The present invention provides a method for improving visibility of an image display device which is capable of providing an image display device excellent in anti-reflection properties and bright-field contrast even using an optical layered body including a light-transmitting substrate having in-plane birefringence, such as a polyester film. The method of the present invention is a method for improving visibility of an image display device that has an optical layered body including a light-transmitting substrate having in-plane birefringence and an optical functional layer disposed on one surface of the substrate. The method includes the step of disposing the optical layered body such that the slow axis showing a greater refractive index of the light-transmitting substrate is in parallel with the vertical direction of a display screen of the image display device.

The present invention provides a method for improving visibility of an image display device which is capable of providing an image display device excellent in anti-reflection properties and bright-field contrast even using an optical layered body including a light-transmitting substrate having in-plane birefringence, such as a polyester film. The method of the present invention is a method for improving visibility of an image display device that has an optical layered body including a light-transmitting substrate having in-plane birefringence and an optical functional layer disposed on one surface of the substrate. The method includes the step of disposing the optical layered body such that the slow axis showing a greater refractive index of the light-transmitting substrate is in parallel with the vertical direction of a display screen of the image display device.

A device for controlling a production system for planar or strand-shaped bodies comprises a measurement region and a conveying apparatus configured to convey the body through the measurement region. A transmission apparatus is configured to irradiate the body with measurement radiation in the measurement region. A detection apparatus is configured to detect the measurement radiation reflected by the body. An evaluation apparatus is configured to use the measurement radiation detected by the detection apparatus to determine at least one of: (1) a refractive index of the body; and (2) an absorption of the measurement radiation by the body. A control apparatus is configured to control at least one production parameter of a production system based on the at least one of: (1) the refractive index of the body; and (2) the absorption of the measurement radiation by the body.

The invention relates to a process for making an opaque and glossy film from a thermoplastic polyester composition, comprising the steps of a) extruding the polyester composition through a slot die, and quenching to form a substantially amorphous film having a crystallinity of at most 5%; b) rapidly heating the amorphous film to a drawing temperature in the range from T.sub.g to (T.sub.g+50) C. while applying a draw ratio in the range of from .sub.initiation to .sub.max. in longitudinal direction, and a drawing rate of at least 1 m/min to form an oriented film showing stress-whitening, wherein .sub.initiation is the draw ratio at which a transfer from a transparent product to a stress-whitened product occurs and .sub.max. is the draw ratio at which failure of the stress whitened film occurs; and c) heat-setting the oriented stress-whitened film; the thermoplastic polyester composition substantially consisting of at least one crystallizable polyester derived from at least one aliphatic diol and at least one aromatic dicarboxylic acid. With this process it is possible to make a unitary, glossy, opaque film from a polyester composition that does not contain void-forming additives like high amounts of fine pigment particles or dispersed non-miscible polymer particles. The film obtained also has very good mechanical properties. It is a further advantage that the process can be performed continuously on conventional extrusion and stretching equipment used for making transparent film from polyesters. The invention also relates to an opaque polyester film obtainable by said process.