Summary of current corrugated box packaging printing methods
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The color of corrugated carton packaging is now more and more vivid and eye-catching, because corrugated carton packaging has a new task - to display goods and promote sales. In large supermarkets, beautifully printed colored cartons are more attractive to customers, attracting customers' interests and stimulating purchase desires. This requires that the corrugated box not only has the function of transport packaging, but also has excellent surface printing quality.
In order to safely transport items packed in folding cartons or items packed in plastic bags (such as liquid milk) to the point of sale, they are usually packaged in corrugated boxes. The reason for choosing corrugated boxes is that they are solid with the same weight. Compared to cardboard, corrugated cardboard is more resistant to impact and better protects the contents from impact damage. However, you may notice a considerable contradiction, that is, a beautifully printed, sales-promoting folding carton or liquid milk pouch wrapped in a box that has not been printed or printed with some simple text, if not Open the box and leave it at the point of sale, so no matter how attractive the folding carton or liquid milk bag is, the print is so beautiful and unattractive. In this case, the design of the corrugated carton packaging is extremely important. This is why more and more corrugated boxes are now printed. At present, the printing of corrugated cardboard in China is divided into: offset printing and bonding into cardboard, flexographic direct printing, pre-printing and several special printing and boxing methods.
The main methods and characteristics of carton production at home and abroad
1.1 Offset printing indirect corrugated box
The process of offset printing indirect printing carton is: single-faced corrugated cardboard (single sheet), ten offset printing, color printing paper (single sheet), bonding to cardboard, die-cutting, slotting, bonding nail box
This method uses offset printing of corrugated boxboard paper and then uses a single machine to retanning corrugated sheets. It can print beautifully designed cartons and improve the printing quality of carton products. At present, most of the high-grade corrugated boxes used in China for sales packaging are offset products.
a. Offset printing Corrugated box has the following advantages: 1 The printing product is very fine, and the number of screen lines can reach 200 lines/inch. 2 plate making is easy, for the PS plate conventional plate making 3 can be surface finishing, such as film, glazing and so on. Printing quality is relatively stable.
b. Offset printing corrugated carton has the following deficiencies: 1 It is not suitable for the use of cardboard linkage production line, only suitable for single-face corrugating machine, and the production efficiency is low. 2 The production process is complicated and the production cycle is long. 3 The carton has low strength, high scrap rate and high production cost. 4 The production site is large and the labor intensity is high. 5 printing format is limited; delivery time is not flexible enough.
From the above analysis, it can be seen that offset printing indirect printing cartons are economically uneconomical for a company. Especially for the production of large-scale carton and the export of packaging carton, due to high production cost, low efficiency, long cycle, and can not meet the needs of production.
1.2 Flexographic printing corrugated box
The process of flexo printing box production is as follows: corrugated board production, direct printing of cardboard (flexible version), die-cutting and slotting, bonding nail box
The conventional flexographic printing corrugated box process is directly printed on corrugated cardboard, using water-based inks, and is currently widely used in carton factories in China.
a. Flexographic direct printing has the following advantages: 1 large, wide flexographic printing press with a maximum width of up to 2.5 to 2.8 m. 2 The price is low, the flexo printing plate has high printing durability and can be reused; the ink price is also low. 3 can be linked to production, such as printing, grooving, indentation, binding (sticking) boxes, bundling and other machines can be completed. 4 carton strength reduction is relatively small. Since flexo printing is light press printing, the effect on the strength of corrugated board is small.
b. Flexographic printing of corrugated cardboard directly, although the printing quality is higher and the efficiency is higher, there are three difficulties in printing the pattern comparable to offset printing:
1 corrugated board is difficult to maintain stable during high-speed printing, resulting in excellent overprint accuracy of four colors or more. In multi-color overprinting, when the carton printing press cannot guarantee sufficient multi-color overprinting accuracy, carton printing cannot meet higher requirements.
2 control of printing pressure. Unlike other printing methods, flexographic printing transfers ink to paper by means of flexible dots. Due to the rough surface characteristics of the corrugated board, it is difficult for the printing machine to keep the stability of the paperboard, and the fine dots can be attached to the rough corrugated paper surface with the best printing pressure to achieve the minimum dot spread. possible. This makes most of the current direct printing carton printing quality in the middle and low-end state, can only deal with the printing of the field, lines and simple patterns, which greatly reduces the printing quality of the carton.
3 printing accuracy is not high, the number of conventional offset printing network lines is 175 lines / inch, and the number of conventional screen printing lines of flexo printing boxes is only 35 ~ 75 lines / inch, which is a low-precision printing method, most suitable for printing text lines, four-color image printing Although quality has improved in recent years, it still has limitations.
1.3 pre-printed corrugated boxes
Pre-printing, including two printing methods: gravure pre-printing, flexo pre-printing. The method of producing a color corrugated box by gravure printing is to use a gravure printing machine to print on a web, and after receiving the printing, it is still collected into a web, and then the printed web is used as a corrugated paper production line on the carton paper. The corrugated cardboard box is cut into a box shape by a die cutter. The method of producing a color corrugated box by flexo preprinting is to print on a web using a flexographic printing machine, and still receive the web after printing, and then use the printed web as a corrugated paper production line on the carton paper. Make a corrugated cardboard box and cut it into a box shape with a die-cutting machine. The carton made by these two methods has high printing quality and molding quality, and is suitable for high quality and mass production.
The process of flexo printing box production is: web pre-printed paper (gravure, flexo) Ten corrugated composite bonding produced by the production line Computer slitting Computer crosscutting Die-cutting slotting Bonding nail box
(1) Pre-printing conditions are already available
a. Pre-printing requirements for paper and ink
Pre-printing has special requirements on paper. The printed surface of coated white paper has good color expression, but in the process of bonding through corrugated high-temperature drying tunnel, the coating will have different degrees of change, which directly affects the color surface pattern effect. It is not the most suitable paper; although it can meet the requirements of the corrugated high-temperature drying process, it has a rough surface, which causes the printing pattern to lose dots, false, poor display, and large ink consumption. It is also not the most ideal preprinted paper. Practice has proved that a good pre-printing paper should be white cardboard, which can fully demonstrate the color of the printed pattern and withstand the test of the corrugated high-temperature drying process.
Printing is inseparable from ink. Pre-printing has special requirements on the heat resistance and rubbing resistance of ink. When the pre-printed facial paper is flattened on the corrugated paper production line and passed through the drying tunnel section, the required ink is resistant to high temperature and resistance. Good grinding, otherwise the color surface will be pulled, and the ink will become waste. Pre-printed inks have mature experience in foreign countries, but they are still blank in China in recent years. In recent years, Tianjin Toyo Ink Co., Ltd. has developed pre-printed water-based gravure inks and preprinted water-based flexographic plates that can meet the requirements of corrugated paper production lines. Ink and varnish. It can be used for gravure pre-printing and flexo pre-printing respectively. The cost of ink is similar to that of offset printing. Pre-printing ink is mainly based on water-based ink. Water-based inks are favored by people for their non-toxic, odorless, easy to operate, and environmentally friendly. With the advent of “green food and green products”, “green packaging and green printing materials” will inevitably be required. The water-based ink of Tianjin Toyo Ink Co., Ltd. is a non-toxic ink approved by the American Food and Drug Association. With this ink, it can print beverage boxes, food boxes, medicine boxes, export boxes and other internationally accepted green carton products.
b. Equipment required for pre-printing
The equipment currently used for gravure preprinting is mainly web gravure printing machine. This type of machine is classified according to the arrangement of roller parts. There are mainly two types of machines: satellite gravure printing machine and unit gravure printing machine. Among the two models, the unit gravure printing machine has a more reasonable layout and a higher technical level. It is the standard model of the current web gravure printing machine. There are also many manufacturers in China that manufacture such equipment, such as Zhongshan Jiangnan Packaging Machinery Factory and Xi'an Aerospace Huayang Printing and Packaging Company.
Flexo Preprinting The equipment currently used is mainly roll-to-roll flexo presses. It is mainly available in three models: satellite flexo presses, unit-type flexo presses, and cascading flexo presses. Among the three models, the satellite flexo printing machine can meet the requirements of width and repeat length, and the central imprinting cylinder constant temperature can ensure the stability of the substrate shrinkage and is reasonable. The roll-to-roll wide-format flexographic printing equipment currently used in China mainly relies on imports.
c. Auxiliary equipment required for pre-printing
Pre-printing must first print the pattern, then the corrugated paper production line for corrugated composite bonding, and then cut, in this case, we must consider the pattern factor. The previous corrugated paper production line computer cross-cutting is mostly fixed length and cross-cut, so it must be horizontal The photoelectric tracking and cross-cutting control system is installed on the cutter. The main control mechanism is to identify the cross-cut mark on the printed pattern of the corrugated board by the photoelectric eye, and transmit the time when the cross-cut mark reaches the photoelectric eye to the control computer, and then the control computer The cutting time of the cross cutter is controlled to achieve accurate cutting of the corrugated cardboard at the boundary of the pattern.
At present, domestic and foreign cross-cutting machine manufacturers can easily add this function. The crosscutting accuracy can be controlled within 1mm. Computer slitting and computer crosscutting are the same principle.
Gravure products have the characteristics of bright colors and high gloss. Gravure has unique advantages in printing high-grade packaging. This type of pre-printing is increasingly favored by people.
(2) Features of gravure preprinting
a. The advantages of gravure preprinting
1 color printing carton produced by gravure printing can obtain high quality and green ink printing
The amount of ink on the gravure printing is larger than other printing methods, the ink color of the gravure printing is full, the ink layer is thick, and the three-dimensional feeling is strong; the color is colorful, the layer is rich, and the definition is high. Among various printing methods, the printing quality is the best and the printing quality is stable. The tension control system of the gravure printing machine controls the stable operation of the machine, and the automatic color registration control system can ensure the overprinting precision reaches ± 0.1 mm. The gravure printing is fully dried after each color printing, and the printed product is firmer. Under normal gravure printing, the number of printed mesh lines can reach 200L/in. Even with the paper with high surface smoothness, gravure printing can achieve high printing quality. The printing uses pre-printed water-based gravure ink, which is non-toxic and non-polluting, and meets environmental protection requirements. At present, domestically produced gravure papers and inks are relatively mature, and can withstand the requirements of 200 ° C high temperature and hot plate friction on corrugated paper production lines. Gravure printing can also be done in one print and varnish.
2 gravure preprinted printing plate with high printing durability, suitable for large-volume printing production requirements of carton
Since the gravure plate is a steel chrome plated gravure plate, the entire plate is protected by a hard layer of metal chrome, so even if there is a constant contact between the blade and the plate during printing, the printing resistance is still high. 3 to 4 million impressions, suitable for high-quality, high-volume printing production requirements for cartons.
3 gravure preprinting for continuous printing of continuous patterns
Offset printing encloses a finished plate on a plate cylinder. Therefore, there is always an area on the surface of the plate for fixing the plate. The gravure plate is different. Since the plate-making operation of the gravure plate is performed directly on the drum cylinder, as long as the images on the drum are seamlessly spliced, a continuous stretch pattern can be obtained on the substrate.
4 corrugated boxes produced by gravure preprinting have higher strength
Because the pre-printed corrugated box is completed on the production line, there is a certain heating and forming time when making the corrugated board, so the corrugated box obtained by the conventional method of using the veneer is stronger, and the direct printing to the carton can be avoided. Injury caused by strength, improve and improve the strength and stamping strength of corrugated boxes.
5 gravure preprint printing speed, high production efficiency
Because the pre-printing method is printed by a web gravure printing machine, after each color printing, there is a drying device, which does not require dusting, and can enter the next process, and the printing speed can reach 150 m/min. In the high-speed gravure printing process, a roll of material can be printed in a short period of time, and the replacement of the coil material by the non-stop automatic roll changing device can greatly improve the printing efficiency. After printing, the upper corrugated paper production line is made of corrugated cardboard, which is much faster than the traditional veneer.
b. Insufficient gravure preprint:
The gravure printing plate is complicated, the cycle of making a pair of steel chrome-plated electric gravure cylinders is generally 5 to 10 days, and the price is higher, which is 8 to 10 times that of the flexo printing; the gravure printing technology is more complicated and the process is relatively more The investment in the entire production line is relatively large.
(3) Features of flexo preprinting
a. Advantages of flexo preprinting:
1 Non-toxic, non-polluting, and conducive to environmental protection, is a green printing method, which has great advantages in the printing of green cartons such as food boxes and medicine boxes.
2 can print large-format multi-color, high-quality color boxes. Foreign web flexo presses can be up to 1.8 meters in width and satellite-type flexographic printing units can be made in 6 colors. Can print wide format, multi-color, high quality, high precision color carton
3 low cost. The low cost of flexo printing has formed a broad consensus in foreign countries, and there are different opinions in China. Mainly because most of the flexo printing machines and flexographic printing plates used in China are imported, the cost is high. Offset and gravure are relatively low cost in this regard. With the flexo printing equipment and its plates and local production in China, the cost will gradually decrease.
4 It is printed by different network lines, the print pattern is fine, and the print consistency is strong. It can be used in 100L/in, 133L/in, and 175L/in. The dots are delicate and the colors are dazzling.
5 Re-bonding the face paper and corrugation on the corrugated paper production line can improve and improve the strength and stamping strength of the corrugated box.
6 printing speed, high output. The speed of the satellite flexo press is generally 250 to 300 m / min, which can meet the needs of multiple automatic corrugated production lines.
7 The range of printing materials is wide, and paper can be printed from 80 to 400g/m2.
b. Insufficient flexo preprinting
1 For the meta-draft in the plate-making process, the highlights of the pattern, the dots are obviously polarized, or the small dots (the dots below 8%) have been lost during the printing, and become the net; or the dot gain rate Big, become a network point that is close to the middle tone. In the dark adjustment part, the outlets will be leveled at about 85% and will be in the field. It can be seen that the flexographic printing can use the amplitude modulation dot to replicate the tone range of the tone copy, which is about 8% to 85%. That is to say, when printing more than 85% of the area, due to the increase of the dot, a level phenomenon will occur, so that the dark area is dead and no layer; when printing the area below 8%, it is difficult to print on the plate because the dot is too small. "Stand up". Less than 8% of the dots in the design are not shown in the actual printing process. Therefore, some rich manuscripts are difficult to present in a flexible version of their rich layers and colors.
2 From the number of printing screens, the highest number of offset and gravure lines are higher than flexo. The ideal number of screen lines for flexo printing is generally below 150L/in, and over 175L/in, it will increase the difficulty of flexographic plate making, and will also shorten the service life of the plate.
3 It is not advisable to use thin lines and too small text. Since the flexographic plate is deformed during the printing process, too thin lines and characters are easily deformed. If it is a small anti-white or anti-white line, because the relief is shallow, it is easy to cause a dead phenomenon. So try to use a thicker line, the decorative line and the main line color contrast is larger.
It can be seen from the above analysis that pre-printing is an ideal way to produce corrugated boxes in high quality and in large quantities.
2. Several special printing methods
2.1 plastic gravure composite carton process
When the single-face corrugated production line is used, if the glossy film is required to be coated after the printing of the facial paper is completed, and the production batch is large, the printing on the surface paper can be omitted, and the gravure printing is performed on the plastic film by the gravure printing method. Apply the white base, then combine the printed plastic film with the facial tissue, and then complete the box according to the conventional carton forming process.
The characteristics of this process are:
1 carton production costs are low. When the production batch size is large, such a process can greatly reduce the printing cost of the face paper and the material cost of the face paper. Since the face paper does not need to be printed, non-coated whiteboard paper can be used, so that the cost of the face paper is greatly reduced.
2 beautifully printed. Because the plastic gravure is used, the printing effect is comparable to the offset printing effect. Special attention should be paid to the use of this process. In the process of plate making, the dimensional change and deformation of the plastic film should be fully considered. Otherwise, the carton paper will be misaligned with the lower paperboard.
2.2 coated paper gravure composite carton process
This process can be used when the production batch size is relatively large, no film is required, and the printing effect is good and the cost is low. The process is to first print a thin (60-90g/m2) coated paper with a paper gravure printing machine, and then combine the beautifully printed coated paper with ordinary slag paper or cardboard paper, and use it as a carton paper as a whole. For sputum and normal carton forming processing.
The characteristics of this process are:
1 carton production costs are low. The main reason for the cost reduction is to convert the whiteboard paper into a low-weight coated paper and a cheap cardboard paper, which reduces the material cost.
2 beautifully printed. The printing of paper gravure is very beautiful.
3 Gravure plate making is more complicated and costly, and is not suitable for printing carton products that are often revised.
4 The printing plant's operation and control methods for the process of paper composite, box making, etc. should be carefully explored, accumulating and rationally implemented, otherwise it will easily lead to an increase in scrap rate.
2.3 Direct offset corrugated box process
The corrugated carton direct offset printing process is now relatively mature abroad. It is to directly print corrugated cardboard onto a special offset printing machine, which is suitable for processing thin corrugated boxes.
The process not only ensures the formability of the carton, but also completes the exquisite paper printing, but the printing machine used is relatively expensive. In the next few years, this process may become a new development direction for high-end carton printing in China.
2.4 Screen printing corrugated box
The screen printing corrugated box process uses direct printing. Since the ink-injection rate of the screen plate is proportional to the pitch of the screen, the resolution of the screen printing is not high, and the image accuracy is low, and the conventional screen line number is 60 to 80 lines/inch.
Screen printing corrugated boxes have the following advantages:
1 printing format can be large or small.
2 It can be printed before the box is placed, or it can be printed after the box is placed.
3 Screen printing ink is thick, its color saturation is high, and the visual effect is strong, especially in the field of spot color printing, the effect is better.
4 plate making is easy, and the plate making cost is low.
5 printing costs are low.
6 printing quality is relatively stable. The disadvantage of screen printing corrugated boxes is that they are not suitable for linkage production lines and have low production efficiency.
3. Conclusion
It can be seen from the above analysis that there are many methods for carton printing, each of which has its advantages and disadvantages, and it is necessary to select a suitable printing method according to the characteristics of the produced carton. Especially for high-quality, high-volume corrugated boxes, pre-printing is undoubtedly the best way.