WO2017091428A2

WO2017091428A2 - Moisture barrier film articles and methods of making

Info

Publication number: WO2017091428A2
Application number: PCT/US2016/062395
Authority: WO
Inventors: Karnav D. KANUGA; Moses M. David
Original assignee: 3M Innovative Properties Company
Priority date: 2015-11-24
Filing date: 2016-11-17
Publication date: 2017-06-01
Also published as: WO2017091428A3

Abstract

A barrier film article comprising a polymeric substrate, a coating layer, and a barrier layer. The coating layer is disposed over a major face of the polymeric layer, and includes EAA copolymer. The barrier layer is disposed over the coating layer opposite the polymeric substrate, and includes silicon and oxygen. In some non-limiting embodiments, the barrier layer may be a diamond-like carbon (DLC) or a diamond-like glass (DLG). The barrier film articles are well suited for use with various electrical devices, for example as the backsheet of a PV module. The barrier film articles of the present disclosure can optionally provide a significant barrier to moisture vapor, for example exhibiting a MVTR of less than about 2.5 g/m²/day.

Description

MOISTURE BARRIER FILM ARTICLES AND METHODS OF MAKING

Background

The present disclosure relates to barrier articles for protection of moisture or oxygen sensitive devices. Certain embodiments, for example, relate to barrier film articles exhibiting moisture vapor transmission rates at desired levels appropriate for use with various devices, such as the backsheet of a photovoltaic module.

Harnessing the energy of sunlight can be accomplished by the use of photovoltaic (PV) cells (also referred to as solar cells), which are used for photoelectric conversion. PV cells are relatively small in size and are typically combined into a physically integrated PV module (or solar module) having a correspondingly greater power output. PV modules are generally formed from two or more "strings" of PV cells surrounded by an encapsulant and opposing, front and back protective sheets or layers. The two sheets are typically referred to as the front-side layer and the backsheet. This laminated construction provides mechanical support for the PV cells and also protects them against damage due to environmental factors such as wind, snow, and ice. The backsheet further serves to electrically insulate the PV module.

Available barrier films useful as a PV module backsheet are typically a polymeric material (e.g., polyethylene terephthalate (PET) polymers, polyethylene naphthalate (PEN) polymers, polyesters, and polyamides), and are readily capable of protecting the PV cells from harsh environmental conditions over extended periods of time. However, PV module manufacturers and end users continue to demand ever- increasing performance. For example, a "snail trail" or "snail track" effect sometimes observed in PV modules over time has been attributed, at least in part, to transmission of moisture vapor through the backsheet. Though the long term ramifications of the snail trail issue is not fully understood, manufacturers have begun to demand improvements in the Moisture Vapor Transmission Rate (MVTR) properties of barrier film backsheets. Increasing the thickness of available barrier film backsheets can help reduce MVTR, but is not a viable option from a cost standpoint.

A challenge exists to develop barrier thin films that are compatible with the traditional backsheet materials because of the intrinsic roughness of the backsheet substrates arising from the particulate filler material added to the backsheet to impart opacity and white color. The intrinsic roughness of the backsheet substrate presents a problem with barrier thin films since the moisture barrier properties are dominated by defects on the substrate, which are difficult to coat conformally, and the barrier thin films are prone to mechanical damage.

Summary

The inventors of the present disclosure recognized that a need exists for a barrier film article that overcomes one or more of the above-mentioned problems.

Some aspects of the present disclosure relate to a barrier film article comprising a polymeric substrate, a coating layer, and a barrier layer. The coating layer is adjacent a first major face of the polymeric substrate, and includes ethylene acrylic acid (EAA) copolymer. The barrier layer is adjacent the coating layer opposite the first major face, and includes silicon and oxygen. In some non-limiting embodiments, the barrier layer further includes at least 5% carbon, and may be a diamond-like carbon (DLC) or a diamond-like glass (DLG). In related optional embodiments, the coating layer has a thickness of less than 500 nanometers, for example a thickness in the range of 50 - 250 nanometers. The barrier film articles are well suited for use with various electrical devices, for example as the backsheet of a PV module. The barrier film articles of the present disclosure can optionally provide a significant barrier to moisture vapor, for example exhibiting a Moisture Vapor Transmission Rate of less than about 2.5 g/m²/day (at 37.8 °C and 100% relative humidity). The barrier film articles of the present disclosure can optionally provide a significant barrier to oxygen, for example exhibiting an oxygen transmission rate of less than about 2 cc/m²/day (at 23 °C and ambient relative humidity).

Other aspects of the present disclosure relate to a method of making a barrier film article. The method includes coating a major face of a polymeric film substrate with a coating material including EAA copolymer to provide a coated substrate. The coated substrate is then stretched. A barrier layer is applied on to the coating material of the stretched coated substrate, and includes silicon and oxygen. In some embodiments, the polymeric film substrate is stretched in a first direction (e.g., machine direction) prior to the step of applying the coating material, and the coated substrate is stretched in a second direction (e.g., transverse direction)following the step of applying the coating material and prior to the step of applying the barrier layer.

Brief Description of the Drawings

FIG. 1A is a simplified side view of a barrier film article in accordance with principles of the present disclosure;

FIG. IB is a simplified side view of another barrier film article in accordance with principles of the present disclosure;

FIG. 2 is a simplified cross-sectional view of a portion of a PV module in accordance with principles of the present disclosure and including a backsheet comprising a barrier film article; and

FIG. 3 is a schematic view of one exemplary process in accordance with principles of the present disclosure.

Detailed Description

The present disclosure generally relates to barrier film articles capable, for example, for use in

PV modules as backsheets, as well as methods of making such articles. The barrier film articles of the present disclosure can be used in any type of PV module.

In one exemplary embodiment, the barrier film articles of the present disclosure are capable of use as a backsheet in a PV module. In these and other embodiments, the barrier film articles of the present disclosure exhibit, via a barrier layer as described below, a Moisture Vapor Transmission Rate (MVTR) of less than about 2.5 g/m²/day at 37.8 °C and 100% relative humidity. In some embodiments, the barrier film article has a MVTR of less than about 1.0 g/m²/day, alternatively less than about 0.5 g/m²/day, at 37.8 °C and 100% relative humidity. In related embodiments, the barrier film articles of the present disclosure exhibit an oxygen transmission rate of less than about 2 cc/m²/day at 23 °C and ambient relative humidity, and optionally further exhibit the MVTR properties described above. In yet other embodiments, the barrier film articles of the present disclosure have a thickness of less than about 0.010 inch (0.254 mm) and provide the MVTR and oxygen transmission rate properties described above. In other embodiments, the barrier film articles of the present disclosure provide both a moisture vapor transmission barrier and an oxygen transmission barrier, and may have, for example, a MVTR of less than about 2.5 g/m²/day at 37.8 °C and 100% relative humidity and an oxygen transmission rate of less than about 2 cc/m²/day at 23 °C and ambient relative humidity.

One embodiment of a barrier film article 20 in accordance with principles of the present disclosure is shown schematically in FIG. 1A, and includes a polymeric substrate or film 30, a coating layer 32, and a barrier layer 34. In general terms, the coating layer 32 is highly thin and adheres the barrier layer 34 relative to a first major face 40 of the polymeric substrate 30. As described in greater detail below, in some embodiments, the coating layer 32 is applied to the polymeric substrate prior to one or more processing steps (e.g., stretching, tenting or other biaxial orienting operations), and the barrier layer 34 is applied after the processing step(s). Thus, in some embodiments, the polymeric substrate 30 and the coating layer 32 can be collectively viewed as tenter coated substrate 50, with the barrier layer 34 being applied, deposited or formed on the tenter coated substrate 50. Regardless, the coating layer 32 is adjacent to the first major face 40 of the polymeric substrate 30, and the barrier layer 34 is adjacent to the coating layer 32. The term "adjacent" reflects a general relationship between two materials or components, and is inclusive of the two materials or components in contact with one another (e.g., in some embodiments, the coating layer 32 contacts the polymeric substrate 30) and a third material or component disposed between the two materials or components (e.g., in some embodiments, an additional layer is optionally disposed between the coating layer 32 and the polymeric substrate 30).

The barrier film article 20 is capable of use as a backsheet in a PV module. For example, the barrier layer 34 exhibits an MVTR and/or oxygen transmission rate appropriate for long term protection of the PV module as described above. In this regard, the barrier layer 34 can include silicon and oxygen (e.g., silica), and optionally carbon, with the coating layer 32 including an ethylene acrylic acid (EAA) polymer that surprisingly enhances MVTR properties of the barrier layer 34. Further, the barrier film article 20 is configured to provide a dielectric breakdown voltage of at least 10 kV or at least 20kV. The barrier film articles of the present disclosure can optionally include additional layers and/or materials as described below. For example, another barrier film article 200 in accordance with principles of the present disclosure is shown schematically in FIG. IB and includes the coating layer 32 and the barrier layer 34 disposed over the first major face 40 of the polymeric substrate 30. In addition, an optional functional layer 202 is adjacent to an opposing, second major face 42 of the polymeric substrate 30, and can assume various forms described below. In some embodiments, adhesion between the polymeric substrate 30, the coating layer 32 and the barrier layer has a value of at least 4 as measured under ASTM D 3359, Test Method A.

Polymeric Substrate or Film 30

The polymeric substrate or film 30 can assume various forms appropriate for use with a PV module backsheet. In the context of the present disclosure, the term "polymeric" will be understood to include organic homopolymers and copolymers, as well as polymers or copolymers that may be formed in a miscible blend, for example, by co-extrusion or by reaction, including transesterification. The terms "polymer" and "copolymer" include both random and block copolymers.

In some embodiments, the polymeric substrate 30 includes at least one polyester layer. In other embodiments, the polymeric substrate 30 is a multilayer polyester film. Regardless, the polyester of the polymeric substrate 30 is a polyethylene terephthalate (PET) polymer layer in some exemplary embodiments. The PET layer may include additional polymers in some embodiments. Some exemplary additional polymers include: polyethylene napthalate (PEN), polyarylates; polyamides, such as polyamide 6, polyamide 11, polyamide 12, polyamide 46, polyamide 66, polyamide 69, polyamide 610, and polyamide 612; aromatic polyamides and polyphthalamides; thermoplastic polyimides; polyetherimides; polycarbonates, such as the polycarbonate of bisphenol A; acrylic and methacrylic polymers such as polymethyl methacrylate; polyketones, such as poly(aryl ether ether ketone) (PEEK) and the alternating copolymers of ethylene or propylene with carbon monoxide; polyethers, such as polyphenylene oxide, poly(dimethylphenylene oxide), polyethylene oxide and polyoxymethylene; and sulfur-containing polymers such as polyphenylene sulfide, polysulfones, and polyethersulfones.

Other exemplary materials useful as the polyester layer include polyethylene naphthalate (PEN), polyetheretherketone (PEEK), polyaryletherketone (PAEK), polyarylate (PAR), polyetherimide (PEI), polyarylsulfone (PAS), polyethersulfone (PES), polyamideimide (PAI), and polyimide.

The polymeric substrate 30 can optionally include pigment particles (or filler particles). For example, the pigment particles can be white pigment particles (e.g., titanium dioxide, barium sulfate, etc.). Typically, the polymeric substrate 30 may contain from about 1% to about 15% or up to 20% weight based on the weight of the white pigment particles. In related embodiments, the polymeric substrate 30 is a white PET. Other formats or colors are equally acceptable, and other useful pigment particles include carbon black and calcium carbonate. In some embodiments, the barrier film article 20 is black in color due the presence of substantial amounts of carbon particles (available, for example, from Mitsubishi Polymers under the trade designation :BIN 175 EHB). The carbon particles may be modified, for example surface treated, coated or may contain functionalized groups (e.g., by chemical reaction with chemical modifiers or by adsorption of chemicals). Carbon particles include graphite, fullerenes, nanotubes, soot, carbon blacks (e.g., carbon black, acetylene black, and ketjen black). Typically, the polymeric substrate 30 (or other layer of the barrier film article) may contain from about 1% to about 6% or up to about 10% weight based on the weight of the layer of carbon particles. The loading with carbon particles may be increased but in that case the layer may become electron conductive. In this case the layer can be earthed when it is incorporated into a solar module. However, the barrier film articles of the present disclosure can be of a different color if pigments or paints are used. The pigment or filler particles can affect a surface roughness of the polymeric substrate 30 (e.g., where the pigment or filler particles have a mean particle size on the order of at least 0.2 microns; for example, in some non-limiting embodiments, the polymeric substrate 30 has a surface roughness characterized by a maximum roughness or mean roughness depth Rz of at least 500 nm.

The substrate 30 may further comprise any of the additives conventionally employed in the manufacture of polyester films. Thus, agents such as: cross-linking agents; optical brighteners, dyes; pigments; lubricants; anti-oxidants; radical scavengers; thermal stabilisers; end-capping agents; flame retardants and inhibitors; anti-blocking agents; surface active agents; slip aids; gloss improvers; prodegradents; viscosity modifiers; and dispersion stabilisers may be incorporated as appropriate. The substrate 30 may further comprise UV absorbers preferably organic UV absorbers. Suitable examples of organic UV absorbers include benzophenones, benzotriazoles, benzoxazinones and triazines. The substrate 30 optionally comprises a light stabilizer, preferably a hindered amine light stabilizer (HALS), typically having a hindered piperidine skeleton in the molecule. Specific examples of HALS include bis- (2,2,6,6-tetramethyl-4-piperidyl)sebacate, bis-(N-methyl-2,2,6,6-tetramethyl-4-piperidyl)sebacate, bis- (l,2,2,6,6-pentamethyl-4-piperidyl)sebacate, l,2,2,6,6-pentamethyl-4-piperidyl-tridecyl-l,2,3,4- butanetetracarboxylate- , tetrakis-(2,2,6,6-tetramethyl-4-piperidyl)-l,2,3,4-butanetetracarboxylat- e, and tetrakis-(N-methyl-2,2,6,6-tetramethyl-4-piperidyl)-l,2,3,4-butanet- etracarboxylate.

The polymeric substrate 30 can be oriented, such as biaxially oriented or alternatively uniaxially oriented. As described below, orientation may be effected by any process known in the art for producing an oriented film. In general terms, biaxial orientation is effected by drawings or stretching in two mutually perpendicular directions in the plane of the film to achieve a desired combination of mechanical and physical properties.

In some embodiments, the polymeric substrate 30 has a thickness in the range of 2 - 300 micron, and the corresponding barrier film article exhibits the MVTR and oxygen transmission properties described above. In other embodiments, the polymeric substrate 30 can have a thickness above or below this range.

Coating Layer 32

The coating layer 32 includes or comprises an ethylene acrylic acid (EAA) polymer (such as an EAA copolymer), and is suitably applied to the polymeric substrate 30 via a coating technique. The coating layer 32 can thus be viewed as a solidified form of an aqueous coating composition including EAA polymer (such as an EAA copolymer) particles as described below.

Useful EAA copolymers can include from about 2 to about 30 wt% acrylic acid comonomer. In some embodiments, the EAA copolymer comprises only ethylene and acrylic acid co-monomers. However, the copolymers may further comprise one or more additional co-monomers. Suitable EAA copolymers for use with the present disclosure are available from Michelman, Inc. of Cincinnati, OH, under the trade designation "Michem® Prime", such as Michem® Prime 4983R and Michem® Prime 5931.

As mentioned above, in a final form of the barrier film article 20, the coating layer 32 is solidified. The solidified structure can result from an aqueous coating composition including the EAA polymer or EAA copolymers described above along with other ingredients that promote coating and subsequent solidification. The aqueous coating composition can comprise at least 1 wt% of the EAA particles, such as at least 3 wt% or at least 6 wt% of the EAA particles. In some embodiments, the aqueous coating compositions of the present disclosure are water-based, and include other components such as surfactants, waxes, inorganic particles, etc. The aqueous coating compositions are substantially free of organic solvents (i.e., less than 1 wt% organic solvent).

An adhesion promotor is optionally included with the aqueous coating composition, and can be silane-based. Exemplary materials useful as a silane adhesion promoter include A-J_86 beta-(3,4- Epoxycyclohexyl)ethyltrimethoxysilane - CH2CH2Si(OCH3)3 246.1, A-187* gamma- glycidoxypropyltrimethoxysilane CH2CHCH20CH2CH2CH2Si(OCH3)3 236.1, A-1871 gamma- glycidoxypropyltriethoxysilane 278.1, WetLink* 78 3-glycidoxypropylmethyldiethoxysilane 248.4, and CoatOSil* 1770 beta-(3,4-epoxycyclohexyl)ethyltriethoxysilane 288.

UV absorbers are optionally added to the aqueous coating composition. UV absorbers are typically organic UV absorbers. Suitable examples of organic UV absorbers include benzophenones, benzotriazoles, benzoxazinones and triazines. The coating composition optionally comprises a light stabilizer, preferably a hindered amine light stabilizer (HALS), typically having a hindered piperidine skeleton in the molecule. Specific examples of HALS include bis-(2,2,6,6-tetramethyl-4- piperidyl)sebacate, bis-(N-methyl-2,2,6,6-tetramethyl-4-piperidyl)sebacate, bis-(l,2,2,6,6-pentamethyl-4- piperidyl)sebacate, l,2,2,6,6-pentamethyl-4-piperidyl-tridecyl-l,2,3,4-butanetetracarboxylate- , tetrakis- (2,2,6,6-tetramethyl-4-piperidyl)-l,2,3,4-butanetetracarboxylat- e, and tetrakis-(N-methyl-2,2,6,6- tetramethyl-4-piperidyl)- 1 ,2,3 ,4-butanet- etracarboxylate .

As described below, the coating layer 32 can serve as a primer for the polymeric substrate 30, promoting adhesion of the barrier layer 34 in a highly smooth form. In some embodiments, a thickness of the coating layer 32 is less than 500 nanometers, optionally in the range of about 50 - 250 nanometers, alternatively in the range of 100 - 250 nanometers. As described above, the polymeric substrate 30 can include pigment or filler particles that affect surface roughness. In some embodiments, a thickness of the coating layer 32 is less than an average particle size of the pigment or filler particles of the polymeric substrate. In yet other embodiments, a thickness of the coating layer 32 is less than the mean roughness depth Rz at the first major face 40 of the polymeric substrate 30. With these and related embodiments, the coating layer 32 may not entire "cover" pigment or filler particle(s) at the first major face 40 and thus may not establish a truly planar or planarizing layer for the barrier layer 34; it has surprisingly been found that even though a planarizing layer for the barrier layer 34 may not be present, the coating layers 32 of the present disclosure promote adhesion of the subsequently-applied barrier layer 34 (otherwise including at least silicon and oxygen as described below) in a format that enhances or improves performance of the barrier layer 34 in terms of MVTR and/or oxygen transmission rate.

Barrier Layer 34

The barrier layer 34 can assume various forms, and in some embodiments includes or comprises at least silicon and oxygen. In related embodiments, the barrier layer includes or comprises at least silica. In other embodiments, the barrier layer 34 additionally includes carbon (e.g., at least 0.1 atomic percent carbon, alternatively at least 5 atomic percent carbon, alternatively at least 10 atomic percent carbon, alternatively at least 20 atomic percent carbon). A particularly advantageous form of the barrier layer 34 is a diamond-like film, which is very high in atomic packing density, having superior adhesion to the substrate, flexibility, and abrasion resistance. In related embodiments, the barrier layer 34 is diamondlike carbon (DLC), or alternatively is diamond-like glass (DLG).

The term "diamond-like glass" (DLG) refers to substantially or completely amorphous glass including carbon, silicon and oxygen, and optionally including one or more additional components selected from the group including hydrogen, nitrogen, fluorine, sulfur, zirconium, titanium, copper, etc. Other elements may be present in certain embodiments. The amorphous diamond-like glass films may contain clustering of atoms to give it a short-range order but are essentially void of medium and long range ordering that lead to micro or macro crystallinity which can adversely scatter radiation having wavelengths of from 180 nanometers (nm) to 800 nm.

The term "diamond-like carbon" (DLC) refers to an amorphous film or coating comprising approximately 50 to 90 atomic percent carbon and approximately 10 to 50 atomic percent hydrogen, with a gram atom density of between approximately 0.20 and approximately 0.28 gram atoms per cubic centimeter, and composed of approximately 50% to approximately 90% tetrahedral bonds.

With optional embodiments in which the barrier layer 34 is DLG, diamond-like glass is an amorphous carbon system including a substantial quantity of silicon and oxygen that exhibits diamondlike properties. In these films, on a hydrogen-free basis, there is at least 30% carbon, a substantial amount of silicon (typically at least 25%) and no more than 45% oxygen. The unique combination of a fairly high amount of silicon with a significant amount of oxygen and a substantial amount of carbon makes these films highly transparent and flexible (unlike glass).

Diamond-like glass thin films may have a variety of light transmissive properties. Depending upon the composition, the thin films may have increased transmissive properties at various frequencies. However, in specific implementations the thin film (when approximately one micron thick) is at least 70% transmissive to radiation at substantially all wavelengths from about 250 nm to about 800 nm and more preferably from about 400 nm to about 800 nm. The extinction coefficient of DLG film is as follows: 70% transmission for a one micron thick film corresponds to an extinction coefficient (k) of less than 0.02 in the visible wavelength range between 400 nm and 800 nm.

The DLG can optionally be an amorphous carbon system including a substantial quantity of silicon and oxygen that exhibits diamond-like properties. In these films, on a hydrogen-free basis, there is optionally at least 5% carbon, a substantial amount of silicon (typically at least 25%) and no more than 65% oxygen. In some embodiments, the DLG is created by depositing a dense random covalent system comprising carbon, silicon, hydrogen, and oxygen under ion bombardment conditions by locating a substrate on a powered electrode in a radio frequency ("RF") chemical reactor. In one non-limiting implementation, DLG is deposited under intense ion bombardment conditions from mixtures of tetramethylsilane and oxygen, or from mixtures of hexamethyldisiloxane and oxygen. Typically, DLG shows negligible optical absorption in the visible and ultraviolet regions (250 to 800 nm). Also, DLG usually shows improved resistance to flex-cracking compared to some other types of carbonaceous films and excellent adhesion to many substrates, including ceramics, glass, metals and polymers.

Other possible compositions, features, manufacturing techniques and additives useful with the optional DLG formats of the present disclosure are described, for example, in U.S. Patent No. 6,696, 157, entitled "Diamond-Like Glass Thin Films" ("the Ί57 Patent") and in U.S. Patent No. 8,034,452, entitled "Moisture Barrier Coating" ("the '452 Patent"), the entire teachings of each which are incorporated herein by reference.

With other optional embodiments in which the barrier layer 34 is DLC, diamond and DLC differ significantly due to the arrangement of carbon atoms in the specific material. Carbon coatings contain substantially two types of carbon-carbon bonds: trigonal graphite bonds (sp²) and tetrahedral diamond bonds (sp³). Diamond is composed of virtually all tetrahedral bonds, DLC is composed of approximately 50% to 90% tetrahedral bonds, and graphite is composed of virtually all trigonal bonds. The type and amount of bonds are determined from IR and nuclear magnetic resonance (NMR) spectra.

Other possible compositions, features, manufacturing techniques and additives useful with the optional DLC formats of the present disclosure are described, for example, in the '452 Patent, the entire teachings of which are incorporated herein by reference.

Optional Functional Layer 202

Where provided, the optional functional layer 202 can assume various forms. In some embodiments, the functional layer 202 can be any of the formats described above with respect to the barrier layer 34 (e.g., a material including at least silicon and oxygen), and in some embodiments the functional layer 202 and the barrier layer 34 are identical (at least in terms of composition). With end use applications in which the barrier film article 200 is used as a backsheet in a PV module, the so- constructed functional layer 202 can promote adhesion with an encapsulant material (e.g., EVA or polyolefin) conventionally used in PV module assembly. In other embodiments, the functional layer 202 can assume other forms that promote adhesion with conventional PV module encapsulants, such as an acrylic coating or a polyester coating.

Optional Fluoropolymer Layer

In some embodiments, a fluoropolymer layer (not shown) is provided adjacent to (e.g., directly over) the barrier layer 34. Not all embodiments include a fluoropolymer layer; this layer is optional. A fluoropolymer layer is not required, but may be included in some embodiments. Where a fluoropolymer layer is included, the fluoropolymer can be selected from a variety of fluoropolymers. Such fluoropolymers are typically homopolymers or copolymers of TFE (tetrafluoro ethylene), VDF (vinylidene fluoride), VF (vinylfluoride), (chlorotrifluoroethylene), or CTFE with other fluorinated or non-fluorinated monomers. Representative materials include copolymers of tetrafluoroethylene-ethylene (ETFE), tetrafluoroethylene-hexafluoropropylene (FEP), tetrafluoroethylene-perfluoroalkoxyvinlyether (PFA), copolymers of vinylidene fluoride and chlorotrifluoroethylene, tetrafluoroethylene- hexafluoropropylene -ethylene (HTE), polyvinyl fluoride (PVF), copolymers of vinylidene fluoride and chlorotrifluoroethylene, or a copolymer derived from tetrafluoroethylene (TFE), hexafluoropropylene (HFP), and vinylidene fluoride (VDF), such as the THV series available from 3M Company, Saint Paul, Minn.

The fluoropolymer layer may be capable of providing or enhancing low moisture permeability characteristics ("barrier" properties) to the construction in order to protect internal components of the film or of the preferred solar cell application.

A preferred class of fluorinated copolymers suitable as the fluoropolymer layer are those having interpolymerized units derived from tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride, and optionally a perfluoro alkyl or alkoxy vinyl ether. Preferably these polymers have less than about 30 weight percent (wt %) VDF, more preferably between about 10 and about 25 wt %, of its interpolymerized units derived from VDF. A non-limiting example includes THV 500 available from Dyneon LLC, Oakdale, Minn.

Another preferred class of materials suitable for use as the fluoropolymer layer include various combinations of interpolymerized units of TFE and ethylene along with other additional monomers such as HFP, perfluoro alkyl or alkoxy vinyl ethers (PAVE or PAOVE). An example is HTE 1510, available from Dyneon LLC, Oakdale, Minn.

Optional Additives

Optionally, other materials can be included with barrier film articles of the present disclosure, as part of one or more of the polymeric substrate 30, the coating layer 32, the barrier layer 34, the optional functional layer 202, or as part of an additional layer. Exemplary optional adjuvants include, for example, antioxidants, UV-absorbers, light stabilizers, conductive materials, flame retardants, photoluminescent additives, fillers, lubricants, plasticizers, processing aids, stabilizers, and the like including combinations of such materials. In addition, metallized coatings and reinforcing materials also may be used in or with the barrier film articles of the present disclosure. These include, e.g., polymeric or fiberglass scrim that can be bonded, woven or non-woven.

The barrier film articles of the present disclosure are useful, for example, with various electronic devices. In some embodiments, the barrier film articles of the present disclosure can be employed as the backsheet for a PV module. FIG. 2 is a simplified representation of a PV module 250. The PV module includes a plurality of PV cells 252 that can be interconnected by electrical leads 254 (e.g., flat copper ribbons). Overlying the PV cells 252 is an optional front cover 256 that may be a planar light- transmitting and electrically non-conducting cover in sheet form that also functions as part of the cell support structure of the PV module 250. The PV cells 252 overlie a backsheet 258. The backsheet 258 is a barrier film article of the present disclosure, such as the barrier film article 20, 200 as described above. Interposed between the backsheet 258 and the front cover 256 and surrounding the PV cells 252 and their electrical connector ribbons 254 is an encapsulant 260 that is typically made of suitable light-transparent, electrical non-conductive material (e.g., ethylene vinyl acetate copolymer known in the trade as "EVA" or an ionomer).

Methods of Making

FIG. 3 is a diagram of a system 300, illustrating methods in accordance with principles of the present disclosure for making the barrier film articles described above. A continuous supply or length of the polymeric substrate 30 is provided to the manufacturing line using conventional techniques (e.g., the polymeric substrate 30 can be provided as an extruded film). The polymeric substrate 30 is directed to a first coating station 302. The first coating station 302 is configured and arranged to apply an aqueous coating composition 304 onto the first major face 40 of the polymeric substrate 30 via conventional coating techniques known in the art. The aqueous coating composition can have any of the formats described above with respect to the coating layer 32 (it being understood that the coating layer 32 later results from solidification of the aqueous coating composition 304) and generally includes EAA copolymer particles, along with other components (e.g., water, surfactant(s), etc.). The applied aqueous coating composition 304 and the substrate 30 combine to define a coated substrate 306 immediately downstream of the first coating station 304.

The coated substrate 306 is next subjected to stretching at a stretching station 310. The stretching station 310 can have any form typically employed for stretching film (e.g., a tenter), and subjects the coated substrate 306 (including the aqueous coating composition 304 in a non-solidified form) to biaxial or uniaxial stretching (e.g., the coated substrate 306 is stretched or oriented longitudinally (i.e., the machine direction of the substrate 30) and/or transversely (i.e., perpendicularly to the machine direction)). In some embodiment, the polymeric substrate 30 is subjected to stretching in one direction prior to deposition of the aqueous coating composition 304 (e.g., at an optional initial stretching station 312), and the coated substrate 306 is subjected to stretching in a second direction (transverse to the first direction) at the stretching station 310. For example, the polymeric substrate 30 can be longitudinally stretched at the initial stretching station 312, and the coated substrate 306 is transversely stretched at the stretching station 310. Regardless, and in accordance with some aspects of the present disclosure, a step of film stretching or tenting occurs after the aqueous coating composition 304 (otherwise including the EAA copolymer particles), in contrast to conventional PV module backsheet barrier layer film manufacturing practices.

The stretched coated substrate 306 can then be subjected to various drying and heat setting conditions to solidify the aqueous coating composition 304 into the coating layer 32 (e.g., processing the stretched coated substrate through an oven or similar elevated heat conditions). Next, the stretched coated substrate 306 is delivered to a second coating station 314. While FIG. 3 implicates the second coating station 314 being in-line with the stretching station 310, it will be understood that in some embodiments, the second coating station 314 (at which the barrier layer 34 is applied) is off-line relative to the stretching station 310 (e.g., the stretched coating substrate 306 is subjected to processing at the second coating station 314 at a later point in time on a different machine). The second coating station 314 is configured and arranged to apply the barrier layer 34 onto the coating layer 32, with the coating layer 32 thus serving as a primer for the polymeric substrate 30. The second coating station 314 can assume various known in the art and appropriate for applying the particular format of the barrier layer 34 (e.g., a plasma enhanced chemical vapor deposition process as described, for example, in U.S. Application Publication No. 2009/0186209, the entire teachings of which are incorporated herein by reference).

Following application of the barrier layer 34, a continuous sheet 320 of barrier film is provided. Optionally, one or more additional layers can be applied to the sheet 320 as described above (e.g., the functional layer 202 of FIG. IB). The sheet 320 of barrier film can be cut into discrete sections (that serve as the barrier film articles of the present disclosure), or can be stored in roll (or other) form for subsequent processing in to barrier film articles.

Embodiments and advantages of features of the present disclosure are further illustrated by the following non-limiting examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit the scope of the present disclosure. Unless otherwise noted, all parts, percentages, and ratios reported in the following examples are on a weigh basis. Flow rates are in standard cubic centimeters per minute, abbreviated "seem". Reagents were obtained from Sigma Aldrich Company of St. Louis, MO unless otherwise noted.

EXAMPLES Materials

White PET Film: Polyethylene terephthalate film pigmented with titanium dioxide filler particles having a mean particle size of 0.22 microns. EAA Copolymer Dispersion 1 : Ethylene acrylic acid copolymer dispersion available under the trade designation Michem® Prime 5931 from Michelman, Inc. of Cincinnati, OH.

EAA Copolymer Dispersion 2: Ethylene acrylic acid copolymer dispersion available under the trade designation Michem® Prime 4983R from Michelman, Inc. of Cincinnati, OH.

Silane: Adhesion promoter available under the trade designation A- 187* gamma- glycidoxypropyltrimethoxysilane from Momentive Performance Materials Inc. of Waterford, NY.

Rhoplex Dispersion: Dispersion of Rhoplex 3208 available from Dow Chemical Co., surfactant, crosslinker and crosslinking catalyst.

THV Dispersion: A fluoropolymer dispersion available under the trade designation Dyneon™ THV 340Z from 3M Company of St. Paul, MN.

Cymel® 350: Highly methylated, monomelic melamine resin crosslinker available from Allnex Belgium SA/VN.

Tomadol: Ethoxylated alcohol surfactant available from Air Products and Chemicals, Inc. of Allentown, PA.

Dynol: Ethoxylated, acetylenic diol surfactant available from Air Products and Chemicals, Inc. of Allentown, PA.

Urethane Emulsion: A urethane emulsion available under the trade designation NeoRex® R966 from DSM Coating Resins of The Netherlands.

HMDSO: hexamethyldisiloxane.

Moisture Vapor Transmission Rate

Moisture vapor transmission rate was determined according to ASTM F 1249-06 at 37.8 °C and 100% relative humidity.

Example 1

A White PET Film (with titanium dioxide as a filler) was extruded and longitudinally stretched at a stretch ratio of 3.25 : 1. The stretched film was coated on one side with an aqueous coating composition of 7% solids by weight, which contained 71% by weight EAA Copolymer Dispersion 1, 28.7% by weight Cymel® 350 crosslinker, and 0.3% Tomadol surfactant based on the dried coating. The film was then dried and then stretched transversely at a stretch ratio of 4: 1 and finally heat set to obtain a biaxially oriented film. The final thickness of the White PET Film was 75 micron. The average thickness of the coating layer (containing the EAA copolymer) was calculated to be in the range of 100-120 nm. The primed film was then further coated with a barrier layer containing 0.5 atomic percent carbon, 68 atomic percent oxygen and 31.5 atomic percent silicon using an ion-enhanced plasma deposition process. MVTR for Example 1 was obtained. The deposition conditions for the barrier layer and determined MVTR of Example 1 are provided in Table 1. Example 1 HMDSO 0₂ Speed Power MVTR

(seem) (seem) (feet/minute) (watts) (g/m²-day)

200 2000 10 10000 1 .59

TABLE 1

Example 2

A White PET Film (with titanium dioxide as a filler) was extruded and longitudinally stretched at a stretch ratio of 3.25 : 1. The stretched film was coated on one side with an aqueous coating composition of 7% solids by weight, which contained 96.8% by weight EAA Copolymer Dispersion 2, 3% Cymel® 350 and 0.2% Dynol surfactant based on the dried coating. The film was then dried and then stretched transversely at a stretch ratio of 4: 1 and finally heat set to obtain a biaxially oriented film. The final thickness of the White PET Film was 147.5 micron. The average thickness of the coating layer (containing the EAA copolymer) was measured to be 110 nm. The primed film was then further coated with a barrier layer containing carbon, oxygen and silicon using an ion-enhanced plasma deposition process. The effect of barrier layer process conditions was established by depositing the barrier layer on the primed White PET Film while varying: 1) plasma power, 2) line speed, and 3) HDMSO/O2 ratio. Seven sets of conditions were examined, including a determination of MVTR. The deposition conditions for the DLG layer and determined MVTR for each of the seven sets of conditions of Example 2 are provided in Table 2.

Table 2

Example 3

A White PET Film (with titanium dioxide as a filler) was extruded and longitudinally stretched at a stretch ratio of 3.25 : 1. The stretched film was coated on one side with an aqueous coating composition of 7% solids by weight, which contained 83.8% by weight EAA Copolymer Dispersion 1, 8% by weight Cymel® 350 crosslinker, 8% by weight Silane and 0.2% Dynol surfactant based on the dried coating. The film was then dried and then stretched transversely at a stretch ratio of 4: 1 and finally heat set to obtain a biaxially oriented film. The final thickness of the White PET Film was 147.5 micron. The average thickness of the coating layer (containing the EAA copolymer) was measured to be 110 nm. The primed film was then further coated with a barrier layer using an ion-enhanced plasma deposition process. The effect of differing barrier layer processing conditions and barrier layer constituents on MVTR was evaluated. The deposition conditions and components for the barrier layer and determined MVTR of Example 3 are provided in Table 3.

Table 3

Example 4

A White PET Film (with titanium dioxide as a filler) was extruded and longitudinally stretched at a stretch ratio of 3.25: 1. The stretched film was coated on both sides with an aqueous coating composition of 7% solids by weight, which contained 83.8% by weight EAA Copolymer Dispersion 1, 8% by weight Cymel® 350 crosslinker, 8% by weight Silane and 0.2% Dynol surfactant based on the dried coating. The film was then dried and then stretched transversely at a stretch ratio of 4: 1 and finally heat set to obtain a biaxially oriented film. The final thickness of the White PET Film was 147.5 micron. The average thickness of the coating layer (containing the EAA copolymer) was calculated to be 110 nm. The primed film was then further coated on both sides with a barrier layer containing 0.5 atomic percent carbon, 68 atomic percent oxygen and 31.5 atomic percent silicon using an ion-enhanced plasma deposition process. The deposition conditions for the barrier layer and determined MVTR of Example 4 are provided in Table 4.

Table 4

Comparative Example 1

A White PET Film (with titanium dioxide as a filler) was extruded and longitudinally stretched at a stretch ratio of 3.25 : 1. The stretched film was further stretched transversely at a stretch ratio of 4: 1 and finally heat set to obtain a biaxially oriented film. The final thickness of the White PET Film was 75 micron. The unprimed film was then further coated with a barrier layer containing 0.5 atomic percent carbon, 68 atomic percent oxygen and 31.5 atomic percent silicon using an ion-enhanced plasma deposition process. MVTR for Comparative Example 1 was obtained. The deposition conditions for the barrier layer and determined MVTR for Comparative Example 1 are provided in Table 5. Comparative HMDSO 0₂ Forward Speed Thickness MVTR

Example 1 (seem) (seem) Power (feet/minute) (g/m²-day)

(watts)

200 2000 10000 10 125 nm 2.45

Table 5

Comparative Example 2

A clear PET Film was extruded and longitudinally stretched at a stretch ratio of 3.25 : 1. The stretched film was coated on one side with an aqueous coating composition of 7% solids by weight, which contained 94.8% by weight Rhoplex Dispersion, 5% by weight Cymel® 350 crosslinker and 0.2% by weight Tomadol based on the dried coating. The film was then dried and then stretched transversely at a stretch ratio of 4: 1 and finally heat set to obtain a biaxially oriented film. The final thickness of the PET Film was 125 micron. The average thickness of the coating layer (containing the EAA copolymer) was calculated to be 110 nm. The primed film was then further coated with a barrier layer containing 0.5 atomic percent carbon, 68 atomic percent oxygen and 31.5 atomic percent silicon using an ion-enhanced plasma deposition process. MVTR for Comparative Example 2 was obtained. The deposition conditions for the barrier layer and determined MVTR of Comparative Example 2 are provided in Table 6.

Table 6

Comparative Example 3

A White PET Film (with titanium dioxide as a filler) was extruded and longitudinally stretched at a stretch ratio of 3.25 : 1. The stretched film was coated on one side with an aqueous coating composition of 12.9% solids by weight, which contained 70% by weight THV Dispersion, 27.8% by weight Urethane Emulsion, and 2.7% by weight Cymel® 350 crosslinker based on the dried coating. The film was then dried and then stretched transversely at a stretch ratio of 4: 1 and finally heat set to obtain a biaxially oriented film. The final thickness of the White PET Film was 147.5 micron. The average thickness of the coating layer (containing the EAA copolymer) was calculated to be 110 nm. The primed film was then further coated with a barrier layer containing 0.5 atomic percent carbon, 68 atomic percent oxygen and 31.5 atomic percent silicon using an ion-enhanced plasma deposition process. MVTR for Comparative Example 3 was obtained. The deposition conditions for the barrier layer and determined MVTR of Comparative Example 3 are provided in Table 7.

Table 7 A testing matrix was established by which samples of PET Film: 1) were coated with one of the aqueous composition of Example 1 (containing EAA Copolymer Dispersion 1), the TUV/urethane aqueous coating composition of Comparative Example 3, or the Rhoplex aqueous coating composition of Comparative Example 2, and MVTR obtained, and 2) the coated layers were dried and then coated with a barrier layer containing carbon, silicon and oxygen, and MVTR obtained. MVTR for the PET Film prior to coating with primer coating was also obtained. MVTR for all samples of the testing matrix were obtained and are reported in Table 8 below.

Table 8

Without wishing to be bound by theory, the inventors believe that a reduction in MVTR by adding the coating layer (containing EAA copolymer) is achieved because the coating layer with EAA copolymer surprisingly acts as a highly appropriate adhesion agent between the PET substrate surface and the barrier layer that is surprisingly independent of a surface roughness of the polymeric substrate. Table 9 below reports surface roughness measurements for White PET Film coated with the EAA Copolymer coating composition of Example 1, the Rhoplex coating composition of Comparative Example 2, or the THV coating composition of Comparative Example 3 (prior to application of a barrier layer), as well as measured MVTR following application of a barrier layer to the primed sample.

Table 9

Although the present disclosure has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the present disclosure.

Exemplary Embodiments

1. A barrier film article comprising:

a polymeric substrate defining opposing, first and second major faces; a coating layer adjacent the first major face, wherein the coating layer includes ethylene acrylic acid (EAA) copolymer; and

a barrier layer adjacent the coating layer opposite the first major face, wherein the barrier layer includes silicon and oxygen.

2. The barrier film article of embodiment 1, wherein the barrier layer further includes at least 5 atomic percent carbon.

3. The barrier film article of embodiment 2, wherein the barrier layer includes at least 10 atomic percent carbon.

4. The barrier film article of embodiment 3, wherein the barrier layer includes at least 20 atomic percent carbon. 5. The barrier film article of embodiment 2, wherein the barrier layer is diamond-like carbon (DLC).

6. The barrier film article of embodiment 2, wherein the barrier layer is diamond-like glass (DLG). 7. The barrier film article of embodiment 1, wherein the coating layer is configured to adhere the barrier layer relative to the polymeric substrate.

8. The barrier film article of embodiment 1, wherein the coating layer has a thickness of less than 500 nanometers.

9. The barrier film article of embodiment 8, wherein the thickness of the coating layer is in the range of 50 - 250 nanometers.

10. The barrier film article of embodiment 8, wherein the thickness of the coating layer is in the range of 100 - 250 nanometers.

11. The barrier film article of embodiment 1, wherein the coating layer is a solidified form of an aqueous coating composition including EAA copolymer particles. 12. The barrier film article of embodiment 11, wherein the aqueous coating composition further includes at least one of a surfactant, a crosslinking agent consisting of melamines, isocyantes, aziridines, a coupling agent consisting of epoxy functional silanes, a wetting agent, a radical scavenger, a UV absorber, HALS, an antioxidant, an antistatic agent, an antiblocking agent, and a matting agent.

13. The barrier film article of embodiment 11, wherein the aqueous coating composition is substantially free of organic solvents.

14. The barrier film article of embodiment 1, wherein the polymeric substrate includes at least one layer of polyester. 15. The barrier film article of embodiment 14, wherein the polymeric substrate is a multilayer polyester film.

16. The barrier film article of embodiment 14, wherein the polyester is polyethylene terephthalate (PET).

17. The barrier film article of embodiment 1, wherein the polymeric substrate further includes pigment particles.

18. The barrier film article of embodiment 17, wherein the pigment particles include a material selected from the group consisting of titanium dioxide, barium sulfate, carbon black, and calcium carbonate.

19. The barrier film article of embodiment 1, wherein a maximum surface roughness Rz of the first major face is greater than a thickness of the coating layer.

20. The barrier film article of embodiment 1, wherein the polymeric substrate includes PET and pigment particles, and further wherein the coating layer is a solidified from of an aqueous coating composition including EAA copolymer particles, and even further wherein the barrier layer further includes carbon.

21. The barrier film article of embodiment 1, wherein the polymeric substrate is a biaxially oriented film.

22. The barrier film article of embodiment 1, wherein the barrier film article exhibits a moisture vapor transmission rate of less than about 2.5 g/m²/day at 37.8 °C and 100% relative humidity. 23. The barrier film article of embodiment 1, wherein the barrier film article exhibits a moisture vapor transmission rate of less than about 1.0 g/m²/day at 37.8 °C and 100% relative humidity.

24. The barrier film article of embodiment 1, wherein the barrier film article exhibits a moisture vapor transmission rate of less than about 0.5 g/m²/day at 37.8 °C and 100% relative humidity.

25. The barrier film article of embodiment 1, wherein the barrier film article exhibits an oxygen transmission rate of less than about 4 cc/m²/day at 23 °C and ambient relative humidity. 26. The barrier film article of embodiment 1, wherein the barrier film article exhibits an oxygen transmission rate of less than about 2 cc/m²/day at 23 °C and ambient relative humidity.

27. The barrier film article of embodiment 1, wherein the barrier film article exhibits an oxygen transmission rate of less than about 1 cc/m²/day at 23 °C and ambient relative humidity.

28. The barrier film article of embodiment 1, wherein the barrier film article exhibits:

a moisture vapor transmission rate of less than about 2.5 g/m²/day at 37.8 °C and 100% relative humidity; and

an oxygen transmission rate of less than about 4 cc/m²/day at 23 °C and ambient relative humidity.

29. The barrier film article of embodiment 28, wherein the barrier film article exhibits a moisture vapor transmission rate of less than about 1.0 g/m²/day at 37.8 °C and 100% relative humidity. 30. The barrier film article of embodiment 29, wherein the barrier film article exhibits a moisture vapor transmission rate of less than about 0.5 g/m²/day at 37.8 °C and 100% relative humidity.

31. The barrier film article of embodiments 29 or 30, wherein the barrier film article exhibits an oxygen transmission rate of less than about 2 cc/m²/day at 23 °C and ambient relative humidity.

32. The barrier film article of embodiment 31, wherein the barrier film article exhibits an oxygen transmission rate of less than about 1 cc/m²/day at 23 °C and ambient relative humidity.

33. The barrier film article of embodiment 1, wherein the barrier film article has a thickness of less than about 0.011 inch. 34. The barrier film article of embodiment 1, wherein the barrier film article is configured for use as a backsheet of a photovoltaic module.

35. The barrier film article of embodiment 1, further comprising a fluoropolymer layer adjacent the barrier layer.

36. The barrier film article of embodiment 1, further comprising a second barrier layer adjacent the second major face of the polymeric substrate. 37. The barrier film article of embodiment 36, wherein the second barrier layer is configured to promote adhesion to an encapsulant of a photovoltaic module.

38. The barrier film article of embodiment 1, further comprising an adhesion coating adjacent the second major face of the polymeric substrate, the adhesion coating selected from the group consisting of an acrylic coating and a polyester coating.

39. The barrier film article of embodiment 1, wherein the polymeric substrate further comprises at least one additive selected from the group consisting of an antioxidant, a light stabilizer, and optical brightener and a UV stabilizer.

40. The barrier film article of embodiment 1, wherein the coating layer contacts the first major face.

41. The barrier film article of embodiment 40, wherein the barrier layer contacts the coating layer. 42. The barrier film article of embodiment 1, wherein an adhesion between the polymeric substrate, the coating layer and the barrier layer has a value of at least 4 as measured under ASTM D 3359, Test Method A.

43. A method for making a barrier film article, the method comprising:

providing a polymeric film substrate defining opposing, first and second major faces;

coating the first major face with a coating material including ethylene acrylic acid (EAA) copolymer to form a coated substrate;

stretching the coated substrate; and

applying a barrier layer on to the coating material of the stretched coated substrate, wherein the barrier layer includes silicon and oxygen.

44. The method of embodiment 43, wherein the step of stretching is performed by a tenter machine. 45. The method of embodiment 43, wherein the barrier layer further includes carbon.

46. The method of embodiment 45, wherein the barrier layer is diamond-like carbon (DLC) or diamond-like glass (DLG).

47. The method of embodiment 43, wherein the coating material is an aqueous coating composition including EAA copolymer particles. 48. The method of embodiment 47, wherein the aqueous coating composition further includes at least one of a surfactant, a crosslinking agent consisting of melamines, isocyantes, aziridines, a coupling agent consisting of epoxy functional silanes, a wetting agent, a radical scavenger, a UV absorber, HALS, an antioxidant, an antistatic agent, an antiblocking agent, and a matting agent. 49. The method of embodiment 47, wherein the aqueous coating composition is substantially free of organic solvents.

50. The method of embodiment 43, wherein the polymeric film substrate includes a polyester. 51. The method of embodiment 50, wherein the polyester is polyethylene terephthalate (PET).

52. The method of embodiment 50, wherein the polymeric film substrate further includes pigment particles. 53. The method of embodiment 52, wherein the pigment particles include a material selected from the group consisting of titanium dioxide, barium sulfate, carbon black, and calcium carbonate.

54. The method of embodiment 43, wherein a coating thickness of the coating material is less than a maximum surface roughness Rz of the first major face.

55. The method of embodiment 43, further comprising stretching the polymeric film substrate in a machine direction prior to the step of coating the first major face with a coating material.

56. The method of embodiment 55, wherein the step of stretching the coated substrate includes stretching the coated substrate in a transverse direction perpendicular to the machine direction.

57. A method of making a primed biaxially oriented polyester film, the method comprising: providing a uniaxially oriented polyester film defining opposing, first and second major faces, the uniaxially oriented film having been stretched in a machine direction;

coating the composition of embodiment 1 onto the first major face;

partially drying the coating composition to provide a coated uniaxially oriented film; and stretching the coated uniaxially oriented film in a transverse direction.

58. The method of embodiment 57, further comprising coating the composition of embodiment 1 onto the second major face.

59. A backsheet for a photovoltaic module, the backsheet comprising:

a polymeric substrate defining opposing, first and second major faces;

a coating layer adjacent the first major face, wherein the coating layer includes ethylene acrylic acid (EAA) copolymer; and

60. A photovoltaic module comprising:

a backsheet including:

a polymeric substrate defining opposing, first and second major faces,

a coating layer adjacent the first major face, wherein the coating layer includes ethylene acrylic acid (EAA) copolymer,

a barrier layer adjacent the coating layer opposite the first major face, wherein the barrier layer includes silicon and oxygen; and

a plurality of photovoltaic cells.

Claims

What is claimed is:

1. A barrier film article comprising:

a polymeric substrate defining opposing, first and second major faces;

2. The barrier film article of claim 1, wherein the barrier layer is diamond-like carbon (DLC).

3. The barrier film article of claim 1, wherein the barrier layer is diamond-like glass (DLG).

4. The barrier film article of claim 1, wherein the thickness of the coating layer is in the range of 100 - 250 nanometers.

5. The barrier film article of claim 1, wherein the coating layer is a solidified form of an aqueous coating composition including EAA copolymer particles.

6. The barrier film article of claim 1, wherein a maximum surface roughness Rz of the first major face is greater than a thickness of the coating layer.

7. The barrier film article of claim 1, wherein the barrier film article exhibits a moisture vapor transmission rate of less than about 2.5 g/m²/day at 37.8 °C and 100% relative humidity.

8. The barrier film article of claim 1, wherein the barrier film article exhibits an oxygen transmission rate of less than about 4 cc/m²/day at 23 °C and ambient relative humidity.

9. The barrier film article of claim 1, wherein the barrier film article has a thickness of less than about 0.011 inch.

10. The barrier film article of claim 1, further comprising a fluoropolymer layer adjacent the barrier layer.

11. The barrier film article of claim 1, wherein the coating layer contacts the first major face, and wherein the barrier layer contacts the coating layer.

12. A method for making a barrier film article, the method comprising:

stretching the coated substrate; and

13. The method of claim 12, wherein the barrier layer is diamond-like carbon (DLC) or diamond-like glass (DLG).

14. The method of claim 12, wherein a coating thickness of the coating material is less than a maximum surface roughness Rz of the first major face.

15. A method of making a primed biaxially oriented polyester film, the method comprising:

providing a uniaxially oriented polyester film defining opposing, first and second major faces, the uniaxially oriented film having been stretched in a machine direction;

coating the composition of claim 1 onto the first major face;