Colloid systems and wetting agents; subcombinations thereof; pro – Continuous liquid or supercritical phase: colloid systems;... – Aqueous continuous liquid phase and discontinuous phase...
Reexamination Certificate
2000-07-26
2002-07-16
Lovering, Richard D. (Department: 1712)
Colloid systems and wetting agents; subcombinations thereof; pro
Continuous liquid or supercritical phase: colloid systems;...
Aqueous continuous liquid phase and discontinuous phase...
C106S013000, C106S287190, C106S440000, C106S448000, C252S588000, C502S350000
Reexamination Certificate
active
06420437
ABSTRACT:
TECHNICAL FIELD
This application is a 35 U.S.C. 371 of PCT/JP99/00342 filed Jan. 27, 1999 which designated the U.S.
The present invention relates to a titanium dioxide sol and a method of producing the same. More particularly the present invention relates to a titanium dioxide colloid sol usable as a semiconductor photocatalyst and a method of producing the same. The titanium dioxide colloid sol can be used as a material for various functional coating agents for the purpose of ultraviolet ray-absorption, stain prevention, hydrophilization, preventing fogging, preventing fungus, deodorizing and for water treatment.
BACKGROUND ART
AS ceramic coating materials which are excellent in heat resistance and wear resistance in comparison with organic coating materials, alkali metal silicate salts, phosphate salts, silica sol and metal oxide coating materials are known.
These ceramic coating materials have the characteristics of inorganic coating materials, for example, excellent heat resistance and wear resistance. Currently, attempts to impart new functions to ceramic coatings has been made mainly for metal oxide coatings.
Among the various ceramics, titanium dioxide can exhibit an excellent photocatalytic effect and when ultraviolet rays are irradiated thereto, the titanium dioxide exhibits a high oxidizing activity. Accordingly, it is known that when the titanium dioxide having an excellent photocatalytic activity is located on a surface of a material, for example, a metal, glass or ceramics, to be coated, the titanium dioxide contributes to enhancing the stain prevention, decomposition of odor-generating substances, water-treatment, rust prevention, prevention of fungus, prevention of algae propagation and the decomposition of hard decomposable waste materials. A plurality of titanium dioxide coating materials for the purpose of forming titanium dioxide coatings having the above-mentioned characteristics on substrate surfaces and methods of producing the coating materials have been provided.
As a method of forming a titanium dioxide coating, the method in which a hydrolysis product of a titanium alkoxide is coated, namely a sol-gel method, is most popular. As a method similar to the sol-gel method, Japanese Unexamined Patent Publication No. 4-83,537 discloses a method in which a mixture of a titanium alkoxide with an amide or glycol is employed, and Japanese Unexamined Patent Publication No. 7-100,378 discloses a method in which a mixture of titanium alkoxide with an alcohol amine is employed.
Also, as a method for producing a titanium dioxide sol, other than the above-mentioned methods, Japanese Unexamined Patent Publication No 6-293,519 discloses a method in which fine titanium dioxide particles crystallized by water heat-treatment are dispersed in an acid solution having a pH value of 3 or less, and the resultant dispersion can be employed for coating.
However, the above-mentioned sol-gel method or the method in which the titanium dioxide colloid particles are deagglomerated or dispersed are greatly disadvantageous in that since the colloidal solution is an acidic solution, when the colloidal solution, is coated on a metal or paper surface, the coated material is corroded or deteriorated. Also, there is a disadvantage that even when the colloidal solution is coated on a material having a high acid resistance, for example, a resin, a ceramic or glass, the coating device, for example, a coater or a spray gun, and a printing machine are corroded and the working atmosphere for the coating workers is degraded.
As a means for solving the above-mentioned problems, Japanese Unexamined Patent Publication No. 9-71,418 discloses a sol liquid comprising hydrogen peroxide and titanium dioxide and a method of producing the sol liquid. The sol liquid is advantageous in that the sol liquid can be neutralized. However, since an oxidizing agent is contained, the sol liquid is disadvantageous in that the effect of the sol liquid for preventing the metal corrosion is low, the sol liquid is colored yellow, and a colorless coating is difficult to be formed from the sol liquid unless the coating is heat-dried.
DISCLOSURE OF THE INVENTION
An object of the present invention is to solve the above-mentioned problems of the conventional photocatalytic titanium dioxide solution and to provide a titanium dioxide colloid sol which is stable in a neutral condition to allow the coating procedure with the sol to be safely carried out and enables a colorless transparent coating to be formed even when dried at room temperature, and a method of producing the same.
The above-mentioned object can be attained by the titanium dioxide sol and the methods of producing the same, of the present invention.
The titanium dioxide colloid sol of the present invention comprises 50 to 100 parts by weight of titanium dioxide colloidal particles charged with negative electricity and 5 to 50 parts by weight of a complexing agent and 1 to 50 parts by weight of an alkaline substance.
The titanium dioxide colloid sol of the present invention preferably has a pH value of 5 to 10.
The method (1) of the present invention for producing a titanium dioxide colloid sol comprises mixing an alkaline substance into an acid titanium dioxide colloid sol containing 50 to 100 parts by weight of titanium dioxide colloid sol and 5 to 50 parts by weight of a completing agent, to adjust the pH value of the sol to a level of 5 to 10, to thereby cause the titanium dioxide colloidal particles to be charged with negative electricity.
The method (2) of the present invention, for producing a titanium dioxide colloid sol, comprises mixing an alkaline substance into an acid titanium dioxide colloid sol comprising 50 to 100 parts by weight of titanium dioxide colloidal particles and 5 to 50 parts by weight of a complexing agent to adjust the pH value of the resultant sol to a level of 6 to 12, and applying a deionization treatment to the sol to thereby cause the titanium dioxide colloidal particles to be charged with negative electricity.
BEST MODE OF CARRYING OUT THE INVENTION
The inventors of the present invention prepared a titanium dioxide colloid solution by reacting an inorganic titanium salt, for example, titanium chloride or titanium sulfate, or titanium alkoxide with water under an acid condition to hydrolyze the titanium salt or alkoxide, and analyzed the electricity-charging behavior of the acid colloid sol of the titanium dioxide. As a result of the analysis, it was confirmed that the titanium dioxide colloidal particles are stably charged with positive electricity in an acid range and, when the colloid solution is neutralized with an alkaline solution into a pH range of from 3 to 5 the titanium dioxide colloidal particles lose almost all of the electric charge and become significantly unstable and are firmly agglomerated with each other to such an extent that the agglomerated particles are difficult to separate from each other; and when the alkaline property of the colloid solution is further enhanced, the above-mentioned agglomerated titanium dioxide colloidal particles are charged with negative electricity.
Then, the inventors of the present invention further researched means for imparting both a stable electric charge and a high dispersibility to the titanium dioxide colloidal particles even in a neutral range.
As a result of the further research, a phenomenon that, when an acid titanium dioxide colloid sol is mixed with an aqueous solution of an alkali metal hydroxide or ammonia to shift the pH value of the sol to alkaline range, the titanium dioxide colloidal particles are strongly agglomerated with each other to such an extent that the agglomerated particles cannot be separated from each other, and a slurry-like suspension is formed, was found. Also, it was found that the above-mentioned phenomenon is due to the titanium ions Ti
4+
present in the sol liquid forming colloidal titanium hydroxide, and the titanium dioxide particles are bonded to each other through the colloidal titanium hydroxide, and that, since the charge of the colloida
Mori Kazuhiko
Nakamura Mitsuru
Tanaka Masanobu
Lovering Richard D.
Manelli Dension & Selter & PLLC
Nihon Parkerizing Co. Ltd.
White, Jr. Paul E.
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