Why the white thermoplastic marking paint comes out not white but gray, dark, or slightly yellow ???

The core reasons are the combined effects of six factors: thermal-oxidative aging of resin, insufficient titanium dioxide, ultraviolet exposure, excessive construction temperature, surface contamination, and equipment mixing.

Incorrect or impure resin selection: C5 aliphatic petroleum resin should be used. If mixed with C9 aromatic resin or impurities, it is prone to yellowing and has poor heat and weather resistance.

Insufficient or low-grade titanium dioxide: Whiteness depends on titanium dioxide for coverage and UV protection. Low content, anatase type, or inferior titanium dioxide results in poor whiteness and easy aging/yellowing.

Lack of anti-UV additives in the formula: Without UV absorbers or light stabilizers, the resin is easily oxidized by UV, forming yellow chromophoric groups.

Excessive heating temperature / overly long heating time: The standard temperature is 180–200°C. If it exceeds 220°C or is repeatedly cooked for long periods, thermal degradation of the resin accelerates, directly causing yellowing.

Mixing new and old materials / repeated reheating: Old material is already aged; mixing it with new material or reheating multiple times worsens yellowing.

Poor equipment cleaning: After marking yellow lines, if the hot-melt kettle, line marking machine, and filters are not thoroughly cleaned, residual yellow material contaminates the white material.

Long-term UV exposure: Sunlight UV (270–380 nm) continuously oxidizes the resin, especially under high-temperature exposure, accelerating yellowing.

Road surface contamination: Oil bleeding from new asphalt surfaces, tire dust, oil stains, and dirt can attach and penetrate the coating, causing surface yellowing.

Rainwater and humid heat aging: Long-term rainwater immersion and wet-dry cycles cause resin hydrolysis and aging, reducing whiteness and gradually turning yellow.

If yellowing occurs immediately after construction: it is mostly due to equipment mixing, overheating, impure resin, or insufficient titanium dioxide.

If yellowing occurs after several months of use: the main causes are UV aging, poor resin weather resistance, or low-grade titanium dioxide.

Localized yellowing: likely caused by road surface oil bleeding or contamination.

Key solutions:

• Use qualified coatings with pure C5 resin + titanium dioxide + anti-UV additives.
• Strictly control construction temperature at 180–200°C, avoid prolonged cooking and reuse of old material.
• Thoroughly clean equipment before construction; keep yellow and white materials separately dedicated.
• Wait 1–3 months after opening a new asphalt road to allow stabilization before construction.