EVA 發泡為什麼會收縮？

Why Does EVA Foam Shrink?

PART 2

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

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.

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.

七、IUS‑4065 如何改善超軟 EVA／POE 配方？

VII. How Does IUS-4065 Improve Ultra-Soft EVA/POE Formulations?

圖 5｜供應商對 IUS‑4065 的定位：以較高熔點降低貼合／二次加工後的熱收縮風險。

Figure 5 | Supplier positioning for IUS-4065: a higher melting point reduces the risk of thermal shrinkage after lamination or secondary processing.

依使用者提供的 INNOARK 比較資料，IUS‑4065 原料硬度約 Shore A 40、熔點約 64°C；DF 640 與 ENGAGE 8842 約 Shore A 54–56、熔點低於 50°C。這代表 IUS‑4065 的核心不是單純降硬，而是在更軟的條件下，把主要熔融支撐區間往上移。

According to the INNOARK comparison data provided by the user, the raw-material hardness of IUS-4065 is approximately Shore A 40 and its melting point is about 64°C; DF 640 and ENGAGE 8842 are approximately Shore A 54-56 with melting points below 50°C. This means the core value of IUS-4065 is not simply lower hardness; it shifts the principal melt-support range upward while delivering a softer material.

八、導入 IUS‑4065 時，建議如何重做配方？

VIII. How Should the Formulation Be Redesigned When Introducing IUS-4065?

1. 建立原配方基準：記錄原 POE、EVA VA 含量、DCP／發泡劑／活化劑、密度、硬度及 72 h 收縮。

Establish a baseline for the existing formulation: record the original POE, EVA VA content, DCP/blowing agent/activator levels, density, hardness, and 72 h shrinkage.

2. 設計三個 IUS 比例：不要只做等量替換，至少包含等比例、目標硬度等效與降低總軟質相三組。

Design three IUS loading levels: do not perform only a one-for-one substitution; include at least an equal-ratio replacement, a target-hardness-equivalent formulation, and a formulation with a lower total soft-phase content.

3. 設計三階 DCP：以低／中／高有效添加量，搭配 MDR 或流變曲線找交聯—產氣平衡。

Design three DCP levels: use low, medium, and high effective dosages with MDR or rheology curves to identify the crosslinking-gas generation balance.

4. 固定密度再比性能：比較回彈、壓縮永久變形、撕裂、延伸及泡孔，避免倍率差製造假性優勢。

Compare performance at a fixed density: evaluate resilience, compression set, tear strength, elongation, and cell structure so that differences in expansion ratio do not create a false advantage.

5. 加入二次熱歷史：依客戶貼合條件做溫度 × 時間測試，而非只量剛開模尺寸。

Include a secondary thermal history: run temperature × time tests based on the customer's lamination conditions instead of measuring only immediately after demolding.