PVC has poor thermal stability and light resistance. Hydrogen chloride began to decompose at 150 ℃, and adverse reactions occurred with the content of plasticizer. In addition, the influence of pigment on PVC is reflected in whether the pigment reacts with PVC and other components constituting PVC products, as well as the migration resistance and heat resistance of the pigment itself. Some components in the colorant may promote the degradation of the resin. For example, iron ions and zinc ions are catalysts for the degradation of PVC resin. Therefore, the use of iron oxide (red, yellow, brown and black) pigments or white pigments such as zinc oxide, zinc sulfide and lithopone will reduce the thermal stability of PVC resin. Some colorants may interact with degradation products of PVC resin. For example, ultramarine pigments have poor acid resistance, so they will interact with hydrogen chloride produced by PVC decomposition and lose their due color in the process of PVC coloring. Therefore, in terms of PVC coloring, considering the characteristics of the resin and related additives, combined with the characteristics of pigments. The following problems should be paid attention to when selecting colorants. [4]

1. Some metal ions in the pigment will promote the thermal oxygen decomposition of PVC resin.

The determination method is the hue change of polyethylene with pigment when heated to 180 ℃. Because the pigment contains metal ions, the decomposition of PVC is accelerated, resulting in hue change. At the same time, it should also be noted that the same addition of Lake red can make the color difference of PVC different. For example, if it contains calcium, the color difference is small; The color difference is large when containing manganese, which is caused by manganese and other metals promoting the dehydrochlorination of PVC.

Sulfide Colorants (such as cadmium red, etc.) are used for coloring PVC, which may release hydrogen sulfide due to the decomposition of colorants. Such colorants should not be mixed with lead stabilizers to avoid the formation of black lead sulfide.

2. Effect of pigments on electrical insulation of PVC

As a cable material, PVC and polyethylene should consider the electrical properties after coloring. In particular, PVC has a greater impact on pigment because of its poor insulation than polyethylene. It shows that the electrical insulation of PVC colored with inorganic pigment is better than that of organic pigment (except furnace black and anatase titanium dioxide).