To obtain the excellent performance of UV inks in applications requires close attention to the properties of printed materials and related chemical reactions.
UV inks that were applied to printing in the early 1970s are increasingly being used in offset printing. Cheng Tun's materials range from paperboard, plastics to metals, etc. UV ink printing has vivid colors, bright colors, and high gloss.
In the past, UV inks were only used for the printing of materials such as car profiles, company annual reports, and advanced cosmetics packaging boxes. Now almost every printing process uses a large amount of UV inks to print a wide variety of prints. Rad Tech International Association (Radiation and Drying Industrial Trade Organization) estimates that about 4,000 T of UV/EB (e-beam curing and drying) ink was used in North American offset printing in 1997, and 3000 T was used in 1994.
With the development of science and technology, UV inks and their curing and drying system technologies are increasingly perfect, which is the main reason for the dramatic increase in the use of UV inks. Professionals pointed out that "UV inks have overcome many difficulties in curing and drying, such as the skin's allergic nature to certain chemical components of UV inks, which has caused headaches for the industry; UV inks are more difficult to clean; it is difficult Obtaining good quality of typographical printing, etc. Now most of the above issues have been satisfactorily resolved."
The energy crisis 25 years ago, together with environmental issues, for the first time attracted the web offset printing industry to the field of UV inks. “Because the evaporation of gases from the offset drying unit was not well captured and the printing company was facing new emission standards for factory chimneys, the web printing industry was seriously shutting down the use of UV inks for the first time.
Environmental issues are the main reason for promoting the large-scale use of UV inks. In fact, a recent survey by the RadTech Association shows that the main reason why 89% of UV ink users apply UV/EB ink technology is to comply with environmental regulations. The pressure to eliminate the issue of volatile organic compounds (Vocs) emissions has made UV inks an advantage in market competition because UV inks hardly emit Vocs when they cure and dry. In some areas, printing companies can only allow printing with UV inks. In the United States, as the federal or local air quality standards become more stringent, more printing companies may use UV ink technology to print products.
Another advantage of UV inks is their excellent drying characteristics, that is, if UV light is not applied, UV inks will not solidify, which can reduce the number of cleaning rollers relatively. Other types of ink rely mainly on evaporation, penetration in the substrate, oxidation, or a combination of these methods to achieve ink drying. In contrast, UV inks cure polymerization reactions almost instantaneously under UV light (wavelengths between 200 and 400 nm), and different chemical UV inks require different UV wavelengths to cure. The active ingredient of the UV ink consists of a polymer resin (conventional ink composition is a hard resin), a diluent that participates in the curing reaction, a phototrigger that reacts to UV irradiation, an additive (such as paraffin wax that improves ink abrasion resistance), and a pigment. And other material components.
The durability of UV inks is another advantage. Many prints printed on coated paper by UV inks for direct mailing can withstand multiple folds and can withstand strong radiation when re-lasered. UV ink can make the ink layer of printing ink solid, fast dry and cross-linked, so that the ink layer has strong abrasion resistance.
UV ink system manufacturers recommend the following basic maintenance methods:
1. Open and check the light box once every 300 working hours. Pay special attention to the mirror pad, which determines the output of half the UV light energy. Use a paper towel, isopropyl alcohol, or other solvents that leave no residue after evaporation to clean the UV lamp and its reflector.
2. Check once a week for dirty spots caused by the accumulation of dust, and use compressed air to wash dirty spots every month.
3. Use a voltmeter and ammeter as a diagnostic tool to measure the operating voltage and current value of each UV lamp and compare the reading with the previous value curve.
4. Determine if each device or component connection is tightly connected.
5. An air dryer is installed to provide clean, dry compressed air to drive the opening and closing of UV lamps. Water is drained from the dryer once a week.
6. Save the system maintenance diary to record the UV lamp usage time (hours).
Although UV inks are two to three times more expensive than conventional heat-curable inks, their many excellent features make up for the costly disadvantages. UV inks can be printed on substrates that other inks cannot print.
For example, it can be printed on nylon and credit cards. Recently, printing companies have used single-sided printing with oil-based ink on some materials for direct mailing, and then printed a large amount of Uv ink on them to seal the printed content. (For example, after printing the original password of some magnetic card telephone cards in China, a layer of UV ink is printed to achieve the purpose of sealing. The user can scrape off this layer of UV ink when using a magnetic card.)
New users often need to change the printing process to meet the printing technology requirements of UV inks. For example, UV ink printing needs to use a blanket, ink roller, printing plate, etc. different from conventional printing, in which the printing plate is changed from the original plano-convex plate to the bimetal plate. In addition, special attention should be paid to ink roll adjustment, ink balance, fountain solution, and other issues that need to be summarized. In addition, since UV inks can be applied to different printing processes, the sellers should be consulted about the applicability of UV inks for specific applications.
The most common problem caused when using UV inks is its adverse effect on blankets and ink rollers. Most of the ink rollers used in traditional inks are made of synthetic rubber. However, when UV inks encounter this type of rubber, the UV inks contain components such as acetate monomers and photoinitiators. This kind of rubber reacts chemically, causing the ink roller to expand. After the ink roller expands, it will cause the roller to disengage, which will affect the accuracy of registration and make the edges of the image unclear. Users should use special blankets and ink rollers when printing with UV inks. The material should be composed of a polymer with anti-oxidant solvent and high concentration of acid. The oxidizing solvent and high concentration of acid can easily damage the rubber. Some compounds.
UV inks can cause the same problems with photopolymers on the surface of the plate. Monomers and photoinitiators in UV inks rapidly decompose dot sites in the same manner, so that the range of imprint resistance of printing plates after using UV inks is reduced to 300 to 100,000 sheets. The reason for the large change in the range of the imprint resistance rate is mainly caused by the following factors: , namely roller pressure, paper, printer type, printer's working status and its service life.
Another obvious change when using UV inks is the use of bimetal plates. The inert steel surfaces of these plates are not attacked by UV inks. This bimetal plate can greatly improve the printing rate, while the print quality is almost not reduced. According to statistics, the printing rate of this bimetal plate has reached 400,000 sheets.
Bimetal plates can be sharpened during the platemaking process to overcome dot gain during the printing process. In the plate making process, the normal and bimetal plates are subjected to an exposure treatment, and the unexposed photopolymer is removed with a developer, since the photopolymer is attached to a thin layer of a copper-aluminum or copper stainless steel plate. So the bimetal version will last longer. In addition, the etching liquid can be used to remove some copper material on the printing plate without image area, and the etching thickness is 0 2020 μm to control the degree of the copper plate material to be removed/removed under the polymer dot, so that the user can control the size of the printing dot size.
Prints made with this bimetal plate have clear, vivid images. The degree of blotting (spreading) at the outlets is also tolerable. This bimetal plate overcomes the stencil failure and the layout is very clean during the printing process.
Because UV inks can be used on different types of printers, the use of UV inks should be carefully consulted when selecting UV inks. Appropriate adjustments to blankets, rollers, plates, ink fountain solutions, and inks are very important for UV ink printing. For example, UV ink suppliers often provide training and even adjust their ink formulations to help users meet special printing requirements.
UV inks have many advantages. Knowing in advance that process requirements will help users who are using UV inks for the first time fully understand the benefits of UV inks. G
(Author: Shanghai Jiaotong University)
Editor/Ou Dingjun
Rongqi Ceramic Co., Ltd. , http://www.sz-ceramics.com