Improvement measures for severe matte surface of PVC injection molded parts
A severe matte surface color on PVC injection-molded parts can significantly impact the product’s appearance quality and market competitiveness. Effective improvement measures are needed in terms of raw material selection and processing. First, ensure that the selected PVC resin has high purity and a uniform molecular weight distribution. Excessive impurities or an uneven molecular weight distribution in the PVC resin can lead to uneven melt flow during the injection molding process, resulting in a matte surface color. Furthermore, the type and amount of additives such as plasticizers and stabilizers in the PVC resin must be strictly controlled. Excessive or insufficient plasticizers can affect the material’s fluidity and stability. Improper addition of plasticizers can lead to precipitation or defects on the surface of the molded part, manifesting as a matte color. Before use, the PVC raw materials should be thoroughly mixed and stirred to ensure that all additives are evenly dispersed throughout the resin to avoid surface matte problems caused by localized concentrations of excessive or insufficient amounts.
Optimizing injection molding process parameters is a key step in improving the matte surface color of PVC injection-molded parts. Controlling the melt temperature is particularly important. If the melt temperature is too low, the PVC material will not fully melt, resulting in poor melt flow and significant resistance when filling the mold cavity, resulting in an uneven surface and a matte color. Excessively high melt temperatures can cause thermal decomposition of the PVC material, producing decomposition products that adhere to the part surface, causing a matte color. Therefore, the melt temperature must be precisely set based on the specific properties of the PVC material, generally within an appropriate range to ensure sufficient melting and prevent decomposition. Furthermore, the injection pressure and speed must be properly adjusted. Insufficient injection pressure can lead to incomplete melt filling, resulting in surface defects and a matte color. Excessive pressure can prevent gas from escaping the mold in a timely manner, forming bubbles and affecting surface gloss. Excessively high injection speeds can lead to unstable melt flow in the mold cavity, creating turbulence and resulting in a rough and matte surface. Excessively slow injection speeds can cause the melt to cool too quickly during filling, forming a cold layer on the surface and also causing a matte color.
Mold design and maintenance have a direct impact on the surface quality of PVC injection molded parts. Mold optimization can effectively improve the surface dullness of PVC injection molded parts. First, the mold cavity surface roughness should be kept to a low level. If the cavity surface is too rough, the molded part will replicate the mold surface defects, resulting in a dull color. Therefore, the mold cavity needs to be finely polished to improve its surface finish. Second, the mold’s gate and runner design must be appropriate to ensure smooth and even melt flow into the cavity. Improper gate placement or improper runner dimensions can cause eddy currents or excessive shear forces during melt flow, leading to material degradation or uneven distribution, which in turn causes a dull surface color. Furthermore, the mold’s exhaust system is crucial. If exhaust is not smooth, gas trapped in the cavity cannot be promptly expelled, resulting in bubbles or scorch marks on the molded part surface, which manifests as a dull color. Sufficient exhaust slots should be placed in appropriate locations within the mold to ensure smooth exhaust. Furthermore, molds should be regularly maintained and cleaned to prevent oil and impurities adhering to the mold surface from contaminating the molded part surface and causing a dull color.
During the PVC injection molding process, strengthening equipment maintenance and management can effectively ensure a matte finish on molded parts. The screw and barrel of the injection molding machine are critical components that affect melt quality. Severe wear of the screw and barrel can lead to uneven plasticization of the PVC material, resulting in a matte finish on the part. Therefore, regular inspection of the screw and barrel for wear is essential, and repair or replacement is necessary. Furthermore, the injection molding machine’s temperature control system must remain stable. Inaccurate temperature control, resulting in fluctuating temperatures, can affect the melt state of the PVC material and degrade surface quality. Components such as temperature sensors and heater coils must be regularly calibrated and maintained to ensure accurate and reliable temperature control. Furthermore, the injection molding machine’s nozzle and nozzle must be kept clean to prevent residual cold material or impurities from clogging the channel, disrupting the proper flow of the melt and causing a matte finish on the molded part.
In addition to the measures mentioned above, proper post-treatment of PVC injection-molded parts can also improve the surface matte problem to a certain extent. For example, for injection-molded parts with a less severe surface matte, polishing can be performed. This can be done through mechanical grinding or chemical polishing to remove surface defects and improve surface finish. However, it is important to avoid excessive polishing, as this can affect the dimensional accuracy and mechanical properties of the injection-molded part. Furthermore, for products requiring high surface quality, a coating process can be used to apply a transparent coating to the surface of the injection-molded part. This not only conceals the surface matte but also improves the product’s weather resistance and abrasion resistance. During the coating process, ensure good adhesion between the coating and the PVC substrate to avoid peeling. Furthermore, strict control of process parameters during post-treatment ensures stable and reliable treatment results.
