Brief analysis of carton printing plate

With the improvement of people's life quality and the improvement of printing and packaging requirements for environmental protection, flexographic printing has developed rapidly all over the world in these years. In the field of flexographic printing, there are different types, such as: direct multicolor printing of cartons, preprinted cartons, flexible packaging, thin film printing (plastic bags, tablecloths, etc.), trademark printing, and coating of conductive liquids for LCDs in the electronics industry. Cloth and so on. The above flexo printing uses different printing equipment and uses different thicknesses and hardness plates to print different substrates.

So far, the product field of flexographic printing is mainly in the three aspects of carton, flexible packaging and labeling. Three aspects are different consumer products. Corrugated box printing has gradually developed toward higher levels of multicolor and dot-to-dot. From the use of flexo media, carton version accounted for 80%, flexible packaging, labels and other only 20%. According to incomplete statistics on the carton industry in Shanghai in the past 10 years, it is growing at a rate of 20% every year. The reason why the flexo is preferred for carton printing is because the surface of the carton is rough, and general metal plates such as offset aluminum plates or gravure copper plates are difficult to print such substrates. Flexo printing originally originated from simple text logos and was the best choice for carton printing. Later, it gradually transformed this printing method into a wide format and a narrow format of environmental protection printing, mainly used for printing flexible packaging and trademarks. We have seen that the flexographic printing plates are evolving day by day, and also make the flexo printing products more exquisite. The plate making is simpler, faster, more convenient and more environmentally friendly.

The following is a brief introduction of the development of flexible carton plates.
Development and evolution of carton flexo: hand-engraved rubber plate → cast rubber plate → photosensitive resin plate (digital plate, solid/liquid plate) → laser direct engraving rubber plate.

The hand-carved version is simple to make and belongs to rubber products. It is a graphic engraving of the front side of the plate and engraving with a cutting knife. This plate-making method can only produce simple text and patterns, and the hardness is about 20 to 50 degrees in Xiao. Its raw material is natural rubber or synthetic rubber. It has good elasticity, but the craftsmanship of the production is particularly strong and requires skilled techniques and rich experience. Therefore, this type of printing has a large limitation and can only be made larger. Since it is hand-carved, irregular fonts are a common phenomenon. The hand-engraved version uses a low-hardness plate, and the reproduction of the graphic is limited and not suitable for dot printing. However, it has the advantages of convenience, speed, and low cost. There is already a simple single laser head engraving on the market to replace manual engraving with simple text.

For the casting rubber plate, the production process is to design the pattern first, make a metal relief plate, press a concave paper or a metal stencil, and press the rubber plate through a concave stencil. The process of heating, pressurizing, vulcanizing, hardening, and molding of rubber is contaminated by the water produced by the concave stencil and the residue formed during the final processing. This is not environmental protection. Casting rubber plates are produced into various rubber plates according to the inks used in different substrates, such as artificial nitrile rubber plates and solvent inks. Natural rubber plates are suitable for water-based alcohol-based inks. Normally, the hardness value of the rubber plate is 50 degrees Shore, and the difference in thickness is generally 0.045 mm. Due to the complex production process, the uniform thickness properties of the cast rubber plate are difficult to control, so the uniformity of the thickness is poor. Generally, the back of the plate is polished to achieve a uniform thickness. Due to the cumbersome typesetting, long plate-making time, and uneven thickness, casting rubber has gradually been eliminated. Now it is difficult to see it in printing houses.

Photopolymer, 1972 United States DuPont company launched the first Cyrel photosensitive resin, with its transfer of high-resolution images, a wide range of media, with a variety of sizes and thickness, can be reproduced in the 175 lines / inch condition of 2% ~ 95% of outlets, Yinxianxian and Yangxian are also excellent. Overprinting accuracy, excellent ink transfer performance, high printing rate and good performance, occupy more than 50% of the global flexible media market.

Cyrel photosensitive resin plate composition: Synthetic rubber, acrylic monomer, photoinitiator, etc., can reproduce fine text and fine dot layer, exposure only requires negative film to complete, stable size, uniform thickness, short plate making time, hardness is Xiao 34 to 42 degrees, thickness tolerance 0.03 mm. Plate making process: back exposure (UV-A light source) - main exposure (UV-A light source) - cleaning (tetrachloroethylene 75% + n-butanol 25%) - drying (60 °C) - post-processing (UVA + UVC light source ).

Comparing the photosensitive resin plate and the engraved rubber plate: The shrinkage of the photosensitive resin plate is small, and the expansion and contraction of the plate is not generated. The plate of the accurate size can be produced, and the dimensional stability is good. The photosensitive resin plate making process is relatively simple, and the reproduction accuracy of the original is high. The side of the photosensitive resin plate is flat, and the compensation problem can be considered in the making of the bottom plate. It is not necessary to grind the plate back. Even if it is thinner than the plate, it can make a high-precision plate.

How to determine the quality of photosensitive resin? The first is to look at hardness and elasticity. Hardness will directly affect the pressure, print times, and recovery level during printing. The hardness of the plate is a key indicator of the plate. Different equipment and different substrates must be equipped with plates of different hardness. The hardness of the resin plate depends on the hardness of the photopolymer and can be controlled by adding a hardness control agent. Elasticity is a counter indicator of hardness, that is, the higher the hardness, the smaller the elasticity. The elasticity of the printing plate is even when it comes into contact with the substrate, and the printed ink is also uniform. However, the reproducibility of the image layer is poor, and the dot enlargement is more remarkable. When the elasticity is small, the hardness is high, which is suitable for printing high-level four-color graphic dots. Followed by the uniformity of the thickness of the plate is an important indicator of the quality of the plate. Take DuPont Cyrel photosensitive resin plate as an example: The thickness error range can be controlled at: ± 0.03 mm. Different printing equipment, you should choose different thickness specifications of the plate, generally 0.7 mm ~ 7 mm to choose from. Finally, the depth of the relief, improper printing plate embossed, will cause the ink paste version or the graphics of the local due to pressure and damage; the stability of the polymer directly affects the plate printing effect and the printing rate.

Liquid photic printing plate, liquid version of the late 1980s began to rise, and the same as the hand-carved version of Japan, Malaysia and other Asian Pacific markets. A printing plate made of a liquid photosensitive resin is called a liquid photosensitive resin plate. Its plate making process flow is: paving → backside mask exposure → front exposure → backside full exposure → recovery of uncured resin → development → drying and post exposure. The production of the liquid plate takes one hour to complete all the work, and the cost of raw materials is reduced by more than half compared to the solid version (according to Australia's liquid polymer LF32/37), but this material can only print short-term products. Later, the introduction of new TF series of high-quality photosensitive liquid raw materials, due to increased costs, the market is difficult to see. The limitation of the liquid version is that it is impossible to make larger-size printing plates. Due to the reason of the process, the large-format plate-making process will result in non-uniform thickness of the plate, which is the most difficult problem for the users, and many waste products. It is also caused from here. In addition, the production of plates of different thickness requires the replacement of a lot of cumbersome raw materials, so the production of thin plates is relatively less.

DuPont Photoresist Digital Version (Cyrel Digital Image) was launched in the late 1990s. It solves the vacuum problem of film in the production of common photosensitive resin plates and the problem of dot enlargement in the process of photolithography. It is a new version of the photosensitive resin plate. breakthrough. The plate is coated with a black photopolymer film instead of the traditional negative film. When the plate is made, the film is omitted, the computer inputs the graphic data, the laser scorches the black film, forms the graphic, and then the main exposure → washing → drying → Post-processing process to complete the plate making. It is characterized by high contrast in printing, anti-white characters are not easily filled, the control of the dot gain is minimized, high resolution can be obtained, tedious preparations are eliminated, the problem of vacuum suction is solved, and the determination based on graphic judgment is resolved. Exposure time and other issues. At present, there are nearly 10 CDI plate-making systems in mainland China. I believe there will be more such devices in the future.

The laser directly sculpts the rubber plate. Laser technology began to be used in printing in the 1990s. Laser engraving ceramic anilox roller is a new breakthrough in flexo printing. In recent years, laser engraving rubber plate has been used instead of photosensitive resin plate. The advantage is that computer input graphic information directly engraving, eliminating the need for output film vacuum suction exposure and washing version and other procedures. The direct engraving of the seamless stencil simplifies the affixing time. Since the stencil is a fiber fabric, the size is very stable, the printing rate is high, the stencil making process is simple, the graphic and text accuracy is high, and the stencil making time is short and efficient. Luscher of the United Kingdom has used laser-engraved anilox technology to improve the laser engraving of the rubber plate directly, 300W CO2 beam, two laser heads producing 0.7 m2 per hour, and can be engraved on the sleeve plate, which can simplify the paste time. The rubber plate direct engraving technology has been listed as the most advanced flexographic plate making technology in the European and American markets. However, due to its sophisticated equipment, high cost, and the import of raw materials, engraving rubber version of the price is higher than the photosensitive resin version, so the use of the Chinese mainland market has a process. ※

Author: Xiaolin Wen

Author: Shenzhen Jiuheng Equipment Equipment Co., Ltd.

Reprinted from: Chinese Flexo