Discussion on sand mesh quality of PS plate base o

Discussion on the quality of the base grit of the prefabricated photosensitive plate (PS version) - a brief discussion on the experience of learning the national standard GB 3505-83 "surface roughness, terminology, surface and its parameters"

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discussion on the quality of the base grit of the prefabricated photosensitive plate (PS version) - a brief discussion on learning the national standard GB 3505-83 "surface roughness, terminology, surface and its parameters" Author's note: I have made a preliminary analysis on the quality of the sand mesh of the base of the prefabricated photosensitive plate in the fourth issue of printing technology in 2000. About this article, I would like to borrow the "printer" magazine to make a simple explanation: first, the article recognizes the "centerline part" as "the horizontal intercept is 5%". When the horizontal intercept is 50%, it is 50% of the maximum height ry of the contour. Different centerlines coincide, which are two different concepts. Second, the calculation of SM in "(3) analysis of peak valley average spacing of sand mesh [table (2)] in this paper is based on the calculation formula SM = L/D that the density (d) of contour peak valley is within the" sampling length "specified in article 3.9 of the national standard GB 3505-83. In fact, the data quoted in this article is measured by the Japanese "Oriental Precision Co., Ltd. e-30a" roughness instrument. The peak valley density number (i.e. peak number PC) given by the roughness instrument is the peak valley density number intercepted in the "measurement length", and the measurement length = sampling length × 5 times. In this way, the SM data given in [table (2)] should be expanded by 5 times. According to this, the data in [table (3)] should also be expanded by 5 times. Please refer to page 52 of the fourth issue of printing technology, 2000. This is the author's mistake of not being proficient in reading. The statement is hereby corrected

to evaluate the quality of PS version, it is easier to intuitively judge that Binjiang economic development zone is Changzhou new chemical materials export base, and its appearance quality, that is, dirty white spots, scratches, folds and other problems. However, as a printer, we should also try our best to understand and master the internal quality of PS plate, that is, the quality of photosensitive film and oxide film of PS plate, as well as the micro quality of sand mesh structure and other comprehensive indicators. Among the indicators of the overall quality of PS plate, there is no doubt that its appearance quality, the quality of photosensitive adhesive and oxide film are extremely important. They are directly related to the photochemical reaction of PS plate in the actual printing application, as well as the ink transfer state and wear-resistant and durable state of the plate during printing. However, from the perspective of the structural composition of the PS version, the oxide film and photoresist are successively attached to the plate base sand mesh. The author believes that in addition to supporting the oxide film and photosensitive adhesive layer, the sand pits on the surface of the plate base should also meet the requirements of "ink water balance" in offset printing without special treatment on the surface of the plate base. In terms of the function of "water and water retention" on the surface of the plate base, the internal quality of the grit structure cannot be lower than that of the oxide film and photosensitive adhesive. Next, we discuss the effect of sand mesh on the surface of PS plate base on printing

we know that offset printing is based on the principle that the water (fountain solution) in the blank area of the printing plate is insoluble with the ink in the graphic area, and achieves a balance to realize the transfer of graphic information. That is to say, the blank area of the layout is hydrophilic and water retaining through rough sand holes, so that the blank area of the layout is not polluted by ink. The graphic area of the layout is firmly attached to the sand pit of the plate base through physical force (van der Waals force), and the photosensitive adhesive layer (point) on the surface of the oxide film is used to affinity a certain amount of ink, so as to realize the purpose of graphic information transfer. To be exact, rough surface sand pits mainly have the following four functions:

1. Reduce the surface tension of the fluid (photosensitive glue and fountain solution) on the surface of the plate base, and increase the wettability of the fluid on the surface of the plate base. That is to say, it can improve the leveling performance of photoresist coating and the hydrophilicity of white area in printing

2. Expand the specific surface area of the layout, greatly improve the adhesion between the photosensitive adhesive layer and the fountain solution and the plate base, and achieve the purpose of not easy to drop and dirty

3. with its high durability and easy protection, it has a certain volume of sand pits, which can store a certain amount of fountain solution, so that the fountain solution in the blank area of the layout will not dry during the high-speed operation or short-term shutdown of the printing machine, so that the layout will not be polluted by ink and external oil pollution. (of course, when the machine is shut down for a long time, you should smear the plate protection liquid on the plate)

4. Because the cured photosensitive adhesive layer is mainly composed of organic substances (2.1.5 photosensitive agent, phenolic resin, etc.), its friction resistance is far lower than that of the alumina layer made on the surface of amoufenggu. Therefore, the layout has a certain depth of sand mesh large and medium wave pits, which can also reduce the wear of the photosensitive adhesive layer by the rubber roller of the printing machine

it can be seen from the function of the above plate base surface sand mesh on printing that the quality of the PS plate base surface sand mesh for offset printing is the basis of the overall quality of the PS plate. If the base hammer return is abnormal, the structure quality of the sand mesh is poor, and the quality of the oxide film and photosensitive adhesive is difficult to reflect, even there will be problems such as insufficient water content in the sand mesh in the blank area and dirty, and the photosensitive adhesive layer in the image and text area will be worn off

in the actual production and manufacturing (roughening) of the sand on the base surface of the PS version, we can't make the test range and uniform micro peak and valley structure that touch the body, chassis, frame, car interior, seat belt, window glass, etc. as the machined parts, but can only process the disordered and uneven three-dimensional space structure. In article 1.30 of the national standard GB 3503-83, the definition of surface roughness is "refers to the micro geometric characteristics composed of small spacing and peaks and valleys on the machined surface"

it has three conceptual parameters:

1. Surface roughness parameters related to the height characteristics of micro roughness: such as contour arithmetic mean deviation RA; Micro unevenness ten point height RZ; The maximum height of the contour ry (the Japanese standard adopts the maximum height Rmax), etc

2. Surface roughness parameters related to the spacing characteristics of micro unevenness: such as average spacing SM; Density D of contour peak (the peak height and valley depth adopted by Japanese standard exceed 0.635 respectively μ Peak number of M (PC), etc

3. Surface roughness parameters related to the shape characteristics of micro unevenness: such as the profile skewness sk for evaluating the wear-resistant strength characteristics of the surface (the average peak height above the center line rpm is adopted by the Japanese e-30a roughness instrument); Contour horizontal intercept (c) for evaluating peak valley shape characteristics μ M or C/ry) - contour support length ratio plus TP% curve

for the application of the above surface roughness parameters in the PS edition industry, there are many contents and limited space, This paper would like to focus on the following three issues:

1. About RA contour arithmetic mean deviation:

in article 2.9 of the national standard GB, RA is defined as "arithmetic mean deviation of the absolute value of contour offset within the sampling length L" (see Figure <1). Its numerical expression is: RA =

from higher mathematics, we know that (x) |dx is expressed within the sampling length (o-l), The micro integrated area between the crest and trough divided by the center line (x-axis) of the contour curve and the center line. Look at this area as a rectangle whose long side is the sampling length L, then the "height" of this rectangular area is defined as RA, Rd × L＝∫LO|y（X）|dx。 Therefore, RA is different from the equivalence of ry, RZ and RP. although it is also a concept of roughness depth, it is an abstract and purely computational concept of mathematical arithmetic mean deviation. Ra value represents the magnitude of the arithmetic mean deviation between peak and valley, and its value can only be measured and calculated by the integration program of the precision roughness instrument. It does not have intuitive measurement significance

as we all know, the concept of surface roughness was introduced by our industry pioneers from the machinery industry to the PS version industry. Without their efforts, we could not have such a deep understanding of the PS version today. However, from the perspective of the impact of surface roughness on the function of parts in the machinery industry, in addition to "for the power seal surface with relative sliding, due to relative motion, its micro unevenness is generally 4 ~ 5 μ m. It is more beneficial to store lubricating oil ", no matter 1) the influence on the matching property; Or the effect of 2> on wear resistance; 3> resist the influence of fatigue strength; 4) influence on contact stiffness: 5> influence on impact strength; 6 ＞ resist the influence of corrosion; 7> for static sealing surfaces without relative sliding, it is required that "the lower the Ra value, the better". (please refer to Volume I of mechanical design manual, 3rd Edition, January, 1993) that is to say, the function of mechanical parts requires that the smaller the arithmetic mean deviation Ra of peak valley and pit on the surface of machined parts, the better the surface is smooth. Therefore, as a mechanical industry, "within the commonly used parameter value range of height characteristic parameters (RA is 0.025 ~ 6.3 μ m. RZ is 0.1-25 μ m) It is recommended to choose "RAA" preferentially, and "average spacing of contour micro unevenness (SM)" and "contour support length ratio (TP)" are selected as "additional evaluation parameters". (see article 4.3 and 4.6 of GB 1031-1995 for details). However, as a PS version, the surface function of the plate base is quite different from that of machined parts. The purpose of surface roughness of PS plate base not only needs to produce a sand mesh surface with a certain roughness Ra value to support the oxide film and photosensitive adhesive layer, but also needs to meet the functional requirements of four aspects of micro peaks, valleys and pits of sand mesh on the surface of PS plate base mentioned above. That is to say, it is required to have a certain micro three-dimensional spatial structure for the produced sand mesh peak valley pits