Fine mesh screen printing (3)

● Influence of printing materials on screen printing

Regardless of the coarse or fine mesh, most of the time, the impact of printing materials is relatively large. Unfortunately, we have to face the reality that the printed materials are often not controllable by screen printing workers. .

The selection of printing materials is often based on the use of the final print product and some of the customer's specific needs. Screen printers often have to choose between one or two. Only the printer can explain and put forward the reasonable reasons for selection, the customer is willing to accept the choice of screen printing staff, for example, our company explains to the customer why we use PVC foam printed label with a relatively smooth surface, that is to say, the surface is smooth Can print fine mesh tones.

However, in addition to these choices, there are many variable parameters that have an important influence on the printing effect:

(1) The surface condition of the printing material (thick or thin);

(2) Physical properties of paper and plastic materials, including textiles;

(3) It is flexible or rigid and determines the type of printing machine (platform or roller);

(4) size (size);

(5) Chemical properties determine the choice of ink;

(6) The dimensional stability.

The controllable variable of the printing material - the surface condition is an important parameter, related to the shape and quality of the printed dots.

Microporous substrates, such as coated paper and optical disks, are better than coarse-pored substrates. Like coarser paper, non-woven fabrics, and some stretchy textiles and plastics, the first printed ink “eats” part of the aesthetic fiber and some openings so that this color will become The main color is said. In other words, it will be more prominent in the entire printed pattern.

To control this problem means to reduce the density of the first color, or the density of the color itself, or both, by correcting the template on the one hand, and reselecting the printing order of the color on the other hand. The color of the first print is selected according to its importance in the final printed image. For example, printing a bright mesh on a highly hygroscopic paper, preferably printing magenta or pink first. However, if it is a natural landscape, it is better to print black first.

It should be emphasized that the flatness, stability, and thickness of printed materials are also important.

Screen printers should stand on the customer's behalf to decide whether a certain material can be used or not, and tell customers as much as possible.

The smoothness of the material and the flatness of the surface are inconsistent. How can we ensure that the quality of the halftone print image is always consistent?

Unfortunately, production tolerances such as cardboard, hard corrugated, or thick plastic materials are often close to ±7 (especially for some stretchy products, the actual stretch causes the thickness to be difficult to control). In contrast, screen printers cannot fully control these variables. This is an almost uncontrollable variable. However, when customers request four-color screen printing on these substrates, you must pay special attention to ensure that the other party provides the required print quality, which is absolutely necessary.

This problem is not that simple, because, especially in fine-mesh printing, the screens and templates must be adapted to the material to be printed. This means that many pro-related factors must be taken into account, such as those commonly used in screen printing. Materials, such as cotton paper, all kinds of plastics, stretchable products, and textiles.

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.