JP2711903B2 - Image forming device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as an electrophotographic copying machine, and more particularly to an improvement in a transfer apparatus in a color image forming apparatus.

2. Description of the Related Art Conventionally, when copying images of a plurality of colors, a multiple transfer method using a transfer drum in which a high-resistance film (transfer material carrying sheet) is wound around a drum-shaped frame is used. The fed transfer material is gripped by a gripper 151 provided on a part of the peripheral surface of the transfer drum 150 as shown in FIG. 14, for example. Such a gripper-based transfer drum is disclosed, for example, in Japanese Patent Application Laid-Open No. 61-150354. Means for applying a charge to the transfer material carrying sheet and the transfer material without using a gripper, and means for electrostatically adsorbing the transfer material to the transfer material carrying sheet and transporting the transfer material are also disclosed in, for example, 32079
No. 6,086,045. The transfer device in the image forming apparatus shown in FIG. 15 is this example. Of course, there are cases where the electrostatic attraction means is provided by a gripper system.

In FIG. 15, reference numeral 51 denotes an adsorption charger of the transfer device 30,
An electric charge is applied to the transfer material carrying sheet 34 from the inside using the adsorption charger 51, and the charge
The transfer roller P is provided with a charge having a polarity opposite to that of the suction charger 51 by using the conductive roller 52 facing the transfer roller 51. Conductive roller 52
Is grounded and is also used as a counter electrode of the adsorption charger 51. The transfer material P is electrostatically attracted to the transfer material carrying sheet 34, and is conveyed to the transfer area, whereupon the toner image on the photosensitive drum 1 is transferred.

In order to obtain a color image, so-called multiple transfer in which a transfer process is repeated is performed, and the transfer material P is transferred to a transfer material carrying sheet.
As a pretreatment for separation from the AC power, the AC neutralization is performed by a pair of neutralizing corona dischargers (pair chargers) 16 to neutralize the electric charge and weaken the electrostatic attraction force. A push-up member 53 is operated to separate the leading end of the transfer material provided on a part of the transfer drum frame from the transfer material carrying sheet 34, and the separating claw 42 is moved between the transfer material P and the transfer material carrying sheet 34. Insertion completes the separation. The transfer material P is conveyed to the fixing device 18, discharged after fixing, and copying is completed.

Problems to be Solved by the Invention However, in the above conventional example, the image quality is deteriorated due to a change in transfer efficiency due to a change in environment or the type of transfer material, or a charge-up of the transfer material carrying sheet or the like. Further, there is a disadvantage that the charge efficiency of the transfer material carrying sheet at the time of continuous copying lowers the transfer efficiency every time the toner of each color is transferred, thereby deteriorating the image quality.

Means for detecting a change in the environment or the type of the transfer material may be used, but such a method has a disadvantage that the cost is significantly increased.

Accordingly, an object of the present invention is to prevent the transfer efficiency from being changed every time toner of each color is transferred and the image quality from deteriorating due to a change in environment, the type of transfer material, or by continuous copying, and to stabilize a high-quality image. An object of the present invention is to provide an image forming apparatus that can be obtained by performing the above steps.

Means for Solving the Problems The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides an image carrier capable of carrying a toner image of a plurality of colors, a transfer material carrier carrying a transfer material, and applying a charge to the transfer material carrier so that the transfer material carries the transfer material. An adsorbing and charging means for adsorbing to the body, a contact member provided to face the adsorbing and charging means via the transfer material carrier, and capable of contacting the transfer material carrier, and the plurality of colors on the image carrier. Transfer charging means for sequentially superimposingly transferring the toner image onto the transfer material carried on the transfer material carrier, and when the transfer material passes between the suction charging means and the contact member, the suction charging means and And a current detection unit for detecting a current flowing between the contact member and the contact member, based on the current detected by the detection unit,
A first output of the transfer charging unit when transferring the first color toner to the transfer material, and a second output of the transfer charging unit when transferring the second color toner to the transfer material. An image forming apparatus comprising a control unit for making a difference variable.

According to another aspect of the present invention, an image carrier that can carry a plurality of color toner images, a transfer material carrier that carries a transfer material,
An adsorbing and charging unit for applying a charge to the transfer material carrier and adsorbing the transfer material to the transfer material carrier; and an opposing charging device provided with the transfer material carrier via the transfer material carrier. A contact member capable of contacting a body, a transfer charging unit for sequentially superimposingly transferring the plurality of color toner images on the image carrier onto a transfer material carried on the transfer material carrier, and An image forming apparatus, comprising: a voltage detecting unit that detects a voltage between the attraction charging unit and the contact member when the transfer material passes between the member and the transfer material; On the basis of,
A first output of the transfer charging unit when transferring the first color toner to the transfer material, and a second output of the transfer charging unit when transferring the second color toner to the transfer material. There is provided an image forming apparatus having control means for making the difference variable.

Next, an image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

Embodiment 1 FIG. 1 shows an embodiment in which the image forming apparatus according to the present invention is embodied in a color electrophotographic apparatus. In the present embodiment, an image carrier rotatably supported and rotated in the direction of the arrow,
That is, the electrophotographic photosensitive drum 1 is uniformly charged by the primary charger 2, and is irradiated with a light image 3 corresponding to image information by exposure means such as a laser beam exposure device or the like. A latent image is formed. The electrostatic latent image is visualized as a toner image on the photosensitive drum 1 by, for example, the movable developing device 4.

The movable developing device 4 includes four developing devices 4M, 4C, 4Y, and 4B that specifically store four color developers of a magenta color developer, a cyan color developer, a yellow color developer, and a black color developer.
And a guide (not shown) that can hold these four developing units and move in the horizontal direction. The movable developing device 4 conveys a desired developing device to a developing position facing the outer peripheral surface of the photosensitive drum 1 and develops an electrostatic latent image on the photosensitive drum 1.

A visible image on the photosensitive drum 1, that is, a toner image, is carried by a transfer device 30, which will be described in detail later, and is conveyed by the transfer device 30 in the direction of the arrow in FIG. Transferred to P. The transfer material P is supplied to the transfer device 30 in synchronization with the image by the registration roller 6a.

The photosensitive drum 1 is subjected to the color image process again after the residual toner on the surface is cleaned by the cleaning device 20.

An embodiment of the transfer device 30 used in the color electrophotographic apparatus of the present invention will be described with reference to FIGS. In the present embodiment, the transfer device 30 includes cylindrical rings 31 and 32 provided at both ends, and a connecting portion that connects the rings 31 and 32.
33. These cylindrical rings 31, 32 and connecting portion 33
Constitutes a transfer material carrier made of a derivative film, that is, a drum frame for winding the transfer material carrier sheet. The transfer device 30 further has a separating unit 40. The separation means 40,
Separation claw support 41 provided along the axial direction of the transfer drum 30D, and a plurality of peeling members fixed to the support 41,
In the present embodiment, there are provided three separation claws 42, and a separation outer pressing roller for the purpose to be described later is provided at the tip of the separation claw 42.
42a is provided integrally. At both ends of the support 41, as shown in FIGS. 2 and 4, abutting rollers 45, 46 are provided via appropriate support plates 43, 44. The abutting rollers 45 and 46 are provided with a separation claw operation clutch (not shown).
When the is operated, it comes into contact with the cylindrical rings 31, 32 of the transfer drum 30D and guide grooves 35, 36 formed in the rings 31, 32.
To rotate the tip of the separation claw 42 downward, that is, in the normal direction of the transfer drum 30D.

A notch 37 is formed in the connecting portion 33 so that the separation claw 42 can be easily inserted between the transfer material carrying sheet 34 and the transfer material P adsorbed and carried by the transfer material carrying sheet 34. As shown in FIGS. 1 and 5, the leading end of the transfer material carrying sheet 34 has a cut 34a along the notch 37 of the connecting portion 33 up to the transfer material non-image area. 34 (the hatched portion in FIG. 5) is fixed to the connecting portion 33 so that the curvature becomes locally large.

Further, the transfer device 30 will be described. In the present embodiment, the transfer device 30 includes a transfer material suction unit 50 for sucking and holding the transfer material P fed to the transfer device 30 on the transfer material carrying sheet 34. . As shown in FIG. 1, the transfer material adsorbing means 50 is provided inside the transfer drum 30D, and applies a charge having a polarity opposite to that of the toner image on the photosensitive drum 1 to the back surface of the transfer material carrying sheet 34. It has an adsorption charging means, that is, an adsorption corona charger 51, and a conductive roller 52 provided outside the transfer drum 30D. The contact member, that is, the conductive roller 52, is grounded via the current detecting means 80, and becomes a counter electrode of the suction corona charger 51 and a voltage applied to the transfer material to the suction corona charger. Has the function of applying a charge of the opposite polarity and electrostatically adsorbing the transfer material P to the transfer material carrying sheet 34.

The transfer material P adsorbed by the transfer device 30 is transferred to the transfer charger 15.
Is transferred to the transfer area where the toner image of the first color, for example, the magenta toner image on the photosensitive drum 1 is
In order to transfer to the transfer material P of the sheet, a charge of the opposite polarity to the toner is transferred to the back surface of the transfer material carrying sheet 34 by transfer charging means, that is,
It is given by using a corona charger 15 for transfer. Subsequently, the same latent image is formed on the photosensitive drum 1 again, developed with the first color toner, and the first color toner image is similarly transferred to the second transfer material. By the time the first transfer material reaches the position of the conductive roller 52 for the second time, the conductive roller 52 is released, and a position where the toner image transferred onto the transfer material P is not disturbed, for example, from the transfer material carrying sheet 34 Separated outward by more than 2mm.

Next, a second image on the photosensitive drum 1 formed in synchronization with the first transfer material on which the first color toner image has been transferred is formed.
The toner image of the second color is transferred onto the first transfer material P using the corona charger 15 for transfer, and the toner image of the second color is also transferred to the second transfer material on which the toner image of the first color has been transferred. Is transferred. Thereafter, similarly, toner images of four colors are respectively transferred to the two transfer materials P.

According to the present invention, the transfer current value is determined as follows, and the magnitude transfer current is supplied to the transfer charger 15.

 An example of determining the transfer current value will be described below.

In the case of plain paper and OHP, FIG. 6 shows a current value (adsorption charging current value) flowing through the adsorption corona charger 51 and a current value (adsorption inflow current value) flowing into the transfer material P from the conductive roller 52.
The relationship was shown. The solid line is for plain paper and the broken line is for OHP. From this, it can be seen that when the adsorption charging current value is constant, the adsorption inflow current value changes depending on the type of the transfer material.

FIG. 7 is a graph showing an example of a relationship between a transfer current value when a fixed amount of toner image is formed on the photosensitive drum 1 and a density (reflection density) of the toner image transferred onto the transfer material P. is there. From this, depending on the type of the transfer material, an area having a high density, that is, an appropriate transfer current value area having a high transfer efficiency (in FIG. 7,
This is the area indicated by the arrow. If the solid line is plain paper,
OHP) is different.

Therefore, for example, when the adsorption charging current value is 200 μA, the current detection means 80 detects the adsorption inflow current value, the detected value is taken into the CPU 100, and the CPU 100 transfers the detected value through the transfer constant current source 90, for example. As shown in Table 1, the transfer current value is switched at the boundary of the adsorption inflow current value of 6.5 μA. That is, in the present embodiment, when the attracting current value is 6.5 μA or more, the transfer current value of the second color is increased by 30 μA with respect to the transfer current value of the first color. The transfer current value of the fourth color is increased by 30 μA with respect to the transfer current values of the second color and the third color, respectively. When the adsorption current value is 6.5 μA or less, the transfer current value of the second color is
The transfer current value of the first color is increased by 50 μA, and the transfer current values of the third and fourth colors are respectively increased by 80 μA and 120 μA with respect to the transfer current values of the second and third colors.

Referring to FIG. 1, the transfer device 30 includes a pair of AC coronas opposed to each other with a transfer material carrying sheet 34 interposed therebetween in order to weaken the attraction force of the transfer material to the transfer material carrying sheet after the transfer process. The discharger 16 is provided, and the transfer material P and the transfer material carrying sheet 34 are discharged.

When the transfer is completed as described above, in order to separate the first transfer material P from the transfer material carrying sheet 34, as shown in FIGS.
45, 46 are actuated by a separating claw operating clutch (not shown), abut against the cylindrical rings 31, 32 of the transfer drum 30D, and are guided by guide grooves 35, 36 formed in the rings 31, 32. . As a result, the tip of the separation claw 42 is rotated downward, that is, in the direction of the normal to the transfer drum 30D toward the transfer material carrying sheet 34, and the separation outer pressing roller 42a is driven integrally with the separation claw 42. Is pressed against the transfer material carrying sheet. Further, the outer separation pressing roller 42a moves along the notch 37 of the connecting portion 33, and when the curvature of the transfer material carrying sheet 34 is locally changed, the leading end of the transfer material and the transfer material carrying sheet 34 The transfer material P is separated from the transfer material carrying sheet 34.

When the transfer material P is separated, it is preferable to perform an AC corona discharge using a corona discharger 54 in order to prevent image disturbance due to peeling discharge generated when the transfer material P and the transfer material carrying sheet 34 are separated.

After the transfer and separation steps, the transfer material P is conveyed to the fixing device 18 and is heated, whereby the toner is mixed and fixed, and the paper is discharged to complete image formation.

Embodiment 2 FIG. 8 shows a configuration example of an image forming apparatus according to the present embodiment.

As shown in FIG. 8, in this embodiment, a DC constant current source 85 is provided between the conductive roller 52 of the transfer device 30 and the ground in the image forming apparatus, and a voltage detecting means 86 is provided. In FIG. 8, the same reference numerals as those in FIG. 1 indicate the same members.

Current value to be applied to the adsorption corona charger (adsorption charging current value)
FIG. 9 shows the relationship between the voltage detected by the voltage detecting means 86 and the environmental change, particularly the relative humidity change, when the current value flowing from the conductive roller 52 into the transfer material P is 10 μA. It can be seen that the adsorption inflow current is less likely to flow without lowering the relative humidity.

FIG. 10 shows the relationship between the transfer current value when a fixed amount of toner image is formed on the photosensitive drum 1 and the density (reflection density) of the toner image transferred onto the transfer material P, when the relative humidity is 15% and 50%. %, 80
% (The broken line is 80%, the solid line is 50%, and the alternate long and short dash line is 15%). Thus, it can be seen that the appropriate range of the transfer current value changes according to the relative humidity. Relative humidity
The appropriate ranges of 80%, 50%, and 15% are indicated by broken lines, solid lines, and dashed-dotted arrows.

Therefore, depending on the value detected by the voltage detecting means 86, as shown in Table 2, for example, less than 1.4 KV (A region), 1.4 KV or more and less than 2.0 KV (B region), or 2.0 KV or more (C
In each case, the transfer current value to the transfer charger 15 is switched by the CPU 100 via the transfer constant current power supply 90. That is, in this embodiment, when the conductive roller applied voltage value is less than 1.4 KV, the transfer current values of the first to fourth colors are the same, and the conductive roller applied voltage value is 1.4 KV or more and less than 2.0 KV. In this case, the transfer current value of the second color is increased by 30 μA with respect to the transfer current value of the first color.
The transfer current value of the color is increased by 30 μA with respect to the transfer current values of the second color and the third color, respectively. When the applied voltage value of the conductive roller is 2.0 KV or more, the transfer current value of the second color becomes Is increased by 50 μA with respect to the transfer current value of the first color,
Similarly, the transfer current values of the third and fourth colors are increased by 50 μA with respect to the transfer current values of the second and third colors, respectively.

Embodiment 3 In this embodiment, a case of continuous copying will be described.

This embodiment is possible with the configuration of the second embodiment, but the same configuration as the first embodiment, that is, the current detection means 80 is provided between the conductive roller 52 and the ground.

A pair of corona dischargers for static elimination shown in FIG. 1 during continuous copying
If the static elimination capability of 16 is low, the transfer material carrying sheet 34 (see FIG. 2) charges up. This tendency is remarkable in a low humidity environment.

The tendency is remarkable in a low humidity environment.

In FIG. 11, for example, the relative humidity 15%, the transfer material carrying sheet 34
AC voltage is applied to the discharger (inner static eliminator) 16
The DC constant current is superimposed on Vpp = 12.0 KV so that the DC difference current becomes −100 μA. The discharger (external static eliminator) 16 disposed outside the transfer material carrying sheet 34 has an internal static neutralizer 16. When Vpp = 10.0 KV is applied with the phase shifted by π from the applied AC voltage,
The relationship between the number of continuous copies and the suction inflow current value measured by the current detection means 80 is shown.

FIG. 12 shows the change in density when the transfer current value was fixed at, for example, 150 μA when a certain amount of toner image was formed on the photoconductor at that time.

Thus, the suction inflow current value changes according to the number of copies during continuous copying, and the density decreases.

Therefore, at the time of continuous copying, for example, as shown in FIG. 13, the transfer current is changed in accordance with the difference between the suction inflow current value flowing into the transfer material and the suction inflow current value at the time of the first sheet. Here, the solid line is the transfer current of the first color, the broken line is the transfer current of the second color,
The dashed line indicates the transfer current of the third color, and the two-dot chain line indicates the transfer current of the fourth color.

Hereinafter, after the separation and fixing steps are completed, the sheet is discharged, and after the input number of copies is repeated, the copying is completed.

Effect of the Invention As described above, in the image forming apparatus of the present invention, the current flowing between the adsorption charging means for adsorbing the transfer material to the transfer material carrier and the contact member or the current flowing between the adsorption charging means and the contact member Detecting a voltage and, depending on the detected current or voltage, a first
Since the difference between the first output of the transfer charging means at the time of transferring the toner of the second color and the second output of the transfer charging means at the time of transferring the toner of the second color is made variable, the environment may fluctuate or Even if the resistance value of the transfer material fluctuates due to different types of materials,
The output of the transfer charging unit can be properly adjusted each time toner of each color is transferred, and a high-quality image can be stably obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of the image forming apparatus of the present invention. FIG. 2 is a perspective view showing a main part of a transfer device provided in the image forming apparatus of FIG. FIG. 3 is a perspective view showing a guide frame in the transfer device of FIG. FIG. 4 is a side view of the transfer device of FIG. FIG. 5 is a perspective view showing a sheet portion at a connecting portion of a guide frame of a transfer material carrying sheet of the transfer device of FIG. FIG. 6 is a graph showing an example of a relationship between an attraction charging current value and an attraction inflow current value in the transfer device of FIG. FIG. 7 is a graph showing a relationship between a transfer current value and a density of a transferred toner image in the transfer device of FIG. FIG. 8 is a schematic configuration diagram showing another embodiment of the image forming apparatus of the present invention. FIG. 9 is a graph showing the relationship between the relative humidity and the voltage applied to the suction conductive roller when the suction current value is constant in the transfer device provided in the image forming apparatus of FIG. FIG. 10 is a graph showing a relationship between a transfer current value and a density of a transferred toner image in the transfer device. FIG. 11 is a graph showing the relationship between the number of copies and the inflow current value during continuous copying in a transfer device provided in still another embodiment of the image forming apparatus of the present invention. FIG. 12 is a graph showing the relationship between the number of copies and the density of a transferred toner image during continuous copying in the same transfer device. FIG. 13 is a graph showing the relationship between the suction inflow current value and the transfer current value during continuous copying in the same transfer device. FIG. 14 is a perspective view showing a transfer drum in a transfer device provided in a conventional image forming apparatus. FIG. 15 is a schematic configuration diagram showing another conventional image forming apparatus. 1: Photosensitive drum 4: Developing device 15: Transfer charger 16: Discharger 30: Transfer device 51: Adsorption charger 52: Adsorption conductive roller 80: Current detection means 90: Transfer constant current power supply 100: CPU

Claims (2)

(57) [Claims] An image carrier capable of carrying toner images of a plurality of colors; a transfer material carrier for carrying a transfer material; and a charge applied to the transfer material carrier, and the transfer material is transferred to the transfer material carrier. An attraction / charging unit for adsorbing, a contact member provided to face the attraction / charging unit via the transfer material carrier, and capable of contacting the transfer material carrier; and the toner of the plurality of colors on the image carrier. A transfer charging means for sequentially superimposingly transferring an image onto a transfer material carried on the transfer material carrier, and when the transfer material passes between the suction charging means and the contact member, the suction charging means and the contact member And a current detecting means for detecting a current flowing between the first color toner and the first color toner based on the current detected by the detecting means. A first output of the charging means and a toner of a second color; An image forming apparatus comprising: a control unit configured to vary a difference between the transfer output and the second output of the transfer charging unit when transferring the image to a transfer material. 2. An image carrier capable of carrying a toner image of a plurality of colors, a transfer material carrier carrying a transfer material, and applying a charge to the transfer material carrier to transfer the transfer material to the transfer material carrier. An attraction / charging unit for adsorbing, a contact member provided to face the attraction / charging unit via the transfer material carrier, and capable of contacting the transfer material carrier; and the toner of the plurality of colors on the image carrier. A transfer charging means for sequentially superimposingly transferring an image onto a transfer material carried on the transfer material carrier, and when the transfer material passes between the suction charging means and the contact member, the suction charging means and the contact member Voltage detection means for detecting a voltage between
A first output of the transfer charging unit when transferring a first color toner to a transfer material based on the voltage detected by the detection unit; An image forming apparatus comprising: a control unit configured to change a difference between a second output of the transfer charging unit and a second output of the transfer charging unit when transferring toner to a transfer material.