The hottest flexo gravure ink and related technica

Gravure printing ink and related technical problems

gravure printing in Japan is mainly used in packaging printing, and its ratio is close to 90%. In Europe and the United States, flexographic printing occupies most of the packaging printing market, and the market formation is different. Intaglio printing in Japan has entered a mature stage. Flexographic printing has also stepped out of the low-quality printing in the past, or changed its image as a special purpose, and has made quite gratifying improvements. Now it is the third largest printing method after offset printing and gravure printing. 1、 Background of gravure and flexographic printing inks in 1995, the total volume of printing inks on the market in Japan was more than 400000 tons, of which packaging gravure printing inks accounted for 1/3. Since the late 1960s, gravure printing ink has been popularized rapidly because polyethylene, polypropylene, polystyrene, polyester, vinyl chloride, nylon and other plastic film materials have replaced cellophane, and has greatly increased as the mainstream of packaging printing. However, the growth rate slowed down after 1985, and its growth rate has been lower in the past five years. The number of flexographic inks is still small, but its growth is extremely strong (Table 1). Gravure inks are low viscosity inks using resins soluble in fast drying organic solvents as color carriers. In the past, its color carrier mainly used derivatives of natural resins such as nitrocellulose and rosin. However, with the popularity of various film packaging materials and the increasing demand for inks with better adhesion, suitable for various purposes and able to maintain physical properties, all resins soluble in solvents have been able to be applied to various gravure inks. In recent years, due to environmental requirements and health problems, water-based inks are being actively developed. The history of flexographic printing can be traced back to 1890. At that time, flexographic printing was also called aniline printing, which was limited to rubber relief printing, so it was rarely used in the field of film packaging, and it was only used as a printing means attached to kraft paper bag making machine for a long time. In the 1970s, flexographic printing gradually developed in the field of corrugated paper printing, and now this field has accounted for 70% of flexographic printing. Since flexographic printing used rubber relief plates at the beginning, it was impossible to make high-quality images. It was not until 1973 that DuPont developed a resin plate with UV curing method that high-precision prints could be obtained, and the printing inks were mainly water-based inks and alcohol based inks. The so-called alcohol refers to the ratio of 3 parts of ester solvent with strong solubility to alcohol (because there are very few resins that can be dissolved in a single solvent of alcohol), and the use of nitrocellulose, alkyd amine, polyamide and other resins as color carriers. However, most resins used for gravure inks cannot be used for flexographic printing. Table 1 Change and growth rate of main printing ink market volume (thousand tons) growth rate (Times) 85 year 90 year 95 year 85 year 90 year 9 can automatically draw marks on the table 5 year offset ink 73.7 108.4 119.7 1.47 1.10 1.62 packaging gravure ink 83.2 115.9 121.3 1.39 1.05 1.46 publishing gravure ink 20.9 25.6 28.5 1.22 1.11 1.36 metal plate ink 28.3 44.1 45.5 1.56 1.03 1.61 printing ink 43.8 50.5 45.7 1.15 0.90 1.04 rubber relief flexographic ink 16.5 21.2 25.6 1.28 1.21 1.56 II. Gravure inks 1 The development of gravure printing inks gravure printing inks not only use low-cost hydrogen carbide such as toluene, but also use all fast drying organic solvents such as esters, ketones and alcohol. Therefore, gravure printing and ink production are restricted by laws and regulations such as fire protection law and labor safety, and organic solvents such as toluene often remain in the printing film. If this kind of printing material is used in food packaging, it will bring great harm, so it is also restricted by health law. 2. The development of water-based gravure printing inks water-based gravure printing inks were widely used in the printing of packaging paper and cardboard boxes in the 1970s. Due to the better evaporation drying and absorption drying in paper printing, the drying of water-based ink is relatively easy to solve and popularized earlier, but the characterization of oil ink in packaging film printing has not yet reached the real practical stage. Water based printing in the field of flexible packaging can improve the adhesion and humidity of the film and maintain its physical properties in various applications. Although the requirements for ink are higher, in the application of this high evaporation energy water-based ink (the evaporation energy of water is about 5 times that of organic solvents), the matching of desiccant and printing plate system is very important. In addition, the lubrication performance is reduced and the friction resistance is increased due to water, which will cause the printing plate fog and the relative friction between the doctor blade and the plate to increase. Therefore, the improved doctor blade system is an integral part of the whole printing system (above right). Although the water-based gravure printing ink has entered the stage of use, it has not been further popularized. This is because the promotion and use of water-based printing ink not only needs to enhance the performance of the existing dryer, but also needs to be equipped with high-precision shallow hole printing plates, and the improvement of the whole printing system requires considerable investment. In the near future, gravure printing will be completely separated from organic solvents, and now a variety of printing tests are being carried out. It is believed that the printing industry will soon usher in the era of full use of water-based inks. 3、 Flexo printing ink 1. The directionality of flexo printing ink flexo printing ink is not completely different from gravure printing ink, but rather similar. However, due to different printing systems, it has different printability from gravure printing. Flexo printing basically uses water-based ink and alcohol ink. Water based flexographic ink has long been used in the printing of corrugated board and paper bags, while the water-based ink for flexible packaging film printing is still under development. The flexographic printing of packaging film now uses alcohol solvent ink, but it is difficult to maintain its physical properties to be suitable for multi-purpose film packaging materials, especially after various composite processing, cooking and other processing. Another reason why flexographic inks are rarely used in packaging film printing is that the printing quality is far inferior to gravure printing. The quality comparison of the two printing images is shown in Table 2. The films used for flexible packaging are basically lipophilic, and hydrogen carbide such as toluene is easy to adhere. This gravure printing ink has good transferability, while the flexible printing ink based on polar solvents such as water and alcohol is difficult to ink the film, which has the disadvantages of poor transferability and uniformity. In color printing, it is very difficult to deal with large format point enlargement with high-precision image processing technology. In addition to these shortcomings, coupled with many changing factors of flexo printing, as the whole printing system, it is necessary to carry out precise management and transformation in operation. The new choice of flexographic printing is to use general UV (ultraviolet curing) ink (the so-called general ink is an ink that can be applied from paper to film printing). It has entered the practical stage in Europe and America, and some reports think it is good. UV ink has good printability, which will not change the physical properties at all in printing, and can be used for printing with high viscosity (such as honey). Therefore, the dot enlargement in color printing is greatly reduced, so as to improve the printing quality. In addition, after using UV ink, there is no problem of solvent emission, which is conducive to environmental protection for equipment manufacturers of recycled plastic granulator. In short, the trend of UV ink will attract constant attention. 2. The problem of water-based ink in flexo printing is called kiss touch. Soft press printing. The inking property of soft press printing ink has a great impact on the quality of printed images. In the printing of hydrophilic paper, there is no big obstacle to the transfer of water-based ink, but it is difficult to ink the film with strong lipophilicity, which is prone to inking, and the ink remaining on the printing plate becomes the cause of blocking. In addition, flexo printing has less ink transfer than gravure printing, and the ink path is long. The ink is dispersed due to evaporation during the transfer, resulting in changes in the composition of the ink, blocking, poor transfer and poor uniformity. Therefore, the water-based ink with good re solubility, less changes on the machine, good inking and adhesion can maintain its physical properties at the end of the experiment of the bellows ring stiffness tester, and good dryness is the current demand target. However, the contradiction is that both printability and physical properties should be maintained, and the functional requirements of ink are just the opposite, so the difficulty of water-based ink in design technology is conceivable. Table 2: gravure and flexo printing quality comparison project gravure flexo printing field (including thick lines) uniformity · good (good inking) · changes due to the viscosity and fluidity of the ink · there is ink blotting phenomenon · pinholes are easy to occur · increasing the printing pressure can improve the ink squeezing phenomenon at the edge of the field · good (no ink squeezing) · excessive printing pressure, occurs when the ink volume is too large · use a fine roller to improve the ink viscosity, It is expected to improve the fuzzing of the edge part of the field. It is good (does not happen) · the printing press is small, and it is easy to happen when the ink volume is small · the surface of the printing plate is deformed due to the printing press. The hollowed out part is dotted and jagged. It is easy to be too thin. Too much ink is easy to produce ink pile. After the hollowed out line is slightly thickened, it can improve the reproduction of thin convex words (including thin lines) · the edge appears points, and there are jagged. It is good, Straight lines can be used. Excessive ink will pile up. With thin lines, clear lines can be printed. Barcode reproduction. Edge shape. Good. Overprinting is too heavy and coarsens. Printing density. Ink density can be adjusted by the depth of ink holes in the printing plate. Ink density can be adjusted by the volume of ink holes in the embossing roller. Registration accuracy can be adjusted by the color control mechanism. It is easy to stretch, Unequal thickness · accuracy depends on plate pasting · inaccurate printing cover with CI machine. Very few printing plate fogs · non image parts of printing plate are prone to occur due to discomfort such as accuracy, poor doctor blade, ink viscosity, etc. 3 Detect micro damage or even non-destructive · good (no) blocking · good (no) · appropriate printing pressure · minimum ink transfer · ink drying balance · ink re solubility gradient image overprint · good · poor drying balance occurs · pay attention to ink intrusion · overprint occurs on the field when the speed increases · good · printing pressure should be high · pay attention to drying balance color printing · good (175 lines/inch) · pay attention to blocking, The ink mark of the doctor blade, the printing plate fog, and the number of thick lines are good. For example, 85 lines/inch · 100 ~ 150 lines are fashionable. Pay attention to the occurrence of blocking. Use the fine line roller to perform the color gradation. Good. The ink hue is balanced. The concentration is expressed through the size and depth of the ink hole. More technical accumulation. The high light part is good. The occurrence point is enlarged. The high light part reproduction is difficult. Most of the image correction values need to be modified. The ink hue is balanced, Concentration 1. Performance in point size. Less technical accumulation. 4. Problems of related technologies. 1. Ceramic roller has been used in flexographic printing for more than ten years. It can be said that ceramic roller is a trump card to improve and stabilize the quality of flexographic printing. At present, although chrome plating roller and laser engraving ceramic roller have their own markets, it can be predicted that the large market is gradually turning to the application of ceramic roller. At first, the uneven ink holes of the ceramic roller cause poor printing, and the uneven thickness of the roller surface will cause abnormal wear of the scraper, or pinholes and other faults. Now the ceramic roller has been able to maintain a stable quality, but the ink color is often shallow or uneven due to ink blocking in printing, so the cleaning and management after printing cannot be ignored. In case of ink hole blockage, ultrasonic cleaning can be used to restore the capacity of the ink hole, and Nu Skin can be used. The manufacturing process of ceramic roller has superior hardness due to its material characteristics, so there is no report of corrugation roller deterioration due to wear so far. So a ceramic roller to