Color masterbatch discoloration problem and solution
Blow the film with white masterbatch, the whole film becomes red after the product is placed for a month, the red distribution gradually becomes lighter from the edge to the inside, or after using white masterbatch, the blown film will become longer with time, the color becomes yellow. What causes plastic film to turn red or yellow? The main ingredients of white masterbatch are carrier resin LDPE, 60% titanium dioxide, plus a small amount of calcium carbonate and dispersant.
Blow transparent and opalescent film with the same formula, i.e., transparent without color masterbatch. In the open environment of high temperature placed for a month or so, if only the milky white film yellow, is the use of anatase qinbai powder. If yellowing occurs, it is necessary to suspect that the antioxidant of the resin has BHT or other unstable types, or that other antioxidants have been added; At the same time, you can compare the yellow situation of the film without printing and printing, and try to use 100-200 layers of overlap when comparing, so that the color difference is more obvious.
The solution of yellow film is as follows:
Pay attention to the match and ratio of antioxidant and titanium dioxide. Part of antioxidant is phenolic, phenolic group is easy to be oxidized into quinone group, resulting in yellow products, some auxiliary antioxidant can be added, such as :168. Domestic antioxidants are not very stable. In addition to the quality of antioxidant itself, and the use of antioxidant dosage and varieties also have a relationship, antioxidant and titanium dioxide action can produce an impact. Domestic chin white powder is easy to yellowing, so it is suggested to use imported chin white powder with yellowing resistance.
Calcium carbonate can also be problematic because the calcium carbonate in the masterbatch is usually stearic acid coated. Calcium carbonate is generally added with whitening agent will not change color. Trace metals contained in calcium carbonate act as catalysts to speed up the oxidation reaction. The effect of common antioxidant is not obvious, and the effect of metal passivating agent is also limited.
Other aspects may also be related to carrier resin, processing temperature, processing environment, titanium dioxide impure, film blowing raw materials dry, raw materials use and preservation problems.
Reasons and solutions for the film turning red may be as follows:
When hydrogen free radicals are given by blocked phenolic antioxidant, it is easy to heteroform quinones, which turn yellow or red. It may also be antioxidant and raw material water;
It may be the problem of the proportion of antioxidant in PE for blowing film, which can be solved by changing the brand. Adding some stearates can solve the redness problem.