How to Dry TPV Particles Before Processing

2026-06-04 10:28:25

　　Proper drying of TPV (Thermoplastic Vulcanizate) particles before processing (extrusion or injection molding) is essential to prevent surface defects, foam, and hydrolysis, even though TPV is less hygroscopic than nylons or polyesters.

　　Below is a step-by-step guide based on industry best practices for automotive weather strip and seal manufacturing.

　　1. Do You Actually Need to Dry TPV?

　　General rule:

　　Most TPV grades (e.g., Santoprene, Sarlink) are not hygroscopic but can absorb surface moisture if stored improperly.

　　Drying is required if:

　　Bags show signs of water exposure or condensation.

　　Material has been stored in open containers >2 hours in humid conditions (>60% RH).

　　Processing equipment shows moisture-related issues (splay marks, bubbles, rough surface).

　　You are co-extruding with a hygroscopic material (e.g., PP carrier with TPV lip).

　　Tip: Many automotive Tier 1 suppliers dry TPV prophylactically to eliminate any risk, even though data sheets often state "normally not required."

　　2. Recommended Drying Parameters for TPV

　　ParameterValue

　　Temperature80–90°C (176–194°F)

　　Time2–4 hours (3h typical)

　　Dew point-30°C or lower (desiccant dryer)

　　Maximum moisture content before processing<0.08% (800 ppm)

　　Caution: Do not exceed 100°C for more than 1 hour, as this can cause partial softening, agglomeration, or degradation of the PP phase.

　　3. Drying Methods

　　A. Hopper Dryer (Desiccant) – Recommended

　　Best for continuous production.

　　Use a closed-loop desiccant dryer with dew point monitoring.

　　Set hot air flow to ensure uniform temperature across the hopper.

　　B. Tray Oven (Batch Drying)

　　Spread particles in a thin layer (≤25 mm / 1 inch deep).

　　Do not overfill trays – moisture cannot escape from deep beds.

　　Stir every 30 minutes if possible.

　　C. Vacuum Dryer – Optional

　　Lower temperature (70–80°C) and shorter time (1–2h).

　　Useful for heat-sensitive or regrind TPV.

　　More expensive, usually not necessary for standard TPV.

　　4. Step-by-Step Drying Procedure

　　Step 1 – Check moisture before drying

　　Use a moisture analyzer (loss-on-drying) or a capacitance meter if available. Target:<0.08% (800 ppm).

　　Step 2 – Pre-heat the dryer

　　Bring your hopper or oven to 80–85°C before adding TPV.

　　Step 3 – Load TPV particles

　　Do not mix with regrind that has unknown moisture history.

　　Step 4 – Dry for 3 hours at 85°C

　　Adjust time based on moisture load:

　　1–2 hours for dry bags stored in climate-controlled room.

　　3–4 hours for material from open bins or humid environment.

　　Step 5 – Verify moisture after drying

　　Quick check: Perform a “purge test” – extrude a small amount through a screen pack (40–60 mesh). No splay, bubbles, or steam means dry enough.

　　Step 6 – Keep dry

　　Feed directly from dryer to extruder/hopper. Minimize exposure to ambient air for >15 minutes.

　　5. What Happens If You Don’t Dry TPV?

　　DefectCauseAppearance

　　Surface splay / silver streaksFlash steam from water vaporizing at the dieStreaks along flow direction

　　Internal bubbles / voidsTrapped moisture expanding under heatVisible bubbles in cross-section

　　Poor adhesion (co-extruded seals)Moisture interfering with bonding between TPV and rigid PPDelamination at interface

　　Rough surface textureMicro-voids collapse unevenlyOrange peel or matte spots

　　Extrudate swelling variationSteam expansion altering melt rheologyInconsistent profile dimensions

　　In automotive weather seals, bubbles or voids are a direct scrap cause – no cosmetic fix possible.

　　6. Special Cases

　　Regrind / Recycled TPV

　　More surface area → absorbs moisture faster.

　　Dry at 70–75°C for 2–3 hours (lower temp to prevent degradation).

　　Maximum regrind ratio typically 20–30% for exterior seals.

　　TPV with Adhesive or Overmolding

　　If TPV is overmolded onto a substrate (e.g., metal or rigid plastic), moisture must be<0.05% to prevent bubble formation at the interface.

　　Flame-retardant TPV grades

　　May have lower thermal stability. Check supplier datasheet – drying temperatures often reduced to 70°C max.

　　7. Common Mistakes to Avoid

　　MistakeConsequence

　　Drying >100°CParticles stick together, block hopper.

　　Drying<70°CIneffective – moisture not removed.

　　Exceeding 4 hours at high tempColor shift, loss of elongation.

　　Drying in uninsulated hopperCondensation forms when cold material enters.

　　Opening dryer door during cycleMoist air re-enters, resets process.

　　8. Quick Checklist for Production

　　Hopper dryer set to 80–85°C

　　Dew point ≤ -30°C (desiccant active)

　　Residence time ≥ 2 hours for fresh pellets

　　Moisture verified <0.08%(or purge test clean)

　　Extruder temperature profile starts ≥180°C melt zone

　　Screen pack 40–60 mesh to catch any degraded gels

　　Final Recommendation for Automotive Weather Seal Lines

　　Dry TPV for 3 hours at 85°C in a desiccant dryer, regardless of supplier claims. This eliminates moisture as a variable, reduces scrap by 2–5%, and ensures bubble-free, dimensionally stable extrusions – especially critical for Class A visible seals like flush glass runs or decorative weather strips.