雙面微結構超薄件微射出成型之實驗探討

黃勝田(Sheng-Tien Huang)

指導教授 ： 楊申語

國立臺灣大學/工學院/機械工程學研究所/碩士(2004年)

https://doi.org/10.6342/NTU.2004.10140

摘要

本研究致力於超薄件(100μm、250μm、500μm)微射出成型之實驗探討。首先藉由短射方式觀察PS融膠充填對稱一模四穴與一模八穴的波前，並改變模具溫度、射出速度及融膠溫度觀察成型條件對充填的影響。本研究接著定義不同塑料(PS、PMMA、PC)、厚度(250μm、100μm、60μm)的成型操作窗，並比較表面有微結構與無微結構時的差異性。依據可成型範圍，本研究進一歩探討製程參數對微結構轉寫性的影響，也量測射出件應力光彈分佈，最後使用變模溫系統的快速加熱冷卻模具，探討如何所短製程時間。
短射觀察發現在低模溫(80℃)充填100μm厚的一模四穴時，模穴內波前形狀不對稱，偏向模穴外側，主因是薄壁間流動常見的遲滯現象所引起。當提高模溫或模穴變厚時，這種不對稱波前的現象消失。在低模溫(80℃)充填100μm厚一模八穴時，內側四模穴有遲滯現象，外側四模穴持續充填，波前對稱，反而超越內側四模穴；然後內側模穴也突破遲滯，開始另一波充填，波前不對稱，偏向模穴外側。當模溫提高或模穴厚度加厚時，回復一般射出內側四模穴先充填，並且波前對稱。
操作窗是以模具溫度與射出速度為二軸的可成型範圍，越薄模穴操作窗越小；雙面微結構使極薄件(60μm厚)充填射速需要大幅調高。三種材料(PS、PMMA、PC)所得操作窗大小、面積、形狀均異，而且PS所需射速最小。本實驗也成幼g出30μm超薄件。
在微結構轉寫實驗方面，微透鏡結構的轉寫效果都很好，因為微透鏡結構深寬比小。藉光彈實驗觀察分子定向及殘留應力，發現模具溫度的影響最明顯，隨著模溫的升高，光彈條紋逐漸減少，表示高模溫減少分子定向及殘留應力。射出超薄件時，使用變模溫系統，要縮短製程時間，可藉由盡量降低模具溫度與提高開模溫度而得。

關鍵字

雙面微結構 ； 多模穴 ； 薄件 ； 微射出成型

並列摘要

This study is devoted to investigating the micro-injection molding of ultra-thin parts. The thin rectangular (36 mm × 60 mm) sheets with thicknesses of 500, 300, 200, 100 and 60 μms are molded with a 15-ton injection molding machine. There are several aspects in this study: First of all, with aid of short shots, the shapes of melt fronts are observed to trace the process during filling an H-type symmetric four-cavity mold and a symmetric eight-cavity mold. The effects of thickness, mold temperature, injection speed and melt temperature on filling patterns are systematically investigated. Secondly, the moldability is defined and the operation windows of different melts (PS, PMMA, PC) in molding thin parts of different thicknesses are compared. Also the moldability in molding parts with features and without features on part surfaces are investigated. The effects of processing parameters on transcription ratio (TR) of micro features, and on the distribution of orientation and residual stress of the injection parts are studied. Finally, the cycle times of the molding process using a mold with rapid mold-heating and cooling system are measured.
Based on the short shots, it is noticed that when filling the symmetrical 4-cavity mold for the cavity of 100μm thick in the mold at low mold temperature (80℃), the melt fronts in the four cavities are not asymmetrical and bends outward. The major cause is the hesitation effect of flow between thin-walls. When the mold temperature is raised or the thickness of runners and cavities is increased, the melt fronts become symmetrical. When filling the symmetrical 8-cavity of 100μm thick in the mold at low mold temperature, hesitation phenomenon occurs in the 4 inner cavities; but the filling of the 4 outer cavities continues with symmetric melt fronts, overtaking the 4 inner cavities. Afterwards, the inner 4 cavities experience a pierce-through and are filled again with the asymmetric melt fronts bending outward. Similarly, after raising the mold temperature or increasing the cavity and runner thickness, conventional filling pattern are observed; the inner 4 cavities are filled with symmetrical melt fronts, overtaking the melt fronts in outer 4 cavities.
Moldability is defined as the “molding area” on the mold temperature-injection speed plane. The thinner the cavity thickness is, the smaller the operation window is. The operation windows are different in size, area and shape for three materials (PS, PMMA and PC). The required injection speed for PS is the lowest. In this study, the thinnest part ever successfully molded is the ultra-thin part of 30μm thickness. Molding parts with or without micro-features make no significant difference if the feature size is small compared to the thickness. But molding micro ultra-thin (60μm) parts with micro-lenses (25μm radius, 2.8μm deep) and grating (3μm pitch, 1μm deep) features on surfaces demands much higher injection speed than other thicker parts.
The transcription of micro-features is satisfactory as long as the operation conditions is inside the molding area, since the micro-features is of low aspect-ratio. The molecular orientation and residual stress are compared with aid of birefringence observed with polarized light, it is found that the moldings molded with high mold temperature yields least orientation and residual stress. For injection molding ultra-thin parts with lowest cycle time, a rapid mold-heating and cooling system must be employed, and lowest mold temperature and highest demold temperature allowed should be used.

並列關鍵字

Thin part ； Molding parts with micro-features on both surfaces ； Micro-injection molding ； Multi-cavity

參考文獻

蔡明宏，“射出成形模具模穴內（Intra-Cavity）流動不平衡問題探討與改善對策”，科盛科技股份有限公司。

Becker, E.W., Ehrfeld, W., Hagmann, P., Maner, A., Muenchmeyer, D., “Fabrication of microstructures with high aspec ratios and great structural heights by synchrotron radiation lithography, golvanoforming and plastic molding (LIGA process)”, Microelectronic Engineering, Vol. 4, No. 1, pp. 35-56 (1986).

Despa, M.S., Kelly, K.W., Collier, J.R., “Injection Molding of polymeric LIGA HARMs”, Microsystem Technologies, Vol. 6, No. 2, pp. 60-66 (1999).

Flaman, A., “Buildup and Relaxation of Orientation in Injection Molding”, Polymer Engineering and Science, Vol. 33, No. 4, pp. 193-201 (1993).

Friesenbichler, W., Knappe, W., Rabitsch, R., “Injection Molding with Reduced Packing and without Packing”, International Polymer Science and Technology, No. 3, p. 191 (1988).