Abstract:
The present disclosure provides a method of fabricating closed-molded translucent fiber-reinforced plastic (FRP) material and parts for use in various applications, such as for use in waterslides and architectural fascia and signage. The method includes: (a) providing a first mold half mateable with a second mold half to define a mold having an internal cavity; (b) disposing a glass fiber pre-form within the internal cavity of the mold, the glass fibers of the pre-form having a preselected refractive index; (c) selecting a transparent thermoset resin having a refractive index when cured that is substantially similar to the refractive index of the glass fibers of the pre-form; (d) injecting the thermoset resin into the internal cavity of the mold until the void space defined within the internal cavity is substantially filled with the resin; (e) allowing the resin to cure; and (f) removing the part from the mold.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application No. 61/199,119, filed on Nov. 12, 2008, the disclosure of which is hereby expressly incorporated herein by reference. 
    
    
     FIELD OF TECHNOLOGY 
     The present disclosure relates to translucent, closed-molded fiber-reinforced plastic (FRP), and parts made thereof for various applications, including waterslides and architectural fascia and signage applications. 
     BACKGROUND 
     Fiber-reinforced plastic (FRP) is a composite material comprising a thermoset plastic reinforced with glass or other fibers. Such material is also referred to by other names, including fiberglass, glass-reinforced plastic (GRP), reinforced-thermoset plastic (RTP) and reinforced thermoset resin (RTR). These materials will be herein after collectively referred to as “FRP” for ease of description. 
     Various methods can be used to fabricate FRP parts. Open-mold processes are the most commonly used methods. In open-mold processes a one-sided mold is used. The mold can be made of various well-known materials including, for example, tooling grade FRP, epoxy or metal. Typically, a release agent is first applied to the mold, followed by a layer of gelcoat. The gelcoat is typically a clear or pigmented resin, and gives the finished surface of the part a harder, more durable and attractive, glossy finish. 
     Open-mold fabrication may typically be done using either a hand lay-up or spray-up process. In a hand lay-up open-mold process, after the gelcoat layer is dry, a layer of glass fiber pre-form (also known as a mat or veil) is laid on the gelcoat layer and wetted with catalyzed resin. Additional layers of glass fiber pre-form are added and wetted with resin until the desired thickness is achieved. 
     A spray-up open-mold process is much faster and less labor-intensive than a hand lay-up open-mold process. In a spray-up process, chopped glass fibers and catalyzed resin are sprayed directly onto the mold after application of the gelcoat. The resin and glass can be applied separately or can be simultaneously “chopped” in a combined stream from a chopper gun. In both a spray-up and hand lay-up processes, once the desired thickness is achieved, the part is cured, cooled and removed from the mold. With spray-up, the resulting parts have a thickness that tends to be less consistent throughout the part than with hand lay-up. 
     Open-mold spray-up processes are suitable for high volume part production. However, with open-mold processes, the side of the part that was in contact with the mold has a smooth surface, whereas the other side has a much rougher surface, typically showing a distinct three-dimensional random fiber pattern. A blue-tinted, translucent FRP part (a flume segment of a waterslide) formed using an open-mold, spray-up process is shown in the photographs in  FIGS. 1A and 1B . As can be seen in the photographs in  FIGS. 1A and 1B , the FRP parts include a textured exterior surface. 
     For applications which require a smooth or predefined surface finish on both sides and/or close dimensional tolerances, a closed-mold process is more suitable. A photograph of an opaque, blue-colored FRP part (a flume segment of a waterslide) formed using a standard closed-mold process is shown in  FIG. 1C . Resin transfer molding (RTM) is a closed-mold process where a glass fiber pre-form is placed in a two-part closed-mold, which is then injected with a catalyzed thermoset resin. As in the open-mold processes described above, a release agent and optionally a clear or pigmented gelcoat layer are first applied to the inside surfaces of the mold. The resin is allowed to cure and then the mold is opened and the part is removed. Typically the resin is injected under pressure. The resin may also be heated, for example, to help control resin cure times for achieving consistent production rates and/or to lower the viscosity of the resin for better flow. The mold is also sometimes preheated, for example, to achieve shorter cycle times. 
     Light RTM (LRTM) is a vacuum-assisted RTM low-pressure resin injection technique that also uses a two-part mold comprising a mold and a counter-mold, or a first mold portion and a second mold portion. A vacuum is used for mold closure and to assist resin flow through the glass fiber pre-form which is placed inside the mold. A low pressure pump is used to inject the resin which is then drawn through the mold cavity by a vacuum, limiting the pressure needed for injecting the resin. Because limited pressure is used, LRTM molds tend to be less heavy-duty and costly to produce. In LRTM the counter mold is typically semi-rigid, and because it is relatively lightweight, it is easy to handle. 
     Although the tooling costs can be significantly less for LRTM in comparison to conventional RTM, the part production rate is generally lower. This is because in LRTM, the resin flow rates cannot be speeded up above a certain level in order to fill the mold more quickly. The mold construction and the atmospheric mold clamping pressures limit the overall in-mold pressures that can be applied, for example, typically to less than 0.5 bar (8 psi). 
     Closed-mold fabrication through conventional RTM is suitable for high volume manufacturing of FRP parts. Light RTM is now the most commonly used closed-mold process for low to medium volume applications, such as marine, automotive, industrial, wind, power, and medical composite molding applications. 
     Closed-mold fabrication of FRP parts through conventional RTM or LRTM offers a number of advantages over open-mold spray-up fabrication, including some or all of the following:
         Closed-molded parts can be produced with a smooth or deliberately textured, (gelcoated or non-gelcoated) engineered surface on both sides. This is practically important for some applications, and also provides an improved visual appearance and a better looking product.   Closed-mold processes result in reduced material waste and are a more environmentally-friendly process, as they produce less styrene and other volatile organic compound (VOC) emissions. This improves the working environment, reduces or eliminates the need for ventilation systems, and enhances regulatory compliance.   Closed-mold processes allow for superior design flexibility to create complex shapes and forms.   Closed-mold processes provide more uniform dimensional tolerance. The parts typically have tighter tolerances to design specifications (for example, +/−1.0 mm or 0.04 inches) and greater consistency in part thickness.   Parts produced via closed-mold processes can have high fiber content, which creates a strong and light-weight finished product. For example, the fiber content of closed-molded parts is typically in the range of 25% to 50% fiber content by volume. Parts formed from open-mold processes, by comparison, have glass fiber content by volume typically in the range of 15-35%, with spray-up at the lower end and hand lay-up at the higher end.   LRTM closed-mold processes have short mold-cycle times that can help increase production volumes and throughput.       

     It is well known that adding glass fibers to transparent or clear plastic resin improves the stiffness and strength of the material. However, this improvement generally goes hand in hand with diminished optical properties of the FRP part. The term “optical properties” refers to the ability of the material to transmit visible light. Materials can be “transparent”, in which case they will transmit visible light without significant scattering such that items lying beyond are clearly visible. Materials can also be “opaque”, in which case visible light will be blocked and one cannot see through an object made from those materials. In between are materials that transmit some visible light, such that items lying beyond can be seen, but perhaps not perfectly clearly or at a distance. Such materials are referred to a “translucent”. The degree of translucency a material can provide will often be a function of the thickness of a part made from that material. 
     Until now, FRP panels have not been produced with sufficient translucency and optical quality for certain applications, such as for use in architectural fascia and waterslide applications. Most closed-molded and open-molded FRP parts are opaque, and are made in a variety of colors. To create opaque FRP parts, typically only the surface gelcoat layer is colored, or the parts are instead sanded and then painted with the desired color after being made. 
     There have been attempts to make translucent FRP parts via open-mold processes for various applications including waterslides, roof and wall panels, skylights, and tanks or vessels (where the translucency enables vision of the liquid level inside). Translucent FRP samples fabricated using a conventional open-mold process are shown in the photograph of  FIG. 2 . Although the translucent open-molded FRP samples similar to those in shown in  FIG. 2  could be made using suitable variations of a conventional open-mold FRP process using readily available materials, the method and materials used to create the FRP samples of  FIG. 2  will be hereinafter described for reference in the discussion below. 
       FIG. 3  illustrates a cross-sectional view of a portion of an open-molded translucent FRP sample  18  of  FIG. 2 . The sample  18  includes a clear gelcoat layer  20  (about 0.5 mm, or 0.02 inches thick) and an FRP layer  24  (about 3.5 mm, or 0.14 inches thick). The FRP layer  24  was formed using a conventional open-mold hand lay-up process using three layers of an FRP supply E-Glass chopped strand/fiber pre-form available from Ashland Inc. of Columbus, Ohio. The Ashland FRP supply E-Glass chopped strand/fiber pre-form exhibits at least the following known characteristics:
         It has randomly oriented chopped glass fibers   It has a 1.5 oz. per square yard (per 0.84 square meter) fiber content mat   The glass fibers have a diameter of about 13 micron   The fibers have a silane-based coating that is styrene soluble (for bonding the fibers to the resin)   The “E-Glass” grade glass fibers are suitable as an electrical insulator       

     It should be appreciated that other suitable glass chopped fiber pre-forms having similar characteristics may instead be used. 
     The resin used to create the FRP layer  24  has certain characteristics to enhance the translucency of the FRP layer  24 . In the sample  18  of  FIG. 2 , a surf board resin available from Reichhold of Research Triangle Park, North Carolina was used. The resin is known to exhibit at least the following characteristics:
         It is a thermoset polyester resin   It cures to a colorless, transparent plastic   The cured refractive index of the resin is between about 1.55 and 1.57   The viscosity of the resin is between about 400-500 CPS at 77° F.   It has a thix index of about 5.0 (wherein the thix index is a measure of anti-sag properties)       

     It should be appreciated that the resin may be altered to accommodate the end-use requirements of the open-molded translucent FRP part. For example, the resin may be modified using well-known techniques to increase water resistance, temperature resistance, and/or UV stability. In some cases the translucent material is tinted, in which case a pigment is incorporated into the resin so that the material is tinted throughout its thickness. 
     The translucent FRP open-molded samples fabricated as described had about 33% fiber content by weight, and the material is therefore sufficiently strong for a variety of applications, including waterslides and architectural fascia and signage applications. However, as can be seen in the photograph of  FIG. 2  and as will be more fully appreciated by the description below, although the materials formed using an open-mold hand lay-up process have very little color, these materials have a low degree of translucency. This is due at least in part to the rough surface created on the unfinished surface of the material (which also causes varied thickness throughout a part or sample made from the material), and a visible fiber pattern within the FRP layer  24 . The low degree of translucency results in a low degree of light transmission and optical quality that makes open-molded translucent FRP materials, like the samples shown in  FIG. 2 , insufficient for some applications. 
     Attempts to make closed-molded translucent FRP parts have likewise been unsuccessful. More specifically, FRP samples with low translucency fabricated using a conventional RTM or LRTM closed-mold process are shown in  FIG. 4 . Although the low-translucency closed-molded FRP samples similar to those shown in  FIG. 4  could be made using variations of conventional closed-mold RTM or LRTM processes using readily available materials, the method and materials used to create the FRP samples of  FIG. 4  will be hereinafter described for reference in the discussion below. 
       FIG. 5  illustrates a cross-sectional view of a portion of a closed-molded FRP sample  26  of  FIG. 4 . The sample  26  includes inner and outer clear gelcoat layers  28  and  32  (each about 0.5 mm, or 0.02 inches thick), inner and outer FRP layers  36  and  40  (each about 1 mm, or 0.04 inches thick), and a flow media layer  44  (about 1 mm, or 0.04 inches thick) interposed between the FRP layers  36  and  40  consisting of 180 g/m 2  polypropylene. The FRP layer  36  and  40  and flow media layer  44  were formed using a conventional closed-mold process using a Rovicore® 600/D3/600 fiber glass pre-form that consists of large diameter glass fibers mechanically stitched together with flow media (as is well known in the art) for helping the resin flow through the mold when vacuum is applied. The pre-form was infused with a resin used to create the FRP layers  36  and  40  having certain characteristics to enhance the translucency of the FRP layers  36  and  40 . In the sample of  FIG. 4 , an Ashland Aropol CL 70502-25 clear ISO resin was used, which is known to exhibit at least the following characteristics:
         It is a thermoset isophthalic polyester resin   It cures to a colorless, transparent plastic   The viscosity of the resin is between about 90-120 CPS at 77° F.,       

     The FRP closed-molded samples fabricated as described above with reference to  FIGS. 4 and 5  have about 32% fiber content by weight, and the material is therefore sufficiently strong for a variety of applications, including waterslides and architectural fascia and signage applications. However, as can be seen in  FIG. 4  and as will be more fully appreciated by the description below, these translucent closed-molded FRP materials have a degree of translucency that is considerably less than would be desirable for many situations. The low degree of translucency is due at least in part to visibility of the glass fibers within the material after the resin has cured. 
     Where transparent or highly translucent plastics are needed, typically acrylic, polycarbonate and other thermoplastics have been used. However, these materials do not have the same strength and durability as FRP. Also, parts made from acrylic and polycarbonates (or other similar materials) generally have a much larger coefficient of thermal expansion which can be problematic in some applications. These materials also tend to pose limitations in part geometry due to limited draw depth, which causes problems in thickness control, as the material is often “stretched” over corners and mold features. 
     Translucent FRP parts are desirable in many applications, which include, for instance, waterslides or architectural signage or fascia. Waterslides are popular ride attractions for water parks, theme parks, family entertainment centers and destination resorts. The popularity of waterslide rides has increased dramatically over the years, and park patrons continue to seek out more exciting and stimulating ride experiences. Thus, there is an ever present demand for different and more exciting waterslide designs that offer riders a unique ride experience and that give park owners the ability to draw larger crowds to their parks. 
     Transparent waterslides have been fabricated using clear or color-tinted acrylic flume segments. This can provide an entertaining and exciting waterslide experience, allowing waterslide users to seek out and experience thrilling sensations such as flying, as well as allowing other patrons to have a pleasing and exciting view of riders as they descend. Sometimes transparent sections of the waterslide pass through underwater features such as shark tanks or aquariums so that the user has the feeling of being inside that feature. It can also allow the slide structure to blend more with the surroundings and have a more subtle visual impact. 
     FRP is generally a preferred material for waterslide construction over acrylic or other thermoplastics. Acrylic slides are often cost prohibitive and, as noted above, lack the strength and durability of FRP products. As also noted above, FRP has better structural properties and therefore thinner and lighter weight parts can be used. Furthermore, FRP does not have the same limitations in thickness control as acrylic or other thermoplastics, which provides greater design flexibility for unique waterslide parts. 
     Translucent waterslide flume segments have been fabricated using open-molded spray-up FRP materials such as those described above in reference to  FIGS. 1A and 1B  as well as  FIGS. 2 and 3 . As can be seen in  FIGS. 1A and 1B  and  2 , the open-mold spray-up FRP process creates parts having a low degree of light transmission and translucency. 
     For plastic signage and architectural fascia applications, thermal-formed acrylic or other thermoplastic panels are commonly used. As noted above, FRP offers numerous advantages (ability to be formed into more complex shapes, strength, light-weight properties, less thermal expansion issues) that are also advantageous in architectural fascia and signage applications. Because FRP is stronger, panels that would have to be made and installed in several pieces in acrylic can be made in a single large panel. Moreover, translucent FRP materials could be used to create architectural fascia panels and signage with lenses and shaded light transmission features such as up-lighting or wash, and can be used to produce backlit graphics using post-applied or integral graphics or decals. 
     Thus, it can be appreciated from the foregoing that it is desirable to develop an improved translucent FRP material that can be used to create parts for various applications, such as for waterslides and architectural fascia and signage, as well as a method of fabricating the improved translucent FRP material and parts. 
     SUMMARY 
     The present disclosure provides a method of fabricating closed-molded translucent fiber-reinforced plastic (FRP) material and parts for use in various applications, such as for use in waterslides and architectural fascia and signage. The method includes: (a) providing a first mold half mateable with a second mold half to define a mold having an internal cavity; (b) disposing a glass fiber pre-form within the internal cavity of the mold, the glass fibers of the pre-form having a preselected refractive index; (c) selecting a transparent thermoset resin having a refractive index when cured that is substantially similar to the refractive index of the glass fibers of the pre-form; (d) injecting the thermoset resin into the internal cavity of the mold until the void space defined within the internal cavity is substantially filled with the resin; (e) allowing the resin to cure; and (f) removing the part from the mold. 
     The present disclosure further discloses a closed-molded translucent FRP material that may be, for example, in the form of a waterslide flume segment or architectural fascia and signage. The closed-molded translucent FRP material and parts include first and second layers of a cured substantially clear gelcoat and an FRP layer formed between the first and second layers of gelcoat. The FRP layer includes a glass fiber pre-form comprising glass fibers having a preselected refractive index, and a cured transparent resin bonded to the glass fibers of the pre-form, wherein the cured resin has a refractive index when cured that is substantially similar to the refractive index of the glass fibers of the pre-form. 
     This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee. 
       The foregoing aspects and many of the attendant advantages of the present disclosure will become more readily appreciated by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
         FIGS. 1A and 1B  are photographs of a prior art open-molded blue-tinted FRP part, specifically a waterslide flume segment; 
         FIG. 1C  is a photograph of a prior art closed-molded, opaque, blue-colored FRP part, specifically a waterslide flume segment; 
         FIG. 2  is a photograph of low-translucency, open-molded FRP samples (prior art); 
         FIG. 3  is an illustrated cross-sectional view of a portion of one of the samples of  FIG. 2 ; 
         FIG. 4  is a photograph of low translucency, closed-molded FRP samples; 
         FIG. 5  is an illustrated cross-sectional view of a portion of one of the samples of  FIG. 4 ; 
         FIG. 6  is a photograph of translucent, closed-molded FRP samples formed in accordance with a preferred embodiment of the present disclosure; 
         FIG. 7  is an illustrated cross-sectional view of a portion of one of the samples of  FIG. 6 ; 
         FIG. 8  is a photograph of a translucent, closed-molded FRP architectural fascia panel formed in accordance with a preferred embodiment of the present disclosure; 
         FIGS. 9A and 9B  are photographs of translucent, closed-molded FRP waterslide parts formed in accordance with a preferred embodiment of the present disclosure, wherein the waterslide parts are tinted blue; 
         FIG. 10  is an isometric view of a test fixture for use in measuring light transmission of samples of translucent FRP materials; 
         FIG. 11  is a cross-sectional view of the test fixture of  FIG. 10 ; wherein the light transmission through an FRP sample is shown being tested; 
         FIG. 12A  is an isometric view of a test fixture for use in measuring optical properties of samples of translucent FRP materials; 
         FIG. 12B  is planar view of a sheet have text printed thereon in a standard font of increasing size, the sheet for use with the test fixture of  FIG. 12A ; 
         FIG. 13  is a photograph of one of the prior art translucent open-molded FRP samples of  FIG. 2  shown in a first configuration within the test fixture of  FIG. 12A ; 
         FIG. 14  is a photograph of the prior art sample of  FIG. 13  shown in a second configuration within the test fixture of  FIG. 12A ; 
         FIG. 15  is a photograph of one of the a low translucency closed-molded FRP samples of  FIG. 4  shown in a first configuration within the test fixture of  FIG. 12A ; 
         FIG. 16  is a photograph of the sample of  FIG. 15  shown in a second configuration within the test fixture of  FIG. 12A ; and 
         FIG. 17  is a photograph of one of the translucent closed-molded FRP samples of  FIG. 6  shown in a first configuration within the test fixture of  FIG. 12A . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 6 , a plurality of samples of an improved RTM closed-molded translucent FRP material formed in accordance with a preferred embodiment of the present disclosure is depicted. The overall general process for fabricating the improved translucent closed-molded FRP samples shown in  FIG. 6  will first be described.  FIG. 7  depicts a cross-sectional view of a portion of a translucent closed-molded RTM FRP sample  48  of  FIG. 6 . The translucent closed-molded RTM FRP sample  48  includes inner and outer clear gelcoat layers  50  and  54  (each about 0.5 mm, or 0.02 inches thick) and an FRP layer  58  (about 3 mm, or 0.12 inches thick) formed between the gelcoat layers  50  and  54 . 
     The FRP layer  58  is formed using a closed-mold RTM process in which a glass fiber pre-form is placed in a mold (after the clear gelcoat layers have cured), which is then closed and injected with a catalyzed resin. The resin can be drawn through the glass fiber pre-form by applying a vacuum in a light RTM process. Alternatively, the resin may be injected under pressure in a regular RTM process. 
     The glass fiber pre-form and the resin are selected so that the glass fiber in the pre-form becomes almost or entirely visually absent when incorporated into the cured resin. It is believed by the inventors that closely matching the refractive indices of the cured resin and the glass fibers of the glass fiber pre-form reduces the visibility of the glass fibers in the finished product and improves its translucency. It is also been found that it is beneficial if the glass fiber pre-form does not include flow media, binders, or stitching and consists of glass fibers with a small filament size. 
     The resin is chosen so that it is optically transparent when cured, and it is of suitable viscosity for injection. The resin can include one or more additives, for example, catalysts, coupling or cross-linking agents, UV-blockers, pigments or dyes, anti-oxidizing agents, weathering agents, and/or air release or surface tension reducers which can reduce the tendency for air bubbles to be trapped in the finished product. Preferably the additives do not unduly adversely affect the optical characteristics, moldability or physical properties of the material. The glass fiber content of the finished part is preferably in the range of 35-50% by weight. 
     Although the translucent closed-molded FRP sample  48  shown in  FIG. 6  may be formed using materials having the same or similar properties as described above, a specific example of the formulation of a closed-molded RTM translucent FRP sample  48  having desirable optical and light transmission properties will be hereinafter provided. 
     EXAMPLE 
     The closed-molded RTM translucent FRP samples shown in  FIG. 6  were fabricated using one layer of a Uniconform® UM2A glass fiber pre-form available from Owens Corning of Toledo, Ohio. The Uniconform® UM2A glass fiber pre-form exhibits at least the following known properties:
         It has randomly oriented continuous E-glass fibers   The glass fibers have a maximum diameter of about 18 micron   It has a filament bundle size of 25 tex at the surface, 50 tex in the core (wherein “tex” is a measure of the fiber bundle size, and is defined by the weight (in grams) of 1 kilometer of fiber bundle, wherein a fiber bundle is simply a grouping of individual glass fibers)   The pre-form has no stitching or binder materials, but rather, the glass strands are held together by a suitable method such as needle punching   The fibers have a silane-based coating that is styrene soluble (for bonding the fibers to the resin)   The glass fibers have a refractive index of 1.56+/−0.02   The pre-form has a substantially uniform fiber distribution per unit area       

     The resin chosen to create the closed-molded RTM translucent FRP samples shown in  FIG. 6  was an Ashland Aropol CL 70502-25 clear ISO resin. The chosen resin is known to exhibit at least the following characteristics:
         It is a thermoset isophthalic polyester resin   It cures to a colorless, transparent plastic   The cured refractive index of the resin is between about 1.55 and 1.57   The viscosity of the resin is between about 90-120 CPS at 77° F.       

     The resin may further include some methyl methacrylate (MMA), to suitably adjust the viscosity. It should be appreciated that the resin could be further altered in formulation to accommodate end-use requirements. For example, the resin may be modified using well-known techniques to increase water resistance, temperature resistance, and/or UV stability. 
     It has also been discovered that closed-molded RTM translucent FRP parts that are substantially uniform in thickness have increased levels of translucency. Parts that are uneven in thickness may result from increased or decreased amounts of glass fibers in certain areas which cause the resin to deform when curing. To adjust the thickness in areas of the closed-molded RTM translucent FRP part, the amount of glass fibers can be increased or decreased to create a part of substantially uniform fiber content. This can be done by taking a cross-section of a finished closed-molded RTM translucent FRP part, measuring the fiber content in different areas of the part (especially comparing fiber content in areas of varying thickness), and increasing or decreasing the amount of glass fibers in those areas accordingly. 
     The closed-molded RTM translucent FRP samples formed using the above-described method and materials had about 30% fiber content by weight, and the material is therefore sufficiently strong for a variety of applications. Moreover, as can be seen in the photograph of  FIG. 6 , and as will be more fully appreciated by the experiments discussed below, these materials have a high degree of translucency that results in an FRP material having superior level of light transmission and optical quality. 
     The closed-molded RTM translucent FRP material has been found to be particularly suitable for waterslides and architectural fascia and signage. In a waterslide application, a glass fiber pre-form (OCV Uniconform UM2A 1800 from Owens Corning was injected with a clear polyester resin (Ashland Aropol CL 70502-25 clear ISO resin) in a light RTM production process using a vinyl ester matched mold set. Initially, both halves of the mold were coated with a clear gelcoat, and then the glass fiber pre-form was laid on the “A” side (lower half) of the mold. The mold was closed and a vacuum applied (for example, −0.8 bar cavity, −0.9 bar flange). The resin was mixed with an MEKP (methyl ethyl ketone peroxide) initiator at varying ratios depending on the part size and ambient temperature, and was infused under vacuum pressure. The part was then cured (with the cure time varying depending on part size) and the waterslide part was removed from the mold. 
     In a signage or architectural fascia application, closed-molded RTM translucent FRP parts were fabricated using methods similar to the above-described method with respect to waterslide parts. Typically, for architectural parts the resin was injected with a low pump pressure, and was allowed to cure for about 90 minutes. An architectural fascia panel formed in accordance with this method is shown in the photograph of  FIG. 8 . 
     For parts that are intended to be substantially colorless, slight resin discoloration or yellowing due to the curing process can be offset by the addition of a slight blue tint to the resin prior to injection so that the material is tinted throughout its thickness. For example, the tint can be a pigment solution in a glycol carrier with the pigment ratio typically varying from about 1% to 3%, depending on the final color requirements. In one example, 2 mL of tint (a 1% pigment solution) per liter of resin was used to produce clear parts. 
     In some cases, it may be desirable to tint the translucent material, in which case one or more pigments can be added to the resin prior to injection. The particle size of the pigment is important, both for the optical characteristics of the finished part and so that, during the fabrication process, the tinted resin flows through the pre-form without clogging (which would otherwise cause unevenness in the color of the finished part). Preferably pigment particle sizes of not more than about 8 microns are used. This typically enables the tint to disperse evenly throughout the part during the resin infusion stage. A portion of a waterslide formed in accordance with the above-described method and having a blue tint is shown in the photographs of  FIGS. 9A and 9B . 
     Combinations of opaque and tinted or clear areas may be combined in one part to provide special visual or graphic effects depending on end-use requirements. Post-applied paints can also be used to obtain unique appearance features when combined with the translucent base material. Thus, it should be appreciated that closed-molded RTM translucent FRP parts formed in accordance with the above-described method can be used in a variety of applications having different structural and aesthetic requirements. 
     A number of tests and comparative tests were performed to investigate the characteristics and properties of closed-molded RTM translucent FRP materials formed in accordance with the above-described method and materials, and to compare them with FRP materials formed also using substantially transparent resins but in combination with other glass fiber pre-forms and made using other fabrication methods. These test results are included below in EXPERIMENTS 1 and 2. In that regard, EXPERIMENT 1 describes results from a light transmission test performed on samples shown and described with respect to  FIGS. 2 ,  4 , and  6 . EXPERIMENT 2 describes results from an optical quality test performed on samples shown and described with respect to  FIGS. 2 ,  4 , and  6 . It will become apparent from the experiments described below that the closed-molded RTM FRP samples of  FIG. 6  have superior light transmission and optical quality characteristics, and therefore significantly superior translucency, when compared to the open-molded FRP materials shown and described with respect to  FIG. 2  and the closed-molded FRP materials shown and described with respect to  FIG. 4 . 
     Experiment 1 
     Light Transmission 
     The purpose of this experiment was to determine the amount of visible light permitted through FRP samples shown and described with respect to  FIGS. 2 ,  4 , and  6 , as one indicator of the translucency of the materials. Referring to  FIGS. 10 and 11 , a test fixture  60  was developed to measure the light permittivity of the samples. The test fixture  60  consisted of a hollow housing  64 , preferably rectangular-shaped, having a cover (not shown) to enclose the interior chamber. A slot  68  was defined in the center of the fixture  60  that was suitable for slidably receiving a test sample S therein. The slot  68  received the sample S such that it was substantially parallel to the first and second ends of the housing  64 . 
     A first opening  72  was formed in a first end of the housing  64  that was in substantially coaxial alignment with a second opening  76  formed in the second end of the housing  64 . The first opening  72  was sized to receive a light sensor of a visible light transmission and power meter  78  (“VLT meter”). Although other suitable VLT meters may be used, the experiment was conducted with EDTM Model #VP1165. A light meter support  80  was secured to the first end of the housing  64  to support the VLT meter  78  in a substantially horizontal position such that the light sensor of the VLT meter  78  was substantially aligned with the first opening  72 . 
     A light source  84  was aligned with the second opening  76  such that the light from the light source was directed through the opening  76  toward the light sensor of the VLT meter  78 . The light source used in this experiment was a common incandescent projector type light bulb, rated at 100W. The fixture  60  held the sample S, the VLT meter  78 , and the light source  84  at constant distance and angle relative to one other. For instance, in the experiment conducted, the fixture  60  held the sample S 150.4 mm (5.92 inches) from the light source  84  and 150.4 mm (5.92 inches) from the VLT meter  78 . 
     The samples S used in the experiment were samples of materials formed as described above with respect to  FIGS. 2 ,  4 , and  6 . Thus, the samples S tested will be hereinafter referred to as a “ FIG. 2  sample,” a “ FIG. 4  sample,” and a “ FIG. 6  sample.” The samples were of substantially the same thickness, size and shape. 
     To conduct the experiment, the samples S were placed in the slot  68  and light transmission measurements were taken using the VLT meter  78 . The VLT meter  78  measured light transmission as a percentage of the light emitted from the light source  84 . More specifically, the experiment was conducted by carrying out the following steps:
         1) Turning on the light source  84  and VLT meter  78 ;   2) Placing the cover over the opening in the test fixture housing  64  and calibrating the VLT meter  78  following an established calibration procedure for the VLT meter  78 ;   3) Removing the cover, placing the first  FIG. 2  sample into the slot  68 , and replacing the cover;   4) Observing and recording the reading on the VLT meter  78 ;   5) Removing the cover and removing the first  FIG. 2  sample;   6) Replacing the cover and recalibrating the VLT meter  78 ;   7) Loading the second  FIG. 2  sample and replacing the cover;   8) Observing and recording the reading on the light meter;   9) Repeating steps 2 through 8 as desired to test other  FIG. 2  samples;   10) Performing steps 2 through 8 on  FIG. 4  and  FIG. 6  samples.       

     Data was gathered for each of the samples and is tabulated in TABLE 1 below. 
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Average Thickness  
                 % Light 
               
               
                   
                 Sample 
                 (mm)/(inches) 
                 Transmitted 
               
               
                   
                   
               
             
             
               
                   
                 FIG. 2 SAMPLE - 1 
                 4.0150/0.1581 
                 60% 
               
               
                   
                 FIG. 2 SAMPLE - 2 
                 3.9300/0.1547 
                 59% 
               
               
                   
                 FIG. 2 SAMPLE - 3 
                 4.2100/0.1657 
                 61% 
               
               
                   
                 FIG. 2 SAMPLE - 4 
                 4.0900/0.1610 
                 61% 
               
               
                   
                 FIG. 4 SAMPLE - 1 
                 3.1720/0.1249 
                 49% 
               
               
                   
                 FIG. 4 SAMPLE - 2 
                 3.2600/0.1283 
                 47% 
               
               
                   
                 FIG. 6 SAMPLE - 1 
                 3.7775/0.1487 
                 72% 
               
               
                   
                 FIG. 6 SAMPLE - 2 
                 4.2700/0.1681 
                 70% 
               
               
                   
                 FIG. 6 SAMPLE - 3 
                 4.1150/0.1620 
                 73% 
               
               
                   
                 FIG. 6 SAMPLE - 4 
                 3.9275/0.1546 
                 72% 
               
               
                   
                   
               
             
          
         
       
     
     As can be understood by referring to the results shown in TABLE 1, the  FIG. 6  samples transmitted on average 11.5% more light than the  FIG. 2  samples, and the  FIG. 6  samples transmitted on average 23.75% more light than the  FIG. 4  samples. Thus, it can be concluded that the closed-molded RTM translucent FRP materials shown and described with respect to  FIG. 6  consistently allow more light to be transmitted because they have a considerably higher level of translucency. 
     Experiment 2 
     Optical Quality 
     The purpose of this experiment is to further characterize and compare the transparency qualities of the materials by determining the ability to read text through samples shown and described with respect to  FIGS. 2 ,  4 , and  6 . The same nomenclature for the samples ( FIG. 2 ,  4 , or  6  samples) will be used as above for EXPERIMENT 1. Moreover, similar to above, the samples used in this experiment were of substantially the same thickness, size and shape. 
     Referring to  FIG. 12A , a graduated height test fixture  90  was developed to measure the optical qualities of the samples. The test fixture  90  consisted of a base  94  having first and second upright supports  98  and  102  extending upwardly therefrom. A plurality of horizontal slots were defined on the upright supports  98  and  102  by a plurality of opposing protrusions  106  extending from the inner opposing surfaces of the upright supports  98  and  102 . The protrusions  106  were spaced equidistant from one another to define slots increasing in height at one inch increments along the length of the supports  98  and  102 . In the experiment conducted, twelve slots were used at one inch increments. The protrusions  106  defined slots substantially transverse to the upper surface of the base  94  that were configured to slidably receive samples S therein. 
     Referring additionally to  FIG. 12B , a sheet  110  having text printed thereon in a standard font of increasing size was placed on the base  94  such that it was substantially aligned with the sample S when it was received within a slot. The optical quality of the sample S was assessed by placing the sample S at increasing distances (in increments of one inch) away from the sheet  110  to subjectively determine the readability of different sized fonts through the sample S. The printed text on was evaluated at varying distances from the sample S, until the largest text size was not readable. The output of the experiment was to measure the smallest font readable through the sample S, at the greatest distance away from the sample S. The test environment and lighting conditions remained substantially constant throughout the comparative experiment. 
     More specifically, the experiment was conducted as follows:
         1) Placing the sheet  110  in the base  94  of the test fixture  90 ;   2) Placing the sample S into the lowest slot in the test fixture  90 , which effectively placed the sample S directly on the sheet  110 ;   3) Attempting to read the text on the sheet  110  with your chin resting on the top of the fixture  90 ;   4) Moving the sample S up to the next graduation in height and attempting to read the text again;   5) Continuing this process, recording at what height text could no longer be read, for each font size;   6) Performing steps 1 through 6 with all of the samples;   7) Recording observations.       

     Data was gathered for each of the samples and is tabulated in TABLE 2 below. 
     
       
         
               
               
               
               
             
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                   
                 FIGURE 2 SAMPLE 
                 FIGURE 4 SAMPLE 
                 FIGURE 6 SAMPLE 
               
             
          
           
               
                   
                 Text Font Size  
               
             
          
           
               
                 Sample 
                 8 pt 
                 10 pt 
                 12 pt 
                 14 pt 
                 16 pt 
                 8 pt 
                 10 pt 
                 12 pt 
                 14 pt 
                 16 pt 
                 8 pt 
                 10 pt 
                 12 pt  
                 14 pt 
                 16 pt 
               
               
                   
               
             
          
           
               
                  0″ 
                 Y 
                 Y 
                 Y 
                 Y 
                 Y 
                 N 
                 Y 
                 Y 
                 Y 
                 Y 
                 Y 
                 Y 
                 Y 
                 Y 
                 Y 
               
               
                  1″ 
                 N 
                 N 
                 N 
                 N 
                 N 
                 N 
                 N 
                 N 
                 N 
                 N 
                 Y 
                 Y 
                 Y 
                 Y 
                 Y 
               
               
                  2″ 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 Y 
                 Y 
                 Y 
                 Y 
                 Y 
               
               
                  3″ 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 N 
                 N 
                 Y 
                 Y 
                 Y 
               
               
                  4″ 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 N 
                 N 
                 Y 
                 Y 
                 Y 
               
               
                  5″ 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 N 
                 N 
                 N 
                 Y 
                 Y 
               
               
                  6″ 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 N 
                 N 
                 N 
                 Y 
                 Y 
               
               
                  7″ 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 N 
                 N 
                 N 
                 Y 
                 Y 
               
               
                  8″ 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 N 
                 N 
                 N 
                 N 
                 Y 
               
               
                  9″ 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 N 
                 N 
                 N 
                 N 
                 Y 
               
               
                 10″ 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 N 
                 N 
                 N 
                 N 
                 N 
               
               
                 11″ 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 12″ 
               
               
                   
               
               
                 Legend: 
               
               
                 Y = text is readable 
               
               
                 N = text is unreadable 
               
             
          
         
       
     
     As can be appreciated by referring to the results shown in TABLE 2, the  FIG. 6  samples had far greater translucency than the  FIG. 2  and  FIG. 4  samples. At less than a 1″ distance from the sheet  110 , no text was discernable through the  FIG. 2  or  FIG. 4  samples. The  FIG. 4  sample showed the worst optical properties of all, with the smallest font unreadable at a 0″ distance. 
     To illustrate the poor optical qualities of the  FIG. 2  and  FIG. 4  samples, a photograph of a  FIG. 2  sample at a 0″ distance from the sheet  110  (in other words, directly upon sheet  110 ) is shown in  FIG. 13 , where it can be seen that the text is somewhat readable, and a photograph of a  FIG. 2  sample at a 1″ distance from the sheet  110  is shown in  FIG. 14 , where it can be seen that the text is not readable. Similarly, a photograph of a  FIG. 4  sample at a 0″ distance from the sheet  110  (in other words, directly upon sheet  110 ) is shown in  FIG. 15 , where it can be seen that the text is somewhat readable, and a photograph of a  FIG. 4  sample at a 1″ distance from the sheet  110  is shown in  FIG. 16 , where it can be seen that the text is not readable. 
     In contrast, it can be seen by referring to the photograph of  FIG. 17 , which shows a  FIG. 6  sample at a 4″ distance from the sheet  110 , that the text (at least down to a 12 point font size) is still readable through the sample. Thus, although this experiment is rather subjective, the experiment clearly demonstrates that the closed-molded RTM translucent FRP materials shown and described with respect to  FIG. 6  have higher optical qualities and a higher degree of translucency than FRP materials formed also using substantially transparent resins, but in combination with other glass fiber pre-forms and made using different fabrication methods. 
     While illustrative embodiments have been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the present disclosure.