UV printing technology

Industrial Applications UV Hardening Technology Since the early 1960s, the German Wood Company has applied a hardened coating to the surface of wood. The world's first use of UV lithography was in the United States, and the United Kingdom was successfully used by the company in 1970 (Holland, 1997). Compared with the traditional lithography, it is only a very young technology, but development has become a very important printing technology.

In general, UV is not specifically used for lithography. It is a UV light source that irradiates chemicals. The scale of the chemicals contained in the chemical, Photoinitiator, is stimulated by a UV light source and is extremely short. Within a period of time (less than one second), the "Radiation Curing" of the "Polymer" contained in the chemical to produce a glue-hardening is commonly referred to as UV Curing. Internationally, it has also been classified as "Electronic Beam Curing" in the same category, collectively known as UV/EBCuring.

UV curing can be used in various traditional printing formats, including letterpress, flexo (Flexo), lithographic, screen printing, etc., as long as the use of UV ink, with the UV light source to complete the main part. The lithographic UV printing is a lithographic structure that uses UV inks and UV light sources. Of course, some very important matching conditions need to be achieved at the same time. In addition to printing, the use of transparent material for UV coating is also widely used in the market.

First, the characteristics of lithographic UV printing

In general, UV printing has the following advantages:

1. The color saturation is high and the color effect is good. Compared with traditional lithography, lithographic UV printing can achieve higher color effects. For print products with stricter color requirements, more satisfactory results can be obtained.

2. High print gloss, visually beautiful. When paired with an extinction background, a visually compelling contrast is obtained, which is extremely helpful in enhancing the high quality image of the product (Tolliver, 1998).

3. Applicable to various types of objects with completely different physical properties and chemical properties, including paper, paperboard, plastic, Sailuluo, PVC, PE, etc. Paper and film. This feature can print more product types than traditional lithography and has a broader market future.

4. Drying immediately at the same time as printing can greatly improve production efficiency (RadTech, 1998). Because there is no need to wait for the ink drying time, the production time can be greatly shortened, and the printing company can also save a lot of space for storing dry prints, which is helpful for cost savings.

5. Due to immediate drying during printing, it is not necessary to use dusting, which can be avoided by improving the quality problems caused by dusting.

6. Due to immediate drying during printing, color change may not occur within 48 hours of printing, unlike conventional lithography (Ehrlitzer, 1998).

7. The print has better light resistance.

8. The print has better abrasion resistance.

9. Be more environmentally friendly (RadTech, 1998).

In addition to the aforementioned advantages, does lithographic UV printing have no shortcomings? The answer is of course there are some drawbacks:

1. The cost of investment in lithographic UV printing is higher than that of traditional lithography equipment, and investment decisions need to be more careful.

2. The types of markets that can use offset UV printing are wider and more dispersed than the traditional lithography market. Therefore, if manufacturers want to invest in the development of this technology, they should first conduct market analysis and research so as to avoid the risk of placing orders after investing in equipment. .

3. The cost of ink for lithographic UV printing is about 3 to 4 times that of traditional lithographic printing inks, and the material cost is high. The production management technology, process technology, and cost control in print production need to be more rigorous, otherwise the proportion of cost loss will be higher than traditional lithography.

4. The ink storage area must be subject to stricter temperature control, which should be kept below 20°C, and the storage cost is higher (Hostmann Steinberg, 1992).
5. If the UV leaks out, it will have a health impact on people.
6. Lithographic UV printing is not as popular as traditional lithographic printing. Familiarity with the manpower supply of operating technology requires its own training.

In general, the types of technologies that UV printing will apply to are briefly described below:

1. UV light source equipment: including lamp, reflector, energy control device, temperature control device (or cooling device).

(1) Tube: The most common type of tube used for UV light sources is Mercury Lamp filled with mercury. Sometimes, other metals are added, such as Gallium. Metal halide lamps and quartz lamps are also common types. At present, many rely on imports. The electromagnetic wavelength emitted by UV lamps must be between 200 and 400 nm.

(2) Reflector: The main function of the reflector is to reflect the UV electromagnetic wave back to increase the efficiency of the UV light source (UV Tech Publications, 1991). Another important function is to maintain the operating temperature of the lamp. The surface of the reflector is usually made of aluminum and the reflectance requirement usually needs up to 90%.

There are two basic types of reflectors, one is the focusing type and the other is the defocusing type. Along with the development of the manufacturer, there are other extension types.

(3) Energy control device: The main energy supply of this device is to control the UV energy emitted by the UV lamp to be stable, so as to maintain the efficiency and stability of hardening, in order to meet the needs of different printing speeds. There are electronic designs, but also use microcomputer control.

2. Cooling device:

Since the UV lamp emits IR (infrared wave) when it emits UV electromagnetic waves, the UV equipment will operate at a high temperature (for example, the temperature of the quartz lamp can reach 600~800°C), which will not only shorten the life of the equipment However, the importance of the cooling device is evident in the fact that prints are also prone to stretching.

3. Ink supply system:

Since UV inks have higher viscosity, higher friction, and damage to the components of the printing press (including blankets, ink rollers, etc.) than conventional lithographic inks, the ink in the ink tank should be treated in addition to printing. Should continue to be stirred, the ink roller and blanket used in the ink supply system should be designed for UV printing.

In order to maintain the stability of the UV ink, so as not to affect the viscosity of the ink, the temperature control device of the ink roller is also an important device.

4. Heat dissipation and exhaust device:

The main function is to remove excessive heat from the inside of the machine and eliminate the ozone generated when the ink cures and polymerizes. Usually consists of an exhaust motor and an exhaust pipe.

5. Ink printing:

Whether the quality of the ink is good or not is the most critical factor that directly affects the UV printing. In addition to affecting the traditional quality factors such as color performance and color gamut, the printability of printing ink directly affects the adhesion, strength, and anti-friction force of printed materials after printing is completed. Photoinitators and polymer monomers and their properties are key basic materials.

To control the adhesion of the UV ink, when the wet UV ink is in contact with the object to be printed, the surface tension of the object to be printed (unit: dynes/cm) must be higher than the surface tension of the ink (Schilstra, 1997) to produce Good ink adhesion, so controlling the surface tension of the ink and the printed material is an important technology for UV printing.

6. UV energy measuring equipment:

In UV printing, because the UV lamp aging, power supply, printer speed and other factors, need to control the UV energy to remain stable, so the measurement of UV energy technology has become a very important part.

7. Foreign Technology Development Trends:

(1) The stable growth of the market.
(2) Separation technology using multi-color printing and high-precision performance. Including Hi-Fi Color, and Stochastic Screening Technology.
(3) Cold UV Curing (Holland, 1997):

Heraeus Company develops Excimer Lamp, which does not generate infrared light, so it will not generate heat. For the printing of thin film or the printed material with the effect of shrinkage, it is an effective and good regulatory control result. Other advantages are: energy saving, no erosion of the printing machine Parts, no smell, etc. However, its efficiency has not been able to replace mercury lamps so far, and it has great potential for future development.

China's current use of the lower version of UV printing, compared with the traditional lithography, is a very small number of technology types. To date, there are few manufacturers of lithographic printers designed specifically for the characteristics of lithographic UV printing. Most of them are used to produce magnetic cards, films, and high-quality cosmetic packaging boxes.

Domestic printing companies use more lithographic UV applications, most of which are used in glazing applications. Most of them are offline UV glazing. When a traditional lithographically printed paper print requires a high-gloss finish (including full gloss and partial gloss), this approach is mostly used. Its investment amount is relatively small, and most of them are invested by Shanghai Everglades, so the printing company does not need to invest, and Shangguang is more cost-effective because the equipment can be efficient. The disadvantage is that the production process is long and the quality is unstable. Due to the use of dusting in traditional lithographic printing, the coating effect will be affected. This type of combination is often used in commercial advertising and packaging.

At present, there are no major problems on the current situation regarding the use of lithographic UV printing technology in China. As the leading international manufacturers (printers such as Heidelberg, Roland; UV equipment: IST METZ, Eltossch, Spectral; UV lamps: OSRAM... etc.) all have professional complete equipment, these equipments have also experienced foreign printing companies. The rigorous test of its use, its use efficiency and stability have no major problems, in addition to the financial problems of high investment in equipment. At present, the application of lithographic UV printing technology in China mainly focuses on issues related to material supply and printability.


Source: Shenzhen Kaidia Electric Light Source Co., Ltd.