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/m2 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.
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