Abstract:
A method of manufacturing a composite sheet includes using a porous reinforcement panel of thermoplastic. A mold surface onto which the composite sheet will be formed is provided. At least one outer coat of material is applied onto the mold surface. At least one coat of resin and reinforcement material is applied over the outer coat to form a reinforcement layer. A porous thermoplastic reinforcement panel is applied to the reinforcement layer, and is bonded to the reinforcement layer. An additional coat of resin may optionally be applied onto the reinforcement panel. If the optional coat is applied onto the reinforcement panel, the reinforcement material may or may not be used with resin. Vacuum force or compression force may be applied to the laminate to assist the resin curing and the bonding, or curing may be performed without the application of pressure.

Description:
TECHNICAL FIELD 
       [0001]    This is a continuation-in-part of Ser. No. 12/192,734, filed Aug. 15, 2008, the entire content of which is incorporated herein by reference. This invention relates in general to a method and apparatus for the manufacture of fiber-reinforced panels, and in particular, to a method and apparatus for the manufacture of a composite sheet suitable for such uses as a recreational vehicle wall. 
     
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    It is commonplace in the manufacture of recreational vehicles to use composite sheets, such as glass fiber-reinforced wall panels, for the exterior surface of the recreational vehicle. These wall panels vary in dimensions up to, and including, from 2.4 to 3 meters (8 to 10 feet) wide, and can have a length as great as 15 meters (50 ft.) or more. 
         [0003]    For a number of years, various manufacturers have produced sheet glass panels for RV exterior walls, in which the panels contain a layer of lauan plywood. These panels have the structure of (i) a gel coat with (ii) chopped glass and resin composite reinforcement with (iii) a lauan plywood substrate, and are made by an open-mold-spraying and vacuum-bagging process (i.e., applying a vacuum using a bag for pressure containment). The low-viscosity liquid unsaturated polyester resin that is mixed with the chopped glass to provide the reinforcement can fill the gaps between the edges of the lauan panels, and partially penetrate the plywood. 
         [0004]    The process of making such a composite material begins with an elongate mold. The mold is somewhat larger than the panels to be made, but large enough to accommodate the 3×15 meter (10×50 ft.) panels. The upper surface of the mold is a finished surface to provide a substantially flat and smooth surface, as it is this surface which forms the exterior surface of the panels to be made. 
         [0005]    The mold is first sprayed with a coating known as a gel coating, which cures to form a high gloss exterior surface for the panel. Once cured, a resin and fiberglass are placed on the back (exposed) side of the gel coating, and then a plurality of panels of lauan are positioned side by side on top of the fiberglass. A vacuum bag is then placed over the top of the panels and a slight vacuum is introduced, which draws resin into the lauan panels to form a finished product. The completed product is then pulled off of the mold and cut and trimmed to the proper size. 
         [0006]    In addition to such composite panels, Crane Composites also produces a type of all-composite exterior wall panel (sold under the trademark CTEC) for use in recreational vehicles. This material has uniform and consistent properties, does not crack, does not absorb water and will not rot. However, the raw-material costs are high, and the manufacture of this product requires considerable investment, and requires a longer molding cycle time than is encountered in manufacturing panels reinforced with lauan. 
         [0007]    Despite the relatively low cost of lauan plywood, the present inventors note various disadvantages in using that material. Aside from requiring the cutting of trees to make the lauan, that material is not entirely uniform or consistent in its properties from panel to panel. In addition, lauan can emit certain amounts of formaldehyde, and has a strong propensity to absorb and retain water, and thus is susceptible to rotting. In addition, the lines between adjoining panels of lauan may be visible in the finished product, which is unesthetic, and voids in the lauan may turn into cracks and spread (commonly referred to as “telegraphing”), applying a high stress to the composite layer, with the potential to cause micro-cracking of the gel coat surface upon exposure to hot, cold and damp weather conditions. 
       SUMMARY OF THE INVENTION 
       [0008]    The object of providing an advance over existing composite materials that incorporate lauan, as well as other objects not specifically enumerated, is achieved by a method and apparatus for manufacturing a composite sheet according to the present invention. The method of manufacturing a composite sheet includes using a porous reinforcement panel made of a thermoplastic material. A mold surface onto which the composite sheet may be formed is provided. At least one outer coat of material is applied onto the mold surface. At least one coat of resin and reinforcement material, preferably although not necessarily glass fibers, is applied over the outer coat to form a reinforcement layer. The porous thermoplastic reinforcement panel or substrate is applied to the reinforcement layer when the reinforcement layer is still wet. The resin of the reinforcement layer works as a glue to bond the reinforcement layer to the reinforcement panel through application of a vacuum. A coat of wet resin with or without a layer of glass mat can be applied on the top surface of the reinforcement panel before application of a vacuum. 
         [0009]    In another embodiment of the invention, a mold surface onto which the composite sheet may be formed is provided. One or more dispensing mechanisms (which may themselves be conventional equipment) dispense at least one outer coat of material onto the mold surface, and at least one coat of resin over the outer coat. At least one applicator mechanism is provided to apply reinforcement material (again, preferably glass fibers) over the outer coat, where the resin and the reinforcement material together form a reinforcement layer. A vacuum mechanism is used to bond a porous thermoplastic reinforcement panel to the reinforcement layer, via the resin from the reinforcement as glue. A layer of wet resin with or without a layer of glass mat can be applied on the top surface of the reinforcement panel before application of a vacuum. 
         [0010]    In another embodiment of the invention, a composite sheet includes a layer of outer coat material. A layer of resin and reinforcement material is applied to the outer coat layer, the layer of resin and reinforcement material forming a reinforcement layer. A porous reinforcement panel of thermoplastic material is applied to the reinforcement layer, and the liquid resin from the reinforcement layer secures the reinforcement layer to the reinforcement panel. A layer of wet resin with or without a layer of glass mat can be applied on the top surface of the reinforcement panel before application of a vacuum. 
         [0011]    Various additional objects, features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments, when read in light of the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a schematic view in elevation, partially in cross-section, of an the manufacture of a composite sheet according to the invention, illustrating the application of several layers of the composite sheet. 
           [0013]      FIG. 2  is an enlarged cross-sectional view in elevation of a portion of the apparatus shown in  FIG. 1 , illustrating the use of a vacuum bag attached to the mold. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0014]    Referring now to the drawings, there is shown in  FIG. 1  an apparatus  10  for manufacturing a composite sheet  11  according to the invention. The illustrated manufacturing process involves passing a series of manufacturing operations over an elongate mold  12  in a direction indicated by the arrow  13  in  FIG. 1 . The mold  12  is made of any suitable material, such as fiberglass composite. Typically the mold  12  is somewhat larger than the composite sheet to be made, and large enough to accommodate a 3×15 meter (10×50 ft.) composite sheet. An upwardly facing surface  14  of the mold  12  has a smooth face to provide a substantially flat and smooth surface to the composite sheet  11 . The surface  14  forms the exterior surface of the composite sheet to be made. 
         [0015]    In a first step of the manufacturing process, an outer coat of material is applied to the surface  14  of the mold  12 . Typically, the outer coat is a gel coat  16 , but may be any suitable material such as a veneer or a composite material. The gel coat  16  is a commercially available quick setting polymer applied to the surface of the mold. The gel coat  16  cures to form a high gloss exterior surface for the finished composite sheet  11 . The gel coat  16  may include a pigment and provides a durable and esthetically pleasing outer surface for the finished composite sheet  11 . Preferably, the gel coat  16  is applied in two layers by a sprayer  18  (although it is within the invention to apply a different number of layers thereof). Typically, the sprayer  18  is moved longitudinally along rails and sprays the entire length of the elongate mold  12 . The sprayer  18  may be a conventional sprayer, such as one that is commercially available from Magnum Venus of Kent, Wash. The spray head of the sprayer  18  preferably traverses across the width of the mold  12  and discharges the gel coat  16  in a spray pattern and with a substantially uniform thickness. Preferably, the gel coat  16  is a polymer having a catalyst which sets to a gel in about 20 minutes and cures, or hardens, in about 35 minutes. 
         [0016]    It will be understood that more than one sprayer  18  may be used to apply the gel coat  16 , and that other methods for applying the gel coat  16  can be used. 
         [0017]    In a second step of the manufacturing process, a composite mixture of resin  20  and reinforcement material, such as chopped fiberglass  22 , is applied to the gel coat  16  to form a reinforcement layer  28 . The resin  20  may comprise a polymer similar to the gel coat  16 , but without a pigment. The resin  20  may be any suitable commercially available polyester resin, such as CoREZYN COR61-AA-830 DCPD laminating resin, from Interplastic Corporation, Minneapolis, Minn. Preferably, however, a polyester/epoxy blend resin having a low shrink characteristic, such as AME 2000 LB 6527-017, from the Ashland Specialty Chemical Company, Composite Polymers Division, Bartow, Fla., will be used. 
         [0018]    Preferably, the resin  20  is applied by a resin sprayer  24 , and the fiberglass  22  is applied by a fiberglass applicator  26 . The resin sprayer  24  and the fiberglass applicator  26  can both be conventional. The fiberglass applicator  26  is designed for chopping fiberglass into fibers  22  of a desired length and dispensing the chopped fibers  22  in various sizes to form a laminate or reinforcement layer  28  consisting of a mixture of the resin  20  and the fiberglass fibers  22 . Such dispensing and spray apparatus may be obtained commercially, for example from Magnum Venus. 
         [0019]    Like the sprayer  18 , the sprayer  24  and applicator  26  preferably move longitudinally along rails, and traverse across the mold  12 , and discharge resin  20  and chopped fiberglass  22 , respectively, in a pattern and with a substantially uniform thickness. In another embodiment, the mold  12  can move longitudinally along rails, and the sprayer  18 , the sprayer  24  and applicator  26  stay in the designated position, and just traverse across the mold  12 . It will be understood that more than one resin sprayer  24  and fiberglass applicator  26  may be used to apply the resin  20  and the fiberglass fibers  22 . 
         [0020]    When applying the resin  20  and the chopped fiberglass  22 , either the resin  20  or the fiberglass  22  can be applied first, or the resin  20  and the fiberglass  22  can be applied simultaneously. The reinforcement layer  28  may be rolled with weighted rollers (not shown) to remove air from the reinforcement layer  28 . 
         [0021]    In an alternative embodiment of the invention (not shown), the chopped fiberglass fibers are replaced by a glass mat or other suitable reinforcement material. The mat is applied to the resin in a manner similar to the chopped fiberglass fibers described above, that is, so as to produce a substantially uniform reinforcement layer. In a further such alternative embodiment, such a glass mat is saturated with the polymer resin  20  and applied on top of the gel coat material  16 , thereby eliminating the steps of applying the chopped fiberglass  22  and spraying the resin  20 . Furthermore, the mat may comprise non-woven mat, or a stitched or knitted mat so as to provide strength characteristics as desired. 
         [0022]    In a third step of the manufacturing process, a plurality of porous thermoplastic reinforcement panels  29  are applied to the reinforcement layer  28  in a side-by-side manner to cover the reinforcement layer  28  when the resin  20  is still wet, so the resin works with fiberglass forming the reinforcement layer and as glue bonding the reinforcement panels  29  with the reinforcement layer  28 . The reinforcement panels  29  are preferably panels made of porous fiberglass thermoplastic composite, and are commercially available from Azdel under its SuperLite VGX trademark, from Owens-Corning under its AcoustiMax trademark and from Quadrant Plastic Composites, Inc. under its SymaLITE trademark (the panels can instead be made of a porous fiberglass thermosetting plastic composite). Each panel  29  typically has a thickness of about 1 to 5 mm. The surfaces  30  and  31  may be smooth, but need not be. The panels  29  are abutted together along their respective edges, and typically have a length equal to the width of the composite panel  11  that is being manufactured. Thus, for example, the reinforcement panels may be 1.2×2.4 meter (4 ft.×8 ft.) panels, and the 2.4 m (8 ft.) length of the panel  29  corresponds to the width of the composite sheet  11 . 
         [0023]    As shown in  FIG. 1 , the panels  29  can be lowered onto the reinforcement layer by mechanical means, but it is also within the broad scope of the invention for them to be put in place manually. 
         [0024]    If desired, strips of webbing  32 , such as strips of fiberglass mat, are wetted with a catalyzed resin and applied at each seam between adjacent reinforcement panels  29  to reinforce the composite sheet  11 . 
         [0025]    Although the composite sheet  11  is described as having a plurality of reinforcement panels  29 , it will be understood that a continuous reinforcement backing may be provided instead, thereby eliminating the seams between panels and eliminating the webbing  32 . If this embodiment is adopted, then the continuous reinforcement backing that is used instead of discrete panels  29  may be applied to the reinforcement layer  28  by being taken straight from a roll, or applied in any other manner that is convenient. 
         [0026]    Furthermore, the panels  29  may comprise substantially thicker panels, depending on the application; for example 19 mm (¾ inch) thick sheets may be used if the product is intended for incorporation in a truck body. 
         [0027]    In a fourth step, one layer of resin  33  is sprayed on the exposed surface  31  of the panels  29  by an additional sprayer  25 , which is the same as sprayer  18 . The resin  33  also can be used with a layer of glass  34  for increasing the bending stiffness of the composite sheet  11 . The glass  34  will be chopped glass sprayed by an applicator  27 , which is like applicator  26 . Alternatively, the glass  34  can be a continuous glass mat, such as a fiberglass veil mat, chopped fiberglass strand mat or fiberglass woven roving, applied by a roll. If desired, this fourth step can be eliminated, or just the additional layer of resin  33  may be applied, without glass. 
         [0028]    It is possible that pockets of air may become trapped between the reinforcement panel  29  and the gel coat layer  16  of the composite sheet  11 . More particularly, air may become trapped between the reinforcement panel  29  and the reinforcement layer  28 . Such trapped air can cause a distorted appearance on the finished surface  16  of the composite sheet  11 , and this results in composite sheets  11  that must be scrapped or remanufactured, adding cost and time to the manufacturing process. The distorted appearance may worsen over time due to the effects of heat related expansion and contraction of both the trapped air and the composite sheet  11 . 
         [0029]    In a fifth step of the manufacturing process, therefore, means for applying a vacuum, such as the vacuum bag  66 , is placed around the mold  12 , as illustrated in  FIG. 2 . The vacuum bag  66  may be secured to the mold  12  by any suitable means, such as an elastomeric band  67  or clamps (not shown). The vacuum bag  66  includes a plurality of vacuum lines  68 . The vacuum lines  68  are connected to a vacuum pump  70 . The vacuum pump  70  creates a vacuum pressure, preferably within the range of from about 5.0 cm (2.0 in.) Hg to about 77.8 cm (30.0 in.) Hg. More preferably, the vacuum pump  70  creates a vacuum pressure of about 13 to 39 cm (5 to 15 in.) Hg. One piece of plastic breath sheet  62  is used for covering the entire mold  14  (and thus the entire composite panel  11 ). The breath sheet may be of the material sold under the trademark Mylar (which is a trademark of E.I. DuPont de Nemours &amp; Co.), although other materials can be used in addition, as is known to those in the art. The vacuum pump pulls the air from between the bag  66  and the top composite layer  33 / 34 . The vacuum draws the layers of the composite sheet  11  together, and pulls out any air trapped anywhere between the top composite layer  33 / 34  and the gel coat  16 . 
         [0030]    After the reinforcement layer  28  and the top composite layer  33 / 34  harden, the vacuum bag  66  is removed from the mold  12 . When the composite sheet  11  is fully cured, the sheet  11  is removed from the mold  12 . The sheet  11  may be removed from the mold  12  by a lifting mechanism (not shown) and moved to a location for additional processing, such as trimming and inspection. 
         [0031]    Alternatively, a press platen may be used to apply pressure to the composite sheet  11  to aid in eliminating air bubbles. It is also within the scope of the invention, however, to allow free curing of the resin without the application of pressure. 
         [0032]    The principle and mode of operation of this invention have been described with reference to the preferred embodiments. However, it should be noted that this invention may be practiced otherwise than as specifically illustrated and described without departing from its scope. For example, the mold  12  may be movable relative to a plurality of stationary manufacturing operations, such as the gel coat sprayer  16 , the resin sprayer  24  and  25 , and the fiberglass applicator  26  and  27 , as described in commonly-assigned U.S. Pat. No. 6,854,499, or may be used in a continuous molding process as described in commonly-assigned U.S. Pat. No. 6,755,633, both of which are incorporated herein by reference. 
         [0033]    The inventors have found that this invention provides an all-composite sheet suitable for use as an RV exterior wall panel, and does so using a well-understood high-productivity mold process. In addition, a sheet made according to the present invention has advantages over conventional lauan-backed panels, being lighter in weight, more consistent in quality and properties of the material, better moisture resistance, greater durability, thermal stability and thermal insulation, as well as better surface appearance, with very minor border lines. In addition, a sheet according to the present invention has no formaldehyde emission. 
         [0034]    Many additional variations and modifications of the foregoing embodiments will now be apparent to those skilled in the art, and thus, the scope of this invention is not to be limited by the details of the foregoing embodiments, but rather is set out by the scope of the following claims.