JPH11300969A - Electrostatic ink jet printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably supply liquid toner and to efficiently fly flocculated color particles to form printing or an image free from density irregularity. SOLUTION: A lurality of projections 4 comprising a dielectric regularly arranged on a plane, liquid toner 8 containing charged color particles P to wet the surfaces of the projections 4, a bias electrode 13 applying voltage having the same polarity as the charged color particles to flocculate the color particles in the liquid toner on the tips of the projections 4 by coulomb force and the ultrasonic generation parts 16 provided corresponding to the base parts of the projections 4 to generate ultrasonic waves in the protruding direction of the projections 4 to separate the liquid droplets containing the flocculated color particles are provided. By this constitution, the color particles flocculated by the electric field of bias voltage are separated by ultrasonic waves and efficiently allowed to fly to form printing or an image free from density irregularity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a liquid toner in which charged colored particles are dispersed, aggregates the colored particles at the tip of the ejection projection by electrostatic force, and separates the tip from the tip of the ejection projection by ultrasonic vibration. The present invention relates to an electrostatic ink jet printer that performs recording by flying over a recording medium.

[0002]

2. Description of the Related Art In recent years, as an output device of a personal computer, an ink jet recording type printer which forms a character or an image on a recording paper by ejecting ink particles toward a recording medium such as a recording paper opposed thereto has been widely used. ing. Among them, an electrostatic ink jet printer apparatus that performs recording by ejecting colored particles onto recording paper by electrostatic force using liquid toner in which charged colored particles are dispersed has attracted attention. The reason for this is that a piezo printer that ejects ink from a nozzle due to thermal expansion of a bubble or a bubble jet printer that ejects ink from a nozzle using a piezo pump must use a nozzle that causes liquid clogging. Not only must a large number of nozzles with different inner diameters be provided to provide light and shade (gradation) of recording, whereas an electrostatic printer device not only requires no nozzles but also This is because shading can be easily realized only by changing the voltage pulse width and the pulse height.

[0003] This electrostatic printer is disclosed in, for example, Japanese Patent Application Laid-Open No. 8-149253 and Japanese Patent Application Laid-Open No. 7-502218.
And the like, and supplies a liquid toner obtained by dispersing charged colored particles in an insulating liquid to the injection point of the electrode body having a sharp tip, and the charged colored particles are supplied to the electrode of the electrode body. A liquid toner is ejected and recorded by applying a voltage of the same polarity and using the Coulomb force generated at that time. In order to form an image, a bias voltage for aggregating the charged colored particles at the emission point is applied to the electrode,
Recording is performed by applying an ejection voltage to the electrodes according to the image input signal. In this electrostatic method, high-density printing can be performed by aggregating and ejecting the charged colored particles, and since the structure of the electrode body is simple, the number of injection points is increased by arranging a large number of electrodes in a line to form a multi-emission point. It has the feature that high-speed printing can be easily performed.

As another inkjet printer, a printer using ultrasonic waves has been proposed in the following English literature [ACOSTIC INK PRINTI].
NG: PRINTING BY ULTRASONIC
INK EJECTION] (IS &T's Eig
hth International Congres
s on Advances in Non-Impa
ct Printing Technologies
(1992), 411-415). This device is
Ultrasonic waves are generated from an ultrasonic generator submerged in the ink, and the ultrasonic waves are narrowed down to the liquid surface of the ink by an ultrasonic lens to locally vibrate the ink to separate and fly fine ink droplets. It has become.

[0005]

An important point for stably ejecting the liquid toner in this type of electrostatic printer is how to supply the liquid toner to the surface of the ejection projection in a stable manner. And whether the colored particles can be efficiently blown off. This is because if the supply amount of the liquid toner including the colored particles fluctuates, the amount of the ejected colored particles also fluctuates, and density unevenness occurs in prints and images.
In this regard, at present, the printer disclosed in the above-mentioned publication cannot provide a sufficient result.

Further, in the above-described printer using ultrasonic waves, since ink droplets are ejected by mechanical vibration, it is not necessary to charge the colored particles. In order to eject fine ink droplets, the ultrasonic waves must be precisely focused on the ink liquid surface using a high ultrasonic vibration frequency of 150 MHz. For this reason, not only must the height of the ink liquid level be controlled with high precision on the order of submicrons, but also the ultrasonic lens system must be of high precision, which poses great difficulties in practical use. Furthermore, it is difficult to use highly viscous ink to eject droplets from the horizontal ink level with only the energy of ultrasonic waves. Can only be used,
In order to obtain high printing quality, it is not possible to use a highly viscous pigment that does not easily cause bleeding.

[0007] The present invention focuses on the above problems,
It was created to solve this effectively. SUMMARY OF THE INVENTION An object of the present invention is to provide an electrostatic ink jet printer capable of stably supplying a liquid toner and efficiently printing out aggregated colored particles and performing printing and image formation without density unevenness. Is to do.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a plurality of projections made of a dielectric material regularly arranged in a plane, and the projections including charged colored particles. A liquid toner that wets the surface of the projection, a bias electrode that applies a voltage of the same polarity as the charged colored particles and agglomerates the colored particles in the liquid toner at the tip of the emission projection by Coulomb force, and each of the emission projections And an ultrasonic generator for generating ultrasonic waves in the direction in which the ejection projections protrude to separate droplets containing the aggregated colored particles.

As a result, the entire surface of each ejection protrusion is wetted by the liquid toner in which the charged colored particles are dispersed by capillary action or the like, and a conical meniscus of thin liquid toner is formed on the entire surface of the ejection protrusion. By applying a bias voltage having the same polarity as the charging of the colored particles to the bias electrode, an electric field is generated by the bias voltage, and the colored particles are aggregated at the tip of the meniscus. Since the surface tension of the liquid toner is larger than the force of pushing the charged particles by the electric field, the aggregated colored particles accumulate at the tip of the meniscus.
In this state, the driving voltage is supplied to the ultrasonic wave generator to generate an ultrasonic wave. As a result, an ultrasonic wave is applied to the tip of the ejection projection to advance the tip of the ejection projection, and vibration is generated to separate the colored particles aggregated by the bias electric field from the tip of the meniscus. Since the agglomerated colored particles are easily released by the bias electric field, the separation easily occurs when an ultrasonic vibration serving as a trigger is applied. Since the separated colored particles (liquid toner droplets) are charged, they are accelerated by the electric field of the bias voltage and fly far, and adhere to a recording medium arranged in the ejection direction to form a print or an image. .

[0010] Then, the control of applying or stopping the ultrasonic vibration is performed to control the emission of the colored particles. As described above, since the detachment and the flying of the colored particles can be performed efficiently, for example, a pigment having a relatively high viscosity can be used as the liquid toner, and high-density fine printing or image formation without bleeding can be performed. it can.

In this case, a land having a height lower than that of the ejection projections is provided between the plurality of ejection projections so as to form a canal for transferring the liquid toner by capillary action. Since it flows through the canal and wets the surface of the ejection projection, the aggregation of the colored particles is performed promptly, the image quality can be increased without causing unevenness in density, and printing at a high frequency is also possible. .

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the electrostatic ink jet printer according to the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a plan view showing an electrostatic ink jet printer of the present invention, and FIG.
FIG. 3 is a schematic cross-sectional view taken along line A of FIG.
FIG. 4 is a cross-sectional view taken along a line and showing details of a substrate portion. FIG. 4 is a cross-sectional view showing the operation of the printer device of the present invention. FIG.
As shown in FIG. 2 and FIG. 2, the inkjet printer device 1 has a substrate portion 2 on which various electrodes and the like are provided, and an injection projection plate 3 bonded thereon. The injection projection plate 3
A plurality of (many) injection protrusions 4 are regularly and vertically arranged in the vertical and horizontal directions at an equal pitch. Each of the injection projections 4 has a truncated conical shape in which the tip of a cone is cut off in a flat shape. However, the tip 5 may have a curved surface shape, or may have a truncated pyramid shape in which the tip of a pyramid is cut off. Good.

At the approximate center between the projections 4, a rectangular land 6 having a height lower than the height of the projections 4 is provided upright from the bottom. A canal 7 having a fine groove width is formed. The canal 7 communicates with the entirety of the ejection protruding plate 3, and the liquid toner 8 formed by dispersing the charged colored particles in an insulating liquid made of, for example, isoparaffin or the like is formed in the canal 7 by capillary action. It is designed to be supplied by flowing. Further, the ejection projection plate 3 has, at the center in the oblique direction of the arrangement of the ejection projections 4, a spout hole 10 for spouting the liquid toner 8 onto the ejection projection plate 3, and an absorption hole 11 for sucking and collecting the liquid toner. Are formed, so that the liquid toner can be sufficiently supplied to each of the ejection projections 4 without bias. By supplying the liquid toner 8 to the surface of the ejection projection plate 3, the entire surface of each ejection projection 4 is wetted by the liquid toner 8 due to the capillary phenomenon, and the meniscus 12 whose surface becomes uneven due to surface tension is formed. become.

On the other hand, a bias electrode 13 made of, for example, copper foil is provided on one surface of the upper surface of the substrate portion 2 to be joined to the bottom surface of the ejection projection plate 3.
Is connected to a bias power supply 14 to apply a DC bias voltage having the same polarity as the colored particles. Due to the application of the bias voltage, an electric field is generated upward in FIG. 2, and the colored particles in the liquid toner 8 are moved by Coulomb force and aggregated at the tip 5 of the ejection projection 4.

Under the bias electrode 13, an ultrasonic generator 16 is individually provided corresponding to each of the emission projections 4 via an insulating layer 15. Each ultrasonic generator 16 is made of, for example, a piezoelectric ceramic such as PZT or barium titanate. When a voltage is applied thereto, the ultrasonic generator 16 mechanically vibrates at a high frequency in a tip direction A of the ejection projection 4 to generate ultrasonic vibration. It has become. As shown in FIG. 2, the upper surface of each ultrasonic generator 16 is commonly connected to form a common electrode 17, and the lower surface is formed with an individual electrode 18 to which a terminal 19 is connected. Then, by applying an ultrasonic excitation signal as a drive voltage to the individual electrode 18 via the terminal 19, the colored particles aggregated at the tip 5 of the ejection projection 4 can be separated.

In the substrate section 2, a supply path 20 for supplying the liquid toner 8 toward each of the wells 10 and a collection path 2 for collecting the liquid toner absorbed from each of the absorption holes 11 are provided.
1 are formed, each supply hole 20 communicates with each spring hole 10, and each recovery hole 21 communicates with each absorption hole 11. In order to manufacture the substrate portion 2, as shown in FIG. 3, for example, a thin plastic substrate 23 may be laminated in multiple layers by thermocompression bonding or the like. And holes forming vertical communication paths 24 and 25 communicating with the well 10 and the absorption hole 11. Further, if a printed circuit board subjected to a patterning process is used at a position where the bias electrode 13, the common electrode 17, and the like are provided, the substrate unit 2 can be easily manufactured.

The dimensions of each part in this embodiment are as follows: the pitch L1 between the ejection projections 4 is about 0.5 to 1.0 mm; the height L2 of the ejection projections 4 is about 0.2 to 1.0 mm;
Alternatively, the diameter L3 of the absorption hole 11 is about 0.2 to 0.3 mm, and the diameter of the tip 5 of the ejection projection 4 is about several tens of μm. For example, a droplet corresponding to the minimum gradation at an image density of 600 DPI (dot per inch) The formation is possible.

Next, the operation of the embodiment constructed as described above will be described. First, the liquid toner 8 is supplied to the upper surface of the ejection protruding plate 3 from each of the spout holes 10 through the supply path 20 as shown in FIG. 3, and is supplied into the canal 7 (see FIG. 2) using the capillary phenomenon. At the same time, the entire surface of each ejection protrusion 4 is wetted, and the used liquid toner 8 is collected from the absorption hole 11 into the collection path 21. The liquid toner 8 that wets the surface of each of the ejection projections 4 forms a meniscus 12 (see FIG. 2) which becomes uneven due to the surface tension of the medium. Here, when no voltage is applied to the bias electrode 13, there is no aggregation of the colored particles P on the top of the meniscus 12, as shown in FIG. 2, and the top is not swollen. And
When a bias voltage is applied to the bias electrode 13, an electric field is generated, and the colored particles P charged to the same polarity as the electric field are pushed away from the bias electrode 13. As shown in FIG. As shown by reference numeral 30, the colored particles P are aggregated and swell.

Here, when an ultrasonic excitation signal is applied to the individual electrode 18A via a predetermined selected terminal 19A among the terminals 19, the ultrasonic generator 16A causes vibration in the direction of arrow A to generate ultrasonic waves. 31 is fired toward the tip of the ejection projection 4A. Since the cross-sectional area of the tip of the ejection projection 4A and the meniscus 12 is gradually reduced and is a free end, the ultrasonic vibration intensity is gradually increased. This vibration breaks the balance of retention of the colored particles due to the surface tension of the toner solvent, and the colored particles are detached to generate droplets 8A. This droplet 8A
Is charged, the solvent surface tension is released, and it is accelerated by the bias electric field and flies upward in the drawing, and adheres to a recording medium such as recording paper (not shown) to form characters and images. . At this time, the ultrasonic excitation signal applied to the individual electrode 18A is, for example, shown in FIG. 5A. For example, a burst high-frequency signal of about 10 MHz of the power W is applied, and the droplet 8A has a large amplitude. The print density is controlled by changing this length. Further, instead of the signal as shown in FIG. 5A, an ultrasonic signal as shown in FIG. 5B may be applied. In this case, when the droplet 8A is generated, the same signal of the power W as described above is applied, and at other times, the signal of the power Wo having a small amplitude is applied. To prevent injection. According to this, in the portion of the electric power Wo, the ultrasonic waves release the constraint between the solvent and the colored particles in the liquid toner 8 and reduce the friction between the particles. Since the aggregation of the particles P by the Coulomb force can be performed at a higher speed, the injection interval can be reduced.

As described above, the ultrasonic wave is mainly used for separating the agglomerated colored particles P to form the droplets 8A, and the bias voltage is used for aggregating the charged colored particles in the liquid toner 8. And by using the formed droplet 8A to accelerate and fly toward the recording medium,
It is possible to efficiently form droplets of the liquid toner 8 to perform printing and image formation on a recording medium. In this case, since the liquid droplets can be efficiently formed as described above, a pigment having a higher viscosity than the dye can be used as the liquid toner 8, so that no blur occurs in the image or print, and the quality of the liquid toner 8 can be improved. A good image or the like can be formed.

Further, since the generated ultrasonic waves are gradually narrowed down toward the tip of the emission projection 4, the formation of the ultrasonic generating section 16 is not required to be so high in precision as compared with the conventional apparatus. , Making the design easier. Also, since the colored particles in the liquid toner 8 are vibrated as a secondary effect of the ultrasonic wave, the liquid toner moves smoothly in the canal 7 due to the capillary phenomenon and the colored particles in the meniscus 12 are smoothly aggregated. Yes, and this facilitates injection at higher frequencies.

Further, by providing the land 6, since the liquid level fluctuation generated in the meniscus 12 when the droplet 8A is detached is absorbed by the land 6, the liquid level fluctuation is caused by the adjacent ejection protrusion. 4, and the occurrence of adverse effects such as crosstalk can be prevented. Further, the land 6 may be eliminated and the base of the ejection projection 4 may be made thicker. In this case, the structure is an efficient structure for the propagation of ultrasonic waves, and a high-efficiency head is obtained. Further, the bias electrode 13 and the common electrode 17 can be used in common without being individual. According to this, since the ultrasonic wave generator 16 approaches the emission protrusion, interference of the ultrasonic wave with the adjacent emission point is reduced. In the above embodiment, the tip of the ejection projection 4 is
Although the structure protrudes sharply, the present invention is not limited to this. The cross-sectional shape of the tip 36 of the injection protrusion 35 may be formed to be substantially a right angle (90 degrees) as shown in FIGS.
The shape of the ejection projection 35 is a pyramid or a cone. Then, the distance L5 between the ultrasonic generator 16 and the tip 36 is
The setting is made to be an integral multiple of a half wavelength of the ultrasonic signal applied to the ultrasonic generator 16. This half-wavelength is
It is the wavelength when propagating inside. Although no land is provided in the illustrated example, it may be provided in the same manner as in the previous embodiment. 6 and 7 show only the main components, and the other components are configured in the same manner as in the previous embodiment.

As described above, since the cross-sectional shape of the distal end 36 of the emission projection 35 is substantially right angle and the whole is shaped like an isosceles triangle, the plane wave emitted from the ultrasonic wave generator 16 as shown in FIG. The ultrasonic wave 38 is reflected on the surface of the liquid toner that wets the slope of the ejection protrusion 35 and the tip 3 of the ejection protrusion 35
From 6, they meet on the vertical line 39 lowered to the ultrasonic generator 16. The further advanced ultrasonic wave 38 is reflected downward on the opposite slope and returns to the upper surface of the ultrasonic generator 16. Therefore, an ultrasonic standing wave is generated inside the ejection projection 35.
Since the vibration antinode is formed on the perpendicular line 39 and a large amount of vibration energy is accumulated, the action of separating the droplets agglomerated at the tip 36 becomes large, and efficient droplet ejection can be performed.

In particular, if the injection projection 35 is formed in a conical shape having a vertical angle of 90 degrees by a plastic molded product or the like, all ultrasonic waves pass through the center line of the conical shape, so that the resonance energy on this line becomes extremely large. More efficient droplet ejection can be performed. It should be noted that each dimension in the above embodiment is merely an example, and is not limited to this.

[0025]

As described above, according to the electrostatic ink jet printer of the present invention, the following excellent functions and effects can be exhibited. The colored particles are aggregated at the tip of the ejection protrusion by the bias electric field, and the agglomerated colored particles are separated by vibrating the tip of the meniscus of the ejection protrusion by ultrasonic waves, and the separated colored particles are accelerated and fly by the bias electric field. Since printing and image formation are performed by performing this, high-density, fine print without bleeding can be performed on any recording medium such as absorbent paper and non-absorbable art paper. In particular, since a pigment that is more viscous than a dye and does not cause bleeding can be used as the liquid toner, the image quality can be significantly improved. Further, since the flying of the agglomerated colored particles is accelerated by the bias electric field, the recording medium can be separated from the ejection head, and an inexpensive printer that does not require precise adjustment and assembly for assembling the ejection head can be realized. Furthermore, since a precise acoustic lens element for converging the ultrasonic wave is not required, and the distance between the liquid surface and the ultrasonic wave generating section does not need to be made with high accuracy, the configuration of the injection head is simple and an inexpensive product can be realized. . Further, since it is not necessary to converge the ultrasonic wave, it is not necessary to have an extremely short wavelength (10 μm) and a high frequency (150 MHz) like the ultrasonic wave of the conventional device, and the frequency is several tens of M
Hz or less, and therefore easier and cheaper to manufacture than conventional devices. Also, unlike the liquid toner jet method, a high voltage (about 300 V to 900 V) for a driving electric field for releasing colored particles is not required, and the ultrasonic generator can be driven at a relatively low voltage (several tens of volts or less). There is an advantage that the head drive control circuit can be easily realized at low cost. Also, the cross-sectional shape of the tip of the injection projection is set to be substantially right angle,
By specifying the distance between the tip and the ultrasonic generator, an ultrasonic standing wave is generated in the emission protrusion, and the emission point exists on the antinode line (or on the plane) of the vibration amplitude of the standing wave. The resonance energy at the ejection point can be increased, and as a result, efficient droplet detachment can be achieved with a small ultrasonic output.

[Brief description of the drawings]

FIG. 1 is a plan view showing an electrostatic ink jet printer of the present invention.

FIG. 2 is a schematic sectional view of the device shown in FIG.

FIG. 3 is a cross-sectional view of the apparatus shown in FIG. 1 taken along line BB, showing details of a substrate portion.

FIG. 4 is a sectional view showing the operation of the printer device of the present invention.

FIG. 5 is a waveform diagram showing an ultrasonic excitation signal applied to an ultrasonic generator.

FIG. 6 is a sectional view showing a main part of another device of the present invention.

FIG. 7 is a sectional view showing an operation state of the device shown in FIG. 6;

FIG. 8 is an enlarged view of a part of the device shown in FIG. 7;

[Description of Symbols] 1 ... Inkjet printer device, 2 ... Substrate unit, 3 ... Ejection projection plate, 4,35 ... Ejection projection, 6 ... Land, 7 ... Canal, 8 ... Liquid toner, 10 ... Spout hole, 11 ... Absorption Hole, 1
2: Meniscus, 13: Bias electrode, 16: Ultrasonic wave generator, 17: Common electrode, 18: Individual electrode, P: Colored particles.

Claims (6)

[Claims] 1. A plurality of projections made of a dielectric material regularly arranged in a plane, a liquid toner containing charged coloring particles and wetting the surface of the projections, and the same polarity as the charged coloring particles. And a bias electrode for applying the voltage of the above to agglomerate the colored particles in the liquid toner at the tip of the ejection protrusion by the Coulomb force. And an ultrasonic generator for generating a sound wave to release droplets containing the aggregated colored particles. 2. A land having a height lower than that of the ejection projections is provided between the plurality of ejection projections to form a canal for transferring the liquid toner by capillary action. 2. The electrostatic inkjet printer according to claim 1. 3. The electrostatic ink jet printer according to claim 1, wherein the bias electrode comprises a single electrode commonly provided on a base side of each of the ejection projections. 4. The electrostatic ink jet printer according to claim 1, wherein the liquid toner is made of a pigment obtained by dispersing charged colored particles in an insulating liquid. apparatus. 5. The electrostatic ink jet printer according to claim 1, wherein a burst high-frequency signal is applied to the ultrasonic generator as an ultrasonic excitation signal. 6. The cross section of the tip of the emission projection is formed at a right angle, and the distance between the tip and the ultrasonic generator is set to a length that is an integral multiple of a half wavelength of the ultrasonic wave. The electrostatic inkjet printer according to any one of claims 1 to 5, wherein: