Metal packaging is an important branch of the country's light industry and is indispensable in the development of industrial production and social life.
With the iteration of modern business needs, the requirements for metal packaging are no longer simply limited to providing reliable storage conditions for the contents. From the perspective of an information carrier, manufacturers hope to enhance brand value, convey corporate culture and future trends to a certain extent through careful design and perfect manufacturing.
Tinplate packaging, mainly three-piece cans, is the most typical representative. Through a series of operations such as surface treatment, cutting, printing and welding of the metal substrate, packaging products that meet specific design requirements can be obtained.
At present, the inner and outer coatings used in traditional coating processes basically require thermal baking and centralized VOC treatment, so tinplate printing factories are usually large local energy consumers and VOC emitters.
In view of increasingly stringent emission reduction regulations, whether for the purpose of reflecting social responsibility or further expanding production capacity, adopting green coating technology to reduce VOC and energy consumption, and achieving carbon footprint traceability are very important issues for industry benchmark companies and influential brand owners.
From the information learned from the market, in the process of printing and coating iron, most of the iron printing inks have switched to UV inks, and the inner coating, primer and varnish are still hot-baked solvent-based coatings. In view of the particularity of the inner coating, the next technical direction should be the transformation of primer and varnish to light-curing technology. At present, light-cured iron printing varnish is a hot spot in the industry, and the development progress is rapid. The following content introduces the detailed introduction of light-cured iron printing varnish.
UV cationic coating is the best solution to meet the needs of tinplate packaging products
Ultraviolet light-curing cationic (UV cationic) coating is the most suitable green coating product for tinplate packaging. Its technical features such as food contact safety, good post-processing performance, zero VOC emissions, no heating and ultra-high curing efficiency all cover the needs of the product just right.
At present, Europe and the United States have taken the lead in commercializing this technology for many years with their leading position in light-curing application technology. With the popularization of technology and the reduction of comprehensive costs, the market penetration rate of UV cationic tinplate coating will be further improved in the future.
Ultraviolet light-curing free radical (UV free radical) coating is another common light-curing system. The core difference between the two systems in the application of tinplate is that UV cationic can be applied to all types of tinplate packaging, while UV free radical coating cannot be used for food and packaging with high tensile requirements.
1)Low migration characteristics - meets food safety requirements
The curing mechanism of UV coatings is a process of polymerizing small molecules into macromolecules in an ultra-short time. The conversion rate of UV cationic coatings can be nearly 100%. The cured film-forming substances have good low migration characteristics, while the free radical system Usually only about 80% can be completed, and safety requirements cannot be met due to the residue of small molecules.
The reason for the ultra-high conversion rate of UV cationic coatings is that the monomers or resin molecules in the system often have two or more functional groups. They have post-curing (or dark curing) characteristics and will initiate polymerization when exposed to UV light. , produces a chain reaction, and in a very short time (about 0.02 seconds), the conversion rate of functional groups will reach more than 80%; the remaining unreacted functional groups will continue to react even if they no longer receive UV energy, 48 hours at room temperature Afterwards, the conversion rate of functional groups will be greater than 99%, and proper heating can significantly shorten the time.
This is fundamentally different from the curing mechanism of UV free radicals. Under ultraviolet light irradiation, the functional groups of UV free radicals have a conversion rate of about 80%. After the ultraviolet light irradiation stops, the reaction stops immediately, and the unreacted monomers, functional groups and resins remain in the film-forming material. These residues will not only cause the mechanical properties and resistance of the coating to decrease, but also easily migrate to the contact surface to cause safety risks.
In addition, UV cationic coatings have low volatility and low odor, and have a better operating environment and health and safety, and are more
acceptable to operators on the production line.
2)High tensile strength and durability - good post-processing performance
The main resins used in UV cationic systems are epoxy materials, and therefore have the excellent properties of epoxy materials such as high adhesion and high mechanical strength. Engineers can make a combination of alicyclic epoxy, bisphenol A epoxy, hydrogenated epoxy and oxygen heterocycle materials according to the specific application scenarios. Among them, alicyclic epoxy resins have the highest reaction activity, high Tg and do not contain bisphenol A. At the same time, they overcome the problem of poor weather resistance of ordinary epoxy materials and are the most suitable epoxy resin materials for cationic reactions.
Current Market Overview
UV cationic tinplate varnish is maturely applied on tinplate packaging abroad. Domestic cationic varnish has an advantage in the comprehensive cost of products. Although there are few light-curing coating equipment in the domestic market, downstream manufacturers are actively expanding their layout and choosing UV cationic or UV free radical varnish according to their own business structure. In addition, UV cationic varnish is also applicable to aluminum substrates, and there are corresponding products for aluminum cans and aluminum screw caps.
UV cationic transparent primer and Bai Keting products are still under development, and there are few commercial varieties on the market