JPH075770A - Image forming device - Google Patents

Abstract

PURPOSE:To provide an image forming device which steadily separates a material on which an image is to be transpferred (expressed as transfer material hereinafter) irrespective of the type of the transfer material and changes in environment, etc., forms a high quality image and is small in size. CONSTITUTION:The device is equipped with: an image carrier 10 which holds a developer image and has a prescribed potential, a transfer roller 14 which transfers the developer image from the image carrier 10 to a transfer material 15, a separation means 16a which is arranged near the downstream from the transfer roller 14 and immediately near the transfer material 15 between the transfer roller 14 and the transfer material 15, generates an electric field in a gap between the transfer material 15 and transfer roller 14, and attracts the transfer material 15 by means of an electrostatic force, thereby separating the material 15 from the image carrier 10, and a discharge preventing means 16b which is provided so as to cover the separation means 16a and prevents the separation means 16a from causing discharge between the transfer material 15 and the transfer roller 14.

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 or a printer, which forms an image by an electrophotographic method.

[0002]

2. Description of the Related Art Image forming apparatuses of this type are disclosed, for example, in JP-A-58-10765 and JP-A-60-903.
No. 71, JP-A-2-213879 and the like are known.

A conventional example of an image forming apparatus will be described with reference to FIGS. 9 and 10.

FIG. 9 is a side view of a first conventional example in which a corona transfer charger is used to transfer a developer image from an image carrier onto a transfer material.

In FIG. 9, the charging member 71 uniformly charges the surface of the image carrier 70, and the exposure means 72 irradiates a laser beam according to an image signal to attenuate the surface potential of the image carrier 70 so that it is static. Form a latent image. Next, the developer charged by the developing means 73 is caused to fly onto the image carrier 70 by electrostatic force to visualize the electrostatic latent image, and a developer image is formed on the surface of the image carrier 70.

The corona transfer charger 74a is a bias power source 7
5, a transfer voltage is applied by the transfer member 5, and the transfer target material 7 is transferred to a proximity portion (hereinafter referred to as a transfer nip) between the image carrier 70 and the corona transfer charger 74a by a transfer unit (not shown).
Charge 6 As a result, the developer image on the image carrier 70 is attracted by the electrostatic force due to the back surface charge of the transferred material 76, and the developer image on the image carrier 70 is transferred to the transferred material 7.
6 is transferred. The image carrier 70 on which the developer remains after the transfer is removed of the residual developer by the cleaning unit 78, and is again used in the next step. The transferred material 76 that has been transferred is
It is fixed by the fixing means 80 via the paper discharge guide 79.

On the other hand, a separating member 77 which is a grounded conductor
d is the transferred material 7 that has been transferred and has been discharged from the transfer nip.
As the 6 approaches the separating member 77d, the transferred material 7
A charge having a polarity opposite to that of the back surface charge of 6 is induced, and the transferred material 76
The electrostatic attraction force starts to act between the back surface charges of the transfer target material and the transfer target material 76, and the transfer target material 76 receives the electrostatic attraction force by the separating member 77d and the transfer target material 7.
6 and the restoring force due to the rigidity of 6 itself act to separate from the image carrier 70.

In the first conventional example, the separating member 7
It is also proposed that a voltage is applied to 7d to generate the electrostatic attraction force of the separating member 77d with respect to the transferred material 76.

FIG. 9 is a side view of a second conventional example in which a transfer roller is used to transfer a developer image from an image carrier onto a transfer material.

In FIG. 10, the same components as those in FIG. 9 are designated by the same reference numerals. 74b is a transfer roller, 77
Is a grounded SUS plate 77a, Al plate 77b and PET
It is a separation plate constituted by a plate 77c.

First, as in FIG. 9, a developing member image is formed on the image carrier 70 by the charging member 71, the exposing means 72 and the developing means 73.

A bias power supply 75 applies a transfer voltage having a polarity opposite to that of the developing material to the transfer roller 74b. The transferred material 76 is a contact portion (hereinafter referred to as a transfer nip) between the image carrier 70 and the transfer roller 74b by a conveying unit (not shown).
Be transported to. At the transfer nip, the developer image on the image carrier 70 is transferred from the back surface of the transfer material 76 to the transfer roller 74.
The electrostatic attraction force due to the transfer voltage having the opposite polarity of b acts, and the developer image on the image carrier 70 is transferred to the transfer material 76. The image carrier 70 on which the developer remains after the transfer is removed of the residual developer by the cleaning unit 78, and is again used in the next step. The transferred material 76 that has been transferred passes through a paper discharge guide 79,
It is fixed by the fixing means 80.

On the other hand, the material to be transferred 76, which has been transferred and carries the developer image on the surface and is discharged from the transfer nip, approaches the separation plate 77 in which the Al plate 77b is connected to the grounded SUS plate 77a. The transferred material 76 is placed on the Al plate 77b.
Are induced from the transfer roller 74b and have a polarity opposite to that of the back surface charge, and an electrostatic attraction force between the back surface charge of the transfer material 76 and the charge of the opposite polarity of the Al plate 77b acts on the transfer material 76. The transferred material 76 is separated from the image carrier 70. A PET plate 77c is provided on the Al plate 77b of the separation plate 77, and the PET plate 77c serves as a transfer material 76 and SU.
By the contact with the S plate 77a or the Al plate 77b, the back surface charge of the transferred material 76 is discharged with the opposite polarity charge of the SUS plate 77a or the Al plate 77b, and the transferred material 76 carries a developer image. It prevents the unfixed developer from scattering by losing the back surface charge.

[0014]

However, in the structure of the first prior art example described above, since the corona transfer charger 74a supplies the excessive charge to the back surface of the transfer material, the charge is discharged from the transfer nip. A large amount of residual charge remains on the back surface of the transferred material 76, and the transferred material 76 is liable to be discharged when contacting the discharge guide provided between the transfer nip and the fixing means and the fixing means, By this discharge, the transferred material 7
6 has a problem in that the image quality is deteriorated due to the loss of the back surface charge carrying the developer image and scattering of the unfixed developer, and the transfer material 76 wandering due to electrostatic force.

Further, in the configuration of the second conventional example described above, the transferred material 76, the transfer roller 74b, the SUS plate 77a, and the Al plate 7 are used.
In order to prevent discharge between 7b, it is necessary not only to provide the PET plate 77c but also to set the distance between the transfer roller 74b or the transferred material 76 and the separation plate 77 of the SUS plate 77a or the Al plate 77b to a certain extent or more. Yes, (1) The amount of charges induced in the SUS plate 77a and the Al plate 77b is small, and the transferred material 76 and the SUS plate 77a and the Al plate 7 are small.
There is a problem that the electrostatic attraction force acting between 7b becomes small, and the transfer material 76 having low rigidity such as thin paper causes separation failure between the image carrier 70 and the transfer material 76.

(2) As described above, the transferred material 76 and the SU
Since it is necessary to set the distance between the S plate 77a and the Al plate 77b and the separation plate 77 to a certain extent or more, the space required for the transfer means and the separation means becomes large, which causes a problem that the device cannot be downsized. I have a problem.

(3) When the PET plate 77c comes into contact with the transferred material 76 and the back surface charge of the transferred material 76 leaks to the PET plate 77c, the PET plate 77c is only partially connected to the Al plate 77b. Therefore, the distribution of the lines of electric force is biased, the leaked back surface charges appear on the surface of the PET plate 77c, and the developer floating in the image forming apparatus is attracted to the PET plate 77c.
There is a problem that this developer stains the back surface of the transferred material.

Further, when the back surface charge amount of the transferred material 76 after being discharged from the transfer nip changes due to a change in environment such as humidity, a change in current value into the transfer roller and a change in the transferred material 76, Due to this change, the separation effect of the transferred material 76 from the image carrier 70 fluctuates, and there is a problem that a separation failure of the transferred material 76 from the image carrier 70 occurs.

Further, when there is a change in the rigidity of the transferred material 76 due to an increase in the thickness of the transferred material 76, a decrease in the width of the transferred material 76, etc., the transferred material from the image carrier 70 due to electrostatic force. Since the separation effect of 76 does not change, there is a problem that the overall separation effect due to the rigidity and the electrostatic force varies and a separation failure occurs.

Further, the discharge guide 79 is charged by the back surface charge of the transferred material 76 after being discharged from the transfer nip, and an electric field is formed, and by this electric field, the unfixed developer formed on the transferred material 76. There is a problem that is scattered.

The present invention solves the above-mentioned problems and provides an image forming apparatus capable of forming a high-quality image, stably separating a transfer material from an image carrier, and reducing the size of the apparatus. The purpose is to provide.

[0022]

In order to solve the above-mentioned problems, an image forming apparatus of the present invention includes an image carrier carrying a developer image and having a predetermined potential, and the developer image carrying the developer image. From the transfer roller to the transfer material, and in the vicinity of the transfer roller and the transfer material in the vicinity of the transfer roller in the vicinity of the transfer roller, an electric field is generated in the gap between the transfer roller and the transfer material. Separation means for sucking the transfer material and separating it from the image carrier, and preventing the separation means from being discharged between the transfer material and the transfer roller provided so as to cover the separation means. And a discharge prevention unit that operates.

In order to solve the above problems, the image forming apparatus of the present invention preferably generates an electric field in the gap between the transferred material and the separating means by the back surface charge of the transferred material.

In the image forming apparatus of the present invention, in order to solve the above problems, it is preferable that the separating means is a grounded conductor.

Further, in order to solve the above problems, the image forming apparatus of the present invention preferably has a first bias power source for applying a voltage having a polarity opposite to that of the transfer roller to the separating means.

Further, in the image forming apparatus of the present invention, in order to solve the above problems, it is preferable that the discharge prevention means is an insulating layer coated on the surface of the separation means.

Further, in order to solve the above-mentioned problems, the image forming apparatus of the present invention may have a first control means for controlling the voltage applied to the separating means in accordance with the amount of charges flowing into the material to be transferred. It is suitable.

Further, in order to solve the above-mentioned problems, the image forming apparatus of the present invention preferably has a second control means for controlling the voltage applied to the separating means in accordance with the humidity.

In order to solve the above-mentioned problems, the image forming apparatus of the present invention preferably has a third control means for controlling the voltage applied to the separating means according to the value of the current flowing into the transfer roller. Is.

Further, in order to solve the above-mentioned problems, the image forming apparatus of the present invention preferably has fourth control means for controlling the voltage applied to the separating means in accordance with the rigidity of the material to be transferred. .

Further, in order to solve the above problems, the image forming apparatus of the present invention preferably has a fifth control means for controlling the voltage applied to the separating means according to the thickness of the material to be transferred. .

Further, in order to solve the above problems, the image forming apparatus of the present invention preferably has a sixth control means for controlling the voltage applied to the separating means according to the width of the material to be transferred. .

Further, in order to solve the above problems, the image forming apparatus of the present invention applies a DC voltage to the separating means only when the paper is passed and applies an AC voltage to the separating means when the paper is not passed. It is preferable to have a power supply.

Further, in order to solve the above-mentioned problems, the image forming apparatus of the present invention preferably has a seventh control means for controlling the applied voltage applied to the transfer roller as a transfer potential with a constant current.

In order to solve the above-mentioned problems, the image forming apparatus of the present invention fixes a transfer path for transferring the transfer material downstream of the separating means in the advancing direction of the transfer material and a developer image on the transfer material. It is preferable to form the transport path into a plate-shaped member.

[0036]

In the image forming apparatus of the present invention, since the separating means is provided so as to cover the separating means and prevents the separating means from generating an electric discharge between the material to be transferred and the transfer roller, the separating means is covered. Even if it comes into contact with the transfer material and transfer roller,
The separating means does not discharge between the transfer material and the transfer roller, and the separating means can be arranged in the vicinity of the transfer roller and the transfer material near the transfer material in the vicinity of the downstream of the transfer roller. That is, when a grounded conductor is used as the separating means and an insulating layer coated on the surface of the separating means is used as the discharge preventing means, the separating roll transfers from the transfer roll to the transfer material to transfer the developer image. A charge with the opposite polarity to the applied transfer voltage is generated, but since the separation means, which is a grounded conductor, is in the immediate vicinity of the material to be transferred after it has been transferred, there is a large amount of electric charge that is generated in the vicinity. Combined with this, the electrostatic attraction force acting between the separating means and the transfer material becomes large,
Further, the electrostatic attraction force between the image carrier and the transfer material can be reduced, and the transfer material can be reliably separated from the image carrier. Since the distance between the separating means and the material to be transferred or the transfer roller can be reduced, the transfer means and the separating means can be downsized.

A transfer roller is used to transfer the developer material image from the image carrier to the transfer material, and the transfer roller can supply the necessary and appropriate amount of charge to the transfer material. The back surface charge of the material to be transferred later can be sufficiently reduced as compared with the case where the corona transfer charger is used, which is a problem in the conventional example in which the back surface charge is too large using the corona transfer charger. It is possible to prevent the developer from scattering in the discharge guide and the fixing device and the wobbling of the material to be transferred, thereby preventing image deterioration.

Further, since the first, second, and third control means for controlling the voltage applied to the separating means are provided according to the amount of charges flowing into the material to be transferred, the humidity, the amount of charges flowing into the transfer roller, and the like, The back surface charge of the transfer material changes according to changes in the amount of charges flowing into the transfer material, humidity, the amount of charges flowing into the transfer roller, etc., and the electrostatic attraction force between the image carrier and the transfer material changes. However, since the amount of electric charge supplied to the separation means can be controlled to an appropriate amount according to this variation, the electrostatic attraction force between the transfer material and the separation means is electrostatically attracted between the image carrier and the transfer material. The necessary and appropriate value for the force can be set, and the transferred material can be stably separated from the image carrier.

Since the fourth, fifth, and sixth control means for controlling the voltage applied to the separating means according to the rigidity, thickness, width, etc. of the material to be transferred are provided, the rigidity, thickness, width, etc. of the material to be transferred are provided. Even if the restoring force due to the elasticity of the material to be transferred fluctuates in accordance with the above, the amount of charge supplied to the separation means can be controlled to an appropriate amount in accordance with this fluctuation, so electrostatic attraction between the material to be transferred and the separation means The force can be set to a necessary and appropriate value for the restoring force of the transferred material,
The transferred material can be stably separated from the image carrier.

Further, since there is a quadrature switching bias power source that applies a DC voltage to the separating means only when the paper is not passing and an AC voltage is applied to the separating means when the paper is not passing, the developer to the separating means is not supplied when the paper is not passing. Adhesion can be suppressed and dirt can be prevented from adhering to the back surface of the transferred material.

Further, since the seventh control means for controlling the voltage applied to the transfer roller at a constant current is provided, it is possible to suppress the fluctuation of the back surface charge amount of the transfer material after being discharged from the transfer nip, and to stabilize the stable transfer. The transfer material can be separated from the image carrier.

Further, since the transfer material transporting path from the transfer nip to the fixing device is formed by a plate-shaped member, each part of the plate-shaped member uniformly contacts the transfer material and the charge from the transfer material is transferred. As a result, the local increase in the potential of the plate-shaped member can be prevented, and the unfixed developer of the transfer material being conveyed can be prevented from scattering due to the local increase in the potential.

[0043]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the image forming apparatus of the present invention will be described with reference to FIG.

FIG. 1 is a side view of the image forming apparatus of the first embodiment.

In FIG. 1, 10 is an image carrier, 11 is a charging means, 12 is an exposing means for irradiating the image carrier 10 with a laser beam, and 13 is a magnetic latent image of the electrostatic latent image formed on the image carrier 10. Developing means for visualizing with a component developer, 14 is a transfer means composed of a transfer roller 14a composed of a cored bar and a conductive rubber foam and a bias power source 14b, 15 is a material to be transferred, and 16a is grounded. Separating means consisting of
Reference numeral b denotes a discharge preventing means configured to cover the separating means 16a, and in this embodiment, a SUS plate or the like having a thickness of 0.1 (mm) is grounded and the surface is covered with an insulating layer such as a fluororesin. . 17 is a cleaning device, 18 is a paper ejection guide, 1
9 is a fixing device.

The operation of the first embodiment will be described with reference to FIG.

First, similarly to the conventional example, the image carrier 1 which has been negatively charged by performing the charging, exposing and developing processes by a known technique.
0, the negatively charged developer is reversely developed.

The transfer roller 14a includes a bias power source 14
A positive voltage is applied by b, and the transfer target material 15 transported to the transfer nip by a transport unit (not shown) is positively charged from the back surface. Therefore, the transferred material 15 and the image carrier 1
An electric field is formed in the gap with 0, and the developer image on the image carrier 10 is transferred onto the transfer material 15 by the electrostatic attraction force of this electric field.

After the transfer of the developer, a positive charge is left on the back surface of the transfer material 15, and is discharged from the transfer nip while being electrostatically adsorbed to the image carrier 10. afterwards,
With the rotation of the transfer roller 14a, the transferred material 15
When reaching the vicinity of the separating means 16a, a negative charge is induced in the separating means 16a by the positive charge of the transferred material 15. Due to this phenomenon, the lines of electric force that have been emitted toward the image carrier 10 from the positive charges of the material 15 to be transferred are also distributed to the separating means 16a, and the material 15 to be transferred and the image carrier 10 are distributed.
The electrostatic attraction force between them is reduced, and the electrostatic attraction force is generated between the back surface charges of the transferred material 15 and the induced charges of the separating means 16a. Therefore, the transferred material 15 is
The material to be transferred 1 is opposed to the electrostatic attraction between the image carrier 10 and the image carrier 10.
5, the electrostatic attraction force between the separating means 16a and the transfer material 1
There is a restoring force due to the rigidity of 5, and these act as a force for separating the transferred material 15 from the image carrier 10, and separate the transferred material 15 from the image carrier 10.

The transfer material 15 separated from the image carrier 10 by the separating means 16a is conveyed from the paper discharge guide 18 to the fixing means 19, and the developer image is thermally fixed on the surface of the transfer material 15 by the fixing means 19. Then, the image forming process is completed.

As described above, according to the first embodiment, the material to be transferred 1 is transferred by the induced charges induced in the separating means 16a.
A part of the lines of electric force that have been directed from the positively charged charges on the back surface of the image carrier 5 toward the image carrier 10 are directed in the direction of the induced charges induced in the separating means 16a, whereby the transferred material 15 and the image carrier 10 are transferred. The electrostatic attraction force between them is reduced, and furthermore, the electrostatic attraction force acts between the transferred material 15 and the separating means 16a.
The transfer material 15 can be reliably separated from the image carrier 10. In an image forming apparatus using a conventional corona transfer charger or the like, a large amount of electric charge is supplied to the back surface of the material to be transferred, so that it is necessary to apply a bias voltage to the separating means. However, according to the present invention, by using the transfer roller 14a in the transfer device 14, the transferred material 15
Since the amount of electric charge supplied to the image carrier 10 is reduced to a necessary and appropriate amount, it is possible to reliably separate the transfer material from the image carrier 10 without applying a bias voltage to the separating means 16a.
Therefore, the separating means 16a can have a simple structure.

Further, the discharge preventing member 16b prevents discharge between the separating means 16a and the transfer material 15, and even if the separating means 16a comes into contact with the transferred material 15, the discharge preventing means 16b covers the entire separating means 16a. Since it is provided so as to cover, the back surface charge of the transferred material 15 can be prevented from leaking to the separating means 16a, and the separating means 16a can be arranged close to the transfer material 15. Therefore, the back surface charge of the transferred material 15 is held, the separation characteristic by the separating means 16a arranged in proximity is improved, the toner scattering due to the discharge can be prevented, and the space can be further saved.

Further, the discharge prevention member 16b can prevent the charges supplied to the transfer material 15 by the transfer roller 14a from leaking to the separating means 16a, so that the transfer failure due to the leakage of the charges on the back surface of the transfer material 15 is prevented. It can be effectively suppressed, and the voltage applied to the transfer roller 14a can be reduced.

Further, by using a fluororesin coating on the discharge prevention member 16b, the toner releasing property is good, and the discharge prevention member 16
Since b is not contaminated with toner, it is possible to prevent the back surface of the transferred material 15 from being contaminated. The thickness of the fluororesin coating varies depending on the amount of charges flowing into the transferred material 15 and the distance between the transfer path of the transferred material 15 and the separating means 16, but is preferably approximately 10 μm or more.

In this embodiment, the separating means 16a
Any material can be used as long as it is a conductive material, and is not limited to the configuration of this embodiment.

Further, in the present embodiment, the transfer means 14 is composed of the transfer roller 14a, but any contact transfer system such as a belt transfer system may be used, and it is not limited to the structure of this embodiment.

Further, the discharge preventing member 16b is not limited to a fluororesin or the like, and may be an insulating resin such as PET, but a material having a high releasability and a small friction coefficient is preferable. Further, these coatings may be any such as sheet adhesion or coating.

A second embodiment of the present invention will be described with reference to FIG.

FIG. 2 is a side view of the image forming apparatus of the second embodiment.

In FIG. 2, 10 is an image carrier, 14 is transfer means, 15 is a material to be transferred, 16a is separating means, and 16b is discharge preventing means, which have the same construction as in FIG.

The difference from the configuration of FIG. 1 is that the separating means 16a.
The point is that a DC bias power source 20 for applying a bias is provided. Similar to FIG. 1, charging, exposing, developing and cleaning means are installed around the image carrier 10.

The operation of the image forming apparatus of the second embodiment constructed as described above will be described with reference to FIG.

First, similarly to FIG. 1, each step of charging, exposing, developing and transferring the image carrier 10 is performed by a known technique to form a developer image on the transfer material 15. Further, the transferred material 15 conveyed while being electrostatically attracted to the image carrier 10 is discharged from the transfer nip and reaches the vicinity of the separating means 16.

A bias power source 20 applies a separation bias voltage having a polarity opposite to that of the back surface charges of the transfer material 15 to the separation means 16a. Therefore, an electrostatic attraction force acts due to the separation bias voltage between the transfer material 15 and the separating means 16 a, and the resultant force of the restoring force due to the rigidity of the transfer material 15 causes the transfer material 15 from the image carrier 10 to move. Separation is ensured.

When the transfer material 15 is thin paper or the like, the restoring force due to the rigidity becomes small, and the restoring force due to the rigidity of the transfer material 15 becomes small. In addition, the reduction of the restoring force increases the gap between the separating means 16 and the transferred material 15, and the amount of electric charges induced in the separating means 16 decreases, so that the static force acting between the separating means 16 and the transferred material 15 is reduced. Electric attraction is reduced. Therefore, in the configuration of the first embodiment in which the separating means 16a is grounded,
As the restoring force decreases, the electrostatic attraction force decreases, and the image carrier 1
Although it becomes difficult to separate the transferred material 15 from 0, in the second embodiment, the separating means 16 is provided by the DC bias power source 20.
Since a separation bias voltage is applied to a, the separation means 16a
Can exert a stable electrostatic attraction force on the transfer material 15, and can reliably separate the transfer material having low rigidity from the image carrier 10.

Further, in the configuration of FIG. 1, the fluctuation of the gap between the transferred material 15 and the separating means 16a due to wrinkles or the like greatly affects the separating force. Therefore, if the transferred material 15 has wrinkles,
The position where the transfer material 15 is separated from the image carrier 10 is changed, and the transfer material 15 is flapping. However, according to the second embodiment, since a stable separation force can be imparted by the separation bias voltage as described above, fluttering of the transfer material 15 can be suppressed, and a high quality image can be formed without causing toner scattering. You can

Further, if the separation force is increased by increasing the separation bias voltage, the transfer material 15 and the separation means 1 are separated.
The gap between 6a can be made large. Therefore, the separating means 1
Even when the toner adheres to the surface of the discharge preventing means 16b covering 6a, the transfer material 15 is not in contact with the discharge preventing means 16b, and the toner adhered to the discharge preventing means 16b adheres to the back surface of the transfer material 15. Can be prevented. In addition, the separating means 16a can be freely arranged, and the margin of the transfer material 15 with respect to the conveying path is widened.

An image forming apparatus according to the third embodiment of the present invention is shown in FIG.
It will be described based on.

FIG. 3 is a side view of the image forming apparatus of the third embodiment.

In FIG. 3, 10 is an image carrier, 14 is a transfer means, 15 is a transfer material, 16a is a separating means, 16b is a discharge preventing means, 20 is a DC bias power source, and the above is the same as in FIG.
The configuration is the same as that of.

2 is different from the structure shown in FIG. 2 in that the inflow charge detection means 31 to the transfer material, the humidity detection means 32 to detect the atmospheric humidity, the inflow current value detection means 33 to the transfer roller, and the transfer material to the transfer material are different. First control means 21 that controls the separation bias voltage based on the amount of inflow charges, second control means 22 that controls the separation bias voltage based on the atmospheric humidity, and control the separation bias voltage based on the current value flowing into the transfer roller. Third
The control means 23 is provided.

The operation of the image forming apparatus of the third embodiment constructed as above will be described with reference to FIG.

First, each step of charging, exposing, developing and transferring the image carrier 10 is performed by a known technique to form a developer image on the transfer material 15. In the transfer step, transfer charges are supplied from the transfer roller 14a to the transfer material 15, but a part thereof leaks to a peripheral member (not shown) depending on the conductivity of the transfer material 15. Therefore, when the atmospheric humidity decreases, the conductivity of the transfer material 15 decreases, and the amount of charge remaining on the back surface of the transfer material 15 increases, and the electrostatic attraction force with the image carrier 10 increases.

The transfer material 15 is conveyed by the image carrier 10 while being electrostatically adsorbed to the image carrier 10, discharged from the transfer nip, and reaches the vicinity of the separation electrode 16a.
The separation force acts on the separation electrode 16a by the DC bias power source 20 by the separation bias voltage having the opposite polarity to the back surface charge of the transferred material 15. The separation bias voltage of the bias power source 20 is detected by the inflow charge detecting means 31 to the transfer material.
Humidity detecting means 32 for detecting the atmospheric humidity, the first control means 21 for estimating the back surface charge amount of the transfer material 15 based on the detection result of the inflow current value detecting means 33 to the transfer roller,
The second control means 22 and the third control means 23 control to a separation bias voltage adapted to the estimated back surface charge amount of the transfer material 15.

Therefore, the transfer material 15 has a separating means 16a.
An electrostatic attraction force corresponding to the amount of back surface charge acts between and, and the separation is surely performed by the resultant force of the restoring force due to the rigidity of the transferred material 15.

In the present embodiment, the inflow charge to the transfer material, the atmospheric humidity, the inflow current value to the transfer roller, etc. were detected, but the object to be detected is one that can estimate the back surface charge amount of the transfer material 15. Any material may be used, for example, a transfer material guide plate (not shown) or the amount of charges flowing into the fixing device, the image carrier 10.
The back surface charge amount can also be estimated by detecting the amount of charge flowing into the device, and the control means described above are not limited to the configuration of this embodiment.

When the bias power source 14b is controlled to a constant voltage, the bias power source 14b causes the transfer roller 14a to move due to the circumferential resistance distribution of the transfer roller 14a.
Since the amount of charges supplied to the transfer material fluctuates, the amount of charges on the back surface of the transfer material 15 also changes and the separation of the transfer material 15 becomes unstable. However, when the transfer current value is detected by the detection unit 33, it is possible to estimate the back surface charge amount of the transferred material 15 and control the separation bias voltage.
The transfer material can be reliably separated even when the resistance value unevenness is large.

If the separating operation is stable, the transfer material 15
Since the separation position can be stabilized, fluttering during transfer of the transfer material 15 can be suppressed, and toner scattering does not occur, and a high-quality image can be formed.

FIG. 4 shows an image forming apparatus according to the fourth embodiment of the present invention.
It will be described based on.

FIG. 4 is a side view of the image forming apparatus of the fourth embodiment.

In FIG. 4, 10 is an image carrier, 14 is a transfer means, 15 is a transfer material, 16a is a separation means, 16b is a discharge prevention means, 20 is a DC bias power source, and the above is the same as the configuration of FIG. It is a thing.

The difference from the configuration of FIG. 3 is that the rigidity detecting means 24 for detecting the rigidity of the transferred material 15, the thickness detecting means 25 for detecting the thickness of the transferred material 15, and the width of the transferred material 15 are detected. Width detection means 26, fourth control means 24 for controlling the separation bias voltage based on the rigidity of the transferred material 15, fifth control means 25 for controlling the separation bias voltage based on the thickness of the transferred material 15, transfer target The sixth control means 26 controls the separation bias voltage based on the width of the material 15.

The operation of the image forming apparatus of the fourth embodiment constructed as described above will be described with reference to FIG.

First, each step of charging, exposing, developing and transferring the image carrier 10 is performed by a known technique to form a developer image on the transfer material 15. Further, the transferred material 15 is discharged from the transfer nip and reaches the vicinity of the separating means 16a, and at this time, the separating means 16a has a DC bias power supply 2
A separation bias voltage of 0 is applied.

When the transfer material 15 is a thin paper such as tracing paper, the rigidity is low and the transfer material 15 is the image carrier 10.
The gap between the separating means 16a and the material to be transferred 15 becomes large due to the close contact with the material to be transferred 1 by the separation bias voltage.
As the separating force acting on 5 becomes smaller, the restoring force due to the rigidity becomes smaller and the separation failure easily occurs.

Therefore, in the fourth embodiment, the rigidity detection means 24, the thickness detection means 25 and the width detection means 26 detect the rigidity, thickness and width of the transfer material 15, and the fourth control means 24, The fifth control unit 25 and the sixth control unit 26 estimate the rigidity of the transferred material 15, and the bias power source 20 receives the separation bias voltage corresponding to the estimated rigidity from the separation unit 16a.
Control so that it is applied to.

As described above, according to the fourth embodiment, the separation bias voltage applied to the separating means 16a can be controlled according to the rigidity of the material 15 to be transferred.
Even if the rigidity of the fluctuates, reliable separation can always be performed.

Further, in the fourth embodiment, the transfer material 15
Although the thickness and width are detected, the thickness or width may be detected independently, and the present invention is not limited to the fourth embodiment.

Further, in the fourth embodiment, the rigidity is detected by the detecting means, but the user may input the rigidity data of the material to be transferred in advance and control the separation bias voltage according to the input rigidity data. Well, it is not limited to the configuration of the fourth embodiment.

FIG. 5 shows an image forming apparatus according to the fifth embodiment of the present invention.
It will be described based on.

FIG. 5 is a side view of the image forming apparatus of the fifth embodiment.

In FIG. 5, 10 is an image carrier, 14 is transfer means, 15 is a transfer material, 16a is separating means, 16b is discharge preventing means, and 20 is a DC bias power source. It is a thing.

The difference from the configuration of FIG. 2 is that an AC bias power supply 40 for applying an AC bias voltage to the separating means 16a at the time of non-transfer is provided.

The operation of the image forming apparatus configured as described above will be described with reference to FIG.

First, each of the steps of charging, exposing, developing and transferring the image carrier 10 is performed by a known technique to form a developer image on the transfer material 15, and the transfer material 15 is discharged from the transfer nip. To be done.

The DC bias power source 20 is provided in the separating means 16a.
The separation bias voltage is applied by the separation bias voltage and exerts a separation force on the transferred material 15 that has reached the vicinity. After that, the transfer roller 1
When the rear end of the transferred material 15 passes over the separating means 16a as the 4a rotates, the separating means 16a is connected to the AC bias power supply 40. The AC bias power supply 40 generates an AC voltage having a center value of 0 (V). Therefore,
Since an AC voltage is applied to the separating means 16a at the time of non-transfer, an AC electric field is formed in the gap between the separating means 16a and the image carrier 10 and the floating toner is discharged.
To prevent adherence to. At the same time, the discharge prevention means 1
The toner already attached to 6b is caused to fly by the alternating electrostatic force.

As described above, according to the fifth embodiment, it is possible to prevent the discharge prevention means 16b covering the separating means 16a from being contaminated with toner, so that the toner may adhere to the rear surface of the transfer material 15 that follows. It is possible to form a high quality image. When the surface of the separating means 16a is conductive,
The AC bias voltage causes a discharge between the image carrier 10 and the image carrier 10 to form a pinhole. However, in the fifth embodiment, the insulating layer of the discharge preventive means 16b is formed on the surface. Since such a defect is formed, such a problem does not occur, so that a good result can be obtained.

FIG. 6 shows an image forming apparatus according to the sixth embodiment of the present invention.
It will be described based on.

FIG. 6 is a side view of the image forming apparatus of the sixth embodiment.

In FIG. 6, 10 is an image carrier, 14 is a transfer means, 15 is a transfer material, 16a is a separation means, and 16b is a discharge prevention means. The above is the same as the configuration of FIG.

The bias power supply 1 is different from the configuration of FIG.
4c is a constant current power source.

The operation of the image forming apparatus of the sixth embodiment constructed as described above will be described with reference to FIG.

First, each step of charging, exposing and developing the image carrier 10 is performed by a known technique to form a developer image on the image carrier 10. The material to be transferred 15 reaches the transfer nip by a conveying unit (not shown), and the bias power source 14
The charge is supplied to the back surface by b, and the developer image is transferred. The bias power source 14c is controlled so that the amount of electric charge applied to the transfer roller 14a is constant, and when the resistance value unevenness in the circumferential direction of the transfer roller 14a is large, or in accordance with the environment such as atmospheric humidity, the material to be transferred 15 is transferred. Even when the impedance changes, the amount of charge supplied to the back surface of the transfer material 15 is kept constant. The transferred material 15 reaches the vicinity of the separating means 16a while holding a constant charge on the back surface thereof, and an electrostatic attraction force is generated between the transferred material 15 and the charges induced in the separating means 16a to perform separation.

As described above, according to the sixth embodiment, the bias voltage 14c controls the transfer bias voltage at a constant current, so that the back surface charge amount of the transferred material 15 after being discharged from the transfer nip changes due to environmental fluctuations. Or, it becomes constant regardless of the roller resistance value unevenness, and the transferred material 15 is stably held on the image carrier 10.
Can be separated from. In the sixth embodiment, the separating means 16a
However, good results can also be obtained by applying the separation bias voltage, and the structure is not limited to that of the sixth embodiment.

Further, by combining the control of the transfer bias voltage in the sixth embodiment with each of the aforementioned embodiments, more stable transfer material separation can be performed.

An image forming apparatus according to the seventh embodiment of the present invention will be described with reference to FIGS.

FIG. 7 shows a paper discharge guide 1 according to the seventh embodiment.
8a and 8 are perspective views of a conventional paper ejection guide 18b.

The paper discharge guides 18a and 18 shown in FIGS.
b is installed in the image forming apparatus shown in FIG. 1, for example.
In the conventional example, ribs are formed on the paper discharge guide 18b as shown in FIG. 8, and in the seventh embodiment, the paper discharge guide 18a is formed.
Has a flat surface as shown in FIG.

An image forming apparatus equipped with the paper discharge guides 18a and 18b shown in FIGS. 7 and 8 will be described with reference to FIG.

First, the transfer material 15 is subjected to the steps of charging, exposing, developing and transferring the image carrier 10 by a known technique.
A developer image is formed on top. The transfer material 15 carrying the unfixed developer image on the surface is separated by the separation electrode 16a, and then further conveyed by the rotation of the transfer roller 14a and reaches the paper discharge guide 18.

The paper discharge guides 18a and 18 shown in FIGS.
As a result of performing image formation by installing b in the image forming apparatus shown in FIG.
18b and leaks to the paper ejection guides 18a and 18b. However, in the case of the paper ejection guide 18b in which protrusions such as ribs are formed as shown in FIG. It was found that the unfixed image formed on the transfer material 15 was disturbed. However, when the surface is formed as a flat plate like the paper discharge guide 18a as shown in FIG. 7, a local electric field is not formed even by contact with the transfer material 15, and the unfixed developer image is disturbed. It turned out that no.

As described above, according to the seventh embodiment, even when the transfer target material is separated with the back surface charges remaining on the transfer target material 15 due to the charges induced in the separating means 16a,
By forming the surface of the paper discharge guide 18a in a flat plate shape, it is possible to prevent the unfixed developer image from scattering and form a high quality image.

Although all of the embodiments have been described with respect to the image forming apparatus for performing the reversal development, the same effect can be obtained for the image forming apparatus for performing the regular development, and the configuration of the present embodiment is limited. It is not something that will be done.

[0114]

According to the image forming apparatus of the present invention, by transferring the developer image by the transfer roller, the back surface charge amount at the time of transferring the transfer material can be appropriately reduced, and the back surface of the transfer material can be reduced. An electrostatic attraction force generated between the charge induced in the separating means grounded by the charge and the back surface charge of the transfer target material acts on the transfer target material as a separation force, thereby stably separating the transfer target material. You can Further, by covering the surface of the separating means with the discharge preventing means made of an insulating layer, the back surface charges of the material to be transferred are prevented from leaking to the separating means, so that it is possible to provide a separating device in which no transfer failure occurs. . Furthermore, since the discharge between the separating means and the transfer roller is also prevented, the distance between the separating means and the material to be transferred and the transfer roller may be narrow, and the space required for the separating / transferring process can be reduced to reduce the image forming apparatus. This has the effect of realizing miniaturization.

By applying a separation bias voltage to the separation means, the separation force acting on the transferred material is increased,
Separation may be difficult in some cases. Thin paper can be separated stably, and due to the increase in separation force, the material to be transferred is always separated immediately after being discharged from the transfer nip, and the separation position is constant. This has the effect of suppressing the flapping of the material and forming a high-quality image.

Further, since the separation force is enhanced by the separation bias voltage, the separation means can be arranged at a position away from the transfer path of the transfer material, and even when toner adheres to the discharge prevention means, the back surface of the transfer material is removed. Can be prevented from becoming dirty.

By controlling the separation bias in accordance with the amount of charge on the back surface of the transfer material or the rigidity of the transfer material,
It is possible to reliably prevent the occurrence of separation failure.

Further, by applying an AC voltage to the separating means at the time of non-transfer, it is possible to prevent the scattered toner from adhering to the separating means, so that it is possible to form a high quality image without back stain. Play.

Further, by controlling the transfer bias voltage applied to the transfer roller at a constant current, it is possible to prevent fluctuations in the amount of electric charge supplied to the back surface of the transfer material, so that even when the resistance value of the transfer roller is uneven. It is possible to perform stable separation of the transferred material.

Further, since the surface of the discharge guide is formed in a flat plate shape, there is no place where an electric field is concentrated and discharged between the rear surface charge of the transfer material and the discharge guide, and there is no fixing on the transfer material. The effect that the toner image scattered by the discharge of the developer image is eliminated is obtained.

[Brief description of drawings]

FIG. 1 is a side view of a first embodiment of an image forming apparatus of the present invention.

FIG. 2 is a side view of a main part of a second embodiment of the image forming apparatus of the invention.

FIG. 3 is a side view of a main part of a third embodiment of the image forming apparatus of the invention.

FIG. 4 is a side view of a main part of a fourth embodiment of the image forming apparatus of the invention.

FIG. 5 is a side view of a main part of a fifth embodiment of the image forming apparatus of the invention.

FIG. 6 is a side view of a main part of a sixth embodiment of the image forming apparatus of the invention.

FIG. 7 is a perspective view of a paper discharge guide of a seventh embodiment of the image forming apparatus of the invention.

FIG. 8 is a perspective view of a paper discharge guide of a conventional image forming apparatus.

FIG. 9 is a side view of an image forming apparatus of a first conventional example.

FIG. 10 is a side view of an image forming apparatus of a second conventional example.

[Explanation of symbols]

 10 image carrier 11 charging means 12 exposure means 13 developing means 14 transfer means 14a transfer roller 14b bias power supply 14c bias power supply 15 transferred material 16a separation means 16b discharge prevention means 17 cleaning means 18 paper ejection guide 18a paper ejection guide 18b paper ejection Guide 19 Fixing Means 20 DC Bias Power Supply 21 First Control Means 22 Second Control Means 23 Third Control Means 24 Fourth Control Means 25 Fifth Control Means 26 Sixth Control Means 31 Means for Inflowing Charge into Transferred Material 32 Humidity Detecting means 33 Detecting current flowing into transfer roller 34 Stiffness detecting means 35 Thickness detecting means 36 Width detecting means 40 AC bias power source

Claims (14)

[Claims] 1. An image carrier that carries a developer image and has a predetermined potential, a transfer roller that transfers the developer image from the image carrier to a transfer material, and a transfer roller near the transfer roller in the vicinity of the transfer roller. Separation means for disposing the electric field in a gap between the transfer material and the transfer material, the electric field being generated in a gap between the transfer material and the transfer material, and separating the transfer material from the image carrier; An image forming apparatus comprising: a discharge preventing unit that is provided so as to cover the unit and that prevents the separating unit from causing a discharge between the transfer target material and the transfer roller. 2. The image forming apparatus according to claim 1, wherein an electric field is generated in a gap between the transferred material and the separating means by a back surface charge of the transferred material. 3. The image forming apparatus according to claim 1, wherein the separating unit is a grounded conductor. 4. The image forming apparatus according to claim 1, further comprising a first bias power source for applying a voltage having a polarity opposite to that of the transfer roller to the separating unit. 5. The image forming apparatus according to claim 1, wherein the discharge prevention unit is an insulating layer coated on the surface of the separating unit. 6. The image forming apparatus according to claim 4, further comprising a first control unit that controls a voltage applied to the separation unit according to an amount of charges flowing into the transfer material. 7. The image forming apparatus according to claim 4, further comprising a second control unit that controls a voltage applied to the separating unit according to humidity. 8. The image forming apparatus according to claim 4, further comprising a third control unit that controls a voltage applied to the separating unit according to a current value flowing into the transfer roller. 9. The image forming apparatus according to claim 4, further comprising a fourth control unit that controls the voltage applied to the separating unit according to the rigidity of the material to be transferred. 10. The image forming apparatus according to claim 4, further comprising a fifth control unit that controls the voltage applied to the separating unit according to the thickness of the material to be transferred. 11. The image forming apparatus according to claim 4, further comprising a sixth control unit that controls the voltage applied to the separating unit according to the width of the material to be transferred. 12. The image forming apparatus according to claim 4, further comprising a quadrature switching bias power source that applies a DC voltage to the separating means only when the paper is passed and applies an AC voltage to the separating means when the paper is not passed. 13. The method according to claim 1, further comprising a seventh control means for controlling a constant voltage applied to the transfer roller as a transfer potential. 12. The image forming apparatus according to item 12. 14. A transport path for transporting the transfer material and a fixing means for fixing a developer image on the transfer material are provided downstream of the separating means in the traveling direction of the transfer material, and the transport path is formed in a plate-like member. Claims 1, 2, 3, 4, 5, 6, 7, 8, 9, 1
The image forming apparatus according to 0, 11, 12 or 13.