The material treatment of high-gloss PVC baseball needs to be carried out around four core links: material selection, processing technology optimization, surface treatment and quality inspection. The following is an analysis of the specific technical points:
Raw material selection and formula design
High transparency PVC resin: Select PVC resin with a narrow molecular weight distribution and low impurity content to ensure that the substrate itself has high light transmittance (light transmittance ≥88%). This type of resin has better fluidity during processing, which is conducive to forming a smooth and flat surface.
Optimization of plasticizers and stabilizers: High-efficiency plasticizers such as dioctyl phthalate (DOP) are used, with the addition amount controlled at 30-40 PHR (parts per 100 parts of resin) to balance flexibility and gloss. Meanwhile, calcium-zinc composite stabilizer is added to prevent surface yellowing caused by thermal degradation during processing.
Lubricants and impact modifiers: Add lubricants such as calcium stearate with a pH of 0.5-1 to reduce the friction between the melt and the equipment and improve the surface finish. Add an appropriate amount of MBS or ACR impact modifier (5-8 PHR) to enhance toughness while avoiding a decrease in gloss.
2. Processing technology control
Injection molding temperature and pressure optimization: The injection molding temperature is set at 175-190℃ to ensure that the PVC is fully plasticized and does not decompose. The mold temperature is controlled at 60-70℃ to promote rapid cooling of the melt and reduce surface shrinkage marks. The injection pressure needs to be adjusted according to the size of the baseball (usually 80-120 mpa) to avoid surface flow marks caused by insufficient pressure.
Holding pressure and cooling time: The holding pressure time is set at 5 to 8 seconds to ensure that the melt fully fills the mold and compacts the surface. The cooling time should be controlled at 15 to 20 seconds to prevent surface deformation caused by excessive demolding.
Screw speed and back pressure: The screw speed should be controlled at 30-50 RPM, and the back pressure should be set at 5-10 mpa to ensure uniform mixing of the melt and reduce bubbles and impurities.
3. Surface treatment technology
Mirror polishing mold: The surface of the mold needs to undergo precise polishing treatment, with a roughness Ra≤0.05μm, to ensure that there are no microscopic defects on the formed surface. The polishing process can combine mechanical grinding with electrolytic polishing to enhance the surface finish.
Coating technology: UV-curable coatings or fluorocarbon resin coatings are applied to the surface of PVC, and a transparent protective film with high hardness and low friction is formed through light curing or thermal curing. The coating thickness is controlled at 10-20μm, which can not only enhance the gloss but also improve the wear resistance.
Plasma treatment: Plasma activation treatment is carried out on the PVC surface before coating to enhance the adhesion between the coating and the substrate and prevent the decline in gloss caused by coating peeling.
4. Quality inspection and post-treatment
Gloss detection: Use a 60° Angle gloss meter to measure the surface gloss, with a target value of ≥90GU (gloss unit). If the standard is not met, the polishing accuracy of the mold or the coating formula needs to be adjusted.
Defect repair: Local grinding and polishing of minor surface blemishes (such as flow marks, bubbles), or reapplication of the repair layer.
Environmental adaptability test: Place the baseball in a high-temperature and high-humidity environment (50℃, 90%RH) for 72 hours, and measure the gloss attenuation rate (which should be ≤5%) to ensure long-term performance.
Technical difficulties and solutions
Poor thermal stability of PVC: By adding organotin stabilizers or phosphite ester auxiliary stabilizers, the thermal degradation during processing can be inhibited.
Insufficient adhesion of the coating: Pre-apply a primer (such as polyurethane) on the PVC surface to enhance the chemical bonding ability between the coating and the substrate.
Balance of gloss and wear resistance: Nano-scale silica fillers are used to enhance the hardness of the coating, while the particle size of the fillers (≤50nm) is controlled to avoid a decrease in gloss caused by scattering.
Through the above-mentioned technical means, high-gloss PVC baseball can achieve a surface gloss of ≥90GU and a wear resistance loss of ≤10% (rotating 1000 times under a 500g load of Taber), meeting the demands of professional events and the high-end consumer market.