The effect of the PS version of the sand state on the printing durability of the printing plate
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The sand-eye state on the PS plate base refers to the sand-mesh feature formed by roughening the surface of the aluminum plate. The PS version of the sand structure determines many of the properties of the plate, especially for the printing durability of the plate. In order to investigate the relationship between the PS state and the printing durability of the printing plate, we designed the PS sanding abrasion test, which was studied in depth.
PS version sand eye wear experiment design
1. Experimental content
(1) Using the surface roughness measuring instrument to measure the roughness value of the surface sand of some domestic brand PS plates, and analyze its characteristics.
(2) The roughness value of the PS plate sand before and after printing was measured by a surface roughness measuring instrument, and the change of the roughness of the sand before and after printing was analyzed.
(3) Using the surface roughness measuring instrument to print the contour curve of the PS plate sand before and after printing, and analyze the change of the contour curve of the sand.
(4) The state of the sand structure of the PS plate before and after printing was photographed by electron microscopy, and the wear of the microstructure was analyzed.
2. Experimental equipment
(1) Surface roughness measuring instrument
1 Instrument accuracy: ≤ 10%.
2 Measurement method: The measurement is performed at different positions of the PS plate before and after printing, and each position is measured at three angles of 45°, 90° and 135°, and the arithmetic mean value is taken as the final roughness value.
(2) AMRAY-1000B scanning electron microscope
1 magnification: 20,000 times.
2 resolution: 6 nm.
3 PlateDot X-RiteDot (ccDot) measuring instrument
Experimental process and results analysis
1. Measure the roughness and the same plate difference of some brands of PS sand
See Table 1 for comparison of the sand roughness and the same plate difference of some domestic brand PS plates. It can be seen from Table 1 that the roughness of the sand mesh of each brand PS version is very different. The same version of the large PS plate production plant has good control, mainly because its production line is a reel production line with relatively good stability.
2. Measuring the roughness of the PS plate sand before and after printing
The wear rate of the sand was calculated by measuring the roughness of the sand before and after printing of a certain PS plate, as shown in Table 2. The sand contour curve of the PS plate before and after printing measured by a three-parameter surface roughness meter is shown in Fig. 1. Combining the data and the contour curve of the sand, and analyzing the change of the contour curve of the sand before and after printing, the following conclusions can be obtained.
(1) Before the printing, the wave profile curve of the PS plate has a large fluctuation range, and the contour curve of the fine sand surface of the sand surface is clear, and the peaks and troughs are more obvious.
(2) After printing, the PS profile has a smoother contour profile, and the wear at the peak is more serious. The upper sandstone is subject to greater wear and the number of peaks is reduced relative to that before printing.
3. Electron microscopy experiments to analyze the state of the PS version before and after printing
The image shown in Fig. 2 was obtained by taking a picture of the sand state of the PS plate before and after printing with a scanning electron microscope.
A comparative analysis of the two electron micrographs in Fig. 2 is carried out, and the conclusions are as follows.
(1) The sand-eye structure on the PS plate before printing shows obvious honeycomb shape, and the thick and fine sand-eye structures overlap each other, high and low, and the peaks and corners are distinct. The bottom of the sand is also compounded with fine pores, which greatly increases the specific surface area.
(2) After printing, the overall structure of the PS plate sand has been greatly worn, the peak of the sand has been ground down, and even some fine sands at the peak have been smoothed, and the entire surface of the sand has become relatively smooth.
The sand-eye structure before printing generally has both coarse sand and medium sand and fine sand. The coarse sand has a good water retention property, which makes the printing plate not easy to get dirty in printing. The medium sand mesh can not only improve the developing performance of the printing plate during the printing process, but also ensure the wear 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 printing plate, the fine sand mesh greatly improves the hydrophilicity and water retention performance of the printing plate, and can maintain a large ink even when the amount of the printing plate is small. The amount ensures the balance of ink and water during printing, so that the printing plate has good printability.
By analyzing and comparing the roughness of the sand before and after printing, the change of the contour curve of the sand, and the photos of the sand before and after printing, it can be concluded that after the printing, the sand is subject to wear and the entire sand structure is damaged. The wear of the coarse sand peak is heavier, the upper surface of the sand becomes smoother, the fine sand is seriously worn, and the middle sand wears a part. The hydrophilicity and water retention performance of the sand are reduced, which affects the printing suitability of the printing plate. When printing, it is easy to produce printing problems such as paste and dirt.
4. Changes in the dots on the plate before and after printing
The PlateDot X-RiteDot (ccDot) meter was used to measure the dot on the PS plate before and after printing (take 20% of the dots as an example), as shown in Figure 3. The photosensitive layer on the PS plate before and after printing was photographed by a scanning electron microscope to obtain an image as shown in FIG.
It can be seen from Fig. 3 and Fig. 4 that the dot shape of the photosensitive layer before printing is relatively complete, and the edge is relatively clear. The edges of the photosensitive layer are not closely attached to the substrate, so that the edges of the photosensitive layer are easily subject to abrasion. After printing, the photosensitive layer on the PS plate wears, and the wear mainly occurs at the edge portion of the dot, so that the edge of the dot is relatively blurred, and there is no obvious boundary line with the sand, which affects the ink affinity of the photosensitive layer, resulting in a printed image. The density of the text drops. Therefore, the adhesion between the photosensitive layer at the edge of the dot and the substrate should be strengthened to reduce the wear of the edge of the photosensitive layer of the PS plate. The sand-eye structure has a great influence on the adhesion of the photosensitive layer. It is better to form a composite sand-eye structure when roughening the sand mesh to enhance the adhesion of the photosensitive layer to the plate base and improve the printing durability of the printing plate.
In addition, through the microscopic structure of the sand mesh taken by electron microscopy, the analysis and comparison of the PS mesh sandpaper structures of different brands can be concluded as follows.
(1) The variation of the sand structure of the PS plate produced by different manufacturers is very large, mainly due to the different production lines. The plates of “Huaguang” and “Zhuguang” are produced by the reel production line, which is more stable than the continuous production of single sheets.
(2) The sand-eye structure of Huaguang and other plates belongs to the composite sand-eye structure, which can be combined with the photosensitive layer better, improve the printing durability of the PS plate, and effectively improve the resolution of the plate. Some of the fine mesh structures of the plate are not so obvious, and the peaks of the sand structure are sharp, and the peaks are easily worn at the time of printing, resulting in a decrease in the contact area between the photosensitive layer and the plate base, thereby causing a decrease in the printing durability of the printing plate. Therefore, it is necessary to improve the manufacturing process, eliminate the platform structure of the sand, and promote the process improvement of the fine structure of the sand.