JPH0726178A - Ink, ink jet recording method using the same, and method for preventing dye association - Google Patents

Abstract

PURPOSE:To obtain a high-quality ink causing no blurs even for plain paper, good in settability, capable of recording free from variations in denseness, by incorporating specified amounts of an alkali metal compound in a composition comprising a sparingly water-soluble dye, water-soluble organic solvent and water. CONSTITUTION:The objective ink can be obtained by incorporating a composition comprising (A) a sparingly water-soluble dye [pref. an azo dye of the formula (A, B and C are each H; D is SO3NH4; M is NH4)], (B) a water-soluble organic solvent (pref. containing a water-soluble, high-boiling organic solvent like diethylene glycol) and (C) water with (D) 0.8-6mol, per mol of the component A, of an alkali metal compound (pref. a sodium compound like NaOH, or lithium compound like Li2CO3). It is preferable that the component A account for 2-5wt.% of the whole ink.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink suitable for an ink jet printer and an ink jet recording method for recording on a recording material by ejecting the ink from the orifice of a recording head by the action of energy, preferably heat energy. More specifically, it is possible to print uncoated paper such as copy paper, report paper, notebooks, notepaper, bond paper, continuous slip paper, and so-called plain paper, which are commonly used in offices and homes, without bleeding and uneven density. Possible inks and inkjet recording methods.

The invention also relates to a method of preventing dye association.

[0003]

2. Description of the Related Art Conventionally, ink jet inks having various compositions have been reported, and a recording liquid mainly composed of a pigment or a water-soluble dye, a water-soluble organic solvent and water is used. The same applies to the recording liquid for the writing instrument.

When this kind of ink is used in an ink jet recording system and recorded on plain paper on which no special ink receiving layer is formed, there are some differences depending on the composition.
There are common problems such as bleeding and uneven density.
Therefore, a method has been proposed in which a high-viscosity solvent such as a water-soluble polymer compound or a water-soluble natural product is added to the ink in order to suppress bleeding. However, by increasing the viscosity, bleeding can be suppressed, but since a considerable amount of high-viscosity solvent is required for that, the viscosity of the ink becomes too high, the ink ejection speed at the nozzle decreases, and the ink ejection amount increases. And the surface tension is lowered, resulting in unstable ejection.

US Pat. No. 4,963,189, US Pat. No. 5,062,893, US Pat. No. 50
In No. 62892, kogation on the heater of an inkjet printer is reduced, or 0.2 wt% (0.02%) of sodium borate is used as an ink pH buffer.
A technique of adding mol / 1, 0.58 mol / dye) is disclosed. Also disclosed is a technique of adding an oxoanion in order to reduce kogation on the heater of an inkjet printer.

[0006]

With the above technique, there is no unevenness in the density of the image, and a satisfactory print density cannot be obtained.

Therefore, an object of the present invention is to prevent the formation of an associated state of a dye, such as a J-aggregate, in a fine nozzle of an ink jet, to reduce the dynamic viscous resistance, and to obtain various recording characteristics. It is an object of the present invention to provide an ink capable of excellent recording and capable of recording without density unevenness, and an ink jet recording method using the ink, which can be applied to various recording papers.

[0008]

[Means and Actions for Solving the Problems]
The following is achieved by the present invention.

That is, the present invention contains at least a non-water-soluble dye, a water-soluble organic solvent, water and an alkali metal compound,
An ink containing an alkali metal compound in an amount of 0.8 to 6.0 mol per mol of a dye, and by applying energy corresponding to a recording signal, preferably heat energy, to the ink. This is an inkjet recording method in which recording is performed by ejecting ink as droplets from fine holes.

Further, it is a method of preventing the association of the dye in the liquid composition by adding 0.8 to 6.0 mol of the alkali metal compound to 1 mol of the dye.

As a result, it is possible to obtain a stable recorded image without lowering the print density.

The present invention will be described in detail below.

The inventors of the present invention have conducted extensive studies on various ink compositions in order to improve ink bleeding, drying properties, and penetrability on plain paper. As a result, when a poorly water-soluble dye was used as a coloring agent, an alkali metal was used. The ink that used the compound together,
The present invention has been found to prevent a decrease in the amount of ink ejected from nozzles, bring good results against bleeding and uneven density, and have high reliability with no adverse effect in preventing clogging. It came to.

That is, according to the research conducted by the present inventor, the dye molecules in the ink are likely to exist in multiple molecules due to the chemical phenomenon of association in order to maintain the energy stable state. In particular, when the ink moves at a high shear rate in a fine nozzle such as an ink jet printer, this phenomenon seems to be remarkable. That is,
The dye molecule in the ink interacts with the π electron cloud of another dye molecule in the vicinity through the π electron cloud spreading on the plane, and a J-aggregate of dye molecules is formed. Therefore, the solubility of the dye molecule in the ink is further lowered, resulting in an increase in the viscosity of the ink. Therefore, when an alkali metal ion is added to the ink, it interferes with the interaction of the π electron cloud spreading on the dye molecule,
Decreases the formation of J-aggregates. As a result, the solubility of the dye is improved and the dynamic viscous resistance of the ink is reduced.

In the present invention, the alkali metal compound means lithium carbonate, sodium carbonate, potassium carbonate, rubidium carbonate, cesium carbonate, lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, lithium chloride. , Sodium chloride, potassium chloride, rubidim chloride, cesium chloride, lithium phosphate,
Examples thereof include, but are not limited to, sodium phosphate and potassium phosphate. Further, the effect of preventing the formation of the J-aggregate of the water-insoluble azo dye by the alkali metal ion depends on the size of the Stokes radius of each ion, and the effect is large in the order of Li>Na>K>Rb> Cs. is there. That is, it is preferable to add lithium ions and sodium ions in order to achieve the object of the present invention.

The amount of the above alkali metal compound added to the ink is preferably 0.8 to 6.0 mol / day. When the addition amount is 0.8 mol / dye or less, the effect of preventing the association of the dye becomes weak, which is an object of the present invention.
It is difficult to obtain a satisfactory print density without density unevenness. Furthermore, the alkali metal ion concentration in the ink is
It is more preferably 1.0 mol / dye or more with respect to the dye concentration. This is because when a fluid (ink) moves at a high shear rate in a fine nozzle such as an inkjet head, a phenomenon called J-association, in which dye molecules are stacked in a card shape, and the viscosity of the ink is reduced. In order to prevent the height from increasing, it is necessary that at least one alkali metal ion be present between all the dye molecules stacked in a card shape. In addition, the upper limit is the sum of the alkali metal ions that act to prevent the association of the dyes described above and the alkali metal ions that can replace the ammonia (or organic ammonia) ionically bonded to the dissociative groups in the dye molecules. But,
Depends on pH of ink (pH of recording liquid is 10
The following is a prerequisite). Although it depends on the kind of the alkali metal compound to be added, the amount of the alkali metal compound added is limited by adjusting the pH after the addition to 10 or less. That is, when the pH of the ink is 10 or more, a phenomenon such as corrosion of the constituent material of the inkjet head occurs.

Examples of the water-soluble organic solvent used by mixing with water include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol and the like. Alkyl alcohols having 1 to 4 carbon atoms; amides such as dimethylformamide and dimethylacetamide; ketones or keto alcohols such as acetone and diacetone alcohol; ethers such as tetrahydrofuran and dioxane; polyalkylenes such as polyethylene glycol and polypropylene glycol Glycols; ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol Alkylene glycols in which the alkylene group such as diethylene glycol contains 2-6 carbon atoms; glycerin; ethylene glycol monomethyl (or ethyl) ether, diethylene glycol methyl (or ethyl) ether, triethylene glycol monomethyl (or ethyl) ether, etc. Lower alkyl ethers of polyhydric alcohols; N-methyl-2-pyrrolidone, 2-pyrrolidone, 1.3-dimethyl-2-imidazolidinone and the like can be mentioned.

The above media can be used alone or as a mixture, but the solvent is at least one water-soluble high-boiling organic solvent such as diethylene glycol, triethylene glycol, glycerin, 1,2,6-hexanetriol. , Polyhydric alcohols such as thiodiglycol,
It contains 2-pyrrolidone and the like.

As the color material constituting the ink of the present invention,
Examples include water-insoluble azo dyes. The term "water-retardant" as used in the present invention means that the solubility in water is 10% or less. As such a dye, an azo dye having almost no hydrophilic group and having a dissociative group such as a carboxyl group, a sulfone group or a hydroxyl group at the terminal is desirable. Preferred structural formulas of such azo dyes are shown in the following (1) and (2).

[0020]

[Outside 3] (Wherein, A represents a hydroxyl group or a hydrogen atom, B represents a hydroxyl group or a hydrogen atom, C is H, SO ₃ M, D is selected from SO ₃ M. However, M represents ammonium or an organic ammonium.)

[0021]

[Outside 4] (Here, R ₁ , R ₂ , and R ₃ are each a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a methoxy group, a halogen group, or COO.
It represents a group selected from the group consisting of M and COOR ₄ . However, R ₄ represents an alkyl group having 1 to ₄ carbon atoms, and M represents ammonium or organic ammonium. ) As a preferred specific example, Direct Black 51, B-
2 (manufactured by Mitsubishi Kasei Co., Ltd.), Pro-jet fast
Black 2 liquid (manufactured by ICI) and the like can be given, but the present invention is not limited to this. Among the above dyes, the most suitable for the present invention are A, B, and
C-H, D-SO ₃ NH ₄ and M-NH ₄ Pro-jet fast Black2 Liqu
id (manufactured by ICI).

The content of these dyes is the kind of liquid medium component,
Although it is determined depending on the properties required for the ink, etc., it is generally in% by weight in the total weight of the ink, preferably 2 to 5
It is the ratio that accounts for%.

The main components of the ink of the present invention are as described above, but various other dispersants, surfactants, viscosity modifiers,
A surface tension adjusting agent, a fluorescent whitening agent and the like can be added according to the purpose of the present invention.

For example, viscosity adjusting agents such as polyvinyl alcohol, celluloses and water-soluble resins; surface tension adjusting agents such as various cationic, anionic or nonionic surfactants, diethanolamine and triethanolamine; pH adjustment with a buffering agent. Agents; antifungal agents and the like can be mentioned.

Further, the ink of the present invention solves the problems of ink bleeding and dryness and permeability of recorded matter when recorded on plain paper, and at the same time, improves the matching with the ink jet recording head. As the physical properties of the ink itself, the surface tension at 25 ° C. is 30 to 68 dyn.
e / cm, viscosity is 15 cP or less, more preferably 5 cP
The following adjustments are desirable.

A recording apparatus suitable for recording using the ink of the present invention is an apparatus for applying thermal energy corresponding to a recording signal to the ink in the chamber of the recording head and generating a droplet by the energy. To be

An example of the head structure, which is the main part, is shown in FIGS. 1, 2 and 3. The head 13 includes glass, ceramics, or a plastic plate having a groove 14 through which ink passes, and a heating head 15 used for heat-sensitive recording (thin film is shown in the drawing, but not limited to this). It is obtained by bonding and. The heating head 15 includes a protective film 16 formed of silicon oxide, an aluminum electrode 1 and the like.
7-1, 17-2, heat generating resistor layer 18 formed of nichrome or the like, heat storage layer 19, substrate 2 of good heat dissipation such as alumina
The ink 21 consisting of 0 reaches the ejection orifice (fine hole) 22 and forms the meniscus 23 by the pressure P.

When an electric signal is applied to the electrodes 17-1 and 17-2, the area indicated by n of the heating head 15 rapidly generates heat, and bubbles are generated in the ink 21 in contact therewith, and the pressure thereof is generated. Then, the meniscus 23 protrudes, the ink 21 is ejected, and becomes a recording droplet 24 from the orifice 22 and flies toward the recording medium 25. FIG. 3 shows an external view of a multi-head in which many heads shown in FIG. 1 are arranged. The multi-head is made by bonding a glass plate 27 having multi-grooves 26 and a heating head 28 similar to that described in FIG.

Incidentally, FIG. 1 shows the head 13 along the ink flow path.
2 is a cross-sectional view of FIG. 2, and FIG. 2 is a cross-sectional view taken along the line AB of FIG.

FIG. 4 shows an example of an ink jet recording apparatus incorporating such a head. In FIG. 4, reference numeral 61 is a blade as a wiping member, and one end of the blade is held by a blade holding member to become a fixed end, which is in the form of a cantilever. The blade 61 is arranged at a position adjacent to the recording area by the recording head, and in the case of this example,
The recording head is held in a protruding form in the moving path of the recording head.
Reference numeral 62 denotes a cap, which is arranged at a home position adjacent to the blade 61, and has a configuration in which it moves in a direction perpendicular to the moving direction of the recording head and comes into contact with the ejection surface to perform capping. Further, 63 is an ink absorber provided adjacent to the blade 61, and like the blade 61, is held in a form protruding in the moving path of the recording head. The blade 61, the cap 62, and the absorber 63 constitute an ejection recovery unit 64, and the blade 61 and the absorber 63 remove water, dust, and dust on the ink ejection port surface. Reference numeral 65 denotes a recording head which has an ejection energy generating means and ejects ink to a recording material facing the ejection port surface where the ejection ports are arranged for recording, and 66 denotes a recording head 65 mounted to move the recording head 65. It is a carriage for performing. The carriage 66 slidably engages with the guide shaft 67, and a part of the carriage 66 is connected (not shown) to a belt 69 driven by a motor 68. As a result, the carriage 66 can move along the guide shaft 67, and the recording head 65 can move the recording area and its adjacent area.

Reference numeral 51 is a paper feed section for inserting a recording material, and 52 is a paper feed roller driven by a motor (not shown). With these configurations, the recording material is fed to the position facing the ejection opening surface of the recording head, and is ejected to the ejection portion provided with the ejection roller 53 as the recording progresses.

In the above structure, when the recording head 65 returns to the home position due to the end of recording or the like, the carriage 62 of the head recovery unit 64 is retracted from the moving path of the recording head 65, but the blade 61 projects into the moving path. ing.
As a result, the ejection port surface of the recording head 65 is wiped. When the cap 62 comes into contact with the ejection surface of the recording head 65 to perform capping, the cap 62 moves so as to project into the moving path of the recording head.

When the recording head 65 moves from the home position to the recording start position, the cap 62 and the blade 61 are at the same positions as the above-mentioned position during wyoing. As a result, even during this movement, the ejection port surface of the recording head 65 is wiped.

The above-mentioned movement of the recording head to the home position is performed not only at the end of recording and at the time of ejection recovery, but also at the home adjacent to the recording area at a predetermined interval while the recording head moves in the recording area for recording. The wiper is moved to the position, and the wiping is performed along with the move.

FIG. 5 shows an ink cartridge 4 containing ink to be supplied to the head through an ink supply tube.
It is a figure which shows an example of 5. Here, 40 is an ink bag containing the supply ink, and a rubber stopper 42 is provided at the tip thereof.
Is provided. By inserting a needle (not shown) into this stopper 42, the ink in the ink bag 40 can be supplied to the head. An ink absorber 44 receives the waste ink.

The ink jet recording apparatus used in the present invention is not limited to the above-described head and ink cartridge which are separate bodies, and those in which they are integrated as shown in FIG. 6 are also preferably used. To be

In FIG. 6, reference numeral 70 denotes an ink jet cartridge in which an ink absorber impregnated with ink is housed, and the ink in the ink absorber is discharged from a head portion 71 having a plurality of orifices. It is configured to be ejected as an ink droplet. Reference numeral 72 is an atmosphere communication port for communicating the inside of the cartridge with the atmosphere.

The ink jet cartridge 70 is
It is used in place of the recording head 65 shown in FIG. 4, and is detachable from the carriage 66.

[0039]

EXAMPLES Next, the present invention will be described more specifically with reference to Examples and Comparative Examples. In the text, "part" and "%" are based on weight unless otherwise specified.

Examples 1 to 5 After mixing the following components and stirring for 5 hours, the pore size was 0.
Inks A to E of the present invention were obtained by pressure filtration with a 22 μm membrane filter (trade name: Fluoro Filter, manufactured by Sumitomo Electric Industries, Ltd.).

Next, an ink jet printer BJ-10v (trade name: Canon Inc.) using the obtained inks A to E as a heat generating element as an ink discharge energy source.
Manufactured) ink cartridge (BC-01),
Recording on commercially available copy paper and bond paper using the above printer, the amount of ink ejected from the nozzles, the print density of the obtained recorded matter, the occurrence rate of bleeding, and the eye when reprinting after pausing printing The clogging and frequency response were evaluated. The results are shown in Table 1.

Ink A Pro-jet fast black 2 liqu
id (manufactured by ICI) 2 parts Ethylene glycol 15 parts Lithium phosphate 0.5 parts Water 82.5 parts Ink B Pro-jet fast black 2 liqu
id (manufactured by ICI) 2 parts Ethylene glycol 15 parts Sodium phosphate 0.5 parts Water 82.5 parts Ink C Pro-jet fast black 2 liqu
id (manufactured by ICI) 2 parts Ethylene glycol 15 parts Potassium phosphate 0.5 parts Water 82.5 parts Ink D Pro-jet fast black 2 liqu
id (manufactured by ICI) 2 parts Ethylene glycol 15 parts Rubidium phosphate 0.5 parts Water 82.5 parts Ink E Pro-jet fast black 2 liqu
id (manufactured by ICI) 2 parts Ethylene glycol 15 parts Cesium phosphate 0.5 parts Water 82.5 parts

Comparative Example 1 Ink F of Comparative Example 1 was prepared in the same manner as in Examples 1 to 5 except that the alkali metal compound was not used. The results are shown in Table 1.

Examples 6 and 7 After mixing the following ingredients and stirring for 5 hours, the pore size was 0.
Inks G and H of the present invention were obtained by pressure filtration with a 22 μm membrane filter (trade name: Fluoro Filter, manufactured by Sumitomo Electric Industries, Ltd.). Then, the same experiment as in Examples 1 to 5 was performed, and the results are shown in Table 2.

Ink G Pro-jet fast black 2 liqu
id (manufactured by ICI) 2.2 parts Ethylene glycol 5 parts Glycerin 5 parts Urea 5 parts Lithium phosphate 0.6 parts Water 82.2 parts Ink G lithium ion concentration = 0.16 mol / l,
The dye concentration is 0.035 mol / l, and lithium ions are contained in an amount of 4.6 mol / dye.

Ink H Pro-jet fast black 2 liqu
id (manufactured by ICI) 2.2 parts Ethylene glycol 5 parts Glycerin 5 parts Urea 5 parts Sodium phosphate 0.6 parts Water 82.2 parts Ink H sodium ion concentration = 0.11 mol /
1, dye concentration = 0.035 mol / l, and sodium ion was contained in 3.1 mol / dye.

Comparative Example 2 Ink I of Comparative Example 2 was prepared in the same manner as in Examples 6 and 7. The results are shown in Table 2.

Ink I Pro-jet fast black 2 liqu
id (manufactured by ICI) 2.2 parts Ethylene glycol 5 parts Glycerin 5 parts Urea 5 parts Sodium phosphate 0.1 parts Water 82.7 parts Ink H sodium ion concentration = 0.018 mol /
1, dye concentration = 0.035 mol / l, and sodium ion was contained at 0.51 mol / dye.

(Evaluation) * 1 Ink ejection amount Using the above ink jet recording apparatus, Canon: N
Several prints were made on P-DRY copy paper, and the amount of ink ejected from one nozzle was estimated from the weight change of the ink cartridge (BC-01).

* 2 Evaluation of printing density Using the above ink jet recording apparatus, Canon: N
Printing was performed on P-DRY copy paper, and the print density of the print was measured with a Macbeth densitometer (TR918).

* 3 Bleeding occurrence rate Regarding the bleeding occurrence rate, 300 dots were printed discontinuously on a commercially available copy paper and bond paper with a printer, left for 1 hour or more, and then bleeding occurred with a microscope. The number of dots was counted, and the ratio to the total number of dots was displayed in%, and evaluated as follows.

(Printing under environmental conditions of 25 ° C. and 60% RH) ◯ ・ ・ ・ 10% or less △ …… 11 to 30% × …… 31% or more

* 4 Clogging property Clogging property refers to the clogging property at the time of reprinting after a temporary stop of printing. The printer was filled with a predetermined ink, and alphanumeric characters were printed continuously for 10 hours. After that, the printing was stopped, and after leaving it for 10 minutes without a cap or the like, when the alphanumeric characters were printed again, it was evaluated by the presence or absence of defective parts such as scratches or chips of the characters.

(Printed under the environmental conditions of 25 ° C. and 60% RH) ◯ ・ ・ ・ No defective part from the first character △ …… Part of the first character is scratched or chipped × …… No printing is possible from the first character

* 5 Frequency Responsiveness The printed matter thus obtained was visually observed and evaluated for the printing state, that is, the state of scratches or white spots and the state of defective landing points such as splashes and twists.

⊚: The state of ink following the frequency was good, and neither smearing, white spots, nor defective landing points were found in both solid printing and character printing.

∘: The state of following the frequency is almost good, and there is no blur, white spots, or landing defect in character printing, but slight blur in solid printing.

Δ: No fading or white spots are seen in character printing, but some defective landing points are seen. or,
In solid printing, blurring and white spots are seen in about 1/3 of the whole solid printing.

X: A lot of blurring and white spots are seen in solid printing, and a lot of blurring and defective landing points are also seen in character printing.

[0060]

[Table 1]

[0061]

[Table 2]

[0062]

As described above, when the ink according to the present invention is used, it can be applied to plain paper such as copy paper, report paper, notebook, notepaper, bond paper, and continuous slip paper which are generally used in offices and the like. Also, it is possible to perform recording with no blurring, excellent quality, and good fixability.

Further, according to the present invention, it is possible to obtain an ink having high safety even when used in an office or a home.

Furthermore, according to the ink of the present invention, various problems can be solved without deteriorating other characteristics such as ink ejection stability, solidification at the head tip, and quality deterioration of printed matter. Have.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a head portion of an inkjet recording apparatus.

FIG. 2 is a cross-sectional view of a head portion of an inkjet recording device.

FIG. 3 is an external perspective view of a head portion of the inkjet recording apparatus.

FIG. 4 is a perspective view showing an example of an inkjet recording apparatus.

FIG. 5 is a vertical sectional view of an ink cartridge.

FIG. 6 is a perspective view of a recording unit.

Claims (10)

[Claims] 1. An ink containing at least a hardly water-soluble dye, a water-soluble organic solvent and water, wherein the ink contains an alkali metal compound in an amount of 0.8 to 6.0 mol per mol of the dye. 2. The ink according to claim 1, wherein the alkali metal compound is contained in an amount of 1.0 to 6.0 mol with respect to 1 mol of the dye. 3. The alkali metal compound is lithium,
The ink according to claim 1, which is selected from carbonates, hydroxides, chlorides of sodium, potassium, rubidium and cesium, and phosphates of lithium, sodium and potassium. 4. The ink according to claim 1, wherein the poorly water-soluble dye is an azo dye having a molecule having a planar structure and having a π-conjugated system on the molecular plane. 5. The water-repellent dye comprises 2.
The ink according to claim 1, wherein the ink is contained in an amount of 0 to 5.0 wt%. 6. The ink according to claim 1, wherein the pH is adjusted in the range of 7 to 10. 7. The water-repellent dye has the following structural formula (1):
The ink according to claim 1, which is selected from (2). [Outer 1] (Here, A and B represent a hydroxyl group or a hydrogen atom, C represents a hydrogen atom, SO ₃ M and D represent SO ₃ M. However, M represents ammonium or organic ammonium.) [External 2] (Here, R ₁ , R ₂ and R ₃ are each a hydrogen atom and a carbon number 1 respectively.
~ 4 alkyl group, methoxy group, halogen, COOM,
COOR ₄ is shown. However, R ₄ is an alkyl group having 1 to ₄ carbon atoms, and M is ammonium or organic ammonium. ) 8. An ink jet recording method for recording by applying energy to ink to eject the ink as droplets from fine holes, wherein the ink according to any one of claims 1 to 7 is used. Inkjet recording method. 9. A method for preventing association of dyes in a liquid composition containing a poorly water-soluble dye, wherein the alkali metal compound is contained in an amount of 0.8 to 6.0 mol per mol of the dye. And a method for preventing association of dyes. 10. The method for preventing association of dyes according to claim 9, wherein the pH of the liquid composition is adjusted to 7 to 10.