JPH1020633A - Image forming device provided with developing bias control function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device forming an excellent image without lowering developing efficiency even when a resistance value rises because of the resistance fluctuation of a load body on which developing bias is impressed by environmental change. SOLUTION: This image forming device is provided with a photoreceptor or a developing roller or a toner supply roller constituted of the electric load body 29, and a developing bias impressing means 19 impressing the developing bias for developing a latent image formed on the photoreceptor on the load body, and provided with a developing bias control function to control the impressing means 19 to control the developing bias. It is provided with resistance value change detection means 24 and 27 detecting the change of the resistance value of the load body 29 before a developing process, and developing bias control means 20 and 27 controlling the impressing means 19 according to output from the detection means 26 and 27, so that the developing bias is varied in accordance with the change of the resistance value of the load body.

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 having a developing bias control function for controlling a developing bias for developing a latent image formed on a photosensitive member.

[0002]

2. Description of the Related Art Conventionally, an electrophotographic apparatus based on the so-called Carlson process, which is a kind of image forming apparatus, is well-known. It is necessary to apply a high voltage of 8 KV or more to the wire, and as a result, ozone and nitrogen oxides and ammonium salts, which are discharge products thereof, are generated, and these are adsorbed on the surface of the photoreceptor, so that image flow is likely to occur.

In order to solve such a drawback, a roller configured to contact a conductive roller on a photosensitive drum and apply a DC voltage to the conductive roller to perform contact charging of the photosensitive drum in a dark place. Although there is a charging method, even in this charging method, since there is a minute wedge-shaped gap between the photosensitive drum and the charging roller, a slight discharge phenomenon occurs in that portion, and the generation of ozone is recognized. However, the disadvantages described above cannot always be eliminated.

On the other hand, in recent years, there has been a photosensitive drum used in an electrophotographic apparatus which uses an a-Si drum in order to improve durability and achieve free maintenance.
Si has a high hygroscopicity compared to an organic semiconductor, so that the image flow is likely to occur in the a-Si drum more frequently.
A sheet heater or other heating element is disposed on the back side of the photosensitive drum, and the photosensitive drum is heated to prevent the occurrence of the image deletion.

However, providing a heater requires heat control means and the like, which not only complicates the configuration, but also makes the system complicated when a heater is used especially in miniaturization and personalization of copiers and printers. turn into.
In addition, a certain time is required for raising the temperature of the heater, and the time from when the power is turned on to when printing is performed (warm-up time) is long, which requires power consumption. When the photoconductor is heated, the TG temperature (glass transition temperature) of the toner is increased.
Since the temperature is raised to a value close to the temperature, toner adheres to the surface of the photoconductor. Various problems occur.

Further, even in a state in which image deletion does not occur, in this type of electrophotographic apparatus, toner adheres to a developing area of an electrostatic latent image formed on a photosensitive member in a developing step, and a toner adheres to a non-developing area. In order to prevent adhesion, the photosensitive member surface potential is set to 400 V or more in the charging step, and the difference between the high potential portions of the electrostatic latent image formed in the exposure step is set to 400 V.
As described above, the developing potential was required to be 200 V or more. Therefore, a photoconductive material having a charging ability of 400 V or more is required for the photoreceptor, and there are great restrictions on material selection and film thickness setting.

Further, a-Si tends to cause a so-called “fogging” phenomenon in which toner adheres to a white background. This is a phenomenon in which the toner in the apparatus adheres to the surface of the photoreceptor due to an image force or the like. The image power of the toner is greatly affected by the relative permittivity of the photosensitive layer, and the higher the relative permittivity, the higher the image power. This relative dielectric constant is usually 3 to 3 for an organic photoreceptor.
Since it is 3.5, and a-Si is as large as about 10 to 12, a-fogging phenomenon easily occurs in a-Si.

Conventionally, a pulverized toner has been used. This pulverized toner is obtained by cooling a kneaded material obtained by mixing small particles such as a resin, a colorant and a charge control agent, and then coarsely pulverized by a hammer mill, a cutter mill or the like, and further jet-milled. 8 to 1 depending on the size
It is made by finely pulverizing it to about 5 μm. Although it is relatively easy to make, it is made into an irregular shape with irregularities, and the charge tends to concentrate on the protrusions, and the surface of the photoreceptor may come into contact with a plurality of protrusions for one particle. In some cases, the image power increases.

On the other hand, in the polymerization toner, at the stage of polymerizing a polymer from a monomer, a toner is manufactured by incorporating a colorant, a charge control agent, and the like into the polymer particles.
Spherical particles are obtained, and the charge is uniformly charged on the spherical particles. Therefore, point contact with the surface of the photoreceptor results in few contact points with one particle and small mirror image power.

Under such circumstances, the applicant of the present application has used an a-Si drum prior to the present application, and particularly, uniformly charged the photosensitive member including a discharge phenomenon, such as a corona discharger, a charging roller, and a charging brush. An application has been filed for the purpose of providing an electrophotographic apparatus capable of forming a clear image without causing image deletion and a 'fogging' phenomenon even in an electrophotographic apparatus which has performed the above. That is, the thickness of the surface layer of the electrophotographic photoreceptor obtained by laminating and covering the photoconductive layer and the surface layer on the substrate is set to 25.
μm or less of an a-Si layer, the surface potential of the photoreceptor is set to about 400 V or less, and a developing roller with a development potential of about 150 V or less is brought into rolling contact with the surface layer. Roller volume resistivity is 3 × 1
Set to 0 ⁷ [Omega] cm or less, on the developing roller, discloses an electrophotographic apparatus configured to perform development of the latent image of the photosensitive body while forming a thin layer of toner particles created by a polymerization method I have. An apparatus according to this application is a non-magnetic one-component developing method combining a-Si and a polymerized toner, and provides an image forming apparatus having high developing efficiency, realizing development by a low electric field, and having high transfer efficiency. Can be.

[0011]

However, a-S
i has an electrical resistance of 10 ⁹ Ωcm, and an OPC (organic photoreceptor) has an electrical resistance of 10 ¹² to ¹³ Ωcm.
The electrical resistance of the developing roller used for the a-Si photosensitive member is also low because the electrical resistance is lower than that of the a-Si photosensitive member. Therefore, the degree of fluctuation of the resistance value due to the leak resistance in environmental changes such as high temperature and high humidity or low temperature and low humidity is large. .

In particular, when the resistance value increases due to a change in resistance of the developing roller due to a change in environment, the developing bias changes in a direction in which the potential difference between the photosensitive member and the developing roller decreases,
The recovery of toner in a white background portion of the image on the surface of the photoreceptor is reduced to lower the development efficiency.

Further, in the case of a developing mechanism for recovering the residual toner which is the transfer residual toner of the photoconductor at the same time as the development, when the transfer efficiency of the photoconductor decreases and the residual toner increases, the residual toner is removed from the surface of the photoconductor. Cannot be collected and ghosts occur. As described above, this phenomenon is particularly remarkable because the developing bias decreases due to an increase in the resistance value of the developing roller.

In view of the above circumstances, the present invention provides a good image without lowering the development efficiency even if the resistance value increases due to a change in resistance of a load to which a development bias is applied during development due to a change in environment. It is an object of the present invention to provide an image forming apparatus for forming an image. Another object of the present invention is to form an image forming apparatus using an a-Si drum while forming a clear image which does not cause image deletion and a 'fogging' phenomenon while considering simplification of the configuration and safety. It is another object of the present invention to provide an obtained image forming apparatus.

[0015]

According to the present invention, there is provided a photosensitive member or a developing roller or a toner supply roller comprising an electric load member, and a developing device for developing a latent image formed on the photosensitive member on the load member. A developing bias applying means for applying a bias, and a developing bias control function for controlling the developing bias by controlling the developing bias applying means. And a developing bias control means for controlling the developing bias applying means based on the output of the resistance change detecting means, and the developing bias is varied according to the resistance change of the load. It is characterized by the following.

It is also an effective means of the present invention that the developing bias applied to the load is applied between the developing roller and the supply roller.

As described above, according to the present invention, as shown in FIG. 3, the photosensitive member (photosensitive drum) 1, which is an electric load member (load) 29 to which a developing bias is applied, or the developing mechanism (developing mechanism) The developing bias applying means 19 for applying a developing bias to the developing roller 40 or the supply roller 45 in the unit 4 includes a resistance change detecting means (detecting a resistance change of the load body 29) prior to the developing process. 2
4, 27) and a developing bias control means (20, 2) for controlling the developing bias by the output of the resistance value change detecting means.
7).

Therefore, prior to the development process, the load 29
Is detected. Then, when a resistance value higher than a predetermined resistance value of normal temperature and normal humidity at a temperature of 20 ° C. and a humidity of 60% is detected, a voltage lower than a predetermined voltage value of normal temperature and normal humidity is applied to the load body 29 during the development process, and a developing bias is applied. Control within a predetermined range. When a resistance value lower than the predetermined resistance value of the normal temperature and the normal humidity is detected, a voltage higher than the predetermined voltage of the normal temperature and the normal humidity is applied to the load body 29 during the development process, and the development bias is controlled to a predetermined range.

Since the developing bias is made variable in accordance with the change in the resistance value of the load body 29, the developing bias is applied in such a direction that the potential difference between the photosensitive member and the developing roller or between the developing roller and the supply roller decreases. Therefore, the recovery of the toner on the white background portion of the image on the surface of the photoreceptor is reduced, so that the development efficiency and the toner recovery rate are not reduced.

Further, the photoreceptor is formed of a-Si,
A layer of toner particles on the developing roller that rubs against the surface of the photoconductor is set to 0.3 to 0.9 mg / cm ² , or a developing mechanism having the developing roller and the toner supply roller is provided. It is an effective means of the present invention that the developing mechanism is provided with a collecting means for collecting the residual toner of the photoreceptor, or that toner particles produced by a polymerization method are used.

The present invention, as shown enlarged in FIG.
In the a-Si photoreceptor, a photoconductive layer 1b and a surface layer 1c are generally laminated on a conductive substrate 1a made of an aluminum cylinder, and the surface layer 1c is formed of an α-SiC-based inorganic high resistance or Using an insulating material, the photoconductive layer 1b
The surface potential Vo and the latent image potential distribution above are maintained.

Conventionally, discharge products such as nitrate ions and ammonium ions generated by corona discharge during the image forming process are adsorbed on the surface of the photoreceptor, and they are deposited on the photoconductive layer under a high temperature and high humidity environment. The latent image charges formed on the surface layer move based on the surface potential and the latent image potential distribution in the surface direction, causing a charge flow, that is, an image flow. In this case, the image flows around the latent image, and a phenomenon of “bleeding” of the image occurs.

That is, in the present invention, since the surface layer of the photoreceptor is formed of an a-Si layer having a lower electric resistance than that of the OPC, the volume resistivity of the developing roller rubbing the surface layer is reduced. Since it can be set to a low value (for example, 3 × 10 ⁷ Ωcm or less), an excessive voltage drop in the roller layer is prevented, and a synergistic effect with the low relative dielectric constant of the a-Si photoreceptor is used. The potential and the developing potential of the developing roller can be set low, and the occurrence of the image deletion phenomenon can be suppressed.

As a result, according to the present invention, the surface potential of the photosensitive member is set to about 400 V or less, preferably 300 to 350 V, and the developing potential of the developing roller is set to about 150 V.
V or less, desirably from 80 to 120 V, whereby the thickness of the photoreceptor can be reduced to 25 μm or less, and the layer of toner particles on the developing roller can be set to 0.1 V or less.
3 to 0.9 mg / cm ² , desirably 0.4 to 0.8
mg / cm ² , and a low-cost image forming apparatus can be provided.

Further, in the developing container 41 of the developing mechanism (developing unit) 4, a developing roller 40 operating as a toner collecting means rubs against the surface of the photoreceptor 1 while scraping off the residual toner on the photoreceptor 1. Since the development is performed by applying new toner, the toner can be collected in the developing container, and the residual toner not used for the development can be reused. In addition, by adopting such a configuration, it is possible to form an image without causing image deletion even in a state where a heater is not built in the base supporting the photoconductive layer 1b.

In the present invention, the latent image on the photosensitive member is developed while forming a thin layer of toner particles formed by a polymerization method on the developing roller. It is uniformly charged, and has a point contact with the surface of the photoreceptor, so that there are few points of contact with one toner particle, the image power is small, and the 'fogging' phenomenon is small.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be illustratively described in detail with reference to the drawings. However, unless otherwise specified, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention, but are merely illustrative examples. Not just.

FIG. 1 shows an embodiment of an image forming apparatus to which the present invention is applied. Exposure is performed along a rotation direction around an a-Si photosensitive drum (photosensitive body) 1 rotating clockwise in FIG. An optical system including the LED head 2 and the SELFOC lens 3, a developing unit 4, a transfer roller 5, a cleaning member 6, a neutralizing lamp 7, and a charging unit 8 are provided.

Next, each component will be described.
As shown in A, the photosensitive drum 1 has a conductive support 1a.
A photoconductive layer 1b and a surface layer 1c are laminated and formed thereon, a carrier injection blocking layer 1e is provided between the conductive support 1a and the photoconductive layer 1b, and a photoconductive layer 1b and the surface layer 1c are formed.
A transition layer 1f is interposed between them. The support 1a is generally made of an aluminum cylindrical body.
It is formed of a metal material such as S, Ti, Ni, Au, Ag, etc., an inorganic material such as glass having a conductive film adhered on the surface, or a transparent resin such as epoxy, and has a thickness of 3 mm in this embodiment.
To set the outer diameter to 30 mm and 254 in the axial direction.
An aluminum cylindrical body having a length of mm is used.

The carrier injection blocking layer 1e is a photoconductive layer 1
Various materials are used depending on the material of b. When an a-Si-based material is used for the photoconductive layer 1b, it is preferable to use the a-Si-based carrier injection blocking layer 1e.

The a-Si-based photoconductive layer 1b is formed into a film by a glow discharge decomposition method, a sputtering method, an ECR method, an evaporation method, or the like. In forming the film, an element for terminating a dangling bond, for example, (H) And halogen 5 to 40w
It is better to contain t%. That is, a-
A photoconductor made of Si: H is used. When the developing bias is positive, non-doped or Va group elements are contained in order to increase the mobility of electrons. When the developing bias is negative, the movement of holes is performed. In order to increase the degree, it is preferable to include a group IIIa element. If necessary, elements such as C, O, and N may be contained in order to obtain desired characteristics such as electric characteristics such as dark conductivity and photoconductivity, and optical band gap.

The thickness of the entire photoconductive layer 1b is:
The thickness is preferably about 3 to 50 μm in order to ensure necessary charging and insulation withstand voltage, absorb exposed light, and suppress the above-described residual potential.

The surface layer 1c has a thickness of 25 μm.
Below, glow discharge decomposition method, sputtering method, ECR
A film is formed by a method, a vapor deposition method, etc., and the element ratio composition formula (a-
When expressed as Si _{1 -X} C _X : H), x is 0.95 ≦
It is composed of hydroxide amorphous silicon carbide having x <1 and a dynamic indentation hardness of the outermost surface (free surface layer) of 50 to 200 Kgf / mm ² , and particularly has a resistance value of 10 ¹² to 10 ^13. Set to a resistance value in the Ω · cm range. The surface layer 1c is formed from the photoconductive layer 1b from the outermost surface side.
The hardness is set so as to gradually increase as it goes to the far side of the side.

In order to form a gradient of the hardness as described above (a gradient such that the hardness gradually increases from the outermost surface toward the photoconductive layer 1b side), for example, the surface layer 1c is glowed. When a film is formed by the discharge decomposition method, the ratio of the C-containing gas to the Si-containing gas in the source gas is gradually increased with time, the gas pressure during film formation is gradually increased, and the hydrogen gas as the source gas is used. , The discharge power is gradually reduced, and the substrate temperature of the aluminum cylindrical drum is gradually lowered.

Further, between the photoconductive layer 1b and the surface layer 1c,
It is preferable to provide a transition layer 1f in which the C content in a-SiC: H is smaller than the C content in the surface layer 1c. Further, the C content of the transition layer 1f may be changed in the layer to have a gradient of the content. Such a transition layer 1
By providing f, the traveling of the photocarriers generated in the photoconductive layer 1b becomes smooth, the photosensitivity is high, the residual potential is low, and the image characteristics are good. The thickness of such a transition layer 1f is 1 μm or less, preferably 0.05 to
It is set in the range of 0.5 μm.

The exposure LED head 2 has an exposure wavelength of 6
A head array of 85 nm is used, and the head array is configured to perform a dynamic drive to divide the exposure into 64 bits × 40 times for each scanning line.

The developing mechanism (developing unit) 4 includes a developing container 41 containing a non-magnetic one-component toner, a developing roller 40 composed of an elastic body 42 made of an elastic material such as urethane rubber, A developing blade 17 that regulates the thickness of the toner layer, a supply roller 45 that supplies toner to the developing roller 40, and the like are provided.
DC developing bias power supplies E1 (350V), E2 (350V), E3 (1
20V) to perform development.

In the developing unit 4, as shown in FIG. 2, a new toner 50 is supplied to the developing roller 40 by a supply roller 45 rotating counterclockwise, and the developing blade 17 for regulating the toner layer thickness. , it is regulated by the toner layer thickness ^{0.3mg / cm 2 ~0.9mg / cm 2} ,
It is supplied to the photoconductor 1.

On the other hand, the residual toner 49 of the toner not transferred to the recording paper 9 comes into contact with the elastic body 42 of the developing roller 40 again. Rotates rapidly, the residual toner 49 is scraped off by the elastic body 42 of the developing roller 40 as indicated by reference numeral 51, and new toner 48 develops the latent image on the surface of the photoconductor 1.

Further, as shown by 51, the residual toner 52 adhered to the developing roller 40 without dropping to the lower portion in the developing container 41 is removed in a nip area where the developing roller 40 and the supply roller 45 affect each other. Reference numeral 53 denotes a supply roller 45 which rotates in a direction opposite to the developing roller 42.
As shown in (1), it is dropped below the developing container 41 and collected.

In this embodiment, the photosensitive member 1 and the developing roller 40
Is of a rubbing type, and if the resistance value is too low, the toner may be a polymerized toner and a high resistance of 10 ⁶ Ωcm or more or an insulating toner may be used in view of leakage. In the polymerized toner, at the stage of polymerizing a polymer from a monomer, toner particles are produced by incorporating a colorant, a charge control agent, and the like into the polymer particles, so that spherical particles are obtained, and the charges are uniformly charged on the spherical particles. Therefore, due to point contact with the surface of the photoreceptor, the number of contact points with respect to one particle is small and the image force is small.

The developing roller 40 is provided on the surface layer 1 of the photosensitive member 1.
c is rubbed with a nip width of 1 mm or more (preferably 1 to 2 mm), and rotates in the same direction at the rubbing position. (Preferably, the toner layer thickness is 0.3 mg / cm ^{2 to} 0.9 mg /
The speed is set to 1.1 to 6.0 times of cm ² . More preferably, the toner layer thickness is 0.7 mg.
/ Cm ² is set to a speed of 1.2 to 5.0 times.

The layer thickness of the toner particles is 0.3 mg / c.
m ^{2 to} 1.0 mg / cm ² , preferably 0.3 mg / c
m ^{2 to} 0.9 mg / cm ² , more preferably 0.4 mg / cm ²
cm ^{2 to} 0.8 mg / cm ² . Transfer roller 5
Uses a conductive roller to increase the transfer efficiency to the recording paper 9, applies a transfer bias having a polarity opposite to the charging potential of the toner, and uniformly presses the peripheral surface of the photosensitive drum 1. It is configured to be rotatable in synchronization with 1.

The cleaning member 6 is located on the downstream side of the transfer roller 5 and rotates conductive fibers such as polyester, acrylic, carbon-containing rayon, nylon, and vinylon around a rotation axis or by winding the fibers. It is formed as a paper dust removing roller 6a in a roller shape, and its outer peripheral surface contacts the surface of the photoreceptor 1, and is arranged so as to rotate in a direction opposite to the rotation direction of the photoreceptor 1 at the contact position. Since the paper dust of the recording paper 9 does not adhere to the opening 1 as much as the toner,
The conductive roller 6a can remove the toner with a force smaller than the toner removing force.

The charging unit 8 was uniformly charged on the photoreceptor by a well-known scorotron charger. In the figure, 81 is a corona discharge wire, 82 is a control grid, 8
3 is a discharge bias and 84 is a charge control bias.

Since the roller 6a of the cleaning member 6 is made of a conductive material, the roller 6a may also serve as a charge removing roller for removing charge on the surface of the photosensitive member 1 instead of the charge removing lamp 7. Alternatively, the charge removing lamp 7 and the charging unit 8 may be removed, and the photosensitive member 1 may be charged by the roller 6a.

In this embodiment, as shown in FIG. 3, a developing bias applying means 19 is provided. The developing bias applying means 19 is provided for the photosensitive member (photosensitive drum) 1 or
The developing roller 40 in the developing mechanism (developing unit) 4 or the supply roller 45 or the like functions to adjust and apply the developing bias to a load body (load) 29 to which the developing bias is applied.

The developing bias applying means 19 has an emitter follower type transistor 20 having a collector C connected to a terminal for outputting a DC voltage of E5 and a base connected to a transmitter 30 having a base drive circuit. The emitter E of the transistor 20 is grounded via a diode 32 and is connected to a transformer 21 via a filter circuit 31.
Is connected to one terminal of the first coil, the other terminal is connected to the collector of the oscillation transistor 22, the emitter of the oscillation transistor 22 is grounded, and the base is
It is connected to a transmitter 23 having a drive circuit.

The second coil side of the transformer 21 is a diode,
A third coil unit 25 is provided on the output side of the transformer 21 as a reference voltage for A / D conversion. A connection point between the diode and the capacitor 26 is connected to one end of a load 29, and the other end is grounded via an Rs resistor 24. The connection point between the resistor 24 and the load 29 is connected to a CPU (central processing element) 27, and the transmitter 30 is connected to an output terminal of the CPU 27.
7, the ON time t of the transistor 20, the switching cycle T, and the like are changed so that different voltages are applied to the first coil side of the transformer 21.

The output terminal of the CPU 27 is connected to the transmitter 2
3 and controls the oscillation of the oscillation transistor 22. Therefore, the developing bias applying means 19
Step-down type chopper type switching power supply circuit and D
A combination of C-DC converters, where E5 = 2
The DC voltage of 4 V is reduced to 8 to 10 V, and the
To the primary coil, and 80 to 10 in the secondary coil.
The voltage is raised to 0 V and applied to the load 29. And the third
The output voltage of the coil unit 25 and the terminal voltage of the resistor 24 are configured to be input to the input terminals of the CPU 27, respectively.
The control of the input voltage value to the transformer 21 and the voltage value applied to the load 29 are performed according to the program.

Since the developing bias applying means 19 of FIG. 3 is configured as described above, the CPU 27 oscillates the transmitter 23 and drives the transmitter 30 to operate the transistor 20 by operating a power switch (not shown). onof
f, and the input voltage Vio is applied to the transformer 21.
A transformed AC voltage is generated in the second coil, and this AC voltage is converted to DC through a diode, and the DC voltage Voo is applied to the load 29.

The current I flowing through the load 29 generates the terminal voltage Vs of the resistor 24. The terminal voltage Vs is subjected to A / D conversion in the CPU 27 and is subjected to arithmetic processing. When this Vs is equal to the reference voltage Vso, the ON time of the transistor 20 is set so that the DC voltage Voo is continuously applied to the load. t and the switching period T are adjusted and controlled.

The above operation is performed before the developing mechanism 4 starts the developing operation. Now, when the environmental conditions are low temperature and low humidity, the load resistance increases, the terminal voltage Vs of the resistor 24 decreases, and when the terminal voltage reaches Vsd, a voltage Vod lower than the applied voltage Voo is developed to reduce the terminal voltage between the load resistors 29. Sometimes applied. In addition, environmental conditions become high temperature and high humidity,
When the load resistance decreases and the terminal voltage Vs of the resistor 24 increases and becomes Vsu, a voltage Vou higher than the applied voltage Voo is applied during development in order to increase the terminal voltage between the load resistors 29.

As described above, prior to the development process, the load 29
Is detected. Then, when a resistance value higher than a predetermined resistance value of normal temperature and normal humidity at a temperature of 20 ° C. and a humidity of 60% is detected, a voltage lower than a predetermined voltage value of normal temperature and normal humidity is applied to the load body 29 during the development process, and a developing bias is applied. Control within a predetermined range. When a resistance value lower than the predetermined resistance value of the normal temperature and the normal humidity is detected, a voltage higher than the predetermined voltage of the normal temperature and the normal humidity is applied to the load body 29 during the development process, and the development bias is controlled to a predetermined range.

In the control of the developing bias, if the load is between the photosensitive member and the developing roller, the load is the developing roller or the photosensitive member.
The load is a developing roller or a supply roller, and the developing bias is made variable according to a change in the resistance value of the load body 29 as the load. Therefore, the potential difference between the photosensitive member and the developing roller, or the developing roller and the supply roller Needless to say, a voltage may be appropriately applied to the load body 29 in a direction in which the potential difference decreases to control the developing bias to change. As a result, the recovery of the toner in the white background portion of the image on the photoreceptor surface is reduced, and the development efficiency and the toner recovery rate are not reduced.

When the developing bias is determined, the process proceeds to the developing step.
Since the bias is appropriately set between around 00V,
By applying the high-voltage discharge bias to charge the surface potential Vk of the photoconductor drum 1 to the above-mentioned set value, a predetermined latent image is exposed by the exposure head 2. Thereafter, a toner image created by a polymerization method is attached to the latent image by the developing unit 4 and transferred to a recording medium (recording paper) 9 inserted between the photoconductor 1 and the transfer roller 5.

The recording paper 9 is sent out from a storage (not shown), inserted between the photosensitive member 1 and the transfer roller 5, and sent out to a fixing step (not shown) after the transfer. In this process, especially before and after including the transfer process, the paper dust is separated from the recording paper by pressure contact with a roller or the like. Then, the separated paper dust adheres to the surface of the photoconductor 1 and is transferred to the cleaning member 6 located on the downstream side of the transfer roller 5.

The paper dust removing roller 6a of the cleaning member 6
Is that the outer periphery contacts the surface of the photoreceptor 1 and rotates at the contact position in a direction opposite to the rotation direction of the photoreceptor 1, so that the paper dust of the recording paper 9 is not as closely adhered to the opening 1 as the toner. ,
It is removed by the conductive roller 6a described above.

On the other hand, in FIG. 2, the residual toner 49 which is not transferred to the recording paper 9 contacts the elastic body 42 of the developing roller 40 again. The developing roller 40 is a photosensitive member 1
Since the peripheral speed of the photosensitive member 1 is higher than that of the photosensitive member 1 at the contact position, the residual toner 49 is scraped off by the elastic member 42 of the developing roller 40 as indicated by reference numeral 51 and new toner 48 is removed. Develop the latent image on the surface.

Further, the residual toner denoted by reference numeral 51 contains a small amount of photoreceptor powder obtained by polishing the surface of photoreceptor 1. The residual toner 51 is scraped off by the developing roller 40 and falls below the developing container 41. However, the residual toner 51 may adhere to the surface of the developing roller 40 as indicated by reference numeral 52 and may be transferred. In a nip region where both rollers affect each other, the supply roller 45 is rotated in a direction opposite to the developing roller 40, and is dropped and collected below the developing container 41 as indicated by reference numeral 53.

The residual toner 53 is mixed with the new toner in the developing container 41, but is diluted because the amount is small relative to the amount of the new toner. Therefore,
It is desirable that the residual toner 53 be recirculated in the developing container 41, injected into the new toner near the entrance where the new toner is supplied, and stirred.

The present embodiment can prevent image deletion. Here, the cause of the image deletion will be described. As shown in an enlarged manner in FIG. 1A, in the a-Si photosensitive member, a photoconductive layer 1b and a surface layer 1c are laminated on a conductive substrate 1a generally formed of an aluminum cylinder. The surface layer 1c is made of an α-SiC-based inorganic high resistance or insulating material to maintain the surface potential Vk and the latent image potential distribution on the photoconductive layer 1b.

Accordingly, discharge products such as nitrate ions and ammonium ions generated by corona discharge during the image forming process are adsorbed on the surface layer 1c, and they are deposited on the photoconductive layer 1b under a high temperature and high humidity environment. The latent image charge formed on the surface layer 1c moves toward the surface based on the surface potential Vk and the latent image potential distribution, and a charge flow, that is, an image flow occurs. It is also considered that the photoreceptor surface is oxidatively degraded by continuous printing and becomes hydrophilic, which is also a factor of image deletion.

Due to this image deletion phenomenon, the latent image charge flows around the latent image in the case where there is no image deletion, and “bleeds” of the image.
The phenomenon occurs. On the other hand, in the present embodiment, since the surface layer of the photoreceptor is formed of the a-Si layer, the electric resistance of the developing roller that rubs against the surface layer is low, for example, the volume resistivity is low. Can be set to 3 × 10 ⁷ Ωcm or less) to prevent an excessive voltage drop in the roller layer, and to have a synergistic effect with the low relative dielectric constant of the a-Si photoreceptor so that the surface potential of the photoreceptor and the developing roller Even if the developing potential is set low, a sufficient image density can be obtained.

As a result, in the present embodiment, the surface potential of the photosensitive member is set to about 400 V or less, preferably 300 to 350 V, and the developing potential of the developing roller is set to about 15 V.
The voltage can be set to 0 V or less, preferably 80 to 120 V, whereby the thickness of the photoreceptor can be reduced to 25 μm or less, and a low-cost image forming apparatus can be provided. In addition, by adopting such a configuration, it is possible to form an image without causing image deletion even in a state where a heater is not built in the base supporting the photoconductive layer 1b.

In this embodiment, the developing roller 4
0 to the surface of the surface layer 1c of the photoreceptor 1 and
Since the surface layer of the photoconductor 1 is developed with a peripheral speed difference with respect to the photoconductor 1, the developing container 41
In addition, the toner can be collected in the developing container together with the development, and the residual toner not used for the development can be reused.

In the present embodiment, the latent image of the photosensitive member 1 is developed while forming a thin layer of toner particles formed by a polymerization method on the developing roller 40 in the present embodiment. Charge is uniformly charged on the spherical toner particles,
In addition, due to point contact with the surface of the photoreceptor, the number of contact points with one toner particle is small, the mirror image force is small, and the 'fogging' phenomenon is small.

Further, in this embodiment, when the image formed on the photosensitive member is transferred to a recording medium, the cleaning member 6 for removing the peeling powder of the recording medium adhered to the photosensitive member is used.
Therefore, the amount of toner transferred to the developing roller 40 while being attached to the photoreceptor 1 and collected by the developing roller 40 together with the residual toner in the developing container 41 is extremely small. It is extremely less likely that the peeling powder is mixed and disturbs the image.

Further, when the developing roller 40 is
The effective developing state of the developing roller 40 can be maintained by setting the nip width in contact with the developing roller to 1.5 to 2.0 mm.

In this embodiment, the change in the resistance value of the load body 29 is detected before the development process,
When a resistance value higher than the predetermined resistance value of normal temperature and normal humidity of 60% is detected, a voltage lower than the predetermined voltage of normal temperature and normal humidity is applied to the load body 29 during the development process, and the developing bias is controlled to a predetermined range. When a resistance value lower than the predetermined resistance value of the normal temperature and the normal humidity is detected, a voltage higher than the predetermined voltage of the normal temperature and the normal humidity is applied to the load body 29 during the development process, and the development bias is controlled to a predetermined range. Therefore, a good image can be formed without reducing the potential difference of the developing bias and making it difficult to pull back the toner.

Further, according to the present embodiment, even if image formation is performed without using a heater, fogging or the like does not occur. Therefore, in addition to greatly reducing power consumption, a thermistor for detecting the temperature of the heater and the surface of the drum is provided. In addition to reducing the number of electrical components such as a heater control circuit based on the temperature detected by the thermistor and simplifying the circuit configuration, a warm-up time is not required because the heater is not used, and the start-up time of the device is greatly reduced. Can be done.

[0072]

【Example】

Example (1) An a-Si photoreceptor having a surface layer having a thickness of 25 μm was prepared and charged by a scorotron method Vk: 350.
V, development is a non-magnetic one-component system, and the developing roll is a conductive roller having a diameter of 18 mm and a volume specific resistance of 5 × 10 ⁶ Ω · c.
m, surface roughness 10 microns or less, development nip about 1 mm,
Developing linear speed 120mm / sec (Photoconductor linear speed 60mm / s
ec), the developing blade has a thickness of 1.3 mm and a resistance value of 1
0 ⁴ Ω · cm or less, supply roll diameter 12 mm, resistance value: 10 ⁴ Ω · cm or less, nip about 1 m with development roll
m, each bias value used was a developing blade 350V, a supply roller 350V, and a toner produced to have an average particle diameter of 8 microns by a polymerization method based on a styrene acrylic material. Set to ~ 30 microamps.

After printing 5000 sheets under normal temperature and normal humidity, and after leaving for 8 hours at high temperature and high humidity, the toner layer on the developing roller was changed by changing the method of applying the developing blade to the developing roller in the above condition setting. By adjusting the thickness, the potential difference Vs between the photosensitive member and the developing roller was changed, and the image forming state was measured. Table 1 shows the results.

[0074]

[Table 1] From Table 1, the layer thickness of the developing roller is 0.2 mg / cm ²
In this case, the image density is low, the rubbing effect of the photoreceptor is low, and image deletion occurs. At 1.0 mg / cm ² , the cleaning power was weak, and a small amount of residual toner remained on the photoconductor.
At 1.2 mg / cm ² , the fog removal electric field was high, the cleaning power was weak, and the residual toner remained on the photoconductor. Therefore, the toner layer thickness on the developing roller is
1.0 to 0.3 mg / cm ² , preferably 0.4 to
1.0 mg / cm ² , more preferably 0.4 to 0.8 m
It can be seen that a good image is obtained at g / cm ² .

Example (2) The film thickness of the surface layer was 25 μm
A-Si photoreceptor is prepared and charged by scorotron method V
k: 350 V, development is a non-magnetic one-component system, the development roll is a conductive roller having a diameter of 18 mm, and the volume resistivity is 5 × 1.
0 ⁶ Omega · cm, the surface roughness 10 microns or less, the developing nip of about 1 mm, developing linear speed 120 mm / sec (photoconductor linear velocity 6
0 mm / sec), the developing blade has a thickness of 1.3 mm,
Resistance value: 10 ⁴ Ω · cm or less, supply roll 12 m in diameter
m, resistance value: 10 ⁴ Ω · cm or less, nip with the developing roll about 1 mm, each bias value
Supply roller 350V, potential difference 2 between photoconductor and developing roller
20V, the toner layer thickness is 0.7mg / cm2, and the toner is
Using a styrene-acrylic material produced by polymerization with an average particle size of 8 microns and a pulverized method, the transfer is performed by a roller method and the transfer current is 20-30.
Set to microamps.

Normal temperature and normal humidity (N / N) at a temperature of 20 ° C. and a humidity of 60%
N), the transfer efficiency of each toner was measured at a high temperature and a high humidity (L / L) of 33 ° C. and a humidity of 85%, and the results are shown in Table 2.

[0077]

[Table 2] From Table 2, it can be seen that the transfer efficiency of the polymerization toner is superior.

[0078] Example (3) of the surface layer, the element ratio composition formula _{(a-Si 1 - X C} X: H) when expressed as, x is from 0.9
5 ≦ x <1 and dynamic indentation hardness of the outermost surface is 3
An electrophotographic photoreceptor having a hardness of not more than 00 Kgf / mm ² , and having a higher hardness on the back side of the photoconductive layer side than the outermost surface side, and having a hardness gradually increasing toward the back side, is prepared.
Charging is a scorotron method Vk: 300 to 350 V, developing is a non-magnetic one-component method, developing roller is 18 mm in diameter, resistance value is 10 ⁶ Ω · cm to 10 ⁷ Ω · cm, surface roughness is 10 μm or less, and developing nip is about 1 mm, the developing blade has a thickness of 1.3 mm, the resistance value is 10 ⁴ Ω · cm or less, the supply roll is 12 mm in diameter, the resistance value is 10 ⁴ Ω · cm or less, the nip with the developing roll is about 1 mm, and each bias value is , Developing roller 100V, developing blade 350V, supply roller 350
V. The toner used had a mean particle size of 8 microns by polymerization based on a styrene acrylic material, and the transfer was set at a transfer current of 20 to 30 microamps by a roller method.

After performing a running test with 5,000 sheets at room temperature under the above settings, the test was carried out under an environment of 33 ° C. and 85% humidity.
When the image was evaluated after being left for more than an hour, a good image without image deletion was obtained.

[0080]

As described above, according to the present invention, even if the resistance value increases due to a change in the resistance of the load to which the developing bias is applied due to a change in the environment, a good image can be obtained without reducing the developing efficiency. Another object of the present invention is to provide an image forming apparatus using an a-Si drum, in which simplification of the configuration and safety are taken into consideration while preventing image deletion and the phenomenon of fogging. It has various remarkable effects such as the ability to form an image.

[Brief description of the drawings]

FIG. 1 is an embodiment of an image forming apparatus to which the present invention is applied.

FIG. 2 is a configuration diagram illustrating a configuration inside a developing container.

FIG. 3 is a diagram illustrating an embodiment of a developing bias control circuit.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photoconductor drum 1a conductive substrate 1b photoconductive layer 1c surface layer 2 exposure head 3 optical system 4 developing unit 6 cleaning member 8 charging device 19 developing bias applying means 27 CPU 29 load (loading body) 40 developing roller 41 developing container

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Keiji Itsukushima 704-19 Noshino, Tamaki-cho, Machi Prefecture Mie Prefecture Inside the Mie Tamaki Plant, Kyocera Corporation (72) Inventor Yoshio Ozawa 704-19 Noshino, Tamaki-cho, Tamaki-cho, Mie Prefecture Kyocera Corporation Mie Tamaki Factory

Claims (5)

[Claims] 1. A photosensitive member or a developing roller or a toner supply roller constituted by an electric load member, and a developing bias applying means for applying a developing bias to develop a latent image formed on the photosensitive member to the load member. An image forming apparatus having a developing bias control function of controlling the developing bias by controlling the developing bias applying means, wherein a resistance value change detecting means for detecting a resistance value change of the load body prior to a developing process. And developing bias control means for controlling the developing bias applying means based on the output of the resistance value change detecting means, wherein the developing bias is made variable in accordance with the resistance value change of the load body. An image forming apparatus having a bias control function. 2. The image forming apparatus according to claim 1, wherein the developing bias applied to the load is applied between a developing roller and a supply roller. 3. The method according to claim 1, wherein the photoconductor is formed of a-Si, and a layer of toner particles on the developing roller that rubs against the surface of the photoconductor is set to 0.3 to 0.9 mg / cm ^2. An image forming apparatus having a developing bias control function according to claim 1. 4. The image forming apparatus according to claim 1, further comprising: a developing mechanism having the developing roller and the toner supply roller, wherein the developing mechanism includes a collecting unit for collecting residual toner on the photoconductor. An image forming apparatus having a developing bias control function. 5. The image forming apparatus according to claim 3, wherein the toner particles are manufactured by a polymerization method.