At present, modern design tends to lightweight requirements, the use of plastic proportion is increasing, no matter what industry, as long as the plastic can replace the absolute metal, plastic another advantage is the process of low cost, molding easier.

Among the many polymer plastic materials, nylon is the leader, especially in the automotive industry, basically can not be separated from the nylon material.

Polyamide resin, known in English as polyamide, or PA for short, is commonly known as nylon (Nylon). It is a general term for polymers containing amide groups in the repeating units of the main chain of macromolecules. It is one of the five major engineering plastics with the largest production, the most varieties, the most versatile species, with other polymer blends and alloys, etc., to meet different special requirements, widely used as a substitute for metal, wood and other traditional materials.

The main varieties of nylon are nylon 6 (PA6) and nylon 66 (PA66), which occupy the absolute dominant position.

So what is the essential difference between PA6 and PA66?

The basic difference in physical properties

Nylon 6 (PA6) is a polycaprolactam, while nylon 66 (PA66) is a polyhexanediamine, PA66 is 12% harder than PA6.

The chemical and physical properties of PA6 are very similar to PA66, however, it has a lower melting point and a wide range of process temperatures. It has better impact and dissolution resistance than PA66, but is also more hygroscopic.

PA66 is a semi-crystalline - crystalline material that has a higher melting point and maintains high strength and stiffness at higher temperatures.


Product performance differences

PA6: excellent thermal stability, high heat resistance; good dimensional stability; high surface quality; good anti-warping properties.

Melting point: 210 - 220 ℃

Decomposition temperature: >300 ℃

Flash point: >400 ℃

Self-ignition temperature: >450 ℃

Physical state: solid particles 

Odor: Non-toxic:

No recycling: Can

Final disposal: soil (harmless industrial waste)

Extinguishing agent: Available in various extinguishing agents (water, foam, powder, CO2, sand)

Transportation: Non-hazardous goods, suitable for various means of transportation 

EC standard: non-dangerous goods

PA66 has excellent wear resistance, good high impact resistance and good dimensional stability.

Melting point: 250-270 ℃

Decomposition temperature: >350 ℃

Flash point: >400 ℃

Self-ignition temperature: >450 ℃

Physical state: solid particles 

Odor: Non-toxic:

No recycling: Can

Final disposal: soil (harmless industrial waste)

Extinguishing agent: Available in various extinguishing agents (water, foam, powder, CO2, sand)

Transportation: Non-hazardous goods, suitable for various means of transportation 

EC standard: non-dangerous goods



Usage difference

PA6 is generally used for automotive parts, mechanical parts, electronic and electrical products, engineering parts and other products.

PA66 is more widely used in automotive industry, instrument housing and other products that need to have impact resistance and high strength requirements, such as marine propellers, gears, rollers, pulleys, rollers, impellers in pump bodies, fan blades, high pressure sealing enclosures, valve seats, gaskets, bushings, various handles, support frames, inner layers of wire packages, etc.


Molding process difference

PA6-Molding process conditions

PA6 is subject to moisture absorption because of many quality characteristics of the molded parts, so it is important to take this into account when designing products using PA6. To improve the mechanical properties of PA6, a variety of modifiers are often added. Glass fiber is the most common additive, and sometimes synthetic rubber, such as EPDM and SBR, is added to improve impact resistance.



For products without additives, the shrinkage of PA6 ranges from 1% to 1.5%. The addition of glass fiber reinforced nylon can reduce the shrinkage to 0.3% (but slightly higher in the direction perpendicular to the process). The shrinkage of the molded assembly is mainly influenced by the crystallinity and moisture absorption of the material.



Drying treatment

Since PA6 absorbs moisture very easily, special attention should be paid to drying before processing. If the material is supplied in a waterproof package, the container should be kept airtight. If the humidity is greater than 0.2%, drying in hot air at 80°C or higher for 16 hours is recommended. If the material has been exposed to air for more than 8 hours, vacuum drying at 105°C for more than 8 hours is recommended.



Melting temperature

230~280℃, for reinforced nylon is 250~280℃.



Mold temperature

80~90℃. The mold temperature significantly affects the crystallinity, which in turn affects the mechanical properties of the molded part, and the crystallinity is important for structural parts, so the recommended mold temperature is 80~90℃. Higher mold temperatures are also recommended for thin-walled parts with longer processes. Increasing the mold temperature will improve the strength and stiffness of the part, but will reduce the toughness. If the wall thickness is greater than 3mm, it is recommended to use a low temperature mold of 20~40℃. For glass reinforced material mold temperature should be greater than 80℃.



Injection pressure

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



Injection speed

High speed (to be reduced slightly for reinforced nylon).



Runners and gates

Due to the short solidification time of PA6, the location of the gate is very important. The gate aperture should not be smaller than 0.5*t (where t is the thickness of the molded part). If using a hot runner, the gate size should be smaller than with a conventional runner, because the hot runner can help stop the material from solidifying too early. If submerged gates are used, the minimum diameter of the gate should be 0.75mm.



PA66 - Injection Molding Process Conditions

PA66 remains hygroscopic after molding, the extent of which depends primarily on the composition of the material, wall thickness, and environmental conditions. The effect of moisture absorption on geometric stability must be considered when designing the product.



PA66 has a low viscosity and therefore flows well (but not as well as PA6). This property can be used to process very thin components. Viscosity is sensitive to changes in temperature.



The shrinkage of PA66 ranges from 1% to 2%, and the addition of glass fiber modification can reduce the shrinkage to 0.2% to 1%. The difference in shrinkage is large in the process direction and in the direction perpendicular to the process direction.



PA66 is resistant to many solvents, but is less resistant to acids and some other chlorinated agents.



Drying treatment

If the material is sealed prior to processing, then drying is not necessary.

If the storage container is opened, then it is recommended that the material be dried in hot air at 85°C.

If the humidity is greater than 0.2%, vacuum drying at 105°C for 12 hours is also required. Melting temperature

260~290℃.

For glass modified products 275~280℃.

Melting temperature should be avoided higher than 300℃.



Mold temperature

80℃ is recommended.

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 40°C is used, the crystallinity of the plastic part will change over time and annealing is required to maintain the geometric stability of the part. Injection Pressure

Usually in the range of 750 to 1250 bar, depending on the material and product design.



Injection speed

High speed (should be slightly lower for reinforced materials). Runners and gates

Since the solidification time of PA66 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 molded part).

If using a hot runner, the gate size should be smaller than with a conventional runner, because the hot runner can help stop the material from solidifying prematurely.

If submerged gates are used, the minimum diameter of the gate should be 0.75mm.