JPH05150565A - Developing method for image forming device - Google Patents

Abstract

PURPOSE:To obtain high-quality images at a low cost by lessening the adhesion of a carrier to a photosensitive drum. CONSTITUTION:A developer which consists of a toner and the carrier and satisfies the conditions of 2<rho<3, 10<14>>Dv>10<10>, 25rho<psi<70rho when the true sp. gr. of the carrier is designated as rho(g/cm<3>), the electric resistance of the carrier as Dv(OMEGA.cm) and the density on a developing sleeve as psi(g/cm<3>) is used in the developing method for the image forming device. The developer is napped on the developing sleeve 21 toward the photosensitive drum 8 while the conditions of BP>RP and 0.15 <={BP/(SP-RP)}<=0.25 are satisfied when the surface potential of the photosensitive drum 8 is designated as SP(V) and the white part latent image potential of the photosensitive drum 8 as RP(V).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing method, and more particularly, to an image forming apparatus for developing a toner by using a developer composed of a toner and a carrier, by making the developer stand on the developing sleeve against the photoreceptor. It relates to a developing method.

[0002]

2. Description of the Related Art As a method of developing a toner on the surface of a photoreceptor using a developer composed of toner and carrier, a multipolar magnet is arranged in a developing sleeve, and the developer is put on the developing sleeve. There is a method in which the ears are raised and the developing sleeve is brought into sliding contact with the photoconductor by rotating the developing sleeve. In the double rotation developing method in which the multi-pole magnet in the developing sleeve is also rotated, the carrier is transported while rotating on the developing sleeve. For this reason, the toner at the base of the ears can be supplied to the development, and the development efficiency is improved.

In the conventional dual rotation developing method, since the movement of the developer becomes unstable during development, the carrier easily adheres to the surface of the photosensitive member. In particular, in the case of iron powder type carrier or ferrite type carrier having a large true specific gravity, the centrifugal force acting on the carrier becomes large, so that the carrier adheres to the photosensitive member more. If the carrier adheres to the photoconductor, it adversely affects the copy image quality.Therefore, as a means for recovering the carrier adhering to the photoconductor, for example, a carrier recovery means using magnetic force, electromagnetic force, or electrostatic force is used in the vicinity of the developing sleeve. There is one provided in. However, when these collecting means are used, when the carrier is collected from the photoconductor, the toner image developed on the photoconductor is disturbed and the image quality is deteriorated. Further, such a recovery means has a complicated mechanism, and therefore increases the cost of the device.

An object of the present invention is to reduce the adhesion of the carrier to the photoreceptor and obtain a high quality image at a low cost.

[0005]

A developing method for an image forming apparatus according to the present invention includes a developing device having a developing sleeve and a multi-pole magnet arranged in the developing sleeve, and a developing device arranged opposite to the developing sleeve. It is used in an image forming apparatus having a photoconductor. In this developing method, the toner is composed of toner and carrier, and the true specific gravity of the carrier is ρ (g / cm ³ ),
When the electric resistance of the carrier is Dv (Ω · cm) and the density on the developing sleeve is ψ (g / cm ³ ), 2
<Ρ <3, 10 ¹⁴ >Dv> 10 ¹⁰ , 25ρ <ψ <70ρ
A developer satisfying the condition of is used. Also, with this method,
When the bias potential applied to the developing sleeve is BP (V), the surface potential of the photoconductor is SP (V), and the latent image potential of the blank portion of the photoconductor is RP (V), BP> RP and 0. While satisfying the condition of 15 ≦ {BP / (SP-RP)} ≦ 0.25, the developer is made to stand on the developing sleeve with respect to the photoconductor.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a copying machine to which an embodiment of the present invention is applied. In the figure, a document table 2 is fixed to the upper surface of the copying machine main body 1. A document retainer 3 is arranged on the document table 2 so as to be openable and closable. A pair of paper feed cassettes 4 and 5 are detachably mounted on the right side of the copying machine body 1 in the drawing. On the left side of the copying machine body 1 in the drawing, a paper discharge tray 6 for discharging copied paper is mounted. An optical system 7 for reading a document is provided on the top of the main body 1 of the copying machine. This optical system 7
Is composed of a light source, a lens, a mirror, and the like. Further, a photosensitive drum 8 on the surface of which an electrostatic latent image is formed is arranged at substantially the center of the apparatus main body 1. Around the photosensitive drum 8, a main charger 9 that charges the photosensitive drum 8 to a predetermined charge, a developing device 10 that develops an electrostatic latent image,
A transfer discharger 11 that transfers a toner image onto a sheet, a separation discharger 12 that separates the sheet from the photosensitive drum 8, and a cleaning device 13 that removes residual toner on the photosensitive drum 8 are arranged. A paper feeding and conveying device 14 including a plurality of rollers is arranged between the paper feeding cassettes 4 and 5 and the transfer discharger 11. Further, between the separating discharger 12 and the discharge tray 6, the discharge conveying device 15 and the fixing device 1 are provided.
6 and 6 are arranged.

Next, the developing device 10 will be described in detail with reference to FIG. In the case 20 that constitutes the developing device 10,
A developer composed of toner and carrier is contained.
As the carrier, a binder-based carrier in which magnetic powder is dispersed in a binder polymer is used. Case 2
In FIG. 0, a cylindrical developing sleeve 21 facing the surface of the photosensitive drum 8 with a predetermined gap, and a magnet roller (multipolar magnet) 2 arranged in the developing sleeve 21.
2 and are arranged. The developing sleeve 21 rotates in a rotation direction B opposite to the rotation direction A of the photosensitive drum 8. A power source 28 for applying a bias voltage is applied to the developing sleeve 21.
Are connected. This power source 28 is used for the developing sleeve 21.
This is to prevent toner fogging by adjusting the bias potential to the toner. Generally, when the bias potential is increased, toner fogging is prevented but carrier adhesion is increased, and when the bias potential is decreased, carrier adhesion is reduced but toner fogging is likely to occur.

The magnet roller 22 is a uniformly magnetized magnet in which an equal number of N poles and S poles are arranged. The magnet roller 22 is rotatable in the rotation direction C opposite to the developing sleeve 21. On the right side of FIG. 2 in the case 20, a stirring roller 24 for stirring and mixing the developer in the case 20 and conveying the developer to the developing sleeve 21.
a and 24b are arranged. Stirring rollers 24a, 24
A toner hopper 25 containing replenishment toner is fixed to the case 20 on the b.
A toner replenishing roller 26 is provided at the bottom of the unit 5.
A doctor blade 23 is provided obliquely above the developing sleeve 21 to control the height of the surface of the developing sleeve 21. A toner concentration sensor 27 that detects the toner concentration by detecting the magnetic flux density of the developer is provided above the developing roller 20. When the toner is consumed by the development and the toner concentration of the developer decreases, the toner replenishing roller 26 rotates based on the detection result from the toner concentration sensor 27, and the toner is supplied from the toner hopper 25 into the case 20.

In this embodiment, the true specific gravity of the carrier is ρ (g / cm ³ ), and the electric resistance of the carrier is Dv (Ω
Cm) and the density of the developer on the developing sleeve 21 is ψ (g / cm ³ ), 2 <ρ <3, 10 ¹⁴ > Dv
The conditions of> 10 ¹⁰ and 25ρ <ψ <70ρ are satisfied. When the developer density ψ decreases to 25ρ or less, the image density decreases. The developer density ψ is 7
If it is equal to or greater than 0ρ, problems such as the carrier being conspicuous in the image or the characters being crushed occur.

The bias potential applied from the power source 28 to the developing sleeve 21 is BP (V), the surface potential of the photosensitive drum 8 is SP (V), and the blank sheet latent image potential of the photosensitive drum 8 is RP (V). ), BP> RP and 0.15
Each potential is set so that the condition of ≦ {BP / (SP-RP)} ≦ 0.25 is satisfied. BP / SP-RP
When the value P is less than 0.15, toner fogging of the image increases. When the value P exceeds 0.25, the carrier comes to adhere to the photosensitive drum 8,
As a result, the carrier becomes noticeable in the image.

Here, if the value P is set within the range of 0.15≤P≤0.25, both carrier adhesion and toner fogging of the image are slightly generated, but they are sufficiently within the allowable range. Further, when the value P is set within the range of 0.16 ≦ P ≦ 0.24, neither carrier adhesion nor toner fogging occurs. When the value P is set within the range of 0.18 ≦ P ≦ 0.22, neither carrier adhesion to the photosensitive drum 8 nor toner fogging on the image occurs, and the most preferable result is obtained.

Next, the operation will be described. When the copying operation is started, first, the original document on the original document table 2 is scanned by the optical system 7. The obtained image information is irradiated on the photosensitive drum 8 as a change in the intensity of the light beam. As a result, the charge of the portion corresponding to the blank portion of the original is erased on the photosensitive drum 8 which has been given a predetermined surface potential by the main charger 9, and an electrostatic latent image is formed on the photosensitive drum 8. .. In the developing device 10, the developing sleeve 21 rotates in the arrow B direction, and the magnet roller 22 rotates in the opposite arrow C direction. As a result, the developer conveyed by the rotation of the developing sleeve 21 is erected by the magnet roller 22 rotating in the reverse direction and slidably contacts the photoconductor drum 8. As a result, the toner in the developer is transferred to the photoconductor drum 8 side. Move to.

In this embodiment, since the magnet roller 22 is rotating in the direction opposite to the developing sleeve 21, the ears of the carrier continue to rotate. Therefore, the developing efficiency is improved. Moreover, since the true specific gravity ρ of the carrier is low, the ears are softened and the developing efficiency is further improved. Further, the bias potential applied to the developing sleeve 21 and the photosensitive drum 8
Surface potential of the photosensitive drum 8 and the latent image potential of the blank portion of the photosensitive drum 8 are set within the range satisfying the above conditions, the toner fogging phenomenon of the blank portion of the image does not easily occur, and the carrier adheres to the photosensitive drum 8. Hateful. Therefore, image deterioration due to carrier adhesion is prevented, and it is not necessary to provide a conventional carrier recovery means. Experimental example Carrier true specific gravity 2.5 to 2.7 (carrier resistance: 10 ¹²
Experiments were conducted using the binder-based carrier of (10 ¹³ ). The composition of the carrier used here and other conditions are as follows. The carrier is composed of 100 parts by weight of a resin (styrene acrylic) as a binder, 5 parts by weight of carbon black for controlling resistance, and 200 parts by weight of magnetite for imparting magnetism. The above materials were used, melt-kneaded, and crushed and classified to obtain target particles. The carrier had a central particle diameter of 55 μm, a resistance value of 1.2 × 10 ¹⁸ (1000 V) Ω, and a saturation magnetization of 43 (5000 Oe) emu / g.

The voltage level applied to the developing sleeve 21 is BP (V), the latent image voltage level on the surface of the photosensitive drum 8 is SP (V), and the blank sheet latent image voltage level on the photosensitive drum 8 is the residual potential. The following equation was set as RP (V).
The plane density of the developer on the developing sleeve was measured as the developer density (g / cm ³ ). Table 1 shows the value P of the equation P = BP / (SP-RP), the adhesion of the carrier to the photosensitive drum, and the state of the image.

[0015]

[Table 1]

In Table 1, No. 21-No. As shown in 29, when the developer density is less than the predetermined value, the carrier does not adhere to the photosensitive drum regardless of the value of P, but the image density becomes too small. In addition, No. Thirty
~ No. As shown in 37, when the developer density exceeds a predetermined value, the carrier adheres to the photoconductor drum regardless of the value of P, so that the carrier becomes conspicuous in the image.

No. 1-No. In the range shown by 20, the developer density is set within the predetermined range, and within that range, toner fogging on the image decreased as P increased from a small value to a good state. However, when the value of P exceeds the predetermined range, the amount of carrier adhered to the photosensitive drum increases, and the carrier becomes conspicuous in the image.

A more detailed analysis of the above experimental results shows that
In the range of 0.15 ≦ P ≦ 0.25, both carrier adhesion and toner fogging of the image are slightly generated, but they are within the allowable range. When the value P is out of this range, both carrier adhesion and toner fog increase. In addition, 0.
In the range of 16 ≦ P ≦ 0.24, neither carrier adhesion nor toner fogging occurred. 0.18 ≦ P ≦
In the range of 0.22, neither carrier adhesion to the photosensitive drum nor toner fogging on the image occurred, which was the most preferable area. The experimental data showing this most preferred region is No. It was 4, 11, 12, and 18.

[Other Embodiments] Although the magnet roller is rotated in the opposite direction to the developing sleeve in the above embodiment, the present invention may be adopted in a system in which the magnet roller is rotated in the same direction.

[0020]

According to the developing method of the image forming apparatus of the present invention, the true specific gravity and electric resistance of the carrier, the developer density on the developing sleeve, the bias potential applied to the developing sleeve, and the surface potential of the photosensitive drum. Since the potential of the latent image on the blank portion of the photoconductor drum is set to the above condition, the carrier adhesion to the photoconductor drum can be reduced, and it is not necessary to provide the carrier collecting means. Further, a high-quality image can be obtained at low cost without causing toner fogging of the image and reduction of the image density.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of a copying machine to which an embodiment of the present invention is applied.

FIG. 2 is a schematic vertical sectional view of a developing device.

[Explanation of symbols]

 8 photoconductor drum 10 developing device 21 developing sleeve 22 magnet roller

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Toyonori Inoue 1-228, Chuo-ku, Osaka City Mita Industrial Co., Ltd. Within Mita Engineering Co., Ltd.

Claims (1)

[Claims] 1. A developing method for an image forming apparatus, comprising: a developing device having a developing sleeve; and a multi-pole magnet arranged in the developing sleeve; and a photoconductor arranged so as to face the developing sleeve. The toner has a true specific gravity of ρ (g / cm ³ ), the electric resistance of the carrier is Dv (Ω · cm), and the density on the developing sleeve is ψ (g / Cm ³ ), 2 <ρ <3, 10 ¹⁴ > D
v> 10 ¹⁰ and 25ρ <ψ <70ρ are used, and the bias potential applied to the developing sleeve is set to BP.
(V), the surface potential of the photoreceptor is SP (V),
When the blank image latent image potential of the photoconductor is RP (V),
BP> RP and 0.15 ≦ {BP / (SP-RP)} ≦
A method of developing an image forming apparatus, which comprises causing the developer to stand on the developing sleeve with respect to the photoconductor while satisfying the condition of 0.25.