JPS649953B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention uses a multicolor printing method using a letterpress, or more specifically, a photolithography method, to create a halftone separation negative through a screen for each separated color, and through that negative, a letterpress plate of the color including the intermediate area near the highlight area is created. The present invention relates to a multicolor overlapping printing method in which a relief plate of a color excluding an intermediate area close to a highlight area is produced, inks of respective colors are supplied to each relief plate, and the inks are transferred to the printing surface. When printing methods are classified by plate, there are letterpress printing, planographic printing, and intaglio printing. Letterpress printing uses a metal plate such as zinc that has a convex printing area, and ink is attached to the relief plate of the plate, and the ink is applied to the plate. Between the letterpress and the impression cylinder,
It is a method of printing by sandwiching and pressing a flexible printing material such as paper, and in lithographic printing, the plate has no unevenness, and the areas other than the image area covered with ink are moistened with water, and the image line is Intaglio printing is a method of printing by transferring ink on a rubber blanket, and then transferring the ink on this blanket to a printing medium.
Supplying ink to the concave portion of the plate with the image area concave,
This is a method of printing by transferring this ink onto a printing material. By the way, lithographic printing using a rubber blanket is used to print on hard materials such as tin plates. This is because in letterpress printing, when the plate is pressed against a hard material, the letterpress of the plate is worn out and deformed, making it impossible to print in large quantities. However, unlike planographic printing, letterpress printing has the advantage that it does not require dampening water, making printing operations and management easier. A method will be found. In this regard, the present inventors have studied the use of a blanket to transfer ink from letterpress to the blanket, and the practical application of this method in photolithography. Photoengraving uses color filters to create color separation negatives for red, yellow, blue, and black ink from a colored photographic original, and from these negatives, color separation positives for each color are created. These positives are created through a process of passing them through a screen (which is arranged in a grid as shown in Figure 1) to create plates (halftone plates) of each color. The width of the grid on the screen is equal to the width of the space between the grids, and the number of grids per inch is called the number of lines. If a screen with a line count of 70 is used, 4,900 (70 x 70) convex points will be formed at equal intervals on the area of the plate, and if a screen with a line count of 150 is used, 22,500 convex points will be formed at equal intervals.
convex points are formed. The more convex points (or ink dots) that are formed in a unit area, the tighter the print will be, and the more beautiful it will be.
Moreover, a printed color close to the original color can be obtained. This is why a screen with a large number of lines is used to make a plate when trying to bring the print finish closer to the original photograph, which has continuous color tones. Also, the shade of color is reflected in the size of the raised dots on the plate. For example, in a plate produced using a screen with 150 lines, the printing area has 22,500 convex dots per square inch everywhere, but in dark areas, the width of the convex dots is larger than that of the convex dots. It is larger than the distance between the points, and as the color becomes lighter, the width of the raised points becomes smaller and the distance between the raised points becomes larger. At the darkest point, the convex points touch each other and there is no space between them. This part with no intervals is called a shadow part. On the other hand, where there is no color, there are no convex points. This part is called the highlight part. The part between the shadow part and the highlight part is called the intermediate part. FIG. 2 shows a state in which the convex portion gradually becomes smaller from the shadow portion toward the highlight portion. The left end of the figure is the shadow part. The ink adhering area per unit area is large in the shadow part, and the ink adhering area becomes smaller toward the highlight part. As mentioned above, lithography is used for multicolor printing on hard materials such as tinplate, but when photoengraving this, the number of lines is usually 100 to 150.
A mesh plate made from a screen in between is used. Therefore, the inventors of the present invention, as an experiment, produced halftone letterpress printing plates for each of the four colors separated according to the conventional method of photoengraving using a screen with a line count of 150, and transferred the ink from these letterpress plates to a rubber blanket. Then, when we transferred the ink from the blanket to a tin plate and overprinted four colors, and examined the color tone of the print, we found that only the blurred areas looked extremely different compared to the original photo, and we highlighted the cause of this. There is no middle part (the part where the ink adhesion area is less than 5% of 1 square inch of the unit area) near the middle part, and the part that does not include the middle part immediately becomes the highlight part, and the blurring ends in the middle. I learned that it was for the purpose of being there. The reason why this blurring ends midway is considered as follows. In letterpress halftone printing, when ink is transferred from the letterpress to the blanket and from the blanket to the tin plate, a phenomenon occurs in which the dots become thicker, that is, dot gain (according to experiments by the present inventors, The diameter of the halftone dots of the ink transferred to the tin plate is approximately 45μ larger than the halftone dots of the letterpress.) The dot gain ratio (the rate at which the halftone dots that are transferred become larger) is larger for the halftone dots that are closer to the highlight. So, if you print as is,
Compared to the original, the color density of the print is particularly dark in the areas near the highlights, and the tonal balance is disrupted.
The printing function of reproducing the original is not performed. As a countermeasure against this problem, the size of the halftone dots of the relief plate is usually reduced in advance by the amount of the dot gain (reduced power) at the stage of plate making. The table shows the area ratio and size of halftone dots that can be reproduced on negatives, and the table shows the size of halftone dots when the dot gain (thickness of halftone dots after printing) is reduced. show. In addition, it has been confirmed through experiments that the thickness of halftone dots on the printed surface by letterpress is approximately 45μφ, so the reduction in force is
It was set to 45μφ.

【table】

[Table] Based on the table results and the fact that the size of halftone dots that can be reproduced with partial exposure on negatives is approximately 18μφ or more, negatives using a screen with a large number of lines (fine halftone dots) are close to highlights. Halftone dots, for example, halftone dots of less than 5% are lost. As a result, using a screen with 150 lines,
In the produced plate, the halftone dots in the highlighted areas disappear when the correction negative is reduced during plate making, and they remain erased on the printing plate, so the printing on the tin plate printed with this plate does not show the highlighted areas. This results in an image with an unbalanced color tone that lacks an intermediate area close to that of the original image (see Figure 5). However, this countermeasure method is undesirable because it requires a lot of time and effort to produce and modify the plate. The present invention makes it easier than lithographic printing to print the blurred portions on a smooth printing surface as closely as possible to the original photograph, under the condition that a photograph is separated into colors and printed in multiple colors using a letterpress. The purpose of the present invention is to provide a printing method that enables printing using a color separation photolithography method, and a letterpress plate a of a color including an intermediate area close to the highlight area, and a printing method in which the highlight area is printed. In a multicolor overprinting method in which ink is transferred onto the printing substrate using letterpress b of a color that does not include a near intermediate area, letterpress b is produced using a screen with a line count of 100 or more, and letterpress b is produced using a screen with a line count of 100 or more. and a letterpress plate A produced using a screen with a smaller number of lines than the screen used to produce letterpress plate B, and transfer from each plate to a smooth printing surface via a rubber blanket. A letterpress multicolor overlapping printing method characterized by the following can be obtained. In the present invention, even if a mesh negative (original negative) is created using a screen with a large number of lines, and the power is reduced by the amount of dot gain from the screen negative (creating a reduced power corrected negative), there will be no problem in the resolution of the corrected negative. A letterpress plate that can obtain halftone dots of a size that can be resolved on a corrected negative, that is, a letterpress plate B whose color does not include the intermediate area near the highlight area, can obtain a printed color that is closer to the original color. On the other hand, if a screen with a large number of lines is used to make a net negative, when the power is reduced by the amount of dot gain, halftone dots with a small area ratio near the highlight area will be produced. However, the color letterpress a containing the middle part (portion with halftone dots with a small area ratio) near the highlight part, which cannot be resolved on the corrected negative, is later reduced in strength by the dot gain (on the corrected negative). The screen is manufactured using a screen with a line count that allows halftone dots of a size that does not cause problems in the resolution of the corrected negative (halftone dots with a small area ratio are resolved on the corrected negative) even if the screen is created. Using these letterpress plates B and A, multiple colors of ink are transferred from each plate to a smooth printing surface through a rubber blanket, so the transferred ink causes dot gain and becomes different from each original. (original negative), from the middle part near the shadow part to the middle part near the highlight part, from the middle part near the shadow part to the middle part near the highlight part, and from the middle part near the highlight part to the highlight part. The area ratio of halftone dots decreases smoothly and naturally, and as a result, the color density becomes comparable to that of the original, and a printed matter with good color reproducibility is obtained. Figures 5 and 6 show the halftone dots with a halftone dot area ratio of 5% when the original negative is made using a screen with 150 lines and a screen with 100 lines, respectively. Plate making Shows how each process changes during printing. If a letterpress is produced using a screen with a line count of 150 (see Figure 5), the halftone dots with an area ratio of 5% will disappear at the stage of producing a corrected negative, which is reduced in power, but when a screen with a line count of 100 is used, the halftone dots will disappear. When a letterpress is produced using a screen (see Figure 6), the halftone dots with an area ratio of 5% become smaller at the stage of creating a corrected negative, which reduces the force, but returns to the size of the original negative during printing. I understand. In the above explanation, we have described the case where a net negative (original negative) is created using a screen and then a corrected negative is created by reducing the force. It is also possible to optically reduce the halftone dots to create the same version of the corrected negative all at once. Here, the number of lines of the screen is set to 100 or more because
There is no point in using the method of the present invention when making a letterpress using a screen with a line count of less than 100. In other words, in the case of a screen with a line count of less than 100, the entire printing surface becomes blurred when compared with the original photograph. This is because it does not feel particularly strange even if the blur level of the blurred part changes rapidly.
Furthermore, a smooth printing surface is an essential requirement for printing to resemble an original photograph, and the number of lines can be reduced.
Related to specifying 100 or more (if you are targeting a rough surface, even if you increase the number of lines, there are advantages of increasing the number of lines,
In other words, there is no advantage of being able to approximate the original photograph. )
It is something. The present invention solves the conventional concept that when a manuscript photograph is separated into colors and letterpress plates of each color are produced, plates that can produce beautiful printed pictures cannot be produced unless the plates are made using a screen with the same number of lines for each color. Regardless, you can use a screen with fewer lines (but not less than 100) than the number of lines required to make a letterpress of a color that has an intermediate area close to the highlight area, and a letterpress of a color that does not include such an intermediate area. Produced using
In addition, by using a blanket, which was unimaginable in letterpress printing, and printing with plates made using screens with different number of lines, it is possible to print on a smooth printing surface with blurred areas just like the original photo. It made it possible to do so. Next, an example of printing using the method of the present invention will be shown. To make a plate using an offset printing machine,
An original still life photograph as shown in Figure 3 was color separated.
As a result, four colors are obtained: red, yellow, indigo, and ink, and the unblurred parts (colored parts that do not include the middle part near the highlights) are red and yellow, and the blurred parts (highlights part of the color including the middle part near the part)
was made of indigo and ink. Therefore, the red version and the yellow version have a line count of 1.
In addition, an indigo plate and a black plate were made using a screen with a line count of 100, respectively, and the ink from these letterpress plates was transferred to a rubber blanket, and then red and yellow were printed on the smooth surface of the tinplate. , indigo, and ink were overprinted in that order. In the resulting print, even the blurred areas were smoothly blurred. Comparative Example As a comparative example, an indigo version and a black version were produced using a screen with a line count of 120 like the red and yellow versions, and printed in the same manner as in the above example. The result was a photograph with no parts, giving an impression quite different from the original photograph. According to the present invention, it is now possible to perform multicolor overlapping printing that closely resembles original photographs using letterpress printing techniques that do not use dampening water, even in fields that were conventionally thought to be impossible with letterpress printing. In this sense, the present invention can be said to be extremely significant. The present invention is particularly effective when the printing material is hard and has a smooth surface, but it can also be applied to soft materials such as plastic film as long as it has a smooth surface.
It can also be applied to printing.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an example of a screen, FIG. 2 is an explanatory diagram showing an example of a state in which the size of a convex portion changes from a shadow part to a highlight part, and FIG. 3 is a plan view showing an example of a screen according to an embodiment of the present invention. FIG. 4 is a sketch of the printed image obtained in the comparative example, and FIGS. 5 and 6 are original images obtained using a screen with 150 lines and a screen with 100 lines, respectively. This is a schematic diagram illustrating how halftone dots with an area ratio of 5% when a negative is produced change during the processes of reducing force correction negative production, printing plate production, and printing.

Claims (1)

[Claims] 1. A relief plate a of a color that includes an intermediate area close to the highlight area and a relief plate b of a color that does not include an intermediate area close to the highlight area, which are produced by a color separation photolithography method. In the multi-color overprinting method, which involves transferring ink onto a printing substrate, the letterpress b produced using a screen with a line count of 100 or more, and the screen having a line count of 100 or more and used to produce the letterpress b. A letterpress multicolor printing method characterized by using letterpress plates A and A made using a screen with a small number of lines, and transferring from each plate to a smooth printing surface via a rubber bracket. . 2. The method according to claim 1, in which the number of colors is four. 3. In the method described in claim 1,
The number of lines of the screen used to make letterpress b is 120, and the number of lines of the screen used to make letterpress a is 120.
How to be 100. 4. The method according to claim 1, wherein the printing material is a hard material such as a tin plate.