JPS61196248A - Direct manufacture of multicolor printing plate - Google Patents

Abstract

PURPOSE:To enable a good black printing plate to be formed from a perfect block copy original composed of continuous tone multicolor images and line image mixed with each other by covering the line images with a masking material lower in light reflectance and the continuous tone images with a masking material higher in reflectance and using this original for exposure. CONSTITUTION:Since the original part of letters A are used to expose a yellow plate as a line image, it is covered with a black masking material M-1 having an optical density of 2.0 and a light reflectance of 1%. Since the original part of letters B is formed as a black plate, it is covered with a white masking material M-2 having an optical density of 0.07 and a reflectance of about 85% to prevent the yellow plate from being exposed as the line image. The original thus prepared is used to give flash exposure with a reflection exposure light source, and then, the original having the part B covered with M-2 but the part A freed of M-1, and a part of a photograph covered with M-1, thus permitting the letter A to be photographed, and the yellow plate to be obtained by using this original for exposure.

Description

[Detailed Description of the Invention] ^ Industrial Application Field The present invention relates to a method of making a lithographic plate plate directly from a draft original, a so-called direct plate making method.

More specifically, the present invention relates to a method for creating a black plate in a multicolor direct plate making method.

However, prior art and its problems Today, a wide variety of lithographic printing plates are known and put into practical use. Examples include gresencitized plates (so-called PS plates) using diazonium compounds, electrophotographic printing plates using zinc oxide or organic photoconductors, and silver salt photolithographic printing plates using silver halide emulsions. It is listed as a typical example. However, like the latter two, lithographic printing plates with high photosensitivity can be easily and quickly made using an automatic plate-making machine, from photographing the original to be printed to processing. It has become rapidly popular as a lithographic printing plate suitable for the so-called direct plate making method.

In particular, lithographic printing plates for direct plate making using silver salt as a photosensitive component are useful because they have extremely high photosensitivity, contrast, and resolution.

It has been proposed to perform multicolor printing by taking advantage of the advantages and features of the direct plate making method.

According to this method, a contact screen is placed in close contact with a lithographic printing plate having panchromatic light sensitivity, and a draft original containing a continuous tone color image (for example, a color photograph) and a line image (for example, a middle line of text) is color-separated. A cyan plate, a magenta plate, a yellow plate, and a black plate are made by exposure using a filter.

By the way, when color printing is performed using a well-known PS plate, images such as photographs (hereinafter referred to as continuous tone images) and characters and lines (hereinafter referred to as line images) are printed. They are printed separately on lithographic film as intermediate documents, and these lithographic films are printed on P.
The image was printed on the S version, closely following the composition.

However, in the direct plate making method, since the entire intermediate original such as lithographic film is not used, it is necessary to use a complete original in which continuous g images and line images are assembled into the desired composition to be printed. It requires continuous tone image exposure using a screen and line image exposure without using a contact screen. When exposing these two images separately, it is sufficient to cover one unexposed image with a mask and expose the other image. There were problems in that halftone dots were formed, halftone dots in continuous tone images became smaller, and halftone dots disappeared.

This problem occurs in the cyan, magenta, and yellow versions when the mask body with a light reflectance of 2% or less and the light-reflecting main fishing 8
We have separately proposed that the problem can basically be solved by using a mask body with a density of 0% or more.

However, in black printing, it is difficult to solve the problem using only the above solution, and a special method is required.

(Q. Purpose of the Invention The purpose of the present invention is to provide a method for creating a black plate in a multicolor direct plate making method.

0 Structure of the Invention The inventors of the present invention have conducted intensive studies on the method of creating a black plate, and have discovered that the method described below can be used.

That is, the present invention is a method of exposing an original having a continuous tone image and a line image to a photosensitive lithographic printing plate (G) for a black plate, and exposing the line image to a mask body (M) having a light reflectance of 2% or less. -1)
CM-2)
exposing the printing plate (G) to light through a contact screen while covered with a line image t-nuclear mask body (M-1), and exposing the printing plate (T) to light through a contact screen with no mask body used for a continuous tone image; The printing plate (g) without going through
and a line image exposure comprising exposing the printing plate to light with the continuous tone image being exposed to the mask body (M-1). This is a multicolor direct plate making method characterized by the following.

The present invention will be explained in more detail below.

The method of the present invention - For performing rituals, for example, Japanese Patent Application No. 59
A plate making camera capable of attaching and detaching a contact screen under bright room light, as described in detail in Japanese Patent Application No. 126208, can be used, but is not limited to this. Any plate-making camera may be used as long as it is capable of attaching and detaching a contact screen to the lithographic printing plate (P).

The present invention is illustrated using the plate-making camera described in the above specification and a photosensitive lithographic printing plate (CP) utilizing a silver complex diffusion transfer method having a (chromatically spectrally sensitized) 10-silver-genide emulsion layer. do.

(G) An example manuscript was prepared on a manuscript rack with continuous tone multicolor photographs and characters (-) arranged in the composition to be printed.

The heading text shall be printed in red, and the text B shall be printed in black using a black plate. In this case, the text document may have text in a desired color instead of black.

First, I will explain how to create the yellow version. A 150 t/inch gray contact screen (CS) was set on a horizontal exposure platen, and then conveyed and superimposed on the printing plate (T) tC8 stored in a magazine, so that it was vacuum-adhered and ready for exposure. do. In front of the lens, an f-color filter is set by rotating a color filter rack. On the other hand, since the part of the original with characters is exposed as a line image on the yellow plate, the original with 0 characters B is covered with a black mask body (M-1) with an optical density of 2.0 (light reflection ￥A1%). Since the part is created using a black plate, the yellow plate has an optical density of 0.07 (light reflectance, approximately 85%) so that it will not be exposed as a line image.
) is covered with a white mask body (M-2).

The document prepared in this way is exposed to the aperture f using a reflective exposure light source.
=16,100 seconds of photographic original (q exposure is performed. Then, by a well-known method, a flat exposure of f=16.3 seconds is given.

Next, the vacuum contact state is released, and the printing plate (P) is pulled out of the C84 machine while being maintained at the same position. For the original, the part with the letter B is covered with a white mask (M-2), the black mask with the letters (M-1) is removed, and the photo part is covered with a black mask with the same light reflectance as above. Mask body (M-1
), you will be able to photograph the letter A.

−f=16, a 10 second exposure is carried out on the above printing plate P).

The printing plate surface, which has been exposed in this manner, is transported to a plate-making processing section, where it is subjected to processing such as development, stopping, and desensitization to become a yellow plate.

The magenta version can also be obtained by the same operation as the yellow version.

The cyan version uses the white mask body (M-
2) and exposing the photographic original (C).

Next, a method for creating a black plate according to the present invention will be described.

As is well known, the black plate increases the contrast in the high-density areas of continuous-tone multicolor originals, that is, the shadow parts, and hides errors in gray balance caused by the three-color ink of cyan, magenta, and yellow. used for

Normally, a black plate is created so that the optical density in the shadow part of the document is around 1.0 and has a halftone dot area of 5%, and around 2.0 has a halftone dot area of 50qIb. However, in the direct plate-making method, the complete draft manuscript often includes line images printed in black, such as the letter B1.
Character Bt-Even when covered with the mask body (M-1),
Simply exposing the printing plate (G) to a continuous tone image through a contact screen would result in the formation of halftone dots in the portion of the letter B.

However, an important feature of the present invention is that while the character B is covered with the mask body (M-1), a continuous tone multicolor original is covered with the mask body (M-2) and exposed through C8 gold. (This method forms only a halftone image, and is hereinafter referred to as "cotton exposure") and the image exposure of the original document itself without going through C8 2
By performing two exposures, a black plate with halftone dots formed on a portion of the shadow of the original as described above is created. Specifically, the original part of the character A and the photograph is covered with the white mask body (M-2), and the original part of the character B is covered with the black mask body CM-1).

(f=16, 3 seconds). Then C8
Take a photo of the photo original with only the white mask body (M-2) removed (f = 16.4 seconds) without removing the money.
. Subsequently, the photo original was covered with the black mask body (M-1), and with the black mask body (M-1) of the letter B removed, the line image exposure of the letter B (f = 16.3 seconds) was performed. It can be obtained by rubbing.

The text is printed using the white mask (M-2) described above so as not to be formed using a black plate, but it is sufficient to use it at least once during exposure without using CS6. For cotton exposure, halftone dots (dots) with a halftone dot area of about 70% to about 90% are used.
It is preferable to apply it so as to form a .

In creating the black plate mentioned above, a white mask body (M-2) with a light reflectance of 85 cm was used for exposing the cotton cloth and masking the letters A'i, but a black mask body (M-2) for the letter B was used.
Since the light reflectance of -1) is extremely low and the portion with letters can be exposed to light multiple times, a mask body (M-2) having an even lower light reflectance may be used. In general,
It is possible to use a mask body with a light reflectance of 50% or more (a mask body with a light reflectance of this level or higher is referred to as a mask body with a high light reflectance), but preferably a mask body with a light reflection rate of 70% or more is used. .

In addition, for exposure of continuous tone color originals that do not use C8, the exposure amount of the line image can be used as a guide, and it is added to the cotton exposure amount to create halftone dots (dots) around the optical density of the original 1.0. It should be done so that the amount is about 5%. The amount and ratio of these two exposures should be appropriately determined according to preference, since there are large subjective judgment factors for color printed matter. Further, the order of these two exposures is arbitrary.

In this specification, the light reflectance of the mask body used when creating a black plate refers to the rate at which the exposure light from the light source of the plate-making camera is reflected by the mask body. It is the percentage of light that passes through it. Usually, a neutral black mask body and a white mask body are used. The mask body may be made of any material such as paper or film.

In either version, the continuous tone image and line image exposure order can be reversed.

As a result of performing color printing using the yellow plate, magenta plate, cyan plate, and publication obtained in this way, no halftone images were formed in both heading letters A (red) and body letters B (black). Not a good line image,
The color photograph was a one-of-a-kind Inryu product with good halftone quality and faithful color reproduction to the original.

The above operation is performed as a black mask body (M-1) and the light reflectance is 2.
When the same procedure was repeated except that % of the light reflectance was used, similar good results were obtained. Dots were formed, the halftone dots of the color photograph became smaller overall, and the fine halftone dots disappeared, resulting in printed matter with poor color reproducibility.

(F') Effects of the Invention According to the present invention, it has become possible to create a good black plate from a complete original containing a mixture of continuous tone multicolor color images and line images.

Claims (1)

[Claims] (1) A method in which an original having a continuous tone image and a line image is exposed to a photosensitive lithographic printing plate (P) for a black plate, and the line image is exposed to a mask body (M-1) with a light reflectance of 2% or less. Then, the continuous tone image is covered with a mask body (M-2) having a large light reflectance, and the printing plate (P) is exposed through a contact screen.
and covering the line image with the mask body (M-1) and exposing the printing plate (P) without using the mask body for the continuous tone image without passing through a contact screen. Multicolor color direct plate making, characterized in that it consists of image exposure and line image exposure, which includes exposing the printing plate (P) with a continuous tone image covered with the mask body (M-1). Law.