Corrugated packaging, three printing methods, big competition
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Since the beginning of this century, the market demand for domestic corrugated paperboard has been increasing, and the production concept of cardboard boxes has also undergone great changes. Before 2000, the production purpose of corrugated packaging was mainly to facilitate transportation. As time went by, the printing of corrugated packaging became more and more important, and the choice of printing method directly affected the printing quality, speed, cost and other factors. The three most commonly used printing methods - offset printing, flexo printing and pre-printing - are compared, hoping to provide a reference for the corrugated packaging printing industry.
Before the turn of the century, corrugated packaging used a transmission printer, and the quality and efficiency of production were not high. The new corrugated packaging uses better printing machinery, more advanced printing technology, and newer printing methods, which are more diverse than the old corrugated packaging. At present, corrugated board is the most widely used in offset printing and flexo printing. Pre-printing has not been widely popularized in China's corrugated printing field. According to its current application, the trend and prospects are very gratifying.
First, offset printing
Offset printing of corrugated cardboard has two types: direct offset and indirect offset.
Direct offset printing uses corrugated cardboard as a substrate and is printed directly with a special offset press. Direct offset printing is relatively mature in foreign countries, and the country is still in its infancy. As a new technology, it has no extensive offset printing in the corrugated packaging and printing field, but the direct offset printing effect is ideal, suitable for thin corrugated cardboard (such as G-type and F-type micro corrugated cardboard) can be used to make packaging boxes and gift boxes for home appliances, toys, food, electronic products, etc. It is likely to become the development direction of high-grade corrugated box printing in China.
Conventional offset printing corrugated boxes use indirect printing, that is, printing the carton paper first, and then attaching it to the corrugated board. The machinery required includes a general offset printing machine and a fully automatic, semi-automatic laminating machine.
Second, flexo
Flexo printing is flexographic printing, which is letterpress printing, but the printing plate is soft. Corrugated cardboard is uneven due to thickness. If a rigid printing plate is used, the pressure on the paper surface is inconsistent, the partial imprint of the corrugated sheet is smeared, the empty part is in contact with the bad imprint, the embossing force is difficult to control, and the corrugation of the carton is Cause damage. The pressure of flexographic printing is only l/30 of the pressure of conventional letterpress printing, and the deformation of corrugated cardboard after imprinting is small. The water-based ink used in flexo printing is almost completely absorbed by corrugated paper by light contact with corrugated board. The commonly used flexographic plates are photosensitive resin and rubber.
Third, preprint
Pre-printing refers to printing the roll paper before the corrugated board is produced, printing the finished paper into a roll, and then sending the printed facial paper to the corrugated paper production machine for veneer molding. The pre-printed corrugated board is not subjected to printing pressure, so the corrugated box after molding has an ideal appearance.
Both preprinted and gravure preprinted are preprinted. Flexo preprinting is the process of printing a face paper into a corrugated board after printing it on a corrugated printing machine. Many foreign corrugated packaging and printing companies prefer to use flexo preprinting.
Gravure preprinting is the process of printing the finished paper with a gravure press and rolling it into corrugated cardboard on the corrugated board. For China, gravure is more mature than flexo, so the current corrugated packaging printing is more in line with the actual situation in China.
Fourth, corrugated packaging offset, flexo, preprint comparison
1. Printing quality
Among the three, flexo printing is the most inferior, and offset and pre-print quality are ideal.
The quality of flexographic printing cannot meet the requirements of high-grade corrugated packaging. First of all, this is the water-based ink used in corrugated packaging flexo printing, resulting in poor gloss of printed products; secondly, the number of screen printing lines for flexo printing is generally 30 ~ 65LPI, no more than 150LPI, lower than offset printing and pre-printing; third The dot density of flexo printing is more serious and difficult to grasp (for example, the dot size of the 50% dot is increased by 30% to 40%).
Offset printing is already a relatively mature printing technology in China, and it is also a printing method with a large advantage in the printing field. Therefore, the high quality of corrugated packaging offset printing is normal. First of all, the PS version of offset printing has a high resolution, can print very fine patterns, and can also be used for surface finishing such as laminating and glazing. Therefore, most of the high-grade corrugated box printing used in domestic sales packaging is Offset printing; secondly, the number of screens for corrugated packaging offset printing can reach 150-200LPI; thirdly, the increase of offset dot is much lighter than flexo printing, and the dot size at 50% is increased by 15%~2O%; fourth, corrugated packaging offset printing can The range of dot reproduction is large, reaching 2% to 98%, or even 1% to 99% (the range of dots that can be reproduced by flexo printing is 3 to 95%).
The printing pressure of the corrugated packaging preprinted is uniform and is not affected by the height of the corrugated, so the printing quality is good. The number of screens for flexo preprinting can reach 150LPI, and the 50% dot gain is 15% to 25% lower than that of traditional flexo printing, but the range of tone can only be between 8% and 85% when copying continuous tone images; The pre-printing is stronger than the flexo pre-printing, and the network cable can reach 300LPI, which reflects the advantages of full gravure ink color, strong stereoscopic effect and high overprinting precision. The gravure pre-printing can even exceed the offset printing effect.
2. Printing machinery costs
Pre-printed machinery costs the most, and flexographic printing machinery has the lowest.
China's pre-printing is still in its infancy. The pre-printing method requires a web-printing press. After printing, it is re-rolled to form a roll of printed matter, and then the corrugated board production line is re-laid. The existing corrugated board production line is not suitable for pre-printing. The cardboard composite requires technical improvements. The pre-printed printing equipment introduction fee and renovation fee are very large, and the general flexo preprinting machine is priced at about 10 million yuan.
The flexographic printing press has a simple structure and low cost.
Offset presses (especially direct offset presses) cost about twice as much as flexo presses.
3. Plate cost and printing durability
The flexo version has the highest cost and the preprinted version has the highest print durability.
Flexo rubber and photosensitive resin versions cost the most.
The printing durability of offset printing is generally only a few hundred thousand sheets; the flexographic printing durability is about 1 million printed sheets; the flexographic printing plate has high printing durability and can be reused, such as gravure preprinting with a printing durability of 300-400. Wan Yin Zhang.
4. Ink performance
Offset inks are resin type, bright type inks, etc., which often contain benzene, which has certain pollution. Both flexographic printing and pre-printing can use water-based inks. Domestic ink can meet the high temperature and friction of corrugated paper. Therefore, China's corrugated board printing uses water-based inks, which is beneficial to the loose and corrugated cardboard corrugated and non-toxic. It is tasteless, non-polluting and low in cost.
5. Printing speed
The slowest speed is offset printing. Offset printing is only suitable for single-face corrugating machines, and it is not suitable for cardboard linkage production lines, so production efficiency is low. The domestic offset paper production line has an offset speed of 5,000 to 9000 sheets per hour, a high-speed production line of up to 16,000 sheets per hour, and a processing carton speed of 300 to 1000 inches per minute.
Preprinting speed is the fastest. Since the pre-printing avoids the influence of the conventional printing on the flat pressing strength of the paperboard, the printing speed can reach 200 to 400 m/min.
Followed by the flex version. The flexo printing machine can work continuously with die-cutting, indentation, grooving, gluing, folding, stapling boxes, baling and other post-press processing equipment at an ideal speed. Because of the fast printing speed of the flexo printing plate, it is difficult to maintain stability, resulting in low printing accuracy in multi-color printing.
6. Printing format
Pre-printing can satisfy the largest printing format, followed by flexo printing and minimum offset printing.
Both flexographic and preprinted presses are available for wide format printing. Flexographic printing corrugated paperboards are available in widths up to 2.8 m and gravure preprinted presses have a maximum print width of up to 3.4 m. Offset printing is not possible for large format printing.
In summary, corrugated packaging has its advantages and disadvantages in offset printing, flexo printing and pre-printing. We need to choose the appropriate printing method according to different needs. Pre-printing is especially suitable for high-quality, high-volume corrugated packaging. If there are many types of products and the printing quantity of a single variety is small, it is not economical to use pre-printing; offset printing is suitable for high-quality, small-volume corrugated packaging; flexo printing Suitable for corrugated boxes with low printing accuracy requirements (such as text lines), large quantities, fast requirements, large area, and low cost. These three corrugated packaging and printing methods will coexist for a long time in the future, and their market share will be adjusted according to changes in social needs, let us continue to pay attention.