JPH06171159A - Two-side image forming device - Google Patents

Abstract

PURPOSE:To perform a superior transfer even if resistance values change due to attachment of oil to a transfer material by a method wherein, when an image is transferred to a first side of the transfer material and then an image is transferred to a second side, a constant-current control means e gives a predetermined current to the transfer material during the transfer of image to the second side. CONSTITUTION:When a toner image on a photosensitive drum 3 is transferred to one side of a transfer material held on a dielectric sheet 6' of a transfer drum 6 and thereafter an image is transferred to the other side, an electroconductive roller 21 is used and voltage from a power source 30 is applied to the roller 21 to generate a transfer electric field, wherein current of equal magnitude is supplied from the power source 30 by constantcurrent control in the transfer for both the first and second sides. As a result, the current is fed directly into the transfer material from the roller 21 via the sheet 6' and hence even if there are changes in resistance values of the transfer material between the transfer of the first side and that of the second sides, transfer current of equal magnitude can be supplied.

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 or a laser beam printer, and more particularly to an image forming apparatus capable of forming a multicolor image on both sides of a transfer material.

[0002]

2. Description of the Related Art Conventionally, as a full-color image forming apparatus, it is known to transfer a toner image on a photoconductor, which is an image carrier, onto a transfer material carried on a transfer material carrier of a transfer drum by a transfer corona charger. . After the yellow, magenta, cyan, and black toner images are transferred onto the transfer material carried by the transfer material carrier, the transfer material is conveyed to the fixing device. In the fixing device, the four color toner images are melt-mixed and fixed on the transfer material.

As colorization has progressed in recent years, there is an increasing demand for forming multicolor images on both sides of a transfer material in the above-mentioned full-color image forming apparatus.

However, when a multicolor image is formed on both surfaces of the transfer material, the transfer material is transferred between the first surface of the transfer material and the second surface of the transfer material. The resistance value of the transfer material is different due to the difference in water content, transfer toner amount, fixing oil adhesion amount, and the like.

Therefore, when a multi-color image is formed on both sides by a conventional image forming apparatus, a transfer failure such as scattering or transfer omission may occur. In order to prevent this, it is necessary to match the resistance value of the transfer material. The transfer conditions such as the transfer electric field of the transfer charger including the corona charger have to be controlled differently, and there has been a problem that the control of the transfer condition becomes troublesome.

On the other hand, when it is attempted to continuously form a multicolor image on both surfaces of a transfer material with respect to a plurality of transfer materials, for example, the first surface of the transfer material is transferred and fixed to form an image carrier or an image carrier. There has been a problem that it takes a considerable amount of time to perform the transfer and the fixing after performing the preparatory operation for starting the second surface of the transfer material after cleaning the transfer drum and removing the charge.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of excellent transfer regardless of a change in the resistance value of the transfer material due to a difference in the amount of oil adhered to the transfer material.

Another object of the present invention is to provide an image forming apparatus capable of easily controlling the transfer of the second surface of the transfer material.

Another object of the present invention is to provide an image forming apparatus capable of forming a good image on both surfaces of a transfer material.

Another object of the present invention is to provide an image forming apparatus in which the image forming speed on both surfaces of the transfer material is improved.

Another object of the present invention is to provide a first surface and a second surface of the transfer material.
An object of the present invention is to provide an image forming apparatus that forms a good image without changing the transfer condition of the surface.

The different objects and features of the present invention will become more apparent by reading the following detailed description with reference to the accompanying drawings.

[0013]

According to the present invention, an image carrier capable of carrying a toner image, a transfer material carrier which is a dielectric material carrying a transfer material, and the toner image on the image carrier are transferred to the transfer material. In order to transfer to a transfer material carried on a carrier, a transfer member that can be contacted with the back side of the transfer material carrier, and a constant current control unit that applies a predetermined current to the transfer member to control a constant current, In the image forming apparatus having the image forming apparatus, the apparatus can perform image transfer on the first surface of the transfer material and then perform image transfer on the second surface of the transfer material opposite to the first surface. The constant current control means applies a predetermined current to the transfer member during image transfer on the surface.

Further, the present invention comprises an image carrier capable of carrying a toner image and a transfer material carrier for carrying and transporting a transfer material to a transfer position, and the toner image on the image carrier is In an image forming apparatus in which the transfer material carried on the transfer material carrier is transferred at the transfer position, the apparatus transfers an image onto the first surface of the transfer material and then reverses the first surface of the transfer material. Image transfer can be performed on the second surface on the side, and the transfer material carrier can transfer the image to the second surface at a different position, and the first transfer material can transfer the image to the second surface. It is characterized in that it can simultaneously carry two transfer materials.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

For example, FIG. 4 shows a device configuration of a main part of an image forming apparatus capable of forming a multicolor image on both surfaces of the transfer material P. In the figure, reference numeral 3 is a photosensitive drum that is an image bearing member that rotates in a predetermined direction. Around the photosensitive drum 3, a primary charger 2, magenta, yellow, cyan, black developing devices 1M, 1Y, 1C, 1K, and cleaning are provided. A container 4 is provided.

A transfer drum 6 which rotates and conveys the transfer material P while being held by the grip 6a is arranged so as to come into contact with the photosensitive drum 3. Inside the transfer drum 6, a transfer electric field is applied to the transfer material P. As a result, the transfer charging member 21 that transfers the toner image on the photosensitive drum 3 onto the transfer material P is provided. As shown in FIG. 5, the transfer drum 6 has a dielectric sheet 6'consisting of a dielectric material as a transfer material carrying member stretched in a space on the outer peripheral surface of the frames 61a and 61b in which a pair of rings are connected by a connecting member. The transfer material P is held on the dielectric sheet 6 '. The grip 6a is provided on the connecting member 6b.

A separating claw 7, a conveying section 8 and a fixing device 9 are arranged downstream of the transfer drum 6 in the transfer material moving direction, and a paper feed cassette 10 and a paper feed roller 1 are provided on the paper feed side of the transfer drum 6.
1, registration roller 12, first and second guides 13, 1
4 are provided. In addition, the transfer material P
A reversing guide 15 is provided to convey the sheet to the sheet discharge tray 16 side or the re-conveying line side including the third guide 17, the intermediate tray 18, the feeding roller 19, and the like.

The fixing device 9 has a built-in heater as a heat source and rotates in a predetermined direction, and a fixing roller 90.
A pressure roller 91 which rotates in pressure contact with the fixing roller 9 and a fixing roller 9
0, abutting against the pressure roller 91, these rollers 90, 9
1 is composed of first and second rollers 92, 93, etc., which are coated with a release agent such as oil and can move back and forth in the vertical direction in the figure.

First, the operation in the case of forming a multicolor full-color image on only one surface (first surface) of the transfer material P in this image forming apparatus will be described. When the image light L based on magenta information is exposed from a laser scanner unit (not shown) onto the photosensitive drum 3 uniformly charged by the primary charger 2, an electrostatic latent image based on magenta information is exposed on the photosensitive drum 3. The formed electrostatic latent image is developed by a magenta developing device 1M having magenta toner and visualized as a magenta toner image. This toner image is formed by applying the transfer electric field formed by the transfer charging member 21 to the transfer material P held on the dielectric sheet 6 ′ of the transfer drum 6.
The image is transferred onto the transfer material P.

After the transfer, the photosensitive drum 3 is cleaned by the cleaning device 4, and then uniformly charged again by the primary charging device 2. The scanner unit similarly exposes the image light L based on the yellow information to the photosensitive drum. An electrostatic latent image based on yellow information is formed on 3. This electrostatic latent image is developed by a yellow developing device 1Y having yellow toner, and visualized as a yellow toner image,
The yellow toner image is transferred by the transfer charging member 21 onto the transfer material P on the dielectric sheet 6 ′ from the above magenta toner image in an overlapping manner.

Similarly, cyan information on the photosensitive drum 3,
By forming an electrostatic latent image based on black information, developing the latent image by the cyan developing device 1C and the black developing device 1K, and transferring the obtained cyan toner image and black toner image onto the transfer material P, A color image is obtained by superimposing and transferring the toner images of four colors on the first surface of the transfer material P.

The transfer material P is supplied from the paper feed cassette 10. The transfer materials P are taken out one by one from the paper feed cassette 10 by the paper feed roller 11, and then transferred to the first guide 13
From the registration roller 12 to the registration roller 12
Thus, the toner image is sent out at the same timing as the formation of the toner image on the photosensitive drum 3, and is supplied to the transfer drum 6 via the second paper feed guide 14. The transfer material P supplied to the transfer drum 6 is positioned and held by the gripper 6a of the transfer drum 6, and then is rotated by the rotation of the transfer drum 6 to pass through an image transfer portion facing the photosensitive drum 3 and pass there. While passing, the toner image on the photosensitive drum 3 is transferred.

The transfer material P on which the four color toner images have been transferred in this manner is separated from the transfer drum 6 by the separation claw 7 and then sent to the fixing device 9 via the conveying section 8 and fixed there. . The transfer material P sent to the fixing device 9 is heated and pressed while being sandwiched and conveyed by the fixing roller 90 and the pressure roller 91 and passed between them, and the toner image is melted and mixed with the color. The image is fixed on the transfer material P, fixing is completed, and a full-color permanent image is formed. A first application roller 92 abuts on the fixing roller 90 to apply fixing oil as a release agent.
The transfer material P on which the toner image has been fixed is stacked on the paper discharge tray 16 via the reversing guide 15.

For example, in an environment where the humidity is 60% RH, 10 ⁶
When a transfer material of about Ω · cm passes through the fixing roller pair whose temperature is adjusted to 180 ° C. once, the resistance is increased to 10 ⁷ to 10 ⁸ Ω · cm. This is because the transfer material was exposed to a high temperature and the water content decreased. It is also known that when toner particles using a resin or silicone oil such as dimethyl type is used, the resistance of the transfer material becomes higher than that before the fixing in the same manner when a large amount of the fixing oil adheres. In order to apply a transfer electric field that transfers the same high image quality as that of the first surface to the second surface of the transfer material having high resistance as described above, the increase in impedance must always be considered.

FIG. 1 is an enlarged sectional view of the vicinity of the transfer portion of the image forming apparatus shown in FIG.

As shown in FIG. 1, in this embodiment, a conductive roller 21 is provided as a transfer charging member in the transfer drum 6, and the conductive roller 21 is a transfer drum of a transfer portion facing the photosensitive drum 3. The inside of 6 is in contact with the back surface of the dielectric sheet 6 ′. A bias power supply 30 that applies a voltage to the conductive roller 21 is connected to the conductive roller 21, and the conductive roller 21 generates a transfer electric field when a voltage is applied from the power supply 30. In FIG. 1, reference numeral 6b is a connecting member that connects a pair of rings (not shown) of the transfer drum 6.

The volume resistivity of the above conductive roller 21 is
If it is higher than 10 ⁸ Ω · cm, transfer failure will occur.
10 ⁸ Ω · cm or less is preferable, and 10 ² to 10 ⁷ is preferable.
Ω · cm is good. In this embodiment, the conductive roller 21 has a diameter of 20 mm and a volume resistivity of 10 ⁵ Ω · cm.
Apply 10g of pressure (transfer pressure) to the back of the dielectric sheet 6 '.
/ Cm ² It was made to contact.

The conductive roller 21 is arranged at the transfer portion between the position where the transfer material held on the dielectric sheet 6'starts contact with the photosensitive drum 3 and the position at which the transfer material has finished contacting, and as close as possible. The conductive roller 21 is brought into contact with the back surface of the dielectric sheet 6 ′ by pressing the back surface of the dielectric sheet 6 ′. The conductive roller 21 may be driven at the same speed as the dielectric sheet 6 ′ that is rotationally moved with the rotation of the transfer drum 6, or may be rotationally driven with a peripheral speed difference.

In this embodiment, the toner images of the respective colors on the photosensitive drum 3 are transferred onto one surface (first surface) of the transfer material held on the dielectric sheet 6'of the transfer drum 6, and then the front and back are reversed. When transferring the toner images of the respective colors on the photosensitive drum 3 to the other surface (second surface) of the transfer material held by the above, the conductive roller 21 as described above is used, and a voltage from the power supply 30 is applied thereto. Transfer is performed by applying and generating a transfer electric field. At that time, the power source 30 causes the same current as the transfer current to flow through the constant current control for both the first surface and the second surface.

According to this, unlike the transfer charger composed of the corona charger, the current applied at the time of transfer is directly injected from the conductive roller 21 to the transfer material through the dielectric sheet 6 '. Even if there is a change in the resistance value of the transfer material between the transfer on the first surface and the transfer on the second surface, the same transfer current can be supplied by controlling the applied current at a constant current. Therefore, it is possible to secure the required transfer current amount, which largely depends on the toner charge amount, on both sides by the same control value and perform the transfer.

In this embodiment, the transfer material conveying speed of the image forming apparatus of FIG. 4 is 180 mm / sec, and the polyvinylidene fluoride resin film as the dielectric sheet 6'is 150 μm thick.
m, volume resistance value of about 10 ¹⁴ Ω · cm, toner is about −25
The μc / g two-component resin toner and the transfer material used were plain paper having a basis weight of 80 g / cm ² of 10 ⁶ Ωcm.

Formation of almost black image on transfer material (solid image)
The case of transferring the image to both surfaces of the transfer material will be described.

When the power source controls the transfer charging member with a constant current on both the first and second sides of the transfer material 1
The constant current appropriate for the transfer of the surface was 20 μA.
At this time, the output voltage of the power supply was about 2 kV.

When the second surface image is transferred, the resistance value of the transfer material increases due to the adhesion of the fixing oil and the drying of the transfer material after passing through the fixing device. When the same 20 μA constant current as on the first surface was applied to the transfer charging member to transfer the image on the second surface, the output voltage of the power supply increased to 3 kV, but proper transfer was obtained.

On the other hand, a case will be described in which a constant voltage control is performed by supplying a constant voltage of 2 kV to the transfer charging member by the power source when transferring a solid black image on both the first and second sides of the transfer material. On the first surface of the transfer material, when the resistance of the transfer material was 10 ⁶ Ωcm as in the above example, the transfer current flowing through the transfer charging member was 20 μA, and proper transfer was obtained. When the image was transferred to the second surface of the transfer material, the resistance of the transfer material became higher than that of the first surface, so that the transfer current was about 13 μA. Thus, the transfer current decreases as the resistance of the transfer material increases. Therefore, in the transfer of the second surface, non-uniform transfer of the solid portion, reduction of transfer efficiency, and the like occurred.

In the above description, the case where the solid image was transferred to both surfaces of the transfer material was described. However, when the character image (highlight part) is transferred, the transfer charging member is similarly controlled with constant current. Then, proper transfer is performed on both surfaces of the transfer material, but if constant voltage control is applied to the transfer charging member, deterioration of the line image due to toner scattering at the time of transfer of the second surface of the transfer material and roughness at the time of halftone reproduction occur.

In the above description, the black monochromatic image is formed both when the constant current control and the constant voltage control are performed at the time of double-sided transfer of the transfer material. However, the transfer characteristic tendency of these is the image formation described in FIG. It becomes more prominent in a color image forming apparatus in which toner images are sequentially superimposed and transferred like an apparatus.
Therefore, when image transfer is performed on the second surface of the transfer material, it is preferable to perform constant current control on the transfer charging member.

Further, even on the first surface of the transfer material, the resistance value of the transfer material changes according to the environment of temperature and humidity. It is desirable to perform constant current control.

FIG. 6 shows the output applied voltage value when the transfer current of the image recording apparatus described in this example is controlled to constant current and the control current value is changed. As shown in the figure, the applied voltage increases sequentially, and for example, at 20 μA, the applied voltage is doubled or more for the first color and the fourth color. Thus, the present invention is
It is more effective when applied to a color image forming apparatus.

FIG. 2 is a sectional view showing a transfer drum provided with a transfer charging member in another embodiment of the image forming apparatus of the present invention. This embodiment is characterized in that a conductive brush 22 is installed as a transfer charging member. Similarly, the conductive brush 22 is brought into contact with the back surface of the dielectric sheet 6 ′ inside the transfer drum 6 of the transfer portion facing the photosensitive drum 3,
A bias power supply 30 that applies a voltage to the conductive brush 22 is connected to the conductive brush 22.

The conductive brush 22 is made of fine fibers having elasticity and conductivity. In this embodiment, the conductive brush 22 is used.
As the conductive fibers, conductive fibers obtained by dyeing acrylic fine fibers with copper sulfide to make them conductive were used. Other conductive fibers include stainless steel fibers having a diameter of about 8 to 15 μm, fibers obtained by metal-plating resin fibers such as acrylic, nylon, polyester, rayon, and conductive fine particles such as carbon and metal powder in the resin. It is possible to use those which are kneaded or compounded into fibers, and further carbon fibers obtained by carbonizing resin fibers or the like to impart conductivity. The volume resistivity of the conductive fiber may be 10 ¹⁰ Ω · cm or less, preferably 10 ⁸ Ω · cm or less.

The conductive brush 22 is arranged at the transfer portion by a transfer material carried on the dielectric sheet 6 ', with the brush tip extending from the introduction side of the dielectric sheet 6'to the downstream side in the moving direction. Is a position where the contact with the photosensitive drum 3 is started and a position where the contact is ended, and the position is as close as possible, and the conductive brush 22 is pressed by the elasticity to the back surface of the dielectric sheet 6 '. Contacted.

The contact state of the conductive brush 22 with the dielectric sheet 6'is different from the contact made by the elastic sheet-shaped, blade-shaped, or roller-shaped contact conductive member which is close to a straight line. Because of the contact, the inclination of the contact pressure in the longitudinal direction of the contact area and the dielectric sheet 6 '
Irrespective of the surface roughness, the step difference of the connecting portion 6b of the transfer drum 6, and the like, the contact state of individual fine fibers can be maintained uniformly and softly.

Therefore, the contact state with the dielectric sheet 6'can be made closer than in the case of the conductive roller 21 of the embodiment shown in FIG. 1, and the transfer omission due to abnormal discharge can be prevented more reliably. It is possible to secure a wider transfer latitude (especially when the humidity is low).

Also in this embodiment, under the environment of temperature of 20 ° C. and humidity of 60%, the conductive brush 22 applies a transfer current of 20 μA to both the first surface and the second surface of the transfer material, and the first surface and the second surface. The toner images of four colors were transferred to each of the surfaces, and a good double-sided full-color image without transfer defects on both surfaces could be obtained.

FIG. 3 is a sectional view showing a transfer drum provided with a transfer charging member in still another embodiment of the image forming apparatus of the present invention. This embodiment is characterized in that a conductive fur brush 23 is installed as a transfer charging member.
Similarly, the conductive fur brush 23 is brought into contact with the back surface of the dielectric sheet 6 ′ inside the transfer drum 6 of the transfer portion facing the photosensitive drum 3, and the conductive fur brush 23 is applied with a bias power source for applying a voltage thereto. 30 is connected.

In this embodiment, the conductive fur brush 23 is used.
Is a metal round bar wrapped with a conductive adhesive cloth that is raised with a conductive adhesive, and is adhered to it, and the fiber length is adjusted to 5 mm.
It is an 8 mm cylindrical brush.

In this embodiment, as the conductive fiber cloth of the conductive fur brush 23, a cloth of conductive fibers obtained by dyeing acrylic fine fibers with copper sulfide to make them conductive is used. Similarly, as the fibers of the conductive fiber cloth, a diameter of 8 to
About 15 μm stainless steel fiber, or resin fiber such as acrylic, nylon, polyester, rayon, etc., which is metal-plated, or conductive fine particles such as carbon, metal powder, etc. are kneaded into the resin or made into a composite fiber. Further, carbon fibers obtained by carbonizing resin fibers or the like to impart conductivity can be used. Similarly, the conductive fiber having a volume resistivity of 10 ¹⁰ Ω · cm or less can be used.
It is preferably 10 ⁸ Ω · cm or less.

Similarly, the conductive fur brush 23 is arranged at the transfer portion between the position where the transfer material held on the dielectric sheet 6'starts contact with the photosensitive drum 3 and the position where the transfer material finishes contacting. Also, the conductive fur brushes 23 are located as close to each other as possible, and due to their elasticity, the conductive fur brushes 23 are pressed against the back surface of the dielectric sheet 6 ′ and brought into contact therewith. The conductive fur brush 23 may be driven at the same speed as the dielectric sheet 6'which is rotationally moved as the transfer drum 6 is rotated, or may be rotationally driven with a peripheral speed difference.

By using the conductive fur brush 23 as the transfer charging member in this embodiment, the same effect as in the previous embodiment can be obtained, and the first and second surfaces of the transfer material under the same conditions are obtained. By transferring the four-color toner image to each surface, a good double-sided full-color image without transfer defects on both surfaces could be obtained. Further, instead of the fur brush 23, a blade-shaped or sheet-shaped transfer charging member can be used.

Further, the present invention is not necessarily limited to the color image forming apparatus using one photosensitive drum described above. The present invention is particularly effective for a high speed color image forming apparatus. Next, as a typical example of a high-speed color copying machine, a case where it is applied to an apparatus equipped with a photosensitive drum for each color toner will be described.

An example of such a color electrophotographic recording apparatus will be briefly described with reference to FIG. 7. In the main body of the color electrophotographic recording apparatus, the first, second, third and fourth image forming portions Pa are provided. , Pb, Pc, and Pd are provided side by side, and images of different colors are formed through the processes of latent image, development, and transfer.

The structure of the main body will be described. Image forming unit Pa,
Pb, Pc, and Pd are respectively provided with dedicated image carriers, electrophotographic photosensitive drums 3a, 3b, 3c, and 3d in this example, and electrophotographic images formed by the image forming portions Pa, Pb, Pc, and Pd. The images on the photosensitive drums 3a, 3b, 3c and 3d are transferred onto the recording material P carried and conveyed on the recording material carrier 130 moving adjacent to each image forming section. Further, the fixing unit 9 heats and pressurizes and the fixed recording image is discharged.

The latent image forming section will be described below. The outer periphery of the photosensitive drums 3a, 3b, 3c, and 3d is the exposure lamp 1
11a, 111b, 111c, 111d, drum chargers 2a, 2b, 2c, 2d, a light source device (not shown), a polygon mirror 117 for scanning light emitted from the light source device, and potential sensors 113a, 113b, 113.
c and 113d are provided. Laser light emitted from a light source device (not shown) is scanned by rotating a polygon mirror 117, and scanning light whose light flux is deflected by a reflection mirror is exposed to the photosensitive drums 3a, 3b, 3c and 3d.
A latent image corresponding to the image signal is formed via the fθ lens that collects light on the mother.

The developing section will be described below. Developer 1
Supply of cyan (hereinafter abbreviated as C), magenta (hereinafter abbreviated as M), yellow (hereinafter abbreviated as Y), and black (hereinafter abbreviated as K) color developers to a, 1b, 1c, and 1d, respectively. A predetermined amount is filled by the device. The developing devices 1a, 1b, 1c, 1d form a visible image on the photosensitive drums 3a, 3b, 3c, 3d according to the latent image formed by the scanning light.

The transfer section will be described below. The recording material P in the recording material cassette 10 is sent to each transfer portion by the recording material carrier 130 via the registration roller 12.

Here, the recording material carrier 130 is a polyethylene terephthalate resin film sheet (PET sheet), a polyvinylidene fluoride resin film sheet,
It is a dielectric resin film such as a polyurethane resin film sheet, and both ends thereof are overlapped and joined to each other to have an endless shape, or a seamless belt (seamless) is used. In the case of a belt having no seams, it is not only difficult to manufacture a belt having uniform physical properties, but also a belt having a stable circumference and mass production such as manufacturing time are not suitable in terms of cost and the like. On the other hand, in the case of a belt having a seam, when forming an image on the seam position, changes in physical properties such as unevenness and resistance value of the seam portion are unavoidable, and image formation on the seam disturbs the image. In order to obtain high image quality, it is general to provide a means for detecting a joint position (not shown) so that an image is not formed on the joint. Therefore, as a means for detecting this joint, an opaque recording material carrier 130
In the case of, a reflection type optical sensor is used, and the recording material carrier 1
Providing a detection mark having a light reflection characteristic different from 30, and providing a transmission type optical sensor in the case of being transparent, or using a mechanical sensor such as a displacement sensor having a shape (for example, a cutout or a protrusion is provided) There are many. Therefore, it is preferable that the belt circumference is an integral multiple of the distance between the recording material and the paper.

When the recording material carrier 130 is confirmed to rotate and reach a predetermined position, the recording material P is conveyed from the registration roller 12 onto the recording material carrier 130.
At this time, the image writing signal is turned on, and an image is formed on the first photosensitive drum 3a at a certain timing. Then, the visible image on the photosensitive drum 3a is transferred by the transfer charging member 24a under the first photosensitive drum 3a applying an electric field or electric charge. At this time, the recording material P is held on the recording material carrier 130 by electrostatic attraction, and the second image forming portion Pb
After that, it is transferred and conveyed. Hereinafter, the recording material P on which the image is formed by the fourth image forming portion Pd by the same method as described above is discharged by the separation charger 32, and is separated from the recording material carrier 130 by the attenuation of the electrostatic attraction force. Then, it is conveyed to the fixing unit 9. The fixing unit will be described below. The fixing unit 9 includes a fixing roller 51, a pressure roller 52, and a heat resistant cleaning member 5 for cleaning each of them.
Heaters 56 and 57 for heating the rollers 4 and 55, an oil application roller 51 for applying a release agent oil such as dimethyl silicone to the fixing roller, an oil reservoir 53 for supplying the oil, and a thermistor for fixing temperature control. It is composed of 58. The cleaning unit will be described below. After the transfer, the developer remaining on the photosensitive drum is removed by the photoconductor cleaning units 4a, 4b, 4c, and 4d to prepare for the subsequent latent image formation. or,
The developer remaining on the recording agent carrier 130 is written off by the abutting nonwoven fabric 34. As other means, a blade or a fur brush and a combination thereof may be used.

When performing double-sided transfer, the transfer material after the transfer of the first surface has passed through the fixing device 9 and is not conveyed to the paper discharge tray 63, but the transfer paper P is reversed by a flapper or the like. Then, the transfer material P is once stored in the intermediate tray 65.

For example, when recording 10 sheets on both sides continuously,
Once the transfer material 6 that has been fixed on the first side is transferred to the intermediate tray 6
It is accumulated to 5. After that, the transfer material P is transferred to the registration roller 12
After that, the image is transferred to the transfer position of each image forming portion to transfer the second surface, and then fixed by the fixing device 9.

In order to realize high-speed recording in this color image forming apparatus, the time to turn on / off the output of the transfer current cannot be kept up when the transfer material is successively conveyed, or Since the high voltage rise time is shortened, very expensive high pressure control is required. Therefore, if the transfer current when continuously transferring a plurality of transfer materials P is configured to keep the output state constant during recording, a stable transfer image can be obtained at low cost. Furthermore, the present invention becomes more effective when applied to a double-sided high speed machine. When performing double-sided image output, 1 on the transfer material carrier that can carry multiple transfer materials.
It is more efficient to mix the first side and the second side. For example, when a plurality of manuscripts are 2 m sheets, O ₁ , O ₃ , O ₅ , and O _2m-1 , and these are copied and output on m sheets of copy paper, C ₁ , C ₂ , ..., C _m. think of. Here, the high-speed color copying machine shown in FIG.
It can be carried. At this time, the originals O ₁ , O ₃ , O ₅ , ...
..O _{2 m -1} minute, image formation is _{first performed on} the first surface P ₁ , P ₂ , ... P _m of the transfer paper C ₁ ... C _m , and then the original O ₂ ,
When outputting O ₄ , O ₆ , ... O _2m to the second side P ₁ ′, P ₂ ′, ... P _m ′ of the copy paper C ₁・ ・ ・ C _m , it is placed in the intermediate tray 65. Since P _m is recorded by feeding from the lower side of the accumulated copy paper that has been output to the first side, the P ₁ ′, P ₂ ′, ... Are recorded immediately after the fed C _m. Therefore, by feeding the copy sheets C ₁ , C ₂ , ..., Efficient recording and output can be achieved. Alternatively, first, C ₁ , C ₂ and C ₃ are fed, the originals O ₁ , O ₃ and O ₅ corresponding to P ₁ , P ₂ and P ₃ are copied and output, and then the copy is returned to the intermediate tray 65. Paper C ₁ is fed, O ₂ corresponding to P ₁ ′ is copied, then C ₄ is fed for copying O ₇ (P ₄ ), and thereafter C ₂ (P ₂ ′) and C ₅ are alternately printed. (P ₅ ), C ₃ (P ₃ ′), C
By recording ₆ (P ₆ ), ..., Normally, the same number of originals can be output at substantially the same speed as continuous recording of the first side.

As described above, at the time of double-sided recording, it is possible to carry out double-sided recording more efficiently by carrying the first side and the second side in a mixed manner on the copying material carrier. However, the present invention is not necessarily limited to the above two examples. In order to make the best use of such characteristics of the high-speed machine, for example, when performing continuous double-sided copying of one side of a plurality of different originals, the image of the first original is transferred to the first side of the transfer material. After that, when the second image of the original is transferred to the second surface of the first transfer material, the image is fed from the intermediate tray 65 to the recording material carrier 130. On the other hand, almost simultaneously with this, the image of the third sheet of the document is transferred to the first surface of the transfer material of the second sheet.
The first transfer material is supplied from the paper feed cassette 10 to the recording material carrier 13
Transported to 0. At this time, the first transfer material for transferring the image on the second surface and the second transfer material for transferring the image on the first surface are sequentially carried on the transfer material carrying member 130, and the transfer material carrying member 130 An appropriate interval is provided between the rear end of the first transfer material and the front end of the second transfer material. According to this embodiment, the power source is the transfer charging member 2 on the first and second sides of the transfer material.
Since the transfer currents applied to 4a, 24b, 24c, and 24d are the same, the transfer charging member is composed of the first transfer material for image transfer on the second surface and the second transfer material for image transfer on the first surface. The transfer currents applied to 24a, 24b, 24c, and 24d are the same. Since it is not necessary to switch the transfer current as described above, it is possible to reduce the distance between the rear end of the first transfer material and the front end of the second transfer material on the transfer material carrier 130. Therefore, when images are continuously formed on both surfaces of a plurality of transfer materials, the image forming speed can be increased and the productivity can be improved.

Further, as described above, the transfer material for transferring the first surface and the transfer material for transferring the second surface can be simultaneously carried on the recording material carrier so that the transfer currents on the first and second surfaces are constant. This can be applied to the automatic double-sided image forming apparatus configured to be able to carry a plurality of sheets on the transfer material carrier as shown in FIG. 4, and the same effect can be obtained. In that case, it is more effective to set the same transfer control conditions for the toner images of the respective colors.

In the apparatus shown in FIGS. 4 and 7, a transfer path is provided for automatically transferring the image to one surface of the transfer material and then automatically transferring it to the transfer position for transferring the image to the second surface of the transfer material. There is. However, after this image is transferred onto one surface of the transfer material without providing this conveyance path, the transfer material is once discharged to a paper discharge tray, and the operator puts the second surface of the transfer material face up in the paper feed cassette and the second surface. Image transfer may be performed.

[0066]

According to the present invention, it is possible to easily control the transfer of the second surface of the transfer material, and the good transfer can be performed regardless of the change in the resistance value of the transfer material due to the difference in oil adhesion of the transfer material. I was able to do it.

Further, the transfer conditions for the first surface and the second surface of the transfer material can be kept unchanged, and the image forming speed on both surfaces of the transfer material can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a transfer charging member and a transfer drum in a first embodiment of an image forming apparatus of the present invention.

FIG. 2 is a cross-sectional view showing a transfer charging member and a transfer drum in a second embodiment of the image forming apparatus of the invention.

FIG. 3 is a cross-sectional view showing a transfer charging member and a transfer drum in a third embodiment of the image forming apparatus of the invention.

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

FIG. 5 is a perspective view of a transfer drum.

FIG. 6 is a graph showing the relationship between the output current and the output voltage of the transfer power supply.

FIG. 7 is an overall configuration diagram showing another embodiment of the image forming apparatus of the present invention.

[Explanation of symbols]

 3 Photosensitive Drum 6 Transfer Drum 6'Dielectric Sheet 21 Conductive Roller 22 Conductive Brush 23 Conductive Fur Brush 30 Transfer Power Source

Claims (28)

[Claims] 1. An image carrier capable of carrying a toner image, a dielectric transfer material carrier carrying a transfer material, and a transfer of the toner image on the image carrier carried by the transfer material carrier. An image forming apparatus comprising: a transfer member that can be contacted with the back side of the transfer material carrier for transferring to a material; and a constant current control unit that applies a predetermined current to the transfer member to control the constant current. The apparatus is capable of performing image transfer to the second surface of the transfer material opposite to the first surface after performing the image transfer to the first surface of the transfer material. An image forming apparatus, wherein the current control means applies a predetermined current to the transfer member. 2. The image forming apparatus according to claim 1, wherein the constant current control means applies a predetermined current to the transfer member during image transfer on the two surfaces of the transfer material. 3. The image forming apparatus according to claim 2, wherein the constant current value given to the transfer member during image transfer of the first surface and the second surface of the transfer material is the same. 4. A toner image of a first color and a toner image of a second color can be formed on the image carrier, and the toner image of the first color and the toner image of the second color are transfer materials. 4. The predetermined currents given to the transfer member by the constant current control means when superposed and transferred on the second surface are the same.
Image forming device. 5. The constant current control means applies the same predetermined current to the transfer member when the first color toner image and the second color toner image are superimposed and transferred on the first surface of the transfer material. The image forming apparatus according to claim 4, wherein the image forming apparatus is provided. 6. The apparatus is capable of forming a full color toner image on a transfer material, and the constant current control means transfers the toner image of each color when the image is transferred to the first surface and the second surface of the transfer material. The image forming apparatus according to claim 1, wherein the predetermined currents applied to the members are the same. 7. The apparatus comprises fixing means for fixing a toner image on a transfer material, and the transfer material having the image transferred onto the first surface of the transfer material is subjected to image fixing by the fixing means. 7. The image forming apparatus according to claim 1, wherein the image transfer on the second surface is performed. 8. The image forming apparatus according to claim 7, wherein the fixing unit includes a fixing member that holds and conveys the transfer material, and a unit that applies release oil to the fixing member. 9. The apparatus according to claim 1, further comprising a conveying unit that conveys the transfer material, which has been subjected to the image fixing by the fixing unit, to the transfer material carrying member in order to transfer the image on the second surface. Item 7. The image forming apparatus according to item 7. 10. The transfer material carrier comprises a first transfer material for transferring an image onto the second surface at different positions thereof, and the second transfer material.
10. The image forming apparatus according to claim 1, wherein the second transfer material that transfers the image onto the surface can be simultaneously carried. 11. The image forming apparatus according to claim 10, wherein the constant current control means applies the same predetermined current to the transfer member during image transfer of the first transfer material and the second transfer material. . 12. A toner image of a plurality of colors can be formed on the image carrier, and the constant current is applied when the toner images of the plurality of colors are transferred to the first transfer material and the second transfer material in an overlapping manner. 12. The image forming apparatus according to claim 11, wherein the control means applies the same predetermined current to the transfer member. 13. The transfer member has a volume resistivity of 10 ⁸ Ω.
The image forming apparatus according to any one of claims 1 to 12, wherein the image forming apparatus has a size of not more than cm. 14. The image forming apparatus according to claim 1, wherein the transfer member has a brush shape. 15. The image forming apparatus according to claim 1, wherein the transfer member has a sheet shape or a blade shape. 16. An image carrier capable of carrying a toner image, and a transfer material carrier for carrying and transporting a transfer material to a transfer position, wherein the toner image on the image carrier is carried by the transfer material. In an image forming apparatus for transferring a transfer material carried on a body at the transfer position, the apparatus transfers a second image on a side opposite to the first surface of the transfer material after performing image transfer on the first surface of the transfer material. The image can be transferred onto the surface, and the transfer material carrying member is provided with the second
An image forming apparatus capable of simultaneously carrying a first transfer material that transfers an image onto a surface and a second transfer material that transfers an image onto the second surface. 17. The apparatus according to claim 16, further comprising a transfer member that applies an electric charge to the transfer material carrier to transfer the toner image to the transfer material carried on the transfer material carrier. Image forming device. 18. The apparatus has a constant current control means for applying a predetermined current to the transfer member to control a constant current, the constant current control means during the image transfer of the first transfer material and the second transfer material. 18. The image forming apparatus according to claim 17, wherein the predetermined currents applied to the transfer members are the same. 19. A toner image of a plurality of colors can be formed on the image carrier, and the constant current is applied when the toner images of the plurality of colors are transferred onto the first transfer material and the second transfer material in an overlapping manner. 19. The image forming apparatus according to claim 18, wherein the control means applies the same predetermined current to the transfer member. 20. The transfer member is capable of contacting the back side of the transfer material carrier.
9. Image forming apparatus. 21. The apparatus has a fixing means for fixing the toner image on the transfer material, and the transfer material having the image transferred to the first surface of the transfer material is subjected to image fixing by the fixing means. 21. The image forming apparatus according to claim 16, wherein the image transfer on the second surface is performed. 22. The image forming apparatus according to claim 21, wherein the fixing unit includes a fixing member that holds and conveys the transfer material, and a unit that applies release oil to the fixing member. 23. The apparatus according to claim 1, further comprising a transporting unit that transports the transfer material, which has been subjected to the image fixing by the fixing unit, to the transfer material carrying member in order to transfer the image on the second surface. Item 21. The image forming apparatus according to item 21. 24. The transfer member has a volume resistivity of 10 ⁸ Ω.
21. The image forming apparatus according to claim 17, wherein the image forming apparatus has a size of not more than cm. 25. The image forming apparatus according to claim 16, wherein the transfer member has a brush shape. 26. The image forming apparatus according to claim 16, wherein the transfer member has a sheet shape or a blade shape. 27. The image forming apparatus according to claim 16, wherein toner images of a plurality of colors are superimposed and transferred onto the first transfer material and the second transfer material carried by the transfer material carrier. 28. The image forming apparatus according to claim 27, wherein the apparatus is capable of forming a full-color toner image on the first transfer material and the second transfer material.