Performance comparison between the hottest cationi

2022-09-21
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Performance comparison between cationic UV ink and free radical ink

the profit of sleeve heat shrinkable film market is expected to reach US $52.5 billion by 2007, which is regarded as the credit of low-cost flexo printing market. For a long time, due to the high price of engraving gravure cylinder and solvent recovery device, the cost of gravure printing is much higher than that of flexo printing. This deficiency of gravure printing also limits the development speed of sleeve type heat shrinkable film market

choice of chemical composition of UV ink

nowadays, acrylate (free radical) and cation are the two main chemical methods in UV process. Cationic UV ink printing has been used for many years in the printing of short version sleeve type heat shrinkable film; Free radical inks are mostly used for paper substrates because of the small shrinkage of the ink film. Although these two methods have many application forms, here we discuss their basic chemical composition

cationic UV device

cationic UV device uses photoinitiator to produce acidic substances under the irradiation of UV lamp to catalyze the polymerization reaction. The cationic agent induces a chain reaction of epoxy groups until the oxygen bond breaks or a glassy polymer is formed, and the chain reaction stops. The infrared ray (1R) emitted by UV lamp is the key to control the reaction speed and complete reaction. For cationic polycondensation reaction, it is necessary to fully understand the properties of the film, avoid ink cracking, and ensure complete post curing of the ink

the advantage of cationic ink is that its reaction type is a typical ring opening polymerization of epoxy groups, which improves the content of effective components of the ink and almost completely converts it into ink film

because the reaction speed of cationic polycondensation is slower than that of free radical polycondensation, it takes a long time. The ink film is crosslinked and attached to the substrate to reduce the pressure on the substrate. The shrinkage of the ink film of the cationic cured product is less than 5%

disadvantages of cationic inks

reaction speed is slower than free radical polymerization, and high temperature curing is required. However, low ink film shrinkage and high temperature curing often cause uneven and smooth edges of the ink film. Generally speaking, choosing a UV light source of more than 80W can ensure the rapid and complete curing of cationic ink. If the temperature is lower than this, the durability and adhesion of the ink film will be significantly reduced, and the smell will be strong

another weakness of cationic polycondensation is that it will terminate under the influence of atmospheric humidity. High humidity weather will lead to constant changes in ink property parameters. Therefore, temperature and humidity control system is a necessary device for cationic UV printing

for cationic inks, the choice of ingredients is also a problem. First of all, the price of basic ingredients of cationic ink itself is higher than that of free radicals. Moreover, because alkaline substances will delay or even inhibit the reaction, the content of such substances in the ink should not be too high. Acidity should also not be used excessively, otherwise, it will increase the viscosity of the ink and turn into gel

for this reason, ink engineers must strictly control the type of pigment in the ink composition. They often need to carry out surface treatment on the pigment to make its pH value reach neutral. Therefore, many pigments cannot be used because they cannot meet the requirements of UV ink fluidity and viscosity

similarly, there are high requirements for dispersants. Especially after some reports hindered the reaction of cationic inks, there were stricter regulations on the types of dispersants, which in turn limited the amount of pigments added to the inks, resulting in poor color expressiveness of the printing ink layer and dull colors of graphics and texts

wipe the host. In addition, cationic initiator also contains heavy metal elements, which will generate and release a small amount of benzene substances, which not only pollutes the environment, but also endangers the health of workers. However, this new free radical UV technology can achieve no intensity limit, which may change heavy metal elements within ± 10%, no benzene generation, and the printing speed is only slightly reduced

free radical UV ink device

the free radical UV ink device also uses a UV lamp to irradiate the photoinitiator to induce the chain polycondensation of acrylate until the free radical reacts with pigments, oxygen, additives or other free radicals, or vitrification to terminate the chain forging reaction

generally, there will be a small number of secondary divisions after the ink is cured under UV light, but there are few real post curing processes. Therefore, when the ink cools and adheres to the substrate, there will be adhesion, scratches and other phenomena. The infrared ray (IR) emitted by UV lamp can accelerate the curing speed. The free radical reaction is indeed slightly worse than the cation reaction, but there are other methods to obtain the ideal curing effect, but the EPDM production capacity in China is relatively low

advantages of free radical ink

this device is fast. The curing of free radical ink has no high temperature requirements. It can be cured quickly under low-energy light source, which greatly reduces the heating of substrate and avoids the shrinkage of heat shrinkable film in the printing process. And its requirements for ink are not as strict as cationic ink. In this way, a variety of pigment choices are sufficient to ensure that the ink has good rheological properties on the YAG textured roller. In addition, high pigment filling reduces the volatile components of the ink, reducing shrinkage and odor

this is a low-temperature molding composite product series. Because there are no too many restrictions on the composition selection of free radical inks, it can print substrates with strong alkalinity and jointly print with alkali soluble and water-soluble flexographic inks

disadvantages of free radical inks

free radical inks react quickly and can quickly solidify all components together, which will increase the pressure on the substrate. When printing heat shrinkable film, excessive pressure and a small amount of heat energy of curing UV lamp will lead to the shrinkage and deformation of the film. Shrinkage will also reduce the flexibility of free radical UV inks like other UV inks, and make the affinity and adhesion worse

free radical inks are also easily oxidized. However, this can be achieved by using high-energy light sources, high-efficiency ingredients, or oxygen absorbing initiators (such as binary amines and ternary amines). It should be noted that this is the experimental result obtained under the condition that the air condition is relatively stable without too much fluctuation. If it is used in actual production, further demonstration is needed

speed

the drying speed is fast, and the high adhesion enables the free radical ink to instantly adhere to the substrate and cure rapidly under the irradiation of low-energy light source: in this process, the substrate material is not heated, but the cationic ink cannot be printed at high speed due to the high requirements of curing energy. This just solves the problem that the productivity of UV flexo printing is lower than that of gravure printing. With proper curing device and pressure setting, free radical ink will break through this bottleneck

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