The cause of the stencil phenomenon in the screen printing process

The paste version, also known as plugging, refers to the phenomenon that the hole of the screen printing plate can not 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 squashing can be analyzed from the following aspects:

1 Glass: The glass surface is not clean, and there are watermarks, paper prints, mimeographs, fingerprints, dust particles, and other contaminants. Thus resulting in paste version;

2 Reasons for workshop temperature, humidity and ink properties: The screen printing workshop requires a certain temperature of about 20°C and a relative humidity of about 50%. If the temperature is high and the relative humidity is low, volatile solvents in the ink will evaporate quickly. The viscosity of the ink on the screen becomes high, 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. Secondly, if the ambient temperature is low, the ink flowability is also poor and it is easy to produce paste.

3 Reasons for the screen printing plate: The prepared screen plate can be used only after being rinsed with water and dried before use. If you make a good version, do not print it too late. In the process of preservation, dust adheres more or less, and if it is not cleaned during printing, it will cause a paste.

4 The reason of printing pressure: In the printing process, the imprinting force is too large, it will make the squeegee bent, the squeegee is not in line contact with the screen plate and the glass, and is in surface contact, so that each squeegee can clean the ink. , leaving residual ink, after a certain period of time will cause conjunctiva caused paste plate.

5 Reasons for improper clearance between screen plate and glass: The gap between the screen plate and the glass should not be too small. The gap is too small. After the squeegee is printed, the screen plate cannot be separated from the glass in time. When the screen plate is lifted, the ink is printed. A certain amount of ink is stuck on the bottom of the plate, which can easily cause a paste.

6 The reason of the ink: When the pigment and other solid particles in the screen printing ink are relatively large, the phenomenon of blocking the mesh hole easily occurs. 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.

In the printing process, the increase in ink viscosity caused by paste version, the main reason is that the screen printing ink solvent evaporation, resulting in increased ink viscosity, and closure of the network 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 paste printing. The countermeasure is to use a small amount of ink refilling principle.

Poor flow of 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 without affecting the print quality.

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 every time it is scrubbed, and if it is wiped off, it causes a major defect in the plate.