JP3363604B2 - Image forming device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic method such as a copying machine or LBP.

[0002]

2. Description of the Related Art As an output means of an external device such as a copying machine or a computer, an image forming apparatus using an electrophotographic method as shown in FIG. 5 has been conventionally proposed.

This image forming apparatus has a photosensitive drum 2 which is uniformly charged by a charging roller 1. After uniformly charging the photosensitive drum 2, the exposure device 3 corresponds to image information input from an external device, for example. Then, light irradiation is performed to form an electrostatic latent image on the photosensitive drum 2. The latent image on the photosensitive drum 2 is subjected to so-called reversal development using the toner 6 in the developing device 16, that is, the toner 6 having the same polarity as the voltage applied to the charging roller 1 is applied to the latent image portion (exposure portion) of the photosensitive drum 2. ), And the latent image is visualized as a toner image.

The obtained toner image is transferred by the transfer roller 15 onto the transfer material 7 supplied to the photosensitive drum 2.
The transfer material 7 onto which the toner image has been transferred is separated from the photosensitive drum 2 and conveyed to the fixing device 17, where it is fixed to form a permanent image. On the other hand, the photosensitive drum 2 is subjected to the next image forming process after cleaning and removing the residual toner remaining without being transferred by the cleaning device 12.

The developing method used in the developing device 16 is as follows.
A constant gap is provided between the developing sleeve 5, which is a developer carrying member, and the photosensitive drum 2, and the thin toner layer carried on the developing sleeve 5 is not directly contacted with the photosensitive drum 2, but an electrostatic latent image is formed. A developing method has been put into practical use, in which toner is selectively caused to fly by the electric field of an image to prevent background fogging, and at that time, an alternating electric field is applied to the developing gap, which is known as a jumping developing method. (JP-A-58-323)
75).

According to this jumping developing method, the toner is reciprocated by causing transfer and reverse transfer of the toner between the developing sleeve 5 and the image portion and the non-image portion on the photosensitive drum 2. An appropriate edge effect is generated in the image portion, and the sharpness of the edge of the image portion and the reproducibility of the halftone image close to the non-image portion are significantly improved.

In recent years, it has been actively practiced to reduce the particle size of the toner to improve the definition of the output image or to use the non-magnetic toner to colorize the image output device. However, since the toner having a small particle diameter or the non-magnetic toner has a weak or non-existent binding force to the developing sleeve due to the magnetic force, the fog is more likely to occur due to the adhesion to the non-image portion than the magnetic toner having the normal particle diameter. Therefore, a developing method has been proposed in which fog is less likely to occur than the jumping developing method.

The applicant has applied for the following developing method in the proposal of the image forming apparatus. That is, reversal development in which a developer having the same polarity as the charging polarity of the photosensitive drum is attached to the image portion (exposure portion) having the bright portion potential VL of the latent image formed on the photosensitive drum charged to the dark portion potential Vd for development. In the system, the first voltage V1 and the second voltage V1 are generated by the voltage generating means.
This is a developing method in which 2 is alternately generated and applied between the developing sleeve and the photosensitive drum, and the first voltage V1 and the second voltage V2 thereof satisfy the following formula.

Α × (Vd-V1)> 0 (Formula 1) α × (VL-V2) ≧ 0 (Formula 2) In the above formula, α is an index corresponding to ± of the charging polarity of the toner, Α = −1 for the negative polarity toner and α = + 1 for the positive polarity toner. The dark portion potential Vd is the non-image portion potential, and the light portion potential VL is the image portion potential. The above-mentioned developing method is called a PID developing method.

The PID developing method will be described below in comparison with the jumping developing method and the DC developing method. still,
The PID developing method satisfies the above formula regardless of the toner polarity in the reversal developing system, but here, for the sake of simplicity of description, a photosensitive drum having a negative polarity toner and a negative polarity photoreceptor such as OPC is used. The following is an example.

The first expression shows that in the PID developing method in which the developing bias shown in FIG. 6B is applied, the toner does not fly from the developing sleeve to the non-image area on the photosensitive drum. That is, the toner of negative polarity flies in the direction of higher electric potential (in the direction of increasing absolute value in the negative direction).
In the jumping developing method of applying the developing bias shown in (a), there is a section in which the potential of the developing sleeve is lower than the potential Vd of the non-image portion within one cycle of the developing bias. Adheres to the non-image area of
Fog is likely to occur. On the other hand, in the PID developing method, as shown in FIG.
As shown in (b), the potential of the developing sleeve is always the non-image portion potential Vd on the photosensitive drum within one cycle of the developing bias.
Therefore, the negative polarity toner does not fly to the non-image area. Therefore, the fogging of the non-image area can be prevented.

The second expression shows that in the PID developing method, the toner reciprocates between the developing sleeve and the photosensitive drum in the image portion which is the exposed portion. In the DC developing method in which the developing bias shown in FIG. 6C is applied, the toner does not fly to the non-image area on the photosensitive drum, so fog does not occur, but the toner flying to the image area does not cause the latent image. It is difficult to fly with high fidelity, resulting in an image with poor edge sharpness. In the PID developing method, the toner can be reciprocated in the image area to achieve an image quality equivalent to that of jumping development.

That is, according to the second equation, when the developing sleeve potential is V1, the toner flies to the image portion and develops because VL> V1. Next developing sleeve potential is V2
At this time, since V2> VL, the toner on the photosensitive drum flies back to the developing sleeve. Therefore, this voltage V1
And V2 are alternately applied to the developing sleeve,
Since the transfer of toner to the image area and the reverse transfer from the image area occur repeatedly, while the good image quality by the edge effect similar to the jumping development is reproduced in the image area, the toner is transferred to the photosensitive drum in the non-image area. Development that achieves background fog prevention by not flying is achieved.

[0014]

As described above, as described above,
By using the PID developing method, it is possible to suppress the toner from flying to the non-image portion without deteriorating the image quality and to reduce the fog even when the toner has a small particle size or is made non-magnetic. There is.

However, since the toner is the toner charged to the regular polarity, the toner reciprocates only between the developing sleeve and the image portion on the photosensitive drum, and the toner flying to the non-image portion is generated. Compared with the jumping development method, the amount is much less and fog is less likely to occur.

However, when the rubbing by the developer regulating member (regulating blade) is incomplete and the toner is charged in the opposite polarity, the toner of the opposite polarity is transferred from the developing sleeve to the photosensitive drum even in the PID developing method. Fog occurs in the non-image area because the object flies to the upper non-image area. Hereinafter, if necessary, the toner charged with the opposite polarity is referred to as “reversed toner”.
And the fog on the non-image portion due to the reversal toner is called "reversal fog". The toner charged to the regular polarity is called "regular toner".

When used in a normal temperature and humidity environment, the charge polarity of the toner is controlled by the charge control agent, external additive, etc. in the toner, so that reversal toner is less likely to occur. It exhibits excellent developability such as. However, in a low-humidity environment, even if the charge polarity of the toner is controlled by a charge control agent or the like, reversal toner is likely to occur, and thus reversal fog is likely to occur.

That is, in the one-component developing method which is widely used in the electrophotographic apparatus at present, the toner is mainly charged by frictional charging with the regulating blade. However, in general, the amount of electrostatic charge imparted to each of the toner particles by triboelectrification depends on the shape of the regulating blade, the contact state with the toner, dirt,
Depending on the environment and the like, as shown in FIG. 7A, the toner charge amount is distributed with a certain spread, and even if the amount of the reverse toner charged in the opposite polarity is small as indicated by the diagonal line, it occurs. To do. In a low-humidity environment, the amount of water in the toner resin is small and the toner resistance value rises. Therefore, as shown in FIG. 7B, it is possible to have a large amount of charge as compared with a normal-humidity environment. , The reverse toner acquires the developing property. In the PID developing method of FIG. 6B, the reverse toner flies to the non-image portion Vd of the photosensitive drum when the developing sleeve potential is V2, and reverse fog occurs.

The above is the reason why it is difficult to obtain a high-quality image in the PID developing method, especially in a low humidity environment, where reversal fog is likely to occur.

The object of the present invention is to prevent the background fog in the non-image area while reproducing a good image quality due to the edge effect similar to the jumping development even when a small particle size or non-magnetic one-component developer is used. An object of the present invention is to provide an image forming apparatus capable of developing and obtaining a high quality image.

[0021]

The above object can be achieved by an image forming apparatus according to the present invention. In summary, according to the present invention, a charging member that charges an image bearing member to a potential Vd and an electrostatic latent image including an image portion having a potential VL and a non-image portion having a potential Vd are formed by exposing the image bearing member. Exposure means, a developer carrying body carrying a one-component developer for developing the electrostatic latent image on the image carrying body, and carrying it to a developing section facing the image carrying body, and a developer carrying body at the time of development. In the image forming apparatus having a bias applying unit for applying a developing bias to the developing bias, the developing bias is a voltage that generates an electric field for urging the developer from the developer carrier to the image portion on the image carrier, A voltage of a level positioned between the potential VL and the potential Vd is V1, and a voltage for generating an electric field for urging the developer from the image portion on the image carrier to the developer carrier, which is a voltage with respect to the potential VL. The voltage at the level opposite to V1 is V2, the voltage V1 and the voltage V Where V3 is a voltage of a level located between and, and α is an index corresponding to ± of the charging polarity of the developer, α × (Vd-V1)> 0 α × (VL-V2) ≧ 0 α × VL ≦ The image forming apparatus is characterized in that the voltage V1, the voltage V2, and the voltage V3 satisfying α × V3 ≦ α × Vd α = ± 1 are repeated, and the voltage V3 is a variable bias.

According to one embodiment of the present invention, the voltage V
The duty ratio of 1 and the voltage V2 is larger than 1.
Further, according to another embodiment, the developing bias is a bias that is repeated in the order of the voltage V1, the voltage V3, and the voltage V2.

[0023]

【Example】

Example 1 FIG. 1 is a diagram showing a developing bias used in an example of the present invention. FIG. 2 is a schematic configuration diagram of an image forming apparatus usable in the present invention, and the image forming apparatus is an electrophotographic apparatus. In this embodiment, the image forming apparatus is basically the same in mechanical structure as the conventional image forming apparatus shown in FIG. 5, except that the image forming apparatus includes a developing power source 8 having a developing bias introduced therein. 2, the same reference numerals as those given in FIG. 5 denote the same members.

The image forming apparatus has a photosensitive drum as a latent image carrier indicated by reference numeral 2. The photosensitive drum 2 can be formed of a photoconductive semiconductor material such as an organic semiconductor or amorphous silicon. is there. In this embodiment, the photosensitive drum 2 is formed using a negatively chargeable organic semiconductor. A charging roller 1 is in contact with the photosensitive drum 2 with a predetermined pressure, and the charging roller 1 is a conductive roller having a resistance value of 10 ⁵ to 10 ⁷ Ω. The charging roller 1 is driven to rotate in accordance with the rotation of the photosensitive drum 2, and by applying a charging bias from the charging power source 13 to the charging roller 1, the belt photosensitive drum 2 is charged to a predetermined dark portion potential. The charging bias applied to the charging roller 1 is a voltage obtained by superimposing an AC voltage (2 kV) having a peak value twice or more the discharge threshold value on a DC voltage corresponding to the charging potential in order to uniformly charge the photosensitive drum 2. Used. In the first embodiment, as an example, the DC voltage −
A charging bias in which an AC voltage of 2 kV (Vpp) was superimposed on 500 V was applied to the charging roller 1. The photosensitive drum 2 charged to a predetermined dark portion potential receives image exposure from the exposure device 3 to form an electrostatic latent image having an image portion having a predetermined light portion potential.

A developing device 16 accommodating the negatively chargeable toner 6 is installed around the photosensitive drum 2. The developing device 16 has a developing sleeve arranged with a gap of 100 μm from the photosensitive drum 2. 5 is provided. The developing sleeve 5 contains a magnet (not shown) extending in the longitudinal direction, and the negatively charging toner 6 having the magnetic substance internally added thereto is attracted by the scooping pole of the magnet, so that the surface of the developing sleeve 5 is attracted. Is carried by. The toner 6 carried on the developing sleeve 5 is regulated in layer thickness by the regulation blade 4 to form a uniform thin toner layer having a thickness of 50 μm. The toner 6 formed in a thin layer is conveyed to the developing area facing the photosensitive drum 2 by the rotation of the developing sleeve 5 and the action of the conveying pole of the magnet, where the developing bias is applied by the developing power source 8 to the photosensitive drum. The electrostatic latent image on 2 is developed.

The negatively chargeable toner 6 used in this embodiment contains a magnetic material such as magnetite and ferrite and a charge control agent such as an azo type alloy-containing dye, and has an average particle diameter of 6 μm.
It is a small particle size toner. By using such a toner having a small particle diameter, it is possible to obtain a high-quality image faithful to the latent image from the viewpoint of the developer.

The toner image formed on the photosensitive drum 2 by development is transferred onto the transfer material 7 supplied to the photosensitive drum 2 by the transfer roller 15 to which a transfer bias is applied from the transfer power supply 10. The transfer material 7 on which the toner image is transferred is
After being separated from the photosensitive drum 2, the toner image is conveyed to the fixing device 17, where the toner image is fixed to be a permanent image. On the other hand, the photosensitive drum 2 is subjected to the next image forming process after cleaning and removing the residual toner remaining without being transferred by the cleaning device 12.

In the present embodiment, as described above, the toner 6 having a small particle size is used in the developing device 16, and thereby the development of the image faithful to the latent image and having a high resolution is realized as compared with the conventional case. There is. However, it is generally known that the smaller the particle size of the toner, the stronger the cohesive force and the adhesive force acting on the toner as compared with the magnetic force and the electrostatic force, and the more difficult the development becomes. For example, when the particle size of the toner was r, the magnetic force is proportional to r ³ proportional to the magnetic substance content in the toner, the frictional charge of the electrostatic force toner surface, thus r ² proportional to the toner surface area Although proportional, the van der Waals force is the main factor in the cohesive force and the adhesive force, and the van der Waals force is considered to be proportional to r. Therefore, the smaller the toner particle size, the more
Cohesive force and adhesive force are relatively larger than magnetic force and electrostatic force.

The toner 6 used in this embodiment is a small particle size toner, and has a larger cohesive force and adhesive force than the conventional toner,
Since the magnetic force and the electrostatic force are small, applying the conventional developing method may cause the toner to adhere to the non-image area even if a good image with high resolution is obtained in the image area on the photosensitive drum. It causes fog. Therefore, in the present embodiment, development is performed using the developing bias shown in FIG. 1 to realize an image with less fog even with a small particle size toner. This will be described below.

According to the developing bias of FIG. 1, as in the PID developing method, first, the toner (regular toner) negatively charged by the effect of the charge control agent or the like flies to the non-image portion on the photosensitive drum 2. There is nothing to do. That is, the negative polarity toner flies to a portion having a higher potential, but as shown in FIG. 1, the charging potential Vd, which is the potential of the non-image portion on the photosensitive drum 2, is
Toner flying potential V1 applied to the developing sleeve 5 (first
Voltage), the regular toner does not fly to the non-image area. Further, by holding the photosensitive drum 2 and the developing sleeve 5 at an appropriate distance, V1 forms a sufficient developing electric field with respect to VL, so that the fog in the non-image area is significantly improved and the image area is developed. can do.

Next, the potential of the developing sleeve is set to V2 (second voltage) to cause the regular toner to fly to the developing sleeve, causing the toner to reciprocate between the developing sleeve and the photosensitive drum in the image portion. This makes it possible to obtain a clear line image accompanied by an appropriate edge effect.

The conditions satisfied by the first voltage V1 and the second voltage V2 described above are as follows, as described in the section of the description of the prior art.

Α × (Vd−V1)> 0 (Formula 1) α × (VL−V2) ≧ 0 (Formula 2) Here, the application times t ₁ and t ₂ of V1 and V2 are t ₁ > t. ₂
By setting (that is, the duty ratio> 1), a larger amount of toner can be attached to the image portion.
It is possible to reduce the potential by 1 to make it difficult for discharge from the developing sleeve to occur. Further, by making the duty ratios of V1 and V2 changeable, the density adjustment becomes easy.

However, when the developing sleeve potential is set to V2, when the reverse toner charged to the opposite polarity is generated due to a low humidity environment or the like, the reverse toner is transferred from the developing sleeve 5 to the non-image portion (potential Vd on the photosensitive drum 2). )
This will cause reversal fog. Therefore, in the present invention,
As the third voltage, a rest potential V3 that satisfies the following third expression
Of the first voltage V1 and the second voltage V
It was inserted between the two to prevent reversal fog.

Α × VL ≦ α × V3 ≦ α × Vd (Formula 3) In the above, α is an index α = ± 1 corresponding to ± of the charging polarity of the toner, and the exposed portion on the photosensitive drum is developed. In the reversal development system, the third formula is satisfied regardless of the polarity of the toner. That is, the rest potential V3 is an intermediate potential between the dark portion potential Vd and the light portion potential VL, and both the normal toner and the reversal toner are set to a potential at which they are unlikely to fly to the non-image portion (Vd) on the photosensitive drum. In this embodiment, the rest potential V3 is set to V
By setting the average value of 1 and V2, the density was set to the same level as in the conventional PID developing method. It is also possible to freely change the concentration by changing the magnitude of the rest potential V3. Therefore, by applying the rest potential V3, it is possible to simultaneously suppress the ground fog and the reverse fog even in a low humidity environment.

What is important here is the application time t ₃ of the rest potential V3. The longer the rest potential V3 is applied, the more the fog-preventing effect increases, but the PID developing method is adopted because it approaches the DC developing system. The goodness of the line sharpness that it had is reduced.

Further, in order to obtain the line sharpness equivalent to that of the conventional PID developing method, it is necessary to cause the toner to reciprocate a proper number of times. The number N of times the toner reciprocates between the developing sleeve 5 and the image portion of the photosensitive drum 2 is represented by the following equation.

N = f × L / v FIG. 3 is an enlarged view of the developing section of the developing device 16. The developing sleeve 5 conveys the thin toner layer 19 carried on the developing sleeve 5 to the vicinity of the photosensitive drum 2, and has a width L with which a developing electric field of sufficient strength can be obtained by applying a developing bias from the developing power source 8 of FIG. In the developing area, toner flies to the photosensitive drum 2. When the developing power source 8 forms an alternating electric field, toner transfer and reverse transfer occur, and the number N of reciprocal movements of the toner is the number of transfer and reverse transfer. The developing area width L is measured as a width developed when the photosensitive drum 2 is stopped, and the number N of reciprocating movements of the toner is the developing frequency f.
And the peripheral speed v of the photosensitive drum 2 is used to define the above equation.

In the present invention, the number N of reciprocating movements of the toner is N ≧ 10 in order to obtain a good image due to the edge effect caused by the reciprocating movement of the toner. In this embodiment, L = 4 m
m, f = 1000 Hz, v = 100 mm / sec, N
= 40 times, good line sharpness was obtained.

As described above, the toner withdrawal potential V2, which causes the reversal fog in the PID developing method, while suppressing the density change and the deterioration of the image quality as compared with the conventional PID developing method.
It was possible to reduce the time and prevent the reversal fog. Further, by providing the rest potential V3 immediately after the toner flying potential V1, the probability that toner is present on the photosensitive drum at the end of the developing area is increased, and the reproducibility of one dot or a halftone image which is a shallow latent image is improved. It became possible to do.

As described above, by using the developing bias of the present invention, not only the toner charged to the regular polarity but also the toner charged to the opposite polarity is attached to the non-image portion on the photosensitive drum. Can be prevented, and in the image part, sharp line images and halftone images can be reproduced,
As a result, it has become possible to obtain high-quality images without fog.

In the above, the photosensitive drum 2, the charging roller 1,
Although the developing device 16 and the cleaner 12 are individually incorporated in the image forming apparatus, the present invention can be applied to a process cartridge by integrally incorporating them. Similarly, a high-quality image without fog can be stably obtained, and maintenance such as toner replacement can be simply performed.

Example 2 In this example, a case where the present invention is applied when color development is performed by using a non-magnetic toner as a developer of a developing unit for each color will be described. FIG. 4 is a schematic configuration diagram of an image forming apparatus that can be used in this embodiment.

The image forming apparatus is a color electrophotographic apparatus, which sequentially forms yellow, magenta, and cyan toner images on the photosensitive drum 2 and collectively transfers the toner images of the three colors. 7 to obtain a color image. The photosensitive drum 2 is made of a negatively chargeable organic semiconductor, but a photoconductive semiconductor material such as amorphous silicon can also be used.

First, the formation of a yellow toner image will be described. The surface of the photosensitive drum 2 is uniformly charged to a predetermined dark portion potential by the primary charger 14, and light is irradiated by the exposure device 3 based on the yellow image information input from the external device, and the latent image of the yellow image is formed on the photosensitive drum 2. An image is formed. This latent image is developed by the yellow developing device 16a using the non-chargeable non-magnetic yellow toner 6.

The yellow developing device 16a is provided with a developing sleeve 5 arranged at a distance of 100 μm from the photosensitive drum 2, and the yellow toner 6 is rubbed by a coating roller 20 in contact with the developing sleeve 5 to develop the developing sleeve. The yellow toner 6 is electrostatically adhered and carried on the surface 5. The toner 6 carried on the developing sleeve 5 is conveyed to the location of the regulating blade 4 as the developing sleeve rotates, and the toner 6 has a thickness of 2 mm.
After being regulated to a toner thin layer of 0 μm, the toner is conveyed to a developing unit facing the photosensitive drum 2. And the changeover switch 18
Is connected to the side of the yellow developing device 16a, the yellow toner 6 flies from the developing sleeve 5 to the photosensitive drum 2 by the developing bias applied to the developing sleeve 5 from the developing power source 8 and the electrostatic latent image on the photosensitive drum 2 is discharged. The image is developed as a yellow toner image. The yellow toner 6 used in this example has a negative charge control agent such as an azo-based alloy-containing dye and a yellow pigment internally added to a binder resin such as styrene acrylic.

The photosensitive drum 2 rotates while holding the yellow toner image, and the next magenta toner image is formed thereon. The surface of the photosensitive drum 2 holding the yellow toner image is recharged to a predetermined dark part potential by the primary charger 4,
Light exposure based on magenta image information is performed by the exposure device 3 to form a latent image of a magenta image on the photosensitive drum 2. Then, the magenta developing device 16b develops the latent image using a non-magnetic magenta toner similar to the yellow toner to form a magenta toner image on the photosensitive drum 2.
The same process is performed for the cyan toner image. Thus, a color image is obtained in which toner images of three colors of yellow, magenta and cyan are formed on the photosensitive drum 2 in an overlapping manner.

The three color toner images formed on the photosensitive drum 2 are collectively transferred onto the transfer material 7 supplied to the photosensitive drum 2 by the transfer charger 9. The transfer material 7 onto which the toner images of the three colors have been transferred is separated from the photosensitive drum 2 and sent to the fixing device 17, where it is fixed and becomes a full-color permanent image.

The developing units 16a, 16b and 16c in this embodiment all use non-magnetic toner as a developer. With magnetic toner, magnetic force can prevent toner from adhering to non-image areas and causing fog, but with non-magnetic toner, there is no pullback of toner due to magnetic force. Fogging easily occurs on the non-image area of the drum, and fog easily occurs. In the present embodiment, since the developing bias shown in FIG. 1 is used for development, an image with less fog can be realized even if non-magnetic toner is used.

That is, according to the developing bias of FIG. 1, as described above, the charging potential Vd, which is the potential of the non-image portion on the photosensitive drum 2, is set lower than the toner flying potential V1 applied to the developing sleeve 5. Therefore, the regular toner does not fly to the non-image portion on the photosensitive drum 2. Since V1 forms a sufficient developing electric field with respect to VL, the image area can be developed while the fog in the non-image area is significantly improved. Also, by setting the developing sleeve potential to V2,
The regular toner is caused to fly to the developing sleeve to cause the toner to reciprocate between the developing sleeve and the photosensitive drum in the image portion, whereby a clear line image accompanying an appropriate edge effect can be obtained.

At this time, when the developing sleeve potential is V2, the reversal toner may fly from the developing sleeve 5 to the non-image portion (potential Vd) on the photosensitive drum 2 and cause reversal fog. In the developing bias, the above-mentioned third
Since the rest potential V3 satisfying the formula: α × VL ≦ α × V3 ≦ α × Vd is provided, inversion fog can be prevented.

That is, the rest potential V3 is a potential intermediate between Vd and VL in which both the normal toner and the reversal toner are less likely to fly to the non-image portion (Vd) on the photosensitive drum.
Since it is provided as the average value of V1 and V2, it is possible to simultaneously suppress the ground fog and the reverse fog even in a low humidity environment.

Then, in order to obtain a line sharpness equivalent to that of the conventional PID developing method, the reciprocating motion of the toner is caused for an appropriate number of times N ≧ 10. In this embodiment, as in the previous embodiment, Development area width L = 4 mm, development frequency f
= 1000 Hz, peripheral speed v of the photosensitive drum 2 = 100 mm /
A good line sharpness was obtained by setting the number of reciprocating movements of the toner to N = f × L / v = 40 times per second.

As described above, by using the developing bias of the present invention, not only the non-magnetic toner but also the toner charged to the regular polarity and the toner charged to the opposite polarity are on the photosensitive drum. It is possible to prevent adhesion to non-image areas, reproduce sharp line images and halftone images, and obtain high-quality images without fog. Therefore, it is possible to provide an image forming apparatus having a simpler developing device and lower cost than an image forming apparatus using a conventional developing device such as a two-component developing method.

[0055]

As described above, according to the present invention,
In addition to achieving a sharp and precise image in the image area and preventing background fog in the non-image area, it is possible to prevent toner charged with the opposite polarity from adhering to the non-image area in a low humidity environment. It has become possible to reduce significantly. Therefore, it has become possible to form a high-definition image using a small particle diameter toner and a non-magnetic toner, which have been difficult to use because of a large amount of fog.

[Brief description of drawings]

FIG. 1 is a diagram showing a developing bias used in an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram showing an image forming apparatus usable in the present invention.

3 is an enlarged view showing a developing unit of a developing device installed in the image forming apparatus of FIG.

FIG. 4 is a schematic configuration diagram showing an image forming apparatus usable in the present invention.

FIG. 5 is a schematic configuration diagram showing a conventional image forming apparatus.

FIG. 6 is a diagram showing developing biases used in a jumping developing method, a PID developing method, and a DC developing method, which are used in a developing device of a conventional image forming apparatus.

FIG. 7 is a diagram showing a difference in toner charge amount distribution depending on the environment.

[Explanation of symbols]

1 charging roller 2 photosensitive drum 3 exposure equipment 5 Development sleeve 8 Development power supply 16 Developing device 16a to 16c developing device 20 coating roller

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-5-150624 (JP, A) JP-A-60-134262 (JP, A) JP-A-2-129655 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G03G 15/06 101 G03G 15/08

Claims (3)

(57) [Claims] 1. A charging member for charging an image carrier to a potential Vd, and an exposure for exposing the image carrier to form an electrostatic latent image including an image portion having a potential VL and a non-image portion having a potential Vd. Means, a developer carrying body carrying a one-component developer for developing an electrostatic latent image on the image carrying body, and carrying the developer to a developing section facing the image carrying body; In an image forming apparatus having a bias applying unit for applying a bias, the developing bias is a voltage for generating an electric field for urging the developer from the developer carrier to the image portion on the image carrier, and the potential VL. Between the voltage Vd and the potential Vd is V1,
A voltage for generating an electric field for urging the developer from the image portion on the image carrier to the developer carrier, which is a voltage V with respect to the potential VL.
Let V2 be the voltage of the level located on the side opposite to 1 and V3 be the voltage of the level located between voltage V1 and voltage V2, and let α be the exponent corresponding to ± of the charging polarity of the developer. −V1)> 0 α × (VL−V2) ≧ 0 α × VL ≦ α × V3 ≦ α × Vd α = ± 1 is a bias in which the voltage V1, the voltage V2, and the voltage V3 are repeated, and the voltage V3 is An image forming apparatus having a variable bias. 2. The image forming apparatus according to claim 1, wherein a duty ratio between the voltage V1 and the voltage V2 is larger than 1. 3. The image forming apparatus according to claim 1, wherein the developing bias is a bias repeated in the order of the voltage V1, the voltage V3, and the voltage V2.