UV ink application in screen printing

China's rare earth resources are very abundant. There are many types of rare earth luminescent materials and their applications are also extensive. The rare earth luminescent material can be combined with the ink, and a photoluminescent safety signboard can be produced through screen printing, and PVC hard low-foamed polyvinyl chloride sheet or flame-retardant ABS material can be used according to different requirements of the use place, environment and customers. Fire sign board. At present, there are broad prospects for the development of photoluminescent safety signs in China, and their social and economic benefits are inestimable. In the past, light-emitting security signs mostly used thermosetting light-emitting inks, which had the disadvantages of large solvent volatilization, complicated process, time-consuming, and large energy consumption. Therefore, development of a simple, clean, environmentally friendly, energy-saving ink has become the focus of attention.

UV inks use ultraviolet light as an energy source, and the photoinitiator in the ink is irradiated with ultraviolet light to generate radical or cation-initiated polymer solidification. In the UV curing system, there is no need to add volatile solvents. The prepolymer and the diluent in the raw materials all have the polymerization reaction activity. When cured, all cross-linked and formed into films, so that there is no solvent volatilization, and it is known as “facing the 21st century. Green Industry New Technology."

Combining UV curable inks with rare earth luminescent materials to produce UV luminescent inks enables the printing process to be clean, environmentally friendly, low in energy consumption, suitable for continuous production, and has excellent UV curing properties in gloss, abrasion resistance, hardness, and solvent resistance. Aesthetics and other aspects have other excellent quality unmatched by the curing method, UV Luminescent Ink is a new type of ink suitable for modern industrial production.

1. Application of UV Luminous Ink in Screen Printing

Adding luminescent powder to ink is a common method for preparing luminescent ink. In the past, luminescent ink was mixed with luminescent powder to prepare luminescent ink. With the development of UV technology, the combination of a luminescent powder and a UV ink to prepare a UV luminescent ink has been gradually adopted by a large number of printers. In particular, the use of a UV luminescent ink instead of a thermosetting luminescent ink in the production of a luminescent sign has considerable advantages. The use of screen printing technology for the printing of UV light inks is a common method for preparing light emitting signs.

1.1 Luminous powder selection

The UV light ink should consider the choice of luminescent powder in screen printing. The basic requirement of luminescent powder is high brightness and moderate particle size. The large particle size cannot be leaked from the screen, and the small print thickness is not enough. It is necessary to increase the number of prints to achieve the thickness requirement and waste time. It is appropriate to use 50-80 μm luminescent powder. The rare earth luminescent powder is light yellow-green, so the choice of substrate for making logos should be blue or green.

1.2 Screen Production

Luminous signs generally require that the luminescent layer be printed thicker. Therefore, a screen of 80 mesh polyester monofilament is usually used so that the luminescent powder can pass through the screen and the printed luminescent layer is also relatively thick. In the plate-making process, it is necessary to consider the general label products. For example, some place name plates are often not printed consecutively in the same pattern. In this case, the low-grade oil-resistant photosensitive plastic can be used to save costs.

1.3 Precoat

A layer of white underlayer needs to be printed before the light emitting layer is printed, and the light emitting layer is printed on the white underlayer. The bottom layer is one of the necessary steps for printing a luminescent ink. Precoating the substrate surface to the substrate will help improve the luminescent properties of the coating. The experimental results show that the use of different pigments of the primer on the luminescent properties of the coating is not the same, the white primer added titanium dioxide is most conducive to improve the coating's luminescence, because white coating can make the incident through the coating The light and the emitted fluorescence are reflected more fully, and the effect of the fluorescent coating is maximized.

It should be noted here that UV-emitting inks need to have good adhesion on the white base layer, otherwise the light-emitting layer will easily fall off after curing, and general PVC inks are generally used because most UV inks have good adhesion on PVC. Efforts are made so that the light-emitting layer can be prevented from falling off the signage.

1.4 curing method

At present, the production process of thermosetting inks is the printing of the first color (usually printed dark color) → sending high-efficiency infrared or far-infrared dryer (conveyor drying tunnel) surface drying → printing the second color (color sequence is usually deep And light) →Send high-efficiency infrared or far-infrared dryer surface drying →Print n-th color →n-time send high-efficiency infrared or far-infrared dryer surface drying → Last color complementary color cover (finishing color) →High efficiency infrared or far infrared Drier surface drying → send infrared or far infrared drying oven completely cured and dried. It can be seen that the curing process is cumbersome and energy-intensive, and UV inks can be cured immediately after being printed directly through the UV curing machine. The cured product can immediately proceed to the next procedure, and the process is simple, which greatly saves time.

1.5 Other issues

In the use of UV light ink to pay attention to a very important issue, label production often need to reach a certain thickness of the light-emitting layer, then need to be printed multiple times to achieve the thickness requirements. Since the UV ink is cured immediately after printing, the cured surface is smooth, and the next printing is performed on the basis of the previous layer. In this case, UV ink is required to have good adhesion between each layer. Efforts can not be stratified. Therefore, in the selection of UV inks, special attention should be paid to the problem of interlayer adhesion.

2. Comparison of UV Luminous Inks and Traditional Thermo-Solid Luminous Inks

The composition of UV inks is very different from that of traditional inks. The filming of UV inks is a chemical action. Polymerization of monomers and polymers takes place under the action of initiators. The filming of traditional inks is a physical action and the resin is already polymerized. Body, solvent The solid polymer is dissolved into a liquid polymer, printed on the substrate, and then the solvent is volatilized or absorbed, allowing the liquid polymer to revert back to its original solid state.

2.1 UV Luminous Ink Composition and Advantages

The structure of UV inks includes resins, monopolymers instead of solvents, additives, and photoinitiators. The resin in the UV ink is very different from the resin of the solvent-evolving ink. It is reactive and it can react with a certain product in other chemical reactions. In UV ink, it can react with the monomer. Monomer is a low molecular weight chemical that can replace the solvent to some extent and reduce the viscosity for printing. But in addition to serving as a solvent or diluent, it also has a very important role to play in chemical reactions. Each component of the UV ink can react chemically because it is 100% cured and all components will become solid by chemical reaction.

2.2 Advantages of UV inks in printability

Compared with solvent inks, UV inks have greatly improved printability and print quality. Since UV inks are 100% solids and there are no volatile solvents, ink viscosity does not change with changing environmental conditions. In the past, printers had to complete a very long cycle of printing, especially when printing fine patterns. The problem of viscosity change was always encountered. Before and after the printing, the ink was drawn and the solvent volatilized to change the viscosity. From time to time, The thickness of the ink layer will be different. With UV inks, the ink viscosity does not change during the working day, and the quality of printed products is exactly the same. In terms of cleaning, UV inks are immediately put into the curing equipment for curing after printing, so the printed materials are not exposed to impurities and the products are kept clean. The solvent-based inks need to be dried for a long time after printing. When there are more dust in the environment, the products will be contaminated. When a luminous signboard is manufactured, it is often required to print thicker, and multiple prints are required to achieve the thickness requirement. At this time, printing with a traditional ink must be performed in a drying tunnel once after each printing, which requires a lot of time and energy. The use of UV-curing inks for printing does not require drying in a drying tunnel, and can be cured immediately after each printing to proceed to the next step, which greatly saves time and energy.

In general, UV inks have the following advantages: 1) Free of volatile organic solvents, little pollution, no harm to human health, 100% solid content, no inconsistency in printing ink film thickness due to volatilization of solvents 2) The ink is not blocked, which is conducive to the printing of fine products; 3) During printing, the solvent is not worried about the damage to the substrate, the ink quality is stable, the dry ink film gloss is good, and the ink film is abrasion-resistant, water-resistant and oil-resistant. Good resistance to solvents; 4) Instantaneous drying of ink, rapid printing production line can be organized, greatly improving printing efficiency; 5) Printing ink saving, solvent ink can print about 50 m2 per kilogram, and UV ink can be printed under the same conditions. M2.

Conclusion

Ultraviolet radiation curing technology is a brand-new green technology developed in the world since the 1970s. The UV-curable inks produced by this technology, referred to as UV inks, have no volatile organic compounds (VOC) and have little environmental pollution. , Curing speed, saving energy, curing product performance is good, suitable for high-speed automated production and other advantages. Traditional inks are volatile and have a slow curing speed, which is not conducive to environmental protection. Therefore, UV inks can be said to be the main alternative to traditional inks. At present, UV ink has become a more mature ink technology and its application range is expanding. With the advancement of UV ink production technology and the development of UV ink raw materials, UV curing technology will make greater progress in the future. UV-curing light-emitting inks, as a type of UV ink, also have a greater application in screen printing.

Information Source: Screen Printing