Corrugated board flexo printing requirements and pre-printing (on)

In general, the flexographic printing corrugated box process prints directly on corrugated board, using a water-based ink. Corrugated carton production processes now also use web preprinting methods. Corrugated cartons use flexographic printing technology in the United States accounted for about 95%, Western Europe accounted for 85%, Japan accounted for more than 93%. In China, it is gradually accepted by corrugated box manufacturers. Rapid development in recent years, the current use of this technology is estimated to account for more than 50% of companies, and now more use of corrugated board multi-color flexo printing slot machine.

1. Flexographic printing features

Corrugated board flexo printing has the following favorable factors: Flexible version can not only copy the field version but also copy the cable version; corrugated paper printing has been developed from single-color, double-color to multi-color screen version, changing the past monotonous ink, simple graphic The situation satisfies the requirements for sales packaging. This is an inevitable law of development. Corrugated paper (boxes, boxes) are now printed on cable screens, which can be printed on 100 lines/inch on E-tiles and 40 lines/inch on A, B, and C corrugated lines. Flexible version can make solid version, but also can make cable version, in line with corrugated box printing requirements.

Flexible plates can be compressed and deformed. Corrugated paper is the worst in thickness and surface flatness in printed substrates. Especially for A and C tiles, the thickness error is 0.5mm or even higher. Because the flexible printing plate is made of synthetic rubber as the main body, it can compensate for the thickness error and surface unevenness of the corrugated paper in the printing process by its own compressive elastic deformation, thus satisfying the imprinting requirement of each corrugated paper, making the ink color more uniform and ensuring Print quality and reduce bad film. The characteristics of flexible printing plates can be compressed and deformed, which is absolutely impossible to do with plain printing and gravure printing. Therefore, the thickness of the flexible plate used on corrugated boxes is relatively thick, generally 4-7 mm, while the thickness of flexible printing flexible printing plate is only 1.14 mm. 1.7mm. Why do we need to use thick plates on corrugated paper, or use it for compression deformation? Now, in order to reduce costs, we use 4mm plates and 3mm air-cushioned rubber linings (not plastic linings). Of course, we should promote the consistency of the thickness of corrugated paper. In foreign countries, thin corrugated paper is printed on corrugated paper. The key is to control the surface smoothness of corrugated paper.

Flexo printing belongs to light pressure printing. Corrugated paper is due to corrugated, but also has uneven pressure of the printing base material, corrugated high pressure, low corrugated light pressure, but also produce low corrugated sheet can not touch the ink, ink is not printed, so plain printing, gravure The defects of corrugated paper thickness error and uneven pressure cannot be overcome. Flexo printing belongs to light pressure printing, which is the lightest printing pressure in traditional printing, commonly known as “0” pressure printing. The corrugated height won't produce excessive pressure, and the printed ink will be soft and flat. Corrugated cartons are printed on a cable screen. Why should we use fine corrugated cardboard? Because the screen printing requirements are higher, the finer the corrugation, the more uniform the press.

Flexographic printing can use aqueous inks. Paper is made of fibers intertwined, and its hydrophilicity is better than that of lipophilicity. Therefore, by gently touching the corrugated paper, the water-based ink is almost completely absorbed by the corrugated paper, so the ink is uniform, flat, and thick. Water-based ink is not contaminated, low cost, quick drying, and operational use. Flexographic printing uses a short ink path ink transfer system with a metal anilox roller that can use water-based inks and is also a feature of flexo printing. Lithography of the long ink, oil ink (oxidation and drying ink) can not do.

High-efficiency, high-quality, high-speed process technology. At present, the corrugated box printing process technology lines are: First, screen printing. Suitable for small-batch and low-demand transport packaging. Second, corrugated paper after the use of flexographic printing. Since it is a printing process after corrugated paper forming, the process is simple, and the requirement for the development of corrugated paper printing from a single color to a multi-color screen version can be basically satisfied, and therefore high efficiency and high quality can be achieved. Together with high printing speeds, 350 sheets per minute, and 170-220 sheets per minute, this is an ideal printing process technology. Third, leaflets are preprinted. This process is due to the use of sheet-fed lithographic screen printing, although the printing quality is high, but later still use a sheet of corrugated board, and then indentation, slotting, die cutting, can not reach high speed. Moreover, there are not many large-format typographers and the cost is high, which restricts the development and is starting in China. The main advantage is that the printing quality is high. But it is suitable for large-volume packaging, and the cost is higher than that of corrugated paper after printing.

The flexo printer has a simple structure and is suitable for making it large. The corrugated box is large in area and its length is 1.6-3.5m. If a long-path ink-transfer system with lithography is used, the equipment is huge and manufacturing, operation, and maintenance are difficult. The flexo printing press has a simple structure, and four rollers can form a color group. The diameter of the roller is suitable to be large, just to meet the requirements of the plate roller, and can improve the mechanical accuracy and stability. Due to the simple structure of the machine and the large space of the equipment, it can meet the requirements of plate loading and adjustment, and it is convenient for cleaning and use.

Flexo printing can be combined with other processes to form a production line, but also a major feature. Corrugated paper is heavier, and each sheet has a large labor intensity and cannot meet the requirements for mass production. It also cannot be scaled. Due to its simple structure, the flexo printing press can be combined with other processes to form a production line, which greatly improves work efficiency and reduces labor intensity. Most of the corrugated flexo presses now work in conjunction with the indentation notches. Good performance of indentation, slotting, die cutting, gluing, box making, counting and other processes. The finished products can be removed from the machine and can be carried directly on the bus.

2. Flexo printing related requirements

(1) Plate

The corrugated board has a certain elasticity in the direction perpendicular to the paper surface, and has cushioning effect on the package. This is the main reason for the wide application of corrugated cardboard packaging boxes. However, this elasticity brings certain difficulties to printing. In order to adapt to the elasticity of the print and to have good ink transfer, the printing plate must be softer than the plate used in general flexographic printing. Except for special fine prints, the corrugated board has a plate hardness of 30±5 Shore.

(2) Brush

Corrugated board flexo printers come in a variety of sizes. Smaller, 610 mm × 1620 mm corrugated cardboard can be printed, up to 2030 mm × 4830 mm. Because of the large printing format, the plate cylinder is also large. In general, the plate cylinder cannot be disassembled. When printing a new job, the flexible plate on the plate cylinder can be replaced.

Corrugated cardboard has enough stiffness, so in order to adapt to the substrate with a certain stiffness, the paper feeding system of the corrugated cardboard printing machine adopts a single-sheet feeding method. The paper feed condition is to push the end of the paperboard into a pair of paper feed rollers so as to feed the paper to the printing member. Throughout the entire paper printing process, corrugated cardboard is placed on a horizontal plane through the press.

Corrugated board can be printed on a single machine, but nowadays, many carton factories often combine the printing process of the corrugated box with the equipment of other processes of the box making a box production line. For example, printing, slitting, molding, folding, gluing, bonding, labeling, tying, and the like. (to be continued)