TW202235392A - Ion exchangeable silicate glass - Google Patents

Abstract

The present invention describes a chemically strengthened cover glass composition that has high Three Dimensional Forming Parameter (TDFP). The TDFP is defined as 1 / (Glass Transition Temperature (Tg) * Coefficient of Thermal Expansion (CTE)). When the TDFP of the glass is greater than 220, the glass has high three-dimensional (3D) forming capabilities. The 3D forming capabilities of a cover glass can be enhanced by lower glass transition temperature and decreasing CTE. The glass composition is well suited for 3D forming and has high toughness, better service durability and high impact strength.

Description

ion exchangeable silicate glass

The present invention relates to a silicate glass capable of chemical strengthening. More specifically, the present invention relates to cover glass compositions with good 3D formability. Even more specifically, the present invention relates to the three-dimensional forming parameter (TDFP) which determines the 3D formability of glass.

In recent years, glass substrates have been widely used to protect display screens of various electronic devices such as mobile phones, entertainment devices, tablet computers, laptop computers, digital cameras, and wearable devices. As the size of display screens increases and the thickness of electronic devices decreases, the cover glass becomes more susceptible to scratches and cracks when subjected to impact (eg, contact with hard, angular objects). For this reason, a need has been raised for chemically strengthened glass with high strength and durability. In addition, the use of curved or flexible displays is gaining more and more attention in the consumer electronics market. Accordingly, cover glasses used in electronic devices are now evolving from flat (2D) to curved (3D) forms or shapes. Since the cover glass in 3D form helps to strengthen the corners/edges of curved or flexible displays, there is a need for glass compositions with good 3D formability.

Furthermore, the properties of the cover glass are highly dependent on the reaction temperature and glass composition. Compounds in various proportions have been used as raw materials for the production of cover glasses. In addition, the cover glass is chemically strengthened by various processes such as ion exchange process. This chemically strengthened glass has excellent performance properties. There is a need for cover glass compositions with appropriate 3D formability, thermal expansion properties, and annealing glass temperatures. In view of the foregoing, there is a need for a method of determining the 3D formability of glass compositions.

Objects of the Invention Some of the objects of the invention are described herein. One object of the present invention is to provide a cover glass composition. Another object is to provide cover glass compositions with high strengthening properties.

Another object of the present invention is to provide cover glass compositions having a high three-dimensional forming parameter (TDFP) describing high 3D formability. TDFP is defined as 1/(glass transition temperature (Tg) x coefficient of thermal expansion (CTE)).

Another object of the present invention is to provide a cover glass composition having a TDFP value greater than 220. The cover glass with TDFP value greater than 220 has good 3D molding ability.

Another object of the present invention is to provide a cover glass composition with higher toughness, lower density and longer service life.

Another object of the present invention is to subject the cover glass composition to multiple ion exchange processes.

Other objects and advantages of the present invention will be more apparent from the following description, which is not intended to limit the scope of the present invention.

In one embodiment of the present invention, a cover glass composition has been disclosed. The present invention discloses cover glass compositions with high three-dimensional forming parameters (TDFP).

In one embodiment, TDFP is defined as 1/(glass transition temperature (Tg)×coefficient of thermal expansion (CTE)).

In one embodiment, the TDFP of the glass should be greater than 220. When the TDFP is greater than 220, the glass has good 3D forming properties. When the TDFP is less than 220, the glass is not suitable for 3D molding. Glass with high strength and excellent 3D molding ability has better durability, high crack resistance, high post-damage retention strength and high sharp impact strength, and the glass can withstand more device drops before failure.

In one embodiment, the cover glass composition has reduced non-bridging oxygen (NBO), which increases the toughness of the glass.

In one embodiment, the cover glass composition has a reduced amount of SiO ₂ which is compensated by increasing the amount of B ₂ O ₃ and Al ₂ O ₃ . An increase in the amount of Al ₂ O ₃ makes the alkalinity of the glass constant. An increase in the amount of Al ₂ O ₃ leads to a good ion exchange process during the preparation of the glass composition.

In one embodiment, the glass composition further includes an alkali metal oxide. In one embodiment, the alkali metal oxide is selected from the group consisting of Li ₂ O, Na ₂ O or K ₂ O. In one embodiment, the glass composition further includes an alkaline earth metal oxide. In one embodiment, the alkaline earth metal oxide may be at least one of MgO, CaO, SrO or BaO.

In one embodiment, the cover glass composition includes about 40 mol % to about 70 mol % SiO ₂ , about 1 mol % to about 18 mol % B ₂ O ₃ , and about 10 mol % to About 32 mole % Al ₂ O ₃ . In one embodiment, the glass composition further comprises an alkali metal _oxide , wherein the sum R2O of the total alkali metal oxides present in the glass composition is from about 6 mole % to 38 mole %, and wherein R is At least one of Li, Na or K. In one embodiment, the alkali metal oxide is selected from the group consisting of Li ₂ O, Na ₂ O or K ₂ O. In one embodiment, the glass composition further includes an alkaline earth metal oxide, wherein MgO is about 0 mol% to about 5 mol%. In one embodiment, the glass composition further includes about 0 mol % to about 7 mol % of P ₂ O ₅ and about 0 mol % to about 5 mol % of ZnO. In one embodiment, the glass composition further includes about 0 mol % to about 2.5 mol % of one or more refining agents, such as SnO ₂ , Fe ₂ O ₃ , CeO ₂ , chlorides, and sulfates. The glass composition further includes from about 0 mole % to about 5 mole % _Ti02 .

In one embodiment, the cover glass may be provided with high strength through chemical strengthening through multiple ion exchanges. In one embodiment, the glass composition is well suited for dual ion exchange processes.

In one embodiment, the double ion exchange process comprises a first step of ion exchange followed by a second step of ion exchange on the outer surface region of the glass. In one embodiment, the ion exchange process is based on the size of the ions. When larger ions from an external ion exchange bath are exchanged with smaller ions in the glass, the larger ions wrap around the surface area previously occupied by smaller ions, causing compressive stress on the surface of the glass material with a corresponding increase in The strength of the glass material. The resulting compressive stress is reported to be proportional to the volume of the ion-exchanged glass.

In one embodiment, the cover glass can be used as a substrate for touch panel displays and as a back cover for such displays, such as Liquid Crystal Displays (LCDs), Field Emission Displays (FEDs), Plasma Displays (PDs), Electromagnetic Displays (PDs), Light Emitting Displays (ELD), Organic Light Emitting Diode (OLED) displays, Micro LEDs or similar displays. The glass can also be used as a substrate of a solar cell cover glass, a magnetic disk substrate, and a window glass plate. Furthermore, glass is also used as protective windows in connection with various modes of transportation, such as air, sea or land, and for wind protection in non-transportation applications. In addition, it is also used as fireproof glass. However, cover glasses are not limited to the above-mentioned applications, and can also be used, for example, as coated substrates, cooktops, semiconductor interposers, semiconductor carriers, hard disks, internal displays, automotive windshields, and many other applications.

These and other aspects, advantages and salient features of the invention will become apparent from the following detailed description.

In the following description, the same reference numerals designate the same or corresponding parts in several views shown in the drawings. It should also be understood that terms such as "top", "bottom", "outwardly", "inwardly" and the like are words of convenience and should not be construed as terms of limitation unless otherwise specified. Furthermore, whenever a group is described as comprising at least one of a group of elements and combinations thereof, it is to be understood that the group may comprise, consist essentially of, or consists of it. Similarly, whenever a group is described as consisting of at least one of a group of elements or a combination thereof, it will be understood that the group may consist of any number of those said elements, alone or in combination with each other. When a range of values is recited, unless otherwise stated, the upper and lower limits of the range and any range therebetween are included. As used herein, the indefinite article "a/an" and the corresponding definite article "the" mean "at least one" or "one or more" unless stated otherwise. It should also be understood that the various features disclosed in the specification and drawings can be used in any and all combinations.

As used herein, the term "glass article/glass articles" is used in its broadest sense to include any object made entirely or in part of glass. All compositions are expressed in mole percent (Mole %) unless otherwise indicated. All temperatures are expressed in degrees Celsius (° C.) unless otherwise indicated. Unless otherwise specified, the coefficient of thermal expansion (CTE) is expressed in 10-7/°C, and represents a value measured in a temperature range of about 50°C to about 300°C. As used herein, the term "annealing point" refers to the temperature at which the viscosity of the glass is about 1×10 ^13.2 poise.

It should be noted that the terms "substantially" and "about" may be used herein to denote the inherent degree of uncertainty attributable to any quantitative comparison, value, measurement or other representation. These terms are also used herein to denote the degree by which a quantitative representation may differ from a stated reference without resulting in a change in the basic function of the subject matter at issue.

Recently, with the advancement of technology, glass has been molded to form 3D curved cover glass. The 3D curved cover glass has the advantages of being light, thin, transparent, clean, anti-fingerprint, anti-glare, hard, scratch-resistant and weather-resistant. In addition, the curved surface of the 3D curved cover glass provides the display with additional functionality for sub-display applications or better aesthetics. As described below, cover glass is used to protect the display screens (eg, touch-based displays) of electronic devices such as mobile phones, smartphones, tablet computers, wearable devices, digital cameras, and the like. The cover glass used on the back is required for better electromagnetic transmission in addition to providing strength to the device. However, the cover glass is not limited to the above-mentioned applications, and can also be used for touch panel displays, glass for solar cells, magnetic disks, interior and exterior parts of automobiles, signs, windows in vehicles, and other applications.

Various cover glass compositions are described in detail herein. The present invention generally describes lithium aluminum borosilicate (LABS) glasses and compositions thereof. Glass compositions include one or more chemical components, such as SiO ₂ , B ₂ O ₃ , Al ₂ O ₃ , Li ₂ O, and Na ₂ O. It may also contain other chemical components such as K ₂ O, ZnO, MgO, SrO, BaO, CaO, P ₂ O ₅ and TiO ₂ and the like. In addition, it may also contain refining agents such as SnO ₂ , Fe ₂ O ₃ , CeO ₂ , chlorides, sulfates, and the like.

The production process of the cover glass is greatly influenced by the molar percentage content of the components of the glass composition. The molar percentage content of the components and the reaction temperature are important factors affecting the properties of the cover glass.

3D formability is an important aspect of LABS cover glass compositions in order to use the glass compositions in various applications. In order to ensure that the cover glass composition has 3D formability, it is necessary to know the mole % range and properties of the components of the glass composition. Coefficient of thermal expansion (CTE) and glass transition temperature are key parameters to characterize glass materials.

(1) Accordingly, the present invention describes a model for calculating a three-dimensional forming parameter (TDFP) to predict the 3D formability of a cover glass. Specifically, the present invention discloses a cover glass composition with higher TDFP. TDFP is defined as the inverse ratio of the product of glass transition temperature (Tg) and coefficient of thermal expansion (CTE). For example, TDFP can be represented by the following equation (1):

(1)

The calculated TDFP values may be helpful in understanding the 3D formability of glass compositions. The above equation is understood as follows: Tg represents the viscosity of the glass (10 ¹³ Poise or 10 ¹² Pa.s) constant at this temperature. Therefore, if the Tg is low, the viscosity at the same 3D molding temperature is expected to be low. Therefore, 3D molding will be easier. On the other hand, lower CTE will lead to lower residual stress of glass products after 3D forming. Therefore, the reciprocal of the product of Tg and CTE, that is, TDFP represents the 3D formability of glass, and the higher the TDFP, the better the 3D formability.

In one embodiment, when the TDFP is greater than 220, the glass has good 3D forming properties. When the TDFP is less than 220, the glass is not suitable for 3D molding. Glass with high strength and excellent 3D formability has better durability, high crack resistance, high post-damage retention strength and high sharp impact strength, and the glass can withstand more device drops before failure.

In one embodiment, the lower the Tg and CTE of the glass, the higher the 3D formability of the glass. Lower Tg and CTE values can be obtained by increasing the content of B ₂ O ₃ or by decreasing the content of at least one of Al ₂ O ₃ or SiO ₂ .

In one embodiment, the cover glass has reduced non-bridging oxygen (NBO), which increases the toughness of the glass.

In one embodiment, the glass composition used to obtain the cover glass includes various components such as SiO ₂ , Al ₂ O ₃ and B ₂ O ₃ . In one embodiment, the glass composition further includes other components, such as at least one of R ₂ O, RO, P ₂ O ₅ , ZnO, ZrO ₂ , SnO ₂ , TiO ₂ , CeO ₂ or Fe ₂ O ₃ .

In one embodiment, SiO ₂ is a glass network forming component. In the case where the SiO ₂ content is too high, the glass is difficult to melt and form, or the glass has too low a thermal expansion coefficient and it is difficult to have the same thermal expansion coefficient as the surrounding material. On the other hand, when the content of SiO ₂ is too low, vitrification becomes difficult. In addition, the coefficient of thermal expansion of such glass increases, and the thermal shock resistance tends to decrease. Therefore, the glass composition requires an optimal molar % of _SiO2 . In one embodiment, the cover glass composition has a reduced amount of SiO ₂ which is compensated by increasing the amount of B ₂ O ₃ and Al ₂ O ₃ . In one example, the glass composition can include about 40 mol % to about 70 mol % SiO ₂ . In the case of low _SiO2 content, the glass composition has higher acid loss.

In one embodiment, B ₂ O ₃ is a component that has the effect of lowering the liquidus temperature, high-temperature viscosity, and density of the glass, and further has the effect of improving the multiple ion exchange adaptability of the glass. _B2O3 may help to scavenge non _- bridging oxygen atoms (NBO). B ₂ O ₃ converts NBOs into bridging oxygen atoms via the formation of BO ₄ tetrahedra, thereby increasing the toughness of the glass by minimizing the number of weak NBOs. B ₂ O ₃ reduces the hardness of the glass, which, combined with the higher toughness brought about by the removal of NBO, reduces brittleness, resulting in a mechanically durable glass. The B ₂ O ₃ content thereof may range from about 1 mol % to about 18 mol %. _In the case where _SiO2 is replaced by B2O3, the _acid loss of the glass composition increases.

_In one embodiment, the amount of _Al2O3 in the glass composition is increased such that the alkalinity of the glass is kept constant. _In one embodiment, _Al2O3 is a component that enhances suitability for multiple ion exchanges. In an example, the glass composition may include about 10 mol % to about 32 mol % Al ₂ O ₃ . In the case where _SiO2 is replaced by _Al2O3 , the _acid loss of the glass composition increases.

In one embodiment, the glass composition further includes alkali metal oxides, wherein the sum R ₂ O of the alkali metal oxides ranges from about 6 mol% to about 38 mol%. In one embodiment, the alkali metal oxide is selected from the group consisting of Li ₂ O, Na ₂ O or K ₂ O.

Higher alkali oxide content promotes melting, which softens the glass, enables ion exchange, reduces melt resistivity, and disrupts the glass network, which increases thermal expansion and reduces durability. The glass composition may include about 3 mol% to about 18 mol% Na2O, about ₃ mol% to about 18 mol% _Li2O , and about 0 mol% to about 2 mol% K ₂ O. In one embodiment, for the glass composition to be the cover glass, the Al/R2O ratio is from about _0.5 to about 1.7.

In one embodiment, the glass composition further includes an alkaline earth metal oxide, wherein MgO is in a range of about 0 mol% to about 5 mol%. In one embodiment, the alkaline earth metal oxide may be at least one of MgO, CaO, SrO or BaO. Alkaline earth oxides may help produce a steeper viscosity curve for the glass. Replacing alkali metal oxides with alkaline earth metal oxides results in higher annealing and strain points of the glass, while lowering the melting temperature required to produce high-quality glass.

In one embodiment, the glass composition further includes about 0 mol % to about 7 mol % of P ₂ O ₅ . P ₂ O ₅ is a component that improves the ion exchange suitability of glass, and is particularly effective in increasing the depth of a compressive stress layer. In the case where SiO ₂ is replaced by P ₂ O ₅ , higher P ₂ O ₅ content may lead to higher devitrification temperature of the glass composition.

In an embodiment, the glass composition may or may not include ZnO. In an exemplary embodiment, the glass may be free of ZnO. In another exemplary embodiment, the glass may include ZnO at about 0 mol % to about 5 mol %. In one embodiment, the glass composition further includes about 0 mol % to about 2.5 mol % of one or more refining agents, such as SnO ₂ , Fe ₂ O ₃ , CeO ₂ , chlorides, and sulfates. In one embodiment, the glass composition further includes about 0 to 5 mol % TiO ₂ , which facilitates the preparation of glass-based articles, such as glass ceramics.

The present invention describes the optimal mole % of the various components of the composition. The cover glass composition includes about 40 mol % to about 70 mol % SiO ₂ , about 10 mol % to about 32 mol % Al ₂ O ₃ , and about 1 mol % to about 18 mol % B ₂ O ₃ . In one embodiment, the glass composition further includes an alkali metal oxide, wherein the sum R ₂ O of the total alkali metal oxides present in the glass composition is about 6 mol% to 38 mol%. In one embodiment, the alkali metal oxide is selected from the group consisting of Li ₂ O, Na ₂ O or K ₂ O. In one embodiment, the glass composition further includes an alkaline earth metal oxide, wherein MgO is about 0 mol% to about 5 mol%. In one embodiment, the glass composition further includes about 0 mol % to about 7 mol % of P ₂ O ₅ and about 0 mol % to about 5 mol % of ZnO. In one embodiment, the glass composition further includes about 0 mol % to about 2.5 mol % of one or more refining agents, such as SnO ₂ , Fe ₂ O ₃ , CeO ₂ , chlorides, and sulfates. The glass composition further includes from about 0 mole % to about 5 mole % _Ti02 .

Table 1 illustrates non-limiting exemplary glass compositions and their corresponding physical properties, including glass transition temperature (Tg), density, Young's modulus (YM), coefficient of thermal expansion (CTE), annealing temperature, Poisson's ratio , shear modulus, acid test loss and TDFP. Mole % 1 2 3 4 5 6 7 8 SiO ₂ 45.54 49.61 54.02 41.35 50.20 48.01 54.20 55.21 B ₂ O ₃ 10.29 8.18 6.81 11.20 7.27 8.22 9.21 7.81 Al ₂ O ₃ 25.74 23.70 21.17 27.89 23.25 23.44 20.00 17.48 Na ₂ O 10.71 9.75 8.68 10.89 8.70 9.81 10.00 9.00 Li ₂ O 7.42 8.04 8.05 7.74 8.30 6.84 6.50 7.60 K ₂ O 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.33 ZnO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 MgO 0.00 0.00 0.00 0.00 0.03 0.17 0.00 0.00 P ₂ O ₅ 0.22 0.64 1.18 0.85 2.17 3.43 0.00 2.50 _SnO2 0.080 0.080 0.080 0.080 0.080 0.080 0.080 0.080 TiO ₂ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 total 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 Al/ R ₂ O 1.42 1.33 1.27 1.50 1.37 1.41 1.21 1.03 nature Tg ( °C ) 552 554 560 550 558 556 588 554 CTE (×10 ^-7 ) / ℃ (50-300 ℃ ) 73.0 75.0 77.0 72.0 76.0 74.0 72.0 76.0 Density (g/cc) 2.43 2.42 2.42 2.43 2.42 2.41 2.40 2.38 YM (GPa) 79.7 77.5 - - - - 75.9 73.0 Annealing temperature ( °C ) 562 564 570 560 568 566 598 564 Poisson's ratio 0.25 0.23 - - - - 0.24 - Shear modulus (GPa) 31.9 31.5 - - - - 30.6 - Acid test loss (5% HCL , 24 hours, 95 ℃ ) (mg/cm ² ) - - - - - - - 53.6 TDFP 248.2 240.7 231.9 252.5 235.8 243.0 236.2 237.5 Table 1: Exemplary compositions and physical properties of glasses

Table 2 illustrates non-limiting exemplary glass compositions and their corresponding physical properties, including glass transition temperature (Tg), density, Young's modulus (YM), coefficient of thermal expansion (CTE), annealing temperature, Poisson's ratio , shear modulus, acid test loss and TDFP. Mole % 9 10 11 12 13 14 15 16 SiO ₂ 54.29 55.09 55.25 55.50 55.60 57.75 57.20 65.42 B ₂ O ₃ 7.81 7.10 6.17 8.00 7.20 6.17 7.00 1.78 Al ₂ O ₃ 18.00 18.20 18.20 18.10 18.50 17.40 17.40 12.00 Na ₂ O 9.00 9.00 9.90 8.50 8.50 9.40 8.50 8.39 Li ₂ O 8.00 8.00 7.30 7.42 7.42 7.30 7.42 6.82 K ₂ O 0.33 0.33 0.90 0.40 0.40 0.90 0.45 0.00 ZnO 0.00 0.00 0.00 0.50 0.80 0.00 0.45 3.51 MgO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 P ₂ O ₅ 2.50 2.20 2.20 1.50 1.50 1.00 1.50 2.00 _SnO2 0.080 0.080 0.082 0.082 0.082 0.082 0.082 0.073 _{Fe2O3 _} 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.009 TiO ₂ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 total 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 Al/ R ₂ O 1.04 1.05 1.01 1.11 1.13 0.99 1.06 0.79 nature Tg ( °C ) 550 570 577 574 583 577 579 630 CTE (×10 ^-7 ) / ℃ (50-300 ℃ ) 77.0 77.9 78.0 71.0 73.0 81.6 76.0 74.0 Density (g/cc) 2.38 2.38 2.40 2.40 2.40 2.39 2.39 2.44 YM (GPa) 74.0 - 74.4 74.0 75.0 75.0 75.0 76.0 Annealing temperature ( °C ) - - 587 584 593 587 589 637 Poisson's ratio - - 0.22 0.22 0.24 0.22 0.22 0.23 Shear modulus (GPa) - - 30.5 30.3 30.2 30.7 30.7 30.7 Acid test loss (5% HCL , 24 hours, 95 ℃ ) (mg/cm ² ) - - 45.6 - - - - - TDFP 236.1 225.2 222.2 245.4 235.0 212.4 227.3 214.5 Table 2: Exemplary compositions and physical properties of glasses

Table 3 illustrates non-limiting exemplary glass compositions and their corresponding physical properties, including glass transition temperature (Tg), density, Young's modulus (YM), coefficient of thermal expansion (CTE), annealing temperature, Poisson's ratio , shear modulus, acid test loss and TDFP. Mole % 17 18 19 20 twenty one twenty two twenty three twenty four SiO ₂ 60.42 60.42 58.42 58.42 59.00 57.25 57.99 56.91 B ₂ O ₃ 3.20 3.20 5.20 5.20 4.50 5.41 6.44 7.10 Al ₂ O ₃ 19.11 19.11 18.11 17.11 18.00 17.45 17.68 18.10 Na ₂ O 8.56 8.56 9.56 9.56 9.50 9.21 9.33 8.50 Li ₂ O 6.35 5.35 6.35 7.35 6.50 8.35 6.20 7.10 K ₂ O 0.14 0.14 0.14 0.14 0.22 0.13 0.14 0.14 ZnO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 MgO 0.82 1.32 0.82 0.82 0.60 0.79 0.80 0.76 P ₂ O ₅ 1.37 1.87 1.37 1.37 1.60 1.32 1.34 1.37 _SnO2 0.020 0.020 0.020 0.023 0.080 0.084 0.0849 0.023 TiO ₂ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 total 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 Al/ R ₂ O 1.27 1.36 1.13 1.00 1.11 0.99 1.13 1.15 nature Tg ( °C ) 648 652 616 585 608 - - 589 CTE (×10 ^-7 ) / ℃ (50-300 ℃ ) 73.0 74.1 71.6 76.3 76.0 - - 71.2 Density (g/cc) 2.41 2.40 2.40 2.40 2.40 - 2.39 2.39 YM (GPa) - - - 76.5 - - 75.0 72.5 Annealing temperature ( °C ) 658 662 626 595 618 - - 599 Poisson's ratio - - - 0.23 - - 0.23 0.26 Shear modulus (GPa) - - - 31.1 - - 30.5 28.9 Acid test loss (5% HCL , 24 hours, 95 ℃ ) (mg/cm ² ) - - - - - - - TDFP 211.4 206.9 226.7 224.0 216.4 - - 238.5 Table 3: Exemplary compositions and physical properties of glasses

Table 4 illustrates non-limiting exemplary glass compositions and their corresponding physical properties, including glass transition temperature (Tg), density, Young's modulus (YM), coefficient of thermal expansion (CTE), annealing temperature, Poisson's ratio , shear modulus, acid test loss and TDFP. Mole % 25 26 27 28 29 30 31 32 SiO ₂ 57.63 57.00 57.85 57.43 57.43 58.70 55.16 59.42 B ₂ O ₃ 7.10 6.00 5.20 5.20 5.20 5.77 4.24 4.20 Al ₂ O ₃ 17.11 17.74 17.25 18.10 18.10 17.11 17.59 18.11 Na ₂ O 8.90 9.50 9.70 9.56 9.56 9.00 9.10 9.56 Li ₂ O 6.90 7.35 7.70 7.35 6.91 7.35 11.50 6.35 K ₂ O 0.14 0.51 0.65 0.14 0.58 0.14 0.08 0.14 ZnO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 MgO 0.82 0.45 0.45 0.82 0.82 0.48 1.14 0.82 P ₂ O ₅ 1.37 1.37 1.37 1.37 1.37 1.37 1.07 1.37 _SnO2 0.023 0.080 0.025 0.023 0.025 0.075 0.020 0.020 TiO ₂ 0.00 0.00 0.00 0.00 0.00 0.0006 0.11 0.00 total 100.00 100.00 100.20 100.00 100.00 100.00 100.00 100.00 Al/ R ₂ O 1.07 1.02 0.96 1.06 1.06 1.04 0.85 1.13 nature Tg ( °C ) 575 - 585 600 601 585 566 618 CTE (×10 ^-7 ) / ℃ (50-300 ℃ ) 70.0 - - 79.0 79.0 71.1 73.9 75.0 Density (g/cc) 2.38 2.40 2.40 2.40 2.40 2.39 2.42 2.40 YM (GPa) 71.3 73.5 73.5 75.0 75.6 75.0 76.9 73.3 Annealing temperature ( °C ) 585 - - 610 611 595 576 628 Poisson's ratio 0.25 0.25 0.24 0.25 0.23 0.22 0.22 0.24 Shear modulus (GPa) 28.5 29.5 29.5 30.0 30.8 30.7 31.5 29.5 Acid test loss (5% HCL , 24 hours, 95 ℃ ) (mg/cm ² ) 37.4 49.9 - TDFP 248.4 - - 211.0 210.6 240.4 239.1 215.7 Table 4: Exemplary compositions and physical properties of glasses

In an exemplary embodiment, when the glass composition of the cover glass includes about 58.70 mol % of SiO ₂ , about 5.77 mol % of B ₂ O ₃ , about 17.11 mol % of Al ₂ O ₃ , about 9.00 mol % Mole % of Na ₂ O, about 7.35 mol % of Li ₂ O, about 0.14 mol % of K ₂ O, about 0.48 mol % of MgO, about 1.37 mol % of P ₂ O ₅ , about 0.075 mol When mol% SnO ₂ and about 0.0006 mol% TiO ₂ , the properties of the glass include a glass transition temperature of 585°C, a CTE of 71.1×10 ^-7 /°C, a density of 2.39 g·cm ^-3 , a density of 75 GPa Young's modulus, annealing point of 595°C, Poisson's ratio of 0.22, and shear modulus of 30.7 GPa. Here, TDFP of the glass composition was 240.4. Since the TDFP value is greater than 220, the glass composition has good 3D formability.

In another exemplary embodiment, when the glass composition of the cover glass includes about 57.43 mole % of SiO ₂ , about 5.20 mole % of B ₂ O ₃ , about 18.10 mole % of Al ₂ O ₃ , about 9.56 mol% of Na ₂ O, about 7.35 mol% of Li ₂ O, about 0.14 mol% of K ₂ O, about 0.82 mol% of MgO, about 1.37 mol% of P ₂ O ₅ and about 0.023 When the mole% of SnO ₂ is present, the properties of the glass include a glass transition temperature of 600°C, a CTE of 79×10 ^-7 /°C, a density of 2.40 g·cm ^-3 , a Young's modulus of 75 GPa, and a CTE of 610°C. Annealing point, Poisson's ratio of 0.25, and shear modulus of 30.0 GPa. Here, the TDFP of the glass composition was 211.0. Since the TDFP value is less than 220, the glass composition is not suitable for forming a 3D arc shape.

3D Formability Test An experiment was conducted on the first and second cover glass formed from two different glass compositions to determine their 3D formability in a furnace.

The first cover glass 102 is formed from a glass composition 30 comprising about 58.70 mol % SiO ₂ , about 5.77 mol % B ₂ O ₃ , about 17.11 mol % Al ₂ O ₃ , About 9.00 mol% of Na2O, about 7.35 mol% of _Li2O , about 0.14 mol _% of K2O, about 0.48 mol% of MgO, about _1.37 mol _% of _P2O5 , about 0.075 mol % SnO ₂ and about 0.0006 mol % TiO ₂ .

The second cover glass 104 is formed from a glass composition 16 comprising about 65.42 mol % SiO ₂ , about 1.78 mol % B ₂ O ₃ , about 12.00 mol % Al ₂ O ₃ , About 8.39 mole % of Na ₂ O, about 6.82 mole % of Li ₂ O, about 3.51 mole % of ZnO, about 0.073 mole % of SnO ₂ , about 0.009 mole % of Fe ₂ O ₃ and about 2.00 mole % of P ₂ O ₅ .

1A-1C illustrate images of a first cover glass and a second cover glass under different furnace conditions according to an embodiment of the present invention. The first cover glass 102 and the second cover glass 104 were kept in a furnace for 3D formability testing. As shown in FIG. 1A , before the furnace is turned on, the first cover glass 102 and the second cover glass 104 are planar at room temperature. Once the furnace was turned on, the first cover glass 102 and the second cover glass 104 were kept in the furnace at 650° C. for 10 minutes. Referring to FIG. 1B , compared to the second cover glass 104 , the first cover glass 102 is curved to some extent. The first cover glass 102 and the second cover glass 104 were further kept in the furnace at 670° C. for 10 minutes. Referring to FIG. 1C , the first cover glass 102 is further curved than the second cover glass 104 . Then close the furnace, and gradually cool the first cover glass 102 and the second cover glass to room temperature.

1D shows an image of a perspective view of a first cover glass and a second cover glass after a 3D formability test according to an embodiment of the present invention. 1E shows an image of a side view of a first cover glass and a second cover glass after a 3D formability test according to an embodiment of the invention. As shown in FIG. 1D and FIG. 1E , the first cover glass 102 is arc-shaped, and the second cover glass 104 is planar. As mentioned in Table 2 and Table 4, the TDFP value of the first cover glass 102 is greater than 220, while the TDFP value of the second cover glass 104 is less than 220. Tests have shown that glass with a TDFP value greater than 220 has higher 3D formability than glass with a TDFP value less than 220.

In one embodiment, for the two-step ion exchange process of alkali metal silicate glass, such as lithium aluminosilicate glass material, the alkali metal ions to be replaced are lithium ions (Li+). The salt bath preferably used is a sodium ion (Na+) bath and a potassium ion (K+) bath. More preferably, the salt bath used comprises salts of NaNO ₃ and KNO ₃ . In the first step of ion exchange, lithium ions are replaced by at least sodium ions within the surface of the glass material. Furthermore, in the second step of ion exchange, lithium ions or sodium ions are replaced by at least potassium ions within the surface of the glass material.

In one embodiment, during the two-step ion exchange process, one ion pair is exchanged first, followed by another ion exchange that reintroduces the original ion or introduces another ion in the outermost surface layer. In one embodiment, the ion exchange process is based on the principle that ions present in the glass are exchanged by ions of different sizes. When the larger ions from the external ion exchange bath exchange the smaller ions in the glass, the larger ions completely fill the surface, causing it to compress using the internal equilibrium tensile stress. The resulting compressive stress is reported to be proportional to the volume of the ion-exchanged glass. Once ion exchanged, the glass exhibits high resistance to cracking.

In an exemplary embodiment, glass sample compositions were subjected to a two-step ion exchange process in which the glass was first immersed in a molten salt bath containing more than 45% by weight _KNO3 and less than ₅₅ % by weight NaNO3 (which was maintained at a temperature between and 500°C) for a fixed number of hours, such as greater than 1.5 hours, followed by immersion in a molten salt bath containing more than 85% by weight _KNO3 and less than 15% by weight NaNO3 (which is maintained at a temperature between ₃₀₀ °C and at a temperature between 500° C.) for a fixed number of hours, such as greater than 0.3 hours. The process of this double ion exchange method increases the compressive stress (CS), wherein each compressive layer of the surface has a compressive stress of at least 150 MPa. Furthermore, in the double ion exchange process, the depth of the first layer extends from the glass surface to a minimum depth of 130 μm to a depth of the second layer at a maximum depth of 10 μm.

Table 5 illustrates exemplary samples defining the maximum depth of layer (DOL) and compressive stress (CS) for each step of the dual ion exchange process under different reaction conditions for a particular glass composition, eg, glass composition 30 of glass. Sample serial number Step 1 _ Step 2 _ Step 1 _ Step 2 _ Fitted data from step 1 and step 2 CT (MPa) KNO ₃ ( wt %) temperature ( °C ) time ( minutes ) KNO ₃ ( wt %) temperature ( °C ) time ( minutes ) CS (MPa) DOL (μm) CS (MPa) DOL (μm) CS (MPa) DOC (μm) CS _k (MPa) DOL (μm) 1 60% 415 110 97% 380 40 179.728 154.271 1182.665 5.156 1182.853 153.252 166.386 6.750 85.977 2 60% 415 110 97% 380 40 195.937 151.785 1163.035 5.292 1163.779 150.669 180.689 6.950 86.769 3 60% 415 110 97% 380 60 192.822 154.568 1170.113 5.876 1170.236 154.897 179.005 7.547 87.197 4 60% 415 110 97% 380 60 188.093 147.879 1164.822 5.782 1164.825 146.279 176.147 7.750 86.079 5 60% 415 110 97% 390 60 235.679 130.667 1175.610 5.587 1176.488 130.848 219.605 7.150 89.072 6 60% 415 110 97% 390 60 186.628 148.281 1164.203 5.563 1165.695 146.102 171.411 7.500 85.079 7 60% 415 110 97% 380 90 169.358 161.101 1164.668 5.945 1165.029 154.322 159.426 6.100 80.020 8 60% 415 110 97% 380 90 176.456 143.478 1156.285 5.979 1156.306 140.211 182.356 6.500 89.442 9 60% 415 110 97% 380 90 191.756 140.102 1170.932 5.921 1171.023 137.757 184.914 6.950 89.168 10 60% 415 110 97% 390 90 186.463 146.722 1179.938 5.990 1179.980 145.862 176.524 5.900 82.996 11 60% 415 110 97% 390 90 180.436 152.597 1162.249 6.052 1163.474 149.316 161.079 6.275 84.091 12 60% 415 110 90% 390 60 202.292 149.740 965.955 4.901 966.225 150.494 192.793 3.875 89.672 13 60% 415 110 100% 390 20 191.958 138.020 1528.341 3.126 1528.365 136.837 191.144 4.425 81.755 14 60% 415 110 100% 390 40 185.925 145.557 1500.696 4.541 1528.737 145.698 183.104 3.425 83.132 15 60% 415 150 97% 380 60 167.823 158.851 1121.418 5.227 1121.842 152.590 153.097 7.875 83.050 16 60% 415 150 97% 380 60 186.958 156.959 1127.874 5.338 1128.273 154.243 166.458 7.250 87.400 17 60% 415 150 97% 380 60 194.227 148.199 1134.173 5.795 1135.226 146.337 180.430 5.200 91.386 18 60% 415 150 97% 380 60 171.324 163.485 1135.180 5.759 1136.856 158.881 165.333 5.325 82.221 19 60% 415 150 97% 380 60 217.056 139.274 1102.399 5.990 1103.405 138.878 199.769 5.275 87.457 20 60% 415 150 97% 380 60 175.242 162.763 1135.176 5.799 1144.815 156.950 160.583 5.275 83.165 twenty one 50% 415 150 97% 380 60 187.144 149.175 1096.187 5.153 1097.519 148.069 175.771 7.375 89.176 twenty two 50% 415 150 97% 380 60 178.084 155.878 1098.605 5.160 1100.845 153.821 168.646 7.250 91.213 twenty three 55% 415 150 97% 380 60 183.496 148.025 1053.368 5.109 1053.386 146.585 172.590 7.925 88.763 twenty four 55% 415 150 97% 380 60 176.726 155.367 1088.811 5.133 1091.140 154.234 166.570 7.200 90.100 25 65% 415 150 97% 380 60 244.113 132.252 1107.595 5.126 1108.068 133.247 231.458 7.750 94.203 26 65% 415 150 97% 380 60 208.194 142.937 1118.563 5.190 1118.565 143.187 194.397 7.500 91.554 27 70% 415 150 97% 380 60 170.377 149.838 1077.927 6.254 1078.299 147.425 159.172 7.600 92.460 28 70% 415 150 97% 380 60 166.458 149.984 1052.971 6.498 1053.761 148.586 160.679 7.900 92.102 29 70% 415 150 97% 380 60 230.975 132.835 1113.418 5.935 1113.428 132.869 215.512 5.575 87.561 30 70% 415 150 97% 380 60 218.530 135.843 1110.074 6.013 1110.882 136.321 204.205 5.325 86.712 31 75% 415 150 97% 380 60 224.002 130.396 1140.791 7.182 1140.842 131.276 206.163 8.325 86.232 32 75% 415 150 97% 380 60 186.301 146.308 1119.884 7.089 1121.143 146.815 168.578 8.950 86.500 33 80% 415 150 97% 380 60 161.257 155.608 1144.334 8.019 1150.638 153.901 156.257 6.075 86.699 34 60% 430 130 97% 380 60 173.766 157.539 639.414 4.761 641.577 156.412 172.394 4.550 90.716 35 75% 415 150 97% 380 60 176.693 147.860 1143.228 7.316 1143.350 148.459 163.865 9.300 90.312 36 75% 415 150 97% 380 60 169.434 148.493 1118.239 7.075 1119.504 148.070 157.182 8.930 87.892 37 75% 415 150 97% 380 60 169.771 139.629 1123.578 7.980 1123.652 139.819 153.230 9.080 84.374 38 75% 415 150 97% 380 60 154.663 146.360 1131.141 7.943 1131.683 143.664 150.948 8.980 89.309 39 75% 415 150 97% 380 60 200.652 139.662 1153.731 7.915 1154.606 140.394 184.862 8.350 89.284 40 75% 415 150 97% 380 60 159.448 146.718 1137.348 7.951 1124.025 144.096 154.053 8.780 89.890 41 75% 415 150 97% 380 60 188.845 141.773 1130.485 7.305 1130.488 142.603 170.681 8.850 86.245 42 75% 415 150 97% 380 60 236.213 131.103 1131.929 7.210 1132.422 132.579 209.946 8.230 88.576 43 75% 415 150 97% 380 20 202.955 128.832 1097.609 8.509 1097.609 130.109 189.811 10.050 89.444 44 75% 415 150 97% 380 20 183.800 135.493 1077.412 8.094 1078.135 140.144 182.902 8.725 81.878 Table 5: Exemplary samples and DOC and CS for each step of the double ion exchange process

In an exemplary embodiment, the glass composition of the cover glass includes about 58.70 mole % SiO ₂ , about 5.77 mole % B ₂ O ₃ , about 17.11 mole % Al ₂ O ₃ , about 9.00 mole % mol% of Na ₂ O, about 7.35 mol% of Li ₂ O, about 0.14 mol% of K ₂ O, about 0.48 mol% of MgO, about 1.37 mol% of P ₂ O ₅ , about 0.075 mol% % of SnO ₂ and about 0.0006 mole % of TiO ₂ . The cover glass undergoes a double ion exchange process. For the first ion exchange process, the alkali metal bath contained 25% NaNO ₃ and 75% KNO ₃ by weight. This glass substrate was immersed in an alkali metal bath at a temperature of 415° C. for a period of 2.5 hours. The compressive stress of the glass is 186.301 MPa, and the corresponding depth is 146.308 μm. After immersion in the first bath, a second ion exchange treatment of the cover glass is performed. The second ion exchange bath contained 3% NaNO ₃ and 97% KNO ₃ by weight. The glass substrate was immersed in the second ion exchange bath at a temperature of 380° C. for 1 hour. The material bears a compressive stress of 1119.884 MPa, corresponding to a depth of 7.089 μm. The fitting compressive stress and compressive depth (DOC/DOL_zero) of the first ion exchange treatment are 1121.143 MPa and 146.815 μm. The fitted compressive stress (CS _k ) and depth of compression (DOC) of the second ion exchange treatment are 168.578 MPa and 8.950 μm. Since the central tension determines the fragmentation of the glass, the central tension of this double ion exchange glass is 86.500 MPa.

The cover glass composition is used for the back cover of touch panel display and display screen, such as liquid crystal display (LCD), field emission display (FED), plasma display (PD), electroluminescence display (ELD), organic light emitting Diode (OLED) displays, micro LEDs or the like. However, the cover glass is not limited to the aforementioned applications, and can also be used, for example, as a substrate of a touch panel display, a cover glass of a solar cell, a magnetic disk substrate, and a window glass.

In a particular embodiment, the cover glass is used as a protective window in connection with various modes of transportation, such as air, sea or land, as well as for wind protection in non-transportation applications. In addition, it is also used as fireproof glass. In addition, cover glass is also used as a substrate for hard disks. In addition, it can also be used in semiconductor interposers and semiconductor carriers. By adding nucleating agents, it can also be used as a cooktop in ceramized form. Finally, cover glass is used as a coated substrate in a variety of applications.

In a specific embodiment, the present invention further focuses on a back cover glass for protecting the back of electronic devices such as mobile phones, smart phones, tablet computers, wearable devices, digital cameras, and the like. The cover glass used on the back is required for better electromagnetic transmission in addition to providing strength to the device. A tinted opaque appearance may be possible for design reasons. One way to achieve this is to include one or more transition elements in the glass melt. The one or more transition elements may be Nb ₂ O ₅ , ZrO ₂ , Fe ₂ O ₃ , V ₂ O ₅ , Y ₂ O ₃ , MnO ₂ , NiO, CuO, Cr ₂ O ₃ , Co ₃ O ₄ , CoO, Co At least one of ₂ O ₃ and the like.

The present invention provides a cover glass composition having excellent 3D formability. By determining the TDFP of a glass composition, the present invention helps to control the composition in a more efficient manner. In particular, the present invention relates to a silicate glass composition capable of better durability, high crack resistance, high post-damage retention strength, and high impact strength.

While typical embodiments have been described for purposes of illustration, the foregoing description should not be considered as limiting the scope of the invention or of the appended claims. Therefore, those skilled in the art can think of various modifications, adjustments and substitutions without departing from the spirit and scope of the present invention.

102: First cover glass 104: Second cover glass

The features of the invention which are believed to be novel are set forth with particularity in the appended claims. Embodiments of the present invention will be described below in conjunction with the accompanying drawings to illustrate but not limit the scope of the claims, wherein the same reference numerals represent the same elements, and in these drawings: 1A-1C show images of a first cover glass and a second cover glass under different furnace conditions according to an embodiment of the present invention; 1D shows an image of a perspective view of a first cover glass and a second cover glass after a 3D formability test according to an embodiment of the present invention; and 1E shows an image of a side view of a first cover glass and a second cover glass after a 3D formability test according to an embodiment of the invention.

Claims (8)

An ion exchangeable silicate glass comprising: 40 to 70 molar % SiO ₂ , 1 to 18 molar % B ₂ O ₃ , 10 to 32 molar % Al ₂ O ₃ , wherein the glass favorably has a three-dimensional (3D) form when the glass has a three-dimensional forming parameter (TDFP) greater than 220, and wherein the TDFP is defined by the following expression: TDFP=1/(glass transition temperature ( Tg) x coefficient of thermal expansion (CTE)). The glass of claim 1, further comprising: 3 mol% to 18 mol% of Na ₂ O, 3 mol% to 18 mol% of Li ₂ O, 0 mol% to 2 mol% of K ₂ O, 0 mol% to 5 mol% MgO, 0 mol% to ₅ mol% ZnO, 0 mol% to 7 mol% _P2O5 , 0 mol% to 2.5 mol% % of SnO ₂ , and 0 mol% to 5 mol% of TiO ₂ . The glass of claim 2, wherein the glass composition comprises 6 mol% to 38 mol% of R ₂ O, wherein R ₂ O represents the sum of alkali metal oxides present in the glass composition. The glass according to claim 3, wherein the ratio of Al ₂ O ₃ to R ₂ O (Al ₂ O ₃ (mol%)/R ₂ O (mol%)) is in the range of 0.5 to 1.7. The glass according to claim 1, wherein the glass transition temperature Tg is lower than 700°C. The glass according to claim 1, wherein the coefficient of thermal expansion (CTE) is less than 100×10 ^-7 /°C. The glass according to claim 1, wherein the glass undergoes a double ion exchange process. The glass according to claim 1, wherein the glass is a lithium aluminum borosilicate cover glass used for displays.

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