JPS5924415B2 - Color electrophotographic copying method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for color copying by repeating the steps of exposing a color original through a color separation filter and developing it with color toner, and particularly to a color copying method that is excellent in reproducing black images.

Conventionally, in order to obtain a color copy from a color original by electrophotography, the light reflected from the color original is first separated and exposed using a color separation filter, and the resulting electrostatic latent image is in a complementary color relationship to the color separation filter. Developed with toner.

This process is repeated using a blue filter, a green filter, and a red filter, which are developed with a yellow toner, a magenta toner, and a cyan toner, respectively, and then superimposed to obtain a color copy. However, when a color copy is reproduced using this method, for example, if black text exists at the same time as in a color image and its explanatory text, the black text part is reproduced by superimposing yellow, magenta, and cyan toner images. However, it is difficult to maintain a balance between yellow, magenta, and cyan, making it difficult to reproduce pure black characters.

It is also known to overlay an image that has been exposed without a filter and developed with black door i or shadow toner (pale black toner) on top of the above color image to intensify the black tone, but it is still difficult to obtain pure black tone. This is difficult, and if you apply enough black toner to reproduce complete black, the black toner will also adhere to colored areas, which will adversely affect color reproduction.

Therefore, either excessive exposure without a filter is applied so that no black toner is deposited on the colored areas, or shadow toner (pale black toner) is used to prevent staining of the colored areas.

However, with this method, the text will be overexposed, or
Since it is reproduced using pale black toner, the black tone is insufficient and it is not possible to reproduce complete black. The purpose of the present invention is to
The object of the present invention is to provide a color copying method capable of reproducing complete black, which solves the drawbacks of the conventional methods as described above.

The present invention achieves the above object in a color copying method in which a color copy is obtained by repeating the step of developing with each color toner corresponding to each color separation of a color original. This method includes the steps of forming an electrostatic latent image corresponding to the black image in the original, and developing this electrostatic latent image with black toner.

Here, the following method is available as a method of not placing black toner on the color image area and placing a black toner image only on the portion corresponding to the black image.

That is, by performing image exposure with near infrared rays, an electrostatic latent image is formed only in the portion corresponding to the black image, and the black portion is reproduced by developing with black toner.

In order to reproduce a color image using the method of the present invention, the three colors yellow, magenta, and cyan may be reproduced in any appropriate order, but it is preferable to reproduce the black toner last.

In this case, if the image reflection density of the black toner is higher than 0.7, the underlying cyan, magenta, and yellow toners are well hidden, and the black image area is reproduced in pure black tone. The present invention will be specifically explained below using examples. [Example] CdSlOO7 vinyl chloride monovinyl acetate copolymer 107 (trade name) was placed on an aluminum plate.
Vinylite VMCN. Union Carbide ◆Methyl Ethyl Ketone 20y A photosensitive liquid in which methyl isobutyl ketone 307 is uniformly dispersed,
It was applied using a blade and dried to a dry thickness of 40 μm.

Next, a polyester film having a thickness of 25 μm was adhered onto this photosensitive layer using an adhesive having the following formulation.
A photosensitive plate for P process was obtained. Epoxy resin
1007 (Product name: Epicoat 828, manufactured by Ciel Chemical Co., Ltd.) Hardening agent 20V (Product name: Acmetsu H-92, manufactured by Nippon Gosei Chemical Co., Ltd.) This photosensitive plate was heated to +6,
It was charged by a 5 KV corona discharge, and then imagewise exposed through a filter at the same time as a 6.5 KV alternating current corona discharge to perform full exposure, and then developed with a complementary color toner of the filter.

This image was transferred onto high-quality paper by +6.0 KV corona discharge, and this was repeated four times to obtain a color copy. The combinations of the filter, lens aperture, and toner in this example were as follows.

Illuminance without filter at F-4.5 is 300tU
The effective exposure time during slit exposure with X was 0.3 seconds. Order Filter 1 Aperture Toner 4/Near infrared 878F-2.8 Black There was no black toner on the image area.

The black text portion of the text image area had an image density of 0.8 due to the black toner, and the reproduced black text had a pure black tone. still,
The toner used in this experiment is as follows.

Colored Pigment Coumaron Resin 40
y (Product Name: Kumaron VMl/2, Nippon Steel? Natural Rubber 50t Low Molecular Weight Polyethylene 407 (Product Name: AC Polyethylene Manufactured by Allied Chemical) Aromatic Solvent
150y (Product name: Solbetsuso S-100
After dispersing the above components for 1 hour using a dispersion machine (trade name: Atraita I, manufactured by Mitsui Miike Seisakusho), 1 ton of dispersion medium (trade name: Isopa I H, manufactured by Etsuo Oil) was added for another 30 minutes. A concentrated toner was obtained by dispersion.

20 ml of this concentrated toner was dispersed in 1 t of Isopa-H, and 20 ml of lecithin was added thereto to prepare a developer. The colored pigments used here and their amounts were as follows. face
Quantity Yellow toner 50r (product name, Benzidine Yellow I G toner, manufactured by Toyo Ink) Magenta toner 507 (product name He)
liOFastPinkE vinyl cyan toner
407 (Product name, Heliogeso Blue 7040, manufactured by BASF) Black toner 507 (Product name,
MA-100, manufactured by Mitsubishi Kasei) As described above, according to the present invention, it is possible to form a latent image while sufficiently distinguishing a black image in a color original from a color image, which is particularly useful for reproducing black images. It has now become possible to form color images, which had previously been a problem.

Claims (1)

[Claims] 1 In a color copying method in which a color copy is obtained by repeating the process of developing with each color toner corresponding to each color separation of the color original, the color original is exposed to near-infrared light to correspond to the black image in the color original. A color copying method comprising the steps of forming an electrostatic latent image and developing the electrostatic latent image with black toner.