JPH05281790A - Developing method and image forming device - Google Patents

Abstract

PURPOSE:To obtain high-grade images having good character reproducibility and graininess, etc., while suppressing the generation of image abnormality, such as so-called fogging and drop-out, in the developing method which visualizes the electrostatic latent image formed by irradiation with a laser beam by using a two component developer formed by mixing an insulating toner and magnetic particles. CONSTITUTION:The insulating toner having <=8mum average grain size is used. The frequency of the AC component of the bias voltage to be impressed between an electrostatic latent image carrying member and a developer carrying member is specified to >=4000Hz and the relation between the electric resistivity rho(OMEGA.cm) of the magnetic particles incorporated into the developer and the diameter r(mum) of the laser beam is specified to a range of r<=-12mulog(rho)+196 (r<=100).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing method for visualizing an electrostatic latent image on a photoconductor by using a two-component developer in which an insulating toner and magnetic particles are mixed, and an image forming apparatus using the developing method. Regarding

[0002]

2. Description of the Related Art Conventionally, as a developing method using a two-component developer, there has been known a method of using a developer carrier to attach toner to an electrostatic latent image on a photoconductor adjacent thereto.
The outline of this method is as follows. A developer containing a mixture of insulating toner and magnetic particles is supplied to the surface of the developer carrier, and the magnetic particles of the magnet housed inside the developer carrier are fixed at a fixed position to form a magnetic particle on the surface of the developer carrier. Forming a magnetic brush that has become. On the other hand, an electrostatic latent image is formed on the electrostatic latent image holder by irradiating the surface thereof with light based on an image signal, due to a difference in charging potential. The magnetic brush is brought into contact with or in close proximity to the surface of the electrostatic latent image holding member, and a bias voltage is applied between the developer carrying member and the electrostatic latent image holding member to convert the insulating toner into an electrostatic latent image. The image is visualized by attaching it.

It is known that the insulating toner used in the above developing method generally improves the image quality, the reproducibility of characters, and the graininess, which is the smoothness of the appearance of characters, when the average particle size of the toner particles is reduced. There is. For this reason, the toner used in recent years tends to have a smaller diameter, but if toner particles having a small diameter are used and only the DC component is applied as the bias voltage, it becomes difficult to obtain the required image density. On the other hand, as a method of increasing the image density, there are known methods such as increasing the rotation speed of the developer carrying member and narrowing the gap between the developer carrying member and the electrostatic latent image holding member. However, the former is likely to cause toner smoke and developer spillage, and the latter requires the developer layer on the developer carrier to be thin, which narrows the gap that regulates the thickness of the developer layer. There is a drawback in that streaky non-developed portions are likely to occur on an image due to clogging of foreign matters other than lumps and developers, such as lint.

For this reason, in order to obtain a sufficient image density, a bias voltage containing an AC component is applied between the developer carrying member and the electrostatic latent image holding member to form the electrostatic latent image holding member. Due to an oscillating electric field formed at a close position (development area), toner having a charge adheres to the electrostatic latent image. The frequency of the AC component of the bias voltage is in a range suitable for obtaining a required image density and forming a high quality image. For example, JP-A-62-19275.
In general, as disclosed in Japanese Patent Publication No. 8-200,
It is set within the range of 0 Hz.

Further, when the electric resistance (volume resistance) of the magnetic particles of the developer used in such a developing method is low, discharge under a developing bias may occur, and electric charges to the magnetic particles may be generated. A phenomenon such as injection or deterioration of gradation reproducibility may occur, and therefore, JP-A-61-73975, JP-A-62-289858, and JP-A-63-12306.
Generally, it is set to 10 ¹² Ω · cm or more as disclosed in Japanese Patent Laid-Open No. 9-29762 and Japanese Patent Laid-Open No. 2-29762.

[0006]

In the above developing method, when a toner having a small diameter is used, that is, when a toner having an average particle diameter of toner particles of 8 μm or less is used,
The frequency of the AC component of the bias voltage is 200 to 300
When set in the range of 0 Hz, a phenomenon called so-called fogging in which a non-image portion on the image is stained with toner occurs, and the graininess of the image quality is not effectively improved,
Rather, the problem of becoming worse arises.

In order to solve this problem, it can be considered to increase the frequency of the AC component to about 4000 to 8000 Hz. However, when the frequency of the AC component is increased, the occurrence of fogging and the improvement in graininess can be seen, but the image abnormality as shown in FIG. 4 is likely to occur. This image abnormality is caused by developing an image having a high-density portion 30 and a halftone portion 31 in contact with the high-density portion on the downstream side of the developing process.
This is a phenomenon in which the portion 32 in contact with the high density portion of the low density portion becomes blank and is not developed. This image abnormality becomes particularly noticeable when a line screen is used to irradiate the electrostatic latent image holder with light. Therefore, there is a problem in that it is difficult to obtain a high-quality image having good graininess without any of the above-mentioned white spots and fog using a toner having an average particle diameter of 8 μm or less. The present invention has been made in view of the above drawbacks in the prior art, and suppresses the occurrence of image abnormalities such as stains in non-image areas called so-called fog and the above-mentioned white spots, while improving character reproducibility and graininess. An object of the present invention is to provide a developing method capable of obtaining a good and high-quality image and an image forming apparatus using the method.

[0008]

In order to solve the above problems, the invention according to claim 1 provides an insulating toner and magnetic particles on the surface of a developer carrier having a magnetic pole whose position is fixed. A magnetic brush of developer mixed with is formed, and the magnetic brush is brought into contact with or in proximity to an electrostatic latent image holding member on the surface of which an electrostatic latent image is formed by uniform charging and laser beam irradiation based on a digital signal. In the developing method, a bias voltage containing an AC component is applied between the electrostatic latent image holding member and the developer carrying member, and the insulating toner is adhered to the electrostatic latent image for visualization. An insulating toner having an average particle size of 8 μm or less is used, and the frequency f of the AC component of the bias voltage is 40
00 Hz or more, the magnetic particles have an electrical resistivity ρ
(Ω · cm) is used in the range of r ≦ −12 × log (ρ) +196 (r ≦ 100) with respect to the diameter r (μm) of the laser beam.

According to a second aspect of the present invention, an electrostatic latent image holding member having a photoconductive photoconductor layer on its surface, and a laser beam based on a digital signal irradiating the electrostatic latent image holding member on the electrostatic latent image holding member. A writing device that forms an electrostatic latent image on the
A developer carrier for forming a magnetic brush of a developer in which a magnetic pole whose position is fixed and which has a mixture of insulating toner and magnetic particles is formed on the surface is provided with the magnetic brush in proximity to the electrostatic latent image holder or A developing device to be brought into contact, a bias power source for applying a bias voltage containing an AC component between the electrostatic latent image holding member and the developer carrying member, and a toner image formed on the electrostatic latent image holding member. In an image forming apparatus having a transfer device for transferring to a recording medium, the insulating toner has an average particle diameter of 8 μm or less, a frequency f of an AC component of the bias voltage is 4000 Hz or more,
The electrical resistivity ρ (Ω · cm) of the magnetic particles and the diameter r (μm) of the laser beam are in the range of r ≦ −12 × log (ρ) +196 (r ≦ 100).

In the developing method, the electrostatic latent image to be developed is formed by irradiating light based on a digital signal, and may be one using a line screen,
It may be one using a dot screen. As the waveform of the bias voltage, a rectangular wave, a sine wave, a triangular wave, a sawtooth wave, or the like can be selected. The electrical resistivity ρ (Ω · cm) of the magnetic particles is such that the magnetic particles are put in a cell having a constant volume sandwiched between two electrodes and the applied voltage between the electrodes is 1
The resistance value is (V / μm). The diameter r (μm) of the laser beam is defined as follows.
As shown in FIG. 5, the energy density of the beam decreases as it moves away from the center of the beam in the radial direction, but the energy density is 1 / e ² ≈1 of the maximum value (center of the beam).
The diameter at the position of 3.5%, that is, r shown in FIG.

[0011]

In the developing method according to claim 1, since the insulating toner used in the two-component developer has an average particle diameter of 8 μm or less, the character reproducibility is good and at the same time the graininess improving effect is obtained. Becomes noticeable and the image quality is improved. Also,
Even if the above-mentioned insulating toner having a small particle size is used, the frequency of the AC component of the bias voltage applied between the developer carrying member and the electrostatic latent image holding member is set to 4000 Hz or more. Therefore, the occurrence of a so-called fogging phenomenon can be prevented and the graininess can be effectively improved.

Further, according to the experiment, the white spots are generated when the developed toner returns to the developer carrier again due to a reverse electric field due to the residual electric charge left on the magnetic particles, and the developed toner returns to the high density portion. It was found that the reverse electric field is stronger as the potential difference between the low concentration part and the low concentration part is larger. On the other hand, when the electrical resistivity of the magnetic particles is reduced, the residual charge is reduced, and the smaller the diameter of the laser beam used for writing the electrostatic latent image, the smaller the difference in potential between the high-concentration portion and the low-concentration portion. And white spots are less likely to occur. Therefore, the lower the resistivity of the magnetic particles and the smaller the diameter of the laser beam, the less the occurrence of white spots, and the values of the resistivity ρ (Ω · cm) of the magnetic particles and the diameter r (μm) of the laser beam are reduced. , R ≦ −12 × log (ρ) +196 (r ≦ 100), it is possible to obtain a good image in which white spots are not substantially a problem.

According to another aspect of the image forming apparatus of the present invention,
The development according to claim 1 can be carried out, and a high-quality image having good character reproducibility and graininess can be obtained without occurrence of image abnormalities such as so-called fog in non-image areas such as stains and white spots. Be done.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. 1 is an image forming apparatus that can be used in a developing method that is an embodiment of the invention described in claim 1, and is a schematic configuration showing an image forming apparatus that is an embodiment of the invention described in claim 2. It is a figure. In this image forming apparatus, the electrostatic latent image carrier 1 has a photosensitive member (OP
It is a cylindrical body having a (C photoconductor), and is capable of forming an electrostatic latent image by once uniformly charging the peripheral surface and exposing the image portion. Four developing devices are provided around the electrostatic latent image holding member 1 so as to face the electrostatic latent image holding member 1. The developing devices use cyan, magenta, yellow, and black toners, respectively. is there.

A charger for uniformly charging the electrostatic latent image carrier 1 around the electrostatic latent image carrier 1 at the upstream side in the rotational direction from the position where the developing devices 4, 5, 6, 7 are provided. 2 (strocolon charger), a writing device 3 for irradiating a laser beam based on a digital image signal to form an electrostatic latent image is provided, and a line screen is used for irradiating light based on the image signal. ing. Further, on the downstream side in the rotation direction, a transfer device 9 that faces the transfer drum 8 and that transfers the developed toner image to a sheet is provided at the facing position. Further on the downstream side, a cleaning device 10 for removing the toner remaining on the electrostatic latent image holder 1 after transfer.
Is provided. On the other hand, a paper feeding device 11 for carrying the paper carried out from the transfer section is provided in the paper carrying path, and a fixing device 12 for fixing the transferred toner image onto the paper is provided downstream thereof. ing. The charger 2 is set to uniformly charge the electrostatic latent image carrier 1 to -650V. The writing device 3 emits a laser beam based on a digital signal,
A laser diode is used as a light source, and a laser beam having a wavelength of 780 nm is used. The potential of the entire exposed image portion is set to -200 V by the irradiation of this laser beam.

FIG. 2 is a schematic structural view showing a developing device used in the above image forming apparatus. This developing device is attached to the surface of the cylindrical developer carrier 16 that conveys the developer by adsorbing the developer on the surface and rotating it in a housing 18 that houses the developer. A developer regulating member 17 that regulates the amount of the developer, and screw augers 13 and 14 that rotate to stir and convey the developer and supply the developer to the developer carrying member 16 are provided.

The developer carrying member 16 has a built-in magnet roll which is fixed so as not to rotate, and a sleeve which is rotatably supported around the magnet roll. This sleeve is arranged so as to face the electrostatic latent image carrier 1 with a gap of 0.5 mm, and the portions where the surfaces of the sleeves are close to each other are the development area. Further, the magnet roll disposed inside has a plurality of magnetic poles 15, a magnetic brush of magnetic particles is formed on the surface of the sleeve by a magnetic field formed between the adjacent magnetic poles, and the developer is conveyed by rotation of the sleeve. You can do it. The rotation speed of the sleeve is set so that the peripheral speed ratio between the electrostatic latent image carrier 1 and this sleeve is about 2: 1.

A DC weight AC voltage as a developing bias voltage is applied to the developer carrying member 16 from a DC power source 19 and an AC power source 20, and is formed at a position (developing area) close to the electrostatic latent image holding member 1. Due to the generated electric field, the charged toner adheres to the electrostatic latent image. This applied voltage has a DC component as a negative voltage, and the development potential contrast (the DC component voltage and the overall exposure potential of the electrostatic latent image holding member) with respect to -200V which is the entire exposed image portion voltage of the electrostatic latent image holding member. Difference) is about 300V, that is, the DC component is -500V. This development contrast is determined as a value at which good gradation is obtained when the photosensitive member of this embodiment has a gradation of 350 V or more. The AC component of the applied voltage has an amplitude value of 1.5 KV in peak-to-peak value and a frequency of 6 kHz, and the waveform is a rectangular wave.

One end of the developer regulating member 17 is fixedly supported and the other end is attached so as to project close to the surface of the developer carrying member 16, and the developer adsorbed on the surface of the developer carrying member is fixed. The amount is regulated.

In the image forming apparatus as described above, an image is formed by the following steps. Electrostatic latent image holder 1
Is uniformly charged by the charger 2, and the writing device 3 irradiates a laser beam to form an electrostatic latent image. This electrostatic latent image is obtained by extracting only a single color component of the color image to be formed. When the electrostatic latent image holder 1 rotates, the surface of the electrostatic latent image holder on which the electrostatic latent image is formed moves to the developing area facing the developing device. Of the four developing devices, only the developing device corresponding to the electrostatic latent image operates, and the electrostatic latent image is visualized by the adhesion of the toner. The developed toner image is moved by the rotation of the electrostatic latent image holder 1, and is transferred onto the paper held on the transfer drum 8 by the transfer device 9. The electrostatic latent image holder 1 after the transfer is cleaned by the cleaning device 10 and charged again by the charger 2. Such a process is repeated four times, and the toner images of the components of the respective colors are transferred onto the sheet in an overlapping manner to form a full-color toner image. The formed toner image is conveyed to the fixing device 12, heated and pressed, and fixed on the paper.

In the above-mentioned image forming apparatus, the diameter of the laser beam of the writing device 3 and the resistivity of the magnetic particles are changed to form an electrostatic latent image and develop the result. The developer used in this case is a mixture of toner having an average particle diameter of 7 μm and magnetic particles (ferrite carrier) having an average particle diameter of 50 μm, and the toner concentration is 7%. In FIG. 3, the diameter of the laser beam is set to three types of 40 μm, 64 μm, and 95 μm, and the resistivity of the magnetic particles of the developer is set to 10 for each.
^{This is} a result of observing the state of occurrence of white spots by forming and developing an electrostatic latent image while changing the range of ⁷ to 10 ¹⁵ Ω · cm. In this figure, the state of occurrence of white spots is evaluated by dividing it into the following three grades. Grade 1: No white spots (○ in the figure)
Grade 2): White spots occur, but acceptable range (△ in the figure)
Grade 3: Out of the allowable range due to white spots (× in the figure)
Indicated by)

As shown in this figure, the resistivity ρ of the magnetic particles is
The lower (Ω · cm), the diameter r of the laser beam
The smaller (μm), the less likely whiteout occurs. In this figure, the broken line shown in the figure is represented by r = -12 × log (ρ) +196 (r ≦ 100), and the occurrence of white spots is within the allowable range because the resistivity of magnetic particles or The diameter of the laser beam is in a small range.

[0023]

As described above, in the developing method or the image forming apparatus of the present invention, a small particle size toner having an average particle size of 8 μm or less is used, so that clear image quality with good character reproducibility and graininess can be obtained. In addition, by setting the frequency f of the AC component of the developing bias voltage to 4000 Hz or more, it is possible to prevent the occurrence of so-called fog phenomenon and effectively improve the graininess. In addition, since the electrical resistivity ρ (Ω · cm) of the magnetic particles and the diameter r (μm) of the laser beam are in the range of r ≦ −12 × log (ρ) +196 (r ≦ 100), the white spot occurrence level Can be maintained within an acceptable range.

[Brief description of drawings]

FIG. 1 is a schematic view showing an image forming apparatus which can be used in a developing method which is an embodiment of the invention described in claim 1, and which is an embodiment of the invention described in claim 2. It is a block diagram.

FIG. 2 is a schematic configuration diagram showing a developing device that can be used in the image forming apparatus of the above embodiment.

FIG. 3 is a diagram showing the developing method according to claim 1 and the developer and writing device used in the image forming apparatus according to claim 2, wherein the electrical resistivity ρ (Ω · cm) of the magnetic particles and the diameter r of the laser beam are used. It is a figure which shows the relationship with (micrometer).

FIG. 4 is a diagram showing an image sample for explaining a problem in a conventional developing method or image forming apparatus.

FIG. 5 is a diagram showing a definition of a laser beam diameter r.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrostatic latent image holder 2 Charging device 3 Writing device 4, 5, 6, 7 Developing device 8 Transfer drum 9 Transfer device 10 Cleaning device 11 Paper feeding device 12 Fixing device 13 Screw auger 14 Screw auger 15 Magnet 16 Developer carrying Body 17 Developer regulating member 18 Housing

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical display location G03G 15/06 101 15/09 Z (72) Inventor Yoshiro Yamaguchi 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Zero Co., Ltd. Ebina Office

Claims (2)

[Claims] 1. A magnetic brush of developer, which is a mixture of insulating toner and magnetic particles, is formed on the surface of a developer carrier having a magnetic pole whose position is fixed, and the magnetic brush is uniformly charged and digitally charged. By irradiating a laser beam based on a signal, the electrostatic latent image is brought into contact with or in proximity to the electrostatic latent image holding member formed on the surface, and an AC component is formed between the electrostatic latent image holding member and the developer carrying member. In the developing method of applying a bias voltage including the above, and making the insulating toner adhere to the electrostatic latent image to make it visible, the insulating toner having an average particle size of 8 μm or less is used. The frequency f (Hz) of the component is in the range of 4000 ≦ f, and the magnetic particles have an electrical resistivity ρ (Ω · cm) of r ≦ −12 × log with respect to the diameter r (μm) of the laser beam. (Ρ) +196 A developing method, wherein a developing agent having a range of (r ≦ 100) is used. 2. An electrostatic latent image carrier having a photoconductive photoconductor layer on its surface, and writing for forming an electrostatic latent image on the electrostatic latent image carrier by irradiation of a laser beam based on a digital signal. An apparatus and a developer carrier that contains a magnetic pole whose position is fixed and that forms a magnetic brush of developer on the surface of which a mixture of insulating toner and magnetic particles are formed. And a bias power source for applying a bias voltage containing an AC component between the electrostatic latent image holding member and the developer carrying member, and a developing device formed on the electrostatic latent image holding member. An image forming apparatus having a transfer device for transferring a toner image to a recording medium, wherein the insulating toner has an average particle size of 8 μm or less, and a frequency f (Hz) of an AC component of the bias voltage is 4000 ≦ f. Range of The electrical resistivity ρ (Ω · cm) of the magnetic particles and the diameter r (μm) of the laser beam are in the range of r ≦ −12 × log (ρ) +196 (r ≦ 100). Image forming apparatus.