JPH068469A - Ink jet head - Google Patents

Abstract

PURPOSE:To realize a high recording speed and simplify the constitution and control of a device without damaging reliability by providing ink feed tanks feeding the ink inside into a recovery line through a nozzle by means of gravity while retaining the ink level above the outlet end position of the ink recovery line. CONSTITUTION:A recording head 2 is provided with seven ink tanks 21-27 when ink is fed to the recording head 2, and ink is fed from an ink reservoir 3 into tanks 21-27 at both ends through a pump 4. The level of ink tanks at both ends is raised by feeding the ink, and when the level reaches ink communication windows 38, the ink flows into an adjacent tank 22. When the ink level of the tank 22 is beyond the communication window 38, the ink further flows into an adjacent tank 23. Thus all ink levels reach the ink communication windows 38, and further the ink levels are raised, and when the ink levels are beyond drain opening 43 formed slightly higher than the ink communication windows 38, the ink is flowed into a recorery tank 28 and recovered into the tank reservoir 3 through drain pipngs 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet recording apparatus, and more particularly to ink supply for an ink jet head.

[0002]

2. Description of the Related Art Ink ejected from an ink jet head must be chemically stable without changing physical properties such as viscosity in order to maintain good ejection characteristics. However, after a long period of time, the ink changes its physical property values due to solvent evaporation or chemical alteration, bubbles are generated inside the ink due to temperature changes, and further foreign matter is deposited. Hereinafter, this is referred to as ink deterioration.
The deteriorated ink deteriorates the ejection characteristics. In addition, nozzle clogging, which is a fatal malfunction, is caused.

In order to prevent this, the ink in the head is collected at a predetermined time interval and the inside of the head is constantly replaced with fresh ink. Hereinafter, this is referred to as an ink replacement operation.

In the apparatus disclosed in JP-A-3-187761, as shown in FIG. 8, in an ink jet head having an ink supply passage 100, an ink discharge passage 101, and a nozzle 102, the nozzle 102 is sealed by means for sealing the nozzle 102. The ink is sealed and a high pressure ink is supplied to the ink supply passage 100 by a pump to force the ink to flow away to perform an ink replacement operation.

[0005]

However, in such an apparatus, since the nozzle is closed during the ink replacement operation, it is necessary to suspend the printing operation. Therefore, there is a problem that the recording speed is lowered due to the ink replacement. Furthermore, in order to ensure reliability, it is necessary to control the device so that the ink replacement operation is performed periodically at a predetermined time interval, which causes a problem that the device configuration and device control become complicated. Further, since the ink replacement operation cannot be performed very frequently in order to secure the recording speed, there is a problem in that reliability is deteriorated if this time interval is made large.

The present invention solves these problems, and an object thereof is to realize a high recording speed without impairing reliability. Yet another purpose is the device configuration,
It is to realize a highly reliable device with simple device control.

[0007]

An ink jet head of the present invention communicates with a plurality of nozzles capable of independently controlling ejection of ink droplets, and the ink surface is opened to atmospheric pressure below the nozzles. An ink recovery path having an outlet,
An ink supply tank that holds an ink liquid level above the outlet end position of the ink recovery path, communicates with the nozzle, and supplies the internal ink by gravity to the ink recovery path via the nozzle. The configuration.

More preferably, the ink supply tank holds the ink surface below the nozzle position.

[0009]

According to the above construction, the ink always moves from the ink supply tank provided on the upper side to the ink collecting path on the lower side by gravity. Therefore, the nozzle portion is filled with fresh ink from the ink supply tank. Since the above operation is performed without sealing the nozzle, the printing operation is not suspended.

Further, by arranging the ink supply tank below the nozzle, it is possible to maintain the nozzle portion at a negative pressure and increase the reliability of ink leakage from the nozzle portion.

[0011]

EXAMPLES Examples of the present invention will be described.

FIG. 1 is a perspective view of the ink jet printer of the first embodiment.

This printer is constructed such that an ink image is formed on the transfer drum 1 and then transferred onto a recording paper 8 which is a recording medium, and the recording head 2 scans the transfer drum 1. The ink is an emulsion in which colored particles are dispersed in an ink dispersion medium. The ink dispersion medium is a petroleum solvent, that is, a high resistance low dielectric constant aliphatic hydrocarbon solvent (for example, Isopar G manufactured by Exxon Chemical Co.). The colored particles are Raven 125 from Colombian Carbon Co. as a pigment.
5 and ethyl cellulose as a resin, which are made into fine particles having an average particle diameter of 1 μm, and are dispersed in the above ink dispersion medium together with an organic amine which is a dispersion stabilizer as an additive.

The ink is diluted with a dispersion medium so that the solid content concentration defined by the following definition is 25 wt% so that the ink can be ejected from the recording head 2.

Solid content concentration = (weight of colored particles) / (weight of colored particles + weight of dispersion medium + weight of additive) The transfer drum 1 has an image forming layer 17 formed of a silicone rubber layer around a metal tube 16. Consists of Silicone rubber does not repel ink drops and has the property that ink drops do not spread greatly. Furthermore, the ink image releasability is good, and pressure transfer to a recording medium is possible at low pressure. In addition, since the surface of the recording paper is deformed due to the unevenness of the surface of the recording paper due to elasticity, the transfer drum 1 is not affected by the smoothness of the recording paper.
It has the characteristic that the above ink image can be faithfully transferred to the recording paper. Therefore, it is suitable for the image forming layer 17. A pressure roller 9 is provided as a pressure applying unit that presses the recording paper 8 toward the transfer drum 3.

Next, the structure of the recording head 2 will be described with reference to FIGS. 2, 3 and 4.

In FIG. 2, an electromechanical conversion means 31 is provided corresponding to each nozzle 20 so that ink can be ejected independently from each nozzle 20. This uses a piezo element to expand in the direction of arrow B by the applied voltage control to deform the metal thin film 44 and increase the pressure in the pressure chamber 35 (the space between the metal thin film 44 and the nozzle filled with ink). , Eject ink drops. The pressure chamber 35 communicates with a nozzle group composed of specific nozzles through an ink supply path 32, and the ink supply path 32 is located in the rear portion of the recording head 2 with ink tanks 21, 22, 23, 24, 25, 26. Two
It communicates with 7. As shown in FIG. 2, the ink tank (which will be described as a representative of 24) is separated by a partition having an ink communication window 38 at its upper portion, and drain ports provided in the ink tanks 21 and 27 at both ends. Except for 43, they have the same sectional shape. Each ink tank is configured to communicate with a specific nozzle group through each ink supply path 32 and supply ink to the corresponding nozzle group.

In FIG. 3, the recording head 2 has a plurality of nozzles (typically represented by 20) on the front surface facing the transfer drum 1. A supply pipeline 6 for supplying ink from the ink container 3 using a pump 4 is connected to the ink tanks 21 and 27 at both ends. The supply conduit 6 has an ink end detector 51, which issues an ink end signal when the liquid level in the ink container 3 has dropped. As a detector used for this purpose, a pair of light emitting and light receiving elements having an optical path orthogonal to the transparent portion of the supply conduit 6 is used. When the ink flows through the conduit, the emitted light is absorbed by the ink and does not reach the light receiving element, but when the air flows through the conduit, the light is transmitted through the conduit and is received, thereby performing detection. The air sent immediately before the ink end signal floats on the liquid surface immediately after being sent to the ink tanks 21 and 27 and escapes to the atmosphere, so that it does not enter the ink supply passage 32.
Since the ink according to this embodiment has a light absorption characteristic of absorbing almost all infrared light, a pair of light emitting and light receiving elements using infrared light is suitable. It is needless to say that even in the case of using an ink other than this embodiment, such as color, it can be applied by using light having a wavelength suitable for the light absorption characteristics of the ink used in the light emitting element.

The ink tanks 21 and 27 at both ends are provided on the wall 4
It has recovery tanks 28 and 29 through 3,44,
The recovery tanks 28 and 29 are connected to the ink container 3 via the drain conduit 5. During the printing operation, the discharge amount of the pump 4 is increased / decreased by the overflow detector 52 so that a small amount of ink always flows out to the drain conduit 5. As the detector, a detector having the same configuration as the ink end detector 51 is used.

As shown in FIG. 4, the pressure chamber 35 communicates with the return channel 81 through the ink recovery channel 80 and further with the recovery tank 28. The return flow passage 81 has a large pipe cross-sectional area for ensuring sufficient air permeability, and the recovery tank 28 is open to the atmospheric pressure in the upper portion. Therefore, the ink recovery passage 80 is filled with ink, and the lower end is kept at atmospheric pressure.

Next, the operation will be described.

First, the image forming operation will be described.

In FIG. 1, the transfer drum 1 rotates in the direction of arrow A during operation. The recording head 2 selectively ejects ink droplets from a plurality of nozzles, and the recording head 2 transfers the ink onto the transfer drum 1
Form an ink image. Since the ink dispersion medium has an evaporating property and the image forming layer 17 has a property of absorbing the ink solvent, the ink solvent is removed from the ink image on the transfer drum 1 and colored particles are formed on the transfer drum 1. An ink image having a high density is formed. Next, the recording paper 8 is brought into contact with the transfer drum 1 and pressed by the pressure roller 9 to transfer the ink image.

Since the ink image has a high density on the transfer drum 1, the ink is soaked in the recording paper fiber in the transfer step and the image is faithfully transferred without blurring the edges. The image is obtained.

Next, the ink supply operation to the recording head 2 will be described with reference to FIGS. 3 and 5. FIG. 5 is a view seen from the direction of arrow G in FIG.

The recording head 2 includes an ink tank 21, ...
Ink is supplied from the ink container 3 to the ink tanks 21 and 27 at both ends by using the pump 4. Ink tanks at both ends (represented by 21) are raised in level by the supply of ink, and when they reach the ink communication window 38, they flow into the adjacent ink tanks 22. Further, when the ink level in the ink tank 22 exceeds the communication window 38, the ink level flows into the adjacent ink tank 23. Thus, all the ink tank liquid level reaches the ink communication window 38, the ink level further rises, and when it exceeds the drain port 43 which is set slightly higher than the ink communication window 38, the recovery tank 28
To the ink container 3 through the drain conduit 5.

The ink in the ink tank advances in the ink supply path 32 by the capillary force to fill the pressure chamber 35, and the ink filling operation before the operation is performed. Furthermore, the ink recovery path 80
And reaches the return flow path 81.

According to an experiment conducted by the present inventor, the ink supply path 3
2. When the gap between the flow passages forming the pressure chamber 35 and the ink recovery passage 80 (the gap dimension on which the capillary force acts) is 0.2 mm,
If the height from the ink tank liquid surface is within 25 mm,
The ink could be smoothly pulled up, and the pressure chamber 35 could be filled with the ink. The nozzle 20 is open to atmospheric pressure, but has a nozzle diameter of 50 μm and a small diameter, so that the inside of the pressure chamber 35 is filled with ink without leaving air.

Next, the ink replacement operation will be described. A predetermined amount of ink is held in the ink tank as described above. The ink filled in the ink supply path 32, the pressure chamber 35, and the ink recovery path 80 causes a steady flow by the siphon principle and reaches the return flow path 81 provided below,
It is led to the recovery tank 28. Therefore, ink replacement is always performed.

In the ink jet head of this embodiment, since the ink liquid level in the ink tank is kept horizontal even if the installation posture is changed, the ink that has passed the lower portion of the ink communication window 38 is adjacent to the ink tank. Flowing into 26,
The liquid level of each ink tank is almost the same, and there is no difference between the nozzle groups.

Next, the ink jet head of the second embodiment will be described with reference to FIG.

In the configuration of this embodiment, the nozzle 20 is configured to eject the ink droplet upward.

The ink tank 85 has a vent hole 83 that can be controlled to be opened and closed, and an ink liquid surface position detection sensor 86. The other members that are the same as those of the inkjet head of the first embodiment are designated by the same reference numerals and the description thereof is omitted.

The ink filling operation will be described. Before the operation, when the ink is not filled in the head, the plug 82 for sealing the vent hole 83 is driven by the driving means 84 to seal the vent hole 83. Ink is supplied from the ink container 3 to the ink tank 85 by the pump 4. The ink is supplied with pressure by the ink supply passage 32, the pressure chamber 35, and the ink recovery passage 8.
Proceed 1 to satisfy these. After that, by opening the vent holes 83, the upper part of the ink tank becomes atmospheric pressure, the ink liquid level is lowered, the ink passes through the pressure chamber 35, flows into the ink recovery passage 81, and is drained from the drain conduit 5 to the ink container 3. Will be collected. That is, the ink moves steadily by the siphon principle, and the ink replacement operation of the ink inside the head 2 is performed. The liquid level position sensor 86 detects the amount of ink in the ink tank, and the ink is supplied by the pump 4 so that the amount of ink in the ink tank 85 becomes constant, whereby the ink replacement operation is continuously performed.

Other operations are the same as those in the first embodiment,
The description is omitted.

Next, the ink jet head of the third embodiment will be described with reference to FIG.

In the configuration of this embodiment, the nozzle 20 is configured to eject the ink droplet upward.

Although a positive pressure acts at the nozzle position, the front surface 71 of the nozzle is water-repellent to prevent ink from leaking.

The ink tank 85 is arranged so that the ink liquid surface is above the nozzle 20 and has an ink liquid surface position detection sensor 86. The other members that are the same as those of the inkjet head of the second embodiment are designated by the same reference numerals and the description thereof is omitted.

The ink is supplied to the ink container 3 by the pump 4.
To the ink tank 85. The ink fills the ink supply path 32, the pressure chamber 35, and the ink recovery path 81 by gravity. The upper part of the ink tank 85 is kept at atmospheric pressure. The ink passes through the pressure chamber 35, flows into the ink recovery passage 81, and is recovered into the ink container 3 through the drain conduit 5. That is, the ink constantly moves due to gravity, and the ink replacement operation of the ink inside the head 2 is performed. The liquid level position sensor 86 detects the amount of ink in the ink tank, and the ink is supplied by the pump 4 so that the amount of ink in the ink tank 85 becomes constant, whereby the ink replacement operation is continuously performed.

Other operations are the same as those in the first embodiment,
The description is omitted.

[0042]

According to the ink jet head of the present invention, an ink recovery passage which communicates with a nozzle and has an outlet for opening the ink liquid surface to the atmospheric pressure below the nozzle, and above the ink liquid surface position of this ink recovery passage. An ink supply tank is provided that holds the ink surface and communicates with the nozzle, and supplies the ink inside by gravity to the ink recovery path via the nozzle. According to this configuration, the ink constantly moves from the ink supply tank provided on the upper side in the lower ink recovery path by gravity. Therefore, the pressure chamber and the vicinity of the nozzle are filled with fresh ink from the ink supply tank, and foreign matters and bubbles are removed from this portion. Since the above operation is performed without sealing the nozzle, the printing operation is not suspended. Therefore, it is not necessary to suspend the printing operation, the ink replacement operation is performed, the recording speed does not decrease, and high reliability can be realized. Further, it is not necessary to control the device so that the ink replacement operation is periodically performed during the operation, and the device configuration and the device control can be simplified.

Further, by disposing the ink supply tank below the nozzle, the nozzle portion can be kept at a negative pressure, and the reliability of ink leakage from the nozzle portion can be improved.

[Brief description of drawings]

FIG. 1 is a perspective view of an inkjet recording apparatus using an inkjet head of the present invention.

FIG. 2 is a diagram showing an internal configuration mainly of an ink supply path of the inkjet head according to the first embodiment of the present invention.

FIG. 3 is a perspective view showing the configuration of the inkjet head according to the first embodiment of the present invention.

FIG. 4 is a diagram showing an internal configuration of the inkjet head according to the first embodiment of the present invention, mainly centering on an ink recovery path.

FIG. 5 is a diagram illustrating ink supply of the inkjet head according to the first embodiment of the present invention.

FIG. 6 is a diagram showing an internal configuration of an inkjet head according to a second embodiment of the present invention.

FIG. 7 is a diagram showing an internal configuration of an inkjet head according to a third embodiment of the present invention.

FIG. 8 is a diagram showing a configuration of a conventional inkjet head.

[Explanation of symbols]

1: Transfer drum 2: Recording head 3: Ink container 4: Pump 5: Drain pipe line 6: Ink supply pipe line 8: Recording paper 21, 22, 23, 24, 25, 26, 27, 85: Ink tank 28, 29: Recovery tank 32: Ink supply channel 38: Communication window 43: Drain port 62: Ink 80: Ink recovery channel 81: Return channel

Claims (2)

[Claims] 1. An ink recovery path having a plurality of nozzles capable of independently controlling ejection of ink droplets, an outlet communicating with the nozzle and having an ink liquid surface below the nozzle and being opened to atmospheric pressure, and the ink recovery path. An ink supply tank, which holds an ink liquid level above the outlet end position of the passage, communicates with the nozzle, and supplies the internal ink by gravity to the ink recovery passage through the nozzle. And inkjet head. 2. The ink jet head according to claim 1, wherein the ink supply tank holds an ink surface below the nozzle position.