化學發泡 vs. 超臨界發泡

Chemical Foaming vs. Supercritical Foaming

不只是泡孔大小：從原理、設備、成本到材料回收性的完整選擇指南

Not Just Cell Size: A Complete Selection Guide from Principles, Equipment, and Cost to Material Recyclability

適用於 EVA、POE、TPU、TPE、PP、PE 與工程發泡材料開發

Applicable to the Development of EVA, POE, TPU, TPE, PP, PE, and Engineering Foams

先說結論｜化學發泡的核心優勢是設備成熟、配方彈性與投資門檻較低；超臨界發泡的核心優勢是可不依賴殘留型化學發泡劑，並具備形成高細胞密度微孔結構的潛力。最終選擇仍由材料的氣體溶解度、熔體強度、產品外觀及產量決定。 Bottom line | The core advantages of chemical foaming are mature equipment, formulation flexibility, and a lower investment threshold; the core advantages of supercritical foaming are that it does not rely on residual chemical blowing agents and has the potential to form microcellular structures with high cell density. The final choice still depends on the material’s gas solubility, melt strength, product appearance, and production volume.

一、為什麼這個比較值得關注？

I. Why Is This Comparison Worth Attention?

當品牌要求產品更輕、更高回彈、低氣味、減少添加劑，甚至希望提升回收再利用的可能性時，傳統化學發泡是否仍是最佳答案，便成為研發與採購共同面對的問題。另一方面，超臨界發泡常被包裝成「更環保、更細孔、更高性能」，但若忽略高壓設備、材料氣體溶解度與製程控制，其量產風險可能被嚴重低估。

When brands require products to be lighter, more resilient, lower in odor, and lower in additives, or even seek greater potential for recycling and reuse, whether traditional chemical foaming remains the best answer becomes a question jointly faced by R&D and procurement. On the other hand, supercritical foaming is often promoted as “more environmentally friendly, finer-cell, and higher-performance,” but if high-pressure equipment, material gas solubility, and process control are overlooked, its mass-production risks may be seriously underestimated.

本文所稱化學發泡，是指發泡劑受熱分解或反應產生氣體；超臨界發泡則是使用處於特定溫度與壓力狀態的 CO₂ 或 N₂ 作為物理發泡介質。兩者最大的差異，不在於有沒有氣泡，而在於氣體如何進入聚合物、何時成核，以及泡孔如何被凍結固定。

In this article, chemical foaming refers to generating gas through the thermal decomposition or reaction of a blowing agent; supercritical foaming refers to using CO₂ or N₂ under specific temperature and pressure conditions as a physical foaming medium. The biggest difference between the two is not whether bubbles exist, but how the gas enters the polymer, when nucleation occurs, and how the cells are frozen and stabilized.

二、化學發泡：用反應在材料內部產生氣體

II. Chemical Foaming: Generating Gas Inside the Material Through a Reaction

化學發泡劑（Chemical Blowing Agent, CBA）混入樹脂後，在設定溫區內分解或反應並釋放氣體。常見放熱型系統包括 ADC，吸熱型系統則可由碳酸氫鹽／有機酸組合產氣。選擇發泡劑時，分解溫度必須與樹脂的加工溫度、交聯速度及熔體強度相匹配。

After a Chemical Blowing Agent (CBA) is mixed into the resin, it decomposes or reacts within the designated temperature range and releases gas. Common exothermic systems include ADC, while endothermic systems can generate gas through bicarbonate/organic-acid combinations. When selecting a blowing agent, its decomposition temperature must match the resin processing temperature, crosslinking rate, and melt strength.

化學發泡的控制核心

Core Control Factors for Chemical Foaming

· 發泡劑必須均勻分散，否則容易產生局部大泡孔或表面缺陷。

· The blowing agent must be uniformly dispersed; otherwise, localized large cells or surface defects can easily occur.

· 產氣太早，熔體尚未具備強度，容易合泡、破泡或塌泡。

· If gas is generated too early, the melt may not yet have sufficient strength, making cell coalescence, rupture, or collapse more likely.

· 產氣太晚，材料已過度交聯或冷卻，發泡倍率會受到限制。

· If gas is generated too late, the material may already be excessively crosslinked or cooled, limiting the expansion ratio.

· ADC 等發泡劑會留下分解副產物，可能影響氣味、顏色、霧度或長期性能。

· Blowing agents such as ADC leave decomposition by-products that may affect odor, color, haze, or long-term performance.

三、超臨界發泡：先溶解氣體，再用壓降觸發成核

III. Supercritical Foaming: Dissolve the Gas First, Then Trigger Nucleation by Pressure Reduction

CO₂ 的臨界點約為 31.1°C、7.38 MPa；高於臨界點後不再有明確液氣界面，可呈現氣體般擴散及液體般密度。實際聚合物發泡不一定每一階段都維持在嚴格超臨界狀態，但產業通常仍以「超臨界發泡」統稱高壓 CO₂／N₂ 的物理發泡技術。

製程先將 CO₂ 或 N₂ 在高壓下溶入聚合物。氣體會降低聚合物黏度或玻璃轉移溫度，形成塑化作用；當壓力快速下降或溫度改變，系統進入過飽和狀態並產生大量氣泡核，隨後經泡孔成長與冷卻定型形成微孔材料。

The process first dissolves CO₂ or N₂ into the polymer under high pressure. The gas lowers the polymer viscosity or glass-transition temperature, producing a plasticizing effect. When pressure drops rapidly or temperature changes, the system becomes supersaturated and generates a large number of bubble nuclei, followed by cell growth and cooling/setting to form a microcellular material.

 

圖 1｜化學發泡由發泡劑熱分解產氣；超臨界發泡由高壓氣體溶解及壓降成核

Figure 1 | Chemical foaming generates gas through thermal decomposition of a blowing agent; supercritical foaming generates nuclei through dissolution of high-pressure gas and pressure reduction

四、兩種技術的本質差異

IV. Fundamental Differences Between the Two Technologies

五、泡孔一定是超臨界發泡比較細嗎？

V. Are Cells Necessarily Finer with Supercritical Foaming?

通常具有這個潛力，但不能視為必然結果。泡孔大小與密度同時受氣體溶解度、成核速率、降壓速度、熔體強度、結晶行為、成核劑及冷卻速度控制。超臨界 CO₂ 可在適當條件下形成大量氣泡核；如果材料熔體強度不足，這些泡核仍可能合併、破裂或在脫模後收縮。

This is generally possible, but it should not be regarded as an inevitable outcome. Cell size and density are simultaneously controlled by gas solubility, nucleation rate, depressurization rate, melt strength, crystallization behavior, nucleating agents, and cooling rate. Supercritical CO₂ can form a large number of bubble nuclei under appropriate conditions; if the material lacks sufficient melt strength, these nuclei may still coalesce, rupture, or shrink after demolding.

 

圖 2｜典型泡孔趨勢示意；實際結果取決於材料、氣體溶解度與製程窗口

Figure 2 | Schematic of typical cell-size trends; actual results depend on the material, gas solubility, and process window

重要提醒｜「微孔」指的是結構尺度，不等於產品一定更柔軟、更高回彈或更耐久。成品性能取決於相對密度、泡孔壁厚度、開閉孔比例、結晶度與材料本體性能。 Important reminder | “Microcellular” refers to the structural scale; it does not mean the product will necessarily be softer, more resilient, or more durable. Finished-product performance depends on relative density, cell-wall thickness, open/closed-cell ratio, crystallinity, and the inherent properties of the material.

六、性能比較：應看哪些數據？

VI. Performance Comparison: Which Data Should Be Examined?

若只比較密度或顯微照片，很容易做出錯誤結論。不同製程應在相近密度與相近硬度條件下進行公平比較，並建立泡孔結構—力學性能—長期耐久性之間的關係。

七、環保與可回收性：不要只看「是否使用 CO₂」

VII. Environmental Performance and Recyclability: Do Not Look Only at Whether CO₂ Is Used