EP2593302A1

EP2593302A1 - Method for improving heat-protection glazings by preventing glass corrosion caused by alkaline glass attack and by priming

Info

Publication number: EP2593302A1
Application number: EP11731239.7A
Authority: EP
Inventors: Horst Seidel
Original assignee: Gevartis AG
Current assignee: Gevartis AG
Priority date: 2010-07-16
Filing date: 2011-06-16
Publication date: 2013-05-22
Also published as: WO2012006748A1; TW201213260A

Abstract

The invention relates to a translucent and preferably transparent fire protection element, which has at least two glass panes, between which there is at least one transparent fire-resistant protection layer made of a cured and water-containing alkali polysilicate, wherein each glass surface in contact with the protection layer is provided with a lye-resistant coating (a blocking layer) having a thickness of less than 100 nm, said coating being substantially made of oxides of multivalent cations and the reaction product thereof with the silicate of the glass surface. Said layers are preferably applied by means of reactive sputtering and are used to reduce (or prevent) glass corrosion and to provide priming that improves tear-off behavior in the event of a fire, thus increasing fire resistance capability.

Description

Method for improving heat protection glazings by preventing glass corrosion caused by alkaline glass attack, and by priming background

The present invention relates to a method for reducing or preventing alkaline glass attack by surface treatment, preferably while improving the properties in case of fire.

State of the art Glass attack, be it acidic or alkaline, has long been known and various approaches have been tried to reduce this corrosion. These include in particular special additives to the glass, such as alumina and / or boron oxide, but also corrosion-reducing additives to detergents for use in dishwashers.

For large-scale application, the use of special corrosion-resistant glasses has prevailed to a large extent until today.

In the case of fire protection glazings or heat protection glazings which are equipped with an intumescent layer based on alkali silicate and which are often distinguished by high pH, the problem of alkaline glass corrosion is of great importance. Dependent on the pot life, the alkaline glass attack sooner or later shows up.

The aim of the present invention was therefore to reduce the glass corrosion in fire protection or heat protection glazings, without having to change to more expensive glasses, or the provision of such glazing. Presentation of the invention

This objective has been achieved by providing fire-resistant glazings or elements which are more corrosion-resistant or corrosion-resistant by the use of glass plates provided with a special surface treatment.

Another object of the invention is a method for producing such surface-modified glasses.

As a result, the terms fire protection and heat protection are used interchangeably in the context of the present invention.

A translucent and preferably transparent fire protection element according to the invention has at least two glass panes, between which there is at least one transparent fire-resistant protective layer made of a hardened and water-containing alkali polysilicate. A suitable protective layer, usually an intumescent layer, has a SiC> 2: alkali metal oxide (Me 2 O) ratio of at least 2: 1 and a water content of up to 60% by weight. The glass surface which is in contact with the alkali polysilicate layer is provided according to the invention with a coating (a blocking layer or diffusion barrier layer) consisting essentially of oxides of polyvalent cations and their reaction product with the silicate of the glass surface, both the oxides and the oxides Reaction products in the alkaline medium are sparingly soluble, and the alkali-resistant blocker layer has a thickness of less than 100 nm.

For the purposes of the present invention, it is understood that the oxides and / or their reaction products with the silicate of the glass surface are sparingly soluble compounds that the coated side of a glass sheet is left to stand for 24 hours at 60 ° C. can be exposed to medium of pH 12, in particular even pH 13, without subsequently a glass attack is detected by light microscopic observation.

The coating materials are also referred to as network formers or network converters. These are oxides of polyvalent cations which, as such, are sparingly soluble compounds in the alkaline range or form sparingly soluble compounds by reaction with the glass surface in the alkaline region and which act as blocking or diffusion barrier layers which are present in the glass / glass interface. Protective layer preferably reduces or preferably prevents ion exchange of sodium and potassium ions for hydrogen ions or of sodium ions for potassium ions, and blocks competition adsorption of hydroxide ions and in particular of the foreign ions sodium and potassium.

With regard to the mode of action of these blocking layers, it is assumed that they break the oxygen bridges of the siloxane groups through the fire-resistant basic protective layer and thus the

Cleavage in Si-O-Me groups (Me = alkali metal, insbeson ^¬ particular Na) and silanol groups prevent. This assumption is not intended to limit the subject invention in any way.

Since such blocker layers - in order to be invisible to the human eye - must be very thin (<100 nm) or transparent and at the same time have very good adhesion to the glass surface, not every method can be used for their production. Very good properties were obtained with the so-called "reactive sputtering", which has the advantage that the content of the individual cations in the oxide can thus be largely determined by the composition of the target Control oxidation.

In the reactive sputtering process, in particular, two variants are distinguished, the DC and the HF Method. These are both suitable. In addition, there is the possibility of performing sputtering as magnetron sputtering.

Alternative coating methods are Chemical Vapor Deposition (CVD) or sol-gel methods.

In the CVD method, a suitable, easily volatile ^¬ Beschichtungsguelle such SnCl4 or S Cl2Et2 is. (Et = ethylate), evaporated and deposited in the presence of oxygen as SnC> 2 on the substrate to be coated.

In the sol-gel process, the coating is preferably carried out by immersion using a suitable precursor (eg for aluminum: aluminum (2-propylate), aluminum (2-butoxide), for zirconium: zirconium propylate or for titanium: Titanium ethylate, titanium (2-propylate), iCl2Et2), at a certain dip angle and at a certain speed and preferably at a temperature of about 25 ° C -30 ° C and a humidity of 8-10 g / cm ^. The metal alkoxides react with water to form M-OH groups, which crosslink with each other by dehydration condensation Kgs ^¬ NEN. The coating process is followed by a drying at about 175 ° C, then an annealing at temperatures of about 450 ° C to a maximum of about 500 ° C, in particular up to a maximum of about 480 ° C with subsequent controlled cooling.

Both the CVD and the sol-gel process have the disadvantage that they depend on special output products, in the CVD method on volatile compounds, in the sol-gel process on hydroxy-convertible metal-containing precursors. In contrast, reactive sputtering allows virtually any composition, as it is primarily determined by the metal or the alloy of the target.

The coating method such as the reactive sputtering, CVD or ^'sol-gel method, a heat treatment or a thermal tempering can downstream be turned on. These processes improve the adhesion, chemistry and cohesiveness of the blocker layer on the substrate and, at thermal tempering, improve the glass quality at the same time. Suitable conditions are:

for heat treatment a temperature treatment at a temperature below the transformation point (Tg)

- a temperature for the thermal toughening turbehandlung at a temperature below the Erwei ^¬ monitoring point (softening point, abbreviated Ew) in Before ^¬ voltage.

Basically suitable coatings are:

Oxides of aluminum, bismuth, boron, titanium, zinc, tin or zirconium and mixtures thereof,

Zinc oxide-containing mixed oxides, such as zinc aluminum oxide (ZnAlO _x ),

- Aluminum. doped connections like Zn _x Sny_

Al _z O _n,

Aluminates, borates, bismuthates, titanates,

Zincates, stannates and zirconates, particularly with more ^¬ valent cations selected from aluminum, boron, bismuth, titanium, zinc, tin and zirconium.

Such compounds may be considered. individual laminations or - one above the other - as

Layer systems be present.

Also suitable are mixtures of at least ^¬ least two of the following oxides.

Alumina, boric oxide, bismuth oxide, titanium oxide, zinc oxide, zirconium oxide, tin oxide.

Summarize Examples of suitable blocking layers to ^¬:

Aluminum oxide (AI2O3), bismuth oxide (81203), boron oxide (B2O3), titanium oxide (T1O2), zinc oxide (ZnO), tin oxide (SnO2) or zirconium oxide (ZrO2) and mixtures thereof,

- zinc aluminum oxide (ZnA10 _x) Aluminum doped compounds such as Zn _x Sny_

Al _z O _n,

Aluminum borates, aluminum titanates, aluminum zincates, aluminum stannates, aluminum zirconates, boron aluminates, bismuth aluminates, bismuth titanates, bismuth stannates, bismuth irconates, titanium stannates, titanium zirconates, zinc borates, zinc titanates, zinc stannates, zinc zirconates, tin zincates, tin zirconates, zirconium aluminates, zirconium borates, zirconium titanates , Zirconium zinc and / or zirconium stannates.

Preferred blocking layers include tin oxide

(Sn02), alumina (Al2O3), bismuth oxide (B12O3), titanium oxide (T1O2), zinc oxide (ZnO), zirconium carbide (ZrC> 2), boron oxide (B2O3) or their mixtures, zinc oxide-containing mixed oxides, such as zinc aluminum oxides (ZnA10 _x) , Aluminum-doped compounds such as Zn _x SnyAl _z O _n , zinc stannates (ZnSnO _x ), cerium aluminates, zirconium aluminates, zirconium borates and / or Zirkonzinkate.

Especially preferred blocker layers are layers of tin oxide (SnC> 2), alumina

(Al2O3), bismuth oxide (B12O3), titanium oxide (Ti02), zinc oxide (ZnO), zirconium oxide (Zr02) and mixtures thereof, zinc oxide-containing mixed oxides and particularly aluminum doped compounds, such as Zn _x SnyAl _z O _n, zirconates or Zinkstan- naten (ZnSnO _x ).

Preferred overall layer thicknesses of one or more blocker layer (s) arranged one above the other are in the range from 10 to 100 nm, preferably from 10 to 60 nm and in particular from 10 to 30 nm.

The inventive fire-resistant glazings can be produced by either coating a glass sheet with a casting material which is curable to a water-containing alkali polysilicate having a SiC> 2: Me20 ratio of at least 2: 1 and a water content of up to 60% by weight, whereupon above this casting material before, during or after curing, a second glass pane is placed, or wherein two or more panes of glass are edge-sealed at a distance from each other (eg, except at least one fill opening), and the at least one space formed therein is filled with the hardenable casting material, and then cured;

wherein the glass sheets are provided on at least one side and preferably at least on the air side with a blocking layer and the glass sheets are arranged such that their blocker layer provided side (s) in contact with the optionally cured to the protective layer casting material.

The air side is the side of the glass which has been turned away from the tin bath during manufacture. The tin bath facing side is referred to as the bath side.

Particularly suitable as a protective layer together with the glasses provided with blocking layer (s) are layers which are produced from nanoparticulate SiO 2 in the form of dispersions of pyrogenic SiO 2, precipitated silica, silica sol and mixtures of 2 or all 3 of these SiO 2 s, and alkali metal hydroxide , especially potassium hydroxide. Such layers are described in WO 2009/155719, the disclosure of which is included here in its entirety.

Preferably, the blocking layer is applied by means of a reactive DC, HC and / or magnetron sputtering process and is especially preferably subsequently tempered.

For blocker layers applied in this way, not only was prevention or at least reduction of the glass corrosion found, but at the same time a prevention or at least a strong reduction of the tear of the protective layer in case of fire. The properties of fire protection elements of glass panes coated according to the invention in the event of fire were comparable to the properties of primed glass panes, for example produced according to O99 / 04970. Another object of the present invention is therefore the use of coatings containing polyvalent cations and oxygen, as defined above for the blocking layer, to reduce the adhesion of the protective layer and thus the breaks from the glass surfaces both from the firing side also from the glass pane facing away from the fire side in case of fire.

Ways to carry out the invention

Various blocking layers were prepared by reactive sputtering and compared with each other and with untreated glass with respect to glass corrosion (white spots).

Example 1: Preparation of a glass provided with a stannate layer

In a continuous flow industrial magnetron plant, a blocking layer was applied to the fire side by means of reactive sputtering (with the fire side the non-tin bath side facing away from the tin bath). Blocker layer can also be understood as a multilayer coating. According to prior art methods (e.g., EP 1 889 818), various layers were applied to 5mm thick float glass sheets, namely:

Glass / 30nm ZnSnO _x

Glass / 40 nm SnC> 2,

Glass / 40 nm SnC> 2/3 nm Zn _x Sn _y Al _z O _n ,

All layers were deposited by means of reactive sputtering, the SNG ^ layer with a pure tin target, the ZnSnO _x layer with a target of 53 wt .-% zinc and 47 wt .-% tin and the Zn _x SnyAl _z O _n was reactively sputtered from a target made of an alloy 68 wt .-% Zn, 30 wt .-% Sn and 2 wt .-% Al consisted. Sputtering of this layer did not reveal any nuisance impressions (from the glass transport system). Example 2: Production of transparent heat protection elements with protective layers with module S1O2: 2O = 5.1: 1

2. Resources:

Si02 ~ dispersions:

10 1 reactor, equipped with an anchor stirrer, a heating and cooling unit, a glass flow cooler with a 2 1 round bottomed flask as a collecting vessel and a vacuum pump based on compressed air with a venturi system. Such a pump is suitable for efficiently evacuating large volumes while achieving a good vacuum of about 70 mbar.

Ultra Turrax stirrer as disperser, which works according to a rotor / strator principle.

KOH:

5 1 stirred tank

2. He position of the components:

SiO 2 dispersion of solid silicic acid:

Both as precipitated silica and as pyrogenic silica, a S1O2 with a BET 50 m2 / g and a primary particle size of 55 nm was used.

In a 10 1 container were submitted:

3.23 kg of water demineralized conductance <10 pS / cm

0.05 kg of aqueous emulsion of a polydimethylsiloxane (50% by weight of polydimethylsiloxane)

1.96 kg of glycerol> 99.9% pure 0.06 kg KOH> 99, 9% pure

With a stirrer, this solution was stirred for about 5 minutes until homogeneous. While dispersing with an Ultraturrax stirrer, 4.7 kg of silica powder was slowly added to the solution. The dispersion was continued until a homogeneous dispersion had formed.

Silica sol (provided with additives):

In a 10 1 reactor were set up:

9.35 kg of silica sol (BET 50 m ² / g, primary particle size 55 nm, 50% S1O2 in water, adjusted to pH 9 to 11 with KOH)

Demineralized 0.59 kg of water, conductance <10 pS / cm

1.96 kg glycerol> 99.9% pure.

With a stirrer, the mixture was stirred for about 5 minutes to homogeneity and then heated with further heating with the heating module to about 50 - 60 ° C. This temperature was maintained, the sol brought un ^¬ ter vacuum to boiling and 1.96 kg of water abge ^¬ evaporated. Subsequently, the mixture was cooled down to 20 ° C without vacuum.

potassium hydroxide solution:

In a 5 1 stirred tank were submitted:. 1.85 kg KOH> 99.9% pure

Demineralized 1.85 kg of water, conductance <10 S / cm While stirring, the KOH was stirred until complete dissolution.

3. Manufacture the Hitzeschatzglessmasse or Hitzescho.tzgla.ses

There were following SiC> 2 dispersions manufactured provides the following ^'SiC> 2-Zusammenset wetting or quantity be ^¬ subjected to the above under 2. Preparation of the component quantities:

(a) 100% fumed silica

(b) 100% precipitated silica

(c) 50% fumed silica and 50% precipitated silica

(d) 100% silica sol

(e) 50% silica sol and 50% fumed silica

(f) 50% silica sol and 50% precipitated silica

By hardening the abovementioned S1O2 sources (a) to (f) with the amount of KOH solution indicated above under 2. Preparation of the components, an intumescent layer having a modulus S1O2: K2O of 5.1: 1 was obtained.

One of each of the dispersions / sols (a) to (f) was initially charged and mixed with potassium hydroxide solution. The stirrer was turned on and stirred until the mixture was homogeneous. While stirring, the heating module was heated to about 50-55 ° C. When reaching 50 ° C, the mixture was kept for 30 min with stirring at a temperature of 50-55 ° C until the mass became very liquid. Then the vacuum pump was turned on and a vacuum of 50-90 mbar was generated. The mixture was cooled to 20 ° C under vacuum and with stirring. After 90 minutes under vacuum, the material was ready and could be filled between at least two or more glass sheets. be used. The elements produced in this way were then cured at 80 ° C. for 8 hours per 6 mm layer thickness until transparent. The properties of such heat protection casting compounds are shown in Table 1:

Table 1:

Pot life at 55 ° C for 30 min and then 20 ° C

Example 3: Differences of properties with coated / uncoated glasses and with respect to the tin bath side.

Exemplary embodiments for glasses with and without blocking layer will be described below.

For evaluating the coating properties, various tests were carried out on the glasses, namely

A Rxtz hardness

In this case, a weight-loaded needle is pulled over the layer at a defined speed. The weight at which scratch marks are visible serves as a measure of the scratch hardness.

B scratch hardness after water storage Test procedure as for A, but after 30 minutes storage of the samples in water at 20 ° C.

C Eriehsen washing test according to ASIM 2486,

Visual assessment

D Schwitztrassertest (SWT)

The samples are exposed for 140 h at a temperature of 60 ° C at a relative humidity of 100%.

Visual assessment. E Zo ⁺ leaching

The measurement is carried out according to the plate method according to Kimmel et al. Z. Glastechnische Berichte 59 (1986) p. 252 et seq.

The test allows a statement about the hydro ^¬ lytic resistance Zn-containing coating systems. F hydrochloric acid test

Here, the glass sample is immersed for 8 min in 0.01 N HCl of 38 ° C and found the loss of emissivity in%. G hydrochloric acid test visual assessment

The glass sample is immersed as in G in hydrochloric acid. The assessment criterion is the visibility of the immersion edge. B water film

The coated side of the samples is brought into contact with a thin film of water for 24 hours. The test allows a statement about the storage behavior of coated and stacked glass panes when traces of water get between the panes of glass. The assessment is done visually. Examined samples:

The following glass sides were examined:

(a) the stannate layer of a coated according to Example 1 glass (5 mm float glass)

(b) the tin bath side of a 5 mm float glass

(c) the fire side of a 5 mm float glass.

The test results obtained with a glass coated according to the invention in comparison with the tin bath or non-tin bath side of uncoated glasses are shown in Table 2 below

Table 2:

1) Not relevant as there is no coating.

Table 2 shows that the glass coated by reactive sputtering with metal oxide shows better results in almost all tests than the glasses without metal oxide coating, insofar as they were measurable. Example 4: Investigation of heat protection elements

By casting with Hit zeschut zgiessmasse as set forth in Example 2, heat protection glasses were made with a heat protection layer between two panes of glass. The protective layer was in contact with

(a) different blocker or diffusion barrier layers of coated according to Example 1 by means of reactive sputtering glasses (5 mm float glass, further processed by coating ^(¬ thermally stressed) to ESG quality)

(b) the tin bath side of a 5 mm ESG

(c) the fire side of a 5mm tempered glass. The test results obtained with an inventively provided with blocking layer glass in Ver ^¬ coincide with the Zinnbad- or non-tin side uncoated glasses of different ages arising from the following Table 3. The structure of the heat protection element used for these experiments was 2 x 5 mm glass with a layer thickness of the fire protection zgiessmasse of 6 mm. The accelerated aging took place at 60 ° C.

Table 3:

Blocker or diffusion barrier layer: Zinc stannate (ZnSnO _x ) of 30 nm thickness obtained with target of the composition about 53 wt .-% zinc and 47 wt .-% tin.

Blocker or diffusion barrier layer: Tin oxide (Sn.C> 2) of 40 nm thickness obtained with target of 100 wt .-% tin. Blocker or Diffusion Barrier Layer: Glass Side Tin oxide (SnO 2) of 40 nm obtained with target of 100 wt% tin and over it applied an additional barrier layer of 3 nm thickness of Zn _x Sn y Al _z O _n obtained with a target of composition 68 % By weight of Zn, 30% by weight of Sn and 2% by weight of Al.

Giaskorrosion manifests itself in the form of white spots

1-6 days refers to glass directly from the last manufacturing step. The actual age is probably around 2-3 days

> 6 days refers to glass that is older than 6 days and has been stored and transported. The actual age is estimated at about 1 month previous trial period, trial continues

The alkaline glass attack by the heat / fire protection layer shows up in the form of white spots and bands (in the case of previously damaged glass surfaces) and less severe cloudiness and clouds on the surfaces

Interfaces Glass / Hit Zeschutzschicht.

Example 5: Fire tests

There were fire tests according to EN 1363 and

1364 in the glass dimensions 120 cm x 220 cm and in the pane structure 5 mm ESG / 6 mm protective layer / 5 mm tempered safety glass. The protective layers used were potassium polysilicates with a modulus SiO 2: K 2 O = 5.1: 1 with and without additives based on polydimethylsiloxane and as blocking layers 30 nm ZnSnO x, 40 nm SnO 2 and 40 nm SnO 2/3 nm Zn x Sn x Al z.

The results are summarized in Table 4. Table 4:

¹ see legend) to Table 3

2 see legend 2) _to Table 3

³ see legend 3) _to Table 3

⁴ breaks with temperature passage of> 180 K above the starting temperature

⁵ FWK = Fire resistance class according to EN 13501-2

While preferred embodiments of the invention are described in the present application, it is to be understood that the invention is not limited thereto and may be embodied otherwise within the scope of the following claims.

Claims

claims

1. Translucent and preferably transparent fire protection element having at least two glass panes, between which at least one transparent fire-resistant protective layer of a cured and aqueous alkali polysilicate with a SiO 2: Me20 ratio of at least 2: 1 and a water content up to 60 wt. %, with the respective glass surface in contact with the alkali polysilicate layer being provided with a coating (a blocking layer) consisting essentially of polyvalent cation oxides and their reaction product with the silicate of the glass surface, both the oxides and the oxides the reaction products in the alkaline medium are sparingly soluble, and the alkali-resistant blocker layer has a thickness of less than 100 nm.

2. fire protection zverglasung according to claim 1, characterized in that the at least one blocker layer is selected from at least one layer from the group consisting of

Zinc oxide-containing mixed oxides, such as zinc aluminum oxide (ZnA10 _x ),

Aluminum doped compounds such as Zn _x Sny_

Al _z O _n,

Aluminates, borates, bismuthates, titanates, zincates, stannates and zirconates, in particular with polyvalent cations selected from aluminum, boron, bismuth, titanium, zinc, tin and zirconium.

3. fire protection zverglasungen according to claim 1 or 2, characterized in that the blocking layer or the blocking layers are selected from the group consisting of Aluminum oxide (AI2O3), bismuth oxide (B12O3), boron oxide (B2O3), titanium oxide (T1O2), zinc oxide (ZnO), tin oxide (SnO2) or zirconium oxide (ZrC> 2) and mixtures thereof,

Zinc alumina (ZnAlO _x ),

Aluminum doped compounds such as Zn _x Sny_

Al _z O _n,

4. Fire-resistant glazings according to any one of claims 1 to 3, characterized in that the

Blocker layer or the blocking layers are selected from the group consisting of tin oxide (SnC> 2), alumina (Al2O3), bismuth oxide (61203), titanium oxide (T1O2), zinc oxide (ZnO), zirconium oxide (ZrO2>, boron oxide (B2O3) or mixtures thereof , Zinc oxide-containing mixed oxides, such as zinc aluminas (ZnA10 _x ), aluminum-doped compounds such as Zn _x Sn _y Al _z O _n , zinc stannates (ZnSnO _x ), Boraluminate, zirconium aluminates, zirconium borates and / or Zirkonzinkate.

5. fire protection zverglasungen according to any one of claims 1 to 4, characterized in that the

Blocker layer or the blocking layers are selected from the group consisting of tin oxide (SnO 2), aluminum ^¬ oxide (Al 2 O 3), bismuth oxide (B12O3), zirconium oxide (ZrÜ2), titanium oxide (T1O2) or zinc oxide (ZnO) and mixtures thereof, zinc oxide-containing mixed oxides , aluminum doped Ver ^¬ bonds, such as Zn _x SnyAl _z O _n, zirconates or Zinkstannaten (ZnSnO _x).

6. fire protection glazings according to any one of claims 1 to 5, characterized in that the blocking layer or the blocking layers have total layer thicknesses of 10 to 100 nm, preferably from 10 to 60 nm and in particular from 10 to 30 nm.

7. A method for producing fire-resistant glazings according to any one of the preceding claims 1 to 6, wherein either a glass with a water-containing alkali polysilicate having a SiO 2: Me20 ratio of at least 2: 1 and a water content of up to 60 wt. % hardenable casting composition is coated, and wherein above this casting material before, during or after curing, a second glass pane is arranged, or wherein two or more glass sheets are sealed at a distance from each other, and the at least one space formed with the curable Giessmasse filled, and this is then cured,

characterized in that the glass sheets are provided on at least one side with a blocking layer, and that the glass sheets are arranged such that their provided with a blocking layer side in contact with the optionally cured to the protective layer casting material.

8. The method according to claim 7, characterized in that the blocking layer is applied by means of a reactive DC or HC sputtering process.

9. The method according to claim 7 or 8, characterized in that the blocking layers are tempered after application by means of reactive sputtering or thermally biased.

Use of glass sheets provided with a coating as defined in any one of claims 1 to 6 for preventing or reducing glass corrosion.

11. The use of coatings containing polyvalent cations and oxygen as defined in any one of claims 1 to 6 for reducing the adhesion of the protective layer and thus the breaks from the glass surfaces of both the fire side and the glass side facing away from the fire side in case of fire.