NEWSPRINT 257
importance of groundwood for giving good printing qualities, the sulphite
percentage has been steadily reduced. Improvements in groundwood manu-
facture, resulting from scientific research, and also the development of reliable
methods of pulp evaluation, have helped to make the reduction in sulphite
content practicable.
Non-Fibrous Raw Materials.—Mention must be made of the two other raw
materials that occur in appreciable proportions in newsprint. They are loading
and water.
Loading is added to newsprint to increase ink receptivity, to help to give
satisfactory opacity, and to fill up inter-fibre spaces so that a smoother surface
may be obtained; it also helps to make a sheet of paper as economically as
possible. China cky is the most common loading for newsprint, although in
some American mills calcium carbonate is used, because china cky is expensive;
the reason being that it occurs only to a limited extent in the United States, and
a good deal has, therefore, to be imported from Cornwall. In one American
mill, calcium carbonate is made from carbon-dioxide recovered from the flue
gases of the boiler plant. In other mills, loading is not used at all, because
of the expense of transporting it to the mill site.
The cheaper grades of clay, even down to mica ckys, are quite satisfactory
for newsprint, provided the abrasive grit content is not too high. This is an
important point to watch, otherwise excessive wire wear may result. The
colour of the clay, unless it is exceptionally bad, has no appreciable effect on
the shade of the finished newsprint paper, and it is, therefore, only a secondary
consideration. The amount of loading carried may range from 2 or 3 per cent
up to 12 per cent or more, depending on the properties desired, the basis weight
of the paper, and other factors.
The last of the four major constituents of newsprint, water, is the cheapest,
but it is by no means unimportant, neither is it put in primarily for reasons of
economy. Newsprint devoid of water would, like any other paper, be of
very inferior quality. The presence of the correct amount of water, which
should be between about 8 per cent and 10 per cent, is helpful in obtaining
a satisfactory finish; it gives paper a mellow handle (if it is too dry it will be
harsh and brittle; if too wet it will be soft and flabby); it minimises the possibility
of troubles due to static electricity during printing, and it reduces the tendency
to cockle during transport and storage.
The analysis below gives the proportions in which the four constituents
mentioned occur in a typical sample of newsprint.
Groundwood ...... 70 % or 84 %\ expressed as a percentage of the
Sulphite pulp ...... 13% ori6%J fibrous furnish only
China day ...... 8%
Moisture........ 9%