JP2003300321A - Electrostatic ink jet recorder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an electrostatic ink jet recorder in which an ink drop is ejected under optimal conditions while sustaining a specified resolution. <P>SOLUTION: Assuming the width of each slit 104 is a and the projecting height from the end face 107a of an ink supporting part 107 between the slits 104 to the forward end 102a of an ink ejecting part 102 is b, following conditions are satisfied: 30 μm≤a≤150 μm and 10 μm≤b≤60 μm. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet recording apparatus, and more particularly to an electrostatic ink jet recording apparatus which forms an electric field and ejects ink charged by Coulomb force.

[0002]

2. Description of the Related Art In an electrostatic ink jet recording apparatus, a plurality of ejection electrodes for ejecting ink droplets are arranged in the width direction of a recording sheet to form a print head.
An electric field is formed between the ejection electrode and a counter electrode arranged so as to face the ejection electrode, and the Coulomb force of this electric field forms a charged ink droplet in front of each ejection electrode. The ink is ejected from the ink ejection unit to form an image on the recording paper. Each ink ejecting section is provided so as to correspond to one pixel of the image, and the gradation of each pixel can be changed by controlling the amount of ink ejected from the ink ejecting section.

In order to eject ink droplets from the print head, ink is attached to the vicinity of the tip of each ink ejecting portion (wet the vicinity of the tip of the ink ejecting portion) by utilizing the capillary phenomenon and surface tension, and the state is maintained. An electric field is applied to overcome the surface tension. Then, the charged ink is drawn from the print head toward the recording paper, and becomes a substantially spherical ink droplet due to surface tension during flight.

[0004]

The ink ejecting portion projects more toward the recording paper than other portions so that the electric field is likely to concentrate in order to eject ink droplets from this portion. However, if the protrusion height of the ink ejection portion is too high,
Ink does not adhere to the tip of the ink ejecting unit, the amount of ink ejected from the ink ejecting unit is reduced, and in order to obtain an image with an appropriate density, the applied electric field must be increased. On the contrary, when the protrusion height of the ink ejection portion is low, the electric field is not concentrated on the ink ejection portion, and even from a portion other than the ink ejection portion, for example, an edge portion of the ink support that constitutes a slit for supplying ink. Ink is ejected and the ink droplets become too large, or the position where the ink droplets adhere on the recording paper is displaced, and the image quality deteriorates.

The present invention has been made to solve the above problems, and in an electrostatic ink jet recording apparatus, obtains a shape in the vicinity of an ink ejecting portion of a print head which can eject ink droplets under optimum conditions. The purpose is to

[0006]

In order to achieve the above object, an electrostatic ink jet recording apparatus of the present invention applies an electric field to charged ink, and ejects the ink by the Coulomb force generated by the electric field, thereby ejecting the ink. In an electrostatic ink jet recording apparatus for recording on a recording medium surface facing a recording medium portion, a plurality of ink ejected from an end face of the print head facing the recording medium surface to the recording medium surface side and arranged at a predetermined pitch. Section and a plurality of slits formed on both sides of the ink ejection section for supplying ink to the ink ejection section, the width of each slit is a, and an ink support section between the slits is provided. Let b be the protrusion height from the end face of the ink jet head to the tip of the ink discharge portion, and 30 μm ≦ a ≦ 150 μm and 10 μm ≦ b ≦ 6.
It is characterized in that each condition of 0 μm is satisfied.

In the above structure, 0.5 ≦ b / a ≦ 1.
It is preferable that the condition 5 is further satisfied.

[0008]

DETAILED DESCRIPTION OF THE INVENTION An electrostatic ink jet recording apparatus according to an embodiment of the present invention will be described. The configuration of the print head in the electrostatic ink jet recording apparatus of this embodiment is shown in FIG. Further, FIG. 2 shows a schematic configuration of an ink ejection mechanism in the electrostatic ink jet recording apparatus.

As shown in FIG. 2, in the electrostatic ink jet recording apparatus of the present embodiment, the recording paper P is shown in FIG.
It is assumed that the sheet is conveyed at a constant speed in the direction indicated by the middle arrow (for example, the vertical direction, hereinafter referred to as the “sub-scanning direction”). The print head 10 is arranged so that ink is ejected in a direction orthogonal to the recording surface of the recording paper P (eg, horizontal direction, hereinafter referred to as “main scanning direction”). The counter electrode 20 is provided so as to face the print head 10 with the recording paper P in between. A secondary electrode 30 is provided between the print head 10 and the counter electrode 20 so as to face the print head 10. The counter electrode 20 and the secondary electrode 30 are substantially parallel to the recording surface of the recording paper P.

The print head 10 is fixed and has a printing width longer than the width of the recording paper P in the main scanning direction. As an example, when the electrostatic inkjet recording apparatus according to the present embodiment prints a high-quality print similar to a photo quality, if the width of the recording paper P in the main scanning direction is 3.5 inches (about 89 mm), the print is performed. The print width of the head 10 is
The length is 90 mm or more so as to be longer than that. Ink is ejected from an ink ejecting unit 102, which will be described later, onto the recording paper P all at once, and printing is performed for each line of an image. In addition, from the print head 10, a predetermined color (1 color)
Since only the above ink can be ejected, in the case of color printing, it is assumed that the print heads 10 corresponding to the respective color inks are arranged in the sub-scanning direction.

As shown in FIG. 1, the printhead 10
Is a base member 10 formed of, for example, a ceramic material.
1 and the cover member 105. At the end of the base member 101 on the ink ejection side, a plurality of ink ejection portions 102 are formed at a predetermined pitch so as to eject in the ink ejection direction. In addition, the upper surface 1 of the base member 101
A plurality of ejection electrodes 103 and the like are formed at 01a at a predetermined pitch corresponding to each ink ejection portion 102.

The ink ejecting portion 102 is formed into an isosceles triangle whose tip is the apex, for example, by cutting the end surface of the base member 101 or the cover member 105, and the solid component in the ink is ejected. By concentrating on the top of the portion 102, the solid component in the ink is concentrated. Assuming that the resolution of this electrostatic ink jet recording apparatus is 600 dpi, the ink ejection unit 1
The pitch of 02 is about 40 μm.

The ejection electrode 103 is made of a highly conductive material such as gold, and is laminated on the upper surface 101a of the base member 101 and the side surface of the ink ejection portion 102. As shown in FIG. 2, each ejection electrode 103 has
A bias voltage source E1 for applying a bias voltage, a pulse voltage source E2 for applying a pulse voltage at the time of ink ejection, and a reverse bias voltage for applying a reverse bias voltage for diluting solid components in ink, respectively. Source E3 is connected. The positive electrode of the pulse voltage source E2 and the negative electrode of the reverse bias voltage source E3 are switchably connected by a switch S1. The negative electrode of the bias voltage source E1 and the positive electrode of the reverse bias voltage source E3 are the voltage source E for applying a predetermined voltage (for example, 500 V) to the secondary electrode 30.
5 is connected to the positive electrode. The bias voltage source E1 applies a bias voltage of, for example, 1500 V to the ejection electrode 103. The pulse voltage source E2 has a voltage (eg, 500 V) sufficient to eject ink from the ink ejecting unit 102.
Is applied to the ejection electrode 103. Therefore, the voltage applied to the ink ejection unit 102 when ejecting ink is 2500V.

Inside the cover member 105, a cavity 105a functioning as an ink storage portion is formed. Further, on both side portions 105c of the cover member 105, an ink supply pipe 106a and an ink discharge pipe 106b are respectively provided.
Is provided, and the ink flows in the direction indicated by the arrow in FIG. 1 (ink circulation direction). The ink supply pipe 106a and the ink discharge pipe 106b are connected to an ink tank and a pump (not shown), respectively, and are configured so that ink circulates between the ink tank and the cavity 105a at a predetermined flow rate.

In this embodiment, a bias voltage is applied to the ejection electrode 103 to forcibly collect the solid component charged with, for example, + in the vicinity of the ink ejection portion 102, and a predetermined concentration (for example, about 20%). Discharge electrode 1 after concentrated to
Ink is applied by applying a pulse voltage to 03.

The counter electrode 20 is grounded and functions as an electrode facing the ejection electrode 103. Counter electrode 20
Is formed in a flat plate shape by a conductor such as copper, and the recording paper P slides on it. The secondary electrode 30 is
It is provided to strengthen the electric field in the vicinity of the ink ejecting portion 102, and a predetermined voltage (500 V) is applied by the voltage source E5 to increase the potential gradient between the print head 10 and the secondary electrode 30. . The secondary electrode 30 is also formed in a flat plate shape with a conductor such as copper. In addition, the print head 1 is provided near the center of the secondary electrode 30.
A slit 31 is formed in parallel with the width direction (main scanning direction) of the recording paper P for allowing the ink ejected from the zero ink ejecting unit 102 to pass therethrough.

The ink discharge control section 40 switches the switch S1 to the pulse voltage source E2 side when the main switch of the apparatus is turned on or when a print start signal is received, and the discharge electrode 10 is discharged.
A bias voltage is applied to 3 to concentrate the solid components in the ink near the ink ejection portion 102. Further, when printing of one image of the apparatus is completed, the switch S1 is switched to the reverse bias voltage source E3 side, and the reverse bias voltage is applied to the ejection electrode 103 to remove the solid components in the ink in the vicinity of the ink ejection portion 102. Dilute. Also, during printing, for example, 256
The pulse voltage source E2 is controlled based on a gradation image signal or the like, and a signal having a pulse width corresponding to the gradation of each pixel signal is applied to the corresponding ejection electrode 103.

Next, the operation of the electrostatic ink jet recording apparatus of this embodiment will be described with reference to FIG.
First, as ink, the solid component charged to + is 3-1.
A pigment-based ink containing 0% is used.

When the main switch of the apparatus is turned on or the print start signal is received, the switch S1 is switched to the pulse voltage source E2 side, and a predetermined bias voltage is applied to each ejection electrode 103 by the bias voltage source E1. As a result, an electric field is generated near the ink ejection portion 102 in the ink ejection direction, and the concentration of the solid component in the ink is concentrated to about 20% near the ink ejection portion 102.

Next, when a predetermined signal voltage is applied to each ejection electrode 103 by the pulse voltage source E2, the electric field in the vicinity of the ink ejecting section 102 becomes stronger, and the electric field receives the Coulomb force and is concentrated. The ink droplet k is ejected from the ink ejection unit 102 toward the recording paper P.

The ejected ink droplet k is accelerated by the Coulomb force due to the electric field formed between the secondary electrode 30 and the ejection electrode 103, and passes through the slit 31 of the secondary electrode 30. The ink droplet k that has passed through the slit 31 receives Coulomb force due to the electric field formed between the secondary electrode 30 and the counter electrode 20, and further advances forward, and eventually the recording paper P.
To reach. As a result, printing for one line in the sub-scanning direction is completed. Next, the recording paper P is conveyed by one line in the sub-scanning direction, and the next line is printed. An image is formed on the recording sheet P by repeating these operations.

Next, FIG. 3 shows a structure in the vicinity of the ink ejecting portion 102 of the print head 10. FIG. 3 is a plan view showing the configuration near the ink ejection unit 102.

As shown in FIG. 3, in the print head 10, a plurality of ink ejection portions 102 and slits 104 arranged alternately at a predetermined pitch are alternately formed on the end surface of the base member 101 constituting the head main body on the recording paper P side. It is formed so as to guide the ink to the tip of the ink ejection unit 102 by utilizing the capillary phenomenon.

The ink protruding portion 102 is formed so as to protrude more toward the recording paper P than the ink supporting portion (wall portion) 107 between the two adjacent slits 104 and has a cross section of a substantially isosceles triangle. Has been done.

As shown by hatching in FIG. 3, ink 2
When 00 is introduced into the slit 104, the ink 200 rises in a meniscus shape from the ink supporting portion 107 toward the tip portion 102a of the ink protruding portion 102 due to surface tension. The meniscus shape of the ink varies depending on the material of the ink protruding portion 102 and the characteristics of the ink 200 (so-called “wettability”), but from the end surface 107a of the ink supporting portion 107 between the slits 104 to the tip 102a of the ink ejecting portion 102. The protrusion height depends on b, and the width of each slit 104 depends on a.

If the width a of the slit 104 is smaller than a predetermined value depending on the fluidity of the ink 200, the ink 200 does not sufficiently flow and the ink droplet k cannot be projected. On the other hand, when the width a of the slit 104 is increased, the flow rate of the ink 200 can be sufficiently secured and the ink droplet k can be ejected, but the pitch of the ink ejecting unit 102 in the print head 10 becomes coarse and the resolution becomes high. descend. Therefore, the value of the width b of the slit 104 is limited to some extent due to the relationship between the fluidity of ink and the resolution.

Generally, when the ejection height b of the ink ejection portion 102 is too high, the meniscus 200a of the ink becomes an acute angle, and the ink 2 reaches the tip 102a of the ink ejection portion 102.
00 does not reach and ink droplet k cannot be ejected. Conversely, if the ejection height b of the ink ejection portion 102 is too low, the ink meniscus 200a becomes an obtuse angle, and the difference between the tip 102a of the ink ejection portion 102 and the end surface 107a of the ink support portion 107 disappears, and the ink ejection portion Ink is ejected not only from the front end 102a of the ink 102 but also from the end surface 107a of the ink support 107, the ink droplet k becomes too large, or the position where the ink droplet k adheres on the recording paper is displaced, resulting in poor image quality. to degrade.

Therefore, the present inventors experimentally determined the ejection height b of the ink ejection portion 102 capable of ejecting an optimum amount of the ink droplet k with respect to the limited width a of the slit 104. As a result, 30 μm ≦ a ≦ 150 μm, and 10 μm
By satisfying the respective conditions of m ≦ b ≦ 60 μm, the ink droplet k having a suitable size can be ejected while ensuring a resolution (pitch of the ink ejection portion 102) which is practically no problem, and on the recording paper P. It was confirmed that ink droplets could be attached to the correct position of. Further, by further satisfying the condition of 0.5 ≦ b / a ≦ 1.5, the angle of the ink meniscus 200a can be set to a suitable angle while ensuring high resolution, and the image quality is improved. be able to.

[0029]

As described above, according to the electrostatic ink jet recording apparatus of the present invention, an electric field is applied to charged ink, and the ink is ejected by the Coulomb force generated by the electric field, so that the recording portion faces the ejection portion. In an electrostatic ink jet recording apparatus for recording on a medium surface, a plurality of ink ejecting portions which are projected at a recording medium surface side from an end surface of a print head facing the recording medium surface and arranged at a predetermined pitch, and the ink. In order to supply ink to the ejection portion, the ink ejection portion has a plurality of slits formed on both sides thereof, the width of each slit is a, and the ink is applied from the end face of the ink support portion between the slits. Assuming that the protrusion height up to the tip of the discharge portion is b, 30 μm ≦ a ≦ 1
Since the conditions of 50 μm and 10 μm ≦ b ≦ 60 μm are satisfied, the ink droplet k having a suitable size is ejected while ensuring a resolution that is practically no problem, and the ink droplet is located at the correct position on the recording paper P. Can be attached.

By further satisfying the condition of 0.5 ≦ b / a ≦ 1.5, it is possible to improve the image quality while ensuring high resolution.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration example of an ink head in an electrostatic ink jet recording apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a schematic configuration of an ink ejection mechanism in the electrostatic ink jet recording apparatus.

FIG. 3 is a plan view showing a configuration near an ink ejection unit in the above embodiment.

[Explanation of symbols]

a: width of slit b: protrusion height of the ink ejection portion K: Ink drop P: Recording paper 10: Ink head 20: Counter electrode 30: Secondary electrode 101: Base member 102: Ink ejection section 102a: tip of ink ejection unit 103: discharge electrode 104: slit 105: cover member 107: Ink support part (wall) 107a: end face of ink support portion

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kazuhiro Kimura             No. 1 at 579 Umehara, Wakayama City, Wakayama Prefecture             Inside Ritsu Koki Co., Ltd. (72) Inventor Yuji Yamamoto             No. 1 at 579 Umehara, Wakayama City, Wakayama Prefecture             Inside Ritsu Koki Co., Ltd. F-term (reference) 2C057 AF30 AF33 AG04 AG05 BD05                       BD07 BD12 BD14

Claims (2)

[Claims] 1. An electrostatic ink jet recording apparatus, wherein an electric field is applied to charged ink, the ink is ejected by a Coulomb force generated by the electric field, and recording is performed on a surface of a recording medium facing an ejection portion. A plurality of ink ejecting portions that protrude from the end surface facing the recording medium surface to the recording medium surface side and are arranged at a predetermined pitch, and both sides of the ink ejecting portion for supplying ink to the ink ejecting portion. A plurality of slits each formed, and the width of each slit is a, and the protrusion height from the end face of the ink support portion between the slits to the tip of the ink ejection portion is b, 30 μm ≦ a ≦ 150 μm, and 10 μm ≦ b ≦ 60
An electrostatic ink jet recording apparatus characterized by satisfying each condition of μm 2. 2. The electrostatic ink jet recording apparatus according to claim 1, further satisfying the condition of 0.5 ≦ b / a ≦ 1.5.