How to correctly distinguish and choose injection moulding materials PA6 and PA66?

Time:2019-03-22 14:20:05 / Popularity: / Source:

With development of modified nylon technology become more mature, scope of use PA6 and PA66 has gradually expanded. Many plastic mold factory or units using nylon injection moulding materials have no clear distinction between PA6 and PA66. In addition, PA6 and PA66 are very similar in appearance. Obvious difference has caused a lot of confusion. How to distinguish PA6 and PA66, how to choose?
  • Tips of identification for PA6 and PA66:
Burn with burnt wool and nails, PA6 is a light yellow flame, while PA66 is a blue flame. PA6 has good toughness, is cheaper than PA66, and has a low melting point (225 degrees). PA66 has good strength, wear resistance and high melting point (255 degrees).
  • Physical difference between PA6 and PA66:
PA66 has a melting point of 260 to 265℃ and a glass transition temperature (dry state) of 50℃. The density is 1.13~1.16 g/cm3.
PA6 is translucent or opaque milky crystalline polymer particles, melting point 220℃, thermal decomposition temperature greater than 310℃, relative density 1.14, water absorption (24℃ water 24 hours) 1.8%, with excellent wear resistance and self-lubricating. It has high mechanical strength, good heat resistance and electrical insulation performance, excellent low temperature performance, good self-extinguishing and chemical resistance, especially excellent oil resistance.
Compared with PA66, PA6 is easy to process and form, has good gloss on surface of product, and has a wide temperature range, but has high water absorption rate and poor dimensional stability. It has low rigidity, low melting point, long-term use in harsh environments, and sufficient stress in a wide temperature range. Continuous use temperature is 105℃.
  • How to judge whether to use PA66 or PA6?
Performance comparison between PA6 and PA66:
Mechanical properties: PA66 > PA6
Thermal media performance: PA66 > PA6
Price: PA66 > PA6
Melting point: PA66 > PA6
Water absorption: PA66< PA6
Weather resistance: PA66< PA6
Condensation time: PA66< PA6
Molding performance: PA66 < PA6
  • How to choose PA6 and PA66?
1. When high temperature resistance is not required to reach 187 degrees or more, please use PA6+GF, which is more cost-effective and easy to process.
2. When high temperature resistance is required, use PA66+GF.
3. HDT (heat distortion temperature) of PA66+30GF is 250 degrees, PA6+30GF is about 220 degrees.
Chemical and physical properties of PA6 are similar to those of PA66. However, it has a low 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 quality characteristics of injection molded parts are affected by hygroscopicity, this should be taken into account when designing products using PA6. In order to improve mechanical properties of PA6, various modifiers are often added. Glass is the most common additive, and sometimes synthetic rubber is added to improve impact resistance. For products without additives, PA6 shrinks between 1% and 1.5%. Addition of a glass fiber additive reduces shrinkage to 0.3% (but slightly higher in direction perpendicular to flow). Shrinkage of molded assembly is mainly affected by crystallinity and hygroscopicity of material.
  • Application range distinction of PA6 and PA66:
PA6 engineering injection moulding materials have high tensile strength, good impact resistance, excellent wear resistance, chemical resistance and low friction coefficient. They can be modified by glass fiber, mineral filler modification and flame retardant. It makes it more comprehensive, mainly used in automotive industry and electronic appliances by plastic mold factory.
PA66 has good comprehensive performance, high strength, good rigidity, impact resistance, oil and chemical resistance, wear resistance and self-lubrication, especially hardness, rigidity, heat resistance and creep performance. PA66 is more used for production of industrial yarns such as cords because of its higher strength than PA6.
  • Difference between PA6 and PA66 injection molding process.
1. PA6 and PA66 drying treatment:
PA6 absorbs moisture easily, so special attention should be paid to drying before processing. If material is supplied in a waterproof material, container should be kept closed. If humidity is greater than 0.2%, it is recommended to dry in hot dry air above 80℃ for 3-4 hours. If material has been exposed to air for more than 8 hours, it is recommended to dry at 105℃ for 1-2 hours or more. It is best to use a dehumidifying dryer.
If material of PA66 is sealed before processing, then there is no need to dry. If storage container is opened, it is recommended to dry in a hot, dry air at 85℃. If humidity is greater than 0.2%, it is also necessary to carry out vacuum drying at 105℃ for 1 to 2 hours. It is best to use a dehumidifying dryer. Molding temperature: 260~310℃, 280~320℃ for enhanced varieties.
2. Mold temperature:
PA6: 80~90℃. Mold temperature significantly affects crystallinity, which in turn affects mechanical properties of part. For thin-walled, longer-flowing parts, it is also recommended to apply higher mold temperatures. Increasing mold temperature increases strength and stiffness of part, but reduces toughness. If wall thickness is greater than 3mm, it is recommended to use a low temperature mold of 20~40℃. For glass reinforcement mold temperature should be greater than 80℃.
PA66: 80℃ is recommended. Mold temperature will affect crystallinity, which will affect physical properties of product. For thin-walled injection molded parts, if a mold temperature lower than 40℃ is used, crystallinity of injection molded parts will change with time. In order to maintain geometric stability of injection molded parts, annealing treatment is required.
3. Melting temperature:
PA6: 230~280℃. 250~280℃ for enhanced varieties.
PA66: 260~290℃. Product with glass additives is 275~280℃. Melting temperature should be avoided above 300℃.
4. Injection pressure:
Injection pressure of PA6 and PA66 is generally between 750 and 1250 bar (depending on material and product design).
5. Injection speed:
Both PA6 and PA66 injection speeds are high speed (slightly lower for reinforced materials).
6. Flow path and gate:
Since solidification time of PA6 and PA66 is very short, position of gate is very important. Gate aperture should not be less than 0.5*t (t is thickness of injection molded parts). If a hot runner is used, gate size should be smaller than with a conventional runner because hot runner can help prevent premature solidification of material. If a submerged gate is used, minimum diameter of gate should be 0.75 mm.

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