JP2003255627A - Image forming method and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming method having stable developability, and capable of preventing a noise feeling from getting worse and preventing the occurrence of a void. <P>SOLUTION: As for the image forming condition for forming a toner image on an image carrier in a developing process, a developing bias condition is set as follows so as to perform an image stabilization control. (1) A developing AC bias condition is established by fixing a developing AC frequency to be ≤1 kHz, setting the using extent of the developing AC bias (effective value Vac) to be ≥0 V and ≤750 V, and having the Vac value capable of obtaining the prescribed image density within the aforesaid extent. (2) A developing AC bias condition is established by fixing the developing AC bias to nearly the maximum value in the using extent in the case the prescribed image density is not obtained by nearly the maximum effective value in the developing AC bias using extent, and then, increasing the developing AC frequency Fac from the low frequency up to the AC frequency capable of obtaining the prescribed image density. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method and an image forming apparatus for forming an image on a recording material by an electrophotographic method, and more particularly to a technique for controlling developing conditions.

[0002]

2. Description of the Related Art In an example of an image forming process for forming an image by an electrophotographic method, an electrostatic latent image is formed on an image bearing member such as a photoconductor, and the formed electrostatic latent image is developed by a developing means. A toner image is formed on the image carrier, the formed toner image is transferred to a recording material by a transfer unit, and the transferred toner image is fixed on the recording material by a fixing unit to form an image on the recording material. In another example, a toner image on an image forming body such as a photoconductor is transferred to an intermediate transfer body as an image carrier, and then transferred from the intermediate transfer body to a recording material by a transfer means to be fixed, thereby recording the recording material. To form an image.

In the developing step in the image forming step,
Development using a two-component developer containing toner and carrier is often used, and a development bias voltage in which a DC bias is superimposed on an AC bias is often applied.

The development bias voltage is often used as a control parameter for the maximum density, gradation, fog removal, etc. The AC bias of the development bias voltage in which the DC bias is superimposed on the AC bias is the development for controlling the image density. It is controlled as a parameter. That is, the AC bias is a parameter that controls the chance of the toner coming into contact with the image forming body carrying the latent image by applying vibration to the toner in the developing area, and by increasing the voltage of the AC bias, Alternatively, the image density is adjusted by controlling the AC bias by utilizing the phenomenon that the image density tends to increase in many cases by increasing the frequency of the AC bias.

[0005]

The developing bias is D
In the conventional development process in which the C bias and the AC bias are superposed and developed, AC is aimed at improving the developability.
Although the effective value Vac of the bias is set to be high, when the effective value Vac is set to be high, the "noise feeling" in which the image solid part feels rough is deteriorated, and the high density part and the low density part of the image are deteriorated. There was an image defect such as "white spot" at the boundary of the image. This phenomenon has been particularly prominent in a polymerized toner and a toner having a small particle diameter, which are used for obtaining a high quality image, and have been a problem.

The present invention solves such a problem and has a stable developability, stable "image noise" in the image solid portion and stable "white spots" which do not occur in the high density portion / low density portion boundary portion. An object of the present invention is to provide an image forming method and an image forming apparatus capable of obtaining a good image.

[0007]

The above object of the present invention is achieved by the following image forming method and image forming apparatus.

1. The latent image forming step of forming a latent image on the image bearing member and the developing step of applying a developing bias voltage in which a DC bias is superimposed on an AC bias to the developer bearing member to develop the toner causes the toner on the image bearing member. An image forming method characterized in that the image forming condition for forming an image is set by a developing bias condition by the following steps (1) and (2) to perform image stabilization control. (1) A step of selecting a certain value on the low frequency side of a variable range of the AC frequency of the AC bias, changing the effective value of the AC bias, and determining the AC bias effective value at which a desired image density is obtained (2) ) When the desired image density is not obtained in the step (1), the AC bias effective value is determined to be the maximum value or a value close to the maximum value in the range changed in (1), and the AC frequency is changed to obtain the desired value. 1. Determine the AC frequency at which the concentration of Image carrier, charging means for uniformly charging the image carrier, exposing means for exposing the uniformly charged image carrier to form a latent image, developing bias in which DC bias voltage is superimposed on AC bias The controller has a developing unit that applies a voltage to a developer carrier that conveys the developer to the developing nip portion to develop the toner image, and an image density sensor that detects the toner adhesion amount of the toner image. An image forming apparatus characterized by setting image forming conditions using a developing condition setting program (1) and (2) recorded in a memory and performing image stabilization control. (1) The image density detection pattern latent image is formed by forming an image density detection pattern latent image, selecting a certain value on the low frequency side of the variable range of the AC frequency of the AC bias, and changing the effective value of the AC bias. And determining the AC bias effective value at a value at which the toner adhesion amount detected by the image density sensor reaches a predetermined value (2) When the desired image density cannot be obtained in the step (1), The AC bias effective value is determined to be the maximum value or a value close to the maximum value in the range changed in (1), the AC frequency is changed, and when the toner adhesion amount detected by the image density sensor reaches a predetermined value, AC The process of determining the frequency

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION (1) The experimental study conducted by the present inventors prior to the description of the present invention will be described.

In a developing device for developing by applying a DC bias and an AC bias in a superimposed manner as a developing bias, the relation between the effective value (Vac value) of the AC bias and the noise sensation of the solid portion of the patch image is shown. It is a graph of FIG. The noise sensation is recognized as roughness (granularity) with respect to a solid matte toner adhesion state in the solid part, and is numerically calculated from the density distribution measured by the microdensitometer. .

From the graph of FIG. 1, it is shown that when the effective value (Vac value) of the AC bias is increased, the noise sensation deteriorates almost linearly.

Further, the effective value of AC bias (Vac value)
FIG. 2 is a graph showing the relationship between the toner adhesion amount M / A for the solid portion on the image carrier with respect to. V
As the ac value is increased, the developability is also improved, and the toner adhesion amount M / A is increased. However, if the Vac value is further increased with a certain value as a peak, the toner adhesion amount may be decreased. Is recognized.

At the time of image formation, a feeling of noise with respect to the effective value (Vac value) of the AC bias and the toner adhesion amount M /
It is necessary to determine the optimum Vac (V) in consideration of the relationship of A.

From the graphs of FIGS. 1 and 2, Vac (V)
It can be seen that when the value is set low, the noise feeling is improved but the toner adhesion amount (mg / cm ² ) is decreased. Further, regarding the toner adhesion amount, the effective value Va of the AC bias is
At c = 1000V, the toner adhesion amount has a peak value, and if an excessive AC bias is applied, the image is disturbed and the toner adhesion amount decreases.

Based on the results of this examination, in the present invention, the application region of the effective value Vac (V) of the AC bias is set to 0 to 0.
It is set to 750V or less. However, the developability varies greatly depending on the usage time of the developer and environmental conditions, and Vac = 7.
In some cases, the required toner adhesion amount (for example, the toner adhesion amount on the image carrier of 0.6 mg / cm ² required to obtain the image density of 1.3) may not be obtained even at 50V. In such a case, the AC bias frequency (Hz) is changed to obtain the required toner adhesion amount. In addition,
The graphs of FIG. 1 and FIG. 2 show the AC bias frequency of 2.0 k.
It is data at Hz.

It is possible to judge whether or not the required amount of toner has been adhered by setting the developing bias conditions as described above. The solid patch image on the image bearing member is developed, and the developing portion is subjected to a reflection type micro image. It is performed by reading with a photo sensor. By setting the development bias conditions and performing image stabilization control in this way,
The developability is ensured, the deterioration of noise and the occurrence of white spots are prevented, and the image stabilization control is performed.

(2) Next, an image forming apparatus to which the image forming method of the present invention is applied will be described.

A color image forming apparatus shown as an embodiment of the present invention forms toner images composed of yellow (Y), magenta (M), cyan (C) and black (K) toners on a plurality of image carriers, respectively. A tandem type color image forming apparatus in which toner images formed and formed on a plurality of image bearing members are superposed on a transfer material via an intermediate transfer member or directly.

The color image forming apparatus shown in FIG. 3 is a tandem type color image in which the toner images formed on the image carrier are transferred onto the intermediate transfer member in an overlapping manner, and the superimposed toner images are transferred together. It is called a forming device, and includes a plurality of sets of image forming units 10Y, 10M, 10C and 10K, an intermediate transfer unit 7, a sheet feeding and conveying unit and a fixing unit 24. Image forming apparatus body (hereinafter referred to as apparatus body)
A document image reading device SC is arranged above A.

Image forming unit 1 for forming a yellow image
0Y has a charging unit 2Y, an exposing unit 3Y, a developing unit 4Y, a primary transfer unit 5Y, and a cleaning unit 6Y arranged around an image carrier (photoconductor) 1Y. The image forming unit 10M that forms a magenta image includes an image carrier (photoconductor) 1M, a charging unit 2M, an exposing unit 3M, and a developing unit 4.
M, primary transfer means 5M, and cleaning means 6M. The image forming unit 10C that forms a cyan image includes an image carrier (photoconductor) 1C, a charging unit 2C, an exposing unit 3C,
Developing means 4C, primary transfer means 5C, cleaning means 6
Has C. The image forming unit 10K that forms a black image,
Image carrier (photoreceptor) 1K, charging means 2K, exposure means 3
K, developing means 4K, primary transfer means 5K, and cleaning means 6K. In each image forming unit 10, charging, exposure and development are performed to form an image of each color on the image carrier 1.

The intermediate transfer unit 7 has a semiconductive endless belt-shaped intermediate transfer member 70 which is wound by a plurality of rollers and is rotatably supported.

Image forming units 10Y, 10M, 10C, 10
The image of each color formed by K is transferred to the primary transfer means 5Y, 5
By M, 5C, and 5K, a superimposed color image is transferred onto the rotating intermediate transfer member 70 in synchronism with each other and sequentially superimposed and transferred. A recording medium (hereinafter, referred to as paper) P housed in the paper feeding cassette 20 is a paper feeding unit 21.
Is fed by a plurality of intermediate rollers 22A, 22B, 2
The color images superposed on the paper P are collectively transferred by being conveyed to the secondary transfer unit 5A via the 2C and 22D and the registration roller 23. Paper P on which a color image has been transferred
Is subjected to a fixing process by the fixing means 24, and the paper discharge roller 25
The sheet is sandwiched between the sheets and placed on the sheet discharge tray 26 outside the machine.

On the other hand, after the color image is transferred onto the paper P by the secondary transfer means 5A, the residual toner is removed by the cleaning means 6A from the intermediate transfer body 70 in which the paper P is separated by the curvature.

During the image forming process, the primary transfer means 5K is constantly in pressure contact with the photoconductor 1K. Other primary transfer means 5
Y, 5M and 5C are pressed against the corresponding photoconductors 1Y, 1M and 1C only when forming a color image.

The secondary transfer means 5A is brought into pressure contact with the intermediate transfer member 70 only when the sheet P passes therethrough and secondary transfer is performed.

(3) FIG. 4 shows a set of image forming portions 10 taken out. An OPC photosensitive member or the like is used as the drum-shaped photosensitive member 1 as an image bearing member that rotates in the arrow direction,
Uniform charging is performed by the charging means 2 using a scorotron charger or the like. As the exposure means 3, an exposure means for performing dot exposure such as a laser or a light emitting diode is used, and an electrostatic latent image is formed by the image exposure of the exposure means 3. Subsequent to the latent image forming step, development is performed by the developing unit 4 which will be described in detail below, and the electrostatic latent image becomes a toner image. An image density sensor SD using a reflection type microphotosensor or the like for detecting the toner adhesion amount adhering to the surface of the photoconductor 1 is provided on the downstream side of the developing means 4, and the toner adhesion amount is detected if necessary. Is done.

(4) The developing means 4 includes a developing device frame 40,
A developer carrier 41 composed of a developing roller, a magnetic field generating means (magnet roll) 42, a regulating means 43 composed of an ear cutting plate, a water wheel type supply means 44, a supply / conveyance means 45 composed of a screw, and an agitation / conveyance composed of a screw. Means 4
6, a conveying roller 47, a stripping plate 48, a collecting means 49 including a screw, and the like.

The developer carrying member 41 is arranged so as to face the photoconductor 1 and is rotatably supported. The developer carrying member 41 rotates to convey the developer to the developing area DR as indicated by an arrow, and the developing area D
In R, a developer is carried to form a layer of the developer required for development.

The supplying means 44 is a rotatable water wheel type conveying means for supplying the developer to the developer carrying body 41, and the developer carried from the supplying / conveying means 45 is supplied to the developer carrying body 4.
The developer is uniformly supplied in the vicinity of the developer receiving magnetic pole S3.
The supply means 44 may be a screw having a conveying function in the rotation axis direction.

The supplying / conveying means 45 is arranged in parallel with the supplying means 44, and conveys the developer conveyed from the stirring / conveying means 46 to the supplying means 44 while conveying the developer in the rotation axis direction thereof.

The stirring / conveying means 46 mixes the new toner to be replenished with the developer refluxed from the supplying / conveying means 45, agitates them, and conveys them to the upstream portion of the supplying / conveying means 45.

A transport roller 47 is arranged near the developer stripping magnetic pole S2 of the developer carrier 41. The transport roller 47 is a rotatable rotating member (sleeve) 47.
A and the developing device frame 4 housed inside the rotating member 47A.
It is composed of a cylindrical magnet body 47B fixed to 0.

The collecting means 49 rotatably arranged in the collecting section 403 collects the developer which is peeled off by the conveying roller 47 and the peeling plate 48 and drops, and supplies it.
The developer is carried to the downstream side of the carrying means 45 in the carrying direction and to the outside of the image forming area of the developer carrying body 41. At the position where the developer does not return to the developer carrier 41, the collected developer is put in the developing region of the developer carrier 41 on the downstream side in the transport direction of the supply / transport means 45. Good. Alternatively,
The developer collected by the collecting means 49 may be returned to the upstream portion of the stirring / conveying unit 402.

Supply / transport means 45, stirring / transport means 46
Each of the collecting means 49 and the collecting means 49 is composed of a spiral screw, conveys the developer in the rotation axis direction while stirring, and discharges the developer in a direction substantially perpendicular to the rotation axis.

The developing device frame 40 includes a developer carrier 41,
A lower frame 40A that supports the transport roller 47, the supply unit 44, the supply / transport unit 45, and the stirring / transport unit 46, and an inner frame 40B that supports the stripping plate 48 and the recovery unit 49.
And an upper lid 40C that closes the upper opening of the middle frame 40B.

The lower frame 40A forms a supply section 401 for accommodating the supply means 44 and the supply / conveyance means 45, and a stirring / conveyance section 402 for accommodating the stirring / conveyance means 46. The supply unit 401 and the stirring / conveying unit 402 are formed on both sides with the first partition wall 404 standing upright from the bottom of the lower frame 40A.

The second partition wall 405 formed at the bottom of the middle frame 40B for rotatably supporting the collecting means 49 is the supply section 4.
01 and the collection unit 403 are partitioned. Further, a part of the middle frame 40B closes the upper opening of the stirring / conveying unit 402.

The downstream side of the developer transport of the recovery section 403 and the downstream side of the developer transport of the supply section 401 communicate with each other through a first opening 406 formed near the end of the second partition 405.

Stirring with the developer transport downstream side of the supply unit 401
The developer transport upstream side of the transport unit 402 means the first partition 404.
An opening (not shown) provided near one end of one of the two communicates with each other.

The developer peeled off by the conveying roller 47 and the stripping plate 48 is collected in the collecting section 403, and the collected developer is conveyed to the downstream side of the developer conveying by the collecting means 49, and further, the supplying section 401. Reflux to.

The developer in the supply section 401 is fed into the stirring / conveying section 402 through an opening (not shown) formed at one end of the first partition 404 by the supplying / conveying means 45 into an arrow W.
It is conveyed as indicated by 1. The developer conveyed into the stirring / conveying unit 402 is mixed and stirred by the stirring / conveying means 46 with the toner replenished from the toner replenishing opening 409, and then conveyed to the first partition 404. Is discharged from an opening (not shown) formed at the other end of the sheet and is recirculated into the supply section 401 as indicated by an arrow W2. In the supply unit 401, the supply / conveyance means 45 conveys the developer in the axial direction and discharges the developer to supply it to the supply means 44. The supply unit 44 radiates the developer while conveying the developer in the axial direction to supply the developer to the developer carrier 41.

B (DC) is a DC bias power source for applying a DC bias to the developer carrying member 41, and D (AC) is an AC bias power source for applying an AC bias to the developer carrying member 41, which is controlled by a control unit described later. Then, the AC bias is superimposed on the DC bias and applied, and the development is performed.

The developing means 4 of the image forming apparatus according to the present embodiment develops using a two-component developer containing toner and carrier.

The toner has a mass average particle diameter of 3 to 8 μm.
m polymerized toner is preferred. By using the polymerized toner, it is possible to form an image having a high resolution and a stable density and very little fog.

The polymerized toner is manufactured by the following manufacturing method. The formation of the binder resin for the toner and the shape of the toner are obtained by polymerizing the raw material monomer or prepolymer of the binder resin and the subsequent chemical treatment. More specifically, it is obtained through a polymerization reaction such as suspension polymerization or emulsion polymerization and, if necessary, a fusion step of particles to each other, and in a polymerized toner, a raw material monomer or a prepolymer is uniformly dispersed in an aqueous system. By polymerizing the toner later, a toner having a uniform particle size distribution and shape can be obtained.

In the present embodiment, the mass average particle size is 3
-8 μm toner is used. The mass average particle diameter is an average particle diameter on a mass basis, and is a value measured by a "Coulter Counter TA-II" or a "Coulter Multisizer" (both manufactured by Coulter, Inc.) equipped with a wet disperser.

If the mass average particle diameter is less than 3 μm, fogging and toner scattering are likely to occur. The upper limit of 8 μm is the upper limit of the particle size that enables formation of high image quality that is the target of the present embodiment.

The carrier has a mass average particle diameter of 10 to 10.
A carrier consisting of 50 μm magnetic particles is preferred. 10
Carrier adhesion is likely to occur with a carrier having a particle size smaller than μm. Further, with a carrier having a particle size larger than 50 μm, an image having a uniform density may not be formed in some cases.

(5) FIG. 5 is a block diagram for setting the developing bias condition of the present invention and performing image stabilization control. FIG. 6 shows the developing bias of the present invention for performing image stabilization control. The flowchart is shown.

The image stabilization control of the present invention is performed during the warming-up time when the power switch is turned on or after a predetermined number of copies have been printed, and the control section C1 calls the developing condition setting program recorded in the memory C2. The steps according to the program are performed. (F1) Development AC frequency Fac is 1 kHz or less (for example, 500 H
z), the solid patch is formed, and the development of the solid patch is performed while changing the use range of the developing AC bias (effective value Vac) from 0 to 750 V or less (for example, 750 V) from the low voltage side. (F2) The reflection density (sensor output) of the solid patch image developed by the image density sensor SD is detected. Control unit C
1 checks whether or not the detected sensor output has a predetermined sensor output value (adhered toner amount). (F
3) When it is determined that the sensor output has a predetermined sensor output value (toner adhesion amount), the AC frequency Fac for developing the solid patch and the AC bias effective value Vac are set as the AC bias developing condition. , The image density adjustment is completed. (F3, YES) When it is not determined that the sensor output has reached the predetermined sensor output value (toner adhesion amount) (F3, NO), the control unit C1
Is the AC bias effective value Vac, which is almost the maximum value of the use range,
Alternatively, the effective value close to the maximum value (for example, 750 V) is set, and the frequency Fac is set to 1 kHz or less (for example, 500 V).
The solid patch is developed again while the solid patch is raised at a predetermined Hz interval (e.g., 500 Hz) at a predetermined Hz interval.
(F4) The reflection density (sensor output) of the solid patch image developed by the image density sensor SD is detected. Control unit C
1 checks whether or not the detected sensor output has a predetermined sensor output value (adhered toner amount). (F
5) When it is determined that the sensor output has a predetermined sensor output value (toner adhesion amount), the control unit C1 develops the AC frequency Fac of the solid patch and the AC bias which is almost the maximum value of the use range. The effective value, for example, 750 V is set as the AC bias developing condition, and the image density adjustment is completed. (F5, YES) When it is not determined that the sensor output has reached the predetermined sensor output value (toner adhesion amount) (F5, NO), the control unit C1
Sets the AC frequency Fac to the maximum value of the variable range (F
6), together with the AC bias effective value (for example, 750 V) which is almost the maximum value of the use range, is set as the AC bias developing condition, and the image density adjustment is completed.

By the above image density adjustment, a high quality developing performance is secured, and an image with good image quality without noise or white spots is formed.

(6) The image density adjustment described above is performed in a state where the rotational peripheral speed ratio between the photoconductor 1 and the developer carrying member 41 is kept constant. When the peripheral speed of the developer carrying member 41 is increased, the image density also increases and the developability tends to improve, but on the other hand, toner scattering and carrier adhesion tend to increase, so
The optimum peripheral speed of the developer carrying member 41 is determined in advance, and the peripheral speed is not changed during the above adjustment.

Further, although the stable image development performance and the high quality image are secured by the image density adjustment control described above, it is necessary to newly set the developing condition when the environmental conditions such as temperature and humidity greatly change. Becomes An environmental condition measuring means C4 for measuring temperature and humidity is provided in the image forming apparatus, and the control unit C1 records the environmental condition measured during the image density adjusting process performed in the morning in the memory and measures during the printing operation. The above environmental conditions are compared with the stored environmental conditions, and when a change exceeding the threshold value is recognized, a message indicating that image density adjustment is to be performed is displayed on the display panel, and image density adjustment is performed.

The characteristics of the developer are fatigued by use,
Appropriate developing conditions also vary. Therefore, it is necessary to newly set the developing condition after the developing means 4 is operated for a long time. The developing means 4 is provided with a developer use time detecting means C3 for integrating and measuring the operating time, and the control section C1 detects that the developer use time has reached a predetermined time after the image density adjusting step performed in the morning etc. Then, the display panel displays that the development density adjustment is to be performed, and the image density adjustment is executed. The image density adjustment is executed subsequent to the end of the job. The detection of the developer use time can be substituted by the number of prints of the transfer paper printed during that time.

The image density adjustment described above is executed for each of the Y, M, C, and K image forming sections 10 in the color image forming apparatus shown in FIG.

[0056]

EXAMPLE A drum-shaped OPC photosensitive member is used, and an AC bias of a developing bias voltage in which a DC bias is superimposed on an AC bias is set by the image stabilization control method described above.
An image forming experiment was conducted. -Linear velocity of photoconductor: 180 mm / sec-Linear velocity ratio between photoconductor and developer carrier: Forward rotation, fixed at linear velocity ratio of 1.8 for variable range 0.5 to 3.0-Developer carrier Amount of developer carried on the body: 20 mg / cm ²・ Gap between photoconductor and developer carrier: 0.35 mm ・ Developer: two-component developer ・ Toner: polymerized toner having a mass average particle size of 6.5 μm ・Carrier: Iron powder carrier having a mass average particle diameter of 30 μm ・ Toner concentration of developer: 8.0 mass% ・ Development bias: AC bias + DC bias, where A
The waveform of the C bias is a rectangular wave. ・ DC bias: Variable range -200 to -700 V is set to -500 V. ・ AC bias effective value Vac: Variable range 0 to 750 V. ・ AC bias frequency Fac: Variable range 500 to 3000.
Hz AC bias was set according to the flow of FIG. 6 under the above conditions. In F2, Fac was set to 500 Hz, and the solid patch was developed while increasing Vac from 0 V to 750 V at 125 V intervals at 750 V.
In F3, the toner adhesion amount of the patch image is 0.6 mg / cm
^It was detected whether a sensor output corresponding to ² was obtained, but no satisfactory sensor output was obtained for any AC effective value. (F3 ・ NO) In F4, set Vac = 750V and set Fac to 1 kHz, 1.5 kHz ...
The solid patch was developed while raising it at z intervals. In F5, toner adhesion amount 0.6 mg / cm ² at Fac = 2 kHz
A sensor output corresponding to Therefore, in the image stabilization control, as the developing AC bias condition, Vac = 7
It was set to 50 V and Fac = 2 kHz.

The above-mentioned image density adjustment shows one embodiment thereof, and the image forming apparatus for carrying out the image density adjusting method performed during warm-up or the like is 200
During the printing operation of Kc (200,000 sheets), good developability is maintained for all print images, there is no problem with image quality such as noise and white spots, and stable print images are the same as at the start. Was obtained.

[0058]

As a result of the image stabilization control of the present invention, there is no white spot phenomenon that occurs at the boundary between the high density portion and the low density portion, with stable developing property and no deterioration of noise feeling in the image solid portion. It is possible to obtain a stable print image without any noise.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between an AC bias effective value and a feeling of noise.

FIG. 2 is a graph showing a relationship between an AC bias effective value and a toner adhesion amount.

FIG. 3 is a cross-sectional configuration diagram of a color image forming apparatus.

FIG. 4 is a cross-sectional configuration diagram of an image forming unit.

FIG. 5 is a block diagram for performing image stabilization control according to the present invention.

FIG. 6 is a flowchart for performing image stabilization control according to the present invention.

[Explanation of symbols]

1 photoconductor 2 charging means 3 exposure means 4 developing means 41 developer carrier SD image density sensor C1 controller C2 memory

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 15/08 507 G03G 9/08 384 (72) Inventor Nobuyasu Tamura 2970 Ishikawa-cho, Hachioji-shi, Tokyo Konica In-house F-term (reference) 2H005 AB06 EA05 FA01 2H027 DA10 DA13 DA14 DA38 DE02 EA05 EB04 EC03 2H073 AA02 BA04 BA06 BA13 BA28 BA33 BA43 CA03 CA22 2H077 AD06 AD36 DA05 DA18 DA20 DA47 DA63 DA81 DB08 EA03 GA13

Claims (12)

[Claims] 1. An image is formed by a latent image forming step of forming a latent image on an image carrier and a developing step of applying a developing bias voltage in which a DC bias is superimposed on an AC bias to the developer carrier to develop the image. An image forming method characterized in that the image forming condition for forming a toner image on a carrier is set by a developing bias condition by the following steps (1) and (2) to perform image stabilization control. (1) A step of selecting a certain value on the low frequency side of a variable range of the AC frequency of the AC bias, changing the effective value of the AC bias, and determining the AC bias effective value at which a desired image density is obtained (2) ) When the desired image density is not obtained in the step (1), the AC bias effective value is determined to be the maximum value or a value close to the maximum value in the range changed in (1), and the AC frequency is changed to obtain the desired value. Of determining the AC frequency at which the concentration of 2. The image forming method according to claim 1, wherein the image bearing member and the developer bearing member maintain a constant rotational peripheral speed ratio. 3. The image forming method according to claim 1, wherein in the developing step, development is performed using polymerized toner. 4. In the developing step, the mass average particle diameter is 3 to 8.
The image forming method according to claim 1, wherein development is performed using a two-component developer having a toner having a particle size of 10 μm and a carrier having a mass average particle diameter of 10 to 50 μm. 5. The image forming method according to claim 1, wherein the image stabilization control is performed when the environment changes. 6. The image stabilization control is carried out for each predetermined length of time the developer is used.
The image forming method according to any one of 1. 7. An image carrier, a charging unit for uniformly charging the image carrier, an exposing unit for exposing the uniformly charged image carrier to form a latent image, and a DC bias voltage for the AC bias. A developing unit that applies the superimposed developing bias voltage to a developer carrier that conveys the developer to the developing nip portion to develop it to form a toner image, and an image density sensor that detects the toner adhesion amount of the toner image are provided. The image forming apparatus is characterized in that the control unit sets image forming conditions by using the developing condition setting programs (1) and (2) recorded in the memory and performs image stabilization control. (1) The image density detection pattern latent image is formed by forming an image density detection pattern latent image, selecting a certain value on the low frequency side of the variable range of the AC frequency of the AC bias, and changing the effective value of the AC bias. And determining the AC bias effective value at a value at which the toner adhesion amount detected by the image density sensor reaches a predetermined value (2) When the desired image density cannot be obtained in the step (1), The AC bias effective value is determined to be the maximum value or a value close to the maximum value in the range changed in (1), the AC frequency is changed, and when the toner adhesion amount detected by the image density sensor reaches a predetermined value, AC The process of determining the frequency 8. The image forming apparatus according to claim 7, wherein the image bearing member and the developer bearing member maintain a constant rotational peripheral speed ratio. 9. The image forming apparatus according to claim 7, wherein a polymerized developer is used as the developer. 10. The developer has a mass average particle diameter of 3 to 8 μm.
10. A toner having a particle size of m, a carrier having a mass average particle diameter of 10 to 50 .mu.m, and a two-component developer are used.
The image forming apparatus according to claim 1. 11. The image stabilization control according to claim 7, wherein the image stabilization control is performed when the environment changes.
The image forming apparatus according to item. 12. The image stabilization control is carried out every predetermined length of time the developer is used.
10. The image forming apparatus according to any one of 10.