1.What are the emergency response and on-site verification procedures?
Immediate Isolation and Labeling:
Immediately isolate rolls (or cut sheets) with excessive color difference from the production line or finished product area, and clearly label them "Color Difference Abnormal, Pending Handling" to prevent confusion or misdelivery with qualified products.
If the problem occurs at the customer's location, immediately suspend the use of this batch of material and notify the supplier.
Preliminary Assessment and Recording:
Standardized Measurement: Use a portable colorimeter to perform multiple measurements at multiple points under a standard light source box (e.g., D65 illuminator). Record the values of ΔE (total color difference), ΔL (lightness difference), Δa (red-green difference), and Δb (yellow-blue difference).
Establish Acceptable Standards: Refer to the standards agreed upon in the contract between both parties (usually ΔE ≤ 1.0 or 1.5, depending on industry and customer requirements). If there is no explicit agreement, refer to general standards such as GB/T 9761 and ASTM D2244.
Photography and Sampling: Take high-resolution photographs of the color difference area from different angles under standard light and natural light. Simultaneously, cut small samples (at least 10cm x 10cm) including the color difference boundary as physical evidence.
Preliminary Cause Investigation:
Batch Consistency: Check for color differences between the problematic roll and the qualified sample, between rolls within the same batch, and between the beginning/end or edge/middle of the same roll.
2.What could be the reasons from the manufacturer?
Paint-related factors: Color differences exist between different batches of paint; uneven mixing of paint; improper addition of solvent or hardener ratio.
Process-related factors:
Uneven coating thickness: Caused by fluctuations in roller coater settings, roller wear, or vibration.
Uneven/Inadequate curing: Oven temperature deviations and uneven airflow rates lead to different degrees of cross-linking in the coating, affecting color and gloss.
Pretreatment residue: Residue of degreasing or passivation solution on the surface affects the coating appearance.
Substrate-related factors: Inconsistent surface conditions (e.g., zinc flower size, roughness) of the substrate (galvanized sheet, aluminum-zinc sheet).
3.What could be the reasons from the user/storage/transporter?
Mixed batch use: Mixing rolls from different production batches on the same visible surface can lead to noticeable color differences, even if each roll is合格 (qualified/up to standard).
Improper storage: Prolonged exposure to direct sunlight and high temperature/humidity environments causes premature aging and yellowing of the coating (especially light colors and white).
Processing contamination: Lubricating oil and coolant used during cutting and stamping contaminate the surface.
Installation factors: Visual effects vary under different orientations and lighting angles; failure to remove the protective film promptly during installation can cause discoloration due to temperature differences.
4.What preventative measures can be taken for the production side?
Establish a color database: Retain samples from each batch of paint and establish internal standards for the allowable range of color difference (ΔE) (which should be stricter than customer standards).
Enhance online monitoring: Install online colorimeters and film thickness gauges after the coating line and curing oven to achieve real-time monitoring and automatic feedback adjustment.
Strict batch management: Ensure "first-in, first-out" (FIFO) production; the same order must use the same batch of paint, and the batch number must be clearly marked upon shipment.
Provide application guidance: Provide written instructions with the goods, emphasizing the principle of "ordering from the same batch, using from the same batch" and correct storage, transportation, and installation requirements.
5.What preventative measures should be taken for users?
Ordering and Acceptance: Order the entire project's required quantity at once, and request the manufacturer to guarantee production from the same batch. Upon receipt, randomly check for color difference under standard light.
On-site Management: After arrival, stack goods separately by batch. Always verify the batch number on the roll material before use to ensure that only the same batch of material is used on the same visible surface.
Standardized Processing and Installation: Avoid contamination and remove the film promptly.