Overview of post printing and pre printing of the

Overview of post printing and pre printing of corrugated paperboard

a single corrugated paperboard is composed of a layer of face paper pasted on both sides of the corrugated base paper. Such a structure results in greater strength than the three-layer paper used, while maintaining a relatively light weight at this thickness. Ordinary corrugated types include g, F, e, B, C and A. among them, the height of G type corrugated is the smallest and that of a type corrugated is the largest. Different ridge heights combined with different face paper thicknesses and types, such as bleached/unbleached kraft paper or high tear resistant paperboard, will produce a series of paperboard thicknesses and strengths by sticking coated and uncoated paperboard. Double corrugated board can be used when greater strength is required. The thickness of corrugated board and the properties and thickness of the used face paper material have a significant impact on the printability of the board

most corrugated cardboard is used for production and transportation packaging. Simple patterns are enough for such packaging, which is mainly used for identification and brief introduction. The printing pattern of transportation packaging is composed of 1-3 color line drafts, usually including a company logo and a bar code. About 6% of corrugated board is used in the field of point of sale display and retail packaging, which has high requirements for printing quality, usually including line four-color images

post printing

printing directly on corrugated board is called post printing. Most printed corrugated board packages are produced in this way, and flexographic printing and water-based ink are used. Flexographic printing is economical and effective because it is very suitable for live parts with different printing numbers, and can be printed in 1 ~ 8 colors on any thickness of cardboard (depending on the printing machine). When printing directly on the corrugated board, because too much printing pressure will crush the corrugated board and damage its strength, and successfully complete the temperature measurement, sampling and other work with a high risk factor, the following balance must be achieved: use enough pressure to effectively transfer the ink, and minimize the occurrence of pinhole (refers to the phenomenon of bead like pinhole exposure caused by the ink not properly wetting the surface of the substrate); At the same time, the pressure is not high enough to damage the cardboard structure

a certain degree of adhesion can usually be seen on the corrugated board printed after flexo printing, especially in the online area, which is the result of the point expansion becoming more serious where the top of the corrugated base paper touches the face paper. The adhesion phenomenon is most obvious when using light tissue paper, which is immersed between the tips of corrugated base paper, which intensifies this washboard phenomenon

for corrugated board printed after flexo printing, the recommended quantity of face paper should be at least 180g/m2, and the feed direction of corrugated board should be consistent with that of corrugated base paper. This project is an environmental friendly renewable resource utilization project supported by the state and local governments, so as to minimize the washboard phenomenon

corrugated board used for transportation packaging only needs to print 1 ~ 2 colors and simple pictures. A large number of carton processing plants buy Dazhong corrugated board and specialize in printing and producing live parts of transportation packaging type. The printing machines used include monochrome, two-color or three-color corrugated board printing machines, which are usually used online with folding machine/gluing machine without any form of drying auxiliary equipment. This type of equipment has limited printing performance, and is only suitable for printing live parts with simple lines and blockwork colors, as well as fairly rough light color flat

for the corrugated board used for sales and packaging, end users continue to require that they can print higher quality pictures for most state-owned enterprises. The industry also requires that they purchase new equipment that adopts the latest technology, can print more colors and has enhanced production performance, such as the latest single sheet corrugated board printing machines such as boster's MASTERFLEX series. This machine can print up to 8 colors, and can be used for online or offline die cutting. This kind of flexographic printing equipment is suitable for printing various types of paperboard. Plates of different thicknesses can be used, and it has the function of pulling and skewing. They are capable of high-quality flexographic printing at a speed of up to 10000 sheets/hour. The corrugated roller can be replaced within a few minutes without the intervention of the operator; At the same time, the cavity scraper makes automatic cleaning easier, thereby reducing downtime; The independent servo motor allows to correct the printing length and ensure the accuracy of overprinting, and can also set the unused unit when the equipment is running; With the ability to use thin printing plates, supplemented by fine texturing rollers, it can print high-quality four-color movable parts with 85 ~ 120 lines/inch of lines, and its printing quality can compete with that of printing with face paper pre printing equipment

other printing processes

corrugated cardboard can also be used in the form of single sheet cardboard for silk screen printing, offset printing and digital printing. But at present, these printing processes only occupy a relatively small market share

silk printing can produce printed matter with high quality, high gloss and good color strength. Products are usually used for sales, display and packaging. The speed of silk printing is slower than flexographic printing, and the unit cost is higher. It is only suitable for live parts with relatively small number of prints

offset printing is currently only used for direct printing of micro corrugated cardboard, and offset printing machines suitable for printing of thicker cardboard are being developed. The materials produced by direct offset printing can be die-cut, avoiding the additional cost caused by offset mounting, so that the offset printing process is very suitable for the high quality requirements of short version, small size, light carton and the demand for timely delivery

working side by side with incadigital, sunchem has developed an inkjet printer with UV ink and a fixed print head array for the printing of single corrugated board. This technology is aimed at the short version and high-quality corrugated board market. It was introduced to the market as a complementary technology, and now its linear speed has reached 100 meters/minute, equivalent to 60000 square meters/hour. With the cooperation of first-class flexographic printing equipment suppliers, the mechanical requirements of paperboard feeding and transmission have been met. It can carry out four-color printing with 300dpi and 300dpi printing accuracy. The maximum paper size that can be printed is 80 inches and 48 inches (length and width, 120cm and 170cm). Inkjet printing is digital printing, so there is no printing plate cost. Sunchem believes that this technology is cost-effective for live parts with a printing area of no more than 3000 square meters (40000 square feet)

industry insiders believe that if the average printing number of some sheet fed printing machines is less than 5000, if this technology is strong enough, it may occupy an important market share in a relatively short time

pre printing

the so-called pre printing means that the face paper of corrugated board is printed by flexographic press in the form of drum, using water-based ink, satellite printing machine, and then on the corrugated board production line to make corrugated board. The most important reason for printing the finished products of face paper rather than corrugated board is that pre printing can obtain higher and more stable quality and better overprint accuracy. Preprint also has the advantages of eliminating faults such as washboard phenomenon and printing metal ink and seamless design patterns. Preprint is an ideal method for long plate printing, which is suitable for all corrugated base paper and double corrugated board

some of the latest printing machine technologies have been adopted on the flexpress96s eight color satellite flexograph designed by German Fischer krecke company for the pre printing of tissue paper. The company claims that flexpress96s is the only satellite flexographic machine with lateral bearing system, servo drive and sleeve technology. The servo drive realizes stepless speed change with repetition length between 750 ~ 2000mm, and an expansion module can increase the repetition length to 3500mm The maximum printing width of this flexographic press is 2750mm, and the speed can reach 400 m/min. the speed of 600 m/min can also be selected. Other options include an automatic cleaning system to make cleaning faster; An accesssystem can make the unused unit ready when the printing machine is running; And a cascade unit that prints additional colors

offset printing can also be used for pre printing of corrugated board. If this process is selected, the paper will be mounted into corrugated board through a separate process after pre printing, which is 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 lines added to offset preprint is 175 lines/inch. In terms of printing small area line four-color images, it can obtain higher printing quality than corrugated board direct printing or flexographic preprint. Offset preprint and flexo preprint face paper can be mounted on the surface of corrugated materials of any grade or thickness

each has its own advantages

when it comes to determining the best printing method for a live part, the number of copies printed, carton size and printing quality requirements are the main determinants. Flexographic post printing can meet the most requirements and obtain the greatest printing quality improvement. Due to the remarkable performance of post flexo printing in recent years, the demand for pre printing of flexo printing has also been impacted by the market development trend due to the reduction of the number of copies printed. However, the printing quality of corrugated board is very important for the success of post printing, especially for high-quality four-color moving parts

pre printing is a more economical choice than post printing, and it still has advantages in dealing with high-quality long version live parts or special requirements such as printing seamless design patterns. When it is necessary to make more than 3/4 of the hot-air plastic granulator reproduce a large number of image details with a very high number of lines, offset mounting becomes the best choice with its ability to print up to 175 lines/inch. When offset printing is used directly on the micro corrugated board, it shows the characteristics of high printing quality; At the same time, the low prepress production cost makes it very suitable for medium and long edition printing of micro corrugated board. Because digital printing has no printing plate cost problem, and has reached the printing speed of 100 meters/minute, it is extremely suitable for seizing the high-end business market of short edition. 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 board packaging and printing market in the next few years