Injection Molding
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Low Hardness of Polypropylene Injection-Molded Products
Problem Phenomenon
The surface hardness test value of the product is lower than the standard requirement, and the surface is easily scratched or indented.
Low hardness affects the wear resistance and surface scratch resistance of the product, and affects the use performance in products requiring surface hardness.
Cause Analysis
(1) The mold temperature is too low, and the low crystallinity of polypropylene leads to a decrease in hardness
(2) The barrel temperature is too high, and the material partially degrades and the molecular weight decreases
(3) The holding pressure is insufficient, and the product density is low
(4) The cooling time is insufficient, and the crystallization process is not completed
(5) The material grade is selected improperly, and the hardness index does not meet the requirements
Solution
(1) Appropriately increase the mold temperature to the higher value within the range of 40-90°C to increase crystallinity
(2) Control the barrel temperature at a reasonable value within the range of 200-280°C to avoid overheating
(3) Increase the holding pressure to 80-120MPa to ensure the product is dense
(4) Extend the cooling time to ensure full crystallization
(5) Select a suitable grade, and add a nucleating agent to increase crystallinity when necessary
Key Takeaway
Low hardness is mainly caused by insufficient crystallinity or material degradation, and needs to be improved by increasing the mold temperature and holding pressure.
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