The light that we are familiar with includes infrared, visible and ultraviolet light. The energy of violet visible light is higher than that of red visible light. The spectrum of light that contains higher energy than that of violet visible light is called “ultraviolet light.” Artificial light sources emitting ultraviolet light that can be made use of by titanium dioxide photocatalyst are stipulated in JIS (Japanese Industrial Standard) R1709.

As evidenced by strong sunlight’s tanning effects in summer, sunlight contains ultraviolet light. Titanium dioxide photocatalyst makes use of the ultraviolet light.

A state in which bacterial growths are curbed on product surfaces

Photocatalyst is supported through a variety of methods, including application, impregnation and kneading, in order to make use of its antibacterial function.

Test methods that judge whether photocatalyst antibacterial treatments are “antibacterial” are stipulated for plate-shaped and fibrous products respectively in JIS R1702. Antibacterial effects are judged based on “antibacterial activity values” that are found by the test methods. The relationship among the terms is shown in Table 1. In the same way, another test method that judges whether photocatalyst antibacterial treatments are “antifungal” is stipulated in JIS R1705.

Bacteria are inoculated on two products, one of which has received the photocatalyst antibacterial treatment and the other which has not, and the live bacterial numbers are measured after the products have been exposed to light. The antibacterial activity value is the difference between logarithmic values of the live bacterial numbers on the two products. This value includes decreases in bacterial numbers, which are obtained in conditions where the products are not exposed to light.

Bacteria are inoculated on two plate-shaped products, and live bacterial numbers on the two products are measured after one of the products is exposed to light and the other is placed in a dark place. The light exposure effect is the difference between logarithmic values of the live bacterial numbers on the two products.

Test methods that evaluate the “phenomenon in which stains are dissolved” and “phenomenon in which stains are washed out” are stipulated in JIS R1703-2 (wet dissolution performance) and JIS R1703-1 (water contact angle measurement) respectively.

Hydrophilic character of materials when water contacts the surface

It is the angle between a tangential line on a curved surface of liquid placed on a horizontal solid matter and the surface of the solid matter. The contact angle of water is called “water contact angle.”