Plastic Packaging Tube Extrusion: From Die to Finished Tube

Two families of packaging tube, and only one is extruded

Walk into a tube plant and you will find one of two production models. They look similar in the finished product and are completely different in how they are made.

Extruded tubes are made the way you would expect: plastic granules go into a screw, a melt comes out of an annular die as a continuous tube, it is sized and cooled, and it is cut to length. The body is seamless. Wall thickness is set by the die and the haul-off speed. This is the process this article is about.

Laminate tubes start as a flat sheet. The sheet is printed, then rolled into a cylinder and the longitudinal seam is welded — usually ultrasonically — into a tube. The body has a seam. The sheet itself may be an aluminium foil laminate (ABL) or a co-extruded all-plastic film (PBL).

Table 1 — The two tube families. The choice is usually made by the brand's artwork, not by the engineer.

The rest of this article covers the extruded tube line, because that is the part an extrusion supplier controls. The head, the cap and the decoration are separate supply chains that happen to meet at the same filling line.

The body: what happens between die and cutter

The tube body is a thin-wall pipe with two special requirements: the wall has to be concentric to within a few hundredths of a millimetre, and the surface has to be good enough to print on without preparation. Both of those are decided in the first two metres after the die.

The die

Most tube lines use a crosshead die — the melt enters from the side and turns 90° to flow around a mandrel before exiting through an annular gap. The alternative is a spider die, where the melt flows around support legs and re-joins downstream. Crosshead is preferred for tubes because it leaves no weld line; spider legs always leave a faint longitudinal line that shows up as a defect after printing.

The die gap sets the wall. For a 35 mm tube with a 0.5 mm wall, the die gap is typically 1.5 – 2.5 mm — considerably larger than the finished wall, because the tube is drawn down between the die and the haul-off. Draw-down ratio is the die gap divided by the finished wall, and it is usually between 3:1 and 6:1. Higher draw-down gives better orientation and a thinner wall from the same die, but it also amplifies any concentricity error in the die.

Sizing and cooling

Two methods dominate. Vacuum sizing pulls the tube onto a cooled sleeve with a vacuum applied through slots; the outside diameter is set by the sleeve and the wall is set by the draw-down. Pressure sizing pushes air inside the tube so it expands against an external sleeve; this holds the bore round but requires a reliable seal at the die and at the haul-off.

For packaging tubes vacuum sizing is more common, because the outside diameter is what the cap and the filling nozzle care about. The cooling trough is usually 3 – 6 m long with spray rings, and the water temperature is held at 12 – 18 °C. Cold water cools faster but increases internal stress, which shows up later as ovality after the tube is cut.

Table 2 — Line settings for a 35 mm PE tube. Note that haul-off speed and die gap both change the wall — operators often change speed when they should change the die.

The head is not extruded

The shoulder and neck of a tube — the part the cap screws onto — is almost always injection moulded in HDPE or PP, then welded to the extruded body. It is not extruded with the body, and there are three good reasons.

First, the neck needs a precise thread and a sealing lip. Extrusion cannot hold those tolerances. Second, the shoulder is thick — 1.5 to 3 mm at the transition — and an extruded thin wall cannot thicken locally without a very complex die. Third, colour: the head is often a different colour from the body, and moulding it separately avoids a two-material extrusion.

The head is moulded on a multi-cavity tool, typically 8 – 32 cavities, in a cycle of 12 – 20 seconds. It is the single most expensive tool in the project and the longest lead time — 8 to 12 weeks is normal, against 3 to 5 weeks for an extrusion die.

Table 3 — Attaching the head. Ultrasonic welding dominates because it is fast, clean and needs no consumables.

The weld is the first place a tube leaks. A tube that passes a pressure test at 0.5 bar when new can fail at 1.2 bar after two weeks on a shelf, because the weld interface creeps under sustained load. If the product is a cream with a preservative system that is sensitive to oxygen ingress, the weld quality matters more than the body barrier.

Decoration decides the line layout

Extruded tubes cannot be printed flat, so they are printed as finished cylinders. That single constraint drives most of the equipment decisions downstream.

Table 4 — Decoration routes for an extruded tube. Anything above four colours pushes the cost up sharply because each colour needs its own print station.

Because printing happens on the finished cylinder, the tube must be round and concentric before it reaches the printer. An oval tube prints with a gap on one side and a squeeze on the other. This is why ovality tolerance — not wall thickness — is often the specification that rejects the most tubes.

The full line, in order

1. Ekstrüzyon — granules to tube, cut to length, packed loose in boxes
2. Head moulding — separate operation, usually a different supplier
3. Head welding — ultrasonic, on a rotary or linear machine
4. Baskı — offset, screen or flexo, on mandrels
5. Varnish / lacquer — UV or solvent, for gloss and scuff resistance
6. Capping — automatic, with torque control
7. Tail sealing — happens at the filler, not the tube maker

Note that tail sealing is the filler's job. The tube maker ships an open tube with a cap on; the brand fills it and crimps the tail closed. This is why the tube's cut length tolerance matters: a tube 1 mm short will not reach the crimping jaws cleanly, and the seal will be weak on one corner.

What actually gets inspected

Table 5 — Inspection plan for an extruded tube body. Ovality is measured after 24 hours because it develops as residual stress relaxes.

The 24-hour wait on ovality is not bureaucracy. A tube measured straight off the line is round because it is still constrained by the cooling history. Cut it, leave it, and the stress relaxes over a few hours — a tube that was 0.1 mm oval at the machine can be 0.4 mm oval the next morning. Any plant that measures ovality immediately after cutting is measuring the wrong number.

Where the cost sits

For a 35 mm × 150 mm PE tube with a moulded head, cap and two-colour print, a rough split at 100,000 pieces looks like this:

Table 6 — Cost structure of a printed extruded tube. Printing is the most compressible line and the one brands change most often.

The two levers that move the price most are print colours and wall thickness. Dropping from six colours to four saves more than thinning the wall from 0.5 to 0.45 mm, and it is easier to do. Thinning the wall below 0.4 mm starts to affect the feel of the tube in the hand, which consumers notice even when they cannot say why.

Choosing between an extruded and a laminate tube

The decision usually comes down to three questions, in this order:

Does the artwork need photographic print? If yes, laminate. An extruded tube cannot reproduce a halftone image at retail quality, and no amount of print tuning fixes it.

Does the formula need a real oxygen barrier? If the product is a retinol serum, a probiotic or anything oxygen-sensitive, the foil in an ABL tube gives an absolute barrier that no co-extruded plastic matches. PBL with EVOH comes close and is recyclable, but it is not the same number.

What is the annual volume? Below about 50,000 pieces, laminate print cylinders cannot be amortised and the extruded tube wins on tooling. Above 500,000, laminate becomes competitive on piece price and better on graphics.

Between those two extremes both options work, and the decision is usually made on the brand's packaging brief rather than on engineering. That is worth knowing before you spend two weeks optimising a tube the marketing team will reject for the wrong shade of white.