Screen printing plate production

In addition to the selection of plate-making materials, the key to improving the quality of screen printing products lies in the rationality of the screen printing plate production process. At present, screen printing plates are mostly hand-made, and there is an urgent need for the improvement of plate-making techniques. Here, some of the problems encountered in the manual platemaking process are discussed briefly.

We have used three kinds of plate-making materials: dichromate silk screen film (film paper), diazo film screen glass and alcohol-soluble nylon screen film (hereinafter abbreviated as F, D, N). In the production process, various kinds of materials should pay attention to the following issues:

First, the choice of the number of screen mesh and stretch the impact on the quality of the printing plate l, the choice of silk screen mesh number of screens to choose according to the printed pattern and the requirements of the pattern to decide. If the pattern is larger and the lines are thicker, and the requirements for the pattern are not as accurate, a mesh with a lower mesh number may be used. Conversely, if the pattern is small, the lines are narrow, and the pattern needs to be precise, a mesh with a higher mesh number should be used. The number of screen meshes directly affects the printing quality. Because of the relatively low screen mesh, the printing ink permeability is good and the mesh is not easy to plug. However, the number of meshes is too low, and it is easy to infiltrate the printing material too much, resulting in unclear pattern edges and pattern distortion. The high number of screen meshes can meet the requirements of clear edges and lines. However, the number of screen meshes cannot be higher than the number of printed materials. Otherwise, it will easily block the mesh. Therefore, a moderate number of meshes should be selected, generally between 120 mesh and 300 mesh. The dichotomy in the single-factor merit selection method can be used as a selection test. 2. When the stretch net mesh is stretched and the net frame is stretched, the degree of tightness should be appropriate, and it should be noted that the tension in each point in the net frame should be the same. If the screen is stretched too tightly or too loosely, or the tension at each point is inconsistent, the following problems may arise: the screen is stretched too tightly: the elasticity of the printing plate is lost, and the pattern is distorted during printing; Too loose or the tension is not the same: 1 Fine lines can not be developed; 2 The edges of the pattern appear zigzag, pattern distortion; 3 In the printing process, there is a phenomenon of leakage of the slurry 4 For the F version, the adhesion of the film and the screen Poor, resulting in film peeling off during development; for the D, N version, the layout is difficult to evenly flattening. The glue cannot adhere tightly to the screen. D version of the film caused by the development of the phenomenon of smooth slipping off the N version of the layout is also very easy to produce trachoma. 5 In terms of F and D, the net is loose and it also affects the reuse of the screen.

Second, the impact of temperature on the quality of the printing plate. The quality of the production of printing plate quality and production of various types of temperature. This temperature includes: 1, the operating room temperature; 2, the oven temperature; 3, the exposure chamber temperature; 4, the developer temperature. l, operating room temperature; operating room temperature should generally be maintained at about 25 °C is appropriate. Winter and summer seasons should pay attention to the regulation and control of temperature. For F version, the influence of room temperature is not obvious. For the D version, in hot weather, if the room temperature control is not good, the following problems will occur: 1 Preparation of glue can easily produce thermal cross-linking, resulting in difficulty or no obvious development; 2 a lot of bubbles in the glue, Causes the layout to produce bubbles or trachoma. For the N version, when the room temperature is lower than 2O°C, the following problems will occur: 1 The difficulty in developing the film due to the uneven thickness of the squeegee will cause the display to be difficult to appear: Not uniform, resulting in inconsistent print pattern color. 2. Temperature in the oven The drying temperature set according to the respective performance index of the plate-making material should be gradually tested from the lower limit of the specified range according to local conditions, and the optimum drying temperature should be selected. Normal drying N version without blowing; drying F or D version should be added to the blast, in order to speed up the speed of the layout of the water, as soon as possible to make the layout dry. If the drying temperature is too high, the following problems may occur: 1) Development is difficult, and blinding occurs; or 2) The screen loses its elasticity, resulting in distortion of the printed pattern. If the drying temperature is too low, the drying time must be prolonged, otherwise the layout will not be fully dried. For F, D version, it will cause the phenomenon of film layer or glue layer falling off; for N version, the glue layer is also easy to thin when developing, thus shortening the service life of the printing plate. 3, the temperature inside the exposure box This temperature can easily be ignored. The drying temperature is often better, and the temperature of the exposure box will eventually make the plate-making failure. The temperature in the exposure chamber depends on the type of light source. If it is a cold light source, it is generally not considered; if the source of heat is relatively intense, such as a high-pressure mercury lamp, special attention should be paid. Because the high-pressure mercury lamp cannot ignite instantaneously, several plates of continuous exposure methods are usually used. In this way, the temperature of the surface of the plate at the time of exposure can be as high as 85°C or higher. This temperature is extremely unfavorable for the three layouts of F, D, and N. It will cause similar problems such as development difficulties due to excessively high temperatures in the oven, and will seriously affect the quality of the printing plate. Therefore, exhaust equipment must be installed in the exposure box to reduce the plate surface temperature. In general, the surface temperature of the plate cannot exceed the drying temperature. ; 4, developer temperature development: is the final condition for the success of the printing plate. When the process is inadvertently performed due to the previous process, the method of increasing the temperature of the developer is often adopted in order to accelerate the development speed. The temperature of the developer should be controlled with caution, and the drying temperature should generally be the upper limit. If the temperature of the developer is too high, the following problems will easily occur: For the F and D plates, the plate will easily swell and the pattern will be serrated around; for the N plate, the edges of the pattern will become hairy and cause pattern distortion. .

Third, the time on the quality of the printing plate quality and the quality of the produced plate is also very much related to the time. The control of time is the same as the temperature, and the requirements are relatively strict, mainly including: 1, the drying time in the oven; 2, the exposure time; 3, the development time. l, in the oven time, this time should first depend on the degree of drying of the layout, and then consider the drying range. For D and N, since the squeegee is manually operated, the thickness of the squeegee is not completely controlled. In general, the glue layer is thicker and the drying time is also properly lengthened. Each time the glue is not too thick, it should be thin and uniform. Again, the squeegee should be done on the basis of the previous full drying, otherwise there will be inconsistent surface dryness. For the F version, it should also pay attention to the amount of sensitizer. Otherwise the layout is difficult to dry. If the F and D editions are not fully dried, they will cause the film or adhesive layer to slip off during development. If the drying time is too long, it may easily cause difficulties in development or may not appear. For the N version, since it does not have a drying limit, it depends only on its degree of drying. Therefore, under the normal drying temperature control, it can be stored in the oven for a long time to ensure that its layout is fully dried. If it is not fully dried, the layout is easily thinned and blisters appear. 2, exposure time Exposure process is a photochemical reaction process. Regardless of the type of media, the exposure time, despite having a specified value, must be tested several times. In the plate making process to be able to be aware of the entire process, estimate the problems that will occur after the development, so as to finally determine the appropriate exposure time. To judge from the condition when developing: the exposure time is appropriate. Fast development, clear patterns, crisp lines, proved that the exposure time is appropriate; development is difficult or not to show that the exposure time is too long;; exposure time is not enough, for the F, D version, the reaction in the development of the film layer or layer The surface is loose or easy to fall off. For the N version, the layout is blank and the non-patterned parts are glued. 3, development time A successful printing plate, the most obvious expression is the relative development time is short. This means that the adhesive film has good adhesion and development. If the development time is long, it not only indicates that there are problems in the production process, but also affects the service life of the printing plate, and even results in failure of the production. Because the photochemical reaction is not sufficient during the exposure process, the developer dissolves the film of the non-light-transmitting portion and also affects the portion where the reaction is insufficient. Therefore, the long development time will affect the fastness of the printing plate. If the development time is too long, for the F and o plates, the following problems will occur: 1 The edges of the pattern will swell and the lines will be unclear. 2 The surface of the film or adhesive layer will be smooth and the adhesion to the screen will be reduced; The adhesive layer is easy to fall off. If the development time is too long, for the N version, the following problems will occur: 1 The layout will be thinned and the trachoma will appear; 2 The pattern will have a frizzy edge and the lines are not stiff. The process of making a printing plate is a complex physical and chemical process that involves many factors. In addition to the above-mentioned factors, there are also exposure luminosity, humidity in the process of making plate, and so on. Especially in the plate making process, many processes are manual operations, and many factors are directly controlled by people. Therefore, many factors cannot be measured accurately in the manufacturing process. For example, the thickness of the squeegee is difficult to measure during operation. Therefore, how much time can be dried can not be specifically determined; for example, how thick the film after squeegee is, how long the exposure time should be, and it is not proportional. Incremental, but after repeated trials. However, due to the Other preparation factors in the plate making process in the previous stage, the conclusions reached are only a reference.

In short, to make the screen printing process to be as complete and reasonable as possible, it is necessary to continuously summarize, explore, and find out some rules through long-term practice.