Preliminary study on the new pre printing process

2022-08-22
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Preliminary study on the new process of carton preprint

intaglio printing carton preprint is to use intaglio printing technology to pre print the required exquisite patterns on the wide web paper (carton face paper) before making the corrugated cardboard, and then make the corrugated cardboard production line on the web printed face paper into the corrugated carton board, and then use the die-cutting machine to cut and indentation into the carton shape

at present, 30% of the total output of corrugated boxes in some developed countries, such as Europe and the United States, have adopted the new pre printing technology. With the rapid development of China's paper product packaging industry, in recent years, many carton factories with stable customers, such as Mengniu, Budweiser, Tsingtao beer, have turned their attention to the new pre printing technology. With the stability of the packaging of products such as beverages, beer, household appliances and food in the design and consumption of corrugated boxes, Using web preprint to produce high-grade color corrugated boxes will become the trend of the future packaging industry

● web preprint is better than flat sheet offset preprint

at present, the vast majority of domestic color cartons adopt the flat sheet offset preprint method, and its process flow is: cut the web into single sheets → offset printing machine prints single sheets of face paper → at the same time, single-sided machine rolls two layers of corrugated board → face paper and single-sided corrugated board are mounted on the veneer or veneered on the veneer machine → die cutting indentation molding → nailing box/gluing box; The technological process of web gravure printing preprint technology is: gravure printing machine printing surface layer paper roll → cardboard production line cutting into three (or five) layers of cardboard → die cutting and indentation molding → nailing box/gluing box

so why do you need gravure preprint? There are two main reasons. First, gravure printing can easily provide high-quality color prints. Weng Yunxuan, Secretary General of the degradable plastics special committee of China Plastics Association, introduced it; Second, the electronic engraving technology has greatly reduced the production cycle and cost of the metal plate roller, which is close to or even lower than that of the flexo plate. Moreover, the domestic northerners of Shaanxi have produced high-speed wide width paper concave machines, and the price is only one third of that of imported flexographic printing machines. The use of intaglio pre printing may be more suitable for the reality of China's packaging enterprises

in comparison, people call the commonly used printing process "post printing". Compared with post printing, pre printing has some obvious advantages:

-- higher printing quality and wider adaptability can be obtained. The pre printing adopts the gravure printing machine or flexo printing on the smooth paper surface. Compared with the post printing, which adopts the printing slotting machine to print on the uneven cardboard surface, it can carry out the exquisite color printing with richer layers and brighter colors, and the printing quality will be more stable and reliable

-- it can obtain the highest strength of corrugated cardboard. Because pre printing does not need to imprint the cardboard after it is formed, it can avoid corrugating deformation and weakening of cardboard strength. After using corrugated board printing slotting machine for printing, each color printing will cause more or less deformation of corrugated board, and the more the number of colors, the greater the influence on the deformation of corrugated board

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

compared with the traditional color offset printing, the production method of intaglio printing carton preprint has the following remarkable characteristics:

-- high production efficiency. The printing speed of gravure printing web paper is up to m/min, which basically matches many domestic corrugated board production lines. Compared with the offset printing and veneer tiling of traditional flat paper, it has shorter processes, lower labor cost and higher efficiency

-- the color cartons produced by intaglio printing pre printing can get high-quality ink and water prints. Due to the high overprint accuracy of intaglio printing, which is no more than 0.2mm, intaglio printing can also complete printing and varnish coating at one time. Generally, the printing line after intaglio printing can reach 300 lines, and the inking volume of intaglio printing is larger than that of other printing methods, up to 4 G/m2, the ink color of the print is full, soft, bright and firm, and after gravure printing (3) place the test piece in the center of the ball shaped support plate of the movable table of the experimental machine, and there is a sufficient drying system for each color. Therefore, on the premise of selecting paper with high surface smoothness for printing, gravure printing can obtain high ink printing quality. Most cigarette packs are made by intaglio printing on paper. At present, the domestic paper gravure printing ink has been relatively mature, and the domestic water-based paper gravure printing ink that can meet the pre printing of corrugated board line has been manufactured, which can fully meet the friction between 180 ℃ high temperature and hot plate on the corrugated board production line

-- large scale multicolor color printing can be carried out. The maximum format of traditional color offset printing can generally reach 1.2 × 0.9m (full size sheet) and mostly four-color printing. The maximum width of the printing material of the unit gravure printing machine used for carton pre printing is 2.5m. (Shaanxi beiren printing machine company has produced various specifications of pre printing machines 1300mm, 1650mm, 1800mm, 2000mm, 2200mm, 2500mm and they are in good operation). The number of printing colors can reach the color group, and it can also print gold ink, silver ink and other special inks

-- it is more suitable for large-scale long edition printing. The pre printing plates are made of steel chrome plated engraving intaglio plates, with a printing resistance of 10000 printing times, which reduces the time of changing plates, and is especially suitable for large quantities of long plate printing

-- the corrugated box produced has higher strength. Because the production of corrugated boxes for pre printing is completed on the production line, there is a certain heating and forming time during the production, the final corrugated boxes have high strength, and can avoid the uneven gelatinization, carton reinforcement, cardboard warping and other phenomena produced during the production of veneering machine

● production equipment and process of carton pre printing

-- the main equipment used for carton pre printing is a large unit gravure printing machine, and its auxiliary equipment is corrugated paper production line computer-controlled cross cutting and longitudinal cutting. The pre printed face paper is loaded on the noodle station of the corrugated board line, and is finally made into color paperboard through the processes of sizing, veneering, flattening, drying, cutting, etc., and then the carton is made through the subsequent processing processes such as die cutting, gluing, etc

-- requirements of carton preprint on corrugated board line. The important configuration of the pre printing production line of intaglio printing carton is the computer crosscutting on the expensive corrugated board production line, that is, the identification crosscutting control function must be added to the crosscutting knife of the corrugated board production line. Its main control principle is that the photoelectric eye identifies the crosscutting mark on the printed pattern of corrugated board, transmits the time when the crosscutting mark reaches the photoelectric eye to the control computer, and then the control computer controls the crosscutting time, Thus, the corrugated board is accurately cut off at the boundary of the pattern. At present, cross cutting machine manufacturers at home and abroad can install this function for carton factories, and the cross cutting accuracy can be controlled within 0.5mm. At present, the corrugated board production lines currently produced in China can install computer cross cutting devices according to customer requirements

computer longitudinal cutting and computer transverse cutting are the same principle

-- ink and varnish: the inks used in the pre printed gravure printing machine are mainly alcohol soluble inks or special gravure printing inks for water-based paper

when the pre printed paper is pressed and dried on the corrugated paper production line, the ink used is required to have good high temperature resistance and friction resistance, otherwise the color surface will be scratched or dragged. At present, the "Tiens" brand ink produced by Tianjin Dongyang ink factory can meet the requirements of water-based paper gravure printing, with low cost and no pollution, and meets the national environmental protection requirements. The intaglio carton pre printing ink produced by essence industry and Trade Co., Ltd. is based on cellulose and the main solvents are alcohol and ester. Compared with water-based ink and offset printing ink, this ink has bright color, high gloss, abrasion resistance, high temperature resistance of 180 ℃ -250 ℃, good printing adaptability, clear printing patterns, delicate color performance, etc., and has excellent adhesion to most printing surfaces. Some domestic manufacturers of glazing oil adopt high-temperature glazing oil of American cprecision in technology company, and some domestic brands are also widely used, with good results

-- printing plate: the pre printed printing plate adopts steel chrome plated electric engraving intaglio, and the number of lines of the intaglio can reach more than 300 lines, which is completely suitable for field printing and point level printing of color transition. However, the intaglio printed on paper is deeper than the intaglio printed on general plastic during engraving. The price of intaglio plate making has been reduced from 0.7 yuan/cm2 to about 0.35 yuan/cm2, which is close to flexo, while the number of intaglio plates is times that of flexo, up to 10000 prints, The glazing roller can use a fixed number of line rollers, and adopts shaftless transmission. At present, there are many domestic plate making manufacturers, such as Shanghai Yuncheng, Nanfang plate making, Sanmenxia Lanxue and other manufacturers, whose electric engraving has reached the international advanced level

-- paper: the substrate of gravure pre printing must use coated white paper with good surface smoothness, strong printing adaptability and stable moisture content (6%-7%). The imported coated kraft linerboard and domestic gray bottom whiteboard can meet the paper matching requirements of high-grade color corrugated box face paper. Finnish M-real forestry company is famous for producing coated paper with high hygienic standards all over the world. 185g coated paper has been widely used in domestic prepress machines, and the quantitative range of paper is 150g-350g/m2. Mead paper industry in the United States has been using 500 grams of raw wood pulp to coat kraft linerboard gravure printing cartons and tinned beer portable cartons, with strength higher than corrugated cartons

● problems and solutions

the printing products of the paper concave machine include pre printed paper rolls such as decorative paper, bubble sugar paper, beer and beverage boxes, cigarette boxes, medicine boxes, milk boxes and fruit boxes, household appliances and daily necessities, which are characterized by exquisite design, bright colors and large demand. For some common problems in the application of paper concave machine, the following solutions are for reference

wrinkling: the tension of High-g pre printed paper roll is about 50kg, which is more difficult to control than film (10kg) and thin paper (25kg). When the moisture content is uneven and the thickness is uneven, greater tension changes will cause the paper to swing laterally, forming the wrinkle of the print surface. The installation of preheating device on the paper concave machine helps to reduce the tension change caused by moisture loss (if the moisture is too low, install the increase pair rising and falling buttons, if there is no humidifier); If the deflection adjusting and flattening roller is added, it will help the paper roll to flatten as much as possible and reduce the swing

ink embossing: 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 intensity when the paperboard passes through the hot end. The process is that an air spraying channel is set at the gap between the heating plate and the paperboard, which can spray air instantly to form an air film to hold up the paperboard, so as to avoid scratches, ink drawing and other defects caused by excessive heating and pressure of the paperboard

whitening: it is mainly caused by dust on the surface of the paper roll and ink blocking. Installing dust removal and explosion-proof electrostatic ink suction devices in the field printing group can respectively blow and dust, improve the inking effect, and reduce the phenomenon of point loss

spiral winding: the gravure printing machine for preprinting shall adopt a closed-loop control system to ensure the taper control of the winding tension

uneven edge trimming: if the section edge trimming is uneven, the standby pressure roller (receiving rubber roller) can be added to drive the air out of the paper roll, so as to eliminate the surface static electricity. When the paper roll is collected and pulled, it is close to the roller device to reduce the edge trimming swing

installing the PLC computer deviation correction device also helps to alleviate the uneven edge. Another way to solve the uneven edge is offline rewinding

paper roll lapping: improper paper roll lapping during the printing process will cause downtime and slow down, and affect the consistency of prints at the same time. Zero number docking can be used to connect paper without interrupting printing

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