=In the production of silicone two-tone straps, cross-contamination between different colored silicones is a core issue affecting product appearance quality. This primarily stems from raw material residue, insufficient equipment cleaning, process design flaws, and inadequate environmental control. To address this issue, a multi-dimensional prevention and control system needs to be built, encompassing raw material management, equipment cleaning, process optimization, environmental control, operational procedures, quality inspection, and continuous improvement, to ensure the color purity and appearance consistency of the silicone two-tone straps.
Raw material management is fundamental to avoiding color contamination. Different batches of masterbatch may exhibit color differences or uneven particle size distribution. Without rigorous screening, this can easily lead to uneven color or residue during mixing. Before production, batch consistency testing of the masterbatch is necessary to ensure color differences meet standards and to filter impurities, preventing the agglomeration of large masterbatch particles. Simultaneously, the ratio of liquid silicone to color paste must be precisely controlled using automated metering equipment to avoid color deviations caused by manual weighing errors. For solid silicone, a "pre-dispersion + secondary mixing" process is required to ensure full integration of the masterbatch and base silicone, reducing residue.
Equipment cleaning is a crucial step in preventing color cross-contamination. During color change production, residual silicone or colorant from the previous batch may remain in the mold runner, injection molding machine barrel, and screw. If not thoroughly cleaned, this can lead to discoloration or color spots in subsequent products. Cleaning requires a specialized silicone cleaner, used in conjunction with ultrasonic cleaning equipment, for deep cleaning of the mold runner. If necessary, disassemble the mold and manually clean corners and venting channels. For the injection molding machine barrel, high-temperature baking combined with screw idling is required to completely evaporate residual solvents. After cleaning, wipe the mold surface with alcohol to ensure no dust or oil adheres.
Process optimization can reduce the risk of color contamination. In two-color injection molding, an improper runner design, such as a single-point gate causing color gaps at the far end or inconsistent flow rates across multiple gates, can easily lead to color separation or uneven mixing. The runner layout needs to be optimized using mold flow analysis software to ensure balanced melt filling. Simultaneously, injection speed and pressure should be controlled to avoid turbulence causing colorant separation. For liquid silicone, a static mixer must be used to ensure uniform online mixing of the colorant and substrate. The mixing tube length must meet requirements, and dynamic mixing efficiency must be up to standard. In addition, mold temperature needs to be controlled evenly to avoid color differences caused by inconsistent curing speeds.
Environmental control is equally important for reducing color contamination. The production workshop must be kept clean to reduce dust particles adhering to the mold surface. Simultaneously, workshop humidity must be controlled to prevent the silicone raw material from absorbing moisture, leading to yellowing or bubbles. For color change production, a separate production area or isolation enclosure should be set up to reduce the risk of cross-contamination between different color products. Furthermore, the equipment's sealing performance must be checked regularly, such as the feed pipe seals and the gap between the material cylinder and the screw, to prevent material leakage and air suction that could cause color contamination.
Standardized operating procedures are crucial to avoiding human error. Operators must receive professional training and master the key points of "color matching" and "bubble detection" to avoid incorrect mixing sequences or misadjustment of equipment parameters. During color changes, the cleaning process must be strictly followed, and the cleaning time and responsible person must be recorded to ensure traceability. In addition, the equipment's operating status must be checked regularly, such as the temperature control system and pressure sensors, to prevent color contamination due to equipment malfunctions.
Quality inspection is the last line of defense against color contamination. The first piece must undergo full inspection for color and bubbles. Color difference is measured using a colorimeter, and surface bubbles are visually inspected under specific light sources. Process control requires hourly sampling inspections, using a magnifying glass to examine the surface and record bubble locations and color fluctuation data. For non-conforming products, the causes must be analyzed and corrective measures implemented, such as adjusting process parameters or cleaning the equipment again.
Continuous improvement is a long-term strategy to enhance color purity. A material traceability table should be established to record the density, moisture content, and color masterbatch batch of each batch of silicone, facilitating problem tracing. Molds should be maintained regularly; venting channels should be cleaned after a certain number of mold production cycles, and the mold surface should be polished annually to reduce the risk of residue. Simultaneously, attention should be paid to new industry technologies, such as plasticizer-free, biodegradable liquid silicone materials, or digital production systems, to improve the accuracy and efficiency of color control.
