In-Mold Labeling (IML) — How Do You Integrate Labels, Films and Decorations Directly Into the Injection Molding Cycle, and What Are the Design and Process Requirements?
Last updated: 2026-09-03 · Reading time: about 6 min
In-mold labeling (IML) and in-mold decoration (IMD) place a pre-printed film or label into the cavity before injection, so the melt bonds it into the part surface. That eliminates a secondary labeling step, saves $0.02–0.08 a part, and yields a graphic that cannot peel, fade or be removed.
See also related article.
Key facts
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Warpage — Part deformation after ejection caused by uneven shrinkage. Amorphous resins warp less (0.4–0.7% shrinkage). Semi-crystalline resins warp more (1.0–2.5% shrinkage). Fix: uniform wall thickness, balanced cooling, optimized gate location, adequate packing pressure. See also related guide.
What are the IML types — and how do they differ?
Four variants cover the range from a recyclable food tub to a hard-coated keypad overlay.
| Type | How it works | Label material | Typical use |
|---|---|---|---|
| Film IML (thin-film) | Pre-printed film placed in the mold; melt flows over and bonds it | PP or PE film (same resin as the part) | Food containers, tubs, lids |
| Paper/card IML | Pre-printed paper or board placed in the mold; melt flows behind it | Coated paper, cardboard | Packaging, cosmetic containers |
| IMD (film insert) | Hard-coated film placed in the mold; melt flows behind it | PC or PET film (100–200 μm) | Keypads, control panels, auto interiors |
| Roll-fed IML | Labels fed from a roll, cut and placed by a robot | PP or PE film | High-volume food packaging (10M+/year) |
Film IML is the standard for food containers because the label is the same resin as the part — PP on PP — so the whole thing recycles together with no separation. At 20–50 μm it is thin enough to conform and thick enough to handle, and the ink sits on the back of the film, protected from food and environment.
IMD is the decorative cousin: a thicker PC or PET film with a scratch-resistant hard-coat, resin injected behind it. It is what forms a keypad (keys printed on the film, resin forming the body), a control panel, or wood-grain and carbon-fiber automotive trim.
What are the design and process requirements?
Four requirements, in the order they cause failures. Get the first one wrong and nothing else matters.
- Match the label resin to the part. A PP label goes on a PP part, a PE label on PE. A mismatched film — PVC on PP — will not bond and peels or delaminates. A PP film melts at 160–170 °C; when 220–260 °C melt flows over it, the film surface softens just enough to fuse, giving a 2–4 N/mm bond you cannot peel without tearing.
- Automate placement and hold it by vacuum. A pick-and-place robot with a vacuum gripper sets the label to ±0.2 mm in 0.5–1.0 s before the mold closes. Vacuum holes (0.5–1.0 mm diameter, 0.4–0.6 bar) hold it flat; without them, injection pressure shifts the label 1–5 mm and the graphic misaligns.
- Keep the gate off the label. A gate on the label lets a high-velocity melt jet hit and shift or tear it. Put the gate at the label edge or opposite side, and prefer a fan or film gate that spreads the melt into a wide, thin front at 50–100 mm/s. Profile the speed: slow for the first 60–80% of fill, faster for the last 20–40%.
- Control mold temperature (40–80 °C). Too cold (below 30 °C) and the resin freezes before it flows into the film texture, so the bond is weak; too hot (above 100 °C) and the film softens, wrinkles or shrinks. PP IML runs 40–60 °C, PC/PET IMD 60–80 °C; keep cooling channels 15–25 mm behind the surface for a uniform label area.
Resin match is the rule that makes IML work. The label fuses because it is the same polymer as the part — PP to PP, PE to PE. A mismatched film will not bond no matter how you tune the process, and it peels or delaminates in service. Matching resin is also what lets the finished part recycle as one material, with no label to separate.
“IML looks simple — drop a label in the mold — but the failures come from the same three places: a film that does not match the resin, a gate that jets onto the label, and a vacuum that does not hold it flat. In the DFM we settle the film, the gate and the vacuum scheme before we cut, so the graphic lands in register on shot one and stays bonded for the life of the part.”
— Project Engineer, aCatMould
Frequently asked questions
What are the common IML defects — and how do you fix them?
Wrinkling, where the melt folds the film as it flows over: slow the injection speed, raise the mold temperature so the film softens and flattens, or use a thicker, stiffer film.
Shifting, where the label moves 1–5 mm and the graphic misaligns: raise the vacuum holding force, slow the fill, or add 0.5 mm locating pins that fit registration holes in the label.
Air traps behind the label — a bubble or silver streak where air is caught between film and melt: add vent holes or a vented insert behind the label area, or raise the melt temperature so the resin pushes the air out before it freezes. Poor adhesion, where the label peels: confirm resin match, raise melt temperature, or add a tie layer.
How does IML compare to pad printing and adhesive labels?
Pad printing lays 5–15 μm of ink straight on the part at $0.01–0.03, which suits short runs — but the ink wears off (1,000–10,000 abrasion cycles) and each pad covers only about 100 × 100 mm. Adhesive labels stick on after molding at $0.02–0.05 — but the adhesive degrades in heat and humidity and the label must be separated before recycling.
IML protects the ink under the film, wraps the whole part, and recycles with it. It earns the investment above about 500,000 parts a year (the IML mold runs $5,000–15,000 more and the robot $20,000–50,000, recovered in 1–2 years), for full-wrap decoration pad printing cannot do, or where the graphic must survive food contact, outdoor exposure or chemical cleaning.
What mold modifications does IML need — and can an existing mold convert?
Yes, but a conversion takes four changes: drill vacuum holes (0.5–1.0 mm) into the cavity at the label and plumb them to a 0.4–0.6 bar pump ($500–1,500); relocate a gate that sits on the label to the edge or opposite side ($1,000–3,000); adjust cooling behind the label so temperature is uniform ($500–2,000); and machine locating pins or shoulders for ±0.2 mm placement ($300–800).
Total conversion runs $2,500–7,500 for a single-cavity mold. A new IML mold costs $5,000–15,000 more than a standard one, but arrives with the vacuum system, the optimized gate and IML-specific cooling designed in from the start.
Key takeaways
- IML and IMD fuse a pre-printed film into the part surface during molding — no secondary labeling, a graphic that cannot peel or fade, and, with matched resin, a part that recycles as one material.
- Choose the type by job — film IML for food tubs, IMD film-insert for keypads and panels, roll-fed for high volume — and always match the label resin to the part resin.
- Design for robot-plus-vacuum placement (±0.2 mm), a gate that never jets onto the label, and 40–80 °C mold temperature; it pays above about 500,000 parts a year or for full-wrap, peel-proof decoration.
IML turns a separate decorating operation into part of the molding cycle — one shot, one part, one graphic bonded in rather than stuck on. The four rules (matched resin, vacuum placement, gate position, mold temperature) separate a label that fuses on shot one from one that wrinkles, shifts or peels. If you are weighing IML against pad printing or adhesive labels, a DFM review checks the film, the gate and the vacuum scheme before the mold is built.
Sources
Plastics Technology — in-mold labeling and decoration process practice
MoldMaking Technology — IML mold design, vacuum and gating
Plastics Industry Association — in-mold decoration industry resources
Society of Plastics Engineers — IML process engineering
MatWeb — PP, PE, PC and PET film material properties
Sources: Plastics Technology · Plastics Technology Online · Society of Plastics Engineers (SPE) · ThomasNet