After UV coating treatment, the appearance effect of paper packaging products can be largely improved, make the printing quality thick and full, gloss and rich, improve the decoration effect of paper products, and can significantly improve the folding and chemical resistance, and improve its performance , To reduce the loss of products in the process of transportation and storage. For products with high requirements for moisture resistance (such as electrical appliances, etc.), the paper packaging products are treated with UV coating to improve the moisture resistance of the packaging.
Advantages of UV coating
1. No environmental pollution, no solvent volatilization, which is safe and environmentally friendly.
2. Fast drying speed and high production efficiency. Since the photo-curing reaction can be completed in an instant, the UV varnish can be directly stacked or entered into the next process after printing and curing, which speeds up the production process and improves production efficiency.
3. Not limited by the types of substrates, not only can be used to polish the surface of paper, aluminum, plastic materials, but also can be used to polish the surface of polymer plates, furniture, metal materials, wireless materials, etc.
4. Save space and energy, because the UV varnish does not need auxiliary equipment such as drying tunnels for ordinary oily varnish during the curing process, and the volume of the UV curing machine is small, and the effective utilization rate is high, so it greatly saves space and energy. , To reduce the investment in early equipment.
5. Good quality, the printed matter surface after UV coating is smooth and bright, without warping, wrinkling, blistering, etc., and the surface hardness is high, abrasion resistance, not easy to scratch, and chemical corrosion resistance is good. Compared with the laminating film, the cost is only about 1/4-1/3 of the laminating film.
Disadvantages of UV coating
1. The first is the security issue. At present, the active diluents used in UV varnishes have certain volatility or irritation, which still pollutes the environment. The water-based UV varnish that is currently being researched and developed uses water or thickener instead of active diluent to solve the problem of volatility and irritation. It is an ideal environmentally friendly product.
2. Next is the smell problem. Now it is gradually developing in the direction of low odor. At present, the packaging products of UV glazing have not been fully recognized by the International Food and Drug Administration, and they cannot be in direct contact with food. Therefore, it is necessary to improve the working conditions and environment, improve the drying effect, and obtain thorough curing, thereby reducing the odor.
3. The third is the adhesion problem on the oxidative polymerization ink. Not only there are problems such as odor and low gloss, but also difficult to attach glue. Nowadays, double coating is often used to improve the quality of UV coating, but it also increases the cost. Therefore, it is necessary to improve the adaptability of UV varnish and ink.
4. Finally, there is the issue of cost reduction. Although the cost has dropped a lot, it is cheaper than the cost of BOPP composite film composite. But in China, there are many types of UV varnishes and their performance is different. So the price difference is big. In general, the cost is still too high, and it is necessary to further reduce the cost of varnish, coating costs and equipment operating costs.
The influence of UV coating on the color of printed matter
Prints with UV glazing sometimes show yellowing. There are two main reasons: one is that the UV glazing oil itself turns yellow; the other is that the glazing oil is only cured on the surface of the printed matter during the glazing process. The inside is not completely cured.
The yellowing of the glazing oil is related to the certain yellowness of the oligomers and reactive diluents used, so colorless oligomers and reactive diluents should be used to prepare the glazing oil. In addition, the influence of photoinitiators is also great. Some photoinitiators will cause the system to turn yellow after curing, such as benzoin dimethyl ether. Therefore, avoid using such photoinitiators to prepare varnishes.
During the glazing process, when the interior of the glazing oil is not fully cured, the glazing oil diluent inside will gradually be absorbed by the ink and paper, and at the same time it will have an effect on the binder in the ink, causing the loss of grease. The pigment is not sufficiently protected and the pigment particles are free. At this time, the smoothness of the surface of the paper coating and the ink layer will be reduced. The rough surface will diffusely reflect the light, so that some white components are added to the color, which increases the brightness and decreases the saturation, giving people a feeling of yellowing and lightening of the color. Therefore, the curing speed of UV varnish should be increased or an efficient UV curing light source should be selected. In addition, the use of water-based UV varnish can avoid the chemical effect of the thinner ink layer and the paper coating, and can avoid the yellowing of the printed matter.