The different types of varnishes available on the market are cured in different processes, so the properties of the paper and cardboard that use the varnish must be different accordingly. Since printing materials, inks and varnishes interact with each other, the optimization of the relationship between these three can significantly improve the overall performance, because changing one of the three at will not all get the same good results. If you choose an unverified substrate, the result may be bad. Therefore, printing companies need to cooperate with paper manufacturers and distributors to find possible printing materials for all varnishes.
Process practice shows that the quality and characteristics of paper directly affect the quality of glazing products to a large extent. For example, due to its smooth surface, the gloss effect of coated paper is obviously improved after glazing. While the surface of whiteboard or offset paper is rough, the effect after glazing is relatively poor, and the brightness is not significant enough. This is because the varnish is almost completely absorbed by the rough paper fibers.
In order to make up for the defect that the paper is easy to absorb oil and make the printed product lack gloss, you can first apply the casein primer on the surface of the printed product and then polish it, or you can take the method of two varnish passes to increase the printed product Brightness to ensure the quality of glazing.
The operation of coating and drying varnish requires a certain level of knowledge and printing press operation skills. When switching to a different varnish, it is important to test its compatibility with the substrate and all other required finishing forms.
It is also necessary to ensure that the acidity of the printing material does not delay the drying or curing process. Nowadays, paper and cardboard are usually pH-neutral because calcium carbonate can be used as a filler and coating at a lower cost. In an acid medium, calcium carbonate will decompose, and the bubbles of carbon dioxide will cause the ink and varnish to foam.
The rough surface of the paper will directly affect the leveling performance of UV varnish on the surface of the paper. When the surface of the paper is too rough, the flow rate of UV varnish on the paper surface is slow, and almost all the UV varnish transferred to the paper surface is absorbed by the rough paper, so that the film-forming substance in the UV varnish—photosensitive resin penetrates into the fiber. In time, the gloss and brightness of the printed product surface after UV curing are not good. In addition, the rough surface of the paper will also affect the reflection, diffraction and interference of ultraviolet rays, and affect the multiple reflection of UV light on the varnish layer, thereby affecting the curing effect.
The smoothness of the paper surface is not as high as possible. Paper with a surface that is too smooth is generally not very absorbent, and the printing ink cannot penetrate effectively on its surface, causing the ink to crystallize on its surface and form a non-absorbent surface. When UV coating is performed on such a surface, the penetrating components in the varnish will stay on the surface of the paper together with the photosensitive resin, which will make the curing of the varnish incomplete.
Choose paper with good printing suitability, or pre-print diluted white ink on the surface of the paper to change its surface roughness and delay the absorption speed. In addition, water-based varnish can be used as a primer to improve the printability of the paper surface, which can also improve the flexural resistance of printed matter.
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