Papers capable of reversibly displaying digital information, which are so-called digital papers, are being actively studied at present because their importance will increase in the digital information era in the future. Representative examples of the mode include an electrophoresis display mode based on the movement of electrically charged fine particles, a thermally rewritable display mode utilizing the thermally reversible color development process of a leuco dye, and a mode utilizing the volume expansion of a high-molecular weight gel.
Among them, the thermally rewritable display mode utilizing the thermally reversible color development process of a leuco dye has been eagerly studied because white display on a basis of scatter close to paper can be utilized.
Leuco dyes are widely used as various display materials because they can realize a color development system by the acid-base reaction. For example, there are enumerated thermosensitive papers, pressure-sensitive papers, and thermosensitive printing materials. In addition, since the leuco dyes can realize a reversible color development system of the acid-base reaction, for example, reversible thermosensitive display materials comprising a combination of the leuco dye with a developer are known. The details of the reversible thermosensitive display materials are described in, for example, Polymer Preprints, Japan, Vol. 42, p. 736 (1993).
As the display material comprising a polymer having a leuco dye connected thereto by covalent bond are enumerated those disclosed in JP-A-11-181031. However, the display materials disclosed in this patent are of an irreversible color development system.
Further, as a display mode utilizing the phase change of a high-molecular weight gel are enumerated those disclosed in JP-A-11-236559 and JP-A-9-160081. However, the display materials disclosed in these patents still involve a problem such that the display contrast is low, and hence, its improvement has been demanded.
As the technology of complexing a high-molecular weight gel with a photo-functional material, high-molecular weight gels having a residue that can be ionically dissociated upon irradiation with light are disclosed in JP-A-62-55967. However, this residue involves a problem in stability of the chromophore, and hence, its improvement has been demanded.
As materials comprising a polymer having a leuco dye and a developer connected thereto by covalent bond are enumerated those disclosed in JP-A-11-181031. However, the materials disclosed in this patent relate to an irreversible display material comprising a combination with a functional group having an acid-proliferating function.