JPS5937830B2 - Charge latent image developing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a charge latent image developing device, and more particularly to a charge latent image developing device capable of performing reversal development.

2. Description of the Related Art A developing device is known in which a charged colored powder (insulating toner) is attached using electrostatic force in order to make a latent charge image visible on the surface of a photoconductor or an insulator.

In such a developing device, when a charge latent image is formed with positive polarity charges, if the charge polarity of the toner is negative, the toner adheres to the area where the charges exist (regular development).
However, when the charge polarity of the toner is positive, the toner adheres to areas where no charge exists (reverse development). The opposite is true if the charge latent image is a negative charge. Therefore, by selecting the charge polarity of the toner, a normal or reversed image can be obtained, but it is extremely difficult to achieve this with one type of toner. Further, it is extremely difficult to prepare two types of toner because the structure becomes large. On the other hand, a developing device that uses a conductive toner instead of an insulating toner has been proposed, but since the charged state of this conductive toner changes depending on the polarity of the latent charge image, there is no relationship between the positive and negative sides of the latent charge image. Normal development will be performed.

When a bias development electrode is used in combination, the image density changes with this bias voltage and there is a possibility of reversal development, but since this toner adheres to the charge latent image of either positive or negative polarity, stable reversal development must be performed at all times. It has the disadvantage that it is difficult to An object of the present invention is to propose a developing device that can perform stable reversal development using conductive toner. The present invention relates to a device in which a latent charge image is developed by bringing a conductive toner attached to a conductive support into contact with a charge latent image surface of a recording medium, in which an anti-charge latent image formed between the conductive support and the recording medium is provided. By providing a bias power supply electrically connected to the conductive support and an insulating layer that covers the surface of the conductive support and isolates the conductive toner from the conductive support in terms of direct current, Prevent short circuit of bias voltage of
Further, by providing a developing current circuit formed between the conductive toner and the oppositely charged latent image surface of the recording medium and flowing a developing current, charges are accumulated on the insulating layer and in the toner. The invention is characterized in that unstable characteristics caused by this can be prevented and stable reversal development can be realized.

In the following explanation based on the drawings, first, reversal development will be explained based on FIGS. 1 and 2. A magnetic roll 1 and a conductive sleeve 2 that rotate relative to each other are provided concentrically,
The magnetic conductive toner 4 in the toner container 3 is transported along the outer periphery of the sleeve 2. The conductive toner 4 is adhered (magnetically attracted) to the outer periphery of the sleeve 2 without forming a layer, and the toner layer 4 comes into contact with the charge latent image surface of the recording medium 5 and develops it. The recording medium 5 is composed of a photoconductive layer forming a latent charge image and a conductive substrate, and a bias power source 6 is connected between the sleeve 2 and the opposite charge latent image surface (substrate) of the recording medium 5. FIG. 2 shows the development retention in such a developing device.

This characteristic occurs when the charge polarity of the latent image is positive, and when the bias voltage applied to the sleeve 2 from the power supply 6 is increased to a positive polarity, the image density in the charge existing area decreases and the density in the charge absent area decreases. increase This tendency continues until a certain voltage value Vb is reached, at which point the concentration of the charge existing region becomes minimum, and thereafter the concentration of the charge existing region increases. The best state for reversal development is when the bias voltage Vb is close to the image voltage in the charge existing region, but this value depends on the structure of the developing device and the physical properties of the toner. It varies depending on.

When the bias voltage is increased to a negative value, the density of the charge-absent region increases and the "fogging" increases. Therefore, in the characteristics shown in FIG. Range where there is little change in image density (
Δ) is in the range of about 50V. However, if there is a defective part (low resistance part) in the recording medium 5, the bias voltage is short-circuited through the conductive toner, which not only prevents the correct bias voltage from being applied but also causes heat generation of the toner and destruction of the recording medium. ing. The present invention proposes a developing device that does not have such drawbacks, and its basic configuration will be explained below with reference to FIG. 3. (Those with the same reference numerals as in FIG. 1 in the same drawing are equivalent, so detailed explanation thereof will be omitted.) 21 covers the outer surface of the conductive sleeve 2 with an insulating layer, and the toner layer 4 and the conductive sleeve 21 are covered with an insulating layer. 2 is cut off in terms of direct current. Reference numeral 22 denotes an electrode provided inside the toner container 3, and this electrode 22 is electrically connected to the oppositely charged latent image surface of the recording medium 5.

Although this electrical connection may be direct or indirect, it is necessary to construct a circuit in which the current flowing from the charge latent image surface through the toner layer 4 and the electrode 22 flows to the opposite charge latent image surface of the recording medium 5. Actually, this is realized by grounding the anti-charge latent image surface of the recording medium 5 and the electrode 22, respectively. The electrode 22 is connected to the toner container 3
It does not need to be located inside the sleeve, and may be located between the container of the toner layer 4 on the sleeve surface and the developing area (the contact area between the toner layer 4 and the recording medium 5). In the above configuration, the bias voltage from the bias power supply 6 is indirectly applied to the recording medium 5 via the insulating layer 21, so that a desired correct bias voltage can be applied without causing a short circuit phenomenon. .

In addition, since it is grounded through the toner layer 4, a self-bias is applied by the current flowing through the toner layer 4 during development, and the range of the appropriate range ΔV expands, thereby widening the range in which good development can be performed. The bias voltage from the bias power source 6 can be either semi-solid or fixed to achieve the objective, but in order to bring about even better results, it should be controlled according to the surface voltage of the charge latent image surface of the recording medium 5. It's better to.

In this case, it is easier to implement the measuring device by measuring the image potential before exposure or before developing an unexposed area unrelated to the image (such as outside the image frame) than by measuring the image potential after exposure. Then, it is best to be able to set, adjust, and control the voltage of the bias power supply 6 in accordance with the measured potential. In this case, once adjusted, the best reversal development can be performed by simply adjusting the light amount. becomes possible. Fourth
In the figure, the surface potential of the recording medium 5 is measured before image exposure and the magnitude of the bias voltage applied to the conductive sleeve 2 is controlled.

The recording body 5 is formed into a drum shape, and this drum rotates in the direction of the arrow.

As the drum 5 rotates, it is uniformly charged by a charger 7,
The surface potential is detected by the probe 8, imaged by the optical system 10, developed by the toner layer 4, and the toner image is transferred onto the recording paper 13 at the position of the transfer roller 14. After the transfer, the drum surface is irradiated by an erasing lamp 15 to remove residual charges on the surface, and then cleaned by a fur brush. The detection output of the probe 8 is amplified by an amplifier 9 to change the output voltage of the bias power supply 6. According to the above configuration, the bias voltage can be changed according to the voltage of the unexposed portion (charge existing region), so a high quality image can be obtained.

Although the above embodiments have been described using magnetic conductive toner, it does not need to be magnetic.

Further, although the embodiment shown in FIG. 4 is an example in which a toner image is transferred to recording paper, it is clear that the toner image may be fixed to a recording medium (recording paper). As described above, according to the present invention, in a device for developing a charge latent image by bringing a conductive toner attached to a conductive support into contact with the charge latent image surface of a recording medium, the conductive support a bias power supply electrically connected to the oppositely charged latent image surface of the body, and an insulating layer that covers the surface of the conductive support and cuts off the conductive support and the conductive toner in terms of direct current. This prevents short-circuiting of the bias voltage during reversal development, and furthermore, by providing a developing current circuit formed between the conductive toner and the oppositely charged latent image surface of the recording medium to flow the developing current. Since unstable characteristics due to charge accumulation on the insulating layer and in the toner are prevented, the effect of realizing stable reversal development without fogging can be obtained.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the reversal developing device, Figure 2 is a development characteristic diagram,
3 and 4 are schematic diagrams showing two embodiments of the reversal developing device according to the present invention.

Claims (1)

[Scope of Claims] 1. A device in which a latent charge image is developed by bringing a conductive toner attached to a conductive support into contact with a charge latent image surface of a recording medium, wherein the conductive support and the recording medium have opposite charges. a bias power supply electrically connected to the latent image surface; an insulating layer that covers the surface of the conductive support to cut off direct current between the conductive support and the conductive toner; and a conductive toner and a recording layer. 1. A charge latent image developing device comprising: a developing current circuit formed between opposite charge latent image images of a body. 2. The charge latent image developing device according to claim 1, wherein the developing current circuit is formed between the conductive toner in the toner container and the oppositely charged latent image surface of the recording medium.