JP2001105623A - Ink jet recording apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink jet recording apparatus preventing the clogging of ink flow channels caused by the floc of colorant particles or foreign matter in ink and simple in maintenance. SOLUTION: In an ink jet recording apparatus equipped with an ink jet recording head wherein a plurality of ink discharge electrodes are arranged and grounded counter electrodes are arranged at a predetermined interval, a filtering means is provided on the way of the circulating passage to an ink tank. As a result, the clogging of ink flow channels caused by the floc of colorant particles or foreign matter in ink is prevented and ink flying characteristics are stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet type recording head device, and more particularly to an ink jet type recording head device for printing by discharging a pigment-based ink containing charged colorant particles onto a recording medium by electrostatic force.

[0002]

2. Description of the Related Art An apparatus that forms recording dots and records an image by discharging liquid ink as small droplets onto a recording medium has been put to practical use as an ink jet printer. This ink jet printer has advantages such as lower noise compared to other recording methods, and realization of the printer with a smaller number of parts than other recording methods because recording is performed directly on a recording medium. Therefore, it is attracting attention as plain paper recording technology. As a recording method of an ink jet printer, a method of ejecting ink droplets at a pressure of a bubble generated by heat of a heating element (for example,
56-9429) and a method of ejecting ink droplets by mechanical pressure accompanying a volume change caused by distortion of a piezoelectric element (for example, Japanese Patent Publication No. 53-12138). In the above two methods, since the ejection amount of the ink droplet for each recording dot on the recording medium is constant,
In printing a color image, pseudo gradation expression is performed by spatially changing the density between recording dots. However, with this gradation expression method, it is difficult to print a high gradation color image equivalent to a photograph. In order to print an image with higher gradation, gradation expression by so-called area modulation for changing the area of the recording dot is required. But,
In the above two methods, since the ejection amount of the ink droplet is constant, it is extremely difficult to express gradation by area modulation.

As a recording method for overcoming this drawback, a method has been devised in which a voltage is applied to a plurality of electrodes arranged in parallel on a substrate, and ink or colorant particles in the ink is discharged using electrostatic force. . Specifically, JP-A-56-4467
JP-A-7-502218 discloses a method of ejecting ink by electrostatic attraction as disclosed in Japanese Patent Application Laid-Open Publication No. 7-502218. A method of increasing the density and performing ejection has been proposed. As a specific shape of the ink jet type recording head in the latter type, a multi-head having a plurality of discharge electrodes is formed by laminating an insulating electrode substrate having an ink discharge electrode formed on one side via a spacer. Alternatively, there has been known a method in which ink discharge electrodes are formed in parallel as thin film electrodes at a printing interval of a desired resolution on a flat insulating substrate, and are configured as a multi-head. In this method, a bias voltage of, for example, about 1.5 to 2.0 kV is commonly applied to all the ink discharge electrodes, and when ink is to be discharged, for example, 300 to 500 ( A pulse voltage of about V) is superimposed. Here, it is an advantage of this method that the amount of ejected ink can be controlled by changing the width of the pulse voltage, and the area of the recording dots formed on the recording medium can be controlled.

[0004]

In an ink jet recording apparatus utilizing electrostatic force as in the present invention, a type in which colorant particles are dispersed in a petroleum organic solvent is used as an ink. Such inks are generally classified as pigment-based inks. Such a pigment-based ink has an advantage in that a printed image is less likely to be discolored since it has light resistance as compared with a dye-based ink used in another inkjet recording apparatus. Incidentally, the constitution of the pigment-based ink used in the present invention will be described in more detail as follows. The coloring agent particles are obtained by adding a charge controlling agent, a dispersing agent, and the like to the pigment particles, and the individual coloring agent particles are contained in the organic solvent in a charged state. Therefore, the colorant particles are dispersed in the organic solvent without aggregation due to the electrostatic repulsion between the colorant particles. However, after a period of about 1 to 2 months, for example, the charge amount of some colorant particles decreases due to a decrease in the charge holding power of the charge control agent, or the dispersant separates from the colorant particles. Resulting in. Therefore, the electrostatic repulsion between the colorant particles is weakened, and the colorant particles aggregate with each other in the ink tank. Further, since the ink ejection portion of the ink jet recording head is exposed to the air, foreign matters such as dust and paper powder in the air are likely to be mixed into the ink. As described above, if the aggregates of the colorant particles or the foreign matters are mixed, clogging occurs in the ink flow path, and the ink flow becomes unstable. As a result, the ink cannot be stably ejected from the ink ejection electrode, which causes a problem that the printed image is deteriorated.

As a method for solving such a problem, Japanese Patent Application Laid-Open No. Hei 8-207307 discloses a configuration in which a porous member is adhered to the vicinity of an ink collecting portion of a recording head. Here, an attempt is made to remove agglomerates of colorant particles, foreign matters, and the like mixed in the ink by passing through the porous member at the time of ink recovery. However, in such a configuration, the inside of the porous member is filled with agglomerates of colorant particles or foreign substances while being repeatedly used, and the filtering ability gradually deteriorates. In addition, since it is attached to the tip of the head, it is structurally difficult to replace only the porous member, which is inconvenient in terms of maintenance.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and removes agglomerates and foreign matters of colorant particles mixed into ink to obtain stable ink ejection.
An object is to simplify maintenance associated with ink removal.

[0007]

SUMMARY OF THE INVENTION The present invention provides an ink jet recording head having a plurality of ink discharge electrodes arranged in parallel on an insulating substrate via an insulating thin film member, an ink tank for storing ink, An ink circulating unit that circulates the ink, a plurality of pulse power supplies connected to the individual ink discharge electrodes, a bias power supply connected to the plurality of ink discharge electrodes via a common wire, and the plurality of A counter electrode disposed to face the ink discharge electrode, and the ink circulation unit includes an ink filtering unit.

As described above, by providing the filtering means, it is possible to always supply the ink discharge electrode with the ink which does not contain the aggregates of the colorant particles and the foreign matter in the ink flow path.

Further, since the filtering means is of a cartridge type, maintenance is facilitated.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described with reference to the drawings.

FIG. 2 is a top view showing the basic structure of the ink jet recording head 1 according to the first embodiment.
As shown in FIG. 2, the ink jet recording head 1 has a configuration in which the ink discharge electrodes 3 are arranged in parallel in the main scanning direction of printing at intervals of, for example, 500 μm. FIG. 3 is a perspective view showing a detailed structure around one ink discharge electrode 3 in the ink jet recording head 1 according to the first embodiment. A shield electrode 7 is provided between two adjacent ink discharge electrodes 3. The entire surface of the shield electrode 7 is covered with the insulating covering member 4. Further, the space other than the space on the upper surface of the ink discharge electrode 3 is filled with the covering member 4. The gap on the upper surface of the ink discharge electrode 3 forms an ink flow path of each ink discharge electrode 3. This ink flow path sucks up the ink 6 supplied into the recording head 1 through the ink circulation path 14a shown in FIG. 1 toward the tip of the ink discharge electrode 3 by capillary action, and the ink 6 The tip is always wet. The ink discharge electrode 3 is formed on a single insulating substrate 17 covered with an insulating thin film member 18. For example, glass is used for the insulating substrate 17, and an organic thin film such as polyimide is used for the insulating thin film member 18. here,
For example, high relative dielectric constant such as glass (ε _s = 7 to 10)
By coating the extent) substrate, for example, low dielectric constant, such as polyimide (epsilon _s = about 3.4) thin film, the electric field at the tip of the ink ejection electrode 3 when ejecting the ink in a state of being aggregated Can be prevented from lowering the concentration. The ink discharge electrode 3 is formed as a thin film electrode on the insulating thin film member 18 in the manufacturing process of the ink jet recording head 1. The electrode 3 for ink ejection is provided on the insulating substrate 17 so as to strengthen the electric field at the tip.
Protrudes from the end face of, for example, about 50 to 200 μm.
Further, as shown in FIG.
7 protrudes, for example, by about 20 to 40 μm.
This is to enhance the effect of suppressing electrical mutual interference between adjacent ink ejection electrodes. The projecting portion of the shield electrode 7 is also covered by the covering member 4. Further, the covering member 4 at the protruding portion of the shield electrode 7 serves to mechanically separate the ink flow between the adjacent ink discharging electrodes 3. Therefore, it is possible to prevent the ink surface shape (ink meniscus) between the adjacent ink discharge electrodes 3 from being connected to form a bridge (liquid junction), and to influence the ink meniscus between the ink discharge electrodes 3 during ink discharge. To prevent them from affecting each other. Further, as shown in FIG. 2, an individual pulse power supply 9 and a common bias power supply 8 are connected to each ink discharge electrode 3.

FIG. 1 shows one configuration example of an ink jet printer according to the first embodiment. The ink 6 used in the printer according to the present invention is one in which charged coloring agent particles are dispersed in an organic solvent. In particular,
The coloring agent particles are obtained by adding a charge controlling agent, a dispersing agent, and the like to the pigment particles, and the individual coloring agent particles are contained in the organic solvent in a charged state. Therefore, the colorant particles are dispersed in the organic solvent without aggregation due to the electrostatic repulsion between the colorant particles. The ink 6 is sucked from the ink tank 12 by the supply pump 13a,
a to the inkjet recording head 1. The ink 6 is supplied to the recording head 1 through an ink introduction path 15 between the ink circulation path 14a and the recording head 1, and flows inside the recording head 1 from top to bottom in the drawing.
In the ink jet recording head 1, a plurality of ink discharge electrodes 3 are arranged in parallel at a constant arrangement pitch in the main scanning direction of printing (the direction of arrow A in the drawing). An individual pulse power supply 9 and a common bias power supply 8 are connected to each ink ejection electrode 3. Further, a control signal from the drive circuit 11 is connected to the pulse power supply 9, and the control signal is transmitted to each pulse power supply 9 independently according to print data transmitted from a personal computer or the like. The application of a voltage to the ink discharge electrode 3 is controlled. From the ink discharge electrode 3 to which a voltage is applied from the pulse power supply 9, charged colorant particles (not explicitly shown in the figure) dispersed in the ink 6 by an electric field near the tip of the ink discharge electrode 3 are formed. The aggregated colorant particles are discharged toward the counter electrode 2 that is grounded.
As a result, dots are formed on the recording medium 5 on the counter electrode 2 by aggregates of colorant particles, and printing is performed. When printing of one line in the main scanning direction is completed in this manner,
The recording medium 5 is moved in the sub-scanning direction (the direction of arrow B in the figure) by one dot pitch of the printing resolution by a transport mechanism not explicitly shown in the figure. Then, printing for the next one line is started. By repeating such a printing operation in the printing area on the recording medium 5, printing for one page is performed. At the time of the printing operation, the coloring material particles which are not consumed in the ink discharging process and remain at the tip of the ink discharging electrode 3 flow from the tip of the ink discharging electrode 3 to the back surface of the recording head 1 together with the ink circulation flow. . The ink 6 flowing to the back surface of the recording head 1 is sucked from an ink lead-out passage (not shown) by the collection pump 13b and flows into the ink circulation passage 14b. The ink 6 flowing through the ink circulation path 14b is returned to the ink tank 12 and used again for printing. The above procedure is for printing of only one color. However, in the case of multicolor printing such as a color image, yellow (Y), magenta (M), cyan (C) and black (K) are used.
A plurality of ink jet recording heads 1 for printing the respective inks may be provided in parallel, for example, in the sub-scanning direction of printing.

The feature of this embodiment is that a filtering means 20a is provided in the middle of an ink circulation path 14a for supplying the ink 6 to the ink jet recording head 1. Filtration means 20a
For example, a porous member such as a sponge or a member such as filter paper is used. The members used for these filtering means 20a have holes having an inner diameter of about several times the particle size of the colorant particles, so that the dispersed colorant particles can pass through, but the colorant particles have Aggregates are not allowed to pass. Therefore, when the agglomerates of the colorant particles as described above are included in the ink 6, when the ink 6 is sucked from the ink tank 12 by the supply pump 13a, the colorant is dispersed together with the colorant particles dispersed therein. Aggregates of particles are also in the ink circulation path 14.
a. However, the ink circulation path 14a
Since the filtering means 20a is inserted in the middle of the process, it is possible to prevent the aggregate of the colorant particles from being sent to the ink jet head. As a result, since only the dispersed colorant particles are supplied to the ink flow path in the ink jet recording head, clogging in the ink flow path does not occur. Further, by forming the filtering means 20a into a form like a cartridge, even if the filtering ability is reduced, it can be easily replaced.

As described above, according to the present embodiment, it is possible to prevent agglomerates of colorant particles from entering the ink flow path in the ink jet type recording head 1, so that clogging in the ink flow path does not occur. As a result, stable ink ejection can be obtained over a long period of time, and the life of the recording head device can be extended. Further, the maintenance of the printer device can be simplified by forming the filtering means 20a in the form of a cartridge.

Next, a second embodiment of the present invention will be described. FIG. 4 shows one configuration example of an ink jet printer according to the second embodiment. The configuration of the printer device is the same as that of the first embodiment except for the filtering means 20b, so that the description of the overlapping portions will be omitted.

The feature of this embodiment resides in that a filtering means 20b is provided in the middle of an ink circulation path 14b for collecting the ink 6 from the ink jet recording head 1. Filtration means 20
For b, a porous member such as a sponge or a member such as filter paper is used. The members used for these filtering means 20b have holes having an inner diameter of about several times the particle diameter of the colorant particles, so that only the dispersed individual colorant particles can pass through. . Therefore, if the colorant particles in the state of being aggregated at the tip of the ink discharge electrode 3 are collected as they are, or if dust or paper dust enters the ink 6 from the collection port, the dispersed color is These foreign substances along with the agent particles also pass through the ink circulation path 14b. However, since the filtering means 20b is inserted in the middle of the ink circulation path 14b, foreign substances such as aggregates of colorant particles and dust can be prevented from being sent into the ink tank 12. As a result, only the dispersed colorant particles are collected in the ink tank 12, so that the ink 6 can be reused without causing clogging in the ink flow path in the ink jet recording head 1.

As described above, according to the present embodiment, the ink tank 12
It is possible to prevent foreign substances such as aggregates of colorant particles and dust from being mixed into the ink 6 in the inside. As a result, clogging of the ink flow path in the ink jet type recording head is prevented, and stable ink ejection over a long period of time can be realized.

Next, a third embodiment of the present invention will be described. FIG. 5 shows one configuration example of the ink jet recording apparatus according to the second embodiment. The configuration of the ink jet recording apparatus is the first except for the periphery of the filtering means 20c.
Since the embodiment is the same as that of the first embodiment, the description of the overlapping parts will be omitted.

The present embodiment is characterized in that, in addition to a normal ink circulation system, an ink filtration system comprising pumps 13c and 13d, ink circulation paths 14c and 14d, filtration means 20c, and a controller 30 for controlling these. It has a circulatory system. In FIG. 5, during the printing operation, only the circulation system that passes through the ink circulation paths 14a and 14b is operating, and the above-described circulation system for filtration is not operating. When the ink 6 is filtered, the controller 30
A signal for operating the pumps 13c and 13d is transmitted from the controller, and the circulating system for filtration is operated. The procedure for controlling the operation of the circulation system for filtration will be described below.

FIG. 6 is a block diagram showing the circuit configuration of the controller 30 as a block diagram. The central processing unit 301 is an integrated circuit device that controls peripheral circuits according to a certain program such as a microcomputer or a PLD. The data unit 302 sends data such as date and time back to the central processing unit 301 in response to a request from the central processing unit 301. The counter section 303 is connected to the drive circuit 11 for controlling ink ejection as shown in FIG. The drive circuit 11 transmits a single pulse signal to the controller every time one page is printed. On the controller 30 side, the pulse signal is received by the counter section, and the number of times of printing one page at the time of turning on the power once is integrated. The memory unit 304 is a nonvolatile memory, and is an electrically rewritable element such as an EEPROM. The memory unit 304 records the date of last use and the total number of times one page has been printed so far. In such a circuit configuration, the controller 30 executes the control sequence shown in the flowchart of FIG. When the power switch of the printer is turned on,
The central processing unit 301 in FIG. 6 loads data stored in the memory unit 304. The central processing unit 301 compares the integrated number of printings N1 up to that point with the specified number of printings N0 that requires ink filtration. N1 ≧ N
In the case of 0, a signal for operating the pumps 13c and 13d is transmitted to activate the circulating system for filtration. Also,
If N1 <N0, the number of days D1 elapsed from the previous use date is calculated using the previous date and the date at that time. Then, the prescribed number of elapsed days D0 at which ink filtration is required
Compare with When D1 ≧ D0, a signal for operating the pumps 13c and 13d is transmitted to start the circulating system for filtration. When D1 <D0, the state shifts to the printing state. After that, the number of prints N2 integrated by the counter unit 303 at certain time intervals is stored in the central processing unit 30.
1 and added to the total number of times N1 so far, and this is compared again with the specified number of times N0 that requires ink filtration as the total number of prints N1 to determine whether or not the ink filtration operation is necessary. . Here, when the integration number N2 is loaded from the counter unit 303 to the central processing unit 301,
The count number in the counter unit 303 is reset. This operation is repeated until it is detected that the power switch of the ink jet recording apparatus is turned off. When it is detected that the power switch of the ink jet recording apparatus is turned off, the controller 30 stores data such as the accumulated number of times of printing and date in the central processing unit 301 in the central processing unit 301 before the power supply to the circuit is cut off. The data is rewritten with the previous data stored in the unit 304. Even with the method of filtering ink with the minimum necessary frequency by the ink filtering means described above,
As long as clogging due to aggregates of colorant particles and foreign matter does not occur in the ink flow path in the ink jet recording head 1, it is possible to delay the deterioration of the filtration ability of the filtration means 20 used for ink filtration and to extend the life. Can be

Therefore, according to the present embodiment, the ink is filtered at the minimum necessary frequency within a range where clogging due to aggregates of colorant particles or foreign matter does not occur in the ink flow path. Deterioration of performance can be delayed to extend the life. As a result, the frequency of replacement due to the deterioration of the filtering means 20 can be reduced, so that the simplicity of maintenance can be further improved.

[0022]

As described above, according to the present invention, it is possible to prevent the aggregates of the colorant particles from entering the ink flow path in the ink jet type recording head 1.
Clogging in the ink flow path does not occur. As a result, stable ink ejection can be obtained over a long period of time, and the life of the recording head device can be extended. Further, the maintenance of the printer device can be simplified by forming the filtering means 20a in the form of a cartridge.

[Brief description of the drawings]

FIG. 1 is a view showing one configuration example of an ink jet recording apparatus according to a first embodiment of the present invention.

FIG. 2 is a top view of a basic structure of an ink jet recording head according to the present invention.

FIG. 3 is a perspective view showing a three-dimensional structure near an ink discharge electrode in an ink jet recording head.

FIG. 4 is a diagram illustrating a configuration example of an ink jet recording apparatus according to a second embodiment of the present invention.

FIG. 5 is a diagram illustrating a configuration example of an inkjet recording apparatus according to a third embodiment of the present invention.

FIG. 6 is a block diagram showing an internal configuration of a controller used in an ink jet recording apparatus according to a third embodiment of the present invention.

FIG. 7 is a flowchart illustrating a control sequence of a controller used in an inkjet recording apparatus according to a third embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Ink jet recording head, 2 ... Counter electrode, 3
... Electrode for ink discharge, 4 ... Partition member, 5 ... Recording medium, 6
... Ink, 7 ... Shield electrode, 8 ... Bias power supply, 9 ...
Pulse power supply, 11 drive circuit, 12 ink tank, 1
3a, 13b, 13c, 13d ... pumps, 14a, 14
b, 14c, 14d: ink circulation path, 15: ink introduction path, 17: insulating substrate, 18: insulating thin film member, 20
a, 20b, 20c: filtration means, 30: controller, 3
01: central processing unit, 302: data generation unit, 303: counter unit, 304: memory unit.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Mamoru Okano 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture F-term in Hitachi Research Laboratory, Hitachi Ltd. 2C056 EA14 EA26 KB16 KB26 2C057 AF72 AG21 AH07 BD06

Claims (4)

[Claims] 1. An ink jet recording head having a plurality of ink discharging electrodes arranged in parallel on an insulating substrate via an insulating thin film member, an ink tank for storing ink, and an ink circulating unit for circulating the ink A plurality of pulse power supplies connected to the individual ink discharge electrodes; a bias power supply connected to the plurality of ink discharge electrodes via a common wiring; and a plurality of pulse power supplies facing the plurality of ink discharge electrodes. An ink-jet recording apparatus, comprising: a counter electrode disposed; and the ink circulating unit having an ink filtering unit. 2. The ink jet recording apparatus according to claim 1, wherein said ink filtering means is provided in an ink circulation path for supplying ink from said ink tank to said ink jet recording head. 3. An ink jet recording apparatus according to claim 1, wherein said ink filtering means is provided in an ink circulation path for recovering said ink from said ink jet recording head to said ink tank. 4. An ink jet recording apparatus according to claim 1, wherein said ink filtering means is a detachable cartridge type.