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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for purifying aqueous dye
solutions. More particularly, the present invention provides a high purity
water-soluble dye for use as a coloring component of a recording agent.
The recording agent can be used, for example, in an ink-jet recording
system or a manual writing implement (hereinafter, the recording liquid is
referred to as "ink").
2. Description of the Prior Art
Water-soluble dyes such as direct cotton dyes, acid dyes, basic dyes,
reactive dyestuffs and the like have conventionally been used for the
dyeing of fibers, woven cloths, etc. Further, these dyes are recently used
as coloring components in ink jet recording wherein an ink is discharged
by various discharging means to form ink droplets and the ink droplets are
deposited to a recording medium such as a paper or the like in accordance
with image signals. Furthermore, the water-soluble dyes are used as
coloring components of inks used in writing, such as fountain pen, felt
tip pen, ball point pen and the like.
As coloring component dyes of inks, particularly inks which are used in ink
jet recording, there are generally utilized dyes for dyeing of fibers.
These dyes contain large amounts of additives or impurities. Therefore,
when such commercially available dyes are used for ink jet recording, the
inks cause various troubles. One of the most serious is clogging of the
ink-discharging orifice, and another is deposition of impurities on the
heat-generating head in the ink jet recording method utilizing heat energy
for ink discharge. In order to prevent such troubles, purification of dyes
used in these inks have heretofore been proposed and carried out.
Accordingly, some improvements have been achieved and problems caused by
inks have been reduced by using dyes of higher purity. However, there
still exists a phenomenon that inks which are pure after production, when
delivered from ink manufacturers and stored for several months or years,
frequently cause unanticipated problems. These troubles are significant
particularly in the ink jet recording method employing heat energy for ink
discharge.
SUMMARY OF THE INVENTION
The main object of the present invention is to provide a dye capable of
giving an ink which remedies the above mentioned shortcomings. This ink,
even at a high dye concentration does not the orifice, etc. of ink jet
recording equipment during use and also during long term storage, forms no
deposit on the heat-generating head of ink jet recording equipment
utilizing heat energy, and has excellent stability.
According to one aspect of the present invention, there is provided a
method for purifying a dye solution, comprising dissolving a dye in a
solvent to prepare a dye solution, and treating the dye solution by
addition of a flocculant.
According to another aspect of the present invention, there is provided a
method for purifying a dye solution, comprising the steps of dissolving a
dye in a solvent to prepare a dye solution, treating the dye solution by
addition of a flocculant, and removing insoluble matters .from the dye
solution by filtration or centrifugation.
According to further aspects of the present invention, there is provided a
method for producing an ink by utilizing the above method for dye
purification.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In order to attain the above objects the present inventor undertook
extensive research. Commercially available dyes contain various impurities
(e.g. various inorganic and organic substances such as dispersing agents
and leveling agents) and the above mentioned problems are caused mainly by
these impurities. Hence, the adverse effects of the impurities were
investigated. It was found that the greatest cause for clogging of nozzles
and orifices, for formation of precipitates during ink storage and for
deposition of impurities on heat-generating heads in the ink jet recording
method utilizing heat energy is the presence in ink of Fe, Si, P,
polyvalent metal ions, and colloidal substances consisting of these
compounds and that these harmful substances can be efficiently removed
from dyes used in inks by using a particular method. Thus the present
invention has been completed.
The main characteristic of the present invention lies in the use of a
flocculant for purification of a water soluble dyes. The dyes to which the
present invention is applicable are water-soluble dyes conventionally used
mainly for the dyeing of various fibers, such as direct cotton dyes, acid
dyes, basic dyes, reactive dyestuffs and the like. As dyes which are
preferably used in inks for ink jet recording and satisfy such
requirements as distinctness, water solubility, stability, light
resistance and the like, there are mentioned, for example, C. I. Direct
Black 17, 19, 32, 51, 71, 108 and 146; C. I. Direct Blue 6, 22, 25, 71,
86, 90, 106 and 199; C. I. Direct Red 1, 4, 17, 28 and 83; C. I. Direct
Yellow 12, 24, 26 and 98; C. I. Direct Orange 34, 39, 44, 46 and 60; C. I.
Direct Violet 47 and 48; C. I. Direct Brown 109; C. I. Direct Green 59; C.
I. Acid Black 2, 7, 24, 26, 31, 52, 63, 112 and 118; C. I. Acid Blue 9,
22, 40, 59, 93, 102, 104, 113, 117, 120, 31, 52, 63, 112 and 118; C. I.
Acid Blue 9, 22, 40, 59, 93, 102, 104, 113, 117, 120, 167, 229 and 234; C.
I. Acid Red 1, 6, 32, 35, 37, 51, 52, 80, 85, 87, 92, 4, 115, 180, 256,
317 and 315; C. I. Acid Yellow 11, 17, 23, 25, 29, 42, 61 and 71; C. I.
Acid Orange 7 and 19; C. I. Acid Violet 49; C. I. Basic Black 2; C. I.
Basic Blue 1, 3, 5, 7, 9, 24, 25, 26, 28 and 29; C. I. Basic Red 1, 2, 9,
12, 13, 14 and 37; C. I. Basic Violet 7, 14 and 27; C. I. Food Black 2;
etc. These dyes are preferably used in the present invention. However, the
present invention is not restricted to such dyes.
The water-soluble dyes mentioned above generally are available in the
market. The commercially available products contain large amounts of
sodium chloride, sodium sulfate and other inorganic salts and further
contain inorganic substances such as alkaline earth metal salts, various
metal compounds and the like as well as many organic substances such as
various surfactants, dispersing agents, leveling agents and the like.
Since the above mentioned additives contained in the conventional
water-soluble dyes are also water-soluble, purification of these dyes is
not simple. When such dyes are thoroughly purified by employing a
conventionally known purification method such as filtration, salting-out,
ion exchange or the like and are then immediately used as inks for ink jet
recording, such inks show excellent performance, as intended. When stored
for several months or longer after their preparation, however, these inks
cause troubles as, mentioned previously. These troubles caused by stored
inks occur, in many cases, after the inks have been distributed to the
market and hence it is a serious problem. In order to solve this serious
problem, the present inventors undertook extensive research. As the
result, it was found that (1) the troubles caused by an ink deteriorated
by storage over a long period of time cannot be alleviated by treating the
ink by ordinary filtration, ion exchange, etc., (2) the main cause of the
troubles comes from a colloidal substance which is present in ink with a
relatively high stability but the substances lose their stability when the
ink encounter environmental changes such as temperature change,
concentration change at a discharging nozzle, thermal shock at a heating
head and the like, and (3) said troubles can be completely removed by
adding a flocculant to a dye solution to be purified, prior to or during
ink preparation to flocculate colloidal substances present in the dye
solution and, if necessary, separating the resulting flocculates of any
size by means of centrifugation or the like to remove the colloidal
substances completely.
The flocculant used in the present invention can be any of ions of bi- or
higher-valent metals (e.g. iron, manganese, aluminum, magnesium), ions of
metal compounds, ions of oxides of metals (semimetals such as silicon and
phosphorus and the like are included), their hydrates and substances which
will neutralize electric charges of colloidal substances present in dye
solutions, as long as the above ions, hydrates and substances are stable
in water. There are preferably used, for example, conventionally known
flocculants such as inorganic flocculants (e.g. aluminum hydroxide,
aluminum sulfate, ferrous sulfate, ferrous chloride, ferric sulfate,
ferric hydroxide, calcium sulfate, calcium carbonate, calcium hydroxide,
Fe.sub.2 (SO.sub.4).sub.3.FeCl.sub.3 and organic flocculants (e.g. starch,
gelatin, sodium alginate, a polyacrylamide, chitosan). Particularly
preferably used in the present invention are flocculants of iron type and
aluminum type.
In the present invention method, mainly colloidal substances are changed,
by the use of a flocculant, to flocculates which can mostly be removed by
filtration. However, in a treatment with a flocculant alone, not all the
colloidal substances changes to flocculates removable by filtration; fine
and insufficiently grown flocculates of colloidal substances pass through
a filter membrane or cause clogging of the membrane when an ordinary
filtration is conducted; consequently, the filter membrane need be
replaced frequently. The present inventors made a research to solve such
problems and found that when a centrifugation is conducted subsequently to
the treatment with a flocculant, the fine flocculates of colloidal
substances which pass through a filter membrane or cause clogging of the
membrane are captured by larger flocculates and separated together with
the larger flocculates, whereby an aqueous dye solution substantially free
from colloidal substances can be obtained. Such a purified aqueous dye
solution cannot be obtained only by treatment with a flocculant or only by
the treatment using a centrifuge alone but can be obtained only when these
two treatments are conducted in succession in this order.
In the centrifugation treatment, there can be effectively used any
commercially available centrifuges.
In the method for dye purification according to the present invention, a
dye to be purified is dissolved in water or in a mixed solvent of water
and a water-soluble organic solvent in an amount of 0.1 to 10% by weight,
preferably 1 to 5% by weight; to the resulting aqueous dye solution is
added 0.01 to 1 part by weight, based on 100 parts by weight of the dye,
of a flocculant; and the resulting mixture is thoroughly stirred. Such a
treatment will eliminate the electric charges from a majority of stable
colloidal substances and the like as mentioned above and accordingly the
substances lose the colloidal properties to flocculate. The above aqueous
dye solution treated with a flocculant is subjected to a filtration
treatment. In cases when the previously mentioned troubles arise even
after the filtration treatment, there may be successively conducted a
centrifugation treatment. In the centrifugation, neither heating nor
cooling is required. A centrifugation of 5,000 to 20,000 rpm for about 10
to 60 min can satisfactorily achieve the object of the present invention.
Thus an aqueous dye solution from which mainly colloidal substances have
been removed can be obtained. The present invention method can be
conducted batchwise or continuously.
The purified aqueous dye solution obtained as above, when the dye had been
subjected, prior to the above purification method of the present
invention, to other purification method to remove other impurities, can be
used as it is as an ink for ink jet recording or as an ink for writing
pens. When the dye had not been subjected to the other purification
method, the purified aqueous dye solution obtained above contain, in many
cases, impurities which cannot be removed by a flocculant, such as sodium
chloride, sodium sulfate, other metal salts and organic substances;
therefore, it is preferable that the purified aqueous dye solution be
further purified, as necessary, by a method such as salting-out,
fractional precipitation with a water-soluble organic solvent,
ultrafiltration, reverse osmosis, ion exchange, exposure to air, lime
softening, electrolysis or the like.
The purified aqueous dye solution thus obtained can be made into an ink as
it is or after adding thereto necessary additives such as a water-soluble
organic solvent and the like, or can be made into a powder by removing the
water present in the solution. The amount of impurities remaining in the
purified aqueous dye solution or in the purified powder can easily be
determined by the use of atomic absorption spectrometry, inductively
coupled plasma emission spectral analysis or the like. It is preferable
that the concentration of impurities in the purified dye of the present
invention be about 200 ppm or below (each of iron, magnesium and
phosphorus), 250 ppm or below (silicon), about 1,000 ppm or below (total
colloidal substances including these metal compounds) and about 2% by
weight or below (total inorganic substances), all based on powdery dye. A
purified dye containing impurities so as not to exceed the above limits
can provide an ink useful for use particularly in the ink jet recording
method using a heat energy. Use of such an ink can eliminate the
previously mentioned troubles even when the ink has been stored for a long
period of time after its preparation.
Hereinafter the present invention will be described more specifically b way
of Examples. Parts or % in the following refer to parts or % by weight.
EXAMPLES 1A TO 6A (DYE PURIFICATION)
The commercially available dyes listed in Table 1A which appears later were
purified according to an ordinary method such as salting-out, fractional
precipitation, ultrafiltration, reverse osmosis, ion exchange or the like.
Then, these purified dyes were made respectively into a 2% aqueous
solution. To each 500 ml of these solutions was added 10 ml of an aqueous
solution containing 10 ppm of a flocculant shown in Table 1A, and they
were stirred for 2 hrs. Thereafter, the mixture was subjected to pressure
filtration or centrifugation to separate flocculates. The filter for
pressure filtration was Fluoropore filter (pore diameter of 0.45 .mu.m)
manufactured by Sumitomo Electric Industries, Ltd. and centrifugation was
conducted at 12,000 rpm for 30 min. The content (based on powder dye) of
inorganic substances in the purified dye was measured with iron picked up
as a representative inorganic substance. The results are shown in Table
1A.
EXAMPLE 1A (INK EVALUATION)
Using the purified dye obtained in Example 1A (dye purification), there was
prepared an ink for ink jet recording having the following composition.
______________________________________
Dye 2 parts
Diethylene glycol
40 parts
Water 60 parts
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This ink was subjected to the following T1 to T5 evaluation tests, using a
recording equipment having an on-demand type multi-head (discharging
orifice diameter: 35.mu., resistance of heat-generating resistor: 150
.OMEGA., driving voltage: 30 V, frequency: 2 KHz) wherein the ink stored
in the recording head was given a heat energy to generate ink droplets for
evaluation of recording. The ink gave good results in all the tests.
(T1) Long term storage stability: The ink was sealed in a plastic film bag
and stored for 6 months at -30.degree. C. and 60.degree. C., separately.
No insoluble appeared and further there was no change in ink properties
and color.
(T2) Discharging stability: The ink was subjected to continuous discharging
of 24 hours in atmospheres of room temperature, 5.degree. C. and 40.degree.
C., separately. Constantly stable and high quality recording could be
conducted in all the conditions.
(T3) Discharging response Two cases of intermittent discharging of 2 sec
and discharging after 2 month standing were examined. In each case, there
was no clogging at the orifice tip and there was obtained stable and
uniform recording.
(T4) Quality of recorded image: Using the ink, recording was conducted on
the recording media listed in Table 2 which appears later. Each recorded
image had high optical density and distinctness. When each image was
exposed to an indoor light for 6 months, the reduction of its density was
1% or less.
(T5) Fixing on various recording media: Using the ink, printing was
conducted on the recording media of Table 2 which appear later. After 15
sec, the printed portion on each recording medium was rubbed with fingers
to see image aberration and spreading. In all the cases, there was neither
image aberration nor image spreading, and fixing was excellent.
EXAMPLES 2A TO 6A (INK EVALUATION)
Using the purified dyes obtained in Examples 2A to 6A (dye purification)
according to the present invention method, inks were prepared in the same
manner as in Example 1A (ink evaluation). Each ink was subjected to the
same T1 to T5 evaluation tests as in Example 1A (ink evaluation). All the
inks showed the same excellent results as in Example 1A (ink evaluation).
EXAMPLE 7A (INK EVALUATION)
The yellow ink, magenta ink, cyan ink and black ink obtained in Examples
1A, 2A, 3A and 5A (ink evaluation), respectively, were subjected to the
same T1 to T5 evaluation tests as in Example 1A (ink evaluation), using a
recording equipment having an on-demand type recording head (discharging
orifice diameter: 50 .mu., driving voltage for piezoelectric vibrator: 60
V, frequency: 4 KHz) wherein each ink was discharged by the piezoelectric
vibrator. All the inks showed excellent results.
EXAMPLE 8A (INK EVALUATION)
Using the yellow ink, magenta ink, cyan ink and black ink obtained in
Examples 1A, 2A, 4A and 6A (ink evaluation), respectively, and the same
ink jet recording equipment as in Example 1A (ink evaluation), a
photograph of full color was reproduced. In the recorded image, each color
was very clear and color reproduction was good.
EXAMPLE 9A (INK EVALUATION)
Each of the inks of different color prepared in Examples 1A to 6A (ink
evaluation) was charged into a felt pen. With the cap removed, each felt
pen was left standing for 10 days. Then, recording was made on a paper
using these felt pens. There was no ink skipping and the recording was
smooth.
COMPARATIVE EXAMPLE A (INK EVALUATION)
Using the dyes of Table 1A before purification with a flocculant and in the
same manners as in Examples 1A to 6A (ink evaluation), 6 different inks for
comparison were prepared.
These inks were subjected to the same T1 to T5 evaluation tests as in
Example 1A (ink evaluation). Each ink formed precipitation of insolubles
in one month. In the test (T2), missing of ink discharge was often
observed, at which time the driving voltage had to be raised. Upon
observation of the surface of the heat-generating head using a microscope,
adherence of brown deposits was observed.
In the test (T3), clogging occured at the orifices after standing for 1
month and discharging of ink was unstable.
EXAMPLES 1B TO 6B (DYE PURIFICATION)
The commercially available dyes listed in Table 1B which appears later were
purified according to an ordinary method such as salting-out, fractional
precipitation, ultrafiltration, reverse osmosis, ion exchange or the like.
Then, these purified dyes were respectively made into a 2% aqueous
solution. To each 500 ml of these solutions were added 10 ml of an aqueous
solution containing 10 ppm of a flocculant shown in Table 1B, and they were
stirred for 2 hrs. Thereafter, the mixture was subjected to centrifugation
to separate flocculants. The content (based on powery dye) of inorganic
substances in the purified dye was measured for iron as a representative
inorganic substance. The results are shown in Table 1B.
EXAMPLE 1B (INK EVALUATION)
Using the purified dye shown in Example 1B (dye purification), there was
prepared an ink for ink jet recording having the following composition.
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Dye 2 parts
Diethylene glycol
40 parts
Water 60 parts
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This ink was subjected to the same T1 to T5 evaluation tests as in Example
1A (ink evaluation). The results were excellent similarly to those of
Example 1A (ink evaluation). In the tests T4 and T5, the recording mediums
of Table 2 were used.
EXAMPLES 2B TO 6B (INK EVALUATION)
Using the purified dyes obtained in Examples 2B to 6B (dye purification)
according to the present invention method, inks were prepared in the same
manner as in Example 1B (ink evaluation). Each ink was subjected to the
same T1 to T5 evaluation tests as in Example 1B (ink evaluation). All the
inks showed the same excellent results as in Example 1B (ink evaluation).
EXAMPLE 7B (INK EVALUATION)
The yellow ink, magenta ink, cyan ink and black ink obtained in Examples
1B, 2B, 3B and 5B (ink evaluation), respectively, were subjected to the
same T1 to T5 evaluation tests as in Example 1B (ink evaluation), using a
recording equipment having an on-demand type recording head (discharging
orifice diameter 50 .mu., driving voltage for piezoelectric vibrator 60 V,
frequency: 4 KHz) wherein each ink was discharged by the piezoelectric
vibrator. All the inks showed excellent results.
EXAMPLE 8B (INK EVALUATION)
Using the yellow ink, magenta ink, cyan ink and black ink obtained in
Examples 1B, 2B, 4B and 6B (ink evaluation), respectively, and the same
ink jet recording equipment as in Example 1B (ink evaluation), a
photograph of full color was reproduced. In the recorded image, each color
was very clear and color reproduction was good.
EXAMPLE 9B (INK EVALUATION)
Each of the inks of different color prepared in Examples 1B to 6B (ink
evaluation) was charged into a felt pen. With the cap removed, each felt
pen was left standing for 10 days. Then, recording was made on a paper
using these felt pens. There was no ink skipping and the recording was
smooth.
COMPARATIVE EXAMPLE B (INK EVALUATION)
Using the dyes of Table 1B before purification with a flocculant and in the
same manners as in Examples 1B to 6B (ink evaluation), 6 different inks for
comparison were prepared.
These inks were subjected to the same T1 to T5 evaluation tests as in
Example 1B (ink evaluation). When stored, each ink showed precipitation of
insolubles in one month. In the test (T2), missing of ink discharge was
often observed, at which time the driving voltage had to be raised. Upon
observation of the surface of the heating head using a microscope,
adherence of brown deposits was seen.
In the test (T3), clogging occured at the orifice after standing for 1
month and discharging of ink was unstable.
TABLE 1A
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Example Iron content
No. (dye (ppm based on dye)
purifi- Post- Before
After
cation
Dye Flocculant
treatment
purification
purification
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1A Acid Yellow
Ferric chloride
Pressure
23 filtration
525 71
2A Acid Red
Ferrous sulfate
Centrifugation
362 68
35
3A Direct Blue
Aluminum sulfate
Centrifugation
416 98
86
4A Direct Blue
Sodium aluminate
Centrifugation
318 110
199
5A Food Black
Ferric sulfate
Pressure
292 61
2 filtration
6A Food Black
Aluminum Centrifugation
292 50
2 hydroxide
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TABLE 1B
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Example Iron analytical value
No. (dye (ppm based on dye)
purifi- Before
After
cation)
Dye Flocculant Centrifugation
purification
purification
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1B Acid Yellow
Ferric chloride
(1) 525 66
23
2B Acid Red 35
Ferrous sulfate
(2) 362 68
3B Direct Blue
Aluminum sulfate
(2) 416 98
86
4B Direct Blue
Sodium aluminate
(1) 318 110
199
5B Food Black
Ferric sulfate
(1) 292 55
2
6B Food Black
Aluminum hydroxide
(2) 292 49
2
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(1) Continuous centrifuge (A251, manufactured by Kokusan Enshinki) 16,000
rpm, 30 min, 20.degree. C.
(2) Centrifuge (18RR2, manufactured by Hitachi Koki, Co., Ltd.) 15,000 rpm
45 min, 20.degree. C.
TABLE 2
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Recording medium
(brand name) Classification
Manufacturer
______________________________________
Ginkan High quality Sanyo-kokusaku
paper Pulp Co., Ltd.
Seven Star High quality Hokuetsu Paper
paper Mills Co., Ltd.
Hakubotan Intermediate Honshu Paper Co.,
quality paper
Ltd.
Toyo Roshi No. 4
Non-sized Toyo Roshi K. K.
paper
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