Twenty Kinds of Plastics and Their Properties—(4) PA66
4.PA66 polyamide 66 or nylon 66
Typical application range:
Compared with PA6, PA66 is more widely used in automobile industry, instrument shell and other products requiring impact resistance and high strength.
Injection molding process conditions:
Drying process: if the material is sealed before processing, it is not necessary to dry. However, if the storage container is opened, it is recommended to dry in the hot air at 85 °C centigrade. If the humidity is greater than 0.2%, it is also necessary to do a 105 °C and 12-hour vacuum drying.
Melting temperature: 260~290 °C. The product of glass additive is 275~280 °C. The melting temperature should be avoided above 300 °C.
Mold temperature: recommended 80 °C. The mold temperature will affect the crystallinity, and the crystallinity will affect the physical properties of the product. For thin walled plastic parts, if the mold temperature below 40 °C is used, the crystallinity of the plastic will change with time. In order to maintain the geometrical stability of the plastic part, annealing treatment is needed.
Injection pressure: usually in 750~1250bar, depending on the material and product design.
Injection speed: high speed (for reinforced material should be slightly lower).
Runner and gate: the location of the gate is very important because of the short solidification time of the PA66. The gate diameter of the gate should not be less than 0.5*t (here t is the thickness of the plastic part). If the hot runner is used, the gate size should be smaller than the conventional channel, because the hot runner helps prevent the premature solidification of the material. If the subsurface gate is used, the minimum diameter of the gate should be 0.75mm.
Chemical and physical properties:
PA66 has a high melting point in polyamide. It is a kind of semicrystal crystal material. PA66 also maintains strong strength and stiffness at higher temperatures. PA66 is still hygroscopic after forming, and its degree depends mainly on the composition of the material, the thickness of the wall and the environmental conditions. When the product is designed, it is necessary to consider the effect of Hygroscopicity on the geometric stability. In order to improve the mechanical properties of PA66, a variety of modifiers are often added. Glass is the most common additive, and sometimes in order to improve the impact resistance also added to synthetic rubber, such as EPDM and SBR. The viscosity of PA66 is low, so the fluidity is very good (but not as good as PA6). This property can be used to process very thin components. Its viscosity is sensitive to temperature change. The shrinkage rate of PA66 is between 1%~2% and the addition of glass fiber additive can reduce the shrinkage to 0.2%~1%. The contraction rate is larger in the direction of the flow and in the direction perpendicular to the direction of the flow. PA66 is anti – soluble for many solvents, but is weak in resistance to acids and other chlorinating agents.