Cleaning compositions for solid surfaces – auxiliary compositions – Cleaning compositions or processes of preparing – For cleaning a specific substrate or removing a specific...
Reexamination Certificate
2000-04-06
2003-02-18
Boyer, Charles (Department: 1751)
Cleaning compositions for solid surfaces, auxiliary compositions
Cleaning compositions or processes of preparing
For cleaning a specific substrate or removing a specific...
C510S175000, C510S186000, C510S253000, C510S257000, C423S488000
Reexamination Certificate
active
06521575
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method and apparatus for regenerating a glass cleaning solution containing hydrofluoric acid, and a method and apparatus for cleaning silicate glass. In particular, the present invention relates to a method and apparatus for providing a glass surface requiring high cleanness as in a panel for a cathode-ray tube (CRT), for example. Furthermore, the present invention relates to a CRT equipped with the above-mentioned panel.
BACKGROUND ART
Hydrofluoric acid is used for etching a glass surface in producing glass for interior decoration, due to its property of dissolving silicate. Hydrofluoric acid also is used for cleaning glass, due to its property of corroding a glass surface. For example, when something remains adhering to the inner surface of a CRT glass panel for various displays and the like, a phosphor layer and the like formed on the panel are degraded, which results in a decrease in the performance of the CRT. Accordingly, a cleaning step using hydrofluoric acid is indispensable for producing a glass product requiring a very clean surface as in a CRT panel.
When cleaning a CRT panel, a glass cleaning solution containing hydrofluoric acid is circulated by a circulation apparatus connected to a panel cleaning tank so as to be used repeatedly for cleaning panels. However, when a cleaning solution is thus used repeatedly, substances adhering to glass surfaces and glass components are dissolved in the cleaning solution with an increasing number of cleaning cycles, which degrades the cleaning ability of the cleaning solution. Impurities such as dissolved glass components may adhere to a CRT panel to cause a panel defect. Under such circumstances, when cleaning a CRT panel, the cleaning solution is exchanged periodically. A used cleaning solution containing impurities is disposed of as industrial waste.
If a degraded cleaning ability is enhanced by supplying a cleaning solution with hydrofluoric acid, it becomes possible to extend the exchange cycle of a cleaning solution to some degree. However, simply supplying hydrofluoric acid will not overcome the problems related to reduction of industrial waste. Furthermore, supplying hydrofluoric acid cannot remove impurities in a cleaning solution to prevent a panel defect.
Among impurities in a cleaning solution, in particular, fluorosilicic acid (hexafluorosilicic acid; H
2
SiF
6
) generated by the reaction between silica (SiO
2
) in glass and hydrogen fluoride (HF) causes a serious problem. Fluorosilicic acid binds with various cations contained in the cleaning solution to form a fluorosilicate in a gel state. This gel with low flowability is transparent. Therefore, when it adheres to a glass surface, the gel is difficult to recognize visually when the glass surface is wet, which is likely to cause defects in a glass product.
As described in Japanese Publication for Opposition No. 46-15768, for example, it is possible to remove impurities in hydrofluoric acid by utilizing electrolysis. However, electrolysis is not suitable as a method for removing large amounts of impurities efficiently from an exhausted glass cleaning solution. Furthermore, although electrolysis is excellent as a method for removing a trace amount of cations from hydrofluoric acid, it is not effective as a method for removing fluorosilicic acid.
Cleaning a CRT panel is applied for reusing not only a newly molded panel but also a CRT panel on which a black matrix layer or a phosphor layer has been formed. By cleaning the panel with a cleaning solution containing hydrofluoric acid, the black matrix layer and the like are removed by etching together with glass on a panel surface layer. However, these layers contain substances (e.g., carbon in the black matrix layer) which are sparingly soluble in hydrofluoric acid. Therefore, in the cleaning step for reusing a CRT panel, minute insoluble substances are likely to be generated in a large amount in the cleaning solution. If the insoluble substances are left, the surface of a panel will be damaged; therefore, it is necessary to remove insoluble substances floating in the solution. As a method for removing insoluble substances, settling them in a settling tank and filtering them with a filter are considered.
The method for settling insoluble substances in a settling tank is effective when they are large insoluble particles; however, this method is not suitable for minute insoluble substances floating in a glass cleaning solution. Furthermore, according to the method for filtering insoluble substances with a filter, a filter is clogged more quickly if it has a high filtering ability, and a filter having a low filtering ability cannot remove insoluble substances.
As described above, conventionally, a method for regenerating efficiently a glass cleaning solution containing hydrofluoric acid is not known. Reduction of industrial waste has already become a social task, and it also has become a task for the purpose of continuing enterprise activities, in response to the implementation of International Standard for Environment (ISO14001). Under such a situation, an effective method for recovering the cleaning ability of a glass cleaning solution, other than that for exchanging a glass cleaning solution, has not been found. This is becoming a serious problem in the production of glass products.
DISCLOSURE OF INVENTION
In order to overcome the above-mentioned problem, an objective of the present invention is to provide an efficient method and apparatus for regenerating a glass cleaning solution containing hydrofluoric acid that is exhausted in a large amount, utilized for cleaning and treating silicate glass. In particular, an objective of the present invention is to provide an efficient method and apparatus for regenerating a glass cleaning solution containing floating insoluble substances and fluorosilicic acid.
Another objective of the present invention is to provide a method and apparatus for cleaning silicate glass with a regenerated cleaning solution.
Still another objective of the present invention is to provide a cathode-ray tube using a panel cleaned with a regenerated cleaning solution.
In order to achieve the above-mentioned objective, a method for regenerating a glass cleaning solution of the present invention is characterized by adding fluoride to a glass cleaning solution containing hydrofluoric acid after being used for cleaning a surface of silicate glass, allowing fluorosilicic acid in the glass cleaning solution to react with the fluoride to precipitate fluorosilicate, and removing the fluorosilicate from the glass cleaning solution.
According to the above-mentioned regeneration method, a large amount of glass cleaning solution can be regenerated efficiently. In particular, according to the above-mentioned method, hydrogen fluoride is generated in the precipitation of fluorosilicate, and the hydrogen fluoride contributes to the recovery of the cleaning ability of the glass cleaning solution. According to the regeneration method, since the glass cleaning solution can be regenerated by an industrial procedure, the exchange cycle of the glass cleaning solution can be extended.
In the regeneration method, it is preferable that fluoride is provided from at least one compound selected from the group consisting of lithium fluoride, sodium fluoride, potassium fluoride, rubidium fluoride, cesium fluoride, magnesium fluoride, strontium fluoride, barium fluoride, cobalt fluoride, manganese fluoride, copper fluoride, and ammonium fluoride. This is because fluorosilicic acid can be removed efficiently by using these fluorides.
Furthermore, in the above-mentioned regeneration method, it is preferable that hydrofluoric acid is supplied to the glass cleaning solution from which fluorosilicate has been removed. Furthermore, in the above-mentioned regeneration method, it is preferable that fluoride is added together with hydrofluoric acid. Hydrogen fluoride generated by the above-mentioned regeneration method does not cover all the hydrogen fluoride consumed, for example, in the ge
Arai Osamu
Fujiwara Kenji
Gotoh Masao
Sasada Juichi
Taguchi Takuji
Boyer Charles
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
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