JPS60147738A - Direct plate making method - Google Patents

Abstract

PURPOSE:To reproduce a block copy original including at least a halftone dot picture more than 100 lines per inch accurately by exposing a lithographic plate from the back of the light-transmissible block copy original having the halftone dot picture through a lens. CONSTITUTION:A lighting light source (halogen lamp) is arranged on the back of an original setting board of an exclusive automatic plate making machine (reflecting mirror system) of a printing board independently of an already set-up light source (front side) for reflecting exposure. The reflected original and the transmitted original are exposed by the reflecting exposure light source and the transmitting exposure light source respectively so that 50% area of the halftone dot can be reproduced in plate making processing. In said method, the block copy original including the halftone dot picture 100 lines or more per inch can be accurately reproduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of making a lithographic printing plate directly from a draft, a so-called direct plate making method.

BACKGROUND OF THE INVENTION Today, a wide variety of lithographic printing plates are known and put into practical use. Examples include gresencitized plates (so-called P8 plates) using diazonium compounds, electrophotographic printing plates using zinc oxide or organic photoconductors, and silver salt photolithographic printing plates using silver halide emulsions. This is listed as a typical example. 9. Lithographic printing plates with high photosensitivity, such as the latter two, can be easily and quickly made using an automatic plate-making machine, from photographing the document to be printed to processing. It has become rapidly popular as a lithographic printing plate suitable for direct plate making.

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. Although lithographic printing plates for direct platemaking have such excellent characteristics and improved printing durability, it is still believed that they are destined to be unable to match the image quality of the P8 plate, and to this day, they are still There is. In other words, high image reproducibility can be obtained (by contact printing from expensive lithographic film as an intermediate manuscript for P8 printing companies), whereas direct platemaking has poor image reproducibility because it is photographed with a camera through a lens. What you can't get is a well-known fact. Furthermore, JP118
48- & 9007, a prepress camera has a built-in prism or reflective mirror in order to obtain the correct print on the left and right sides of the image, and this prism or reflective mirror does not affect the optical properties, It is known that this also deteriorates image reproducibility.

Inferior image 1# in this direct plate making method! Even if the reproducibility is practically acceptable for line drawing manuscripts such as characters and ruled lines, there is a significant difference in reproducibility from the 28th edition for images obtained by converting continuous tone originals into minute halftone dots. In fact, even silver halide lithographic printing plates, which are lagging behind in resolution, can at best reproduce halftone originals with 1,100 lines per inch; It has not been possible to recreate the elephant, and users have been requesting its realization for many years. If this is to be achieved using something other than printing materials, that is, an automatic plate-making machine, it would be beneficial from the user's perspective if there was a method that could be used by simply making a few changes to the large number of existing plate-making machines. .

OBJECTS OF THE INVENTION An object of the present invention is to provide a direct plate-making method that can faithfully reproduce a draft manuscript containing at least a halftone image of 100 lines per inch or more.

Another object of the present invention is to provide a direct plate-making method that can achieve the above-mentioned purpose by only slightly improving an existing automatic plate-making machine.

Structure of the Invention The above object of the present invention has been achieved by a direct plate making method characterized by exposing a lithographic printing plate to light through a lens from the back side of a light-transmissive original having at least a halftone image.

The present inventors have continued to conduct intensive research into improving the image reproducibility of direct plate-made lithographic printing plates, and it is true that the reason for the poor image reproducibility is due to optical systems such as lenses and reflective mirrors. However, as a result of discovering that there are also important causes in areas that have traditionally been common knowledge in direct plate making, such as the draft original and exposure method, we have discovered that there are important causes that can be used without changing the optical system such as lenses. We have now discovered a method by which the objects of the present invention can be achieved.

All of the cameras for direct plate making that are commercially available or already installed today use a reflected light photography method.

Therefore, the originals to be used include characters and lines created with high-contrast image-forming materials using light-impermeable supports such as phototypesetting paper and positive paper produced by silver complex diffusion transfer. It is only a so-called reflected image of an image obtained by converting a continuous tone image such as a TNH photograph into a halftone image (this is called a halftone image), and these reflected images are assembled into a desired composition. The reality was that it was a printed manuscript.

If such halftone dot reflection image is used as a manuscript and is directly plate-made using a silver halide lithographic printing plate or an electrophotographic lithographic printing plate, there will be 80 halftone dots per inch, or at most 100 fiI halftone dots. The image could only be reproduced to an acceptable level for practical purposes, and a manuscript with 133 lines could not be reproduced.
The paper had to be printed in an expensive 28-plate version, which was economically disadvantageous.

The present invention is different from the conventional direct plate making method in that it uses a light-transmitting original as the original. Therefore,
Halftone images are created in photographic materials on light-transmissive supports such as transparent films. The photographic material used is one that can provide a transmission density of 2 or more. Generally, most original documents are combined with not only halftone images (photographs) but also negative line images.

This line image is also preferably created using a photographic material capable of obtaining a transmission density of 2 or more.

Since such a light-transparent original is used, an automatic plate-making machine requires a light source for illumination on the back side of the original when viewed from the printing plate, and this light source can be easily installed in an existing automatic plate-making machine. be able to.

However, some existing self-plate making machines are equipped with a light source on the back side of the manuscript shelf. However, the purpose of this light source is different from the light source for exposing the reflected image on the front side; it is only intended to shine light from the back side of the mount in order to erase the shadows of the manuscript pasted on the mount for the original manuscript. This is completely different from the purpose of image exposure in the present invention.

Effects of the Invention The present invention succeeded in successfully reproducing a halftone image with 9133 lines per inch or more than 150 lines per inch, which could not be achieved by conventional direct plate making methods using silver salt lithographic printing plates or electrophotographic lithographic printing plates. This will bring about dramatic progress in improving the quality of direct plate making in the field of light printing.

The present invention can also improve the resolution of line images, and can obtain high-quality printed matter by greatly improving image reproducibility.

The present invention is an advantageous method from the user's perspective because it can be achieved by simply installing a new light source for diffused illumination in an existing automatic plate making machine.

Example A commercially available lithographic printing plate that utilizes surface transfer silver as an ink-receiving agent using the silver complex diffusion transfer method and a dedicated automatic plate making machine (reflection mirror) for the above printing plate that is equipped with development, neutralization, and desensitization treatment tanks. An illumination light source (halogen lamp) was attached to the back side of a manuscript rack (one-sided type) separately from the existing light source for reflective exposure (on the front side).

50 micron ruled lines and 1 inch as a block manuscript! D8
An image-receiving material for silver complex diffusion transfer having a halftone image of 0, 100, 133, or 150 lines was prepared on polyethylene laminate paper (reflective original) and polyester film (transparent original) as supports. The maximum reflection density of the reflective original was 1°37, and the maximum transmission density of the transparent original was 3.4.

The reflective original was exposed to light W for reflective exposure, and the transparent original was exposed to light using a light source for transmission exposure so that halftone dots with an area of 50 cm were clearly visible. As a result of printing these lithographic printing plates with an offset printing machine, in the case of reflective originals, 80 lines and 1
For the 00 line, the image was reproduced without any practical problem, but for the 133 or more lines, the small halftone dot area (area 5 to 20%) of the document could not be obtained, and the large halftone dot area (area 80%) could not be obtained.
~95cm) were crushed, and the resulting halftone dots also had disordered edges. Furthermore, the ruled lines were all thick, ranging from 60 to 70 microns.

On the other hand, in the case of transparent originals, all halftone dot images of 80 to 150 lines are reproduced almost exactly as the original from 5q6 to 95%, the halftone dots are also solid, and all ruled lines are 50 to 150 lines.
TL was reproducing the micron.

Procedural amendment issued April 9, 1985, Commissioner of the Japan Patent Office1, Indication of the case, Patent Application No. 4168, 1982,2, Name of the invention, Direct plate making method3, Amendment made by Mitsubishi Paper Mills Co., Ltd.5, Amendment In the subject ``Detailed Description of the Invention,'' the column ``Also, the ruled lines were 60 to 70 microns thick.'' was deleted.

Claims (2)

[Claims] (1) A direct plate-making method characterized by exposing a lithographic printing plate to light through a lens from the back side of a light-transparent draft manuscript having at least a halftone image. (2) The direct plate-making method according to claim 1, wherein the draft manuscript has a line image in addition to a halftone image.