JPH11102115A - Electrophotographic equipment - Google Patents

Abstract

(57) Abstract: An electrophotographic apparatus capable of obtaining a uniform image over a long period of time and extending the life of a blade member such as a rubber blade constituting an organic photoconductive photoreceptor or a cleaner. provide. A moving direction of a first developing roller is opposite to a moving direction of a photosensitive drum, and two developing rollers are rotated in opposite directions. The peripheral speed ratio of the photosensitive drum 1 to the peripheral speed of the photosensitive drum 1 is 0.1.
5 to 2.5, the moving direction of the second developing roller 62 is the same as the moving direction of the photosensitive drum 1, and the peripheral speed ratio of the circumferential speed to the circumferential speed of the photosensitive drum 1 Is 1.
According to the relationship of the peripheral speed ratio, an action of removing unnecessary toner remaining on the photosensitive drum 1 is generated, and the load on the cleaning blade member is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus for forming a toner image on recording paper by using an electrophotographic method or an electrostatic recording method, and more particularly, to a method for forming an electrostatic latent image formed on a photoreceptor. The present invention relates to an electrophotographic apparatus in which a first developing roller and a second developing roller which are arranged along the direction of movement of a photoreceptor and rotate in opposite directions to each other develop with a developer containing a magnetic carrier and a toner as main components.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic method or an electrostatic recording method, a charge latent image is formed on a photoreceptor, and a magnetic carrier and a toner are used as main components by two developing rollers rotating in opposite directions. A method of developing with a two-component magnetic developer is disclosed in Japanese Patent Publication No. Sho 54-10869 and Japanese Patent Publication No. 1-503811.
And Japanese Patent Publication No. 63-15881 and U.S. Pat. No. 4,442,790.

[0003]

However, in the above-mentioned conventional method, the development capability is increased, so that the occurrence of unevenness in the developing direction in a high image density region can be prevented. Therefore, improvement has been desired in order to obtain a stable image over a long period of time.

An object of the present invention is to provide an electrophotographic apparatus capable of obtaining a uniform image for a long period of time and extending the life of a blade member such as a rubber blade constituting an organic photoconductive photosensitive member or a cleaner. To provide.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to expose a charged organic photoconductive photoreceptor by exposure means to form an electrostatic latent image comprising a combination of a light exposed portion and a non-exposed portion on the photoreceptor. A first developing roller and a second developing roller that are arranged along the direction of movement of the photoconductor and rotate in opposite directions to each other, and mainly include a magnetic carrier and a toner containing magnetite fine particles. Develop with developer
Developing means for forming a toner image on the photoreceptor; and a blade member provided to be in pressure contact with the photoreceptor surface and removing toner remaining on the photoreceptor after the toner image is transferred to recording paper. An electrophotographic apparatus having a cleaning means, wherein the moving direction of the first developing roller is opposite to the moving direction of the photoconductor, and the peripheral speed (Vd1) of the first developing roller and the peripheral speed of the photoconductor are changed. Peripheral speed ratio with speed (Vp) (S1
= Vd1 / Vp) is regulated in the range of 0.5 to 2.5, the moving direction of the second developing roller is the same as the moving direction of the photoconductor, and the peripheral speed (Vd2 ) And the peripheral speed (Vp) of the photosensitive member (S2 = Vd2 / Vp) is 1.
The first developing roller and the second developing roller are controlled within a range of 5 to 3.5, and are achieved by generating an action of removing unnecessary toner remaining on the photoconductor according to the relationship of the peripheral speed ratio. You. This makes it possible to reduce the pressure of the blade member against the photoreceptor and to reduce the abrasion amount of the photoreceptor to 1 / 100,000 rotations even when toner containing magnetic fine particles is used. ~ 3
It can be suppressed to about μm.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a laser printer according to an embodiment of the present invention. As shown in FIG. 1, a photoconductive photosensitive drum 1 (hereinafter, simply referred to as a "drum").
Is rotated in the direction of arrow A (clockwise), and a charger 2, a laser beam (optical writing system) 3, a developing device 4, a transfer device 19, and a cleaner 29 are arranged around the device in the order of the electrophotographic process. After the drum 1 is uniformly charged by the charger 2, an electrostatic charge latent image is formed by the laser beam 3. Here, the moving speed (peripheral speed) of the drum 1 suitable for the present invention is 10
５０50 cm / s, preferably about 20-40 cm / s. This is because image defects are less likely to appear at low speeds such as less than 10 cm / s, and the developing capability is insufficient at high speeds exceeding 50 cm / s.

The diameter of the drum 1 is 40 to 150 mm, and the diameter suitable for realizing a high-speed small printer is 50 to 120 mm.
mm, preferably 60 to 100 mm. The charging polarity may be either positive or negative, but in this embodiment, the charging polarity is positive. Charging voltage is 500-1000
V, for example, 700V. The exposure is image writing, that is, image area exposure.

The electrostatic charge latent image formed on the drum 1 is reversely developed by the developing device 4 to form a positive polarity toner image on the drum 1. Exposure may be performed using background lighting for regular development, but the present invention is more effective in the case of reversal development.

In the developing machine 4, the first developing roller 61 which moves in the opposite direction to the drum 1 (both are in the same direction because they are both clockwise rotations in terms of rotational direction).
And a second developing roller 62 that moves in the same direction as the drum 1 (the two developing rollers 62 are “opposite directions” in terms of rotational direction). The second developing roller 62 has magnets 51 and 52 fixed inside, respectively. Due to the magnetic force of 51, 52, the developing roller 6
A two-component magnetic developer mainly composed of a magnetic carrier and a colored toner (magnetic or non-magnetic) is adsorbed to the first and second rollers 62, and further conveyed by the rotation of the first and second developing rollers 61 and 62. The developer is brought into contact with the drum 1 to develop the electrostatic latent image.

The magnetic flux density of the developing magnetic pole is 700 to 1200 gauss, the center of the drum 1 and the first and second developing rollers 61 and 62.
Angle between the center of the developing pole and the line connecting the center of
(Not shown), the first developing roller 61
At 0 °, the second developing roller 62 is set at ± 10 °. The charge polarity of the toner is a plus having the same polarity as the charge polarity of the drum 1. The amount of the developer transported is controlled by the regulating plate 8 and the first,
It is adjusted by the gap between the second developing rollers 61 and 62. The first developing roller 61 has a bias power supply 71
A bias power supply 72 is connected to the developing roller 62, and a positive voltage having the same polarity as that of the toner is applied to the developing roller 62.
For example the charging voltage to the drum 1 when V ₀ = 700 V is, 250～600V is applied. An AC voltage of 100 Hz to 10 kHz may be superimposed on these bias voltages, and the magnitude of the effective voltage is 1/2 to 1/1 / of the DC voltage.
4.

The developer in the developing machine 4 is mixed and stirred left and right, and back and forth by a pair of screw augers 11 and 12 having a notched blade structure. The screw augers 11 and 12 have a greater effect of mixing and dispersing the toner in the developer and charging the developer than the screw auger of a simple shape.
Therefore, when the toner is supplied from the feed roller 13, the toner can be quickly dispersed in the developer, and the toner can be started up to a predetermined charge amount in a short time. Can be prevented.

The developer mixed and stirred as described above is
The developer sucked and transported by the developing roller 62 and passed through the gap between the regulating plate 8 and the second developing roller 62 develops the electrostatic charge latent image on the second developing roller 62 and is returned to the developing device 4. . The developer regulated by the regulating plate 8 is sucked and conveyed toward the first developing roller 61, and the developer that has passed through the gap between the regulating plate 8 and the first developing roller 61 is charged by the electrostatic force of the first developing roller 61. The charge latent image is developed, and the scraper 10 is developed.
Is returned into the developing device 4 through

Excess developer regulated by the second developing roller is returned to the screw auger by the guide plate 9.
Further, in a developing machine having a structure in which two developing rollers are vertically arranged as described above, the shape and setting position of the guide plate 9 are also important. That is, the surplus developer whose supply to the second developing roller 62 is regulated by the regulating plate 8 is smoothly transferred to the first developing roller 61, and the supply to the first developing roller 61 is regulated by the regulating plate 8. It is necessary to reduce the force applied to the developer when returning the surplus developer, and to reduce the load required for transportation. To this end, as shown in the figure, the leading end of the guide plate 9 has a bent portion for guiding the surplus developer from the second developing roller 62 to the first developing roller 61,
It is preferable that the upper portion is located approximately at the center of the two developing rollers, and the upper portion has a shape capable of temporarily holding the developer.

When developing with the first and second developing rollers 61 and 62, not only toner but also a carrier may adhere to the drum 1. Such a carrier has a fixed magnet 53 built therein. While being pulled back by the catch roller 63, it is transported and collected into the developing device 4 by the rotation of the catch roller 63.

A bias power supply 73 having the same polarity as the photosensitive member charging voltage is connected to the catch roller 63 in order to help the attached carrier to be pulled back, and the same as the photosensitive member charging voltage or the bias voltage of the second developing roller 62. Voltage is applied. The provision of the catch roller 63 is effective in preventing problems such as transfer failure and photoconductor damage due to the carrier adhered to the drum 1 and in preventing toner scattering from the developing machine 4. As described above, when developing with the two developing rollers 61 and 62, an inexpensive plastic magnet is used as the magnet 53, or a small catch roller with a diameter of about 63 can be used. Alternatively, a simple conductive roller without the magnet 53 can be used. When an AC voltage similar to that in the case of the first and second developing rollers 61 and 62 is superimposed on the applied voltage, the carrier removing effect is increased.

In the developing device 4 having the above structure, the peripheral speed of the drum 1 is 20 to 40 cm / s, and the diameter is 60 to 100 mm.
In this case, the diameters of the first and second developing rollers 61 and 62 suitable for obtaining a large developing capacity in a small developing machine are １ ／ to の of the diameter of the drum 1. For example, when the diameter of the drum 1 is 100 mm, the first and second developing rollers 61,
The diameter of 62 is preferably 25 to 30 mm.

The set position of the developing machine 4 is as shown in FIG.
Two developing rollers 6 from the exposure position with the laser beam 3
If the center positions of the lenses 1, 62 are set so as to form an angle θ, and are set so as to substantially correspond to the photoresponse time of the photoreceptor, the space can be used efficiently and the whole can be made compact. This is possible because reversal development is employed.

The relationship between the number of rotations (peripheral speed) of the two developing rollers 61 and 62, the developing gap, the applied bias voltage, the developing magnetic pole, the photosensitive member, and the developer will be described later, but the layer thickness is 20 to 60 μm.
Using a thick organic photoconductive photoreceptor and semiconductive developer
The peripheral speed ratio of the developing roller 61 is made equal to or smaller than that of the second developing roller 62, and the frictional force between the magnetic brush of the developer formed by the first developing roller 61 and the drum 1 and the second developing roller 62 Magnetic brush and drum 1 of developer to be formed
By setting the ratio to the rubbing force between 1 and 2, and setting the bias voltage of the first developing roller 61 to be equal to or 70% of the bias voltage of the second developing roller 62, the image density is changed from low image density to high image density. , A uniform image without unevenness in the developing direction can be obtained. Further, in the present embodiment employing the reversal development, the toner filming phenomenon on the drum 1 can be suppressed because the cleaning function occurs during the development by the first developing roller 61, so that the life of the photosensitive member can be extended. Can be planned.

The recording paper 14 includes registration rollers 15, 1
6. The toner image on the drum 1 and the recording paper 14 are conveyed while being aligned by the paper guide plate 17, and the toner image is transferred to the recording paper 14 under the action of the transfer device 19. Paper guide plate 1
7 is connected to a ground resistance of 20 to 100 MΩ to prevent electric charges required for transfer from leaking through the recording paper 14 at high humidity.

A high direct current voltage of -4 to -7 kV is applied to the transfer unit 19, and charges of the opposite polarity to the toner are transferred to the recording paper 14.
And electrostatically attracts and transfers the toner on the drum 1 to the surface of the recording paper 14. Subsequently, the recording paper 14 is separated and separated from the photoreceptor drum 1 while the charge charged by the charger 19 is removed by the action of the separating charge remover 20 as the drum 1 rotates. 100 to 500 for static eliminator 20
AC voltage with an effective value of 4 to 6 kV superimposed with a DC voltage of V
(Frequency 200 to 1000 Hz) is applied to generate an AC corona. At the time of the transfer static elimination, the drum 1 is irradiated with light by an erasing lamp 21 installed on the back side of the transfer unit 19. As a result, the charge on the drum corresponding to the interval between the recording sheets and the leading end of the recording sheet is attenuated. When thin recording paper is used, light is also irradiated through the paper, so that a part of the charge is erased.

The charge decay on the drum 1 has the effect of reducing the electrostatic attraction between the recording paper 14 and the drum 1 and assists in separating the recording paper 14 from the drum 1. In addition,
In order to erase the charge remaining on the drum 1 and prepare for the next image forming cycle, the toner and the photosensitive member are electrostatically used together with the erase lamp 24 or in such a manner that the efficiency of removing the residual toner by the cleaner 29 is improved. In order to further reduce the adhesive force, it is preferable to use the erase lamp 23 together. In any case, the charging polarity of the transfer unit 19 is opposite to the charging polarity of the charger 2 (in the case of the present embodiment in which the charging polarity of the photoconductor is positive, the charging polarity is negative). May be negatively charged to the opposite polarity. In this case, since the drum 1 usually has no sensitivity to this charging polarity, no charge can be removed by any erase lamp. Therefore, since the surface voltage of the drum 1 before charging by the charger 2 is not uniform, the charger 2 whose charging voltage is controlled by a screen (grid) 2a close to the surface of the drum 1 as shown in FIG. Is required.

After the transfer, the recording paper 14 is heated and pressed by a fixing device 25 via a conveyor belt 22, and the toner image is transferred to the recording paper 1
4 is fixed. The fixing device 25 includes, for example, a heater 2 inside.
And a backup roller 26 pressed against the heat roller 27. Unnecessary toner remaining on the surface of the drum 1 after the transfer is removed by a cleaner 29.
And is provided for the next image formation.

The cleaner 29 includes a blade member 30 such as a rubber blade, a brush 31 which rotates while being in contact with the surface of the drum 1, and a discharge cleaner 32 which discharges the removed toner.

In order to extend the life of the organic photoreceptor in the printer having the above configuration, it is necessary to increase the thickness of the organic photoreceptor, secure the electrophotographic characteristics, and reduce the abrasion caused by contact with the blade member 30. Desired. For this purpose, the film thickness is between 20 and 60 μm, preferably between 25 and 50 μm
It is preferable to use an organic photoconductive photoreceptor having a relative dielectric constant of 3 to 5 as well as abrasion and electrophotographic characteristics.
This is also a preferable value in that the toner is uniformly charged at a high speed, and that image chipping during development is suppressed.

Further, the amount of wear should be 1 to 3 μm per 100,000 rotations.
As m, it is required to ensure good image quality over a long period of time. For this purpose, the toner must have a small polishing effect due to contact with the blade member 30, but in such a case, the charging stability of the toner is reduced, and it becomes difficult to obtain a long-life developer. On the other hand, although the amount of wear can be suppressed by lowering the pressure contact of the blade member 30 to the photoconductor, problems such as image fogging, black stripes, and photoconductor filming due to insufficient cleaning (slipping) occur.

The present invention is to prevent the above-mentioned problems from occurring. That is, image defects (fog, black streaks, chipping) and photoreceptor filming do not occur while using a toner and a low pressure blade cleaner having excellent charge stability.
This realizes a long-life photosensitive drum, developer, and cleaner.

FIG. 8 is an explanatory diagram for explaining an image defect often seen in a conventional electrostatic latent image developing device. FIG. 8A shows a white solid portion 34 having a line width of 1 to 2 mm recorded in a black solid portion 33 having a size of about 3 cm in length and width. The moving direction of the photosensitive drum and the relative moving direction of the developing brush are different. Both are examples in the direction of the arrow. The phenomenon that the rear end portion of the solid black portion 33 is not clearly developed, the rear end chipping 35, the phenomenon that the front end portion of the white portion 34 is hardly developed, and the leading end omission 36 occur. These phenomena appear on the basis of the relative movement direction of the developing brush and the lines of electric force around the image area. For example, when the image density is D ≦ 1.2, especially when the image density is low at D ≦ 1, it is remarkable. When the developing capacity is increased to achieve a high image density such as D ≧ 1.2, the image becomes inconspicuous, but has drawbacks such as difficulty in reproducing a thin white outline image and an increase in toner consumption.

FIG. 8 (b) shows about 100 thin wires 37 (about 20 mm wide) with a length of about 10 mm and a width of about 0.1 mm, and an interval of about 0.2 mm, with a width of 3 mm and a length of 10 mm.
It is an example of an image when a thick line 39 of a degree is recorded. In this case, the rear end chipping 38 has few places where the thick line 39 exists.
This phenomenon appears based on the relative moving direction of the developing brush, the lines of electric force around the image area, and the charges induced in the carrier of the developer. For example, when the image density is low (D = 1 or less), it is remarkable. If the developing capacity is increased to increase the image density, the image becomes inconspicuous, but it becomes difficult to reproduce fine lines.

FIG. 8C shows a halftone dot portion 4 of 100 to 600 lines.
11 is an example of a defect image generated when a solid black portion 41 is recorded in 0. In addition to the above-mentioned lack of the rear end, a fringe image 42 due to a decrease in image density around the solid black area or white spots is generated, but the rear end is more remarkable, and the left, right, and front ends are few. This phenomenon appears based on the relative movement direction of the developing brush and the lines of electric force around the image area. For example, this phenomenon is remarkable when the image density D is lower than 1 and is conspicuous when the developing capacity is increased to increase the image density. However, it has disadvantages such as the halftone dots being easily crushed.

[0030] Such an image defect shown in FIG. 8, using a low resistance developer (dynamic hereinafter electric resistance 10 ⁶ Ω · cm), 2 pieces of developing roller from each other rotation direction as shown in FIG. 1 different 6
It is improved by developing at 1,62, but it is not perfect in low density images, and the life of the developer is short, discharge between the photoconductor and the life of the photoconductor is shortened, and bias leak is apt to occur. There's a problem. In addition to the high resistance developer, a high image density cannot be obtained, and there is a problem that a defect in a low image density and halftone of a halftone dot or fine line structure cannot be eliminated. In the case of an organic photoconductive photoreceptor (dielectric) having a dielectric constant of 3 to 5, it is easy to occur when the layer thickness is less than 20 μm. It achieves a longer life.

First, a photoreceptor having a dielectric constant of 3 to 5 has a thickness of 20 to 60 μm, preferably 25 to 50 μm. This is to reduce the peripheral effect of the lines of electric force, secure a margin against abrasion by the developer and the cleaner blade, and extend the life of the photoconductor. When the thickness of the photoreceptor is less than 20 μm, the peripheral effect is large, the above-described image defects are likely to occur, and the life is short. If the thickness of the photoreceptor exceeds 60 μm, the photoresponse is greatly reduced and the residual voltage is greatly increased, making it difficult to manufacture.
Decreased light response caused by thickening the photosensitive layer,
The adverse effects caused by the increase in the residual voltage can be eliminated by properly setting and correcting the set position θ of the developing device 4 and the developing bias voltage.

According to the present invention, a combination of the above-described and the following developing systems and a cleaner is used.
The amount of wear is μm, and the life of the drum 1 can be reduced to 200 to 1,000,000 pages.

The carrier of the developer has a volume average particle size of 70 to
A ferrite or magnetite carrier of 120 μm, preferably 80 to 100 μm is used. If it is less than 70 μm, the carrier adhesion to the photoreceptor will increase and the fluidity of the developer will decrease. If it exceeds 120 μm, the image density will decrease and the image will be disturbed.

Of these carriers, the saturation magnetization density is 50 to
100 emu / g (an external magnetic field of 3000 Oersted) can be used. If it is less than 50 emu / g, it is difficult to transport
If it exceeds 00 emu / g, the rigidity of the developing brush becomes large and the image quality is deteriorated. The strength suitable for the magnetic flux density of the developing magnetic pole is 700 to 900 Gauss. Also, if water-soluble ions are attached to the surface of the carrier, the change in the amount of charge over time with respect to the number of prints at the initial use of the developer is large. Is desirable.

As the toner, a volume average particle diameter containing a resin, a coloring material, a charge control material and the like is 5 to 12 μm, preferably 8 to 12 μm.
The thing of 10 μm is used. If it is less than 5 μm, it is difficult to manufacture, and the fluidity of the developer decreases. If it exceeds 12 μm, the resolution decreases, and it is difficult to record at a high resolution of 16 lines / mm or more. Styrene, acrylic, butadiene, styrene acrylic copolymer, polyester, etc. are used for the resin,
Styrene acrylic copolymers, for which charge control is relatively easy, are preferred.

The coverage of the carrier covered with the toner is set to 0.1.
2 to 0.5, preferably 0.25 to 0.4. If it is less than 0.2, the toner supply amount is insufficient, and it is difficult to obtain a high image.
If it exceeds 0.5, adverse effects such as lowering of the charging rise speed, occurrence of image fogging, and toner scattering are likely to occur.

The charge amount of the toner is preferably 10 to 25 μC / g (measured the charge amount of the toner developed on the photoreceptor). For example, when the toner particle size is 8 to 10 μm, 15 to 2
0 μC / g gives good results. If it is less than 10 μC / g, excessive toner adhesion and toner scattering occur, and
Is exceeded, the image density becomes insufficient.

The charge amount is printed for a long time (20 to 1).
(Million pages), conductive magnetic fine particles Fe ₃ O ₄ (magnetite, 50 to 100 emu) are contained in the toner.
/ G, an external magnetic field of 1000 to 3000 Oersted) is preferably added externally or internally. That is, in the configuration of the present developing machine,
High-speed development is performed with a small developer capacity of 1 to 2 kg. However, stirring is performed sparingly to reduce the load on the developer, and development is performed to prevent the occurrence of image defects in the development direction as described later. Since it is preferable to suppress the rotation speed of the roller as much as possible, the toner as a developer has a rapid charge rise when the toner is replenished with the developer, and is within a certain range without a large charge amount with time. It is necessary to subside. In order to obtain this characteristic, various experiments were conducted. As a result, the particle size was 0.05 to 2 μm, and preferably 0.5 to 2 μm.
It was found that it is better to externally add 0.1 to 2 wt% of magnetite of 2 to 0.7 μm or to add 0.5 to 20 wt% of magnetite. The life of the developer was 200,000 to 500,000 pages per kg. When the particle size is smaller than this, or when the amount of addition is small, the rise of charging is poor and the fluctuation value of the charge amount is large. Further, when the particle size is large, not only the fluctuation is large, but also the amount of wear of the blade member of the photoreceptor becomes large, and there is a practical problem.

When the addition amount was too large, the charge amount was small, and the abrasion of the photoreceptor was large, so that the photoreceptor could not be used. In the case of the above addition amount, the linear pressure of the blade member having a hardness of around 70 is 5 to 15
g, the OPC wear amount is 3 to 10 per 300,000 rotations.
μm, and the photoreceptor life is 20 to 10
100,000 pages can be secured. In addition, in combination with the magnetic powder, SiO 2
₂ (silica) and TiO ₂ (titanium oxide) in an amount of 0.1 to 0.5 wt%
It may be added.

The dynamic electric resistance of the developer suitable for the present invention is 10 ⁸ to 10 ¹¹ Ω · cm, and the dynamic electric resistance of the carrier at that time is 10 ⁷ to 10 ¹⁰ Ω · cm. Here, the dynamic electric resistance value is the current when a DC voltage of 100 V is applied in a state where a metal (for example, aluminum) drum is used instead of the drum 1 and a developer or a carrier is transported by the developing rollers 61 and 62. It is a value calculated from the value, gap, contact width, and contact length.

As will be described later with reference to FIG. 5 for this resistance value, there is an appropriate developing gap, but if it is lower than this, the photoconductor damage due to discharge, bias leak, and developer life are short (spent (A large change in the resistance value due to the toner), and if it is high, the image density becomes insufficient.

When the above-described photoconductor and developer are used, the image shown in FIG.
The results obtained by examining the rotation speed of the developing roller that can suppress the occurrence of the image defect described above will be extended. First developing roller 6
1, the peripheral speed ratio S1 = Vd1 / Vp, which is the ratio of the peripheral speed Vd1 of the photosensitive drum 1 to the peripheral speed Vp of the photosensitive drum 1, and the ratio of the peripheral speed Vd2 of the second developing roller 62 to the peripheral speed Vp of the photosensitive drum 1. The investigation was performed in a relationship of a certain peripheral speed ratio S2 = Vd2 / Vp. The peripheral speed ratio S
1, S2 and the moving direction of the photosensitive drum 1 are indicated by (+) in the direction of the arrow in FIG.

When developing with the two developing rollers 61 and 62 rotating in opposite directions to each other, in order to suppress an image defect based on the moving direction of the developer, a portion where the defect occurs in the first developing roller 61 is removed. 2 In order to compensate by the developing roller 62, the relative speeds with respect to the drum 1 are opposite to each other,
It is preferable that 1> 0 and S2> 1. FIG. 2 shows various cases in which the possible ranges of S1 and S2 have been confirmed by experiments.

In this experiment, the image density of the solid portion was set to a developing bias voltage of D = 1.1, which is relatively low, so that an image defect can be easily identified. The experimental conditions are as follows.

S1: 1.5 Photoconductor photoconductor drum diameter: 100 mm Organic photoconductor thickness: 30 μm Relative permittivity: about 3 Photoconductor photoconductor drum peripheral speed Vp: 250 mm / s First and second developing roller diameters: 30 mm Flux density of developing magnetic poles of first and second developing rollers: 900 gauss Angle between first developing roller and photosensitive drum: 5 ° Angle between second developing roller and photosensitive drum: 0 ° Photoconductor Photoconductor drum charging voltage V0: 650 V Baice voltage b1 of the first developing roller b1: 300 V Baice voltage b2 of the second developing roller b2: 350 V Developer carrier: magnetite Volume average particle diameter 100 μm Saturation magnetization density 90 emu / g Dynamic electric resistance Value 1.5 × 10 ⁸ Ω · cm Developer toner: Volume average particle diameter 9 μm Charge 15 μC / g Developer: Toner coverage 0.3 Dynamic electric resistance value 1.2 × 10 ¹⁰ Ω · cm Developer filling density in the developing section of the first developing roller: 41% Developer filling density in the developing section of the second developing roller: 35% An image was formed under these conditions. Chipped black solid front end (see FIG. 8A), chipped black solid rear end (see FIG. 8A), white front end (see FIG. 8A), white rear end (see FIG. 8A).
(A), the thin line configuration (see FIG. 8 (b)), the solid rear end of the halftone dot (see FIG. 8 (c)), and the solid front end of the halftone dot (see FIG. 8 (c)).印, good ones, slightly good ones
Marks and bad ones are represented by x marks.

As is clear from the evaluation results, S1 =
The range of S2 at which an image acceptable for 1.5 is obtained is 1.5 ≦ S2 ≦ 3.5, preferably 2 ≦ S2 ≦ 3.
That is, S2 = (S1 + 1) ± 0.5.

When the peripheral speed of the drum 1 is set at 20 to 40 cm / s, the good range obtained under various experimental conditions and each developing roller has a sufficient developing ability, and In order to achieve a range in which the load can be suppressed as much as possible, 0.5 ≦ S1 ≦ 2.5, 1.5 ≦ S2 ≦ 3.5, preferably 0.5 ≦ S1 ≦ 2, 1.5 ≦ S2. It was confirmed by experiment that ≦ 2.5.

Further, the relationship between the first developing roller 61 and the drum 1 can be achieved by making the sliding force of the first developing roller 61 equal to or more than that of the second developing roller 62 due to the difference in the relative speed, thereby providing a cleaning effect. The peripheral speed ratio difference is larger than the peripheral speed ratio difference between the second developing roller 62 and the drum 1 (S1).
+ 1.gtoreq.S2-1) and a condition (S1.ltoreq.S2) in which the peripheral speed ratio is equal to or greater than that in order to increase the developing ability of the second developing roller 62 rotating in the same direction as the drum 1 by the toner conveying ability , The range indicated by the hatching shown in FIG. The range of the square in the figure is 0.5 ≦ S1 ≦ 2.5 and 1.5 ≦ S2 ≦ 3.5.
Range.

On the other hand, increasing the rubbing force of the magnetic brush to provide a cleaning effect on the first developing roller 61 or an appropriate abrasion effect on the drum 1 prevents filming on the drum 1, Although useful for suppressing fogging, if too large, the balance against image defects may be lost or the drum 1 may be worn too much. The rubbing force can be changed by the difference in relative speed difference and the developer density in the developing area as described above.

FIG. 4 is an experimental example in which these relationships were examined. In this experiment, the rubbing force was changed by changing the developer density in the developing area. The rubbing force is determined by attaching a torque meter to the drum 1 and measuring a change in the rotational force of the drum 1 when the first developing roller 61 or the second developing roller 62 is operated. The sliding force is expressed per unit length of the magnetic brush.

In this experiment, S1 = 1.5, S2 = 2,
Sliding force F2 of second developing roller 62 = 7.33 gf / cm
(Filling density 35%), and the other conditions were the same as those in the experiment of FIG. As is apparent from this figure, the first developing roller 61
Of the rubbing force F1 of the second developing roller 62 to the rubbing force F1 of the second developing roller 62
(F1 / F2) is 0.9 to 2.1, preferably 1.2 to 1.6.
It is good to do.

FIG. 5 shows the gap relationship between the two developing rollers and the drum. The gap d1 of the first developing roller 61 is set to be equal to the gap d2 of the second developing roller 62 or wider than 0.1 to 0.5 mm as shown in FIG. This is based on the ease with which the developer flows due to the difference in the moving direction with respect to the drum 1. The hatched area in FIG. 5 is a preferable area.

When the setting of the second developing roller 62 is performed accurately (for example, ± 0.05 mm) when the developing machine 4 is set,
The accuracy of the first developing roller 61 may be reduced (for example, ± 0.1 mm). In the figure, a is a range where fringe is easily suppressed, b is a range where high image density is easily ensured, c is a range where edge chipping can be suppressed, and stable conveyance is difficult at 0.5 mm or less. Therefore, preferably, d1, d2
Both are preferably set to 0.5 to 1.5 mm.

Although the development gap is shown here, as another measure, it is more preferable to consider the packing density of the developer or carrier in the development gap region. That is, when the gap is the same as in FIG. 3, the filling density of the carrier in the first developing roller 61 is set to be equal to or less than 1.5 times the value in the second developing roller 62. As a result, the developing ability, sliding force, and cleaning effect of the first developing roller 61 can be secured. Specifically, the carrier filling density in the first developing roller 61 is 30 to 60%,
That at the developing roller 62 is 15 to 50%.

FIG. 6 is a diagram for explaining the light response characteristics of the photosensitive drum and the set positional relationship of the two-roller developing machine.
FIG. 6 shows an example of the photoresponse characteristics of an organic photoconductive photoconductor suitable for use in the present invention. The time t is the moving time of the photosensitive drum, that is, the time from the exposure point.
When the laser scanning exposure is performed at time t = 0, the charging voltage attenuates as time elapses and reaches a constant value (residual value) according to the exposure light amount. Further, even by increasing the amount of light and _{E 1, E 2, E 3} ...... E n not attenuated. Voltage V _r at this time is a so-called saturation residual voltage. Normally, giving exposure amount 80-100% of the contrast voltage is obtained for V ₀ -V _r, to allow time to decay to the 90-100% as the time before the start developer. However, to secure this time means to secure a considerable distance from exposure to development, and therefore, it is necessary to increase the diameter of the photosensitive drum, resulting in an increase in the size and cost of the apparatus. become. Alternatively, the peripheral speed of the photosensitive drum must be reduced, which limits high-speed recording.

[0056] In FIG. 6, an extension of a portion V ₀ is attenuated approximately linearly with time t as _{(V 0 (V 0 -V R} ) / e
(Where e = 2.718) and a tangent (extension) of the residual voltage V _R (saturated residual voltage or a value near this) with respect to the set light quantity (E _{n-1 in the} figure). the intersection of the time t _r and optical response time. In a recording apparatus combining an organic photoconductor photoreceptor and a blade cleaner, the photosensitive layer of the photoreceptor has one layer.
Since there is abrasion of 0.1 to 1 μm per million pages printed, if the thickness of the photosensitive layer is 25 μm or more, preferably 30 to 60 μm, the photoresponse becomes poor in order to obtain a long-life photoreceptor. , _Tr increase.

When the ambient temperature is low (15 ° C. or less, especially 10 ° C. or less), or depending on the type of photoreceptor, the light response is poor when the humidity is low (50% or less, especially 30% or less). For example, the time may be from 0.1 second to 0.3 second, which is a problem in mounting the device.

In the present invention, the photosensitive member having a long light response time is used, and the first developing roller 61 is moved from the position where the laser beam 3 is exposed.
To realize a high-speed compact recording apparatus. That is, from the exposure to the developing roller 6
The time (angle θ) between 1 and the developing roller 62 is set to be _tr . Particularly, it preferred to correspond to θ to t _r at a low temperature and low humidity. By doing so, the first developing roller 61 can be brought closer to the exposure section, which is extremely effective when a system combining a photosensitive drum having a short diameter and two developing rollers is desired to be used at higher speed.

In the developing roller 61, reversal development is performed in a state where the voltage of the photosensitive member is higher than a desired value. Therefore, it is important to increase the development efficiency for high-speed recording. When the first developing roller rotates in the same direction as the photoconductor and the second roller rotates in the opposite direction to perform reverse development, the disadvantage can be compensated for. That is, when the photosensitive drum and the developing roller rotate in the same direction (the moving directions of the developer and the photosensitive member in the developing area are opposite to each other), the developing property is higher than when the photosensitive drum and the developing roller rotate in the opposite directions. It has good characteristics and less fogging. On the other hand, in the development by the second developing roller rotating in the opposite direction, a smooth and uniform image is obtained. Therefore, in the present developing machine, development with good development efficiency and uniformity can be achieved, and the problem of the residual voltage described above is reduced.

Further, in the case of reversal development, the developability can be further improved by making the bias voltage applied to the first developing roller equal to or higher than that of the second developing roller, for example, by 20 to 100 V. since, it is also possible to eliminate the disadvantages of setting the t _r by adopting this method between two developing rollers.

If the layer thickness of the photoreceptor is increased, the residual voltage (charge voltage after exposure) becomes large at a low temperature, and there is a problem that the image density is lowered. I have. FIG. 7 is a diagram showing a bias application circuit for that purpose.

A resistor 44 is connected in series with the developing bias power supply 43.
The thermistor 46 is connected, and the resistor 45 is connected in parallel with the thermistor 46. In some cases, the resistor 45 can be omitted. The voltage generated in the thermistor 46 is applied to two developing rollers 61,
62. At this time, the thermistor 46 is attached so as to be in contact with the developing device 4, near the developing device 4, or a part of the developer flow, so that the resistance value changes depending on the temperature of the developer.

During the operation of the printer, the temperature of the photosensitive drum 1 is almost close to the temperature of the developer, so that when the temperature decreases, the bias voltage increases, and the operation is performed to compensate for the decrease in image density. In this manner, if the thermistor 46 is configured to be integrally attached to the developing device 4, a developing device unit that automatically compensates for a change in residual voltage due to a change in temperature of the photosensitive drum 1 can be obtained.

Further, in the developing machine having two developing rollers according to the present invention, as described above, a high quality image with less occurrence of image defects and good uniformity can be obtained, but the toner remaining on the photoreceptor before development. In contrast, the cleaning effect of the first developing roller 61 is large, so that the cleaning performance of the cleaning member 29 can be combined with the cleaning performance of the blade member without causing problems such as image fogging and toner filming on the photosensitive member. , Reduction of photoreceptor wear, and long life can be achieved.

The toner to be used in the present developing machine is preferably a toner to which magnetic powder is added. In this case, the organic photosensitive layer is easily scraped off by the cleaner blade. To suppress this, it is preferable to reduce the blade pressure. But,
If the pressure is low, the toner is not removed but remains. This limit is due to the residual toner exceeding the fog visibility limit,
This is a place where filming does not occur due to accumulation.

When these conditions were examined, when the toner amount before cleaning was 0.5 to 1 mg / cm ² and the number of toner particles remaining after cleaning was about 100 to 1000 particles / cm ² , It has been found that the generation of fogging and the formation of filming can be prevented by the cleaning action of the developing roller, particularly the first developing roller 61. Also, it was confirmed that there was no hindrance during exposure.
The toner amount of 0.5 to 1 mg / cm ² before cleaning is the case where the toner image formed by development reaches the cleaner portion without being transferred. Such a case corresponds to forming a patch image for detecting image density between sheets when there is a sheet running trouble. At the time of actual printing, the developed toner image is transferred to the paper, so there is no problem even if the cleaning efficiency is further worse, but if this performance is secured, the image is formed to fill the paper or even to the outside. At this time, there is no adverse effect when the image density detection patches are formed continuously or without interrupting the actual printing operation. This cleaning performance must be ensured during the life of the blade.

On the other hand, the relationship between the cleaning performance, the wear amount of the organic photoconductive photoconductor (OPC), and the blade life was examined. Magnetic powder externally added toner (average volume toner particle diameter 8 μm, average volume magnetic powder particle diameter 0.4 μm, external addition amount 0.5 wt%), diameter 10
A 0 mm photosensitive drum (binder composition: 50% polycarbonate resin having a molecular weight of about 100,000) is used.
0 ± 5 degree urethane rubber, thickness 2mm, free end length 12m
m, and the toner amount before cleaning was 0.8 mg / cm ² . To reduce the remaining amount of toner after cleaning to about 100 particles / cm ² or less, a blade linear pressure of 15 g / cm or more is required. At this time, the amount of wear of the OPC is about 5 μm per 100,000 rotations, and the life of the blade is 10 minutes. It was less than 10,000 revolutions.

In order to reduce the remaining amount of toner to about 1000 / cm ² or less, a blade linear pressure of 5 g / cm or more is required.
The amount of wear was 1 μm or less per 100,000 rotations, and the life of the blade was 300,000 rotations or more. Similarly, when the magnetic powder of the toner was changed using the above-described range, the cleaning performance was secured, and the amount of abrasion was set to about 1 to 3 μm per 100,000 rotations. ~ 15g / c
m, preferably 8 to 12 g / cm, and the life of the blade was found to be equal to or longer than the life of the drum.

Next, a description will be given of a developing bias condition for achieving both the residual toner removing effect in the developing machine and the developing property. First, the bias voltage Vb1 applied to the first developing roller 61 has a large effect of removing residual toner after cleaning the larger the difference to the charging voltage V ₀ which the photoreceptor. This is because the force acting on the developing roller side from the photoconductor to the toner on the photoconductor increases.

However, if the difference is too large, the developing action is reduced. Since the moving direction of the first developing roller 61 is opposite to that of the photosensitive drum 1, both the cleaning action and the developing action are larger than those of the second developing roller 62. Therefore, the voltage difference can be made relatively large.

About 100 to 1000 particles / cm of residual toner
, The residual toner is taken into the first developing roller 61 side to prevent fogging and OPC filming from occurring, and the bias voltage Vb1 at which a practical developing action can be ensured is determined by the experiment. result, when the charging voltage V ₀ which photoreceptor is 500V～1000V, about 1 V ₀
/ 3 to 2/3. Second developing roller 6
The required image density and uniform image can be obtained by applying a voltage equal to or higher than the bias voltage of the first developing roller as the bias voltage Vb2 applied to the second developing roller.
Incidentally, the reproducibility of fine lines is about V ₀ -Vb is V ₀ 1 / 3~1 /
2, it is possible to keep the thickness of the line based on the light quantity distribution of the laser spot and the thickness of the line within an acceptable range.
It is desirable that b2 also satisfies this condition.

Regarding the bias voltage applied to the developing roller, a more desirable method is that at the time of initialization such as when the printer is started, when a print job is started, or when printing is interrupted due to a paper jam, etc. One of the second developing rollers, preferably the first developing roller 61,
More preferably, the bias voltage applied to both is set lower than the bias voltage at the time of steady printing. By doing so, it is possible to quickly and reliably remove the residual toner and dirt.

[0073]

As described above, according to the present invention, the pressure contact of the cleaner blade member to the photosensitive member can be reduced, and the life of the photosensitive member and the blade member can be extended. Can be.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a laser printer according to an embodiment of the present invention.

FIG. 2 shows the laser printer shown in FIG. 1 in which the peripheral speed ratio S2 between the second developing roller and the photosensitive drum is varied with respect to the peripheral speed ratio S1 between the first developing roller and the photosensitive member (photosensitive drum). FIG. 9 is a characteristic diagram summarizing evaluation of an image state when an image is formed by changing the image state.

FIG. 3 shows a peripheral speed ratio S1,
FIG. 4 is a characteristic diagram showing a preferable range of S2.

FIG. 4 is a ratio of a sliding force F1 of a first developing roller to a photosensitive drum and a sliding force F2 of a second developing roller to a photosensitive drum in the laser printer of FIG.
FIG. 9 is a characteristic diagram summarizing evaluations of (F1 / F2) and other characteristics.

FIG. 5 is a characteristic diagram showing a preferable range of a gap between two developing rollers and a photosensitive drum in the laser printer of FIG. 1;

FIG. 6 is a characteristic diagram showing a light response characteristic of a photoconductor and a set position of a developing machine.

FIG. 7 is a circuit diagram of a bias application circuit in the laser printer of FIG. 1;

FIG. 8 is an explanatory diagram showing a state of an image defect.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photoreceptor drum, 2 ... Charger, 3 ... Laser beam, 4 ... Developing machine, 14 ... Recording paper, 19 ... Transfer device, 25 ...
Fixing device, 29 Cleaner, 61 First developing roller, 62
... Second developing roller.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Katsuya Kawai, 1060 Takeda, Hitachinaka-shi, Ibaraki, Hitachi Koki Co., Ltd. (72) Inventor Tsutomu Nakagawa 1060 Takeda, Hitachinaka-shi, Ibaraki, Hitachi Koki Co., Ltd. (72) Inventor Seiki Hohashi 1060 Takeda, Hitachinaka City, Ibaraki Prefecture Within Hitachi Koki Co., Ltd.

Claims (6)

[Claims] 1. A method comprising: exposing a charged organic photoconductive photoreceptor to light by an exposing means to form an electrostatic charge latent image comprising a combination of a light-exposed portion and a non-exposed portion on the photoreceptor; By a first developing roller and a second developing roller that are arranged along the moving direction of the photoconductor and rotate in opposite directions to each other, development is performed with a developer containing a magnetic carrier and toner containing magnetite fine particles as main components, Developing means for forming a toner image on the photoreceptor; and a blade member provided in pressure contact with the surface of the photoreceptor, for removing toner remaining on the photoreceptor after the toner image is transferred to recording paper. An electrophotographic apparatus having a cleaning unit, wherein the moving direction of the first developing roller is opposite to the moving direction of the photoconductor, and the peripheral speed (Vd1) of the first developing roller and the peripheral speed of the photoconductor are changed. Peripheral speed ratio with speed (Vp) ( S1 = Vd1 / Vp) is regulated in the range of 0.5 to 2.5, the moving direction of the second developing roller is the same as the moving direction of the photoconductor, and the peripheral speed of the second developing roller ( Vd2) and a peripheral speed ratio (S2 = Vd2 / Vp) of the peripheral speed (Vp) of the photoconductor are restricted to a range of 1.5 to 3.5, and the first developing roller and the second developing roller An electrophotographic apparatus, wherein an action of removing unnecessary toner remaining on the photoreceptor is generated according to a relationship of a peripheral speed ratio. 2. An electrophotographic apparatus according to claim 1, wherein an unnecessary toner removing action of said first developing roller is larger than that of said second developing roller. 3. A developing device according to claim 1, wherein a developing bias is applied to said first and second developing rollers, and a developing bias voltage applied to said first developing roller is changed with respect to a latent image voltage of said non-exposed portion. To about 1/3 to 2/3,
An electrophotographic apparatus, wherein a developing bias voltage applied to the second developing roller is specified to be equal to or higher than a developing bias voltage applied to the first developing roller. 4. An electrophotographic apparatus according to claim 1, wherein said blade member is arranged in counter contact with said photoreceptor surface, and its linear pressure is regulated to 5 to 15 g / cm. . 5. The toner according to claim 1, wherein the toner has a volume average particle size of 5 to 12 μm, and the number of toner particles remaining after cleaning a toner weight of 0.5 to 1 mg / cm ² on the photoreceptor. The electrophotographic apparatus is characterized in that when the life of the blade member is about 100 to 1000 pieces / mm ² . 6. An organic photoconductive photoreceptor having a thickness of 20 to 60 μm, charging means for charging the organic photoconductive photoreceptor, exposing the charged photoreceptor to a light-exposed portion and a non-exposed portion A first developing roller and a second developing roller that are arranged along the moving direction of the photoconductor and rotate in opposite directions to each other;
Magnetic particles of 0.5 to 2 Wt% are added externally or 0.5 to 20 Wt%.
Developing means for developing the light-exposed portion using a developer containing a toner in which Wt% of magnetic fine particles are internally added; and a developing means provided in pressure-contact with the surface of the photoreceptor; A cleaning unit having a blade member for removing the toner remaining on the photoreceptor after the obtained toner image is transferred to the recording paper, wherein the moving direction of the first developing roller is The peripheral direction ratio (S1 = Vd1 / Vp) between the peripheral speed (Vd1) of the first developing roller and the peripheral speed (Vp) of the photoconductor is opposite to the moving direction of the photoconductor.
The moving direction of the second developing roller is the same as the moving direction of the photoconductor, and the peripheral speed (Vd2) of the second developing roller and the peripheral speed (Vp2) of the photoconductor are regulated. ) And the peripheral speed ratio (S2 = Vd2 / Vp) is 1.
5 to 3.5, the developing bias voltage applied to the first developing roller is regulated to about 35 to 70% with respect to the latent image voltage of the non-exposed part, and the second developing roller The applied developing bias voltage is regulated to be equal to or higher than the developing bias voltage applied to the first developing roller, and the linear pressure of the blade member pressed against the surface of the photoreceptor is regulated to 5 to 15 g / cm. Electrophotographic equipment.