Market Opportunities and Challenges of UV Spraying Inks

As an important member of the eco-friendly ink family, UV inks are occupying the digital ink jet printing market step by step thanks to their attractive advantages such as fast drying speed and low VOC (volatile organic compounds).

UV technology development

UV curing technology has been used in the printing industry for more than 20 years. The key advantage of this technology is the absence of solvents, which reduces VOCs. Its working principle is: UV ink is selectively absorbed by UV light, and its curing is affected by the total energy of UV light and the distribution of light energy of different wavelengths. Under the irradiation of UV light, the photopolymerization initiator in the UV ink absorbs photons of a certain wavelength and is excited to an excited state to form radicals or ions. Then, a polymer such as a polymerizable prepolymer and a photosensitive monomer is brought into an excited state by energy transfer between molecules, and a charge transfer complex is produced. These complexes are continuously crosslinked and eventually cured into a film. Because it avoids the environmental impact of traditional solvent inks, it is considered a "green technology." Another advantage of UV technology is that it can reduce production costs, mainly in terms of improving production efficiency, saving energy, and reducing solvent recovery costs. Based on these excellent properties, the application of UV technology in the field of ink has made considerable progress. According to statistics, from 1999 to 2004, the growth rate of U.S. UV ink applications was 25% to 50%. Among them, flexographic printing inks accounted for 32%; offset inks accounted for 50%; screen printing inks accounted for 25%. It is expected that the application of UV inks in these three printing markets will continue to grow.

The development of the inkjet market

Since the 1950s, the American A.B. Dick company successfully developed inkjet printing, the inkjet printing market has developed rapidly and has become a famous brand in printing technology. At present, the digital inkjet market in some developed countries is quite mature; in China, although the digital printing market has not yet been fully standardized, there is still no standard industry standard concerning product quality, but it is when the market is developing rapidly.

Inkjet printing is generally divided into continuous printing and on-demand printing in two ways (Figure 1). It is directly connected to the computer to solve the needs of high-speed, small-batch printing and on-demand printing, because it is a non-contact printing method. Can be printed on a three-dimensional object, which is actually its greatest merit. Moreover, most of the equipment for inkjet printing is provided for office work and household occupation. In the future, it is estimated that in addition to expanding in these areas, the printing sector will also grow accordingly.

The potential of inkjet printing technology is endless and it has a very broad market prospect. According to a survey by IT Strategy, screen printing currently accounts for about 50% of the entire POP market. Digital inkjet printing and flexo printing almost equally divide the rest of the market. However, by 2008, the market demand for large-format inkjet print will double compared to 2003. In 2003, about 1.1 billion square feet of material was used for inkjet printing, and by 2008, this demand is expected to increase to US$3.3 billion. The corresponding sales value of the market is expected to increase from 2.03 billion U.S. dollars in 2003 to 5.13 billion U.S. dollars in 2008. Obviously, digital inkjet printing technology will show its edge in the flourishing printing industry.
Application of UV ink

With the emergence and development of UV technology, printers have attempted to bring UV technology to the door of digital ink jet printing. However, due to the constraining of the ink viscosity of continuous inkjet (CIJ) nozzles, the application of UV ink jet technology has been limited. The restrictions apply only to the label, cable and wire printing industry. Until the advent of drop-on-demand (DOD, also known as intermittent ink jet) nozzles, the scope of the ink viscosity was expanded, providing a great deal of convenience for the development of UV inks. For a time, many manufacturers of inkjet heads, including Spectra, Xaar, HKIS, IJT, Brother, Canon, Konica, Seiko, Trident, and Sharp, have developed such nozzles that can be used for higher viscosity inks. Some can even eject inks with a viscosity of up to 100 cps at room temperature. Since then, inkjet inks have begun to play a major role in the inkjet printing market.

The advent of drop-on-demand inkjets has expanded the range of UV ink materials. Many ink manufacturers have focused on this opportunity to research and develop UV inkjet inks. They have been successfully applied to the printing of flexible materials and rigid materials. Subsequently, digital ink jet equipment manufacturers also developed a wide flatbed ink jet printer that can use UV jet ink. With the advent of this equipment, the demand index for UV inks has been rising in a straight line in recent years. In the United States, the market share of UV inks in all jet ink products has increased from 25% in 1999 to 2004. 30%.

There is no doubt that UV technology will become a key factor in wide-format digital printing.

Since UV printing can be printed on rigid materials as well as on flexible materials, print resolution up to 600d pi, productivity up to 1000 sq ft per hour, durable printed images, ability to print unprocessed substrates, and The low price and many other leading advantages make it a good application prospect. Numerous screen printers have begun to use this technology to seize new market opportunities for short-run printing and apply it to the growing number of personalized, regional advertising prints. At the same time, commercial photo agencies and commercial printers have begun buying UV printers to compete with screen printers in the field of short-run printing.

The advantages of UV ink jet

The ideal UV jet ink can make the printed image waterproof, anti-fading and other characteristics, its advantages over other types of inkjet ink include: low VOC; low energy requirements; instantaneous drying; applicable to a variety of substrates; before curing Will not dry; does not block the nozzle; does not need to clean the nozzle; ink composition is stable; printing quality is high (lightfastness, rub resistance); no pollution.

One of the most worth mentioning is the instant curing characteristics, which make the UV ink from the nozzle has no component penetrate into the surface of the substrate and has nothing to do with the substrate, so there is no need to worry about the ink will infiltrate into the substrate and thus the surface of the substrate Performance affects.

The greatest advantage of UV inks for inkjet devices is that they do not cure at the nozzles, eliminating the need to clean the nozzles to remove insoluble components. From an industrial point of view, due to the shortened maintenance time of inkjet equipment, inkjet printing using UV inks can achieve greater production efficiency. Types of UV Ink Jets There are mainly three kinds of UV inks for inkjet printing, namely, water-based inkjet inks, hot-melt inkjet inks, and low-viscosity inkjet inks.

1. Water-based UV ink jet

Water-based UV inks use water as a solvent to reduce the viscosity of the ink. Its components are mainly UV-curable resin emulsions. However, this technique has two disadvantages. First, the ink jet system requires the moisture in the ink to evaporate before the UV light source is irradiated. The moisture in the ink is an annoying problem. Only the rapid removal of moisture can prevent printing defects such as dot gain and moisture penetration into the substrate. If the moisture is not removed in time, the ink cannot adhere well to the substrate. , Which affects the quality of printed matter; Second, there are still some technical difficulties in the dispersion of photoinitiators.

2. Hot melt UV ink

The use of hot-melt UV inks is mainly dependent on the generation of large droplets of viscous ink droplets. The use of such ink jets can bring strong rub resistance and burst resistance to flexible substrate prints. The difficulty in production is how to find the balance between the two opposites of ink stability and low viscosity at high temperatures.

3. Low viscosity UV ink jet

How to make traditional UV ink directly applied to inkjet printing technology? The key problem is to try to make UV inks have good printing performance, namely low VOC, excellent curing performance, low viscosity and so on. One of the biggest difficulties is how to obtain a lower viscosity. In this regard, researchers have developed a UV-curing resin with a lower viscosity, which provides ink manufacturers with new options, but the practical application of this research results is still very difficult.

Low-viscosity UV-jet ink is a type of jet ink modified by conventional UV inks. Low-viscosity UV inks are developed specifically for intermittent inkjet heads, while high-viscosity inks are often printed with industrial ink jet heads, such as those manufactured by Spectra.

The advantage of low-viscosity UV ink jets is that it introduces UV inks into the wide-format inkjet printing market, allowing it to compete with the ultra-wide inkjet and flat panel inkjet markets. The viscosity of ordinary UV inks is high. They are only suitable for industrial printing, ultra-wide-format inkjet and flat-panel inkjet printing markets. The emergence of low-viscosity UV-jet inks has opened up a broad field of development for wide-format inkjet printing methods. . In addition, there are still some gaps in application fields in the printing market, and researchers need to further improve the UV inks.

UV inkjet ink challenges

Viscosity

The biggest problem with formulating ink jets is to keep their viscosity low. In general, the viscosity of the ink is usually between 10 and 20 cps, but this is mainly achieved by raising the operating temperature of the ink jet device to approximately 40 to 45°C. In foreign countries, it is generally required that the thermal foaming ink jet must be maintained at a viscosity of 3 to 5 cps at 25°C; the piezoelectric ink jet has a viscosity of 3 to 30 cps at 25°C. Only maintaining such a relatively low viscosity can ensure that the ink components can be ejected from the showerhead. Due to the potential volatility and irritation of the cured component, the ink is preferably not above 65[deg.]C, and some are ejected at no more than 50[deg.]C.
2. Pigment wetting

Another factor that affects the performance of UV jet ink is the problem of pigment wetting, which is also a direct factor that affects the durability of the print surface. Therefore, the difficulty in manufacturing UV-jet inks lies in the selection of suitable pigments and their good wetting in low-viscosity solvents.

3. Surface durability

Wide-format and ultra-wide-format inkjet technology is commonly used in the production of advertising banners and slogans. Banners generally do not need to be posted for many years, and usually only need to maintain the printed image for a few months of surface durability. For this reason, manufacturers often introduce fatty chains into the composition of the ink.

Surface tension

The formation of ink droplets is mainly affected by surface tension. Too much surface tension causes the ink to be less prone to droplet formation and may exhibit longer break lengths or break off into "tailed" droplets. Too low a surface tension will cause the droplets to become unstable and even form a "satellite" shape, creating a sputtering spot and affecting the pattern. The ink satisfies the following surface tension range: (2.0 to 5.0) 10-2 N/m, more preferably (2.2 to 4.0) 10-2 N/m.

5. Curing speed

The curing speed of inks is very important for the label industry. Label printers typically run at speeds of 300 to 600 ft/min. For such fast printing speeds, UV inks can exhibit excellent printing performance. To achieve this rapid cure rate, high-functionality cured materials are used in the formulation. Wide-format inkjets typically print at less than 50 feet per minute, so the cure speed requirements are not very high. However, the need for low viscosity ink jets means that low-viscosity, low-functionality cured materials are used to make the ink, but this will inevitably reduce the curing speed.