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Amazing diversity

Bayer MaterialScience AG : 24 March, 2005  (Company News)
Bathrooms are increasingly becoming places for relaxation and wellness. As such, the fixtures and fittings of these feel-good oases have to meet high esthetic and technical requirements.
Nowadays, plastic is the material of choice when it comes to manufacturing high-quality bathtubs and shower trays. Plastics not only give designers a lot of freedom, they also meet the high strength requirements that this sanitaryware has to fulfill. Bathtubs are generally manufactured by thermoforming a polymethyl methacrylate (PMMA) or acrylonitrile-butadiene-styrene (ABS) thermoplastic film.

To ensure the molded part has the necessary stability, the reverse side of the thermoformed film has to be reinforced. Till now, this was generally performed using a time-intensive manual process that involved laminating the film with unsaturated polyesters and cut glass fibers. However, the time- and labor-intensive hand lay-up process is not the only downside to this method as it also relies on styrene as a solvent and co-reactant. The value for the maximum workplace concentration of styrene was recently lowered quite considerably.

The Baytec® RS polyurethane system from Bayer MaterialScience AG has been established on the market for ten years and offers a tried-and-tested alternative for reinforcing thermoformed bathtub blanks. With Baytec® RS, the polyurethane mixture is sprayed on to the ABS or PMMA component to be reinforced either by hand or using a robot, thereby eliminating the need for time-intensive manual work and post-curing.

“Baytec® RS, which contains inorganic fillers as strengthening materials, has been renamed and now comes under the umbrella brand of the Multitec® structural spray applications,” says Dr. Marc Schütze, a polyurethanes expert at Bayer MaterialScience. The filler-containing system is now being supplied under the name Multitec® Filler Reinforced Spraying. In addition, Bayer MaterialScience is also offering a new sprayable polyurethane system – Multitec® Short Fiber Spraying – for manufacturers who still rely on glass fiber reinforcement. “The Multitec® series provides us with an extensive range of versatile materials for the cost-effective and environmentally friendly production of large plastic components,” says Dr. Schütze.

Among the companies already using Multitec® Short Fiber Spraying and Multitec® Filler Reinforced Spraying is Formtec Kunststoffe GmbH & Co. KG of Dornstetten, Germany, which manufactures bathtubs under contract. Formtec recognized the exceptional benefits of polyurethane spray coating for thermoformed acrylic bathtubs some years ago and is now in a position to offer customers the most cost-effective and creative solution by using both Multitec® variants.

The reinforced coating is achieved with Multitec® Short Fiber Spraying by spraying a quick-curing polyurethane to the reverse side of the thermoformed sheets at room temperature. This polyurethane typically comprises an isocyanate and two polyols, with a foam additive being optional. “By modifying the type and quantity of these components, the molded part can be given a variable structure by combining solid, glass fiber-reinforced and foamed layers,” says Dr. Schütze. “This efficient process enables the characteristics of the molded part to be varied for different customers and requirements.”

Traditional production methods generally require the molded part to be post-cured at high temperature following manual production so as to ensure the unsaturated polyester resin cures completely. This process is both energy- and time-intensive: it takes between two and three hours to manufacture a complete bathtub or shower tray. The Multitec® Short Fiber Spraying System on the other hand requires just three to five minutes to cure at room temperature. This cuts the time taken to produce bathtubs to just twenty or so minutes. The polyurethane spray system can also be processed with the aid of a robot, thereby improving productivity and reproducibility – both important criteria for ensuring the quality of the molded part.
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