How to choose the screen properly (below)

How to choose the screen properly (below)

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In the second step, the minimum dot diameter D that can be printed by different meshes is calculated.

First, the relationship between the minimum dot diameter D and the mesh diameter d and the number M of meshes will be discussed.

Since the screen printing mesh is disturbed by the wire diameter, the small mesh point is easily blocked by the wire and is lost, and the degree of loss is related to the position of the mesh at the wire mesh.

As shown in Figure 2 on the following page, the mesh has a diameter d and a pore size of m. The circle with the diameter Dmin shown includes the four, 2, 3, and 4 mesh nodes of the wire mesh, and Dmin is the minimum dot diameter to obtain a relatively complete footprint.

Table 3 Data calculated using equation (2)

Screen line number

Line / cm   wire / inch        5% tone dot diameter (μm)   10% tone dot diameter (μm)      20% tone dot diameter (μm)

     30            76                          84                                      119                                       168

     34            86                          74                                      105                                       148

     40            63                          63                                        89                                       126

     48            53                          53                                        74                                       105

     54            47                          47                                        66                                         93

     60            42                          42                                        59                                         84

Available from the illustration:

Due to the mesh number, mesh diameter, and aperture, the following relationships exist:

m=1/M—d

Substituting into (3) can be obtained:

Table 4 data can be calculated according to equation (4) for comparison selection.

When selecting the appropriate mesh size, consider Tables 3 and 4 to make a choice.

2.3 selection of screen grade

The number of stages of the screen refers to the fineness of the wire mesh. For the mesh with the same mesh number, according to the thickness of the mesh, it is divided into the following four different levels: S fine, M fine, T medium coarse, HD coarse, ie S, M, T, HD Four levels. The diameter of the mesh is usually expressed in microns. After selecting a mesh of a certain number of meshes, the following factors should be considered when selecting the number of stages:

a. The smaller the diameter of the mesh, the larger the relative opening area, the more suitable for subtle copying;

b. The smaller the diameter of the mesh, the worse the corrosion resistance of the corrosive cleaning agent, and the worse the wear resistance of the ink and the doctor blade;

c. The larger the diameter of the mesh, the higher the printing durability of the screen.

In general, in addition to considering the above factors, the choice of screen should also consider its plate making method, ink type, film plate life, production cost requirements and so on. After comprehensive consideration, the correct choice can be made to achieve the best printing results and economic benefits.

Table 4 List of minimum dot diameter calculations

M (mesh / inch)      Aperture m (μm)      Mesh diameter d (μm)     Minimum dot diameter Dmin (μm)

        305S                         40                                  32                                              163

        305T                         45                                  37                                              170

        330T                         40                                  37                                              161

        355S                         38                                  32                                              146

        355T                         33                                  37                                              153

        380S                         34                                  32                                              140

        380T                         30                                  37                                              147