The colors of corrugated carton packaging are now more and more eye-catching, this is because corrugated carton packaging has a new task-to display goods and promote sales. In large supermarkets, beautifully printed colored carton boxes can attract customers 'attention, raise customers' interest, and stimulate their desire to buy. 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 plastic bags (such as liquid milk) to the point of sale, they are usually packed in corrugated boxes. The reason for choosing corrugated boxes is that they are solid with the same weight Compared with cardboard, corrugated cardboard is more impact-resistant and can better protect the contents from impact damage. However, you may notice a considerable contradiction, that is, a beautifully printed, salesable folding carton or liquid milk packaging bag is wrapped in a carton that has not been printed or only printed with some simple text. Open the box and leave it at the point of sale, so no matter how attractive the folding carton or liquid milk packaging is, and how beautifully it is printed, it is also unattractive. On this occasion, the pattern design of corrugated carton packaging is extremely important. This is why more and more corrugated boxes are now printed with patterns. At present, the printing of corrugated cardboard in our country is divided into: offset printing and then bonding and bonding into cardboard, flexographic direct printing, pre-printing and several special printing box making methods.
The main methods and characteristics of carton production at home and abroad
1.1 Offset printing indirectly printing corrugated boxes
The process of offset printing indirect printing carton is as follows: single-sided corrugated cardboard (single sheet) ten offset printing color printing paper (single sheet) bonded to the cardboard die-cut slotted adhesive nail box
This method uses offset printing to print corrugated box face paper, and then use a single machine to mount the corrugated paper. It can print carton with exquisite patterns and improve the printing quality of carton products. At present, a considerable part of high-end corrugated carton used for sales and packaging in China is offset printing products.
a. Offset printing corrugated boxes have the following advantages: â‘ The printed products are very fine, and the number of screen lines can reach 200 lines / inch. â‘¡Easy plate making, regular plate making for PS plate â‘¢ Surface finishing, such as coating, glazing, etc. The printing quality is relatively stable.
b. Offset printing corrugated boxes have the following disadvantages: ①It is not suitable for the use of cardboard linkage production line, only suitable for single-sided corrugated machine, and the production efficiency is low. ②The production process is complicated and the production cycle is long. ③Carton has low strength, high scrap rate and high production cost. ④ Large production site and high labor intensity. ⑤ The printing area is limited; the delivery time is not flexible enough.
From the above analysis, it can be seen that offset printing of carton boxes is economically uneconomical for an enterprise. Especially for high-volume carton production and export packaging carton production, due to high production costs, low efficiency, long cycle, can not meet the needs of production.
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1.2 Flexible printing corrugated boxes
The production process of flexo printing carton is as follows: corrugated cardboard production cardboard direct printing (flexible version) die-cut slotted adhesive nail box
The conventional flexographic printing corrugated carton process is to print directly on corrugated cardboard, using water-based ink, which is currently widely used in carton factories in China.
a. The direct printing of flexographic printing plate has the following advantages: ①Large format, and the maximum width of flexographic printing machine with wide format can reach 2.5 ～ 2.8m. ②The price is low, the flexographic printing plate has high durability, and can be reused; the ink price is also low. ③Can be linked production, such as printing, slotting, creasing, ordering (sticking) boxes, bundling, etc. can be completed in one machine. ④ The carton strength is reduced less. Because flexo printing is light pressure printing, it has little effect on the strength of corrugated cardboard.
b. Flexo printing directly corrugated board, although the printing quality is higher and the efficiency is higher, but it is difficult to print a pattern comparable to offset printing in the following three aspects:
â‘ Corrugated cardboard is difficult to maintain stability during high-speed printing, resulting in excellent overprint accuracy of more than four colors. In multi-color overprinting, when the carton printing machine cannot guarantee sufficient multi-color overprinting accuracy, the carton printing cannot meet the higher requirements.
â‘¡Control of printing pressure. Unlike other printing methods, flexographic printing relies on flexible dots to transfer ink to paper. Due to the rough nature of the corrugated cardboard surface, it is difficult for the printing press to maintain the stability of the cardboard, so that the fine dots can be attached to the rough corrugated paper surface with the best printing pressure to achieve the minimum dot spread, so printing beautiful patterns is not possible. This makes the printing quality of most of the flexographic direct printing cartons in the low-end state, which can only deal with the printing of solid ground, lines and simple patterns, which greatly reduces the printing quality of the carton.
③The printing precision is not high. The number of screen lines for conventional offset printing is 175 lines / inch, while the number of screen lines for flexographic printing cartons is only 35 ～ 75 lines / inch. It belongs to the low-precision printing method. Although the quality has improved in recent years, there are still limitations.
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1.3 Pre-printed corrugated boxes
Pre-printing includes two printing methods: gravure pre-printing and flexo pre-printing. The method of producing color corrugated cardboard boxes by gravure pre-printing is: use gravure printing machine to print on the roll paper, after printing, it is still collected into roll paper, and then the printed roll paper is used as the carton face paper on the corrugated paper production line. Corrugated cardboard box board, and then cut into box shape with die cutting machine. The method for producing color corrugated carton by flexo pre-printing is: use flexo printing machine to print on the roll paper, after printing, it is still collected into the roll paper, and then the printed roll paper is used as the carton face paper on the corrugated paper production line It is made into corrugated carton board, and then cut into a box shape with a die-cutting machine. The printing quality and forming quality of the carton made by these two methods are relatively high, which is suitable for high-quality and mass production.
The production process of flexo printing carton is as follows: roll paper pre-printed facial paper (gravure printing, flexo printing) Corrugated composite adhesive computer slitting computer cross-cutting die-cutting slotted adhesive nail box produced by ten production lines
(1) The pre-printing conditions are already in place
a. Paper and ink requirements for pre-printing
Pre-printing has special requirements on paper, and the printing surface of coated whiteboard paper has a good color expression, but during the bonding process through the corrugated high-temperature drying tunnel, the coating will change to varying degrees, directly affecting the color surface pattern effect , Not the most suitable paper; hanging whiteboard paper, although it can meet the requirements of the corrugated high-temperature drying tunnel bonding process, but due to its rough and uneven surface, the printed pattern loses dots, unrealistic, poor display power, and the ink consumption is large , Is not the most ideal preprinted paper. Practice has proved that a good pre-printing paper should be white cardboard, which can not only fully display the color of the printed pattern, but also withstand the test of the corrugated high-temperature drying tunnel bonding process.
Printing is inseparable from the ink. Preprinting has special requirements on the heat resistance and friction resistance of the ink. When the preprinted facial paper is flattened on the corrugated paper production line and passes through the drying tunnel section, the ink used requires high temperature resistance and resistance. Good abrasiveness, otherwise the colored surface will be drawn and the ink will become waste. Pre-printing inks already have mature experience abroad, but were still blank in China a few years ago. In recent years, Tianjin Toyo Ink Co., Ltd. has developed pre-printed water-based gravure inks and pre-printed water-based flexographic printing plates that can meet the needs of corrugated paper production lines Ink and varnish. It can be used for gravure pre-printing and flexo pre-printing. The cost of ink is similar to that of offset printing. The pre-printing ink is mainly based on water-based ink. Water-based ink is favored by people because of its non-toxic, odorless, easy to operate, green and environmental protection. With the emergence of "green food and green products", it is bound to require "green packaging and green printed materials" corresponding to it. The water-based ink of Tianjin Toyo Ink Co., Ltd. is a non-toxic ink approved by the American Food and Drug Association. This ink can be used to print internationally accepted green carton products such as beverage boxes, food boxes, medicine boxes, and export packaging boxes.
b. Equipment required for pre-printing
The equipment currently used for gravure pre-printing is a web gravure printing machine. This machine is classified according to the arrangement of the cylinder parts. There are two main models: satellite gravure printing machine and unit-type gravure printing machine. Among the two models, the layout of the unit-type gravure printing machine is more reasonable and has a higher technical level. It is the current standard model of the web gravure printing machine. At present, there are many domestic manufacturers of such equipment, such as Zhongshan Jiangnan Packaging Machinery Factory and Xi'an Aerospace Huayang Printing and Packaging Company.
The equipment currently used for flexo pre-printing is mainly roll-to-roll flexo printing machines. It mainly has three models: satellite-type flexo printing machines, unit-type flexo printing machines, and laminated flexo printing machines. Among the three models, the satellite-type flexo printing machine can meet the requirements of width and repeat length, and the constant temperature of the central impression cylinder can ensure the stability of the expansion and contraction of the printing material, which is more reasonable. The roll-to-roll wide-flexo printing equipment currently used in China mainly relies on imports.
c. Ancillary equipment required for pre-printing
Pre-printing must first print the pattern, and then go to the corrugated paper production line for corrugated composite bonding, and then cut. At this time, it is necessary to consider the factor of the pattern. In the previous corrugated paper production line, computer cross-cutting is mostly fixed-length cross-cutting, so it must be in horizontal A photoelectric tracking cross-cutting control system is installed on the cutter. Its main control mechanism is that the photoelectric eye recognizes the cross-cut mark on the corrugated cardboard printed pattern, and transmits the cross-cut mark to the control computer when it reaches the photoelectric eye, and then the control computer Control the cutting time of the cross cutter, so as to achieve accurate cutting of corrugated cardboard at the boundary of the pattern.
At present, domestic and foreign manufacturers of cross-cutting machines can easily install this function. The cross-cutting precision can be controlled within 1mm. Computer longitudinal cutting and computer transverse cutting are the same principle.
Gravure products have the characteristics of bright colors and high gloss, etc. In printing high-end high-quality packaging, gravure printing has unique advantages. This pre-printing method is increasingly favored by people.
(2) Features of gravure pre-printing
a. Advantages of gravure pre-printing
â‘ The color carton produced by gravure pre-printing can get high-quality, green and environmentally friendly ink-and-wash prints
The inking volume of gravure printing is larger than other printing methods. The color of gravure printing ink is full, the ink layer is thick and has a three-dimensional sense; 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 register control system can ensure that the register accuracy reaches & # 177; 0.1 mm. The gravure printing has sufficient drying after each color printing, and the printed matter is firmer. After ordinary gravure printing, the number of printed screen lines can reach 200L / in. Even if paper with high surface smoothness is used, gravure printing can still obtain very high printing quality. Pre-printed water-based gravure ink is used for printing, 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 ℃ high temperature and hot plate friction on the corrugated paper production line. Gravure printing can also complete printing and varnishing at once.
â‘¡The gravure pre-printed printing plate has high durability, suitable for the production requirements of carton mass printing
Since the gravure printing plate is a steel chrome-plated electrogravure gravure plate, the entire layout is protected by a hard metal chrome layer, so even during the printing, there is a constant contact between the blade and the layout to maintain a high printing resistance, generally up to 3 ~ 4 million prints, suitable for high-quality carton and high-volume printing production requirements.
â‘¢ Gravure pre-printing is suitable for printing of continuous stretched patterns
Offset printing is to wrap the prepared plate on the plate cylinder, so there is always an area on the plate roller surface for fixing the plate. The gravure printing plate is different. Because the plate making operation of the gravure printing plate is directly carried out on the cylinder of the cylinder, as long as the images on the cylinder are seamlessly spliced, a continuous stretched pattern can be obtained on the substrate.
â‘£The corrugated paper box produced by gravure pre-printing has higher strength
Because the pre-printing production of corrugated boxes is completed on the production line, there is a certain heat forming time when making corrugated cardboard, so it is stronger than the corrugated boxes obtained by the traditional method of laminating machine, and can avoid direct printing to the carton. Damage caused by strength improves and improves the strength and punching strength of corrugated boxes.
⑤ Gravure pre-printing printing speed, high production efficiency
Because the pre-printing printing method uses a web gravure printing machine, after each color is printed, there is a drying device, without powder spraying, you can enter the next process, the printing speed can reach 150 meters / minute. In the high-speed gravure printing process, a roll of material can be printed in a short period of time. The use of a non-stop automatic roll changing device to replace the roll material can greatly improve the printing efficiency. After printing, the corrugated cardboard production line is made into corrugated cardboard, which is much faster than the traditional laminating machine.
b. Insufficiency of gravure printing:
The gravure platemaking is complicated. The period of making a pair of steel chrome-plated electrogravure gravure cylinders is generally 5 to 10 days, and the price is higher, which is 8 to 10 times that of flexo printing. 3. The investment in the entire production line is relatively large.
(3) Features of flexo preprint
a. Advantages of flexo pre-printing:
â‘ It is non-toxic, non-polluting and conducive to environmental protection. It is a green printing method and has great advantages in the printing of green cartons such as food boxes and medicine boxes.
â‘¡Can print large-format multi-color, high-quality color packaging boxes. The widest web flexo printing machine in foreign countries can reach 1.8 meters wide, and the satellite flexo printing unit can be made into 6 colors. Can print wide-format, multi-color, high-quality, high-precision color carton
â‘¢ Low cost. The low cost of flexo printing has formed a broad consensus abroad, and there are still different opinions at home. The main reason is that most of the flexo printing machines and flexographic printing plates currently used in China rely on imports, resulting in higher costs. The offset and gravure printing costs are relatively low in this regard. With the flexo printing equipment and its plates and local production in China, its cost will gradually decrease.
â‘£Printed with different screens, the prints have fine patterns and strong consistency. 100L / in, 133L / in, 175L / in can be used to express the pattern, the dots are exquisite and the colors are eye-catching.
⑤The face paper and the corrugated paper are laminated and bonded at one time on the corrugated paper production line, which can improve and improve the strength and punching strength of the corrugated paper box.
⑥ The printing speed is fast and the output is high. The speed of satellite flexo printing machine is generally up to 250 ～ 300m / min, which can meet the needs of multiple automatic corrugated production lines.
⑦The printing material has a wide range, and the paper can be printed from 80 to 400g / m2.
b. The shortage of flexo pre-printing
â‘ In the tone-making process of gradation drafting, the dots of the pattern are clearly polarized. Either small dots (dots below 8%) have been lost during printing, and they have become extinct; or the dot increase rate is too high. Large, becoming an outlet close to the middle tone. In the dark part, about 85% of the outlets will be graded, on the ground. It can be seen from this that flexographic printing uses amplitude modulation dots to reproduce the tone range of the tone, and the tone range can be narrow, which is about 8% to 85%. That is to say, when printing more than 85% of the area, due to the increase of the dots, there will be a gradation phenomenon, so that the dark areas are dead and no layers; when printing less than 8% of the area, because the dots are too small, it is difficult to print on the plate "Stop". Less than 8% of the dots in the design cannot be expressed in the actual printing process. Therefore, it is difficult for some manuscripts with rich layers to present their rich layers and colors with the flexible version.
â‘¡ Judging from the number of screen printing lines, the highest number of lines for offset printing and gravure printing is higher than that for flexo printing. The ideal screen printing line number for flexo printing is generally below 150L / in, more than 175L / in, will increase the difficulty of flexo plate making, and also will greatly shorten the service life of the printing plate.
â‘¢Do not use too thin lines and too small text. Since the flexographic plate will be deformed during the printing process, lines and text that are too thin are highly susceptible to deformation. If it is small anti-white characters or anti-white lines, due to the shallow relief, it is easy to cause stagnation. Therefore, try to use thicker lines, and the contrast between the decorative lines and the main line should be larger.
It can be seen from the above analysis that pre-printing is an ideal method for high-quality, high-volume production of corrugated boxes.
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2. Several special printing box making methods
2.1 Plastic gravure composite carton process
When the single-sided corrugated production line is used, if the glossy paper needs to be coated after the printing of the facial paper is completed, and the production volume is large, you can not print on the facial paper, but use the gravure method to complete the gravure printing on the plastic film, and add Coat on white base, and then compound the printed plastic film with facial paper first, and then complete the box making according to the conventional carton forming process.
The characteristics of this process are:
â‘ Low cost of carton production. When the production volume is large, this process can greatly reduce the printing cost of facial tissue and the material cost of facial tissue. Because facial paper does not require printing, non-coated whiteboard paper can be used, which greatly reduces the cost of facial paper.
â‘¡ Beautifully printed. Because plastic gravure printing is used, the printing effect is comparable to that of offset printing. Special attention should be paid to the adoption of this process. During plate-making and printing, the dimensional change and deformation of the plastic film must be fully taken into account. Otherwise, the carton face paper will be misaligned with the underlying cardboard.
2.2 Craft of gravure composite carton of coated paper
This process can be used when the production volume is relatively large, no lamination is required, and the printing effect is good and the cost is low. The process is to print a thin (60 ~ 90g / m2) coated paper with a paper gravure printing machine, and then compound this beautifully printed coated paper with ordinary slag board paper or box board paper, and the whole is used as carton face paper before proceeding. For mounting and normal carton molding processing.
The characteristics of this process are:
â‘ Low cost of carton production. The main reason for the cost reduction is to change the whiteboard paper to low-gage coated paper combined with cheap boxboard paper, which reduces the material cost.
â‘¡ Beautifully printed. The printing effect of paper gravure printing is very beautiful.
â‘¢ Gravure plate making is relatively complicated and costly, so it is not suitable for printing carton products that are frequently revised.
â‘£The operation and control methods of the printing plant on the process of face paper compounding and box making should be carefully explored, accumulated, and implemented reasonably, otherwise it will easily lead to an increase in the scrap rate.
2.3 Direct offset printing corrugated box process
The direct offset printing process of corrugated cardboard boxes is relatively mature abroad. It is to directly print corrugated cardboard onto a special offset printing machine, which is suitable for processing thin corrugated cardboard boxes.
This process can not only ensure the good formability of the carton, but also complete the exquisite facial 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 boxes
The screen printing corrugated box process uses direct printing. Since the ink drop rate of the screen is proportional to the pitch of the screen, the resolution of screen printing is not high, the image accuracy is low, and the number of conventional screen lines is 60 to 80 lines / inch.
The screen printing corrugated box has the following advantages:
â‘ The printing area can be large or small.
â‘¡The printing can be completed before the boxing, or after the boxing.
â‘¢ The ink color of screen printing is thick, the color saturation is high, and the visual effect is strong, especially the spot printing of spot color, the effect is better.
â‘£Easy plate making and low cost.
⑤ Low printing cost.
â‘¥ The printing quality is relatively stable. The disadvantage of screen-printed corrugated boxes is that it is not suitable for linked production lines and the production efficiency is low.
3. Conclusion
It can be seen from the above analysis that there are many methods of carton printing, and each method has its advantages and disadvantages. It is necessary to select the appropriate printing method according to the characteristics of the carton produced. Especially for high-quality, high-volume production of corrugated boxes, pre-printing is undoubtedly the best way.
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