The present invention relates to double glazing.
This application claims priority from the following U.S. provisional patent applications:
Application No. 60/224949, dated Aug. 11, 2000 and
Application No. 60/238269, dated Oct. 5, 2000.
In a double glazed window, two sheets of glass are arranged parallel to each other with a narrow gap therebetween. A peripheral seal is provided for trapping gas between the panes, to prevent flow of gas degrading the heat transfer, i.e insulation, properties of the assembly, referred to as a doubling glazing unit.
A problem with present double glazing units is that the seal can leak, allowing the ingress of moisture. This can then condense on the inside of the glass, interfering with the transparency of the unit.
The object of the present invention is to provide an improved double glazing unit with an improved seal.
A double glazing unit of the invention comprises two parallel sheets of glass peripherally sealed to each other, the seal being of fused glass frit.
Glass frit is comminuted glass and a binder. The binder is carried in a solvent, whereby the frit can be tape cast in continuous lengths either for subsequent positioning or in situ or screen printed. On heating, the binder is driven off. The frit can be heated to higher temperature for fusing it to a substrate on which it is carried.
Our preferred method of fusing the frit is by laser irradiation. However, we anticipate that it will prove possible to fuse the frit by heating the entire unit in an oven to the frit fusing temperature.
In accordance with a preferred feature, the frit is of colored glass, whereby it absorbs heat on irradiation.
It should be noted that certain double glazing units have three sheets of glass, in effect forming triple glazing units. The invention is equally as applicable to production of triple glazing units as double glazing units.
In accordance with another preferred feature of the invention, the frit is chosen to have substantially the same coefficient of thermal expansion—CTE—as that of the glass to be sealed. On the other hand, the softening point of the glass of the frit is preferably markedly less than that of the glass to be sealed, for example 250° C. as against 500° C.
Further, the degree of preheat of the glass is preferably maintained below the temper firing temperature, whereby the surface compressive stresses induced to strength the glass on tempering are not relieved, at least in the bulk of the glass. Typically, the temper firing temperature is of the order of 500 to 600° C. for a glass with a softening temperature of 750° C.
In accordance with another aspect of the invention, there is provided:
a method of producing a double glazing unit comprising two parallel sheets of glass peripherally sealed to each other, consisting in the steps of:
applying the frit to one of the sheets of glass,
positioning the other sheet of glass over the first sheet on the frit and
locally heating the frit to fusing temperature by traversing it with laser irradiation, whereby the two sheets of glass become peripherally sealed together
Preferably, the sheets are preheated to close to the frit fusing temperature, whereby the energy supplied by the laser is only that required to raise the temperature of the frit locally to its fusing temperature from the preheat temperature.
Again, preferably the degree of preheat of the glass is maintained below the temper firing temperature of the glass, whereby the surface compressive stresses induced to strength the glass on tempering are not relieved, at least in the hulk of the glass.
Subsequent to irradiation, the sealed unit is cooled in a controlled manner.
Normally, the laser irradiation will be carried out in a dry, inert atmosphere whereby such an atmosphere is enclosed within the double glazing unit.
The frit can be preliminarily tape cast and positioned on the glass in continuous lengths. Alternatively, it can be positioned by tape casting direct onto the first sheet of glass. Again, the frit can be positioned by screen printing onto the first sheet of glass.
Normally, the frit is preliminarily heated to drive off its binder, prior to positioning of the other sheet of glass on it.
According to a third aspect of the invention, there is provided a double glazing sealing machine comprising:
a frit application station for applying frit peripherally to a glass sheet to form one side of a double glazing unit;
an assembly station for assembling the double glazing unit from the two glass sheets on top of each other with the frit between them;
a preheating station for preheating the assembled pairs of sheets;
a laser irradiation station for fusing the frit to seal the sheets to each other; and
a cooling station for cooling the sealed units to room temperature.