JPS6134672B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gravure screen, and particularly to a screen for net gravure plate making.

In order to obtain a halftone gravure printing plate, it is well known to use not only a halftone positive for gravure, but also a halftone positive for lithography or letterpress printing, as shown in Japanese Patent Laid-Open No. 50-26603. As shown in FIG. 1, in a halftone positive 1 for planography or letterpress printing, opaque halftone dots 2 are grafted or overlapped in the shadow area to the halftone area. The opaque halftone dots 2 become independent halftone dots toward the light portion. When performing net gravure plate making using such a net positive 1 for planography or letterpress printing, a gravure screen 4 having transparent lines 3 as shown in FIG. 2 and other parts being opaque is used. There is a need. The reason for this is that in the halftone dots 1 for planography or letterpress printing, the opaque halftone dots 2 touch or overlap from the shadow area to the halftone area.
This is to prevent ink from flowing in these areas during printing.

However, net positive 1 for planography or letterpress
When used in combination with the gravure screen 4, it not only has the disadvantage that moiré is likely to occur from the light area to the intermediate tone area, but also the halftone dots in the light area may be missing or disappear due to the transparent lines of the gravure screen. This has the disadvantage that the tone reproducibility of the light section is impaired.

Considering the above points, as a method to prevent the light section from being affected by the gravure screen, it is possible to overlap the negative on the gravure screen when printing the gravure screen with transparent lines on the carbon tissue. , Japanese Patent Application Publication 1973-
This is shown in Publication No. 161303.

Alternatively, a gravure screen with transparent lines and a negative are overlapped and printed on a photosensitive film.
Furthermore, by printing the net positive, a negative net with black lines from the original shadow area to the halftone area is created, and this is inverted to create a negative net with transparent lines from the shadow area to the halftone area. Japanese Patent Application Laid-Open No. 131703/1983 discloses that this net positive is used for net gravure plate making.

According to these methods, the problems of preventing moiré and reproducibility of tone in light areas can be solved. However, in the former case, when printing the gravure screen on the carbon tissue, the light part is not burned, so the gravure screen is printed on the necessary parts and the gravure screen is printed on the unnecessary parts. It is difficult to confirm that this is not the case until the carbon film is transferred to a gravure cylinder and developed after printing the net positive. Therefore, the gravure screen may not be printed in the necessary areas,
On the other hand, if the gravure screen is printed on unnecessary parts, it will be necessary to start over from the beginning, resulting in a large waste of materials and working time.

Furthermore, in the latter case, the transparent lines of the gravure screen are inserted into the halftone positive itself, so that the opaque halftone dots in the shadow to halftone areas of the halftone positive are also divided into minute independent points by the transparent lines. On the other hand, when printing a net positive onto a photosensitive material, there are many methods including blurring the dots of the net positive to give the same effect as a continuous tone positive. Disclosed in the literature. If the above-mentioned halftone positive (i.e., the halftone positive with transparent lines of a gravure screen) is used in such a method, when blurring the halftone dots of the halftone positive, redundant light will be emitted from the transparent line portions from the shadow areas to the halftone areas. This results in a disadvantage that tone reproducibility from shadow areas to halftone areas is impaired.

The present invention was completed as a result of various researches aimed at solving the above-mentioned drawbacks. That is, the present invention has discovered that the various drawbacks mentioned above can be overcome by using a special gravure screen, and has also discovered a method for manufacturing this special gravure screen.

The gravure screen of the present invention is suitable for net gravure plate making, and is particularly suitable for use in net gravure plate making, especially when using net positives in which opaque halftone dots are in contact or overlap from shadow areas to halftone areas, such as net positives for planography or letterpress printing. Suitable for obtaining a net gravure version.

As illustrated in FIG. 3, the gravure screen 5 of the present invention includes a portion A corresponding to the shadow portion of the net positive to be used and a portion B corresponding to the halftone portion.
There is a transparent line 6 up to the point C, and there is no transparent line in the part C corresponding to the light part of the net positive used. The portion other than the transparent line 6 is an opaque portion 7.

The halftone area of halftone positive has a halftone percentage of approximately 50%.
It has a certain width around the center. Therefore, the percentage of halftone dots to include the transparent line 6 within the range of part B corresponding to the halftone part should be determined by considering the pattern to be printed and the quality required for the printed material. and select appropriately. In addition, in the above-mentioned part, the expression that the opaque halftone dots in the halftone part of halftone positive for planography or letterpress are touching or overlapping means that the halftone dots in the halftone part having a certain width are It should be noted that the point percentage is for a portion greater than approximately 50%.

It is important for the gravure screen of the present invention to have transparent lines 6 in the area corresponding to the halftone dot percentage range of 100% to 50% of the halftone positive for the purpose of preventing ink flow during printing. However, if the print is of a quality that can be tolerated even if a slight ink flow occurs, it may not be necessary to have transparent lines up to the 50% area, for example, approximately 60%. In some cases, it is good to have the ability to do so. In addition, the transparent line 6 has a portion corresponding to a halftone dot percentage of 50% of the positive halftone dot, and does not have a transparent line in a portion corresponding to a halftone dot percentage of less than 50% of the halftone positive. It's okay to be.

Furthermore, the gravure screen of the present invention may have transparent lines 6 up to a portion corresponding to a halftone dot percentage smaller than 50% of the halftone positive. In this case, the desired percentage of the transparent line 6 to be included may be appropriately selected depending on the pattern to be printed, quality, and other conditions.

The reason why the transparent line 6 is provided even in the part corresponding to the halftone dot percentage less than 50% is that depending on the pattern to be printed, it is necessary to have the transparent line 6 in the part corresponding to the halftone dot percentage less than 50%. However, if the transparent line suddenly disappears in the area corresponding to fewer halftone dots than the 50% boundary, the gradation of the printed material will suddenly change at that boundary, making it more desirable and affecting the image. Because there is. Therefore, as long as there is no such problem, it is preferable that it be close to 50%.

Further, the opaque portion of the gravure screen of the present invention preferably has a density of 2.5 or more, and more preferably has a density of 3.0 or more.

In order to obtain the gravure screen of the present invention, the fourth
As illustrated in the figure, in addition to requiring a so-called black line screen 10 having opaque lines 8 and transparent portions 9 other than the opaque lines 8, a positive screen such as a continuous tone positive screen or a net positive screen is also required. shall be. These black line screens and positives are each printed separately on the same photosensitive film.
In this case, either the black line screen printing or the positive printing may be performed first. For positive printing, either continuous tone positive or net positive may be used.

FIG. 5 is an explanatory cross-sectional view showing the state of printing on a photosensitive film when a continuous tone positive film is used as the positive film. As shown in FIG. 5, a continuous tone positive film 13 is brought into close contact with the photosensitive layer 12 side of the photosensitive film 11, and light is irradiated from the continuous tone positive film side as shown by the arrow in the figure. A shaded area 14 in the photosensitive layer 12 schematically represents the amount of light that has passed through the continuous tone positive plate 13 and reached the photosensitive layer 12.

In other words, the amount of light is the lowest in the shadow area a.
In the light portion c, the amount of light is large, and in the halftone portion b, the amount of light is between the shadow portion and the light portion.

When a net positive is used as a positive,
When printing this net positive onto a photosensitive film, the halftone dots of the net positive are diffused and printed. The purpose of diffusing the halftone dots of a halftone positive is to create an effect similar to that of printing a continuous tone positive.

A method of printing a photosensitive material by diffusing the halftone dots of a halftone positive has already been disclosed in various documents, so that method may be employed. For example, as shown in FIG.
Diffusion sheet 15 on the photosensitive layer 12 side of 1
The net positive 16 may be brought into close contact with the net through the net, and light may be irradiated from the net positive side as shown by the arrow in the figure. In FIG. 6, a hatched portion 14 in the photosensitive layer 12 schematically represents the amount of light that has passed through the net positive and reached the photosensitive layer 12, as in FIG. 5.

Another known method for diffusing halftone dots is to use a transparent sheet instead of a diffusion sheet and irradiate the dots with diffused light, and such a method may also be used.

Note that the diffusion sheet refers to a sheet that has the property of diffusing light, and is usually a milky white sheet, such as matte film, opal glass, etc.
It is sufficient to select an appropriate material such as ground glass.

When the positive is brought into close contact with the photosensitive film 12, the selection of which of the base layer 17 and the emulsion layer 18 of the positive should be directed toward the photosensitive film 11 is determined by the pattern of the net positive used for plate making and the gravure screen of the present invention. The pattern should be visible in the same direction as viewed from the emulsion surface (or base surface).

To print the black line screen, as shown in FIG. 7, the black line screen 19 is brought into close contact with the photosensitive layer 12 side of the photosensitive film 11, and light is irradiated from the black line screen side as shown by the arrow in the figure. .

The part 20 indicated by diagonal lines on the lower left in Fig. 7
1 schematically represents the amount of light that has passed through the transparent portion 21 of the black line screen 19 and reached the photosensitive layer 12 of the photosensitive film 11.

Since the opaque portion 22 of the black line screen 19 does not transmit light, the portion of the photosensitive layer 23 corresponding to the opaque portion 22 is not irradiated with light during this printing process.

When the black line screen 19 is brought into close contact with the photosensitive film 11, it is preferable to place the emulsion layer 24 of the black line screen 19 on the photosensitive layer 12 side of the photosensitive film because the image of the black line screen will not be blurred.

Note that the black line screen 19 is replaced by a photosensitive film 11.
The amount of exposure when printing differs depending on the type of photosensitive film used, so apply the amount appropriate for each photosensitive film used.

As the photosensitive film used in the present invention, it is desirable to use a film that is used for making ordinary gravure screens, that is, a film that has a large gamma value and a strong contrast. Such a film is usually called a lithium type film.

Among photosensitive films having a large gamma value, in addition to silver salt type films, for example, vesicular films can also be used.

The photosensitive film used in the present invention preferably has a gamma value of 3.0 or more, and more preferably has properties similar to those of a lithium type film for contact reversal of halftone positives or for halftone photography.

The photosensitive film 11, which has undergone positive printing and black line screen printing as described above, is developed. As shown in FIG. 8, the screen of the present invention is obtained by this development process. This screen has a transparent line 25 from a part corresponding to a positive shadow part to a part corresponding to a halftone part,
There is no transparent line in the part corresponding to the positive light part. The area other than transparent line 25 is opaque area 2
6.

The screen of the present invention is used when obtaining a net gravure plate using a net positive, particularly a net positive for planography or letterpress printing. Therefore, it is preferable to use this net positive as the positive used in the present invention.

The screen of the present invention is printed in close contact with carbon tissue, roto film, or other photoresist during net gravure plate making. The pattern of the net positive printed on carbon film or other photoresist and the pattern of the screen of the present invention must be printed in register.

The screen of the present invention is not limited to having orthogonal transparent lines as shown in FIG. 3, but may also have diagonal transparent lines or a so-called backstein screen that looks like stacked bricks. It's okay.

As with the usual gravure screen, various numbers of lines can be adopted for the screen of the present invention.

The screen of the present invention has a transparent line from the shadow area to the intermediate tone area, and does not have a transparent line in the light area, so it not only does not generate a moire pattern but also has excellent gradation reproducibility in the light area. You can get prints.

The conventional method of preventing moiré by overlapping a gravure screen and a negative and printing them on the photoresist not only has poor workability in the process of printing onto the photoresist, but also has a problem in that the gravure screen only covers a certain percentage of the net positive. Although it has been difficult to confirm whether or not the image has been printed completely, this problem can be solved by using the screen of the present invention.

Next, examples of the present invention will be shown.

Example 1 A 200 μm thick matted film was inserted between a 150 line/inch lithographic screen positive and a lithographic film, and a vacuum pump was used in a printer to bring them into close contact with each other. Next, light was irradiated for 5 seconds from a distance of 80 cm using a 12 V, 50 W halogen lamp.

Next, after removing the net positive and the matte film, a 250 line/inch black line screen having an angle of 45 degrees is placed on the same lith type film so that the emulsion layer of the black line screen and the photosensitive layer of the lith type film are in close contact with each other. overlap each other in such a manner as to make them adhere to each other using a vacuum pump in the printer,
It was irradiated with the same amount of light that was used to print the net positive.

Next, the lithographic film on which the net positive and black line screen had been printed was developed and fixed according to the instructions, washed with water, and dried. An automatic developing machine was used for these developing treatments.

In this way, the screen of the present invention was obtained. This screen has 50% positive halftone dots.
It had a transparent line in the part corresponding to the part exceeding , and had no transparent line in the part corresponding to the part where the halftone dot of the halftone positive was about 0% to 50%. Using the screens obtained in this way, we performed net gravure printing in the usual manner by combining them with 150 line/h lithographic net positives having various angles, and were able to obtain printed matter with almost no noticeable moiré. .

Example 2 Instead of printing the net positive and matte film used in Example 1, a continuous tone positive having the same size and the same pattern as the net positive used for net gravure plate making was used to print at 25 lux. A screen of the present invention was obtained in the same manner as in Example 1 except that the screen was irradiated with light for 5 seconds. The screen thus obtained was also almost the same as the screen obtained in Example 1.

[Brief explanation of the drawing]

Fig. 1 is a schematic plan view of a net positive for lithography or letterpress printing, Fig. 2 is a plan view of a normal gravure screen, Fig. 3 is a plan view of the screen of the present invention, and Fig. 4 is a plan view of a black line screen. Figures 5 and 6
FIG. 7 is an explanatory diagram of a positive printed state, FIG. 7 is an explanatory diagram of a black line screen printed state, and FIG. 8 is a cross-sectional diagram of the screen of the present invention. 1... Halftone positive, 2... Halftone dot, 3... Transparent line, 4... Gravure screen, 5... Gravure screen of the present invention, 6... Transparent line, 7... Opaque part, 8... Opaque line , 9...transparent part, 10
...Black line screen, 11...Photosensitive film,
12...Photosensitive layer, 13...Continuous tone positive, 15
... Day fusion sheet, 16 ... Net positive, 17 ... Base layer, 18 ... Emulsion layer, 19 ...
...Black line screen, 21...Transparent part, 22...
Opaque portion, 24... Emulsion layer, 25... Transparent line,
26...opaque area.

Claims (1)

[Scope of Claims] 1. A gravure screen having transparent lines for forming dots of a gravure plate, and parts other than the transparent lines being opaque, corresponding to the shadow part to the halftone part of the halftone positive used. A screen for net gravure plate making that has transparent lines in some parts and does not have transparent lines in the part corresponding to the light part of the net positive used. 2. A step of contact-printing a continuous-tone positive film on a photosensitive film or diffusing halftone dots of a net positive film, and a step of contact-printing a black line screen for gravure onto the photosensitive film are carried out in any order. A method for manufacturing a screen for net gravure plate making, characterized in that the photosensitive film is then processed to produce transparent lines in areas corresponding to the halftone areas from the shadow areas of the net positive.