Patent Publication Number: US-2016221275-A1

Title: Method of manufacturing a polyimide film

Description:
FIELD 
     The present disclosure relates to composite materials, and more particularly, to methods of manufacturing polyimide composite materials. 
     BACKGROUND 
     Composite materials have various advantageous properties over conventional metal materials. In particular composite materials may be lighter than metals such as aluminum. However, some composite matrix materials do not perform well at high sustained temperatures. For example, epoxy-based thermoset resin composites are typically not suitable for environments with sustained temperatures over 250° F. (120° C.). 
     Polyimide-based resin composites are known to operate effectively at higher temperatures than epoxy composites. However, known polyimide-based resins in their liquid state typically have very low viscosity, rendering them very difficult to convert into a film to be used in later phases of manufacturing a composite component. This has been a practical impediment to wide spread use of polyimide-based resin systems. 
     SUMMARY 
     A method of manufacturing a polyimide film may comprise adding nanomaterials to a polyimide resin and forming the polyimide resin and the nanomaterials into a film through a first nip roller. 
     In various embodiments, adding the nanomaterials to the polyimide resin may increase a viscosity of the polyimide resin. The nanomaterials may comprise at least one of carbon nanotubes, carbon nanofibers, and graphene nanoplatelets. The method may comprise co-extruding the polyimide resin and a carbon veil through a second nip roller. The polyimide resin may be extruded into the polyimide film. The polyimide film may be uncured. The polyimide film may be partially cured. The polyimide resin may be heated prior to the extruding. 
     A method of manufacturing a composite laminate may comprise adding nanomaterials to a polyimide resin, extruding the polyimide resin into a polyimide film, laying together a plurality of composite plies each comprising a carbon fabric and polyimide resin, wherein each composite ply comprises either separate layers or carbon fabric and the polyimide resin film, or each composite ply comprises a prepreg fabric made from a prior infusion of the polyimide resin film into a carbon fiber fabric, and compressing, heating and curing the plies together to form a laminate. 
     In various embodiments, the polyimide film may be coupled to a surface of the composite laminate. The polyimide film may be interleaved between adjacent dry fiber layers. The dry fiber layers may comprise carbon fiber. The polyimide film and the dry fiber layers may be resin film infused. 
     The foregoing features and elements may be combined in various combinations without exclusivity, unless expressly indicated otherwise. These features and elements as well as the operation thereof will become more apparent in light of the following description and the accompanying drawings. It should be understood, however, the following description and drawings are intended to be exemplary in nature and non-limiting. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter of the present disclosure is particularly pointed out and distinctly claimed in the concluding portion of the specification. A more complete understanding of the present disclosure, however, may best be obtained by referring to the detailed description and claims when considered in connection with the drawing figures, wherein like numerals denote like elements. 
         FIG. 1  illustrates a schematic view of a system for filming a polyimide resin in accordance with various embodiments; 
         FIG. 2  illustrates a schematic view of a system for manufacturing a polyimide film with a carbon veil in accordance with various embodiments; 
         FIG. 3  illustrates a cross-section view of a composite laminate with a surface film in accordance with various embodiments; and 
         FIG. 4  illustrates a flowchart of a process for manufacturing a polyimide film in accordance with various embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The detailed description of various embodiments herein makes reference to the accompanying drawings, which show various embodiments by way of illustration. While these various embodiments are described in sufficient detail to enable those skilled in the art to practice the inventions, it should be understood that other embodiments may be realized and that logical, chemical and mechanical changes may be made without departing from the spirit and scope of the inventions. Thus, the detailed description herein is presented for purposes of illustration only and not of limitation. For example, the steps recited in any of the method or process descriptions may be executed in any order and are not necessarily limited to the order presented. 
     Furthermore, any reference to singular includes plural embodiments, and any reference to more than one component or step may include a singular embodiment or step. Also, any reference to attached, fixed, connected or the like may include permanent, removable, temporary, partial, full and/or any other possible attachment option. Additionally, any reference to without contact (or similar phrases) may also include reduced contact or minimal contact. 
     A method for manufacturing a polyimide film may comprise adding nanomaterials to a polyimide resin. The nanomaterials may increase the viscosity of the polyimide resin. The polyimide resin with the nanomaterials may be extruded through a nip roller. The nip roller may produce an uncured or semi-cured polyimide film comprising nanomaterials. In addition to increasing the viscosity of the polyimide resin which is beneficial in producing the film, the nanomaterials may improve microcracking resistance in the polyimide composites, may improve ultraviolet resistance in the polyimide composites, and may increase thermal and electrical conductivity. 
     Referring to  FIG. 1 , a system  100  for filming a polyimide resin is illustrated according to various embodiments. Nanomaterials  112  may be added to a polyimide resin  110 . In various embodiments, the nanomaterials  112  may be at least one of carbon nanotubes, carbon nanofibers, or graphene nanoplatelets. The nanomaterials  112  may be introduced to the polyimide resin  110  by a variety of methods. In various embodiments, the nanomaterials  112  may be distributed in a solvent, such as alcohol or acetone. The solvent may be mixed with the polyimide resin  110 . The solvent may be removed from the polyimide resin  110  by heating the mixture, leaving the nanomaterials  112  dispersed in the polyimide resin  110 . In various embodiments, the nanomaterials  112  may be introduced directly into the polyimide resin  110 , and the polyimide resin  110  and nanomaterials  112  may be mixed using a high shear mixing method. 
     The nanomaterials  112  may increase the viscosity of the polyimide resin  110 . Without the nanomaterials  112 , the viscosity of the polyimide resin  110  may be too low to create an uncured film using a nip roller. The high surface area to volume ratio of the nanomaterials  112  may provide many interfaces between the nanomaterials  112  and the polyimide resin  110 , which results in the higher viscosity of the polyimide resin  110 . 
     The polyimide resin  110  may be extruded through the nip roller  120 . The nip roller  120  may comprise two or more rollers  121 , which compress and flatten the polyimide resin  110  into a thin sheet  115 . In various embodiments, the polyimide resin  110  may be temporarily heated prior to or during extrusion of the polyimide resin  110  through the nip roller  120 . Heating the polyimide resin  110  may temporarily decrease the viscosity of the polyimide resin  110 , which may allow for easier processing of the polyimide resin  110 . In various embodiments, the polyimide resin  110  may be extruded through a series of nip rollers  120 ,  130 . Each nip roller  120 ,  130  may successively form the polyimide resin  110  into a thinner film. After extrusion through the nip rollers  120 ,  130 , the polyimide resin  110  may be a polyimide film  117  comprising nanomaterials dispersed throughout. In various embodiments, the polyimide film  117  may cool after being extruded, and the viscosity may increase as the polyimide film  117  cools. In various embodiments, the polyimide film  117  may be at least partially cured. The partially cured polyimide film  117  may allow for handling of the polyimide film  117  which may be formed into a desired shape on a substrate. 
     Referring to  FIG. 2 , a system  200  for manufacturing a polyimide film with a carbon veil is illustrated according to various embodiments. Although described primarily as a carbon veil, those skilled in the art will appreciate that various materials may be suitable for the veil, such as glass fibers or polymer fibers. Nanomaterials  212  may be introduced into a polyimide resin  210 , as discussed with reference to  FIG. 1 , with respect to nanomaterials  112  and polyimide resin  110 . The polyimide resin  210  may be extruded through a first nip roller  220 . A carbon veil  240  may be introduced to the polyimide resin  210 , and the polyimide resin  210  and the carbon veil  240  may be co-extruded through a second nip roller  230 . In various embodiments, the carbon veil  240  may be a carbon fiber veil or a carbon nanofiber veil. The co-extrusion through the second nip roller  230  may cause the polyimide resin  210  with the nanomaterials  212  to impregnate the carbon veil  240 . The carbon veil  240  may provide a support layer for the polyimide resin  210 . The polyimide resin  210  and the carbon veil  240  may be extruded into an uncured or partially cured polyimide film  217 . 
     Referring to  FIG. 3 , a composite laminate  300  is illustrated according to various embodiments. The composite laminate  300  may comprise a plurality of composite plies  350 . Each composite ply or ply layer  350  may comprise a resin matrix material reinforced with fibers, such as carbon fibers. Each ply layer  350  is formed either from a separate polyimide resin film and a woven or non-woven carbon fiber fabric, where the resin film is infused into the fabric as part of the cure cycle, or formed from a polyimide and carbon fiber prepreg fabric. The prepreg fabric itself may be formed in a known manner in a separate step where a film of polyimide resin is incorporated into a carbon fiber woven or nonwoven fabric layer, and then stored as a prepreg until incorporated into a layup as shown in  FIG. 3 . The composite laminate may further comprise a surface layer  317 . The surface layer  317  may be formed from incorporating on top of the layup a layer of polyimide film comprising nanomaterials, prepared in the manner explained with reference to  FIG. 1  and  FIG. 2 . In various embodiments, the surface film  317  may comprise a polyimide resin and nanomaterials with or without a carbon veil. After all the layers  350  and  317  are prepared, the whole layup may be vacuum bagged, heated, compressed and consolidated, and cured according to a suitable cure cycle and setup. 
     The surface layer  317  may improve the performance of a multi-ply composite laminate  300  by protecting against the formation of microcracks at the surface thereof. A resin rich surface, in combination with nanomaterials incorporated therein in the manner previously explained, is believed to provide additional resistance to microcracking, due in part to the ability of the nanomaterials to form a reinforcing high-strength and interlinked matrix within the resin itself. Additionally, the surface layer  317  with the nanomaterials may provide enhanced protection against ultraviolet radiation as the nanomaterials are known to do. The composite laminate  300  may be used in environments at sustained temperatures of 500° F. (260° C.) or higher with decreased degradation as compared with polyimides without nanomaterials. 
     Referring to  FIG. 4 , a flowchart of a process for manufacturing a polyimide film illustrated according to various embodiments. Nanomaterials may be added to a polyimide resin (step  410 ). Adding the nanomaterials to the polyimide resin may increase the viscosity of the polyimide resin. In various embodiments, the nanomaterials may be distributed in a solvent, such as alcohol or acetone. The solvent may be mixed with the polyimide resin. The solvent may be removed from the polyimide resin by heating the mixture, leaving the nanomaterials dispersed in the polyimide resin. In various embodiments, the nanomaterials may be introduced directly into the polyimide resin, and the polyimide resin and nanomaterials may be mixed using a high shear mixing method. 
     The polyimide resin may be extruded through a first nip roller (step  420 ). In various embodiments, the polyimide resin may be heated prior to or during extrusion through the nip roller to temporarily decrease the viscosity of the polyimide resin. The polyimide resin may be extruded through a second nip roller (step  430 ). In various embodiments, any number of nip rollers may be used to film the polyimide resin. In various embodiments, the polyimide resin may be co-extruded through the second nip roller with a carbon veil. After extrusion, the polyimide resin may be in the form of a polyimide film comprising nanomaterials. 
     The polyimide film may be coupled to a composite laminate (step  440 ). In various embodiments, the polyimide film may be a surface film which is coupled to a composite laminate. The surface film and the composite laminate may be co-cured, or the composite laminate may be cured first, and the surface film may be subsequently added to the composite laminate and cured. In various embodiments, the polyimide film may be interleaved between dry fabric layers, and the composite laminate may be manufactured via a polyimide resin film infusion process. 
     In the detailed description herein, references to “one embodiment”, “an embodiment”, “various embodiments”, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. After reading the description, it will be apparent to one skilled in the relevant art(s) how to implement the disclosure in alternative embodiments. 
     Benefits, other advantages, and solutions to problems have been described herein with regard to specific embodiments. Furthermore, the connecting lines shown in the various figures contained herein are intended to represent various functional relationships and/or physical couplings between the various elements. It should be noted that many alternative or additional functional relationships or physical connections may be present in a practical system. However, the benefits, advantages, solutions to problems, and any elements that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as critical, required, or essential features or elements of the inventions. The scope of the inventions is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” Moreover, where a phrase similar to “at least one of A, B, or C” is used in the claims, it is intended that the phrase be interpreted to mean that A alone may be present in an embodiment, B alone may be present in an embodiment, C alone may be present in an embodiment, or that any combination of the elements A, B and C may be present in a single embodiment; for example, A and B, A and C, B and C, or A and B and C. Different cross-hatching is used throughout the figures to denote different parts but not necessarily to denote the same or different materials. 
     Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. 112(f) unless the element is expressly recited using the phrase “means for.” As used herein, the terms “comprises”, “comprising”, or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.