溶劑鑄模之研究

黃元昌

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溶劑鑄模之研究

Research on Solvent Casting

黃元昌 , Ph.D　　Advisor：劉大佼　　

繁體中文

溶劑鑄膜；牛頓流體；非牛頓流體；黏彈性； Solvent Casting ； Newtonian fluid ； non-Newtonian fluid ； viscoelasticity

Abstract │ Reference (90) │ Altmetrics

Abstract 〈TOP〉

本論文是從流體力學、流變學與高分子結構觀點對於溶劑鑄膜之行為進行研究。實驗塗液包含牛頓流體與非牛頓流體；牛頓流體是採用甘油與玉米糖漿水溶液，黏度範圍是在110~10500mPa•s，研究鑄膜起始狀態、預潤濕、黏度與鑄膜間隙對於溶劑成膜之影響。在非牛頓流體將使用Polyacrylamide (PAA)伯格流體與簡稱Carboxymethyl cellulose (CMC)黏彈性流體進行研究，並以不同方式改變分子結構、黏度、彈性等了解其對於溶劑鑄膜對於獲得良好成膜區域，即操作視窗之影響。
    在甘油流體溶劑鑄膜研究中可發現操作窗外有不同的鑄膜缺陷如空氣滲入、不穩定水窪、抖邊。另外研究兩種不同起始方式對於溶劑鑄膜的影響。並研究最大鑄膜速度Vmax之影響，結果發現在模具與基材間的鑄膜間隙在600μm以下，Vmax可能隨著黏度增加而增加。但在鑄膜間隙在1000μm時Vmax會隨著黏度增加而上升。起最大鑄膜速度Vmax時之Capillary No. Camax(=μVmax/σ，μ為黏度、σ為表面張力)小於1時會產生不穩定水窪，Camax大於1則缺陷改變為空氣滲入。同時從流場觀測中塗佈液珠面積與動態接觸角證實Vmax與黏度之間關係，證明Vmax與兩者之間關係。
    玉米糖漿牛頓流體研究中，因為玉米糖漿之表面張力為72 mN/m 較甘油63 mN/m為高，因此Vmax與鑄膜視窗都高於甘油水溶液，且與甘油水溶液相同一樣有著局部最大Vmax現象。且Camax>1時鑄膜缺陷同為空氣滲入。
   非流頓流體研究結果中，發現具彈性之PAA流體可增加Vmax與鑄膜視窗，但增加效果會與Vmax時無因次群Camax與Weissenberg No. Wimax有關。若是Camax>1彈性效應可明顯抵銷黏滯力所帶來的負面效果，增加Vmax與鑄膜視窗，且隨著彈性與Wimax上升Vmax與鑄膜視窗將隨之減小。若是Camax≤1黏滯力較小情況下，彈性效應僅可小幅增加Vmax與鑄膜視窗。
    第二種非牛頓CMC黏彈性流體中，同樣發現上述Camax>1彈性可增加鑄膜視窗與Vmax現象。且CMC牽涉到剪切稀效應，因此與PAA相比將有更大的鑄膜視窗。且高分子結構的差異若是不會產生黏彈性、表面張力不同，對於鑄膜視窗將不會有影響，因此CMC每重複單元羥基被羧甲基取代之取代度(degree of substitution，DS)對於溶劑鑄膜無影響，但分子量大小確有明顯的差異。

Parallel Abstract 〈TOP〉

In this research, the effect of hydrodynamics, rheology and polymer structures on the solvent casting of Newtonian and non-Newtonian fluids have been investigated. The main focus of the present study is on the evaluation of the operating window, i.e., a region for stable and uniform processing. The experimental aqueous solutions were Newtonian fluids, such as glycerin and corn syrup with viscosities of 110~10500 mPa•s and Non-Newtionian fluids, such as polyacryamid (PAA) and carboxymethyl cellulose (CMC). 
Different types of defects, such as stable or unstable poolings, vibrating edges and air entrainment outside the operating windows were observed. The effects of two different start-up approaches on the operating window were studied. One of the key operating parameters is the maximum casting velocity Vmax for stable operation. The fluid viscosity is the most critical parameter on Vmax. It was found that if the gap between the slot die exit and the moving film substrate is smaller than 600μm, Vmax may go down and then go up as the fluid viscosity increases. On the other hand, if the gap is larger than 600μm, Vmax will decrease as the fluid viscosity increases. It found that casting defects of glycerin solutions were determined by critical maxium capillary number Camax(=μVmax/σ, Vmax is maxium casting speed, μ is viscosity, σ is surface tension). If Camax>1, the defect of casting is air entrainment, otherwise is unstable pooling. Competition of two different types of defects, i.e., unstable pooling and air entrainment can decide Vmax, as evidenced by the observation on the fluid motion and dynamic contact angles of different cases. The importance of different forces on Vmax was also analyzed.
The surrface tension of corn syrup solution is 72 mN/m more than 63 mN/m of glycerin. According to other literatures, lower capillary number can improve the Vmax . We found the same result and critical Camax with glycerin solutions.
We also investigated PAA of Boger fluids (elastic fluid with the constant viscosity) to understand the effect of elasticity on solvent casting process. It shows that the operating windows and Vmax of non-Newtonian solutions are higher than the Newtonian fluids. Especially, in high viscous force (Camax>1), the Vmax could raise significantly, because the elastic force offsets the viscous force. But higher elastic force will reduce the stability of coating beads.
The CMC of viscoelastic fluids have shear thinning and elasticity to affect the solvent casting process. Because of shear thinning, the Vmax of CMC solutions are higher than PAA. However, there are similar critical capillary numbers as PAA solution. If Camax>1, the Vmax could increase greatly, and decrase as the fluid elasticity increase. We also studied on the effect of polymer structures such as difference degree of substitution (DS) and molecular weight.

Reference ( 90 ) 〈TOP〉

2. Z Tadmor, C. G. Gogos “Principles of polymer processing,” John Wiley & Sons: New Jersey, 2006; Chapter 12.
連結：
7. O.J. Romero, W.J. Suszynski, L.E. Scriven, M.S. Carvalho, “Low-flow limit in slot coating of dilute solutions of high molecular weight polymer,” J. Non-Newtonian Fluid Mech., 118, 137–156, 2004.
連結：
9. K. J. Ruschak, “Limiting flow in pre-metered coating device,” Chem. Eng. Sci. 31, 1057-1064, 1976.
連結：
10. L.D. Landau, V.G. Levitch, “Dragging of a liquid by a moving plate,” Acta Physicochimi. U.R.S.S., 17, 42, 1942.
連結：
11. B. G. Higgin and L. E. Scriven, “Capillary pressure and viscous pressure drop set bounds on coating bead operability,” Chem. Eng. Sci., 35, 673-682, 1980.
連結：

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