JP3624932B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as an electrophotographic copying machine or a laser printer, and more particularly to an image suitable for preventing image deterioration that may occur during fixing processing of an unfixed toner image transferred to a recording medium. The present invention relates to a forming apparatus.
[0002]
[Prior art]
In an image forming apparatus such as an electrophotographic copying machine or printer, there is a method in which a printed image is obtained by transferring an unfixed toner image formed on a latent image carrier such as a photosensitive drum onto a recording medium such as paper. It is done. FIG. 4 is a schematic diagram illustrating an example of an electrophotographic printer. In the figure, the surface of a photosensitive drum (hereinafter referred to as “photosensitive member”) 1 as an image carrier is uniformly charged with a predetermined charge by a charging roll 2 as a charging device, and the laser beam emitted from the exposure device 3 An electrostatic latent image corresponding to the image signal is formed by writing scanning. The electrostatic latent image reaches the developing position by the rotation of the photosensitive member 1 and is developed with toner by the developing device 4. The toner image on the photoconductor 1 reaches the contact portion, that is, the transfer position between the transfer roll 5 as a transfer device and the photoconductor 1 by the rotation of the photoconductor 1.
[0003]
On the other hand, the recording paper is stored in the recording paper tray 6, and the recording paper is pulled out to the conveyance path by the paper supply roll 7 in accordance with the image forming operation on the photoreceptor 1. A conveyance roll 8 is provided in the conveyance path, and the recording paper drawn from the recording paper tray 6 is conveyed to the transfer position. A transfer bias having a polarity opposite to the charged polarity of the toner image on the photosensitive member 1 is applied to the transfer roll 5 at the transfer position, and the toner image is transferred onto the recording paper. Sensors 9 and 10 for detecting the recording paper are provided in the conveyance path, and are used to adjust the image formation on the photosensitive member 1 and the conveyance timing of the recording paper. After the transfer roll 5, an electrode 11 as a peeling device for peeling the recording paper from the photoreceptor 1 is provided.
[0004]
The recording paper on which the toner image on the photoreceptor 1 is transferred is sent to the fixing device 12 and is heated and pressurized by the pressure roll 13 and the heating roll 14. The recording paper on which the toner image is fixed by the fixing device 12 is discharged to the face-up tray 16 or the face-down tray (upper surface of the main body housing) 17 according to the switching of the gate 15. A transport path 18 for discharging the recording paper to the face-down tray 17 and a sensor 19 for detecting the position of the recording paper are provided in the transport path downstream of the fixing device 12. In order to supply the recording paper, a manual feed tray 20 can be provided in addition to the recording paper tray 6. A half-moon roll 21 is provided to pull out the recording paper from the manual feed tray 20.
[0005]
In the apparatus having the above configuration, when the recording paper passes through the contact portion (nip portion) between the pressure roll 13 and the heating roll 14 in the fixing device 12 and the rear end of the recording paper leaves the heating roll 14 side, The electric charge falls on the heating roll 14 as peeling discharge, and an electrostatic history remains on the heating roll 14. This electrostatic history remains even after the heating roll 14 makes one turn, and the toner image on the recording paper is attracted to the history portion when it next contacts the recording paper. As a result, the toner image may be transferred from the heating roll 14 to the recording paper after the next round, and the image may be disturbed. Such retransfer to recording paper is known as "offset".
[0006]
[Problems to be solved by the invention]
In order to prevent the offset, for example, the pressure roll and the heating roll are electrically connected and grounded via a rectifying element so as to hold the charge having the same polarity as that of the toner particles, or the heating roll or It has been considered to apply a voltage to the pressure roll. An example of an image forming apparatus in which a pressure roll and a heating roll are grounded via a rectifying element is disclosed in JP-A-2-253283.
[0007]
However, the image forming apparatus to which the bias voltage is applied has the problems that the number of parts increases and the structure becomes complicated.
[0008]
SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of solving the above-described problems and preventing an offset due to peeling discharge without increasing the number of parts and obtaining a good image.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides an image forming apparatus having a fixing device that pressurizes a recording medium carrying an image made of charged particles and fixes the charged particles to the recording medium. A pair of pressurizing means arranged so as to be in contact with the back surface and sandwiching the recording medium, and on the downstream side of the pressurizing means in the recording medium conveyance direction, the recording medium is not flat in the width direction. The present invention is characterized in that it includes recording medium deformation means for imparting such deformation.
[0010]
According to this feature, the recording medium exiting the pressurizing means is deformed non-flatly in the width direction. Therefore, when passing through the pressurizing unit, the trailing edge of the recording medium is unevenly separated from the pressurizing unit. As a result, peeling discharge that has occurred in a wide range in the width direction of the recording medium is suppressed to a narrow range.
[0011]
Further, the present invention provides a recording medium urging unit that is on the downstream side of the pressurizing unit in the recording medium conveyance direction and presses the recording medium in a direction facing the back surface of the charged particle carrying surface of the pressurizing unit. There is a second feature in that
[0012]
According to the second feature, the rear end of the recording medium in the pressurizing unit is pressed toward the opposite side of the charged particle carrying surface, so that the recording medium is conveyed along one of the pressurizing units. As a result, peeling discharge is caused to the pressurizing means that does not face the charged particle carrying surface, and no “offset” occurs due to this peeling discharge.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a color image forming apparatus to which the present invention is applied will be described in detail with reference to the accompanying drawings. Here, the configuration and operation described with reference to FIG. 4 are used, and the description will be made with reference to FIG. 4 as appropriate.
[0014]
Conventionally, when the recording paper is detached from the fixing device, the entire width direction of the recording paper is separated from the heating roll almost at the same time, so that a strip-like peeling discharge occurs along the axial direction of the heating roll, and in a wide range. It is considered that an offset of Therefore, in the present embodiment, the recording paper trailing edge is prevented from being separated from the heating roll at a time when the recording paper comes out of the fixing device.
[0015]
FIG. 1 is a perspective view illustrating a configuration of a fixing device of the image forming apparatus according to the present exemplary embodiment. The fixing device 12 includes a pressure roll 13 and a heating roll 14. The heating roll 14 is formed by coating a surface of a metal pipe such as aluminum or stainless steel with a material having good heat resistance and releasability such as fluorine resin, and a lamp heater 14a is disposed at the center. . The pressure roll 13 is formed by laminating a high friction material such as foamed resin on a metal core, and is elastically pressed in the direction of the heating roll 14 by a spring means (not shown). The recording paper P conveyed from the transfer position is conveyed while being heated and pressurized at the nip portion of the pressure roll 13 and the heating roll 14, and the toner image on the recording paper P is fixed.
[0016]
A discharge chute 22 and two pairs of discharge rolls 23 and 24 are disposed after (downstream) the pressure roll 13 and the heating roll 14, and the recording paper P that has passed through the fixing device 12 runs along the discharge chute 22. It is conveyed and guided to the nip portion of the discharge roll pair 23, 24.
[0017]
In the discharge roll pair 23, 24, either one of the upper and lower sides is a driving side, and the other is a pressing side. Here, discharge rolls 23a and 24a as drive-side rolls are arranged on the upper side, and pinch rolls 23b and 24b as press-side rolls are arranged on the lower side. The discharge rolls 23a and 24a and the pinch rolls 23b and 24b are all formed in a conical shape having a taper. Accordingly, the recording paper passing through the discharge roll pair 23, 24 is deformed along the shapes of the discharge rolls 23a, 24a and the pinch rolls 23b, 24b.
[0018]
FIG. 3 is a perspective view showing a state of deformation of the recording paper when passing through the discharge roll pairs 23 and 24. As shown in this figure, the recording paper P is bent from the central portion when passing through the discharge roll pairs 23 and 24 to form a mountain shape. That is, the recording paper P has a non-flat shape in the cross section in the width direction, that is, in the direction orthogonal to the transport direction. When the recording paper P passes through the fixing device 12, at the rear end Pre, when both ends are separated from the heating roll 14, the central portion that is raised in a mountain shape still follows the heating roll 14. Accordingly, the central portion of the rear end Pre is separated from the heating roll 14 later than both ends, and as a result, the peeling discharge generated between the rear end Pre of the recording paper P and the heating roll 14 is suppressed only in the vicinity of the central portion. can do. Since the recording paper P is forcibly deformed by the discharge roll pair, the position of the peeling discharge can be reliably controlled. Further, by changing the recording paper P into a mountain shape, the peeling discharge can be limited to one place, and the “offset” can be made inconspicuous.
[0019]
Next, a second embodiment will be described. In the second embodiment, the recording paper is deformed by changing the upper surface of the discharge chute 22 from a flat one to a three-dimensional shape. In FIG. 2, the upper surface of the discharge chute 22, that is, the surface on which the recording paper slides is made higher than the central portion at both ends in the width direction of the recording paper. That is, as shown in FIG. 2B, the discharge chute 22 is formed so that the XX cross-sectional shape is concave. With such a shape of the discharge chute 22, the recording paper that has passed through the fixing device 12 is conveyed along the discharge chute 22 and the central portion in the width direction is deformed into a concave shape. As a result, both end portions of the rear end of the recording paper are separated from the heating roll 14 later than the central portion, and peeling discharge generated between the rear end of the recording paper and the heating roll 14 is suppressed only in the vicinity of both end portions. The Since the recording paper P is aligned with the shape of the discharge chute 22, the deformation applied to the recording paper P is gentle, unlike the forced one. Further, by suppressing the position of the peeling discharge at both ends, it is possible to avoid the disadvantage that an “offset” occurs in the center of the image. In this embodiment, the discharge roll pair 23, 24 has a cylindrical outer shape.
[0020]
In each of the first and second embodiments, the recording paper may be deformed in the reverse direction. That is, in the first embodiment, the combination of cones may be changed so that the central portion in the width direction of the recording paper is recessed, and in the second embodiment, the upper surface of the discharge shooter 22 is made convex. Good. In short, the shape of the discharge roll pairs 23 and 24 or the discharge chute 22 is determined so that the recording paper when discharged from the fixing device 12 does not become flat in the width direction, that is, the axial direction of the heating roll 14. Good.
[0021]
Next, a third embodiment will be described. When the recording paper leaves the fixing device 12, if the electric charge is dropped not on the heating roll 14 but on the pressure roll 13, the “offset” due to the peeling discharge does not occur. Therefore, in the third embodiment, a measure for causing the recording paper to follow the pressure roll 13 is taken.
[0022]
FIG. 5 is a cross-sectional view of a main part in the vicinity of the fixing device according to the third embodiment. In this embodiment, the heating roll 14 is disposed on the lower side, and the pressure roll 13 is disposed on the upper side. The discharge chute 22 is provided with a mountain 25 near the heating roll 14 and the pressure roll 13. That is, the part which protruded in the pressurization roll 13 side rather than the tangent L in the nip part of the heating roll 14 and the pressurization roll 13 was formed.
[0023]
The recording paper P that has passed through the nip portion between the pressure roll 13 and the heating roll 14 is urged by the peak 25 in the direction of rotating toward the pressure roll 13 with the peak 25 as a fulcrum, that is, in the direction of the arrow R. As a result, the rear end of the recording paper P is displaced while contacting the pressure roll 13. Accordingly, the charge of the recording paper P falls on the pressure roll 13 and no electrical history remains on the heating roll 14 side. In this way, peeling discharge can be easily avoided by simply making the upper surface shape of the discharge chute 22 unique.
[0024]
It is preferable that the mountain 25 be approximately the same as the width of the discharge chute 22 or be intermittently arranged in the entire width direction. Further, the mountain 25 may be configured as an extension of a linear rib usually formed on the discharge chute 22 in order to improve the sliding property of the recording paper. FIG. 6 is a perspective view of the discharge chute 22 and shows a rib 26 extending to the peak 25. In short, in order to urge the recording paper that has slipped out of the fixing device 12 toward the pressure roll 13, the recording paper once enters the pressure roll 13 side beyond the tangential line L, and immediately thereafter returns to the heating roll 14 side. The path may be formed by the outer shape of the discharge chute 22.
[0025]
In order to reliably urge the recording paper toward the pressure roll 13, the recording paper conveyance speed by the discharge roll pair 23, 24 is faster than the recording paper conveyance speed by each roll 13, 14 of the fixing device 12. It is preferable to do this. This is because a tensile force acts on the recording paper, and this tensile force increases a force for rotating the recording paper with the mountain 25 serving as a fulcrum.
[0026]
The present invention is not limited to a heat fixing method using a heating roll, but can be similarly applied to a pressure fixing method in which a toner image is fixed only by pressure. Furthermore, the recording paper is not limited to the above-described method using a pair of rolls as a means for sandwiching the recording paper, and the recording paper may be pressed by a belt device and a heating roll. However, when the recording paper is pressed by the belt and the heating roll, the shape of the backup member of the belt is deformed, and the rear end shape of the recording paper when the recording paper leaves the nip portion is preferably processed. While there is a degree of freedom, in the above-described embodiment in which pressure is simply applied by a pair of rolls, it is difficult to process the recording paper at the nip portion, so the advantage of applying the present invention is even greater. .
[0027]
In addition to the above-described image forming apparatus that transfers an image formed on a photosensitive member to a recording medium, a method of directly forming an image on a recording medium, for example, a process of exposing and developing uniformly charged photosensitive recording paper The present invention can also be applied to an image forming apparatus that employs a method of obtaining an output image through the above. Furthermore, the present invention can also be applied to an image forming apparatus that ejects charged powder toner or charged liquid ink directly onto a recording medium under electric field control according to an image signal.
[0028]
【The invention's effect】
As is apparent from the above description, according to the present invention, the movement of electric charges from the recording medium to the pressurizing means is controlled, and the “offset” due to the peeling discharge is suppressed or eliminated, thereby improving the image quality.
[Brief description of the drawings]
FIG. 1 is a perspective view of a fixing device of an image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a perspective view of a fixing device according to a second embodiment.
FIG. 3 is a perspective view illustrating a deformation mode of a recording sheet that has passed through a fixing device.
FIG. 4 is a schematic diagram illustrating a configuration of an image forming apparatus.
FIG. 5 is a cross-sectional view showing the shape of a recording paper discharge chute according to a third embodiment.
FIG. 6 is a perspective view showing ribs formed on the surface of the recording paper discharge chute.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Photoconductor, 12 ... Fixing device, 13 ... Pressure roll, 14 ... Heating roll, 14a ... Lamp heater, 22 ... Discharge chute, 23, 24 ... Discharge roll pair

Claims (1)

In an image forming apparatus having a fixing device that pressurizes a recording medium carrying an image made of charged particles and fixes the charged particles to the recording medium.
A pair of pressurizing means disposed so as to contact the front and back surfaces of the recording medium and sandwiching the recording medium;
A recording medium disposed in a pair in the width direction of the recording medium , which is downstream of the pressurizing unit in the recording medium conveyance direction and imparts deformation to the recording medium so as to be non-flat in the width direction. A transport roll,
The image forming apparatus according to claim 1, wherein a shape of a nip portion of the recording medium conveyance roll is formed to be inclined with respect to an axial direction of the recording medium conveyance roll .

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