Controlled Rheology Visbreaking Degradation Risks in Food Contact Packaging Resins
Visbroken polypropylene risks organoleptic contamination and thermal degradation; verify residual peroxide, NIAS limits, and OIT before food contact use.
Plate Out
Meaning
Surface deposits of chemical additives or degradation products build up on the metal surfaces of extrusion dies or injection moulds during processing. This phenomenon, known as plate out, occurs when incompatible substances migrate out of the polymer melt under high pressure or temperature. Moulders must identify and resolve this issue to avoid surface defects on finished parts.
Deposit Formation
Migration of additives occurs when they exceed their solubility limit in the polymer matrix. This residue accumulates on the polished mold surface and transfers to the moulded parts. This transfer results in surface haze or gloss variations.
Processing Mitigation
Optimizing melt temperature and injection speed helps minimize the rate of additive migration. High melt temperatures can accelerate the decomposition of peroxides, which increases the likelihood of plate out occurring during high-speed runs. Vacuum venting on the injection mould or compounding extruder helps remove volatile elements before they can deposit on the metal.
Proper selection of stable additives and slip agents also reduces the rate of residue accumulation.
Maintenance Cost
Frequent tool cleaning is required to maintain part quality once these deposits begin to form. Production downtime increases when the mould must be pulled from the press for manual polishing. Using self-cleaning vents or mould coatings can extend the time between cleanings.