GLASS SHEET CAPABLE OF HAVING CONTROLLED WARPING THROUGH CHEMICAL STRENGTHENING

Abstract

A float glass sheet having a boron- and lithium-free glass composition comprising the following in weight percentage, expressed with respect to the total weight of glass: 65SiO.sub.278% 5Na.sub.2O20% 1K.sub.2O<8% 1Al.sub.2O.sub.3<6% 2CaO<10% 0MgO8%; K.sub.2O/(K.sub.2O+Na.sub.2O) ratio which is from 0.1 to 0.7; wherein the glass sheet has:

[00001]$0.01<.Math.\frac{{\left({\mathrm{Na}}_2.Math.O\right)}_{\mathrm{air}}}{{\left({\mathrm{Na}}_2.Math.O\right)}_{\mathrm{tin}}}-1.03.Math.3.$

The glass sheet may be a chemically-temperable soda-silica type glass composition suitable for mass production that shows reduced or controlled increased warping effect.

Claims

1. A float glass sheet comprising the following in weight percentage, expressed with respect to the total weight of glass: 65SiO.sub.278%; 5Na.sub.2O20%; 1K.sub.2O<8%; 1Al.sub.2O.sub.3<6%; 2CaO<10%; 0MgO8%; and K.sub.2O/(K.sub.2O+Na.sub.2O) ratio of from 0.1 to 0.7, wherein the glass sheet has: $0.01<.Math.\frac{{\left({\mathrm{Na}}_2.Math.O\right)}_{\mathrm{air}}}{{\left({\mathrm{Na}}_2.Math.O\right)}_{\mathrm{tin}}}-1.03.Math.3,$ and wherein the glass sheet is boron- and lithium-free.

2. A float glass sheet according to claim 1, wherein the composition comprises total iron (expressed in the form of Fe.sub.2O.sub.3) in a content ranging from 0.002 to 1.7% by weight.

3. A float glass sheet according to claim 2, wherein the composition comprises total iron (expressed in the form of Fe.sub.2O.sub.3) in a content ranging from 0.002 to 0.06% by weight.

4. A float glass sheet according to claim 3, wherein the composition comprises total iron (expressed in the form of Fe.sub.2O.sub.3) in a content ranging from 0.002 to 0.02% by weight.

5. A float glass sheet according to claim 1, wherein the composition comprises an alumina content such that 1Al.sub.2O.sub.34 wt %.

6. A float glass sheet according to claim 5, wherein the composition comprises an alumina content such that: 2Al.sub.2O.sub.33 wt %.

7. A float glass sheet according to claim 1, wherein the composition comprises: 5CaO<10 wt %.

8. A float glass sheet according to claim 1, wherein the composition comprises: 1K.sub.2O<6 wt %.

9. A float glass sheet according to claim 1, wherein the composition comprises a K.sub.2O/(K.sub.2O+Na.sub.2O) ratio of from 0.1 to 0.5.

10. A float glass sheet according to claim 1, wherein the composition comprises a K.sub.2O/(K.sub.2O+Na.sub.2O) ratio of from 0.2 to 0.5.

11. A float glass sheet according to claim 1, wherein the composition comprises a K.sub.2O/(K.sub.2O+Na.sub.2O) ratio of from 0.2 to 0.4.

12. A float glass sheet according to claim 1, wherein the glass sheet has: $\frac{{\left({\mathrm{Na}}_2.Math.O\right)}_{\mathrm{air}}}{{\left({\mathrm{Na}}_2.Math.O\right)}_{\mathrm{tin}}}1.$

13. A float glass sheet according to claim 1, wherein the float glass sheet is chemically tempered.

14. An electronic device comprising the float glass sheet according to claim 13.

15. An electronic device comprising the float glass sheet according to claim 1.

Description

EXAMPLES

[0118] Powder raw materials were mixed together and placed in melting crucibles, according to the compositions specified in the following tables 1-4. The raw material mix was then heated up in an electrical furnace to a temperature allowing complete melting of the raw material.

[0119] In a first series (examples 1.x), the base molar composition was kept constant, and the proportion between Na.sub.2O and K.sub.2O was varied in the range of the invention while keeping constant the molar fraction of alkali (Na.sub.2O+K.sub.2O13.3 mol %) over the total composition. Example 1.1 is a comparative example, similar to state-of-the-art soda-lime float glass composition, with a classical K.sub.2O/(K.sub.2O+Na.sub.2O) ratio.

[0120] In a second series (examples 2.x.x), the molar composition in SiO.sub.2 and Al.sub.2O.sub.3 was kept constant. The molar fraction of total alkali (Na.sub.2O+K.sub.2O13.3 mol %) and total alkali-earth (MgO+CaO15 mol %) were as well kept constant, but the proportion between K.sub.2O and Na.sub.2O and between MgO and CaO were varied. As replacement of CaO by MgO is known to improve DoL, 3 levels of CaO/MgO (sub-series 2.1.x, 2.2.x and 2.3.x) were tested to show the beneficial impact of an improved K.sub.2O/(K.sub.2O+Na.sub.2O) ratio over a large range of compositions. Examples 2.1.1, 2.2.1, 2.3.1 are comparative examples, for each sub-series, with a classical K.sub.2O/(K.sub.2O+Na.sub.2O) ratio.

[0121] The third series (examples 3.x) is similar to the series 2.2.x, but with a higher content of Al.sub.2O.sub.3. Example 3.1 is a comparative example, with a classical K.sub.2O/(K.sub.2O+Na.sub.2O).

[0122] In a fourth series (examples 4.x), the base molar composition was kept constant, and the proportion between Na.sub.2O and K.sub.2O was varied in the range of the invention while keeping constant the molar fraction of alkali (Na.sub.2O+K.sub.2O13.3 mol %) over the total composition. Two glass tints were prepared, characterized by their levels of iron: 0.2% wt % of Fe.sub.2O.sub.3 (light green glass), and 0.45 wt % of Fe.sub.2O.sub.3 (green glass). In this series, examples 4.1 and 4.4 are comparative examples, similar to state of the art float compositions, with a classical K.sub.2O/(K.sub.2O+Na.sub.2O) ratio.

TABLE-US-00001 TABLE 1 EX1.1 Wt % (comp) EX1.2 EX 1.3 EX 1.4 SiO.sub.2 71.9 71.7 71.3 70.6 Al.sub.2O.sub.3 1.1 1.1 1.2 1.2 CaO 8.1 7.8 7.1 6.7 MgO 4.0 4.0 4.2 4.3 Na.sub.2O 14.3 13.3 11.3 9.4 K.sub.2O 0.2 1.7 4.6 7.4 Fe.sub.2O.sub.3 0.038 0.034 0.031 0.030 K.sub.2O/(Na.sub.2O + K.sub.2O) 0.01 0.11 0.29 0.44

TABLE-US-00002 TABLE 2 EX EX EX 2.1.1 EX EX 2.2.1 EX EX 2.3.1 EX EX Wt % (comp) 2.1.2 2.1.3 (comp) 2.2.2 2.2.3 (comp) 2.3.2 2.3.3 SiO.sub.2 71.8 71.6 70.9 72.0 71.7 71.0 73.0 72.7 71.4 Al.sub.2O.sub.3 1.1 1.1 1.2 1.1 1.2 1.2 1.1 1.2 1.2 CaO 8.1 7.8 6.5 7.2 6.9 5.7 3.4 3.3 2.8 MgO 4.1 4.2 4.2 4.7 4.8 4.8 7.1 7.2 7.3 Na.sub.2O 14.3 13.3 9.3 14.4 13.4 9.4 14.8 13.7 9.6 K.sub.2O 0.2 1.7 7.6 0.2 1.7 7.6 0.2 1.7 7.6 Fe.sub.2O.sub.3 0.034 0.003 0.027 0.035 0.032 0.028 0.034 0.033 0.028 K.sub.2O/(Na.sub.2O + K.sub.2O) 0.01 0.11 0.45 0.01 0.11 0.45 0.01 0.11 0.44

TABLE-US-00003 TABLE 3 EX3.1 Wt % (comp) EX3.2 EX3.3 SiO.sub.2 70.4 69.9 68.7 Al.sub.2O.sub.3 3.1 3.1 3.2 CaO 7.3 6.9 5.9 MgO 4.8 4.7 4.8 Na.sub.2O 14.2 13.4 9.4 K.sub.2O 0.2 1.7 7.6 Fe.sub.2O.sub.3 0.0 0.0 0.0 K.sub.2O/(Na.sub.2O + K.sub.2O) 0.01 0.11 0.45

TABLE-US-00004 TABLE 4 EX4.1 EX4.4 Wt % (comp) EX4.2 EX4.3 (comp) EX4.5 EX4.6 SiO.sub.2 72.1 71.4 71.0 71.9 71.2 70.6 Na.sub.2O 14.2 11.2 9.3 14.3 11.2 9.3 K.sub.2O 0.1 4.8 7.9 0.1 4.8 7.9 Al.sub.2O.sub.3 1.1 1.1 1.1 1.1 1.1 1.1 CaO 8.1 7.1 6.4 8.0 7.1 6.5 MgO 4.2 4.2 4.2 4.1 4.2 4.2 Fe.sub.2O.sub.3 0.21 0.19 0.18 0.48 0.45 0.42 K.sub.2O/(Na.sub.2O + K.sub.2O) 0.01 0.30 0.46 0.01 0.30 0.46

[0123] After the melting and the homogenization of the composition, the glass was cast in several small samples of 40*40 mm and annealed in an annealing furnace. Subsequently, the samples were polished up to a surface state similar to floated glass (mirror polishing). Several samples were produced for each composition, in order to allow to perform different tempering treatment for each composition.

Chemical Tempering

[0124] The samples prepared in above section were chemically tempered under two different tempering conditions, and for each of them the different samples were treated at the same time and in the same conditions. The samples of different compositions were placed in a cassette, preheated and then dippen in a molten KNO.sub.3 (>99%) bath. After the ion exchange, the samples were cooled down and washed.

[0125] Two types of treatments were applied on the different glass compositions. The first one was carried out at 420 C. during an immersion time of 220 minutes (so called low temperature). The second one was carried out at 465 C. during 480 minutes (so called high temperature). Subsequently the surface compressive stress (CS) and the depth of exchanged layer (DoL) were measured via photoelasticimetry. The following tables 5-7 summarize the average value of CS and DoL for 3 random samples of each composition and each treatment.

TABLE-US-00005 TABLE 5 EX1.1 (comp) EX1.2 EX1.3 EX 1.4 CS.sub.465 C. (MPa) 501 523 481 427 DOL.sub.465 C. (m) 21.4 25.4 31.6 37.9 CS.sub.420 C. (MPa) 747 706 588 495 DOL.sub.420 C. (m) 8.6 9.7 13.0 16.1

TABLE-US-00006 TABLE 6 EX EX EX 2.1.1 EX EX 2.2.1 EX EX 2.3.1 EX EX (comp) 2.1.2 2.1.3 (comp) 2.2.2 2.2.3 (comp) 2.3.2 2.3.3 CS.sub.465 C. (MPa) 502 541 417 511 527 438 537 468 425 DOL.sub.465 C. (m) 20.8 22.5 37.7 21.7 27.4 38.8 31.6 34.9 51.2 CS.sub.420 C. (MPa) 740 687 462 749 697 471 743 695 465 DOL.sub.420 C. (m) 8.4 9.3 16.0 9.0 10.2 16.7 13.0 14.3 23.9

TABLE-US-00007 TABLE 6 EX3.1 (comp) EX3.2 EX3.3 CS.sub.465 C. (MPa) 579 585 450 DOL.sub.465 C. (m) 18.9 25.5 41.3 CS.sub.420 C. (MPa) 827 722 501 DOL.sub.420 C. (m) 8.2 9.8 18.8

TABLE-US-00008 TABLE 7 EX4.1 EX4.4 (comp) EX4.2 EX4.3 (comp) EX4.5 EX4.6 CS.sub.465 C. (MPa) 516 512 476 517 526 489 DOL.sub.465 C. (m) 22.1 29.6 38.6 21.9 29.6 36.4 CS.sub.420 C. (MPa) 811 671 525 809 662 533 DOL.sub.420 C. (m) 7.9 10.6 14.7 7.7 10.6 14.5

[0126] Based on the measured values of the chemical tempering properties (CS and DoL), the ratio R between the high temperature and low temperature compressive stresses can be computed: R=CS.sub.465 C./CS.sub.420 C.. This R ratio is an image of the surface compressive stress preservation at high temperature. A value of R close to 1 means that the glass tends to limit stress relaxation at high temperature, and that low and high temperature treatment finally yields the same level of compressive stress. On the other hand if the R ratio is small, it means that the glass submitted to a high temperature treatment tends to relax the generated stresses to a large extent.

[0127] The gain in DoL (G factor) can also be computed for each composition according to the invention by using the corresponding comparative sample: G=(DoL.sub.sampleDoL.sub.comparative)/DoL.sub.comparative. This G factor as to be as high as possible in order to improve the resistance of the glass pieces versus mechanical solicitations.

[0128] The R ratios and G factors for the different examples are summarized in the following tables 8-11.

TABLE-US-00009 TABLE 8 EX1.1 (comp) EX1.2 EX 1.3 EX 1.4 K.sub.2O/(Na.sub.2O + K.sub.2O) 0.01 0.11 0.29 0.44 R (CS.sub.465 C./CS.sub.420 C.) 0.67 0.74 0.82 0.86 G.sub.465 C. (DoL improvement) 0% 19% 48% 77% G.sub.420 C. (DoL improvement) 0% 13% 51% 86%

TABLE-US-00010 TABLE 9 EX EX EX 2.1.1 EX EX 2.2.1 EX EX 2.3.1 EX EX (comp) 2.1.2 2.1.3 (comp) 2.2.2 2.2.3 (comp) 2.3.2 2.3.3 K.sub.2O/(Na.sub.2O + K.sub.2O) 0.01 0.11 0.45 0.01 0.11 0.45 0.01 0.11 0.44 R (CS.sub.465 C./CS.sub.420 C.) 0.68 0.79 0.90 0.68 0.76 0.93 0.72 0.67 0.91 G.sub.465 C. (DoL improvement) 0% 8% 81% 0% 26% 79% 0% 10% 62% G.sub.420 C. (DolLimprovement) 0% 10% 90% 0% 13% 86% 0% 10% 84%

TABLE-US-00011 TABLE 10 EX3.1 (comp) EX3.2 EX3.3 K.sub.2O/(Na.sub.2O + K.sub.2O) 0.01 0.11 0.45 R (CS.sub.465 C./CS.sub.420 C.) 0.70 0.81 0.90 G.sub.465 C. .sub.(DoL improvement) 0% 35% 118% G.sub.420 C. (DoL improvement) 0% 19% 128%

TABLE-US-00012 TABLE 11 EX4.1 EX4.4 (comp) EX4.2 EX4.3 (comp) EX4.5 EX4.6 K.sub.2O/(Na.sub.2O + K.sub.2O) 0.01 0.30 0.46 0.01 0.30 0.46 R (CS.sub.465 C./CS.sub.420 C.) 0.64 0.76 0.91 0.64 0.79 0.92 G.sub.465 C. (Dol improvement) 0% 34% 86% 0% 37% 87% G.sub.420 C. (Dol improvement) 0% 34% 75% 0% 35% 66%

[0129] From the above tables 8-11, the beneficial effect of the composition of the invention is highlighted: by increasing the K.sub.2O/(K.sub.2O+Na.sub.2O) ratio while keeping the rest of the composition stable on a molar point of view, the G factors (420 C. and 465 C.) of the composition increases significantly, meaning that the composition according to the invention allows faster ion exchange at the two tested temperatures. Moreover, this surprising effect is also observed and similar for the different glass tints, i.e. for the two different iron levels in series of samples 4.x (Table 11).

[0130] Similarly, the R ratio increases with higher values of K.sub.2O/(K.sub.2O+Na.sub.2O), highlighting the effect of stress conservation for high temperature treatment. In this set of experiments, the comparative examples present a R ratio around 0.65-0.7, meaning that increasing the treatment temperature from 420 C. to 465 C. will reduce the surface compressive stress by 30-35%. On the other side, examples according to the invention present a R ratio up to 0.92, meaning that the higher temperature treatment only reduces the compressive stress by 10% or less with respect to low temperature treatment.

[0131] By this way, interesting combinations of DoL (up to 50 m) and CS (kept higher than 400 MPa) can be obtain with the composition according to the invention, by applying higher temperature treatments.

Warping Behaviour

[0132] FIG. 2 shows evolution of warp (on 0.7 mm thickness sheet and for 200 mm sample length) vs. Na.sub.2O.sub.air/Na.sub.2O.sub.tin ratio for (i) classical soda-lime float glass from the state-of-the-art (plain line) and (ii) classical alumino-silicate float glass from the state-of-the-art (in particular, a DragonTrail glass from Asahi Glass Co.) (dashed line). In view of this figure, the behaviour from the composition of the invention will be intermediate between both shown trendlines.

Other Properties

[0133] The following properties were evaluated for the series of examples 4.x on the basis of glass composition using Fluegel model (Glass Technol.: Europ. J. Glass Sci. Technol. A 48 (1): 13-30 (2007); and Journal of the American Ceramic Society 90 (8): 2622 (2007)): [0134] Glass melt density evaluated at 1200 and 1400 C.; [0135] Viscosity through the Melting point temperature T2; [0136] Working point temperature T4; [0137] Devitrification temperature T0;

[0138] Table 12 summarizes obtained results.

[0139] In a general manner:

[0140] The melting point temperature T2 is preferably at most 1550 C., more preferably at most 1520 C., the most preferably at most 1500 C.

[0141] The Working point temperature T4 is preferably at most 1130 C., more preferably at most 1100 C., the most preferably at most 1070 C.

[0142] The devitrification temperature T0 is preferably at most T4, more preferably at most T4-20 C., the most preferably at most T4-40 C.

[0143] The compositions according to present invention are suitable for forming by a float process and while using existing furnace tools for production of soda lime glass because of: [0144] their melting point temperature T2 being lower than 1500 C. and which are close to the one of classical soda lime glass (Comparative ex.1.1 and 2.1). [0145] their working point temperature T4 which is lower than 1100 C. and which are close to a classical soda lime glass (Comparative ex.1.1 and 2.1). [0146] their devitrification temperature T0 are suitable because lower than working point temperature T4; [0147] their glass density which is very close to soda lime glasses (Comparative EX4.1 and 4.4), thereby avoiding/limiting density defects during composition change (transition).

TABLE-US-00013 TABLE 12 EX4.1 EX4.4 (comp) EX4.2 EX4.3 (comp) EX4.5 EX4.6 Glass melt density (1200 C.) 2.37 2.35 2.34 2.36 2.35 2.34 Glass melt density (1400 C.) 2.33 2.32 2.31 2.33 2.32 2.32 Melting point T2 ( C.) 1450 1480 1500 1449 1479 1498 Working point T4 ( C.) 1028 1041 1049 1027 1040 1047 Devitrification temperature T0 ( C.) 993 988 975 989 988 980

[0148] Finally, compositions according to the invention allow to get sulfate fining ability during their manufacture/melting, thanks to an adequate solubility of sulfate and suitable high-temperature viscosity.