JPH11268277A - Ink-jet recording apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink-jet recording apparatus wherein reaching distance of ink droplets is long and fluctuation of reaching positions is small and high quality of image is obtd. SOLUTION: An ink 18 is stored in a nozzle 10 and a thin filmy heat generating resistance element 13 is fitted on the inner wall face of the nozzle 10. A nozzle plate 11 is fitted on the front face of the nozzle 10 and an opening part 12 being an injection outlet of ink droplets 19 is provided on the nozzle plate 11. This nozzle plate 11 is constituted of an electrically conductive body and is also used as an electrode for generating electric field at the front of the nozzle 10. A cylindrical platen 20 is arranged at the front of the nozzle 10 and the inside of the platen 20 is a counter electrode 21 being a pair with the nozzle plate 11. A recording paper 25 is arranged by being brought into close contact with the outer peripheral side of the platen 20. In addition, instead of using the heat generating resistance element 13, a laminated piezoelectric element can be also used.

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 forming an image by ejecting ink droplets from nozzles, and more particularly to a drop-on-demand type apparatus for discharging ink only when necessary. The present invention relates to an ink jet recording apparatus capable of stably landing ink droplets having a small particle diameter on a recording medium such as recording paper.

[0002]

2. Description of the Related Art Conventionally, there has been known an ink jet printer which forms recording dots by flying small ink droplets (ink droplets) on recording paper. This ink-jet printer has advantages in that it has less noise than other recording methods and does not require processing such as development and fixing, and is widely used as plain paper recording technology.

An ink jet printer is of a type in which ink droplets fly by static electricity (for example, Japanese Patent Publication No. 36-137).
No. 68) has been put to practical use,
Various recording methods based on each of the various principles have been proposed. These can be broadly classified into two types: a continuous type and a drop-on-demand type.

In the continuous type, high-speed thread-like ink is ejected from a small nozzle by applying pressure, and disturbance is caused by ultrasonic waves or the like to generate continuous ink droplets in a row. By removing unnecessary ink droplets by using a means for modulating the flight direction of the image, ON / OFF control of an image point is performed to form an image. As a typical example of the continuous type, Japanese Patent Publication No. 42-8350
There is a so-called sweet system described in Japanese Patent Application Laid-Open No. H10-260, 1988.

[0005] The continuous type has a relatively high flying speed of ink droplets (20 to 60 m / sec) and is therefore less susceptible to disturbance by air or viscous drag. Therefore, the fluctuation of the landing position is small, and the flying distance is small. Can be long. For this reason, the continuous type has a track record as a printer for high definition and large screen. However, it is said that it is difficult to make the characteristics of each nozzle uniform when a multi-nozzle is used.

[0006] On the other hand, unlike a continuous type such as a continuous type, a type called a pressure pulse type has been put into practical use as a dot-on-demand type which discharges ink only when necessary. In particular, a method in which an ink droplet is caused to fly by the pressure of steam generated by heating using a heating element (for example, Japanese Patent Publication No. 56-9429, Japanese Patent Publication No. 61-1986)
No. 59911) and a method in which an ink droplet is caused to fly by a mechanical pressure pulse using a piezoelectric body (for example, Japanese Patent Publication No.
No. 3-12138) is a typical example. The pressure pulse type has a track record as a multi-nozzle type for forming a plurality of recording dots in parallel, and is currently widely used.

As described above, the continuous type has a relatively high ink flying speed of 20 to 60 m / sec, whereas the conventional drop-on-demand type has a flying speed of ink droplets. Is up to about 15m / sec,
Normally, the value is lower. Further, it is said that it is necessary to limit the flying speed to about 2 to 5 m / sec in order to generate good ink droplets without scattering in order to improve image quality.

When the flying speed of the ink is low, the landing position is likely to fluctuate due to the influence of the air flow, and the flying distance is set short because the speed is further reduced by the viscous resistance of the air during the flight. Must. In particular, when flying small ink droplets to form a high-definition image, the smaller the particle size, the greater the effect of air resistance. Even if it is shortened, it does not reach the recording medium.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the conventional ink jet recording apparatus as described above, and an object of the present invention is to provide a long flying distance using small ink droplets. Accordingly, it is an object of the present invention to provide a drop-on-demand type ink jet recording apparatus having high image quality by realizing the above-described method and suppressing the fluctuation of the landing position.

[0010]

According to the present invention, there is provided an ink jet recording apparatus comprising: first driving means for applying pressure to ink contained in a nozzle to eject ink droplets from the nozzles; and recording on the ejected ink droplets. An ink jet recording apparatus including a second driving unit that further applies a force flying in a medium direction, wherein the second driving unit includes a first electrode disposed on a back side of the recording medium, And a second electrode that is disposed in front of the nozzle opposite to the one electrode, and that applies an electrostatic force to the ink droplet.

[0011] The second electrode may be composed of a plurality of electrodes arranged along the flight direction of the ink droplet. According to the inkjet recording apparatus of the present invention, the ink droplets ejected from the nozzle by the first driving unit are formed by the second driving unit (that is, the first electrode and the second electrode facing each other). Accelerated by electrostatic forces in an electric field. As a result, deceleration due to air resistance can be suppressed or compensated, and the speed can be increased to an initial speed or more.

Therefore, according to the present invention, a long flight distance can be realized and small fluctuations in the landing position can be suppressed while using small ink droplets, so that image quality can be improved.

[0013] The second electrode may be composed of a plurality of electrodes arranged along the direction of flight of the ink droplet. Further, a heating element or a piezoelectric element arranged in the nozzle can be used as the first driving means.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Some examples of an ink jet recording apparatus according to the present invention will be described below in detail with reference to the drawings. (Example 1) FIG. 1 shows an example of an ink jet recording apparatus according to the present invention. FIG. 1 is a cross-sectional view (a cross-sectional view in the nozzle axis direction) of a nozzle constituting a main part of the ink jet recording apparatus and its periphery.

An ink 18 is contained inside the nozzle 10, and a thin-film heating resistor 13 is provided on the inner wall surface of the nozzle 10.
(Heating element) is attached. A nozzle plate 11 (second electrode) is attached to the front surface of the nozzle 10, and the nozzle plate 11 is provided with an opening 12 serving as a discharge port of an ink droplet 19. The nozzle plate 11 is formed of a conductor, is connected to a voltage supply 16, and is also used as one electrode for generating an electric field in front of the nozzle 10.

A cylindrical platen 20 is disposed in front of the nozzle 10, and the inside of the platen 20 is a counter electrode 21 (first electrode) that forms a pair with the nozzle plate 11. The counter electrode 21 is connected to the ground. The recording paper 25 (recording medium) is held in close contact with the outer peripheral surface of the platen 20.

FIG. 2 is a schematic diagram showing the configuration of a recording head (a set of nozzles) using a heating element as the first driving means. An insulating layer 32 is uniformly provided on a substrate 31, on which a heating resistor 13 and an electrode 34 for supplying a current to the heating resistor 13 are provided. The heating resistors 13 and the electrodes 34 are formed in a number corresponding to the recording dots formed at a time. Furthermore, an oxidation prevention film 35, a shock absorption film 36, and a reaction prevention film 37 are sequentially provided thereon. As described above, the multilayer substrate 3
0 is configured.

Separately, the partition 38 and the upper lid 3
A recording head is constituted by attaching a member 40 made of a material 9 or the like to a multilayer substrate 30 made of the above-described heating resistor 13 and attaching a nozzle plate 11 provided with an opening 12 to the front surface thereof. ing.

Next, the recording operation of this ink jet recording apparatus will be described with reference to FIG. Ink 18
Is supplied into the nozzle 10 through the ink supply hole 14. When a current pulse is sent to the heating resistor 13, the temperature of the heating resistor 13 rises sharply, the ink in contact with it boils, and bubbles are generated on the upper surface of the heating resistor 13. As the bubble grows in a short time, the pressure in the nozzle 10 sharply increases, and the ink droplet 19 is ejected from the opening 12.

At this time, a voltage is applied to the nozzle plate 11 to
When an electric field is generated in front of the nozzle 10 with the counter electrode 21, the ejected ink droplet 19 is accelerated in the direction of the counter electrode 21 by the electrostatic force received from the electric field, flies, and flies. Reaches (landing). Thus, recording dots are formed on the recording paper 25.

When the bubbles in the nozzle 10 disappear after the ejection of the ink droplets 19, the ink 18 is supplied from the ink supply holes 14 to prepare for the next ejection operation. If the recording pause time exceeds a certain value,
In order to prevent clogging in the nozzle 10, a head cap (not shown) is attached to the nozzle 10, and the ink whose density has increased in the nozzle 10 is sucked out to the head cap.

FIG. 3 is a diagram for explaining the force that an ink droplet receives from an electric field formed in the flight direction. In the case of ink having a relatively low volume resistance, for example, 10 ⁶ to 10 ⁷ Ωcm or less, charges are injected from the electrode (nozzle plate 11) in contact immediately before flying, and the charged state as shown in FIG. And receives a force in an electric field. According to the theory of electromagnetism, the magnitude f of the force is represented by f = q · E, where q is the amount of charge and E is the electric field strength.

On the other hand, the volume resistance is relatively high, for example, 10
^{In the case} of ink of ⁸ to 10 ⁹ Ωcm or more, since the property as a dielectric is strong, as shown in FIG. 3B, a polarization charge is generated and a force is applied in an electric field. The magnitude f of the force is represented by r as the radius of the ink droplet, k as the relative permittivity of the ink, and 傾 き as the gradient of the electric field.
If E, f = 2πε ₀ r ³ {(k−1) / (k + 2)} E ·} E.

However, these two forces are not clearly divided by the value of the volume resistance, and do not exist exclusively, but actually coexist. According to this example, the ink droplets are separated from the nozzles and fly separately from the first driving means (a heating element that applies thermal energy to generate the pressure of bubbles) used to separate the ink droplets from the nozzles. A force in the flight direction is applied to the ink droplet by the electrostatic force of the second driving means to suppress or compensate for the deceleration due to the air resistance applied to the ink droplet, and further increase the ink droplet to an initial speed or more. I have. In this way, by providing the second driving means using the electrostatic force,
Even with a small ink droplet having a particle size of 0 μm or less, a long reach distance and small fluctuation of the landing position can be realized. Therefore, according to the present invention, a high-quality image can be formed.

Example 2 FIG. 4 shows an example of an ink jet recording apparatus according to the present invention. FIG. 1 is a cross-sectional view (a cross-sectional view in the nozzle axis direction) of a nozzle constituting a main part of the ink jet recording apparatus and the periphery thereof.

In this example, in addition to the pair of electrodes (nozzle plate 11 and counter electrode 21) in the previous example, a plurality of auxiliary electrodes (in this example, three auxiliary electrodes having an opening through which ink droplets pass) are provided. : 41a, 41b, 41c) are arranged in parallel with each other along the flight direction of the ink droplet 19. Each of these auxiliary electrodes is connected to a drive element 42 for controlling a respective potential. An electrostatic force can be applied to the flying ink droplet 19 by sequentially applying an alternating voltage to each of the auxiliary electrodes as described below.

A method of accelerating the ink droplet when the auxiliary electrode is arranged as described above will be described with reference to FIG. Each of these auxiliary electrodes 41a to 41c has a structure shown in FIG.
(B) As shown in (c), pulse voltages are applied in order. As a result, the position of the electric field for accelerating the ink droplet 19 moves with time, and the ink droplet 19 receives a force in order from the moving electric field and flies in the recording paper direction as shown in FIG.

Specifically, as in various examples shown in FIG. 6, the voltage applied to the plurality of auxiliary electrodes 41a to 41c is controlled. That is, in the example shown in FIG. 6A, the position of the electric field moves in the direction of the recording paper sequentially with time.
The driving element 4 outputs a three-phase voltage pulse train controlled by the transfer shift.
2 to the auxiliary electrodes 41a to 41c. In this example, the shape of the voltage pulse is determined so that the voltage pulse is applied to only one of the three phases at any time.

Further, in the example shown in FIG. 6B, instead of the above method, at any time, two out of three phases are used.
The applied voltage is controlled so that a voltage pulse is applied to the phase.

Further, the voltage waveform applied to each auxiliary electrode does not necessarily have to be a rectangular pulse shape.
As shown in FIG. 6C, sine waves having different phases can be used.

In each of the above examples, the number of auxiliary electrodes is three.
In addition, the number of phases of the voltage pulse applied to each auxiliary electrode is three, but is not limited to this. For example, the number of auxiliary electrodes is set to 4 and FIG.
As shown in (d), four-phase voltage pulses can be used.

(Example 3) FIGS. 7 and 8 show another example of an ink jet recording apparatus according to the present invention. In this example,
As the first driving means used to separate the ink droplet from the nozzle, a piezoelectric element is used in place of the heating element in the above example.

FIG. 7 is a schematic diagram of a cross section of a nozzle which is a main part of the ink jet recording apparatus and its periphery.
A part of the inner wall of the ink chamber 77 is constituted by a vibration plate 74, and the vibration plate 74 has a laminated piezoelectric element 75 (piezoelectric element).
Is attached. A nozzle plate 72 (second electrode) is attached to the front side of the ink chamber 77, and an opening 71 for discharging ink is formed in the nozzle plate 72. The nozzle plate 72 is made of metal and also serves as one electrode.
A flat counter electrode 80 (first electrode) is arranged to face the nozzle plate 72. A platen 79 is attached to the front surface of the counter electrode 80, and the recording paper 78 is held on the surface of the platen 79.

The multilayer piezoelectric element 75 is driven to eject ink from the opening 71, and a voltage is applied between the nozzle plate 72 and the counter electrode 80 to generate an electric field between them, thereby opening the opening. The ink droplets 19 ejected from 71 are accelerated. The counter electrode 80 is grounded,
A voltage of about 500 to 1000 V is applied to the nozzle plate 72.

FIG. 8 shows a configuration of a nozzle portion of the above-described ink jet recording apparatus. The recording head 70 (collection of nozzles) includes a nozzle plate 72 having an opening 71 formed therein, a substrate 73 forming a supply and discharge path of ink into the ink chamber 77, a laminated piezoelectric element 75, and inner walls of the ink chamber 77. And a diaphragm 74 driven by the laminated piezoelectric element 75, and the like. The substrate 73 and the laminated piezoelectric element 75 are supported by a member 76. The tip of the laminated piezoelectric element 75 is fixed to the back surface of the diaphragm 74.

When a voltage signal is applied to the laminated piezoelectric element 75,
The laminated piezoelectric element 75 expands and contracts in the longitudinal direction, changes the volume in the ink chamber 77, and pressurizes the ink inside. The pressurized ink is discharged from the opening 71.

According to this example, apart from the first driving means (piezoelectric element for generating a pressure pulse in the nozzle) used to separate the ink droplet from the nozzle, the ink droplet flies separately from the nozzle. By applying a force in the flight direction to the ink droplet by the electrostatic force of the second driving means,
The ink droplets are suppressed or compensated for the deceleration due to the air resistance, and the ink droplets are accelerated to an initial speed or more.
As described above, by providing the second driving unit using the electrostatic force, it is possible to realize a long reach distance and a small fluctuation of the impact position even for an ink droplet having a small particle diameter of 20 μm or less. Therefore, according to the present invention, it is possible to realize a high quality image.

Further, when the piezoelectric element is used as the first driving means as in this example, the driving force to be generated by the piezoelectric element in order to eject ink droplets can be set small. Therefore, reducing the load on the first driving means,
Specifically, the drive voltage of the piezoelectric element can be kept low. As a result, it is possible to form a well-controlled ink flow inside the nozzle by adjusting the voltage waveform applied to the piezoelectric element, and to be less affected by the voltage applied to the adjacent piezoelectric element. In addition, an inherent effect that ink droplets with small size and shape fluctuations can be generated can be obtained.

In the various examples described above, a cylinder or a plate having a shape corresponding to the platen is used as the counter electrode disposed on the back surface of a recording medium such as recording paper. Is not limited to these. For example, as shown in FIG. 9A, the shape of the counter electrode 80a can be configured so that a knife-edge electric field is formed linearly in the same direction as the arrangement direction of the nozzle rows. Especially when using dielectric ink,
Since an attractive force acts on the ink droplet in proportion to the gradient of the electric field strength,
Such an electric field having a shape concentrated in the flight direction is effective.

Further, as shown in FIG.
0b may be configured by arranging the same number of linear electrodes as the dot resolution in a direction orthogonal to the arrangement direction of the nozzle rows. If an electrode having such a shape is used, it is possible to effectively guide the ink droplet having a reduced speed to the landing position. In particular, the effect is great in the case of the division driving method in which the recording within one main scanning width is divided into a plurality of timings and recorded.

[0041]

As described above, according to the ink jet recording apparatus of the present invention, in addition to the first driving means (heating element or piezoelectric element) for discharging ink droplets from the nozzles, the discharged ink The provision of the second driving means for applying electrostatic force to the droplet in the flight direction suppresses or compensates for the deceleration due to the air resistance that the ink droplet receives while flying, and further increases the ink droplet above the initial speed. Can be faster. As a result, even with a small ink droplet of 20 μm or less, it is possible to realize a long reaching distance and a small fluctuation of the landing position. Therefore, according to the present invention, the image quality can be improved.

According to the ink jet recording apparatus of the present invention, the driving force for landing the ink droplets ejected from the nozzles and flying on the recording medium is borne by the second driving means common to all the dots. Therefore, the first driving means required for each individual dot is assigned only the role of ejecting ink droplets from the nozzles, and the driving force can be set small. Therefore, it is possible to reduce the load on the first driving means, for example, to lower the driving voltage of the piezoelectric element.

In particular, when a piezoelectric element is used as the first driving means, it is possible to form a well-controlled ink flow inside the nozzle by adjusting the voltage waveform applied to the piezoelectric element. In addition, since it is less likely to be affected by the voltage applied to the adjacent piezoelectric element, it is possible to generate ink droplets with small size and shape fluctuations.

[Brief description of the drawings]

FIG. 1 is a partial sectional view showing a first example of an ink jet recording apparatus according to the present invention.

FIG. 2 is a schematic diagram showing a configuration of a recording head used in the ink jet recording apparatus shown in FIG.

FIG. 3 is a diagram illustrating electrostatic force acting on ink droplets in the ink jet recording apparatus according to the present invention;
(A) shows a case where the volume resistance of the ink is relatively low, and (b) shows a case where the volume resistance of the ink is relatively high.

FIG. 4 is a partial sectional view showing a second example of the ink jet recording apparatus according to the present invention.

5A to 5C are diagrams illustrating a method of accelerating ink droplets using a plurality of auxiliary electrodes in the ink jet recording apparatus illustrated in FIG. 4; FIGS. FIG. 4 is a diagram illustrating a relationship with a voltage pulse applied to an auxiliary electrode.

FIGS. 6A to 6C are diagrams showing voltage waveforms applied to each auxiliary electrode in the ink jet recording apparatus shown in FIGS.
(D) shows examples of various voltage waveforms.

FIG. 7 is a partial sectional view showing a third example of the ink jet recording apparatus according to the present invention.

FIG. 8 is a schematic diagram showing a structure of a nozzle unit of the ink jet recording apparatus shown in FIG.

FIG. 9 is a diagram showing another example of the shape of the counter electrode used in the ink jet recording apparatus according to the present invention, (a).
Shows an example of an electrode forming a knife-edge electric field in the arrangement direction of the nozzle rows, and (b) shows an example in which a plurality of electrodes are arranged in the main scanning direction.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Nozzle, 11 ... Nozzle plate (2nd electrode), 12 ... Opening, 13 ... Heating resistor (heating element), 14 ... Ink supply hole, 16 ... Voltage supply source, 18: ink, 19: ink drop, 20 ...
・ Platen, 21 ... Counter electrode (first electrode), 25
... Recording paper (recording medium), 30 ... Multilayer substrate, 31
... substrate, 32 ... insulating layer, 34 ... electrode (for current supply), 35 ... oxidation prevention film, 36 ... shock absorption film, 37 ... reaction prevention film, 38 ... .Partitions, 39
· Upper lid, 40 ... members, 41a, 41b, 41c ···
Auxiliary electrodes, 42 driving elements, 70 recording heads (nozzles), 71 opening parts, 72 nozzle plates, 73 substrates, 74 diaphragms, 75 plates ..Laminated piezoelectric elements (piezoelectric elements), 76 members, 77 ...
Ink chamber, 78: recording paper, 79: platen, 8
0 ... electrode.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasuo Hosaka 1st location, Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture. (72) Inventor Kazushi Nagato Toshiba Komukai, Sai-ku, Kawasaki-shi, Kanagawa. No. 1 in the Toshiba R & D Center (72) Inventor Kazuhiko Higuchi 1 in Komukai Toshiba-cho in Koyuki-ku, Kawasaki-shi, Kanagawa Prefecture In-Toshiba R & D Center (72) Inventor Koichi Ishii Kawasaki-shi, Kanagawa 1, Komukai Toshiba-cho, Ward Inside Toshiba R & D Center

Claims (4)

[Claims] A first driving unit that applies pressure to ink contained in a nozzle to eject ink droplets from the nozzle;
And an ink jet recording apparatus provided with a second driving means for further applying a force to the ejected ink droplet in the direction of the recording medium, wherein the second driving means is disposed on the back side of the recording medium. An ink-jet recording apparatus comprising: a first electrode; and a second electrode disposed in front of the nozzle so as to face the first electrode and applying an electrostatic force to the ink droplet. 2. The ink-jet recording apparatus according to claim 1, wherein the second electrode includes a plurality of electrodes arranged along a flying direction of the ink droplet. 3. The method according to claim 1, wherein the first driving unit is a heating element disposed in the nozzle, and causes the ink to boil and eject ink droplets by the pressure of the vapor. The inkjet recording apparatus according to claim 2. 4. The first driving means is a piezoelectric element disposed in the nozzle, and applies a voltage to the piezoelectric element to pressurize ink to discharge ink droplets. The ink jet recording apparatus according to claim 1.