JPH0212281A - Image producing method - Google Patents

Abstract

PURPOSE:To produce a high-quality image and to miniaturize a device by bringing a destaticized electrostatic latent image carrier into contact with a magnetic brush retained on the developing sleeve of a first developing unit, of which the impressed bias voltage is switched so as to be higher than during developing. CONSTITUTION:A toner image is transferred on an image-transferred body 17 in a transfer area Y, while the surface of an electrostatic latent image carrier 2 of which the toner image is deprived is destaticized by an eraser lamp 8. When toner retaining electrostatic charge comes in a first developing area X1, the developing bias voltage VB1 of a first developing sleeve 41 is already switched so as to be higher than during the developing. Electrostatically charged toner is recovered to the developing sleeve 41 by means of static electricity based on a voltage difference between the developing bias voltage VB1 and the surface potential of the electrostatic latent image carrier 2, and the scrape- off action of the magnetic brush on the developing sleeve 41. As a result, the necessity of a cleaning device is eliminated when two units of developing units are provided on the device to obtain the high-quality image, and the device can be thereby made compact and multifunctional.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention comprises two developing devices around an electrostatic latent image carrier,
The present invention relates to an image forming method for forming an image by driving these developing devices.

(Prior Art and its Problems) Conventionally, as an image forming apparatus, a magnetic brush-like two-component developer held on the surface of a developing sleeve is brought into contact with the surface of an electrostatic latent image carrier to form an electrostatic latent image. Electrostatic toner supply devices have been provided.

In this type of image forming apparatus, the developer filling rate (P, D) of the developing area where the electrostatic latent image carrier and the developing sleeve face each other is P, D=Vd/Ds d: The developer passes through the developing area per unit time. Developer amount Ds: The distance between the developing sleeve and the electrostatic latent image carrier has a great effect on the image quality of the created image, and increasing the developer filling rate (P, D) will improve density reproducibility. Thin line reproducibility decreases, and conversely, if the developer filling rate (P, D) is lowered, density reproducibility decreases but fine line reproducibility improves.

In other words, in the image forming apparatus, density reproducibility and fine line reproducibility are opposite to each other; if density reproducibility is prioritized, fine line reproducibility decreases, and conversely, if priority is given to fine line reproducibility, density reproducibility decreases. The image quality tends to decrease, and which image quality is prioritized depends on the value of the developer filling rate.

Therefore, conventionally, as long as a single magnetic brush type developer using a two-component developer is used, an image that satisfies both density reproducibility and fine line reproducibility cannot be obtained. Ta.

Therefore, the present inventors conducted various studies to obtain images with good density reproducibility and fine line reproducibility using a magnetic brush type developer, and as a result, they installed two developing devices around the electrostatic latent image carrier. The developing devices are arranged such that the developer filling rate of the first developing device, which has priority in the development order, is set high, while the developer filling rate of the second developing device located downstream of the first developing device is set to the first developing device. By driving the first and second developing devices simultaneously to develop the same electrostatic l() image on the electrostatic latent image carrier twice with toner of the same color, the density reproducibility is lower than that of the developing device. It has been found that images with excellent fine line reproducibility can be obtained.

That is, according to this method, the image density is ensured in the first developing device, and the reproducibility of fine lines is ensured in the subsequent second developing device.

However, in order to obtain high-quality images with excellent density reproducibility and fine line reproducibility as described above, at least 2
A standalone developer is required.

However, in recent years, there has been a demand for miniaturization of image forming apparatuses, and it is necessary to provide a compact and multifunctional apparatus that is equipped with the above-mentioned high-quality image creation function.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a compact image creation method that is capable of creating high-quality images.

(Means for Achieving the Object) The image forming method of the present invention has been made to achieve the above object, and will be described with reference to FIG. 1 showing one embodiment. (1) First development The developing sleeve (41) of the device (4) supplies toner to the electrostatic latent image formed on the surface of the electrostatic latent image carrier (photosensitive drum) (2) in the opposing first development area (X+). (11) The developer filling rate of the developing area is lower than the developer filling rate (P, Dυ) of the first developing area (xl).
(iii) supplying toner of the same color as that of the first developing device (4) to the electrostatic latent image from the developing sleeve (51) of the second developing device (5); The supplied toner is transferred to the transfer object [transfer paper] (17) in the transfer area (Y).
(1v) Discharge the surface of the electrostatic latent image carrier (2) that has passed through the transfer area (Y), and (v) transfer this discharged electrostatic latent image carrier (2) to the surface of the electrostatic latent image carrier (2) that is The magnetic brush is brought into contact with the magnetic brush held on the developing sleeve (42) of the first developing device (4) whose bias voltage (VB,) is switched to a higher voltage than that during development.

(Function) According to the image forming method, toner is successively supplied to the electrostatic latent image on the electrostatic latent image carrier (2) from the first developing device (4) and the second developing device (5). .

Here, the developer filling rate (P, D,) of the first development area (Xl) where the development sleeve (41) of the first development device (4) faces the electrostatic latent image carrier (2) is Since the developing sleeve (51) of the developing device (5) is set higher than the developer filling rate (P, Dt) of the second developing area (X,) facing the electrostatic latent image carrier (2), The electrostatic latent image has density reproducibility,
Poor reproducibility of thin lines! It is reproduced as a high-quality toner image.

The toner image is transferred to the transfer target (17) in the subsequent transfer area (Y).
The surface of the electrostatic latent image carrier (2), which has thus lost its toner image, is charged with an eraser lamp (8).

However, it is not possible to remove the charge of the toner remaining on the surface of the electrostatic latent image carrier (2) without being transferred in the transfer area (Y).

Therefore, the charged toner is transferred to the first development area (
When reaching X, ), the first developing sleeve (
The developing bias voltage (Van) of 41) is switched to a higher voltage than that during development, and static electricity is generated due to the 7 μ pressure difference between the developing bias voltage (■ゎ1) and the surface potential of the electrostatic latent image carrier (2). Due to the force and the scraping action of the magnetic brush on the developing sleeve (41), the charged toner is transferred to the developing sleeve (41).
1) is recovered.

(Example) An example of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a sectional view showing the main parts of an electrophotographic copying machine, in which a photosensitive drum (2) is arranged approximately in the middle of the copying machine (1) so as to be rotatable in the direction of arrow (a). The body drum (2) used has a circumferential length longer than the maximum length of transfer paper that can be used in the copying machine (1).

Around the photoreceptor drum (2), there is a charger (3).
, first developer (4), second developer (5), transfer charger (6), separation charger (7), eraser lamp (8)
) are placed.

Above the photoreceptor drum (2), the opening/closing cover (10
) An optical system (12) having an exposure lamp (13) is disposed below the document table glass (11) covered with a glass plate (11).

The developers R3 (4) and (5) are magnetic brush type developers that use a two-component developer consisting of toner and carrier, in which the toner is charged positively and the carrier is charged negatively by frictional contact with each other. There is a developing sleeve (4
1) and (51) are respectively arrows (C).

It is housed so as to be rotatably driven in the direction (d), and has a predetermined height regulating gap (D b ,) on its upper outer circumferential surface.

(Db2), the height regulating portions (42) and (52) are opposed to each other.

Further, the developing sleeves (41) and (51) are respectively opposed to the photoreceptor drum (2) with predetermined developing gears (Ds, ), (Dst), and the developing sleeves (
41), developer filling rate (p,
Dt) is the developer filling rate of the development area (Xυ) (P, D
), the developer filling rate of the development area (X2) is (p, Dt)
Then, the relationship is set as P, D, > P, D.

Note that the developer filling rate (P, D) is expressed by the following formula.

P, D=Vd/Ds V(1・Amount of developer passing through the development area per unit time.

Ds/Development gap.

In addition, the developing sleeves (41) and (51) are powered by a power source (43).
, (53), the developing bias voltage (v I11+)+
(V a,) are applied, respectively, and their values are variable.

Copying machine (1) with the above configuration? The 9-photographing operation will be explained with reference to FIG.

i (J) When the print switch (not shown) of machine (1) is turned on and the main motor (not shown) starts,
After the photoreceptor drum (2) starts rotating in the direction of arrow (a), the charger (3) is turned on and the photoreceptor drum (
2) No (surface is at a predetermined potential (Vo--500 (V))
is charged with electricity.

Next, scanning is performed in the direction of arrow (b) while the exposure lamp (13) is turned on, and a document (not shown) placed on the document table glass (11) is irradiated with light, and the reflected light (1 m )
is exposed onto the surface of the photoreceptor drum (2) from an exposure point (14) through a lens and a mirror, and an electrostatic latent image corresponding to the original image is formed.

Next, the first. As the second developing units (4) and (5) start, the power supplies (43) and (44) apply a predetermined developing bias 7u to their developing sleeves (41) and (51).
A pressure [■B1, v, , -15o(v)] is applied, and the surface potential of the photoreceptor drum (2) and the developing bias voltage (V
Toner charged to a positive polarity is electrostatically supplied based on the potential difference of B+)+ (v ot).

Here, the developer filling rate (P, D,
) is higher than the developer filling rate (P, D, ) of the development area (X2).

Therefore, in the first development area (Xυ), there is a high probability of contact between the electrostatic latent image and the developer, and a toner image of sufficient density is formed.However, while the development efficiency is high, the photoreceptor drum ( In 2), there is a high probability that toner adhering to the surface will be scraped off by the magnetic brush, and in particular, toner adhering to thin lines is more easily scraped off than solid images or ordinary character images.

However, charges are still retained on the photosensitive drum (2) where the toner has been scraped off in this manner.

Next, in the second development area (X2), the first
Toner of the same color as the first developer 2a (4) is supplied onto the toner image formed in the development area (X,) and on the traces where the toner was scraped off.

However, the developer filling rate (P, D2) here is low, and the probability that the developer comes into contact with the photoreceptor drum (2) is low.

Therefore, the probability that the toner running parallel to the surface of the photoreceptor drum (2) will be scraped off by the magnetic plan is low, and the fine line static
Enough toner is applied to the F1 latent image to make it into an inkstone image.

From the above, the electrostatic latent images of normal character images and area images that have passed through the development areas (X +) and (X t) are reproduced with sufficient density, and the electrostatic latent images of thin lines are also reproduced with sufficient density. Reproduced in a visualized state.

The toner image formed in the development area (Xυ, (X,) is conveyed to the transfer area (Y) opposite to the transfer charger (6), and is synchronized with the toner image based on the discharge of the transfer charger (6). The image is then transferred onto a transfer paper (17) that is conveyed by a timing roller (15).

The transfer paper (17) on which the toner image has been transferred is separated from the surface of the photoreceptor drum (2) by the discharge of the separation charger (7), and is conveyed to a regular feeding device (not shown) by the transfer conveyor (16). The toner image is fused and fixed on the transfer paper (17) and discharged to the stray paper section.

On the other hand, when the scanning operation of a predetermined length by the exposure lamp (13) is completed and all the developed images to be printed are exposed, the charger (3) and the exposure lamp (13) are turned off one after another. Note that the circumference of the photosensitive drum (2) is greater than or equal to the maximum length of the transfer paper (17) planned for the machine (1), so when the scanning operation is completed, the leading edge of the document The electrostatic latent image corresponding to has not yet reached the exposure point (14).

Next, when the electrostatic latent image corresponding to the end of the original image passes through the first development area (Xl), the development bias voltage (V
at) is switched from -150 (V) to -400 (V).

On the other hand, the eraser lamp (8) has been kept in the on state since the main motor started, and any residual charges are removed from the surface of the photoreceptor drum that has passed through the transfer area (Y) by the light irradiation from the eraser lamp (8). Ru.

Here, even after the transfer, some untransferred positively charged toner remains on the surface of the photoreceptor drum (2), and the charge of the charged toner cannot be completely removed even by light irradiation from the eraser lamp (8). However, it remains electrostatically attached to the surface of the photoreceptor drum (2) while still being positively charged.

The surface of the photoreceptor drum (2) that has passed through the portion facing the eraser lamp (8) passes through the portion facing the charging roller (3) and reaches the development area (Xυ).

In the developing area (X,), a magnetic brush held on the surface of the developing sleeve (41) rotating in the direction of arrow (C) is in contact with the surface of the photoreceptor drum (2), and the untransferred surface is removed by the magnetic brush. charged toner is scraped off. Note that the untransferred charged toner has a positive charge, and a developing bias voltage of -400■ is applied to the developing sleeve (41).
V at) is applied, and the charged toner is electrically drawn to the developing sleeve (41). Therefore, the binding force between the charged toner and the photoreceptor drum (2) is weakened, and the toner is easily scraped off by the magnetic brush.

Therefore, the surface of the photoreceptor drum (2) that has passed through the first development area (Xl) has been cleaned so that there is almost no untransferred toner.

As described above, when the outer circumference of the photoreceptor drum (2), where at least an electrostatic latent image corresponding to the original image is formed, is cleaned in the development area (Xυ), the main motor When the developing device (4) and the second developing device (5) are stopped, the developing bias '11 pressure (V-, ),
(V112) is shut off and the developing operation ends.

(Experiment) Hereinafter, the developer filling rate was set to P by setting the first developing device (1) and the second developing device (2) to the following conditions.

When D, > P, D2 are set in the relationship, and the development IH (1) and (2) set in this way are driven individually, and when these development as (1) and (2) are driven simultaneously. 100μm 150μm when the same electrostatic latent image is developed twice
The fine line reproducibility of fine lines and the degree reproducibility of image density (1, D) were evaluated using copied images.

, Photosensitive drum (100) Peripheral speed -150mm/sec 1, Developing sleeve (10) Outer diameter...2D5mm Rotation speed...143.64rpm Developing gap [)S, -Q, 4mm D S 2"' 1, 2 mm Bread height regulation gap ob +... 0, 5 mm D b t-0, 45 mm Bottom casing (3) and interval... 1.Qmmiii
, magnetic body (11) Second developer (2) See Figure 2.3 First developer (1) Remove the magnetic poles (N, ) and (S5) from the second developer (1).

iv, Bucket roller (13) Outer diameter...34mm Rotation speed...179.55rpm V Screw (15) Outer diameter...20.0mm Rotation speed...100100 rp, Developer toner...Positive charging Insulating non-magnetic toner carrier...
・Average particle size: 57 μm Binder-type insulating magnetic carrier resistance: to”Ω-cm The results of the experiment are shown in FIG. 4.

Note that, as shown in the figure, fine line reproducibility is determined by the copy image density (1
, D) with different line widths of 50 μm and 100 μm in the vertical and horizontal directions, and was evaluated based on the following evaluation based on the reproducibility of the lines perpendicular to the paper feeding direction.

Rank Evaluation Contents 1 1, Dl, 5 lines are perfectly reproduced 2 1D1.5~1. The line of Dl, 2 is completely reproduced 3
1, Dl, 5-1. Do, the line of 9 is completely reproduced 4
1, Dl, 5-1. Do, 6 line is completely reproduced 5 1
, Dl, 5-1. DQ, the line of 4 is completely reproduced.As a result,
When the first developing device (1) is driven alone, A in FIG.
As shown in the column, the fine line reproducibility is ranked "3.5" for 100 μm fine wire and "4.5" for 50 μm fine wire.
q photo image density 1. D) was "1.47".

Next, when the second developing device (2) is driven independently, the fourth developing device
As shown in column B of the diagram, the 1100u thin line has a rank of “4.5”.
°°, 50 μm thin line is ranked “5”, copy image production +3
1i(1,D) was 0.62.

Subsequently, when the same electrostatic latent image is developed twice by driving the first developing device (1) and the second developing device (2) at the same time, the image becomes 100 μm.
A thin line has a rank of “5”, a 50 μm thin line has a rank of “4.5”
The values were the same as those of the second developing device (2). Also, the copy image density (1, D) is 1.48, which is the first
The value was almost the same as that of developer (1).

In this way, the first development 11ffl(
1) and a second developing device (2) with a lower developer filling rate than this.
) is used to develop the same electrostatic latent image twice, the density reproducibility of the reproduced image is the same as the image obtained by driving the first development Mu (1) alone, and the fine line reproducibility is Second developer (2
), an image with excellent density reproducibility and fine line reproducibility was obtained, which was the same as the image obtained by driving the 3000A alone.

In the above embodiment, the first and second developing units (1), (2
), the developer filling rate was changed by changing the developing gap (1)sυ, (DS2), or the height regulating gap (Db) and the rotation speed of the developing sleeve (10) were changed to the 1st and 2nd developing device. The developer filling rate may be changed by changing (1) and (2).

(Effects of the Invention) As is clear from the above explanation, according to the image forming method according to the present invention, it is not necessary to provide an IJ-ning device on the side of the electrostatic latent image carrier, and a high-quality image can be obtained. Therefore, even if two developing devices are provided, space is saved since a cleaning device is not required, and a compact and multifunctional image forming apparatus can be provided.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the main parts of the copying machine, FIG. 2 is a timing chart, and FIG. 3 is a diagram showing the results of experiments regarding l button reproducibility and fine line reproducibility. ■...'ta photosensitive drum, 4...first developing device, 5...second developing device, 6...transfer charger, 8...erasing lamp, 13...・Exposure lamp, 1
7... Transfer paper, 41, 51... Developing sleeve, 42.
52...Hot height regulation part, X,,X,-...Development area, D
s,,Ds. ...Development gap, Vb, , V, 1. ...Bear height regulation gap, V[11+V, 2...Bias voltage. Patent applicant Minolta Camera Co., Ltd.

Claims (1)

[Claims] (1) The developing sleeve of the first developing device supplies toner to the electrostatic latent image formed on the surface of the electrostatic latent image carrier in the opposing first developing area, and adjusts the developer filling rate of the developing area. Supplying toner of the same color as that of the first developing device to the electrostatic latent image from a developing sleeve of a second developing device whose developer filling rate is lower than that of the first developing area, and supplying the same color toner to the electrostatic latent image carrier. The toner is transferred to a transfer target in a transfer area, the surface of the electrostatic latent image carrier that has passed through the transfer area is neutralized, and the applied bias voltage is applied to the electrostatic latent image carrier from which the static electricity has been removed during development. An image forming method characterized in that the magnetic brush is brought into contact with a magnetic brush held on a developing sleeve of a first developing device whose pressure has been switched to a higher voltage than that of the first developing device.