JPS58214159A - Method of making inverted halftone gravure plate - Google Patents

Abstract

PURPOSE:To form easily a photosensitive layer for transferring an image to a plate material, by bringing a contact screen and a screen positive into intimate contact with the photosensitive layer and printing it. CONSTITUTION:A gravure contact screen S in contact with a sensitized carbon tissue C is contact printed with a UV light source from the direction of arrow E to form a hardened part as shown by hatches 2 in the first step. Then, the screen positive P for use in lithographic, letterpress, and gravure printings in intimate contact with the side of the tissue C opposite to the emulsion layer is contact printed to form printed parts 6 corresponding to dots 4a, 4b, 4c in the second final step. Since a transparent film base 7 diffuses transmitted light as a spacer, the hardened parts 6 are changed in depth in accordance with the dots 4a, 4b, 4c different in area, and the form of the hardened parts 6 approaches a continuous gradation. Then, it is transferred to the plate material and etched.

Description

[Detailed description of the invention] The present invention relates to a net gravure plate making method.

The net gravure plate making method involves the first step of contact-printing a special contact screen (screen) with a grid-like array of halftone dots with a loose outline onto a sensitized carbon tissue; A second step of contact-printing the screen positive; an eighth step of contact-printing the carbon chip with a diffusion sheet and the top of the screen positive; the carbon chip thus obtained is transferred to a plate material, and the printing process is performed. A method is known which consists of a fourth step of corrosion, and a fourth step of corrosion. However, with this method, there are 8 steps involved in baking the contact screen, baking the net positive, applying the diffusion sheet, and printing the net positive.
All steps must be completed.

In addition, a vacuum baking frame is normally used for contact baking, but between the second and eighth steps, the vacuum is returned to atmospheric pressure, the carbon tissue is removed, and a diffusion sheet is installed. ,
In order to place the carbon chip in a predetermined position again and vacuum it, the location and degree of distortion are different in the second and eighth steps, where the distortion occurs when the carbon chip is made into close contact with the positive. , therefore exact registration is difficult.

On the other hand, Japanese Patent Publication No. 56-26016 discloses one process in which a net negative is closely printed onto a sensitized carbon tissue through a diffusion sheet and a contact screen for gravure, and a screen positive is attached to the baked carbon tissue through a transparent film. A net gravure plate making method is described that includes a second step of printing. in this way,
The process only requires two steps, but in the first step, eight
In addition, since a net negative and a net positive are used, it is necessary to register them, and printing the contact screen cannot be done in a separate process. In this method, image information is printed on the carbon tissue in both the first and second steps, so the screen is printed on the entire carbon tissue at a certain angle in advance, as in the conventional gravure platemaking method, and the screen is printed each time it is needed. It is not possible to set up a work such as printing a positive onto a carbon tissue, and the carbon tissue that has gone through the first process must be printed in the second process using a corresponding mesh positive, resulting in a troublesome registration process. The problems associated with this still remain unresolved.

Furthermore, the net gravure plate making method described in Japanese Patent Publication No. 58-67504 corresponds to the method described in Japanese Patent Publication No. 56-26016 using a diffusion sheet instead of the transparent film used in the second step. However, this method also has the same problems as mentioned above.

First, the present invention is intended to provide a simple method of the above-mentioned known net gravure plate making method.

According to the present invention, a first step of contact printing a contact screen having a fixed array of halftone dots with a blurred outline on a photosensitive layer such as a sensitized carbon tissue or an autofilm; In the second step, in which the halftone positive is layered and contact-baked so that the surface opposite to the emulsion layer is in contact with the photosensitive layer, a photosensitive layer is carefully prepared for transfer to the plate material. Ru.

Next, a detailed explanation of the present invention will be given with reference to the drawings.
The figure shows the first step 8'e of the net gravure plate making method of the present invention, in which a gravure contact screen is printed in close contact with the sensitized carbon tissue C. Arrow B indicates the direction of exposure The contact screen S is a screen that has a constant array of halftone dots whose density decreases from the center toward the outline, and the outline is blurred and the density is 0.
．． Each halftone dot, which continuously changes in the range of 1 to 8.0, is a square or a square with rounded apex corners. The number of lines of this contact screen is 1o.

selected from the range of 5850 lines/inch. The number of lines is typically on the order of 250 lines/inch. Also, the ratio of the width of the line part to the non-line part of the contact screen is 1
+2.8 or so can be used, but if +8 to +5 is used, the possibility of halftone dots being cut off is reduced. It should be noted that other photosensitive layers such as autofilm can be used in place of ~-Bontechno. When the contact screen SL is baked on the carbon tissue 0, a hardened part 2 shown by diagonal lines is formed on the carbon tissue. In order to fully improve the parallelism of the light beam using a light source, the intensity of ultraviolet rays on the exposed surface is 2 to 6 mW.
It is best to use it as far away as possible to maintain /ci and expose for 5 to 10 minutes.

The use of a contact screen in the first step prevents the halftone dots from becoming too sharp and provides an overall relatively round halftone dot than if a white line screen had been used instead.

Continuing the contact printing in the first step as described above, in the second step shown in FIG. 2, a net positive P for planography, letterpress printing, or gravure is closely printed on the carpon chip 0. Through this second step, the halftone dots 4a and 4b of the halftone positive P are
, 4c is formed on the carbon tissue.

The important point in this second step is that the mesh positive P is placed so that its surface opposite to the emulsion layer surface is in contact with the carbon tissue 0. In other words, the net positive P is the eighth
The process shown in the figure has an emulsion layer surface (film surface) only on one side of the base film 7 (the top surface in the figure), and during development, halftone dots 4a, 4b, and 4c are formed only on that emulsion layer surface. Although a light-transmitting film is formed, in the second step of the method of the present invention,
The surface of this emulsion layer is placed on the side opposite to carbon tissue 0, that is, on the side of the exposure light source, and is exposed to light in the direction E.

The base thickness of commercially available films is usually 100°15
0.175 μm, etc., and the thinnest one is 75-μm.
In any case, the film has a certain thickness, so place the net positive P on the surface of the carbon film C with the emulsion layer side facing the exposure source as shown in Figure 2. When brought into close contact, a kind of spacer is formed in the transparent base film 7 between the non-transparent film of the halftone dots 4a, 4b, 4c on the surface of the emulsion layer and the surface of the carbon tissue C. The thickness of this spacer then corresponds to the thickness of the base mentioned above.

During the second step of contact baking, the light that has passed through the transparent part of the net positive P reaches the carbon chip C while being diffused by the spacer function of the base film 7, and the hardened part 6 described above. is formed.

That is, the hardened area immediately below the halftone dot 4a in the shadow area is the shallowest, the hardened area immediately below the halftone dot 4b in the intermediate gradation area has an intermediate depth, and the hardened area immediately below the halftone dot 4c in the light area is the shallowest. is the deepest. 1. Due to the diffusion of light by the transparent base film 7, the light forms the halftone dots 4a.

4b and 4c, the shape of the hardened portion 6 approaches continuous gradation.

That is, in performing the contact printing in the second step of the present invention, in addition to transmitting the halftone dot image information in the conventional halftone positive contact printing, in other words, the shape and size of the halftone dot,
The exposure in the second step, which simultaneously transmits the generation and production of pseudo-continuous gradation in halftone positive printing through the diffusion sheet) 1, may be normal exposure, but preferably a combination of parallel light exposure and diffused light exposure. do.

For determining the formation of halftone dots in highlight areas, it is preferable to use parallel light exposure to avoid crushing the small halftone dots. A light source with a lens is used. On the other hand, since a light diffusion effect cannot be obtained with parallel light alone, diffuse light exposure is used in combination as described above. An example of a diffused light source is one in which a satin reflective plate is provided behind the lamp and a diffuser plate is further provided in front of the lamp.A more preferable diffused light source is a scanning light source. When the exposure surface is scanned with a point light source or a line light source, the angle of incidence of light on the carpon tissue changes continuously for each halftone dot, making it possible to perform exposure from various directions.

The ratio of parallel light exposure and diffused light exposure is 80-90/20-1
It is better to set it to 0. That is, the amount of exposure due to parallel light is greater than the amount of exposure due to diffused light.

By using parallel light exposure and diffused light exposure in combination as described above, it is possible to prevent a decrease in resolution while obtaining a sufficient diffusion effect without using a light diffusing sheeter other than halftone positive P.

In addition, if necessary, flash exposure may be performed on the carpon tissue after exposure in the first or second step.
The depth of the shadow portion can be controlled.

As the exposure source, for example, an ultraviolet light source such as a mercury lamp or an arc lamp is used, and exposure is preferably performed for about 8 to 8 minutes at a distance *fli of 2 to 5 m and an ultraviolet intensity of 2 to 6771 W/crl on the exposed surface.

As a net positive, for example, 150 fRJ/inch
A line of about 175 lines/inch is used. Note that if the number of halftone positive lines is too large, it is difficult to form halftone dots in highlighted areas. The installation angle when printing the net positive P is
The angle of the screen is varied within the angle range of 0° to 90° for the valley color halftone positive, and the screen angle is usually varied within the angular range of θ° to 4° for each color halftone positive. In order to suppress the occurrence, the same result can be obtained even if the first and second steps are performed in the reverse order.

After the carbon tissue is cured by exposure to light as described above, the carbon tissue is transferred to a plate material, developed, and then eroded. A gravure printing plate 8 having the following properties is obtained.

When using the method of the present invention, it becomes difficult to form halftone dots in highlighted areas due to the diffusion of light, so instead of the serial dilution method, a multi-liquid corrosion method is used as the corrosion method. In either method, the corrosive liquid is gradually thinned as the corrosion progresses, and this allows for smooth penetration of the corrosive liquid into the highlighted areas, allowing the correct formation of cells in the illuminated areas. Furthermore, when comparing the method of the present invention in which a white line screen is used as a substitute for the blur screen and the method of the present invention, the transfer was better when printing using a gravure cylinder made using a brush screen. The shape of the halftone dots is soft (meaning there are no corners), making it difficult for moiré to occur.Furthermore, the cells formed on the surface of the gravure cylinder use a white line screen, so the halftone dots are not cut sharply during the process. The rounded corners improve the transferability of the ink, making it more stable and capable of reproducing good tone than the general gravure printing method, and also preventing the printed material from feeling rough. Therefore, the drawback that the overall smoothness is lost can be solved.

As described above, in the present invention, there are only two steps: a step of printing only the contact screen as a filler screen, and a step of printing only the net positive, and each step requires only one film. The method of the present invention can be said to be overall simpler and easier to implement than conventional methods. Since it is only a process, even if there are multiple colors, if the screen angle and net positive angle are determined for each color, the screen printing can be performed in advance, and the net positive can be printed as needed. Benefits in terms of work setup can also be maintained.

In addition, if you use an offset net positive,
In addition to the sense of mass that gravure has, it is possible to incorporate the advantages of offset, and it is possible to improve the reproducibility of originals. It also becomes possible to use offset net positives and proof printing by offset.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the first step of the net gravure plate making method of the present invention, FIG. 2 is a diagram showing the second step, FIG. 8 is a cross-sectional view of the net positive used in the second step, and FIG. The figure is a cross-sectional view of the obtained gravure printing plate. C... Carbon tissue, 8... Contact screen, P-... Net positive, 2.6-... Cured part, 4a, 4
b. 4C...halftone dot, 7...base film, 8...gravure printing plate. Applicant's agent Kiyoshi Inomata

Claims (1)

[Claims] contact printing a contact screen having an array of halftone dots with frayed contours onto a photosensitive layer such as sensitized carbon tissue or autofilm;
A step of contact-baking the entire screen positive for planography, letterpress or gravure onto the photosensitive layer so that its surface opposite to the emulsion layer surface is in contact with the photosensitive layer, and the above two contact-baking steps. A net gravure plate-making method that consists of a process of transferring the photosensitive layer onto a plate material and corroding it.