JP2842318B2 - Electrostatic ink jet recording head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic ink jet recording head, and more particularly, to an electrostatic ink jet recording head which prints on recording paper by flying color material particles by electrostatic force.

[0002]

2. Description of the Related Art The non-impact recording method has recently attracted attention in that noise during recording is extremely small to a negligible level. In particular, an ink jet recording method capable of performing high-speed recording on plain paper with a simple mechanism is an extremely effective recording method, and various methods have been proposed so far. For example, there is a method in which a voltage is applied between an electrode provided on the back surface of a recording paper and a needle-like electrode facing the electrode, and a coloring material such as ink is caused to fly by electrostatic force of an electric field generated thereby, thereby performing recording.

FIG. 6 shows a conventional example of this kind. In FIG. 6, the surface of a substrate 52 is covered with a cover 54, and a slit-shaped ink ejection port 55 for holding ink is provided. On the surface of the substrate 52, a plurality of recording electrodes 53 are arranged in parallel along the ink ejection direction. These recording electrodes 53 are connected to a voltage driver (not shown), and a high voltage pulse is selectively applied to the recording electrodes 53 during recording. on the other hand,
On the extension of the recording electrode 53, a counter electrode 51 is provided via a recording paper P.
Are provided, and an electric field is generated between the recording electrode 53 and the recording electrode 53 during recording. Here, since the recording electrode 53 has a needle shape, an electric field concentrates on the tip of the recording electrode 53 during recording, and charges are accumulated in the ink near the recording electrode.

[0004] The process of accumulating the electric charge differs depending on the type of ink. The conductive ink uses electrostatic induction, and the dielectric ink uses dielectric polarization. Further, in the ink in which the coloring material particles (toner and the like) are dispersed, the coloring material particles themselves have an apparent charge due to the zeta potential, and the migration of the charged coloring material is energized by the electric field.

[0005] Any of the above-mentioned types of ink can be used for recording. However, recording by jetting the liquid ink itself has a disadvantage that ink bleeding occurs on recording paper, and feathering and color bleeding specific to multicolor recording occur, thereby deteriorating print quality. In such a case, since the degree of bleeding differs depending on the recording paper, there is a disadvantage that the printing result differs depending on the recording paper. Further, there is an inconvenience that the recording speed is limited due to the necessity of drying time of the ink. On the other hand, when printing is performed by ejecting color material particles using ink in which color material particles are dispersed, it is possible to perform printing without bleeding regardless of the recording paper.
For this reason, it is desirable to use ink in which coloring material particles are dispersed.

[0006] These inks or the color material particles in the ink are formed by the Coulomb force acting on the accumulated electric charges.
When the Coulomb force overcomes the surface tension of the ink, the ink flies,
It adheres on the recording paper P. By controlling the high voltage pulse applied to the recording electrode according to the image to be recorded, desired recording can be performed.

However, since the conductivity and permittivity of the ink used for recording are higher than the conductivity and permittivity of air, strictly speaking, the location where the electric field concentrates is not determined only by the arrangement of the recording electrodes. Is affected by the shape of the ink meniscus formed on the substrate. In the recording head 50 shown in FIG. 6, it is desirable that the ink meniscus be uniform in the longitudinal direction of the ink ejection port. However, actually, the processing accuracy of the opening,
The surface of the ink meniscus has minute irregularities due to vibration of the meniscus that has performed the ink ejection, natural fluctuation of the meniscus, and the like.

In such a case, the electric field is concentrated on the minute meniscus convex portion generated near the recording electrode due to the relationship between the conductivity and the dielectric property of the ink. Then, when the meniscus starts to deform due to the Coulomb force, the concentration of the electric field is further strengthened, so that the initial flying portion of the meniscus shifts due to the minute unevenness of the meniscus. According to this, even if a high voltage pulse is applied to a certain recording electrode, the ink flies from a position shifted from the recording electrode, so that it may not be possible to perform recording at a desired position, resulting in a decrease in print quality. was there.

On the other hand, Japanese Patent Laid-Open Publication No. Sho 60-228162 discloses an example of a solution to the above problem. In this publication, as shown in FIG. 7 , a convex portion 66 is provided at a position corresponding to the recording electrode 63 at the front end portion of the substrate 62 so that the ink meniscus is provided with irregularities in advance. The electric field diverged from is concentrated at a desired position.

In such a system, when an ink containing coloring material particles is used, the ejection is performed only when the charged coloring material particles in the ink move to the tip of the meniscus according to the electric field in the ink. .

[0011]

However, in the conventional example described in the above publication, when the resolution of the printer is set to 300 dpi, for example, the arrangement pitch of the recording electrodes is set to about 8
It is necessary to set it to about 5 μm. In such a case, in order to process fine irregularities corresponding to such a recording electrode having a fine pitch, there is a disadvantage that a substrate material and a processing process are limited, and a manufacturing cost is increased. Also, in order for the substrate to have sufficient mechanical strength, a thickness of 100 μm or more is required, whereas the pitch of the unevenness to be processed is less than a fraction of this thickness, making processing extremely difficult. Again, there was an inconvenience that led to an increase in manufacturing costs.

The above-mentioned publication also discloses that the substrate 62 is formed of a thin and flexible material by disposing a reinforcing plate 67 at a position separating the recording electrodes 63 as shown in FIG. However, the strength of the convex portion at the front end of the substrate is reduced by this, so that there is an inconvenience that the convex portion at the front end of the substrate is easily damaged when cleaning the front end portion of the head or when a recording paper jam occurs.

Further, the direction of the electric field around the recording electrode is shown in FIG.
Direction diverging from the recording electrode as shown in the figure (arrow in the figure)
Therefore, the color material particles do not move or move smoothly to the tip of the meniscus on the recording electrode axis, which leaves room for improvement in the performance of continuously ejecting ink at high speed. Was.

[0014]

An object of the present invention is to improve the disadvantages of the prior art described above, and in particular, to provide an electrostatic processing device which can be easily processed and manufactured at a low cost, and can stably and promptly eject color material particles in ink. It is an object of the present invention to provide an ink jet recording head of the type.

[0015]

According to the first aspect of the present invention,
A substrate, a recording electrode formed on the substrate surface for generating an electric field for ink ejection, a cover member for forming a slit-shaped ink flow path in the ink ejection direction on the substrate surface on which the recording electrode is formed, and a slit-shaped member. An ink ejection port provided at the tip of the ink passage on the ink ejection side. In addition, a configuration is adopted in which the tip of the ink ejection side of the cover member is set so as to protrude in the ink ejection direction from the tip of the ink ejection side of the substrate.

According to the present invention, when the ink containing the color material particles is filled in the ink flow path, an ink meniscus is formed in the ink ejection port with the cover member side protruding as shown in FIG. The electric field radiated from is concentrated at the tip of the cover member along the surface shape of the ink meniscus due to the conductivity and the dielectric constant of ink and air. By the action of the electric field, the charged coloring material particles in the ink migrate to the tip of the meniscus, and the ink (toner) flies from the tip of the cover member.

In addition, according to the first aspect of the present invention, the recording electrode is formed in a needle shape with the ink jetting direction as a longitudinal direction, and a plurality of the needle-shaped recording electrodes are arranged in parallel. Is formed in a saw-tooth shape, and a plurality of protrusions having the saw-tooth shape are arranged on the extension of the needle-like recording electrode.

Therefore, in the present invention, as shown in FIG. 2, since a convex ink meniscus is formed corresponding to the sawtooth shape formed at the tip of the cover member, the electric field diverging from the recording electrode is reduced by the ink meniscus. Concentrated on the tip of the convex part,
Ink (toner) flies from the tip of the projection.

According to the second aspect of the present invention, the cover member is formed by a mold member.

In the present invention, in particular, the saw-tooth-shaped projection formed at the tip of the cover member has sufficient strength.

[0021] With the above, the above object is to be achieved.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

The electrostatic ink jet recording head shown in FIGS. 1 to 5 has a substrate 1, a recording electrode 2 formed on the surface of the substrate 1 for generating an electric field for ink ejection, and the recording electrode 2 formed thereon. A cover member 4 that forms a slit-shaped ink flow path 3 in the ink jetting direction (the direction of the arrow A) on the surface of the substrate 1 and an ink jet port 5 provided at the tip end of the slit-shaped ink flow path 3 on the ink jet side. Have. The front end of the cover member 4 on the ink ejection side is set to project from the front end of the substrate 1 on the ink ejection side in the ink ejection direction.

In this embodiment, the recording electrodes 2 are formed in a needle shape with the ink jetting direction as a longitudinal direction, and a plurality of the needle-shaped recording electrodes 2 are arranged in parallel on the surface of the substrate 1. The tip of the cover member 4 on the ink jetting side is formed in a sawtooth shape, and a plurality of protrusions 12 having the sawtooth shape are arranged on the extension of the needle-like recording electrode 2. Here, the cover member 4 is formed of a mold member. Here, reference numeral 8 indicates an ink meniscus, and reference numeral 9
Denotes an ink, and reference numeral 10 denotes a flying toner group.

More specifically, in this embodiment, the substrate 1 is formed of an insulator such as glass, and a plurality of recording electrodes 2 are formed on the surface thereof. This recording electrode 2
Is obtained by patterning a dielectric material such as nickel or chromium sputtered on the entire substrate 1 by a photolithography method, and is arranged at a pitch of 300 dpi, that is, at an interval of about 85 μm. The tip of the recording electrode 2 is covered with an insulator layer 6.

The cover member 4 is formed of a resin such as polysulfone by molding, and is attached to the substrate 1 so as to form a slit-shaped ink flow path 3 and an ink ejection port 5. The three sides of the cover member 4 other than the ink ejection ports 5 are in close contact with the substrate 1, whereby the ink flow path 3 is in a state where only the ink ejection ports 5 are opened. Further, two ink circulation ports 7 are provided on the upper surface of the cover member 4, and are connected to an ink tank and a tube (not shown). Then, the ink in the ink flow path 3 is forcibly circulated while a negative pressure of about 1 cmH ₂ O is applied to the ink. Here, the recording ink is preferably one in which fine particles (toner) of a thermoplastic resin colored with a charge controlling agent in a petroleum organic solvent (isoparaffin hydrocarbon) are dispersed in the liquid. In the present embodiment, the toner is apparently positively charged by the zeta potential.

The cover member 4 is provided with a plurality of reinforcing columns 4a in contact with the insulator layer provided on the substrate 1 at positions separating adjacent recording electrodes 2 and 2.

The other structure is the same as that of the above-described conventional example.

Next, the overall operation of the recording head in this embodiment will be described.

When the ink is filled in the ink flow path 3, the ink 9 forms an ink meniscus 8 in the ink ejection port 5 by the surface tension. Here, a negative pressure is applied to the ink 9 in the ink flow path 3 and the end of the cover member 4 protrudes from the end of the substrate 1 in the ink ejection direction.
As shown in FIGS. 3 to 5, the ink meniscus 8 has a concave surface shape obliquely upward with the convex portion 12 as a vertex when viewed from the side. Further, a convex portion 1 is provided at an end of the cover member 4.
2 is formed, the ink meniscus 8 is
As seen from the top, as shown in FIG. Further, since the convex portion 12 is set at a position corresponding to the recording electrode 2, an ink meniscus 8 protruding corresponding to the recording electrode 2 is formed.

Subsequently, when a voltage pulse is applied to an arbitrary recording electrode 2, a counter electrode (not shown)
That is, an electric field directed toward the recording paper is formed. The direction of the electric field around the recording electrode is a direction diverging from the recording electrode 2, and the toner particles move in the ink along this electric field. As indicated by the arrows in FIG. 5, some toner goes directly to the meniscus tip, and some toner goes first to the ink meniscus surface, and then moves to the meniscus tip along the surface shape of the meniscus. .

The toner particles collected at the tip of the meniscus are drawn out by a strong electric field concentrated at the tip of the meniscus, and fly as a group of toner particles 10 to a counter electrode (not shown), that is, a recording sheet, thereby performing recording. . The toner adhering to the recording paper and forming the recording dots is heated and fixed by a heater (not shown).

On the other hand, the electric charge corresponding to the electric charge held by the flying toner particle group 10 is supplied to the ink 9 near the ink ejection port from the portion of the recording electrode 2 not covered by the insulator layer 6, As a result, the electrical balance is always maintained.

As described above, according to the present embodiment, since the tip of the cover member 4 on the ink jetting side is set at a position protruding from the tip of the substrate 1 having the recording electrode 2, the ink meniscus to be formed is formed. 5 has a shape in which the cover member side protrudes as shown in FIG. 5, whereby the electric field tangential direction component at the meniscus portion is directed toward the tip of the meniscus 8 and the component is also increased. The toner particles can be supplied quickly, and high-speed and high-precision recording can be performed.

Further, the tip of the cover member 4 on the ink jetting side is formed in a saw-tooth shape, and the position of the protruding portion 12 having the saw-tooth shape is set on the extension of the acicular recording electrode 2, so that the ink meniscus 8 As shown in FIG.
Thus, the electric field diverged from the recording electrode 2 can be more efficiently concentrated for each recording electrode 2, and the toner particles can be more quickly supplied to the tip of the meniscus. In addition to this, higher-speed and higher-precision recording can be performed using the plurality of recording electrodes 2.

Since the sawtooth shape for concentrating the electric field is formed on the cover member 4 side instead of the substrate 1, the range of choice of the substrate material can be widened, and the recording electrodes 2 precisely arranged on the substrate 1 can be formed. There is more choice in the process of forming
The manufacturing cost can be reduced by selecting an inexpensive material and an easy forming process, which in the prior art were considered to be inappropriate due to processing problems.
Further, by setting the plate thickness of the cover member 4 to a thickness suitable for processing, the processing of the saw-tooth-shaped uneven portion can be facilitated,
The manufacturing cost can be further reduced.

Further, since the cover member 4 employs a mold member, the saw-tooth-shaped portion formed at the front end of the ink jetting side can have sufficient strength.
It is possible to prevent damage to the saw-toothed uneven portion due to cleaning of the head end portion and paper jam.

In addition, since the tip of the recording electrode 2 is covered with the insulator layer 6, the withstand voltage between the recording electrode 2 and the counter electrode is increased, and an overcurrent flows due to the occurrence of recording paper jam or the like, and a driving device or the like is used. Inconvenience such as breakage of the image can be effectively prevented.

Here, the present invention is not limited to the present embodiment, and the shape of the tip portion of the cover member on the ink jetting side does not have to be a saw-tooth shape, and the material for forming the cover member does not have to be a mold. Further, in the electrostatic ink jet recording head according to the present embodiment, first, the recording electrode 2 is printed on the surface of the substrate 1 and then the insulator layer 6 is formed, and thereafter, the insulating layer 6 is formed separately from these. It may be manufactured by a procedure of attaching the cover member 4 on the substrate 1.

[0040]

Since the present invention is constructed and functions as described above, according to the present invention, the front end of the ink jetting side of the cover member is set at a position protruding from the front end of the substrate having the recording electrodes. The formed ink meniscus has, for example, a shape in which the cover member side protrudes as shown in FIG. 5, whereby the component of the electric field tangent in the meniscus portion faces the tip direction of the meniscus, and the component also increases. The toner particles can be quickly supplied to the tip of the meniscus, and high-speed and high-precision recording can be performed.

Further, the tip of the cover member on the ink jetting side is formed in a saw-tooth shape, and the position of the protruding portion having the saw-tooth shape is set on the extension of the needle-shaped recording electrode. As shown in the figure, a shape having vertices corresponding to the convex portions of the cover member is obtained, so that the electric field radiated from the recording electrode can be more efficiently concentrated for each recording electrode, and the toner particles Supply can be performed more quickly, and higher-speed and higher-precision recording can be performed using a plurality of recording electrodes.

Further, since the saw-tooth shape for concentrating the electric field is formed on the cover member side instead of the substrate, the range of choice of the substrate material can be widened, and the process of forming the recording electrodes precisely arranged on the substrate can be performed. Since there is a wider range of choices, manufacturing costs can be reduced by selecting inexpensive materials and easy forming processes, which in the prior art were considered unsuitable due to processing problems. Further, by setting the thickness of the cover member to a thickness suitable for processing, the processing of the saw-toothed uneven portion can be facilitated, and the manufacturing cost can be further reduced.

According to the second aspect of the present invention, since the mold member is employed as the cover member, the saw-tooth-shaped portion formed at the tip end on the ink jetting side can have sufficient strength. It is possible to provide an unprecedented excellent electrostatic ink jet recording head which can prevent the leading edge from being cleaned and prevent the saw-tooth-shaped uneven portion from being damaged due to paper jam.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of the present invention.

FIG. 2 is a partially cutaway plan view of the embodiment shown in FIG.

FIG. 3 is a sectional view taken along line CC of FIG. 2;

FIG. 4 is a cross-sectional view taken along line DD of FIG. 2;

FIG. 5 is an enlarged view of a portion indicated by reference numeral B in FIG.

FIG. 6 is a partially omitted perspective view showing a conventional example.

FIG. 7 is a perspective view showing another conventional example.

8 is a schematic cross-sectional view showing a state of an ink meniscus formed in an ink ejection port and a state of an electric field diverged from a recording electrode in the conventional example shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Recording electrode 3 Ink flow path 4 Cover member 5 Ink ejection port 6 Insulator layer 12 Convex part A Ink ejection direction

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hitoshi Minemoto 5-7-1 Shiba, Minato-ku, Tokyo NEC Corporation (72) Inventor Yoshihiro Hagiwara 5-7-1 Shiba, Minato-ku, Tokyo Japan (56) References WO 93/11866 (WO, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B41J 2/06

Claims (2)

(57) [Claims] 1. A substrate, a recording electrode formed on the surface of the substrate for generating an electric field for ink ejection, and a cover for forming a slit-shaped ink flow path in the ink ejection direction on the surface of the substrate on which the recording electrode is formed. and the member, and an ink ejection port provided on the ink ejection side end portion of the slit-shaped ink passage, an ink ejection side end portion of the cover member in the ink ejecting direction from the ink ejection side end portion of the substrate In the electrostatic ink jet recording head set so as to protrude , the recording electrode is formed in a needle shape with the ink jetting direction as a longitudinal direction.
As well as arranging multiple needle-shaped recording electrodes in parallel
Then, the front end of the ink jetting side of the cover member is formed in a sawtooth shape.
And the plurality of protrusions forming the sawtooth shape are recorded in the needle-like form.
Characterized by being arranged on the extension of the electrode respectively
Type inkjet recording head. 2. The cover member is formed by a mold member.
The electrostatic ink jet according to claim 1, wherein
Jet recording head.