Status of label printing inks
Label printing inks are rapidly developed along with the rapid growth of label and label printing. In order to better discuss and understand the use of label inks, it is necessary to understand the label classification and label printing methods, by the type and printing method of the labels. The analysis determines the variety of label printing inks and the technical routes and solutions used.
Label classification
Although there are many kinds of labels, they can be easily divided into absorption labels and non-absorbent labels according to the printing materials. Absorbent label materials can be subdivided into paper, synthetic paper, non-woven fabric, etc., and paper label materials can be divided into coated paper, mirror coated paper, wet strong paper, fragile paper, white paper and thermal transfer paper. Non-absorbent label materials can be divided into laser film, PP film, PE film, PVC film, PET film and other plastic film, as well as aluminum foil.
Label printing method
Although there are many kinds of labels, the printing materials are varied and the quality requirements are very different, but their printing methods mainly include lithographs. Offset , gravure, letterpress, flexo, screen printing, transfer and pad printing, and digital printing. UV-cured lithographic offset printing, letterpress printing, flexographic printing, screen printing and digital printing have been used more and more in label printing for more than a decade. The ink curing relies mainly on UV curing. The reaction, because it does not contain a low-boiling organic solvent, can be cured instantaneously, has outstanding advantages in environmental protection, and can be printed on both absorbent materials and non-absorbent materials, and is expected to become label-printed in the near future. One of the main ways. Digital printing is a promising printing method in label printing. Because it is computer-controlled, there is no flexibility, it can be printed on flat materials, curved surfaces, etc. Direct printing on shaped materials allows label printing to be adapted to the variety and individuality of the product.
Label printing ink
Label printing materials are required, so label printing inks are required to have good printability on paper materials, plastic film materials, metal materials (such as electrochemical aluminum foil, metal foil). In the following, we will take the gravure ink used in the gravure beer neck label and the gravure heat shrink sleeve label which are often encountered in daily life, from the selection of resin, the selection of pigments, the selection and matching of conventional solvents, and additives. The label printing ink is discussed in terms of screening, formula optimization and other aspects.
It is critical to master and apply the mechanism of action (50-80%) of the solvent that accounts for the largest proportion of ink composition. The role of the solvent is to dissolve the resin in the ink, but care should be taken to control the solvent's ability to dissolve (ie, solubility). It can neither dissolve nor dissolve well. Solubility is the primary condition for the choice of solvent. Second, use The solvent volatilization speed adjusts the drying speed of the ink, and selects a gradual process from fast to slow according to the volatilization speed. It is impossible to choose a solvent that is too fast and too slow to be transitioned. The third is to adjust the viscosity by using a solvent during the printing process. According to the depth of the gravure and the number of mesh lines, weather conditions, printing speed, etc., the viscosity of the ink can be adjusted to achieve the best printing effect. Generally, the solvent with better solubility is lower, and the dilution viscosity is lower; It is to improve the wetting property of the printing substrate. The organic solvent can improve the wetting substrate. The solvent has a certain ability to penetrate or dissolve on the surface of the substrate, which enhances the adhesion of the ink and thus improves the ink. The adhesion fastness.
Label printing requires good color rendering, hiding rate, image clarity, and is resistant to light (sun), water, acid and alkali. These properties are reflected in the viscosity (adhesion), adhesion fastness, and drying of the ink. Speed, color density, overprint ratio, chromaticity and color gamut, surface tension and other properties.
It is true that the gravure beer neck mark requires ink drying very quickly, the film is smooth, and the die-cutting performance is good (the cut is smooth and smooth, which is good for the winery about 40,000 bottles/hour high-speed labeling), and has excellent alkali water solubility (residue can not be Adhered to the inner wall of the recycled bottle).
The gravure heat shrink sleeve requires the ink to have excellent abrasion and scratch resistance, and the shrinkage ratio is matched with the printed substrate. At present, the heat shrinkable sleeve label is developed from the traditional affordable PVC film to the easily degradable PET and PETG film. In view of the large shrinkage rate of the latter, the shrinkage temperature is relatively high (typically 95 ° C, 10 ° C higher than PVC film). It is easy to deform, so pay special attention to the correct matching of resin and additive when designing ink formulation.
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