JPS621663B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an inkjet recording ink composition,
In particular, the present invention relates to an inkjet recording ink composition that has been improved to prevent nozzle clogging and to enable high-speed recording.

An inkjet recording method in which ink droplets are ejected from a nozzle by rapidly reducing the volume of a pressure chamber of a printer head is known and is described, for example, in Japanese Patent Laid-Open No. 47-2006. Several ink compositions for use in such recording methods have been proposed (for example, Japanese Patent Publication No. 8361/1983, Japanese Patent Publication No. 18396/1986, etc.). These ink compositions aim to achieve satisfactory recording by providing characteristics such as no nozzle clogging, clear recorded fonts, and excellent storage stability of recorded fonts. There is. The present invention also shares this goal.

The prior art states that the content of polyhydric alcohol in an ink composition should not exceed a maximum of 80 weight percent. This is explained as follows: If there is too much polyhydric alcohol, the viscosity will exceed the proper viscosity range of the ink, resulting in inability to print, slowdown, and abnormalities (Japanese Patent Publication No. 18396/1983). And, such an ink composition has a temperature of the surroundings and the ink composition itself.
When the temperature is 20-25℃, it will certainly prevent nozzle clogging and give stable jetting.

However, with the inkjet recording method,
Temperature control is typically performed to maintain the ink composition at a temperature of about 35°C. This is to prevent the viscosity from increasing or decreasing when the temperature of the ink composition changes due to a change in ambient temperature, causing ejection failure. In that case, the temperature near the nozzle increases locally, and the saturated vapor pressure of water increases there.
Relative temperature decreases. For example, 20 heated in winter
Assuming that the humidity in a room at 25°C is approximately 20% RH, and the humidity in an air-conditioned room at 25°C in summer is 70% RH, approximately
Assuming that the temperature is adjusted to 35℃, the humidity near the print head nozzles is approximately 8.3%RH and approximately
Decreases to 39%RH. In conventional ink compositions,
When the humidity decreases to such a large extent, the viscosity of the ink composition in the nozzle increases rapidly due to water evaporation, making it impossible to eject the ink composition. In a multi-nozzle print head, depending on the printing conditions, there are nozzles that eject frequently and nozzles that eject frequently, and thickening of the ink composition can at least cause clogging in those nozzles that eject frequently. Make it easier.

On the other hand, in the prior art, the viscosity of the ink composition is, for example, 100 centipoise or less in the aforementioned Japanese Patent Publication No. 50-8361, and 4 centipoise or less in the aforementioned Japanese Patent Publication No. 56-18396.
~20 centipoise is considered appropriate. However, according to experiments conducted by the inventors, if the pressure exceeds 10 centistokes, it is necessary to apply an excessive pressure pulse during injection, which increases the vibration time, which is inappropriate. In a drop-on-demand print head, vibrations remain due to the shaking of the ink after it is ejected. When the next ink droplet is ejected while the vibration remains, the size and flying speed of the droplet change compared to the previous droplet, and the vibration resonates and becomes larger, causing air to be sucked into the pressure chamber from the nozzle. Therefore, the next particle cannot be ejected until the vibration has damped down to a certain level. Second
The figure shows the relationship between ink viscosity and vibration decay time. In order to increase printing speed, it is better to have a shorter decay time. From FIG. 2, it can be seen that there is a viscosity range suitable for high-speed printing. vibration time
It can be said that the viscosity needs to be 3 to 10 cSt in order to reduce the number of injections to 0.5 msec or less (injection number of 2000 pieces/sec or more). Furthermore, if the ink exceeds 10 cSt, there is also the problem that the recorded ink bleeds significantly onto the paper and the quality of the recorded font deteriorates.

The present invention aims to overcome the above disadvantages and deficiencies in the prior art. In particular, it is an object of the present invention to reduce or eliminate jetting failures of printers in temperature-controlled inkjet recording methods.

In the present invention, the temperature of the printer head is 30℃ during operation of the device.
An ink composition for a drop-on-demand inkjet printer whose temperature is adjusted as described above, the ink composition containing a polyhydric alcohol having 2 to 6 carbon atoms, water, and a dye; is more than 80 weight percent of said ink composition,
The above object is achieved by providing an ink composition having a viscosity of 3 centistokes or more and 10 centistokes or less at a temperature of 30° C. or higher at which the temperature of the printer head is adjusted. It is something to do.

The ink composition for inkjet recording contains a polyhydric alcohol having 2 to 6 carbon atoms, water, and a dye. The dye used in the present invention is a water-soluble dye that dissolves in a medium of polyhydric alcohol having 2 to 6 carbon atoms and water, and is selected from known or conventional dyes. For example, as a blue dye, CIDirect
Blue86, CIAcid Blue182, CIAcid Blue112,
CIAcid Blue90, CIReactive49, as red dye, CIDirect Red89, CIDirect Red225,
CIAcid Red37, CIAcid Red265, CI
Reactive Red29, as a black dye, CIDiret
Black19, CIDirect Black38, CIAcid
Black2, CIDirect Yellow86 as yellow dye,
CIDirect Yellow87, CIDirect Yellow50, C.
I.Acid Yellow17, CIReactive Yellow81 can be used. These can be used alone or in combination. The selection should be made taking into consideration the clarity and preservation of the recorded font. In the constitution of the present invention, the content of the dye is usually about 1 to 5% by weight.

Polyhydric alcohols having 2 to 6 carbon atoms are used because of their hygroscopic properties, low vapor pressure properties, and thickening properties. It's important. Attached Figure 1 shows a typical relationship between glycol equilibrium water content and relative humidity. Under normal office conditions, the RH near the nozzle will be less than approximately 40%,
According to Figure 1, the equilibrium water content of glycol does not exceed 20% by weight below 40%RH. Therefore, in order to prevent the viscosity of the ink in the nozzle from increasing even if the ejection signal is not applied for a while while the printer is operating, the glycol concentration must be at least 80% by weight. That is understood.

Examples of polyhydric alcohols having 2 to 6 carbon atoms that can be used in the ink composition of the present invention include ethylene glycol, glycerin, diethylene glycol, propylene glycol, triethylene glycol, hexylene glycol, and triethanolamine.

One of the characteristics of the ink composition of the present invention is that the kinematic viscosity at the usage temperature is 3 centistokes or more and 10 centistokes or less. In order to achieve this, the ink composition of the present invention uses a polyhydric alcohol having 2 to 6 carbon atoms. This ensures more stable injection. In addition,
The operating temperature (temperature control temperature) is 30°C or higher. This is because temperature control by heating is easier. Generally the temperature is 30 to 40°C, preferably 35°C.

In addition to the polyhydric alcohol, water and dye, various additives can also be added to the ink composition of the present invention. For example, preservatives, antifungal agents, surfactants, etc.

The ink composition of the present invention is produced by a method commonly used for producing ink jet recording ink compositions, such as stirring and mixing the respective components, and preferably performing filtration thereafter. However, since the ink composition of the present invention has high hygroscopicity, it is preferable to stir and mix in a closed container and store it in a closed container.

The ink composition of the present invention makes it possible to significantly reduce evaporation at high temperatures and low humidity compared to conventional ink compositions, thereby significantly reducing clogging in printers using temperature-controlled inkjet recording methods. Prevented. In particular, clogging is largely prevented even in nozzles that eject ink infrequently when the printer is used. Note that clogging can be easily prevented by capping the nozzles when the printer is not in use. Furthermore, the ink composition according to the present invention enables printing of clear fonts at high speed.

The present invention will be described below with reference to specific examples.

In the following examples, various prototype inks were all tested under the following conditions. The printer head used was a drop-on-demand head using a cylindrical piezo vibrator.

A. Clogging test The ambient conditions of the printer were set to a temperature of 20°C and humidity of 20% RH using a constant temperature and humidity chamber, and the temperature of the printer head was adjusted to 35±3°C using a tape heater. Then, ink droplets of 60 ± 3 μmφ are ejected at a speed of 3.0 ± 0.1 m/sec, paper is placed in front of the nozzle, and 10 single pulses are applied for several seconds until a dot appears on the paper. It was confirmed whether the nozzle was clogged by checking whether the nozzle was clogged. The injection pause time was then varied to determine the time until injection became impossible.

B. Printing test Under the same ambient conditions, controlled temperature, and jetting conditions (droplet diameter and speed) as in the clogging test, a high-quality coded paper without supercalender treatment was placed at a distance of 2 mm from the nozzle, and the recording density was 8 dots/mm. A printing test was performed by looking at what was recorded.

Example 1 Prior art ink compositions were tested for comparison. An ink composition described in Example 1 of Japanese Patent Publication No. 56-18396 was prepared and tested. Its composition and properties are as follows.

Composition: Ethylene glycol 64.0ωt% Distilled water 31.9ωt% Nigrosine 4.0ωt% Dioxine 0.1ωt% Viscosity: 7.0cps (25℃) Surface tension: 47.7dyne/cm (25℃) The content of polyhydric alcohol in this case is 68.1ωt
%. When the injection was stopped for 5 to 7 minutes, the injection became impossible.

Example 2 An ink composition having the following composition and characteristics was prepared.

Composition: Ethylene glycol 82.0ωt% Distilled water 16.0ωt% Dye (CIDirect Black19 acid-precipitated) 1.8ωt% Lithium hydroxide (LiOH・H ₂ O) 0.2ωt% Kinematic viscosity: 6.5 centistokes (35℃) The polyhydric alcohol content is 82.0ωt%. The injection downtime before injection became impossible was about 30 minutes. The ink dot diameter on the recording paper is 150~
The diameter was 200 μm, and high resolution recording was possible.

Example 3 An ink composition having the following composition and characteristics was prepared.

Composition: Ethylene glycol 50.0ωt% Diethylene glycol 35.0ωt% Dye (CIReactive176) 3.0ωt% Distilled water 12.0ωt% Kinematic viscosity: 9.3 centistokes (35°C) Polyhydric alcohol content is 85.0ωt%. The injection suspension time before injection became impossible was approximately 1 hour. The results of the printing test were similar to Example 2.

Example 4 An ink composition having the following composition and characteristics was prepared.

Composition: Ethylene glycol 63.0ωt% Glycerin 19.0ωt% Dye (CIReactive Red13) 2.5ωt% Distilled water 15.5ωt% Kinematic viscosity: 9.8 centistokes (35°C) Polyhydric alcohol content is 82.0ωt%. The results of the clogging test and printing test obtained were the same as in Example 2.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between relative moisture content and relative humidity for various glycols at 70 to 80 degrees. FIG. 2 is a graph showing the relationship between the kinematic viscosity of the ink composition and the meniscus vibration reduction time.

Claims (1)

[Claims] 1. An ink composition for a drop-on-demand inkjet printer in which the temperature of the printer head is adjusted to 30°C or higher during device operation, the ink composition comprising a polyhydric alcohol having 2 to 6 carbon atoms and water. and a dye, the polyhydric alcohol exceeds 80 percent by weight of the ink composition, and the ink composition has a viscosity of 3 centistokes or more at the temperature of 30° C. or higher at which the printer head is temperature conditioned. An ink composition characterized in that it has a density of 10 centistokes or less.