JPS6365143B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A method of printing a conventional lithographic or letterpress halftone positive and a gravure screen image onto a photoresist such as carbon film, and then using the photoresist to create a gravure printing plate is disclosed in Japanese Patent Publication No. 1970-
This method is known from Japanese Patent Application Laid-open No. 26603, Japanese Unexamined Patent Publication No. 155305/1980, and the like. When making a gravure printing plate by such a method, it is inevitable that a moiré pattern will occur between the halftone positive used and the gravure screen. Therefore, in practice, it is necessary to appropriately adjust the screen angle of the net positive and the screen angle of the gravure screen so that the moire pattern is as inconspicuous as possible, which makes the work cumbersome. As a way to solve these shortcomings,
Publication No. 13026 discloses that when a gravure screen is printed on a photoresist such as carbon film, a negative image is interposed to prevent the gravure screen from being printed in the light to middle tone areas where moiré patterns are likely to occur. A method is disclosed. However, this method not only requires an extra continuous tone negative or a screen negative, thus increasing the cost, but also the printing of the screen positive after screen printing through the negative is not in register with the image of said negative. The disadvantage is that it is necessary and the work is cumbersome.

One way to solve these problems by improving gravure screens is to increase the number of lines as much as possible.
This is because the moiré pattern described above is basically an interference pattern caused by the intersection of two types of parallel lines. For example, as shown in Figure 1, the parallel lines of pitch a and the parallel lines of pitch b are arranged at an angle. The pitch d of moiré that occurs when crossing at θ is This can be said from the fact that the number of lines of the gravure screen is larger than that of the net positive, that is, the finer the pitch, the finer the pitch of the moire that occurs will be kept.
However, the current situation is that making gravure screens finer causes various problems and restrictions in the quality of printed matter.
Publication No. 14005 discloses a method of using a halftone dot pattern created with a screen with a very large number of lines, such as 300 lines/inch to 600 lines/inch, as a gravure screen in order to eliminate the occurrence of moire patterns. However, since the halftone dot pattern in this case has a blackened area ratio of about 40 to 45%, it is blacker than the blackened area ratio of 56.3% on a regular gravure screen with a black-and-white line ratio of 1:3. The area ratio of the printed parts is extremely reduced, resulting in a significant deterioration in quality such as a decrease in the density of printed matter.

The present invention provides an extremely large number of lines when producing a gravure printing plate using the above-mentioned halftone positive for planography or letterpress printing and a gravure screen, compared to conventional gravure screens. Moreover, this method attempts to provide high-quality gravure prints by using an improved method in which the area ratio of the blackened portion is maintained at the same level or higher than that of the conventional method.
That is, the present invention provides a method for producing a net gravure printing plate using the photoresist after printing a gravure screen and a halftone positive image for planography or letterpress on a photoresist such as carbon tissue. The width of the white line in one direction is narrower than the width of the white line in the other direction, and the width of the thicker white line is about 9μ to 20μ, and the number of lines is 300.
line/inch or more, the width of the thinner white line is 0.1 to 0.5 times the width of the thicker white line, and the area ratio of the blackened part is 56% or more. This is a plate-making method. Increasing the number of screen lines means that in addition to keeping the moiré pattern thin as mentioned above, it also improves the resolution of the image and allows you to obtain sharper and smoother printed matter. Increasing the area ratio of the printed parts leads to an increase in the cell capacity of the printing plate, which means that it is possible to obtain printed matter with a more voluminous feel, or in other words, with a richer amount of color.

However, in general, increasing the number of screen lines and increasing the area ratio of blackened portions are accompanied by a decrease in the white line width.

However, there is a limit to simply reducing the white line width. The reason for this is explained as follows.
As is well known, gravure printing plates are produced by transferring a gravure screen and a carbon tissue with a positive printed onto a copper-plated cylinder, and etching with a ferric chloride solution or the like through a gelatin resist obtained by developing this. It is generally obtained by During this etching, a phenomenon called side etching inevitably occurs, and the width of the dots on the plate is always narrower than the width of the white lines on the gravure screen. For example, when a gravure printing plate is prepared using an ordinary gravure screen as shown in Fig. 2a to Fig. 2d, the surface condition of the solid area of the plate is shown in Fig. 3a to Fig. 3d, respectively. It becomes like this. Second
In the figure, the ratio m:n of one side n of the blackened portion 1 to the width m of the white line 2 is 1:3. In FIG. 3, dots 3 are formed continuously from a to c, and cells 4
are independent, but due to the side etching, the width of the dot is narrower than the width of the white line of the gravure screen, and in Figure 3 d, due to the side etching, only the part of dot 3 corresponding to the intersection of the white lines remains, and the rest are It has disappeared. It is no longer possible to carry out gravure printing with a printing plate such as that shown in FIG. 3d.

The characteristics of side etching are represented by an etching factor F, which takes a constant value when certain etching system conditions are determined. Figure 4 is an explanatory diagram of side etching.
The etching factor F when the copper 5 on the gravure cylinder is etched by the etching solution through the resist 6 is determined by the following simple formula: F=2d/V (2) based on the etching depth d and the side etching amount V. It is expressed as

As is clear from the above equation (2), there exists a relationship in which the side etching amount V is proportional to the etching depth d. FIG. 5 shows an example of the relationship between the etching depth d and the side etching amount V, which varies depending on the etching factor F, in other words, depending on the etching conditions.

If the dots become too thin due to side etching, the printing durability of the plate will decrease. Some literature states that the ratio of the dot width on the plate to the side of the cell is limited to about 1:6 to 1:8. Therefore, under certain etching conditions, it is necessary to use a screen with a white line width that takes into account the thinning of the dots by the amount of side etching estimated from the etching factor.

Here, there is a contradictory conflict between the quality requirement of increasing the number of screen lines and the area ratio of blackened areas, and the technical requirement of not being able to produce a small white line width. As a result of a compromise between the above conflicting demands, gravure screens are now used with a screen of about 175 lines/inch or 250 lines/inch, both with a black-to-black line ratio of around 1:3, that is, the width of the white line is about 25μ to 40μ. Most of them do.

In addition, as a special gravure screen, the use of a gravure screen in which the width of the white line is reduced to about 9.3μ to 17μ and the number of lines is about 250 to 500 lines/inch is disclosed in Japanese Utility Model Application Publication No. 55-1297. This method is disclosed in Japanese Patent Application Publication No. 50-155301.

This kind of gravure screen has fine white lines and a large number of lines, so gravure printing plates using it are expected to produce printed matter of significantly improved quality. Since this is close to the limit when etching is taken into account, it is impossible from a practical standpoint to increase the number of screen lines any further.

The present invention differs from the conventional gravure screens described above in that it uses a gravure screen that has been greatly improved in terms of the number of screen lines and/or the area ratio of blackened areas. That is, the present invention provides a method for producing a net gravure printing plate using the photoresist after printing an image of a gravure screen and a halftone positive for lithography or letterpress on a photoresist such as carbon tissue. The width of the white line in one direction is narrower than the width of the white line in the other direction, and the width of the thicker white line is
The thickness is about 9μ to 20μ, the number of lines is 300 lines/inch or more, and the width of the thinner white line is the width of the thicker white line.
The purpose of the present invention is to provide a net gravure plate-making method characterized in that the area ratio of the blackened portion is 0.1 to 0.5 times and the area ratio of the blackened portion is 56% or more.

FIG. 6a is an enlarged explanatory diagram of an example of a gravure screen used in the method of the present invention, in which the width of the horizontal white line 8 is 5 μm, and the width of the vertical white line 7 is 5μ.
It is narrower than 15μ, with a vertical black-and-white line ratio a:b1:1.8 and a horizontal black-white line ratio (c:d) of 1:7.4. The number of lines is 610 lines/inch in both the vertical and horizontal directions, and the area ratio of blackened areas is approximately 57%, as shown in Figure 2 (black and white line ratio 1:3). This is approximately 56% of the total.

FIG. 6b is an enlarged explanatory view showing a gravure printing plate surface which has been corroded to a solid depth of approximately 20 μm. As shown in this figure, on the gravure printing plate made by the plate making method of the present invention, the vertical dots 9 due to gravure screen baking remain firmly, but the horizontal dots 9 are due to side etching during corrosion. Therefore, it is not formed as a dote but remains as a protruding portion 10. This means that, as an effect of the present invention, in addition to the aforementioned prevention of moiré caused by the large number of screen lines and the reproduction of voluminous color tones due to the large blackened area ratio, small halftone dots in the light area can be used for gravure. This shows that halftone dot reproducibility is improved by reducing the frequency of screen division to approximately 1/2. In order to improve halftone dot reproducibility in light areas in a method of producing a gravure printing plate by printing a halftone positive for planography or letterpress and a screen for gravure on a photoresist such as carbon tissue, JP-A No. 52-9503 The publication states that a halftone positive is printed in close contact with a carbon film on which a gravure screen has been printed in advance to form a change in the area of halftone dots, and then a continuous tone image is printed on the same carbon film to form a change in depth. In order to prevent the halftone dots from becoming even smaller, a method is disclosed in which a negative mask is used when printing a continuous tone image. However, this method does not eliminate or reduce the degree of division of the halftone positive halftone dot image into smaller halftone dots by the gravure screen image; This method is intended to prevent the value from becoming any smaller, so this method does not fundamentally solve the problem.

Furthermore, according to FIG. 6b, the portion corresponding to the horizontal direction of the gravure screen in the solid portion is not formed as a dot, but remains as a protruding portion 10, which is due to the method of the present invention. According to this method, even if the dots corresponding to the thinner white lines of the gravure screen are not sufficiently formed on the gravure printing plate, the ink packed in the ink receiving portion 11 is prevented from flowing by the protruding portions 10. This indicates that the ink flow problem is limited and that good printed matter can be obtained in practice without any ink flow problems. It is considered possible to make a gravure printing plate using a line screen having white lines in only one direction, but in this case, the protruding portions 10 formed in the method of the present invention will not be produced, and therefore the ink will not be able to be used. Therefore, restrictions on plate-making conditions, printing conditions, etc. are extremely narrow. According to experimental examples of gravure plates using line screens, the number of lines should be 300 lines/inch or more, the angle should be between 15° and 165° with respect to the doctor of the printing machine during gravure printing, and This results in restrictions such as the plate depth being 15μ or less.

FIG. 7 is an enlarged explanatory view of another example of the gravure screen used in the method of the present invention, in which the width of the horizontal white line 8 is 5 μm, and the width of the vertical white line 7 is 15 μm.
The line ratio of the vertical white line is a:
b is 1:1.5, horizontal white line ratio c:d is 1:
15. The blackened area ratio of this gravure screen is about 56, which is the same as the regular screen shown in Figure 2.
%, but the number of screen lines for vertical white line 7 is approximately
677 lines/inch, and the screen line count of horizontal white line 8 is approximately 318 lines/inch.

FIG. 8 is an enlarged explanatory view of still another example of the gravure screen used in the method of the present invention, in which the horizontal white line 8 and the vertical white line 7 are each 5 μm.
and 15μ, and the line ratio c of the horizontal white line 8:
d is 1:15, and the line ratio a:b of the vertical white line 7 is 1:
It is 2.7. The number of white lines in the vertical direction of this gravure screen is 460 lines/inch, the number of white lines in the horizontal direction is 320 lines/inch, and the blackened area ratio is about 68%. As shown in FIGS. 7 and 8, according to the method of the present invention for producing a net gravure printing plate using a gravure screen and a net positive for planography or letterpress printing, the density of printed matter obtained by the conventional gravure plate making method is It is possible to obtain a density of the same level or higher than that of the above method, and to obtain a smooth printed matter in which moiré is not noticeable and halftone dots are well reproduced in light to halftone areas.

The width of the thicker white line of the gravure screen used in the present invention is 9μ to 20μ; if it is narrower than 9μ, it will not be possible to form a sufficient dot on the gravure printing plate, and if it is wider than 20μ, the width of the light halftone dot will be Problems arise in terms of reproducibility. On the other hand, the width of the thinner white line is 0.1 to 0.5 times the width of the thicker white line, and in this range, an extremely thin dot is formed on the gravure printing plate, or a protrusion with a part of it cut off. However, the flow of printing ink can be sufficiently restricted. Furthermore, the screen frequency of the thicker white lines is 300 lines/inch or more, thereby making it possible to make moire patterns less noticeable and to obtain smooth printed matter.

Further, according to the method of the present invention, the following advantages can be obtained by increasing the number of screen lines of halftone positive for planography or letterpress printing. In other words, when using conventional gravure screens, even if you increase the number of screen lines of the halftone positive for lithography or letterpress printing, the number of screen lines of the gravure screen cannot be increased, so the print quality will be affected. Although much improvement could not be expected, and rather problems were caused such as problems with halftone dot reproducibility in the light area, the method of the present invention was able to improve the 150-line halftone positive halftone for ordinary planography or letterpress printing. / inch, 175 lines/inch, as well as 200 lines/inch, 300 lines/inch, or more, there is no problem when using positive halftones, and by taking advantage of their characteristics, delicate gradation reproduction is possible in printed matter. Ta.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing that when the parallel lines of pitch a and the parallel lines of pitch b intersect at an angle of θ, moiré of pitch d occurs, and Figure 2 is the moiré pattern used in the conventional method. 3 is an explanatory diagram of various examples of gravure screens; FIG. 3 is an explanatory diagram of the solid area of a gravure printing plate after etching when the gravure screen of FIG. 2 is used; FIG. 4 is an explanatory diagram of side etching; FIG. 5 is a graph showing the relationship between etching depth d and side etching amount V; FIG. 6 is an explanatory diagram showing an example of a gravure screen used in the present invention and a gravure printing plate made by the method of the present invention using the screen; FIGS. 7 and 8 are explanatory diagrams showing other examples of the gravure screen used in the present invention. 1...blackened part, 2...white line, 3...dote, 4...
... Cell, 5 ... Copper, 6 ... Resist, 7 ... Vertical white line, 8 ... Horizontal white line, 9 ... Dote, 1
0...Protruding portion, 11...Ink receiving portion.

Claims (1)

[Claims] 1. In a method of making a net gravure printing plate using the photoresist after printing a gravure screen and a halftone positive image for planography or letterpress on a photoresist such as carbon film, the gravure screen is unidirectional. The width of the white line is narrower than the width of the white line in the other direction, the width of the thicker white line is 9μ to 20μ, the number of lines is 300 lines/inch or more, and the width of the thinner white line is narrower than the width of the thicker white line. width of
A net gravure plate making method characterized by using a plate having a magnification of 0.1 to 0.5 times and a blackened area ratio of 56% or more.