Improvements in the Method of and Means for Reclaiming India- rubber and Rendering the Reclaimed India-rubber Dissolvable by Ordinary Rubber Solvents.
Year: 1898

page_text: Date of Application, 22nd Aug., 1898
Complete Specification Left, 23rd May, 1899-Accepted, 8th July, 1899
INVOVIRA DUITIVATION.
Improvements in the Method of and Means for Reclaiming India-
rubber and Rendering the Reclaimed India-rubber Dissolvable by
Ordinary Rubber Solvents.
I, JOSEPH ANDERSON, Junior, of Clayton, Manchester, in the County of Lancaster,
Manufacturing Chemist, do hereby declare the nature of my said invention to
be as follows:-
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My said invention relates to the devulcanisation and (or) desulphurisation of
vulcanised india-rubber, or to the recovery of india-rubber from waste or scrap
rubber for re-manufacturing purposes. Heretofore it has been the custom to use
oil, resin or other bodies containing oil, or of an oily or greasy nature, but.
experience has shewn that such bodies have a very injurious effect upon the.
rubber, deteriorating the same at the time, of devulcanisation, and afterwards
decomposing it, or other rubber with which it is mixed. Besides the injurious
effects the devulcanisation is only partial, a large portion of the rubber still
remaining chemically combined with the sulphur and in consequence depriving
it of its essential properties and rendering it unsuitable for many purposes for.
which unvulcanised rubber could be used.
The object of this invention is to produce a devulcanised rubber, having as
nearly as possible all the properties the said rubber possessed previous to being.
vulcanised, and in consequence being adapted for many other purposes for which
it cannot be used by the present mode of recovery.
According to my experiments I have discovered that the essential conditions
required to attain the object in view, are as follows:-1. To employ a substance,
such as calcium sulphide, which will combine with sulphur at devulcanising heat.
2. To employ a volatile solvent (such as coal tar naptha) partly or wholly free
from oil or grease, and capable of being evaporated at about 300° F., or other
high temperature at which rubber will be devulcanised without being injured.
3. In grinding the rubber into a powder before treatment, and operating upon
it whilst in intimate contact or association with the calcium sulphide and spirit.
In proceeding to treat say a hundred-weight of old rubber of average quality,
I first introduce the same into a grinding, or disintegrating mill until reduced to
a powder..
To such powdered rubber I then add in a suitable vortex or mixing
machine about 4 lbs. of (by preference) calcium sulphide, and three gallons of
spirit or naptha (coal-tar naptha preferred), and thoroughly mix the whole
together. I then transfer the mixture to a series of trays or vessels, and in a
suitable steam tight devulcanising chamber stack such trays one above another,
with intervening supports to keep them apart. The door, or cover of the chamber
is then tightly closed and. the temperature within the chamber raised to about
300° F., or higher if desired, at which heat, the spirit or naptha dissolves the
rubber and sets free the sulphur which then combines with, or is absorbed by,
the calcium sulphide and produces calcium per-sulphide or calcium penta-sulphide.

page_text: The rubber thus freed of sulphur is thoroughly devulcanised and only requires to
have the spirit or naptha taken from it to make it as good as new unvulcanised
rubber, and to that end, after the devulcanisation is complete, I reduce the
pressure in the devulcanising chamber until the spirit can freely evaporate, and
mixing with the steam pass out of the chamber. For the quantity and quality
of rubber aforesaid the process of devulcanisation occupies from 12 to 16 hours
and the evaporation one or two hours, but I do not leave the rubber in the devul-
canising chamber until the spirit is entirely evaporated, but transfer it to another
closed chamber, partly filled with water, into which I place the rubber, and by
special heat, or the heat from the exhaust steam of the devulcanising, chamber,
I boil and wash the rubber, primarily for the purpose of removing the per-sulphide
or penta-sulphide of calcium and secondarily for further removing the spirit, which
in evaporating is carried away with the steam. Before this last named treatment
I knead, press or masticate the reclaimed rubber by passing it through heated
rollers and after which washing as aforesaid the reclaimed rubber is then ready
for use and is in a condition absolutely free from oil or other deteriorating agent,
entirely devulcanised, and can be dissolved as, and when, required, by the
ordinary solvents of rubber which has not been possible by any previous methods
of reclaiming rubber.
Although I prefer to grind the rubber previous to treatment I may treat it
in its rough state, but the operation is only partially successful as the calcium
sulphide cannot properly reach the rubber.
In practise I prefer to obtain the desired heat by the use of super-heated steam
at a pressure of about 60 lbs. per sq. inch, or by using steam at a pressure of
about 120 lbs. per sq. inch.
To maintain a slight circulation of steam through the devulcanising chamber
I provide a small outlet pipe and the exhaust steam may serve for heating the
washing chamber as aforesaid. To effect the utmost economy in using naptha
I arrange for the spirit as it is evaporated off, to pass along with the steam into
a condenser and there be collected for further use.
A modification of my invention consists in using an excess of naptha or spirit
and leaving out the calcium sulphide and subsequent evaporation of the solvent,
and pressing the rubber between rolls or sheeting with the sulphur still chemically
combined & the resulting product is a semi-fluid which only requires the evapora-
tion of the solvent to become re-vulcanised. Or, I leave out the kneading and
cause the resulting product to be a fluid.
Rubber so treated is particularly advantageous for waterproofing garments, or
cementing rubber surfaces together, and saves the trouble and expense of special
vulcanisation.
Improvements in the Method of and Means for Reclaiming India- 4
rubber and Rendering the Reclaimed India-rubber Dissolvable by
Ordinary Rubber Solvents.
I, JOSEPH ANDERSON, Junior, of The Lodge, Clayton, Manchester, in the County
of Lancaster, Manufacturing Chemist, do hereby declare the nature of this inven-

page_text: tion and in what manner the same is to be performed, to be particularly described
and ascertained in and by the following statement: —
My said invention relates to the dissolving (devulcanisation and disulphurisation)
of vulcanised india-rubber, or to the recovery of india-rubber from waste or
scrap rubber for re-manufacturing purposes. Heretofore it has been the custom
to use oil, resin or other bodies containing oil or of an oily or greasy nature,
but experience has shewn that such bodies have a very injurious effect upon the
rubber, deteriorating the same at the time of devulcanisation, and afterwards
decomposing it, or other rubber with which it is mixed. Besides the injurious
effects the devulcanisation is only partial, a large portion of the rubber still
remaining chemically combined with the sulphur and in consequence depriving
it of its essential properties and rendering it unsuitable for many purposes for
which unvulcanised rubber could be used.
The object of this invention is to produce a devulcanised rubber, having as
nearly as possible all the properties the said rubber possessed previous to being
vulcanised, and in consequence being adapted for many other purposes for which
it cannot be used by the present mode of recovery.
According to my experiments I have discovered that the essential conditions
required to attain the object in view, are as follows:--1st. To employ a substance
such as calcium sulphide which will combine with sulphur or sulphur compounds
at devulcanising heat. 2nd. To employ a volatile solvent (such as coal tar naptha)"
capable of being evaporated at about 300° F., or other high temperature at which
the rubber will not be injured. 3rd. To grind the rubber into a powder before:
treatment and heat it whilst in intimate contact or association with the calcium
sulphide and spirit.
In proceeding to treat say one hundred-weight of old rubber of average quality
I first introduce the same into a grinding or disintegrating mill until reduced to
a powder. To such powdered rubber I then add a in a suitable vortex or mixing
machine about 4 lbs. of (by preference) calcium sulphide and about three gallons
of naptha (coal tar naptha preferred) and then thoroughly mix the same together.
I then transfer the mixture to a series of trays or vessels, with, or without lids
or covers, and in a suitable steam tight devulcanising chamber stack such trays
one above another, with intervening supports to keep them apart. The door or
cover of the chamber is then tightly closed and the temperature within the chamber
raised to the heat at which the naptha dissolves the rubber and sets free the
sulphur, which then combines with or is absorbed by the calcium sulphide. The
rubber thus freed of sulphur is devulcanised and only requires to have the spirit
or naptha taken from it to make it as good as unvulcanised rubber, and to that
end after the devulcanisation is complete I reduce the pressure in the devulcanising
chamber until the spirit can freely evaporate. For the quantity of rubber afore-
said the process of devulcanisation occupies from 12 to 16 hours and the evapora-
tion one or two hours, but I do not always leave the rubber in the devulcanising
chamber until the spirit is entirely evaporated, but transfer it to another closed
chamber, partly filled with water into which I place the rubber and by special
heat or the heat from the exhaust steam of the devulcanising chamber boil and
wash the rubber, primarily for the purpose of removing the per-sulphide or penta-
sulphide of calcium, and secondarily for further removing the spirit which in
evaporating is carried away with the steam and for further carrying out the
devulcanising process and giving the rubber desirable properties.
Before this last named treatment I knead, press or masticate the reclaimed
rubber by passing it through heated or otherwise rollers and after washing as
aforesaid the reclaimed rubber is ready for use and is in a condition free from oil
or other deteriorating agent, devulcanised and capable of being dissolved as and
when required by the ordinary solvents of rubber.
Whilst calcium sulphide is effective for the purposes aforesaid, other substances
which combine with sulphur or compound of sulphur in the manner aforesaid
may be used, such as compounds of soda, or other such body; or substances which

page_text: like calcium sulphide is alkaline in character, as I have found in practise that
whilst the substance above named act as aforesaid they also serve to neutralise
any acid which may be formed during the devulcanisation, and which in a free
state would ruin the rubber, but by the neutralising effect of the alkaline sub-
stance is rendered harmless.
Although I prefer to grind the rubber previous to treatment I may treat it in its
rough state, but the operation is only partially successful as the calcium sulphide
or other disulphurising and (or) alkaline substance cannot properly reach the
rubber. The proportions of spirit calcium sulphide and rubber, will vary with
the quality of the rubber (according to the percentage of sulphur or degree of
vulcanisation) and will be readily determined by those familiar with the treatment
of rubber.
To maintain a slight circulation of steam through or around the devulcanising
chamber and to regulate the heat I provide a small outlet pipe and the exhaust
steam may serve for heating the washing chamber as aforesaid. "To effect the
utmost economy in using naptha I arrange for the spirit as it is evaporated off
to pass along with the steam into a condenser and there be collected for further
use.
In conclusion I would point out that the devulcanising heat may vary with the
quality of rubber, or time allowed for devulcanisation and that the high tempera-
ture at which the spirit evaporates is simply to preserve the spirit against undue
evaporation before devulcanisation takes place.
Having thus particularly described the nature of my said invention and in what
manner the same is to be performed I declare that what I claim is:-
1: In a process of reclaiming waste india-rubber, mixing such rubber in
(by preference) ground state with a volatile solvent of the kind described and
a desulphurising and (or) alkaline substance, placing the mixture in a heated
devulcanising chamber, subjecting the mixture to the action of heat sufficient
to allow the india-rubber to dissolve under the action of the solvent substantially
as set forth.
2: In a process of reclaiming waste india-rubber, mixing such rubber in a
(by preference) ground state with a volatile solvent of the kind described and
a desulphurising and (or) alkaline substance, placing the mixture in a heated
devulcanising chamber, subjecting the mixture to the action of heat sufficient
to allow the india-rubber to dissolve under the action of the solvent, and then
washing the devulcanised rubber and evaporating the solvent in a separate steam
heated chamber, substantially as and for the purposes herein set forth.
Dated this 18th day of May 1899.
JOSEPH ANDERSON, JUNIOR,
By John G. Wilson & Co.,
Agents.