JPH09269671A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make an image forming device always exhibit stable transferring/ peeling performance, regardless of the influence of environment and the kind of paper by making a difference in a feeding speed for carrying a recording medium between a peeling roll and a destaticization roll and peeling the recording medium from an electrostatic latent image carrier. SOLUTION: The peeling roll 8 is in contact with a photoreceptor drum 1 with a very low load and setting in a central processing unit(CPU) is attained for rotating the roll 8 at a uniform speed with the drum 1. The leading edge of a paper sheet 4 carried with the difference in speed faster than that of the drum 1 by about 0.5% for instance by a transfer roll 6, etc., forms a loop in front of the peeling roll 8 rotated at the uniform speed with the drum 1. After that, the paper 4 is attracted to the side of the peeling roll by its electrostatic attracting force and carried to the succeeding fixing device 10. The difference in the feeding speed is made among the transfer roll 6, the destaticization roll 7 and the peeling roll 8, so that a part for separation from the periphery of the drum 1 can be formed and peeling with electrostatic attraction by the peeling voltage of the periphery of the peeling roll 8 can be surely attained.

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, a facsimile, a laser beam printer, and the like, and more specifically, an unfixed toner image formed on the surface of an electrostatic latent image carrier is used as a recording medium. The present invention relates to an apparatus provided with a mechanism for transferring the image onto the surface, removing the charge, and peeling.

[0002]

2. Description of the Related Art Generally, in an image forming apparatus, as shown in FIG. 6, a peripheral surface of a photosensitive drum (electrostatic latent image bearing member) 1 rotating in an arrow direction is charged by a corona charger 2 and then exposed. The electrostatic latent image is formed on the peripheral surface of the photosensitive drum 1 by being exposed by the container 3. 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. ing. This transfer corotron is advantageous in that the paper can be uniformly charged, but it requires a high voltage power source because a high voltage of several kV must be applied in order to give a predetermined charge to the paper. Further, since ozone is generated by corona discharge, there is a problem that the ozone deteriorates the rubber parts and the photosensitive drum inside the apparatus.

Therefore, recently, as an alternative transfer method to the transfer corotron, a conductive transfer roll made of an elastic material, a conductive rubber belt, a conductive resin belt, or the like is pressed against the photosensitive drum to form an unfixed toner image on the paper. A contact transfer method for transferring has attracted attention. Such a contact transfer method has an advantage over the method using a conventional transfer corotron in that highly efficient transfer can be performed with a small transfer current and that ozone is not generated by corona discharge.

However, in the contact transfer method using the transfer roll, the paper passing between the photosensitive drum and the transfer roll has both the electrostatic attraction force on the peripheral surface of the photosensitive drum and the pressure contact force of the transfer roll. Is strongly attracted to the peripheral surface of the photoconductor drum, and if the diameter of the photoconductor drum is increased to increase the process speed, the peripheral surface of the photoconductor drum becomes flatter than that of a normal size photoconductor drum. As a result, the deformation repulsive force stored in the paper becomes small when the paper is attracted to the peripheral surface of the photoconductor drum. Therefore, when attempting to separate the paper from the peripheral surface of the photoconductor drum, the force of the paper itself to peel from the peripheral surface of the photoconductor drum becomes weak due to the stiffness of the paper itself, that is, bending rigidity, and the paper after transfer is There is a problem that it becomes difficult to peel from the peripheral surface of the photoconductor drum.

[0006] As one of the methods for improving the peeling property when using this transfer roll, a "detack saw" having a needle-like or saw-toothed tip on the downstream side of the transfer device in the sheet moving direction is conventionally used. Hereinafter, a plate-shaped charge removing member called "DTS" will be provided.
A discharge voltage is applied to the paper to remove excess charges on the paper, reducing the electrostatic attraction between the paper and the peripheral surface of the photoconductor drum,
As a result, the DTS method is used in which the bending rigidity of the paper is utilized to separate the paper from the peripheral surface of the photoconductor drum.

This DTS method has an advantage that the amount of ozone generated is small because the discharge current is small, but since the peeling performance is low, image defects called "finger marks" may occur when the diameter of the photosensitive drum is large. There is This "finger mark" is a phenomenon that occurs when the electrostatic peeling current, that is, the discharge current in the case of the DTS method is small and the force for peeling the paper from the peripheral surface of the photosensitive drum is insufficient, and the paper is exposed to light. This is a phenomenon in which a sheet is conveyed while being adsorbed to the peripheral surface of the photosensitive drum to the disposition position of the peeling claw because it cannot be separated from the peripheral surface of the body drum, and the sheet collides with the peeling claw to leave a mark on the edge of the sheet.

As a method of preventing the generation of the finger mark, generally, a method of increasing the discharge voltage applied to the DTS to increase the amount of discharge to the paper and strengthening the peeling force from the peripheral surface of the photosensitive drum is adopted. However, since the discharge of the DTS is concentrated from the saw-toothed tip portion, when the discharge voltage is increased, a strong discharge may be locally applied to the paper, and excessive static electricity may be partially removed. . Then, the electrostatic force for holding the toner is lost from the part where the excessive static electricity removal is performed, so that the toner once transferred to the paper side is again attracted to the peripheral surface of the photosensitive drum and re-adhered. A phenomenon called “retransfer” occurs, which causes a problem of image quality such as white streaks and a decrease in density, which makes it difficult to maintain stable peeling performance.

On the other hand, of the contact transfer methods, in the case of a belt transfer method using a transfer belt instead of a transfer roll, the transfer / separation performance is stable, but a mechanism for cleaning the belt to recover residual toner. However, there is a problem that the device becomes complicated and the manufacturing cost becomes high.

As a peeling means other than the above, Japanese Patent Laid-Open No. 58-10764 and Japanese Patent Laid-Open No. 58-10765 disclose a conductive brush method for removing static electricity by using a conductive brush. There is. This conductive brush method has the advantage that it can reduce the amount of ozone generated, but when high moisture content paper with a high water content is used, transfer defects occur, and depending on the type of paper, sufficient peelability is not achieved. There is a problem that you cannot get it.

Further, Japanese Unexamined Patent Publication No. 6-102773 discloses a system in which a needle electrode and a separating roll are combined, and Japanese Unexamined Patent Publication No. 6-274046 discloses a system in which an electrostatic separating roll is used. Has been done. However, in the method using the separation rolls such as these, the electrical resistance of the separation rolls changes due to changes in the environment such as temperature and humidity, the potential difference between the paper and the separation rolls fluctuates, and the paper Since the potential difference between the paper and the separation roll varies depending on the type, it is not possible to obtain a stable electrostatic attraction force with respect to changes in the environment and the type of paper, and the peelability varies. There is.

[0012]

Therefore, the present inventors have solved the problems as described above, and can be used in an image forming apparatus in which the diameter of the photosensitive drum is increased and the process speed is increased. As a result of earnest research on an image forming apparatus that has low cost and stable peeling performance, a mechanism for performing each process of transfer, charge removal and peeling by using a plurality of rolls is provided, and the peeling roll and the recording medium moving direction upstream. The present invention has been completed by finding that the above problems can be solved by providing a feed speed difference between adjacent rolls on the side and providing a trigger for the peeling of the recording medium.

Therefore, an object of the present invention is an ozone-less type apparatus which can be used in a high-speed processing type image forming apparatus using a large-diameter type photosensitive drum, and is low in cost, low in power consumption, and capable of producing images such as finger marks and retransfer. An object of the present invention is to provide an image forming apparatus having a peeling mechanism that does not cause defects.

[0014]

SUMMARY OF THE INVENTION According to the present invention, an electrostatic latent image carrier on which an unfixed toner image is formed on a carrier surface according to image information and an electrostatic latent image carrier at least sandwiching a recording medium in a transfer region. A transfer roll, which is in pressure contact with the surface of the latent image carrier to transfer the unfixed toner image to the recording medium side and has a transport function for this recording medium, is adjacent to the transfer roll on the downstream side in the recording medium moving direction, The static electricity image carrier is pressed against the surface of the electrostatic latent image carrier to remove electricity from the recording medium, and the static electricity removing roll having the function of transporting the recording medium is adjacent to the static elimination roll on the downstream side of the direction of movement of the recording medium to keep the recording medium stationary. An image forming apparatus having a plurality of rolls each of which electrically suctions and peels off the recording medium from the surface of the electrostatic latent image carrier, and which comprises a plurality of rolls for performing the steps of transfer, charge removal and peeling, Roll carries recording medium Is provided and a feed speed difference imparting means for imparting a feed speed difference between the feed speed at which the roll adjacent to the upstream side of the peeling roll in the recording medium moving direction conveys the recording medium is provided. The image forming apparatus has a mechanism in which a recording medium is bent between a peeling roll and a roll adjacent to the peeling roll to separate the recording medium from the surface of the electrostatic latent image carrier 1.

In the present invention, a plurality of rolls are attached in contact with the surface of the electrostatic latent image carrier,
These plural rolls perform various operations such as transfer, charge removal and peeling of the recording medium. The plurality of rolls include at least three rolls of a transfer roll, a charge eliminating roll, and a peeling roll in order to perform the above-mentioned steps of transfer, charge elimination, and peeling.

The transfer roll is pressed against the surface of the electrostatic latent image carrier to form a transfer area, and the transfer medium is sandwiched between the transfer roller and the transfer medium to convey the recording medium. It is a member applied to a recording medium. At least the outer peripheral surface of the transfer roll is made of a conductive material such as conductive urethane or conductive rubber, and a transfer voltage for applying an electric charge to the recording medium is applied to the outer peripheral surface from a power source.

The charge eliminating roll is a member for removing the electric charge applied from the transfer roll in the transfer area. The charge eliminating roll removes the electric charge applied to the recording medium from the transfer roll in the transfer area to reduce or eliminate the electrostatic attraction force between the electrostatic latent image bearing surface and the surface of the electrostatic latent image bearing member. Makes it easier to peel off the recording medium from the body surface. The charge eliminating roll is attached to the downstream side of the transfer roll in the recording medium moving direction. Further, at least the outer peripheral surface of the charge eliminating roll is made of a conductive material, and normally a charge eliminating voltage for removing charges of the recording medium is applied to this outer peripheral surface from a power source. Depending on the conditions, the static elimination effect may be obtained just by grounding the static elimination roll.

The peeling roll is a member for peeling the recording medium which has undergone the transfer and static elimination steps from the surface of the electrostatic latent image carrier. This peeling roll is attached on the downstream side of the charge eliminating roll in the recording medium moving direction, and the recording medium conveyed through the charge eliminating roll is adsorbed by the peeling voltage applied to the peripheral surface of the electrostatic latent image carrier. It is a roll that is peeled from the surface and sent to the subsequent fixing device.

One or more auxiliary transfer rolls may be provided on the upstream side of the transfer roll in the recording medium moving direction. The auxiliary transfer roll is a member that guides the recording medium conveyed from the recording medium container by the paper feeding mechanism to the transfer area, and assists the function of the transfer roll. Therefore, the auxiliary transfer roll may be in contact with the surface of the electrostatic latent image carrier, but it is not necessarily in contact with the surface of the electrostatic latent image carrier as long as it is arranged at a position where the transfer roll can be assisted. . A voltage can also be applied to the auxiliary transfer roll, but it is not always necessary to apply it.

Further, one or more auxiliary charge eliminating rolls or auxiliary peeling rolls may be provided between the charge eliminating roll and the peeling roll. The auxiliary charge eliminating roll and the auxiliary peeling roll assist the functions of the charge eliminating roll and the peeling roll, respectively. Therefore, these auxiliary charge-eliminating rolls and auxiliary peeling rolls may also be in contact with the surface of the electrostatic latent image bearing member. Do not have to be in contact with each other.
Further, a voltage can be applied to these auxiliary charge eliminating rolls and auxiliary peeling rolls, but it is not always necessary to apply them.

A rotation driving force is applied to each roll that controls the above-mentioned transfer, charge removal and peeling process, and a driving source may be attached to each roll, and the rotation driving force is transmitted from the same driving source. You may. When rotating each roll that controls the process from transfer to charge removal at a constant speed,
It is convenient to transmit the rotational drive force from the same drive source via a gear train, a belt, etc. to rotate the drive force.

The feeding speed difference giving means is a feeding speed at which the peeling roll conveys the recording medium, and a roll adjacent to the peeling roll on the upstream side in the moving direction of the recording medium (hereinafter abbreviated as "adjacent roll") is the recording medium. Is a means for providing a difference between the feeding speed for transporting the sheet, that is, a feeding speed difference. here,
Adjacent roll, in the device that arranges the charge eliminating roll between the transfer roll and the peeling roll, refers to the charge eliminating roll, but if further rolls are arranged between the charge eliminating roll and the peeling roll, that roll Point to. Further, it is preferable that each of the transfer roll and the auxiliary transfer roll located upstream of the adjacent roll in the recording medium moving direction has the same feed speed as the adjacent roll.

When the recording medium transferred in the transfer area is conveyed to a region where the peeling roll and the electrostatic latent image carrier are brought into pressure contact with each other through the adjacent rolls (hereinafter abbreviated as "peeling region"), the peeling is carried out. Although sandwiched in the area, a feeding speed difference is provided between the adjacent roll and the peeling roll, and the recording medium is conveyed from the adjacent roll to the peeling area at a speed faster than the feeding speed that the peeling roll conveys. . Therefore, the recording medium conveyed at an excessive ratio bends in an arc shape as shown in FIG. 3 between the peeling area, that is, between the adjacent roll and the peeling roll to form a so-called “loop”, and this loop is formed. The part to be separated is separated from the surface of the electrostatic latent image carrier.

The portions forming the loop and separated from each other are completely separated from the surface of the latent electrostatic image bearing member, and the charge is removed by the charge eliminating roll to electrostatically attract the surface of the latent electrostatic image bearing member. Since the force is weakened, the entire recording medium can be easily peeled off by sucking the peeling voltage of the peeling roll and pulling the separated portion in the direction away from the surface of the electrostatic latent image carrier. That is, the part that forms a loop between the adjacent roll and the peeling roll and is separated is a part that becomes a trigger when peeling the entire recording medium, and when the separated part is sandwiched in the peeling region, the peeling roll It is attracted to the peeling voltage on the peripheral surface and easily peeled from the surface of the electrostatic latent image carrier.
Since the separated portion is the tip portion of the recording medium, when the tip portion is peeled off, the portion after the tip portion is also peeled off from the surface of the electrostatic latent image carrier following the tip portion, and eventually the recording medium The whole is smoothly separated from the surface of the electrostatic latent image carrier.

As a method of giving a difference in the feeding speed of the recording medium by the feeding speed difference giving means, any method may be used as long as the feeding speed of the peeling roll is slowed with respect to the adjacent roll. For example,
The rotational speed of the adjacent roll is adjusted so that the moving speed of the peripheral surface of the adjacent roll is the same as the surface moving speed of the electrostatic latent image bearing member, while the moving speed of the peripheral surface of the peeling roll is the moving speed of the electrostatic latent image bearing member surface. A method of adjusting the rotation speed of the peeling roll so as to be slower can be considered.

As another method, the frictional resistance between the adjacent roll and the recording medium is made larger than the frictional resistance between the peeling roll and the recording medium, for example, the peripheral surface of the adjacent roll is rubbed against the peripheral surface of the peeling roll. Method of making with material with large resistance,
A method of making the peripheral surface of the adjacent roll have a larger surface roughness than the peripheral surface of the peeling roll, the force of pressing the adjacent roll to the surface of the electrostatic latent image carrier is the force of pressing the peeling roller to the surface of the electrostatic latent image carrier. It is possible to make it higher.

As yet another method, the rotation of the peeling roll is momentarily stopped immediately before the recording medium is pinched in the peeling region based on a signal from the recording medium conveyance detector to form a loop, and then the adjacent rolls are formed. A method of peeling the recording medium from the surface of the electrostatic latent image bearing member by rotating it so that the feeding speed is the same as that of the roll, or an outer diameter of the peeling roll is made larger than that of the other roll and the same rotation speed is applied to the other roll. A method of increasing the peripheral speed of the peeling roll can be considered.

The degree of difference in the feed rate is required to be such that the loop having an appropriate size can be formed. That is, if the loop is too small, it is not sufficiently separated from the surface of the latent electrostatic image bearing member and cannot be peeled from the surface of the latent electrostatic image bearing member by suction with the electrostatic suction force of the peeling roll. It is required to be large enough to be peeled off from the surface of the electrostatic latent image bearing member by force. On the other hand, if the loop is too large, it becomes wrinkled between the adjacent roll and the peeling roll or when the recording medium is sandwiched in the peeling region, so it is required to have a size that does not cause wrinkles before and after the peeling region. To be Therefore, the feeding is such that the electrostatic attraction force of the peeling roll can peel the surface of the electrostatic latent image carrier from the surface of the latent electrostatic image bearing member, and the loop can be formed before and after the peeling area so as not to wrinkle. It is required to be a speed difference.

The value of such a feed speed difference is the diameter of the electrostatic latent image carrier, the rotational speed, the diameter of the adjacent roll and the peeling roll, the material, the distance between the adjacent roll and the peeling roll, the electrostatic latent image carrier. Although it depends on various conditions such as the pressure contact force to the surface, the peeling voltage, the type of toner, etc., the optimum value should actually be determined experimentally. Generally, for example, the feeding speed of the peeling roll is 100%. And the feed rate of the adjacent roll is 10
An example of the case is 0.1% to 101.5%.

This feed speed difference is, for example, generally "CP
Using an electronic central control device called "U", the voltage and frequency of the driving power source for each of the adjacent roll and the peeling roll are controlled so that an appropriate feed speed difference is given. . Further, the program installed in the CPU can appropriately change the feed speed difference in accordance with the recording medium and environmental conditions such as temperature and humidity.

It is preferable that all of the plurality of rolls that control the steps of transfer and charge removal / peeling are compatible common parts having the same material and shape. Typically, these rolls are made by applying a peripheral surface made of a conductive elastic material such as conductive urethane or conductive rubber having an electrical resistance of about 10 ⁵ to 10 ¹⁰ Ωcm to a core material such as metal or resin. Is mentioned. For example, an elastic material containing an ion conductive agent has a volume resistance of 1
A urethane foam of about 0 ⁵ to 10 ¹⁰ Ωcm, an electronic conduction type foam roll, or a surface coated with fluorine or tubing may be used. By using the common parts in this way, the manufacturing cost of the roll can be reduced and the maintainability can be simplified.

Further, these plurality of rolls are, for example, shown in FIG.
It is preferable that they are attached to the same roll support member as shown in FIG. By mounting them on the same roll support member and using a solenoid or an eccentric cam to attach and separate the roll support member to and from the surface of the electrostatic latent image carrier, the plurality of rolls can simultaneously carry the electrostatic latent image. It is possible to bring it away from the body surface. As a result, for example,
When the developing patch is formed in the non-image area and the density is adjusted, the density can be adjusted while the plurality of rolls are completely separated from the surface of the electrostatic latent image carrier at the same time. It is possible to prevent adhesion to a plurality of rolls.

Further, in a state where the roll supporting member is separated from the electrostatic latent image bearing member and a plurality of rolls which are integrally supported by the roll supporting member and are in charge of the steps of transfer and charge removal / peeling are separated from the surface of the electrostatic latent image bearing member. By applying a voltage having the same polarity as the toner to each roll and rotating each roll, the toner adhering to the peripheral surface of each roll is caused to fly from the peripheral surface of the roll, thereby eliminating the need for a dedicated cleaning member such as a scraper. It is possible to perform a cleaning operation on the roll peripheral surface.

As an operation effect of the image forming apparatus of the present invention, the recording medium is peeled from the electrostatic latent image carrier by providing a difference in the feed speed for conveying the recording medium between the peeling roll and the adjacent roll. In the peeling step, a mechanical peeling force is obtained in addition to the electrostatic attraction force, so that stable transfer and peeling performance can always be exhibited regardless of the influence of the environment and the type of paper. In particular, when a rotation driving force is applied to the rolls included in the adjacent rolls such as a transfer roll and a charge eliminating roll to give an equal feed speed, the paper is conveyed with a large conveyance force of the plurality of rolls relative to the peeling roll. A loop having an appropriate size can be reliably formed between the peeling roll and the adjacent roll, and the peeling operation by the peeling roll can be performed more reliably. Further, since the corotron is not used as the charge eliminating member and the charge eliminating roll is used, ozone is not generated. Further, since the transfer roll is used as the transfer means, a special cleaning device required for the belt type transfer device is not required, and the cost of the device can be reduced.

[0035]

[Embodiment]

(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. 1 is a schematic cross-sectional view showing the configuration of the image forming apparatus of this embodiment. The image forming apparatus according to the present exemplary embodiment is configured such that an unfixed toner image is formed on a carrying surface according to image information.
The (electrostatic latent image carrier) and at least the paper (recording medium) 4 at least in the transfer area are pressed against the peripheral surface of the photoconductor drum 1 to transfer the unfixed toner image to the paper 4 side and the paper 4 Is adjacent to the transfer roll 6 having a transporting function of the transfer roll 6 on the downstream side of the transfer roll 6 in the moving direction of the paper 4, and is pressed against the peripheral surface of the photoconductor drum 1 with the paper 4 interposed therebetween to remove the charge of the paper 4 and Of the charge removing roll 7 and a peeling roll adjacent to the charge removing roll 7 on the downstream side in the moving direction of the paper 4 and electrostatically attracting the paper 4 to separate the paper 4 from the peripheral surface of the photosensitive drum 1. 8 is an image forming apparatus including a plurality of rolls for performing the steps of transfer, charge removal and peeling.

In the image forming apparatus of this embodiment, the peeling roll 8 feeds the paper at a feed speed and the peeling roll 8
Is provided with a feed speed difference imparting means for imparting a feed speed difference to the feed speed at which the roll adjacent to the upstream side of the sheet moving direction conveys the paper. The feed speed difference imparted by the feed speed difference imparting means is provided. To bend the paper between the peeling roll and the roll adjacent to the peeling roll so that the photosensitive drum 1
Away from the surrounding surface. Further, in the image forming apparatus of this embodiment, the auxiliary transfer roll, the transfer roll, the charge eliminating roll, and the common roll are used as the peeling roll. Furthermore,
As a feeding speed difference imparting means, the auxiliary transfer roll, the transfer roll, and the charge eliminating roll are rotated at a constant speed, while the rotation speed of the peeling roll is made slower than the rotation speed of these rolls. A central control unit (CPU) was used to electronically control the supply voltage of the.

The operation when a copy operation is performed using the image forming apparatus of this embodiment will be described below. The peripheral surface of the photosensitive drum is uniformly negatively charged by the charger 2 arranged above the photosensitive drum 1 in FIG. 1, and an electrostatic latent image is formed by an exposure device (not shown) based on image information from the original. An unfixed toner image is formed by forming and developing with negatively charged toner supplied from the developing device 3, and the unfixed toner image is conveyed to the transfer area. On the other hand, the sheet 4 is conveyed toward the transfer area by a sheet feeding device (not shown) at the timing when the unfixed toner image is conveyed to the transfer area.

In the image forming apparatus of this embodiment, the auxiliary transfer roll 5 is mounted at a position before the transfer area. Therefore, when this sheet is conveyed to the vicinity of the transfer area, the sheet is first transferred to the auxiliary transfer roll 5. It is received by and is guided by this to be sent to the transcription area. In the transfer area, a transfer roll 6, a charge eliminating roll 7 and a peeling roll 8 arranged so as to sandwich the paper with the photoconductor drum are used for cleaning the residual toner on the peripheral surface of the photoconductor drum after transfer, charge removal and peeling. The cleaning device 9 completes one cycle, and after the paper passes through the transfer roll, the fixing device 10 fixes the paper under heat and pressure to fix an unfixed toner image on the paper and records it on the paper, thus completing a series of copying operations. .

FIG. 2 is a schematic view showing the positional relationship between one of the transfer and charge removing / peeling rolls and the photosensitive drum 1. The roll includes a conductive elastic layer 22 in which a conductive elastic material is applied on a peripheral surface of a core material 21 made of a conductive material, and the core material is rotatably supported by a roll supporting member (not shown). A driving force is supplied through the gear 23 to rotate the photosensitive drum in the opposite direction. Further, since each roll holds the paper by sandwiching the paper with a predetermined pressure between the roll and the peripheral surface of the photosensitive drum, the roll is elastically abutted on the peripheral surface of the photosensitive drum by a pressing member such as a spring. A power supply member 24 for applying a bias voltage to the roll is arranged near the roll, and the voltage is applied to the peripheral surface of the roll via the core material.

The auxiliary transfer roll 5 shown in FIG. 1 is located upstream of the transfer roll 6 and serves to reliably press the paper 4 conveyed by a paper feeding device (not shown) against the peripheral surface of the photosensitive drum. Since the auxiliary transfer roll surely feeds the paper to the transfer area, the paper called "blurring" in the pre-nip area, that is, the auxiliary transfer area that guides the paper to the transfer area on the upstream side of the transfer area. It is possible to prevent the unfixed toner from scattering due to the charging of the toner. Further, in the apparatus of this embodiment, a bias voltage is applied from the power source 51 to the peripheral surface of the auxiliary transfer roll.

A transfer voltage is applied to the transfer roll 6 from a power source 61 to perform constant current control, and the transfer roller 6 is pressed against the photosensitive drum during transfer, and a transfer current is applied from the back surface of the paper to undetermine the paper on the photosensitive drum. The transferred toner image is transferred. In addition, a cleaning cycle is performed after the transfer of the sheet, and a reverse bias application for applying a reverse bias voltage is performed after the image forming cycle.

The destaticizing roll 7 is for destaticizing the sheet 4 which has been positively charged by the transfer roll. In the apparatus of this embodiment, the static elimination voltage was applied from the power source 71. Further, the rotational speeds of the transfer roll and the charge eliminating roll 7 are set to have a speed difference of about 0.1 to 10% faster than the rotational speed of the photoconductor drum. 0.1 to drum feed rate
The central control unit (CPU) was set so that the feed rate difference would be about 1.5% faster.

A reverse bias voltage having a polarity opposite to the transfer voltage is applied to the peeling roll 8 from a power source 81. As a result, the sheet 4 that has been discharged by the discharging roll 7 is peeled off by the electrostatic attraction force on the peripheral surface of the peeling roll. The peeling roll 8 is in contact with the photoconductor drum with a small load, and the central control unit (CPU) is set so as to rotate at a constant speed with the photoconductor drum 1. FIG. 3 is a diagram schematically showing the state of the paper in the peeling area. The leading edge of the sheet 4 conveyed by a transfer roll or the like with a speed difference about 0.5% faster than the photosensitive drum,
A loop is formed in front of the peeling roll that is rotating at the same speed as the photosensitive drum, and then the electrostatic attraction of the peeling roll 8 sucks the loop toward the peeling roll and conveys it to the subsequent fixing device 10. By providing a feeding speed difference between the transfer roll, the charge removing roll, and the peeling roll, it is possible to form a part separated from the peripheral surface of the photosensitive drum at the leading edge of the paper that is in close contact with the peripheral surface of the photosensitive drum. It is possible to more reliably perform electrostatic attraction and peeling by the peeling voltage on the roll peripheral surface.

FIG. 4 is a block diagram of the image forming apparatus of this embodiment. Rolls 5-8 for auxiliary transfer, transfer, charge removal, and peeling
Are integrally provided on the roll supporting member 25.
The roll support member is configured to be brought into contact with and separated from the photoconductor drum 1 by a direct-acting motor, an eccentric cam mechanism, or the like, and is formed on each roll circumferential surface by forming a development patch for toner concentration adjustment performed in a non-image area. Prevents the adhesion of the toner.

FIG. 5 is a timing chart showing the operation of the image forming apparatus of this embodiment. A voltage is applied to the charger 2 at the same time when the main motor is turned on. Transcription,
The roll supporting member that supports each of the static elimination / peeling rolls is separated from the photoconductor drum until just before the paper is conveyed to the photoconductor drum 1, and the paper conveyance detector disposed in the middle of the paper conveyance path detects the paper. When the carrier signal is received, the photosensitive drum approaches the photosensitive drum. In the transfer mode in which the unfixed toner image formed on the peripheral surface of the photosensitive drum is conveyed to the transfer area,
A transfer voltage having a polarity opposite to that of the toner is applied to the transfer roll to transfer the unfixed toner image on the peripheral surface of the photosensitive drum to the paper side. In addition, in the case of performing a copy operation between images in the transfer mode, that is, on a plurality of sheets of paper, after completion of copying the first sheet,
In addition, before the start of the second copy, when the electrostatic latent image is not formed on the peripheral surface of the photoconductor drum, the transfer voltage applied to the transfer roll is decreased to 0 V to prevent the fog toner from being transferred to the transfer roll. Prevents adhesion.

After the last sheet has passed the transfer roll, a voltage having the same polarity as the toner is applied to the transfer roll for two rounds of the roll. As a result, the toner adhering to the peripheral surface of the transfer roll can be electrostatically repelled and re-adhered to the peripheral surface of the photosensitive drum. After that, a voltage having a polarity opposite to that of the toner is applied to the transfer roll for one round of the roll, and the toner attached to the peripheral surface of the transfer roll is transferred to the photosensitive drum. In this way, after applying a voltage having a polarity opposite to that of the time of transferring two rolls of the roll, idling for one revolution of the roll, that is, applying the voltage at the time of transfer to rotate the roll is performed by changing the voltage state of the roll peripheral surface after the cleaning cycle. This is to keep it stable. The toner reattached to the peripheral surface of the photosensitive drum during the cleaning cycle is removed by the cleaning device attached to the peripheral surface of the photosensitive drum. By performing the cleaning cycle at the end of the image forming cycle as described above, it is possible to reliably remove the toner adhering to the peripheral surface of the transfer roll, and to obtain a high-quality image without the occurrence of dirt on the back surface of the paper. It can be stably obtained. Although the cleaning cycle has been described here by exemplifying the case of the transfer roll, the same effect as that of the transfer roll can be obtained by performing the same cleaning cycle on the other charge eliminating / peeling rolls.

(Second Embodiment) Instead of continuously rotating the peeling roll, the position of the paper is recognized by a detector, and the paper passing through the adjacent roll is detected in the peeling area based on the signal from this detector. By immediately stopping the rotation of the peeling roll immediately before being sandwiched, a loop in a proper state is formed between the adjacent roll and the peeling region, and the loop is separated from the peripheral surface of the photoconductor drum, so that the paper sheet An image forming apparatus having the same structure as that of the first embodiment was prepared except that the image forming apparatus was peeled from the peripheral surface of the drum. When a copy operation was performed using this image forming apparatus, the same good results as in the first embodiment were obtained. Further, as the effect peculiar to this embodiment, the effect of the speed fluctuation among the transfer roll, the peeling roll and the fixing roll is small, and the effect that the sheet feeding after the leading edge peeling is stable is obtained.

[0048]

EXAMPLE An image forming apparatus of this example has a diameter of 84 mm.
OPC (Organic Photo Conductor) type photosensitive drum
And the process speed is 300 mm / sec.
Was. In addition, EPDM with conductive particles dispersed in the charger
(Ethylene Propylene DieneMethylene linkage) Rubber
Using a charging roll coated with a surface layer on the
Applying 1350V, the potential of the photosensitive drum is set to -750.
It was charged to V. This time, the developer is polyester or
A two-component developer based on ethylene was used. Each roll
Is a metal core material having a diameter of 10 mm and a conductive elastic layer 22.
The conductive elastic layer 22 is made of an ionic conductive agent.
Volume resistance of 10 with an elastic roll containing ^Five-10^TenΩc
A urethane foam of about m was used.

The power supply of the auxiliary transfer roll 5 is set to a high resistance value of about 100 MΩ so that it does not drop below a certain resistance value even under high temperature and high humidity. The generation of transfer defects at the rear end is prevented. The transfer roll is pressed against the photosensitive drum with a load of 500 g on one side at the time of transfer, and is +30 μm from the back surface of the paper.
A transfer current of A was applied. In addition, a cleaning cycle was performed in the non-image area after transfer, and a reverse bias voltage of −2000 V was applied after the image formation cycle. 1.5kV from the power source 71 for the static elimination roll
An alternating voltage of / 600 Hz was applied. For the peeling roll,
A reverse bias voltage of −750 V having a reverse polarity to the transfer voltage was applied from the power source. The peeling roll was brought into contact with the photosensitive drum with a minute load of 100 g or less on one side. When a copy operation was performed using the image forming apparatus of this example, a good result was obtained that stable peeling performance was obtained without generating finger marks even on thin paper.

[0050]

EFFECTS OF THE INVENTION Since the recording medium is separated from the electrostatic latent image carrier by providing a difference in the feed speeds for conveying the recording medium between the peeling roll and the static eliminator roll, electrostatic adsorption is performed in the peeling step. In addition to the force, mechanical peeling force is obtained, and stable transfer and peeling performance can always be exhibited regardless of the influence of the environment and the type of paper. Further, since the corotron is not used as the charge eliminating member and the charge eliminating roll is used, ozone is not generated. Furthermore, since a transfer roll is used as the transfer means,
A special cleaning device required for the belt type transfer device is not required, and the cost of the device can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of an image forming apparatus of the present invention.

FIG. 2 is a schematic view showing the structure of a transfer / peeling roll of the present invention.

FIG. 3 is a diagram showing a state of a sheet between a peeling roll of the present invention and an adjacent roll.

FIG. 4 is a schematic diagram showing a configuration of an image forming apparatus of the present invention.

FIG. 5 is a timing chart showing the operation of the image forming apparatus of the present invention.

FIG. 6 is a schematic sectional view of a conventional image forming apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum (electrostatic latent image carrier), 4 ... Paper (recording medium), 5 ... Auxiliary transfer roll, 6 ... Transfer roll, 7 ... Static elimination roll, 8 ... Separation roll.

Claims (3)

[Claims] 1. An electrostatic latent image carrier on which an unfixed toner image is formed according to image information on the carrier surface, and a pressure contact with the surface of the electrostatic latent image carrier sandwiching a recording medium at least in a transfer area. Then, an unfixed toner image is transferred to the recording medium side, and a transfer roll having a function of conveying the recording medium is adjacent to the transfer roll on the downstream side in the recording medium moving direction, and the electrostatic latent image carrier is sandwiched across the recording medium. The recording medium is pressed against the surface of the recording medium to remove electricity from the recording medium and is adjacent to the discharging roller having the function of transporting the recording medium and the downstream side of the discharging roller in the moving direction of the recording medium. An image forming apparatus having a plurality of rolls for peeling the medium from the surface of the electrostatic latent image carrier and performing the steps of transfer, charge removal and peeling, in which the peeling roll conveys the recording medium. Speed and this peeling A feed speed difference giving means for giving a feed speed difference between the roll adjacent to the upstream side of the recording medium moving direction of the recording medium and the feed speed for conveying the recording medium, and the peeling roll and the peeling roll by this feed speed difference. An image forming apparatus, characterized in that a recording medium is bent between adjacent rolls to separate the recording medium from the surface of the electrostatic latent image carrier 1. 2. The image forming apparatus according to claim 1, wherein each of the rolls that control the steps of transfer, charge removal and peeling is a compatible common roll-shaped member having a resistance of 10 ⁵ to 10 ¹⁰ Ωcm. 3. The image forming apparatus according to claim 1, wherein all the rolls that control the steps of transfer, charge removal and peeling are integrally mounted so as to be able to come into contact with and separate from the electrostatic latent image carrier.