Why Does Varnish Turn Yellow? Professional Anti-Yellowing Solutions for Printing & Coating Industries

Why Does Varnish Turn Yellow? Key Causes & Solutions

• Component Defects: Low-quality resins (aromatic types), amine-based curing agents, or inferior photoinitiators tend to oxidize and form colored substances. Opt for aliphatic urethane acrylate resins and acylphosphine oxide photoinitiators to minimize yellowing risk.
• Improper Curing Process: Mismatched UV lamp wavelength (needs 365-405nm), insufficient energy (below 800mJ/cm²), or overly thick coating (exceeding 15μm) leads to incomplete curing. Residual monomers are prone to oxidation and yellowing. Use 500-600 mesh screens for uniform film thickness.
• Environmental Factors: Long-term exposure to UV radiation, high temperature (>35℃), high humidity (>60%), or pollutants accelerates oxidation and aging of varnish.
• Substrate Issues: Substrates containing lignin, yellowing-prone plastics, or residual oil/moisture on the surface can cause discoloration through the varnish layer or chemical reactions.

Professional Anti-Yellowing Solutions

1. Choose High-Quality Materials: Select "UV-resistant" or "non-yellowing" varnish. Add 0.5-2% UV absorbers (e.g., UV-P) and antioxidants (e.g., 1010) to enhance protection synergistically.
2. Optimize Curing Parameters: Match UV lamp wavelength with photoinitiator requirements, control curing energy at 800-1200mJ/cm², and avoid thermal degradation from over-irradiation.
3. Standardize Application & Storage: Maintain application environment at 20-30℃ and 50-60% humidity; ensure substrates are clean and dry. Store finished products in sealed containers at 10-25℃ in a cool, dark place.
4. Targeted Protection: For light-colored materials or outdoor applications, use laminating technology or aliphatic polyurethane varnish, achieving a yellowing resistance grade of ≥4.5.

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