Deep understanding of PA6, PA66
First, the background
PA66 was successfully polymerized into a PA66 polymer by adipic acid and hexamethylene diamine in 1935. The process of manufacturing PA66 by melt spinning was discovered from 1936 to 1937, and was commercialized by DuPont in the United States at the end of 1939.
A6 is a PA6 polymer synthesized by Schrack of IG Corporation of Germany in 1939. Taking caprolactam as a starting material and ε-aminocaproic acid as an initiator, it is heated. The production of PA6 fiber began in 1939 and was commercialized by French companies in 1943.
Second, the structure
In order to analyze their differences, we need to start with their structure. It is well known that nylon PA66 is formed by polycondensation of adipic acid and hexamethylene diamine. PA6 has the same molecular formula as PA66, but its structure is different, as shown in the following figure:
The performance difference between PA66 and PA6 is as follows:
Mechanical properties, thermal media properties, price, melting point and other properties PA66 are greater than PA6;
However, the water absorption, weather resistance, condensation time and molding processability of PA66 are lower than PA6.
Fourth, the process conditions
PA6 is easy to absorb moisture, and should pay special attention to drying before processing. If the material is supplied in a waterproof package, the container should remain closed. If the humidity is higher than 0.2%, it is recommended to dry in hot dry air above 80 °C for 3-4 hours. If the material is exposed to air for more than 8 hours, it is recommended to vacuum dry at 105 ° C for 1-2 hours or more. It is best to use a dehumidifier.
If the PA66 is sealed prior to processing, then no drying is required. If the storage container is opened, it is recommended to dry it in dry hot air at 85 degrees Celsius. If the humidity is greater than 0.2%, it needs to be vacuum dried at 105 ° C for 1-2 hours. It is best to use a dehumidifier. Molding temperature: 260 ~ 310 ° C, 280 ~ 320 ° C indicates enhanced varieties.
PA6: 80~90 °C. Mold temperature significantly affects crystallinity, and crystallinity also affects the mechanical properties of plastic parts. For thin-walled plastic parts with long process flows, it is recommended that the mold temperature be higher. Increasing the mold temperature can increase the strength and stiffness of plastic parts, but reduce toughness. If the wall thickness is greater than 3 mm, a low temperature mold of 20 to 40 ° C is recommended. For glass reinforcements, the mold temperature should be above 80 °C.
PA66: 80 °C is recommended. The mold temperature will affect the crystallinity, which will affect the physical properties of the product. For thin-walled plastic parts, if the mold temperature is below 40 °C, the crystallinity of the part will change with time. In order to maintain the geometric stability of the part, annealing is required.
PA6: 230~280°C, 250~280°C for enhanced varieties.
PA66: 260~290 °C. The product for glass additives is 275~280 °C. The melting temperature should be avoided above 300 °C.
Both are generally between 750 and 1250 bar (depending on material and product design).
Both are high speed (slightly lower for reinforced materials).
Runner and gate
Since the setting time of PA6 and PA66 is very short, the gate position is very important. The gate aperture should not be less than 0.5*t (where t is the thickness of the plastic part). If a hot runner is used, the gate size should be smaller than a conventional runner because the hot runner can help prevent premature curing of the material. If a flood gate is used, the minimum diameter of the gate should be 0.75 mm.
Fifth, the application
PA66 has the advantages of high strength, good rigidity, impact resistance, oil resistance, chemical resistance, wear resistance and self-lubrication, especially hardness, rigidity, heat resistance and creep properties. Since PA66 has higher strength than PA6, it is more used to produce industrial yarns such as cords.