JP2000255066A - Ink jet recorder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower the ink ejection voltage while stabilizing the flying characteristics of ink by arranging an ink ejecting part such that a dielectric ejection member is assisted by an assisting member, a coating member is arranged to hold the ejection member between and an ejection electrode is wrapped in the coating member. SOLUTION: An ink ejection cell 3 comprises ejection electrodes 31 arranged on the opposite sides of a dielectric ejection member 32. The ejection member 32 is formed on an assisting member 19 of polyimide, or the like, by production process of ink jet recording head while projecting from the end face of an insulating substrate 17 in order to enhance the field at the forward end thereof and the ejection electrodes 31 is wrapped in the coating member 4. More specifically, the gap between the adjacent ink ejection cells 3 is filled with the coating member 4. According to the structure, the ink ejection voltage can be lowered while stabilizing the flying characteristics of ink.

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 ink droplets for each recording dot on the recording medium is constant, in printing a color image, the density between recording dots is spatially changed to generate a pseudo The gradation expression is performed. 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. However, in the above two methods, since the ejection amount of the ink droplet is constant, it is extremely difficult to express the gradation by the 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.

In the actual printing operation, it is necessary to control the above-mentioned pulse-like high-voltage on / off operation in a very fast cycle, for example, a printing cycle of 4 to 10 (kHz). Further, since such an operation must be controlled in parallel for all the ink ejection electrodes arranged in parallel, a dedicated IC for high voltage driving is used for the pulse voltage control circuit. . However, when the magnitude of the voltage to be controlled becomes 300 (V) or more, the price of the high-voltage driving IC rapidly increases, so that there is a problem that the price of the printer body also becomes expensive. As an invention for solving such a problem, Japanese Unexamined Patent Publication No. 9-234870 discloses a grid having a hole-shaped slit through which an ink droplet passes between an ink discharge electrode and a counter electrode placed at a position opposite thereto. A configuration for disposing electrodes is disclosed. Also, Japanese Patent Application Laid-Open No. H10-12879 discloses a method for stabilizing the flight of ink in a similar configuration. In Japanese Patent Application Laid-Open No. H10-12879, a plurality of ink ejection electrodes are arranged in parallel at a fixed arrangement pitch in an ink jet recording head. A flat counter electrode is arranged at a position along the longitudinal direction at a certain distance from the tip of the ink discharge electrode, and a recording medium is placed on the counter electrode. A grid electrode having a plurality of slits is placed between the ink ejection electrode and the counter electrode. The grid electrode is grounded (0 V). Here, the second electrode is
Is connected so that the potential of the counter electrode becomes lower than the potential of the grid electrode. As a result, the ink droplets ejected from the ink ejection electrode move by receiving a force by the electric field between the grid electrode and the counter electrode, so that the flight is stabilized.

[0005]

By the way, in each of the above two patent publications, a conductor or a conductor coated with a thin film of an insulating material is used as an ink discharge portion in each case, but a high voltage is applied. Ink ejection electrode 2
When the ink 0 and the ink 6 come into direct contact, the surface of the ink discharge electrode 20 is corroded or deteriorated by a chemical reaction,
The shape of the discharge unit may change. Therefore, there is a problem that the dot diameter of the ejected ink changes. On the other hand, when the ink discharging electrode 20 is coated with an insulating thin film, in the configuration of Japanese Patent Application Laid-Open No. H10-128979, there is a potential difference between the ink discharging electrode 20 and the grid electrode due to the bias voltage V _b1 . The ink discharge electrode 20
The insulating thin film is always subjected to stress by the electric field at the tip of the substrate. In such a configuration, there is a possibility that deterioration over time in long-term use may progress quickly,
There is a problem that the life of the ink discharge unit cannot be expected much.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and aims at lowering the ink discharge voltage and stabilizing the ink flying characteristics, and at the same time, ensures stable ink discharge over a long period with little deterioration of the ink discharge portion. It is intended to be realized.

[0007]

According to the present invention, there is provided an ink jet recording head having a plurality of ink discharge sections for discharging an ink containing a pigment in a solvent, and an ink tank for storing the ink. A power supply unit for applying the ink to an ink discharge unit to discharge the ink;
A counter electrode disposed to face the ink discharge unit, and a grid electrode disposed between the ink discharge unit and the counter electrode, wherein the ink discharge unit includes a discharge member that is a dielectric; A configuration including an auxiliary member for assisting the discharge member, a covering member disposed to sandwich the discharge member, and a discharge electrode included in the covering member and to which a voltage is applied from the power supply unit. I have.

Since the ejection member is a dielectric, corrosion and deterioration of the surface of the ejection member due to a chemical reaction with ink can be suppressed, and deformation of the tip of the ejection member can be reduced even when used for a long period of time.

Further, according to the present invention, since the grid electrode has a switch section for selecting between grounding and connection to the power supply section, it is possible to prevent unnecessary ink ejection during a period during which ink does not fly, such as a pause time. .

[0010]

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

FIG. 5 shows one configuration example of a printer using the ink jet recording head 1 according to the present invention. Ink 6 used in the printer according to the present invention
Is a dispersion of charged coloring agent particles in an organic solvent. Pump 6 for supplying ink 6 from ink tank 12
The ink is sucked by 3a and supplied to the recording head 1 through the ink circulation path 14a. The ink 6 is supplied to an ink introduction path 15 between the ink circulation path 14a and the recording head 1.
Through the recording head 1, and flows through the recording head 1 from top to bottom in the drawing. In the ink jet recording head 1, a plurality of ink discharge cells 3 are arranged in parallel in the main scanning direction of printing (the direction of arrow A in the drawing) at a constant arrangement pitch. Each ink discharge cell 3 is connected to an individual pulse power supply 9 and a common bias power supply 8. Further, a control signal from the drive circuit 11 is connected to the pulse power supply 9, and the control signal is transmitted independently to each pulse power supply 9 in accordance with print data transmitted from a personal computer or the like. Thus, application of a voltage to the ink discharge cells 3 is controlled. From the ink discharge cell 3 to which the voltage is applied from the pulse power supply 9, charged colorant particles dispersed in the ink 6 by an electric field near the tip of the ink discharge cell 3 (not explicitly shown in the drawing) ) Are aggregated, and the aggregated colorant particles are discharged toward the grounded counter electrode 2. 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 for 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. Just be moved. 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 colorant particles which are not consumed in the ink discharge process and remain at the front end of the ink discharge cell 3 flow from the front end of the ink discharge cell 3 to the back surface of the recording head 1 together with the circulating flow. The ink 6 that has flowed to the back surface of the recording head 1 is sucked from an ink outlet passage (not shown) by a collection pump 13b and flows into an ink circulation passage 14b. The ink circulation path 14b
Is returned to the ink tank 12 and used again for printing. The above procedure is for printing only one color. However, in the case of multicolor printing such as a color image, each ink of yellow (Y), magenta (M), cyan (C) and black (K) is used. For example, a printer configuration in which a plurality of inkjet recording heads 1 for printing are provided in parallel in the sub-scanning direction of printing may be used.

FIG. 2A is a top view showing the basic structure of an ink jet recording head 1 and a recording apparatus using the ink jet recording head 1 according to the first embodiment. The inkjet recording head 1 includes:
As shown in FIG. 2A, the ink discharge cells 3
The print head is arranged in parallel in the main scanning direction of printing at intervals of 0 (μm). FIG. 2B is a perspective view of one ink discharge cell 3 in the ink jet recording head 1 according to the first embodiment. The ink ejection cell 3 includes an ejection member 32 and ejection electrodes 31 arranged on both sides of the ejection member 32. For example, 2 is provided between the discharge electrode 31 and the discharge member 32.
A gap of 0 (μm) is formed, and this gap becomes an ink flow path. The ink flow path sucks up the ink 6 supplied into the recording head 1 through the ink circulation path 14a shown in FIG. 5 toward the tip of the ejection member 32 by the capillary phenomenon, so that the ink 6 reaches the tip of the ejection member 32. It is always wet. The ink discharge cells 3 are formed on one insulating substrate 17 covered with an insulating thin film member 18. The insulating substrate 17 is made of, for example, glass, and the insulating thin film member 18 is made of, for example, an organic thin film such as polyimide. Here, for example, high relative permittivity such as glass (ε _s = about 7 to 10)
For example, low dielectric constant, such as a polyimide substrate (epsilon _s
(Approximately 3.4) By coating with a thin film, it is possible to prevent the concentration of the electric field at the tip of the ejection member 32 from being reduced when the ink in the aggregated state is ejected. The ejection member 32 is formed on the auxiliary member 19 in a process of manufacturing the inkjet recording head 1. The auxiliary member 19 is made of, for example, polyimide. The material of the ejection member 32 is also a dielectric material. Like the auxiliary member, an organic material such as polyimide may be used, or an inorganic material such as silicon nitride (Si ₃ N ₄ ) may be used. good. The tip of the discharge member 32 projects from the end face of the insulating substrate 17 by, for example, about 50 to 200 (μm) so as to strengthen the electric field at the tip. On the other hand, the discharge electrode 31 has a structure included in the covering member 4. As shown in FIG. 2A, one covering member 4 includes one ejection electrode 31 belonging to an adjacent ink ejection cell 3 at a time. In other words, the space between the adjacent ink discharge cells 3 is filled with the covering member 4. The strength of the electric field at the tip of the ejection electrode 31 is about 1 to 2 (MV / m), which is almost the same as that of the tip of the ejection member 32. Therefore, when the ink 6 is filled around the ejection electrode 31, the ink 6 may be ejected from the tip of the ejection electrode 31. Therefore, the ink 6 is prevented from penetrating by filling the periphery of the discharge electrode 31 with the covering member 4. In FIG. 2A, the discharge member 32 extends along the longitudinal direction of the discharge member 32.
The counter electrode 2 at a position about 1 (mm) away from the tip of
Is provided, and a recording medium 5 is provided on the counter electrode 2.
Is placed. The opposing electrode 2 is connected to a power supply 10 for accelerating a droplet for applying a constant bias voltage _-Vacc for a reason described later. Further, a grid electrode 7 having a plurality of slits 71 is provided between the recording head 1 and the counter electrode 2, and the grid electrode 7 is grounded (0 V). FIG. 3 shows a grid electrode 7.
FIG. 2 is a perspective view illustrating an arrangement relationship between the recording head and the recording head. The slit 71 is provided on the grid electrode 7 on the ink discharge cell 3.
Are provided so as to correspond one-to-one with the same array pitch. The grid electrode 7 is, for example, 50-100 (μ)
m) is a metal plate having a thickness of m, and is held by the support member 16 together with the recording head 1 so that the distance between the recording head 1 and the grid electrode 7 is kept constant.
The slit 71 is formed in the grid electrode 7 by a method such as electric discharge machining or etching. Alternatively, in the method of forming the slit 71 by electroforming, there is no overhang (whiskers due to etching) at the edge of the hole, and processing with higher precision is possible. In FIG. 5, a recording medium 5 is sent to the front of the recording head 1 on a counter electrode 2 by a paper feed mechanism (not shown), and the ink 6 discharged from the recording head 1 is printed. As described above, the pair of discharge electrodes 31 in the plurality of ink discharge cells 3 are provided with a common bias power supply 8 for assisting the discharge of the ink 6 and a pulse power supply used for discharging the ink 6. 9 is connected. When printing on the recording medium 5 in the present invention, a printing signal is given from the drive circuit 11 to the pulse power supply 9 connected to the ink discharge cell 3 corresponding to the position of the dot to be printed in one line.
As a result, the ejection members 3 in the ink ejection cells 3 connected to all of the pulse power sources 9 to which the print signal has been given.
The ink 6 in which the independently charged colorant particles are simultaneously concentrated is discharged from the two tips and printed on the recording medium 5.

A feature of the present invention is that, in a configuration in which a grid electrode grounded (0 V) is inserted between an ink jet recording head and a counter electrode to which a negative bias voltage is applied, the ink jet recording head is a pair. In this structure, ink discharge cells composed of discharge electrodes and a dielectric discharge member sandwiched between these discharge electrodes are arranged at predetermined intervals in the main scanning direction on an insulating substrate. is there. Specifically, in the above-described configuration, not only the pulse voltage but also the bias voltage can be reduced, and the droplets of the ink 6 fly through the grid electrode and reach the recording medium on the counter electrode. In addition to maintaining the stability of the tip, there is no deformation of the tip due to aging degradation such as peeling of the coating, and stable for a long time compared to the case where the discharge part is a conductor coated with an insulating thin film Thus, the discharged ink is obtained. The reason will be described in detail below.

FIG. 4A is a configuration diagram of an experimental apparatus for measuring an ink discharge starting voltage when a grid electrode is used. Here, one needle electrode 25 was used as a substitute for the inkjet recording head 1 having a multi-head configuration. The needle electrode 25 has an outer diameter of 460 (μm) and an inner diameter of 25.
It has a cylindrical shape of 0 (μm), and the ink 6 is supplied from the ink tank 12 into the tube of the needle electrode 25.
Further, a first high voltage source 23 is connected to the needle electrode 25, and a voltage V _ej for discharging the ink 6 from the tip of the needle electrode 25 is applied. On the other hand, a second high voltage source 24 is connected to the grid electrode 7, and the ink 6
A voltage V _grid for facilitating the discharge is applied. In this experiment, the voltage applied from the first high voltage source 23 to the needle electrode 25 was gradually increased from 0 (V) to ground (0
V) The applied voltage value of the first high-voltage source 23 when the formation of dots by the ink 6 on the recording medium 5 on the counter electrode 2 was started was defined as an ink ejection start voltage _Vej . At this time, the distance D _grid between the needle electrode 25 and the grid electrode 7, the voltage V _grid applied to the grid electrode 7, and the diameter W of the slit 71
_When three parameters of the _grid were changed, the ink discharge start voltage V _ej was measured. FIG. 4 (b)
7 is a graph in which the measurement results of the ink discharge start voltage V _ej when the above-described parameters related to the grid electrode 7 are changed are plotted against the distance D _grid between the grid electrode and the discharge point. Here, the circle (●) and the triangle (black triangle) indicate that the diameter W _{grid of the} slit 71 is 900 (μm) and 60, respectively.
This is the case of 0 (μm). Further, the measurement results when the applied voltage V _grid to the grid electrode 7 is set to 0 (V), 400 (V), and 900 (V) are shown in the graph. In the graph, a horizontal line near 1.4 (kV) indicates the value of the ink discharge start voltage when the grid electrode 7 is not provided. It can be seen from the graph of FIG. 4B that the _{smaller the} distance D _grid between the grid electrode and the discharge point, the lower the ink discharge start voltage _Vej . Further, it can be seen that as the voltage V _grid applied to the grid electrode 7 becomes lower, the ink ejection start voltage V _ej becomes lower. These results are because the potential distribution around the tip of the needle electrode 25 changes depending on the potential of the grid electrode 7, and the potential gradient at the tip of the needle electrode 25, that is, the electric field is affected. And the needle electrode 25
This indicates that the closer the distance between the grid electrode 7 and the grid electrode 7, the stronger the influence. Therefore, as the distance D _grid between the grid electrode and the discharge point is smaller and the voltage V _grid applied to the grid electrode 7 is lower, the electric field at the tip of the needle electrode 25 is strengthened. Indicates that you are starting. Also, the diameter W _{grid of the} slit 71 is 90
A comparison between the case of 0 (μm) (●) and the case of 600 (μm) (black triangle) shows that the voltage V _grid applied to the grid electrode 7 is
It can be seen that the ink ejection start voltage V _ej is lower in the case of W _grid = 600 (μm) (black triangle) than in the case of W _grid = 900 (μm) (●). This indicates that the electric field is strengthened because the relative distance between the grid electrode 7 and the tip of the needle electrode 25 is reduced by reducing the diameter W _grid of the slit 71.
The above measurement results are obtained when the discharge portion of the ink 6 is a conductor. However, it is considered that similar results can be obtained for the ink discharge cells 3 used in the present embodiment. Therefore, in this embodiment, the voltage applied to the discharge electrode 31 in the ink discharge cell 3 for discharging the ink 6 is about 800 by grounding the grid electrode 7 (0 V) as shown in FIG. The voltage can be reduced up to 900 (V). This is illustrated, for example, in FIG.
Pulse such as pulse power source 9 in (a) Voltage V _p =
When driving at 200 (V), which means that the bias voltage of the bias power source 8 may be a V _B = 600~700 (V). As a specific form of the bias power supply 8, a power supply module is used. However, there is an advantage that the power supply module for generating the above-described voltage is smaller and lighter than one (1 kV) or more.

When the grid electrode 7 is also grounded (0 V) with the counter electrode 2 grounded (0 V), no electric field exists between the grid electrode 7 and the counter electrode 2. Therefore, after the droplet of the ink 6 passes through the grid electrode 7, it moves by inertia until it reaches the recording medium 5 on the counter electrode 2. When the droplet of the ink 6 moves by inertia, the velocity of the droplet gradually decreases due to air resistance. In actual printing, droplets of the ink 6 are often continuously ejected from the ink ejection cell 3 at short intervals. The speed of the ink drop is attenuated, and the distance between the subsequent ink drop is reduced. As a result, there is a possibility that the droplets of the ink 6 may interfere with each other, or in the worst case, the droplets may be combined. Such a problem arises as the distance between the ink discharge cell 3 and the counter electrode increases.
The probability of occurrence is high. Therefore, as shown in FIG. 2A, a power supply 10 for accelerating the droplet is connected so that a negative bias voltage is applied to the counter electrode 2. FIG. 1 is a diagram showing how the potential changes from the tip of the ejection member 32 in the ink ejection cell 3 to the counter electrode 2 in the above-described configuration. Since an electric field is generated between the grid electrode 7 and the counter electrode 2 by the power supply 10 for accelerating the droplet, the droplet of the ink 6 undergoes acceleration motion due to the electric field. Therefore, coupling and interference between droplets can be prevented. For example, if the distance between the ejection member 32 and the grid electrode 7 is 100 (μm) and the thickness of the grid electrode 7 is 100 (μm), the distance between the grid electrode 7 and the counter electrode 2 is 800 (μm). When a specific value of the voltage −V _acc applied to the counter electrode 2 is, for example, −80 (V), the strength of the electric field between the grid electrode 7 and the counter electrode 2 is 100 (kV /
m). As an electric field for accelerating the droplet of the ink 6,
This size is sufficient.

On the other hand, in the prior art, a metal coated with an insulating thin film is used for the discharge portion of the ink 6, whereas in the present embodiment, the dielectric of the bulk member is formed in the discharge portion of the ink 6 as described above. Used. Where the discharge portion of the ink 6 is a metal coated with an insulating thin film, when the discharge portion of the ink 6 is a dielectric of a bulk member, the colorant particles in the ink 6 under a high electric field The possibility that problems such as deterioration and corrosion of the surface of the ejection member due to the chemical reaction of the above will occur is extremely low. Therefore, the occurrence of the problem that the shape of the tip of the ejection member is deformed due to the change in diameter can be extremely suppressed, and the reliability of the recording head is enhanced.

As described above, according to this embodiment, not only the pulse voltage for ink discharge but also the bias voltage can be reduced, so that an inexpensive high-voltage drive IC can be used for the drive circuit for pulse voltage control. And
Power supply module for bias voltage
Lightweight ones can be used. As a result, a low-priced, small-sized and lightweight printer can be provided. In addition, the configuration in which a negative bias voltage is applied to the opposing electrode 2 causes ink droplets flying from the ejection member 32 toward the opposing electrode 2 to always undergo acceleration motion due to an electric field. Thus, the flying state of the droplets of the ink 6 can be stabilized. Furthermore, by using a bulk member dielectric for the ink 6 discharge section, the ink 6 under a high electric field can be used.
The possibility that problems such as deterioration or corrosion of the surface of the ejection member due to a chemical reaction with the colorant particles in the inside can be extremely reduced. As a result, the life of the recording head device can be prolonged, and it is easy to maintain stable ink ejection characteristics of the recording head even when used for a long time.

Next, a second embodiment of the present invention will be described. FIG. 6 is a top view showing the basic structure of an ink jet recording head 1 according to the second embodiment and a recording apparatus using the ink jet recording head 1. The ink jet recording head 1 has a configuration in which the ink discharge cells 3 are arranged in parallel in the main scanning direction of printing on an insulating substrate (not explicitly shown in the drawing) at intervals of, for example, 250 (μm). ing. The ink ejection cell 3 includes an ejection member 32 and ejection electrodes 31 arranged on both sides of the ejection member 32. Between the discharge electrode 31 and the discharge member 32, for example, 20 (μ)
A gap m) is formed, and this gap becomes an ink flow path. The ink flow path is formed by the recording head 1 due to a capillary phenomenon.
The ink 6 supplied inside is sucked up toward the tip of the ejection member 32 so that the ink 6 always wets the tip of the ejection member 32. The material of the ejection member 32 is a dielectric material. For example, an organic material such as polyimide may be used, or an inorganic material such as silicon nitride (Si ₃ N ₄ ) may be used. The tip of the ejection member 32 projects from the end face of the insulating substrate by about 50 to 200 (μm), for example, so as to strengthen the electric field at the tip. On the other hand, the discharge electrode 31 has a structure included in the covering member 4. As shown in FIG. 6, one covering member 4 is formed by a discharge electrode 3 belonging to an adjacent ink discharge cell 3.
1 is included one by one. In other words, the space between the adjacent ink discharge cells 3 is filled with the covering member 4. The strength of the electric field at the tip of the ejection electrode 31 is about 1 to 2 (MV / m), which is almost the same as that of the tip of the ejection member 32. Therefore, when the ink 6 is filled around the ejection electrode 31, the ink 6 may be ejected from the tip of the ejection electrode 31. Therefore, by filling the periphery of the discharge electrode 31 with the covering member 4, the ink 6 is filled.
To prevent penetration. In FIG. 6, a counter electrode 2 is provided at a position, for example, about 1 (mm) away from the tip of the discharge member 32 along the longitudinal direction of the discharge member 32, and a recording medium is provided on the counter electrode 2. 5 is placed. The opposite electrode 2 has a constant bias voltage -V _acc
Is connected to the power supply 10 for applying a droplet. Further, a grid electrode 7 having a plurality of slits 71 is provided between the recording head 1 and the counter electrode 2. The slits 71 are provided on the grid electrode 7 at the same arrangement pitch as the ink discharge cells 3 so as to correspond one-to-one. The grid electrode 7 is, for example, 50 to
It is a metal plate having a thickness of 100 (μm) and is held together with the recording head 1 by a support member not shown in the drawing, so that the distance between the recording head 1 and the grid electrode 7 is kept constant. I have. The slit 71 is formed in the grid electrode 7 by a method such as electric discharge machining or etching. Or electroforming (electroforming)
According to the method of forming the slits 71, there is no overhang (whiskers due to etching) at the edges of the holes, and processing with higher precision can be performed.

This embodiment is characterized in that a pair of ejection electrodes 31
An ink jet recording head 1 in which ink discharge cells 3 each composed of a discharge member 32 of a dielectric material sandwiched between these discharge electrodes 31 are arranged in a main scanning direction at predetermined intervals on an insulating substrate. applying the included configuration the grid electrode 7 in the negative between the opposed electrodes 2 a bias voltage is applied to said grid electrode 7 the ejection electrode 31 in a state of being grounded (0V) to a bias voltage V _B and Switching means 21 for switching between a state of connection to the bias power supply 8 and a state of connection. Hereinafter, a printing operation using the switching means 21 will be described. FIG. 7 is a diagram illustrating a state of a voltage applied to the discharge electrode 31 and the grid electrode 7 with the passage of time.
Here, the voltage applied to the ejection electrode 31 means the recording head 1
2 illustrates data on one of the ink ejection cells 3. The bias voltage _Vb is always applied to the ejection electrode 31 by the bias power supply 8 not only during the printing period but also during the pause period. Once in print period, it said the ejection electrode 31 is pulsed voltage V _p which is pulse width modulated at each printing position by the pulse power supply 9 is superimposed. On the other hand, during the standby period or the idle period, the grid electrode 7
The switching means 21 is connected to the bias power supply 8 to apply the bias voltage _Vb . Then, when the recording head 1 enters the printing operation, as soon as a certain ejection preparation period before the pulse voltage V _p starts to be superimposed to the ejection electrode 31, the grid electrode 7 by the switching means 21
Is grounded (0 V). FIG. 8 is a diagram showing how the potential changes from the tip of the ejection member 32 in the ink ejection cell 3 to the counter electrode 2 in the configuration shown in FIG.
In the graph showing the change in the potential with respect to the position x, the solid line represents the potential during the printing operation, and the dashed line represents the potential during the idle period. During the printing operation,
As in the first embodiment, the pulse voltage _Vp and the bias voltage _Vb can be reduced by setting the grid electrode 7 to the ground (0 V) state. In addition, the ground (0
V) and the negative bias voltage −V _acc
An electric field is generated between the counter electrodes 2 to which the ink is applied, so that the droplets of the ink 6 are accelerated by the electric field while the droplets of the ink 6 fly between the grid electrode 7 and the counter electrode 2. As a result, the flight characteristics become stable. On the other hand, when the standby period or the printing of one page ends and the pause period starts,
The switching means 21 connects the grid electrode 7 to the bias power supply 8 which is common to the discharge electrode 31 and applies the bias voltage _Vb . As a result, potential near the center of the slit 71, V _b and substantially equal to or, alternatively, the degree number 10 (V) lower than V _b. Therefore, as shown in FIG. 8, the discharge member 32 and the grid electrode 7 are at rest.
And the electric field at the tip of the discharge member 32 becomes almost zero. Therefore, even when disturbance or the like acts, the ink 6 is not ejected from the tip of the ejection member 32 during the standby period or the halt period. Further, the electric field around the ejection member 32 is also substantially equal to 0, so that the colorant particles in the ink 6 are discharged from the ejection member 32.
The electrostatic repulsive force between the colorant particles is stronger than the force for concentrating at the tip. Therefore, since the colorant particles are dispersed in the ink 6, the rate of occurrence of fixation of the colorant particles to the tip of the ejection member 32 is extremely low. By the way, when the printing operation is started from the standby period or the pause period, the switching means 2 is used.
1, the grid electrode 7 is again grounded (0 V). At this time, in order to print dots having a sufficient image density on the recording medium 5, the colorant particles need to be concentrated at the tip of the discharge member 32. However, it takes time to shift from a state where the colorant particles are dispersed to a state where the colorant particles are concentrated. Therefore, as shown in FIG. 7, the timing for switching the grid electrode 7 to the grounded (0 V) state is advanced by a fixed time from the start of the printing operation,
Before the start of the printing operation, an electric field is generated at the tip of the ejection member 32 and around it. Since it is possible to shift to a state where the colorant particles are concentrated at the tip of the ejection member 32 during the ejection preparation period, it is possible to form dots having sufficient image density on the recording medium 5 from the first printing. it can.

The ink jet recording head 1 according to the present embodiment can be used in a printer having the configuration shown in FIG. A recording medium 5 is sent to the front of the recording head 1 on the counter electrode 2 by a paper feeding mechanism (not shown), and the ink 6 discharged from the recording head 1 is printed. As described above, a common bias power supply 8 for assisting the discharge of the ink 6 and a pulse power supply 9 used for discharging the ink 6 are provided to the pair of discharge electrodes 31 in the plurality of ink discharge cells 3. Is connected. When printing on the recording medium 5 according to the present invention, the pulse power supply 9 connected to the ink discharge cell 3 corresponding to the position of the dot to be printed in one line.
Is supplied with a print signal from the drive circuit 11. as a result,
The ink 6 in which the independently charged concentrated colorant particles are simultaneously ejected from the tip of the ejection member 32 in the ink ejection cell 3 connected to all the pulse power supplies 9 to which the print signal is given, is recorded. It is printed on the medium 5.

As described above, according to the present embodiment, not only the voltage of the bias power supply but also the voltage of the pulse power supply can be reduced, and the stability of the flight characteristics of the ink 6 droplets between the grid electrode 7 and the counter electrode 2 can be improved. . In addition, since ink is not ejected due to disturbance or the like during the suspension period, erroneous printing can be prevented. At the same time, by suppressing the rate of occurrence of colorant particles sticking to the tip of the discharge member 32 during the suspension period, problems such as unstable ink discharge characteristics and clogging are less likely to occur. Further, by providing a discharge preparation period and shifting to a state where the colorant particles in the ink 6 are concentrated before the start of the one-page printing operation, dots having a sufficient image density are formed from the first printing. And high quality images without density unevenness can be printed.

Next, a third embodiment of the present invention will be described. FIG. 9 is a top view showing the basic structure of an ink jet recording head 1 according to the third embodiment and a recording apparatus using the ink jet recording head 1. In the present embodiment, since the configuration is the same as that of the second embodiment except for the structure of the ink jet recording head 1, description other than the structure of the ink jet recording head 1 is omitted. The ink jet recording head 1 has a configuration in which the ink discharge electrodes 20 are arranged in parallel in the main scanning direction of printing on an insulating substrate (not explicitly shown in the drawing) at intervals of, for example, 250 (μm). Has become. A conductor or a conductor whose surface is covered with an insulating thin film is used for the ink ejection electrode 20. The ink discharge electrode 20 has a width of, for example, 100 (μm).
(Μm). The partition member 26 is higher than the ink discharge electrode 20 in the direction perpendicular to the plane of the paper, and the adjacent partition member 2
A space is formed in the space of No. 6, and this space becomes an ink flow path. The ink flow path sucks up the ink 6 supplied into the recording head 1 toward the tip of the ink discharge electrode 20 by capillary action, so that the ink 6 always wets the tip of the ink discharge electrode 20. I have. Also,
The tip of the ink discharge electrode 20 is, for example, 50 to 2 mm from the end face of the insulating substrate so as to strengthen the electric field at the tip.
It protrudes by about 00 (μm).

In the present embodiment, in the structure of the ink jet type recording head 1, the ink ejection electrode 20 is replaced with an ink ejection cell composed of a dielectric ejection member and ejection electrodes arranged on both sides thereof. Is used.
In this case, even when the same voltage is applied to the ink ejection electrode 20 as that of the ejection electrode 31 shown in FIG. 7, a potential gradient similar to that in FIG. 8 can be obtained. In addition, since the configuration of the recording head is simpler than the case of the ink discharge cells, the number of steps in the manufacturing process can be reduced.

Therefore, according to this embodiment, not only the pulse power source but also the bias power source can be reduced in voltage, and the stability of the flight characteristics of the ink 6 droplets between the grid electrode 7 and the counter electrode 2 can be improved. Furthermore, since the number of steps in the manufacturing process of the ink jet recording head can be reduced, the production cost of the recording head can be reduced and the throughput can be improved.

[0025]

As described above, according to the present invention,
Since the bias voltage as well as the pulse voltage can be reduced, an inexpensive high-voltage drive IC can be used for the drive circuit for controlling the pulse voltage, and a low-cost power supply module for the bias voltage can be used. Small and light weight can be used. As a result, it is possible to provide a low-cost, compact and lightweight printer device. Further, the configuration in which a negative bias voltage is applied to the counter electrode 2 can stabilize the flying state of the ink 6 droplets. Furthermore, by using a bulk member dielectric material for the discharge portion of the ink 6, the possibility of causing a problem such as deterioration or corrosion of the discharge member surface due to a chemical reaction with the colorant particles in the ink 6 under a high electric field is extremely low. can do. As a result, the life of the recording head device can be prolonged, and it is easy to maintain stable ink ejection characteristics of the recording head even when used for a long time.

According to the second embodiment of the present invention, it is possible to prevent a printing malfunction during a pause period.
At the same time, the rate of occurrence of the colorant particles sticking to the tip of the discharge member 32 during the suspension period can be suppressed, and problems such as unstable ink discharge characteristics and clogging are less likely to occur.
Further, by providing the ejection preparation period, dots having a sufficient image density can be formed from the first printing, and a high-quality image without density unevenness can be printed.

According to the third embodiment of the present invention, the stress caused by the electric field on the insulating thin film at the tip of the discharge portion is reduced, so that even if the ink discharge portion is a conductor coated with the insulating thin film, the length is long. Life can be extended. Further, since the number of steps in the manufacturing process of the ink jet type recording head can be reduced, the production cost of the recording head can be reduced and the throughput can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a potential gradient between an inkjet recording head and a counter electrode according to a first embodiment of the present invention.

FIG. 2A is a top view of a basic structure of a recording apparatus using an ink jet recording head according to a first embodiment of the present invention, and shows a three-dimensional structure of an ink discharge cell in the ink jet recording head. Perspective view (b).

FIG. 3 is a perspective view showing a three-dimensional arrangement of ink discharge cells and grid electrodes in the ink jet recording head according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a configuration (a) and a measurement result (b) of an experimental apparatus for measuring an ink discharge start voltage when a grid electrode is used.

FIG. 5 is a diagram showing a configuration of a printer using an ink jet recording head according to the present invention.

FIG. 6 is a top view of a basic structure of a recording apparatus using an inkjet recording head according to a second embodiment of the present invention.

FIG. 7 is a view for explaining a change in a state of a voltage applied to an ejection electrode and a grid electrode over time in a second embodiment of the present invention.

FIG. 8 is a diagram showing a potential gradient between an inkjet recording head and a counter electrode according to a second embodiment of the present invention.

FIG. 9 is a top view of a basic structure of a recording apparatus using an inkjet recording head according to a third embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Ink jet recording head, 2 ... Counter electrode, 3
... Ink discharge cell, 4 ... Coating member, 5 ... Recording medium, 6 ...
Ink, 7 grid electrode, 8 bias power supply, 9 pulse power supply, 10 droplet acceleration power supply, 11 drive circuit, 1
2 ... ink tank, 13a, 13b ... pump, 14a,
14b: ink circulation path, 15: ink introduction path, 16: support member, 17: insulating substrate, 18: insulating thin film member, 1
9 Auxiliary member, 20 Ink ejection electrode, 21 Switching means, 23 First high voltage source, 24 Second high voltage source, 25 Needle electrode, 26 Partition wall member, 27 Second Bias power supply, 31 ... Ejection electrode, 32 ... Ejection member, 7
1 ... Slit.

 ────────────────────────────────────────────────── ─── 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. 2C057 AF55 AF65 AF70 AF72 AG22 AG90 AM03 AM18 AR06 BD06

Claims (4)

[Claims] 1. An ink jet recording head having a plurality of ink ejection units for ejecting ink containing a pigment in a solvent, an ink tank for storing the ink, and a power supply unit for applying the ink to the ink ejection unit to eject the ink. And a grid electrode disposed between the ink discharge unit and the counter electrode. The ink discharge unit is a dielectric discharge. Inkjet recording, comprising: a member, an auxiliary member for assisting the ejection member, a covering member disposed to sandwich the ejection member, and an ejection electrode included in the covering member and to which a voltage is applied from the power supply unit. apparatus. 2. The ink jet recording apparatus according to claim 1, wherein said grid electrode is grounded. 3. The ink jet recording apparatus according to claim 1, wherein said grid electrode has a switch section for selecting between grounding and connection to said power supply section. 4. An ink jet recording apparatus according to claim 1, wherein said discharge electrode is a conductor coated with an insulating thin film.