Homopolymer or copolymer for a Portable PP case?

Answer: It depends on service temperature. Above freezing, homopolymer gives more stiffness per millimetre; for cold stores, specify block copolymer with minus 25 °C impact data.

How does melt index change the part?

Answer: A high index fills long thin sections but sacrifices impact; a low index risks short shots. At 2.0 mm, 12–18 balances both.

Can regrind go into the body?

Answer: Yes, near 20 percent and matched to the same grade, or index and shrinkage drift. Keep it out of hinges and wheel bosses.

Why do two batches differ in colour?

Answer: Pigment dispersion and mould temperature. Colder moulds darken deep colours; weighing masterbatch by mass holds delta E under 1.0.

Does a thinner wall hurt impact?

Answer: Yes, but ribs soften the trade. A 2.0 mm ribbed panel weighs ten percent less than a 2.4 mm flat one with similar drop results; thinning without ribs cracks the corner first.

Portable PP case buying guide: 5 checks on resin grades

Quick answer: The difference between suppliers usually sits in the resin bag. Confirm homopolymer or block copolymer, check melt index against the 8–25 g/10min window, then ask about low-temperature modification. A 2.0 mm wall, index 12–18 and 6 kJ/m² at minus 25 °C are the lines to hold.

Resin families behind a Portable PP case
Matching melt index to wall and machine
Low-temperature impact modification
Shrinkage control on the mould
Incoming and first-article checks
FAQ

1. Resin families behind a Portable PP case

Two Portable PP case samples can look identical and behave nothing alike. Homopolymer is stiff at 1500 MPa, so a thin wall holds shape but turns brittle in the cold. Block copolymer grafts ethylene into the chain, drops modulus to 1100 MPa and multiplies cold impact.

Melt index separates them. Homopolymer runs 8–12 g/10min at 230 °C and 2.16 kg, copolymer 15–25. A high index fills thin sections; a low one starves the flow end.

Resin	Melt index	Modulus	Cold behaviour
Homopolymer	8–12	1500 MPa	brittle at minus 10 °C
Block copolymer	15–25	1100 MPa	usable at minus 20 °C
Random copolymer	20–30	1000 MPa	clear, moderate toughness
Talc-filled	10–15	1800 MPa	stiff, lower toughness

2. Matching melt index to wall and machine

A 2.0 mm wall over a 1.2 m flow is stable at index 12–18. Below 8 the thin end short-shots and shows weld lines; above 25 a Portable PP case fills easily but short chains split along ribs.

Portable PP case: orange and black shell open flat, black foam in the lid, cut-outs for a gauge, valve and coiled tube, two black latches

Clamp force sets machine size: 0.18 m² at 35 MPa needs 380 to 650 tonnes. Melt runs 210–230 °C, mould 40–60 °C; a cold mould dulls the grain.

Watch batch drift: lots differing by over ±2 g/10min need a new fill profile, or the next short-shots.

3. Low-temperature impact modification

Homopolymer embrittles near minus 10 °C, a line winter transport crosses daily. The answer for a Portable PP case is 8–12 percent polyolefin elastomer, lifting notched impact at minus 25 °C above 6 kJ/m² so corners stop breaking off whole.

Modification costs modulus and gloss. Adding 10–15 percent talc restores modulus above 1600 MPa and pulls shrinkage from 1.6 to about 1.0 percent. Push the filler further and impact falls again.

System	Addition	Impact	Cost
Unmodified	none	3 kJ/m²	lowest
Elastomer	8–12%	6–8 kJ/m²	modulus down 20%
Elastomer and talc	8 and 12%	5–7 kJ/m²	duller surface
Heavy talc	above 20%	3 kJ/m²	toughness lost

Drying is not optional: two hours at 80 °C holds moisture under 0.05 percent, or silver streaks show.

4. Shrinkage control on the mould

Polypropylene shrinks 1.4–1.8 percent, so a 500 mm body needs a cavity 7–9 mm oversize. Get it wrong and hinges sit off position while latches miss.

Portable PP case: close view of the orange lid rim, black foam seated inside the frame, mould parting line visible on the orange edge

Anisotropy beats the average: flow and cross direction differ by 0.2–0.4 percent, so a square part drifts towards a diamond. A Portable PP case hinge seat carries 0.3 mm of compensation.

5. Incoming and first-article checks

Three incoming values block most failures: index, density and moisture. In range the window repeats; out of range, tuning moves the problem.

Item	Criterion	Method
Melt index	8–25 g/10min	230 °C, 2.16 kg
Density	0.905 ± 0.005	immersion
Moisture	0.05% max	loss on drying
Wall	2.0 ± 0.1 mm	ultrasonic, nine points
Cold drop	1 m, six faces at minus 25 °C	2 h soak first
Hinge life	50,000 cycles	3 kg load
Colour	delta E within 1.0	light booth

First-article work measures six faces, floor 1.85 mm. Hinges are overlooked: failures cluster near cycle 20,000 because a weld line sits at the root.

Conclusion

There is no best resin, only a match: temperature picks the family, wall and flow pick the index window, tolerance picks filled or unfilled, hinges pick the toughening level. Put those four into the technical agreement and ask for measured values, not a sample in the hand. Screen them in that order, and a Portable PP case becomes comparable on paper.

This article discusses only the container (case body) side of specifications and design intent, and does not cover any handling, loading or use of the contents.