DE102007009785B4 - Process for the production of coated glass with increased strength, and according to the method produced glass product - Google Patents

Abstract

A process for producing a coated sodium-containing glass, in which the glass is provided with a sol-gel coating in the form of a multilayer interference layer and the glass with the sol-gel coating for curing the coating at a temperature of more than 200 ° C. is tempered, characterized in that the thus coated glass is chemically biased after annealing the sol-gel coating by the coated glass is stored in a potassium-containing medium, so that sodium ions of the glass at the surface and in the near-surface Regions are at least partially replaced by potassium ions, wherein the ion exchange through the annealed multilayer sol-gel coating is carried out.

Description

The invention relates generally to optically coated glasses, in particular sol-gel coated glasses. The coating of glass sheets by sol-gel methods is known to the person skilled in the art. In this coating, a sol is applied to a glass substrate to be coated. From this sol, or the forming gel is then produced by annealing an oxide layer. For example, SiO ₂ layers can be produced by means of a sol which contains TEOS (tetraethoxysilane) as precursor. For high-index layers, titanium oxide layers can be produced by the sol-gel method. A common precursor for such layers is titanium tetraisopropoxide. Such coatings are used inter alia as interference layers, for example for the antireflection of glasses.

It would be desirable to give such coated glasses further advantageous properties. An important feature is the strength of the glass. In order to increase strength, the chemical and thermal tempering of glasses is generally known. The thermal bias, or thermal curing is based on that the glass to be hardened is quenched. In the process, the surface of the glass first cools, while liquid or soft glass is still inside. The temperature difference to the environment is then greater inside than outside. The interior of the glass would contract more in the following, but this is prevented by the already solid surface. This results in a tensile stress on the inside, while a compressive stress forms on the surface. Chemical curing is based on replacing a smaller ion present in the glass with a larger one on the surface. Due to the increased space requirement of these ions, a compressive stress is generated on the surface.

Although thermal tempering is a comparatively inexpensive method for increasing the strength, it also has some disadvantages compared to chemical tempering. Thus, thin glasses can not or at best only inadequately thermally prestressed, since when cooling the glass, a sufficient temperature gradient can not be achieved in the glass. Furthermore, thermally tempered glasses can not be cut. In the case of chemically tempered glasses, on the other hand, subsequent heating of the glass results in relaxation of the built-up stresses. Thus, temperatures of over 200 ° C are used for the tempering of sol-gel layers.

The document DE 698 18 541 T2 discloses a method of producing very thin glass on a roll. Here, after a chemical toughening, a sol-gel coating is applied, but the method is only practicable with very thin glasses, ie with glass thicknesses below 1.2 mm. The document DE 10 2005 020 168 A1 relates to a process for producing a substrate with an anti-reflective coating. The coating is applied by means of a sol-gel process. Chemical hardening of the coated substrate does not take place.

The invention is therefore based on the object, in view of the above-mentioned problems, to provide optically coated glasses with increased strength. This object is already achieved in a surprisingly simple manner by the subject matter of the independent claims. Advantageous embodiments and further developments of the invention are specified in the dependent claims.

Accordingly, the invention provides a process for producing a multilayer coated sodium-containing glass in which the glass is provided with a sol-gel coating and the glass with the sol-gel coating for curing the coating at a temperature of more than 200 ° C is annealed. The glass thus coated is chemically tempered after annealing of the sol-gel coating by storing the coated glass in a potassium-containing medium, so that sodium ions of the glass at the surface and in near-surface regions are at least partially covered by potassium. Ions are exchanged. As a medium in particular a potassium-containing melt, such as a corresponding molten salt is suitable. Other media, such as potassium-containing solutions come into consideration. The preferred bias in a molten salt generally uses high temperatures above 350 ° C. At these temperatures, the ion mobility increases accordingly, so that the ion exchange accelerates.

Accordingly, the ion exchange takes place according to the invention through the tempered sol-gel coating. Accordingly, the coated sodium-containing glass obtainable by this process is provided with a sol-gel coating and is chemically tempered, the chemical bias being carried out after coating with the sol-gel coating in a potassium-containing medium such that sodium Ions of the glass in near-surface regions are at least partially replaced by potassium ions, wherein the ion exchange has taken place through the tempered sol-gel coating, wherein the sol-gel layer due to the chemical bias Contains potassium from the medium used for the bias. The potassium ions in the sol-gel coating are a characteristic of this manufacturing process.

It is an unexpected effect that a chemical biasing of the glass is still possible through the cured sol-gel coating. It has further been found that the chemical bias can be done both by a silicon oxide-containing sol-gel coating produced on the glass, as well as by a titanium oxide-containing sol-gel coating. This applies in general to many metal oxide-containing coatings, such as those which can be prepared by the sol-gel process, and in particular also to those metal oxides which are used for optical, in particular also interference-optical coatings.

In general, the coating composition for producing the sol-gel coating may contain hydrolyzable compounds or salts of at least one of the elements of main groups III to V, for example Al, In and / or subgroups II to V, for example Sn, Zn, Zr, Nb, Ta, V and / or hydrolyzable compounds of the lanthanides, such as Ce included. Other hydrolyzable compounds can be used, such as those of elements of main groups I and II of the Periodic Table, z. B. Na, Ca, Mg and subgroups VI to VIII of the periodic table, such as Mn, Cr, Ni. The finished tempered and cured sol-gel coating then contains corresponding oxides of the aforementioned elements. Particularly important for optical, in particular interference-optical coatings are oxides of the metals Ti, Si, Nb, Ta, Al, Zr.

It can be a multilayer sol-gel coating, in particular made with the above-mentioned metal oxides and after annealing the chemical bias can be performed. In particular, the individual layers of the multilayer coating may have different compositions with oxides of the abovementioned elements. In particular, the aforementioned elements can also be mixed to produce desired layer properties, such as a specific refractive index, so that corresponding mixed oxide layers are obtained.

Such multilayer coatings can be formed as interference layers. For example, by means of the invention, glass panes can be provided with antireflection coatings in this manner and then be chemically hardened.

In a preferred embodiment of the invention, the ion exchange is carried out for the chemical curing in a potassium nitrate-containing medium, in particular a potassium nitrate-containing melt. Preferably, the glass is stored for several hours in the potassium-containing medium. Regardless of the nature of the potassium-containing medium, the glass should be stored in the medium for more than 30 minutes, preferably at least 2 hours, more preferably at least 3 hours to achieve a good tempering effect. Depending on the case, even much longer preload times, for example up to 16 hours, can be selected. Typical bias times are often in the range of 4 to 16 hours. These biasing procedures can be used to the same extent for the glasses coated according to the invention.

In order to apply the sol-gel coating, it is further preferred to use dip coating. In dip coating, the glass sheet to be coated is dipped in the sol and then slowly pulled out. In this method, the desired layer thickness, for example, an interference-optical acting λ / 4 layer can be set very accurately by adjusting the pulling speed. But there are also other application methods into consideration. In particular, the spray coating should be mentioned here. Even with this coating method, a fairly accurate adjustment of the applied amount of coating material is possible, this method at the same time allows a much faster order.

The invention is particularly suitable for coating lime-soda glasses. The high sodium content of such glasses predestines them for chemical toughening. In addition, the sol-gel layers adhere very well to such a glass.

With the invention, an increase in the breaking strength by at least a factor of 2.5 compared to a similar, not inventively tempered glass can be achieved.

The invention will be explained in more detail by means of embodiments and with reference to the accompanying drawings. Show it:

1 a cross section through an inventively coated and chemically toughened glass,

2 a bar graph with strengths of uncoated, coated and additionally chemically toughened glass,

1 shows a product produced according to the invention 1 which is a glass pane 3 with pages 5 . 7 includes. On the glass 3 is both sides on the pages 5 . 7 a three-layer coating 9 with layers 11 . 12 . 13 applied by sol-gel coating. The coating can be designed in particular as a three-layer antireflection coating. For this purpose, the layers 11 . 12 . 13 different refractive indices and have an optical thickness of preferably each an integer multiple of a quarter wavelength. According to one exemplary embodiment of a three-layer antireflection coating, a mixed oxide layer is the first 11 with silica and titania 11 , then a high refractive titanium oxide layer 12 and then a silicon oxide layer 13 applied by sol-gel coating in a dipping process. The refractive index of the situation 11 lies between the refractive indices of the layers 12 and 13 , Preferably, for an effective anti-reflection the optical thickness of the layers 11 and 13 each quarter wavelength and the optical thickness of the layer 12 a half wavelength for one wavelength of the optical spectral range. The layer system thus obtained is then tempered at a temperature above 200 ° C and cured.

A sol-gel process, as used according to the invention, is a wet-chemical coating process, with which inorganic oxide layers can be produced. The preparation of the coating starts in each case from a liquid sol, which is converted by a sol-gel transformation into a solid gel state. The sol represents a dispersion of particles, which typically have sizes in the range well below 1 micrometer. In many cases, organometallic compounds are used as precursor substances for the coating, in which case the term "metal" also includes semiconductors, in particular silicon. In the transformation of the sol into a gel, crosslinking of the dispersed particles in the solvent occurs. If the sol is applied and converted into a gel, the coating thus obtained is still - preferably tempered under air or in another oxidizing environment, so that organic residual constituents of the coating pyrolyze and a densified inorganic oxide layer is obtained. The reaction of the organometallic precursor is typically carried out by hydrolysis and condensation reactions.

The starting compound (the precursor) for preparing a coating solution contains a metal or transition metal, for example silicon. The most commonly used precursor compounds are metal alkoxides and salts. To prepare the sol, one or more starting compounds, if appropriate with acidic or basic catalysis, are hydrolyzed in aqueous or organic solvents and optionally at least partially condensed. The coating compositions may generally, without limitation to the embodiment of the 1 be varied. Inter alia, mixed oxide layers can also be produced. For the preparation of silicon oxide layers, suitable precursors include TEOS (tetraethoxysilane). Titanium oxide layers can be prepared, for example, with titanium tetraisopropoxide as precursor. It then forms by hydrolysis and condensation, a colloidal dispersion of metal alkoxides, which is applied to the glass to be coated. Subsequently, the glass is tempered. In the temperature range between 200 ° C and 550 ° C, in which the heat treatment is preferably carried out, the residual organics pyrolyzed from the coating and the coating densifies.

Following the sol-gel coating with curing is the coated glass sheet 3 chemically toughened.

This is the glass 3 stored in a potassium nitrate-containing melt, preferably a potassium nitrate melt for several hours. The potassium ions of the melt diffuse through the sol-gel coating 9 into the glass of the glass pane 3 into it. Conversely, sodium ions of the glass diffuse through the coating 9 through into the melt. It forms accordingly on the sides 5 . 7 near-surface areas 15 in which sodium is at least partially replaced by potassium. These ranges are generally much deeper than the layer thicknesses of the individual layers of an interference-optical sol-gel coating, which typically have thicknesses smaller than the optical wavelengths of the optical spectral range. In contrast, typical exchange depths are in the range of 10 to 100 μ.

2 shows a bar graph with strengths of different glasses with a thickness of 6 mm. Strength measurement was performed by placing the glass panes on a 100 millimeter inner diameter ring and then applying pressure to the glass sheet on the point of the surface above the center of the ring until the glass broke. In the 2 given values are given relative to an untreated, uncoated float glass, used as a reference (reading A) for measurements on other glass panes. Measurement B is the measurement on a similar glass pane, which was provided with a three-layer anti-reflection coating by sol-gel coating. The sol-gel coating has little effect on the strength. The slight deviations of the strength with respect to the untreated glass are within the scope of the measurement uncertainty. Measured value C is the measured strength on a glass sheet treated according to the invention, which was first provided with a three-layer antireflection coating and then chemically tempered. This was the glass 4 Hours stored in the potassium nitrate-containing bath. The comparison with measured value A shows that the strength is higher by a factor of 3 than in the case of the untreated float glass pane. Also, the strength is surprisingly comparable to that of uncoated, chemically tempered glasses (measured value D). Although the strength measured to measure D Density is sometimes even higher, but also a much longer biasing time, 16 hours in the potassium salt-containing molten salt, was used. It turns out that even a three-layer sol-gel coating surprisingly has little effect on the achievable strength, although here the potassium ions must diffuse through the coating into the glass and vice versa sodium ions through the coating into the melt.

Claims (17)

A process for producing a coated sodium-containing glass, in which the glass is provided with a sol-gel coating in the form of a multilayer interference layer and the glass with the sol-gel coating for curing the coating at a temperature of more than 200 ° C. is tempered, characterized in that the thus coated glass is chemically biased after annealing the sol-gel coating by the coated glass is stored in a potassium-containing medium, so that sodium ions of the glass at the surface and in the near-surface Regions are at least partially replaced by potassium ions, wherein the ion exchange through the annealed multilayer sol-gel coating is carried out. Process according to Claim 1, characterized in that a sol-gel coating is prepared which comprises an oxide of at least one of the elements of main groups III to V, in particular Al, In and / or subgroups II to V, in particular Sn, Zn, Zr , Nb, Ta, V and / or the lanthanides, in particular Ce, and / or an element of the main groups I and II of the Periodic Table, in particular Na, Ca, Mg, and / or the subgroups VI to VIII of the Periodic Table, in particular Mn, Cr Contains Ni. Process according to the preceding claim, characterized in that a sol-gel coating is produced which contains at least one of the elements Si, Ti, Al, Ta, Nb, Zr as oxide. Method according to one of claims 2 or 3, characterized in that a sol-gel coating is produced with a mixed oxide of at least two of the elements mentioned in the two preceding claims. Method according to one of the preceding claims, characterized in that the ion exchange takes place in a potassium nitrate-containing medium, preferably a potassium nitrate-containing melt. Method according to one of the preceding claims, characterized in that the glass is coated with a multilayer sol-gel coating whose layers have different compositions of one or more oxides of the elements mentioned in claims 2 and / or 3. Method according to one of the preceding claims, characterized in that the glass is coated with an antireflection coating in the sol-gel process. Method according to one of the preceding claims, characterized in that the sol-gel coating is applied by dip coating or spray coating. Method according to one of the preceding claims, characterized in that the glass for the chemical toughening is stored for longer than 30 minutes, preferably for at least 3 hours, in a potassium-containing solution. Coated sodium-containing glass obtainable by a process according to any one of the preceding claims, which is provided with a sol-gel coating in the form of a multilayer interference layer and is chemically tempered, characterized in that the chemical prestressing after the preparation of the sol-gel Coating is carried out in a potassium-containing medium, so that sodium ions of the glass in the near-surface regions are at least partially replaced by potassium ions, wherein the ion exchange is carried out through the tempered sol-gel coating, wherein the multilayer sol-gel Layer due to chemical biasing potassium from the solution. Coated sodium-containing glass according to claim 10, characterized in that the coating comprises a sol-gel coating comprising an oxide of at least one of the elements of main groups III to V, in particular Al, In and / or subgroups II to V, in particular Sn, Zn, Zr, Nb, Ta, V and / or the lanthanides, in particular Ce, and / or an element of the main groups I and II of the Periodic Table, in particular Na, Ca, Mg, and / or the subgroups VI to VIII of the Periodic Table , in particular Mn, Cr, Ni. Coated sodium-containing glass according to claim 11, characterized in that the coating contains at least one of the elements Si, Ti, Al, Ta, Nb, Zr as oxide. Coated sodium-containing glass according to claim 11 or 12, characterized in that the sol-gel coating contains a mixed oxide of at least two of the elements mentioned in the two preceding claims. Coated sodium-containing glass according to one of the preceding claims, characterized in that the glass is coated with a multilayer sol-gel coating. Coated sodium-containing glass according to one of the preceding claims, characterized in that the glass is coated with an anti-reflection coating in the sol-gel process. Coated sodium-containing glass according to one of the preceding claims, characterized in that the glass has a breaking strength which is at least a factor of 2.5 higher than that of a similar, non-tempered glass. Coated sodium-containing glass according to any one of the preceding claims, characterized in that the glass is soda-lime glass.

Images