PREPREG MASTER ROLLS AND SLIT TAPE AND METHOD

Abstract

Thick thermoset prepreg sheets and slit tapes and methods and apparatus for the production thereof.

Claims

1. A method for the production of thick thermoset prepreg master rolls which method comprises aligning two or more sheets of conventional thermoset prepreg, one over the other along their length, each sheet having a mating surface, and mating the sheets along their mating surfaces to form the thick thermoset prepreg sheet material.

2. The method of claim 1 wherein the mating surface of at least one of the sheets of conventional prepreg material is heated prior to the mating.

3. The method of claim 2 where the mated sheets are subjected to pressure to press the sheets of material to one another.

4. The method of claim 1 where the mated sheets are subjected to pressure to press the sheets of material to one another.

5. The method of claim 1 wherein the thick thermoset prepreg material is wound into a master roll.

6. The method of claim 1 wherein the thick thermoset prepreg material is to passed through a slitter to form slit tape which is then wound.

7. The method of claim 1 wherein the thickness of the resulting prepreg material is not attainable using convention prepreg sheet manufacture.

8. The method of claim 1 wherein the resulting prepreg material has less voids and/or better wetting that a prepreg sheet material of the same thickness and composition made using convention prepreg sheet manufacture.

9. A thick prepreg master sheet material formed in accordance with the method of claim 1.

10. The master sheet material of claim 9 wherein the thickness of the prepreg sheet material is greater than is attainable using convention prepreg sheet manufacture and the same composition.

11. The master sheet material of claim 9 wherein the prepreg sheet material has less voids and better wetting as compared to a similar master sheet material of the same thickness prepared using convention prepreg sheet manufacture.

12. A master roll of thick thermoset prepreg material formed in accordance with the method of claim 5.

13. The master roll of claim 12 wherein the thickness of the prepreg sheet material is greater than is attainable using convention prepreg sheet manufacture and the same composition.

14. The master roll of claim 12 wherein the prepreg sheet material has less voids and better wetting as compared to a similar master sheet material of the same thickness prepared using convention prepreg sheet manufacture.

15. A thick thermoset prepreg slit tape formed in accordance with the method of claim 6.

16. The slit tape of claim 15 wherein the thickness of the prepreg slit tape material is greater than is attainable using prepreg sheet material made using conventional prepreg sheet manufacture.

17. The slit tape of claim 15 wherein the prepreg slit tape has less voids and better wetting as compared to slit tape made using prepreg sheet material of the same thickness prepared using conventional prepreg sheet manufacture.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings which form a part of the specification are to be read in conjunction herewith. Like reference numerals are employed to indicate like parts in the various views.

[0019] FIG. 1 is a schematic side view of an apparatus for mating two continuous sheets of prepreg material.

[0020] FIG. 1A is a close-up view of the mated thick prepreg sheet material of FIG. 1 at A.

[0021] FIG. 1 is a cross-sectional view of the mated thick prepreg sheet material at A1-A1 of FIG. 1A.

[0022] FIG. 2 is a schematic side view of an alternate apparatus for mating two continuous sheets of prepreg material with the removal of a liner from each.

[0023] FIG. 3 is a schematic side view of an apparatus for concurrently mating three continuous sheets of prepreg material with liner removal.

[0024] FIG. 3A is a close-up view of the mated thick prepreg sheet material of FIG. 3 at B.

[0025] FIG. 3B is a cross-sectional view of the mated thick prepreg sheet material at B1-B1 of FIG. 3A.

[0026] FIG. 4 is a schematic side view of an alternate apparatus for sequentially mating three continuous sheets of prepreg material with liner removal.

DETAILED DESCRIPTION

[0027] As used herein and in the appended claims, the term conventional when used in relation to prepreg sheet and/or tape means a prepreg sheet or tape made in a manner conventional as of the date of the discovery of the present teaching where the liquid matrix resin is combined and infused into a plurality of fibers/fiber bundles or a fabric, typically on a backing or support, and excess resin removed to produce continuous sheets and tapes of defined widths and thickness. Backing or support materials are commonly paper or a polymer film, especially polyolefin, polyamide, polyester, vinyl polymer, and polyacetate films. Specific exemplary polymer films include polyethylene (PE), including low density polyethylene, high density polyethylene, and linear low density polyethylene; polypropylene, biaxially oriented polypropylene, polyethylene-propylene copolymer, polytetrafluro-ethylene, polyvinyl acetate, polyvinyl chloride, polyvinyl alcohol, ethylene vinylacetate (EVA), EVA-PE blends, polystyrene, biaxially oriented polystyrene, polyethylene terephthalate, polyamide 6, polyamide 6,6, and cellulose triacetate, just to name a few. Most preferably, the polymer film is a polyolefin, especially polyethylene. Generally speaking conventional prepreg sheets and slit tapes will have the physical characteristics mentioned above in the Background.

[0028] As noted above, conventional prepreg sheet materials are formed on a backing or support layer. Sometimes the original support layer or backing is replaced with a liner, most typically a polymer liner. Additionally, it is common to place a liner on the opposite surface of the prepreg sheet material during or subsequent to the prepreg formation process to protect the exposed surface of thermoset resin. For convenience, in an effort to avoid referencing backings, supports and liners and their iterations, the term liner as used herein and in the appended claims is intended to embrace all three, particularly as context allows.

[0029] As used herein and in the appended claims, the term continuous when used in reference to the prepreg sheet material and slit tape refers to long lengths of such materials for either immediate use/processing, such as slitting in the case of the sheet materials, or wound for storage and/or transportation. Typically, continuous prepreg sheets and tapes to be slit will have lengths of from at least about 10 meters, more typically 25 meters, up to about 100 meters or more, and with newer technologies now typically from at least about 100 meters, more typically 250 meters, up to 1000 meters and more, and widths of from about 0.1 meters, more typically 0.35 meters, to 2.5 meters, preferably from about 0.7 meters to about 1.5 meters. Meanwhile continuous slit tapes, depending upon their widths and whether they are coil wound or transverse wound will have lengths similar to those of the sheet materials up to, typically in excess of, 200 meters or more, more typically up to 1500 meters or more, or well in excess of 1000 meters, more typically up to or in excess of 3500 meters, even up to and exceeding 6000 meters, respectively. Typical widths range from about 0.1 cm to about 10 cm or more, more typically from about 0.3 cm to 10 cm. Additionally, although specific reference herein is made to prepreg sheet materials of unidirectional carbon fibers impregnated with curable epoxy resins, it is understood that the present teachings are not so limited. Indeed, the present teachings are equally applicable to other prepreg sheet materials, including those made of glass fibers, polymer fibers, and combinations of fibers, all of which may be unidirectional along the length or angled relative to the length of the tape, woven, non-woven, etc., as well as those wherein the matrix resin is any of number of curable or thermosetting matrix resins including, but not limited to epoxies, cyanate esters, bismaleimides, phenolics, polyimides, and the like. Most especially the present teachings are particularly suited for and will be discussed with respect to prepreg sheets and tapes of unidirectional carbon fibers in an epoxy thermoset resin matrix.

[0030] As used herein and in the appended claims, the term thick and thicker when used in reference to prepreg sheet materials and slit tapes refers to such sheet materials and tapes formed in accordance with the teaching of the present disclosure.

[0031] Finally, the use of the terms align and aligned in reference to the positioning of the master sheet materials by the alignment or guide rollers means that the master sheet materials are positioned relative to one another so that they effectively overlay one another along their length, especially at the point. Where two master sheets of the same width are to be mated, the alignment will position the master sheet materials so that the edges of each directly or as closely as reasonably possible align one over the other.

[0032] While few details are provided herein with respect to the elements of the apparatus as well as the apparatus as a whole, all of the elements are known and commercially available: it is their combination and orientation as well as the use thereof that is novel. Other apparatus referenced herein are well known and commercially available; for example, slitting and winding apparatus are well known.

[0033] According to the present teachings there is provided: [0034] a method for the production thick prepreg master sheet material wherein two or more conventional prepreg sheets are aligned and mated to form a thick master sheet material; [0035] a method for the production master rolls of thick prepreg master sheet material wherein two or more conventional prepreg sheets are aligned and mated to form a thick master sheet material which is then wound to form the rolls; [0036] a method for the production thick prepreg slit tape wherein thick master sheet material is slit into tapes of desired widths and either directed to use or wound for subsequent use; [0037] an apparatus for the production of thick master sheet from conventional master sheet; [0038] thick prepreg master sheet materials; [0039] master rolls of thick prepreg master sheet materials; and [0040] thick prepreg slit tapes.

[0041] Another aspect and benefit of the present teaching is that one is able to customize the thickness of the thick prepreg master sheet material and the resultant thick prepreg slit tape by the selection of the number and thicknesses of the conventional master sheet materials used in the production thereof. In this respect, it is to be appreciated that the description above of typical thicknesses, particularly the upper limits thereof, is primarily based upon the maximum thicknesses that can be suitably and efficaciously attained given the aforementioned concerns with resin infiltration and wetting. However, thicknesses of less degree can readily be produced without or with less concern for the previously discussed problems and shortcomings and, thus, are readily suitable for use in the practice of the present teachings.

[0042] For convenience and ease of understanding, the methods, apparatus and products of the present teachings are now explained in conjunction with reference to the appended Figures, which are incorporated herein,

[0043] FIG. 1 presents a side-view schematic of the simplest of the methods for producing thick prepreg master sheet materials. Here two master rolls 1 of conventional thermoset prepreg master sheet materials 2, each having aligner 11 on one surface, as more clearly shown in FIG. 1A and FIG. 18, are aligned by a plurality of alignment rollers 4 and mated at a pair of pinch rollers 6. Optionally, as shown in FIG. 1 a heater element 8 is positioned to warm the thermoset resin to enhance the tackiness thereof. In those methods and apparatus where the heating element is present, the extent and duration of the heating is limited to improve the tackiness of the thermoset resin and, in any event is controlled to ensure that the temperature does not accidently initiate cure of the thermoset resin. Generally, the resin is heated to no more than 120 C., preferably no more than 100 C., more preferably no more than 65 C., most preferably no more than 50 C., again depending upon the activation temperature of the cure catalyst/activator for the thermoset resin. Furthermore, although FIG. 1 shows both prepreg sheet materials being subjected to the heating, it is to be appreciated that only one sheet need be heated to benefit from the increased tackiness.

[0044] As previously noted, the two prepreg sheet materials are mated and pass through a pair of pinch rollers 6. The pinch rollers help ensure proper face to face mating across the full width of the sheet materials. The pinch rollers are spaced to provide a slight interference fit or may be constructed to allow the upper pinch roller to float whereby the weight of the roller itself presses down on the mated master sheet materials. Additionally, the pinch rollers may be controlled to impart a force whereby the two master sheet materials are pressed into one another. Whether weight induced or pressure induced, the force acting upon the mated sheet materials in the pinch rollers is generally from about 1 psi to about 4 psi, though lesser force is sufficient where the tack of the thermoset is high. Higher forces are possible, however, are discouraged to avoid undesired resin flow.

[0045] The resulting thick master sheet material 9 is shown in FIGS. 1A and 1B wherein a liner 11 is present on both surfaces of the thick prepreg sheet material 12. Although accentuated, FIG. 18 presents a cross-sectional view of the master tape wherein a distinct thermoset resin layer 15 is present intermediate the two resin infused unidirectional fiber layers 16.

[0046] Finally, FIG. 1 shows the thick prepreg master sheet advancing to Box 18 for further processing. Such further processing could be merely the winding of the thick prepreg master sheet on a core element to form a master roll, with or without removing one of the remaining liners. Alternatively, the thick prepreg master sheet material could be advanced to a slitting apparatus for converting the wide master sheet into a plurality of slit tapes of one or more widths. Further still, the master sheet may be advanced to a manufacturing process where the master sheet material is fed to an ATL apparatus or AFP apparatus, particularly one with an integrated slitter, for building a composite structure.

[0047] FIG. 2 presents a side-view schematic of a similar apparatus and method to that shown in FIG. 1 except in this instance the conventional prepreg sheet materials 21 have a liner on each surface of the thermoset prepreg master sheet material. In this instance, it is necessary to remove the liner from the mating surfaces before the two master sheets are mated. Here two take-up winders 22 for the liner are provided with the liner separating from the master sheet material at a alignment rollers 24.

[0048] This apparatus also employs a different means to press the sheets of master sheet material into one another. Specifically, in this apparatus the master sheet materials are mated at a set of serpentine rollers 26. Here the mated sheets pass through the serpentine rollers where the serpentine-like or wave-like motion of the mated sheets through the rollers is occasioned by the offsetting of the serpentine rollers, i.e. the extent to which the lower surface of the upper roller elements extends below the upper surface of the lower roller elements. This serpentine-like or wave-like motion of the mated sheets through the serpentine rollers creates a compression in the mated materials which serves to press the mated surfaces of the prepreg master sheet material to one another. Although not necessary, it is also contemplated that one or more of the rollers is associated with a weight or a pneumatic or spring activated element which acts upon and forces one or more of the roller against the mated materials. As shown FIG. 2, the serpentine or wave motion of the mated materials through the serpentine rollers is fairly shallow, thereby exerting a lower pressure on the mated sheet materials. However, it is to be appreciated that the offsetting of the rollers can be made more pronounced so as to create a wave action having an higher amplitude whereby a higher pressure or force is imparted against and to the mated sheet materials.

[0049] For the purpose of exemplification, the apparatus of FIG. 2 does not incorporate a heating element to warm and make more tacky either or both of the mating surface(s) of the prepreg sheet material. However, it is to be appreciated that a heater element could be incorporate at or near the mating point of the master sheet materials or anywhere intermediate the mating point and the roller at which the liner is removed.

[0050] In the embodiment shown in FIG. 2 the formed thick prepreg sheet material is wound on a winder 29 to form master rolls 30 of the thick prepreg sheet material. Although not shown, if desired, one could also insert an additional liner removal apparatus and liner winder intermediate the serpentine rollers and the winding apparatus in order to remove one of the two remaining liners before winding the master roll. Of course, also as discussed above with respect to the apparatus and method of FIG. 1, the thick prepreg master sheet material of this apparatus could equally be fed directly to additional apparatus for subsequent processing and/or use rather than being wound as shown.

[0051] FIG. 3 presents a side-view schematic of an apparatus and method for producing thick prepreg master sheet materials from three master rolls 40, 41, 42 of conventional prepreg sheet material 45. In this particular depiction, each of the conventional thermoset prepreg master sheet materials 45 has a liner 11 on one surface. In the case of the master roll 41 sourcing the intermediate layer for the thick prepreg sheet material, it is necessary to remove the liner 47 prior to mating that sheet material with the other two sheet materials. As shown, the liner that is removed is taken up by winder 49. Of course, if any or all of the master sheet materials had a liner on both surfaces, it would be necessary to remove the liner from the other surface in the case of the middle roll of master sheet material 41 and from the mating surfaces of the other master sheet materials before mating. In these instances, there would be a liner removal apparatus and liner take-up winder intermediate those master rolls and the mating point for the sheet materials.

[0052] As with the embodiment of FIG. 1, the sheets of conventional prepreg sheet materials are aligned by a plurality of alignment rollers 50 and mated at a pair of pinch rollers 53, the same as or comparable to those described above. Furthermore, it is to be appreciated that the apparatus and method is not limited to pinch rollers. For example, as with the previous embodiment, a set of serpentine rollers or other like functioning elements could be employed in place of the pinch rollers.

[0053] The apparatus and method depicted in FIG. 3 also employs a heater element 55 on each side of the conventional sheet material, post liner removal, sourced from the middle master roll 41. As described with respect to the apparatus and method of FIG. 1, the heater element 55 is positioned to warm and thereby enhance the tackiness of the thermoset resin. In this case, the heater(s) is positioned to warm both surfaces of the sheet material. Of course, it is also to be appreciated that a heater element could also be employed with each of the other master sheet materials. Again, any heating is limited to improve the tackiness of the thermoset resin without initiating cure of the thermoset resin.

[0054] As previously noted, the three prepreg sheet materials are mated and pass through a pair of pinch rollers 53. Again, the pinch rollers help ensure proper face to face mating across the full width of the sheet materials and are spaced to provide a slight interference fit or may be constructed whereby a pressure is exerted by one roller relative to the other to press the mated layers into one another.

[0055] The resulting thick master sheet material 60 is shown in FIGS. 3A and 38 wherein a liner 62 is present on both surfaces of the thick master prepreg material 64. Although accentuated, FIG. 38 presents a cross-sectional view of the master tape wherein a distinct thermoset resin layer 65 is present intermediate each of the opposing resin infused unidirectional fiber layers 66.

[0056] Finally, as in FIG. 1, FIG. 3 shows the thick prepreg master sheet advancing to Box 18 for further processing. As previously mentioned, such further processing could be merely the winding of the thick prepreg master sheet on a core element to form a master roll, with or without removing one of the remaining support or liners. Alternatively, the thick prepreg master sheet material could be advanced to a slitting apparatus for converting the wide master sheet into a plurality of slit tapes of one or more widths. Further still, the master sheet could be advanced to a manufacturing process where the master sheet material is fed to an ATL apparatus or AFP apparatus, particularly one with an integrated slitter, for building a composite structure.

[0057] FIG. 4 presents a side-view schematic of an alternate apparatus and method for producing thick prepreg master sheet materials from three master rolls 80, 81, 82 of conventional prepreg sheet material 85. In this particular depiction, each of the conventional thermoset prepreg master sheet materials 85 has a liner 87 on both surfaces. Further this embodiment differs from the previous in that the build is a sequential build wherein an intermediate two layer thick prepreg sheet is formed and then a third layer mated to the intermediate prepreg sheet material.

[0058] In the iteration shown in FIG. 4, the two layered thick prepreg intermediate sheet 86 is formed as depicted in FIG. 2 wherein conventional prepreg sheet material is fed from two master rolls 80, 81 and the liner on the mating surface removed and taken up by liner winders 83 before the two sheets are mated at a serpentine roller assembly 88. Guide rollers 92 are employed to align the sheet materials for proper mating. In this particular embodiment, a heater 90 is also present to enhance the tackiness of the two surfaces to be mated.

[0059] The resulting thick prepreg intermediate master sheet 86 is then advanced to a set of pinch roller assemblies 94: in this case the pinch roller assembly comprises two pair of pinch rollers 95, to press the third sheet of prepreg sheet material 93 to the intermediate prepreg sheet material. In advance of this second mating point, the liner 98 on the mating surface of the third conventional prepreg master sheet material is removed and wound on liner winder 99 to expose the thermoset resin. As shown, the backing or liner is removed in close proximity to the mating point as this will reduce the opportunity for debris and other possible contaminants from settling on the surface of the thermoset resin prior to the mating. Of course, if desired one could remove the backing liner as the conventional master sheet material comes off the master roll 82 as with the other two master rolls.

[0060] As noted, this particular embodiment employs a pinch roller assembly 94 to mate the third master sheet material with the intermediate thick sheet material. Although not necessary, given the increased thickness of the thick prepreg master sheet material at this point, having two pair of pinch rollers 95 provides better certainty that air is not trapped and all the layers of the thick prepreg sheet material are firmly bonded to one another. Of course, other press means could be used as well such as a set of serpentine rollers, etc. Additionally, one could add a heater to heat the mating surface of the conventional prepreg sheet, of the intermediate thick prepreg sheet or both, to enhance tackiness.

[0061] In the depiction in FIG. 4, the resulting thick master sheet material 100 is advanced to a winder 101 for winding into a master roll 102 for subsequent use and/or processing. Of course, as noted before, the resulting thick master sheet material could be directly advanced for further processing and use as described above with respect to the Box 18 in FIGS. 1 and 3. Furthermore, in this instance, since both surfaces of the resulting thick master sheet material have a liner, one is removed and wound on liner winder 104 before actually winding the thick master sheet material.

[0062] Although each of the depicted embodiments show the conventional master sheet materials being fed from master rolls, it is also to be appreciated that the apparatus and processes described above could be integrated into a prepreg sheet manufacturing plant and process where each feed of conventional sheet material comes directly from its manufacture to the mating process. This allows for a continuous operation and process.

[0063] Alternatively, a continuous operation and process is provided by temporarily suspending the mating process when a master roll is expended to provide time to replace the expended roll with a new master roll. In these instances a splicer is also integrated into the apparatus and splicing operation into the process so that a continuous source of conventional master sheet material is attained. Splicers and splicing operations are conventional in the art and are, e.g., present in typical slitting apparatus and operations for forming slit tape. In those instances where a conventional splicing operation is integrated into the apparatus and process it is especially desirable to stagger the initial feed of conventional master sheet material into the mating section so as to avoid or lessen the chance that two splices will overlap in the mating operation. The stagger may be attained by initiating the feed of one conventional sheet material into the pinch rollers or serpentine rollers prior to advancing the other(s). Alternatively, one may attach a lead sheet material to one or more of the conventional sheet materials whereby when priming the apparatus for commercial production, all master sheet materials are started at once, but the use of the lead prevents the lead edge of prepreg materials arriving at the mating point at the same time.

[0064] The thick master sheet materials and slit tapes produced by the process of the present teaching allow for faster production of parts since one is laying substantially thicker sheets and tapes in the layup operation. Hence, fewer passes are needed to achieve the same part thickness when laying the thick prepreg sheets and tapes of the present teaching than with the conventional prepreg sheet and tapes from which they are produced. Of course, it is contemplated that any given AFP or ATL apparatus could also have multiple sources of slit tape, both those of conventional thickness and the enhanced thickness of the present sheet and tapes to control overall part thickness in accordance with their design specifications.

[0065] Following on the foregoing, another benefit of the present teaching is that one can customize the thickness of the thick prepreg master tapes to be produced. As noted above, issues with voids and wetting, among others, are associated with trying to produce conventional tapes of greater thicknesses. However, one can generally prepare sheets which are thinner without concern. In this respect, one can select and use conventional prepreg sheet materials of different thicknesses to build a thick prepreg master sheet material of a given or desired thickness in accordance with the present teachings. These thick prepreg sheets are thicker than attainable with conventional prepreg sheet materials and avoid or lessen the concern with voids and wetting, among other issues as noted. For example, when using a thermoset resin for which one can only attain a maximum thickness of 250 micrometers without a marked adverse effect on the resulting prepreg material, one could mate a prepreg sheet of 250 micrometers with another sheet of 100 micrometers to produce a thick prepreg sheet material of 350 micrometers thickness. These sheets would have characteristics relative to wetting and voids consistent with that of the starting materials, e.g., conventional sheets, from which they are formed, not as would be found if one attempted to produce such a thickness in a conventional sheet manufacture. Accordingly, from a general perspective, the present method and resulting thick prepreg sheet and slit tape materials have better and improved properties and characteristics, particularly from a fiber wetting and resin infiltration standpoint than sheet material and slit tape of the same thickness, particularly of the same and composition, made according to the conventional method.

[0066] In the foregoing description many embodiments and alternative iterations are discussed in terms of what one could do. It is to be noted that the use of the word could is not to be misconstrued as indicating or inferring that the subject matter is merely theoretical or nothing more than a supposition; rather, these are embodiments, iterations and alternatives that are fully contemplated and workable. Similarly, the methods and apparatus are presented with a number of interchangeable elements, e.g., the pinch rollers and the serpentine rollers as well as the box and the master roll winder; in these instances, the specification is to be read and understood as if each interchangeable element were in fact presented. Similarly, throughout the specification certain characteristics and properties of the various elements and process steps are presented in detail with one embodiment but not another, e.g., the temperature for the heating elements or the pressure for the pinch rollers or serpentine rollers thereof. In these instances, it is to be understood that the same characteristics and properties exist for each embodiment unless otherwise specifically mentioned. Generally speaking, it would be nearly impossible and, in any event, would take an extensive specification to describe each and every iteration or embodiment. Hence, one is to construe this specification as if each of the interchangeable element and properties has, in fact, been is specifically embodied.

[0067] Although the method and apparatus of the present specification have been described with respect to specific embodiments and figures, it should be appreciated that the present teachings are not limited thereto and other embodiments utilizing the concepts expressed herein are intended and contemplated without departing from the scope of the present teaching. In following, true scope of the present teachings is defined by the claimed elements and any and all modifications, variations, or equivalents that fall within the spirit and scope of the underlying principles set forth herein.