Drug – bio-affecting and body treating compositions – Preparations characterized by special physical form
Reexamination Certificate
1997-02-28
2002-02-12
Naff, David M. (Department: 1651)
Drug, bio-affecting and body treating compositions
Preparations characterized by special physical form
C435S262500
Reexamination Certificate
active
06346253
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a photoreactive agent for removing harmful materials comprising at least a photoreactive semiconductor which can decompose and remove harmful materials such as malodorants and environmental pollutants by utilizing the photocatalytic reaction of the photoreactive semiconductor.
With an increase of interest in environmental problems, there has recently been an increasing demand for not only the removal of a low concentration of industrial environmental pollutants such as industrial waste gas and waste water but also the removal of malodors and indoor pollutants in daily life. As an agent for removing a low concentration of such harmful materials, in particular, malodors in daily life, there have been generally used, for example, inorganic adsorbents obtained by compositing activated carbon, silica, alumina, a metal oxide, etc.
A removing method using such an adsorbent, however, involves various problems during its employment, for example, as follows. In proportion as harmful materials are adsorbed on the adsorbent, the adsorbability is gradually decreased. Therefore, when the practical adsorbability is lost, the adsorbent has to be renewed. Accordingly, it is necessary to ascertain the duration of effectiveness of the adsorbability.
On the other hand, a method for removing harmful materials using a photoreactive semiconductor has recently been noted. Japanese Patent Laid-Open No. 61-135669 discloses a method for decomposing sulfur compounds, malodorants by irradiating a photoreactive semiconductor such as zinc oxide with ultraviolet light. Japanese Patent Examined Publication No. 2-62297 discloses a method for removing a low concentration of nitrogen oxides by using a mixture of a titanium oxide and activated carbon. Since the decomposition of such malodorants by the photoreactive semiconductor such as a titanium oxide or zinc oxide is caused by oxidative decomposition by positive holes or radicals generated on the surface of the photoreactive semiconductor by the ultraviolet irradiation, materials decomposable by the photoreactive semiconductor are not only organic substances but also sulfides and nitrogen-containing compounds such as ammonia. Moreover, the photoreactive semiconductor itself is not consumed or deteriorated by the decomposition of the malodorants, and its capability is not basically deteriorated so long as its irradiation with ultraviolet light is continued. Thus, the above-mentioned method is markedly advantageous as compared with the case of using only an adsorbent.
The decomposing capability of such photoreactive semiconductors is improved with an increase of their chance of coming into contact with harmful materials, i.e., materials to be decomposed. Therefore, the photoreactive semiconductors are most effective when used in a powder form in which the area of reaction by the contact with the harmful materials is not decreased.
However, powder of the photoreactive semiconductor is not usable as it is in practice. Moreover, in general, the photoreactive semiconductors are not substantially able to form a self-coating film unless at least calcined. Accordingly, for handling the photoreactive semiconductors, they have to be subjected to some processing, for example, employment of a structure-forming agent capable of forming a structural material, together with the photoreactive semiconductors. Japanese Patent Laid-Open No. 3-75062 discloses a photoreactive semiconductor-supporting sheet obtained by supporting a photoreactive semiconductor by the use of a latex having a minimum film-forming temperature of 60° C. or lower.
In general, since latices have a high film-forming capability and are easily dispersible in water, they can easily be applied. However, when the photoreactive semiconductor is mixed with the latex and supported on a sheet according to the above method, a resin contained in the latex is decomposed in itself owing to the powerful oxidative effect of the photoreactive semiconductor. When the photoreactive semiconductor is a titanium oxide or the like which has a particularly high photocatalytic activity, the photoreactive semiconductor-supporting sheet is not fit for long-term use.
In addition, when the photoreactive semiconductor is used for removing harmful materials in the air, its effective photocatalytic capability cannot be obtained because the photoreactive semiconductor surface is coated with the resin, so that direct contact of the harmful materials with the photoreactive semiconductor is remarkably inhibited.
Japanese Patent Laid-Open No. 6-315614 has proposed the following purging agents for purging pollutants from the air or water: a purging agent produced by forming photocatalyst powder composed mainly of a titanium oxide (a photoreactive semiconductor) or a mixture of a titanium oxide and activated carbon into a sheet or a panel by the use of synthetic resin powder, and a purging agent obtained by adhering the same photocatalyst powder as above to the surface of a sheet material or a panel material with an adhesive.
Since a fluororesin such as polytetrafluoroethylene is used as the synthetic resin powder, the former purging agent has a structure hardly attackable by the powerful oxidative effect of the photocatalyst. This purging agent, however, is difficult to process to a large area necessary for cleaning the air, and it involves a problem of environmental pollution due to itself because it cannot be subjected to a discarding treatment such as combustion because of the too high durability of the fluororesin.
In the purging agent obtained by adhering photocatalyst powder with an adhesive, the photocatalyst powder exhibits substantially no photocatalytic capability as in the above when buried in the adhesive, and it is poor in strength as a structural material when merely sticked to the adhesive. Thus, it is impossible to increase the amount of the photocatalyst powder in which the powder acts effectively.
Further, Japanese Patent Laid-Open No. 2-187147 discloses a denitration catalyst obtained by supporting vanadium oxide on solid-supporting paper prepared by impregnating ceramic paper with a mixture of titania sol and silica sol and firing the ceramic paper.
The ceramic paper and silica sol are not photocatalytically attacked by titania sol, and the denitration catalyst is unlikely to cause environmental pollution because of such a structure. However, although a mixed film of titania sol and silica sol is rather good in strength in a dry state, it is poor in water resistance when formed by mere drying. For removing such a defect, an after-treatment such as firing is necessary as described in the above reference, but the fired ceramic paper is poor in flexibility and hence processability.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a photoreactive agent for removing harmful materials which utilizes the photocatalytic capability of a photoreactive semiconductor, is excellent in ability to remove harmful materials such as malodor, is water-resistant, is not changed in characteristics over a long period of time, and can easily be produced.
The present inventors earnestly investigated and consequently have achieved the above object with a photoreactive agent for removing harmful materials which comprises a substrate and a layer containing a photoreactive semiconductor and organic fine particles coated with inorganic fine particles which is formed on at least one side of the substrate.
Basically, the photoreactive agent for removing harmful materials of the present invention is obtained by coating or impregnating a substrate with an aqueous dispersion containing a photoreactive semiconductor and organic fine particles coated with inorganic fine particles. The organic fine particles coated with inorganic fine particles according to the present invention are fine particles obtained by coating the surfaces of organic fine particles with inorganic fine particles by the interaction between the organic fine particles and the inorganic fine particles. The
Aizawa Yasuhiro
Azuma Yoichiro
Sato Michihiko
Takaoka Kazuchiyo
Foley & Lardner
Mitsubishi Paper Mills Limited
Naff David M.
Ware Deborah K.
LandOfFree
Photoreactive agent containing photoreactive semiconductor... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Photoreactive agent containing photoreactive semiconductor..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Photoreactive agent containing photoreactive semiconductor... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2983005