Process for preparation of water soluble dyes containing lithium sulfonate group or ammonium sulfonate group by cation exchange, neutralization and reverse osmosis

In accordance with this invention an aqueous solution of a water-soluble dye containing lithium sulfonate group or ammonium sulfonate group can be obtained by a very simple and economical process in such a way that an aqueous solution of a water-soluble dye containing sodium sulfonate group is fed to a packed column packed with acid type cation exchange resin (H-form) to form an aqueous solution of a dye containing a free sulfonic acid group, and after neutralizing the resulting solution with LiOH or NH.sub.4 OH, the aqueous solution of the dye thus obtained is concentrated according to a process for separation through reverse osmotic membrane.

FIELD OF THE INVENTION 
This invention relates to a process for preparation of water-soluble dyes 
containing lithium sulfonate group or ammonium sulfonate group. More 
particularly, this invention relates to a process for preparation of 
water-soluble dyes containing lithium sulfonate group or ammonium 
sulfonate group which have large solubility adapted for use in an ink-jet 
printing ink. 
BACKGROUND OF THE INVENTION 
Recently, there are seen many cases where water-soluble dyes containing 
sulfonate group are utilized in the field of information recording 
materials. 
In most of these cases, as the sulfonate, sodium sulfonate is used. This is 
not only because the sodium salt is inexpensive but also because most of 
the dyes, though they are used in the field of electronic materials, have 
been diverted from the commercially available dyes for fibers. 
When water-soluble dyes containing sodium sulfonate group (hereinafter 
abbreviated to "sodium type of dyes") are used, for example, as an ink 
composition for ink jet recording, heretofore, not a few dyes have proved 
unfit for practical use because of their insufficiency in solubility, 
especially the solubility in glycols that may be added as liquid medium, 
in spite of the fact that they are excellent in the aspect of qualities 
such as color tone, light fastness, etc. However, with regard to these 
dyes, it was found that when the sodium salt is replaced by lithium salt 
or ammonium salt, their solubilities in glycols and amides can be 
remarkably improved making it possible to obtain an ink composition having 
a dye concentration satisfactory from the practical viewpoint. 
As the conventional process for preparation of the water-soluble dyes 
containing lithium sulfonate group or ammonium sulfonate group 
(hereinafter, referred to as "lithium type of dyes" and "ammonium type of 
dyes", respectively), there are known a process of separation by acid and 
a process of separation by salt (salting out process). 
However, in the former process, the dye deposits in most of cases and 
usually as the deposited dye is considerably difficult to filter, it takes 
a long period of time for the separation, and moreover, as the wet cake of 
the separated dye contains a considerable amount of acid therein, a large 
amount of expensive lithium hydroxide or ammonium hydroxide is required 
for the neutralization. Also, by the operation being carried out under a 
strongly acidic condition the materials of the machinery and apparatus are 
inevitably greatly restricted. 
In the latter process, usually by adding LiCl, NH.sub.4 Cl, etc. to an 
aqueous solution of a water-soluble dye containing sodium sulfonate group, 
i.e., by salting out, there are obtained the crystals of Li salt, NH.sub.4 
salt, which are recovered by filtration, and after washing, are required 
to be redissolved and then purified by desalting. Thus, in this process, 
not only are the expensive LiCl, NH.sub.4 Cl, etc. needed in large 
quantities, but also the operations such as washing, redissolving, 
purification by desalting, etc. are troublesome and industrially 
disadvantageous. 
SUMMARY OF THE INVENTION 
An object of this invention is to provide a process wherein an efficient 
salt exchange can be achieved in the manufacture of a water-soluble dye 
containing lithium sulfonate group or ammonium sulfonate group from a 
water-soluble dye containing sodium sulfonate group. 
An another object of this invention is to provide a process for 
manufacturing a water-soluble dye containing lithium sulfonate group or 
ammonium sulfonate group which has a large solubility useful for an 
ink-jet printing ink. 
In accordance with this invention these objects can be achieved by feeding 
an aqueous solution of a water-soluble dye containing sodium sulfonate 
group to a packed column packed with a cationic exchange resin to form an 
aqueous solution of a dye containing free sulfonic acid group, and 
neutralizing the resulting aqueous solution with LiOH or NH.sub.4 OH, 
followed by concentrating the aqueous solution of a dye thus obtained 
according to a process for separation through reverse osmotic membrane. 
DETAILED DESCRIPTION OF THE INVENTION 
As the raw material of the water-soluble dye in this invention any of the 
dyes containing sodium sulfonate group may be used. For example, there may 
be mentioned direct dyes, acid dyes, or food dyes having the structure of 
azo dyes such as monoazo, disazo, trisazo, tetrakisazo compounds, etc.; 
anthraquinone dyes, anthrapyridone dyes, quinophthalone dyes, methane 
dyes, phthalocyanine dyes, etc. (See Yutaka Hosoda: "Theoretical Treatment 
of Manufacturing Chemistry of Dyes", published by Gijutsu-Do 5th Ed., July 
15, 1968; "Colour Index" 3rd Ed. Vol. 1, The Society of Dyers and 
Colourists (1971), etc.) 
As examples of these dyes there may be mentioned: 
C.I. Direct Black -19, -38, -154 
C.I. Direct Blue -86, -199 
C.I. Direct Red -4, -80 
C.I. Direct Yellow -50, -86, -142 
C.I. Acid Black -2, -24, -26 
C.I. Acid Blue -9, -185, -254 
C.I. Acid Red -8, -35, -37 
C.I. Acid Yellow -1, -38 
C.I. Food Black -2. 
In accordance with this invention aqueous solutions of these water-soluble 
dyes containing sodium sulfonate group are fed to a packed column of an 
ion exchange resin, whereby the concentration of the water-soluble dye in 
the aqueous solution employed in the operation is 0.5 to 20 wt %, and 
preferably 1 to 10 wt %. 
Also, the pH of the aqueous solution employed in the operation is below 
7.5, and preferably 6 to 7.5. 
As the cation exchange resin used for converting the sodium sulfonate group 
to free sulfonic acid group use can be made of acid type cation exchange 
resin, and usually use is made of strong acid type cation exchange resin. 
These resins are usually formed in particles of cross-linked copolymer of 
styrene and divinylbenzene as the matrix, into which the ion exchange 
group such as sulfonic acid group, etc. have been introduced. There are 
two types, i.e., gel-type and porous-type, either of which may be used in 
the process of this invention. 
The contact treatment of the aqueous solution of a dye and the cation 
exchange resin is, after the ion exchange resin packed in the packed 
column has been made into the H-form, carried out by feeding thereto the 
aqueous solution of a dye containing sodium sulfonate group. In the above 
case the treating temperature is usually 0.degree. to 50.degree. C., and 
preferably 10.degree. to 30.degree. C., and the feeding rate is usually 1 
to 15 (hr.sup.-1), preferably 2 to 8 (hr.sup.-1), and more preferably less 
than 5 (hr.sup.-1) in terms of space velocity (hereinafter referred to as 
S.V.) 
The neutralization is carried out by adding a basic aqueous solution of 
lithium hydroxide or ammonium hydroxide to the aqueous solution of a dye 
which has passed through the cation exchange resin bed and contains free 
sulfonic acid group, and then mixing with stirring. The neutralization 
temperature is 0.degree. to 80.degree. C., and preferably 10.degree. to 
30.degree. C. 
Next, the procedure in the process for concentration in this invention will 
be briefly described below. 
After the raw material solution, i.e., the aqueous solution of a dye 
containing lithium sulfonate group or ammonium sulfonate group, which was 
obtained by the above neutralization, has been adjusted to a predetermined 
pH, it is placed in an apparatus for reverse osmosis provided with a 
reverse osmotic membrane, and allowed to pass through the reverse osmotic 
membrane by applying a predetermined pressure at a predetermined 
temperature, whereby there is obtained a concentrated aqueous solution of 
a water-soluble dye containing lithium sulfonate group or ammonium 
sulfonate group. 
As the reverse osmotic membrane various kinds of prior known membranes that 
can pass water, salts, etc. but dyes can be used. For example, use is made 
of those membranes which are composed of a high polymer such as cellulose 
acetates, e.g., cellulose diacetate, triacetate, etc.; polyamides, 
polybenzimidazolones, polybipheny ethers, etc. and do not pass most, or 
preferably 98% or more, of dye. 
When the concentration process is carried out by the use of a reverse 
osmotic membrane in accordance with this invention, almost all the salts 
in the dye that were either present in the raw materials or contaminated 
during the manufacturing step can be removed. 
The reverse osmotic membrane may be of any desired shape or form. Namely, 
it may be of the form of hollow fiber, tubular membrane, coil-shaped 
module, branched frame module, or various many others. 
The pressure varies depending on the membrane or module used, usually 10 to 
50 kg/cm.sup.2, and preferably 15 to 35 kg/cm.sup.2. The pH should 
preferably be adjusted to not less than 6, and preferably 6 to 8 from the 
consideration of the durability of the membrane and the solubility of the 
dye. Also, the temperature is 10.degree. to 50.degree. C., and preferably 
15.degree. to 35.degree. C. 
In accordance with the process of this invention the concentrated aqueous 
solution of the water-soluble dye containing lithium sulfonate group or 
ammonium sulfonate group is very pure since the impurities accompanied 
with the raw dye are removed through the step of contact with ion exchange 
resin and the step of concentration by the reverse osmotic membrance. 
Further, in accordance with the process of this invention the amount of the 
alkali consumed is no more than necessary, and ho particular operation is 
required between the individual steps, so that the operation is simple and 
yet the aimed product can be obtained in high yield. Therefore, the 
process of this invention is industrially an extremely advantageous 
process. 
The water-soluble dye containing lithium sulfonate group or ammonium 
sulfonate group which was obtained in the above described way is adapted 
for use as an information recording ink, especially as an ink-jet printing 
ink. Also, it is advantageous when in use as a coloring matter used in the 
field of the electronic material such as the color filter, etc. in a solid 
image-pickup device. 
To be concrete, in the ink used in an ink jet printer which contains water 
and glycols as the main component, in the case where the printer is 
allowed to stand over a long period of time, the water evaporates at the 
pointed end of the nozzle, so that the glycols become rich. In the 
conventional sodium type dyes, while the solubility in water is large, the 
solubility in glycols is comparatively small, so that the dyes depositing 
at the pointed end of the nozzle may cause the clogging of the nozzle. 
On the other hand, in the case of the lithium type dyes or the ammonium 
type dyes obtained in accordance with the process of this invention their 
solubilities in glycols are so large, that no clogging is caused, and 
therefore, it may be said that this invention can markedly improve the 
reliability of the ink jet printer. 
With reference to some examples this invention will be explained in more 
detail below, but it should be understood that this invention is not 
limited thereto. 
The color index in examples is abbreviated to C.I.

EXAMPLE 1 
250 kg of 2% aqueous solution of C.I. Direct Black -19 was fed to a packed 
column (10 cm in diameter, and 140 cm high) packed with sulfonic acid type 
cation exchange resin, Diaion SK-1B (H-form, gel-type, manufactured by 
Mitsubishi Chemical Industries Limited, trade name), from the top at 
25.degree. C. at S.V. 2 (hr.sup.-1). 
Then, the recovered liquid was neutralized to pH 7.5 with a 5% aqueous 
solution of lithium hydroxide. The aqueous solution of dye thus obtained 
was concentrated at 25.degree. C. under a pressure of 24 kg/cm.sup.2 in an 
apparatus for reverse osmosis provided with polybenzimidazolone membrane 
having 1.25 m.sup.2 of surface area, which gave 27.7 kg of concentrated 
aqueous solution of a dye containing lithium sulfonate group. The yield of 
dye was 98% (as measured by O.D. value). 
Also, the coloring matter obtained by evaporating the above aqueous 
solution of dye to dryness was analyzed for sodium and lithium by atomic 
absorption method, whose results are shown together with the solubilities 
of the dye in water and diethylene glycol in Table 1 below. 
TABLE 1 
______________________________________ 
Analytical Value 
by Atomic Solubility 
Absorption Method 
(wt %) 
(wt %) Diethylene 
Na Li Water Glycol 
______________________________________ 
Coloring Matter 
5.5 0 21.0 8.4 
Before Treatment 
Coloring Matter 
0.01 1.6 22.3 18.1 
After Treatment 
______________________________________ 
EXAMPLE 2 
100 kg of 2% aqueous solution of C.I. Food Black -2 was fed to a packed 
column (10 cm in diameter, 110 cm high) packed with sulfonic acid type 
cation exchange resin, Diaion SK-1B (H-form), from the top at 25.degree. 
C. at S.V. 2 (hr.sup.-1). 
Then the recovered liquid was neutralized to pH 7.3 with a 5% aqueous 
solution of ammonium hydroxide. The aqueous solution of dye thus obtained 
was concentrated at 25.degree. C. under a pressure of 24 kg/cm.sup.2 in an 
apparatus for reverse osmosis provided with polybenzimidazolone membrane 
having 1.25 m.sup.2 of surface area, which gave 11.1 kg of concentrated 
aqueous solution of a dye containing ammonium sulfonate group. The yield 
of the dye was 97% (as measured by O.D. value). 
As in the case of Example 1, the analytical values by atomic absorption 
method and the solubilities are shown in Table 2 below. 
TABLE 2 
______________________________________ 
Analytical Value 
by Atomic Solubility 
Absorption Method 
(wt %) 
(wt %) Diethylene 
Na Water Glycol 
______________________________________ 
Coloring Matter 
11.2 29.5 6.9 
Before Treatment 
Coloring Matter 
0.3 26.3 20.5 
After Treatment 
______________________________________ 
Further, the result of the elementary analysis is also shown in Table 3. 
TABLE 3 
______________________________________ 
C H N 
______________________________________ 
Calculated Value (%) 
38.8 3.9 15.7 
Analytical Value (%) 
39.0 3.6 15.2 
______________________________________ 
EXAMPLE 3 
250 kg of 2% aqueous solution of C.I. Direct Blue -86 was fed to a packed 
column (15 cm in diameter, and 85 cm high) packed with sulfonic acid type 
cation exchange resin (H-form), Diaion SK-1B, from the top at 23.5.degree. 
C. at S.V. 2 (hr.sup.-1). 
Then the recovered liquid was neutralized to pH 8.0 with a 2% aqueous 
solution of lithium hydroxide. The aqueous solution of dye thus obtained 
was concentrated in an apparatus for reverse osmosis provided with 
polybenzimidazolone membrane having 1 m.sup.2 of surface area at 
23.degree. C. under a pressure of 25 kg/cm.sup.2, which gave 22 kg of 
concentrated aqueous solution of a dye containing lithiuim sulfonate 
group. The yield of the dye was 96% (as measured by O.D. value). The 
analytical values of sodium and lithiuim in the coloring matter by atomic 
absorption method and the solubilities of the dye in water and diethylene 
glycol are shown in Table 4. 
TABLE 4 
______________________________________ 
Analytical Value 
by Atomic Solubility 
Absorption Method 
(wt %) 
(wt %) Diethylene 
Na Li Water Glycol 
______________________________________ 
Coloring Matter 
8.1 0 41.5 7.3 
Before Treatment 
Coloring Matter 
0.2 2.3 36.0 22.3 
After Treatment 
______________________________________ 
While the invention has been described in detail and with reference to 
specific embodiments thereof, it will be apparent to one skilled in the 
art that various changes and modifications can be made therein without 
departing from the spirit and scope thereof.