Preform yellowing and discoloration

In the stretch '2079851475616104457 production process, the product exhibits the quality defect of "Preform yellowing and discoloration". The specific manifestation is that the preform color is yellowish. This defect is relatively common when processing materials such as PET, PP, PC, and its occurrence conditions are usually related to the unreasonable settings of stretching temperature, stretch ratio, blowing pressure, and preform heating uniformity. When the "Preform yellowing and discoloration" situation is severe, it will cause a series of chain quality defects in the product in terms of appearance, dimensional accuracy, mechanical properties, etc., which not only reduces the functionality and safety of the product in use, but also directly increases the scrap rate and production cost. Therefore, this problem requires systematic diagnosis and optimization from multiple dimensions such as material selection, the status of the stretch '2079851475616104457 machine, heating oven, stretch rod, and blow mold, and stretching temperature, stretch ratio, blowing pressure, and preform heating uniformity.

1. Melt temperature too high. Temperature is the core factor affecting melt fluidity and viscosity. A temperature set too high will cause the melt viscosity to decrease, insufficient melt strength, and even thermal degradation; a temperature that is too low results in poor melt fluidity and insufficient plasticization, making it impossible to fill or form smoothly. A reasonable temperature window should be optimized and determined within the recommended range according to the melting characteristics and thermal stability of the material. 2. Long residence time. This factor causing the problem reflects that certain process conditions or material characteristics in stretch blow '2079851475616104453ing have not met the optimal molding requirements. Such problems are often cumulative and hidden, and should be investigated and verified as key focus items during process debugging and finalization to ensure that hidden dangers are eliminated at the source. 3. Poor thermal stability of the raw material. The selection and handling of materials is the foundation of molding quality. The intrinsic characteristics of the resin, such as molecular weight, molecular weight distribution, and melt index, determine its processing window and final properties. Factors such as raw material moisture content exceeding the standard, impurity mixing, and improper regrind ratio will all cause various defects during processing. In terms of equipment maintenance, the regular overhaul and precision confirmation of the stretch '2079851475616104457 machine, heating oven, stretch rod, and blow mold are not in place, causing the actual operating parameters of the equipment to deviate from the process requirements, which will also become a potential inducement of the "Preform yellowing and discoloration" problem.

1. Reduce the melt temperature. Adjustments should follow the principle of gradual progress; the amplitude of each adjustment should not be too large, and it is recommended to decrease by 5%~15% of the current value. After each adjustment, observe the product quality changes stably for at least 5~10 mold cycles, and continue adjusting only after confirming that the improvement direction is correct; avoid one-step excessive adjustment. 2. Shorten the residence time. Adjustments should follow the principle of gradual progress; the amplitude of each adjustment should not be too large, and it is recommended to decrease by 5%~15% of the current value. After each adjustment, observe the product quality changes stably for at least 5~10 mold cycles, and continue adjusting only after confirming that the improvement direction is correct; avoid one-step excessive adjustment. 3. Add a heat stabilizer. The adjustment of formulas and proportions should be determined on the basis of laboratory small-scale tests, and then verified by on-line pilot tests. Any change in the formula should be recorded and its impact on all aspects of product performance should be evaluated. Automatic metering and batching devices can effectively reduce errors in manual batching and batch-to-batch fluctuations. In terms of material management, incoming inspection of raw materials upon arrival and in-process inspection of work-in-progress should be strengthened, and the key performance indicators of PET, PP, PC should be strictly controlled to ensure the stability of molding quality from the source.

In summary, the causes of the "Preform yellowing and discoloration" problem can be attributed to the combined action of multiple factors such as Melt temperature too high, Long residence time. Solving this problem requires starting from aspects such as Reduce the melt temperature, Shorten the residence time and adopting systematic governance measures. In actual production, it is recommended to establish a prevention and rapid response mechanism for this problem, and achieve stable production and continuous improvement through preform heating uniformity and biaxial stretch orientation control.