Common Problems and Countermeasures in Screen Printing (2)

Second, the ink is not firmly fixed on the substrate

1 When printing on printed materials, it is very important that the printed materials are subjected to strict degreasing and pre-treatment inspection before printing. When the surface of the substrate adheres to substances such as oils, adhesives, and dust, poor adhesion between the ink and the substrate can result. Inadequate surface treatment of plastic products before printing can also result in poor ink fixation.

2 As the printing material, polyethylene strands must be surface flame treated in order to improve the adhesion with ink. For metal materials, they must be degreased and dust-removed before they can be printed. After printing, they should be baked according to the required temperature of the ink. Dry handling can also cause ink film peeling failure if improperly handled. In addition, in the textile printing, in order to make the textile waterproof, silicon processing is generally performed, so that the phenomenon of ink sticking is not likely to occur during printing.

3 Items such as glass and ceramics must be sintered at high temperatures after printing, so as long as the temperature is properly treated, adhesion will be good. A simple method to test the good or bad fixing fastness of the ink film: When the material to be printed is paper, the printing surface can be repeatedly bent to see whether the ink at the fold is peeled off. If the ink is peeled off, its bonding strength is weak. In addition, the printed matter is exposed to rain to see if the ink is easily peeled off. This is also a way to check the firmness of the ink film.

4 Insufficient adhesion of the ink itself causes the ink film to be hardened, and it is better to replace other types of ink for printing. Improper use of diluting solvent may also result in the phenomenon that the ink film is not firmly fixed. When selecting the diluting solvent, the properties of the ink must be taken into consideration so as to avoid the phenomenon that the ink and the substrate are not firmly bonded.

Third, the ink film edge defects

In screen printing products, a common problem is the occurrence of jagged gross margins (including defects or breaks) at the edges of the printed ink film. There are many reasons for glitches, but the main reason is the quality of screen printing.

1 The sensitivity of the photosensitive adhesive is not high, resulting in broken lines or incomplete lines.

2 The exposure time is insufficient or the exposure time is too long, the development is not sufficient, and the edge of the screen printing graphic is not neat, and appears jagged. For a good screen printing plate, the edges of the graphic should be smooth and neat.

3 When the surface of the screen printing plate is uneven, when printing is performed, there is still a gap between the screen printing plate and the substrate. Due to the penetrating infiltration of the ink, burrs occur on the edges of the printing ink.

4 During the printing process, due to the swelling of the printing film after exposure to the solvent, and the degree of swelling in the latitude and longitude are different, the surface of the printing film is uneven. During the printing, the screen printing plate and the substrate contact surface appear locally; Infiltration, the ink film will appear burrs.

In order to prevent the appearance of jagged haircuts, the solution can be considered from the following aspects:

1 Use high mesh screen plate making;

2 Select high-sensitivity photosensitive material plate making;

3 Make a certain thickness of screen printing plate to reduce the expansion deformation;

4 Stretching the net by stretching the net as much as possible, the best angle is 22.5°;

5 Fine line printing, as far as possible the use of indirect plate making law, because the indirect law plate burr may be smaller;

6 In the process of plate making and printing, try to control the temperature expansion factor and use a photosensitive material with a small expansion coefficient;

7 Improve the quality of plate making, ensure that the surface of the screen plate is smooth, and the edges of the screen lines must be neat;

8 Spray the screen printing plate with a water jet gun to improve the development effect;

9 The distance between the screen plate and the substrate, the angle of the squeegee, and the printing pressure should be appropriate.

Fourth, ink uneven

Ink film thickness is uneven due to a variety of reasons. In terms of ink, the ink is poorly formulated, or the normally formulated ink is mixed with ink. When printing, the ink expands and softens due to the effect of the solvent. Mesh hole is blocked, play the role of the plate, so that the ink can not pass.

In order to prevent such failures, the formulated ink (especially the old ink) should be screen-filtered before use. When you reuse a used plate, you must completely remove the old ink that has adhered to the plate. When the plates are stored after printing, they must be fully washed (including scrapers). If done according to the above requirements, the incident of inking wood will not happen.

If the tip of the razor plate is damaged, a trace will appear along the direction of movement of the squeegee. In particular, when printing transparent materials, there will be obvious ink inconsistencies. Therefore, the front end of the plate must be well protected from damage, and if it is damaged, it must be ground carefully with a grinder.

The unevenness of the printing table also affects the uniform ink. The convex ink layer is thin and the recessed ink layer is thick. This phenomenon is also called ink inhomogeneity. In addition, if the back surface of the substrate or the printing table adheres with dust, the above failure may occur. (to be continued)