JPH09258565A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of a finger mark, etc., caused by contact with a peeling pawl by discharging electricity only for the top end part of a recording medium with a tooth-shaped discharge member (DTS), so as to peel the top end part from an electrostatic latent image carrier and receiving the top end part, and guiding it to a fixing means side, with a paper guide. SOLUTION: This image forming device is provided with a discharge voltage applying means for attaining the discharge of a region over a corona discharge area, only in the top end part of a paper sheet 6, to peel the top end part from a drum 1, by the tooth-shaped discharge member DTS. The paper guide 5 for receiving the top end part of the paper 6 peeled by the DTS, to guide the paper 6 to a fixing means, by attracting force by the application of a voltage having the same polarity as that of the potential of the drum 1 is disposed on the downstream side in the moving direction of the paper 6, of the DTS. The discharge-voltage-applied DTS starts to discharge the electricity, when the top end of the paper approaches a discharge position and in the paper having the discharge, a charge is removed from the top end. The voltage-application- stopped DTS stops to discharge the electricity and the end part of the paper is destaticized and received by the paper guide.

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 utilizing an electrostatic transfer system such as an electrostatic copying machine or an electrostatic printer,
In particular, it relates to an image forming apparatus equipped with a transfer and peeling device.

[0002]

2. Description of the Related Art Generally, in an image forming apparatus, as shown in FIG. 8, a surface of an electrostatic latent image carrier 1 of a photosensitive drum rotating in an arrow direction is charged by a corona charger 2 and then an exposure device 3 is used. And an electrostatic latent image is formed on the peripheral surface of the photosensitive drum 1. Then, the latent image is developed by the developing device 4 to form an unfixed toner image 6 on the peripheral surface of the photosensitive drum 1. Next, the unfixed toner image 6 moves to a transfer area in which a transfer device 7 is provided, is transferred onto a sheet (recording medium) 8 in this transfer area, and is then peeled off from the peripheral surface of the photosensitive drum 1. And is conveyed to the fixing device 9, where it is fixed on the paper 8 and discharged to the outside of the device.

A corona transfer method using a corona charger called "transfer corotron" is known as one of electrostatic transfer methods for transferring an unfixed toner image formed on the peripheral surface of a photosensitive drum onto a sheet. However, the transfer corotron used in this corona transfer method attracts and transfers the unfixed toner image to the paper side only by the electrostatic attraction force, and the transfer corotron itself has no force for conveying the paper. Therefore, the image forming apparatus is downsized to reduce the distance between the transfer device and the fixing device, and the structure in which the leading end of the paper in the moving direction is sandwiched by the fixing device before the entire paper is completely transferred by the transfer device is downsized. When this transfer corotron is used in the device, the fixing device has a stronger carrying force than the attraction force between the transfer corotron and the photoconductor drum, so when the leading edge of the paper is caught in the fixing part A change in speed or vibration may be applied to cause a deviation in the moving speed from the unfixed toner image on the peripheral surface of the photoconductor drum, resulting in image smearing called "smear". In some cases, a high water content paper containing a large amount of water is used as the recording medium. However, in such a high water content paper, the electric resistance value decreases due to the water content, so that the transfer charge imparted on the paper is diffused. Transfer defects may occur.

In order to solve such problems as image disturbance and transfer failure, one of the electrostatic transfer type devices is called a "bias roll" in which a constant DC bias voltage is applied to the roll peripheral surface. A contact transfer method is used in which a transfer member in the form of a roll is used, and the transfer member is pressed against the photosensitive drum to perform transfer while rotating the transfer member. In addition to electrostatic attraction, this bias roll conveys paper strongly while holding the paper strongly with a nip force that sandwiches the paper in the transfer portion that is in pressure contact with the photoconductor drum. Even when used in an image forming apparatus in which the fixing device and the fixing device are arranged in close proximity,
There is no image distortion like smear. Further, in the transfer area where the bias roll and the paper are in contact with each other, the transfer charge does not diffuse even when the high water content paper is used, and there is an advantage that the transfer failure can be prevented when the high water content paper is used.

However, in the electrostatic transfer type contact transfer system using the bias roll, an electrostatic force is generated between the paper and the peripheral surface of the photoconductor drum by the charge, and the paper itself contacts the peripheral surface of the photoconductor drum. Since the paper is attracted and the bias roll presses the paper strongly against the peripheral surface of the photoconductor drum, the attraction force between the paper and the electrostatic latent image carrier becomes stronger than when a transfer corotron is used, and the paper is exposed to light. There is a problem that it becomes difficult to peel from the body drum.

Therefore, in order to improve the peeling property, various peeling means such as a mechanical peeling means and an electrostatic peeling means have been proposed. However, in order to meet the demand for downsizing of the image forming apparatus, a static peeling means has been proposed. Electrolytic stripping means are often employed.
For example, a "detack saw" having a needle-shaped or saw-toothed tip on the downstream side of the transfer device in the sheet moving direction.
Hereinafter, it is abbreviated as “DTS”. ), And a discharge voltage is applied to the DTS to remove excess charges on the paper to reduce the electrostatic attraction force between the paper and the peripheral surface of the photosensitive drum. The DTS method in which the stiffness of the paper, that is, the bending rigidity is used to separate it from the peripheral surface of the photoconductor drum, or the grounded conductive member is brought into contact with the paper to eliminate excess electric charges at the leading end of the paper and the paper and the photoconductor drum After reducing the electrostatic adsorption force with the peripheral surface, a voltage is applied to the conductive member arranged further downstream in the paper movement direction to apply the electrostatic adsorption force and peel off. The method etc. are used.

However, the electrostatic attraction force acting between the paper and the peripheral surface of the photosensitive drum is strong, and when developing the non-image portion of the original document, that is, the white paper portion on which characters and pictures are not drawn, unfixed toner is used. Since the image is not formed on the peripheral surface of the photosensitive drum and the paper is directly pressed against the peripheral surface of the photosensitive drum in the transfer area, the adhesion between the photosensitive drum and the paper is improved. In particular, there is no image in the blank area from the edge of the paper to the characters, and the paper strongly adheres to the peripheral surface of the photoconductor drum in this blank area. Is reduced. Therefore, when a document having a large proportion of the non-image portion, especially the blank portion is transferred, the peeling property of the paper from the peripheral surface of the photoconductor drum is significantly lowered regardless of whether the DTS method or the conductor separation method is used. The sheet is conveyed to the portion having the peeling claw while being attracted to the peripheral surface of the photosensitive drum.
When the leading edge of the paper reaches the position where the peeling claw is attached, the peeling nail sequentially peels from the leading edge, but the part after the leading edge of the paper is attracted to the peripheral surface of the photosensitive drum until it is peeled by the peeling nail. Therefore, the entire sheet eventually comes into contact with the lower portion of the peeling claw before the peeling of the sheet is completed. Therefore, the unfixed toner image transferred onto the paper is also rubbed by the lower part of the peeling claw, and at this time, the unfixed toner image may be disturbed to cause an image defect called “finger mark”.

Further, with the increase in speed of image forming apparatuses, there is a tendency to increase the process speed such as development and transfer in order to increase the print speed of the image forming apparatus. In order to increase the moving speed of the body drum surface, a method of increasing the diameter of the photosensitive drum may be adopted. When the diameter of this photoconductor drum is increased, the amount of deformation that the paper receives from the time when the leading edge of the paper is adsorbed to the peripheral surface of the photoconductor drum in the transfer area until the position of the peeling claw is reduced. , The force of peeling from the peripheral surface of the photoconductor drum becomes small due to the bending rigidity of the paper itself, and the entire paper is conveyed to the position of the peeling claw while being attracted to the peripheral surface of the photoconductor drum. It tends to occur. On the other hand, in order to prevent the generation of this finger mark, the transfer area is moved to the upstream side in the rotation direction of the photosensitive drum, or
If the distance between the transfer area and the peeling claw is increased by moving the peeling claw to the downstream side in the rotation direction of the photoconductor drum, it becomes difficult for the peeled paper to enter the subsequent fixing device, and the paper called "jam" Clogging easily occurs.

By the way, as a method of preventing the generation of finger marks while maintaining good transferability by the conductor separation method, Japanese Patent Application Laid-Open No. 62-237468 discloses that a static eliminating brush is provided on the downstream side of a transfer device and the static elimination is performed. A transfer / separation device is disclosed in which a conductive paper guide is disposed on the downstream side of a brush. However, this method has a drawback that the back surface of the paper is soiled when the paper is jammed because the brush comes into contact with the paper. In addition, as the process speed of transfer and peeling increases, the frictional resistance between the brush and the paper increases, the brush bristles bend and the contact with the paper becomes uneven, resulting in insufficient charge removal from the paper and peeling. If the high water content paper is used, the electrical resistance is lowered, and there is a defect that a transfer omission occurs at a portion in contact with the static elimination brush.

On the other hand, since the DTS does not come into contact with the paper, the above-mentioned problem that the back surface of the paper becomes dirty does not occur, but the discharge voltage is high at the tip of the DTS, and the discharge is concentrated at the tips of the teeth. Therefore, the paper may be locally excessively discharged. Since there is no force to electrically hold the toner on the paper in the excessively discharged portion of the paper, the toner once transferred onto the paper is attracted to the electricity on the peripheral surface of the photoconductor drum, and then the toner is again attracted to the peripheral surface of the photoconductor drum. The image may return to the surface, and streak-shaped image defects called “DTS marks” may occur on the sheet portion.

As means for preventing this DTS mark,
Japanese Unexamined Patent Publication No. 62-8180 discloses a method of applying a voltage lower than that at which DTS starts self-discharge. However, in this method, since the peeling effect due to the discharge of DTS is low, the diameter of the photoconductor drum is increased to increase the printing speed of the image forming apparatus and the process speed, and the peripheral surface of the photoconductor drum becomes flat. If the distance becomes closer, the bending rigidity of the paper itself weakens the force of peeling from the peripheral surface of the photoconductor drum, and therefore it cannot be used in an apparatus equipped with a photoconductor drum having a large diameter.

[0012]

Therefore, as a result of intensive studies on the image forming apparatus which does not have the above-mentioned problems, the present inventors have found that the peeling of the recording medium due to the discharge and charge removal of the DTS is performed only on the leading end portion of the recording medium. Then, the front end portion of the peeled recording medium is received by a paper guide to which a voltage having the same polarity as the potential of the ground or the electrostatic latent image carrier is applied, and the paper guide transfers the recording medium to the subsequent fixing device. The present invention has been completed by finding that the above problems can be solved by adopting a guiding mechanism.

Therefore, an object of the present invention is to provide a finger mark or D in an electrostatic peeling type image forming apparatus using a DTS even if the diameter of a photosensitive drum as an electrostatic latent image carrier is increased.
An object of the present invention is to provide an image forming apparatus capable of reliably peeling a recording medium from the peripheral surface of a photosensitive drum without causing image defects such as TS marks.

[0014]

SUMMARY OF THE INVENTION According to the present invention, an electrostatic latent image carrier on which an unfixed toner image is formed according to image information on a carrying surface, and the unfixed toner image is an electrostatic latent image carrier. A transfer roll that is disposed in a transfer area that is transferred from the body surface to the recording medium, presses against the surface of the electrostatic latent image carrier while sandwiching the recording medium during transfer, and a bias voltage is applied to the transfer roll. A sawtooth discharge member (DTS), which is disposed on the downstream side in the moving direction of the recording medium, applies a discharge voltage to separate the recording medium from the electrostatic latent image carrier, and an unfixed toner image on the recording medium. In the image forming apparatus provided with a fixing means for fixing to the sawtooth discharge member, the sawtooth discharge member discharges only a tip portion of the recording medium in a region beyond the corona discharge region to form a tip portion. Is removed from the electrostatic latent image carrier. And a discharge voltage applying means disposed downstream of the sawtooth discharge member in the moving direction of the recording medium, and a voltage having the same polarity as the potential of the ground or the electrostatic latent image carrier is applied. The image forming apparatus is provided with a paper guide that receives the separated leading end of the recording medium and guides the recording medium to the fixing unit side.

In the present invention, the discharge voltage applying means is D
It is a means for applying a predetermined voltage to this DTS so that the TS discharges in a region beyond the corona discharge region only at the tip of the recording medium. The discharge voltage applying means applies the discharge voltage to the DTS at the same timing as the recording medium passes through the discharge position of the DTS. The timing for applying the discharge voltage to the DTS is based on the method of transporting the recording medium, or the signal is taken out from the control system for writing, developing, transferring, etc., an image on the electrostatic latent image carrier. And the method based on this.

As a method based on the conveyance of the recording medium, for example, the leading end portion of the recording medium is just DTS based on a detection signal of a detector for detecting the position of the recording medium provided in the image forming apparatus. This is a method in which the timing of passing the discharge position is determined by actual measurement or calculation, and the discharge voltage is applied so that the DTS is discharged at that timing.

As a method of extracting a signal from a control system for writing, developing, transferring, etc. an image on the electrostatic latent image carrier and using this as a reference, image information is written on the electrostatic latent image carrier. Sometimes, the signal sent from the control system to the exposure device or the signal received by the electrostatic latent image carrier determines the time when the surface portion of the electrostatic latent image carrier on which the image information is written passes the discharge position of the DTS. In this method, the discharge voltage is applied so that the DTS is discharged in the portion just before the surface portion passes the discharge position.

Further, a method combining the above two methods is also possible. For example, while determining the time when the edge of the recording medium passes the discharge position on the basis of the signal from the recording medium conveyance detector, from the signal issued from the control system when the image information is written to the electrostatic latent image carrier. The time when the surface portion of the electrostatic latent image carrier on which the image information is written passes through the discharge position of the DTS is determined, and discharge is performed in the portion from the edge of the recording medium to immediately before the portion where the image information is written. This is a method of applying a discharge voltage.

The "front end portion of the recording medium" to which the discharge voltage is applied from the DTS is a so-called recording medium from the upstream end in the moving direction of the recording medium to the position where the unfixed toner image is transferred. Refers to the blank area. The length of the leading end portion in the recording medium moving direction is given by the bending rigidity of the recording medium, the conveyance speed, the diameter of the electrostatic latent image carrier when it is a photosensitive drum, the pressure contact force of the transfer roll, and the transfer roll. It is determined based on data such as test operation, taking into consideration conditions such as the amount of electric charge, the distance from the transfer area to the fixing unit, and the potential of the photosensitive drum. Generally, a length of about 6 mm from the tip is used. If so, it can be sufficiently peeled off by discharging this portion and removing the charge.

The discharge voltage applied to the DTS from the discharge voltage applying means is a voltage that allows the DTS to discharge in a region beyond the corona discharge region, and the leading edge of the paper is completely discharged from the surface of the electrostatic latent image carrier. The discharge is such that it can be peeled off.

The discharge phenomenon of the present invention will be described in detail with reference to FIG. FIG. 1 shows the discharge voltage applied to the DTS on the horizontal axis and the discharge current when discharge occurs from the DTS to the surface of the electrostatic latent image bearing member on the vertical axis. The solid line graph shows the discharge voltage. The relationship with the discharge current is shown. As shown in this graph, the discharge voltage is 0 to 1.
Only a weak discharge current of less than 100 μA flows up to around 9 kVrms. This region is a region called a corona discharge region where a weak discharge occurs, but such a weak discharge cannot separate the recording medium from the surface of the electrostatic latent image carrier. On the other hand, when the discharge voltage is made higher than 1.9 kVrms, the discharge current sharply increases. A region where this discharge occurs is called a transition region, and a relatively large discharge current flows.

In the present invention, it is necessary to cause discharge by the DTS in a region beyond the corona discharge region such as this transition region. In the present invention, only the tip portion of the recording medium is DT
Since it is a system in which the sheet is separated by the discharge of S and the portion other than the leading end is sucked by the paper guide, the DTS is discharged only at the leading end in the moving direction of the recording medium. If the leading end of the recording medium is not peeled off, it is difficult to peel off the recording medium only by the suction force of the paper guide.
The leading edge of the recording medium must be reliably peeled off. Moreover, normally, images such as characters and pictures are rarely drawn at the tip of the recording medium in the moving direction, and since this tip is strongly attracted to the surface of the electrostatic latent image carrier, it exceeds the corona discharge range. This is because it is necessary to surely peel off by applying the discharge in the different region.

The value of the voltage capable of "discharging the region beyond the corona discharge region" is the distance between the DTS and the electrostatic latent image carrier and the bias applied to the surface of the electrostatic latent image carrier. Voltage, diameter of the electrostatic latent image carrier when it is a photoconductor drum, amount of charge applied to the paper by the transfer roll, D
Although it depends on various conditions such as the position of TS, the conveyance speed of the paper, the moisture content of the paper, etc., it is actually preferable to experimentally determine the optimum value.

As an application example of the discharge voltage applying means, an ion conductive type bias roll is used as a transfer roll, and this ion conductive type bias roll is used as a moisture content sensor of the paper. The peelability can be compensated by detecting that it is difficult to peel.
That is, it is possible to detect an increase or decrease in the electric resistance of the paper from the change of the transfer voltage or the transfer current applied to the transfer roll, and to detect the moisture content of the paper from the electric resistance value. For example,
When the moisture content of the paper is lower than the preset range, the electrical resistance of the paper increases due to the decrease of the moisture content, and the leakage of the transferred charges is reduced, and electrostatic adsorption with the electrostatic latent image carrier is performed. The force may increase and the releasability may decrease.In such a case, the difference between the moisture content of the paper and the moisture content in the above setting range is recognized from the electric resistance value, and the degree of this deviation is recognized. Accordingly, by increasing the discharge voltage and increasing the peeling function of the DTS, it is possible to compensate for the decrease in peelability.

Further, as another application example of the discharge voltage applying means, a detector for detecting the bending rigidity of the sheet is arranged in the sheet conveying portion, and the peeling property is compensated by using the signal of this detector. You can also As such a detector, for example, there is a detector in which a weight for pressing the paper is arranged in the paper transport portion and the bending rigidity of the paper is detected by the change in the position of the weight. Then, when the bending rigidity of the paper, which is grasped from the position change of the weight, is lower than the preset range, the discharge voltage applied to the DTS is increased and the peeling function of the DTS is increased, so that the peeling property due to the decrease in the bending rigidity is increased. Can also be used as a mechanism for compensating for the decrease in

The paper guide has the electrostatic attraction force due to the voltage of the same polarity as the potential of the electrostatic latent image carrier grounded or applied, that is, the electrostatic attraction force generated between the electrostatic charge and the transfer charge of the sheet. It is a member that receives the leading end of the recording medium separated by DTS from the surface of the electrostatic latent image carrier and guides the recording medium to the fixing device. The paper guide is D
The DTS is provided on the downstream side of the TS in the moving direction of the recording medium.
The leading end portion of the recording medium that has been peeled off can be reliably received, and the recording medium is attached to a position where it can be reasonably guided to the subsequent fixing device. More specifically, at this paper guide attachment position, when the leading end portion of the recording medium is peeled off due to the discharge of DTS, and when the leading end portion is peeled off from the surface of the electrostatic latent image carrier due to the bending rigidity of the recording medium. At a position where the leading end portion of this recording medium can be reliably received and the recording medium can be reasonably guided to the fixing device by the suction force due to the grounding or the application of a voltage having the same polarity as the potential of the electrostatic latent image carrier. is there. As such a position, for example, in a space formed between the surface of the electrostatic latent image carrier and a plane in contact with the surface of the electrostatic latent image carrier in the transfer area, on the downstream side of the recording medium moving direction of the DTS. The position is such that a part of the paper guide exists.

This paper guide is connected to the electrostatic latent image carrier surface or D
When the electrostatic latent image carrier is a photosensitive drum, the diameter, the type of the electrostatic latent image carrier, the electrostatic latent image carrier, and the positional relationship with respect to the TS, particularly the distance, are determined. Although it depends on various conditions such as the moving speed of the surface, the bending rigidity of the recording medium, the mounting position of the transfer roll, the mounting position of the DTS, etc., it is actually preferable to experimentally determine the optimum value.

The shape of the paper guide can surely receive the leading end portion of the recording medium separated by the DTS,
The shape is not particularly limited as long as it can guide the recording medium to the subsequent fixing device without difficulty. The material of the paper guide is not particularly limited, but at least the surface part of the part that receives the recording medium and guides it to the fixing device is formed of a material having a semiconductive resistance value intermediate between the conductor and the insulator. Has been done. The reason why a material having such a resistance value is used is that a resistance value lower than this causes a leakage of a transfer current through the guide and disturbs the transferred image.
On the contrary, if the resistance value is higher than this, the transfer charge is accumulated on the guide and the electrostatic attraction force does not act.

As an example of the material of the paper guide, A
A material in which carbon black is dispersed as a conductive powder in a resin such as BS, polycarbonate, or noryl to appropriately adjust the resistance value can be used.

The surface of the paper guide is grounded or a voltage having the same polarity as the voltage applied to the peripheral surface of the electrostatic latent image carrier is applied to the recording medium whose front end is peeled off by the DTS. This is because the guide is sucked, and the guide is surely received and guided to the fixing unit. As an example of the structure of the paper guide, a resin having the above-mentioned electrical properties, a coating of a resin having the above-mentioned electrical properties on the surface of an insulating material, or a shape such as a rib is provided, and a contact portion of the paper is provided. Examples include a shape that reduces paper stains and makes the paper stains inconspicuous.

As described above, the recording medium is pressed against the surface of the electrostatic latent image carrier by the transfer roll in the transfer area, and at the same time, an electric charge is applied to the recording medium, and after the unfixed toner image is transferred, the recording medium is conveyed to the leading end portion. When it reaches the discharge position, it receives discharge from the DTS. At this time, the electric charge at the tip of the recording medium is completely removed by the discharge of the DTS, and the electrostatic force that attracts the tip to the surface of the electrostatic latent image carrier disappears. The tip portion is in a state of being easily peeled off from the surface of the electrostatic latent image carrier. Therefore, when this tip portion is conveyed to the position of the paper guide on the downstream side of the DTS, it is sucked toward the paper guide by the suction force of the paper guide and the tip portion is peeled off. Then, the peeling of the leading edge causes the portion after the leading edge to be sucked toward the paper guide along the leading edge, and eventually the entire recording medium is sucked toward the paper guide, and the electrostatic latent image is reasonably pressed. It is peeled off from the surface of the carrier and guided to the subsequent fixing device.

As described above, the leading end portion of the recording medium is the DTS.
Of the recording medium is separated by the electric discharge of the paper, and the separation after the leading end is sucked and separated by the suction force of the paper guide, and the recording medium is above the paper guide (the space between the paper guide and the surface of the electrostatic latent image carrier). Since the recording medium is peeled off from the surface of the electrostatic latent image carrier at a position where the recording medium passes, the recording medium is hardly conveyed to the position of the peeling claw while being adsorbed on the surface of the electrostatic latent image carrier. As a result, image defects of the finger marks caused by friction with the lower part of the peeling claw are prevented.

On the other hand, the leading edge portion that receives the discharge by the DTS is only the very leading edge portion of the recording medium or the blank portion where the unfixed toner image is not transferred. Even if it does, since it does not affect the image actually formed on the recording medium, the image defect called the DTS mark does not occur.

[0034]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) The present invention will be described below based on the image forming apparatus according to the first embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing the configuration of the image forming apparatus according to this embodiment. The image forming apparatus according to the present exemplary embodiment includes a photoconductor drum 1 (electrostatic latent image carrier) on which an unfixed toner image is formed on a carrying surface according to image information, and the unfixed toner image. A transfer roll 2 which is disposed in a transfer area where the sheet 6 (recording medium) is transferred from one circumferential surface, is pressed against the photosensitive drum 1 with the sheet 6 sandwiched therebetween, and is applied with a bias voltage. The photoconductor drum 1 is arranged downstream of the transfer roll 2 in the moving direction of the paper 6 and is applied with a discharge voltage.
DTS3 (sawtooth discharge member) for peeling the paper 6 from the paper
And a fixing device (fixing means) for fixing the unfixed toner image on the sheet 6 onto the sheet 6.

In the image forming apparatus according to the present embodiment, the DTS discharges the area beyond the corona discharge area only to the leading end of the sheet 6 to separate the leading end from the photosensitive drum 1. A voltage applying means is attached, and at the downstream side of the sheet 6 in the moving direction of the sheet 6, the front end portion of the sheet 6 separated by the DTS is received by the suction force by the application of the voltage having the same polarity as the potential of the photosensitive drum 1. And a paper guide 5 for guiding the paper 6 to the fixing means. Further, in the image forming apparatus according to the present exemplary embodiment, as a discharge voltage applying unit, a detector that detects passage of a sheet, and the leading end portion of the sheet is DTS based on a signal from the detector.
Of the ion conductive type urethane foam is used for the transfer roll 2 by using a central control unit (CPU) that electronically controls the application of the discharge voltage so that the DTS is discharged at the time when the discharge position of the DTS passes. Was used.

The photosensitive drum 1 carrying the unfixed toner image on its peripheral surface rotates and the unfixed toner image is transferred to the transfer roll 2.
When it reaches the transfer region where the photosensitive drum 1 and the photosensitive drum 1 come into pressure contact with each other, the paper 6 is supplied from the paper container to the transfer region through the transport path at the same timing. A detector for detecting the passage of the paper is attached in the middle of the conveying path through which the paper 6 is supplied from the paper storage container, and when the paper passes the detection portion of the paper detector, the paper is detected by the detector. Of the central control unit (CP
U) is signaled. When the central control unit (CPU) receives the signal from the detector, it recognizes the time when the paper passes the detector from this signal, and from this time, the paper measured in advance passes the detection position. The leading edge of the paper is DT
At the time when the time required to reach the S discharge position has elapsed, DT
A discharge voltage is applied to the DTS so that the discharge from S is started. The DTS to which the discharge voltage is applied starts discharging just when the leading edge of the sheet approaches the discharging position, and the discharged sheet is discharged from the leading edge. This discharge continues from the leading edge of the paper to a predetermined position. Next, at the time when the paper passes the discharge position for a predetermined length from the leading edge, the central control unit (CPU) stops applying the voltage to the DTS so as to stop the discharge. The DTS, to which the voltage application has been stopped, stops the discharge, and only the leading end portion of a predetermined length of the edge of the paper is discharged.

When the paper is further conveyed by the rotation of the photoconductor drum and the transfer roll, the leading end of the static-free paper reaches the vicinity of the paper guide attached on the downstream side of the DTS. The force of adhering to the photosensitive drum at the leading edge of the paper is weakened by the charge removal, so that the paper can be easily peeled off. On the other hand, the paper guide is given a force to attract the paper by applying a voltage having the same polarity as the potential of the photoconductor drum, and the paper guide is at a position where the paper peeled off from the photoconductor drum can be reliably received. Since it is attached to the paper, the leading edge of the paper is naturally received by the paper guide.

Since the portion of the paper after the front end of the paper is not discharged by the discharge of DTS, it is conveyed while being attracted to the peripheral surface of the photosensitive drum by electrostatic force, but the front end is guided by the paper guide. Since it is received and guided to the subsequent fixing device, the paper portion after the leading edge portion is naturally guided by the paper guide and guided to the fixing device.

(Second Embodiment) An ion conductive type bias roll is used as a transfer roll, an electric resistance value of a sheet is detected from a change in a transfer voltage or a transfer current applied to the transfer roll, and from this electric resistance value. When the moisture content of the indexed paper is lower than the preset range, the discharge voltage is increased according to the degree of deviation between the moisture content of the paper and the value of the moisture content in the above-specified range, and the DTS An image forming apparatus having the same structure as that of the first embodiment was prepared and a copy operation was performed, except that the discharge voltage applying means had a function of compensating for the deterioration of the peeling property by increasing the peeling function. As a result, it is possible to obtain an image forming apparatus that can always obtain a stable copy image regardless of the change in the water content of the paper.

(Third Embodiment) A mechanism for pressing a sheet with a weight is attached in the middle of a sheet conveying path, the bending rigidity of the sheet is detected by the position change of the weight, and the detected bending rigidity of the sheet is preset. If it is lower than the above range, the discharge voltage applying means is provided with a function of increasing the discharge voltage applied to the DTS and increasing the peeling function of the DTS to compensate for the deterioration of the peeling property due to the decrease of the bending rigidity. Manufactured an image forming apparatus having the same structure as the first embodiment and performed a copy operation. As a result, it is possible to obtain an image forming apparatus which can always obtain a stable paper peeling property even when a paper having a low bending rigidity is used.

[0041]

EXAMPLES The results of a copying operation using the image forming apparatus according to the first embodiment of the present invention will be described below.

In this embodiment, an image forming apparatus having a schematic structure as shown in FIG. 2 was used. An OPC (Organic Photo Conductor) photosensitive layer is provided on a photosensitive drum 1 having an outer diameter of 84 mm and having an axis line in the direction perpendicular to the plane of the drawing and rotating in the direction of the arrow shown. Charged. The process speed of this image forming apparatus was 300 mm / s. As the transfer roll, a roll made of conductive urethane foam and having an outer diameter of 18.7 mm was used. The resistance value of this transfer roll was 1.0 × 10 when measured under the condition corresponding to the state of being pressed against the photosensitive drum 1.
¹⁰ Ω. The tribo value of the toner used in this image forming apparatus, that is, the toner charge amount was 22 to 30 μC / g, and the developing amount was 0.86 × 10 ⁻⁵ g / mm ² . The DTS has a shape shown in FIG. 3 in which a triangular plate having a height of 2.5 mm and an angle of 25 ° is provided at one end of a stainless steel plate having a thickness of 0.1 mm, a length of 314 mm, and a height of 9.1 mm at 3.3 mm intervals. I used the one. The electrode tip has a photosensitive drum 1 and a transfer roll 2
They were arranged at a position of 20 degrees from the transfer region where and are pressed against each other, and a distance of 1.7 mm from the photosensitive drum 1. Further, the peeling claw 4 was arranged at a position of 48 degrees from the transfer area.

The paper guide 5 was arranged so that its tip was 4.6 mm from the tip of the DTS electrode and its surface was flush with the DTS electrode surface. Then, the surface of the paper guide 5 is 10 ¹¹ Ω · c.
m semiconductive sheet, and the same voltage of −750 V as that of the photosensitive drum 1 was applied to the sheet. D in this state
When the relationship between the voltage of TS and the discharge current was measured, the discharge mode transitioned from the corona discharge region from around the applied voltage of 1.9 kVrms as shown in FIG. Therefore, after detecting the leading edge of the paper by a paper registration sensor (not shown) on the DTS, 600 Hz, 2.0 k for 20 ms corresponding to 6 mm of the leading edge of the paper.
An AC voltage of Vrms was applied. The transferability and peelability were evaluated using a chart in which a black belt having a width of 15 mm at a position 7 mm from the front end of the paper and a square having a width of 25 mm at the center were used to evaluate transferability and peeling property. As shown in FIG. No defect was generated and no finger mark was generated. Further, as shown in FIG. 5, the transfer efficiency in this state is 91%.
Met. The transfer efficiency is determined by performing the development and transfer operations using the square pattern shown in FIG. 4, and determining the toner weight of the image transferred on the paper by the unfixed toner carried on the photosensitive drum in the developing process. It is calculated by dividing by the weight.

(Comparative Example 1) In the image forming apparatus having the same structure as that of the first embodiment, the DTS is 6 over the entire area of the sheet.
When an AC voltage of 00 Hz and 2.0 kVrms was applied and transferability and peelability were evaluated using the same chart as in the first embodiment, no finger mark was generated, but as shown in FIG. There has occurred.

(Comparative Example 2) In the image forming apparatus having the same configuration as that of Comparative Example 1, 600H was applied to the DTS over the entire area of the paper.
When an alternating voltage of z and 1.5 kVrms was applied and transferability and peelability were evaluated using the same chart as in the first embodiment, no DTS mark was generated, but as shown in FIG. There has occurred.

[0046]

EFFECTS OF THE INVENTION Since the tip portion of the recording medium is removed by the DTS to separate the recording medium, no finger mark is generated due to contact with the separation claw. Further, the portion which is discharged and separated by the DTS is only a tip portion having a slight length from the tip of the recording medium, and the portion after the tip portion of the recording medium is applied with a voltage of the same polarity as the ground or the electrostatic latent image carrier. The applied paper guide sucks and guides it toward the fixing means.
The image defect of the discharge mark caused by the S discharge does not occur.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a DTS applied voltage and a discharge current in the present invention.

FIG. 2 is a schematic cross-sectional view of the image forming apparatus according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a DTS used in the first embodiment of the present invention.

FIG. 4 is a diagram showing a copy sample when a copy operation is performed using the image forming apparatus according to the first embodiment of the present invention.

FIG. 5 is a diagram showing transferability measurement data when a copy operation is performed using the image forming apparatus according to the first embodiment of the present invention.

6 is a diagram showing a copy sample according to Comparative Example 1. FIG.

7 is a diagram showing a copy sample according to Comparative Example 2. FIG.

FIG. 8 is a schematic sectional view of a conventional image forming apparatus.

[Explanation of symbols]

1 ... Photosensitive drum (electrostatic latent image carrier), 2 ... Transfer roll, 3 ... DTS (sawtooth discharge member), 4 ... Peeling claw, 5 ...
Paper guide, 6 ... Paper (recording medium).

Claims (3)

[Claims] 1. An electrostatic latent image bearing member on which an unfixed toner image is formed on a bearing surface according to image information, and the unfixed toner image is transferred from the electrostatic latent image bearing member surface onto a recording medium. The transfer roll is disposed in the transfer area, is pressed against the surface of the electrostatic latent image carrier while sandwiching the recording medium at the time of transfer, and is provided with a transfer roll to which a bias voltage is applied and on the downstream side of the transfer roll in the recording medium moving direction. Image formation including a sawtooth discharge member that is provided and that applies a discharge voltage to separate the recording medium from the electrostatic latent image carrier, and a fixing unit that fixes the unfixed toner image on the recording medium onto the recording medium. In the device, the saw-tooth discharge member discharges the region beyond the corona discharge area only to the tip portion of the recording medium by the saw-tooth discharge member to separate the tip portion from the electrostatic latent image carrier. Voltage applying means, the sawtooth shape It is arranged on the downstream side of the recording medium in the moving direction of the recording medium, and is applied with a voltage of the same polarity as the ground or the potential of the electrostatic latent image carrier. An image forming apparatus comprising: a sheet guide that guides the recording medium toward the fixing unit. 2. The image forming apparatus according to claim 1, wherein the discharge voltage applying means is means for changing the discharge voltage applied to the sawtooth discharge member according to the bending rigidity or the water content of the recording medium. 3. The transfer roll is an ion conductive type transfer roll which functions as a detector for detecting the water content of the recording medium by the change of the transfer voltage or transfer current of the roll.
An image forming apparatus according to claim 1.