Three common plate materials

Screen making method

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 screen mesh number and the impact of stretch net on the quality of the printing plate

l, the choice of screen mesh number

The number of screen meshes to be selected depends on the printed pattern and the requirements on the pattern. 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, stretch net

When the screen is stretched over the frame, the degree of tightness should be appropriate, and it should be noted that the tension at each point in the frame should be the same. If silk

If the net is stretched too tight or too loose, or if the tension at each point is inconsistent, the following problems may arise:

The screen is stretched too tightly: to make the printing plate lose its elasticity, resulting in distortion of the pattern during printing;

The mesh is too loose or the tension is not the same:

1 fine lines cannot be developed;

2 The edges of the pattern appear zigzag, and the pattern distortion;

3 Leakage phenomenon during the printing process;

4 In terms of F plates, the adhesion between the film and the screen is poor, resulting in the phenomenon of film peeling during development;

For D and N versions, the layout is difficult to evenly flatten when squeegeeing. 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 temperature on the quality of the printing plate

The quality of the printing plate is related to the various temperatures during production. 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

The operating room temperature should generally be maintained at about 25 °C. 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 D version, if the room temperature control is not good in hot weather, the following problems will occur:

1 Preparation of glue can easily produce thermal cross-linking, resulting in difficult or obvious development;

2 A large amount of air bubbles are generated in the glue solution, causing bubbles or blisters on the plate.

For the N version, when the room temperature is lower than 2O°C, the following problems will occur:

1 Difficult to develop or difficult to develop due to uneven thickness

Trachea appeared on the 2nd surface, which caused the phenomenon of slurry leakage in the printing process;

3 uneven layout, resulting in inconsistent print pattern color.

2, the oven temperature

According to the drying temperature set by the respective performance index of the plate-making materials, the temperature 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:

1Development difficulties, resulting in ignorance;

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 is easily overlooked. 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

Developing: It is the last condition for the success or failure 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 developer temperature is too high, the following problems can easily occur:

For F and D plates, it is easy to make the plate swell, and a zigzag pattern appears around the pattern.

For the N version, it is easy to make the pattern edge frizzy, resulting in pattern distortion.