Process chemicals: auxiliaries outside the formulation
Anti-tack agent, inside and outside tire paint, mold release agent and marking ink are not in the compound formulation as phr; they are applied to surfaces during production. Which group is used where, and what drives the selection?
Difference between a formulation component and a process auxiliary
Accelerator, antioxidant or sulfur goes into the compound; its ratio is written in phr and it determines the properties of the vulcanizate. Process chemicals do not go into the compound: they are applied on the compound, the mold or a surface, and after doing their job they either do not remain in the product at all or remain as a washable film.
This difference has two practical consequences. First, a process chemical is not weighed like a formulation material; its consumption depends on line speed, sheet surface and dilution ratio. Second, because it is a mixture and not a single substance, it is not defined by a single CAS number. The substance pages on this site describe compounds tied to a single CAS; process chemicals are therefore treated as use groups, not classes.
Four groups and where they are used
Four groups of process chemicals are used regularly in tire production. Each comes into play at a different point of the line and solves a different problem.
| Group | Applied to | Problem solved |
|---|---|---|
| Anti-tack (batch-off) | Surface of sized compound sheets and strips | Compound sticking to itself in the stack, on the pallet or on the conveyor |
| Inside tire paint | Inner surface of the green tire | Bladder sticking to the inner surface during curing, trapped air |
| Outside tire paint and mold release agent | Outer surface of the green tire and mold surface | Friction on entering the mold, release after curing, surface stains |
| Marking ink | Tread surface after extrusion | Line and batch identification mark before curing |
Four questions that drive the selection
When choosing a process chemical, the line and the next process are discussed, not the product code. Two products in the same group do the same job but are not interchangeable.
First question: can a mark remain on the surface? A powder film is not wanted on light-colored, white or transparent products; a liquid type that leaves a transparent film is needed. Second question: is adhesion needed in the next process? If two compounds are to join at the building stage, the anti-tack film must not be too slippery or too thick.
Third question: how fast does the mold foul? A paint with high solids clogs the mold vent holes and shortens the cleaning interval. Fourth question: what is the application method? Dipping, spraying and brushing do not need the same viscosity; the dilution decision is made according to the equipment.
Common traps of water-based systems
Most of this group is water-based. In a water-based product, the process water is part of the quality: hardness, chloride and pH change film formation. If the same product gives different results in two plants, the first thing to check is not the product but the preparation water.
The second trap is foam. In circulating tanks and spray lines, foam makes film thickness uneven; in this case, instead of adding an antifoam right away, review the dilution and the pump pressure. The third trap is shelf life: an opened drum spoils with freezing or excessive heat, and a separated product leaves a flaky film when diluted.