Improvement: ADC Foaming Agent for EVA Shoe Sole Production

One chemical. One reaction. The difference between a midsole that performs and one that fails at the shelf. Here is what every EVA formulation engineer needs to know about ADC — fast.

The numbers that matter

~220 mL/g

Gas yield of ADC — highest among common chemical blowing agents

155 – 175 °C

Effective decomposition range (activated) — aligned with EVA crosslinking window

3 – 8 phr

Typical ADC loading for midsoles targeting 0.15 – 0.25 g/cm³ density

ADC vs OBSH — which to pick?

ADC: high yield, low cost, high expansion. OBSH: lower temp, cleaner residue, better whiteness. Combine both for finest cell structure.

Why does density shift summer vs winter?

Warmer compound triggers early ADC decomposition in summer. Lower mix temp by 3–5 °C and limit compound hold time to under 4 hours before pressing.

01 · Decomposition Mechanism

ADC thermal decomposition reaction

Thermal decomposition equation (pure: ~200 °C · activated system: 155–175 °C)C₂H₄N₄O₂ → N₂ ↑ + CO ↑ + CO₂ ↑ + NH₃ ↑Gas yield ~220 mL/g · N₂ is the primary blowing gas — it drives cell nucleation and structural stability

N₂ released by ADC nucleates fine, uniform cells in the EVA melt. CO₂ and NH₃ jointly influence cell morphology. Activators (ZnO, zinc soaps) depress decomposition temperature by 20–40 °C, precisely aligning gas release with the DCP crosslinking window for optimal cell structure.

02 · Key Process Parameters

Critical control points at a glance

ADC loading3 – 8 phr

Activator ZnO ratio1 – 3 phr (approx. 1:3 vs ADC)

Effective foaming temperature (activated)155 – 175 °C

Mold press time8 – 15 min (thickness-dependent)

Mold press pressure150 – 200 kg/cm²

Target expansion ratio (midsole)1.5 – 2.5 ×

Target density0.15 – 0.25 g/cm³

03 · Production Process Flow

One-step compression molding route

Mixing

EVA + ADC + ZnO + DCP + additives; internal or open mill dispersion

80 – 100 °C

Pre-form

Cut compound to size; precise weighing for batch consistency

Ambient

Compression

ADC decomposition + DCP crosslinking occur simultaneously in the closed mold

165 – 175 °C

Demold

Rapid mold opening; EVA foam expands to target volume

Instant

Cooling

Cold press or natural cooling; stabilize cell structure and final dimensions

< 40 °C

04 · Quality Improvement

How ADC drives product performance

Finer, more uniform cells

Ultrafine ADC (D50 3–7 µm) with controlled activator loading achieves cell diameters of 100–300 µm, directly improving resilience and energy return.

Precise density control

Each +1 phr ADC reduces density ~0.02 g/cm³. Synchronize DCP adjustment to maintain mechanical strength as density decreases.

Reduced surface defects

ADC dispersion quality during mixing directly governs skin layer uniformity. Insufficient mill time causes coarse cells or surface collapse.

Lower compression set (C-set)

Balance crosslink density with foam density: under-crosslinked → high C-set; over-crosslinked → excessive hardness and poor underfoot feel.

05 · Defect Diagnosis

Common defects, root causes, and corrective actions

Defect	Root cause	Corrective action	Priority
Coarse / large cells	Poor ADC dispersion; activator excess causes premature decomposition	Extend mixing time; reduce activator loading	High
Density variation	Weighing error; uneven mold temperature distribution	Tighten to ±0.5 g tolerance; calibrate mold temperature zone by zone	High
Surface collapse	Insufficient ADC loading; premature demolding	Increase ADC loading; extend press hold time	Medium
Yellowing	BIUREA byproduct accumulation; mold temperature too high	Lower mold temp; switch to low-residue ADC grade; add optical brightener	Medium
High compression set	Insufficient DCP; low crosslink density	Increase DCP by 0.1–0.2 phr; extend press cycle duration	Low