Fine halftone screen printing analysis (4)

Therefore, a direct photosensitive adhesive plate is used for printing general images on any material.

As mentioned before, in most cases the printing materials are either already established or specified by the customer rather than screen printers. In this case, screen printers can only provide their opinions and suggestions to customers who provide materials, or report that these materials are harmful to the quality of screen printing.

Screen printers should explain to customers why this material is more suitable than the other one. Therefore, we say that choosing a certain substrate for screen printing is a half-controllable factor.

In most cases, involving numerous physical and chemical variables, you want to explain to the customer as clearly as possible, for example, why choose polystyrene instead of PVC, why is pH neutral paper superior to Higher pH paper, or why a cotton spun material is better than another (textile), etc., because it can send and improve the print quality, sending the final image quality.

Of course, the surface of relatively coarse and porous materials can also achieve good printing quality, but the screen printer must adjust the screen exposure intensity, the choice of screen printing technology, the density and viscosity of the ink, and print parameters such as the doctor blade. Factors such as pressure and printing speed also need to be adjusted. These naturally relate to the physical properties of the substrate, the surface properties, including the flexibility or rigidity of the material. For example, with regard to the choice of printing press, if the substrate is sufficiently flexible, it can be printed on a cylinder printing press, which is better for half tone printing. The 0.7mm thick material can be printed on a small roll press, and the 1.5mm thickness can be printed on a big roll press. Harder printing materials should be chosen platform presses.

In short, the use of automatic platform printing machine, we must absolutely consider the thickness of the material, according to the maximum release of the press gripper. In other words, the nature of the surface of the substrate should also be adjusted according to whether it is a platen printer or a cylinder printer.

The size of the substrate is also a physical variable that affects the type of printer used, the screen, the plate making method, and the ink selection. For example, to print a museum-customized bus station stop sign advertisement (120cm x 176cm) or a large-format map (120cm x 160cm), I usually use a 110-150 lines/inch (44-60 lines/cm) screen. Number, in order to be able to get the customer's desired quality.

This means that when printing a large-format halftone, it must be treated like other small-sized halftones.

Especially when solvent inks or water-based inks are used, it is necessary to accurately select other important variables related to the chemical nature of the substrate materials.

This simple fact shows that printing of some plastic materials cannot use water-based inks or use solvent inks. However, to carefully and accurately select the type of ink, it is necessary to select a chemically compatible ink for the printing materials. Consider solutions to other parameters such as thixotropy.

For me, I usually use UV ink to solve this problem. I can use a UV ink to print various substrates. This means that the variables that need to be controlled are greatly reduced.

The dimensional stability of the substrate should also be tested and well controlled. In addition, in the four-color screen printing, whether it is fine-tuning or not, accurate positioning registration is very important.

If it is possible to choose between two substrates with similar physical and chemical properties, the most stable one should be chosen.

Editor's note: The author Michel Casa was born in France in 1935 and graduated from the French Press University and the Swedish Social University. In 1954 he entered the field of screen printing in Stockholm.

In 1979 and 1984, two printing plants were established to work on art and POP printing. Mr. Casa printed a total of about 3,000 fine works of art. It specializes in particularly complex screen printing. Since 1983, its print products have received more than 300 awards.

Mr. Casa also publishes technical publications and thousands of technical articles, publishes technical CDs in several languages, and regularly conducts technical lectures around the world. He served as PESPA President from 1996 to 2002 and is currently a member of PESPA.

Source: Silkscreen World