twigs, soil, etc.; these require removing before the manufacturing
processes can be carried out. The first operation, after rough washing,
is to shred the raw material into small strips, so as to enable the
impurities to be washed out. This process is carried out by pressing
the rubber against the surface of a revolving drum (_A_, Fig. 1),
carrying a number of diagonally arranged knives, _B_, on its surface. A
lever, _C_, presses the rubber against the knives; _D_ is the fulcrum
on which _C_ works, _E_ being a weight which throws back the lever on
the pressure being removed. During {744} this operation a jet of water
is kept playing onto the knives to cool and enable them to cut.
Following this comes the passage between a pair of corrugated steel
rollers (as shown in Fig. 2). These rollers have each a different
speed, so that the rubber gets stretched and squeezed at the same time.
Immediately over the rollers a water pipe is fixed, so that a steady
stream of water washes out all the sand and other extraneous matter.
In Fig. 2, _AA_ are the steel rollers, while _B_ is a screw working
springs which regulate the pressure between the rollers. The power is
transmitted from below from the pulley, _C_, and thence to the gearing.
[Illustration: Fig. 3.]
The next operation, after well drying, is to thoroughly masticate the
shredded rubber between hot steel rollers, which resemble those already
described, but usually have a screw-thread cut on their surfaces. Fig.
3 shows the front view of this masticating machine, _A_ being the
rollers, while the steam pipe for heating is shown at _B_. Fig. 3_a_
gives a top view of the same machine, showing the two rollers.
[Illustration: Fig. 3A.]
After passing several times through these, the rubber will be in the
form of homogeneous strips, and is then ready either for molding or
dissolving. As we are dealing solely with waterproofed textiles, the
next process which concerns us is the dissolving of the rubber in a
suitable solvent. Benzol, carbon bisulphide, oil of turpentine, ether,
and absolute alcohol, will each dissolve a certain amount of rubber,
but no one of them used alone gives a thorough solution. The agent
commonly employed is carbon bisulphide, together with 10 per cent of
absolute alcohol. Whatever solvent is used, after being steeped in it
for some hours the caoutchouc swells out enormously, and then requires
the addition of some other solvent to effect a complete solution.
A general method is to place the finely shredded rubber in a closed
vessel, to cover it with carbon bisulphide, and allow to stand for some
hours. Toward the end of the time the vessel is warmed by means of a
steam coil or jacket, and 10 parts absolute alcohol are added for every
100 parts of carbon bisulphide. The whole is then kept gently stirred
for a few hours. Fig. 4 shows a common type of the vessel used for
dissolving rubber. In this diagram _A_ is the interior of the vessel,
and _B_ a revolving mixer in the same. The whole vessel is surrounded
by a steam jacket, _C_, with a steam inlet at _D_ and a tap for
condensed water at _E_. _F_ is the cock by which the solution is drawn
off.
[Illustration: Fig. 4.]
After the rubber is dissolved, about 12 to 24 per cent of sulphur is
added, and thoroughly incorporated with the solution. The sulphur may
be in the form of chloride of sulphur, or as sulphur pure and simple.
A very small quantity of sulphur is required to give the necessary
result, 2 to 3 per cent being sufficient to effect vulcanization; but a
large quantity is always added to hasten the operation.
Even after prolonged treatment with the two solvents, a solution of
uniform consistency is never obtained: clots of a thicker nature will
be found floating in the solution, and the next operation is to knead
it up so as to obtain equal {745} density throughout. Fig. 5 will give
an idea of how this mixing is done.
[Illustration: Fig. 5.]
At the top of a closed wooden chamber is a covered reservoir, _A_,
containing the solution of rubber. A long slit at the base of this
reservoir allows the solution to fall between sets of metal rollers,
_BBB_ below. Neighboring rollers are revolving in opposite directions,
and at different speeds, so that, after passing all three sets of
rollers, and emerging at the bottom, the solution should be of uniform
consistency. _CCC_ are the guiding funnels, and _EE_ are scrapers to
clear the solution from the rollers. _D_ is a wedge-shaped plug worked
by a rack and pinion, and regulates the flow of the solution.
[Illustration: Fig. 6.]
It now remains to apply the rubber to the fabric and vulcanize it.
Up to this stage the sulphur has only been mechanically mixed with
the rubber; the aid of heat is now required to bring about chemical
combination between the two. This process, which is known as “burning,”
consists in subjecting the rubber-covered fabric to a temperature of
about 248° F. Sulphur itself melts at 239° F., and the temperature at
which combination takes place must be above this. Fig. 6 shows one
of the methods of spreading the rubber on the cloth. _A_ is the tank
containing the solution with an outlet at the bottom arranged so as
to regulate the flow of solution. The fabric passes slowly underneath
this, receiving as it travels a thin coating of the waterproofing. The
two rollers at _B_ press the solution into the fabric and distribute
the proofing evenly over the entire surface.
After leaving the two squeezing rollers, the cloth travels slowly
through a covered chamber, _C_, having a series of steam pipes, _EE_,
underneath, to evaporate the solvent; this condenses on the upper
portion of the chamber, which is kept cooled, and flows down the sides
into suitable receptacles. After this the proofed cloth is vulcanized
by passing round metal cylinders heated to the necessary temperature,
or by passing through a heated chamber. Fig. 7 shows the spreading of
rubber between two fabrics. The two cloths are wound evenly on the
rollers, _BB_; from this they are drawn conjointly through the rollers,
_D_, the stream of proofing solution flowing down between the rollers,
which then press the two fabrics together with the rubber inside. The
lower rollers marked _CC_ are heated to the necessary degree, and cause
the rubber and sulphur to combine in chemical union.
[Illustration: Fig. 7.]
So far the operation of proofing has been described as though pure
rubber only was used; in practice the rubber forms only a small
percentage of the proofing material, its place being taken by cheaper
bodies. One of the common ingredients of proofing mixtures is boiled
linseed oil, together with a small quantity of litharge; this dries
very quickly, and forms a glassy flexible film. Coal tar, shellac,
colophony, etc., are all used, together with India-rubber varnish, to
make {746} different waterproof compositions. Oil of turpentine and
benzol form good solvents for rubber, but it is absolutely essential
that both rubber and solvent be perfectly anhydrous before mixing. Oil
of turpentine, alcohol, etc., can be best deprived of water by mixing
with either sulphuric acid or dehydrated copper sulphate, and allowing
to stand. The acid or the copper salt will absorb the water and sink
to the bottom, leaving a supernatant layer of dehydrated turpentine or
whatever solvent is used. All the sulphur in a rubber-proofed cloth
is not in combination with the rubber; it is frequently found that,
after a lapse of time, rubber-proofed material shows an efflorescence
of sulphur on the surface, due to excess of sulphur, and occasionally
the fabric becomes stiff and the proofing scales off. Whenever a large
proportion of sulphur is present, there is always the danger of the
rubbers forming slowly into the hard vulcanite state, as the substance
commonly called vulcanite consists only of ordinary vulcanized rubber
carried a stage further by more sulphur being used and extra heat
applied. If after vulcanizing, rubber is treated with caustic soda, all
this superfluous sulphur can be extracted; if it is then well washed
the rubber will retain its elasticity for a long period. With the old
methods of proofing, a sheet of vulcanized rubber was cemented to a
fabric with rubber varnish, and frequently this desulphurizing was
performed before cementing together. The result was a flexible and
durable cloth, but of great weight and thickness, and expensive to
produce.
The chemistry of rubber is very little understood; as mentioned
previously, rubber is a highly complex body, liable to go through many
changes. These changes are likely to be greater in rubber varnish,
consisting of half a dozen or more ingredients, than in the case of
rubber alone. The action of sunlight has a powerful effect on rubber,
much to its detriment, and appears to increase its tendency to oxidize.
Vulcanized rubber keeps its properties better under water than
when exposed to the air, and changes more slowly if kept away from
the light. It appears as though a slight decomposition always takes
place even with pure rubber; but the presence of so many differently
constituted substances as sometimes occur in rubber solutions no
doubt makes things worse. Whenever a number of different bodies with
varying properties are consolidated together by heat, as in the case
of rubber compositions, it is only reasonable to expect there will be
some molecular rearrangement going on in the mass; and this can be
assigned as the reason why some proofings last as long again as others.
Some metallic salts have a very injurious action on rubber, one of the
worst being copper sulphate. Dyers are frequently warned that goods
for rubber-proofing must be free from this metal, as its action on
rubber is very powerful, though but little understood. As is generally
known, grease in any form is exceedingly destructive to rubber, and it
should never be allowed in contact in the smallest proportion. Some
compositions are made up by dissolving rubber in turpentine and coal
tar; but in this case some of the rubber’s most valuable properties
are destroyed, and it is doubtful if it can be properly vulcanized.
Owing to rubber being a bad conductor of heat, it requires considerable
care to vulcanize it in any thickness. A high degree of heat applied
during a short period would tend to form a layer of hard vulcanite on
the surface, while that immediately below would be softer and would
gradually merge into raw rubber in the center.
The different brands of rubber vary so much, especially with regard
to solubility, that it is always advisable to treat each brand by
itself, and not to make a solution of two or more kinds. Oilskins and
tarpaulins, etc., are mostly proofed by boiled linseed oil, with or
without thickening bodies added. They are not of sufficient interest
to enlarge upon in this article, so the second, or “water-repellent,”
class has now to be dealt with.
All the shower-proof fabrics come under this heading, as well as
every cloth which is pervious to air and repulsive to water. The most
time-honored recipe for proofing woollen goods is a mixture of sugar of
lead and alum, and dates back hundreds of years. The system of using
this is as follows: The two ingredients are dissolved separately, and
the solutions mixed together. A mutual decomposition results, the
base of the lead salt uniting with the sulphuric acid out of the alum
to form lead sulphate, which precipitates to the bottom. The clear
solution contains alumina in the form of acetate, and this supplies
the proofing quality to the fabric. It is applied in a form of machine
shown in Fig. 8, which will be seen to consist of a trough containing
the proofing solution, _C_, with a pair of squeezing rollers, _A_, over
the top. The fabric is drawn down through the solution and up through
the squeezers in the direction of the arrows. At the {747} back of the
machine the cloth automatically winds itself onto a roll, _B_, and then
only requires drying to develop the water-resisting power. _D_ is a
weight acting on a lever which presses the two rollers, _A_, together.
The water-repelling property is gained as follows:
[Illustration: Fig. 8.]
Drying the fabric, which is impregnated with acetate of alumina, drives
off some of the volatile acetic acid, leaving a film of basic acetate
of alumina on each wool fiber. This basic salt is very difficult to
wet, and has so little attraction for moisture that in a shower of
rain the drops remain in a spheroidal state, and fall off. In a strong
wind, or under pressure, water eventually penetrates through fabrics
proofed in this manner; but they will effectually resist a sharp
shower. Unfortunately, shower-proofed goods, with wear, gradually lose
this property of repelling water. The equation representing the change
between alum and sugar of lead is given below. In the case of common
alum there would, of course, be potassium acetate in solution besides
the alumina.
Alum. Sugar of lead.
Al_〈2〉K_〈2〉(So_〈4〉)_〈4〉 + 4 Pb(C_〈2〉H_〈3〉O_〈2〉)_〈2〉
Lead Potassium Aluminum
sulphate. acetate. acetate.
= 4 PbSo_〈4〉 + 2 KC_〈2〉H_〈3〉O_〈2〉 + Al_〈2〉(C_〈2〉H_〈3〉O_〈2〉)_〈6〉
Now that sulphate of alumina is in common use, alum need not be used,
as the potash in it serves no purpose in proofing.
There are many compositions conferring water resisting powers upon
textiles, but unfortunately they either affect the general handle of
the material and make it stiff, or they stain and discolor it, which
is equally bad. A large range of waterproof compositions can be got
by using stearates of the metals; these, in nearly every case, are
insoluble bodies, and when deposited in the interior of a fabric form
a water-resisting “filling” which is very effective. As a rule these
stearates are deposited on the material by means of double baths;
for example, by passing the fabric through (say) a bath of aluminum
acetate, and then, after squeezing out the excess of liquid, passing
it through a bath of soap. The aluminum salt on the fabric decomposes
the soap, resulting in a deposit of insoluble stearate of alumina. This
system of proofing in two baths is cleaner and more economical than
adding all the ingredients together, as the stearate formed is just
where it is required “on the fibers,” and not at the bottom of the bath.
One of the most important patents now worked for waterproofing purposes
is on the lines of the old alumina process. In this case the factor
used is rosin, dissolved in a very large bulk of petroleum spirit. The
fabrics to be proofed (usually dress materials) are passed through a
bath of this solution, and carefully dried to drive off the solvent.
Following this, the goods are treated by pressing with hot polished
metal rollers. This last process melts the small quantity of rosin,
which is deposited on the cloth, and leaves each single fiber with an
exceedingly thin film of rosin on it. It will be understood that only
a very attenuated solution of rosin is permissible, so that the fibers
of the threads and not the threads themselves are coated with it. If
the solution contains too much rosin the fabric is stiffened, and the
threads cemented together; whereas if used at the correct strength
(or, rather, weakness) neither fabric nor dye suffers, and there is no
evidence of stickiness of any description.
[Illustration: Fig. 9.]
Fig. 9 shows a machine used for spreading a coat of either proofing or
any other fluid on one side of the fabric. {748} This is done by means
of a roller, _A_, running in the proofing solution, the material to
be coated traveling slowly over the top and just in contact with the
roller, _A_, which transfers the proofing to it. Should the solution
used be of a thick nature, then a smooth metal roller will transfer
sufficient to the fabric. If the reverse is the case, and the liquid
used is very thin, then the roller is covered with felt, which very
materially adds to its carrying power. As shown in Fig. 9, after
leaving the two squeezing rollers, _BB_, the fabric passes slowly round
a large steam-heated cylinder, _C_, with the coated side uppermost.
This dries the proofing and fastens it, and the cloth is taken off at
_D_.
Besides stearates of the metals, glues and gelatins have been used for
proofing purposes, but owing to their stiffening effect, they are only
of use in some few isolated cases. With glue and gelatin the fixing
agent is either tannic acid or some metallic salt. Tannic acid converts
gelatin into an insoluble leather-like body; this can be deposited in
the interstices of the fabric by passing the latter through a gelatin
bath first, and then squeezing and passing through the tannic acid.
Bichromate of potash also possesses the property of fixing the proteid
bodies and rendering them insoluble.
The following are special processes used to advantage in the
manufacture of waterproof fabrics:
I.—Ordinary Fabrics, Dressing Apparel, etc.—Immerse in a vat of acetate
of alumina (5° Bé.) for 12 hours, lift, dry, and let evaporate at a
temperature of from 140° to 149° F.
II.—Sailcloth, Awnings, Thick Blankets, etc.—Soak in a 7 per cent
solution of gelatin at 104° F., dry, pass through a 4 per cent solution
of alum, dry again, rinse in water, and dry.
III.—Fabrics of Cotton, Linen, Jute, and Hemp.—Put into a bath of
ammoniacal cupric sulphate of 10° Bé. at a temperature of 87° F.; let
steep thoroughly, then put in a bath of caustic soda (20° Bé.) and dry.
To increase the impermeability, a bath of sulphate of alumina may be
substituted for the caustic-soda bath.
IV.—Saturate the fabrics with the following odorless compound,
subjecting them several times to a brushing machine having several
rollers, where the warp threads will be well smoothed, and a waterproof
product of fine sheen and scarcely fading will be the result. The
compound is made with 30 parts, by weight, of Japan wax, 22 1/2
parts, by weight, of paraffine, 12 parts, by weight, of rosin soap, 35
parts, by weight, of starch, and 5 parts, by weight, of a 5 per cent
solution of alum. Fabrics thus prepared are particularly adapted to the
manufacture of haversacks, shoes, etc.
V.—White or Light Fabrics.—Pass first through a bath of acetate of
alumina of 4° to 5° Bé. at a temperature of 104° F., then through the
rollers to rid of all liquid; put into a warm solution of soap (5
parts, by weight, of olive-oil soap to 100 parts, by weight, of fresh
water) and finally pass through a 2 per cent solution of alum, dry for
2 or 3 days on the dropping horse, and brush off all particles of soap.
VI.—Dissolve 1 1/2 parts, by weight, of gelatin in 50 parts, by
weight, of boiling water, add 1 1/2 parts, by weight, of scraped
tallow soap and 2 1/2 parts, by weight, of alum, the latter being put
in gradually; lower the temperature of the bath to 122° F., lift out
the fabric, dry, and calender.
VII.—Tent Cloth.—Soak in a warm solution of 1 part, by weight, of
gelatin, 1 part, by weight, of glycerine, and 1 part, by weight, of
tannin in 12 parts, by weight, of wood vinegar (pyroligneous acid) of
12° Bé. The whole is melted in a kettle and carefully mixed. The mass
is poured into the receiver of the brushing machine, care being taken
to keep it liquid. For a piece of 500 feet in length and 20 inches in
width, 50 to 80 parts, by weight, of this compound are needed.
VIII.—To freshen worn waterproof material, cover with the following:
Fifty-five thousand parts, by weight, of gelatin; 100 parts, by weight,
of bichromate of potash; 100 parts, by weight, of acetic acid (to keep
glue from congealing), and from 3,000 to 5,000 parts, by weight, of
water; to this add 500 parts, by weight, of peroxide of ammoniacal
copper, 100° Bé. This compound is put on the fabric with a brush and
then exposed to air and light.
IX.—Soft Hats.—The hats are stiffened as usual, then put through the
following three baths: Dissolve 1/2 part, by weight, of tallow soap
in from 40 to 50 parts, by weight, of warm water (140° F.). Put 3 to
4 dozen hats into this solution, leave them in it for half an hour,
then take out and put them as they are into another bath prepared
with 40 to 50 parts, by weight, of water and 1/2 part, by weight,
of alum and heated to 86° to 104° F. After {749} having been left in
the second bath for 1/4 or 1/2 hour, take out as before, put into
the third bath of 40 to 50 parts, by weight, of water, 1/2 part, by
weight, of alum, and about 13 parts, by weight, of fish glue. In this
cold bath the hats are left for another 1/2 hour or more until they
are completely saturated with the liquid, then dried and the other
operations continued.
X.—Woolen cloth may be soaked in a vat filled with aluminum acetate,
of 5° Bé., for 12 hours, then removed, dried, and dried again at a
temperature of 140° F.
XI.—Wagon covers, awnings, and sails are saturated with a 7 per cent
gelatin solution, at a temperature of 104° F., dried in the air, put
through a 4 per cent solution of alum, dried again in the air, carried
through water, and dried a third time.
XII.—Cotton, linen, jute, and hemp fabrics are first thoroughly
saturated in a bath of ammonio-cupric sulphate, of 10° Bé., at a
temperature of 77° F., then put into a solution of caustic soda, 2°
Bé., and dried. They may be made still more impervious to water by
substituting a solution of aluminum sulphate for the caustic soda.
XIII.—White and light-colored fabrics are first put into a bath of
aluminum acetate, 4° to 5° Bé., at a temperature of 102° F., the
superfluous liquid being removed from the fabric by press rollers. The
fabric is put into a soap solution (5 parts of good Marseilles soap
in 100 parts of soft water). Finally it is put through a 2 per cent
alum solution, and left to dry for 2 or 3 days on racks. The adhering
particles of soap are removed by brushing with machinery.
XIV.—Dissolve 1.5 parts of gelatin in 50 parts of boiling water, add
1.5 parts of shavings of tallow grain soap, and gradually, 2.5 parts
of alum. Let this cool to 122° F., draw the fabric through it, dry and
calender.
XV.—Cellular tissues are made waterproof by impregnating them with a
warm solution of 1 part, by weight, of gelatin, 1 part, by weight, of
glycerine, and 1 part, by weight, of tannin, in 12 parts, by weight, of
wood vinegar, 12° Bé.
XVI.—Linen, hemp, jute, cotton, and other fabrics can be given a
good odorless waterproof finish by impregnating them, and afterwards
subjecting them to the action of several mechanical brush rollers. By
this process the fabric is brushed dry, the fibers are laid smooth,
the threads of the warp brought out, and a glossy, odorless, unfading
waterproof stuff results. Fabrics manufactured in the usual way from
rough and colored yarns are put through a bath of this waterproof
finish, whose composition is as follows: Thirty parts, by weight, of
Japanese wax; 22.5 parts, by weight, of paraffine; 15 parts, by weight,
of rosin soap; 35 parts, by weight, of starch, and 5 parts, by weight,
of a 5 per cent alum solution. The first three components are melted in
a kettle, the starch and, lastly, the alum added, and the whole stirred
vigorously.