Curved surface screen printing process of the most

Surface printing process of rotating and non rotating plastic containers

Abstract: This paper briefly describes the process and essentials of surface printing, explains the pre press surface treatment method of plastic containers, and explains the printing process of rotating and non rotating plastic containers in detail

key words: packaging container; Plate printing; Rotating body

all the printing decoration on containers (cups, bottles, cans, cylinders, etc.) made of various materials (plastic, glass, ceramics, etc.) whose appearance surface is not flat, but concave, convex, arc, can be called curved printing

I. process and essentials of surface printing

the following takes cylindrical and conical objects as examples to illustrate the method of surface printing. The printing method of cylinder and cone is the same, because both substrates need to rotate when printing. When the scraper is pressed, the printing pattern on the plate is in close contact with the substrate, and the plate moves and drives the substrate to rotate for printing. After printing, remove the substrate. At this time, the scraper and the plate return to the original position at the same time, and the printing process is completed. In this process, it should be noted that before printing, the plate cannot contact the substrate, and a gap of 2~3 mm should be left. This is the same as the requirement of separating the plate from the substrate in plane printing. The center line of the acute angle of the scraper, civil aircraft and high-tech ships is in line with the center of the substrate, and then the plate drives the substrate to rotate for printing, as shown in Figure 1

the application scope of curved surface printing not only includes cylinders and cones, but also exquisite printing of concave and quite irregular products. There is no difference in printing principle between surface printing and plane printing, but the former is more difficult

for example, when printing cylinder and cone substrates, there is a certain limit to the area of the substrate stamped by the scraper. In addition, the strength and straightness of the scraper should also be considered. Otherwise, when printing, the printing patterns at both ends of the object will be blurred, and the handwriting will lack pens and strokes. In addition, if the type and variety of silk used in plate making are not selected well, printing quality problems will occur

to make the plate printing work smoothly, the following three conditions must be met (Essentials of curved surface printing):

(1) the vertical center line of the scraper must be perpendicular to the rotation center line of the substrate

(2) the substrate must be able to rotate, but the central axis that needs suction cannot rotate

(3) the printing plate or substrate must be able to rotate

in addition, during the printing process, the frame should move back and forth smoothly and evenly. The printing pressure of the scraper should be kept constant, and the substrate should not shake back and forth

when printing on curved surface, it is necessary to design and manufacture special frame and supporting device of substrate according to the shape of substrate to ensure printing accuracy

II. Prepress surface treatment of plastic containers

1. Degreasing treatment

greasy dirt or film remover on the surface of plastic products will affect the adhesion of ink. The purpose of surface cleaning and degreasing can be achieved through alkaline aqueous solution, surfactant, solvent cleaning and sandpaper polishing

plastics with good adhesion to printing ink, such as ABS, polystyrene, plexiglass (polymethylmethacrylate), are mostly wiped with low-grade alcohol solvents (such as methanol, ethanol, isopropanol, etc.) or polished with sandpaper to achieve the purpose of degreasing

2. Dust removal treatment

the existence of dust not only affects the adhesion of ink on plastic products, but also affects the printing effect

washing with surfactant can remove dust and static electricity, but there is the possibility of dust in the drying process

the compressed air nozzle equipped with high-voltage electrode to generate spark discharge is used for dust blowing, which is fast, easy to operate, and can remove both dust and static electricity. In addition, there is a kind of electric brush, which can remove dust at the same time as long as it passes on the print, and the effect is also very good

3. Treatment to improve the printability of plastic products

appropriate surface treatment methods should be selected according to different plastics and process requirements: for example, polyolefin (PE, PP) non-polar plastics, flame or corona treatment can be used; Because polyester plastic contains benzene ring, its optical activity is large, and it can be treated by ultraviolet light. Pingmei Shenma is a large state-owned enterprise group dominated by energy and chemical industry; Nylon can be treated with phosphoric acid to improve the printability of plastic products with bending center diameter specified by relevant standards

flame treatment is applicable to the surface treatment of small plastic containers. Its purpose is to use high temperature to decontaminate the surface and melt the film surface, so as to improve the performance of surface adhesion ink

put the container to be treated into the gas flame. The length of the inner core of the flame is controlled to be 6~19 mm, the distance between the top of the flame core and the surface is 6~25 mm, the contact time is 0.1~1 s, and the rotation speed is 100~150 rpm. The operation requirements are strict. If you are not careful, the product will be deformed and scrapped. This method has good treatment effect, no pollution and low cost. At present, it is mainly used for the surface treatment of thick plastic products

(to be continued)