Analysis of direct and indirect offset printing ch

Analysis of direct/indirect offset printing characteristics of corrugated board (Part 2)

III. problems and solutions of direct offset printing of corrugated board

the first consideration of direct offset printing of corrugated board is the uneven surface of corrugated board. Different from the printing of ordinary paperboard, the printing of corrugated paperboard must be carried out on the uneven surface caused by corrugated peaks and troughs. Offset printing is difficult to print uneven substrates, and the printing quality is also difficult to guarantee

the unevenness of the substrate is a major challenge for corrugated board printing. The printing machine must deal with the structure composed of grooves and ridges, which corresponds to the solid plate structure. Another difficulty lies in the fact that the transfer of ink from blanket to corrugated paper requires a certain contact pressure in order to achieve a clear image in the grooved part. This pressure is higher than the pressure for effective printing on the smooth paper on the ridge, and it will not weaken the structure and stability of the corrugated board. This condition is the starting point of corrugated board direct offset printing. Many corrugated paper suppliers have provided the necessary material quality to adapt to uninterrupted printing

the blanket required for direct offset printing of corrugated board should be quite elastic. It enables the printing process to use the highest printing pressure without causing too much increase in back pressure. This avoids excessive compression of the grooves. So as to maintain the stability of corrugated board chromaticity and box type. Due to the optimization of blanket, the ink can be transferred well to achieve the highest quality of corrugated board printing

another problem is that ink needs to be transferred to the substrate through certain pressure during printing. In order to make the part of the corrugated paper surface relative to the corrugated trough can also print the image completely, its printing pressure must be higher than the printing pressure required by the material with flat surface, which will inevitably produce a large pressure at the wave crest of the corrugated board, resulting in the reduction of the strength of the corrugated board

in order to solve the above problems, a special blanket has been developed, which has a very flat elastic curve. Therefore, even if greater pressure is applied during printing, the pressure will not increase greatly at the peak of the paperboard, which avoids the damage of the strength of the corrugated paperboard and ensures the accuracy of overprint and the flatness of the corrugated paperboard. The emergence of this kind of blanket has greatly promoted the development of corrugated board direct offset printing

one of the most important conditions for corrugated board direct offset printing is to optimize the ink so as to minimize the washboard effect. The development of blanket is mainly for corrugated board printing, through its high compressibility to compensate for the change of printing pressure between corrugated board ridge and groove. However, the remaining pressure difference can still lead to ridge and recess dot enlargement and ink overprint to varying degrees. This needs to be compensated by ink when printing corrugated board. Printing tests show that the optimized ink significantly reduces the washboard effect. It finishes printing in a wider color gamut and has been proved to be the most suitable for corrugated board printing

the successful application of the technology of direct printing corrugated board by offset press has made the packaging and printing of corrugated box and bag with a variety of flame retardants enter a new stage of development. Due to the high quality and low cost of direct offset printing of corrugated board, the printing and packaging industry can no longer ignore this technology

the design concept and market demand of displaying products and publicizing products through storage and transportation packaging have also promoted the rise of offset press direct printing corrugated board technology, and also established a new printing quality standard for the corrugated box packaging field. Of course, this does not mean that only offset printing will have the future of corrugated board direct printing. Thick cartons are still printed directly by flexographic printing, and many thin cartons will still use flexographic printing because of their simple shape and design pattern. Similarly, high-quality corrugated boxes will also adopt the processing method of offset printing and then mounting. Despite various restrictions, offset direct printing corrugated board has occupied a certain market share and will continue to grow

IV. indirect offset printing of corrugated board

indirect printing method of corrugated board, that is, first print the surface paper of the carton, and then mount the printed surface paper on the corrugated paper. Offset printing uses conventional PS board. Due to the high resolution of PS board, very fine printing patterns can be printed. At present, the vast majority of high-end corrugated boxes used for sales and packaging in China are offset printing. In the production process of corrugated boxes, offset printing is a pre printing method, that is, printing on the opposite paper first, and then mounting on the corrugated board. It is not much different from the general offset printing process, so I don't think much about it here, but only make a simple analysis of its main characteristics

offset printing corrugated boxes have the following characteristics:

① it is easy to make plates, and the technical version is routinely made for PS version

② surface finishing can be carried out, such as film coating, polishing, etc

③ high printing cost

④ it is not suitable to use the paperboard linkage production line, but only the single-sided corrugating machine, with low production efficiency

⑤ the format is limited, which is generally smaller than that of flexo cartons

⑥ printing products are very fine, and the number of lines added can reach 150-200 lines/inch

printing quality is relatively stable

⑦ due to more post processes, the strength of paperboard decreases

⑧ ink generally contains benzene, which has certain pollution

when printing directly on corrugated board, the strength of the carton will certainly decrease due to the printing pressure, which is a major disadvantage of corrugated board direct printing. The influence of printing on the strength of corrugated board is mainly reflected in the printing area and printing position. Generally speaking, with the increase of printing area, the strength of paperboard decreases proportionally. Full printing decreased by about 40%; For horizontal strip printing, the width at the center is 50mm, with a decrease of about 35%; The width of the lower edge is 50mm, with a decrease of about 30%; The printing width on the upper and lower sides is 50mm, with a decrease of about 37%; On the side and the center of the end face of the carton, 50mm is printed longitudinally, a decrease of about 5%

with the continuous development of printing technology and process, the printing of corrugated board will also further develop. There will also be more competition among several printing methods of corrugated board, which also promotes the development of corrugated board printing. Several printing methods of corrugated board will occupy a certain market by virtue of their own characteristics

(author/caihuiping, School of printing and packaging engineering, Beijing Institute of printing)

China Packaging

according to statistical data