HK1173474A - Loaded film cassette for gaseous vapor deposition - Google Patents

Description

Load film cassette for gas vapor deposition

Cross Reference to Related Applications

The subject matter disclosed herein is disclosed in and claimed by the claims of the following co-pending patent applications, all filed concurrently herewith and assigned to the assignee of the present invention:

a film cassette (CL-4584) for gas vapor deposition;

a method (CL-4819) of manufacturing a film cassette for gas vapor deposition;

an apparatus for gas vapour deposition (CL-4821);

an apparatus and method (CL-4820) for loading a film cassette for gas vapor deposition; and

an apparatus and method (CL-4822) for unloading a film cassette for gas vapor deposition.

Background

Field of the invention the present invention relates to a film cassette for supporting a film substrate during a gas vapour deposition process, a method for manufacturing said cassette, an apparatus for depositing one or more materials on a substrate using a gas vapour deposition method, and an apparatus and method for loading and unloading said cassette.

Description of the prior art to manufacture a popular thin film photovoltaic module, a roll of ultra-barrier film is required to have an industrial length (about 10-200 meters or more) and a width of about 350-1650 mm. An acceptable ultra-barrier film should be capable of limiting the water vapor transmission rate of water vapor and/or oxygen into the photovoltaic layer of a thin film photovoltaic module to less than 5 x 10^-4g-H₂O/m²Day(s). The ingress of water vapor or oxygen is detrimental because it tends to rapidly destroy the photovoltaic layer of the module.

Currently, the roll-to-roll process is used to produce water vapor transmission rates as low as only 10^-3g-H₂O/m²Day coating films (e.g. bags for edible snack products) are possible. It has been demonstrated that efforts to manufacture ultra-barrier films for Organic Light Emitting Diodes (OLEDs) using efficient roll-to-roll techniquesCommercial length rolls have not been successful, far short of the threshold required for films that exhibit super-barrier utility (5X 10)^-4g-H₂O/m²-day units).

In previous efforts to roll-to-roll manufacture coated ultra-barrier films for OLEDs, a material was deposited onto the surface of a film substrate using chemical or gas vapor deposition, such as a process known as atomic layer deposition. During previous roll-to-roll manufacturing attempts, the process roll was in contact against the entire surface of the substrate, creating surface scratches on the substrate. Furthermore, as the substrate is guided from one roll to another, the substrate undergoes significant bending, thereby creating additional cracks throughout the deposited barrier coating. Such scratches, abrasions, creases or cracks destroy the ability of any deposited barrier coating to resist the ingress of moisture or oxygen.

Film cassettes capable of supporting silver halide films of various lengths (typically between 35-100mm in width) during chemical batch development are known in the photographic arts. Such cartridges typically support the film to be developed in a spiral fashion. In a spiral wound cassette, the film being processed is held edgewise in the spiral groove of the cassette without contact with the surface of the film. Representative of such prior art film cassettes are metal cassettes sold by Hewes Photographic Equipment manufacturers (Bedfordshire, England) and plastic cassettes sold by Paterson Photographic Limited (west midlands, England).

However, there are difficulties in measuring either metal wire (stainless steel) or commonly used plastic spiral cassettes for films having a width greater than 100 mm.

While the high rib pitch to spoke spacing ratio (about 2.5-6.5%) of these silver halide cassettes is ideal for allowing the processing solution to penetrate into the spaces between the turns of spirally wound film stock, such a high pitch to spoke spacing ratio is very inefficient for industrial rolls used to process ultra-barrier films. Only a small piece of film can be carried on the cassette at such a high pitch to spoke spacing ratio.

It has proven difficult to process wire cassettes and cryogenic plastic cassettes wider than 100mm because small variations in the flow lines on the wound/welded wire or injection molded plastic cassettes can cause distortion of the end plates. These structural distortions will make the membrane difficult to load. The film will also have a tendency to fall off the spiral groove.

Although wire cassettes can take the relatively rough processing regime of vapor deposition, their symmetrical rib geometry (aspect ratio 1: 1) does not have sufficient rib pitch to maintain film width as it expands from room temperature to processing temperature, especially for rib pitches less than about 6 mm. Plastic cassettes distort under the relatively rough processing conditions of vapor deposition, which conditions greatly exceed the heat distortion temperature of the plastic. In addition, the self-threading nature of some cassettes creates debris as the film substrate slides along the flexible plastic ribs of the cassette.

Thus, in light of the foregoing, it is believed to be advantageous to provide a film cassette capable of edgewise supporting an industrial length roll of spirally wound film substrate during a vapor deposition process to minimize scratching of the film surface during processing and the risk of creasing or cracking of the film or coating during loading and unloading, thereby enabling the manufacture of an industrial length ultra-barrier film.

Summary of The Invention

In one aspect, the present invention relates to a cassette for supporting a length of a film substrate during a gas vapor deposition process. The cassette includes a central shaft having first and second end plates mounted thereon. Each end plate includes a central hub from which radiate a plurality of angularly spaced spokes. The spokes have an inner surface that lies on a reference plane oriented substantially perpendicular to the axis of the shaft. The inner surfaces of the spokes are disposed in facing relation and spaced apart by a predetermined inter-spoke spacing defined between the reference surfaces.

Each end plate has a helical rib mounted thereon to the inner surface of the spoke. Each helical rib has a predetermined number of evenly spaced turns and a predetermined pitch associated therewith. The spaces between adjacent turns of the helical ribs define helical grooves on each end plate that can receive the edges of the membrane.

Each rib has a cross-sectional configuration in a radial plane containing the axis of the shaft. The cross-sectional configuration has a substantially linear major edge. Each rib exhibits a predetermined width dimension, a predetermined average thickness dimension, and a width to thickness aspect ratio of at least 2: 1. In one embodiment, the cross-sectional configuration of the rib is generally rectangular and may further include a flow spoiler at a free end thereof. In an alternative embodiment, the cross-sectional configuration of each rib is generally wedge-shaped.

The spacing between the spokes is at least three hundred millimeters (300mm) and is also greater than the width dimension exhibited by the film substrate at the vapor deposition temperature. The ribs have a width dimension on each end plate of between about 0.5% and about 2.0% of the interspoke spacing.

In other aspects, the invention relates to a cassette loaded with a predetermined length of a membrane substrate and to a vapour deposition apparatus having an insert in which the loaded cassette is received.

In yet other aspects, the present invention relates to an apparatus and method for loading a film cassette and to an apparatus and method for unloading a film cassette and immediately laminating it to a protective cover sheet.

Brief Description of Drawings

The present invention will be more fully understood from the following detailed description of the invention taken together with the accompanying drawings which form a part of this patent application, in which:

FIG. 1 is a stylized, diagrammatic illustration of an apparatus for coating a film substrate using a gaseous fluid vapor deposition method with a film cassette in accordance with the present invention;

FIG. 2 is a front view of an optional diffuser plate for use in the vapor deposition apparatus of FIG. 1;

FIG. 3 is a cross-sectional view taken along section line 3-3 of FIGS. 1 and 4 showing a membrane cassette according to the present invention for supporting a length of membrane substrate during exposure to gaseous fluids;

FIG. 4 is an elevation view taken along line 4-4 of FIG. 3;

FIG. 5 is a cross-sectional view taken along section line 5-5 in FIG. 4, showing the edges of the membrane substrate received by the cassette and further showing vapor flowing through the diffuser plate and into the flow channels defined between adjacent turns of the membrane substrate when supported by the cassette;

FIG. 6 is a cross-sectional view generally similar to FIG. 5 showing the relative position between the edges of the film substrate received by the cassette during the vapor deposition process and when the final substrate is removed from the cassette;

FIGS. 7A and 7B are cross-sectional views illustrating alternative cross-sectional configurations of ribs of a film cassette;

FIGS. 8A and 8B are diagrammatic views showing the steps for manufacturing an end plate of a cassette and manufacturing a cassette including two end plates according to the method of the present invention;

fig. 9A, 9B and 9C are diagrammatic views showing an apparatus for supporting a film cassette according to the present invention; and is

Fig. 10 is a diagrammatic view showing an apparatus for unloading a film cassette and immediately laminating it to a protective cover sheet in accordance with the present invention.

Detailed Description

In the following detailed description, like reference numerals designate like elements throughout the figures.

FIG. 1 is a stylized, diagrammatic illustration of an insert (generally designated by reference character 10) according to the present invention for coating a predetermined, continuous length of a film substrate F with one or more materials using a gaseous fluid vapor deposition process. A film substrate F in roll form is shown in the drawings, which is shown supported inside the insert 10 by the cassette 100 according to the present invention.

The insert 10 is useful in a gas vapor deposition apparatus for manufacturing ultra-barrier films of industrial length, i.e., having less than 5 x 10^-4g-H₂O/m²-membrane of the natural water vapour transmission rate. The ultra-barrier film itself serves to protect the radiation collection surface of the photovoltaic module. To fabricate such ultra-barrier films, a transparent material (e.g., aluminum oxide, Al) is deposited using a method such as atomic layer deposition₂O₃) Deposited on both surfaces of a polymer film substrate. Aluminum oxide Al₂O₃Atomic layer deposition on polyethylene terephthalate (PET) has a gaseous deposition temperature in the range of about 80-120 degrees celsius.

Industrial film roll substrate F (i.e., an industrial scale process that can be used to manufacture photovoltaic modules) should have a minimum length of about ten to two hundred meters or more (10-200 m). Preferably, the film F has a thickness in the range of about 0.002 inch to about 0.010 inch (about 0.05 to about 0.25 mm), and more preferably about 0.005 inch (0.13 mm). The film substrate for such use may have a predetermined nominal width dimension W (i.e., a width dimension at room temperature) in a range of at least three hundred millimeters (300mm) to about one thousand six hundred fifty millimeters (1650 mm). It should also be appreciated that the width dimension of the substrate F may increase by approximately 0.4-0.6% due to thermal effects during the deposition process.

As diagrammatically suggested in fig. 1 and 3 and as will be described herein, the structural features of the cartridge 100 are sized and arranged such that, when the membrane substrate F is edgewise supported by the cartridge 100, adjacent turns T of the spirally wound roll of membrane F define open (unobstructed) fluid conducting channels C through which gaseous vapor can propagate. Such unobstructed channels are very important to ensure that the coating is deposited on both surfaces of the film without forming discontinuities.

It is also important to prevent the imposition of bowing, surface abrasion and/or other forces that may cause wrinkles or cracks in the film and/or coating when the film is loaded and unloaded from the cassette. Such abrasion, creases or cracks (even nano-sized cracks) can compromise the protective effect of the ultra-barrier film deposited by the vapor deposition process. The size and arrangement of the structural features of the cassette 100 according to the present invention are therefore also selected.

As illustrated in fig. 1, an insert 10 for a gas vapor deposition apparatus includes a pressure vessel 12 having a process fluid inlet 14 and a process fluid outlet 16. One suitable atomic layer deposition device for use with the insert 10 is a device known as "Planar 400" or "Planar 800" available from Planar Systems Inc.

A diversion guide 18 is connected to the process fluid inlet 14. The diversion guide 18 serves to direct and evenly distribute the laminar flow of gaseous fluid toward the first end plate 106-1 of the cassette 100, as indicated by flow arrows 26. The diversion guide 18 contacts against or is within a predetermined proximity of the outer surface of the end plate 106-1.

The confluence guide 28 may be disposed in the insert 10 adjacent to an end plate 106-2 disposed at the other end of the cassette 100. The converging flow director 28 serves to conduct vapor originating from the end plate 106-2 to the vent 16, as indicated by flow arrow 30. Preferably, the bus guide 28 contacts against the outer surface of the end plate 106-2 or is located within a predetermined close distance.

In the illustrated embodiment, the flow diversion guide 18 includes an optional diffuser plate 22 that is surface-engaged against or within a close proximity of the end plate 106-1. The diffuser plate 22 is shown in the front view of fig. 2 and includes a plurality of openings 22P arranged in a spiral configuration. The plate may be made of a material having a coefficient of thermal expansion similar to alumina, such as aluminum or titanium.

Fig. 3 shows a side elevation view entirely in section of the film cassette 100. Cassette 100 includes a central shaft 102 on which first end plate 106-1 and second end plate 106-2 are mounted.

In the illustrated embodiment, each end plate 106-1, 106-2 is a generally circular member that includes a central hub 106H from which a plurality of angularly spaced spokes 106S radiate. The radially outer ends of the spokes 102S may be connected by an outer rim 106M. The shaft 102 extends through an opening in each hub 106H. Once positioned, the hub 106H is conveniently secured to the shaft 102, such as by an adhesive or fasteners 108. Preferably, the position of each end plate 106-1, 106-2 is selectively adjustable along axis 102.

The shaft 102 is an elongated hollow member having first and second ends 102A, 102B thereon and a reference axis 102R extending therethrough. The shaft 102 is preferably machined from aluminum or titanium, although any other suitable rigid metal or polymeric material capable of withstanding the machining temperatures may be used. The surface of the shaft 102 is interrupted by a slot 102S that extends a predetermined distance 102D along the length of the shaft. The slot 102S is parallel to the reference axis 102R.

The rim 106M and each of the spokes 106S have respective outer surfaces 106E thereon_MAnd 106E_SAnd respective inner surfaces 106I_MAnd 106I_S. Outer surface 106E of rim 106M_MActing as a convenient surface against which the shunt guide 18 and the merge guide (if provided) can be contacted.

Inner surface 106I of rim and spoke on each end plate_MAnd 106I_SAre disposed facing each other. In the illustrated embodiment, the inner surface 106I of each end plate 106-1, 106-2_M、106I_SOn the respective reference plane 112-1, 112-2. Each end plate 106-1, 106-2 has at least an inner surface 106I mounted to the spoke 106S_SUpper spiral rib 106R. Inner surface 106I of rim 106M_MCan be offset from the reference surfaces 112-1, 112-2 as the case may be, so long as the surface 106I of the rim_MDoes not extend inwardly beyond the end 106R of the rim. The reference planes 112-1, 112-2 are oriented substantially perpendicular to the axis 102R of the shaft 102.

For the end plates 106-1, 106-2 to be secured at desired locations on the shaft 102, a predetermined axial inter-spoke spacing 114 is defined between the facing reference planes 112-1, 112-2. Once the cassette is configured to exhibit the desired predetermined inter-spoke spacing 114 between the end plates, the hub and shaft should be fixed such that the inter-spoke spacing 114 does not vary by more than a quarter to three millimeters (0.25-3mm) around the perimeter of the end plates.

The outer diameter of the shaft 102 should be radially equal to the outer diameter of the hub 106H of the end plates 106-1, 106-2 so that the hub and shaft present a radially uniform surface between the end plates. To this end, the shaft 102 in the illustrated embodiment has a sleeve 110 disposed on the shaft 102 between facing reference planes 112-1, 112-2. The sleeve 100 has the same outer diameter as that of the hub 106H. The sleeve 110 provides a slot that aligns with the slot 102S on the shaft 102.

As previously described, each end plate 106-1, 106-2 has at least an inner surface 106I mounted to the spoke 106S_SUpper spiral rib 106R. A portion of the rib may also be mounted to the inner surface 106I of the rim 106M_M. The helical rib 106R on each end plate 106-1, 106-2 has a predetermined number of evenly spaced turns having a predetermined pitch dimension 116. The pitch dimension 116 is measured at a given angular position on the end plate in a radial direction relative to the axis 102R of the shaft 102. For example, the pitch dimension 116 may be taken between the centers of adjacent turns of the helical rib.

The open spacing 118 between adjacent turns of the helical rib 106R defines a continuous helical groove 106G on each end plate 106-1, 106-2. The groove 106G has a first outer end 106F and a second inner end 106N (fig. 4). The helical grooves 106G on the end plate are arranged such that the first and second ends 106F, 106N of each respective groove are axially aligned.

Each rib 106R has a cross-sectional configuration in a radial plane that includes the axis of the shaft. Generally, the cross-sectional configuration of the ribs 106R exhibits generally linear major edges, as perhaps best shown in fig. 5, 7A, 7B. Ribs on each end plate106R have a predetermined width dimension 106W and a predetermined average thickness dimension 106T. Width dimension 106W is measured from an inner surface 106I of spoke 106S on which rib 106R is mounted_SMeasured (i.e., from reference planes 112-1, 112-2) to the free ends of the ribs and taken in a direction parallel to the axis of the shaft. The predetermined minimum thickness dimension 106T is measured in a radial direction relative to the axis of the shaft 102. The average thickness dimension is an average of the thickness dimensions obtained at predetermined points across the width of the rib. According to the invention, the ribs have a width to average thickness aspect ratio of at least 2: 1.

In the embodiment shown in fig. 3-6, each rib 106R has a generally rectangular cross-sectional configuration. By substantially rectangular, it is meant that the major edges of the cross-sectional configuration of the rib are substantially parallel to each other along substantially the entire width and that the thickness dimension 106T of the rib is substantially uniform across substantially the entire width of the rib. The free ends of the ribs may have rounded edges if desired.

A modified embodiment of a rib having a generally rectangular cross-section is shown in fig. 7A. Such a modified rib includes a spoiler 106P disposed at a free end thereof. The role of the spoiler 106P is discussed in detail herein.

Ribs according to the present invention can also be configured to exhibit a generally wedge-shaped cross-sectional configuration 106D. An embodiment of such an alternative configuration of ribs is shown and discussed in connection with fig. 7B.

As described above, according to the present invention, various structural features of the cassette 100 are sized and arranged to exhibit dimensions within the following ranges.

The inter-spoke spacing 114 is at least as large as the nominal width dimension of the film substrate supported by the cassette. Thus, in general, the cassette according to the present invention has an inter-spoke spacing 114 of at least about three hundred millimeters (300 mm).

In addition, the inter-spoke spacing 114 is also greater than the width dimension exhibited by the film substrate F at the gaseous deposition temperature, such that a clear distance 106C (FIG. 3) is defined between the edges of the substrate F and the inner surfaces of the spokes when the substrate F is received in the cassette.

The width dimension 106W of the ribs 106R on each end plate is also important. As shown in table 1 below, the width dimension 106W should be in the range of about 0.5% to about 2.0% of the inter-spoke spacing in accordance with the present invention.

TABLE 1

The effect of the configuration having a rib width 106W and an inter-spoke spacing 114 within the above-defined range can be understood from fig. 5 and 6.

As shown in fig. 6, the cassette having ribs 106R with a width dimension 106W within a prescribed range ensures that a film substrate F of a given stiffness will be supported edgewise and not sag or interfere with the fluid conduction channels C defined between adjacent turns T of the film F when received in the spiral groove 106G. The free outer end of a film roll having a film width greater than about 500mm may require support provided by an axially extending stiffening member V (fig. 3).

The gap distance 106C accommodates any amplification of the film width dimension due to thermal expansion at the processing temperature during processing of the film. Providing edgewise support to the membrane also minimizes the possibility of contact by the membrane operator, which may leave harmful organics on the membrane surface. The edgewise support of the membrane may minimize damage/chipping and yield loss to the membrane.

The flow path of the vapor through the cartridge 100 according to the present invention is best shown in fig. 5. It is noted that, due to the stiffness of the film F, it is possible that the edges of the film may not be in contact with the same surface of the ribs throughout the entire length of the film. Thus, as shown in fig. 5, the edges of the film F may contact either the radially inner or outer surface of the ribs or may reside in the interstices between adjacent turns of the ribs.

Currently, gas vapor deposition equipment relies on a diffusion mechanism to transport the gaseous fluid into contact with the surface being coated. However, diffusion-based processing requires a relatively long cycle time to coat a layer on a film. The insert 10 of the present invention can be used to reduce coating cycle time.

As described with respect to FIG. 1, the insert 10 includes a flow diversion guide 18 having a diffuser plate 22, the diffuser plate 22 being disposed in face contact against or within a close proximity of the end plate 106-1. The presence of the flow splitting guide 18 serves to direct and evenly distribute the laminar flow 26 of the gaseous fluid toward the passages 22P in the diffuser plate 22, as indicated by the flow arrows in fig. 5. As the process gas rushes out of the plate and into the spaces (defined by the axial dimensions of the spokes) existing between the diffuser plate 22 and the ribs 106R, the laminar flow of the process gas is accelerated as it is forced through the passages 22P and transitions to turbulent flow. The transition from laminar to turbulent flow is indicated by a fan-shaped array of fluid arrows 27. This turbulent flow 27 of gas is directed through the spaced openings 118 defining the spiral grooves on the end plate 106-1 to the flow channels C formed between adjacent turns of the membrane F. Gas permeation is minimized by positioning plate 22 in contacting relationship with (or within a close proximity of) end plate 106-1.

Thus, when the flow splitting guide 18 is used in conjunction with the diffuser plate 22, the gas flows into the spaces 118 between the ribs and into the channels C having radial as well as axial flow components, as indicated by flow arrows 28. The radial component of flow into the flow channel C is required to bring the precursor carried in the gas into direct contact with the substrate. Since only a small percentage of the precursor gas is actually absorbed into the substrate when the precursor impacts the substrate, a radial component of flow is necessary to increase the chance of absorption, thus making the flow through the channels C more efficient and reducing the overall cycle time for the ultra-barrier layer to grow properly. It is noted that laminar flow alone will cause a majority of the precursor to travel the length of the flow channel rather than impinge significantly on the substrate, thereby reducing overall coating efficiency.

The diffuser plate 22 may be omitted if a modified rib configuration as shown in fig. 7A or 7B is utilized on the end plate 106-1. When the rib 106R is shaped as shown in these figures, the laminar flow from the flow director 18 is converted to turbulent flow as it enters the channel C. The switching is effected by either a spoiler 106P (fig. 7A) or a rib wedge 106D (fig. 7B).

The interspoke spacing 114 within the specified range also allows the film to be inserted into the groove without over-bending the film surface. This is illustrated in fig. 6. This means that the risk of wrinkles or cracks forming on the film when it is loaded into the cassette or the risk that the coating on the substrate will break when the film is unloaded from the cassette is minimized.

In summary, by sizing the cassette according to the present invention, both the inter-spoke spacing 114 and the rib width 106W are wide enough to support the film edgewise without sagging as it expands throughout the temperature range of the process temperature, yet narrow enough to minimize film compression as the film is inserted into and removed from the cassette, thereby reducing wrinkles or tears.

The capacity of the cassette is thus controlled by the pitch and thickness dimensions of the ribs 106R, in terms of the length of the film roll that can be supported. The ribs are as thin as possible to allow maximum gaseous fluid flow and maximum loaded membrane length but also strong enough not to break off when loaded or unloaded.

The relationship between rib pitch and film length is shown in the table in table 2.

TABLE 2

The relationship between rib pitch and spoke spacing is shown in table 3. Generally, the pitch of each helical rib is less than about 1.2% of the interspoke spacing, and more specifically less than about 0.5% of the interspoke spacing. The dimension 106T of the ribs 106R on each end plate is less than about fifty percent of the pitch. When the inter-spoke spacing is increased to accommodate wider membranes, the rib pitch, and therefore the radial dimension of the channel C, should be proportionally increased to maintain the same flow resistance of the channel C.

TABLE 3

As discussed, when the film roll F is spirally wound on the cassette 100, the spaces between adjacent turns of film cooperate to define an air flow channel C extending axially across the cassette between the end plates. As best seen in fig. 4 and 5, portions of each spiral groove 106G exposed between angularly adjacent spokes 106S on each end plate define a plurality of openings 118 for the flow of gaseous fluid into and out of the gas flow channel C. The angular size of the spokes 106S is selected such that the extent of the area of the exposed portion of the groove (i.e., the total area of the openings 118) is at least fifty percent of the predetermined area of the end plate.

Cassette 100 may be fabricated from high temperature polymeric materials such as polycarbonate, liquid crystals, polyimide, acetal copolymers, nylon 6, polypropylene, and polyether ketones. The cassette may also be machined from metal or ceramic.

Scraping between the film and the cassette can result in debris being generated within the cassette. Debris can result from abrasion of the film and/or abrasion of the cassette material.

Such debris can degrade the properties of the coating to be formed on the film. To minimize such scraping and debris generation, at least the spiral ribs 106R on each end plate are coated with a hard, abrasion resistant layer 120 of a suitable ceramic or other protective material. The thickness of coating 120 ranges from about 100 angstroms to about 2000 angstroms.

Atomic layer deposition methods can be used to apply coating materials such as Al₂O₃、TiO₂、ZrO₂、HfO₂And SiO₂. Can be prepared by chemical reactionA vapor deposition process to apply a SiN or SiC coating. If the coating is alumina, the coating thickness is in the range of about 100 angstroms to about 1000 angstroms.

The coating has a predetermined surface roughness of less than about fifty microns (50 microns) and a hardness of greater than 30 Shore D. In a preferred case, the coating is provided on the entire surface of the end plate.

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In another aspect, the present disclosure is directed to a method for manufacturing an end plate (e.g., end plates 106-1, 106-2) of a cassette according to the present disclosure that is capable of supporting a length of membrane during exposure to a gaseous fluid at a temperature of 80 degrees celsius or greater. The end plates and the cassette made of two end plates are very useful in a method for atomic layer deposition of an inorganic coating on a polymer film.

As described above, the end plate includes the center hub 106H, the outer rim 106M, and the ribs 106R. The center hub 106H and outer rim 106R are connected by spaced spokes 106S. The ribs are in the form of spirals extending from the central hub to the outer rim. The ribs are mounted against the inner surface of the spaced apart spokes and have spiral ends adjacent the outer rim.

The end plates are made of polymeric materials such as polycarbonate, liquid crystals, polyimide, acetal copolymers, nylon 6, polypropylene, and polyether ketones. Since the coating process that can be used for the end plates operates at temperatures of 80 degrees celsius or higher, the polymer should be suitable for use at these temperatures. The selected polymer should have a heat distortion temperature at low pressure above 80 degrees celsius.

A method for manufacturing an end plate is schematically illustrated in fig. 8A. The first step in the method is to shape the uncoated end plate. For example, filaments 202 originating from a forming device 203 are deposited onto a substrate 201 to begin building the end plate. The end plates may be formed by known techniques such as rapid prototyping, powder sintering, injection molding or laser polymerization. In rapid prototyping, a forming machine reads data from a CAD drawing and lays down successive layers of liquid, powder, filament, or sheet material to build up an object such as an end plate. In powder sintering, powder is injected into a mold and strengthened by heating. In injection molding, molten polymer is injected into a mold. In laser polymerization, a laser beam is irradiated in a pattern to deposit a polymer from a vapor. For example, a fused deposition modeling apparatus available from Stratasys, inc. (Eden Prairie, MN) as a Stratasys "Vantage" type FDM may be used.

In an optional second step, shown in fig. 8A, the end plate is heat treated to reduce residual stresses. In the figure, the end plates 106-1, 106-2 are located in the furnace 204. An industry standard (Blue-M) convection oven may be used.

Suitable heat treatment temperatures are at least twenty degrees higher than the temperature of the inorganic coating deposition process in which the end plate may be used. For example, atomic layer deposition methods used to form the super-barrier layer are used at a minimum of 80 degrees celsius. Thus, the heat treatment temperature for such end plates will be a minimum of 100 degrees celsius.

The next step in the process is to use, for example, alumina, silicon nitride, TiO₂、ZrO₂、HfO₂And SiO₂Such as an inorganic coating, to coat the polymer end plate. If the coating is alumina, the coating thickness is in the range of about 100 angstroms to about 1000 angstroms.

This is schematically illustrated in fig. 8A. The end plates 106-1, 106-2 are placed in the coating apparatus 205. The coating serves to smooth and harden the surface of the polymer end plate so that debris is not generated by wear of the end plate when a length of film is loaded into or unloaded from the cassette. The surface roughness of the inorganic coating should be less than about fifty microns (50 microns) and the hardness of the inorganic coating should be greater than 30 on the shore D hardness scale. Debris can cause defects in the coating applied to the film in the cartridge. Coating system 205 may implement known techniques for depositing inorganic coatings on end plates such as chemical vapor deposition, physical vapor deposition, or plasma deposition. The thickness of the alumina coating can be 100-2000 angstroms, preferably 100-1000 angstroms. The coating may be deposited using a Planar P-400A atomic layer deposition platform.

Another aspect of the invention is a method of manufacturing a cassette (e.g., cassette 100) for supporting a length of membrane during exposure to a gaseous fluid having a temperature of 80 degrees celsius or greater. Cassette 100 includes two end plates, each of which is manufactured as in the method described above. The method of manufacturing a cassette further comprises the steps of: each endplate 106-1, 106-2 is mounted near each end 102A, 102B of the central axis 102 as shown in fig. 8B. The central shaft 102 may also be machined from metal or the same polymer as the end plates. The hole in the center hub of the end plate may be sized to closely match the diameter of the center hub. The end plates are mounted near the ends of the central shaft as shown in fig. 8B.

The next step in the method of manufacturing a cassette shown in fig. 8B is to align the helical ends of the ribs 106R. The spiral ends 106F of the grooves of both end plates should be arranged at the same axial position with respect to the central axis. This is necessary to accommodate loading and unloading of the film into and from the space inside the spiral of ribs. One of the end plates is rotated about the shaft until the helical ends are aligned. After aligning the helical ends of the ribs, the end plates may be secured to the central shaft by fasteners 108 (e.g., set screws) or adhesive. The central shaft may be slotted to secure the ends of the membrane to facilitate loading of the membrane into the cassette. The size of the slots on the central shaft may range from about one hundred to about fifteen hundred fifty millimeters (100 and 1550 mm).

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Another aspect of the present invention is an apparatus and method for loading a film cassette 100 for use in a vapor deposition process. The apparatus is shown in fig. 9A, 9B and 9C.

The apparatus includes an unloaded cassette 100 for supporting a length of film F during the gas vapor deposition process as described above. The unloaded cassette 100 itself includes a central shaft 102 having an axis 102R. The shaft includes an axially extending slot 102S. Unloaded cassette 100 also includes first and second end plates 106-1, 106-2 mounted to shaft 102. Each end plate 106-1, 106-2 has a helical groove 106G. The helical grooves 106G on each end plate are axially aligned. The end plates 106-1, 106-2 are spaced apart by a predetermined inter-spoke spacing 114. The cassette is mounted in a cassette mounting bracket 301 which allows the cassette to rotate freely about the axis 102R of the central shaft. Cassette mounting bracket 301 is adjustable for lateral alignment. An example of a technique for lateral alignment adjustment may be to insert a washer or o-ring on the shaft 102. Lateral alignment moves the edge of the unloaded cassette end plate relative to the datum plane 306. The center points of the supply roll 303 and the shaft 102 of the cassette should be aligned within about 3mm on a reference plane 306 perpendicular to the two axes and passing through the two center points. The apparatus also includes a supply roll mounting bracket 302, which supports a supply roll of film 303. The supply roll 303 has an axis 304. The axis of the supply roll 304 is spaced a predetermined distance from the axis of the unloaded cassette 102R. The distance between the supply roll 304 and the axis of the unloaded cassette 102R is selected according to the width of the film F to be coated. The distance between the supply roll 303 and the axis of the unloaded cassette 100 should be between about 0.25 and 3 times the width of the film F.

Both the cassette mounting bracket 301 and the supply roll mounting bracket 302 have an axis. These axes should be parallel with an accuracy of up to 0.5 degrees in orbit (x-direction) and horizontal (z-direction). Possible misalignment in the orbital direction of the axes 304, 305 is shown in fig. 9B. Possible misalignment in the horizontal direction of the axes 304, 308 is shown in fig. 9C. The mounting bracket may include a mechanical mechanism to adjust the parallelism of the axes.

Examples of mechanical mechanisms to adjust axis parallelism include leveling threads, set bolts, and shims.

The brackets 301, 302 themselves may be mounted to the base plate 300 if desired.

Film F is taken from the top of the supply roll 303 and enters the unloaded cassette 100 at the bottom as shown in fig. 9A. The leading edge of the film is tapered and inserted into the slot 102S of the shaft 102 of the unloaded cassette 100.

The tensioning device 307 is connected to the supply roll 303 of film. During the loading of the film into the cassette, the film F is tensioned so that the edges of the feed film remain secured within the spiral grooves on the two end plates without creating creases in the surface of the film as it is wound onto the cassette. Examples of the tensioning device include a pluronic brake, a pneumatic brake, a magnetic particle clutch, a wire brake, and a drum brake. Dynamic tensioning may also be employed. The tensioning device 307 must be capable of tensioning the film F over a film width of about 0.02-0.36 newtons/mm.

The invention also relates to a method of loading a film cassette for use in a gas vapour deposition method. In order to eliminate the scratching of the film F, the conventional film alignment technique and the tensioning technique using a roll contacting the film cannot be employed. In addition, this method requires stricter specifications in terms of parallelism calibration and allowable offset than conventional web handling methods. Both requirements must be satisfied in order to avoid scratching or creasing the film F.

The first step in the method is to mount a supply roll 303 of film on a first mounting bracket 302. The supply roll 303 of film has a tapered free end. The supply roll has an axis 304 and a reference plane 306 perpendicular to the axis 304 and passing through a center point of the supply roll.

The next step in the method is to mount the unloaded film cassette 100 on a second mounting bracket spaced a predetermined distance 309 from the first mounting bracket. The unloaded film cassette has an axis 102R and a central reference plane 306 perpendicular to the axis and passing through the center point of the unloaded cassette. The unloaded cassette includes a central shaft 102 having axially extending slots 102S. The unloaded cassette also includes a first 106-1 end plate and a second 106-2 end plate mounted to shaft 102. Each end plate has a spiral groove 102G. The helical grooves 102G on each end plate are axially aligned. The end plates are spaced apart by a predetermined inter-spoke spacing 114. The mounted supply roll and mounted cassette can be seen in fig. 9A and 9B.

The third step in the method is to insert the tapered free end of the film F into the slot 102R on the central shaft 102 of the unloaded cassette 100. The film F should follow a path from the top of the supply roll 303 to the bottom of the cartridge 100 as shown in fig. 9A. The length of the taper from the free end of the film to the non-tapered (i.e. full width) portion of the film should be fifteen to twenty centimeters. The angle between the non-tapered edge and the tapered edge should be in the range of fifteen to thirty degrees.

The fourth step in the method is to align the center reference plane 306 (shown in FIG. 9B) on each roll to within a predetermined allowable skew. The allowable offset is the distance between a plane perpendicular to the supply spool line 304 and passing through the center point of the supply roll 303 and perpendicular to the unloaded cassette axis 102R and passing through the center point of the cassette shaft 102. The predetermined allowable standoff distance is about three millimeters. This alignment may be achieved by inserting gaskets, o-rings, or shims between the supply roll mounting bracket 302 and the supply roll 303 and the cassette mounting bracket 301 and the unloaded cassette 100.

The fifth step in the method is to align the axis of the supply roll and the axis of the unloaded cassette with respect to each other with a parallelism in both the track (x-direction) and the horizontal (z-direction) within 0.5 degrees. Alignment is shown in fig. 9B and 9C. Such alignment may be achieved by adjusting leveling threads, set bolts, or shims associated with the mounting bracket.

The sixth step in the method is to apply a predetermined tension to the film. The tension is imparted by a tensioning device 307 located on the supply roll 303. Examples of the tensioner 307 include a pluronic brake, a magnetic particle clutch, a wire brake, and a drum brake. Dynamic tensioning may also be employed. The film F is tensioned within a film width range of about 0.02-0.36 newtons per millimeter.

The seventh step in the method is to rotate the unloaded cassette 100 relative to the supply roll 303, drawing the film into the spiral grooves 102G on both end plates 106-1, 106-2 without creasing or scratching the surface of the film F. The unloaded cassette can be rotated manually as long as the film F is not touched.

For film widths greater than about 500mm, axially extending stiffening members V (in fig. 3) are inserted around the outer ends of the film, now loaded into the cassette. This rigid element minimizes the unwinding of the film F from the cassette during processing and coating deposition.

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Another aspect of the invention is an apparatus and method for unloading a film cassette from a gas vapor deposition process and laminating it with a protective film to minimize scratching of the ultrabarrier coating. In order to eliminate the scratching of the film F, the conventional film alignment technique and the tensioning technique using a roll contacting the film cannot be employed. In order to protect the coated film until lamination, equipment to avoid contacting the film super barrier coating U on one surface of the film is required. The apparatus is shown in figure 10.

The unloaded apparatus includes a cassette mounting bracket 401 supporting the loaded cassette 100 from the gas vapor deposition method. The load cassette 100 includes a central shaft 102 having axially extending slots 102S. Load cassette 100 also includes a first 106-1 end plate and a second 106-2 end plate mounted to shaft 102. In each end plate there is a helical groove 102G. The helical grooves 102G on each end plate are axially aligned. The end plates are spaced apart by a predetermined inter-spoke spacing 114. The coating film F is supported by the spiral groove 102G. The membrane has a free outer end. The load cassette further includes a central shaft 102 having an axis 102R.

The unloaded device also includes a tensioner brake 402 connected to the loaded cassette 100. The tensioning device is an active tensioning device such as a magnetic particle brake, a pneumatic brake or a friction brake. The tensioner includes a load cell 412. Such an integrated tensioner with a brake and load sensor is available from Dover Flexo Electronics (Rochester, NH). The film should be tensioned to between 0.175 to 0.50 newtons per millimeter.

The unloaded device also includes a mounting bracket 403 that supports a roll of protective film 404. The protective membrane has a free end. The protective film can be any polymer that can be subsequently laminated at room temperature or above using an adhesive. For use as a barrier layer in photovoltaic modules, fluoropolymer protective films such as FEP, ETFE, and PFA are desirable. The fluoropolymer protective film must be corona treated (Enercon Surface Treatment Inc, Germantown, WI) for lamination.

The unloaded apparatus further includes a nip roll 406 into which the free ends of the coated film F and the protective film 405 are inserted so that they form a laminate 407. Nip roll 406 should operate at room temperature or higher. The load on the nip roll should be greater than 0.10 n/mm of film width. The nip rolls and tensioning devices should be operated to minimize the curling of the laminate.

The unloaded apparatus also includes a take-up roll 408 to collect the laminate from the nip roll.

The take-up roll 408 is connected to a take-up roll tension control device 409. The take-up tension control device may be controlled by a load cell, as is available from MagPowr Inc. The tension on the laminate 407 should be greater than 0.10 newtons per millimeter of film width.

The unloaded apparatus also includes an adhesive applicator 410 to apply adhesive to the protective film 404 between the protective film roll 404 and the nip roll 406. The adhesive applicator may be a slot-jet applicator, a gravure applicator, or a reverse gravure applicator. The coater should be adapted to the adhesive selected for a given application. For a single-sided corona treated FEP protective film laminated to a PET substrate coated with alumina, an adhesive available from national Starch (Bridgewater, NJ) under the trademark Duro-Tak was used. Slot-die coaters are available from Egan Film and Coating Systems & BlowMolding Systems (Somerville, N.J.). The adhesive coater may also apply a solid adhesive to the protective film.

The unloaded apparatus also includes an optional dryer 411 to dry the adhesive between the adhesive coater and laminator. The drying parameters depend on the binder chosen.

The present invention also relates to a method of unloading and laminating the film cassette 100 for a gas vapor deposition method to a protective film. See fig. 10 for a method description. Dust or debris on the membrane contaminates the process. The method should be carried out in a clean room environment or a cleaning machine should be provided prior to the lamination step. The rolls in this method should be aligned as described above so that the loading method includes parallelism in the track (x) and horizontal (z) directions and lateral alignment between the cassette nip rollers and all rollers in between.

The first step in the method is to provide a load cassette 100 that holds the coating film F. Load cassette 100 includes a central shaft 102 having an axially extending slot 102S and first 106-1 and second 106-2 end plates mounted to shaft 102. In each end plate there is a helical groove 102G. The helical grooves 102G on each end plate are axially aligned. The end plates 106-1, 106-2 are spaced apart by a predetermined inter-spoke spacing 114. The coating film F is supported by the spiral groove 102G and has a free end. A sacrificial leader may be bonded to the free end of the coating film to establish a running set-up.

The next step in the method is to provide a roll of protective film 404. The protective film 404 can be any polymer that can be cross-laminated at room temperature or above. For use as a barrier layer in photovoltaic modules, fluoropolymer protective films such as FEP, ETFE, and PFA are desirable. The fluoropolymer protective film must be corona treated (Enercon Surface Treatment Inc, Germantown, WI) for lamination.

The third step in the method is to apply an adhesive to the protective film to form a coated protective film. The adhesive is applied with an adhesive applicator 410. The adhesive coater 410 may be a slot-jet coater, a gravure coater, and a reverse gravure coater. The coater 410 should be adapted to the adhesive selected for a given application. For a single-sided corona treated FEP protective Film laminated to a PET substrate coated with alumina, a durotac 80-1194(National Starch, Bridgewater, NJ) adhesive was used in combination with a slot-jet coater from Egan Film and Coating Systems.

Especially for fluoropolymers, static eliminators should be used in cases where flammable solvents are present in, for example, the adhesive.

In the fourth step, the adhesive is dried in the dryer 411. The drying temperature should be above about 60 degrees celsius. The drying conditions vary with the binder chosen.

The fifth step in the method is to laminate the coated film and the coated protective film to form a laminate 407. This is done by feeding the adhesive coated protective film and the coating film to nip roll 406. Nip roll 406 should operate at room temperature or higher. The load on nip roll 406 should be greater than 0.10 n/mm of film width. For a given material selected, nip rollers 406 (temperature and pressure) and tensioning device 412 should be operated to minimize laminate curl. The curl of the laminate depends on the adhesive, film matrix properties, protective film properties, temperature, pressure, and film tension. One of ordinary skill in the art can determine the optimal process parameters for the selected material.

In the sixth step, the laminate is collected on a take-up roll 408. The take-up roll 408 is controlled by a take-up roll tension control device 409. When available from MagPowr inc. (Oklahoma City, OK), the take-up tension control device 409 may be controlled by a load cell. The tension in the laminate 407 should be greater than 0.12 newtons per millimeter of film width. There is an upper limit to the tension applied to the laminate; when this upper limit is reached, the inorganic coating on the membrane substrate is broken. This limit depends on the inorganic coating material and its thickness.

Examples

The following example illustrates the effect of using a cassette according to the present invention to support a film substrate during an atomic layer deposition process.

Example 1Polyethylene terephthalate (PET), uncoated plastic film, 0.005 inches thick, available from DuPont Teijin Films (Hopewell, Va.),manual loading was performed on a spiral cassette with an inner diameter of about 62mm and an outer diameter of about 200mm as shown in fig. 3-6. The end plate with spiral grooves, the cassettes made of polycarbonate had a pitch of 4.0mm between the spiral grooves and the width of the cassettes was about 350 mm. The spacing between the turns of the helical rib, i.e., the spacing 118 (fig. 3) defining the radial width of the groove, is 2.5 mm. The rib thickness was 1.5 mm and the rib width was 6.5 mm. The length of uncoated PET fully wound on a cassette with a 4mm pitch was about 7 meters. This cassette was loaded with a PET film into a reactor (Planar P400A) for Al deposition by Atomic Layer Deposition (ALD)₂O₃A thin film coating of barrier layer was deposited on both sides of the PET. Prior to ALD deposition, the temperature in the ALD reactor was raised to 100 ℃ and incubated for 3 hours prior to ALD coating to remove any residual moisture absorbed by the PET plastic film.

For Al₂O₃The reactor was maintained at 100 c. For Al₂O₃The reactants and precursors for ALD deposition of (a) are trimethylaluminum vapor and water vapor. These precursors were introduced sequentially into the ALD reactor, which was continuously purged with nitrogen and pumped with a mechanical pump to a background pressure of about 1 torr (no reactants or precursors). Nitrogen is used as a carrier for the reactants and also as a purge gas. More specifically, the PET substrate was injected with water vapor carried by nitrogen for 4 seconds, and then the reactor was purged with flowing nitrogen for 20 seconds. The substrate was then sparged with nitrogen-loaded trimethylaluminum vapor for 4 seconds, followed by a 20 second sweep with flowing nitrogen. This reaction sequence produced a layer of Al on both sides of the PET substrate₂O₃. The reaction sequence was repeated 200 times, which formed an Al2O3 barrier layer whose thickness on both sides of a 7 meter long PET substrate was determined by ellipsometry to be approximately 29nm thick.

To evaluate Al coated with water vapor by ALD coating on a dark box₂O₃Permeability of the film, which was spread and 2 specimens (about 100mm x 100mm) were cut from the center of a 7 meter long PET. Further, 2 cuts were made at the coating place near the outside or larger diameter portion of the cassetteTest specimens (about 100 mm. times.100 mm). The Water Vapor Transmission Rate (WVTR) of all four samples was measured in a commercial instrument (MOCON Aquatran-1, Minneapolis, MN). The instrument has a size of 5 × 10^-4g-H₂O/m²Day WVTR sensitivity. All four samples tested were below this limit. That is, they all have a WVTR of less than 5X 10^-4g-H₂O/m²Day(s). This is in contrast to Al on a full 4mm pitch cassette₂O₃The coating is uniform and consistent with high quality.

Example 2The experiment described in example 1 was repeated with a cassette having a 2mm pitch between the helical grooves. The rib thickness was 1.0mm and the rib width was 6.5 mm. That is, the uncoated PET loaded on such a cassette was 350mm wide by about 14m long. I.e., the spacing 118 (fig. 3) defining the radial width of the groove, is 1.0 mm. A2 mm spiral with uncoated PET was loaded into the ALD reactor and heated in the ALD reactor at 100 ℃ to remove residual water vapor absorbed by the PET, followed by Al₂O₃Deposited on both sides of PET by ALD method at 100 ℃. The ALD deposition process included 8 seconds of injection with water vapor carried by nitrogen followed by purging the reactor for 50 seconds under flowing nitrogen. The PET substrate on a 2mm pitch cassette was then infused with nitrogen-loaded trimethylaluminum for 8 seconds followed by a 50 second purge in flowing nitrogen. This reaction sequence produced a layer of Al on both sides of the PET substrate₂O₃. The reaction sequence was repeated 200 times, which formed Al₂O₃The thickness of the barrier layer, on both sides of the 14 meter long PET substrate, was determined by ellipsometry to be about 30nm thick.

After it was unwound from the cassette, the Water Vapor Transmission Rate (WVTR) was measured on four samples on ALD coated PET. Two samples were measured from the middle of the unrolled PET and two samples were taken from the coated PET at a position near the outer diameter of the helix. All four measurements were at 5X 10^-4g-H₂O/m²Day MOCON Aquatran-1 instrument. That is, they all have a WVTR of less than 5X 10^-4g-H₂O/m²Day(s). This is in contrast to Al on a full 2mm pitch cassette₂O₃The coating is uniform and consistent with high quality.

These examples demonstrate that cassettes loaded and processed in a vapor deposition apparatus (all as described according to the invention) are used to produce substrates having a surface roughness of less than 5 x 10^-4g-H₂O/m²Excellent barrier film for water vapour transmission rate of day.

Having the benefit of the teachings of the present invention as set forth above, those skilled in the art will appreciate numerous modifications therefrom. Such modifications are intended to be understood as being within the contemplation of the invention as defined by the appended claims.

Claims (14)

1. A film cassette for use in a gas vapor deposition process, the cassette comprising:

a central shaft having an axis therethrough;

a first end plate and a second end plate, each end plate mounted to the shaft, each end plate including a central hub from which a plurality of angularly spaced spokes radiate,

the spokes of each end plate having an inner surface lying on a reference plane oriented substantially perpendicular to the axis of the shaft,

each end plate has a helical rib mounted to the inner surface thereof,

each helical rib has a predetermined number of evenly spaced turns and a predetermined pitch associated therewith,

the spaces between adjacent turns of the helical rib define a helical groove on each end plate;

a film substrate having first and second edges thereon and having a predetermined width dimension greater than three hundred millimeters (300mm),

each edge of the membrane matrix is received within a helical groove on one of the end plates to define a helical membrane winding having a plurality of turns,

spaces between adjacent turns of the spiral membrane winding cooperate to define a gas flow guide channel extending axially across the cassette between the end plates,

each rib having a cross-sectional configuration in a radial plane containing the axis of the shaft, the cross-sectional configuration exhibiting a substantially linear major edge,

each rib having a predetermined width dimension measured in a direction parallel to the axis of the shaft from the inner surface of the spoke on which the rib is mounted, a predetermined average thickness dimension measured in a radial direction with respect to the axis of the shaft, and a width to average thickness aspect ratio of at least 2: 1, wherein

The inner surfaces of the spokes are spaced apart by a distance greater than a width dimension exhibited by the film matrix at a gas deposition temperature, and

the ribs on each end plate having a width dimension of from about 0.5% to about 2.0% of the spacing between the inner surfaces of the spokes; and is

The spaces between adjacent turns of the helically mounted ribs disposed between adjacent spokes on one end plate define a plurality of inlet openings for gaseous fluid,

the spaces between adjacent turns of the helically mounted ribs extending between adjacent spokes on the other end plate define a plurality of outlet openings for gaseous fluid,

the inlet opening and the outlet opening are in communication with the gas flow guide channel.

2. The cassette of claim 1 wherein the helical rib has a predetermined pitch,

the pitch of each helical rib is less than about 1.2% of the interspoke spacing.

3. The cartridge of claim 2 wherein

The pitch of each helical rib is less than about 0.5% of the interspoke spacing.

4. The cartridge of claim 2 wherein

The ribs on each end plate have a thickness dimension that is less than about fifty percent of the pitch.

5. The cassette of claim 1 wherein each helical rib has a coating thereon of a predetermined thickness, the coating thickness being in the range of about 100 angstroms to about 2000 angstroms,

the coating has a predetermined surface roughness of less than about fifty microns (50 microns) and a hardness of greater than 30 Shore D.

6. The cassette of claim 5 wherein the coating is alumina and wherein the coating thickness is in the range of about 100 angstroms to about 1000 angstroms.

7. The cartridge of claim 1 wherein

The one end plate has a predetermined area defined thereon, and wherein

The area of the inlet opening is at least fifty percent of the predetermined area of the one end plate.

8. The cassette of claim 1 wherein the film wrap has an inner end, and wherein

The shaft is a hollow member having an axially extending slot disposed therein, the slot extending parallel to the axis of the shaft, and wherein

The inner end of the film wrap is received in a slot in the shaft.

9. The cassette of claim 1 wherein each end plate is made of a polymeric material sufficient to withstand a gas vapor deposition process using water vapor and Trimethylaluminum (TMA) having a minimum processing temperature of at least 80 degrees celsius.

10. The cassette of claim 1 wherein the interspoke spacing between the end plates does not vary by more than one to three millimeters (1-3 mm).

11. The cassette of claim 1 wherein each end plate has an outer rim, the hub and rim being connected to each other by the angularly spaced spokes.

12. The cassette of claim 1 wherein each rib is generally rectangular in cross-sectional configuration.

13. The cassette of claim 12 wherein each rib has an outer end, and wherein each rib has a spoiler at its outer end.

14. The cassette of claim 1 wherein the cross-sectional configuration of each rib is generally wedge-shaped.