Things to note when color correcting and producing injection molded purple PVC parts
Color calibration for injection-molded purple PVC parts is crucial for ensuring the product’s appearance quality. Purple is a sensitive color and is easily affected by factors such as the type of masterbatch, addition ratio, and process parameters. Therefore, the calibration process requires exceptional care. First, a dedicated purple masterbatch for PVC should be selected, avoiding generic masterbatches, as these have poor compatibility with PVC resin and can easily lead to color shifts and color variations in the finished product. The addition ratio of the masterbatch must be precisely controlled. Generally, the addition level for purple masterbatch ranges from 1% to 3%, with the specific ratio determined based on the target color depth. When testing colors, a small trial run should be conducted. Color swatches should be prepared and compared to a standard swatch. If the color appears lighter, the masterbatch addition level can be increased; if it appears darker, the addition level can be reduced. Furthermore, attention should be paid to the masterbatch’s dispersibility. Increasing the screw speed and back pressure can be used to promote uniform dispersion of the masterbatch in the PVC melt to avoid defects such as color spots and streaks.
During color calibration, it’s also important to consider the impact of environmental factors on color perception. Lighting conditions are a crucial factor influencing color observation. Different light sources (such as natural light, fluorescent lighting, and incandescent lighting) produce varying visual effects. Therefore, color calibration should be performed in a standard light booth to ensure consistent observation. Standard light booths typically feature a variety of light sources, including D65 (simulated natural light), TL84 (European store lighting), and CWF (American cool white fluorescent). Comparing color charts under different light sources can prevent color misjudgments caused by varying lighting sources. Furthermore, subjective factors can also affect color judgment, so it’s best to have multiple people perform comparative observations to minimize individual subjective errors. For demanding purple PVC parts, a colorimeter can be used for quantitative testing. By measuring the L* (lightness), a* (redness-greenness), and b* (yellowness-blueness) values of the color chart and comparing them with those of a standard color chart, color differences can be precisely controlled to remain within acceptable limits (typically, a ΔE value of less than 1.5).
During the injection molding process of purple PVC parts, controlling barrel temperature is particularly important. PVC is a heat-sensitive plastic and can easily decompose at high temperatures, leading to defects such as yellowing and black specks in the finished product. Purple is particularly sensitive to yellowing, and even a slight yellowing can darken the purple and dull its luster. Therefore, the temperature of each section of the barrel must be strictly controlled within a reasonable range. Generally, the feeding section should be 140-160°C, the compression section 160-180°C, and the metering section 170-190°C. The nozzle temperature should be 5-10°C lower than the metering section to prevent molten material from decomposing at the nozzle. Before production, the barrel must be thoroughly cleaned to remove any remaining plastic or impurities. PVC-specific cleaning compounds should be used during cleaning, and excessively high temperatures should be avoided. During production, close monitoring of barrel temperature is crucial. If abnormal temperature increases are detected, the machine should be shut down for inspection to prevent PVC decomposition.
The settings of injection molding pressure and injection speed will also affect the quality of purple PVC parts. Excessively high injection pressure will cause greater internal stress in the product, which is prone to cracking during use. At the same time, excessive pressure may also prevent the gas in the mold cavity from being discharged in time, resulting in defects such as bubbles and burning in the product, affecting the uniformity of the purple color. Generally speaking, the injection pressure of injection molded purple PVC parts should be controlled at 50-80MPa. The specific value needs to be adjusted according to the structure of the product. The injection speed should be moderate. Too fast an injection speed will cause the melt to produce severe shearing effects in the cavity, causing the PVC to decompose; too slow an injection speed will cause the melt to cool too quickly, affecting the filling effect. The injection speed is usually set at 30-80mm/s. For products with complex structures, multi-level injection speeds can be used to ensure smooth filling of the melt.
The cooling and demolding processes for purple PVC parts also require special attention. Insufficient cooling time will result in incomplete cooling of the product, making it prone to deformation during demolding, affecting dimensional accuracy and appearance quality. Excessive cooling time will reduce production efficiency. The cooling time is determined based on the wall thickness of the product and is generally 10-30 seconds. Thin-walled products can be shortened, while thick-walled products require longer. Mold temperature is typically controlled between 30-50°C and regulated through cooling water channels to ensure uniform mold temperature and avoid problems such as internal stress and warping caused by uneven cooling. During demolding, the demolding mechanism should operate smoothly and excessive demolding force should be avoided to prevent surface defects such as scratches and abrasions that affect the glossiness of the purple color. Furthermore, the production environment should be kept clean to avoid contamination from dust and impurities. A small amount of release agent may be applied to the mold cavity and demolding mechanism. However, be careful with the type of release agent and avoid oil-based release agents, as they may affect the surface quality and subsequent processing (such as printing and spraying). After production, purple PVC parts should be properly stored away from direct sunlight and high temperature environments to prevent color change.
