching across the machine from one side to the other. The edge of the disc is about half an inch wide. The felt carries the thin sheet of pulp from the guideroll C past the disc, which revolves in contact with the felt, and a thin strip of pulp adheres to the edge of the disc, so that the sheet is divided into two smaller sheets. The pulp attached to the disc is washed off by a continuous stream of water. The position of the disc K on the shaft M can be varied so as to cut the sheet as required. The diagram illustrates the position necessary for cutting the sheet of 72 inches into 42 inches and 30 inches respectively.

The wet boards removed from the machine are piled up, with pieces of coarse sacking between them, and subjected to great pressure, in order to remove the excess of water and at the same time to "close up" the sheet and produce a

hard solid board. The pressed boards are then dried either by simple exposure to air for the production of what are known as air-dried boards, or by exposure to a current of heated air passing through a closed chamber. After drying, the boards are glazed by heavy calender-rolls.

Vulcanised Boards.-The heavy dense material known as vulcanised board is prepared by soaking damp boards or sheets of paper in strong solutions of zinc chloride. Two or three thicknesses of board or paper are treated in this way, placed together and passed through heavy rollers, which squeeze out the excess of solution and press the thin boards into a compact mass which, when dried and glazed, is exceedingly hard.

Panel Boards and Roofing.-A cheap waterproof board is made by soaking boards in a hot mixture of rosin and tallow. Paper barrels are rendered hard and waterproof by this means.

Middles and Thin Boards.-Thin cards and cheap middles are now produced in very large quantities on the continuous board machine, which resembles an ordinary Fourdrinier paper-machine in every respect, except as to the endless wire. Instead of the wire, two or three cylinder moulds are used, and the sheets of wet pulp are brought into close contact, carried through heavy press-rolls which cause the two or three sheets to combine into one compact mass, and then dried over heated cylinders in the usual manner.

Wood-pulp Boards.-These are manufactured on the board machines of the intermittent type, or on continuous machines, according to the bulk and weight required.

CHAPTER VIII

"ART" PAPERS

Process of manufacture Materials used - Qualities of Art paper-Defects in Art paperInfluence of mineral constituents-Surface- Printing process.

Process of Manufacture.-These special papers are now made in large quantities to supply the demand for a paper having a smooth surface suitable for the printing of half-tone blocks. The clearness of detail, and the sharpness of outline required in an illustration produced by process printing cannot be obtained on ordinary paper, however highly glazed and finished, since the surface is not sufficiently smooth, but by the application of a mineral coating an enamelled surface is obtained which is perfectly even and level, and capable of

taking an extremely high polish. The machinery employed in the production. of these papers is not complicated, and the operation appears to be quite simple, though, as a matter of fact, the difficulties connected with the manufacture and use of "Art" papers are

numerous.

The coating applied to the surface of the paper varies in composition according to the quality of the work, the mixture consisting of some inert mineral substance, such as china-clay, blanc fixe, or enamel, mixed with the proper quantity of an adhesive such as glue or casein. For high-class papers in which good colour and extra finish are the desired qualities, blanc fixe and satin white are used in conjunction with glue, commoner qualities being coated with chinaclay.

The machine for the manufacture of coated paper consists of three parts. The first is the coating section proper, the second is the drying apparatus, and the third the appliance for reeling up the paper. (Fig. 72.)

The reel of paper to be coated is placed in any convenient manner upon a shaft at the back of the coating apparatus, which is a large drum about 4 feet diameter, and 1 feet wide. The paper is led round under the drum and then over the top, and as it passes over it is brought into close contact with a short endless felt, which transfers the enamel mixture to the paper. The mixture is continuously fed into a narrow copper trough fixed to the front of the machine, and this is maintained at a suitable temperature. A copper roll rotating in the