In recent years, infection diseases caused by various viruses such as new type influenza viruses or bacteria such as O157 threaten human life, so that a measure against the threat is urgently needed on a global basis. From such a point of view, a demand for antibacterial and antiviral materials increases, and antibacterial and antiviral properties are required for various products. Currently, application with respect to the antiviral property has advanced, but a material having sufficient performance with respect to the antiviral property has not been developed, yet.
A photocatalyst has a function of decomposing organic matters by light irradiation, and is a material in which antibacterial and antiviral effects are expected, and an antiviral product in which a titanium oxide-based photocatalyst is mixed, and the like have been put into practical use. However, the photocatalyst made of titanium oxide is excited only by ultraviolet rays, so that sufficient performance cannot be obtained in indoor environments having only a small amount of ultraviolet rays. Antiviral performance of a filter using titanium oxide is known. However, the antiviral performance uses ultraviolet rays contained in a fluorescent lamp, and cannot exhibit a sufficient effect under practical illuminance or in room space in which ultra violet rays are cut by a shade or the like, resulting in that the performance is insufficient.
In order to improve visible light responsiveness of titanium oxide, visible light response-type photocatalysts based on titanium oxide carrying platinum compounds exhibiting performance even by visible light, titanium oxide doped with nitrogen or sulfur, and the like have been developed. However, the visible light response-type photocatalyst based on titanium oxide has a narrow excitation wavelength range, and thus sufficient performance has not been obtained under low illuminance of general interior lighting. With respect to the antiviral property as well, similarly, practical products have not been obtained under the present circumstances.
Products required for the antiviral property are touched by people, or used in an environment where people exist, and a product that exhibits antiviral performance regardless of in an outdoor environment or indoor environment is preferable. The photocatalyst material is one in which its performance is exhibited by light irradiation, and a material that exhibits antiviral performance regardless of a light irradiation amount of a usage environment is more preferable. It is said that viruses are inactivated by alcohol, but this is a temporary effect at the time when alcohol is applied to a product, and the product itself does not inactivate the viruses, and thus there is a possibility that viruses attach to the product again. Further, the effect varies also according to types of viruses. An Ag ion or the like is also said to be effective for the virus inactivation, but has a problem of low duration of the effect.
Tungsten oxide has a band gap narrower than that of titanium oxide, so that it receives attention as a material capable of obtaining photocatalysis by visible light. As for an antiviral function of tungsten oxide, it has been known that growth of sulfur oxidizing bacteria is inhibited under an environment of pH 2.5. Further, it has also been known that tungsten oxide is mixed with titanium oxide to obtain an antiviral property by photocatalysis. However, an antiviral material based on tungsten oxide has not been known. As described above, as for a conventional antiviral material, it has been difficult to evaluate an antiviral effect, so that a practical antiviral material has not been obtained so far. Development of an antiviral material having an antiviral effect regardless of an outdoor environment or indoor environment has been expected.