JPH0925441A - Recording ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a recording ink good in long term stability, not generating clogs at the tip of an ink jet printer head and in the passage for the ink, and excellent in ejecting stability and ejecting response by adjusting the content of potassium. SOLUTION: This recording ink is obtained by regulating the content of potassium contained in the ink composition to <5ppm. To adjust the content of potassium, e.g. sodium sulfate is added to an aqueous dye solution for salting the dye out to remove NaCl which is the most representative impurity in the dye, sodium sulfate is removed by dissolving the precipitated dye with a water soluble organic solvent such as alcohols and filtering the solution, and finally ionized potassium is removed by adding water to the filtrate and by treating with a cation exchanging resin. Further, as the dye, usually a water soluble dye can be used. As the solvent used for the ink composition, a mixed solvent consisting of a deionized water with alkyleneglycols or lower alkyl ethers of a polyhydric alcohol is preferable.

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 potassium in an ink composition.

[0002]

2. Description of the Related Art Ink jet recording methods include various ink ejection methods (for example, an electrostatic suction method, a method in which a piezoelectric element is used to mechanically vibrate or displace ink, and air bubbles are generated by heating ink at that time. The ink droplets are formed by a method utilizing the pressure generated in the recording medium), and a part or all of them are attached to a recording material such as paper for recording.

As an ink composition used in such an ink jet recording system, there is known an ink composition obtained by dissolving or dispersing various water-soluble dyes or pigments in water or a liquid medium comprising water and a water-soluble organic solvent. And used. 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 substances are likely to deposit on the surface of the heating element due to temperature changes.

[0004]

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 above conditions, and various impurities are contained in these additives and the dyes used. There are problems such as clogging and precipitation during long-term storage. Further, in the ink jet method using heat energy, there is a problem that deposits are generated on the surface of the heating element. 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-described problems and prevents ink from being clogged at the tip of the head of an ink jet printer or in the ink flow path during use and during long-term storage, and particularly, an ink jet using heat energy. It is an object of the present invention to provide a recording ink having excellent stability in which a precipitate is not generated on a heating element of a printer.

[0006]

In order to achieve this object, the first aspect of the present invention is characterized in that the content of potassium contained in the ink composition is less than 5 ppm.

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

According to a third aspect, the invention is used in an ink ejecting apparatus for ejecting ink 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.

[0010]

According to the present invention having the above-mentioned constitution, by setting the content of potassium contained in the ink composition to less than 5 ppm, the tip of the head of the ink jet printer or the ink flow path can be used even during long-term storage. It is possible to provide a recording ink having excellent stability in which no clogging occurs, and in particular, no precipitate is generated on the heating element of an inkjet printer which uses heat energy.

[0011]

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.

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.

As the water-soluble organic solvent used by mixing with water, for example, methyl alcohol, ethyl alcohol,
n-propyl alcohol, isopropyl alcohol, n
-Butyl alcohol, sec-butyl alcohol, te
Lower alcohols such as r-butyl alcohol, amides such as dimethylformamide and dimethylacetamide, ketones or keto alcohols such as acetone and diacetone alcohol, ethers such as tetrahydrofuran and dioxane, polyglycol such as polyethylene glycol and polypropylene glycol. Alkylene glycols, ethylene glycol, propylene glycol, butylene glycol,
Alkylene glycols such as diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, thiodiglycol and hexylene glycol, ethylene glycol monomethyl ether,
Ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether,
Lower alkyl ethers of polyhydric alcohols such as triethylene glycol monoethyl ether and 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 water content at this time is determined in a wide range depending on the kind of the solvent component, its composition, or the desired properties 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 of the present invention is as described above, but various other conventionally known additives such as dispersants, surfactants, viscosity modifiers, surface tension modifiers, pH modifiers and anti-corrosion agents. 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.

The method for adjusting the potassium content in the ink composition according to 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 a cation exchange resin. The solution subjected to the cation 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 potassium content in the ink is less than 5 ppm by an atomic absorption spectrophotometer and then used.

In the treatment procedure described above, the first salting-out treatment is a treatment 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. Subsequent cation exchange resin treatment is one method for reducing the potassium content in the ink composition, which is the object of the present invention, and is treatment for removing ionized potassium.

The representative method for adjusting the potassium 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 ionized potassium can be used. All can be used effectively.

The source in which potassium is mixed as an impurity is
In addition to the dye, water to be used and additives such as a surfactant and a water-soluble resin are considered. With respect to water, it is possible to avoid mixing of potassium by using distilled water, ion-exchanged water, or the like as water for producing the ink. As for the surfactant, it is possible to avoid mixing of potassium by using a substance other than potassium salt, for example, a nonionic surfactant. Further, regarding water-soluble resins and the like, there are some in which potassium is mixed when manufacturing these resins and the like, but these resins and the like can also be potassium-removed by the same purification procedure as the above dye, and then added. It can be used as an agent. However, the largest source of potassium contamination is dyes,
In particular, when the dye is a commercial product, the potassium content is often large, and in the analysis examples, several thousand p is contained in the dye powder.
Some are known to reach pm.

Although the removal of the potassium component contained in the ink composition has been mainly described above, it is preferable to remove iron, calcium, barium, etc. substantially in addition to the removal of potassium.

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

Example 1 A 10% aqueous solution of a commercially available dye "Sumiacrylic Black G" (manufactured by Sumitomo Chemical Co., Ltd.) 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, and 60 parts of water is added to 40 parts of the filtrate and stirred to obtain a cation exchange resin “C-464”.
(Made by Sumitomo Chemical Co., Ltd.). Then, the pH was adjusted to 8.5 with triethanolamine and filtered through a 0.7 μm membrane filter to obtain an ink composition. When the potassium content in this ink composition was measured by an atomic absorption spectrophotometer, it was 3.0 ppm.

An on-demand type multi-head (ejection orifice diameter 35 μm, heating resistor resistance value 150 ohms) in which thermal energy is applied to ink in a recording head to generate droplets by using this ink composition for recording. 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
Although continuous ejection was performed for 24 hours at each ambient temperature, stable and high-quality recording could be performed under all conditions.

(3) Discharge responsiveness: 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 without passing through the cation exchange resin in Example 1, the potassium content in the ink composition was 8.0 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 element was observed with a microscope, it was found that a brown substance was attached.

Example 2 An ink composition was prepared in the same manner as in Example 1 by using a commercially available dye "Astrazone Yellow 3G" (manufactured by Bayer Co.), and the potassium content in the ink composition was 4.8 ppm. Met. 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 without passing the cation exchange resin in Example 2, the potassium content in the ink composition was 9.2 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 element was observed with a microscope, it was found that a yellow substance was attached.

Example 3 An ink composition was prepared in the same manner as in Example 1 by using a commercially available dye “Paramagenta Base” (manufactured by Orient Chemical Industry Co., Ltd.), and the potassium content in the ink composition was 1. 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 cation exchange resin, the potassium content in the ink composition was 5.4 ppm. When the same examination as in Example 1 was conducted using this ink composition, it was found to be −30 in (1).
The color tone changed after storage at ℃, and the difference was ΔE = 5.5. A printing test was conducted using this ink composition in the same manner as in Example 3. As a result, ΔE of the obtained image was changed by 8.0 as compared with the case of using the ink composition before storage, and the appearance was visually observed. However, the difference was clearly recognized.

Example 4 An ink composition was prepared in the same manner as in Example 1 by using a commercially available dye "Aizen Victoria Blue BH" (manufactured by Hodogaya Chemical Co., Ltd.). It was 2.7 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 4 When an ink composition was prepared without passing through the cation exchange resin in Example 4, the potassium content in the ink composition was 7.2 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 element was observed with a microscope, it was found that a blue substance was attached.

Example 5 An ink composition was prepared in the same manner as in Example 1 by using a commercially available dye "Diacryl Supra Black BSL" (manufactured by Mitsubishi Kasei Kogyo Co., Ltd.). The content of potassium in the ink composition was found to be It was 2.2 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 5 When an ink composition was prepared without passing through the cation exchange resin in Example 5, the potassium content in the ink composition was 6.5 ppm. When the same examination as in Example 1 was carried out using this ink composition, non-ejection of ink was often observed in the intermittent ejection of 1 minute of (2) and (3). When the surface of the heating element was observed with a microscope, it was found that a brown substance was attached.

Example 6 In Examples 2 to 5, the ink of Example 2 was used as the yellow ink, the ink of Example 3 was used as the magenta ink, the ink of Example 4 was used as the cyan ink, and the ink of Example 5 was used as the black 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 6 As in Example 6, the ink of Comparative Example 2 was used as the yellow ink, the ink of Comparative Example 3 was used as the magenta ink, the ink of Comparative Example 4 was used as the cyan ink, and the ink of Comparative Example 5 was used as the black 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 6, which had good long-term stability, ejection stability, and ejection response, the potassium content was less than 5 ppm.

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

As described above, in Examples 1 to 6, since the potassium content in the ink composition was less than 5 ppm, recording inks excellent in long-term stability, ejection stability and ejection response were obtained. Obtainable.

In Examples 1 to 6 and Comparative Examples 1 to 6,
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.

[0046]

According to the recording ink of the present invention having the above constitution, the content of potassium in the ink composition is 5 pp.
Since it is less than m, long-term stability as an ink is good, and an ink ejecting apparatus using this recording ink is
Ink can be satisfactorily ejected without being clogged in the ejection port and the ink flow path through which the ink is ejected.

Claims (4)

[Claims] 1. A recording ink, wherein the content of potassium contained in the ink composition is 5 pp.
A recording ink which is less than m. 2. The recording ink according to claim 1, wherein the recording ink is subjected to a treatment of passing a cation 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.