JPH05265303A - Color image forming device - Google Patents

Abstract

PURPOSE:To prevent sticking of color toner to an image end part and to obtain a high quality multicolor image by making the first area of a photosensitive body, where a first developing means carries out development, wider than the second area of the photosensitive body, where a second developing means carries out development. CONSTITUTION:The photosensitive body 1 is uniformly electrified by an electrifier 2, a latent image is formed by image exposure 3, and it is reversely developed by a first developing unit 4. The black image information is formed on the photosensitive body 1. Next, color image information is exposed imagewise on the photosensitive body 1 by second image exposure 6, and the color image is reversely developed by a second developing unit 7. The second developing unit 7 contains nonmagnetic one-component color toner. The width of laser scan is narrow compared to the case of the black image, since a light shielding plate 19 is provided. By providing the light shielding plate 19 between the photosensitive body 1 and the image exposure means, the formation of a latent image in the end part of an image area is prevented and, therefore, sticking of color toner to the image end part can be restrained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as an electrophotographic apparatus, and more particularly to a multicolor image forming apparatus for performing multicolor printing. More specifically, for example, a first electrostatic latent image is formed by performing a first exposure on a uniformly charged electrostatic latent image holder, and the first electrostatic latent image is developed with a developer (hereinafter referred to as “toner”). To form a first toner image and then to recharge it, and then perform a second exposure to form a second electrostatic latent image, which is formed into a second toner of a color different from that of the first toner. The present invention relates to a multicolor image forming apparatus that forms a second toner image by developing with toner to form a multicolor image of at least two colors in one copy cycle.

[0002]

2. Description of the Related Art Conventionally, computers, facsimiles, C
In a printer as a terminal device of information equipment such as AD, an electrostatic recording method using electrophotography is often applied. These printers send information signals to laser beams,
A recorded image is obtained by writing on a photoconductor as an electrostatic latent image holder by an LED, LCD, etc., visualizing it by a developing device, transferring it to a transfer paper, and fixing it by a fixing device. The recorded image used to be a solid black color before.

However, recently, because the recorded image becomes clearer and the information is easier to understand, for example, the color of the format and the color of the calculated value or the data value are expressed in different colors. , A part of the drawing output by CAD is output in another color, and a printer capable of obtaining a recorded image of two or more colors is desired.

The main one of such an electrophotographic apparatus capable of recording two or more colors is image exposure of an image portion (here, image exposure in which light is applied to a portion corresponding to a dark portion of an original image). A method of performing reversal development afterward (hereinafter referred to as "image exposure / reverse development method") and a method of performing regular development after image-exposing (background exposure) the non-image area (hereinafter referred to as "background exposure / regular development method"). ")
There is.

First, based on FIG. 4, image exposure
The outline of the reversal development method will be described. In FIG. 4, reference numeral 1 denotes a drum-shaped (or belt-shaped) photosensitive member as an image carrier having a photoconductive layer such as amorphous silicon,
It rotates in the direction of arrow a in the figure. 6 to 11 show changes in the surface potential of the photoconductor 1 in the following steps. The photoconductor 1 is first uniformly charged to, for example, +400 V by the first charger 2 (FIG. 6), and then subjected to the first image exposure 3.

The first image exposure 3 is a first laser beam modulated by a first image signal using the first semiconductor laser 11 as a light source, and the first laser beam is made constant by the motor 14. Polygon mirror 1 that rotates at the number of revolutions
After being polarized by 3, reflected by the folding mirror 16 through the image forming lens 15, the photoconductor 1 is raster-scanned,
The surface potential of the exposed portion is attenuated to, for example, +100 V (FIG. 7) to form an image-shaped first latent image.

The first latent image is developed by the first developing device 4 using, for example, positively charged black one-component magnetic toner, and the first developing device 4 has, for example, 200
A bias voltage in which a DC voltage of +340 V is superimposed on an AC voltage of 0 Hz · 1300 V _PP is applied to reverse-develop the first latent image (FIG. 8). The potential of the first toner image T1 formed by this is around + 200V, which is increased by about + 100V due to the toner charge (FIG. 8).

After the first development, the second charger 5 recharges the photosensitive member 1 to raise the potential of the first toner image T1 to, for example, +420 V (FIG. 9). Then, a second image exposure 6 is performed. The second image exposure 6
Is a second laser beam modulated by a second image signal using the second semiconductor laser 12 as a light source. The second laser beam is polarized by the rotating polygon mirror 13 and is passed through the imaging lens 15 to be exposed. Raster scan over body 1,
The potential of the exposed portion is attenuated to, for example, +60 V (see FIG.
0), a second latent image is formed.

The second latent image is developed by the second developing device 7 using, for example, positively charged red one-component non-magnetic toner. +400 for AC voltage of 1600Hz / 1300V _PP
The second latent image is reversely developed by applying a bias voltage on which a DC voltage of V is superimposed to obtain a second toner image T2 (see FIG. 1).
1).

The two color toner images T1 and T2 formed on the photoconductor 1 as described above are transferred onto the transfer paper P by the transfer device 8 and fixed by the fixing device 9. Further, the toner or the like remaining on the photoconductor 1 is cleaned by the cleaning device 10.
Will be collected at.

Next, the background exposure / regular development system will be described with reference to FIG. 4 similarly to the above. 12 to 17 show changes in the surface potential of the photoconductor 1 in the following steps.

In this method, the first charger 2 uniformly charges the photosensitive member 1 to, for example, +400 V (FIG. 12), and then the first image exposure 3 is applied to the non-image area.
The first image exposure 3 is a first laser beam modulated by a first image signal using the first semiconductor laser 11 as a light source, and the first laser beam is the motor 1
4 is polarized by the polygon mirror 13 rotating at a constant rotation speed, is reflected by the folding mirror 16 through the imaging lens 15, and is raster-scanned on the photoconductor 1 to set the surface potential of the exposed portion to, for example, + 40V. It is attenuated (FIG. 13) to form a reverse latent image of the first latent image.

The first latent image is developed by the first developing device 4 using, for example, a negatively charged black one-component magnetic toner, and the first developing device 4 has, for example, 200
A bias voltage in which a DC voltage of +110 V is superimposed on an AC voltage of 0 Hz · 1300 V _PP is applied (FIG. 14) to normally develop the first latent image. Toner image T obtained by this
The potential of 1 drops to about 320 V due to the toner charge, which is about 80 V (FIG. 14).

After the first development, the second charger 5 recharges the photosensitive member 1 to raise the potential of the first toner image T1 to, for example, +420 V (FIG. 15), and then the photosensitive member 1 is recharged. Then, a second image exposure 6 is performed. The second image exposure 6
Is a second laser beam modulated by a second image signal using the second semiconductor laser 12 as a light source, and the second laser beam is polarized by the rotating polygon mirror 13,
The photoconductor 1 is raster-scanned via the imaging lens 15, and the potential of the exposed portion is attenuated to, for example, +40 V (see FIG. 1).
6), a second inverted latent image is formed.

The second latent image is developed by the second developing device 7 using, for example, negatively charged red one-component non-magnetic toner, and the second developing device 7 has, for example, 1600 Hz.・ + 150V for AC voltage of 1300V _PP
The second latent image is normally developed by applying a bias voltage superposed with the DC voltage of (2) to obtain a second toner image T2 (FIG. 17).

The two color toner images T1 and T2 formed on the photoconductor 1 as described above are simultaneously transferred onto the transfer paper P by the transfer device 8 and fixed by the fixing device 9. Further, the toner and the like remaining on the photoconductor 1 are collected by the cleaning device 10.

[0017]

Certainly, it is possible to obtain a two-color image by following both of the above equations.
However, when an image was obtained by the above-mentioned conventional method, color toner adhered to the area at the end of the image where there should have been no image, and the obtained two-color image was very difficult to see. This phenomenon similarly occurred in the case of reversal development as well as in the case of regular development. There are several possible causes for this, for example, reading a document placed on the document table from a scanner,
When converting to an image signal, especially in a thick document, it is easy to form a shadow on the edge of the document, and the shadow is recognized as an image signal. In particular, depending on the color recognition method, it is recognized as a color signal. It is easy. When the color toner adheres to the edge of the image, the image becomes very unimpressive.

The present invention has been made in order to solve the above problems of the conventional example, and prevents the color toner from adhering to the edge portion of the image, thereby obtaining a high quality multicolor image. The purpose is to provide.

[0019]

SUMMARY OF THE INVENTION The present invention which achieves the above object is a color image forming apparatus in which an electrostatic latent image is formed based on an electrophotographic photosensitive member and an original image obtained by reading an original by original reading means. Image forming means for forming an electrostatic latent image formed on the photoconductor, a first developing means applying black toner for developing the electrostatic latent image formed on the photoconductor, and a first developing means applying color toner for developing the electrostatic latent image formed on the photoconductor. 2 developing means, and the first area of the photoconductor developed by the first developing means is made wider than the second area of the photoconductor developed by the second developing means.

[0020]

【Example】

(Embodiment 1) The present invention will be described below based on the illustrated embodiment. In addition, about the code | symbol in a figure, the same thing as what was used by the prior art example is used unless there is particular notice.

The first embodiment according to the present invention is based on an image exposure / reversal development system and uses a semiconductor laser as an image exposure means. FIG. 1 is a diagram showing a laser scanning width 20 on the photoconductor 1 when image exposure in a color mode is performed. The light shield plate 1 is provided between the photoconductor 1 and the image exposure means.
9 is provided to regulate the image exposure to the end portion 21 of the photoconductor 1. FIG. 2 is a diagram showing the laser scanning width 22 for the photoconductor 1 when performing image exposure in the black mode.

As described above, an operation example of the present embodiment using the light shielding plate 19 in the color mode image exposure portion will be described with reference to FIGS. 5 and 6 to 1.
This will be described using 1. First, the charging unit 2 uniformly charges the photosensitive member 1 with +400 V (FIG. 6), and then the image exposure 3 forms a latent image of +100 V (FIG. 7), and the first developing unit 4 reversely develops the latent image. .. A black one-component magnetic toner is used as a developer in the first developing device 4 as in the conventional example, and black image information is formed on the photoconductor 1. As shown in FIG. 2, the laser scanning width 22 covers almost the entire image area 24. Next, the photoconductor 1 and the toner image T1 thereon are charged to + 460V and + 420V by the charger 5, respectively (FIG. 9). In the second image exposure 6, the color image information is image-exposed on the photoconductor 1, and the color image is reversely developed by the second developing device 7.
The second developing device 7 contains non-magnetic one-component color toner (toner of a color other than black), and as shown in FIG. ,
It is narrower than the black image.

In this way, 2
The color image is transferred onto the transfer paper P by the transfer charger 8.
It is fixed by the fixing device 9. When the light shielding plate 19 is provided between the photoconductor 1 and the image exposing means in this way, a latent image is not formed at the end of the image area 24, and therefore the shadow of the end of the document is recognized as a color signal. Also in the above, it is possible to suppress the adhesion of the color toner to the end portion of the image. Therefore, the image obtained in this example is much better than the conventional image.

The extent to which the laser scanning width 20 in the color mode is made shorter than the laser scanning width 22 in the black mode depends on the characteristics of the device, but for example, the degree to which the end of the photosensitive member 1 is scratched. , Or the possibility that the color information is at the end, etc.
It is preferable that the laser scanning width 20 in the color mode is set so as to be narrowed by about 5 mm, and the light shielding plate 19 is provided so as to correspond thereto.

(Second Embodiment) Next, a second embodiment according to the present invention will be described. This embodiment is based on the background exposure / regular development system, and uses a semiconductor laser as an image exposure means. FIG. 2 is a diagram showing the laser scanning width 22 for the photoconductor 1 when performing image exposure in the black mode. FIG. 3 is a diagram showing a laser scanning width 26 for the photoconductor 1 when performing color mode image exposure.
The image signal is set so that the end portion 21 of the photoconductor 1 is always irradiated with the laser.

As described above, FIGS. 4 and 12 to 12 show an operation example of the present embodiment in which the end portion 21 of the photosensitive member 1 is always irradiated with the laser during image exposure in the color mode.
This will be described with reference to FIG. First, a uniform charging of + 400V is applied to the photoconductor 1 by the charger 2 (FIG. 12), and an inverted latent image is formed by image exposure 3 on the background (FIG. 13).

Next, the negatively charged toner is normally developed by the first developing device 4. In this first developing device, a black one-component magnetic toner is used as a developer as in the conventional example, and black image information is formed on the photoconductor 1. In this case, the laser scanning width 22 covers the entire image area 24 as shown in FIG. Next, by the charger 5, the photoconductor 1 and the developer T1 are +460 V and +4, respectively.
It is charged to 20V (FIG. 15). The second image exposure 6
The color image information is written as a reverse latent image on the photoconductor 1 by background exposure, and the color image is normally developed by the second developing device 7. The second developing unit 7 contains a non-magnetic one-component color toner, and by constantly irradiating the laser as shown in FIG. 3, the image area 27 is always blackened by the laser irradiation width 28. It is narrower than the image. In this way, the two-color image developed on the photoconductor 1 is transferred to the transfer paper P by the transfer charger 8 and fixed by the fixing device 9.

By constantly irradiating the end portion 21 of the photosensitive member 1 with a laser beam in this way, the surface potential of the end portion 21 of the photosensitive member 1 drops sufficiently, so that the shadow of the end portion of the document is recognized as a color signal. Even in the case where the color toner is left, it is possible to suppress the adhesion of the color toner to the edge portion of the image. Therefore, the image obtained in this example is several times better than the conventional image.

How narrow the image area in the color mode is made smaller than the image area in the black mode depends on the characteristics of the apparatus, but for example, the degree of scratches on the end 21 of the photosensitive member 1 or the color. Considering the possibility that the information is at the edges, etc., it is preferable to always set the laser irradiation width 28 and set the image signal so that both ends are about 3 to 5 mm from the image area 24 of the black image.

In each of the above embodiments, a black image for the first color and a color image for the second color were formed on the photoconductor.
The present invention is not limited to this, and the toner image is formed so that the toner image does not adhere to the edge of the image by regulating the image area of the color image for the first color, and then the black image for the second color is formed on the photoreceptor. It may be configured to be formed over the entire surface of No. 1. In that case, since a color image is formed in the first color, a better image can be obtained without being affected by the black toner when forming each image.

Further, in each of the above-mentioned embodiments, the image forming apparatus provided with two steps of charging, exposing and developing, and thus capable of obtaining a two-color image has been described, but the present invention is not limited to this. , 3 steps of charging, exposure and development
The present invention can be applied to an apparatus having three or more and capable of obtaining images of three or more colors. For example, a black image is formed as the first color, a red image is formed as the second color, and a blue image is formed as the third color. Then, at the time of image exposure for forming a red image and a blue image, the laser scanning width is regulated by providing a light shielding plate 19 between the photoconductor 1 and the image exposing means as shown in FIG. Prevent the toner from adhering. Further, even if the laser scanning widths of the second color and the third color are the same or slightly different, there is no significant difference in the effect. However, when compared with the black image of the first color, it is necessary to shorten both the laser scanning widths of the second color and the third color.

The developing system is not limited to the above-described embodiments, and various developing systems such as two-component developing or elastic blade coating can be applied.

Further, as the image exposing means, besides the semiconductor laser, various image exposing means such as an LED array and a liquid crystal shutter can be applied.

Since the present embodiment is configured as described above, it is possible to prevent the color toner from adhering to the end portion of the image area and obtain a high quality multicolor image.

(Embodiment 3) The multicolor image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

This embodiment will be described as being embodied in the multicolor electrophotographic apparatus shown in FIG.

FIG. 18 shows a schematic structure of an example of the developing devices 4 and 7 which can be used in the present invention. Developing device 4, 7
Have the same configuration. That is, the developing device 4 stores the developer T in the developing container 4a, and the magnet roller 4b.
A developing sleeve containing a toner, that is, a developer carrying member 4c is rotatably carried in the developing container 4a.

The developing sleeve 4c holds the developer T in the developing container 4a on its surface, and after the layer thickness is made constant by the developer layer thickness regulating blade 4d, an image carrier, that is,
It is conveyed to a developing position facing the photoconductor 1. At the developing position, the electrostatic latent image on the photoconductor 1 is made into a developed image by the developer on the developing sleeve 4c. The developer carrying member is usually the developing sleeve 4c as described above, but it may be formed in a belt shape.

Since the structure and operation of the developing device are well known to those skilled in the art, detailed description thereof will be omitted.

FIG. 19 is a view of the first developing device 4 and the second developing device 7 shown in FIG. 4 as seen from the direction of the photoconductor 1, respectively. The developer layer thickness regulating blades 4b and 7b and the first developing device 4 are shown in FIG. , End seal members 4e and 7e provided at both ends of the second developing sleeves 4c and 7c, and developer non-application areas 4f and 7f.
And the areas 4g and 7g of the developing sleeves 4a and 7a that can actually carry the developer.

As shown in FIG. 19, the developer carrying area 4g of the first developing device 4 is the same as the image area, whereas the developer carrying area 7g of the second developing device 7 is ,
It is shorter than the developer carrying area 4g of the first developing device 4. The developer carrying area 4g on the developing sleeve 4c covers the entire image area. Then, the developer carrying area 7 of the developing sleeve 7c of the second developing device 7
g is shorter than the developer carrying area 4g of the first developing device 4 and the image area.

2 thus developed on the photoconductor 1
The color image is transferred to the transfer paper P by the transfer charger 8 and fixed by the fixing device 9 as in the above-described embodiment.

With this structure, it is possible to prevent the second color toner from adhering to the edge of the image area. Especially, as described above, in order to obtain a high quality image, the first
Even when the AC bias voltage is applied to the developing device 4, the toner scattering can be prevented, and the black toner leaking from the end portion of the first developing device 4 can be prevented from entering the second developing device 7. Also, the second charger 5 that is easily formed at the end
It is possible to suppress development of stains and scratches on the photoconductor 1 with color toners, and obtain a high-quality two-color image with a good impression.

The developer carrying area 7g of the second developing device 7.
Is shorter than the developer carrying area 4g of the first developing device 4, depending on the characteristics of the device. For example, the degree of scratches on the end of the photosensitive member or the end of color information In consideration of the possibility that
It is preferably about 5 mm.

The developing system of each developing device is not limited to the above-mentioned embodiment, and various developing systems such as two-component developing or elastic blade coating can be adopted.

(Embodiment 4) FIG. 20 shows another embodiment of the developing devices 4 and 7 usable in the present invention.

In this embodiment, the developing sleeve 7c itself of the second developing device 7 is replaced by the developing sleeve 4c of the first developing device 4.
The developer carrying area 7g of the second developing device 7 is made shorter than that of the first developing device 4 by making the size of the end seals 4e, 7e and the developer non-carrying areas 4f, 7f identical to each other. It is shorter than the developer carrying area 4g.

The operation and effect are similar to those of the third embodiment, but there is an advantage that productivity is increased by making the end dimensions uniform in manufacturing the developing sleeve.

(Embodiment 5) FIG. 21 shows still another embodiment of the developing devices 4 and 7 usable in the present invention.

In the fifth embodiment, the first developing device 4
Is a two-component developing device using color toner and carrier, and the second developing device 7 is a developing device using black one-component magnetic toner.

As shown in FIG. 21, the length in the longitudinal direction of the developer carrying region 4f of the first developing device 4 using the color toner is changed to the development of the second developing device 7 using the black toner. It is shorter than the agent carrying region 7f.

With this structure, the same effect as that of the third embodiment can be obtained.

(Embodiment 6) Further, according to the present invention, also in the case of an image forming apparatus having three or more developing devices, the developer carrying region of the developing device having the color toners in the longitudinal direction is also the same. By making the length shorter than the length in the longitudinal direction of the developer carrying region of the developing device having the black toner, it is possible to obtain a high quality multicolor image as in each of the above embodiments.

For example, in FIG. 22, in a multicolor image forming apparatus in which three image forming steps such as charging, exposure and development are provided, the first and the first described above are constructed according to the present invention. 2 shows an embodiment having two developing devices 4 and 7, and further a third developing device 17 having the same structure as the developing devices 4 and 7.

As the image forming operation, the image forming process of the second embodiment described with reference to FIG. 4 is further increased by the image forming process of charging, exposing and developing.
During rotation, a three color image is created on the photoreceptor.

Referring to FIG. 22, the first developing device 4,
The second developing device 7 and the third developing device 17 are respectively attached to the developer layer thickness regulating blades 4d, 7d and 17d and the end portions of the first, second and third developing sleeves 4c, 7c and 17c. The provided end seal members 4e, 7e, 17e,
Non-developer coated areas 4f, 7f, 17f and developer carrying areas 4g, 7g, 17 of the developing sleeves 4c, 7c, 17c.
have g.

With this arrangement, the first developing device 4 contains one-component magnetic black toner, and the second and third developing devices 7 and 17 contain one-component non-magnetic red and blue toners. ..

In the sixth embodiment, as in the first embodiment, after the first charging, the black image information is converted into a latent image by the first exposure, and the latent image is transferred to the first developing device. And develop with black toner. At this time, as in the first embodiment, a developing bias voltage is applied to the developing sleeve 4c of the first developing device 4 by superposing an AC voltage of V _PP = 1300V and a frequency of 2000 Hz on a DC voltage of + 340V. There is.

Further, successively, similarly to the first image forming step, the second image forming steps of charging, exposing and developing are performed.
Next, an image forming step of third charging, exposure and development is performed to obtain a three-color image of black, red and blue.

According to this embodiment, as shown in FIG.
The developer carrying region 4 of the developing sleeves 4c, 7c, 17c
g, 7g, 17g are developing sleeves 4c, 7c, 17c
The second and third color toners are prevented from adhering to the end regions of the developing sleeves 7c and 17c, and the black toner leaks from the end portion of the first developing device to prevent the second and third color toners from adhering to the end regions. Second, it is possible to prevent the third developing devices 7 and 17 from being mixed with each other, and it is possible to obtain a high-quality image with a good impression in which the color toner is not attached to the end portions.

As described above, according to the multi-color image forming apparatus of the second to fifth embodiments, the length in the longitudinal direction of the developer carrying region of the developer carrying body of the developing device having the black toner. Compared with the above, since the length of the developer carrying region of the developer carrying member of the developing device having the color toner in the longitudinal direction is made shorter, the adherence of the color toner to the end portion of the image is prevented, and A high quality multicolor image can be obtained.

According to the above-described embodiment, the charging wire of the charging device is apt to be contaminated at the end portion, so that the recharging device 5 before the second color development is apt to be contaminated by the first color developer. This stain also causes color toner to adhere to the edges of the image. When the color toner adhered particularly to the edge portion of the image, the image did not have a very bad impression.

The first developing device usually uses a black developer and is often used for producing a normally used image such as a black image, so that the image quality is also severely demanded. Therefore, it is necessary to use a direct current bias with an alternating current superposed as the developing bias, but the alternating current component tends to scatter toner at the time of development, and in particular, the end of a developer carrying member such as a developing sleeve. Although the parts are easily scattered, the above-described embodiment also solves this problem.

A seal member is provided at the end of the developing sleeve to prevent toner from leaking. However, due to the seal leak at this portion, toner often leaks from the end of the developing sleeve to the outside of the developing device. This is a problem that occurs. Therefore, the problem that the toner leaked from the end seal from the first developing device is mixed into the second developing device has been solved.

(Embodiment 7) In the above embodiment, 1
The multi-developing method in which a two-color image is formed on one photoconductor and is transferred live is described. However, the present invention
Not limited to this shape, all image forming apparatuses capable of outputting a multicolor image of at least two colors of a black image and a color image are included.

For example, as in Embodiment 7 of the present invention shown in FIG. 23, an image forming apparatus having two image forming means for charging, exposing, developing, transferring and cleaning and forming a multicolor image is also included. The image forming process of the image forming apparatus as shown in FIG. 23 is as follows.

The original is read from the scanner to obtain a black image signal and a color image signal. For example, the image formation of a black image as the first image formation is performed as follows. Then, after the photoconductor 30 is uniformly charged by the charger 32, a latent image of a black image is formed by the semiconductor laser 42, for example.

This latent image is developed by a developing device 31 containing black toner.
It is also possible to make it narrower than the area to be visualized by the transfer means 34 and transferred onto the transfer paper P by the transfer means 34.

As described above, by making the color image area narrower than the black image area, even if the color information in the edge area is erroneously determined or the shadow of the original is determined as the color, the color toner is not used. No longer adheres to the edges and causes image deterioration.

In each of the above embodiments, an example of adjusting the area in the longitudinal direction (rotational axis direction) of the photoconductor is shown. However, the adjustment of the moving direction of the photoconductor is also performed at the ON / OFF timing of light image irradiation. Alternatively, it can be performed by the ON / OFF timing of the developing bias and the contact / separation operation of the developing device with respect to the photoconductor.

Subsequently, the transfer paper on which the black image is formed is conveyed to the second image forming means. A color image is formed in the second image forming means. First, the photoconductor 36 is uniformly charged by the charger 38. Next, the semiconductor laser 41 forms a latent image of a color image. At the time of forming this latent image, the laser irradiation width was narrowed by the light shielding plate 47 in the same manner as in Example 1, so that the image forming area of the color image was made narrower than the black image in the longitudinal direction of the photoconductor. The latent image of the formed color image is developed by the developing device 37 containing the color toner to form a color toner image on the photoconductor 36. The color toner image thus formed is transferred onto the transfer paper on which the black image has been formed, and is fixed by the fixing device 45 to form a two-color image.

Also in the case of such a process, as in the second embodiment, a method of constantly exposing the image end portion at the time of latent image of a color image by background exposure, or the third, fourth, and fifth embodiments. As for the adjustment of the developable area of the developing means for the color image as shown in Nos. 6 and 6, the developable area of the developing means for the black image can be carried out by the following method for adjusting the moving direction of the photoconductor.

For example, in the case where a document placed on a document table is read from a scanner and converted into an image signal, when the color image signal is recognized in the image end area, the color image as described above is used. In addition to the means for narrowing the latent image area in the longitudinal direction of the photoconductor at the time of forming the latent image for It is OFF, and when background exposure is performed, image exposure is always ON. As a result, the area can be narrowed, so that it is possible to suppress the adherence of color toner due to a shadow or the like on the edge of the document.

Further, as another example, it is possible to attach and detach the developing device in the developing process. In this case, when the color image signal is recognized in the image edge area in the moving direction of the photoconductor, the developing device for color image development is used in the image edge area during the color image development.
The timing of turning on is delayed and the timing of turning off is advanced so as to be in the off state. As described above, by changing the mounting / removing timing of the developing device, it is possible to prevent the adherence of color toner in the moving direction of the photoconductor.

As described above, in the longitudinal direction and the moving direction of the photoconductor, the area where the color image is developed is made narrower than the area where the black image is developed, which causes adverse effects such as adhesion of color toner to the end portions. Can be prevented.

In the above-described embodiment, the area of the color image is narrowed, whereas the area of the black image is left as the image area. Since the black image information is mainly character information, the area is narrowed. This also has the effect of not losing character information.

[0077]

According to the present invention, it is possible to prevent the shadow portion of an original image, which is likely to occur when copying an original, and the periphery of the image forming area of the photosensitive member, which is likely to cause a fogged image, from being developed by color toner. did it. As a result, it has become possible to reduce the adhesion of color toner on the peripheral portion of the formed image, which has been a cause of deterioration in image quality.

[Brief description of drawings]

FIG. 1 is a plan view showing a laser scanning width in a color mode for a photoconductor according to an exemplary embodiment of the present invention.

FIG. 2 is a plan view showing a laser scanning width in a black mode with respect to the photoconductor according to the embodiment.

FIG. 3 is a plan view showing a laser scanning width and a constant laser scanning width in a color mode for a photoconductor according to an exemplary embodiment of the present invention.

FIG. 4 is a device diagram of a conventional example and an embodiment of the present invention.

FIG. 5 is a device diagram of an embodiment of the present invention.

FIG. 6 is a graph showing the surface potential of a photoconductor according to an example of the present invention.

FIG. 7 is a graph showing the surface potential of a photoconductor according to an example of the present invention.

FIG. 8 is a graph showing the surface potential of a photoconductor according to an example of the present invention.

FIG. 9 is a graph showing the surface potential of a photoconductor according to an example of the present invention.

FIG. 10 is a graph showing the surface potential of a photosensitive member according to an example of the present invention.

FIG. 11 is a graph showing the surface potential of a photoconductor according to an example of the present invention.

FIG. 12 is a graph showing the surface potential of a photoconductor according to an example of the present invention.

FIG. 13 is a graph showing the surface potential of a photoconductor according to an example of the present invention.

FIG. 14 is a graph showing the surface potential of a photoconductor according to an example of the present invention.

FIG. 15 is a graph showing the surface potential of a photosensitive member according to an example of the present invention.

FIG. 16 is a graph showing the surface potential of a photoconductor according to an example of the present invention.

FIG. 17 is a graph showing the surface potential of a photoconductor according to an example of the present invention.

FIG. 18 is a sectional view of the developing device.

FIG. 19 is a developer layer thickness regulating blade in one embodiment of the developing device used in the multicolor image forming apparatus of the present invention;
FIG. 6 is a front view of the developing device showing the relationship between the end seal members provided at both ends of the first and second developing sleeves, the developer non-application area, and the developer carrying area of the developing sleeve.

FIG. 20 is a developing layer used in the multi-color image forming apparatus of the present invention, in which the developer layer thickness regulating blade and the end portions of the first and second developing sleeves are provided. FIG. 6 is a front view of the developing device showing a relationship among a seal member, a developer non-application region, and a developer carrying region of a developing sleeve.

FIG. 21 is a developing layer used in a multicolor image forming apparatus according to another embodiment of the present invention, wherein a developer layer thickness regulating blade and end portions provided at both end portions of the first and second developing sleeves. FIG. 6 is a front view of the developing device showing a relationship among a seal member, a developer non-application area, and a developer carrying area of a developing sleeve.

FIG. 22 is a view showing a developing device used in the multi-color image forming apparatus of the present invention, which is provided on both ends of the developer layer thickness regulating blade and the first, second and third developing sleeves in another embodiment. FIG. 6 is a front view of the developing device showing the relationship among the end seal member, the developer non-application region, and the developer carrying region of the developing sleeve.

FIG. 23 is a diagram showing an apparatus used in Example 7 of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrophotographic photoreceptor 2 Charging device 3 First image exposure 4 First developing device 6 Second image exposure 7 Second developing device 11 First semiconductor laser beam 12 Second semiconductor laser beam 13 Polygonal mirror 15 Imaging lens 16 Folding mirror 20 Laser scanning width 22 Laser scanning width 24 Image area 30 Photoconductor 31 Developer 32 Charger 36 Photoconductor 37 Developer 38 Charger 41 Semiconductor laser 42 Semiconductor laser 43 Folding mirror P Transfer paper

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H04N 1/23 103 C 9186-5C

Claims (4)

[Claims] 1. A color image forming apparatus comprising: an electrophotographic photosensitive member; a latent image forming unit that forms an electrostatic latent image based on an original image obtained by reading an original by an original reading unit; and a latent image forming unit formed on the photosensitive member. A first developing unit applying black toner for developing the electrostatic latent image formed on the photosensitive member, and a second developing unit applying color toner for developing the electrostatic latent image formed on the photoconductor. A color image forming apparatus, wherein the first area of the photoconductor developed by the means is made wider than the second area of the photoconductor developed by the second developing means. 2. The color image forming apparatus according to claim 1, wherein the first and second area difference changes a latent image forming area formed on the photoconductor. 3. The color image according to claim 2, wherein the difference between the formation areas of the first and second latent images is changed by setting the exposure area of the optical means with respect to the photosensitive member for forming the latent image. Forming equipment. 4. The color image forming according to claim 2, wherein the difference between the first and second areas is set so that a developable area by the first developing means is larger than a developable area by the second developing means. apparatus.