GB2029861A

GB2029861A - A heat reflecting pane and a method of manufacturing the same

Info

Publication number: GB2029861A
Application number: GB7848384A
Authority: GB
Original assignee: BFG Glassgroup GIE
Current assignee: BFG Glassgroup GIE
Priority date: 1977-12-23
Filing date: 1978-12-13
Publication date: 1980-03-26
Also published as: FR2412508A2; DE2757750B2; JPS54106527A; JPS5532656B2; GB2029861B; DE2757750A1; BE873035R; FR2412508B2; DE2757750C3

Abstract

A heat reflecting pane is formed by vacuum deposition of a first Ti film on a glass substrate relatively slowly at a vacuum of the order of 10<-4> Torr, and subsequent deposition of a second Ti film on the first Ti film relatively quickly at a vacuum of the order of 10<-5> Torr. The pane is then heated in air in a conventional thermal toughen- ing furnace to oxidize the first Ti film to an intermediate TiO2 film in the anatase form and said second Ti film to an outer TiO2 film in the rutile form, the pane then being chilled to toughen the glass. The invention overcomes the problem of the dulling of the TiO2 film which occurs in reflective TiO2 coated glass panels prepared conventionally.

Description

SPECIFICATION A heat-reflecting pane and a method of manufacturing the same The invention relates to a heat-reflecting pane and to a method of manufacturing such a pane.

Heat-reflecting panes, on which a thin titanium film is deposited in vacuo and subsequently oxidized at elevated temperatures in air to form a heat-reflecting TiO2 film, are known and described e.g. in a publication by G. Hass entitled: "Preparation, Properties and Optical Applications of Thin Films of Titanium Dioxide" (G. Hass, Vacuum, Volume II, No.

4, pages 331-345, 1952). Oxidation of the Ti film in air may result in two TiO2 forms, depending on the conditions under which the Ti film has previously been vacuum-deposited.

If the titanium is rapidly deposited at a high vacuum, i.e. - 10-5 Torr or better, the rutile form is produced, whereas relatively slow evaporation at a lower vacuum, e.g. approximately 10-4 Torr, results in the anatase form.

TiO2 films produced in the aforementioned manner have received various optical applications as coatings of glass panes, e.g. as lightdividers and as sunlight-reflecting coatings. In order to obtain maximum reflectivity, a quarter-wave interference film is used, the thickness being relative to that region of the spectrum in which it is desired to modify the reflection properties of the substrate.

One special application of heat-reflecting panes of the aforementioned kind is to use them in facade units or spandrel panels.

Spandrel panels of the aforementioned kind are preferably made of TiO2-coated glass panes having high, neutral-colour reflectivity in the visible spectral region, with a slight blue or yellow tint if required. In spandrel panels of the aforementioned kind, the TiO2 interference film is usually disposed on the outside of the building, whereas the back of the glass pane is covered with opaque enamel or lacquer, to hide the parts of the building behind the spandrel panel.

TiO2 films having a rutile structure are very advantageous, particularly for the last-mentioned embodiment, since rutile TiO2 films have a higher refractive index than anatase films and thus have higher reflection coefficients, which are greatly desired in facade units or spandrel panels. It has also been found that rutile films have much greater hardness and wear-resistance than anatase films. Consequently panes having a rutile TiO2 interference film at the outside of the building can be directly exposed to atmosphere without damage, even for long periods. In addition, the panes or spandrel panels can be cleaned with the substances normally used for outer glass surfaces.

In various applications of TiO2-coated panes of the aforementioned kind, more particularly when used as facade units or spandrel panels, it is necessary to toughen the glass in compliance with the safety regulations. Toughening of this kind is necessary if spandrel panels coated with rutile are enamelled at the back, since the enamel layer is opaque to radiation so that sunlight may heat the glass so much that heat flaws may occur if the glass substrate is not toughened. Accordingly, the glass is toughened in known manner by heating it above the transformation point to temperatures at which softening begins, followed by abrupt cooling. In the case of soda-lime silicate glass having the normal sheet-glass chemical composition, the temperatures required are approximately 570 to 620"C.

Theoretically, panes of the aforementioned kind can be toughened in two different ways during manufacture. Firstly, the toughening process may advantageously be combined with the oxidation of the vacuum-deposited Ti film. Alternatively, of course, the deposited Ti film can first be oxidized at an adequate temperature, e.g. 400 to 500"C, after which the TiO2-coated pane can be cooled and then, in an additional process step, be heated in an additional furnace to the required toughening temperaturc approximately 570 C to 620 C in the case of soda-lime silicate glass.

Theoretically, of course, it is desirable to oxidize the Ti film to rutile TiO2 as quickly as possible. It is known (G. Hass, Vacuum, Volume II, No. 4, page 335, Fig. 3) that the speed of oxidation increases with the oxidation temperature. However, if, in the known method, the oxidation temperature is increased to the value required for rapid oxidation, i.e. above approximately 550"C, changes occur in the rutile films. The films become dull and opaque and scatter so much transmitted and reflected light that the resulting panes are unsuitable for the aforementioned applications, more particularly as spandrel panels or facade units. Surprisingly, the aforementioned changes occur only in rutile films.If the vacuum deposition conditions are changed, more particularly if the vacuum is lower and/or the deposition rate is less, so that oxidation in the aforementioned manner results in TiO2 films having an anatase structure, the resulting coated panes can be heated oven to high temperatures such as 550"C and above without changing in the aforementioned manner.

Of course, the same difficulties (i.e. the change in rutile films) occur if the panes have to be thermally toughened in the aforementioned manner, since, as previously stated, this requires temperatures above approximately 550"C or preferably 570 to 620"C in the case of soda-lime silicate glass. These disadvantageous changes occur when the panes are heated to the thermal toughening temperatures, whether or not the oxidation of the Ti films to TiO2 films and the heating to the toughening temperature occur in a single step or whether the Ti films are first oxidized at a relatively low temperature (below 550"C) and then, after further processing if necessary, the panes are heated to the temperature required for thermal toughening.

In British Patent Specification No.

1,534,122 there is disclosed a method of manufacturing heat-reflecting panes of the aforementioned kind; suitable more particularly as spandrel panels or facade units, and wherein the TiO2 film is mostly or entirely in the rutile form and undesirable changes are effectively prevented from occurring in the films when heated to temperatures above 550"C, as required for rapid oxidation of the Ti film, more particularly for thermal toughening. To this end, in the method of Patent No.

1,534, 122, a vapour-deposited silicon oxide layer which does not cause interference is deposited upon the glass substrate before deposition of the Ti film so that the silicon oxide layer is disposed between the glass substrate and the TiO2 film in the finished panel.

It is among the objects of the present invention to provide a heat reflecting pane and a method of producing the same, which also overcome the problems mentioned in a different manner from that disclosed in Specification No. 1,534,122.

According to one aspect of the invention there is provided a heat reflecting pane comprising a glass substrate, a film of TiO2 in the anatase form on the glass substrate and a film of TiO2 in the rutile form on the side, remote from the glass substrate, of the film of TiO2 in the anatase form, said films of TiO2 having been formed by deposition of respective Ti films in vacuo and subsequent oxidisation.

According to another aspect of the invention there is provided a method of manufacturing a heat reflecting pane according to the first mentioned aspect, and wherein a first Ti film is vapour-deposited in vacuo on to a glass substrate under a first set of conditions after which a second Ti film is deposited on said first Ti film, in vacuo, and the thus-coated glass pane is heated in air to oxidize the first Ti film to an intermediate film of TiO2 and simultaneously oxidize the second Ti film to a further film of TiO2, the first and second sets of conditions respectively and the conditions during oxidation being such that said intermediate film of TiO2 formed in said oxidation is in the anatase form and such that said further film of TiO2 formed in said oxidation is in the rutile form.

The invention is based on the surprising discovery that the disadvantageous changes in a rutile TiO2 film after heating to temperatures above 550"C, as required more particularly for thermal toughening, can be avoided if an intarmediata film of TiO2 in the anatase modification is disposed between the glass pane and the rutile film. In preferred embodiments, the two films are produced as follows: A first Ti film is deposited on to the glass pane relatively slowly and at a relatively low vacuum, after which a second Ti film is deposited relatively fast at a relatively high vacuum. As a result of subsequent oxidation, the anatase intermediate film is formed from the first Ti film on the glass pane and the rutile film is formed from the second Ti film.

It has been shown that the feature of providing an anatase film between the glass pane and the rutile film completely obviates the disadvantages of the prior art, and that, as in the method and product disclosed in Specification No. 1,534,122, no changes occur in the films at the temperatures required for oxidation or thermal toughening. In addition, however, the TiO2 coating does not crack or become loose even when it has a considerable total thickness of up to 600 , as is desirable in order to obtain a neutral-colour external appearance. Since, in the preferred embodiments of the present invention, the same titanium-filled evaporator devices are preferably used for depositing both Ti films, the films can be applied even more easily and economically than in the case of the heat-reflecting pane and the method according to Patent No.

1,534,122. In addition, titanium coating material is available in wire form, whereas silicon monoxide, when used for paper-coating, is in granulate form, so that it is easier according to the invention to weigh the amount of material required for the evaporator devices.

The double TiO2 coating according to the invention has the same hardness and wear resistance as a rutile film without an anatase intermediate film, provided the rutile film is applied in a thickness of at least approximately 80 . The total thickness of the rutile film inside the total TiO2 coating preferably should not be more than approximately 300 since otherwise the rutile film may crack. The maximum permissible thickness of the rutile film is slightly dependent on the temperature chosen for oxidizing the films or for thermal toughening-the maximum permissible thickness is somewhat lower if the temperature is increased. In addition, the maximum permissible thickness of the rutile film before cracking is slightly influenced by the surface state of the glass before coating i.e. if the glass surface is corroded or has not been carefully cleaned, the maximum permissible thickness is reduced.

Another special advantage of the coating utilized in embodiments of the invention is that the glass pane is directly adjacent the TiO2 coating, resulting in particularly firm adhesion. In addition, the Ti films, even before being oxidized, adhere very firmly to the glass, so that it is easier to handle the Ticoated panes before the Ti films have oxi dized.

Some embodiments of the invention will now be described in detail with reference to the drawing.

The single drawing is a view in section, showing the structure of a heat-reflecting pane according to the invention.

As the drawing shows, a heat-reflecting pane according to the invention comprises a glass substrate in the form of a glass pane 10, more particularly of soda-lime silicate glass, covered in succession by an intermediate film 12 of anatase TiO2 and a film 14 of rutile TiO2. The system of films can be produced by depositing a first titanium layer relatively slowly at a vacuum of the order of 10-4 Torr and then depositing a second Ti layer relatively rapidly in a vacuum of the order of 10-5 Torr, after which the two layers are oxidized at a temperature sufficient to produce the anatase and rutile TiO2 forms respectively. The film system shown in the drawings, in the example described herein, is made up of thermally toughened glass, i.e.

the glass pane is heated after coating to a temperature in the range from 570 to 620"C (550"C in the present case) and then ther mally toughened by chilling. Preferably, the glass pane coated with the two Ti films is first heated to a temperature in the range from 570 to 620"C (in the case of soda-silicate glass) thus converting the deposited Ti films into the anatase film 1 2 and the rutile film 14 and also heating pane 10 to the temperature required for thermal toughening, so that it can immediately be chilled. No disadvantageous changes have been observed in rutile TiO2 films 14 prepared in this way. Even long-term tests do not show any changes in the TiO2 coating.

Two examples will now be described. Example 1 illustrates a technique according to the prior art whereas Example 2 illustrates a technique embodying the invention.

Example 1 A float glass pane 8 mm thick and having external dimensions of 300 x 245 cm was first cleaned in conventional manner by a flow discharge at a pressure of 3 X 10-2 Torr in a vacuum deposition plant. Next, a Ti film was vacuum-deposited at a pressure of 5 x 10-5 Torr for 35 seconds. Next the coated pane was heated to 620do in a conventional thermal toughening furnace and then chilled. During the heating process, the titanium film was oxidized to a titanium film 470 A thick having a rutile structure. However, the film was dull and opaque, so that the pane could not be used i.e. was unsuitable for architectural reasons, more particularly for use as a spandrel panel or facade unit.

Example 2 The procedure was the same as for Example 1 except that after the flow discharge purification, a first Ti film was deposited at a pressure of 1.5 X 10-4 Torr in 2 minutes, after which the deposition process was interrupted, the vacuum was made more intense, and a second Ti film was deposited at a pressure of 5 X 10-5 Torr in 20 seconds. The thus coated pane was then toughened in the same manner as in Example 1. The outer TiO2 film, which was produced from the Ti film applied in a high vacuum, had a rutile structure, whereas the intermediate film had an anatase structure. In contrast to the pane produced according to Example 1, the pane produced by the procedure of Example 2 was completely transparent after toughening, and was therefore very suitable as a spandrel panel or facade unit. The pane had a neutral-colour, silvery shining appearance. Its reflective power, relative to the sensitivity of the human eye to brightness, was 40%. The pane had the characteristics required to render it very useful for architectural purposes, in conjunction with neutral-colour insulating glass planes.

Claims

1. A heat reflecting pane comprising a glass substrate, a film of TiO2 in the anatase form on the glass substrate and a film of TiO2 in the rutile form on the side, remote from the glass substrate, of the film of TiO2 in the anatase form, said films of TiO2 having been formed by deposition of respective Ti films in vacuo and subsequent oxidisation.

2. A heat-reflecting pane according to claim 1, in which the total thickness of the TiO2 coating, comprising the anatase film and the rutile film is 300 to 600 .

3. A heat-reflecting pane according to claim 2, in which the anatase film has a thickness of at least 30 .

4. A heat-reflecting pane according to claim 3, in which the rutile film has a thickness of at most 300 .

5. A heat-reflecting pane according to claim 4, in which the rutile film has a thickness of at least 80 .

6. A heat-reflecting pane according to claim 5, in which the rutile film has a thickness of 220 to 250 .

7. A heat-reflecting pane according to any of the preceding claims, in which the glass substrate is thermally toughened by heating to a temperature of at least 550"C, followed by chilling.

8. A heat-reflecting pane according to any of claims 1 to 6 in which the temperature to which the glass substrate is heated for toughening is between 570"C and 620"C.

9. A heat reflecting pane according to any of claims 1 to 8 wherein said glass substrate is of soda-lime silicate glass.

10. A method of manufacturing a heatreflecting pane according to any of the preceding claims, wherein a first Ti film is va pour-deposited in vacuo on to a glass substrate under a first set of conditions after which a second Ti film is deposited on said first Ti film, in vacuo, and the thus-coated glass pane is heated in air to oxidize the first Ti film to an intermediate film of TiO2 and simultaneously oxidize the second Ti film to a further film of TiO2, the first and second sets of conditions respectively and the conditions during oxidation being such that said intermediate film of TiO2 formed in said oxidation is in the anatase form and such that said further film of TiO2 formed in said oxidation is in the rutile form.

11. A method according to claim 10, in which the first Ti film is deposited relatively slowly at a relatively low vacuum, of the order of 10-4 Torr, and the second Ti film is deposited relatively quickly at a relatively high vacuum of the order of 10-5 Torr.

1 2. A method according to claim 11, in which the first Ti film is deposited in more than 60 seconds and the second Ti film in less than 30 seconds, and the pressure in the vapour-cating device is between 1 and 2 x 10-4 Torr when the first Ti film is deposited and not more than 6 x 10-5 Torr when the second Ti film is deposited.

1 3. A method according to any of claims 10 to 12, in which the two Ti films are vapour-deposited in succession, using the same vapour-coating device filled with Ti vapour, and after the first Ti film has been applied the evaporation process is stopped, the vacuum is made more intense, and then the second Ti film is deposited.

14. A method according to any of claims 1Q to 13, in which the Ti-coated glass pane is heated in air to a temperature of at least 550"C in order to oxidize the Ti films.

1 5. A method according to any of claims 10 to 13, in which the Ti-coated glass pane is heated in air to a temperature of between 570 and 620"C in order to oxidize the Ti films.

16. A method according to claim 14 or 1 5 in which the glass pane is thermally toughened by chilling after heating it to the oxidation temperature.

1 7. A method according to any of claims 10 to 15, in which the Ti-coated glass substrate is first heated to a temperature sufficient to oxidize the Ti films, then further processed if required and then, in an additional heating step, thermally toughened by being heated to a temperature of at least 550"C, and then chilled.

1 8. A method according to claim 1 7 in which the glass substrate is thermally toughened by being heated to a temperature of between 570 and 620"C.

1 9. A method according to any of claims 10 to 1 8 wherein the glass substrate used is of soda-lime silicate glass.

20. A heat-reflecting pane substantially as herein before described with reference to Example 2 herein.

21. A method of manufacturing a heatreflecting pane, substantially as hereinbefore described with reference to Example 2 herein.

22. Any novel feature or combination of features described herein.