Application of UV Technology in Printing Iron Can Industry

First, the introduction of UV technology for printing

UV is the abbreviation of English UltravioletRays, that is, UV rays. Ultraviolet light (UV) is invisible to the naked eye and is a period of electromagnetic radiation other than visible violet light, with a wavelength in the range of 210-400 nm.

The technology of applying UV in the printing process is to use a special ink to quickly form a three-dimensional network of macromolecules with a stable physical and chemical properties and a high surface ink brightness under the irradiation of ultraviolet rays in a certain wavelength range.

Second, printing application of UV technology and development

The earliest developed UV ink in the world was the United States, probably in the early 1960s. At the end of the 1960s, UV inks had begun industrial production in the United States and were developed primarily to meet regulatory requirements for environmental pollution. Japan began industrial production of UV inks in the early 1970s and manufactured UV ink printing equipment.

China began to introduce UV glazing and UV ink printing processes and equipment in the 1980s. At the same time, domestic ink companies such as the Tianjin Ink Factory also developed UV inks and varnishes. So far, China has developed into the world's largest installed base of UV printers and UV inks.

The application of UV technology in the printing and canning industry was mainly marked by the introduction of the metalstar2 six-color UV iron printing machine of the world’s most advanced KBAMetalprint company in 2004 by Shanghai Baoyin Metallic Coating Co., Ltd., and was subsequently introduced by Hangzhou Zhongyin Packaging Co., Ltd. The British company Lai Wu has five-color UV iron-printing machines. At this point, the UV-printing iron technology has entered a new period of development in China.

Third, the traditional printing process and control points

1. Coating

Apply before printing. Under normal circumstances, the front of the tinplate needs to be coated and printed, and the inner surface is decided to be coated according to requirements. If necessary, the resistance welding blank must be designed scientifically and reasonably to ensure that the tinplate product has good canning, canning, and appearance. Decoration requirements. Coatings are classified by resin as oily, phenolic, epoxy, polyester, vinyl, acrylic, amino, etc. According to the application, there are inner coating, outer coating, color coating, covering coating and special coating.

2. Plate making

Printed iron platemaking and ordinary offset plate making are basically the same, but since the printed iron products must be made into cans at the end, the plated iron plates must meet the canning requirements. The basic characteristics of metal packaging containers should be clearly understood during plate making. For example, in most tinplate cans, the requirements for blank resistance welding are taken into consideration when making plates. There is a certain gap between the patterns, which facilitates the need for cutting and canning after the printing process. The battery case, for example, is In order to arrange as many as possible in the size range of the tinplate, it is also convenient to cut and punch the battery case. In addition, for art jars and gift boxes, it is necessary to understand the size of the blanking edge of the lid, and to leave a certain amount of excess material in accordance with this, otherwise it will cause troubles for the stamping of the lid.

3. print

Tinplate can be printed on the machine (except for special processes) after it has been coated by the inner coating. Iron printing machine is divided into monochrome machine, two-color machine and multi-color machine (generally refers to more than 3 units). The structure of the iron printing machine is similar to the offset printing machine. When printing, ink balance adjustment, printing pressure adjustment and overprinting adjustment are required. Since the surface of tinplate is different from paper, there is no absorptivity of the kind of capillary pores of the paper. Therefore, in consideration of the color sequence, a large area wet wet multicolor overprint cannot be arranged, and a wet-wetting process can be performed only for a dot area of ​​50% or less. When arranging the color sequence, it is generally necessary to comprehensively consider the main colors of the layout, the accuracy of overprinting, and the advantages and disadvantages of the operation, and conduct a detailed analysis according to the characteristics of the product itself and the machine performance.

4. Polishing

After finishing all the trapping, a layer of varnish must be applied on the surface of the stamping iron to increase the gloss of the surface of the printing product. At the same time, the hardness of the surface of the product can be improved, so that the surface of the stamped iron product is not only scratch-resistant but also has a certain flexibility. .

5. dry

Paints and inks are dried in a tunnel oven. The drying conditions of the printing ink are usually between 130°C and 160°C, the time is controlled at about 10-12 minutes, and the drying condition of the coating is between 170°C and 210°C. The tunnel oven is about 30 meters long and consists of three sections: a temperature rise zone, a constant temperature zone, and a cooling zone. The warming zone is the first zone after the tinplate enters the oven. The main role is to raise the tinplate from room temperature to the set temperature; the main function of the constant temperature zone is to maintain the temperature reached in the warming zone for a certain period of time; the function of the cooling zone It is to make the dried tinplate stamps fully cooled. Once the cooling is not enough, the paint film can be easily scratched when the tinplate is piled. After the stacking, the sticky film phenomenon easily occurs.

IV. Application of UV Technology in Printed Iron Can Making

1. Application prospect

With the increasing pressure of environmental protection in China, the environmental protection of UV printing iron has been fully recognized by the metal packaging industry. More and more printing and tinning companies have the desire and demand to adopt UV printing technology to achieve green production. The goal. In addition, UV technology can also save companies considerable cost. If UV technology is used, there is no need to bake up to more than 30 meters of tunnel-type drying room to save equipment footprint, save energy, and reduce noise. Due to the non-absorption of tinplate and its coating, multi-color printing such as printing paper cannot be adopted, so conventional printing iron production lines are mostly monochrome or two-color machines, and production of a product often requires printing several times. The use of UV printing technology can be used after the four-color or even six-color printing machine, so that printing a product can be completed at one time, can greatly increase production efficiency and product quality.

Due to the advanced nature of the UV printing technology and its applicability to the printing and canning industry, some companies in the metal packaging industry have transformed the traditional printing line into the UV printing line since 2004. Since the development of the UV printing technology, the metal packaging industry has entered the fast lane.

2. UV printing materials

At present, the materials used in UV printing are mainly inks, coatings, and related auxiliary materials. Since UV inks, paints and traditional inks and coatings are quite different, we will introduce them in detail here.

The main components of UV inks and coating oils are polymeric prepolymers, photosensitive monomers, and photoinitiators. The auxiliary ingredients are coloring pigments, fillers, additives (leveling agents, defoamers, polymerization inhibitors, lubricants). Wait.

UV printing inks have high requirements for storage. They must be stored in an environment of 5-25°C and the ink should not be exposed to the air; heat sources and sunlight should be avoided.

The technical indicators of UV iron varnishes 971-0461 mainly include: main components: UV acrylic; solids: 97.5±2.5% (ASTMD-5403; METHODA); VOC: 0.08Kg/L; viscosity: 65-95 seconds (25 °C4? Ford Cup); Curing conditions: 300 ± 75mj/cm2; Coating thickness: 5.4-7.0 g/m2; Preheating oil temperature: 32-38°C; Flash point: 93°C (closed cup); Film properties: Good adhesion and mechanical processing properties, high gloss, high hardness, excellent surface smoothness.

3. UV printing equipment

The main difference between UV iron printing equipment and traditional iron printing equipment is that there are UV UV drying equipments between each printing unit, which is less than the traditional equipment. Of course, UV printing iron rollers, blankets and other auxiliary materials should be dedicated, the PS version also need to be dealt with separately, mainly to improve its printability and resistance to India.

4. UV printing process

Since the ink of each unit of UV printing can be dried under ultraviolet light, it can be printed together in multiple colors, and the problem of wet pressing and wet production in the traditional printing iron process can not be considered when arranging the color sequence, and it can be freely arranged according to actual conditions.

5. UV printing iron FAQ

(1) Bad drying, incomplete photocuring, and sticky surface

Causes: UV light intensity is not enough; UV lamp aging, strength weakened; UV ink storage time is too long; Toner is added too much; machine speed is too fast.

Solution: In the case of curing speed requirements less than 0.5s, must ensure that the power of high-pressure mercury lamp is generally not less than 120w/cm, the lamp must be updated, do not wait for the bad to change, if necessary, add a certain amount of UV light Oil curing accelerator accelerates drying.

(2) The surface of the printed product is not painted with UV light oil

Causes: UV light oil viscosity is small, the coating is too thin; the ink contains too much ink or dry oil; ink surface has been crystallized; ink surface anti-stick material (silicone oil, dusting) and more.

Solution: When printing products that require UV coating, appropriate measures must be taken to create the conditions. When applying UV varnish, apply thicker coatings. If necessary, use oil on the base or replace special varnish to solve the problem.

(3) Large residual odor

Causes: Drying and curing is not complete; UV light source is insufficient or the lamp tube is aging; UV varnish oil has poor anti-oxidation capability; UV varnish contains too much non-reactive diluent.

Solution: UV inks and varnish must be thoroughly dried and cured, and ventilation must be strengthened. If necessary, replace the UV varnish type.

V. Comparison between traditional iron printing and UV technology

Compared with the traditional printing iron, UV printing iron technology has obvious advantages:

Reduce costs: UV metal ink can reduce the cost and save energy. The use of UV inks, first of all, no longer needs the drying room part of the traditional printing iron production line, which can save the company the cost of buying drying rooms, and can reduce the space occupation and save plant investment.

Speed ​​increase: The use of UV printing ink can increase the printing speed. Nowadays ordinary iron printing machines generally have a speed of about 4,000 sheets/hour, and after using UV technology, the speed can reach more than 5000 sheets/hour. In addition, because ordinary iron printing ink needs drying room drying, when printing 6 color finished products, if you use two-color printing machine, you need to go through three drying rooms, if it is a monochrome printing machine, you must go through six drying rooms; after using UV technology, not only It can greatly increase production efficiency and reduce the chance of surface scratches on the printed iron products.

Green: The environmental performance of UV printing ink is its excellent quality, because UV ink is basically free of organic solvents.