Electric heating – Heating devices – With heater-unit housing – casing – or support means
Reexamination Certificate
1999-09-24
2001-07-31
Walberg, Teresa (Department: 3742)
Electric heating
Heating devices
With heater-unit housing, casing, or support means
C219S205000, C312S236000, C052S171200
Reexamination Certificate
active
06268594
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to multipane insulating glass for appliances with an inner-chamber temperature which is lower than ambient temperature, in particular for viewing doors of refrigerators and freezers. The glass comprises at least two panes which are of approximately equal size and are arranged at a distance from one another, the distance being maintained by a spacer which runs continuously around the vicinity of the edge. One of the two outer panes is provided with an electrically conductive, transparent coating on its side which faces towards the space between the panes. The present invention furthermore relates to a process for producing coated flat glass materials for such insulating glass materials.
2. Background Information
In particular, upright and chest refrigerators and freezers have viewing doors with multipane insulating glass materials of the type described in the introduction. These materials delimit the cold area in the inner chamber from the higher ambient temperature.
In refrigerators, and in particular in freezers, the temperature difference between the inner chamber and the environment often results in the formation of condensation. The condensation from the atmospheric humidity which is precipitated on the pane makes it difficult or impossible to see the cooled articles in the inner chamber. In order to substantially prevent this, or in order for the precipitated condensation to be removed again quickly, in the appliances which are commercially available, the pane of the multipane insulating glass which faces towards the outside area is heated. This is achieved by means of a treatable, electrically conductive, transparent coating on the inside of the pane, i.e. on its side which faces towards the space between the panes. Such a coating consists, for example, of doped SnO
2
which is applied, for example, using a hot-spray process and is then fired.
To this end, before the coating operation, the pane of glass is cut to the desired size and a mask which covers the peripheral area is applied to the pane, so that the coating is kept off the subsequent contact surface for the spacer. This is necessary, despite the standard adhesive bonding using adhesives which are non-conductive in the cured state, in order to prevent the metal spacers used from causing spark-overs onto the spacers when the pane is heated, so that voltage is passing through the spacers, which may lead to overheating.
OBJECT OF THE INVENTION
Therefore, the object of the present invention is to provide multipane insulating glass which reduces the formation of condensation, can be produced with little process outlay and is electrically insulated reliably with respect to the outside.
SUMMARY OF THE INVENTION
The object can be achieved by means of multipane insulating glass which comprises at least two panes which are of approximately equal size and are arranged at a distance from one another. The distance is maintained by a spacer which runs continuously around the vicinity of the edge, and one of the two outer panes is provided with an electrically conductive, transparent coating on its side which faces towards the space between the panes. The conductive coating, which can be applied to the entire surface, is deactivated in the peripheral area of the pane, containing the contact surface for the spacer. The object can be further achieved by means of a process for producing coated flat glass materials for the production of multipane insulating glass materials including the steps of application of an electrically conductive, transparent coating to the entire surface of a flat glass pane, cutting the pane to size, and deactivation of the coating in the peripheral area of the pane, including the subsequent contact surface for the spacer.
In contradistinction to the treatable multipane insulating glass materials which have hitherto been known for appliances having an inner-chamber temperature which is lower than the ambient temperature, when flat glass materials for the production of the multipane insulating glass materials according to the invention are being produced, the electrically conductive, transparent coating is applied to the entire surface. It can be applied to the entire surface of commercially available flat glass which is only cut to the particular dimensions once it has been coated.
This eliminates the step of applying the mask prior to coating, which has hitherto been required. Also, it is not necessary to coat panes of numerous different, small formats.
The transparent coating, which can consist, for example, of doped tin oxide, e.g. with fluorine (SnO
2
:F), is applied, for example, using the hot-spray process or the dip-coating process. Other coatings may be possible within the scope of the invention.
Such coated flat glass materials with sheet resistances of, for example, approx. 10
106
/□ (ohm/square) to 40 &OHgr;/□ (ohm/square) are commercially available. Further suitable coating materials are, for example, silver or indium-tin oxide (ITO). It is advantageous for the coatings which are mentioned here by way of example to be not only electrically conductive but also heat-reflecting. Usually, such coatings are referred to, with reference to their scratch resistance, as hard coatings (with a high scratch resistance) and soft coatings (with a low scratch resistance).
For example, the doped tin oxide coatings are hard, and Ag layers and ITO layers represent soft coatings.
Panes with hard coatings are preferred in the context of the invention, since they are more suitable for thermal prestressing, and since multipane insulating glass materials usually comprise prestressed panes.
According to the invention, the electrically conductive, transparent coating, which was originally applied to the entire surface, can be deactivated, i.e. be made no longer electrically conductive, all the way around the peripheral area, specifically including the contact surface for the spacer. This allows commercially available spacers, for example made from metal, to be used in order to ensure the distance between the panes of the multipane insulating glass, without spark-overs onto the spacer when the pane is heated.
In addition to the deactivated direct contact surface for the spacer, the deactivated surface can extend at least another about 2 mm to about 3 mm, on both sides, beyond the contact surface for the spacer. Since the spacer does not directly adjoin the edge of the pane, but rather is slightly set back from the edge of the pane in the vicinity of this edge, in order to form a gap for insulating and sealing material, the deactivated surface preferably extends all the way to the edge of the pane, in order to increase the electrical safety.
In standard pane formats and with standard spacer sizes, the width of the deactivated zone is usually between about 5 mm and about 10 mm, and preferably between about 8 mm and about 10 mm.
Various processors are suitable for deactivation of the described partial area of the coating.
By way of example, soft coatings, e.g. silver coatings, can be removed by being ground off by means of a rotating grinding head tipped with, for example, corundum or diamond.
Such mechanical removal is not advantageous for hard coatings on glass, since it causes many panes to break.
To deactivate the coating, i.e. to remove its electrical conductivity, the coating does not necessarily have to be removed completely, but rather it is sufficient to destroy the coating in such a way that it is no longer electrically conductive.
This may be effected, for example, by the application of a glaze or of an enamel to that area of the coating which is to be deactivated and by subsequent heating of the pane. The glaze or the enamel can be fired in at temperatures which are below the deformation point of the glass of the pane, the vitreous composition of the glaze or of the enamel melting, penetrating into the coating and destroying its conductivity while being joined stably to the surface of the pane of glass.
Glazes c
Leroux Roland
Leutner Kurt
Melson Sabine
Fuqua Shauntina T.
Nils H. Ljungman & Associates
Schott Glas
Walberg Teresa
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