JPH045669A - Color image forming device - Google Patents

Abstract

PURPOSE:To obtain a high-definition image as for a black image part according to the type of the image by providing two different black developing means for forming a full color image and monochrome image as for the black developing means in a developing means. CONSTITUTION:The black developing unit 17 is used as a pair with respect to a yellow developing unit 14, a magenta developing unit 15, a cyan developing unit 16, etc., at the time of a full color mode, etc. The black toner B of the developing unit 17 has the same type characteristic as the yellow toner E of the developing unit 14, the magenta toner D of the developing unit 15, and the cyan toner C of the developing unit 16, and the gamma characteristic as for respec tive toners B, C, D, and E is almost one. The developing unit 18 is used at the time of a monochrome copy mode, black toner A housed in the developing unit 18 has a characteristic different from a group of the above-mentioned respective toners B, C, D and E and the toner having the characteristic of gamma>1 suitable for a monochrome copy is used. Thus, the high-definition image is obtained according to the type of images of full color and monochrome records.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a color image forming apparatus.

(Prior Art) A color image forming apparatus generally includes a writing device for writing an original image on an image carrier, a developing device for visualizing the latent image written on the image carrier as a toner image, and a developing device for visualizing the latent image written on the image carrier as a toner image. It has a transfer means for transferring onto the material to be transferred, and is roughly divided into analog type and digital type.

■ As an example of an analog color copying machine, JP-A-62-
No. 182766, US Pat. No. 4,697,920, etc.

These analog color copying machines have a black developing device for black-and-white monochrome copying, but are not equipped with a black developing device for full-color copying.

In other words, color masking is extremely difficult with analog color copying machines, and with normal dry development, black is reproduced by overlapping cyan, magenta, and yellow toners, etc. It does not have a full-color black developing device.

■ A digital color image forming apparatus that writes an original image that has been converted into an electrical signal in advance onto an image carrier is equipped with a black developing device for full color, contrary to the technology described in (■) above, but a black developing device for black and white monochrome recording Some printers do not have a developing device, and use full-color black toner for monochrome black and white recording.

(Problem M to be Solved by the Invention) In the above technique (■), due to the difficulty of color masking, the black toner in the black developing device for black-and-white single-color copying cannot be used to reproduce black images in full-color images. , reproduction of this black image is done exclusively by overlapping the colors of cyan, magenta, and yellow toners.

Therefore, there are problems such as color bleeding in the image due to subtle image shifts due to overlapping colors, and the black color resulting from the synthesis feels unnatural due to the balance with other surrounding colors.

On the other hand, with the technique (2) mentioned above, color masking is possible, so even if there is no problem since full-color black toner is used during full-color recording, this toner has a gamma characteristic of 1 and is inferior in durability. This causes problems in black and white monochrome recording, especially in terms of line image reproducibility and image gloss.

SUMMARY OF THE INVENTION An object of the present invention is to provide a color image forming apparatus that can obtain high quality black image portions depending on the image format such as full color recording, black and white monochrome recording, etc.

(Means for Solving the Problems) In order to achieve the above object, in the color image forming apparatus of the present invention, among the developing means, the black developing means is used for forming a full-color surface image and for forming a black-and-white monochrome surface image. 2 different
It was decided to provide two black developing means.

In this case, the two different black developing means are preferably selected depending on at least the glossiness and toner adhesion surface density of the final formed image.

(for production) Black developing devices are used differently depending on the image characteristics.

(Example) Examples of a digital color image forming apparatus according to the present invention are shown in FIGS. 1 and 2, respectively.

Although these two apparatuses differ in the arrangement and configuration of the developing units serving as developing means, other basic configurations include common parts, so the same functional members will be given the same reference numerals and the overall outline will be explained.

When forming an image, the original 1 placed on the contact glass 2 is irradiated with the illumination lamp 3 while the mirror group 4 is moved and scanned. Then, the reflected light passes through a reduction lens 5, reaches a color CD image sensor 6, is controlled by a scanner controller 7, and is converted into electrical signals corresponding to blue, green, red, and black original images.

This electrical signal is further processed by the image processing section 8, sent to the writing section 9 which is a writing means, and converted into an optical signal.
Polygon mirror 10. as a laser beam. A belt-shaped photoreceptor 11 is connected via an fθ lens IOA, a mirror 10B, etc.
irradiated on top.

Here, around the photoconductor 11, there is a static eliminator 12 that eliminates static electricity from the photoconductor by irradiating light, a charger 13 that charges the photoconductor after neutralization, and a black developer equipped with black toner for forming a black and white monochromatic surface image. A developing device 27 having a plurality of developing devices for forming a color surface image, a photoreceptor cleaning device 19, and the like are arranged.

In the above, the developing means 27 includes a yellow developing device 14 having yellow toner, a magenta developing device 15 having magenta toner, and a cyan developing device 1 having cyan toner.
6 and a black developing device 17 having black toner for forming a full-color surface image. When forming a full-color image, each of these developing devices sequentially faces the photoreceptor 11 and collects the photosensitive material written by the writing means. Visualize latent images on the body.

When creating a color image, each time a latent image of one color is visualized, the visualized toner image is transferred to the intermediate transfer belt 20 disposed close to the photoreceptor 11.

The intermediate transfer belt 20 is supported by a support roller 26, and around it is a first transfer device 21 and a second transfer device 21 by a bias roll.
Transfer device 22, intermediate transfer belt cleaner 23, bias roll cleaner 24. A waste toner bottle 25 and the like are provided. In the example shown in FIG. 2, a part of the first transfer device 21 is also used as a support roller for the belt.

The first transfer device 21 is for transferring the toner image from the photoreceptor 11 onto the intermediate transfer belt 20, and the second transfer device 22 is for transferring the toner image transferred onto the intermediate transfer belt to transfer paper. It is for transferring.

That is, a monochrome image, a two-color image, a three-color image, and a four-color image (for monochrome copying, multicolor copying, and full-color copying) are formed on the intermediate transfer belt 20 depending on the copy mode.

The transfer paper 30 is stocked in a predetermined paper feed section, and is moved to the paper feed roller 3 in synchronization with the intermediate transfer belt 20.
1, the sheets are separated one by one and fed. A manual feed table device 32 is used for special size paper, etc. The transfer paper 30 sent out in this manner passes through a guide plate, a conveyance roller, and a registration roller 33, and reaches the second transfer section, that is, the second transfer device 22, where the toner image is transferred from the intermediate transfer belt 20.

The transfer paper 3o on which the toner image has been transferred in this manner is transported by the transport device 34 to the fixing device 100, where the toner image is fixed, and then discharged outside the machine via the discharge roller 35 and placed in the copy stacker 36. It is ejected and stocked as a copy 37.

The above is an overview of the configuration and copying process, but the black developing devices 17 and 18 contain the same black toner but with different characteristics.

That is, the black developing device 17 is used in pairs with the yellow developing device 14, the magenta developing device 15, the cyan developing device 16, etc. in the full color copy mode, etc., and the black toner B stored therein is As shown in FIG. 3, yellow toner E in the yellow developer 14, magenta toner D in the magenta developer 15, and cyan toner C in the cyan developer 16.
It has the same characteristics as .

Here, the characteristics of the same system include electrical characteristics (electrical resistance, dielectric constant, amount of charge, etc.), thermal characteristics (softening point, melting point, shrinkage rate, etc.),
Refers to mechanical properties (particle size, particle shape, particle size distribution, etc.).

The γ characteristic of each of these toners B, C, D, and E is approximately 1.

On the other hand, the black developing device 18 is used in the black and white monochrome copy mode, and the black toner A contained therein is
As shown in the figure, each of the above toners B.

Those exhibiting characteristics different from those of groups C, D, and E are used, and those with γ>1, which are suitable for black-and-white monochrome copying, are used.

The specific usage of each of these developing devices is determined by the selection means according to at least the glossiness and toner adhesion surface density of the final formed image to be transferred to the transfer paper 30.

This selection means includes a selection switch, control and drive means (not shown).

The selection switch includes at least a mode switch that instructs full-color copying or black-and-white single-color copying, a switch that instructs high gloss or low gloss of the copy, and a low density toner adhesion surface density. There is a switch ■ to indicate whether it is a ``text'' image or a high-density ``picture'' image.

By using switches I, n, or H, you can make black and white monochrome copies,
When either low gloss or "text" image is selected,
The black developer 17 is used, and if a full color copy, high gloss, or "picture" image is selected, the black developer 18 is used.

The following benefits can be obtained by forming an image according to the instructions given by the above switches.

(1) A high-quality full-color copy image can be obtained.

This is because the image is formed using black toner B, which is the same type of developer as yellow toner E, magenta toner D, and cyan toner C. Color masking through digital image processing, especially UCR (undercolor removal) Since this effect is most noticeable, it is possible to express a natural black that is well-balanced with other colors.

(2) High-quality black-and-white copies can be obtained.

This is due to the use of black toner A having high γ characteristics.

(3) In (2), high gloss or low gloss copies can be obtained. This can be achieved by selecting black toner B when a high-gloss black-and-white copy is required, and by selecting black toner A when a low-gloss black-and-white copy is required.

(4) In (2), line images (text, line drawings, etc.)
Alternatively, the optimum reproduction state can be selected for each solid image (design, photograph, etc.). Usually, black and white monochrome copies are mostly line images, and color copies are mostly solid images.

Therefore, this requirement is automatically satisfied by selecting switch (2).

(5) Regarding the creation of black and white copies, which are used most frequently by users, when manufacturing black toner A corresponding to this,
Developer formulations and materials that can be expected to have the highest developer durability can be used, and reliability and economical efficiency can be improved.

Although the above description has been made regarding a copy image, the present invention is not limited to copy images and is widely applicable.

(Effects of the Invention) According to the present invention, a high quality black image portion can be obtained depending on the image format such as full color recording, black and white monochrome recording, etc.

[Brief explanation of drawings]

FIGS. 1 and 2 are overall schematic diagrams of a color image forming apparatus illustrating an embodiment of the present invention, and FIG. 3 is a characteristic diagram of a developer. 9...Writing section, 17. 18...Black developer. (idiot name)

Claims (1)

[Scope of Claims] 1. A writing device that writes a document image that has been converted into an electric signal in advance on an image carrier, and a developing device that visualizes the latent image written on the image carrier as a toner image. , in a color image forming apparatus having a transfer means for transferring the toner image to a transfer material, the black developing means in the developing means has two different black developing means, one for forming a full color surface image and the other for forming a black and white monochrome image. A color image forming apparatus characterized by comprising: means. 2. The color image forming apparatus according to claim 1, wherein the two different black developing means are selected depending on at least the glossiness and toner adhesion surface density of the final formed image.