Defining Paint Discoloration and “Dark Yellowing” in Storage
Paint discoloration during storage refers to the deviation from the initial color state, a critical quality issue for manufacturers. This phenomenon often manifests as “dark yellowing” or specific failures like green paint appearing blue after opening or metallic pigments losing luster, turning dark or green.
Root Causes: From Chemical Reactions to Formula Imbalance
Troubleshooting in-can color drift requires a systematic analysis of the following technical triggers:
- Formulation and Compatibility:
- Issues arise from poor compatibility between resins and pigments, or density differences in compound colors where lighter pigments float and heavier ones sink.
- Chemical Reactions:
- Pigments like Iron blue can fade due to reduction in insufficient air. Additionally, shellac varnish and nitrocellulose lacquer often darken when reacting with bare iron containers.
- Metallic Pigment Failure:
- Gold and aluminum powders can react with certain varnishes, leading to a complete loss of their characteristic metallic luster.
Professional Solutions for Color Stability and Preservation
To solve paint discoloration, manufacturers should implement these authoritative process optimizations:
- Formulation and Process Optimization:
- Add 0.2%-1% wetting and dispersing agents, such as: silicone oil, polyacrylates, polymeric polycarboxylates, polyaminoamide phosphates, fatty alcohol sulfates
- Avoid moisture incorporation, appropriately extend dispersion and grinding time
- For metallic pigment paints, use neutral paints and add metallic pigments at the final stage
- Packaging Improvement:
- Use galvanized or tin-plated iron drums
- Package special paints (shellac varnish, nitrocellulose lacquer) in plastic drums, porcelain jars or glass bottles
- Separate packaging for metallic pigments and paints, mix before use
- Problem Identification:
- Compound color paints returning to uniform color after thorough stirring are not true discoloration
- Color restoration after air exposure is normal phenomenon
FAQ: Identifying True Discoloration
Not necessarily. If compound color paints return to a uniform state after thorough stirring, it is considered physical separation rather than true chemical discoloration.
No. Color restoration after air exposure (common with certain reduction-sensitive pigments) is a normal phenomenon and not a quality failure.
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