Is the gap necessary?

There should be a certain gap between screen and substrate. The mesh is stretched on screen frame. When the screen is in a horizontal state, there will be a certain sag. Especially during the scraping process, the sag will increase.

To prevent the substrate from sticking to the ink before scraping and thus ensure the printing quality, the lowest part of the screen must leave the substrate.

In silkscreen printing, the squeegee and the screen are in mobile line contact. They cannot be in contact with the substrate before and after printing. The screen moves away from the substrate as the squeegee moves.

If the screen does not leave the pattern before printing, the ink will continue to penetrate and diffuse, causing inaccurate pattern and distortion of the substrate.

There gap between screen and substrate is closely related to the movement of the substrate. When printing (especially when printing on the curved surface), the substrate must make a circular motion while printing. A certain gap won't cause blurring of the pattern or deformation on the substrate.

How to determine the gap?

The gap is necessary, but its size cannot be arbitrary. If the gap is too small, it is easy to cause penetration and sticking along the direction of the squeegee movement.

If the gap is too large, the mesh cannot recover after printing. It will sag and make the size of the pattern small. In severe cases, the screen will be damaged and unable to print.

If you use stainless steel screen with low elasticity, the screen will not contact the surface of the substrate, and printing cannot be carried out.

Factors that determine the amount of gap between screen and substrate:

1. Size of the screen

2. Tension of the mesh

3. Center sag of the screen

4. Shape of the substrate

5. Material properties of the substrate

6. Surface morphology of the substrate

7. Ink viscosity

The gap varies due to different printing conditions. Generally, for substrates with hard surfaces, such as ceramics, glass, metal surfaces, and hard plastics with low ink absorption, the printing requirement is high. For substrates with soft surfaces, such as cloth, paper, and soft plastics with high ink absorption, the printing gap is not so strict.

Usually, the gap with high accuracy is between 1-3 mm. For ordinary printed products, the gap can be 2-6 mm. The value is smaller when printing on curved surfaces, while the gap value is larger when printing on flat surfaces.

Ink drying

There are some ways of ink drying, such as natural drying, heating drying, ultraviolet drying, electron beam drying, infrared drying, and microwave drying.

In addition to the above drying methods, there are physical drying and chemical drying according to different ink resins contained in ink. According to the different properties of ink, there are penetration drying, oxidation film drying, volatile drying, etc..

Inks with special properties have other drying methods, such as photopolymerization drying and ultraviolet drying. Most inks usually use only one drying method, but some inks use a certain drying method as the main drying method, accompanied by other auxiliary methods.

Generally, volatile drying inks, water-based inks, oxidative polymerization inks, and two-component reaction inks are dried naturally, or by hot or cold air, or by infrared irradiation. Heat curing inks are dried by infrared irradiation. UV curing inks are dried by ultraviolet irradiation.

We should choose right drying method based on the actual conditions such as the ink, drying equipment, and workplace.