Preparation before transparent plastic injection molding
Transparent plastic injection molding places extremely high demands on the production environment and material handling. Any minor impurities or operational errors can affect the product’s transparency and surface quality, so pre-molding preparations require meticulous attention to detail. First, material pretreatment is essential. Transparent plastics such as PMMA and PC easily absorb moisture from the air during storage. Direct injection molding can lead to defects such as bubbles and silver streaks in the finished product. Workers place the raw materials in a dryer and set the appropriate temperature and time based on the characteristics of each plastic. For example, PMMA is typically dried at 80-90°C for 4-6 hours, while PC requires 120-130°C for 6-8 hours. The dried material should be used immediately to prevent further moisture absorption. Raw materials must also be screened to remove any impurities, off-color particles, or lumps that may have entered. This can be achieved through filtration or manual selection to ensure raw material purity.
Inspecting and cleaning the mold is another key preparation. The cavity surface of the transparent plastic injection mold must maintain an extremely high degree of finish. Any scratches, oil stains, or residual release agent will leave marks on the surface of the product and affect its transparency.
The operator must first disassemble the mold and carefully wipe the cavity, core, and parting surface with a dedicated cleaning agent (such as alcohol or mold cleaner). Use a soft cloth or sponge if necessary to avoid scratching the surface. Then, check the mold’s cooling system to ensure unobstructed waterways and uniform cooling. Uneven temperature distribution can lead to inconsistent shrinkage in the product, internal stress, and even cracking. Also, verify that the mold’s exhaust system is functioning properly. Transparent plastic melts have a high viscosity, and poor exhaust can easily cause bubbles. Clear any debris from the exhaust slots to ensure smooth exhaust.
The equipment debugging process should not be neglected either. The barrel and screw of the injection molding machine need to be thoroughly cleaned, especially when plastics of other colors or materials have been processed before. Residual materials must be removed to prevent contamination of transparent raw materials. When cleaning, you can first flush with recycled transparent plastic or special cleaning materials until the extruded plastic is uniform in color and free of impurities. Then set the barrel temperature according to the characteristics of the transparent plastic. For example, the barrel temperature of PMMA is usually 180-230℃, and that of PC is 260-320℃. Too high a temperature will cause the plastic to degrade, produce black lines or discoloration, and too low a temperature will cause the melt to have poor fluidity and make it difficult to fill the cavity. At the same time, it is necessary to adjust parameters such as injection speed, pressure, and holding time to prepare for formal production.
Environmental control is also an important component of the preparations before transparent plastic injection molding. Because transparent products require extremely high cleanliness levels, production workshops must remain dust-free. Air purification systems are typically installed to control airborne dust particles within a certain range. The workshop’s temperature and humidity must also be stable, generally maintained at 20-25°C and 50-60%. Excessively high humidity can cause the raw materials to absorb moisture again, while excessively low humidity can easily generate static electricity and attract dust. Operators must wear clean work clothes, gloves, and hats before entering the workshop to prevent hair, dandruff, or clothing fibers from mixing with the raw materials or molds. Furthermore, equipment and tools within the workshop require regular cleaning to prevent the accumulation of contaminants.
Finally, a small-batch trial production run is necessary to verify the effectiveness of the preliminary preparations. During trial production, the product’s exterior quality is closely observed, inspecting for defects such as bubbles, silver streaks, scratches, and black spots. The dimensional accuracy of the product is also measured to ensure compliance with design requirements. If any problems are discovered, the cause is promptly analyzed and relevant parameters or treatment measures are adjusted. For example, if bubbles appear, this may indicate insufficient drying of the raw materials or poor venting, requiring re-drying of the raw materials or cleaning of the venting slots. If scratches are present, the mold surface must be inspected for damage or foreign matter, and these must be repaired or cleaned promptly. Only after the trial-produced products have fully qualified can large-scale production begin, thus ensuring the consistent quality of transparent plastic injection molded products.
