Part B The characteristics and application of shrink label printing ink
At present, there are four types of inks that can be used as heat-shrinkable materials: cationic UV inks, radical UV inks, solvent-based inks, and water-based inks.
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Free Radical ink advantages
(1) Fast response. Radical ink curing without too high temperature requirements, low-energy light, you can quickly solidify, which greatly reduces the heat of the substrate, to avoid shrinkage of the heat shrink film in 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 ink volatility, reducing shrinkage and odor.
(2) Wide printability. Since free radical ink does not have too many restrictions on its ingredient selection, it can print substrates with strong alkalinity and co-print with alkali-soluble, water-soluble flexographic printing inks.
(3) Fast drying. The high adhesion allows the radical ink to adhere to the substrate instantaneously and cure rapidly under irradiation with a low-energy light source. 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 ink will break through 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.
Free radical ink disadvantages
(1) The free radical ink reacts quickly and quickly cures all components together, which increases the pressure on the substrate. When printing a heat-shrink film, excessive pressure and a small amount of thermal energy of the UV lamp can cause shrinkage and deformation of the film. The shrinkage will also make the free radical UV ink soft as the same as other UV inks, and the affinity and adhesion will be worse.
(2) Free radical inks are easily oxidized. This can be done with high-energy light sources, high-efficiency ingredients, or oxygen-absorbing initiators (such as diamines and triamines). It should be noted that this is an experimental result obtained under the conditions of relatively stable air conditions and no significant fluctuations. If it is used in actual production, further demonstrations are needed.
Now some companies, such as XSYS's Flexocure XS UV radical polymerization flexographic inks, have been tested and found to achieve 70% shrinkage, and the products also have good adhesion, with a wide range of applicable materials, such as PVC, OPS, OPP, PETG and so on.
Even at a shrinkage rate of up to 70%, these new-technology free-radical-polymerized flexographic printing inks can exhibit good abrasion 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 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. Instead, alcohol-soluble composite plastic inks, benzene-free solvent inks, and water-based inks are used.