Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having voids in a component
Reexamination Certificate
1998-12-28
2001-04-17
Copenheaver, Blaine (Department: 1771)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having voids in a component
C427S213340, C427S213360, C428S317900, C428S328000, C428S403000, C430S138000, C502S350000, C502S439000
Reexamination Certificate
active
06217999
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a photochemical reactor element containing microcapsulated TiO
2
photocatalyst.
Titanium dioxide has long been used as a white pigment. It is known that intact TiO
2
crystals or particles have a strong photocatalytic activity and, therefore, may cause photochemical degradation of paint films known as “chalking” when the TiO
2
-containing films are exposed to sunshine in the presence of oxygen and water. Consequently, almost all commercial TiO
2
pigments have been coated with one or more dense layers of SiO
2
, Al
2
O
3
, ZrO
2
or other metal oxides to retard the photochemical degradation of the paint film.
The TiO
2
photocatalyst finds unique use, instead, in photochemically decomposing or destroying malodorous substances, air pollutants or microorganisms. TiO
2
photocatalyst may also be used in producing superhydrophilic surfaces on a substrate which are hardly susceptible to soiling. See, WO96/29375 published Sep. 26, 1996. In these applications, the TiO
2
photocatalyst occurring as powder not only needs to be immobilized on a substrate but also needs to be exposed at least in part to the atmosphere and light. It is also necessary for a matrix or binder used to immobilize the TiO
2
particles to be hardly susceptible to TiO
2
catalyzed photochemical reactions.
Several attempts have been made to meet these conditions. JP-A-05253544 discloses a method of forming a TiO
2
photocatalyst layer on a ceramic substrate such as building tiles by applying titania sol onto the glaze layer of the tile before melting the glaze layer, and then firing both layers. WO96/29375 discloses a similar method comprising applying a mixture of TiO
2
sol and SiO
2
sol onto the surface of a heat resistant substrate to form a film and then firing the film. This method is used to form a superhydrophilic coating on ceramic or glass substrates such as building tiles, mirrors or glass lenses. The above two methods suffer from disadvantages that the substrate is limited to ceramics, glass or other fire-resistant materials and that the photocatalyst layer is frangible and susceptible to abrasive wear. JP-A-08067835 and JP-A-08141503 disclose the use of an inorganic binder material to immobilize the photocatalyst particles, while WO96/29375, discloses silicone polymers as a binder or matrix of TiO
2
photocatalyst particles to form photoreactive films on a substrate. Although films formed of silica or silicone polymers are less susceptible to the photochemical degradation than organic binder resins conventionally used in the paint industry, only a portion of the photocatalyst particles that are exposed to the atmosphere can participate in the photochemical reaction and the remainder of particles that have been fully embedded in the matrix body are not available to the photochemical reaction.
JP-A-08131842 discloses a photochemically active coating film formed of a thermoplastic or thermosetting resin. To expose the photocatalyst particles adjacent to the surface, the film is irradiated with UV light to photochemically decompose the matrix resin surrounding the photocatalyst particles. Obviously, this treatment is intentional “chalking” which remarkably impairs the film integrity.
JP-A09031335 and JP-A-10005598 disclose TiO
2
photocatalyst particles having a porous coating of photochemically inert inorganic materials. The porous coating layer prevents direct contact of the photocatalyst particles with the surrounding matrix and, therefore, may decrease the photochemical degradation of matrix. This treatment compromises the photocatalytic activity of TiO
2
particles as in the case of conventional TiO
2
pigments. However, the photochemical degradation of matrix is not fully avoidable when used at a concentration sufficient to exhibit a desired photocatalytic activity.
All of the above-discussed prior art commonly suffer from disadvantages associated with the fact that only a portion of the photocatalyst particles that are exposed to the atmosphere can participate in the photochemical reaction and the reminder is not available to the photochemical reaction.
A need exists, therefore, for a TiO
2
photocatalyst composition and a system which may elimate or ameliorate various problems associated with the above-discussed prior art.
SUMMARY OF THE INVENTION
In one aspect, the present invention provides a photochemical reactor element using TiO
2
photocatalyst particles. According to the present invention, the photochemical reactor element comprises a composition containing microcapsulated TiO
2
photocatalyst particles having a porous shell layer of photochemically inert inorganic material, said microcapsulated TiO
2
photocatalyst particles being dispersed in a polysiloxane matrix having a permeability to oxygen gas not less than 1×10
−14
mol·m·m
−2
·s
−1
·Pa
−1
. The polysiloxane matrix is preferably formed of a three-dimensional polysiloxane network comprised of a recurring unit of the formula: RnSiO
(4−n)/2
wherein R is methyl, ethyl, n-propyl, isopropyl, phenyl or vinyl, and n is a number represented by the equation 0<n≦1.7.
The photochemical reactor element of the present invention may take any desired shape such as coating films, self-sustained films, bulk bodies, filaments or other shaped bodies.
In another aspect, the present invention provides a method for preparing the photochemical reactor element of the present invention. The method comprises providing microcapsulated TiO
2
photocatalyst particles having a porous shell layer of a photochemically inert inorganic material, providing a hydrolyzate-polycondensate sol of a trialkaoxysilane of the formula RSi(OR′)
3
wherein R is methyl, ethyl, n-propyl, isopropyl, phenyl or vinyl, and R′ is methyl or ethyl, or a mixture of said trialkoxysilane with a tetraalkoxysilane of the formula Si(OR′)
4
and/or a dialkoxysilane of the formula R
2
Si(OR′)
2
wherein R and R′ are as defined, dispersing an amount of said microcapsulated TiO
2
photocatalyst particles in said sol, and shaping and converting the mixture into the photochemical reactor element. Alternatively, the microcapsulated TiO
2
photocatalyst particles may be produced in situ in the matrix using naked TiO
2
photocatalyst particles. In this case, the above method is followed using naked TiO
2
photocatalyst particles. The in situ microcapsulation step comprises irradiating the shaped element with light having an energy greater than the band gap of TiO
2
photocatalyst at a dose sufficient to decompose the hydrocarbon groups of surrounding matrix in the vicinity of the TiO
2
particles while retaining the polysiloxane network of the matrix.
It will be appreciated that the present invention achieves significant advantages over the prior art. Microcapsulation of TiO
2
photocatalyst particles within a porous shell layer of photochemically inert inorganic material and the use of a polysiloxane material having a high permeability to oxygen gas as matrix contribute, on one hand, to decreased susceptibility to photochemical degradation of the matrix and, on the other hand, to the availability of the entire photocatalyst particles including fully embedded particles to the photochemical reaction.
Other advantages of the present invention will become apparent as the description proceeds.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
TiO
2
particles used as pigment normally have a particle size from about 0.2 to about 0.3 &mgr;m, while TiO
2
photocatalyst particles have much smaller particle size and thus much greater specific surface areas than the TiO
2
pigment.
The TiO
2
photocatalyst particles have a primary particle size less than 100 nm, normally several tens nm or less in average. The crystalline form thereof is normally anatase which is photochemically more active than rutile as is well-known in the pigment industry. The TiO
2
based photocatalyst is commercially available, for example, under the brand name of TAIPEK™ ST-01, ST-11, ST-21 or ST-31 from Ishihara Sangyo
Nishino Hiroyuki
Tanigami Yoshinori
Yamada Hideo
Zhang Zuyi
Copenheaver Blaine
Millen White Zelano & Branigan
Nihon Yamamura Glass Co., Ltd.
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