塑胶卷盘注塑模具设计【说明书+CAD+UG】
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Microsystem Technologies 10 (2004) 531535 _ Springer-Verlag 2004DOI 10.1007/s00542-004-0387-2Replication of microlens arrays by injection moldingB.-K. Lee, D. S. Kim, T. H. KwonB.-K. Lee, D. S. Kim, T. H. Kwon (&)Department of Mechanical Engineering,Pohang University of Science and Technology (POSTECH),San 31, Hyoja-Dong, Nam-Gu, Pohang, 790-784, Koreae-mail: thkwonpostech.ac.krAbstract Injection molding could be used as a mass production technology for microlens arrays. It is of importance, and thus of our concern in the present study, to understand the injection molding processing condition effects on the replicability of microlens array profile. Extensive experiments were performed by varyingprocessing conditions such as flow rate, packing pressure and packing time for three different polymeric materials (PS, PMMA and PC). The nickel mold insert of microlens arrays was made by electroplating a microstructure master fabricated by a modified LIGA process. Effects of processing conditions on the replicability were investigated with the help of the surface profile measurements. Experimental results showed that a packing pressure and a flow rate significantly affects a final surface profile of the injection molded product. Atomic force microscope measurement indicated that the averaged surface roughness value of injection molded microlens arrays is smaller than that of mold insert and is comparable with that of fine optical components in practical use.1 Introduction Microoptical products such as microlenses or microlens arrays have been used widely in various fields of microoptics, optical data storages, bio-medical applications, display devices and so on. Microlenses and microlens arrays are essential elements not only for the practical applications but also for the fundamental studies in the microoptics. There have been several fabrication methods for microlenses or microlens arryas such as a modified LIGA process 1, photoresist reflow process 2, UV laser illumination 3, etc. And the replication techniques, such as injection molding, compression molding 4 and hot embossing 5, are getting more important for a mass production of microoptical products due to the cost-effectiveness. As long as the injection molding can replicate subtle microstructures well, it is surely the most cost-effective method in the mass production stage due to its excellent reproducibility and productivity. In this regard, it is of utmost importance to check the injection moldability and to determine the molding processing condition window for proper injection molding of microstructures. In this study, we investigated the effects of processing conditions on the replication of microlens arrays by the injection molding. The microlens arrays were fabricated by a modified LIGA process, which was previously reported in 6, 7. Injection molding experiments were performed with an electroplated nickel mold insert so as to investigate the effects of some processing conditions. The surface profiles of molded microlens arrays were measured, and were used to analyze effects of processing conditions. Finally, a surface roughness of microlens arrays was measured by an atomic force microscope (AFM).2 Mold insert fabricationMicrolens arrays having several different diameters were fabricated on a PMMA sheet by a modified LIGA process 6. This modified LIGA process is composed of an X-ray irradiation on the PMMA sheet and a subsequent thermal treatment. The X-ray irradiation causes the decrease of molecular weight of PMMA, which in turn decreases the glass transition temperature and consequently causes a net volume increase during the thermal cycle resulting in a swollen microlens 7. The shapes of microlenses fabricated by the modified LIGA process can be predicted by a method suggested in 7. The microlens arrays used in the experiments were composed of 500m -(a 2 2 array), 300m -(2 2) and 200m (5 5) diameter arrays, and their heights were 20.81, 17.21 and 8.06 m, respectively. Using the microlens arrays fabricated by the modified LIGA process as a master, a metallic mold insert was fabricated by a nickel electroplating for the injection molding. Typical materials used in a microfabrication process, such as silicon, photoresists or polymeric materials, cannot be directly used as the mold or the mold insert due to their weak strength or thermal properties. It is desirable to use metallic materials which have appropriate mechanical and thermal properties to endure both a high pressure and a large temperature variation during the replication process. Therefore, a metallic mold insert is being used rather than the PMMA master on silicon wafer for mass production with such replication techniques. Otherwise special techniques should be adopted as a replication method, e.g. a low pressure injection molding 8.The size of final electroplated mold insert was 30 30 3 mm. The electroplated nickel mold insert having microlens arrays is shown in Fig. 1.Fig.1.Moldinsert fabricated by a nickel electroplating (a) Real view of the mold insert (b) SEM image of 200 m diameter microlens array (c) SEM image of 300 mdiameter microlens array3 Injection molding experimentsA conventional injection molding machine (Allrounders 220 M, Arburg) was used in the experiments. A mold base for the injection molding was designed to fix the electroplated nickel mold insert firmly with the help of a frametype bolster plate (Fig. 2). Shape of aperture of the bolster plate (in this study, a rectangular one) defines the outer geometry of the molded part on which the profiles of microlens arrays are to be transcribed. The mold base itself has delivery systems such as sprue, runner and gate which lead the molten polymer to the cavity formed by the bolster plate, the mold insert and amoving mold surface. The mold base was designed such that mold insert replacement is simple and easy. Of course, one may introduce an appropriate bolster plate with a specific aperture shape. Fig. 2. Mold base and mold insert used in the injection molding experimentThe injection molding experiments were carried out with three general polymeric materials PS (615APR, Dow Chemical), PMMA (IF870, LG MMA) and PC (Lexan 141R, GE Plastics). These materials are quite commonly used for optical applications. They have different refractive indices (1.600, 1.490 and 1.586 for PS, PMMA and PC, respectively), giving rise to different optical properties in final products, e.g. different foci with the same geometry. The injectionmolding experiments were performed for seven processing conditions by changing flow rate, packing pressure and packing time for each polymeric material. Furthermore, same experiments were repeated three times for checking the reproducibility. It may be mentioned that the mold temperature effect was not considered in this study since the temperature effect is relatively less important for these microlens arrays due to their large radius of curvature than other microstructures of high aspect ratio. For high aspect ratio microstructures, we are currently investigating the temperature effect more closely and plan to report separately in the future. Therefore, flow rate, packing pressure and packing time were varied to investigate their effects more thoroughly with the mold temperature unchanged in this study. Table 1 shows the detailed processing conditions for three polymeric materials. Other processing conditions were kept unchanged during the experiment. The mold temperatures were set to 80, 70 and 60 _C for PC, PMMA and PS, respectively.It might be mentioned that we carried out the experiments without a vacuum condition in the mold cavity considering that the large radius of curvature of the microlens arrays in the present study will not entrap air in the microlens cavity during the filling stage.Table 1. Detailed processing conditions used in the injection molding experimentsCaseFlow rate (cc/sec)Packing time (sec)Packing pressure(MPa)112.05.010.0212.05.015.0312.05.020.0PS412.02.010.0512.010.010.0618.05.010.0724.05.010.0PMMA16.010.010.026.010.015.036.010.020.046.05.010.05676.09.012.015.010.010.010.010.010.0PC 16.05.05.026.05.010.0356.06.09.05.010.015.05.065.05.0712.05.05.04Results and discussionBefore detailed discussion of the experimental results, it might be helpful to summarize why flow rate, packingpressure and packing time (which were chosen as processing conditions to be varied in this study) affect thereplication quality. As far as the flow rate is concerned, there may exist an optimal flow rate in the sense that too small flow rate makes too much cooling before a complete filling and thus possibly results in so-called short shot phenomena whereas too high flow rate increases pressure fields which is undesirable.The packing stage is generally required to compensate for the volume shrinkage of hot molten polymer whencooled down, so that enough material should flow into a mold cavity during this stage to control the dimensionalaccuracy. The higher the packing pressure, the longer the packing time, more material tends to flow in. However, too much packing pressure sometimes may cause uneven distribution of density, thereby resulting in poor opticalquality. And too long packing time does not help at all since gate will be frozen and prevent material from flowing into the cavity. In this regard, one needs to investigate the effects of packing pressure and packing time.4.1Surface profilesFigure 3 shows typical scanning electron microscope (SEM) images of the injection molded microlens arrays for different diameters for PMMA (a) and different materials (b). Cross-sectional surface profiles of the mold insert and all the injection molded microlens arrays were measured by a 3D profile measuring system (NH-3N, Mitaka).Fig. 3. SEM images of theinjection molded microlensarrays and microlenses (a)Injection molded microlensarrays (PMMA) (b) Injectionmolded microlenses of 300 mdiameter for different materialsAs a measure of replicability, we have defined a relative deviation of profile as the height difference between the molded one and the corresponding mold insert for each microlens divided by the mold insert one. The computed relative deviations for all the microlenses are listed in Table 2.Diameter ( m)Relative deviation (%)1234567PS200300500-7.625.862.38-7.592.03-0.382.082.860.51-5.611.47-8.6660161.47-11.444.291.47-5.731.95PMMA2003005007.205.77-0.661.315.60-1.62-3.886.453.98-5.805.952.80-0.975.95-0.72-8.536.68-0.904.86-2.62-0.72PC20030050023.026.20-0.9316.054.965.0916.872.66-1.8619.664.531.8833.974.786.9618.671.792.43-2.944.15-1.55It may be mentioned that the moldability of polymeric materials affects the replicability. Therefore, the overall relative deviation differs for three polymeric materials used in this study. It may be noted that PC is the most difficult material for injection molding amongst the three polymers. The largest relative deviation can be found in PC for the smallest diameter case, as expected. In that specific case, the largest value is corresponding to the low flow rate and low packing pressure. Packing time in this case does not significantly affect the deviation. The relative deviation for PS and PMMA with the smallest diameter is far better than PC case.Table 2 indicates that the larger the diameter, the smaller the relative deviation. The larger diameter microlens is, of course, easier to be filled than smaller diameter during the filling stage and packing stage. Microlenses of larger diameters were generally replicated well regardless of processing conditions and regardless of materials. The best replicability is found for the case of PS with 500 m diameter. Generally, PS has a good moldability in comparison with PMMA and PC.It may be mentioned that some negative values of relative deviation were observed mostly in the smallest diameter case for PS and PMMA according to Table 2. In these cases, however, the absolute deviation is an order of 0.1 m in height, which is within the measurement error of the system. Therefore, the negative values could be ignored in interpreting the experimental data of replicability. Surface profiles of microlens of 300 m diameter are shown in Figs. 4 and 5 for PC and PMMA, respectively. As shown in Fig. 4, the higher packing pressure or the higher flow rate results in the better replication of microlens for the case of PC, as mentioned above. Packing time has little effect on the replication for these cases. For the case of PMMA, the packing pressure and packing time have insignificant effect as shown in Fig. 5; however, flow rate has the similar effect to PC. It might be reminded that packing time does not affect the replicability if a gate is frozen since frozen gate prevents material from flowinginto the cavity. Therefore, the effect of packing time disappears after a certain time depending on the processing conditions.Fig.4ac(leftside).Surface profiles of microlens (PC with diameter (/) of 300 m). a effect of packing pressure, b effect of flow rate, c effectof packing timeFig.5ac.(rightside)Surface profiles of microlens (PMMA with diameter(/) of 300 m). a effect of packing pressure, b effect of flow rate,c effect of packing time4.2Surface roughnessAveraged surface roughness, Ra, values of 300 m diameter microlenses and the mold insert were measured by an atomic force microscope (Bioscope AFM, Digital Instruments). The measurements were performed around the top of each microlens and the measuring area was 5 m 5 m. Figure 6 shows AFM images and measured Ra values of microlenses. PMMA replicas of microlens have the lowest Ra value, 1.606 nm. It may be noted that AFM measurement indicated that Ra value of injection molded microlens arrays is smaller than the corresponding one of the mold insert. The reason for the improved surface roughness in the replicated microlens arrays is not clear at this moment, but might be attributed to the reflow caused by surface tension during a cooling process. It may be further noted that the Ra value of injection molded microlens arrays is comparable with that of fine optical components in practical use.Fig. 6. AFM images and averaged surface roughness, Ra, values of the mold insert and injection molded 300 m diameter microlenses. a Nickel mold insert, b PS, c PMMA, d PC4.3Focal lengthThe focal length of lenses can be calculated by a wellknown equation as follows:where f, nl, R1 and R2 are focal length, refractive index of lens material, two principal radii of curvature, respectively.For instance, focal lengths of the molded microlenses were approximately calculated as 1.065 mm (with R1 0.624 mm and R2 11 ￥) for 200 m diameter microlens, 1.130 mm (with R1= 0.662 mm and R2=) for 300 m microlens and 2.580 mm (with R1=1.512 mm and R2=) for 500 m microlens according to Eq. (1). These calculations were based on an assumption that microlenses are replicated with PC (nl= 1.586) and have the identical shape of the mold insert. It might be mentioned that the geometry of the molded microlens might be inversely deduced from an experimental measurement of the focal length.5ConclusionThe replication of microlens arrays was carried out by the injection molding process with the nickel mold insert which was electroplated from the microlens arrays master fabricated via a modified LIGA process.The effects of processing conditions were investigated through extensive experiments conducted with various processing conditions. The results showed that the higher packing pressure or the higher flow rate is, the better replicability is achieved. In comparison, the packing time was found to have little effect on the replication of microlens arrays.The injection molded microlens arrays had a smaller averaged surface roughness values than the mold insert, which might be attributed to the reflow induced by surface tension during the cooling stage. And PMMA replicas of microlens arrays had the best surface quality (i.e. the lowest roughness value of Ra =1.606 nm). The surface roughness of injection molded microlens arrays is comparable with that of fine optical components in practical use. In this regard, injection molding might be a useful manufacturing tool for mass production of microlensarrays.References1. Ruther P; Gerlach B; Gottert J; Ilie M; Muller A; Omann C (1997) Fabrication and characterization of microlenses realized by a modified LIGA process. Pure Appl Opt 6: 6436532. Popovic ZD; Sprague RA; Neville Connell GA (1988) Technique for monolithic fabrication of microlens array. Appl Opt27: 128112843. Beinhorn F; Ihlemann J; Luther K; Troe J (1999) Micro-lens arrays generated by UV laser irradiation of doped PMMA. Appl Phys A68: 7097134. Moon S; Lee N; Kang S (2003) Fabrication of a microlens array using micro-compression molding with an electroformed mold insert. J Micromech Microeng 13: 981035. Ong NS; Koh YH; Fu YQ (2002) Microlens array produced using hot embossing process. Microelectron Eng 60: 3653796. Lee S-K; Lee K-C; Lee SS (2002) A simple method for microlens fabrication by the modified LIGA process. J MicromechMicroeng 12: 3343407. Kim DS; Yang SS; Lee S-K; Kwon TH; Lee SS (2003) Physical modeling and analysis of microlens formation fabricated by a modified LIGA process. J Micromech Microeng 13: 5235318. Bauer W; Knitter R; Emde A; Bartelt G; Gohring D; Hansjosten E (2002) Replication techniques for ceramic microcomponents with high aspect ratio. Microsyst Technol 7: 85 90 微透镜阵列注塑成型的复制 B.-K. Lee, D. S. Kim, T. H. Kwon朴航科技大学(POSTECH) 机械工程学院San 31, Hyoja-Dong, Nam-Gu, Pohang, 790-784, Korea电子邮箱l: thkwonpostech.ac.kr摘要 微透镜阵列注塑成型，可作为一种非常重要的大量生产技术。因此我们在近来的研究中非常关注， 为了进一步了解注塑成型在不同的加工条件下对可复制的微透镜阵列剖面的影响，如流量、填料压力和填料时间，对3种不同的高分子材料(PS，PMMA和PC)进行了大量的试验。 镍金属模具嵌件微阵列就是利用改良的LIGA技术电镀主装配的显微结构制造的。在表面轮廓得到测量的前提下，研究工艺条件对可复制的微透镜阵列的影响。实验结果表明， 填料压力和流速对注射模塑的终产品的表面轮廓有重要的影响。 原子力显微镜测量表明， 微透镜阵列注塑成型的平均表面粗糙度值小于模具嵌件成型， 并在实际运用中，能与精细的光学元件相媲美。1 说明 微型光学产品，如微透镜或微透镜阵列已广泛应用于光学数据存储、生物医学、显示装置等各个光学领域。微透镜和微透镜阵列不仅在实践应用上，而且在微型光学的基础研究上都是非常重要的。有几种微透镜或微透镜阵列的制作方法，如改良的LIGA技术1 ，光阻回流进程2，紫外激光照射3等。还有复制技术，如注塑模压成型4和热压5技术 ，这种方法对于减少大规模生产的微型光学产品的成本尤为重要。由于其优越的生产和再生产能力，只要注塑成型过程中能很好的复制微观结构，那么肯定是最适合于降低大量生产成本的方法。基于这点，检查注塑成型能力并确定成型加工条件是注塑成型微观结构过程中最重要的步骤。在本次研究中，我们考察了工艺条件对可复制的微透镜阵列的注射成型的影响。微透镜阵列是用之前介绍过6，7的改良的LIGA技术来编制的。注塑成型实验采用的是一种镀镍金属模具，来探讨了几种不同工艺条件对成型的影响。通过对微透镜阵列的表面轮廓测量，用来分析工艺条件产生的影响。最后，利用原子力显微镜(AFM)测量微透镜的表面粗糙度值的大小。2 模具嵌件的制造利用改良的LIGA技术6，在一个有机玻璃板上制造出具有几种不同直径微透镜阵列。此种技术是先用X光照射有机玻璃板，然后再进行热处理两部分构成的。X-射线照射引起有机玻璃分子质量的减少，同时降低了玻璃化转变温度，并因此导致净含量的增加，在热循环的作用下，微透镜发生微膨胀7。利用7中提出的方法，结合改良的LIGA技术可以预测微透镜形状的变化过程。 在试验中使用的微透镜阵列，有500m (22阵列)，300m (22)和200m (55)的直径阵列，高分别是20.81m，17.21m和8.06m。采用改良的LIGA技术制造微透镜阵列作为一个主要的技术，用来制作镀镍的金属模具的注塑成型。另一些特殊材料，因为它们的强度不够或热性能差而不能直接进行微细加工，当作模具或金属模具使用，如硅、光阻剂或高分子材料。尽量使用具有良好机械性能和热性能的金属材料，因为它们能在可复型加工过程中经受高压力和不断变化的温度。因此，为了利用这种复制技术进行大批量生产，我们选择使用金属模具材料而不是有机玻璃硅晶体。一些特殊技术，如低压注塑成型8技术，应该作为良好的复制加工方法被采纳。电镀模具的最终大小为30 mm30 mm3mm。镀镍金属模具所具有的微透镜阵列如图1所示。图1 镀镍模具嵌件的制造 （a）直接观察；（b）直径为200m的微透镜阵列电子显微镜图像；（c）直径为300m的微透镜阵列电子显微镜图像3 注塑成型实验 传统注塑机(Allrounders 220 M，Arburg)多用做实验机。注塑模具设计的模架就是利用一块框形支撑板固定镀镍模具(如图2所示)。 图2 注塑模具实验中使用的模架和嵌件用修改的微透镜阵列确定模具零件孔形加强板(在这次实验中，是一块矩形板)的外部形状。模架本身已含有传输系统，如注射口，流道及浇口，通过支撑板、模具流道和滑动的模具表面将熔融聚合物引入模腔。用这种方法设计的模架，能够使模具零件更换起来简单容易。 不过，有时候也使用具有特定孔径形状的支撑板。 实验主要用三种普通高分子材料，PS(615APR，陶氏化学)，有机玻璃(IF870， LG MMA)和PC(Lexan 141R)进行注塑成型。这些高分子材料通常在光学元件上使用，它们有不同的折射率(PS，PMMA和PC的折射率分别为1.600，1.490和1.586)，能生产出具有不同的光学特性的产品，例如:具有相同的几何尺寸却有不同的焦距的光学元件。通过改变每个高分子材料的流速，充填压力和充填时间获得7种加工条件进行注塑成型试验。此外，为了检查是否能可再生产，同一实验往往需要重复三次。可能有人会指出，实验中没有考虑模具温度的影响，这是因为温度效应相对来说不是主要因素，而且微透镜阵列曲率半径比其他微观结构的高宽纵横比大。正是因为较大的微观结构高宽纵横比，使我们目前研究的温度效应更加可靠，并计划在将来实验时进行单独报告。 因此，在这项研究中，我们保持模具温度不变，而流速、充填压力和充填的时间都变化的情况下，能更清楚的观察其产生效果。表1详细的列出了三种高分子材料PC，PMMA和PS在其他加工条件都保持不变，将模具温度分别设定为80，70和60的情况下的实验结果。表1注塑模具实验中详细的工艺条件序号流 速 (cc/s)充填时间 (/s)充填压力 (MPa)112.05.010.0212.05.015.0312.05.020.0PS412.02.010.0512.010.010.0618.05.010.0724.05.010.0PMMA16.010.010.026.010.015.036.010.020.046.05.010.0566.09.015.010.010.010.0续表1序号流 速 (cc/s)充填时间 (/s)充填压力(MPa)712.010.010.0PC 16.05.05.026.05.010.0356.06.09.05.010.015.05.065.05.0712.05.05.0可能有人会指出，我们的实验没有考虑型腔出现真空状态时的情况，其实大可不必担心，因为在本研究中的注射阶段，大曲率半径的微透镜阵列不会把空气引入到型腔中。4 讨论和结果在详细讨论实验结果之前，认真思考一下，可能有助于总结为什么流速、充填压力和充填时间(在这项研究中被选为不同的加工条件)影响复制的质量。就流速而言，可能存在一个最佳流速，而在完成充填之前，流速太小会使得熔融聚合物过冷却，从而可能导致所谓的短暂的不连续现象，而过高的流速增大了压力面积，这是不可取的。充填阶段是一般要求，是要在冷却时能够弥补热熔融聚合物的体积收缩 。 因此，在这个阶段应有足够的熔融聚合物流入型腔并控制产品的尺寸精度。 越高的充填压力，越长的充填时间，将使更多的材料持续不断的流向型腔。然而， 过高的充填压力，有时可能造成不均匀的密度分布，从而产生劣质的光学质量。过长的充填时间，不利于在各自浇口处的冷凝，并且会阻止熔融聚合物流入型腔。因此，我们需要研究不同的充填压力和充填时间所产生的影响。4.1 表面轮廓图3所示的是用电子显微镜(SEM) 扫描的不同注塑微透镜的直径的PMMA图像(a)以及不同 材料的图像(b)。代表性的模具表面轮廓以及所有注塑微阵列都是通过三维轮廓测量系统(NH-3N， Mitaka)测定的。图3 注塑模具的微透镜阵列和微透镜的电子显微镜图像（a）PMMA微透镜阵列 （b）不同材料直径为300m微透镜阵列的注塑模具作为一个可复制阵列的测量工具，我们已经确定了在模具与相应的模具嵌件分开的微阵列之间轮廓的相对高度偏差，所有的微透镜阵列相对偏差值列在表2中，具体见表所示： 表2 表面轮廓相对偏差直径 (m)相对偏差(%)1234567PS200300500-7.625.862.38-7.592.03-0.382.082.860.51-5.611.47-8.6660161.47-11.444.291.47-5.731.95PMMA2003005007.205.77-0.661.315.60-1.62-3.886.453.98-5.805.952.80-0.975.95-0.72-8.536.68-0.904.86-2.62-0.72PC20030050023.026.20-0.9316.054.965.0916.872.66-1.8619.664.531.8833.974.786.9618.671.792.43-2.944.15-1.55值得一提的是，高分子材料的塑性会影响其重复使用性能。 因此在研究中，三种高分子材料总的相对误差是各不相同的。PC是三种聚合物中最难注塑成型的材料。在直径最小的例子中产生最大的相对偏差，那都是意料之中的事。 在这种特殊情况下，充填时间并不对偏差产生显著影响，最好的解决方法是采用相对低的流速和充填压力。PS和PMMA最小的直径的相对偏差要比PC小的多。 从表2可以看出，直径越大，相对偏差越小。当然，在注射和保压阶段，直径大的微透镜阵列容易比直径小的更容易填补，不管是在什么加工条件下和使用什么材料，大直径的微透镜阵列一般都能得到较好的复型。研究发现直径500m的PS最好复型，一般而言，与PMMA和PC相比较，PS具有良好的成型性能。根据表2的数据，在考察最小的直径的PS和PMMA的相对偏差时，可能会有人提出一些消极的观点，认为偏差过大，但是在这些数据中可以得到，高度上的绝对偏差在0.1m左右，这是在测量系统误差范围以内。 所以，在解读复型实验数据时可以忽略这些消极的观点。 直径为300m的PC和PMMA微透镜表面轮廓分别如图4和图5所示。正如之前所述，在图4所示
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