JPH0677171B2 - Image forming device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a color electrophotographic copying apparatus, a color recording apparatus having a computer output section, and the like, and in particular, it is possible to use two or more kinds of toner. The present invention relates to a transfer and separation device for an image forming apparatus.

2. Description of the Related Art A conventional transfer and separation device for an image forming apparatus is a latent image carrier on which a visible powder image of toner is formed by a developing device, usually a photosensitive surface of a photosensitive drum. After exposure or DC discharge of the same polarity as the polarity of the toner or AC discharge is added to this to perform pre-transfer charging to enhance the charge amount of the toner and eliminate the charge on the photosensitive surface where the toner is not attached. The transfer paper is brought into close contact with the photosensitive surface, the polarity of the toner is opposite to that of the back surface of the transfer paper, and the electrostatic force is used to transfer the toner on the photosensitive surface to the transfer paper.

Next, the back surface of the transfer paper that has been transferred is charged with AC discharge or DC discharge with the same polarity as the toner polarity to charge the transfer paper and remove the static electricity between the transfer paper and the latent image carrier. The transfer force is removed, and the elastic force of the transfer paper is used to separate the transfer paper from the photosensitive surface.

Problems to be Solved by the Invention However, when the image forming apparatus uses, for example, a multicolor developing apparatus, two or more kinds of toners are used. In this case, the electrical characteristics of different types of toner,
Since the grain shape, size, and other characteristics are not the same,
The adhesion between the transfer sheet and the latent image carrier after transfer is largely different, and thus the separability is also significantly different. Therefore, if the transfer and separation conditions are the same for all toners as in the above-described conventional configuration, transfer and separation can be performed for a certain toner, but other conditions are also applied to the toner. However, there is a drawback in that stable transfer and separation cannot be performed, and retransfer and separation defects frequently occur, resulting in remarkable deterioration and hindrance in image condition and paper feeding.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an image forming apparatus capable of always performing stable transfer and separation regardless of the type of toner used.

Means for Solving the Problems The above object is completely achieved by the image forming apparatus according to the present invention. In summary of the present invention, the present invention selectively develops an electrostatic latent image formed on an image carrier by using a non-magnetic toner and a magnetic toner having a smaller charge amount than the non-magnetic toner, In an image forming apparatus that transfers a toner image on an image carrier to a transfer material, a pre-transfer charging unit that charges a toner image after development and a magnetic toner toner image rather than a non-magnetic toner toner image An image forming apparatus comprising: a control unit that controls the output of the pre-transfer charging unit so as to give a large increase in the charge amount.

An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

The attached drawings are schematic configuration diagrams showing an example of an electrophotographic apparatus embodying the present invention. A cylindrical drum type latent image carrier 10 rotates in the direction of the arrow shown in the figure, and first a latent image is formed by a primary charger 11. The carrier, that is, the photosensitive surface of the photosensitive drum 10 in this embodiment is uniformly charged, and the image corresponding to the original is exposed in the next exposure unit 1 to form an electrostatic latent image. The electrostatic latent image on the photosensitive surface is selectively developed by the following first developing device 13 or second developing device 14 to form a visible powder image of a toner image.

Next, a pre-transfer exposure device 16 and a pre-transfer charger 15 that performs a DC discharge having the same polarity as the toner of the visible powder image or a discharge obtained by adding an AC discharge to the photosensitive surface on which the visible powder image is formed. To expose and charge the toner to enhance the electric charge of the toner and to remove static electricity from the portion of the photosensitive surface where no toner is attached. Is transcribed. This transfer is a transfer charger 18
Then, apply a charge of the opposite polarity to the toner on the back of the transfer paper 20,
This is achieved by transferring the visible powder image on the photosensitive surface to the transfer paper 20 using electrostatic force.

After that, the back surface of the transfer paper 20 is charged by AC discharge or a D discharge having the same polarity as the toner added thereto by a separation charger 19, and the transfer paper is charged.
The charge of 20 is removed to remove the electrostatic attraction between the transfer paper 20 and the photosensitive surface, and the elastic force of the transfer paper 20 is used to separate the transfer paper 20 from the latent image carrier 10. The toner remaining on the photosensitive surface is removed by the cleaning device 21, and the photosensitive surface is cleaned to prepare for the next cycle.

In the electrophotographic apparatus having the above structure, different kinds of toner are contained in the first developing device 13 and the second developing device 14.
Therefore, since various characteristics of both toners are different from each other, if pre-transfer charging, transfer charging and separation charging are performed under the same conditions, one toner can be stably transferred and separated, but the other toner can be stably transferred. Stable transfer and separation cannot be performed on the toner. Therefore, in the present invention, a high-voltage control device 30 is provided, and by this control device 30, the pre-transfer charging, transfer charging, and separation charging current values that are optimal for various characteristics of the toner used are selected. The pre-transfer charging device 15, the transfer charging device 18, and the separation charging device 19 are configured to discharge at a selected current value.

For example, when a one-component magnetic toner (magnetic toner) is used for the first developing device 13 and a two-component non-magnetic toner (non-magnetic toner) is used for the second developing device 14, it is photosensitive. The latter has a larger charge amount of toner on the surface, and the transfer paper 20 and the latent image carrier may differ depending on the type of external additive of the toner.
Since the latter also has better adhesion to the photosensitive surface of 10, the latter developing device, that is, the second developing device 14 is more likely to cause retransfer or defective separation.

However, in the present invention, the high voltage control device 30 allows the second
When the developing device 14 is used, the discharge current of the DC component of the pre-transfer charging is selected to be smaller than that when the developing device 13 is used, and the toner charge amount becomes excessive. The transfer current is selected to be a small value to prevent toner scattering and the like, and the separation charging is performed by selecting a large value of the AC component current or increasing the frequency, so that the transfer paper 20 To enhance the static elimination effect against. Therefore, even when the image is developed by the second developing device 14, it is possible to stably perform the transfer and the separation without causing the retransfer or the separation failure unlike the conventional case.

The following table shows an example of transfer and separation conditions when the present invention is carried out.

When the pre-transfer, transfer and separation discharges were performed under the conditions specified in the above table, the first component magnetic toner was used.
In the case of the development by the developing device 13 of the above, or in the case of the development by the second developing device 14 using the two-component non-magnetic toner,
Stable transfer and separation were possible, and there was no retransfer or defective separation.

As described above, according to the present invention, according to the type of the developed toner, the discharge current value of the pre-transfer charging, the transfer charging, and the separation charging and the AC
Since the component frequency is selected to be the optimum value, there is no occurrence of toner scattering, retransfer, improper separation, etc. during transfer.
It is possible to always perform stable transfer and separation, and obtain a high quality image, especially a color image. Further, since the discharge voltage value and frequency that match the type of toner used are simply selected by the high voltage control device 30, the configuration is simple, and there is no problem in terms of manufacturing and price.

In the above embodiment, two developing devices are used,
Although two kinds of toners are used, it goes without saying that the present invention can be applied to an electrophotographic apparatus that selectively develops using three or more kinds of toners. Further, the discharge current values of the pre-transfer charging, the transfer charging, and the separation charging shown in the above table should be controlled differently from the above values depending on the characteristics of the toner or the discharge distribution of various chargers. It should be noted that a larger effect may be chosen. Further, by controlling the wavelength of pre-transfer exposure, the exposure amount, etc. depending on the type of toner, it is possible to perform more stable transfer and separation.

[Brief description of drawings]

The accompanying drawings are schematic configuration diagrams showing an example of an electrophotographic apparatus embodying the present invention. 10: Latent image carrier 11: Primary charger 12: Exposure unit 13: First developing device 14: Second developing device 15: Pre-transfer charger 16: Pre-transfer exposing device 18: Transfer charger 19: Separation Charger 20: Transfer paper 30: High voltage controller

Claims (1)

[Claims] 1. A non-magnetic toner and a magnetic toner having a smaller amount of electric charge than the non-magnetic toner are selectively used to cause an electrostatic latent image formed on the image carrier to develop a phenomenon. In an image forming apparatus that transfers a toner image to a transfer material, a pre-transfer charging unit that charges a toner image after development and before transfer, and a large amount of charge increase for a toner image of a magnetic toner rather than a toner image of a non-magnetic toner And a control unit that controls the output of the pre-transfer charging unit so as to provide the image forming apparatus.