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Causes of discoloration of plastic containers

Update:20 Mar 2020
Summary:

Generally speaking, there are many factors that affect […]

Generally speaking, there are many factors that affect the fading of plastic containers, and the fading of plastic colored products is related to the light resistance, oxygen resistance, heat resistance, acid and alkali resistance of pigments and dyes, and the characteristics of the resin used. In the production of color masterbatches, the above-mentioned properties of the required pigments, dyes, surfactants, dispersants, carrier resins and anti-aging additives are comprehensively evaluated before they can be used.

Reasons affecting the discoloration of plastic containers:
① Lightfastness: The lightfastness of the colorant directly affects the fading of the product. For outdoor products exposed to strong light, the lightfastness (lightfastness) level of the colorant used is an important indicator. The lightfastness level is poor, and the product will be fast in use. fade. However, during blow molding, a certain amount of anti-UV ingredients will be added to ensure the durability of product color retention time.
② Heat resistance: Due to the thermal stability of the pigment, it refers to the degree of thermal weight loss, discoloration, and discoloration of the pigment at the processing temperature. The composition of inorganic pigments is metal oxides and salts with good thermal stability and high heat resistance. The pigments of organic compounds undergo molecular structure changes and a small amount of decomposition at a certain temperature. Actually, we need in the production process. If it is a plastic product that requires high temperature heating, we need to choose a pigment with more heat resistance to ensure that the color is discolored and faded, and the overall appearance of the product is guaranteed.
③ Oxidation resistance; some organic pigments gradually fade due to the degradation of macromolecules or other changes after oxidation. This process is one of high temperature oxidation during processing and the other is oxidation in the presence of strong oxidants. After the use of lakes, azo pigments and chrome yellow, the red will gradually decrease.

Compared with ordinary plastic containers, the discoloration of colored plastic products and the chemical resistance of colorants, such as molybdenum chromium red are resistant to dilute acid, but sensitive to alkalis, cadmium yellow is not resistant to acid, these two pigments and phenolic resin are These colorants have a strong reducing effect, which seriously affects the heat resistance and weather resistance of the colorants and discoloration occurs.