Staining mould material

Basic materials such as lime or magnesium oxide increase the hardening rate of novolak-hexa compositions and are sometimes referred to as accelerators. They also function as neutralising agents for free phenols and other acidic bodies which cause sticking to, and staining of, moulds and compounding equipment. Such basic substances also act as hardeners for resol-based compositions. 

The principal application of melamine-formaldehyde moulding compositions is for the manufacture of tableware, largely because of their wide colour range, surface hardness and stain resistance. The stain resistance does, however, leave something to be desired and one aim of current research is to discover alternative materials superior in this respect. Cellulose-filled compositions also find a small outlet for trays, clock cases and radio cabinets and other purposes. The mineral-filled powders are used in electrical applications and knobs and handles for kitchen utensils. 

Pentachlorophenol and its salt, sodium pentachlorophenate, are used primarily as wood preservatives on telephone poles, pilings and fence posts. In Europe, pentachlorophenol and its derivatives, sodium pentachlorophenate and pentachlorophenyl laurate are used to control sap stain in green lumber. It is also used in Europe on millwork to prevent the growth of mould and fungi, and as a preservative for waterproof materials (i.e., tarpaulins) that are used in outdoor applications. In the United States, it is used almost entirely for treatment of utility poles (Agency for Toxic Substances and Disease Registry, 1994). 

Because the RIM materials enter the mould as low viscosity liquids, they accurately reproduce the mould surface. This characteristic is an advantage when a stained or textured surface is desired for aesthetic reasons. Secondly, both mould halves must be closely fitted to avoid excess leakage and fiash of the low-viscosity liquid mixture. This close-fit requirement must be balanced with the need to dispel all the air in the mould within the 5 s or less fill time. Some provisions for the release of mould air must be made. Also mould release must be applied to the mould surface to effect release of the parts, and mould cleaning is required to control flash removal and polymer build-up. 

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