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Nylon has special performance,so it is widely used in automobiles, electronic and electrical equipment, mechanical structures, sports equipment, textiles, etc. However, miniaturization of automobiles, high-performance of electronic and electrical equipment, and lightweight of mechanical equipment accelerates, the demand and performance requirements for nylon are gradually increasing. So the modification of nylon seems particularly important.
Precautions for nylon modification
1. Barrel temperature setting
(1) Because nylon is a crystalline polymer, it has an obvious melting point. The temperature of nylon in barrel during injection depends on the resin itself performance,machine and the shape of the product.
(2) If the material temperature is too high,it can easily cause discoloration, brittleness and silver threads in plastic parts, and if the material temperature is to low ,it can make the material very hard and may damage the mold and screw.
(3) Generally, the minimum melt temperature of PA6 is 220℃, and that of PA66 is 250℃. Due to the poor thermal stability of nylon, it is not suitable to stay in the barrel at high temperature for a long time to avoid discoloration and yellowing of the material. At the same time, because nylon has good fluidity, it flows rapidly after the temperature exceeds its melting point.
2. Mold temperature setting
(1) Mold temperature has a certain impact on crystallinity and molding shrinkage. The mold temperature ranges from 80 to 120°C.
Choose high mold temperature, high crystallinity, increased wear resistance, hardness, elastic modulus, decreased water absorption, increased molding shrinkage of the product, suitable for thick products; choose low mold temperature, low crystallinity, good toughness, elongation Higher, shrinkage rate is reduced, suitable for thin products with good transparency.
(2) If the wall thickness is greater than 3mm, it is recommended to use a low-temperature mold at 20~40℃. For glass reinforced materials, the mold temperature should be greater than 80°C.
(3) Temperature control of molds where the wall of the product is thin and difficult to form or requires high crystallinity. If the product requires a certain degree of flexibility, cold water temperature control is generally used.
3. Product wall thickness
The flow length ratio of nylon is 150 to 200, and the wall thickness of the product is not less than 0.8mm, usually 1 to 3.2mm. Moreover, the shrinkage of the product is related to the wall thickness of the product. The thicker the wall thickness, the greater the shrinkage.
4. Exhaust
The overflow value of nylon resin is about 0.03mm, so the vent slot should be controlled below 0.025.
5. Runners and gates
The gate hole diameter should not be less than 0.5t (t is the thickness of the plastic part). With submersible gates, the minimum gate diameter should be 0.75mm.
6. Glass fiber filling range
During the molding process of nylon, lowering the mold temperature, increasing the injection pressure, and lowering the material temperature will reduce the shrinkage rate of nylon to a certain extent, making the product more prone to deformation due to increased internal stress. For example, the shrinkage rate of PA66 is 1.5% to 2%, and the shrinkage rate of PA6 is 1% to 1.5%. After adding glass fiber additives, the shrinkage rate can be reduced to about 0.3%.
Practical experience tells us that the more glass fiber is added, the smaller the molding shrinkage of nylon resin. However, adding too much glass fiber will cause floating fibers on the surface and poor compatibility. Generally, adding 30% has a relatively good effect.
7. Use of recycled materials
It is best not to exceed three times to avoid discoloration of the product or a sharp decline in physical and mechanical properties. The application amount should be controlled below 25%. Excessive application will cause fluctuations in process conditions. The mixture of recycled materials and new materials must be dried.
8. Safety instructions
When starting up the nylon resin, you should first turn on the nozzle temperature, and then heat the barrel. When the nozzle is blocked, do not face the nozzle hole to prevent the melt in the barrel from being suddenly released due to pressure accumulation and causing danger.
9. Use of release agent
Using a small amount of release agent can sometimes improve and eliminate defects such as bubbles. The release agent for nylon products can be zinc stearate, white oil, etc., or it can be mixed into a paste and used. The amount must be small and even when used to avoid surface defects of the product. The screw should be emptied when the machine is shut down to prevent the screw from being broken during next production.
10. Post-processing
(1) Heat treatment is required after the product is formed.
Commonly used methods: In high boiling point liquids such as mineral oil, glycerin, and liquid paraffin, the heat treatment temperature should be 10 to 20°C higher than the use temperature. The treatment time varies depending on the wall thickness of the product. The thickness is 10 to 15 minutes if the thickness is less than 3 mm, and the thickness is 3 to 20 minutes. The 6mm time is 15 to 30 minutes. The heat-treated products should be slowly cooled to room temperature to prevent the regeneration of stress in the products caused by sudden cooling. (2) Humidity control treatment should be carried out after the product is formed.
Humidity conditioning treatment is mainly performed on products with relatively high environmental humidity. There are two methods: one is the boiling water humidity conditioning method; the other is the potassium acetate aqueous solution humidity conditioning method (the ratio of potassium acetate to water is 1.25:1, Boiling point 121°C).
The boiling water humidity control method is simple, as long as the product is placed in an environment with a humidity of 65% to achieve the equilibrium moisture absorption, but it takes a long time, while the potassium acetate aqueous solution humidity control method requires acetic acid at a processing temperature of 80 to 100°C Potassium aqueous solution humidity control method, the processing time mainly depends on the wall thickness of the product, about 2 hours when the wall thickness is 1.5 mm, about 8 hours when the wall thickness is 3 mm, and 16 to 18 hours when the wall thickness is 6 mm.
With nearly 20 years in the intelligent extrusion equipment industry, he has held key roles at Jwell Machinery, including General Manager and Rotating Chairman. Since 2024, he has managed multiple subsidiaries, driving business expansion and industrial upgrades, while leading innovation in intelligent manufacturing and global growth.
