外文翻譯原文微透鏡陣列注塑成型技術(shù)

1、編號(hào)： 畢業(yè)設(shè)計(jì)(論文)外文翻譯（原文）學(xué) 院： 國(guó)防生學(xué)院 專 業(yè)： 機(jī)械設(shè)計(jì)制造及其自動(dòng)化 學(xué)生姓名： 黃志勇 學(xué) 號(hào)： 1000110103 指導(dǎo)教師單位： 機(jī)電工程學(xué)院 姓 名： 曹泰山 職 稱： 講 師 2014年 3 月 9 日the technology of microlens array injection moldingabstract injection molding could be used as a mass production technology for microlens arrays. it is of importance, and thus of o

2、ur 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 m

3、aterials (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 res

4、ults 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 c

5、omparable 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 a

6、rrays 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.

7、 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

8、 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 t

9、his 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

10、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 (af

11、m).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

12、 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 i

13、n 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

14、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

15、 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 rep

16、lication 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

17、 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

18、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

19、 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 cour

20、se, 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 p

21、c (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.

22、 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 temperatu

23、re 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 temperatur

24、e 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

25、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 ra

26、dius 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)112.05.010.0212.05.015.031

27、2.05.020.0ps412.02.010.0512.010.010.0618.05.010.0724.05.010.0pmma16.010.010.026.010.015.036.010.020.046.05.010.05676.09.012.015.010.010.010.010.010.0pc 16.05.05.026.05.010.0356.06.09.05.010.015.05.065.05.0712.05.05.04 results and discussionbefore detailed discussion of the experimental results, it m

28、ight 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 t

29、oo 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 tha

30、t 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 resultin

31、g 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.4.1 surface profilesfigure 3 shows typical scanning electron

32、 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).(a)inje

33、ction molded microlensarrays (pmma) (b) injectionmolded microlenses of 300 mdiameter for different materialsfig. 3. sem images of theinjection molded microlensarrays and microlensesas a measure of replicability, we have defined a relative deviation of profile as the height difference between the mol

34、ded 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 (%)1234567ps200300500-7.625.862.38-7.592.03-0.382.082.860.51-5.565.611.47-8.6660161.47-11.444.291

35、.47-9.475.731.95pmma2003005007.205.77-0.661.315.60-1.62-3.886.453.98-5.805.952.80-0.975.95-0.72-8.536.68-0.904.86-2.62-0.72pc20030050023.026.20-0.9316.054.965.0916.872.66-1.8619.664.531.8833.974.786.9618.671.792.43-2.944.15-1.55it may be mentioned that the moldability of polymeric materials affects

36、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

37、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 indi

38、cates 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 condition

39、s 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

40、 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 30

41、0 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

42、 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 th

43、e cavity. therefore, the effect of packing time disappears after a certain time depending on the processing conditions.fig.4ac(leftside).surfce 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)surfac

44、e profiles of microlens (pmma with diameter(/) of 300m). a effect of packing pressure, b effect of flow rate,c effect of packing time4.2 surface roughnessaveraged surface roughness, ra, values of 300 m diameter microlenses and the mold insert were measured by an atomic force microscope (bioscope afm

45、, 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

46、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

47、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.a nickel mold insert, b ps, c pmma, d pcfig. 6. afm images and averaged surface roughness, ra, values of the mold insert and injection molded 30

48、0 m diameter microlenses.4.3 focal 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 we

49、re approximately calculated as 1.065 mm (with r1 0.624 mm and r2 ￥) 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

50、 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.5 conclusionthe replication of microlens arrays was carried out by the

51、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

52、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 mol

53、d 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 t

54、hat of fine optical components in practical use. in this regard, injection molding might be a useful manufacturing tool for mass production of microlensarrays.modern mold technologyintroductionalong with the global economy development, the new technological revolution made the new progress and the b

55、reakthrough unceasingly, the technical leap development already becomes the important attribute which the impetus world economics grew. the market economy unceasing development, urges the industry product more and more to the multi- varieties, high grade, the low cost direction to develop, in order

56、to maintain and strengthens the product in market competitive power, product development cycle, production cycle more and more short, thereupon to makes each kind of product the essential craft equipment mold request to be more and more harsh. on the one hand the enterprise for the pursue scale bene

57、fit, causes the mold to turn towards high speed, is precise, the long life direction develops; on the other hand enterprise in order to satisfy the multi- varieties, the product renewal quickly, wins the market the need, requests the mold to turn towards the manufacture cycle to be short, the cost low fast economy direction develops. the computer, the laser, electronic, the new