Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Organic compound containing
Reexamination Certificate
1999-12-10
2001-04-03
Wood, Elizabeth D. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Organic compound containing
C502S527120, C502S527150
Reexamination Certificate
active
06211112
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a photocatalyst carrier for supporting a substance having a photocatalytic function (for example, titanium dioxide), and manufacturing method therefor.
DESCRIPTION OF RELATED ART
Conventionally known photocatalyst carriers include (1) those obtained by methods in which a porous membrane is impregnated with a stock solution of a photocatalytic particulate substance, and this stock solution is then subjected to a pulverization reaction; (2) those obtained by methods in which voids in a porous membrane are impregnated with a dispersion of a photocatalytic particulate substance, and the product is dried and supported; and (3) those obtained by methods in which a photocatalytic particulate substance is mixed, for example, with polytetrafluoroethylene (hereinafter “PTFE”), and is then made into a woven article after being calendered into a sheet or porosified and fibrillated.
Carriers obtained by methods in which a porous membrane is merely impregnated with a stock solution of a photocatalytic particulate substance, which is then subjected to a pulverization reaction, or carriers obtained by methods in which a photocatalytic particulate substance is directly supported by impregnation are disadvantageous, however, in that the photocatalytic substance and the porous membrane are not bonded together particularly strongly, and the photocatalytic substance tends to peel off. To address this problem, a method in which a photocatalytic particulate substance is tacked on to the surface of a PTFE porous membrane or the like, and this particulate substance is then compression-bonded with the PTFE porous membrane by being pressed with rolls is disclosed, for example, in Japanese Patent Application (Tokugan) 1-101342. In such a method, however, fixing is achieved by mechanical pressure alone, making it impossible to achieve sufficient bonding between the photocatalytic particulate substance and the PTFE porous membrane.
In addition, porous products made by premixing a photocatalytic particulate substance with a substrate resin such as PTFE develop strong bonding force between the photocatalytic particulate substance and the PTFE resin itself, but the surface of the photocatalytic particulate substance is not exposed adequately, and the resulting efficiency of the photocatalytic function is low. Furthermore, admixing large amounts of photocatalytic substances in order to raise the efficiency of the photocatalytic function tends to cause problems associated with a marked reduction in the mechanical strength of the PTFE porous article.
An object of the present invention is to provide a highly durable photocatalyst carrier in which sufficient exposure to the surrounding atmosphere is achieved for the surface of the photocatalytic substance on the surface and/or in the pores of a hot-melt resin porous article, optionally provided with a reticulated layer, and in which the photocatalytic substance is firmly supported by the photocatalytic substance.
SUMMARY OF THE INVENTION
According to the present invention, a substance having a photocatalytic function (such as titanium dioxide particles) is applied to a hot-melt resin porous article, and the article is then heated to the softening temperature of the resin surface, whereupon the pores of the hot-melt resin porous article shrink somewhat, and the surface softens at the same time, with the result that the applied titanium dioxide particles are supported by, and firmly bonded to, the hot-melt resin porous article while somewhat embedded in the pore walls.
Compared with cases in which the resin surface is merely coated with deposited titanium dioxide, therefore, the photocatalyst carrier pertaining to the present invention can develop a stronger bonding force, and the titanium dioxide can maintain its catalytic function for a long time with virtually no peeling or separation from the hot melt resin porous article, even under fairly rigorous service conditions.
In addition, when the hot-melt resin porous article that supports the aforementioned titanium dioxide is used in the form of a flat membrane, it is possible to fabricate a reticulated product with high mechanical strength, such as a photocatalyst-carrying sheet that is resistant to stretching or deformation and that is obtained by integrating a layer of glass fabric with the aid of a laminator. In the photocatalyst-carrying sheet thus fabricated, the photocatalytic substance remains resistant to peeling when stretched or the like. Another benefit is that in contrast to the mixing and molding of titanium dioxide and resins, large areas on the surface of the titanium dioxide are not penetrated into the resin, and thus, are exposed on the surface, making it possible to increase the surface area of the titanium dioxide functioning as a photocatalyst.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The present invention will now be described in detail through specific embodiments.
A hot-melt resin porous article is used as the substrate for the photocatalyst carrier of the present invention. Using a fluororesin as the hot-melt resin is particularly preferred because of the need to afford oxidation resistance, taking into account the decomposition power of the active oxygen produced by titanium dioxide. Specific examples of resins that can be used as such hot-melt fluororesins include tetrafluoroethylene-hexafluoroethylene copolymers (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers (PFA), tetrafluoroethylene-hexafluoroethylene-perfluoroalkyl vinyl ether copolymers (EPA), and tetrafluoroethylene-ethylene copolymers (ETFE). In addition, the aforementioned hot-melt fluororesins, and PFA and FEP in particular, exhibit good transmission properties at a wavelength of 385 nm, which corresponds to the light (UV light) needed to achieve photocatalysis, and are thus suitable as such photocatalyst carrier substrates. Another feature of such hot-melt fluororesins is that their melt viscosity falls within a range of about 102 to 107 poise; that is, these resins behave similarly to common macromolecular materials and, unlike low-molecular substances, melt within a fairly wide temperature range, with the result that these resins can be adequately softened by heating without causing the collapse of the pores in the porous article.
A porous article used as a substrate can be obtained from the aforementioned fluororesin by a method in which hot-melt fluororesin particles and a thermoplastic resin soluble in organic solvents are heated to a temperature above the melting point of the thermoplastic resin soluble in organic solvents but below the melting point of the hot-melt fluororesin. Pressure and shearing force are optionally applied at the same time as heat is applied to perform molding. The system is subsequently heat-treated at a temperature above the melting point of the hot-melt fluororesin, and the resin soluble in organic solvent is then dissolved away with an organic solvent, yielding a hot-melt fluororesin porous article.
It is also possible to obtain a hot-melt fluororesin porous sheet reinforced with glass fabric by performing the following operations during the manufacturing steps. A sheet is first molded when the system is heated and molded at a temperature below the melting point of the hot-melt fluororesin, as described in the molding steps above. Glass fabric is then sandwiched and integrated between two such sheets, then this system is heat-treated at a temperature above the melting point of the hot-melt fluororesin, and the resin soluble in organic solvents is then dissolved away with an organic solvent. The pores and/or the surface of the porous article are/is coated with titanium dioxide by a method in which the resulting hot-melt fluororesin porous article, optionally reinforced with glass fabric, is impregnated with a solution obtained by dispersing fine titanium dioxide particles in water, and the system is then dried, or by a method in which a titanium compound serving as a starting material for fine titanium dioxide part
Junkosha Inc.
Lewis White Carol A.
Wood Elizabeth D.
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