Unlike paper, corrugated cardboard is first processed into corrugated base paper, and then the surface and the middle corrugated layer are bonded from both sides with an adhesive to make the middle layer of the cardboard have a hollow structure, which has high strength, stiffness and resistance Compressive strength, etc. Because of its special properties, it is now widely used in product packaging, and direct printing on corrugated paper has become the mainstream printing method for packaging boxes.
In recent years, especially in Europe and the United States, ultra-thin and ultra-strong micro-corrugated cardboard has quietly occupied more and more corrugated cardboard market, because it has better physical properties and printing performance of corrugated cardboard and thick cardboard at the same time. Compared with the traditional thick cardboard, it has the characteristics of good strength, strong cushioning force, good elasticity, material saving, light weight and good printing effect. Compared with traditional corrugated cardboard, micro corrugated cardboard has the characteristics of small corrugated shape, high stiffness, compact structure, strong and flat, light and thin materials, good compression resistance, and the ability to use offset printing machines to print directly. The production process of printing directly on the printing machine and only printing after mounting on the offset printing machine simplifies the process, shortens the production cycle, and improves the production efficiency.
Commonly used mini corrugated cardboards are F-type (0.75mm), G-type (0.5mm), N-type (0.46mm), O-type (0.3mm), etc., which are all three-layered, namely, face paper, corrugated paper and bottom paper . At the same time, micro corrugated cardboard also has the following characteristics: (1) high strength, which can enhance the protection function of the product, which is 40% stronger than thick cardboard; (2) light weight, 40% lighter than thick cardboard, and 20% lighter than laminated corrugated cardboard %; (3) The surface is smooth, the patterns are exquisite, the colors are colorful, and it has the characteristics of strong visual effects.
1. The principle of offset printing and its requirements for corrugated cardboard printing
At present, the methods commonly used in corrugated cardboard printing include flexographic printing, gravure printing, offset printing paper and laminating. Among them, flexographic printing is the most commonly used, but the printing accuracy is not very high, generally only some low-grade rough cartons can be printed, and gravure printing and offset printing are pre-printing processes, that is, printing the facial paper first and then performing Although the bonding process can obtain better quality, the process is complicated and the cost is higher. Therefore, offset printing directly on corrugated cardboard is a brand-new process pursued by the packaging and printing industry. The current KBA Rapida 105 and Manroland 700 and 900 can be directly offset printed on mini corrugated cardboard, and the printing quality can reach a very high level.
Offset printing is based on the natural law of immiscibility of oil and water. On the printing plate on almost the same plane, the graphic part only absorbs ink, and the blank part only absorbs water, and the graphic ink is transferred to the substrate through the blanket . Due to its high image restoration and color reproduction capabilities, offset printing is currently the most widely used and most mature printing method. At present, it accounts for more than 50% of all printing in China, mainly paper printing. In recent years, with the rapid development of packaging and printing, flexographic printing, gravure printing, and screen printing have achieved tremendous development, and the development momentum and proportion of offset printing have declined.
At present, the offset printing technology has made a breakthrough in printing directly on micro corrugated paper, so that the offset printing process will return to life. In the field of traditional fiber cardboard boxes, such as wine, small appliances, footwear, hardware tools, microelectronics, computer software, counter sales, fast food, etc., offset printing has begun to cooperate with Traditional thick corrugated cardboard competes for the market.
However, fountain solution should be used in offset printing (the fountain solution is mainly used to keep the blank part of the printing plate clean and the main component of the fountain solution is water), which makes the offset printing process very complicated. The mixing of ink and water will cause emulsification of the ink, which will cause deformation of the water absorption of the cardboard and change in strength, which will affect the color, viscosity and drying performance of the ink. Therefore, the control of the water-ink balance becomes very critical. If the amount of water is too large, the ink will be excessively emulsified, the drying will become slower, and the color will become lighter. In particular, the corrugated cardboard will absorb more water and reduce the compressive strength and surface strength. It will not even withstand the printing pressure and collapse. [next]
The size of the cardboard becomes larger, which makes the deformation of the face paper and the backing paper inconsistent, making its printing suitability worse. Therefore, the water volume control of direct offset printing of corrugated cardboard is more strict than that of ordinary paper printing. If the amount of ink is too large, it will cause failures such as dot expansion, gradation and gradation, and dirt. Therefore, it is necessary to control the water-ink balance in the printing process, especially the amount of water.
Direct offset printing on corrugated cardboard requires lighter than ordinary paper in pressure control. Since the middle corrugation of corrugated cardboard is empty, if the pressure is too large, it will cause failures such as network expansion and level grading. At the same time, it will produce a "washing board" phenomenon, which will cause crushing in serious cases. Therefore, the pressure control should be more precise.
Due to the special structure and special requirements of corrugated cardboard, this type of offset press generally uses a special rubber blanket with better compressibility and a certain hardness, so that the different compression resistance of the corrugated cardboard surface can be compensated by the compression deformation of the rubber blanket Performance and deformation performance to improve printing quality.
2. The effect of offset printing on corrugated cardboard printing
(1) Influence on the strength of corrugated cardboard
The huge pressure of offset printing will reduce the compressive strength of corrugated cardboard; the use of fountain solution will reduce the surface strength and compressive strength of the cardboard due to water absorption.
(2) "Washboard" phenomenon
The phenomenon of the washboard is the most common quality problem in corrugated cardboard printing. This phenomenon may occur if the pressure and the amount of ink are not well controlled in the printing.
(3) Ink and ink unbalance
The biggest impact on quality in offset printing is the water-ink balance, especially if the amount of water is too large, it will have a greater impact on the micro-corrugated cardboard.
(4) Acidity and alkalinity of fountain solution
If the acidity is too strong, the drying will slow down and corrode the printing plate; if the acidity is too weak, an effective hydrophilic protective layer cannot be formed on the blank part of the printing plate.
(5) Performance of blanket
The performance of the blanket includes surface performance and compression deformation performance. The surface performance is the guarantee of absorbing ink and transferring ink, and the compression deformation performance is the basis of whether high-quality images can be obtained on corrugated cardboard.
Direct offset printing micro corrugated cardboard is a brand-new printing process, which has reached a very high level in printing effect and printing quality. It can basically be comparable to the printing quality of paper. It will become a high-end corrugated carton and carton. The first choice of packaging paperboard can bring huge economic benefits to packaging and printing companies. It is one of the main directions of the development of offset printing in the future. This will re-ignite the bright light for the development of offset printing.
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