JPH07188595A - Conductive ink for ink jet printing - Google Patents

Abstract

PURPOSE:To obtain an ink for ink jet printing composed of a water-soluble dye, a water-soluble organic solvent, a conductivity-imparting agent and water, having specified physical properties, excellent in conductivity, discharge response, shelf life, quality of printing and weather resistance and free from occurrence of clogging of a discharge orifice. CONSTITUTION:This aqueous ink is composed of preferably 1 to 5wt.% water-soluble dye (e.g. the compound of the formula), preferably 5 to 20wt.% witer-soluble organic solvent (e.g. dimethyl sulfoxide or diethylene glycol), preferably 1 to 7wt.% conductivity imparting agent (preferably ionic salt, e.g. lithium sulfate) and water and has 20 to 60mS/cm electrical conductivity, 1.6 to 2.4cP viscosity, 35 to 50dyn/cm surface tension and 6 to 10pH.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aqueous ink for ink jet. More specifically, when used as an inkjet ink, it has excellent conductivity, and does not cause clogging of the ejection orifice, and ejection response, ejection stability, storage stability, print quality,
The present invention relates to a conductive ink for inkjet having excellent weather resistance.

[0002]

2. Description of the Related Art The non-impact recording method has an advantage that noise during recording is small, and among them, high-speed recording is possible, and the so-called plain paper can be recorded without requiring a special fixing process. The inkjet recording method that can be performed is an extremely powerful recording method, and various methods have been devised and improved so far, and some have been commercialized. Some have.

The ink jet recording method as described above is a recording method in which droplets of a recording liquid, so-called ink, are ejected and adhered to a recording material.
Such a recording liquid is a recording agent (a dye or a pigment is used)
Also, a liquid medium (water or various water-soluble organic solvents or a mixture thereof) which dissolves or disperses it is used as a basic component, and various additives are added as necessary. There are various types of such recording methods depending on the method of generating droplets of the recording liquid and the method of controlling the flight direction of the droplets.

For example, a so-called drop-on-demand method (pressure pulse method) in which a recording signal is applied to a recording head section having a piezo-vibrator, and droplets of a recording liquid are generated in accordance with the signal to perform recording, A so-called electric field control method in which ink is ejected by utilizing an electric attraction force, a droplet is continuously generated while being charged, and the charged ink droplet is controlled by a control electrode to record a part of the ink droplet. Charge control method (continuous method) used for recording, so-called bubble jet method that ejects ink using pressure generated by applying high heat to the recording liquid in the recording head chamber and forming and growing bubbles, high voltage application state There is known a so-called spark jet method in which a spark is generated in ink and the ink is ejected by its explosive force.

There are various types of recording devices according to such various systems. Therefore, in order to perform good recording, it depends on the method of generating droplets or the method of controlling the flight direction of droplets. It is necessary that the recording liquid has appropriate physical properties (for example, electric conductivity, viscosity, surface tension, pH, etc.). In particular, the recording liquid used for the electric field control method, the charge control method, the spark jet method, etc. in the above-mentioned ink jet method has an ink conductivity within an appropriate range in order to perform good droplet generation and flight direction control. Have to control.
Originally, the water-soluble dye used in the water-based ink shows a certain degree of conductivity because the dye itself ionizes in an aqueous solution, but in the electric field control method, the charge control method, the spark jet method, etc. Is insufficient,
It is necessary to impart higher conductivity. In particular, in the method of applying a high voltage to ink such as the spark jet method, the recording liquid needs to have high conductivity in order to control the voltage to some extent. In addition, it is necessary to adjust the viscosity in order to generate recording droplets and fly. If the viscosity is too high, droplets may not be ejected at all, and if the viscosity is too low, good droplet formation cannot be achieved.

Furthermore, proper adjustment of the surface tension is necessary for good droplet formation and recording image formation.
If the surface tension is too high, when the droplets are ejected and land on the recording medium, the dots do not spread, the penetration into the recording medium is hindered, the drying property is poor, and a recorded image with a high contrast cannot be obtained. On the other hand, if the surface tension is too low, so-called bleeding occurs, such as dot spreading being too large, so that good quality of the recorded image cannot be obtained. The pH of the recording liquid is also an important issue. This is because when the pH is too high, there is a problem such as corrosion of the nozzle that comes into contact with the recording liquid, and further, safety is not provided when a person touches it by mistake during handling. Further, if the pH is too low, problems such as corrosion of the electrodes in the head and influence on the recording medium occur. As described above, it is not easy to set all of these physical property values in the water-based ink within proper ranges.

In addition, the ink should not have a solid content due to vaporization of the components of the liquid medium or chemical changes of the components of the ink during storage for a long period of time or suspension of recording. Generally, since the discharge orifice of this type of recording apparatus is a fine hole (generally, a diameter of several tens of μm), the solid content may cause clogging, and the droplet may not be discharged at all.

Even if the ejection stop does not occur, the generation of the solid content adversely affects the generation of uniform droplets or the stable flight of the droplets, and the recording property, the ejection stability, and the ejection response property. Alternatively, continuous recordability may decrease. Alternatively, when the constituent components of the recording liquid undergo a chemical change, the physical property value of the ink adjusted to a desired value during preparation may change, and the recording property, ejection stability, and ejection responsiveness may also deteriorate. Therefore, there is a demand for a liquid medium component that is difficult to vaporize, a chemically stable recording agent, or a combination of a liquid medium and a recording agent that does not cause the above-mentioned drawbacks.

By the way, in order to impart conductivity as an ink physical property in the ink jet recording method, it is known to add conductivity imparting agents such as inorganic salts such as lithium chloride, ammonium chloride and sodium chloride to the ink. . Further, JP-A-62-109870 also describes a conductivity-imparting agent such as an organic salt such as an organic quaternary ammonium salt. However, when it is attempted to obtain a high conductivity such as 20 to 60 mS / cm using these known conductivity-imparting agents, the physical properties of other inks are set within appropriate ranges, and recording properties, ejection stability, ejection It is extremely difficult to make adjustments so that the responsiveness and the quality of the recorded image are all kept good.
This is because, for example, the following methods can be considered in order to obtain high conductivity, but each has a serious problem.
One is to add a large amount of the conductivity-imparting agent, but in this case, addition of salts causes an increase in viscosity, and a desired viscosity value cannot be obtained, and solid precipitation occurs as described above. It is easy to cause clogging and has a problem in discharge stability. The second method is to suppress the amount of water-soluble organic solvent contained in the recording liquid to some extent instead of suppressing the addition of salts, but in that case, the surface tension inevitably shows a high value, usually exceeding 55 dyn / cm. It is impractical. For example, Japanese Patent Application Laid-Open No. 59-129274 proposes an ink having high conductivity, but has a surface tension of 60 to 70 dyn /
cm, and when the surface tension is set to about 60 dyn / cm, the viscosity becomes 2.5 cp or more, so that it is difficult to satisfy all the truly desired physical properties. Further, as a method of reducing the viscosity to 2.5 cp or less, adjustment of the amount of the water-soluble organic solvent contained in the ink and the amount thereof is disclosed in JP-A-62-116676. Also has a high surface tension of 60 dyn / cm or more.
As described above, the conductivity, viscosity, surface tension, and pH of the conductive ink are all set to appropriate values, and ejection responsiveness, ejection stability, storage stability, and printing can be performed without causing clogging of the ejection orifice. To date, no conductive ink for inkjet having excellent quality and weather resistance has been obtained.

[0010]

DISCLOSURE OF THE INVENTION The present invention has excellent electroconductivity for ink jet recording, and by setting various physical properties within appropriate ranges, the ejection orifice is not clogged, and ejection response and ejection are prevented. An object of the present invention is to provide a conductive ink for inkjet which is excellent in stability, storage stability, printing quality and weatherability.

[0011]

DISCLOSURE OF THE INVENTION The inventors of the present invention have a high conductivity, and are excellent in discharge response, discharge stability, storage stability, print quality, and weather resistance without causing clogging of a discharge orifice. As a result of earnest research efforts to obtain a conductive ink for inkjet, it has been found that an ink having the following various physical properties exhibits desired recording performance. That is, the present invention is a water-based ink comprising at least a water-soluble dye, a water-soluble organic solvent, a conductivity-imparting agent and water, (1) electric conductivity is 20 to 60 mS / cm, and (2) viscosity is 1. .6 to 2.4 cp, (3) surface tension is 35 to 50 dyn / cm, and (4) p
The gist is a conductive ink for inkjet having H of 6 to 10.

In the prior art, adjusting these physical property values to a specific range and its effect were not known, but surprisingly, the water-based ink adjusted to the above-mentioned various physical property values was used for ink jet recording. It has been found that this is an excellent conductive ink for inkjet which can solve the above problems.

For example, as a conventionally known ink composition for ink jet recording, there is a composition using a dye, glycerin, water and the like. As described in JP-A-62-116676, these dyes 3 to 5 are used. %, Glycerin 10 to 20% and the balance water.
Such an ink composition has a viscosity of approximately 1.8 to 2.6 cp,
The surface tension is 60 dyn / cm or more. To these ink compositions, if a conductivity-imparting agent is added to give high conductivity, the viscosity increases, and if a lower alcohol is added to reduce the surface tension, the conductivity decreases. When recording with ink, there were many problems such as impairing ejection stability.

The water-soluble dye to be used in the present invention includes
Various materials generally used for inkjet inks can be used. Among them, azo dyes and phthalocyanine dyes are preferable, although not particularly limited thereto. Typical examples of the structures of these dyes include azo dyes represented by the following [A], [B] and [C] in the form of free acid.

[0015]

[Chemical 1] Further, for example, a phthalocyanine dye represented by the following [D] in the form of a free acid can also be preferably used.

[0016]

[Chemical 2]

Any other water-soluble dye can be used as long as it is water-soluble, and it can be selected from acid dyes, basic dyes, direct dyes, reactive dyes, disperse dyes, food dyes and the like. it can. For example, C.I. I. Acid Black 2, 16, 17, 28, 41, 94, 119; C.I.
I. Acid Yellow 4, 11, 12, 13, 14,
17, 18, 23, 25, 29, 34, 40, 41, 5
3,55,61,76,111,122; C.I. I. Acid Red 4,8,15,19,21,30,32,
34, 37, 40, 42, 54, 82, 106, 10
8,110,119,133,172,176,18
7; C.I. I. Acid Blue 7,23,25,41,
43, 45, 49, 51, 53, 55, 56, 62, 7
8, 80, 81, 90, 102, 111, 124, 14
5,167; C.I. I. Basic Black 2,8;
C. I. Basic Yellow 2, 12, 32; C.I.
I. Basic Red 1, 9, 13; C.I. I. Basic Blue 3, 5, 24, 28; C.I. I. Direct Black 2,9,11,14,19,22,27,3
6,38,41,48,49,56,75,77,7
8, 80, 106, 154; C.I. I. Direct Yellow 1,2,4,8,12,26,33,34,41,
42, 48, 50, 51, 72, 87; C.I. I. Direct Red 4,8,11,15,23,31,46,
59, 62, 73, 75, 77, 81, 84, 85, 9
0, 101, 108, 110, 145, 189, 22
5; C.I. I. Direct Blue 1,2,8,22,3
4,69,70,71,72,75,76,78,8
1, 82, 83, 90, 98, 110, 120, 16
5,195,218,239,258; C.I. I. Hood Black 1; C.I. I. Food Yellow 2,4,5;
C. I. Hood Red 2,3,7,14,52,8
7,94,105; C.I. I. Food Blue 1, 2 and the like can be mentioned. The concentration of these water-soluble dyes in the recording liquid is usually 0.5 to 10% by weight, preferably 1 to 5% by weight, based on the total composition. Further, these water-soluble dyes may be used not only in one kind but also in a mixture of two or more kinds.

Further, the water-soluble organic solvent contained in the ink of the present invention ensures the solubility of the dye, the conductivity-imparting agent, etc., prevents solid deposition, and also prevents clogging of the discharge orifice, thus causing clogging. Even if it is, it is used so that it can be easily reproduced. Further, in forming a recorded image, it is used in order to improve the penetrability and dryness of the recording liquid into the recording medium, maintain proper spread of dots, and obtain good quality and sharpness of the recorded image.

Specific examples of these water-soluble organic solvents include dimethyl sulfoxide, dimethylformamide, ketones such as acetone and methyl ethyl ketone, ethylene glycol, diethylene glycol, propylene glycol, polyethylene glycol, thiodiglycol, glycerin, 1, 2, Polyols such as 6-hexanetriol, glycol ethers such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether and ethylene glycol monobutyl ether, alkanolamines such as triethanolamine and ethyldiethanolamine, methanol, ethanol, 1-propanol, 2- Alcohols such as propanol, N-hydroxyethylmorpholine, N-methyl-2-pyrrolidone, etc. That. These water-soluble organic solvents are
It is not particularly limited as long as it is suitable for adjusting within the range of the physical property values of the present invention, and there is no problem in using not only one kind but also a mixture of two or more kinds. The concentration of the water-soluble organic solvent in the recording liquid is usually 1 to 4 with respect to the total composition in order to adjust it within the range of physical properties of the present invention.
The range is 0% by weight, preferably 3 to 30% by weight, more preferably 5 to 20%. If it exceeds 40% by weight, it is difficult to obtain high conductivity, and if it is less than 1% by weight, clogging of the ejection orifice is likely to occur, and the penetrability and dryness of the recorded image deteriorate.

The conductivity-imparting agent used in the present invention is an ionizable salt, and either an inorganic salt or an organic salt may be used. Alkali metal and alkaline earth metal halides, nitrates, thiocyanates and There are organic ammonium salts and the like. These conductivity-imparting agents are not particularly limited as long as they are adjusted within the range of the physical properties of the present invention, and there is no problem in using not only one kind but also a mixture of two or more kinds. The concentration of these conductivity-imparting agents in the recording liquid is usually 0.2 to 15% by weight, preferably 0.5 to the total composition, in order to adjust the ink within the range of physical properties of the present invention. The range is preferably 10 to 10% by weight, more preferably 1 to 7%. If it exceeds 15% by weight, precipitates are easily generated in the ink, and if it is less than 0.2% by weight, it is difficult to obtain sufficient conductivity. Examples of additives such as wetting agents include urea and thiourea. In addition to the above, additives such as a surfactant, a pH adjuster, an antiseptic, an antifungal agent, an evaporation accelerator, and a chelating agent may be added, if necessary. The conductive ink for inkjet of the present invention has high conductivity, and by adjusting the above-mentioned various physical properties to the appropriate ranges, the discharge orifice is not clogged, and discharge responsiveness, discharge stability, print quality, and penetrability. , The drying property is improved.

[0021]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1 An ink having the following composition was prepared using the sodium type of the water-soluble azo dye [A] in which H of the sulfonic acid group in the above structural formula [A] was replaced with sodium. Table 1 shows the results of the physical property measurement and the printing test performed on this.

[0023]

[Table 1] Ink composition Water-soluble azo dye [A] Sodium type 3.0% by weight Glycerin 5.0% by weight Diethylene glycol 5.0% by weight Lithium sulfate 5.0% by weight Urea 1.0% by weight 2-propanol 3. 0% by weight Demineralized water 78.0 % by weight 100.0% by weight

Example 2 An ink having the following composition was prepared using the sodium type of the water-soluble azo dye [A] in which H of the sulfonic acid group in the above structural formula [A] was replaced with sodium. Table 1 shows the results of the physical property measurement and the printing test performed on this.

[0025]

Table 2 Ink composition Water-soluble azo dye [A] Sodium type 3.0% by weight Glycerin 5.0% by weight N-methyl-2-pyrrolidone 3.0% by weight Lithium nitrate 3.5% by weight 2-propanol 3. 0 wt% Demineralized water 82.5 wt% 100.0 wt%

Example 3 An ink having the following composition was prepared by using the sodium type of the water-soluble azo dye [A] in which H of the sulfonic acid group in the above structural formula [A] was replaced with sodium. Table 1 shows the results of the physical property measurement and the printing test performed on this.

[0027]

[Table 3] Ink composition Water-soluble azo dye [A] Sodium type 3.0% by weight Glycerin 5.0% by weight N-methyl-2-pyrrolidone 3.0% by weight Lithium sulfate 5.0% by weight 2-propanol 3. 0 wt% demineralized water 81.0 wt% 100.0 wt%

Example 4 An ink having the following composition was prepared by using the sodium type of the water-soluble azo dye [A] in which H of the sulfonic acid group in the above structural formula [A] was substituted with sodium. Table 1 shows the results of the physical property measurement and the printing test performed on this.

[0029]

Table 4 Ink composition Water-soluble azo dye [A] Sodium type 3.0% by weight Glycerin 8.0% by weight Urea 1.0% by weight Lithium sulfate 5.0% by weight 2-Propanol 3.0% by weight Demineralized water 80 0.0 wt% 100.0 wt%

Example 5 An ink having the following composition was prepared using the sodium type of the water-soluble azo dye [A] in which H of the sulfonic acid group in the above structural formula [A] was replaced with sodium. Table 1 shows the results of the physical property measurement and the printing test performed on this.

[0031]

[Table 5] Ink composition Water-soluble azo dye [A] Sodium type 3.0% by weight Diethylene glycol 5.0% by weight N-methyl-2-pyrrolidone 3.0% by weight Lithium chloride 2.0% by weight 2-propanol 3. 0 wt% demineralized water 84.0 wt% 100.0 wt%

Example 6 An ink having the following composition was prepared by using the sodium type of the water-soluble azo dye [B] in which H of the sulfonic acid group in the above structural formula [B] was replaced with sodium. Table 1 shows the results of the physical property measurement and the printing test performed on this.

[0033]

[Table 6] Ink composition Water-soluble azo dye [B] Sodium type 2.0 wt% Glycerin 5.0 wt% Ethylene glycol 3.0 wt% Lithium nitrate 3.5 wt% Urea 1.0 wt% 2-Propanol 3 0.0 wt% demineralized water 82.5 wt% 100.0 wt%

Example 7 An ink having the following composition was prepared using the sodium type of the water-soluble azo dye [A] in which H of the sulfonic acid group in the above structural formula [A] was replaced with sodium. Table 1 shows the results of the physical property measurement and the printing test performed on this.

[0035]

[Table 7] Ink composition Water-soluble azo dye [A] Sodium type 3.0% by weight Glycerin 5.0% by weight N-methyl-2-pyrrolidone 3.0% by weight Ammonium chloride 2.0% by weight 2-propanol 3. 0 wt% demineralized water 84.0 wt% 100.0 wt%

Comparative Example 1 An ink having the following composition was prepared using the sodium type of the water-soluble azo dye [A] in which H of the sulfonic acid group in the above structural formula [A] was replaced with sodium. Table 1 shows the results of the physical property measurement and the printing test performed on this.

[0037]

[Table 8] Ink composition Water-soluble azo dye [A] Sodium type 3.0% by weight Glycerin 5.0% by weight Diethylene glycol 3.0% by weight Lithium sulfate 7.0% by weight Urea 4.0% by weight 2-propanol 3. 0 wt% Demineralized water 75.0 wt% 100.0 wt%

Comparative Example 2 An ink having the following composition was prepared by using the sodium type of the water-soluble azo dye [A] in which H of the sulfonic acid group in the above structural formula [A] was substituted with sodium. Table 1 shows the results of the physical property measurement and the printing test performed on this.

[0039]

[Table 9] Ink composition Water-soluble azo dye [A] Sodium type 3.0% by weight Diethylene glycol 5.5% by weight N-methyl-2-pyrrolidone 3.0% by weight Lithium nitrate 3.5% by weight 2-propanol 1. 5% by weight Demineralized water 83.5 % by weight 100.0% by weight

Comparative Example 3 An ink having the following composition was prepared using the sodium type of the water-soluble azo dye [A] in which H of the sulfonic acid group in the above structural formula [A] was substituted with sodium. Table 1 shows the results of the physical property measurement and the printing test performed on this.

[0041]

Table 10 Ink composition Water-soluble azo dye [A] Sodium type 3.0 wt% Diethylene glycol 5.0 wt% N-methyl-2-pyrrolidone 3.0 wt% Lithium sulfate 7.0 wt% 2-propanol 3. 0 wt% demineralized water 79.0 wt% 100.0 wt%

Comparative Example 4 An ink having the following composition was prepared using the sodium type of the water-soluble azo dye [A] in which H of the sulfonic acid group in the above structural formula [A] was replaced with sodium. Table 1 shows the results of the physical property measurement and the printing test performed on this.

[0043]

Table 11 Ink composition Water-soluble azo dye [A] Sodium type 3.0 wt% Glycerin 2.0 wt% Diethylene glycol 6.0 wt% Lithium sulfate 5.0 wt% Urea 1.0 wt% 2-Propanol 1. 0% by weight Demineralized water 82.0 % by weight 100.0% by weight

Printing test Clogging test Inkjet printer HG using the prepared ink
-300 (trade name, Epson's product) was continuously printed with 300 characters, and the recorded image sample was visually evaluated. ◯: Printing can be performed without clogging of the discharge orifice until the end of the printing test. Δ: Clogging occurs during the printing test, but it is easily restored by the cleaning operation. X: Clogging occurred during the printing test, and the printing operation did not recover. Dryability Test A recorded image printed with the prepared ink was printed and then rubbed by hand, and the time at which the disorder of the recorded image does not occur was measured and judged. ◯: Dry immediately after printing (less than 10 seconds after printing). B: Drying time after printing takes 10 seconds or more and less than 20 seconds. X: It takes 20 seconds or more and less than 30 seconds to dry after printing. Judgment of print quality A recorded image sample (character print) was visually judged. ◯: Print quality is good. Δ: Some blurring, feathering, and twisting are observed. X: Blushing, feathering, and twisting are very noticeable.

[0045]

[Table 12]

Further, the same effect can be obtained by using other azo dyes and phthalocyanine dyes as the dyes in the above embodiment.

[0047]

EFFECTS OF THE INVENTION According to the present invention, by having high conductivity and by setting various physical properties within a specific range, the ejection orifice is not clogged, and ejection response, ejection stability, print quality, and penetrability. Thus, a conductive ink for inkjet having excellent drying property can be obtained.

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[Procedure amendment]

[Submission date] February 13, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0044

[Correction method] Change

[Correction content]

Printing Test Clogging Test Using the prepared ink, 300 characters of character printing were continuously printed with an ink jet printer, and a recorded image sample was visually judged. ◯: Printing can be performed without clogging of the discharge orifice until the end of the printing test. Δ: Clogging occurs during the printing test, but it is easily restored by the cleaning operation. X: Clogging occurred during the printing test, and the printing operation did not recover. Dryability Test A recorded image printed with the prepared ink was printed and then rubbed by hand, and the time at which the disorder of the recorded image does not occur was measured and judged. ◯: Dry immediately after printing (less than 10 seconds after printing). B: Drying time after printing takes 10 seconds or more and less than 20 seconds. X: It takes 20 seconds or more and less than 30 seconds to dry after printing. Judgment of print quality A recorded image sample (character print) was visually judged. ◯: Print quality is good. Δ: Some blurring, feathering, and twisting are observed. X: Blushing, feathering, and twisting are very noticeable.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeru Tonohira 1-1 Kurosaki Shiroishi, Hachimansai-ku, Kitakyushu City Mitsubishi Kasei Co., Ltd. Kurosaki Plant

Claims (3)

[Claims] 1. A water-based ink comprising at least a water-soluble dye, a water-soluble organic solvent, a conductivity-imparting agent, and water,
(1) The electric conductivity is 20 to 60 mS / cm,
(2) The viscosity is 1.6 to 2.4 cp, (3) the surface tension is 35 to 50 dyn / cm, and (4) the pH is 6 to 10, which is a conductive ink for inkjet. . 2. The water-soluble dye is an azo dye.
The conductive ink for inkjet according to the above. 3. The conductive ink for inkjet according to claim 1, wherein the water-soluble dye is a phthalocyanine dye.