Patent Publication Number: US-2004058182-A1

Title: Glass preform with living hinge

Description:
TECHNICAL FIELD  
       [0001] The present invention relates to glass preforms used in composite applications and more specifically to a glass preform having a living hinge for use in composite applications.  
       BACKGROUND OF THE INVENTION  
       [0002] In the manufacture of pickup trucks, truck boxes are typically secured to the frame of the pickup truck directly behind the cab region. Because these truck boxes are required to hold and support heavy tools or the like, the strength of the truck box and the dividers is of great concern. Further, because these truck boxes are placed in open air environments in the truck beds, corrosion resistance is another important consideration. Further, it is also highly desirable to use lightweight materials to improve fuel economy and emissions. Because of these concerns, molded plastic materials are commonly used to form the truck boxes.  
       [0003] It is a primary drawback of the present state of the art with respect to containers in general, and truck boxes in particular, that the containers themselves are somewhat complex in nature. Because of this, the molds and tools used to form the containers are quite complex in nature and in most instances require multi-plane flow and forming of the polymer being molded. For this reason, the plastic materials that can be used in the molding process must be somewhat flexible in nature or must be able to flow to fill complex molds. Most plastic materials used in today&#39;s industry do not contain the strength necessary for truck box applications unless reinforced with a straight enhancing material such as glass or carbon fiber and the like.  
       [0004] To increase the strength of moldable plastic materials, it is common practice to introduce glass or other reinforcement materials to the plastic either prior to or during the molding process. One process that is used is a structural reaction injection molding (SRIM) process. In this process, a two component matrix polymer resin is injected into a mold containing a matrix of reinforcing fibers. The mold is maintained at an elevated temperature to activate and react together the two component matrix polymer resin. The mold is also subjected to higher pressure to ensure total wetout of the fibrous matrix. The mold is shaped to the proper dimension and configuration required for the finished composite part. One common two component matrix system consists of polyol and polyisocyanate reacting to form a finished polyurethane composite part. The SRIM process has many drawbacks, however. For example, it is difficult and expensive to form complex shapes. Further, equal dispersion of the fibrous reinforcing material throughout the part is essential or structural weakness in portions where fiber content is limited may be experienced. Also, it is difficult to achieve class A surface parts with the SRIM process.  
       [0005] One difficulty with these systems is that the fiber reinforcing member must first be formed substantially into the shape of the truck box prior to injection of the resinous component to form the preform. This shaped glass element is commonly known as a preform. To form the preform, a vacuum is directed to different portions of a preform screen containing the fiberglass material to compress and hold the fiberglass on the screen surface, a process that requires a large vacuum pressure over a large area. Compaction screens are then required to keep the fiberglass in place on the screen surface.  
       [0006] Another problem is that the method of forming the preform must be capable of applying the fiber coating equally over a three dimensional area. Typically, a 6-axis robot is required to accomplish this task, a process that is both time consuming and expensive. Also, a vacuum must be maintained on the glass preform and compaction screen to maintain the preform on the compaction screen until the resinous component of the preform hardens (or cures) to form the preform.  
       [0007] It is thus highly desirable to form fiber reinforced polymer materials in a simple, cost effective manner that does not require complex spraying equipment and large vacuums. It is also desirable that the materials formed may be subsequently shaped to form relatively complex three dimensional parts such as truck beds and bedliners.  
       SUMMARY OF THE INVENTION  
       [0008] The present invention enables the manufacture of a glass preform with a “living hinge section” for input to a truck box structural reinforced injection molding process.  
       [0009] The concept incorporates a continuous strand that is sprayed onto a preform at an area that will become a hinge line. The entire preform is then sprayed with a string binder. The preform is then introduced into a three-dimensional injection type mold and conformed to the desired part shape. The continuous strand is flexible and allows for easy shaping in the hinge area.  
       [0010] The foregoing and other advantages of the invention will become apparent from the following disclosure in which one or more preferred embodiments of the invention are described in detail and illustrated in the accompanying drawings. It is contemplated that variations in procedures, structural features and arrangement of parts may appear to a person skilled in the art without departing from the scope of or sacrificing any of the advantages of the invention. 
     
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
     [0011]FIG. 1 is a perspective view of a truck constructed in accordance with one embodiment of the present invention;  
     [0012]FIG. 2 is a side view of a screen corresponding to the truckgate as shown in FIG. 1;  
     [0013]FIG. 3 is a top view of FIG. 2;  
     [0014]FIGS. 4 and 5 are a illustrate the process for forming a glass fiber matted structure onto the screen of FIG. 3;  
     [0015]FIG. 6 is a logic flow diagram for making a preform from the glass fiber matted structure of FIG. 5;  
     [0016]FIG. 7 is a perspective view of the preform formed in FIG. 6; and  
     [0017]FIG. 8 is a logic flow diagram for forming a composite bedliner from the preform of FIG. 7. 
    
    
     DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS OF THE INVENTION  
     [0018]FIG. 1 illustrates a pickup truck  10  having a truckgate  11  and a cab section  15 . The truckgate  11  typically has an open truck box  12  and a tailgate  24 . The truck box  12  is typically secured to the vehicle frame and cab section  15  by methods well known in the art. The truck box  12  has a pair of sidewalls  14 ,  16  and a bottom wall  17 . A pair of wheel wells  20 ,  22  are also typically contained within the truck box  12 . The truck box  12  of the present invention is comprised of a fiber reinforced thermoplastic material that is made from a novel fiberglass preform  50 . The method for forming the fiberglass preform  50  is shown below in FIGS.  2 - 6 .  
     [0019]FIGS. 2 and 3 illustrate a cross-sectional and top view of a glass preform screen  30  that is used to make a matted structure  70  that is subsequently processed to form a preform  50  according to one preferred embodiment of the present invention. The preform screen  30  is semi-flat in profile and is sized to substantially match the dimensions of the truck box  12 . As best shown in FIG. 2, a portion  32  of the screen  30  corresponding to the junction between each of the sidewalls  14 ,  16  and bottom wall  17  is formed in a hinge out pattern that will subsequently form a living hinge section  77  on the preform  50  as described below.  
     [0020]FIGS. 4 and 5 illustrates the method for making a fiberglass matting structure  70  using the preform screen  30  according to one preferred embodiment of the present invention. As shown in FIG. 4, a continuous strand  52  of fibrous material is sprayed along the portion  32  of a metal screen  30  within a chamber  60  featuring a down draft of air, preferably at about 150 cfm, through the screen  30 .  
     [0021] Next, as shown in FIG. 5, a string binder  54  is applied in chopped segments of about 3 inches in length over the entire surface of the preform screen  30  using a spray up process. In a preferred embodiment, the segments of string binder  54  are blown or spread by conventional means over the semi-flat preform screen  30  by supplying a down draft of air, preferably at about 150 cfm, through the screen  30  to form a predetermined vacuum pressure. Also, a sufficient level of heat is applied to the segments of string binder  54  as they are sprayed so as to soften the binder resin enough to permit fusing of some segments. Preferably, suction is applied to promote compacting of the segments as they fuse. The process of fusing allows the layered material to conform to the shape of the screen  30 , and the material is then set in a solid matted structure  70  that can be physically transported if necessary. The matting structure  70  may be subsequently processed to form a preform  50  having a living hinge section  77  as shown below in FIG. 6.  
     [0022] The continuous strand  52  of fibrous material is preferably in the form of a continuous strand composed of multiple filaments. The strands may take the form of yarns, or rovings, including two-end and four-end rovings. Typically, such reinforcing strands are formed by combining filaments of the reinforcing fiber material as they are attenuated from a fiber-forming apparatus such as a bushing or orifice plate, although they may also be made by any method conventionally known in the art. The filaments may be coated with a sizing composition comprising functional agents such as lubricants, coupling agents and film-forming polymers, after which they are gathered into strands. These strands may then be formed into yarns or rovings.  
     [0023] One preferred continuous strand  52  is a glass-roving product such as K75 S-O forming cake fibrous glass (7500 yds./lb.). Another preferred strand is a yarn product such as G-75 glass yarn (7500 yds./lb.). Both of these products are commercially available from Owens Corning. Alternatively, the continuous strand  52  may be in the form of a string binder, in which strand has a thermoformable binder resin deposited thereon prior to application to the screen  30 .  
     [0024] The string binder  54  comprises a fibrous carrier material with a thermoformable binder material to form a solid product that may be used in continuous or chopped form as a raw material in the preparation of preforms for molding process. In such an embodiment, the binder material is solidified on at least a portion of the fibrous carrier material. A catalyst that effects the cure of the binder resin during the manufacture of a reinforcing article is also present and is either directly incorporated into the thermoformable binder resin or incorporated into a separately applied layer to the fibrous carrier material. As used herein, the term “thermoformable” is intended to mean a resin that can be formed by heating, such as a thermoplastic, or a resin that is irreversibly set using heat, such as a thermosetting resin. The term “fibrous carrier material” is defined to mean a fibrous substrate selected from materials that are commonly used in the art. The “binder resin material” is a polymer that is used to fuse the fibers or strands of the fibrous carrier material such that the mixture of fibrous carrier material and the binder resin material may be solidified and cured to form a reinforcing article such as a preform, which may be used in a further manufacturing process to form a composite article. The ratio of the amount of fibrous carrier material to the amount of binder resin material is preferably about 50:50 in the string binder  54 .  
     [0025] One preferred string binder  54  that is commercially available and may be used is ME 2000, available from Owens Corning. This string binder  54  is fused to form the preform  50  in the downward forced air oven at approximately 230 to 235 degrees Celsius (about 450 degrees Fahrenheit) for about 5 minutes.  
     [0026] Another preferred string binder  54  is disclosed in U.S. patent application Ser. No. 09/280,808 entitled “String Binders”, which is herein incorporated by reference. In this application, the binder resin material is a crystalline resin that has been modified to have an acid value of less than about 30 mg KOH/g resin, and more preferably less than about 10 mg KOH/g resin. The preferred binder resins that may be used in the practice of this invention include one or acid-modified thermoplastic or thermosetting resins, such as a crystalline polyester resin. Preferably, the low-acid crystalline polymers are manufactured by controlling the proportions of ingredients and processing conditions during polymerization. The resulting modified resin comprises particularly desirable molar properties of the monomers that are condensed to form the polymer. Exemplary combinations of polymers that may be formed by a combination of different monomers is set forth below:  
                                                   Monomers   Molar Ratios                          ethylene glycol/fumaric acid   1.0/1.0           1,6-hexanediol/fumaric acid   1.02/1.0           1,6-hexanediol/ethylene glycol/fumaric acid   0.82/0.2/1.0           1,6-hexanediol/ethylene glycol/fumaric acid   0.92/0.1/1.0           1,6-hexanediol/1,4-butanediol/fumaric acid   0.82/0.2/1.0           1,6-hexanediol/1,4-butanediol/fumaric acid   0.92/0.1/1.0           1,6-hexanediol/1,4-cyclohexanedimethanol/   0.92/0.1/1.0           fumaric acid           1,6-hexanediol/1,4-cyclohexanedimethanol/   0.82/0.2/1.0           fumaric acid           1,4-butanediol/fumaric acid   1.03/1.0           1,4-butanediol/ethylene glycol/fumaric acid   0.82/0.2/1.0           1,4-butanediol/ethylene glycol/fumaric acid   0.70/0.3/1.0           1,4-butanediol/ethylene glycol/fumaric acid   0.92/0.1/1.0           1,4-butanediol/1,6-hexanediol/fumaric acid   0.82/0.2/1.0           1,4-butanediol/1,6-hexanediol/fumaric acid   0.92/0.1/1.0           1,4-cyclohexanedimethanol/ethylene   0.93/0.1/1.0           glycol/fumaric acid           1,4-cyclohexanedimethanol/ethylene   0.83/0.2/1.0           glycol/fumaric acid           1,4-cyclohexanedimethanol/1,6-hexanediol/   0.83/0.2/1.0           fumaric acid           1,4-cyclohexanedimethanol/1,6-hexanediol/   0.90/0.1/1.0           fumaric acid           1,4-cyclohexanedimethanol/1,4-butanediol/   0.83/0.2/1.0           fumaric acid           1,4-cyclohexanedimethanol/1,4-butanediol/   0.90/0.1/1.0           fumaric acid                      
 
     [0027] Referring now to FIG. 6, a logic flow diagram for forming a preform  50  from the matted structure  70  is illustrated. First, in Step  100 , the matted structure  70  is removed from the screen  30 . Next, in Step  110 , the matted structure  70  is placed into a downward forced air oven set a predetermined temperature and time to further soften the binder resin on the string binder  54  to fuse together adjacent string binder  54  segments and fuse the string binder segments to the strand  52 , thereby forming the preform  50 . The time and temperature necessary to form the preform  50  are dependent upon many factors, including the thickness of the preform  50 , the composition of the binder component of the string binder  54 , and to a lesser extent the type of fibrous reinforcement used. For most preferable systems, a temperature of approximately 225 to 250 degrees Celsius for about 4-6 minutes is sufficient to ensure fusing of the string binder  54  to both the strands  52  and other segments of the string binder  54  to form the preform  50 .  
     [0028] As shown in FIG. 7, the preform  50  formed according to the logic as shown in FIG. 6 is preferably maintained in the shape of the screen  30 . The preform  50  has a living hinge section  77  and a fused fiber section  79  surrounding the living hinge section  77 . The living hinge section  77  comprises the continuous strands  52  fused to a portion of the plurality of fused chopped segments of string binder  54  while the fused fiber section  79  is comprised entirely of fused segments of string binder  54 . The presence of the continuous strand  52  in the region of the living hinge section  77  provides the living hinge section  77  with increased flexibility and can be easily manipulated into complex shapes.  
     [0029] As shown in FIG. 8, the resulting preform  50  may then be subsequently processed to form a composite article, here truck box  12 , using an otherwise conventional molding process, for example liquid resin molding or injection molding process. In Step  200 , the preform  50  is placed in a mold cavity of a mold, preferably an injection mold. In Step  210 , a matrix resin is injected into the mold in a method well known to those of skill in the art. Any moldable materials which are compatible with the thermoset binder material of the preform  50  can be used as the matrix resin  78  system of the composites. Typical matrix resins  78  that can be used include vinyl esters, polyesters, polyurethanes and phenolic thermoplastics.  
     [0030] Next, in Step  220 , the preform  50  is molded at a desired pressure and temperature to form a composite article. In these molding techniques, the living hinge section  77  of the preform  50  provides the preform  50  with added flexibility in which to form more complex three-dimensional shapes such as those used in truck boxes  26 .  
     [0031] The mold used in a preferred molding process as shown in FIG. 8 is a 4000-ton press fitted for structural reaction injection molding. The press is closed and the injection cycle injected with Baydur 425, a 2-part polyurethane available from Bayer, as the matrix resin  78 . Molding is accomplished at 200° F. at 100 psi to form the composite truck box  26 .  
     [0032] The technique for forming the preform  50  and truck box  12  used in the present invention offers many advantages over prior art processes. First, the semi-flat profile of the screen  30  allows for a reduction in vacuum pressure and airflow required to secure the glass in the form of strands  52  and string binder  54  to the screen  30  as compared with those required to form complex shapes. The semi-flat profile also allows for directed vacuum pressure to minimal areas of the preform screen  30 . Also, the semi-flat profiles simplify the equipment used to spray the matted structure  70 , in that the use of six-axis robotic sprayers for spraying a complex three-dimensional shape is eliminated. Further, the semi-flat profile allows for elimination of compaction screens that are commonly used to compress and hold the preform glass on the screen surface.  
     [0033] While the invention has been described in terms of preferred embodiments, it will be understood, of course, that the invention is not limited thereto since modifications may be made by those skilled in the art, particularly in light of the foregoing teachings.