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Cost-effective manufacturing process combines spraying and foaming

Bayer MaterialScience AG : 28 March, 2006  (Company News)
By applying a tailor-made skin of high-grip Baytec Reactive polyurethane spray-on elastomer directly during manufacture, there is no need to cover the foam with watertight film post-manufacture. The viscoelastic Bayfit padding still remains permanently sealed.
In recent years, viscoelastic foams have added another powerful variant to the broad range of standard- and high-resilience grades in the field of molded foams. Bayer MaterialScience AG, the market leader in polyurethane raw materials, is once again extending the range of application for these “memory foams” by intelligently combining a high-quality VE foam from the Bayfit program with Baytec Reactive, the easy-to-apply, plasticizer-free and yet highly elastic polyurethane spray-on elastomer. Combining these two high-tech materials has resulted in VE foams that combine the superior qualities of a viscoelastic product with a particularly stable, watertight surface.

“Viscoelastic foams are currently in the process of conquering more and more new areas of application,” says Dr. Dagmar Ulbrich, an expert in flexible molded foam at Bayer MaterialScience. “They show a smaller increase in force at higher deformations than corresponding HR foams and adjust superbly to every contour. This means that the weight of a body resting on it is distributed over the largest possible area. The innovative VE foams have therefore recently found use in high quality furniture for homes, offices and public areas, where they provide improved grip and a pleasing ‘wow factor’ when people sit down. However, mattresses and pillows remain an important area of application for Bayfit MEMORY foams.”

In many areas, the material’s properties include not only its excellent pressure release but also its optimized surface properties. “Up to now, waterproof shells made of PVC were applied to the foams post-production to protect them from contact with liquids, for example. However, large amounts of plasticizers must be added to these shells if they are even to come close to the elasticity of the viscoelastic core. By applying a tailor-made skin of high-grip Baytec Reactive polyurethane spray-on elastomer directly during manufacture, it is possible to permanently seal the viscoelastic Bayfit padding without later having to cover the foam with the vulnerable film,” says Ulbrich. “The customer is also spared the problems arising from gradual embrittlement.”

All that is required to produce the long-life foam/spray-on skin composite is to spray the filler-free Baytec elastomer into an open mold, possibly using robots. “The material’s special thixotropic formulation prevents it from running down the upright faces of the mold, enabling end products to assume complex geometries too,” says Dr. Marc Schütze, a polyurethane spray systems expert. The high mixing viscosity is achieved without compromising the reactivity of the reactive mixture. If particularly robust zones are required, the thickness of the spray-on skin can be varied between 0.2 and a few millimeters - even within one and the same product. The skin’s final hardness can generally be set between extra soft (35 Shore A) and extra hard (60 Shore D). Favorable isocyanate/polyol mixing conditions that are largely unaffected by mixing ratios in the dosing unit also make for a low-waste production process.

Once the spray-on skin has been applied, a liquid mixture of polyurethane raw materials is inserted into the mold, and viscoelastic Bayfit MEMORY foam with optimal cell size distribution is produced in the ensuing reaction. Alternatively, elastic grades from the Bayfit product range can also be used for back-filling. In all cases, the result of this reaction is a foam/elastomer composite in which the core is sealed against air and moisture, and is responsive to all the user’s movements. A combination with a colorfast in-mold coating as an additional top layer is also possible in the same production process.

“Truly high-tech materials like Bayfit and Baytec enable customers to benefit from the polyurethane expertise we as raw material manufacturers and our partners in the polyurethane industry have honed over decades working with this versatile family of plastics,” states Schütze. “We’ll be showcasing this innovative combination of materials at JEC 2006 in Paris. We hope to see further applications for watertight padding in the future, e.g. outdoors in areas such as gardening or camping.”
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