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Why Does EVA Foam Shrink?

Sep 07,2026 | Published in：Advanced Foaming Solutions for OEM Manufacturing

EVA 發泡為什麼會收縮？

Why Does EVA Foam Shrink?

PART 3

從 POE 熔點、DCP 交聯密度到冷卻定型的完整分析

A Complete Analysis: From POE Melting Point and DCP Crosslink Density to Cooling and Stabilization

並解析 IUS‑4065 如何改善超軟配方的二次收縮與尺寸穩定

Including How IUS-4065 Improves Secondary Shrinkage and Dimensional Stability in Ultra-Soft Formulations

核心觀點｜EVA 發泡收縮不是「發泡劑太少」這麼簡單，而是泡孔內壓下降、氣體擴散、鏈段回復、晶體重整、交聯固定能力與冷卻梯度共同疊加。IUS‑4065 的價值，在於以約 Shore A 40 的柔軟度搭配約 64°C 的較高熔點，降低超軟 POE 配方在二次受熱時失去晶區支撐的風險。

Core insight | EVA foam shrinkage is not simply a matter of "too little blowing agent." It results from the combined effects of falling cell pressure, gas diffusion, molecular-chain recovery, crystal reorganization, the fixation capacity of the crosslinked network, and cooling gradients. The value of IUS-4065 lies in pairing a softness of approximately Shore A 40 with a relatively high melting point of about 64°C, reducing the risk that ultra-soft POE formulations lose crystalline support during secondary heating.

五、交聯與產氣必須同步：真正重要的是反應窗口

V. Crosslinking and Gas Generation Must Be Synchronized: What Matters Is the Reaction Window

理想狀態不是先完全交聯再發泡，也不是先大量產氣才成網，而是在發泡劑快速產氣之前建立最低必要熔體強度，並在泡孔成長階段持續增強網路。DCP、ADC／其他發泡劑、活化劑與實際料溫共同決定這個時間差。

The ideal state is neither complete crosslinking before foaming nor extensive gas generation before network formation. Instead, the minimum necessary melt strength should be established before the blowing agent begins rapid gas generation, and the network should continue strengthening as the cells grow. DCP, ADC/other blowing agents, activators, and the actual compound temperature jointly determine this timing difference.

失配情況

Mismatch

泡孔結果

Cell-Structure Outcome

可能收縮表現

Likely Shrinkage Behavior

優先檢查

First Items to Check

產氣早於成網

Gas generation precedes network formation

泡孔過大、併孔或破孔

Oversized cells, cell coalescence, or rupture

開模後快速回縮

Rapid shrink-back after demolding

料溫、活化劑、DCP 半衰期、混煉熱史

Compound temperature, activator, DCP half-life, and mixing thermal history

成網過早

Network forms too early

泡孔成長受限、倍率不足

Restricted cell growth and insufficient expansion

密度高、內應力大

High density and high internal stress

DCP 用量、模溫、模壓時間

DCP dosage, mold temperature, and molding time

成網不均

Nonuniform network formation

中心與表皮泡孔差異

Different cell structures at the core and skin

局部凹陷、翹曲

Localized depressions and warpage

分散、批次混煉、厚度與升溫均勻性

Dispersion, batch mixing, thickness uniformity, and heating uniformity

後硫化不足

Insufficient post-cure

初期正常、停放後漂移

Initially normal, then drifts during storage

24–72 h 後收縮

Shrinkage after 24-72 h

中心溫度、保壓時間、凝膠率

Core temperature, pressure-hold time, and gel content

研發上應先固定的三件事

Three Factors to Fix First in R&D

固定成品密度，而不是只固定配方重量；密度不同會直接改變硬度與收縮。

Hold finished-product density constant, not merely formulation weight; changes in density directly alter hardness and shrinkage.

記錄實際膠料與模芯溫度，而不是只記錄機台設定值。

Record the actual compound and mold-core temperatures, not just the machine setpoints.

以相同停放條件量測 0 h、24 h、72 h 及二次加熱後尺寸。

Measure dimensions at 0 h, 24 h, 72 h, and after secondary heating under identical conditioning conditions.

六、冷卻定型：為什麼表面冷了，成品仍會繼續縮？

VI. Cooling and Stabilization: Why Does the Product Keep Shrinking After the Surface Feels Cool?

圖 4｜厚件的中心熱量、氣體擴散及結晶定型均落後於表面。

Figure 4 | In thick parts, core heat dissipation, gas diffusion, and crystallization-based stabilization all lag behind the surface.

泡棉導熱係數低，厚件中心降溫慢。對相似幾何，可用 t ∝ L²/α 作工程近似：特徵厚度 L 增加一倍，達到相似中心溫度所需時間可能接近四倍。提早堆疊、裝袋或進入貼合，會使中心熱量無法逸散，也讓晶體在受拘束狀態下重整，造成批次間尺寸差。

Foam has low thermal conductivity, so the core of a thick part cools slowly. For similar geometries, t ∝ L²/α can be used as an engineering approximation: doubling characteristic thickness L may require nearly four times as long to reach a similar core temperature. Premature stacking, bagging, or lamination prevents core heat from dissipating and allows crystals to reorganize under constraint, causing batch-to-batch dimensional variation.

九、建議 DOE：把收縮問題量化，而不是憑手感調料

IX. Recommended DOE: Quantify Shrinkage Instead of Adjusting the Formulation by Feel

因子

Factor

建議水準

Recommended Levels

主要觀察值

Primary Responses

POE／IUS‑4065 比例

POE/IUS-4065 ratio

低／中／高；或等硬度替代

Low/medium/high; or equal-hardness replacement

硬度、回彈、DSC、尺寸

Hardness, resilience, DSC, and dimensions

DCP 有效量

Effective DCP dosage

低／中／高

Low/medium/high

t10、t90、凝膠率、倍率、撕裂

t10, t90, gel content, expansion ratio, and tear strength

模壓條件

Compression-molding conditions

溫度 × 時間

Temperature × time

中心溫度、泡孔、開模回縮

Core temperature, cell structure, and demolding shrink-back

冷卻方式

Cooling method

治具／風冷／水冷；不同停放時間

Fixture/air cooling/water cooling; different conditioning times

0 h、24 h、72 h 長寬厚

Length, width, and thickness at 0 h, 24 h, and 72 h

二次加熱

Secondary heating

50／60／70°C × 30／60 min

熱收縮、翹曲、硬度漂移

Thermal shrinkage, warpage, and hardness drift

建議判定公式

Recommended Evaluation Formula

線性收縮率｜S_L (%) = (L₀ − L_t) / L₀ × 100%。長、寬、厚度要分別量測；若要比較體積穩定，另計 V₀ 與 V_t。量測前應規定調節溫濕度、停放時間與取點方式。

Linear shrinkage | S_L (%) = (L₀ - L_t) / L₀ × 100%. Measure length, width, and thickness separately; to compare volumetric stability, calculate V₀ and V_t as well. Specify the conditioning temperature and humidity, conditioning time, and measurement locations before testing.

至少應建立的量產規格

Minimum Production Specifications to Establish

1. 開模後 30 分鐘、24 小時與 72 小時的長／寬／厚尺寸。

Length, width, and thickness at 30 minutes, 24 hours, and 72 hours after demolding.

2. 貼合或熱處理後的尺寸收縮率及平整度。

Dimensional shrinkage and flatness after lamination or heat treatment.

3. 同模不同穴、中心與邊緣的密度及泡孔差異。

Differences in density and cell structure among cavities in the same mold and between the center and edges.

4. 成品密度、硬度、回彈、壓縮永久變形、撕裂與延伸。

Finished-product density, hardness, resilience, compression set, tear strength, and elongation.

5. 連續三批的平均值、標準差與製程能力，而不只看單次最佳樣。

Mean, standard deviation, and process capability across three consecutive batches, rather than only the best individual sample.

十、現場快速診斷：看到哪種症狀，先查什麼？

X. Rapid On-Site Diagnosis: What Should Be Checked First for Each Symptom?

症狀

Symptom

高機率原因

Most Likely Cause

第一優先動作

First-Priority Action

出模立刻縮

Shrinks immediately after demolding

交聯不足或產氣太早

Insufficient crosslinking or gas generation occurs too early

查 MDR／料溫；做 DCP 三階與發泡時序

Check MDR/compound temperature; test three DCP levels and foaming timing

隔日才縮

Shrinks the next day

氣體擴散、後結晶、中心未冷

Gas diffusion, post-crystallization, or an inadequately cooled core

統一 72 h 調節；量中心溫度與堆疊方式

Standardize 72 h conditioning; measure core temperature and review stacking practices

貼合後縮

Shrinks after lamination

POE 熔融區間太低、熱歷史過高

POE melting range is too low or thermal history is excessive

做 DSC＋實際貼合溫度曲線；導入 IUS‑4065 對照

Run DSC plus an actual lamination-temperature profile; compare against IUS-4065

局部翹曲

Localized warpage

模溫／厚度／冷卻不均

Nonuniform mold temperature, thickness, or cooling

查模穴熱分布、治具與冷卻接觸

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