Moulding compounds, commercially

Following the success in blending rubbery materials into polystyrene, styrene-acrylonitrile and PVC materials to produce tough thermoplastics the concept has been used to produce high-impact PMMA-type moulding compounds. These are two-phase materials in which the glassy phase consists of poly(methyl methacrylate) and the rubbery phase an acrylate polymer, usually poly(butyl acrylate Commercial materials of the type include Diakon MX (ICI), Oroglas... 

Currently, one of the most important commercially available materials today are the urea-formaldehyde (U-F) resins. Their applications include coatings, adhesives, castings, moulding compounds and textiles. Maciel et al. have produced a series of extensive papers in this area concentrating on both and CP/MAS [13-16]. 

Reinforced plastics first became commercially available in the 1940s. Unsaturated polyester reinforced with fibrous glass is the most widely used reinforced plastic today. Chopped glass mats are used for sheet moulding compounds (SMC), bulk moulding compounds (BMC) and hand lay-up composites. 

Parallel to thermosetting SMCs and BMCs are thermoplastic moulding compounds in sheet form, known as glass mat thermoplastics (GMTs), and compounded into standard granules for injection moulding and extrusion. Most thermoplastics are theoretically capable of such combination with reinforcement, but the main types used commercially at present are polyamide (PA) and polypropylene (PP). 

The major commercial interest continues to be centred on poly(ethylene terephthalate) 2GT and its use in fibres, films, and as a moulding material. Poly(tetramethylene terephthalate) 4GT has, however, found use recently as a moulding compound, and the lower members of the aliphatic series continue to find use in urethane technology. 

There is thus an optimum filler loading at which minimum internal stress performance is achieved and by utilising this fact it is possible to significantly improve the stress performance of epoxide moulding compounds. The properties of two commercially available low stress epoxide moulding compounds are compared to a standard material in Table 10.1. 

In commercial use are a wide variety of machines which transfer fixed volumes of compound to clamped moulds, by the operation of a ram in a cylinder fed with pre-heated slugs. These machines are capable of high speed semi-automatic cycling and are a great advance over the use of loose transfer moulds in conventional presses. The components which are produced are to a large degree flash-free, it only being necessary, in the majority of cases, to remove the injection feed and runner system. 

In 2004, Sony and Mitsubishi Plastics teamed up to develop a flame retardant PLA biodegradable resin claimed to be as strong as ABS. The new material will be used in the front panel of Sony standalone DVD players. The resin employs an aluminium hydroxide flame retardant, is rated UL94 V-2 and complies with the EU s Restrictions on Hazardous Substances (RoHS) directive. Sony says the use of additives and modifications to moulding parameters allows it to process PLA compound on conventional injection presses in commercially viable cycle times. 

Though useful as model compounds, PF resins have many commercial uses in their own rights, these include thermal insulation, mouldings, and use as wood resins. Therefore the systematic understanding of their molecular structure gives an insight into their physical properties. One important physical property is the resistance of the resin towards acid and bases understanding this enables a better approach to the correct formulation of the resins. 

The production of MF was first patented in 1935 by Henkel (Brydson, 1999). Today, MF polymers have commercial applications in decorative laminates for chipboard (a low cost substitute for solid wood) and unbreakable tableware. During synthesis, an excess of formaldehyde is heated with melamine at 80°G in alkaline conditions to produce an aqueous, syrup-like prepolymer. The prepolymer contains melamine-formaldehyde in a molar ratio of 1 2 (Figure 3.8). It is compounded with fillers, pigments, lubricants, stabilizers and sometimes accelerators, dried and milled to powder. Heating the powder to mould it at 145-165°C and 30-60 MPa produces a solid, thermosetting network. 

Phenol-formaldehyde was reported as the first commercially synthetic polymer (1899) which was introduced as BakeliteT by Baekeland in 1909. This was the period which marked the dawn for the production of commercial synthetic thermosetting polymers. Other advances in the field included the discovery of urea-formaldehyde resins in 1884 and the beginning of their commercialization as Beetle moldable resin in 1928, followed by thiourea-formaldehyde (1920), aniline-formaldehyde (Cibatine by Ciba, 1935) and melamine-formaldehyde (1937) moulding powders. The year 1909 marked the discovery of epoxy compounds by Prileschaiev, which were not used until World War 2. The first thermoset polyesters, invented by Ellis, date back to 1934 and in 1938 was reported their first use in the forms of glass-reinforced materials [1]. 

Most of these systems use the one-shot technique and are based on MDI with either a polyether or a polyester. Crude or polymeric MDI or other liquid variants of MDI predominate. Formulations usually contain high catalyst concentrations of either tin or mercury salts to give a very rapid cure at room temperature within a few minutes. It is usual to use additives to provide specific properties of density and lower the cost. Applications are commercial vehicle floor mats, cable jointing and potting compounds, sealants, moulds and the like. 

The resin system developed with BP for Lucas is a special one, which delivers a high surface gloss with mechanical strength. If the (confidential) formulation is varied, the properties suffer. The compound formulation --glass content etc. and its application to headlights by injection moulding are protected by patents, which places the product in a strong commercial position. 

---