JPH0481875A - Image forming device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [1! The present invention involves forming a latent image on an image carrier using electrophotography or electrostatic recording, converting the latent image into a visible image, that is, a toner image, using a developing means, and transferring the toner image. It relates to an image forming device that obtains an image by transferring it to a material, and in particular, it is a device that supports a transfer material on a transfer material support, conveys it to a transfer area, and transfers the toner image on the image carrier onto the transfer material. The present invention relates to an image forming apparatus that transfers images. Various multicolor image forming apparatuses have heretofore been proposed and are commercially available, and FIG. 4 shows an example of a typical color electrophotographic copying machine or printer. In FIG. 4, the color electrophotographic copying machine forms a latent image on an image bearing member 3, which is an electrophotographic photosensitive drum, and develops the latent image using a plurality of colors, for example, four types of development: yellow, magenta, cyan, and black. 4 developing units IY, IM, IC containing agent
A visible image, that is, a color toner image is formed in a rotary developing device l equipped with 1IBK, and these toner images are transferred to a sheet-like transfer material such as paper attached to a drum-shaped transfer device 9 disposed close to the surface of the photosensitive drum 3. The structure is such that a color image is obtained by superimposing the image on the image. As schematically shown in FIG. 5, the transfer device 9 used in such a color electrophotographic copying machine includes a pair of annular members, cylindrical members 9a and 9b in this example, arranged concentrically. Both are integrally connected by a connecting member 9c, and the entire circumference is usually made of polyvinylidene fluoride (PVdF).
a transfer material support formed of a dielectric material such as a sheet;
That is, a cylindrical transfer drum covered with a transfer sheet 93 is used. Further, a gripper 91 is disposed on the outer surface of the connecting member 9c of the transfer drum 9, and grips and conveys the transfer material P supplied in synchronization with the toner image on the photosensitive drum 3.
The photosensitive drum 3 is placed at the transfer position where the transfer charger 10 is placed.
After the toner image of each color is transferred to the transfer material each time the transfer material approaches to form a color image, the gripper 91 is opened to separate the transfer material from the transfer drum. The separated transfer material is fed to the fixing means 17 by the conveying means 16. Conventionally, in the transfer drum 9, in order to make the transfer sheet 93 uniform and to shorten the transfer nip to increase the transfer efficiency and obtain a clear transferred image, the transfer drum 9 is heated from the inside of the transfer drum 9 in the vicinity of the transfer charger 10. In order to push up the transfer sheet 93 toward the photosensitive drum 3, a pressing member 18 is provided as shown in FIG. This pressing member 18 is made of an elastic material such as a synthetic resin sheet, and applies appropriate pressure to the transfer sheet 93. However, in the above conventional example, although the pressing member 18 is detachable so that it can be removed as necessary,
Since the pressure of the pressing member 18 to press the transfer sheet 93 toward the photosensitive drum 3 is constant, changes in temperature and humidity,
In particular, in order to increase transfer efficiency in response to changes in humidity,
The only method available was to control the strength or weakness of the transfer current of the transfer charger 10. For example, at high temperatures and high humidity, the volume resistivity of the transfer material used decreases to about 1/100 of that at room temperature (for example, 23° C./60% RH) in the case of transfer paper. Furthermore, the surface resistance of the transfer sheet 93 itself also decreases because it absorbs moisture. Therefore, a weak transfer current is sufficient, and a weak pressing force of the transfer sheet 93 and the transfer material P against the photosensitive drum 3 is sufficient. However, in the past, the pressing force of the pressing member 18 is fixed, so that the pressing force of the pressing member 18 due to long-term use
8), and the stability of the transfer cannot be guaranteed during long-term use.Also, at low temperatures and low humidity, the surface resistance of the transfer material and transfer sheet increases, so strong current However, even when a strong current is applied, the desired transfer efficiency may not be achieved in some cases, and it is necessary to increase the pressing force of the pressing member 18. The purpose of the invention is to make the pressing member that presses the transfer material support against the image carrier movable in response to changes in temperature and humidity, and to change the pressing force on the image carrier, thereby changing the strength of the conventional transfer current. The purpose of the above is to provide an image forming apparatus that can perform more appropriate transfer, improve transfer efficiency, and always obtain high-quality images than when controlling transfer conditions by This is achieved by an image forming apparatus according to the present invention.In summary, the present invention includes an image carrier on which a toner image is formed, a transfer material support that supports and conveys a transfer material, In an image forming apparatus that transfers a toner image on a body to a transfer material on a transfer material support, a pressing member that presses the transfer material support toward an image carrier, and the transfer material support of the pressing member. The image forming apparatus is characterized in that it has a moving means for moving the pressing member according to changes in the installation environment of the image forming apparatus in order to adjust the pressing force against the image forming apparatus. The image forming apparatus according to the above 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 is also equipped with the transfer device 9 shown in FIG. 5, whose structure and operation are as follows. As described above, the structure and operation of the multicolor electrophotographic copying machine and transfer device 9 will be briefly explained below. In this embodiment, the photosensitive drum 3 constituting the image carrier is The rotating photosensitive drum 3 is surrounded by a primary charger 4, a rotary developing device 1 including developing devices IY, LM, Ic, and IBK, a transfer drum 9 constituting a transfer device, and a cleaning device 12. Image information signals color-separated by a laser optical system consisting of a polygon mirror unit 8 and a laser reflection mirror 7 are irradiated onto the photosensitive drum 3 to form a latent image on the photosensitive drum 3. As the rotary developing device 1 rotates, the image is developed by a predetermined developing device at a developing position facing the photosensitive drum 3 to form a visible toner image. On the other hand, the transfer material P in the cassette (hereinafter referred to as "transfer paper") is sent out from the cassette by a paper feed roller, passes through the second registration roller pair 19 and the second registration roller pair 6, and is transferred to the paper feed guide 20. Sent. The transfer paper P is timed by the first and second registration rollers 9.6, and its leading edge is gripped by the gripper 91 on the transfer drum 9 described in connection with FIG. The upper transfer material support is made of polyvinylidene fluoride resin (P
It is held on a transfer sheet 93 made of VdF) or the like. The transfer paper P held on the transfer sheet 93 is transferred to the transfer charger 1
0, the toner image on the photosensitive drum 3 is transferred. The transfer process is repeated for each color, and once the transfer is complete, the gripper 91 opens and the corona charger 11.13.1
4, the conveying means 16 is removed by the separating claw 15.
be guided by The transfer paper guided to the conveyance means 16 is fixed by a fixing means 17 having a pair of rollers, and then discharged onto a tray. The toner image remaining on the photosensitive drum 3 after the transfer process is cleaned by a cleaning device 12, and the photosensitive drum 3 is prepared for the next image formation. According to the present invention, as shown in FIG. 1, within the discharge width of the transfer charger 10, extending from the introduction side in the movement direction of the transfer sheet 93 of the transfer drum 9 toward the downstream side in the movement direction. A pressing member 18 having elasticity is arranged. This pressing member 18 is made of an insulating sheet, such as Mylar (
Polyethylene terephthalate, which is commercially available as a registered trademark, can be used, and the thickness is approximately 1100L.
A material of about L is suitable. According to the present invention, the pressing member 18 at high temperature and high humidity,
Move to the lower left direction (direction a) in FIG.
3 onto the photosensitive drum 1.
Also, when the temperature is low and humidity is low, it moves to the upper right direction (b direction),
The configuration is such that the force for pressing the transfer sheet 93 against the photosensitive drum 1 is strong. According to the invention, therefore, the pressing member 18 is attached to the displacement means 30, as shown in detail in FIGS. 2 and 3. In this embodiment, the moving means 30 includes a moving table 31 to which the pressing member 18 is fixed, and a fixed table 32 to which the moving table 31 is slidably attached. As shown in FIG. 3, the movable base 31 and the fixed base 32 are provided with uneven fitting grooves 31a and 32a formed in complementary shapes.
is slidably guided along the Further, the moving table 31 includes an actuating piece 33, which is in contact with the tip of a pressing screw rod 35 driven by a stepping motor 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 presses the transfer sheet 93 toward the photosensitive drum 3. Conversely, when the stepping motor 34 is driven in the opposite 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 b direction together with the pressing member 18 by the return spring 36, Photosensitive drum 3 of transfer sheet 93
This reduces the pressing force towards. The stepping motor 34 is controlled based on a signal from a temperature/humidity sensor (not shown) that can automatically detect the environment in which the copying machine is installed, and the movement of the pressing member 18 is controlled when the transfer material is at the transfer position. Complete before reaching. 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 is
As shown in the figure, there are four image forming units I to (2). Each of the image forming units I to IV has photosensitive drums 38 to 3d, which are surrounded by primary chargers 48 to 4d and exposure means 88.
~8d, developing units 1a~ld, transfer chargers lOa~10d
, static eliminators 11a to 11d and 13a to 13d, and cleaning devices 12a to 12d are arranged, and furthermore, an endless belt that carries and conveys the transfer paper P below the photosensitive drum in a manner that penetrates each image forming unit. transfer material support 4
0 is placed. On the other hand, pressing members 18a to 18d are provided within the discharge width of the transfer charger 10a=10d to press the endless belt-shaped transfer material support 40 toward the corresponding photosensitive drum. The pressing members 18a to 18d are the same as the pressing member 18 having the structure shown in FIGS. 2 and 3, for example, and the moving means 30a to 30 have the same structure as the moving means 30.
It is possible to move at d. Then, the pressing members 18a to 1
8d is driven by moving means 308 to 30d, so that the pressing force against the transfer material support 40 is varied in accordance with changes in temperature and humidity. After being fed by a paper feeding roller, the transfer paper P is conveyed by the endless belt-shaped transfer material support 40 through a transfer section where transfer chargers 10a to 10d of each image forming unit are arranged. In the case of this example, 4 colors of M, C, Y, and BK in full color are used.
In each color image forming area, the pressing members 18a to 18a are individually pressed.
18d, it is possible to set the position of the pressing member according to each toner, and the optimum position of the color name can be set more easily than in the first embodiment. Another embodiment of the moving means 30 is shown in FIG. According to this embodiment, the moving means 30 has three setting positions 50a,
The cam 50 includes 50b and 50c, and is driven to rotate in the direction of the arrow by a driving means (not shown) such as a motor.
set in place. The cam 50 has a spring member 36
, the support member 31 to which the pressing member 18 is fixed is brought into contact, and the supporting member 31 is moved to a predetermined height position by the cam 50, thereby making it possible to move the pressing member up and down. When the humidity is high, the pressing member is lifted upward, and when the temperature is low and humid, the pressing member is lowered, and the same effects as in the previous embodiment can be achieved. 1. As explained above, the image forming apparatus according to the present invention uses a moving means to move the pressing member for pressing the transfer material support carrying the transfer material toward the image carrier. Since the transfer current of the transfer charger can be controlled in accordance with environmental changes, or the pressing force of the pressing member can be changed without the need to control the transfer current.
It has the characteristics of being able to significantly expand the transfer tolerance range, and also reducing the wear of the pressing member due to long-term use, making it possible to form reliable and high-quality images. ing. Furthermore, in the past, the pressing member could be partially deformed depending on the shape of the transfer sheet, giving an impact to the image carrier and causing blurring of the latent image, but according to the present invention, the pressing force can be reduced. By reducing this, it has become possible to prevent image deterioration due to this latent image blur.

[Brief explanation of the drawing]

FIG. 1 is an enlarged sectional view of a main part of a transfer device portion of an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a front view of the pressing member and the moving means. 3 is a partially enlarged sectional view taken along line 11T-III of FIG. 2. 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: 9: 10: 18: 40, Image carrier transfer device Transfer charger Pressing member 93: Transfer material support Fig. 2 Fig. 7

Claims (1)

[Claims] 1) Image formation that includes an image carrier on which a toner image is formed and a transfer material support that carries and conveys a transfer material, and that transfers the toner image on the image carrier to the transfer material on the transfer material support. In the apparatus, 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 are installed in the installation environment of the image forming apparatus. An image forming apparatus comprising: a moving means for moving according to fluctuations in the image forming apparatus.