How to gradually improve the quality and efficiency of flexographic plate making
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The traditional rubber version advantage no longer fades out of the market
The earliest flexographic version was a vulcanized rubber plate, which was used in the industry as a rubber plate and was originally carved by hand. With the birth of the photosensitive resin plate and the price drop, as well as the market demand for quality, the use of the rubber plate is gradually reduced. In recent years, users' demand for seamless printing plates has increased. The rubber version of computer engraving has once again entered our field of vision. There are also a small number of applications in China, but there are still great challenges in the overall cost and printing quality of equipment.
In the early 1970s, the liquid photosensitive resin plate first entered the market. Compared with the rubber plate at that time, the plate making speed of the liquid plate was greatly improved, and the printing quality was generally improved. However, the liquid version also brings many challenges. For example, the thickness of the printing plate is completely controlled by the plate making equipment. Therefore, the precision of the plate making equipment is relatively high. The promotion of the liquid plate in China is not ideal, but the domestic plate making equipment is not related. A big relationship, after all, high-end imported equipment is expensive, and customers who are willing to invest are very limited.
Solid photosensitive flexible resin plate opens a new era
In 1973, DuPont invented the solid photosensitive flexible resin plate (hereinafter referred to as "flexo") and entered formal commercial production in 1974. In the following 40 years, several large chemical companies have entered the field of flexible plate production, such as Asahi Kasei of Japan, BASF of Germany (later related business was acquired by Flint Company of the United States), American Medme and Kodak, etc. The company has developed unique technologies and products that promote the development of flexographic plate making technology. The breakthrough of flexo is mainly manifested in two aspects. Firstly, the precision of image printing is greatly improved. Compared with the previous rubber plate, flexo can easily produce more than 80lpi. Secondly, there has been a significant increase in ink transfer, print durability and plate making speed.
In the early days of the flexible version, there were only 1.7mm and 2.28mm thickness plates. In order to meet the needs of different printing equipment and printing materials, there are many kinds of plates from 0.76mm to 7mm thickness. Thick plates of 2.28 mm or more are usually used in corrugated board printing, while plates of 0.76 mm and 1.14 mm thickness are more widely used in labels and flexible packaging. It is worth mentioning that throughout the global flexo printing, the European and North American markets and our Asia-Pacific region, there is a big gap in the demand for flexo thickness. For example, the North American market uses a 1.7mm thickness version for printing labels and films. The materials are more common; most European users prefer a 1.14mm thick plate. The 0.76mm thick plate for flexible packaging can meet the high-speed printing needs due to the fast plate making speed and small dot expansion, and is also widely used in Europe. Large-scale flexible packaging printing companies in China use almost 1.14mm thick plates to print film products. Thicker plates are also used in some old equipment, while 0.76mm thickness plates are rarely used. The influence of printing equipment and process flow has a great impact on this.
Computer direct plate making breaks through flexo limitations
With the development of computer-to-plate technology, the printing quality has been greatly improved, which has further boosted the quality requirements of the packaging and label market. The direct platesetter and digital version brought many benefits to flexo printing. At that time, the limitations of flexographic printing quality were solved, and major breakthroughs were made, such as printing smaller light spots, longer tonal range, and finer Anti-white lines and text. In terms of plate making and printing operations, better plate-making tolerance, better registration, and shorter preparation time have also been recognized by the industry. These features have greatly promoted the improvement of flexo quality and production efficiency. effect.
With the gradual expansion of the flexographic application market, different printing requirements have begun to impose different requirements on the performance of the printing plate. Some requirements have the opposite requirements for the same performance of the printing plate. Currently, there is no flexographic printing plate on the market. Able to meet all flexo needs. Therefore, a wide range of flexographic plates for different application types have been developed to meet the different needs of users.
At the same time as the digital version was introduced, the environmental protection problems of long-term flexo plate making and the need to use organic solvent washing were also paid attention to by the industry. The flexographic plate-making process using organic solvents usually takes 3 to 4 hours. The intermediate drying process is the most time-consuming. Although there is also a water-washing process, it usually takes more than one hour to process. Obviously, flexographic printing is too long for offset printing, and most of the organic solvents used for washing are still unsafe. Especially, the mixed solvent of tetrachloroethylene and n-butanol used in China is more toxic.
Thermal technology improves environmental protection and platemaking efficiency
In order to solve the two problems of plate making cycle and environmental protection, the solventless thermal plate washing technology was first introduced by DuPont in 2000. The biggest advantage of thermal technology is that it does not use solvents. It does not worry about the safety hazards of solvent use and recycling process. There is no environmental problem, and there is no time-consuming problem of drying. The printing plate has no swelling and recovery process, so the plate making process The speed is fast and the plate produced is stable.
The core of thermal technology is the formulation of the photosensitive resin and the control of the plate washing process. Figure 1 illustrates the working principle of the thermal plate-making system. The plate after the main exposure is clamped on the roller of the thermal washer, the unexposed resin melts under high temperature, and then the non-woven fabric will be thick. The melted resin is taken away to realize the development of the embossed characters.
High-definition flexo plate-making technology enhances flexo quality
After entering the year 2000, the voice of improving the quality of flexographic prints resounded. In the face of competition from other printing methods, in order to further enhance the fineness of flexographic printing, in 2009, Esko released the engraving machine with a 4000dpi resolution. HD Flexo technology, before that, for high-definition flexo, Kodak and screen companies have also had different screening technologies, but they are not widely used. The biggest problem in fine dot printing in the past is that the paste and the printing durability are low. The high-definition flexo printing adopts the technology of large-scale dot-spinning and screening in the high-light part, and uses the way of supporting each other to enhance the printing durability of the printing plate. High nets to slow down the pressure on small outlets and extend the life of small outlets, as shown in Figure 2. Although high-definition flexo printing technology has brought another improvement in quality, it has presented an unprecedented challenge to the plate making process: how to accurately make small dots without appearing in the plate making process? How to effectively control the dot size, Ensuring the stability of the plate making process? These problems were challenged by all the plate suppliers at that time. A large number of tests showed that there are not many materials and plate-making equipment that can fully meet the requirements of high-definition flexographic plate making. Repeatability is a question that must be considered. Practical experience also confirms that high-definition plates must be made of medium-high hardness, high-resolution flexo plates; high-energy exposure equipment is the second necessary condition; for washing, small dots are guaranteed. It is also very challenging to completely remove the unexposed resin between the dots. Therefore, in addition to high-precision laser engraving machines and software technology, high-quality plates and fine back-plate equipment are also necessary for the production of high-definition flexo plates.
Another direction for the development of HD flexo is the field screening technology, which improves the ink transfer rate by engraving extremely fine dots on the surface of the flexographic solid part to increase the surface area of the plate. At the beginning of this technology, the increase in solid density was only 0.1 to 0.2, but it was very helpful to reduce pinholes and improve the uniformity of the ink layer in the field. However, the problem of printing resistance of small dots has not been completely solved due to the introduction of HD. In the actual printing work of a large number of laser plates, the printing durability is still plaguing users, and the voice of reducing the paste is getting higher and higher.
Flat top dot technology increases plate printing durability and printing stability
After long-term use of the laser version of the Dome outlet, people gradually realized that the flexo printing made by the traditional film also has the advantage of high printing durability. If the advantages of both can be combined to develop new technology, it can break through the dome point. bottleneck. Flat top dot technology was developed to address these issues.
The main exposure of the conventional laser version is done in the air, and the presence of oxygen causes the dots on the black film to fail to replicate 1:1. By removing or controlling the effects of oxygen, widening the shoulders of the dots, and improving the durability and stability of the dots, a more stable printing can be achieved. At present, the similar technologies on the market mainly include DuPont's DigiFlow technology using nitrogen gas (the purpose of removing oxygen by flushing nitrogen into the exposure machine during exposure), and Medtech's Lux technology (using a conventional laser printing plate, Using a composite film to isolate oxygen), Flint's NExT technology (using a high-intensity exposure device to "suppress" the effects of oxygen), Esko's built-in high-intensity exposure lamps in laser engraving machines also use NExT-like Technical design ideas. These open platemaking methods can be used to make any laser film based on black film, and users need to compare cost, quality and efficiency.
In China, some users have adopted this flat-topping technology based on plate-making equipment, and have carried out a large number of productions. From the actual effect, the performance of the flat-top dot has reached the expected level, and it has a good print durability and printing stability. Performance, see Figure 5; In addition, thanks to the smaller dot expansion of the flat top outlet, in the gradual effect, it can also be seen that the flat top dot is smoother than the traditional laser version of the dome, and for the field screening technology With the use of flat-top dot technology, it can also be greatly improved. The recently introduced more precise engraving technology Pixel+ and flat top dot technology have made significant breakthroughs in the field of flexible packaging. For example, for the four-color blue monochrome test, the density value can be obtained under the same printing conditions. Increased from 1.1 to 1.5, while looking more uniform on the ground, solves the problem of uneven density within the common large solid patch.
At the same time as the breakthrough in the field screening technology, another plate technology for the improvement of ink density has also made progress, that is, the multi-layer technology, that is, adding a layer of resin on the surface of the flexographic plate to enhance the ink. The transfer rate, DuPont's PLS, EXL plates, and Medtech's EPIC plates have all used this technology.
Self-contained flat top dot plate material to enhance the efficiency of choice
In 2014, with the promotion of equipment-based flat-top network technology, the bottleneck of such technology gradually emerged. The biggest problem customers face in their use is the balance of cost, quality and efficiency. From the existing equipment solutions, there is still no perfect solution to meet the needs of customers in the above three aspects. As a result, almost all flexo plate suppliers have turned to developing media technology that does not require additional equipment and comes with flat-top dots. In the past two years, major flexo suppliers have introduced plates with flat-top dots, such as Flint's FTF and Medtech's ITP.
The plate with its flat top outlet first solves the investment problem of purchasing equipment, and improves the plate making efficiency by reducing various oxygen removal links. At the same time, combined with the multi-layer version technology, a layer of frosted resin layer is added on the surface of the plate with the flat top dot, which can more effectively improve the ink transfer rate.
In 2015, DuPont launched the flat-top digital flexo-Easy series flat top dot flexo plate. The new resin-coated plate maintains the high resolution of the digital flexo and combines the advantages of a traditional flexo. No special screening procedures are required, and no special plate making equipment is required to get the best performance.
The text magnified under the high magnification magnifying glass is printed on the coated cardboard by ink. The new plate material solves the phenomenon of “double eyelid” on the edge of the text in flexographic printing, which greatly improves the performance of small characters and lines.