1. Polyester wire mesh (polyester) PET1000 (SL / S / T / HD)-Taking 120/305 mesh as an example, it is divided into three specifications: 120-31 (S ultra-thin type) PW120-34 ( T standard type) PW120-40PW (HD thick type)
characteristic:
--High tensile strength (tension)
--Good wear resistance, not sensitive to climate
--Good acid resistance (sulfuric acid, hydrochloric acid, nitric acid), good performance and can resist common solvents
2. Nylon wire mesh PA1000 (S / T)
Take 120/305 mesh as an example: it is divided into two specifications: 120-30 (S pole) 120-35 (T pole standard)
characteristic:
-Very good wear resistance (good wear resistance on rough or curved surfaces)
-Good surface tension and high resilience
--Good solvent resistance
-Better alkali resistance
Second, how to choose wire mesh
1. Wire mesh structure and mesh
The geometric structure of the wire mesh refers to all two-dimensional and three-dimensional appearances of the wire mesh. The basic elements of the geometric structure are the mesh number of the wire mesh and the diameter of the wire mesh.
For example: 120-34 means 120 meshes in each centimeter, and the nominal diameter of each mesh is 34um.
** The mesh number of the wire mesh refers to how many silk threads are in each centimeter,
** The diameter of the mesh refers to the nominal value of the diameter of the unwoven mesh.
** The geometric structure of the wire mesh is divided into: flat knot wire mesh (1: 1) oblique knot wire mesh (2: 1, 2: 2, or 3: 3)
The mesh sizes of different weaving methods are inconsistent, which determines the amount of ink penetration of the screen (the amount of ink penetration is an important factor in determining the printing effect)
2. The decision of opening the wire mesh: (W)
** Maximum size of particles in screen printing ink (the average particle size of ink in printing must be less than 1/3 of mesh).
** The fineness of the printing level of lines and dots (too large openings leak too much ink, and fine lines cannot be obtained)
** Ink peeling performance (e.g. large particles of ink lead to blockage of the mesh and affect the penetration of ink in the next printing)
** The thickness of the printing ink layer (the opening is too small and the amount of ink penetrating is also small, so a thick ink layer cannot be obtained)
In general, a mesh with a mesh opening larger than the mesh diameter can reproduce a higher resolution than a mesh with mesh openings smaller than the mesh diameter. (Of course, the fluidity, viscosity and other factors of ink will also affect) [next]
3. Stretch the net correctly
1. Standard stretching steps:
The wire mesh can be stretched to the desired tension value within 1-3 minutes, but before the wire mesh is fixed to the frame, it must wait for more than 15 minutes before increasing the tension to the final desired tension value. Repeating it several times will reduce the tension loss in the future.
*** If the sticky net stays for 5 minutes after the net is stretched, the tension loss is more than 28%.
*** If the sticky net stays for 15 minutes after the net is stretched, the tension loss is 15% -20%.
*** If the sticky net stays for 30 minutes after the net is stretched, the tension will lose 10%.
The above tension loss refers to the tension loss when sticking the net and just after being pulled, not the tension loss value after 24 hours after sticking the net. Generally, the minimum of screen printing for overprinting is to reprint the screen after 24 hours, otherwise there will be inaccurate overprinting or line distortion.
After stretching the screen, the printed screen should be fixed to the screen frame, and the tensile force it bears is determined by the tensile resistance of the screen (that is, it can withstand the maximum tension). The tension of the screen is an important factor to ensure accurate overprinting and determine the appropriate screen pitch.
Generally speaking, the higher the mesh, the finer the mesh. The thicker mesh is pulled tighter than the fine mesh.
Correctly stretch the net according to the stretch net procedure. The standard screen tension loss is 15 * 20%, and the PET1000 screen tension loss is 10-12.5%.
2. If the loss of tension is serious, you should understand whether the following causes:
*** The aluminum material used in the mesh frame is very weak and cannot withstand large tensions, resulting in repeated tensions
*** The method of inserting the wire mesh into the head is improper, and the tensile forces on the four sides are inconsistent.
*** The tension of the edge mesh clamp is uneven, and the mesh frame is unevenly placed.
*** Insufficient waiting time before sticking to the net.
3. Problems that may occur when tension is unstable:
*** The positioning register cannot be controlled. (In case of misalignment, the line or chart is stretched or shrunk)
*** The ink layer on the printed matter has a net pattern, and the thickness of the ink layer is inconsistent
*** Increase the mechanical abrasion of the screen by the rubber scraper, shorten the service life of the screen
4. Correctly select the angle of the screen
*** When the lines on the negative film are parallel or overlapping with the wire diameter of the screen, when the light passes through the photosensitive coating during printing, the light will be scattered and the light will be scattered (refraction of light), which will cause aliasing. Therefore, it is necessary to choose the screen angle of the screen.
*** The angle of the screen is generally 45 °, 22.5 °, 12.5 °, 7.5 °, etc. We can choose the required angle according to the thickness of the line. It is difficult to have a standard for the angle of the screen. 45 ° or 22.5 ° is not the best angle.
The general approach is:
Prepare a few screens with different meshes that have been drawn at a right angle of 90 °. Before pulling the screen, compare the negative and the screen against the light source to select the best screen angle.
*** If the photosensitive paste is too thin during printing, it will also cause jaggedness, and the screen angle is only one of the factors.
5. Stick the net correctly
*** Before applying viscose, the printed screen frame must be thoroughly cleaned and free of dust and grease.
*** The net yarn must be in close contact with the surface of the screen frame after sticking the net. If there is still a gap, it should be pressed with a heavy object, instead of using 502 glue as the medium for sticking the net. Because the 502 glue is too hard, the wire mesh loses its elasticity, resulting in an unbalanced tension.
*** After applying the glue, there must be sufficient time for the adhesive to cure, and then apply the edge filler on the four sides. Then, the removed frame must be pasted with a complete label. In order to identify in the next work. [next]
4. The correct printing method
1. The maximum printed pattern should be 70% of the inner diameter of the screen, otherwise overprinting difficulties and image distortion on the four sides will occur. (In the general case of tension balance, except for Wushu fabric printing.)
2. The correct sizing method:
*** The sizing should be as slow as possible. The edge of the sizing device should be as blunt as possible. The angle of the blunt edge is 90 ° at right angles to the screen. The flatness of the screen from this angle is the best and not too thin.
*** The purpose of slow sizing is to allow the photosensitive agent to fully fill the holes of the screen. Too fast sizing will squeeze air into the mesh and cause trachoma.
*** For the precision screen printing, after the first paste is dried, the photosensitive paste must be scraped one or three times at a sharp angle on the patch surface to ensure the smoothness of the screen.
*** Generally, the photosensitive emulsion layer on the printing surface of the screen is thicker than the ink layer to serve as the medium layer of the ink.
*** The cleaned screen must be sealed to avoid dust.
*** The screen with the photosensitive paste must be exposed as soon as possible. If it is temporarily unavailable, it must be covered and sealed with black adhesive paper to prevent it from being contaminated by dust and re-moisture or pre-exposure.
3. Choose the appropriate exposure time:
*** Unexposed screens will never harden. During the development process, the photosensitive emulsion on the scraped surface will be washed away.
The roughness and blur of the emulsion layer is the exact sign of underexposure. Insufficient rinsing, some of the dissolved emulsion sticks to the through-hole area of ​​the screen, after drying, leaving only visible debris, unevenness appears to hinder the fluidity of the ink and saw teeth appear.
*** Unexposed screens are poorly resistant to solvents, printing inks, and abrasion. Moreover, the screen which is not fully exposed to the photosensitive paste is difficult to remove.
*** How to calculate the correct printing time
Take an idle screen, after applying the photosensitive paste, perform exposure test in stages to get the best printing time.
1. Record the usage time of the light source so that the light source can be replaced at an accurate time.
2. Regularly clean rubber skin, glass, lampshade and reflector.
3. Regularly clean the net room, repair the net-drawing machine, printing machine and other equipment.
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