JP2002256180A - Ink for ink jet recording and recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink jet recording liquid that always exhibits good jetting stability under a low humidity environment and can easily be restored to a normal state of jetting under such an extraordinary condition that the recording liquid is left to stand in a nozzle cap-off condition and an ink jet recording method, provide an evaluating method for simply selecting a recording liquid excellent in anti-clogging properties and ejection restoration in case of emergency, and provide a recording method capable of performing a stable recording without clogging in an ink jet recording method using a static head which is expected to enable provision of a recorded image having a higher density as the most promising device for the coming generation. SOLUTION: An aqueous ink for ink jet comprises as the essential components water, a water-soluble organic solvent and a pigment, wherein a surface shear viscosity is not more than 3 g/s after evaporating a volatile component contained in the ink while left to stand at an ordinary temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aqueous ink jet ink comprising water, a water-soluble organic solvent and a pigment as essential components, and an ink jet recording method for performing recording by flying the ink jet aqueous ink as fine droplets. About.

[0002]

2. Description of the Related Art Inkjet printers are most important in that they are smaller and less expensive than recording devices for electrophotography, etc., are excellent in personalization, and have been recognized as the most familiar recording device in recent years. It is spreading rapidly. There are two types of printing methods for inkjet printers: a continuous method that deflects constantly ejected ink droplets to determine the presence or absence of a recording device, and an on-demand method that ejects ink only when recording is desired. It has become.

[0003] Typical types of ink jet heads include a thermal head (bubble head), a piezoelectric head, and an electrostatic head. In the thermal head, an individual heater is provided for each bit for ejecting ink. The individual heater instantly boiles the ink and ejects the ink by the pressure of bubbles. The piezoelectric head type literally uses a piezoelectric body. The piezoelectric body can be displaced in the thickness direction of the piezoelectric body as it is or by giving it to the ink pressure chamber through a diaphragm to eject ink, and the piezoelectric body can be displaced in the in-plane direction. (Surface bending)
There is a method in which the diaphragm is curved to make use of the ink jetting method. The electrostatic head performs ink ejection by bending the diaphragm surface using electrostatic attraction. The thermal head type and the piezoelectric head type have already been mass-produced and put into practical use. However, a heater element and a piezoelectric element must be individually incorporated in each bit, and the processing limit is further increased by an on-demand method. Hindered above. On the other hand, the electrostatic head method is expected as a next-generation device capable of achieving the highest density by using a fine processing technology of a semiconductor or a micromachine.

As an ink used in such an ink jet recording method, an aqueous ink using water as a main solvent has been actively developed. Water-based inks for ink-jet printing should be capable of stable ejection without clogging at the head of the recording device or in the ink flow path, and to provide a sufficiently high-density recorded image with a clear color tone. Performance is required.

It is common to use a water-soluble dye as a colorant for an aqueous ink for ink jet. Since the water-soluble dye is completely dissolved in the ink medium, if the impurities in the water-soluble dye are controlled to a certain amount or less, the dye ink is less likely to be clogged at the tip of the ink jet printer head or in the ink flow path, It is possible to obtain a high-density recorded matter with a clear color tone. For this reason, there are many examples of commercialization of aqueous inks for inkjet using a highly purified water-soluble dye as a colorant for inkjet printers. However, water-soluble dyes originally have poor light fastness,
Even with these techniques, further improvement in image fastness is desired. An aqueous pigment ink using a pigment such as carbon black has been proposed in order to impart light resistance and water resistance to such recorded images.

Here, an ink jet recording apparatus using an aqueous ink is generally provided with a mechanism for covering a jetting orifice of a head with a nozzle cap in a closed state when not jetting. This is to prevent nozzle clogging and ejection bending due to drying and thickening of the ink component at the nozzle tip of the inkjet head, and it functions sufficiently effectively under normal use conditions.

On the other hand, in the case of pigment inks, the problem of nozzle clogging and ejection bending due to drying and thickening of ink components as described above becomes more important. For example, if the ink jet head is left for a long time without the nozzle cap attached, thickening of the ink, generation of precipitates,
Nozzle clogging due to drying or the like occurs, and it is almost impossible to recover to a normal injection state. Also, even under such abnormal use conditions, in normal printing,
There are few cases where ink is ejected from all nozzles of the head, and even when ink is ejected based on an image signal from a nozzle that has not been ejected for a relatively long time, nozzle clogging, ejection bending, or ejection speed is caused. Degradation may occur. In particular, this is a serious problem in printing in a low humidity environment.

In particular, recently, in order to further increase the density of an image, the nozzle diameter and the ink dot size are becoming finer. In addition, as mentioned above, in the electrostatic head, which is expected in the future, the ink ejection force may not be so large compared to other methods, and the above-mentioned problem of ejection stability due to nozzle drying will be more and more. It's getting bigger. To solve such a problem, Japanese Patent Laid-Open Publication No. 2000-9
No. 5983 discloses that in a water-based inkjet ink comprising water, a water-soluble organic solvent and a water-soluble dye as essential components, the residue after evaporation of volatile components in the ink is a liquid, and the viscosity of the residue is based on the viscosity. Water-based ink for inkjet, characterized in that the viscosity is 10 times or less of the ink viscosity of (1). However, in the case of pigment ink, according to the experiments performed by the present inventors, the increase in ink viscosity was 10%.
In some cases, the ejection state may not recover even if the ink viscosity is less than 2 times, or there is ink that does not cause any problem even if the increase in ink viscosity is 10 times or more, and the rate of increase in viscosity does not always correspond to nozzle clogging. was there. In addition, the technique disclosed in Japanese Patent Application Laid-Open No. 2000-95983 has hardly improved the disturbance of the ejection of the first droplet due to drying of an unused nozzle in a relatively short time during printing. When conducting an experiment based on the technique described in Japanese Patent Application Laid-Open No. 2000-95983, observing an ink obtained by evaporating a volatile component from an ink in a bulk state, an ink in which the entire bulk becomes viscous and a film is formed on the surface. As a result, it was presumed that the viscosity of the ink inside the ink did not increase so much, and that this difference might be related to nozzle clogging.

On the other hand, Japanese Patent Application Laid-Open No. 11-158423 has developed a special device capable of measuring the viscosity in a minute area, and when the end face of an aqueous pigment ink placed in a capillary having an inner diameter of 700 μm is opened indoors, 20 from the end
An ink is disclosed in which the viscosity at a depth of 0 μm is 100 cp or less. This method is considered to be more realistic in that the viscosity is measured by defining the depth from the ink surface. Further, according to the invention described in JP-A-11-158423, based on the finding that, in a capillary having an inner diameter of 1000 μm or less, the pigment dispersion liquid shows a specific behavior such as dispersion and aggregation different from the bulk state. As described above, a measurement method in a capillary having an inner diameter of 700 μm has been newly developed. However, considering that the nozzle diameter of the printer head is several tens of microns, it is difficult to say that the behavior of the capillary having an inner diameter of 700 μm necessarily reflects the behavior of an actual inkjet printer head. In consideration of this point, the measurement using the special device as described above is complicated, and a simpler evaluation method is desired. Furthermore, the drying of unused nozzles in a relatively short time during printing may cause
No mention is made of turbulence in eye drop ejection.

[0010]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and always shows good jetting stability even in a low humidity environment and is left without a nozzle cap. It is an object of the present invention to provide an ink jet recording liquid and an ink jet recording method capable of easily recovering to a normal ejection state even under abnormal conditions such as the case where the ink jet recording liquid is used. Another object of the present invention is to provide an evaluation method for easily selecting a recording liquid excellent in clogging property and ejection recovery property in an emergency. Still another object of the present invention is to provide a recording method capable of performing stable recording without clogging in an inkjet recording method using an electrostatic head which is expected as a next-generation device capable of achieving the highest density. Is to provide.

[0011]

SUMMARY OF THE INVENTION The object of the present invention is to provide (1) an aqueous inkjet ink comprising water, a water-soluble organic solvent and a pigment as essential components, wherein volatile components in the ink remain at room temperature in a standing state. A water-based inkjet ink characterized in that the surface shear viscosity after evaporation is 3 g / s or less ", (2)" the pigment is dispersed to have an average particle diameter of 200 nm or less by a dispersion stabilizer. The aqueous ink for inkjet according to the above item (1) ".

Another object of the present invention is to provide an ink-jet recording method according to the present invention, which is directed to (3) an ink-jet recording method in which an ink-jet aqueous ink comprising water, a water-soluble organic solvent and a colorant as essential components is jetted as fine droplets for recording. And (4) "water, a water-soluble organic solvent, and a colorant as essential components," wherein the water-based ink for inkjet described in the above (1) or (2) is used. In the inkjet recording method for performing recording by flying the aqueous inkjet ink as fine droplets, the head for flying the ink is an electrostatic head, and the head according to the above item (1) or (2) is used. Ink jet recording method characterized by using aqueous ink jet ink ".

[0013]

Embodiments of the present invention will be described below. In an ink jet recording apparatus using a general water-based ink, the viscosity at which normal ejection is possible is about 1 to 10 cPs, but a long time of several days or more when the nozzle at the tip of the ink jet head is filled with ink. If the ink is left without being sealed with a cap or the like, the ink on the nozzle electrode surface will increase in viscosity significantly with the evaporation of volatile components, and in the worst case, a precipitate may be formed or may be dried. It is almost impossible to forcibly discharge the ink in such a thickened, precipitated and dried state by a conventionally known purge device and to return to normal jetting. Also,
Even under such abnormal use conditions, in normal printing, there are few cases where ink is ejected from all nozzles of the head, and there are nozzles that hardly eject ink depending on the image. In such a nozzle, the meniscus is constantly blown by the scanning of the head, and the ink dries quickly. When ink ejection based on an image signal is performed from such a nozzle where ink ejection has not been performed for a relatively long time, nozzle clogging, ejection bending, or ejection speed reduction may occur, and as a result, an image may be disturbed. . In particular, in recent years, the nozzle diameter and the ink dot size have been miniaturized in order to achieve higher image density. In addition, as mentioned above, in the electrostatic head, which is expected in the future, the ink ejection force may not be so large compared to other methods, and the above-mentioned problem of ejection stability due to nozzle drying will be more and more. It's getting bigger.

The present inventors have examined the drying process of the aqueous ink for inkjet on the nozzle surface of the inkjet head. As a result, regardless of the degree of drying of the ink in bulk, the ink easily forms a film on the outermost surface of the ink. It has been found that there are inks that are not so, and that the degree greatly contributes to the jetting stability of the ink, leading to the present invention. That is, when the volatile components such as moisture are dried from the ink meniscus at the nozzle surface at the tip of the inkjet head, the surface of the ink is significantly thickened to form a film, and when the next ejection signal is given, While the ejection speed may be significantly reduced or ejection may not be performed, ink that does not form a film on the surface even if drying proceeds to some extent can be ejected normally when the next ejection signal is given. I found it.

The state of the film formation after drying the ink on the nozzle surface at the tip of the ink jet head is described in Shin-Jikken Kagaku Koza Vol. 18 (interface and colloid), page 460 (Showa 54).
−6-20, published by Maruzen). In addition, the measurement can be performed using a commercially available device such as a surface viscoelasticity meter SVR-A (manufactured by Kyowa Interface Science Co., Ltd.) or an interface rheometer CIR-100 (manufactured by Eiko Seiki Co., Ltd.).

In the present invention, it is a new discovery that when the ink is allowed to stand at room temperature and dried, the viscosity of the surface is remarkably increased, and some inks do not.
That is, as shown in FIGS. 1 and 2, in the ink drying process (thick line), the bulk ink viscosity gradually increases in the initial stage, as shown by the solid line,
It rises sharply as it approaches equilibrium drying. In contrast, the surface viscosity rises relatively slowly and continuously as shown in FIG. 1 and the ink rapidly rises in the first half of drying and becomes almost constant after drying as shown in FIG. Things exist. The reason for this is not clear, but as drying progresses,
The pigment in the ink or a substance having a hydrophobic portion contained as a pigment dispersant migrates to the interface with air, that is, to the surface, and the concentration on the ink surface increases. It is believed that this degree depends on the dispersion stability of the pigment in the ink with reduced water content or the dissolution stability of the pigment dispersant. Further, it is considered that whether the viscosity is remarkably increased when the concentration on the surface of the ink is increased to form a film or the viscosity is kept low is due to the properties of the dispersion stabilizer. That is, it is considered that there is a difference in the coatability of the ink surface based on the mutual properties of the water-soluble organic solvent and the dispersion stabilizer in the ink.

The ink of the present invention comprises water, a water-soluble organic solvent and a pigment as essential components. As the water in the ink of the present invention, it is desirable to use deionized water (pure water). At this time, the content of water is desirably 40% by weight or more based on the total weight of the ink in order to keep the viscosity of the ink at normal time low enough to allow normal ejection.

As the water-soluble organic solvent in the present invention, a solvent which is mainly used for the purpose of preventing the ink from drying at the tip of the ink jet head and therefore has low volatility and good miscibility with water is selected. It is desirable to do. Examples of such water-soluble organic solvents include polyalkylene glycols such as polyethylene glycol; ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, 1,2,6-hexanetriol. Alkylene glycols such as thiodiglycol, 1,3-butanediol, 1,5-pentanediol, and hexylene glycol; glycerin; and pyrrolidones such as 2-pyrrolidone and N-methyl-2-pyrrolidone. These water-soluble organic solvents may be used alone or in combination of two or more.

The content of the water-soluble organic solvent in the ink is 5 to 40% by weight, preferably 7 to 40% by weight, more preferably 10 to 30% by weight based on the total weight of the ink. If the amount is less than 5% by weight, the wetting action becomes insufficient, and problems such as drying occur. In addition, 40% by weight
If it exceeds, the ink thickens more than necessary, and it becomes impossible to eject the ink, and the drying on the recording paper becomes extremely slow.

As the pigment used as a coloring material in the present invention, carbon black is preferably used as a black pigment.
In addition, a color pigment can be used as the pigment of the present invention. Examples of color pigments include, for example, C.I. I. Pigment Ye
llow 1, C.I. I. Pigment Yellow
2, C.I. I. Pigment Yellow 3,
C. I. Pigment Yellow 13, C.I. I.
Pigment Yellow 16, C.I. I. Pig
Ment Yellow 83, pigments used as magenta inks include C.I. I. Pigment R
ed 5, C.I. I. Pigment Red 7, C.I.
I. Pigment Red 12, C.I. I. Pigm
entRed 48 (Ca), C.I. I. Pigment
Red 48 (Mn), C.I. I. Pigment R
ed 57 (Ca), C.I. I. Pigment Red
112, C.I. I. Pigment Red 122 and pigments used as cyan inks include C.I. I. P
Pigment Blue 1, C.I. I. Pigment
Blue 2, C.I. I. Pigment Blue
3, C.I. I. Pigment Blue 15: 3
C. I. Pigment Blue 16, C.I. I. P
Pigment Blue 22, C.I. I. Vat Bl
ue 4, C.I. I. Vat Blue 6 and the like.

These pigments are preferably added to the ink as a pigment dispersion obtained by dispersing in an aqueous medium with a dispersant or a surfactant. Preferred dispersants include those commonly used to prepare pigment dispersions,
For example, a polymer dispersant can be used. Examples of dispersants include polyacrylic acid, polymethacrylic acid, acrylic acid-acrylonitrile copolymer, vinyl acetate-acrylic ester copolymer, acrylic acid-alkyl acrylate copolymer, styrene-acrylic acid copolymer. Copolymer, styrene-methacrylic acid copolymer, styrene-acrylic acid-alkyl acrylate copolymer, styrene-methacrylic acid-alkyl acrylate copolymer, styrene-α-methylstyrene-acrylic acid copolymer, styrene -Α-methylstyrene-acrylic acid-acrylic acid alkyl ester copolymer, styrene-maleic acid copolymer, vinylnaphthalene-maleic acid copolymer,
Examples include vinyl acetate-ethylene copolymer, vinyl acetate-fatty acid vinyl ethylene copolymer, vinyl acetate-maleic acid ester copolymer, vinyl acetate-crotonic acid copolymer, and vinyl acetate-acrylic acid copolymer.

As the surfactant, nonionic surfactants are preferably used. Examples thereof include polyoxyethylene alkyl phenyl ethers, polyoxyethylene alkyl ethers, polyoxyethylene alkyl esters, and polyoxyethylene. It can be arbitrarily selected from alkyl sorbitan esters, polyoxyethylene alkylamines, glycerin fatty acid esters, sorbitan fatty acid esters, propylene glycol fatty acid esters, polyoxyethylene glycol fatty acid esters, and the like.

The pigment in the aqueous pigment ink composition of the present invention has a particle size of 50 to 200 nm, particularly 75 to 150 nm.
It is preferable to use the compound finely dispersed in nm. When the particle size of the pigment is 50 nm or less, the recorded matter becomes transparent, and a sufficient optical density cannot be obtained. On the other hand, if it exceeds 200 nm, sedimentation of the pigment particles tends to occur.

Fine dispersion of the pigment is carried out by adding a dispersion stabilizer as if the pigment was slightly aired, and wet-pulverizing the aqueous medium for 3 to 10 hours using a mill medium and a pulverizer. As a mill medium, glass beads, zirconia beads, magnetic beads and the like are used. Examples of the pulverizing device include a ball mill, an attritor, a jet jet mixer, an impeller mill, a colloidal mill, and a sand mill (for example, a bead mill, a sand glider, a super mill, an agitator mill, a Dyno mill (trade name)) and the like.

In the present invention, in order to control the ink surface viscosity after evaporation of the volatile components to a low level, first, the dispersion stabilizer should be of a relatively low molecular weight having a low film-forming ability. It is effective to reduce as much as possible. Second, it is effective to select a component having a relatively low viscosity as a low-volatility, room-temperature liquid component such as the water-soluble organic solvent. It is also effective to select a type according to characteristics such as solubility of the two.

The basic constitution of the ink used in the present invention is as described above. In addition, various conventionally known various penetrants, resin binders, viscosity modifiers, surface tension regulators, pH regulators, antiseptic / antifungal agents, etc. Can be added as needed.

As the penetrant, it is desirable to use polyhydric alcohols having a vapor pressure at 20 ° C. of 0.1 mmHg or less. The polyhydric alcohols improve the quick drying property of the ink on the paper by effectively increasing the ink penetration rate into the recording paper, and the bleeding (the boundary between different colors) caused by the slow drying property on the recording paper. Those which prevent bleeding and are less likely to cause feathering (whisker-like bleeding along paper fibers) due to penetration are preferably used.

Specific examples of the above polyhydric alcohols include:
For example, diethylene glycol monomethyl ether (2
Vapor pressure at 0 ° C. 0.1 mmHg, diethylene glycol monobutyl ether (vapor pressure at 20 ° C. 0.01 mm)
Hg), diethylene glycol monoisobutyl ether (vapor pressure at 20 ° C. 0.01 mmHg), dipropylene glycol monomethyl ether (vapor pressure at 20 ° C.
06 mmHg), dipropylene glycol monopropyl ether (vapor pressure at 20 ° C. 0.02 mmHg), dipropylene glycol monoisopropyl ether (20 ° C.
Vapor pressure at 20 ° C., dipropylene glycol monobutyl ether (vapor pressure at 20 ° C. 0.05 mmHg)
Hg), triethylene glycol monomethyl ether (vapor pressure at 20 ° C. less than 0.01 mmHg), triethylene glycol monobutyl ether (vapor pressure at 20 ° C. less than 0.01 mmHg), tripropylene glycol monomethyl ether (vapor at 20 ° C.) Pressure 0.02mmH
g), tripropylene glycol monobutyl ether (vapor pressure at 20 ° C. of less than 0.01 mmHg) and the like.

The content of the penetrant in the ink is preferably 1 to 5% by weight based on the total weight of the ink. if,
If the amount is less than 10% by weight, the ink penetrates into the recording paper at a low speed, causing problems in drying time and bleeding. Also,
If it exceeds 5% by weight, the ink will penetrate into the recording paper intensely, causing the ink to reach the back of the recording paper and causing problems in feathering.

[0030]

Embodiments of the present invention will be described below. In the examples, "%" in the table is based on weight. Table 1 shows the evaluated inkjet pigment inks.
It was shown to. The composition shows the value estimated by Tg-DTA analysis.

[0031]

[Table 1] Table 2 shows the results of measuring the viscosity of these inks before and after drying.

<Equilibrium loss on drying> About 180 g of an ink was placed in a petri dish having a radius of 70 mm, allowed to stand in an environment of 25 ° C. and 30%, and the weight was recorded every day. Daily loss on drying is 0.1
% Or less was defined as equilibrium drying. <Viscosity before and after drying> Measured with an E-type viscometer. After drying, the ink in the equilibrium dry state was well stirred and measured. <Surface viscosity before and after drying> It was measured using an automatic surface viscoelasticity meter SVR-A type (manufactured by Kyowa Interface Science Co., Ltd.). After drying, the ink in the equilibrium dried state was measured as it was without stirring.

[0033]

[Table 2]

Evaluation of Dry Clogging Inkjet Printer IPS Using Piezo Type Head
The evaluation ink was put into iOJET300 (manufactured by Ricoh Company), and after confirming the ink ejection, it was left at room temperature for 30 days without capping the nozzle surface. Then 10
After purging with 000 drops, an image was printed. For those that could not be printed, a cleaning operation was performed, and an image was further printed. At this point, a mark was printed when the printing was successful, and a mark was printed when the ink was not ejected and printing was not possible.

Evaluation of Jet Stability After confirming ink ejection in the same manner as described above, head scanning similar to printing for 5 minutes was performed without inputting an ejection signal. Thereafter, an image was printed immediately. A: the ink was printed from the first drop, ○: the ink was discharged several drops later, and x: the ink was not printed.

Evaluation of Injection Stability Using an Electrostatic Head Using an electrostatic head described in Japanese Patent Application Laid-Open No. 11-348284, ink ejection was confirmed, and the apparatus was allowed to stand for 5 minutes. Thereafter, an image was printed immediately. A: the ink was printed from the first drop, ○: the ink was discharged several drops later, and x: the ink was not printed.

[0037]

[Table 3]

[0038]

As is apparent from the detailed and concrete description, in the present invention of claim 1, since the ink surface viscosity after drying is controlled to be low, the ejection stability of the ink is ensured. (Ink ABCDGI)
According to the second aspect of the present invention, by using a pigment dispersant, the ejection stability can be reliably improved even in an ink in which the particle diameter of the pigment is easily reduced to 200 nm or less.
According to the present invention, the ink jet recording method using the inks according to the first and second aspects enables printing without image disturbance, and the fourth aspect of the present invention provides an electrostatic head which can be expected to have a high density. In the printing experiment used, printing without image disturbance was made possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing how a surface viscosity increases in the present invention.

FIG. 2 is another diagram showing how the surface viscosity increases in the present invention.

Continued on front page F-term (reference) 2C056 FA02 FC01 FC02 2H086 BA52 BA53 BA55 BA59 BA60 4J039 AD01 AD02 AD03 AD08 AD09 AD10 AD11 AD14 AE07 BA04 BC07 BC09 BC12 BC20 BC50 BE01 BE22 CA06 DA02 DA08 EA15 EA16 EA17 EA24 EA44 EA44

Claims (4)

[Claims] 1. An aqueous ink jet ink comprising water, a water-soluble organic solvent and a pigment as essential components, wherein the surface shear viscosity after evaporation of volatile components in the ink at room temperature is 3 g / s or less. A water-based ink for ink-jet printing, characterized in that: 2. The aqueous ink according to claim 1, wherein the pigment is dispersed by a dispersion stabilizer to an average particle diameter of 200 nm or less. 3. The ink jet recording method according to claim 1, wherein the ink jet aqueous ink comprising water, a water-soluble organic solvent, and a colorant as essential components is jetted as fine droplets for recording. An ink jet recording method using an aqueous ink. 4. An ink jet recording method in which an ink jet aqueous ink comprising water, a water-soluble organic solvent and a colorant as essential components is jetted as fine droplets for recording, wherein the head for jetting the ink is an electrostatic head. An inkjet recording method using the aqueous ink for inkjet according to claim 1 or 2.