JPH0667492A - Image formation method - Google Patents

Abstract

PURPOSE:To reduce a voltage to be impressed to an electrifying roller, in a method for carrying out development and exposure simultaneously and forming a sharp image. CONSTITUTION:The image forming method in which magnetic toner is carried to the image forming area of a photosensitive body 1 by a development roll 5 incorporating a permanent magnet, the photosensitive body 1 is uniformly electrified, and then the magnetic toner is selectively attached to the surface of the photosensitive body 1 by means of light irradiation carried out by an LED array is characterized in that the photosensitive body 1 is auxiliarily electrified by the electrifying roller 21 in advance and also toner contains a fixed amount of conductive, magnetic powder.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method for forming a toner image on a photoconductor using an optical image as a signal.

[0002]

2. Description of the Related Art A conventional general image forming apparatus includes a photosensitive member,
It consists of a corona charger, an optical writing head, a developing device, a transfer device, a cleaner, etc., and the device is complicated, large, and expensive.

Japanese Patent Laid-Open No. 58-987 discloses a device which solves such a problem and realizes downsizing and cost reduction of the device.
No. 46 or Japanese Patent Laid-Open No. 58-153957 discloses an image forming apparatus for forming a toner image on a photosensitive member by performing development and exposure substantially at the same time.

FIG. 2 shows the outline of this image forming apparatus. An optical writing head 3 such as an LED array is arranged inside a belt-shaped photoconductor 1, and a negative roller is applied to a developing roll 5 with the photoconductor 1 as a reference. Photoconductor 1 with a bias voltage applied
To form a visible image on the photoconductor 1 by simultaneously performing charging to the photoconductor 1, writing of image information to the photoconductor 1 by the optical writing head 3, and accumulation of toner in the image area by the developing device 4. is there. This visible image is picked up from a paper feed tray 9 by a paper feed roller 10 and transferred to a transfer position by a transfer roller 8 to which a bias voltage is applied, and the transferred toner image is then fixed by a fixing device. 1
It is fixed by 1. FIG. 3 shows the principle of charging the photoreceptor, writing image information, and developing in this image formation. The photoconductor 1 has a transparent support 12, a transparent conductive layer 13, and a transparent photoconductor layer 14. The developing roll 5 has a structure in which a hollow conductive sleeve 16 and a magnet roll 17 are concentrically housed therein, and is arranged to face the photoconductor 1 with a predetermined gap. Magnetic powder toner is attracted to the periphery thereof by a magnetic attraction force from the magnet roll 17 to form a magnetic toner layer 6,
The toner layer 6 fills the voids. Further, a bias voltage is applied between the conductive sleeve 16 and the transparent conductive layer 13 by a DC power source 20 having a voltage V _S0 . In such a structure, when the photoconductor 1 moves in the direction indicated by the arrow A in FIG.
Since the voltage of the potential difference V _S0 is applied to both surfaces of the photoconductor layer 14, the photoconductor layer 14 is charged. The charge amount of the photoconductor increases as the photoconductor moves in the contact region 18, but the potential difference on both sides at the maximum charge is V _S0 . Next, when the photoconductor moves to a position facing the optical writing head 3, an optical latent image is formed by the optical writing head 3, and thereafter, the toner moves from the toner layer 6 to the optical latent image and adheres to the visible image. An image is formed.

FIG. 4 is a diagram for explaining changes in the potential of the photoconductor layer 14 in the above-described process from charging to formation of a visible image. However, since a negative bias is applied to the surface of the photoconductor with reference to the transparent conductor and the toner is also negatively charged, the potentials related to the following description are all negative potentials. ， For convenience of explanation, we will treat it as positive. In FIG. 4, the potential V _S0 indicated by the broken line is the maximum possible voltage level on the surface of the photoconductor layer 14 obtained in the charging process as described above, and V _S is the actually obtained voltage level. _VL is the voltage level of the portion where optical writing is performed. This figure, the optical writing is performed portion, a result of the toner is accumulated by an electrostatic attraction force corresponding to the initial potential difference V _S0 -V _L, and shows a state in which the voltage of that portion increases to V _H . At this point, the toner has V
_The attraction force corresponding to _S0 - _VH is acting.

[0006]

On the other hand, the toner does not always accumulate only in the optically written portion, but adheres to the unwritten portion where the potential is V _S. This is because the electrostatic attraction force corresponding to V _S0 −V _S acts on the toner when the potential of the non-writing portion is V _S with respect to the potential V _S0 of the toner. Such toner adhesion to the non-written portion causes recording on an unnecessary portion and fogging phenomenon. Thus, as V _S is as close as possible to V _S0, it is preferable to perform sufficient charge. However, the conventional two-component toner uses magnetic particles having a positive charging property as a carrier and is mixed with insulating toner particles having a negative charging property, which is applied to the charging method handled in the present invention. In this case, the chargeability was not necessarily good because the negatively chargeable toner particles, which serve as a path for injecting charges into the photoconductor, are insulators.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of these problems, and reduces the fog phenomenon by preventing toner adhesion to unnecessary portions of the photosensitive layer 14 as much as possible. The main purpose is to do.

In the present invention, firstly, by using a mixture of conductive particles having both negative charging properties and two kinds of insulating particles, the charging efficiency and the transfer property are improved. It is a feature.

A second feature is that an auxiliary charging process by a charging roller is provided prior to the conventional main charging process of the photoconductor via toner.

[0010]

According to the present invention, both the process of efficient auxiliary charging by the charging roller and the process of charging by toner make the potential of the photosensitive member immediately before optical writing as close as possible to V _S0 of the toner potential. Toner adhesion to the writing portion is reduced.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. The difference from the conventional example of FIG. 2 is that from the facing portion of the photoconductor and the developing roller,
An auxiliary charging roller 21 is provided at a fixed distance point in the direction opposite to the moving direction of the photoconductor, and the auxiliary charging roller 21 further biases the bias voltage in the same direction as the bias voltage applied to the photoconductor by the developing roller in the conventional example. The auxiliary charging power source 22 is connected to the auxiliary roller so that the voltage is applied to the photoconductor. For convenience of explanation, the charging part by the auxiliary charging roller will be referred to as auxiliary charging below, and this part will be referred to as the auxiliary charging part. On the other hand, charging by the conductive sleeve used in the conventional device will be called main charging. Further, this portion will be referred to as a main charging portion.

In such a structure, the charging operation of the auxiliary charging section will be described first. Prior to the present invention, there is a known example of the method of charging by means of a charging roller. For example, in Japanese Patent Laid-Open No. 1-267667, the result of a study on uniform charging of the surface of the photoconductor required for high quality recording is described. . It is described that uniform charging is difficult in the range of DC 450 V to 750 V, and charging is made uniform by superimposing an AC voltage of 1100 V or more. However, a low operating voltage is desirable for equipment maintenance. Therefore, the present inventor conducted a study including experiments to effectively combine the voltage conditions of the auxiliary charging and the main charging, and by using the conductive toner, the above system requires the high voltage as described above. It was found that excellent recording quality with less fog can be obtained without any problem. A concrete experimental example will be described below. In the experiment, the rotation speed of the photosensitive member was set to 30 mm / sec, a charging roller with a volume resistivity of 10 ³ Ω · cm was used, a bias of −600 V was applied to the charging roller, and 350 Vp-p was applied by an AC power supply (not shown). After superimposing the AC voltage of, the main charging was performed with a bias of -350V. With the above process, a record with less fog was obtained.

As described above, the device of the present invention is used in the entire device, as compared with the case of applying the AC bias of 1100 Vp-p in addition to the DC bias of about 600 V in Japanese Patent Laid-Open No. 1-267667. Maximum voltage to be 600+
It is possible to keep it as low as 350/2 = 775V.

That is, in this apparatus, the charging is not concentrated on a specific portion as in the Carlson method, but is distributed at two places, so that the time spent for charging is substantially extended, resulting in low charging. There is an effect that sufficient charging can be obtained even by the applied voltage.

Another reason why the applied voltage at the time of charging can be kept low is that the conductive toner is used. Regarding the effect of conductive toner on the charging potential due to auxiliary charging, the following results were obtained from the experiment. The charging potential was measured when the insulating toner and the conductive toner were 5: 1 and 1: 1 as the toner mixing ratio (weight ratio).
The value of V was obtained. From this result, it can be seen that the higher the ratio of the conductive toner, the higher the potential obtained. The reason for this is that in the apparatus of FIG. 1, most of the toner transferred to the photoconductor in the developing process is transferred to the recording paper in the transferring process. However, the transfer is not complete, and part of the transfer proceeds to the auxiliary charging process while remaining on the photosensitive member. Therefore, in the auxiliary charging, charging is performed with the toner interposed between the photosensitive member and the charging roller. It will be. in this case,
When the ratio of the conductive toner is large, the charge injection can be easily performed. As described above, the characteristic of the auxiliary charging by the charging roller is considered to be due to the action of the conductive toner remaining on the photoconductor after the transfer.

In the above description, the minimum requirement for the toner is that it has magnetism and conductivity, but if only conductive toner is used, the transfer efficiency will decrease. For this reason, it is considered desirable to use it in the form of being mixed with insulating particles, and the form of being mixed with insulating toner is adopted.

Here, it is desirable that the conductive toner has a high conductivity for its purpose, but in practice, a volume resistivity of 10 ² to 10 ⁹ Ω · cm is practical. is there. Insulating toner has a volume resistivity of 10 ¹⁵
Ω · cm or more. Experiments were conducted on conductive toner with a volume resistivity of 10 ³ Ω · cm and 10 ⁷ Ω.
・ The results were good for both cases of cm. Of course, it is preferable to adjust the mixing ratio of the conductive toner and the insulating toner according to the level of conductivity,
The inventor has determined that the weight ratio of the conductive toner is such that the volume resistivity is 1
20% for 0 ³ Ω · cm, 40% for 10 ⁷ Ω · cm
I am trying.

[0019]

As described above, according to the present invention, as a result of using the conductive toner, the auxiliary charging is efficiently performed, so that the apparatus can be configured at a lower voltage than the conventional roller charging. It is possible. Moreover, in this device, the charging is not concentrated in a specific part like the Carlson method, but is distributed in two places, so the time spent for charging is substantially extended, and as a result, a low applied voltage is applied. However, there is an effect that sufficient charging can be obtained.

As a result, the charging potential of the photoconductor can be made higher than that in the conventional apparatus, thereby preventing the fog phenomenon.

[0021]

[Brief description of drawings]

FIG. 1 is a schematic diagram of a device configuration example of a turtle for carrying out the present invention.

FIG. 2 is a schematic diagram of a device configuration example of a turtle for explaining a conventional image forming method.

FIG. 3 is a schematic configuration diagram of main charging, exposure, and developing sections in a conventional image forming method.

FIG. 4 is a diagram illustrating changes in the potential of the photosensitive member from main charging to development in a conventional image forming method.

[Explanation of symbols]

 1: Photoconductor 3: Optical writing head 4: Developing device 5: Developing roll 6: Toner layer 8: Transfer roll 9: Paper feeding tray 10: Paper feeding roll 11: Fixing device 21: Auxiliary charging roller 22: Auxiliary charging power source

Front page continuation (72) Inventor Yoshiko Meguro 1-3-1, Gotenyama, Musashino City, Tokyo NTT Advanced Technology Co., Ltd.

Claims (1)

[Claims] 1. A light-transmissive photoconductor is provided so as to be capable of endless rotation, and the photoconductor is formed into a hollow cylindrical shape with a non-magnetic material while incorporating a permanent magnet member having a plurality of magnetic poles on its surface. The magnetic toner supplied onto the sleeve is conveyed to the recording area formed between the sleeve and the photoconductor by the relative rotation of the sleeve and the permanent magnet member so that the surface of the photoconductor is cleaned. After charging like
By irradiating a recording area with an optical signal corresponding to the original image from the back surface of the photoconductor, the magnetic toner is selectively adhered to the surface of the photoconductor to form a toner image, and the toner image is transferred to a recording paper. In an image forming method for performing image formation for post-fixing, a charging roller is provided so as to face the photoconductor, the photoconductor is preliminarily auxiliary charged by the charging roller, and then the photoconductor and the sleeve are The image forming method is characterized in that the toner is made to face each other and the toner contains at least a certain amount of magnetic powder having conductivity.