This invention relates to solutions for the production of fire resistant glazings, interlay ers produced from said solutions, fire resistant glazings comprising said interlay ers and methods for the preparation of said solutions, interlayers and fire resistant glazings. This invention also relates to buildings and fire resistant glazing assemblies incorporating said fire resistant glazings.

Glass laminates incorporating an intumescent inorganic silicate interlayer sandwiched between two opposed panes of glass are sold under the trade marks PYROSTOP and PYRODUR by the Pilkington group of companies. When such laminates are exposed to a fire the inorganic interlayer intumesces and expands to form a foam layer. The foam provides a thermally insulating layer which protects the pane of glass remote from the fire so that the structural integrity of the glass unit, which acts as a barrier preventing the propagation of the fire, is maintained for a longer period. Glass laminates incorporating such intumescent interlayers have been used successfully as fire resistant glass structures. These laminates may comprise more than two panes of glass sandwiching more than one intumescent interlayer. Laminates comprising up to eight intumescent interlayers have been employed. These multi layered laminates are relatively thick and correspondingly expensive.

The intumescent inorganic layer is normally formed from a sodium silicate waterglass or a mixture thereof with potassium or lithium silicate waterglasses. The layer is commonly formed by preparing a solution of the silicate, spreading that solution on the surface of the glass and drying excess water from the solution so as to form the intumescent inorganic layer.

US 4190698 discloses fire resistant glazings comprising an intumescent inorganic layer obtained by drying a silicate solution. The authors suggest the use of various additives in silicate solutions such as the addition of glycerine and saccharose, or glucose but no mention is made of the addition of lithium sources.

WO 2001/10638 and WO 2004/014813 both disclose fire resistant glazings comprising an intumescent layer obtained by drying a silicate solution. WO 2001/10638 discloses the use of a zirconium containing aggregate whilst WO 2004/014813 mentions the use of aluminate additives such as sodium aluminate and lithium aluminate.

There exists the need to provide improved fire performance of layers of intumescent material produced by a drying process, or indeed other processes such as casting into a sealed cell and solidifying, without having to modify existing equipment and plants. One area that could be enhanced is the control of the rate of water loss from such layers during the early stages of a fire (i.e. up to around 20 minutes). Greater control in this regard provides improved foam structure in the event of a fire whilst maintaining the impact performance of a glazing. Consequently larger sized fire resistant glazings may be able to pass standard fire tests. It is of course essential that any fluid compositions used to prepare silicate layers for fire resistant glazings are stable otherwise they will form a precipitate immediately or on standing. Since the dried layer is used as part of a glazing it must be optically transparent, whereas the presence of particulate material such as a precipitate does not afford transparency and is therefore not acceptable.

According to a first aspect of the present invention there is provided an aqueous solution for the production of fire resistant glazings comprising:

at least one sodium and/or potassium silicate,

at least one water soluble lithium-containing compound,

at least one water soluble aluminate, and

water,

wherein the molar ratio of Si:Li of the solution is at least 10: 1 but at most 100: 1, wherein the molar ratio of Si:Al of the solution is at least 20: 1 but at most 100: 1, and wherein the molar ratio of Si0 ₂ :M20 of the at least one sodium and/or potassium silicate, where M represents a sodium and/or potassium cation, is at least 2.0: 1 but at most 4.0:1.

According to another aspect of the present invention there is provided a transparent intumescent material for the production of fire resistant glazings comprising:

at least one sodium and/or potassium silicate,

at least one water soluble lithium-containing compound,

at least one water soluble aluminate, and

water,

wherein the molar ratio of Si:Li ofthe interlayer is at least 10:1 but at most 100:1, wherein the molar ratio of Si:Al of the solution is at least 20: 1 but at most 100: 1, and wherein the molar ratio of Si0 ₂ :M20 of the at least one sodium and/or potassium silicate, where M represents a sodium and/or potassium cation, is at least 2.0: 1 but at most 4.0:1.

The inventors of the present invention have surprisingly found that the addition of a water soluble lithium-containing compound and a water soluble aluminate, in the ratios detailed above, to a sodium and/or potassium silicate with a molar ratio of Si0 ₂ :M ₂ 0 of at least 2.0: 1 but at most 4.0:1 enables better control of the foam structure of a layer of the material during the early stages of a fire, keeping glazings incorporating said layer flatter. The presence of both the water soluble lithium- containing compound and the water soluble aluminate, in the ratios described, provides a synergistic effect on foaming, which affords increased fire performance, enabling larger sized glazings to pass standard fire tests. A key feature of the invention is the ability of the lithium-containing compound and the water soluble aluminate to control the rate of water loss from a layer of material in the early stages of a fire, thereby improving

(1) the spatial distribution of uneven intumescence of the layer of material on the non- fire side (the pane of glass on this side ultimately cracks), and

(2) the minimisation of excessive intumescence of the layer of material,

which leads to better mechanical resilience of the glazing in a fire.

The present invention is additionally suited to the production of fire resistant glazings since the solution is stable and the subsequently obtained material is transparent. In the context of the present invention the term "stable" means that the solution does not generate a precipitate and therefore is readily pourable.

In the following discussion of the invention, unless stated to the contrary, the disclosure of alternative values for the upper or lower limit of the permitted range of a parameter, coupled with an indication that one of said values is more highly preferred than the other, is to be construed as an implied statement that each intermediate value of said parameter, lying between the more preferred and the less preferred of said alternatives, is itself preferred to said less preferred value and also to each value lying between said less preferred value and said intermediate value.

The at least one water soluble lithium-containing compound may be selected from the group consisting of lithium hydroxide, lithium carbonate, lithium oxide, lithium hydride, lithium halides, lithium borate, lithium silicate, lithium nitrate, and lithium salts of organic acids such as lithium citrate, lithium tartrate and lithium acetate.

Preferably the molar ratio of Si:Li in the solutions and materials according to the present invention is at least 15: 1, more preferably at least 20:1, even more preferably at least 25:1, but preferably at most 60:1, more preferably at most 40:1, even more preferably at most 30:1. These preferred ratios enable greater control of the degree of foaming in the event of a fire, influencing foam uniformity, density and ultimately the mechanical resilience and integrity of the glazing when exposed to fire load conditions.

The molar ratio of Si0 ₂ :M ₂ 0 of the at least one sodium and/or potassium silicate in the solutions and the materials of the present invention, where M represents a sodium and/or potassium cation, is preferably at most 3.5: 1, more preferably at most 3.25:1, even more preferably at most 3.0:1, even more preferably at most 2.9:1, but preferably at least 2.25: 1, more preferably at least 2.4: 1, even more preferably at least 2.5: 1. The present invention is particularly useful for materials derived from less colloidal silicates (generally at most 3.0: 1 molar ratio of Si0 ₂ :M ₂ 0) which have a tendency to retain a relatively higher water content.

The water soluble aluminate of the solutions and materials of the present invention is preferably an alkali metal aluminate such as potassium aluminate, caesium aluminate, lithium aluminate and most preferably sodium aluminate. Other water soluble aluminates notably ammonium aluminate and alkyl ammonium aluminates may also be employed.

Preferably the aluminate has been partially neutralised with a carboxylic acid. Preferably the partial neutralisation occurred prior to mixing the aluminate with the sodium and/or potassium silicate. Aluminates are very reactive towards silicates but can be controlled by forming co-ordination compounds. The hydroxy carboxylic acid may be carried in glycerol. It is preferable to carry out the neutralisation under low water conditions to avoid aluminium hydroxide polymerisation. Preferably the at least one water soluble lithium-containing compound is added to an aqueous solution of the at least one sodium and/or potassium silicate, followed by addition of the partially neutralised aluminate. Preferably the molar ratio of Si:Al of the solutions and materials is at least 25:1, more preferably at least 30:1, even more preferably at least 35:1, but preferably at most 60: 1, more preferably at most 40:1, even more preferably at most 30:1. These preferred ratios enable greater control of the degree of foaming in the event of a fire, influencing foam uniformity, density and ultimately the mechanical resilience and integrity of the glazing when exposed to fire load conditions.

Accordingly, the solutions and materials of the present invention may further comprise at least one carboxylic acid. The carboxylic acid of the solutions and materials of the present invention is preferably a hydroxy carboxylic acid and more preferably an a-fiydroxy carboxylic acid. Examples of preferred carboxylic acids include tartaric acid, malic acid, gluconic acid, lactic acid, saccharic acid and most preferably citric acid.

The solutions and materials of the present invention may further comprise at least one polyhydric organic compound. The most preferred polyhydric organic compound is glycerol. Other compounds which can be used but whose use is less preferred include other polyols such as ethylene glycol, monosaccharides and polysaccharides.

Preferably the concentration of the polyhydric compound in the solution is at least 8% by weight, more preferably at least 10% by weight, even more preferably at least 12% by weight, most preferably at least 14% by weight, but preferably at most 30% by weight, more preferably at most 25% by weight, even more preferably at most 20% by weight, most preferably at most 18% by weight. Preferably the concentration of the polyhydric compound in the material is at least 15% by weight, more preferably at least 17%) by weight, even more preferably at least 18% by weight, but preferably at most 30% by weight, more preferably at most 25% by weight, even more preferably at most 20%) by weight. As the concentration of polyhydric compound increases, the flexibility of the material which is produced when the solution is dried and/or cured increases. This tends to improve the impact resistance properties of laminates incorporating at least one layer of the material. However the incorporation of an excessive proportion of the polyhydric compound can be disadvantageous particularly if the layer is relatively thick.

These thicker, heavier layers suffer from a tendency to slump particularly when used in larger sized laminates and such laminates are not acceptable in use. Furthermore although the laminates of this invention that comprise a polydric organic compound have surprisingly good fire resistant properties, increasing the quantity of polyhydric compound present contributes to the flammability of the material, and this may reduce the performance of the laminate in a fire test. For these reasons it is preferred that the solution comprises no more than 20% of polyhydric organic compound. Most preferably the solution comprises from 14 to 18% by weight of polyhydric organic compound.

The water content of the solution will generally be at least 30% by weight, preferably at least 40% by weight, but generally not more than 70% by weight, preferably not more than 60% by weight.

The material of the present invention may comprise a water content of at least 15% by weight, preferably at least 20% by weight, more preferably at least 22.5% by weight, but at most 35% by weight, preferably at most 30% by weight, even more preferably at most 27.5% by weight.

The material of the present invention may be in the form of a layer. The thickness of the layer may vary through a wide range such as from 0.3 to 10.0 mm. Generally thicknesses of from 0.5 to 2.5 mm are preferred. Additionally two such layers can be laminated face to face which leads to a thicker overall interlayer.

According to another aspect of the present invention there is provided a fire resistant glazing comprising at least one layer of an intumescent material according to the present invention attached to at least one glass sheet.

The layer of intumescent material may be an interlayer attached to at least two glass sheets.

According to another aspect of the present invention there is provided a fire resistant glazing assembly comprising at least one fire resistant glazing according to the present invention attached to a frame.

According to another aspect of the present invention there is provided a building incorporating at least one fire resistant glazing according to the present invention. According to another aspect of the present invention there is provided a method of preparing a solution according to the present invention comprising:

providing an aqueous solution of at least one sodium and/or potassium silicate; and adding

at least one water soluble lithium-containing compound, and

at least one water soluble aluminate,

wherein the molar ratio of Si:Li of the resultant solution is at least 10: 1 but at most 100: 1,

wherein the molar ratio of Si:Al of the resultant solution is at least 20: 1 but at most 100: 1, and

wherein the molar ratio of Si0 ₂ :M ₂ 0 of the at least one sodium and/or potassium silicate, where M represents a sodium and/or potassium cation, is at least 2.0: 1 but at most 4.0:1.

According to another aspect of the present invention there is provided a method of preparing a transparent intumescent material according to the present invention comprising:

drying and/or curing an aqueous solution in accordance with the present invention.

The material may conveniently be produced by spreading the solution onto the surface of a sheet of glass and subsequently evaporating water from the solution. In order to produce a layer of material of the desired thickness upon the glass it is sometimes necessary to provide an edge barrier on the glass which will retain the solution during evaporation. The evaporation of water from the solution is preferably carried out by drying it in an oven at a temperature of from 70 to 110°C for a period of from 12 to 24 hours. By drying to higher residual water content, long drying times can be reduced, but it is necessary to improve the mechanical stability of the resultant material. This can be achieved by the use of the additives described herein.

When the material is produced by removing excess water the rate of evaporation of the water may conveniently be controlled by varying the relative humidity in the atmosphere. When the evaporation is complete the coated glass sheet may be removed from the oven and the retaining edge barrier removed by cutting the edges from the sheet. The resulting product is a fire resistant glazing comprising a layer of material attached to a glass sheet. Another method of forming a fire resistant glazing is the so called cast in place method in which a solution or mixture is introduced into the space between two opposed panes with a peripheral seal and cured to form an interlayer of material. In a cast in place process the water content of the solution is retained in the cured interlayer. This high water content absorbs a quantity of heat during a fire.

EP 620781 discloses a cast in place method for the production of a fire resistant glazing comprising a silicate interlayer. The method comprises applying a sealant around the entire circumference of two opposed glass panes thereby defining a cavity between them and pouring a silicate solution into that cavity. The silicate solution is then allowed to cure. The curing may be accelerated by raising the temperature of the glazing.

In an alternative process the solutions may be dried and/or cured on the surface of a substrate and, provided that the interlayer has sufficient mechanical strength, it can be separated from the substrate and placed between two glass sheets to form a fire resistant glazing. Suitable substrates on which the solution could be dried include glass, metals such as stainless steel and polymeric materials such as PTFE and polyolefins such as polypropylene. Where the substrate is transparent e.g. when the substrate is a transparent polymeric film, the film with the interlayer dried upon one surface may be mounted between two glass panes so as to form a fire resistant glazing without the need to separate the dried interlayer from the substrate.

According to another aspect of the present invention there is provided a method of preparing a fire resistant glazing according to the invention comprising:

drying and/or curing an aqueous solution in accordance with the present invention upon at least one glass sheet.

A second sheet of glass may be bonded to the dried/cured layer of material to produce a laminated fire resistant glazing. Alternatively a second sheet of glass having a dried/cured intumescent layer attached can be bonded to the layer of material of the first sheet of glass and then a top sheet can be added to form a laminate having two interlayers. This process can be continued to produce however many interlayers are desired. Another alternative is to bond the second sheet with the interlayers in contact with one another and thus form a single interlayer having twice the thickness of the original. The glass sheets used to form these laminates will normally be conventional sheets of soda-lime float glass. However other glass compositions may be employed in particular those having a higher strain temperature as these will increase the fire resistance of the laminate. Coated glasses, in particular those having a coating which reflects heat may also be used.

According to a further aspect of the present invention there is provided the use of a solution according to the present invention in the preparation of a fire resistant glazing.

According to a further aspect of the present invention there is provided the use of a fire resistant glazing according to the present invention to prevent the spread of fire.

It will be appreciated that optional features applicable to one aspect of the invention can be used in any combination, and in any number. Moreover, they can also be used with any of the other aspects of the invention in any combination and in any number. This includes, but is not limited to, the dependent claims from any claim being used as dependent claims for any other claim in the claims of this application.

Embodiments of the present invention will now be described with reference to the following examples:

Examples

A mixture was prepared consisting of a commercial sodium silicate molar ratio of 2.85, 8010g), a commercial potassium silicate (SiC^lV O molar ratio of 1.43, 2300g), glycerol (87% aqueous, 798g) and an aqueous lithium solution (360g containing 11.9g Li). These components were mixed with a paddle stirrer until a homogenous mixture was obtained.

This mixture was stirred and a prepared solution containing sodium aluminate (38% aqueous, 345g), citric acid (195g) and glycerol (87% aqueous, 390g) was added slowly. This afforded a clear and transparent solution with a molar ratio of SiC^ilV^O of the sodium and potassium silicate, where M represents sodium and potassium cations, of 2.63:1, a molar ratio of Si:Li of 30:1 and a molar ratio of Si:Al of 35:1. The solution was dried on a glass pane (lm x 2m x 2.6mm) under controlled conditions of temperature and humidity to produce a hard solid interlayer, approximately 1.5mm thick and containing 25% water. A second glass pane (lm x 2m x 2.6mm) was then laminated on to the dried interlay er.

Other samples were prepared in a similar fashion, varying the ratios of Si:Al and Si:Li by proportional variation of the amount of aluminium and lithium containing compounds added where required. The molar ratio of Si02:M ₂ 0 of the sodium and potassium silicate was varied as necessary using different commercial silicates.

Glazings containing these interlay ers were fire tested according to BS-E 1364 part 1 : 1999. The time to failure defined by loss of integrity is given in table 1. Only transparent glazings were fire tested; opaque or translucent glazings are not deemed suitable for use as fire resistant glazings.

Si0 ₂ : M ₂ 0 Duration Molar Ratio Appearance before

Si : Li Si : Al

of Sodium of glazing integrity of

Example Molar Molar

and prior to fire glazing fails Ratio Ratio

Potassium test in fire test Silicate (minutes)

1 20:1 2.74 Transparent 16

(Comparative)

2 20:1 2.74 Transparent 27

(Comparative)

3 20:1 2.74 Transparent 33

(Comparative)

4 15:1 35:1 2.74 Transparent 47

5 20:1 35:1 2.74 Transparent 48

6 30:1 35:1 2.74 Transparent 46

7 5:1 35:1 2.74 Opaque Not applicable

(Comparative)

8 40:1 17:1 2.74 Translucent Not applicable

(Comparative)

9 35:1 2.74 Transparent 34

(Comparative)

10 35:1 4.1 Opaque Not applicable

(Comparative)

Table 1 : BS-EN 1364 Pt ] : 1999 fire test results for a number of examples Summary of results

Table 1 illustrates clearly that in the event of a fire the glazings of the present invention (Examples 4-6) retain their integrity for much longer than the comparative glazings (Examples 1-3 and 7-10). The fire test results for Examples 4-6 clearly demonstrate the synergistic effect that the presence of both the water soluble lithium- containing compound and the water soluble aluminate has on fire performance. This improved integrity is due to better control of the foam structure of the silicate layer during the early stages of the fire test which keeps the glazings flatter. It is worth noting that all of the glazings of the present invention are transparent whereas a number of the comparative glazings are opaque or translucent and therefore would not be suitable for glazing applications, where transparency is essential. Furthermore, comparative examples 7, 8 and 10 show such instability in fire tests that they delaminate and explosively eject glass.