PA6 and PA66 are both polyamide fibers, PA66 is polycondensed from hexamethylenediamine adipate, and PA6 is formed by polycondensation of caprolactam. From the molecular structure, the two fibers are very similar, so the physical and chemical properties of the two are similar. The difference is that the hydrogen bonding between adjacent molecules of PA66 is stronger, so its melting point is as high as 260 ° C, which is about 40 ° C higher than that of PA6, and the heat resistance is superior. Both weaving and sewing performance are good, but PA66 has a higher melting point, better heat resistance and better modulus of elasticity. It is more suitable for the manufacture of heat-resistant strain products such as tire cords and heat-resistant water-washed fabrics. And woven fabric. However, this is different from the subtle aspects. In fact, the difference between the two in the textiles for clothing is not large. The main use difference is in industrial applications, especially in the use of cords, PA66 is even better. PA6 is a kind of toughness, which is commonly used in climbing hands and automotive structural parts. PA66 is a toughness and hardness for industrial gears such as marine propellers.
PA6
For products without additives, PA6 shrinks between 1% and 1.5%. The addition of a glass fiber additive reduces the shrinkage to 0.3% (but slightly higher in the direction perpendicular to the flow). The shrinkage of the molded assembly is mainly affected by the crystallinity and hygroscopicity of the material.
Injection molding process conditions
Drying treatment: Since PA6 absorbs water easily, special attention should be paid to drying before processing. If the material is supplied in a waterproof material, the container should be kept closed. If the humidity is greater than 0.2%, it is recommended to dry in hot air above 80C for 16 hours. If the material has been exposed to air for more than 8 hours, it is recommended to perform vacuum drying at 105 C for more than 8 hours.
Melting temperature: 230~280C, 250~280C for enhanced varieties.
Mold temperature: 80~90C. The mold temperature significantly affects the crystallinity, which in turn affects the mechanical properties of the part. Crystallinity is important for structural components, so it is recommended that the mold temperature be 80~90C. For thin-walled, longer-flowing parts, it is also recommended to apply higher mold temperatures. Increasing the mold temperature increases the strength and stiffness of the part, but reduces the toughness. If the wall thickness is greater than 3mm, it is recommended to use a low temperature mold of 20~40C. For glass reinforcement the mold temperature should be greater than 80C. Injection pressure: generally between 750 and 1250 bar (depending on material and product design).
Injection speed: high speed (slightly lower for reinforced materials).
Runners and gates: Because the solidification time of PA6 is very short, the location of the gate 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 with a conventional runner because the hot runner can help prevent premature solidification of the material. If a submerged gate is used, the minimum diameter of the gate should be 0.75 mm.
PA66
PA66 has a higher melting point in polyamide materials. It is a semi-crystalline-crystalline material. PA66 also maintains high strength and stiffness at higher temperatures. PA66 is still hygroscopic after molding, the extent of which depends primarily on the composition of the material, the wall thickness and the environmental conditions. When designing a product, it is important to consider the effect of hygroscopicity on geometric stability. In order to improve the mechanical properties of PA66, various modifiers are often added. Glass is the most common additive, and sometimes synthetic rubbers such as EPDM and SBR are added to improve impact resistance. PA66 is less viscous and therefore has good fluidity (but not as good as PA6). This property can be used to machine very thin components. Its viscosity is sensitive to temperature changes. The shrinkage of PA66 is between 1% and 2%. The addition of glass fiber additives can reduce the shrinkage to 0.2%~1%. The shrinkage ratio is large in the flow direction and in the direction perpendicular to the flow direction. PA66 is resistant to many solvents, but is less resistant to acids and other chlorinating agents.
Injection molding process conditions
Drying: If the material is sealed before processing, there is no need to dry. However, if the storage container is opened, it is recommended to dry it in hot air at 85C. If the humidity is greater than 0.2%, it is also necessary to carry out vacuum drying at 105 C for 12 hours.
Melting temperature: 260~290C. The product for glass additives is 275~280C. The melting temperature should be avoided above 300C.
Mold temperature: 80C is recommended. The mold temperature will affect the crystallinity, which will affect the physical properties of the product. For thin-walled plastic parts, if a mold temperature lower than 40C is used, the crystallinity of the plastic part will change with time, and in order to maintain the geometric stability of the plastic part, annealing treatment is required.
Injection pressure: usually between 750 and 1250 bar, depending on material and product design.
Injection speed: high speed (slightly lower for reinforced materials).
Runners and gates: Because of the short settling time of the PA66, the location of the gate 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 with a conventional runner because the hot runner can help prevent premature solidification of the material. If a submerged gate is used, the minimum diameter of the gate should be 0.75 mm.
Application difference
The chemical and physical properties of PA6 are similar to those of PA66, however, it has a lower melting point and a wide process temperature range. It has better impact resistance and solubility resistance than PA66, but it is also more hygroscopic. Because many of the quality characteristics of plastic parts are affected by hygroscopicity, this should be taken into account when designing products using PA6. In order to improve the mechanical properties of PA6, various modifiers are often added. Glass is the most common additive, and sometimes synthetic rubbers such as EPDM and SBR are added to improve impact resistance.
PA6 material can achieve translucent effect, but temperature resistance is not ideal. If PA66 is used, it will not achieve translucent effect. PA66 has better heat resistance than PA6, PA66 has good rigidity, PA6 has good toughness, and PA66 price ratio. PA6 is expensive, feels softer than PA6, can be made of microfiber, and is made of high-grade fabrics. Nowadays, the quality of the down fabrics on the market is PA66, which is smooth, soft and soft, and has anti-feather effect. However, dyeing is difficult, difficult to color, high temperature dyeing is required, and color fastness is not very good.
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