Screen layout shape selection before plate making
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The quality of the screen is the premise of the quality of the printing. Without the good quality of the screen, it is impossible to print high-quality works. In the process of screen printing, it is important to select the net, stretch net, cleaning to gluing, exposure, development and other processes, but the screen shape is also one of the factors affecting the printing quality. This article discusses the problem of screen shape selection before screen making.
The screen shape is also the plane shape of the frame. The selection box is generally based on the net content of the draft and the width of the ink area to determine the size of the frame, and then consider what material is used in the frame, how much material is used, and so on. The shape of the frame is mostly rectangular, and only a few shapes that are rare are selected when encountering a special substrate. For example, the handkerchief printing adopts a square shape; the printed advertisement on the finished umbrella is triangular or isosceles trapezoid due to the influence of the rib; the large color printing is to strengthen the bearing capacity of the net frame to prevent the inward deformation from being selected as a hexagon; the concave bottom of the bucket, The bottom of the basin is round and so on. In fact, the special screen shape is not only suitable for special printing, but also in the production of fine lines and tone color printing, which is used for high-order screens, especially in the production of tension nets, tension uniformity, screen printing resolution, and amount of ink. It is also practical for ordinary planes. The following is a description of the three aspects of force analysis, screen printing experiment and practical application.
First, the screen plane force analysis
Screen printing plate is a kind of elastic plate. Stretching and squeegee both deform the screen and require the screen to return to its original shape. The frame is subjected to the restoring force transmitted by the screen. This restoring force can be regarded as the sum of the tension of the stretched net and the component of the squeegee and the shearing force generated by the friction between the squeegee and the running of the squeegee. Since the force of the motion is an instantaneous value, the squeezing force can be manually controlled, and the frame is stressed. Can be seen as a tension similar to static. From the 90° stretch net, within the elastic limit of the screen, the tension of the stretcher is larger, the tighter the screen, the more uniform the tension, and the better the quality of the screen. However, the tension of the stretcher will not be transferred to the screen 100%. The loss of tension is mainly caused by the deformation of the frame and the fatigue of the screen. In response to this contradiction, the high-strength screen and the trapezoidal section frame are created, which can be improved. Screen quality. However, if the frame material is infinitely increased, the weight will increase and the actual operation will be affected. The deformation of the frame is proportional to its length. The longer the frame is, the larger the deformation is, and the greater the tension loss. Therefore, the deformation of the frame shape is different.
On the circular frame, each action point is subjected to the recovery force of the screen in both the longitudinal and transverse directions, and the resultant force of the restoring force is directed to the center of the circle to reach equilibrium, so that no inward deformation occurs. The intersection point on the hexagonal frame is not subject to force, and the six sides are relatively short, and are subjected to vertical resultant force to minimize deformation. The sides of the square mesh frame are equal in length, which is the smallest deformation in the rectangular mesh frame, and the tension uniformity after deformation is the best. The smaller the ratio of the short side to the long side of the rectangular frame, the larger the deformation, and the greatest influence on the tension uniformity of the entire screen.
Second, screen printing experiment
Steps:
1. Using a 2 cm x 2 cm metal square tube, bend into a semicircular frame of 40 cm in diameter on a round bender, and then weld them together. The same material is then made into hexagonal, square and rectangular mesh frames.
2. After the frame is made, sand the sand, glue the mesh twice, select the 300 mesh wire mesh on the same stretcher, and the tension is about 8kg. After the stretched screen, the screen is left to stand for 3 to 4 days.
3. The empty version scrapes out 4 pieces of land.
4. Use 60 lines of 1 to 9 to make the picture of the net, and make the same version of the plate on the four kinds of frames, and use each version to print the two clearest tones on the 3mm white glass. Samples printed on various shapes of screens were compared. Experimental results: the rectangular screen version of the underground ink and uniformity is slightly worse, the dot is deformed, not complete enough, and the order is narrowed. The quality of other screen samples is close to the same.
Third, the actual use of the screen shape
The circular and hexagonal mesh frame is tight, the tension is uniform, and the printing effect is good. However, in practical applications, the circular frame is made by bending the circular machine, and the process is complicated, and the effective printing area is an inscribed rectangle. Waste material consumption; although the hexagonal mesh frame is welded by straight edge, the welding points are many, the angle is difficult to control, and there are also problems of the round frame, which lacks practicality. Only the square version has the advantages of the above version, and the processing technique is the same as that of the rectangular version. Therefore, it is preferable to select a square having a side length of 1:1 when making a frame or a rectangle having a side length ratio close to 1:1.
When I was just engaged in screen printing, I used a large number of large, medium and small mesh screens to make large-scale maps. In order to be faithful to the manuscript and to meet the mathematical precision of the figure, the screen prints a non-serrated criss-crossing square mesh, as thick as a hairline, clearly reflecting rivers, beaches, roads, residential areas, etc. Heap, all night long. Turn over the print records in the less-than-successful, and count the success rate of each numbered screen. The square plate printing was found to have the highest success rate and the best quality. After analysis and experiment, the layouts were all changed to 80cm×80cm, 90cm×90cm, 100cm×120cm, and 3 groups of 12 screens were recycled. When you typeset, you can put together as many pieces as possible, or a content that consists of several rows and several times to form a layout. The pattern that cannot be spliced by overprinting is a large version of the small image, as long as it is successful and worthwhile. Due to the change of the shape of the screen, the monthly screen printing task of the month is as high as 80 editions, and 3,000 sheets of paper are opened, with a success rate of 100%. The screen printing accuracy is 2‰, and the negative error is zero. The picture content is clear, the lines are smooth, the characters are full, and the inspections are sent to the provincial bureaus and ministerial agencies to meet the normative standards. Later, the author used the screen version close to the square to make the four-screen effect of the flower and bird, and it also laid the foundation for the large-scale color screen printing in the future.