Injection Molding
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Low hardness of homopolymer polypropylene injection 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 product wear resistance and surface scratch resistance, and affects use performance in products requiring surface hardness.
Cause Analysis
(1) Mold temperature too low; low crystallinity of homopolymer polypropylene causes hardness decrease
(2) Barrel temperature too high; partial material degradation reduces molecular weight
(3) Insufficient holding pressure, low product density
(4) Insufficient cooling time, crystallization process incomplete
(5) Improper material grade selection; hardness index does not meet requirements
Solution
(1) Appropriately increase mold temperature to the higher value within the 40-90°C range to increase crystallinity
(2) Control barrel temperature at a reasonable value within the 200-280°C range, avoid overheating
(3) Increase holding pressure to 80-120MPa, ensure the product is dense
(4) Extend cooling time, ensure full crystallization
(5) Select an appropriate grade; add nucleating agent when necessary to increase crystallinity
Key Takeaway
Low hardness is mainly caused by insufficient crystallinity or material degradation; it needs to be improved by increasing mold temperature and holding pressure.
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