Polypropylene is the lightest of the volume thermoplastics and the cheapest per part once you account for density. It shrugs off acids, bases and most solvents, and a properly gated living hinge will flex a million cycles without cracking. The catch is shrinkage of one to two percent and a tendency to warp — both manageable, but only if the tool is designed for them from the start.
Typical values for standard moulding grades. Exact figures depend on the specific compound or grade — confirm against your drawing before quoting.
Key properties
| プロパティ | Typical value |
|---|---|
| 密度 | 0.90 – 0.91 g/cm³ |
| Tensile strength | 25 – 40 MPa |
| Flexural modulus | 1.2 – 1.7 GPa |
| HDT at 0.45 MPa | 100 – 110 °C |
| Mould shrinkage | 1.0 – 2.5 % |
| Water absorption (24 h) | < 0.02 % |
Values are typical for unfilled moulding grades at 23 °C unless stated. Glass-filled and specialty grades differ.
Typical applications
- Bottle caps and closures
- Food containers and thin-wall packaging
- Living-hinge lids and flip tops
- Automotive battery trays and interior panels
- Chemical tanks and laboratory ware
Processing notes
- No drying needed in most cases — PP absorbs almost no water. Skip the dryer and save a process step.
- Melt 200 – 260 °C, mould 20 – 60 °C. A cold mould gives the best gloss and the shortest cycle.
- Shrinkage of 1.5 % means a 100 mm span moves 1.5 mm. Design ribs and bosses so that differential shrinkage pulls the part flat rather than into a banana.
- For living hinges, gate so the melt flows across the hinge line, and keep the hinge thin — 0.25 to 0.4 mm — with a sharp entry radius.
Frequently asked questions
Why does my PP part warp even though the tool is correct?
Almost always differential shrinkage between a thick boss and a thin wall, or uneven cooling between the two halves. Packing profile and mould temperature balance fix it more often than a tool change does.
Is PP suitable for food contact?
Yes, in a food-contact grade with the appropriate declaration. We supply the migration documentation your market requires, whether that is EU 10/2011 or FDA 21 CFR.
Related materials
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