TITLE Development of long-term stable fixation technology of photocatalyst with high-level environmental purification function
(Joint Program to Promote Technological Development with the Private Sectors)
AUTHOR RITE - AKASHI LABORATORY in Kawasaki Heavy Industries, Ltd.

Titanium dioxide photocatalyst has attracted a lot of interest for environmental cleanup catalysis. For the use of titanium dioxide coating agents, it has to be coated on substrates properly. We focused attention on the development of an undercoat agent fixing to the substrate and the top layer of titanium dioxide photocatalyst for a long time. The undercoat film is also used to prevent the decomposition of an organic substrate due to the photocatalytic oxidation.

In this fiscal year, we carried out to find out the optimum condition of producing the undercoat agent, designed and fabricated a bench-scale production plant for the undercoat agent, operated the plant to obtain data for scale-up, as well as investigated the optimum condition for coating the undercoat agent on substrates.

Firstly, we investigated the optimum condition for producing the undercoat agent which is stable for a long period. We tested various undercoat agents prepared with using some kinds of additives. We evaluated a shelf life of the undercoat agent by measuring  viscosity and absorbance ratio with time. In a performance of the coating film, we evaluated by measuring the decomposition ability of methylene blue. We selected 0.5 wt% of acetyl acetone as a final candidate material.

Secondly, the life of the coating film was evaluated by an accelerated weathering test. Test samples were prepared by coating with the undercoat agent and the photocatalytic coating agent on organic substrates (clear acrylic sheets ). Test results show that the coating film with the undercoat agent selected was highly adhesiveness to the substrate and had an enough performance as a barrier layer, which prevented the decomposition of the substrate due to photocatalytic oxidation.

Thirdly, refer to the results of optimization tests for producing undercoat agents, we designed and fabricated the bench-scale production plant. Through running of the bench-scale plant with changing mixing rates of raw materials, conditions of stirring reactants, and so on, we obtained data required for designing of the main reactor, feed pumps, and etc. for scale-up.

Finally, in case of applying photocatalyst to organic substrates, we defined the quantity of the undercoat agent required for protecting the substrate from the attack of photocatalytic oxidation. In addition, we obtained data for designing of an automatic spray coating machine which is capable of coating undercoat agents efficiently.