By Herbert W. Mason.
The word "paper" derives its name from the ancient Greek word
"papyrus," the name of the material used in ancient times for writing
purposes, and manufactured by the Egyptians from the papyrus plant,
and which was, up to the eighth century, the best-known writing
material. Probably the earliest manufacturers of paper were the
Chinese, who used the mulberry tree and other like plants for this
purpose, and may be called the inventors of our modern paper
manufacturing, as they have practised the art of paper making for
almost two thousand years.
In the ordinary book papers of to-day the materials used are largely
rags and wood fibres. "Esparto," a Spanish grass, is used in England
to a great extent, but it is too expensive to import to this country,
and is, therefore, not used here. Many other materials could be used
to advantage, such as "bagasse," the waste material of sugar cane, and
corn stalks, both of which make good book paper; also hemp, wild
clover, and other plants which have a good fibre.
Only two kinds of rags are used, linen and cotton, of both of which
there are several grades. Linen rags make a very strong paper, and are
mostly used in manufacturing fine writing papers, ledgers, and covers
for books where strength is necessary. Cotton rags may be divided into
three distinct kinds, whites, blues, and colors, and these in turn are
subdivided into several grades. Most of the blue rags are now imported
from Germany, Belgium, and France; none from Japan as formerly. The
whites and colors are bought in this country.
Wood fibres are divided into two classes, the harder woods, such as
spruce, fir, etc., and the softer, such as poplar, cottonwood, etc.
There are three ways of reducing or disintegrating wood fibres: first,
by sulphurous acid or bi-sulphite of lime fumes, which gives the name
"sulphite fibre"; second, by caustic soda, which is called "soda
fibre"; and third, by grinding. The last is usually only used for
stock in very low grades of paper, such as newspaper and wrapping
paper; it is rarely used for book paper. Many persons think that this
ground wood, which is merely spruce ground very fine into pulp, is
used in book papers; but if it were, the paper would not last long,
and would almost immediately discolor on exposure to light and air.
There is a theory that no paper made from wood fibres is lasting, and
that therefore high grades of paper for fine books should be made
only of rags, but this is erroneous, for wood stock and rag stock
nowadays are treated and prepared in the same way, and only
practically pure cellulose matter goes into the paper. It would be a
different matter, however, if _ground_ wood were used for fine papers,
for in this stock the cellulose matter is not separated.
Rags are usually purchased by the paper manufacturer in solid bales,
which have been graded into whites, blues, or colors. After being
opened, they are thrown into a thrashing machine, which thrashes and
shakes out the greater part of the loose dust and dirt. Later, they
are sorted more carefully by hand into several grades, according to
their colors and cleanliness. All the woollens, gunny, buttons, hooks
and eyes, silks, and foreign materials are thrown aside. As the rags
are usually too large to be thrown into the boilers to be cooked, they
are cut into very small pieces by means of sharp revolving knives, to
which they are fed rapidly from an endless belt. When cut, they are
packed into a revolving kettle or boiler, called a "rotary," and
cooked with caustic soda and lime for several hours, to disintegrate
the fibres, separate the cellulose matter, and "start" the colors. The
rags, after coming out of the boiler, look very dark, and are all
mashed together. They are then thrown into a tub of water and revolved
horizontally by means of a large wheel fitted with radial knives,
which tear and bruise them while water continually runs in and out,
carrying away the dirt. In a few hours the rags look much cleaner, and
a small amount of chlorate of lime and sulphuric acid is run in to
bleach them white. After having been thoroughly stirred for a while,
the stock is run into what is called a drainer, where it is allowed to
stand for several hours to drain off as much water as possible. Liquid
chloride of lime, which is used for bleaching, and sulphuric acid is
then run over the fibre, which in turn is drained and washed off
again. By this time the pulp is white enough to be sent to the
beaters, to be prepared for the paper machines, and is called
"half-stock."
Wood fibres for book papers are usually treated in the same general
way as rags. First, the logs are peeled and are cut into suitable
lengths to be thrown into a wood chopper and cut up in very small
pieces. If the wood is treated by sulphurous acid or bi-sulphite of
lime fumes, it is called the "sulphite process"; if by caustic soda,
the "soda process." This wood is cooked in large upright kettles
called "digesters." In one case the sulphite fumes are allowed to
permeate through the wood under a high pressure, and in the other the
caustic soda is put in "straight," and the wood is cooked under a high
pressure of steam. This is done to dissolve out all the gum and
resins, in order to leave the pure cellulose matter. After the cooking
is done, the stock has to be bleached in very much the same way as
the rags and washed thoroughly before it is ready for the "beaters."
For "beating," the stock is thrown into a large revolving tub. Rag and
wood fibre may be mixed in different proportions, according to the
grade of the paper wanted. The stock is then washed a little to be
sure that it is clean and white. Water at first is mixed in with the
fibre until it is so diluted that it will flow freely; then it is
beaten for several hours by means of an iron wheel covered with iron
or steel knives about one-quarter of an inch thick, which revolves
over an iron bed-plate with similar knives. During this beating
process, clay is mixed with the stock, mainly to give the paper a
well-filled and better appearance, and not, as most people think, to
add weight, although this is sometimes an object. Sizing material is
also added, which helps to keep the fibres together and hold the ink
in printing. If it is desired to give the paper a white shade, a small
amount of aniline blue or pink is mixed in; otherwise it is called
"natural" or "unblued."
The beating part of the process of paper making is the most important.
The stock has to be beaten up so that all the fibres are separated and
broken into just the right lengths according to the weight and
strength of the paper to be made. The harder the roll is set down on
the bed plate, the shorter the fibre will be and _vice versa_, but if
the roll is not put down hard, the stock has to be beaten so much
longer.
"Machining" may be divided into five processes:--
_First._ When the stock leaves the beater it is run into a large
"stuff" chest, and is continually being stirred so that it will not be
lumpy. By this time the pulp is about as clean as possible and is
ready for the paper machines. The first thing to be done on the
machine is to dilute the stock with pure water to the consistency of
buttermilk, according to the thickness of the paper required. Then
this liquid stock runs through what are called "sand settlers," which
are supposed to collect what dirt, iron, etc., remain.
_Second._ From the sand settlers the stock runs on to a screen,
through which it is drawn by means of suction. This process prevents
fibres which are lumpy and too long from getting on to the machine,
and allows only those of a certain size and length to go forward to be
made into paper. An endless and very fine wire cloth, which is
continually moving at the same rate of speed as the rest of the paper
machine, takes the stock after it has been screened. This is the first
step toward making the material into actual paper. Thick rubber straps
on each side of the wire determine the width of the paper. This wire
shakes a little in order to weave the fibres together while in a state
of suspension. At this period the stock looks like thick cream, but
soon changes its appearance to the form of a sheet more or less solid
on coming to the end of the wire, where there is what is called a
"dandy,"--a roll covered with similar wire cloth pressing lightly on
the paper as it runs along the wire. Designs in relief on the surface
of this roll produce the well-known marks called "water marks." Just
beyond the "dandy," underneath the wire, is a suction box which draws
enough of the water out so that the paper can go through the "couch"
roll at the end of the wire without being crumbled.
[Illustration: Cross-section of a Paper Machine.]
_Third._ The couch roll is a small hard roll covered with a thick felt
called a "jacket," and is used on the paper machine to prevent the
paper from being crushed, for it presses out much of the water and
flattens the paper so that it will pass from the wire to the felts
without breaking and through the press rolls without crushing. From
this couch roll the paper leaves the wire and is carried along on an
endless woollen felt to the press rolls, which are made of hard
rubber, steel, or brass. These rolls press the fibres together well,
squeezing out more of the water and flattening the sheet.
_Fourth._ From the press felts the paper is carried to the "dryer
felts," which in turn carry the paper to the "dryers," which revolve
and by means of the felt carry the paper along to the next dryer, and
so on. The dryers are hollow iron or steel cylinders, heated by means
of the exhaust steam from the engines which run the machine. More or
less steam is allowed to run into the dryers, according to the quality
of paper being made.
_Fifth._ As soon as the paper has been carried over all the dryers,
during which time it becomes, perfectly dry, it is run through a set
of so-called steel "chilled rolls," at the end of the machine, which
are under pressure and which give the paper a fairly smooth surface
for ordinary type printing. If a rough surface is desired, the paper
is simply wound on reels from the dryers.
Super-calendered papers are those which have a high finish and smooth
surface, and are used for cuts, lithographic work, magazine papers,
and ordinary illustrations. To calender paper, it is run through a
series of alternate "chilled" and "paper" rolls. The chilled rolls are
made of steel and have a very smooth and even surface. The "paper"
roll is made of circular discs of thin, but strong manila paper,
clamped together on an iron shaft, and then put under hydraulic
pressure, this pressure being increased constantly until it reaches
one hundred tons of pressure to the inch. The rolls are sometimes kept
under this pressure for five or six weeks, and then are turned on a
lathe into a true and smooth cylinder, and finally burnished by being
revolved against each other.
A "cotton" roll, used at times in place of the "paper" roll, is made
in the same manner, except it is made of pieces of cotton cloth
instead of thin manila paper. There is a heavy pressure on these
rolls, and the paper goes through at a high rate of speed. When an
especially smooth surface is wanted, steam is run on the paper as it
unwinds, dampening it and giving the web a surface like that on ironed
linen.
"Coated" paper is treated differently, being covered with a fine
coating, which, after super-calendering, gives the paper a glazed and
smooth surface for fine half-tone illustrations. Clay, mixed with
casein, the product of skimmed milk, or glue, is the chief material
used for coating. It is put on the paper by means of large brushes.
Then it is dried by fans and passed through a long passageway heated
by steam to a high temperature. After being reeled, it is allowed to
stand for a while to harden; then is run several times through the
calenders to get the smooth surface. If a high, glazed finish is
necessary, steam is put on while running through the calenders. This
gives a very bright surface for fine lithographic work. For the best
coated papers, instead of clay, sulphate of lime and sometimes
sulphate of barium is used, with glue or casein. Formaldehyde, a
chemical compound, is used to prevent decomposition in the coating
materials; and soda or borax is used to "cut" or dissolve the casein
or glue.
If the paper is to be printed "from the web," that is, from the roll,
it first has to be trimmed to the correct width, then wound tightly
under a high pressure to a certain thickness, then the rolls are
packed up in wrapping paper ready to be shipped. Some rolls contain as
much as five miles of paper. When the paper is to be put up in
sheets, it has to be cut to exactly the correct width and length on
the cutting machine. It is all very carefully sorted--the imperfect
sheets being thrown out--counted and packed in wooden cases, or done
up with strong wrapping paper in bundles, ready to be sent to the
printer.