Process for dyeing paper with disazo dyes

The dyestuffs of the formula ##STR1## in which A, R.sub.1, M and n are as defined in claim 1, are suitable for dyeing paper with good light-fastness.

Disazo dyes are often used for dyeing paper in blue colour shades. If high 
light-fastnesses of the dyeings are desirable, almost exclusively copper 
complexes of dyes are employed in practice. Light-fast blue dyes for-paper 
which are not copper complexes have recently been sought for economic and 
ecological reasons. The dyes sought furthermore should display a high 
degree of exhaustion under the specific dyeing conditions, they should 
produce dyeings with good wet-fastnesses and they should be so readily 
soluble that the preparation of liquid commercial forms, i.e. concentrated 
solutions of these dyes, is possible. These conditions are not yet met in 
all respects by the blue dyes for paper which are currently obtainable. 
The present invention was based on the object of providing a process for 
dyeing paper in blue colour shades in which the requirements mentioned are 
met as far as possible. This object is achieved by the process according 
to the invention. 
The invention relates to a process for dyeing paper, which comprises using 
a dye of the formula 
##STR2## 
in which A is a radical of the formula 
##STR3## 
X and Y independently of one another are hydrogen, alkyl, alkoxy or 
--NH--CO--Z, 
Z is hydrogen, alkyl, aryl, alkoxy, amino, mono- or dialkylamino or 
arylamino, 
R.sub.1 is hydrogen, alkyl, alkoxy, halogen, SO3M or carboxyl, 
M is hydrogen or one equivalent of a colourless cation, 
n is 1 or 2 and 
m is0or 1. 
Alkyl radicals are generally to be understood, according to the invention, 
as meaning straight-chain, branched or cyclic alkyl groups. Cycloalkyl 
preferably contains 5 to 8 C atoms and open-chain alkyl preferably 
contains 1 to 8 C atoms. 
Unbranched or branched open-chain alkyl is, for example: methyl, ethyl, n- 
and iso-propyl, n-, sec- or tert-butyl, n- and iso-pentyl, n- and 
iso-hexyl or 2-ethylhexyl. 
These alkyl radicals can be mono- or polysubstituted, for example by 
hydroxyl, sulfo, carboxyl, C.sub.1 -C.sub.4 alkoxy, hydroxyl-substituted 
C.sub.1 -C.sub.4 alkoxy, phenyl, phenoxy or phenylaminocarbonyl, it being 
possible for the phenyl group in the last three radicals mentioned to be 
substituted, for example by sulfo, C.sub.1 -C.sub.4 alkyl, C.sub.1 
-C.sub.4 alkoxy or phenoxy. Suitable radicals of this type are, for 
example: hydroxyethyl, 1-hydroxy-isopropyl, ethoxymethyl, 
2-hydroxyethoxypentyl, benzyl, 1-phenylethyl, 2-phenylethyl, 
1-methyl-2-phenylethyl, 1-iso-butyl-3-phenylpropyl, 1,5-diphenyl-3-pentyl, 
1-methyl-2-phenoxyethyl or 1 -methyl-2-phenylaminocarbonyl-ethyl. 
Cycloalkyl is, in particular, cyclopentyl and cyclohexyl; substituents are, 
in particular, C.sub.1 -C.sub.4 alkyl, especially CH.sub.3. 
Suitable alkoxy radicals are preferably those having 1 to 4 C atoms, for 
example methoxy, ethoxy, propoxy, iso-propoxy, n-butoxy, iso-butoxy or 
tert-butoxy. These alkoxy radicals can be substituted, for example by the 
radicals mentioned as substituents of the alkyl groups, in particular by 
hydroxyl or C.sub.1 -C.sub.4 alkoxy. Substituted alkoxy radicals are, for 
example, hydroxyethoxy, methoxyethoxy, 2-hydroxypropoxy, 
1,2-dihydroxy-3-propoxy or 1,2-dimethoxy-3-propoxy. 
Halogen is to be understood as meaning fluorine, bromine, iodine or, in 
particular, chlorine. 
Aryl radicals in this Application are generally to be understood as meaning 
aromatic or heteroaromatic radicals, but especially naphthyl or in 
particular phenyl radicals. All these radicals can be unsubstituted or 
substituted. Substituents are, for example, C.sub.1 -C.sub.4 alkyl, 
C.sub.1 -C.sub.4 alkoxy, bromine, chlorine, nitro, cyano, sulfo, carboxyl 
or C.sub.1 -C.sub.4 alkylcarbonylamino. However, the particularly 
preferred meaning of aryl is phenyl. 
M is hydrogen or one equivalent of a colourless cation, for example 
lithium, sodium, potassium, ammonium or the protonated form of a C.sub.4 
-C.sub.12 trialkylamine, C.sub.4 -C.sub.12 diamine or C.sub.2 -C.sub.15 
alkanolamine. 
A protonated C.sub.4 -C.sub.12 trialkylamine M can be, for example, 
protonated N-ethyldimethylamine, N,N-diethylmethylamine, 
tri-n-propylamine, tri-n-butylamine, tri-isobutylamine and, in particular, 
triethylamine or tri-isopropylamine; mixtures of different protonated 
amines are also suitable. 
A protonated C.sub.4 -C.sub.12 diamine M is, for example, an 
ethylenediamine or 1,3-diaminopropane, in which one or both N atoms are 
additionally substituted by one or two C.sub.1 -C.sub.4 alkyl radicals, 
preferably methyl or ethyl radicals. M here is preferably an 
N,N-dialkylethylenediamine or N,N-dialkyl-1,3-diaminopropane. Examples 
are: N-ethylethylenediamine, N,N-dimethylethylenediamine, 
N,N'-dimethylethylenediamine, N,N-diethylethylenediamine, 
3-dimethylamino-1-propylamine or 3-diethylamino-1-propylamine. 
A protonated C.sub.2 -C.sub.15 alkanolamine M can be, for example, the 
protonated form of a monoalkanol-, dialkanol-, monoalkanolmonoalkyl-, 
monoalkanoldialkyl-, dialkanolalkyl-or trialkanolamine or a mixture of 
different protonated alkanolamines. Examples are protonated 
2-aminoethanol, di(2-hydroxyethyl)amine, N-(2-hydroxyethyl)dimethylamine, 
N-(2-hydroyethyl)diethylamine, N,N-di(2-hydroxyethyl)methylamine, 
N,N-di(2-hydroxyethyl)ethylamine or tri(2-hydroxyethyl)amine, 
2-aminoethoxyethanol or diethylaminopropylamine. Protonated 
polyglycolamines are also possible, for example diethanolamine tris-glycol 
ether. 
M is preferably Na.sup..sym., Li.sup..sym. or a protonated C.sub.4 -C.sub.6 
alkanolamine, preferred C.sub.4 -C.sub.6 alkanolamines being 
tri(2-hydroxyethyl)amine, di(2-hydroxyethyl)amine or a mixture of these 
two amines. 
Z is preferably C.sub.1 -C.sub.4 alkyl, substituted or unsubstituted 
phenyl, amino or substituted or unsubstituted phenylamino, in particular 
methyl, phenyl, amino or phenylamino. 
X and Y are preferably hydrogen, methyl, methoxy, acetylamino, 
benzoylamino, ureido or phenylureido, in particular hydrogen, methyl or 
methoxy. 
R.sub.1 is, in particular, hydrogen, methyl, methoxy, chlorine, SO.sub.3 M 
or carboxyl, especially hydrogen or SO3M. 
A particularly preferred embodiment of the process according to the 
invention comprises using a dye of the formula 
##STR4## 
in which X and Y independently of one another are hydrogen, methyl, 
methoxy or --NH--CO--Z, 
Z is methyl, phenyl, amino or phenylamino, 
R.sub.1 is hydrogen, methyl, methoxy, chlorine or SO.sub.3 M, 
M is hydrogen or one equivalent of a colourless cation and 
n is 1 or2. 
Among these, particularly preferred dyes are those of the formula 
##STR5## 
in which X and Y independently of one another are hydrogen, methyl or 
methoxy, 
R.sub.1 is hydrogen or SO.sub.3 M and 
M is hydrogen or one equivalent of a colourless cation. 
The dyes of the formula (1) used in the process according to the invention 
for dyeing paper are known or can be prepared in a manner known per se. 
However, these dyes have previously been used only for dyeing cotton. 
Surprisingly, they are particularly suitable for dyeing paper and are 
particularly distinguished in this context by a good light-fastness of the 
resulting dyeings. 
In recent years, the use of concentrated aqueous solutions of dyes has 
gained in importance, in particular because of the advantages which such 
solutions have over dyes in powder form. By using solutions, the 
difficulties associated with dust formation are avoided and the user is 
freed from the time-consuming and often difficult dissolving of the dye 
powder in water. The use of concentrated solutions furthermore has been 
prompted by the development of continuous dyeing processes for paper, 
since in these processes it is advantageous to add the solution directly 
to the Hollander or at any other suitable point of papermaking. 
However, difficulties frequently occur when concentrated aqueous solutions 
of anionic dyes are used, since such solutions are not sufficiently 
storage-stable and precipitates occur during storage for several months, 
in particular at about 0.degree. to 5.degree. C. 
It has now been found that concentrated aqueous solutions of the dyes used 
according to the invention have a very good storage stability if they 
comprise at least 0.1 mol of Li.sup..sym. per mol of dye of the formula 
(1), the solutions preferably having a pH of at least 11. 
The invention therefore also relates to aqueous solutions of dyes, which 
comprise 2 to 20 per cent by weight of a dye of the formula 
##STR6## 
and at least 0.1 mol of Li.sup..sym. per mol of dye of the formula (1), in 
which A, M, R.sub.1 and n are as defined above under the formula (1). 
Among these, those which have a pH of at least 11, preferably between 11 
and 13, are preferred. 
Preferred aqueous dye solutions comprise 6 to 15 per cent by weight of a 
dye of the formula (1) and 0.1 to 3 mol of Li.sup..sym. per mol of dye of 
the formula (1) and have a pH of at least 11. 
Those dye solutions which comprise less than 2% by weight, based on the 
weight of the dye solution, of inorganic salts furthermore are preferred. 
If the dye solutions are obtained with a higher salt content during 
synthesis, the solutions can be desalinated in the customary manner, for 
example by a membrane separation process. 
The pH of at least 11 is established in the dye solutions according to the 
invention by addition of a strong base, for example NaOH, KOH, ammonium, 
diethanolamine or triethanolamine, but preferably LiOH. 
The dye solutions according to the invention can additionally comprise 
water-soluble organic solubilizing agents, for example urea, 
.epsilon.-caprolactam, dimethyl sulfoxide, N-methylpyrrolidone, 
water-miscible polyhydric alcohols, such as ethylene glycol, propylene 
glycol or glycerol, alkanolamines, such as ethanolamine or 
triethanolamine, or polyglycolamines, for example reaction products of 
ammonia, as well as alkyl- and hydroxyalkylamines with alkylene oxides, 
such as ethylene oxide, 1,2-propylene oxide, 1,2-butylene oxide or 
2,3-butylene oxide, in suitable quantitative ratios. Such polyglycolamines 
are known, for example from DE-A-2 061 760. 
The concentrated aqueous solutions according to the invention of dyes of 
the formula (1) can be prepared, for example, by a procedure in which the 
dye suspension obtained during preparation of the dye is filtered, 
desalinated, for example by a membrane separation process, if appropriate, 
and stabilized by addition of a lithium salt and/or lithium hydroxide and 
if appropriate a solubilizing agent. However, the isolated dye can also be 
suspended in hydrochloric acid filtered again and the filter cake can be 
mixed with lithium hydroxide and/or a suitable lithium salt and the 
required amount of water. Finally, the coupling can also be carried out in 
the presence of LiOH or alkanolamines and the synthesis solution can then 
be desalinated. 
The aqueous dye solutions according to the invention, which are stable at 
storage temperatures down to -5.degree. C., are suitable for dyeing paper, 
on which they produce attractive blue colour shades with high 
light-fastness with or without the use of a size. 
The dye solutions can be used by all the processes customary in the paper 
industry for direct dyes, in particular for pulp as well as surface dyeing 
of paper for sized and non-sized grades, starting from bleached or 
unbleached cellulose of various origins, such as softwood or hardwood 
sulfite and/or sulfate cellulose. 
The present invention furthermore relates to the dyes of the formula 
##STR7## 
in which X is hydrogen, alkyl, alkoxy or --NH--CO--Z, 
Y' is a C.sub.1 -C.sub.4 alkoxy radical, which is substituted by hydroxyl, 
C.sub.1 -C.sub.4 alkoxy, sulfo, carboxyl, phenyl, phenoxy or 
phenylaminocarbonyl, 
Z is hydrogen, alkyl, aryl, alkoxy, amino, mono- or dialkylamino or 
arylamino, 
R.sub.1 is hydrogen, alkyl, alkoxy, halogen, SO.sub.3 M or carboxyl, 
M is hydrogen or one equivalent of a colourless cation, 
n is 1 or 2 and 
m is0or 1. 
X, Z, R.sub.1, M, n and m are preferably as defined as preferred in the 
dyes of the formula (1), and Y' is preferably C.sub.1 -C.sub.4 alkoxy 
which is substituted by hydroxyl or methoxy. 
The novel dyes of the formula (6) can be prepared in a manner known per se, 
for example by diazotization of an aminoazo compound of the formula 
##STR8## 
and coupling of the product with a compound of the formula 
##STR9## 
In the compounds of the formulae (7) and (8), X, Y', M, n and R.sub.1 are 
as defined under formula (6). 
In the following examples, parts are by weight and temperatures are stated 
in degrees Celsius.

EXAMPLE 1 
60.8 g of the compound of the formula 
##STR10## 
are dissolved with sodium hydroxide solution in 350 ml of water together 
with 6.9 g of sodium nitrite under neutral conditions and diazotized by 
addition of 19.2 g of 32% hydrochloric acid at 20.degree. to 25.degree. C. 
The resulting diazo suspension is added dropwise in the course of 45 
minutes, at 25.degree. to 30.degree. C., to a solution prepared from 34.8 
g of 6-anilino-1-hydroxynaphthalene-3-sulfonic acid and 22 g of 
diethanolamine in 250 ml of water; during this operation, the pH is kept 
at 8.5 to 9.0 by addition of 18.0 g of diethanolamine. When the coupling 
has ended, 40 g of 50% sodium hydroxide solution are added to the 
synthesis solution and hydrolysis is carried out at 75.degree. C. for one 
hour. After cooling to room temperature, the pH is brought to 6.5 to 7 
with 32% hydrochloric acid. A suspension containing the dye of the formula 
##STR11## 
is obtained. 
The dye suspension is desalinated by reverse osmosis over a membrane of 
chemically modified polyacrylonitrile at 50.degree. C. and concentrated to 
a final weight of 750 g. 
A liquid formulation which is storage-stable at 2.degree. to 5.degree. C. 
for several months is obtained. 
EXAMPLE 2 
A dye suspension containing 85.9 g of the trisodium salt of the dye 
described in Example 1 is prepared as described in Example 1, except that 
29 g of 30% sodium hydroxide solution are used instead of 40 g of 
diethanolamine. The resulting suspension is then desalinated by reverse 
osmosis over a membrane of chemically modified polyacrylonitrile at 
50.degree. C. and concentrated to a final weight of 750 g. 3.9 g of 
LiOH.1H.sub.2 O and 3.9 g of anhydrous Li.sub.2 SO.sub.4 are added and the 
solution is stirred at 50.degree. C. for one hour. It is then cooled to 
25.degree. C., made up to 780 g with deionized water and filtered. 
The resulting dye solution is stable for several months at a storage 
temperature of 2.degree. to 5.degree. C. and dyes paper with excellent 
light-fastness. 
EXAMPLE 3 
The procedure described in Example 1 is repeated, except that 11.7 g of 
anhydrous Li.sub.2 SO.sub.4 are used in place of 3.9 g of LiOH.1H.sub.2 O 
and 3.9 g of anhydrous Li.sub.2 SO.sub.4, likewise affording a 
storage-stable liquid formulation. 
EXAMPLE 4 
The procedure described in Example 1 is repeated, except that a total of 
9.9 g of LiOH.1H.sub.2 O is used for the coupling in place of 
diethanolamine, likewise affording a storage-stable liquid formulation. 
EXAMPLE 5 
70 parts of chemically bleached sulfite cellulose (from softwood) and 30 
parts of chemically bleached sulfite cellulose (from birch wood) are 
beaten in 2000 parts of water in a Hollander. 2.5 parts of the dye 
solution described in Example 1 are added to this pulp. After a mixing 
time of 20 minutes, paper is produced from this pulp. The absorbent paper 
obtained in this manner is dyed blue. The dyeing has a high 
light-fastness. The waste water is practically colourless. 
EXAMPLE 6 
3.0 parts of the dye solution from Example 1 are dissolved in 100 parts of 
water and the solution is added to 100 parts of chemically bleached 
sulfite cellulose which has been beaten with 2000 parts of water in a 
Hollander. After thorough mixing for 15 minutes, sizing is carried out in 
the customary manner with resin size and aluminium sulfate. Paper produced 
from this pulp has a blue shade with good wet-fastnesses and good 
light-fastness. 
EXAMPLES 7-13 
The following dyes which dye paper in blue colour shades with good 
fastnesses are prepared in a manner analogous to that described in Example 
1. 
______________________________________ 
##STR12## 
Example A 
______________________________________ 
7 
##STR13## 
8 
##STR14## 
9 
##STR15## 
10 
##STR16## 
11 
##STR17## 
12 
##STR18## 
13 
##STR19## 
______________________________________ 
EXAMPLES 14-16 
The following dyes which dye paper in blue colour shades with good 
fastnesses are prepared in a manner analogous to that described in Example 
1. 
__________________________________________________________________________ 
##STR20## 
Example 
R 
__________________________________________________________________________ 
14 CH.sub.3 
15 SO.sub.3 H 
16 COOH 
__________________________________________________________________________ 
EXAMPLES 17-22 
The following dyes which dye paper in blue colour shades with good 
fastnesses are prepared in a manner analogous to that described in Example 
1. 
______________________________________ 
##STR21## 
Beispiel A 
______________________________________ 
17 
##STR22## 
18 
##STR23## 
19 
##STR24## 
20 
##STR25## 
21 
##STR26## 
22 
##STR27## 
______________________________________ 
EXAMPLES 23-25 
The following dyes which dye paper in blue colour shades with good 
fastnesses are prepared in a manner analogous to that described in Example 
1. 
______________________________________ 
##STR28## 
Example D 
______________________________________ 
23 
##STR29## 
24 
##STR30## 
25 
##STR31## 
______________________________________