EP2490988A1

EP2490988A1 - Tempered glass spacer

Info

Publication number: EP2490988A1
Application number: EP10785133A
Authority: EP
Inventors: Serge Valladeau; Xavier Brajer
Original assignee: Saint Gobain Glass France SAS; Compagnie de Saint Gobain SA
Current assignee: Saint Gobain Glass France SAS; Compagnie de Saint Gobain SA
Priority date: 2009-10-22
Filing date: 2010-10-18
Publication date: 2012-08-29
Also published as: CN102639456A; US20120202049A1; JP2013508250A; KR20120098642A; WO2011048313A1; FR2951715A1

Abstract

The invention relates to an object including at least one glass spacer between a first element of said object and a second element of said object, said spacer including a concentration gradient in alkaline ions from the surface thereof and perpendicular to the surface thereof. The object can be a vacuum solar collector. The invention also relates to a glass ball including a concentration gradient in alkaline ions from the surface thereof and perpendicular to the surface thereof and to the use of said ball as a spacer withstanding a pressure force between two elements, said pressure pushing the two elements towards one another.

Description

TEMPERED GLASS SPACEUR

The invention relates to the field of glass spacers. Spacers are used to maintain a distance between two solid elements, in particular two walls, generally parallel, of an object such as double-glazing, a flat lamp, a solar thermal collector, etc.

Glass spacers are known. As documents of the state of the art, mention may be made of WO96 / 12862 and US4683154. Spacers can be metal or ceramic like zirconia. The chemical quenching technique is known to reinforce glass objects in applications where the glass is biased in tension or bending, but not in compression. The glass spacers have the advantage of being little visible given the natural transparency of the glass. In addition, they improve energy efficiency for solar collectors because they let in solar radiation. Thus, for application in a solar collector, the spacer is a transparent element at least in the wavelength ranges of solar radiation which are useful for the conversion of energy from solar radiation into thermal energy by means of solar radiation. absorption means.

We have now had the idea of treating glass spacers by a chemical quench for an application where they are stressed in compression as is particularly the case when the space between the two solid elements is under sub-atmospheric pressure. Glass spacers are relatively fragile and their implementation in a production process or operation in the final application generates breakages. On the other hand, for vacuum glazing and vacuum planar collectors, the necessary presence of the spacers is associated with a loss of thermal performance by conduction. It is therefore advantageous to seek to increase the mechanical strength of the spacers to be able to reduce the number.

It was not obvious a priori that the ion exchange imparted by chemical quenching makes it possible to obtain an improvement in the compressive strength of the spacers, in particular in the form of a sphere. It is known to those skilled in the art that ion exchange at a temperature below the glass Tg can introduce compression into the surface layers of the treated glass, which causes reinforces in the case where it is subjected to a tensile stress, or bending, as is the case of aircraft cockpit glass for example. This superficial compression due to the ion exchange makes it possible to compensate for a part of the stress applied on the surface which is a tension in the case of applied external forces of traction or bending. On the other hand, in the case where the external forces are compression or crushing, it is not obvious a priori that the ion exchange makes it possible to obtain a reinforcement.

FR2103574 teaches chemical quenching treatment of grains to increase their tensile strength.

The spacer is placed between two elements (said first and second element with which it is in contact) to separate, as two walls to ensure a distance between them. The space between these elements contains the spacers and gas at atmospheric pressure or reduced pressure or vacuum. The free space between the elements (that is to say the free space in the immediate environment of the spacer) can therefore be at sub-atmospheric pressure (pressure below atmospheric pressure). The spacer according to the invention is particularly recommended for any object comprising a vacuum or low-pressure glazing, such as for example a vacuum flat lamp, a vacuum solar collector, a vacuum insulator (freezer door, habitat, door of oven), etc. These objects are indeed under pressure because of the vacuum (pressure of the atmosphere) on their main faces that directly or indirectly compress the spacer. If the vacuum is formed between two outer walls, the pressure exerted on each wall towards the other is an atmosphere and therefore less than 1, 2 bar. The pressure internal to the object is typically between 1 .10 ^"8 bar and 1, 2 bar.This external pressure can be communicated to the spacer according to the invention via internal elements to the object of which the walls participate in the outer casing A solar collector generally comprises a glass pane as the first outer wall, which is intended to receive the sunlight, and as the second outer wall a metal plate (which can be integrated into a window). This collector generally contains absorption means traversed by a coolant, said absorption means being heated by solar energy. the spacers are used to prevent crushing due to external pressure and which is communicated directly (in which case they are in contact with an external wall) or indirectly (when other elements internal to the object communicate pressure to them). The spacers according to the invention may be considered to be point spacers insofar as they do not participate in the outer envelope of the object. In addition, the spacer can be compressed under the effect of additional forces, in particular those due to bending deformation of the object or those due to thermal stress or those due to the manufacturing process (in some cases case, especially when the object must undergo a laminating operation with PVB (polyvinyl butyral), it must support the pressure of the autoclave).

Thus, the invention relates to an object comprising at least one glass spacer between a first element of said object and a second element of said object, said spacer comprising a concentration gradient of alkaline ions from its surface and perpendicular to its surface. In particular, the first element may be a glass wall. In particular, the glass of this wall may comprise less than 200 ppm of iron. This is useful when it is desired that the glass allows the maximum of solar radiation to pass.

The reinforcing method used for the spacers according to the invention aims, by ion exchange (also called "chemical quenching"), to replace ions initially present in the glass with larger ions, in order to induce high stresses. surface compression. This technique is in itself known to those skilled in the art. For this treatment by chemical quenching, the glass must contain before said quenching an alkaline oxide. This oxide may be Na ₂ O or Li ₂ O, and may be present in the glass at, for example, from 1 to 20% by weight. The chemical quenching treatment consists of replacing alkaline ions initially in the glass with other larger alkaline ions. If the initial oxide is Na2O, chemical quenching is applied by KNO3 treatment so as to at least partially replace Na ⁺ ions with K ⁺ ions. If the initial oxide is Li ₂ O, a chemical quench is applied by treatment with NaNO 3 or KNO 3, so as to replace at least partially Li ⁺ ions as appropriate by Na ⁺ ions where K ⁺ . The chemical quenching leads to a concentration gradient in alkaline ion (especially K ⁺ or Na ⁺ ) perpendicular to the treated and decreasing surfaces for one of the ions from said surface and increasing for another alkaline ion when one goes from the heart of the glass to the surface. This ion exchange alkali exists from any point on the chemically treated surface of the spacer. Thus, the term "alkaline ion gradient" means that the concentration of one ion (exchanger ion) decreases from the surface towards the core, while the concentration of another ion (ion exchanged) increases from from the surface towards the heart. The exchanger ion and the exchanged ion form a pair. In the case of a sodium / potassium exchange, the exchange is carried out by quenching spacers in a bath of potassium salt brought to temperatures between 390 and 500 ° C. In the context of the present invention, the exchange parameters (temperature and duration) are chosen so as to favor a high surface stress and a relatively low exchange depth for chemical quenching. We therefore favor the intensity of the surface stress at the expense of the exchange depth. Conventionally, the exchange depth is the depth p such that if, after chemical quenching

C _p is the concentration in the exchanger ion at the depth p,

C _c is the concentration of the ion exchanger to the heart of the glass (thus corresponding to the concentration of the ion exchanger in the glass prior to chemical quench, this concentration may be zero),

Co is the concentration of the exchanger ion on the surface of the glass,

then = 0.05

Co - C _c

In other words, the exchange depth is the depth at which the exchanger concentration overconcentration is only 5% of its value at the treated surface (overconcentration: additional concentration relative to the initial concentration).

To do this, it is preferred to perform the chemical quenching at relatively low temperature. For example, in the case of the exchange of Na ⁺ ions by K ⁺ ions (soaking of the glass in a potassium nitrate bath), the temperature of the chemical quenching can be chosen between 350 and 420 ° C. Ion exchange may not be assisted by an electric field, or be assisted by an electric field.

The use of an electric field accelerates the exchange, which makes it possible to obtain a higher surface stress and a greater exchange depth, or a duration of lower treatment. On the other hand, it introduces an asymmetry in the treatment of the spacer. In this way, certain surface areas may be more chemically hardened than others. Without being excluded, the use of an electric field does not appear however necessary. The non-use of an electric field favors a treatment identical to the entire surface of the spacer and therefore the obtaining of an identical alkaline ion gradient from any point on the surface towards the core of the spacer. .

In the context of the invention, the alkaline ion exchange depth may be between 1 micron and 20 microns, and preferably from 5 to 17 microns.

The ion exchange can be carried out from molten liquid or pasty salts comprising the ion that it is desired to diffuse into the glass. Such salts are, for example, sodium or potassium nitrate or sulfate or chloride or mixtures of these compounds.

Generally, the starting glass contains:

-50 to 80 mass of S1O2,

5 to 25% by weight of alkaline oxide, preferably chosen from Na ₂ O and K ₂ O, preferably Na ₂ O in large quantity (thus up to 25% by mass) in the context of Na / Na exchange; K;

1 to 20% and preferably 4 to 10% by weight of alkaline earth oxide, preferably CaO.

The glass may comprise at least one other oxide and in particular Al 2 O 3

For solar collector application, the starting glass (and thus the final glass as well) contains less than 200 ppm by weight of iron oxide (sum of all forms of iron oxides).

It is noted that the starting glass preferably contains CaO, whereas usually the glasses to be chemically quenched have little or no CaO.

By way of example, the starting glass (before chemical quenching) may comprise: balls 2ηηηη ± 7μηη

SiO2 67.5% by weight

Na ₂ O 10.5% by weight

K2O 5.5% by weight

BaO 3.8 mass%

CaO 5.8 mass%

B2O3 0.1% by weight

AI2O3 0.6% by weight

Fe2O3 0.02% by weight

On the alkaline level, it is preferred to use the Na / K couple for chemical quenching (exchanges of Na ⁺ ions initially in the glass with K ⁺ ions initially in the chemical quenching bath) rather than on the couple. Li / Na (ion exchange Li ⁺ initially in the glass by Na ⁺ ions initially in the chemical quench bath) because the latter couple may cause instability if the glass has to be heated during the setting spacers (such as heat sealing the final solar collector for the purpose of evacuating the interior). By the use of the Na / K pair, it is possible to implement the spacers according to the invention up to about 400 ° C, especially between 100 and 400 ° C, without too much loss of the reinforcement provided by the chemical quenching . Indeed, the implementation may involve heating to hermetically seal two parts of a solar collector (for example) and be able to evacuate thereafter. In the same vein, the presence of CaO in the starting composition is preferred because this oxide slows ion diffusion. Thus, although its presence is not desired by those skilled in the art because it is deemed to hinder the chemical quenching, in the context of the invention, it is desired because it actually stabilizes the gradient of surface ions for the case. or the spacers must be heated during their implementation.

Overall, the composition of the spacer does not really change by chemical quenching since this treatment produces only an alkaline ion exchange surface and a fairly moderate depth.

It can therefore be said that the spacer according to the invention comprises:

-50 to 80 mass of S1O2,

5 to 25% by weight of alkaline oxide, 1 to 20% and preferably 4 to 10% by weight of alkaline earth oxide, preferably CaO.

The spacer may have any suitable shape: parallelepiped, shaped like a cross, shaped like a sphere (like a ball), etc. The spherical shape is particularly preferred for several reasons:

the contact area with the spaced walls is minimized, limiting the thermal and electrical exchanges by thermal or electrical conduction from one wall to the other,

the spherical shape allows the spacers to roll, which provides an ease of conveyance appreciable in the manufacturing process.

the spherical shape is less visible to the eye.

The spacer has, before chemical quenching, generally the desired shape in the final application, since it is indeed not recommended to be obliged to cut it. Indeed, a chemically tempered glass is usually not cut by conventional techniques using a diamond or a wheel at the risk of uncontrolled breakage.

The spacers may be glued to at least one of the elements with which they must be in contact. This bonding can take place beforehand or concomitantly with a seal and a vacuum. In particular, in the case of vacuum collectors, the spacers may be prior to the evacuation made bonded (gluing) of the absorption means.

The balls generally have a diameter of between 0.4mm and 15mm. A small diameter of 1 to 5 mm is well suited and allows to achieve an object according to the invention thin. This is a significant advantage when the object is intended to be integrated into a roof as in the case of a solar collector.

In the case of glass beads of the prior art (without chemical tempering according to the invention) to be placed between two walls in vacuo, generally placed at least 1000 beads per m ² between the two walls, in particular in the case where the object must be autoclaved. The chemical quenching according to the invention makes it possible to divide this number by 4, which is accompanied by an improvement in the production yields. Thus, it is possible to place in particular between 200 and 1000 beads per m ² (of course relative to the area of only one of the walls) according to the invention between the two elements communicating to them pressure. We can also in place more than 250 per m ^2. One can also place less than 800 m ^2. Thus, according to the invention, one of the elements may be plane and the object may comprise between 200 and 1000 spacers per m ^{2 of} said planar element. In addition, in the case of vacuum insulating glazing units and vacuum planar solar collectors, the use of chemically quenched spacers according to the invention, because of the possible reduction in their number, leads to a considerable reduction (sometimes by a factor 4) from the loss of thermal performance due to the necessary presence of the spacers.

The invention also relates to the use of a ball according to the invention as a spacer for supporting a pressure force between two elements pushing them towards each other.

FIG. 1 represents glass beads 1 according to the invention acting as a spacer between two elements 2 and 3 which are glass sheets acting as external walls, the vacuum being applied at 4 between the two glass sheets.

Figure 2 shows the percentage of cumulative breaks as a function of the breaking force (compressive force) in the case of 2 mm diameter glass balls quenched chemically in two different ways compared to untreated (reference) beads.

Figure 3 is a section of a solar collector 101 as an object according to the invention. The solar collector 101 comprises a first transparent upper outer wall 102 and a second transparent outer wall 104 also transparent, formed by two identical plates of thermally tempered glass. The walls 102 and 104 delimit between them and with a metal frame 105, to which they are fixed by a sealing gasket 1 10 sealed, a sealed housing 103 receiving the absorption means 106 and 107 of the collector. The outer envelope of the object according to the invention is therefore formed of the walls 102, 104 and 105. The absorption means comprise an absorber panel 106 and a conduit 107 for circulating a heat transfer fluid. The conduit 107 is in thermal contact with the absorber panel 106 on the underside side 106A thereof. The collector 101 comprises a plurality of upper spacers 108 according to the invention and a plurality of lower spacers 109 according to the invention, intended to maintain a constant distance between the upper wall 102 and the bottom wall 104 when the collector 101 is placed. under vacuum. These spacers 108 and 109 are aligned in pairs along the thickness Z direction of the manifold 101, so that each upper spacer 108 is positioned between the top wall 102 and a portion 161 of the absorber panel 106 which is in thermal contact with the conduit 107, while each lower spacer 109 is positioned between the bottom wall 104 and the conduit 107. The spacers 108 and 109 are in the form of glass beads reported on the walls 102 and 104, for example by gluing. In order to resist the compressive force exerted on the walls 102 and 104 when the vacuum is made in the housing 103, the glass beads are reinforced by a chemical quenching according to the invention. The pressure exerted on the outer walls 102 and 104 is indeed communicated to the spacers 108 and 109 by internal elements of the solar collector, the absorption means 106 and 107. The chemical quenching makes it possible to significantly increase the resistance to compression of the balls acting as spacers.

EXAMPLES

Glass beads corresponding to those described in Table 1 were used. A sodium / potassium ion exchange was carried out on these beads by dipping in a potassium nitrate bath at 405 ° C. for 8 hours.

The operating protocol for dipping 100 balls of 2mm in diameter was as follows:

- weighing 100 balls,

- introduction of the balls on a sample holder,

placing the sample holder in a bath of molten potassium nitrate placed in an oven at the desired temperature (405 ° C. or 435 ° C. according to the tests),

- stirring the sample holder every hour, for 8 hours,

- output of the sample holder,

- washing with demineralized water,

weighing of the 100 beads and determination of the weight gain for control of the ion exchange, and possible soaking in the bath to continue the chemical quenching, if necessary.

In the case of a treatment of 8 hours at 405 ° C, the weight gain is 0.06%, the depth exchanged measured by scanning electron microscope is about 5μηη. The beads thus treated were subjected to a compression test, the results of which are shown in FIG. 2. The percentage of cumulative breaks is plotted as a function of the breaking force (compression force).

It can be seen that chemical quenching makes it possible to significantly increase (by more than 500 N) the average values of breakages of the balls. The use of these chemically reinforced beads as a spacer in flat lamps (between two glass sheets separated by vacuum) shows a significant decrease in the number of breakages of these beads during the manufacturing process, significantly increasing the yield of production. On the other hand, in this case of flat lamps, the number of necessary spacers could be divided by 4. In the case of non-quenched balls, the production yield was 85% whereas it was 99% with the same beads treated chemically according to the invention.

Claims

1. An object comprising at least one glass spacer between a first element of said object and a second element of said object, said spacer comprising a concentration gradient of alkaline ions from its surface and perpendicular to its surface.

2. Object according to the preceding claim characterized in that the spacer has the shape of a sphere.

3. Object according to the preceding claim, characterized in that one of the elements is flat and in that it comprises between 200 and 1000 spacers per m ^{2 of} said planar element.

4. Object according to one of the preceding claims characterized in that the alkali ion exchange depth is between 1 micron and 20 microns.

5. Object according to one of the preceding claims, characterized in that the first element is a glass wall.

6. Object according to the preceding claim characterized in that the glass of the wall comprises less than 200 ppm by weight of iron oxide.

7. Object according to one of the two preceding claims, characterized in that the glass wall is a wall of the outer shell of the object

8. Object according to one of the preceding claims, characterized in that the concentration gradient exists from any point on the surface and towards the heart of the spacer glass.

9. Object according to one of the preceding claims, characterized in that the free space around the spacers is at sub-atmospheric pressure, the atmospheric pressure exerted on the object being communicated to said spacers.

10. Object according to one of the preceding claims, characterized in that it is a solar collector.

1 1. Object according to one of the preceding claims, characterized in that the glass of the spacer comprises less than 200 ppm by weight of iron oxide.

12. A glass ball comprising an alkaline ion concentration gradient from its surface and perpendicular to its surface.

13. Ball according to the preceding claim characterized in that the glass comprises less than 200 ppm by weight of iron oxide.

14. Ball according to one of the preceding claims ball characterized in that the glass comprises 50 to 80 by weight of S1O2, 5 to 25% by weight of alkaline oxide, 1 to 20% and preferably by weight of alkaline earth oxide.

15. Use of a ball according to one of the preceding ball claims as a spacer supporting a pressure force between two elements, said pressure pushing the two elements towards each other.