JP3164705B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to relates to an image forming apparatus which applies an electrophotographic, especially, image forming instrumentation by low charging potential
About the installation .

[0002]

2. Description of the Related Art F. Since the invention of electrophotography by Carlson (U.S. Pat. No. 2,297,691),
Various devices have been proposed based on this method. An electrophotographic method represented by the Carlson method is widely used at present, and its basic process is to uniformly charge a photosensitive member, form a latent image by selective exposure, form a toner image with a developer, transfer and fix.

Conventionally, as a developing method, a two-component developing method using a carrier and a toner, a one-component jumping developing method, and the like have predominantly been used. In these developing methods, in the developing step, a toner (colored resin powder) is attached to a developing area of the electrostatic latent image formed on the photoreceptor. It is considered necessary to charge the photoreceptor to a surface potential of 400 V or more, and to form and develop a high-contrast electrostatic latent image having a large potential difference between the highly charged portion and the lowly charged portion in the electrostatic latent image process. Have been.

[0004] For this reason, a photoconductive material having a charging ability of 400 V or more is required for the photoreceptor, and the selection of the material is greatly restricted. Further, since the required charging potential is large, it is necessary to increase the film thickness of the photosensitive layer. For example, in the case of an amorphous silicon (a-Si) based photosensitive layer, since the film withstand voltage is 12 V / μm, it is 400 V In order to perform the above charging, a film thickness of 34 μm or more is required. In the case of an organic photoreceptor (OPC), a film thickness of 20 μm or more is required. In the case of an a-Si type photoreceptor, a film is generally formed by a plasma glow method, and the deposition rate of the film is low, so that the manufacturing cost increases in proportion to the film thickness,
Also, the rate of occurrence of film defects increases.

On the other hand, the OPC-based photoreceptor has a low hardness of the photosensitive layer, and the film thickness is reduced at a rate of 1 μm in about 10,000 prints by use. It is not possible to maintain the dark charge amount on the surface of the photoreceptor, resulting in image defects. Therefore, the initial film thickness 20
In the case of an OPC photoreceptor of μm, there is a problem that charging failure occurs in printing of 50,000 sheets or less, and the life is short. OPC
Although it is conceivable that the thickness of the system photoreceptor layer is thicker than 20 μm, for example, about 40 μm, there is a limit in increasing the film thickness with the current film forming technology by the coating method.

Further, in order to charge the photoreceptor to a high potential of 400 V or more, a charging device having a large output and a corresponding charging time are required, resulting in an increase in the size of the device and high power consumption. In particular, the a-Si-based photoreceptor has a low charging ability, and thus requires a large charging area. Also, in the exposure step, a light quantity for quickly eliminating a surface charging potential of 400 V or more is required, which again causes a restriction on the selection of a light source, an increase in the size of the exposure apparatus, and a high power consumption. Further, the situation is the same because the developing bias voltage requires a high voltage, which leads to an increase in the size of the entire apparatus and high power consumption.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of forming an image with a low surface charging potential.

[0008]

The inventors of the present invention have conducted intensive studies to solve the above technical problems, and as a result, have found that a potential difference between a high potential portion and a low potential portion of an electrostatic latent image (hereinafter referred to as a latent image contrast potential). Has been found to be able to solve the above problem by forming a small electrostatic latent image and developing it using a predetermined conductive developer and applying a predetermined bias voltage. That is, the image forming apparatus of the present invention comprises a charging unit for uniformly charging the photosensitive member, and an electrostatic device comprising a low potential portion and a high potential portion by selectively lowering the charging potential of the photosensitive member by selective light irradiation. A latent image forming means for forming a latent image on the photoconductor, a photoconductor on which the electrostatic latent image is formed, and a two-component developer comprising a toner and a conductive magnetic carrier are brought into contact with each other;
Developing a toner image by selectively adhering toner to the electrostatic latent image while applying a developing bias voltage to the contact portion;
In the image forming device including means, wherein the latent image forming means, a potential difference between the high potential portion and a low potential portion 30
Forms an electrostatic latent image of 0 volts or less, and the two-component developer
Product specific resistance is 10 ³ to 10 ⁷ Ω · cm and volume specific resistance is
10 ¹⁴ Omega · and more toner cm, volume resistivity 10 ¹
~10 ⁵ Ω · cm, the maximum magnetization in the magnetic field of 5KOe 50
emu / g or more, maximum magnetization in a magnetic field of 1 KOe is 40 e
mu / g or more carrier, and the developing means
By applying a developing bias voltage higher than the potential of the low potential portion
The toner of the two-component developer is selectively adhered to the electrostatic latent image.
It is characterized by squeezing .

[0009]

FIG. 1 is an explanatory view showing an embodiment of the image forming apparatus of the present invention. Photosensitive layer 1 on conductive support 13
The charging unit 21 and the exposure unit (the LED exposure optical system 4)
1) A developing unit 51, a transfer unit 71, and a fixing unit 81 are provided. The photoconductor 11 may be a belt-shaped (sheet-shaped).

As the photoconductor, an a-Si photoconductor, OP
Appropriate ones such as C-based photoconductors and Se-based photoconductors can be adopted,
Further, since the surface charging potential in the charging step may be low as described later, it is also possible to use an organic or inorganic photoconductor or a photoconductive material which has been conventionally unusable due to low charging ability. it can.

Further, since the low surface charging potential provided by the charging potential is sufficient at a low potential, the thickness of the photosensitive layer 15 may be small. For example, in the case of an a-Si photosensitive member, 2 to 24 μm
Is sufficient, and the film deposition time can be reduced and the occurrence of film defects can be improved, leading to a significant cost reduction. Further, in the case of the OPC-based photoreceptor, it is possible to sufficiently form an image even with a photosensitive layer having a significantly smaller film thickness than before, and even if the photosensitive layer of the OPC-based photoreceptor becomes significantly thin due to repeated image formation. An image can be formed, and a long life can be realized.

The photoreceptor is charged by the charging unit 21 in the dark. The charging unit 21 includes the mag roller 2
5, a magnetic brush roller 23 having a conductive charging sleeve 27 and a conductive and magnetic charging particle 29,
And a charging bias power supply 31. The charging particles 29 are a conductive member to which a voltage is applied from a charging bias power supply 31 via a charging sleeve 27, which is in contact with the photoconductor 11, injects charges into the photoconductor 11, and charges the magnetic brush roller 23. The magnetic brush roller 23 rotates while contacting the photoconductor 11 with the rotation of the magnetic brush roller 23.

The surface charge potential of the photoreceptor 11 is less than 400 V, preferably 350 V or less, more preferably 300 V or less.
V or less. The image forming method of the present invention aims at lowering the surface charging potential, and the required minimum surface potential is not particularly limited as long as an image can be formed.

In the embodiment shown in FIG. 1, a case is shown in which a contact charging device using magnetic conductive particles is used in the charging unit 11, but other contact charging devices using a conductive brush or a conductive roller, a corotron charger, A corona charging device using a scorotron charger can also be used. Since the required amount of charging is small, contact charging is easy, and the size and power consumption of the apparatus can be reduced in both contact charging and corona charging.
Furthermore, even when corona charging is used, the amount of generated ozone is significantly reduced as compared with the conventional case. Further, even when a photoreceptor having a low chargeability such as an a-Si type photoreceptor is used, the required charging area (charging time) can be shortened, and the whole apparatus can be made compact.

The photoreceptor 11 whose surface is uniformly charged is then subjected to image exposure by an LED exposure optical system 41. By the image exposure, the surface potential of the exposed portion is selectively reduced, and an electrostatic latent image composed of a low potential portion and a high potential portion is formed.

The potential difference between the low potential portion and the high potential portion of the electrostatic latent image, that is, the latent image contrast potential is 300 V or less, preferably 30 to 300 V, more preferably 50 to 250 V, but it is used. It also depends on the characteristics of the photoreceptor. For example, the above range is preferable for an OPC-based photoreceptor, but 20% for an a-Si based photoreceptor.
A latent image contrast potential of up to 300 V is suitable, more preferably 30 to 250 V. As described above, since the amount of potential lowered by exposure can be reduced, the amount of exposure can be reduced, and the degree of freedom in selecting an exposure apparatus, miniaturization, and energy saving can be achieved.

In the embodiment shown in FIG. 1, the potential of a portion corresponding to a future image portion is lowered by the LED exposure optical system 41 with the use as a printer in mind. The LED exposure optical system 41 is a combination of an LED array in which LED chips are linearly arranged by the number of recording pixels and an imaging optical system such as a selfoc lens, but a rotating mirror is used instead of the LED exposure optical system. And a laser exposure optical system using an f-θ lens, or a copying optical system that irradiates reflected light from an original document when applied to a copying machine. The photoreceptor 11 on which the electrostatic latent image is formed is developed by the developing unit 51.

The developing unit 51 supplies a two-component developer 91 composed of a conductive magnetic carrier and a high-resistance or insulating toner to the surface of the photoreceptor 11 by a developing roller 53. A developing bias power source 59 for applying a developing bias voltage between the photoconductor 11 and the developing roller 53 is connected to the conductive developing sleeve 57 of the developing roller 53. The developing roller 53 includes a mag roller 55 having several magnetic poles (N and S poles) in a conductive developing sleeve 57. In the present embodiment, the photosensitive member 11 and the developing roller 53 are rotated in the directions of the arrows P and S (forward direction), respectively, to transport and supply the developer 91 to the surface of the photosensitive member 11. The developing roller 53 may rotate either the mag roller 55 or the developing sleeve 57, or both.

The developer 91 has a volume resistivity value of 1
0 ³ to 10 ⁷ Ω · cm is used.
Those having ³ to 10 ⁶ Ω · cm are preferred. The specific volume resistance of the developer was determined by placing 1.5 g of a carrier in a Teflon cylindrical body having an inner diameter of 20 mm and having an electrode of
This value is obtained by inserting a φ electrode and applying a load of 1 kg from above to measure.

At the time of development, a bias voltage is applied from a developing bias power supply 59 to develop the developing roller 53 and the photosensitive member 1.
1, a developing bias electric field is generated. This development
The bias voltage is a voltage equal to or higher than the low potential portion of the electrostatic latent image.

By the development, the toner in the developer 91 selectively adheres to the electrostatic latent image on the photoconductor, and an image formed of the toner is formed on the photoconductor 11. For example, photoconductor 1
1 is negatively charged, the potential of the image forming section is reduced by image exposure to form an electrostatic latent image, and the image is formed by the reversal developing method using negatively charged toner. The toner is selectively transferred and adhered to the low potential portion of the photoconductor 11 to form a toner image using the potential difference between the high potential portion of the photoconductor 11 and the developing bias potential. As a driving force, the negatively charged toner that is in contact with the high potential portion on the photoconductor 11 shakes off affinity with the photoconductor 11 such as van der Waals force, and the developer 9
1, and the occurrence of "fogging" in the background portion is prevented.

The following experiment was conducted using the apparatus shown in FIG. 1 in order to more specifically explain the behavior in the above-mentioned developing step. Developing method: Two-component reversal developing method Carrier: Conductive ferrite carrier (manufactured by Idemitsu Petrochemical Co., Ltd .; manufactured according to JP-A-2-187771) Toner: negatively-chargeable magnetic toner Developer specific volume resistance: 5 × 10 ⁴ Ω · cm Photoreceptor: negatively chargeable OPC photoreceptor (manufactured by Dainippon Ink and Chemicals, Inc.) Vo: absolute value of the potential of the high potential portion of the latent image (volts) Vl: low potential portion of the latent image Absolute value of the potential (volt) Vb: Absolute value of the developing bias voltage (volt), and by changing the value of Vb, the value of Vo−Vb is adjusted. The degree of “fog” was measured, and the results are shown in FIG. FIG. 2 shows that there is a minimum value Vmin that minimizes the level of “fog”. Under the conditions of this experimental example, the voltage was 30 volts, and -30 volts in consideration of the positive and negative.

When Vo>Vb> Vl (Vo-Vb> 0), the magnetic force of the toner and the magnetic force of the carrier are compared.
-Coulomb force received based on the potential difference of -Vb
As the toner is attracted to the carrier, the toner in the background portion (high potential portion) can be pulled back into the developer at the moment when the photoconductor and the developer are separated, thereby preventing "fogging" in the background portion. It is easy to set the development conditions as much as possible.

On the other hand, Vb>Vo> Vl (Vo-Vb <
In the case of 0), the direction of the Coulomb force received based on the potential difference of Vo-Vb is opposite to the above, and a force acts to leave the toner in the high potential portion (background portion) of the photoconductor. Therefore, depending on the setting conditions, as shown in FIG. 2, the fog level sharply increases. Therefore, it is desirable that the developing bias voltage be set to an intermediate value between the low potential portion and the high potential portion.
However, on the other hand, measures such as increasing the magnetic material content of the toner and increasing the magnetic force of the mag roller 55,
Even when Vb>Vo> Vl (Vo-Vb <0), the toner on the high potential portion is pulled back into the developer when the photoconductor is separated from the developer, thereby preventing the occurrence of "fog". it can. Further, as shown in FIG. 2, Vo−Vb> 0
Even in the region of, the value of the bias voltage Vb is reduced,
As the value of the horizontal axis Vo-Vb is increased, the fog level increases. This is due to the non-uniformity of the charge distribution of the toner.

That is, when performing reversal development, charging control is performed so as to negatively charge the toner, but a part of the charge is reversely charged and a part of the toner is positively charged. When the developing bias voltage is large, the positively charged toner is Vo-
The latent image is attracted by the Coulomb force of Vb (negative polarity) from the high potential portion (background portion) of the latent image. Does not occur. However, Vo-
When Vb becomes too large, the Coulomb force for attracting the positively charged toner to the high potential portion of the latent image becomes large, and "fogging" occurs in the background portion. When Vl> Vb, toner cannot be adhered to the latent image portion to perform development.

Therefore, it is necessary to set the developing bias voltage to a value higher than the potential of the low potential portion of the latent image, and it is preferable to set the developing bias voltage to a value between the potential of the low potential portion and the potential of the high potential portion of the latent image. In the range of Vo>Vb> Vl, an appropriate value is obtained. The reason why an image can be formed by a low surface charging potential and a low developing bias potential in the present invention is as follows.
It is considered as follows, and as a schematic diagram in FIG.
It was shown to.

In the two-component developing system, FIG.
As shown in (A), the photoconductor and the sleeve are electrically coupled via a carrier chain. Conventionally, even when a conductive carrier is used as the carrier, the degree of conductivity has a higher resistance than that of the present invention. Thus, as shown in FIG. 3B, the potential drops almost uniformly from the developing roller sleeve, which is a developing electrode, to the surface of the photoconductor. Assuming the case of reversal development, the gradient of the potential (electric field strength) between the sleeve and the photoconductor caused by the difference between the latent image low potential portion potential Vl and the development bias potential Vb causes the charged toner to be deposited on the photoconductor. It becomes the driving force for developing. On the other hand, the gradient of the potential between the sleeve and the photoconductor caused by the potential difference between the latent image high potential portion potential Vo and the developing bias potential Vb causes the toner in contact with the non-exposed portion to be collected in the developer and the fog to be removed. It becomes the driving force to prevent. Conventionally, since the potential is uniformly reduced between the sleeve and the photoconductor, unless the charging potential is set sufficiently high and the post-exposure potential is set sufficiently low, the development bias potential required for developing and preventing fogging is required. Cannot be set, and the developing bias potential also has a high value in order to increase the gradient of the potential for development (to increase the electric field).

On the other hand, in the present invention, since the magnetic brush made of the carrier has high conductivity, the same effect as when the proximity electrode is provided near the surface of the photoreceptor can be obtained. Therefore, as shown in FIG. 3 (C), the potential does not drop or rise uniformly between the sleeve and the photoconductor, but changes from a virtual proximity electrode near the photoconductor surface toward the photoconductor surface. The amount rises sharply and a large slope is obtained.
Since the magnitude of this inclination corresponds to the magnitude of the driving force for developing the toner and preventing fogging, a good image is formed even when the potential difference between the high potential portion and the low potential portion of the latent image of the photoconductor is set small. This makes it possible to inevitably set the developing bias potential low.

The toner image 93 formed on the photoreceptor 11 by the developing unit 51 is transferred to paper 95 by a transfer roller 73 to which a positive bias voltage is applied by a transfer bias power supply 75 by a transfer unit 73. Reference numeral 69 denotes a registration roller that sends out the paper 95.

Next, the transfer toner is transferred to the fixing unit 81.
Is fixed on the paper 95 by the fixing roller 83 (heating roller). Reference numeral 85 denotes a pressure roller. The residual toner remaining on the photoconductor 11 without being transferred at the time of transfer is removed by the cleaning blade 99. In the above description, the case where the photoreceptor 11 is negatively charged and an image is formed by reversal development using a two-component developer has been described. However, the reversal development method in which the a-Si photoreceptor is positively charged and the regular development method Other developing processes can also be applied.

Next, an example of the developer used in the present invention will be described. In the present invention, as the developer 91, a two-component developer containing at least a conductive magnetic carrier and a toner is used. The conductive magnetic carrier may be particles having both conductivity and magnetism, such as iron powder stabilized by forming a surface resistance layer, or a conductive layer may be formed on the surface of core particles having magnetism. The following two types are typical as core particles of the latter. (1) A magnetic resin particle core in which magnetic material fine particles are dispersed and supported in a binder resin. (2) A magnetic powder particle core made of magnetic powder particles such as ferrite and magnetite.

On the other hand, any of the following (a) to (c) can be applied as a method for forming a conductive surface layer on the particle core, that is, a method for making the particle core conductive. (A) Conductive fine particles such as conductive carbon black are fixed to the surface of the magnetic particle core. This method is particularly suitable for the magnetic resin particle core of the above (1). The adhesion of the conductive fine particles to the particle core is performed by uniformly mixing the conductive fine particles with the magnetic particle core in which the magnetic material fine particles are dispersed in a binder resin, and attaching the conductive fine particles to the surface of the particle core. This is performed by applying a thermal and thermal impact force to drive and fix the conductive fine particles into the surface layer of the magnetic particle core. As such a surface reforming apparatus, for example, there is a hybridizer (manufactured by Nara Machinery Co., Ltd.). Such conductive magnetic carriers are described in EP 0 492 665.

(B) A conductive resin coating layer in which conductive fine particles are dispersed in a synthetic resin is formed on the surface of the magnetic particle core. This method can be applied to both the magnetic resin particle core (2) and the magnetic resin particle core (1). Specifically, the following methods (1) to (3) can be adopted. (1) A method in which a resin is dissolved in a solvent or the like, conductive fine particles are dispersed therein, and the dispersion is applied on a particle core, and the solvent is volatilized and removed by heating to form a conductive resin coating layer. (2) Dissolve the resin in a solvent or the like, disperse conductive fine particles therein, apply it on the particle core, remove the solvent by heating, promote crosslinking and polymerization of the resin component, A method for forming a conductive resin coating layer. (3) A method in which a monomer is directly polymerized on the surface of a particle core such as ferrite particles in the presence of conductive fine particles such as carbon black, and a conductive resin coating layer is grown and formed so as to involve the conductive fine particles. This method is described in, for example, Japanese Patent Application Laid-Open No.
No. 6808 is cited and described.

(C) ITO (Indium-T) is formed by a thin film forming method such as a CVD method, a vapor deposition method, and a sputtering method.
io-Oxide), a conductive thin film of indium oxide, tin oxide, aluminum, nickel, chromium, gold, etc.
Formed on the surface of the magnetic particle core.

The average particle size of the conductive magnetic carrier is 15 to 7
0 μm, and preferably 25 to 40 μm. The magnetic force of the conductive magnetic carrier needs to be larger than a certain level. Preferably, the maximum magnetization (magnetic flux density) in a magnetic field of 5 KOe (Oersted) is 50 emu / g or more.
More preferably, it is 50 to 200 emu / g, and still more preferably 60 to 180 emu / g. The maximum magnetization in a magnetic field of 1 KOe is preferably at least 40 emu / g, preferably from 40 to 90 emu / g, and more preferably from 45 to 70 emu / g. If the magnetic force of the carrier is too small, development occurs in which the carrier is attracted to the photoconductor side during development and moves onto the photoconductor (hereinafter, referred to as carrier pulling).

The conductive magnetic carrier has a volume resistivity of 1
0 ¹ to 10 ⁵ Ω · cm, more preferably 10 ² to 10 ⁴ Ω · cm
cm. If the volume resistivity is too large, the bias potential required for development is not sufficiently applied, while if it is too small, the low potential portion of the photoconductor formed by exposure is recharged. The volume specific resistance of the conductive magnetic carrier was measured by placing 1.5 g of the carrier in a Teflon cylindrical body having an inner diameter of 20 mm and having an electrode at the bottom, inserting an electrode having an outer diameter of 20 mm, and applying a load of 1 kg from the top. It is the value when doing.

The toner has a volume resistivity of 10 ¹⁴ Ω.
・ High-resistance or insulating toner of cm or more is suitable,
Preferably, 10 ¹⁵ Ω · cm or more is used. This value is measured as in the case of the carrier. The insulating toner may be a magnetic toner or a non-magnetic toner. As the toner, a toner having the same configuration as that of the related art is used.
A binder resin, a colorant, a charge control agent, an offset preventing agent, and the like can be added. Further, a magnetic material can be added to form a magnetic toner, which is effective for improving the developing characteristics and preventing the toner from scattering in the machine.

As the binder resin, a vinyl resin or a polyester resin represented by a polystyrene resin such as a styrene / acrylic copolymer is used. Various pigments and dyes including carbon black are used as colorants; quaternary ammonium compounds, nigrosine, nigrosine base, crystal violet, and the like are used as charge control agents.
Triphenylmethane compounds and the like; olefin waxes such as low molecular weight polypropylene and low molecular weight polyethylene or modified products thereof as anti-offset agents and fixing aids; magnetite and ferrite as magnetic materials. The average particle size of the toner is preferably 20 μm or less, more preferably 5 to 15 μm.

[0039]

According to the present invention, a good image can be formed at a low charging potential. As a result, it is possible to simplify the processing in each of the charging, exposure, and development processes, to reduce the size of the apparatus used, and to save power, and to achieve excellent effects such as simplification of the photoconductor and increased flexibility. However, it has a significant ripple effect on the improvement of the entire image forming system.

Experimental Example 1 An image was formed using the apparatus shown in FIG. 1 under the following conditions. Developing method: two-component reversal developing method Photoconductor: negatively chargeable OPC photoconductor (manufactured by Dainippon Ink and Chemicals, Inc.) Developer: two-component developer composed of carrier and toner Developer specific resistance: See Table 1. Description (Volume resistivity is changed by selecting a carrier) Carrier: a conductive magnetic carrier in which ferrite particles are coated with a carbon black-containing resin layer (JP-A 2-1877)
71), and the resistance is controlled by adjusting the amount of carbon black in the surface conductive layer. Average particle diameter 37 μm Toner: negatively chargeable magnetic toner Charge amount in charging step: amount at which high potential portion potential Vo shown in Table 1 is obtained Exposure amount in latent image forming step: low potential portion potential shown in Table 1 V
Developing bias voltage Vb: Vo-30 volts (however, Vo
(Vb = Vo-20 volts only when -Vl = 40 volts)

By changing the charge amount, an image is formed by changing the difference Vo-Vl between the high potential portion potential Vo and the low potential portion potential of the electrostatic latent image, and the result is evaluated based on the following criteria. The results are shown in Table 1. Table 2 shows the values of Vc, Vl, and Vb (setting conditions) for each Vo-Vl value for reference. ：: Good image was obtained even after printing 100,000 sheets in the initial stage. △: Image density was slightly insufficient from the initial stage, or image was good in the initial stage, but image defect occurred after 100,000 sheets. Image defect

[0042]

TABLE 1 Evaluation Results Vo-Vl (V) 40 50 70 100 150 200 250 300 350 developer ^{resistance: 10 2 Ω · cm × ×} × × × × × × × 10 3 Ω · cm △ ○ ○ ^{○ ○ ○ ○ ○ × 10 4} Ω · cm △ ○ ○ ○ ○ ○ ○ ○ △ 10 5 Ω · cm × ○ ○ ○ ○ ○ ○ ○ △ 10 6 Ω · cm × ○ ○ ○ ○ ○ ○ ○ △ 10 7 Ωcm × ○ ○ ○ ○ ○ ○ ○ ○ △ 10 ⁸ Ωcm × × × × × × × × ×

[0043]

[Table 2] Table 2: Setting conditions Vo-Vl (volt) 40 50 70 100 150 200 250 300 350 Setting condition value: Vo (volt) 70 80 100 130 180 230 280 330 380 Vl (volt) 30 30 30 30 30 30 30 30 30 Vb (volt) 50 50 70 100 150 200 250 300 350

EXPERIMENTAL EXAMPLE 2 The thickness of the a-Si photosensitive layer was 5 μm in place of the OPC photosensitive member.
m-positive a-Si type photoreceptor, and forming an image in the same manner as in Experimental Example 1 except that the charging characteristics of the toner, the charging polarity, the developing bias voltage, and the polarity of the transfer bias voltage are adjusted to this. The results are shown in Tables 3 and 4.

[0045]

[Table 3]

[0046]

[Table 4]

Experimental Example 3 When the thickness of the photosensitive layer was 30 μm, 25 μm, 20 μm,
A charging condition for preparing an OPC photoconductor of 10 μm or 10 μm, forming an electrostatic latent image by performing charging and image exposure using a photoconductor of 30 μm, and obtaining 100 V as a high potential portion potential of the electrostatic latent image. (100 V condition). Hereinafter, similarly, 200 V condition, 300 V condition, 380 volt condition, 40
The 0V condition was determined.

Next, the photosensitive member is coated with a film having a thickness of 25 μm,
m, 15 μm, and 10 μm, respectively, sequentially form an electrostatic latent image under each of the above-described conditions of 100 V to 400 V, and measure the high potential portion potential Vo of the electrostatic latent image. The results are shown in FIG. Under the condition of forming a low Vo, the same high potential portion Vo can be obtained regardless of the thickness of the photosensitive layer. From this, the reproducibility of image performance can be improved even by the thickness reduction due to the wear of the OPC photosensitive layer. It can be seen that it can be obtained. On the other hand, under the 400 V condition, the high potential portion potential Vo changes greatly due to the decrease in the film thickness, and it is not expected to maintain the image performance. When the thickness of the photosensitive layer is too large, sufficient light attenuation cannot be obtained even by image exposure, and ghost occurs.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an image forming method of the present invention.

FIG. 2 is a graph showing a relationship between a difference (Vo−Vb) between a high potential portion potential Vo of an electrostatic latent image and a developing bias voltage Vb, and a fog level.

FIG. 3 is an explanatory diagram showing the principle of image formation of the present invention.

FIG. 4 is a graph showing the relationship between the thickness of a photosensitive layer of a photosensitive member and the potential of a high potential portion of an electrostatic latent image.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Photoreceptor 13 Conductive support 15 Photosensitive layer 21 Charging unit 23 Magnetic brush roller 25 Mag roller 27 Charging sleeve 29 Charging particle 31 Charging bias power supply 41 LED exposure optical system 51 Developing unit 53 Developing roller 55 Mag roller 57 Sleeve 59 Developing bias power supply 71 Transfer Unit 73 Transfer Roller 77 Transfer Bias Power Supply 81 Fixing Unit 83 Fixing Roller 85 Pressure Roller 91 Developer 93 Toner Image 95 Paper 99 Cleaning Blade

Continuation of the front page (56) References JP-A-4-102865 (JP, A) JP-A-2-109060 (JP, A) JP-A-4-178653 (JP, A) (58) Fields investigated (Int) .Cl. ⁷ , DB name) G03G 13/08-13/095 G03G 15/06-15/06 101 G03G 15/08-15/095 G03G 9/08-9/113

Claims (2)

(57) [Claims] A charging means for uniformly charging the photosensitive member; and selectively charging the photosensitive member to selectively lower a charging potential of the photosensitive member by irradiating the photosensitive member with an electrostatic latent image comprising a low potential portion and a high potential portion. A latent image forming means formed thereon, a photosensitive member having an electrostatic latent image formed thereon, and a two-component developer comprising a toner and a conductive magnetic carrier are brought into contact with each other, and a developing bias voltage is applied to the contact portion. Developing means for selectively adhering toner to an electrostatic latent image to form a toner image
If, in the image forming apparatus having a said latent image forming means, the potential difference between the high potential portion and a low potential portion to form the following electrostatic latent image 300 volts, two-component developer, the specific volume Resistance is 10 ³ to 10 ⁷ Ω · cm
With a volume resistivity of 10 ¹⁴ Ω · cm or more
Insulating toner and volume resistivity of 10 ¹ to 10 ⁵ Ω · c
m, maximum magnetization in a magnetic field of 5 KOe is less than 50 emu / g
Above, the maximum magnetization in a 1 KOe magnetic field is 40 emu / g or more
The developing means applies a developing bias voltage equal to or higher than the potential of the low-potential portion to transfer the toner of the two-component developer to an electrostatic latent image.
Imaging instrumentation, characterized in that allowed to selectively adhere to the
Place . 2. The photosensitive member according to claim 1, wherein the surface charge potential of said photosensitive member is 400 volts.
The image forming apparatus according to claim 1, wherein
Place.