SankalpYes, a compression liner seals to a cold-end treated bottle with or without hot-end treatment, provided the rim is flat, smooth and not heavily coated. A compression liner, such as the TPE liner in an aluminium roll-on closure, seals by being squeezed onto the rim, not by sticking to it. What coating changes is friction and adhesion: lubricant on the finish lowers opening torque, and it weakens seals that depend on a bond, such as an induction foil or a pressure-sensitive liner. Hot-end treatment is a thin metal oxide laid on hot glass; cold-end treatment is a lubricating layer applied after annealing, and it holds on best over the oxide.
The two treatments
Glass bottles are treated twice on the way through the plant. CETIE’s data sheet DT13.00 describes surface treatment as what preserves glass strength and improves handling through manufacture and filling: a hot-end metallic oxide deposit, then a cold-end lubrication layer.
| Hot-end treatment | Cold-end treatment | |
|---|---|---|
| Where on the line | Between the forming machine and the annealing lehr, on glass still at several hundred degrees | At the exit of the lehr, on cooled glass |
| What it is | A very thin tin or titanium oxide layer, formed from a vapour | A lubricating film, such as a polyethylene wax emulsion, oleic acid vapour or a stearate |
| What it is for | Protects the surface and anchors the cold-end layer | Lets bottles slide past each other on conveyors instead of scratching |
| Where it should be | Body and shoulder. Glassmakers aim to keep it off the finish | The outside of the bottle; some reaches the finish unless controlled |
| Survives washing? | More durable than the cold-end layer | Depends on type. Stearates are water soluble; a hot caustic wash on returnable glass can strip much of it |
The two work as a pair. A cold-end layer without the oxide underneath bonds less durably to bare glass, so it wears unevenly and transfers more readily, which is the situation behind the question this page answers.
What each does to the sealing surface
The rim is where the liner meets the glass, and Indian roll-on finishes already carry a requirement for it: IS 7511 (Part 4) asks for the sealing surface to stay flat and as regular and smooth as possible.
Hot-end oxide on the finish is a glass fault, not a design choice. Coating on the neck and thread can interfere with closure application, and a heavy iridescent band on the rim is worth raising with the glass supplier before blaming the cap.
Cold-end lubricant on the finish is more common and harder to see. It lowers friction between liner and rim and in the thread, so opening torque reads lower, and in larger amounts some closures back off in storage. For a bonded seal it is worse, because the wax film is what the adhesive meets instead of glass.
Compression seals and bonded seals
Whether the coating matters depends on how the closure seals.
| Seal type | How it seals | Sensitivity to lubricant on the rim | Sensitivity to missing hot-end oxide |
|---|---|---|---|
| Compression liner in an aluminium roll-on closure (TPE or PVC compound) | Liner squeezed onto the rim by the capping head | Low for the seal; opening torque reads lower | Low |
| Foam or pulp wad in a screw cap | Wad squeezed by the screwed-down cap | Low for the seal; higher back-off risk, as thread friction holds the cap | Low |
| Induction heat-seal foil | Heat-activated layer bonds foil to the rim | High | Moderate, as an unanchored cold-end layer transfers more readily |
| Pressure-sensitive liner | Adhesive bonds to the rim under closing force | High | Moderate |
So “can you seal a liner to a cold end treated bottle without hot end treatment” depends on the liner. A compression liner will seal. A bonded liner may not, and a trial on that glass is the only reliable answer. Liner materials are compared in EPE, PE, PVC and pulp liners compared, and the component itself in what a cap liner is.
For an aluminium roll-on closure on treated glass, a moulded compound liner is the practical choice. If a brand also wants a bonded inner seal for tamper evidence, specify a heat-seal layer made for glass, ask the glassmaker in writing how cold-end coating is kept off the finish, and trial both together. The finish geometry is set out in glass bottle neck finishes for ROPP closures and the Indian standards behind it in neck finish standards on Indian glass bottles.
What it means for torque
A roll-on cap has no application torque in the screw-cap sense. The head presses the shell down and rollers form the thread against the glass, so the settings are head load and roller pressure, as the ROPP capping process describes. Coating shows up in what you measure afterwards: opening torque on a lubricated finish reads lower for the same settings.
So set the removal torque window on the glass you will actually run, and re-establish it when the glass supplier, mould set or coating changes. Cap torque specifications covers how the window is set.
When a seal fails because of the coating, and how to tell
Coating faults follow the glass lot, not the capping head.
| What you see | Points to the coating when | Check |
|---|---|---|
| Opening torque low on every head | It starts with one glass lot and stops when the lot changes | Run the same caps and settings on a lot from another production date |
| Induction foil lifts clean off the rim | The foil leaves no heat-seal residue on the glass | Ask the glassmaker for the cold-end coating type and how the finish is protected |
| Caps loosen in storage | Packs were warm-cycled on heavily lubricated glass | Measure removal torque at capping and again after storage |
| Leaks cluster on particular capping heads | Never; that pattern is the machine | Trace packs by head before raising the glass question |
When the pattern follows the head, why water bottle caps leak walks through the capper. Testing a ROPP closure sets out the torque, leak and secure-seal tests that separate the two, and cap dimension tolerances and QC sampling the plan for incoming lots.
R Vision’s Bev Cap and Aqua Cap are 28/15 mm aluminium ROPP closures that seal with a TPE compression liner, rated to 8 bar, for hot fill, cold fill and carbonated products on standard roll-on machinery. To trial them on your glass, send the finish drawing and the glassmaker’s coating details through contact us.
Frequently asked questions
Can you seal a liner to a cold-end treated bottle without hot-end treatment?
A compression liner, such as the liner in an aluminium roll-on cap or a foam wad in a screw cap, will seal, because it works by being squeezed onto the rim; expect lower opening torque. A bonded seal, such as an induction foil or pressure-sensitive liner, may not bond well to a lubricated rim, and without the oxide layer the coating transfers more easily. Trial the exact liner on that glass.
What is hot-end coating on glass bottles?
A very thin layer of tin or titanium oxide deposited from a vapour onto bottles just after forming, while the glass is still hot and before the annealing lehr. It protects the surface and anchors the cold-end coating applied later. Glassmakers try to keep it off the finish, because coating on the neck can interfere with closure application.
What is cold-end coating?
A lubricating film applied to bottles as they leave the annealing lehr, commonly a polyethylene wax emulsion, oleic acid vapour or a stearate. It lets bottles slide past each other on conveyors without scratching, which preserves strength. It bonds best over a hot-end oxide layer, and some types wash off in water or a caustic bottle wash.
Does cold-end coating affect cap torque?
Yes. Lubricant on the finish lowers friction between the liner and the rim and in the thread, so opening torque reads lower for the same capping settings, and heavy amounts can let some closures back off in storage. Set the removal torque window on the glass you will run, and re-check it when the glass or coating changes.
Sources
- CETIE general data sheets: DT13.00, glass containers surface treatment, and DT31.00, main types of sealing on glass containers.
- BIS, IS 7511 (Part 4): 1986, roll-on threads pilferproof finishes, for the sealing surface clause.