Recently, we encountered a strange phenomenon where the customer used our white masterbatch to blow film. After one month of product placement, the entire film turned red, and the red distribution gradually became lighter from the edge to the inside; The previous situation was that after using a white masterbatch, the blown film would become longer and yellow in color over time.
What causes plastic film to turn red or yellow? The main components of white masterbatch are carrier resin LDPE, 60% titanium dioxide, and a small amount of calcium carbonate and dispersant.
The following methods can be used to find the cause of yellowing:
Try blowing transparent and milky white films using the same formula, that is, transparent without color masterbatch. If only the opal film turns yellow after being placed in an open environment at high temperature for about one month, it means that anatase titanium dioxide is used as the color master. If all of them turn yellow, it is necessary to suspect whether the antioxidant in the resin has BHT or other unstable types, or if other antioxidants have been added; At the same time, it is possible to compare the yellowing of non printed and printed films. When comparing, try to overlap them with 100-200 layers as much as possible, so that the color difference is more obvious.
The solution for yellowing the film is as follows:
Pay attention to the matching and proportion of antioxidant and titanium dioxide. Some antioxidants are phenolic, which can easily be oxidized to quinones, causing the product to turn yellow. Some auxiliary antioxidants, such as 168, can be added. Domestic antioxidants are not very stable. In addition to the quality of antioxidant itself, it is also related to the amount and variety of antioxidant used. The effect of antioxidant and titanium dioxide will have an impact. Domestic titanium dioxide is prone to yellowing, so it is recommended to use imported titanium dioxide resistant to yellowing, such as 2220 titanium dioxide of European KONUSS Company; The anatase titanium dioxide is prone to yellowing. It is better to use rutile titanium dioxide outdoors, but the color is not as good as the anatase, so you can consider adding more titanium dioxide;
Calcium carbonate may also have problems, as the calcium carbonate in the master batch is generally coated with stearic acid. Calcium carbonate generally does not change color when added with a whitening agent, but it must be imported. The trace metals contained in calcium carbonate serve as catalysts to accelerate oxidation reactions. The effect of ordinary antioxidants is not significant, and the effect of metal passivators is also limited;
Other aspects may also be related to carrier resin, processing temperature, processing environment, impure titanium dioxide, dry blown raw materials, use and preservation of raw materials, etc.
There are several possible reasons and solutions for the film turning red:
Hindered phenolic antioxidants are prone to isomerization into quinones after giving hydrogen free radicals, and quinones appear to turn yellow or red; It may also be antioxidants and raw materials containing water;
It may be a problem with the proportion of antioxidants in PE used for film blowing, and changing the brand should be able to solve it;
Adding some stearate can solve the problem of turning red.
