Stable dye solution

A stable dye solution which has a high concentration of dye and which is miscible with water in any proportion, is described which dye solution contains PA1 (a) 20 to 40 percent by weight of at least one azo, nitro or anthraquinone dye containing acid groups, in particular sulphonic acid groups, PA1 (b) 20 to 80 percent by weight of N-cyclohexylpyrrolidone, PA1 (c) optionally 0.1 to 20 percent by weight of water, and PA1 (d) optionally 0.1 to 50 percent by weight of a glycol or glycol ether or of a mixture thereof, As well as, optionally, further additives; the said dye solution is suitable in particular for the continuous dyeing of carpets.

The invention relates to a stable dye solution of acid dyes, which is 
miscible with water in any proportion, to processes for producing this dye 
solution, as well as to its use for the preparation of dye baths and 
printing pastes for dyeing and printing of, in particular, textile 
materials. 
Many dyes are put on the market usually in the form of dried and finely 
ground powders, which have to be dissolved or dispersed for dyeing in the 
dye bath. This form of application has however considerable disadvantages. 
Apart from the unpleasant release of dust caused by the weighing, 
transferring or charging of the deeply coloured dye powders, and the risk 
of the finely ground dye powders becoming caked together due to the action 
of moisture or heat resulting from incorrect storage, the dissolving or 
dispersing of the powders in the dye bath gives rise to considerable 
difficulties since the dyes in most cases are insufficiently soluble in 
water, particularly when high dye concentrations are required, such as are 
necessary, e.g., for continuous dyeing or for printing. If it is not 
possible to get the undissolved dye constituents of a padding liquor or of 
a printing paste into an adequately fine dispersion, irregular and 
skittery dyeings and printings are obtained. 
It has therefore already been suggested that dyes, for example acid dyes, 
be used in the form of concentrated solutions. It is possible in this way 
to avoid certain disadvantages, such as the generation of dust and the 
dissolving difficulties, associated with the use of dye powders. 
From DOS 2,335,512 is thus known a dye solution which contains at least one 
azo, nitro or anthraquinone dye, each containing sulphonic acid groups, 
dissolved in a solvent mixture that is miscible in any proportion with 
water and consists of an aprotic solvent, a glycol and, optionally, water. 
It has now been found on the one hand that with the use of 
N-cyclohexylpyrrolidone as an aprotic solvent, this can be employed on its 
own as solvent and not necessarily in combination with a glycol; and on 
the other hand that in the case of other organic solvents present, these 
can be at least partially replaced by water. 
Surprisingly, as a result of the application of N-cyclohexylpyrrolidone, 
the capacity of the dye solution to be diluted with water is improved, and 
furthermore the diluted solution -- also in the acid pH range -- is more 
stable. The consequence of this is that such a solution can be used 
particularly in the continuous dyeing of carpets. 
The invention thus concerns a dye solution which consists essentially of 
a. 20 to 40 percent by weight of at least one azo, nitro or anthraquinone 
dye containing acid groups, in particular sulphonic acid groups, 
b. 20 to 80 percent by weight of N-cyclohexylpyrrolidone, 
c. optionally 0.1 to 20 percent by weight of water, and 
d. optionally 0.1 to 50 percent by weight of a glycol or glycol ether or of 
a mixture thereof. 
An especially preferred dye solution is composed of: 
a. 25 to 35 percent by weight of an azo, nitro or anthraquinone dye 
containing sulphonic acid groups, 
b. 20 to 30 percent by weight of N-cyclohexylpyrrolidone, 
c. 0.1 to 10 percent by weight of water, and 
d. 30 to 50 percent by weight of a glycol or glycol ether. 
The dye solutions according to the invention are highly fluid, have a pH 
value of about 6 to 8, have a high concentration of dye, are miscible with 
water in any proportion, are storage-stable over 3 to 4 months and are 
temperature-stable from -20.degree. C to +50.degree. C. 
The azo, nitro and anthraquinone dyes containing acid groups, in particular 
sulphonic acid groups, can according to the invention be present in the 
dye solution in the form of the free sulphonic acid, advantageously 
however in the form of their metal salts, e.g. sodium, potassium or 
magnesium salts. 
Azo dyes containing sulphonic acid groups are, for example, disazo dyes, 
particularly however monoazo dyes which belong, e.g., to the following 
classes: benzene-azobenzene, benzene-azo-naphthalene, 
naphthalene-azo-naphthalene, benzene-azo-pyrazolone, 
benzene-azo-aminopyrazole, benzene-azo-acetoacetic acid amide, 
benzene-azobenzene-azobenzene, benzene-azo-naphthalene-azo-benzene or 
benzene-azo-benzene-azo-naphthalene; and which can contain further 
substituents such as amino, hydroxy, alkylsulphonyl, arylsulphonyl, alkyl 
or alkoxy groups having 1 to 6 carbon atoms, halogen atoms such as 
chlorine, bromine or fluorine, or nitro groups. 
As acid nitro dyes are mentioned in particular nitrophenylamine compounds 
which can contain further substituents, e.g. amino groups. 
The anthraquinone dyes from a colouristic point of view can belong to the 
most diverse classes. Of interest from a chemical point of view are in 
particular the 1-amino-4-arylamino-anthraquinones. 
Suitable glycols or glycol ethers optionally usable according to the 
invention are those which are miscible with water in any proportion. 
Examples of these are: ethylene glycol, 1,2-propylene glycol, diethylene, 
glycol, triethylene glycol and tetraethylene glycol, 
2-methylpentanediol-3,4, ethylene glycol monomethyl ether, ethylene glycol 
monoethyl ether or ethylene glycol mono-n-butyl ether, diethylene glycol 
monomethyl ether, diethylene glycol monoethyl ether or diethylene glycol 
monobutyl ether, diethylene glycol monoethyl ether acetate, triethylene 
glycol monobutyl ether, tetraethylene glycol dimethyl ether dipropylene 
glycol, glycerin, glycerin-1,3-diethyl ether or thiodiglycol. 
Of the glycols or glycol ethers mentioned, which may also be used mixed 
with or among each other, those preferably employed are tetraethylene 
glycol, diethylene glycol monomethyl ether and tetraethylene glycol 
dimethyl ether. 
To the dye solutions according to the invention can also be added 
water-soluble additives for improving properties, such as anti-foaming 
agents or dispersing agents. 
The dye solutions according to the invention are obtained by mixing the 
commercial dye or pure dye as defined, preferably in the dried powder 
form, into N-cyclohexylpyrrolidone, optionally in the presence of water 
and/or of a glycol or glycol ether, at a temperature of about 20 to 
60.degree. C, and stirring until the solution is homogeneous. The solution 
temperature and the time required to obtain the solution depend on the 
employed dye and on the solvents. Both values can be easily determined by 
preliminary tests. 
The insoluble constituents, such as inorganic salts, impurities, etc., are 
if necessary filtered off to finally obtain the homogeneous dye solution 
according to the invention. 
By virtue of the existence of a solution, the danger, often present in the 
case of dispersions, of flocculation and sedimentation is avoided. 
The dye solution according to the invention is miscible with water in any 
proportion, without precipitation of the dye, and can be easily 
volumetrically measured out, irrespective of whether it is diluted with 
water or is poured into water. The adding of the dye solution according to 
the invention to the liquor can be carried out even at room temperature 
without any risk of lumps being formed. In the case of dye preparations in 
powder form, however, it is frequently necessary, before addition of the 
dye to the dye bath, to prepare a stock solution at elevated temperature 
in water, in order to ensure that the dyes are completely dissolved or 
dispersed in the dye bath. 
Before its subsequent use, the dye solution according to the invention has 
to be diluted with water approximately in the ratio of 1:10 to 1:50, i.e. 
1 part of dye solution and 10 to 50 parts of water. 
A dye solution of this kind is used, in particular, for the preparation of 
a dye bath, or, before dilution with water and after the addition of 
suitable thickening agents, for the preparation of aqueous, 
organic-aqueous or pure organic printing inks. 
In continuous dyeing, the use of highly concentrated dye solutions 
extraordinarily simplifies the preparation of padding liquors. A 
particular requirement in this respect is that these padding liquors 
should be stable, a requirement which the dye solution according to the 
invention, after dilution with water, satisfies. This is especially of 
advantage when, for example, floor coverings of polyamide fibre material, 
such as tufted carpets, are being continuously dyed in long lengths, with 
several cubic meters of padding liquor being required for each batch. 
Thus the dye solution according to the invention is suitable, in 
particular, for the continuous dyeing of carpets. It can however be used 
for other purposes, e.g. for producing dye baths for the continuous and 
discontinuous process applicable to textile materials which are dyeable 
with acid dyes. Furthermore, such a dye solution can be used to produce 
inks or printing inks for recording instruments, stamp pads and typewriter 
ribbons.

In the following Examples which illustrate the invention without its scope 
being limited to them, parts are by weight, except where otherwise stated, 
and temperatures are in degrees Centigrade. 
EXAMPLE 1 
A storage-stable solution is obtained by introducing 35 parts of the 
salt-containing dye powder of the formula 
##STR1## 
into a mixture of 25 parts of N-cyclohexylpyrrolidone, 10 parts of water 
and 30 parts of tetraethylene glycol dimethyl ether at 60.degree. while 
stirring is maintained. 
The solution is then further stirred for 1 hour at room temperature, and 
subsequently filtered off from the residue remaining. The dye does not 
crystallise out from the resulting solution even after 3 months at 
temperatures of -20, 25 and 50.degree.. If the dye solution is poured into 
water, a homogeneous dispersion occurs instantly. 
The colouristic properties of the solution are better than those of the 
corresponding standardised dye-powder type. 
EXAMPLE 2 
31 parts of the dry salt-containing dye of the formula 
##STR2## 
are introduced at room temperature into a mixture of 20 parts of 
N-cyclohexyl-2-pyrrolidone and 49 parts of diethylene glycol monomethyl 
ether. The mixture is stirred during one hour at room temperature. The dye 
goes into solution and the solution is subsequently filtered. On 
filtration, practically no residue remains on the filter. The resulting 
solution is highly fluid, storage-stable, miscible with water in any 
proportion and, in its diluted form, is characterised by a particularly 
good stability in storage. It is very suitable for the continuous dyeing 
of carpets. 
EXAMPLE 3 
25 parts of the salt-containing dye powder of the formula 
##STR3## 
are dissolved, by stirring, in a mixture of 10 parts of water, 25 parts of 
N-cyclohexyl-2-pyrrolidone and 40 parts of tetraethylene glycol at room 
temperature. The mixture is further stirred for one hour, and the 
undissolved (salt) is then removed by filtration. The solution obtained is 
storage-stable and, if diluted with water, remains stable. 
EXAMPLE 4 
25 parts of the salt-containing dye powder according to Example 3 are 
dissolved by stirring at room temperature in 75 parts of 
N-cyclohexyl-2-pyrrolidone. The mixture is stirred for a further hour, and 
then separated by filtration from the undissolved (salt). The solution 
obtained is storage-stable and, if diluted with water, remains stable. 
EXAMPLE 5 
28 parts of the salt-containing dye powder of the formula 
##STR4## 
are dissolved by stirring in a mixture of 10 parts of water, 20 parts of 
N-cyclohexylpyrrolidone and 42 parts of tetraethylene glycol at a 
temperature of about 40 to 50.degree.. The mixture is stirred for a 
further hour, and is then separated by filtration from the undissolved 
(salt). The solution obtained is storage-stable and, when diluted with 
water, remains stable.