REINFORCED SHOWER TRAYS AND BATHTUBS
15 June 2004 - Bayer MaterialScience AG

The versatile group of polyurethanes plays a key role in converting the "wet cell" to a pleasurable oasis, even though they are not always visible. In many applications they take a back seat, but are nevertheless instrumental in providing the customary comfort of a bath. One example of their use is in the stabilization of bathtubs and shower trays made of thermoformed thermoplastics.

A new sprayable polyurethane system with the name Multitec® Short Fiber Spraying, recently introduced by Bayer MaterialScience AG, now supplements the existing range of filled reinforcing materials. Because of its glass fiber reinforcement, Multitec® Short Fiber Spraying can absorb considerable forces and ensures dimensional stability on a lasting basis. The new sprayable system has found an interesting application in, for example, Duscholux® shower trays from the well-known Luxembourg specialist, Belaton SA, Sandweiler.

"Nowadays, the usual way to manufacture tough but attractive shower trays is to reinforce a high-grade thermoformed thermoplastic film by applying a suitable material on the back," says Dr. Marc Schütze, a polyurethane specialist with Bayer MaterialScience. This reinforcement is absolutely essential, because a PMMA film, which is only a few millimeters thick after thermoforming, will find it very difficult indeed to bear the weight of an adult without changing shape. "Shower trays must, however, have good shape retention under high concentrated loads – and also, of course, under heat," says Dr. Schütze.

To guarantee this stability, many manufacturers still opt for the complicated hand lay-up process with glass fiber-reinforced polyesters (GRP), which need styrene as a solvent and co-reactant. "However, this technology could almost be described as antiquated today," says Schütze. The production of a single shower tray or bathtub using these manual techniques can take up to one hour. Following the manual production step, the product then has to be subjected to an energy- and time-consuming annealing process so that the unsaturated polyester resin can cure completely.

Modern polyurethane chemistry offers a major advantage in this respect. With its sprayable Multitec® Short Fiber Spraying system, Bayer MaterialScience has developed a future-oriented GRP alternative that also relies on glass fiber reinforcement. The new polyurethane system has a property level comparable with the GRP polyester resins, but is both economically and ecologically superior. The process involves the production of a reinforcing layer by spraying a fast-curing polyurethane at room temperature – possibly by a robot – onto the back of the thermoformed film. With this efficient process, the properties of the molded part can be varied to suit the customer's requirements and the specific application. Layers with or without glass fibers, solid or cellular, can be produced individually, seamlessly and in a single process.

"In the case of the Duscholux® shower trays, the outstanding material properties of the Multitec® Short Fiber Spraying coat result from the addition of glass fibers to the jet of polyurethane material immediately it leaves the spray head. This makes the new system an environmentally friendly, sprayable GRP alternative, adding another particularly economical variant to the existing polyurethane spray systems. Nor is it in any way inferior to conventional reinforcing systems as far as its processing speed is concerned.

The excellent properties of the coating are attained immediately the polyurethane cures, in other words less than 15 minutes after the Multitec® reaction mix has been produced. Nor is there any need for an annealing process with this method, "making production of the high-quality shower tray up to five times faster than the conventional manual method of GRP hand lay-up," says Dr. Schütze. "Consequently, attractively designed sanitary furniture now goes hand in hand with efficient, ecological production."

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