Chemically strengthened substrate and method for chemically strengthening substrate

Abstract

The invention relates to a chemically strengthened substrate and a method for chemically strengthening a substrate. A method of chemically strengthening a substrate having a thickness of 10 [mu] m to 100 [mu] m includes contacting the substrate with a molten salt solution maintained at 350 DEG C to 400 DEG C for 10 minutes to 90 minutes. In an aspect, the molten salt solution comprises at least two anions associated with at least two potassium salts. The concentration of the first potassium salt and the second potassium salt is at least 2% by weight of the molten salt solution. In an aspect, a method includes transferring a substrate to a cooling chamber having a temperature decreasing from 4 DEG C / min to 20 DEG C / min. In an aspect, a method includes contacting a substrate with an acidic solution having a pH of 3.5 to 4.5 for 10 seconds to 3.5 minutes. A chemically strengthened substrate having a thickness of 10 [mu] m to 100 [mu] m has a maximum compressive stress of 650 megapascal to 1200 megapascal.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of priority of Chinese application No. 202311773622.3 filed on December 21, 2023, the contents of which are taken as the basis and incorporated herein by reference in their entirety. Technical Field

[0003] The present disclosure relates generally to chemically strengthened substrates and methods of chemically strengthening substrates, and more particularly to chemically strengthened substrates comprising a thickness of 100 microns or less and methods of chemically strengthening substrates comprising a thickness of less than 100 microns. Background Art

[0004] Glass-based substrates are widely used, for example, in display devices such as liquid crystal displays (LCDs), electrophoretic displays (EPDs), organic light emitting diode displays (OLEDs), or plasma display panels (PDPs).

[0005] It is desirable to develop foldable versions of displays and foldable protective covers mounted on foldable displays. Foldable displays and covers should have good impact resistance and puncture resistance. At the same time, foldable displays and covers should have a small minimum bending radius (e.g., about 10 millimeters (mm) or less). Plastic displays and covers with a small minimum bending radius tend to have poor impact resistance and / or puncture resistance. In addition, common sense suggests that ultra-thin glass-based sheets (e.g., about 75 micrometers (μm) or thinner) with a small minimum bending radius tend to have poor impact resistance and / or puncture resistance. In addition, thicker glass-based sheets (e.g., greater than 125 micrometers) with good impact resistance and / or puncture resistance tend to have a larger minimum bending radius (e.g., about 30 mm or more). Therefore, there is a need to develop foldable devices with a low minimum bending radius, good impact resistance, and good puncture resistance. Summary of the Invention

[0006] Chemically strengthened substrates (e.g., foldable substrates) and methods for chemically strengthening substrates (e.g., making thereof) are described herein. Providing glass-based substrates and / or ceramic-based substrates can provide good dimensional stability, can reduce the incidence of mechanical instability, and / or can provide good impact resistance and puncture resistance. The methods of the present disclosure can increase the pen drop height that foldable devices and / or foldable substrates can withstand, can increase the survival rate of substrates folded to parallel plate spacings of 5 mm, 3 mm, 2 mm, and / or 1 mm, and / or can increase the foldability of the substrate.

[0007] In one aspect, a substrate can be chemically strengthened with a molten salt solution comprising two anions associated with at least a first potassium salt and a second potassium salt. Providing a plurality (i.e., two or more) of potassium atoms per anion to the first potassium salt can increase the effective concentration and / or activity of potassium in the molten salt solution, which can contribute to an increase in the maximum compressive stress in the resulting chemically strengthened foldable substrate. Providing the first potassium salt in the molten salt solution with a pKa of about 9 or greater and / or a molten salt solution pH of about 9 to 12 can improve the strength and / or foldability of the resulting chemically strengthened foldable substrate, for example, by selectively etching defects inherent in the foldable substrate (which might otherwise be amplified due to the chemical strengthening treatment). As discussed herein with reference to the Examples, potassium carbonate (K2CO3) has a more pronounced and unexpected increase in compressive stress than other components in the molten salt solution. Furthermore, without wishing to be bound by theory, it is believed that carbonate anions facilitate the precipitation of other cations (e.g., lithium, sodium) exchanged from the foldable substrate, which can increase the lifespan of the molten salt solution (e.g., by removing components from the solution phase that would otherwise "poison" the molten salt solution). As demonstrated in the examples discussed herein, providing a first temperature of the molten salt solution below 400° C. can increase the maximum compressive stress established for a predetermined depth of layer and / or compression depth. Furthermore, for some of the molten salt solutions discussed herein, temperatures of 350° C. or higher can be used to ensure salt melting.

[0008] It was observed that foldable substrates having a thickness of about 50 μm or less (e.g., about 10 μm to about 50 μm or about 10 μm to about 30 μm) were unexpectedly sensitive to events that occurred after the foldable substrate was removed from the molten salt solution. For these thin foldable substrates, even relatively small differences in compressive stress on their surfaces can result in ripples and / or warping, which can produce optical distortion that is visually visible to users of consumer electronic products that may incorporate the foldable substrate. Therefore, the controlled temperature of the cooling chamber can contribute to relatively uniform compressive stress on the surface of the foldable substrate. In addition, providing an initial cooling chamber temperature of 180°C or higher (e.g., 200°C or higher or 220°C or higher) can facilitate the removal of residual portions of the molten salt solution before it solidifies. Without wishing to be bound by theory, the first potassium salt can have a higher melting temperature than the second potassium salt, which means that incorporating the first potassium salt into the molten salt solution can increase the viscosity of the molten salt solution and / or can cause the molten salt solution to solidify at a higher temperature than a molten salt solution without the first potassium salt. Thus, when the molten salt solution comprises a first potassium salt, it may be particularly useful to allow a residual portion of the molten salt solution to remain on the foldable substrate after it is removed from the molten salt solution. Lowering the temperature of the cooling chamber to a final temperature of about 100°C or less (e.g., about 25°C to about 100°C or about 60°C to about 90°C) can allow subsequent treatment of the foldable substrate with an aqueous solution (e.g., relatively quickly or immediately) (e.g., rinsing with water or an alkaline detergent solution, contacting with an aqueous acidic solution). Providing a cooling rate of about 4°C / minute to about 20°C / minute can allow the temperature of the cooling chamber (and the foldable substrate) to drop rapidly while maintaining a relatively uniform temperature throughout the cooling chamber (and / or the foldable substrate), for example, thereby generating a relatively uniform compressive stress on the surface of the foldable substrate.

[0009] Providing an etch rate of about 1 μm / minute or less (e.g., about 1.0 μm / minute or less) can promote substantially uniform material removal from the surface(s) of the foldable substrate. As discussed above, a foldable substrate having a thickness of about 50 μm or less (e.g., about 10 μm to about 50 μm or about 10 μm to about 30 μm) is quite sensitive to compressive stress differences and thickness variations on its surface. Therefore, providing an etch rate of about 1 μm / minute can remove relatively uniform thickness and compressive stress portions from the surface(s), thereby reducing the probability of the occurrence of ripples and / or warping that would produce optical distortion that is visually visible to users of consumer electronic products that may incorporate the foldable substrate. Without wishing to be bound by theory, providing a lower temperature of the acidic solution (e.g., about 20°C to about 40°C or about 20°C to about 25°C) can reduce the SiF6 - The concentration of anions, because H2SiF6 and 2H + +SiF6- The reaction is endothermic. - The concentration of anions can be associated with a reduction in the deposition (e.g., redeposition) of silicon dioxide or silicon dioxide-like materials on the surface, which would otherwise produce variations in thickness and / or compressive stress across the surface of the foldable substrate. Providing a higher pH (e.g., from about 3.5 to about 4.5, from about 3.6 to about 4.3, or from about 3.7 to about 4.0) can reduce the etch rate, which can help produce relatively uniform compressive stress and thickness across the foldable substrate. Providing a total concentration of HF and NHF of about 4.0 wt% or less, about 3.5 wt% or less, about 3.0 wt% or less, about 2.5 wt% or less, or about 2.0 wt% or less (e.g., about 1.25 wt% to about 4.0 wt%, about 1.3 wt% to about 3.5 wt%, about 1.35 wt% to about 3.0 wt%, about 1.4 wt% to about 2.5 wt%, about 1.5 wt% to about 2.0 wt%) can provide relatively controlled and uniform etching of the foldable substrate and / or can reduce the deposition of materials on the foldable substrate that can detract from the optical properties of the foldable substrate (e.g., silicon dioxide, materials similar to silicon dioxide, ammonium fluoride crystals).

[0010] In aspects, the substrate can have a substrate thickness of about 50 μm or greater (e.g., about 50 μm to about 100 μm, about 50 μm to about 90 μm, or any corresponding subranges therebetween as discussed above) and is combined with one or more of the following properties: (1) a compression depth of about 10% to about 30%, about 16% to about 26%, or any corresponding subranges therebetween as a percentage of the substrate thickness 209; (2) a depth of layer (e.g., a first depth of layer and / or a second depth of layer) of potassium in a range of about 3 μm to about 20 μm, about 10 μm to about 15 μm, or any corresponding subranges therebetween; and / or (3) a maximum compressive stress (e.g., a first maximum compressive stress and / or a second maximum compressive stress) in a range of about 650 MPa to about 1200 MPa, about 800 MPa to about 1100 MPa, about 850 MPa to about 1200 MPa, or any corresponding subranges therebetween as discussed above. In aspects, the substrate thickness can be about 50 μm or less (e.g., about 10 μm to about 50 μm, about 10 μm to about 30 μm, or any corresponding subranges therebetween as discussed above) and is combined with one or more of the following properties: (1) a depth of compression, as a percentage of the substrate thickness, of about 10% to about 30%, about 12% to about 19%, or any corresponding subranges therebetween as discussed above; (2) a depth of layer of potassium in the range of about 3 μm to about 20 μm, about 5 μm to about 9 μm, or any corresponding subranges therebetween; and / or (3) a maximum compressive stress (e.g., a first maximum compressive stress and / or a second maximum compressive stress) in the range of about 650 MPa to about 1200 MPa, about 750 MPa to about 1100 MPa, about 750 MPa to about 1,000 MPa, or any corresponding subranges discussed above.

[0011] Some exemplary aspects of the present disclosure are described below, and it is to be understood that any features of the various aspects may be used alone or in combination with each other.

[0012] Aspect 1: A method for chemically strengthening a substrate, the substrate comprising a thickness defined between an existing first major surface and an existing second major surface opposite the existing first major surface, the method comprising:

[0013] The existing first major surface of the substrate is contacted with a molten salt solution maintained at a first temperature for a first time period, the molten salt solution comprising at least two anions associated with at least a first potassium salt and a second potassium salt, the concentration of the first potassium salt and the concentration of the second potassium salt being 2% or greater by weight of the molten salt solution, the first temperature being in the range of about 350° C. to about 400° C., and the first time period being in the range of about 10 minutes to about 90 minutes.

[0014] Aspect 2: The method of aspect 1, wherein the first potassium salt comprises two or more potassium atoms per anion, and the pKa of the potassium salt is 9 or greater, and the concentration of the first potassium salt ranges from about 2 wt% to about 12 wt% of the molten salt solution.

[0015] Aspect 3: The method of any of Aspects 1-2, wherein the first potassium salt is potassium carbonate K2CO3, and the concentration of the first potassium salt ranges from about 2 wt% to about 12 wt% of the molten salt solution.

[0016] Aspect 4: The method of any of Aspects 1-3, wherein the concentration of the first potassium salt ranges from about 2.5 wt% to about 5.0 wt%.

[0017] Aspect 5: The method of any of Aspects 1-3, wherein the concentration of the first potassium salt ranges from about 5 wt% to about 12 wt%.

[0018] Aspect 6: The method of Aspect 5, wherein the concentration of the first potassium salt ranges from about 8 wt% to about 12 wt%.

[0019] Aspect 7: The method of any of Aspects 3-6, wherein the molten salt solution further comprises 0 wt% to 5 wt% of a third potassium salt associated with a third anion, wherein the third anion is different from anions associated with the first potassium salt and the second potassium salt, and the third potassium salt comprises two or more potassium atoms per anion.

[0020] Aspect 8: The method of Aspect 7, wherein the third potassium salt comprises potassium sulfate, K2SO4, and the concentration of the third potassium salt is about 0.5 wt% to about 5 wt%.

[0021] Aspect 9: The method of any of Aspects 1-8, wherein the second potassium salt is potassium nitrate KNO 3 , and the concentration of the second potassium salt ranges from about 50 wt % to about 98 wt % of the molten salt solution.

[0022] Aspect 10: The method of Aspect 9, wherein the concentration of the second potassium salt ranges from about 88 wt% to about 98 wt%.

[0023] Aspect 11: The method of any of Aspects 1-10, wherein the pH of the molten salt solution at the first temperature is in the range of about 9 to 12.

[0024] Aspect 12: The method of any of Aspects 1-11, wherein the presence of the first potassium salt increases the compressive stress imparted by contact of the existing first major surface with the molten salt solution by about 5% or more relative to immersing the substrate in a comparative molten salt solution having the same composition as the molten salt solution without the first potassium salt.

[0025] Aspect 13: The method of any of Aspects 1-12, wherein the substrate has a thickness in the range of about 15 μm to about 50 μm.

[0026] Aspect 14: The method of any of Aspects 1-12, wherein the substrate has a thickness in the range of about 50 μm to about 90 μm.

[0027] Aspect 15: The method of any of Aspects 1-13, further comprising: heating the substrate at a temperature in a range of about 250°C to about 350°C for a period of about 10 minutes to about 4 hours before contacting the first major surface with the molten salt solution.

[0028] Aspect 16: The method of any of Aspects 1-13 or 15 (inclusive), further comprising, after the first major surface has been contacted with the molten salt solution:

[0029] The substrate is transferred from the molten salt solution to a cooling chamber, and the temperature of the cooling chamber is reduced from an initial temperature to a final temperature at a cooling rate of about 4°C / minute to about 20°C / minute, the initial temperature ranges from about 180°C to about 300°C, and the final temperature ranges from about 25°C to about 100°C.

[0030] Aspect 17: A method of chemically strengthening a substrate, the substrate comprising a thickness defined between an existing first major surface and an existing second major surface opposite the existing first major surface, the method comprising:

[0031] subjecting the substrate to strengthening in the molten salt solution maintained at a first temperature for a first period of time, the first temperature being in a range of about 350° C. to about 400° C., and the first period of time being in a range of about 10 minutes to about 90 minutes; and

[0032] The substrate is transferred from the molten salt solution to a cooling chamber, and the temperature of the cooling chamber is reduced from an initial temperature in the range of about 180°C to about 300°C to a final temperature in the range of about 25°C to about 100°C at a cooling range of about 4°C / minute to about 20°C / minute.

[0033] Aspect 18: The method of any of Aspects 16-17, wherein the final temperature is in the range of about 60°C to about 90°C.

[0034] Aspect 19: The method of any of Aspects 16-18, wherein the initial temperature is in the range of about 180°C to about 220°C.

[0035] Aspect 20: The method of any of Aspects 16-19, further comprising: rinsing the substrate with water, an alkaline detergent solution, or a combination thereof after the cooling chamber reaches the final temperature.

[0036] Aspect 21: The method of any of Aspects 1-20, wherein the initial maximum compressive stress of the substrate after the first major surface has been contacted with the molten salt solution is from about 800 megapascals to about 1500 megapascals.

[0037] Aspect 22: The method of Aspect 21, wherein the initial maximum compressive stress is from about 900 megapascals to about 1200 megapascals.

[0038] Aspect 23: The method of any one of Aspects 1-20, further comprising:

[0039] contacting the existing first major surface with an acidic solution for a second time period to remove the outer layer from the existing first major surface to form a new first major surface, the acidic solution having a pH in the range of 3.5 to 4.5, and the second time period being from about 10 seconds to about 3.5 minutes; and then

[0040] The new first major surface is cleaned with water.

[0041] Aspect 24: A method of chemically strengthening a substrate, the substrate comprising a thickness defined between an existing first major surface and an existing second major surface opposite the existing first major surface, the method comprising:

[0042] chemically strengthening the substrate in a molten salt solution maintained at a first temperature for a first time period, the first temperature being in a range of about 350° C. to about 400° C., and the first time period being in a range of about 10 minutes to about 90 minutes;

[0043] contacting the existing first major surface with an acidic solution for a second time period to remove the outer layer from the existing first major surface to form a new first major surface, the acidic solution having a pH in the range of 3.5 to 4.5, and the second time period being from about 10 seconds to about 3.5 minutes; and then

[0044] The new first major surface is cleaned with water.

[0045] Aspect 25: The method of any of Aspects 23-24, wherein the second temperature of the acidic solution is from about 20°C to about 40°C.

[0046] Aspect 26: The method of Aspect 23, wherein the second temperature is in the range of about 20°C to about 25°C.

[0047] Aspect 27: The method of any of Aspects 23-26, wherein the acidic solution comprises a buffered HF solution.

[0048] Aspect 28: The method of any one of Aspects 23-27, wherein the acidic solution comprises, in weight percent of the acidic solution:

[0049] about 0.5 wt% to about 1.5 wt% HF; and

[0050] About 0.75 wt% to about 2.5 wt% NH4F.

[0051] Aspect 29: The method of Aspect 28, wherein the acidic solution comprises, in terms of weight percent of the acidic solution:

[0052] from about 0.5 wt% to about 0.75 wt% HF; and

[0053] About 0.9 wt% to about 1.5 wt% NH4F.

[0054] Aspect 30: The method of any of Aspects 23-29, wherein the acidic solution removes the outer layer at a rate of about 1.0 micron / minute or less.

[0055] Aspect 31: The method of any of Aspects 23-30, wherein the substrate comprises an initial maximum compressive force prior to contacting the acidic solution, the substrate comprises a final maximum compressive stress after contacting the acidic solution, and the final maximum compressive stress is about 10% to about 25% less than the initial maximum compressive stress as a percentage of the initial maximum compressive stress.

[0056] Aspect 32: The method of Aspect 31, wherein the final maximum compressive stress is about 15% to about 20% less than the initial maximum compressive stress, as a percentage of the initial maximum compressive stress.

[0057] Aspect 33: The method of any of Aspects 31-32, wherein the final maximum compressive stress ranges from about 700 megapascals to about 1200 megapascals.

[0058] Aspect 34: The method of any of Aspects 23-33, further comprising rinsing the substrate with water or another acidic solution after the first major surface has been contacted with the acidic solution.

[0059] Aspect 35: The method of any of Aspects 23-34, wherein 95% or more of the substrate sample is able to withstand a parallel plate spacing of 5 mm.

[0060] Aspect 36: The method of any of Aspects 23-35, wherein the substrate exhibits a pen-down threshold height of 10 centimeters or greater in a pen-down test.

[0061] Aspect 37: The method of any of Aspects 23-35, wherein the substrate exhibits a pen-down threshold height of 20 centimeters or greater in pen-down height.

[0062] Aspect 38: The method of any of Aspects 23-37, wherein about 30% or more of the substrate sample is able to withstand a parallel plate spacing of 3 mm when the thickness ranges from about 50 microns to about 100 microns.

[0063] Aspect 39: The method of any of Aspects 23-36, wherein the thickness is 10 microns to 50 microns.

[0064] Aspect 40: The method of Aspect 39, wherein the thickness is 10 microns to 30 microns.

[0065] Aspect 41: The method of any of Aspects 39-40, wherein 90% or more of the substrate sample can withstand a parallel plate spacing of 2 mm.

[0066] Aspect 42: The method of any of Aspects 39-40, wherein 10% or more of the substrate sample is able to withstand a parallel plate spacing of 1 mm.

[0067] Aspect 43: The method of any of Aspects 1-42, wherein the substrate is a glass-based substrate.

[0068] Aspect 44: The method of Aspect 43, wherein the composition of the substrate comprises, in terms of mole % of the substrate:

[0069] about 60 mol % to about 70 mol % SiO2;

[0070] about 8 mol% to about 16 mol% Al2O3;

[0071] about 12 mol % to about 18 mol % Na2O;

[0072] about 2 mol% to about 6 mol% MgO; and

[0073] About 0.1 mol % to about 2.0 mol % CaO.

[0074] Aspect 45: The method of Aspect 44, wherein the composition comprises, in mole % of the substrate:

[0075] about 64 mol % to about 69 mol % SiO2;

[0076] about 9 mol% to about 15 mol% Al2O3;

[0077] about 14 mol % to about 17 mol % Na2O;

[0078] about 2.5 mol% to about 5.5 mol% MgO;

[0079] about 0.3 mol % to about 1.2 mol % CaO; and

[0080] 0.0 mol % to about 0.5 mol % K2O.

[0081] Aspect 45: Chemically strengthened substrates, comprising:

[0082] a thickness defined between the first major surface and a second major surface opposite the first major surface, the thickness being from about 10 micrometers to about 100 micrometers; and

[0083] a first compressive stress region extending from the first major surface to a first compressive depth, the first layer depth of potassium being about 5 microns or greater, and a maximum first compressive stress being about 650 MPa to about 1200 MPa,

[0084] The chemically strengthened substrate includes a glass-based material, 95% or more of the chemically strengthened substrate samples are able to withstand a parallel plate spacing of 5 mm, and the substrate exhibits a pen drop threshold height of 10 cm or greater in a pen drop test.

[0085] Aspect 47: The chemically strengthened substrate of Aspect 46, wherein the composition of the chemically strengthened substrate is, in terms of mol % of the chemically strengthened substrate:

[0086] about 60 mol % to about 70 mol % SiO2;

[0087] about 8 mol% to about 16 mol% Al2O3;

[0088] about 12 mol % to about 18 mol % Na2O;

[0089] about 2 mol% to about 6 mol% MgO; and

[0090] About 0.1 mol % to about 2.0 mol % CaO.

[0091] Aspect 48: The chemically strengthened substrate of Aspect 47, wherein the composition comprises, in terms of mole % of the chemically strengthened substrate:

[0092] about 64 mol % to about 69 mol % SiO2;

[0093] about 9 mol% to about 15 mol% Al2O3;

[0094] about 14 mol % to about 17 mol % Na2O;

[0095] about 2.5 mol% to about 5.5 mol% MgO;

[0096] about 0.3 mol % to about 1.2 mol % CaO; and

[0097] 0.0 mol % to about 0.5 mol % K2O.

[0098] Aspect 49: The chemically strengthened substrate of any of Aspects 46-48, wherein the maximum first compressive stress is from about 800 megapascals to about 1100 megapascals.

[0099] Aspect 50: The chemically strengthened substrate of any of Aspects 46-49, wherein 90% or more of the substrate samples are able to withstand a parallel plate spacing of 3 mm.

[0100] Aspect 51: The chemically strengthened substrate of any of Aspects 46-50, wherein the thickness is from about 10 microns to about 50 microns.

[0101] Aspect 52: The chemically strengthened substrate of Aspect 51, wherein the thickness is from about 10 microns to about 30 microns.

[0102] Aspect 53: The chemically strengthened substrate of any of Aspects 51-52, wherein the maximum first compressive stress is from about 750 megapascals to about 1100 megapascals.

[0103] Aspect 54: The chemically strengthened substrate of any of Aspects 51-53, wherein 90% or more of the substrate samples are able to withstand a parallel plate spacing of 2 mm.

[0104] Aspect 55: The chemically strengthened substrate of any of Aspects 51-54, wherein 10% or more of the substrate sample is able to withstand a parallel plate spacing of 1 mm.

[0105] Aspect 56: The chemically strengthened substrate of any of Aspects 46-50, wherein the maximum first compressive stress is from about 850 megapascals to about 1200 megapascals.

[0106] Aspect 57: The chemically strengthened substrate of any of Aspects 46-50, wherein the maximum first compressive stress is from about 1000 megapascals to about 1200 megapascals.

[0107] Aspect 58: The chemically strengthened substrate of any of Aspects 46-50 or 56-57, inclusive, wherein about 30% or more of the chemically strengthened substrate samples are able to withstand a parallel plate spacing of 3 mm.

[0108] Aspect 59: The chemically strengthened substrate of any of Aspects 46-50 or 56-57, inclusive, wherein about 50% or more of the chemically strengthened substrate samples are able to withstand a parallel plate spacing of 3 mm.

[0109] Aspect 60: The chemically strengthened substrate of any of Aspects 46-59, wherein the chemically strengthened substrate exhibits a haze of about 1% or less.

[0110] Aspect 61: The chemically strengthened substrate of any of Aspects 46-60, wherein the chemically strengthened substrate exhibits a transmittance of 90% to 95%.

[0111] Throughout this disclosure, the accompanying drawings are used to emphasize certain aspects. Therefore, unless otherwise explicitly stated, it should be assumed that the relative sizes of different regions, parts, and substrates shown in the drawings are not to scale with their actual relative sizes. BRIEF DESCRIPTION OF THE DRAWINGS

[0112] The above features and advantages and other features and advantages of the present disclosure will be better understood from the following detailed description with reference to the accompanying drawings, in which:

[0113] Figure 1 is a schematic diagram of an exemplary foldable device in a flat configuration according to aspects, wherein a schematic diagram of the folded configuration can be seen in FIG. Figure 5 As shown;

[0114] Figure 2 An exemplary foldable device comprising a foldable substrate according to aspects Figure 1 A cross-sectional view taken along line 2-2;

[0115] Figure 3 An exemplary foldable device according to aspects Figure 1 A cross-sectional view taken along line 2-2;

[0116] Figure 4 is a schematic diagram of an exemplary foldable device in a folded configuration according to aspects of the present disclosure, wherein a schematic diagram of a flat configuration can be seen in FIG. Figure 1 As shown;

[0117] Figure 5 is a cross-sectional view of a test device used to determine the cross-sectional view of an exemplary improved foldable device and / or foldable substrate along Figure 4 The minimum parallel plate spacing of line 5-5;

[0118] Figure 6 It is a schematic elevation view of the pen-dropping device;

[0119] Figure 7 It is a schematic elevation view of a foldable consumer electronic product;

[0120] Figure 8 is a schematic plan view of an exemplary consumer electronic device according to aspects;

[0121] Figure 9 yes Figure 8 A perspective schematic diagram of an exemplary consumer electronic device;

[0122] Figure 10 Flowchart showing an exemplary method of chemically strengthening a substrate to form a foldable substrate and / or a foldable device according to aspects of the present disclosure;

[0123] Figure 11Schematic diagram showing a method for chemically strengthening a substrate including a step of heating the substrate;

[0124] Figure 12 Schematically showing a method for chemically strengthening a substrate including the step of contacting the substrate with a molten salt solution;

[0125] Figure 13 Schematically showing a method for chemically strengthening a substrate including steps of lowering the temperature of a cooling chamber and / or causing a molten salt solution to drip from the substrate;

[0126] Figure 14 Schematic diagram showing a method for chemically strengthening a substrate including a step of cleaning the substrate;

[0127] Figure 15 Schematic diagram showing a method for chemically strengthening a substrate including the step of contacting the substrate with an acidic solution;

[0128] Figure 16 Is a foldable device in Figure 12 After the steps shown and / or Figure 15 a cross-sectional view prior to the step shown;

[0129] Figure 17 Schematic diagram showing the compressive stress (in megapascals) of Examples 1-6 and Comparative Examples AA-DD (vertical axis - y-axis);

[0130] Figure 18 Schematic representation of the layer depth (in micrometers) of Examples 1-6 and Comparative Examples AA-DD (vertical axis - y-axis);

[0131] Figure 19 Schematic diagram showing the functional relationship between the compressive stress (in megapascals) (vertical axis - y axis) and the concentration of K2CO3 in the molten salt solution (in weight %) (horizontal axis - x axis);

[0132] Figure 20 Schematic representation of the functional relationship between the layer depth (in micrometers) (vertical axis - y axis) and the concentration of K2CO3 in the molten salt solution (in weight %) (horizontal axis - x axis);

[0133] Figure 21 Schematic representation of the survival rate (percentage, vertical axis - y axis) as a function of the parallel plate spacing (in micrometers) (horizontal axis - x axis);

[0134] Figure 22 Schematic representation of the survival rate (percentage, vertical axis - y axis) as a function of the parallel plate spacing (in micrometers) (horizontal axis - x axis);

[0135] Figure 23Schematic representation of the survival rate (percentage, vertical axis - y axis) as a function of the parallel plate spacing (in micrometers) (horizontal axis - x axis);

[0136] Figure 24 Schematic representation of the survival rate (percentage, vertical axis - y axis) as a function of the parallel plate spacing (in micrometers) (horizontal axis - x axis);

[0137] Figure 25 Schematic representation of the survival rate (percentage, vertical axis - y axis) as a function of the parallel plate spacing (unit: micrometers) (horizontal axis - x axis); and

[0138] Figures 26A-26C Schematic representation of visually observable reflections from chemically strengthened substrates exhibiting different levels of waviness.

[0139] Throughout this disclosure, the accompanying drawings are used to emphasize certain aspects. Therefore, unless otherwise explicitly stated, it should be assumed that the relative sizes of different regions, parts, and substrates shown in the drawings are not to scale with their actual relative sizes. DETAILED DESCRIPTION

[0140] Aspects will now be described more fully with reference to the accompanying drawings, in which exemplary aspects are shown. Whenever possible, the same reference numerals are used throughout the drawings to represent the same or similar parts. However, the claims may include many different aspects of various aspects and should not be construed as limited to the aspects set forth herein.

[0141] Figure 1-5 Schematic diagrams showing foldable devices 101, 301, and / or 401 including a foldable substrate 201 according to aspects of the present disclosure. Unless otherwise noted, discussions of features in one aspect of a foldable device and / or foldable substrate are equally applicable to corresponding features in any aspect of the present disclosure. For example, throughout the present disclosure, identical part numbers may indicate that, in some aspects, the referenced features are identical to one another, and discussions of referenced features in one aspect are equally applicable to referenced features in any other aspect of the present disclosure, unless otherwise noted.

[0142] like Figure 1-3 As shown, exemplary aspects of the foldable device 101 and / or 301 may include a foldable substrate 201 according to the present disclosure in an unfolded (eg, flat) configuration, while Figure 5 A foldable device 401 according to the present disclosure comprising a foldable substrate 201 is demonstrated in a folded configuration. Figure 4-5 As shown, the foldable device 401 may include and / or be composed of the foldable substrate 201. In aspects, as Figure 3As shown, the foldable device 310 may include a layer (e.g., a PET sheet 321) attached to the foldable substrate 201 via an adhesive layer 311, it being understood that other layers (e.g., a release layer, a display device, additional substrates) may be used in addition to or in place of the layers shown.

[0143] Throughout this disclosure, see Figure 1 , the width 103 of the foldable device 101 and / or 301 is considered to be the dimension of the foldable device selected between opposite edges of the foldable device in the direction 104 of the folding axis 102 of the foldable device, wherein the direction 104 also includes the direction of the width 103. Moreover, throughout this disclosure, the length 105 of the foldable device 101 and / or 301 is considered to be the dimension of the foldable device 101 and / or 301 selected between opposite edges of the foldable device 101 and / or 301 in the direction 106 perpendicular to the folding axis 102 of the foldable device. In aspects, such as Figure 1-3 As shown, the foldable device of any aspect of the present disclosure may include a folding plane 109 that includes the folding axis 102 and the direction of the substrate thickness 209 when the foldable device is in a flat configuration (e.g., see Figure 2 ). The folding surface 109 may include the central axis 107 of the foldable device, which is located at, for example, the second major surface 205 of the foldable device 101 and 301 (see Figure 2-3 In the aspect, the foldable device can be folded in a direction 111 about a folding axis 102 extending in a direction 104 of width 103 (see Figure 1 ), thereby forming a folded structure (see, for example, Figure 4-5 ). In aspects, such as Figure 2-3 As shown, the foldable device 101 and / or 301 and / or the foldable substrate 201 may include a substantially flat first major surface 203 and / or second major surface 205, wherein a central portion of the foldable device may be indistinguishable from adjacent portions. Figure 1-5 As shown, the foldable device can include a single fold axis to allow the foldable device to include a bifold, wherein, for example, the foldable device can be folded in half. In other aspects, the foldable device can include two or more fold axes, for example, each fold axis including a corresponding central portion similar to or consistent with the central portion discussed herein. For example, providing two fold axes can allow the foldable device to include a trifold, wherein, for example, the foldable device can be folded such that a first portion, a second portion, and a third portion similar to or consistent with the first portion or the second portion are folded, respectively, by a central portion and another central portion similar to or consistent with the central portion positioned between the first portion and the second portion and positioned between the second portion and the third portion.

[0144] The foldable device 101 and / or 301 of the present disclosure includes a foldable substrate 201. In one aspect, the foldable substrate 201 may include a glass-based substrate having a pencil hardness of 8H or higher (e.g., 9H or higher). In one aspect, the foldable substrate 201 may include a glass-based substrate. As used herein, "glass-based" includes both glass and glass-ceramics, wherein the glass-ceramics have: one or more crystalline phases, and an amorphous residual glass phase. Glass-based materials (e.g., glass-based substrates) can include an amorphous material (e.g., glass) and optionally one or more crystalline materials (e.g., ceramics). Amorphous materials and glass-based materials can be strengthened. As used herein, the term "strengthened" can refer to a material that has been chemically strengthened by, for example, ion-exchanging smaller ions in the surface of the substrate with larger ions, as discussed below. However, other strengthening methods can also be used, such as thermal tempering or mismatching of thermal expansion coefficients between substrate portions to produce compressive stress and central tension regions to form a strengthened substrate. Exemplary glass-based materials (which may be lithium oxide-free or lithium oxide-containing) include soda-lime silicate glass, alkali aluminosilicate glass, alkali-containing borosilicate glass, alkali-containing aluminoborosilicate glass, alkali-containing phosphosilicate glass, and alkali-containing aluminophosphosilicate glass. In one or more aspects, the glass-based material may comprise, by mole percentage (mol%), about 40 mol% to about 80 mol% SiO2, about 5 mol% to about 30 mol% Al2O3, 0 mol% to about 10 mol% B2O3, 0 mol% to about 5 mol% ZrO2, 0 mol% to about 15 mol% P2O5, 0 mol% to about 2 mol% TiO2, 0 mol% to about 20 mol% R2O, and 0 mol% to about 15 mol% RO. As used herein, R2O refers to alkali metal oxides such as Li2O, Na2O, KO, Rb2O, and Cs2O. As used herein, RO refers to MgO, CaO, SrO, BaO, and ZnO. In aspects, the glass-based substrate may also optionally include 0 mol% to about 2 mol% of each of the following: Na2SO4, NaCl, NaF, NaBr, K2SO4, KCl, KF, KBr, As2O3, Sb2O3, SnO2, Fe2O3, MnO, MnO2, MnO3, Mn2O3, Mn3O4, Mn2O7. "Glass-ceramics" include materials produced by controlled crystallization of glass. In aspects, the glass-ceramics have a crystallinity of about 1% to about 99%.Examples of suitable glass-ceramics may include Li2O-Al2O3-SiO2 system (i.e., LAS system) glass-ceramics, MgO-Al2O3-SiO2 system (i.e., MAS system) glass-ceramics, ZnO×Al2O3×nSiO2 (i.e., ZAS system) and / or glass-ceramics including a primary crystalline phase comprising a β-quartz solid solution, β-spodumene, cordierite, petalite, and / or lithium disilicate. A chemical strengthening process may be used to strengthen the glass-ceramic substrate. In one or more aspects, the MAS system glass-ceramic substrate may be strengthened in a Li2SO4 molten salt, thereby generating 2Li. + Mg 2+ exchange.

[0145] In aspect, the glass-based substrate (e.g., foldable substrate 201) has SiO2 as the largest component, and thus SiO2 is the main constituent component of the glass network formed by the glass-based composition. Pure SiO2 has a relatively low CTE. However, pure SiO2 has a high melting point. Therefore, if the concentration of SiO2 in the glass-based composition is too high, the formability of the glass-based composition may decrease because the higher SiO2 concentration increases the difficulty of melting the glass, which in turn has a negative impact on the formability of the composition. If the concentration of SiO2 in the glass-based composition is too low, the chemical durability of the glass-based material may decrease, and the glass-based material may be prone to surface damage during post-forming processing. In aspects, the glass-based substrate can include SiO in an amount of 60 mol% or more, 61 mol% or more, 62 mol% or more, 63 mol% or more, 63.5 mol% or more, 64 mol% or more, 70 mol% or less, 69 mol% or less, 68 mol% or less, 67 mol% or less, 66 mol% or less, or 65 mol% or less. In aspects, the glass-based substrate can include SiO in a range of 60 mol% to 70 mol%, 61 mol% to 70 mol%, 62 mol% to 69 mol%, 63 mol% to 69 mol%, 64 mol% to 69 mol%, 65 mol% to 69 mol%, 64 mol% to 68 mol%, 65 mol% to 67 mol%, or any range or subrange therebetween. In preferred aspects, the glass-based substrate includes SiO in an amount of 60 mol% to 70 mol% or 64 mol% to 69 mol%.

[0146] A glass-based substrate (e.g., foldable substrate 201) can include Al2O3. Similar to SiO2, Al2O3 can act as a glass network former. Al2O3 can increase the viscosity of the glass-based composition because it is tetrahedrally coordinated in the glass melt formed from the glass-based composition, and when the amount of Al2O3 is too high, the formability of the glass-based composition is reduced. However, when the concentration of Al2O3 is balanced with the concentration of SiO2 and the concentration of alkali oxides in the glass-based composition, Al2O3 lowers the liquidus temperature of the glass melt, thereby enhancing the liquidus viscosity and improving the compatibility of the glass-based composition with certain forming processes. Including Al2O3 in the glass-based composition can achieve high fracture toughness values ​​as described herein. In aspects, the glass-based substrate comprises Al2O3 in an amount of 8 mol% or more, 9 mol% or more, 10 mol% or more, 11 mol% or more, 12 mol% or more, 16 mol% or less, 16 mol% or less, 15 mol% or less, 14 mol% or less, or about 13 mol% or less. In aspects, the glass-based substrate comprises Al2O3 in an amount ranging from 8 mol% to 16 mol%, 9 mol% to 15 mol%, 10 mol% to 15 mol%, 11 mol% to 14 mol%, 12 mol% to 13 mol%, or any range or subrange therebetween. In preferred aspects, the glass-based substrate comprises Al2O3 in an amount ranging from 8 mol% to 16 mol% or from 9 mol% to 15 mol%.

[0147] A glass-based substrate (e.g., foldable substrate 201) can include Na2O. Na2O can contribute to the ion exchangeability of the glass-based composition and can improve formability, thereby improving the manufacturability of the glass-based composition. However, if too much Na2O is added to the glass-based composition, the CTE may be too low and the melting point may be too high. In addition, if too much Na2O is included in the composition relative to the amount of Li2O, the ability of the glass-based substrate to achieve a deep compression depth when ion exchanged may be reduced. In aspects, the glass-based substrate includes Na2O in an amount of: 12 mol% or more, 13 mol% or more, 14 mol% or more, 15 mol% or more, 18 mol% or less, 17 mol% or less, 16 mol% or less, or 15 mol% or less. In aspects, the glass-based substrate comprises Na2O in an amount ranging from 12 mol% to 17 mol%, from 13 mol% to 18 mol%, from 14 mol% to 17 mol%, from 15 mol% to 16 mol%, or any range or sub-range therebetween. In preferred aspects, the glass-based substrate comprises Na2O in an amount ranging from 12 mol% to 18 mol% Na2O or from 14 mol% to 17 mol%.

[0148] Glass-based substrates (e.g., foldable substrate 201) may include K2O. Including K2O in glass-based compositions increases potassium diffusivity in glass-based materials, enabling deeper compressive stress peak depths (DOLs) to be achieved with lower ion exchange times. SP ). If too much KO is included in the composition, the amount of compressive stress imparted during the ion exchange process may be reduced. In aspects, the glass-based substrate may include KO in an amount of 0.0 mol% or more, 0.1 mol% or more, 0.25 mol% or more, 1 mol% or less, 0.75 mol% or less, 0.5 mol% or less, or 0.3 mol% or less. In aspects, the glass-based substrate may include KO in an amount in the range of 0.0 mol% to 1 mol%, 0.0 mol% to 0.75 mol%, 0.0 mol% to 0.5 mol%, 0.1 mol% to 0.3 mol%, or any range or sub-range therebetween. In preferred aspects, the glass-based substrate may include KO in an amount in the range of 0.0 mol% to 1 mol% or 0.0 mol% to 0.5 mol%.

[0149] Glass-based substrates (e.g., foldable substrate 201) may include MgO. MgO may reduce the viscosity of the glass, which enhances the formability and manufacturability of the composition. Including MgO in a glass-based composition may also improve the strain point and Young's modulus of the glass-based composition. However, if too much MgO is added to the glass-based composition, the liquidus viscosity may be too low for compatibility with the desired forming technology. Adding too much MgO may also increase the density and CTE of the glass-based composition to undesirable levels. Including MgO in a glass-based composition also helps improve fracture toughness. In aspects, the amount of MgO included in the glass-based substrate may be: 2 mol% or more, 2.5 mol% or more, 3.0 mol% or more, 3.2 mol% or more, 3.5 mol% or more, 4.0 mol% or more, 6 mol% or less, 5.5 mol% or less, 5.0 mol% or less, or 4.9 mol% or less. In aspects, the glass-based substrate may include MgO in an amount ranging from 2 mol% to 6 mol%, 2.5 mol% to 5.5 mol%, 3.0 mol% to 5.0 mol%, 3.2 mol% to less than or equal to 4.9 mol%, 3.5 mol% to 4.9, or any range or sub-range therebetween. In preferred aspects, the composition includes MgO in an amount ranging from 2 mol% to 6 mol% or from 2.5 mol% to 5.5 mol%.

[0150] The glass-based substrates described herein (e.g., foldable substrate 201) can include CaO. CaO can reduce the viscosity of the glass, which can enhance formability, strain point, and Young's modulus. However, if too much CaO is added to the glass-based composition, the density and CTE of the glass-based composition can increase to undesirable levels, and the ion exchangeability of the glass-based substrate can be undesirably hindered. Including CaO in the glass-based composition also improves fracture toughness. In aspects, the amount of CaO included in the glass-based substrate can be: 0.1 mol% or more, 0.2 mol% or more, 0.3 mol% or more, 0.4 mol% or more, 0.5 mol% or more, 0.7 mol% or more, 2.0 mol% or less, 1.5 mol% or less, 1.2 mol% or less, 1.1 mol% or less, 1.0 mol% or less, or 0.9 mol% or less. In aspects, the glass-based substrate may include CaO in an amount ranging from 0.1 mol% to 2.0 mol%, 0.2 mol% to 1.5 mol%, 0.3 mol% to 1.2 mol%, 0.4 mol% to less than or equal to 1.1 mol%, 0.5 mol% to 1.0 mol%, 0.7 mol% to 1.0 mol%, or any range or sub-range therebetween. In preferred aspects, the glass-based substrate includes CaO in an amount ranging from 0.1 mol% to 2.0 mol% or from 0.3 mol% to 1.2 mol%.

[0151] In one aspect, the glass-based substrate can be substantially free of or free of one or more of: P2O5, B2O3, TiO2, ZnO, ZrO2, Ta2O5, HfO2, La2O3, and / or Y2O3. As used herein, the term "substantially free" means that the component is not purposefully added as a component of the batch material, although very small amounts of the component (e.g., less than 0.1 mol%) may be present as a contaminant in the final glass-based composition. For example, the inclusion of ZrO2 in the glass-based composition may result in the formation of undesirable zirconium oxide in the glass-based material, at least in part due to the low solubility of ZrO2 in the glass-based material. In addition, the inclusion of Ta2O5, HfO2, La2O3, and / or Y2O3 may increase the raw material costs associated with the glass-based substrate.

[0152] In one aspect, a glass-based substrate (e.g., foldable substrate 201) can include: about 60 mol% to about 70 mol% SiO2, about 8 mol% to about 16 mol% Al2O3, about 12 mol% to about 18 mol% Na2O, about 2 mol% to about 6 mol% MgO, and about 0.1 mol% to about 2.0 mol% CaO. In one aspect, a glass-based substrate (e.g., foldable substrate 201) can include: about 64 mol% to about 69 mol% SiO2, about 9 mol% to about 15 mol% Al2O3, about 14 mol% to about 17 mol% Na2O, about 2.5 mol% to about 5.5 mol% MgO, about 0.3 mol% to about 1.2 mol% CaO, and 0.0 mol% to about 0.5 mol% KO.

[0153] The foldable substrate 201 may include a glass-based substrate, and the first major surface 203 and / or the second major surface 205 may include one or more compressive stress regions. In one aspect, the compressive stress region can be generated by chemical strengthening. Chemical strengthening may include an ion exchange process in which ions in the surface layer are replaced or exchanged with larger ions having the same valence or oxidation state. Chemical strengthening methods will be discussed later. Without wishing to be bound by theory, chemical strengthening of the foldable substrate 201 can achieve good impact resistance and / or puncture resistance (e.g., resistance to failure at a 20 cm pen drop height). Without wishing to be bound by theory, chemical strengthening of the foldable substrate 201 can achieve a small (e.g., less than about 10 mm or less) bending radius because the compressive stress from chemical strengthening can offset the bending-induced tensile stress on the outermost surface of the substrate. The compressive stress region can extend into a portion of the first portion and / or the second portion to a depth referred to as the compression depth. As used herein, the compression depth refers to the depth at which the stress in the chemically strengthened substrate and / or portion described herein changes from compressive stress to tensile stress. Depending on the ion exchange treatment and thickness of the article being measured, the depth of compression can be measured using a surface stress meter or a scattered light polarizer (SCALP, wherein the values ​​reported herein were obtained using a SCALP-5 manufactured by Glasstress, Estonia). The depth of compression is measured using a surface stress meter (e.g., FSM-6000 (Orihara Industries, Ltd., Japan)) when stress is generated in the substrate and / or part by exchanging potassium ions into the substrate. Unless otherwise stated, compressive stress (including surface CS) is measured using a surface stress meter (FSM), using, for example, a commercial instrument such as the FSM-6000 manufactured by Orihara Corporation. Surface stress measurement relies on the accurate measurement of the stress-optical coefficient (SOC), which is related to the birefringence of the glass. Unless otherwise stated, SOC is measured according to Protocol C (Glass Disc Method) as described in ASTM Standard C770-16, entitled "Standard Test Method for Measurement of Glass Stress-Optical Coefficient," the entirety of which is incorporated herein by reference. When stress is generated by exchanging sodium ions into the substrate and the measured article is thicker than about 400 μm, SCALP is used to measure the depth of compression and central tension (CT). When stress is generated in the substrate and / or part by exchanging both potassium and sodium ions into the substrate and / or part and the measured article is thicker than about 400 μm, SCALP is used to measure the depth of compression and CT. Without wishing to be bound by theory, the depth of exchange of sodium can represent the depth of compression, while the depth of exchange of potassium ions can represent the change in the magnitude of the compressive stress (but not the change in stress from compression to tension).A graph representing the stress distribution can also be obtained using the refracted near field (RNF; RNF method) described in U.S. Patent No. 8,854,623, entitled “Systems and methods for measuring a profile characteristic of a glass sample” (the entirety of which is incorporated herein by reference). When the RNF method is used to obtain a graph representing the stress distribution, the maximum central tension value provided by SCALP is used in the RNF method. The graph representing the stress distribution obtained by RNF is force balanced and calibrated using the maximum central tension value provided by the SCALP measurement. As used herein, “depth of layer” (DOL) refers to the depth of exchange of ions (e.g., sodium, potassium) into the substrate and / or part. In the present disclosure, when the maximum central tension cannot be directly measured by SCALP (when the article being measured is thinner than about 400 μm), the maximum central tension can be approximated by dividing the product of the maximum compressive stress and the compression depth by the difference between the substrate thickness and twice the compressive stress, where the compressive stress and the compression depth are measured by FSM. Throughout this disclosure, the absolute value of the compressive stress is reported as the compressive stress, and the absolute value of the central tensile stress is reported as the central tensile stress.

[0154] In terms of Figure 2 As shown, the first major surface 203 of the foldable substrate 201 may include a first compressive stress region 212 extending from the first major surface 203 to a first compressive depth 216. Although not shown, the first compressive stress region 212 may also include a first layer depth of one or more alkali metal ions (e.g., potassium) associated with the first compressive stress region. Figure 2 As shown, the second major surface 205 of the foldable substrate 201 may include a second compressive stress region 214 extending from the second major surface 205 to a second compressive depth 218. Although not shown, the second compressive stress region 214 may also include a second layer depth of one or more alkali metal ions (e.g., potassium) associated with the first compressive stress region. Figure 2 As shown, dashed lines 213 and 215 correspond to the locations where the stress in the foldable substrate switches from compression to tension (or vice versa), corresponding to the boundaries of the corresponding compressive stress region (i.e., the compression depth). It is to be understood that Figure 2 The first compressive stress region 212 and / or the second compressive stress region 214 of the foldable substrate 201 of the foldable device 101 shown may also be present in other foldable devices (e.g., Figure 3-5 In the foldable devices 301 and / or 401 shown, although Figure 3-5 not clearly marked).

[0155] In aspects, the first compression depth 216 and / or the second compression depth 218 can be, as a percentage of the substrate thickness 209, about 5% or greater, about 10% or greater, about 12% or greater, about 14% or greater, about 16% or greater, about 18% or greater, about 20% or greater, about 30% or less, about 26% or less, or about 22% or less, about 20% or less, about 19% or less, about 18% or less, about 17% or less, or about 16% or less. In aspects, the first compression depth 216 and / or the second compression depth 218 can be, as a percentage of the substrate thickness 209, in a range of about 5% to about 30%, about 10% to about 26%, about 12% to about 22%, about 14% to about 20%, about 16% to about 19%, about 16% to about 19%, about 16% to about 18%, or any range or sub-range therebetween. In other aspects, the first compression depth 216 and / or the second compression depth 218 can be about 15% or greater, such as in the range of about 16% to about 30%, about 16% to about 26%, about 18% to about 24%, about 20% to about 22%, or any range or sub-range therebetween, as a percentage of the substrate thickness 209. In exemplary aspects, the first compression depth 216 and / or the second compression depth 218 can be in the range of about 10% to about 30%, about 12% to about 19%, or about 16% to about 26%, as a percentage of the substrate thickness 209.

[0156] In aspects, the first compression depth 216 and / or the second compression depth 218 can be: about 1 μm or greater, 3 μm or greater, about 4 μm or greater, about 5 μm or greater, about 6 μm or greater, about 7 μm or greater, about 10 μm or greater, about 11 μm or greater, about 12 μm or greater, about 13 μm or greater, about 30 μm or less, about 25 μm or less, about 20 μm or less, about 17 μm or less, about 15 μm or less, about 14 μm or less, about 13 μm or less, about 12 μm or less, about 10 μm or less, about 9 μm or less, about 8 μm or less, or about 7 μm or less. In aspects, the first compression depth 216 and / or the second compression depth 218 can be in a range of about 1 μm to about 30 μm, about 3 μm to about 25 μm, about 3 μm to about 20 μm, about 4 μm to about 17 μm, about 5 μm to about 15 μm, about 6 μm to about 14 μm, about 6 μm to about 13 μm, about 7 μm to about 12 μm, about 7 μm to about 10 μm, or any range or sub-range therebetween. In aspects, the first compression depth 216 and / or the second compression depth 218 can be about 10 μm or less, for example, in a range of about 3 μm to about 10 μm, about 5 μm to about 10 μm, about 6 μm to about 9 μm, about 7 μm to about 8 μm, or any range or sub-range therebetween. In certain aspects, the first compression depth 216 and / or the second compression depth 218 can be about 10 μm or greater, such as, for example, a range of about 10 μm to about 20 μm, about 10 μm to about 17 μm, about 11 μm to about 15 μm, about 12 μm to about 14 μm, about 12 μm to about 13 μm, or any range or sub-range therebetween. In certain aspects, the first compression depth 216 and / or the second compression depth 218 can be a range of about 3 μm to about 20 μm, about 5 μm to about 9 μm, or about 10 μm to about 15 μm.

[0157] In aspects, the first layer depth and / or the second layer depth of the one or more alkali metal ions (e.g., potassium) can be about 5% or more, about 10% or more, about 12% or more, about 14% or more, about 16% or more, about 18% or more, about 20% or more, about 30% or less, about 26% or less, or about 22% or less, about 20% or less, about 19% or less, about 18% or less, about 17% or less, or about 16% or less, as a percentage of the substrate thickness 209. In aspects, the first layer depth and / or the second layer depth of the one or more alkali metal ions (e.g., potassium) can be in the range of about 5% to about 30%, about 10% to about 26%, about 12% to about 22%, about 14% to about 20%, about 16% to about 19%, about 16% to about 19%, about 16% to about 18%, or any range or sub-range therebetween, as a percentage of the substrate thickness 209. In one aspect, the first layer depth and / or the second layer depth of the one or more alkali metal ions (e.g., potassium) can be about 15% or greater, such as in the range of about 16% to about 30%, about 16% to about 26%, about 18% to about 24%, about 20% to about 22%, or any range or sub-range therebetween, as a percentage of the substrate thickness 209. In a preferred aspect, the first layer depth and / or the second layer depth of the one or more alkali metal ions (e.g., potassium) can be in the range of about 10% to about 30%, about 12% to about 19%, or about 16% to about 26%, as a percentage of the substrate thickness 209.

[0158] In aspects, the first layer depth and / or the second layer depth of one or more alkali metal ions (e.g., potassium) can be: about 1 μm or greater, 3 μm or greater, about 4 μm or greater, about 5 μm or greater, about 6 μm or greater, about 7 μm or greater, about 10 μm or greater, about 11 μm or greater, about 12 μm or greater, about 13 μm or greater, about 30 μm or less, about 25 μm or less, about 20 μm or less, about 17 μm or less, about 15 μm or less, about 14 μm or less, about 13 μm or less, about 12 μm or less, about 10 μm or less, about 9 μm or less, about 8 μm or less, or about 7 μm or less. In aspects, the first layer depth and / or the second layer depth of one or more alkali metal ions (e.g., potassium) can be in the range of about 1 μm to about 30 μm, about 3 μm to about 25 μm, about 3 μm to about 20 μm, about 4 μm to about 17 μm, about 5 μm to about 15 μm, about 6 μm to about 14 μm, about 6 μm to about 13 μm, about 7 μm to about 12 μm, about 7 μm to about 10 μm, or any range or sub-range therebetween. In aspects, the first layer depth and / or the second layer depth of one or more alkali metal ions (e.g., potassium) can be about 10 μm or less, for example, in the range of about 3 μm to about 10 μm, about 5 μm to about 10 μm, about 6 μm to about 9 μm, about 7 μm to about 8 μm, or any range or sub-range therebetween. In one embodiment, the first compression depth 216 and / or the second compression depth 218 can be about 10 μm or greater, such as in the range of about 10 μm to about 20 μm, about 10 μm to about 17 μm, about 11 μm to about 15 μm, about 12 μm to about 14 μm, about 12 μm to about 13 μm, or any range or sub-range therebetween. In a preferred embodiment, the first layer depth and / or the second layer depth of one or more alkali metal ions (e.g., potassium) can be in the range of about 3 μm to about 20 μm, about 5 μm to about 9 μm, or about 10 μm to about 15 μm.

[0159] In one aspect, the first compressive stress region 212 can include a first maximum compressive stress and / or the second compressive stress region 214 can include a second maximum compressive stress. In other aspects, the first maximum compressive stress can be substantially equal to the second maximum compressive stress. In other aspects, the first maximum compressive stress and / or the second maximum compressive stress can be about 500 megapascals (MPa) or greater, about 600 MPa or greater, about 650 MPa or greater, about 700 MPa or greater, about 750 MPa or greater, about 800 MPa or greater, about 850 MPa or greater, about 900 MPa or greater, about 950 MPa or greater, about 1,000 MPa or greater, about 1050 MPa or greater, about 1,500 MPa or less, about 1,300 MPa or less, about 1,200 MPa or less, about 1,150 MPa or less, about 1,100 MPa or less, about 1,050 MPa or less, about 1,000 MPa or less, about 950 MPa or less, about 900 MPa or less, about 850 MPa or less, or about 800 MPa or less. In other aspects, the first maximum compressive stress and / or the second maximum compressive stress can be in the range of about 500 MPa to about 1,500 MPa, about 600 MPa to about 1,300 MPa, about 650 MPa to about 1,250 MPa, about 650 MPa to about 1,200 MPa, about 700 MPa to about 1,150 MPa, about 750 MPa to about 1,100 MPa, about 800 MPa to about 1,050 MPa, about 850 MPa to about 1,000 MPa, about 900 MPa to about 950 MPa, or any range or sub-range therebetween. In other aspects, the first maximum compressive stress and / or the second maximum compressive stress can be about 700 MPa or greater, such as in the range of about 700 MPa to about 1500 MPa, about 700 MPa to about 1300 MPa, about 700 MPa to about 1200 MPa, about 750 MPa to about 1150 MPa, about 800 MPa to about 1100 MPa, about 850 MPa to about 1100 MPa, about 900 MPa to about 1050 MPa, or any range or sub-range therebetween. In other aspects, the maximum first compressive stress and / or the maximum second compressive stress can be about 1000 MPa or greater, such as in the range of about 1000 MPa to about 1500 MPa, about 1000 MPa to about 1300 MPa, about 1000 MPa to about 1200 MPa, about 1050 MPa to about 1150 MPa, or any range or sub-range therebetween. In preferred aspects, the first maximum compressive force and / or the second maximum compressive stress can be in a range of about 650 MPa to about 1200 MPa, about 750 MPa to about 1100 MPa, or about 850 MPa to about 1200 MPa.

[0160] In aspects, the substrate thickness 209 can be about 50 μm or thicker (e.g., about 50 μm to about 100 μm, about 50 μm to about 90 μm, or any corresponding subranges therebetween as discussed above) and combined with one or more of the following properties: (1) a compression depth (e.g., the first compression depth 216 and / or the second compression depth 218) of about 10% to about 30%, about 16% to about 26%, or any corresponding subranges therebetween as discussed above, as a percentage of the substrate thickness 209; 2) the depth of layer (e.g., the first depth of layer and / or the second depth of layer) of potassium ranges from about 3 μm to about 20 μm, from about 10 μm to about 15 μm, or any corresponding sub-ranges discussed above; and / or (3) the maximum compressive stress (e.g., the first maximum compressive stress and / or the second maximum compressive stress) ranges from about 650 MPa to about 1200 MPa, from about 800 MPa to about 1100 MPa, from about 850 MPa to about 1200 MPa, or any corresponding sub-ranges discussed above. In aspects, the substrate thickness 209 can be about 50 μm or less (e.g., about 10 μm to about 50 μm, about 10 μm to about 30 μm, or any corresponding subranges therebetween as discussed above) and combined with one or more of the following properties: (1) a compression depth (e.g., the first compression depth 216 and / or the second compression depth 218) of about 10% to about 30%, about 12% to about 19%, or any corresponding subranges therebetween as discussed above, as a percentage of the substrate thickness 209; (2) the depth of layer (e.g., the first depth of layer and / or the second depth of layer) of potassium is in the range of about 3 μm to about 20 μm, about 5 μm to about 9 μm, or any corresponding sub-ranges discussed above; and / or (3) the maximum compressive stress (e.g., the first maximum compressive stress and / or the second maximum compressive stress) can be in the range of about 650 MPa to about 1200 MPa, about 750 MPa to about 1100 MPa, about 750 MPa to about 1000 MPa, or any corresponding sub-ranges discussed above.

[0161] Throughout this disclosure, ASTM D638 is used to determine the tensile strength, ultimate elongation (e.g., failure strain), and yield point of polymeric materials (e.g., adhesives, polymer-based parts) using a tensile testing machine (e.g., Instron 3400 or Instron 6800) at 23° C. and 50% relative humidity using a Type I dog-bone shaped sample. Throughout this disclosure, ISO 527-1:2019 is used to measure elastic modulus (e.g., Young's modulus) and / or Poisson's ratio. Throughout this disclosure, the resonant ultrasonic spectroscopy technique proposed in ASTM E2001-13, entitled “Standard Guide for Resonant Ultrasound Spectroscopy for Defect Detection in Both Metallic and Non-metallic Parts,” is used to measure the Young's modulus of glass-based materials and ceramic-based materials. In aspects, the foldable substrate 201 can comprise an elastic modulus of about 10 gigapascals (GPa) or more, about 40 GPa or more, about 60 GPa or more, about 70 GPa or more, about 100 GPa or less, about 80 GPa or less, about 60 GPa or less, or about 20 GPa or less. In other aspects, the foldable substrate 201 can comprise a glass-based portion comprising an elastic modulus in the range of about 10 GPa to about 100 GPa, about 40 GPa to about 100 GPa, about 60 GPa to about 100 GPa, about 80 GPa to about 100 GPa, or any range or sub-range therebetween.

[0162] The transmittance and haze values ​​reported herein were measured using a BYK Haze-Gard Dual (BYK Gardner). In aspects, an "optically transparent material" or "optically clear material" can have an average transmittance of 75% or greater, 80% or greater, 85% or greater, or 90% or greater, 92% or greater, 93% or greater, 94% or greater, 95% or greater, or 96% or greater, through a 0.7 mm thick sheet of the material over the wavelength range of 400 nm to 700 nm. The average transmittance over the wavelength range of 400 nm to 700 nm is calculated by measuring the transmittance at integer wavelengths from about 400 nm to about 700 nm and averaging the measurements. In aspects, the foldable substrate can be optically transparent. In aspects, the foldable substrate 201 can comprise an average transmittance (averaged over a wavelength of light between 400 nm and 700 nm) of about 80% or greater, about 90% or greater, about 91% or greater, about 92.0% or greater, about 92.2% or greater, about 92.5% or greater, about 92.8% or greater, about 93.0% or greater, about 99% or less, about 96% or less, about 95% or less, or about 94% or less. In aspects, the foldable substrate 201 can comprise an average transmittance (averaged over a wavelength of light between 400 nm and 700 nm) of about 80% to about 99%, about 90% to about 96%, about 90% to about 95%, about 91% to about 95%, about 92.0% to about 95%, about 92.2% to about 94%, about 92.5% to about 94%, about 92.8% to about 93%, or any range or sub-range therebetween.

[0163] As used herein, haze refers to transmission haze, which is measured according to ASTM D1003-21 through the first major surface 203 at 0° normal to the first major surface 203. Haze was measured using a BYK Haze-Gard Dual (BYK Gardner). CIE D65 illuminant was used as the light source for illuminating the foldable substrate 201. The haze values ​​reported herein were measured through a substrate comprising a thickness of 0.7 mm, with light incident on the first major surface 203 measured as it exits the first major surface 203. In other aspects, the haze of the foldable substrate 201 can be: about 5% or less, about 2% or less, about 1% or less, about 0.8% or less, about 0.5% or less, or about 0.3% or less. In other aspects, the haze of the foldable substrate 201 can be in the range of about 0.01% to about 5%, about 0.05% to about 2%, about 0.1% to about 1%, about 0.1% to about 0.8%, about 0.2% to about 0.5%, or any range or sub-range therebetween.

[0164] like Figure 2-3As shown, foldable substrate 201 can include a first major surface 203 and a second major surface 205 opposite first major surface 203. In one aspect, first major surface 203 can extend along a first plane, and / or second major surface 205 can extend along a second plane. In other aspects, the second plane (second major surface 205) can be parallel to the first plane (first major surface 203). As used herein, substrate thickness 209 of foldable substrate 201 is defined as the average distance between first major surface 203 and second major surface 205. In one aspect, foldable substrate 201 can be an ultra-thin substrate, meaning substrate thickness 209 is approximately 100 microns or less. In aspects, substrate thickness 209 can be about 10 micrometers (μm) or thicker, about 15 μm or thicker, about 20 μm or thicker, about 25 μm or thicker, about 30 μm or thicker, about 40 μm or thicker, about 50 μm or thicker, about 60 μm or thicker, about 70 μm or thicker, about 100 μm or thinner, about 95 μm or thinner, about 90 μm or thinner, about 85 μm or thinner, about 80 μm or thinner, about 75 μm or thinner, about 70 μm or thinner, about 60 μm or thinner, about 50 μm or thinner, about 40 μm or thinner, about 30 μm or thinner, or about 25 μm or thinner. In aspects, the substrate thickness 209 can range from about 10 μm to about 100 μm, about 15 μm to about 95 μm, about 20 μm to about 80, about 25 μm to 75 μm, about 30 μm to about 70 μm, about 40 μm to about 60 μm, about 40 μm to about 50 μm, or any range or sub-range therebetween. In aspects, the substrate thickness 209 can be about 50 μm or thicker, which can exhibit better impact resistance and / or puncture resistance and reasonable foldability compared to even thinner foldable substrates (e.g., a parallel plate spacing of 5 mm as discussed below), such as the range from about 50 μm to about 100 μm, about 50 μm to about 95 μm, about 50 μm to about 90 μm, about 60 μm to about 80 μm, about 70 μm to about 75 μm, or any range or sub-range therebetween. In aspects, substrate thickness 209 can be about 50 μm or less, which can exhibit increased foldability (e.g., parallel plate spacing of 3 mm or less or 2 mm or less, as discussed below) compared to thicker substrates, such as a range of about 10 μm to about 50 μm, about 15 μm to about 50 μm, about 20 μm to about 45 μm, about 25 μm to about 40 μm, about 30 μm to about 40 μm, or any range or sub-range therebetween. In aspects, as shown, the local thickness of foldable substrate 201 can be substantially uniform (e.g., substantially equal to substrate thickness 209) across first major surface 203 and / or second major surface 205.

[0165] As used herein, if a first layer and / or component is described as being “disposed above” a second layer and / or component, there may or may not be other layers between the first layer and / or component and the second layer and / or component. In addition, as used herein, “disposed above” does not indicate a relative position with reference to gravity. For example, a first layer and / or component may be considered to be “disposed above” a second layer and / or component when the first layer and / or component is disposed below, above, or to one side of the second layer and / or component. As used herein, describing a first layer and / or component as being “bonded to” a second layer and / or component refers to mutual bonding of the layers and / or components, either by direct contact and / or bonding between the two layers and / or components or via an adhesive layer. As used herein, describing a first layer and / or component as being “in contact with” or “in contact with” a second layer and / or component refers to direct contact and includes mutual bonding of the layers and / or components.

[0166] like Figure 3 As shown, foldable device 301 can include adhesive layer 311. As shown, adhesive layer 311 can include a first contact surface 313 and a second contact surface 315 that can be opposite first contact surface 313. In aspects, as shown, first contact surface 313 of adhesive layer 311 can include a flat surface, and / or second contact surface 315 of adhesive layer 311 can include a flat surface. Adhesive thickness 319 of adhesive layer 311 can be defined as the average distance between first contact surface 313 and second contact surface 315. In aspects, adhesive thickness 319 of adhesive layer 311 can be: about 1 μm or thicker, about 5 μm or thicker, about 10 μm or thicker, about 100 μm or thinner, about 60 μm or thinner, about 30 μm or thinner, or about 20 μm or thinner. In aspects, the adhesive thickness 319 of the adhesive layer 311 can be in the range of about 1 μm to about 100 μm, about 5 μm to about 60 μm, about 10 μm to about 30 μm, about 10 μm to about 20 μm, or any range or sub-range therebetween. Figure 3 As shown, the first contact surface 313 of the adhesive layer 311 can face and / or contact the first major surface 203 of the foldable substrate 201. Figure 3 As shown, the second contact surface 315 of the adhesive layer 311 can face and / or contact another layer (eg, the PET sheet 321 discussed below).

[0167] In one embodiment, the adhesive layer 311 may include one or more of the following: polyolefins, polyamides, halogenated polymers (e.g., polyvinyl chloride or fluoropolymers), elastomers, urethanes, phenolic resins, polyparaxylene, polyethylene terephthalate (PET), and polyetheretherketone (PEEK). Exemplary aspects of polyolefins include low molecular weight polyethylene (LDPE), high molecular weight polyethylene (HDPE), ultra-high molecular weight polyethylene (UHMWPE), and polypropylene (PP). Exemplary aspects of fluoropolymers include polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), perfluoropolyether (PFPE), perfluorosulfonic acid (PFSA), perfluoroalkoxylate (PFA), fluorinated ethylene propylene (FEP) polymer, and ethylene tetrafluoroethylene (ETFE) polymer. Exemplary aspects of elastomers include rubbers (e.g., polybutadiene, polyisoprene, chloroprene rubber, butyl rubber, nitrile rubber) and block copolymers (e.g., styrene-butadiene, high impact polystyrene, poly(dichlorophosphazene)). In other aspects, the adhesive layer 311 may include an optically clear adhesive. In even other aspects, the optically clear adhesive may include one or more optically clear polymers: acrylics (e.g., polymethyl methacrylate (PMMA)), epoxides, silicones, and / or polyurethanes. Examples of epoxides include bisphenol-based epoxies, phenolic-based epoxies, cycloaliphatic-based epoxies, and glycidylamine-based epoxies. In even other aspects, the optically clear adhesive may include, but is not limited to, acrylic adhesives (e.g., 3M's 8212 adhesive) or optically clear liquid adhesives (e.g., LOCTITE optically clear liquid adhesive). Exemplary aspects of optically clear adhesives include transparent acrylics, epoxies, silicones, and polyurethanes. For example, the optically clear liquid adhesive may include one or more of the following: LOCTITE AD 8650, LOCTITE AA 3922, LOCTITE EA E-05MR, LOCTITE UK U-09LV, all available from Henkel.

[0168] In aspects, although not shown, the coating can be disposed over the second major surface 205 of the foldable substrate 201. In even other aspects, the coating can have a coating thickness of about 0.1 μm or greater, about 1 μm or greater, about 5 μm or greater, about 10 μm or greater, about 15 μm or greater, about 20 μm or greater, about 25 μm or greater, about 40 μm or greater, about 50 μm or greater, about 60 μm or greater, about 70 μm or greater, about 80 μm or greater, about 90 μm or greater, about 200 μm or less, about 100 μm or less, or about 50 μm or less, about 30 μm or less, about 25 μm or less, about 20 μm or less, about 20 μm or less, about 15 μm or less, or about 10 μm or less. In other aspects, the coating can have a coating thickness in the range of about 0.1 μm to about 200 μm, about 1 μm to about 100 μm, about 10 μm to about 100 μm, about 20 μm to about 100 μm, about 30 μm to about 100 μm, about 40 μm to about 100 μm, about 50 μm to about 100 μm, about 60 μm to about 100 μm, about 70 μm to about 100 μm, about 80 μm to about 100 μm, about 90 μm to about 100 μm, about 0.1 μm to about 50 μm, about 1 μm to about 50 μm, about 10 μm to about 50 μm, or any range or sub-range therebetween.

[0169] In aspects, coating can include polymer coating. In other aspects, polymer coating can include one or more of the following: ethylene-acid copolymer, polyurethane-based polymer, acrylate resin and mercapto-ester resin. Exemplary aspects of ethylene-acid copolymer include: ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, and ethylene-acrylic acid-methacrylic acid terpolymer (e.g., Nucrel (DuPont (DuPont))), ionomer of ethylene acid copolymer (e.g., Surlyn (DuPont)) and ethylene-acrylic acid copolymer amine dispersion (e.g., Aquacer (BYK)). Exemplary aspects of polyurethane-based polymer include water-based modified polyurethane dispersion (e.g., Eleglas (Axalta)). Exemplary aspects of UV-curable acrylate resins include acrylate resins (e.g., Uvekol resins (Allinex Corporation)), cyanoacrylate adhesives (e.g., Permabond UV620 (Krayden Corporation)), and UV free radical acrylic resins (e.g., Ultrabond windshield repair resins, such as Ultrabond (45CPS)). Exemplary aspects of mercapto-ester resins include mercapto-ester triallyl isocyanurate (e.g., Norland Optical Adhesive NOA61). In other aspects, the polymer coating may include ethylene-acrylic acid copolymers and ethylene-methacrylic acid copolymers, which may be ionomerized by neutralization of carboxylic acid residues with typical alkali metal ions (e.g., sodium and potassium) and also zinc to form ionomer resins. Such ethylene-acrylic acid and ethylene-methacrylic acid ionomers may be dispersed in water and applied to a substrate to form an ionomer coating. Alternatively, such acid copolymers may be neutralized with ammonia, which releases the ammonia to reform the acid copolymer as a coating after application and drying. By providing a coating comprising a polymer coating, the foldable device can include low energy rupture.

[0170] In aspect, coating can comprise the polymer coating that comprises optically transparent polymer coating.Suitable material for optically transparent polymer coating includes but is not limited to: solidified acrylate resin material, inorganic-organic hybrid polymer material, aliphatic or aromatic six-functional urethane acrylate, hybrid material based on siloxane, and nano composite material (for example, epoxy and urethane material with nano silicate). In aspect, optically transparent polymer coating can be made up of one or more of these materials basically. In aspect, optically transparent polymer coating can be made up of one or more of these materials. As used herein, " inorganic-organic hybrid polymer material " refers to the polymer material comprising monomer with inorganic and organic components. Obtain inorganic-organic hybrid polymer by polymerization reaction between monomer with inorganic group and organic group. Inorganic-organic hybrid polymer is not the nano composite material (for example, inorganic particles are dispersed in organic matrix) that comprises separated inorganic and organic composition or phase. More specifically, suitable materials for optically transparent polymer (OTP) coatings include, but are not limited to, polyimide, polyethylene terephthalate (PET), polycarbonate (PC), polymethyl methacrylate (PMMA), organic polymer materials, inorganic-organic hybrid polymer materials, and aliphatic or aromatic hexafunctional urethane acrylates. In one aspect, the OTP coating may be essentially composed of an organic polymer material, an inorganic-organic hybrid polymer material, or an aliphatic or aromatic hexafunctional urethane acrylate. In one aspect, the OTP coating may be composed of a polyimide, an organic polymer material, an inorganic-organic hybrid polymer material, or an aliphatic or aromatic hexafunctional urethane acrylate. In one aspect, the OTP coating may include a nanocomposite material. In one aspect, the OTP coating may include at least one of a nanosilicate, an epoxide, and a urethane material. U.S. Patent Publication No. 2015 / 0110990 describes suitable compositions for such OTP coatings, the entirety of which is incorporated herein by reference. As used herein, "organic polymer material" refers to a polymer material comprising monomers having only organic components. In one aspect, the OTP coating may include an organic polymer material having a hardness of 9H manufactured by Gunze Co., Ltd., for example, Gunze's "High Durability Transparent Film". As used herein, "inorganic-organic hybrid polymer material" refers to a polymer material comprising monomers having inorganic and organic components. Inorganic-organic hybrid polymers are obtained by polymerization reactions between monomers having inorganic groups and organic groups. Inorganic-organic hybrid polymers are not nanocomposites comprising separate inorganic and organic components or phases (for example, inorganic particles dispersed in an organic matrix). In one aspect, the inorganic-organic hybrid polymer material may include polymerized monomers comprising inorganic silicon-based groups, for example, silsesquioxane polymers.The silsesquioxane polymer may be, for example, an alkyl-silsesquioxane, an aryl-silsesquioxane, or a silsesquioxane having the following chemical structure (RSiO. 1.5 )n arylalkyl-silsesquioxane, wherein R is an organic group such as, but not limited to, methyl or phenyl. In one aspect, the OTP coating may include a silsesquioxane polymer bound to an organic matrix, such as, for example, SILPLUS manufactured by Nippon Steel Chemical Co., Ltd. In one aspect, the OTP coating may include: 90 wt% to 95 wt% of an aromatic hexafunctional urethane acrylate (e.g., PU662NT (aromatic hexafunctional urethane acrylate) manufactured by Miwon Specialty Chemicals), and 10 wt% to 5 wt% of a photoinitiator (e.g., Darocur 1173 manufactured by Ciba Specialty Chemicals), with a hardness of 8H or greater. In one aspect, an OTP coating comprising an aliphatic or aromatic hexafunctional urethane acrylate can be formed as a free-standing layer by spin coating the layer onto a polyethylene terephthalate (PET) substrate, curing the urethane acrylate, and removing the urethane acrylate layer from the PET substrate. The OTP coating can have a coating thickness ranging from 1 μm to 150 μm, including subranges; for example, 10 μm to 140 μm, 20 μm to 130 μm, 30 μm to 120 μm, 40 μm to 110 μm, 50 μm to 100 μm, 60 μm to 90 μm, 70 μm to 80 μm, or any range or subrange therebetween. In one aspect, the OTP coating can be a monolithic single layer. In one aspect, the OTP coating can be a layer of an inorganic-organic hybrid polymer material or a layer of an organic polymer material having a thickness ranging from 80 μm to 120 μm, including subranges. For example, an OTP coating comprising an inorganic-organic hybrid polymer material or an organic polymer material can have a thickness of 80 μm to 110 μm, 90 μm to 100 μm, or any range or sub-range therebetween. In aspects, the OTP coating can be a layer of an aliphatic or aromatic hexafunctional urethane acrylate material having one or more thickness ranges discussed in this paragraph or above for coating thickness.

[0171] In aspects, if provided, the coating may further comprise one or more of the following: an easy-to-clean coating, a low-friction coating, an oleophobic coating, a diamond-like coating, a scratch-resistant coating, or a wear-resistant coating. The scratch-resistant coating may comprise an oxynitride, such as aluminum oxynitride or silicon oxynitride having a thickness of about 500 μm or more. In such aspects, the wear-resistant layer may comprise the same material as the scratch-resistant layer. In aspects, the low-friction coating may comprise a highly fluorinated silane coupling agent, such as an alkylfluorosilane having oxymethyl groups as side chains on the silicon atom. In such aspects, the easy-to-clean coating may comprise the same material as the low-friction coating. In other aspects, the easy-to-clean coating may comprise protonatable groups, such as amines, such as alkylaminosilane having oxymethyl groups as side chains on the silicon atom. In such aspects, the oleophobic coating may comprise the same material as the easy-to-clean coating. In aspects, the diamond-like coating comprises carbon and may be produced by applying a high voltage potential in the presence of a hydrocarbon plasma.

[0172] In terms of Figure 3As shown, a layer (e.g., PET sheet 321) can be disposed over the first major surface 203 of the foldable substrate 201 and / or the layer (e.g., PET sheet 321) can be attached to the foldable substrate 201 via the adhesive layer 311. In other aspects, the layer (e.g., PET sheet 321) can be disposed over and / or in contact with the second contact surface 315 of the adhesive layer 311. In other aspects, as shown, a first surface area 323 of the PET sheet 321 can face the first major surface 203 of the foldable substrate 201, can face the second contact surface 315 of the adhesive layer 311, and / or can contact the second contact surface 315 of the adhesive layer 311. The thickness 329 of the PET sheet 321 is defined as the average distance between the first surface area 323 and a second surface area 325 opposite the first surface area 323. As discussed below with reference to the pen drop test, the adhesive thickness 319 of the adhesive layer 311 (e.g., optically clear adhesive 8212 available from 3M) can be 50 μm, and the thickness 329 of the PET sheet 321 can be 100 μm, although other materials and / or thicknesses are possible in other aspects of the foldable device. For example, in other aspects, the layer (e.g., the PET sheet) can include a polymer material (not limited to PET), such as polyester (e.g., polyethylene terephthalate (PET)) and polyolefin (e.g., low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP)). Furthermore, in other aspects, the layer (e.g., the PET sheet 321) can be replaced by a release liner, which can include paper and / or polymers. Exemplary aspects of paper include kraft paper, machine-finished paper, multi-layer coated paper (e.g., polymer-coated paper, glassine paper, siliconized paper), or clay-coated paper. Additionally or alternatively, the layer may include and / or comprise a display device, such as a liquid crystal display (LCD), an electrophoretic display (EPD), an organic light emitting diode (OLED) display, or a plasma display panel (PDP). The display device may be part of a portable electronic device (e.g., a consumer electronic product, a smartphone, a tablet, a wearable device, or a laptop computer).

[0173] Aspects of the present disclosure may include consumer electronic products. The consumer electronic product may include a front surface, a back surface, and side surfaces. The consumer electronic product may also include an electronic component at least partially located within a housing. The electronic component may include a controller, a memory, and a display. The display may be located on the front surface of the housing or adjacent to the front surface of the housing. The display may include: a liquid crystal display (LCD), an electrophoretic display (EPD), an organic light emitting diode (OLED) display, or a plasma display panel (PDP). The consumer electronic product may include a cover substrate arranged above the display. In aspects, at least one of a portion of the housing or the cover substrate includes a foldable device discussed throughout this disclosure. The consumer electronic product may include a portable electronic product, such as a smartphone, a tablet, a wearable device, or a laptop computer.

[0174] The foldable devices disclosed herein can be incorporated into another article, such as an article having a display screen (or display article) (e.g., consumer electronics, including mobile phones, tablets, computers, navigation systems, and wearable devices (e.g., watches), etc.), a building article, a transportation article (e.g., a vehicle, a train, an aircraft, a marine vehicle, etc.), an electrical article, or any article that can benefit from partial transparency, scratch resistance, wear resistance, or a combination thereof. Exemplary articles incorporating any of the foldable devices 101 and / or 301 and / or foldable substrates 201 disclosed herein are as follows: Figure 8-9 Specifically, Figure 8-9 A consumer electronic device 800 is shown, which includes a housing 802 having a front surface 804, a back surface 806, and side surfaces 808. Although not shown, the consumer electronic device may include electronic components that are at least partially located within the housing or completely located within the housing. For example, the electronic components may include at least a controller, a memory, and a display. Figure 8-9 As shown, display 810 can be located on or adjacent to the front surface of housing 802. The consumer electronic device can include a cover substrate 812 located on or above the front surface of housing 802, such that it is located above display 810. In one embodiment, at least one of cover substrate 812 or a portion of housing 802 can include any foldable device disclosed herein (e.g., foldable substrate 201).

[0175] also, Figure 7A schematic diagram of a foldable consumer electronic product 701 is shown in elevation. The consumer electronic product 701 can include a foldable device 101 and / or 301 and / or a foldable substrate 201 according to aspects of the present disclosure. As shown, the consumer electronic product 701 can include a front surface 703 and a side surface 705. The consumer electronic product 701 can include electronic components, including a display screen 702 that can be viewed through the front surface 703. In aspects, as shown, the consumer electronic product 701 can be folded in a direction 712 to form a folded configuration in which a first end 727 and a second end 727 (opposite the first end 737) are closer to each other (compared to a non-folded configuration). In addition, as shown, the consumer electronic product 701 can be folded so that the front surface 703 and / or the display screen 702 face toward itself, but the consumer electronic product can also be folded in the opposite direction 712 so that the front surface 703 is located on the outside of the consumer electronic product when in the folded configuration. Figure 15 The illustrated consumer electronic product 701 can be folded about a fold axis 102, wherein a central portion 781 is located between a first portion 721 including a first end 727 and a second portion 731 including a second end 737. The position of the fold axis 102 determines a first distance 713 between the first end 727 and the fold axis 102 (e.g., in direction 106) relative to a second distance 715 between the second end 737 and the fold axis 102 (e.g., in direction 708). The overall length of the consumer electronic product (e.g., Figure 1 The length 105 in FIG. 105 may be the sum of the first distance 713 and the second distance 715. Additionally, as shown, the consumer electronic product is shown in a folded or partially folded configuration with the front surface 703 forming an angle A about the fold axis 102.

[0176] Throughout this disclosure, refractive index is measured according to ASTM E1967-19, wherein the first wavelength includes 589 nm. In aspects, the first refractive index of the foldable substrate 201 can be about 1.4 or greater, about 1.45 or greater, about 1.48 or greater, about 1.49 or greater, about 1.50 or greater, about 1.6 or less, about 1.57 or less, or about 1.55 or less, about 1.53 or less, or about 1.52 or less. In aspects, the first refractive index of the foldable substrate 201 can be in the range of about 1.4 to about 1.6, about 1.45 to about 1.57, about 1.48 to about 1.55, about 1.49 to about 1.53, about 1.50 to about 1.52, or any range or sub-range therebetween.

[0177] In aspects, adhesive layer 311 can include a second refractive index within one or more of the ranges discussed above with respect to the first refractive index of the foldable substrate. In aspects, the difference in absolute value equivalent to the difference between the second refractive index of adhesive layer 311 and the first refractive index of foldable substrate 201 can be about 0.1 or less, about 0.07 or less, about 0.05 or less, about 0.001 or greater, about 0.01 or greater, or about 0.02 or greater. In aspects, the difference can be in the range of about 0.001 to about 0.1, about 0.001 to about 0.07, about 0.01 to about 0.07, about 0.01 to about 0.05, about 0.02 to about 0.05, or any range or sub-range therebetween. In aspects, the second refractive index of adhesive layer 311 can be greater than the first refractive index of foldable substrate 201. In aspects, the second refractive index of adhesive layer 311 can be less than the first refractive index of foldable substrate 201.

[0178] Figure 5 Aspects of a foldable device 401 comprising and / or consisting of a foldable substrate 201 according to aspects of the present disclosure are schematically shown in a folded configuration. Figure 4 As shown, foldable device 401 is folded such that second major surface 205 of foldable substrate 201 is located on the outside of foldable device 401, while first major surface 203 is located on the inside of foldable device 401. In the folded configuration, although not shown, if the display device is located on the inside of the curve, the user would view the display device through foldable substrate 201 and would therefore be located to the side of second major surface 205. Alternatively, if the display device is located on the outside of the curve, the user would view the display device through foldable substrate 201 and would therefore be located to the side of first major surface 203. Alternatively, although not shown, the foldable device can be folded such that the first major surface of the foldable substrate is located on the outside of the folded foldable device, wherein the user would view the display device through the foldable substrate and would therefore be located opposite the display device.

[0179] As used herein, "foldable" includes fully foldable, partially foldable, curved, bent, or multiple folding functions. As used herein, the terms "failure" and "fault" and the like refer to rupture, destruction, delamination, or crack propagation. If the foldable device resists failure when maintained at a parallel plate spacing of "X" for 10 minutes at about 25°C and about 50% relative humidity, the foldable device achieves a parallel plate spacing of "X", or withstands a parallel plate spacing of "X", or has a parallel plate spacing of "X", or includes a parallel plate spacing of "X". Similarly, if the foldable device resists failure when maintained at a parallel plate spacing of "X" for 10 minutes at about 50°C and about 50% relative humidity, the foldable device achieves a parallel plate spacing of "X", or has a parallel plate spacing of "X", or includes a parallel plate spacing of "X". In aspects, the foldable substrate and / or the foldable device may be rollable. As used herein, a foldable substrate or foldable device is "rollable" if it can achieve a threshold parallel plate spacing over a corresponding foldable substrate and / or foldable device length that is greater than 10 mm or 10% of the length of the corresponding foldable substrate and / or foldable device. Throughout this disclosure, the "survival rate" or % of samples that survived a parallel plate spacing of X mm refers to the percentage of at least 20 samples that survived bending to a parallel plate spacing of X mm.

[0180] As used herein, a parallel plate apparatus 501 (see Figure 5 ) is used to measure the "parallel plate distance" of a foldable device and / or foldable substrate, wherein the parallel plate device 501 includes a pair of parallel rigid stainless steel plates 503 and 505, which includes a first rigid stainless steel plate 503 and a second rigid stainless steel plate 505. When measuring the "parallel plate distance", the foldable device or foldable substrate is placed as is (without modification) between the pair of parallel rigid stainless steel plates 503 and 505. For example, Figure 4 As shown, it will be Figure 2 A foldable device 101, shown as being comprised of a foldable substrate 201, is placed in an unmodified manner between a pair of parallel rigid stainless steel plates 503 and 505, with the second major surface of the foldable substrate 201 contacting the pair of parallel rigid stainless steel plates 503 and 505 as a foldable device 401. To determine the "parallel plate spacing," the spacing between the parallel plates is reduced at a rate of 1 millimeter per second (mm / second) until the parallel plate spacing 511 equals the "parallel plate spacing" to be tested. The parallel plates are then maintained at the "parallel plate spacing" to be tested for 10 minutes at approximately 85°C and approximately 85% relative humidity. As used herein, the "minimum parallel plate spacing" is the minimum parallel plate spacing that the foldable device can withstand without failure under the conditions and configurations described above.

[0181] In aspects, the foldable device 101, 301, and / or 401 and / or the foldable substrate 201 can achieve a parallel plate spacing of 20 mm or less, 10 mm or less, 7 mm or less, 5 mm or less, 3 mm or less, 2 mm or less, or 1 mm or less. In aspects, the foldable device 101, 301, and / or 401 and / or the foldable substrate 201 can include a minimum parallel plate spacing of about 5 mm or less, 4 mm or less, about 3 mm or less, about 2 mm or less, or about 1 mm or less. In aspects, the foldable device 101, 301, and / or 401 and / or the foldable substrate 201 can include a minimum parallel plate spacing in a range of about 0.5 mm to about 5 mm, about 0.5 mm to about 4 mm, about 0.5 mm to about 3 mm, about 0.5 mm to about 2 mm, about 1 mm to about 2 mm, or any range or sub-range therebetween.

[0182] In aspects, at a parallel plate spacing of 5 mm, the foldable substrate 201 can exhibit a survival rate of about 90% or more, about 92% or more, about 95% or more, about 97% or more, about 98% or more, about 99% or more, or about 100% (i.e., about 90% or more, about 92% or more, about 95% or more of a sample of the foldable substrate can survive a parallel plate spacing of 5 mm, etc.). In aspects, at a parallel plate spacing of 3 mm, the foldable substrate 201 can exhibit a survival rate of about 90% or more, about 92% or more, about 95% or more, about 97% or more, about 98% or more, about 99% or more, or about 100% (i.e., about 90% or more, about 92% or more, about 95% or more of a sample of the foldable substrate can survive a parallel plate spacing of 3 mm, etc.). In aspects, at a parallel plate spacing of 3 mm, the foldable substrate 201 can exhibit a survival rate of about 30% or more, about 35% or more, about 40% or more, about 50% or more, about 55% or more, about 60% or more, about 65% or more, about 70% or more, about 75% or more, about 80% or more, about 85% or more, about 90% or more, about 95% or more, or about 100% (i.e., about 30% or more, about 35% or more, about 40% or more of the samples of the foldable substrate can withstand a parallel plate spacing of 3 mm, etc.). In aspects, at a parallel plate spacing of 2 mm, the foldable substrate 201 can exhibit a survival rate of about 90% or more, about 92% or more, about 95% or more, about 97% or more, about 98% or more, about 99% or more, or about 100% (i.e., about 90% or more, about 92% or more, about 95% or more of a sample of the foldable substrate can survive a parallel plate spacing of 2 mm, etc.). In aspects, at a parallel plate spacing of 1 mm, the foldable substrate 201 can exhibit a survival rate of about 10% or more, about 15% or more, about 20% or more, about 25% or more, about 30% or more, about 40% or more, or about 50% (i.e., about 10% or more, about 15% or more, about 20% or more of a sample of the foldable substrate can survive a parallel plate spacing of 1 mm, etc.).

[0183] In aspects, when the foldable substrate 201 includes a substrate thickness 209 of about 50 μm or greater (e.g., about 50 μm to about 100 μm, about 50 μm to about 90 μm, or any corresponding sub-ranges discussed above), it can exhibit: (1) a survival rate of about 90% or greater, 92% or greater, and / or 95% or greater (e.g., about 90% to about 100%, about 92% to about 99%, about 95% to about 97%) at a parallel plate spacing of 5 mm, and / or (2) a survival rate of about 30% or greater, 35% or greater, or about 40% or greater (e.g., about 30% to about 50%, about 35% to about 45%) at a parallel plate spacing of 3 mm. In aspects, when the foldable substrate 201 includes a substrate thickness 209 of about 50 μm or less (e.g., about 10 μm to about 50 μm, about 10 μm to about 30 μm, or any corresponding sub-ranges discussed above), it can exhibit: (1) a survival rate of about 90% or greater, 92% or greater, 95% or greater, 97% or greater, 98% or greater, or 99% or greater (e.g., about 90% to about 100%, about 92% to 100%, or about 95% to about 99%) at a parallel plate spacing of 5 mm; (2) a survival rate of about 80% or greater, about 90% or greater, or about 95% or greater at a parallel plate spacing of 3 mm. (e.g., about 80% to about 100%, about 90% to 100%, or about 95% to about 99%); (3) a survival rate of about 90% or greater, about 92% or greater, about 95% or greater, or about 97% or greater at a parallel plate spacing of 2 mm (e.g., about 90% to about 100%, about 92% to 100%, about 95% to about 99%, or about 97% to about 99%); and / or (4) a survival rate of about 10% or greater, about 15% or greater, or about 20% or greater (e.g., about 10% to about 50%, about 15% to 40%, about 20% to about 30%) at a parallel plate spacing of 1 mm.

[0184] When measured according to a "pen drop test," a foldable device and / or foldable substrate can have impact resistance defined as the ability of a region of the foldable device and / or foldable substrate to avoid failure at a pen drop height (e.g., 5 centimeters (cm) or greater, 10 centimeters or greater, 20 cm or greater). As used herein, a "pen drop test" is performed in the following manner: a sample of the foldable device and / or foldable substrate is tested such that a load (i.e., a pen dropped from a certain height) strikes a major surface (e.g., the second major surface 205 of the foldable substrate 201 and / or the foldable device 101 and / or 301), the foldable substrate 201 being configured as shown. Figure 3As shown, a PET sheet 321 having a thickness 329 of 100 μm is attached to an adhesive layer 311 having a thickness of 50 μm and composed of an optically clear adhesive 8212 (available from 3M) and in contact with the first major surface 203 of the foldable substrate 201. Thus, the purpose of the PET sheet in the pen drop test is to simulate a foldable electronic display device (e.g., an OLED device). During the test, the foldable substrate 201 bonded to the PET sheet was placed on an aluminum plate (6063 aluminum alloy, polished to a surface roughness of 400 grit paper), with the PET sheet 321 in contact with the aluminum plate. No tape was used on the side of the sample that was on the aluminum plate.

[0185] The pen drop test uses a guide tube to guide the pen to the outer surface of the foldable device. Figure 2-3 5 and the foldable device 101, 301 and / or 401 and / or the foldable substrate 201 (as modified as described in the previous paragraph), the pen is guided to the second major surface 205 of the foldable substrate 201, and the conduit is placed in contact with the second major surface 205 of the foldable substrate 201 so that the longitudinal axis of the conduit is substantially perpendicular to the second major surface 205, and the longitudinal axis of the conduit extends in the direction of gravity. Figure 6 The writing device 601 includes a ballpoint pen 603, which is a BIC Easy Glide Pen, Fine, including a 0.7 mm (0.68 mm) diameter tungsten carbide ballpoint tip 605 and a weight of 5.73 grams (g) including the pen cap. The ballpoint pen 603 is held at a predetermined height 609 (see FIG. 1 ) from the outer surface of the sample (e.g., the second major surface 205 of the foldable device 201). Figure 3 The foldable device 301 is shown. A guide tube (not shown for clarity) is used as part of the pen drop device 601 to guide the ballpoint pen 603 to the outer surface of the sample (e.g., the second major surface 205 of the foldable substrate 201), and the guide tube is placed in contact with the outer surface so that the longitudinal axis of the guide tube is substantially perpendicular to the outer major surface, and the longitudinal axis of the guide tube extends in the direction of gravity. The guide tube has an outer diameter of 1 inch (2.54 cm), an inner diameter of 9 / 16 inches (1.4 cm), and a length of 90 cm. For each test, the ballpoint pen 603 was held at a predetermined height 609 using an acrylonitrile butadiene ("ABS") washer (not shown). After each drop, the guide tube was repositioned relative to the sample to guide the pen to a different impact location on the sample.

[0186] For the pen drop test, the pen is dropped with the cap attached to the top (i.e., the end opposite the pen tip) so that the ballpoint tip can interact with the test sample. In the drop sequence according to the pen drop test, the pen is dropped once at an initial height of 1 cm, followed by drops in 0.5 cm increments (up to 20 cm), and then after 20 cm, in 2 cm increments until the test sample fails. After each drop, any observable evidence of cracks, failures, or other damage to the sample is recorded, as well as the specific height of the drop. Using the pen drop test, multiple samples can be tested according to the same drop sequence to produce groups with improved statistical accuracy. For the pen drop test, the pen is replaced with a new pen after every five drops and for each new sample tested. In addition, all pen drops are made at a random position on the sample at or near the center of the sample, and no pen drops are made at or near the edge of the sample.

[0187] For the purposes of the pen drop test, "failure" refers to the formation of a visible mechanical defect in the laminate. A mechanical defect can be a crack or plastic deformation (e.g., a surface indentation). A crack can be a surface crack or a through-crack. Cracks can form on the interior or exterior surface of the laminate. Cracks can extend through all or a portion of the foldable substrate 201. A visually visible mechanical defect has a minimum dimension of 0.2 mm or greater.

[0188] In aspects, the foldable substrate 201 and / or foldable device 101 and / or 301 resists failure for a pen drop height of 10 centimeters (cm), 12 cm, 14 cm, 16 cm, or 20 cm. In aspects, the maximum pen drop height that the foldable substrate 201 and / or foldable device 101 and / or 301 can withstand without failure can be about 10 cm or greater, about 12 cm or greater, about 14 cm or greater, about 15 cm or greater, about 16 cm or greater, about 18 cm or greater, about 20 cm or greater, about 40 cm or less, or about 30 cm or less, about 25 cm or less, about 20 cm or less, or about 15 cm or less. In aspects, the maximum pen drop height that the foldable substrate 201 and / or foldable device 101 and / or 301 can withstand without failure can be in the range of about 10 cm to about 40 cm, about 12 cm to about 40 cm, about 14 cm to about 30 cm, about 16 cm to about 30 cm, about 18 cm to about 30 cm, about 20 cm to about 25 cm, or any range or sub-range therebetween. In aspects, when the substrate thickness 209 of the foldable substrate 201 is about 50 μm or greater (e.g., about 50 μm to about 100 μm, about 50 μm to about 90 μm, or any corresponding sub-ranges discussed above), the foldable substrate 201 can withstand pen drops from a pen drop height of 15 cm or greater, or even 20 cm or greater. In aspects, when the substrate thickness 209 of the foldable substrate 201 is about 50 μm or less (e.g., about 10 μm to about 50 μm, about 10 μm to about 30 μm, or any corresponding sub-ranges discussed above), the foldable substrate 201 can withstand a pen drop from a pen drop height of 10 cm or more.

[0189] Will refer to Figure 10 Flowchart and Figure 12-15 The exemplary method steps shown and Figure 16 The cross-sectional view shown in FIG. Figure 2-3 5 (e.g., in the method of manufacturing the foldable device 101, 301 and / or 401) are discussed.

[0190] In the first step 1001 of the method of the present disclosure, Figure 11-12As shown, the method can begin by providing a foldable substrate 1111. In one aspect, the foldable substrate 1111 can be provided by purchasing or obtaining the substrate in any other manner or by forming the foldable substrate. In one aspect, the foldable substrate 1111 can include a glass-based substrate. In other aspects, the glass-based substrate can be provided by forming it through various strip forming processes, such as: slot drawing, down drawing, fusion down drawing, up drawing, roller pressing, redrawing or float glass. In other aspects, a glass-based substrate containing ceramic crystals can be provided by heating the glass-based substrate to crystallize one or more ceramic crystals. The foldable substrate 1111 can include an existing first major surface 1113 and an existing second major surface 1115 opposite the existing first major surface 1113. In other aspects, the initial thickness 1119 of the foldable substrate 1111 (defined as the average spacing between the existing first major surface 1113 and the existing second major surface 1115) can be within one or more of the ranges discussed above and / or can be within 5 μm of the final thickness (e.g., substrate thickness 209) (i.e., 0.1 μm to about 5 μm or about 0.5 μm to about 4 μm greater than the final thickness). In other aspects, the existing first major surface 1113 and / or the existing second major surface 1115 can extend along a plane. In aspects, the foldable substrate 1111 can have a composition within one or more of the ranges discussed above with respect to glass-based substrates (e.g., foldable substrate 201). In aspects, at the conclusion of step 1001, the foldable substrate 1111 can be substantially unreinforced. As used herein, substantially unreinforced refers to a substrate comprising no depth of layer, no compression depth, a depth of layer ranging from 0% to about 5% of the substrate thickness, or a compression depth ranging from 0% to about 5% of the substrate thickness.

[0191] After step 1001, Figure 11 As shown, the method can optionally proceed to step 1003, including heating the foldable substrate 1111 at a predetermined temperature for a predetermined period of time. Figure 11As shown, heating the foldable substrate 1111 can include placing the foldable substrate 1111 in an environment (e.g., oven 1101) maintained at a predetermined temperature for a predetermined period of time. In one aspect, the predetermined temperature can be about 250°C or higher, about 270°C or higher, about 280°C or higher, about 290°C or higher, about 300°C or higher, about 350°C or lower, about 330°C or lower, about 320°C or lower, about 310°C or lower, or about 300°C or lower. In one aspect, the predetermined temperature can be in the range of about 250°C to about 350°C, about 270°C to about 330°C, about 270°C to about 320°C, about 280°C to about 310°C, about 280°C to about 300°C, or any range or sub-range therebetween. In one aspect, the predetermined temperature can be less than the first temperature maintained by the molten salt solution used in step 1005 (discussed below). In one aspect, the predetermined time period can be about 10 minutes or more, about 20 minutes or more, about 30 minutes or more, about 45 minutes or more, about 1 hour or more, about 4 hours or less, about 2 hours or less, about 1.5 hours or less, or about 1 hour or less. In one aspect, the predetermined time period can be in the range of about 10 minutes to about 4 hours, about 20 minutes to about 2 hours, about 30 minutes to about 1.5 hours, about 45 minutes to about 1 hour, or any range or sub-range therebetween. Heating the foldable substrate prior to the chemical strengthening treatment of step 1005 can reduce thermal shock to the foldable substrate and contribute to a more uniform compressive stress region on the surface of the foldable substrate.

[0192] After step 1001 or 1003, if Figure 12 As shown, the method can proceed to step 1005, including contacting at least the first major surface 1113 with a molten salt solution 1203 maintained at a first temperature for a first period of time to establish at least an initial compressive stress region. Figure 12 As shown, the molten salt solution 1203 can be contained in the molten salt bath 1201. In aspects, as Figure 12As described above, contacting at least the existing first major surface 1113 with the molten salt solution 1203 may include immersing the foldable substrate 1111 in the molten salt solution 1203, for example, contacting both the existing first major surface 1113 and the existing second major surface 1115 with the molten salt solution 1203. However, in other aspects, only a portion of the foldable substrate (e.g., the existing first major surface) may be in contact with the molten salt solution. When first cations within the surface depth of the foldable substrate 1111 are exchanged with second cations in the molten salt solution 1203 having a larger radius than the first cations, the foldable substrate 1111 is chemically strengthened by ion exchange. For example, lithium cations within the surface depth of the foldable substrate 1111 may be exchanged with sodium cations or potassium cations in the molten salt solution 1203. Similarly, sodium cations within the surface depth of the foldable substrate 1111 may be exchanged with potassium cations in the molten salt solution 1203, thereby establishing compressive stress in the foldable substrate 1111. Therefore, the surface of the foldable substrate 1111 is in compression and thus chemically strengthened by the ion exchange process because the radius of the lithium cations is smaller than the radius of the exchanged sodium or potassium cations in the molten salt solution 1203.

[0193] In one aspect, the first temperature of the molten salt solution 1203 can be about 350°C or greater, about 360°C or greater, about 370°C or greater, about 380°C or greater, about 400°C or less, about 390°C or less, or about 380°C or less. In one aspect, the first temperature of the molten salt solution 1203 can be in the range of about 350°C to about 400°C, about 360°C to about 400°C, about 370°C to about 390°C, about 380°C to about 390°C, or any range or sub-range therebetween. As demonstrated in the embodiments discussed herein, providing a first temperature of the molten salt solution below 400°C can increase the maximum compressive stress established for a predetermined depth of layer and / or depth of compression. Furthermore, for some of the molten salt solutions discussed herein, a temperature of 350°C or greater can be used to ensure salt melting. Without wishing to be bound by theory, it is believed that lower temperature molten salt solutions (eg, about 400°C or lower, about 350°C to about 400°C) improve substrate properties by preventing stress relaxation and providing more controlled and uniform compressive stress across the substrate.

[0194] In aspects, the first time period that foldable substrate 1111 (e.g., having first major surface 1113) is in contact with molten salt solution 1203 can be about 10 minutes or more, about 15 minutes or more, about 20 minutes or more, about 30 minutes or more, about 45 minutes or more, about 60 minutes or more, about 90 minutes or less, about 75 minutes or less, about 60 minutes or less, about 45 minutes or less, about 30 minutes or less, about 20 minutes or less, or about 15 minutes or less. In aspects, the first time period that foldable substrate 1111 (e.g., having first major surface 1113) is in contact with molten salt solution 1203 can be in the range of about 10 minutes to about 90 minutes, about 15 minutes to about 75 minutes, about 20 minutes to about 60 minutes, about 30 minutes to about 45 minutes, or any range or sub-range therebetween. In aspects, the first time period in which the foldable substrate 1111 (e.g., having the first major surface 1113) is in contact with the molten salt solution 1203 can be about 30 minutes or less, such as in the range of about 5 minutes to about 30 minutes, about 10 minutes to about 20 minutes, about 10 minutes to about 15 minutes, or any range or sub-range therebetween.

[0195] In one embodiment, the molten salt solution 1203 may include at least two anions associated with different salts. In other aspects, the at least two anions may be associated with different potassium salts, and the molten salt solution 1203 may include potassium ions in addition to the at least two anions. In even other aspects, the concentration of the first potassium salt and the concentration of the second potassium salt in the molten salt solution 1203 may be 2% or more (e.g., 2.0% or more), 2.5% or more, 3.0% or more, 4.0% or more, 5.0% or more, 7% or more, 8% or more, or 10% or more by weight, based on a total of 100% by weight of the molten salt solution 1203 (i.e., before immersion in the foldable substrate 1111). Unless otherwise specified, the composition of the molten salt solution 1203 refers to the composition before immersion in the foldable substrate 1111 and is based on a total of 100% by weight of the molten salt solution 1203. It is to be understood that the molten salt solution may include additional components beyond the two potassium salt components discussed herein, such as sodium salts, lithium salts, silicic acid, or combinations thereof. For example, the molten salt solution may include silicic acid in an amount, based on the weight percent excess addition of the molten salt solution excluding silicic acid, of 0.1 weight percent or more, about 0.3 weight percent or more, about 0.5 weight percent or more, about 1.0 weight percent or less, about 0.7 weight percent or less, or about 0.5 weight percent, such as in the range of about 0.1 weight percent to about 1.0 weight percent, about 0.3 weight percent to about 0.7 weight percent, about 0.3 weight percent to about 0.5 weight percent, or any range or sub-range therebetween.

[0196] In other aspects, the concentration of the first potassium salt in the molten salt solution 1203 can be about 2 wt % or more (e.g., about 2.0 wt % or more), about 2.5 wt % or more, about 3.0 wt % or more, about 4.0 wt % or more, about 5.0 wt % or more, about 7 wt % or more, about 8 wt % or more, about 10 wt % or more, about 12 wt % or less, about 10 wt % or less, about 8 wt % or less, about 5 wt % or less (e.g., about 5.0 wt % or less), about 4.0 wt % or less, or about 3.0 wt % or less. In other aspects, the concentration of the first potassium salt in the molten salt solution 1203 can be in a range from about 2 wt % to about 12 wt %, about 2.5 wt % to about 10 wt %, about 3.0 wt % to about 8 wt %, about 4.0 wt % to about 5 wt %, or any range or sub-range therebetween. In other aspects, the concentration of the first potassium salt in the molten salt solution 1203 can be about 5 wt% or more, such as in the range of about 5 wt% to about 12 wt%, about 7 wt% to about 12 wt%, about 8 wt% to about 10 wt%, or any range or sub-range therebetween. In other aspects, the concentration of the first potassium salt in the molten salt solution 1203 can be about 5.0 wt% or less, such as in the range of about 2.0 wt% to about 5.0 wt%, about 2.5 wt% to about 5.0 wt%, about 3.0 wt% to about 4.0 wt%, or any range or sub-range therebetween. In preferred aspects, the concentration of the first potassium salt in the molten salt solution (based on 100 wt% of the molten salt solution before immersing the foldable substrate therein) can be about 2 wt% to about 12 wt%, about 2.0 wt% to about 5.0 wt%, or about 5 wt% to about 12 wt%.

[0197] In other aspects, the first potassium salt may include two or more potassium atoms per anion. Providing the first potassium salt with multiple (i.e., two or more) potassium atoms per anion can increase the effective concentration and / or activity of potassium in the molten salt solution, which can contribute to an increase in the maximum compressive stress in the resulting chemically strengthened foldable substrate. Throughout this disclosure, the pKa of potassium salts is measured according to OPPTS 830.7370 "Dissociation Constants in Water" (August 1996) of the U.S. Environmental Protection Agency, available from the National Environmental Publications Service. In other aspects, the first potassium salt may include a pKa of about 9 or greater, about 10 or greater, about 10.5 or greater, about 11 or greater, about 20 or less, about 15 or less, about 13 or less, or about 12 or less. In other aspects, the first potassium salt can include a pKa in the range of about 9 to about 20, about 10 to about 15, about 10.5 to about 13, about 11 to about 12, or any range or sub-range therebetween. Providing a pKa of about 9 or greater for the first potassium salt in the molten salt solution can improve the strength and / or foldability of the resulting chemically strengthened foldable substrate, for example by selectively etching defects inherent in the foldable substrate that might otherwise be amplified by the chemical strengthening process. Exemplary aspects of potassium salts having more than two potassium atoms per anion and a pKa of about 9 or greater include potassium carbonate (K2CO3) and potassium phosphate (K3PO4). A preferred aspect of the first potassium salt is potassium carbonate (K2CO3), and the concentration of potassium carbonate (as the first potassium salt) can be within one or more of the corresponding ranges discussed in the previous paragraphs (e.g., about 2 wt% to about 12 wt%, about 2.0 wt% to about 5.0 wt%, or about 5 wt% to about 12 wt%). As discussed herein with reference to the Examples, potassium carbonate (K2CO3) provides a more pronounced and unexpected increase in compressive stress than other components in the molten salt solution. Furthermore, without wishing to be bound by theory, it is believed that carbonate anions facilitate the precipitation of other cations (e.g., lithium, sodium) exchanged from the foldable substrate, which can increase the lifespan of the molten salt solution (e.g., by removing components from the solution phase that would otherwise "poison" the molten salt solution).

[0198] In other aspects, the molten salt solution comprises a second potassium salt associated with the two or more anions, wherein the anion of the first potassium salt is different from the anion of the second potassium salt. In even other aspects, the second potassium salt can be one or more potassium nitrate (KNO3) and / or potassium chloride (KCl). A preferred aspect of the second potassium salt is potassium nitrate (KNO3). In other aspects, the concentration of the second potassium salt (e.g., potassium nitrate) in the molten salt solution can be about 50 weight % or more, about 60 weight % or more, about 70 weight % or more, about 80 weight % or more, about 84 weight % or more, about 88 weight % or more, about 89 weight % or more, about 90 weight % or more, about 91 weight % or more, about 92 weight % or more, about 93 weight % or more, about 94 weight % or more, about 95.0 weight % or more (e.g., about 95 weight % or more), about 96.0 weight % or more, about 97.0 weight % or more, about 97.5 weight % or more, or about 98.0 weight % or more (e.g., 98 weight % or more). In other aspects, the concentration of the second potassium salt (e.g., potassium nitrate) in the molten salt solution can be in the range of about 50 weight % to about 98.0 weight %, about 60 weight % to about 98 weight %, about 70 weight % to about 98 weight %, about 80 weight % to about 98 weight %, about 84 weight % to about 98 weight %, about 88 weight % to about 98.0 weight %, about 89 weight % to about 97.5 weight %, about 90 weight % to about 97.0 weight %, about 91 weight % to about 96.5 weight %, about 92 weight % to about 96.0 weight %, about 93 weight % to about 95.5 weight %, about 94 weight % to about 95.0 weight %, or any range or sub-range therebetween. In other aspects, the concentration of the second potassium salt (e.g., potassium nitrate) in the molten salt solution can be about 88% by weight or higher, such as in the range of about 88% by weight to about 98% by weight, about 88% by weight to about 97.5% by weight, about 88% by weight to about 97.0% by weight, about 88% by weight to about 96.0% by weight, about 88% by weight to about 95.0% by weight, about 88% by weight to about 94.0% by weight, about 88% by weight to about 93.0% by weight, about 88% by weight to about 92.0% by weight, about 89% by weight to about 91% by weight, about 90% by weight to about 91% by weight, or any range or sub-range therebetween. In other aspects, the concentration of the second potassium salt (e.g., potassium nitrate) in the molten salt solution can be about 95.0% by weight or higher, such as in the range of about 95.0% by weight to about 98.0% by weight, about 95.0% by weight to about 97.5% by weight, about 96.0% by weight to about 97.0% by weight, or any range or sub-range therebetween. In preferred aspects, the concentration of the second potassium salt (eg, potassium nitrate) in the molten salt solution can be in the range of about 50 wt % to about 98 wt %, about 88 wt % to about 98 wt %, or about 95 wt % to about 98 wt %.

[0199] In other aspects, the molten salt solution 1203 can include a third potassium salt associated with a third anion of the at least two anions, wherein the third anion is different from the anions associated with the first and second potassium salts (discussed above). In even other aspects, the third potassium salt can have two or more potassium atoms per anion (similar to the first potassium salt). An exemplary aspect of the third potassium salt is potassium sulfate, K2SO4. For example, the molten salt solution 1203 can include K2CO3 as the first potassium salt, KNO3 as the second potassium salt, and K2SO4 as the (optional) third potassium salt. In even other aspects, the concentration of the third potassium salt (e.g., potassium sulfate) in the molten salt solution can be: 0 weight % or more, about 0.1 weight % or more, about 0.3 weight % or more, about 0.5 weight % or more, about 0.8 weight % or more, about 1.0 weight % or more, about 1.2 weight % or more, about 1.5 weight % or more, about 1.8 weight % or more, about 2.0 weight % or more, about 2.5 weight % or more, about 3.0 weight % or more high, about 3.5 wt % or more, about 4.0 wt % or more, about 5 wt % or less (e.g., about 5.0 wt % or less), about 4.5 wt % or less, about 4.0 wt % or less, about 3.5 wt % or less, about 3.0 wt % or less, about 2.5 wt % or less, about 2.0 wt % or less, about 1.5 wt % or less, about 1.0 wt % or less, about 0.8 wt % or less, or about 0.5 wt % or less. In even other aspects, the concentration of the third potassium salt (e.g., potassium sulfate) in the molten salt solution can be in the range of about 0 weight % to about 5 weight %, about 0.1 weight % to about 5.0 weight %, about 0.2 weight % to about 5.0 weight %, about 0.5 weight % to about 5.0 weight %, about 0.8 weight % to about 4.5 weight %, about 1.0 weight % to about 4.0 weight %, about 1.2 weight % to about 3.5 weight %, about 1.5 weight % to about 3.0 weight %, about 1.8 weight % to about 2.5 weight %, about 2.0 weight % to about 2.5 weight %, or any range or sub-range therebetween. In even other aspects, the concentration of the third potassium salt (e.g., potassium sulfate) in the molten salt solution can be about 2.0 wt % or less, such as a range from about 0 wt % to about 2.0 wt %, about 0 wt % to about 1.5 wt %, about 0.1 wt % to about 1.0 wt %, about 0.1 wt % to about 0.8 wt %, about 0.2 wt % to about 0.5 wt %, or any range or sub-range therebetween.

[0200] Due to the presence of the first potassium salt (e.g., potassium carbonate having a pKa of 9 or greater), in one aspect, the molten salt solution 1203 can be alkaline (i.e., a pH greater than 7). In other aspects, the pH of the molten salt solution 1203 can be about 8 or greater, about 9 or greater, about 10 or greater, about 10.5 or greater, about 11 or greater, about 15 or less, about 13 or less, or about 12 or less. In other aspects, the pH of the molten salt solution 1203 can be in the range of about 8 to about 15, about 9 to about 13, about 9 to about 12, about 10 to about 13, about 10.5 to about 12, or any range or subrange therebetween. In preferred aspects, the pH of the molten salt solution can be in the range of about 9 to 12 or about 10 to 12. Providing a molten salt solution having a pH of about 9 to 12 can improve the strength and / or foldability of the resulting chemically strengthened foldable substrate by, for example, selectively etching defects inherent in the foldable substrate that might otherwise be amplified by the chemical strengthening process. Figure 13-14 16, the chemical strengthening treatment of step 1005 can produce an initial first compressive stress region 1212 and / or an initial second initial compressive stress region 1214. For example, the presence of the first potassium salt can increase the compressive stress imparted by contacting the existing first major surface with the molten salt solution 1203 (at least in step 1005) by about 5% or more (e.g., about 10% or more, about 5% to about 20%, about 5% to about 15%, or about 7% to about 10%) relative to immersing the foldable substrate in a comparative molten salt solution having the same composition as the molten salt solution without the first potassium salt.

[0201] In the aspect, after step 1005, as Figure 13 As shown, the method can proceed to step 1007, which includes transferring the foldable substrate 1111 to the cooling chamber 1301 and allowing the temperature of the cooling chamber to decrease from the initial temperature to the final temperature. Figure 13 As shown, the foldable substrate 1111 may still contain residual portions of the molten salt solution (represented by droplets 1305) and / or deposits 1303 on the surface (e.g., the existing first major surface 1113) resulting from contact with the molten salt solution in step 1005. In even other aspects, such as Figure 13 As shown, the foldable substrate 1111 can be suspended in the cooling chamber 1301, for example, to facilitate removal of residual portions of the molten salt solution (shown by droplets 1305) from the foldable substrate 1111, which will move in the direction of gravity (not shown, but assumed to be Figure 13 The liquid crystal material flows away from the foldable substrate 1111 (center downward).

[0202] In aspects, the initial temperature of the cooling chamber 1301 (e.g., when the foldable substrate 1111 is placed therein) can be about 300° C. or less, about 280° C. or less, about 260° C. or less, about 240° C. or less, about 220° C. or less, about 180° C. or more, about 190° C. or more, about 200° C. or more, about 210° C. or more, or about 220° C. or more. In aspects, the initial temperature of the cooling chamber 1301 (e.g., when the foldable substrate 1111 is placed therein) can be in the range of about 180° C. to about 300° C., about 190° C. to about 280° C., about 200° C. to about 260° C., about 210° C. to about 240° C., about 210° C. to about 220° C., or any range or sub-range therebetween. In preferred aspects, the initial temperature of cooling chamber 1301 can be in the range of about 180° C. to about 300° C. or about 180° C. to about 220° C. In other aspects, the difference between the first temperature maintained at molten salt solution 1203 in step 1005 and the initial temperature of cooling chamber 1301 in step 1007 (i.e., the first temperature minus the initial temperature) can be about 50° C. or greater, about 75° C. or greater, about 100° C. or greater, about 120° C. or greater, about 140° C. or greater, or about 160° C. or greater. Providing an initial temperature of the cooling chamber that is lower than the molten salt solution (e.g., by about 50° C. or greater, about 100° C. or greater, or about 140° C. or greater) can reduce residual chemical strengthening that occurs due to any residual portion of the molten salt solution or deposits from the molten salt solution on the foldable substrate after removal from the molten salt solution. Specifically, it was observed that foldable substrates having a thickness of about 50 μm or less (e.g., about 10 μm to about 50 μm or about 10 μm to about 30 μm) were unexpectedly sensitive to events that occurred after the foldable substrate was removed from the molten salt solution. For these thin foldable substrates, even relatively small differences in compressive stress on their surfaces can result in ripples and / or warping, which can produce optical distortion that is visually visible to users of consumer electronic products that may incorporate the foldable substrate. Therefore, the controlled temperature of the cooling chamber can contribute to relatively uniform compressive stress on the surface of the foldable substrate. In addition, providing an initial cooling chamber temperature of 180°C or higher (e.g., 200°C or higher or 220°C or higher) can facilitate the removal of residual portions of the molten salt solution before it solidifies. Without wishing to be bound by theory, the first potassium salt can have a higher melting temperature than the second potassium salt, which means that incorporating the first potassium salt into the molten salt solution can increase the viscosity of the molten salt solution and / or can cause the molten salt solution to solidify at a higher temperature than a molten salt solution without the first potassium salt. Thus, when the molten salt solution comprises the first potassium salt, allowing a residual portion of the molten salt solution on the foldable substrate after it is removed from the molten salt solution can be particularly useful.

[0203] In other aspects, the final temperature of the cooling chamber 1301 can be about 25°C or higher, about 40°C or higher, about 60°C or higher, about 70°C or higher, about 100°C or lower, about 90°C or lower, or about 80°C or lower, about 70°C or lower, or about 60°C or lower. In other aspects, the final temperature of the cooling chamber 1301 can be in the range of about 25°C to about 100°C, about 40°C to about 90°C, about 60°C to about 90°C, about 60°C to about 80°C, about 70°C to about 80°C, or any range or sub-range therebetween. Lowering the temperature of the cooling chamber to a final temperature of about 100°C or lower (e.g., about 25°C to about 100°C or about 60°C to about 90°C) can allow for subsequent (e.g., relatively quick or immediate) treatment of the foldable substrate with an aqueous solution (e.g., rinsing with water or an alkaline detergent solution, contact with an aqueous acidic solution).

[0204] In other aspects, the cooling rate of the temperature of the cooling scheme can be achieved by using an environment with sufficient ventilation and / or circulation (e.g., air) through the cooling chamber. In other aspects, the cooling rate of the temperature of the cooling scheme (e.g., from the initial temperature to the final temperature) can be: about 4°C per minute (°C / min) or greater, about 6°C / min or greater, about 8°C / min or greater, about 10°C / min or greater, about 12°C / min or greater, about 14°C / min or greater, about 20°C / min or less, about 18°C / min or less, about 16°C / min or less, about 14°C / min or less, or about 10°C / min or less. In other aspects, the cooling rate of the temperature of the cooling scheme (e.g., from the initial temperature to the final temperature) can be in the range of about 4°C / minute to about 20°C / minute, about 6°C / minute to about 18°C / minute, about 8°C / minute to about 16°C / minute, about 10°C / minute to about 14°C / minute, about 12°C / minute to about 14°C / minute, or any range or sub-range therebetween. Providing a cooling rate of about 4°C / minute to about 20°C / minute can allow the temperature of the cooling chamber (and the foldable substrate) to decrease rapidly while maintaining a relatively uniform temperature throughout the cooling chamber (and / or the foldable substrate), for example, to generate a relatively uniform compressive stress on the surface of the foldable substrate.

[0205] In the aspect, after step 1005 or 1007, as Figure 14As shown, the method can proceed to step 1009, including (e.g., after removing the foldable substrate from the molten salt solution in step 1005 and / or after the cooling chamber reaches the final temperature) washing the foldable substrate 1111 with the solution 1403. In other aspects, the solution 1403 can be contained in the bath 1401 and / or the foldable substrate 1111 can be immersed in the solution 1403 (e.g., with the first major surface 1113 and the second major surface 1115 in contact with the solution 1403). In other aspects, as Figure 13 and 14As shown in the figure, solution 1403 can remove (e.g., dissolve and / or replace) deposits 1303 from the molten salt solution left on the foldable substrate 1111. In some aspects, solution 1403 can be subjected to oscillation (e.g., ultrasonic oscillation) to further promote the removal of deposits 1303 and / or contaminants on the surface that may interfere with the uniform treatment of the surface of the foldable substrate in subsequent steps. In other aspects, solution 1403 can be: water (e.g., purified water, filtered water, deionized water and / or distilled water), an alkaline detergent solution, or a combination thereof. As used herein, the pH of a solution is measured according to ASTM E70-90 at 25°C with a standard solution extending to a pH of at least 14. In even other aspects, the alkaline detergent solution (e.g., solution 1403) can comprise an alkaline detergent and a pH of about 11 or greater, about 12 or greater, about 12.5 or greater, about 12.8 or greater, about 14 or less, about 13.5 or less, or about 13.2 or less. In aspects, the alkaline detergent solution (e.g., solution 1403) can comprise a pH range of about 11 to about 14, about 12 to about 14, about 12.5 to about 13.5, about 12.8 to about 13.2, or any range or subrange therebetween. In aspects, the alkaline detergent solution (e.g., solution 1403) can comprise an alkaline detergent at a concentration of about 0.5% by weight or greater, about 1% by weight or greater, about 1.5% by weight or greater, about 2% by weight or greater, about 4% by weight or less, about 3% by weight or less, or about 2.5% by weight or less. In aspects, the alkaline detergent solution (e.g., solution 1403) can comprise an alkaline detergent in a concentration range of about 0.5% to about 4% by weight, about 1% to about 4% by weight, about 1.5% to about 3% by weight, about 2% to about 3% by weight, about 2.5% to about 3% by weight, or any range or sub-range therebetween. Exemplary aspects of the alkaline detergent solution include SemiClean KG (Yokohama Oil & Fats Industries). Exemplary aspects of ultrasound can include ultra-sound and megasonication. Without wishing to be bound by theory, ultrasound (e.g., ultra-sound, megasonication) can aid in the removal of contaminants (e.g., particles, oils) from surfaces by forming microscopic bubbles on the surface, by increasing circulation of the alkaline detergent solution through oscillation, and / or by loosening the contaminants through direct vibration. In aspects, the alkaline detergent solution and / or water can be substantially free of rheology modifiers. As used herein, a rheology modifier is a component other than the solvent or listed components (e.g., acid, hydroxide-containing base, H2SiF6, fluorine-containing compound) that changes the viscosity or shear-dependent behavior (dilatancy, thixotropy) of a solution.Exemplary aspects of rheology modifiers that the solution will be substantially free of include one or more of cellulose, cellulose derivatives (eg, ethyl cellulose, methyl cellulose, and AQUAZOL (poly-2-ethyl-2-oxazine)), hydrophobically modified ethylene oxide urethane modifiers (HUER), and ethylene acrylic acid.

[0206] In other aspects, solution 1403 can comprise a cleaning temperature and / or be in contact with foldable substrate 1111 for a cleaning period. In other aspects, ultrasound can be applied for at least half of the cleaning period, such as the entire first period. In other aspects, the cleaning period can be about 2 minutes or longer, about 3 minutes or longer, about 4 minutes or longer, about 5 minutes or longer, about 60 minutes or less, about 40 minutes or less, about 20 minutes or less, about 10 minutes or less, about 8 minutes or less, or about 6 minutes or less. In other aspects, the cleaning period can range from about 2 minutes to about 40 minutes, about 2 minutes to about 20 minutes, about 3 minutes to about 20 minutes, about 3 minutes to about 10 minutes, about 4 minutes to about 8 minutes, about 4 minutes to about 6 minutes, or any range or subrange therebetween. Providing a cleaning period of at least 2 minutes can effectively remove contaminants and / or deposits from the surface. Providing a cleaning period of less than 40 minutes can keep the probability of damage or cracking within an acceptable range. In one aspect, the first temperature can be about 20° C. or higher, about 25° C. or higher, about 30° C. or higher, about 35° C. or higher, about 65° C. or lower, about 60° C. or lower, about 55° C. or lower, or about 45° C. or lower. In one aspect, the first temperature can be in the range of about 20° C. to about 65° C., about 25° C. to about 60° C., about 30° C. to about 55° C., about 35° C. to about 45° C., or any range or subrange therebetween. Providing an alkaline detergent solution can selectively act on (e.g., remove, round, blunt) surface imperfections before removing material from other portions of the surface, which can increase the impact resistance of the substrate without removing significant thickness from the surface of the foldable substrate.

[0207] like Figure 14 and 16As shown, after and / or at the conclusion of steps 1005, 1007, and / or 1009, the chemically strengthened foldable substrate (i.e., foldable substrate 1111) can include (e.g., as a result of the chemical strengthening treatment described above) an initial first compressive stress region 1212 extending from the existing first major surface 1113 to an initial first compressive depth 1216 and an initial first depth of one or more alkali metal ions (e.g., potassium) associated with the initial first compressive stress region 1212, and / or the foldable substrate 1111 can include an initial second compressive stress region 1214 extending from the existing second major surface 1115 to an initial second compressive depth 1218 and an initial second depth of one or more alkali metal ions (e.g., potassium) associated with the initial second compressive stress region 1214. In other aspects, the maximum initial first compressive stress of the initial first compressive stress region 1212 and / or the maximum initial second compressive stress of the initial second compressive stress region 1214 can be within one or more of the ranges discussed above with respect to the maximum first compressive stress. In other aspects, the maximum initial first compressive stress of the initial first compressive stress region 1212 and / or the maximum initial second compressive stress of the initial second compressive stress region 1214 can be: about 800 MPa or greater, about 850 MPa or greater, about 900 MPa or greater, about 950 MPa or greater, about 1000 MPa or greater, about 1500 MPa or less, about 1300 MPa or less, about 1200 MPa or less, about 1100 MPa or less, about 1050 MPa or less, about 1000 MPa or less, or about 950 MPa or less. In other aspects, the maximum initial first compressive stress of initial first compressive stress region 1212 and / or the maximum initial second compressive stress of initial second compressive stress region 1214 can be in the range of about 800 MPa to about 15,000 MPa, about 850 MPa to about 1,300 MPa, about 900 MPa to about 1,200 MPa, about 950 MPa to about 1,100, about 1,000 MPa to about 1,050 MPa, or any range or sub-range therebetween. In other aspects, the presence of the first potassium salt can increase the compressive stress imparted by contacting the first major surface with the molten salt solution 1203 (at least in step 1005) by about 5% or more (e.g., about 10% or more, about 5% to about 20%, about 5% to about 15%, or about 7% to about 10%) relative to immersing the foldable substrate in a comparative molten salt solution having the same composition as the molten salt solution without the first potassium salt.In other aspects, the maximum initial first compressive stress of the initial first compressive stress region 1212 and / or the maximum initial second compressive stress of the initial second compressive stress region 1214 can be greater than the resulting maximum first compressive stress and / or the resulting maximum second compressive stress by about 5% or more, about 8% or more, about 10% or more, about 12% or more, about 15% or more, about 17% or more, or about 20% or more, such as in the range of about 5% to about 30%, about 8% to about 25%, about 10% to about 22%, about 12% to about 20%, about 15% to about 18%, or any range or sub-range therebetween.

[0208] After step 1005, 1007 or 1009, if Figure 15-16 As shown, the method can proceed to step 1011, including contacting at least the existing first major surface 1113 with an acidic solution 1503 maintained at a second temperature for a second period of time to remove the outer layer (e.g., extending to Figure 16 1603 of the initial first compressive stress region 1212 as shown) to form a new first major surface (e.g., first major surface 205) and first compressive stress region 212. In aspects, as shown, the existing second major surface 1115 can also be contacted with the acidic solution 1503 to remove the outer layer (e.g., extending to the first outer depth 1603 of the initial first compressive stress region 1212 as shown) to form a new first major surface (e.g., first major surface 205) and first compressive stress region 212. Figure 16 The outer compressive layer of the second outer depth 1605 of the initial second compressive stress region 1214 is shown to form a new second major surface (e.g., second major surface 205) and a second compressive stress region 214. Figure 15 As shown, the acidic solution 1503 can be contained in the bath 1501 and the foldable substrate 1111 can be immersed in the acidic solution 1503, although the acidic solution can be brought into contact with the foldable substrate (e.g., having the first major surface 1113) in other situations in other aspects. In other aspects, such as Figure 16 As shown, the first outer depth 1603 and / or the second outer depth 1605 of the outer layer removed by the acidic solution 1503 (see Figure 15 ) can be about 3.5 μm or less, about 3.0 μm or less, about 2.5 μm or less, about 2.0 μm or less, about 1.5 μm or less, about 1.0 μm or less, about 0.8 μm or less, about 0.1 μm or more, about 0.3 μm or more, about 0.5 μm or more, about 0.8 μm or more, about 1.0 μm or more, or about 1.5 μm or more. In other aspects, such as Figure 16 As shown, the first outer depth 1603 and / or the second outer depth 1605 of the outer layer removed by the acidic solution 1503 (see Figure 15) can be in the range of about 0.1 μm to about 3.5 μm, about 0.3 μm to about 3.0 μm, about 0.5 μm to about 2.5 μm, about 0.8 μm to about 2.0 μm, about 1.0 μm to about 1.5 μm, or any range or sub-range therebetween. Figure 16 As shown, first outer depth 1603 and / or second outer depth 1605 are less than initial first compression depth 1216 and / or initial second compression depth 1218, respectively, and foldable substrate 201 is less than initial first compression depth 1216 and / or initial second compression depth 1218 after contacting with acidic solution 1503 (see Figure 15 ) can include a first compressive stress region 212 and / or a second compressive stress region 214 having a reduced compressive stress relative to the corresponding initial compressive region. In other aspects, the reduction in compressive stress (i.e., removed by the acidic solution) as a percentage of the maximum initial first compressive stress and / or the maximum initial second compressive stress can be about 10% or more, about 12% or more, about 15% or more, about 17% or more, about 20% or more, about 22% or more, about 25% or less, about 22% or less, about 20% or less, about 17% or less, or about 15% or less. In other aspects, the reduction in compressive stress (i.e., removed by the acidic solution) as a percentage of the maximum initial first compressive stress and / or the maximum initial second compressive stress can be in the range of about 10% to about 25%, about 12% to about 22%, about 15% to about 20%, about 17% to about 20%, or any range or sub-range therebetween. In other aspects, the resulting compressive stress region can include a corresponding maximum compressive stress within one or more of the ranges discussed above with reference to the maximum first compressive stress.

[0209] The etch rate of the acidic solution (i.e., the rate of material removal from each surface (presumably a major surface) of the foldable substrate) can be adjusted based on the second temperature, the contents of the aqueous solution comprising the selected components, the concentrations of the components, and the resulting pH of the acidic solution. In aspects, the etch rate of the acidic solution 1503 can be about 1 μm per minute (μm / min) or less (e.g., about 1.0 μm / min or less), about 0.9 μm / min or less, about 0.8 μm / min or less, about 0.7 μm / min or less, about 0.6 μm / min or less, about 0.5 μm / min or less, about 0.4 μm / min or less, about 0.1 μm / min or more, about 0.2 μm / min or more, about 0.3 μm / min or more, about 0.4 μm / min or more, about 0.5 μm / min or more, or about 0.6 μm / min or more. In one embodiment, the etch rate of the acidic solution 1503 can be in the range of about 0.1 μm / minute to about 1.0 μm / minute, about 0.2 μm / minute to about 0.9 μm / minute, about 0.3 μm / minute to about 0.8 μm / minute, about 0.4 μm / minute to about 0.7 μm / minute, about 0.5 μm / minute to about 0.6 μm / minute, or any range or sub-range therebetween. Providing an etch rate of about 1 μm / minute or less (e.g., about 1.0 μm / minute or less) can promote substantially uniform material removal from the surface(s) of the foldable substrate. As discussed above, foldable substrates having a thickness of about 50 μm or less (e.g., about 10 μm to about 50 μm or about 10 μm to about 30 μm) are quite sensitive to compressive stress differences and thickness variations on their surfaces. Thus, providing an etch rate of approximately 1 μm / minute can remove relatively uniform thickness and compressive stress portions from the surface(s), thereby reducing the likelihood of waviness and / or warping that would produce optical distortion that is visually visible to users of consumer electronic products that may incorporate the foldable substrate.

[0210] In one aspect, the second temperature of the acidic solution 1503 can be about 20°C or higher, about 22°C or higher, about 25°C or higher, about 28°C or higher, about 30°C or higher, about 40°C or lower, about 35°C or lower, about 30°C or lower, about 28°C or lower, about 25°C or lower, or about 23°C or lower. In one aspect, the second temperature of the acidic solution 1503 can be in the range of about 20°C to about 40°C, about 20°C to about 35°C, about 20°C to about 30°C, about 20°C to about 28°C, about 20°C to about 25°C, about 22°C to about 23°C, or any range or sub-range therebetween. Without wishing to be bound by theory, providing an acidic solution at a lower temperature (e.g., about 20°C to about 40°C or about 20°C to about 25°C) can reduce SiF -The concentration of anions, because H2SiF6 and 2H + +SiF6 - The reaction is endothermic. - The concentration of anions may be associated with a reduction in the deposition (eg, redeposition) of silica or silica-like materials on the surface, which would otherwise produce variations in thickness and / or compressive stress on the surface of the foldable substrate.

[0211] In one aspect, the second time period during which foldable substrate 201 or 1111 (e.g., having first major surface 1113 or first major surface 203) is contacted with acidic solution 1503 can be about 20 seconds or longer, about 30 seconds or longer, about 45 seconds or longer, about 60 seconds or longer, about 75 seconds or longer, about 90 seconds or longer, about 120 seconds or longer, about 3.5 minutes or less, about 3 minutes or less, about 2.5 minutes or less, about 2 minutes or less, about 1.5 minutes or less, or about 1.0 minute or less. In one aspect, the second time period can be in the range of about 20 seconds to about 3.5 minutes, about 30 seconds to about 3 minutes, about 45 seconds to about 2.5 minutes, about 60 seconds to about 2 minutes, about 75 seconds to about 1.5 minutes, or any range or sub-range therebetween. In one aspect, acidic solution 1503 can be agitated (e.g., stirred, sonicated) during the second time period. Without wishing to be bound by theory, agitating the acidic solution may reduce supersaturation of silica-like compounds near the surface.

[0212] As discussed above, the pH of the solution is measured according to ASTM E70-90 at 25° C. In aspects, the pH of the acidic solution 1503 can be about 3.5 or more, about 3.55 or more, about 3.6 or more, about 3.65 or more, about 3.7 or more, about 3.75 or more, about 3.8 or more, about 4.5 or less, about 4.3 or less, about 4.0 or less, about 3.9 or less, about 3.8 or less, or about 3.7 or less. In aspects, the pH of the acidic solution 1503 can be in the range of about 3.5 to about 4.5, about 3.55 to about 4.3, about 3.6 to about 4.0, about 3.65 to about 3.9, about 3.7 to about 3.8, about 3.75 to about 3.8, or any range or sub-range therebetween. Providing a higher pH (eg, about 3.5 to about 4.5, about 3.6 to about 4.3, or about 3.7 to about 4.0) reduces the etch rate, which can help produce relatively uniform compressive stress and thickness across the foldable substrate.

[0213] In aspects, the acidic solution may include a buffered HF solution and / or an aqueous acidic solution. As used herein, buffered HF means that the solution contains NH4F or F is generated in the acidic solution. -In one aspect, the acidic solution can comprise an amount of HF in an amount, based on the weight percent of the acidic solution, of about 0.5 wt % or more, about 0.55 wt % or more, about 0.6 wt % or more, about 1.5 wt % or less, about 1.25 wt % or less, about 1.0 wt % or less, about 0.75 wt % or less, about 0.7 wt % or less, or about 0.65 wt % or less. In one aspect, the acidic solution can comprise an amount of HF in an amount, based on the weight percent of the acidic solution, of about 0.5 wt % to about 1.5 wt %, about 0.5 wt % to about 1.25 wt %, about 0.5 wt % to about 1.0 wt %, about 0.5 wt % to about 0.75 wt %, about 0.55 wt % to about 0.70 wt %, about 0.6 wt % to about 0.65 wt %, or any range or sub-range therebetween. In aspects, the acidic solution can contain NH4F in an amount, based on the weight percent of the acidic solution, of about 0.75 wt% or more, about 0.8 wt% or more, about 0.85 wt% or more, about 0.9 wt% or more, about 0.95 wt% or more, about 1.0 wt% or more, about 1.1 wt% or more, about 2.5 wt% or less, about 2.25 wt% or less, about 2.0 wt% or less, about 1.75 wt% or less, about 1.5 wt% or less, about 1.3 wt% or less, about 1.2 wt% or less, about 1.1 wt% or less, or about 1.0 wt% or less. In aspects, the acidic solution can contain an amount of NH4F in the range of about 0.75 wt% to about 2.5 wt%, about 0.8 wt% to about 2.25 wt%, about 0.8 wt% to about 2.0 wt%, about 0.85 wt% to about 1.75 wt%, about 0.9 wt% to about 1.5 wt%, about 0.95 wt% to about 1.3 wt%, about 1.0 wt% to about 1.2 wt%, about 1.0 wt% to about 1.1 wt%, or any range or sub-range therebetween. In exemplary aspects, the acidic solution can contain about 0.5 wt% to about 1.5 wt% or about 0.5 wt% to about 0.75 wt% HF, and / or about 0.75 wt% to about 2.5 wt% or about 0.9 wt% to about 1.5 wt% NH4F.Providing a total concentration of HF and NHF of about 4.0 wt% or less, about 3.5 wt% or less, about 3.0 wt% or less, about 2.5 wt% or less, or about 2.0 wt% or less (e.g., about 1.25 wt% to about 4.0 wt%, about 1.3 wt% to about 3.5 wt%, about 1.35 wt% to about 3.0 wt%, about 1.4 wt% to about 2.5 wt%, about 1.5 wt% to about 2.0 wt%) can provide relatively controlled and uniform etching of the foldable substrate and / or can reduce the deposition of materials on the foldable substrate that can detract from the optical properties of the foldable substrate (e.g., silicon dioxide, materials similar to silicon dioxide, ammonium fluoride crystals).

[0214] In aspects, after step 1011, the method can further proceed to step 1013, comprising washing the foldable substrate with water, an alkaline detergent solution, or a combination thereof. Figure 12 Step 1013 may include washing the foldable substrate (eg, foldable substrate 201 is replaced herein) with a solution 1203 (eg, alkaline detergent solution, water) contained in a bath 1201. Figure 12 foldable substrate 1111 in FIG. In other aspects, step 1013 can include: washing with water followed by washing with an alkaline detergent solution, in reverse order, or multiple washes involving water and / or an alkaline detergent solution. In other aspects, step 1013 can include one or more of the aspects discussed above with reference to step 1009. For example, providing the alkaline detergent solution in step 1013 can neutralize residual etchant from step 1011, which can prevent surface defects and / or produce a more uniform thickness of the foldable substrate. Providing the alkaline detergent solution in step 1013 can neutralize and / or remove hydrogen (e.g., hydronium ion) accumulation at the surface of the foldable substrate, which could otherwise result in large defects as a result of stress corrosion during a subsequent chemical strengthening process. Providing the alkaline detergent solution can selectively act on (e.g., remove, round, passivate) surface defects before removing material from other portions of the surface, which can increase the impact resistance of the substrate without removing significant thickness from the surface of the foldable substrate.

[0215] In some aspects, after steps 1009, 1011, or 1013, the method can proceed to step 1015, which includes assembling a foldable device from the foldable substrate. In other aspects, step 1015 can include disposing an adhesive layer 311 or polymer-based portion over the foldable substrate 201 (e.g., the first major surface 203). In other aspects, step 1015 can also include disposing an adhesive layer 311 (see FIG. 10A ) disposed earlier in step 1015. Figure 3) or a polymer-based portion disposed over a layer (e.g., a display device, another substrate, PET sheet 321). In other aspects, step 1015 may also include an adhesive layer 311 disposed earlier in step 1015 (see Figure 3 ) or a polymer-based portion. In aspects, step 1015 can include disposing a coating over the foldable substrate (eg, the second major surface).

[0216] After steps 1009, 1011, 1013, and / or 1015, the method can be completed at step 1017. In certain aspects, method 1017 can also include assembling the foldable device, such as by disposing the coating opposite a release liner or a display device, or by disposing the release liner or a display device opposite a coating. At the conclusion of steps 1009, 1011, 1013, and / or 1015, the foldable substrate 201 can be assembled with a foldable device such as a foldable device. Figure 2-3The foldable substrate 201 shown is similar or identical. In one aspect, the method can proceed along the steps discussed above, for example, sequentially through steps 1001, 1003, 1005, 1007, 1009, 1011, 1013, 1015, and 1017. In one aspect, if the foldable substrate 1111 is to be chemically strengthened without preheating, the method can proceed along arrow 1002 from step 1001 to step 1005. In one aspect, if, for example, the chemically strengthened foldable substrate is washed in step 1009 without placing the foldable substrate in a cooling chamber with a controlled temperature profile, the method can proceed along arrow 1004 from step 1005 to 1009. In aspects, for example, if the foldable substrate is to be chemically strengthened directly from step 1015 to etching with an acidic solution (e.g., without cleaning and / or placement in a cooling chamber with a controlled temperature profile), the method can proceed from step 1005 to step 1011 along arrow 1006. In aspects, for example, if the foldable substrate is to be transferred from the cooling chamber to the acidic solution (e.g., without intermediate cleaning of the foldable substrate), the method can proceed from step 1007 to step 1011 along arrow 1008. In aspects, for example, if the method is complete at the end of step 1011, the method can proceed from step 1011 to step 1017 along arrow 1010. In aspects, for example, if the foldable substrate is to be assembled as part of a foldable substrate after etching with an acidic solution (e.g., without intermediate cleaning), the method can proceed from step 1011 to step 1015 along arrow 1012. In aspects, for example, if the method is completed at the end of step 1013, the method can follow arrow 1014 from step 1013 to step 1017. In aspects, for example, if the method is completed at the end of step 1009, the method can follow arrow 1016 from step 1009 to step 1017. Any of the above options can be combined to make chemically strengthened foldable substrates and / or foldable devices according to aspects of the present disclosure.

[0217] In aspects, the method according to aspects of the present disclosure may consist of the steps discussed above. For example, in the above reference Figure 10 There may be no further treatment of the foldable substrate between one or more (or even all) steps described in the flowchart. Throughout this disclosure, the phrase "no further treatment" or "no other treatment" excludes treatment of the first major surface other than the stated contact with a solution and rinsing with water (e.g., purified water, filtered water, deionized water, distilled water). Exemplary aspects of treatment that may be excluded by "no further treatment" or "no other treatment" include treatment with additional acidic solutions, alkaline solutions, fluorine-containing solutions, detergents, and mechanical polishing of the foldable substrate.

[0218] Example

[0219] Various aspects are further illustrated by the following examples.

[0220] Examples 1-3, 21-24, 29-43, and 48-50, and Comparative Examples AA-BB, II-JJ, MM-NN, QQ, and TT comprise a glass-based substrate having Composition 1 (nominal, in mol %): 68.9% SiO, 10.1% AlO, 4.9% MgO, 0.5% CaO, 15.5% NaO, and 0.1% SnO. Examples 1-3, and Comparative Examples AA-BB and QQ comprise a substrate thickness of 80 μm. Examples 21-24, 40-43, and Comparative Example II-JJ comprise a substrate thickness of 75 μm. Examples 29-39, 49-50, and Comparative Example MM-NN comprise a substrate thickness of 30 μm.

[0221] Examples 4-20, 25-28, 44-47, and 51-74, as well as Comparative Examples CC-HH, KK-LL, OO-PP, and RR-SS, comprised a glass-based substrate having Composition 2 (nominal, in mol %): 65.0% SiO, 14.1% AlO, 3.4% MgO, 1.0% CaO, 16.4% NaO, and 0.1% SnO. Examples 4-6 and Comparative Examples CC-DD and RR comprised a substrate thickness of 80 μm. Examples 14-20 and 25-28, as well as Comparative Example GG-HH, comprised a substrate thickness of 75 μm. Examples 44-47 and Comparative Example KK-LL comprised a substrate thickness of 70 μm. Examples 7-13 and 51-74, as well as Comparative Examples EE-FF, OO-PP, and SS, comprised a substrate thickness of 30 μm.

[0222] Table 1-2 and Figure 17-18 The processing conditions and properties of Examples 1-6 and Comparative Examples AA-DD are presented. The remainder of the molten salt solution (after accounting for the second potassium salt) is potassium nitrate (KNO3), with any silicic acid added thereto in superaddition. For example, Example 1 is 95 wt% KNO3 and 5 wt% K2CO3, with 0.5 wt% superaddition of silicic acid. Figure 17 , the vertical axis 1703 (e.g., y-axis) corresponds to compressive stress in MPa, and the horizontal axis 1701 (e.g., x-axis) corresponds to different embodiments, with the embodiments using composition 1 separated from those using composition 2 by a dashed line. Figure 18 , the vertical axis 1803 (eg, y-axis) corresponds to layer depth in μm, and the horizontal axis 1801 (eg, x-axis) corresponds to different embodiments, with embodiments employing composition 1 separated from those employing composition 2 by a dashed line.

[0223] Table 1 presents the properties of Composition 1 (Examples 1-3 and Comparative Examples AA-BB). Comparing Example 1 with Comparative Example AA, the further addition of K2CO3 at 420°C reduces compression and depth of layer (relative to Comparative Example AA). The molten salt solutions of Comparative Example BB and Examples 2-3 were maintained at 380°C rather than 420°C. As demonstrated in Comparative Example BB, a longer chemical strengthening treatment (69 minutes versus 30 minutes) at a lower temperature (380°C versus 420°C) can achieve approximately the same (or even slightly higher) compressive stress with a reduced depth of layer. As discussed above, it is believed that the lower molten salt solution temperature improves the properties of the substrate by preventing stress relaxation and by providing a more controlled and uniform compressive stress across the substrate. The addition of a second potassium salt in Examples 2-3 improves the compressive stress and (improves or maintains) the depth of layer (relative to Example 1 and Comparative Example BB). Furthermore, Examples 2-3 improve the compressive stress (relative to Comparative Example AA).

[0224] Table 1: Processing conditions and properties of Examples 1-3 and Comparative Examples AA-BB (Composition 1 at 80 μm thickness)

[0225]

[0226] Table 2: Processing conditions and properties of Examples 4-6 and Comparative Examples CC-DD (80 μm thickness of Composition 2)

[0227]

[0228] Table 2 presents the results for Composition 2 (Examples 4-6 and Comparative Examples CC-DD). Comparing Example 4 with Comparative Example CC, the further addition of KCO at 420°C reduced both compression and depth of layer (relative to Comparative Example CC). The molten salt solutions for Comparative Example DD and Examples 5-6 were maintained at 380°C rather than 420°C. As demonstrated in Comparative Example DD, a longer chemical strengthening treatment (69 minutes versus 30 minutes) at a lower temperature (380°C versus 420°C) can achieve higher compressive stress with reduced depth of layer. As discussed above, it is believed that the lower molten salt solution temperature improves substrate properties by preventing stress relaxation and providing a more controlled and uniform compressive stress across the substrate. Examples 5-6 added a second potassium salt. For Example 6, the addition of KCO improved both compressive stress and depth of layer (relative to Example 4), as well as compressive stress (relative to Comparative Examples CC-DD). However, the addition of KPO increased the depth of layer but reduced the compressive stress (relative to Example 4) (while maintaining properties substantially identical to Comparative Example DD). Thus, the addition of K3PO4 did not improve the properties of Composition 2 (Example 5 compared to Comparative Example DD, although it did improve the compressive stress of Composition 1), while K2CO3 improved the compressive stress (and depth of layer) for both Composition 1 (Example 3 compared to Comparative Example BB) and Composition 2 (Example 6 compared to Comparative Example DD).

[0229] Table 3-4 and Figure 19-20 The processing conditions and properties of Examples 7-20 are presented. Figure 19-20 , the vertical axis 1903 or 2003 (eg, y-axis) corresponds to the compressive stress in MPa, and the horizontal axis 1901 or 2001 (eg, x-axis) corresponds to the weight % of K 2 CO 3 in the molten salt bath.

[0230] Table 3 and Figure 19 Results for Composition 2 are presented for a substrate thickness of 30 μm. Curves 1907 correspond, from left to right, to Comparative Example EE and Examples 7-9, respectively, which were chemically strengthened at 400°C for 12 minutes. As shown, for Example 10 with 5 wt% K2CO3, a maximum compressive stress of 975 MPa in curve 1907 was unexpectedly achieved (approximately 4% or more greater than Comparative Example EE). Based on this result, it is expected that adding about 2 wt% to about 5 wt% (e.g., about 2.5 wt% to about 5.0 wt%) of K2CO3 to the molten salt bath will also exhibit an unexpected increase in compressive stress when chemically strengthening substrates having a thickness of less than 50 μm (e.g., about 10 μm to about 50 μm or about 10 μm to about 30 μm) at 400°C.

[0231] Curves 1909 correspond, from left to right, to Comparative Examples FF and Examples 10-12, respectively, which were chemically strengthened at 380°C for 18 minutes. As shown, for K2CO3 contents of 10 wt% or greater (e.g., 12 wt% or greater or less than 15 wt%), curve 1909 (380°C) is higher than curve 1907 (400°C). As discussed above, chemical strengthening at a lower temperature (e.g., 380°C instead of 400°C) achieves the same or greater compressive stress with an additional time (e.g., 18 minutes instead of 12 minutes). For curve 1909, a maximum compressive stress of 984 MPa is unexpectedly observed for 10 wt% K2CO3 (Example 11), although 5 wt% K2CO3 (Example 10) also has a high compressive stress (e.g., approximately 980 MPa or greater). Based on this result, it is expected that the addition of about 2 wt % to about 12 wt % (e.g., about 2.5 wt % to about 12 wt %, about 5 wt % to about 12 wt %, or about 8 wt % to about 12 wt %) K2CO3 to the molten salt bath will also exhibit an unexpected increase in compressive stress when chemically strengthening substrates having a thickness of less than 50 μm (e.g., about 10 μm to about 50 μm or about 10 μm to about 30 μm) at 380°C. Figure 19 Also exhibited is a difference 1917 between the compressive stress of Comparative Example EE (line 1905) and the compressive stress of Example 11 (line 1915) of approximately 50 MPa (i.e., 47 MPa), corresponding to an increase in compressive stress of approximately 5% or greater from Comparative Example EE to Example 11.

[0232] As shown in Table 3 (but Figure 19 3 ), Example 13 corresponds to Example 11 without silicic acid, and Example 13 still exhibits an increase in compressive stress (relative to Comparative Example EE, but not relative to Comparative Example FF or Example 11). Table 3 also shows the pH measured for solutions prepared by diluting 5 g of the molten salt solution (cooled to ambient temperature) in 100 grams of deionized water using the criteria discussed above. As shown, the pH of pure KNO3 (Comparative Example EE) is 7.51, which is approximately neutral. In contrast, the pH of 10 wt% K2CO3 and 90 wt% KNO3 (Examples 11 and 13) is approximately 11. The pH of the other molten salt baths was not measured. As discussed above, it is believed that the increase in pH of Examples 11 and 13 (relative to Comparative Example EE) can improve the strength and / or foldability of the resulting chemically strengthened foldable substrate by, for example, selectively etching defects inherent in the foldable substrate (which might otherwise be amplified by the chemical strengthening treatment).

[0233] As shown in Table 3 (but not plotted), Examples 73-74 used a lower concentration (2.5 wt %) of the second potassium salt (K2CO3 and K2SO4, respectively). At 2.5 wt %, K2CO3 (Example 73) produced greater compressive stress and depth of layer than K2SO4. Comparing 2.5 wt % K2CO3 (Example 73) and 5.0 wt % K2CO3 (Example 10), the compressive stress and depth of layer were essentially the same. This demonstrates that the K2CO3 concentration can be reduced from 5 wt % to 2.5 wt % without negatively impacting the stress-related properties of the resulting article.

[0234] Table 3: Processing conditions and properties of Examples 7-13 and 73-74 and Comparative Examples EE-FF (Composition 2 at 30 μm thickness)

[0235]

[0236]

[0237] * = pH value measured by dissolving 5 g of molten salt solution cooled to ambient temperature in 100 g of deionized water

[0238] --=Untested

[0239] Table 4: Processing conditions and properties of Examples 14-20 and Comparative Examples GG-HH (75 μm thickness of Composition 2)

[0240]

[0241]

[0242] Table 4 and Figure 20 The substrate thickness is 75 μm (instead of Tables 3 and Figure 19 30 μm) in question. Curve 2007 corresponds, from left to right, to Comparative Examples GG and Examples 14-16, respectively, which were chemically strengthened at 400°C for 12 minutes. As shown, for Example 14 with 5 wt% K2CO3, the unexpected maximum compressive stress of 1123 MPa in curve 2007 was achieved (approximately 5% or more, or 4.75% greater, relative to Comparative Example EE). Example 15 also exhibited a compressive stress of approximately 1120 MPa. Based on this result, it is expected that adding from about 2 wt% to about 12 wt% (e.g., from about 2.5 wt% to about 12 wt%, from about 5 wt% to about 12 wt%, or even from about 2.5 wt% to about 5.0 wt%) K2CO3 to the molten salt bath would also exhibit an unexpected increase in compressive stress when chemically strengthening substrates having a thickness greater than 50 μm (e.g., from about 50 μm to about 100 μm or from about 50 μm to about 90 μm) at 400°C.

[0243] Curve 2009 corresponds from left to right to Comparative Examples HH and Examples 17-19, respectively, which were chemically strengthened at 380°C for 18 minutes. As shown, for a K2CO3 content of approximately 10 wt% (e.g., about 8 wt% to about 12 wt%), curve 2009 (380°C) is higher than curve 2007 (400°C). This is different from Figure 19 and the trends observed for thinner substrates in Table 3. For curve 2009, a maximum compressive stress of 1131 MPa was unexpectedly observed for 10 wt% K2CO3 (Example 18). Based on this result, it is expected that the addition of about 5 wt% to about 12 wt% (e.g., about 8 wt% to about 12 wt%) K2CO3 to the molten salt bath will also exhibit an unexpected increase in compressive stress when chemically strengthening substrates having a thickness greater than 50 μm (e.g., about 50 μm to about 100 μm or about 50 μm to about 90 μm) at 380°C. Figure 20 Also exhibited is a difference 2017 between the compressive stress of Comparative Example GG (line 2005) of about 50 MPa or greater (e.g., about 60 MPa or greater, 59 MPa) and the compressive stress of Example 18 (line 2005), which corresponds to an increase in compressive stress of about 5% or greater (i.e., 5.5%) from Comparative Example GG to Example 18.

[0244] As shown in Table 4 (but Figure 20 (not plotted in the graph), Example 20 corresponds to Example 18 without silicic acid, and Example 20 still exhibits an increase in compressive stress (relative to Comparative Examples GG-HH, but not relative to Example 18). This suggests that thinner substrates (Table 3) are more sensitive to silicic acid content, while thicker substrates (Table 4) are less sensitive.

[0245] Examples 1-20 and Comparative Examples AA-HH were cooled relatively quickly (e.g., quenched) in air before being rinsed in deionized water. However, cooling substrates in an industrial environment is not always feasible, particularly when the molten salt bath can contain several tons and present a significant thermal mass. Although not shown, residual molten salt deposits and / or optical distortions were observed to form on substrates cooled in air under industrial conditions (where cooling rates are believed to be slower). Therefore, controlled cooling conditions are described in Tables 5-6.

[0246] Tables 5-6 present the processing conditions and properties of Examples 21-28. In addition to the chemical strengthening detailed in Tables 5-6, Examples 21-28 were also processed as follows: the substrate was removed from the molten salt solution (380°C or 420°C) and transferred to a cooling chamber (which was initially physically located above the molten salt solution for 5 minutes, allowing the residual molten salt bath to drip from the substrate back into the molten salt bath when the substrate was transferred to the cooling chamber), and held at 285°C for 5 minutes, followed by cooling from an initial temperature of approximately 270°C to a final temperature of approximately 70°C (an approximately linear cooling profile with a cooling rate of approximately 4°C / minute), followed by rinsing in a deionized water bath and cooling to ambient temperature.

[0247] Table 5 presents the results for Composition 1 having a thickness of 75 μm (and having undergone the cooling treatment described in the previous paragraph). As shown, the molten salt solution having 5 wt% K2CO3 (both with and without silicic acid, Examples 22-24) exhibited an increase in compressive stress of about 5% or more (e.g., 4.8% or more for Examples 22-24), and a compressive stress increase of about 7% or more relative to Example 21 was confirmed by chemical strengthening with K2CO3 at 380°C (Examples 22 and 24).

[0248] Table 5: Processing conditions and properties of Examples 21-24 with cooling treatment (75 μm thick composition 1)

[0249]

[0250]

[0251] Table 6: Processing conditions and properties of Examples 25-28 with cooling treatment (75 μm thick composition 2)

[0252]

[0253] Table 6 presents the results for Composition 2 with a thickness of 75 μm (and after the cooling treatment described above). As shown, the molten salt solution with 5 wt% K2CO3 (with and without silicic acid, Examples 26-28) exhibited an increase in compressive stress, with chemical strengthening of 380°C K2CO3 demonstrating an increase in compressive stress of about 3.5% or more (Examples 26 and 28), and Example 28 exhibiting an increase in compressive stress of about 5% or more (i.e., 6.5%) (relative to Example 25). In addition, although not shown, visual inspection of Examples 21-28 with the naked eye did not detect any residual or optical distortion from the molten salt solution. Examples 21-28 (Tables 5-6) demonstrate that controlled cooling conditions do not result in optical distortion (for substrate thicknesses of 50 μm or greater), and that the addition of K2CO3 (e.g., from about 2 wt% to about 12 wt%, from about 2 wt% to about 5 wt%, or from about 2.5 wt% to about 5.0 wt%) still produces an increase in compressive stress (particularly at temperatures less than 400°C).

[0254] Table 7 presents the processing conditions and properties of Examples 29-39, which explore the cooling process (in combination with a second potassium salt) for thinner (30 μm thickness) composition substrates. Figures 26A-26C This conveys the level of deformation recorded in the "Visual Inspection" column of Table 7. Figures 26A-26C , the outline of the fluorescent tube light reflected from the substrate is shown schematically. Figure 26A A substrate 2601 is shown with "slight deformation" where contours 2603 and 2605 are relatively smooth with little to no local deviations of the contours from their general shape, which is the target condition. Figure 26B A substrate 2611 is shown with "medium deformation" where profiles 2613, 2615, and 1617 exhibit waviness (e.g., waviness 2614), which is a noticeable localized deformation in the general shape of the profile (e.g., compared to the Figure 26A ), other contours (e.g., contour 219) may be relatively unaffected. Figure 26C A substrate 2621 with "high deformation" is shown, wherein contours 2623, 2625, 2627, and 2629 exhibit extreme waviness, e.g., the contours appear discontinuous (or nearly discontinuous) and / or the local shapes of the contours have little to no resemblance to shapes of less deformed substrates (e.g., compared to Figures 26A-26B ).although Figure 26A The angle of observation of the substrate is different from that of observation Figures 26B-26C perspective, but the general principles discussed above apply.

[0255] In Table 7, the compressive stress differences are relative to the properties of Example 29. In Table 7, Examples 32, 34-36, and 38 exhibit high deformation. In addition, Examples 32, 34-36, and 38 exhibit waviness in the surface, which is observed when the surface is viewed at an oblique angle. It is noted that Examples 34 and 36, which have high deformation, cool in ambient air, which is relatively slow (e.g., much less than 4°C / min) under the industrial conditions used (for Examples 29-39). Similarly, Example 35, which has high deformation, cools at a rate of less than 4°C / min (e.g., less than 3°C / min). The high deformation observed for Example 32, combined with the waviness, suggests that the chemical strengthening was too rapid (e.g., reaching high temperatures (400°C for 8 minutes) in too short a time for thicknesses less than 50 μm) to achieve a uniform compressive stress layer. Examples 30 and 39 exhibit moderate deformation. Examples 29, 31, 33, 37, and 39 exhibit slight deformation. It is noted that Examples 29-31, 33, and 37, which have moderate or slight deformation, have cooling rates of 4°C / min or greater. Examples 31, 33, and 37 suggest that a cooling process in which the temperature is rapidly reduced by about 100°C or more (e.g., about 120°C or more) relative to the temperature of the molten salt solution is associated with reduced deformation. Compared to Examples 21-28 in Tables 5-6, which have a thickness of 75 μm, Examples 29-39 in Table 7 demonstrate that thinner substrates (e.g., having a thickness of about 50 μm or less, about 10 μm to about 50 μm, or about 10 μm to about 30 μm) are much more sensitive to the conditions of the cooling process. As discussed above, it is believed that small differences (e.g., non-uniformity) in the compressive stress established in thinner substrates can lead to optical distortion. Therefore, in addition to decreasing the temperature of the cooling chamber at about 4°C / minute or more (e.g., about 4°C / minute to about 20°C / minute), rapidly lowering the temperature (e.g., by about 100°C or more or about 120°C or more) when removing the substrate from the molten salt solution can reduce residual chemical strengthening.

[0256] Table 7: Processing conditions and properties of Examples 29-39 with cooling treatment (30 μm thick composition 1)

[0257]

[0258]

[0259]

[0260]

[0261] Figure 21-22Tables 8-9 show the performance of Examples 40-47 and Comparative Example II-LL for various parallel plate spacings (% survival rate - % of samples that survived). For Examples 40-47 and Comparative Example II-LL, a sample size of 30 sheets was used for testing. Figure 21-22 In the graph, the vertical axis 2103 or 2203 (e.g., the y-axis) corresponds to the percentage of samples that survived the parallel plate spacing (i.e., the % survival rate), and the horizontal axis 2101 or 2202 (e.g., the x-axis) corresponds to the parallel plate spacing (in mm) at which the test was performed. It should be noted that the horizontal axis 2101 or 2202 is not linear; rather, the axis labels correspond to the different spacings at which the samples were measured, which is roughly logarithmic (but not exactly).

[0262] Table 8 presents the processing conditions and properties of Examples 40-43 and Comparative Examples II-JJ having composition 1 and a substrate thickness of 70 μm (for non-industrial conditions, rapid cooling in air). Table 8 presents the % survival (i.e., % of samples that survived) for parallel plate spacings of 5 mm and 3 mm, with additional points (e.g., a total of about a dozen different parallel plate spacings) highlighted. Figure 21 The trend shown in Figure 21 In the figures, curves 2105 and 2107 correspond to Comparative Examples II-JJ, respectively; while curves 2109, 2111, 2113, and 2115 correspond to Examples 40-43, respectively. Unless otherwise noted, the etching of the examples involved a 2 wt% HF (unbuffered) solution. As shown, curve 2107 (Comparative Example JJ, etching removed 0% of the CS) has 0% of the samples withstanding even a 5 mm parallel plate spacing. Curve 2105 (Comparative Example II, etching removed 18% of the CS) has 100% of the samples withstanding a 5 mm parallel plate spacing, but 3% of the samples withstanding a 3 mm parallel plate spacing. Examples 40-43, which were chemically strengthened with 5 wt% K2CO3 and had different amounts of compressive stress (CS) removed by etching, had 90% or more (e.g., 95% or more, about 97% or more) of the samples withstanding a 5 mm parallel plate spacing. Specifically, Examples 42-43 (Example 42 having a compressive stress relief substantially equivalent to that of Comparative Example II) had 10% or more (e.g., about 20% or more) of the samples withstanding a parallel plate spacing of 3 mm, which is much higher than that observed for Comparative Example II. Thus, the addition of 5 wt% K2CO3 can improve the foldability of the substrate, as evidenced by the parallel plate behavior (e.g., 3 mm for a substrate thickness of 70 μm (about 50 μm to about 100 μm or about 50 μm to about 90 μm)).

[0263] Table 8: Processing conditions and properties of Examples 40-43 and Comparative Examples II-JJ (70 μm thickness of Composition 1)

[0264]

[0265]

[0266] Table 9: Processing conditions and properties of Examples 44-47 and Comparative Examples KK-LL (70 μm thickness of Composition 2)

[0267]

[0268]

[0269] Table 9 presents the processing conditions and properties of Examples 40-43 and Comparative Examples II-JJ having Composition 2 and a substrate thickness of 70 μm (for non-industrial conditions, rapid cooling in air). Table 9 presents the % survival (i.e., % of samples that survived) for parallel plate spacings of 5 mm and 3 mm, with additional points (e.g., a total of about a dozen different parallel plate spacings) highlighted. Figure 22 The trend shown in Figure 22 In the graph, curves 2205 and 2207 correspond to Comparative Examples KK-LL, respectively; while curves 2209, 2211, 2213, and 2215 correspond to Examples 44-47, respectively. As shown, curve 2207 (Comparative Example LL, 0% CS removed by etching) has 0% of the samples withstanding even a 5 mm parallel plate spacing. Curve 2105 (Comparative Example LL, 18% CS removed by etching) has 97% of the samples withstanding a 5 mm parallel plate spacing, and 60% of the samples withstanding a 3 mm parallel plate spacing. Examples 44-47, which were chemically strengthened with 5 wt% K2CO3 and had varying amounts of compressive stress (CS) removed by etching, had 90% or more (e.g., 95% or more, approximately 97% or more, or approximately 100% for Examples 45 and 47) of the samples withstanding a 5 mm parallel plate spacing. Examples 46-47 had 10% or more (e.g., about 20% or more, about 30% or more, or about 40% or more) of the samples survive a parallel plate spacing of 3 mm. Example 47 had 63% of the samples survive a parallel plate spacing of 3 mm, which is much higher than that observed for Comparative Example KK. Thus, the addition of 5 wt % K2CO3 can maintain or improve the foldability of the substrate, as evidenced by the parallel plate behavior (e.g., 3 mm for a substrate thickness of 70 μm (about 50 μm to about 100 μm or about 50 μm to about 90 μm)).

[0270] Figure 23-24Tables 10-11 show the performance of Examples 47-52 and Comparative Example MM-PP for various parallel plate spacings (% survival rate - % of samples that survived). For Examples 48-53 and Comparative Example MM-PP, a sample size of 30 sheets was used for testing. Figure 23-24 In the example, the vertical axis 2303 or 2403 (e.g., the y-axis) corresponds to the percentage of samples that survived the parallel plate spacing (i.e., the % survival rate), and the horizontal axis 2301 or 2402 (e.g., the x-axis) corresponds to the parallel plate spacing (in mm) at which the test was performed. Note that the horizontal axis 2301 or 2402 is linear (corresponding to a measurement for each 0.2 mm decrease in the parallel plate spacing, which is different from the Figure 21-22 Scale bar used).

[0271] Table 10 presents the processing conditions and properties of Examples 48-50 and Comparative Examples MM-NN having composition 1 and a substrate thickness of 30 μm (for non-industrial conditions, rapid cooling in air). Table 10 presents the % survival (i.e., % of samples that survived) at parallel plate spacings of 2 mm and 1 mm, with additional points (e.g., a total of about seven different parallel plate spacings) highlighted. Figure 23 The trend shown in Figure 23 In the graph, curves 2305 and 2307 correspond to Comparative Examples MM-NN, respectively; while curves 2309, 2311, 2313, and 2315 correspond to Examples 48-50, respectively. As shown, curve 2307 (Comparative Example NN, 0% CS removed by etching) has 30% of the samples withstanding a parallel plate spacing of 2 mm, and 0% of the samples withstanding a parallel plate spacing of 1 mm. Curve 2305 (Comparative Example MM, 18% CS removed by etching) has 100% of the samples withstanding a parallel plate spacing of 2 mm, but 10% of the samples withstanding a parallel plate spacing of 1 mm. Examples 47-49, which were chemically strengthened with 5 wt% K2CO3 and had varying amounts of compressive stress (CS) removed by etching, had 90% or more of the samples withstanding a parallel plate spacing of 2 mm. Specifically, Example 50 had 95% or more (e.g., about 100%) of the samples withstanding a parallel plate spacing of 2 mm and more than 10% (e.g., 15% or more or about 20% or more) of the samples withstanding a parallel plate spacing of 1 mm, which is much higher than that observed in Comparative Examples 2 and 3. Thus, the addition of 5 wt% K2CO3 can improve or maintain the foldability of the substrate, as evidenced by the parallel plate behavior (e.g., 1 mm for a substrate thickness of 30 μm (about 10 μm to about 50 μm or about 10 μm to about 30 μm)).

[0272] Table 10: Processing conditions and properties of Examples 48-50 and Comparative Examples MM-NN (30 μm thickness of Composition 1)

[0273]

[0274]

[0275] Table 11: Processing conditions and properties of Examples 51-53 and Comparative Example OO-PP (Composition 2 at 30 μm thickness)

[0276]

[0277] Table 11 presents the processing conditions and properties of Examples 51-53 and Comparative Example 00-PP with composition 2 and 30 μm substrate thickness (fast cooling in air for non-industrial conditions). Table 11 presents the % survival (i.e., % of samples that survived) at parallel plate spacings of 2 mm and 1 mm, with additional points (e.g., a total of about seven different parallel plate spacings) highlighted. Figure 24 The trend shown in Figure 24 In the graph, curves 2405 and 2407 correspond to Comparative Examples 00-PP, respectively; while curves 2409, 2411, 2413, and 2415 correspond to Examples 51-53, respectively. As shown, curve 2407 (Comparative Example PP, 0% CS removed by etching) has 60% of the samples withstanding a 2 mm parallel plate spacing, and 0% of the samples withstanding a 1 mm parallel plate spacing. Curve 2405 (Comparative Example 00, 18% CS removed by etching) has 95% of the samples withstanding a 2 mm parallel plate spacing, and 25% withstanding a 1 mm parallel plate spacing. Examples 51-53, which were chemically strengthened with 5 wt% K2CO3 and had varying amounts of compressive stress (CS) removed by etching, had 90% or more of the samples withstanding a 2 mm parallel plate spacing. Specifically, Examples 52-53 had 95% or more (e.g., approximately 100%) of the samples withstanding a 2 mm parallel plate spacing. For Example 53, the lower % survival rate at 1 mm parallel plate spacing is believed to be due to handling issues. Based on the results in Table 10 and the 2 mm survival rate in Table 11, the addition of 5 wt % K2CO3 can improve or maintain the foldability of the substrate, as evidenced by the parallel plate performance (e.g., for a substrate thickness of 30 μm (about 10 μm to about 50 μm or about 10 μm to about 30 μm)).

[0278] Table 12 presents the threshold pen drop heights for Example 3 and Comparative Examples AA and MM, each having a substrate composition of 1 and a thickness of 80 μm. In Table 12, the samples were not etched to isolate the effect of the molten salt solution on impact resistance, which was evaluated by the pen drop test. As shown, Example 3 had a threshold pen drop height of 16.6 cm, which is 3.1 cm higher than Comparative Example MM (a 23% increase) and 2 cm higher than Comparative Example AA (a 14% increase). Therefore, adding 5 wt% KCO can increase the impact resistance of the substrate, as measured by the pen drop threshold height.

[0279] Table 12: Threshold Pencil Drop Height for Example 3 and Comparative Examples AA and MM (Composition 1 and 80 μm Thickness)

[0280]

[0281] Table 13: Pen drop height of Example 6 and Comparative Examples CC and NN (Composition 2 and 80 μm thickness)

[0282]

[0283] Table 13 presents the threshold pen drop heights for Example 6 and Comparative Examples CC and NN, each having a substrate composition of 2 and a thickness of 80 μm. In Table 13, the samples were not etched to isolate the effect of the molten salt solution on impact resistance, as assessed by the pen drop test. As shown, Example 6 had a threshold pen drop height of 21.1 cm, which is 12.8 cm higher than Comparative Example NN (a 152% increase) and 4.9 cm higher than Comparative Example CC (a 30% increase). Therefore, the addition of 5 wt% K2CO3 can increase the impact resistance of the substrate, as measured by the pen drop threshold height. Specifically, Example 6 was able to withstand pen drop heights of 20 cm or greater.

[0284] For the remaining examples, unless otherwise stated, the examples (and comparative examples) were chemically strengthened for 12 minutes in 100 wt % KNO 3 maintained at 400° C. Furthermore, etching was performed at 22° C. unless otherwise stated.

[0285] Table 14 presents the etchant compositions and conditions for Examples 54-56 and Comparative Example SS. Comparative Example SS is an unbuffered HF solution, while Examples 54-56 are buffered HF solutions due to the addition of NH4F. As shown, the buffered HF solutions (Examples 54-56) have a higher pH than Comparative Example SS. However, as shown in the "Visual Inspection" column, these samples have various issues. Example 54 and Comparative Example SS have a blue color, which disappears when the HF concentration in Examples 55-56 is reduced to less than 2 wt% HF. Example 55 exhibits perceptible warping. Example 56 is turbid, which is attributed to precipitate formation from the patterned etching, which may be due to its higher NH4F concentration.

[0286] Table 14: Etching conditions and properties of Examples 54-56 and Comparative Example SS (Composition 2 at 30 μm thickness)

[0287]

[0288]

[0289] Therefore, the etching conditions of Examples 57-61 shown in Table 15 were varied (Example 56 and the comparative example are presented again for comparison). For Examples 57-58, the substrate was cleaned mid-etch (after 50 seconds), then etched for the remaining time (another 50 seconds), and then cleaned again; while Examples 56 and 59-61 were cleaned only after the entire etching time. In Example 57, deionized water (DI) was used for mid-etch cleaning, which reduced haze but also caused the surface to have slight wrinkles. Example 58 used HNO3 instead of DI for mid-etch cleaning, but Example 58 also showed low haze and low wrinkles. It is believed that the following situations may exist: (1) multiple substrate transfers between the etchant and the cleaning solution allow residual etchant on some parts of the surface to continue to etch while other parts are not etched; (2) some precipitates still accumulate on the surface, effectively masking the progress of etching; or (3) both situations. Furthermore, despite the same total etching time (50 seconds times 2 cycles = 100 seconds), Examples 57-58 removed more compressive stress than Example 56. Conversely, Examples 59-61 used shorter overall etching times to reduce the ability of precipitates formed on the surface to mask the etching. In Example 59, the substrate was cleaned with DI; in Example 60, the substrate was cleaned with oxalic acid; and in Example 61, the substrate was cleaned with nitric acid. Furthermore, Examples 59-61 exhibited perceptible wrinkles on the surface.

[0290] Table 15: Etching conditions and properties of Examples 56-61 and Comparative Example SS (Composition 2 at 30 μm thickness)

[0291]

[0292]

[0293] Table 16 further explores modifications to the etching conditions and buffered HF compositions of Examples 62-66 (Example 56 was repeated for comparison). In Examples 62-63, the etching temperature was increased, which reduced the haze, but there was still perceptible haze and some surface wrinkling (Example 63 additionally warped). Examples 64-66 reduced the etchant concentration (i.e., the concentration was halved relative to Example 56), without any perceptible defects to the naked eye. The same was true for etching times of 100 seconds to 200 seconds (studied) and temperatures of 22°C to 30°C (studied). Furthermore, as noted in Table 16, Examples 64-66 had etching rates of about 1.0 μm / min or less, while Examples 56 and 62-63 had higher etching rates. Thus, an etching rate of about 1.0 μm / min or less unexpectedly provided an etched substrate without visually observable defects. Note that this is only a problem for thinner substrates (e.g., about 50 μm or less, about 10 μm to about 50 μm, or about 10 μm to about 30 μm) and certain compositions (e.g., Composition 2, but not necessarily Composition 1).

[0294] Table 16: Etching conditions and properties of Examples 56 and 62-66 (Composition 2 at 30 μm thickness)

[0295]

[0296] Table 17 captures the etching compositions and cleaning conditions for Examples 65 and 67-68, as well as Comparative Example TT (all of which have a substrate thickness of 30 μm). Comparative Example TT has Composition 1 and demonstrates the blue color seen with Composition 2 (Comparative Example SS) that was not seen with Composition 1. For Example 67, the substrate was cleaned twice (evenly spaced) during the etching process and again at the end (effectively three etch-clean cycles). Despite having a lower etchant concentration (Example 67 vs. Example 62), Example 67 had noticeable haze and surface wrinkling. This suggests that some uneven etching occurred when the substrate was transferred from the etching solution to the DI cleaning. Example 68 was the same as Example 67, but the cleaning solution was 5 wt% nitric acid instead of DI, but Example 68 also had noticeable wrinkling on the surface. Although wrinkling was seen in Examples 67-68, both Examples 67-68 had higher survival rates for a parallel plate spacing of 1 mm than Comparative Example TT (68% and 23%, respectively). However, Example 65 (discussed above) was able to have over 20% (eg, about 30% or more, about 40% or more) of the samples survive a parallel plate spacing of 1 mm without any visually observable defects.

[0297] Table 17: Processing conditions and properties of Examples 65 and 67-68 and Comparative Example TT (30 μm thickness)

[0298]

[0299] Table 18: Processing conditions and properties of Examples 70-73 and Comparative Examples AA and SS (Composition 2 at 30 μm thickness)

[0300]

[0301] Table 18 and Figure 25 The properties of Examples 69-72 and Comparative Examples AA and SS are presented. As noted above, Examples 69-72 and Comparative Examples AA and SS were chemically strengthened in 100 wt% KNO3 maintained at 400°C for 12 minutes before rapid cooling (not the industrial setting). Table 18 presents the composition of the etching solution and the time the etching solution was in contact with the substrate. Figure 25 In FIG, the vertical axis 2503 (e.g., y-axis) presents the survival rate (i.e., the percentage of samples that survived a specific parallel plate spacing), while the horizontal axis 2501 (e.g., x-axis) presents the parallel plate spacing (in mm) at which the test was performed on a linear scale. Figure 25 In the figure, curves 2505 and 2515 correspond to comparative examples AA and SS, respectively. Curves 2507, 2509, 2511, and 2513 correspond to examples 69-72, respectively. Figure 18 and Figure 25 As shown, Comparative Example AA had 35% of the samples survive a 2 mm parallel plate spacing, but 0% survived a 1 mm parallel plate spacing. Comparative Example SS performed better, with 93% of the samples surviving a 2 mm parallel plate spacing and 15% of the samples surviving a 1 mm parallel plate spacing.

[0302] Examples 69-72 used the lower concentration buffered HF solution of Examples 64-65, with different treatment times, increasing from 50 seconds to 175 seconds from Example 69 to Example 72. As shown, all of Examples 69-72 had more than 90% (e.g., about 95% or more) of the samples withstanding a parallel plate spacing of 2 mm. Examples 70-72 had more than 20% of the samples withstanding a parallel plate spacing of 1 mm, which is better than Comparative Examples AA and SS. In addition, Examples 71-72 had about 30% or more (e.g., about 40% or more or about 50% or more) of the samples withstanding a parallel plate spacing of 1 mm, which is more than twice the proportion of Comparative Example SS. This demonstrates that lower concentration buffered HF etching solutions (e.g., treatment times less than 3.5 minutes and etching rates of about 1.0 μm / minute or less) provide unexpected improvements in foldability and reliability, as demonstrated by the increased survival rate at a 1 mm parallel plate spacing.

[0303] The above observations can be combined to provide chemically strengthened substrates (e.g., foldable substrates) and methods of chemically strengthening substrates (e.g., making the same). Providing glass-based substrates and / or ceramic-based substrates can provide good dimensional stability, can reduce the incidence of mechanical instability, and / or can provide good impact resistance and puncture resistance. The methods of the present disclosure can increase the pen drop height that foldable devices and / or foldable substrates can withstand, can increase the survival rate of substrates folded to parallel plate spacings of 5 mm, 3 mm, 2 mm and / or 1 mm, and / or can increase the foldability of the substrate.

[0304] In one aspect, a substrate can be chemically strengthened with a molten salt solution comprising two anions associated with at least a first potassium salt and a second potassium salt. Providing a plurality (i.e., two or more) of potassium atoms per anion to the first potassium salt can increase the effective concentration and / or activity of potassium in the molten salt solution, which can contribute to an increase in the maximum compressive stress in the resulting chemically strengthened foldable substrate. Providing the first potassium salt in the molten salt solution with a pKa of about 9 or greater and / or a molten salt solution pH of about 9 to 12 can improve the strength and / or foldability of the resulting chemically strengthened foldable substrate, for example, by selectively etching defects inherent in the foldable substrate (which might otherwise be amplified due to the chemical strengthening treatment). As discussed herein with reference to the Examples, potassium carbonate (K2CO3) has a more pronounced and unexpected increase in compressive stress than other components in the molten salt solution. Furthermore, without wishing to be bound by theory, it is believed that carbonate anions facilitate the precipitation of other cations (e.g., lithium, sodium) exchanged from the foldable substrate, which can increase the lifespan of the molten salt solution (e.g., by removing components from the solution phase that would otherwise "poison" the molten salt solution). As demonstrated in the examples discussed herein, providing a first temperature of the molten salt solution below 400° C. can increase the maximum compressive stress established for a predetermined depth of layer and / or compression depth. Furthermore, for some of the molten salt solutions discussed herein, temperatures of 350° C. or higher can be used to ensure salt melting.

[0305] It was observed that foldable substrates having a thickness of about 50 μm or less (e.g., about 10 μm to about 50 μm or about 10 μm to about 30 μm) were unexpectedly sensitive to events that occurred after the foldable substrate was removed from the molten salt solution. For these thin foldable substrates, even relatively small differences in compressive stress on their surfaces can result in ripples and / or warping, which can produce optical distortion that is visually visible to users of consumer electronic products that may incorporate the foldable substrate. Therefore, the controlled temperature of the cooling chamber can contribute to relatively uniform compressive stress on the surface of the foldable substrate. In addition, providing an initial cooling chamber temperature of 180°C or higher (e.g., 200°C or higher or 220°C or higher) can facilitate the removal of residual portions of the molten salt solution before it solidifies. Without wishing to be bound by theory, the first potassium salt can have a higher melting temperature than the second potassium salt, which means that incorporating the first potassium salt into the molten salt solution can increase the viscosity of the molten salt solution and / or can cause the molten salt solution to solidify at a higher temperature than a molten salt solution without the first potassium salt. Thus, when the molten salt solution comprises a first potassium salt, it may be particularly useful to allow a residual portion of the molten salt solution to remain on the foldable substrate after it is removed from the molten salt solution. Lowering the temperature of the cooling chamber to a final temperature of about 100°C or less (e.g., about 25°C to about 100°C or about 60°C to about 90°C) can allow subsequent treatment of the foldable substrate with an aqueous solution (e.g., relatively quickly or immediately) (e.g., rinsing with water or an alkaline detergent solution, contacting with an aqueous acidic solution). Providing a cooling rate of about 4°C / minute to about 20°C / minute can allow the temperature of the cooling chamber (and the foldable substrate) to drop rapidly while maintaining a relatively uniform temperature throughout the cooling chamber (and / or the foldable substrate), for example, thereby generating a relatively uniform compressive stress on the surface of the foldable substrate.

[0306] Providing an etch rate of about 1 μm / minute or less (e.g., about 1.0 μm / minute or less) can promote substantially uniform material removal from the surface(s) of the foldable substrate. As discussed above, a foldable substrate having a thickness of about 50 μm or less (e.g., about 10 μm to about 50 μm or about 10 μm to about 30 μm) is quite sensitive to compressive stress differences and thickness variations on its surface. Therefore, providing an etch rate of about 1 μm / minute can remove relatively uniform thickness and compressive stress portions from the surface(s), thereby reducing the probability of the occurrence of ripples and / or warping that would produce optical distortion that is visually visible to users of consumer electronic products that may incorporate the foldable substrate. Without wishing to be bound by theory, providing a lower temperature of the acidic solution (e.g., about 20°C to about 40°C or about 20°C to about 25°C) can reduce the SiF6 - The concentration of anions, because H2SiF6 and 2H + +SiF6- The reaction is endothermic. - The concentration of anions can be associated with a reduction in the deposition (e.g., redeposition) of silicon dioxide or silicon dioxide-like materials on the surface, which would otherwise produce variations in thickness and / or compressive stress across the surface of the foldable substrate. Providing a higher pH (e.g., from about 3.5 to about 4.5, from about 3.6 to about 4.3, or from about 3.7 to about 4.0) can reduce the etch rate, which can help produce relatively uniform compressive stress and thickness across the foldable substrate. Providing a total concentration of HF and NHF of about 4.0 wt% or less, about 3.5 wt% or less, about 3.0 wt% or less, about 2.5 wt% or less, or about 2.0 wt% or less (e.g., about 1.25 wt% to about 4.0 wt%, about 1.3 wt% to about 3.5 wt%, about 1.35 wt% to about 3.0 wt%, about 1.4 wt% to about 2.5 wt%, about 1.5 wt% to about 2.0 wt%) can provide relatively controlled and uniform etching of the foldable substrate and / or can reduce the deposition of materials on the foldable substrate that can detract from the optical properties of the foldable substrate (e.g., silicon dioxide, materials similar to silicon dioxide, ammonium fluoride crystals).

[0307] In aspects, the substrate can have a substrate thickness of about 50 μm or greater (e.g., about 50 μm to about 100 μm, about 50 μm to about 90 μm, or any corresponding subranges therebetween as discussed above) and is combined with one or more of the following properties: (1) a compression depth of about 10% to about 30%, about 16% to about 26%, or any corresponding subranges therebetween as a percentage of the substrate thickness 209; (2) a depth of layer (e.g., a first depth of layer and / or a second depth of layer) of potassium in a range of about 3 μm to about 20 μm, about 10 μm to about 15 μm, or any corresponding subranges therebetween; and / or (3) a maximum compressive stress (e.g., a first maximum compressive stress and / or a second maximum compressive stress) in a range of about 650 MPa to about 1200 MPa, about 800 MPa to about 1100 MPa, about 850 MPa to about 1200 MPa, or any corresponding subranges therebetween as discussed above. In aspects, the substrate thickness can be about 50 μm or less (e.g., about 10 μm to about 50 μm, about 10 μm to about 30 μm, or any corresponding subranges therebetween as discussed above) and is combined with one or more of the following properties: (1) a depth of compression, as a percentage of the substrate thickness, of about 10% to about 30%, about 12% to about 19%, or any corresponding subranges therebetween as discussed above; (2) a depth of layer of potassium in the range of about 3 μm to about 20 μm, about 5 μm to about 9 μm, or any corresponding subranges therebetween; and / or (3) a maximum compressive stress (e.g., a first maximum compressive stress and / or a second maximum compressive stress) in the range of about 650 MPa to about 1200 MPa, about 750 MPa to about 1100 MPa, about 750 MPa to about 1,000 MPa, or any corresponding subranges discussed above.

[0308] Directional terms used herein, such as up, down, left, right, front, back, top, and bottom, are only used with reference to the drawings and are not intended to indicate absolute orientations.

[0309] It will be understood that the various aspects disclosed may relate to specific features, elements or steps described in conjunction with a particular aspect. It will also be understood that although specific features, elements or steps are described in conjunction with one aspect, different aspects may be interchanged or combined with each other in various combinations or permutations not shown.

[0310] It is also to be understood that the terms "the," "a," or "an" as used herein mean "at least one" and should not be limited to "only one" unless expressly specified to the contrary. Thus, for example, reference to "a" component includes aspects having two or more such components, unless the context clearly indicates otherwise. Similarly, "plurality" is intended to mean "more than one."

[0311] As used herein, the term "about" indicates that amounts, sizes, formulations, parameters and other variables and characteristics are not and need not be exact, but may be approximate and / or larger or smaller as needed, reflecting tolerances, conversion factors, rounding and measurement errors, etc., as well as other factors known to those skilled in the art. Herein, ranges can be expressed as starting from "about" another specific value and / or ending at "about" another specific value. When expressing such a range, aspects include starting from a specific value and / or ending at another specific value. Similarly, when the antecedent "about" is used to indicate that a value is approximate, it should be understood that the specific value constitutes another aspect. Regardless of whether the numerical value or the endpoint of a range of this specification is stated with "about", the numerical value or the endpoint of the range is intended to include two aspects: one modified with "about" and one not modified with "about". It should also be understood that the endpoint values ​​of each range are meaningful both in relation to the other endpoint value and in relation to the other endpoint value.

[0312] As used herein, the terms "substantially," "substantially," and variations thereof are intended to indicate that the described feature is identical or approximately identical to the value or description. For example, a "substantially flat" surface is intended to indicate a flat or approximately flat surface. Furthermore, as defined above, "substantially similar" is intended to indicate that two values ​​are equal or approximately equal. In aspects, "substantially similar" can mean that the values ​​are within about 10% of each other, such as within about 5% of each other, or within about 2% of each other.

[0313] Unless otherwise expressly stated, it is not intended that any method described herein be construed as requiring that its steps be performed in a specific order. Therefore, when a method claim does not actually recite that its steps follow a certain order or when it does not specifically indicate in any other way in the claims or description that the steps are limited to a specific order, it is not intended to imply any particular order.

[0314] Although the transitional term "comprising" may be used to disclose various features, elements, or steps of a particular aspect, it is understood that this implicitly includes alternative aspects that may be described using the transitional terms "consisting of" or "consisting essentially of." Thus, for example, implicit alternative aspects for a device comprising A+B+C include aspects where the device consists of A+B+C and aspects where the device consists essentially of A+B+C. As used herein, unless otherwise indicated, the terms "comprising" and "including" and variations thereof should be understood to be synonymous and open-ended.

[0315] The above-described aspects and features of those aspects are exemplary and may be provided alone or in any combination with any one or more features of the other aspects provided herein without departing from the scope of the present disclosure.

[0316] It will be apparent to those skilled in the art that various modifications and variations may be made to the present disclosure without departing from the scope and spirit of the present disclosure. Therefore, the present disclosure encompasses modifications and variations to aspects herein as long as they fall within the scope of the appended claims and their equivalents.

Claims

1. A method for chemically strengthening a substrate, the substrate comprising a thickness between an existing first major surface and an existing second major surface opposite the existing first major surface, the method comprising: The existing first major surface of the substrate is contacted with a molten salt solution maintained at a first temperature for a first time period, the molten salt solution comprising at least two anions associated with at least a first potassium salt and a second potassium salt, the concentration of the first potassium salt and the concentration of the second potassium salt being 2% or greater by weight of the molten salt solution, the first temperature being in the range of about 350° C. to about 400° C., and the first time period being in the range of about 10 minutes to about 90 minutes.

2. The method according to claim 1, wherein The first potassium salt includes two or more potassium atoms per anion, and the pKa of the potassium salt is 9 or greater, and the concentration of the first potassium salt ranges from about 2 wt % to about 12 wt % of the molten salt solution.

3. The method according to any one of claims 1 to 2, wherein The first potassium salt is potassium carbonate K2CO3, and the concentration of the first potassium salt ranges from about 2 wt% to about 12 wt% of the molten salt solution.

4. The method according to any one of claims 1 to 3, wherein The concentration of the first potassium salt ranges from about 2.5 wt % to about 5.0 wt %.

5. The method according to any one of claims 1 to 3, wherein The concentration of the first potassium salt ranges from about 5 wt % to about 12 wt %.

6. The method according to any one of claims 2 to 5, wherein The molten salt solution also includes 0 wt % to 5 wt % of a third potassium salt associated with a third anion, the third anion being different from anions associated with the first potassium salt and the second potassium salt, and the third potassium salt includes two or more potassium atoms per anion.

7. The method according to claim 6, wherein: The third potassium salt includes potassium sulfate, K2SO4, and the concentration of the third potassium salt is about 0.5 wt% to about 5 wt%.

8. The method according to any one of claims 1 to 7, wherein The second potassium salt is potassium nitrate KNO 3 , and the concentration of the second potassium salt ranges from about 50 wt % to about 98 wt % of the molten salt solution.

9. The method according to any one of claims 1 to 7, wherein The pH range of the molten salt solution at the first temperature is about 9 to 12.

10. The method according to any one of claims 1 to 9, wherein The presence of the first potassium salt increases the compressive stress imparted by the existing first major surface in contact with the molten salt solution by about 5% or more relative to immersing the substrate in a comparative molten salt solution having the same composition as the molten salt solution without the first potassium salt.

11. The method according to any one of claims 1 to 10, wherein The thickness of the substrate ranges from about 15 μm to about 50 μm.

12. The method of any one of claims 1 to 11, further comprising, after the first major surface is contacted with the molten salt solution: The substrate is transferred from the molten salt solution to a cooling chamber, and the temperature of the cooling chamber is reduced from an initial temperature to a final temperature at a cooling rate of about 4°C / minute to about 20°C / minute, the initial temperature ranges from about 180°C to about 300°C, and the final temperature ranges from about 25°C to about 100°C.

13. The method of claim 12, wherein: The initial temperature ranges from about 180°C to about 220°C.

14. The method according to any one of claims 12 to 13, further comprising: After the cooling chamber reaches the final temperature, the substrate is rinsed with water, an alkaline detergent solution, or a combination thereof.

15. The method according to any one of claims 1 to 14, wherein After the first major surface has been contacted with the molten salt solution, the substrate has an initial maximum compressive stress of about 800 megapascals to about 1500 megapascals.

16. The method of any one of claims 1 to 15, further comprising: contacting the existing first major surface with an acidic solution for a second time period to remove an outer layer from the existing first major surface to form a new first major surface, the acidic solution having a pH in the range of 3.5 to 4.5, and the second time period being from about 10 seconds to about 3.5 minutes; and then The new first major surface is cleaned with water.

17. A method of chemically strengthening a substrate, the substrate comprising a thickness defined between an existing first major surface and an existing second major surface opposite the existing first major surface, the method comprising: chemically strengthening the substrate in a molten salt solution maintained at a first temperature for a first time period, the first temperature being in a range of about 350° C. to about 400° C., and the first time period being in a range of about 10 minutes to about 90 minutes; contacting the existing first major surface with an acidic solution for a second time period to remove an outer layer from the existing first major surface to form a new first major surface, the acidic solution having a pH in the range of 3.5 to 4.5, and the second time period being from about 10 seconds to about 3.5 minutes; and then The new first major surface is cleaned with water.

18. The method according to any one of claims 16 to 17, wherein The second temperature ranges from about 20°C to about 25°C.

19. The method according to any one of claims 16 to 18, wherein In terms of weight % of the acidic solution, the acidic solution comprises: about 0.5 wt% to about 1.5 wt% HF; and About 0.75 wt% to about 2.5 wt% NH4F.

20. The method according to any one of claims 16 to 19, wherein The acidic solution removes the outer layer at a rate of about 1.0 micron / minute or less.

21. The method according to any one of claims 16 to 20, wherein The substrate comprises an initial maximum compressive stress before contacting the acidic solution, the substrate comprises a final maximum compressive stress after contacting the acidic solution, and the final maximum compressive stress is about 10% to about 25% less than the initial maximum compressive stress as a percentage of the initial maximum compressive stress.

22. The method of any one of claims 16 to 21, wherein: The ultimate maximum compressive stress ranges from about 700 MPa to about 1200 MPa.

23. The method of any one of claims 16 to 22, wherein: The substrate exhibits a pen-down threshold height of 20 cm or greater in the pen-down height.

24. The method of any one of claims 16 to 23, wherein: When the thickness ranges from about 50 microns to about 100 microns, about 30% or more of the substrate samples can withstand a parallel plate spacing of 3 mm.

25. The method of any one of claims 16 to 23, wherein The thickness was 10 microns to 50 microns, and 90% or more of the substrate samples were able to withstand a parallel plate spacing of 2 mm.

26. A chemically strengthened substrate comprising: a thickness defined between a first major surface and a second major surface opposite the first major surface, the thickness being from about 10 microns to about 100 microns; as well as a first compressive stress region extending from the first major surface to a first compressive depth, the first layer depth of potassium being about 5 microns or greater, and a maximum first compressive stress being about 650 MPa to about 1200 MPa, The chemically strengthened substrate includes a glass-based material, 95% or more of the chemically strengthened substrate samples are able to withstand a parallel plate spacing of 5 mm, and the substrate exhibits a pen drop threshold height of 10 cm or greater in a pen drop test.

27. The chemically strengthened substrate according to claim 24, wherein The composition of the chemically strengthened substrate is, in terms of mole % of the chemically strengthened substrate: about 60 mol % to about 70 mol % SiO2; about 8 mol% to about 16 mol% Al2O3; about 12 mol % to about 18 mol % Na2O; about 2 mol% to about 6 mol% MgO; and About 0.1 mol % to about 2.0 mol % CaO.

28. The chemically strengthened substrate according to any one of claims 26 to 27, wherein 90% or more of the substrate samples were able to withstand a parallel plate spacing of 5 mm.

29. The chemically strengthened substrate according to any one of claims 26 to 28, wherein The thickness was from about 10 microns to about 50 microns, and 90% or more of the substrate samples were able to withstand a parallel plate spacing of 2 mm.

30. The chemically strengthened substrate according to any one of claims 26 to 29, wherein About 30% or more of the chemically strengthened substrate samples were able to withstand a parallel plate spacing of 3 mm.

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