Screen Printing Frequently Asked Questions (1)

Screen printing failures are caused by many factors, including screen printing plates, screen printing, screen printing inks, screen printing equipment, screen printing materials, and operating techniques. There are single reasons for the occurrence of silk screen failures, but more are the result of the cross-cutting effects of intricate causes. This is where the operator pays special attention to determining the cause of the fault and taking appropriate countermeasures.

First, paste version

The paste version, also known as plugging, refers to the phenomenon that the hole of the screen printing plate can't transfer ink to the printing material during printing. The appearance of this phenomenon will affect the printing quality, even if it is severe, it will not be able to print normally.

The cause of the stencil phenomenon in the screen printing process is intricate. The reasons for plagiarism can be analyzed from the following aspects.

1 The reason for the substrate. Screen printing substrates are diverse, and the texture characteristics of substrates are also a factor in the stencil phenomenon. For example: paper, wood. The substrates such as fabrics have low surface smoothness and poor surface strength, and are prone to powdering and hair loss during the printing process, thus resulting in stencil printing.

2 The reason for workshop temperature, humidity and ink properties. Screen printing shop requires a certain temperature and relative humidity. If the temperature is high and the relative humidity is low, the volatile solvent in the ink will evaporate quickly and the viscosity of the ink will become high, thus blocking the mesh. Another point that should be noted is that if the downtime is too long, it will produce a paste version phenomenon, the longer the paste version becomes more serious. Second, if the ambient temperature is low, the ink flowability is also poor, it is easy to produce paste.

3 reasons for screen printing plate. The prepared screen plate can be used after being rinsed with water and dried before use. If the printed version is left over for a long time and is not printed in time, the dust will adhere to more or less during the preservation process. If printing is not performed, it will cause a paste plate.

4 reasons for printing pressure. Excessive embossing force during the printing process will cause the blade to bend. The blade and the screen plate and the substrate are not in line contact, but are in surface contact, so that each time the ink is scraped, the ink can be scraped and left behind. Residual ink, after a certain period of time will cause conjunctiva caused paste plate.

5 screen printing plate and the substrate gap due to improper reasons. The gap between the screen printing plate and the substrate should not be too small. The gap is too small. After the squeegee is printed, the screen plate cannot be separated from the substrate. When the screen plate is lifted, some ink adheres to the bottom of the plate. This is also easy. Create a paste board.

6 ink reasons. When the particles of the pigments and other solid materials in the screen printing ink are large, the phenomenon of blocking the mesh holes is likely to occur. In addition, the mesh size and through-hole area of ​​the selected mesh are smaller than those of the ink, so that it is one of the reasons why the coarse-grained ink does not easily pass through the mesh. For stencils caused by large particles of ink, it is possible to solve the problems when manufacturing the ink. The main method is to strictly control the fineness of the ink.

The ink is dried too fast during the printing process, which can easily cause stencil failure. This is particularly true when using volatile drying inks, so it is important to choose the right solvent to control the drying speed when printing. In the selection of ink to take into account the impact of climate, generally in the winter using fast-drying ink, in the summer should be added to the ink in the dryer, if the use of late drying agent also occurs paste version, you must change to other types of ink.

Oxidation-drying inks are used, and the phenomenon of stencil printing does not appear much. However, if the desiccant is used excessively in summer, stencil printing may occur, and desiccants must be controlled in summer.

When using a two-fluid reactive type ink, since the ink itself is slow to dry, there is almost no stencil printing, but occasionally, stencil printing occurs.

In the printing process, the viscosity of the ink is increased, resulting in a paste plate. The main reason is that the solvent of the ink on the plate evaporates, resulting in an increase in the viscosity of the ink and a screen-sealing phenomenon. If the area for printing graphics is large, the ink on the screen printing plate will consume more, and the stencil printing will be less. If the picture area is small, the ink consumption on the screen printing plate is small, it is easy to cause the paste plate, and the countermeasure is to change the ink frequently. Poor flow of the ink will cause the ink to produce a paste when not passed through the screen. This can be solved by lowering the viscosity of the ink and improving the fluidity of the ink.

After a paste failure occurs, an appropriate solvent scrub can be used depending on the nature of the ink on the plate. The method of scrubbing starts from the printing surface and gently wipes from the center to the periphery. Check the plate after wiping, if any defects should be promptly repaired, and re-start printing after repair. It should be noted that the plate is thinned each time it is scrubbed, and if it is wiped out, it causes a major defect in the plate.

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.