Conventionally proposed light reflector plates for use in backlights for illumination signboards, lighting fixtures, displays and the like, include those fabricated such that a light-reflecting synthetic resin film or sheet is formed into a three-dimensional shape to thereby yield a light reflector plate (refer to, for example, Patent Reference 1).
Known light-reflecting synthetic resin films and sheets include thermoplastic resin film or sheet having numerous fine bubbles or pores therewithin (for example, refer to Patent Reference 2), and thermoplastic resin film containing fillers wherein numerous voids are formed with the filler as the core (for example, refer to Patent Reference 3).
The former thermoplastic resin film or sheet having numerous fine bubbles or pores is obtained by placing molten or solid thermoplastic resin in contact with inert gas under increasing pressure then depressurizing, and subsequently foaming the resin by heating the resin at a temperature higher than the softening temperature thereof under normal pressure. The obtained thermoplastic resin foam film or sheet has high reflectance due to a fine mean bubble diameter of 50 μm or less, as well as superior shape-retention properties because the thickness thereof can be 200 μm or more, and therefore, the thermoplastic resin foam film or sheet can be singly processed into a three-dimensional shape. The light reflectance of the thermoplastic resin foam film or sheet generally tends to indicate higher values as the number of bubbles per unit volume increases. Therefore, high light reflectance can be achieved because the smaller the bubble diameters are, the more the number of bubbles per unit volume of the resin is. Because thinner film or sheet can be obtained as a result, thermoplastic resin foam having numerous finer bubbles or pores is desired.
On the other hand, the latter thermoplastic resin film containing fillers can be obtained by forming an un-stretched film containing fillers such as calcium carbonate or barium sulfate and forming numerous voids with the fillers as the core by stretching this un-stretched film. However, because stretch processing is performed, the thickness of the obtained film becomes thin, under 200 μm and thus, the film alone does not have shape-retention properties and light leaking to the back surface of the film increases. Therefore, this film is implemented by placing a plate having sufficient strength and light-shielding properties to the back surface thereof.
Known thermoplastic polyester resin includes thermoplastic polyester resin loam formed by mixing an elastomer therewithin (for example, refer to Patent Reference 4). However, it is merely stated that impact-resistance is enhanced by mixing an elastomer with polyester, and there are no statements or implications regarding the bubble diameters of the obtained foam. It is difficult to make the bubbles fine and to disperse the bubbles evenly with the extrusion foaming method described in Patent Reference 4, and in reality sheet formed by mixing an elastomer with polyester and performing extrusion foaming has large bubble diameters. Ever when a reflecting plate is formed from this extrusion foamed sheet the reflecting plate does not have sufficient functions as a reflecting plate because the reflectance is low.    [Patent Reference 1] Japanese Patent Laid-Open Publication 2002-122863    [Patent Reference 2] WO Publication 97/01117    [Patent Reference 3] Japanese Patent Laid-Open Publication Heisei 4-296819    [Patent Reference 4] Japanese Patent Laid-Open Publication Heisei 11-49883