BACKGROUND OF THE INVENTION

l. Field of the Invention

This invention relates to a polyester backed acrylic composite molded structure. More particularly, it relates to a composite structure having a polyester polymeric backing material applied during a molding process to an acrylic shell for manufacturing of lightweight durable articles such as sanitary fixtures including bathtubs, sinks, shower receptors, lavatories and the like which are a lightweight, and resist damage and delamination when subjected to impact, the weight of the user and thermal shock.

2. Background of the Related Art

In the development of bathroom and kitchen fixtures, as well as bathtubs, whirlpool tubs and other composite articles, the traditional porcelain-cast iron fixtures have gradually been replaced by lighter and more resilient composite structures. One of the difficulties with the porcelain-cast iron and enameled fixtures has been their susceptibility impact damage and extreme weight which causes great difficulties in moving and installing large fixtures such as sinks, bathtubs and whirlpool tubs. The porcelain-cast iron and enameled fixtures did have the advantage of having a very solid feel and a high weight bearing capability.

Initial attempts by the industry to replace these porcelain-cast iron fixtures proved difficult. The early composite structures had a plastic, hollow feel and would deform, crack, chip or delaminate when subjected to impact, thermal shock, or the weight of the typical bather. Also, these composite structures would often delaminate, crack, craze or chip when subjected to impact from the outside of the structure during manufacturing, transportation and installation of the fixture.

A successful solution to these problems is disclosed in U.S. Patent No. 4,664,982 to Genovese et al., and in U.S. Patent Application Serial No. 07/400,289 to Kuszaj et al., the disclosure of both of these documents are incorporated by reference herein. Both disclose composite enamelled steel or stainless steel fixtures which have the look and feel of the earlier porcelain-cast iron fixtures. The structures are light, have high structural strength, and resist delamination, chipping and denting due to impact or thermal shock. The composite structures are formed from a steel or stainless steel which may be enamelled on one or both of its faces. The excellent physical and mechanical properties are imparted to these shells as a result of the chemical bonding of a plastic layer to a non-finish side of the shell. The preferred plastic layer is an isocyanate-modified thermosetting unsaturated polyester or polyether foam which is introduced into a mold containing the shell by Reaction Injection Molding (RIM), or by reinforced reaction injection molding ("RRIM") processing. The foamed plastic is chemically bonded to the shell by the action of silane, a coupling agent which creates chemical linkages between the metallic groups or the SiOH groups in the enamel and the reinforced foamed plastic to form the laminate. These composite structures possess excellent physical and mechanical properties as a result of the chemical bonding of the reinforced foamed polymeric layer to the enamel steel or stainless steel shell. These

disclosures do not relate, however, to the manufacture of a composite structure in which an acrylic layer is bonded to a polymeric or plastic molded structure. Additionally, these reaction molding processes are carried out under high pressures and require a large and expensive hydraulic press to keep the mold closed and prevent the escape of the reacting polymeric foam during the molding process. Although these molding procedures result in a very fast cure time, the equipment required, such as the hydraulic mold press is expensive, requiring a high capital investment.

Another solution to these problems was the use of a polymeric, cosmetic surface layer bonded directly to a foamed plastic substrate, described as a cross-linked isocyanate-modified thermosetting unsaturated polyester or polyether resin layer to provide a high impact strength, delamination-resistant structure. These structures and their process of manufacture are disclosed in U.S. Patent Nos. 4,844,944 and 4,844,955 both to Graefe et al., the disclosure of which is incorporated by reference herein. Methylmethacrylate and commercially available adhesive Thixon 416, manufactured by hittaker Corp., West Alexandria, Ohio, which contains a blend of 65% solvents, 35% solids including polyurethane phenolic and epoxy resins, was used as a primer to cross-link and chemically bond the polymeric cosmetic layer to the isocyanate groups in the foamed plastic while plastic is cured. The isocyanate was provided in the foamed plastic to provide a very fast cure of the plastic layer during RIM, or RRIM molding. These reaction molding processes are carried out under high pressures and require a large and expensive hydraulic press to keep the mold closed and prevent the escape of the reacting polymeric foam during the molding process. Although these molding procedures result in a very fast cure time, the equipment required, such as the hydraulic mold press is expensive, requiring a high capital investment.

Accordingly, a feature of the present invention is to provide a polyester backed acrylic composite molded structure which has a solid feel and sound of the porcelain-coated cast iron and enameled fixtures without the weight and delamination problems associated with such structures.

Another feature of the present invention to provide a polyester backed acrylic composite molded structure which can be molded under low pressures without the need for expensive hydraulic mold press which is needed for RIM or RRIM molding.

SUMMARY OF THE INVENTION

These and other features are achieved by the present invention which provides a polymeric composite structure, preferably formed in the configuration of a bathtub and a method manufacturing such composite structure. The polymeric composite strucutre includes a polymeric shell layer, preferably made from a thermoformable acrylic polymer of polymethylmethacrylate having a finish-side and a non-finish side. A fiber reinforced resin layer which may include a layer of fibers such as fiberglass, carbon, ceramic, boron, graphite, woolastonite, aromatic polya ide and mixtures of these fibers adhered to the non-finish side of the acrylic shell. Preferably such layers are made of chopped fiberglass in a resinous backing. A weight bearing reinforcing structure is adhered to the non-finish side of the shell and to the fiber reinforced resin layer. This weight bearing reinforcing strucutre can include wood, such as chip-board, particle-board, plywood and wooden planks or it may include a polymeric composite or inorganic weight bearing structures. Preferably, the weight bearing structure is a rectangular wooden structure made from chip-board placed below the floor portion of the bathtub. Additionally, a plurality of reinforcing wooden planks are placed below the deck portion of the shell of the tub.

Preferably, the non-finish side of the shell is bonded to the fiber reinforcing layer by a silane based coupler which is made from a silane based primer and a methylmethacrylate and solvent blend. The methylmethacrylate and solvent blend preferably includes methylene chloride, styrene and water, while the silane based primer composition suitably includes 3[2(vinyl benzylamino)ethylamino] propyltri ethoxy silane dissolved in a solution of toluene, butanol, 2-butoxy ethyanol and ethyl alcohol.

The polymeric composite also includes a molded, cross-linked thermosetting polymeric backing layer which surrounds the fiber reinforcing resin layer and the weight bearing reinforcing structure. The cross-linked thermosetting polymeric layer is bonded to the non-finish side of the polymeric shell and includes at least one of the following components: polyester, epoxy, acrylic, or vinyl esters, alone or blended in combination, but does not contain isocyonate. Preferably, this cross-linked thermosetting backing, prior to curing includes a rigid unsaturated polyester resin, flexible unsaturated polyester resin, a curing promoter, a peroxide cross- linking promoter and a filler in a ratio from about 2:1 resin to filler to about a 1:30 resin to filler. The filler may include calcium carbonate, aluminum trihydrate, glass spheres, sand, ceramic, mica, talc, silica, and mixtures containing one or more of these fillers.

The polymeric composite structure, preferably formed in the shape of the bathtub, is manufatured by a process of the present invention. The manufacturing process includes forming a polymeric shell, preferably a thermoformable acrylic shell of polymethylmethacrylate, to a suitable shape such as the configuration of a bathtub. The non-finish side of the polymeric shell is preferably primed with the above-described silane based coupler. The primed (or unprimed) polymeric shell is then reinforced on its non-finish side with a resinous mixture of reinforcing fibers by suitable spray-up and roll down, or by other suitable techniques. After the reinforced shell has sufficiently cured, the shell is arranged in a mold with the non-finish side covering a weight bearing reinforcing structure, such as chip-board, placed below the weight bearing portion of the shell, for instance, the floor of the tub. Other reinforcing structures such as wooden boards may be placed below the deck of the shell. An uncured mixture of unsaturated thermosetting polymeric

backing material and cross-linking promoter, as described above, is injected into the mold at a sufficient pressure to force the backing material to coat the non-finish side of the shell and cover the fiber reinforcing material and the weight bearing reinforcing structures. The molded thermosetting polymeric backing material is cured at suitable temperatures and for a sufficient time to allow hardening and cross-linking of the thermosetting material and bonding of the fiber reinforcing layer structural reinforcing non-finish side of the shell. After sufficient curing, the composite structure is removed from the mold for trimming.

In an alternative embodiment of this manufacturing process, the polymeric shell, preferably primed (or unprimed) is arranged in the molding cavity with the non- finish side covering a fiberous reinforcement, such as a fiberglass or other fiberous mat. An additional fiberglass mat may be, preferably, placed between the weight bearing reinforcing structure, such as the chip¬ board, and the floor of the bathtub. The thermosetting polymeric material is injected into the mold, coating the non-finish side of the shell and embedding the fiberous mat and the weight bearing board to bond these reinforcing and weight bearing materials to the non-finish side of the shell. It is also contemplated that the fiberous reinforcing material such as fiberglass mat may be inserted as a preformed fiberous structure made by a thermoforming process, or the spray-up of fiberglass and resin onto a suitably shaped screen.

For better understanding of the present invention, references made to the following description, taken in conjunction with the figures, the scope of which is pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic partial perspective cross- sectional view illustrating the preferred polyester backed acrylic composite bathtub of the present invention.

Figure 2 is a schematic flow chart illustrating the low pressure resin transfer molding apparatus used to carry out the molding process of the present invention.

Figure 3 is a top perspective view of the preferred molding receptacle in accordance with the present invention.

Figure 4 is a perspective view of the mold according to the present invention shown in the open position, illustrating the molding receptacle, shell support and mold closing means of the present invention.

Figure 5A shows the non-finish side of the acrylic shell of the present invention; and

Figure 5B shows the non-finish side of the acrylic shell of the present invention after the application of fiberglass spray-up reinforcement.

Figure 6 shows the freshly demolded polyester backed acrylic composite bathtub of the present invention positioned on a trimming table with a horizontally oriented circular saw for trimming excess polyester backing produced during the molding process, shown with blind bolts in place.

Figures 7A, 7B and 7C are orthogonal views of the trimmed polyester backed acrylic composite bathtub of the present invention, shown without the blind bolts in place.

DETAILED DESCRIPTION OF THE INVENTION

The polyester backed acrylic composite molded structure according to the present invention, preferably molded in the configuration of a bathtub .10 is illustrated in Figure 1. Bathtub JLO includes a polymeric shell, preferably a thermoformable shell, most preferably an acrylic shell 12 having a polished finish side 20 which is normally exposed to the user. The shell 12 also includes a non-finish side 21 which is bonded to molded thermosetting polymeric backing which does not contain isocyonate, preferably a blended polyester backing material 14. Additionally a fiberglass, graphite fiber, carbon fiber, boron fiber, ceramic fiber, woolastonite fiber, aromatic polyamide fiber or similar reinforcing material (not shown) is preferably attached by spray-up prior to molding. Alternatively, the fiber reinforcing material is molded to the acrylic shell 12 by the polyester backing material 14 during the molding process. A floor reinforcing means 16 preferably made of chip¬ board, particle-board or plywood is molded into the polyester backing 14 below the acrylic shell 12 under the floor of the bathtub 10. Preferably, deck supporting means 18, such as wooden boards are molded under the deck area of the acrylic shell 12 within the polyester backing 14. In an especially preferred embodiment blind bolts 22 are placed, after the molding process has been completed, through a portion of the molded polyester backing material 14 and into the floor reinforcing means 16. Feet 24 are attached to the blind bolts 22 for supporting the weight of the tub, user and water during bathing.

A schematic flow chart illustrating the preferred low pressure resin transfer molding (LPRTM) apparatus 25. suitable for carrying out the molding process of the present invention is shown in Figure 2. The molding apparatus 2J5 includes a mixer 26, such as a 110 gallon capacity NAUTA mixer manufactured by Daymixing Corp. ,

Cincinnati, Ohio. The uncured, mixed polyester and filler backing material is transferred from mixer 26 to a pressure pot liner 28 which suitably fits within a pressure pot 29, Model No. QM 5744 both of which are manufactured by Devilbiss Corp., Toledo, Ohio. After the addition of cross-linking promoter, the pressure pot 29 is closed and compressed air 30 is pumped into the pressure pot 29. Once pressure pot 29 is sufficiently charged, throttle valve 32 is opened allowing the compressed air to force the uncured polyester and filler mixture through polymer delivery hose 34 and into the mold 3_6. Preferably polymer delivery hose 34 is a flexible PVC hose having a one (1") inch diameter which is disposed of and replaced following the molding process. Mold 3_6 preferably includes a molding receptacle 38, shown in Figure 3 made from cast aluminum having a cavity for receiving the acrylic shell 12, leaving a molding space between the non- finish side 21 of acrylic shell 12 and an interior face 44 of the molding receptacle 38.

As illustrated in Figure 3, molding receptacle 38 is preferably made from a good heat dissipating material, such as cast aluminum and has a relatively smooth interior face 44 for forming the shape of the polyester backing 14. Preferably, molding receptacle 38 also includes a water jacket 45 or other temperature regulating means for maintaining the mold 3_6 at a desired temperature (see Figure 4) . The uncured polyester backing and filler mixture is introduced into the molding receptacle from polymer delivery hose 34 into a molding aperture 46 which is located approximately in the geometric center of a portion of the molding receptacle 38 for molding the tub floor. As shown in Figure 3, the interior face 44 of the molding receptacle 38 includes a rectangular indentation 48 of suitable dimension to retain a tub floor reinforcement 16, preferably a rectangular piece of chip¬ board, or alternatively particle-board, plywood, wooden plank, fiberboard or a composite, plastic, fiberglass or

other suitable weight bearing structural reinforcing material. The molding receptacle may suitably also include positioners or slots (not shown) for retaining deck supports 18, which preferably include wooden reinforcing 1" by 1" boards illustrated in Figure 1.

Due to the low pressure molding process utilized in the present invention, mold seals are not required, and in fact may impede the flow of the uncured polyester resin and filler mix into the cavity formed between the non- finish side 21 of the acrylic shell 12 and the interior face 40 of the molding receptacle 38. Due to the absence of mold seals, there is some spillover of polyester backing material 14 and adherence of the hardened backing material to portions of the molding receptacle 38 due to the molding and curing process. Accordingly, hydraulic lifters are not ordinarily utilized. Rather, after the polyester backing 14 is sufficiently cured the molded tub is loosened or cut from the molding receptacle 38 and removed by hand.

The mold 3_6_ also includes a shell support and mold closing means 40 which maintains the shape of the thin acrylic shell 12 during the molding process, and holds the acrylic shell in proper orientation within the molding receptacle 38. The mold may be kept closed by any suitable means, however, due to the low molding and curing pressures, an expensive hydraulic mold press which is required in RIM and RRIM molding, although useful, is not required. Rather four C clamps 42, rated at 500 lbs. each, are entirely satisfactory for keeping mold 3_6 closed during the molding and curing process.

The mold 3_6 as viewed in the open position is illustrated in greater detail in Figure 4, showing the molding receptacle 38, and shell support and mold closing means 40 suitably held above the molding receptacle by a mold opening and lifting means, such as a chain hoist 50.

As well known by those skilled in the art other mold opening and closing means such as a pivoting or levered systems, electro-mechanical or hydraulic mold clamps may be suitably utilized to carry out the molding process of the present invention instead of the chain hoist 50 and clamps 42.

The shell support and mold closing means 40 shown in Fig. 4 is typically made of a cast aluminum core 52 which is coated with a urethane skin 54 which matches the shape and supports the finish side 20 of the acrylic shell 12, without scratching or otherwise damaging the polished finish. Teflon strips 56, or other non-abrasive materials are included around the periphery of the urethane skin 52 for contacting and urging a deck portion of the shell 12 towards the molding receptacle 38 during the molding process without causing damage to the finish side 22 of deck portion of shell 12. A detailed description of other suitable molding apparatus which may be adapted for use with the present invention is described and commonly assigned co-pending U.S. Patent Application Serial No. 07/467,384 filed January 19, 1990 the disclosure of which is incorporated by reference herein.

In accordance with the process of the present invention acrylic shell 12 is formed from a cell cast acrylic sheet preferably made from polymeth lmethacrylate which has a highly polished finish side and a non-finish side. The shell preferably has a thickness of approximately 3.2 millimeters. The acrylic sheet may be made from other materials such as those described in United States Patent Nos. 4,844,955 and 4,844,944 the disclosure of which is incorporated by reference herein. The acrylic sheet is thermoformed using well known vacuum thermoforming apparatus into the desired shape of the acrylic shell 12 which is illustrated in Figure 5A.

The thermoformed acrylic shell 12 is preferably treated on its non-finish side 21 with a bonding primer composition. One suitable primer composition includes a silane based primer AP-134, manufactured by Lord Corp. in Erie, Pennsylvania. It contains a silane compound at a 10% concentration in a solvent of 75% toluene, 5% butanol, 5% 2-butoxy ethanol and 5% ethyl alcohol. A suitable silane compound is 3[2(vinyl benzylamino)ethylamino] propyltrimethoxy silane at a preferred 10% concentration, although the concentration of this silane compound may range from about 1% to about 20%, preferably from about 5% to about 15%. The silane primer AP-134 is most preferably mixed at a 1% concentration by weight with 1% water, 9.8% styrene, 29.4% methylene chloride and 58.8% methylmethacrylate. The concentration of these components may range from about 0.1% to 10%, preferably from about 0.5% to about 2% silane primer such as AP-134; from about 0.1% to about 10%, preferably from about 0.5% to about 2.0% water; from about 0.1% to about 98%, preferably from about 5% to about 15%, styrene; from about 2.5% to about 98%, preferably from about 25% to about 35% methylene chloride; and from about 98% to about 5%, preferably from about 70% to about 40% methylmethacrylate. This primer solution promotes cross-linking and improves bonding between the polyester reinforced backing and the non- finish side 21 of the acrylic shell. Other compositions useful as bonding primer solutions are described in the above-referenced U.S. Patent Nos. 4,844,955 and 4,844,944 to Graefe et al. The purpose of the primer is improve bonding to the acrylic shell 12 allowing for faster demolding times. However, if the demolding times are increased, or if sufficient bonding occurs during the spray up reinforcing step, the bonding primer is not required.

The thermoformed and preferably primed acrylic shell is reinforced with a resinous mixture of fiberous material, including chopped fiberglass, ceramic fibers,

boron fibers, graphite or carbon fibers, woolastonite fibers, or aromatic polyamide fibers. Preferably, the reinforcing materials include a sprayed on and rolled out mixture of chopped fiberglass from about 10% to about 40%, preferably from about 15% to about 35%, and most preferably about 30% by weight; and polyester resin from about 60% to about 90%, preferably from about 85% to about 75%, and most preferably about 70% by weight. The sprayed on fiberglass is typically designated as fiberglass reinforced plastic (FRP) or glass reinforced plastic (GRP) . The polyester resin preferably includes a mixture of a rigid unsaturated polyester resin and styrene monomer designated 31-439 by the Reichold Corp. ; and may also include a flexible unsaturated resin designated 97- 088 by Reichold Corp. and a styrene monomer. The polyester resin is combined with a curing or cross-linking promoter containing from about 0.01% to about 1%, preferably from about 0.05% to about 0.5%, most preferably about 0.2% cobalt naphthanate; and from about 0.1% to about 5%, preferably from about 0.5 to about 3%, most preferably about 1% methyl ethyl ketone peroxide, percentages based on weight of resin only. The resin and chopped fiberglass mixture is typically applied by suitable spray equipment such as Venus Model HI SSCW 2100 manufactured by Venus-Gusmer Corp. , Kent, Washington. After curing for approximately one hour, the reinforced acrylic shell 58 illustrated in Figure 5B is placed in the molding receptacle 38 with reinforcing weight bearing structures 16 and 18 placed below the tub floor and deck regions, respectively.

In an alternative embodiment, the acrylic shell 12, preferably primed as described above, is reinforced with a matted or woven fiberous reinforcing material, as described above, preferably a 1 & 1/2 ounce (per square foot) fiberglass mat. The fiberous reinforcing material is placed inside the molding receptor, preferably below the weight bearing floor supporting board 16, and another

fiber reinforcing mat is placed above the reinforcing board 16 and below the floor of shell 12. The fiberglass or similar mat of fiberous reinforcing material is adhered to the acrylic shell 12 during the molding step. A further alternative is that the fiberous reinforcing material is preformed prior to the molding step and placed as a single unit inside the molding receptacle 38 prior to the placement of the reinforcing board 16 and acrylic shell 12 within the molding receptacle 38. Preforming of the fiberglass reinforcing material may be obtained using thermoformable fiberglass and plastic composite or similar fibrorous composite which is shaped using thermoforming techniques which are well known to those skilled in the art. Alternatively, preforming may be accomplished by spray-up of a resinous mixture of chopped fiberglass or other fibers onto a shaped mesh or screen by known techniques.

After the acrylic shell has been suitably arranged within the molding receptor, the mold 3_6 is closed by placing the urethane coated surface 54 and TEFLON strips

56 of the shell support and mold closing means 40 in suitable contact with the finish-side 21 of the acrylic shell 12. The mold is suitably clamped to provide sufficient venting by four heavy duty C clamps 42 to secure the shell support and mold closing means to the molding receptacle 38. After the mold has been secured and properly vented, the temperature of the mold is stabilized between 100° and 120° F using a water jacket 45 in the molding receptacle 38.

The low pressure resin transfer molding (LPRTM) process suitable for the present invention is described below, however, other low pressure injection, gravity casting or displacement molding processes may also be suitably adapted for use in the present invention. The preferred resin, filler and catalyst formulation is described below.

Typically, approximately 100 lbs. of material is mixed in mixer 26, thus the percentages are based on weight. The most preferred polyester resin and filler formulation includes rigid unsaturated polyester resin and styrene monomer, sold under the name Reichhold 31-439, 35.20%; flexible unsaturated polyester resin and styrene monomer sold under the name Reichhold 97-088, 11.90%; styrene monomer, 2.48%; calcium carbonate (filler), sold under the name Vicron 15-15, 49.6%; dimethylparatoluidene (DMPT) (activator/promoter), 0.6%; benzoyl peroxide, sold under the name Cadox 40 E (40% benzyl peroxide solution) , 0.76%. Suitable ranges of this preferred combination of materials include from about 0% to about 98%, preferably from about 25% to about 45% Reichnold 31-439; from about 98% to about 0%, preferably from about 20% to about 5% Reichnold 97-088; from about 0% to about 40%, preferably from about 1% to about 10% styrene; from about 0% to about 75% , preferably from about 40% to about 60% Vicron 15-15; from about 0.05% to about 5%, preferably from about 0.2% to about 1% DMPT; and from about 0.05% to about 5%, preferably from about 0.2% to about 2% Cadox 40E.

Depending on the type of filler used, the ratio of resin to filler may range from no filler at all, or it may be as high as 1:30, depending upon the filler particle size. Preferably the ratio of resin to filler may be from about 2:1 to about 1:3. Other fillers may be added in addition to or instead of calcium carbonate, including aluminum trihydrate, glass spheres, sand, ceramic, mica, talc, silica and other suitable filling materials.

Various other fillers are described in U.S. Patent Nos.

4,844,955 and 4,844,944 to Graefe et al. which are incorporated by reference herein. The preferred polyester resin mixture is not foamed, although foaming agents may be utilized to decrese the weight of the molded composite article. Additionally, other polyester blends may be used with additional fillers, foaming agents and other

catalysts without departing from the scope of the present invention, as long as these resin and catalyst formulations have a sufficiently long cure time to allow low pressure molding of the molded article of present invention. The use of isocyanate in the resin system is undesirable since such compounds speed up the curing process to such an extent that high pressure and high speed molding processes would be needed, such as RIM or RRIM, requiring use of the expensive RRIM or RIM high pressure molding apparatus.

Other suitable thermosetting polymeric materials can include epoxy, acrylic and vinyl esters and blends thereof which do not contain isocyanate. Additional useful resin compositions suitable for the present invention are also described in the aforementioned U.S. Patent Nos. 4,844,944 and 4,844,955 to Graefe et al.

In preparing the preferred polyester resin of the present invention, the rigid unsaturated polyester and flexible unsaturated polyester resins are mixed in mixer 26 and the styrene monomer is then added. DMPT is also added and thoroughly mixed, and the filler material, such as calcium carbonate is then mixed typically for about 45 to 1 & 1/2 hours. One hundred (100) pounds of the material is then dispensed into the lined pressure pot 29. Approximately 3/4 pounds of benzoyl peroxide (CADOX 40E) cross-linking promoter is added and mixed for about one minute. The pressure pot 29 is closed and pressurized by compressed air source 30 to about 5 psi. Throttle valve 32 is opened and the air pressure to the pressure pot 29 is increased to about 10 psi. The air pressure is continuously increased by approximately 5 psi at one minute intervals up to a pressure of from about 20 to about 25 psi, the pressure is maintained for about 5 to 8 minutes until the mold is filled. After the mold is filled and some resin mixture spills, the throttle valve is closed and the clamps are tightened to seal the mold.

The molded article is then cured. Curing time after the mold is filled for the above-described mixture is approximately for about 2 minutes to about 22 minutes, preferably from about 2 minutes to about 6 minutes, but it may be maintained in the mold for longer times. If the silane based primer is not utilized, curing may range from about forty-five (45) minutes to about 8 or more hours when cured overnight. The longer cure times allow a stronger bond to be formed between the polyester resin and the non-finish side 21 of the acrylic shell. After curing has been completed, the mold 3J5 is opened and the shell support mold closing means is removed. Any overflow of hardened polyester resin adhering to the outside of the molding receptacle 38 is cut away and the molded bathtub JLQ. is removed by hand from the molding receptacle 38.

The freshly demolded bathtub JLO, is trimmed of excess polyester hardened backing material 14 using suitable equipment. Suitable trimming equipment may include the trimming table 60 and horizontally mounted circular saw 62 shown in Figure 6. The finished polyester backed composite bathtub ljO of the present invention is shown in Figure 7A through 7C. Blind Bolts 22 and feet 24, illustrated in Figures 1 and 6 are inserted on the bottom surface of the bathtub through the molded polyester backing 14 and into deck supporting board 18.

In a preferred embodiment of the present invention the acrylic shell 12 has a thickness of about 3.2 millimeters while the fiber reinforcement is typically from about 1.0 to 2.0 millimeters measured from the non- finish side 21 of the shell. Typically the total thickness of the molded bathtub is about 8 to 10 millimeters in the side wall region and 20-25 millimeters on the floor region. The total thickness of the deck region may range from about 5 millimeters to about 35 millimeters, preferably from about 8 millimeters to about 30 millimeters. The thickness of the polyester molded

material in the walls is typically from about 4.4 to about 7 millimeters. The preferred tub floor support weight bearing reinforcing structure is typically made from chip¬ board, particle-board, plywood or wooden plank having a preferred thickness of about 7/16 inches, but may range from about 1/4 inch to about 1/2 half of an inch in thickness, depending on the desired thickness of the floor of the molded article and its underlying backing. The preferred deck supports are typically 1 inch x 1 inch wooden boards as illustrated in Figure 1.

Thus, while we have described what are the presently contemplated preferred embodiments of the present invention, further changes and modifications may be made by those skilled in the art without departing from the scope of the invention, and it is contemplated to claim all such changes and modifications.