JPH01165452A - Ink jet recording head - Google Patents

Abstract

PURPOSE:To enable a delayed timing of start of ink discharge to be reduced without increasing the voltage of an ink discharge signal by providing a standby electrode at the rear of an electrode in an air discharge port, and connecting signal sources which output an ink discharge signal simultaneously, with the same polarity, between an electrode in the ink discharge port and a standby electrode as well as the standby electrode and the air discharge port. CONSTITUTION:An ink discharge signal is applied between an ink electrode 22 and a standby electrode 61 using a signal source 24. At the same time, an ink discharge signal is applied between the standby electrode 61 and a common electrode 23 using another signal source 24A. As a result, a strong magnetic field is added to an ink meniscus. A large electrostatic power acts upon the meniscus, causes the ink to start its discharge at a short delayed timing TD and maintains the discharging action until an ink discharge signal disappears. An air pressure and an ink pressure are set in such a manner that the flying speed of discharged ink becomes 10m/sec. If a voltage for the ink discharge signal from each signal source 24, 24A is set to 500V, the time delay is 30musec, thus reducing the delayed timing for start of ink discharge.

Description

Detailed Description of the Invention <Industrial Application Field> The present invention relates to an inkjet recording head that uses electrostatic force and air flow, and in particular, to reduce the time delay of ink ejection relative to an ink ejection signal in order to improve gradation. related to technology.

<Prior Art> Conventionally, inkjet recording heads have been proposed that use air flow in addition to electrostatic force to improve high-speed response. FIG. 6 is a schematic configuration diagram showing an example of a conventional multi-nozzle type inkjet recording head of this type.

As shown in FIG. 6, the body 11 has an orifice plate 1.
The orifice plate 12 and the nozzle plate 14 each have a plurality of ink chambers 13 covered by an ink chamber 13 and an air chamber 15 covered by a nozzle plate 14 on the outside of the ink chamber 13. An ink discharge port 16 and an air discharge port 17 are provided. High-pressure air is supplied into the air chamber 15 from an external supply source 19 via an air supply path 18, and air is constantly jetted out from the air outlet 17 at high speed. On the other hand, an ink supply path 20 is provided in the ink chamber 13.
Oil-based ink is supplied from an external ink tank 21 via an air chamber 15 near the ink discharge port 16.
A constant pressure is applied to the ink tank 21 from the air supply source 19 so that the air pressure in the ink chamber 13 is made almost equal to the ink pressure in the ink chamber 13, so that the meniscus of ink generated at the ink discharge port 16 can be kept stationary. There is. Also,
An independent ink electrode z2 is attached to the rear of each ink discharge port 16, and one common electrode 23 is attached to the front of each air discharge port 17.
A signal source 24 that generates a pulse voltage as an ink ejection signal is provided between the common electrode 23 and the ink ejection signal.

In such an inkjet recording head, a desired signal source 24 causes a common f! 4tI
When an ink ejection signal is applied between the ink ejection signal and the air ejection port 23 to generate a pulse-like potential difference, the meniscus of ink generated at the ink ejection port 16 is stretched in the direction of the air ejection port 17 due to the electrostatic force caused by the potential difference. At this time, since a rapid air flow is generated in the space from the ink discharge port 16 to the air discharge port 17, the ink meniscus generated in the ink discharge port 16 is stretched while the ink discharge signal is applied. , and is torn off by the air flow, and the air outlet 1
7, the ink pops out in a string-like shape.

To perform gradation modulation, the dot diameter is controlled by changing the pulse width of the ink ejection signal to change the length of ejected ink. For example, the main scanning speed for drawing one line is 40 cm/s, and the pixel density is 8 pixels/w.
If it is a, there is a time of 300Its per pixel, so the pulse width of the voltage pulse generated at 3.31 & is changed. When reproducing the maximum density, the pulse width is 300 p, and therefore a DC voltage is applied. For example, if the flying speed of the ejected ink is 10 m/s, the ink is continuously ejected with a length of 3 mm per pixel. Decreasing the pulse width shortens the ejected ink, ejecting ink in the shape of droplets and reproducing low density.

<Problems to be Solved by the Invention> However, if the pulse width is reduced below a certain level, ink will no longer be ejected. The reason for this is that even if an ink ejection signal is applied, the ink is not ejected immediately due to the viscosity, inertia, etc. of the ink, but there is a time delay in the start of ejection. Therefore, it is necessary to apply an ink ejection signal with a pulse width longer than the time delay, which limits the gradation. This tendency is remarkable when the meniscus of the ink is concave.

In order to shorten the time delay, the voltage of the ink ejection signal may be increased to, for example, 100 OV or more, but it is not possible to apply a very high voltage because the insulation of the electric wire may be insufficient or discharge may occur. Further, it is not necessarily easy to increase the voltage of the signal source 24.

The present invention is intended to solve the problems of the prior art described above, and aims to provide an ink jet recording head that can reduce the voltage of the ink ejection signal (but can shorten the time delay in starting ink ejection). There is.

Means for Solving the Problems> An inkjet recording head according to the present invention for solving the above-mentioned problems has an air jet recording head that jets an air stream outward facing an ink ejection port provided in an ink chamber. While an ejection port is provided, an electrode is provided on each of the ink ejection port and the air ejection port, and an ink ejection signal is applied between both electrodes to draw out the ink meniscus from the ink ejection port by electrostatic force. In an inkjet recording head that ejects a meniscus from an air discharge port using an air flow, an auxiliary electrode is provided behind the electrode of the air discharge port with an insulator interposed between the electrode of the ink discharge port and the auxiliary electrode, and Auxiliary electrode and air outlet? An inkjet recording head characterized in that signal sources that output ink ejection signals at the same time are connected to S i with the same polarity.

Function: The auxiliary electrode is closer to the ink outlet electrode than the air outlet electrode. Therefore, if the voltage of the ink ejection signal is the same, it is better to connect the signal source between the ink ejection port electrode and the auxiliary electrode than to connect the signal source between the ink ejection port electrode and the air ejection port electrode. , the electric field applied to the ink meniscus becomes stronger, the electrostatic force acting on the meniscus becomes stronger, and the meniscus is quickly drawn out from the ink ejection port.

Moreover, an electric field is generated between the auxiliary electrode and the 'rs pole of the air discharge port to accelerate the extraction of the meniscus due to an ink discharge signal from another signal source.

Therefore, ink ejection starts with a short time delay without increasing the voltage of each ink ejection signal. Moreover, it is more advantageous to use a plurality of No. 41 voltage sources, which are easy to manufacture, than to use one extremely high voltage signal source in terms of cost, wire insulation, and discharge.

Embodiment Hereinafter, an embodiment of the present invention will be specifically described with reference to the drawings.

First, the overall configuration of an example of an inkjet recording apparatus to which an inkjet recording head according to the present invention can be applied will be described with reference to FIG. 5, which is a schematic diagram thereof. As shown in FIG. 5, this inkjet recording apparatus includes a digital color scanner 31, an image information processing device 32, and an inkjet printer 33.

The digital color scanner 31 scans each part of the color original image 34 to measure the density values of blue, green, and red. , an illumination light source 37, lenses 38, 39, and a three-color separation photometry section 40
The photoelectric conversion head 41 has a photoelectric conversion head 41 attached thereto, and a drive device that reciprocates the photoelectric conversion head 41 in a direction parallel to the axial direction of the rotating cylinder 36 by a sub-scanning pulse motor 43 via a feed screw shaft 42. There is. Therefore, the rotating cylinder 3
Each time the photoelectric conversion head 41 rotates once, the rotating cylinder 36
The color original image 34 is moved by one scanning line in the axial direction to two-dimensionally scan each part of the color original image 34, and the blue, green, and red reflection densities of each part of the color original image 34 are measured.

The image information processing device 32 is composed of a central processing unit 44, an internal storage device 45, an OCR circuit 46, and a table memory circuit 47. The color density signal is written into the internal storage device 45, and the UCR circuit 46 performs gradation correction, undercolor removal, and smudge correction on the signal read out from the internal storage bag M45 to produce cyan, magenta, yellow, and black. The table memory circuit 47 determines the pulse width of the ink ejection signal by referring to the table memory for each level with respect to the density signal from the UCR1il path 46, and determines the pulse width of the ink ejection signal.
An ink ejection signal is supplied to 3.

The inkjet printer 33 reproduces a color image by attaching ink droplets ejected from the head unit 5o to a white paper 49 wrapped around a rotating cylinder 48, and includes a rotating cylinder 48 that is rotationally driven by a main scanning pulse motor 51 and ,
A yellow inkjet recording head 5 is arranged along the axial direction of the rotating cylinder 48 so as to be close to its outer peripheral surface.
2. A head unit 50 including an inkjet recording head 53 for magenta, an inkjet recording head 54 for cyan, and an inkjet recording head 55 for black, and this head unit 50 is rotated by a sub-scanning pulse motor 57 via a feed screw shaft 56. It has a drive device that reciprocates in a direction parallel to the axial direction of the cylinder 48. Then, the rotating cylinder 48 is rotated by the signal from the central processing unit 44.
Each time the head unit 50 rotates, the head unit 50 moves by one scanning line, and in the process, each of the recording heads 52 to 5
5 are driven to eject ink droplets at the same time and deposit the ink onto the white paper 49 to perform recording. Note that since the four inkjet recording heads 52 to 55 are shifted in position in the scanning direction of the head section 50, each inkjet recording head 52 to 55 stores data in the internal storage device 45 according to the pixels to be recorded at each scanning position. Addressing is done sequentially.

Next, an inkjet recording head according to the present invention will be explained. FIG. 1 is a sectional view of a main part of an inkjet recording head according to an embodiment of the present invention, FIG. 2 is a layout diagram of auxiliary electrodes, and FIG. 3 is an operation explanatory diagram. However, in FIGS. 1 and 2, the same parts as those of the conventional head shown in FIG. 6 are given the same reference numerals.

As shown in FIGS. 1 and 2, the inkjet recording head 60 is of a multi-nozzle type, and an orifice plate 12
At the same time, one common electrode 23 for each air outlet 17 is attached to the front surface of the nozzle plate 14, and one common electrode 23 is attached to each air outlet 17 on the rear surface of the nozzle plate 14. An independent auxiliary electrode 61 is attached to the air outlet 17. Furthermore, each ink electrode 22 and each auxiliary electrode 61 are connected to a positive terminal and a negative terminal of a signal source 24, respectively, and each auxiliary electrode 61 and common electrode 23 are connected to a positive terminal of another signal source 24A, respectively. This is a continuation of the negative terminal. The nozzle plate 14 is an insulator. Reference numeral 61a in FIG. 2 indicates a lead portion of the auxiliary electrode 61.

By the way, as an example, the diameter of the ink discharge port 16 is 50μ.
m1 Diameter of air discharge port 17 is 150 μm1 Distance between orifice plate 12 and nozzle plate 14 is 80 μm1 Common electric current W71
The distance between the auxiliary electrode 61 and the ink electrode 22 was 480 μm, and the distance between the auxiliary electrode 61 and the ink electrode 22 was 280 μm.

Further, the auxiliary electrode 61 was made to have a thickness of several μm by vapor deposition.

Both the orifice plate 12 and the nozzle plate 14 have a thickness of 200 Alm.

A pair of signal sources 24 and 24A corresponding to each nozzle are configured to simultaneously output ink ejection signals. However, the voltages v1 and (2) of each ink ejection signal do not necessarily have to be equal. In the case of a multi-nozzle type, the time delay may vary between nozzles, and the time delays can be made equal by setting the ink ejection signal voltages (1) and (2) independently for each nozzle.

Next, the operation will be explained with reference to FIG.

When the signal source 24 applies an ink ejection signal between the ink electrode 22 and the auxiliary electrode 61, and at the same time, another signal vX24A applies an ink ejection signal between the auxiliary electrode 61 and the common electrode 23, a strong electric field is applied to the ink meniscus. . As a result, a larger electrostatic force than before acts on the meniscus, and ink starts to be ejected with a short time delay TD. Ink is ejected until the ink ejection signal disappears.

With the dimensions mentioned above, the flying speed of the ejected ink is 10
Set the air pressure and ink pressure so that it is m/s, and set the voltage of the ink ejection signal of each signal source 24, 24A to 50 m/s.
When set to 0V, the time delay TD was 30. It was cm. On the other hand, when the auxiliary voltage Fj61 is connected (the signal source 24 is connected only between the ink electrode 22 and the common electrode 23 (conventional)), there is a long time delay of 50 to 100 JIs.

From this, for example, the peripheral speed of the rotating cylinder 48, which is the main scanning speed, is 40 am/s-, the pixel density is 8 pixels/hazy,
Ink ejection signal l! When the dynamic wave number is set to 3.3, the gradation is significantly improved compared to the conventional method.

If the gradation is still insufficient, matrix recording such as 2X2, 3X3, or 4X4 (dots) is performed, although the resolution is reduced.

Next, an inkjet recording head according to another embodiment will be described with reference to FIG. In this embodiment, the auxiliary Ti electrode 61 is formed in multiple layers, and another signal source 24B is connected between the auxiliary electrodes 61 and 61 with the same polarity as the other signal sources 24 and 24A. One set of signal sources 24.24 for each nozzle
A and 24B simultaneously output ink ejection signals. Reference numeral 62 in FIG. 4 is an insulator provided between the eyebrows. In this way, when the auxiliary electrode 61 has a multilayer structure, the signal sources 24, 24A
.

24B can be of relatively low output voltage.

<Effects of the Invention> As described above in detail with reference to embodiments, according to the present invention, an auxiliary electrode is provided behind the electrode of the air discharge port via an insulator, and the electrode is connected to the electrode of the ink discharge port. Signal sources that output ink ejection signals at the same time are connected with the same polarity between the auxiliary electrode and between the auxiliary electrode and the air ejection port electrode, so the voltage of the ink ejection signal from each signal source does not have to be high. However, the time delay in starting ink ejection can be shortened, and the gradation can therefore be improved.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of essential parts of an inkjet recording head according to an embodiment of the present invention, FIG. 2 is a layout diagram of auxiliary electrodes, and FIG.
4 is a cross-sectional view of essential parts of an inkjet recording head according to another embodiment, FIG. 5 is a general schematic diagram of an example of an inkjet recording apparatus to which the present inkjet recording head can be applied, and FIG. 6 is an illustration of the operation. 1 is a schematic configuration diagram of an inkjet recording head according to a conventional example. In the drawing, 12 is an orifice plate, 13 is an ink chamber, 14 is a nozzle plate, 15 is an air chamber, 16 is an ink discharge port, 17 is an air discharge port, 22 is an ink electrode, 23 is a common electrode, 24.24A and 24B is a signal source, 61 is an auxiliary electrode, and 62 is an interlayer insulator. Patent application Agent: Fuji Photo Film Co., Ltd.

Claims (1)

[Claims] An air ejection port is provided to face the ink ejection port provided in the ink chamber and eject air to the outside, and an electrode is provided to each of the ink ejection port and the air ejection port, and the ink is discharged between the two electrodes. In an inkjet recording head that draws out an ink meniscus from an ink ejection port by electrostatic force by applying an ejection signal and ejects the drawn out meniscus from the air ejection port using an air flow, an insulating film is provided on the rear side of the electrode of the air ejection port. An auxiliary electrode is provided through an object, and signal sources that simultaneously output ink ejection signals are connected with the same polarity between the ink ejection port electrode and the auxiliary electrode, and between the auxiliary electrode and the air ejection port electrode. An inkjet recording head characterized by: