WO2012038718A2

WO2012038718A2 - Coating glass

Info

Publication number: WO2012038718A2
Application number: PCT/GB2011/051700
Authority: WO
Inventors: John Andrew Ridealgh; John Buckett
Original assignee: Pilkington Group Limited
Priority date: 2010-09-20
Filing date: 2011-09-12
Publication date: 2012-03-29
Also published as: WO2012038718A3; GB201015657D0

Abstract

A process for producing a coated glass, the process comprising providing a glass substrate, depositing a pyro lytic coating on at least one surface of the glass substrate to produce a pyrolytically coated glass, ageing the pyrolytically coated glass for a predetermined period, and depositing a further coating on the surface of the aged pyrolytically coated glass, wherein depositing the further coating comprises sputter depositing one or more layers, wherein at least one of said layers is a reflective metal layer.

Description

COATING GLASS

The present invention relates to a process for producing a coated glass and coated glasses produced by the process. In particular, the present invention relates to a process for coating glass on an aged substrate and coated, aged glasses.

At present fresh glass is supplied to sputter coating plants. This is because the glass surface deteriorates during storage leading to poor sputtered coating properties when depositing a coating stack containing reflective metal layers (e.g. silver layers). The poor properties of the sputtered coating are visible as patterns on the coated glass. These patterns are particularly noticeable in (toughenable) coatings after toughening or heat treatment. As a consequence glass colours and thicknesses that are not made regularly have to be made specifically if they are to be coated so the coating can take place very soon after manufacture. This problem reduces the flexibility of glass coating manufacturers .

Glass surface condition is important for imparting good properties to thin film coatings deposited upon the surface. Poor surface quality may be associated with surface corrosion during storage in the ambient conditions of temperature and humidity present in standard glass warehousing. Sometimes this corrosion is so serious it can be seen with the naked eye as patterns while viewing uncoated glass. These patterns are invariably worse after coating with a coating stack containing a metal layer such as silver.

The patterns produced are usually patches or blotches of corrosion of non-uniform size and distribution. In the worst cases they have been compared to the pattern seen on a Leopard skin.

For this reason it is accepted practice within the large area glass coating industry to use only fresh glass, usually defined as glass less than a month, preferably less than four weeks old. The problem becomes even more apparent for toughenable coatings. Toughenable coatings have to survive the thermal toughening (tempering) process which includes heating to temperatures in the region of 650°C, in an air atmosphere, for a number of minutes. During this process patterns in the coating can be produced, or increased. Patterns from an aged glass surface are particularly noticeable after toughening. For this reason a standard test during toughenable coating development is the observation of the development of specular-haze following an oven heat treatment, in vertical orientation, at 650°C for 5 mins (for 4 mm glass thickness). Specular- haze may be considered as a milky or finely dappled spot pattern covering the majority of the coated glass surface. As the name suggests its nature appears to be predominantly, but not completely, specular rather than diffuse. This means the patterns can frequently have a strong angular component to their behaviour i.e. if the illumination and observer's viewing angle is at normal incidence the specular- haze may be strongly apparent whereas if the illumination moves to a very different angle, such as 45°, it may not be. After heating, and after allowing the glass to cool to room temperature, the coated sample is appraised by illumination with a powerful lamp against a dark background. The level of specular-haze is numerically ranked against other samples and experience. A sample showing no specular-haze at all would be ranked at zero. Although it is common to get non-zero specular-haze scores this is not a problem at low value as long as the haze is evenly and randomly distributed. If it is concentrated into patterns, or has regions of very high haze, this becomes visually distracting and is unacceptable. These localised and/or non-uniform patterns in the haze may take the form of patches, spots or blotches. Known methods of trying to maintain or recover surface quality of relatively old glass substrates have involved application of preservatives such as adipic acid. However use of preservatives can lead to the creation of specular-haze patterns based on the non- uniformities in the adipic acid deposition process or polishing of the surface with fine ceramic particle slurries (e.g. of ceria or alumina: this improves aged surfaces but never recovers the state of the original surface) before coating. Both of these techniques add cost and can lead to further problems with unwanted patterning of the coating. They can also lead to absorption and worsening of emissivity in the functional silver films used in low-e and solar-control coatings.

For this reason the usual method of avoiding poor quality surfaces is to avoid long storage of glass substrates. Clearly this is not preferable as flexibility is lost in terms of logistics of glass manufacture and storage. This is particularly problematic for "campaign" products - rarely made glass thicknesses and compositions.

It is an aim of the present invention to address the ageing problem.

The inventors of the present invention have surprisingly discovered that a pyro lytic coating on a glass surface alleviates or solves the ageing problem.

The present invention accordingly provides a process for producing a coated glass, the process comprising: providing a glass substrate, depositing a pyrolytic coating on at least one surface of the glass substrate to produce a pyrolytically coated glass, ageing the pyrolytically coated glass for a predetermined period, and depositing a further coating on the surface of the aged pyrolytically coated glass, wherein depositing the further coating comprises sputter depositing one or more layers, wherein at least one of said layers is a reflective metal layer.

Surprisingly depositing subsequent coatings on a pyrolytically deposited coating on the surface of the glass substrate alleviates the problems associated with depositing coatings on aged glass substrates.

Aged glass substrates will usually be two weeks old or more (i.e. the predetermined period will usually be two weeks or longer). The process is particularly effective wherein the predetermined period is four weeks or longer. Samples considerably older than this also exhibit the beneficial properties of the invention. For example, a three year old substrate comprising a pyrolytically deposited coating has been successfully deposited with a subsequently sputtered coating (see Examples). Usually, the pyrolytic coating will comprise one or more layers. The layers may be selected from one or more of silicon oxide (for example silicon oxycarbide, silica, or silicon oxynitride), titanium oxide, tin oxide and/or zinc oxide. Usually, the pyrolytically deposited coating is deposited to a thickness of between 10 and 50 nm. Preferably, the thickness of the pyrolytic coating will be between 15 and 30 nm, more preferably 15 and 25 nm.

It is particularly beneficial if the pyrolytic coating is deposited during the glass production process. If the glass substrate comprises a float glass substrate, conveniently the pyrolytic coating will be deposited during the float glass deposition process either in the float bath, in the lehr or in the lehr gap. The preferred method of pyrolytic coating is chemical vapour deposition, in particular atmospheric pressure chemical vapour deposition (e.g. online CVD as performed during the float glass deposition process).

Usually the surface of the glass substrate will be the gas side surface. Coated glass manufacturers usually prefer depositing coatings on the gas side surface (as opposed to the tin side surface for float glass) because it is thought that deposition on the gas side surface improves the properties of the coating.

Usually sputter depositing the further coating further comprises depositing one or more layers selected from a dielectric layer, a metallic protective layer, and/or a substoichiometric oxide protective layer. The protective layers may be metals sputtered from a metal target or metal oxides sputtered from conductive ceramic targets in a predominantly argon atmosphere (e.g. nichrome, titanium, zinc-aluminium sub-oxide, titanium sub-oxide, indium-tin sub-oxide).

The dielectric layer or layers in a sputter coating will usually be selected from oxides, nitrides and/or oxynitrides of the following metals and/or their mixtures: Al, Ti, Si, Zn, Sn.

Usually the reflective metal layer in the sputter coating will comprise a silver layer. Sputter coatings may be single reflective sputter coatings (usually a silver layer deposited between dielectric layers with optional protective layers). Alternatively, the sputter coating may comprise one or more additional silver layers (each silver layer preferably being sandwiched between dielectric and protective layers). Usually, the reflective metal layer will be deposited to a thickness of between 6 and 30 nm.

Coated glasses produced according to the first aspect of the present invention find uses in many areas of glass use.

The present invention accordingly provides, in a second aspect, a coated glass comprising, a glass substrate, an aged pyrolytically deposited coating on at least one surface of the substrate, and a sputter deposited coating on the aged pyrolytically deposited coating, wherein the sputter deposited coating comprises one or more layers, wherein at least one of said layers is a reflective metal layer.

The present invention provides in a third aspect the use of at least one pyrolytically deposited undercoating on at least one surface of a glass substrate to reduce the specular haze exhibited by at least one subsequently deposited overcoating on the at least one surface of the glass substrate after the resultant coated glass substrate has undergone a heat treatment.

It is believed that the use of at least one pyrolytically deposited undercoating on at least one surface of a glass substrate maintains the smoothness exhibited by the substrate prior to depositing at least one overcoating.

The reduction in the specular haze may be the reduction in the degree of localised and/or non-uniform patterning of said haze exhibited by said at least one subsequently deposited overcoating on a lm x lm sized glass substrate.

The at least one overcoating may be sputter deposited and may comprise one or more layers. At least one of said layers may be a reflective metal layer. The pyrolytically deposited coating may have been aged for at least two or at least four weeks, but preferably at most five years, more preferably at most 3 years, before depositing the at least one overcoating.

Preferably the heat treatment exposes the substrate to a temperature of at least 450°C, more preferably at least 550°C, even more preferably at least 625°C, but preferably at most 750°C, more preferably at most 700°C, even more preferably at most 675°C. The invention is illustrated by the attached drawings in which: Figure 1 illustrates the general principle of the invention compared to conventional designs, and Figure 2 illustrates the normal emissivity (according to EN12898) as a function of sheet resistance for sputtered silver coatings. Figure 1 shows cross sections of a coated glass substrate according to the invention (A) and a coated glass substrate of a standard design (B). Coated substrate A is a glass substrate 1 coated on one of its surfaces with a CVD layer 2 which has been aged before a sputter multi-layer coating 3 has been deposited on said same surface. Coated substrate B is a glass substrate 1 coated on one of its surfaces with a sputter multi-layer coating 3.

The invention is further illustrated by the following examples in which sputter coatings were deposited on CVD-coated glass and four week old uncoated float glass. Surprisingly the CVD coated substrate was better than the fresh glass despite being much older. Estimates of age for the CVD glass are 3 years and 6 months, for 2 different substrates.

Samples were compared to a sample deposited in the same coating run, but using a standard float glass substrate with no protective CVD film overcoat. The sputtered stack deposited on all substrates was an experimental film made to survive a laboratory heat treatment that simulates the commercial toughening process by exposure to a temperature of 650°C for 5 mins (for 4 mm thick glass) in an air atmosphere. The sputtered stack deposited contains an Ag layer as one of its layers. This layer is responsible for giving the coating its low-emissivity properties. It is also the layer most likely to show damage during heating. This damage shows up as an increase in sheet resistance (related to conductivity and therefore emissivity) and as visible damage that can be seen in bright light against a dark background with the naked eye. This visible damage is known as specular-haze (although it is not necessarily purely specular in nature) and is sometimes called red- haze or white-haze to describe a certain colour cast associated with it. Specular-haze is determined visually and ranked using a number system in which relatively worse specular- haze has a larger number. Besides a general uniform background level of haze there can be localised and/or non-uniform patterns in the haze that are very visible and hence unacceptable. These can take the form of patches, spots or blotches. A totally transparent sample showing no evidence of specular-haze would have a value of zero.

Besides the appearance of patterns from the glass there are other important aspects of coating performance that can be affected by toughening. These are visible transmittance and emissivity. Visible transmittance is an important feature of any coating. Toughenable coatings often contain layers of metal or sub-stoichiometric material that oxidise on heating. This usually results in transmittance rising on heating, or staying the same if there is no metallic/substoichio metric layer. Coatings are designed to take this into account. If there is a problem with glass surface quality the transmittance can be seen to fall on heating. This is obviously a problem as the coating will not necessarily meet its claimed performance - a performance which can be legally binding.

The specular-haze, sheet resistance and transmittance results for the samples are shown below.

After heating all samples had similar changes in sheet resistance and specular-haze, but the CVD baselayer samples had greatly improved transmittance and no patterns. The plain glass substrate had a poorer transmittance improvement and showed unacceptable specular-haze blotch patterns. Coating emissivity controls the thermal performance of a window, and is therefore the main functional property of a low-emissivity window coating. It is usually declared with a legally binding value. Emissivity depends on the electrical charge transport properties of the silver layer. Another attribute dependant on these properties is sheet resistance. As sheet resistance is easier to measure it is usual to quote these values in experimental work. There is an approximate theoretical relationship between the two (Hagen-Rubens Relation), but it is straightforward to empirically derive an accurate relationship by measuring the emissivity of a number of samples with differing sheet resistance, as illustrated in Figure 2. Figure 2 makes it is clear that sheet resistance can be accurately used as a proxy measurement of normal emissivity.

When the glass surface quality is poor a worse emissivity/sheet resistance (higher) is obtained in the coating. For toughenable coatings it is normal for the sheet resistance to decrease on heating as the silver layer at least partially recrystallises. However, when glass surface quality is poor the sheet resistance can stay the same or increase. This can take the coating performance outside the allowable value for emissivity.

The invention utilises a CVD coating deposited during glass manufacture onto the pristine glass surface. Although these coatings may be made from materials very similar in composition to glass (such as Si0₂) they surprisingly reduce the specular-haze patterning to the level of fresh glass or better. In the examples given here the same silver based toughenable coating stack was deposited onto plain glass less than a month old and onto two pieces of Si0₂ coated glass that were approximately 3 years and 6 months old respectively. The coating on the fresh plain glass showed Specular-Haze blotches whereas the CVD coated substrate samples did not. All samples showed a fall in sheet resistance and an increase in transmittance. However the CVD substrate samples showed a larger increase resulting in a higher transmittance for the same sheet resistance/emissivity - a preferable product attribute. As Deposited Heat Treated Tvis Tvis

Specular-

Substrate (AD) Rs (HT) Rs AD HT Comment

Haze

Type ohms/square ohms/square % %

CVD Si0₂

Substrate 3 No years old 8.2 5.2 81 86 1 Patterns

CVD Si0₂

Substrate 6 No months old 8.3 5.1 80 85 1-2 Patterns

Uncoated

Float Glass Blotchy

Substrate 8.2 5.1 80 83 1 Pattern

Table 1 - Physical properties of sputtered Ag-stacks deposited on various substrates

All substrates were prepared in the same way by passing them through a "Bentler" flat bed washing machine. The washing machine uses heated water and a multistage washing process finishing with pure water and an air-knife drier. The CVD Si0₂ underlayers were approximately 25 nm in thickness.

All samples were coated with the same sputtered coating stack in the same coating run. The coating plant was a "Von Ardenne GC 120 V/CSE" equipped with 3400 cm² WSM and SDM magnetrons hooked up to DC and MF Power supplies. DC supplies were used when sputtering in pure Ar. The coating stack had the following design: Substrate/28 SiN/5 ZnSnO_x/5 ZnO/12 Ag/1.5 NiCrO_x/3 ZAO/10 ZnSnO_x/25 SiN (with all thickness in nm).

The deposition conditions were as described in Table 2.

First figure for layer closest to substrate, 2ⁿ figure for layer further away. Table 2

Claims

1. A process for producing a coated glass, the process comprising,

a) providing a glass substrate,

b) depositing a pyrolytic coating on at least one surface of the glass substrate to produce a pyrolytically coated glass,

c) ageing the pyrolytically coated glass for a predetermined period, and d) depositing a further coating on the surface of the aged pyrolytically coated glass,

wherein depositing the further coating comprises sputter depositing one or more layers, wherein at least one of said layers is a reflective metal layer.

2. A process as claimed in claim 1 wherein the predetermined period is four weeks or longer.

3. A process as claimed in either claim 1 or claim 2 wherein the pyrolytic coating comprises one or more layers.

4. A process as claimed in claim 3, wherein the pyrolytic coating comprises silicon oxide, titanium oxide, tin oxide and/or zinc oxide.

5. A process as claimed in any one of the preceding claims when the pyrolytic coating is deposited to a thickness of between 10 and 50nm.

6. A process as claimed in any one of the preceding claims wherein the pyrolytic coating is deposited during the glass production process.

7. A process as claimed in any one of the preceding claims wherein the glass substrate comprises a float glass substrate.

8. A process as claimed in claim 7, wherein the surface of the glass substrate is the gas side surface.

9. A process as claimed in any one of the preceding claims wherein sputter depositing the further coating further comprises depositing one or more layers selected from a dielectric layer, a metallic protective layer, and/or a substoichiometric oxide protective layer.

10. A process as claimed in claim 9 wherein the dielectric layer or layers comprise oxides, nitrides and/or oxynitrides of the following metals and/or their mixtures: Al, Ti, Si, Zn, Sn.

11. A process as claimed in any one of the preceding claims wherein the reflective metal layer comprises a silver layer.

12. A process as claimed in any one of the preceding claims wherein the reflective metal layer is deposited to a thickness of between 6 and 30 nm.

13. A coated glass comprising,

a) a glass substrate;

b) an aged pyrolytically deposited coating on at least one surface of the substrate, and

c) a sputter deposited coating on the aged pyrolytically deposited coating, wherein the sputter deposited coating comprises one or more layers, wherein at least one of said layers is a reflective metal layer.

14. Use of at least one pyrolytically deposited undercoating on at least one surface of a glass substrate to reduce the specular haze exhibited by at least one subsequently deposited overcoating on the at least one surface of the glass substrate after the resultant coated glass substrate has undergone a heat treatment.

15. The use as claimed in claim 14, wherein said reduction in the specular haze is the reduction in the degree of localised and/or non-uniform patterning of said haze exhibited by said at least one subsequently deposited overcoating on a lm x lm sized glass substrate.

The use as claimed in claim 14 or claim 15, wherein the at least one overcoating sputter deposited.

17. The use as claimed in any one of claims 14 to 16, wherein the at least one overcoating comprises one or more layers, wherein at least one of said layers is a reflective metal layer.

18. The use as claimed in any one of claims 14 to 17, wherein the pyrolytically deposited coating has been aged for at least two weeks before depositing the at least one overcoating.

19. The use as claimed in claim 18, wherein the pyrolytically deposited coating has been aged for at least four weeks before depositing the at least one overcoating.

20. The use as claimed in any one of claims 14 to 19, wherein the heat treatment exposes the substrate to a temperature of at least 550°C.