Patent Description:
Aircraft face a harsh environment in use, often subject to aggressive chemicals (e.g., paint strippers, deicing fluids, jet fuel) and environmental conditions including lightning strikes and other potential degradation mechanisms due to environmental stresses (e.g., UV, salt, acid or thermal degradation). In addressing these issues, aircraft manufacturers are under increasingly difficult pressures to reduce manufacturing costs, and to reduce weight and improve performance of the aircraft.

<CIT> and <CIT> disclose, a surfacing material including a porous conductive layer embedded in the curable resin layer and a mold-releasable layer. The mold-releasable layer is in contact with the mold surface of the molding tool during composite part manufacturing. The mold-releasable layer consists of a woven fabric that is bonded on one side to a curable epoxy-thermoplastic layer; a curable resin layer in contact with the opposite side of the woven fabric; and a conductive layer laminated to or embedded in the curable resin layer.

<CIT> discloses a lightning strike protection surfacing layer comprising a curable epoxy resin coating and combined with a polyester mat carrier and expanded copper screen. As the outer layer a polyester peel ply was coated.

The present disclosure is directed toward multifunctional surfacing films that not only protect composite parts/substrates against environmental stresses and chemical exposures, but also provide a peelable porous sheet that reduces downstream manufacturing processes and cost, particularly during surface finishing. The surfacing films are also able to provide even more functions / benefits / properties, including but not limited to improved performance after impact, lightning strike protection, electric current dissipation, EMI shielding, heat transfer performance, or combinations thereof. These surfacing films represent a step forward in aircraft manufacture and performance. The present disclosure describes these surfacing films, as well as methods for making and using them.

The present invebntion is directed to a multifunctional surfacing film (<NUM>) comprising:.

"Beneath" with respect to describing relative positions of the various sheets will be understood to mean behind or covered by and not necessarily under a reference sheet. Various embodiments discussed herein include the wide range of materials and characteristics of the surfacing films generally and of the individual components specifically. The surfacing films may contain additional additives distributed within the curable polymer composition, as well as the interlayer porous sheets. The surfacing films may be conformable to contoured substrates and can have structural attributes and areal weights that provide significant advantages over conventional laminated materials.

Independent embodiments include those where the curable polymer compositions are not yet cured, partially cured, or fully cured.

Other embodiments include methods of modifying a substrate surface using these surfacing films to provide functionality to a substrate surface. In one set of embodiments, the methods comprise:.

In another embodiment, the methods of using these surfacing films comprise.

Certain embodiments incorporate at least one sheet of a second functional material onto a substrate, desirably as part of the multifunctional film, and all described embodiments should be read as optionally containing this feature. The multifunctional surfacing film accomplishes this with minimal weight, and with the additional benefit of providing a peel-ply feature that facilitates simplified downstream manufacturing operations.

In some embodiments, these multifunctional surfacing films can be made by:.

These methods provide the unique advantage of being able to incorporate the peelable porous sheets and porous sheets of the second functional materials at independently defined depths within the curable polymer layer to tune the performance of the surfacing layer.

The present application is further understood when read in conjunction with the appended drawings. For the purpose of illustrating the subject matter, there are shown in the drawings exemplary embodiments of the subject matter; however, the presently disclosed subject matter is not limited to the specific methods, devices, and systems disclosed. In addition, the drawings are not necessarily drawn to scale. In the drawings:.

The present invention is directed to multifunctional surfacing films, and methods of making and using the same.

The present disclosure may be understood more readily by reference to the following detailed description taken in connection with the accompanying Figures, which form a part of this disclosure. It is to be understood that this invention is not limited to the specific products, methods, conditions or parameters described and / or shown herein, and that the terminology used herein is for the purpose of describing particular embodiments by way of example only and is not intended to be limiting of any claimed invention. Similarly, any description as to a possible mechanism or mode of action or reason for improvement is meant to be illustrative only, and the invention herein is not to be constrained by the correctness or incorrectness of any such suggested mechanism or mode of action or reason for improvement. Throughout this text, it is recognized that the descriptions refer both to the multifunctional surfacing films and to the methods of preparing and using the same.

In the present disclosure the singular forms "a," "an," and "the" include the plural reference, and reference to a particular numerical value includes at least that particular value, unless the context clearly indicates otherwise. Thus, for example, a reference to "a material" is a reference to at least one of such materials and equivalents thereof known to those skilled in the art, and so forth.

When values are expressed as approximations by use of the antecedent "about," it will be understood that the particular value forms another embodiment. In general, use of the term "about" indicates approximations that can vary depending on the desired properties sought to be obtained by the disclosed subject matter and is to be interpreted in the specific context in which it is used, based on its function, and the person skilled in the art will be able to interpret it as such. In some cases, the number of significant figures used for a particular value may be one non-limiting method of determining the extent of the word "about. " In other cases, the gradations used in a series of values may be used to determine the intended range available to the term "about" for each value. Where present, all ranges are inclusive and combinable. That is, reference to values stated in ranges includes each and every value within that range.

It is to be appreciated that certain features of the invention which are, for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any subcombination. Finally, while an embodiment may be described as part of a series of steps or part of a more general composition or structure, each said embodiment may also be considered an independent embodiment in itself.

In certain embodiments, the multifunctional surfacing film comprises:.

As used herein, the term "single layer" of curable polymer composition refers both the composition and the associated integrity of the curable polymer composition. Unless otherwise specified herein, a single layer of curable polymer composition refers to a layer having no observable interlayer discontinuities as would be seen in laminate of two similar or dissimilar polymer compositions. This characteristic provides additional strength and stability during environmental challenges (e.g., thermal shock or cycling), relative to laminate composites, by minimizing or eliminating mismatches of, for example, thermal expansion coefficients of different layers or adhesives therebetween. The single layer of curable polymer composition may also be described as a single cohesive polymer layer or a unitary structured layer. Depending on the manner in which the polymer layer is made, the polymer itself may be compositionally homogeneous throughout the film or may vary continuously - i.e., without abrupt polymer compositional discontinuities -- either along the length of the film, or across the width of the film (i.e., from the first to second surfaces). As used herein, the term "opposing," as in "opposing first and second surfaces," refers to the planar surfaces (faces) on either side of a film, sheet, or layer; for example on opposite faces of the single layer of curable polymer composition.

In other embodiments, the requirement that the multifunctional surfacing film have a single layer of curable polymer composition may be relaxed, and laminates comprising similar or dissimilar polymers may be considered. Alternatively, the multifunctional surfacing film may itself be laminated to another curable polymer composition comprising the same or different polymers as the surfacing film.

Also, while most of the embodiments are described in terms of "curable" polymer compositions," additional embodiments include those where the composition is either partially or fully cured, either within itself or co-cured with another curable polymer composition.

In certain embodiments, the curable polymer composition may comprise one or more thermoset or thermoplastic resins, or a blend or mixture of both. The polymer composition may comprise monomers, oligomers, or polymers of such materials. Exemplary, non-limiting curable polymers comprise benzoxazines, bismaleimide, epoxies, (meth)acrylates, (meth)acrylamides, polyamides, polyesters, polyimides, polyurethanes, vinyl esters, or copolymers or mixtures thereof. Epoxies are especially suited for the methods described herein. The polymers associated with Hysol® EA <NUM>, EA9895, and EA9897 resins show promising results. In some independent embodiments, the curable polymer composition is predominantly epoxy resin. For the sake of clarity, the use of the parenthetical "meth," as exemplified in the term "(meth)acrylates," refers to independent embodiments of acrylates, methacrylates, or mixtures or copolymers comprising both.

Owing to the aromatic nature of some of the polymers used, and in some cases, the methods of making the films, in some embodiments, the polymer chains within the curable polymer composition may adopt organized, almost liquid-crystalline orientations, in the film, where the aromatic moieties partially or completely align in a parallel array within the film. In other embodiments, either because of the crosslinking or the nature of the polymer, the polymers may adopt a more randomly oriented array within the film.

The polymer composition is preferably curable (e.g., cross-linkable) by the application of light (UV, visible, or infrared) or heat. This allows for the use of sheet materials and control over the time of curing / co-curing with other substrates. It is preferred that the polymers retain their flexibility prior to application, so that uncrosslinked or only partially crosslinked polymers are preferred. In some embodiments, the curable polymers comprise partially cured (cross-linked) resins, prepared by mixing complementary resins and/or catalysts immediately prior to incorporation of the porous interlaminar first peelable sheets and the porous sheets of the second functional materials, and cure by free-radical processes.

The polymers may contain various additives, either or both organic or inorganic in nature, in addition to the peelable porous sheets and porous sheets of functional materials. These are discussed further elsewhere herein, but can include UV absorbers or stabilizing additives (e.g., as described in <CIT>or <CIT>), reinforcing fibers, or electrically conductive materials.

As described herein, the porous sheets of the first peelable and second functional materials are disposed within the matrix of the curable polymer composition. These sheets are most preferably aligned parallel with one another, within the film, and with respect to the first and second surfaces. Given this disposition, the sheets of first peelable and second functional materials may also be referred to collectively as interlaminar sheets, because these sheets form laminar structures within the otherwise unitary film structure.

As described elsewhere herein, at least a portion, and preferably all, of both the first peelable sheets and the sheets of the second functional materials are porous or preferably porous. While these materials can also comprise non-porous materials (e.g., including cross-hatched solid ribbons or sheets) or sections of non-porous materials (e.g., patches or sub-areal portions), the presence of porosity is at least useful, if not necessary, during manufacturing, when the processing involves impressing the porous sheets from the surfaces into the body of the curable polymer compositions. The pores allow for flow of the polymer through the sheets as the sheets are disposed in the polymer composition, desirably impressed into the polymer composition, like a semi-solid through a sieve or screen, optionally wetting or saturating the sheet material. Once formed, and ultimately cured, the polymers contained within the openings provide physical connectivity between the polymer molecules on either side of the sheets, and may provide enhanced stability to the resulting cured films. The porosity within each sheet is preferably distributed homogeneously. Porosity may be the same or different across two types of sheets. In some cases, high densities of small pores, slits, or apertures are preferred over lower density larger pores, slits, or apertures, for a given total open area. In other cases, the opposite is true, while in still other cases, a balance of the two size classifications may also provide advantages. In some embodiments, either or both porous sheets of the first peelable and second functional materials independently have nominal pore sizes having diameters in a range of from <NUM> to <NUM> microns. In other embodiments, these dimensions may be characterized as ranging from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, or any combination of two or more of these ranges, for example, from <NUM> to <NUM> microns. Where the openings are slits or other-shaped configurations, at least one dimension of these openings may also be within these ranges.

As described elsewhere herein, the first peelable porous sheet is contained beneath the first surface. The distance beneath the first surface may be specifically pre-determined and controlled during manufacturing. The purpose of this peelable porous sheet is to provide the surfacing film with the functionality of a sacrificial peel-ply layer in the post-cured composition, and at least have the attributes normally associated with that function. The peelable porous sheet is positioned between <NUM> and <NUM>% of the distance between the first and second surfaces; i.e., closer to the first surface, such that when the composition is cured and the peelable sheet removed, approximately <NUM> to <NUM> wt%, <NUM> to <NUM> wt%, <NUM> to <NUM> wt%, <NUM> to <NUM> wt%, or <NUM> to <NUM> wt% of the cured resin is also removed). In some embodiments, this pre-determined positioning is accomplished by physically embedding the fabric or expanded film upon or into the surface of the curable polymer composition, desirably the cast polymer composition, as described elsewhere herein.

In some embodiments, the peelable porous sheet includes materials comprising one or more fluorinated or perfluorinated polymer (such as a polytetrafluoroethylene (PTFE or Teflon®), a polyvinylidene difluoride (PVDF), a polyvinyl fluoride (PVF or Tedlar®)), (meth)acrylate, (meth)acrylamides, polyester, polyamide, polyethylene, polypropylene, polyethylenenaphthalate (PEN), polyethylenterephthalate (PET), polybutylenterephthalate (PBT) polyether etherketone (PEEK), polyaryletherketone (PAEK), polyethersulfone (PES), polyethylenenimine (PEI), poly (p-phenylene sulfide), polyvinyl chloride, or a co-polymer or mixture thereof. Preferred exemplary fabrics may comprise a polyester, a polyamide, a polyaramid such as Kevlar®, a polyimide such as Kapton®, carbon fibers, or glass or other inorganic fibers. In some embodiments, the fabric or expanded film may be coated or impregnated by laminating adhesive resin. In other embodiments, no such additional laminating adhesive resin is employed. Coating or impregnating the expanded films or fabrics may be accomplished by any of the various means well-known to those skilled in the art. The polymer surface of either the fabrics or expanded films may optionally be coated with silica, siloxane, aluminum oxide, or metal, or treated with plasma or silane. Polyesters, nylons, or mixtures thereof are especially useful as fabrics or expanded films in this application.

In various embodiments, the peelable porous sheet has a thickness in the range of <NUM> microns to <NUM> microns, or may be defined by one or more ranges from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, or from <NUM> to <NUM> microns, for example from <NUM> to <NUM> microns or from <NUM> to <NUM> microns. The pore, slit, or aperture openings are described elsewhere herein.

The peelable porous sheet typically comprises a fabric or expanded film.

As used herein, the term "expanded film" refers to a sheet or film containing perforations or through-hole porosity, for the reasons provided elsewhere herein.

As used herein, the term "fabric" most typically refers to woven material. Non-woven materials may also be used, but are less preferable, since they have a greater tendency to leave behind fiber residues / ends on the surface during post-cure removal of the peelable sheet.

In some embodiments, where the fabric is a woven fabric, the woven fabric comprises tightly woven mono- or multi-filament tows. Tightly woven, high-density weaves are preferred so as to provide a smooth finish, compatible with the finish desired for the final painted product. Accordingly, preferred weaves include a plain weave, a harness satin weave, a crow-foot satin weave, ripstop weave, or a twill, with a crow-foot satin weave style being most preferred. The fabric may also comprise, in independent embodiments mono- or multifilament/twisted yarns, or a combination of mono- or multifilament/twisted yarns, wherein each yarn surface can be independently flat or textured. In separate embodiments, the yarn has a maximum size of <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> denier.

The tightness of the weave can be described in terms of warp ends and fill ends per inch, both terms being readily understood by those skilled in the art of woven fabrics. Fabrics or films of this invention comprise those that independently contain at least <NUM> warp ends per inch, or at least <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> warp ends per inch, and at least <NUM> fill ends per inch, or at least <NUM>, <NUM>, or <NUM> fill ends per inch, and/or the fabric comprises a yarn having a minimum of <NUM> yarns/inch in both warp and fill directions, the yarn having a maximum <NUM> denier in either warp or fill directions. For example, good results are obtained wherein the fabrics or films contain at least about <NUM>-<NUM> warp ends per inch and at least about <NUM> fill ends per inch. More preferred embodiments include those weaves wherein the fabric is woven with at least <NUM> warp ends per inch and at least <NUM> fill ends per inch. Such weaves are commercially available, for example, from Precision Fabrics Group of Greensboro, North Carolina. Exemplary compositions include polyester style <NUM> and nylon style <NUM> materials that have been scoured and heat set. Fiber or yarn thicknesses are such as to provide minimally open weaves, given the warp end / fill end parameters, and consistent with the thickness of the overall fabric.

The final surface finish of the article resulting from removal of the sacrificial peel ply layer can be further improved by using fabrics for the peel ply layer which undergo additional calendaring methods such that removal of the peel ply layer of these fabrics creates even smoother, very low porosity article surfaces.

Another characteristic of the peelable porous sheet is that it has a tensile strength that is greater than that of the cured polymer composition, so that, for example, the peelable sheet does not shred during its subsequent removal or leave behind individual filament strands that compromise the cleanliness of the surface finish when peeled.

It is preferred that the peelable porous sheet exhibits a tensile strength in a range of from <NUM> N to <NUM> N, when tested according to ASTM-D5034, so as to provide the physical integrity to serve its intended function. In other embodiments, the tensile strength is described in terms of one or more ranges of from <NUM> to <NUM> N, from <NUM> to <NUM> N, from <NUM> to <NUM> N, from <NUM> to <NUM> N, from <NUM> to <NUM> N, from <NUM> to <NUM> N, from <NUM> to <NUM> N, from <NUM> to <NUM> N, from <NUM> to <NUM> N, from <NUM> to <NUM> N, from <NUM> to <NUM> N, from <NUM> to <NUM> N, from <NUM> to <NUM> N, from <NUM> to <NUM> N, for example from <NUM> N to <NUM> N,.

The multifunctional surfacing film of the present disclosure optionally comprises at least one sheet of a second functional material at least a portion of which is in the form of a porous woven or non-woven fabric, expanded metallic foil or polymer film, grating, mesh, screen, or web. Again, and for the same reasons as described elsewhere herein, desirably most if not all of the functional sheet(s) have a high degree of porosity for ultimate product stability and manufacturability. In certain preferred embodiments, these porous sheets of additional functional materials are present.

In some embodiments, a plurality of sheets of functional materials may be employed. Or, a single sheet may comprise materials (including so-called hybrid materials) having different functions. It is appreciated that the first peelable porous sheets provide a functional capability of the multifunctional surfacing film (i.e., peelability), but in the context used in this section, the term "functional" refers to an attribute of the sheet material which imparts some character to the film that improves performance, e.g. impact stability, dimensional stability, electrical conductivity, and heat transfer capability, so as to provide improved strength, EMI shielding material, and static and lightning strike protection to a substrate to which it is ultimately attached. Further, the phrase "at least one sheet of a second functional material" can be one or more sheets of a non-peelable functional material, as to distinguish from the peelable sheet. That is, it represents embodiments including (a) one sheet of one or more (non-peelable) functional materials, as described below; (b) two or more sheets of the same (non-peelable) functional material, (c) two or more sheets of different (non-peelable) materials, or (d) two or more sheets of two or more (non-peelable) functional materials.

The physical attributes of these second functional materials are similar to those described elsewhere herein for the first peelable porous sheets, at least in terms of thickness and porosity characteristics, but the compositions and architectures of these porous sheets of functional materials reflect the need for a different range of properties. For example, the sheet of second functional material(s) may not need the same tensile strength as required for the peelable porous sheet.

Again, the porous sheets of the second functional materials may comprise woven fabrics and expanded films, but additionally these sheets may also comprise non-woven fabrics, meshes, screens, or webs of continuous or chopped organic or inorganic fibers, including the same or similar materials to those useful for the peelable porous sheets - i.e., one or more fluorinated or perfluorinated polymer (such as a polytetrafluoroethylene (PTFE or Teflon®), a polyvinylidene difluoride (PVDF), a polyvinyl fluoride (PVF or Tedlar®)), (meth)acrylate, (meth)acrylamides, polyester, polyamide, polyethylene, polypropylene, polyethylenenaphthalate (PEN), polyethylenterephthalate (PET), polybutylenterephthalate (PBT) polyether etherketone (PEEK), polyaryletherketone (PAEK), polyethersulfone (PES), polyethylenenimine (PEI), poly (p-phenylene sulfide), polyvinyl chloride, or a co-polymer or mixture thereof. Other useful organic materials include polyaniline, polypyrrole, polythiophene, or a copolymer or mixture thereof, either alone, or in mixtures with any of the other materials described for this purpose. Aramids (e.g., Kevlar® fibers) and imide fibers (e.g. Kapton ®) are also attractive in this application. Since it is intended that the second functional materials will remain in the multifunctional film after curing and during ultimate use, the physical integrity or woven nature of these sheets is less critical than those of the peelable materials; i.e., they do not need to withstand a peeling operation.

The functional materials may also comprise ceramic or glass fibers - e.g., oxides, carbides, nitrides, oxycarbides, oxynitrides, carbonitrides, or oxycarbonitrides comprising aluminum, boron, silicon, and/or titanium - cermet fibers, carbon, or metallic fibers - e.g., comprising aluminum, copper, iron, silver, tin, or zinc, or mixtures, alloys - or coated hybrids comprising these materials. Exemplary materials include fibers or whiskers of alumina, aramid, boron, carbon, glass, silicon carbide, aluminum nitride, coated hybrids or mixtures thereof, preferably glass, carbon or metal-coated fibers. As used herein, the term "fibers" includes those of macro, micro, or nanodimensions, and include wires through elongated single crystals also known as whiskers. In some cases, these materials are composites of the various material classes, for example, including carbon coated metals, glass, or polymers; metal coated polymers, carbon, or glass; polymer coated glass, carbon, or metals, etc. In some cases, the functional materials are electrically conductive. In some embodiments, the functional materials impart a magnetic character to the surfacing film.

Typically, and in preferred embodiments, at least one porous sheet of the second functional material is positioned close to but beneath the second surface of the curable polymer composition. The sheet of the second functional material should be of a depth in the film so as to provide that the overlaying curable polymer composition is sufficiently thick to be able to co-cure with a later provided substrate. The second functional sheet is positioned typically between the peelable porous sheet and the second surface within the polymer composition. In separate embodiments, the at least one porous sheet of second functional material is disposed at a position that is <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, or <NUM>% of the distance between the second surface and the peelable porous sheet. For example, in some embodiments, the at least one second functional material is disposed at a position substantially equidistant between the first surface and the peelable porous sheet. The positioning of the porous sheet of functional material is deliberately controlled and specific. Preferably, as described above, it is disposed in a plane substantially parallel to the first and second surfaces of the multifunctional film and disposed between these surfaces; i.e., such that the sheet is disposed at a pre-determined location within the polymer composition and runs lies in a plane substantially parallel to the second surface. In independent individual embodiments, local variances of the position of the function sheets within the surfacing film are less than <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, or <NUM>% from the mean position within the film.

In some embodiments, the multifunctional surfacing film further comprises at least one particulate filler within the curable polymer composition, in addition to the peelable porous sheets and the sheets of second functional materials. These fillers may comprise nano-, micro-, and/or macro-dimensioned particulate materials distributed substantially uniformly throughout the curable polymer, between the peelable porous and functional material sheets. Owing to one way in which these surfacing films are constructed, the particulate filler(s) may be concentrated between and adjacent to the peelable porous sheet and functional material sheets, resulting from the sieving action of incorporating of these sheets into the curable polymer layer. These particulates fillers may comprise one or more of any of the functional materials described herein, e.g., ceramic, polymer, glass, or metal/metalloid material or alloy thereof, or coated hybrid materials, more specifically including a carbide, nitride, or oxide of aluminum, boron, silicon, tin, zirconium, or aluminum, carbon, copper, nickel, Sn-Zn, or stainless steel, or aramid, and composite versions thereof.

The surfacing film, at least before curing, is designed to be sufficiently flexible / pliable to conform to a shaped or contoured substrate, including flat or essentially flat panels, curved contours, including convex or concave shapes or surfaces comprising combinations thereof. The curable surface coating composition may be applied to substantially conform to the contour shape of the substrate. This feature results from a combination of the degree of curing of the curable polymer composition and the thickness of the surfacing film, both of which are described elsewhere herein.

Additionally, in some embodiments, the multifunctional surfacing film has a total thickness in a range of from <NUM> to <NUM>,<NUM> microns (<NUM> to <NUM> mils), preferably from <NUM> to <NUM> microns (<NUM> to <NUM> mils). In other embodiments, the total thickness may be described in terms of a range of from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, from <NUM> to <NUM>,<NUM> microns, from <NUM>,<NUM> to <NUM>,<NUM> microns, or a combination of two or more of these ranges, for example, from <NUM> to <NUM> microns, from <NUM> to <NUM> microns, or from about <NUM> to <NUM> microns.

In other embodiments, the multifunctional surfacing film can have an areal weight in a range of from <NUM> to <NUM> lb. /ft<NUM> (psf), or this weight may be defined by one or more ranges of from <NUM> to <NUM> psf, from <NUM> to <NUM> psf, from <NUM> to <NUM> psf, from <NUM> to <NUM> psf, from <NUM> to <NUM> psf, from <NUM> to <NUM> psf, from <NUM> to <NUM> psf, from <NUM> to <NUM> psf, from <NUM> to <NUM> psf, <NUM> to <NUM> psf, from <NUM> to <NUM> psf, from <NUM> to <NUM> psf, from <NUM> to <NUM> psf, <NUM> to <NUM> psf, from <NUM> to <NUM> psf, from <NUM> to <NUM> psf, from <NUM> to <NUM> psf, <NUM> to <NUM> psf, from <NUM> to <NUM> psf, from <NUM> to <NUM> psf, from <NUM> to <NUM> psf, from <NUM> to <NUM> psf, from <NUM> to <NUM> psf, from <NUM> to <NUM> psf, from <NUM> to <NUM> psf, from <NUM> to <NUM> psf, from <NUM> to <NUM> psf, from <NUM> to <NUM> psf, or from <NUM> to <NUM> psf. For aircraft applications, preferred ranges include those from <NUM> to <NUM> psf, from <NUM> to <NUM> psf, from <NUM> to <NUM> psf, from <NUM> to <NUM> psf, from <NUM> to <NUM> psf, or from <NUM> to <NUM> psf, or some combination of two or more of these ranges. Herein <NUM> pound per square foot (psf) corresponds to <NUM>/m2.

The relative amounts of the curable polymer and the porous sheets is not necessarily critical, provided that there are sufficient amounts of each to allow each to perform their respective purposes. But in some embodiments, the ratio of the thickness of the curable polymer to the total thickness of the porous sheets ranges from <NUM>:<NUM> to <NUM>:<NUM>, from <NUM>:<NUM> to <NUM>:<NUM>, from <NUM>:<NUM> to <NUM>:<NUM>, from <NUM>:<NUM> to <NUM>:<NUM>, from <NUM>:<NUM> to <NUM>:<NUM>, from <NUM>:<NUM> to <NUM>:<NUM>, or from <NUM>:<NUM> to <NUM>:<NUM>, or the ratio is characterized by two or more of these ranges, for example, from <NUM>:<NUM> to <NUM>:<NUM>.

In independent embodiments, the multifunctional surfacing film comprises at least one releasable liner on the first surface, the second surface, or on both the first and second surfaces. One or both of these releasable liners may be made of a cellullosic or plastic film (e.g., paper, polyethylene or polyester). Such liners are provided to protect the film and facilitate handling thereof during manufacture, shipment, or application/use and/or to prevent reaction between adjacent layers on a roll or stack.

As described above, the multifunctional surfacing films may comprise curable, partially cured, and fully cured polymer compositions. In separate embodiments, these films may physically contact, be physically affixed to, or co-cured with other substrates, including laminate substrates, optionally where the substrate is a laminate, and optionally where the substrate is part of an aircraft or automotive vehicle.

To this point, the disclosure has highlighted some of the characteristics of the multifunctional surfacing film itself, but the invention also contemplates the methods of making and using these surfacing films. As stated elsewhere, it should be appreciated that the various features as pertaining to the surfacing films are also appropriate to both the methods and making, and comments / characteristics of the surfacing films are also applicable in the methods of making and using these surfacing films, without the need to repeat them in the corresponding sections of this disclosure.

These surfacing films may be applied to pre-formed structures (e.g., <FIG>), or may be used with tools / molds onto which structures are constructed (e.g., <FIG>). In either case, it is intended that the second surface of the surfacing film physically contacts and becomes attached to the ultimate structures. This results in the first surface being disposed on the outside of the article or structure to which the film is attached as the outer surface layer of the article, and provides that the sheet of second functional material becomes attached to the structure beneath, i.e. internal to, the first peelable porous sheet, such that the first peelable porous sheet can be subsequently removed to provide the first revealed surface leaving the sheet(s) of second functional material attached to the structure with the remainder of the surfacing film.

Accordingly, certain embodiments provide methods of providing functionality to a substrate surface, some method comprising:.

In some embodiments, the substrate is a fiber reinforced composite part. The substrate may also comprise at least one of the following: a curable polymer matrix composition, reinforcement fibers impregnated with a curable polymer matrix, a honeycomb core, an expandable film, a potting compound, or a metal or ceramic surface.

In some embodiments, the substrate is a shaped structure comprising or at least presenting a surface that is the same or complementary polymer composition as is the curable polymer composition of the surfacing film, as described elsewhere herein. The substrate may be a laminate.

In other embodiments, the methods comprise:.

In either or both methods, the conditions sufficient to permit co-curing comprise exposing the intermediate composition to sufficient thermal or radiative conditions to co-cure the curable polymer compositions of the substrate and the multifunctional surfacing film, thereby forming a permanent bond therebetween. Such conditions depend on the specific materials chosen and the skilled artisan will be able to determine the best conditions for forming such a bonded interface. Exemplary processes that can be used to co-cure the materials include thermal or radiative curing, such as typically employed for the materials discussed. The nature of the bond between the co-cured substrate polymer and the multifunctional surfacing film depends on several factors, including processing conditions and the nature of the individual components, ranging from largely or entirely physical to largely or entirely chemical. The skilled artisan will appreciate those materials and processing conditions necessary to achieve the desired bonding between the substrate and the surfacing film.

After the functionalized co-cured structure is prepared, and at a time to be selected by the user, the first peelable porous sheet can be removed from the cured composition to leave behind a revealed first surface of the cured polymer composition of the multifunctional surfacing film. Typically, this removal is done by a peeling action to leave behind the remaining cured surfacing film containing the second functional material on the substrate, with this revealed first surface acting as a site for application of paint. Desirably, little or no sanding, primer paint or other surface treatment of the revealed new first surface is required or present before application of additional layers. By way of non-limiting example, preferably less than <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM> microns of surface treatment or primer paint is added and/or cured polymer composition is removed from the revealed new first surface prior to application of additional layers of surface finish/decoration, e.g. paint. Depending on the pre-defined depth of the first peelable porous sheet in the films, or the nature of the fabric, removing peelable porous sheet removes between about <NUM> wt% and about <NUM> wt% of the pre-cure areal weight of the multifunctional film and about <NUM>-<NUM> wt% of the cured polymer composition, or as otherwise described herein. Incremental wt% ranges are considered additional embodiments, e.g., from <NUM> to <NUM> wt%, from <NUM> to <NUM> wt%, from <NUM> to <NUM> wt%, from <NUM> to <NUM> wt%, from <NUM> to <NUM> wt%, from <NUM> to <NUM> wt%, from <NUM> to <NUM> wt%, from <NUM> to <NUM> wt%, from <NUM> to <NUM> wt%, from <NUM> to <NUM> wt%, from <NUM> to <NUM> wt%, or two or more of these ranges. Desirably the at least one optionally porous sheet of a second functional material is positioned in the multifunctional surfacing film such that it remains covered by the remaining cured surfacing film after removal of the first porous peelable sheet, preferably uniformly covered, most preferably covered by a selected thickness of the remaining cured surfacing film. Achieving a requisite surface suitable for painting without further treatment depends, at least in part, on the smoothness of the weave or surface of the fabric or film used for the first porous peelable sheet. It is also important that the peelable porous sheet exhibit sufficient structural integrity such that when it is removed from the cured surfacing film, it can be removed without leaving behind individual filament strands. It is preferred that the surface is free; desirably essentially free, meaning less than <NUM>%, preferably <NUM>%, of individual filament strands of the fabric or film.

In specific embodiments, removal of the first peelable porous sheet after curing the surfacing film provides a revealed first surface that is suitable for painting without additional surface conditioning or treatment. Where some fabric strands are left behind, these may be removed by mild abrasion. Additional embodiments include the additional step of applying such paint or other filled or unfilled or clear coat finish, and the articles derived therefrom. In some embodiments, the revealed first surface is suitable for painting without the need for a primer coat. The characteristics associated with these suitabilities include that the revealed first surface has mean surface roughness (e.g., from fabric impression) (Ra) in a range of from about <NUM> to about <NUM> microns, which may also be characterized as having a mean surface roughness in one or more of the ranges from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM> (<NUM> microns), from <NUM> microns to <NUM> microns, from <NUM> microns to <NUM> microns, from <NUM> microns, to <NUM> microns, from <NUM> microns to <NUM> micron, from <NUM> micron to <NUM> microns, from <NUM> microns to <NUM> microns, from <NUM> microns to <NUM> microns, or from <NUM> microns to <NUM> microns. One such exemplary range includes, for example, from <NUM> microns to <NUM> microns. The term "suitable for painting" means that the resulting paint coating exhibits a paint adhesion to the revealed first surface having a rating of at least <NUM>, preferably at least <NUM>, and more preferably at least <NUM>, either as applied and/or after stress, or both, as measured by ASTM D3359. Such stresses include one or more of thermal cycling (e.g., <NUM> cycles from -<NUM> to +<NUM>°F), UV exposure to the revealed surface, water immersion and/or extreme temperature exposure, salt or acid spray exposure after application of paint (with / without primer) as described in ASTMs B117, B287, D7869, F483, F1110.

The methods for applying the paints are not limited to any particular means, though spray painting is typically used to allow for smooth coverage over large areas, or through the use of decals. Similarly, the choice of paint is not limiting, so long as the paint is compatible with the final surface composition. Preferred paints are those comprising a polyacrylate, a polyester, a polymethacrylate, a polyurethane, or a co-polymer or mixture thereof. The bonding of the paint to the exposed surface can be physical or chemical, or both, depending on the nature of the paint chosen. The post-cure removal of the peelable sheet leads to the revealed surface have a larger contact surface area, which promotes physical paint adhesion, as compared to the first surface. It is then expected that the revealed surface will expose a higher concentration of chemical groups that promote paint adhesion than it would otherwise have had in the absence of the process described herein. As a result, it is also expected that the increased chemical interaction between the revealed surface and the paint will likely lead to a more integral bond, hence the ability to negate the need for primer.

One of the many advantages of the present invention is that the co-cured surfacing film can stay on the substrate throughout manufacture and assembly to protect said part from contaminants and chemical/environmental exposures, particularly to UV sources, until the part is ready for painting or other surface coating. In some embodiments, the lesser the amount of cured material removed with the peelable sheet is preferred to enable the remaining cured surfacing material to continuously protect the composite part through successive processing during its lifetime.

To this point, the various embodiments have been described in terms of the methods for preparing and/or using the multifunctional surfacing films and the surfacing films themselves. It should also be appreciated that various intermediate structures described herein are considered within the scope of the present disclosure as separate embodiments as articles of manufacture. Various embodiments of this invention also include those articles produced by the methods described herein. The invention is suited for structures of any size, but is especially attractive in its ability to accommodate large structures. It is envisioned that such objects produced using the methods described herein are contained within the scope of this present invention. Structures contemplated include those which may be one of more of any of a primary structure element, secondary structure element, exterior element, interior element and parts forming those elements in commercial and personal aircraft and aerospace applications, motor vehicles, watercraft (including ships), railroad cars, tankers, storage tanks, and wind turbines. It may also be used to prepare smaller articles, including, but not limited to, sports equipment (e.g., fishing rods, bicycle frames). Each of these structures, when containing such a partially or fully cured multifunctional film is considered a separate embodiment of this disclosure.

Additional embodiments include those methods for making the multifunctional surfacing films described herein. <FIG> and <FIG> provide two representations of examples of such methods. One such method comprises:.

In such methods, the at least one porous sheet of the second functional material becomes at least partially embedded into the cast polymer composition beneath the second surface after the peelable porous sheet is impressed into the first surface of the curable polymer composition. The depth of impregnation controlled to a pre-defined depth, at least in part, by viscosity of the curable polymer composition (which depends at least in part on the temperature, the specific polymer composition, and the degree of curing in the polymer composition), degrees of porosity of the interlaminar sheets, and pressure applied by the individual nip rollers used to impress the interlaminar sheets into the curable polymer composition.

In related embodiments, the method or methods further comprise passing the multifunctional surfacing film between at least one pair of non-porous rollers (<NUM>, <NUM>), optionally comprising non-porous liners, further embedding the at least one porous sheet of second functional material (<NUM>, <NUM>), the peelable porous sheet (<NUM>, <NUM>), or both the at least one porous sheet of second functional material and the peelable porous into the cast curable polymer composition, each at a pre-selected distance from the respective surface of the curable polymer composition.

Claim 1:
A multifunctional surfacing film (<NUM>) comprising:
(a) a single layer of curable polymer composition (<NUM>) having opposing first and second surfaces:
(b) a first peelable porous sheet (<NUM>) disposed beneath the first surface wherein the peelable porous sheet (<NUM>) is positioned between <NUM> and <NUM>% of the distance between the first and second surfaces of the single layer (<NUM>); and
(c) at least one porous sheet of a second functional material (<NUM>) disposed within the single layer of curable polymer composition (<NUM>) and positioned between the second surface and the peelable porous sheet (<NUM>).