2. Screen printing

2.1 selection of blade width

The choice of scraper width mainly considers two aspects. From the perspective of the frame: The basic condition is that the width of the blade must be smaller than the frame in order to print. The ideal condition for the frame is that the smaller the blade width is, the better, that is, the larger the distance between the left and right ends of the blade and the frame is, the better; because in this state, the mesh can be soft when squeegeed. Contact with the substrate, mesh stretch is also smaller. Conversely, if the distance between the scraper and the net frame is too small, the nets at the two ends of the scraper will be subjected to force and the angle will be too large, which will cause the shape to be distorted. This is one of the reasons that the net frame has a short service life and is easy to break.

From the substrate considerations: the width of the scraper must be greater than the width of the substrate 2 to 10 cm. The smaller the width of the scraper, the better. In general, the width of the scraper exceeds the size of the substrate by 3 to 5 cm per side to ensure the printing quality. , and leave a certain margin of error. The width of the ink return blade should be wider than the width of the printing blade so that the ink spilled from both ends of the printing blade can be completely transported back.

2.2 Squeegee speed and angle

The speed and angle of the squeegee motion mainly affect the amount of ink reaching the substrate through the web. Squeegee printing speed is faster and less ink and thin, slower printing speed is more ink and thicker. However, if the squeegee speed is too fast, the thickness of the ink is not enough, and the printing pattern is unclear. However, if the squeegee is too slow, it may easily cause bleeding and the printing pattern is not sharp enough. The general printing and squeegee speed should be adjusted according to the test result at that time.

The angle of the blade also affects the amount of ink. When the angle is small, the amount of ink is large. When the angle is large, the amount of ink is small. The angle usually used is between 45 degrees and 75 degrees. Scratch printing must pay attention to uniform speed requirements, and the angle must be the same before and after, it will not produce different shades of ink in the same print.

2.3 Squeegee pressure

The squeegee pressure has an effect on the quality of the print pattern. First of all, silk screen printing does not rely on the pressure of the squeegee to press the printing ink onto the substrate. Instead, it pushes the ink against the squeegee to generate a hydraulic pressure inside the ink. The ink is pushed through the mesh and is formed between the substrate and the ink. The adhesive force reaches the purpose of printing. Therefore, the printing pressure should be as light as possible within the scope of the better, and the scraper surface and the substrate is in contact with the line, or the printing pressure is too large, so that the blade tip too much bending, resulting in print patterns are not clear, or shorten the screen life And increase the loss of the blade. When printing pressure is insufficient, it is inevitable that the pattern cannot be printed.

2.4 Ink

At present, UV inks do not have long shelf life because UV inks are prone to gelation and deterioration. When using, should pay attention not to let the ink expire, use within the shelf life, the stock can't backlog, guarantee the ink quality.

UV ink ink film thickness, transparency: ink ink film thickness is too thick, it will also affect the speed of UV light irradiation, causing ink hardening is not easy. As for the transparency of the ink, the transparent UV ink cures faster than the opaque UV ink. In ink, the speed of UV light irradiation is not only faster but also more uniform. The color that is currently hardest to cure is the blue in color four-color printing, followed by magenta and yellow. The black ink cures slowly, and the hardest to harden is opaque white. Not only that, the opaque white will have a tendency to yellow when exposed to UV light.

3. other aspects

3.1UV lamp

In order to make the printing ink fully dry, the UV lamp must be designed with sufficient strength so that the printed UV ink or coating oil is completely dried, and the printing speed, the thickness of the ink film, and the color of the ink also have a certain influence on the drying effect. General installation of UV lamps should consider the type of printing machine and select the appropriate UV lamp on the finished product.

In multicolor overprinting, if the color density is high and the dark color is printed on one or two superimposed colors, the overall difficulty of drying is particularly increased, because the UV light is quickly absorbed by the dark pigment of the ink. Generally four-color UV ink drying difficulty is magenta, yellow, blue and black.

Some blending colors are also very difficult to dry. For example, green is made of yellow and cyan tones; opaque colors are also difficult to dry because it reflects off all UV light. The same metallic, gold, and silver colors have the same problem.

An excessively aged lamp cannot dry UV ink or coating oil, which can cause printing troubles. Most instructions on the UV lamp indicate that about 1,000 hours are required to replace the UV lamp. In fact, if the print cannot be completely dried at the printing speed, you must consider replacing the UV lamp so as not to affect the overall quality of the printing.

3.2 Reflector

If there is no UV lamp reflector, about 80% of the UV light will not be able to reach the substrate because of the diffusion. Therefore, the UV lamp must be installed with a lamp cover to reflect the UV light and focus on the surface of the substrate. The importance of the reflector is important. Sex can't be ignored.

The reflector must be cleaned and maintained. It is best to maintain the same features as the new one. Some dust or dust generated during drying tends to adhere to the reflective cover, which affects the efficacy of UV light reflection. UV lamps should be cleaned frequently to prevent dust and dust from affecting the drying effect.
(Author: Guo detached)