In a liquid crystal display (LCD), a polarizing plate or a phase-contrast plate is used to control optical rotation and birefringence of beam that passes through liquid crystals. Also, in an organic electroluminescent device (OLED), a circularly polarizing plate is used to avoid reflection of external light.
Conventionally, in such a polarizing plate, a polarizer obtained by dissolving or adsorbing iodine or a dichromatic organic dye in a polymeric film, such as a polyvinyl alcohol or the like and stretching the obtained film in one direction (stretching method) to orient dye molecules or the like has been widely used.
However, there has been a problem that polarizers produced by the stretching method are poor in heat resistance and light resistance depending on the dye or the polymeric material used. Further, a bad yield of overlapping films when producing a display panel has been raised a problem. Moreover, a film with a wide width is needed to be stretched as the display panel becomes bigger, so that a large film forming apparatus is needed, which has caused a problem.
In contrast, a method for orienting a dichromatic dye in a thin film (coating method) by coating a solution containing a dichromatic dye on a substrate, such as a glass plate or a transparent film and the like to form a thin film utilizing intermolecular interaction is well known. The coating method is getting attention because the method can produce thin polarizing plates excellent in heat resistance compared with the stretching method. It is known that a polarizing plate having preferable optical anisotropy can be obtained when using a substance for forming dye aggregates caused by intermolecular interaction, such as a lyotropic liquid crystal phase in a coating fluid as a dichromatic dye.
However, in many cases, the solution containing a dichromatic dye exhibiting a lyotropic liquid crystal phase exhibits acidity, so that a coater made of stainless steel that is ordinarily used easily becomes corrosive. Accordingly, an acid solution containing a lyotropic liquid crystal compound is neutralized with an alkaline agent, such as sodium hydroxide or the like before coating (JP 2006-328157 A (Example 1)).
The concentration range exhibiting liquid crystallinity becomes narrower when neutralizing the acid solution containing a lyotropic liquid crystal compound with sodium hydroxide, resulting in irregularity in orientation of the lyotropic liquid crystal compound in a coating film. This leads to a problem with a decrease in dichroic ratio of the coating film. Thus, processes for production of a coating fluid and an optically anisotropic film without a reduction of the dichroic ratio have been demanded.