JPH10301374A - Image forming device and process cartridge used therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image satisfied with the reproducibility of a line image, a fog and a solid black density by prescribing a developing bias applied to a developer carrier. SOLUTION: At the time of developing an electrostatic latent image formed on the surface of a photoreceptive drum 1 by a developing device 6, the maximum voltage Vmax on a developing acceleration side, of the AC bias of the developing bias applied to the developing sleeve of the developing device 6 from bias supply is adjusted and the gap G between the drum 1 and the developing sleeve, in a developing region is adjusted, so that an acceleration-side maximum electric field Vmax/G shown by the maximum voltage Vmax/the gap G is set to be a value within the range of 4.0<=Vmax/G<5.0 and the AC bias is adjusted so that the effective value Vfm of the acceleration-side wavelength of the AC bias and the acceleration-side maximum voltage Vpf of the AC bias are at values within the range of 0.75×Vpf<=Vfm<=0.90×Vpf. Thus, a high- resolution and -accuracy image can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus using an electrophotographic system for developing an electrostatic latent image formed on an image carrier by a developing device and visualizing the electrostatic latent image, and a process cartridge used for the same.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus using an electrophotographic method, an electrostatic latent image formed on an image carrier (photosensitive drum) is developed by a developing device and visualized as a toner image. I have. There are various developing systems using one-component and two-component developers as this developing device.
As one of the developing methods using a one-component developer, a jumping developing method for developing a latent image on an image carrier while holding a developer carrier (developing sleeve) of a developing device in non-contact with the image carrier. It has been known.

In this jumping development method, a one-component developer is layered on a developing sleeve, and a developing bias in which an AC component is superimposed on a DC component is applied to the developing sleeve on which the developer is layered, so that a developing region is formed in a developing region. The developer (toner) flies and adheres to the electrostatic latent image on the photosensitive drum, and the latent image is visualized as a toner image.

As the AC voltage superimposed on the DC voltage, a sine wave shown in FIG. 11, a triangular wave shown in FIG.
The rectangular wave shown in FIG. 13 and the duty bias shown in FIG. The duty bias is different from a half value of the maximum voltage of the waveform and the integrated average value Vdc, and is a first peak value which forms an electric field for urging the toner from the developing sleeve to the photosensitive drum in FIG. Vma
The bias is composed of the time during which x is applied and the time during which Vmin, which is the second peak value that forms an electric field that urges the toner in the direction from the photosensitive drum toward the developing sleeve, is applied.

Further, with the recent development of computer graphics technology, there is a demand for an electrophotographic image forming apparatus having higher image quality. Therefore, a high-resolution and high-definition developing method is required to achieve higher image quality.

By the way, in the one-component magnetic developing system, the toner is developed in a chain form (generally called "spikes") at the time of development. This causes a tailing phenomenon that runs off in the state of the ears and a phenomenon that the toner scatters around the peripheral portion of the image rubber, which causes a reduction in resolution. Therefore, as a method for further improving the image reproducibility, it is necessary to shorten the ears of the magnetic toner.

As a developing device, a thin layer forming method for thinning the application of the toner on the developing sleeve has been developed. A blade made of an elastic material is brought into contact with the developing sleeve, and the toner on the sleeve is triboelectrically charged. An elastic blade method or the like that regulates the amount of coating while giving the same has been put to practical use.

Further, with respect to the toner, when the magnetization strength of the magnetic toner is large, a strong attractive force along the direction of the magnetic field and a strong repulsive force in the direction perpendicular to the magnetic field are generated between the magnetic toner particles. The magnetic toner particles formed on the sleeve form ears due to the magnetic force and the Coulomb force due to the charged charges. At this time, the ears become shorter and denser as the toner becomes finer.

Further, as the particle size of the toner becomes smaller, the amount of fine powder having a higher charge amount increases, which is suitable for higher image quality.

[0010]

However, when the thickness of the toner applied on the developing sleeve is reduced, the frictional charging of the toner may be excessive, and the developing property may be deteriorated.

In this case, a low-quality image such as scattering of a line image or deterioration of sharpness, a decrease in image density of a solid image, or an increase in fog (in particular, a tendency to increase ground fog) is caused. . This is because, when the toner tribo is greater than a certain level, the reflection force of the toner on the sleeve is increased due to an increase in the reflection power of the toner, and the tribo distribution of the toner on the sleeve becomes broad.

In order to solve these problems, as a developing bias, a method of increasing the amplitude of an AC component and a method of changing a DC component have been conventionally known. However, if the amplitude of the AC component of the developing bias is increased or the DC component is changed, the fog is further deteriorated, and a leak may occur between the developing sleeve and the photosensitive drum (referred to as SD). There is. Therefore, conventionally, it has been difficult to satisfy all of the requirements (1) to (4). In particular, in the case of an image forming apparatus in which the particle size of the toner is reduced and the charge amount is increased in order to improve the image quality, it has been difficult to satisfy the above-mentioned requirements.

The image forming apparatus of the present invention and the process cartridge used therein are excellent in preventing scattering of line images and in sharpness reproducibility, have sufficiently high image density of solid images, have sufficiently low fog, and have high resolution and high definition. An object of the present invention is to provide an image forming apparatus and a process cartridge capable of obtaining a high-quality image at a low cost.

[0014]

According to a first aspect of the present invention, the above object is achieved by providing an image carrier and a developer carrier arranged at a predetermined distance from the image carrier. And a developing bias applying means for applying a developing bias in which an AC component is superimposed on a DC component to the developer carrier, and a developing bias is applied to the developer carrier by applying a developing bias to the developer carrier. An image forming apparatus for developing an electrostatic latent image, wherein an interval between an image carrier and a developer carrier is G (μm)
When the maximum voltage on the accelerating side on the accelerating side which is applied from the developing bias applying means and urges in the direction from the developer carrier to the image carrier is Vmax, the accelerating maximum electric field is Vmax.
When the effective voltage of the waveform on the AC bias accelerating side is Vfm, and the maximum voltage on the AC bias accelerating side is Vpf, the developing bias is applied to the developer carrier. In this case, the promotion-side maximum electric field Vmax / G
Is set to a value satisfying the range of 4.0 ≦ Vmax / G <5.0, and the effective voltage Vf of the waveform on the AC bias promoting side is set.
m and the maximum voltage Vpf on the acceleration side of the AC bias are 0.7
This is achieved by setting a value satisfying a range of 5 × Vpf ≦ Vfm ≦ 0.90 × Vpf.

Further, according to the second aspect of the present invention, the above object is achieved by setting the time from the start of the application of the AC bias accelerating voltage to the reaching of the accelerating maximum voltage Vpf to tpf and the AC bias being 1 When the cycle is T, tpf
Is set to a value satisfying tpf ≦ T / 4.

Further, according to the third invention of the present application, the above object is to reduce the peak voltage of the voltage applied on the acceleration side to Vpf
When the peak voltage applied on the return side that urges in the direction from the image carrier toward the developer carrier is Vpb, the peak voltage Vpf on the promotion side and the peak voltage Vpb on the return side are defined as: This can be achieved by expressing the relationship | Vpf |> | Vpb |.

According to a fourth aspect of the present invention, the object is to achieve a weight average of a developer sealed in a developing device provided in an image forming apparatus and used for developing an electrostatic latent image. This is achieved by using a one-component magnetic toner having a particle size of 3.5 to 7.0 μm.

According to a fifth aspect of the present invention, the object is to provide a process cartridge for use in the image forming apparatus according to the first to third aspects of the present invention, which is integrated into a shape that can be housed in the image forming apparatus. A cartridge is formed, and a developing device having a developer carrier is provided in the cartridge at least in place of the developing device provided in the image forming apparatus, and a process cartridge is provided in the image forming apparatus. The developer carrying member in the cartridge and the developing bias applying means provided at an arbitrary position are connected so as to be able to be input in a state where the developing bias is accommodated in the cartridge, so that the developing bias under the conditions of the first to third inventions is changed to This is achieved by allowing application to the agent carrier. Further, the developing device provided in the cartridge has a weight average particle diameter of the developer used for developing the electrostatic latent image of 3.5 to 3.5.
This is achieved by using a 7.0 μm single-component magnetic toner.

That is, in the first invention of the present application,
The acceleration-side maximum electric field Vmax, which is represented by the distance G (μm) between the image carrier and the developer carrier and the promotion-side maximum voltage Vmax that urges the developer carrier toward the image carrier.
/ G (V / μm) so that 4.0 ≦ Vmax / G <5.0, the distance between the image carrier and the developer carrier and the maximum voltage on the accelerating side are adjusted, and the AC bias is adjusted. The relationship between the effective voltage Vfm of the waveform on the promotion side and the maximum voltage Vpf on the promotion side of the AC bias is 0.75 × Vfp ≦ Vf
By adjusting the AC bias so that m ≦ 0.90 × Vpf to optimize the developing bias applied to the developer carrier, scattering of line images can be prevented, and sharpness and solid image can be prevented. High-resolution and high-definition image formation excellent in image density is performed without increasing fog.

Further, according to the second aspect of the present invention, the time from the start of the application of the AC bias accelerating voltage to the reaching of the accelerating maximum voltage Vpf is tpf, and one cycle of the AC bias is T. At this time, if the AC bias is adjusted so that the relationship of tpf ≦ T / 4 is satisfied, the peak of the voltage on the promoting side comes to the first half of the promoting side in the cycle of the AC bias, so that the high resolution, High-definition image formation is performed.

According to the third aspect of the present invention, the AC bias is adjusted so that the relationship between the peak voltage Vpf on the promotion side and the peak voltage Vpb on the return side is | Vpf |> | Vpb |. Accordingly, scattering of line images is prevented, high-resolution and high-definition image formation excellent in sharpness and solid image density is performed without increasing fog, and reversal fog is reduced.

Further, according to the fourth invention of the present application, by using a one-component magnetic toner having a weight average particle diameter of the developer of 3.5 to 7.0 μm in the developing device, it is possible to more effectively improve the toner density. Resolution and high-definition image formation are performed.

According to the fifth aspect of the present invention, a process cartridge is formed so as to be housed in an image forming apparatus.
A state in which a developing device having a developer carrier is provided in the cartridge, at least in place of the developing device provided in the image forming apparatus, similarly to the developing apparatus, and the process cartridge is housed in the image forming apparatus. 3. By connecting the developer carrier in the cartridge and the developing bias applying means at an arbitrary position so as to be able to be input,
The distance between the image carrier and the developer carrier and the maximum voltage on the accelerating side are adjusted so that 0 ≦ Vmax / G <5.0, and 0.75 × Vfp ≦ Vfm ≦ 0.90 × Vpf. To adjust the AC bias, tpf ≦ T / 4
Tpf is adjusted so as to satisfy the relationship of | Vpf |>
The developing bias adjusted to be | Vpb | can be applied to the developer carrying member in the cartridge. This makes it possible to form high-resolution and high-definition images with excellent sharpness and solid image density without increasing fog. An image forming apparatus having easy maintainability is configured. Further, by using a one-component magnetic toner having a weight average particle diameter of 3.5 to 7.0 μm of a developer used for developing an electrostatic latent image in a developing device provided in the cartridge, more effectively. High resolution and high definition image formation is performed.

[0024]

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

(First Embodiment) First, a first embodiment of the present invention will be described with reference to FIGS.

FIG. 6 is a schematic diagram showing an example of a laser beam printer (hereinafter, referred to as LBP) which is an image forming apparatus using an electrophotographic process to which the present invention is applied. As the electrophotographic photosensitive member 1 (hereinafter, photosensitive drum) provided as an image carrier for forming an electrostatic latent image on the surface, for example, an OPC photosensitive member is used. The rotation speed (hereinafter, process speed) of the photosensitive drum 1 is set to 100 mm / sec.

In the LBP image forming process, the photosensitive drum 1 is uniformly charged by the roller charger 2. Next, exposure is performed by a laser scanner 101 according to an image signal, and the laser scanner 101 scans the blinking of the semiconductor laser with a polygon scanner and forms an image on the photosensitive drum 1 by an optical system. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 1. The electrostatic latent image formed on the photosensitive drum 1 is developed by the developing device 6. Development is performed using a development method such as jumping development.
Turn on the laser and use the developer (toner) on the side with less charge
Is used.

The developed image is transferred to a transfer material 104 using, for example, paper. The transfer material is the cassette 103
Are fed one by one by a paper feed roller 105. When a print signal is sent from the host to the LBP, the paper is fed by the paper feed roller 105, and the paper is fed by the transfer roller 107. The toner image is transferred onto the transfer material. The transfer roller 107 is a conductive elastic body, and is a nip portion formed by the photosensitive drum 1 and the transfer roller 107. The transfer is performed electrostatically by a bias electric field. Transfer material 104 on which the image has been transferred
Is fixed by the fixing device 109. On the other hand, the transfer residual toner is cleaned by the blade 5 with a cleaner.

FIG. 5 is an enlarged view of a main part near the developing device 6. The photosensitive drum 1 is uniformly charged to a charging potential Vd = 1600 V by a primary charger. Next, exposure is performed with a laser according to the image signal, and the potential of the exposed portion is changed to the image portion potential Vl =
The voltage becomes -100 V, and an electrostatic latent image is formed on the photosensitive drum 1 as an image portion where toner adheres to the exposed portion. The electrostatic latent image formed on the photosensitive drum 1 is developed by the developing device 6.

As the toner 7 which is a developer sealed in the developing device 6, for example, a negatively chargeable magnetic one-component toner is used. The binder resin of the toner 7 is, for example, 100 parts by weight of a styrene n-butyl acrylate copolymer, 100 parts by weight of magnetic particles, 2 parts of a negative charge control agent of a monoazo iron complex, and 3 parts of low molecular weight polypropylene as a wax. Is melt-kneaded in a twin-screw extruder heated to 140 ° C., the cooled kneaded material is coarsely pulverized by a hammer mill, the coarsely pulverized material is finely pulverized by a jet mill, and the obtained finely pulverized material is subjected to air classification. To obtain a classified powder having a weight average diameter of 5.0 μm. It is obtained by mixing 1.0 part by weight of a hydrophobic silica fine powder with a Henschel mixer with a classified product having an average particle size of 5.0 μm. Higher image quality can be achieved by using a toner having a weight average diameter of 3.5 to 7.0 μm in each embodiment of the present invention. Even when the amount is high, high-resolution and high-definition image formation can be performed effectively.

The toner 7 in the developing device 6 is sent to the vicinity of the developing sleeve 3 by stirring 10 and then supplied to the developing sleeve 3 by the action of the magnetic field formed by the magnet roll 4 and conveyed with the rotation of the sleeve. You. Thereafter, the toner is conveyed to the developing area at a contact portion with the developing blade 8 with a low tribo application and a reduced thickness regulation. The amount of toner on the sleeve is M / S
(M / S: toner coat weight (mg) per 1 cm ^{2 of} sleeve surface), and in the present embodiment, M / S
The contact force and the contact width between the developing blade 8 and the developing sleeve 3 are adjusted so that S has a value of 0.4 to 2.0, preferably 0.6 to 1.50. The toner 7 has a charge amount Q / M per unit volume = −10−30 μC /
g is given.

The developing sleeve 3 for carrying the toner 7 is, for example, a non-magnetic aluminum sleeve of φ16.0 having a surface coated with a resin layer containing conductive particles.
A 1.0 μm sleeve is used, and the developing sleeve 3 is rotated at a peripheral speed of 100 to 140% of the drum. A magnet roll 4 is fixedly arranged in the developing sleeve 3, and one magnetic pole of the magnet roll 4 is arranged so as to face the photosensitive drum 1, so that the magnetic flux density of the pole on the sleeve surface in the radial direction is reduced. By setting the peak value to be 750 to 950 G, it is possible to form the ears of the toner in the developing area and to pull the fog toner back toward the developing sleeve 3.

The photosensitive drum 1 and the developing sleeve 3 are arranged in a developing section in a non-contact manner with a gap of 100 to 500 μm. In a gap between the developing sleeve 3 and the photosensitive drum 1 of the developing section (between SDs or SD), a bias power supply 1 provided in a developing bias applying unit is provided.
From 1, frequency f: 800 to 3500 Hz, amplitude Vp
p: 500 to 3000 V, DC voltage Vdc: -150 to
A developing bias in which a DC voltage of -550 V and an AC voltage are superimposed is applied, and a developing electric field is generated between SD.

In this embodiment, a developing bias having the waveform shown in FIG. 1 was applied. That is, development Vdc = −450
(V), SD = 300 μm, Vpp = 1800 V, f
= 2.4 kHz, and a developing bias of Vmax = -1350 V was applied. At this time, the accelerating maximum electric field that urges in the direction from the developing sleeve 3 toward the photosensitive drum 1 is:
Efmax = Vmax / G = 4.5 (V / μm), and the effective voltage of the waveform on the AC bias promoting side is Vfm = 0.85.
× Vpf.

Here, the words used in the description of the waveform are defined as follows.

Promoting side f: Direction from developing sleeve to photosensitive drum Returning side b: Direction from photosensitive drum to developing sleeve Vpf: Peak voltage on AC bias facilitating side Vpb: Peak voltage on AC bias returning side Vpp: AC Vpp is the sum of the accelerating side and the returning side of the bias.
= Vpf + Vpb Vfm: Effective voltage of waveform on AC bias promoting side Vdc: DC voltage Vmax: Maximum voltage on promoting side, Vmax = Vpf + Vd
c G: The distance between the developing sleeve and the photosensitive drum, G (μm) Emax: The maximum electric field on the acceleration side, Efmax = Vmax /
G (V / μm).

Hereinafter, the present embodiment will be described in detail.

In this embodiment, the bias power source 11 is
An experiment was performed using a combination of a waveform generator and an amplifier and monitoring the waveform of the developing bias with an oscilloscope connected between the amplifier and the developing sleeve. As experimental conditions, Vd = −600 (V), Vl = −10
0 (V), development Vdc = -450 (V), SD = 300
μm and a toner having a weight average particle diameter of 6.0 μm.
M / S of toner coat layer = 1.10 mg / cm ² , Q /
The experiment was performed under a low-temperature and low-humidity environment where M = −15 μC / g and fog and an image deteriorated.

Under the above conditions, in order to examine the relationship between the waveform of the AC bias, the AC bias Vpp and the image based on the frequency f, the image was evaluated by changing Vpp and f as follows.

F: 1.5 to 3.5 kHz 0.2
kHz step Vpp: 1000 to 2000 V... 100 V step The image evaluation of the above experimental results will be described below.

Sharpness of line image: The character image and dot image of the durability evaluation sample were magnified about 30 times and evaluated according to the following criteria. 優 Excellent: The line was very sharp and almost no scattering was observed. Slightly scattered, the line is relatively sharp. △ Acceptable: Slightly scattered, and the line looks sloppy. × Bad: Less than △ level Fog: Fog on drum and paper was measured. ◎ Excellent : 3% on the drum, 1% or less on the paper ○ Good: 5% on the drum, 2% or less on the paper △ Acceptable: 7% on the drum, 3% or less on the paper × Bad: More than solid black density: The density is Macbeth reflection densitometer (優 Excellent: 1.45 or more ○ Good: 1.40 or more △ Acceptable: 1.35 or more × Bad: Less than 1.35

The evaluation was performed as described above.
The above is OK. FIGS. 2 to 4 show the relationship between f, Vp-p and the OK region of the image characteristic. Arrows in FIGS. 2 to 4 indicate an OK region of a line image, an OK region of a fog, and an OK region of a solid image, respectively. The shaded areas in FIGS. 2 to 4 indicate the f and Vpp areas satisfying all the image characteristics (experimental results can be obtained).

FIG. 3 shows a comparative example 1 in which a rectangular wave shown in FIG. 10 was used as an AC bias. As shown in FIG. 3, it can be seen that the range of f and Vpp (shaded area) that satisfies all of the image characteristics is small.

FIG. 4 shows a comparative example 2 in which a sine wave shown in FIG. 11 was used as an AC bias. As shown in FIG. 4, it can be seen that the range of f and Vpp (the shaded area) satisfying all of the image characteristics to is smaller than that of Comparative Example 1.

The following can be seen from Comparative Examples 1 and 2.

In order to improve the reproduction of the line image, it is necessary to increase Vpp to a certain value or more in both Comparative Examples 1 and 2. Also, the dependence on Vpp is greater than the dependence on the waveform. The fog and density have a relationship with the waveform. Comparing Comparative Examples 1 and 2, it was found that the fog deteriorated with the rectangular wave of Comparative Example 1 and the density became insufficient with the sine wave of Comparative Example 2. Was. The fog here is mainly ground fog (toner charged to normal polarity reaches the non-image portion on the drum and remains as fog).

Therefore, the present inventor has proposed that while maintaining Vpp at a certain level or more to improve image quality, fog,
Considering a waveform that satisfies the concentration, an experiment was performed using a waveform obtained by changing the effective voltage of the AC bias accelerating side waveform as shown in FIG. 1 (this embodiment).

FIG. 2 shows the results of image characteristics when the effective voltage Vfm of the acceleration waveform is set to 0.85 × Vpf (Vpf is the acceleration-side maximum voltage). As can be seen from FIG. 2, in the present embodiment, the area of Vpp and f where fog and density are compatible (satisfies all image characteristics) is larger than in Comparative Examples 1 and 2. Further, when the image characteristics were examined by changing the effective voltage of the acceleration-side waveform, Vfm was found to be 0.90 of Vpf.
In the range of 0.75 times, desirably 0.90 to 0.80 times, the effect of expanding the range of Vpp and f in which fog and density are compatible was confirmed. Note that Vfm is set to 0.90 of Vpf.
If it is larger than 2 times, the fog will be worse, and if it is smaller than 0.75 times, the image density will be worse.

Further, the distance G between SDs is set to 200 or 40
As a result of conducting an experiment by changing the value to 0 μm, the electric field intensity Vmax on the development promoting side
/ G. The results are summarized as follows.

That is, the promotion-side maximum electric field Vmax / G
(V / μm) is 4.0 ≦ Vmax / G <5.0 (Vm
ax / G ≧ 5.0, there is a risk of leakage between SDs), and the effective voltage V
fm and promotion-side maximum voltage Vpf are 0.75 × Vpf
By setting ≦ Vfm ≦ 0.90 × Vpf, an effect of improving image quality can be obtained.

The charge amount of the toner on the developing sleeve has a non-uniform distribution, and the force from the electric field received by the toner and the mirroring force received from the developing sleeve vary depending on the charge amount of each toner. However, since the toner having a large amount of charge has a large reflection power, it cannot reciprocate away from the sleeve surface unless the force received from the electric field is strong.

Therefore, the maximum electric field Vmax / G (V
/ Μm) is set to 4.0 ≦ Vmax / G, it is possible to separate the toner from the sleeve surface by overcoming the mirror force even with a toner having a large charge amount. Furthermore, 0.75 × Vp
By reducing the effective voltage of the acceleration-side waveform with a waveform such that f ≦ Vfm ≦ 0.90 × Vpf, the flying speed of the toner can be made appropriate and the latitude of the image and fog can be enlarged.

This is because if the toner having a large charge amount can be separated from the surface of the sleeve, the mirroring force decreases in inverse proportion to the square of the distance. It is thought that. That is, the acceleration-side maximum electric field V
max / G (V / μm) is 4.0 ≦ Vmax / G <
It suffices if Vpf is such that it becomes 5.0. Conversely, Vpf
In the following square wave, fog toner reaching the drum increases, and ground fog worsens.

As described above, in the developing device of this embodiment, the accelerating-side maximum electric field Vmax / G (V / μm) is used as a developing bias in which a DC voltage and an AC voltage applied to the developer carrier during development are superimposed. ) Is 4.0 ≦ Vmax / G
<5.0, the effective voltage Vfm of the waveform on the AC bias promoting side and the maximum voltage Vpf on the AC bias promoting side are
By setting 0.75.times.Vpf.ltoreq.Vfm.ltoreq.0.90.times.Vpf, high-resolution and high-definition image formation excellent in prevention of line image scattering, sharpness, and solid image density is performed without increasing fog. be able to.

(Second Embodiment) A second embodiment of the present invention will be described with reference to FIG.

This embodiment is designed so that the maximum voltage on the promotion side reaches a peak within a time period of T / 4 of the AC bias.
It is characterized in that the position of the peak of the promotion-side maximum voltage is defined.

FIG. 7 shows a developing bias waveform used in this embodiment. Here, the time from the start of the application of the AC bias accelerating voltage to the time when the maximum voltage Vpf is reached is tpf, and one cycle of the applied AC bias is T.

Under the same conditions as in the first embodiment, the effective voltage of the facilitating side waveform is fixed at 0.85 × Vpf, and the time tpf until the AC bias facilitating side voltage reaches the maximum voltage is variously changed to examine the image characteristics. Was. At this time, tpf is tpf ≦ T
In the range of / 4 (the peak reaches the first half of T / 2 (promoting side cycle)), Vpp and f at which both fog and density are compatible are obtained.
The effect of area expansion was confirmed. This is because the high tribo toner used in the present invention cannot be separated from the sleeve surface unless a strong electric field is applied, but the waveform (promotion) in which the maximum electric field Vmax / G on the promotion side is in the first half of the cycle on the promotion side. In the case where the applied voltage peaks in the first half of the cycle on the side, the time until the reverse electric field is generated after the toner having a large charge amount is separated from the sleeve surface is sufficiently secured.
It is considered that a necessary amount of toner can adhere to the photosensitive drum side.

On the other hand, if tpf satisfies tpf ≧ T / 4 (waveform having a peak in the latter half of T / 2), the electric field on the return side is switched to the electric field on the return side in a short time after reaching the peak, and the developability deteriorates. However, it was found that the image quality deteriorated and the density became low. In this regard, the promotion-side maximum electric field Vmax /
In the waveform in which G is in the latter half (when the peak of the applied voltage reaches the latter half of the cycle on the acceleration side), the toner having a large charge amount separates from the surface of the sleeve and immediately returns to the sleeve due to the reverse electric field. It is considered that the toner cannot adhere to the photosensitive drum side.

(Third Embodiment) A third embodiment of the present invention will be described with reference to FIG.

In this embodiment, the acceleration-side peak voltage Vpf
Is characterized in that the relationship between the promotion-side and return-side peak voltages is defined such that the absolute value of the peak voltage Vpb becomes greater than the absolute value of the return-side peak voltage Vpb.

FIG. 8 shows a developing bias waveform used in the present embodiment. As shown in FIG. 8, the maximum voltage Vpf on the promotion side of the AC bias and the maximum voltage Vpb on the return side are | Vp
f |> | Vpb |. Thereby, the reproducibility of the line image and the solid image and the characteristics of the background fog are not changed as compared with the first and second embodiments, and the reverse fog can be reduced. This is because the effective voltage on the return side is equal to that of the first and second embodiments.
, The effect of returning the toner reciprocating between the SDs can be obtained. On the other hand, if there is an inverted toner charged on the sleeve in the opposite polarity to the normal polarity, the maximum voltage Vpb is reduced, so that the effect of reducing the amount of the inverted toner reaching the non-image portion can be obtained.

(Fourth Embodiment) A fourth embodiment of the present invention will be described with reference to FIG.

In this embodiment, the developing device described in the first embodiment is provided in an integral type cartridge which can be exchanged together with a photosensitive drum, a cleaner, a charging device and the like, and can be housed in an image forming apparatus. In addition, it is characterized in that a developing bias under the conditions described in the above embodiments can be applied.

FIG. 9 shows an example of a process cartridge using an integrated cartridge housed in an image forming apparatus. Note that members having the same configuration as the image forming apparatus described in the first embodiment are denoted by the same reference numerals.

An outer package 100 is formed as an integrated cartridge that can be housed in the image forming apparatus. Inside the exterior 100, the developing device 6, the photosensitive drum 1, the cleaning device 5, and the charging device 2 are arranged at appropriate positions to form an integrated cartridge. The developing device 6, the photosensitive drum 1, the cleaning device 5, and the charging device 2 are provided in a cartridge instead of being provided in the image forming apparatus.

In the case of this integral type cartridge, when the toner 7 is used up, the other devices are designed to have almost the same life as the other devices, and by removing the outer package 100 from the image forming apparatus and replacing it with a new cartridge. , So that an image can be formed. Therefore,
The user can always obtain a stable image while the toner in the cartridge is present, and since the cartridge is integrated, there is an advantage that the replacement can be easily performed.

The developing bias applied to the developing device in the cartridge is applied, for example, from the bias power supply 11 of the developing bias applying means disposed in the image forming apparatus. 4.0 ≦ V
The distance between the image carrier and the developer carrier and the maximum voltage on the accelerating side are adjusted so that max / G <5.0.
The AC bias is adjusted so as to satisfy 0.75 × Vfp ≦ Vfm ≦ 0.90 × Vpf, the tpf is adjusted so as to satisfy the relationship of tpf ≦ T / 4, or | Vpf |> | Vp
By applying the developing bias adjusted so as to satisfy b | to the developer carrier in the cartridge, there is an advantage that high-definition image formation can be stably performed in addition to the inherent advantage of the integrated type cartridge. Incidentally, the developing device in the cartridge has a weight average particle size of 3.5 as a developer.
By using a one-component magnetic toner of about 7.0 μm,
Higher resolution and higher definition images may be formed more effectively. Further, the developing bias applying means may be arranged in the process cartridge so that the developing bias shown in each of the above embodiments can be applied.

It should be noted that only the developing device may be provided in the cartridge, and the photosensitive drum, cleaner, charging device and the like may be fixedly provided in the image forming apparatus. Further, a cartridge provided with a developing device and a cartridge provided with a photosensitive drum, a cleaning device, and a charging device may be provided separately so that each can be accommodated in the developing device.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made within the technical concept of the present invention.

[0071]

As described above, according to the first aspect of the present invention, the distance between the image carrier and the developer carrier is G (μm), and the distance from the developer carrier to the image carrier is increased. Assuming that the maximum voltage on the accelerating side energized in the direction is Vmax, the maximum electric field Vmax / G (V / μm) is 4.0 ≦ Vmax / G
<5.0, the effective voltage Vfm of the waveform on the AC bias promoting side, and the maximum voltage Vp on the promoting side of the AC bias.
f is 0.75 × Vpf ≦ Vfm ≦ 0.90 × Vpf
By applying a developing bias so as to prevent the scattering of line images, high-resolution and high-definition images with excellent sharpness and solid image density can be formed without increasing fog. .

Further, according to the second aspect of the present invention, after the start of the application of the AC bias accelerating voltage,
Assuming that the time required to reach pf is tpf, and one cycle of the AC bias is T, the application of the accelerating voltage is adjusted so that tpf satisfies the range of tpf ≦ T / 4. Images and high-definition images can be formed.

According to the third aspect of the present invention, the peak voltage Vpf on the promotion side and the peak voltage Vpf on the return side are set.
By adjusting pb so that | Vpf |> | Vpb |, the reversal fog can be reduced without impairing the effects of the first and second aspects of the invention.

According to the fourth aspect of the present invention, the developer has a weight average particle diameter of 3.5 to 7.0 in the developing device.
The use of the μm one-component magnetic toner makes it possible to form a high-resolution and high-definition image more effectively.

According to the fifth aspect of the present invention, at least the developing device is provided in the integrated type cartridge, and the developer carrying member in the cartridge is supplied with the developing bias under the same conditions as those of the first to third aspects. In addition to the advantages of the cartridge, such as image stability and easy maintenance, it is possible to provide a process cartridge capable of obtaining an even higher quality image.

Further, according to the sixth aspect of the present invention, a one-component magnetic toner having a weight average particle diameter of the developer of 3.5 to 7.0 μm is used for the developing device in the cartridge. High resolution and high definition image formation can be performed effectively.

[Brief description of the drawings]

FIG. 1 is a graph showing a developing bias waveform according to a first embodiment of the present invention.

FIG. 2 is a graph showing experimental results of the embodiment of the present invention.

FIG. 3 is a graph showing experimental results of Comparative Example 1 of the present invention.

FIG. 4 is a graph showing experimental results of Comparative Example 2 of the present invention.

FIG. 5 is a schematic sectional view showing a developing device of the present invention.

FIG. 6 is a schematic sectional view showing an image forming apparatus according to an embodiment of the present invention.

FIG. 7 is a graph showing a developing bias waveform according to a second embodiment of the present invention.

FIG. 8 is a graph showing a developing bias waveform according to a third embodiment of the present invention.

FIG. 9 is a schematic sectional view showing a process cartridge according to a fourth embodiment of the present invention.

FIG. 10 is a graph showing a developing bias waveform using a conventional rectangular wave.

FIG. 11 is a graph showing a developing bias waveform using a conventional sine wave.

FIG. 12 is a graph showing a developing bias waveform using a conventional triangular wave.

FIG. 13 is a graph showing a developing bias waveform using a conventional duty bias.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 3 Developing sleeve 6 Developing device 7 Toner 11 Bias power supply Vpf Peak voltage of AC bias promoting side Vpb Peak voltage of AC bias returning side Vfm Effective voltage of waveform on AC bias promoting side Vmax Promoting side maximum voltage tpf AC bias From the start of voltage application to the Vpf

Claims (6)

[Claims] A developing device having an image carrier, a developer carrier disposed at a predetermined distance from the image carrier, and a developing bias in which an AC component is superimposed on a DC component. An image forming apparatus comprising: a developing bias applying unit configured to apply a developing bias to a body, and developing an electrostatic latent image on the image carrier by applying a developing bias to the developer carrier. When the distance from the carrier is G (μm), and the maximum voltage on the accelerating side on the accelerating side, which is applied from the developing bias applying unit and urges in the direction from the developer carrier to the image carrier, is Vmax, Side maximum electric field is Vm
ax / G (V / μm), when the effective voltage of the waveform on the AC bias accelerating side is Vfm and the maximum voltage on the AC bias accelerating side is Vpf, a developing bias is applied to the developer carrier. In this case, the promotion-side maximum electric field Vmax / G becomes a value satisfying the range of 4.0 ≦ Vmax / G <5.0, and the effective voltage Vfm of the waveform on the AC bias promotion side.
And the maximum voltage Vpf on the acceleration side of the AC bias is 0.75
An image forming apparatus, wherein the value satisfies a range of × Vpf ≦ Vfm ≦ 0.90 × Vpf. 2. The time from the start of the application of the AC bias accelerating voltage to the reaching of the accelerating maximum voltage Vpf is defined as t.
2. The image forming apparatus according to claim 1, wherein tpf is a value that satisfies tpf ≦ T / 4, where T is one cycle of pf and the AC bias. 3. The peak voltage of the voltage applied on the accelerating side is defined as Vpf, and the peak voltage of the voltage applied on the return side for urging in the direction from the image carrier toward the developer carrier is Vpb.
3. The image forming apparatus according to claim 1, wherein the peak voltage Vpf on the promotion side and the peak voltage Vpb on the return side are expressed by a relation of | Vpf |> | Vpb |. 4. A developing device provided in the image forming apparatus, wherein a developer used for developing an electrostatic latent image formed on the image carrier has a weight average particle diameter of 3.5 to 7.0 μm. The image forming apparatus according to claim 1, wherein the one-component magnetic toner is used. 5. A process cartridge used in the image forming apparatus according to claim 1, wherein an integrated cartridge is formed in a shape that can be housed in the image forming apparatus, Has a developing device having a developer carrier similarly to the developing device in place of the developing device provided at least in the image forming apparatus, and accommodates the process cartridge in the image forming apparatus. The developer carrying member in the cartridge is connected to the developer carrying member in the cartridge and the developing bias applying means provided at an arbitrary position in the state so as to be able to input the developing bias under the condition described in claim 1 to 3. A process cartridge which can be applied to a body. 6. A developing device provided in a cartridge uses a one-component magnetic toner having a weight average particle diameter of 3.5 to 7.0 μm as a developer used for developing an electrostatic latent image. The process cartridge according to claim 5, wherein: