Application of Corrugated Cardboard Direct and Indirect Offset Printing Technology

Third, corrugated board direct offset problems and solutions

The first thing that should be considered in the direct offset printing of corrugated board is the uneven surface of corrugated board. Unlike the printing of plain paperboard, the printing of corrugated board must be done on uneven surfaces caused by corrugations and troughs. Offset printing on uneven substrates is difficult and print quality is difficult to guarantee.

Substrate irregularities are a major challenge for corrugated board printing. The structure that the printer must handle the grooves and backs corresponds to the three-dimensional plate structure. Another difficulty lies in the fact that the ink must transfer from the blanket to the corrugated paper with a certain contact pressure in order to achieve a clear image in the grooved portion. This pressure is higher than the effective printing pressure on the smooth surface of the ridge, and it does not weaken the structure and stability of the corrugated board. This condition is the starting point for direct offset printing on corrugated board. Many corrugated paper suppliers already provide the necessary material quality to accommodate non-stop printing.

The blankets needed for direct offset printing on corrugated board should have fairly good elasticity. It enables the printing process to use the highest printing pressure without causing too much pressure on the spine. This avoids excessive compression of the groove. In order to maintain the color of the corrugated board and the stability of the box type. Due to the optimization of the blanket, the ink can be well transferred to the highest quality of corrugated board printing.

Another problem is that the printing needs to transfer ink to the substrate with a certain pressure. In order to make the corrugated paper surface completely printable with respect to the part of the corrugated trough, the printing pressure must be higher than the printing pressure required for the flat surface material, which inevitably generates a greater pressure at the crest of the corrugated paperboard. As a result, the strength of the corrugated board is reduced.

In order to solve the above problems, a special rubber blanket was developed. The elasticity of the blanket was smooth. Therefore, even if a large pressure is applied at the time of printing, the pressure at the crest of the paperboard will not be greatly increased. This avoids the damage of the strength of the corrugated paperboard, and ensures that the overprinting accuracy and the corrugated paperboard are piled up flat. The emergence of such blankets has greatly promoted the development of direct offset printing of corrugated board.

One of the most important conditions for the direct offset printing of corrugated board is to optimize the ink so that the effect of the washboard is minimized. The development of blankets is primarily for corrugated board printing, compensating for variations in the printing pressure between the ridges and grooves of corrugated board through its high compressibility. However, the remaining pressure difference can still cause the ridges and recesses to expand and ink overprint to varying degrees. This needs to be compensated by ink when printing on corrugated board. Print tests show that optimizing the ink significantly reduces the washboard effect. It prints in a wider color gamut and has been found to be best suited for printing on corrugated cardboard.

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

The design concept and market demand for displaying products and promoting products through storage and transportation packaging also promoted the rise of direct printing of corrugated board technology by offset presses, and also established new printing quality standards for corrugated box packaging. Of course, this does not mean that only offset printing will have the future of direct printing on corrugated cardboard. Thick cardboard boxes are still printed mainly by flexo printing. Many long-lasting cardboard boxes will still use flexo printing because of their relatively simple shapes and design patterns. Similarly, high-quality corrugated cartons will also be offset-printed and then processed. Despite all the restrictions, direct offset printing corrugated board has occupied a certain market share and will continue to grow.

Fourth, indirect offset printing of corrugated board

The indirect printing method of corrugated paperboard is to print the carton paper first, and then paste the printed paper paper to the corrugated paper. Offset printing uses conventional PS plates. Since the resolution of PS plates is relatively high, very fine printing patterns can be printed. At present, most of the high-grade corrugated boxes used in sales packaging in China are offset printing. In the production process of corrugated cartons, offset printing is a pre-printing method. That is, first printing on facing paper and then on corrugated cardboard, it is not much different from the general offset printing process. There is no more consideration in this regard, only Its main features are simple analysis.

Offset printing corrugated boxes have the following characteristics:

1 Plate making is easy, and the PS plate is a conventional plate making.

2 can finish the surface decoration, such as coating, polishing and so on.

3 high printing costs.

4 It is not suitable to use paperboard linkage production line. It is only suitable for single-faced corrugating machine and the production efficiency is low.

5 format is limited, generally smaller than the flexo printing carton format.

6 printing products are very fine, the number of screen lines can reach 150-200 lines / inch.
The printing quality is relatively stable.

7 Due to more post-processes, the strength of the board is reduced.

8 ink generally contains benzene, there is a certain degree of pollution.

Direct printing on corrugated board, due to the effect of printing pressure, the strength of the carton will certainly decline, which is a major drawback of direct printing corrugated board. The effect of printing on the strength of corrugated board is mainly reflected in the printed area and the printed position. In general, as the printing area increases, the board strength decreases proportionately. The total printing is reduced by about 40%; transverse belt printing is reduced by about 35% at the center width of 50mm; about 30% at the width of the lower edge of 50mm; and the width of printing is reduced by about 30% at the upper and lower sides by 50mm; on the side and end of the carton. The central part is reduced by about 5% in vertical printing of 50mm.

With the continuous development of printing technology and processes, the printing of corrugated board will further develop. There will be more competition between several printing methods of corrugated cardboard, and this kind of competition 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.

Excerpt from: Feilang carton design