Slik screen tension control is an important aspect to improve the quality of screen printed matter, to make four-color network version of the same tension,and it will make the network edition of tension decline in print quality to a minimum, which is the key of most screen printing companies that need improvement in.It needs adequate screen tension and appropriate network distance to make full colors on the substrates, images, network integrity and reproducibility of fine level. Just when the screen there is enough tension, the mesh in order to overcome the rapid separation of the ink viscosity to make a stencil and substrate. When the lack of screen tension, screen scraper scratch can not be well separated with the substrate, so that printed images blurred edges, the ink overflow is serious, the picture’s quality can not reach customer requirements.
First, Screen tension due to reduced quality
The tension decreased has two main cases: First, the stretching is not in right place. lacking of tension; Second: After a lot of printing, screen decreased elasticity lead to tension decreased. In the former case, it can be avoided as long as the stretching process was in strict accordance with the requirements of the printing process. Tension decreased, the printing operation is often to increase net margin to compensate for lack of tension, thus ensuring the rapid separation of the stencil and substrate. While this would solve the adhesion problems, but will also bring the following question.
1.Increased costs
In order to compensate for lack of tension, It often used to increase the net. Increases network distance, only by a large squeegee pressure to make a stencil contact with the substrate. Scraping pressure has led to serious wear and tear of the mesh, particularly severe for large-volume print jobs. When using adjustable tension screen frame, the operator often had to twist the tension screw to increase the tension of the screen. It directly affects the printing speed, printing efficiency is greatly decreased. To can not adjust the tension of the screen frame, too much scraping pressure to reduce the network version of the life. not only reduce the printing speed but also resulting in material waste, greatly increasing the cost of printing.
2.Misregistration and image distortion
In above discussed, the tension decreased and had a large network from the network version of tensile deformation in the direction of the squeegee, so print out the pattern appears to be elongated phenomenon. The resulting image is much larger than the projected image misregistration printing, printing can not locate the printing fault. When a serious shortage of screen tension in the role of the squeegee will produce a shift in the direction of the squeegee. Printed image not only tone in the hierarchy, but also a serious distortion in the clear.
3.Colour cast
Lack of tension caused another printing failure is sticky dirty. Nets distance than the net from the small squeegee contact angle. Squeegee angle smaller extrusion through mesh ink is more. Relaxation of screen tension increased the net away from the printing process will be to squeeze too much ink. The increase in printing ink resulting in dot gain, blurred image edge, the image color cast.
4.Blade wear
Blank portion on the screen is composed of mesh can drain the relatively rough surface. While the rough surfaces is similar of nature of sandpaper. When the squeegee scraper force in the Web version, the scraper blade wear and tear is inevitable. We have dealt In front, declining screen tension eventually led to a large squeegee pressure, squeegee pressure greatly accelerate the wear of the scraper. Use different ink blade wear is also different, experiments show that the UV ink is more obvious wear and tear on the scraper. It can be observed by Judging scraper wear the printed pattern, such as blurred edges, resulting in flash phenomenon instructions to replace scraper.
Second, Measures of Control screen tension decreased
1.Prepress preparations
Have already corrected the good accurate reading of the tensiometer. The tension meter is sinking through the mesh of its own weight to the following Shen values indicate tension, the standard unit is N / cm. Measuring at least should be test 5 point, and finally calculate the tension value of the screen. The test method will not repeat again.
Through several experiments to develop a reasonable and prepared the tension parameter table.In general, the tension in order to get the high quality of the print screen is bigger is better, but the stretching tension is too large, the silk net easy to broke when printing.If you want to make sure the screen tension, you should make reference to several parameters.
The type of screen net, now the most commonly used synthetic mesh stretching tension can be slightly larger, but the poor quality of polyester mesh is necessary to use a smaller tension. Secondly, the different screen mesh screen, the best tension values are different. The larger the mesh, stretching the tension should be the greater. Re-printed image of a different nature should also use different stretching tension. In general, such as printing a simple block of color, the tension should not be too large, but the pattern of printed lines and mesh tone graphics, requiring great tension. Besides, the screen printing process, tension decreased, the need to replace the screen when the screen tension decreased to a certain tension value or tighten the mesh screws; When the adjusting screw to increase tension, but also to determine which tension value is the most suitable, these are slowly study the problem.
If you want to get reasonable and accurate tension reference table, take it as a day-to-day work. Firstly, the operator should for a mesh screen version of the record every time stretching tension values, and then record their normal printing prower. After several different production attempts to be the most reasonable value of initial tension in the screen version of this mesh according to the printing quality and printing prower, and other reference factors. For those adjustable tension screen, records the same way each time and then adjust the tension value (generally adjust tension value of the initial tension value, the tension value is slightly larger). To other mesh screen version, this method to get their best tension value. In order to establish the types of different mesh, different mesh screen stretching tension reference value for creating the necessary conditions to guarantee the continuity of high-quality printing.
2.The printing proces
When all prepared in the control of the printing process is to ensure that the tension accurate key. The first is the choice of the scraper and scraping pressure to determine and select the scraper type and quality, we must consider the different screen types, image feature and the printing process, and many other aspects, such as squeegee hardness, edge shape should be based on different substrates to be taken into accountand choice. Printing on fabric and other soft substrates, generally strong hardness scraper. The hard material of the substrate should choose the lesser hardness of the squeegee.
When you choose a good scraper, squeegee process is more difficult to determine a reasonable pressure. First of all, we should to adhere to a principle is as far as possible with minimal squeegee pressure, printing. When a transfer ink is insufficient, you can increase squeegee angle and appropriate increase in the pressure of ink reclaiming blade to increase the pre-plus network holes ink.If the results are not obvious, you can switch to a smaller hardness of the squeegee printing. These measures can increase the amount of ink transfer. Make sure only to increase the scraping pressure to resolve the lack of ink, but also try little by little. Scraping pressure will not only appeared earlier in this article some of the fault, but also the image produce pinhole printing failure.
Then, determine the reasonable network distance. Experiments show that when the screen when the tension is enough, the best network from 0.32cm. Not only improve high-quality of printed product, and can effectively extend the life of screen printing. But now general printing factory can not get this requirement, the main reason in this paper before half has been discussed.
Beside,we should strengthen the management to pay attention to cultivating the technical quality of the operator. The technical level of operator influence all aspects of the smooth conduct of an important part. Enterprises should often carry out some technical training or skill competitions and other activities to improve the skills of the skilled workers. Only in this way, enterprises can ensure the stability of the printing quality, the improvement of the printing process into a virtuous cycle .