JP2660938B2 - Image forming device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a latent image on an image carrier by an electrophotographic or electrostatic recording method, and developing the latent image into a visible image, that is, a toner image. The present invention relates to an image forming apparatus that obtains an image by transferring the toner image to a transfer material,
The present invention relates to an image forming apparatus of a type in which a transfer material is carried on a transfer material support, and is conveyed to a transfer area to transfer a toner image on an image carrier onto the transfer material.

2. Description of the Related Art Conventionally, various multicolor image forming apparatuses have been proposed and commercially available. FIG. 4 shows an example of a typical color electrophotographic copying machine or printer.

In FIG. 4, a color electrophotographic copying machine forms a latent image on an image carrier 3 which is an electrophotographic photosensitive drum, and develops the latent image into a plurality of development images of, for example, four types of yellow, magenta, cyan and black. Developing units 1Y, 1M, 1C, 1B
A visible image, that is, a color toner image, is formed by the rotary developing device 1 provided with K, and these toner images are transferred to a drum-shaped transfer device 9 disposed close to the surface of the photosensitive drum 3, such as a sheet-like transfer material such as paper. To obtain a color image by superimposing and transferring the color image.

As schematically shown in FIG. 5, as a transfer device 9 used in such a color electrophotographic copying machine, a pair of annular members, in this example, cylindrical members 9a and 9b are arranged concentrically. Both are integrally joined by a connecting member 9c, and further covered with a transfer material support, which is usually formed of a dielectric material such as a polyvinylidene fluoride resin (PVdF) sheet, that is, a transfer sheet 93 over the entire circumference. A transfer drum formed into a cylindrical shape is used.

Further, a gripper 91 is disposed on the outer surface of the connecting member 9c of the transfer drum 9 to grip and transfer the transfer material P supplied in synchronization with the toner image on the photosensitive drum 3 and transfer the transfer material. Each time the toner image of each color is transferred to the transfer material at a transfer position where the transfer drum 10 is located to form a color image, a gripper 91 is opened to separate the transfer material from the transfer drum. The separated transfer material is fed to the fixing unit 17 by the conveying unit 16.

Conventionally, in the transfer drum 9, the transfer sheet 93 is made uniform from the inside of the transfer drum 9 in the vicinity of the transfer charger 10 in order to increase the transfer nip by increasing the transfer efficiency and obtain a clear transfer image. In order to push up the transfer sheet 93 in the direction of the photosensitive drum 3, a pressing member 18 is provided as shown in FIG. The pressing member 18 is formed of an elastic body such as a synthetic resin sheet, and applies an appropriate pressure to the transfer sheet 93.

Problems to be Solved by the Invention However, in the above conventional example, although the pressing member 18 is detachable so that it can be removed as needed,
Since the pressure for pressing the transfer sheet 93 of the pressing member 18 toward the photosensitive drum 3 is constant, in order to increase the transfer efficiency in response to changes in temperature and humidity, particularly changes in humidity, a transfer charger is required. Only the method of controlling the strength or weakness of the ten transfer currents could be taken.

For example, at the time of high temperature and high humidity, the volume resistivity of the transfer material used is reduced to about 1/100 in the case of the transfer paper as compared with that at normal temperature and normal humidity (for example, 23 ° C./60% RH). Also, transfer sheet 9
3 itself also reduces surface resistance due to the absorption of moisture.
Therefore, a small transfer current is sufficient, and a small pressing force of the transfer sheet 93 and the transfer material P against the photosensitive drum 3 is sufficient.

However, in the related art, since the pressing force of the pressing member 18 is fixed, there is a disadvantage that the setting of the pressing member 18 due to long-time use occurs, and transfer stability during long-time use cannot be guaranteed. .

In addition, at low temperature and low humidity, it is necessary to apply a strong current to increase the surface resistance of the transfer material and the transfer sheet. However, even when a strong current is applied, the desired transfer efficiency may not be improved in some cases, and it is necessary to increase the pressing force of the pressing member 18.

Therefore, an object of the present invention is to make it possible to move a pressing member for pressing a transfer material support against an image carrier in accordance with changes in temperature and humidity, to change the pressing force on the image carrier, and to perform conventional transfer. An object of the present invention is to provide an image forming apparatus capable of performing more appropriate transfer, improving transfer efficiency, and always obtaining a high-quality image, as compared with a case where transfer conditions are controlled by current and strength.

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 comprises an image carrier on which a toner image is formed, and a transfer material support for carrying and transporting a transfer material, and transferring the toner image on the image carrier to the transfer material support. In an image forming apparatus for transferring to a material, a pressing member for pressing the transfer material support toward the image carrier, and a pressing member for adjusting a pressing force of the pressing member against the transfer material support, Moving means for moving the image forming apparatus in accordance with a change in the installation environment of the image forming apparatus.

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

The present invention can be suitably implemented in a multicolor electrophotographic copying machine having the rotary developing device described above with reference to FIG.
Therefore, in this embodiment, the image forming apparatus is embodied in the multicolor electrophotographic copying machine shown in FIG. 4, and has the transfer device 9 shown in FIG. It is as follows.

Therefore, the configuration of the multicolor electrophotographic copying machine and the transfer device 9 and the operation thereof will be briefly described below.

In this embodiment, the photosensitive drum 3 constituting the image carrier
Rotates in the direction of the arrow, and a rotary developing device 1 provided with a primary charger 4, developing devices 1Y, 1M, 1C, and 1BK around the photosensitive drum 3, a transfer drum 9 constituting a transfer device, a cleaning device
12 are located.

An image information signal color-separated by a laser optical system including a polygon mirror unit 8 and a laser reflecting mirror 7 is irradiated onto the photosensitive drum 3 to form a latent image on the photosensitive drum 3. The latent image on the photosensitive drum 3 is moved at a developing position facing the photosensitive drum 3 by rotation of the rotary developing device 1.
The image is developed by a predetermined developing device to form a visible toner image.

On the other hand, the transfer material P (hereinafter, referred to as “transfer paper”) in the cassette is sent out of the cassette by a paper feed roller, and the first registration roller pair 19 and the second registration roller pair 6 are fed.
And is sent to the paper feed guide 20. The transfer paper P is timed by the first and second registration rollers 19 and 6, and the leading end is held by the gripper 91 on the transfer drum 9 described with reference to FIG. Material support, that is, polyvinylidene fluoride resin (PVd
F) is held on a transfer sheet 93 made of, for example, F).

The transfer paper P held on the transfer sheet 93 is transferred to the transfer charger 10.
As a result, the toner image on the photosensitive drum 3 is transferred.

The transfer process is repeated for each color, and when the transfer is completed, the gripper 91 is opened and guided by the separation claw 15 to the transporting means 16 while being discharged by the corona chargers 11, 13, and 14. The transfer paper guided to the transport means 16 is fixed by a fixing means 17 having a pair of rollers, and is discharged onto a tray.

The toner image remaining on the photosensitive drum 3 after the transfer process is cleaned by the cleaning device 12, and the photosensitive drum 3 is ready for the next image formation.

According to the present invention, as shown in FIG. 1, the transfer drum 9 extends from the introduction side in the movement direction of the transfer sheet 93 to the downstream side in the movement direction within the discharge width of the transfer charger 10. A pressing member 18 having elasticity is arranged.

As the pressing member 18, an insulating sheet, for example, polyethylene terephthalate commercially available as Mylar (registered trademark) can be used, and the thickness is about 100 μm.
A degree is preferred.

According to the present invention, at the time of high temperature, high humidity,
In FIG. 1, the transfer sheet 93 moves in the lower left direction (the
To the photosensitive drum 1 so that the force of pressing
Also, at low temperature and low humidity, it moves in the upper right direction (b direction),
The transfer sheet 93 is configured to have a strong pressing force against the photosensitive drum 1.

Thus, according to the present invention, the pressing member 18 is attached to the moving means 30, as shown in detail in FIGS.

In this embodiment, the moving means 30 includes a moving table 31 on which the pressing member 18 is fixed, and a fixed table 32 on which the moving table 31 is slidably mounted.
And As shown in FIG. 3, the movable base 31 and the fixed base 32 are provided with concave and convex fitting grooves 31a, 3
2a, the movable table 31 is slidably guided along the fixed table 32.

The moving table 31 includes an operation piece 33 and a stepping motor.
It is in contact with the tip of the pressing screw rod 35 driven by 34. Therefore, when the stepping motor 34 is driven and the pressing screw rod 35 is pushed out in the direction of the arrow, the moving table 31
That is, the pressing member 18 is moved in the direction a, and the transfer sheet
93 is pressed toward the photosensitive drum 3. Conversely, when the stepping motor 34 is driven in the reverse direction and the pressing screw rod 35 is retracted in the direction opposite to the direction of the arrow, the movable table 31 is moved in the direction b together with the pressing member 18 by the return spring 36, The pressing force of the transfer sheet 93 toward the photosensitive drum 3 is reduced.

The stepping motor 34 is controlled based on a signal from a temperature and humidity sensor (not shown) capable of automatically detecting the environment in which the copying machine is installed, and the movement of the pressing member 18 causes the transfer material to reach the transfer position. Complete before you do.

FIG. 7 shows a high-speed color electrophotographic copying machine according to another embodiment of the present invention. In this embodiment, the electrophotographic copying machine has four image forming units I to IV as shown in the figure.

Each of the image forming units I to IV has a photosensitive drum 3a to 3d, around which a primary charger 4a to 4d, an exposure unit 8a to 8d, a developing unit 1a to 1d, a transfer charger 10a to 10d, and a discharging charger. 11a-11d
And 13a to 13d, cleaning devices 12a to 12d, and an endless belt-shaped transfer material support 40 that carries and transports the transfer paper P below the photosensitive drum in a manner penetrating each image forming unit. Be placed.

On the other hand, pressing members 18a to 18d are provided within the discharge width of the transfer chargers 10a to 10d to press the endless belt-shaped transfer material support 40 toward the corresponding photosensitive drums. The pressing members 18a to 18d are, for example, the same as the pressing member 18 having the configuration shown in FIGS. 2 and 3, and can be moved by moving units 30a to 30d having the same configuration as the moving unit 30. . The pressing members 18a to 18d are driven by the moving units 30a to 30d, so that the pressing force on the transfer material support 40 is changed according to the change in temperature and humidity.

After the transfer paper P is fed by a paper feed roller, the transfer paper P is conveyed by the endless belt-shaped transfer material support 40 through a transfer section in which the transfer chargers 10a to 10d of each image forming unit are arranged.

In the case of this embodiment, M, C, Y, and BK in full color
In each image forming area of the color, the pressing members 18a to 18d are individually
Is provided, the position of the pressing member corresponding to each toner can be set individually, and the optimum position of each color can be set more easily than in the first embodiment.

FIG. 8 shows another embodiment of the moving means 30. According to the present embodiment, the moving means 30 has three setting positions 50a, 50b,
The cam 50 is provided with a cam 50c, and is driven to rotate in a direction indicated by an arrow by driving means (not shown) such as a motor, and is set at a predetermined position. A support member 31 to which the pressing member 18 is fixed is abutted on the cam 50 by a spring member 36, and the support member 31 is moved to a predetermined height position by the cam 50, whereby the pressing member is moved. It can be moved up and down, raising the pressing member upward at high temperature and high humidity, and lowering the pressing member downward at low temperature and low humidity, so that the same operation and effect as the previous embodiment can be obtained.

Effect of the Invention As described above, the image forming apparatus according to the present invention has
Since the pressing member for pressing the transfer material support supporting the transfer material toward the image carrier is configured to be movable by the moving means, the transfer current of the transfer charger is controlled according to the environmental change. In addition, the pressing force of the pressing member can be changed without requiring the control of the transfer current, and the allowable range of the transfer can be greatly expanded. This makes it possible to reduce the sag due to image formation and to form a high-quality image with high reliability.

Further, in the related art, the pressing member is partially deformed due to the shape of the transfer sheet and gives an impact to the image carrier, which may cause blurring of the latent image. With the reduction, it is possible to prevent the image deterioration due to the latent image blur.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view of a main part of a transfer device according to an embodiment of the image forming apparatus according to the present invention. FIG. 2 is a front view of the pressing member and the moving means. FIG. 3 is a partially enlarged sectional view taken along line III-III in FIG. FIG. 4 is a schematic configuration diagram of an image forming apparatus that can embody the present invention. FIG. 5 is a perspective view of the transfer device. FIG. 6 is an enlarged sectional view of a main part of a transfer device portion of a conventional image forming apparatus. FIG. 7 is a sectional view of another embodiment of the image forming apparatus according to the present invention. FIG. 8 is a front view of another embodiment of the moving means for the pressing member. 3: Image carrier 9: Transfer device 10: Transfer charger 18: Pressing member 40, 93: Transfer material support

Claims (1)

(57) [Claims] An image carrier on which a toner image is formed; and a transfer material support for carrying and transporting a transfer material, wherein the toner image on the image carrier is transferred to a transfer material on the transfer material support. A pressing member for pressing the transfer material support toward the image carrier, and a pressing member for adjusting the pressing force of the pressing member against the transfer material support, the image forming apparatus comprising: And a moving means for moving in accordance with a change in the installation environment of the image forming apparatus.