In the production of PVC soft rubber products, such as panda nightlights, controlling surface defects is crucial to the product's appearance quality and market competitiveness. These defects may manifest as pitting, bubbles, flow marks, silver streaks, or surface roughness, and their causes involve multiple factors, including raw materials, mold design, molding processes, and environmental control. To avoid these problems, collaborative improvements are needed across multiple dimensions, including raw material selection, mold optimization, process parameter control, and production environment management.
The purity and proportion of raw materials are fundamental to the surface quality of soft rubber. PVC soft rubber typically consists of PVC resin, plasticizers, stabilizers, and fillers. If the impurity content in the raw materials is too high or the proportions are improper, it can easily lead to uneven melt flow, resulting in pitting or bubbles during molding. For example, insufficient plasticizer will cause the soft rubber to have higher hardness, poorer flowability, and a tendency for flow marks to appear on the surface; while improper selection of stabilizers may lead to decomposition and gas generation during processing, forming bubbles. Therefore, it is necessary to strictly screen suppliers to ensure that raw materials meet quality standards and to use high-precision metering equipment during the mixing stage to ensure uniform mixing of all components.
Mold design directly affects the flow and filling effect of the melt within the mold cavity. The panda nightlight design typically includes complex curved surfaces and detailed structures, such as ears and eyes. If the mold runner design is unreasonable, such as too narrow a runner, too many corners, or poor venting, turbulence or trapped air can occur during melt filling, leading to flow marks or silver streaks on the surface. Mold optimization requires addressing three aspects: runner balance, venting system, and cooling efficiency. Using hot runner technology can reduce pressure loss within the runner and improve filling uniformity. Adding venting grooves at key locations such as the parting line and core end can effectively expel gas from the cavity. A reasonable cooling water channel layout can shorten the molding cycle and prevent surface shrinkage and depressions caused by uneven cooling.
Precise control of molding process parameters is crucial to avoiding surface defects. Parameters such as injection speed, pressure, temperature, and holding time need to be dynamically adjusted according to the product structure and material properties. For example, excessively fast injection speeds can lead to high melt shear rates, resulting in streaks; while excessively slow speeds may cause flow marks due to the melt front cooling and solidifying. Injection pressure must balance filling requirements with mold capacity; insufficient pressure will result in short runs, while excessive pressure may cause flash or mold damage. Temperature control includes barrel and mold temperatures. Excessively high barrel temperatures can degrade the material, while excessively low temperatures result in poor flowability. Mold temperatures need to be adjusted according to product thickness; thin-walled parts require higher mold temperatures to improve flowability, while thick-walled parts require lower mold temperatures to avoid shrinkage and sink marks. Properly setting holding time and pressure can reduce internal stress in the product, preventing deformation or cracking after demolding.
The humidity and cleanliness of the production environment also significantly affect the surface quality of PVC. PVC is sensitive to moisture; if the raw materials are damp or the workshop humidity is too high, the moisture will evaporate during processing, forming bubbles. Therefore, raw materials must be stored in a dry environment and dried before use; the workshop must be equipped with dehumidification equipment to maintain relative humidity within a reasonable range. Furthermore, insufficient cleanliness in the workshop can lead to dust, oil, and other impurities adhering to the mold or raw material surface, resulting in stains or defects on the product surface. Regular cleaning of molds, equipment, and floors, along with requiring operators to wear dust-proof clothing and gloves, can effectively reduce contamination.
The operational procedures during demolding are equally crucial. The soft rubber surface of panda nightlights is typically quite flexible; excessive demolding force or insufficient draft angle can easily cause the product surface to be scratched by the mold, resulting in scratches or whitening. Sufficient draft angles should be included in the mold design, and the core and cavity surfaces should be polished to reduce the coefficient of friction. The demolding mechanism should employ a flexible ejection method, such as pneumatic ejection or elastic ejector rods, to avoid rigid impacts. Operators must master the correct demolding techniques, handling the product gently to prevent deformation or surface damage.
Optimizing post-processing can further improve product surface quality. Minor defects such as parting lines and burrs can be addressed through manual trimming, sanding, or polishing. For bubbles or pitting, the causes need to be analyzed, and process parameters or mold structure adjusted accordingly. In addition, surface coating or electroplating processes can conceal some defects while enhancing the product's aesthetics and added value, but it is essential to ensure that the coating adhesion and weather resistance meet requirements.
Continuous improvement and quality monitoring are the long-term mechanisms for preventing surface defects. A comprehensive quality traceability system must be established during production, conducting visual inspections on each batch of products, recording the type and location of defects, and analyzing defect rate trends through statistical process control (SPC) to adjust process parameters or mold conditions promptly. Regular cross-departmental quality analysis meetings should be organized to collaboratively optimize processes from design, production, and quality inspection, forming a closed-loop management system to gradually reduce the defect rate and improve the first-pass yield.
