Preliminary Study on Preprinting Technology of Gravure Printing Carton

Keywords: corrugated carton preprinting process gravure printing paper gravure printing machine electronic engraving

The preprinting of gravure printing carton is to print the corrugated carton on the wide web (carton paper) in advance using a gravure printing technology before making the corrugated cardboard, and then printing the good paper in roll shape. The upper corrugated board production line is made of corrugated boxboard, and then die-cut by a die-cutting machine into a box type.

At present, 30% of the total output of corrugated boxes in some developed countries such as Europe and America are produced using preprinted technology. In recent years, with the rapid development of China's paper product packaging industry, many carton factories with stable customers, such as Mengniu, Budweiser, and Tsingtao Brewery, have set their sights on preprinting new technologies. With the stability in the design and consumption of corrugated cartons for the packaging of beverages, beer, home appliances and food products, the use of web pre-printing methods to produce high-grade colored corrugated cartons will become a trend in the future of the packaging industry.

Web preprinting is better than single offset printing

At present, the vast majority of domestic color carton uses a sheet-fed offset printing preprinting method. The process flow is: cutting the web into single sheets, offset printing, printing single sheets, simultaneous single-roller rolling, two-layer corrugated cardboard, facing paper, and single-faced corrugated cardboard on the veneer, backing or veneering. Machine veneer → Die cutting indentation molding → Nail box / stick box. The technical process of the web gravure printing preprinting technology is: gravure printing machine printing surface layer paper roll → cardboard line production cut into cardboard → die cutting indentation forming → nail box/adhesive box.

So, why should we use gravure preprinting? There are two main reasons: First, gravure printing can easily provide high-quality color prints; second, electronic engraving technology can significantly reduce the production cycle and cost of metal plate rollers. Close to or even lower than the flexo version. At present, high-speed wide-format paper gravure printing machines have been produced in China, and the price is only one-third that of imported flexographic printing machines. The use of gravure preprinting may be more suitable for the actual situation of packaging companies in China.

In comparison, people use the past commonly used paperboard molding printing process as "post-printing". Pre-printing has some obvious advantages over post-printing:

1. Get better print quality and adaptability. Pre-printing uses a gravure printing machine or flexo printing on a smooth paper surface. Compared with printing with a printing slotting machine for printing on uneven paperboard surfaces, pre-printing can be performed in fine-grained printing with richer colors and vivid colors. Printing quality will also be more stable and reliable.

2. Makes corrugated board the highest strength. Since the preprinting is not imprinted after the cardboard is formed, deformation of the corrugated board and weakening of the cardboard strength can be avoided. After printing with corrugated board printing slot machine, each color printing will cause more or less deformation of corrugated board, and the more color number, the greater the effect on the deformation of corrugated board.

3. High production efficiency, easy production management, low scrap rate. Preprinting has become an important trend in the printing of corrugated board, especially the printing of high-grade cartons (including large and special-shaped cartons).

The use of intaglio printing carton preprinting has the following salient features compared to traditional color offset printing:

1. high productivity. Gravure printing web printing speed of 150 ~ 200m/min, basically with many domestic corrugated cardboard production line match, than traditional sheetfed offset printing and veneer tile and other short process, low labor costs, high efficiency.

2. The color carton produced by gravure preprinting can get high quality ink prints. The high accuracy of gravure overlay printing is not more than 0.2mm. It can also finish the printing and varnishing once. The printed wire can reach 300 lines and the amount of ink is larger than other printing methods. The highest is 4.5~6g/m2. The printed ink is full, soft, bright, and firm, and there is a sufficient drying system for each color after gravure printing. Therefore, under the premise of choosing the paper with higher surface smoothness for printing, gravure printing can obtain high printing quality of ink and ink. Most cigarette packs are made from paper gravure printing. At present, the domestic production of paper gravure printing inks has been relatively mature, domestic has been able to meet the corrugated board line preprinted with water-based paper gravure ink, can fully meet the corrugated board production line 180 °C high temperature and hot plate friction.

3. Large-format, multi-color printing is possible. The maximum size of traditional color offset printing is generally up to 1.2 m×0.9 m (envelopment), and most of them are four-color printing. Carton pre-printing unit gravure printing machine maximum printing material width of 2.5m, printing color number can reach 4 to 10 color group. At the same time, special inks such as gold ink and silver ink can also be printed.

4. More suitable for long-run printing in large quantities. The pre-printed plates are all made of steel chrome-plated electrogravure. The number of prints resistant to printing is 3 million to 4 million, which reduces the time for changing plates and is particularly suitable for long-lived large-volume printing.

5. The corrugated boxes produced are stronger. Since preprinted corrugated cartons are produced on the production line, there is a certain amount of heat-forming time during production, and the final production of corrugated cartons is high in strength. And can avoid the veneer machine produced when the coating uneven, cardboard cramp, cardboard warping and so on.

Carton preprinted production equipment and process

The main equipment used for carton preprinting is a large-sized unit gravure printing press. Its auxiliary equipment is a computer controlled cross cut and slitting of a corrugated paper production line. The pre-printed face paper is placed on the noodle station of the corrugated board line, and after sizing, veneering, flattening, drying, cutting and other processes, the colored cardboard is finally made, and the post-passage is obtained through die-cutting, sticking, and the like. The production process completes the production of the carton.

Carton preprinting requirements for corrugated cardboard lines. The important configuration of the gravure printing carton preprinting production line is the computer cross-cutting on the corrugated board production line, that is, the crosscutting control function must be installed on the cross cutting knife of the corrugated board production line. Its main control principle is to identify the cross-cut mark on the printed pattern of the corrugated cardboard by photoelectric eyes, transmit the timing of the cross-cut mark to the photoelectric eye to the control computer, and then control the cross-cutting time by the control computer, thereby demarcating the pattern. Accurately cut corrugated cardboard. At present, China's current production of corrugated board production lines can be installed according to customer requirements computer cross-cutting device, cross-cutting accuracy can be controlled within 0.5mm. The same principle applies to computer slitting and computer crosscutting.

Ink and Varnish. The ink used in the preprinted gravure printing machine is mainly based on alcohol-soluble inks or water-based paper-specific gravure inks.

The preprinted paper is subjected to flattening and drying processes on the corrugated paper production line. Therefore, the ink used requires high temperature resistance and good rubbing resistance, otherwise the colored surface may be pulled or ink dragging occurs. At present, the "Tianshi" brand ink produced by the Tianjin Toyo Ink Factory can meet the requirements for waterborne paper gravure printing. Its low cost and no pollution, in line with national environmental protection requirements. The gravure carton preprinted inks produced by Shanxi Essence Industry & Trade Co., Ltd. are based on cellulose. The main solvents are alcohols and esters. Compared with water-based ink and offset ink, this ink has bright color, high gloss and abrasion resistance, high temperature resistance of 180°C~250°C, good printing adaptability, clear printing patterns, delicate color, etc. The product surface has excellent adhesion. Some of China's glazing oil manufacturers use high-temperature varnish from Cprecision In & Technology of the United States. Some domestic brands have also been widely adopted, and the effect is also very good.

Plate: The preprinted plate is made of steel chrome-plated electric gravure, and the number of gravure screens can reach more than 300 lines. It can be completely suitable for printing on the ground and continuously adjusted dot printing. Only the gravure printed by the paper is deeper than the gravure printed by the general plastic during the carving. The price of gravure platemaking has dropped from 0.7 yuan/cm2 to about 0.35 yuan/cm2, which is close to the flexographic version. The gravure print is 3 to 4 times the flexo, up to 3 million to 4 million prints. The glazing roller can use a fixed number of cable rollers and uses a shaftless drive. At present, there are many domestic plate-making manufacturers, such as the electric carving plates produced by the manufacturers such as Haicheng, Nanban, and Sanmenxia Lanxue, which have reached the international advanced level.

Paper: Intaglio preprinted substrates must use coated white paper with good surface smoothness, strong printability, and stable moisture content (6% to 7%). Imported coated cattle card and domestic gray board can meet the high-end color corrugated cardboard paper distribution requirements. Finland M-REAL Forestry Co., Ltd. is famous for producing coated paper with high hygiene standards. 185g/m2 of coated paper has been widely used in domestic preprinting machines. The quantitative range of paper is 150~350g/m2. U.S. Mead Paper has been using 500g/m2 wood pulp to coat cowskin gravure printing cartons and canned beer cartons, which are stronger than corrugated boxes.

Problems and Solutions

The printing products of paper gravure printing machines include preprinted paper rolls such as decorative paper, bubble gum paper, beer and beverage boxes, cigarette cases, medicine boxes, milk boxes, and fruit boxes, household appliances, and daily necessities. The features are exquisite design, colorful colors, and large demand. The following solutions are available for reference for some common problems in the application of current gravure printers.

Wrinkling: High gram preprinted paper roll tension is approximately 50 kg, which is more difficult to control than film (10 kg) and thin paper (25 kg). When the moisture is uneven and the thickness is not uniform, greater tension changes will cause the paper to swing laterally, forming a crease on the printed surface. The addition of a preheating device to the paper gravure press helps to reduce the change in tension caused by loss of water (when the moisture content is too low, install a humidifier): If you add a misalignment flattening roller, it will help to flatten the roll as it moves. Wobble reduction.

Ink draw: In addition to the above-mentioned temperature-resistant ink and varnish, the latest air-cushion heating plate heat conduction control system can reduce the heating temperature and stress strength of the cardboard through the hot end. The process is that an air spray channel is arranged at the gap between the heating plate and the cardboard, and air can be sprayed in an instant to form a gas film to hold the cardboard, so as to avoid defects such as scratches, inks and the like caused by overheated pressure of the cardboard.

Lu Bai: Mainly due to dust on the surface of the paper roll and blocked by ink. In the field printing group, dust and explosion-proof electrostatic ink-absorbing devices are separately installed to blow air and dust to improve the ink-in effect and reduce the dot-loss phenomenon.

Spiral rewinding: Preprinted gravure printing presses should use a closed-loop control system to ensure tension taper control.

Incomplete edges: The edges of the cross section are not uniform, and the backup roller (receiving rubber roller) can be added to remove air from the paper roll and eliminate static electricity on the surface. When the paper roll receives the material, the roller device is tightened to reduce the edge swing.

The installation of a PLC correction device also helps to alleviate the problem of uneven edges. Another solution to the problem of missing edges is offline rewind.

Roll overlap: If the roll is improperly overlapped during printing, it will cause downtime and affect the consistency of the printed product. Zero-butt connection can be used to pick up the paper without interrupting the printing process.

Conclusion