KR102224613B1 - Method for adjusting a curvature of a chemically strengthened glass pane and glass pane manufactured according to said method - Google Patents

Abstract

An object of the present invention is to provide a glass pane that can be simply manufactured in the form of a thin glass plate having a very small curvature. For this purpose, a float glass pane 1 made of chemically strengthenable glass 2 is provided, in which case the glass pane 1 has a pout thickness of 0.25 mm to 1.5 mm, and oppositely disposed faces of the float glass panes ( The difference in the imaginary temperature of the two planes 10, 11 inside the glass 2 in 4, 5) is less than 7 K, preferably less than 5 K, the planes being each of the float glass panes 1 It is formed by faces 4, 5, or extends in a depth of up to 50 μm below the surface of faces 4, 5 and parallel to faces 4,5.

Description

A method for adjusting the curvature of a chemically strengthened glass pane, and a glass pane that can be manufactured according to the above method.

The present invention relates to a method for adjusting the curvature of a chemically strengthened glass pane and to a glass pane that can be produced according to the method.

Chemically strengthened glass generally has some degree of curvature (also referred to as warp) depending on the manufacturing technique, geometry, glass thickness and stress conditions.

Chemically strengthened glass is used in particular as a protective- or cover pane for display composites for respective applications (eg smartphones, tablets, computers, etc.).

Depending on the manufacturing- and stress conditions, the deflection may exceed the device manufacturer's specifications. On the other hand, a certain curvature of the glass pane (convex or non-concave) is sometimes required. The predetermined curvature can be adjusted by the processing process.

Warping is achieved by asymmetric ion exchange on the upper or lower surface of the glass. This causes a difference in compressive stress and/or ion exchange depth, which can be measured as dCS (difference in compressive stress) or dDoL (difference in exchange depth). Thus, "relaxation" or balancing of the difference in compressive stress of the glass is achieved in the form of curvature (bending).

This effect can also be observed in float glass. The cause of the asymmetric ion exchange in US 3 453 095 A and DE 3 607 404 C2 lies in the presence of a so-called tin layer caused by the diffusion of tin from the float bath into the glass.

US 3 453 095 A proposes to insert tin into the surface at both sides for symmetric ion exchange.

DE 3 607 404 C2 proposes to activate the surface affected by tin by ion exchange preceding the original stress process, i.e. to carry out a two-stage ion exchange process. In the case of exchanging sodium ions for potassium ions in the surface layer of the float glass, tin interferes with the replacement of sodium ions with potassium ions, and the action is prevented by the preceding ion exchange.

For glass 1 mm thick and 300 x 300 mm in size, according to DE 3 607 404 C2, a stress zone depth of 20-30 µm and a surface tension of 20-35 kg/mm2 (196-343 MPa) 0.4- A deflection of 0.6 mm is measured. In the method according to DE 3 607 404 C2, the percent warpage is 0.13-0.20 %.

SG 155800 A proposes a special sample holder during stress processing to reduce curvature.

US 2009 0220761 A1 proposes to rapidly cool or quench the glass in order to increase the implantation depth and compressive stress area of ions over a given period of time. On the other hand, for rapidly cooled glass, the achievable compressive stress is lower, unlike slowly cooled glass. It is not suggested whether the method proposed in this prior art can be applied to float glass as well.

WO 2012/073624 A1 discloses a housing installed around a float bath and a subsequent cooling furnace, in which case the housing wall is arranged spaced apart from the outlet of the cooling furnace, and a cutting unit is arranged outside the housing. This arrangement should prevent undesired cooling air flow opposite to the direction of traction of the float glass ribbon. This device is used to keep the temperature condition inside the cooling furnace constant over time. A reduction in curvature must be achieved by means of such a device.

In WO 2013/005608 A1, it is proposed to reduce the feed rate inside the cooling furnace or to later stress relieve the glass, whereby the glass at a distortion point or higher temperature is maintained for a predetermined duration and then cooled.

An object of the present invention is to provide a glass pane that can be simply manufactured in the form of a thin glass plate having a thickness of up to 1.5 mm with a very small curvature.

This problem is solved by the subject of the independent claim.

Preferred embodiments and improvements of the invention are presented in the dependent claims.

By means of the invention the disadvantages of the prior art are avoided, or an improved value with respect to curvature is achieved. In the case of removing a layer of float glass on the side of a tin bath containing tin impurities according to the proposal of DE 3 607 404 C2, for example by polishing, a significant reduction in curvature is expected. Surprisingly, however, the warpage is reduced by 5 to 30% only when a layer of tin several micrometers thick is completely removed by polishing (eg by removing glass of 5 μm).

The warpage can be reduced to less than 50% of the initial value only when thicker removals exceeding 10 μm are removed.

In this regard, the curvature of chemically strengthened float glass seems to be caused not only by tin-impurities, but also by differences in the adjacent glass structure between the float side and the atmosphere side, and these differences have a significant effect on the formation of warpage. . Here the present invention begins.

In the present invention, the virtual temperatures on the two sides may be different due to manufacturing, and if the virtual temperatures on the two sides become uniform, the warpage can be significantly reduced without complicatedly removing the glass on the tin bath side of the float glass. It is based on facts.

“Virtual temperature” is a general characteristic value of the dependence of the glass structure on the cooling state or cooling rate, in this case, ie high fictive temperatures correspond to fast cooling rates and loose atomic glass composites, and low fictive temperatures are slow cooling rates and dense Corresponds to atomic glass composites (see G. Scherer, "Relaxation in Glass and Composites" Krieger Publishing, Malaba, Florida, 1992).

In the case of cooling of the pane according to the invention is characterized by the uniformity of the hypothetical temperature across the thickness of the pane.

According to the present invention, a float glass pane made of chemically strengthenable glass is provided, the glass pane being a sheet glass, in particular as a sheet glass, having a pane thickness of 0.25 mm to 1.5 mm, and inside the glass on opposite sides of the float glass pane. The difference between the imaginary temperature of the two planes of is less than 7 K, preferably less than 5 K, the planes being each formed by the face of the float glass pane, or within a depth of up to 50 μm below the surface of the face and to the face. It extends parallel to.

In other words, a float glass pane having the aforementioned small difference in imaginary temperature is provided on the oppositely disposed side. This difference does not necessarily have to exist between the surfaces of the two planes exactly, but the hypothetical temperature may be determined in a region or plane located up to 30 μm below the plane, each adjacent to the surface. To determine the hypothetical temperature under the plane, simply because the glass can be removed to an appropriate thickness, a new surface is formed, which surface coincides with the aforementioned plane in the depth region up to 50 μm. Determination of the hypothetical temperature difference inside the glass rather than on the original surface is particularly desirable when the glass has already been strengthened. In this case, the fictive temperature can be determined at the new surface after the glass in the compressive stress region has been removed. This is desirable because otherwise the measured value of the hypothetical temperature is affected and distorted by the compressive stress. Since the ion exchange depth is usually up to 50 μm, even in the case of tempered glass, after removal of a layer of a corresponding thickness of up to 50 μm, the virtual temperature between the oppositely placed faces of the float glass panes on the new surface thus formed. The difference can be determined with certainty.

Further, on the tin bath side of the float glass that has not yet been strengthened, also referred to as the bottom surface, the layer can be removed to prevent tin impurities from distorting the measured values.

A sheet having a curvature of up to 0.1% normalized to a peep thickness, preferably in a state fully reinforced with a compressive stress of> 30 µm DoL (DoL = "Depth pf Laher", exchange depth) and> 700 MPa by the present invention Glass panes may be provided. In particular, standardized curvatures of up to 0.075% or up to 0.05% can be formed at an exchange depth of >30 μm and a compressive stress of 700 MPa or more.

Since the removal of the glass on the side of the tin bath can be omitted, as another characteristic in the improved example of the present invention when such removal is not carried out, the tin content of the glass appears different on the oppositely disposed side.

The curvature depends on the glass thickness. The following approximation is applied for the percent curvature at a glass thickness of 0.25-1.5 mm:

W[%] = W _norm [%/mm] / d [mm].

In the above equation, W is the curvature expressed as a percentage, W _norm is the curvature normalized to the pane thickness expressed as a percentage per millimeter, and d is the glass thickness in millimeters.

When the glass thickness is 1 mm, the curvature (W) corresponds to the _{normalized curvature (W norm).}

For a reinforced float glass pane according to the invention with a normalized curvature less than 0.1%, the following maximum curvature is given depending on the glass thickness:

Glass thickness mm Maximum standardized curvature Maximum curvature 1.00 0.10% 0.10% 0.70 0.10% 0.14% 0.55 0.10% 0.18%

The homogenization of the hypothetical temperatures starts approximately at the slow cooling point by adjusting the symmetrical cooling profile within the glass transition range according to the invention. Preferably the float glass pane is given a symmetrical temperature profile or a symmetrical temperature-time profile in the viscosity range ^{of 10 11.3} dPas to 10 ^{14.5 dPas.}

The temperature corresponding to the viscosity range of 10 ^11.3 dPas is called the expansion and softening point of the glass, and ^{the temperature corresponding to the viscosity range of 10 14.53} dPas is called the distortion point of the glass. There is a slow cooling point in between, and the slow cooling point corresponds to a viscosity of ^{10 13 dPas.} The softening point, which should not be confused with the expansion softening point, corresponds to a viscosity of ^{10 7.6 dPas.}

In particular there is provided a method for the production of a float glass pane according to the invention, said method comprising the following steps:

-Drawing a glass ribbon from which the float glass pane is separated from the glass melt by floating,

-Cooling the glass ribbon or the float glass pane separated from the glass ribbon,

^{-On the oppositely disposed two sides of the float glass pane in the viscosity range of 10 11.3} dPas to 10 ^14.5 dPas during the cooling step, so that the difference in surface temperature between the oppositely disposed surface areas of the two sides is less than 10 K, A symmetrical temperature-time profile is given such that it is preferably less than 7 K and particularly preferably less than 5 K.

Since the maximum difference of the hypothetical temperatures of the surface is at least less than or equal to the maximum difference of the surface temperatures, in the case of starting cooling above the expansion softening point, the difference of the hypothetical temperature is 7, especially on the demand of a surface temperature difference of less than 7 K According to the demand of the surface temperature difference smaller than K and smaller than 5 K, it is guaranteed that the difference in the hypothetical temperature is smaller than 5 K.

The cooling may take place in a float glass ribbon or in a float glass pane that was first separated. Thus, in general, the separation of the float glass-pane from the glass ribbon can be made symmetrically or according to the same temperature-/time-curve before or after cooling. In addition, separation may be carried out during the cooling process. Since the preceding heating can also take place in both cases, controlled cooling can be carried out according to a symmetrical temperature-time profile with respect to the two sides of the glass ribbon or float glass-pane.

The temperature control or symmetric cooling process is preferably ensured immediately after thermoforming at the end of the float bath or after shaping in the drawing process. This may be done at the beginning of the cooling process at each process run.

It is also possible to control the temperature of the two sides, i.e. the top and bottom, as intended, either by asymmetric heating of one glass side or by different heating of the two sides of a glass ribbon, in some cases already separated float glass panes. It may be desirable. This allows a symmetrical temperature distribution to appear from one side to the other, at least temporarily during cooling, preferably continuously during cooling in the critical regions of the structural control of the glass in the viscosity range of ^{10 11.3} dPas to 10 ^{14.5 dPas.} This allows the structures of the surface, or the upper and lower surfaces, to be uniform.

On cooling it is also possible according to the invention for subsequent tempering by means of a correspondingly symmetrical profile. Accordingly, according to an embodiment of the present invention, the float glass pan or glass ribbon is heated again past the slow cooling point after the first cooling and then cooled again. When the temperature of the two opposing facets of the float glass pane is in the range between the expansion softening point and the distortion point, cooling is carried out in which the faces are given a symmetrical temperature-time profile.

The present invention relates to a symmetrically cooled float glass-pane having the same or approximately the same fictive temperature on two sides and a chemically strengthened glass-pane formed by incubation in a salt bath from said intermediate product. The chemical strengthening step is, of course, carried out after controlled cooling by means of a temperature-time-curve, which is symmetrical or uniform on the two sides of the pan. Thus, in a refinement of the present invention, the float glass pane is chemically strengthened in the salt bath after a cooling step in which a symmetrical temperature-time profile is given to the two oppositely disposed faces of the float glass pane in the temperature range between the expansion softening point and the distortion point. .

The strengthening can take place in a potassium containing molten salt, for example in a potassium nitrate melt. For strengthening, the float glass panes are preferably incubated at least 350° C. in a potassium containing salt melt for at least 3 hours.

It is also particularly preferred when the imaginary temperature inside the glass between the two sides is lower than the imaginary temperature of the two planes or two planes in the surface area. According to an embodiment of the present invention, the imaginary temperature along the cross-section has a concave curve when viewed from one facing surface to the other surface, and the lowest value of the imaginary temperature in the curve is located in a region between the two surfaces. Since the curve is preferably as symmetric as possible, the lowest value of the hypothetical temperature is located in the middle 1/3 of the distance between the faces, preferably in the middle of the depression with a maximum deviation of 10%. This curve can be adjusted by controlling the temperature during cooling.

The curve is preferred because this provides a stress relief glass in the center on the one hand, but the glass structure expanded in plane promotes ion exchange and high exchange depth and compressive stress values.

The present invention is described below with reference to examples and the accompanying drawings. In this case, the same reference numerals in the drawings indicate the same or corresponding members.

1 schematically shows a device for adjusting a symmetrical temperature-time profile upon cooling of a float glass ribbon.
2 shows a curved float glass strip.
3 is a cross-sectional view of a chemically strengthened float glass pane.
4 is a diagram showing a curve of an imaginary temperature along a cross section of a float glass pane.
5 is a diagram showing a measure of the curvature of a float glass pane chemically strengthened according to various tempering programs.
6 shows measurements of compressive stress and ion exchange depth in chemically strengthened samples.

1 schematically shows a device for adjusting a symmetrical temperature-time profile during cooling of a continuous float glass ribbon 3. The float glass ribbon 3 is a thin plate glass having a thickness of 0.25 to 1.5 mm. Symmetry means in this connection that the temperature profile of the glass 2 of the face 4 becomes uniform with the temperature profile of the opposing face 5 at a given point in time.

In the float glass ribbon, which is guided out from the float glass trough through the roller 16 along the conveying direction 15, the side 4 is the upper side or the atmosphere side, and the oppositely disposed side 5 is the lower side or It is the tin bath side.

Symmetrical cooling is preferably carried out immediately after shaping in the manufacture of the glass. In the embodiment shown in Fig. 1, two temperature sensors (21, 22) are provided, and the sensors are on the upper surface (surface; 4) or under the lower surface (surface; 4) guided through the roller 15. It is placed and measures the temperature of the two sides (4, 5). The temperature value is provided to the control device 20, which determines the difference in surface temperature from the measured value. Heating devices 23 and 24 are arranged above and below the upper surface of the glass ribbon 3, and the heating device is controlled by the control device 20. When the temperature of one of the surfaces 4 and 5 is lower than the temperature of the oppositely disposed surface, the control device 20 can heat the lower temperature surface as intended by increasing the heat output of the heating device. Therefore, the surface temperatures of the two surfaces 4 and 5 can be uniform. The homogenization is achieved by making the difference in surface temperature between the oppositely arranged surface areas of the two sides 4 and 5 less than 10 K, preferably less than 7 K, and particularly preferably less than 5 K, so that the float glass The ribbon 3 is given a symmetrical temperature-time profile. Since the heat output of the heating devices is, on average, less than the heat released from the glass ribbon, cooling occurs. Alternatively or additionally, as shown in FIG. 1, cooling devices 25, 26 may be provided, which cooling devices are provided with a control device 20 for cooling each side of the glass ribbon 3. Controlled by Fans or water coolers are particularly suitable as cooling devices 25 and 26.

If the heat dissipation on one of the sides is greater than on the continuously opposed side, for example due to the structure of the cooling device, in some cases the heating device may be omitted on the side where the heat dissipation is smaller. Further, only the heating device or cooling device on one side of the float glass ribbon 3, that is, on the top or bottom, can be controlled by the control device, and the other heating device can be operated with a defined heat output.

It is not limited to the embodiment of FIG. 1, and in the improved example of the present invention, the surface temperature of the glass ribbon 3 is determined by sensors 21 and 22 on both sides, and at least one heating device 23, 24 or At least one cooling device (25, 26) uses the temperature measurement value by the control device (20) to ensure that the difference in surface temperature between the oppositely disposed surface areas of the two sides (4, 5) is less than 10 K. To be controlled. In general, not limited to the embodiment, by cooling the glass ribbon 3 or the glass pane 1 separated from the glass ribbon, the virtual temperatures of the glass in the oppositely disposed regions of the faces 4 and 5 become uniform, and thus The temperatures differ from each other by a maximum of 7 K, preferably a maximum of 5 K.

Cooling regime between ^{viscosity 10 12} dPas and 10 ^14.5 dPas by controlling one or more heating devices 23, 24 as intended and blowing as intended by one or more cooling devices 25, 26 Because this is implemented, the stress inside the glass is minimized and the glass structure is symmetrically adjusted.

According to an embodiment, the curvature normalized to the glass thickness is adjusted to a value less than 0.1% by increasing the heat output at the upper surface of the glass ribbon by 150-200% compared to the heat output at the lower surface of the glass ribbon. The sample strengthened after being cut from the glass ribbon has a size of 160 mm x 260 mm. In the table below, the properties of the symmetrical temperature control exhibited by different cooling on the two sides 4 and 5 of the glass ribbon 3 in this example are described together with the comparative example. Uniform heating was applied during cooling in the comparative example, and thus different surface temperatures appeared due to different heat release rates in the cooling device.

Example 5.1 (Comparative Example) Example 5.2 Example 5.3 (Comparative Example) Yes 5.4 Heat output
Upper limit-lower limit 100% 150-200% 100% 150-200% Size(mm) 160 x 260 x 0.7 160 x 260 x 0.7 160 x 260 x 0.55 160 x 260 x 0.55 CS after strengthening (MPa) 850 850 850 850 DoL(um) after strengthening 42 42 33 33 curvature(%) 0.25 0.12 0.27 0.14 Relative curvature (%) 0.17 0.08 0.15 0.08

From the table values, it can be seen that the glass pane according to the present invention has a much smaller curvature than the float glass pane cooled in a conventional manner.

Particularly preferably, without being limited to the examples, the low temperature difference between the opposingly disposed surface regions is maintained while passing through the entire viscosity range between ^{10 11.3} dPas and 10 ^{14.5 dPas.} By means of the cooling according to the invention a difference in hypothetical temperatures of less than 7 k, preferably less than 5 K can be achieved at the surfaces of the two sides 4 and 5. After the float glass ribbon 3 has cooled, the float glass ribbon can be subdivided into float glass panes according to the invention, and thus the float glass panes can be chemically strengthened in a salt bath. The reinforced float glass panes according to the invention have an exchange depth of >30 μm and a curvature of up to 0.1% normalized to the peep thickness at a compressive stress of at least 700 MPa.

The glass structure is homogenized on the upper and lower surfaces of the glass by means of a symmetrical cooling profile, that is to say on the two sides 4 and 5. Accordingly, it is ensured that during chemical strengthening, the ion exchange proceeds uniformly on the upper and lower surfaces of the glass, and that the difference in compressive stress-and/or ion exchange depth-can be minimized. As a result, the glass body is not severely curved.

The virtual temperature is particularly easily measured by infrared reflective spectroscopy. In the silicate glass preferred for the present invention, in particular the spectral range of 800/cm to 1200/cm stands out. In this range, the reflection band may be related to the stretching vibration of the tetrahedral network (for pure silicate, see A. Agarwal et al., /Journal of Non-Crystalline Solids 185 (1995) 191-198, and in particular as a glass material in the present invention. For preferred aluminosilicates see Fujita et al.,/ Journal of Non-Crystalline Solids 330 (2003) 252-258).

The relationship between the infrared spectrum and the hypothetical temperature is that a fluctuation of 1 K in the hypothetical temperature causes a shift of the maximum peak of approximately 0.02/cm in that spectral range (for pure silicates A. Agarwal et al., /Journal of Non- See Crystalline Solids 185 (1995) 191-198 and Fujita et al., / Journal of Non-Crystalline Solids 330 (2003) 252-258 for aluminosilicates).

From the analysis of the pane in the unstrengthened state, since the hypothetical temperature non-uniformity in the unstrengthened state causes the curvature of the float glass pane in the unstrengthened state, and the curvature of the float glass pane in the unstrengthened state is usually of the same magnitude as the curvature in the strengthened state. An approximate relationship between the curvature and the virtual temperature non-uniformity of the reinforced pane can be derived.

To this end, the strip of the float glass pane 1 is analyzed with reference to FIG. 2, and the virtual temperature of the strip is changed to have a maximum value for "upper" and a minimum value for "lower" along the thickness. The difference is called _{ΔT f.} Here, the difference in the virtual temperature due to the shape part of the thermal expansion called CTE (shape) or CTE (K) for short causes non-uniform expansion of the glass strip, and the expansion causes CTE (K) in the "top" rather than the "bottom" It is as large as _{ΔT f.} For the shape part of the thermal expansion, reference is made to the aforementioned part of Scherrer. In other words, representative values are also presented there.

For clarity, a long and narrow glass strip is used, and only the larger of the two face dimensions is shown.

The longitudinal extension of the strip preferably represents a circular section. Depending on the relationship between the circumference and the radius, if the thickness (d) is much less than the radius (R), then for the strip thickness (D) and radius (R) of the circle described above and the two variables ΔT _f and CTE (K) The following relationship is established:

2·π·D = CTE(K)·ΔT _f ·2·π·R

If you place the strip on the base 30 and look at the circle segment 33 formed by the direct connection (i.e. chord) between the strip and the two support points 31, 32, the deflection of the strip is the length of the chord (reference numeral 35). It corresponds to the height (H) of the circle segment (reference numeral 34) subdivided by (L).

If L is much less than R,

H = L ² /(8R) holds,

Or about warping

H/L = L/(8R) holds.

ΔT less than 7 K using representative values, i.e. CTE(K) = 10 ppm/K, D = 0.01 m and L = 0.1 m (see above) for alkali-containing aluminosilicate glass (from actual measurements) _{For f} less than 0.1% warpage, for ΔT _f less than 5K, much less than 0.1% warpage, and for ΔT _f less than 2 K, much less than 0.1% warpage.

From thereon the infrared spectral peak-shift of two oppositely arranged faces (4, 5), the peak shift is less than 0.14/cm (in _{the case of ΔT f} less than 7 K), or less than 0.1/cm (5 K). than in the case of small ΔT _f) or less than 0.04 / cm appears (in the case of smaller than the ΔT _f 2 K). When the movement does not reach the limiting resolution of the measuring device, the measurement accuracy can be further increased by interferometric measurement. In particular, it is not necessary to determine the absolute position of the peak of the infrared spectrum, because in this case, the absolute position is not important when irradiating the upper or lower surface or the surface (4, 5) of the strip, but the relative movement of the peak is important. Because. It is possible to measure the small wave number difference caused by the difference in imaginary temperature, because on the one hand, the absolute position of the peak does not need to be determined as described above. In addition, shifts in the spectrum can be detected by multiple peaks in the absorption spectrum, and thus the measurement accuracy can be significantly increased.

In order to determine the symmetry of the structure of the upper and lower surfaces or small differences in imaginary temperatures, in particular IR-reflection spectra can be recorded. The maximum values of the reflection spectrum at a wavenumber of 800/cm to 1200/cm, i.e., the positions of the peaks corresponding to the highest in the wavenumber range, are at most 0.14/cm, preferably at most 0.1 in the case of the float glass pane according to the present invention. /cm or more preferably by 0.04/cm.

In order to be able to determine the smaller shifts of the peaks, a highly precise device described in, for example, Kirckpatrick et al. Journal of Molecular Spectroscopy 281 (2012) pages 51-62, is suitable, in this case, which is operated upon transmission of such Kirckpatrick et al. The high-resolution Fourier transform analyzer Bruker IFS 125 (Fa. Brucker Corporation, 40 Manning Road Billerica, MA 01821, USA) can be operated even in reflections by means of suitable components.

The float glass pane according to the present invention is not limited to the embodiment, is measured when reflected from the plane (10, 11) or plane by an infrared spectrum, and preferably an absorption spectrum of a wavelength number of ^{800 cm -1} to 1200 cm ^-1 The peaks of can be characterized as different by ^{at most 0.14 cm -1} , preferably at most 0.1 cm ^-1 and particularly preferably by at most 0.04 cm ^-1 at the position of the spectrum.

In irradiation analysis it may be considered that the surface effect may shift the reflection peak, in which case the inventive uniformity of cooling or hypothetical temperature may not be relevant. Surface effects are described, for example, in S. Fujita et al./Journal of Non-Crystalline Solids 330 (2003) pages 252-258.

This applies in particular to the ion exchange bed. It is thus observed that only when a glass layer of for example 5 μm is removed as the glass pane according to the invention, the uniformity of the hypothetical temperature or the corresponding uniformity of the infrared spectrometer reaction is achieved. In particular, this uniformity may be confirmed when the entire ion exchange layer (typical exchange depth 30 µm to 50 µm) is ground or polished, and therefore within a depth of up to 50 µm below the surface of the faces 4 and 5 and Each plane extending parallel to the is exposed. 3 schematically shows a cross-section of a float glass pane 1 with ion exchange layers 13, 14 and planes 10, 11, chemically strengthened to illustrate this. Since the glass 2 is removed from the right side of the float glass pane 1, the exchange layers 13, 14 are removed, and the planes 10, 11 form faces 4, 5 in the region 9 . In the region 9, the difference in imaginary temperature, ΔT _f , can be measured, in which case the ion exchange layer does not affect the measurement.

4 schematically shows in the form of a diagram a curve of an imaginary temperature in the cross-sectional direction (position coordinate x). The positional coordinates of the two sides 4 and 5 are shown by arrows in the abscissa. _{The difference ΔT f} of the imaginary temperatures on the two sides 4 and 5 is less than 7 K, preferably less than 5 K, and particularly preferably less than 2 K, as described above. Also, the imaginary temperature inside the glass between the two sides is lower than the imaginary temperature of the two planes on the side. The imaginary temperature inside the float glass pane at position 6 is the lowest. Since the lowest fictive temperature T _f,min is in particular lower than the two fictitious temperatures of planes 4 and 5, a concave curve of fictive temperature across the cross section is obtained. According to a refinement of the invention the lowest fictive temperature is at least 15 K lower than the fictitious temperature of the faces 4 and 5 or the planes 10 and 11.

The measurement results in the diagram of Fig. 5 show the effect of asymmetric cooling. Later, the curvature decreases due to tempering, or increases during asymmetric cooling.

In addition, the glass was heated at 640° C.-680° C. and cooled as intended, in which case no tampering was performed for the reference sample (marked with “Ref”). The temperature difference between the upper and lower surfaces was 10-20 ℃ in the experiment. In the case of the sample containing the additional item "bot.", the lower side was hotter, and when cooled, the T _g later passed, while the sample not containing the additional item had a higher temperature on the upper side than the lower side. The temperature mark of the sample always defines the temperature of the hottest side.

The size of the sample was 260 mm x 160 mm x 0.8 mm. All samples were chemically strengthened for 6 hours in a salt melt consisting _{of 100% KNO 3} at 420° C. after the subsequent tampering described above.

The following values of curvature (W) in the sample were measured in micrometers, compressive stress (CS) in MPa, and exchange depth (DoL) in micrometers:

Sample: W[㎛] CS[MPa] DoL[㎛] Ref. 550 850 46 640℃ 212 842 46 660℃bot. 843 839 45 660℃ 168 843 46 680℃bot. 1343 Not determined Not determined 680℃ 68 841 45

The achievable compressive stress increases due to subsequent tampering. The faster the top surface cools, the higher the value of the curvature compared to the reference sample, depending on the starting temperature. In the opposite case, the value of curvature decreases. This effect is intensified with increasing temperature. In the tampering program, a reduction in curvature of 80% or more is achieved. The curvature is causally related to the uniformity of cooling up to a temperature of approximately 600° C. representing a distortion point with a viscosity ^{of 10 14.5 dPas.}

6 shows measurements of compressive stress (CS) and ion exchange depth (DoL) in a chemically strengthened sample, in which case the hypothetical temperatures of the plane in the sample were not uniform according to the present invention.

For this example, a glass sample having a size of 100 mm x 100 mm x 5 was strengthened at 420° C., and the ion exchange depth and compressive stress were measured on the top and bottom surfaces of the sample, respectively. Since the warpage depends on the glass thickness and becomes almost zero from a thickness of 5 mm (or because it is only a few micrometers thick), the difference between the compressive stress and the ion exchange depth can be determined relatively accurately. For the compressive stress condition, the difference in ion exchange depth (dDoL) is 2.2 μm, and the difference in compressive stress (dCS) is 29 MPa. In particular, it appears that the compressive stress area (DoL) and the compressive stress are greater in the glass upper surface, which is the atmospheric side of the float glass disposed opposite to the float bath side.

1 float glass pan
2 glass
3 glass ribbon
4, 5 sides
6 Location of the lowest fictive temperature range including the removed ion exchange layer
9 ion exchange bed
10, 11 flat
13, 14 ion exchange bed
15 feed direction
16 rollers
20 control unit
21, 22 temperature sensor
23, 24 heating device
25, 26 cooling system
30 base
31, 32 support points
33 circle segment
Height of 34 to 33
35 33 string length

Claims (13)

A float glass pane (1) made of chemically strengthenable glass (2), the glass pane (1) having a pane thickness of 0.25 mm to 1.5 mm, and the glass on opposite sides (4, 5) of the float glass pane. (2) The difference between the virtual temperature of the two inner planes 10 and 11 is less than 7 K, and the planes are respectively formed by the planes 4 and 5 of the float glass pane 1, or the plane ( 4, 5) extending in a depth of up to 50 μm below the surface and parallel to the surface 4, 5,
Float glass pane, characterized in that the tin content of the glass (2) is different on two opposite sides (4, 5). The float glass pane according to claim 1, wherein the float glass pane is reinforced and has a curvature of 0.1% or less normalized to the pane thickness at an exchange depth of >30 μm and a compressive stress greater than 700 MPa. The float glass pane according to claim 1 or 2, wherein the imaginary temperature inside the glass between the two sides is lower than the imaginary temperature of the two planes on the side. Float glass according to claim 3, characterized in that the lowest imaginary temperature inside the glass of the float glass pane is at least 15 K lower than the imaginary temperature of the two planes (10, 11) on the side (4, 5). Pain. delete The peaks of the absorption spectrum according to claim 1 or 2, measured upon reflection from the plane (10, 11) or the plane (4, 5) and in ^{the wavenumber range of 800 cm -1} to 1200 cm ^-1 Float glass panes, characterized in that they differ by at most 0.1 cm ^{-1 in position.} A method for manufacturing a float glass pane (1) according to claim 1, comprising:
-Drawing a glass ribbon (3) from which the float glass pane (1) is separated from the glass melt by floating,
-Cooling the glass ribbon (3) or the float glass pane (1) separated from the glass ribbon (3),
-During the cooling step, in ^{the viscosity range of 10 11.3} dPas to 10 ^14.5 dPas, on the two opposing faces (4, 5) of the float glass pane (1) the surface between the opposing surface areas of the two faces (4, 5) A method of making a float glass pane, characterized in that a symmetrical temperature-time profile is given such that the temperature difference is less than 10 K. The glass ribbon (3) or separated float glass according to claim 7, so that a symmetrical temperature distribution appears from one of the facing faces toward the other during cooling in a viscosity range of ^{10 11.3} dPas to 10 ^{14.5 dPas.} A method for manufacturing a float glass pane, characterized in that by different heating of the two sides (4, 5) of the pane (1), the temperature is controlled on the two sides (4, 5). 9. The virtual temperatures of the glass according to claim 7 or 8, in which the virtual temperatures of the glass are made uniform in the oppositely arranged areas of the side (4, 5) by cooling of the glass ribbon (3) or the glass pane separated from the glass ribbon. A method for producing a float glass pane, characterized in that it has a difference of at most 7 K. 9. The method according to claim 7 or 8, wherein the surface temperature of the glass ribbon is determined by sensors (21, 22) on both sides, at least one heating device (23, 24) or at least one cooling device (25, 26). ) Is a float glass, characterized in that the difference in surface temperature between the oppositely disposed surface areas of the two sides 4 and 5 is controlled to be less than 10 K using the temperature measurement value by the control device 20 How to make a pane. 10. The method according to claim 7 or 8, wherein the glass ribbon (3) or the float glass pane (1) is _{heated again after the first cooling to a glass transition temperature (T g} ) or higher and then cooled again, in this case 10 ^A method for producing a float glass pane, characterized in that a cooling step is carried out in which a symmetrical temperature-time profile is given to two opposite faces (4, 5) of the float glass pane in a viscosity range of 11.3 dPas to 10 ^{14.5 dPas.} 9. A symmetrical temperature-time according to claim 7 or 8, wherein the float glass pane (1) has a symmetrical temperature-time on two opposite sides (4, 5) of the float glass pane in the viscosity range of ^{10 11.3} dPas to 10 ^{14.5 dPas.} Method for producing a float glass pane, characterized in that after the cooling step to which the profile is given, it is chemically strengthened in a salt bath. 13. Float according to claim 12, characterized in that the strengthening takes place in a potassium-containing salt melt, in which case the float glass pane (1) is incubated at a temperature of at least 350° C. in a potassium-containing salt melt for at least 3 hours. A method of manufacturing a glass pane.

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