Screen tension troubleshooting

Of all the variables that can change and cause problems on the printing press, those associated with the screen always bring the greatest trouble. When printing, your screen changes and the prints change accordingly.

Mesh tension is the biggest variable you need to focus on. In the production process, when the screen tension drops, the following problems will occur:

1. The screen tension drops, the pushing and pulling force of the squeegee becomes larger, and the dots increase, resulting in hue shift in the printing process.

2. The screen tension drops, causing the screen cutting ability to decrease, resulting in insufficient ink coverage.

3, the screen tension drops, the scratch resistance becomes smaller, but also in the image of the squeegee end of the shadow.

4. Instability of the screen causes registration problems.

In the case of monochrome printing, slight changes in tension have little effect on the quality of the print. However, in multi-color (color printing) printing, the color shift of the prints can easily reveal the change of the screen tension. As a compensation for low tension, you must increase the pressure of the squeegee and/or increase the off-gauge gap. Alternatively, you can try to stabilize the screen tension by using a repetitive stretched net frame to prevent problems in advance.

The discovery and overhaul of moire

Moiré is always one of the most frustrating appearances when printing on colour printing. There are three forms of moiré:

The first kind of moire: When two or more halftone patterns appear on a positive picture, the conflict between them will cause moiré.

The second type of moiré arises from the conflict between the number of image lines and the screening angle.

The third kind of moire: This kind of moire is easily found. It results from the conflict between the pattern appearing on the screen and the weaving pattern on the garment.

Before the screen exposure, a simple positive image detection method was used. The first type of moiré was easier to find. If you line up the positives and find any type of pattern that is different from what you expected, you will immediately know that these unwanted patterns will be copied to the screen and will appear in the clothing. on.

Many print shops can almost completely eliminate the second type of moiré by using the correct screen tension and number of screens. If you add screens, make color separations, and use appropriate screens and correct (stable) screen tensions in the correct angle, in fact, the second type of moire problem will be printed from your clothing. Disappeared in production.

The third type of moiré is the most common and difficult to find in production. This is especially true if you miss the management of the first and second types of moiré in the production process. The first aspect to consider in the tortoise pattern is the repetitiveness of irregular patterns. If this pattern remains consistent from one printing platen to another, it is very likely due to screen and/or color separation. If the pattern changes from one printing platen to another, the result may be due to the conflict between the weaving of the printing substrate and the screening angle of the separation printing plate. It is assumed here that the printing platen is horizontal and the screen plate is parallel to the printing platen.

From this point of view, the relevant variables include the number of lines of the design work, the angle of the screening, and the weaving method of the clothing. If you are aware of the first few variables in the operation of color registration printing, your best bet now is to look at other garments with higher fabric quality or stitching to solve this problem.

Choosing the right fabric for the chromatic printing is critical because there are many fabric structures available. Fabrics with a high number of needles (1000/in. or more) perform better during trap printing because the printing surface characteristics of the fabric minimize the impact of the printing on the screen or the number of lines.

Registration issues

For printers, registration is also a common problem that hinders productivity in print jobs. When misprint occurs, it may be because the squeegee pressure is too high and/or the screen tension is too low.

The solution is to maximize screen tension, minimize off-slot clearance, and minimize squeegee pressure. This situation is common when using wooden frames on automatic printing machines. Wooden frames are not dimensionally stable, so they can only give minimal support to the screen. The resulting low tension condition requires a larger squeegee pressure to push the ink through the screen.

Change in registration has also resulted from a number of reasons, including the fact that the printing platen is not kept horizontal, the screen plate is not parallel to the platen, and the printing machine is displaced.