Fire-resistant glazing and method for manufacturing fire-resistant glazing

Description

[0001] The invention relates to the field of fire-resistant glazing. It relates to fire-resistant glazing with a transparent fire-resistant layer arranged between two transparent supports (e.g., glass panes).

[0002] In fire-resistant glazing with a fire-resistant layer sandwiched between transparent supports (especially glass panes), the side of the glass facing the fire shatters, and in the event of a fire, the fire-resistant layer foams and / or cloudes. The fire-resistant layer then has a cooling and / or insulating or reflective effect. This fire-resistant layer can be based on silicates or hydrogels, for example. Both have their advantages and disadvantages.

[0003] A fire-resistant glazing based on hydrogels is described, for example, in DE 2713849, in which a space between at least two parallel glass panes is filled with a gel. The gel is formed during the polymerization of methacrylamide and acrylamide, with the polymerization taking place with the aid of peroxides or persalts with the addition of an accelerator (e.g., diethylaminopropionitrile) and, optionally, a crosslinking agent (e.g., methylenebisacrylamide, MBA).

[0004] DE 10237395 describes a process for producing fire-resistant glazing, wherein a fire-resistant composition is created between two adjacent glass panes. The fire-resistant composition is formed by the polymerization of acrylic acid and / or methacrylic acid and / or their respective alkali metal salts and / or ammonium salts of acrylic acid. A salt solution, a polymerization initiator, and a crosslinking agent are additionally used, with basic salt solutions being indicated as preferred. Similar processes are also described in WO 03 / 061963, DE 4001677, and DE 6916816.

[0005] Previously known hydrogels are partly made from toxic, carcinogenic, or mutagenic raw materials (e.g., based on acrylamide / DE 2713849), or they use raw materials (water-soluble monomers) that preferentially polymerize in alkaline conditions. However, high pH values ​​can trigger undesirable reactions with glass surfaces (glass corrosion) and thus lead to cloudiness. Another disadvantage of the hydrogels used to date is their poor adhesion to the glass surface. Hydrolysis reactions caused by high pH values, in particular, either destroy chemical bonds to the glass surface or prevent them from forming at all.

[0006] Hydrogels based on methylolacrylamide are also known. Methylolacrylamide, for example, can be produced from the starting materials acrylamide and formaldehyde, both of which are substances of very high concern. They have been classified as SVHCs (Substances of Very High Concern). SVHCs are chemical compounds (or part of a group of chemical compounds) identified under the REACH regulation (Registration, Evaluation, Authorisation and Restriction of Chemicals) as having particularly hazardous properties. Therefore, acrylamide is also referred to as an acinogen and mutagen, and formaldehyde is classified as toxic and probably carcinogenic.

[0007] Exposure of people to these substances, for example during production or after the fire-resistant glass pane bursts in the event of a fire, is therefore harmful and should be avoided.

[0008] Furthermore, when manufacturing hydrogel-based fire-resistant glazing, great haste is required once the polymerization initiator is added to the gel reactants, as crosslinking and thus the curing of the gel begins immediately. This is particularly disadvantageous if the reactants, or some of them, are toxic, as hectic activities are much more prone to errors.

[0009] It is therefore an object of the invention to provide a fire-resistant glazing and a method for its production which eliminate the above-mentioned disadvantages.

[0010] These objects are achieved by a fire-resistant glazing and a method for producing a fire-resistant glazing as defined in the patent claims.

[0011] The fire-resistant glazing comprises at least two transparent supports, between which a transparent layer of a fire-resistant coating is arranged. The fire-resistant coating comprises a hydrogel. This hydrogel comprises a polymer polymerized from at least one monofunctional monomer and at least one bifunctional or polyfunctional monomer in an aqueous salt solution or in an aqueous salt dispersion in an acidic environment, and contains 5-20 wt.% salt.

[0012] The monomers are non-toxic, non-carcinogenic, and non-mutagenic. Polymerization of the polymer from the monomers is thermally activated, and thermal activation occurs above room temperature. The monofunctional monomers contain at least acrylic acid or an acrylic acid derivative and methacrylamide or a methacrylamide derivative.

[0013] Glass panes, especially flat glass panes, are particularly suitable as transparent substrates. Ceramic glass can also be used, and special curved glass can be applied. Thermally or chemically toughened glass panes can be particularly advantageous. Alternatives to silicon oxide-based glass panes include transparent polymer-based substrates (e.g., polycarbonates or polymethyl methacrylate (PMMA; acrylic glass), partially crystalline "glasses" (ceramic glass), or composite systems with glass panes and plastic substrates.

[0014] The term "fire-resistant glazing" is therefore functional and should not be understood as being limited to certain materials (specifically: glass in the narrower sense), but explicitly also includes structures with transparent or translucent supports made of the above-mentioned and other materials.

[0015] A hydrogel is a water-containing, but water-insoluble (but water-compatible) polymer whose monomers are linked to form a three-dimensional network. An acidic solution has a pH < 7. Particularly preferably, the hydrogel is polymerized in a solution with a pH of less than 6.5, for example, a pH of at most 6 or, for example, at a pH of at most 4.7.

[0016] A non-toxic monomer, for example, is a chemical compound that, according to the United Nations' Globally Harmonized System of Classification, Labelling and Packaging of Chemicals (GHS), is not classified in the "Acute Toxicity" hazard class with the hazard designation toxic (code letter: T) or very toxic (code letter: T+). Likewise, the monofunctional and, for example, bi- or polyfunctional monomers of the fire protection layer are not classified as carcinogenic (cancer-causing) and / or mutagenic (genetic damage).

[0017] One of the underlying insights of the invention is that it is possible for the fire protection layer to be non-toxic both before conversion to a hydrogel (educts) and in the fully converted hydrogel form. This has the advantage that the formation of toxic compounds is also reduced in the event of a fire. This provides better protection against poisoning for both a worker involved in the production of the fire protection layer and a person in the event of a fire or if the fire protection panels break during use.

[0018] Furthermore, it is possible for the polymerized fire-resistant layer to have a pH value of less than seven. Surprisingly, it has been found that this can achieve significant advantages. Firstly, the fire-resistant layer forms a polar surface. The polarity of the fire-resistant layer is influenced by the polarity of the ligands in the polymer chain. This polar surface can interact efficiently with the surface of the glass pane, thereby greatly improving the adhesion of the fire-resistant layer to the glass pane. The improved adhesion can be particularly important in the event of a fire, as the fire-resistant layer remains bonded to the other glass pane after the fire-side glass pane shatters or bursts and does not simply fall into the fire chamber (which would correspond to a total failure of the fire-resistant glazing). This improved adhesion is achieved without the use of additional adhesion promoters.

[0019] A second advantage of a fire-resistant coating with a pH value of < 7 is that, in acidic environments, the glass pane that comes into contact with the fire-resistant coating is less susceptible to attack than with state-of-the-art technology, since glass corrosion occurs less severely in acidic than in alkaline environments. This prevents aging-related clouding of the glass / pane.

[0020] Methylenebisacrylamide (MBA), for example, can be used as a bifunctional monomer. This bi- or polyfunctional monomer causes or accelerates three-dimensional crosslinking of the fire-resistant layer. This makes it possible for the fire-resistant layer to no longer flow after polymerization. Therefore, the dimensional stability of the fire-resistant layer and thus of the fire-resistant glazing is significantly improved.

[0021] The initiation of polymerization can be promoted by an initiator. The initiator can, for example, be a water-soluble UV initiator of a UV radical chain polymerization (after irradiation with ultraviolet radiation).

[0022] Advantageously, the initiator (or the polymerization process in general) is thermally activated. This makes it possible to require only one initiator to initiate the polymerization of the fire-resistant layer. In contrast, initiators are known that act as a redox system and have at least two reactants. By using fewer starting materials (educts) for the fire-resistant layer, homogenization of the reactants can be achieved more easily, thereby improving the efficiency of the polymerization and thus the quality of the fire-resistant glazing.

[0023] Thermal activation preferably occurs above room temperature (standard room temperature is defined as 23°C). This allows for polymerization to occur during homogenization of the reactants (including the initiator) at room temperature. Therefore, there is no need to rush the careful production of fire-resistant glazing, which reduces the risk of errors and allows for additional flexibility in the production process.

[0024] The fire protection compound that forms the fire protection layer after polymerization (i.e., the hydrogel, possibly with additives) is therefore particularly preferably designed such that essentially no polymerization occurs at room temperature. "Essentially no polymerization" can mean, for example, that the viscosity of the hydrogel does not reach or exceed a value of 200 mPa s within 12 hours. In other words, the reactants of the fire protection layer do not cure within an acceptable period of time (approximately 12 hours) without undergoing thermal activation.

[0025] The activation temperature for initiating polymerization is advantageously below 100°C. This prevents the formation of bubbles in the fire protection layer due to any evaporating water. For example, it can be advantageous if the polymerization starts at a temperature of 40°C to 75°C. The activation temperature can be considered the lowest temperature at which the viscosity of the freshly mixed compound increases by a factor of 1000 within one to two hours, i.e., reaches a viscosity of 400 mPa s. At a viscosity of 400 mPa s and above, the fire protection compound is difficult or impossible to process, and its flow is virtually nonexistent.

[0026] If only a single initiator is used to initiate polymerization of the fire protection layer, a reactant for the initiator can be omitted. This eliminates the need to adjust a redox system when composing the fire protection layer, where, for example, an excess of a reactant can lead to undesirable side reactions.

[0027] A persalt can be used as an initiator; peroxydisulfates are particularly well-suited for initiating polymerization. Persalts are the salts of a peracid, with the term peracid being a collective term. Peracids can include both oxoacids with a higher oxygen content and peroxoacids (as well as peroxycarboxylic acids). Persalts are strong oxidizing agents that, in a redox system with a reducing agent, can initiate the radical conversion of the hydrogel reactants into a polymer. Peroxydisulfates, in particular, can also be thermally activated.

[0028] Another key advantage is that activation can occur precisely when the reactants of the fire-resistant layer are located at their intended location, for example, between the at least two panes of glass. This allows processing steps such as mixing and homogenizing the reactants and filling them between the at least two panes of glass to be carried out with great care and without haste. Therefore, the quality of the fire-resistant glazing can be ensured at a reproducibly high level.

[0029] Furthermore, in various embodiments of the invention, not only with thermal activation, the at least two glass panes of the fire-resistant glazing can have a layer of organofunctional silane on the side facing the fire-resistant layer. The organofunctional silane can be applied to the glass pane, for example, by spraying, roller application, or wiping.

[0030] This makes it possible to further improve the adhesion of the fire-resistant coating to the glass pane. This further improved adhesion has a beneficial effect on the fire-resistant glazing's fire-resistant properties, since in the event of a fire, after the glass pane facing the fire has shattered, the fire-resistant coating remains adhered to at least one remaining glass pane, providing heat insulation. The organofunctional silane can also be referred to as a functionalized silane.

[0031] Advantageously, the layer of organofunctional silane is a monomolecular layer. This can be achieved using a highly diluted solution of the functionalized silane in a highly volatile solvent, such as propanol or isopropanol, or a propanol-water mixture. The monomolecular layer allows for a direct and stable bond to the glass pane, as there are no intermediate layers to impair this bond.

[0032] Furthermore, the organofunctional silane can form a covalent bond with the fire-resistant layer. In contrast to purely polar interactions, such a covalent bond can only be broken with a large expenditure of energy. This ensures that the fire-resistant layer adheres particularly well to the coated glass pane. In the event of a fire, a large amount of thermal energy is available, which, on the one hand, breaks the covalent bonds between the fire-resistant layer and the functionalized silane on the side facing the fire, allowing any flaking glass pane to detach from the fire-resistant layer. On the other hand, the bond between the fire-resistant layer and the functionalized silane on the side facing away from the fire remains intact, thus maintaining the thermal insulation of the fire-resistant glazing.

[0033] If the organofunctional silane has at least one double bond on the side facing away from the glass pane, the initiated polymerization can occur not only within the fire-protection layer but also spread to the functionalized silane. This cross-linking between the fire-protection layer and the functionalized silane, and thus with the glass pane, results in the fire-protection layer adhering particularly well to the glass pane, which brings with it the advantages already mentioned. Such a functionalized silane with at least one double bond can be, for example, a vinylsilane.

[0034] The water-soluble, non-toxic monomers from which the fire-protection layer is formed comprise, in one group of embodiments, at least acrylic acid or an acrylic acid derivative and methacrylamide or a methacrylamide derivative. This eliminates the use of toxic acrylamide and ensures, as already mentioned, that the finished hydrogel is also non-toxic, significantly reducing the formation of toxic substances in the event of a fire.

[0035] The fire protection layer before reaction can contain 5-20% by weight of monomers. This ensures good three-dimensional crosslinking, which significantly improves the dimensional stability of the fire protection layer. In particular, the monomer content can also be between 7 and 15% by weight of the fire protection layer before reaction, in which case crosslinking is particularly good. It is advantageous for the monomers to contain both acrylic acid or an acrylic acid derivative and methacrylamide or a methacrylamide derivative. This makes it possible to improve the three-dimensional crosslinking of the fire protection layer. In this case, the proportion of acrylic acid and / or acrylic acid derivative plus methacrylamide and / or a methacrylamide derivative is between 5 and 20% (all values ​​given in weight percent), preferably between 7 and 15%, and particularly preferably between 8 and 12%.The ratio between methacrylamide and / or a methacrylamide derivative on the one hand and acrylic acid and / or acrylic acid derivative on the other hand is preferably between 0.5 and 2.5, in particular between 0.8 and 1.5, particularly preferably between 1 and 1.2.

[0036] The following applies to the proportions of other components of the fire protection compound: Water content between 60-90%, preferably between 70-85%, in particular between 75-82%. Salt (e.g., NaCl or another alkali or alkaline earth salt) 5-20%, preferably between 5 and 15%, in particular between 8 and 13%. Alkali (e.g., NaOH, KOH, or potassium carbonate, etc.) preferably a maximum of 5%, in particular between 0 and 4%, or between 0.8 and 2.5%, e.g., between 1% and 2%. Bi- or polyfunctional monomer (e.g., methylenebisacrylamide MBA), for example, a maximum of 1.5%, in particular between 0%, 0.05% and 0.5%, or between 0.07% and 0.25%. The molar ratio between monofunctional monomer(s) on the one hand and bi- or polyfunctional monomer on the other hand is, for example, between 40 and 1000, in particular between 70 and 300. Initiator: e.g. maximum 1%, in particular between 0.05% and 0.4% or between 0.07% and 0.25%.

[0037] The fire-resistant layer can have a pH value below 7 even after polymerization. This promotes adhesion to the glass due to polar interactions. A layer of organofunctional silane is not necessarily required on the side facing the fire-resistant layer to improve adhesion. In alkaline conditions (pH > 7), the bonds between the fire-resistant layer and any applied layer of functionalized silane can degrade, reducing adhesion to the glass pane in alkaline conditions. Furthermore, in acidic conditions (pH < 7), glass corrosion is reduced, as mentioned above, which increases the aging resistance of the fire-resistant glazing.

[0038] The process for producing fire-resistant glazing comprises the following steps: Providing a fire protection compound comprising water-soluble, non-toxic monomers, as well as at least one bi- or polyfunctional monomer and at least one initiator in an aqueous salt solution or in an aqueous salt dispersion in an acidic environment; providing at least one first transparent carrier (e.g., a glass pane) and at least one peripheral edge border extending along the edge of the first carrier, such that the first carrier and the peripheral edge border form a container; filling the fire protection compound into the container; and controlled initiation of polymerization of the fire protection compound to form a hydrogel fire protection layer containing 5-20 wt.% salt, wherein the first carrier or at least one of the carriers is designed as a glass pane, and wherein in an additional step a layer of organofunctional silane is applied to the at least one glass pane on a side facing the fire protection layer before the glass pane is brought into contact with the fire protection compound.

[0039] According to a first possibility, the container can be formed by the first transparent carrier and an additional second transparent carrier (e.g., also a glass pane) with a circumferential edge seal, wherein the edge seal is interrupted at at least one point to form a filling opening. After filling, the edge seal is then supplemented so that the filling opening is closed. This method has the advantage that space-saving arrangements of multiple fire-resistant glazing units are possible even during production. A possible example of such a filling step is taught (for a different fire-resistant compound than in the method according to the invention), for example, in WO 03 / 031173.

[0040] It is also not entirely impossible that, according to a further embodiment, the first transparent carrier (glass pane or similar) with a surrounding edge border can be laid horizontally, so that the container is formed and filled by the carrier and edge border, similar to a tub. The fire protection compound can then be cured and, if necessary, dried, after which a second transparent carrier is placed on top and, if necessary, an edge seal is applied (the edge seal can also be formed at least partially by the edge border, which then remains on the first carrier). It is also possible to attach the second carrier before or during curing. This process can, for example, be carried out under a protective gas atmosphere to prevent atmospheric oxygen from hindering polymerization.

[0041] This procedure makes it possible to start polymerization in a controlled manner only once the reactants of the fire-resistant layer are homogenized and in contact with at least the first substrate. This allows the production steps for fire-resistant glazing to be carried out with great care, ensuring reproducible quality.

[0042] The controlled start of polymerization can be initiated by heating the fire-resistant layer. This ensures homogeneous polymerization of the fire-resistant layer, for example, in the space between at least two panes of glass. As already mentioned, the temperature must not be set too high to prevent blistering in the fire-resistant layer.

[0043] The method according to the invention comprises a step in which the first support or at least one of the supports is formed as a glass pane (tempered or non-tempered or laminated glass). According to this step, before the respective glass pane comes into contact with the fire-protection compound, a layer of organofunctional silane is applied to the glass pane or at least one of the glass panes on the side facing the fire-protection layer. This can strengthen the adhesion of the fire-protection layer to the glass pane, thereby improving the fire-protection properties of the fire-resistant glazing.

[0044] The procedure according to the invention can of course be applied not only to fire-resistant glazing with two transparent supports and a fire-resistant layer in between, but also to any structures with transparent supports and a fire-resistant layer, in particular also structures with more than two supports and more than one fire-resistant layer.

[0045] Further embodiments emerge from the dependent patent claims. Features of the method claims can be combined mutatis mutandis with the device claims, and vice versa.

[0046] The subject matter of the invention is explained in more detail below with reference to preferred embodiments, which are illustrated in the accompanying drawings. They show schematically: Figures 1a and 1b show various structures of fire-resistant glazing;

[0047] In principle, identical or analogous parts in the figures are provided with the same reference symbols.

[0048] The Figures 1a and 1b show a schematic structure of a fire-resistant glazing 1 having a fire-resistant layer 3 based on a hydrogel. The figures show: Figure 1a A fire-resistant glazing 1 with two glass panes 2.1, 2.2 with a fire-resistant layer 3 with edge seal 4 arranged between them. The fire-resistant glazing can be produced, for example, by curing the reactants of the fire-resistant layer 3, which are first poured in liquid form into the space defined by the edge seal 4 (edge ​​seal) between the glass panes 2.1, 2.2 and thermally cured there. The glass panes 2.1, 2.2 have a layer of organofunctional silane 5 on the side facing the fire-resistant layer 3. This layer of organofunctional silane 5 can alternatively be applied to only one of the two glass panes. Figure 1bFire-resistant glazing 1 with three glass panes 2.1, 2.2, 2.3 with fire-resistant layers 3.1, 3.2 arranged between them, here each with edge sealing 4.1, 4.2; fire-resistant glazing 1 with more than three glass panes 2.1, 2.2, 2.3 and more than two fire-resistant layers 3.1, 3.2 are also possible.

[0049] Structures with more than three glass panes, more than two fire protection layers and / or with transparent supports other than glass panes and / or with additional transparent layers - as described, for example, in DE 20 2012 012 285.1 - are also possible.

[0050] Below are some examples of the production of fire-resistant glazing 1. Example 1

[0051] A fire protection compound is mixed from the following components: 5,42 w[%] Methacrylamide 4,58 w[%] Acrylic acid 0,17 w[%] Methylenebisacrylamide (MBA) 10,00 w[%] NaCl 1,50 w[%] NaOH 78,16 w[%] Water 0,17 w[%] Initiator (peroxide sulfate) Example 2 (comparison example)

[0052] First, the reactants of fire protection layer 3 are mixed to form a fire protection compound with the following weight percentages: 5,4 w[%] Methacrylamide 4,6 w[%] Acrylic acid 0,15 w[%] Methylenebisacrylamide (MBA) 2,5 w[%] KCl 0,1 w[%] NaOH 87,1 w[%] Water 0,15 w[%] Initiator (peroxide sulfate)

[0053] The pH of this acidic mixture is approximately 4.5. The mixture is then poured into the space defined by the edge seal between two panes of glass. During a period of 400 minutes in an oven at 60°C, polymerization is initiated, and the fire-resistant layer hardens between the two panes of glass. Example silanization

[0054] 2 g of vinylsilane (vinyltriethoxysilane) are dissolved in 100 ml of a 1 / 1 water / propanol mixture. The solution is sprayed onto two cured glass panes. After a drying time of 5 minutes, a first glass pane is bonded to a second glass pane using an edge seal (edge ​​seal). The resulting cavity is filled with the mixture of the reactants for fire protection layer 3 listed in Example 1.

[0055] The composite filled with the fire-protection layer is heated in an oven at 55°C for 500 minutes. The polymerization of the hydrogel reactants is initiated by the heating, and the fire-protection layer hardens in the cavity between the panes.

Claims

1. Fire-resistant glazing comprising at least two transparent supports between which a transparent fire-resistant layer is arranged, wherein the fire protection layer comprises a hydrogel, and wherein the hydrogel comprises a polymer and 5-20 wt.% salt, and the polymer is polymerized from at least one monofunctional monomer and at least one bifunctional or polyfunctional monomer in an aqueous salt solution or in an aqueous salt dispersion in an acidic environment, wherein the monomers are non-toxic, non-carcinogenic, and non-mutagenic, and wherein the at least two transparent carriers have a layer of organofunctional silane on the side facing the fire protection layer.

2. Fire-resistant glazing according to claim 1, characterized in that the layer of organofunctional silane is a monomolecular layer.

3. Fire-resistant glazing according to one of the previous claims, characterized in that the organofunctional silane forms a covalent bond with the fire-resistant layer.

4. Fire-resistant glazing according to one of the previous claims, characterized in that the organofunctional silane has at least one double bond on the side facing away from the glass pane, wherein the organofunctional silane is in particular a vinyl silane.

5. Fire-resistant glazing according to one of the previous claims, characterized in that an initiator is additionally present during polymerization of the polymer.

6. Fire-resistant glazing according to one of the previous claims, characterized in that polymerization of the polymer from the monomers is thermally activatable, wherein thermal activation begins above room temperature.

7. Fire-resistant glazing according to claim 6, characterized in that an activation temperature for initiating the polymerization is below 80°C, in particular in a range from 25°C to 80°C, in particular in a range from 40°C to 75°C.

8. Fire-resistant glazing according to one of the previous claims, characterized in that the initiator comprises a persalt, in particular a peroxydisulfate.

9. Fire-resistant glazing according to one of the previous claims, characterized in that the monofunctional monomers comprise at least acrylic acid or an acrylic acid derivative and methacrylamide or a derivative of methacrylamide, wherein the monofunctional monomers comprise 5-20% by weight, in particular 7-15% by weight, of the reactants of the fire-resistant layer.

10. Fire-resistant glazing according to one of the preceding claims, characterized in that the polymerized fire-resistant layer has a pH value of less than 7.

11. Method for producing fire-resistant glazing comprising the steps - providing a fire protection compound with water-soluble, non-toxic, non-carcinogenic and non-mutagenic monofunctional monomers and at least one bi- or polyfunctional monomer and at least one initiator in an aqueous salt solution or in an aqueous salt dispersion in an acidic environment; - providing at least one first transparent carrier and at least one edge boundary extending along the edge of the first carrier so that the first carrier and the edge boundary form a container; - Filling the fire protection compound into the container; and - controlled initiation of a polymerization of the fire protection compound to form a hydrogel fire protection layer containing 5-20% by weight of salt, wherein the first carrier or at least one of the carriers is designed as a glass pane, and wherein, in an additional step, a layer of organofunctional silane is applied to the at least one glass pane on a side facing the fire protection layer before the glass pane is brought into contact with the fire protection compound.

12. Method according to claim 11, characterized in that the first transparent carrier is provided together with at least one second transparent carrier spaced apart from the first carrier, wherein the edge boundary is an edge seal extending between the first and second glass panes along their edge, and the fire protection compound is filled into a space formed between the first and second carriers, which space forms the container, before polymerization.

13. Method according to one of claims 11-12, characterized in that the controlled start of polymerization is initiated by heating the fire protection compound to a temperature above room temperature.

14. Method according to one of claims 11-13, wherein the fire-retardant mass contains monomers which polymerize to a polymer during polymerization, at least one of which is acrylic acid or an acrylic acid derivative and methacrylamide or a derivative of methacrylamide.