The nine-step selection of screens during printing process (2)

Step 8: Screen tension

Appropriate screen tension is required to obtain a stable and consistent off-plan gap and to promote accurate ink transfer. Tension should be the same in warp and weft directions. Without balanced tension, moire and overprinting will occur.

The tension gauge alone can not be used to obtain information on the balance tension of the screen. The precise tension needs to measure the percentage of elongation of the warp and weft cables, and the tension gauge is used to evaluate the geometric performance of the screen (unity, size, and number of screen lines). Using the obtained balance tension data, the probability of occurrence of moiré will be reduced.

If the elastic limit of the screen is exceeded, tension disappears and eventually collapses. This is why it is important to observe static and dynamic tension when printing. The dynamic tension at both ends of the squeegee may exceed the elastic limit first. Especially when the angle of the screen shows absolute tension and the ink pool is too small.

Note that the non-deformable screen should not be used for color overprinting. Once the correct screen geometry is obtained under the required tension, the deformation of the screen will destroy the geometric performance and cause moire.

In general, the minimum static tension level must ensure that the squeegee has similar dynamic tension at both ends and in the middle. The maximum static tension level must ensure that the dynamic tension is below the elastic limit of the screen, and it cannot produce deformation that leads to a decrease in geometric accuracy. .

Step 9: Select the template

After the screen is stretched and the related work is ready, the choice of the template is the next stop in the screen-making journey. For color overprinting, you should produce as thin a stencil as possible to control the emulsion thickness on both sides of the screen and the flatness of the print side. The flat template can ensure that the stencil and the substrate in the printing are relatively parallel.

The EOM (the amount of emulsion deposited on the screen) should be as small as possible on the side of the stencil printing, but it also benefits the flatness of the stencil. The lower the Rz value (surface roughness measurement), the flatter the template, and the easier it is to obtain the resolution and exposure you need. The squeegee side emulsion may have a higher Rz value (unevenness), but it cannot exceed the highest point of the screen fiber.

In short, the thinner and flat the template, the better the printing edge, and the more ink transfer on the screen, the ink accumulation will be reduced for the ink "target="_blank"> UV ink, the default for directly exposing the emulsion template. The parameters should include high cure, dual cure, high resolution, fast drying, and wide exposure range.For overprinting, you want to make the dried coating very transparent.