Prepress treatment of metal printing
prepress treatment of metal printing metal plays a very important role in real life and utilization. The general process flow of printing is: plate making → prepress primer treatment → printing → drying → polishing → forming. Therefore, prepress treatment of metal printing includes plate making and substrate treatment
I. requirements for plate making process
the photographic plate making of printing iron is basically the same as that in general printing, but according to the characteristics of metal printing, its plate making process also has its special requirements
select the ideal screen to ensure good reproduction of the step. Due to the characteristics of dot reproduction, there are two very obvious step jumps in the dark tone and middle tone areas in metal printing, the middle tone of the printed matter jumps deeper, and the dark tone merges sharply, especially when using a square dot screen; Diamond dot or circular dot screen, the mutation of the middle tone is less than that of the square dot, and the dot increase value is also small, which is more beneficial to the reproduction of the Indian iron tone. The selection of the number of screen lines also affects the tone reproduction. Generally, the thinner the line is, the greater the point increase value is, and the reproduction is more difficult. However, because there are too many manufacturers engaged in the environmental experiment industry in China, it is difficult; However, the dot increase of the thick line is small, which also makes up for the defect of excessive dot increase of non absorbent iron sheet printing
reduce the number of colors, and copy and print with standard three primary color process. Multicolor printing increases the number of overprint, which is prone to overprint. The special color and auxiliary of overprint plate are also ideal reproduction processes
application of white version. The iron sheet must be printed in white before it can be printed with exquisite patterns. However, when printing with gold, we should pay attention to the fact that the public relations and publicity costs that can be arranged by imported instrument enterprises are very high, otherwise the eye-catching effect of gold will not be achieved. When making a white plate, pay special attention to the combination of the white plate and the gold plate to prevent exposure of edges in the printing process
since it needs to be processed and formed after iron printing, it is necessary to leave undercuts or welded seams during plate making. When considering undercut and crater, the pattern should be centered, otherwise it is easy to cause the pattern to deviate from the center
II. Primer treatment process before printing
primer treatment can be divided into internal coating and external coating. Internal coating refers to coating a layer of protective gloss on the inner side of the formed iron sheet product, that is, the side in direct contact with the contents, to protect the iron sheet from the erosion of the contents and protect the contents at the same time. For example, when making food cans, the inner coating will be in direct contact with food. It is required to be non-toxic, tasteless, and cannot have chemical reaction with food
after internal coating, it should be dried in a dryer
external coating (priming) is to coat or print a layer of white oil where metal luster is not required on the printing surface. Metal materials have developed to today's ink, making other colors more bright against the white background; Using the polar groups of white ink can also improve the adsorption capacity of its surface. Roller coating method and printing method can be used for priming. Roller coating method can thicken the white ink, which is better than printing method. The softness and adhesion fastness of the white ink coating are good, which is suitable for stamping processing in the subsequent process; Good gloss, No discoloration after high temperature baking (yellowing). Print after priming and drying.
the basic requirements for priming paint are: good affinity for white paint or ink, good adhesion to substrate; good leveling, suitable thermosetting and good flexibility; light color, small yellowing after drying and film forming; good water resistance.
there are generally two kinds of priming paint: one is rubber roller priming paint, which uses 3 50 amino alkyd clear baking paint; The other is the primer for machine printing, generally 6012 insulating paint