JPH03154088A - Image forming device - Google Patents

Abstract

PURPOSE:To always perform stable transfer without depending on environment by providing a current limitation means to a destaticizing means provided at a position obtained before a transfer material advances to a transfer part. CONSTITUTION:The transfer material P is guided by a pair of transfer guides 8 and 9 to reach a transfer part. A destaticizing brush 22 is disposed in the transfer guide 8, and the current limitation circuit C is connected to the brush 22. In the case of performing the destaticization by the brush 22, it is sufficient to set a current Il which flows in a grounding direction at 2muA to the maximum in order to destaticize the charge of the transfer paper P, and the deterioration of an image caused by the splashing of toner is prevented from occurring even under the environment of low humidity. In such a case, the circuit C is made a 2muA constant-current circuit. Even when the resistance R15B of the transfer paper P gets small under the environment of high humidity, a current which flows in a direction shown by an arrow (b) is limited because of the existence of the circuit C and a voltage at the contact point N of the transfer paper P with a transfer roller 5 is not lowered, thereby preventing the faulty transfer from occurring.

Description

DETAILED DESCRIPTION OF THE INVENTION <1) Object of the Invention (Field of Industrial Application) The present invention relates to an image forming apparatus using an electrostatic transfer process, such as an electrostatic copying machine and a printer thereof.

(Prior art and problems to be solved) A transferable toner image formed on the surface of an image carrier is guided to a transfer site constituted by the image carrier and a contact type transfer means such as a transfer roller that comes into contact with the image carrier. , timed to this toner image.

A transfer material such as paper is conveyed to the transfer site, a transfer bias is applied to the transfer means, and the toner image is transferred from the image carrier to the transfer material by the action of the electric field formed. Forming devices are well known in the art.

FIG. 4 is a schematic side view of the main parts of such an image forming apparatus, showing the vicinity of the transfer site. For example, an OPC photosensitive layer on the surface of an image carrier (referred to as a photoconductor) 1 is uniformly negatively charged by a primary charging means (not shown), and a light image is irradiated onto the charged surface by image-modulated scanning laser light or the like. As a result, the potential at that portion is attenuated and an electrostatic latent image is formed.

Next, negatively charged toner is supplied to the latent image from a developing device (also not shown), and by reversal development, the latent image is visualized to become a toner image.

As the photoreceptor 1 rotates, when the toner image arrives at the transfer site where the photoreceptor 1 and the transfer roller 5 come into contact and are formed, the transfer material P is aligned with the toner image by the registration roller pair 10.11. are fed together in the direction of the transfer site, and further guided by a pair of transfer guides 8.9 to reach the transfer site. At the same time, a bias voltage having a polarity opposite to that of the toner is applied to the transfer roller 5 from the back surface of the transfer material, and the toner image is transferred to the transfer material.

The transfer roller is made by dispersing carbon, metal powder, etc. in an elastic material such as rubber, and is adjusted to 10 degrees for low resistance. It is assumed that a transfer bias of 3 to 4 KV is applied.

By the way, when using the above transfer material conveying means,
Before reaching the transfer site, the transfer material inevitably becomes charged due to friction with registration rollers, transfer guides, etc. before reaching the transfer site, so the toner image on the photoconductor side may be disturbed due to the amount of charge and charge polarity. There has been a problem in that floating toner near the transfer site is sucked, resulting in deterioration of image quality.

In order to avoid such inconvenience, as shown in the figure,
As indicated by reference numeral 22 in the drawing, the applicant has already proposed that a grounded static elimination brush be disposed at a suitable location, such as the transfer guide 8, to eliminate static electricity from the charged transfer material that advances to the transfer site. With this configuration, it is possible to achieve a certain effect in preventing deterioration of image quality due to toner scattering as described above.

However, regarding paper, which is most commonly used as a transfer material, it is known that the resistance value of paper changes significantly depending on the environment, especially humidity, and transfer paper that has low resistance in high-temperature environments often suffers from poor transfer. There is a possibility that this may occur.

To explain this, in a high temperature environment, the resistance of the transfer material and the transfer paper (for example, the resistance of 3180 gr/m" paper on a scale of 20 to 35 degrees Celsius compared to the dry state)
, it decreases to 10''Ωcm or less at 85%RH.

The influence of such a change in resistance will be explained using an equivalent circuit diagram.

Figure 5 shows the relationship between the various parts at the transfer site. In the figure, R1 is the resistance of the photoreceptor, R5 is the resistance of the transfer roller, and v
5 is a transfer bias power supply, R15A is the resistance of the transfer material portion sandwiched between the photoreceptor and the transfer roller, and R15B
is the resistance of the transfer material portion between the transfer material portion and the static elimination brush 22.

Therefore, when paper is not passed, R15A, R
15B does not exist.

Generally, R1 is 10 ΩC when the film thickness is about 48 μm.
at%R5 is 10'Ωcm with a low resistance roller in this case.
It is assumed that V5 is a constant voltage power supply of 500V.

The relationship between the resistances R15A and R15B of the transfer paper is R15A<R15B under normal conditions, and R15A410''00111 or more in a low humidity environment and 1012 Ωcm or less in a high temperature environment.

In FIG. 5, in order to perform good transfer, it is necessary that the current flowing in the direction a shown in the figure is sufficient, and in a low humidity environment, R15B is sufficiently large, so the current in the direction indicated by the arrow is small. The necessary transfer current can be obtained.

In a high temperature environment, R15B becomes smaller than R1, so the current in the direction of the arrow also increases.

In such a case, if the power supply V5 does not have sufficient output, the current will increase, the output voltage will drop, and the current in the direction of arrow a necessary for transfer will be insufficient, resulting in a transfer failure.

If the transfer roller is a medium-resistance roller with a resistance of 10' to lOgΩcI11, apply a transfer bias of 3 to 4 KV as described above, but if it is in a low humidity environment and R15B is large, the transfer roller and transfer paper The voltage at contact point N is sufficient for transfer, but if R15B becomes small,
Since the current in the b direction increases and the current passing through R5 also increases, the voltage shared by R5 increases and the voltage at the contact point N decreases, resulting in a transfer defect. .

The present invention provides an image forming apparatus that is equipped with a contact-type transfer means and a pre-transfer static elimination means in the vicinity thereof, and is always stable regardless of the environment by providing a means for limiting the current flowing through the static elimination means. It is an object of the present invention to provide an image forming apparatus capable of performing a high-speed transfer.

(2) Structure of the invention (technical means for solving the problem, its operation) In order to achieve the above objects, the present invention provides a transfer region between an image carrier and the image carrier in contact with the image carrier. In the image forming apparatus, the image forming apparatus is provided with a static eliminator for removing static from the transfer material at a position before the transfer material enters the transfer site, and a means for restricting the current flowing through the static eliminator. This is a characteristic feature.

With this configuration, it is possible to prevent toner scattering and poor separation in a low-humidity environment, and also to prevent poor transfer in a high-temperature environment, so that stable transfer can be performed at all times regardless of the environment.

(Description of Embodiments) FIG. 1 shows an image forming apparatus showing an embodiment of the present invention.
It is a schematic side view showing the vicinity of the separation site, and parts corresponding to those of the above-mentioned known device are given the same reference numerals.

In the illustrated device, a current limiting circuit C is connected to the static elimination brush 22, and the circuit C is connected to a trough filter 23. It includes an operational amplifier 24, a resistor 25, a constant voltage power supply V, and a resistor RL.

When removing static electricity with the static eliminating brush 22, a maximum of 2 μA of current II2 flowing in the ground direction is sufficient to eliminate the charge on the transfer paper P, and even in a low humidity environment, image deterioration such as toner scattering is prevented. It will never occur.

Since Rt, = V / Iβ, V and RL can be set appropriately according to the value of II. Here, to set ■β to 2 μA as shown in the example, for example, if ■ = 5v, then RL = It becomes 2.5MΩ.

FIG. 2 shows an equivalent circuit of the above device, in which the resistors and the like are the same as in the previous case, and C is a 2 μA constant current circuit.

Even if the resistance R15B of the transfer paper becomes small in a high-temperature environment, the presence of the constant current circuit C limits the current flowing in the direction of the arrow, and the voltage at the contact point N between the transfer roller and the transfer paper does not drop. , it is possible to prevent the occurrence of transfer defects.

In other words, the illustrated apparatus prevents deterioration of image quality due to poor separation and toner scattering in low humidity or room temperature environments, and also prevents image quality deterioration due to toner scattering in low humidity or room temperature environments. Since the hook does not change the upper resistance, it is possible to prevent the transfer current from decreasing and avoid the occurrence of transfer defects.

FIG. 3 shows another embodiment of the present invention, in which the image forming apparatus portion has the same structure as the apparatus of the previous embodiment, and corresponding parts are designated by the same reference numerals.

In the illustrated device, a constant current diode 26 is connected to the static eliminating brush 22.

A constant current diode has a characteristic of supplying a constant current within a certain voltage range, and exhibits a characteristic curve as shown in FIG. The vertical axis of the graph shows the current, and the horizontal axis shows the applied voltage.
is the constant current value, and ■ is the maximum constant current region voltage.

In this way, a constant current diode outputs a constant current within a certain voltage range, so select a constant current diode whose maximum voltage value is equal to or greater than the voltage applied to the transfer roller. However, by connecting multiple diodes in series to increase the voltage in the constant current region (and configuring it as described above, the resistance of the transfer material can be reduced as in the case of the embodiment device described above). Even in this case, the transfer current flowing from the transfer roller to the photoreceptor via the transfer material is not reduced, and it is possible to prevent the occurrence of transfer defects.

According to this embodiment, it is possible to avoid deterioration of image quality due to toner scattering, and also to prevent transfer failures in high-temperature environments.Furthermore, the entire device can be configured to be small and compact, which greatly contributes to cost reduction. .

Although an embodiment using a transfer roller as the transfer means has been described above, the present invention is not limited to this. There is no doubt that it is applicable.

(3) Effects of the Invention According to the present invention, in an image forming apparatus using a contact type transfer means such as a transfer roller, a current limiting means is provided in the pre-transfer static elimination means arranged adjacent to the transfer means. Regardless of the environment, it is possible to always perform stable, high-quality transfer without deterioration of image quality due to toner scattering, or transfer failure due to moisture absorption, which contributes to obtaining high-quality images. However, it is large.

[Brief explanation of the drawing]

FIG. 1 is a schematic side view showing the main parts of an image forming apparatus according to an embodiment of the present invention, FIG. 2 is an equivalent circuit diagram of the transfer and separation section of the same, and FIG. 3 is a main part showing another embodiment. FIG. 4 is a schematic side view of the main parts of a known image forming apparatus; FIG. 5 is an equivalent circuit diagram of the transfer and separation section shown above; FIG. 6 is a graph showing the characteristics of a constant current diode. . DESCRIPTION OF SYMBOLS 1... Photoreceptor, 5... Transfer roller, 8.9... Transfer guide, 1O111... Registration roller pair, 22.
... Static elimination brush, 26... Current limiting circuit, 26...
Constant current diode. Figure 1 Figure 2 Figure 3 Figure Figure Figure Figure t, IIF-p

Claims (1)

[Scope of Claims] A charge removal method that forms a transfer region between an image carrier and the image carrier in contact with the image carrier, and removes charge from the transfer material at a position before the transfer material enters the transfer region. What is claimed is: 1. An image forming apparatus comprising: a means for restricting a current flowing through the static eliminating means;