Pinking refers to the appearance of a pink tint on the surface of white rigid PVC products. In practice, this defect is most often discussed in relation to window and building profiles that are exposed to light and moisture over long periods.
The issue is particularly important for manufacturers of white PVC products because the color change may not appear immediately after extrusion but only after extended service. Color stability should therefore be considered as early as the formulation development stage.
Why Pinking Occurs
Pinking is associated with a combination of factors:
- the type and surface treatment of the titanium dioxide;
- the PVC heat-stabilization system;
- exposure to moisture;
- UV and visible light;
- the service conditions of the finished product.
Historically, the problem was particularly characteristic of certain formulations containing lead stabilizers. However, it is incorrect to attribute pinking to a single component: the change in shade results from interactions between formulation components and external factors.
Titanium dioxide serves several functions in white PVC. It provides whiteness and opacity and also helps determine the product’s resistance to light exposure. The choice of TiO2 grade should therefore take into account not only the pigment’s initial whiteness but also its behavior in the specific PVC compound.
Why the Stabilizer System Matters
Modern calcium-zinc stabilizers enable lead-free PVC formulations while helping control the compound’s thermal stability, color and processability. However, switching to another stabilizer system does not eliminate the need to select the formulation as a whole.
When developing a white profile, it is important to assess how the stabilizer, titanium dioxide, lubricants, modifiers and other components work together. Changing one ingredient can affect both the initial color and its stability after ageing.
How to Reduce the Risk of Color Change
When selecting a formulation for white PVC products, consider:
- the type of titanium dioxide and whether it is intended for outdoor or indoor applications;
- the compatibility of TiO2 with the stabilizer system used;
- the compound’s resistance to light and moisture;
- the results of accelerated and natural weathering;
- color stability under actual processing and service conditions.
If long-term whiteness is critical for the product, assessing its shade immediately after extrusion is not enough. Comparing compounds after climatic and light-exposure tests is more informative.
Revada Plastic’s Approach
REVADA PLASTIC supplies titanium dioxide and calcium-zinc stabilizers for PVC processing. Our specialists help select components based on the formulation, processing technology and requirements for the finished product’s appearance and durability.
