Production of Azo Colors in Discharge-printing on Indigo Dyed Fabrics.
Year: 1891

page_text: Date of Application, 16th Feb., 1891
Complete Specification Left, 14th Nov., 1891-Accepted, 19th Dec., 1891
PROVISIONAL SPECIFICATION.
Production of Azo Colors in Discharge-printing on Indigo Dyed
Fabrics.
[Communicated from abroad by THE FARBWERKE VORMALS MEISTER LUCIUS
AND BRUNING, of Hoechst-am-Maine, in the Empire of Germany.]
I, OLIVER IMRAY of No. 28 Southampton Buildings, Chancery Lane in the
County of London, Fellow of the Institute of Patent Agents, do hereby declare
the nature of this invention to be as follows:-
The printing in discharge-style on indigo-dyed cloth is one of the most important
businesses in printing works; the object of this process is to produce patterns
coming out in bold relief from the indigo-blue by printing with thickened caustic
materials giving off oxygen.
When it is desired not only to produce white patterns but also colored ones,
there are added to the printing color coloring matters that in the discharge
operation are easily fixed on the fibre. On this account it was hardly possible
to use any other coloring matters than those commonly known as albumen
colours, a great number of which do not resist rubbing and therefore separate in
washing.
Beautiful and brilliant colours can only be obtained on condition that the indigo
be completely removed from the printed places by the chemical discharge, as only
in that case will the red, orange, claret red etc. etc., stand out in bold relief from
the dark blue."
It is therefore absolutely necessary that the coloring matter employed shall resist
in every respect the action of the oxygen which converts the indigo into isatin, and
causes its solution in this form.
This result depends on the nature of the oxidising agent and on the conditions
under which the oxygen is set free. As oxidising agents were used up to now
chromic acid and chromates.
The printing in discharge-style on indigo-dyed cloth is effected as follows:-
The cloth is printed upon with a thickening containing a greater or less quantity
of chromate solution according to the depth of the blue color. After having been
dried, the cloth is passed through a moderately hot solution of sulphuric and oxalic
acids, whereby the chromic acid is set free, the indigo is oxidised without difficulty,
and the printed places rendered colorless.
As before stated, coloured opaque pigments can be fixed on the places treated
during the same operation; this is done by thickening the solution of the neutral
chromate with albumen and admixing insoluble metallic colors, which resist the
action of the chromic acid.
The acid bath, through which the cloth is afterwards passed, must be kept at the
temperature necessary for coagulating the albumen completely.
For red colors, which are mostly printed on indigo, there was used vermilion,
for which of late has been substituted, a cheap lake prepared from azo coloring
matters, which also resists the action of chromic acid.
This lake however not only has, like
the disagreeable quality of. falling off
but, moreover, it is decomposed by the
dissolved.
the body for which it was substituted,
when the cloth is rubbed in washing
action of the warm soap solution and

page_text: Another method very interesting in theory but impracticable on account of its
great cost, is to print alumina-mordants on the indigo blue and afterwards to dye
with alizarine.
On account of the great importance of the method of printing in discharge-style
on indigo to the trade, a universal want is felt for the devising of a simple and
cheap process for producing on indigo-ground bright colors that shall be permanent
in washing and shall resist the action of light as much as possible.
The inventor of the process described in German Letters Patent No. 55779
endeavoured to effect some improvement in this direction, by trying to fix on the
indigo-ground the azo colors to be developed on the fibre, excelling by their beauty
permanency and cheapness. But he did not succeed in producing a suitable red or
other current shades, as experience shews that none of the diazo compounds resist
the action of chromic acid; and, as the patentee himself acknowledges, there is but
one body, namely amidoazobenzene which possesses sufficient resistance and can be
employed for producing a red shade when using chromic acid; but unfortunately
the shade obtained, though fast, cannot satisfy even the most moderate require-
ments as to beauty. The patented process substantially consists in that, to the
usual chromate solution, there is admixed a solution of diazotized hydrochlorate of
amidoazobenzene, the naphthol-prepared cloth being printed therewith and then
passed through the usual acid bath.
The present invention relates to a process which, in contradistinction to that
above referred to, allows of the employment of all the diazo compounds for producing
on the indigo ground insoluble azo colors, and at the same time the obtaining
of shades equalling in beauty those produced in the ordinary manner on white
cloth.
The invention is carried out in the following manner. Instead of adding to the
thickened diazo compounds a chromate solution, alkaline ferri-cyanides are added,
and after the colour has formed, the oxidation is proceeded with in an alkaline
bath. In this process the beauty of the azo colors is in no way affected, and
moreover there are obtained shades that hitherto could not be produced on indigo
blue.
The essential feature of the invention consists in that, in contradistinction to the
process heretofore employed, oxidising agents are used, which in acid solution do
not set free oxygen, so that the diazo compounds are not decomposed; the develop-
ment of the oxygen only begins when the azo colors have formed, in which condition
they are not affected by the oxygen which oxidises the indigo and removes it from
the fibre
In the following is described, by way of example, the manner in which the inven-
tion is carried out for the production on indigo ground of an azo red from diazotised
paranitraniline and beta naphthol.
The indigo blue-dyed cloth is padded on the hotflue with a betanaphthol solution
prepared as follows.

page_text: nitraniline base and molecules of nitrite of sodium with 5 per cent. of nitrite
in excess of the theoretical quantity) are mixed with:
037
305 cubic centimeters of water.
The mixture I is slowly mixed with the mixture II and when the whole has
dissolved, there is added :-
300 grammes of red-ferri-cyanide of potassium and 60 grammes of crystallised
acetate of soda.
After being printed upon, the cloth is passed through a soda lye of from 5° to
10° Bé. at a temperature of from 50° to 60° C.; by which means the indigo is
totally destroyed at the printed places; the cloth is then well washed and, if
necessary, passed through a boiling soap bath, washed again and dried.
The other diazo compounds that can be employed for producing on the fibre azo
colors behave in an analogous manner to the diazo compound produced from para-
nitraniline, that is to say, by mixing thickened diazo solutions with alkaline-ferri-
cyanides there are produced printing colours, which on being printed on naphthol-
prepared indigo ground and subsequently passed through an alkaline bath, furnish
discharge-colours which resist rubbing and washing.
16th
falar 1901
ABEL & IMRAY,
Agents for the Applicant.
COMPLETE SPECIFICATION.
Production of Azo Colors in Discharge-printing on Indigo Dyed
Fabrics.
I, OLIVER IMRAY of No. 28 Southampton Buildings, Chancery Lane, in the
County of London, Fellow of the Institute of Patent Agents, do hereby declare
the nature of this invention and in what manner the same is to be performed to
be particularly described and ascertained in and by the following statement:
-
The printing in discharge-style on indigo-dyed cloth is one of the most important
businesses in printing works; the object of this process is to produce patterns
coming out in bold relief from the indigo-blue by printing with thickened caustic
materials giving off oxygen.
When it is desired not only to produce white patterns but also colored ones,
there are added to the printing color coloring matters that in the discharge operation
are easily fixed on the fibre. On this account it was hardly possible to use any
other coloring matters than those commonly known as albumen colours, a great
number of which do not resist rubbing and therefore separate in washing.
Beautiful and brilliant colours can only be obtained on condition that the indigo
be completely removed from the printed places by the chemical discharge, as only
in that case will the red, orange, claret red etc. etc. stand out in bold relief from
the dark blue.
It is therefore absolutely necessary that the coloring matter employed shall resist

page_text: in every respect the action of the oxygen which converts the indigo into isatin, and
causes its solution in this form.
This result depends on the nature of the oxidising agent and on the conditions
under which the oxygen is set free. As oxidising agents have heretofore been used
chromic acid and chromates.
The printing in discharge style on indigo-dyed cloth is effected as follows:-
The cloth is printed upon with a thickening containing a greater or less quantity
of chromate solution according to the depth of the blue color. After having been
dried, the cloth is passed through a moderately hot solution of sulphuric and oxalic
acids, whereby the chromic acid is set free, the indigo is oxidised without difficulty,
and the printed places are rendered colorless.
As before stated, colored opaque pigments can be fixed on the places treated
during the same operation; this is done by thickening the solution of the neutral
chromate with albumen and admixing insoluble metallic colors, which resist the action
of the chromic acid.
The acid bath, through which the cloth is afterwards passed, must be kept at the
temperature necessary for completely coagulating the albumen.
For red colors, which are mostly printed on indigo, there was used vermilion,
for which of late has been substituted a cheap lake prepared from azo coloring
matters, which also resists the action of chromic acid. This lake however not only
has, like the body for which it was substituted, the disagreeable quality of falling
off when the cloth is rubbed in washing but moreover, it is decomposed by the
action of the warm soap solution and dissolved.
Another method very interesting in theory but impracticable on account of its
great cost, is to print alumina-mordants on the indigo blue and afterwards to dye
with alizarine.
On account of the great practical and commercial importance of the method
of printing in discharge style on indigo, a universal want is felt for the devising
of a simple and cheap process for producing on indigo-ground bright colors that
shall be permanent in washing and shall resist the action of light as much as
possible.
The inventor of the process described in German Letters Patent No. 55779
endeavoured to effect some improvement in this direction, by trying to fix on the
indigo ground the azo colors to be developed on the fibre, excelling by their beauty,
permanence and cheapness. But he did not succeed in producing a suitable red or
other current shades, as experience shews that none of the diazo compounds resist
the action of chromic acid; and, as the patentee himself acknowledges, there is but
one body namely amido azo benzene which possesses sufficient resistance and can be
employed for producing a red shade when using chromic acid; but unfortunately
the shade obtained, though fast, cannot satisfy even the most moderate require-
ments as to beauty. The patented process substantially consists in that, to the
usual chromate solution, there is admixed a solution of diazotised hydrochlorate of
amido-azo-benzene, the naphthol prepared cloth being printed therewith and then
passed through the usual acid bath.
The present invention relates to a process which, in contradistinction to that
above referred to, allows of the employment of all the diazo compounds for pro-
ducing on the indigo ground insoluble azo colors, and at the same time the
production of shades equalling in beauty those produced in the ordinary manner on
white cloth.
-
The invention is carried out in the following manner. Instead of adding to the
thickened diazo compounds a chromate solution, alkaline ferro-cyanides are added,
and after the color has formed the oxidation is proceeded with in an alkaline
bath. In this process the beauty of the azo colors is in no way affected and
moreover there are obtained shades that hitherto could not be produced on indigo
blue.
The essential feature of the invention consists in that, in contradistinction to the

page_text: process heretofore employed, oxidising agents are used which in acid solution do
not set free oxygen, so that the diazo compounds are not decomposed; the develop-
ment of the oxygen only begins when the azo colors have formed, in which condition
they are not affected by the oxygen which oxidises the indigo and removes it from
the fibre.
In the following is described, by way of example, the manner in which the
invention is carried out for the production on indigo ground of an azo red from
diazotised paranitraniline and beta-naphthol.
The indigo blue dyed cloth is padded on the hot flue with a beta naphthol
solution prepared as follows

page_text: washing by padding the fabric in alkaline phenol solution, printing it with thickened
diazo compound mixed with ferri cyanide, and passing it through an alkaline bath,
substantially as described.
Dated this 10th day of November 1901
ABEL & IMRAY,
Agents for the Applicant.