Large format screen printing plate production method (below)

Fourth, large-format screen printing photosensitive adhesive

The high-sensitivity SBQ (single liquid) sensitizer, which is compatible with large-format direct-projection and magnifying exposure plate-making machines, is a new generation of screen-printed photographic materials and has patents registered in various countries. It is predicted that in the 21st century, this type of non-diazophobic photosensitive adhesive will replace diazo type photosensitive adhesive and become a new type of photosensitive material.

The new non-diazo SBQ emulsion can produce high-quality large format screen printing plates (large outdoor advertising plates). One-component SBQ photopolymers do not use diazo resins as sensitizers, and they are combined with PVA (polyvinyl alcohol) emulsions in a single liquid form before exposure. When exposed to UV light at wavelengths of 330 nm to 400 nm, a "bridge" reaction occurs between molecules of SBQ, forming a network-like molecule (macromolecule) structure that produces a hard film that is insoluble in water, that is, after the screen is exposed. The formed screen printing plate film.

SBQ single liquid emulsion characteristics:

1. Since it is a single liquid emulsion, it eliminates the trouble of mixing and can be used directly.

2. Sensitive glue speed, compared with the general diazo photosensitive emulsion compared to only 1/3-1/5 exposure time, improve productivity and save energy.

3. With high resolution, it is possible to faithfully reproduce originals or negatives and print products with high quality requirements.

4. Due to the high concentration, the coated thick plate has good workability, smooth film surface and clear lines.

5. The adhesive uses SBQ as a sensitizer, so the stability is good, the emulsion can be stored at room temperature for more than one year, and pre-coated version can be produced. Under the condition of keeping dry, it can be used normally within 6 months ( Keep away from light).

V. Computer direct inkjet large format screen printing plate plate making technology

Another ideal large-format screen printing platemaking technology is computer direct inkjet (spray wax) plate making technology.

The Swiss JetScreen computer direct plate-making system is a new type of plate-making technology that directly sprays a screen printing screen from a computer to a plate (Computer-to-plate, CTP for short). With the continuous enhancement of the economic strength of the screen printing industry, it is believed that screen printing CTP will become the mainstream of screen printing plate making technology.

JetScreen's computer-to-plate system breaks the traditional screen-making mode, completely abandoning the film bottom plate, uses the computer digital processing technology to design screen printing graphics and text symbols, and performs color separation and screen printing according to the requirements of the screen printing plate. After being processed and stored by a specialized computer, the digital output is converted, a dedicated inkjet device is driven, and images, etc. (through a wax liquid or other special liquid with high hiding power) are sprayed on the coated emulsion. On screen mesh screens, screen printing plates used for screen printing can be obtained through direct exposure and development (flushing). The following figure shows the comparison between the traditional screen production process and the JetScreen screen production process. From the comparison of the above two process flows, it can be seen that in the production of a traditional large-scale color screen plate, whether it is the use of film splicing or enlargement film film, or even direct-magnification exposure plate-making, must first output high precision The film's film is premised. The quality of the film output directly affects the quality of the screen printing plate. For example, due to improper control of the process of film exposure or development at the time of film output, the film thickness on the film is not insufficient or the contrast is not good (grey degree is large). This kind of film bottom version will often make the screen that is not a small dot easily washed away, that is, the subtle leakage points will not be able to pass through. As a result, the printed screen will lose the subtle details of the canal in the bright tone area or the dark tone area, or the color cannot be Correctly restore.

There is no need for a screen-printed CTP film at the bottom of the film, and the size of its sprayed stencil ranges from 1800mm x 2200mm to 3500mm x 5200mm. The JetScreen system is equipped with a very precise Piezo nozzle, with a pixel resolution of up to 533 x 633 dpi. The alignment repeatability can reach 0.02mm. The number of screen lines can reach 75 lines/inch. The dot shape can be arbitrarily selected circular, square, prismatic heart elliptical dot. In operation, a special hot melt wax was sprayed onto the screen plated emulsion film. The special hot-melt wax has a high optical density. When the nozzle sprays images onto the screen, the hot-melt wax immediately solidifies and adheres tightly to the emulsion. And the hot melt wax contains a special ultraviolet blocking agent, which can completely prevent the diffraction of ultraviolet rays during exposure and avoid the photo-cathode side wall photo-corrosion. JetScreen does not have the process of splicing films, but also completely solves the insurmountable issues such as network distortion and virtual images caused by objective factors such as image distance and lens spherical aberration in magnified film or spotting screens, effectively preventing network expansion. Guaranteed the fine level of detail of the image. At the same time, JetScreen provides an effective solution to the occurrence of moiré in screen printing.

The features of JetScreen's screen printing plates are as follows:

1. The computer design process is simple. The pattern (printing information) is easy to save and can be freely changed as needed. The previous film stock is easy to store, dirty, and sometimes deformed.

2. Users can obtain print data from disk, CD-ROM, and other forms of the heart of the user. The communication between the enterprise and the customer is easy and convenient, which helps to shorten the work cycle.

3. You can set the spray pattern at any position of the screen, and ensure the repetitive screen reset accuracy, making it easier to adjust the printing alignment.

4. Brightroom operation (but to avoid sunlight, strong light, indoor yellow light source for safe work), no special darkroom requirements.

5. Without the need for a vacuum drying frame (vacuum precision printing machine), the exposure is more direct, resulting in an increase in the resolution of the emulsion and the resistance of the screen to India.

6. No special emulsion, solvent-resistant, water-resistant emulsion can be used.

7. The size of output screen size can be accurate as required, and it can be adjusted freely.

8. Select the dot type and dot size that are most suitable for screen printing. At present, the screen output maximum number of screen lines is up to 75 lines/inch. Yin and Yang charts can be produced.

9. Hue grayscale (dot tone value) can reach 2% - 95%, to ensure the contrast of the print screen, the heart of the screen to adjust the dark tone of the subtle level of complete reproduction.

10. In theory, JetScreen is suitable for all screen-printed plates. JetScreen has unique advantages for large-format screen printing.

Screen printing CTP is not unique to the JetScreen family. For example, screen printing CTPs have been developed by Polaroid and Gerber Technologies. At the same time, domestically produced CTP systems have also entered commercialization.

Source: "Printing World"

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