Chapters on Papermaking by Clayton Beadle

Author:Clayton Beadle
Language: eng
Format: epub
Published: 1907-03-25T05:00:00+00:00

one loaded with the same chemical substance, but not precipitated in the beater.

"(^2) The kind of material employed is, perhaps, one of the most important factors affecting the opacity of the sheet. Chemical wood pulps are all more transparent than cotton and rag papers, or jute papers, and—to take an extreme instance—than mechanical wood pulp.

" Here, again, sulphate pulp is more opaque than sulphite or soda. Bleached pulps more transparent than naif-bleached pulps or unbleached pulp. Stuff made from old rags is less transparent than stuff from new rags.

"Mechanical pulp stands by itself; it is the most opaque of paper-making fibres (if it can be classed as a fibre), since it consists of wood with all the lignine matters just aB it is found. Mechanical pulp made from the fir species is more transparent than that made from the pine species.

"(8) The treatment in the beater has also an important bearing on the question, and I think the chief factor. Stuff beaten * wet' is more transparent than stuff beaten * free.' Wet stuff has the property of forming an amorphous-looking sheet, and, as you remarked in commenting in Chapter V., that * as a sheet of paper approaches a sheet of amorphous cellulose the more transparent it becomes,' one would conclude that viscose sizing tends to make the finished paper more transparent than it would be if sized with ordinary resin size.

" From the above conditions under which paper may be made, it is not difficult to understand why semi-transparent papers, as Banks and imitation parchments, are made from sulphite pulps beaten wet."

W's answer is somewhat confusing. "A paper made with all clear furnish and beaten fairly fine will be more transparent than the same beaten long and with the addition of a lot of broke and loading." He must not conclude from this that the long stuff gives a more opaque paper. The fact is that the broke and loading give the paper its opacity, and the long stuff is really serving to hold the mineral in suspension. If you were to leave out the broke and loading and merely compare the long stuff with the short stuff, you would probably find that, other things being equal, the long stuff would be the more transparent of the two.

To gain the necessary knowledge of the principles of optics, the reader could not do better than read the little book by A. H. Church on "Colour" (Cassell and Co.), also the little

book on " Colour Measurement and Mixture," by Capt. Abney, published by the Society for Promoting Christian Knowledge ; but if you find even these two books too much for you to understand, you need not be discouraged, because although they are of very great value to a proper understanding of the subject, you can advance your knowledge considerably without them. There are one or two references in Church's book to the subject of paper. **TVhen the rays of parallel light from the sun strike upon a rough, that

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