JPH11277747A - Ink-jet recording apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink-jet recording apparatus which can supply a coloring material component in ink stably to an ink drop discharge position and record parts of required different resolutions with image points of respective optimum sizes without changing a driving voltage waveform specially. SOLUTION: A first, a second ink drop discharge parts 6a, 6b of different shapes are provided, which include individual electrodes 9a, 9b formed in the circumference of through holes 8a, 8b on an insulating substrate 7 for acting an electrostatic force to ink, and projecting ink guides 10a, 10b with leading end parts projecting in an ink drop fly direction from the through holes 8a, 8b for guiding ink supplied from an ink chamber 5. The projecting ink guides 10a, 10b have slits 11a, 11b of different widths.

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 a liquid ink in which a coloring material is dispersed,
The present invention relates to an ink jet recording apparatus that performs recording by flying at least a color material component in the ink as an ink droplet on a recording medium.

[0002]

2. Description of the Related Art Pixels (recording dots) are formed by flying liquid ink as small droplets called ink droplets on a recording medium.
A device that records an image by forming a color image has been put to practical use as an inkjet printer. Ink jet printers have the advantage that they are less noisy than printers of other recording methods and do not require processing such as development and fixing, and are receiving attention as plain paper recording technology. Many ink jet printer systems have been proposed so far. In particular, (a) a system in which ink droplets are ejected by the pressure of steam generated by the heat of a heating element (for example, Japanese Patent Publication No.
9429, JP-B-61-59911, etc.) and (b) a method in which ink droplets are caused to fly by a mechanical pressure pulse generated by a piezoelectric element (for example, JP-B-53-1213).
8) are typical.

[0003] A recording head used in an ink jet printer is mounted on a carriage and is perpendicular to the conveying direction of recording paper (sub-scanning direction) (main scanning direction).
A serial scanning type head that performs recording while moving to a computer has been put to practical use. With this serial scanning head, it is difficult to increase the recording speed. Therefore, a printer that uses a line-scanning head whose recording head length is equal to the width of the recording paper to increase the speed has been considered, but such a line-scanning head is realized. This is not easy for the following reasons.

In general, a recording head for ink jet recording is provided with a large number of individual nozzles corresponding to the resolution. However, evaporation or volatilization of a solvent is liable to cause local concentration of ink by nature, which is a problem of the nozzle. It may cause clogging. Furthermore, in the method using the pressure of steam for forming the ink jet, the adhesion of the insoluble substance formed by reacting with the ink thermally or chemically induces nozzle clogging, and the method using the pressure by the piezoelectric element In addition, a complicated structure such as an ink flow path makes it easier to induce clogging. Among inkjet heads, the line scanning head, which requires thousands of nozzles, which is even more than the serial scanning head that uses tens to hundreds of tens of nozzles, has a very high probability. This causes clogging and lacks practical reliability.

[0005] Further, in the method using the pressure of steam, a diameter of 20 μm corresponding to a recording dot having a diameter of 50 μm on recording paper is used.
Since it is difficult to generate ink particles having a particle diameter of μm or less, it is difficult to manufacture a recording head having high resolution. Further, in the method using the pressure generated by the piezoelectric element, since the recording head has a complicated structure, it is difficult to manufacture a high-resolution head due to a problem in processing technology. For this reason, the conventional recording head has a problem that it is difficult to improve the resolution by any method.

In order to solve these problems, a voltage is applied to an electrode array formed by arranging a plurality of individual electrodes formed of a thin film on a substrate, and the ink or the ink contained therein is applied from an ink liquid surface using an electrostatic force. An ink jet recording system in which a color material component flies as an ink droplet has been proposed. Specifically, a method of causing ink droplets to fly by electrostatic attraction (see JP-A-49-62024 and JP-A-56-4467), or a method using an ink containing a charged coloring material component, A method of flying ink droplets by increasing the density of the material (Tokuheihei 7-
No. 502218) has been proposed.

In these systems, the recording head has a slit-shaped nozzle structure which does not require a nozzle for each individual dot, or a nozzleless structure which does not require a partition wall of an ink flow path for each individual dot. Therefore, it is effective for preventing and recovering from clogging which is a major obstacle in realizing the line scanning type recording head. In addition, the latter can stably generate and fly ink droplets having a very small diameter, and thus is suitable for high resolution.

However, in the ink jet recording apparatus of the type in which the color material component is ejected as ink droplets by the above-described electrostatic force, since the recording head is nozzleless, it is effective in preventing clogging. There is a problem that the ink droplet discharge position becomes unstable because the ink can move freely in the main scanning direction on the substrate. In addition, since the ink droplets are ejected with a voltage having the same polarity as the charging polarity of the coloring material and fly to the recording medium, the coloring material component repels and escapes from the electrode position on the recording head, and the coloring material component is repelled. Cannot be stably supplied to the ink droplet ejection position. Accordingly, it is difficult to eject and fly a sufficient amount of ink droplets from a predetermined ejection point in a stable state, and there is a problem that characters and images cannot be recorded well on a recording medium.

[0009] On the other hand, an image generally includes a portion where high resolution is required and a portion where low resolution is sufficient. Therefore,
At the time of recording, it is desirable to be able to change the size of an image point to be recorded according to the required resolution. By recording a plurality of pixel sizes in this manner, it is possible to record a high-definition, high-quality image rich in gradation expression. As one method of changing the size of a recording image point, a method of changing a drive voltage waveform is known (for example, Journal of the Institute of Electrophotography, Vo1.34, No. 3, p. 226, 1995). However, this method has a problem that the configuration of the driving circuit is complicated because the driving voltage waveform is changed, which leads to an increase in cost.

[0010]

As described above, in a conventional ink jet recording apparatus of the type in which a color material component flies as ink droplets by electrostatic force, ink is applied to a recording head substrate in a main scanning direction. The ink droplet ejection position becomes unstable because it can move freely, and the ink droplet is ejected with a voltage of the same polarity as the charging polarity of the coloring material and flies over the recording medium. Since the color material component repels from the position and escapes, and the color material component cannot be stably supplied to the ink droplet ejection position, the ink droplet is ejected by a sufficient amount in a stable state from a predetermined ejection point to fly. It is difficult to record characters and images on a recording medium well.In addition, the method of changing the drive voltage waveform in order to change the size of the recorded pixel corresponding to the required resolution is The configuration of the dynamic circuit is complicated, there is a problem that the price of the device is increased.

According to the present invention, the color material component in the ink can be stably supplied to the leading edge of the individual electrode, which is the discharge position of the ink droplet,
It is another object of the present invention to provide an ink jet recording apparatus capable of recording portions having different required resolutions with image points of optimum sizes without particularly changing a drive voltage waveform.

[0012]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a plurality of ink droplet ejection sections provided individually corresponding to pixels to be formed on a recording medium, and these ink droplet ejection sections. An ink supply means for supplying ink to the ejection unit, wherein an electrostatic force is applied to the ink in which the coloring material component is dispersed in the solvent, so that an ink droplet containing at least the coloring material component is caused to fly toward the recording medium. In this case, the ink droplet ejecting unit includes at least a first ink droplet ejecting unit and a second ink droplet ejecting unit having different shapes. The first and second ink droplet ejection units are:
For example, they are arranged at different positions with respect to the relative movement direction of the recording medium in a direction orthogonal to the relative movement direction.

[0013] Each of the first and second ink droplet ejection sections is provided with an individual electrode for applying electrostatic force to ink formed around the through hole on the insulating substrate having the through hole, and a through hole. Is provided so as to protrude in the ink droplet flight direction from
And a convex ink guide for guiding the ink supplied from the ink supply means.

The first and second ink droplet ejection portions have different shapes of convex ink guides. Specifically, the convex ink guide has (a) a slit formed along the ink droplet flight direction, and the width of the slit is different between the first and second ink droplet ejection portions, or b)
The first and second ink droplet ejection sections are configured such that the widths of the tips protruding from the through holes are different.

In the ink jet recording apparatus according to the present invention, the width of the slit of the convex ink guide at the first and second ink droplet ejection portions and the front end protruding from the through hole of the convex ink guide are provided. By making the width of
The size of the pixel formed by both can be changed, and the portions having different required resolutions can be recorded with the pixel having the optimum size.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a plan view of a line scanning type recording head section in an ink jet recording apparatus according to a first embodiment of the present invention, and FIGS.
It is A 'and BB' sectional drawing.

Referring to FIG. 2, a head block 1 is made of an insulating material such as plastic or ceramics, and receives ink 4 which is recirculated through an ink supply port 2 and an ink discharge port 3 by an ink recirculation mechanism including a pump and an ink flow path (not shown). It has an ink chamber 5 for storing. Ink 4
For example, a positively-chargeable coloring material component is colloidally dispersed together with a charge control agent, a binder, and the like in an insulating solvent having a resistivity of 10 ⁺⁸ Ωcm or more. On the head block 1, there are provided first and second ink droplet ejection sections 6a and 6b individually provided corresponding to image points to be formed on a recording medium described later.

First and second ink droplet discharge units 6a and 6b
As shown in FIGS. 1A and 1B, the main scanning direction x (sub-scanning direction) is set at a different position in the sub-scanning direction y (direction of relative movement of the recording paper), that is, at a position shifted by a predetermined distance in the sub-scanning direction. (A direction orthogonal to the direction y), each of which is configured as described below.

On the head block 1, for example, 25 μm
An insulating substrate 7 made of polyimide having a thickness of about m is provided. The insulating substrate 7 has through holes 8a, 8 at positions corresponding to the first and second ink droplet ejection portions 6a, 6b.
b is formed, and a through hole 8 on the insulating substrate 7 is formed.
Individual electrodes 9a and 9b are formed around a and 8b. The diameter of the through holes 8a and 8b is, for example, 200 to 300.
It is about μmφ. The individual electrodes 9a and 9b are made of copper and have a thickness of about 18 μm, and have an inner diameter substantially equal to the diameter of the through holes 8a and 8b. To the individual electrodes 9a and 9b, lead wires for connection to a head drive circuit described later are connected.

On the other hand, convex ink guides 10a and 10b are provided with their tips protruding from the through holes 8a and 8b in the ink droplet flying direction (the direction perpendicular to the paper surface in FIG. 1, and the upward direction in FIG. 2). Convex ink guides 10a, 10b
Is made of an insulating material such as plastic or ceramics, and has a root portion located in the ink chamber 5 and integrally formed in the ink chamber 5 and fixed to the head block 1 by an appropriate method. The protruding ink guides 10a and 10b have a pointed tip protruding from the through holes 8a and 8b as shown in the figure, and further have a slit 11a extending to the tip in the ink drop flying direction at the center. 11b is formed.

As described above, the first ink droplet discharge portion 6a is composed of the through hole 8a, the individual electrode 9a, and the first convex ink guide 10a. Similarly, the second ink droplet discharge portion 6b is formed of the through hole 8b. It comprises an individual electrode 9b and a second convex ink guide 10b. Here, the first convex ink guide 1
0a and the second ink guide 10b have different shapes as described later, and can form image spots of different sizes.

Hereinafter, first and second convex ink guides 10 will be described.
More specifically, the first convex ink guide 10a has a width of, for example, 160 μm and a thickness of about 60 μm.
The flat plate of m is cut into a triangular or trapezoidal shape, and a slit 11a having a width of 40 μm is formed at the center. The second convex ink guide 10b has basically the same configuration as the first convex ink guide 10a, but has a width of 18 mm.
A flat plate having a thickness of 0 μm and a thickness of 60 μm is cut into a triangular or trapezoidal shape, and a slit 11 b having a width of 60 μm is formed at the center.
Are formed, and the width of the slit 11b is larger than the width of the slit 11a in the first convex ink guide 10a. In addition, the first and second convex ink guides 10a and 10b both have through holes 8a and 8b.
The tip protruding from the position is the ink droplet flying position.

On the other hand, the convex ink guides 10a, 1a of the first and second ink droplet ejection sections 6a, 6b of the recording head section.
0b, a recording paper 21 as a recording medium is disposed as shown in FIG.
And a counter electrode 22 also serving as a platen for guiding the light.

Next, the recording operation of the ink jet recording apparatus according to the present embodiment will be described with reference to FIG. FIG.
FIG. 7 is a diagram for explaining a recording operation by a first ink droplet ejection unit 6a. The same applies to the recording operation by the second ink droplet ejection unit 6b. At the time of recording, the ink 4 filled in the ink chamber 5 shown in FIG. 2 passes through the through-hole 8a, and is further guided by the first convex ink guide 10a to the ink flying position 14 at the tip of the convex ink guide 10a. Supplied. Here, a voltage of, for example, DC 1.5 kV is always applied as a bias to the individual electrode 9 a from a bias voltage source 12 provided in the head drive circuit, and an image signal is supplied from a signal voltage source 13 also provided in the head drive circuit. For example, a pulse voltage of 500 V is superimposed at the time of ON as a signal voltage corresponding to. On the other hand, the counter electrode 22 provided on the back surface of the recording medium 21 has a ground potential (0 V) as shown in FIG.
Is held in.

Now, the individual electrode 9a is turned on (in a state where 500 V is applied) and the bias DC is set to 1.5 kV.
When a total voltage of 2 kV on which a pulse voltage of 00 V is superimposed is applied, an ink droplet 15 centered on a positively charged coloring material component is ejected from an ink droplet flying position 14 at the tip of the convex ink guide 10a. Discharge by electrostatic repulsion. The ejected ink droplet 15 is pulled by the electric field formed by the counter electrode 22, flies toward the recording medium 21, and
Image points are formed on the recording medium 21. An image is recorded on the recording medium 21 by repeating such a series of operations.

Here, the flow path of the ink 4 to the ink droplet flying position 14 is determined by the convex ink guide 10a, and the ink droplet flying position 14 is determined substantially at the center of the convex ink guide 10a. Sometimes, the color material component does not escape in the main scanning direction due to the application of the voltage to the individual electrode 9a.

Further, the ink 4 is conveyed to the independent through hole 8a, and the surface of the convex ink guide 10a projecting substantially perpendicularly from the through hole 8a and the convex ink guide 10a
The ink is supplied to the ink droplet flying position 14 by wetting or surface tension in the slit 11a formed in the center of the ink droplet, so that the size and position of the ink meniscus formed at the ink droplet flying position 15 It is kept stable without being affected by pressure, atmospheric pressure and mechanical vibration. Therefore, the flight of the ink droplet 15 is stabilized, and a good image with a stable density can be recorded on the recording medium 21.

Furthermore, the amount and size of the flying ink droplet 15 depends on the shape of the convex ink guide 10a,
The amount and the size of the ink droplet 15 are small in the first ink droplet ejection unit 6a having the convex ink guide 10a in which the width of the slit 11a is relatively small and the width of the slit 11a is relatively small. Therefore, the size of the image point formed on the recording paper 21 is also relatively small, which is suitable for recording a high resolution portion. On the other hand, as shown in FIGS. 1 and 2, the convex ink guide 10b has a relatively wide slit 11b.
In the second ink droplet ejection section 6b having the above, since the amount and size of the ink droplets are larger, the size of the image spot formed on the recording paper 21 is also larger, which is suitable for recording in a low resolution portion. Become.

As described above, according to the present embodiment, the first and second ink droplet ejection portions 6a and 6b are used to form the convex ink guide 10
By making the widths of the slits 11a and 11b of a and 10b different, it is possible to change the size of the pixel formed by the slits 11a and 11b, and to record the high-resolution part and the low-resolution part with the pixel of the optimum size. It becomes possible.

(Second Embodiment) FIGS. 4 (a) and 4 (b)
FIGS. 2A and 2B of a line scanning type recording head unit in an ink jet recording apparatus according to a second embodiment of the present invention.
2 shows a cross-sectional view similar to FIG.

Hereinafter, portions corresponding to those in FIG. 2 will be described by assigning the same reference numerals. In the present embodiment, the first ink droplet ejection section 6a shown in FIG. 4A is the same as that in the first embodiment. Although the configuration is different from that of the first embodiment, the configuration of the convex ink guide 10b in the second ink droplet ejection unit 6b is different.

In other words, the convex ink guide 10a in the first ink droplet discharge section 6a has a pointed tip projecting from the through hole 8a, and the tip has a very small width (diameter). On the other hand, the convex ink guide 10b in the second ink droplet ejection section 6b is
The tip of the ink guide 10a is flattened and the width (diameter) of the tip is larger than that of the convex ink guide 10a.

With such a configuration, the size of the ink meniscus formed at the ink droplet flying position at the tip of the convex ink guide 10b in the second ink droplet discharging section 6b is increased by the convexity in the first ink droplet discharging section 6a. The size is larger than the size of the ink meniscus formed at the ink droplet flying position at the tip of the ink guide 10a, and the amount and size of the ink droplet ejected from the ink meniscus are also larger. Therefore, the first ink droplet ejection unit 6a is suitable for printing a high resolution portion, and the second ink droplet ejection unit 6b is suitable for printing a low resolution portion.

(Third Embodiment) FIGS. 5 and 6 show the first and second ink droplet ejection sections 6a of a line scanning recording head section in an ink jet recording apparatus according to a third embodiment of the present invention. , 6b are plan views respectively showing the configuration of FIG.

In the above-described first and second embodiments, the first and second ink droplet ejection portions 6a and 6b are formed in a line in the main scanning direction. In the present embodiment, however, FIGS. As shown, the first and second ink droplet ejection sections 6a and 6b are shifted from each other by a half pitch in the main scanning direction, that is, formed in two rows in a staggered manner. The staggered first and second ink droplet ejection sections 6a and 6b are arranged on the same insulating substrate 7 with their positions shifted in the sub-scanning direction.

By doing so, the arrangement pitch of the first and second ink droplet ejection sections 6a and 6b in the main scanning direction can be made fine, and printing with higher resolution can be performed. In addition, when the resolution is the same as compared with the case where the first and second ink droplet ejection units 6a and 6b are each arranged in one row, the arrangement pitch of each row can be increased. Manufacturing becomes easy.

In this example, the first and second ink droplet ejection sections 6a and 6b are formed in two rows, respectively, but it goes without saying that three or more rows may be formed. In addition, the first ink droplet ejection section 6a and the second ink droplet ejection section 6b are combined in a line and arranged in a zigzag pattern.
A pair may be prepared and these may be shifted in the sub-scanning direction.

Further, in FIGS. 5 and 6, the convex ink guides 10 in the first and second ink droplet ejection portions 6a and 6b are shown.
Regarding the shapes of a and 10b, the widths of the slits 11a and 11b are made different from each other in the same manner as in the first embodiment, so that the size of the pixel formed by each is made different. Similarly, the convex ink guides 10a,
The width of the tip of 10b may be made different, and the size of the pixel formed by each may be made different.

In addition, the present invention can be implemented with various modifications. For example, in the above embodiment, two types of ink droplet discharge units (first and second ink droplet discharge units) are provided, but three or more types of ink droplet discharge units having different shapes of the convex ink guide are provided. You may comprise so that the image point of a different magnitude | size corresponding to a kind or more resolution may be formed.

Further, as an example in which the shape of the ink droplet discharge section is made different, the example in which the slit width and the width of the tip of the convex ink guide are made different is shown. However, the present invention is not limited to this. Any shape change may be provided as long as the shape and size of the droplet can be varied.

[0041]

As described above, in the ink jet recording apparatus according to the present invention, the wetting or surface tension is applied to the surface of the convex ink guide and the slit of the ink droplet ejection section for applying electrostatic force to the color material component in the ink. By carrying the ink to the ink droplet flying position and applying a predetermined voltage to the individual electrode, the ink droplet is made to fly on the recording medium,
There is no clogging in the nozzles, and the meniscus at the ink drop flying position and the ink drop flying position is determined uniformly,
The flying of the ink droplets is stabilized without being affected by the pressure and atmospheric pressure of the ink, mechanical vibration, and adjacent dots, and high-quality recording with stable density can be performed.

Further, in the present invention, at least two types of ink droplet ejection portions having different shapes are provided, and the shape of the convex ink guide in each of these ink droplet ejection portions, specifically, the width of the slit and the tip of the convex ink guide are provided. By changing the width of the part, it is possible to form multiple types of pixels without changing the drive voltage waveform, so that it is possible to record with the optimal pixel according to the required resolution, and it is rich in gradation expression High-definition·
An inkjet recording apparatus capable of recording high-quality images can be provided at a low price.

[Brief description of the drawings]

FIG. 1 is a plan view of a recording head unit in an ink jet recording apparatus according to a first embodiment of the present invention.

FIG. 2 shows AA ′ and BB ′ in the embodiment.
Arrow cross section

FIG. 3 is an exemplary view for explaining a basic recording operation in the embodiment.

FIG. 4 is a plan view of a recording head unit in an inkjet recording apparatus according to a second embodiment of the present invention.

FIG. 5 is a plan view illustrating a configuration of a first ink droplet ejection unit of a recording head unit in an inkjet recording apparatus according to a third embodiment of the present invention.

FIG. 6 is a plan view illustrating the configuration of a second ink droplet ejection unit of the recording head unit in the inkjet recording apparatus according to the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Head block 2 ... Ink supply port 3 ... Ink discharge port 4 ... Ink 5 ... Ink chamber 6a, 6b ... Ink droplet discharge part 7 ... Insulating substrate 8a, 8b ... Through hole 9a, 9b ... Individual electrode 10a, 10b ... Convex ink guides 11a, 11b Slit 21 Recording paper (recording medium) 22 Counter electrode

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasuo Hosaka 1st Toshiba R & D Center, Komukai-ku, Kawasaki City, Kanagawa Prefecture (72) Inventor Hideyuki Nakao Toshiba Komukai, Koyuki-ku, Kawasaki City, Kanagawa Prefecture Koichi Ishii, Kochi Toshiba-cho, Kawasaki-shi, Kanagawa Prefecture, Japan Toshiba R & D Center (72) Inventor Kazuhiko Higuchi, Kawasaki-shi, Kanagawa 1, Komukai Toshiba-cho, Ward Inside Toshiba R & D Center

Claims (4)

[Claims] 1. An image forming method in which an electrostatic force is applied to an ink in which a color material component is dispersed in a solvent to cause at least an ink droplet containing the color material component to fly toward a recording medium, thereby forming an image point. In the ink jet recording apparatus, a plurality of ink droplet ejection units individually provided corresponding to image points to be formed on the recording medium, and an ink supply unit that supplies the ink to the ink droplet ejection unit Wherein the ink droplet ejection section comprises at least first and second ink droplet ejection sections having different shapes, and each of the first and second ink droplet ejection sections is provided on an insulating substrate having a through hole. An individual electrode for applying an electrostatic force to the ink formed around the through-hole; and an electrode provided to protrude from the through-hole in an ink droplet flying direction, to guide the ink supplied from the ink supply means. An ink jet recording apparatus comprising: a convex ink guide that is driven by a first ink droplet ejecting unit; 2. The method according to claim 1, wherein the first and second ink droplet ejection units include:
2. The ink jet recording apparatus according to claim 1, wherein the recording medium is arranged at a position different from the relative movement direction of the recording medium in a direction orthogonal to the relative movement direction. 3. A method according to claim 2, wherein said convex ink guide has a slit formed along said ink droplet flight direction, and said first and second ink droplet discharge portions have different widths of said slit. The ink jet recording apparatus according to claim 1 or 2, wherein 4. The projection-shaped ink guide according to claim 1, wherein the first and second ink droplet ejection portions have different widths at the tip portions protruding from the through holes. Ink jet recording device.