The resolubility of ink is an important indicator of ink quality, which has a non-negligible impact on the printing and composite quality of flexible packaging composite materials. Many colleagues in the industry have paid attention to this, but it is difficult to make a clear explanation in theory. Write down the problems and understanding related to ink resolubility encountered in many years of work, in order to arouse more attention and discussion.
1. The concept of ink resolubility
The resolubility of the ink refers to the ability of the ink after printing and drying to re-dissolve after encountering the solvent. Generally, the following methods can be used to compare and judge the degree of ink re-dissolution-cut two printed films (printed with different inks) Place it flat on the desktop, and add two drops of ethyl acetate on the printing ink layer respectively. After 3 or 4 seconds, the two films will stand upright. If the ink flows down more, it means that the resolubility is stronger, and the ink flows down. Less means that the resolubility is weaker.
There is no clear quantitative index for the resolubility of inks. The resolubility of inks of different manufacturers may be significantly different. Because the resolubility of the ink has a certain impact on the quality of printed and compounded products, flexible packaging companies may wish to use the resolubility of the ink as a reference index for selecting inks, and choose inks with moderate resolubility to reduce the adverse effects on product quality.
Because the effect of the resolubility of the ink on printing and compounding is the same or similar to some phenomena that occur when the printing ink is not completely dried, the problems discussed below will exclude the factors that the printing ink is not completely dried.
2. The effect of the resolubility of the ink on the printing process
Ink with strong resolubility, the ink remaining at the bottom of the mesh will be dissolved again by the ink in the ink tank during printing, so the blocking phenomenon is relatively light, and the reproducibility of the shallow mesh part will be better (of course with ink The fineness is also directly related).
For the ink with weaker resolubility, the ink remaining at the bottom of the mesh hole is more difficult to be dissolved again by the ink in the ink tank, so it is easy to block the plate, and the reproduction of the shallow mesh portion is poor.
The ink with strong resolubility is also prone to "bite" phenomenon when printing (that is, the back color dissolves some of the front color). In severe cases, the pattern will be transferred to the printing film again, causing pollution to the product. And the color of the latter set of ink will change due to the mixing of the previous ink, which will affect the hue of the printing.
The solution to the ink bite is to increase the printing speed, and reduce the pressure of the platen roller to reduce the contact time. It can also be solved by pulling the scraper back a bit. It can also add a faster volatilization speed to the ink. Solvent.
3. The influence of the resolubility of the ink on the compounding process
The resolubility of the ink is strong, and the solvent and glue will penetrate into the ink together during compounding. First, it will cause an insufficient amount of glue on the surface. Second, the curing agent will interact with the ink binder and the residual solvent (such as isopropyl alcohol and moisture ) A reaction occurs, causing the glue to not dry.
For such inks, the amount of glue can be increased to ensure the composite strength, and the working concentration of the glue can be increased to reduce its dissolution and penetration of the ink. In addition, more curing agent should be added to ensure the glue is dry.
If the resolubilization of the ink is too strong, the phenomenon of "bite" will also occur during the application of glue, which is manifested by the blurred printing pattern on the surface of the applicator roll. Products and affect transparency.
The solution is to increase the compound speed and reduce the pressure of the platen roller to reduce the contact time. It can also be solved by pulling the scraper back a little, and increasing the working concentration of the glue will also have a certain effect on this problem.
When doing peel strength inspection, composite products processed with inks that are too soluble are often easily separated from the middle of the ink layer, resulting in low peel strength of the product.
For inks that are too soluble and reproducible, the printing film cannot be used with a squeegee roller during compounding, because the ink is easily reconstituted after coating, and the reconstituted ink will be scratched by the squeegee roller.
White ink with too much resolubilization will become non-uniform due to the re-dissolution of the white ink after coating, or the coverage rate will decrease. It is easy to cause "white spots" when it is compounded with aluminum coating.
In solvent-free compounding, due to the strong fluidity of solvent-free adhesives, inks with higher resolubility are more prone to "inking" phenomenon with the flow of glue, that is, the printing boundary of the ink of this color becomes jagged And cross the printed border into other colors.
The resolubility of the ink is only one of the factors that affect the quality of printed composite products. I hope that the above discussion will be helpful for flexible packaging companies to find the cause of the problem.
In the process of material organization, I received the help of technical personnel from several ink production enterprises, and I would like to express my gratitude! Some opinions are improper and I still ask my colleagues in the industry to correct them.
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