What issues should I pay attention to when coloring PVC?

2024-01-07 10:07:04

Polyvinyl chloride ( PVC ) is relatively inferior in thermal stability and light resistance, and begins to decompose hydrogen chloride at 140 Â° C, so it is not possible to react adversely with itself when a colorant is selected. In addition, it should be noted that the influence of pigment on PVC is mainly reflected in whether the pigment can chemically react with PVC and other components constituting the PVC product, and whether the pigment itself has excellent migration resistance and heat resistance. Therefore, in terms of PVC coloring, considering the characteristics of the resin used and related additives, in combination with the characteristics of the pigment, we should pay attention to the following three major problems when selecting the coloring agent.

First, the stability of processing

Certain components of the colorant may contribute to the degradation of the resin. For example, iron ions and zinc ions are catalysts for the degradation reaction of PVC resins. Therefore, the use of iron oxide (red, yellow, brown and black) pigments or zinc oxide, zinc sulfide and lithopone white pigments reduces the thermal stability of PVC resins. Some colorants may interact with degradation products of PVC resins. For example, the ultramarine pigments have poor acid resistance, so in the PVC coloring process, they will interact with the hydrogen chloride generated by the decomposition of PVC and lose the color they deserve.

Second, mobility

Mobility occurs only in plasticized PVC articles and when dyes or organic pigments are used. The so-called migration is a partially soluble dye or organic pigment present in the surrounding solvent. The plasticizer penetrates into the surface of the PVC product, and the dissolved dye particles are also brought to the surface of the product, which leads to the osmosis. Color, solvent bleeding or blooming. Another problem is "fouling." It means that the coloring agent is freed from the system during the coloring process because of the poor compatibility or incompatibility of the coloring matter, and is deposited on the surface of the processing equipment (such as the inner wall of the barrel of the extruder and the inner wall of the die hole). .

Third, weather resistance

Refers to the ability of pigments to withstand various climates. These include visible and ultraviolet light, moisture, temperature, atmospheric chlorination, and chemicals encountered during the use of the product. The most important weatherability, including non-fading, powdering resistance and durability of physical properties. Organic pigments are different due to their different structures. In addition, in formulations containing white pigments, the weatherability of the pigments is more severely affected.

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