Shrinkage label printing ink (below)

The free radical UV ink device also utilizes a UV lamp to irradiate the photoinitiator to induce an acrylate-linked polycondensation reaction until the free radicals react with pigments, oxygen, additives or other free radicals, or vitrification to terminate the chain reaction.

Under normal circumstances, there will be a small number of secondary splits after the ink has cured under UV light, but there are few true post-curing processes. Therefore, when the ink cools and adheres to the substrate, sticking, scratches, etc. may occur. The infrared light emitted by the UV lamp can speed up the curing process. The free radical reaction is slightly inferior to the cation reaction, but there are other ways to obtain the desired curing effect.

● free radical ink advantages

1 The reaction speed is fast. The curing of radical ink does not require too much temperature, and it can be quickly cured under low-energy light sources, which greatly reduces the heat of the substrate and avoids the shrinkage of the heat-shrinking film during the printing process. Its ink requirements are also less demanding than cationic inks. In this way, a wide selection of pigments is sufficient to ensure that the ink has a good rheology on the YAG anilox roll. In addition, high pigment filling reduces the volatile components of the ink, reducing shrinkage and odor.

2 wide printability. Because free radical ink does not have too many restrictions on ingredient selection, it can print substrates with strong alkalinity, or alkali-soluble, water-soluble flexographic printing inks.

3 Drying speed. High adhesion enables radical inks to adhere instantly to substrates and rapidly cure under low energy light sources. In this process, substrates are not exposed to heat, and cationic inks cannot be printed at high speed because of the high energy requirement for curing. This precisely solves the problem of lower productivity of UV flexo printing than gravure printing. With proper curing equipment and pressure settings, free radical inks will overcome this bottleneck.

4 The new free-radical UV technology can produce heavy metal-free and benzene-free materials, but the printing speed is slightly reduced.

● The disadvantages of free radical ink

1 Free radical ink reacts quickly and quickly cures all ingredients together, which increases the pressure on the substrate. When printing a heat-shrink film, excessive pressure and a small amount of heat energy from the UV lamp can cause shrinkage and deformation of the film. The contraction will also make the free radical UV ink as soft as other UV inks, and the affinity and adhesion will be worse.

2 Free radical ink is easily oxidized. This can be done with high-energy light sources, high-efficiency ingredients, or oxygen-absorbing initiators (such as diamines and triamines). To illustrate, this is an experimental result obtained under the condition that the air condition is relatively stable and there is no great fluctuation. If it is used in actual production, further demonstrations are needed.

Now some companies, such as XSYS's Flexocure XS UV free-radical polymer flexographic ink, have been tested and found to achieve 70% shrinkage, and the product also has good adhesion, with a wide range of applicable materials, such as PVC, OPS, OPP, PETG and so on.

Even at a shrinkage of up to 70%, these new-technology free-radical-polymer flexographic printing inks can exhibit good rub resistance without the use of primers and varnish. These products have the advantages of high color strength, fast curing speed, excellent printability and print performance. It can realize both surface and in-print processes, while its excellent curing performance and low viscosity are effective guarantees for productivity.

3. Solvent type ink

Solvent-based inks are generally used in gravure printing and consist of pigments, solid resins, volatile solvents, fillers and additives. Gravure ink pigments are mostly organic pigments. Organic pigments contain lead, chromium, mercury, copper and other metal elements, which have certain toxicity. Solvent-based inks are the largest source of pollution in the printing industry. In 2004, the world’s annual ink production was approximately 3.5 million tons, solvent-based inks accounted for an average of 30% to 40%, and the amount of organic solvents used by ink worldwide reached 1 million each year. More than tons. In addition, the ink also contains heavy metal elements that are harmful to the human body. The linking material contains 40% to 50% of organic solvents, and long-term exposure can damage the human skin. The high content of organic solvents in the air, passive inhalation will cause harm to the respiratory system. In addition, more organic solvents are used in the ink, and chemical reactions may occur with some gases in the air, resulting in the generation of foul chlorine and fumes, which seriously pollute the air, have a great influence on the growth of various plants, and destroy the ecological balance. Therefore, traditional gravure solvent inks tend to be eliminated, and alcohol-soluble composite plastic inks, benzene-free solvent inks, and water-based inks are being replaced.

Since water-based gravure inks are not yet fully capable of replacing toluene inks, the ink industry has been working hard to develop alcohol-soluble inks that can be accepted by the environment. Alcohol-soluble inks can effectively solve the health problems caused by toluene inks and the influence of solvent residues on the quality of packaged foods. In Europe and the United States, this development has become a trend. In Asia, such as Singapore, South Korea and other countries, toluene ink is being eliminated, will be replaced by alcohol-soluble gravure ink. Alcohol-soluble inks have been widely used in the domestic gravure printing industry. It can be foreseen that in the near future, alcohol-soluble inks will occupy a certain share of the shrink label ink market in China.

4. Water-based ink

Water-based inks are generally used in flexographic printing. The fundamental difference between water-based inks and solvent-based inks is that the solvents used in water-based inks are water rather than organic solvents, which significantly reduces VOC emissions, prevents air pollution, does not affect human health, is not easy to burn, is stable in ink, and is vivid in color. It does not corrode plate material, has simple operation, low price, good adhesion after printing, strong water resistance, and rapid drying, so it is especially suitable for packaging prints such as foods, beverages, medicines, etc. It is a world-recognized environment-friendly printing material and is also currently all printing. The only ink in the ink approved by the American Food and Drug Association. At present, 40% of U.S. shrink film products use water-based inks, and other economically developed countries (such as Japan, Germany, and France) use more water-based inks for film printing. According to relevant data, in the United States, water-based inks that meet the VOC emission regulations must reach a level of less than 25% of the volatile components in the used ink composition and have a moisture content of more than 75%; the ink with low moisture content will not be volatile under the conditions of use. The ingredients are above 60% of these two standards.

Gravure inks have also made considerable progress. The WE-type plastic film gravure aqueous ink produced by Beijing Incofan Chemicals Co., Ltd. uses water as the main solvent, a variety of high-molecular polymers as the film-forming substance, and is accompanied by high-grade organic pigments, inorganic pigments, and various additives. It meets the requirements of environmental protection and has good printing performance and adhesion fastness on plastic films such as BOPP, PE and PET with surface tensions of (3.6 to 4.2)×10-2N/m. After being printed on a BOPP film at a speed of 70 meters per minute by a color printing and packaging factory, the printing effect and performance can reach the level of similar products using aromatic hydrocarbon as the main solvent.

However, not only the water-based ink itself requires advanced technology in gravure printing, but the gravure printing equipment and printing plate rollers also need to be improved. For example, changing a corrugated or engraved platen drum with a groove depth of about 38 to 42 μm to a laser patterning drum with a groove depth of about 24 to 28 μm requires a more effective and powerful drying equipment and a printing plate cylinder and ink that must be made of corrosion-resistant materials. Components such as pumps and scrapers require considerable investment.

Drying time is still the biggest problem in aqueous ink applications. Unless the press is equipped with enough drying equipment, the printing speed will be affected. This is also the most important factor affecting the speed of water-based inks to replace solvent-based inks.

Since aqueous inks are soluble in alkaline solutions, the use of aqueous inks in highly magnetic environments is limited.

Water-based inks also have poor weatherability on frozen food packages.