JP7105534B2 - screen printing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a screen printing method, and more particularly to a screen printing method capable of enhancing image reproduction without degrading image quality and reducing printing costs.

In recent years, illuminated signboards have been developed that clearly display advertising images printed on a transparent or translucent sheet attached to a translucent plastic plate to station users and passers-by by irradiating light from the back side. , Many are installed in the station premises and underpasses.

With offset printing, gravure printing, and screen printing, the amount of ink applied is small, and with single-sided printing, there is a limit to the color density of the printed area. The color density of the advertising image displayed on the illuminated signboard was increased by matching the two images. For example, in offset printing, after printing an advertising image on the surface of a transparent or translucent sheet using a printing plate, the ink is sufficiently dried for a while, and then a printing plate opposite to the printing plate is used. Since the back side of a transparent or translucent sheet with a printed front side is printed to increase the color density by printing on the front and back sides (see, for example, Patent Document 1), a preliminary printing sheet is also required for double-sided printing.

Japanese Utility Model Publication No. 49-15273

However, the technique described in Patent Document 1 requires double-sided printing plates and the number of printing spare sheets, which is a factor in increasing the manufacturing cost of the illuminated signboard. In addition, it is extremely difficult to print the same advertisement image on both sides, and the two images do not match perfectly, resulting in blurring of the boundaries of the patterns in particular. Furthermore, even if it is possible to match both images by printing precisely, when viewed from a direction other than the front direction, for example, from an oblique direction, the pattern will be shifted by the thickness of the transparent or translucent sheet. As a result, the borders of the patterns in particular became unclear.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a screen printing method capable of improving image reproduction without degrading image quality and reducing printing costs.

In order to achieve the above object, the screen printing method according to the present invention is a screen printing method for printing the same image multiple times on one side of a semi-transparent sheet fixed to an electrical signboard panel, wherein the semi-transparent sheet At least part of the printing plate used for printing the image on one side is plate-making using an AM (Amplitude Modulation) screen that displays gradation by changing the size of halftone dots arranged at equal intervals. and the screen ruling indicating the number of halftone dots arranged per inch in the AM screen is 700 lines/inch or more.

Further, in the above screen printing method, at least a part of the printing plate used for printing the image on one side of the translucent sheet displays density by changing the density of randomly arranged halftone dots. A FM (Frequency Modulation) screen may also be used for plate making. In the FM screen, it is preferable that the screen ruling, which indicates the number of halftone dots arranged per inch, is about 400 lines/inch, or that the size of the halftone dots is 20 μm or less.

Further, in the above screen printing method, it is preferable that an ink having a transmittance of 30% or less is used for printing the image on one side of the translucent sheet . In addition, it is preferable to use an ink for reducing the transparency of the conventional ink for printing the image on one side of the semi-transparent sheet .

In the screen printing method described above, the ink used for printing the image on one side of the translucent sheet may be any ink that is produced by mixing white ink with transparent ink.

According to the present invention, it is possible to provide a screen printing method capable of enhancing image reproduction without degrading image quality and reducing printing costs.

A method for manufacturing an illuminated signboard according to an embodiment of the present invention will be described below.

The illuminated signboard according to the present embodiment is produced by printing an advertising image on one side of a translucent sheet multiple times using an offset printing machine, and fixing the translucent sheet on which the advertising image is printed to a panel. manufactured. In this embodiment, printing of an advertisement image on one side of a translucent sheet is described as being performed by offset printing, but the present invention is not limited to this, and includes gravure printing, screen printing, and may be performed by inkjet printing or the like.

Specifically, first, four original printing plates are prepared. The original printing plate should preferably have a recording layer capable of forming an image by CTP (Computer To Plate). For example, as the original printing plate, it is possible to form an image directly from digital data by semiconductor laser exposure or the like, and it has a thermal positive recording layer in which the solubility of the exposed area in an alkaline developer is improved. Examples include those having a thermal negative type recording layer that is cured to form an image.

Next, the image data representing the advertisement image is input to the CTP setter to perform color separation processing and halftone dot generation. ) screen is used to generate plate-making data indicating halftone dots for each of the colors used in the offset printing press (in this embodiment, the four colors of cyan, magenta, yellow, and black). In this embodiment, the offset printing press uses four colors of cyan, magenta, yellow, and black. is arbitrary and may be three colors or less, or may be five colors or more including special inks.

Here, in the AM screen, screen ruling (the number of halftone dots arranged per inch) is used as a method of expressing resolution. In the manufacture of illuminated signboards, relatively low-resolution halftone dots of 175 lines/inch are generally used, but in this embodiment, high-fine halftone dots of 200 lines/inch or more are used. there is As a result, even when an advertisement image is printed multiple times on one side of a translucent sheet, as in the method for manufacturing an illuminated signboard according to the present embodiment, interference moiré and rosette patterns can be generated to improve the texture of the image, the sense of existence, and the appearance of the image. It is possible to prevent deterioration of reproducibility of details and the like.

Note that the screen ruling is arbitrary as long as it is 200 lines/inch or more, and in order to more reliably prevent the deterioration of the texture of the image, the sense of existence, and the reproducibility of details due to the occurrence of interference moiré and rosette patterns. is preferably 700 lines/inch or more, such as 700 lines/inch, 900 lines/inch, and 1000 lines/inch. However, if the screen ruling is increased, problems such as the limitation of the resolution of the CTP setter and the deterioration of the printing durability of halftone dots of a small area occur. good.

In this embodiment, an AM screen is used. However, an FM (Frequency Modulation) screen that displays shades by changing the density of randomly arranged halftone dots may be used. A method combined with an FM screen may also be used. Alternatively, the AM screen may be used for at least some of the colors used in the offset printing press, and the FM screen may be used for the other colors. When using an FM screen, the screen ruling is preferably approximately 400 lines/inch or more in order to stabilize halftone dot reproducibility during plate making and to facilitate management during printing.

Subsequently, the four prepared printing plate originals were set one by one in the CTP setter, and based on the platemaking data, the printing plate originals were exposed, and then developed with an alkaline developer to produce yellow, Cyan, magenta, and black printing plates are made respectively.

Here, the light source used for exposure is selected according to the recording layer of the original printing plate. Currently, various light sources such as xenon for conventional film printing plate exposure are included. As the light source, a light source having an emission wavelength in the near-infrared to infrared region, a solid-state laser, a semiconductor laser, or the like is particularly preferable.

Further, as a developer or a replenisher used for development processing, a known alkaline aqueous solution can be appropriately selected and used. Examples of alkaline agents that can be used in the alkaline aqueous solution include inorganic alkaline salts such as sodium silicate and potassium silicate, and organic alkaline agents such as monomethylamine, dimethylamine, trimethylamine, triethanolamine, ethyleneimine and pyridine. These may be used individually by 1 type, and may use 2 or more types together.

Yellow, cyan, magenta, and black printing plates developed with the developer and replenisher are washed with water, rinsed with surfactants, etc., and desensitized with gum arabic and starch derivatives. is post-processed with

Subsequently, the printing plates of yellow, cyan, magenta, and black are sequentially set from the first printing cylinder of the offset printing press to the final printing cylinder (the fourth printing cylinder in this embodiment), and the ink corresponding to each printing plate is set. , and dampening water is supplied, and the ink supplied to the printing plate is transferred to one side of the semi-transparent sheet held by the impression cylinder through the blanket cylinder, thereby advertising on one side of the semi-transparent sheet. Print an image. Then, the advertisement image is printed on one side of the translucent sheet multiple times. By printing the advertisement image a plurality of times in this manner, the color density can be sufficiently increased even with single-sided printing.

Here, the translucent sheet used for printing is preferably tracing paper, which has high stiffness, excellent printability, and good print appearance. In this embodiment, trace synthetic paper having an opacity (JIS P-8138) of 15 to 35%, which is a stretched film of a thermoplastic resin containing white inorganic fine powder such as calcium carbonate or calcined clay, is used.

In addition, inks with low transparency, specifically, impermeability up to 30% or less are used for printing. Such inks are used as impurities in general-purpose yellow, cyan, magenta, and black UV (Ultra Violet) curable inks (transparent inks) with high transmittance to reduce the transmittance of conventional inks. It is produced by mixing an ink, for example a white ink that reduces the transparency. By printing with ink having a low transmittance in this way, it is possible to prevent the brightness from becoming too high even in single-sided printing. A high-density printed material capable of expressing a clearer image can be obtained as a backlight for the purpose of use.

Then, the translucent sheet on which the advertisement image is printed is fixed to the panel to manufacture the illuminated signboard. In this way, the rear side of the semitransparent sheet fixed to the panel is irradiated with light from a light source such as a fluorescent lamp, a light bulb, a mercury lamp, and a xenon lamp, and the light is transmitted through the semitransparent sheet. , an advertising image printed on a translucent sheet is displayed on the illuminated signboard.

As described above, according to the method for manufacturing an illuminated signboard according to the present embodiment, an advertisement image is printed a plurality of times on one side of a semi-transparent sheet that is a material to be printed, thereby making the conventional method for manufacturing an illuminated signboard. The color density can be sufficiently increased without having to print the advertising images on both sides of the translucent sheet as in . As a result, only a single-sided printing plate is sufficient, and there is no need for a double-sided printing plate unlike the conventional manufacturing method of illuminated signboards. manufacturing cost can be reduced.

In addition, since it is not necessary to print both images on both sides of the translucent sheet so that they match each other, the border of the pattern may be blurred due to the mismatch between the two images, or the pattern may be blurred due to the thickness of the translucent sheet. It is possible to prevent the boundary of the pattern from becoming blurred due to deviation, and not only to prevent the deterioration of the image quality but also to improve the image quality.

Furthermore, at least part of the printing plate used for printing the advertising image on one side of the translucent sheet is plate-made using an AM screen, and the screen ruling of the AM screen is 200 lines/inch or more, more preferably is set to approximately 700 lines/inch or more, it is possible to prevent deterioration of image quality, sense of existence, reproducibility of details, etc. due to the occurrence of interference moiré and rosette patterns. More preferably, by setting the screen ruling of the AM screen to about 700 lines/inch, it is possible to solve problems such as the limitation of the resolution of the CTP setter and the deterioration of printing durability of small-area halftone dots.

At least part of the printing plate used for printing the advertising image on one side of the translucent sheet may be plate-made using an FM screen. The size of is not particularly limited, and can generally be selected arbitrarily. Preferably, the screen ruling is approximately 400 lines/inch, or the halftone dot size is, for example, 10 μm, 15 μm, and 20 μm. For example, if the thickness is 20 μm or less, halftone dot reproducibility can be stabilized during plate making of the printing plate, and control during printing can be facilitated.

Further, the printing of the advertisement image on one side of the translucent sheet may be performed by inkjet printing as described above. In this case, the resolution in inkjet printing is arbitrary as long as it is 1440 dpi or more, Also, the number of colors and the like are not particularly limited. Therefore, the printing method according to the present invention can also be applied to various types of inkjet printing that will be developed in the future.

In addition, inks with an opacity of up to 30% are used for printing an advertising image on one side of a translucent sheet. It is produced by mixing each of the UV curable inks (transparent ink) with a white ink that reduces the transmittance as an impurity. By printing using ink with low transparency in this way, it is possible to express a wide range of printing density, brightness, and saturation for each color even in single-sided printing, and prevent the printing film thickness from becoming too high. It is possible to standardize the printing work environment and suppress excessive consumption of raw materials.

It should be noted that the printing method according to the present invention is not limited to printing on translucent sheets used for illuminated signboards, but can also be applied to printing on various ordinary printing materials such as posters. Needless to say.

Claims (4)

Illuminated signboard Printing the same image multiple times on one side of the translucent sheet fixed to the panelscreenA printing method comprising:
At least a part of the printing plate used for printing the image on one side of the translucent sheet is AM (Amplitude Modulation) that displays gradation by changing the size of halftone dots arranged at equal intervals. made using a screen,
In the AM screen, the screen ruling indicating the number of halftone dots arranged per inch is700Lines/inch or morescreenprinting method. At least part of the printing plate used for printing the image on one side of the translucent sheet also uses an FM (Frequency Modulation) screen that displays shading by changing the density of randomly arranged halftone dots. to be printed,
The screen printing method according to claim 1 , characterized in that: For printing the image on one side of the translucent sheet, an ink with a transmittance of 30% or less is used.
3. The screen printing method according to claim 1 or 2 , characterized in that: The ink used for printing the image on one side of the translucent sheet is produced by mixing white ink with transparent ink.
4. The screen printing method according to claim 1 , 2 or 3 , characterized in that: