JPH06100855B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Object of the Invention (Industrial field of application) The present invention relates to an image forming apparatus such as an electrophotographic copying machine or a printer using an electrostatic transfer process.

(Problems to be Solved with Prior Art) A sheet-shaped transfer material is brought into contact with or brought close to a toner image formed on the surface of a running image carrier to transfer the toner image onto the transfer material, and then the transfer material is transferred. 2. Description of the Related Art An image forming apparatus configured to be separated from an image carrier and conveyed to a fixing device has been widely used.

In this type of image forming apparatus, as a fixing device,
In practice, a pair of rollers are pressed against each other and further heated if necessary, and a transfer material carrying a toner image is inserted into the pressed contact portions of both rollers.

When such a fixing device is used, when the transfer material conveyed from the transfer portion enters the roller pair of the fixing device, the transfer material is momentarily subjected to a braking action, and after the transfer material further enters the pressure contact portion, the transfer material gripping portion is held. Since the force is much larger than the restraining force on the transfer material at the transfer portion, the action of the force applied from the fixing device to the front end of the transfer material may affect the transfer portion and cause transfer deviation.

In order to avoid such an inconvenience, it has been proposed to arrange a transfer material conveying path from the transfer portion to the fixing portion such that the transfer material is intermediately constrained.

FIG. 4 is a schematic side view schematically showing such a structure, in which the toner image formed on the surface of the image carrier 1 formed in the shape of a rotating cylinder is supplied through the conveying path 3 and comes into contact with the toner image. Or, a sheet-like transfer material (not shown) adjacent thereto receives the toner image at the position of the transfer charger 2 and is then separated from the image carrier by the action of the separation charger 4, and is fixed through the transport path 5. To the device 8.

A pressing roller 6, which is a first rotating body, and a conveying roller 7, which is a second rotating body, which is opposed to the pressing roller 6, which are opposed to the pressing roller 6, are arranged in the conveying path 5. The shock absorber is designed to absorb the transfer material so that it does not adversely affect the transfer material.

In such an apparatus, in the illustrated apparatus, a potential having the same polarity as that of the transfer charger is applied to the transport roller 7, and at this position, the toner electrostatically adsorbed to the transfer material is transferred. The toner is further sucked and the toner is not transferred to the pressing roller 6.

However, as a practical problem, the charge of the toner varies, so that it is impossible to prevent a part of the toner from being transferred to the pressing roller 6. For this purpose, the cleaner 9 made of felt, for example, is used as the roller 6
However, if the toner accumulates in the cleaner to some extent, the toner may fall and stain the transfer material.

The present invention has been made to cope with such a situation, and reduces the toner accumulated in the cleaner as much as possible,
It is an object of the present invention to provide an image forming apparatus that prevents toner from falling off and the transfer material from being contaminated due to the toner.

(2) Structure of the Invention (Technical Means for Solving the Problem and Its Action) In order to achieve the above-mentioned object, the present invention transfers a toner image formed on an image carrier onto a transfer material, and then transfers the toner onto the transfer material. An image forming apparatus for fixing an image, comprising: a first rotating body provided on a surface side of the transfer material carrying the unfixed toner image, for transferring the transfer material carrying the unfixed toner image, An image forming apparatus having a second rotary body provided on the opposite side of the first rotary body with a material sandwiched between the first rotary body and a first rotary body that applies a voltage having the same polarity as the toner.
And a second voltage applying means for applying a voltage having a polarity opposite to that of the toner to the second rotating body.

With this configuration, it is possible to positively remove the toner that attaches to the first rotating body, and prevent the occurrence of image distortion before reaching the fixing portion.

(Description of Embodiments) FIG. 1 shows an embodiment of the present invention, in which the position in the image forming apparatus corresponds to the portion surrounded by the two-dot chain line L shown in FIGS. The parts are shown, and the corresponding parts are shown with the same reference numerals and the description thereof is omitted.

The transfer material P, which passes through the transfer portion and electrostatically carries the toner image on the surface of the transfer material (upper part in the drawing), is conveyed in the direction of arrow X and passes between the pressing roller 6 and the conveying roller 7.

In the illustrated case, the toner has a positive charge. In this case, a bias power source 11 applies a potential having the same polarity as the toner to the pressing roller 6 as the first voltage applying means. In this case, if the applied voltage is too high, the repulsive action between the toner and the toner may be excessive and disturb the toner image. Therefore, the applied voltage is appropriately determined to prevent such a situation.

A cleaning blade 10 is provided on the pressing roller to remove the adhered toner, but since the amount is extremely small, it does not substantially affect the image quality. Any appropriate blade such as rubber, mylar or metal plate can be used for the blade.

As shown in the figure, a bias is also applied to the cleaning blade 10 to enhance the scraping action of the toner, and the toner adheres and solidifies between the blade 10 and the pressing roller,
In addition, it is possible to avoid the inconvenience of this dropping.

FIG. 2 shows another embodiment of the present invention, in which it is grounded via a resistor R as a voltage generating element that generates a voltage when a current flows through the pressing roller. As described above, since the transport roller 7 has a potential having a polarity opposite to that of the toner, the above-described configuration causes a potential having a polarity opposite to that of the roller 7 to be induced in the pressing roller 6, so that each of FIGS. It can be easily understood that the same operation as that shown is performed.

Figures 3A and 3B show the optimum bias in response to various conditions such as paper thickness, surface quality, and environmental humidity. An example is shown.

The humidity sensor 14 and the switching switch 15 apply an optimum applied voltage to the pressing roller 6 or the conveying roller 7 via the high-voltage unit 13. FIG. 3B shows the one adjusted in three stages according to the humidity, but of course, the voltage can be continuously changed.

(3) Effect of the Invention Since the present invention has the configuration described above, the transfer material carrying the unfixed toner image, which is conveyed from the image forming portion of the image forming apparatus to the fixing portion, is provided at the intermediate position. Since the grip is firmly held, it is possible to reliably prevent the shock when the transfer material enters the fixing portion from propagating to the transfer portion and deteriorate the image quality, and also to prevent the toner image on the transfer material located in the conveying path. Is held on the transfer material by a uniform and sufficient electrostatic force to prevent the toner image from being disturbed and the toner from scattering, which is a remarkable effect in obtaining a high quality image.

[Brief description of drawings]

FIG. 1 is a side view of an essential part showing an embodiment of the present invention, FIG. 2 is a side view showing another embodiment, and FIGS. 3A and 3B are configuration diagrams and operations showing still another embodiment. FIG. 4 is a schematic side view showing a known image forming apparatus. DESCRIPTION OF SYMBOLS 1 ... Photoconductor, 6 ... Pressing roller, 7 ... Conveying roller, 8 ... Fixing device, 9 ... Cleaner, 10 ... Cleaning blade, 11 ... Bias power supply

Claims (2)

[Claims] 1. An image forming apparatus for fixing a toner image on a transfer material after transferring a toner image formed on an image bearing member to a transfer material, wherein a transfer material carrying an unfixed toner image is nipped and conveyed. To this end, the first rotating body is provided on the surface side of the transfer material that carries the unfixed toner image, and the second rotating body is provided on the opposite side of the first rotating body with the transfer material interposed therebetween. In the image forming apparatus, the first rotating body applies a voltage having the same polarity as that of the toner to the first rotating body.
And a second voltage applying means for applying a voltage having a polarity opposite to that of the toner to the second rotating body. 2. The image forming apparatus according to claim 1, wherein the first voltage applying means has a voltage generating element for generating a voltage when a current flows, and the voltage generating element is grounded.