In recent years, technologies that deal with materials having nanometer size, namely nanomaterials, have been attracting public attention in various industrial fields. New materials having unprecedented new functions have been developed by combining the nanomaterials with a plurality of other materials at the nanometer level. Since nanomaterials dispersed in high degree show different properties from those in a bulk state and hence they are useful, technology to disperse nanomaterials in a composite is indispensable to obtain the composite in which nanomaterials are dispersed in high degree. However, there is a problem that peculiar functions of nanomaterials cannot be realized since they agglomerate when combined to make composite materials because the surface state of the nanomaterials is generally unstable.
Among the nanomaterials, a carbon nanotube has been studied for its physical properties and functions since its discovery in 1991, and research and development for its application have also been carried out extensively. However, in the case of combining the carbon nanotube with a resin or a solution to make a composite material, there is a problem that its characteristic properties cannot be realized because it further agglomerates from its entangled state when it has been produced. Therefore, various attempts to uniformly disperse or dissolve the carbon nanotube into a solvent or a resin have been tried by carrying out physical treatment or chemical modification on the carbon nanotube. For example, a method of dispersing single-walled carbon nanotube by cutting it shortly through its ultrasonic wave treatment in a strong acid has been proposed (Non-patent Document 1). However, this is not an industrially proper method because the operation is complicated owing to the treatment in the strong acid, and the effect of this method on dispersion is insufficient.
Such a shortly cut single-walled carbon nanotube has open edges, each terminated with an oxygen-containing functional group such as a carboxylic group, and taking account of this, it has been proposed to make the shortly cut single-walled carbon nanotube solubilizable in a solvent by changing the carboxylic group into an acid chloride and reacting the acid chloride with an amine compound to introduce a long chain alkyl group into the shortly cut single-walled carbon nanotube (Non-patent Document 2). However, this method has problems unsolved in which there occurs a damage of a graphene sheet structure of the carbon nanotube and in which characteristic properties of the carbon nanotube itself are affected because the long chain alkyl group is introduced into the single-walled carbon nanotube by a covalent bond.
As another attempt, a method has been reported in which, using the fact that pyrene molecule is adsorbed on the surface of the carbon nanotube through a strong mutual interaction, a substituent group containing an ammonium ion is introduced into the pyrene molecule and the resultant molecule is subjected to ultrasonic treatment in water together with the single-walled carbon nanotube so that the resultant molecule is non-covalently adsorbed on the single-walled carbon nanotube to thereby produce a water soluble single-walled carbon nanotube (Non-patent Document 3). According to this method, the damage of a graphene sheet structure and the like can be suppressed owing to a noncovalent bonding type chemical modification, however, there is a problem that electrical conductivity of the carbon nanotube is lowered caused by the existence of a nonconductive pyrene compound.
A method has been proposed in which a dispersion liquid is obtained by dispersing or solubilizing the carbon nanotube in a solvent such as water or an organic solvent without deteriorating the characteristic properties of the carbon nanotube itself using a general-purpose surfactant or polymer dispersant (Patent Document 1 and Patent Document 2). There is a description that the carbon nanotube is stably dispersed in the dispersion liquid, however, there is no description about a dispersed state of the carbon nanotube in a coating film or a composite to be formed from the dispersion liquid or about an application to a conductive material or the like.
Further, there has been proposed a composition composed of carbon nanotube, a conductive polymer, and a solvent, and a composite produced from it (Patent Document 3). It is reported that the composition and the composite can disperse or solubilize the carbon nanotube in a solvent such as water, an organic solvent, or a water-containing organic solvent and can be excellent in long-term storage stability without deteriorating the characteristic properties of the carbon nanotube itself by the coexistence of the conductive polymer. The carbon nanotube composition in which the conductive polymer coexists is excellent in electrical conductivity, film-formability, and moldability and can be applied or coated on a base material with an easy method, however, application to materials that need colorlessness and transparency is difficult owing to a coloring originated from the conductive polymer to be used. Further, there has been a problem that usable solvents are limited because the conductive polymer generally has low solubilities to various solvents.
Further, there has been proposed a composition composed of a nanomaterial, a (meth)acrylic polymer, and a solvent, and a composite produced from it (Patent Document 4). It is reported that the composition and the composite can disperse or solubilize the nanomaterial in a solvent such as water, an organic solvent, or a water-containing organic solvent and can be excellent in long-term storage stability without deteriorating the characteristic properties of the nanomaterial itself by the coexistence of the (meth)acrylic polymer. The nanomaterial composition in which the (meth)acrylic polymer coexists is excellent in film-formability and moldability and can be applied or coated on a base material with an easy method, however, there is a problem that an usable solvent is limited because an amine compound has to be jointly used to raise dispersibility. Further, in the case of using the nanomaterial composition as a coating film (cured film) by adding it to a polymerizable monomer, there has been a problem that water resistance and mar resistance as a coating film are lowered since the nanomaterial composition has no crosslinking point with the film component because the nanomaterial composition is a compound containing sulfonic group and the like.
Further, there has been proposed a photosensitive composition for a black matrix, composed of a binder resin containing a urethane acrylate compound obtained by a reaction between an isocyanate compound and a polyhydroxy compound and a black pigment such as carbon black or carbon nanotube (Patent Document 5). It is described that the photosensitive composition containing the urethane acrylate compound can produce the black matrix at a low cost because it can easily form a pattern having a high light blocking effect with a thin film and has a high sensitivity and a high curing speed, however, there is no description about a dispersion effect of the carbon nanotube and an additional dispersant is separately added to disperse the black pigment. Further, the black matrix has to realize the light blocking effect by a coating film obtained from a composition containing a black pigment, and hence, in the case of applying the composition to a use where transparency is required, a dispersion level of the carbon nanotube is low and accordingly a coating film having a sufficient transparency cannot be obtained. Further, there is a problem that nothing is described concerning an effect of improving electrical conductivity obtained by sufficiently dispersing the carbon nanotube.    Patent Document 1: International Publication No. WO 2002/016257    Patent Document 2: Japanese Patent Application Laid-Open No. 2005-35810    Patent Document 3: International Publication No. WO 2004/039893    Patent Document 4: International Publication No. WO 2006/028200    Patent Document 5: Japanese Patent Application Laid-Open No. 2005-331938    Non-patent Document 1: R. E. Smalley, et. al., Science, 280, 1253 (1998)    Non-patent Document 2: J. Chen, et. al., Science, 282, 95 (1998)    Non-patent Document 3: Nakajima, et. al., Chem. Lett., 638 (2002)