Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1999-06-15
2002-06-04
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S702000, C428S428000, C428S432000, C428S427000, C106S287160, C106S287170, C106S287180
Reexamination Certificate
active
06399229
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a light-transmitting color film exhibiting absorption characteristics within the visible spectrum, a method for producing the film, and a coating solution for forming the color film. More particularly, the present invention relates to a light-transmitting color film having reflectance and reflecting tone which are useful for automobile glass, a method for producing the film, and a coating solution for forming the color film.
2. Description of the Related Art
A transition metal oxide is an inorganic material exhibiting characteristic absorption within the visible spectrum. The theory explaining the absorption mechanism is as follows. When oxygen is coordinated with a transition metal, the d orbital of the transition metal is split into several energy levels. Upon splitting, coloring characteristic to the visible spectrum occurs because the electron transition energy within the orbital, which is 1-3 eV, overlaps the light energy within the visible spectrum. The same theory is considered to account for the phenomenon wherein a complex oxide including two or more kinds of transition metals absorbs visible light.
Examples of industrial application of color films using the same theory include glass products designed to have a privacy-protecting function when used for window glass of vehicles and houses, in which transmittance of visible light is reduced by means of coating transparent glass with the film, as well as glass products having a function of blocking heat rays and ultraviolet rays by shielding sunlight. Since these glass products are used for the windows of houses or vehicles, they require durability, including high wear and abrasion resistance, and high chemical resistance.
Methods for producing the above-described film include a vacuum deposition method and a sputtering method. These dry methods require expensive vacuum systems. Most glass for automobile windows is bend-processed in accordance with design requirements. Therefore, in industrial manufacturing, such glass are not a proper substrate to be processed by dry methods.
In the meantime, a thermal decomposition method is advantageous in that it provides film easily at low cost without need of expensive equipment. In the method, a starting material such as a metal salt is dissolved in a solvent, and the resultant solution is applied to a substrate and heated to high temperature, to thereby obtain metal oxide film. The method permits production of color film at low cost; however, practical application of the method has been successful only in the production of films having high reflectance.
Under these circumstances, a unique coating solution for producing color film and a method for producing color film are disclosed (J. Non-Crystalline Solids, 82, (1986), p 378-p390). The coating solution is produced by addition, to a metal salt solution used in the thermal deposition method, of a metal alkoxide which is vitrifiable by a sol-gel method.
The method is used for producing film having high wear and abrasion resistance and chemical resistance, such as Si oxide film, by use of the sol-gel method. The method is also used for producing an oxide by means of oxidizing a transition metal present in the above-described oxide film as a coloring component, by use of thermal decomposition method. In this method, for example, an Si alkoxide is added to and mixed with a solution in which nitrate salts or sulfate salts of any of several types of transition metals are dissolved as coloring components in accordance with the purpose. When a substrate is coated with the mixture of the metal salt solution and alkoxide hydrolyzate and then heated, a porous gel having a molecular structure of Si—O—Si is produced. When the gel-coated substrate is further heated, ions of the above-described transition metal present in the porous film of the gel undergo crystallization due to heat, to thereby precipitate to form an oxide, which functions as a coloring component. In the process, the above-mentioned gel forms a hard silica film by being densificated through burning. As a result, there can be obtained a silica glass film colored with the above-described transition metal oxide and exhibiting high wear and abrasion resistance and high chemical resistance.
Production of glass by use of the sol-gel method will next be described. First, a metal alkoxide is hydrolyzed, and the hydrolyzate is polymerized, to thereby obtain a three-dimensional network including metal atoms and oxygen atoms. By allowing the reaction to proceed further, the polymer forms a gel, and the resultant porous gel is heated, to thereby produce glass or an oxide polycrystal.
One characteristic feature of the sol-gel method resides in that the method permits low-temperature synthesis. Particularly, in practice, the low-temperature synthesis of silica glass by use of Si alkoxide is widely used for forming a hard coating film on the surface of plastics.
Color films produced by use of the sol-gel method have already been proposed.
For example, Japanese Patent Application Laid-Open (kokai) No. 9406/1993 discloses a colored-glass-gel thin film comprising a metal alkoxide, a condensation polymer of the metal alkoxide, coloring matter, an alcoholic solvent, and a dispersing agent having compatibility therewith. The coloring matter has a particle size of 300-20,000 nm, and metal oxides which serve as inorganic pigments are described as materials therefor.
However, when the technique disclosed in the above-mentioned patent application is used, the particle size of the coloring matter should be adjusted so as to maintain the transparency of the colored-glass-gel thin film.
Japanese Patent Application Laid-Open (kokai) No. 208274/1996 discloses glass having an inorganic pigment including at least CuO—Fe
2
O
3
—Mn
2
O
3
and a thin film prepared from silica sol. However, the fine-particle pigment disclosed therein (elements contained in the pigment: Cu, Mn, Co, Cr, Fe, V, Ti, and Ni) involves the following problems (1) and (2). (1) haze occurs because of scattering due to the size effect of fine particles, which is related to the refractive index of the film. (2) reduction in size of fine particles is essentially required. As a result, the absorption effect of the glass becomes low.
A method for directly forming a color film by use of a transition metal alkoxide is theoretically possible. However, although common alkoxides of Si, Ti, Al, and Zr are inexpensive and relatively easy to handle, most transition metal alkoxides are expensive and difficult to handle. Therefore, the method for producing color film directly from transition metal alkoxides cannot be used as a general method which is widely applicable.
Japanese Patent Application Laid-Open (kokai) No. 169546/1997 discloses the following technique. The specification first points out problems in the above-described techniques; “When a silicon alkoxide and other components other than a coloring component are added in sufficient amounts such that the film attains sufficient durability, the absorbance of the film decreases. Therefore, an increase in the film thickness is required so as to obtain a required decrease in transmittance.”
Claim 1 of the above publication discloses a coating solution for producing oxide film comprising one or more salts of metals selected from the group consisting of Co, Cr, Mn, Fe, Ni, Cu, Zn, and lanthanoids, and an ethylene glycol oligomer.
Further, claim 3 of the publication discloses incorporation of one or more alkoxides or chelates of metals selected from the group consisting of Si, Ti, and Zr to the coating solution.
Further, Examples 14, 15, and 16 of the publication disclose a coating solution comprising Co, Mn, and SiOR, a coating solution comprising Co, Fe, and ZrOR, and a coating solution comprising Co, Ni, and TiOR, respectively.
All films obtained from these Examples are half-mirror, brown transparent films, and have a reflectance of 20%-35%. The obtained films are described to have excellently low haze, excellent adh
Fujita Kennichi
Miyauchi Taro
Muromachi Takashi
Noguchi Tatsuya
Okamoto Hideki
Boss Wendy
Nippon Sheet Glass Co. LTD
Ratner & Prestia
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