Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2003-06-06
2004-08-10
Loney, Donald J. (Department: 1772)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S104000, C156S272200
Reexamination Certificate
active
06773529
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a glass panel including a pair of glass sheets spaced apart from each other with a gap formed between opposing faces of the sheets, the gap being sealed with peripheral edges of the glass sheets and being depressurized. The invention relates also to a method of manufacturing such glass panel.
BACKGROUND ART
Such glass panel including a pair of glass sheets with peripheral edges of opposing faces thereof being sealed along the entire periphery and the gap therebetween being depressurized provides a distinguished heat-insulating performance and sound-insulating performance.
As sealing material thereof, it has been a conventional practice to employ low-melting glass containing lead. However, lead is a strongly poisonous metal, and in recent years, there have been concerns about the effects of lead to the human health and environment.
When such sealing material is used, it is necessary that the sealing material be softened sufficiently to be fused to the opposed glass sheets. The fluidizing temperature of the low-melting glass is generally higher than 400° C. Therefore, after the glass sheets are heated from the room temperature to a temperature higher than 400° C., they need to be cooled slowly so as not to cause detachment between the sealing material and the glass sheets, so that the sealing step is very time-consuming. Here, unless indicated otherwise, the “sealing step” in the context of the present invention relates to the step of sealing the entire peripheral edges of the opposing faces of the pair of glass sheets.
The extremely time-consuming sealing step as described above is an economical disadvantage in the manufacture of a glass panel. For this reason, it has been desired to reduce the temperature of the sealing step as well as the time required for the sealing step.
Further, in order to retain the distinguished heat-insulating and sound-insulating performances of the glass panel, it is necessary that the gap be maintained at a high degree of vacuum (preferably, 1.33 Pa or lower), that is, the glass panel have high vacuum stability. For maintaining such high vacuum stability, it is necessary to eliminate sufficiently in advance any substance which may be adsorbed on the glass surfaces on the side of the gap and which may then be gradually detached therefrom after the sealing of the gap, thus inviting deterioration in the vacuum condition.
If the sealing step is effected at the high temperature higher than 400° C., such substance which may be present on the gap-side glass surfaces can be removed and or reduced to a satisfactory degree in the course of this high-temperature sealing step. However, with reduction in the temperature used in the sealing step, the cleaning of the glass surfaces becomes insufficient, and there arises a need for means of decreasing such substance other than the sealing step.
DISCLOSURE OF THE INVENTION
The present invention has been made to solve the above-described problem of the conventional art. Considering the case of effecting the sealing step at a lower temperature from the economical point of view in the manufacture of a glass panel, the invention has been made based on a discovery concerning a relationship between a contact angle of water on the gap-side glass surface forming the glass panel and the vacuum stability of the glass panel and on a further discovery of means to reduce the contact angle.
Namely, according to the present invention, a glass panel comprises a pair of glass sheets disposed in an opposing and spaced relationship with each other with a gap formed therebetween, the gap being air-tightly sealed by joining peripheral edges of the glass sheets with a sealing material, wherein at least one of the glass sheets has a contact angle of 30 degrees or less of water on a gap-side glass surface thereof.
In the above, the concept: “contact angle of water on a glass surface” is commonly employed, in the application of glass for a mirror, automobile or the like, for the purpose of evaluating appearance and visibility of the glass when water is attached to its surface. The concept allows a quantitative evaluation of wettability of water relative to the glass surface. The water contact angle varies depending on the surface condition of glass. It is generally believed that such substance as of silanol group or other functional group present on the glass surface affects this water contact angle through the magnitude of surface energy dependent thereon. The term “contact angle” refers to an angle formed, at a point of intersection between a surface of solid (the glass surface in the case of the present invention) and a surface of droplet (water droplet in the case of the present invention), between a tangential line drawn therefrom to the droplet surface and the solid surface, the angle including the droplet.
In the field of application of a glass panel having a pair of glass sheets having peripheral edges of their opposing faces sealed and a depressurized gap formed between the glass sheets as a window component, the convention has completely failed to refer to or discuss the relationship between the gap-side glass surface condition of the glass panel and the vacuum stability thereof.
For the first time, the present inventors conducted extensive research into the correlation between the vacuum stability and the water contact angle of the gap-side glass surface of the glass panel and have found out a range of contact angle in which the vacuum stability of the glass panel can be maintained.
In this respect, if such depressurized glass panel is to maintain its vacuum stability for an extended period of time, this requires not only that any such substance inviting vacuum degree deterioration be minimized in advance on the glass sheets forming the glass panel, but also that such minimized condition of vacuum-deteriorating substance be maintained on the gap-side glass surfaces of the glass sheets after the manufacture of the glass panel.
Further, in the appended claims, unless indicated otherwise, the term “water contact angle on the glass surface” refers to a value of water contact angle on the gap-side glass surface which value is determined immediately after the finished glass panel has been broken. Namely, the glass panel is air-tightly sealed after being depressurized. Therefore, it is not possible, under this condition, to determine the water contact angle on the gap-side glass surface. However, the value of contact angle determined after the sealing is smaller than that determined before the sealing since the substance present on the gap-side glass surfaces decreases. Further, the value determined immediately after the breakage cannot become smaller than that determined after the sealing, since the interior of the panel becomes exposed to a certain atmosphere upon the breakage. Then, these relations among the water contact angles in the respective cases can be expressed by the following formula.
before depressurization ≧immediately after breakage ≧after sealing
In case one of the pair of glass sheets is a glass sheet having non-smooth surface such as a frosted glass sheet, it is not possible to determine the water contact angle on the glass surface as proposed by the invention. However, if it is a glass sheet having vacuum-deteriorating substance minimize, such glass too can be employed for forming the glass panel.
That is, in order for a depressurized glass panel to maintain its degree of vacuum for long time, it is essential that at least one of its glass sheets have a water contact angle less than 30 degrees on its gap-side glass surface. The smaller the contact angle, the better, i.e. the less the amount of such substance as water, organic substance etc. which may be detached from the glass surface to invite deterioration of the vacuum degree of the glass panel. In contrast, if the contact angle exceeds 30 degrees, this means that a large amount of such substance as water, organic substance etc. which may be detached from the glass surface to invite deterioration of the vacu
Domi Shinjiro
Misonou Masao
Sakaguchi Koichi
Fulbright & Jaworski L.L.P.
Loney Donald J.
Nippon Sheet Glass Co. Ltd.
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