1. High-gloss molds generally have the following characteristics:
1. The molding temperature of the mold is relatively high (generally about 80-90 degrees). The pressure-holding molding at a higher mold temperature is beneficial to eliminate defects such as weld marks, flow marks, and product internal stress. Therefore, the mold needs to be heated during operation. In order to prevent heat loss, a resin heat insulation board is usually added to the fixed mold side.
2. The surface of the mold cavity is extremely bright (generally mirror level 2 or higher). The products produced by the high-gloss mirror mold can be directly used for installation without any surface treatment. Therefore, it has very high requirements for mold steel and plastic materials. high.
3. There are many hot nozzles in the hot runner system (usually 6-8 nozzles, sometimes more). Each hot nozzle must have a sealing pin and an independent air channel, which is individually controlled by solenoid valves and time relays. , Realize time-sharing glue feeding, so as to achieve the purpose of controlling or even eliminating weld lines.
2. The material selection of high-gloss mold The factors that affect the surface quality of the product In addition to the cavity temperature, the selection of mold steel and plastic materials is also crucial. The following introduces the selection of high-gloss mold steel and plastic materials.
1. Selection of mold steel The performance and life of the mold are directly related to the steel used in the mold. Plastic mold parts are affected by external influences differently due to their different working conditions. Therefore, in addition to some basic requirements for the performance of steel, it is also necessary to focus on it. For example, the steel used for the cavity of large high-gloss plastic molds requires not only good machinability, electrical discharge processability and welding performance, but also excellent polishability and high hardness. This can not only form products with a bright and beautiful surface, but also reduce the wear of the plastic on the cavity surface, which not only prolongs the service life of the mold, but also reduces the injection pressure and protects the injection molding machine. At present, commonly used high-performance mirror plastic mold steels include: POLMAX, LKM838H, LKM818H, S-2, and plastic materials. At present, the plastic materials used for the front shell in TV manufacturing are generally HIPS and ABS.
As two commonly used casing materials, although the cost of ABS will be higher, the molded products are better than HIPS in terms of impact resistance, surface gloss and hardness, so when producing high-gloss products, high-gloss is usually used ABS material. ABS is an amorphous polymer with no obvious melting point. Due to the various grades of its grades, appropriate process parameters should be formulated according to different grades during the injection molding process. Generally, it can be molded at a temperature above 160°C and below 270°C. In the molding process, ABS has good thermal stability, a wide range of options, and is not easy to degrade or decompose. Moreover, the melt viscosity of ABS is moderate, and its fluidity is better than that of polystyrene (PS) and polycarbonate. , and the cooling and solidification speed of the melt is relatively fast, generally it can be frozen and solidified within 5-15 seconds. The fluidity of ABS is related to injection temperature and injection pressure, and injection pressure is slightly more sensitive. For this reason, in the process of injection molding, the injection pressure can be used to reduce the melt viscosity and improve the filling performance. Due to the different components of ABS, the performance of water absorption and adhesion water is different. The surface adhesion water and water absorption rate are 0.2%-0.5%, sometimes up to 0.3%-0.8%. In order to obtain more ideal products, Do drying treatment before molding to reduce the water content to below 0.1%, otherwise, bubbles, silver wires and other defects will appear on the surface of the workpiece.