Colorability Of PVC

PVC has poor thermal stability and light resistance. Hydrogen chloride starts to decompose at 150 ℃, and adverse reactions occur with the amount of plasticizer. In addition, the influence of pigment on PVC is reflected in whether the pigment reacts with PVC and other components of PVC products, and the migration resistance and heat resistance of 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 react with degradation products of PVC resin. For example, ultramarine pigments have poor acid resistance, so they will interact with hydrogen chloride generated from PVC decomposition and lose their proper color during PVC coloring process. Therefore, as far as PVC coloring is concerned, the characteristics of resins and related additives used and the characteristics of pigments are considered. The following issues should be noted when selecting colorants.
1. Some metal ions in the pigment can promote the thermal oxidative decomposition of PVC resin.
The determination method is the color change of polyethylene with pigment when heated to 180 ℃. As the pigment contains metal ions, the decomposition of PVC is accelerated, resulting in color changes. At the same time, it should be noted that the addition of lake red can make the color difference of PVC different. If calcium is contained, the color difference is small; The color difference is large when manganese is contained, which is due to the promotion of dehydrochlorination of PVC by manganese and other metals.
Sulfide colorants (such as cadmium red) 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 producing black lead sulfide.
2. Effect of Pigment on Electrical Insulation of PVC
As cable materials, PVC and polyethylene should consider the electrical properties after coloring. In particular, PVC has a worse insulation than polyethylene, so the influence of pigments is greater. It shows that the electrical insulation of PVC dyed with inorganic pigments is better than that of organic pigments (except furnace black and anatase titanium dioxide).