What are the factors that must be considered when choosing a screen?
Factors that must be considered when choosing a screen:
To achieve the purpose of printing mesh, the choice of screen is not determined by a single factor, and decisions must be considered together. Generally, the following four factors need to be considered.
1. The resolution of the image: the wire diameter is fine, and the number of meshes is high, the resolution is high. The wire diameter is coarse, and the number of meshes is low, and the resolution is low. However, it is not the higher the mesh, the better. If it is too high, the amount of ink generated by screen printing will be insufficient, resulting in defective or broken print. At the same time, under the same mesh number, pay attention to the influence of the wire diameter. The width of the finest line or the diameter of the dot which can be reproduced by the two kinds of screens is: L>2d+w, d is the wire diameter, and W is open. Hole width, when d>W, the opening area of the screen is small, which affects the fluidity of the ink, causing the thread or the dot to become jagged or missing, and the mesh is too high, which will cause the printing result to be the same. The same phenomenon as the net.
In general, a screen having a screen opening larger than the diameter of the wire can replicate a higher resolution than a screen having a mesh diameter smaller than the diameter of the wire. Therefore, the following points should be noted when selecting the network;
A. The larger the mesh/wire diameter value, the better; B. The smaller the contact area between the printed surface and the substrate, the better; C. In order to achieve the resolution requirement, the wire diameter and the opening width of the wire mesh must satisfy a certain relationship; In order to meet the printing requirements, the relationship between the wire diameter and the ultimate tension needs to be considered.
2, the thickness of the ink layer and the hiding rate are thicker, and the hiding rate is good. The thick net and the large net (ie HD level) should be selected.
3. The screen material should be selected according to the surface condition of the substrate: the surface of the curved surface or the undulating surface should be made of elastic nylon mesh, the surface with strong absorption should be selected with a large amount of mesh; the smooth surface should be high tension mesh. The rough surface is made of a low mesh screen; the insulating surface is made of a static electricity screen.
4, the performance requirements of the ink: according to the performance of the ink to select the appropriate ink screen.
Wire mesh weave structure: refers to the weaving method of wire mesh. In the weaving method, it is often divided into: plain weave (indicated by PW) and twill weave (indicated by TW). The plain weave is made up of alternating ones of radial and weft threads, and its structure is 1:1, twill weave. It is composed of alternating radial and latitude lines of 1:2 or 2:2 or 3:3.
The advantages of plain weave: the contact surface with the substrate is small, the ink permeability and the fluidity of the ink are good. The printing quality is high and the mesh is generally below 350 mesh/inch.
The twill weave is generally above 350 mesh/inch, the mesh aperture is small, the mesh is thick, the ink permeability is poor, and the contact surface with the substrate is large, which affects the fluidity of the ink, so the printing quality is not as good as the plain weave in the same mesh.
The color of the screen: very important for the production of high-quality, high-definition screens. Usually the color of the screen is: white is indicated by W and yellow is indicated by Y.
When the white screen is exposed, it will produce reflection and diffuse reflection, which will cause the resolution and clarity of the graphic to be reduced. In severe cases, the fine lines will not be fully developed. The choice of yellow screen, only yellow is reflected, has no effect on the photosensitive film layer, can produce clear images and fine-diameter layers, can produce high-definition reticulated film. Of course, the exposure time of the yellow screen is about 75% longer than the corresponding white screen.
The maximum tension of the screen: refers to the maximum tensile force that the screen can resist. Beyond this pulling force, the screen will break or plastically deform from elastic deformation, losing its elasticity. Therefore, when stretching the net, the tension must not exceed the maximum tension of the screen.
Preservation conditions for the screen: dry at room temperature, avoid direct ultraviolet rays or strong light, and lay flat on a smooth surface.