Pigments or dyes that change the color of plastic materials and give plastic products a beautiful appearance can be called plastic colorants. The production and consumption of plastic products colored by colorants account for more than 80% of the production and consumption of all plastic products.

Due to the different types of chemical elements and chemical structures contained in the colorant molecules, plastic colorant products not only have significant differences in main properties such as use, tinting power, hiding power, coloring durability or firmness, weather resistance, chemical resistance, and toxicity, but also have a certain impact on the processing and forming properties of colored plastic products, the thermal and oxygen stability of the processing process, and the light and oxygen stability of the use process.

Especially for light- and oxygen-stabilized colored plastic products, if the plastic colorant is not properly matched with antioxidants and light stabilizers, it can cause the colored plastic products to fade or discolor prematurely, and can also accelerate the light and oxygen aging of the colored plastic products.

1. The influence of colorants on antioxidants

Chrome yellow is an opaque inorganic colorant that can be used for thermoplastics such as polyolefins, polystyrene, and acrylic resins. It has strong tinting power, good hiding power, and excellent water and solvent resistance.

However, because chrome yellow is a lead compound composed of lead chromate or basic lead chromate and lead sulfate, it is used together with sulfur-containing antioxidants such as DLTP, DSTP, 1035. and 300. Under the high temperature conditions of plastic processing, chemical reactions will occur to generate black lead sulfide, which will affect the appearance of plastic products and greatly weaken the antioxidant's anti-thermal oxidative aging effect. Therefore, chromium-containing colorants cannot be used together with sulfur-containing antioxidants.

In addition, polypropylene molecular chains contain tertiary carbon atoms, which are easily decomposed by oxygen. Antioxidants must be used for anti-aging protection during processing, storage, and application. In colored polypropylene, some colorants will react chemically with low-molecular hindered phenol antioxidants, weakening the effect of the antioxidant.

2. Effect of colorants on the action of light stabilizers

The effect of colorants on the action of light stabilizers in colored plastic products mainly has two aspects.

First, colorants contain heavy metal elements or impurities such as copper, manganese, and nickel, which are photoactive and photosensitized, catalyzing and accelerating the light aging of plastic materials. Phthalocyanine blue containing free copper and impurities will promote the light aging of polypropylene; red iron oxide can reduce the efficiency of benzotriazole, benzophenone, and organic nickel salt light stabilizers in polypropylene by more than 20%; for polyethylene, the use of colorants such as titanium dioxide, ultramarine, chromium oxide green, cobalt green, and iron red will aggravate light aging.

Secondly,colorants with certain molecular structures can react with light stabilizers and directly weaken the effectiveness of light stabilizers.

Acidic colorants can make hindered amine light stabilizers ineffective; in polypropylene, azo red and yellow can react with hindered amine light stabilizers, and azo condensation red BR and azo condensation yellow 3G can reduce the effect of hindered amine light stabilizers by about 25% and 50%, respectively. When the intensity drops by 50%, the radiation dose of the samples is compared. The comparison results show that the stability of polypropylene fibers colored with yellow, red and orange organic pigments is lower than that of uncolored polypropylene fibers, although antioxidants and light stabilizers are added.

For light- and oxygen-stabilized colored plastic products, if the plastic colorant is not properly matched with the antioxidant and light stabilizer, it can cause the colored plastic products to fade or change color prematurely, and can also accelerate the light and oxygen aging of the colored plastic products. How to use additives correctly is crucial to the stability of plastic products. Therefore, in the process of plastic modification, it is very important to understand and master the structure and properties of additives.