JP2768078B2 - Development method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for developing an electrostatic latent image on a photoreceptor with a powdery developer, which is used in an image forming apparatus such as an electrophotographic copying machine. The present invention relates to a developing method using a two-component developer in which particles are mixed.

[0002]

2. Description of the Related Art Conventionally, as a developing method using a two-component developer, there has been known a method in which a developer carrier is used and a toner is transferred to an electrostatic latent image on a photosensitive member adjacent thereto. The outline of this method is as follows. A developer in which insulating toner and magnetic particles are mixed is supplied to the surface of the developer carrier, and the magnetic particles are spiked on the surface of the developer carrier by the magnetic force of a built-in magnet whose position is fixed in the developer carrier. Forming a magnetic brush. On the other hand, the electrostatic latent image holder has
By irradiating the surface with light based on an image signal, an electrostatic latent image is formed due to a difference in charged potential. By contacting or approaching the magnetic brush to the surface of the electrostatic latent image holding member, the insulating toner is attached to the electrostatic latent image,
This is to visualize the image.

In the above-described developing method, as a method of easily obtaining a required density of an image due to toner adhesion, the rotation speed of the developer carrier is increased, or the speed of the developer carrier and the electrostatic latent image carrier is changed. A method for narrowing the gap is generally known. However, the former is liable to cause toner peeling or spilling of the developer, and the latter requires the developer layer on the developer carrier to be thinner, which narrows the gap that regulates the thickness of the developer layer. However, there is a disadvantage that foreign matter clogging due to lump or foreign matter other than the developer, such as lint, is likely to occur, and a problem of whitening on an image is likely to occur.

For this reason, in order to obtain a sufficient image density, a bias voltage containing an AC component is applied between the developer carrier and the electrostatic latent image holder, and the electrostatic latent image holder is An oscillating electric field formed at an adjacent position (developing area) causes toner having electric charge to adhere to the electrostatic latent image. The frequency of the AC component of the bias voltage is set to an appropriate range for obtaining a required image density and forming a high-quality image.
No. 58, as disclosed in US Pat.
It is set within the range of 00 Hz.

The developer used in such a developing method generally has a volume average particle size of about 9 to 15 μm ( hereinafter referred to as “ volume average particle size”).
Below, referred to as an average particle size) ;
A two-component developer mixed with magnetic particles having a particle size of about 0 to 120 μm is used. If the electrical resistivity (volume resistance) of the magnetic particles is low, a discharge may occur under a developing bias, or phenomena such as injection of charges into the magnetic particles and deterioration of gradation reproducibility may occur. Japanese Patent Application Laid-Open
1-73975, JP-A-62-289858, JP-A-63-126969, JP-A-2-29
In general, as disclosed in 762 Patent Publication ^{10 12} Omega
・ Set to cm or more.

[0006]

In the above-described developing method using a two-component developer, the average particle size of the toner particles is a factor affecting the image quality. It is known that image quality is improved. In particular, when the thickness is 8 μm or less, the effect of improving the character reproducibility and the graininess that is the smoothness of the character appearance is remarkable. However, this lower limit is about 6 μm from a technical point of view including the production cost of the toner. However, when the average particle size is 8
In the case where a toner having a size of μm or less is used, if the frequency of the AC component of the bias voltage is set in the range of 200 to 3000 Hz, a phenomenon called so-called fogging that a non-image portion on an image is stained by the toner occurs As for the image quality, there arises a problem that the graininess is not effectively improved, but rather deteriorated.

On the other hand, when the frequency of the AC component is increased, the occurrence of fogging and the graininess can be improved, but the formed image tends to suffer from chipping at the front end and the rear end. This tendency becomes remarkable especially when a line screen is used for irradiating the electrostatic latent image holding member with light. The line screen has an advantage that a pixel writing shift due to a weak vibration or a slight speed fluctuation of the electrostatic latent image holding member is inconspicuous in image output, and is suitable for forming a color image. . Therefore, the average particle size is 8 μm
Using the following toner, there is a problem that it is difficult to obtain a high-quality image with good graininess without any image lack or fog. The present invention has been made in view of such disadvantages in the related art, and suppresses the occurrence of image defects such as toner fouling in a non-image portion and chipping of a front end or a rear end of an image, which is called a fog. It is another object of the present invention to provide a developing method capable of improving character reproducibility and graininess and obtaining a high-quality image without image shift.

[0008]

Means for Solving the Problems To solve the above problems,
For example, the present invention relates to a developing device incorporating a magnetic pole having a fixed position.
Insulating toner and magnetic particles mixed on the surface of the agent carrier
Form a magnetic brush of developer, and apply this magnetic brush uniformly
The electrostatic latent image formed on the surface by charging and exposure
While contacting or approaching the electrostatic latent image carrier,
A bag containing an AC component between the electrostatic latent image carrier and the developer carrier.
A bias voltage is applied, and the insulating toner is transferred to the electrostatic latent image.
In the developing method of visualizing by attaching to the
The toner isVolume average particle sizeIs more than 6μm and less than 8μm
The magnetic particles have an electrical resistivity γ (Ω · c
m) is 10⁸≦ γ ≦ 10¹⁰  Of the AC component of the bias voltage.
The frequency f (Hz) is set in the range of 4000 <f ≦ 8000.

In the developing method, the electrostatic latent image to be developed may be formed by irradiating the electrostatic latent image holding member with light in an analog manner, or by irradiating light based on a digital signal. Although it may be formed by using a line screen, it is preferable to irradiate light based on a digital signal and use a line 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. In addition, a developing mode for implementing such a developing method includes:
Contact development in which the development is performed by bringing the magnetic brush of the developer into contact with the electrostatic latent image holding member, or non-contact jumping phenomenon in which development is performed in a non-contact manner may be used. In addition, the electric resistivity γ (Ω · cm) of the magnetic particles was set to 1 (V / μm) by applying the magnetic particles into a cell having a constant volume sandwiched between two electrodes and applying a voltage per length. It is the resistance value at the time.

[0010]

In the developing method as described above, since an insulating toner having an average particle diameter of 6 μm to 8 μm is used as a two-component developer, the character reproducibility is good and at the same time the graininess is improved. And the image quality is improved.
Even when the above-described insulating toner having a small particle diameter is used, the frequency of the AC component of the bias voltage applied between the developer carrier and the electrostatic latent image carrier is 8000 Hz or less.
Since the frequency is set to be higher than 4000 Hz, the occurrence of a so-called fogging phenomenon can be prevented, and the graininess can be effectively improved. Further, the electrical resistivity of the magnetic particles used in the two-component developer is 10 ⁸ Ω ·
cm or more, the discharge under a developing bias and a decrease in gradation reproducibility that occur when the electric resistivity (volume resistance) is low are prevented, and the electric resistivity (volume resistance) of the magnetic particles is reduced. ) Is 10 ¹⁰ Ω · cm or less, so that the level of occurrence of image edge chipping is within an allowable range.

In the developing method, since a line screen is used for irradiating light for forming an electrostatic latent image, weak vibration and an electrostatic latent image holding member can be provided as compared with a so-called dot type screen. The deviation of pixel writing due to slight speed fluctuation of is inconspicuous, image quality is improved,
The occurrence of image chipping and fogging at the front end portion and the rear end portion of the image in the paper feed direction is prevented, and the graininess is improved, and high image quality is obtained.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram illustrating an example of a developing device used in a developing method according to an embodiment of the present invention. The electrostatic latent image holder 1 can hold an electrostatic latent image due to a difference in charging potential, and the developing device 2 is provided to oppose the electrostatic latent image holder 1. The developing device 2 includes a housing 8 for accommodating a developer, and a magnet roll 5 having a plurality of magnets fixed so as not to rotate. The non-magnetic cylinder is rotatably supported around the magnet roll 5. Developer carrier (sleeve) 6, a developer regulating member 7 for regulating the amount of developer adhering to the surface of the developer carrier 6, a developer carrier that rotates and stirs and transports the developer And 6 screw augers 3 and 4 for supplying a developer.

The electrostatic latent image holder 1 has a photoreceptor (OPC photoreceptor) made of a polymer compound on its surface, and is charged uniformly once, and the image portion is exposed to form an electrostatic latent image. It can be formed. The developer carrier (sleeve) 6 includes:
A portion which is arranged close to the electrostatic latent image holding member 1 and whose surfaces are close to each other is a developing region. Further, the plurality of magnets disposed therein are arranged such that S poles and N poles are alternately disposed, and the magnetic brush of the magnetic particles is moved by the magnetic field formed between the adjacent magnetic poles. Formed on the surface of
The developer can be transported.

A DC weight AC voltage is applied as a developing bias voltage from a DC power supply 9 and an AC power supply 10 to the developer carrier 6, and is formed at a position (developing area) close to the electrostatic latent image holder 1. The charged electric field causes the charged toner to adhere to the electrostatic latent image. This applied voltage has a DC component as a negative voltage, and the developing potential contrast (the difference between the DC component voltage and the overall exposure potential of the electrostatic latent image holding member) is -200 V, which is the light portion charging voltage of the electrostatic latent image holding member. ) Is set to about 300V. In the case of the photoreceptor of this embodiment, if the developing contrast is set to 350 V or more, the gradation deteriorates, and the development contrast is determined as a value at which good gradation can be obtained. The applied voltage has an AC component having an amplitude value of 1.5 KV as a peak-to-peak value, and has a rectangular waveform.

One end of the developer regulating member 7 is fixedly supported,
The other end is attached so as to protrude in the vicinity of the surface of the developer carrying member 6 and regulates a fixed amount of the developer adsorbed on the surface of the developer carrying member.

FIG. 2 is a schematic structural view showing an electrophotographic copying machine using such a developing device. In this image forming apparatus, the developer carrier 6 is mounted so as to be close to and opposed to the electrostatic latent image carrier 1, and the distance between the electrostatic latent image carrier 1 and the developer carrier 6 is 0.5 mm. Is set to Further, the developing device 2 is connected to a toner replenishing device 31 for appropriately replenishing a necessary amount of toner. Around the electrostatic latent image holder 1, a charger 3 for uniformly charging the electrostatic latent image holder upstream of the position where the developing device 2 is provided in the rotation direction.
2. A writing device 33 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.

A transfer unit 34 for transferring the developed toner image to the sheet and a cleaning device 35 for removing the toner remaining on the electrostatic latent image holding member after transfer are provided on the downstream side in the rotation direction. Further, there are provided a paper feeding device 36 for carrying out the paper from the transfer section, and a fixing device 37 for fixing the transferred toner image to the paper. Using such an apparatus, the developer is developed by mixing a toner having an average particle diameter of 7 μm and magnetic particles (ferrite carrier) having an average particle diameter of 50 μm. At this time, the toner concentration is 6 to 11% by weight. The toner uses a polyester resin as a binder.

The results obtained when the development is performed while changing the frequency of the AC component of the development bias voltage will be described below. FIG.
FIG. 4 shows the relationship between the frequency when the frequency of the AC component of the developing bias voltage is changed from 2000 Hz to 8000 Hz and the state of occurrence of fog in the non-image portion.
Shows the relationship between frequency and granularity. The electric resistivity (volume resistance) of the magnetic particles of the developer at this time
Is 10 ⁹ Ω · cm. The levels from 1 to 6 on the vertical axis in FIGS. 3 and 4 are set as indices indicating image quality. 3 and 4, the frequency at which the AC component of the developing bias voltage exceeds 4000 Hz.
, The fog occurrence level and the graininess level in the non-image portion are both within the allowable range, and the image quality becomes good.
At 000 Hz or higher, both levels are almost unchanged, indicating that they are saturated.

FIG. 5 shows that the electric resistivity (volume resistance) of the magnetic particles of the developer is from 10 ⁸ Ω · cm to 10 ¹¹ Ω · cm.
9 shows the relationship between the frequency of the AC component of the developing bias voltage and the level of occurrence of chipping at the end of the image when the value is changed to. In this case, the electric resistivity (volume resistance) of the magnetic particles was determined by putting the magnetic particles in a cell having a fixed volume sandwiched between two electrodes, and applying an applied voltage per length of 1 V / μ.
It is a resistance value when m. Here, the electric resistivity (volume resistance) of the magnetic particles of the developer is set to be 10 ⁸ Ω · cm or more. This is because a discharge occurs during the operation, electric charges are injected into the magnetic particles, and the gradation reproducibility is deteriorated. In FIG. 5, the lower the electrical resistivity of the magnetic particles of the developer, the lower the level of occurrence of chipping at the image end is,
It shows that the allowable range is 10 ¹⁰ Ω · cm or less. At this time, the lower the frequency of the AC component of the developing bias voltage is, the less the chipping of the image end is. If the electric resistivity of the magnetic particles is 10 ¹⁰ Ω · cm or less, the frequency is 800
At 0 Hz or less, it is recognized that the level of occurrence of image chipping is within an allowable range.

As described above, the AC component of the developing bias
Frequency f (Hz) and electric resistivity γ of magnetic particles of developer
(Ω · cm)
In order to obtain the best image quality, the values of f and γ4000 <f ≦ 8000 10⁸≦ γ ≦ 10¹⁰  Is desirably within the range. Also, more preferably4000 <f ≦ 6000 10⁸≦ γ ≦ 10⁹  It is better to be within the range.

[0021]

As described above, in the developing method of the present invention,
Uses a small particle size toner having an average particle size of about 6 to 8 μm.
To obtain clear image quality with good character reproducibility and graininess
And the AC component of the developing bias voltage.
Frequency f (Hz)4000 <f ≦ 8000 The so-called fogging phenomenon
Can be prevented and graininess can be effectively improved.
Can be. Also, the electrical resistivity γ (Ω · cm) of the magnetic particles
To 10⁸≦ γ ≦ 10¹⁰  The range of the image edge chipping is allowed.
It can be maintained within the range. In addition, the electrostatic latent image
When a line screen is used for light irradiation to form
Image due to weak vibration or slight speed fluctuation of the electrostatic latent image carrier
This can prevent the occurrence of element write errors and provide high quality image quality.
Can be

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an example of a developing device that can be used in a developing method according to an embodiment of the present invention.

FIG. 2 is a schematic view showing an example of an electrophotographic copying machine provided with a developing device that can be used in the developing method of the present invention.

FIG. 3 is a diagram illustrating a relationship between the frequency of an AC component of a developing bias voltage and a fogging state of a non-image portion.

FIG. 4 is a diagram showing the relationship between the frequency of an AC component of a developing bias voltage and the granularity of an image.

FIG. 5 is a diagram showing the relationship between the frequency of an AC component of a bias voltage and the occurrence level of chipping at an image end when the electrical resistivity of magnetic particles of a developer is changed.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 electrostatic latent image holder 2 developing device 3, 4 screw auger 5 magnet roll 6 developer carrier 7 developer regulating member 8 housing 9 DC power supply 10 AC power supply

Continuation of front page (72) Inventor Takayuki Yamashita 2274 Hongo, Ebina-shi, Kanagawa Prefecture Fuji Xerox Co., Ltd. Ebina Works (56) References JP-A-4-77752 (JP, A) (58) Fields investigated (Int .Cl. ⁶ , DB name) G03G 15/09 G03G 15/06 101 G03G 15/08 507

Claims (1)

(57) [Claims] Claims: 1. A developing device incorporating a magnetic pole having a fixed position.
Insulating toner and magnetic particles mixed on the surface of the agent carrier
Form a magnetic brush of developer, and apply this magnetic brush uniformly
The electrostatic latent image formed on the surface by charging and exposure
While contacting or approaching the electrostatic latent image carrier,
A bag containing an AC component between the electrostatic latent image carrier and the developer carrier.
A bias voltage is applied, and the insulating toner is transferred to the electrostatic latent image.
In the developing method of visualizing the toner by attaching the insulating toner,Volume average particle sizeIs 8μ at 6μm or more
m, and the magnetic particles have an electrical resistivity γ (Ω · cm) of 10⁸≦ γ ≦ 10¹⁰  Wherein the frequency f (Hz) of the AC component of the bias voltage is set in the range of 4000 <f ≦ 8000.