A study into the process of in-mould decoration (IMD) has been undertaken. The properties of the two components of printed IMD film; namely the ink and the film have been studied. The work has focussed on the heat absorption, visual and mechanical properties of printed IMD film and the changes than occur during the forming stage of the process. The films used in IMD possess mechanical properties typical of plastics. Their mechanical properties are tailored by blending polyesters with polycarbonate. The blended films possess a higher natural draw ratio and elongation before fracture and have lower softening temperatures. Infrared heat absorption by IMD film is dependent on the film type, the ink coating and whether the film is heated from the print or non-printed (first) surface. Heat absorption characteristics affect the temperature of the film and therefore its mechanical strength during forming. Several techniques were used to characterise the appearance of IMD films. The methods are based on measuring the reflected or transmitted light; with each having advantages and disadvantages. The films tested have a surface texture that diffuses incident light, giving a matt appearance to second surface print. Upon heating the texture deteriorates in all films and discoloration occurs in blended films. The ink systems used in IMD had different mechanical and optical characteristics. Solvent-based inks become more ductile with heating but residual solvents make them prone to a "pinhole" effect and weaken the film. UV curable inks become more brittle with heating. Finite element simulations of forming processes have been developed, using material models derived from tensile test data. The simulations predict the geometry and strain distribution in a formed part, which differs depending on the forming method, the temperature and the film. This can then be used to predict the visual changes in the formed part.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:638523 |
| Date | January 2004 |
| Creators | Phillips, C. O. |
| Publisher | Swansea University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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