WO2002050394A1

WO2002050394A1 - Evacuated thermoinsulating glass panel and process for the manufacture thereof

Info

Publication number: WO2002050394A1
Application number: PCT/IT2001/000628
Authority: WO
Inventors: Andrea Conte
Original assignee: SAES Getters SpA
Current assignee: SAES Getters SpA
Priority date: 2000-12-19
Filing date: 2001-12-12
Publication date: 2002-06-27
Anticipated expiration: 2003-06-19
Also published as: ITMI20002750A1; AU2002217442A1

Abstract

A thermoinsulating panel (1) comprises two glass panes (2, 3) spaced apart by means of multiplicity of spacers (5) and sealed along their edges so as to form an evacuated interspace (6) inside which a drying material (9) is provided. The invention also relates to a process for manufacturing said thermoinsulating panel.

Description

"ENACUATED THERMOINSULATING GLASS PANEL AND PROCESS FOR THE MANUFACTURE THEREOF"

The present invention relates to an evacuated thermoinsulating glass panel and to a process for the manufacture thereof. In particular, the invention relates to an evacuated thermoinsulating panel suitable for windows.

It is known that heat exchanges between the air present in the rooms of a building and the external environment take place mainly through the windows, and particularly through their glass panes, because of irradiation and conduction phenomena. The reduction of said heat exchanges is desirable in order to reduce the costs for heating or conditioning the building.

International patent application WO/9102878 describes a thermoinsulating panel comprising two glass panes reciprocally sealed at their edges, between which an interspace that can be evacuated is defined. Besides the peripheral sealing, the two glass panes are connected through suitable spacers arranged inside said interspace, necessary in order to avoid that the glass panes adhere to each other once vacuum has been obtained inside the panel. The panel is further provided with a thin tube for the connection with the pumping means, which connects the interspace to the external environment and thus allows the evacuation of the interspace itself. During evacuation the panel is subjected to a degassing treatment by heating at high temperatures, typically comprised between 200 °C and 300 °C, also known with the definition "bake-out". Said treatment has the purpose of releasing the gases which are dissolved in the glass, as well as in the low-melting vitreous material used for producing the peripheral sealing between the panes, so that also said gases are removed from the inside of the panel.

The interspace of the panel may further contain a chemical getter, suitable for sorbing the gases which can permeate inside the evacuated interspace during the life of the panel. According to the teachings of said international application, the getter can be both of the evaporable and of the non-evaporable type. In the first case, the getter activation is carried out by induction heating with a radiofrequency applied from the outside of the panel after it has been assembled. In the case that non-evaporable getters are used, the international application teaches that the thermal activation at high temperatures requested by this second type of sorbers can be provided by said degassing treatment itself. However, the use of evaporable getters for panels intended to be used in windows of buildings is definitely disadvantageous principally because, as it is known, the evaporation causes the diffusion of the reactive material inside the interspace and the deposition thereof onto the internal walls of the panel. Obviously, this causes a worsening of the functional and aesthetic qualities of the window, which is obscured or at least made opaque. On the other hand in order to guarantee the efficacy of sorption by the evaporable getters, it is necessary that after evaporation these are distributed on a large surface. Therefore, it is not advisable to limit the deposition of the getter on a portion of the internal surface of the panel which is then hidden, for example inside the window frame, because said deposition would be insufficient.

Also using a non-evaporable getter has notable drawbacks. As a matter of fact, if it is inserted into the panel before degassing, it is activated during the sealing treatment of the two glass panes which form the panel; said sealing is normally carried out by placing a low-melting glass paste at the perimetrical area of the two panes, and by melting and then solidifying the paste by a thermal treatment at about 500 °C and subsequent cooling. During this treatment, the getter is exposed to air and to the vapors released by the paste, and its sorbing capacity can be spent in this phase. On the other hand, insertion of the getter into the panel after evacuation is practically impossible to carry out. Object of the present invention is thus to provide a glass thermoinsulating panel which is free from the above mentioned drawbacks, and a process for manufacturing it. Said object is achieved with a panel whose main features are specified in the first claim and a process whose main features are specified in claim 8. Other features of the panel and of the process for the production thereof are specified in the following claims.

A first advantage of the thermoinsulating panel according to the present invention consists in that, thanks to the drying material positioned in the interspace thereof, the increase of thermal conductivity between the two faces of the panel during its life is negligible.

Another advantage of the thermoinsulating panel according to the present invention consists in that said drying material can be positioned in a suitable recess inside the panel interspace, next to the perimetrical sealing and is therefore invisible once the glass panel is mounted in the window frame.

Further, the drying materials used for the thermoinsulating panel according to the present invention are perfectly compatible with the process for manufacturing the panel itself.

Further advantages and features of the thermoinsulating panel and of the process according to the present invention will be evident for those skilled in the art from the following detailed description of some embodiments thereof with reference to the accompanying drawings wherein: - Figure 1 shows a frontal view of the thermoinsulating panel according to a first embodiment of the invention;

- Figure 2 shows a view of the central portion of the thermoinsulating panel according to a cross-section taken along line 11-11 of figure 1;

- Figure 3 shows a view of the peripheral portion of the thermoinsulating panel according to a section taken along line H-TJ of figure 1;

- Figure 4 shows a view similar to that of figure 3 of a thermoinsulating panel according to another embodiment of the invention;

- Figure 5 shows a cut-away view of a device containing drying material which can be used according to a further embodiment of the invention; and

- Figure 6 shows a possible way of using the device of figure 5.

With reference to figures 1 and 2, there is shown that the thermoinsulating panel 1 according to the present invention comprises in a known way two glass panes 2 and 3, sealed to each other along their edges by means of a junction 4 of vitreous material. A multiplicity of spacers 5 is positioned between panes 2 and 3, so that these latter and junction 4 enclose an air-tight interspace 6. In figure 1 there is also shown a small pipe 7 connecting said interspace 6 and the environment outside the panel, which is incorporated into the vitreous material forming junction 4. Obviously, it is essential that junction 4 is impermeable to gases and that the vitreous material perfectly adheres to the external surface of connecting pipe 7 without allowing possible permeation of gases.

According to the invention, the surface of pane 2 facing interspace 6 is provided with a recess 8, which can have circular shape and is intended to contain a drying material. Said material has the purpose of sorbing the water vapor which may be present inside interspace 6. Any drying material known in the art can be used for the thermoinsulating panel according to the present invention. Drying materials comprise physical sorbers, such as zeolites, or chemical sorbers, such as alkali metal oxides and alkaline-earth metal oxides. However, the use of chemical sorbers proved to be particularly advantageous. Differently from the physical sorbers, the chemical sorbers sorb water vapor in an irreversible way; these are therefore particularly suitable in the case the thermoinsulating panel is intended for an environment characterized by variations in temperature in a wide range, because zeolites, when brought at relatively high temperatures, can release at least part of the adsorbed water. Among chemical sorbers, the use of calcium oxide is particularly preferred.

The tests carried out show that although the drying materials sorb only water, they allow to maintain substantially constant the thermal conductivity between the two faces (external surfaces of panes 2 and 3) of the thermoinsulating panel according to the present invention. The reasons of this experimental observation are not completely clear: it may be thought either that water is the most abundant gas inside a double glass panel, or that its quantity is comparable to that of other gases, which however have a thermal conductivity lower than that of water, or finally these two hypothesis could both be true.

As it appears from figure 3, in order to avoid that drying material 9 can come out of recess 8 and invade interspace 6, said recess is closed by means of a shutter 10 suitably made of a material permeable to gases and particularly to water vapor. Therefore, particularly suitable for this purpose is a porous septum, for example made of a vitreous material of the same kind of the material used for panes 2 and 3. This measure has the purpose of avoiding that during the production steps of the thermoinsulating panel, because of possible differences in the coefficients of thermal expansion of the materials of panes 2 and 3 and of shutter 10, uneven expansions of these members and consequent breakings of the glass can occur.

According to the embodiment of the invention shown in figure 3, recess 8 is provided with a widened opening, suitable for forming a seat for shutter 10. Alternatively, as shown in figure 4, it is possible to make a recess 11 having straight walls, inside which a shutter 12 can be inserted, provided at the lower end thereof with a protruding edge suitable for maintaining it raised from the bottom of recess 11.

Finally, it is possible to use a device containing drying material of the kind shown in figure 5, Device 13 is formed of a metal container 14 upperly closed by a member 15 permeable to gases but able to retain powders, such as a metal net or a porous septum, for example of sintered steel; drying material 9 is positioned in the space defined by container 14 and member 15.

Device 13 can be used in panel 1 as shown in figure 6, by making a recess (similar to recess 8 of figure 3) in pane 2, by inserting device 13 inside said recess and by keeping the device 13 inside its seat by means of spacers 5. In order to avoid that the heating of the panel can cause the breaking of the glass because of the different expansion coefficient of this material and of the metal which forms container 14, it is convenient that the recess in pane 2 has a larger diameter than device 13.

A preferred process for manufacturing a thermoinsulating panel according to the present invention comprises the following operative steps:

(a) preparing the two glass panes 2 and 3 and making at least one recess on the surface of one pane; (b) filling said recess with a drying material and closing it with a gas- permeable shutter; (c) positioning a multiplicity of spacers 5 on one of the two panes;

(d) superimposing and sealing to each other the two panes 2 and 3, preparing connecting means 7 of the interspace 6 to the environment outside the panel; (e) evacuating said interspace 6 and eliminating said connecting means 7.

If a device of the kind 13 is used, the process can be adapted, by substituting steps (b) and (c) with the following two steps:

(b¹) inserting in said recess a device (13) containing the drying material (9);

(c¹) positioning a multiplicity of spacers (5) on one of the panes (2) so that some of said spacers (5) maintain said device (13) inside said recess (8).

Preferably, a degassing treatment is carried out at the same time of the evacuation of air, during which panel 1 is subjected to a heating at high temperature so that the gases dissolved into the vitreous material which forms panes 2 and 3 and junction 4 come out and are removed by the evacuation itself. Said sealing between the two panes 2 and 3 can be effected by depositing a strip of vitreous material at the edges of said panes 2 and 3, before having superimposed the panes; subsequently to said superimposition the vitreous material is molten and then allowed to cool, in order to solidify it thus obtaining the sealing. As previously seen, said connecting means can consist of a connecting pipe

7 which is incorporated into the vitreous material making up junction 4 before the solidification thereof, and is closed by hot compression at the end of the evacuation of interspace 6.

Claims

CLAΓMS

1. A thermoinsulating panel (1) comprising two glass panes (2, 3) spaced apart by means of a multiplicity of spacers (5) and sealed along their edges so as to form an evacuated interspace (6), characterized in that a drying material (9) is provided inside said interspace (6).

2. A thermoinsulating panel according to claim 1, characterized in that said drying material is selected in the group consisting of the alkali metal oxides, alkaline- earth metal oxides and the zeolites.

3. A thermoinsulating panels according to claim 2, characterized in that said drying material is calcium oxide.

4. A thermoinsulating panel according to claim 1, characterized in that said drying material is positioned inside at least one recess (8; 11) made on the surface of a pane (2) facing said interspace, said recess being closed by means of a gas- permeable shutter (10; 12).

5. A panel according to claim 4, characterized in that said shutter is a porous septum of vitreous material.

6. A thermoinsulating panel according to claim 1, characterized in that it comprises a device (13) formed of a container (14) and upperly closed by a member (15) permeable to gases but able to retain powders, inside which the drying material is provided.

7. A thermoinsulating panel according to one of the preceding claims, characterized in that the sealing of the edges of said panes is made by means of a junction (4) of vitreous material.

8. A thermoinsulating panel according to the preceding claim, characterized in that said junction is crossed by means (7) for connecting, during a step of evacuation of said interspace, said interspace and the environment outside the thermoinsulating panel.

9. A process for manufacturing a thermoinsulating panel (1) according to claim 1, characterized in that it comprises the following operative steps:

(a) preparing two glass panes (2, 3) and making at least one recess (8; 11) on the surface of one pane (2); (b) filling said recess with a drying material (9) and closing it with a gas- permeable shutter (10; 12);

(c) positioning a multiplicity of spacers (5) on one of the two panes (2);

(d) superimposing and sealing to each other the two panes, preparing means (7) for connecting the interspace (6) to the environment outside the panel (1);

(e) evacuating said interspace and eliminating said connecting means.

10. A process for manufacturing a thermoinsulating panel (1) according to claim 6, characterized in that it comprises the following operative steps:

(a) preparing two glass panes (2, 3) and making at least one recess (11) on the surface of one pane (2); (b¹) inserting into said recess a device (13) containing the drying material (9); (c¹) positioning a multiplicity of spacers (5) on one of the two panes (2) so that some of said spacers maintain said device inside said recess (11);

(e) evacuating said interspace and eliminating said connecting means.

11. A process according to claim 9 or 10, characterized in that during the evacuation, panel is subjected to a degassing treatment at high temperature.

12. A process according to claim 9 or 10, characterized in that said sealing between the two panes is carried out by means of a strip of vitreous material (4) laid at the edges of said panes which is molten and then solidified.

13. A process according to claims 9 or 10, characterized in that said connecting means consist of a small connecting pipe incorporated inside said vitreous material (4), which is closed at the end of the evacuation of the interspace.