First, the ink [1] UV ink retention period is not long: The current UV ink retention period is not long, because the UV ink is more prone to gelation phenomenon.
[2] UV ink ink film thickness, transparency: ink ink film thickness is too thick, it will also affect the speed of UV light irradiation, resulting in ink hardening is not easy. As for the transparency of the ink, the transparency of the UV ink is much faster than the opaque UV ink. In ink, the speed of UV light irradiation is not only faster, but also a more uniform relationship. For example, the color with the fastest hardening speed is blue in color four-color printing, followed by magenta and yellow. The black ink cures very slowly, and the hardest to harden is opaque white. Not only that, opaque whites tend to be yellow when exposed to UV light.
Second, the printing machine in the screen version of the layout of the printed material is different, and there are different printing machine. [Figure 2]
Figure II
The main topic discussed in this paper is screen printing lithography. Separate prepress and postpress for factors that may occur at the time of printing.
[1] Scraper 1. The hardness unit of the hardness blade face is generally measured by a hardness meter of JIS [Japanese Industrial Standards]. If the hardness of the blade surface is larger, the contact between the blade surface and the plate surface will be smaller, so it is suitable for those who print high, and the tangent line is sharper and smaller, and the printing ink is thinner. Conversely, the softer the blade surface, the larger the contact area, it is suitable for printing thick and rough, monotonous imprint pattern. The distinction is as follows: Extra soft 45 degrees to 55 degrees, soft 55 degrees to 65 degrees, medium 65 degrees to 75 degrees, and rigid 75 degrees to 85 degrees.
2. Width In simple terms, the width of the doctor blade must be greater than the width of the imprint and less than the width of the frame, so that the printing requirements can be achieved. However, in order to request quality, reduce the occurrence of imprint distortion, and consider the factors of the width of the doctor blade, there is still a basis for it. The positions of the width of the imprint and the width of the frame are discussed separately.
A. In terms of the frame position: Of course, the width of the scraper must be smaller than the frame in order to print. Ideally, 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, the better, because in this state, the mesh can be in the process of squeegee printing. Soft contact with the printed material, the net cloth stretch is also smaller. On the contrary, when the distance between the scraper and the frame is too small, the net fabric is too rigid, resulting in an excessively large angle of the cloth at both ends of the scraper, resulting in a distorted shape, which is the main cause of the distortion of the print pattern. In general, for every 10 inch increase in the scraper, there is an error of 100 micron, and the width of the scraper is preferably not more than 50 percent of the frame size. If this is not possible, at least the ends of the scraper must be away from the frame. Distance must be 5 cm to ensure print quality.
B. In terms of imprinting positions: Generally, the width of the doctor blade must be greater than the width of the imprinting pattern by 2 to 10 cm. The reason why the width of the doctor blade is smaller, the better, must also be determined depending on the size of the imprint. In the event that a re-inking knife is used, the width of the ink-returning blade should be wider than the width of the printing squeegee, so that the ink overflowed at both ends of the printing squeegee can be completely transported back.
3, squeegee speed and angle The speed and angle of squeegee mainly affect the amount of ink reaching the printed object through the mesh. Squeegee printing speed is less penetrating and thin, slow 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 imprint may be unclear. When the squeegee is too slow, it may easily cause bleeding and the imprint may not be sharp enough. The general print speed is about 60 to 200 cm per second, depending on the conditions at the time. The angle of the squeegee 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 and 75 degrees. Scratching 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.
4, squeegee pressure: First of all must understand a concept, screen printing does not rely on the pressure of the squeegee to press the ink to be printed on the object, but rely on the squeegee to push the ink, in the ink to produce a hydraulic effect, push Through the mesh, and by the adhesion between the printed material and the ink, so that the purpose of printing. Therefore, the printing pressure should be as light as possible within the range of the best possible, and the scraper surface and the printed object can be in line contact, otherwise the printing pressure is too large. When printing pressure is insufficient, it is inevitable that the imprint cannot be printed. When the printing pressure is too large, not only does the extrusion amount of the ink not increase, but the excessive bending of the blade tip causes the surface of the plate to be in surface contact with the object to be printed, resulting in printing. It is not clear, and the squeegee wears too much and the printed surface of the layout may cause peeling.
[2] Mesh screen printing In the aspect of printed body selection, due to its slow speed, most of the objects are not easy to absorb ink. Therefore, the development of ink printing is going in two directions. One is a printing ink containing a solvent. After the printing is completed, the solvent evaporates and the ink is fixed on the printed object. However, because the solvent is harmful to human health and poses a problem of pollution, the ink is developed in the other direction. Or heat to fix ink to reduce the incidence of public hazards. However, the ink is fixed by light or heat, so the thickness of the ink film must be very thin. Therefore, a thin net cloth is required to obtain a good effect, but the fine net cloth is more expensive, and a kind of pass is developed. Pressure-pressed mesh cloth is suitable for the drying of UV printing ink and is called a UV mesh cloth.
1. Advantages The use of a general mesh UV cloth instead of a high mesh cloth can reduce the cost.
2. Disadvantages: After the webbing is flattened, the shape of the mesh is slightly uneven, which affects the linearity of the edge of the print, and is not suitable for fine printing. (To be continued) (Zhongwei Zhong, Department of Print Communication, Chinese Culture University, Taiwan)
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