不同NCO含量的反應型聚胺酯熱熔膠特性研究與探討

反應型聚胺酯熱熔膠(polyurethane reactive hot melt adhesives, PUR)為一種環保、無溶劑的高性能接著劑。本研究以4,4'-二苯基甲烷二異氰酸酯(pure-MDI)、聚酯多元醇(PHA)及聚醚多元醇(PPG)為原料，並固定PHA與PPG之間的比例，藉由pure-MDI的不同添加量製備出不同NCO含量之PUR，並對下列特性進行比較與探討：(1)以ATR-FTIR觀察PUR預聚物之熟化程度，並量測其熔融黏度、開放時間和固著時間；(2)以DSC觀察PUR熟化後的玻璃轉移溫度與熱焓值；(3)不同NCO含量之PUR以PC試片進行貼合，探討其於4小時及168小時的搭接強度(lap shear strength)及破壞模式。研究結果顯示PUR預聚物隨著NCO含量提高，則熔融黏度降低、可操作時間延長。由DSC得知其在不同NCO含量的PUR於熟化後的熱焓值比較依序為PUR42＞PUR30＞PUR10＞PUR17 ≈ PUR23。以拉力試驗機檢測PUR薄膜，得知其隨著NCO含量的提高，當完全熟化後的薄膜，其抗張強度也隨之增加；由接著強度測試的結果得知，當NCO含量增加，可提高其微相分離的程度，並阻礙軟段的聚集，致使PUR的初期強度較低，並且以PUR42的膠膜有較高的內聚力，因此在搭接強度測試有較大的界面破壞。

關鍵字

反應型聚胺酯熱熔膠； 4,4'-二苯基甲烷二異氰酸酯；搭接強度

並列摘要

Polyurethane reactive hot melt adhesives (PUR) are isocyanate-capped prepolymers prepared from polyester and/or polyether glycols and a diisocyanate monomers or polyisocyanate. The different NCO content of PUR have been synthesized by polyhexanediol adipate (PHA), polypropylene glycols (PPG), and 4,4'-methylene diphenyl diisocyanate (pure-MDI) as the main ingredient. The PUR prepolymers are NCO-terminated, and they will be cured in the presence of moisture to generate highly crosslinked structure. The PUR with different isocyanate (NCO) content was studied on rheology, thermal and mechanical properties of PUR film. The effects of NCO/OH molar ratio on the morphology and physical properties of PUR were investigated by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), differential scanning calorimetry (DSC) and universal testing machine. The results showed that the PUR had a high degree of micro phase separation and the hydrogen-bonded urea signal increases significantly under the higher NCO content. As the NCO content increase, the degree of hydrogen bonding of the hard segments and the glass transition temperature (T_g) increase. PUR prepolymer with higher crystalline content showed better green strength and the slower adhesion rate. Because the higher degree of crosslinking can prevent moisture diffusion into the PUR film, so leading to incomplete curing and hinder the crystalline behavior of the soft segment. It hence causes a lower initial adhesive strength.