Reactivation of co-cured films

Abstract

The present disclosure relates to a method for reactivating a co-cured film layer disposed on a composite structure, the method comprising applying a reactivation treatment composition to the co-cured film layer and allowing the reactivation treatment composition to produce a reactivated co-cured film layer, the reactivation treatment composition comprising at least two solvents and a surface exchange agent comprising a metal alkoxide or a chelate thereof, wherein the co-cured film layer is pre-cured at a cure temperature greater than about 50° C. Also provided are a reactivated co-cured film layer and an aircraft component having the reactivated co-cured film layer.

Description

Technical Field

[0001] The present disclosure relates to a method for reactivating a film layer that has been previously co-cured onto a composite structure. A topcoat or other paint layer can then be applied to the reactivated co-cured film layer without any intermediate sanding step. The resulting composite structure can exhibit good adhesion of the co-cured film layer to both the composite structure and the additional coating layer, as well as protection from exposure to environmental conditions or elements, including ultraviolet radiation, rain erosion, moisture, and / or chemicals, such as fuel. The present method for reactivating a film layer that has been co-cured onto a composite structure is particularly useful for marking aerospace parts, such as aircraft parts. Background Art

[0002] Many parts, such as automotive, aerospace (e.g., aircraft, etc.) and other parts, are constructed from strong but lightweight composite materials, which help minimize the overall weight of the structure (e.g., aircraft). These composite materials typically include carbon reinforcement fibers distributed within a polymer matrix.

[0003] Commercial aerospace and vehicle manufacturers often desire to mark or identify aircraft or vehicles with information or markings (e.g., model numbers, company names, company logos, or other decorative or informational markings, including words, numbers, letters, and designs of any kind). However, marking has proven challenging for parts made from composite materials. Painting or printing on these composite structures often results in an increase in manufacturing process time (e.g., painting operation flow time), thereby increasing the cost and time required to manufacture the parts. In some cases, parts may include complex three-dimensional curvatures that may be difficult to print on.

[0004] Furthermore, maintaining desired flow characteristics over coated or painted aircraft surfaces (e.g., coatings or paint on an aircraft's wings or tail) can be challenging. To avoid impacting desired boundary layer characteristics during flight, there are acceptable standards for paint edges and waviness. There may also be restrictions on three-dimensional surface discontinuities, such as those that may result from inclusions of debris, dust, or dried paint overspray, as well as those resulting from multiple layers of applied paint (e.g., multiple colors of paint to create a design or differentiated text).

[0005] Known methods and systems exist for applying flight line designs to the exterior surfaces of aircraft. For example, such known methods and systems may include using tape and / or masking techniques to build up a coating or paint layer over a primer layer or a basecoat color layer. These known methods and systems for applying flight line designs to the exterior surfaces of aircraft may make it difficult to meet or maintain aerodynamic performance requirements, such as requirements for coating or paint edge angles or coating or paint edge peaks that help ensure preferred aerodynamic performance.

[0006] Thus, a marking process can be used that reduces processing time and / or expense while providing sufficient color and design in addition to a smooth aerodynamic surface. Such marking methods may include, for example, the use of co-cured films, such as those disclosed in U.S. Patent Publication No. 2018 / 0345646 (incorporated herein by reference). However, co-cured films may still present difficulties during many types of manufacturing operations. For example, typically, the surface of a co-cured film layer that has been pre-cured to a composite structure does not allow good adhesion of other coating layers. Therefore, conventional processing of co-cured films for applying other coating layers includes sanding to reactivate the surface of the co-cured film layer so that other layers, such as other paint coatings or topcoats, can be applied. However, manual sanding methods can be labor-intensive, create ergonomic issues, generate sanding debris, use consumables for sanding operations, and increase time in the factory. Therefore, current methods for preparing co-cured surfaces for applying other coating layers may lack economic and production efficiency.

[0007] Therefore, there is a need to develop surface treatments for co-cured film layers to improve adhesion of other layers to the co-cured film layer while minimizing commercial viability, health, and safety issues. Summary of the Invention

[0008] In one aspect, the present disclosure relates to a method for reactivating a co-cured film layer on a composite structure, the method comprising: applying a reactivation treatment composition to the co-cured film layer, the reactivation treatment composition comprising at least two solvents and a surface exchange agent, the surface exchange agent comprising a metal alkoxide or a chelate thereof; and allowing the reactivation treatment composition to produce a reactivated co-cured film layer; wherein the co-cured film layer is pre-cured at a curing temperature greater than about 50°C (e.g., at a curing temperature of at least about 121°C or in an autoclave), for example, cured to the composite structure.

[0009] In certain embodiments, the method further comprises applying an additional coating layer (e.g., a clearcoat) to the co-cured film layer. In certain embodiments, the method does not comprise sanding the co-cured film layer prior to applying the reactivation treatment composition. In certain embodiments of the methods disclosed herein, the co-cured film layer, when cured, comprises a polyurethane, a polyimide, a polyester, or an epoxy resin, and in certain embodiments, the co-cured film layer, when cured, comprises a polyurethane.

[0010] In various embodiments disclosed herein, the surface exchange agent is zirconium propoxide, and in certain embodiments, the at least two solvents are dipropylene glycol dimethyl ether and n-propanol.

[0011] In certain embodiments, the methods disclosed herein further comprise applying a cleaning solvent prior to or concurrently with applying the reactivation treatment composition.

[0012] In certain embodiments, the methods disclosed herein include applying an additional coating layer, wherein the additional coating layer has an inter-coat adhesion level of 6 to 10 (eg, 8 to 10) after rain erosion testing.

[0013] In another aspect, the present disclosure relates to a reactivated co-cured film layer comprising: a co-cured film layer disposed on a composite structure, and a reactivation treatment composition layer comprising a surface exchange agent comprising a metal alkoxide or a chelate thereof and disposed on the co-cured film layer to produce the reactivated co-cured film layer, wherein the co-cured film layer is cured to the composite structure at a temperature of at least about 50° C., for example, at a cure temperature of at least about 121° C. or in an autoclave.

[0014] In certain aspects of the reactivated co-cured film layer disclosed herein, the co-cured film layer is not sanded. In certain embodiments, the reactivated co-cured film layer further comprises an additional coating layer disposed on the reactivation treatment composition layer, and in certain embodiments, the additional coating layer has an inter-coat adhesion level of 6 to 10 (e.g., 8 to 10) after the rain erosion test.

[0015] In certain embodiments of the reactivated co-cured membrane layer, the surface exchange agent is zirconium propoxide, and in certain embodiments, the co-cured membrane layer, when cured, comprises a polyurethane, a polyimide, a polyester, or an epoxy resin.

[0016] In yet another embodiment, the present disclosure is directed to an aircraft component having a co-cured film layer thereon, the aircraft component comprising a composite structure and a reactivated co-cured film layer according to an embodiment of the present disclosure cured onto a surface of the composite structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic diagram of a panel portion of a composite structure having thereon a co-cured film layer that has been treated to reactivate its surface properties to facilitate adhesion of other coating layers to the co-cured film layer without compromising the integrity of the co-cured film layer.

[0018] Figure 2 A visual representation is shown relating to a scale of 1 to 10 corresponding to the maximum tear length and percentage of area of the coating removed under the rain erosion test.

[0019] Figure 3AThree composite structures are shown that include a co-cured film layer coated with other coating layers and then subjected to rain erosion testing, wherein the co-cured film layer was not exposed to ultraviolet (UV) light and was sanded prior to application of the other coating layers.

[0020] Figure 3B Three composite structures are shown, which include a co-cured film layer coated with other coating layers and then subjected to rain erosion testing, wherein the co-cured film layer is exposed to 200 kJ / m 2 UV light and was sanded before applying other coating layers.

[0021] Figure 3C Three composite structures are shown, which include a co-cured film layer coated with other coating layers and then subjected to rain erosion testing, wherein the co-cured film layer is exposed to 1,000 kJ / m 2 UV light and was sanded before applying other coating layers.

[0022] Figure 4A Three composite structures are shown, which include a co-cured film layer coated with other coating layers and then subjected to rain erosion testing, wherein the co-cured film layer was not sanded or exposed to UV light, but was coated with Treatment with AP-1 reactivation treatment composition.

[0023] Figure 4B Three composite structures are shown, which include a co-cured film layer coated with other coating layers and then subjected to rain erosion testing, wherein the co-cured film layer was not sanded but exposed to 200 kJ / m 2 UV light and then with Treatment with AP-1 reactivation treatment composition.

[0024] Figure 4C Three composite structures are shown, which include a co-cured film layer coated with other coating layers and then subjected to rain erosion testing, wherein the co-cured film layer was not sanded but was exposed to 1,000 kJ / m 2 UV light and then with Treatment with AP-1 reactivation treatment composition.

[0025] It should be noted that some details of the drawings have been simplified and are drawn to facilitate understanding of the present teachings rather than maintaining strict structural accuracy, detail, and scale. DETAILED DESCRIPTION

[0026] The following description is merely exemplary in nature and is in no way intended to limit the present disclosure, its application, or uses.

[0027] As used throughout, ranges are used as shorthand for describing each and every value within the range. Any value within the range can be selected as the endpoint of the range. In addition, all references cited herein are incorporated herein by reference in their entirety. In the event of a conflict between the definitions of the present disclosure and those of the cited references, the present disclosure shall prevail. Unless otherwise indicated, all percentages and amounts expressed herein and elsewhere in the specification are understood to refer to percentages by weight. The amounts given are based on the active weight of the material.

[0028] Disclosed herein is a method that allows for the reactivation of film layers that have been previously co-cured onto a substrate or intermediate layers cured onto a substrate to improve their adhesion to other coating layers without compromising coating integrity.

[0029] Applying additional coating layers to a co-cured film layer typically requires harsh surface stripping processes, such as mechanical grinding (e.g., sanding) or ablating (e.g., by laser) of the co-cured film layer before the additional coating layers can be applied. Advantageously, the present disclosure provides a method that eliminates the need for conventional methods of mechanically grinding the co-cured film layer before applying subsequent coatings and / or other entities. For example, the reactivation methods disclosed herein can reactivate the surface of a co-cured film layer to improve its adhesion to additional coatings and / or other entities.

[0030] It is well known that when a new coating is applied over a film layer that has been cured in an autoclave or otherwise aged, the adhesion of the coating layer may not meet the in-service performance requirements of the aircraft. This is because, after curing or aging, the co-cured film layer will exceed the application window for adhesion of other coating layers. For co-cured film layers comprising polyurethane, for example, the curing process causes crosslinking between polymer units, creating rigidity in the cured polyurethane film layer. The amount of crosslinking is proportional to the time and / or temperature at which the polyurethane film is cured. Therefore, a co-cured film layer that has been cured in an autoclave (e.g., at a temperature of at least about 121°C) would be expected to have a much higher crosslink density than a comparable film layer cured by other means, such as at a lower temperature (e.g., ambient temperature or a temperature less than 50°C). Furthermore, it would be expected that the higher the crosslink density of the co-cured film layer, the poorer the adhesion of the subsequent coating layer.

[0031] However, disclosed herein is a method for reactivating a co-cured film layer that has been previously cured at elevated temperatures (e.g., in an autoclave), comprising applying a surface reactivation treatment composition comprising a solvent and a surface reactivating agent. In the disclosed method, no additional sanding step of the co-cured film layer is required. Surprisingly and unexpectedly, application of the reactivation treatment composition effectively reactivates a co-cured film layer that has been cured at elevated temperatures and, therefore, has a high crosslink density, without any additional sanding step.

[0032] As used herein, the term "reactivation" refers to improving the adhesion of a coating layer, such as a co-cured film layer. Activation and reactivation are used interchangeably herein. Adhesion can be measured by any method known in the art, including, for example, by the inter-coat adhesion level of a coating. As used herein, "inter-coat adhesion level" refers to the level of adhesion between two coating layers, such as a co-cured film layer and another coating layer disposed directly on the co-cured film layer. As disclosed herein, inter-coat adhesion can be quantified on a scale of 1 to 10 based on, for example, the tear length and removal of the other coating layer after exposure to a rain erosion test.

[0033] In certain aspects, the methods disclosed herein comprise applying a surface reactivation treatment composition comprising a solvent, a surface exchange agent selected from metal alkoxides or chelates thereof, such as titanium or zirconium alkoxides or chelates thereof, and optional additives to the co-cured film layer.

[0034] In certain embodiments, disclosed herein is a method for promoting adhesion of other coating layers to a co-cured film layer present on a substrate, the method comprising applying a reactivation treatment composition comprising a solvent, a surface exchange agent, and an optional additive to the co-cured film layer, wherein the surface exchange agent is selected from a metal alkoxide or chelate, such as titanium or zirconium alkoxide or chelate thereof.

[0035] The methods disclosed herein do not require additional steps such as mechanical grinding or chemical stripping of the co-cured film layer to improve its adhesion to other coating layers.

[0036] like Figure 1 As shown, reactivating the adhesion of a pre-cured film layer (2) on a rigid substrate (1) (e.g., an aircraft composite part) and adhering a new coating layer (4) to the pre-cured film layer (2) using an effective adhesive connection (5) requires not only reactivating the adhesion of the pre-cured film layer (2) to the other coating layer (4), but also requiring not affecting the integrity of the adhesive connection (3) of the original co-cured film layer between the substrate (1) and the pre-cured film layer (2), nor affecting the integrity of any exposed (uncoated) surface (6) of the substrate.

[0037] Composite structures

[0038] In the methods disclosed herein, there is at least one co-cured film layer on a substrate that has been pre-cured to a substrate or an interlayer at an elevated temperature (e.g., at a temperature greater than about 50° C., such as in an autoclave). The substrate can be a support structure, such as a panel configured for use as a structural support portion in a building, vehicle, or aircraft. For example, the substrate can be a panel portion of an aircraft fuselage or wing. In one aspect, the substrate comprises or consists essentially of a composite material.

[0039] The composite material can be a carbon fiber reinforced epoxy resin or a glass reinforced epoxy resin material. The composite material can include glass, wood or fabric. The substrate can be a substantially inelastic or rigid plastic, which can include polyimide or polycarbonate. In one aspect, the substantially inelastic or rigid plastic does not include a plastic film or plastic packaging material that can be stretched or easily manipulated, and / or does not include a plastic film or plastic material that does not have structural rigidity or elastic deformation capability.

[0040] In some embodiments, the composite structure is formed from an organic matrix and fibers, such as an epoxy resin and a carbon fiber reinforced polymer (CFRP). In some embodiments, the composite structure is in the form of a prepreg. As used herein, the term "prepreg" refers to one or more sheets or sheets of fibers that have been impregnated with a matrix material. The matrix can be in a partially cured state to exhibit, for example, a selected adhesion or tack.

[0041] In some embodiments, the prepreg layers are placed adjacent to each other. In certain embodiments, the prepreg layers within a stack can be positioned relative to each other in a selected orientation. For example, a prepreg stack can include prepreg layers having a unidirectional fiber structure, wherein the fibers are oriented at 0°, 90°, a selected angle θ, and combinations thereof relative to the maximum dimension (e.g., length) of the stack. It will be further understood that in certain embodiments, prepregs having any combination of fiber structures (e.g., unidirectional and multidimensional) can be combined to form a prepreg stack.

[0042] In some embodiments, the composite structure is formed by one or more sandwich panels (e.g., honeycomb panels), one or more of which may be composite panels. Each sandwich panel typically includes a core formed of a relatively lightweight material sandwiched between two panel skins. The composite structure may include one or more coatings or layers applied to the underlying panels or material layers. The composite structure may include one or more sandwich panels, joints formed between two or more sandwich panels, and / or a three-dimensional structure formed using one or more sandwich panels.

[0043] As illustrative, non-exclusive examples, composite structures may be used in aircraft structures such as wings, fuselages, horizontal stabilizers, vertical stabilizers, and engine cowlings; however, other parts of the aircraft may additionally or alternatively include composite structures, such as sandwich panels and / or joints formed between two or more sandwich panels. Other applications of composite structures in aircraft include overhead storage bins, floors, interior walls, food handling galley assemblies, wing control surfaces, passenger storage racks, thrust deflector assemblies, bulkheads, ablation protection for fairings, instrument housings and racks, and bulkhead strips. In other industries, one or more composite structures may include or be part of the interior structure of a satellite or aerospace vehicle, a transport vehicle, a shipping container, a shelter, a large antenna or dish reflector, a refrigeration panel, a rapid transit floor, a shipboard electronics deck shelter, a pallet, an automobile body, a ship and other marine vehicles, a building curtain wall, a partition, a partition panel, an expandable hospital shelter, and / or an assembly.

[0044] In some embodiments, a composite structure disclosed herein and a co-curable film layer are placed together and co-cured in a mold, and in certain embodiments, the co-curing can result in the incorporation of a co-curable film layer on the composite material.

[0045] Co-cured film

[0046] As described above, the co-cured film layer that has been cured onto the surface of a substrate (e.g., a composite substrate or an intermediate layer between a composite structure and a co-cured film layer) becomes resistant to forming strong adhesive bonds with other entities (e.g., other coating layers) after the film layer is cured. Based on the chemical properties of their individual components and the curing conditions, the surface properties of the co-cured film layer may become more inert than expected. Without wishing to be bound by any theory, it is believed that this phenomenon may arise from a reduction in the surface energy and amount of reactive surface functional groups of the film, as well as a higher crosslink density that varies with curing time, temperature, and / or aging, which can reduce chemical interactions with other entities and / or the formation of strong adhesive bonds.

[0047] Co-cured film layers that can be reactivated according to the methods disclosed herein include, but are not limited to, fully or partially cross-linked organic film layers. In some embodiments, the co-cured film layers of the present disclosure are formed from a co-curable film composition comprising a thermosetting resin. Typically, thermosetting resins include prepolymers that are in the form of soft solids or viscous liquids at room temperature (about 20° C. to about 25° C.) that typically harden after curing.

[0048] "Curing" is the process of initiating a chemical reaction in a curable material such as a co-curable film composition, resulting in extensive cross-linking between polymer chains, thereby producing an insoluble polymer network. Curing can be carried out by processes including, for example, heating and / or exposure to ultraviolet light. In some embodiments, curing is promoted by high pressure and / or mixing with a curing agent or catalyst. As used herein, the phrase "curing" refers to applying curing conditions to a polymerizable composition, wherein at least a majority of the reactive groups of the composition react to form a solid polymer product. As will be understood by those skilled in the art, applying curing conditions, such as an autoclave, to a polymerizable composition can produce a cured composition in which a higher percentage of reactive groups react, such that the polymerizable composition is cured more than the same composition that has not been exposed to curing conditions or has been exposed to less curing (e.g., curing at a lower temperature (including ambient temperature, such as about 20°C to about 25°C), or for a shorter period of time).

[0049] In some embodiments, curing comprises baking the one or more co-cured film layers and the composite structure together at a temperature greater than about 50° C., such as at a temperature of about 65° C. to about 200° C. or about 121° C. to about 185° C. In some embodiments, curing comprises baking the one or more co-cured film layers and the composite structure for a time of less than 48 hours, such as less than 24 hours, or for a time of about 2 to about 12 hours.

[0050] In some embodiments, co-curing is accomplished using autoclaves, oven curing, or ex-autoclave curing. As used herein, "ex-autoclave" refers to a process whereby a prepreg stack, including, for example, a co-curable film layer of the present disclosure, is laminated within a closed mold. Vacuum, pressure, and heat are then applied using methods known in the art other than autoclaves, such as a resin transfer molding machine. In certain other embodiments, co-curing is accomplished using an autoclave at a temperature of at least about 121°C.

[0051] Examples of suitable thermosetting resins for use in the co-curable film compositions of the present disclosure include polyester resins, epoxy resins, and polyimide resins, such as bismaleimide (BMI) and / or polyetherimide. In certain embodiments, the thermosetting resins used with the co-curable film compositions of the present disclosure include at least one polyisocyanate and at least one polyol, which form a polyurethane upon curing. As used herein, the term "polyurethane" refers to a polymer containing urethane (also known as carbamate) bonds, urea bonds, or a combination thereof, such as polyurethane-urea. Thus, the polyurethanes of the present disclosure may contain at least carbamate bonds and optionally urea bonds.

[0052] In some embodiments, the co-curable film compositions of the present invention comprise from about 5 to about 100 weight percent (wt. %) of the thermosetting resin, e.g., from about 15 to about 75 wt. %, or from about 25 to about 60 wt. %, based on the total weight of the co-curable film composition.

[0053] In some embodiments, the co-curable film compositions of the present invention further comprise non-conductive additives such as fillers, flow control agents, toughening agents, stabilizers (e.g., antioxidants, thermal stabilizers, and ultraviolet (UV) stabilizers), curing agents, and / or catalysts.

[0054] Examples of non-conductive fillers suitable for use with the co-curable film compositions of the present disclosure include ground or precipitated chalk, quartz powder, aluminum oxide, dolomite, carbon fibers, glass fibers, polymer fibers, titanium dioxide, fused silica, carbon black, calcium oxide, calcium magnesium carbonate, barite, and especially silicate fillers of the calcium magnesium aluminum silicate type. Other suitable non-conductive fillers include ceramics and fumed silica. The filler can be in the form of flakes, powders, fibers, microspheres, or glass spheres and can be solid or hollow structures. Further discussion of fillers can be found, for example, in U.S. Patent No. 4,980,234, which is incorporated herein by reference in its entirety.

[0055] In some embodiments, the filler may be present in the co-curable film composition of the present disclosure in an amount of about 0 wt % to about 40 wt %, such as about 5 wt % to about 30 wt %, based on the total weight of the co-curable film composition.

[0056] Flow control agents can be used to modify the rheological properties of the co-curable film composition. Examples of suitable flow control agents include fumed silica and metal powders. The flow control agent can be present in an amount of about 0 wt % to about 40 wt %, for example, about 0.1 wt % to about 10 wt %, based on the total weight of the composition.

[0057] In some embodiments, a toughening agent may be added to the co-curable film composition to adjust the film stiffness and surface hardness after curing. In certain embodiments, the toughening agent may be a polymer or oligomer having a glass transition temperature below about 20° C. (e.g., below about 0° C., below about −30° C., or below about −50° C.), and / or having functional groups, such as carboxylic acid groups, amino groups, and / or hydroxyl groups, that react with other components of the co-curable film composition when the composition is cured by heating.

[0058] Examples of suitable toughening agents include elastomeric toughening agents such as carboxylated nitriles (e.g. 1472, Zeon Chemical, Inc.), carboxyl-terminated butadiene acrylonitrile (CTBN), carboxyl-terminated polybutadiene (CTB), poly(etheretherketone) (PEEK) and polyetherketoneketone (PEKK). Other examples of suitable toughening agents can be found, for example, in U.S. Patent No. 4,980,234; U.S. Patent Application Publication No. 2008 / 0188609; and International Patent Publication WO 2008 / 087467, each of which is incorporated herein by reference in its entirety. In certain embodiments, the concentration of the toughening agent can be from about 5% to about 40% by weight, for example, from about 1% to about 30% by weight, based on the total weight of the composition.

[0059] Ultraviolet (UV) stabilizers can also be optionally added to the co-curable film composition of the present invention. In some embodiments, the UV stabilizer includes a UV absorber, an antioxidant, a pigment, a sealant, and a filler. In some embodiments, the UV stabilizer includes butylated hydroxytoluene (BHT), 2-hydroxy-4-methoxy-benzophenone (UV-9), 2,4-bis(2,4-dimethylphenyl)-6-(2-hydroxy-4-octyloxyphenyl)-1,3,5-triazine, 3,5-di-tert-butyl-4-hydroxybenzoic acid n-hexadecyl ester, titanium dioxide, and carbon black. In some embodiments, based on the gross weight of the composition, the UV stabilizer can be present in an amount of about 0.1 wt % to about 5 wt %, for example, about 0.5 wt % to about 3 wt %.

[0060] Examples of suitable curing agents and / or catalysts that can be added to the co-curable film compositions disclosed herein include aliphatic and aromatic primary amines, and aliphatic and aromatic tertiary amines. For example, amine curing agents and / or catalysts can include dicyandiamide, diureas (e.g., 2,4-toluene bis-(dimethylurea), 4,4'-methylene bis-(phenyl dimethylurea) and 4,4'-diaminodiphenyl sulfone) (4,4-DDS). Other suitable curing agents and / or catalysts include boron trifluoride complexes, guanidine and dicyandiamide. Other examples of curing agents and / or catalysts can be found in, for example, U.S. Patent No. 4,980,234 and U.S. Patent Application Publication No. 2008 / 0188609, each of which is incorporated herein by reference in its entirety. Based on the gross weight of the co-curable film composition, one or more curing agents and / or catalysts can be present in the co-curable film composition in an amount of about 0.1 wt % to about 40 wt %, for example, about 0.5 wt % to about 10 wt %.

[0061] Other suitable additives that may optionally be included in the co-curable film composition include, for example, crosslinking agents (e.g., aluminum or melamine crosslinking agents), binders, corrosion inhibitors, plasticizers, and / or other conventional additives known to those of ordinary skill in the art. In some embodiments, a conductive material is also included in the co-curable film composition as described herein.

[0062] In some embodiments, after curing to the surface of the composite structure, the co-cured film layer of the present invention has a thickness of about 1 mil to about 15 mils, such as about 2 mils to about 10 mils, about 3 mils to about 7 mils, or about 3 mils to about 4 mils, where 1 mil is equal to about 25 microns.

[0063] The co-curable film disclosed herein may further include at least one colorant, such as a pigment or dye, or may include a colored marking material printed thereon. In certain embodiments, at least one colored marking material is printed on the co-curable film, and in certain embodiments, at least one colorant is mixed into the co-curable film composition. The at least one colorant can be used to adjust the color and appearance of the co-curable film. As used herein, "colorant" refers to any substance that gives the co-curable film a color, and may include a colorant (as known in the art) and a pigment. Suitable colorants include, for example, titanium dioxide, carbon black, black pigments and other color dyes and pigments, including inorganic and organic pigments. The colorant can be provided in the form of flakes, powders, fibers or colored masterbatch concentrates. A variety of colorants can be added to a single co-curable film. In certain embodiments, the colorant is a solvent-based or water-based colorant. In certain embodiments, the colorant can impart special effects, such as enhanced reflectivity, pearlescence or gloss, to the co-curable film.

[0064] It should be understood that the co-cured film layer to be reactivated is cured on the substrate. However, there may also be various "underlying" coatings beneath the co-cured film layer, such as other decorative coatings or co-cured films, primers, intermediate layers, and conversion or anti-corrosion coatings.

[0065] Surface reactivation treatment composition

[0066] Disclosed herein is a surface reactivation treatment composition that can be applied to the surface of a co-cured film on a composite structure. As disclosed herein, the surface reactivation treatment composition can include at least two solvents, a surface exchange agent, and optionally one or more other additives. According to the method disclosed herein, at least two solvents, a surface exchange agent, and any optional additives can be combined and applied to the co-cured film layer in the form of a reactivation treatment composition. The reactivation treatment composition disclosed herein can take different physical forms, such as solutions, suspensions, mixtures, aerosols, emulsions, pastes, or combinations thereof. In one aspect, the reactivation treatment composition is in the form of a solution, an emulsion, or an aerosol.

[0067] The reactivation treatment composition can be prepared by mixing the components together using any mixing equipment known to those skilled in the art, such as, but not limited to, stirrers, shakers, high-speed mixers, internal mixers, in-line mixers, such as static mixers, extruders, grinders, ultrasonics, and gas dispersers, or by thorough hand shaking. When the reactivation treatment composition is in the form of a solution, the solution can be prepared as a concentrate and diluted prior to use or prepared for immediate use.

[0068] In certain embodiments, the reactivation treatment composition can be formulated as a spray formulation, and in certain embodiments, the reactivation treatment composition can be formulated to be applied to a co-cured film layer. It should be understood that the ingredients of the formulation can be selected to provide the formulation with a specific rheology or viscosity under specific circumstances so that, in use, the formulation is suitable for spray application or brush application. The spray formulation can be prepared for use with a specific spray gun and system (e.g., pressure, flow rate, and nozzle diameter). The formulation can, for example, provide a wet film that can be dried to form a powder of about 0 microns to about 15 microns thick, such as about 0.1 microns to about 5 microns thick, about 0.5 microns to about 2 microns thick, or about 0.1 microns to about 1 micron thick. The formulation can, for example, provide a powder of about 1 m 2 / L to about 50m 2 / L, for example, about 15m 2 / L to about 30m 2 / L coverage.

[0069] Solvent: The reactivation treatment composition disclosed herein comprises a solvent, which may be a single solvent or a combination of two or more solvents. In certain embodiments, the surface reactivation composition comprises at least two solvents. The at least two solvents may be selected from organic solvents suitable for industrial use. For example, at least two solvents may be selected from esters, ketones, ethers and alcohols, which may provide further advantages for the reactivation treatment composition, such as helping to destroy the surface of the co-cured film layer present on the substrate in certain aspects, or by providing an effective carrier for other components of the reactivation treatment composition (including surface exchange agents and / or any other optional additives). In certain embodiments, the solvent may provide a liquid formulation that can be effectively sprayed onto the surface of the co-cured film layer on the substrate, and in certain embodiments, the solvent may provide a liquid formulation that can be effectively coated (e.g., applied with a brush) on the surface of the co-cured film layer. The solvent may be one or more C 2-H 2 O 2-H 2 O 3-H 2 O 4-H 2 O 5-H 2 O 6-H 2 O 7-H 2 O 8-H 2 O 9-H 2 O 10-H 2 O 11-H 2 O 12-H 2 O 13-H 2 O 14-H 2 O 15-H 2 O 16-H 2 O 17-H 2 O 18-H 2 O 19-H 2 O 20-H 2 O 21-H 2 O 22-H 2 O 23-H 2 O 24-H 2 O 25-H 2 O 26-H 2 O 27-H 2 O 28-H 2 O 29-H 2 O 30-H 2 O 31-H 2 O 32-H 2 O 33-H 2 O 34-H 2 O 35-H 2 O 1-12 It is understood that the alkyl group may be interrupted and / or substituted by one or more functional groups. As used herein, "C 1-12"Alkyl" refers to a straight or branched chain saturated hydrocarbon having 1 to 12 carbon atoms, which may be substituted and / or interrupted by one or more functional groups. In certain embodiments, the solvent may be one or more organic solvents selected from C 3-10 alkyl.

[0070] Suitable organic solvents or solvent combinations may provide further advantages, which may depend on the surfactant and any other optional additives in the reactivation treatment composition, and may include, but are not limited to: (a) ketones, such as methyl ethyl ketone, methyl propyl ketone, methyl amyl ketone, methyl isoamyl ketone, methyl isobutyl ketone, acetylacetone, and acetone; (b) alcohols, such as aromatic alcohols, for example, benzyl alcohol; aliphatic alcohols, for example, C 1-6 or C 1-4 Alcohols, such as tert-butanol, n-butanol, sec-butanol, isopropanol, n-propanol, ethanol and methanol; cyclic alcohols, such as cyclohexanol; and diols, such as ethylene glycol, polyethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol and polypropylene glycol; (c) ethers, such as glycol ethers, for example, glycol diethers, such as di-C 1-6 Alkyl ethers, including diethers of alkylene glycols (e.g., ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, and polypropylene glycol), including but not limited to diethylene glycol dimethyl ether, dipropylene glycol dimethyl ether, or diethylene glycol methyl butyl ether, and cyclic ethers such as tetrahydrofuran; (d) esters, such as ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate, tert-butyl acetate, and glycol ether acetates; or any combination thereof.

[0071] In certain embodiments, at least one solvent may be selected from: alcohols such as ethanol, methanol, ethoxyethanol, propanol, isopropanol or n-propanol, butanol, tert-butanol and sec-butanol; and ether solvents such as C of ethylene glycol and propylene glycol. 1-6 Alkyl ethers or combinations thereof (eg, mixed ethers), including but not limited to glyme (dimethoxyethane), diglyme, triglyme, tetraglyme, and dipropylene glycol dimethyl ether, and cyclic ethers such as tetrahydrofuran.

[0072] Solvent combinations can be provided, including glycol ether:alcohol combinations, such as dipropylene glycol dimethyl ether:isopropyl alcohol or n-propyl alcohol; ether:alcohol combinations, such as dipropylene glycol dimethyl ether:isopropyl alcohol or n-propyl alcohol, methanol, isobutyl alcohol, sec-butyl alcohol, tert-butyl alcohol, ethoxyethanol and / or ethyl hexanol; ethylene glycol monomethyl ether:ethanol, methanol, ethoxyethanol and / or isopropyl alcohol; glycol and monoether combinations, such as dipropylene glycol-monomethyl ether, dipropylene glycol-monobutyl ether and / or dipropylene glycol; ether combinations, such as tetrahydrofuran:triglyme and tetrahydrofuran:dipropylene glycol dimethyl ether; solvent combinations comprising ketones, such as methyl ethyl ketone, methyl amyl ketone, methyl propyl ketone. Typical solvent combinations may include high boiling point and low boiling point solvent combinations.

[0073] The solvent combination can be an ether:alcohol combination, for example a glycol ether, for example a glycol diether, for example a diether of an alkylene glycol, including a dipropylene glycol diether, for example dipropylene glycol dimethyl ether, and an alcohol, for example an aliphatic alcohol, for example C 1-6 or C 1-4 Alcohols, such as isopropyl alcohol or n-propyl alcohol.

[0074] In certain embodiments, the solvent disclosed herein may contain less than about 800 ppm of water, such as less than about 700 ppm, 600 ppm, 500 ppm, 400 ppm, 300 ppm, 200 ppm, or 100 ppm of water, to reduce or prevent precipitation of the surface exchange agent. In certain embodiments, the reactivation treatment composition comprises an anhydrous form of the solvent. In certain embodiments, it is not necessary to add water to the reactivation treatment composition, and in certain embodiments, the reactivation composition does not contain water.

[0075] The at least two solvents may be present in an amount (based on the total weight of the reactivation treatment composition) of less than about 99.5%, such as less than about 99%, 98%, 97%, 96%, 95%, 94%, 93%, 92%, 91%, 90%, 89%, 88%, 87%, 86% or 85%. In certain embodiments, the at least two solvents may be present in an amount (based on the total weight of the reactivation treatment composition) of greater than about 85%, such as greater than about 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99%. In certain embodiments, the at least two solvents may be present in any amount between any two of those values. For example, the at least two solvents may be present in the reactivation treatment composition in an amount of about 86% to about 99.5%, such as about 90% to about 99.5%, about 92% to about 99%, or from about 94% to about 98%. In one aspect, the at least two solvents are present in an amount greater than about 90%, or in an amount from about 95% to about 98%, based on the total weight of the reactivation treatment composition.

[0076] In addition to the at least two solvents mentioned above, the reactivation treatment composition may also include other solvents. The at least two solvents mentioned above without any other solvents may also be referred to as "combination solvents" herein. Therefore, the at least two solvents may include or consist of the "combination solvents" described herein, optional "other solvents", optional incidental impurities and optional small amounts of water. In certain embodiments, "other solvents" may be provided in an amount of less than about 10%, for example, less than about 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2% or 1% (wt% of the total weight of the reactivation treatment composition). In one aspect, the other solvents are the same as those selected for the combination solvents. For example, in certain embodiments, the other solvents may be selected from at least one of acetates and alcohols, such as at least one of methoxypropyl acetate, methoxypropanol and isopropanol.

[0077] Surface exchange agent: In addition to at least two solvents, the reactivation treatment composition disclosed herein also includes at least one surface exchange agent. Suitable surface exchange agents include those that promote surface exchange of the co-cured film layer. Suitable surface exchange agents that promote surface exchange may include ester exchange agents. Exemplary ester exchange agents may be selected from: titanates and zirconates or chelates thereof, such as C 1-10 Alkyl titanate, C 1-10 Alkyl titanate chelate, C 1-10 Alkyl zirconate and C 1-10 Alkyl zirconate chelates. Specific examples may include tetraisopropyl titanate, tetra-n-butyl titanate, tetra(2-ethylhexyl) titanate, tetraethyl titanate, tetra-n-propyl zirconate, tetra-n-butyl zirconate, and combinations thereof. In certain embodiments, at least one surface exchange agent is selected from at least one of tetra-n-propyl zirconate, tetra-n-butyl zirconate, n-propoxy zirconium, tetra-n-propyl titanate, tetraisopropyl titanate, and tetra-n-butyl titanate.

[0078] The amount of the at least one surface exchange agent present in the reactivation treatment composition (based on the total weight of the reactivation treatment composition) can be greater than about 0.001%, for example, greater than about 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%. In certain embodiments, the amount of the at least one surface exchange agent present (based on the total weight of the reactivation treatment composition) can be less than about 10%, for example, less than about 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05% or 0.01%. In certain embodiments, the amount of the at least one surface exchange agent present (based on the total weight of the reactivation treatment composition) can be within the range of any two of these values. For example, the at least one surface exchange agent can be present in an amount of 0.05% to about 10%, for example, from about 1% to about 8%, or from about 2% to about 6%. In one aspect, the at least one surface exchange agent is present in an amount from about 1% to about 8% (based on the total weight of the reactivation treatment composition).

[0079] Optional Additives: The reactivation treatment compositions disclosed herein may contain at least one optional additive, for example, to modify drying time or reduce corrosion. These additives include, but are not limited to, anti-corrosion additives and colorants, such as dyes and pigments. The at least one optional additive may be a colorant, such as a dye, such as a UV fluorescent dye, to indicate where the reactivation treatment composition has been sprayed or brushed.

[0080] In certain embodiments, the at least one optional additive in the reactivation treatment composition disclosed herein may include nanoparticles. As used herein, the term "nanoparticles" refers to particles having a particle size of less than about 500 nm, for example, less than about 450 nm, 400 nm, 350 nm, 300 nm, 250 nm, 200 nm, 150 nm, 100 nm, 90 nm, 80 nm, 70 nm, 60 nm, 50 nm, 40 nm, 30 nm, 20 nm, 10 nm, or 5 nm. Nanoparticles can be organic or inorganic nanoparticles. Examples of organic nanoparticles include carbon-based nanoparticles, such as carbon black. Examples of inorganic nanoparticles include metal oxides of aluminum, zirconium, silicon, antimony, cerium, gadolinium, cobalt, indium, molybdenum, neodymium, tellurium, yttrium, europium, barium, copper, lithium, titanium, tungsten, carbides such as silicon carbide, sulfates such as BaSO4, carbonates such as CaCO3, phosphates such as Ca3(PO4)2 and FePO4, BiOCl, and yttria-stabilized zirconia.

[0081] It should be understood that all additives described below are optional and may be added to further enhance the application of the reactivation treatment composition or to further enhance the performance characteristics of the finished coating system. Suitable additives may include, for example, (a) rheology modifiers such as hydroxypropyl methylcellulose (e.g. 311), modified urea (e.g. ), cellulose acetate butyrate (e.g., Eastman CAB-551-0.01, CAB-381-0.5, CAB-381-20), and polyhydroxycarboxamides (e.g., ); (b) a wetting agent, such as a fluorochemical surfactant (e.g., M ); (c) surfactants, such as fatty acid derivatives (e.g. Bermadol SPS 2543), quaternary ammonium salts, ionic surfactants and nonionic surfactants; (d) dispersants, such as nonionic surfactants based on primary alcohols (e.g. 4481, DuPont) and alkylphenol-formaldehyde-disulfide condensates (e.g. 1494); (e) defoaming agents; (f) leveling agents, such as fluorocarbon-modified polymers (e.g., 3777); (g) pigments, such as those used in aerospace coating compositions, which may include organic phthalocyanines, quinacridones, diketopyrrolopyrroles (DPP) and diarylide derivatives and inorganic oxide pigments (e.g., to enhance the visibility of the reactivation treatment composition and the area to which it has been applied); (h) dyes, including organic and inorganic dyes, such as fluorescers (Royale Pigment and Chemicals) (e.g., to enhance the visibility of the reactivation treatment composition and the area to which it has been applied), fluorescein, and phthalocyanines; and (i) anti-corrosion additives, such as phosphate esters (e.g., ADD APT, C6), (2-benzothiazolylthio) succinic acid alkyl ammonium salts (e.g. 15), triazinedithiols and thiadiazoles.

[0082] In certain embodiments disclosed herein, the at least one optional additive does not comprise or consist of silanes and siloxanes, such that in certain embodiments, the reactivation treatment composition does not comprise silanes or siloxanes.

[0083] When at least one optional additive is present in the reactivation treatment composition, the at least one optional additive can be present in an amount less than about 10%, based on the gross weight of the reactivation treatment composition. For example, if present, the total amount of all optional additives can be provided in an amount less than about 10%, for example, less than about 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1% or 0.05%. In certain embodiments, if present, the total amount of all optional additives can be provided in an amount greater than about 0.01%, for example, greater than about 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8% or 9%. In certain embodiments, if present, the total amount of all optional additives can be provided in an amount between any two of the above values, for example, from about 0.01% to about 10%, for example, from about 0.05% to about 5%, about 0.1% to about 3%, or about 0.5% to about 2%.

[0084] Other coating layers

[0085] According to the reactivation treatment methods disclosed herein, after applying the reactivation treatment composition, at least one additional coating layer can be applied to the co-cured film layer on the substrate. As used herein, the phrase "additional coating layer" is used in its broadest sense and describes: decorative topcoats; basecoats; midcoats; primers; sealers; lacquers; pigmented or transparent coatings (e.g., varnishes); coatings designed for specific purposes, such as corrosion protection, high temperature resistance, or camouflage; coatings with high gloss, matte, textured, or smooth finishes; and / or coatings containing special additives, such as metal, mica, or glass flakes. In certain embodiments, the at least one additional coating layer can be a varnish or a clearcoat.

[0086] In some embodiments, the at least one additional coating layer applied to the co-cured film layer according to the reactivation treatment method disclosed herein can mitigate the effects of environmental conditions, such as chemicals or solar radiation, such as ultraviolet (UV) radiation, compared to other coating layers applied by conventional reactivation methods (e.g., sanding of the co-cured film layer). For example, the surface of the composite structure may be exposed to certain environmental conditions, such as solar radiation, which may cause degradation of the composite structure. However, when compared to other coating layers applied without applying the reactivation treatment composition as disclosed herein, the additional coating layers applied according to the reactivation method disclosed herein can exhibit enhanced resistance to such environmental conditions. In some exemplary embodiments, a composite structure comprising a co-cured film layer and at least one additional layer applied thereto according to the reactivation method disclosed herein has a UV resistance of, for example, from about 200 nanometers to about 800 nanometers, for example, from about 200 nanometers to about 400 nanometers.

[0087] In certain embodiments, the at least one additional coating layer applied to the co-cured film layer according to the reactivation treatment methods disclosed herein can exhibit enhanced adhesion to the co-cured film layer compared to additional coating layers applied by conventional reactivation methods (e.g., sanding the co-cured film layer). As will be discussed in more detail below, the adhesion of the at least one additional coating layer to the co-cured film layer can be measured by any means known in the art (e.g., interlayer adhesion).

[0088] Surface reactivation treatment method

[0089] The reactivation treatment method disclosed herein comprises applying a reactivation treatment composition or individual components of the reactivation treatment composition to the surface of a co-cured film layer that has been pre-cured to a substrate or an intermediate layer that has been pre-cured to a substrate. For example, the reactivation treatment method disclosed herein can be used in situations where the co-cured film layer has been previously adhered to a substrate and aged or cured beyond its application window for adhesion to other coatings or other entities without requiring specific reactivation for adhesion (e.g., harsh surface treatment such as mechanical abrasion).

[0090] It should be understood that the above-mentioned application window provides an environmental duration such that any newly applied film layer ages or cures beyond its acceptable adhesion window for applying any further coating, such that its adhesion does not meet in-service performance requirements, for example, the duration after the co-cured film layer present on the substrate cures such that the adhesion of the additional coating layer will be unsatisfactory for performance requirements. Although not wishing to be bound by theory, it is believed that applying the reactivation treatment composition to the surface of the co-cured film layer can allow the co-cured film layer to swell to a certain extent, thereby causing the entangled network of polymer chains in the co-cured film layer to expand. This swelling of the co-cured film layer can make room for the polymers in the newly applied other coating layers to be incorporated therein. In addition, without wishing to be bound by theory, the reactivation treatment composition in the method disclosed herein can act to activate the co-cured film layer by providing a chemical "bridge" between the reaction sites on the newly applied other coating layers and the reaction sites on the co-cured film layer.

[0091] In certain embodiments, the co-cured film layer has been pre-cured at an elevated temperature. For example, in certain embodiments, the co-cured film layer has been pre-cured at a temperature greater than about 50°C, such as at least about 65°C, about 100°C, at least about 121°C, at least about 150°C, at least about 175°C, at least about 185°C, or at least about 200°C. In certain embodiments, the co-cured film layer has been pre-cured at a temperature of about 65°C to about 200°C, such as about 100°C to about 185°C or about 121°C to about 175°C. In other embodiments, the co-cured film layer has been pre-cured for a period of less than about 48 hours, such as less than about 24 hours, about 12 hours, about 8 hours, or at least about 2 hours. In certain embodiments, the co-cured film layer has been pre-cured for a period of about 2 hours to about 24 hours, such as about 2 hours to about 12 hours or about 2 hours to about 4 hours. In other embodiments, the co-cured film layer has been previously cured at a temperature of about 65° C. to about 200° C., such as about 100° C. to about 185° C. or about 121° C. to about 175° C., and for a period of about 2 hours to about 24 hours, such as about 2 hours to about 12 hours or about 2 hours to about 4 hours. In certain embodiments, the co-cured film layer has been previously cured at a temperature greater than 50° C. In certain embodiments, the co-cured film layer has been previously cured in an autoclave at a temperature of about 185° C. for a period of about 2 hours to 12 hours.

[0092] The co-cured film layer already present on the substrate may be a cured, aged, and / or in-service coating. An in-service coating is understood to be a coating that has been previously applied and cured and is suitable for in-service use or has actually been in-service, such as an aerospace panel that has been provided on an aircraft that has flown at least once. The application window may depend on the type of co-cured film layer and / or the type of substrate, and may, for example, include consideration of time, humidity, temperature, pressure, type of UV exposure, or other factors associated with the curing process.

[0093] It should be understood that the reactivation treatment method of the present disclosure is a chemical method for modifying the surface of the co-cured film layer so that the surface is more susceptible to forming adhesive interactions with other coatings. Without wishing to be bound by any theory, it is believed that the interaction of the solvent and the surface exchange agent with the co-cured film layer changes the surface chemistry and / or surface morphology of the coating layer, making it more receptive to other entities, including but not limited to at least one other coating layer. The solvent, surface exchange agent and optional additives can be selected to maintain the bulk integrity of the co-cured film layer and any underlying coating and substrate structure, and can also include consideration of compatibility with the substrate in the event of any accidental exposure of any uncoated substrate surface to the reactivation treatment composition.

[0094] The reactivation treatment composition or one or more components thereof can be applied by any liquid application method known to those skilled in the art, such as spraying, brushing, dipping, scraping, blade, hose, roller, wiping, curtain coating, blanketing, flow coating, mist coating, pipette, aerosol, and combinations thereof. In one aspect, the reactivation treatment composition is applied by spraying, for example, the reactivation treatment can be a reactivation treatment composition formulated for application as a spray.

[0095] The reactivation methods currently disclosed herein can be carried out at ambient temperature, for example, at a temperature of about 10°C to about 35°C, such as about 15°C to about 30°C, or about 20°C to about 25°C. The reactivation method can also typically be carried out near typical atmospheric pressure (e.g., between about 90kPa to about 105kPa, such as about 101kPa). The curing of the subsequently applied additional coating layers can also be carried out at ambient temperature, such as about 10°C to 35°C. Alternatively, the curing of one or more subsequently applied additional coating layers can be carried out at an elevated temperature, such as the conditions disclosed herein that can be used to cure the co-cured film layer (e.g., an autoclave). In certain embodiments, application of the reactivation treatment composition does not require preheating of the co-cured film layer and the substrate.

[0096] The reactivation treatment composition or one or more of its components can be applied to smaller or larger areas, parts of larger components or parts, or complete facilities, such as facilities related to aerospace (e.g., aircraft), automobiles (e.g., vehicles), shipping (e.g., ships), transportation (e.g., trains), military (e.g., helicopters, missiles) or construction (e.g., buildings, floors). The surface to which the reactivation treatment composition is applied can have simple or complex geometries, including two-dimensional or three-dimensional geometries. The reactivation treatment composition can be applied once or multiple times before interacting with one or more other coating layers. The exposure time of the reactivation treatment composition on the co-cured film layer is not particularly limited, and the exposure time can be very short, such as about 5 minutes, about 10 minutes, or about 15 minutes, or longer, such as about 12 hours, about 18 hours, or about 24 hours, without damaging the integrity of the outermost co-cured film layer, any underlying co-cured film layer or coating structure, and the substrate. On the one hand, the exposure time should be sufficient to evaporate the solvent in the reactivation treatment composition in whole or in part, and the surface of the co-cured film layer is visually dry. This can, for example, depend on the temperature of the airflow and the environment in which the activation treatment composition is applied. It should also be understood that as the relative humidity approaches 100%, the application window for applying other coatings may decrease.

[0097] After the co-cured film layer has been reactivated, one or more additional coating layers may be applied immediately or after a certain amount of time, provided that the reactivated surface of the co-cured film layer remains substantially uncontaminated. Additional coating layers may include entities such as adhesives, sealants, pinhole fillers, stencils, signage, pressure-sensitive decals, and logos.

[0098] Any suitable method known to those skilled in the art can be used to evaluate whether the adhesion quality between the reactivated co-cured film layer and other coating layers or between the reactivated co-cured film layer and the substrate (or any coating therebetween) is suitable for its intended purpose. Such tests include, but are not limited to, ASTM, ISO, or SAE (ASTM G-73) standards, in-house test methods simulating in-service performance, in-service performance itself, and actual or accelerated durability testing.

[0099] In the case of aerospace coatings, water impact-based test methods such as rotating arm rain erosion and single impact jet apparatus (Single Impact Jet Apparatus, SUA) (MIJA Limited, Cambridge, UK) can be used with an immersion time of 16 to 24 hours. In certain embodiments, a rotating arm rain erosion test simulating the rain erosion effects observed on commercial aircraft can be used to evaluate the intercoat adhesion of aerospace coatings. In these cases, the degree of removal of the overcoat is related to the level of interlayer adhesion, wherein a higher degree of removal of the overcoat corresponds to a lower degree of intercoat adhesion, and the overcoat is any other coating layer applied to the reactivated co-cured film layer. For example, these methods are described in the reference, Berry DH and Seebergh JE, "Adhesion Test Measurement Comparison for Exterior Decorative Aerospace Coatings: Two Case Studies," Proceedings 26th Annual Adhesion Society Meeting, Myrtle Beach, SC, pp. 228-230 (2003).

[0100] In certain embodiments, for rain erosion testing, the percentage of area removed or the longest tear length of the topcoat after 30 minutes of exposure to a simulated rain field can be used to determine the degree of intercoat adhesion between the topcoat and the underlying coating (e.g., other coating layers that have been applied to the reactivated co-cured film layer according to the methods disclosed herein). Intercoat adhesion can be quantified by image analysis, including visual inspection or measurement. Figure 2Highlighted are visual representations associated with a scale of 1 to 10 corresponding to the maximum tear length and percentage area of the coating removed in the rain erosion test as described above. Figure 2 In the intercoat adhesion test, a coat-to-coat adhesion value of 10 corresponds to a maximum tear length of 0.02 inches, a coat-to-coat adhesion value of 9 corresponds to a maximum tear length of 0.02 to 0.06 inches with an area loss of no more than 1%, and a coat-to-coat adhesion value of 8 corresponds to a maximum tear length of 0.06 to 0.12 inches with an area loss of no more than 5%. Similarly, a coat-to-coat adhesion value of 7 corresponds to a maximum tear length of 0.12 to 0.25 inches with an area loss of no more than 10%, a coat-to-coat adhesion value of 6 corresponds to a maximum tear length of 0.25 to 0.5 inches with an area loss of no more than 25%, and a coat-to-coat adhesion value of 5 indicates a coating loss of 25% or a maximum loss length of 0.75 inches. A coat-to-coat adhesion value of 4 corresponds to a coating loss of 40% or a loss at any location exceeding 0.75 inches, and a coat-to-coat adhesion value of 3 corresponds to a coating loss of 50%. Finally, a coat-to-coat adhesion value of 2 corresponds to a coating loss of 75%, and a coat-to-coat adhesion value of 1 corresponds to a coating loss of 100%. Depending on various factors, including the type of coating used, the methods of the present disclosure can provide additional coating layers applied to the reactivated co-cured film layer, wherein the additional coating layers have an intercoat adhesion value corresponding to, for example, an intercoat adhesion value of 10, 9, 8, 7, 6, 5, 4, 3, or 2. In one aspect, the scale rating is at least 7, such as at least 8 or at least 9. Depending on various factors, including the type of coating used, the methods of the present disclosure can provide a Rain Erosion Test value corresponding to a % Area Removed of 0%, such as less than about 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, 30%, 40%, 50%, 60%, 70%, 75%, 80%, or 90%, or any range therebetween. Furthermore, the methods of the present disclosure can provide rain erosion test values corresponding to tear lengths of less than about 1 inch, such as less than about 0.5 inch, less than about 0.25 inch, less than about 0.12 inch, less than about 0.06 inch, or about 0.02 inch. It will be appreciated that the more topcoat removed, the worse the intercoat adhesion.

[0101] In certain embodiments, for example, a single impact jet apparatus (SUA, Cambridge) test can be performed using an apparatus configured to use a 0.8 mm nozzle and 0.22 caliber 5.5 mm Crosman Accupell Pointed Pellets (#11246). The test can include immersion in water for approximately 16 to 18 hours and then using a 45° coupon to affect droplet geometry. A single water jet can be used with an impact velocity of approximately 600 + 25 m / s.

[0102] In certain embodiments, the rain erosion test may use a rotating arm rain erosion apparatus employing a 1.32 m (52 in) zero-lift helicopter-like propeller running at 3600 rpm. The topcoat (e.g., one or more additional coating layers applied to the reactivated co-cured film layer) may be applied at a coating thickness of 80 to 120 microns and through a mask to produce a leading edge. A 170 ms delay may be provided at the midpoint of the test sample. -1 The effective rain field density can be about 2 mm droplets, which is equivalent to about 2.54 x 10 -5 kmh -1 (1 inch per hour). In certain embodiments, the effects of rain erosion can be determined after 30 minutes of testing, and the intercoat adhesion of the sample evaluated based on the amount of coating removed or tear length, as described above.

[0103] Adhesion between the co-cured film layer and the substrate (or any layer therebetween) or between the co-cured film layer and other coating layers may also be determined by any other method known in the art, such as a wet and dry cross-hatch test. The dry adhesion of the coating may be determined, for example, according to ASTM D3359, Standard Test Method for Adhesion by Tape Test, Test Method B. In certain embodiments, a cross-hatch pattern may be drawn through the various coating compositions to the substrate. A strip of tape, such as a 1 inch wide tape known as 250-gauge masking tape. The tape can be pressed down using a two-pass roller (e.g., a 4.5-pound rubber-covered roller). The tape can then be removed in one abrupt motion perpendicular to the panel. Adhesion can then be assessed by visually inspecting the coating on the cross-hatch area to determine the percent area of coating removed as described above.

[0104] For aerospace applications, the disclosed reactivation method may provide advantages such as increased flow time for the reactivation process, greater reproducibility and consistency over larger areas and between operators, and improved ergonomics of the process. These and other advantages may together provide net cost savings.

[0105] The methods disclosed herein may include promoting adhesion of one or more additional coating layers to a co-cured film layer present on a substrate by applying a reactivation treatment composition comprising at least two solvents, a surface exchange agent, and optionally at least one additive to the co-cured film layer to reactivate the surface of the co-cured film layer, thereby increasing the surface's adhesion to the additional coating layer. The combination of the solvent and the surface exchange agent may disrupt the surface of the co-cured film layer, thereby activating it for adhesion, such as bonding to the additional coating layer, which may provide effective adhesion for in-service performance, such as the aerospace ASTM intercoat adhesion described herein.

[0106] The methods disclosed herein may further include one or more optional steps, including at least one of cleaning, wiping, and drying the co-cured film layer before applying the reactivation treatment composition to the surface of the co-cured film layer. In certain embodiments, the methods disclosed herein may further include the following steps: cleaning the co-cured film layer by applying a cleaning solvent to the surface of the co-cured film layer before applying the reactivation treatment composition. The cleaning solvent can be any solvent and any optional desired ingredients to facilitate cleaning the surface of the co-cured film layer before reactivation. The cleaning solvent can be applied to the co-cured film layer by any means known in the art, including by wiping or spraying the cleaning solvent onto the surface of the co-cured film layer. In certain embodiments, the cleaning solvent can include a volatile organic solvent, including, for example, methyl ethyl ketone, toluene, isopropyl alcohol, and methyl isobutyl ketone. Applying a cleaning solvent to the surface of the co-cured film layer can help ensure that the co-cured film layer is clean and free of any contaminants or debris. Other pretreatment steps before applying the reactivation treatment composition to the co-cured film layer are also contemplated. For example, other non-reactivation steps, such as mechanical grinding to remove detached surface contaminants, or washing steps, can be performed before applying the reactivation treatment composition. It should be understood that a pretreatment step may not be included in the methods disclosed herein. For example, in certain embodiments of the methods disclosed herein, the co-cured film layer is not sanded or otherwise mechanically abraded after the film layer is cured and before the reactivation composition is applied.

[0107] After applying the reactivation treatment composition to the surface of the co-cured film layer, the method disclosed herein may further include one or more optional steps, including at least one of drying, cleaning, and wiping the surface of the reactivated co-cured film layer. In one aspect, the method includes drying the reactivated surface of the co-cured film layer before applying one or more additional coating layers. In certain embodiments, the drying step may last for at least about 15 minutes, such as at least about 30 minutes, at least about 45 minutes, at least about 1 hour, at least about 2 hours, at least about 4 hours, at least about 8 hours, at least about 1 day, or any time interval within any of those durations, such as about 15 minutes to about 1 day, about 30 minutes to about 8 hours, or about 45 minutes to about 4 hours.

[0108] In certain embodiments, the additional coating layer may be applied to an average dry film thickness (dft) of at least about 1 mil dft (about 25 microns), for example, to an average dft of about 1 mil to about 3 mils ft. One or more additional coating layers may be applied at a thickness sufficient to meet the intended purpose of the additional coating layer, for example, to restore or enhance the gloss of the co-cured film layer. At least one additional coating layer may be applied to a thickness of, for example, at least about 1 mil, for example, from about 2 mils to about 25 mils.

[0109] It should be understood that one or more steps of the method may be repeated to provide additional coating layers to the previously applied co-cured film layer and substrate.It should also be understood that any other aspects described herein may also be applicable to the above method.

[0110] Although the present teachings have been described with respect to one or more exemplary embodiments, changes and / or modifications may be made to the described examples without departing from the spirit and scope of the claimed embodiments. In addition, as used herein, the term "about" indicates that the listed values may vary as long as the variation does not result in a substantial change in the described embodiments.

[0111] Although the method of the present disclosure is described in the context of coating an aircraft, the method can be implemented for coating any type of surface without limitation. In this regard, the surface can be the surface of a motor vehicle (including a tractor-trailer), a building, a banner, or any other type of movable or immovable structure, object, article, or material having a surface on which an image is to be placed. The surface can be flat, simply curved, and / or complexly curved.

[0112] Example

[0113] The following examples are submitted to further define the various species of the present disclosure. The examples are intended to be illustrative only and are not intended to limit the scope of the present disclosure. Unless otherwise indicated, parts and percentages are by weight.

[0114] First, nine samples were prepared, wherein for each sample, a co-cured film layer comprising polyurethane was cured to a composite structure in an autoclave (pressure of up to 100 psi and temperature of up to 121° C. for at least one hour), sanded, and then additional coating layers were applied thereon. The first additional coating layer was a polyamide paint coating, followed by a polyurethane primer and a polyurethane clear coat. After application of the additional coating layers, the composite structure was cured at room temperature for at least 14 days, or at an elevated temperature (38° C. to 55° C.) for at least 3 days. Next, the samples were subjected to a rotating arm corrosion test as described by Berry DH and Seebergh JE, “Adhesion Test Measurement Comparison for Exterior Decorative Aerospace Coatings: Two Case Studies,” Proceedings 26th Annual Adhesion Society Meeting, Myrtle Beach, SC, pp. 228-230 (2003) and similar to ASTM G-73. After the film layers were co-cured into the composite structure, but before sanding, the three samples were not exposed to UV light (see Figure 3A ), three samples were exposed to 200kJ / m 2 of ultraviolet light (see Figure 3B ), and three samples were exposed to 1000 kJ / m 2 of ultraviolet light (see Figure 3C ).

[0115] Figure 3A Three samples are shown in which the co-cured film layer was reactivated by sanding and not exposed to UV light. Figure 3A As shown, at least one of the three samples experienced film degradation. For example, Figure 3A The top graph shows an intercoat adhesion (31) of about a rating of 4 (i.e., about 40% coating loss or more than 0.75 inches at any location), while the middle graph shows an intercoat adhesion (32) of about a rating of 6, and the bottom graph shows an intercoat adhesion (33) of about a rating of 9.

[0116] Figure 3B Three samples are shown where the co-cured film layers were reactivated by sanding and exposed to 200 kJ / m 2 Under ultraviolet light, Figure 3C Three samples are shown where the co-cured film layers were reactivated by sanding and exposed to 1000 kJ / m 2 Under ultraviolet light. Figure 3B As shown, exposure to 200kJ / m 2UV-exposed samples also experienced coating degradation, with exposure to 1000 kJ / m 2 The same is true for samples (see Figure 3C ).For example, Figure 3B The upper graph of shows that the intercoat adhesion (34) is about level 7, while Figure 3B The middle figure shows that the intercoat adhesion (35) is about level 4, Figure 3B The lower graph shows that the intercoat adhesion (36) is about level 6. In addition, Figure 3C In the figure, the upper and lower figures show inter-coat adhesion (37, 39) of about grade 5, and the middle figure shows inter-coat adhesion (38) of about grade 4. The degradation of the coatings indicates that the coatings applied on the sanded co-cured film layer did not adhere adequately to the co-cured film layer.

[0117] Next, an additional nine samples were prepared, wherein for each sample, the co-cured film layer was cured to the above composite structure as described above for the first nine samples (i.e., in an autoclave at a pressure of up to 100 psi and a temperature of up to 121°C for at least one hour) and wiped with Sur-Prep AP-1 provided by Zip-Chem. Sur-Prep AP-1 is a reactivation treatment composition comprising tetra-n-propyl zirconate in a dipropylene glycol dimethyl ether / n-propanol solvent. Next, the additional coating layers were sprayed thereon. The first additional coating layer was a polyamide paint coating, followed by a polyurethane basecoat and a polyurethane clearcoat. After application of the additional coating layers, the composite structure was cured at room temperature for at least 14 days, or at an elevated temperature (38°C to 55°C) for at least 3 days. As with the first nine samples, three samples were not exposed to ultraviolet (UV) light (see Figure 4A ), three samples were exposed to 200kJ / m 2 of ultraviolet light (see Figure 4B ), three samples were exposed to 1000kJ / m 2 of ultraviolet light (see Figure 4C Finally, the samples were subjected to the same rotating arm corrosion test (according to BSS7393).

[0118] like Figures 4A to 4C As shown, all nine samples showed little to no coating degradation, as each panel exhibited an inter-coat adhesion level of about 6 to about 10. Figure 4A In the case where the sample is not exposed to UV light, the top graph shows an inter-coat adhesion (41) of about level 8, the middle graph shows an inter-coat adhesion (42) of about level 9, and the bottom graph shows an inter-coat adhesion (43) of about level 8. Figure 4B In which the samples were exposed to 200 kJ / m 2Under ultraviolet light, the top graph shows an intercoat adhesion (44) of about grade 9, while the middle graph shows an intercoat adhesion (45) of about grade 8. The bottom graph shows an intercoat adhesion (46) of about grade 9. Finally, in Figure 4C In which the sample was exposed to 1000kJ / m 2 Under UV light of 200 kJ / m, the inter-coat adhesion (47) shown in the upper figure is about level 8, while the inter-coat adhesion (48) shown in the middle figure is about level 7, and the inter-coat adhesion (49) shown in the lower figure is about level 7. There is no degradation of the coating layer, indicating that even when the sample is exposed to 200 kJ / m 2 and exposure to up to 1,000 kJ / m 2 After exposure to ultraviolet light, the coating layer applied on the co-cured film layer wiped with the reactivation treatment composition showed good adhesion to the co-cured film layer.

[0119] Furthermore, the present disclosure includes implementations according to the following clauses:

[0120] 1. A method for reactivating a co-cured film layer (2) disposed on a composite structure, the method comprising:

[0121] applying a reactivation treatment composition to the co-cured film layer (2), the reactivation treatment composition comprising at least two solvents and a surface exchange agent, the surface exchange agent comprising a metal alkoxide or a chelate thereof; and

[0122] allowing the reactivation treatment composition to produce a reactivated co-cured film layer (2);

[0123] Wherein, the co-cured film layer (2) is pre-cured at a curing temperature greater than about 50°C.

[0124] 2. The method of clause 1, further comprising applying a further coating layer (4) to the reactivated co-cured film layer (2).

[0125] 3. The method of clause 1 or 2, wherein the curing temperature is at least about 121°C.

[0126] 4. The method of any one of clauses 1 to 3, wherein the method does not comprise sanding the co-cured film layer (2) prior to applying the reactivation treatment composition.

[0127] 5. The method according to any one of clauses 1 to 4, wherein the co-cured film layer (2) is pre-cured in an autoclave.

[0128] 6. The method of any one of clauses 1 to 5, wherein the co-cured film layer (2) comprises polyurethane, polyimide, polyester or epoxy resin when cured.

[0129] 7. The method of any one of clauses 1 to 6, wherein the co-cured film layer (2) comprises polyurethane when cured.

[0130] 8. The method of any one of clauses 1 to 7, wherein the surface exchange agent is zirconium propoxide.

[0131] 9. The process of any one of clauses 1 to 8, wherein the at least two solvents are dipropylene glycol dimethyl ether and n-propanol.

[0132] 10. The method of any one of clauses 1 to 9, further comprising applying a cleaning solvent prior to or simultaneously with applying the reactivation treatment composition.

[0133] 11. The method according to clause 2, wherein the further coating layer (4) is a varnish.

[0134] 12. The method of clause 2, wherein the intercoat adhesion level (31, 32, 33, 34, 35, 36, 37, 38, 39, 41, 42, 43, 44, 45, 46, 47, 48, 49) of the further coating layer (4) is from 6 to 10 after a rotating arm rain erosion test.

[0135] 13. The method of clause 2, wherein the intercoat adhesion level (31, 32, 33, 34, 35, 36, 37, 38, 39, 41, 42, 43, 44, 45, 46, 47, 48, 49) of the further coating layer (4) is from 8 to 10 after the rotating arm rain erosion test.

[0136] 14. A reactivated co-cured film layer (2), comprising:

[0137] a co-cured film layer (2) disposed on the composite structure, and

[0138] a reactivation treatment composition layer comprising a surface exchange agent comprising a metal alkoxide or a chelate thereof and disposed on the co-cured film layer (2) to produce a reactivated co-cured film layer (2),

[0139] Wherein, the co-cured film layer (2) is cured at a temperature of at least about 50°C.

[0140] 15. The reactivated co-cured film layer (2) according to clause 14, wherein the co-cured film layer (2) has not been sanded.

[0141] 16. The reactivated co-cured film layer (2) according to clause 14 or 15, further comprising an additional coating layer (4) disposed on the reactivated co-cured film layer (2).

[0142] 17. The reactivated co-cured film layer (2) of clause 16, wherein the inter-coat adhesion level (31, 32, 33, 34, 35, 36, 37, 38, 39, 41, 42, 43, 44, 45, 46, 47, 48, 49) of the further coating layer (4) is from 6 to 10 after the rotating arm rain erosion test.

[0143] 18. The reactivated co-cured membrane layer (2) according to any one of clauses 14 to 17, wherein the surface exchange agent is zirconium propoxide.

[0144] 19. The reactivated co-cured film layer (2) according to any one of clauses 14 to 18, wherein the co-cured film layer (2) comprises polyurethane, polyimide, polyester or epoxy resin when cured.

[0145] 20. An aircraft component having a co-cured film layer (2) thereon, the aircraft component comprising:

[0146] composite structures; and

[0147] The reactivated co-cured film layer (2) of any one of clauses 14 to 19, cured onto the surface of the composite structure.

Claims

1. A method for reactivating a co-cured film layer (2) disposed on a composite structure, the method comprising: applying a reactivation treatment composition to the co-cured film layer (2), the reactivation treatment composition comprising at least two solvents and a surface exchange agent, the surface exchange agent comprising a metal alkoxide or a chelate thereof; allowing the reactivation treatment composition to produce a reactivated co-cured film layer (2); and applying a further coating layer (4) to the reactivated co-cured film layer (2), The co-cured film layer (2) is pre-cured at a curing temperature greater than 100° C., and the co-cured film layer (2) comprises polyurethane, polyimide, polyester or epoxy resin when cured.

2. The method according to claim 1, wherein The co-cured film layer (2) is pre-cured in an autoclave.

3. The method according to claim 1, wherein The curing temperature is at least 121°C.

4. The method according to any one of claims 1 to 3, wherein The method does not include sanding the co-cured film layer (2) prior to applying the reactivation treatment composition.

5. The method according to any one of claims 1 to 3, wherein The co-cured film layer (2) comprises polyurethane when cured.

6. The method according to any one of claims 1 to 3, wherein The surface exchange agent is zirconium propoxide.

7. The method of claim 1, wherein: The other coating layer (4) is a varnish.

8. The method of claim 1, wherein: The inter-coat adhesion levels (31, 32, 33, 34, 35, 36, 37, 38, 39, 41, 42, 43, 44, 45, 46, 47, 48, 49) of the other coating layers (4) were 6 to 10 after the rotating arm rain erosion test.

9. A reactivated co-cured film layer (2), comprising: a co-cured film layer (2) provided on the composite structure, a reactivation treatment composition layer comprising a surface exchange agent comprising a metal alkoxide or a chelate thereof and disposed on the co-cured film layer (2) to produce a reactivated co-cured film layer (2), and another coating layer (4) disposed on the reactivated co-cured film layer (2), in, The co-cured film layer (2) is cured at a temperature of at least 100° C., and the co-cured film layer (2) comprises polyurethane, polyimide, polyester or epoxy resin when cured.

10. An aircraft component having a co-cured film layer (2) thereon, the aircraft component comprising: composite structures; and The reactivated co-cured film layer (2) according to claim 9 is cured onto the surface of the composite structure.

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