JPH035737B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Conventionally, a method of producing a gravure printing plate using a halftone positive for planography or letterpress printing is known.
Commonly used in this method are:
A method of making a gravure printing plate by printing the image of a gravure screen and the image of a halftone positive for planography or letterpress onto a photoresist such as carbon film, and then etching a gravure cylinder through the photoresist. It is. In this case, there is a problem in that a moiré pattern occurs between the lithographic or letterpress screen positive and the gravure screen.

One possible method for making such a moire pattern less noticeable is to use a grained gravure screen. However, this method has the disadvantage that the use of a grained gravure screen results in printed matter having a rough feel. Therefore, this method is not used for anything other than printed matter where a special grain effect is expected.

Another way to prevent moire is to overlay a negative pattern when printing the gravure screen onto the photoresist, so that the pattern on the gravure screen is not printed in the light to midtone areas where moiré is likely to occur. A method for doing this is disclosed in Japanese Patent Publication No. 13026/1983. However, this method has problems in terms of cost, work efficiency, etc. because it is necessary to further create a negative pattern.

Therefore, in the past, it was necessary to strictly adhere to the operational constraints of regulating and controlling the number of screen lines and screen angle of each halftone positive screen for planography or letterpress printing and the screen for gravure so that moiré would not be noticeable. By using this method, printed matter with inconspicuous moiré patterns was produced.

The present invention aims to provide a gravure screen which has less roughness like a grained gravure screen, and which also has a less noticeable moiré pattern between it and a net positive for planography or letterpress printing than a normal orthogonal screen. be.

That is, the gravure screen of the present invention randomly selects a plurality of types of parallel line patterns in which the line ratio of the transparent part and the opaque part is constant and the line width is different, and the opaque part of the parallel lines arranged in parallel is connected to the parallel line pattern. It has a pattern divided by parallel transparent lines perpendicular or diagonal to the parallel lines.

FIG. 1 is an explanatory diagram of the parallel lines, with transparent parts 11, 21, 31, 41 and opaque parts 12, 2.
2, 32, and 42, and these transparent parts and opaque parts are arranged alternately. The transparent portion 11 and the opaque portion 12 form a parallel line pattern 10 of the parallel lines. Similarly, parallel line patterns 20, 30, and 40 are formed by combining transparent portions and opaque portions. The ratios a:b, c:d, e:f, g:h of transparent parts and opaque parts of these patterns 10, 20, 30, 40 all have constant values, and in the example of the drawing, it is 1. :3
It is becoming. Transparent parts 11, 21, 31, 41
The line width is different. This corresponds to a state in which a plurality of parallel line patterns having a constant line ratio and different line widths are randomly selected and arranged in parallel.

FIG. 2 shows a pattern in which the opaque parts 11, 21, 31, and 41 of the parallel parallel lines shown in FIG. 1 are divided by parallel transparent lines. The opaque portion 12 is divided by parallel transparent lines 11a to form cells 12a. Similarly, the opaque portions 22, 32, 42 are divided by parallel transparent lines 21a, 31a, 41a, respectively, to form cells 22a, 32a, 42a.

Although the parallel transparent lines 11a to 41a in FIG. 2 are perpendicular to the parallel lines, they may be oblique to the parallel lines. When the opaque portions of the parallel parallel lines are divided by parallel transparent lines, the blackened portion area ratios of the cells 12a, 22a, 32a, and 42a thus formed are made to be the same. FIG. 3 is for explaining the method of calculating the area ratio of the blackened part, and the area ratio K of the blackened part is expressed by the following formula using the symbols in the figure.

K=b×n/(2+b)×(m+n)×100(%) In the example shown in FIG. 2, the area ratio of blackened portions in all cell portions is 56.3%. Note that the shape of the molar part does not have to be square, and may be rectangular, diamond-shaped, or the like.

The line ratio of transparent and opaque parts of parallel lines is 1:
It is not limited to 3, but can be freely set within the range of about 1:2 to 1:5. The area ratio of the blackened portion of the cell is not limited to about 56%, but may be larger than that. The width of the parallel transparent lines that divide the opaque parts of the parallel lines is preferably 50 μm or less, and may have a width that prevents dots from being formed by side etching when etching the gravure printing plate.

The gravure screen of the present invention as described above does not cause noticeable moiré even when used in combination with a screen positive for planography or letterpress printing. Furthermore, since the area ratio of the blackened portion is the same, the roughness is reduced compared to a sand-grained screen.

As a method of combining the gravure screen of the present invention and the net positive for planography or letterpress printing, it is possible to print them on the same photoresist such as carbon tissue, or,
A possible method is to create a net positive in which the gravure screen of the present invention is incorporated by overlaying the gravure screen of the present invention in close contact with a net negative and then contact-printing the same onto a photosensitive film.

<Example 1> Parallel line pattern with a line ratio of transparent part and opaque part of 1:3, 150l/inch, 160l/ineh, 170l/inch,
10 randomly selected parallel line patterns with line widths equivalent to six types of screens: 180l/inch, 190l/inch, and 200l/inch and arranged in parallel.
I created a set of 60 parallel lines by arranging them in sequence. FIG. 4 shows a part of the parallel line pattern thus obtained. Next, the opaque portion was divided by parallel transparent lines perpendicular to the parallel line pattern. The method of division in this case was as follows. In other words, the area ratio of the blackened area of the divided cell parts is made to be the same as that of a conventional orthogonal gravure screen with a line ratio of 170/inch and a line ratio of 1:3. The linear ratio (m:n in the example of FIG. 3) was set to 1:3. FIG. 5 shows a partially enlarged view of the pattern thus obtained.

Next, the patterns thus obtained were connected photographically to obtain a film-like gravure screen of practical size (approximately 20 cm x 30 cm).

After the gravure screen thus obtained was closely baked on a carbon tissue, a 175 l/inch lithographic screen positive was closely baked on the same carbon tissue, and the carbon tissue was transferred to a copper cylinder.
After development, it was etched to obtain a gravure printing plate. When gravure printing was performed using this gravure printing plate, smooth printed matter with less noticeable moiré and less roughness was obtained.

In the case of the gravure screen of the present invention, the angle adjustment conditions when used in combination with a lithographic screen positive are relaxed compared to conventional orthogonal gravure screens so that moiré patterns are less noticeable.

<Example 2> Instead of the parallel line pattern having line widths corresponding to the six types of screens used in Example 1, a pattern with a number of lines was used.
250l/inch, 270l/inch, 290l/inch, 310l/
A gravure screen was obtained in the same manner as in Example 1, except that a parallel line pattern was created by selecting from parallel line patterns having line widths corresponding to six types of screens: inch, 330 l/inch, and 350 l/inch. .

When a gravure printing plate was prepared and printed in the same manner as in Example 1 using this gravure screen, a printed matter with less noticeable moiré and less roughness was obtained which was smoother than the printed matter of Example 1.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the parallel line pattern, Fig. 2 is an explanatory diagram of the pattern of the gravure screen of the present invention, Fig. 3 is an explanatory diagram for calculating the area ratio of blackened portions, and Fig. 4 is an explanatory diagram of the pattern of the gravure screen of the present invention. FIG. 5 shows a partially enlarged view of the parallel line pattern according to Example 1, and FIG. 5 shows a partially enlarged view of the gravure screen of the present invention obtained according to Example 1. 10, 20, 30, 40...parallel line pattern, 1
1, 21, 31, 41...transparent part, 12, 22,
32, 42... Opaque portion, 11a, 21a, 31
a, 41a...Parallel transparent line, 12a, 22a, 32
a, 42a...Cell.

Claims (1)

[Claims] 1 Parallel line patterns in which the line ratio of transparent parts and opaque parts is constant and line widths are different are selected irregularly and the opaque parts of the parallel lines are arranged in parallel or perpendicularly to the parallel lines. 1. A gravure screen characterized by having a pattern divided into cell portions having the same area ratio of blackened portions by diagonal parallel transparent lines.