JPH09311556A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of obtaining a uniform and smooth halftone image without any uneven brush mark. SOLUTION: A developing device 1M is constituted of a magnetic brush developing device developing image by impressing DC bias on which AC bias is superposed as developing bias on an opposed part between a photoreceptor drum (image carrier) 3 and a developing sleeve (developer carrier) 25. A stage for impressing voltage to apply force in a direction where two-component developer 22 goes from the drum 3 toward the sleeve 25 on the developer 22 for a specified time and a stage for impressing the voltage to apply force in a direction where the developer 22 goes from the sleeve 25 toward the drum 3 on the developer 22 for the specified time are alternately repeated plural times, and the voltage to apply the force in the direction where it goes toward the sleeve 25 is impressed, then the voltage between the voltage of the image part of the electrostatic latent image on the photoreceptor drum 3 and the voltage of the non-image part thereof is impressed on the sleeve 25 for a fixed time as the developing bias. Thus, the toner is biased and oscillated in the vicinity of an image area and the toner is sufficiently stuck to a highlight halftone area.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine, a printer, a recorded image display for developing an electrostatic latent image formed on an image carrier by an electrophotographic system, an electrostatic recording system or the like to form a visible image. The present invention relates to an image forming apparatus such as an apparatus and a facsimile.

[0002]

2. Description of the Related Art Conventionally, a dry developer as a developer is carried on the surface of a developer carrier, and the developer is conveyed and supplied to the vicinity of the surface of the image carrier carrying an electrostatic latent image. A method of developing an electrostatic latent image and developing the electrostatic latent image while applying an alternating (alternating) electric field between the body and the developer carrying body is generally well known.

Since a developing sleeve is generally used as the developer bearing member, the image bearing member is referred to as a "developing sleeve" in the following description, and a photosensitive drum is generally used as the image bearing member. In many cases,
In the following description, the image carrier will be referred to as "photosensitive drum".

By the way, as a developing method, a magnetic brush developing method using a developer (two-component developer) composed of, for example, a two-component composition (carrier particles and toner particles) has been conventionally known. In this magnetic brush developing method, a magnetic brush is formed on the surface of a developing sleeve in which a magnet is arranged, and the magnetic brush is rubbed or brought close to a photosensitive drum which is opposed to the developing sleeve while holding a minute developing gap. And a photosensitive drum (between S and D) are continuously applied to each other to repeatedly perform transfer and reverse transfer of toner particles from the developing sleeve side to the photosensitive drum side, thereby performing development (for example, (See JP-A-55-306060 and JP-A-59-165082). In addition, a non-contact type alternating electric field development method using a two-component developer for the purpose of simple color development and multiple development is also known (JP-A-56).
-14268, JP-A-58-68051, JP-A-5
6-144452, JP-A-59-181362, JP-A-60-176069).

In recent years, toners produced by a polymerization method (hereinafter referred to as polymerized toners) have been developed for the purpose of further improving transferability and image quality. Since this toner has a spherical shape, it has good releasability from the photosensitive drum, and therefore high transfer efficiency can be obtained.
As a result, a particularly high-quality, high-density, large-area image can be obtained.

On the other hand, if two-component development is carried out using the above toner, the image gradation of highlight and halftone may deteriorate. This phenomenon is remarkable when a method (PWM method) of controlling the light emission time of the exposure means in proportion to the magnitude of the image signal value for each arbitrary pixel is adopted as an analog image exposure or digital image gradation reproduction method. Occurred in. It is considered that this is due to the fact that the electric field component of the peeling electric field of the alternating electric field from the photosensitive drum in the low contrast area is larger than that in the high contrast area, and as described above, the releasing property of the polymerized toner is high. Be done.

The above problem is solved by a so-called counter developing system in which the direction of rotation of the developing sleeve is opposite to the direction of rotation of the photosensitive drum at the portion facing the photosensitive drum.
In the counter developing method, the relative speed difference between the photosensitive drum and the magnetic brush on the developing sleeve becomes larger than that in the conventional forward developing method, so that the rubbing force of the magnetic brush increases and the developing efficiency increases, The image density of the highlight and halftone which is the low contrast area is secured, and the gradation is improved.

Further, it is well known that the counter developing method can prevent the peeling phenomenon which occurs in the forward developing method. Here, the peeling phenomenon is a phenomenon in which the trailing edge of the high-density portion becomes darker when the low-density portion is continuous with the high-density portion, and the high-charge toner enters the developing area of the high-density image area. It is thought that this occurs because it should not occur and stays near the photosensitive drum.

[0009]

As described above, even when the polymerized toner is used, the relative speed between the magnetic brush on the developing sleeve and the photosensitive drum is increased by the magnetic brush counter developing method, so that the density of the low density portion is increased. Although the gradation is improved, the following problems occur depending on the setting conditions of the magnetic brush on the developing sleeve.

That is, when the weight per unit area of the magnetic brush on the developing sleeve is increased in order to secure the density, or in order to suppress toner scattering, the toner density of the magnetic brush on the developing sleeve (hereinafter referred to as T / D ratio). When the value of (1) is lowered, the rubbing force of the magnetic brush against the photosensitive drum becomes excessive, and image deterioration called so-called streaking unevenness occurs in which the toner layer on the photosensitive drum is scraped off after development. This phenomenon was more remarkable when the polymerized toner was used than when the conventional pulverized toner was used.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus capable of obtaining a uniform and smooth halftone image free from unevenness in crimping.

[0012]

To achieve the above object, the invention according to claim 1 has an image carrier and a developing device for developing an electrostatic latent image formed on the image carrier. The developing device holds a rotatable developer carrier that carries and conveys a two-component developer composed of a non-magnetic toner produced by a polymerization method and a magnetic carrier, and is fixed inside the developer carrier. In an image forming apparatus including a plurality of magnetic field generating means provided, the developing device is configured such that both supporting members move in opposite directions at a portion where the image supporting member and the developer supporting member face each other. And a magnetic brush developing device for developing by applying a DC bias with an AC bias superimposed as a developing bias in the facing portion, and the developing bias is changed from the image carrier to the developer carrier to the two-component developer. Give force in the direction A step of applying a predetermined period of time pressure, 2
The step of applying a voltage for applying a force from the developer carrier to the image carrier to the component developer for a predetermined time is alternately repeated a plurality of times, and after applying a voltage for applying a force in the direction to the developer carrier, It is characterized in that a voltage between the voltage of the image portion and the voltage of the non-image portion of the electrostatic latent image on the image carrier is applied to the developer carrier for a certain period of time.

According to a second aspect of the present invention, in the first aspect of the invention, a voltage V1 is applied to the two-component developer for a period of T1 for applying a force in a direction from the carrier to the developer carrier. , The step of applying a voltage V2 for applying a force from the developer carrier to the image carrier to the two-component developer for T2 time is alternately repeated a plurality of times to obtain a voltage for applying a force from the developer carrier to the image carrier. Between the voltage VL of the image portion of the electrostatic latent image and the voltage VD of the non-image portion when the voltage of the image portion of the electrostatic latent image is VL and the voltage of the non-image portion is VD. Means for applying a voltage V3 of 3 to the developer carrier for T3 time, and between the T1 and T2 and T3, Here, m: mass of one toner Q: amount of charge of one toner d: distance between image carrier and developer carrier Lnip: toner flies between image carrier and developer carrier The width of the area of the image carrier in the circumferential direction of the image carrier S: the peripheral speed of the image carrier n: The number of times V1 and V2 are alternately repeated is satisfied.

According to the present invention, the toner is eccentrically vibrated in the vicinity of the image area, and the toner is sufficiently adhered to the highlight / halftone area as well, so that a uniform and smooth halftone image free from scribing unevenness can be obtained.

[0015]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a vertical cross-sectional view of a full-color image forming apparatus adopting an electrophotographic system. The full-color image forming apparatus is provided with a photosensitive drum 3 which rotates in the direction of an arrow shown in the drawing. Is a charger 4, a developing unit 1M,
A rotary developing device 1 equipped with 1C, 1Y and 1BK, a static eliminator 11 and a cleaning means 12 are arranged. A laser beam scanner LS is provided above the photosensitive drum 3.

By the way, the developing units 1M, 1C, 1Y,
1BK supplies a two-component developer containing toner particles and carrier particles to the photosensitive drum 3. The developer of the developing unit 1M develops magenta toner, and the developer of the developing unit 1C develops cyan toner. The developer of the developing device 1Y contains yellow toner, and the developer of the developing device 1BK contains black toner.

Thus, the document reading device having a photoelectric conversion element such as a CCD outputs image signals corresponding to magenta image information, cyan image information, yellow image information, and monochrome image information of the document. Then, the semiconductor laser built in the laser beam scanner LS is controlled by the PWM method in response to these image signals, and emits the laser beam L. The output signal from the electronic computer can also be printed out.

In the entire sequence of the full-color image forming apparatus, the photosensitive drum 3 is first uniformly charged by the charger 4. Next, scanning exposure is performed by the laser light L modulated by the magenta image signal, and the photosensitive drum 3
An electrostatic latent image is formed on the electrostatic latent image, and the electrostatic latent image is reversely developed by the magenta developing device 1M fixed at the developing position to be visualized as a magenta image.

On the other hand, the transfer material taken out from the paper feeding cassette C is fed by the paper feeding guide 5a, the paper feeding roller 6 and the paper feeding guide 5.
It is guided to the transfer drum 9 via b, held by the gripper 7 of the transfer drum 9, and electrostatically wound around the transfer drum 9 by the abutting roller 8 and its opposite pole. The transfer drum 9 rotates in the direction of the arrow in the figure in synchronization with the photosensitive drum 3, and the magenta image developed by the magenta developing device 1M is transferred to the transfer material by the transfer charger 10 at the transfer portion. The transfer drum 9 continues to rotate,
Prepare to transfer the image of the next color (cyan in this embodiment).

On the other hand, the photosensitive drum 3 is neutralized by the static eliminator 11, is cleaned by the cleaning means 12, is charged again by the charger 4, and is charged by the laser beam L modulated by the next cyan image signal as described above. Upon exposure to light, an electrostatic latent image is formed on the photosensitive drum 3. During this time, the developing device 1 rotates, the cyan developing device 1C is fixed at a predetermined developing position, and the electrostatic latent image corresponding to cyan on the photosensitive drum 3 is reversely developed to form a cyan image.

Subsequently, the above steps are carried out for the yellow image signal and the black-and-white image signal respectively, and when the transfer of the four color images (toner images) onto the transfer material is completed, the transfer material is charged by each charger 13. , 14 to release the charge, the gripper 7 releases the holding, the separation claw 15 separates the transfer drum 9, and the conveyance belt 16 sends the fixing device 17 to a fixing device (heat roller fixing device) 17. The transfer material sent to the fixing device 17 receives the fixing of the four-color image superimposed thereon, and is then discharged to the outside by the paper discharge roller 30 and stacked on the paper discharge tray 31. In this way, a series of full-color image forming sequences is completed, and a required full-color image is formed.

Next, based on FIG. 2, the magenta developing unit 1M
Will be described. Incidentally, other developing devices 1C, 1Y, 1BK
Also has the same configuration as the magenta developing unit 1M, the description thereof will be omitted.

The developing device 1M is equipped with a developing container 18,
The inside thereof is partitioned into a developing chamber R1 and a stirring chamber R2 by a partition wall 19, a toner storage chamber R3 is formed above the stirring chamber R2, and a replenishment toner 20 is stored in the toner storage chamber R3. ing. Then, from the replenishing port 21 formed in the lower portion of the toner storage chamber R3, an amount of toner commensurate with the toner consumed in the development is dropped and replenished into the stirring chamber R2.

On the other hand, in the developing chamber R1 and the stirring chamber R2,
The developer 22 in which the toner particles and the magnetic carrier are mixed is contained. As the toner, a known toner in which a colorant, a charge control agent and the like are added to a binder resin is used.

Further, in the developing chamber R1 and the agitating chamber R2, conveying screws 23 and 24 are housed, respectively, and the developer 22 is conveyed along the longitudinal direction of the developing sleeve 25 by the rotational driving of the conveying screw 23. By the rotational driving of the transport screw 24, the development 22 transfers the transport screw 23.
Is conveyed in the direction opposite to the conveying direction.

On the other hand, the partition wall 19 is provided with openings (not shown) on the front side and the back side, and the developer 22 carried by the carrying screw 23 passes through the one opening from the developing chamber R1. It is introduced into the stirring chamber R2, transferred to the conveying screw 24 in the stirring chamber R2, conveyed by the conveying screw 24, passes through the other opening, and is introduced from the stirring chamber R2 into the developing chamber R1. It is delivered to the conveying screw 23 in R1.

By the way, an opening is provided in a portion of the developing container 18 near the photosensitive drum 3, and a non-magnetic developing sleeve 25 made of aluminum, non-magnetic stainless steel or the like is provided in the opening. , The developing sleeve 2
On the surface of No. 5, moderate irregularities are formed.

The developing sleeve 25 rotates in the direction of the arrow b at a peripheral speed Vb, and the developer 22 carried on the developing sleeve 25 has a layer thickness regulating blade 28 provided at the lower end of the opening of the developing container 18. After being regulated to have an appropriate layer thickness by (1), it is conveyed to the developing area 26 and provided for development. In this case, the magnetic brush of the developer 22 carried on the developing sleeve 25 has a circumferential velocity Va in the developing area 26 in the direction of arrow a.
The electrostatic latent image on the photosensitive drum 3 is developed in the developing area 26. The ratio of the peripheral speed Vb of the developing sleeve 25 to the peripheral speed Va of the photosensitive drum 3 (peripheral speed ratio) Vb / Va is 130 to 200%.
Is preferable, and 150 to 180% is more preferable. By the way,
When the peripheral speed ratio Vb / Va is below the above range, sufficient image density cannot be obtained, and above that range, the developer is scattered.

A roller-shaped magnet 29 is fixedly arranged in the developing sleeve 25, and the magnet 29 has a developing magnetic pole S1 facing the developing area 26. A magnetic brush of the developer 22 is formed by the developing magnetic field formed by the developing magnetic pole S1 in the developing area 26, and the electrostatic latent image is developed by bringing the magnetic brush into contact with the photosensitive drum 3. At that time, the toner adhering to the magnetic brush and the toner adhering to the surface of the developing sleeve 25 are also transferred to the image area of the electrostatic latent image and provided for development. Incidentally, in the present embodiment, the magnet 29 includes N1, N2, N in addition to the developing magnetic pole S1.
It has 3, S2 poles.

With this structure, the developer 22 applied at the N3 pole and the S2 pole by the rotation of the developing sleeve 25 as in the conventional case passes through the layer thickness regulating blade 28 to reach the developing magnetic pole S1, and in the magnetic field thereof. The developer 22 that has risen up in step develops the electrostatic latent image on the photosensitive drum 3. After that, N2 pole and N
The developer 2 on the developing sleeve 25 is generated by the repulsive magnetic field between the three poles.
2 falls into the stirring chamber R1. Then, the developer 22 dropped into the stirring chamber R1 is stirred and conveyed by the conveying screws 23 and 24. The magnetic pole configuration of the developing container 18 is not limited to that of the present embodiment, and for example, one of the repulsive magnetic poles may be arranged near the position where the layer thickness regulating blade 28 faces.

Next, the developing bias used in this embodiment will be described in detail including its action.

The developing bias used in the present embodiment is, as shown in FIG. 4, a step of applying a voltage value for applying a force in the direction from the photosensitive drum 3 to the developing sleeve 25 to the toner for a predetermined time, and the developing bias to the toner. An AC bias in which an AC voltage is superposed on a DC voltage in which a step of applying a voltage value for applying a force in a direction from the sleeve 25 to the photosensitive drum 3 for a predetermined time is alternately repeated, and a developing sleeve 25 having the AC bias from the developing sleeve 25 to the photosensitive drum. After applying a voltage value for applying a force in the direction toward the direction 3 for a predetermined time, a DC bias for applying a voltage value between the image portion potential and the non-image portion potential on the photosensitive drum 3 to the developing sleeve 25 for a certain time is repeated. Is.

As described above, in counter development in which the relative speed between the photosensitive drum and the magnetic brush is large, the toner image on the photosensitive drum after development by the magnetic brush is scraped off, which causes image deterioration. In particular, when the density of one pixel is determined by modulating the emission time of the laser (PWM method), high resolution can be obtained, but in the highlight / halftone density area where the potential contrast of the electrostatic latent image is low, The amount of developed toner is small, and streaky unevenness is likely to appear due to scraping of the magnetic brush. Therefore, the developing bias used in the present embodiment is a DC bias that causes toner to fly only to the image area (hereinafter referred to as a blank bias).
After applying, an AC bias that vibrates the toner in the vicinity of the photosensitive drum 3 is applied, so that the T / D ratio of the developer 22 in the image portion is as if increased, and as a result, in the halftone region. In contrast, sufficient toner can be uniformly supplied.

On the other hand, in the non-image area, the developer 22 does not vibrate in the vicinity of the photosensitive drum 3 and is slowly pulled back to the developing sleeve 25 side, so that fog does not increase.
The characteristics of the developing bias, the time of the blank bias, the setting range of the AC bias, and the like will be described based on the movement of the toner.

In the present embodiment, as shown in FIG. 3, the carrier forms ears with the photosensitive drum 3 during development, and the toner can freely reciprocate in more than half of the space. Also, in the following description, the presence of carriers will be ignored. In many past experiments, it has been found that there is no problem even if the existence of carriers is ignored.

Thus, as shown in FIG. 4, the photosensitive drum 3
The potential of the non-image portion in the upper electrostatic latent image is VD, and the potential of the image portion is VL. Further, in order to fly the toner from the photosensitive drum 3 to the developing sleeve 25, a voltage (hereinafter referred to as a return bias) applied to the developing sleeve 25 is V1, and in order to fly the toner from the developing sleeve 25 to the photosensitive drum 3. The voltage applied to the developing sleeve 25 (hereinafter referred to as the feed bias) is V2, the blank bias is V3, and the times for applying the biases V1, V2, and V3 are T1, T2, and T3, respectively.

In the case of reversal development using a negative toner as the developer 22, V2 <VD <V3 <VL <1
The relationship is established, and the opposite relationship is established in positive toner. With this bias, the blank bias V3
Since toner flying on the photosensitive drum 3 is vibrated in the vicinity of the photosensitive drum 3, the time T1 for applying the return bias V1 should be set shorter than the shortest time for the toner on the photosensitive drum 3 to return to the developing sleeve 25. good. When the charge per toner is Q, the mass per toner is m, and the gap between the photosensitive drum 3 and the developing sleeve 25 is d, the time T1 for applying the return bias V1 is given by the following formula;

[0039]

[Equation 1] Should be satisfied.

Further, the time T2 for applying the feed bias V2
Must be longer than the time required for the toner in the image portion separated from the photosensitive drum 3 by the return bias V1 to return to the photosensitive drum 3. Due to the return bias V1, the toner in the image area is transferred from the photosensitive drum 3 to the following formula;

[0041]

[Equation 2] Are separated by the distance indicated by. If the minimum time required to return the toner to the photosensitive drum 3 is T2min, this T2min is calculated as follows.

[0042]

(Equation 3) When the time T2 for applying the feeding bias V2 is shorter than T2min, the toner on the photosensitive drum 3 is returned to the developing sleeve 25 by applying the returning bias V1 and the feeding bias V2 a plurality of times, and sufficient density can be obtained. The image will be uneven.

On the other hand, the time required for the toner on the developing sleeve 25 to fly to the non-image portion of the photosensitive drum 3 is given by the following equation:

[0044]

(Equation 4) If the time T2 for applying the feed bias V2 is longer than this time, image fog occurs.

From the above, the time T2 for applying the feed bias V2 is calculated by the following equation:

[0046]

(Equation 5) Need to satisfy the relationship.

Time T3 for applying blank bias V3
Must be equal to or longer than the time required to pull back the toner, which has started to fly from the developing sleeve 25 to the non-image portion of the photosensitive drum 3 due to the feed bias V2, to the developing sleeve 25.

[0048]

(Equation 6) Needs to be satisfied.

From the result of the examination, 1 on the photosensitive drum 3
When the alternating electric field of the return bias V1 and the feed bias V2 and the blank bias V3 were applied 10 times or less while the point passed through the developing nip portion, the halftone portion was roughened. Therefore, T3 is the following formula;

[0050]

(Equation 7) Here, it is desired that Lnip is the developing nip width, S is the peripheral speed of the photosensitive drum, n is the number of repetitions of the return bias V1 and the feed bias V2.

By repeating the above steps, the toner vibrates in a biased manner in the vicinity of the image area, and the toner is sufficiently adhered to the highlight / halftone density area, so that a uniform and smooth image without scribing unevenness can be obtained. (Hereinafter, this developing bias is referred to as a blank pulse bias).

[0052]

[Embodiment 1] Next, the developing bias used in this embodiment will be described with reference to FIG.

The conditions of the developing bias waveform used in this embodiment are as follows.

Image area voltage: -230V Non-image area voltage: -720V Blank bias: -570V 5 x 10 ^-4 sec. Return bias: 430V 5.00 x 10 ^-5 sec. Feed bias: -1570V 5.00 x 10 ^-5 sec .. Number of alternating bias: 2 times Other developing conditions are shown below.

Developer: polymerized toner + ferrite carrier; T / D ratio = 7% Polymerized toner average particle size: 6.0 × 10 ⁻⁶ m, polymerized toner specific gravity: 1.05 × 10 ³ kg / m ³ per polymerized toner Weight: 9.5 × 10 ^-16 kg Normal charge per unit mass of toner: 2.5 × 10 ^-2 C / kg → Charge per unit: 2.4 × 10 ^-19 C Weight per unit area of developer on sleeve : 6.0 × 10 ^-1 kg / m ² Gap between photosensitive drum and developing sleeve: 5.00 × 10 ^-4 m Peripheral speed of photosensitive drum: 1.50 × 10 ^-1 m / sec. Development nip: 2.0 × 10 ^-3 m condition is,

[0056]

(Equation 8) Meets.

Further, the following rectangular wave was used for comparison.

DC bias: −570 V AC bias: Vpp: 2 kV, frequency: 2.0 kHz In FIG. 6, a blank pulse bias and T ₁ = T ₂ = T ₃
7 shows a γ curve (a curve showing the relationship between the development contrast, which is the potential difference between the image portion potential and the DC bias or the blank pulse bias) when the rectangular wave bias is used. As compared with the case of using a rectangular wave, the blank pulse bias has a density of highlight halftone. This is because the toner is sufficiently developed even in the highlight / halftone image area having a small potential contrast. Therefore, when the rectangular wave bias was used, very noticeable crimping unevenness was observed in the highlight / halftone region, whereas when the blank pulse bias was used, an image in which crimping unevenness was not noticeable was obtained.

[0059]

. Example 2 as a blank pulse bias in this embodiment, the image portion Voltage: -230V non-image area voltage: -720 V blank Bias: -570V 5 × 10 ^-4 sec back bias: 430V 4.16 × 10 ^{- 5} sec. Feed bias: −1570V 4.16 × 10 ⁻⁵ sec. Number of alternating bias: Two times were used.

Other developing conditions are shown below.

Developer: polymerized toner + ferrite carrier; T / D ratio = 5% Polymerized toner average particle size: 6.0 × 10 ⁻⁶ m, polymerized toner specific gravity: 1.05 × 10 ³ kg / m ³ per polymerized toner Weight: 9.5 × 10 ^-16 kg Normal charge amount per unit mass of toner: 3.0 × 10 ^-2 C / kg → Charge amount per unit: 2.85 × 10 ^-19 C Weight per unit area of developer on sleeve : 4.5 × 10 ^-1 kg / m ² Gap between photosensitive drum and developing sleeve: 4.00 × 10 ^-4 m Peripheral speed of photosensitive drum: 1.50 × 10 ^-1 m / sec. Developing nip: 2.0 × 10 ^-3 m In the example, compared with Example 1, the T / D ratio was lowered in order to reduce the toner scattering from the developing sleeve, but a good image free from uneven crimping could be obtained.

[0062]

. Example 3 as a blank pulse bias in this embodiment, the image portion Voltage: -230V non-image area voltage: -720 V blank Bias: -570V 2 × 10 ^-4 sec back bias: 430V 4.16 × 10 ^{- 5} sec. Feed bias: −1570V 4.16 × 10 ⁻⁵ sec. Number of alternating biases: One was used.

Other developing conditions are shown below.

Developer: polymerized toner + ferrite carrier; T / D ratio = 7% Polymerized toner average particle diameter: 6.0 × 10 ⁻⁶ m, polymerized toner specific gravity: 1.05 × 10 ³ kg / m ³ per polymerized toner Weight: 9.5 × 10 ^-16 kg Normal charge per unit mass of toner: 2.5 × 10 ^-2 C / kg → Charge per unit: 2.4 × 10 ^-19 C Weight per unit area of developer on sleeve : 4.5 × 10 ^-1 kg / m ² Gap between photosensitive drum and developing sleeve: 4.00 × 10 ^-4 m Peripheral speed of photosensitive drum: 1.50 × 10 ^-1 m / sec. Developing nip: 2.0 × 10 ^-3 m In the example, the number of alternations is reduced to one, but since the above inequality is satisfied, it is possible to obtain a good image without crimping unevenness. In addition, since the waveform is simpler than those in the first and second embodiments, the cost of the bias waveform high voltage circuit can be reduced.

[0065]

As is apparent from the above description, according to the present invention, the image bearing member and the developing device for developing the electrostatic latent image formed on the image bearing member are provided. A rotatable developer carrier that carries and conveys a two-component developer composed of a non-magnetic toner and a magnetic carrier produced by a polymerization method, and a plurality of members fixedly provided inside the developer carrier. In the image forming apparatus configured to include the magnetic field generating means, the developing device is configured such that both supporting members move in opposite directions to each other at a facing portion between the image supporting member and the developer supporting member, and
A magnetic brush developing device that develops by applying a DC bias superimposed with an AC bias as a developing bias at the facing portion is used, and the developing bias is applied to the two-component developer in the direction from the image carrier to the developer carrier. The step of applying a force-applying voltage for a predetermined time and the step of applying a voltage that gives a force from the developer carrier to the image carrier to the two-component developer for a predetermined time are alternately repeated a plurality of times to apply a force to the developer carrier. Since a voltage between the voltage of the image portion and the voltage of the non-image portion of the electrostatic latent image on the image carrier is applied to the developer carrier for a certain period of time after applying a voltage that gives a force in the direction The toner vibrates in the vicinity of the image region in a biased manner, and the toner adheres sufficiently to the highlight / halftone region as well, so that a uniform and smooth halftone image with no crimping unevenness can be obtained.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a full-color image forming apparatus according to the present invention.

FIG. 2 is a sectional view of a developing device portion of a full-color image forming apparatus according to the present invention.

FIG. 3 is a diagram showing a state of a developer between a photosensitive drum and a developing sleeve in a full-color image forming apparatus according to the present invention.

FIG. 4 is a diagram showing a developing bias waveform applied in the full-color image forming apparatus according to the present invention.

FIG. 5 is a diagram showing a developing bias waveform applied in the full-color image forming apparatus according to the present invention.

FIG. 6 is a diagram showing a developing bias (blank pulse bias) and a γ curve in a rectangular wave used in the present invention.

[Explanation of symbols]

 1 Developing Device (Magnetic Brush Developing Device) 3 Photosensitive Drum (Image Carrier) 22 Two-Component Developer 25 Developing Sleeve (Developer Carrier) 29 Magnet (Magnetic Field Generating Means)

Claims (2)

[Claims] 1. An image carrier, and a developing device for developing an electrostatic latent image formed on the image carrier, the developing device comprising a non-magnetic toner produced by a polymerization method and a magnetic carrier. In an image forming apparatus configured to include a rotatable developer carrier that carries a component developer and conveys the developer, and a plurality of magnetic field generating means fixedly provided inside the developer carrier. In the developing device, at the opposing portion of the image bearing member and the developer bearing member, both bearing members move in opposite directions, and at the facing portion, a DC bias with an AC bias superimposed is applied as a developing bias. And a two-component developer, in which a developing bias is applied to the two-component developer and a voltage is applied to the two-component developer in the direction from the image carrier to the developer carrier for a predetermined time. From the developer carrier The step of applying a voltage for applying a force toward the carrier for a predetermined time is alternately repeated a plurality of times, and after applying a voltage for applying a force in the direction toward the developer carrier, the electrostatic latent image on the image carrier is An image forming apparatus characterized in that a voltage between a voltage of an image area and a voltage of a non-image area is applied to a developer carrier for a certain period of time. 2. A step of applying a voltage V1 for applying a force in the direction from the carrier to the developer carrier to the two-component developer for T1 time, and the two-component developer from the developer carrier to the image carrier. The step of applying the voltage V2 for applying a force toward the image carrier is alternately repeated a plurality of times, and after applying the voltage for applying a force from the developer carrier to the image carrier, the voltage of the image portion of the electrostatic latent image is changed. A means for applying a voltage V3 between the voltage VL of the image portion of the electrostatic latent image and the voltage VD of the non-image portion to the developer carrying member for T3 time when VL and the voltage of the non-image portion are VD. Between T1 and T2 and T3, Here, m: mass of one toner Q: amount of charge of one toner d: distance between image carrier and developer carrier Lnip: toner flies between image carrier and developer carrier 2. The image formation according to claim 1, wherein the following relationship is satisfied: S: circumferential width of the image bearing member in a region to be applied S: circumferential velocity of the image bearing member n: number of times of alternately applying V1 and V2. apparatus.