JP3026644B2 - Image forming device - Google Patents

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,
More specifically, the present invention relates to a visible image processing structure for forming a two-color image.

[0002]

2. Description of the Related Art As is well known, in an image forming apparatus such as a copying machine, there is a two-color image forming apparatus for forming different images by using two different colors. No. 2-48683. According to this, after the first and second visible images are formed by toners having different polarities, collective transfer is performed in a state where the polarities are made uniform by a charger before transfer, and residual toner is removed after the transfer process. in the structure, a structure of the removing means, the pre-transfer Cha - provided discharger supplied offset to the side - the same polarity as the polarity of the charge due Ja previous Cha transfer - residual toner Ja polarity and different polarities The transfer efficiency and the cleaning efficiency after a two-color image is formed by toners of different polarities are improved.

On the other hand, with respect to an apparatus for preventing the occurrence of color mixture of toner when forming the above-described two-color image, JP-A-61-7252, JP-A-63-294579, or JP-A-63-294579. -294580. According to this, the toner used for the second developing means by magnetic brush development is smaller in weight than that of the first developing means, so that the toner reciprocates under the alternating electric field during the second developing process. Prevents color mixing caused by movement, or changes the bulk density or average particle diameter of the toner used in the first development step and the toner used in the second development step, and causes color mixing caused by mixing different kinds of toner. Fog phenomenon is prevented.

Japanese Patent Application Publication No. 45916/94 discloses an apparatus using the same polarity toner instead of the different polarity toner used in the former two-color image forming apparatus. the toner - when the photosensitive member of the developing device for processing a visible image passes, before and re-charged to the same potential as the charging potential of the non-image portion on the photosensitive member before reaching the developing unit of the last stage The potential level at the time of development is eliminated by eliminating the presence of an unsaturated portion to prevent color mixing due to toner at the next development, and the potential level at the time of such development is reduced. As a control method, see JP-A-63-12306.
As described in Japanese Patent Application Laid-open No. 9, the transfer step and the cleaning step for removing the toner after image transfer in a state where the charge-up due to the developing bias to the toner occurs as the number of colors increases. In some of the above, the operation of the static elimination lamp and the static elimination device is controlled according to the color mode because the conditions for transfer and cleaning are different between the case of a single color and the case of a plurality of colors. .

[0005]

The two-color image forming methods described in the above publications have the following problems.

That is, in the image forming method described in the first publication, although the transfer and cleaning efficiency in forming a two-color image can be improved, the toner used for this purpose is A different polarity is used. Therefore, when the two-color image formed on the photoreceptor is transferred collectively, it is necessary to charge the toner before transfer so as to make the polarity of the toner uniform, and the toner having the same polarity as the charged polarity is used between the toners of different polarities. Is higher in charge potential and lower than toner of the same polarity of different polarity, and as a result, the charge amount at the time of collective transfer is different. This means that while toner of one polarity is transferred efficiently, transfer of the toner of the other polarity causes a transfer failure and an image with a strong edge effect is transferred. For this reason, in the device having such a structure, it is difficult to set the conditions of the transfer potential when simultaneously transferring the images of two colors, and there is a possibility that an image having a constant density cannot be obtained. .

In such a structure, a clear
In cleaning, the toner has a lower potential due to the pre-transfer charging, but the toner of the same polarity is charged with a high charge amount and becomes a load for cleaning, and a cleaning blade, brush, etc. , There is a possibility that the toner removal performance may deteriorate. This may occur even in the case of recharging during the development stage in the above-described apparatus.

Further, in such a structure in which recharging is performed before transfer or before reaching a developing device at a later stage, there is a concern that the size and complexity of the device may be increased and the cost of the device may be increased.

On the other hand, in an apparatus in which the mass, bulk specific gravity or average particle diameter of the toner used in the second development step is made different, the toner is obtained by the first development by rubbing with the ears of the magnetic brush development. There is a possibility that the resulting image may be damaged, and an apparatus configured to execute the second development step without using the magnetic brush development (Japanese Patent Application Laid-Open No. 63-12306)
No. 9), it is necessary to make the electricity elimination process before the cleaning process different between a single color and a plurality of colors, and the work may be troublesome.

In view of the above-mentioned problems in the conventional two-color image forming apparatus, an object of the present invention is to provide a two-color image forming apparatus having a structure capable of providing a stable two-color image over time.

Another object of the present invention is to provide a two-color image forming apparatus capable of removing residual toner when forming a two-color image using toners of the same polarity by a simple structure. .

[0012]

In order to achieve the above object, according to the first aspect of the present invention, there is provided a first charging means for uniformly charging a photosensitive member, and a uniform charging by the first charging means. A first exposure unit configured to form a latent image by performing a negative exposure on the photoconductor based on the first image information; and a first development unit configured to develop the latent image formed by the first exposure unit into a first developed image. Developing means, a second charging means for charging the photoreceptor after development processing by the first developing means from above a first developed image, and a photoreceptor charged by the second charging means A second exposure means for negatively exposing a portion other than the first developed image based on the second image information to form a latent image; and a latent image formed by the second exposure means as a first developed image. And a second developing means for developing a second developed image of a different color from the photosensitive member. In the image forming apparatus in which the formed first developed image and the second developed image are collectively transferred to a transfer sheet to obtain a two-color image, the first developing means is a two-component magnetic brush developing system. Wherein the second developing means is of a non-contact developing type, and the average particle diameter of the toner used in the first developing means is larger than the average particle diameter of the toner used in the second developing means. The toner used in the second developing means is small and the particle size distribution of the toner used in the first developing means satisfies the relationship of volume average particle diameter / number average particle diameter ≦ 1.2. It is characterized in that the shape is spherical.

According to a second aspect of the present invention, there is provided a first charging means for uniformly charging a photoreceptor, and a negative exposure based on first image information on the photoreceptor uniformly charged by the first charging means. A first exposure unit for forming a latent image by performing
A first developing unit that develops the latent image formed by the exposing unit into a first developed image, and charges the photoreceptor after the development processing by the first developing unit from the first developed image again A second charging means, and a second exposing means for forming a latent image by negatively exposing the photosensitive member charged by the second charging means to a place other than the first developed image based on second image information And a second developing means for developing the latent image formed by the second exposing means into a second developed image having a different color from the first developed image, and formed on the photoreceptor. A first developed image,
The operation of obtaining a two-color image by collectively transferring the second developed image to transfer paper, and the operation of obtaining a single-color image without operating the second exposure unit and the second development unit In the above-described image forming apparatus, the second charging unit charges the photoconductor during an operation of obtaining the two-color image and an operation of obtaining the single-color image. .

[0014]

[0015]

According to the first aspect of the invention, the toner used in the first developing means has a smaller average particle size and a uniform particle size distribution than the toner used in the second developing means. As a result, the surface area per unit weight (specific surface area) increases, the contact area of the toner with the carrier increases, the charge amount increases, and the second developing unit moves away from the photosensitive member during development by the second developing unit. Toner is prevented from flying to prevent color mixing. Further, the toner used for the second developing means is spherical and has a uniform particle size distribution, so that a uniform charging state between the toners can be set. A good developed image can be obtained even when the developing electric field is small.

According to the second aspect of the present invention, regardless of the operation of obtaining a two-color image and the operation of obtaining a single-color image, the second charging means is operated to perform the operation of obtaining a two-color image. Transfer conditions during operation for obtaining a single color image,
Ning conditions can be the same.

[0017]

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below in detail with reference to FIGS.

FIG. 1 is a layout diagram showing the overall configuration of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus 1 according to the embodiment includes a drum-shaped photosensitive member 2. And
Around the photoconductor 2, a first charging device 3, a first exposure device 4, a first developing device 5, a second charging device 6, A second exposure device 7, a second developing device 8, a paper feeding device 9, a transfer device 10, a cleaning device 11, and a static elimination lamp 12 are arranged. Further, a fixing device 14 and a sheet discharging device 15 for fixing a transfer image on a transfer sheet conveyed via the conveyance belt 13 after the transfer are provided downstream of the transfer position in the rotation direction of the photosensitive member 2 described above. is there.

The above-described first and second charging devices 3 and 6 have the same structure, and the first charging device 4 is used before forming the first color image and in the second charging device. The charging device 6 charges the surface of the photoconductor 2 uniformly after the first color image is developed.

The above-described second charging device 6 is set so as to be uniformly charged in both cases of forming a single color image and forming a two-color image.

The first and second exposure devices 4 and 7
In this embodiment, the negative exposure is performed using a laser light writing device, and image information from a control unit (not shown) is written on the photosensitive member 2.
In the case of the present embodiment, the first exposure device 4 performs exposure according to the image information regarding the black original image, and the second exposure device 7
Perform exposure according to image information relating to a red original image.

On the other hand, both the first developing device 5 and the second developing device 8 perform negative / positive development, that is, so-called reversal development. In the case of this embodiment, the first developing device 5
Is a magnetic brush developing device using a two-component developer in which toner is adhered to a carrier, and the second developing device 8 is a non-contact developing device using a one-component developer. The toner used in each of these developing devices will be described later.

That is, the toner used in the first developing device 5 and the second developing device 8 is manufactured by, for example, a suspension polymerization method and has the same charging polarity. , Toner used in the first developing device 5
Is smaller than the toner used in the second developing device 8 in the average particle size. In this embodiment, the average particle size is 5 to 7.5 μm, and the particle size distribution is It is set so as to satisfy the relationship of volume average particle diameter / number average particle diameter ≦ 1.2.

The condition setting of the toner used in the first developing device 5 described above is based on the following reason. That is, the surface area per unit mass (specific surface area) is increased by reducing the average particle size as compared with the second developing device, and the contact area of the toner with the carrier is increased at the same toner concentration. As a result, the adhesion to the photoreceptor side is increased, and as a result, the visible image processing by the second developing device, that is, the non-contact development using the developing bias, is performed on the photoreceptor by the developing bias. Toner in the first developed image attached to
This is to prevent the second developing device from being sucked into the second developing device and mixing colors.

On the other hand, as shown in FIG. 2, the second developing device 8 is in close proximity to the developing roller 8A and has a toner on the roller surface.
The toner is charged by charge injection through a blade 8B which is a means for reducing the thickness of the toner. The toner used for this is spherical and has a particle size distribution of It is in a state of satisfying volume average particle diameter / number average particle diameter ≦ 1.2.

The conditions for such toner are as follows. That is, as described above, the second developing device 8 is a toner charging method, which is a thin layer forming means.
To be performed using the blade 8B, the toner for the blade 8B is used.
In order to obtain uniform charging, it is preferable to perform uniform treatment. Therefore, by providing a uniform particle size distribution, the toner
, A charge distribution as shown in FIG. 3 is obtained, and as is clear from this result, uniform charging is promoted. FIG. 4 shows the charging characteristics of the conventional pulverized toner with respect to the charging characteristics of the toner used in the second developing device 8 described above. In order to perform the uniform charging, for example, when the second development is a method using a DC developing bias, transfer of the toner to the photosensitive member is performed evenly. In addition, the spherical shape reduces the contact area with the developing roller 8A, so that when a developing bias is applied, the amount of charge is small, and the transfer to the photoreceptor is easy, so that the transfer efficiency is reduced. As a result, as shown in FIG. 5, a margin for the transfer electric field can be given as compared with the conventional pulverized toner.

Since the present embodiment has the above configuration,
As shown in a flowchart showing the copying process in FIG. 6, it is determined whether or not the image has been read, and if it has been determined that the image has been read, it is determined whether or not the image is a single-color image. In the case of a single color, the first charging device 3 and the first developing device 5 are operated. That is, after uniform charging by the first charging device 3, negative exposure corresponding to a single-color original image is performed by the first exposure device 4 to form a latent image on the photoconductor 2, and this latent image is The visible image is processed through the adhesion of the toner in the magnetic brush of the developing device 5. When the photosensitive member 2 rotates and the first developed image carried on its surface reaches the position of the second charging device 6, the second charging device 6 is operated, and the first developed image is actuated. Charges uniformly from above. Then, the first developed image on the photoconductor 2 is transferred. Therefore, the transfer potential and the charge elimination conditions in the transfer step and the cleaning step are performed under the same conditions as in the two-color image formation.

On the other hand, when a single color image is not formed,
As in the case described above, the photoconductor 2 is uniformly charged by the first charging device 3 and is stored in the first developing device 5 by the first exposure device 4, for example. Negative exposure is performed based on image information on a document image of the same color as the black toner. Then, the latent image formed on the photoconductor 2 is subjected to negative / positive development by the first developing device 5 to be a first developed image. Since the toner used in the first developing device 5 has the above-described conditions, the toner has a high charge amount, and the adhesion to the photosensitive member 2 is increased.

After the above-described first developed image is formed, in the process of rotating the photosensitive member 2, the second charging device 6 is operated to uniformly charge the first developed image again from the first developed image. The exposure device 7 performs negative exposure based on image information on a document image of the same color as the red toner accommodated in the second developing device 8. Then, the second developing device 8
Applies a DC bias to the toner thinned on the surface of the developing roller to transfer the toner to a latent image formed on the photosensitive member 2. At this time, since the toner in the first developed image visualized by the first developing device 5 has an increased adhesion to the photoconductor under the above-described conditions, the toner in the second developing device 8 Even under the influence of the developing bias, it does not fly to the second developing device 8 side,
In the developing device 8 is prevented.

When the second developed image is formed by the second developing device 8 described above, the registration roller in the paper feeding device 9
The transfer paper fed together with the paper feed timing set by the roller 9A is collectively transferred together with the first developed image via the transfer device 10, and the first and second developed images on the transfer paper are fixed.

On the other hand, the residual toner is removed from the photoreceptor 2 after the transfer by the cleaning device 11, and the residual charge is removed by the discharge lamp 12.

[0033]

As described above, according to the first aspect of the invention, when forming a two-color image, the toner used in the first developing device is replaced with the toner used in the second developing device. The average particle diameter is smaller than that of the toner, and the particle diameter distribution of the toner used in the first developing device is made uniform. Since the state in which the adhesive force is strengthened can be maintained, there is no need to control the charging of the toner on the photoconductor when the first development image and the second development image on the photoconductor are collectively transferred to transfer paper. Further, it is possible to prevent color mixture between the toner of the first developed image on the photoconductor and the toner in the second developing device. In addition, the toner used in the second developing device of the non-contact developing type is spherical, and the particle size distribution is made uniform, so that the charge amount of the toner can be made uniform and the transfer efficiency can be reduced. As described above, the image characteristics can be improved, and the transfer electric field to the photoconductor can be set with a margin, so that the charging fatigue of the photoconductor can be reduced.

According to the second aspect of the invention, irrespective of the formation of a single-color image or the formation of a plurality of colors, the charging by the second charging means is performed to obtain a two-color image,
Transfer conditions and clear during operation to obtain a single color image
The cleaning conditions can be made the same, whereby the load on the cleaning unit can be reduced without requiring any structural change.

[Brief description of the drawings]

FIG. 1 is a layout diagram for explaining an overall configuration of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a model diagram for explaining the structure of the developing device shown in FIG.

FIG. 3 is a diagram for explaining characteristics of a toner used in the developing device shown in FIG. 2;

FIG. 4 is a diagram corresponding to FIG. 3 for explaining characteristics of a toner used in a conventional developing device.

FIG. 5 is a diagram for explaining a characteristic comparison between a toner used in the developing device shown in FIG. 2 and a conventional toner.

FIG. 6 is a flowchart for explaining an image forming process of the image forming apparatus shown in FIG. 1;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 image forming apparatus 2 photoreceptor 3 first charging device 4 first exposing device 5 first developing device 6 second charging device 7 second exposing device 8 second developing device 10 transfer device 11 cleaning Device 12 Static elimination lamp

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-64-56461 (JP, A) JP-A-63-294579 (JP, A) JP-A-63-149662 (JP, A) JP-A-2- 132459 (JP, A) JP-A-2-208674 (JP, A) JP-A-63-301066 (JP, A) JP-A-3-181952 (JP, A) JP-A-2-302772 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) G03G 13/01 G03G 15/01-15/01 117 G03G 15/08-15/095

Claims (2)

(57) [Claims] A first charging means for uniformly charging a photosensitive member, and a latent image is formed on the photosensitive member uniformly charged by the first charging means by performing negative exposure based on first image information. A first exposing means for developing, a first developing means for developing a latent image formed by the first exposing means into a first developed image, and the photosensitive element after the development processing by the first developing means. Second charging means for recharging the body from above the first developed image;
A second charge is applied to the photoconductor charged by the second charging means.
A second exposure unit that forms a latent image by negatively exposing a portion other than the first developed image based on the image information of the first developed image; and a latent image formed by the second exposure unit is different from the first developed image. A second developing means for developing a second developed image of a color, wherein the first developed image and the second developed image formed on the photoreceptor are collectively transferred to a transfer paper, thereby obtaining two colors. In the image forming apparatus configured to obtain an image, the first developing unit is a two-component magnetic brush developing system, and the second developing unit is a non-contact developing system, and is used for the first developing unit. Toner
Is smaller than the average particle size of the toner used in the second developing means, and the particle size distribution of the toner used in the first developing means is volume average particle size / number average particle. An image forming apparatus which satisfies the relationship of diameter ≦ 1.2 and wherein the toner used in the second developing means has a spherical shape. 2. A first charging means for uniformly charging a photosensitive member, and a negative image is formed on the photosensitive member uniformly charged by the first charging means based on first image information to form a latent image. A first exposing means for developing, a first developing means for developing a latent image formed by the first exposing means into a first developed image, and the photosensitive element after the development processing by the first developing means. Second charging means for recharging the body from above the first developed image;
A second charge is applied to the photoconductor charged by the second charging means.
A second exposure unit that forms a latent image by negatively exposing a portion other than the first developed image based on the image information of the first developed image; and a latent image formed by the second exposure unit is different from the first developed image. A second developing means for developing a second developed image of a color, wherein the first developed image and the second developed image formed on the photoreceptor are collectively transferred to a transfer paper, thereby obtaining two colors. In an image forming apparatus configured to perform an operation of obtaining an image and an operation of obtaining a single-color image without operating the second exposure unit and the second developing unit, the second charging unit may include: An image forming apparatus, wherein the photosensitive member is charged during an operation for obtaining a two-color image and during an operation for obtaining the single-color image.