JPH0931377A - Recording ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a recording ink which has excellent long-term stability and delivery stability and satisfactory response of delivery by regulating the content of formate ions in the ink composition to less than a prescribed value. SOLUTION: The amount of formate ions contained in this ink composition is regulated to less than 6ppm to obtain a highly stable recording ink which neither clogs the tip of the head of an ink-jet printer or the ink passageway during use and long-term storage nor generates a deposit on the heating head of an ink-jet printer employing heat energy. 0.1-20wt.% water-soluble dye is mixed with a solvent which is water or a mixture of water with a water-soluble organic solvent. The content of the organic solvent is 0-95wt.% and that of water is 10-95wt.%. Sodium sulfate is added to an aqueous solution of the dye to conduct salting-out, and the precipitate is taken out by filtration and dried. The solid obtained is dissolved into a water-soluble organic solvent, and the solution is filtered. A prescribed amount of water is added to the filtrate, and the resultant solution is passed through an anion exchange resin. After pH adjustment, the solution is allowed to stand and filtered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet recording ink, and more particularly to the content of formate ion in the ink composition.

[0002]

2. Description of the Related Art Ink jet recording methods use various ink ejection methods (for example, an electrostatic attraction method, a method of mechanically vibrating or displacing ink by using a piezoelectric element, heating ink, and utilizing pressure generated at that time). Method, etc.) to form small ink droplets, and part or all of them are attached to a recording material such as paper for recording. As an ink composition used for such an ink jet recording system, various water-soluble dyes or pigments, which are dissolved or dispersed in water or a liquid medium composed of water and a water-soluble organic solvent, are known and used. Has been done. Such ink compositions are required to have optimal performance characteristics for that purpose. For example, sedimentation or aggregation does not occur even if the ink jet printer is not used for a long period of time, clogging does not occur at the tip of the ink jet printer head and in the ink flow path, and the printing quality is good. Among them, the most required performance is clogging and sedimentation at the tip of the ink jet printer head and in the ink flow path when recording is not performed for a long time when recording is performed using the ink composition. It is liquid-stable that no matter is generated. This problem is particularly important in the inkjet method that uses thermal energy among the inkjet methods, because foreign matter is likely to deposit on the surface of the heating head due to temperature changes.

[0003]

However, in the conventional ink composition, various conditions such as ink ejection conditions, long-term storage stability, image sharpness and density during recording, surface tension, electrical properties, etc. are used. Some additives are required to satisfy the conditions, and various impurities are contained in the dye used, which may cause clogging at the tip of the ink jet printer head or in the ink flow path.
There were problems such as deposits on the surface of the heating head and deposits during long-term storage. This is one of the reasons why its widespread use is not rapid despite the various excellent characteristics of the inkjet recording system.

Therefore, the present invention solves the above problems and does not cause clogging at the tip of the head of an ink jet printer or in the ink flow path during use and during long-term storage, despite the high dye concentration. Another object of the present invention is to provide a recording ink having excellent stability, in which no deposit is generated on the heat-generating head of an inkjet printer which uses heat energy.

[0005]

In order to achieve this object, the first aspect of the present invention is characterized in that the content of formate ion contained in the ink composition is less than 6 ppm.

According to a second aspect of the present invention, the recording ink is subjected to a treatment of passing an anion exchange resin in a manufacturing process thereof.

According to a third aspect of the present invention, it is used in an ink ejecting apparatus for ejecting ink from an ejection port to print on a recording medium.

According to a fourth aspect of the present invention, the ink ejecting apparatus is a thermal ink jet system that ejects ink by using heat energy from a heating element provided in the ink chamber.

[0009]

According to the present invention having the above-mentioned constitution, by controlling the content of formate ion contained in the ink composition to be less than 6 ppm, the ink jet printer can be used at the time of use and long-term storage in spite of the high dye concentration. It is possible to provide a recording ink having excellent stability, which does not cause clogging at the tip of the head or in the ink flow path, and does not cause deposits on the heat-generating head of an inkjet printer that particularly uses thermal energy. .

[0010]

EXAMPLES The basic composition itself of the ink composition in the present invention is already known, and as the dye, a water-soluble dye represented by a direct dye, an acid dye, a basic dye, a reactive dye or the like can be used. Particularly suitable as an ink for an inkjet recording system, and those which satisfy the required performances such as sharpness, water solubility, stability, light resistance, etc. include C.I.
I. Direct Black 17, 19, 32, 51, 7
1, 108, 146; C.I. I. Direct Blue 6, 2
2, 25, 71, 86, 90, 106, 199; C.I.
I. Direct Red 1, 4, 17, 28, 83; C.I.
I. Direct Yellow 12, 24, 26, 86, 9
8, 142; C.I. I. Direct Orange 34, 39,
44, 46, 60; C.I. I. Direct violet 4
7, 48; C.I. I. Direct Brown 109; C.I.
I. Direct Green 59; C.I. I. Acid Black 2, 7, 24, 26, 31, 52, 63, 112, 1
18; C.I. I. Acid Blue 9, 22, 40, 59,
93, 102, 104, 117, 120, 167, 22
9, 234; C.I. I. Acid Red 1, 6, 32, 3
7, 51, 52, 80, 85, 87, 92, 94, 11
5, 180, 256, 315, 317; C.I. I. Acid Yellow 11, 17, 23, 25, 29, 42, 6
1, 71; C.I. I. Acid Orange 7, 19; C.I.
I. Acid Violet 49; C.I. I. Basic black 2; I. Basic Blue 1, 3, 5, 7,
9, 24, 25, 26, 28, 29; C.I. I. Basic Red 1, 2, 9, 12, 13, 14, 37; C.I.
I. Basic Violet 7, 14, 27; C.I. I.
Food Black 1, 2 etc. are mentioned. The above dyes are particularly preferable for the ink composition applicable to the recording method of the present invention, but the present invention is not limited to these dyes.

Such a water-soluble dye is generally used in a conventional ink composition in an amount of about 0.1 to 20% by weight, but in the present invention, it is used within the above range. Needless to say, the stability of the ink composition is exhibited even when the amount used is larger than the conventional amount used, and no precipitate is generated.

The solvent used in the ink composition of the present invention is water or a mixed solvent of water and a water-soluble organic solvent,
Particularly preferred is a mixed solvent of water and a water-soluble organic solvent, which contains a polyhydric alcohol having an ink drying prevention effect as a water-soluble organic solvent. Further, as the water, it is desirable to use deionized water instead of general water containing various ions. 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-
Lower alcohols such as butyl alcohol and ter-butyl alcohol, amides such as dimethylformamide and dimethylacetamide, ketones or keto alcohols such as acetone and diacetone alcohol, ethers such as tetrahydrofuran and dioxane, polyethylene glycol, polypropylene glycol Polyalkylene glycols such as ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, thiodiglycol, hexylene glycol, and other alkylene glycols, ethylene glycol monomethyl ether, ethylene glycol Monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol Lower alkyl ethers of polyhydric alcohols such as rumonoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, glycerin, 2-pyrrolidone, N-methyl-2-pyrrolidone , 1,3-dimethyl-2-imidazolidinone and the like. Among these, alkylene glycols such as glycerin and diethylene glycol, and lower alkyl ethers of polyhydric alcohols such as triethylene glycol monoethyl ether are particularly preferable.

The content of the water-soluble organic solvent in the ink composition is generally 0% by weight based on the total weight of the ink.
The range is from 95 to 95% by weight, preferably from 10 to 80% by weight, more preferably from 20 to 50% by weight.

The content of water at this time is determined in a wide range depending on the kind of the solvent component, its composition, or desired characteristics of the ink, but is generally 10 to the total weight of the ink. The range is 95% by weight, preferably 10 to 70% by weight, more preferably 20 to 70% by weight.

The basic composition of the ink composition according to the present invention is as described above, but various other conventionally known additives such as a dispersant, a surfactant, a viscosity modifier, a surface tension modifier, a pH modifier, and a protective agent. A fungicide or the like can be added if necessary. For example, polyvinyl alcohol, celluloses, viscosity modifiers such as water-soluble resins, cations, anions,
Nonionic surfactants, pH adjusters such as diethanolamine and triethanolamine. When an ink composition used in an inkjet recording method of charging a recording liquid is prepared, a resistivity adjusting agent such as an inorganic salt such as ammonium chloride is added. However, the use of formate salts as these additives leads to an increase in formate ions and must be avoided.

The method for adjusting the formate ion content in the ink composition of the present invention will be specifically described below.

First, sodium sulfate is added to an aqueous dye solution having a desired concentration to salt out the dye. Next, the deposited precipitate is collected by filtration, washed with a saturated aqueous solution of sodium sulfate, and then dried. After dissolving a predetermined amount of the obtained dry solid in a water-soluble organic solvent, the aqueous solution is filtered to obtain a filtrate. In this case, the water-soluble organic solvent may be any solvent as long as it is a poor solvent for sodium sulfate and a good solvent for the dye, and the solvent may be arbitrarily selected in the structure of the dye to be treated. it can. Usually, alcohols, glycols and glycol ethers are preferred water-soluble organic solvents.

Next, a predetermined amount of water is added to the obtained filtrate and the mixture is stirred and then passed through an anion exchange resin. The solution that has been subjected to the anion exchange treatment is subjected to appropriate pH adjustment, and then an additive or the like is added if necessary, and filtered to obtain an ink composition. Then, it is confirmed that the formate ion content in the ink is less than 6 ppm by an ion chromatography measuring device, and the ink is used.

In the treatment procedure described above, the first salting-out treatment is carried out to remove sodium chloride, which is a typical impurity contained in many commercially available dyes. The subsequent treatment with a water-soluble organic solvent is a treatment performed to remove both sodium sulfate originally contained as an impurity in the dye and sodium sulfate added in a large amount in the salting-out treatment. The subsequent anion exchange resin treatment is one method for reducing the formate ion content in the ink composition, which is the object of the present invention, and is a treatment for removing formate ions.

The representative method for adjusting the formate ion content in the ink composition has been described above, but the adjusting method is not limited to this method, and any method capable of removing formate ion can be used. All can be used effectively.

As sources of impurities such as formate ion or formate salt which is a salt thereof, as impurities, dyes, water, additives such as surfactants and water-soluble resins, and impurities of water-soluble organic solvents used. Contamination is possible. For water,
By using distilled water, ion-exchanged water, or the like as the water for producing the ink, it is possible to avoid mixing formate ions. As for the surfactant, if a nonionic formate such as a nonionic surfactant is used, it is possible to avoid the incorporation of formate ions. Further, regarding the water-soluble resin and the like, there are those in which a formate salt is mixed during the production of these resins and the like, but these resins and the like can also be removed by the same purification procedure as the above dye, It can then be used as an additive. Dyes and water-soluble organic solvents are often mixed as impurities, and especially when the dye is a commercial product, the content of formate in the dye is large, and as a result, a large amount of formate ion is contained in the ink.

Although the removal of the formate ion content contained in the ink composition has been mainly described above, the removal of the formate ion is substantially accompanied by the removal of other anions and metals such as sodium, iron, calcium, barium and the like. It is common to remove the.

Next, examples and comparative examples of the present invention will be described.

Example 1 Commercial dye "Daiwa Black MSC" (manufactured by Daiwa Kasei)
5% aqueous solution was prepared, sodium sulfate was added, and the mixture was stirred to salt out the dye. The precipitate was collected by filtration, washed with a saturated aqueous solution of sodium sulfate, and dried. A predetermined amount of the dried solid matter was weighed so that the dye concentration in the obtained ink was 3%, and this was dissolved in a 3: 1 mixed solution of ethylene glycol and N-methyl-2-pyrrolidone.
Next, this aqueous solution is pressure-filtered with a membrane filter having an average pore size of 1 μm, 60 parts of water is added to 40 parts of the filtrate, and the mixture is stirred to give an anion exchange resin “Amberlite IRA-
410 "(manufactured by Organo Corporation). After that, the pH was adjusted to 8.5 with triethanolamine and 0.7 μm
To obtain an ink composition. The formate ion content in this ink composition was measured by an ion chromatography measuring device to be 5.5 pp.
m.

Using this ink composition, heat energy is applied to the ink in the recording head to generate droplets for recording, and an on-demand type multi-head (ejection orifice diameter 35 μm, heating resistor resistance value 150 ohms) is used. The following examinations (1) to (3) were carried out with an inkjet printer having a driving voltage of 30 V and a frequency of 2 kHz), and good results were obtained in all cases.

(1) Long-term stability: No precipitation of insoluble matter was observed even after the ink composition was sealed in a heat-resistant glass bottle and stored at -30 ° C and 60 ° C for 6 months, and the physical properties and color tone of the liquid were almost the same. There was no change.

(2) Discharge stability: 5 ° C, 20 ° C, 40 ° C
In each of the atmospheres, continuous ejection was performed for 24 hours, and stable high-quality recording was always possible under any of the conditions.

(3) Discharge response: intermittent discharge for 1 minute and 2
The ejection after leaving for a month was examined, and in any case, stable and uniform recording was performed without clogging at the tip of the head of the inkjet printer or in the ink flow path.

Comparative Example 1 When an ink composition was prepared in Example 1 without passing through the anion exchange resin, the formate ion content in the ink composition was 8.5 ppm. When the same examination as in Example 1 was carried out using this ink composition, it was often found that ink was not ejected in (2). When the surface of the heating head was observed with a microscope, deposits were found to be attached.

Example 2 An ink composition was prepared in the same manner as in Example 1 by using a commercially available dye "Labacell Fast Yellow R Liquid" (manufactured by Bayer Co.), and it was found that the formate ion content in the ink composition was It was 5 ppm. When the same examination as in Example 1 was carried out using this ink composition, good results were obtained as in Example 1.

Comparative Example 2 When an ink composition was prepared in Example 2 without passing through the anion exchange resin, the formate ion content in the ink composition was 9.5 ppm. When the same examination as in Example 1 was carried out using this ink composition, a small amount of precipitate was observed in (1), and the conductivity of the liquid was reduced. In addition, in (2), ejection failure of ink is often seen,
In (3), after left for 2 months, clogging occurred at the tip of the head of the inkjet printer, and ejection was impossible. When the surface of the heating head was observed with a microscope, deposits were found to be attached.

Example 3 An ink composition was prepared in the same manner as in Example 1 using a commercially available dye "Cyrus Supra Red F3B" (manufactured by Bayer Co.), and the formate ion content in the ink composition was 5. It was 5 ppm. When the same examination as in Example 1 was carried out using this ink composition, good results were obtained as in Example 1.

Comparative Example 3 When an ink composition was prepared in Example 3 without passing through the anion exchange resin, the formate ion content in the ink composition was 8.5 ppm. When the same examination as in Example 1 was carried out using this ink composition, (-3) of (1)
The color tone changes after storage at 0 ° C, and the difference is L * a * when the color is measured twice with a D65 light source specified by CIE.
ΔE = 5.0 in the b * color system. When a printing test was conducted using this ink composition in the same manner as in Example 3, the color tone of solid printing of 5 cm square was changed compared with the case of using the ink composition before storage, and the difference was Δ. E
= 7.5, and the difference was clearly visible.

Example 4 An ink composition was prepared in the same manner as in Example 1 by using a commercially available dye "Labacell Fast Blue HS Liquid" (manufactured by Bayer Co.), and the formate ion content in the ink composition was It was 3.5 ppm. When the same examination as in Example 1 was carried out using this ink composition, Example 1
Similar good results were obtained.

Comparative Example 4 When an ink composition was prepared without passing an anion exchange resin in Example 4, the formate ion content in the ink composition was 9.5 ppm. When the same examination as in Example 1 was conducted using this ink composition, in (3), after left for 2 months, clogging occurred at the tip of the head of the inkjet printer, and ejection was impossible. When the surface of the heating head was observed with a microscope, deposits were found to be attached.

Example 5 In Examples 1 to 4, the ink of Example 1 was used as the black ink, the ink of Example 2 was used as the yellow ink, the ink of Example 3 was used as the magenta ink, and the ink of Example 4 was used as the cyan ink. A full-color photograph was reproduced with the same inkjet recording device as the one used.
The resulting image was extremely clear in each color and had good color reproduction.

Comparative Example 5 The same procedure as in Example 5 was performed using the ink of Comparative Example 1 as the black ink, the ink of Comparative Example 2 as the yellow ink, the ink of Comparative Example 3 as the magenta ink, and the ink of Comparative Example 4 as the cyan ink. When trying to reproduce a full-color photograph, many missing dots were seen and a clear image could not be obtained. The color reproducibility was also poor.

In each of the ink compositions of Examples 1 to 5, which had good long-term stability, ejection stability, and ejection response, the formate ion content was less than 6 ppm.

On the other hand, in each of Comparative Examples 1 to 5, which had problems in long-term stability, ejection stability, and ejection response, the formate ion content in the ink composition was 6 ppm or more.

As described above, in Examples 1 to 5, since the formate ion content in the ink composition was less than 6 ppm, the recording ink excellent in long-term stability, ejection stability and ejection responsiveness was obtained. Can be obtained.

In Examples 1-5 and Comparative Examples 1-5,
An ink jet head having an on-demand type multi-head for recording by applying heat energy to the ink in the recording head to generate droplets has been used, but the Kaiser type disclosed in Japanese Patent Publication No. 53-12138. As a result of conducting the same examination as in the example using the recording ink under the above conditions in the shear mode type ink jet head disclosed in JP-A-2-150355, the same effect was obtained.

[0042]

According to the recording ink of the present invention having the above constitution, the formate ion content in the ink composition is 6 p.
Since it is less than pm, long-term stability as an ink is good, and an ink ejecting apparatus using this recording ink ejects satisfactorily without being clogged in the ejection port and the ink flow path where the ink is ejected. can do.

Claims (4)

[Claims] 1. A recording ink having a formate ion content of 6 p in the ink composition.
A recording ink which is less than pm. 2. The recording ink according to claim 1, wherein the recording ink is subjected to a treatment of passing an anion exchange resin in a manufacturing process thereof. 3. The recording ink according to claim 1, wherein the recording ink is used in an ink ejecting device that ejects ink from an ejection port to print on a recording medium. 4. The recording ink according to claim 3, wherein the ink ejecting device is a thermal ink jet system that ejects the ink by using thermal energy from a heating element provided in the ink chamber.