Choosing an anti-tack agent: powder or liquid?
Why compound sticks together on the batch-off line, the difference between mineral powder and soap-based liquid, and how film thickness affects the next process.
Where sticking comes from
When the compound leaves the batch-off line it is still hot and its surface is fresh. Compounds with a high natural rubber content and a high tack value stick together even while cooling. Stack height, waiting time and ambient temperature increase this tendency.
The anti-tack agent separates this surface: it leaves a thin film on the sheet and acts as if air had entered between the two sheets. If the film is too thin, sticking continues; if it is too thick, adhesion becomes difficult in the next process and marks remain on the surface.
Three types and their character
Products on the market fall chemically into three families. The choice is made according to the color of the product and the next process.
| Type | Leaves on the surface | Strength | Weakness |
|---|---|---|---|
| Mineral powder blend | White, matt, dusty film | Cheap, strong separation, no problem on black compound | Dust escape, white marks, weakens adhesion at building |
| Soap-based liquid | Transparent, thin, dust-free film | Clean surface, suitable for light-colored products | Wipes off easily with water, slippery surface at overdose |
| Polymer or silicone emulsion | Slippery, durable film | High separation, low dust | Cost, risk of sticking in the next process |
Dilution and preparation
Powder types are dispersed in cold or warm water; liquid types are diluted at a higher ratio. The ratio is written in the product's technical data sheet and is not changed in production without verification.
Three points are critical in preparation: water hardness, mixing time and tank cleanliness. In hard water a soap-based product clumps; insufficient mixing lets the powder type settle to the bottom; if film from the previous product remains in the tank, the new mix is diluted unevenly.
Film thickness and the next process
The anti-tack decision affects not a single point of the line but the whole product. If two compounds must join at building, the film left on the surface directly reduces this adhesion. A powder type that leaves a thick film may require refreshing the surface before building.
In light-colored products with visible surfaces (shoe soles, white sidewalls, technical parts), a powder film is not acceptable; a transparent liquid type is preferred. If the film is carried into the mold in a product cured in a mold, mold fouling and surface stains begin; in this case the dose is lowered and the dilution is increased.
Selection checklist
Line name, compound color, stack height and waiting time, whether adhesion is needed in the next process, application method (dipping, spraying, roller) and the hardness of the process water. Without these six pieces of information, choosing a type is guesswork.