Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
2000-06-15
2001-11-06
Jones, Deborah (Department: 1775)
Abrading
Abrading process
Glass or stone abrading
C451S041000, C065S092000, C264S341000, C216S024000, C216S026000
Reexamination Certificate
active
06312317
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for the production of a glass product. More specifically, it relates to a method for the effective production of a glass product having a surface polished highly accurately, particularly a phosphate glass product or a fluorophosphate glass product, as well as a filter formed of the glass product obtained by the above method, and a solid image sensor device for which the filter is adapted.
2. Explanation of Related Art
Generally, glass-containing phosphate as a glass network former has excellent transmission in an ultraviolet region, and it is therefore used in fields where the transmission in an ultraviolet region is important. A colored glass (color filter glass) containing phosphate as a glass network former has been more stably colored with a transition metal ion such as Fe
2+
or Cu
2+
than a color filter glass containing SiO
2
or B
2
O
3
as a glass network former, and is therefore used in various purposes.
Meanwhile, for improving glass in stability, optical constants, transmission characteristics and chemical durability, it is general practice to add alkali metal oxides such as Li
2
O, Na
2
O, K
2
O and Cs
2
O, alkaline earth metal oxides such as CaO, MgO, SrO and BaO, other divalent metal oxides such as ZnO and PbO or F to a glass. When the above components are added as required, the glass can have stability sufficient for shapability and can be mass-produced without causing devitrification.
It is known that the above glass is used for an infrared absorption filter which is a spectral luminous efficiency correction filter of CCD (charge coupled device) for use, e.g., in a color VTR camera. The glass used for the above filter is imparted with the property of absorbing light having a longer wavelength than 700 nm by incorporating CuO as a colorant thereinto and utilizing the absorption by Cu
2+
ion. In this case, the Cu
2+
exhibits excellent absorption only when phosphate is used as a main component of a glass network former. For the above filter, therefore, there is used a phosphate glass or a fluorophosphate glass to which CuO is incorporated. The glass is polished so as to have a thickness of approximately 1.0 to 2.0 mm, and is used as a filter for an image sensor element such as CCD. In the image sensor element, the demand for high density has been increasing, and an area per pixel of photodiode is exceedingly decreased. There is therefore a phenomenon that even a flaw or scratch having a size of the order of several micrometers which has not caused any problem so far causes a detrimental effect on an image. For example, a flaw having a size of greater than about 7 &mgr;m takes or occupies the region for almost one pixel of photodiode, and an image defect in a solid image sensor device is observed. When an infrared absorption filter is disposed close to CCD and when the number of pixels per unit area is large, a filter for use in the above field is therefore required to have a highly accurate polished surface (polish flaw width <7 &mgr;m)
The above phosphate glass containing phosphate as a glass network former essentially has a poor glass structure, and it is therefore liable to have polish-induced flaws and is easily chemically reactive. However, an increase in the hardness of the glass is limited in terms of the glass composition, and unlike a borosilicate glass, it is difficult to obtain a hardness sufficient for easy polishing. When desired transmission characteristics, chemical durability, glass stability adequate for mass-producibility and other optical characteristics are intended to be maintained, an improvement in the composition is limited. It is therefore difficult to impart a phosphate glass or a fluorophosphate glass with a hardness which a borosilicate glass has, and most glasses of this type is so-called least polishable glass having a low hardness. There are therefore limits placed on stably obtaining a highly accurate polished surface (polish flaw width ≦7 &mgr;m) for the glasses of the above type even if the glass composition is improved or the polishing technique is improved.
For polishing the above phosphate glass or fluorophosphate glass, conventionally, there is employed a method in which the glass is polished with a polishing liquid prepared by adding an abrasive such as CeO
2
to water. Generally, as the load for polishing is decreased or as the rotation rate for polishing is decreased, the accuracy of the polished surface of a glass having a low hardness increases. However the phosphate glass and the fluorophosphate glass not only have a considerably low hardness, but also are highly chemically reactive, and therefore, they have the following defects. They show limits in polish accuracy, latent flaws are liable to occur, and it takes a long period of time to polish them.
SUMMARY OF THE INVENTION
Under the circumstances, it is therefore a first object of the present invention to provide a method for effectively producing a glass product having a highly accurately polished surface, a particularly phosphate glass or fluorophosphate glass product.
It is a second object of the present invention to provide a method for the production of a filter which is suitable for a solid image sensor device using CCD and is formed of a glass product obtained by the above method.
It is further a third object of the present invention to provide a filter which is formed of a phosphate glass or fluorophosphate glass having a polish flaws decreased in size and having an ultra-smooth surface and which is suitable for a solid image sensor device using CCD.
Further, it is a fourth object of the present invention to provide a solid image sensor device using the above filter.
For achieving the above objects, the present inventor has made diligent studies on a method of polishing glass surfaces with polishing liquids, and as a result, the following has been found. In conventional polishing methods, relatively large flaws (>width 7 &mgr;m) are liable to remain in a polished surface. This is presumably because a chemical reaction takes place between a glass surface and water during the surface polishing. That is, soluble components such as alkali metal oxide and alkaline earth metal oxide contained in glass components undergo an ion-exchange reaction with hydronium ion (H
3
O
+
) contained in the water to be selectively eluted, and the eluted components corrode the glass network. Further, oxides forming the glass are hydrolyzed so that the entire surface of the glass is dissolved. From the above viewpoint, the rate or velocity of the reaction between the glass and the polishing liquid is decreased by allowing the pH of the polishing liquid used for polishing the glass to approximate to the pH of the glass, and as a result, there can be formed an ultra-smooth surface of which polish flaws are very small (<width 7 &mgr;m). On the basis of the above finding, the present invention has been completed.
That is, according to the present invention, there is provided (1) a method for the production of a glass product, which comprises allowing the pH of a polishing liquid to approximate to the pH of glass of which the surface is to be polished with the polishing liquid, and then polishing the glass surface with the polishing liquid.
According to the present invention, there is also provided (2) a method for the production of a filter, which comprises adapting the glass product obtained by the above method (1) for the filter.
According to the present invention, further, there is provided (3) a filter formed of a phosphate glass or a fluorophosphate glass having a surface of which the hair-like flaws have a width of 7 &mgr;m or less.
Further, according to the present invention, there is provided a solid image sensor device which comprises adapting the above filter (3) for the solid image sensor device.
REFERENCES:
patent: 3673746 (1972-07-01), Highberg
patent: 3685218 (1972-08-01), Gambale et al.
patent: 5227343 (1993-07-01), Osuka et al.
patent: 5
Hoya Corporation
Jones Deborah
Nixon & Vanderhye
Stein Stephen
LandOfFree
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