The state of the sand mesh on the PS plate base refers to the sand mesh feature formed by the surface roughening of the aluminum plate base. The sand mesh structure of the PS version determines many properties of the printing plate, especially has a very important influence on the printing plate's durability. In order to explore the relationship between the PS version of the sand mesh state and the printing plate durability, we designed the PS version of the sand mesh wear test, this in-depth study.
Design of PS version of sand mesh wear experiment
1. Experimental content (1) Use a surface roughness measuring instrument to measure the roughness value of the surface sand of some domestic brands of PS version, and analyze its characteristics.
(2) Measure the roughness value of the PS plate sand mesh before and after printing with a surface roughness measuring instrument, and analyze the change of the sand mesh roughness before and after printing.
(3) Use the surface roughness measuring instrument to print the contour curves of the PS version of sand mesh before and after printing, and analyze the changes of the sand mesh contour curve.
(4) Take photos of the structure of the PS mesh before and after printing by electron microscope experiment, and analyze the wear of the microstructure.
2. Experimental instrument (1) Surface roughness measuring instrument ①Instrument accuracy: ≤10%.
②Measurement method: measure at different positions of the PS version before and after printing, each position is measured at three angles of 45 °, 90 ° and 135 °, and take the arithmetic average as the final roughness value.
(2) AMRAY-1000B scanning electron microscope â‘ Magnification: 20,000 times.
â‘¡ Resolution: 6nm.
(3) PlateDot X-RiteDot (ccDot) measuring instrument
Experimental process and result analysis
1. Measure the roughness and the same version difference of some brands of PS version sand
See Table 1 for the comparison of the roughness of some domestic brands of PS version and the difference between the same version. It can be seen from Table 1 that the roughness of the sand mesh of the PS plates of various brands is very different. The large-scale PS plate production plants have good control of the same plate difference, mainly because their production lines are reel production lines, and the relative stability is better.
2. Measure the roughness of the PS plate sand before and after printing
By measuring the roughness of the sand before and after printing a certain PS plate, the wear rate of the sand is calculated. The contour curves of the PS plate before and after printing measured by a three-parameter surface roughness measuring instrument are shown in Figure 1. Combining the data and the contour curve of the sand mesh, and analyzing the changes of the contour curve of the sand mesh before and after printing, the following conclusions can be obtained.
(1) Before printing, the PS version of the sand mesh contour curve has a large fluctuation range, the fine sand mesh surface contour curve of the sand mesh surface is clear, and the peaks and troughs are more obvious.
(2) After printing, the contour curve of the sand version of the PS plate is relatively smooth, the abrasion at the crest is more serious, the fine sand on the upper layer is subject to greater abrasion, and the number of crests is also reduced compared to before printing.
3. Electron microscopy experiment to analyze the state of PS screen before and after printing
Scanning electron microscope was used to take a picture of the PS version before and after printing.
The two electron micrographs were compared and analyzed, and the conclusions are as follows.
(1) The structure of the sand mesh on the PS plate before printing is obviously honeycomb-shaped, the structure of the coarse and fine sand meshes overlap each other, the height is staggered, and the edges and corners of the wave peak are distinct. The bottom of the sand mesh is also compounded with fine micropores, which greatly increases the specific surface area.
(2) After printing, the overall structure of the PS version of the sand mesh has been greatly abraded. The peaks of the sand mesh have been lowered, and even some fine sand meshes at the peak have been smoothed, and the entire sand mesh surface has become relatively smooth.
The structure of sand mesh before printing generally has coarse sand mesh, medium sand mesh and fine sand mesh. Coarse sand mesh has good water retention, which can make the printing plate not easy to get dirty during printing. Medium sand mesh can not only improve the development performance of the printing plate during the printing process, but also ensure the abrasion resistance of the printing plate during printing and improve the printing durability of the printing plate. On the basis of not changing the surface roughness parameters of the plate grit, the fine grit greatly improves the hydrophilicity and water retention of the plate, and can maintain a large ink even when the amount of plate wetting liquid is small The quantity guarantees the balance state of water and ink during printing, so that the printing plate has good printing suitability.
By analyzing and comparing the roughness of the sand mesh before and after printing, the change of the contour curve of the sand mesh and the photos of the sand mesh before and after printing, the following conclusion can be drawn: after printing, the sand mesh is worn and the entire sand mesh structure is damaged to a certain extent. The crest of the coarse sand mesh is heavily worn, the upper surface of the sand mesh becomes smoother, the fine sand mesh is seriously worn, and the middle sand mesh is worn away. The hydrophilic and water retention properties of the sand mesh are reduced, which affects the printing suitability of the printing plate In printing, it is easy to produce printing faults such as paste and dirty.
4. The changes of the dots on the printing plate before and after printing
Use the PlateDot type X-RiteDot (ccDot) measuring instrument to measure the state of the dots on the PS plate before and after printing (taking 20% ​​dots as an example), as shown in Figure 3. Use a scanning electron microscope to photograph the photosensitive layer on the PS plate before and after printing to obtain the image shown in FIG. 4.
As can be seen from Figure 3 and Figure 4, the dot shape of the photosensitive layer before printing is relatively complete, and the edges are relatively clear. The edges of the photosensitive layer are not tightly attached to the plate base, making the edges of the photosensitive layer vulnerable to wear and tear. After printing, the photosensitive layer on the PS plate is worn, and the wear mainly occurs at the edge of the dot, which makes the edge of the dot more fuzzy, and there is no obvious boundary line with the sand. This affects the ink-absorbing performance of the photosensitive layer, resulting in printed images. The density of the text has dropped. Therefore, the adhesion of the photosensitive layer at the edge of the dot to the substrate should be strengthened to reduce the wear of the edge of the photosensitive layer at the dot of the PS version. The sand mesh structure has a great influence on the adhesion of the photosensitive layer. It is best to form a composite sand mesh structure when roughening to form the sand mesh to enhance the adhesion of the photosensitive layer and the plate base and improve the printing plate's durability.
In addition, through the microstructure of the sand mesh photographed by the electron microscope, the PS version of the sand mesh structure of different brands is analyzed and compared, and the following conclusions can be obtained.
(1) The PS version of the sand mesh structure produced by different manufacturers varies greatly, the main reason is that the production line is different. "Huaguang", "Torchlight" and other plate materials are produced on a reel production line, which is more stable than single-sheet continuous line production.
(2) The sand mesh structure of Huaguang and other plate materials is a composite sand mesh structure, which can be better combined with the photosensitive layer, improve the PS printing plate's durability, and effectively improve the resolution of the printing plate. The fine structure of the sand mesh of some plate materials is not obvious, and the peak of the sand mesh structure is sharp. It is easy to be worn at the wave peak during printing, which reduces the contact area of ​​the photosensitive layer and the plate base, thereby causing the printing plate to have a reduced durability. Therefore, it is necessary to improve the manufacturing process, eliminate the platform structure of the sand mesh, and promote the process improvement of the fine structure of the sand mesh.
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