JPH0717060B2 - Inkjet recording device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inkjet recording device using electrostatic force.

Conventional technology In inkjet recording technology, since ink is ejected from minute nozzles of inkjet head, reliability of ink adhesion that causes clogging near nozzles and adhesion of impurities such as heavy metals in long-term use is ensured. Problems are likely to occur and various efforts have been made to reduce this effect. In this ink jet recording apparatus, as disclosed in JP-A-57-120452 and JP-A-58-101070, there are known ones that utilize electrostatic force.
First, an inkjet head using this electrostatic force will be described.

The figure shows an example of an inkjet recording head having a structure having a plurality of nozzles. In the figure, the meniscus of the ink held along the central axis of the ink ejection port 2 of the ink nozzle member is formed on the surface of the ink ejection port 2 and the common electrode 3 provided on the surface of the air ejection port 1 of the air nozzle member. By being extended by the electric field force generated by the potential difference corresponding to a predetermined electric signal between the control electrode 4 and the control electrode 4, the air flow is sharply bent in the gap between the ink ejection port 2 and the air ejection port 2. Ink is ejected from the air ejection port 1 while being accelerated by the generated air flow having a pressure gradient that decreases in the direction of the air ejection port 2. Further, the plurality of control electrodes 4 provided on the back surface of the ink ejection port 2 are divided corresponding to the respective ink ejection ports 2, and signals are applied to each independently. The shape of the ink flow path portion of the control electrode 4 provided on the back surface of the ink ejection port 2 is circular. Reference numeral 5 is an ink inlet, 6 is an air inlet connected to an air supply source not shown, and 7 is an ink chamber connected to an ink supply source not shown.

In the inkjet recording apparatus having such a configuration,
Conventionally, oil-based ink has been used.

In the ink used for the inkjet head using electrostatic force, the physical properties of the ink such as viscosity, specific resistance, surface tension, and viscosity are strictly defined, which is an important factor for stable ink ejection. Furthermore, it goes without saying that the general properties of the ink are that it is not clogged and is stable when left for a long time. For these inks, by defining the above physical property values,
Oil-based inks of various compositions have been proposed and prototyped.

For example, JP-A-49-50935, JP-A-53-29808, and JP-A-59-64678.
Various inks have been experimentally produced in the publications, and there are various inks having physical properties such as viscosity, specific resistance, surface tension, and specific gravity within a certain range.

Problems to be Solved by the Invention However, by using an electrostatic force, an oil-based ink having characteristic values such as specified viscosity, specific resistance, and surface tension is used for a head having the above-described configuration having a plurality of ink ejection ports 2. It turns out that a stable record cannot be obtained.

This instability is caused by the air ejection port 1 or the ink ejection port 2.
This is not due to the adhered matter on the periphery but to the ink characteristics around the control electrode 4 provided near the ink ejection port 2. That is, the ink around the control electrode 4 causes deposition on the control electrode 4, conductivity of the ink near the control electrode 4, a change in other physical properties of the ink, and further dissolution of the control electrode 4, resulting in ink ejection. The state becomes unstable and changes the recording characteristics.

In other words, since the distance between the control electrodes 4 in this head is very narrow, 1 mm or less, and the control electrodes 4 are provided in the ink, the potentials of the control electrodes 4 adjacent to each other cause one electrode to eject the ink and the other to cause In the case of ejection, a potential difference is generated between the control electrodes, and the potential difference is 100 to 600V. Therefore, an electric current easily flows through the electrodes to cause a chemical reaction of the ink itself or the ink. Therefore, unstable recording occurs. The cause of these instabilities is firstly ink deposition on the electrode surface. As a result, a change in the electrode shape is caused by deposits, bubbles, etc., and the ink flow becomes unstable, causing anxiety in recording. Qualitative occurs. Secondly, due to the electrode reaction, a physical property value such as a specific resistance of the ink itself or a composition change occurs in the vicinity of the ink ejection port, and a state different from the physical property value specified in the initial stage is apparently generated and ejection instability occurs.
Third is the dissolution of the control electrode itself. Instability is usually caused by one or more of these three factors,
As a result, the recording becomes unstable. These causes are complicatedly entangled with the type, combination, dye, impurities, etc. of the solvent in the ink, and it is difficult to clarify them.

The present invention solves the above problems, and an object of the present invention is to provide an inkjet recording apparatus that enables stable recording in inkjet recording using electrostatic force.

Means for Solving the Problems To achieve the above object, the present invention provides an air supply source,
The first member having a plurality of air ejection ports through which the air flow from the air supply source is ejected, the ink supply source, the ink chamber connected to the ink supply source, and the meniscus of the ink from the ink chamber are A second member having a plurality of ink ejection openings which are provided along the central axis of the air ejection openings and are opposed to the air ejection openings and eject ink substantially corresponding to the meniscus of the ink; Located between the air ejection port and the ink ejection port corresponding to the air ejection port, the air flow is ejected from the air ejection port while abruptly bending, so that pressure is applied in the direction of the air ejection port. A plurality of gaps having a pressure gradient such that the first electrode is provided on the surface of the first member opposite to the second member, and the ink discharge port facing the first electrode. Corresponding to each Are formed in the ink ejection port between the first electrode and the second electrode corresponding to a predetermined signal, and a plurality of second electrodes formed of electrodes adjacent to each other provided in the ink chamber. And a voltage generation means capable of applying a voltage to the meniscus of the ink, and the attraction force generated by the potential difference between the first electrode and the second electrode applied in response to the predetermined signal. The ink jet recording in which the meniscus of the ink formed in the ink ejection port is extended toward the air ejection port by the accelerating force generated by the pressure gradient in the gap and the ink is ejected from the air ejection port to fly the ink. A device, wherein a ratio of the voltage to a distance between adjacent electrodes in the second electrode is 100 V / mm or more, and the voltage is large in a range of 100 V to 500 V. When the setting is made, inkjet recording using an oil-based ink having a characteristic that the change in the initial value and the value after 10 minutes of the current flowing between the first and second electrodes with respect to the set voltage is within 30%. It is a device.

Action The ink having the above characteristics has a small change in the ink physical property value due to the voltage for applying the electrostatic force, and has little influence on the electrodes, so that stable ink ejection can be maintained for a long time.

Examples As described above, in ink jet recording using electrostatic force, when an oil-based ink is used, even if the specified physical properties of ink such as viscosity, specific resistance, surface tension, and specific gravity are within the specified range. It cannot be said that it can be used, and it is necessary to define the ink characteristics attributable to the above-mentioned recording instability with the same importance as the above-mentioned physical property values. in this regard,
As a result of various studies on the above-mentioned instability, it was possible to know the correlation between the current change and the actual recording stability by reading the change in the current value of the ink at the specified electrode interval and voltage.

The current change referred to in the present invention is based on the method defined below. First, for the cell for measuring the current value, the same material as the electrode of the actual inkjet head such as gold, platinum, or rhodium is used as the electrode, and the area of each electrode is 0.2 ± 0.15 mm ² , and the applied voltage And the electrode spacing is 100 V / mm or more (the upper limit is about 2000 V / mm for the electrode spacing that can be produced), and the ink is placed on the cells having these electrodes. It was placed,
The change over time of the current when applied in the range of 100 to 500 V is compared with the initial current value and the current value after 10 minutes of application.

Correlation with recording stability can be obtained with the current change obtained by the method specified in this way, while on the other hand, a clear correlation can be obtained with an electrode interval of about 10 mm like a normal conductivity cell for liquids. I can't. That is, as a general conductivity cell for liquid, a standard conductivity cell having an electrode area of 1 cm ² ± 15% and an electrode interval of 1 cm ± 15% has a viscosity of 3 to 8 cp and a specific resistance of 1 × 10 ⁶ to For ink with 1 × 10 ⁷ Ω · cm,
When the current value after 10 minutes was compared with the initial current value when applying 500 V at 25 ° C, it was within 10%. For this ink, the recording characteristics using the inkjet head shown in the figure showed unstable recording. When this ink was used in a cell defined by the above conditions and a change in current was measured, it showed a change of about 70%, which is unsuitable for the inkjet head shown in the figure. On the other hand, when stable ink that shows a change of less than 15% in the specified cell is measured in the same way with the standard conductivity cell, no difference from the above-mentioned unstable ink is found within 10%, and it can be used. It cannot be judged.

As described above, by measuring with the specified cell, that is, by measuring the current characteristics under the above-mentioned conditions, whether the ink can be used for the ink jet recording head using the electrostatic force of the configuration shown in the figure. Can be clarified.

As described above, stable recording can be obtained by using the oil-based ink having a current change whose ink characteristics are regulated.

Next, changes in current as ink characteristics and actual recording stability will be shown.

The physical properties of the ink are as follows: viscosity 2-10 cp, specific resistance 1 × 10 ⁶
~1 × 10 ⁸ Ω · cm, using a variety of oil-based ink having a surface tension 20~40dyn / cm, specific gravity 1.3 following ranges were examined current change pursuant cells described above with the ink. That is, the electrodes are formed so that the ground between the applied voltage and the electrode spacing is 100 V / mm or more, and the ink is put into a cell having an electrode area of 0.2 ± 0.15 mm ² and a voltage of 100 V or more is applied at 25 ° C.
Measure the change in current value after a minute, and change this current by -48%,
It was classified into 6 groups of -28%, -5% or less, 10% or less, 33% and 51%. Here, -indicates a decrease in current value.

These 6 groups of oil-based inks were filled in the ink chamber 7 of the inkjet head shown in the figure, and the ink ejection characteristics were examined. The distance between the control electrodes 4 is 1 mm or less.

When a potential difference is applied between the control electrode 4 and the common electrode 3 in a state where an air flow is made to flow in from the air inlet 6 and an air flow is made to flow out from each air outlet 1, the ink meniscus is drawn toward the air outlet. Ink is ejected from the air ejection port 1 along with the air flow. The ink discharge characteristics at this time are as shown in the table for the 6 groups of oil-based inks.

From this result, it can be seen that the recording stability is obtained when the change in current value is within 30%.

As described above, in the present invention, the change in current as an ink characteristic is
It must be within 30%. Needless to say, the change in current is indicated as a change in resistance value.

As described above, according to the present invention, the plurality of ink ejection ports communicating with the ink chambers, the air ejection ports arranged to face the ink ejection ports, the control electrodes provided in each ink ejection port, and the air An inkjet head equipped with a common electrode provided on the surface of the discharge port has a ratio of applied voltage to adjacent electrode spacing of 100V.
/ mm or more and the applied voltage is 100V or more, the current change after 10 minutes is 30% or less, the ink is filled, and the potential difference between the control electrode and the common electrode The inkjet recording device is provided so that stable ink ejection can be performed for a long period of time.

[Brief description of drawings]

FIG. 1 is a sectional side view showing an example of an inkjet head to which the present invention is applied. 1 ... Air ejection port, 2 ... Ink ejection port, 3 ... Common electrode, 4
... control electrode, 5 ... ink inlet, 6 ... air inlet, 7 ...
Ink chamber.

Claims (2)

[Claims] 1. A first member having an air supply source and a plurality of air discharge ports through which an air flow from the air supply source is discharged.
An ink supply source, an ink chamber communicating with the ink supply source, and a meniscus of ink from the ink chamber are provided facing the air ejection port so as to be formed along the central axis of the air ejection port. Located between the second member having a plurality of ink ejection ports for ejecting ink substantially corresponding to the meniscus of the ink, the air ejection port, and the ink ejection port corresponding to the air ejection port. A plurality of gap portions having a pressure gradient such that the air flow is discharged from the air discharge port while being sharply bent to decrease the pressure toward the air discharge port; and the second member of the first member. A plurality of second electrodes each including a first electrode provided on a surface opposite to the first electrode, and an electrode facing the first electrode and adjacent to each other provided in the ink chamber corresponding to each of the ink ejection ports. Electric When the in response to a predetermined signal first
Voltage generating means capable of applying a voltage to the meniscus of the ink formed at the ink ejection port between the electrode and the second electrode, and the voltage applying means applied in response to the predetermined signal. The meniscus of the ink formed in the ink ejection port is extended toward the air ejection port by the attractive force generated by the potential difference between the first electrode and the second electrode, and the acceleration force generated by the pressure gradient in the gap portion. An ink jet recording apparatus for ejecting ink on an air stream from the air discharge port by means of the voltage, wherein a ratio of the voltage and a distance between adjacent electrodes in the second electrode is 100 V / mm or more. And 100V to 500V
When the size is set within the range, the oiliness has a characteristic that the change in the initial value and the value after 10 minutes of the current flowing between the first and second electrodes with respect to the set voltage is within 30%. Inkjet recording device using ink. 2. The ink jet recording apparatus according to claim 1, wherein the distance between the plurality of electrodes of the second electrode is 1 mm or less.