In mold labeling
- No separate decorating step once the cell is running
- Photo quality artwork over most of the surface
- Needs label handling automation and a mold built for it
- An artwork change means a new label run, not new steel
Process guide
In Mold Labeling
Pick up a margarine tub or a paint pail and try to peel the label. Usually you cannot, because it is not stuck on. It was placed in the mold before the plastic arrived, and the two came out as one wall.
What it is
The label goes in before the plastic
Decoration and molding happen in the same cycle, so there is no labeling line after the press.
An IML label is a thin printed film, usually cut to shape in advance. A robot takes one from a magazine, carries it into the open mold, and holds it against the cavity wall with vacuum or a static charge. The mold closes, hot resin flows in behind the label, and the back of the label melts into the surface of the part. The print sits on the outside, protected by the film it was printed on.
Almost all of it happens in packaging: thin wall tubs, lids, pails, and cups made in large volumes on fast presses. The label can cover most of the outside, stands up to fridges and dishwashers, and does not lift at the edges. Because the label material is normally chosen to match the container, a PP label on a PP tub, the finished pack can go into recycling as one material.
The label's path
From printed sheet to finished wall
Most IML trouble starts before the mold closes.
- 1
Print and die cut
Labels are printed in sheets or on rolls and cut to the flat shape of the surface they will cover. A wrap label for a tapered tub is cut as a curved band, not a rectangle.
- 2
Stack and separate
Cut labels sit in a magazine. Picking one at a time, never two stuck together, is a real design problem for the automation.
- 3
Place and hold
The robot places the label on a mandrel or straight into the cavity. Vacuum ports or an electrostatic charge hold it in place while the mold closes.
- 4
Mold and fuse
Resin fills behind the label and fuses to its back. The part leaves the mold decorated and goes straight to stacking.
Label shapes
Where a label can go, and what each placement asks for
A label is a flat sheet. It can wrap a cone or a cylinder, but it cannot stretch over a dome.
| Placement | Typical part | What to watch |
|---|---|---|
| Lid top | Flat or gently curved lids | The simplest case. Keep the label clear of the snap bead and the gate |
| Side band | Round or oval tubs and cups | Ends meet or overlap at a seam; the taper of the wall sets the curve of the cut label |
| Four side wrap | Square and rectangular containers | Corners need a generous radius or the label creases where it folds |
| Bottom and side | Containers that need a barrier or full coverage | Several labels or a folded blank; placement tolerance tightens at every joint |
Alternatives
IML or printing after molding
IML does not suit every decorated container. The volume and the artwork usually make the call.
Printing or labeling after molding
- Works on parts from an ordinary mold
- Pad printing and silk screening suit small logos and short runs
- Hot stamping adds metallic marks that labels struggle to match
- Adds handling and a second step after the press
Design checks
Before you design a container around IML
These come up in almost every IML review.
Every labeled surface can be unrolled flat: cylinders and cones yes, spheres and domes no
The label material matches the container resin, or you know why it does not
The gate faces the label's back or sits outside the label area, so hot resin does not wash out the print
Artwork leaves room for placement tolerance at seams and edges
Volume is high enough to justify automation and label stock
Keep reading
Related guides
Other ways to decorate a molded part, and the parts IML is usually used on.
In mold decorating
Foil transfer and formed films for durable parts.
In mold decoratingPad printing
Ink transferred onto a molded part by a silicone pad.
Pad printingHot stamping
Heat and pressure for foil marks and metallic trim.
Hot stampingPackaging
Closures, tubs, and thin wall containers.
PackagingLids
Snap beads, hinges, and flat decorated tops.
LidsContainers
Walls, stacking, and draft on molded containers.
ContainersGate location
Where resin enters, and what it does on the way.
Gate locationSecondary operations
Printing, marking, and assembly after molding.
Secondary operationsProcesses hub
Every molding process and secondary operation.
Processes hubFAQ
Questions about in mold labeling
Is an IML label the same as a sticker?
No. A sticker has an adhesive layer and sits on the surface. An IML label has no adhesive; its back melts into the part during molding, so there is no edge to lift.
Can IML go on a curved lid?
On a gentle single curve, yes. A surface that curves in two directions at once, like a dome, would need the label to stretch, and a flat film will wrinkle instead.
Does IML make a container harder to recycle?
Not when the label and the container are the same resin family. That is one of the reasons PP labels on PP packs are so common.
Why does the gate position matter?
Resin comes out of the gate hottest and fastest. Aimed straight at the printed face, it can smear the ink or push the label out of place. The usual fixes are gating through the base or from the unlabeled side.
Next step
Send the part and the artwork area
Upload CAD and mark the decorated faces. The review looks at decorating after molding, with pad printing, silk screening, or hot stamping. NetProto manufacturing is ISO 9001 certified.