Injection molding ingredients and color management
Injection molding batching and color management are critical steps in ensuring the stability and consistency of plastic product quality, directly impacting the mechanical properties, appearance, and production costs of the products. Batching management involves the selection, proportioning, mixing, and drying of raw materials. Color management requires precise control of the addition ratio of masterbatch or color powder to ensure consistent color across batches. Scientific management processes can effectively reduce raw material waste and lower defective product rates, providing reliable support for large-scale production.
Raw material selection and inspection are fundamental to ingredient management. Appropriate resins, additives (such as toughening agents, flame retardants, and fillers), and colorants must be selected based on the product’s intended use. The resin grade must be compatible with the molding process. For example, high-flow PP grades are suitable for thin-walled products, while high-crystalline PP grades are suitable for parts requiring rigidity. Each batch of raw materials must be inspected before entering storage, including melt index (MI), density, and moisture content. For example, the MI deviation of PE should be controlled within ±0.5g/10min, and raw materials with a moisture content exceeding 0.05% must be re-dried. Additive selection must consider compatibility with the resin. For example, adding PC toughening agents to ABS at a ratio exceeding 20% can cause delamination, so the optimal ratio must be determined through pilot testing. For example, a household appliance housing using a formulation of ABS + 10% PC has been shown to increase notched impact strength from 20kJ/m² to 35kJ/m² through impact testing, meeting application requirements.
The ingredient ratio calculation and mixing process must be strictly standardized. Precision weighing equipment (accuracy ≥ 0.1g) must be used for ratio calculation to ensure that the additive ratio deviation is ≤0.5%. For multi-component formulations, the principle of “small additions, larger additions” should be followed: Add a small amount of additives (such as antioxidants and color masterbatch) first, followed by the resin and filler, to avoid uneven dispersion of small amounts of ingredients. Mixing equipment can include a high-speed mixer (800-1500 rpm) or a twin-screw compounder. The mixing time is determined by the material characteristics, generally 5-15 minutes. After mixing, uniformity should be tested, for example, by measuring the melt index difference of sampled materials. The difference should be ≤10%. For example, a flame-retardant PP formulation containing 15% flame retardant was mixed using a high-speed mixer at 1000 rpm for 10 minutes. Testing showed that the flame retardant content deviation in each component was ≤0.3%, ensuring consistent flame retardant properties in the finished product.
Color matching management requires the establishment of a standardized color number system and color matching process. The addition ratio of masterbatch must be measured using a spectrophotometer, and the Lab value deviation must be controlled within ΔE ≤ 1.0 (ΔE represents the color difference; a smaller value indicates closer colors). For the initial color matching, a color palette must be prepared and compared with the standard color sample. The masterbatch ratio is then adjusted by 0.1% to 0.5% until the standard is met. For example, for a blue product with a standard color sample of (-50, 20, -30) Lab values, the initial color matching deviation is 3.2. By adding 0.3% blue masterbatch and reducing 0.2% yellow masterbatch, the final ΔE is 0.8, meeting the requirement. During mass production, masterbatch must be added using an automated metering device with an accuracy of ≥ 0.01%. Samples of color palettes must be inspected for every 100kg of raw material produced to ensure color stability. For light-colored products, the impurity content in the raw materials must be controlled (e.g., black specks ≤ 5 per 100g) to avoid affecting the appearance.
Drying is a critical step in the batching of hygroscopic raw materials (such as PA, PC, and PBT). Drying parameters must be tailored to the raw material type. For PA6, drying conditions are 80-90°C for 4-6 hours, and for PC, 120-130°C for 8-12 hours. The moisture content after drying must be ≤0.02%. Drying equipment must be equipped with dew point monitoring (dew point ≤ -40°C) to prevent reabsorption of moisture during the drying process. Dried materials must be stored in a sealed hopper for ≤4 hours; re-drying is required after this time. For example, a PA66 product developed silver streaks on its surface due to insufficient drying (moisture content 0.05%). After adjusting the drying time to 8 hours, the moisture content dropped to 0.015%, eliminating the silver streak defect.
The record and traceability system for batching and color matching needs to be improved. Each batch of production must record information such as the raw material batch number, ratio parameters, mixing time, masterbatch ratio, and test results, and the retention period must be ≥1 year to facilitate quality traceability. When quality fluctuations occur, the cause can be identified through traceability records. For example, if a batch of products is dark in color, it was found that the masterbatch addition ratio was mistakenly set to 3% (the standard is 2%). After adjustment, it returned to normal. At the same time, the batching equipment needs to be calibrated regularly, the weighing equipment should be calibrated once a year, and the mixer’s agitator wear should be checked quarterly to ensure that the equipment accuracy meets the requirements. Through standardized management of the entire process, the defective rate of ingredients and color matching can be controlled below 0.5%, significantly improving production stability.
