JPH0750360B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is an image forming apparatus capable of forming a good image on a transfer material whose moisture absorption varies depending on environmental conditions without causing transfer defects. It is about.

[Prior Art] Devices to which the electrophotographic method to which the present invention is applicable include electrophotographic copying machines, facsimile receivers, and laser beam printers.

Among them, the laser beam printer is especially in the spotlight because it can perform high-speed image processing as a computer terminal printer in the recent movement of office automation. In this method, a laser beam modulated as a terminal signal is introduced instead of the optical system of a conventional electrophotographic copying machine to obtain a high-quality image by a process process similar to that of a copying machine.

Conventionally, in this main image forming apparatus, when the paper supplied from the paper feed section passes through the transfer guide, the transfer guide is connected to the ground, and therefore when the absorbed paper is passed, the transfer current is transferred through the paper. There was a problem that the sharpness of the line was lowered due to the flow to the guide, and the line was out of focus or the transfer was missing. On the other hand, for example, in the one described in USP4055380, it is proposed to connect the transfer guide to the ground via a large resistance of 100 MΩ to 400 MΩ.

However, when such a large resistance is used, the voltage generated in the transfer guide becomes close to 1000V. For this reason, there is a problem that the toner on the photosensitive drum is adsorbed on the guide, accumulated on the guide, and falls on the transfer paper, so that the image is soiled.

This stain is likely to occur especially in reversal development. This is because, for example, the light portion potential to the dark potential V _d = -700V Vl = -
At 150V, the negative electrode toner adheres to the Vl portion, and the charge on the drum and the charge on the toner tend to repel each other. On the other hand, transfer charging gives a positive corona current to the paper,
In the above-mentioned conventional example, the electric current flowing through the resistance causes the potential of the transfer guide to be around +1000 V, which makes it very easy to adsorb toner. For this reason, in the reversal development, image stains which are particularly troublesome for the transfer guide stains are likely to occur.

In order to solve this problem, a method of connecting a resistance of 80 MΩ or less to the transfer guide has been proposed. However, in this method as well, if there is a transfer roller 11b near the transfer charger and a part of the transfer current flows out as shown in FIG. 5, a voltage is always applied to the transfer guide 11a and the transfer roller 11b. As a result, the tip of the transfer guide 11a is soiled with toner.

[Problems to be Solved by the Invention] The present invention is an image capable of preventing a transfer defect such as image blurring or transfer gap of a hygroscopic paper, which is a drawback of the above-described conventional example, and capable of obtaining an image without image stains. An object is to provide a forming apparatus.

[Means for Solving Problems] A main configuration of the present invention that can achieve the above object is a transfer charging unit that transfers an image of an image carrier to a transfer material at a transfer position, and a transfer material that guides the transfer material to the transfer position. First and second guide plates facing each other in order to do so, and a guide member that is provided between the guide plate and the transfer position and that guides the transfer material on the opposite side of the image carrier side. In the image forming apparatus including the first and second guide plates, the first and second guide plates are grounded via a common first voltage generating element, and the guide member is a second voltage generating element different from the first voltage generating element. And a voltage generated in the guide member is set higher than a voltage generated in the first and second guide plates.

[Examples] Hereinafter, specific examples of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of the present invention. 1 is an image carrier, a photosensitive drum composed of a photosensitive layer 2 and a substrate 3, 4 is a primary charger, 5 is a laser beam, 6 is a developing device including a doctor blade 7, a magnet roller 8 and a sleeve 9, and T is a developing toner. , 10 is a pre-exposure lamp, 11a is a transfer paper guide, 11b is a transfer roller, 12 is a transfer charger, and 13 is a cleaner composed of a rubber blade 14, a magnet roller 15, a screw 16 and a housing 17.

The drum 1 uniformly charged by the primary charger 4 is exposed to the laser beam 5 modulated according to the image signal, and an electrostatic latent image is formed on the drum 1. Subsequently, the drum 1 undergoes a developing process by the developing device 6 to visualize the latent image.

Thereafter, the visible image is transferred by the transfer charger 12 onto the transfer paper (not shown in the figure) guided by the transfer guide 11.

The transfer guide 11a and the transfer roller 11b are made of a conductive material, and are connected to the ground via resistors 20a and 20b, respectively. The transferred toner image is fixed on a transfer sheet by a fixing device (not shown), and is discharged out of the machine to obtain a hard copy.

An example of the image formed in this way is shown in FIG.
18 is a transfer paper, and 19 is a transferred visible image.

On the other hand, the untransferred developing toner remaining on the drum 1 is removed from the surface of the drum 1 by the rubber blade 14, adsorbed to the magnet roller 15, and further screwed by the screw 16 to a toner collecting box (not shown) forming a part of the housing 17. ). The drum 1 thus cleaned is sent to the primary charging step which is the first step and is repeatedly used.

In the process of irradiating the laser beam 5, a laser is applied to a portion of the photosensitive drum corresponding to the visible image 19 on the transfer paper 18, and the background other than the visible image 19 is not irradiated with the laser. Has been done. This method is superior in reproducibility of the visible image to the background image, as compared to the background scan method in which the background is irradiated with laser and only the portion corresponding to the visible image 19 is not irradiated with laser. is there.

FIG. 3 shows the behavior of the surface potential of the drum 1 during latent image formation. Here, an example in which a phthalocyanine-based organic semiconductor is used for the photosensitive layer 2 as the photosensitive drum 1 and the case where the primary charging is performed with a negative polarity is shown. The surface potential obtained by the primary charger 4 is the difference between the dark decay and the bright decay due to laser irradiation (Vd
-Vl), that is, converted to a latent image potential of about 550V in contrast.

As the developing toner T, a magnetic one-component developer is used. The toner T in the developing device is charged by mutual friction and contact friction with the cylinder 9 and the doctor blade 7. The charged toner T is placed on the cylinder 9 by the doctor blade 7 to have a uniform thickness. When the cylinder 9 rotates and the electric attraction force by the electric field between the electrostatic latent image and the developing bias potential applied to the cylinder at the closest position between the drum 1 and the cylinder 9 causes the toner to reach the latent image portion to be developed. Sucked. The portion corresponding to the bright portion potential Vl of the latent image shown in FIG. 3 is developed.

For this purpose, the toner must be charged to a charging polarity (negative in this case) that develops a high potential Vl in a relatively positive direction. FIG. 4 conceptually shows that the toner does not adhere to the negative potential portion of the background Vd, but the negatively charged toner adheres to the laser irradiation portion Vl near the ground potential.

When visualized by such reversal development, the toner is Vl
Since the toner adheres to a portion, the attraction force between the drum and the toner is weak, and transfer can be performed with a smaller transfer current than that of a normally developed toner image, but toner stains on the transfer guide are likely to occur. Especially, in the case where a part of the transfer corona, such as the transfer roller 11b near the transfer portion, directly flows in without passing through the transfer material, the voltage is always applied to the transfer guide and the transfer roller. In particular, toner stains are likely to adhere to the transfer guide.

FIG. 1 shows an embodiment of the present invention, in which the transfer roller 11b has a resistance 2
It is grounded via 0b (resistance value R ₂ ) and the transfer guide 11a has resistance 2
It is grounded via 0a (resistance value R ₁ ). Part of the corona discharge current by the transfer charger flows into the transfer roller 11b and generates a voltage V ₂ . Further, a transfer current flows into the transfer guide 11a via the transfer material when the resistance of the transfer material becomes low, and a voltage V ₁ is generated. These resistors 20a, 20b are 5MR ₁ , R ₂ 2
It should be 00M.

As an experimental example, in the configuration shown in FIG. 5, the dark part potential V _d
= -700V, bright part potential Vl = -150V, current bias voltage V = -450V is used for development. Transfer corona total current 150μA
(Of which, the current in the drum direction is 15 μA). resistance
R ₁ and R ₂ each use a resistance of 20 MΩ and 6
A plain paper of A4 size of 0 g / m ² left in an environment of 32.5 ° C. and 90% RH for 2 days and a paper left in an environment of 25 ° C. and 60% RH for 2 days were used.

When these two types of paper were passed through the main body and the transfer rate of the toner to the paper was checked, in the present example, there was almost no transfer failure and the transfer guide was not contaminated. This is 3
If the paper is left at 2.5 ° C and 90% RH, the transfer roller 11b has about 10
At the same time as the current of .mu.A flows, the corona current also flows into the transfer guide 11a of about 4 .mu.A through the low resistance paper.

However, due to the resistors connected to these guides, bias voltages of 200 V and 80 V are generated, respectively, and transfer defects hardly occur. If the paper is left at 25 ° C and 60% RH, a current of about 10 μA flows into the transfer roller and a voltage of about 200 V is generated.
Only a current of 1 μA or less flows through 11a, and the transfer guide 11a
Voltage of less than 20V is generated, and almost no toner adheres to the transfer guide 11a. Also, when the toner is scattered from the drum, the transfer roller is only between the sheets, and the transfer roller is hardly soiled. Further, since a higher voltage is generated in the transfer roller closer to the transfer than in the transfer guide on the far side, the transfer failure is less likely to occur.

[Other Embodiments] In the above-described embodiments, the resistor is used as the bias generating means, but a constant voltage generating element such as a Zener diode or a varistor may be used. However, electric resistance is better for the element connected to the transfer guide 11a. This is because the resistance changes the bias voltage according to the current and is more advantageous for toner stains. Further, in the above-mentioned embodiment, the transfer roller (conductive) has been described as the guide member for the transfer material close to transfer, but it may be a guide member for the transfer material fixed to the main body.

[Advantages of the Invention] As described above, a member such as a roller, which is near the transfer charger and into which a part of the corona current directly flows, and a transfer guide, which transfers the transfer material to the transfer position, are provided. It is possible to prevent both the roller and the transfer guide from being soiled and prevent the transfer failure by connecting the member that guides to the separate high-voltage generating element.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention, FIG. 2 is a diagram of an image of a hard copy obtained by the same printer, FIG. 3 is a diagram for explaining the potential of the photosensitive drum surface in the image forming step, and FIG. FIG. 5 is a diagram for explaining the state of development, and FIG. 5 is a sectional view of a conventional example. 1 is a photosensitive drum, 4 is a primary charger, 6 is a developing device, 11a is a transfer guide, 11b is a transfer roller, 12 is a transfer charger, 13 is a cleaner, 20 and 21 are resistors, and 22 is a conductive resin film. .

Claims (1)

[Claims] 1. A transfer charging means for transferring an image on an image carrier to a transfer material at a transfer position, first and second guide plates facing each other for guiding the transfer material to the transfer position, and the guide. An image forming apparatus having a guide member that is provided between a plate and the transfer position and that guides the transfer material on the side opposite to the image carrier side, wherein the first and second guide plates are: The guide member is grounded via a common first voltage generating element, and the guide member is grounded via a second voltage generating element different from the first voltage generating element to prevent the voltage generated in the guide member from being generated. The first
And an image forming apparatus characterized in that the voltage is made higher than the voltage generated in the second guide plate.