At present, post-press processing methods in the packaging field are increasingly diversified. Each post-press processing method has its own characteristics, but none of the finishing methods is omnipotent. Therefore, in many cases, people often combine a variety of surface finishing processes, such as the currently popular hot-first-after-print process. This process is to print and polish after hot stamping on paper, cardboard or plastic film. The demand for packaging products for this process continues to grow. Here's how to implement the process of hot stamping before printing.
When implementing the hot-first printing process, first determine which printing method is more appropriate. Commonly used printing methods are offset printing and flexographic printing, and sometimes screen printing is also used, depending on whether the ink used is a traditional drying method or UV curing ink.
1. Ordinary offset printing
When using ordinary offset printing ink to print on hot stamping foil, due to the smooth surface of the hot stamping foil and poor permeability and absorption of ink, special component ink should be selected to avoid affecting the drying of the ink. To this end, ink manufacturers have developed oxidized conjunctival drying inks, also known as hot stamping foil printing inks, which dry by chemical reaction with oxygen in the air. This ink is often used in combination with the online water-based glazing process. Its products can achieve excellent anti-smudge and scratch resistance after 24 hours, and have a very attractive appearance.
When printing on hot stamping foil, in order to obtain the desired effect, one of the prerequisites is to ensure that the hot stamping foil is firmly stamped on paper or cardboard. Otherwise, when the ink is transferred from the blanket of the offset press to the hot stamping foil, if the viscosity of the ink is high, the hot stamping foil will be pulled back. The hot stamping foil powder that is pulled down will quickly accumulate on the blanket, thereby reducing the printing quality. In some cases, adding a tackifier to the ink can alleviate or even eliminate this failure.
Another prerequisite is that the edges of the hot stamping pattern should be as clear and sharp as possible, otherwise the hot stamping foil particles scattered on the hot stamping edge will be pulled down by the rubber band and quickly accumulate on the blanket, thus affecting the printing quality.
2.UV offset printing
When UV offset printing is used to print on hot stamping foil, it is also usually matched with the UV varnish of the connection. At this time, it is necessary to pay attention to the adhesion fastness between the ink and the hot stamping foil. One of the reasons that affect the adhesion fastness is the residue of the hot stamping foil insulation layer. When the hot stamping pattern is peeled off from the hot stamping foil, the substances in the isolation layer will inevitably remain. When printing with oxidized conjunctiva dry ink, due to the longer drying time, these residual substances can be gradually absorbed during the drying process. However, if UV ink is used for printing, because the curing time is very short, these residual substances are too late to be absorbed, which will affect the curing of the ink on the surface of the hot stamping foil.
Another problem with UV offset printing is that UV ink shrinks during rapid curing, which of course affects the quality of the hot stamping foil layer. If you want to apply high gloss glazing on the hot stamping foil, this situation will be more serious because the coated UV varnish layer is thicker. In this case, the scratch resistance of the ink layer is poor whether it is adhered with tape or scratched with nails. In order to improve this situation, the only way is to pretreat the hot stamping foil surface, improve the adhesion of UV ink on the hot stamping foil surface, and improve the adhesion fastness.
3.UV flexo printing
UV flexographic printing is usually achieved with a narrow-width flexographic printing machine, which is much more economical than UV offset printing. However, to obtain satisfactory results, it is necessary to ensure that the ink used matches the hot stamping foil and printing equipment. This requires hot stamping foil suppliers and ink suppliers to work closely to provide customers with tailor-made solutions.
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