Application of UV ink in flexo printing
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Ultraviolet inks, also called UV inks, use a certain wavelength of ultraviolet radiation to turn a liquid UV ink into a solid ink through an instantaneous photochemical reaction.
UV inks have developed rapidly in the past 10 years, have entered the stage of maturity, and are recognized by the world as pollution-free ink varieties. At the 7th International Conference on Radiation Curing in Malaysia last August, much information showed that the world's main application area for radiation curing (including EB curing and UV curing) is the printing industry. Its main varieties include: UV varnish, UV screen printing ink, UV offset ink, UV flexo ink, UV metal printing ink and UV electronic circuit ink. According to the data, in 1997, the United States consumed 3,000 tons of UV flexo inks, and it is increasing at a rate of 9-12% per year.
In recent years, the development of UV materials for printing in China has also been relatively fast. According to statistics, in 1998, domestic UV printing materials consumption exceeded 2,000 tons (including domestic and imported materials), mainly used for UV coating, printed circuit board inks. And UV screen printing inks, in addition, there are some UV offset inks, UV embossing inks, etc., UV flexo inks are used in very small quantities, still in place In the beginning stage.
UV flexo inks have received widespread attention and favor in foreign countries, mainly because they have the following characteristics:
1. UV flexo ink is safe and reliable, solvent-free, non-flammable, non-polluting, suitable for food, beverage, tobacco, alcohol, medicine and other packaging conditions with high hygienic conditions. Flexo UV ink has been used in foreign food packaging for many years without any problems.
2. UV flexo ink has good printability, high printing quality, no change in physical properties during printing, non-volatile solvent, stable viscosity, not easy to paste plate, can be printed with higher viscosity, strong ink, high dot resolution, tone reproduction Good sex, bright and bright ink, strong adhesion, suitable for fine product printing.
3. UV flexo ink can be dried instantaneously, with high production efficiency and wide adaptability. It has good adhesion on different printing carriers such as paper, aluminum foil and plastic. After the product is printed, it can be stacked immediately without blocking.
4. UV flexo inks have excellent physical and chemical properties. The process of UV curing and drying is a photochemical reaction of UV ink, that is, a process from a linear structure to a network structure, so it has many excellent physical and chemical properties such as water resistance, alcohol resistance, alcohol resistance, abrasion resistance, and aging resistance. Kinds of inks are out of reach.
5. The amount of UV flexo ink is reduced. Since there is no solvent volatilization, the active ingredient is high, and it can be converted into an ink film by almost 100%, and the amount thereof is less than half of the ink or solvent ink, and the number of cleaning of the printing plate and the anilox roller can be greatly reduced, so the comprehensive cost is relatively low. Based on the above characteristics, UV flexo inks have obvious advantages and development prospects from the perspective of environmental protection, quality, and technology development.
There is still a process in the promotion and application of UV flexo printing technology in China. On the one hand, it is a further understanding and understanding of UV flexo printing technology, on the other hand, it needs to be improved and improved in terms of equipment, light source, supporting equipment and process technology. The following comprehensive domestic and international information talks about some issues that should be paid attention to in the application of UV flexo printing technology.
First, the UV light source: UV flexo printing each color set must be equipped with an ultraviolet light source. Different colors of UV flexo inks have different ability to absorb ultraviolet light, such as yellow and magenta absorption capacity.
Low, easy to cure and dry, while blue and black absorb UV rays and are not easy to dry. The power of the UV lamp can be distributed according to different colors to ensure proper drying of the UV inks of various colors, and at the same time save energy. Pay attention to the aging of the UV light source, and replace the UV lamp in time to prevent the curing from being incomplete and causing adhesion. The UV lamp has a typical life of 1000 hours, and frequent start-up will significantly shorten the life of the lamp.
Second, Anilox roller: When using UV flexo ink, the mesh angle of the anilox roller is preferably 30° or 60°. The following are ceramic anilox rolls of several common specifications.
2O0 line 9.5-11.0BCM anilox roll: can print opaque solid pattern.
360 line 4.5-6.5BCM anilox roll: printable on the ground and line pattern.
550 line 3.OBCM anilox roll: printable continuous tone image products.
650 line 2.5BCM anilox roll: can print continuous tone image products.
800 line 2.0BCM anilox roll: prints fine continuous image products.
Third, rubber roller: rubber roller must be able to resist UV ink, the commonly used rubber roller is generally made of EPDM rubber (ethylene propylene diene monomer) or silicone rubber.
Fourth, Plate: Although the flexographic printing plate currently used can basically be used for UV flexo printing ink, it is better to use a plate with better anti-UV ink, such as DuPont's UVP-67 open plate. Wait.
Fifth, Ink viscosity UV flexo inks use viscosity slightly larger than water-based inks or solvent-based flexo inks, and the range is wider, which can be in the range of 200 to 1000 CPS.
The viscosity is 30O-500 CPS.
Sixth, storage: UV flexo ink should be strictly protected from light and heat storage. The storage temperature should be controlled at 5 ° C - 30 ° C, and the shelf life of storage is generally half a year.
Seven, additives: UV flexo ink commonly used additives are mainly three: 1. UV reactive diluent; 2. UV curing accelerator; 3. UV ink cleaner.
Eight, safety protection: There are two main points of prevention at present, one is the harm of ultraviolet radiation source to the human body, and the other is the harm of UV ink to the human body. The former needs to use the opaque material to seal the light source and enhance the ventilation discharge treatment. The latter should be operated with gloves to prevent the UV ink from directly contacting the skin. If the UV ink is splashed on the skin, it should be dry and then immediately soaped. Wash with water.
UV flexo inks and their process technology are still being improved and improved, and new varieties and new equipment are also emerging. All of these will promote the UV printing technology to be more complete.
At present, flexo printing machines equipped with UV ink curing systems are increasing, and existing flexographic printing machines are constantly modifying UV ink curing systems. The replacement of water-based inks and solvent-based inks with UV flexo inks has become a trend, and has been widely used in wide-format and narrow-width flexo presses. Undoubtedly, the development prospect of UV flexo printing technology is very good. The promotion and application of domestic UV flexo printing technology needs to be based on our national conditions and product needs, as well as the complete improvement of domestic equipment and equipment. With the increasingly strict environmental protection requirements and quality requirements, it is believed that in the near future, domestic UV flexo printing technology will be adopted. There must also be a big development.