Analysis and thinking of the most popular corrugat

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Analysis and thinking of corrugated board flexographic printing

generally speaking, the flexographic printing corrugated box process is to print directly on corrugated board, using water-based ink. Now corrugated box production process also uses web pre printing method. Corrugated boxes adopt flexographic printing technology, accounting for about 95% in the United States, 85% in Western Europe, and 9% in Japan. DuPont Zytel fr 95g25 v0nh and DuPont crastin fr 684nh are the latest halogen-free brands of DuPont high performance materials division, accounting for more than 3%. It is also gradually accepted by corrugated box manufacturers in China. In recent years, it has developed rapidly. At present, it is estimated that more than 50% of enterprises adopt this technology, and now more enterprises adopt corrugated board multi-color flexographic printing slotting machines

1. Characteristics of flexographic printing

corrugated board flexographic printing has the following advantages: flexographic printing can not only copy the field version, but also copy the line version; Corrugated paper printing has developed from monochrome and two-color to multi-color line version, changing the situation of monotonous ink color and simple graphics and text in the past, and meeting the requirements of sales packaging. This is an inevitable law of development. Now the line version is printed on corrugated paper (box, box), and it can be printed to 100 lines/inch on e corrugated, and 40 lines/inch on a, B, C corrugated. Flexo can make both field version and line version, which meets the printing requirements of corrugated boxes

flexible printing plate can compress and deform. Corrugated paper has the worst thickness error and surface flatness in the printing base material. Especially for a and C corrugated, the thickness error should be 0.5mm or even higher. Because the flexible printing plate is made of synthetic rubber, it is required to choose and design different fixture bodies according to different experimental forces and the shape and size of samples. In the printing process, it can compensate for the thickness error and surface unevenness of corrugated paper with its own compression elastic deformation, so as to meet the stamping requirements of each corrugated paper, make the ink color more uniform, and ensure the printing quality and reduce bad pieces. Flexographic plates can compress and deform, which is absolutely impossible for flat printing and gravure printing. Therefore, the thickness of flexographic plates used on corrugated boxes is relatively thick, generally mm, while the thickness of flexographic plates used for flexible packaging printing is only 1.14mm and 1.7mm. Why thick printing plates should be used on corrugated paper is to use its compression deformation. Now in order to reduce the cost, 4mm printing plates and 3mm air cushion rubber lining (plastic lining is not allowed), the effect is better. Of course, we should advocate that the thickness and quality of corrugated paper should be basically the same. Thin printing plates are also used in corrugated paper printing (fine corrugated) abroad. The key is to control the surface flatness of corrugated paper

flexographic printing belongs to light pressure printing. Due to the corrugated paper, there is also a printing base material with uneven pressure. The pressure at the high part of the corrugated paper is large, and the pressure at the low part of the corrugated paper is light. It will also cause that the low part of the corrugated paper cannot contact the printing plate, and the ink cannot be printed. Therefore, both flat printing and gravure printing cannot overcome the defects of corrugated paper thickness error and uneven pressure. Flexographic printing belongs to light pressure printing, which is the lightest printing pressure in traditional printing, commonly known as "0" pressure printing. There will be no excessive pressure at the height of the corrugation, and the ink color of the print is soft and flat. Corrugated boxes use line printing, why use thin corrugated? Because of the high requirements of line printing, the thinner the corrugated, the more uniform the pressure

water based ink can be used in flexographic printing. Paper is interwoven with fibers, and its hydrophilicity is better than lipophilicity. Therefore, as long as you gently touch the corrugated paper, almost all the water-based ink will be absorbed by the corrugated paper, so the ink color is uniform, flat and thick. Water based ink has no pollution, low cost, quick drying and operation. Flexographic printing uses a short ink path inking system with metal rollers, which can use water-based ink, which is also the feature of flexographic printing. The long ink path of lithography cannot be achieved by oily ink (oxidation drying ink)

high efficiency, high quality and high speed process technology. At present, the technological routes of corrugated box printing in China include: first, silk printing. It is suitable for transportation and packaging in small batches and with low requirements. 2、 Corrugated paper is printed by flexographic printing after forming. Because it is printed after corrugated paper is formed, the process is simple, and can basically meet the requirements of corrugated paper printing from monochrome to multicolor line version, so it can achieve high efficiency and high quality. Coupled with high printing speed, 350 sheets per minute for small specifications and 170-220 sheets per minute for large specifications, it is an ideal printing technology. 3、 Pre print the leaflet. Due to the use of sheet fed lithographic printing line plate, although the printing quality is high, this process still uses sheet mounted corrugated, then indentation, slotting, die cutting, which can not reach high speed. Moreover, there are not many large-scale lithographic presses with high cost, which limits the development. It is also starting in China. The main advantage is high printing quality. However, it is suitable for large batch packaging, and the cost is higher than that of corrugated paper printing after forming

flexo printing machine is simple in structure and suitable for enlargement. The corrugated box has a large area and a length of 1.6-3.5m. If the long ink path ink transmission system of lithography is adopted, the equipment is huge and it is difficult to manufacture, operate and maintain. The flexographic press has a simple structure, and four rollers can form a color deck. The diameter of the roller is suitable to be larger, which just meets the requirements of the printing plate roller, and can improve the mechanical accuracy and stability. Due to its simple structure and large equipment space, the machine can meet the requirements of plate installation and adjustment, and it is convenient to clean and use

flexographic printing can form a linkage production line with other processes, which is another major feature. Corrugated paper is heavy and labor-intensive to move one by one, which can not meet the requirements of mass production and can not form a scale. Due to its simple structure, flexographic printing machine can form a linkage production line with other processes, which greatly improves work efficiency and reduces labor intensity. At present, most corrugated flexographic printing machines are linked with indentation and slotting. For the processes of indentation, slotting, die cutting, gluing, cartoning, counting, etc. with good performance, the finished products can be directly transported to the passenger car from the machine

2. Relevant requirements for flexographic printing

(1) the printing plate

corrugated board has a certain elasticity in the direction perpendicular to the paper surface, which has a cushioning effect on the packaging. This is the main reason why corrugated board is widely used to make packaging boxes. However, this elasticity brings certain difficulties to printing. In order to adapt to the flexible printed matter and make it have good ink transfer, the printing plate must be softer than the printing plate used in general flexographic printing. Except for particularly fine prints, the plate hardness of most corrugated boards is 30 ± 5 shore

(2) brush machine

corrugated board flexographic printing machine has a variety of specifications, and the small one can print 610 mm × 1620 mm corrugated board, up to 2030 mm large × 4830 mm。 Because the printing format is large, the plate cylinder is also large. Generally, the plate cylinder cannot be disassembled. When printing a new job, the flexible plate on the plate cylinder can be replaced

corrugated board has enough stiffness, so in order to adapt to the substrate with a certain stiffness, the paper feeding system of corrugated board printing machine adopts single sheet feeding mode. The paper feeding condition is to push the end of the paperboard into a pair of paper feeding rollers, so as to feed paper to the embossing part. During the whole paper feeding and printing process, the corrugated board passes through the printing machine on a horizontal plane

corrugated board can be printed by a single machine, but now many carton factories often combine the printing process of corrugated boxes with the equipment of other processes of cartoning to form a cartoning production line. For example, printing, slitting, molding, folding, gluing, bonding, labeling, strapping, etc

(3) ink

most corrugated boards are printed with water-based ink. This is because: first of all, the text or simple pattern printed on corrugated board does not need to be very shiny (only for the quality requirements of some cartons), and water-based ink can meet the quality requirements of printing. Secondly, the main machine is similar at home and abroad. Corrugated board is a loose fabric with strong water absorption. After coating water-based ink, its drying method is mainly osmotic drying, with fast drying speed, and there is no need to set a drying device. Again, water-based ink pollution is small, low cost

3. flexographic preprinting

flexographic preprinting, that is, the corrugated board surface paper adopts web paper. First, the flexographic printing machine is used to print and rewind to form web paper, and then the corrugated board production line on the printed web paper is re mounted to produce corrugated board. Simply put, it is to use the printing web paper to replace the face paper of the corrugated board production line, and the other processes are the same as the original. One thing to pay special attention to when using pre printing to produce corrugated board is that it requires relatively high cutting accuracy of the cutting device of the corrugated board production line. The existing corrugated board production lines in many domestic corrugated box production enterprises cannot be suitable for re corrugated after pre printing without technical transformation or modification

there are two forms of flexographic pre printing, unit flexographic printing machine and satellite flexographic printing machine

(1) unit type flexographic printing machine

this kind of printing machine adopts laminated flexographic printing unit combination arrangement. There are one or two sets of printing units on each printing unit rack. The number of printing colors can be combined arbitrarily. The form is similar to that of gravure printing press. Its process flow is:

Web uncoiling device → uncoiling tension control system → pre heating roller (to minimize the paper expansion) → the first printing unit → drying system → the second printing unit → drying system → the third and fourth printing units, and so on → cooling roller → winding tension control system → winding device

the unit type flexographic printing machine has the following characteristics: door width, Its range is best equal to the width of the corrugated board production line. At present, the widest door width can reach 3600mm; The printing perimeter is highly variable. Generally, the repetition cycle is excluded in time. The length is at least 1200 mm, and the large printing perimeter can be more than 1800 mm or even more than 2500 mm; The printing speed is fast, and the general production speed can reach 250-400 M/min; The investment is about 30% lower than that of gravure printing machines and satellite flexographic printing machines with the same color number and specification; Convenient operation and simple process; The overprint accuracy and product printing quality of the unit flexo printing machine are better than those of the corrugated box printing slotting machine, but they are not as good as those of the satellite flexo printing machine

(2) satellite flexographic printing machine

this kind of printing machine is that each printing unit is evenly arranged around both sides of the central impression cylinder. The printing units are arranged symmetrically in even numbers, such as two-color, four-color, six color and eight color. At present, there are also some odd numbers, that is, a group of gravure printing machines or unit flexo printing machines are connected to the main machine of the satellite flexo printing machine, which are used for applying ultraviolet varnish or ordinary varnish

its process flow is:

Web uncoiling device → uncoiling tension control system → auxiliary tension roller (preheating roller) → paper belt guide device (deviation correction device) → paper guide roller → central embossing roller → first color printing → inter color drying → second color printing → inter color drying → third and fourth colors ----- and so on → overall drying (final drying) → cooling roller → winding tension control system → winding device

satellite flexographic printing machine has the following characteristics:

high overprint accuracy. The overprint accuracy of satellite flexographic printing machine is about ± 0.02mm. The high accuracy of the satellite flexographic press is mainly attributed to the following two points: first, the central imprinting cylinder is composed of double walls, and there is circulating water in the cavity to keep the surface temperature of the central imprinting cylinder constant. If the circulating water temperature is not constant, the

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