The products packaged in the carton, when you do n’t need to open the box, just see the appearance of the carton, you know what is inside. It is a very important link in the production of the carton. The embodiment of this link is printing.
Carton printing uses the following three common process methods: offset printing before corrugated cardboard, pre-printing and flexographic printing after corrugated cardboard. There is also a digital plateless printing that is gradually accepted by the market.
The differences between these printing methods are explained below.
We all know that water and oil cannot be mixed (I don't know if modern technology has done it?), Offset printing uses this principle. The graphic and blank parts of the printed version are basically on the same plane, and the ability to contain ink is not good.
The most troublesome is that when doing large-scale on-site dyeing and printing, two plates are often printed on top of each other, otherwise the color saturation required for printing will be insufficient and light. But the small print and halftone dots are printed beautifully.
When printing, first apply water. The graphic portion of the printing plate is water-repellent and water-repellent, and the blank portion is hydrophilic and oil-repellent, forming a relatively stable unit. The graphics on the printing plate are first transferred to the rubber roller, and then transferred to the paper, which is an indirect printing method.
Due to the structural reasons, this printing method has a long route from ink to paper. The most difficult to control is the ink-water balance, that is, it is difficult to print the thickest ink with the minimum amount of water (fountain solution).
Usually, it is printed on a single sheet of paper. After printing, it is mounted on corrugated cardboard, and then the carton is formed. For small batches of carton, the time is too long, the process is too much, and the relative efficiency is low.
There are two methods, gravure preprint and flexo preprint.
a. Gravure pre-printing: usually roll-to-round printing on web.
The printing plate is a chrome-plated roller. Through photo-etching, the electro-engraving process is basically used to make the graphic department lower than the surface of the roller (the graphic section is lower than the blank section).
During printing, the printing plate cylinder is rotated in the ink tank, and the surface of the cylinder is scraped off with an elastic steel scraper (thickness of 0.15 mm, knife edge grinding treatment). Graphic transfer to paper
The inks used are usually solvent-based or UV-based. It is characterized by high efficiency and long plate life. Field dyeing printing is the strength of this method. The ink layer is thick, but it is not as good as offset printing but better than flexographic printing when the printing layer sense is stronger than the halftone dots.
b. Flexographic pre-printing: belongs to the category of letterpress printing. The graphic part is higher than the blank part, like a seal. The reason why it is called a flexible plate is that the photosensitive resin plate has very good elasticity.
The thicker the plate, the lower the hardness, so the pressure control needs to be done well. The thickness of the preprinted printing plate is generally 1.14 mm to 1.7 mm, and the Shore hardness is 55-70.
Because the hardness is high, the network cable can also be made very high. Generally, 133 lines are used, and even 175 lines or more can be printed, which is very delicate. From the visual point of view, it is not much different from offset printing, and in fact, although the ink layer for dyeing and printing is not as thick as gravure, it is much higher than offset printing.
After pre-printing (including varnishing), it is directly applied to the corrugated cardboard production line as a tissue paper and bonded to the corrugated cardboard to form cardboard.
Because the tile line has multiple high-temperature processing links, the temperature resistance of the ink and varnish is also high, and it must be able to withstand a high temperature of 170 degrees.
Then cut at the rear end of the tile line into a single corrugated cardboard, and finally do the forming process.
This printing method is very large for some batches, and the printed patterns are very beautiful. Very beautiful cartons, such as beer and beverage products, are very suitable.
Carton back print
This is also the most widely used carton processing technology, which can realize the processes of wire forming, grooving, round die cutting, flat die cutting, sticky box nailing, and packing.
The printing plate uses a photosensitive resin plate, the difference is that it is directly printed on the finished corrugated cardboard, so the paper feeding and pressure control are more demanding.
Because the corrugated cardboard can not be flattened, the plate should not be too hard. Generally, the hardness of Shaw is 30-35, and the thickness is 3.94 mm. Use with highly resilient printed pads. Because the plate is relatively thick, the printing plate will be greatly deformed in actual printing, which will affect the printing quality. At present, there is a trend of development to thin plates (3.18mm and 2.84mm).
Because these years I mainly do the equipment of this printing method, which is also my expertise. Regarding the plates used in this printing method and related requirements, I will specifically explain it later.
We have all used inkjet printers. This printing method can be simply said to be an enlarged version of an inkjet printer. The difference is that one is printed on paper and the other is printed on cardboard. In addition, ink is expensive and costly, but it is not necessary to make a printing plate.