4/22/2021 0 Comments Ink Formulation Crack
Films commonly used in package printing are polyolefins (polyethylene and polypropylene), polyamide and polyester.All of these materials have similar characteristics that affect the printing process and the physical characteristics of the final printed article.Ink and its components will not soak into film substrates and have a tendency to sit up on the surface.Solvent-borne inks generally have surface energies in the 36-38 dynescm range.
![]() If the film has surface energy below this level, the inks will not lay smoothly and evenly on the surface. The appearance of the printed ink will be pinholed, or fish-eyed (see Figure 1 ). The pinholes and fish-eyes are the result of the ink pulling in on itself. ![]() The most common is corona treatment, but other options include flame and plasma. The purpose of the treatment process is to raise the surface energy of the film by generating oxygen-containing moieties on the surface. This treatment also cleans the surface of the substrate of waxes, processing aids and other chemicals that impact the print quality of the ink. For example, water-borne formulations have very high surface energy, as water has a surface tension of 72 dynescm. In order to overcome high surface energy, the addition of some low-boiling alcohol (often ethanol or isopropyl alcohol) can be utilized when printing on film. Formulators may also use resins with low surface tensions that will wet the surface of films. Resins with low glass transition temperatures, often referred to as soft resins, will wet film surfaces better than those that have high glass transition temperatures, often referred to as hard resins. These additives can be used in both solvent- and water-borne inks, and are often referred to as wetting agents. The materials act as surfactants to modify the surface energy of the ink. Again, the target of these formulation adjustments is to reduce the surface energy of the ink to match that of the film. Therefore, all of the drying of inks printed on film must occur from the surface, which can be a limiting factor. When printing on paper or board stocks, a significant amount of the solvent is absorbed by the stock itself. Therefore, when formulating inks for film printing, the drying process must be considered. The solvents chosen must evaporate rapidly enough to allow the inks to fully dry at press speeds. However, recent improvements in drying capacity allow for very high speeds when printing on film. In water-borne inks, the addition of small amounts of a low-boiling alcohol often increases the evaporation of water, due to the fact that alcohol and water produce a low-boiling azeotrope. The mixture of water and alcohol evaporates faster than water alone.
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