Influence and adjustment of screen spacing in the

2022-07-30
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Influence and adjustment of the pitch in silk printing (Part 1)

in silk printing, many printing variables determine the final printing quality, and the pitch is an important variable. Therefore, in order to ensure good printing quality, it is necessary to accurately adjust the distance in printing. In order to control the distance, it is necessary to fully understand and be familiar with the influence of distance and other variables on the printing quality, so as to print better, faster and more stable products with good quality

function of distance

distance, also known as plate spacing, is the vertical distance between the bottom of the screen printing plate and the surface of the substrate. It is one of the five main variables in silk printing (scraper hardness, distance, printing speed, scraping pressure and ink suitability). In silk printing, the space between the printing plate and the substrate is the key to ensure that the printing plate is not stuck with the substrate in the printing process

if the plate adheres to the substrate, many problems will be caused. This problem has been solved. During the printing process, it can make the wire contact with the substrate only at the edge of the doctor blade. As soon as the doctor blade passes through this area, there will be a stripping area where the wire and the substrate are separated, and then clear prints will be left. Peeling refers to the upward separation movement of the frame during the printing stroke. It occurs at the starting point of the ink scraping stroke and when the ink scraping plate is in motion during the printing cycle. Move the plate until it contacts each gasket. Use different gaskets to adjust different distances. You can also use calibration wedges to adjust the distances. Its accuracy and versatility are good

ruler adjustment. This method is to directly measure the distance from the ruler to the surface of the printing platform by placing the ruler such as wooden column, wooden roof frame, wooden beam, wooden stair, etc. close to the bottom of the frame

use a mechanical distance gauge. Hang the distance meter above the plate, and make the reading of the instrument on the wire surface be 0, then press down until the plate contacts the substrate, read the value at this point from the instrument, and then subtract the thickness of the wire and the template, which is the distance at this point. As long as it is used properly, the data measured by the distance meter is very accurate and has good repeatability. Its disadvantage is that each reading must be reset. The instrument is limited to moving around the plate, which is inconvenient to use and difficult to use on some printing machines. At present, the silk printing technology foundation (SPTF) has launched a new type of distance measuring instrument, which is a more effective and reliable electronic testing instrument. It can measure the distance quickly and accurately at any position of the plate and is easy to operate. The operator of prepress process can know the distance at any time by using this instrument

variables that affect the distance include frame size, plate tension, doctor blade length, image area relative to frame size, and image type (for example, large-area field and reflection, large distance is required due to the large surface area in contact with the substrate). Some of these variables can be changed, and some cannot be changed. The operator of the printing substrate shall make corresponding adjustment according to the requirements, and the distance shall be as small as possible within the acceptable range. The tension of the plate is an important factor affecting the distance adjustment and the printing quality. This should be considered in plate making, but the effect of tension on the plate life will only be shown when printing. If the tension of the version is too low, the wire is easy to degumm under the continuous stretching state. In addition, in order to make the version bounce up quickly, the distance has to be increased, so the pressure of scraping is also required to be increased correspondingly, but this is undoubtedly easier to damage the version and will deform the pattern. The adjustment of general spacing should be based on the tension in 2013. If the tension is large, the spacing will be small, otherwise it will be large; According to the box size, the box spacing is also large. However, it should be noted that when adjusting the spacing, it is necessary to ensure that the spacing of each point on the version is consistent

effect of spacing on printing quality

inappropriate spacing will have an adverse impact on printing quality, which may lead to poor reproduction accuracy. 1. Focus on developing multi-functional, high-performance materials and additives, rubbing, foaming, ghosting, ink bars, lost layers, blurred image edges, incomplete marks, images, inaccurate overprinting, etc

effect of too large distance on printing quality

regardless of the tension, too large distance will cause image expansion and change the image accuracy and size. Under high tension, the separation speed between the wire and the substrate will be faster than the running speed of the scraper, which will cause the deformation of the scraper. Too much pitch will cause serious damage to the wire, which will cause premature damage to the template. The grout may also fall off due to excessive tension

under normal tension, if the distance is too large, it needs a lot of ink scraping pressure to make the printing plate contact with the substrate, which will damage the image hierarchy because of too much ink. Too much pressure on the doctor blade will also damage the image, causing smudging and dot expansion. In addition, if the distance is too large, the plate will bounce back too quickly, so that the ink cannot be fully transferred to the substrate, and the printed matter will have defects such as marks, incomplete images, ink bars, bubbles, blurred image edges, etc. High scraping pressure will also deform the doctor blade, resulting in deformation of the edge of the printing area and large amount of ink adhesion, which will lead to uneven ink layer, which is reflected in the large color variation of the image on the printing crystal and become a defective product. Too large distance will also slow down the printing speed, because the force exerted by the doctor blade is not directly used to transfer the ink, but must first overcome the tension of the plate to make it contact with the substrate, thus dispersing the pressure of the doctor blade and reducing the printing efficiency. In manual printing, the operator must exert greater force to print, which is easy to fatigue

in addition, it should be noted that in silk printing, because increasing the distance has the same effect as increasing the plate tension, some people want to increase the scraper pressure by increasing the distance, so that the plate can obtain a higher tension, but this method has many negative effects (especially point increase), so the plate tension should be increased in printing, rather than increasing the distance

(to be continued)

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