JP2006171787A - Developing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device wherein the occurrence of image defects caused by flaws of an image carrier can be avoided by preventing the image carrier from being flawed by a developer carrier when transporting an image forming apparatus, even in the case that a gap between the image carrier and the developer carrier in the image forming apparatus is narrowed. <P>SOLUTION: A conductive elastic layer 34 which has a higher hardness than a photosensitive drum and has a volume resistivity of ≤10<SP>8</SP>Ωcm is provided as an outer layer on a conductive non-magnetic bade member 32 to obtain a developing sleeve 30 of the developing device. Though the developing sleeve 30 comes into contact with the photosensitive drum because of vibrations during transportation of the image forming apparatus having the developing device built therein, the surface of the photosensitive drum is prevented from being flawed, and thus the occurrence of image defects caused by flaws of the photosensitive drum is avoided. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a developing device for developing an electrostatic latent image formed on an image bearing member of an electrophotographic photosensitive member or an electrostatic recording dielectric.

  Conventionally, jumping development in which a single-component developer is used, the developer-carrying member carrying the one-component developer is opposed to the surface of the image carrier with a required minute gap, and development is performed with the developer flying in the gap. A method is known (for example, Patent Document 1). A developing technique is also known in which a high-frequency pulse bias (frequency 10 kHz to 3000 kHz, etc.) is applied to the gap so that the developer adheres to the image portion of the image carrier but does not adhere to the non-image portion. (For example, Patent Documents 2, 3, 4, etc.).

  Also, a two-component developer containing a toner and a carrier is used, and the two-component developer is indiscriminately brought into contact with the image portion and the non-image portion of the image carrier, and at the same time, between the developer carrier and the image carrier. A developing technique is also known in which a low-frequency alternating electric field is applied, developer is applied substantially only to the image area, and development is prevented from adhering to the non-image area (for example, Patent Document 5). ).

  FIG. 5 is a schematic configuration diagram showing an image forming apparatus provided with a conventional developing device. The developing device provided in the image forming apparatus is an example of a conventional developing device, and applies an alternating electric field to a developing region which is a gap where a developer carrying member and an image carrying member face each other.

  As shown in FIG. 5, the developing device 10 is disposed opposite to a drum-shaped electrophotographic photosensitive member that rotates in the direction of an arrow that is an image carrier of the image forming apparatus, that is, the photosensitive drum 1. The electrostatic latent image is formed by a known electrostatic latent image forming unit 2 including a charger, an exposure unit and the like. As the exposure means, an optical image projection means for an original document, an optical system that scans a laser beam modulated by a recorded image signal, or the like is adopted. The latent image formed on the photosensitive drum 1 is developed by the developing device 10. A toner image is formed.

  The obtained toner image is transferred onto a transfer material such as paper by known transfer means 3 including a transfer charger. The transfer material to which the toner image has been transferred is separated from the photosensitive drum 1 and sent to a known fixing means, where the toner image is fixed to the transfer material.

  The toner remaining on the photosensitive drum 1 after the transfer is removed by a known cleaning means 4 including a cleaning blade and the like.

  The developing device 10 contains an insulating one-component developer 11 that does not contain carrier particles made of magnetic toner in a developing container 12. The developer 11 is mainly composed of an insulating magnetic toner, and preferably a small amount of fine silica powder is externally added thereto. The silica fine powder is externally added for the purpose of controlling the triboelectric charge of the toner or the like so as to increase the image density and obtain an image with less roughness. For example, it is known that gas phase method silica (dry silica) and / or wet method silica (wet silica) are externally added to a toner.

Such as styrene - added to the negative polarity toner containing 60 parts by weight of magnetite acrylic, relative dry silica (e.g., 100 m ² fumed silica exhibiting a strong negative charging property, the HMDS at a rate of 100 m ² per 10 parts by weight The developer to which the heat-treated toner is externally added is suitable for reversal development of a negative electrostatic latent image.

  The one-component developer, that is, the toner 11 is taken out of the container 12 by a non-magnetic developing sleeve 20 such as aluminum or stainless steel that rotates in the direction of an arrow as a developer carrying member, and is conveyed to a developing region 13 facing the photosensitive drum 1. Is done. In the developing region 13, the photosensitive drum 1 and the developing sleeve 20 face each other with a minimum gap of 50 to 500 μm. In the developing area 13, a developer is applied to the electrostatic latent image on the photosensitive drum 1, and the electrostatic latent image is developed.

  The thickness of the toner 11 on the developing sleeve 20 conveyed to the developing region 13 is regulated by the blade 16. The blade 16 is made of a magnetic material such as iron, and is opposed to the magnetic pole N1 of the magnet roller 15 placed stationary in the sleeve 20 with the sleeve 20 interposed therebetween. Accordingly, the magnetic lines of force from the magnetic pole N 1 concentrate on the blade 16, and a strong magnetic curtain is formed between the blade 16 and the sleeve 20. By this magnetic curtain, a toner layer 11 a thinner than the gap between the blade 16 and the sleeve 20 is formed on the sleeve 20.

  The gap between the blade 16 and the developing sleeve 20 is set so that the thickness of the toner layer 11a can be made smaller than the minimum gap between the sleeve 20 and the photosensitive drum 1, that is, the gap between the two in the developing region 13. .

  As described above, in the developing apparatus shown in FIG. 5, so-called non-contact development is performed. That is, since the thickness of the toner layer 11 a conveyed to the developing area 13 is thinner than the minimum gap between the developing sleeve 20 and the photosensitive drum 1, the toner 11 flies from the sleeve 20 through the air gap and reaches the photosensitive drum 1. In order to improve the developing efficiency at that time, and to form a developed image having a high density and a clear image with suppressed fog, a developing bias voltage including an alternating component is applied to the sleeve 20 from a bias power source 18 of constant voltage control. The

  As described above, the development bias is preferably one in which an alternating voltage is superimposed on a DC voltage. The frequency of the alternating voltage is preferably 1 to 2 kHz, and the peak-to-peak voltage (difference between the maximum value and the minimum value) is preferably about 1.1 to 1.8 kV, and the waveform is a rectangular wave, sine wave, triangular wave, or the like. Is done.

  For example, when a latent image having a dark portion potential of −700 V and a light portion potential of −100 V is subjected to reversal development with a negatively charged toner, a DC component is −500 V as a developing bias, and an alternating component has a peak-to-peak voltage of 1. A square wave development bias voltage of 6 kV and a frequency of 1.8 kHz can be used.

  With such a developing bias, an electric field in the direction in which the toner 11 is transferred from the developing sleeve 20 to the photosensitive drum 1 and an electric field in the direction in which the photosensitive drum 1 is reversely transferred to the sleeve 20 act alternately. As a result, a good developed image can be obtained.

  Note that the reversal development is a development method in which a latent image is visualized by attaching a toner charged to the same polarity as the latent image in a light portion potential region of the latent image. On the other hand, a developing method in which a toner charged with a polarity opposite to that of the latent image is attached to the dark part potential region of the latent image and visualized is called normal development.

The toner 11 is charged to a polarity that develops the electrostatic latent image mainly by friction with the developing sleeve 20. As the toner 11, for example, a binder resin mainly composed of a styrene-acrylic copolymer contains 60% by weight of magnetite and 1% by weight of a metal complex salt of a monoazo dye as a negative charge control agent. Basically, an insulating magnetic toner of 10 ¹³ Ωcm is used, which is obtained by adding 0.4% by weight of silica fine particles hydrophobized to increase the fluidity to the toner weight. Such toner is negatively charged by friction with the sleeve 20 described above.

The magnetic pole S1 of the magnet roller 15 forms a magnetic field in the developing area 13 to prevent fogging, and contributes to clear development of a line image. Magnetic poles N2 and S2 contribute to toner conveyance.
Japanese Patent Publication No.41-9476 US Pat. No. 3,890,929 US Pat. No. 3,866,574 US Pat. No. 3,894,318 Japanese Unexamined Patent Publication No. 55-3260

  As described above, in the conventional developing device, the gap (SD gap) between the developing sleeve 15 and the photosensitive drum 1 is as narrow as 200 μm. Therefore, according to a study by simulation, contact between the developing sleeve 20 and the photosensitive drum 1 occurs during transportation of the image forming apparatus incorporating the developing device in the SD gap, and this causes damage to the photosensitive drum 1. On the other hand, it has been found that it causes a defect on the image.

  The damage of the photosensitive drum 1 during transportation is conspicuous in a B4 size process cartridge in which the photosensitive drum and the developing device are assembled into a cartridge.

  Conventionally, in order to prevent this, it has been necessary to wind a polyester sheet (added carbon black or the like for light shielding) around a photosensitive drum.

  The object of the present invention is to prevent the image carrier from being scratched by the developer carrier during transportation of the image forming apparatus, even if the gap between the developer carrier and the image carrier of the image forming apparatus is narrowed. An object of the present invention is to provide a developing device capable of eliminating the occurrence of image defects due to scratches on an image carrier.

  Another object of the present invention is to prevent the image carrier from being scratched by the developer carrier during transportation of the image forming apparatus, and to due to manufacturing variations in the gap of the developer carrier relative to the image carrier and environmental changes. It is an object of the present invention to provide a developing device that can improve changes in development characteristics.

The above object is achieved by the developing device according to the present invention. In summary, according to the present invention, the developer on the developer carrying member is regulated by a regulating member to form a thin layer of the developer, and the developer formed on the thin layer is separated from the developer carrying member to a minute size of 200 μm or less. The developer is transferred to the image carrier while facing the image carrier having a gap and a developing bias is applied between the developer carrier and the image carrier. In the developing device for developing the formed electrostatic latent image, the developer carrying member is provided with a conductive elastic layer on the surface of a conductive substrate, and the conductive elastic layer has a volume resistivity. A developing device having a hardness of 10 ⁸ Ω · cm or less and lower than the surface of the image carrier.

  According to the present invention, the alternating current of the developing bias can be controlled at a constant current so that a constant alternating current flows between the developer carrier and the image carrier, and the maximum value of the alternating current can be controlled. Can be limited.

  Further, when the developing portion of the developer carrying member corresponds to a non-image area of the image carrying member, the alternating current of the developing bias is controlled at a constant current so that a constant alternating current flows between them. The alternating voltage at that time is detected, and when the development site corresponds to the non-image area of the image carrier, the detected alternating voltage or the constant alternating voltage determined thereby is The alternating voltage of the developing bias can be controlled at a constant voltage.

  When the developing portion of the developer carrier corresponds to a non-image area of the image carrier, the alternating voltage of the developing bias is controlled to a constant alternating voltage so that the constant voltage is maintained. When the alternating current is detected, and the development site corresponds to a non-image area of the image carrier, the alternating voltage of the developing bias is set so as to be a constant alternating voltage determined by the detected alternating current. The voltage can be controlled.

  The regulating member is made of an elastic body, the developer is a one-component developer, and the volume-average particle size of the one-component developer can be 9 μm or less.

  According to the developing device of the present invention, even when the gap between the developer carrier and the image carrier of the image forming apparatus is narrowed, the image carrier is prevented from being damaged by the developer carrier during transportation of the image forming apparatus. Thus, the occurrence of image defects due to scratches on the image carrier can be eliminated. Further, when constant current control of alternating current of the developing bias is added, in addition to preventing the image carrier from being damaged by the developer carrier during transportation of the image forming apparatus, the developer carrier to the image carrier It is possible to improve variations in development characteristics due to manufacturing variations of the gaps and environmental changes.

Example 1
FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus including a developing device according to an embodiment of the present invention, and FIG. 2 is an enlarged perspective view illustrating a developing sleeve of the developing device provided in FIG. .

  The configuration of the image forming apparatus is basically the same as that of the conventional image forming apparatus shown in FIG. 5 except that the developing device 10 has a developing sleeve 30 having the configuration shown in FIG. Therefore, in FIG. 1, the same members as those in FIG. 5 are denoted by the same reference numerals, and the description thereof is omitted unless necessary.

  As shown in FIG. 2, according to the present invention, the developing sleeve 30 is formed with a conductive elastic layer 34 as an outer layer on a nonmagnetic sleeve base 32. In this embodiment, the sleeve base 32 is an aluminum cylinder having a thickness of 0.8 mm, an outer diameter of 15 mm, and a straightness of about 20 μm, and the conductive elastic layer 34 is provided on the thickness of about 500 μm.

  The conductive elastic layer 34 is made by kneading urethane rubber with conductive carbon black, for example, conductivetex 975 ub (manufactured by Columbia Carbon Co., Ltd.), diluting the solvent to form a coating liquid, and the coating liquid is used as the sleeve base 32. It is formed by spray coating on top, drying the coating, vulcanizing and curing.

The volume resistivity of the conductive elastic layer 34 obtained by the above-mentioned curing is measured simultaneously with a conductive elastic layer formed on polyethylene terephthalate using a four-terminal resistivity meter (for example, LORESTA AP INTERIGENT manufactured by Mitsubishi Yuka). The volume resistivity was about 10 ⁴ Ω · cm.

  The toner 11 that is a one-component developer housed in the developing container 12 of the developing device 10 is carried on the developing sleeve 30 having the conductive elastic layer 34 by the magnet roller 15 inside thereof, By rotation, the photosensitive drum 1 and the developing sleeve 30 are conveyed to the developing region 13 facing each other with a predetermined minute gap. During the conveyance, the toner 11 is regulated by the magnetic blade 16 to be a thin toner layer 11a having a predetermined thickness. The toner 11 transported to the developing area 13 is used for developing the electrostatic latent image formed on the photosensitive drum 1, and the latent image is visualized as a toner image.

  During development, a developing bias is applied to the developing sleeve 30 by a bias power source 18, and an electric field is applied to the developer in a direction in which the developing sleeve 30 is transferred from the developing sleeve 30 to the photosensitive drum 1. The electric field in the direction of transition to acts alternately. Thereby, a good developed image can be obtained.

  The development bias is set to the following conditions, for example, when a latent image having a dark portion potential of −700 V and a light portion potential of −100 V is negatively charged and developed at a process speed of 47.1 mm / second and an SD gap of 200 μm. As a result, a good developed image can be obtained. The length of the developing sleeve 30 used in the longitudinal direction was 220 mm as an effective length.

Alternating voltage: Square wave, 800V
Alternating frequency: 2000Hz
DC voltage: -500V

The substantial resistance value of the conductive elastic layer 34 of the developing sleeve 30 is the order of volume resistivity × thickness of the elastic layer 34, that is, the order of 10 ² Ω (10 ⁴ Ω · cm × 500 μm ÷ 1 cm ³ = 500Ω). ) Is relatively low, and is a region that can sufficiently withstand high voltage load, and the peak-to-peak of the alternating voltage of the developing bias is in the range of several tens to several hundreds volts. Development is sufficiently possible.

  In the present invention, since the conductive elastic layer 34 is provided as the outer layer on the developing sleeve 30 of the developing device 10 as described above, the developing sleeve 30 is caused by vibration during transportation of the image forming apparatus incorporating the developing device 10. Even if the photosensitive drum 1 is contacted, it is possible to prevent the surface of the photosensitive drum 1 from being scratched, and it is possible to eliminate the occurrence of image defects due to the scratch on the photosensitive drum 1.

  In this embodiment, after carrying out a physical distribution test based on JIS-Z0202, such as frequency: 10 to 100 Hz, acceleration: 1 G, sweep time: 5 minutes, etc., as a result of image formation, the photosensitive drum was brought into contact with the developing sleeve. No image defects due to scratches were observed.

In the above, the conductive elastic layer 34 of the developing sleeve 30 has a volume resistivity of 10 ⁴ Ω · cm, but in general, the upper limit value of the volume resistivity of the conductive elastic layer 34 is the output of the bias power source 18 to be used. It is needless to say that a developing sleeve having a conductive elastic layer having a higher volume resistivity can be used depending on the output of the bias power supply 18.

In the present invention, a developing sleeve having a volume resistivity of the conductive elastic layer 34 of 10 ⁸ Ω · cm or less can be used, and the same effect as described above can be obtained. If the volume resistivity of the conductive elastic layer 34 exceeds 10 ⁸ Ω · cm, leakage is likely to occur locally due to non-uniform resistance, and defects on the image are likely to occur. There is no limit on the lower limit of resistivity.

  Further, in the present invention, since the SD gap is 200 μm or less, the volume resistivity of the developing sleeve 30 can be used higher than that of the conventional developing sleeve. That is, since the distance between the toner to be developed on the developing sleeve 30 (the toner used for development) and the photosensitive drum 1 is reduced, the developability of the toner is improved. It can be higher than the developing sleeve. When the distance between the toner and the photosensitive drum becomes shorter, the developability is improved because the electric field formed by the surface potential of the photosensitive drum on the toner to be developed, that is, the toner farthest from the developing sleeve and closest to the photosensitive drum. One of the factors is considered to be close.

  According to the result of the simulation conducted by the present inventors, when considering the sinusoidal surface potential distribution (normal OPC) in which the dark portion potential on the surface of the photosensitive drum is −700 V and the bright portion potential is −150 V, The distance that the electric field reaches is about 100 to 150 μm from the surface. In other words, when considering the thickness of the toner layer on the developing sleeve, the SD gap is 100 to 150 μm or less, and more generally 200 μm or less is a highly developable region.

  This can be clarified by experimentally examining a VD curve (relation curve of development bias DC voltage V vs. development density D) well known to those skilled in the art. That is, if the developability is high, the VD curve shifts to the low contrast side, but it is so shifted when the SD gap is 200 μm or less, and it is clear that the developability is high when the SD gap is 200 μm or less.

  The developing sleeve 30 provided with the conductive elastic layer 34 according to the present invention and the conventional developing sleeve made of metal (aluminum) are used for development under the condition of 200 μm within the SD gap according to the present invention to form an image. When the test was conducted, the developability and the effect of preventing the photosensitive drum from being damaged due to the contact with the developing sleeve were tested. It shows in Table 1 as 1-2.

  As shown in Table 1, test No. which is an example of the present invention. In 1, the conductive elastic layer according to the present invention is provided on the surface of the developing sleeve, and the SD interval with the photosensitive drum is set to 200 μm within the range of the present invention. The effect which was more than good in the property was acquired.

Example 2
FIG. 3 is a schematic view showing another embodiment of the developing device of the present invention. This embodiment is characterized in that an elastic blade 26 made of an elastic body is used as a developer regulating member. The other configuration of the developing device 10 of this embodiment is basically the same as that of the developing device 10 of the first embodiment shown in FIG. 1, and the same reference numerals as those in FIG. Show.

  In the present embodiment, the elastic blade 26 is fixed at the position of the developing container 12 on the developing sleeve 30, is suspended on the developing sleeve 30 and is brought into contact with a counter direction opposite to the rotation direction thereof. The elastic blade 26 is made of an elastic metal such as SUS or an elastic rubber plate such as urethane rubber.

  Since the developing sleeve 30 in the present invention has a wider contact area with the elastic blade than a conventional aluminum or stainless steel developing sleeve, the elastic blade 26 made of metal or the like can be used effectively.

  The development sleeve 30 provided with the conductive elastic layer 34 according to the present invention and the conventional metal development sleeve 30 were used in combination with an elastic blade 26 made of urethane rubber or SUS thin plate. Development was performed under the same conditions, and an image formation test was performed up to 6000 sheets. The effect on the occurrence of scratches on the developing sleeve due to the difference in the elastic blade at that time was tested. It shows in Table 2 as 3-5.

  The thickness of the elastic blade is 1.0 mm for urethane rubber and 0.1 mm for SUS thin plate. Each elastic blade was brought into contact with the developing sleeve at a pressure of 30 g / cm. The drawing pressure refers to the length of the SUS plate when a SUS plate with a thickness of 30 μm is sandwiched between two plates with a thickness of 30 μm between the developing sleeve and the elastic blade and the SUS plate is pulled out. It is converted per 1 cm.

  As shown in Table 2, even with an elastic blade made of SUS thin plate having a narrow condition range in the conventional developing sleeve, scratches are hardly generated in the developing sleeve of the present invention, and it is sufficiently practical when combined with the developing sleeve of the present invention. It is understood that it is in the range of.

  As described above, in the present invention, since the elastic elastic layer 34 is provided on the surface of the developing sleeve 30, the elastic blade 26 can be easily used. However, the conductive elastic layer 34 is further provided. As a result, the microscopic contact area of the toner, which is regulated by the elastic blade 26, with the developing sleeve increases, so that the specific charge amount (μC / g) due to frictional charging of the toner slightly increases and the development efficiency is improved. I also found that it increased.

  In the above description, the SUS thin plate or the urethane rubber elastic blade 26 is used as the developer regulating member. However, a developer regulating member such as a metal roller may be used and is also effective.

Example 3
In this example, in the developing device 10 of Example 1 described with reference to FIGS. 1 and 2, when a fine toner having a volume average particle diameter of 9 μm or less is used as the toner 11 as the one-component developer, The effect by this invention is demonstrated.

  As the particle size of the toner 11 becomes smaller, the mirroring force with the developing sleeve 30 makes it difficult for the toner to contribute to the development, resulting in a decrease in developability. This phenomenon is particularly markedly dependent on the SD gap under conditions where an alternating electric field is applied.

  In this example, from the viewpoint of toner developability, a solid black pattern image was developed and an image formation test was performed, and the solid black density obtained at that time was examined. As the toner, a fine toner having a volume average particle diameter of about 9 μm was used. Other conditions were the same as in the test of Example 1. Two SD gaps, 200 μm and 300 μm, were tested in order to show the dependence of the fine toner developability on the SD gap.

  The result is shown in FIG. In FIG. 4, the horizontal axis represents the voltage value (kV) corresponding to the alternating voltage of the developing bias, and the vertical axis represents the entire surface solid black density (optical density OD). The DC component of the developing bias was set to -500 V for both the present invention and the conventional one.

  As shown in FIG. 4, when the developing sleeve according to the present invention is used, it can be seen that setting the SD gap to 200 μm is effective for fine toner having a volume average particle diameter of 9 μm. Similarly, image formation tests were performed using toners having a volume average particle size of 6.5 μm and 5.0 μm, and similar results were obtained.

  In the present invention, such a result can be obtained because the developability of the toner decreases as the toner becomes finer.

  In Examples 1 to 3 described above, the frequency of the alternating voltage of the developing bias was 2 kHz (2000 Hz), but good results were obtained in the range of 0.6 kHz to 2.4 kHz. The elastic blade 26 used as the developer regulating member in the second embodiment is in contact with the developing sleeve 30 in the direction opposite to the rotation thereof, but may be in contact with the quasi-direction in the same direction as the rotation. It was effective.

The conductive elastic layer 34 of the developing sleeve 30 uses urethane rubber as a base material. However, the conductive elastic layer 34 is not limited thereto, and a normal conductive raw rubber material such as EPDM or neoprene rubber can be used. Generally, the conductive elastic layer 34 should be softer than the photosensitive drum 1 and have a volume resistivity of 10 ⁸ Ω · cm or less.

  The conductive elastic layer 34 may be formed by a dip method in addition to the spray method, or the conductive elastic layer 34 may be formed on a tube and covered on the sleeve base.

  Although the thickness of the conductive elastic layer 34 was 500 μm, it could be sufficiently applied to 5 to 1000 μm. If the thickness of the conductive elastic layer 34 exceeds 1000 μm, the strength of the magnetic force from the developing pole of the magnet roller 15 in the developing sleeve 30 is weakened, so the upper limit of the thickness of the conductive elastic layer 34 is limited. .

  Although a cylindrical body made of aluminum is used as the base 32 of the developing sleeve 30, a cylindrical body of a fiber reinforced composite material made of carbon fiber or the like and a resin can be used as the base. Alternatively, a conductive layer may be provided on the surface of the cylindrical body of the insulating resin, and this may be used as the sleeve base.

  Needless to say, the present invention is established without depending on the charging polarity of the toner.

As described above, in Examples 1 to 3, the developing sleeve 30 is provided with the conductive elastic layer 34 on the surface of the conductive base 32, and the conductive elastic layer 34 has a volume resistivity of 10 ^8. Since it has a hardness less than Ω · cm and lower than the surface of the photosensitive drum 1, the gap between the developing sleeve 30 and the photosensitive drum 1 is narrow, and even if the developing sleeve 30 contacts the photosensitive drum 1 during transportation of the image forming apparatus, It is possible to prevent the photosensitive drum 1 from being scratched, and it is possible to eliminate the occurrence of image defects due to the scratch on the photosensitive drum 1.

Example 4
FIG. 6 is a schematic configuration diagram showing an image forming apparatus including a developing device according to still another embodiment of the present invention. The developing device of this embodiment is characterized in that it includes a bias power supply 28 having a function capable of controlling the alternating current value of the developing bias to a desired value. Other configurations of the present embodiment are basically the same as those of the first embodiment shown in FIG. 1, and the same reference numerals as those in FIG. 1 in FIG. 6 denote the same members.

  Problems to be solved in this embodiment will be described. In the conventional developing device shown in FIG. 5, a constant voltage alternating voltage is applied as a developing bias alternating voltage to the developing sleeve 20 from the developing bias power source 18, so that the photosensitive drum 1 and the photosensitive drum 1 are rotated depending on the rotational position of the developing sleeve 20. When the SD interval varies, the strength of the alternating electric field varies accordingly, image unevenness occurs at the pitch of the developing sleeve 20, development efficiency varies, and a halftone image or all-solid image. Concentration fluctuation occurred.

  For example, as shown in FIG. 11, the density unevenness of the sleeve pitch in which the high density A portion and the low density B portion appear alternately corresponds to the case where the high density A portion has a narrow SD gap, and the low density B portion. Corresponds to the case where the SD gap is wide. This density unevenness is conspicuously recognized in the case of a halftone image having a darker color such as one dot and one space than the whole solid black image.

  For example, in an image forming apparatus using a cartridge type developing device, the SD gap fluctuation may occur for each cartridge in the cartridge manufacturing process. In this case, it appears as a density fluctuation for each cartridge.

  In this embodiment, the photosensitive drum is prevented from being scratched by the developing sleeve during transportation of the image forming apparatus, and the variation of the developing characteristics due to the variation in the SD gap and the environmental change accompanying the manufacturing of the developing apparatus is improved. .

  The developing device 10 of this embodiment shown in FIG. 6 has a bias that can control the alternating current of the developing bias to a desired value as described above in order to improve the change in the developing characteristics due to the variation in the SD gap and the environmental change. A power supply 28 is provided. The bias power supply 28 is a high-voltage power supply of AC constant current + DC constant voltage that generates a constant alternating current and outputs a desired constant voltage DC voltage superimposed thereon. The alternating output range of the power supply 28 is such that the alternating frequency is about 0.6 to 2.4 kHz and the alternating current value is about 0.05 to 3.0 mA. FIG. 7 shows a bias generation circuit diagram of the bias power supply 28.

  In FIG. 7, a waveform signal used as an alternating current for developing bias is input to the input terminal 41. This input signal is amplified by a variable amplifier 42, and this output current is detected by an alternating current detector / setter 43 and fed back to the amplifier 42 to control the output current value to be constant. An alternating current having a constant waveform having a desired waveform is obtained at the output. On the other hand, a signal of 20 kHz, for example, is input to the input terminal 44, the input signal is input to the variable amplifier 46 in which the DC voltage value is set by the DC variable unit 45, amplified, rectified by the diode 47 in the subsequent stage, and fixed. A direct current voltage is obtained. This DC constant voltage is added to the above alternating constant current, and a development bias on which these are superimposed is output from the output terminal 48. It is also possible to perform constant voltage control of the DC voltage by applying feedback from the alternating current detector / setter 43 to the variable amplifier 46.

  As the alternating current waveform, a rectangular wave, a sine wave, a triangular wave, or the like is used.

  At the time of development, a development bias having a constant alternating current and a constant DC voltage as described above is applied to the developing sleeve 30 to change the volume resistivity of the SD gap of the developing device and the conductive elastic layer 34 of the developing sleeve 30. Even if there is, a predetermined developing bias can be applied to the toner satisfactorily. An electric field in the direction in which the toner is transferred from the developing sleeve 30 to the photosensitive drum 1 and an electric field in a direction in which the toner is transferred from the photosensitive drum 1 to the developing sleeve 30 alternately act on the toner, thereby obtaining a good developed image. It is done.

For example, when toner is negatively charged with a latent image having a dark portion potential of −700 V and a light portion potential of −100 V, and the reverse development is performed at a process speed of 47.1 mm / second and an SD gap of 200 μm, the developing bias is set to
Alternating current: Square wave, 0.6 mA
Alternating frequency: 2000Hz
DC constant voltage: -500V
By satisfying these conditions, a good developed image can be obtained.

  The alternating current value can be detected by the alternating current detector / setter 43 of the circuit of FIG. 7, but here, a digital RMS meter (effective value meter) is inserted between the developing sleeve 30 and the ground. The measured value is shown. The digital RMS meter used was Fluke's 8062A TRUE RMS METER.

In the present invention, the substantial resistance value of the conductive elastic layer 34 of the developing sleeve 30 is relatively low on the order of 10 ² Ω, and it can sufficiently withstand a high voltage load. Since the peak voltage is in the range of several tens to several hundred volts, as described above, the development by applying the development bias as described above is sufficiently possible.

  In this embodiment, since the alternating current of the developing bias applied to the developing sleeve 30 is controlled to a constant current value, the sleeve pitch density unevenness that occurs when the SD gap changes cannot be found (1 dot). It is easy to find with a halftone image of a horizontal line of 1 space). Further, since the conductive elastic layer 34 is provided on the surface of the developing sleeve 30, image formation is performed after a physical distribution test based on JIS-Z0202 such as frequency: 10 to 100 Hz, acceleration: 1 G, sweep time: 5 minutes, etc. In this case, no image defect due to scratches on the photosensitive drum due to contact with the developing sleeve was observed.

  The greatest effect of the present embodiment is to eliminate the dependence on the environment as much as possible. In other words, by eliminating the environmental dependency of the resistance value of the developing sleeve 30, the effect of improving the developability when the SD gap is reduced is always exhibited.

That is, the conductive elastic layer 34 of the developing sleeve 30 has a volume resistivity of 10 ⁴ Ω · cm under a normal environment (J / J environment) of 25 ° C./55%, for example, 15 ° C./10%. Under a low temperature and low humidity environment (L / L environment), the volume resistivity usually increases by 1 to 2 digits and reaches about 10 ⁵ Ω · cm.

  An image similar to that in the J / J environment was obtained in the L / L environment by developing the image by controlling the developing bias with the control method in the present embodiment to form an image. The peak-to-peak voltage of the alternating voltage at this time was in the range of several hundreds to several thousand volts, and development by applying a developing bias was sufficiently possible.

  When a developing sleeve provided with a conductive elastic layer is used and constant current control of alternating current is not performed, the electric field between the developing sleeve and the photosensitive drum changes between the L / L environment and the J / J environment. In addition, the development density changes. It is a well-known fact that there is a change in developability due to an alternating electric field in a developing method in which an alternating voltage is applied. In this embodiment, as described above, the change is eliminated between the developable L / L environment and the J / J environment.

In the above description, the developing sleeve 30 has a conductive elastic layer 34 with a volume resistivity of 10 ⁴ Ω · cm. However, the developing sleeve 30 has a volume resistivity of 10 ⁸ Ω · cm or less. It was possible to use the same effect as described above. When the SD gap exceeds 200 μm, the effect of the conductive elastic layer is reduced, and improvement in developability cannot be expected greatly, but it can be carried out theoretically.

Example 5
FIG. 8 is a diagram showing a bias generating circuit of a developing bias power source in still another embodiment of the developing device of the present invention. The present embodiment is characterized in that a limiter circuit 49 for defining the maximum value of the alternating current value is provided in the bias generation circuit of the developing bias power supply 28 of the fourth embodiment shown in FIG.

  The limiter circuit 49 compares the reference voltage with the voltage of the alternating current detector / setter 43 to turn on / off the operation of the variable amplifier 42 and control the amplifier 42 to output an alternating current having a maximum value equal to or less than a certain value. To do.

  Conventionally, it is known that a leak phenomenon occurs when an alternating voltage is applied to an SD gap that exceeds the Paschen's law. This leak phenomenon appears as a white spot if it is slight when printing solid black on the entire surface, and appears as an elliptical leak mark as shown in FIG. 12 if it is severe.

  Under the condition where a constant alternating voltage is applied, when the developing sleeve shakes, as shown in FIG. 12, no leak occurs in the D region, but a leak occurs in the C region. The C region has a narrow SD gap as in the high concentration A portion shown in FIG. 12 of Example 4, and the D region has a wide SD gap as in the low concentration B portion. It is considered that when a constant alternating voltage is applied, a leak occurs because an electric field strength exceeding the electric field strength of Paschen is generated in a narrow SD gap as in the C region.

  In the present invention, the constant current control of the alternating current of the developing bias shown in the fourth embodiment significantly reduces the occurrence of the sleeve pitch leakage phenomenon as shown in FIG. When a current value is passed, a leak phenomenon similar to that in FIG. 12 occurs. However, since the alternating voltage fluctuates in accordance with the width of the SD gap, there is a high possibility that the leakage from the sleeve pitch shown in FIG.

  However, the above leakage phenomenon can be avoided by lowering the alternating current value. Therefore, in this embodiment, a current limiting circuit that prevents an alternating current exceeding a certain value from flowing, that is, a limiter circuit 49 is provided in the bias generation circuit of the developing bias power supply 28 to eliminate the leak phenomenon.

  As an example of the limit value of the developing bias at which leakage occurs, the alternating frequency is 2000 Hz and the alternating current value is about 2.0 mA. This limit value is a value when a rectangular wave is used and the SD gap is 200 μm. The limit value at which leakage occurs is slightly changed as the SD gap is reduced, and is also changed depending on the type of alternating waveform applied. Therefore, the above numerical values are merely examples.

Example 6
This embodiment is characterized in that the elastic blade 26 is used as the developer regulating member in the fourth embodiment, as in the second embodiment shown in FIG.

  In this example, as in Example 2, development was performed under the same conditions as in the test of Example 1, and an image formation test for up to 6000 sheets was performed. Other conditions such as constant current control of the alternating current of the developing bias were the same as in Example 4. The results are shown in Test No. together with Comparative Example. It shows in Table 3 as 6-8.

  As shown in Table 3, in the conventional developing sleeve, the contact condition is strict, and even an elastic blade made of a SUS thin plate having a narrow condition range is difficult to cause damage to the developing sleeve when combined with the developing sleeve of the present invention. It is in practical use.

  Thus, in this embodiment, the conductive elastic layer is provided on the surface of the developing sleeve, so that the elastic blade can be easily used, and the microscopic contact area of the developer to the developing sleeve is increased. The specific charge amount (μC / g) due to the frictional charging of the toner is slightly increased to increase the development efficiency. However, the constant current control of the alternating current of the developing bias is performed, so that it is always good without depending on the environment. A density image is obtained.

Example 7
The present embodiment is characterized in that fine toner having a volume average particle diameter of 9 μm or less is used as the toner 11 as the one-component developer in the fourth embodiment, as in the third embodiment.

  In this example, an image formation test of a solid black pattern image was performed under the same conditions as in Example 3. Two types of SD gaps of 200 μm and 100 μm were tested. Other conditions such as constant current control of the alternating current of the developing bias were the same as in Example 4.

  The result is shown in FIG. In FIG. 9, the horizontal axis represents the alternating current value of the developing bias, and the vertical axis represents the solid black density (optical density OD) of the entire surface. FIG. 10 shows the result of developability when the alternating voltage is changed. In FIG. 10, the horizontal axis represents the alternating voltage value of the developing bias. Similarly, the vertical axis represents the solid black density (optical density OD). The DC voltage of the developing bias was −500 V for both the present invention and the conventional one.

  As is apparent from a comparison of FIGS. 9 and 10, this example shows that even when a fine toner having a volume average particle size of 9 μm is used, the method of constant alternating current due to variation in the SD gap is effective. The Similarly, image formation tests were performed using toners having a volume average particle size of 6.5 μm and 5.0 μm, and similar results were obtained. In the present invention, such a result can be obtained because the developability of the toner decreases as the toner becomes finer.

  In Examples 4 to 7 described above, the frequency of the alternating voltage of the developing bias was 2 kHz (2000 Hz), but good results were obtained in the range of 0.6 kHz to 2.4 kHz. Further, the elastic blade 26 used as the developer regulating member in the sixth embodiment is in contact with the developing sleeve 30 in the opposite direction to the rotation, but may be in contact with the quasi-direction in the same direction as the rotation. It was effective.

Further, urethane rubber is used as the base material for the conductive elastic layer 34 of the developing sleeve 30. However, the invention is not limited to this, and the same as in Examples 1 to 3, for example, a normal conductive raw rubber material such as EPDM or neoprene rubber. Can be used. In general, the conductive elastic layer 34 should be softer than the photosensitive drum 1 and have a volume resistivity of 10 ⁸ Ω · cm or less.

  Similarly, the conductive elastic layer 34 may be formed by a dip method instead of the spray method, or the conductive elastic layer 34 may be formed on a tube and covered on the sleeve base. . Although the thickness of the conductive elastic layer 34 was 500 μm, it could be sufficiently applied to 5 to 1000 μm. When the thickness of the conductive elastic layer 34 exceeds 1000 μm, the strength of the magnetic force from the developing pole of the magnet roller 15 in the developing sleeve 30 is weakened, so there is a limit to the upper limit of the thickness of the conductive elastic layer 34.

  Further, an aluminum sleeve is used as the base of the developing sleeve 30, but a fiber reinforced composite material sleeve made of carbon fiber or the like and a resin can be used as the base. As described above, a conductive layer may be provided on the surface of the insulating resin sleeve and used as the sleeve base of the developing sleeve 30 of the present invention.

As described above, according to Examples 4 to 7, the conductive elastic layer 34 having a volume resistivity of 10 ⁸ Ω · cm or less and lower hardness than the surface of the photosensitive drum 1 is provided on the surface of the developing sleeve 30. Further, since the alternating current of the developing bias applied to the developing sleeve 30 is controlled at a constant current, the photosensitive sleeve 1 is prevented from being damaged by the developing sleeve 30 during transportation of the image forming apparatus, and the developing device 10 is manufactured. Even if there are SD gap variations and environmental changes associated with the above, it is possible to improve the change in development characteristics and obtain a good image without density variations.

Example 8
FIG. 13 is a diagram showing a developing bias power source in still another embodiment of the developing device of the present invention. The present embodiment is greatly characterized in that a developing bias power source 38 that can switch and apply the developing bias controlled by constant current control and constant voltage control is provided. Since the other configuration of the present embodiment is basically the same as that of the first embodiment of FIG. 1, the drawing of the developing device and the description of each part thereof will be omitted, and a description will be added with reference to FIG. 1 as necessary.

  In the present embodiment, the developing bias power supply 38 includes an alternating power supply (AC power supply) 50, a CPU 51, a constant current controller 52, a constant voltage controller 53, a constant current / constant voltage switch 54, and current detection means. 55 and a voltage detection means 56, the AC power supply 50 is connected to the developing sleeve 30 by the output line L1, and the controllers 52 and 53 are connected to the input side of the AC power supply 50 via the switch 54. 54 is connected to a switching signal line L2 from the CPU 51 for switching the controllers 52 and 53. The constant current controller 52 is connected to the output side of the AC power supply 50 through a connection line L3. The constant current controller 52 is connected to the connection line L3 and grounded. The constant voltage controller 53 is connected to the CPU 51 by connection lines L4a and L4b via A / D converters 57a and 57b, respectively. Between the one connection line L4a and the output line L1 of the AC power supply 50, the constant voltage controller 53 is connected. A voltage detection means 56 and a diode 58 in series therewith are interposed.

  The alternating output range of the developing bias power supply 38 is preferably an alternating frequency of 0.6 to 2.4 kHz and an alternating current value of about 0.2 to 3.0 mA. The peak-to-peak voltage of the alternating voltage at this time is It is about 0.4 kV to 2.0 kV. However, this peak-to-peak value varies depending on the SD gap. As the alternating waveform, a rectangular wave, a sine wave, a triangular wave, or the like is used. Further, the DC voltage of the developing bias is preferably a voltage that exists between the dark part potential and the bright part potential of the latent image formed on the photosensitive drum 1.

  At the time of development, the developing bias is controlled as described below and applied to the developing sleeve 30, whereby the toner has an electric field in a direction in which the toner is transferred from the developing sleeve 30 to the photosensitive drum 1, and the developing from the photosensitive drum 1. An electric field in the direction of reverse transfer to the sleeve 30 acts alternately, whereby a good developed image can be obtained.

For example, when toner is negatively charged with a dark portion potential of −700 V and a light portion potential of −100 V, and the reverse development is performed at a process speed of 47.1 mm / second and an SD gap of 300 μm, the developing bias is set to
Non-image area Alternating constant current: Rectangular wave, 2.0 mA
Alternating frequency: 1800Hz
DC constant voltage: -500V
Image area Alternating constant voltage: about 1600 V (alternating voltage about 1600 when the above alternating constant current is applied)
V (peak-to-peak voltage) held)
Alternating frequency: 1800Hz
DC constant voltage: -500V
By satisfying these conditions, a good developed image can be obtained.

  Next, FIG. 14 shows data when the alternating frequency is constant at 1.8 kHz as an example of the dependency of the SD gap size and the alternating current value. In FIG. 14, the alternating current value was measured by inserting an AC ammeter in series between the developing bias power source 38 and the developing sleeve 30. The vertical line in each plot represents the number of rotations of the developing sleeve. The range of values, and each plot point shows its mean value. The ammeter used was Fluke's 8062A TRUE RMS METER (RMS). The SD gap was held by a holding member having a deflection accuracy of about 10 μm.

  As can be seen from FIG. 14, even when a constant alternating voltage is applied, the alternating current value changes due to a change in the SD gap due to a cartridge difference or the like. In other words, the SD gap can be known by measuring the alternating current value.

  FIG. 15 shows the relationship between the SD gap and the alternating voltage when the alternating current value is constant 2 mA from FIG. According to FIG. 15, if the alternating voltage at that time is obtained in a state where the alternating current is constant, the SD gap is uniquely obtained.

  The present embodiment is characterized in that the SD gap of the developing device is detected using this characteristic, and a constant alternating electric field can always be formed regardless of the change in the SD gap.

  FIG. 16 shows a basic sequence of the image forming apparatus when the developing bias is applied according to this embodiment. As shown in FIG. 16, when the pre-rotation is started by turning on the main motor, charging of the photosensitive drum 1 of FIG. 13 is started almost simultaneously by the charging device, and the surface of the photosensitive drum 1 is charged to -700V. At this time, an alternating constant current of 2 mA is applied to the developing sleeve 30 by a developing bias power source 38 for developing bias. The alternating voltage value at this time is detected in the power supply 38 (SD gap detection). This operation is performed at each sheet interval.

  Next, the charged surface of the photosensitive drum 1 is irradiated with an image-modulated laser beam or the like, and an electrostatic latent image is formed on the photosensitive drum 1. The alternating component of the developing bias is detected during constant current control at the timing until the photosensitive drum 1 rotates and the latent image reaches the developing position of the developing region 13 of the developing device 10 (position facing the developing sleeve 30). Thus, the control is switched to the constant voltage control with the alternating voltage value already held. In the subsequent process, the electrostatic latent image is reversely developed with negatively charged toner, and a toner image is formed on the photosensitive drum 1. The toner image is transferred onto a transfer material (not shown) by the transfer device 3 in FIG. 1, and then the toner image is fixed on the transfer material by a fixing device (not shown) and then discharged outside the image forming apparatus.

  In this embodiment, since the development bias as described above is applied, an image with a constant line width and line density can be obtained even if the SD gap varies. The SD gap was about 250 to 350 μm, but the SD gap was similarly effective up to a range of 50 to 500 μm, and the line width and line density were constant. In addition, the same effect could be confirmed at an alternating frequency of 600-2400 Hz.

  The effect on the line width in this example is shown in a graph in FIG. 17 in comparison with the conventional example. Similarly, a graph of the effect on the reflection density on the transfer material is shown in FIG. 18 in comparison with the conventional example. As shown in FIGS. 17 and 18, according to this embodiment, it can be seen that the line width and the reflection density are constant regardless of the change in the SD gap.

In the present invention, as described above, the substantial resistance value of the conductive elastic layer 34 of the developing sleeve 30 is relatively low on the order of 10 ² Ω, and can sufficiently withstand a high pressure, and the alternating bias of the developing bias. Since the voltage peak-to-peak voltage is in the range of several tens to several hundred volts, development by applying a development bias is sufficiently possible.

  Further, since the conductive elastic layer 34 is provided on the surface of the developing sleeve 30, image formation is performed after a physical distribution test based on JIS-Z0202 such as frequency: 10 to 100 Hz, acceleration: 1 G, sweep time: 5 minutes, etc. Even when the image forming process is performed, image defects due to scratches on the photosensitive drum due to contact with the developing sleeve are not recognized.

Example 9
In this embodiment, in the eighth embodiment, when the developing portion of the developing sleeve 30 corresponds to the non-image area of the photosensitive drum 1, the alternating current of the developing bias is controlled at a constant current, and the detection is detected and held at that time. The alternating voltage V _DO is substituted into a predetermined function to obtain a voltage value V _DT = f (V _DO ), and at the time of correspondence with the image area of the development site, constant voltage control is performed with this voltage value V _DT , A feature is that an alternating electric field is applied to the SD gap between the drum 1 and the developing sleeve 30. Other configurations are the same as those in the eighth embodiment.

  FIG. 19 shows the relationship between the SD gap and the alternating voltage during constant voltage control in this example. In FIG. 19, the solid line is the ninth embodiment, and the hold value is substituted into the function f. The previous Example 8 is shown by a broken line for comparison.

When the function f in this embodiment is V _DT = f (V _DO ) = αV _DO + β, the slope α is
When 250 μm ≦ SD gap ≦ 350 μm α = 1
When SD gap <250 μm or 350 μm <SD gap α = 1.5
It is.

  That is, when the SD gap is 250 to 350 μm, α = 1 and a constant voltage value similar to that in the eighth embodiment is obtained. When the SD gap was less than 250 μm or more than 350 μm, α = 1.5, and the operating voltage was slightly larger than the detected value. The constant β is a numerical value determined in each case.

  The effects of the ninth embodiment are shown in FIGS. FIG. 20 shows the relationship between the SD gap and the line width in this embodiment. In this example, the line width could be made more constant than in Example 8 as well as the conventional example. This is because the alternating electric field is set to be stronger than that in Example 8 when the SD gap exceeds 350 μm and weak when the SD gap is less than 250 μm.

  FIG. 21 shows the relationship between the SD gap and the solid black density. In this embodiment, it is effective to prevent the strength from being lowered when the SD gap exceeds 350 μm.

  As described above, in this embodiment, since the alternating voltage is determined by substituting the detection voltage into a predetermined function, a stable image can be obtained with a wider SD gap.

The above α and β are examples used for the explanation, and the present invention is not limited to this. The function V _DT = f (V _DO ) is a linear function, but it is obvious from the gist of the invention that other functions may be used.

Example 10
The present embodiment is characterized in that the elastic blade 26 is used as the developer regulating member in the eighth embodiment, as in the second embodiment shown in FIG.

  In this example, as in Example 2, development was performed under the same conditions as in the test of Example 1, and an image formation test for up to 6000 sheets was performed. Other conditions such as constant current control of the alternating current of the developing bias were the same as in Example 8. The results are shown in Test No. together with Comparative Example. It shows in Table 4 as 9-11.

  As shown in Table 4, in the conventional developing sleeve, the contact condition is strict, and even an elastic blade made of a SUS thin plate having a narrow condition range is difficult to cause toner fusion when combined with the developing sleeve of the present invention. Is in practical use.

Example 11
The present embodiment is characterized in that, in the eighth embodiment, a limiting circuit for defining a maximum value for the alternating voltage value of the developing bias is provided.

  As described in the fifth embodiment, it is known that a leak phenomenon occurs when an alternating voltage is applied to the SD gap in excess of the Paschen's law. In the eighth embodiment, since the alternating voltage value changes according to the SD gap during constant current control, it is difficult for the leak phenomenon to occur. However, leaks may occur rarely during constant current control. Therefore, in this embodiment, the maximum value of the alternating voltage is limited so as to reliably prevent leakage.

  In this embodiment, the maximum value of the alternating voltage is not instantaneously exceeded the voltage obtained by adding 200 V to the alternating voltage value (Vpp) of each SD gap 200, 300, 400 μm in the graph of FIG. A limiting circuit was provided. As a result, the prevention of leakage was complete, and other effects of the present invention could be obtained as well.

Example 12
In the present embodiment, when the developing portion of the developing sleeve 30 corresponds to the non-image area of the photosensitive drum 1 in the eighth embodiment, the alternating electric field of the developing bias is controlled to a constant voltage with a predetermined value. The alternating current i ₀ that flows is detected and the current value i ₀ is substituted into a certain function to obtain a voltage value V _DT = g (i ₀ ). When the development site corresponds to the image area, the voltage value V It is characterized in that an alternating electric field is applied to the SD gap between the photosensitive drum 1 and the developing sleeve 30 by performing constant voltage control with _DT . Other configurations are the same as those in the eighth embodiment.

In this example, when the development site corresponds to a non-image area, constant voltage control was performed at Vpp = 800 V, and the alternating current value i ₀ at that time was detected. According to the previous FIG. 14, the size of the SD gap is uniquely determined by the value of the alternating current i ₀ , so that the alternating voltage at the time of development is the same as that of the eighth embodiment depending on the size of the SD gap. The function V _DT = g (i ₀ ) was determined.

  As a result, the same effect as in Example 8 could be obtained.

Example 13
In the present embodiment, as shown in FIG. 22 showing the control sequence of the developing bias power source 38 in the eighth embodiment, the alternating current is controlled at a constant current only during the pre-rotation, and the voltage at that time is detected and The feature is not to do so. Others were the same as in Example 8. In this example, the same effect as in Example 8 was obtained.

As described above, according to the eighth to thirteenth embodiments, for example, when the developing portion of the developing sleeve 30 corresponds to the non-image area of the photosensitive drum 1, the developing bias applied to the developing sleeve 30 is set to a constant AC voltage value. Since the development bias is controlled such that the constant current control is performed, the alternating voltage value at that time is detected, and the developing unit corresponds to the image area, the constant voltage control is performed with the detected alternating voltage value. Photoconductive by the developing sleeve 30 during transportation of the image forming apparatus by providing the conductive elastic layer 34 having a volume resistivity of 10 ⁸ Ω · cm or less and a lower hardness than the surface of the photosensitive drum 1 on the surface of the developing sleeve 30. In addition to preventing the drum 1 from being scratched, it improves SD characteristics variation due to the development of the developing device 10 and changes in development characteristics due to environmental changes, further ensuring prevention of density variation, Image can be obtained.

1 is a schematic configuration diagram illustrating an image forming apparatus including a developing device according to an embodiment of the present invention. FIG. 2 is an enlarged perspective view of a surface portion of a developing sleeve provided in the developing device of FIG. 1. It is a schematic block diagram which shows the other Example of the image development apparatus of this invention. It is a graph which shows the developability in further another Example of the image development apparatus of this invention. It is a schematic block diagram which shows the image forming apparatus provided with the conventional developing device. It is a schematic block diagram which shows the image forming apparatus provided with the developing device which concerns on the other Example of this invention. FIG. 7 is a circuit diagram illustrating a bias generation circuit of a developing bias power source provided in the developing device of FIG. 6. It is a circuit diagram which shows the bias generation circuit of the developing bias power supply in the further another Example of the image development apparatus of this invention. It is a graph which shows the developability in further another Example of the image development apparatus of this invention. It is a graph which shows the developability when changing an alternating voltage similarly. It is explanatory drawing which shows the density nonuniformity of the sleeve pitch which has arisen with the conventional developing device. It is explanatory drawing which similarly shows an elliptical leak trace. It is a block diagram which shows the developing bias power supply in further another Example of the developing device of this invention. 14 is a graph showing the dependence of the alternating current value of the developing bias on the SD gap in the developing device of FIG. It is a graph which shows the relationship between SD gap | interval and alternating voltage when alternating current value 2mA created from the graph of FIG. 14 is constant. FIG. 2 is a diagram illustrating a basic sequence of an image forming apparatus when a developing bias is applied in the present embodiment. It is a graph which shows the effect in the line width in a present Example compared with a prior art example. It is a graph which shows the effect in the reflection density on the transfer material in a present Example compared with a prior art example. It is a graph which shows the relationship between the SD gap | interval in the further another Example of this invention, and the alternating voltage at the time of constant voltage control. It is a graph which shows the relationship between SD gap | interval and line width in other Example of this invention. It is a graph which similarly shows the relationship between SD gap | interval and a solid black density. It is a figure which shows the basic sequence of image formation when applying the developing bias in the further another Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 10 Developing apparatus 11 Toner 15 Magnet roller 16 Magnetic blade 18 Bias power supply 26 Elastic blade 28 Bias power supply 30 Developing sleeve 34 Conductive elastic layer 38 Bias power supply

Claims (8)

The developer on the developer carrier is regulated by a regulating member to form a thin layer of developer, and the developer formed in the thin layer is separated from the developer carrier by a minute gap of 200 μm or less. An electrostatic latent image formed on the image carrier by transferring the developer to the image carrier with a developing bias applied between the developer carrier and the image carrier. In the developing device for developing the developer, the developer carrying member is provided with a conductive elastic layer on the surface of the conductive substrate, and the conductive elastic layer has a volume resistivity of 10 ⁸ Ω · cm or less. And a developing device having a lower hardness than the surface of the image carrier.   2. The developing device according to claim 1, wherein the alternating current of the developing bias is controlled at a constant current so that a constant alternating current flows between the developer carrier and the image carrier.   3. The developing device according to claim 2, wherein a maximum value of an alternating current flowing between the developer carrier and the image carrier is limited.   When the developing portion of the developer carrier corresponds to a non-image area of the image carrier, constant current control of the alternating current of the developing bias is performed so that a constant alternating current flows between them, Then, the alternating voltage at that time is detected, and when the development site corresponds to the non-image area of the image carrier, the developed alternating voltage or the constant alternating voltage determined by the detected alternating voltage is obtained. The developing device according to claim 1, wherein the alternating voltage of the bias is controlled at a constant voltage.   When the developing portion of the developer carrier corresponds to a non-image area of the image carrier, constant voltage control is performed so that the alternating voltage of the developing bias becomes a constant alternating voltage, and the alternating at that time When the current is detected and the development site corresponds to a non-image area of the image carrier, the alternating voltage of the developing bias is set to a constant voltage so that the constant alternating voltage is determined by the detected alternating current. The developing device according to claim 1 to be controlled.   The developing device according to claim 1, wherein the regulating member is made of an elastic body.   The developing device according to claim 1, wherein the developer is a one-component developer.   The developing device according to claim 1, wherein the one-component developer has a volume average particle size of 9 μm or less.

Images