Packaging offset printing technology (1)
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Packaging offset printing has been very active both at home and abroad. With the development of the economy and the improvement of people's living standards, people's demand for packaging is increasing, and the requirements for packaging are getting higher and higher. On the one hand, the packaging market has increased demand for offset printing; on the other hand, the development of offset printing technology has made it more suitable for packaging printing.
In addition to the general printing characteristics of packaging printing, the printing range is also very wide, usually requires spot color printing, anti-counterfeiting printing, hot stamping, glazing. The packaging materials of paper products are thicker, and the specifications of printed materials are more varied. Many printed materials require die cutting, indentation, window opening and marking.
In order to meet these needs of packaging printing, both sheetfed offset presses and web offset presses have many innovations and breakthroughs in technology. Many of the connection devices used in web offset presses are now available. It is applied on a sheet of paper offset press.
1. Corona treatment technology
In order to solve the problem of poor adhesion of special materials (such as plastic sheets, etc.), it can be surface-treated first. For example, the KBA Rapida 74 and Rapida 105 models install a corona unit in front of the first printing unit to perform high-pressure discharge treatment on the surface of special materials to improve the adhesion of the ink on the surface of the material, thereby improving the quality and speed of printing.
2. Film coating device
Roland 700 can coat printed materials before color printing begins. The first printing unit prints the glue on the substrate, and the rubber cylinder of the second printing unit is wrapped with a film, and the corresponding portion of the printed material passes over the film. This process is completed at room temperature, completely avoiding the effect of temperature on printed materials such as films.
3. Cold stamping system
The configuration of the cold cold stamping unit is an important feature of the packaging offset press. Connected cold stamping is Manroland's first patented and innovative technology and was awarded the 2006 PIA/GATF InterTech Technology Award. The connection cold stamping unit can be installed at any position of the offset printing machine according to the cold stamping position. The original unit can be printed normally without hot stamping; the printing and hot stamping can be completed once, and the overprint can be realized; and the aluminum foil can be reprinted. Aluminum foil forms any graphics and special color effects.
4. Corrugated board printing
In order to adapt to the thicker packaging materials, many sheetfed offset presses have been improved, such as the use of large transfer rollers, large impression cylinders, roller seven o'clock arrangement, etc., the maximum thickness of the printing material can reach 1.6mm, There are a number of offset presses that add the ability to directly print corrugated cardboard. Because the printing pressure required to directly print on the corrugated board is small, it is difficult to print. In the past, only the flexographic printing machine could print, or the offset printing machine first printed the paper and then stuck it on the corrugated board. After two processes Can be completed. Now the offset press has the function of directly printing corrugated cardboard, which not only reduces the process, but also greatly improves the efficiency.
5.UV offset printing
UV offset printing can not only enhance the decorative nature of printed matter, but also change the situation that offset printing can only print ordinary paper. Now, gold and silver cardboard, aluminized paper, PET, PP, PE and other plastic sheets can be printed on offset printing machine. Greatly expanded the application space of offset printing.
UV printing usually includes UV ink printing and UV coating glazing, which has significant environmental advantages, and the ink layer is thick, bright and wear resistant.
According to several surveys, the UV offset printing market is growing at a rate of 10%, so UV offset printing equipment is also in hot sales. Many equipment suppliers now offer offset presses with UV printing capabilities and can be equipped with different devices depending on the user's different process requirements. However, the UV offset printing process has its own characteristics and needs to gradually accumulate experience. At the same time, the price and energy consumption of the UV offset printing machine are high, and it is necessary to have matching UV ink, UV coating oil, printing plate, blanket, rubber roller, curing device, etc., which invisibly increases the printing cost.
6. Polishing
According to surveys, more than 90% of packaging prints need to be glazed, which fully demonstrates the importance of glazing in packaging printing. In the past, offline special glazing machines were generally used for glazing, and nowadays, wired devices are often used. KBA has conducted a survey of the printing industry in many countries. The order ratio of optical systems with online connection is: folding carton, about 80%; label, about 70%. Table 1 shows the proportion of each of the three main glazing modes of glazing, partial glazing and textured glazing.
Printing companies should combine the printed matter and the company's own conditions to select different configurations of the sheet-fed offset printing machine for packaging. The specific schemes are as follows.
(1) Add a light system to the 5-color machine or the 6-color machine. 1 Add 1 glazing unit (water or UV), 2 add 1 water-based glazing unit and 1 UV glazing unit, 3 add 1 decentralized glazing unit and 1 water-based glazing unit, 4 add 1 water-based unit The glazing unit and a gold glazing unit, 5 add a water-based glazing unit and a lrodin (pigment with pearl glazing effect) glazing unit. The first three methods are mainly used for packaging materials, labels, brochures, covers and calendar printing. The latter two methods are mainly used for printing cigarettes, perfume wrappers and brochures. The fourth method can also be used for labels and chocolates. Wrapping paper printing.
(2) 4-color standard ink + oil glazing + water-based glazing, can produce matt effect, suitable for high-quality labels, packaging materials and brochure printing.
(3) Mixed standard ink + oil glazing + UV glazing, its glazing effect is better than water glazing, suitable for packaging materials, labels, brochures and calendar printing.
(4) Mixed standard ink + UV highlight glazing + UV boring. Hybrid standard ink + UV highlight glazing can achieve the effect of pure UV printing, and the boring effect far exceeds the Drip-off printing process based on heat dispersion glazing.
(5) opaque white + 4 color standard ink + spot color + water glazing + gold glazing. There must be a drying device after glazing, an infrared drying device for water glazing, and a UV curing device for UV glazing. At present, there are three types of drying devices, such as an organic group drying device, an integrated drying device equipped with a long delivery unit, and a dedicated drying unit.
Like sheetfed offset presses, web offset presses can also be used to polish, humidify, and add silicon on one or both sides. The main function of glazing is to improve the gloss of the printed matter and protect the printed matter. It can also be coated with rewet glue (water-repellent glue). If a special additive containing a spice is used, the particle capsule can be destroyed by pressure friction after drying. Stay on the tape. The main function of humidification is to prevent the generation of static electricity, supplement the moisture lost by drying the paper tape, restore the paper performance, reduce the temperature, and create conditions for rewinding and cutting the sheet. Adding silicon (with a silicon content of 2% to 10%) not only has the above functions, but also protects the printed matter from smudging.
7. Post-printing processing
Post-press processing has been a major advantage of web presses, and now sheetfed offset presses have added such features. At present, the post-pressing devices that can be connected to the sheetfed offset printing machine mainly have online slitting, numbering, embossing, punching, cutting, indentation and embossing.
(1) Online cutting
In order to solve the problem that small and medium-sized printed products still need to be cut off offline after printing by large-format offset printing machine, companies such as Manroland and KBA have introduced online slitting devices, which are generally installed on the impression cylinder of the last unit. Manroland's online slitting device has its own drive components; KBA's online slitting device, the pressure of the cutting knife on the impression cylinder is controlled by air pressure.
(2) number, embossing
It is often necessary to type numbers in some packaging and ticket printing. Previously these jobs were done after printing, and number printing was done separately. Now this work can also be processed online, greatly improving production efficiency.
(3) Punching, cutting, indentation, embossing
Some prints sometimes require punching, cutting, indentation, and embossing, and these special requirements can now be processed by wire.