JPH07319299A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent a recording medium from being statically charged by arranging a transfer roller at the lower side periphery of a photoreceptor drum and projectedly composing the paper sheet outlet end part of the one guide plate among a pair of grounded upper and lower guide plates so as to discharge the recording medium toward a transfer part. CONSTITUTION:The base end part of the pair of upper and lower guide plates 33 and 34 are arranged below a tangent C orthogonal to a straight line B that connects the rotation center O1 of the photoreceptor drum 10 and the rotation center O2 of the transfer roller 9, and arranged on the slant in the upward state of approaching to the rotation center O1 of the photoreceptor drum 10 corresponding to the position getting nearer to a transfer region A as the contact point of the photoreceptor drum 10 and the transfer roller 9. Then, the paper sheet outlet end part 34a of the lower side guide plate 34 is projectedly composed so as to come nearer to the rotation center O1 of the photoreceptor drum 10 beyond the tangent C. Moreover, the lower side guide plate 43 is grounded on a ground 38 through a notched crimping piece 37. Furthermore, the upper side guide plate 33 is also grounded on the ground 38.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatographic image forming apparatus such as a laser printer, a copying machine or a facsimile machine, and more specifically, for guiding and feeding a recording medium such as paper to a transfer portion. The present invention relates to the structure of the guide device.

[0002]

2. Description of the Related Art Conventionally, for example, JP-A-4-21128
As shown in FIG. 5 and disclosed in Japanese Patent Publication No. 7, an electrostatic latent image is formed by applying an optical image signal to the surface of the uniformly charged and rotating photosensitive drum 100, and the latent toner is charged toner. Is applied to form a toner image, a high-voltage transfer voltage is applied to the transfer roller 101 while passing the paper P through the transfer portion A where the transfer roller 101 is in contact with the surface of the photosensitive drum 100, and the transfer roller 101 is applied to the paper P. An image forming apparatus is known in which a toner image is transferred, and then the paper P is heated and pressed to fix the toner image on the paper P to form an image.

In this case, as disclosed in the above-mentioned prior art and as shown in FIG. 5, a pair of upper and lower guide plates 102, 103.
The pair of upper and lower guide plates 102 and 103 are arranged in front of the transfer portion A so that the front end of the sheet P passing between them faces the transfer portion A.

[0004]

By the way, normally, the paper on which the image is not formed (the paper stacked in the paper feed cassette) is not charged with static electricity, and when passing through the transfer portion, the transfer roller is Under the influence of the application of the charging voltage to the sheet P, the sheet P is electrostatically charged, and the influence remains after the fixing.

However, in the above prior art, the guide plates 102 and 103 are not grounded.
Therefore, a printer capable of double-sided printing adopting this prior art, that is, a form in which an image is once formed on the front surface of the paper P and the image forming operation is performed again on the back surface of the paper P via a predetermined duplex device (paper reversing device) In this printer, when an image is formed on the back surface of the paper P and then on the back surface, the paper P is already charged with static electricity. Therefore, the paper P is sent to the transfer portion A and transferred by the transfer roller 101. Even if a voltage is applied, the photosensitive drum 1
There is a problem that the charged toner on the surface of No. 00 cannot be properly transferred to the back surface of the paper P, and so-called defective printing occurs.

For example, if negative polarity toner adheres to the surface of the photosensitive drum 100 and a positive transfer potential is applied to the transfer roller 101, the transfer portion A
In the case, the toner of negative polarity is attracted to the surface of the paper P, and then the toner is fixed, but the paper P retains a positive charge. When the next image is formed without removing the charge, the sheet P charged with the positive charge faces the surface of the photoconductor drum 100, and the surface of the photoconductor drum 100 is in front of the transfer portion A (on the upstream side of the sheet conveyance). When the sheet P and the rear surface of the sheet P come close to each other by a predetermined distance, the photosensitive drum 1
The negative polarity toner on the surface of No. 00 is transferred to the back surface of the paper P, and an image cannot be properly formed.

The present invention has been made to solve this technical problem, and an object of the present invention is to provide an image forming apparatus capable of obtaining good image quality.

[0008]

In order to achieve the above object, the image forming apparatus of the present invention according to claim 1 carries a toner image and rotates on a peripheral surface of a photosensitive drum which rotates around a substantially horizontal axis of rotation. A pair of upper and lower guide plates that guide the recording medium such as paper toward the transfer portion between the transfer roller and the transfer roller that are arranged in parallel with each other are provided, and the transfer voltage is applied to the transfer roller to apply toner to the recording medium. An image forming apparatus configured to transfer an image, wherein a transfer roller is arranged on a lower peripheral surface of a photosensitive drum, and a paper exit end of at least one guide plate of a pair of upper and lower guide plates is The recording medium is formed so as to project toward the transfer portion while being in sliding contact with the paper outlet end portion, and the upper and lower guide plates are grounded.

According to a second aspect of the invention, in the image forming apparatus according to the first aspect, the pair of upper and lower guide plates are arranged so as to be inclined from the lower side to the upper side as they approach the transfer portion, and the pair of upper and lower sides is arranged. Of the guide plate, the end of the paper exit portion of the lower guide plate, the rotation center of the photosensitive drum,
It is located above a line perpendicular to the line connecting the center of rotation of the transfer roller, and the lower guide plate is grounded.

[0010]

EXAMPLES Next, examples embodying the present invention will be described. FIG. 1 is a schematic side sectional view of a laser beam printer 1 as an image forming apparatus, and FIG. 2 is an enlarged side sectional view of a main part of a transfer portion. In the printer 1 of this embodiment, a paper feed cassette 3 as a paper feed unit is detachably attached to a lower portion of a main body case 2, and recording sheets stacked in the paper feed cassette 3 by a plurality of paper feed rollers 4 and the like. The paper P as a medium is separated one by one, and the paper midway guide plate 5 and the feeding roller pair 6,
Also, it is sent between the process unit 7 and the transfer roller 9 on the transfer unit base 8 via a pair of upper and lower guide plates 33, 34 described later.

The process unit 7 includes a photosensitive drum 10
A developing device unit 11 including a toner tank and a developing roller 12, and a charging device 13 including a charging roller,
A cleaning (not shown) device and the like are housed in a case as one kit to form a single unit. A scanner unit 22 including a laser emitting section 23, a lens 24, a reflecting mirror 25, and the like is arranged above the process unit 7, and below the transfer unit table 8, the charging device 13 and the transfer roller 9 are elevated. A high voltage substrate 26 for applying a voltage is arranged, and a control substrate 27 is arranged below the fixing unit 15.

The surface of the photosensitive drum 10 precharged by the charging device 13 is irradiated with light emitted from the scanner unit 22 according to image data transmitted from an external device such as a host computer (not shown). The electrostatic latent image is formed on the surface of the photoconductor drum 10, and then the developing roller 12 is rotated to supply the charged powdery toner to visualize the latent image. After that, the toner image is transferred onto the paper P supplied to the transfer site between the photoconductor drum 10 and the transfer roller 9. Next, the paper P conveyed by sliding on the passage guide member 32 of the paper P on the front surface side (upper side) of the transfer unit base 8 is fixed in the fixing unit 15.
Of the paper P by passing between the heating roller 16 and the pressing roller 17 and applying heat and pressure to the transferred image.
Fix the toner image on. After that, the discharge guide plate 18,
The sheet is discharged to the sheet tray 21 on the upper surface of the main body case 2 via the intermediate roller pair 19 and the sheet discharge roller pair 20.

Next, the structure of the transfer portion will be described in more detail with reference to FIGS.
Is formed by injection molding of a synthetic resin having electrical insulation such as ABS resin. One side of the upper surface of the base plate 8a of the transfer unit base 8 is provided with a conductive sponge as shown in FIG. Conductivity of transfer roller 9 (made of metal)
Bifurcated groove-shaped support portion 3 for vertically movingly supporting bearings 30 (only one of which is shown in FIG. 3) on both left and right sides of the shaft 9a.
1 is projected upward. The bearing 30 is configured such that the transfer roller 9 is pressed against the lower circumferential surface of the photosensitive drum 10 by a biasing means 30a such as a metallic (conductive) coil. A plurality of fin-shaped passage guide members 32 for guiding the paper P passing through the transfer portion A toward the fixing unit 15 are provided on the stepped portion on the base plate 8a on the downstream side of the paper conveyance adjacent to 31. It is projected integrally. At least one of the bearings 30 is made of a conductive material (metal or a composite member in which carbon black, graphite, and metal powder are dispersed in a synthetic resin), and the high-voltage board 26 is provided with wiring not shown. The transfer roller 9 is connected to the high voltage circuit in FIG.

A pair of upper and lower guide plates 33, 34 made of a conductive metal such as an iron plate are disposed on the upstream side of the sheet conveyance adjacent to the supporting portion 31 of the transfer roller 9.
As an example, a pair of upper and lower guide plates 3 shown in FIGS.
The base end side of 3, 34 is the rotation center O ₁ of the photosensitive drum 10.
And the rotation center O ₂ of the transfer roller 9 are arranged below a tangent line C perpendicular to a straight line B, and the photosensitive drum 10 approaches the transfer portion A which is a contact point between the photosensitive drum 10 and the transfer roller 9. Are arranged so as to be inclined upward so as to approach the rotation center O ₁ . And the lower guide plate 3
The sheet outlet end portion 34a of _{No. 4} is formed so as to project from the tangent line C so as to approach the rotation center O ₁ of the photosensitive drum 10.

The lower guide plate 34 is fixed to an upward column 35 near the supporting portion 31 of the transfer unit base 8 with a screw 36 or the like, and the base end of the lower guide plate 34 is a metal notch sandwiching piece 37. The clamping piece 37 is grounded to the ground 38 (potential 0). On the other hand, in the vicinity of the paper outlet end 33a of the upper guide plate 33, the tangential line C is crossed to protrude toward the rotation center O ₁ of the photosensitive drum 10 and then slightly downward so as to approach the transfer portion A direction. Bend it.
A contact piece 39 bent downward at a side end of the upper guide plate 33 (a portion where the paper P does not pass) is brought into contact with the upper surface of the lower guide plate 34, and the paper outlet end portions of the upper and lower guide plates 33, 34. The size of the gap between the guide plates 33, 34 near 33a, 34a is regulated so as not to be unnecessarily narrow, and is electrically connected to the lower guide plate 34, so that the upper guide plate 33 is also grounded. Is configured.

In addition, on the downstream side of the sheet conveyance adjacent to the support section 31, a static elimination plate 40 having a sawtooth-shaped upper end is turned upward so as to remove the electrostatic charges charged on the sheet P passing through the transfer portion A. And a flat plate-shaped auxiliary static eliminator plate 41 is arranged on a step portion on the base plate 8a adjacent to the stand plate, and the auxiliary static eliminator plate 41 and the static eliminator plate 40 are electrically connected by the contact portion 42. Then, the static elimination plate 40 or the like is connected to the ground 38 in advance.

With the above structure, the paper P fed from the paper feed cassette 3 is fed between the upper and lower guide plates 33 and 34 via the feeding roller pair 6. Since the tension is applied to the fed sheet P so as to be linear between the transfer portion A and the feeding roller pair 6, the lower surface of the sheet P is the sheet outlet end portion 34 a of the lower guide plate 34. It is sent to the transfer site A while positively contacting the edge, and static electricity can be positively removed from the charged paper P.

A high voltage is applied to the transfer roller 9 to transfer the toner to the upper surface of the paper P, and the paper P is charged with a high potential electrostatic charge.
Immediately after passing through the sheet, the sheet passes above the static elimination plate 40 and the auxiliary static elimination plate 41, so that the electrostatic charge charged on the paper P can be efficiently removed. As shown in FIG. 3, a state in which tension does not act on the sheet P by curving the sheet outlet end portion 34a of the lower guide plate 34 slightly upward (upward beyond the tangent line C) Even in this case, the lower guide plate 34, which is grounded to the ground 38, and the lower surface of the paper P are positively contacted with each other, so that the static elimination action can be improved.

The second embodiment shown in FIG. 4 is an example in which a pair of upper and lower guide plates 33, 34 are arranged in a downwardly inclined shape toward the transfer portion A, and the lower guide plate 34 is once passed over the tangent line C. After being inclined so as to approach the rotation center O ₂ of the transfer roller 9, the vicinity of the paper outlet end 34a of the lower guide plate 34 is projected beyond the tangent line C so as to approach the rotation center O ₁ of the photosensitive drum 10. Let them do it. According to this structure, the lower surface of the sheet P fed obliquely downward is positively brought into contact with the sheet outlet end portion 34a, so that the static elimination effect is not impaired.

It goes without saying that the present invention can also be applied to a transfer device in an electrostatic electrophotographic image forming apparatus such as a facsimile or a copying machine.

[0021]

As described above, claim 1
The image forming apparatus of the invention described above is directed toward a transfer portion between a transfer roller that carries a toner image and that is arranged in parallel so as to face the peripheral surface of the photosensitive drum that rotates around a substantially horizontal rotation axis. It is equipped with a pair of upper and lower guide plates that guide the recording medium such as paper, and is configured to transfer a toner image to the recording medium by applying a transfer voltage to the transfer roller. A roller is disposed, and at least one of the pair of upper and lower guide plates has a sheet outlet end portion formed to project so that the recording medium is ejected toward the transfer portion while slidingly contacting the sheet outlet end portion. In addition, the upper and lower guide plates are grounded.

Therefore, the recording medium charged with static electricity is positively slidably contacted with the sheet exit end of the grounded guide plate on the front side of the conveying position from the transfer portion charged with a high voltage. The recording medium sent will not be charged with static electricity, and the chargeable toner on the surface of the photoconductor drum will properly transfer to the paper only with the high voltage potential applied to the transfer site to form a beautiful image. can do.

In particular, when an image is formed (printed) on both front and back surfaces of a recording medium, the recording medium having an image formed on one side is often charged with static electricity. There is an effect that the charge can be surely removed and the image quality of the recording medium can be improved. According to a second aspect of the invention, in the image forming apparatus according to the first aspect, the pair of upper and lower guide plates are arranged so as to be inclined from the lower side to the upper side as they approach the transfer portion,
Of the pair of upper and lower guide plates, the end portion of the paper exit portion of the lower guide plate is located above a line perpendicular to the line connecting the rotation center of the photosensitive drum and the rotation center of the transfer roller, Moreover, the lower guide plate is grounded.

In this case, when the recording medium is conveyed obliquely upward, the position of the sheet exit end of the lower guide plate connects the center of rotation of the photosensitive drum and the center of rotation of the transfer roller. Since it is above the line perpendicular to the line, the lower surface side of the paper always comes into contact with the paper exit end, and the effect of surely performing the neutralizing action on the recording medium can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic side sectional view of a laser printer.

FIG. 2 is an enlarged side sectional view of a main part of a transfer part.

FIG. 3 is an operation explanatory view.

FIG. 4 is a side view of another embodiment.

FIG. 5 is a side view of the prior art.

[Explanation of symbols]

 1 Printer 2 Body Case 6 Feeding Roller Pair 7 Process Unit 8 Transfer Unit Base 8a Base Plate 9 Transfer Roller 10 Photosensitive Drum 26 High Voltage Substrate 33 Lower Guide Plate 34 Upper Guide Plate 32 Passing Guide Member P Paper

Claims (2)

[Claims] 1. A sheet of paper or the like is transferred toward a transfer portion between a transfer roller, which carries a toner image and is arranged in parallel so as to face the peripheral surface of a photosensitive drum that rotates around a substantially horizontal rotation axis. In an image forming apparatus having a pair of upper and lower guide plates for guiding a recording medium and configured to apply a transfer voltage to a transfer roller to transfer a toner image to a recording medium, the image is transferred onto the lower peripheral surface of the photosensitive drum. A roller is arranged, and the paper exit end of at least one of the pair of upper and lower guide plates is projected so that the recording medium is ejected toward the transfer part while being in sliding contact with the paper exit end. An image forming apparatus, wherein the upper and lower guide plates are grounded. 2. The pair of upper and lower guide plates are arranged so as to be inclined from the lower side to the upper side as they approach the transfer portion, and the sheet outlet end portion of the lower guide plate of the pair of upper and lower guide plates is connected to the photosensitive member. 2. The image according to claim 1, wherein the lower guide plate is located above a line perpendicular to a line connecting the center of rotation of the body drum and the center of rotation of the transfer roller, and the lower guide plate is grounded. Forming equipment.