DE102014116798A1 - Chemically toughened or toughened glass and process for its production - Google Patents

Abstract

The object of this invention is to provide a glass pane which is easy to produce, in particular in the form of a thin glass having a slice thickness of at most 1.5 mm, which has no or only a very slight warping even after prestressing. For this purpose, a glass pane, in particular a float glass pane (1), of a chemically prestressed or tempered glass with two opposite side surfaces (2, 3) is provided, wherein the glass of the glass pane is sodium-containing, wherein the glass on the side surfaces (2, 3 ) having a top (4) (top) and a bottom (5) (bottom) has a different tin content, and wherein the Na 2 O content at the two side surfaces (2, 3) is also different, wherein the Na 2 O content is higher on the side surface (3) with the higher tin content than on the opposite side surface (2), wherein for the surface leaching difference of the Na2O contents (ΔNa2O) of the two side surfaces (2, 3) in percentage by mass: ΔNa2O = -0.00078 · ΔTinCountx, where ΔTinCount is the difference of the TinCounts, which is the difference between the mass-related surface contents of SnO2 of the two side surfaces (2, 3) determined by X-ray fluorescence analysis in ppm (parts p he million), and wherein the exponent x is in the range of 0.5 to 0.7, preferably at 0.62.

Description

The invention generally relates to a chemically toughened or toughened glass and a process for its production.

In particular, the invention relates to an ion exchange chemically preloaded or biased, high-strength glass, preferably as a cover glass with very good scratching behavior. The glass can be used as protective glass (cover) in electronic devices such. As smartphones, tablets, computers, navigation devices, etc., are used.

Smartphones, tablets, computers, navigation devices, etc. are now generally served via touch screens. To protect the display and the sensor, thin, ion-exchanged (chemically tempered) glasses can be used. The chemical bias of the glass is achieved by exchanging small alkali ions (eg, Na ⁺ ) with larger homologs (eg, K ⁺ ). Here, a tension profile is introduced into the glass.

Depending on the manufacturing technology, geometry, glass thickness and prestressing conditions, chemically toughened glasses typically have a more or less large warping, also referred to as "warp".

Depending on the manufacturing and tempering conditions, the warp may exceed the specification of the equipment manufacturer. On the other hand, sometimes a certain warping of a glass pane (convex or concave) is required. By the processing process, a desired warping can be set.

The warp or the warping comes about through asymmetric ion exchange on top or bottom of the glass. This leads to differences in the introduced compressive stress and / or the ion exchange depth, which can be measured as ΔCS (difference of the CS, compressive stress, compressive stress) or ΔDoL (difference of the DoL, depth of layer, exchange depth). As a consequence, it comes to "dodging" or balancing the compressive stress differences of the glass in the form of a warp.

This effect can be observed especially with float glasses.

In the US 3 453 095 A and the DE 3 607 404 C2 The asymmetric ion exchange is attributed to the presence of a so-called tin layer, which is formed by diffusing tin from the float bath into the glass. In the US 3 453 095 A For the purpose of symmetrical ion exchange, it is proposed to incorporate tin into the surface on both sides.

The DE 3 607 404 C2 proposes to activate the tin-influenced side by an ion exchange upstream of the actual tempering process, ie to carry out a two-stage ion exchange process. In the exchange of sodium ions for potassium ions in the surface layers of float glass, tin has a hindering effect on the replacement of sodium ions by potassium ions, which is counteracted by the upstream ion exchange.

The WO 2013/146438 A1 describes that the difference in Na ₂ O contents (ΔNa ₂ O) of the two opposite side surfaces of a glass sheet for non-preloaded and tempered glasses should be between 0.2 and 1.2 percent by mass to effectively suppress warpage to reach. A difference in the Na ₂ O contents (ΔNa ₂ O) of less than 0.7% by mass, more preferably less than 0.3% by mass, is preferably given, in particular from measured data on non-tempered glasses, since a difference of greater as 0.7% by mass apparently also form a kind of "concave sections", in particular if the temperature of the glass does not exceed 650 ° C. For the sodium leaching, a number of possible variants are enumerated, the experimental data being based on fluorine-based sodium leaching and wherein a treatment temperature with the leaching medium of above 650 ° C is recommended, preferably at glass transition temperatures above 700 ° C of 750 ° C.

The DE 694 02 557 T2 describes the sodium leaching of a float glass by applying SO ₃ , in particular generated by SO ₂ gas and an oxygen-containing gas, on the top surface of the float glass, so that substantially the tarnishing of the upper surface of the glass is reduced or is turned off.

The object of this invention is to provide a glass pane which is easy to produce, in particular in the form of a thin glass having a slice thickness of at most 1.5 mm, which has no or only a very slight warping even after prestressing.

This object is solved by the subject matter of the independent claim. Advantageous embodiments and further developments of the invention are specified in the dependent claims.

It was recognized that the intensity of the surface leaching difference of the Na ₂ O- Contents (ΔNa ₂ O) between the two side surfaces (top and bottom / top-bottom) of the glass pane, the primary interactions or the primary asymmetries, which are caused in the float bath in the float process, must be compensated.

The invention will be explained in more detail below with reference to the accompanying figures. Show it:

1 a diagram for the relationship between the force difference (ΔS) in N / mm ([CS _top · DoL _top ] - [CS _bottom · DoL _bottom ]) / 2000 (with the compressive stress CS and the ion exchange depth DoL)) and the TinCount Difference (ΔTinCount) in terms of bottom and top (bottom-top),

2 a diagram of the dependence between the ΔNa ₂ O (relative proportion Na ₂ O _top- relative fraction Na ₂ O _bottom ) and the ΔTinCount (bottom-top) and

3 a schematic representation of the cross section through a chemically tempered float glass sheet with schematic diagrams of the Sn, Na ⁺ and K ⁺ contents in the float glass pane according to the invention.

In series of tests on different deposition intensities in the float bath, in which the compressive stress (CS, Compressive Stress) and the ion exchange depth (DoL, Depth of Layer) were respectively determined on the top (top) and bottom (glass) of the glass pane, the TinCount identified as a well-measurable size, the TinCount the superficial mass-related tin levels measured by X-ray fluorescence, to which a corresponding compensation measure for caused in the float bath primary asymmetries or an optimization of the warpage of the glass can align.

More specifically, TinCount is understood here to mean the mass-related surface content of SnO ₂ in the glass determined by X-ray fluorescence analysis, expressed in ppm (parts per million). The TinCount is a float size, which can be converted as needed into SnO ₂ in weight percent or mass percent by dividing the TinCount value by 10 ^ 4. A TinCount value of 110 is thus equivalent to a proportion of 0.011 wt .-% SnO ₂ in the surface.

There was a clear dependence of the buckling moment or force difference (ΔS in N / mm ([CS _top · DoL _top ] - [CS _bottom · DoL _bottom ]) / 2000)) on the TinCount difference (ΔTinCount) with respect to bottom and bottom Top determined as in 1 shown. The difference of TinCount is used to remain independent of tin contents from the glass synthesis.

No standard FSM (surface stress meter) measurement was used to measure compressive stress (CS) and ion exchange depth (DoL) values on both side surfaces of the glass, as this is significantly systematic even at slight warps Can show measurement error. Instead, a specially optimized for this investigation measuring apparatus was created, in which the glass pane to be measured is leveled to obtain even for thin slices plausible differences in compressive stress and ion exchange depths for the two surfaces of the top and bottom. To measure the compressive stress (CS) and the ion exchange depth (DoL), a commercially available measuring device (manufacturer "Orihara Industrial", model "FSM-6000 LE") was modified to perform reliable measurements on thin and slightly curved glass panes can. The measurement method requires close contact between the sample and the prism (as part of the measuring device for coupling the measuring light), which is not always guaranteed, especially on the concave side of curved samples. The sample is therefore made by placing a small weight in a flat shape. The "leveling" succeeds particularly well when the prism is flush with the surface of the measuring table. For this purpose, the prism holder is reworked in order to install the prism in the desired, for this particular application, particularly favorable position.

By applying the glass sheet with sulfur dioxide (SO ₂ ) or sulfurous acid (H ₂ SO ₃ ), such as in the DE 694 02 557 T2 Sodium is drawn out or leached out of the glass, whereby the relationship between the warping moment (top-bottom) or the force difference (ΔS in N / mm ([CS _top . DoL _top ] - [CS _bottom · DoL _bottom ]) / 2000 (with the compressive stress CS and the ion exchange depth DoL) and the ΔNa ₂ O (relative proportion Na ₂ O _top- relative fraction Na ₂ O _bottom ) gives the following: ΔS = 64 · ΔNa ₂ O

The results of the force difference (ΔS) and the TinCount difference (ΔTinCount) in terms of bottom and top (bottom-top) are in 1 and give the relationship shown in the following formula: ΔS = 0.05 · ΔTinCount ^x , where the exponent x is preferably 0.62 with an upper exponent limit of x = 0.7 and a lower exponent limit of x = 0.5.

If this force difference (ΔS) is to be compensated by a corresponding opposite direction by ΔNa ₂ O, this means that the Na-caused ΔS _Na and the float bath-caused ΔS _TinCount should just compensate _each other to zero, ie ΔS _Na + ΔS _TinCount = 0 or ΔS _Na = -ΔS _TinCount

It results by inserting with the formula: ΔS = 64 · ΔNa ₂ O then the final formula: ΔNa ₂ O = -0.00078 × ΔTinCount ^x , where the exponent x is preferably 0.62 with an upper exponent limit of x = 0.7 and a lower exponent limit of x = 0.5.

This results in the 2 shown illustration with the diagram for the dependence between the ΔNa ₂ O (relative proportion Na ₂ O _top- relative proportion Na ₂ O _bottom ) and the ΔTinCount (bottom-top).

Thus, according to the invention at least the top of the two opposite side surfaces of the glass as long as sulfur dioxide (SO ₂ ) or sulfuric acid (H ₂ SO ₃ ) acted up to the difference of the superficial Na ₂ O contents (ΔNa ₂ O) of the two side surfaces in percentage by mass: ΔNa ₂ O = -0.00078 × ΔTinCount ^x , where ΔTinCounts is the difference of the TinCounts, which denotes the difference of the mass-related surface contents of SnO _{2 of} the two side surfaces determined by X-ray fluorescence analysis in parts per million, and wherein the exponent x is in the range of 0.5 to 0.7 at 0.62.

The most favorable surface leaching difference of the Na ₂ O contents (ΔNa ₂ O) can thus be read directly, knowing the TinCount difference of the glass in question.

3 gives a schematically represented cross section through a float glass pane according to the invention 1 , which is chemically toughened, and their Sn, Na ⁺ and K ⁺ contents in schematic diagrams.

The float glass 1 points to two opposite side surfaces 2 and 3 or at the top 4 (top) and bottom / float glass side 5 (bottom) to a different tin content and a different Na ⁺ content.

In particular, by the diffusion of tin from the float bath is the superficial tin content on the float glass side 5 (Bottom, bottom) higher than on the opposite side, here the top 4 (top) of the float glass 1 , so that a TinCount difference (ΔTinCount) results, which is the difference of the surface tin contents of the two side surfaces 2 and 3 or the float glass side 5 (Bottom, bottom) and the top 4 (top) of the glass pane 1 indicates.

By applying at least the top 4 (top) of the glass pane 1 with sulfur dioxide (SO ₂ ) or sulfurous acid (H ₂ SO ₃ ), in particular in the DE 694 02 557 T2 described, are from the top 4 (top) of the float glass 1 Sodium ions are drawn out or leached out so that there is a surface leaching difference of the Na ₂ O contents (ΔNa ₂ O) between the top 4 (top) and the float glass side 5 (Bottom, bottom) results.

Also in the chemical bias of the glass sodium ions are preferably exchanged on the surface of the glass according to the invention by potassium ions. Consequently, the potassium content (K ⁺ ) also influences the sodium content (Na ⁺ ) and thus the surface leaching difference (ΔNa ₂ O) between the two opposite side surfaces 2 and 3 the float glass 1 ,

The invention avoids the disadvantages of the prior art and achieves better values for warping even after tempering.

With the invention, it is now possible to provide a thin glass pane with a standardized warp (W _s ) after chemical tempering of less than 300 μm, preferably of less than 200 μm and particularly preferably of less than 100 μm, preferably with a compressive stress (CS, Compressive Stress) in the surface of the glass of at least 800 MPa and a depth of exchange (DoL, Depth of Layer) of the alkali ions of the prestressed layer of at least 30 μm.

Preferably, the invention provides a glass with the following constituents in the interior of the glass pane in percent by mass: SiO ₂ 56-70, Al ₂ O ₃ 10-22, B ₂ O ₃ 0-8, P ₂ O ₅ 0-3, Na ₂ O 10-16 K ₂ O 0-6, MgO 0-10, ZnO 0-3, TiO ₂ 0 to 2.1, _SnO2 0-1, F 0-2.

Further favorable secondary conditions result in particular from the quantitative ratios or from the quotients of the total contents of various specific components.

A favorable constraint is the sum of all shares of alkali and alkaline earth oxides. In this case, the alkali oxides include the oxides of the elements Li, Na, K and the alkaline earth oxides, the oxides of the elements Mg, Ba and Ca. The sum of the alkali and alkaline earth oxides should be greater than 13% by mass, preferably greater than 15% by mass. LiO ₂ should be less than 1 mass%, preferably less than 0.1 mass%.

The sum of the alkaline earth oxides is preferably 7% by mass or less.

In addition, the glass contains few impurities, which are unavoidable by the choice of the raw material.

Furthermore, the glass may have 0-2%, preferably 0-1%, further components such as refining agents, chlorides, sulfates, CaO, SrO, BaO. Preferably, as stated above, the glass is free of CaO. It is also preferred that the glass is free of ZrO ₂ . It is obvious to the person skilled in the art that the term "free from" is to be understood in each case as meaning that unavoidable traces of the abovementioned materials CaO and ZrO _{2 can} still be contained by the choice of the raw material and the contact materials.

Although ZrO ₂ is good for the scratching behavior and is neutral with respect to the ion exchange. At too high levels of ZrO ₂ , the devitrification tendency of the glass increases significantly during the melting and shaping process, which is particularly noticeable in hot forming with overflow fusion. Therefore, the glass should be free of ZrO ₂ .

In the following, further aspects of the glass composition and its properties, in particular also the increased scratch tolerance and at the same time good prestressability, will be explained.

SiO ₂ is important as a majority component and glass former for the stabilization of the network. This is advantageous, inter alia, for sufficient chemical resistance of the glass. Insufficient SiO ₂ contents lead to an increased devitrification tendency. On the other hand, very high levels of SiO ₂ also entail high melting temperatures. Furthermore, a glass with a high SiO ₂ content has a very dense structure, which is detrimental to ion exchange.

Al ₂ O ₃ improves the scratching behavior and at the same time proves to be positive for ion exchange. The latter can be seen in an impressive manner when comparing the CS and DoL values of alkali aluminosilicate glasses compared to soda lime variants. The former achieve significantly higher values during ion exchange. Al ₂ O ₃ prevents the formation of non-bridging oxygen (NBO) in the glass structure that results in purely silicatic glasses through the network transducers. However, the melting point is significantly increased by Al ₂ O ₃ , and excessively large amounts deteriorate the devitrification tendency as well as the resistance to acids. Again, the composition of the glasses according to the invention achieves a good balance between not too high softening point and low devitrification tendency on the one hand and good scratch tolerance and good ion exchange on the other.

B ₂ O ₃ shows a strong positive influence with regard to the scratching behavior, the same applies to the melting behavior. However, it interferes with the ion exchange very clearly and the process times become too long. Otherwise, the process temperatures during ion exchange must be increased. To prevent this, the use of B ₂ O _{3 should be} limited to a moderate content. After US 2009/142568 A1 and the US 8,341,976 B2 the absence of non-bridging oxygen (NBO) is ascribed good scratch resistance. This means that a glass with exclusively bridging oxygen (BO, bridging oxygen) would have a very good scratching behavior. It turns out, however, that such a glass is so strong in its structure that the ion exchange is made very difficult, because ions must be able to migrate within the material during an exchange. So NBO should be generated again.

After US 2009/142568 A1 and US 8,341,976 B2 this is attempted by means of a balance of Al ₂ O ₃ and B ₂ O ₃ on the one hand and network converters on the other hand. However, this results in a disadvantageously high B ₂ O ₃ content and associated long process times during ion exchange. In contrast, the solution of this invention is in the balance between B ₂ O ₃ and the element fluorine.

At too high a level, fluorine has a negative influence on the scratch behavior of the glass and, moreover, on ion exchange. At low boron levels in the glass, however, the introduction of fluorine as a glass component is surprisingly positive. If the fluorine content is too low, this results in a poor melting behavior of the glass batch. Furthermore, a bad ion exchange and again a bad scratching behavior is noticeable.

The alkali (Na ₂ O, K ₂ O) and alkaline earth oxides (MgO, CaO, SrO, BaO) reduce the scratch tolerance. This is probably due to the generation of non-bridging oxygen (NBO) in the glass structure. CaO, SrO and BaO as well as ZnO impede the ion exchange and therefore can only be used in small amounts.

P ₂ O ₅ promotes ion exchange. Furthermore, by adding P ₂ O _5, the negative influence of B ₂ O _{3 can be} reduced. Too low amounts of P ₂ O ₅ have a positive effect against devitrification, too high reduce the chemical resistance and increase the evaporation during the melting process.

CeO ₂ and preferably SnO ₂ serve as redox-active refining agents. Too low values lead to many bubbles in the glass, too high produce melting relics and bring unwanted color into the glass.

The glass should preferably also be free from the conventional but harmful or environmentally harmful refining agents As ₂ O ₃ and Sb ₂ O ₃ .

With a glass of the above composition also high bias values and / or a fast chemical bias can be achieved. According to a further aspect, the invention therefore also relates to a chemically toughened glass having the above-mentioned composition for increasing the strength, the glass being chemically toughened by exchanging sodium ions for potassium ions on its surface.

With such a bias by exchanging sodium with potassium ions, the glass has a standard warp (W _s ) after chemical tempering of less than 300 μm, preferably less than 200 μm, and more preferably less than 100 μm, and the compressive stress (CS, Compressive Stress) in the surface of the glass is at least 800 MPa, and the depth of exchange (DoL) of the alkali ions of the prestressed layer is at least 30 μm.

The glasses according to the invention are furthermore distinguished by glass transition temperatures (T _g ) of greater than 580 ° C. Since relaxation processes in the glass become relevant if there are sufficient stresses in the glass, even below the glass transition, a high Tg value for the chemical tempering is relevant and of particular advantage.

In order to serve as a cover glass, in particular for electronic displays, the glass is particularly preferably made disc-shaped. The shaping for such glass panes can be done by floating, pulling (up or downdraw), rolling or overflow fusion.

Glasses according to the invention generally have working temperatures, or an operating point (viscosity of 10 ⁴ dPas) of less than or equal to 1380 ° C. The glasses can thus be melted in common types of special glass jars, and the hot forming can easily be accomplished by the above-mentioned hot forming techniques such as floating, drawing (up- or downdrawing), rolling or overflow fusion.

Therefore, according to yet another aspect, the invention relates to a process for producing a disc-shaped glass in which a glass according to the invention is provided and processed by heat-forming into a glass in the form of a glass pane, wherein the hot-forming of one of the processes comprises floating, drawing, rolling or overflowing. Includes fusion.

• – Ziehen eines Glasbandes, aus welchem die Glasscheibe abgetrennt wird, aus einer Glasschmelze durch einen Float-Prozess,
• – Abkühlen des Glasbandes oder der aus dem Glasband bereits abgetrennten Glasscheibe, wobei

mindestens die Oberseite der beiden gegenüberliegenden Seitenflächen der Glasscheibe so lange mit Schwefeldioxid (SO₂) oder Schwefliger Säure (H₂SO₃) beaufschlagt wird, bis für die Differenz der Na₂O-Gehalte (ΔNa₂O) der beiden Seitenflächen in Massenprozent gilt: ΔNa₂O = –0,00078·ΔTinCount^x, wobei ΔTinCount die Differenz der TinCounts ist, welche die Differenz der über Röntgenfluoreszenzanalyse bestimmten massenbezogenen Oberflächengehalte von SnO₂ der beiden Seitenflächen in ppm (parts per million) bezeichnet, und wobei der Exponent x im Bereich von 0,5 bis 0,7, bevorzugt bei 0,62, liegt.In particular, a method for producing a glass pane according to the invention, in particular a float glass pane, is provided, with the steps:

• Drawing a glass ribbon from which the glass sheet is separated, from a molten glass by a float process,
• - Cooling of the glass ribbon or the already separated from the glass sheet glass, wherein

Sulfur dioxide (SO ₂ ) or sulfuric acid (H ₂ SO ₃ ) is applied to at least the upper side of the two opposite side surfaces of the glass pane until the difference between the Na ₂ O contents (ΔNa ₂ O) of the two side surfaces in percent by mass applies : ΔNa ₂ O = -0.00078 × ΔTinCount ^x , where ΔTinCount is the difference of the TinCounts, which denotes the difference of the mass-related surface contents of SnO _{2 of} the two side surfaces in parts per million determined by X-ray fluorescence analysis, and wherein the Exponent x is in the range of 0.5 to 0.7, preferably at 0.62.

This cooling above can still be done on the float glass ribbon, or on the previously separated float glass. In general, therefore, the separation of the float glass from the glass ribbon before or after cooling can be done with a symmetrical or asymmetrical or similar temperature / time curve. It is also possible to perform the separation during this cooling process. In both cases, a previous heating can be done to then perform the controlled cooling with respect to the two sides of the float glass or the glass ribbon with a symmetrical or asymmetrical temperature-time course.

The temperature setting or the symmetrical or asymmetrical cooling process is preferably ensured directly after the hot forming at the end of the float bath or after shaping in the drawing process. It can also be realized at the beginning of the cooling process, depending on the process.

For this purpose, it may be advantageous, by asymmetrically heating a glass side or by different heating of the two side surfaces of the glass ribbon, optionally also the already separated float glass, the temperatures at the two side surfaces or top and bottom set specifically. In this way, in the critical region of the structural adjustment of the glasses in the viscosity range from 10 ^11.3 dPas to 10 ^14.5 dPas during cooling at least temporarily, preferably continuously, a symmetrical or a defined asymmetrical temperature distribution in the direction from one side surface to the other opposite side surface getting produced. As a result, the structures on the side surfaces, or the top and bottom can adjust accordingly.

In a further development of the invention, it is provided that the float glass pane after the cooling step, wherein in the temperature range between the dilatometric softening point and the lower cooling point, the two opposite side surfaces of the float glass pane with a symmetrical or asymmetric temperature / time history applied be chemically pre-stressed in a salt bath.

The biasing is preferably carried out by exchange of sodium ions contained in the glass by potassium ions from a salt bath. Accordingly, in a further development of the method after the hot forming, in this case preferably after floating, an ion exchange is carried out in a salt bath containing potassium ions to form a glass pane.

According to one embodiment of the invention, a method for producing a chemically tempered glass is provided, wherein a disk-shaped glass, preferably with a length (l ₀ ) of 217 mm, a width (b ₀ ) of 130 mm and a disk thickness (D ₀ ) of 0.7 mm, cut from a glass mentioned above and then stored for a period of at least 1.5 hours, according to a standardized chemical tempering process preferably for 4 hours in a salt bath containing potassium ions. The temperature is at least 300 ° C, preferably 200 K less than the glass transition temperature (Tg). The sodium ions of the glass are at least partially replaced by potassium ions of the salt bath at its surface. The upper side and the tin bath side of the float glass panes are subjected to the same temperature-time profile, so that asymmetries in the chemical pretensioning of the upper side and tin bath side can not result from the tempering process.

Typically, according to the standard chemical tempering process, the exchange depth (DoL) of the alkali ions is at least 30 μm, and the compressive stress (CS) at the surface is typically at least 800 MPa.

For the ion exchange, a temperature of the salt bath in the range of 380 ° C. to 460 ° C. and a storage period of the glass pane in the salt bath in the range of 1 to 10 hours have proven to be particularly favorable.

The chemical toughening is carried out according to an embodiment of the invention by storing in a salt bath containing predominantly KNO ₃ . Optionally, further potassium-containing components such as K ₃ PO ₄ , K ₂ SO ₄ and KOH may be contained in the salt bath. A pure KNO ₃ melt with preferably more than 99.9% KNO _{3 is} preferred. Optionally, a silver-containing salt, such as AgNO ₃ , may be included. By diffusing silver ions during ion exchange, the glass can also be given antibacterial effects in this way.

With the glass according to the invention can continue to be achieved by means of a single-stage biasing a high compressive stress and high penetration depth. A single-stage bias is less expensive and faster compared to multi-stage processes in which the glass is stored successively in different salt baths.

The slices are then removed from the molten salt and cleaned. Subsequently the warp or warp is according to DIN 50441-5: 1998-05 determined, which in principle has a positive sign. According to note in the DIN 50441-5: 1998-05 the definition of the term "warp" corresponds to the warp ASTM F 1390-92 , The "standardized warp after toughening (W _s )" or in short the "standardized warp (W _s )" describes an intrinsic property of an unbiased float glass disk to form a warp after chemical toughening, the standardized warp (W _s ) corresponding to the warp in which the float glass sheet having a given disk dimension with a length (l ₀ ) of 217 mm and a width (b ₀ ) of 130 mm has a predetermined disk thickness (D _o ) of 0.7 mm according to a predefined chemical tempering process ,

The warp values given in this description basically refer to the prestressed condition and not to the unbiased condition, unless explicitly stated.

The standardized warp (W _s ) corresponds in magnitude to the warp DIN 50441-5: 1998-05 , In addition, however, the standardized warp (W _s ) is given a positive sign when the top of the float glass sheet after the chemical tempering is a convex side and a negative sign when the tin bath side of the float glass sheet is the convex side. The orientation of the curvature with respect to the orientation of the float glass pane during the float process is thus in the case of the standardized warp (W _s ) in contrast to the warp according to DIN 50441-5: 1998-05 considered.

For float glass panes of differing slice thicknesses, the standardized warp (W _s ) after chemical tempering can be approximated by determining the warp (W) according to the method described and using the following formula to the given slice thickness (D ₀ ) for the standardized Warp (W _s ) is converted: W _s = W · (D / D _o ) ² , where D ₀ = 0.70 mm

Similarly, the standardized warp (W _s ) after chemical tempering for float glass panes of differing pulley dimensions having a length (1) and a width (b) can be approximated according to the method described and based on the following formula on the given pulley dimension for the standardized pulley Warp (W _s ) to be converted: W _s = W · [(b ² + l ² ) / (b _o ² + l ₀ ² )] ^1/2

However, the dimensions b, 1 and D of the disks should not deviate too much, in particular not more than between 50% and 200%, from the standardized dimensions b ₀ , l ₀ and D ₀ , since these are mathematical approximations.

A possible further processing of the glass sheet may also include the introduction of holes, recesses or depressions, for example by drilling or milling. The further processing, such as, in particular, the cutting to a designated format or milling, drilling, etching, sandblasting can be done prior to storing in a salt bath by at least one of the steps cutting, breaking or grinding. When the glass sheet is formed by floating, polishing of the surface is also advantageous for removing tin impurities. The further processing preferably takes place before the chemical pretensioning in order to avoid damage during processing due to the stresses existing after prestressing.

LIST OF REFERENCE NUMBERS

1

Float glass

2

side surface

3

side surface

4

Top (top)

5

Float glass side / bottom (bottom)

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 3453095 A [0008, 0008]
• DE 3607404 C2 [0008, 0009]
• WO 2013/146438 A1 [0010]
• DE 69402557 T2 [0011, 0023, 0033]
• US 2009/142568 A1 [0047, 0048]
• US 8341976 B2 [0047, 0048]

Cited non-patent literature

• DIN 50441-5: 1998-05 [0071]
• DIN 50441-5: 1998-05 [0071]
• ASTM F 1390-92 [0071]
• DIN 50441-5: 1998-05 [0073]
• DIN 50441-5: 1998-05 [0073]

Claims (10)

Glass pane, in particular a float glass pane ( 1 ), of a chemically toughenable or toughened glass with two opposite side surfaces ( 2 . 3 ), wherein the glass of the glass pane is sodium-containing, wherein the glass at the side surfaces ( 2 . 3 ) with a top side ( 4 ) (top) and a bottom ( 5 ) (bottom) has a different tin content, and wherein the Na ₂ O content at the two side surfaces ( 2 . 3 ) is also different, the Na ₂ O content on the side surface ( 3 ) is higher with the higher tin content than on the opposite side surface ( 2 ), wherein for the surface leaching difference of the Na ₂ O contents (ΔNa ₂ O) of the two side surfaces ( 2 . 3 ) in mass percentage: ΔNa ₂ O = -0.00078 × ΔTinCount ^x , where ΔTinCount is the difference of the TinCounts, which is the difference of the mass-related surface contents of SnO _{2 of} the two side surfaces determined by X-ray fluorescence analysis ( 2 . 3 ) in ppm (parts per million), and wherein the exponent x is in the range of 0.5 to 0.7, preferably 0.62. Glass sheet according to claim 1, wherein the composition of the chemically toughened or tempered glass inside the glass sheet comprises the following components in mass percentage: SiO ₂ 56-70, Al ₂ O ₃ 10-22, B ₂ O ₃ 0-8, P ₂ O ₅ 0-3, Na ₂ O 10-16 K ₂ O 0-6, MgO 0-10, ZnO 0-3, TiO ₂ 0 to 2.1, _SnO2 0-1, F 0-2 and 0-2, preferably 0-1, further components. Glass pane according to one of the preceding claims, wherein the glass has the following features: - the sum of the alkali oxides and alkaline earth oxides is more than 13 percent by mass, preferably more than 15 percent by mass, - the sum of the alkaline earth oxides is at most 7 percent by mass and - the proportion of Li ₂ O. is less than 1 mass%, preferably less than 0.1 mass%. A glass sheet according to any one of the preceding claims, wherein the glass sheet has a disk thickness of 0.25 mm to 1.5 mm. A glass sheet according to any one of the preceding claims, wherein the glass is chemically toughened by exchange of sodium ions for potassium ions on the surface thereof, the glass having a standard warp (W _s ) after chemical tempering of less than 300 μm, preferably of less than 200 μm and particularly preferably of less than 100 μm, and the compressive stress (CS, Compressive Stress) in the surface of the glass is at least 800 MPa and the exchange depth (DoL, Depth of Layer) of the alkali ions of the prestressed layer at least 30 microns. Glass sheet according to one of the preceding claims, wherein the glass sheet produced by a float process comprises a float glass sheet ( 1 ). A process for producing a glass sheet, in particular a glass sheet according to any one of the preceding claims, comprising the steps of: - drawing a glass ribbon from which the glass sheet is separated from a molten glass by a float process, - cooling the glass ribbon or from the glass ribbon already separated glass pane, wherein at least the top ( 4 ) of the two opposite side surfaces ( 2 . 3 ) the glass sheet is exposed to sulfur dioxide (SO ₂ ) or sulfurous acid (H ₂ SO ₃ ) until the surface leaching difference of the Na ₂ O contents (ΔNa ₂ O) of the two side surfaces ( 2 . 3 ) in percentage by mass: ΔNa ₂ O = -0.00078 × ΔTinCount ^x , where ΔTinCount is the difference of the TinCounts representing the difference of the mass-related surface contents of SnO _{2 of} the two side surfaces determined by X-ray fluorescence analysis ( 2 . 3 ) in ppm (parts per million), and wherein the exponent x is in the range of 0.5 to 0.7, preferably 0.62. Process according to the preceding claim, wherein the refining agent used is tin oxide (SnO ₂ ). A method according to any preceding claim, wherein the glass of the glass sheet is chemically tempered by heating the glass for a period of at least 1.5 hours in a potassium-containing salt bath containing potassium ions at a temperature of at least 300 ° C, preferably 380 ° C to 460 C, and sodium ions of the glass at its surface by potassium ions of the salt bath at least partially exchanged, wherein the exchange depth of the alkali ions is at least 30 microns, so that on the surface of the glass, a compressive stress zone with a compressive stress on the surface of at least 800 MPa generated and the glass is chemically biased. Process according to the preceding claim, wherein the glass is stored in a salt bath containing predominantly KNO ₃ , wherein the salt bath optionally further potassium-containing components, preferably at least one of K ₃ PO ₄ , K ₂ SO ₄ and KOH and / or a silver-containing Salt may contain.

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