Patent Publication Number: US-6911175-B2

Title: Methods of hot-melt impregnation of 3-D, woven, textile preforms

Description:
This application is a continuation of application Ser. No. 09/942,332, filed Aug. 28, 2001, now U.S. Pat. No. 6,676,882. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention generally relates to infusion of resin into a woven textile and particularly relates to hot-melt infusion into three-dimensional, woven, textile preforms. 
   2. Description of the Prior Art 
   Generally, laminating resins are used as the matrix material in woven textiles, this also being true for woven preforms used to connect components made of composites or other materials. An example of a commonly-used laminating resin is 977-3, available from Cytec Industries, Inc., of West Paterson, N.J. Typically, the laminating resin is fully infused into a textile product, wetting all of the fiber bundles in the preform and forming a “prepreg,” or pre-impregnated textile. The resin is later cured to form a polymer matrix in the finished composite component. Methods of fully impregnating flat textiles include immersing in a solution, pressing with rollers, and pulling through a die. All of these methods have the advantage of being able to do continuous lengths. 
   In solution impregnation, the resin is dissolved in a solvent, and the textile is immersed in the solution. The textile is then removed from the solution, and the solvent is evaporated, leaving the resin in the textile. The disadvantages of this method are that resin content is difficult to control and that the volatile gases must be removed. 
     FIG. 1  shows a prior art method of infusing resin into a textile  11  by placing resin film  13  against textile  11  and feeding them between a pair of heated rollers  15 . Rollers  15  heat and press resin  13  into textile  11 , transferring the resin  13  into textile  11 . 
     FIG. 2  shows a second prior art method of infusing resin. The pultrusion method of infusing a textile  17  with resin  19  involves pulling textile  17  through a heated die  21 . Resin  19  is placed against textile  17 , and these are fed into the die to heat resin  19  and infuse textile  17 . Die  21  may also cure resin while textile  17  is within die  21 . 
   While these techniques work well for flat textiles, infusion of three-dimensional textile preforms presents different problems. The prior-art methods described above may be used to fully infuse 3-D preforms, but the preforms may have too much resin at intersections, causing the preform to be overly bulky in those areas. Also, a fully-infused preform tends to be stiff and less pliable, making the preform difficult to handle or position during assembly. 
   SUMMARY OF THE INVENTION 
   A method provides for full or partial infusion of resin into three-dimensional, woven, textile preforms. Resin film is placed at selected locations adjacent the preform, and the resin film may be separated from other areas of the preform using separator sheets or other materials. The preform is heated and may be vacuum-bagged to apply pressure, or may be rolled or fed through a die. The heat and pressure cause the resin to infuse into the selected areas of the preform adjacent the resin films. The amount of resin in the partial infusion is the same as is necessary to fully infuse the preform, but the resin remains localized in the selected areas until heated again at cure to cause the resin to flow throughout the preform. The method may also be used to fully infuse the preform with resin by providing sufficient temperature and time at that temperature during the initial infusion. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features believed to be characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings. 
       FIG. 1  is a front view of a prior art method of infusing textiles with resin. 
       FIG. 2  is a perspective view of an alternative prior art method of infusing textiles with resin. 
       FIG. 3  is a perspective view of a three-dimensional, woven textile preform. 
       FIG. 4  is a front, exploded view of a method of fully infusing a three-dimensional textile preform with resin in accordance with the present invention. 
       FIG. 5  is a front view of an alternative embodiment of the method of partially infusing a three-dimensional textile preform with resin in accordance with the present invention. 
       FIG. 6  is a front view of a second alternative embodiment of the method of partially infusing a three-dimensional textile preform with resin in accordance with the present invention. 
       FIG. 7  is a front view of a third alternative embodiment of the method of partially infusing a three-dimensional textile preform with resin in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention provides for infusing a woven preform with laminating resin to form a polymer matrix in the cured preform.  FIGS. 4 through 6  illustrate the preferred embodiments of the method of infusing a three-dimensional (3-D), woven textile preform used for assembling parts into structural joints, the preform being depicted in FIG.  3 . The parts, or components, to be joined may be formed from composites and may be cured or uncured, or the parts may be formed from other materials, e.g., plastics, metals, etc. The infusion may be full or partial. A “full infusion” means that resin is infused through the entire thickness of the infused portions of the preform. A “partial infusion” causes the resin to enter the preform only to a depth that is less than the thickness of the infused portions of the preform or only around the fiber bundles without penetrating the bundles. 
   Referring again to the figures,  FIG. 3  shows a pi-shaped, 3-D, woven preform  23  used to connect two parts (not shown), which may be, for example, a frame member and a skin. While preform  23  is shown as a Pi-shaped preform, the methods of infusion are applicable to other 3-D preform shapes, such as a T-shaped preform (not shown). Preform  23  has a base  25  on its lower portion that has a continuous, flat lower surface  27  and an upper surface  28 . As shown, a pair of spaced-apart planar legs  29  extend vertically upward from base  25 . Each leg  29  is at a position that is offset from, but near to, the center of base  25 . In their installed orientation, legs  29  are typically parallel to each other and are typically perpendicular to base  25 , with inner surfaces  31  of legs  29  facing each other. Outer surfaces  33  of legs  29  face outward when legs  29  are standing upright. A small, upward-facing surface  35  of base  25  lies between the lower ends of legs  29 . Though it is preferable for legs  29  and base  25  to be tapered at their outer edges, as shown, the edges may also be squared. Though not shown, legs  29  may also be installed at an angle other than 90° from base  25 , and legs  29  may not be parallel to each other. 
     FIG. 4  depicts a vacuum-assist method for fully infusing resin into preform  23  by creating a stack of layers of resin and separators and applying a vacuum to the stack. The resin is weighed to provide for the correct resin to fiber ratio. A rigid tool plate  37  is provided, and a non-porous, non-stick film  39 , preferably Teflon-coated, is laid on the upper surface of tool plate  37 . Preform  23  is placed on resin film  41 , which is laid on film  39  and positioned to be under lower surface  27  of preform  23 , film  41  preferably extending to the outer edges of base  25 . Resin film  41  is a carrier sheet having resin on one side, the resin being transferred from the sheet when resin film  41  is heated. The carrier sheet is then removed and discarded. 
   During the infusion process, legs  29  are laid over to a horizontal orientation parallel with base  25 , though legs  29  are each shown in the exploded view of  FIG. 4  at an angle to base  25 . A separator film  43  and a resin film  45  are placed between outer surface  33  of each leg  29  and the corresponding portion of upper surface  28 . Separator film  43  is a non-stick separator film like film  39 , but which is doubled over to provide a non-stick surface against outer surface  33  and upper surface  28  when placed between surfaces  28 ,  33 . Resin films  45 , which are of the same type as resin film  41 , are located between separator film  43  and outer surface  33  on each side of preform  23 , the inner end of each film  43  being positioned to be at the intersection of leg  29  and base  25 . Legs  29  are then laid over onto resin films  45 . 
   A compaction tool  47 , which may be made from rigid or semi-rigid materials, is sized to be placed on upward-facing surface  35  between the lower ends of legs  29 . A layer of thin, Teflon-coated, porous cloth  49 , for example, TX1040, available from Pall Corporation of East Hills, N.Y., is laid on the inner surfaces  31  of legs  29  and is then covered by an upper separator film  51  like films  39 ,  43 . The uppermost layer of the stack is a breather material  53 , for example, dry fiberglass cloth. The entire stack, including tool  39 , preform  23  and all layers of film and separators, is then placed within a bag  55  for creating a vacuum around the stack while the stack is heated. A vacuum vent  57  enters bag  55  and connects to cloth  49  and breather material  53  to assist the vent paths in cloth  49  and material  53 . 
   To cause the resin to infuse into preform, a vacuum is pulled on bag  55  and the stack is heated to around 190° F. to soften the resin on films  41 ,  45 , causing the resin to freely flow through preform  23 . The vacuum within bag  55  allows air pressure outside bag  55  to press inward, forcing the various components of the stack together. The heat causes resin on film  41  to soften and the pressure causes the resin to move into base  25 . The stack is heated to a temperature and held at that temperature for a sufficient length of time to allow the resin to fully wet the fibers of base  25 , from lower surface  27  to upper surfaces  28  and upward-facing surface  35 . Likewise, resin on films  45  softens and flows into legs  29 , from outer surfaces  33  to inner surfaces  31 , fully wetting the fibers of leg  29 . Separator film  39  prevents resin from adhering to tool  37 , whereas separator films  43  prevent resin on films  45  from flowing into base  25  and prevent outer surfaces  33  of legs  29  from tacking to upper surfaces  28  of base  25 . Also this method could be used to partially infuse preform  23  rather than fully infuse. Furthermore the resin could be deposited on inner surfaces  31  of legs  29 , rather than on outer surfaces  33 . By depositing resin on inner surfaces  31 , surfaces  31  can be tacked to the outer surfaces of the frame member (not shown) during assembly. 
   The air pressure outside of bag  55  pushes on bag  55  and forces breather material  53 , separator film  51 , and porous cloth  49  downward toward inner surfaces  31  of legs  29 . This movement forces compaction tool  47  downward onto surface  35 , compacting surface  35  and creating a flat, compacted area having a width equal to the width of tool  47 . When, after infusion, preform  23  is used to join a first component (not shown) under base  25  to a second component (not shown) located between legs  29 , the flat, compacted area at surface  35  ensures that the end of the second component is able to be seated properly against surface  35 . Legs  29  are then moved to a vertical orientation to adhere to the second component. 
   In most applications, it is preferable to have a partially-infused preform, since fully-infused preforms can be stiff and difficult to position during assembly. The partial-infusion method leaves vent paths between the fiber bundles, allowing air, moisture, and volatiles to be removed, thereby limiting porosity after curing. An alternative vacuum-assist method, as shown in  FIG. 5 , can be used to partially or fully infuse Pi-shaped preform  23 , which is shown as inverted from the orientation shown in FIG.  4 . Referring to  FIG. 5 , legs  29  of preform  23  are laid over and resin films  59 ,  61  are placed against base  25  and each leg  29 , respectively. Unlike resin film  41  (FIG.  4 ), each resin film  59 ,  61  has a width less than the width of preform  23 . Resin films  59 ,  61  do not overlie the central portion of base  25  between legs  29 . Each resin film  59  is placed against surface  27  of base  25  and located toward the outer edge of base  25 , leaving no resin film near surface  35 . Resin film  61  is placed against inner surface  31  of each leg  29 . A thin film  63 , preferably polyethylene, is wrapped around preform  23  and resin films  59 ,  61 , a vent material  65  being wrapped around film  63 . Film  63  is inserted into the areas between surfaces  28  of base  25  and outer surfaces  33  of legs  29  to act as a separator film and to contain the resin within preform  23 , preventing the resin from wicking into vent material  65 . A vacuum bag  66  surrounds preform  23 , film  63 , resin films  59 ,  61 , and vent material  65 . 
   To partially infuse preform using the method in  FIG. 5 , the air is removed from within bag  66 , and then bag  66  and its contents are heated to around 120° F. for 15-20 minutes. This temperature permits the resin on films  59 ,  61  to flow enough to be deposited into preform  23  without fully wetting the fiber bundles and keeping the intersections preferably resin-free. This provides within preform  23  the amount of resin necessary to fully infuse preform  23 , but it is located in discrete areas of preform  23 . Partially-infused preform  23  remains more pliable, since no resin is located in the intersections of legs  29  and base  25 . Because base  25  at surface  35  is not infused with resin, no compaction is needed to ensure proper seating on surface  35  of a component (not shown) inserted between legs  29 . The areas lacking resin also become vent paths for air or volatile gases during full wetting and curing after assembly. Preferably, partially-infused preform  23  is simply brought to a curing temperature, allowing the resin to freely flow within preform  23  to fully infuse preform  23 . Another method of fully wetting the fibers of preform  23  after assembly is to bring the temperature of preform  23  up to around 190° F., allowing the resin to fully wet preform  23 , then curing preform  23  in the desired final position in a separate process. 
   Rather than partially infusing preform  23  initially, then heating preform  23  to allow the resin to flow and fully infuse preform  23 , the temperature of the initial heating of preform  23  and resin films  59 ,  61  can be around 190° F. This would allow the resin to fully infuse preform  23  in the initial step, instead of requiring the second heating step. Also, though not shown in  FIG. 5 , resin films having a width nearly that of preform  23  can be used to fully or partially infuse preform  23 . To partially infuse preform  23  using full-width resin films, separator films or other materials are placed between selected portions of preform  23  and the resin films, preventing resin from entering preform  23  at those locations when resin is heated. 
     FIG. 6  shows an alternative embodiment of the present invention for fully or partially infusing resin into preform  23 . Heated rollers  67  provide the heat and pressure to cause resin on films  69 ,  71  to flow into portions of preform  23 . Like resin films  59 ,  61  ( FIG. 5 ) as described above, resin films  69 ,  71  are located against surfaces  27 ,  31 , respectively. Resin films  69 ,  71  have a width less than the width of preform  23  and do not overlie a central space between legs  29 . Separator films  73  are located between resin films  69 ,  71  and rollers  67  for ensuring resin does not adhere to rollers  67 . Preform  23  and resin films  69 ,  71  are fed into the gap between rollers  67 , the gap being sized to compact the stack of films  69 ,  71  and preform  23  as they move between rollers  67 . Like in the method shown in  FIG. 5 , the method shown in  FIG. 6  provides for resin being placed in selected areas of preform  23  when the resin is heated to around 120° F., and resin is absent in base  25  near surface  35  and in the intersections of legs  29  with base  25 . After assembly, preform  23  is heated to around 190° F. to allow resin to fully disperse within preform  23 . 
   As described above, the temperature of the initial heating of preform  23  and resin films  59 ,  61  can be around 190° F., allowing the resin to fully infuse preform  23  in the initial step. Also, resin films having a width nearly that of preform  23  can be used to fully or partially infuse preform  23 . To partially infuse preform  23  using full-width resin films, separator films or other materials are placed between selected portions of preform  23  and the resin films, preventing resin from entering preform  23  at those locations when resin is heated. 
   As shown in  FIG. 7 , another embodiment of the method of the present invention is a pultrusion method. As described above, a pultrusion method uses a heated die  75  to heat resin films  77 ,  79  and cause the resin on films  77 ,  79  to transfer to surfaces  31 ,  27 , respectively, of preform  23 . In the figure, there are no resin films located against surface  28  of base  25  or surfaces  33  of legs  29 , though additional resin films may be located against surfaces  28 ,  33 . Preform  23  may be partially or fully infused by controlling the temperature of die  75 , as described above for the various embodiments. 
   The advantages of the present invention include the ability to fully or partially infuse three-dimensional, woven textile preforms. In the partial infusion, selected amounts of resin are infused into discrete locations of the preforms. The partially-infused preforms provide a tacky surface when the preforms are used to assemble components, are more pliable without resin having been infused into the intersection of planar portions of the preform, and provide for better seating of components being assembled. 
   While the invention has been shown in only some of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit thereof.