About UV printing

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. In the international arena again, the same as "Electronic Beam Curing Technology" (hereinafter referred to as "Electronic Beam Curing") is collectively called UV/EB Curing.

UV hardening can be used in various traditional printing formats, including letterpress, Flexo, lithography, screen printing, etc. As long as using UV printing ink, UV light source completes the main part. The lithographic UV printing is a lithographic structure using UV ink and UV light source. Of course, some very important matching conditions must 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 can be obtained, which is very helpful for enhancing the high quality image of the product (Tolliver, 1998).
3. It is applicable to various types of printed materials with completely different physical properties and chemical properties, including paper and cardboard, plastics, Sailuluo, PVC, PE, etc. 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). Since there is no need to wait for the ink drying time, the production time can be significantly 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 traditional lithography equipment, and investment decisions need to be more careful.
2. The type of market that can use offset UV printing is wider and more dispersed than the traditional lithography market. Therefore, if the manufacturer wants to invest in the development of this technology, it should conduct market analysis and research first, so as to avoid the risk of losing 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) Tubes: The most common type of tube used for UV light sources is Mercury Lamps filled with mercury. Sometimes, other metals are added, such as Gallium. Metal halide lamps and quartz lamps are also commonly used. 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 focusing type and the other is defocusing type. With the development of manufacturers,
There are other extensions.
(3) Energy control device: The main energy supply of this device is to control the UV energy emitted by the UV lamp tube 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 and there are also microcomputer controls.

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 , It is easy for the printed matter to cause stretching, resulting in the timing of printing can not register, so the importance of the cooling device is evident.

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 by the polymerization of the ink. 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 critical 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). 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 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): The development of Excimer Lamp by Heraeus Company does not generate infrared light, so it does not generate heat. It is effective for printing on thin films or for printing materials that are susceptible to shrinkage. Regulatory control results, other advantages are: energy saving, will not erode the printing press parts, do not send off odors ... and so on. 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 off-line UV coatings. 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 is small, and Z is invested by Shanghai Everglades, so the printing company doesn't need to invest, and the Zangguang factory 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 international leading manufacturers (presses such as Heidelberg, Roland; UV equipment: IST METZ, Eltossch, Spectral; UV lamp: OSRAM..., etc.) 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.

Ink roller, blanket or resin plate

The use of UV inks or UV coatings may cause general printing ink rollers, blankets, or resin plates to swell. Swelling may result in peeling or surface cracking. Use appropriate or specific UV-specific blankets and resin plates. It is very important.

Many UV ink suppliers will recommend a standard range. For example, a nitrocellulose or nitrified material used in blankets may be compatible with oils, UV inks, or coatings. Natural rubber and polymeric ethane materials are swollen and cannot be applied to UV inks and coating oils.

Rubber blankets made of EPDM are particularly suitable for UV inks and coatings, but may not be suitable for general ink-based inks. EPDM blankets, in particular, cannot use petroleum-derived lotions, and special lotions should be purchased. In the same way, the selection of the ink roller of the printing press is based on this principle. It is not always possible to alternately use UV inks and general oil inks. If it is necessary to change inks, it must be cleaned very cleanly to remove any chemicals that may remain.

UV tube

The arrangement of the UV lamps between the units and the working intensity of each setting make the UV ink or varnish of the printed matter fully and properly cured, depending on the printing speed, the degree of ink film thickness, and the color of the ink. In general, only the specialized UV technology suppliers in the printing industry will carefully consider the type of printing press and the various finished product requirements for printing, and recommend suitable UV systems.

BEST-UV uses a suitable standard for "Industrial Medium Pressure Mercury Lamps" or "Metal Halide Lamps" for UV printing and coating applications. If the first color (such as cyan), printing standard ink film thickness (1.20-1.40g/m2), speed 100m/min, the use of two 120W/cm medium pressure mercury lamp curing. If we change the color density of the high, dark color printed on 1-2 superimposed color, the difficulty of the overall curing is greatly increased, this is because the UV light is quickly absorbed by the dark pigment of the ink. Generally, the difficulty of curing four-color UV inks is magenta, yellow, cyan, and black, so the color sequence in UV color printing should be black.