The Battle for the Perfect Surface: Why PVI is an Extrusion Engineer’s Best Friend

If you run a rubber extrusion line—whether it’s EPDM automotive seals, high-pressure hydraulic hoses, or intricate NBR profiles—you know the daily battle: Speed vs. Smoothness.

Your boss wants you to crank up the line speed (meters per minute). But as soon as you increase the screw speed, the shear heat spikes. The head pressure rises. Suddenly, your perfectly smooth profile starts to look… rough. You get “shark skin,” scorched edges, or dimensional instability.

So, you slow down. Efficiency drops. It’s frustrating.

But there is a way to break this cycle. It involves rethinking how you use Anti-scorching Agent PVI.

The Enemy is “Micro-Scorch”

We often think of scorching as a binary event: either the rubber is burnt (hard chunks) or it’s fine.

But in extrusion, there is a gray area: Micro-Scorch (Incipient Scorch). When heat builds up in the extruder head/die, the rubber starts to crosslink microscopically just before it leaves the die. This doesn’t create hard chunks, but it destroys the flow. It causes:

Rough surface finish.
Die swell unpredictability.
Poor adhesion to reinforcement layers (in hoses/belts).

PVI: Your “Flow Enhancer” in Disguise

By adding or optimizing PVI (CTP) in your formula, you aren’t just preventing burns; you are modifying the rheology of your process.

Here is what happens when you introduce a high-purity PVI into your EPDM or NBR mix:

Lower Viscosity at High Speed: PVI allows you to run the extruder head hotter without triggering the cure. Warmer rubber flows better.
Self-Healing Flow: Because the crosslinking is firmly delayed, the rubber chains can relax and flow smoothly through the complex die shapes, filling every corner before the heat sets them.
The “Safety Net” for Recycled Material: If you re-feed rework/scrap material (which already has heat history) back into the extruder, PVI is mandatory to neutralize the residual acidity and prevent immediate burning.

A Real-World Example: The EPDM Weatherstrip

We worked with a client producing automotive weatherstrips. They were stuck at a line speed of 12 meters/minute. Any faster, and the thin edges of the profile would become jagged due to heat build-up at the die lip.

The Fix: They didn’t change the extruder. They added 0.15 phr of our Oil-Treated PVI.

The Result:

They increased the die temperature by 5°C.
Viscosity dropped, flow improved.
They ramped speed up to 16 meters/minute (a 33% gain).
The surface came out glass-smooth.

Why “Oil-Treated” is Critical for Extrusion

In extrusion, specks are fatal. A single undissolved particle of PVI looks like a white pimple on a black sealing strip. It’s an instant scrap part.

For extrusion applications, we explicitly recommend our Oil-Treated Powder or Micro-Granule grades.

Zero Dust: Keeps the sensor eyes and laser gauges on your line clean.
Rapid Wetting: The oil coating ensures the PVI melts into the rubber phase instantly, even in short L/D extruders, guaranteeing no “white specks” on the finished product.

Smooth Operations Start Here

Don’t let heat limit your line speed. You might be surprised at how much faster your existing extruders can run with just a minor chemical adjustment.

We have prepared a “Smooth Finish” Sample Pack specifically for extrusion companies. It includes our highest-dispersion grade PVI.