JPH11263016A - Ink jet recording device - Google Patents

Abstract

(57) [Problem] To provide an ink jet recording apparatus capable of stably and favorably recording characters and images on a recording medium. An ink jet recording apparatus according to the present invention flies ink toward a recording medium by an electrostatic field formed by applying a predetermined voltage to an individual electrode provided on a recording head. There, ink guide part 1
0, the height d _{1 of the} portion protruding from the substrate 8 toward the holding means 4
And the distance d ₂ between the recording medium 3 held by the holding means 4 and the substrate 8 satisfies the following inequality. _{d 2/4 ≦ d 1 ≦} 2d 2/3

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 for performing recording by flying ink droplets,
The present invention relates to an ink jet recording apparatus that ejects ink droplets by an electrostatic field formed by applying a predetermined voltage to an individual electrode provided on a recording head.

[0002]

2. Description of the Related Art An ink jet recording system has advantages such as less noise and other processes such as development and fixing than other recording systems. . Numerous studies have been made on the ink jet recording method to date. Typical examples thereof include (a) a method of flying ink droplets using the pressure of steam generated by the heat of a heating element (JP-B-56-9429 and JP-B-61-59911). And (b) a method of flying an ink droplet using a mechanical pressure pulse generated by a piezoelectric element (Japanese Patent Publication No. 53-12138).

As a recording head used in an ink jet recording apparatus, a serial scanning head has been put to practical use. The serial scanning type head is mounted on a carriage, and performs recording by causing ink droplets to fly while moving in a direction (main scanning direction) orthogonal to a recording paper transport direction (sub scanning direction). . However, it is difficult for this serial scanning head to increase the recording speed.

A line scanning type head is expected as a recording head capable of recording at higher speed. The line scanning type head is a long head having the same size as the width of the recording paper. Therefore, unlike the case where a serial scanning type head is used, an ink jet recording apparatus using this does not need to move the head in the main scanning direction at the time of recording, so that high-speed recording is possible. However, there are the following difficulties in putting a line scanning head into practical use.

In general, in an ink jet recording system, an ink obtained by dispersing a colorant component in a solvent is used. Such inks are easily concentrated by evaporation and volatilization of the solvent. Therefore, in the ink jet recording method, clogging of a nozzle provided at the tip of the recording head is liable to occur essentially.

[0006] The occurrence of clogging of the nozzle is promoted for the following reasons. For example, when the pressure of steam is used for forming an ink jet, an insoluble matter is generated by a thermal or chemical reaction of the ink. This insoluble matter easily adheres to the flow path provided in the nozzle or the tip of the nozzle. Therefore, the occurrence of the clogging is promoted. On the other hand, when the pressure of the piezoelectric element is used for forming the ink jet, the structure of the ink flow path and the like becomes complicated. Therefore, even when the pressure of the piezoelectric element is used for forming the ink jet, the occurrence of the clogging is promoted.

The above-described nozzle clogging is more serious when a line scanning head is used than when a serial head is used. That is, although the number of nozzles in a serial type head is about several tens to one hundred and several tens,
In a line scanning type head, the number of nozzles reaches several thousands.
Therefore, clogging occurs much more frequently in a line scanning type head than in a serial type head, which is a serious problem in terms of reliability.

When a line scanning type head is used,
In addition to the nozzle clogging described above, there is a problem that it is difficult to improve the resolution. For example, in a line scanning type head that uses the pressure of steam to form an ink jet, an ink droplet having a particle size of 20 μm or less (the particle size of this ink droplet corresponds to a recording dot having a diameter of 50 μm on recording paper). Is difficult to form. Further, in the case of utilizing the pressure of the piezoelectric element for forming the ink jet, the structure of the ink flow path and the like becomes complicated, so that it is difficult to manufacture a recording head having a high resolution in terms of processing technology.

In order to overcome the above problem, a substrate having a plurality of thin film-shaped individual electrodes (array electrodes) arranged thereon is used, and an electrostatic field formed by applying a voltage to the array electrodes is used. An ink jet recording system has been proposed in which an ink or a colorant component contained therein is ejected from an ink liquid surface as ink droplets (Japanese Patent Application Laid-Open Nos. 49-62024 and 56-4467). As a recording method using the array electrodes, a recording method in which an ink containing a charged colorant component is used and the concentration of the colorant component in the ink is increased to cause ink droplets to fly (WO93 / 11866: PCT / AU92 /
00665: Japanese Patent Publication No. 7-502218).

In these recording methods, an individual electrode for controlling the flight of ink droplets is provided at the tip of a recording head.
Therefore, according to these display methods, it is not necessary to form a nozzle or an ink channel for each individual dot. Therefore, the nozzle can be formed in a slit shape in which the opening is formed in a slit shape, or the recording head can be made nozzle-less.

When the recording head is configured as described above, the above-described nozzle clogging can be prevented. Further, even if the nozzle is clogged, it can be easily recovered. Further, in the case where the nozzle is not used, it is possible to stably fly an ink droplet having a very small particle diameter, so that high resolution can be achieved.

However, when the recording head is nozzleless, there is a problem that the ink droplet ejection position becomes unstable because the ink can freely move in the main scanning direction at the leading end of the recording head. Further, in the above recording method, since the ink droplet is caused to fly by applying a voltage having the same polarity as the charging polarity of the colorant to the individual electrode, the colorant component is generated by an electric repulsion between the individual electrode and the colorant. There is also a problem that the ink cannot be stably supplied to the ejection position.

[0013] Therefore, according to the conventional ink jet recording apparatus, it is possible to fly ink droplets at a desired size.
In addition, it is difficult to cause ink droplets to fly from a desired position on the recording head, and it has not been possible to perform stable and satisfactory recording of characters and images on a recording medium.

[0014]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides an ink jet recording apparatus capable of recording characters and images on a recording medium stably and favorably. The purpose is to:

[0015]

Means for Solving the Problems The present invention has been made to solve the above-mentioned problems, and comprises: a) a substrate having a plurality of openings, and the plurality of substrates being provided on one main surface of the substrate. A plurality of electrodes arranged so as to surround the openings, and an ink supply means for supplying ink containing a colorant component and a solvent to each of the plurality of openings from the other main surface side of the substrate. An ink guide having a plurality of ink guide portions disposed substantially perpendicularly to the substrate surface, each penetrating through the plurality of openings, and having a diameter smaller than the opening diameter of the plurality of openings; A) a recording head having a plurality of electrodes, and b) a holding unit that is arranged to face a surface of the recording head on which a plurality of electrodes are formed and holds a recording medium; and c) a predetermined voltage is applied to each of the plurality of electrodes. Applied voltage applying means Provided, the height d ₁ of the portion projecting from the substrate of the ink guide portion to the holding means side, a distance d ₂ and is represented by the following inequality between the substrate and the recording medium held in said holding means Provided is an ink jet recording apparatus that satisfies the relationship shown below. _{d 2/4 ≦ d 1 ≦} 2d 2/3

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to the drawings. FIG. 1 schematically shows a cross-sectional shape of an ink jet recording apparatus according to an embodiment of the present invention. In FIG. 1, the inkjet recording apparatus 1 includes a recording head 2, a holding unit 4 that is arranged to face the recording head 2 and holds a recording medium 3, and a voltage applying unit 5.

In the above ink jet recording apparatus 1,
The holding unit 4 is not particularly limited as long as it can hold the recording medium 3 such as paper or an OHP sheet with a certain gap from the recording head 2. The holding means 4 can be, for example, in a drum shape or a plate shape. When the holding means 4 is in the form of a drum or a plate, the holding surface for holding the recording medium 3 may be made of a conductor. In this case, a predetermined voltage can be applied to the holding surface, or the holding surface can be grounded. Further, the holding surface may be formed of an insulator so that the holding surface can be charged to a predetermined potential.

In the recording head 2, one surface of an ink tank 7 containing the ink 6 is composed of a substrate 8 on which a plurality of openings (ink discharge ports) are formed. In the ink jet recording apparatus 1, the ink tank 7 is provided as an ink supply unit.

A plurality of electrodes 9 are arranged on the substrate 8 so as to surround the opening. In the ink tank 7, in addition to the ink 6, a plate-like body on which a plurality of protrusions (ink guide portions) 10 are formed is housed as ink guide means 11. The ink guide means 11 is made of, for example, an insulator such as a resin, and is arranged such that the tips of the plurality of ink guide portions 10 project from the plurality of openings formed in the substrate 8.

The ink guide section 10 is usually formed in a column shape. When the ink guide portion 10 is formed in a columnar shape, it is preferable to provide a slit or the like substantially perpendicular to the substrate surface. Thus, ink can be supplied from the ink tank 7 to the tip of the ink guide section 10 by utilizing the capillary phenomenon.

When a slit is formed in the ink guide section 10, it is preferable that the width w of the slit is in the range of 10 μm to 100 μm. If the slit width w is less than 10 μm, the amount of ink supplied into the slit is small, so that a large-sized image dot cannot be formed on the recording medium 3. In addition, clogging due to concentration of ink in the slit is likely to occur.

On the other hand, when the slit width w exceeds 100 μm, the meniscus in the slit becomes large, so that a small-sized image point cannot be formed on the recording medium 3. In addition, since the ink surface at the tip of the slit is low, it is difficult to fly ink droplets.

On the other hand, the width w of the slit is set to 10 μm to
When the thickness is within the range of 100 μm, the amount of ink at the tip of the ink guide unit 10 can always be kept constant. Also,
In this case, by changing the pulse width of the signal voltage applied to the electrode 9, the diameter of the image spot formed on the recording medium 3 can be modulated. That is, a good gradation image can be formed.

Although FIG. 1 shows only three openings formed in the substrate 8, a much larger number of openings are actually arranged in a line. Also, in FIG.
In the ink tank 7, the ink 6 and the ink guide means 1 are provided.
Although only 1 is illustrated, a porous body, fiber, or the like may be accommodated. When the inside of the ink tank 7 is filled with a porous body, a fiber or the like, the position of the ink surface with respect to the opening and the like formed in the substrate 8 can always be kept constant by the capillary phenomenon. When the inside of the ink tank 7 is not filled with a porous body, a fiber, or the like, it is preferable to separately provide a maintenance mechanism for keeping the position of the ink surface constant.

A pipe 15 is connected to one end of the ink tank 7, and a pipe 16 is connected to the other end. Piping 1
Reference numerals 5 and 16 are respectively connected to the ink recirculation mechanism 17 so that the ink 6 in the ink tank 7 can be circulated.

The plurality of electrodes 9 formed on the substrate 8 are electrically connected to the voltage applying means 5, respectively. In FIG. 1, only one of the plurality of electrodes 9 is electrically connected to the voltage applying unit 5. However, in practice, all the electrodes 9 are electrically connected to the voltage applying unit 5. Also,
In this case, it is necessary that a voltage can be selectively applied to a desired electrode 9.

The voltage applying means 5 can apply a bias voltage _Vb to the electrodes 9 and the like formed on the substrate 8.
As described above, the supply of the ink 6 to the tip of the slit provided in the ink guide portion 10 uses the capillary phenomenon. However, the electric field formed by applying the bias voltage _Vb to the electrode 9 and the like also increases. Available.

The voltage applying means 5 can apply _a signal voltage Va to the electrodes 9 and the like formed on the substrate 8. Ink drops fly.

[0029] At the time of actual driving, the signal voltage V _a is applied to the electrode 9 is superposed on the bias voltage V _b. That is, the voltage applying means 5, for example, constantly applies a bias voltage V _b, correspond to the image information to allow superimposing a signal voltage V _a to the electrode 9 formed on the substrate 8. This makes it possible to control the flight of the ink droplet.

Further, the holding surface of the holding means 4 composed of a conductive material, a reverse bias voltage -V _b is applied to the holding surface, only the signal voltage V _a may be capable of applying for the electrodes 9 . Further, the holding surface of the holding means 4 composed of an insulator, a holding surface is charged to -V _b by the charger or the like, may also be capable of applying only the signal voltage V _a is the electrode 9.

In the ink jet recording apparatus 1 configured as described above, as described above, the ink guide means 1
1 is used. By using the ink guide means 11, it is possible to eject ink droplets from a desired position of the recording head 2. Further, since the capillary phenomenon can be used to supply the ink to the tip of the ink guide portion, the ink can be stably supplied to the ejection point.

Further, in the ink jet recording apparatus 1, the height d ₁ protruding holding means 4 side from the substrate 8 of the ink guide part 10, between the recording medium 3 and the substrate 8 held by the holding means 4 The distance d ₂ satisfies the relationship shown in the following inequality.

The picture when _{d 2/4 ≦ d 1 ≦} 2d 2/3 d 1 is less than d _2/4, the meniscus formed between the ink guide part 10 and the substrate 9, the recording medium 3 above Since this contributes to the formation of dots, the flight of ink droplets becomes unstable, and image spots having a large diameter that is bleeding are likely to be formed. On the other hand, if d ₁ is greater than 2d _2/3, which may or cause fogging, flight of ink droplets becomes impossible.

On the other hand, when d ₁ and d ₂ satisfy the relationship shown in the above inequality, it is possible to prevent fogging and to form image points at desired positions on the recording medium 3. That is, according to the ink jet recording apparatus 1, it is possible to record characters and images on the recording medium 3 stably and favorably.

The above d ₁ is preferably from ₂₀₀ μm to 250 μm, and d ₂ is preferably from 300 μm to 400 μm. When d ₁ and d ₂ are within the above range,
The above effect becomes more remarkable.

[0036]

Embodiments of the present invention will be described below. The recording characteristics and the like of the ink jet recording apparatus 1 shown in FIG. 1 were examined by the following method. In this embodiment, the flight of the ink droplet from the ink guide unit 10 is as follows.
Always a bias voltage V _b to the electrode 9 formed on the substrate 8 was controlled by superimposing a signal voltage V _a corresponding to the image information.

First, the height d _{1 of} the ink guide portion 10 protruding from the substrate 8 toward the holding means 4 and the distance d ₂ between the recording medium 3 held by the holding means 4 and the substrate 8 are variously changed. Thus, the image formed on the recording medium 3 was evaluated. The ink guide section 10 was formed in a columnar shape having a diameter of 160 μm, and a slit having a width w = 40 μm was provided at the tip.
The result is shown in FIG.

FIG. 2 is a graph showing conditions under which a good image can be formed in the ink jet recording apparatus according to the embodiment of the present invention. In the drawing, the horizontal axis represents the height d ₁ of the ink guide 10 protruding from the substrate 8 toward the holding means 4.
The vertical axis indicates the distance d ₂ between the recording medium 3 held by the holding means 4 and the substrate 8. In addition, in the drawing, only the conditions under which a good image is formed without causing fog are indicated by black circles.

As shown in FIG. 2, d ₁ is d ₂ / 4~2d
_When it was within the range of 2/3, that is, under the conditions in the region (b), a good image was formed without fogging. In contrast, if d ₁ is less than d _2/4, that is, the recording gap widened under conditions in the region (a), the ink is less likely to fly, becomes unrecordable in the signal as. On the other hand, if d ₁ is greater than 2d _2/3, i.e. under the conditions in the region (c), flight becomes unstable ink droplets for recording gap is narrow, resulting in a background fogging.

Next, the pulse width of the voltage applied to the electrode 9 was modulated, and the change in the diameter of the pixel formed on the recording medium 3 was examined. The result is shown in FIG. FIG. 3 is a graph showing a capability of forming a gradation image of the ink jet recording apparatus according to the embodiment of the present invention. In the figure, the horizontal axis represents the pulse width of the voltage applied to the electrode 9, and the vertical axis represents the diameter of the dot formed on the recording medium 3. Also, the straight lines 20 to 22 are
The slit width w is 60 μm, 40 μm, and 20 μm, respectively.
Data obtained when m is used is shown.

As shown in FIG. 3, the slit width w is 60 μm.
In the case of m, by controlling the pulse width, it was possible to form an image point of a desired size from a small size to a large size. Further, the slit width w is set to 40 μm, 2
When the width was gradually reduced to 0 μm, the maximum diameter of the dot that could be formed gradually became smaller. As a result, even when the pulse width was largely changed, the change in the dot diameter was reduced. When the slit width w was further reduced, it was found that when the slit width was less than 10 μm, clogging in the slit was likely to occur.

Further, when the slit width w was increased, it was possible to form an image point with a larger size. However, on the other hand, since the meniscus of the ink 6 becomes large, if the pulse width is narrow, it is impossible to cause the ink droplets to fly uniformly, and it is difficult to form a small-sized pixel. Was. When the slit width w was further increased, when the slit width exceeded 100 μm, the ink surface at the tip of the ink guide portion 10 was lowered, and it was difficult to cause the ink droplet to fly even when the pulse width was wide.

As described above, according to the ink jet recording apparatus 1, the height d _{1 of} the ink guide portion 10 protruding from the substrate 8 toward the holding means 4, the recording medium 3 held by the holding means 4 and the substrate for 8 and the distance d ₂ between satisfies a predetermined relationship, to prevent the occurrence of fog, and it is possible to form the image dots in a desired position on the recording medium 3.
That is, according to the ink jet recording apparatus 1, it is possible to record characters and images on the recording medium 3 stably and favorably.

Further, by forming a slit having a predetermined width in the ink guide section 10 of the ink jet recording apparatus 1, the amount of ink at the tip of the ink guide section 10 is always kept constant, and a good gradation image is formed. It can be formed.

[0045]

As described above, according to the ink jet recording apparatus of the present invention, the height d ₁ of the ink guide portion protruding from the substrate toward the holding means, and the height d ₁ between the recording medium held by the holding means and the substrate. The distance d ₂ satisfies a predetermined relationship. Therefore, it is possible to prevent the occurrence of fog and to form an image point at a desired position on the recording medium 3. That is, according to the present invention, there is provided an ink jet recording apparatus capable of stably and satisfactorily recording characters and images on a recording medium.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing an inkjet recording apparatus according to an embodiment of the present invention.

FIG. 2 is a graph showing conditions under which a good image can be formed in the ink jet recording apparatus according to the embodiment of the present invention.

FIG. 3 is a graph illustrating a capability of forming a gradation image of the inkjet recording apparatus according to the embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Ink jet recording apparatus 2 ... Recording head 3 ... Recording medium 4 ... Holding means 5 ... Voltage applying means 6 ... Ink 7 ... Ink tank 8 ... Substrate 9 ... Electrode 10 ... Ink guide part 11 ... Ink guide means 15, 16 ... Piping 17: Ink reflux mechanism 20-22: Straight line

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shuzo Hirahara 1st address, Komukai Toshiba-cho, Saiwai-ku, Kawasaki City, Kanagawa Prefecture (72) Inventor Hideyuki Nakao Hideyuki Nakao Toshiba Komukai-shi, Kawasaki-shi, Kanagawa Prefecture Koichi Ishii, Kochi Toshiba-cho, Kawasaki-shi, Kanagawa Prefecture, Japan Toshiba R & D Center (72) Inventor Teruo Murakami, Kawasaki-shi, Kanagawa 1, Komukai Toshiba-cho, Ward Inside Toshiba R & D Center

Claims (2)

[Claims] A) a substrate having a plurality of openings; a plurality of electrodes disposed on one main surface of the substrate so as to surround the plurality of openings, respectively; An ink supply means for supplying an ink containing a colorant component and a solvent to each of the plurality of openings from a surface side; and penetrating the plurality of openings substantially perpendicular to the substrate surface, respectively. A recording head having a plurality of ink guide portions having a diameter smaller than the opening diameter of the plurality of openings; and b) a surface of the recording head on which a plurality of electrodes are formed. C) holding means for holding a recording medium, and c) voltage applying means for applying a predetermined voltage to each of the plurality of electrodes; and Protruding part An ink jet recording apparatus of the height d _1, the distance d ₂ between the recording medium held in said holding means and said substrate characterized by satisfying the relationship shown below inequality. _{d 2/4 ≦ d 1 ≦} 2d 2/3 2. The ink jet recording apparatus according to claim 1, wherein a slit substantially perpendicular to the substrate surface is formed at a tip of the ink guide portion with a width of 10 μm to 100 μm.