Lithography uses the rule of incompatibility of oil and Water for ink transfer. The task of the water delivery device is to provide a uniform layer of water film on the blank part of the printing plate. The task of the inking device is to apply a uniform thickness of ink film to the image and text of the printing plate. The better the task is, the better the quality of the printed matter, because in the imprinting area, the transfer of ink depends on the The amount of ink, ideally, all the printed graphics and text on the printing plate are coated with a uniform thickness of ink film, and the ink film is transferred to the substrate. However, because the wetting fluid and the ink are present on the printing plate at the same time, although the ink and water are not miscible with each other, under the high-speed shear of the ink roller, the water roller and the rubber cylinder, the oil phase and the water phase are mutually The ink is emulsified. 1. The transfer process of ink and water The ink conveying device of the lithographic printing machine is composed of an ink fountain, an ink half roller, a tandem roller and an inking roller; the water conveying device is composed of a water fountain and an inking roller. When the offset press is printing together, there are four nip states of A, B, C and D in the blank part and graphic part of the water roller, ink roller and plate, as shown in Figure 5-2. Ink and water (Wetting fluid) is forcibly mixed between each nip and then separated. Figure 5-2 Transfer of ink and water in an offset press The first type of nip is the gap between the water roller and the blank part of the printing plate. As shown in Figure 5-3 (a), there is a wetting fluid between the nip. After the water roller is separated from the printing plate, the surface of the blank part is wetted by the wetting liquid, leaving a thin layer of water film. If you use coated paper for printing and use ordinary acidic wetting fluid, the experiment shows that when a 3μm ink film is required on the printing plate, the water film is 1μm thick enough to prevent the ink from spreading on the blank part of the plate. The second type of nip is the gap between the water roller and the graphic part of the printing plate. As shown in Figure 5-3 (b), there are both wetting fluid and ink between the nip, and the two phases coexist. Under the strong squeeze of the water roller and the printing plate, a small amount of wetting liquid is squeezed into the ink, causing the first emulsification of the ink. The greater the water supply, the more wetting fluid squeezed into the ink, the more serious the emulsification of the ink. The third type of nip is the gap between the inking roller and the blank portion of the wetted printing plate, as shown in Figure 5-3 (c). Between the nip, the wetting fluid and ink coexist. Under the strong squeeze of the inking roller and the printing plate, a small amount of dampening liquid was squeezed into the ink. Causes the second emulsification of the ink. The fourth type of nip is the gap between the inking roller and the graphic part of the printing plate. As shown in Figure 5-3 (d), there is emulsified ink between the nip and the ink film attached to the graphic part of the printing plate. Wetting fluid beads. When the inking roller rolls over the graphic part of the printing plate, the beads of Lanxian liquid are squeezed into the ink, causing the third emulsification of the ink. After the inking roller is separated from the printing plate, the graphic part of the printing plate has a considerable amount Emulsified ink for wetting fluid. Figure 5-3 The nip between the water roller, ink roller and printing plate The above analysis shows that during the first water supply and ink supply of lithographic printing, the wetting liquid and the ink must be mixed three times. It is obviously impossible to maintain the strict boundary between the water phase and the oil phase, that is, the emulsification of the ink in the lithographic printing The process is inevitable. [next] Figure 5-4 is the water mixing curve of three different inks. The ordinate is the amount of water mixed in 100g of ink after mixing the wetting fluid and the ink. The abscissa is the time for mixing the water and ink. Curve A represents the ink mixed with water. Due to the excessive water content in the ink, the ink head is too short, and the ink is difficult to output from the ink fountain of the printing machine, so it is not suitable for lithographic printing; curve C represents the ink that is the most difficult to mix with water , The ink is almost repulsive to water, the wetting liquid microbeads squeezed into the ink during printing will quickly separate out from the ink, attach to the ink surface and form a layer of water film, which hinders the ink Blanket transfer. Experience has shown that this ink transfer performance is extremely poor, and it may make the printed matter bloom, and can not be used for lithographic printing. Curve B represents an ink that is moderately difficult to mix with water and is most suitable for lithographic printing. This ink can disperse the microbeads of the wetting fluid in the ink and emulsify the ink, which provides a way to exclude the wetting fluid attached to the ink, and the ink transfer performance is good. It can be seen that the emulsification of lithographic ink in the printing process is inevitable, and it is also required for ink transfer. The absolutely non-emulsified ink is not suitable for lithographic printing. Figure 5-4 Curve of ink and water mixing Second, Martin Sevier's flat printing mode Analyzing the transmission and emulsification of ink and wetting fluid on the lithographic printing machine, it is not difficult to see that although the ink transfer of lithographic printing involves water, the key is still the inking process of the graphic part of the printing plate. In order to ensure the smooth transfer of ink, Martin Silver (Mattin Silver) proposed the following flat printing mode: (1) Various solid materials used for rollers and printing plates must have certain free energy of expression, and they must be preferentially wetted by wetting fluid or ink. The blank of the printing plate must be composed of the material that is preferentially wetted by the wetting fluid in the presence of ink; the graphic part of the printing plate must be a material that is preferentially wetted by the ink in the presence of the wetting fluid Pose. (2) The ink and wetting fluid must be incompatible with each other and can be mixed. To a certain extent, a limited mixture or controlled emulsion is formed. That is to say, the wetting liquid is dispersed in the ink with fine water droplets to emulsify the ink, which provides a way to exclude the wetting liquid of the graphic part. (3) In order to form the necessary printing density on the paper, the thickness of the ink printed on the paper is about 1 μm. (4) Ink and dampening fluid are transferred to the printing plate through a series of rollers. The surface of the roller exhibits different wettability to the wetting fluid and ink. Table 5-1 lists the state of the film layer between the nip. There are 16 different states of membrane bonding. Because they are all arranged symmetrically, there are actually only 5 combinations. When there is only one fluid (wetting fluid or ink) between the nip, the fluid film layer splits at the nip outlet, and the thickness of the film layer on each roller is half the total thickness of the nip layer at the nip inlet. Table 5-1 The two roll gaps are the film conditions at the exit When there are ink and wetting fluid between the nip, the conditions of the film layer are listed in Table 5-1. If the No. 1 roller in Table 5-1 is used as the inking roller, it will be preferentially wetted by the wetting fluid, the attached wetting fluid is d, and the ink c is on the roller; if the No. 1 roller is used as the inking roller, Will be preferentially wetted by ink, the attached ink is a, and the moisture on the roller is b. If the No. 2 roller in Table 5-1 is used as the blank part of the printing plate, it will be preferentially wetted by the dampening liquid, the attached dampening liquid is d, and the ink is c; In the graphic part of the text, it will be preferentially wetted by the ink, the attached ink a, with the wetting liquid b. The film layers at the outlets of the four roll gaps shown in Figure 5-3 are dd, db, da, respectively, and the film layer conditions are consistent with the film guide layer conditions listed in Table 5-1. Lithographic printing ink transfer is performed in two steps. First transfer from the printing plate to the blanket, the transfer rate is about 50%, and then transfer from the blanket to the paper surface, the transfer rate is about 76%, the total ink transfer is 38%, this relief printing and gravure printing ink The transfer rate is low. Therefore, the lithographic ink color is lighter than other printed ink colors. According to Martin Sevier's down-printing mode, the ink must be properly transferred between the ink roller and the printing plate. It must be mixed with an appropriate amount of dampening fluid, which must cause a drop in ink color. Therefore, strictly controlling the water supply of the printing plate and maintaining the balance of water and ink are the keys to improving the quality of lithographic printing. Jia Teng Glass Jar is designed for home and kitchen storage. Its body is made of borosilicate glass and matched with bamboo lid. 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No. 1 ink layer No. 2 ink layer ab is the same as ba ac is the same as ca ad and da is opposite a. Ink No. 1 roller is preferably wetted by ink b? Wetting fluid ba
No. 1 contains emulsified wetting fluid film layer No. 2 contains emulsified wetting fluid film layer bb is the same as aa bc and cb is opposite bd is the same as bb b. The wetting fluid No. 2 roller is preferentially wetted by the ink c. The ink ca is the same as aa cb cc is the same as aa cd and dc c. Ink No. 1 is preferentially wetted by the ink d. Wetting fluid da
No. 1 ink layer containing emulsified wetting liquid has wetting liquid No. 2 wetting liquid ink layer db is the same as bb dc dd is the same as bb d? Wetting liquid