Properties of Urea & Melamine Formaldehyde

These thermoset materials give a unique combination of moulded properties which are unmatched by any other plastic raw materials in the same price range making them ideal for a wide range of applications, particularly in the domestic field. Of significant importance is their ability to not soften or melt on heating as thermoplastics do, this being a result of irreversible cross linking of the polymer that takes place during the moulding process (compression or injection) under conditions of heat or pressure.

Urea formaldehyde (UF) materials combine a virtually unlimited range of colours and excellent colour retention with good electrical properties, solvent resistance, high resistance and permanent anti-static properties.

Melamine formaldehyde (MF) materials give mouldings with a superior surface performance to UF materials. Their excellent stain resistance and low formaldehyde extraction properties make them suitable for food contact applications such as table and kitchenware, whilst their greater heat resistance makes then ideal for such items as ashtrays.

The compression moulding process allows the production of large mouldings with good surface appearance, low distortion and excellent stability with an economically priced raw material. Press costs are low and tooling relatively simple. Whilst preheating cycle times can be minimised, they cannot match these achieved by the injection moulding process. With this method the material is very efficiently preheated both by the injection machine screw and barrel and by the further frictional heat generated as the material flows through the sprue, runner and gate. Consequently the material enters the cavity at or near its curing temperature, thus reducing cycle times

However, the injection moulding process has its limitations with mouldings being more prone to flow lines, distortion and cracking at elevated temperatures than the corresponding compression moulded components. Consequently the urea materials are best suited for the moulding of the many smaller, less critical components. Whilst by using an SMX melamine based material the limitations of the urea powders can largely be overcome, there is a cost penalty. Therefore care must be taken to determine accurately the relevant production costs of the two approaches before deciding whether to produce an item by either compression or injection moulding.