JPH04152363A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent mixing of colors, to obtain a high quality image with excellent gradation and to improve image quality by providing multiple color and monochromatic modes, combining most suitably latent images in first, color second and subsequent colors, with developing biases, and carrying out exposure by means of binary writing and multivalue writing respectively. CONSTITUTION:As for a developing means 7 in the second and subsequent colors by applying a DC bias in the case of the multiple color mode, mixing of the colors, which is caused by reverse flying of the first toner on an electrostatic latent image carrier 1, is prevented. By applying periodically varying bias in the monochromatic made, a high quality image with excellent gradation can be obtained. Further, in the case where exposure by the use of laser beams 3 and 6 is carried out, a latent image which has area gradation obtained by the binary writing in the multiple color made or has multivalue gradation obtained by the multivalue writing in the monochromatic mode is exposed. Thus, the high quality image can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (l Lid Color Goryuji! The present invention is an electrostatic latent image formed on an electrostatic latent image carrier by exposure to a plurality of developing means. The present invention relates to an image forming apparatus that forms a multicolor image by sequentially developing the image and then transferring it to a transfer material at once.

BACKGROUND ART As an image forming apparatus capable of obtaining a multicolor image, for example, as a first conventional example, a plurality of developing means are provided around a latent image carrier to obtain a multicolor image. The toner polarity of the developing means on the F flow side is opposite to that of the upstream one, and its toner layer does not come into contact with the latent image carrier. During development, an alternating fL electric field is applied to develop this toner. During development, an electric field is applied to develop the toner on the upstream side, the toner layer thickness is set to 30 to 500 μm, and a two-component developer containing chromatic toner is used in the upstream developing means, and the downstream developing means A method using a one-component developer of male toner has been proposed (see Japanese Patent Laid-Open No. 61-60471).

In addition, as a second conventional example, the thickness of the photosensitive layer is 35 to 90 μm.
A plurality of developing means are disposed around a selenium or arsenic selenide photoreceptor with a capacitance of 20 to 170 pF/i, and charging, exposure, and development are repeated multiple times to form a photoreceptor on the same photoreceptor. An image forming apparatus for obtaining a color image has been proposed in which the developing means is a non-contact DC bias development with a photoreceptor using a thinned toner of 250 IJm or less (Japanese Patent Application Laid-Open No. 63-063-1989). (see publication).

In this device, the rollers that do not contribute to development are stopped! The surface toner is attached outside the image line area to prevent color mixing, the photoreceptor is OPC of 15 to 50 μm, the development is reverse development, the potential contrast is 400V or more, and the toner layer thickness on the photoreceptor is is set to 5 to 30 μm, and the charging is set to scondron.

A third conventional example is an image forming apparatus in which a plurality of developing means are disposed on a recording medium in a non-contact state to obtain a multicolor image, and the peripheral speed of the first developing means on the upstream side is set to the same level. The direction rotation is made faster than the recording medium, black development is applied, and an alternating current bias biased to DC is applied, and the downstream second developing means and subsequent parts are made to be constant-velocity images, color development, and DC bias is applied. An image forming apparatus has been proposed in which only the voltage is applied (see Japanese Patent Application Laid-open No. 85578/1983).

When forming a multicolor image on a carrier with an electrostatic latent image, which is the problem to be solved by the present invention, 2.
The development method after color is non-contact development.

As a developing method, a developing method using non-magnetic toner that can easily be colored is preferred, and a one-component developing method that is particularly advantageous for downsizing and cost reduction is preferable.

In this method, the toner layer and the latent image are developed by making them face each other in a non-contact manner. However, when developing the second color, the toner image is formed on the electrostatic latent image carrier, so for example, When an AC bias is applied as a developing bias as in the first conventional example, the toner moves back and forth between the latent image surface and the toner carrier surface, which not only disturbs the first color toner image but also There is a problem in that the toner of the first color gets mixed into the medium and the image of the second color gradually becomes cloudy.

In order to prevent this problem, as in the second and third conventional examples, development for the second and subsequent colors should be performed using a method in which non-magnetic toner is ejected using a DC electric field. In flying development, the toner does not fly unless the electric field at which the toner starts flying in the development area, that is, the threshold electric field, is exceeded.However, the value of this threshold electric field depends on the charging of each toner,
This value depends on van der Waals forces, etc., and has a large variation. Therefore, if the exposure method is multivalue writing using laser light, the image will have strong graininess in low contrast areas, resulting in a smooth image. I can't get an image.

Therefore, the present invention solves the above problems in the conventional technology, and
It is an object of the present invention to provide an image forming apparatus that can prevent color mixing due to back flight of toner during development of a second color and subsequent colors, and can obtain high-quality images with gradation in monochrome mode.

In order to solve the above-mentioned problem, the invention of claim 1 provides a method for processing an electrostatic latent image formed on an electrostatic latent image carrier by exposure to a plurality of different developing means. An image forming apparatus that forms a multicolor image by sequentially developing with different color toners and then transferring the images to a transfer material at once, the image forming apparatus has a multicolor mode and a monocolor mode, and a second color image among the plurality of developing means is provided. 3. The developing means thereafter performs development by applying only a DC bias when in the multi-color mode, and by applying a periodically changing bias when in the mono-color mode. In addition to the above, the invention provides a method in which the exposure is performed using a laser beam emitted in response to an image signal, and the electrostatic latent image formed for development of the second and subsequent colors is:
The invention according to claim 3 is characterized in that when in the multicolor mode, area gradation is formed by binary writing, and when in the monochrome mode, gradation is formed by multivalue writing. In addition to the above characteristics, the developing means for the second and subsequent colors includes a toner carrier that forms a non-magnetic one-component toner layer, and is of a type that causes the toner layer to fly onto the electrostatic latent image, The toner layer in the development area of the toner carrier has a mass per unit area of 0.5 to 1.5-g/cs, and an absolute value of charge per unit mass of 5 to 30 μC/cs. g range.

According to the invention of claim I, in the developing means for the second and subsequent colors,
In the multicolor mode, only a DC bias is applied, so that the first color toner does not fly backwards onto the electrostatic latent image carrier, and color mixing due to the backward flight is prevented. On the other hand, in the monochrome mode, a high-quality image with gradation can be obtained by applying a periodically changing bias, for example, a DC superimposed AC bias or a pulse bias.

According to the invention of claim 2, in addition to the above, when the exposure is performed with laser light, in the multicolor mode, the exposure is performed so as to form a latent image having area gradation by binary writing; In the monochrome mode, a high-quality image can be obtained by performing exposure to form a latent image with multi-value gradation by multi-value writing.

According to the invention of claim 3, in addition to the effect of the invention of claim 1, since the mass and charge amount of the toner layer are set to numerical values within the predetermined range as described above, the electrostatic latent image carrier and the toner carrier are It is possible to develop a binary image with a DC electric field and obtain sufficient image density even if the image is moved at approximately the same speed. F@2
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Embodiment FIG. 1 shows a schematic structure of an image forming section of a laser printer which is an example of an image forming apparatus to which the present invention is applied.

Around the drum-shaped photoreceptor l as an electrostatic latent image carrier, a first charger 2, a first developer 4 as a plurality of developing means, a second belt container 5. A second developing device 7 as a developing means, a transfer charger 9 and a cleaning device 11
are arranged, and the first exposure 3 and the second exposure 6 as laser light are transmitted between the first charger 2 and the first developer 4 and between the second charger 5 and the second developer 7. The light is irradiated onto the photoreceptor l.

First, a multicolor mode for forming a multicolor image will be explained.

The surface of the photoreceptor 1 is charged by the first charger 2, and the first
Exposure 3 forms a static fl latent image thereon. This first exposure is a laser beam emitted by an optical writing optical system (not shown) in response to an image signal, and can form a latent image having a multilevel wi tone. Next, the first developing device 4
The latent image is developed to form a first toner image. In this first developing device 4, character images are often developed using male toner, so it is preferable to use a system with high image resolution. A contact development method using a magnetic blank of a two-component developer is preferable. Next, the surface of the photoreceptor 1 is charged again from above the first color toner image by the second charger 5, and the first exposure is carried out. Make the potential state of the affected area equal to or higher than that of the surrounding area. Then, a second electrostatic latent image is formed on the photoreceptor l by the second exposure 6. The second exposure 6 is similarly a laser beam emitted by the optical writing optical system, but forms a binary latent image that requires a small memory. In this exposure, by not exposing the portion to which the first color toner is attached, it is possible to prevent the second color toner and the first color toner from colliding with each other on the photoreceptor and causing the color to become muddy.

Subsequently, the second electrostatic latent image is developed by the second developing device 7. As the second developing device 7, it is suitable to use a non-magnetic toner that can be easily colored.In particular, a one-component non-contact type which is advantageous for downsizing and cost reduction is suitable, and as a developing bias. performs flying development using a DC electric field that can prevent the toner of the first color from flying back to the second developing device 7 of the second color.

Through the above process, a multicolor image is sequentially formed on the photoreceptor 1, and the multicolor image is transferred at once to the transfer material on the conveyance path 8 by the transfer charger 9.

The toner image on the transfer material is fixed by a fixing device IO to complete the image. On the other hand, the untransferred toner on the photoreceptor 1 is
It is scraped off by the cleaning device 11, and the photoreceptor 1 is made ready for image formation again.

Next, the image forming order in the monochrome mode will be explained.

The photoreceptor is charged by a first charger 2 and a latent image having a multivalued Fa tone is formed by a first exposure 3.

At this time, it is preferable that the first developing device 4 is retracted so as not to be in contact with the latent image surface. Color development is then performed by the second developing device 7. In this development,
Development is performed by applying a pulse bias that can control the amount of toner adhesion in accordance with the potential of the latent image, and a monochrome image with smooth gradation and high definition is obtained.

FIG. 2 is an enlarged view of the second developing device 7 shown in FIG. 1, and the non-contact developing method for the second and subsequent colors will be explained in more detail.

The second developing device 7 is a developing device that uses non-magnetic one-component toner. A toner 26 of a different color from the first color is supplied to the toner hopper 25 and stirred by an agitator 24.

The toner sent to the toner supply member 22 is charged by friction with the developing roller 2</b>I, which is a toner carrier, and adheres to the developing roller 21 .

The toner adhering to the developing roller 21 is formed into a uniform toner layer by the toner layer forming member 23 and conveyed to the developing area. In this case, the amount of toner attached to the developing roller 211- is preferably such that a partial image density can be obtained even if the developing roller 21 and the photoreceptor I face each other without contacting each other and move at approximately the same speed.

If there is a speed difference between the developing roller 21 and the photoreceptor 1, the toner develops toward the trailing edge, resulting in non-uniform density in solid areas, which is a problem in color images. Therefore, the developing roller 21F has an it (M/A) of 0 per medium area.
．． A toner layer having a density of 5 to 1.5 B/cm2 is formed, and development is carried out by holding the photoreceptor 1 and the toner layer in a non-contact manner.

When the multicolor mode is specified, development is performed from the photoreceptor 1 on which a toner image has already been formed, so that flying development using a DC electric field is used, which can almost completely prevent color mixing due to back flight of toner.

On the other hand, in development using a direct current electric field, the latent image becomes an image with strong graininess in low-contrast areas, resulting in deterioration of reproducibility. For this reason, by forming a latent image by area gradation using a binary incorporation method, it is possible to obtain a good image with uniform density from a low density part to a high density part of the image.

When the monochrome mode is specified, there is no risk of toner color mixing, so the optimum developing bias for reproducing a latent image with multivalued gradation is applied.

This bias preferably has periodic changes, and is a DC superimposed AC bias or a pulse bias.

In order to make the nonmagnetic toner layer fly in accordance with the strength of the electric field, the following bias is preferable. That is, when the toner has the same polarity as the latent image and has a negative charge, the voltage is a high voltage part of -600μ or more, and -
It consists of a low voltage part of 600V or less, and the frequency is 500V.
The bias ranges from 5000 Hz to 5000 Hz, and the high voltage time ratio in one cycle is 50% or less, preferably approximately 30%. By doing so, it is possible to smoothly reproduce a latent image having a multivalued gradation in the range of a charged potential of -800 cm and a writing partial potential of -700 cm to -100 cm.

The toner layer on the developing roller 2I is directly Ili! In both the flying development using an electric field and the flying development using a pulse bias, the character image must be clear and the solid portion must be uniform. Therefore, the toner layer needs to be a multilayer toner layer in which the absolute value of the amount of charge per unit mass (Q/M) on the developing roller 21 is in the range of 5 to 30 μC/g. This is because when the Q/M is 5 IC/g or less, there is a problem that character images become thicker when a periodic bias such as a pulse bias is applied to perform flight development, and the Q/M is 30 IC/g or less. This is due to the problem that if it is more than g, it becomes difficult for the toner to fly under a DC electric field and the image density decreases. In this case, the measurement of Q/M is by the bite method, with 10
The amount of charge was measured by sucking in about mg of toner.

As such a developing roller 21, a roller having a bare aluminum surface subjected to a sandblasting process is known. However, when multiple layers of toner are conveyed using mechanical unevenness, there are problems with durability, such as the toner on the surface layer scattering and contaminating the inside of the device, or the toner getting stuck in the recesses. Therefore, in the present embodiment, the developing roller 21 has at least one of the plurality of portions on the surface having the characteristic of a stomach having a charge retention function, and when a charge is applied to that portion, the characteristic becomes more different than that of 20. The toner is intended to be held by an electric field formed between the parts having .

As shown in FIGS. 3(a) and 3(bl shows an example of such a roller, and the developing roller 2I is shown in the same figure), details of the surface A part are shown, a grid pattern or a fleur-de-lis pattern is formed on the bare aluminum surface. The dielectric portion 21a and the conductive portion 21b are formed by providing a knurled groove in the shape of a shape, and a fluorine-based or Noricon-based resin is embedded as a dielectric material.

By using such a roller, it is possible to form a multi-layered toner layer with high fluidity and good flying efficiency, and to provide the toner for development.

Practical example: In FIG. 1, a drum-shaped organic photoreceptor is used as the photoreceptor l. When the multicolor mode is designated, a latent image having multiple Vi gradations is formed on the charged photoreceptor 1 by the first exposure 3, and this is developed with toner. 20-grade development is performed using a contact development method using a two-component magnetic plano to obtain clear images of characters. Then, the photoreceptor l on which the toner image is formed is charged again, and a second electrostatic latent image is formed by the second exposure 6. This second exposure 6
forms a latent image with area gradation using a binary writing method that requires a small memory. In this case, the potential on the photoreceptor 1 is 1900 V at the toner portion, 1800 V at the charging portion, and 1100 V at the writing portion. In the second color development, the linear velocity of the photoreceptor 1 and the developing roller 21 is made equal by the non-magnetic I component toner layer 120
This is done in mm/sec.

The developing roller 21 that carries this toner layer is as follows. In other words, on top of the aluminum core metal is a width of 0.15 mm x depth of 0.
．． 2mm square groove low left, 0.3mmmm pin 45
It was cut at an angle of 100 degrees, coated with silicone resin, and then machined to expose the aluminum surface. According to this developing roller 21, the resin portion includes the second
A positive charge is accumulated due to the friction between the toner supply member 22 shown in the figure, and this charge forms a fringe electric field between the aluminum surface and the negatively charged toner to form a multi-layered structure and to be transported. I can do it. This toner layer has a Q/M of -15 μC/g and an M/A of 1°0 times g/cm.
It became 2 things. The gap between the developing roller 21 and the photoreceptor 1 was set to 0.12 mm. In this way, when we applied DC -750V as a developing bias and developed the second color, ! Backward flight of toner was prevented, and a color image with uniform density in solid areas was obtained. And photoreceptor l
A good multicolor image was obtained by transferring the above two color toner images onto the recording paper in one go.

When the monochrome mode is designated, the photoreceptor 1 is charged by the first charger 2, and writing is performed by the first exposure 3. This latent image has a multilevel gradation, the charging potential is 1800, and the potential of the exposed part is -600 to -100.
It is within the range of v. In order to develop this with the non-magnetic one-component toner layer, the applied bias was a DC superimposed pulse bias of -100V for 0.5 m
It consists of a part between Sec and a part between -900V and 0.25m Sec. This frequency is approximately 1330
It is Se. Under these conditions, a monochrome image with smooth gradation reproducibility and good line parts was obtained.

According to the present invention as described above, in the invention of claim 1, toner images of different colors are formed on the electrostatic latent image carrier by a plurality of developing means in the multicolor mode. 1 for transfer material
In the case of multiple transfer, since a DC bias is applied as a developing bias for the second and subsequent colors, the toner of the first color does not fly backwards onto the silent latent image carrier, and color mixing is prevented. In the monochrome mode, a DC superimposed AC bias or a pulse bias is applied as a bias having periodic changes, so that a high quality image with smooth gradation can be obtained. In addition, the problems of the prior art can be solved by providing a multicolor mode and a single color mode, and by optimizing the combination of the latent image and developing bias for the first and second colors.

In the invention of claim 2, in addition to the above, when the exposure method is performed using a laser beam emitted in response to an image signal, a latent image with area gradation is formed by binary writing in multicolor mode. A high-quality image can be obtained by exposing to light to form a latent image with multi-value gradation by multi-value writing in the monochrome mode. Furthermore, since an electrostatic layer image having area gradation is formed by binary writing in the multicolor mode, the memory capacity can be reduced.

In the invention of claim 3, the M/A of the non-magnetic toner layer used for development of the second color and subsequent colors on the toner carrier is 0.5.
Since the range is from 1.5 mg/cW+z and the absolute value of the Q/M is from 5 to 30 aC/g, the electrostatic latent image carrier and toner carrier move at approximately the same speed and move directly to 71L.
Even when a binary image is developed using an electric field, sufficient image density can be obtained, and a clear character image can be obtained. Furthermore, even when a latent image with multilevel gradation is developed using a periodic electric field, a good image with smooth III pattern can be obtained.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the image forming section of the laser printer, Fig. 2 is an explanatory diagram of its second developing device, and Fig. 3 (a) is a perspective view of its developing roller. It is an enlarged view of. 440. Photoreceptor (electronic layer image carrier) ・・・First exposure (laser light) ・・・・First developer (plurality of developing means)・・・Second exposure (laser light) 8.・Second developer (developing means for second and subsequent colors)...
Developing roller (toner carrier) U, 2, 2, pu agent Patent attorney Takehisa Ito, PA=/heJi top

Claims (3)

[Claims] (1) The electrostatic latent image formed on the electrostatic latent image carrier by exposure to light is sequentially developed with toner of a plurality of different colors by a plurality of developing means, and then transferred to a transfer material at once to create a multicolor image. An image forming apparatus for forming an image, which has a multicolor mode and a monocolor mode, and develops by applying only a DC bias when in the multicolor mode, using a second and subsequent color developing means among the plurality of developing means. death,
An image forming apparatus characterized in that when in the monochrome mode, development is performed by applying a periodically changing bias. (2) The exposure is performed with a laser beam emitted according to an image signal, and the electrostatic latent image formed for the development of the second and subsequent colors is formed in an area by binary writing in the multicolor mode. The image forming apparatus according to claim 1, wherein the image forming apparatus forms a gradation, and when in the monochrome mode, the gradation is formed by multi-value writing. (3) The developing means for the second and subsequent colors includes a toner carrier that forms a non-magnetic one-component toner layer, and is of a type that causes the toner layer to fly onto the electrostatic latent image, and the toner carrier The toner layer in the development zone of the body has a mass per unit area in the range of 0.5 to 1.5 mg/cm^2 and an absolute value of the amount of charge per unit mass in the range of 5 to 30 μC/g. The image forming apparatus according to claim 1, characterized in that: