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Chongqing Polycomp International Corp (CPIC) has developed a family of fibreglass products with a flat rather than round cross-section that is said to facilitate higher fibre loading levels and better mechanical properties in injection moulded thermoplastic composites and reduce warpage in thin wall sections.
The flat glass enhances thermoplastic processing by lowering resin shear, providing better fluidity (increasing spiral flow), reducing friction and viscosity build-up, and lowering fibre entanglement and breakage since the flat fibres tend to flow in planar sheets like mica rather than rolling and tumbling like conventional round glass filaments. This in turn helps provide for a more isotropic dispersion and also allows higher fibre volume fractions (FVFs) to be achieved with no other change because the fibres pack more closely.
Warpage (differential shrinkage and residual stress relaxation) of a plastic or composite part after demoulding can be a serious problem because it changes final part dimensions and location of mating surfaces, plus negatively affecting aesthetics. It tends to be a function of non-uniform shrinkage between flow and cross-flow directions of a part, which is exacerbated in high-pressure processes like injection moulding because more fibres line up in the direction that polymer flows into the tool than in the cross-flow direction. This, in turn, leads to higher shrinkage and therefore warpage in the cross-flow direction. With thin-wall parts, the cross-flow (through-thickness) direction represents a larger ratio vs. skins aligned with resin flow, so the effects of the non-uniform shrinkage are more pronounced. To an extent, design and gate placements can help reduce warpage, as can process changes such as lowering speed of fill and/or packing pressures. However, CPIC’s new flat glass helps reduce warpage significantly without any other changes just by virtue of how the reinforcement fills parts and how it behaves in conjunction with the resin matrix. It also helps reduce moulding pressures and enables the same part to be moulded on smaller injection presses with fewer gates.
Glass-filled crystalline parts using this flat fibre are being moulded as thin as 1 mm (0.04 inch) without warpage. The flat fibres are said to exhibit excellent resin mechanical properties and are expected to find applications in electrical/electronic industries. In all other properties, the flat strands are said to be equivalent to conventional round glass fibre of the same type at the same loading.
The new products are initially being offered in E-glass (ECT) form with filament widths of 28 μm and filament thicknesses of 7 μm vs. conventional round glass where filaments for chopped strands typically range from 10-13 μm in diameter. The flat strands are subsequently chopped to either 3.0 mm (0.12-inch) (the most common length for short-glass injection grades in Europe) or 4.5 mm (0.18 inch) (the most common length for short-glass injection grades in North America), or it is milled. Three grades of fibre are offered in both the 1:3 and 1:4 length/width ratios as well as milled forms. The fibres feature unique sizing technology for use in polyamide (PA), polyphthalamide (PPA), polybutylene terephthalate (PBT), polyphenylene sulphide (PPS) and polycarbonate (PC) resins.
Fibre shape (flat, round) is only one aspect of glass properties that CPIC can manipulate to create products that meet unique client needs. Other properties that can be modified include the type of sizing used, the type of glass used, and additional special functionality that can be added (e.g. flame retardance and antistatic properties).
Image provided by CPIC
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