JPH07132638A - Printing head in powder jet image forming apparatus - Google Patents

Abstract

PURPOSE:To prevent not only the fluctuations of a developer supply electric field generated on the basis of the difference between the potential of a first electrode and that of a developer supply part by the electric field generated by a second electrode but also the generation of the density irregularity of an image. CONSTITUTION:A matrix like electrode is formed by a plurality of the first electrodes 21 formed on the surface on the side of a developer supply part 1 of an insulating layer 20 and a plurality of the second electrodes 22 formed on the surface on the side of a recording paper feed part 3 of the insulating layer 20 and developer insertion holes 23 are opened at the crossing points of the first and second electrodes 21, 22 to constitute the printing head of a powder jet image forming apparatus. In the printing head, the shield electrodes cutting off the electric fields from the second electrodes 22 are provided so as to cover the gap parts between the adjacent first electrodes 21 on the surface on the side of the developer supply part 1 of the insulating layer 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a print head in a powder jet image forming apparatus.

[0002]

2. Description of the Related Art The present applicant has already developed a powder jet image forming apparatus as shown in FIG. This powder jet image forming apparatus has a print head 2 that controls passage of toner charged with a predetermined polarity, for example, negative polarity.
A toner supply roller 1 for supplying toner to the print head 2, a recording paper transport roller 3 for guiding the recording paper P to the print head 2, and a toner transferred onto the recording paper P. And a fixing roller 4 for fixing.

As shown in FIGS. 6 and 7, the print head 2 includes an insulating substrate 20, a plurality of first electrodes 21 formed on the surface of the toner supply roller 1 of the insulating substrate 20, and an insulating substrate 20. The recording paper conveying roller 3 of No. 2 is provided with a plurality of second electrodes 22 formed on the surface of the hollow. The plurality of first electrodes 21 and the plurality of second electrodes 22 form a matrix electrode. Each first electrode 21 and each second electrode 2
A toner passage hole 23 penetrating the print head 2 is formed at each intersection with the print head 2.

An on-voltage (for example -100V) and an off-voltage (for example + 300V) are selectively applied to each first electrode 21. Each second electrode 22 has an on-voltage (for example, 0 V) and an off-voltage (for example, -200 V).
V) and are selectively applied. FIG. 4 shows each first electrode 21.
Of the applied voltage V1-0 to V1-7. As shown in FIG. 4, each of the first electrodes 21 is subjected to dimic scan control, and the applied voltage is sequentially turned on at predetermined unit time intervals. Then, only when the applied voltage to both the first electrode 21 and the second electrode 22 is the on-voltage, the toner passes through the toner insertion hole 23 at the intersection thereof, and the dot printing is performed.

The recording paper P is moved in the direction perpendicular to the first electrode 21 by the recording paper conveying roller 3 and in the direction in which control by dynamic scanning of the first electrode 21 proceeds (arrow A in FIG. 6).
Is conveyed in the direction indicated by. The recording paper transport roller 3 has
A voltage of + 500V is applied. The toner supply roller 1 is grounded and its surface potential is 0V.

The print head 2 is provided with an ultrasonic vibrator 5 for applying ultrasonic vibration to the print head 2 to prevent the toner insertion hole 23 from being clogged with toner.

[0007]

By the way, the toner is supplied from the toner supply roller 1 to the print head 2 by an electric field (generated by the difference between the potential of the toner supply roller 1 and the potential of the first electrode 21 at the time of off voltage). This is performed by the action of the toner supplying electric field). However, as shown in FIG. 8, the electric field generated by the second electrode 22 affects the toner supply electric field via the insulating layer portion between the adjacent first electrodes 21. Since the voltage applied to the second electrode 22 can be switched between an on voltage and an off voltage according to image information,
The electric field for toner supply changes depending on the voltage state of the electrode 22. Therefore, the above-mentioned powder jet image forming apparatus has a problem that image density unevenness occurs.

According to the present invention, the electric field generated by the second electrode can prevent the developer supplying electric field from changing due to the difference between the electric potential of the first electrode and the electric potential of the developer supplying portion, and thus the image density unevenness can be prevented. An object of the present invention is to provide a print head in a powder jet image forming apparatus that can prevent the generation.

[0009]

A print head in a powder jet image forming apparatus according to the present invention comprises a plurality of first electrodes formed on the surface of a developer supplying portion of an insulating layer, and a recording paper conveying of the insulating layer. Forming a powder jet image in which a matrix-like electrode is formed by a plurality of second electrodes formed on the surface of the portion and a developer insertion hole is formed at each intersection of the first electrode and the second electrode. In the print head of the apparatus, a shield electrode for blocking an electric field from the second electrode is provided in such a manner that the developer supply portion of the insulating layer covers the portion between the adjacent first electrodes on the surface of the insulating layer. To do.

A voltage between an on-voltage and an off-voltage selectively applied to the first electrode is applied to the shield electrode.

[0011]

In the print head of the powder jet image forming apparatus according to the present invention, the developer supplying portion of the insulating layer is arranged so as to cover the portion between the adjacent first electrodes on the surface of the insulating layer.
A shield electrode is provided to block the electric field from the electrode. Therefore, the electric field from the second electrode, which tries to reach the developer supply unit side through the insulating layer portion between the adjacent first electrodes, is blocked by the shield electrode. Therefore, the second
Due to the electric field generated by the electrodes, the electric field for developer supply generated by the difference between the electric potential of the first electrode and the electric potential of the developer supply section does not change. As a result, the occurrence of image density unevenness is prevented.

[0012]

Embodiments of the present invention will be described below with reference to FIGS.

1 and 2 show a print head 200. 1 and 2, the same parts as those in FIGS. 6 and 7 are designated by the same reference numerals. In addition, in this example, the toner supplied to the print head 200 is assumed to be negatively charged.

In this print head 200, like the conventional print head 2 (see FIG. 6), the insulating substrate 20 and the plurality of first electrodes 21 on which the toner supply roller 1 of the insulating substrate 20 is formed on the surface of the wadding are provided. And a plurality of second electrodes 22 formed on the surface of the recording paper carrying roller 3 of the insulating substrate 20. A plurality of first electrodes 21 and a plurality of second electrodes 22
The matrix-shaped electrodes are constituted by. Each first
A toner passage hole 23 penetrating the print head 2 is formed at each intersection of the electrode 21 and each second electrode 22.

An on-voltage (for example -100V) and an off-voltage (for example + 300V) are selectively applied to each first electrode 21. Each second electrode 22 has an on-voltage (for example, 0 V) and an off-voltage (for example, -200 V).
V) and are selectively applied. FIG. 4 shows each first electrode 21.
Of the applied voltage V1-0 to V1-7. As shown in FIG. 4, each of the first electrodes 21 is subjected to dimic scan control, and the applied voltage is sequentially turned on at predetermined unit time intervals. Then, only when the applied voltage to both the first electrode 21 and the second electrode 22 is the on-voltage, the toner passes through the toner insertion hole 23 at the intersection thereof, and the dot printing is performed.

In this print head 200, unlike the conventional print head 2, as shown in FIGS. 1 and 2, the developer supply roller 1 of the insulating substrate 20 has a portion between the adjacent first electrodes 21 on the surface thereof. Adjacent first electrodes 21 so as to cover
Insulating layer 31 is formed across. Further, the insulating layer 31 is formed so that the developer supply roller 1 of the insulating substrate 20 covers the peripheral portion of the group of many toner insertion holes 23 on the surface of the roller.
Are formed. Then, the shield electrode 32 made of a thin metal layer is formed on the insulating layer 31. Insulation layer 3
The sum of the thicknesses of 1 and the shield electrode 32 is 0.1 to 1.0.
There is about mm.

That is, the print head 200 is provided with the shield electrode 32 which covers the portion between the adjacent first electrodes 21 on the surface of the insulating substrate 20 on which the developer supply roller 1 (see FIG. 3) is located.

The shield electrode 32 has an ON voltage (-100 V) applied to the first electrode 21 and an OFF voltage (+30 V).
+ 200V which is an average value of 0V) is applied.

In the print head 200, as shown in FIG. 3, an electric field from the second electrode 22 which attempts to reach the developer supply roller 1 side through the insulating layer portion 20 between the adjacent first electrodes 21. Are blocked by the shield electrode 32. Therefore, the electric field generated by the second electrode 22 causes
Due to the difference between the potential of the first electrode 21 and the potential of the developer supply roller 1, the developer supply electric field generated between the first electrode 21 and the developer supply roller 1 does not change. As a result,
The occurrence of uneven image density is prevented.

[0020]

According to the present invention, it is possible to prevent the developer supplying electric field from varying due to the difference between the potential of the first electrode and the potential of the developer supplying section due to the electric field generated by the second electrode. It is possible to prevent the occurrence of image density unevenness.

[Brief description of drawings]

FIG. 1 is a plan view showing a print head.

FIG. 2 is a sectional view taken along line II-II in FIG.

FIG. 3 is a partially enlarged sectional view of FIG.

FIG. 4 is a time chart showing changes in applied voltage to each first electrode.

FIG. 5 is a configuration diagram showing a schematic configuration of a powder jet image forming apparatus.

FIG. 6 is a plan view showing a conventional print head.

7 is a cross-sectional view taken along the line VII-VII of FIG.

8 is a partially enlarged sectional view of FIG.

[Explanation of symbols]

 200 print head 20 insulating layer 21 first electrode 22 second electrode 23 toner insertion hole 32 shield electrode

Claims (2)

[Claims] 1. A matrix composed of a plurality of first electrodes having a developer supply portion of an insulating layer formed on a wrinkle surface and a plurality of second electrodes having a recording paper conveying portion of an insulating layer formed on a wrinkle surface. In a print head of a powder jet image forming apparatus in which a striped electrode is formed and a developer insertion hole is formed at each intersection of the first electrode and the second electrode, the developer supply portion of the insulating layer A print head in a powder jet image forming apparatus, wherein a shield electrode for blocking an electric field from the second electrode is provided so as to cover a portion between adjacent first electrodes. 2. The powder jet image forming apparatus according to claim 1, wherein a voltage between an on-voltage and an off-voltage selectively applied to the first electrode is applied to the shield electrode. Print head.