Blending equipment materials considerations

Recently, there has been considerable interest in soft-touch materials composed of thermoplastic and mbber blends. These materials when over-molded on hard or stiff stmctures such as hand tools, domestic appliances, writing gadgets, cellular phones, photographic equipments, etc. provide soft and comfortable feeling to the hand. 

In addition to lower capital outlay, dry-blending requires considerably less processing energy. Final product density, which is usually near unity, depends on the density of the starting materials and the nature of equipment used to blend these materials. Modern mixing and blending equipment, if properly controlled, can give product density and particle sizes comparable to spray-dried products. 

Choice of materials, as in any process, is a major consideration. Most resin suppliers and equipment vendors have laboratory to pilot-scale equipment that can screen various resins. Blends of similar resins can also be useful in obtaining greater orientation in the blown film process (9). 

Equipment costs vary widely hut are considerably lower than for comparable injection-molded parts because of the relatively low pressures and temperatures required. Highly automated machines use roll-fed stock. Residual material from trimming can be ground, blended with virgin material, and re-extruded into sheet for subsequent thermoforming use. 

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