- What this coversHow a finished label roll is specified against the machine that applies it, why the unwind numbers on a printer’s order form do not transfer between suppliers, and which figures the co-packer already holds.
- Who this is forBrand owners and operations managers sending finished label rolls to a co-packer, or running them on an in-house filling line.
- Core findingA roll can carry the right artwork on the right material and still stop the line, because unwind direction and roll size are specifications separate from the label itself.
- Bottom lineThe application equipment sets the roll specification. Ask the co-packer for theirs before briefing the printer.
The artwork is signed off. The material is chosen. Then the printer’s order form asks for a roll build: unwind direction one through eight, core size, maximum outside diameter.
Nothing you type into those fields shows up on the proof. The proof shows the flat face of the label, and the artwork sits upright on screen whichever way the roll is wound. A wrong answer stays invisible until the boxes are opened at the co-packer.
SCENARIO
The proof looked right. The colors looked right. The boxes of finished rolls shipped straight to the co-packer for the scheduled filling run.
The phone call comes the morning the line starts. The rolls will not mount on the spindle. The labels land rotated ninety degrees, or the sensor cannot find the gap between one label and the next.
The line slot goes. You pay for downtime, or you pay to ship the rolls back for rewinding, while the printer points at the signed proof showing the exact wind they delivered.
Nothing on that proof was wrong. The roll specification was never on it.
What unwind direction describes
Labels come off a roll in a fixed order. Unwind direction names two things. Which edge of the label leaves the roll first, and whether the printed face sits on the outside or the inside of the roll.
Four possible leading edges, two wind directions, eight combinations in all. That is the whole set, and every printer’s chart is a way of numbering it.
The edges are named against the label artwork as it travels, not against the room. Top means the top of the printed design rather than the top of the roll, which is the first place a conversation about this goes wrong.
The number is not a standard
Printers describe those eight with numbers. Three that publish their charts do not agree on what the numbers mean.
Take position four. Three US converters publish their unwind charts openly. Compare them and two define position four as the left edge leading off the roll, wound outside. The third defines the same number as the right edge leading off, also wound out.
Two of those three put the opposite edge at the same number. That is enough to show the number is not something a buyer can carry between suppliers. Whether every converter diverges is not established and does not need to be.
A number is a reference inside one printer’s system. Someone who reads a wind number off one quote form and repeats it to a different printer can receive a roll wound the opposite way from the one they pictured, with nothing wrong on either side of the transaction.
Specify it by picture. Have the printer mark the orientation on the proof. Send that image to the co-packer and let them check it against the machine before the run.
A worked example: a round container on a conveyor
Take one setup. A cylindrical bottle travels upright down the conveyor past a horizontal dispensing head. The web feeds sideways across the peel plate and the label wraps around the bottle wall.
In that configuration the edge leaving the roll first becomes the edge that meets the bottle first, which fixes how the artwork sits once it is down.
Which edge that needs to be depends on how the artwork was placed on the die line. The leading edge can sometimes be changed by rotating the artwork within the die layout, and the feasible orientation gets confirmed against the actual label and the applicator rather than assumed from the design. A circular or square die leaves room to rotate the design inside the cavity. A custom shape holds the design to the cut outline, so a quarter turn means a different die while the opposite edge may be reached by rewinding.
Core, diameter and what physically fits
Three roll-build figures on the order form are constrained by the machine.
Core inside diameter is the hole the spindle passes through. Three inch is the core I spent ten years handling, with 1 inch and 0.75 inch on smaller or specialty work. The measurement that counts is taken inside the core rather than across it.
Maximum roll outside diameter belongs to the machine. A tabletop unit carries a smaller limit than a line machine, and the figure sits on the equipment rather than on the label. There is no trade number to copy here. The one that governs your job is printed in the documentation for the machine it runs on.
Labels per roll follows from more than the diameter. The repeat, the thickness of the construction, the core and any weight limit all cap it, which is why the count is agreed against the machine rather than chosen by the printer.
A roll wound past the machine’s limit does not shrink to fit. It fouls the frame or sits off the arm, and what happens next depends on the day. Either the rolls go back for rewinding or somebody strips labels off the outside of every roll to get the line moving. Both cost the slot.
Why a clear label can stop the line
An applicator finds each label by detecting the gap between labels on the liner. A minimum gap in the running direction comes from the machine, and the figure differs between machines. The sensing arrangement changes it, so the number to design to is the one for that line.
A standard sensor reads that gap optically, by looking for the drop in light where a label blocks the beam. On clear film on a clear liner there is nothing to block it. The light passes through both and the head never finds an edge, so the web keeps feeding.
Two routes out of it. The printer prints a registration mark on the liner for the optical sensor to find. Or the line carries a sensor built for transparent constructions. Ultrasonic and capacitive heads are the usual alternatives and they work on different principles. Which one suits a given label and liner is a question for the equipment maker.
Which route applies belongs to the co-packer, because it depends on the sensor already fitted to their machine and on the construction being proposed. Two questions before specifying clear-on-clear film. Can the sensor on that line detect this construction, and if not, does the line need a registration mark on the liner or a different sensor.
The liner carries its own failure
The liner gets pulled around the peel plate under tension. A die cut that penetrates too far into the release liner weakens it at the point of highest stress.
Test methods exist for evaluating die strike and release force. A test result tells you about the property measured, not whether the roll will run reliably on your line. The run question belongs to the applicator.
The roll specification your co-packer already has
One row on that sheet carries four measurements that get used as though they were one. Label size is the finished width and length, while web width is the overall width of the liner it sits on. Gap is the space between one label and the next in the running direction, and a multi-lane layout carries a separate gap across the web. Pitch is the repeat, meaning the label length in the running direction plus the running gap. A brief stating only the finished label size has handed the printer one of the four.
| Field | What it controls on the line | Where the number comes from |
|---|---|---|
| Unwind direction | Which edge of the artwork meets the container first, and which way up it lands. | The applicator, settled against a marked diagram rather than a number. |
| Core inside diameter | Whether the roll mounts on the spindle at all. | The machine documentation, measured inside the core. |
| Maximum roll outside diameter | Whether the full roll clears the unwind arm and the frame. | The unwind stand on the machine, not the printer. |
| Roll weight limit | Whether the machine can carry the roll. Weight and unwind behavior both pull on the web at startup, and whether it survives that depends on the construction. | The machine, where one is stated. A roll can reach its weight limit before it reaches its diameter limit, depending on the construction and how much is wound. |
| Labels per roll | How many times the operator stops to change a roll. | The permitted diameter, the weight limit, the repeat and the thickness of the construction. |
| Gap, pitch and web width | How the feed indexes each label and how the web tracks through the head. | The machine documentation. Four separate measurements, not one. |
| Sensor type and eye-mark | Whether the head can find the leading edge of each label. | The sensor fitted to that line, and the construction being proposed. |
| Splice policy | What the operator sees before a join reaches the peel plate. | The co-packer. Permitted count, construction and how it gets flagged. |
Ask for that sheet before briefing the printer. A line running labels automatically has those answers somewhere. On a setup sheet or in the operator’s head, either one is worth more than a guess made at the printer. A brief written without it leaves the printer to pick a default, and unless they have supplied that line before, the default is chosen by somebody who has not seen it.
Before you brief a printer
- What you are solvingGetting the roll specification out of the co-packer and into the brief, alongside the container, the conditions and the volume, so the printer prices your roll build rather than a house default.
- Read nextWhat a label supplier brief should contain before you request a quote
When a roll has already stopped the line
- What you are solvingWorking out what the signed proof actually settled, and tracing a failure that has already happened back to the specification that allowed it.
- Read nextWhy labels pass proof approval and still fail in production · How to diagnose a label failure after the run
FAQ
What is label unwind direction?
It names which edge of the label leaves the roll first and whether the printed face is wound to the outside or the inside. The application equipment needs a specific one so the label lands the right way up on the container.
Is the 1 to 8 unwind numbering the same at every printer?
No. Compare three US converters' published unwind charts and two define position four as the left edge leading off the roll while the third defines it as the right edge. Confirm the orientation against a marked diagram on your proof rather than carrying a number between suppliers.
What core size does a label applicator need?
It depends on the machine. Three inch is the core I spent ten years handling, with 1 inch and 0.75 inch on smaller or specialty work. Your co-packer’s machine documentation carries the answer for your run.
Why do clear labels cause problems on a filling line?
Standard applicator sensors find the gap optically, and light passes straight through a clear label on a clear liner. Two routes out of it. The printer prints a registration mark on the liner for the optical sensor to find, or the line carries a sensor built for transparent constructions. Which one applies depends on the sensor already fitted to that machine.
Who decides the roll specification, the printer or the co-packer?
The co-packer’s equipment decides it. The printer produces to whatever the brief states, so an unstated roll specification becomes the printer’s default rather than the line’s requirement.
A NOTE ON THESE FIGURES
Roll specifications, unwind numbering and liner requirements vary by machine and by converter. Confirm every field against your own applicator documentation and your printer’s proof before releasing a run. This article does not contain affiliate links.
