JPS60147739A - Direct plate making method - Google Patents

Abstract

PURPOSE:To reproduce a block copy original accurately by forming the black copy original actually having a light nontransmissible picture and a light-transmissible picture and exposing a lithographic plate through a lens from the back and front sides of the block copy original. CONSTITUTION:A scattered light lighting light source (halogen lamp) is arranged on the back of an original setting board of an exclusive automatic plate making machine of a printing board incorporating a lithographic plate on the market and developing, nuetralizing and resin-unsensitizing tanks independently of an already set reflecting exposure light source (front side). A picture on the lithographic plate is exposed through a lens from the back and front sides of the block copy original, so that the block copy original can be reproduced accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for directly making an applanation printing plate from a draft manuscript, 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 presensitized plates (so-called PS plates) using diazonium compounds, etc., and plates using zinc oxide or organic photoconductors. Typical examples include electrophotographic printing plates with high photosensitivity and silver halide photolithographic printing plates using silver halide emulsions. Printing plates can be made more easily and quickly than automatic plate-making machines, from photographing the document to be printed to processing, so they have become rapidly popular as lithographic printing plates suitable for so-called direct plate-making methods. A lithographic printing plate for direct plate making using a silver salt as a lithographic printing plate is useful because it has extremely high photosensitivity, contrast, last, and resolution.

Although it can be used with planographic printing plates for direct plate making, which have such excellent properties and improved printing durability, it still remains
It is believed that it is fated to be unable to match the ability of the 8th edition to express one image, and it continues to this day. In other words, the 18th edition achieves high image reproducibility by contact printing from expensive lithographic film as an intermediate manuscript, whereas the direct platemaking method provides poor image reproduction due to the camera photographing through the lens system. It is a well-known fact that only the right side of the image can be printed.As described in Japanese Patent Application Laid-open No. 89007/1989, plate-making cameras use a prism or reflective It has a built-in mirror,
It is known that this prism or reflective mirror affects optical characteristics and also deteriorates image reproducibility.

The poor image reproducibility of this direct plate-making method is acceptable in practice for line drawings such as text and ruled lines, but for images where continuous-tone originals are converted to minute halftone dots, and white areas are printed on black areas. For fine line images (negative images), etc., please contact ps
This appears as a significant difference from the original version. actual,
Even a silver halide lithographic printing plate with excellent resolution can only produce 8 halftone dots of 100 lines per inch, and P
Image reproduction with 133 lines or more than 150 lines cannot be achieved with the A version, and users have been demanding its realization for many years. If this is to be achieved using something other than printing materials, such as an automatic plate-making machine, it is possible to use a method that requires only slight changes to a large number of existing plate-making machines. @ Still, when using a draft manuscript, it would be beneficial for users if there was a method that could be done without using expensive materials such as lithographic film in PS versions as much as possible. OBJECTS An object of the present invention is to provide a direct plate-making method that can faithfully reproduce a draft manuscript containing a sub-dot image or a negative image with 100 lines or more per inch.

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

Still another object of the present invention is to provide a direct plate-making method that can achieve the above-mentioned purpose using a low-lying original.

Structure of the Invention The above-mentioned object of the present invention is to create a draft manuscript having a light-transmitting image and a substantially non-light-transmitting image, and to pass a lens through a lithographic printing plate from the back and front sides of the draft draft. This was achieved by a direct plate-making method characterized by image exposure.

The present invention will be explained in detail below.

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 were other important causes as well, such as the draft original and exposure method, which had been common knowledge in direct plate making methods, we decided to change the optical system such as the lens. We have discovered a method by which the object of the present invention can be achieved without any problems.

Today, all of the cameras for direct plate making that are commercially available or already installed use a photographing method using reflected light. An image obtained by converting a continuous tone image such as a character or line (these are called a line image) or a photograph into a halftone dot image (this is called a halftone image) using a light-impermeable support such as positive paper. (called a point image)
In reality, these reflection images are rarely assembled into a desired composition and used as a draft manuscript.

The reason for this is thought to be that the direct plate making method was originally used mainly in the so-called light printing field, where Pg plates did not have any printing durability, so it was inevitable that the total cost had to be reduced. It will be done. In the present invention, the reproducibility of halftone dot images can be greatly improved while preserving this practical advantage as much as possible. In other words, the above-mentioned dot reflection image plate is used as a manuscript. When direct plate making is performed using a silver halide lithographic printing plate or an electrophotographic lithographic printing plate, there are 80 dots per inch, or at most 10 dots per inch.
The halftone image of 0a could only be reproduced to an acceptable degree for practical purposes, and originals such as 133# could be reproduced using expensive P.
The paper had no choice but to print in 8th edition, which was a huge economic disadvantage when combined with lith film, which was rare.

The present invention differs from the conventional direct plate making method that uses only a reflective surface 11J original, in that the line image is substantially non-light transparent, and the Wakuten image and negative fine line image are light transparent. A draft manuscript is created by combining the above, and the line image is reflected, and the halftone image is exposed through a lens, and the image is exposed onto the planographic printing plate through a lens. Transparency refers to the degree of light transmittance that allows image exposure by reflection exposure or transmission exposure pressure, respectively.〇Such a draft original is a paper support with a line image original on a base for the draft original. At the same time, a halftone image original on a transparent film support is pasted on a desired position of the line image original and cut out at a desired position on a mount. It can be obtained by pasting a manuscript, etc.

Halftone images and negative images are preferably created using a photographic material that can obtain a transmission density of 2 or higher, since a draft manuscript in which a reflection image and a transmission image are combined, such as O, is used, so an automatic plate making machine is used. When viewed from the printing plate, a light source for illumination is required on the front (front) side and the back (back) side of the draft manuscript.The light source on the rear (back) side can easily be installed on an existing automatic plate-making machine. Can be installed on. However, some existing plate-making machines are equipped with light sources on both the front and rear sides, but the purpose of this rear light source is different from that of the front light source for reflective image exposure. The purpose is to eliminate the shadow of the original pasted on the mount by illuminating it from the rear side of the mount, and the purpose is completely different from the purpose of the image exposure from the rear side of the present invention.

In carrying out the present invention, front side (reflection) exposure and back side (reflection) exposure are required.
Transmission) exposure may be performed simultaneously or separately.

Effects of the Invention The present invention has 9133 lines per inch, which is difficult to reproduce such as a halftone image with 150 lines or more, which could not be achieved with the conventional direct plate making method using S scale salt lithographic printing plates or electrophotographic lithographic printing plates. This invention succeeded in reproducing the original image well, and brought about a dramatic progress in improving the quality of the direct plate making method in the field of light printing.〇The present invention adds diffused illumination to an existing automatic plate making machine. This is an advantageous method from the user's perspective as it can be done by simply installing a new light source.

The present invention eliminates the need to create all of the draft manuscripts using expensive films, so the quality can be significantly improved without incurring large economic losses. , a commercially available lithographic printing plate 2 using surface transfer silver as an ink receiving material, development, neutralization,
A special automatic plate making machine for the above-mentioned printing plates with a built-in desensitization tank was equipped with a light source for diffused illumination (halogen lamp) attached to the back side of the document rack separately from the existing light source for reflective exposure (on the front side). Phototypesetting paper (polyethylene laminate paper support) with Mincho typeface characters of grade 8 to 12 printed as a manuscript, and 1 inch drawing υso, io, iaa, and Fixso.
Halftone dot images of @ (each having a halftone dot area of 5 to 95%) were prepared on a transparent polyester film support and a polyethylene laminate paper support as commercially available image receiving materials for silver complex diffusion transfer, and then the above character manuscript and The reflective halftone image original is pasted on the front side of the original mount in an arbitrary composition. In addition, the above-mentioned text original is pasted on the surface of the mount, a cut is made at an arbitrary position on the mount, and a transparent halftone image original is pasted on that part on the long side of the mount. Place the original on the document rack of the machine, and expose the reflective original to the transparent original using a black mask with a light source for reflective exposure, and the transparent original to a diffused light source for transparent exposure so that halftone dots with an area of 50% can be reproduced. Processed by plate making. As a result of printing these lithographic printing plates with an offset printing machine, in the case of reflective manuscripts, characters of any series can be printed as a without any practical problem.
It was reproduced in Jf. However, in the case of a reflective halftone image original, ij80. Image reproduction was practically acceptable for trenches and 100 lines, but for lines 133 and above, small halftone dot areas (area of 5 to 20%) of the manuscript could not be obtained, and thick halftone dot areas (area 80-95%) were crushed, and the obtained halftone dots had disordered edges.@On the other hand, in the case of transparent originals, the halftone images of 80-150 lines were 5%-95%. It was reproduced exactly as in the original manuscript, and the halftone dots were also solid.

The maximum reflection density of text manuscripts was 1.31, which was very high, and the maximum transmission density of fine-mark manuscripts was 3.8.

Claims (1)

[Claims] (1) Create a draft manuscript having a substantially light-opaque image and a light-transmissive image, and expose the image from the back and front sides of the draft manuscript through a lithographic printing plate cough lens.
Direct plate making method with mold 0