UV glazing is a surface finishing process of packaging and printing industry in common. Color printing enterprises (especially the export business in Japan and Europe and other countries and regions of the packaging printing enterprises) will often encounter such problems: UV glazing on printing, UV varnish coating wear resistance and poor adhesion, especially the printed ink is made of metal (gold or silver ink after printing ink) then UV glazing, this phenomenon is particularly prominent.
In general, color box printing enterprises often solve this problem by replacing UV light oil. In fact, we should not limit our thinking to replacing UV varnish. Instead, we should diverge our thinking and transform our thinking to changing the production process of color boxes or adjusting the relevant process parameters.
Solutions
The production process of the conventional corrugated box is: plate making and paper cutting, ordinary printing, over UV bottom oil, over UV surface oil, framed corrugated, die cutting, paste box. After many experiments, the author summarizes the methods to improve the production process of corrugated box.
(1) plate making and cutting paper, UV ink printing + online UV polish. The test proves that this production process can greatly enhance the abrasion resistance and adhesion of UV varnish on metal UV ink, but the metal UV ink is relatively rare in the market. It needs special customization, and the price is high, and UV printing machine is also needed for printing. Generally, most small color box printing enterprises do not have UV printer. Therefore, this production process is only suitable for some color box printing enterprises, and its popularization is of little significance.
(2) plate making and paper cutting, ordinary printing, and net print UV polish. This production process can also solve the problem of poor abrasion resistance and poor adhesion of UV varnish on metal ink, but the cost of screen printing UV varnish is high, and its environmental performance is not as good as that of waterborne UV varnish. In addition, many color box printing enterprises do not have full automatic screen printing machine, only the semi-automatic screen printer with low production efficiency, so this production process can only be applied to some color box printing enterprises, which is not worth popularizing.
Finally, after repeated verification, we made clear the way to solve this problem: using high abrasion resistant UV surface oil to improve wear resistance, and ensuring the adhesion of UV base oil by adjusting process parameters or changing materials. After two times polishing and gloss film thickness, the wear resistance of UV oil with high wear resistance is guaranteed. Next step is to solve the key factors affecting the adhesion of UV varnish, printing ink and UV base oil.
Solutions
Before solving the problem, first of all, we need to know the customer's requirements and detection methods for the color box.
(1) the following resistance detection box UV light oil method: if the box needs shipping, the actual available customs carton installed a box of actual products, or products installed a box weight specification model consistent with the actual products in the transportation simulation test machine (vibration) on the vibration of 2 hours or more no, to box surface UV light oil film or layer of ink drops significantly for the qualified sample is put in a box; friction resistance tester, with a weight of 22N wipe 80 times back and forth (weight and number according to customer requirements), with no apparent UV light oil or ink drop is qualified.
(2) the following detection box UV oil adhesion method: 3M transparent tape hard flat surface in the box, and then at a 45 degree angle to the direction of rapid, tear tape, not sticky out UV varnish coating or ink layer is qualified; using HB pencil in box UV light oil film the surface force not to cross back and forth strokes, UV varnish coating or ink layer is qualified.
At present, there are mainly two kinds of silver powder in the silver and ink sold on the market: one is close to the round granular structure, the other is similar to "fish scale" flaky structure. The former is more beneficial to the adsorption of UV base oil, while the latter is more capable of showing the metallic luster and texture of the ink. At present, there is only one kind of gold powder in the gold ink sold on the market, which is similar to the "fish scale" flake structure. Therefore, the adhesion of UV base oil on the gold ink is much worse than that on the silver ink, and it is also more troublesome to solve it. The author also understands that the adhesion of oil based UV base oil on metal ink is better than that of water based UV bottom oil. However, the oil UV base oil is used in the improved process, but the adhesion problem on the metal ink is still not solved. Therefore, we have to shift the focus to the improvement of the metal ink.
In detecting the adhesion of the color box UV light oil, we found that the adhesive tape of the 3M adhesive tape is not only the layer of the UV light oil film, but also a part of the ink layer. In addition, we found that a thin layer of metal powder was left on the fingers after finishing the conventional printing process and after the metal ink was completely dried. From this we can judge that it is probably not enough in the metal ink. So we added some transparent inks to metal inks. Once again, we found that the adhesion of UV base oil on metal ink has been significantly improved, but it still can't meet customer's requirements. In this regard, we replace the added transparent ink to the fast dry light oil, so that the adhesion of the UV base oil on the metal ink is basically solved. However, the addition of fast drying varnish has weakened the color of the metal ink, resulting in a slight change in the print color. Therefore, a small number of four color inks should be added to the metal ink for redeployment. Besides, in the 3 processes after UV polishing, the moisture content of the color box will affect the wear resistance of UV varnish, so we need to control it.
Scheme summary
Finally, Zhong Ying hardware makes the following summary on the technical points of the wear resistance and adhesion of UV light oil on the metal ink.
(1) production process route: plate making and paper cutting, ordinary printing, over UV bottom oil, and over UV surface oil.
(2) select high wear resistance UV face oil and oil UV bottom oil.
(3) add 10% ~ 20% quick drying varnish in metal ink (the specific proportion to the metallic ink completely dry, fingers gently across the printing surface, the finger does not leave basic metal powder as the standard, if the metal ink color is diluted, can be prepared by adding four-color ink). It should be emphasized that the UV bottom oil must be passed after the metal ink is completely dry.
(4) - light oil contain ink driers, if the metal ink added quick drying varnish is still more difficult to dry, can add the appropriate drying properties like dry white oil driers (add less than 3%), should not be added to the red dryness of the oil, because red dryness oil can only accelerate drying the speed of ink layer surface, and can accelerate the drying rate of ink layer inside.
(5) in the process after the glazing, the water content of the color box must be controlled below 16%.
(6) the brand of all kinds of materials in the fixed production line. And all kinds of process parameters such as general printing, UV bottom oil and UV surface oil must be kept stable, and relevant records should be made.