1 About UV ink
1.1 History of UV printing and UV inks
It is generally believed that the application of UV printing and UV inks to carton printing in the United States in 1969 was the first step in practical use. Today, more than 30 years later, the biggest advantage of UV ink "instant curing" is consistent with market demand, and this demand does indeed have an increasing trend.
1.2 Composition of UV ink
The coloring components include organic pigments, inorganic pigments and filler pigments, etc. The wettability with the binder is important.
The ingredient that determines the nature of the ink is the binder. It plays the role of attaching the pigment to the substrate and has a great influence on the shape and physical properties of the ink. The binder is composed of neutral resin, active oligomer and diluted monomer.
Photopolymerization initiators and sensitizers are "initiators" of photopolymerization. Current UV inks use radical polymerization as the mainstream method.
Pigments, binders, photoinitiators and additives (see Table 1 for their functions) make up the UV ink.
1.3 Drying methods of various types of ink
The drying method of the representative ink used in printing differs depending on the type of printing. Including volatile drying, penetration drying, oxidative polymerization drying and UV curing.
• Volatilization drying method is to dry the solvent or water in the ink by heating. Solvent inks are harmful to the environment because they contain VOCs. In order to dry the water-based solvent or high-boiling solvent ink, a large oven must be configured, and the corresponding energy consumption is also large.
The ink film dried in this way is formed by the solid content of the ink adhering to the substrate, and the strength of the ink film is the strength of the connecting material itself.
• Drying method in which low-viscosity components such as solvent and water in the ink penetrate into the printing material, and solid components such as resin and pigment adhere to the surface of the printing material. This type of ink can be used for paper-based porous absorbent materials, but not for non-permeable materials (such as plastics). The penetration drying method is used as a newspaper printing drying method. The drying time is short and no drying equipment is required. When using this type of ink for color printing, the ink needs to be allowed to dry after printing on the substrate.
• Oxidative polymerization method The oxidative polymerization type uses linkers with double bonds such as linseed oil and soybean oil, which can produce oxidative polymerization reaction with oxygen in the air and dry. Like the infiltration drying method, although drying does not require equipment and consume energy, it requires a certain drying time and cannot immediately enter the next process. In addition, in order to prevent the back side from sticking and spraying, it will cause environmental problems during operation.
• UV curing method UV-curable ink contains active materials and is cured by ultraviolet or electron beam irradiation. Because it does not contain VOC components such as solvents, it has little impact on the environment and can also be used for printing materials such as plastics that are easily affected by organic solvents. Due to the instant curing, it can be transferred to the next process immediately after printing. Since it will not cure without UV irradiation, it will not stick to the printer.
Because UV ink is cured instantaneously, it has the advantage that it can be transferred to the next process immediately after printing. Due to the need for UV irradiation, it consumes more energy than oxidative polymerization and infiltration drying, but compared to volatile drying using a large oven, the energy consumption for drying is much smaller. The printed ink film is very tough because it is formed by UV material cross-linking reaction.
In addition, the ink in this way does not need to be absorbed by the printing material, nor does it need to be heated, and the available printing materials are very wide.
1.4 Advantages and disadvantages of UV ink
The advantages and disadvantages of UV ink are summarized as follows.
1.4.1 Advantages of UV ink
• Fast drying and curing. The printed product is instantly cured and can be immediately transferred to the next process, realizing the improvement of production efficiency.
When printing and packaging products using oxidative polymerization oil-based ink, drying is slow, and the printed matter will be sticky when stacked, so powder spraying is required. By eliminating powder spraying, the purpose of improving the working environment can be achieved, so many companies have switched to UV printing. In addition, because the UV light does not irradiate the ink, it does not harden, so the ink can be stored on the printing machine, and there will be no problems when it is used.
• No solvent, no solvent thinner is used. The use of reactive acrylic monomers forms an ink film when hardened, so no VOCs are generated, which is beneficial to the environment and the operating environment is also improved.
• The ink film is strong. Due to the reactive crosslinking of acrylic resin to form a hard ink film, its abrasion resistance and solvent resistance are excellent.
• Little influence on printing materials. It does not require high temperature when drying, so it can be used for substrates deformed by heat.
• Save energy consumption. Drying does not require a large oven, nor does it require an exhaust treatment device required for permeable ink drying.
1.4.2 Disadvantages and prices of UV inks. Because UV inks use acrylic monomers, photoinitiators, etc., there is a price difference compared to ordinary oil-based inks.
• Use special equipment. Because the composition is different from oil-based ink, special equipment must be used. In order to fully utilize the advantages of UV inks, oily inks are frequently converted to UV inks during use. Due to the different ingredients, if oil-based ink equipment (ink rollers, blankets, printing plates, etc.) is used, the acrylic monomers and photoinitiators in the UV ink will penetrate into these equipments, which often causes the printing to not proceed properly, so it is Use UV ink special or dual-use equipment.
• It is difficult to reduce viscosity. UV inks achieve environmental improvement due to the absence of solvents, but it is difficult to achieve low viscosity without using solvents, especially gravure processes that use liquid inks rarely use it.
• Deinking. When recycling paper, it is necessary to remove the ink (deinking) from the old paper. Generally speaking, since UV ink forms a hardened ink film by crosslinking of acrylic resin, it is difficult to remove the ink film from the substrate. However, inks with improved deinking performance have recently been introduced.
2 Application of UV ink
2.1 Application fields of UV inks and their corresponding ink products
Compared with other inks, the price of UV inks is relatively high, which is due to the more expensive raw materials such as photopolymerization initiators. However, when discussing the price, how do users grasp the comprehensive cost advantage brought by the improvement of production efficiency such as the high-speed printing suitability of UV inks, the reduction of post-press processing time, and the saving of semi-finished product storage space? important.
On the other hand, the price cost of ink in the total cost of printed matter is still an important issue to be considered. If the price of the printed matter is cheap, the larger the area of ​​the image area in the printed area (the greater the amount of ink), the greater the proportion of the price of ink in the price of the printed material; conversely, when the price of the printed matter is high and the amount of ink is small, The price is not a big problem, it is more advantageous to use UV ink printing.
2.2 Environmentally Harmonized UV Ink
UV inks have been used as an environmentally compatible ink from the past. Specifically, this can be explained from the following aspects: 1) From the perspective of global environmental protection (â‘ Control the emission of carbon dioxide generated when the ink is dried; â‘¡Not used Volatile organic solvents); 2) From a sanitary point of view (according to â‘ NL regulations and other industry self-regulation laws, labor safety and health laws, toxic substances ban laws, reduce the use of substances that may cause harm to human bodies or be recorded; Reduce the use of environmental hormones); 3) From the point of view of the operating environment (â‘ do not use powder spray; â‘¡ reduce the workload of storage of dangerous goods; â‘¢ can save space).
However, from the following situation, the environmental coordination of the UV ink is not perfect: the use of petrochemical products that are depleted resources as the main raw material; there are also necessary auxiliary materials for printing engineering, ethanol in the fountain solution, and recycling Increased energy consumption for regeneration.
Take Japan Toyo Ink Company as an example. The company is committed to the development of inks for the purpose of further reducing the environmental load.
First, by introducing vegetable oil (vegetable denatured oil) represented by soybean ink, the SOY of UV ink was established. Secondly, by introducing rosin resin (rosin denatured substance) derived from natural raw materials and vegetable oil (vegetable denatured oil) represented by soybean ink, an ink having both UV and oil properties was established.
The UV and oil-based hybrid ink series contains the above-mentioned oil-based ink components, and the drying performance is worse than that of ordinary oil-based inks. However, due to its good deinking properties, this series of inks has obtained the eco-label and soybean oil SOY mark, which has met the environmental requirements and has become the designated product of the trademark owner. In addition, it has been evaluated as having high similarity to oil-based ink The characteristics of printability, users are indeed increasing. Now it is being repeatedly studied how to improve the drying performance of the mixed ink.
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