PC 241R沙伯基础---The light transmission ability of PC is alsorelated to the smoothness of its product surface. Because thesurface hardness of PC is not high, the wear resistance is notideal, and the surface is easy to hair, which affects its lighttransmission. When PC is under uniaxial tension, birefringenceoccurs due to anisotropy and internal stress. The internal stressof the products can be tested by polarized light. The refractiveindex of PC to visible light varies linearly with temperature. Ithas higher refractive index than other transparent polymers, suchas acrylate, so it is more suitable for lens optical materials.Pure PC products are nontoxic and can be used to package food.Tableware made of PC will not fade or stain when contacting withtea and coffee, and will not affect the original color of food
The melt viscosity of PC is very high, which can reach 103 ~ 104PA · s η It is related to molecular weight, temperature and shearrate. (1) PC η However, when the molecular weight increases atlower temperature, the molecular weight decreases with the increaseof molecular weight η It is more significant than that at highertemperature; PC has high viscosity and is heat sensitive, η It issensitive to the change of temperature, pure PC η A has a larger ↓with the temperature ↑, when the temperature ↓, η Therefore, ahigher injection pressure should be used in the injection moldingto achieve the desired effect η The shear rate has little effect onthe variation, especially at low shear rates γ Therefore, in theprocess of PC molding, it is often better to improve the flow stateby adjusting the temperature than to change the temperature γ Moreeffective, such as simply by increasing the pressure and speed, notonly increase the internal stress, but also can not achieve thepurpose of reducing viscosity.
Although the water absorption of PC is not big, and itsperformance changes little after water absorption, it is verysensitive to water in the molding process. Even if there is a traceof water, the ester group on the main chain of PC will hydrolyze athigh temperature, releasing CO2 and other gases, resulting in asharp drop in molecular weight, discoloration of resin, and silverwire, bubbles and even cracks in the product. The higher themoisture content is, the lower the molecular weight is, and theworse the performance of the product is. Therefore, the rawmaterials must be strictly dried before molding until the moisturecontent is below 0.02%. Boiling bed drying, vacuum drying,circulating blast drying and infrared drying can be used as dryingmethods, among which vacuum drying has better effect. No matterwhich drying method, the temperature should not exceed 135 ℃, andthe thickness of material layer should not exceed 30mm, otherwise,the molecular weight of resin and the impact property of productswill be reduced
