Polyethylene splits into two useful moulding characters. HDPE is stiff and opaque, the material of crates, caps and pipe fittings. LDPE is softer and waxier, chosen where flexibility matters more than rigidity. Both are chemically inert, tolerate freezing temperatures without embrittling, and cost little — which is why they dominate industrial containers and closures.
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 | 0.94 – 0.96 g/cm³ (HDPE) |
| Tensile strength | 20 – 30 MPa |
| Flexural modulus | 0.9 – 1.5 GPa |
| HDT at 0.45 MPa | 43 – 60 °C |
| Mould shrinkage | 1.5 – 3.0 % |
| Water absorption (24 h) | < 0.01 % |
Values are typical for unfilled moulding grades at 23 °C unless stated. Glass-filled and specialty grades differ.
Typical applications
- Closures, caps and tamper-evident bands
- Industrial crates and totes
- Pipe fittings and irrigation components
- Household and garden ware
- Chemical drums and jerry cans
Processing notes
- Melt 180 – 240 °C, mould 20 – 40 °C. PE runs cool and fast; there is no benefit to a hot tool.
- Shrinkage of 2 – 3 % is the largest of the common thermoplastics. Dimensions that must hold need to be quoted with that allowance built in, not trimmed afterwards.
- High shrinkage plus low modulus means warpage is the main defect risk. Uniform wall, balanced cooling and generous radii do more than packing pressure.
- For threaded closures, specify the thread as a unscrewing or collapsing core feature at design stage — retrofitting it later means a new tool.
Frequently asked questions
HDPE or LDPE for a flexible part?
LDPE below about 0.93 g/cm³ for squeeze bottles and soft lids; HDPE above 0.94 for anything that has to hold shape under load. We can also specify a blend when you want stiffness with some give.
Can PE be printed or labelled?
Bare PE has low surface energy and rejects ink. Specify an in-mould label, or plan for corona or flame treatment before printing — this is a finishing decision that belongs in the design review, not after the tool is cut.
Related materials
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