JP2006221147A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize an image forming apparatus which forms a high quality image at high speed by sufficiently reducing worm-shaped image irregularities even in the high-speed developing operation to develop an image by moving an electrostatic latent image bearing member at high speed. <P>SOLUTION: When it is assumed that the frequency of the AC component of developing bias voltage is f(kHz) and the linear velocity of the latent image bearing member is vp(mm/sc), the developing is performed under a condition satisfying vp/f≤70. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrophotographic image forming apparatus, and more particularly to an improvement of a developing device.

  In recent years, there is a growing need for high speed and high image quality in electrophotographic image forming apparatuses. In order to satisfy the need for higher speed, it is necessary to increase the linear velocity of the latent image carrier such as a photoconductor, but when the linear velocity of the latent image carrier is increased, various problems occur in the development process. .

  In the development process, as a problem related to the image quality, a phenomenon that the width of the fogging margin that can be set, which is called an operation window, becomes narrower when the linear velocity of the latent image carrier is increased is a main problem.

  The fog margin is a potential difference between the charging potential of the latent image carrier (the unexposed portion potential on the photosensitive member) and the DC component of the developing bias potential. The fog margin generally does not generate fog and adheres to the carrier. Set to a value that does not occur.

  Thus, there are forward rotation development in which development is performed by moving the latent image carrier and developer carrier in the same development direction in the development areas where they face each other, and reverse development in which development is performed by moving in the opposite direction. In order to widen the operation window of the fog margin and suppress the occurrence of fog and carrier adhesion, reverse development is advantageous.

  In high-speed development, development is performed under an alternating electric field in order to ensure developability.

  As a means for realizing such a high-speed image forming apparatus, it is effective to use a reverse development method in the development process and perform development under an alternating electric field. In high-speed development, it has been found that worm-like image unevenness tends to occur in an image.

  As shown in FIG. 1, such worm-like image unevenness is non-uniform density generated in a low-density solid image, and as a result of pursuing the cause, it is considered that this is caused by the following phenomenon.

  In the reverse development, since the relative speed between the latent image carrier and the developer carrier is high, the friction between the magnetic brush and the latent image carrier increases, and the electrostatic charge of the latent image carrier is likely to occur. When the latent image carrier and the developer carrier are separated from the development area and the gap between the two is enlarged, discharge may occur.

  It is assumed that worm-like image unevenness is caused by such frictional charging and discharging.

  In order to solve the image quality problem in the development process, there have been many studies and many improvements have been proposed.

  For example, in Patent Document 1, the dot image is prevented from being lost by selecting the linear velocity ratio between the latent image carrier and the developer carrier and making the magnetization intensity of the magnetic carrier appropriate.

In Patent Document 2, carrier adhesion is prevented by appropriately setting the relationship between the development bias voltage AC component (Vpp) and the development gap Ds with respect to the difference between the unexposed portion potential and the exposed portion potential of the photoreceptor. ing.
JP-A-9-127793 JP 2001-5295 A

  With respect to worm-like image unevenness that occurs in high-speed development in which a latent image carrier such as a photoconductor is moved at a high speed, it is not a sufficient countermeasure depending on the conventional techniques including Patent Documents 1 and 2 described above. .

  An object of the present invention is to provide an image forming apparatus that prevents the occurrence of worm-like image unevenness even in high-speed development and forms a high-quality image.

The object is achieved by the following invention.
1.
Latent image carrier,
A developer carrier disposed opposite to the latent image carrier;
Magnetic field generating means for generating a magnetic field on the surface of the developer carrying member; and
A bias power source for applying a developing bias voltage in which an AC component is superimposed on a DC component between the latent image carrier and the developer carrier;
An image forming apparatus that uses a two-component developer including toner and carrier, moves the latent image carrier and the developer carrier in opposite development directions in opposite development regions, and performs development by contact development In
When the frequency of the AC component is f (kHz) and the linear velocity of the latent image carrier is vp (mm / sc),
Condition 1 ... vp / f ≦ 70
An image forming apparatus satisfying the requirements.
2.
The development gap Ds (mm) which is the shortest distance between the latent image carrier and the developer carrier, and the maximum value of the height of the head of the magnetic brush formed in the development region by the two-component developer. When h (mm)
Condition 2 ... 0 <h-Ds ≦ 0.3 mm
2. The image forming apparatus as described in 1 above, wherein:
3.
The frequency f and the linear velocity vp are condition 3... 40 ≦ vp / f
3. The image forming apparatus as described in 1 or 2 above, wherein:
4).
The frequency f, the AC component voltage {peak-to-peak voltage (kV)} Vac, and the development gap Ds (mm) which is the shortest distance between the latent image carrier and the developer carrier. Condition 4 ... 1.25 ≦ (f × Ds) /Vac≦1.6
The image forming apparatus according to any one of 1 to 3, wherein:
5.
The peak value Vh (Vh = Vac / 2) of the AC component contributing to the development, the distance between the latent image carrier and the developer carrier, Ds (mm), and the fog margin ΔVdc are as follows: Condition 5 (Vh + ΔVdc) ) /Ds≦3.8
5. The image forming apparatus as described in any one of 1 to 4 above, wherein:
6).
Vp (mm / sc) is condition 6... Vp ≧ 250
The image forming apparatus according to any one of 1 to 5 above, wherein:
7).
When the linear velocity of the developer carrying member is vs (mm / sc), the vp and the vs satisfy the condition 7... 1.5 <vs / vp ≦ 3.0
The image forming apparatus as described in any one of 1 to 6 above, wherein:
8).
9. The image forming apparatus according to any one of 1 to 8, wherein a carrier in which magnetic particles are coated with a resin is used as the carrier.

  According to the present invention, even in high-speed image formation, the occurrence of worm-like image unevenness is sufficiently reduced, and an image forming apparatus that forms a high-quality image is realized.

<Image forming apparatus>
Hereinafter, the present invention will be described with reference to embodiments, but the present invention is not limited to the embodiments. FIG. 2 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention.

  In FIG. 2, 10 is a photosensitive member as a latent image carrier, 11 is a charging device, 12 is an exposure device, 13 is a developing device, 14 is a cleaning device for cleaning the surface of the photosensitive member 10, and 16 is a developing device 13. And a developing sleeve 20 as a developer carrying member constituting the intermediate transfer belt. The image forming unit 1 includes a photoconductor 10, a charging device 11, an exposure device 12, a developing device 13, a cleaning device 14, and the like. Since the mechanical configuration of the image forming unit 1 for each color is the same, FIG. In FIG. 5, reference numerals are assigned to the configuration of only the Y (yellow) series, and reference symbols are omitted for the constituent elements of M (magenta), C (cyan), and K (black). The charging device 11 and the exposure device 12 constitute a latent image forming unit that forms an electrostatic latent image on the latent image carrier.

  The image forming means 1 for each color is arranged in the order of Y, M, C, K with respect to the running direction of the intermediate transfer belt 20, and each photoconductor 10 contacts the stretched surface of the intermediate transfer belt 20. At the contact point, the intermediate transfer belt 20 rotates in the same direction as the traveling direction and at the same linear speed.

  The intermediate transfer belt 20 is stretched around a driving roller 21, an earth roller 22, a tension roller 23, and a driven roller 24, and the belt unit 3 is configured by these rollers, the intermediate transfer belt 20, the transfer device 25, the cleaning device 28, and the like.

  The intermediate transfer belt 20 is driven by rotation of the driving roller 21 by a driving motor (not shown).

  The photosensitive member 10 is formed by forming a photosensitive layer such as a conductive layer, an a-Si layer, or an organic photosensitive member (OPC) on the outer periphery of a cylindrical metal base formed of, for example, an aluminum material, and the conductive layer is grounded. In the state, it rotates counterclockwise as indicated by the arrow in FIG.

  An electrical signal corresponding to image data from the reading device 80 or an external device is converted into an optical signal by an image forming laser, and the exposure device 12 exposes the photoconductor 10 to an image.

  The developing device 13 is a developing sleeve formed of a cylindrical non-magnetic stainless steel or aluminum material that maintains a predetermined interval with respect to the peripheral surface of the photoconductor 10 and rotates in the reverse direction at the closest position to the rotation direction of the photoconductor 10. 16. Details of the developing device 13 will be described later.

The intermediate transfer belt 20 is an endless belt having a volume resistivity of 10 ⁶ to 10 ¹² Ω · cm. It is a semiconductive seamless belt having a thickness of 0.015 to 0.05 mm in which a conductive material is dispersed.

  A transfer device 25 has a function of transferring a toner image formed on the photoreceptor 10 onto the intermediate transfer belt 20 by applying a direct current having a polarity opposite to that of the toner. As the transfer device 25, a transfer roller can be used in addition to the corona discharger.

  A transfer device 26 includes a transfer roller that can be brought into and out of contact with the earth roller 22 and retransfers the toner image formed on the intermediate transfer belt 20 to the recording material P.

  Reference numeral 28 denotes a cleaning device having a cleaning blade 29, which is provided to face the driven roller 24 with the intermediate transfer belt 20 interposed therebetween. After the toner image is transferred to the recording material P, the intermediate transfer belt 20 passes through the cleaning device 28, and the toner remaining on the peripheral surface is cleaned by the cleaning blade 29.

  70 is a paper feed roller, 71 is a timing roller, 72 is a paper cassette, and 73 is a transport roller.

  A fixing device 4 fixes the toner image on the recording material P, onto which the toner image on the intermediate transfer belt 20 has been transferred, by heating and pressing at a nip T formed by the heating roller 41 and the pressure roller 42. . A paper discharge roller 81 discharges the fixed recording material to a paper discharge tray 82.

<Developing device>
Next, the developing device will be described.

  As the developing device, a developing device using a two-component developer mainly composed of carrier and toner is used, but a two-component developing device using a small particle size toner is preferable. In addition, a developing device that performs normal development or reversal development can be used in the developing device. However, a developing bias having the same polarity as the charging of the photosensitive member 10 is applied to the developing sleeve 16 so that the charging of the photosensitive member is the same. Reversal development in which development is performed with toner charged to polarity is preferable. In this embodiment, development is performed by reversal development using negatively charged toner.

  As the toner having a small particle diameter, a toner having a volume average particle diameter of 4.5 μm to 6 μm is preferable.

  The volume average particle diameter was measured by the following method.

  It is measured and calculated using a device in which a computer system for data processing (manufactured by Beckman Coulter) is connected to Coulter Malitz Sizer II (manufactured by Beckman Coulter).

  As a measurement procedure, 0.02 g of toner is blended with 20 ml of a surfactant (for example, a surfactant solution obtained by diluting a neutral detergent containing a surfactant component 10 times with pure water for the purpose of dispersing the toner). After that, ultrasonic dispersion is performed for 1 minute to prepare a toner dispersion. This toner dispersion is poured into a beaker containing ISOTON II (manufactured by Beckman Coulter, Inc.) in a sample stand with a pipette until the measured concentration becomes 5% to 10%, and the measuring machine count is set to 30000 and measured. . The aperture diameter of the Coulter Maltesizer was 100 μm.

  With such a small particle size toner, a high-resolution high-quality image can be formed. A toner having a volume average particle diameter larger than 6 μm weakens the characteristics of high image quality.

  When a toner having a volume average particle diameter of less than 4.5 μm is used, the image quality is liable to deteriorate due to fog or the like.

  It is desirable to use a polymerized toner for the small particle size toner as described above.

  The polymerized toner means a toner obtained by forming a binder resin for toner and forming the toner shape by polymerization of a raw material monomer or prepolymer of the binder resin and subsequent chemical treatment. More specifically, it means a toner obtained through a polymerization reaction such as suspension polymerization or emulsion polymerization and, if necessary, a step of fusing particles between them. In a polymerized toner, a raw material monomer or prepolymer is uniformly dispersed in an aqueous system and then polymerized to produce a toner, so that a toner having a uniform toner particle size distribution and shape can be obtained.

  Specifically, a polymer is produced by emulsion polymerization of a monomer in a liquid of an aqueous medium to which an emulsion is added or a suspension polymerization method, and then an organic solvent, agglomeration is produced. It can manufacture by the method of adding an agent etc. and making it associate. A method of preparing by mixing with a dispersion liquid of a release agent or a colorant necessary for the constitution of the toner at the time of association, or a toner component such as a release agent or a colorant dispersed in a monomer Examples thereof include emulsion polymerization. Here, the association means that a plurality of resin particles and colorant particles are fused.

  As magnetic particles of the magnetic carrier, conventionally known materials such as metals such as iron, ferrite and magnetite, and alloys of these metals with metals such as aluminum and lead are used. Ferrite particles are particularly preferable.

  As the carrier, magnetic particles, those in which magnetic particles are further coated with a resin, or so-called resin dispersion type carriers in which magnetic particles are dispersed in a resin are used, but a carrier in which magnetic particles are coated with a resin is preferable. The resin composition for coating is not particularly limited, and for example, olefin resin, styrene resin, styrene-acrylic resin, silicone resin, ester resin, or fluorine-containing polymer resin is used. The resin for constituting the resin-dispersed carrier is not particularly limited, and known resins can be used. For example, a styrene acrylic resin, a polyester resin, a fluorine resin, a phenol resin, or the like can be used. it can.

In order to enable high-speed development, a carrier having a relatively low resistance is preferable in order to speed up the rise of charging of the toner. That is, a carrier having a resistance measured by the following method of 0.09 × 10 ⁹ to 2 × 10 ⁹ Ω is used.

  FIG. 3 shows an apparatus for measuring carrier resistance.

A magnet roll R2 was disposed opposite to the aluminum cylinder R1, and an interval L between the outer circumferences of the magnet roll R2 including the cylinder R1, the conductive sleeve SR, and the fixed magnet M was set to 0.5 mm. A carrier layer of 800 to 1000 g / cm ² is formed on the surface of the magnet roll R2, the carrier layer is lightly brought into contact with the cylindrical body R1, and a DC voltage of 500 V is applied to the conductive sleeve SR (diameter 35φ, length 55 mm). The resistance of the carrier CR was detected by measuring the current at that time with an ammeter AM.

  Such a relatively low-resistance carrier can be obtained by lowering the resistance of the resin coating layer by means such as containing carbon black in the resin coating layer.

  FIG. 4 is a cross-sectional view of the developing device 13.

  In FIG. 4, reference numeral 130 denotes a casing for accommodating a two-component developer composed of toner and carrier, and a fixed magnet roll 132 as magnetic field generating means is provided inside the developing sleeve 16 as a developer carrier. The The magnet roll 132 has two north poles indicated by N1 and N2, and three south poles indicated by S1 to S3.

  The magnetization center of the magnet roll 132, that is, the center of each magnetic pole in the magnetization direction substantially coincides with the rotation center of the developing sleeve 16.

  The N1 pole is a developing pole where the developing sleeve 16 forms a magnetic brush for the developer in the developing region G where the developing sleeve 16 faces the photoconductor 10, and the S1 pole and the S2 pole are magnetic poles that form a repelling magnetic field. The developer on 16 is peeled off. The S1 pole is a downstream magnetic pole formed immediately downstream of the N1 pole as the development pole. The S2 pole is a layer forming pole for forming a layer by attaching a developer to the developing sleeve 16. The developing sheave 16 rotates as indicated by an arrow W1 to convey the developer. S2, N2, S3, and N1 formed in order in the conveying direction are conveying magnetic pole rows in which different polarities are alternately arranged. The agent is transported by the transport magnetic pole row and supplied to the developing region G. A regulating member 133 is disposed between the S2 pole and the N2 pole so as to face the developing sleeve 16, and the developer conveyed on the developing sleeve 16 is controlled by the regulating action of the S2 pole as the layer forming magnetic pole and the regulating member 133. The amount is regulated, and a uniform developer layer is formed on the developing sleeve 16.

  Reference numerals 135 and 136 denote screws that stir and convey the developer.

  The toner is supplied into the developing device 13 from the opening indicated by 137 in FIG.

  The stirring chamber b in which the screw 135 is disposed and the supply / recovery chamber c in which the screw 136 is disposed are separated by a partition 131. The partition 131 is not illustrated, but a developer is provided at the end in the rotational axis direction of the screws 135 and 136. Passing holes are provided through which.

  In the housing 130, an opening is formed at a portion where the developing sleeve 16 faces the photoconductor 10 to form a developing region G.

  Development is performed as follows.

  In FIG. 4, as the photosensitive member 10 is indicated by W0, the developing sleeve 16 is indicated by W1, the screw 135 is indicated by the arrow W2, and the screw 136 is indicated by the arrow W3, respectively. Are conveyed in the form of screw 135 → screw 136 → developing sleeve 16, and development is performed in the development region G. As shown in the drawing, in the developing region G, the photosensitive member 10 and the developing sleeve 16 move in opposite directions, and reverse development is performed.

  By reverse development, it is possible to form a high-concentration toner image, and carrier adhesion can be suppressed. Also, the reverse development widens the fog margin operation window, which is the difference between the charged potential of the photoconductor 10 and the DC component of the development bias, that is, the width of the fog margin for performing good development that causes fog and carrier adhesion. .

  A developing bias voltage in which a DC voltage is superimposed on an AC voltage is applied to the developing sleeve 16 by bias power supplies E1 and E2. The bias power source E1 is a DC component power source, and the bias power source E2 is an AC component power source.

  In the developing device 13, high-speed image formation, that is, an image forming process in which the photosensitive member 10 is moved at a high linear velocity and development is performed. In addition, it is possible to form a high-quality image in which image quality deterioration phenomena such as carrier adhesion and worm-like image unevenness are sufficiently reduced.

In particular, when development is performed by moving the latent image carrier at a high speed so that the linear velocity of the photoconductor 10 is 250 mm / sc or higher, deterioration of image quality such as worm-like image unevenness is prevented. However, by satisfying the following conditions, it is possible to prevent deterioration in image quality and to form a high-quality image. Although the image formation can be performed by increasing the linear velocity of the latent image carrier to about 450 mm / sc, in the present invention, it is not hindered to perform a higher high-speed development.
Condition 1 (condition in the present invention)... Vp / f ≦ 70
vp is the linear velocity (mm / sc) of the photoconductor 10, and f is the frequency (kHz) of the AC component of the developing bias.

  When the relative speed between the latent image carrier and the developer carrier is high, the friction between the magnetic brush and the latent image carrier increases, and the latent image carrier is more likely to be triboelectrically charged. When the body and the developer carrying member are separated from the developing region and the gap between the two is enlarged, discharge may occur.

  In reverse development in which development is performed by moving the photosensitive member 10 and the developing sleeve 16 in opposite directions in the development region, the relative speed difference between the photosensitive member 10 and the developing sleeve 16 becomes large. Although worm-like image unevenness is likely to occur due to frictional charging and discharge occurring in, the development under Condition 1 can sufficiently suppress the occurrence of worm-like image unevenness.

  Here, the contact development is a development method in which a magnetic brush is brought into contact with the photosensitive member 10 for development, and the condition is set so that the relationship between the development gap Ds and the height h of the brush head of the magnetic brush satisfies h> Ds. Development that is performed.

  As shown in FIG. 5, the height h of the brush head of the magnetic brush is the maximum value of the magnetic brush B of the developer formed on the developing sleeve 16 by the N1 pole as the developing pole. The maximum value h is the rotation of the developing sleeve 16 with the photosensitive member 10 being separated from the developing sleeve 16 and the magnet roll 132 to form the magnetic brush B, and the ear of the magnetic brush B that is not restricted by the photosensitive member 10. It is measured by observing. The developing gap Ds is the shortest distance between the photoconductor 10 and the developing sleeve 16.

  If vp / f exceeds 70, worm-like image unevenness is likely to occur.

Conditions 2 to 7 shown below are preferable conditions.
Condition 2 ... 0 <h-Ds ≦ 0.3 mm
Condition 2 means contact development in which development is performed by bringing the magnetic brush into contact with the photoreceptor 10. When h-Ds is negative, that is, when the magnetic brush is not in contact, a sufficient maximum density cannot be obtained. On the other hand, when h-Ds is larger than 0.3 mm, non-uniform density due to rubbing of the magnetic brush, carrier adhesion, developer clogging at the development nip in the development area, and the like are likely to occur.
Condition 3 ... 40 ≦ vp / f
If vp / f is less than 40, fog, carrier adhesion, discharge traces and the like are likely to occur. In addition, the reproducibility of fine lines tends to be poor.
Condition 4... 1.25 ≦ (f × Ds) /Vac≦1.6
In condition 4, Vac is the voltage (peak-to-peak voltage) (kV) of the AC component in the development bias voltage, and is the output voltage (peak-to-peak voltage) of the power supply E2 in FIG.

Condition 4 is a condition for improving the reproducibility of the fine line. When (f × Ds) / Vac exceeds 1.6, the reproducibility of the fine line is lowered. Further, when (f × Ds) / Vac is lower than 1.25, fog is likely to occur.
Condition 5 (Vh + ΔVdc) /Ds≦3.8
In condition 5, Vh is the peak value of the portion of the AC component of the development bias voltage that contributes to development, and Vh = (1/2) Vac. Further, ΔVdc is a fog margin, and the charging potential of the photoconductor 10, that is, the charging potential of the unexposed portion is the absolute value of the difference between VL and the DC component potential Vdc of the developing bias potential, ΔVdc = | VL−Vdc | It is.

Condition 5 is a condition for preventing carrier adhesion and preventing discharge and leakage through the magnetic brush. When (Vh + ΔVdc) / Ds is greater than 3.8, image loss due to carrier adhesion and discharge or leakage is likely to occur.
Condition 6 ... vp ≧ 250
Condition 6 is a condition for high-speed image formation.
Condition 7: 1.5 ≦ vs / vp ≦ 3.0
In condition 7, vs is the linear velocity of the developer carrier, and in FIG. 4 is the linear velocity of the developing sleeve 16. Although the photosensitive member 10 and the developing sleeve 16 move in opposite directions, the movement in the opposite directions is positive.

  Condition 7 is a condition for ensuring developability in high-speed development and obtaining an image with a sufficient maximum density. When vs / vp is lower than 1.5, the developability is deteriorated and a sufficient maximum density is obtained. Becomes difficult to obtain. On the other hand, if vs / vp is greater than 3.0, density unevenness, developer scattering, etc. are likely to occur.

Hereinafter, experimental examples including examples and comparative examples will be described.
Example 1
In FIG. 4, the linear velocity vp of the photosensitive member 10 is set to 300 mm / sc, and the ratio of the photosensitive member 10 to the developing sleeve 16 is set to vs / vp = 1.8. Images were formed by changing related parameters, and worm-like image unevenness, fine line reproducibility, fogging and the like were evaluated as shown in Table 1.

  In Table 1, ΔVdc is a fog margin, and ΔVd = VL−Vdc. However, VL is a charging potential of the unexposed portion of the photoreceptor 10, and Vdc is a voltage of a DC component of the developing bias.

  Experiment No. 29 indicates that an image is formed but the density is insufficient. The density unevenness at 30 indicates that there was density unevenness due to rubbing of the ears of the magnetic brush. Furthermore, “−” in the evaluation column indicates that evaluation is not possible due to image defects.

  As shown in Table 1, a good image was formed in the experimental example in which vp / f was 70 or less, but in the experimental example in which vp / f exceeded 70, worm-like image unevenness occurred. Also, when vp / f is less than 40, the reproducibility of the thin line is slightly lowered, and when Vac is increased to compensate for this, carrier adhesion, discharge traces, etc. are generated.

  Further, in the experiment example where (f × Ds) / Va is higher than 1.6, the reproducibility of the thin line is not good, and in the experiment example where (f × Ds) / Va is lower than 1.25, Fog is likely to occur.

  Further, in the experimental example where (Vp + ΔVdc) / Ds exceeds 3.8, image loss due to carrier adhesion and discharge or leakage is likely to occur.

It is a figure which shows the image which the worm-like image nonuniformity generate | occur | produced. 1 is a schematic view of an image forming apparatus according to an embodiment of the present invention. It is a figure which shows the resistance measurement apparatus of a carrier. It is a figure which shows a developing device. It is a figure which shows a magnetic brush.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Photoconductor 13 Developing device 16 Developing sleeve 132 Magnet roll G Developing area Ds Distance E1, E2 Bias power supply

Claims (8)

Latent image carrier,
A developer carrier disposed opposite to the latent image carrier;
Magnetic field generating means for generating a magnetic field on the surface of the developer carrying member; and
A bias power source for applying a developing bias voltage in which an AC component is superimposed on a DC component between the latent image carrier and the developer carrier;
An image forming apparatus that uses a two-component developer including toner and carrier, moves the latent image carrier and the developer carrier in opposite development directions in opposite development regions, and performs development by contact development In
When the frequency of the AC component is f (kHz) and the linear velocity of the latent image carrier is vp (mm / sc),
Condition 1 ... vp / f ≦ 70
An image forming apparatus satisfying the requirements. The development gap Ds (mm) which is the shortest distance between the latent image carrier and the developer carrier, and the maximum value of the height of the head of the magnetic brush formed in the development region by the two-component developer. When h (mm)
Condition 2 ... 0 <h-Ds ≦ 0.3 mm
The image forming apparatus according to claim 1, wherein: The frequency f and the linear velocity vp are condition 3... 40 ≦ vp / f
The image forming apparatus according to claim 1, wherein the image forming apparatus satisfies the following. The frequency f, the AC component voltage {peak-to-peak voltage (kV)} Vac, and the developing gap Ds (mm) which is the shortest distance between the latent image carrier and the developer carrier. Condition 4 ... 1.25 ≦ (f × Ds) /Vac≦1.6
The image forming apparatus according to claim 1, wherein: The peak value Vh (Vh = Vac / 2) of the AC component contributing to the development, the distance between the latent image carrier and the developer carrier, Ds (mm), and the fog margin ΔVdc are as follows: Condition 5 (Vh + ΔVdc) ) /Ds≦3.8
The image forming apparatus according to claim 1, wherein: Vp (mm / sc) is condition 6... Vp ≧ 250
The image forming apparatus according to claim 1, wherein: When the linear velocity of the developer carrying member is vs (mm / sc), the vp and the vs satisfy the condition 7... 1.5 <vs / vp ≦ 3.0
The image forming apparatus according to claim 1, wherein: The image forming apparatus according to claim 1, wherein a carrier in which magnetic particles are coated with a resin is used as the carrier.

Images