Editing Slot Die Head for Solution-processed PV Cells Lit Review

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{{MOST literature review notice}}

Slot die coating is a process used to deposit various liquids onto a substrate. They are prevalent in the manufacturing processes of a wide rage of applications including polymer batteries, sensors, optical coatings, and solar cells. It is considered a pre-metered coating technique, where the volume of liquid deposited is predetermined upstream of the deposition site. Slot die coating is desirable primarily due to it's high speed production capabilities along with it's high accuracy. Because slot die coating is industry scalable, it appears to be the best option to obtain economically sensible solution-processed solar cells.

== Additional Resources / External Links ==

* [http://web.archive.org/web/20180730063811/http://www.plasticphotovoltaics.org:80/lc/lc-fabrication/lc-coating/lc-slotdie.html Slot die coating (plasticphotovoltaics.org)]
* [http://web.archive.org/web/20150616065838/http://www.pstc.org:80/files/public/Miller09.pdf SLOT DIE COATING TECHNOLOGY ]

== Literature Review ==

== PV Applications of Slot Dies ==

===[http://www.sciencedirect.com/science/article/pii/S0927024808004704 Polymer solar cell modules prepared using roll-to-roll methods: Knife-over-edge coating, slot-die coating and screen printing]<ref>[1]
F. C. Krebs, "Polymer solar cell modules prepared using roll-to-roll methods: Knife-over-edge coating, slot-die coating and screen printing," Solar Energy Materials and Solar Cells, vol. 93, no. 4, pp. 465–475, Apr. 2009.</ref>===

'''Abstract''' A complete polymer solar cell module prepared in the ambient atmosphere using all-solution
processing with no vacuum steps and full roll-to-roll (R2R) processing is presented. The modules
comprise five layers that were prepared on a 175-mm flexible polyethyleneterephthalate (PET) substrate
with an 80-nm layer of transparent conducting indium–tin oxide (ITO). The ITO layer was first patterned
by screen printing an etch resist followed by etching. The second layer was applied by either knife-over-
edge (KOE) coating or slot-die coating a solution of zinc oxide nanoparticles (ZnO-nps) followed by
curing. The second layer comprised a mixture of the thermocleavable poly-(3-(2-methylhexan-2-yl)-
oxy-carbonyldithiophene) (P3MHOCT) and ZnO-nps and was applied by a modified slot-die coating
procedure, enabling slow coating speeds with low viscosity and low surface tension ink solutions. The
third layer was patterned into stripes and juxtaposed with the ITO layer. The fourth layer comprised
screen-printed or slot-die-coated PEDOT:PSS and the fifth and the final layer comprised a screen-printed
or slot-die-coated silver electrode. The final module dimensions were 28 cm 32 cm and presented four
individual solar cell modules: a single-stripe cell, a two-stripe serially connected module, a three-stripe
serially connected module and finally an eight-stripe serially connected module. The length of the
individual stripes was 25 cm and the width was 0.9 cm. With overlaps of the individual layers this gave a
width of the active layer of 0.6 cm and an active area for each stripe of 15 cm2
increased ten fold compared to mass-produced modules employing screen printing for all five layers of
the device. The processing speeds employed for the R2R processed layers were in the range of
40–50 m h. Finally a comparison is made with the state of the art represented by P3HT–PCBM as the
active layer and full R2R solution processing using slot-die coating.

* All layers of cell coated via slot die method (steel head)
* Steel slot die head capable of 60nm thicknesses
* Humidity while drying creates slightly uneven surfaces

=== [http://onlinelibrary.wiley.com/doi/10.1002/aenm.201401539/full 3D Printer Based Slot-Die Coater as a Lab-to-Fab Translation Tool for Solution-Processed Solar Cells]<ref>D. Vak, K. Hwang, A. Faulks, Y.-S. Jung, N. Clark, D.-Y. Kim, G. J. Wilson, and S. E. Watkins, "3D Printer Based Slot-Die Coater as a Lab-to-Fab Translation Tool for Solution-Processed Solar Cells," Adv. Energy Mater., vol. 5, no. 4, p. n/a–n/a, Feb. 2015.</ref> ===

'''Abstract''' A 3D printer based slot-die coater is developed as a lab-to-fab translation tool for solution-processed solar cells. The modified 3D printer is used to develop the printing process for potential use in large scale roll-to-roll production. Fabrication of a 47.3 cm2 organic solar cell module with 4.56% efficiency and printed perovskite solar cells with 11.6% efficiency are demonstrated.

* Stainless steel slot die head utilized to prevent issues arising from printing organic solutions
* Consistent films of desired thickness (50-200nm) not easily attainable through control of extrusion rate
* To obtain desired thickness, slot die head speed was manipulated

=== [http://apps.webofknowledge.com/InboundService.do?SID=3FfjifeCk1ZMtnxd87r&product=WOS&UT=WOS%3A000318911000024&SrcApp=Wiley_Online_Library&DestFail=http%3A%2F%2Fwww.webofknowledge.com&Init=Yes&action=retrieve&SrcAuth=LinksAMR&customersID=LinksAMR&Func=Frame&IsProductCode=Yes&mode=FullRecord Dependence of opto-electric properties of (semi-)conducting films in polymer based solar cells on viscous shear during the coating process]<ref>L. Wengeler, R. Diehm, P. Scharfer, and W. Schabel, "Dependence of opto-electric properties of (semi-)conducting films in polymer based solar cells on viscous shear during the coating process," Org. Electron., vol. 14, no. 6, pp. 1608–1613, Jun. 2013.</ref> ===

'''Abstract''' Organic photovoltaic is a promising technology for low-cost energy conversion. One of its
major challenges is the transfer of the manufacturing process to a continuous roll-to-roll
process. Previous research showed that the coating method has a significant impact on film
properties, which may be explained by a shear-rate induced crystallization of the polymer–
fullerene-blend.
In this paper we report on a controlled variation of the shear-rate during slot-die coating
of photoactive and conductive layers for polymer solar cells. Light absorption of photoactive
layers increased towards higher coating speed and thus higher shear-rate by up to 28%
from 0.6 m/min to 12 m/min. The currently lower performance of roll-to-roll processed
solar cells, compared to laboratory scale devices may be increased by intentionally applying
a high shear rate during the coating process. In contrast, a shear induced crystallization
is insignificant for conductive (PEDEOT:PSS and Ag-nanoparticle) films, where conductivity
decreased when the operating point approached the stability limit. Thus, a low capillary
number is desirable for PEDOT:PSS layers, whereas the performance of the photoactive
layer increased within the investigated velocity range. These tendencies, shown here for
a standard material system (P3HT:PCBM), are substantial for the design of a roll-to-roll
process for efficient polymer solar cells.

* Covers effect of drying rate and coating speed on light absorption
* Coating method dictates many properties of cell
* May not be useful due to different type of cells being constructed

=== [http://www.sciencedirect.com/science/article/pii/S0927024810006689 ITO-free flexible inverted organic solar cell modules with high fill factor prepared by slot die coating]<ref>N. M. Sammes, S. Vohora, and A. M. Cartner, "Swelling parameter of polypropylene used in household appliances," JOURNAL OF MATERIALS SCIENCE, vol. 29, no. 23, pp. 6255–6258, Jan. 1994.</ref> ===

'''Abstract''' A complete polymer solar cell module prepared in the ambient atmosphere using all-solution processing with no vacuum steps and full roll-to-roll (R2R) processing is presented. The modules comprise five layers that were prepared on a 175-μm flexible polyethyleneterephthalate (PET) substrate with an 80-nm layer of transparent conducting indium–tin oxide (ITO). The ITO layer was first patterned by screen printing an etch resist followed by etching. The second layer was applied by either knife-over-edge (KOE) coating or slot-die coating a solution of zinc oxide nanoparticles (ZnO-nps) followed by curing. The second layer comprised a mixture of the thermocleavable poly-(3-(2-methylhexan-2-yl)-oxy-carbonyldithiophene) (P3MHOCT) and ZnO-nps and was applied by a modified slot-die coating procedure, enabling slow coating speeds with low viscosity and low surface tension ink solutions. The third layer was patterned into stripes and juxtaposed with the ITO layer. The fourth layer comprised screen-printed or slot-die-coated PEDOT:PSS and the fifth and the final layer comprised a screen-printed or slot-die-coated silver electrode. The final module dimensions were 28 cm×32 cm and presented four individual solar cell modules: a single-stripe cell, a two-stripe serially connected module, a three-stripe serially connected module and finally an eight-stripe serially connected module. The length of the individual stripes was 25 cm and the width was 0.9 cm. With overlaps of the individual layers this gave a width of the active layer of 0.6 cm and an active area for each stripe of 15 cm2. The performance was increased ten fold compared to mass-produced modules employing screen printing for all five layers of the device. The processing speeds employed for the R2R processed layers were in the range of 40–50 m h−1. Finally a comparison is made with the state of the art represented by P3HT–PCBM as the active layer and full R2R solution processing using slot-die coating.

* Steel slot die head utilized
* 100nm film thicknesses obtained
* Successfully printed cells on large scale

=== [http://onlinelibrary.wiley.com/doi/10.1002/adma.201404598/abstract Toward Large Scale Roll-to-Roll Production of Fully Printed Perovskite Solar Cells]<ref>K. Hwang, Y.-S. Jung, Y.-J. Heo, F. H. Scholes, S. E. Watkins, J. Subbiah, D. J. Jones, D.-Y. Kim, and D. Vak, "Toward Large Scale Roll-to-Roll Production of Fully Printed Perovskite Solar Cells," Adv. Mater., vol. 27, no. 7, pp. 1241–1247, Feb. 2015.</ref> ===

'''Abstract''' Fully printed perovskite solar cells are demonstrated with slot-die coating, a scalable printing method. A sequential slot-die coating process is developed to produce efficient perovskite solar cells and to be used in a large-scale roll-to-roll printing process. All layers excluding the electrodes are printed and devices demonstrate up to 11.96% power conversion efficiency. It is also demonstrated that the new process can be used in roll-to-roll production.

* Nitrogen used to cool PbI2 immediately after deposition to create more uniform layers
* Obtained coating thicknesses of 20nm via slot die (steel)- ZnO layer
* Perovskite formed by reaction on substrate with 2 separate layers reacting (MAI + PbI2)

=== [http://onlinelibrary.wiley.com/doi/10.1002/adma.201404040/full Fast Printing and In Situ Morphology Observation of Organic Photovoltaics Using Slot-Die Coating]<ref>F. Liu, S. Ferdous, E. Schaible, A. Hexemer, M. Church, X. Ding, C. Wang, and T. P. Russell, "Fast Printing and In Situ Morphology Observation of Organic Photovoltaics Using Slot-Die Coating," Adv. Mater., vol. 27, no. 5, pp. 886–891, Feb. 2015.</ref> ===

'''Abstract''' The mini-slot-die coater offers a simple, convenient, materials-efficient route to print bulk-heterojunction (BHJ) organic photovoltaics (OPVs) that show efficiencies similar to spin-coating. Grazing-incidence X-ray diffraction (GIXD) and GI small-angle X-ray scattering (GISAXS) methods are used in real time to characterize the active-layer formation during printing. A polymer-aggregation–phase-separation–crystallization mechanism for the evolution of the morphology describes the observations.

* Film thickness adjusted by altering temperature, solution concentration, substrate slot die distance, and slot die head speed
* Tuned parameters yielded consistent layers of 100nm
* Mini slot die head (steel) utilized

=== [http://onlinelibrary.wiley.com/doi/10.1002/ente.201500150/full Roll-to-Roll Slot–Die Coated Organic Photovoltaic (OPV) Modules with High Geometrical Fill Factors]<ref>Y. Galagan, H. Fledderus, H. Gorter, H. H. 't Mannetje, S. Shanmugam, R. Mandamparambil, J. Bosman, J.-E. J. M. Rubingh, J.-P. Teunissen, A. Salem, I. G. de Vries, R. Andriessen, and W. A. Groen, "Roll-to-Roll Slot–Die Coated Organic Photovoltaic (OPV) Modules with High Geometrical Fill Factors," Energy Technology, vol. 3, no. 8, pp. 834–842, Aug. 2015.</ref> ===

'''Abstract'''Flexible semi-transparent organic photovoltaic (OPV) modules were manufactured by roll-to-roll slot–die coating of three functional layers [ZnO, photoactive layer, and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)] and either the screen printing or inkjet printing of the top electrodes. A poly(3-hexylthiophene):[6,6] phenyl C61-butyric acid methyl ester (P3HT:PCBM) layer deposited from non-chlorinated solvents was used as the absorber layer. The modules were realized by slot–die coating of the layers onto a laser-patterned polyethylene terephthalate/indium-tin oxide (PET/ITO) substrate, followed by laser structuring of all coated layers. The top electrodes were realized by high-resolution printing, which, combined with laser patterning of other layers, enables manufacturing of the modules with high geometrical fill factor (92.5 %). The modules have an active area of 156 cm2, and contain 13 serially interconnected cells. Two semitransparent electrodes (ITO from the bottom and PEDOT:PSS/Ag-grid from the top side) allow the absorption of photons incident from both sides. The performance of the modules was evaluated and compared among the modules by considering the following factors: (i) roll-to-roll slot–die coated vs. spin-coated layers, (ii) inkjet-printed vs. screen-printed top electrodes, (iii) top vs. bottom illumination. The demonstrated technology is one of the proven feasible ways towards industrial manufacturing of the OPV modules.

* Layer thickness if 60 nm archived via steel slot die
* 3 layers deposited via slot die (PEDOT:PSS, ZnO, and photoactive layer)

=== [http://www.sciencedirect.com/science/article/pii/S1566119909000780 All solution roll-to-roll processed polymer solar cells free from indium-tin-oxide and vacuum coating steps]<ref>F. C. Krebs, "All solution roll-to-roll processed polymer solar cells free from indium-tin-oxide and vacuum coating steps," Organic Electronics, vol. 10, no. 5, pp. 761–768, Aug. 2009.</ref> ===

'''Abstract''' A roll-to-roll process enabling fabrication of polymer solar cells comprising five layers on flexible substrates is presented. The device geometry is inverted and allow for fabrication on both transparent and non-transparent flexible substrates. The process is illustrated in this work by formation of a bottom electrode comprising silver nanoparticles on a 130 micron thick polyethyleneternaphthalate (PEN) substrate. Subsequently an electron transporting layer of zinc oxide nanoparticles was applied from solution followed by an active layer of P3HT-PCBM and a hole transporting layer of PEDOT:PSS. These first four layers were applied by slot-die coating. The final electrode was applied by screen printing a grid structure that allowed for transmission of 80% of the light. The materials were patterned into stripes allowing for formation of a single cell device and serially connected modules comprising 2, 3 and 8 stripes. All five layers in the device were processed from solution in air and no vacuum steps were employed. An additional advantage is that the use of indium-tin-oxide (ITO) is avoided in this process. The devices were tested under simulated sunlight (1000 W m−2, AM1.5G) and gave a typical performance 0.3% in terms of power conversion efficiency (PCE) for the active layer. The low PCE was due to poor transmission of light through the back electrode.

* Obtained coating thicknesses of 100nm via slot die (steel)
* TiO2 and SiO2 layers deposited
* Solution concentration vs viscosity discussed

=== [http://www.sciencedirect.com/science/article/pii/S1369702112700196 Roll-to-roll fabrication of polymer solar cells]<ref>R. Søndergaard, M. Hösel, D. Angmo, T. T. Larsen-Olsen, and F. C. Krebs, "Roll-to-roll fabrication of polymer solar cells," Materials Today, vol. 15, no. 1–2, pp. 36–49, Jan. 2012.</ref> ===

'''Abstract''' As the performance in terms of power conversion efficiency and operational stability for polymer and organic solar cells is rapidly approaching the key 10–10 targets (10 % efficiency and 10 years of stability) the quest for efficient, scalable, and rational processing methods has begun. The 10–10 targets are being approached through consistent laboratory research efforts, which coupled with early commercial efforts have resulted in a fast moving research field and the dawning of a new industry. We review the roll-to-roll processing techniques required to bring the magnificent 10–10 targets into reality, using quick methods with low environmental impact and low cost. We also highlight some new targets related to processing speed, materials, and environmental impact.

* Double slot die coatings have been used to deposit 2 layers simultaneously
* Currently able to produce fill factors of 45–67 %

=== [http://www.sciencedirect.com/science/article/pii/S0255270110002874 Investigations on knife and slot die coating and processing of polymer nanoparticle films for hybrid polymer solar cells]<ref>L. Wengeler, B. Schmidt-Hansberg, K. Peters, P. Scharfer, and W. Schabel, "Investigations on knife and slot die coating and processing of polymer nanoparticle films for hybrid polymer solar cells," Chemical Engineering and Processing: Process Intensification, vol. 50, no. 5–6, pp. 478–482, May 2011.</ref> ===

'''Abstract''' Hybrid solar cells have a high potential to become an inexpensive alternative to conventional photovoltaic. Their major advantage is the possibility to produce them by solvent based deposition in a cost efficient roll to roll (R2R) process. Due to their high optical absorption, high conductivity, tunable particle size and shape they could proof superior to fullerenes. Currently all hybrid cells are produced by spin-coating on laboratory scale. Coating technologies for pilot scale production are discussed. We present an experimental setup that was designed to investigate the coating and drying of hybrid layers with roll to roll compatible methods. Specific problems of processing semiconducting nanoparticle/polymer films such as minimization of hold-up are addressed. First results indicate that the processing conditions determine not only the morphology of the film but also its optoelectric properties such as light absorption, conductivity and eventually cell efficiency. Finally, we can report the preparation of knife and slot die coated hybrid solar cells with up to 1.18% PCE for knife coated devices.

* Discusses the design of the slot die utilized
* Self designed and manufactured
* Produces wet film thicknesses of 5-100µm
* Die cavity volume of 2ml
* Yielded layers ~30nm thick

=== [http://www.sciencedirect.com/science/article/pii/S0927024808003486 Fabrication and processing of polymer solar cells: A review of printing and coating techniques]<ref>F. C. Krebs, "Fabrication and processing of polymer solar cells: A review of printing and coating techniques," Solar Energy Materials and Solar Cells, vol. 93, no. 4, pp. 394–412, Apr. 2009.</ref> ===

'''Abstract''' Polymer solar cells are reviewed in the context of the processing techniques leading to complete devices. A distinction is made between the film-forming techniques that are used currently such as spincoating, doctor blading and casting and the, from a processing point of view, more desirable film-forming techniques such as slot-die coating, gravure coating, knife-over-edge coating, off-set coating, spray coating and printing techniques such as ink jet printing, pad printing and screen printing. The former are used almost exclusively and are not suited for high-volume production whereas the latter are highly suited, but little explored in the context of polymer solar cells. A further distinction is made between printing and coating when a film is formed. The entire process leading to polymer solar cells is broken down into the individual steps and the available techniques and materials for each step are described with focus on the particular advantages and disadvantages associated with each case.

* Typical mask thicknesses range from 10-100µm
* Masks below 20µm and above 50µm become difficult to work with
* Paper discusses polymer solar cells, dimensions may vary with the use of perovskites

=== [http://pubs.rsc.org/en/content/articlehtml/2014/tc/c4tc00817k Organic semiconducting layers fabricated by self-metered slot-die coating for solution-processable organic light-emitting devices]<ref>B. Park, O. E. Kwon, S. H. Yun, H. G. Jeon, and Y. H. Huh, "Organic semiconducting layers fabricated by self-metered slot-die coating for solution-processable organic light-emitting devices," J. Mater. Chem. C, vol. 2, no. 40, pp. 8614–8621, Aug. 2014.</ref> ===

'''Abstract''' We present the results of a study of flat, uniform, and stripe-patternable organic semiconducting layers produced by a slot-die coating method using a self-metered coating mode with blended solutions for the fabrication of bright, efficient, and large-area organic light emitting devices (OLEDs). It is shown that the self-metered slot-die coating process can produce high quality, homogeneous, and stripe-patterned thin films using the downstream meniscus of a blended solution, which can be controlled by adjusting the coating parameters of the capillary number of the coating solution by varying the gap height and coating speed. It is shown that very bright and efficient OLEDs (peak brightness ∼50[thin space (1/6-em)]000 cd m−2 with maximum efficiencies of ∼29 cd A−1 and ∼14 lm W−1) were successfully demonstrated by manipulating the slot-die coated hole-injecting and electroluminescent layers that contained the phosphorescent Ir complex. In view of these results, we believe that the fabrication of organic semiconducting layers using the self-metered slot-die coating process is a promising new technique for high-throughput manufacturing such as via the roll-to-roll process.

* Provides equations for layer thickness relating viscosity, surface tension, and meniscus radius
* The most effective way to alter coating thickness is to change the capillary number (Viscosity*Speed / Surface tension)

== Slot Die Geometries ==

=== [http://link.springer.com/article/10.1007/s11814-015-0079-x Effect of flow rate variation on the frequency response in slot coating process with different upstream sloped die geometries]<ref>W.-G. Ahn, S. H. Lee, J. Nam, and H. W. Jung, "Effect of flow rate variation on the frequency response in slot coating process with different upstream sloped die geometries," Korean J. Chem. Eng., vol. 32, no. 7, pp. 1218–1221, Jun. 2015.</ref> ===

'''Abstract''' The sensitivity of slot coating process with different sloped upstream die configurations has been investigated using the viscocapillary model for a coating liquid with constant viscosity (Newtonian) through frequency response technique. Amplitude ratios of coating thickness with respect to a sinusoidal disturbance at flow rate are compared under different input frequency and upstream die lip angle conditions. Amplitude ratio values decrease as the upstream die lip angle increases, implying that the coating system is less sensitive to the given disturbance due to the larger space condition in the upstream die region. Amplitude ratio curves obtained from various conditions can be usefully unified in a single one with the help of new dimensionless time between fluid time scale in upstream region and perturbed time scale by input frequency.

* Explores effect of tip angle on layer uniformity
* More positive angles typically yield fewer errors

=== [http://onlinelibrary.wiley.com/doi/10.1002/aic.15187/full Coupled fluid-particle modeling of a slot die coating system]<ref>V. Akbarzadeh and A. N. Hrymak, "Coupled fluid-particle modeling of a slot die coating system," AIChE J., vol. 62, no. 6, pp. 1933–1939, Jun. 2016.</ref> ===

'''Abstract''' This work seeks to develop a fundamental understanding of particle motion in the slot die coating process through studying the interaction of forces between particles, with the die walls and the fluid phase. Coupled computational fluid dynamics and the discrete element method is employed for evaluating the motion of individual suspended particles near moving surfaces in a complex three-dimensional flow field, motivated by the flow of particle laden fluid in a slot die coating system, including the presence of free surfaces. Overall, the particles follow the flow streamlines and their final position in the coating depends on the initial entry region of the particles. Particles experiencing adhesion with each other agglomerate in the low velocity regions of the coating gap, and have long residence times near the edge of the die at the end of the feed slot in the coating gap. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1933–1939, 2016

* Explores entry region of slot die
* A feed gap equal to the coating gap provides a more uniform particle distribution than a narrower feed gap.

=== [https://www.jstage.jst.go.jp/article/rheology/30/4/30_4_179/_article Study of the Flow in a Dual Cavity Slot Die]<ref>T. Tsuda, T. Hasegawa, and T. Narumi, "Study of the Flow in a Dual Cavity Slot Die," Nihon Reoroji Gakkaishi, vol. 30, no. 4, pp. 179–185, 2002.</ref> ===

'''Abstract''' One-dimensional flow model for non-Newtonian fluids in a dual cavity slot die is presented. The viscosity of non-Newtonian fluids is treated as the Ellis model. The conservation equations of mass and momentum in a dual-cavity slot die are one-dimensionally simplified by assuming an appropriate mean flow over the cross section of the flow. The flow field in the slot is assumed to be fully developed. The equations of flow for the cavity and the slot are derived separately and then coupled. We use a finite difference method to solve these governing equations. Using this model, we find that the location and the cross-section area of a secondary cavity have large effects on the distribution of outlet flow. It is concluded that the dual cavity die can effectively reduce the flow non-uniformity.

* Explores inner geometry of slot die
* Possible methods to increase layer uniformity include dual cavity and clothes hanger geometry

=== [http://www.sciencedirect.com/science/article/pii/S002197970601099X Three minimum wet thickness regions of slot die coating]<ref>. Y.-R. Chang, H.-M. Chang, C.-F. Lin, T.-J. Liu, and P.-Y. Wu, "Three minimum wet thickness regions of slot die coating," Journal of Colloid and Interface Science, vol. 308, no. 1, pp. 222–230, Apr. 2007.</ref> ===

'''Abstract''' An experimental study was carried out to determine the minimum wet thickness of slot die coating for low-viscosity solutions. There exist three
distinct coating regions (I, II, and III), depending on the physical properties of the coating fluid, die geometry, and flow conditions. A critical
Reynolds number was found, below which viscous and surface tension effects are important. In Region I, the minimum wet thickness increases
with increasing capillary number and becomes independent of capillary number in Region II. Region III exists above the critical Reynolds number
where fluid inertia is dominant. In this region, the minimum wet thickness decreases as Reynolds number increases. Flow visualization on the
coating bead reveals that the position of the downstream meniscus of the coating bead determines the types of coating region, whereas the shape
and position of the upstream meniscus determine the type of coating defects. It was also observed that the downstream meniscus was not located
at the die lip corner and both the static and dynamic contact angles varied under different conditions. These findings are critical for realistic
theoretical study of slot die coating.

* Presents the minimum wet film thickness that can be yielded from various solutions
* Points out that viscosity is the most important factor contributing to film thickness
* Explores different slot die geometries to determine optimum configuration

=== [http://link.springer.com/10.1007/978-94-011-5342-3 Liquid Film Coating]<ref>S. F. Kistler and P. M. Schweizer, Eds., Liquid Film Coating. Dordrecht: Springer Netherlands, 1997.</ref> ===

* Covers a wide range of coating processes
* Provides in depth information on slot die geometries
* Gives optimum coating conditions and variables

=== [http://link.springer.com/article/10.1007/BF02705652 Three-dimensional modelling of Non-Newtonian fluid flow in a coat-hanger die]<ref>S. Y. Na and D. H. Kim, "Three-dimensional modelling of Non-Newtonian fluid flow in a coat-hanger die," Korean J. Chem. Eng., vol. 12, no. 2, pp. 236–243, Apr. 1995.</ref> ===

'''Abstract''' The three-dimensional model of isothermal flow of power-law fluid in a coat-hanger die has been developed using finite element method. The shape of coat-hanger die used in the present model was determined according to the previous analytical design equation which is based on one-dimensional flow model in the manifold and the slot. Because uniform flow rate across the die outlet is most important to achieve uniform thickness of extruded polymer sheet or film, flow rate distribution is mainly examined to determine the valid process condition for the design equation as the design parameters are changed. The effects of fluid property in terms of power-law index and process parameters not considered in one-dimensional design equation such as die inlet size and the presence of land were analyzed. Results show that the manifold angle is the most influencing design parameter on flow rate distribution. When the material of different power-law index from design value is processed, the change of power-law index affects the uniformity of flow rate appreciably.

* Briefly compares internal manifolds of "T" and "coat hanger" slot dies
* Explores the fluid flow through "coat hanger" dies

=== [http://onlinelibrary.wiley.com/doi/10.1002/adv.20173/abstract Operating windows of slot die coating: Comparison of theoretical predictions with experimental observations]<ref>C.-F. Lin, D. S. Hill Wong, T.-J. Liu, and P.-Y. Wu, "Operating windows of slot die coating: Comparison of theoretical predictions with experimental observations," Adv. Polym. Technol., vol. 29, no. 1, pp. 31–44, Mar. 2010.</ref> ===

'''Abstract''' The objective of the present study is to examine the validity of the theoretical predictions on the operating windows of slot die coating. The operating window is defined as a domain inside which stable and uniform coating is possible; different types of coating defects are found outside the window. A flow visualization technique was applied to observe the coating bead, particularly the positions and shapes of the downstream and upstream menisci, just before and after coating defects appear at high coating speeds. Special features of coating bead shapes, which lead to onsets of ribbing and air entrainment, were identified. The two-dimensional flow in the coating bead region was computed by the commercial software package FLOW-3D®. Critical features observed experimentally for the onset of coating defects were used to judge whether the coating flow was within the operating window. The theoretically evaluated operating windows were found to be much larger than those determined experimentally in terms of coating speeds. However, the qualitative trends of theoretical predictions agree with experimental observations. © 2010 Wiley Periodicals, Inc. Adv Polym Techn 29:31–44, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20173

* Provides slot die dimensions

=== [http://link.springer.com/article/10.1007/s11814-015-0079-x, Effect of flow rate variation on the frequency response in slot coating process with different upstream sloped die geometries ]<ref>Ahn, W. G., Lee, S. H., Nam, J., & Jung, H. W. (2015). Effect of flow rate variation on the frequency response in slot coating process with different upstream sloped die geometries. Korean Journal of Chemical Engineering, 32(7), 1218-1221., "http://onlinelibrary.wiley.com/doi/10.1002/pen.760291513/abstract" Adv. Polym. Technol., vol. 29, no. 1, pp. 31–44, Mar. 2010.</ref> ===

'''Abstract''' The sensitivity of slot coating process with different sloped upstream die configurations has been investigated using the viscocapillary model for a coating liquid with constant viscosity (Newtonian) through frequency response technique. Amplitude ratios of coating thickness with respect to a sinusoidal disturbance at flow rate are compared under different input frequency and upstream die lip angle conditions. Amplitude ratio values decrease as the upstream die lip angle increases, implying that the coating system is less sensitive to the given disturbance due to the larger space condition in the upstream die region. Amplitude ratio curves obtained from various conditions can be usefully unified in a single one with the help of new dimensionless time between fluid time scale in upstream region and perturbed time scale by input frequency.

* Discusses the effect of various tip angles on coating quality

=== [http://onlinelibrary.wiley.com/doi/10.1002/pen.760291513/abstract, Design and analysis of a dual-cavity coat-hanger die]<ref>Lee, K. Y., & Liu, T. J. (1989). Design and analysis of a dual‐cavity coat‐hanger die. Polymer Engineering & Science, 29(15), 1066-1075.</ref> ===

'''Abstract''' A method for the design and analysis of a dual-cavity coat-hanger die is presented in this paper. A macroscopic material balance and a microscopic flow analysis using the finite element method are combined to simulate polymeric fluid flow inside the die. Leonard's macroscopic procedure was adopted to include inertial, gravitational, and viscous effects, and the finite element method was then applied to estimate the contributions of inertial and viscous terms. In addition, the flow patterns in the outer cavity were computed by the finite element method so that the appearance of an undesirable vortex could be predicted. The residence time distributions for flow in the die were approximated by a simple, statistical approach. It was found through a case study that a dual-cavity coathanger die can effectively reduce the flow non-uniformities caused by fluid inertia and viscosity variations.

* Design and performance of dual cavity slot dies is discussed.

=== [http://onlinelibrary.wiley.com/doi/10.1002/adv.1987.060070107/abstract, Aspects of the design of coathanger dies for cast film and sheet applications]<ref>Helmy, H. (1987). Aspects of the design of coathanger dies for cast film and sheet applications. Advances in Polymer Technology, 7(1), 59-69.</ref> ===

* Briefly describes adjustable lips

== Possible Slot Die Material ==

=== [http://onlinelibrary.wiley.com/doi/10.1002/pol.1970.150080519/abstract Analysis of nonvolatile oxidation products of polypropylene. II. Process degradation]<ref>J. H. Adams and J. E. Goodrich, "Analysis of nonvolatile oxidation products of polypropylene. II. Process degradation," J. Polym. Sci. A-1 Polym. Chem., vol. 8, no. 5, pp. 1269–1277, May 1970.</ref> ===

'''Abstract''' The nonvolatile products of polypropylene that has been process degraded in the melt by a Brabender torque rheometer have been quantitatively identified by infrared analysis and chemical reactions carried out on molded sheets. The molecular weight changes with degradation have been determined by gel-permeation chromatography (GPC). It was determined that there is only one functional group per chain scission instead of the two groups previously found for thermal oxidation in the solid state. The molecular weight distribution is similar, but the functional groups and the general scheme of oxidation differ slightly from those previously found for polyolefin oxidation carried out below the melting point. The functional group distribution differs from that determined in a process-degraded polyethylene sample.

* Polypropylene will not dissolve into Isopropanol
* May prove to be viable material for slot die head

=== [http://link.springer.com/article/10.1007%2FBF00354568 Swelling parameter of polypropylene used in household appliances]<ref>N. M. Sammes, S. Vohora, and A. M. Cartner, "Swelling parameter of polypropylene used in household appliances," JOURNAL OF MATERIALS SCIENCE, vol. 29, no. 23, pp. 6255–6258, Jan. 1994.</ref> ===

'''Abstract''' Samples of unfilled copolymer polypropylene were immersed in various solvents and the equilibrium swelling was recorded. Two-dimensional solubility maps of the Hildebrand parameter, δ, versus hydrogen bonding parameter, γc, and δh versus δv for polypropylene were plotted. Using the calculated percentage swell values and the solubility maps, the δ and δh values for detergent were postulated. No changes in the polypropylene backbone were revealed by mid- or far-infrared spectra, showing that the polypropylene polymer, when subjected to a number of different solvents, had not altered substantially.

* Polypropylene swelling was characterized
* Polypropylene showed high resistance to swelling when subjected to various solvents

=== [http://www.sciencedirect.com/science/article/pii/S0264127515004037 Fused deposition modeling with polypropylene]<ref>O. S. Carneiro, A. F. Silva, and R. Gomes, "Fused deposition modeling with polypropylene," Materials & Design, vol. 83, pp. 768–776, Oct. 2015.</ref> ===

'''Abstract''' This paper addresses the potential of polypropylene (PP) as a candidate for fused deposition modeling (FDM)-based 3D printing technique. The entire filament production chain is evaluated, starting with the PP pellets, filament production by extrusion and test samples printing. This strategy enables a true comparison between parts printed with parts manufactured by compression molding, using the same grade of raw material. Printed samples were mechanically characterized and the influence of filament orientation, layer thickness, infill degree and material was assessed. Regarding the latter, two grades of PP were evaluated: a glass-fiber reinforced and a neat, non-reinforced, one. The results showed the potential of the FDM to compete with conventional techniques, especially for the production of small series of parts/components; also, it was showed that this technique allows the production of parts with adequate mechanical performance and, therefore, does not need to be restricted to the production of mockups and prototypes.

* The use of polypropylene as a FDM filament is explored
* PP has a relatively high coefficient of shrinkage

=== [http://www.sciencedirect.com/science/article/pii/S0261306903002292 Determination of optimum cutting parameters during machining of AISI 304 austenitic stainless steel]<ref>I. Korkut, M. Kasap, I. Ciftci, and U. Seker, "Determination of optimum cutting parameters during machining of AISI 304 austenitic stainless steel," Materials & Design, vol. 25, no. 4, pp. 303–305, Jun. 2004.</ref> ===

'''Abstract''' High strength, low thermal conductivity, high ductility and high work hardening tendency of austenitic stainless steels are the main factors that make their machinability difficult. In this study determination of the optimum cutting speed has been aimed when turning an AISI 304 austenitic stainless steel using cemented carbide cutting tools. The influence of cutting speed on tool wear and surface roughness was investigated. A decrease in tool wear was observed with increasing the cutting speed up to 180 m/min. Surface roughness (Ra) was also decreased with increasing the cutting speed. Correlation was made between the tool wear/surface roughness and the chips obtained at the three cutting speeds of 120, 150 and 180 m/min.

* Notes stainless steel is difficult to machine for variety of reasons

== Reference ==

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[[Category:MOST literature reviews]]