JPH03192279A - Image forming device - Google Patents

Abstract

PURPOSE:To hold a transfer charge even when humidity is high and to obtain a good image by constituting rollers on which a transfer belt is extended of conductive rollers and directly grounding the conductive rollers by a switching relay or grounding the rollers through a potential holding means. CONSTITUTION:The transfer belt 5 is constituted of a semiconductor belt having a volume resistivity nearly equal to that of the transfer sheet S, and also the rollers 9a, 9b, 11, 12, 13a, 13b, 16 and 17 on which the transfer belt 5 is extended are constituted of the conductive rollers, and the conductive rollers 9a, 9b, 11, 12, 13a, 13b, 16 and 17 are directly grounded by the switching relay 26, or grounded through the potential holding means 27. Thus, by grounding the conductive rollers 9a, 9b, 11, 12, 13a, 13b, 16 and 17 on which the transfer belt 5 is extended by the switching relay 26b through the potential holding means 27 in such a way, the transfer charge can be held even when the humidity is high, so that the good image can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image forming apparatus, and particularly to an image forming apparatus using a transfer belt.

(Prior Art) Image forming apparatuses have heretofore been known in which a toner image formed on a photoconductor is primarily transferred onto a transfer belt, and the toner image on the transfer belt is secondarily transferred onto transfer paper. ing. The transfer belt used is a dielectric type in which a thin dielectric layer with a high volume resistance is formed on the surface of a conductive layer with a low volume resistance as much as possible, and a belt charger is used on this transfer belt. It is configured to perform primary transfer by applying a charge.

However, in the case of using the above-mentioned dielectric type transfer belt, there is a limit to the amount of charge in order to prevent abnormal discharge between the belt and the photoconductor, and the amount of toner that can be absorbed is limited, so it is difficult to form a full-color toner image. There is a problem in some cases.

Therefore, a semiconductor type transfer belt is used, which has a volume resistivity between that of a dielectric layer and a conductive layer, and has a volume resistivity that is approximately the same as that of transfer paper. An image forming apparatus that transfers images has previously been proposed.

Further, there is also known an image forming apparatus in which a transfer paper is supported and conveyed on a semiconductor type transfer bell I similar to the above, and a toner image is transferred from a photoreceptor onto the transfer paper by a transfer charger. There is.

(Problem to be Solved by the Invention) By the way, when a semiconductor type transfer belt as described above is used, as shown in FIG. 3, its volume resistivity changes depending on the humidity, and the volume resistivity decreases at high temperatures. do. In FIG. 3, HH indicates the volume resistance with respect to the applied voltage at high humidity, LL at low humidity, and NN at intermediate times. When the volume resistivity is lower than about 109 Ω-cm, transfer becomes difficult in practice, and even if the volume resistivity does not decrease to that extent, the necessary transfer charge cannot be maintained in high humidity, resulting in insufficient image density. There was a problem.

SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, it is an object of the present invention to provide an image forming apparatus that uses a semiconductor type transfer belt and can perform reliable transfer even in high humidity.

(Means for Solving the Problems) In order to achieve the above object, the image forming apparatus of the present invention transfers a toner image formed on a photoreceptor onto a transfer belt or onto a transfer material supported thereon. In the image forming apparatus, the transfer belt is composed of a semiconductor belt having a volume resistance approximately equal to that of the transfer paper, and the roller around which the transfer belt is wound is composed of a conductive roller, and these conductive rollers are switched. It is characterized in that it is grounded directly by a relay or via a potential maintaining means.

(Function) According to the above structure of the present invention, the transfer charge can be maintained even at high temperatures by grounding the conductive roller around which the transfer belt is wrapped by the switching relay via the potential maintaining means at high temperatures. You can get a good image.

(Example) An example of the present invention will be described below with reference to FIGS. 1 and 2.

In FIG. 1, reference numeral 1 denotes a photosensitive drum, around which a charger 2, an exposure section 3 using an optical system (not shown), a developing section 4, a transfer belt 5, a drum cleaner 6, and an eraser 7 are arranged in the rotational direction. has been done. The developing section 4 includes:
A yellow developer 4Y, a magenta developer 4M, a cyan developer 4C, and a black developer 4B are installed. Further, each developing device is equipped with a developing sleeve, a grain cutting shutter, a toner concentration detector, a toner replenishing device, and the like.

The transfer belt 5 is made of a flexible semiconductor with good environmental resistance, for example, a volume resistivity of 1×10 I0 to 1×10 13 Ω−.
1 x 109 on the surface of a polyurethane rubber belt of about cm
It is composed of an endless heald with a thickness of about 600 μm and a surface coating layer of 10 to 30 μm thick formed by coating a fluorine-based paint with a thickness of about 1×10 12 Ω-cm. The semiconductor belt constituting the transfer belt 5 may have a volume resistivity of 100 to 10'5 Ω-cm. On the inner periphery of the transfer belt 5, there is a primary transfer charger 8 that transfers the toner image from the photoreceptor drum 1 to the transfer belt 5 along the direction of movement, and a primary transfer charger 8 disposed on both sides of the primary transfer charger 8 that transfers the toner image from the photoreceptor drum 1 to the transfer belt 5 along the moving direction. A pair of pressing rollers 9 that press against 1
a, 9b, a drive roller 10, a tension roller 11, a guide roller 12 arranged at the junction with the paper passing path of the transfer belt 5, a conductive belt 14 wound around a pair of rollers 13a and 13b, and a transfer belt 5. A backup roller 16 for the belt cleaner 15 that comes into contact with the surface of the belt cleaner 15 to scrape off residual toner, and a guide roller 17 that is disposed at an appropriate position between the belt cleaner 15 and the pressing roller 9a are provided. The conductive belt 1 is placed around the outer periphery of the transfer belt 5.
A secondary transfer charger 18 and a separation charger 19 are arranged opposite to the transfer charger 4 .

20 is a paper feed cassette, 2L22 is a paper feed roller and a separating plate that takes out the transfer paper S one by one from the paper feed cassette 20 and supplies it to the secondary transfer position between the transfer belt 5 and the secondary transfer charger 18; Registration rollers that feed the transfer paper S to the secondary transfer position in a timely manner; 24 is a transfer paper conveyance belt that transports the transfer paper S after the secondary transfer toward the fixing unit 25; 25a is a fixing unit with a built-in heater; The roller 25b is a pressure roller that presses the transfer paper S against the fixing roller.

A pair of pressing rollers 9 a 19 b contacting the back surface of the transfer belt 5, a tension roller 11, a guide roller 12, at least one of the pair of rollers 13a and 13b around which the conductive belt 14 is wound, and a backup roller. The roller 16 and guide roller 17 are the switching relay 2
One contact 26a of this switching relay 26 is directly grounded, and the other contact 26b is electrically connected to 109 to 6.
It is grounded via a 10"Ω resistor 27. Also, a humidity sensor 28 is placed at an appropriate location inside the aircraft to detect the humidity inside the aircraft, and its detection signal is output as shown in Figure 2. The signal is input to the CPU 29 which controls the entire image forming apparatus, and the CPU 29 is configured to perform switching control of the switching relay 26.

Note that the drive roller IO is made of an insulator.

Next, the operation will be explained.

First, an overview of the process of forming a monochrome image will be explained. The photosensitive drum 1 is charged by a charging charger 2 and exposed by an exposure section 3 using an optical system (not shown) to form an electrostatic latent image. This latent image is developed with toner in the developing section 4. The developing devices used at this time are yellow developing device 4Y,
Any one of the magenta developer 4M, the cyan developer 4C, and the black developer 4B is selected. The toner image on the photosensitive drum 1 is transferred onto the transfer belt 5 by a primary transfer charger 8. Thereafter, the photosensitive drum 1 is cleaned by a drum cleaner 6, residual potential is removed by an eraser 7, and the same process is repeated again.

The toner image transferred to the transfer belt 5 is transferred to the transfer paper S which is sent in synchronization with the toner image by the secondary transfer charger 18.
The image is transferred to the fixing unit 25, fixed by the fixing unit 25, and then discharged. The transfer belt 5 after the secondary transfer is cleaned by the belt cleaner 15, and the same process is repeated again.

Next, an overview of the process of forming a full-color image will be explained. Through the same process as for monochrome images,
A yellow toner image is formed on the photosensitive drum l and transferred onto the transfer heald 5.

Then, while being supported on the transfer belt 5, it goes around once again and returns to the primary transfer position. At this time, paper is not fed and 2
The next transfer charger 18 and the separation charger 19 are not operated, and the belt cleaner 15 is also retracted from the transfer belt 5.

A magenta toner image is formed on the photosensitive drum 1 in synchronization with the yellow toner image on the transfer belt 5, and is transferred onto the transfer belt 5 in an overlapping manner.

Similarly, a cyan toner image and a black toner image are transferred onto the transfer belt 5 in an overlapping manner, and a full-color toner image is formed on the transfer belt 5, which is transferred onto the transfer paper S by the secondary transfer charger 18 and fixed. and discharged. Further, residual toner that has not been transferred to the transfer paper S is cleaned by a belt cleaner 15.

In the case of two colors or three colors, an image is formed by the same operation.

In the above-described image forming process, when the humidity is low, the primary transfer in which the toner image is transferred from the photoreceptor drum 1 onto the transfer belt 5, and the transfer from the transfer belt 5 to the transfer paper S
The secondary transfer to is performed with the switching relay 26 connected to the contact 26a and directly grounded.

On the other hand, when the humidity is high, the switching relay 26 is switched to the other contact 26b based on a detection signal from the humidity sensor 28 and grounded via the resistor 27. As a result, even if the volume resistance of the transfer belt 5 decreases at high temperatures, the transfer charge applied by the primary transfer charger 8 does not escape and remains on the transfer belt 5, preventing deterioration of transfer performance and producing a good image. can be obtained. Note that during secondary transfer, it is better that no charge remains on the transfer belt 5, so the switching relay 2
6 is preferably switched back to contact 26a for direct grounding.

Further, in this embodiment, since the conductive belt 14 grounded is arranged on the back side of the transfer heald 5 at the secondary transfer position, this conductive belt 14 serves as the opposing electrode of the transfer charger 18 and the separation charger 19. functions and ensures high transfer efficiency.

In the above embodiment, the transfer belt 5 is grounded through the resistor 27 at high temperatures, but a constant voltage element of 500 V to 100 OV may be used in place of the resistor 27. It is also possible to use means for applying a voltage of . In these cases, it is necessary to switch to direct grounding during secondary transfer.

Further, in the above embodiment, the switching relay 26 is switched based on the detection signal from the humidity sensor 28, but instead of the humidity sensor, a pair of detection rollers that contact both the front and back surfaces of the transfer belt 5 are provided. The volume resistance of the transfer belt 5 may be detected from the resistance between them, and the switching relay 26 may be switched based on the detection signal. Alternatively, the switching relay 26 may be switched.

Furthermore, in the above embodiments, the toner image on the photosensitive drum 1 is first transferred to the transfer belt 5, and then secondarily transferred from this transfer belt 5 onto the transfer paper S. Even in an image forming apparatus in which a transfer paper S is supported on the transfer paper S and a toner image is transferred from the photoreceptor drum 1 onto the transfer paper S, the electrical potential of the conductive roller around which the transfer belt is wound is maintained at high temperatures. By grounding through a means, the transferred charge can be maintained even in high humidity and a good image can be obtained.

(Effects of the Invention) According to the image forming apparatus of the present invention, as is clear from the above description, the conductive roller around which the transfer belt is wound is grounded by the switching relay via the potential maintaining means when the temperature is high. , the transfer charge can be maintained even at high temperatures, and an image of good quality can be obtained.

[Brief explanation of drawings]

1 and 2 show an embodiment of the image forming apparatus of the present invention, FIG. 1 is an overall schematic configuration diagram omitting the optical system, and FIG.
The figure is a block diagram of the control section of the switching relay, and FIG. 3 is a characteristic diagram of changes in volume resistance with respect to applied voltage with humidity as a parameter. 1・・・・・・・・・−・・−−1−−・・・−・・Photosensitive drum 5−・・−・・−・・・・・・・・・−・・・
Transfer belts 9a, 9b--Press roller 11--Tension roller 12.17--Guide roller 1
3a, 13b-Roller 14--...------- Conductive belt 16------------------
-Backup roller 26---------1...
−・・−Switching relay 27−・−・−・−・・・・・
−・・Resistance S・・・・・・−・−・−・−・・・・・・・
...-Transfer paper Figure 1

Claims (1)

[Claims] (1) In an image forming apparatus that transfers a toner image formed on a photoreceptor onto a transfer belt or onto a transfer material supported on the transfer belt, the transfer belt is a semiconductor having a volume resistance approximately equal to that of the transfer paper. The transfer belt is constructed of a belt, and the roller around which the transfer belt is wound is constructed of conductive rollers, and these conductive rollers are grounded directly by a switching relay or via a potential maintaining means. Image forming device.