Part C Glazing process and analysis of quality factors
The glazing process is a technique and method for applying a layer of uncoated transparent coating on the surface of the printed product, after leveling, drying, calendering, and forming a thin and uniform transparent bright layer on the surface of the printed matter.
UV glazing process knowledge and troubleshooting
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UV glazing is also called UV glazing or curing glazing. The main component of UV varnish is composed of photosensitive resin, reactive diluent, photoinitiator and auxiliaries. The principle is that under the ultraviolet irradiation of a certain wavelength, the light in the system is triggered. The free radical of the agent initiates the unsaturated double bond in the resin, and the bond-locking polymerization reaction rapidly occurs to cure the cross-linked film.
The advantages are: high glazing speed, high brightness of film layer, strong film surface after drying, high production efficiency, small footprint, good mechanical and heat resistance, cold resistance, water resistance, wear resistance, etc. The protective effect, after glazing, can make the surface of the printed product very bright and smooth, and the refractive effect makes the graphic produce a strong three-dimensional sense, the color is more vivid, and the printed product has a high-grade feeling.
The disadvantage is that the UV oil has high self-polymerization degree, poor surface molecular polarity, and no capillary pores, so the UV film layer has poor affinity.
First, the application of UV glazing technology
After UV glazing, the paper packaging can improve the appearance of the product, make the printing quality thick and full, luster and moisturize, improve the decoration effect of the paper products, and obviously improve the folding and chemical resistance and improve the performance. Reduce the loss of products during transportation and storage. For products with high moisture resistance requirements (such as electrical appliances), the paper packaging products can be UV-glazed to improve the moisture resistance of the package.
UV glazing has developed rapidly in recent years, and the proportion in the packaging and printing industry is gradually increasing, but there are still many problems to be solved. The first is the security issue. At present, the reactive diluent used in UV coatings has a certain volatility or irritancy and is still polluting the environment. The water-based UV varnish currently under development is an ideal environmentally friendly product by using a thickener instead of a reactive diluent to solve the problem of volatility and irritation.
Followed by the smell problem. It is gradually moving towards a low odor. At present, UV glazing packaging products have not yet been fully recognized by international food and drug residences and cannot be in direct contact with food. Therefore, it is necessary to improve the working conditions and environment, improve the drying effect, and thoroughly cure, thereby reducing the odor.
Again, the problem of adhesion on oxidative polymerization type inks. Not only the presence of odor, low gloss, etc., but also the difficulty of attaching glue. Double glazing is often used to improve UV glazing quality, but it also increases costs. Therefore, it is necessary to improve the adaptability of UV varnish to ink.
Finally, the cost reduction problem, although the current cost has dropped a lot, compared with the cost of BOPP composite film composite is cheaper. However, in China, there are many types of UV coatings and their performance is different. So the price difference is big. Overall, the cost is still too high, and it is necessary to further reduce varnish cost, coating cost and equipment operating costs.
Second, the advantages of UV glazing
1. No environmental pollution, no solvent evaporation, safe and environmentally friendly.
2. Fast drying speed and high production efficiency. Since the photocuring reaction can be completed in an instant, the UV varnish can be stacked directly or into the next process after printing and curing, which speeds up the production process and improves production efficiency.
3. It is not limited to the type of substrate, it can be used not only on the surface of paper, aluminum plate, plastic material, but also on the surface of polymer board, furniture, metal materials, wireless materials, etc.
4. Saving the site and energy. Because the UV varnish does not require the auxiliary equipment such as the drying tunnel of common oil varnish during the curing process, and the UV curing machine is small in size, the effective utilization rate is high, thus greatly saving the site and energy. Reduce investment in equipment in the early stage.
5. Good quality, the surface of the printed matter after UV glazing is smooth and bright, without curling, wrinkling, foaming, etc., and has high surface hardness, abrasion resistance, scratch resistance, chemical corrosion resistance, and Compared with the lamination, the cost is only about 1/4-1/3 of the lamination.