From the perspective of Europe and the United States, corrugated cardboard is the largest number of supplies in the packaging market, with a total consumption of about 80 million square meters. About 90% of corrugated cardboard needs to be printed. Since flexo printing is the main printing process available, corrugated cardboard is also the largest flexo printing market.

A single sheet of corrugated cardboard consists of corrugated base paper with a layer of paper attached to each side. This structure results in greater strength than the three-layer paper used, while maintaining a relatively light weight at this thickness. Common corrugated corrugated types include G, F, E, B, C and A, among which the corrugated height of G-shaped corrugated is the smallest and the corrugated height of A-shaped corrugated is the largest. Different corrugated heights combined with different tissue thicknesses and types, such as bleached / unbleached kraft paper or highly tear-resistant cardboard, coated with coated tissue and uncoated chipboard, will produce a range of cardboard thicknesses and strengths. When more strength is needed, double corrugated cardboard can be used. The thickness of the corrugated cardboard and the nature and thickness of the tissue material used have a significant impact on the printability of the cardboard.

Most corrugated paperboards are used for the production of transport packaging. This type of packaging has sufficient simple patterns, which are mainly used for identification and brief introduction. The printed pattern of the transportation package consists of line drafts of 1 to 3 colors, usually including a company logo and a bar code. Approximately 6% of corrugated cardboard is used in point-of-sale display and retail packaging, which has high requirements for printing quality and usually contains four-color images of network cables.

Postprint

Printing directly on corrugated cardboard is called post-printing. Most printed corrugated cardboard packaging products are produced in this way, using flexographic printing and water-based inks. Flexo printing is cost-effective because it is very suitable for jobs with different numbers of prints, and can be printed on any thickness of cardboard from 1 to 8 colors (the number of colors depends on the printer). When printing directly on corrugated cardboard, because too much printing pressure will crush the corrugated cardboard and damage its strength, it must achieve the following balance: use enough pressure to effectively transfer the ink, and make the pinhole (referring to the ink is not appropriate The surface of the substrate is wetted and the phenomenon of beaded holes is exposed). The occurrence of this fault is minimized; at the same time, the pressure is not high enough to damage the cardboard structure.

A certain degree of blocking can usually be seen on corrugated cardboard printed after flexo printing, especially in the area of ​​the mesh line, which is caused by the expansion of the dots becoming more serious where the top of the tip of the corrugated base paper hits the facial paper the result of. The blocking phenomenon is most obvious when using lightweight facial paper. The facial paper "immerses" between the tips of the corrugated base paper, thereby exacerbating this "washboard" phenomenon.

For corrugated cardboard after flexo printing, the recommended amount of facial paper should be at least 180g / m2, and the feeding direction of corrugated cardboard should be consistent with the direction of corrugated base paper, so as to minimize the "washing board" phenomenon.

Corrugated cardboard used for transportation and packaging only needs to print 1 to 2 colors and simple drawings. A large number of carton processing plants are buying bulk corrugated cardboard and specializing in printing and producing live parts of transport packaging type. The printing machines used include single-color, two-color or three-color corrugated cardboard printing machines, which usually do not have any form of drying auxiliary equipment and are used online with folding machines / gluing machines. This type of equipment has limited printing performance, and is only suitable for printing jobs with simple lines and large blocks of color (blockwork), as well as relatively rough light-colored flat screens.

For corrugated cardboard for sales and packaging, end users are constantly demanding the ability to print higher-quality drawings, as is the industry's requirement: to purchase new equipment that uses the latest technology, can print more colors, and has enhanced production performance, such as Bost The latest single sheet corrugated cardboard printing machine such as the Masterflex series. This machine can print up to 8 colors, and can be online or offline die cutting. This type of flexo printing equipment is suitable for printing various types of cardboard. It can use different thickness plates and has the function of pulling and skewing. They are capable of high-quality flexographic printing at up to 10,000 sheets / hour. The anilox roller can be replaced within a few minutes without operator intervention; at the same time, the chambered scraper makes automatic cleaning easier, thereby reducing downtime; an independent servo motor allows correction of the printing length and ensures accurate overprinting. Set up unused units when the equipment is running; with the ability to use thin printing plates, supplemented by fine anilox rollers, you can print high-quality four-color screening jobs with screen lines of 85 to 120 lines / inch. Its printing quality can compete with that of printing with facial paper pre-printing equipment.

Other printing processes

Corrugated cardboard can also be used for screen printing, offset printing and digital printing in the form of a single sheet of cardboard. However, these printing processes currently only occupy a relatively small market share.

Screen printing can produce high-quality, high-gloss, good color strength printed products, products are usually used for sales and display packaging. The speed of screen printing is slower than that of flexographic printing, and the unit cost is higher. It is only suitable for printing a relatively small number of jobs.

Offset printing is currently only used for direct printing of micro corrugated cardboard, and an offset printing machine suitable for printing on thicker cardboard is under development. The materials produced by direct offset printing can be die-cut, avoiding the extra cost caused by offset printing mounting, so that the offset printing process is very suitable for the high quality requirements of short version, small size, light weight carton and timely delivery.

Sun Chemical worked side by side with IncaDigital and has developed an inkjet printer that uses UV inks and has a fixed array of print heads for printing on a single sheet of corrugated cardboard. The target of this technology is the short version, high quality corrugated board market. It was introduced to the market as a complementary technology, and its linear speed has reached 100 meters per minute, which is equivalent to 60,000 square meters per hour. In cooperation with first-class flexo equipment suppliers, the mechanical requirements for cardboard feeding and conveying have been met. It is capable of four-color printing with a printing accuracy of 300dpi × 300dpi, and the maximum printable paper size is 80 inches × 48 inches Length × width, 120cm × 170cm). Inkjet printing is digital printing, so there is no cost of printing plates. Sun Chemical believes that this technology is cost-effective for jobs with a printing area of ​​no more than 3,000 square meters (40,000 square feet).

Industry insiders believe that if the average number of sheet-fed printing presses is less than 5,000 copies, if this technology is strong enough, it may occupy an important market share in a relatively short period of time.

Preprint

The so-called pre-printing refers to that the corrugated cardboard face paper is printed by a flexo printing machine in the form of a roll, using water-based ink, a satellite printing machine, and then made into a corrugated cardboard production line. The most important reason for printing face paper instead of printing corrugated board products is that this method of preprinting can achieve higher, more stable quality and better overprint accuracy. Pre-printing also has advantages such as eliminating the "washboard" phenomenon and the advantages of printing metallic inks and seamless design patterns. Preprinting is an ideal method for long-run printing, suitable for all corrugated base paper and double corrugated board.

Some of the latest printing press technologies have been adopted on the Flexpress96S eight-color satellite flexo press designed by German Fischer & Krecke for preprinting of tissue. The company claims that Flexpress96S is the only satellite flexo machine with a lateral load-bearing system, servo drive and sleeve technology. The servo drive realizes a stepless speed change with a repeat length between 750 and 2000mm, and an expansion module can increase the repeat length to 3500mm. The maximum printing width of this flexo printing machine is 2750mm, the speed reaches 400m / min, and the speed of 600m / min can also be selected. Other options include an automatic cleaning system to make cleaning faster; an access system to prepare unused units when the printing press is running; and a cascade unit for printing additional colors.

Offset printing can also be used to preprint corrugated cardboard. If you choose this process, the paper will be mounted on corrugated cardboard after preprinting through a separate process, called offset mounting, due to the cost involved.

Offset mounting is a pre-printing solution with high quality and relatively high output. The number of screen lines for offset printing is more than 175 lines / inch. In printing small area screen four-color images, it can obtain higher printing quality than corrugated cardboard direct printing or flexo printing. Both offset printing and flexographic printing can be mounted on the surface of corrugated materials of any grade or thickness.

Have their own strengths

When it comes to determining the best printing method for a job, the number of copies, carton size and print quality requirements are the main determinants. Post-flexo printing can meet the most requirements and obtain the greatest improvement in printing quality. Since the performance of flexo post-printing in recent years has been extremely compelling, the demand for flexo pre-printing has also decreased as the number of print copies has decreased. This market development trend has been hit. However, the printing quality of corrugated cardboard is critical to the success of post-printing, especially high-quality four-color jobs.

Pre-printing is a more economical choice than post-printing, and it still has advantages in handling high-quality long-form jobs or special requirements such as printing seamless designs. When it is necessary to use a very high number of screen lines to reproduce a large number of image details, offset mounting is the only choice due to its ability to print up to 175 lines / inch. When printing directly on micro corrugated cardboard by offset printing, it shows the characteristics of high printing quality; at the same time, the low pre-press production cost makes it very suitable for medium and long version printing of micro corrugated cardboard. Since digital printing does not have the cost problem of printing plates, and has reached a printing speed of 100 meters per minute, it is extremely suitable for seizing the short version of the high-end business market. With the decreasing number of printed copies and the continuous development of inkjet technology, digital printing is likely to occupy an important share of the corrugated cardboard packaging printing market in the next few years.

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