CA1262843A

CA1262843A - Coated glass

Info

Publication number: CA1262843A
Application number: CA000528493A
Authority: CA
Inventors: Peter Chesworth; Martin Lowe
Original assignee: Pilkington PLC
Current assignee: Pilkington Group Ltd
Priority date: 1986-01-29
Filing date: 1987-01-29
Publication date: 1989-11-14
Also published as: BR8700383A; MX167806B; US4749397A; GB8701486D0; FI870378A0; DE3750823D1; DE3750823C5; FI90655C; FI870378A; ES2000241T3; ES2000241A4; GB2186001A; EP0233003A1; JP2509925B2; DE3750823T2; AU6799187A; AU585426B2; KR870007076A; DE233003T1; EP0233003B1

Abstract

ABSTRACT

Coated Glass Bent and/or toughened silver coated glass having high light transmission and low emissivity is produced by depositing layers of additional metal over, or both under and over, the silver layer.
When the additional metal is used over the silver layer, it is selected from aluminium, titanium, zinc and tantalum. When the additional metal is used both under and over the silver, it is selected from aluminium, titanium, zinc, tantalum and zirconium. The additional metal is used in an amount such that the light transmission of the coated glass increases on bending and/or toughening. The bent and/or toughened coated glass is useful for architectural glazing and as vehicle windows.

Description

~;21~3 CO~ED GLASS

The invention relates to glass fiubstrates coated with light transmitting silver coatlngs, and to the production and proce6~ing of such silver coated glass subs~rates.
It i8 known ehat transparent glass subs~rate3 wlth a thin silver coating, typically 5 nm to 30 nm thick, may be produced with a high light tran~ission and low emlssivity i.e. which reflect a high proportion of infra-red radiation incident upon them but allow visible radiation to pass through. The use of such coatings on window glass (or plastics u~ed in glazings) leads to a reduction in heat 1088 and resultE in valuable savings in heatlng costs. For optimum light transmission, the silver layers are sandwiched between thin anti-reflection layers of metal oxide. Such 1DW emiS9iVitY
coatings including a thin layer of Hilver sandwiched between layers of metal oxide are described9 for example, in European patent speciflcation EP 0 035 906 and UK patent specificatlon GB 2 129 831.
Accordlng to European patent speciflcation EP 0 035 906, a thin layer of materlal ~elected from the group conalstlng of ti~anium, zirconium, silicon, indium~ carbon, cobalt and nlckel ia deposited bPtween the sllver and the overlying metal oxide layer to improve the long term durability of the coating. This addltional thin layer has a tbickness in the range 0.3 nm to 10 nm, preferabIy 1 nm to 5 nm. In :

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each case, the thickness i9 selected to be sufficlent to improve the durability of the coating, but not so great as to cause an unacceptable reduction ln the light tran~mission of the coated product. The specification teaches that the coated substrate should preferably have a light transmission of at least 60% although the specification does include ~ome Examples of coated substrates which have a light transmission of less than 60~; most of these are comparative Examples, but two, Example 56 (light transmisslon 58%) and Example 58 (light transmission 56%) are designated Examples of the inventlon. Their low light tran6missions are due, in part, to the absence of an anti-reflection metal oxide between the silver layer and the glass (Example 56) or over the silver layer (Example 58). In all the Examples, the coatingæ are on plastics substrates.
UK patent speclfication GB 2 129 831 is concerned with problems which arose when attempts were made to apply the metal oxide layer overlying the silver layer by a reactlve sputtering process in the presence of oxygen. Under these condltlon6, the low missivity properties of the silver layer were lost, and the light transmission of the product was æubstantially lower than expected. These problems were overcome, according to patent speclfication GB 2 129 831, by sputtering an additional metal or metals other than ~ilver in an amount equivalent to a layer 0.5 nm to 10 nm thick onto the silver layer.
U.K. patent speclflcation GB 2 129 831 recommends the use o additional metal in an amount Just sufficient t~ achieve the required low emisslvity while obtaining a coating of the maximu~ possible ' ' .

~26`~ 3 light tran6mlsslon. Unfortunately, coated glass produced according to UK patent specification GB 2 129 831 is not stable to heatlng in air, and the coating loaes lts properties of low emissivity and high light transmission when the coated glass 18 subjected to a thermal cycle required for bending or toughening the glass. Thus, in order to obtain a toughened or bent glas3 substrate bearing a silver coating and having high light transmission, it has been necessary to bend and/or toughen the glass substrate ~irst, and then to apply the silver coating to the bent and/or toughened glass.
This di~ficulty has been overcome, in accordance with the present invention, by depositing an additional metal~ in an amount greater than required in accordance with the teaching of UK patent specificatlon GB 21298319 over the silver layerO The presence of the additional metal reduces the light transmission of the coating below the optimum value. However, it is found, surprlsingly, that when the coated glass substrate i8 heated in a bending and/or toughening cycle not only does the coated glass malntain its light transmission, the light transmission of the coating actually increases. The emissivity of the coated glass may simultaneou~ly be reduced.
According to the present invention there is provlded a process for the production of a bent and/or toughened silver coated glass substrate which compri~es sub~ecting a glass substrate with a coating comprising a silver layer 5 nm to 30 nm thlck, a layar of additional metal selected from aluminium, titanium, zinc and tantalum over the ~ilver ~ayer, :

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:~6~ 3 and an anti-reflectlon metal oxide layer over said layer of additional metal to a bending and/or toughening cycle in which it is heated to a temperature above the softening point of the glass, whereby the coated glass develops an increased light: transmission during the bending and/or toughening cycle.
The additional metal i8 preferably deposited substantially free from oxygen i.e. by sputtering ln the absence of oxygen, but may be deposited in partially oxidised for~ (eOg. as a metal oxide which contains a lower proportlon of oxygen than the stolchiometric form of the oxide the metal form~ in lts highest valency state) provided the metal retains su~fic1ent capacity to react with available o~ygen and protect the silver durlng the bending and/or toughening cycle.
The expresslon "softening point" used hereln refers to the temperature at whlch the glass is ~ust beginning to soften. In the present context, it is equivalent, for practical purposes, to the anealing point ~defined in Standard C598-72 of the American Society for Testing Materials). In practice, as is well known in the art, glass is generally heated ~ignificantly above the 60ftening polnt for bending and/or toughening.
In a typical bending process, a coated soda lime silica glass substrate ~s heated ln air at a temperature in the range 570~C to 620C, allowed to sag in a mold of desired curvature, and the bent glass annealed.
In a typical toughenlng process, a coated soda lime silica glass substrate i6 heated in air at a temperature in the ran6e 600C to .
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670C, optionally bent, and rapidly cooled to toughen it. The glass may be cooled by blowing air onto the glass surface.
Samples of glass proce3sed in accordance with the invention were analysed by Auger electron spectroscopy. In Auger analysis, a beam of electrons (the primary beam) is directed onto the aurface to be analysed, and the elements pressnt in the surface are characteri~ed and quantified by examining the energy spectrum of ~econdary electrons emitted from the surface. The surface atomic layers are then removed by argon lon etching to expose sub-surface atoms which are then characterised and quantified Q8 described above. The etching and analysis steps are repeated to bulld up a profile of the composition of the surface layers to the required depth, ~or example the thickness of the coating. The analysis showed that, when the additional metal used was aluminium or zinc, after bending and/or toughen~ng, the additional metal is found both above and below the silver layer. It is believed that the aluminium and zinc migrate through the silver layer during the bending and/or toughening cycle.
Arising from this discovery, it has been found that, instead of depositing all the required additional metal over the silver layer9 part of ~he additional metal may be deposited under the sllver layer.
Moreover, when the additional metal is divided, with part deposited over the silver and part deposlted under the silver, zirconium is also efective as the addltlonal metal.
Thus, according to a further aspect of aspect of the pre~ent invention, there is provided a process for the production of a bent , . :.

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and/or toughened silver coated glass 6ubstrate whlch comprises sub~ectlng a glass substrate with ~ coating comprising a layer oE
additlonal metal selected from aluminium, titanlum, zinc, tantalum and zirconlum over the substrate, a silver layer 5 nm to 30 nm thick over said layer of additional metal, a further layer of additional metal selected from aluminium, titanium, zinc, tantalum and zirconium over the silver layer, and an anti-reflection metal oxlde layer o-ver sald further layer of additional metal to a bending and/or toughenlng cycle ln whlch lt ls heated to a temperature above the softenlng point of the glass, whereby the coated glass develops an lncreased llght transmlsslon durlng the bending and/or toughening cycle.
It ls believed that the additlonal metal deposited over and/or under the sllver layer becomes o~idised during the bending and/or toughening cycle taking up available oxygen; the silver layer is thus lS protected from the effect of oxygen so that the deslred low emisslvlty (high lnfra red reflectlon) of the prod~ct is maintained, with an increase in the llght transmisslon of the product resulting from the oxldation of the additlonal metal to metal oxlde.
The amount of additional metal required depends upon the toughenlng and/or bendlng cycle to which the coated glass ls to be sub~ected, and the degree of oxidatlon of the additlonal metal. In general, the hlgher the temperature and the longer the glass ls hot, the greater the amount of the additional metal required, the lower the temperature, and the ~horter the tlme the gla~s ls hot, the ~maller the amount of additional metal required. The tlme required to heat a glafis pane to the tempPrature requlred for bendlng or toughening will generally be longer the thicker the glass. Thus, , .

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:~Z~ 3 as a general rule, the thicker the glass, the greater amount of additlonal metal requlred~
Thus the amount of additional metal used may be regulated ln accordance with the temperature to whlch the glas6 is heated and the duratlon of the heating cycle employed in the bending and/or toughening cycle to maximise the light transmission of the bent and/or toughened product~
The amount of additional metal used i8 preferably selected so that the coated glass has the maximum possible light transmission after hending and/or toughening; this will generally lnvolve the use of a total amount of additional metal such that the light transmission of the coated glass increases by at least 10% of lts original value on bending and/or toughening.
The coated glass substrate usually has a light transmission of less than 70%~ generally in the range 30% to 70%, before bending and/or toughening, the exact light transmission depending on the particular additional metal used and the bending and/or toughening cycle to be used. On bending and/or toughening, the coated substrates will usually develop an increased light transmission of at least 70%; the preferred products have a light transmlssion of at lea3t 75~, more preferably at least ~0%, with an emissivity of less than 0.2, after bending and/or toughening~
The light transmie~ion figures quoted are for coatings on clear glass substrates. It will be appreciated that the present invention i3 also applicable to the coating of body coloured glass ~which ha~
an lnherently lower llght transmisslon than clear glass) whlch is to .. ..
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8~3 be subsequently bent and/or toLghened. Generally, whether the glass substrate i8 clear or coloured, the total amount of the additional metal used is selected so that the light transmission of the bent and/or toughened coated glass is at least 80%9 and preferably at least 90~, of the light transmission of the uncoated substrate.
The amounts of additional metal deposited over and optionQlly under the silver layer have been referred in terms of thelr effect or the light transmission of the product because the physical thicknesses are, as described hereafter, difficult to determine.
However, from the determlna~ions which have been made, it i8 believed that it will usually be necessary to use the additional metal in an amount equivalent to a slngle metal layer at least 4 nm thic~ or two layers having a total thickness of at leaæt ~ nm) in order to provlde adequate protection for the silver layer during bending and tougheningO It is further believed that the amount o~ additlonal metal used should preferably be less than required to form a single layer 15 nm thick ~being equivalent to two layers having a total thickness of less ehan 15 nm) in order ~o ansure sufficlent oxidation of the metal during bending or toughening to provlde adequate light transmission in the bent and/or toughened product. The more highly oxl~lsed the additional metal present, the greater the amount required to ta~e up available oxygen and protect the silver layer.
When all the additional metal is applied over the silver layer, it ~s prefered to use, as the additional metal~ aluminium or zinc.
When the additional metal is applied partly ovar the silver and partly under the silver, it is preferred to use, as the addltional metal, aluminium, ~inc or titanium.

' ~6215~3 _ 9 _ In a particularly preferred embodiment of the lnvention, the additional metal is aluminiu~ in an amount equivalent to a layer 5 nm to lO nm thick. It is especially preferred, for reasons of convenience, to deposit all the aluminium over the silver layer.
The silver layer in the coating preferably has a thickness of 5 nm to 20 nm.
The anti-reflection layer of metal oxide over the additional metal o~erlying the silver is preferably a layer of tin oxide, titanium oxide, indium oxide (optionally doped wlth tin oxide), bismuth oxide, ~inc oxide or zirconium oxide. If desired9 a mlxture of two or more metal o~ides may be used. The total thickness of any oxide layers overlying the silver layer after bending and/or toughening of the glass, that ls, the thickness of any anti-reflection metal oxide layers overlylng the silver layer plus the thickness of the oxidised additional metal over the silver, will j usually be in the range from lO nm to 80 nm, and preferably from 20 ¦ nm to 60 nm.
If deslred, an anti-reflection layer may be deposited onto the glass before the silver layer or any layer of additional metal under the silver to increase the light transmission o~ the product. When such an anti-reflection layer is deposited, it may conveniently be a metal oxide layer, for example any of the metal oxides described above for use as an anti-reflection layer over the silver layer.
Thls underlayer may serve, not only as an anti-reflection layer, but also as a primer layer to improve the adhesion of the sllver layer to the glass. It wlll usually have a thickness in the range lO nm to 80 :. , '', ' ~ ' ' . .

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nm, especially 20 nm to 60 nm, although, in any particular case, the thickness used will depend on the metal oxide chosen and ths colour and other properties desired in the product. If desired~ a succession of two or more anti-reflection layers of similar total thickness, i.e. usually 10 nm to 80 nm especially 20 nm to 60 nm, may be used under the silver layer.
The coating may be applied to the glass substrate by sputtering the required metal layers, lncluding the silver layer, in the appropriate sequence in an inert atmosphere and reactively sputtering an anti-reflection layer of metal oxide over the addLtional metal overlying the silver. The sputtering operations may be magnetically enhanced.
According to a further aspect of the invention there is provlded a coated glass substrate with a coating comprising a silver layer 5 nm to 30 nm thick, a layer of additional metal selected from aluminium, titanium9 zinc and tantalum over the silver layer, and an anti-reflection metal oxide layer over said additional metal whlch coated glass substrate, when subjected to a bending and/or toughening cycle in which the glass is heated in air to a temperature above the softening temperature of the glass, develops an increased light transmission.
The invention further provides a coated glass substrate with a coating comprising a layer of additional metal selected from aluminium, titanium, zlnc, tantalum and zirconium, a silver layer 5 nm ~o 30 nm thick over the layer of additional metal9 a further layer of additional metal selected from aluminium, titanium, ~inc9 tantalum .

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:~2~2~?43 alld zirconium over the silver layer, and an anti-reflection metal oxide layer over said further layer of addltional metal which coated glass substrate when subjected to a bending and/or toughening cycle in which the glass is heated in air to a temperature abGve the softening temperature of the glass, develops an increased light transmission.
The present invention also providefl, as new products, bent and/or toughened silver-coated glasses which have a light transmission of at least 80% of that of the glass substrate. When aluminium is used as the additional metal (whether applied over the silver or both over and under the silver), it i8 ound to be present in the bent and/or toughened product in oxidised layers over and under the silver. When titanium, tantalum and zirconium are used, and are applied both over and under the silver layer, they are found to be present in the bent and/or toughed product in oxidised layers over and under the silver. Titanium and tantalu~ are also effective when applied only over the siLver layer; in thl6 case, they are found to be present in the bent and/or toughened product in oxldised layers over the silver layer. When ~inc is used as the additional metal ~whether applied over the silver or both over and under the silver) 3 oxidised zinc is found to be present ln the bent and/or toughened product distributed through the layers of the coating.
Thus, according to a further aspect o the present invention, there is provided a bent and/or toughened silver coated glass substrate having a light transmission of at least 80~ of that of the uncoated glass the coating comprlsing an antl-reflection metal oxide layer, an oxidised layer of metal selected from aluminium, , ., , ' ,r .. .
' .~., '''~' ` '' :~Z6~3 titanium, tantalum and zirconium over the anti-reflection layer, a silver layer S nm to 30 nm thick over said oxidised metal layer, a further oxidised layer of metal selected from aluminium, titanium, tantalum and zirconium over said silver layer, and an overlying anti-reflectlon metal oxide layer, tlle said two layers of oxidised metal having a combined total thicknesæ in the range 8 nm to 30 nm.
Preferably, each of the said two oxidisecl layers of metal has a thickness in the range 4 nm to 15 nm.
According to a still further aspect of the present invention, there is provided a bent andtor toughened silver-coated glass substrate having a light transmission of at least 80% of that of the uncoated glass, the coating comprising an anti-reflection metal oxide layer~ a silver layer 5 nm to 30 nm thick over said anti-reflection layer, and an oxidized layer of titanium or tantalum over said silver layer, and an overlying anti-reflection metal oxide layer, the said layer of oxidised metal having a thickness in the range 8 nm to 30 nm.
According to a still further aspect of the present invention, there is provided a bent and/or toughened silver-coated glass substrate havlng a light transmlssion of at least 80~ of that of the uncoated glass, the coating comprising an anti-reflection metal oxide layer, a silver layer 5 nm to 30 nm thick over said anti-reflection layer, and an overlying anti reflection metal layer, with oxidised zinc distributed through all the layers of the coating. The oxidised æinc i9 preferably present in an amount equivalent to a layer of ~inc 4 nm to 15 nm thick.
The bent and/or tou~hened glasses of the lnvention preferably have a light transmission of at least 70%~

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~6Z~3 The present invention enables bent and/or toughened silYer coated glass substrates, with a high light transmlssion and a low emissivity (high in~ra red reflectivity~ to be prepared by a process in which the silver coating ls applied to flat annealed glass which is subsequently bent or toughened. This has two important practical advantages. First, the glass may be coated in stock sizes which are subsequently cut down and bent or toughened as required. Second, the coating is applied to the glass while it is flat, 80 avoiding the problems of forming uniform coatings on a curved glass substrate.
In the present specification and claims, the values quoted for light transmission are for transmission of light from a C.I.E.
Illuminant C Source. The values of emissivity quoted are those obtained by applying the formula Emissivity, E - ~e~B(A~T)d~
B(~,T)d~
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where e~= spectral emittance and B(~T) = black body spectral energy distribution at 300K.

For both light transmission and emissivity, the measurements were made with the radiation source on the coated side of the glass.
It is well known ln the art that very thin layers of metal and metal oxide, particularly layers less than about 5 nm thick, may not be continuous, and it will be understood that the expression 'layer' is used herein to refer to both continuous and non-continous layers.

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8~3 Moreovsr, analysis of coatlngs comprising a plurality of thln layers of metal and/or metal oxide on a glass substrate generally lndicates a substantial overlap or merging of adjacent layers 80 that there is no clear boundary between them; this overlap or merging is particularly marked when the layers are deposited by a high energy process ~uch as magnetically enhanced sputtering. The layer thicknesses referred to in the specification and claims are the equivalent thickness of the continuous layers that would be formed by the material present assuming no overlap with ad~acent layers.
To calculate the amounts of additional metal deposited in the practice of the present invention, the bent and/or toughened products have been analysed by Auger electron spectroscopy and the thicknesæ
of the oxidlsed layers of additional metal determined from the results of the analysis. Flrst9 the atomic ~ of each element detected in the Auger analysis is plotted against etch time to give an Auger depth profile. Then the area under the curve (or curves in the case in which layers of addltional metal are present both under and over the silver) for additional metal is equated to the area of a rectangle (or rectangles) whose height corresponds to the atomic % of additional metal present in the additional metal oxide in which the oxidation state of the additional metal is egual to that observed in the Auger analysis. The thickness of the layer or layers of additional metal oxide is then calculated~from the width of the rectangle(s).
The thickness of the layers of additional metal equivalent to the thickness of the layers of additional metal oxide determlned in this way i8 then calculated from the known bulk densities of the , .; :

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~l2~23~3~3 additional metal and particular oxide of the additional metal found to be present. However, on the basis of experience, the additional metal oxide is assumed, for the purpose of the calculation~ to have a bulk density of 80% of its known bulk deasity.
As noted earlier, it is known that certaln additional metals, deposited over the silver layer, migrate through the silver la~er on bending and/or toughening.
In cases in which all the additlona:L metal has been deposited over the silver, the thickness of the original layer of additional metal deposited is determined by calculating the thickness of the single layer that would be formed by the total additional metal found to be present in the flnal product. In cas2s in which the additional met~l is deposited partly under the silver layer and partly over the silver layer, the thickness of the layers of additional metal originally present are simllarly calculated from ~he results of the analysis, assuming no net migration of the additional metal through the silver on toughening.
For most of the additional metals used, the results calculated are reasonably consistent wlth predictions of layer thickness based on the sputterin~ time and conditions used ln the deposition of the layers of additional metal~ although deviations of up to 25% between the calculated thickness and the predicted thickness are not uncommon. Except in the case of zinc, the calculated thicknesses are believed to be more reliable than the predicted thicknesses. In the case of zinc, the calcuIated thicknesses are about half the value~ of the predicted thicknesses; the zinc is found, in the Auaer analysis, 8'~

- ]6 -to be "smeared out" throughout the coatlng (but with a maximum concentration lmmediately above the coating). It i8 believed that3 with the "smearing out", the calculation of the zinc concentration may not be very relLable and the predlcted values are to be preferred. They have therefore been given, in brackets9 next to the calculated values.
The invention 18 ill~strated but not limited by the followlng Examples. Unles~ otherwlse lndicated, the layer thlckne~ses quoted in the Example~ for ~he addltional metal oxide and addltlonal metal are calculated as indicated above from Auger electron spectroscopy analysis of bent aad/or toughened coated product~, in which the additlonal metal present'has been subs~antially oxidi~ed. The thicknesses of the silver layers and anti-reflectlon tin oxide are similarly calculated from the Auger analysis in conventional manner.
i5 Examples 1 -11 In each of ~hese ~xamples 3 a pane of float glass was prepared for coating by washing and drying and loaded lnto a DC planar magnetron fiputtering apparaeu~O For Examples 1 to 9 and ll, Rn Alrco ILS 1600 apparatus wa~ u~ed; for example 10, a Nordiko NS 2500 apparatus was u~ed.
A layer of tin oxide wa~ reactively sputtered onto the gla~s ~urface from a tin cathode ln the presence of an oxygen atmosphere at 5 x 10 3 torr. In some ca~es a layer of additlonal metal ~as sputtered on to the tln oxlde layer from a cathode of the addltlonal metal In the presence of an argon atmosphere at 4 x 10-3 torr.
A layer of ~ilver ~a~ then spu~tered onto ~he tin oxide frDm a sllver cathode in the preserlce of ~rgon at 4 ~ 1~ 3 torr and a layer of additional metal ~Jas ~puttered onto the sllver from a eathode of * Trade Marks ,.

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the additional metal in the presence of argon at 4 x 10-3 torr.
Finally, a layer of tin oxide was reactively sputtered over the additional metal from a tln cathode in the presence of an oxygen atmosphere 5 x 10-3 torr; and the light transmission and emissivity of the product was measured. The thicknesses of the substrates used and the layers deposited (determined as explained above) are shown in Table 1, together wlth the light transmisslon and emissivity of the resulting products.
Each coated glass was suspended on tongs in a furnace malntalned at 725C and withdrawn when it reached the desired temperature for toughening. Immediately after removal of each glass from the furnace, the glass was rapidly cooled and toughened by blowing air at ambient temperature on to the glass surface. The residence times in the furnace and approximate glass temperature achieved (measured using an infra red radiation thermometer) are shown in Table 2 together with the light transmission and emiss~vity of the coated products. The light transmlssion and emissivity of the products prior to heating are shown in brackets.
In each case, not only is the light transmission maintained on toughening, but it actually increases, for example, by 2B.4% of its original value in Example 1. The emissivity may also be lmproved, as in Example l, where it is reduced from 0.17 to 0.10 on toughening, although ln some cases, as in Example 8, there is an increase in emissivity on toughening. In each caae, the light transmission before toughening i8 substantially lower than would be achieved following the teaching of GB 2,129,B31 to produce a product of optimum light transmission.

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~2~ 3 The thicknesses of the oxidised layers of additional metal found in the toughened products, determlned as described above, are shown below for the products made using aluminium~ titanium, zirconium and tantalum as the additional metal~

ExampleOxidised layer ofOxidised layer of additional metal belowadditlonal metal above silver (nm) silver (nm) 1 3.~ 5.3

2 11.3 7.4

3 6.9 15.~

4 - 14.5 lS 5 12.5 14.0 6 - 15.0 9 5.1 5.4 - 17.3 In Examples 7,8 and 11~ made using zinc as the additional m~tal, oxldised zinc was found to be "smeared out i.e. distributed through all the layers of the coating in the toughened product.
In a comparative Example, a 4 mm pane of float glass was coated with a coating comprising successive layers of tin oxide, sllver, 25 aluminium and tin vxide in accordance with the teachlng of U~K.
patent specificaton GB 2 12~ 831; the amount of aluminium used was, in accordance with the GB patent specification, ~ust sufficient to achieve the required low emissivity while obtaining a coating of the maximum possible light transmission. The emissiv~ty of the coating was 0.1 and the light transmission of the coated glass was 86.8~.
The coated glass was toughened as described above. The residence time in the furnace was 180 seconds and the glaæs achieved a temperature of approximately 650C. After toughening, the coated ., : .

:, glass was found to have an increased emlssivlty of 0.48 and a reduced llght transmission of 79~.
Example 12 A pane of float glass 6 m~ thlck was prepared for coatlng by washing and drying and loaded onto an Airco ILS 1600 D.C. planar magnetron sputtering apparatus.
Tin oxide was reactively sputtered onto the glass surface from a tin cathode in the presence of an oxygen atmosphere at 5 x lO 3 torr to give a tin oxide layer 40 nln thick. ~ layer of sllver 10 nm thick was then sputtered onto the tin oxide from a ailver cathode in the presence of argon at 4 x 10-3 torr and alumlnium was sputtered onto the silver ~rom an aluminium target in the presence of argon at 4 x 10-3 torr to give an aluminium layer 6 nm thick.
Finally a layer of tin oxide 40 nm thick was reactlvely sputtered over the aluminium from a tin cathode in the presence of an oxygen atmosphere at 5 x 10-3 torr. The resulting product was found to have a light transmlssion of 50% and an emissivity of 0.26.
The glass was then suspended on tongs and llfted into a furnace set at 725C. It was withdrawn after 240 seconds at which stage its temperature was measured as 650C. The sample was immediately ; toughened by blowing alr at ambient temperature onto the hot glass surface. The resulting toughened glass product had a light transmlssion of 78% and an emlssivity of 0.11.
In this Example, the layer thicknesses quoted were derlved, by extrapolation~ from the measured layer thicknesses of the same material deposited under similar sputtering conditlons with ~ ...

" ~ , ' : : : ' : ' ~ 20 -appropriate allowance for dif~erent sputtering times.
Example 13 A pane of grey body coloured float glass 6 mm thlk (light transmission 40.8%) was coated with a tln oxide/silver/~inc/tin oxide coating of a composition similar to that described in Example 8. It was found to have a light transmission of 27.8% and an emissivity of 0.16. The coated glass was then toughen~ed as descrlbed wlth reference to Examples l to ll; the resid~ence time in the furnace was 245 seconds and the glass temperature achieved was approximately 650C. After toughening, the coated glass was found to have a increased light transmission of 36%, being approximately 88~ of the light transmission of the base glass, and an emissivity of 0.36. The increase in the light transmission of the glass on toughenlng was 29.5% of the transmlssion before toughenlng.
Example 14 A pane of blue body coloured float glass ~ mm thick ~11ght transmission 56%) was coated with a tin oxide/silver/zinc/tin oxide coating of a composition similar to that described in ~xample 8. It was found to have a light transmission of 28.3% and an emissivity of 0.13. The coated glass was then toughened as described with reference to Examples l to ll; the residence time in the furnace was 250 seconds and the glass temperature achieved was approximately 645C~ After toughening7 the coatea glass waæ found to have an increased light transmission of 43.8%, being approximately 78% of the light transmission of the base glass, and an emissivity of 0.25~ The increase in the light transmission on toughening was 54~7% of the .

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Z~3~3 transmission before toughening. It will be noted that the zinc is apparently not quite so effective in protecting the coatings on body coloured glass in Examples 13 and 14 as the coating on clear float glass in Example 8. Thus 9 in ~xample 13 and 14~ the light transmissions of the toughened products are 88% and 78% of the trans ~issions of the respective uncoated glasses 7 while in Example 8 the light tranmissions of the toughened product is approximately ~3% of the light transmission of the uncoated glass. This may be because the glasses of Examples 13 and 14 are thicker than the glass of Example o and therefore require a longer residence time in the furnace for toughening, so that the amount of additional metal such as zinc required for optimum protection is greater than that used in Example 8.
Example 15 A pane of clear float glass 2.3 mm thick was coated with successive layers of tin oxlde, silver, aluminium and tin oxide as described in Example 1~ using a Temescal in line D.C. magnetron architectural flat glass coater to give a coated pane having a light transmission of 60%. The coated pane was placed on a ring mould and transported through a graduated furnace where it was heated in successive stages to a maximum surface temperature of 600C. The coated pane sagged in the furnace to the required curvatllre. It was withdrawn from the furnace and annealed. The bent, coated pane was found to have a light transmission of 84%.
The emissivity of the coated glass was not measured. However, the sheet resistance of the coating, which is generally related to emissivity, was measured before and after bending. Before bending it was 8 ohms per square and after bendin~ it varied between 5 and 8 , . "~: ,' :.
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2~3 from the furnace and annealed. The bent, coated pane was found to have a light transmis610n of 84%.
The emissivity of the coated glaBs W88 not measured. However, the sheet resistance of the coating, which is generally related to S emissivlty, was mea3ured before and after bending. B~fore bending it was 8 ohms per square and after bending it varied between 5 and 8 ohms per square, corresponding to an emisslvity of less than 0.1. The malntenance of a low sheet reslstance, which generally accompanles a low emissivity, i5 an important advantage of the inventlon, and enables the coatings on bent and/or toughened coated glasse~ of the invention to be used for heating e.g. in vehicle wlndows. When the coating is to be used for heating in a vehicle window, e.g. a windscreen~ the coated glass will be usually laminated, with the coating inwards, after bending.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for the production of a bent and/or toughened silver coated glass substrate which comprises depositing a coating comprising a silver layer 5 nm to 30 nm thick, a layer of a predetermined amount of an additional metal selected from aluminium, titanium, zinc and tantalum over the silver layer, and an anti-reflection metal oxide layer over said layer of additional metal on a glass substrate and subjecting the coated glass substrate to a bending and/or toughening cycle in which it is heated to a temperature above the softening point of the glass, wherein the coated glass develops an increased light transmission during the bending and/or toughening cycle.

2. A process according to claim 1 which comprises depositing the additional metal in an amount such that the coated glass develops an increased light transmission of at least 70% during the bending and/or toughening cycle.

3. A process according to claim 1 which comprises depositing the additional metal in an amount such that the coated glass develops an increased light transmission of at least 80% of the light transmission of the uncoated glass during the bending and/or toughening cycle.

4. A process according to claim 1 which comprises depositing the coating on a soda lime silica glass substrate and heating the coated glass substrate in air at a temperature in the range 570°C to 620°C, allowing it to sag in a mold of desired curvature, and annealing the bent glass.

5. A process according to claim 1 which comprises depositing the coating on a soda lime silica glass substrate and heating the coated glass substrate in air at a temperature in the range 600°C to 670°C, optionally bending the glass, and rapidly cooling the glass to toughen it.

6. A process according to claim 5 which comprises cooling the glass by blowing air onto the glass surface.

7. A process according to claim 1 which comprises regulating the amount of additional metal deposited in accordance with the temperature to which the glass is heated and the duration of the heating cycle employed in the bending and/or toughening cycle, to maximize the light transmission of the toughened and/or bent product.

8. A process according to claim 1 which comprises depositing said additional metal in an amount such that the light transmission of the coated glass increases by at least 10% of its original value on bending and/or toughening.

9. A process according to claim 1 which comprises depositing said additional metal in an amount sufficient to provide a single metal layer having a thickness in the range 4 nm to 15 nm.

10. A process according to claim 1 which comprises depositing aluminium or zinc as the additional metal.

11. A process according to claim 10 which comprises depositing aluminium in an amount equivalent to a layer 5 nm to 10 nm thick as the additional metal.

12. A process for the production of a bent and/or toughened silver coated glass substrate which comprises depositing a coating comprising a layer of a first predetermined amount of additional metal selected from aluminium, titanium, zinc, tantalum and zirconium over the substrate, a silver layer 5 nm to 30 nm thick over said layer of additional metal, a further layer of a further predetermined amount of additional metal selected from aluminium, titanium, zinc, tantalum and zirconium over the silver layer, and an anti-reflection metal oxide layer over said further layer of additional metal, and subjecting the coated glass substrate to a bending and/or toughening cycle in which it is heated to a temperature above the softening point of the glass, wherein the coated glass develops an increased light transmission during the bending and/or toughening cycle.

13. A process according to claim 12 which comprises depositing the additional metal in amounts such that the coated glass develops an increased light transmission of at least 70% during the bending and/or toughening cycle.

14. A process according to claim 12 which comprises depositing the additional metal in amounts such that the coated glass develops an increased light transmission of at least 80% of the light transmission of the uncoated glass during the bending and/or toughening cycle.

15. A process according to claim 12 which comprises depositing the coating on a soda lime silica glass substrate and heating the coated glass substrate in air at a temperature in the range 570°C to 620°C, allowing it to sag in a mold of desired curvature, and annealing the bent glass.

16. A process according to claim 12 which comprises depositing the coating on a soda lime silica glass substrate and heating the coated glass substrate in air at a temperature in the range 600°C to 670°C, optionally bending the glass, and rapidly cooling the glass to toughen it.

17. A process according to claim 16 which comprises cooling the glass by blowing air onto the glass surface.

18. A process according to claim 12 which comprises regulating the amounts of additional metal deposited in accordance with the temperature to which the glass is heated and the duration of the heating cycle employed in the bending and/or toughening cycle, to maximize the light transmission of the toughened and/or bent product.

19. A process according to claim 12 which comprises depositing said additional metal in an amount such that the light transmission of the coated glass increases by at least 10% of its original value on bending and/or toughening.

20. A process according to claim 12 which comprises depositing additional metal in a total amount sufficient to provide a single metal layer having a thickness in the range 4 nm to 15 nm.

21. A process according to claim 12 wherein the additional metal deposited in each layer of additional metal is aluminium, zinc or titanium.

22. A coated glass substrate with a coating comprising a silver layer 5 nm to 30 nm thick, a layer of additional metal selected from aluminium, titanium, zinc and tantalum over the silver layer, and an anti-reflection metal oxide layer over said additional metal which coated glass substrate, when subjected to a bending and/or toughening cycle in which the glass is heated in air to a temperature above the softening temperature of the glass, develops an increased light transmission, the thickness of the anti-reflection metal oxide layer overlying the silver layer plus the thickness of the additional metal layer as oxidized in the cycle over the silver layer being in the range 10 nm to 80 nm.

23. A coated glass substrate according to claim 22 which develops an increased light transmission of at least 70% during the bending and/or toughening cycle.

24. A coated glass substrate according to claim 22 which develops an increased light transmission of at least 80% of the light transmission of the base glass during the bending and/or toughening cycle.

25. A coated glass substrate according to claim 22 wherein the amount of said additional metal is such that the light transmission of the coated glass increases by at least 10% of its original value on bending and/or toughening in air.

26. A coated glass substrate according to claim 22 wherein the amount of additional metal is sufficient to provide a metal layer having a thickness in the range 4 nm to 15 nm.

27. A coated glass substrate according to claim 22 wherein the additional metal is aluminium or zinc.

28. A coated glass substrate according to claim 27 wherein the additional metal is aluminium in an mount equivalent to a layer 5 nm to 10 nm thick.

29. A coated glass substrate according to claim 22 wherein the coating additionally comprises an anti-reflection layer or layers of metal oxide between the glass and the silver layer.

30. A coated glass substrate according to claim 29 wherein the total thickness of any metal oxide layers between the glass and the silver layer is from 20 nm to 60 nm.

31. A coated glass substrate with a coating comprising a layer of additional metal selected from aluminium, titanium, zinc, tantalum and zirconium, a silver layer 5 nm to 30 nm thick over the layer of additional metal, a further layer of additional metal selected from aluminium, titanium, zinc, tantalum and zirconium over the silver layer, and an anti-reflection metal oxide layer over said further layer of additional metal which coated glass substrate, when subjected to a bending and/or toughening cycle in which the glass is heated in air to a temperature above the softening temperature of the glass, develops an increased light transmission, the thickness of the anti-reflection metal oxide layer overlying the silver layer plus the thickness of the additional metal layer as oxidized in the cycle over the silver layer being in the range 10 nm to 80 nm.

32. A coated glass substrate according to claim 31 which develops an increased light transmission of at least 70% during the bending and/or toughening cycle.

33. A coated glass substrate according to claim 31 which develops an increased light transmission of at least 80% of the light transmission of the base glass during the bending and/or toughening cycle.

34. A coated glass substrate according to claim 31 wherein the total amount of additional metal is such that the light transmission of the coated glass increases by at least 10% of its original value on bending and/or toughening in air.

35. A coated glass substrate according to claim 31 wherein the total amount of additional metal is sufficient to provide a metal layer having a thickness in the range 4 nm to 15 nm.

36. A coated glass substrate according to claim 31 wherein the additional metal in each layer of additional metal is aluminium, zinc or titanium.

37. A coated glass substrate according to claim 36 wherein the additional metal is aluminium in a total amount equivalent to a layer 5 nm to 10 nm thick.

38. A coated glass substrate according to claim 31 wherein the coating additionally comprises an anti-reflection layer or layers of metal oxide between the glass and the silver layer.

39. A coated glass substrate according to claim 38 wherein the total thickness of any metal oxide layers between the glass and the silver layer is from 20 nm to 60 nm.

40. A bent/or toughened silver-coated glass substrate having a light transmission of at least 80% of that of the uncoated glass the coating being deposited directly on the glass substrate and comprising an anti-reflection metal oxide layer, an oxidized layer of metal selected from aluminium, titanium, tantalum and zirconium over the anti-reflection layer, a silver layer 5 nm to 30 nm thick over said oxidized metal layer, a further oxidized layer of metal selected from aluminium, titanium, tantalum and zirconium over said silver layer, and an overlying anti-reflection metal oxide layer, the said two layers of oxidized metal having a combined total thickness in the range 8 nm to 30 nm, and the thickness of the anti-reflection metal oxide layers overlying the silver layer plus the thickness of the oxidized metal layer over-the silver layer being in the range 10 nm to 80 nm.

41. A bent and/or toughened silver-coated glass substrate according to claim 40 wherein each of the said two oxidized layers of metal has a thickness in the range 4 nm to 15 nm.

42. A bent and/or toughened silver-coated glass substrate having a light transmission of at least 80% of the uncoated glass, the coating being deposited directly on the glass substrate and comprising an anti-reflection metal oxide layer, a silver layer 5 nm to 30 nm thick over said anti-reflection oxide layer, and an oxidized layer of titanium or tantalum over said silver layer, and an overlyng anti-reflection metal oxide layer, the said layer of oxidized metal having a thickness in the range 8 nm to 30 nm, and the thickness of the anti-reflection metal oxide layer overlying the silver layer plus the thickness of the oxidized metal layer over the silver layer being in the range 10 nm to 80 nm.

43. A bent and/or toughened silver-coated glass substrate according to claim 42 having a light transmission of at least 70%.

44. A bent and/or toughened silver-coated glass substrate having a light transmission of at least 80% of the uncoated glass, the coating being deposited directly on the glass substrate and comprising an anti-reflection metal oxide layer, a silver layer 5 nm to 30 nm thick over said anti-reflection metal oxide layer and an overlying anti-reflection metal oxide layer, with oxidized zinc distributed through all the layers of the coating, the thickness of the anti-reflection metal oxide layers overlying the silver layer being in the range 10 nm to 80 nm.

45. A bent and/or toughened silver-coated glass according to claim 44 wherein the zinc is present in an amount equivalent to a layer of zinc 4 nm to 15 nm thick.

46. A bent and/or toughened silver-coated glass according to claim 44 having a light transmission of at least 70%.