Usually, when development technicians get complex hose drawings, they will evaluate whether they can be printed and what printing method to use to achieve the effect of the design. The hose drawings in production mainly include offset printing, flexographic printing, screen printing, gravure printing, hot stamping, etc. Flexographic printing is a trend that the mainstream is optimistic about in the future, but it has not yet been fully popularized. At present, the main printing method for hoses is still offset printing, and flexographic printing has not yet been popularized in every hose factory. Offset printing is what we usually call letterpress printing. The offset printing process is divided into: dust removal-surface pretreatment (corona treatment and flame treatment)-printing (UV ink)-glazing-varnish UV curing (or thermal curing).
Offset printing uses high-viscosity paste ink. The ink fountain roller transfers the ink from the ink fountain to a group of rubber rollers. Through the ink roller, the ink is evenly distributed to the ink roller. The ink roller transfers the ink to the raised offset image part attached to the plate cylinder. The raised image part is about 0.50mm-0.60mm higher than the blank part. Then the ink on the plate is transferred to the rubber cloth of the rubber roller, and then to the surface of the hose.
The offset printing plate consists of a base and a photosensitive polymer layer. The base is generally metal or photosensitive polymer resin. The printing plate with a metal base has a slightly higher printability. Even if the plate is made of a resin base, the printability can reach 150,000 to 200,000 hoses.
The main reasons why offset printing has become the main printing method for hose printing are as follows:
(1) Good printing effect
The offset printing process combines the characteristics of relief printing and offset printing. Both printing technologies are relatively mature. In four-color printing, four-color dots can be overprinted. Compared with screen printing, the printed images of letterpress offset printing are more delicate, so some art designs with rich gradients and layers can be reproduced.
In the letterpress offset printing process for hoses, the maximum screen count can reach 175 lines/inch when printing in single color; when overprinting in multiple colors, the screen count can reach 100-120 lines/inch. Although the offset printing on hoses is not as delicate as that on paper, it has a rich expressiveness.
(2) Multi-color printing
When printing hoses by offset printing, in addition to the four colors of CMYK, some special colors are often used. At present, eight-color printing machines have appeared in the field of hose offset printing, meeting the specific requirements of some customers.
(3) Fast speed and high production capacity
In the fully automatic hose production line, hose molding and printing are completed in one go. The printing machine, extruder, injection head machine and film capping machine form an automatic hose production line, and the production speed of the entire production line can reach 100 pieces/minute. Some offset printing machines specially designed for hose printing can print at speeds up to 200 pcs/min. The smaller the tube diameter, the faster the printing speed.
(4) Low printing cost
Compared with screen printing, the printing cost of offset printing is relatively low. The reasons are: first, the price of letterpress offset UV ink is cheaper than screen printing UV ink; second, offset printing is an indirect printing method. The ink needs to be transferred from the printing plate to the hose surface twice. Therefore, the ink film layer transferred to the hose surface is obviously thinner, and the ink consumption is much less than that of screen printing; there is no convex feeling when touched by hand. This is also one of the simple ways to distinguish offset printing from screen printing. Third, letterpress offset printing has a fast speed and high production capacity, which reduces the printing cost of each hose.
Compared with flexographic printing, the printing cost is relatively lower. The main reasons are: first, the price of flexographic printing machine is relatively expensive; second, the hose artwork is mainly printed text and logo, and the artwork is simple, which is relatively wasteful compared to offset printing flexographic printing machine; third, the cost of plate making is also relatively expensive.
(5) Stable quality and convenient testing
The fully automatic hose production line is equipped with automatic camera and automatic tube removal devices. The automatic camera stores the image information of standard products, then scans the printed image of each hose, compares it with the stored standard information, automatically makes a judgment on whether the product is qualified, and removes unqualified products, making product quality testing very convenient. The entire printing process ensures that the hose printing quality is within a stable range.
