In the printing of self-adhesive trademarks, if corona treatment is often used when printing film-type adhesive trademarks such as PET self-adhesive trademark materials, what is corona treatment? What is the role of corona treatment? This article will explain the principle and function of corona treatment in the printing of adhesive labels.
Corona treatment is a kind of electric shock treatment, which makes the surface of the self-adhesive trademark have higher adhesion. The principle of corona treatment is electric shock or breakdown. Under the action of high voltage electric field, the strong impact of the electron flow on the plastic film can make the film surface fluff, become rough, and increase the surface area. When the adhesive is in contact with its surface, it can produce good wetting, the adhesive will penetrate into the grooves that have been brushed, and the film will be firmly bonded by the "anchoring" effect. This is a physical effect. Compared with the untreated film, the film after it is obviously uneven and rough, and the electric shock strength can be enhanced with the increase of voltage and current. The surface becomes rough and increases its wetting of polar solvents-these ionic bodies destroy their molecular structure by electric shock and penetration into the surface of the printed object, and then oxidize and polarize the treated surface molecules, and the ionic electric shock erodes the surface So as to increase the adhesion of the substrate surface.
Many people believe that corona treatment makes the surface of the adhesive rough, making it easy to absorb printing inks and adhesives, but this view is denied by the observation results obtained by scanning electron microscopy. The current popular theory is that corona treatment rearranges the molecular structure on the surface of the adhesive to produce more polar parts, which is conducive to the attachment of foreign objects. The unit of measurement for surface energy is dyne. All liquids and most substrates (except the porous type) can be measured to 10 dynes. In order for the printing ink to adhere well to the surface of the substrate, the dyne value of the substrate should be 10 dyne higher than the dyne value of all inks. The surface energy of water-based ink is higher than the surface energy of solvent-based ink, so its substrate must also have a high surface Dyne value. Everything in nature has the characteristic of returning to its original state. The higher the dyne value the paper product processor wants to achieve, the faster the processing energy will decay. Therefore, when printing with water-based ink on films, metal foils and some papers, secondary treatment should be carried out before starting printing. When using a corona treatment device (properly matched) on the printing press, the processing level of the film can be lengthened to the original level or slightly higher.
The purpose of corona treatment is to change the surface energy of many stickers to make it easy to bond with printing inks, coating materials and adhesives. All the self-adhesive labels have better adhesive properties after some processing in the manufacturing process. Corona treatment is a post-processing. It should be pointed out that corona treatment is not the only treatment method that can be used to change the surface energy of the substrate when producing the substrate. Other treatment methods include flame treatment and coating treatment. The specific treatment method mainly depends on the structure of the substrate. Fine depressions are made on the surface of the PET film by voltage, and these small depressions that are not visible to the naked eye increase the adhesion of the ink. The main purpose is to make the self-adhesive trademark materials easy to print.
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