Advantages and Applications of Offset UV Ink

1 About UV ink

1.1 History of UV Printing and UV Ink

It is generally believed that in 1969 UV printing and UV inks were used in carton printing in the United States, and the practical first step was taken. Today, more than 30 years later, the biggest advantage of UV inks is that “instant cure” is in line with market demand, and this demand does have an increasing trend.

1.2 UV ink composition

The coloring components include organic pigments, inorganic pigments, and filler pigments, and the wettability with the binder is important.

The ingredient that determines the nature of the ink is the binder. It plays a role of attaching the pigment to the substrate, and has a great influence on the form and physical properties of the ink. The binder consists of a neutral resin, a reactive oligomer, and a diluting monomer.

Photopolymerization initiators and sensitizers are "primer" for photopolymerization. Today's UV inks use radical polymerization as the mainstream.

Pigments, binders, photoinitiators, and auxiliaries (see Table 1 for the effects) make up the UV ink.

1.3 Drying Methods for Various Types of Inks

The drying method of representative inks used in printing varies depending on the type of printing. Including volatile drying, osmotic drying, oxidative polymerization drying and UV curing.

• Volatile drying

A method in which the solvent or water in the ink is volatilized by heating and dried. Solvent inks are detrimental to the environment because they contain VOCs. In order to dry the water-based solvent or the high-boiling-point solvent ink, a large-scale oven must be configured, and accordingly, the energy consumption is also large.

The ink film after drying in this way is only the solid component in the ink adhered to the substrate. The strength of the ink film is also the strength of the connection material itself.

• Infiltration drying

Low-viscosity components such as solvent and water in the ink penetrate into the substrate, and the solid component such as resin and pigment adheres to the surface of the substrate. This type of ink can be used for paper-based porous absorbent materials, but it cannot be used for non-permeable materials (such as plastics, etc.). The osmotic drying method is used as a newspaper printing drying method, the drying time is short and does not require drying equipment. When using such inks for color printing, the inks need to be dry and do not fade after being printed on the substrates.

• Oxidation polymerization

The oxidative polymerization type uses a binder with double bonds, such as linseed oil and soybean oil, and can be dried by oxidative polymerization reaction with oxygen in the air. As with the osmotic drying method, although drying does not require equipment and energy consumption, it requires a certain drying time and cannot immediately enter the next process. In addition, in order to prevent dirt on the back surface from being dusted, there are environmental problems during operation.

• UV curing

The UV curable ink contains an active material and is cured by irradiation with ultraviolet rays or electron beams. Because it does not contain VOC components such as solvents, it has a low environmental impact and can be used in printing materials such as plastics that are easily affected by organic solvents. Because it is an instant cure, it can be immediately transferred to the next process after printing. Because it will not cure without UV irradiation, it will not adhere to the printing press.

Since UV inks cure instantaneously, they have the advantage of being immediately transferred to the next process after printing. Due to the need for UV irradiation, it consumes more energy than the oxidative polymerization and osmotic drying methods, but the drying energy consumption is much lower compared to the volatile drying using a large oven. The printed ink film is very tough because it is formed by the cross-linking reaction of the UV material.

In addition, this type of ink does not need to be absorbed by the substrate and does not require heating. The available substrates are very extensive.

1.4 advantages and disadvantages of UV ink

The advantages and disadvantages of UV inks are summarized below.

1.4.1 The advantages of UV ink

• Fast drying and curing. Instant curing of the prints can be immediately transferred to the next process, which improves production efficiency.

When printing a packaged product using an oxidative polymerization type oily ink, since the drying is sluggish, the printed product will become sticky when it is placed on top of one another, so it is necessary to spray the powder. The purpose of improving the working environment can be achieved by eliminating dusting, and many companies have turned to UV printing. In addition, since the UV light does not harden when it is not irradiated with ink, the ink can be stored on the printing machine without any problem when used.

• No solvent, no solvent thinner. When an active acrylate monomer is used to form an ink film upon hardening, no VOC is generated, which is favorable for the environment and the operating environment is also improved.

• Strong ink film. Due to the cross-linking of acrylates to form a hard ink film, its abrasion resistance and solvent resistance are excellent.

• Small impact on printing materials. Because it does not require high temperature during drying, it can be used for substrates that are thermally deformed.

• Save energy. Drying does not require a large oven, nor does it require the exhaust gas treatment device required for the drying of the penetrating ink.

1.4.2 The disadvantages of UV ink

•price. Since UV inks use acrylate monomers, photoinitiators, etc., there is a price difference compared to ordinary oil inks.

• Use special equipment. Since the composition differs from the oily ink, special equipment must be used. In order to fully utilize the advantages of UV inks, they are frequently converted from oil inks to UV inks during use. Due to the different composition, if oily ink equipment (ink roller, blanket, printing plate, etc.) is used, acrylate monomer and photoinitiator in the UV ink will infiltrate into these devices, often resulting in printing failures. Use UV ink special or dual-use equipment.

• It is difficult to achieve low viscosity. UV inks achieve environmental improvements due to the absence of solvents. However, it is difficult to achieve low viscosity without the use of solvents. In particular, the gravure process using liquid inks rarely uses it.

• Deinking. It is necessary to remove the ink (deinking) from the old paper when the paper is recycled. In general, since the UV ink forms a hardened ink film by crosslinking of acrylate, it is difficult to remove the ink film from the substrate. However, inks with improved deinking properties have recently been introduced.

2UV ink application

2.1 UV ink applications and their corresponding ink products

UV inks have a relatively high price compared with other inks, which is due to the use of high-priced raw materials such as photopolymerization initiators. However, when discussing prices, how do users grasp the advantages of using UV inks for high-speed printability, shortened post-printing processing time, and saving the production cost of semi-finished product storage space? This is the most comprehensive cost advantage. important.

On the other hand, the price cost of ink in the total cost of printed matter remains an important issue to consider. If the print price is cheaper, the larger the area occupied by the image area in the printing area (the greater the amount of ink), the greater the proportion of ink prices in the print material price; conversely, if the print price is high and the ink usage is small, the ink The price is not a big problem. Printing with UV ink is advantageous.

2.2 Environmentally coordinated UV ink

UV inks have been used as an environment-friendly ink in the past. Specifically, this can be explained in the following aspects: 1) From the perspective of global environmental protection (1) Control of carbon dioxide emissions from ink drying; 2 Do not use (Volatile organic solvents); 2) From the point of view of hygiene (according to industrial self-regulation laws and regulations such as 1NL regulations, labor safety and health laws, toxic substances bans law, reduce the use of substances that may cause harm to the human body or recorded in the book; 2 (Reduce the use of environmental hormones); 3) From the operating environment point of view (1 do not use powder; 2 reduce the burden of the operation of dangerous goods such as preservation; 3 can achieve space savings).

However, from the following point of view, the environmental coordination of the said UV ink is not perfect: the use of petrochemical products that are depleted resources as the main raw material; there must be special materials for printing engineering, ethanol in the fountain solution, and circulation Increased energy consumption for regeneration.

Take Japan's Toyo Ink Company as an example. The company is dedicated to the development of ink for the purpose of further reducing the environmental burden.

First, SOY conversion of UV inks was established by introducing soybean oil as a representative vegetable oil (plant modified oil). Next, by introducing a rosin resin (a rosin-denatured material) derived from a natural material and introducing a vegetable oil (vegetable modified oil) represented by a soybean ink, an ink having both UV and oil properties is established.

Since the UV and oil-based hybrid ink series contain the above-described oil-based ink component, the drying performance deteriorates compared to ordinary oil-based inks. However, this series of inks has obtained the eco mark and soybean oil SOY mark due to its good deinking properties, has met the environmental requirements, has become the designated product of the trademark owner, and has also been evaluated as having a high degree of similarity to oily inks. With the characteristics of printability, users are indeed increasing. It is now being repeatedly studied how to improve the drying performance of the mixed ink.