Preprinting of gravure printing carton is to pre-print the corrugated cardboard box with corrugated paperboard before printing it into corrugated paperboard to print the desired pattern on the wide web (paper box). The paper is then made into a corrugated boxboard from the corrugated board production line and then die-cut by the die-cutting machine into a box type.
At present, 30% of the total output of corrugated cartons in some developed countries such as Europe and the United States adopts preprinted new technologies. With the rapid development of the paper packaging industry in China, in recent years, many manufacturers such as Mengniu, Budweiser and Tsingtao Brewery have Focus on pre-printing 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.
First, the difference between paper preprinting and lithographic offset printing production carton
At present, the vast majority of domestic color cartons use the pre-printing method for sheet-fed offset printing. The process flow is: cutting webs into sheet-fed papers → offset-printing machine printing single-faced papers → simultaneous one-side machine roll-making Corrugated cardboard → face paper and single-faced corrugated cardboard on the veneer back or veneer veneer → die-cutting indentation molding → nail box / adhesive box.
The technological process of the web gravure printing preprinting technology is: gravure printing machine printing surface layer paper roll → cardboard line production cut into three (or five) cardboard → die-cutting indentation molding → nail box/glue box.
Why do you need 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, which is close to or even lower than that of flexographic plates. Moreover, the domestic Shaanxi Beiren has produced a high-speed wide-format paper concave machine, the price is only one-third of the imported flexographic printing press, and the gravure pre-printing method may be more suitable for the actual situation of packaging companies in China.
In comparison, people often refer to the commonly used printing process as “post-printingâ€. Pre-printing has some obvious advantages over post-printing:
1, can obtain higher printing quality, more adaptable. The pre-printing is performed on a smooth paper surface using a gravure printing machine or a flexographic printing plate. Compared with the printing after printing using a printing slotting machine to print on uneven paperboard surfaces, it is possible to perform fine color printing with richer layers and brighter colors. Printing quality will also be more stable and reliable.
2. It can make the corrugated board obtain the highest strength. Because the pre-printing does not need to impress the board after it is formed, it can avoid the deformation of the corrugated board and the strength of the board. 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).
Second, the use of gravure printing carton preprinted this production method features
1, high production efficiency. Gravure printing web printing speeds up to 150-200 m/min, basically matching many corrugated board production lines in China, shorter than traditional flat-sheet offset printing and veneer lapping, low labor cost and high efficiency.
2. The color carton produced by gravure preprinting can get high quality ink prints. Due to the high accuracy of gravure printing, it is not more than 0.2mm. The gravure printing can also be completed by printing and varnishing once, and the printed wire after general gravure printing Up to 300 lines, gravure printing ink than other printing methods, up to 4.5-6g/m2, India ink full, soft, bright, solid, and gravure printing after each color has a full drying system, 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 can be performed. The maximum size of traditional color offset printing is generally up to 1.2m×0.9m (encyclopedia), and most of them are four-color printing. The maximum printing material width of the gravure printing machine for carton preprinting is 2.5 meters (Shaanxi Beiren Printing Machine Co., Ltd.) At present, it has produced a variety of preprinting machines, including 1300mm, 1650mm, 1800mm, 2000mm, 2200mm, and 2500mm, and it runs well. The number of printing colors can reach 4-10 color groups, and gold ink, silver ink, etc. can also be produced. Special ink printing.
4, more suitable for large-scale long-run printing. The preprinted plates are all made of steel chrome-plated electrogravure. The number of prints resistant to printing is 3 million to 4 million times, which reduces the time for changing plates and is particularly suitable for printing long lived prints.
5. The strength of the corrugated boxes produced is higher. Since preprinted corrugated cartons are produced on the production line, there is a certain amount of heat-forming time during the production, and the final production of corrugated cartons is high in strength and can avoid uneven coating and carton creases when the laminator is produced. , cardboard warping and so on.
Third, the carton preprinted production equipment and technology
1. The main equipment used for the preprinting of cartons is a large-sized group-type 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.
2. Carton pre-printing requirements for corrugated cardboard lines.
The important configuration of the gravure printing carton preprinting production line is the computer cross cutting of the corrugated cardboard production line, that is, a 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 corrugated cardboard by the photoelectric eyes. The cross-cut logo on the printed pattern transmits the time when the cross-cut mark reaches the photo-electric eye to the control computer, and then the control computer controls the cross-cutting time, thereby accurately cutting the corrugated cardboard at the border of the pattern. At present, cross-cutting machine manufacturers at home and abroad can install this function for the carton factory, and the cross-cutting accuracy can be controlled within 0.5mm. At present, China's current production of corrugated board production lines can be installed according to customer requirements computer cross-cutting device.
3, the choice of 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.
When preprinted paper is subjected to flattening and drying processes on a corrugated paper production line, the ink used requires high temperature and abrasion resistance, otherwise the colored surface will be pulled or dragged. At present, the "Tianshi" brand ink produced by the Tianjin Toyo Ink Factory can meet the requirements of water-based paper gravure printing. The cost is low, no pollution and meets the 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 inks and offset inks, this kind of ink has bright color, high gloss and abrasion resistance, and is resistant to 180°C. -250°C high temperature, good printing adaptability, clear printing pattern, delicate color, etc., and excellent adhesion to most printing surfaces. Some of China's glazing oil manufacturers use high-temperature light oil from the US company Cprecision & InTechnology. Some domestic brands have also been widely used, and the effect is also very good.
4, the choice of printing plate.
The preprinted plate is made of steel chrome-plated electric gravure, and the number of gravure lines can reach more than 300 lines. It can be completely suitable for dot-printing and dot-tone printing of the ground printing and tone transition, but the gravure of paper printing is more intaglio than the general plastic printing. During carving, the deeper of the cave carvings, the price of the gravure plate has dropped from 0.7 yuan/cm2 to about 0.35 yuan/cm2, which is close to the flexographic version, and the gravure printing is 3-4 times that of the flexographic plate, up to 300 Million - 4 million printing, glazing roller can use a fixed number of wire roller, using a shaftless drive.
At present, there are more domestic plate-making manufacturers, such as the electric engravings produced by the shipping companies, the Southern platemaking industry and Sanmenxia Blue Snow, etc., which have reached the international advanced level.
5, the choice of paper.
Gravure preprinted printing materials must use coated white paper with good surface smoothness, strong printing adaptability, and stable moisture content (6%-7%). Imported coated cattle card and domestic gray board can meet the high-end color corrugated cardboard paper distribution requirements. Finland's M-REAL Forestry Company is world-renowned for producing coated paper with high hygiene standards. 185g of coated paper has been widely used in domestic preprinting machines. The paper's quantitative range is 150g-350g/m2, and the US Mead Paper Industry has been using it. 500 grams of raw wood pulp coated bovine card gravure printing cartons and canned beer cartons are stronger than corrugated cartons.
Fourth, common problems and solutions
The common problems in carton pre-printing are as follows: The solutions are as follows:
1. Wrinkle: Pre-printed paper roll tension of high gram weight is about 50kg, which is more difficult to control than film (10kg) and thin paper (25kg). When the moisture is uneven and the thickness is not uniform, greater tension changes will cause the paper to transverse Swing to form a wrinkle on the printed surface. The preheating device of the paper concave machine can help reduce the tension change caused by moisture loss (when the moisture content is too low, install the humidifier); if you add a flattening roller, you can help the paper roll as far as possible The swing is reduced.
2. 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.
3, Lubai: mainly due to the surface of the paper roll dust and ink blocked version, in the field printing group installed dust and explosion-proof electrostatic suction device can be blown dust, improve the ink effect, reduce network loss.
4, spiral type winding: prepress gravure printing press should use a closed-loop control system to ensure the tension and taper tension control.
5, uneven edges: cross-cutting edges, can increase the pressure roller (receiving rubber roller), the air out of the paper roll, eliminate the static surface, take up the roll when the roller closes the device, reduce Edge swing.
The installation of a PLC correction device also helps to alleviate uneven edges. Another solution to the problem of missing edges is offline rewinding.
6. Paper lap: If the paper roll is improperly lapped in the printing process, 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.
Reprinted from:Gaogong Machine Grid
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