Glazing provided with a low-emissivity multilayer stack

Details Glazing provided with a low-emissivity multilayer stack Glazing provided with a low-emissivity multilayer stack

2000-07-13

2002-08-13

Jones, Deborah (Department: 1775)

Stock material or miscellaneous articles

Composite

Of quartz or glass

C428S428000, C428S448000, C428S450000, C428S472000, C428S698000, C428S702000

Reexamination Certificate

active

06432545

ABSTRACT:

FIELD OF THE INVENTION
The invention is directed to stacks of thin layers having thermal properties, especially solar-control or low-emissivity properties. The stacks being placed on transparent substrates in order to make windows for buildings and vehicles from them. The transparent substrates are organic substrates, of the polyacrylate or polymethyl methacrylate type or preferably, glass substrates. Preferably, the invention is directed to multilayer stacks capable of withstanding heat treatments at high temperatures of at least about 500° C. to about 550° C., which are used for treating glass for the purpose of bending, annealing and/or toughening it.
BACKGROUND OF THE INVENTION
The stacks involved use silver-based functional layers surrounded by coatings made of dielectric material, especially for reducing light reflection, optionally having so-called “blocker” or “sacrificial” metal layers between the functional layer and at least one of the coatings made of dielectric material.
Glazings provided with a low-emissivity multilayer stack make it possible to increase the thermal insulation. In the case of insulating glazing, it is possible, by the use of glass having an emissivity &egr;≦0.1, on the face turned towards the intermediate gas layer, to substantially eliminate radiative exchange between the glass surfaces. Consequently, it becomes possible to manufacture insulating glazing having a K value of 1.1 W/m
2
K. Glazing having optimal low-emissivity multilayer stacks must, moreover, also have an overall energy transmission as high as possible, that is to say a g value as high as possible, in order to be able to use the solar energy within the energy budget. From the optical standpoint, the reflection color of the glazing must be relatively neutral, similar to that of conventional insulating glazing, and it is also attempted to obtain a light transmission as high as possible.
Multilayer stacks which at the very least partially fulfil these conditions have already been studied in various different forms and have, in principle, the general structure mentioned above.
Throughout this text, the term “transparent substrate” will generally be referred to as glass, but it being understood that this term may also encompass substrates made of plastics or other organic polymers. The substrate is only glass in the literal sense when it can withstand a heat treatment, such as bending or toughening at temperatures of about 550° C. to about 650° C.
It is becoming increasingly necessary to develop glazing products having low-emissivity multilayer stacks, which may be subjected to a prestressing heat treatment in order to increase the flexural strength of the glass and to give the glass safety properties. For this purpose, glass panes have to be heated to a temperature of more than 550° C. to 650° C., that is to say heated to their softening temperature, and then have to be suddenly cooled, when a toughening operation is involved. In this case, the layers are exposed to particularly high stresses which cannot always be withstood by the known low-emissivity stacks without deterioration. In the case of thermal stresses, layer modifications may in particular often occur which stem especially from oxidation and/or diffusion phenomena at the interface between the various layers.
Particular importance is attached, during a heat treatment of this kind, to the two sacrificial metal layers adjacent to the silver layer. Document DE 19,632,788 Al discloses a multilayer stack suitable for curved and/or prestressed (toughened) glass in which the sacrificial metal layers above and below the silver layer are composed each time of an AlMgMn alloy and have a thickness of 5 to 10 nm. At least one of the dielectric antireflection layers may be formed from several different oxides of the metals Sn, Zn, Ti, Si and Bi. In the case of this known multilayer system, the silver layer is admittedly protected against corrosion and deterioration by means of the two special layers of blockers at the high temperatures of the heat treatment, but it is not possible to achieve, however, in a satisfactory manner, simultaneously a very high light transmission, a very low emissivity and the desired color neutrality.
The present invention develops a multilayer stack which has a high overall light transmission, an extremely low emissivity and a neutral reflection color. This being so even after the stack has undergone a heat treatment at a moderate or a very high temperature, especially a treatment above about 550° C. in order to curve, toughen or anneal the glass supporting the stack.
SUMMARY OF THE INVENTION
The present invention is directed to a transparent substrate comprising a multilayer stack comprising at least one silver-based functional layer between at least two layers of dielectric material with a metal layer provided between the silver-based functional layer and at least one of the dielectric material layers or coatings. The metal layer is an aluminum alloy of the formula AlM where M is at least one of the elements selected from the group consisting of Mg, Mn, Cu, Zn, Ni and Si. In one embodiment, the stacks can withstand a high-temperature heat treatment and have thermal properties, solar-control properties or low-emissivity properties.
In one particular embodiment, the stack comprises the layer sequence:
D
1
/ZnO/Ag/AlM/D
2
/ZnM′O
wherein Ag denotes the silver-based functional layer, AlM is an aluminum alloy containing at least one of the elements selected from the group consisting of Mg, Mn, Cu, Zn, Ni and Si; ZnM′O is a mixed oxide of zinc and at least one other metal designated at M′, and the ZnM′O has a spinel structure; D
1
, D
2
or both are a layer or a superposition of layers comprising at least one layer made of a metal oxide selected from the group consisting of SnO
2
, Bi
2
O
3
, TiO
2
, ZnO, silicon nitride, a metal nitride, a mixed silicon/metal nitride and mixtures thereof. The mixed silicon/metal nitride can be selected from the group consisting of Si
3
N
4
, AlN, SiAlN, SiZrN and mixtures thereof.
D
1
, D
2
, or both can be a superposition of three layers having a low refractive index of less than 1.75. D
1
, D
2
, or both are made of SiO
2
optionally containing A
1
2
O
3
, flanked by two layers having a refractive index greater than 1.9 and made of compounds selected from the group consisting of SnO
2
, Bi
2
O
3
, TiO
2
, ZnO, Si
3
N
4
, AlN, SiAlN, SiZrN and mixtures thereof.
The aluminum alloy AlM may comprise from about 45% to about 99% by weight of aluminum and from about 55% to about 1% by weight of one or more other metals. Preferably, the aluminum alloy AIM comprises more than about 80% aluminum, from about 2% to about 8% zinc and from 0% to about 3% magnesium.
In another embodiment of the invention, the stacks may further comprise a metal layer inserted between the ZnO layer and the silver layer wherein the metal is Zn.
The mixed zinc oxide ZnM′O is obtained by reactive sputtering using a target made of a metal alloy containing Zn, Sn and Al, Sb, or a mixture thereof. Preferably, the mixed zinc oxide ZnM′O is obtained by reactive sputtering using a target made of a metal alloy containing Zn present in an amount of about 60% to about 80%, Sn present in an amount of about 20% to about 40% and Al or Sb present in an amount of about 1% to 5% by weight of the alloy. Preferably, the metal alloy comprises about 68% Zn, about 30% Sn and about 2% Al or Sb by weight.
The invention also comprises a monolithic, laminated or multiple glazing comprising a transparent glazing sheet that includes on one surface the transparent substrate described herein. Preferably, the glazing sheet is glass or plastic.
DETAILED DESCRIPTION OF THE INVENTION
The invention is directed to a transparent substrate, especially a glass substrate, provided with a multilayer stack having thermal properties, especially solar-control or low-emissivity properties, which is especially capable of undergoing the above-mentioned heat treatments and which comprises at least one silver-based func

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