Molds & Tooling
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Uneven surface gloss of PP products
Problem Phenomenon
The surface brightness of the same product is inconsistent, the gloss difference between near the gate and the flow end is obvious, and the gloss is also unstable between batches.
Cause Analysis
During filling, the front temperature and pressure gradually decay along the flow path, and the melt's ability to replicate the cavity surface is inconsistent at each location; uneven mold temperature, insufficient holding pressure transmission, and a gate that is too small all amplify this difference, and fluctuations in regrind ratio and color masterbatch dispersion also cause batch-to-batch color differences.
Solution
①Increase and even out the mold temperature to reduce the temperature difference between different mold areas; ②optimize the holding pressure curve to ensure the pressure is transmitted to the end; ③enlarge the gate runner or use multi-point gates to shorten the flow length difference of each area; ④stabilize the regrind ratio and strengthen color masterbatch dispersion; ⑤raise the polishing grade of the cavity for high-gloss surfaces.
Key Takeaway
PP gloss consistency = consistency of pressure and temperature distribution: first make the mold temperature uniform and transmit the pressure in place, then talk about polishing; batch-to-batch gloss drift mostly requires going back to check the regrind and color masterbatch, rather than repeatedly adjusting the machine.
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