臺灣博碩士論文加值系統

蠟基黏結劑廣為粉末射出成型所用，但此系統在溶劑脫脂時生胚易軟化變形，且所使用之有機溶劑具有易燃、致癌的危險。有鑑於此，本研究發展一新水溶性黏結劑系統，由聚乙二醇(PEG)、聚氧化乙烯(PEO)、聚乙烯蠟(PE wax)與硬脂酸(SA)所組成，其中PEG與PEO可利用水快速脫脂而無環保上之顧慮。

本論文主要可分為三大部分：第一部份探討PEG與PEO分子量對射料流變行為之影響，並調整最佳射出條件。第二部分為利用動力學確認水脫脂過程之速率控制步驟，第三部分則利用自行組裝的尺寸膨脹儀，同步量測脫脂過程中試片尺寸的變化，並配合前兩部分之結果，提出水脫脂機構。

流變研究結果發現：射料黏度隨PEG與PEO分子量的增加而增大，且隨溫度增加與剪應變速率增大而降低。溫度超過90℃時，由於PEG1K與PEG1.5K的黏度過低，無法附著於氧化鋁顆粒上而降低射料穩定性。
射料的流動活化能隨著PEG與PEO分子量的增加而降低，顯示提高主黏結劑之分子量可有效降低射料對溫度的敏感度，射出時可有較大的工作溫度範圍。綜合各項因素，以PEO4000K為主黏結劑之射料具最高之流變指數，顯示PEO系統為較佳的選擇。

在第二部分，藉由脫脂速率的計算確認以水將PEG從試片內部脫除之速率控制步驟為PEG於水中擴散至表面的速率。本系統PEG與水之相互擴散係數與與溫度之關係顯示相互擴散係數隨著溫度提高而增大，因此在較高的溫度下試片於水中會有較快的脫脂速率。

最後在脫脂機構的方面，試片剛與水接觸時，由於試片與水在溫度上之差異，試片會產生急遽的熱膨脹。而後水分子由外往內與PEG接觸，PEG分子逐漸膨脹成膠體，試片呈現緩慢膨脹的趨勢。當PEG膠體的水濃度到達EWC時，PEG在會溶解而成溶液流出胚體，胚體內部則逐漸有一些空孔形成。隨著脫脂時間增加，水可逐漸深入胚體內部，且孔徑分佈逐漸變廣，最後當所有的PEG分子皆與水分子完成反應後，試片的膨脹量達到最大值。

此外，脫脂溫度越高，試片的熱膨脹量越大，將有較大的孔隙容許水分子進入，可促進脫脂速率；且由於水分子與PEG分子間的相互擴散係數提高，試片尺寸達到最大值的時間亦隨著溫度提高而縮短。

由於PEG高溫下較易溶解，因此在水中之膨脹量隨著水溫的提高而減小，試片膨脹量亦隨之減小。當溫度大於PEG的熔點時，PEG直接以液態脫除，可快速溶解，因此試片並無第二階段之緩慢膨脹。

Wax-based binders are widely used in PIM, but they suffer from a tendency to slump during debinding and the organic solvents most adopted are flammable, carcinogenic and environmental unacceptable. A new water-soluble PEG-based binder for PIM is developed in this study, which is made of PEG, PEO, PE wax and SA. The major binder components PEG and PEO could easily be removed in a short time in water without defects and environmental concern.

This study consists of three parts: (1) the effect of PEG and PEO molecular weights on the rheological behavior of alumina injection molding feedstock (2) to determine the debinding kinetics of water extraction (3) to set up a dilatometer for monitoring the dimensional variations of compacts during water extraction in situ.

The rheological results show that the relative viscosity of feedstock is increased with the increasing molecular weights of PEG and PEO but decreased with increasing both temperature and shear rate. When temperature is above 90℃, the viscosity of PEG1K and PEG1.5K is too low to catch powder, which may induce possible dissociation between the binder and the powder particles.

The activation energy of feedstock decreases with increasing PEG and PEO molecular weights, which indicates that the sensitivity of temperature is lower for PEO binder system. The feedstock based on the PEO4000K binder has the best general rheological index and is most suitable for injection molding. However, they have a poor external property, and a lubricant is more desired to obtain a perfect specimen.

The relationship between dW/dt and W indicates that the isothermal debinding rate varies inversely with the weight of binder removed, which agrees with the equation derived and the extraction process could be described as a diffusion-controlled one. The temperature-dependent inter-diffusion of PEG and water indicates that the inter-diffusion coefficient increases with temperature, as a consequence, a higher temperature increases the debinding rate because of a higher diffusivity.

During solvent debinding based on water extraction, the molded parts expanded drastically as soon as the parts come into contact with preheated water as a result of temperature increase. Then the PEG molecules would swell gradually to form gel from exterior to interior of the specimen when the PEG molecules come into contact with water, consequently, the swell forces the specimen to expand continuously. When the water content in PEG gel is larger than the EWC of PEG, the PEG starts dissolving. As the debinding time increases, the pore size and pore volume are increased and the distribution of pores is broadened obviously. When water penetrates into the center of specimen and the equilibrium between PEG and water is reached, the total dimensional variation reaches the maximum value and the dimension remains constant.

The extent of thermal expansion and solubility of PEG increases with the debinding temperature, which leads to a higher penetration rate of water molecules, shortening the time needed for PEG molecules to interact fully with water. The length of the specimen consequently become stable in a shorter time at a higher temperature.

When the temperature approaches the melting point of PEGs, the crystallinity decreases and the solubility is easily achieved, which decreases the extent of dilation. Once the water temperature exceeds the melting point of PEGs, the swelling curve in the second stage disappears as a result of the melting of PEGs.

總 目 錄
中文摘要----------------------------------------Ⅰ
英文摘要----------------------------------------Ⅳ
總目錄------------------------------------------Ⅶ
圖目錄------------------------------------------Ⅹ
表目錄----------------------------------------ⅩⅥ
英中名詞對照表--------------------------------ⅩⅦ
第一章 緒論-----------------------------------1
第二章 理論基礎-------------------------------6
2-1 粉末性質的影響------------------------------8
2-2 黏結劑的選擇------------------------------ 11
2-3混練----------------------------------------14
2-4射料流變分析--------------------------------15
2-4-1基本流體行為------------------------------15
2-4-2流變量測方法------------------------------19
2-4-3射料的潤滑性------------------------------24
2-5脫脂----------------------------------------28
2-5-1熱脫脂------------------------------------28
2-5-2溶劑脫脂----------------------------------31
第三章 實驗方法與步驟----------------------- 35
3-1原料----------------------------------------35
3-1-1基礎粉末----------------------------------35
3-1-2黏結劑----------------------------------- 35
3-2示差掃瞄量熱儀----------------------------- 40
3-3混練--------------------------------------- 40
3-4流變行為測試--------------------------------40
3-5成型--------------------------------------- 44
3-6脫脂--------------------------------------- 44
3-7脫脂生胚微結構觀察--------------------------44
3-8水銀測孔分析--------------------------------46
第四章 結果與討論----------------------------47
4-1主黏結劑分子量對流變行為的影響--------------47
4-1-1前言--------------------------------------47
4-1-2降伏應力----------------------------------48
4-1-3流動行為指數------------------------------50
4-1-4剪應變速率之影響------------------------- 58
4-1-5溫度的影響--------------------------------68
4-1-6流動活化能--------------------------------69
4-1-7流變行為指數------------------------------70
4-1-8射料的潤滑性------------------------------75
4-1-9小結--------------------------------------78
4-2生胚之水脫脂行為----------------------------80
4-2-1溫度對水脫脂速率的影響--------------------80
4-2-2水脫脂之反應動力學------------------------84
4-2-3 PEG於水中之相互擴散係數------------------85
4-2-4 SEM觀察----------------------------------90
4-2-5水銀測孔儀分析----------------------------94
4-2-6小結--------------------------------------100
4-3水脫脂機構之探討----------------------------102
4-3-1前言--------------------------------------102
4-3-2水脫脂過程試片尺寸的變化------------------104
4-3-3討論--------------------------------------116
4-3-4小結--------------------------------------123
第五章結論-------------------------------------125
參考文獻---------------------------------------128
自述-------------------------------------------137
著作-------------------------------------------138

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