• 2023-05-09
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What is the difference between injection molding material PA6 and PA66?

In modern manufacturing, precision mold manufacturing and injection molding processing is the most common form of batch processing mode, in the injection molding processing | precision injection, often used PA6 (nylon 6) and PA66 material (nylon 66), sometimes adding glass fiber to increase strength, such as GF30%. So what are the differences between PA6 and PA66 materials which are also nylon?

Structural difference

PA6 was obtained from caprolactam ring-opening polymerization, while PA66 was obtained from the condensation polymerization of adipamine and adipic acid. They have the same molecular formula, but the structure is quite different. The number of hydrogen bonds of PA66 is higher than that of PA6, and the molecular force is stronger than that of PA6, so the thermal properties of PA66 are better and higher processing temperature is required.

PA6 has better toughness, while PA66 has better rigidity and hardness, which is due to the different hydrogen bonds in the molecular structure.

Performance difference

The melting point of PA66 is 260~265℃, the glass transition temperature (dry state) is 50℃, and the density is 1.13~1.16 g/cc.

PA6 is a translucent or opaque opalescent crystalline polymer particle with melting point 220℃, thermal decomposition temperature greater than 310℃, relative density 1.14, water absorption rate (24 hours in water at 23℃) 1.8%, excellent wear resistance and self-lubrication, high mechanical strength, good heat resistance, electrical insulation performance, good low temperature performance, self-quenching and chemical resistance. Especially good oil resistance.

Compared with PA66, PA6 has the advantages of easy processing and molding, good surface gloss and wide temperature range, but higher water absorption and poor dimensional stability. Small rigidity, low melting point, can be used in harsh environment for a long time, in a wide range of temperature can still maintain enough stress, continuous use of temperature 105℃.

In general, the performance differences between PA66 and PA6 are as follows.

Mechanical properties: PA66 > PA6

Thermal medium 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

Process difference

1. Dry treatment

PA6 absorbs water easily, so special attention should be paid to drying before processing. If the material is supplied in a waterproof packaging, the container should be kept airtight. If the humidity is greater than 0.2%, it is recommended to dry in hot dry air above 80 ° C for 3 to 4 hours. If the material has been exposed to air for more than 8 hours, it is recommended to vacuum dry it at 105℃ for more than 1 to 2 hours. It is best to use a dehumidifier dryer.

PA66 If the material is sealed before processing, then there is no need to dry. If the storage container is opened, it is recommended to dry it in dry air at 85℃. If the humidity is higher than 0.2%, vacuum drying at 105℃ for 1 to 2 hours is required. It is best to use a dehumidifier dryer.

2. Mold temperature

Mold temperature significantly affects the crystallinity, which in turn affects the mechanical properties of plastic parts.

PA6:80~90℃. For thin-walled, long process plastic parts also recommended to use a higher mold temperature. Increasing the mold temperature can improve the strength and stiffness of plastic parts, but reduce the toughness. If the wall thickness is greater than 3mm, it is recommended to use a low-temperature mold of 20 to 40℃. For glass reinforced material mold temperature should be greater than 80℃.

PA66:80℃ is recommended. For thin-walled plastic parts, if the mold temperature is lower than 40℃, the crystallinity of the plastic parts will change with time. In order to maintain the geometric stability of the plastic parts, annealing is needed.

3, melting temperature

PA6:230~280℃ and 250~280℃ for enhanced varieties.

PA66:260~290℃. For glass fiber additives, the product is 275~280℃. The melting temperature should avoid higher than 300℃.

4. Injection pressure

Generally between 750 and 1250bar (depending on material and product design).

5. Injection speed

Both are high speed (slightly lower for enhanced materials).

6. Runner and gate

Since the solidification time of PA6 and PA66 is very short, the location of gate is very important. Gate aperture should not be less than 0.5*t (where t is the thickness of plastic parts). If a hot runner is used, the gate size should be smaller than if a conventional runner is used, as the hot runner can help prevent premature solidification of the material. If a submerged gate is used, the minimum diameter of the gate shall be 0.75mm.

Application difference

PA6 is used in electronic, automotive and other industrial fields. Its civilian silk industry consumption proportion is higher, clothing with nylon filament, about 58%. PA6 accounts for about 13% of the tire framework nylon cord fabric market. Engineering plastics use PA6 accounted for 12%, including injection materials and modified plastics. PA6 accounted for about 6% of fishing net silk. Plastic film grade PA6 for the production of BOPA film accounted for 4%, short fiber type PA6 for the production of carpets, sweaters, non-woven fabrics and other supplies accounted for 4%, and other PA6 for the production of PA rods, PA tape and other PA6 accounted for 3%.

PA66 is widely used in clothing, decoration, engineering plastics and other fields. The highest proportion is for engineering plastics, accounting for 65 per cent of total consumption, while industrial silk accounts for 20 per cent and others 15 per cent of total consumption.