為什麼 POE 越軟，EVA 發泡成品反而越容易收縮？

Why Does Softer POE Make EVA Foam Products More Prone to Shrinkage?

PART 1

IUS-4065 如何兼顧低硬度、回彈與二次加工尺寸穩定性

How Does IUS-4065 Balance Low Hardness, Resilience, and Dimensional Stability During Secondary Processing?

一、低硬度配方真正困難的，不只是把硬度降下來

I. The Real Challenge of Low-Hardness Formulations Is Not Simply Reducing Hardness

在 EVA 化學交聯發泡配方中，POE 經常被用來調整柔軟度、彈性感與低溫韌性。研發人員直覺上會選擇更軟的 POE，以較少添加量達到目標硬度；但原料硬度只是第一個條件。若材料在後續製程溫度下失去足夠的結晶支撐，即使剛脫模時尺寸正常，也可能在貼合、熱壓、烘箱或長時間高溫存放後發生二次收縮。

In EVA chemically crosslinked foam formulations, POE is often used to adjust softness, elasticity, and low-temperature toughness. R&D personnel may intuitively choose a softer POE to achieve the target hardness with a lower addition level; however, raw-material hardness is only the first consideration. If the material loses sufficient crystalline support at subsequent processing temperatures, secondary shrinkage may occur during lamination, hot pressing, oven treatment, or prolonged high-temperature storage even when the dimensions are normal immediately after demolding.

關鍵判斷｜「低硬度」不等於「低熔點」一定會發生，但許多超軟聚烯烴彈性體確實同時具有較低結晶度及較低熔融區間。選材時必須把硬度、DSC 熔融行為、交聯密度與最終二次加工溫度一起評估。 Key judgment | “Low hardness” does not necessarily mean “low melting point,” but many ultra-soft polyolefin elastomers do have both lower crystallinity and a lower melting range. Material selection must evaluate hardness, DSC melting behavior, crosslink density, and the final secondary-processing temperature together.

二、為什麼低熔點 POE 容易放大二次收縮？

II. Why Does Low-Melting-Point POE Tend to Amplify Secondary Shrinkage?

發泡成品不是完全靜止的結構。材料內部同時存在泡孔壓力、分子取向、交聯網絡、結晶區與冷卻造成的殘留應力。當二次加工溫度接近或超過 POE 的主要熔融區間時，原本提供物理支撐的晶區會逐步減弱，分子鏈開始鬆弛，泡孔壁也更容易重新排列。

A foamed product is not a completely static structure. Cell pressure, molecular orientation, the crosslinked network, crystalline regions, and residual stresses generated during cooling coexist within the material. When the secondary-processing temperature approaches or exceeds the POE's main melting range, the crystalline regions that originally provide physical support gradually weaken, molecular chains begin to relax, and the cell walls become more prone to rearrangement.

圖 1｜超軟、低熔融區間 POE 在發泡與二次加熱後可能產生收縮的機理示意

Figure 1 | Schematic mechanism of potential shrinkage of ultra-soft, low-melting-range POE after foaming and secondary heating

· 結晶相支撐下降：二次加熱使部分晶區熔融，泡孔壁抗變形能力降低。

· Decline in crystalline-phase support: Secondary heating melts some crystalline regions, reducing the cell walls’ resistance to deformation.

· 殘留應力釋放：發泡膨脹、開模及冷卻形成的取向開始回復。

· Release of residual stress: The molecular orientation formed during foaming expansion, demolding, and cooling begins to recover.

· 泡孔氣體逸散：時間與溫度提高擴散速率，可能造成泡孔內外壓差變化。

· Cell-gas loss: Higher time and temperature increase diffusion rates, which may alter the pressure difference between the inside and outside of the cells.

· 交聯不足或不均：若 DCP 網絡無法有效固定尺寸，熱收縮會更明顯。

· Insufficient or non-uniform crosslinking: If the DCP network cannot effectively lock in the dimensions, thermal shrinkage will become more pronounced.

· 冷卻定型不充分：中心溫度、厚度差與堆疊方式都可能造成後續尺寸漂移。

· Insufficient cooling and dimensional setting: Core temperature, thickness differences, and stacking methods can all cause subsequent dimensional drift.

三、IUS-4065 的設計價值：軟，但不必以過低熔點交換

III. The Design Value of IUS-4065: Soft, Without Having to Trade Off for an Excessively Low Melting Point

依供應商提供的比較資料，DF 640 與 ENGAGE 8842 的硬度約為 Shore A 54–56、熔點低於 50°C；IUS-4065 的硬度約為 Shore A 40，熔點約 64°C。換句話說，它的產品主張並不是單純「更軟」，而是希望在更低硬度下仍保留較高的熱支撐區間。

According to comparison data provided by the supplier, DF 640 and ENGAGE 8842 have hardness values of approximately Shore A 54–56 and melting points below 50°C; IUS-4065 has a hardness of approximately Shore A 40 and a melting point of approximately 64°C. In other words, its product proposition is not simply “softer,” but to retain a higher range of thermal support at a lower hardness.

圖 2｜IUS-4065 與 DF 640、ENGAGE 8842 的供應商比較資料（數值須以正式 TDS／批次檢驗與實際配方驗證為準）

Figure 2 | Supplier comparison data for IUS-4065, DF 640, and ENGAGE 8842 (Values should be verified against the official TDS, batch inspection, and actual formulation.)

比較項目 Comparison Item	DF 640／ENGAGE 8842	IUS-4065	研發意義 R&D Significance
原料硬度 Raw Material Hardness	Shore A 54–56	Shore A 40	較低添加量或相同比例下，有機會取得更柔軟觸感 At a lower addition level or the same ratio, there may be an opportunity to achieve a softer feel.
熔點 Melting Point	低於 50°C	約 64°C	二次加工溫度高於 50°C 時，物理支撐潛力較高 At secondary-processing temperatures above 50°C, there is greater potential for physical support.
熱收縮風險 Thermal Shrinkage Risk	供應商標示較高 Supplier indicates higher.	供應商標示較低 Supplier indicates lower.	有利於貼合、熱壓及後加工尺寸控制 Beneficial for dimensional control during lamination, hot pressing, and post-processing.
尺寸穩定性 Dimensional Stability	供應商標示較低 Supplier indicates lower.	供應商標示較高 Supplier indicates higher.	可能降低翹曲、外觀不一致與返工 May reduce warpage, appearance inconsistency, and rework.
加工穩定性 Processing Stability	配方與溫度較敏感 More sensitive to formulation and temperature.	供應商主張較佳 Supplier claims better performance.	仍須由實際 DCP 發泡窗口與量產驗證確認 Still requires confirmation through the actual DCP foaming window and mass-production validation.

四、較高熔點為什麼有助於尺寸穩定？

IV. Why Does a Higher Melting Point Help Dimensional Stability?

在相同的二次加工溫度下，若軟質改質材料仍保留較多未熔融晶區，這些晶區可以視為暫時的物理交聯點，協助泡孔壁抵抗熱鬆弛與形變。IUS-4065 約 64°C 的熔點，相較低於 50°C 的對照材料，理論上能把部分貼合或後加工溫度與主要熔融區間拉開。

At the same secondary-processing temperature, if the soft modifier retains more unmelted crystalline regions, these regions can be regarded as temporary physical crosslinking points that help the cell walls resist thermal relaxation and deformation. Compared with reference materials melting below 50°C, the approximately 64°C melting point of IUS-4065 can theoretically increase the temperature gap between certain lamination or post-processing temperatures and the main melting range.

但熔點不能單獨等同耐熱溫度。DSC 可能呈現寬廣或多重熔融峰，實際尺寸穩定還會受到 POE 添加比例、EVA 的 VA 含量、DCP 交聯密度、發泡倍率、泡孔壁厚度、冷卻條件及受熱時間共同影響。因此，「64°C」應被視為選材優勢與驗證起點，而不是所有成品都能安全承受 64°C 的保證。

However, melting point alone cannot be equated with heat-resistance temperature. DSC may show broad or multiple melting peaks, and actual dimensional stability is also affected by POE addition ratio, EVA VA content, DCP crosslink density, expansion ratio, cell-wall thickness, cooling conditions, and heating time. Therefore, “64°C” should be regarded as a material-selection advantage and a starting point for validation, rather than a guarantee that all finished products can safely withstand 64°C.

圖 3｜發泡配方不能只追求柔軟；回彈與尺寸穩定必須同時成立

Figure 3 | Foaming formulations cannot pursue softness alone; resilience and dimensional stability must be achieved simultaneously.

五、IUS-4065 對 EVA／POE 發泡配方可能帶來什麼？

V. What Could IUS-4065 Bring to EVA/POE Foaming Formulations?

1. 更有效率地降低硬度

1. More Efficient Hardness Reduction

較低的原料硬度有機會讓研發人員用較合理比例達到成品柔軟度，減少為了降硬度而大量增加軟質 POE 或加工油所造成的交聯稀釋與物性損失。實際降硬效率仍須在相同密度下比較。

A lower raw-material hardness may allow R&D personnel to achieve the desired product softness at a more reasonable ratio, reducing the crosslink dilution and property loss caused by adding large amounts of soft POE or processing oil to reduce hardness. Actual hardness-reduction efficiency still needs to be compared at the same density.

2. 保留回彈與柔韌觸感

2. Retaining Resilience and a Flexible, Soft Feel

POE 對 EVA 的價值通常不只是降硬，也包括柔韌、低溫性能與能量回復。IUS-4065 若能在較低硬度下維持適當分子網絡，可用於需要舒適性與回彈的鞋墊、中底、護具與緩衝材料。

The value of POE in EVA is typically not limited to hardness reduction; it also includes flexibility, low-temperature performance, and energy recovery. If IUS-4065 can maintain an appropriate molecular network at lower hardness, it may be used in insoles, midsoles, protective gear, and cushioning materials that require comfort and resilience.

3. 降低貼合後的尺寸漂移

3. Reducing Dimensional Drift After Lamination

對需要布貼合、熱壓、烘烤或其他二次加工的泡棉，較高熔點可提高製程容忍度，降低二次收縮、翹曲、邊緣捲曲與外觀不一致的風險。

For foams requiring fabric lamination, hot pressing, baking, or other secondary processing, a higher melting point can increase process tolerance and reduce the risks of secondary shrinkage, warpage, edge curling, and appearance inconsistency.

4. 提升良率與批次一致性

4. Improving Yield and Batch-to-Batch Consistency

如果現有不良主要來自熱歷史敏感與尺寸回縮，材料窗口改善可能轉化為更高良率、更少整形與返工。但效益必須用同模具、同倍率、同後加工條件進行 A/B 試驗。

If existing defects are mainly caused by sensitivity to thermal history and dimensional shrinkage, an improved material window may translate into higher yield and less reshaping and rework. However, the benefits must be evaluated through A/B testing using the same mold, expansion ratio, and post-processing conditions.