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
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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. |
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.
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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 |
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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 |
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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 |
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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 |
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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 |
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.
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.
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
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.
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.
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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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
建議判定公式
Recommended Evaluation Formula
至少應建立的量產規格
Minimum Production Specifications to Establish
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?
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