JP2003177618A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To impart sufficient attracting force between recording material and image carrier sheet 5f. <P>SOLUTION: The electrifying center of an attracting electrifying brush 5c and an electrifying center of an attracting roll 5g are deviated, respectively. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine such as an electrophotographic system or an electrostatic recording system or a laser beam printer, and an image for forming an image on a recording material carried on a recording material carrier. Forming apparatus

[0002]

2. Description of the Related Art As an image forming apparatus for forming a full-color image, it is known that a recording material such as paper is carried on a recording material carrier such as a dielectric sheet to form an image on the recording material. To form an image on a recording material carried on a recording material carrier, an image formed on an image carrier such as a photoconductor is recorded by a transfer charger provided on the back side of the recording material carrier. Transfer to material.

Further, it is known to provide a corona discharger across a recording material carrier and a roller electrode as a counter electrode as an electrostatic charging means for electrostatically attracting the recording material to the recording material carrier. ing. On the other hand, it has been proposed to provide an adsorption charging brush instead of the corona discharger.

[0004]

As shown in FIG. 2, the charging centers of the suction charging brush 105c and the suction roller 105g as the suction charging means are opposed to each other and coincide with each other. The charging center in FIG. 2 is the center of the contact portion between the attraction charging brush 105c or the attraction roller 105g and the recording material carrier 105f.

However, the recording material carrying is carried out by using the attraction charging means shown in FIG. 2 in which the charging center of the attraction charging brush 105c and the charging center of the attraction roller 105g are aligned in the moving direction of the recording material carrier 105fg. Body 105
When the recording material is electrostatically attracted to f, there is a problem that the recording material cannot be stably conveyed by the recording material carrier 105f due to insufficient attraction force. In addition, this problem is particularly remarkable when an image is formed by carrying a recording material such as thick paper, which requires a large suction force, on the recording material carrier 105f.

(Object of the Invention) Accordingly, the object of the present invention is to
An object of the present invention is to provide an image forming apparatus capable of forming an excellent image on a recording material carried and conveyed by a recording material carrier.

A further object of the present invention is to provide an image forming apparatus provided with an adsorption charging unit capable of stably adsorbing a recording material on a recording material carrier.

[0008]

According to the present invention, there is provided a recording material carrier for carrying and moving a recording material, an image forming means for forming an image on the recording material carried by the recording material carrier, and the recording means. In an image forming apparatus having an adsorption charging unit that electrostatically adsorbs a recording material on a material carrier, the adsorption charging unit includes a first electrode and a second electrode that sandwich the recording material carrier. The charging center of the first electrode and the charging center of the second electrode with respect to the recording material carrier are deviated in the moving direction of the recording material carrier.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a schematic sectional view of a color image forming apparatus according to an embodiment of the present invention.

This example has a digital color image reader section in the upper part and a digital color image printer section in the lower part.

In the reader unit, the original 30 is placed on the original table glass 31 and is exposed and scanned by the exposure lamp 32, so that the reflected light image from the original 30 is condensed by the lens 33 on the full color sensor 34, and color images are obtained. Obtain a decomposed image signal. The color-separated image signal passes through an amplifier circuit (not shown), is processed by a video processing unit (not shown), and is sent to the printer section.

In the printer section, a photosensitive drum 1 which is an image bearing member is rotatably supported in the direction of the arrow, and a pre-exposure lamp 11, a corona charger 2, a laser exposure optical system 3 and a potential sensor 12 are provided around the photosensitive drum 1. , Four developing devices 4y, 4c, 4m, 4Bk of different colors, on-drum light amount detection means 1
3, the transfer device 5, and the cleaning device 6 are arranged.

In the laser exposure optical system 3, the image signal from the reader section is converted into an optical signal by a laser output section (not shown), and the converted laser light is reflected by the polygon mirror 3a, and the lens 3b and the mirror. It is projected onto the surface of the photosensitive drum 1 through 3c.

When forming an image on the printer section, the photosensitive drum 1
Is rotated in the direction of the arrow, the photosensitive drum 1 after the charge is removed by the pre-exposure lamp 11 is uniformly charged by the charger 2, and the light image E is emitted for each separated color to form a latent image.

Next, a predetermined developing device is operated to develop the latent image on the photosensitive drum 1 to form a resin-based toner image on the photosensitive drum 1. The developing device is an eccentric cam 24.
By the operations of y, 24c, 24m, and 24Bk, the photosensitive drum 1 is selectively approached according to each separated color.

Further, the toner image on the photosensitive drum 1 is transferred from the recording material cassette 7 to the recording material supplied to the position facing the photosensitive drum 1 via the conveying system and the transfer device 5. In this example, the transfer device 5 includes a transfer drum 5a, a transfer charger 5b, and an attraction charger 5c, an attraction roller 5g, and an inner charger 5 as attraction charging means for electrostatically attracting a recording material.
d, a recording material carrying sheet 5f made of a dielectric material is integrally stretched in a cylindrical shape in an opening area of a peripheral surface of a transfer drum 5a which is rotatably supported and has an outer charger 5e. ing. The recording material carrying sheet 5f uses a dielectric sheet such as a polycarbonate film.

As the drum-shaped transfer device, that is, the transfer drum 5a is rotated, the toner image on the photosensitive drum 1 is transferred onto the recording material carried on the recording material carrying sheet 5f by the transfer charger 5b.

In this way, a desired number of color images are transferred to the recording material that is adsorbed and conveyed to the recording material carrying sheet 5f to form a full color image.

In the case of forming a full-color image, when the transfer of the four color toner images of yellow, cyan, magenta and black is completed in this way, the recording material is separated from the transfer drum 5a by the separation claw 8a, the separation push-up roller 8b and the separation charger. The toner is separated by the action of 5 h, the four color toners are melted and mixed through the heat roller fixing device 9, and are discharged to the tray 10.

On the other hand, after the transfer, the photosensitive drum 1 is subjected to the image forming process again after the residual toner on the surface is cleaned by the cleaning device 6.

When images are formed on both sides of the recording material,
Immediately after the fixing device 9 is discharged, the transport path switching guide 19 is driven, and after being guided to the reversing path 21a through the transport vertical path 20, the reverse end of the reversing roller 21b causes the trailing end when fed to the beginning. Then, it is withdrawn in the direction opposite to the direction in which it was fed and is stored in the intermediate tray 22. After that, an image is formed on the other surface by the above-described image forming step.

Further, in order to prevent the powder from being scattered and adhered onto the recording material carrying sheet 5f of the transfer drum 5a and the oil from being adhered to the recording material, the fur brush 14 and the recording material carrying sheet 5f are used to interpose the recording material carrying sheet 5f. Cleaning is performed by the action of the backup brush 15 facing the brush 14, and the backup brush 17 facing the roller 16 via the oil removing roller 16 and the recording material carrying sheet 5f. Such cleaning is performed before or after image formation, and at any time when a jam (paper jam) occurs.

Here, in FIG. 3A, the deviation amount x of the center of the nip width y of the charging brush 5c with respect to the center of the contact portion of the suction roller 5g and the suction force of the recording material on the recording material carrier 5f. Shows the relationship between. As shown in FIG. 3A, when the displacement amount x is 0, the suction force of the recording material does not reach the maximum value. That is, the attraction force is larger when the shift amount x is not 0 than when it is 0. This is because the recording material is charged by the suction roller 5g while being in close contact with the recording material carrier 5f, and then the suction is provided on the downstream side in the moving direction of the recording material carrier 5f with respect to the charging center of the suction roller 5g. It is considered to be caused by passing through the charging center of the charging brush 5c. Therefore, it is effective not to set the displacement amount x to 0 when the recording material is stably conveyed or a recording material that requires a large suction force such as thick paper is used.

Here, the adsorption charging means of this embodiment is equipped with
FIG. 3B shows the adsorption charging brush 5c as the first electrode and the adsorption roller 5g as the second electrode.

As shown in FIG. 3B, the charging center of the adsorption charging brush 5c on the recording material carrier 5f (recording material carrier 5).
Nip width y of the adsorption charging brush 5c in the moving direction of f
Center) of the suction roller 5g is displaced from the charging center (center of the contact portion to the recording material carrier 5f) by a distance x downstream in the moving direction of the recording material carrier 5f. Here, in this embodiment, the nip width y of the adsorption charging brush 5c is 2 (mm),
The shift amount x is set to 3.5 (mm). In the adsorption charging means of this embodiment, the deviation amount x is preferably within 5 (mm).

As described above, in this embodiment, the charging center of the attraction charging brush 5c and the charging center of the attraction roller 5g are displaced in the moving direction of the recording material carrier 5f, so that a sufficient attraction force, recording material and recording material can be obtained. Since it can be provided between the recording material carrier 5f and the recording material carrier 5f, the recording material can be stably conveyed.

By the way, in the case of using a pair of adsorption charging means having a deviation of the charging center as in this embodiment, as shown in FIG. The maximum density difference (/ normal density) may become very large. This is because the charge center on the recording material is non-uniform because the charge center by the adsorption charger 5c and the charge center by the opposing roller 5g are distant from each other, and the electric field is also non-uniform at the transfer position. This phenomenon is remarkable in a low humidity environment where the recording material, especially the paper has a high electrical resistance, and in the low humidity environment, it is difficult to support the recording material that requires a large suction force such as thick paper and the image quality. there were.

Therefore, as shown in FIGS. 1 and 6 (b), the image forming apparatus of this embodiment is composed of a charging brush A as a third electrode and a leveling roller B as a fourth electrode facing the charging brush A. The auxiliary charging means is provided. Both the leveling charging brush A and the leveling roller B are electrically conductive. Transfer drum 5
When the recording material enters the sheet a, the attraction charger 5c and the attraction roller 5g, which are separated from the carrying sheet 5f, come into contact with the recording material carrying sheet 5f, and the attraction charger 5c has a constant current of +1.
A constant current is controlled at 5 μA, and an electric charge is injected into the recording material from a suction roller that is grounded. The recording material carrying sheet 5f
Before the adsorption, a negative charge is applied to the inside and a positive charge is applied to the outside by the inner charger 5d and the outer charger 5e. The leveling charging brush A and the leveling roller B, which had been separated from the carrying sheet 5f before the attraction, were brought into contact with the carrying sheet almost at the same time as the attraction charger 5c and the attraction roller 5g, and the charging brush A had a constant current of +10 μA. The electric current is uniformly injected into the recording material from the leveling roller B grounded under constant current control. Adsorption charger 5c, adsorption roller 5g, leveling charging brush A,
The leveling roller B is separated immediately after the paper passes. The center of charge of the leveling charger A coincides with the center of the leveling roller B. FIG. 5 shows the relationship between the deviation amount x of the adsorption charger and the density unevenness when the auxiliary charging means is installed. As shown in FIG. 5, even if the deviation amount x of the charging center between the suction brush 5c and the suction roller 5g was increased, the uneven density could be prevented by providing the auxiliary charger. FIG. 6A shows changes in the potential of the surface of the recording material carrying sheet 5f on the side opposite to the recording material carrying surface in this embodiment. The inside 5f of the carrying sheet is charged to −2 kV by the inside charger 5d before the adsorption, and immediately after the adsorption (see FIG. 6).
(Q in (a)) Approximately -1.5 kV, immediately after normal charge (Fig. 6).
(A) C) -1 kV. T ₁ , T ₂ , T ₃ , T
₄ indicates immediately after the transfer of the first color, the second color, the third color, and the fourth color, respectively, and the potential inside the carrying sheet 5f gradually increases toward the plus side together with the number of times of transfer. After the transfer of the four colors is completed and before the start of the next transfer, the inside of the carrying sheet 5f is charged to −2 kV again by the inside charger 5d.

Next, another embodiment of the leveling charging brush A as the auxiliary charging means is shown in FIG. 6 (d). FIG. 6D shows an example in which a varistor which is a constant voltage device of 1 kV is connected to the charging brush A instead of connecting a high voltage power source.

A ferroelectric film such as polycarbonate, which is a recording material carrying sheet, has an inner charging device 5d and an outer charging device 5e which preliminarily make the inner surface negative and the outer surface positive by about 2 k.
Since it is V-charged, it is possible to inject charges from the brush A into the carrying sheet 5f without using a high-voltage power supply that supplies a voltage to the charging brush A. FIG. 6C shows changes in the potential of the carrying sheet 5f when the charging brush A of FIG. 6D is grounded via a varistor. In the case of FIG.
Compared to the case of (b), cost reduction is expected due to the elimination of the high voltage power supply. In addition, Q, C, T _{1 of} FIG.
T ₂ , T ₃ , and T ₄ indicate the same cases as in FIG.
Further, instead of grounding the charging brush A via a varistor, it may be grounded via a resistor.

Further, FIG. 6 (f) shows an embodiment in which the leveling charging brush A is directly grounded. FIG. 6 (e) is shown in FIG. 6 (f).
Shows the change in the potential of the carrying sheet 5f in the case of,
T ₁ , T ₂ , T ₃ , and T ₄ are the same as those in FIG. 6A.

On the other hand, when the charging brush A and the opposing metal roller B are used as the auxiliary charging means as shown in FIG. 7, the nip width C between the brush A and the carrying sheet 5f, the carrying sheet 5f, and the recording material. It has been empirically known that the above-mentioned charge leveling effect is exhibited only when there is an overlapping portion between the nip widths D of the metal roller B. Basically carrying sheet 5f
Since the metal roller B and the metal roller B are substantially in line contact with each other, by making the nip width C wider than the nip width D, the position latitude of the entire auxiliary charging means can be increased.

Further, since the auxiliary charging means and the attraction charging means are brought into contact with and separated from the carrying sheet 5f at substantially the same timing, if the attraction brush 5C and the leveling brush A are supported by the same support member, the holder is moved. A single drive source can be used. Similarly, it is preferable that the suction roller 5g and the leveling roller B are integrally driven.

As auxiliary charging means, instead of the above-mentioned charging brush A and leveling roller B, a corona discharger connected to a high-voltage power source is grounded to a roller or a brush, and a brush connected to a high-voltage power source is grounded to a corona discharger. Brush,
A combination of a grounded brush and a grounded brush via a varistor, a grounded brush and a grounded brush, and the like can be used. Further, in the above-described combination of two counter electrodes sandwiching the carrying sheet 5f as the auxiliary charging means, either electrode may be inside the carrying sheet 5f.

As described above, according to the image forming apparatus of the present embodiment of the present invention, even thick paper of about 160 g / cm ² is stably electrostatically adsorbed on the recording material carrier 5f and has low humidity. It is possible to form a good image without density unevenness even in an environment.

[0037]

As described above, according to the present invention, the adsorption charging means is provided with the first electrode and the second electrode sandwiching the recording material carrier, and the first charging member is provided with respect to the recording material carrier. By displacing the charge center of the electrode and the charge center of the second electrode in the moving direction of the recording material carrier, it becomes possible to give a sufficient adsorption force between the recording material and the recording material carrier.

[Brief description of drawings]

FIG. 1 is a sectional view of an electrophotographic full-color printer to which an embodiment of the present invention is applied.

FIG. 2 is a partial view showing an arrangement of adsorption charging means.

FIG. 3A is a characteristic diagram showing the relationship between the amount of deviation x of the electrostatic charging position and the electrostatic adsorption force. (B) It is a figure which shows the adsorption charging means of this invention.

FIG. 4 is a characteristic diagram showing the relationship between the amount x of deviation of the adsorption charging position and the density unevenness.

FIG. 5 is a characteristic diagram showing the relationship between the amount x of deviation of the adsorption charging position and the density unevenness.

6A and 6B are a schematic diagram in which a power supply, a varistor, and a ground are connected to the leveling charging brush A, and a characteristic diagram showing the potential of each carrying sheet 5f.

FIG. 7 is a cross-sectional view comparing the nip between the leveling charging brush A and the leveling roller B.

[Explanation of symbols]

1 photosensitive drum 5b Transfer charger 5c Adsorption charging brush 5f Recording material carrying sheet 5g suction roller A charge brush B leveling roller

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takashi Hasegawa             Kyano, 3-30-2 Shimomaruko, Ota-ku, Tokyo             Within the corporation (72) Inventor Isao Kumada             Kyano, 3-30-2 Shimomaruko, Ota-ku, Tokyo             Within the corporation F-term (reference) 2H200 FA17 GA04 GA23 GA34 GA47                       GA50 HA02 HA12 HB02 HB07                       HB12 HB22 HB41 HB48 JA02                       JB03 JB18 JB26 JB27 JB39                       JB42 JB45 JB48 KA03 KA07                       KA13 KA14 LA06 LA15 LB02                       LB12 LB15 MA04 MA20 NA02                       NA08 NA16 NA22                 2H300 EB02 EB08 EB12 ED02 EF02                       EF05 EF09 EF10 EF13 EG03                       EH16 EJ09 EJ12 EJ47 EK03                       GG01 GG02 GG36 GG46 HH09                       HH15 HH28 KK03 PP02 PP08                       PP15 PP20 TT01

Claims (7)

[Claims] 1. A recording material carrying member carrying and moving a recording material, an image forming means for forming an image on the recording material carried on the recording material carrying member, and a recording material on the recording material carrying member. An image forming apparatus having an electrostatically charging means for electrically adsorbing the recording material carrying body, wherein the attractive charging means comprises a first electrode and a second electrode provided so as to sandwich the recording material carrying body. The image forming apparatus is characterized in that the charge center of the first electrode and the charge center of the second electrode are deviated from each other in the moving direction of the recording material carrier. 2. The image forming apparatus according to claim 1, wherein the recording material is adsorbed to the recording material carrier by passing between the first electrode and the second electrode. 3. The second electrode is provided on the recording material carrying surface side of the recording material carrying body so as to come into contact with the recording material,
The image forming apparatus according to claim 2, wherein the first electrode is provided downstream of the second electrode in the moving direction of the recording material carrier. 4. The image forming apparatus according to claim 3, wherein the second electrode has a roller shape. 5. The first electrode is connected to a power source, and the second electrode is electrically grounded.
Alternatively, the image forming apparatus according to claim 4. 6. The color image of a plurality of colors is sequentially overlapped and formed on the recording material carried by the recording material carrying member by the image forming means. Image forming device. 7. The image forming unit includes an image carrier that carries an image, and a transfer charging unit that transfers the image of the image carrier to a recording material carried by the recording material carrier. The image forming apparatus according to any one of claims 1 to 6, which is characterized.