The choice of printing method directly affects printing quality, speed, cost and other factors. This article compares the three most commonly used printing methods for corrugated packaging printing-offset printing, flexo printing, and pre-printing, hoping to provide some reference for the corrugated packaging printing industry.
At present, offset printing and flexo printing are the most widely used for corrugated cardboard, and pre-printing has not yet been widely popularized in the field of corrugated printing in China. Judging from its current application situation, the trend, and prospect are worth looking forward to.
Offset printing: There are two types of offset printing for corrugated cardboard packaging: direct offset printing and indirect offset printing.
Direct offset printing is to use corrugated cardboard as printing material and directly prints it with a special offset printing machine. It is suitable for thin corrugated cardboard (such as G-type and F-type micro-corrugated cardboard) and can be used to make packaging boxes and gift boxes for home appliances, toys, food, electronic products, etc. It will likely become the development direction of high-end corrugated box printing in my country.
Conventional offset printing of corrugated boxes uses indirect printing, that is, printing the carton surface paper first, and then laminating it on the corrugated. The required machinery includes ordinary offset printing machines and fully automatic and semi-automatic laminating machines.
Flexo printing: Flexo printing is flexographic printing, which belongs to letterpress printing, but the printing plate is soft. The pressure of flexographic printing is only 1/30 of that of traditional letterpress printing, and the deformation of corrugated cardboard is very small after embossing. The water-based ink used in flexo printing is almost completely absorbed by the corrugated cardboard as long as it touches the corrugated cardboard lightly. Commonly used flexographic plates include photosensitive resin plates and rubber plates.
Pre-printing: Pre-printing refers to printing the roll face paper before the production of corrugated cardboard, and then sending the printed face paper to the corrugated paper production machine for veneer forming. The pre-printed corrugated box is not affected by the printing pressure, so the appearance of the formed corrugated box is very ideal.
There are two types of pre-printing: flexo pre-printing and gravure pre-printing. Many foreign corrugated packaging and printing companies prefer to use flexo pre-printing. For our country, gravure printing is more mature than flexo printing, so it is more in line with the actual situation of our country to focus on gravure pre-printing in corrugated packaging printing.
1. Printing quality: Among the three, flexo printing is the worst, and the quality of offset printing and pre-printing is ideal.
The quality of flexographic printing cannot meet the requirements of high-grade corrugated packaging. First of all, this is due to the poor gloss of the printed product caused by the water-based ink used in flexo printing for corrugated packaging; secondly, the screen line number of flexo printing is generally 30-65LPI, not exceeding 150LPI, which is lower than offset printing and pre-printing; third, the dot increase of flexo printing is serious and difficult to grasp (such as 30%-40% dot increase at 50% dots).
Offset printing is already a relatively mature printing technology in my country, and it is also a printing method with great advantages in the printing field. Therefore, it is normal for corrugated packaging to have high-quality offset printing. First of all, the PS plate used in offset printing has a high resolution, can print very fine patterns, and can also perform surface finishing work such as lamination and glazing. Therefore, most of the high-end corrugated box printing used in domestic sales packaging is offset printing; secondly, the number of lines of corrugated packaging offset printing can reach 150-200LPI; ~98%, or even 1%~99% (the dot range that can be reproduced by flexo printing is 3~95%).
The printing pressure of corrugated packaging pre-printing is uniform, and it is not affected by the height of the corrugation, so the printing quality is good. The number of screening lines of flexo pre-printing can reach 150 LPI, and the 50% dot gain is 15% to 25% lower than that of traditional flexo printing, but the range of tone when copying continuous tone images can only be between 8% and 85%. Gravure pre-printing is stronger than flexo pre-printing, and the screen line can reach 300 LPI, which reflects the advantages of gravure printing ink full color, strong three-dimensional effect, and high overprinting accuracy. Gravure pre-printing can even exceed offset printing.
2. Printing machinery cost: the cost of pre-printing machinery is the highest, and flexographic printing machinery is the lowest.
my country's pre-printing is still in its infancy. The pre-printing method requires a web printing machine. After printing, it is first rewound to form a web of printed matter, and then corrugated on a corrugated cardboard production line. The existing corrugated cardboard production line is not suitable for pre-printed cardboard compounding, and technical improvement is needed. The cost of introduction and transformation of pre-printed printing equipment is very high, and the price of a general flexo pre-printed machine is around 10 million yuan.
The flexographic printing machine has a simple structure and low cost.
Offset presses (especially direct offset presses) are about twice as expensive as flexo presses.
3. Printing plate cost and printing durability: the cost of the flexographic plate is the highest, and the printing durability of the pre-printed plate is the highest. Flexographic rubber plates and photosensitive resin plates are the most costly.
The printing durability of offset printing is generally only hundreds of thousands of printing sheets; the printing durability of flexo printing is about 1 million printing sheets; the printing durability of flexo printing plate is very high, and can be reused, such as gravure pre-printing printing durability of 3 to 4 million printing sheets.
4. Ink performance: offset printing inks include resin type, glossy ink, etc., flexographic printing and pre-printing can use water-based ink
Offset printing inks include resin type, glossy ink, etc., which often contain benzene, which has certain pollution. Both flexographic printing and pre-printing can use water-based ink. Domestic ink can meet the high temperature and friction on the corrugated paper line. Therefore, water-based ink is mostly used for corrugated cardboard printing in my country. It is conducive to the permeation and drying of loose corrugated cardboard. It is non-toxic, tasteless, pollution-free, and low in cost.
5. Printing speed: Offset printing is the slowest, and pre-printing is the fastest.
Offset printing is only suitable for single-sided corrugating machines, and it is not suitable for cardboard linkage production lines, so the production efficiency is low. The offset printing speed of the domestic general offset paper production line is 5000-9000 sheets/hour, the high-speed production line can reach 16000 sheets/hour, and the speed of processing cartons is 300-1000inch/minute.
Preprint is the fastest. Because pre-printing avoids the influence of traditional printing on the flat pressing strength of cardboard, the printing speed can reach 200-400m/min.
Followed by flexo. The flexographic printing machine can work continuously online with post-press processing equipment such as die-cutting, creasing, slotting, gluing, folding, boxing (gluing), bundling, etc., and the speed is ideal. Because of the high printing speed of the flexo printing plate, it is difficult to maintain stability, resulting in low overprint accuracy during multi-color printing.
6. Printing format: The printing format that can be satisfied by pre-printing is the largest, followed by flexo printing, and offset printing is the smallest.
Both flexographic printing machines and pre-printing printing machines can meet wide-format printing. The width of flexographic printing corrugated cardboard can reach 2.8m, and the maximum printing width of gravure pre-printing printing machines can reach 3.4m. Offset printing cannot be used for large-format printing.
To sum up, offset printing, flexo printing, and pre-printing for corrugated packaging each have their own advantages and disadvantages. We must choose the appropriate printing method according to different needs.
Pre-printing is especially suitable for high-quality, large-volume corrugated packaging. If there are many types of products and the printing volume of a single type is not large, it is not economical to use pre-printing;
Offset printing is suitable for high-quality, smaller batches of corrugated packaging;
Flexo printing is suitable for corrugated cartons that do not require high printing accuracy (such as text line drafts), large quantities, require fast speed, large area, and low cost.