In the process of printing work, sometimes you will come into contact with the surface finishing process of UV glazing, and the development of this process is inseparable from the printing material of UV varnish.
Color box printing companies (especially color box printing companies with export business in Japan, Europe and the United States and other countries and regions) often encounter such problems: after UV coating of the printed products, the wear resistance of the UV varnish film and the Poor adhesion, especially when the printed product is printed with metallic ink (gold ink or silver ink) and then UV coated, this phenomenon is particularly prominent.
Under normal circumstances, color box printing companies often solve this problem by replacing UV varnish. In fact, we should not limit our thinking to only replacing UV varnishes, but should diverge our thinking and switch our thinking to changing the production process route of color boxes or adjusting related process parameters.
The conventional production process route of corrugated color box is: plate making and paper cutting→general printing→UV primer→UV surface finish→corrugated mounting→die cutting→gluing box. After many experiments, the author summarizes the methods for improving the production process of corrugated color boxes as follows.
(1) Plate making and paper cutting→UV ink printing + online UV coating. Tests have proved that this production process can greatly improve the wear resistance and adhesion of UV varnish on metal UV inks, but metal UV inks are relatively rare in the market, requiring special customization, expensive, and UV printing must be used. Printing machine. Generally, most small color box printing companies do not have UV printers, so this production process is only suitable for some color box printing companies, and it is of little significance for general promotion.
(2) Plate making and paper cutting→general printing→screen printing UV coating. This production process can also solve the problems of poor wear resistance and adhesion of UV varnish on metal inks, but the cost of screen printing UV varnish is higher, and its environmental protection performance is not as good as that of water-based UV varnish. In addition, many color box printing companies do not have fully automatic screen printers, but only semi-automatic screen printers with low production efficiency. Therefore, this production process can only be applied to some color box printing companies and is not worthy of general promotion.
Finally, after repeated verifications, we have a clear idea to solve this problem: use high abrasion resistance UV top oil to improve the wear resistance, and adjust the process parameters or replace the material to ensure the adhesion of the UV primer. After two glazing, the varnish film is thicker, which makes the abrasion resistance of the high abrasion resistant UV surface oil more secure. The next step only needs to focus on solving the key factors affecting the adhesion of UV varnish-printing ink and UV primer.
Before solving the problem, it is necessary to understand the customer's requirements for the color box and the detection method.
(1) Test the wear resistance of the color box UV varnish, the method is as follows: ①If the color box needs to be shipped by sea, you can use the carton used in the actual customs declaration to pack a box of the actual product, or pack a box with the same weight and specifications as the actual product. The product model is placed on a simulated transportation test machine (vibration test bench) for more than 2 hours, and the color box has no obvious UV varnish film or ink drop on the surface of the color box as qualified; ②Put the color box sample on the friction resistance tester Use a 22N weight to rub back and forth 80 times (weight and frequency can be determined according to customer requirements), and no obvious UV varnish or ink drop is considered qualified.
(2) To detect the adhesion of UV varnish of the color box, the method is as follows: ①Put the 3M transparent tape flat on the surface of the color box, and then quickly and forcefully tear the tape at a 45 degree angle to prevent the UV varnish film from sticking. Layer or ink layer is qualified; ②Use HB pencil lead to draw back and forth forcefully on the surface of the UV varnish film layer of the color box, and it is qualified if the UV varnish film layer or ink layer is not scratched.
There are two main structures of silver powder contained in silver ink currently on the market: one is a granular structure close to a round shape; the other is a flake structure similar to "fish scales". The former is more conducive to the adsorption of UV primer, while the latter can better show the metallic luster and texture of the ink. However, the gold powder contained in the gold ink currently on the market has only one structure: a flake structure similar to "fish scales". Therefore, the adhesion of UV primer on gold ink is much worse than that on silver ink, and it is more troublesome to solve. The author also learned that the adhesion of oil-based UV primers on metallic inks is better than that of water-based UV primers. However, oil-based UV primers are also used in the improved process, but the problem of adhesion to metal inks has not yet been resolved, so we have to transfer the core to the improvement of metal inks.
When inspecting the adhesion of the UV varnish of the problem color box, we found that it is not only the UV varnish film layer but also a part of the ink layer that is stuck by the 3M scotch tape. In addition, we also found that after finishing the conventional printing process and the metal ink is completely dry, when the surface of the printed product is lightly scratched with the finger, a thin layer of metal powder will be left on the finger. From this we judge: it may be that the linking material in the metal ink is not enough. So we added some transparent inks to the metal ink, and tested again and found that the adhesion of UV primer on the metal ink has been significantly improved, but it still does not meet the customer's requirements. In this regard, we replaced the added transparent ink with a quick-drying varnish. In this way, the adhesion problem of the UV primer on the metallic ink is basically solved. However, the addition of quick-drying varnish dilutes the color of the metal ink, resulting in a slight change in the color of the printed product. Therefore, it is necessary to add a little four-color ink to the metal ink for re-allocation. In addition, in the three processes after UV glazing, it is mainly the water content of the color box that will affect the wear resistance of the UV varnish, so it needs to be controlled to a certain extent.
The author summarizes the technical points of the abrasion resistance and adhesion of UV varnish on metallic inks as follows.
(1) Production process route: plate making and paper cutting→normal printing→UV primer→UV finish.
(2) Choose high abrasion resistance UV face oil and oily UV base oil.
(3) Add 10% to 20% quick-drying varnish to the metal ink (the specific ratio is that after the metal ink is completely dried, the finger lightly scratches the surface of the printed product, and there is basically no metal powder left on the finger. If the color of metal ink is diluted, it can be mixed by adding four-color ink). It should be emphasized that you must wait for the metal ink to dry completely before applying the UV primer.
(4) Quick-drying varnishes all contain ink driers. If metal inks are difficult to dry after adding quick-drying varnishes, you can appropriately add a drier with the same drying properties as white dry oil (additional amount is greater than or equal to 100%). Third), do not add red dry oil, because red dry oil can only speed up the drying speed of the ink layer surface, but not the inside of the ink layer.
(5) In the process after glazing, the water content of the color box must be controlled below 16%.
(6) Fix the brand of various materials in the production process route, and maintain stable various process parameters for ordinary printing, UV primer, and UV finish processes, and make relevant records.
After reading the above analysis, do you have a better understanding of how to improve the abrasion resistance and adhesion of UV varnish?