Glass composition

Abstract

The present invention relates to a glass composition that can form an ultra-thin glass product having excellent bendability and impact resistance.

Description

glass composition

[0001] The present invention relates to a glass composition capable of forming an ultra-thin glass product having excellent bendability and impact resistance.

[0002]

[0003] Ultra-thin glass is being used in a variety of applications, including semiconductor substrates, display protective cover windows for flexible electronic devices such as foldable or rollable devices, fingerprint sensors, and automotive glazing. In particular, cover windows for flexible electronic device displays require excellent flexibility and impact resistance, and extensive research is being conducted to develop ultra-thin glass that satisfies these properties. For example, Republic of Korea Patent Publication No. 10-2020-0014266 discloses an ultra-thin glass article with high sharp contact resistance and high flexibility.

[0004] When a glass object is bent, tensile stress is applied in the direction opposite to the bending direction, and this tensile stress can cause the glass object to break. Furthermore, during the manufacturing and processing of glass, microcracks may form on the surface of the glass object, or micro-defects may develop at the edges of the glass object. The tensile stress generated when the glass object is bent can cause these cracks or defects to elongate, potentially resulting in the glass object's destruction. In this case, if a strong compressive stress exceeding the tensile stress is applied to the glass object, breakage due to bending can be minimized. Therefore, to enhance the bendability and impact resistance required for ultra-thin glass, a method of applying high compressive stress to the glass object is required.

[0005] Thermal strengthening and chemical toughening are used as methods for applying compressive stress to glass articles. Thermal strengthening is a method of applying compressive stress by heating the glass article above the glass transition temperature and then rapidly cooling it to generate stress due to the difference in temperature between the surface and the inside, and is not suitable for application to ultra-thin glass with a thickness of several hundred microns. Chemical toughening is a method of applying compressive stress by the ion exchange method included in the glass article, and is representatively, Na + Contains glass K + By immersing in a base salt bath to induce ion exchange, compressive stress is applied through the filling effect of the ion exchange area.

[0006] Chemical toughening is typically performed at temperatures ranging from 360 to 500°C. However, the appropriate time and temperature depend on the glass network structure that constitutes the glass article, which in turn is determined by the glass composition. Low process temperatures can excessively slow the ion exchange rate between sodium and potassium, while high temperatures can loosen the glass network structure, reducing the compressive stress generated by ion exchange. Furthermore, prolonged chemical toughening can also loosen the glass structure, lowering the compressive stress. Therefore, a glass article is required that can be chemically toughened in a short period of time at low temperatures, or that can be chemically toughened at high temperatures for a long period of time without loosening the glass structure, thereby increasing or at least maintaining the compressive stress.

[0007]

[0008] The present invention provides a glass composition capable of forming an ultra-thin glass product with excellent bendability and impact resistance. In particular, the present invention provides an ultra-thin glass article having high compressive stress by controlling the composition of the glass composition.

[0009]

[0010] The present invention provides a glass composition comprising, with respect to the total content of the glass composition, 60 to 75 mol% of SiO2, 10 to 15 mol% of Al2O3, 10 to 20 mol% of Na2O, 0.01 to 5 mol% of K2O, 3 to 10 mol% of MgO, 0.01 to 3 mol% of CaO, 0.1 to 3 mol% of ZrO2, and 0.01 to 0.5 mol% of SnO2, and wherein [MgO] / ([MgO]+[CaO]) is 0.65 to 0.95. Here, [MgO] is the content (mol%) of MgO with respect to the total content of the glass composition, and [CaO] is the content (mol%) of CaO with respect to the total content of the glass composition.

[0011]

[0012] The present invention provides a glass composition capable of forming an ultra-thin glass product with excellent bendability and impact resistance. The present invention provides an ultra-thin glass article having high compressive stress by controlling the composition of the glass composition.

[0013]

[0014] The present invention will be described in detail below. However, it is not limited to the following description, and each component may be modified or selectively mixed as needed. Therefore, it should be understood that all modifications, equivalents, and alternatives included within the spirit and technical scope of the present invention are included.

[0015] The glass composition of the present invention comprises, based on the total content of the glass composition, 60 to 75 mol% of SiO2, 10 to 15 mol% of Al2O3, 10 to 20 mol% of Na2O, 0.01 to 5 mol% of K2O, 3 to 10 mol% of MgO, 0.01 to 3 mol% of CaO, 0.1 to 3 mol% of ZrO2, and 0.01 to 0.5 mol% of SnO2, and [MgO] / ([MgO]+[CaO]) is 0.65 to 0.95.

[0016] In the above formula,

[0017] [MgO] is the content of MgO (mol%) relative to the total content of the glass composition,

[0018] [CaO] is the content of CaO (mol%) relative to the total content of the glass composition.

[0019] The glass composition of the present invention includes SiO2. SiO2 is a glass-forming oxide in aluminosilicate glass articles, and serves to provide rigidity to the glass. The glass composition may include 60 to 75 mol%, for example, 60 to 70 mol%, of SiO2 based on the total content of the glass composition. If the content of SiO2 is less than the aforementioned range, the strength of the glass may be reduced, and if it exceeds the aforementioned range, the melting temperature may increase, which may impair the formability of the glass article.

[0020] The glass composition of the present invention includes Al2O3. Al2O3 functions as an intermediate, charge balancer, or glass-forming oxide in aluminosilicate glass articles, and together with SiO2, it plays a role in providing strength to the glass. Al2O3 and an alkali metal oxide R2O (R=Li) + , Na + , K + ) content affects the structure and properties of aluminosilicate glasses. When Al2O3 is included in the glass composition in excess of R2O, Al2O3 no longer acts as a Si 4+ Not substituted for, Al 5+ , Al 6+ As the shape changes, the liquid fragility index (m) increases, which can induce crystallization of the glass. In addition, as the content of Al2O3 increases, the melting temperature increases, which can impair the formability of the glass.

[0021] With respect to the total content of the glass composition, Al2O3 may be included in an amount of 10 to 15 mol%, for example, 10 to 13 mol%. If the content of Al2O3 is less than the aforementioned range, the strength of the glass may be reduced, and if it exceeds the aforementioned range, crystallization of the glass may be induced or the melting temperature may be increased, thereby hindering the formability of the glass product.

[0022] The glass composition of the present invention comprises an alkali metal oxide. Alkali metal oxide R2O(R=Li + , Na + , K + ) functions as a modifier or charge compensator. R2O destroys the bonds of the glass former, breaking the Si-O bond to form a non-crosslinked oxide, which lowers the melting point and viscosity of the glass and affects the coefficient of thermal expansion of the glass. For example, Na2O and K2O can be used together as alkali metal oxides, in which case acid resistance can be increased.

[0023] The glass composition may contain 10 to 25 mol%, for example, 13 to 21 mol%, of an alkali metal oxide, based on the total content of the glass composition. For example, the glass composition may contain 10 to 20 mol%, for example, 13 to 18 mol%, of Na2O, and 0.01 to 5 mol%, for example, 0.01 to 3 mol%, of K2O, based on the total content of the glass composition. If the content of Na2O is less than the aforementioned range, the Na content inside the glass may be reduced, thereby reducing the number of alkali metals that can participate in chemical toughening, which may lower the compressive stress. If the content of K2O is more than the aforementioned range, the Si-O bond of SiO2 may be broken, resulting in a reduction in free volume inside the glass, which may lower the compressive stress and ion exchange depth. If the content of K2O is less than the aforementioned range, acid resistance may be weakened, and if the content of K2O is more than the aforementioned range, the compressive stress due to chemical toughening may be lowered, due to a decrease in the Na content inside the glass.

[0024] The glass composition of the present invention comprises an alkaline earth metal oxide. The alkaline earth metal oxide R'O (R'=Mg, Ca, Sr, Ba) can affect the Al-avoidance violation, and as a result, can cause a change in the internal structure of the aluminosilicate glass.

[0025] For example, the alkaline earth metal compound may include MgO. MgO has a lower atomic number than other alkaline earth metals, which can lower the density, reduce the strain point, and lower the high-temperature viscosity, thereby significantly improving the melting property of the glass. However, among alkaline earth metals, Mg 2+ is Ca 2+ , Sr 2+ , Ba 2+ Compared to Al2O3, it has a high ionic field strength and facilitates the formation of 5- and 6-coordinated aluminum. In the aluminosilicate composition, Al2O3 functions as a glass network former or an intermediate oxide to form a strong network structure of the glass, but when it has 5- and 6-coordination numbers, it causes crystallization of the glass. Therefore, when MgO is included, it causes a violation of the Al-avoidance law of the internal structure of the aluminosilicate glass, inducing Si-O-Si and Al-O-Al bonds, so if it is included in large quantities, it can cause crystal precipitation of Mg-Si-O series. In addition, the high ionic field strength reduces the free volume in the glass, resulting in the formation of Na inside the glass. + K has a larger atomic radius than + It becomes difficult for ions to penetrate into the glass, so the substituted K + This may cause the compressive stress caused by ions to be lowered or the ion exchange depth to be lowered.

[0026] For example, the alkaline earth metal compound may include CaO. CaO can significantly improve the melting property of glass by lowering the high-temperature viscosity of the glass. Ca2+ is Mg 2+ Compared to Ca, the electric field intensity is low, so it is less likely to cause violation of the Al-Avoidance law, and as a result, the Si-O-Al structure can be easily formed in the glass. In addition, 2+ It can also serve as a charge compensation system.

[0027] The glass composition may contain 3 to 13 mol%, for example, 3.5 to 9.7 mol%, of alkaline earth metal oxides based on the total content. For example, the glass composition may contain 3 to 10 mol%, for example, 3 to 8 mol%, of MgO, and 0.01 to 3 mol%, for example, 0.5 to 1.7 mol%, of CaO based on the total content. If the content of MgO is less than the above-mentioned range, melting of the glass material may become difficult, and if it exceeds the above-mentioned range, the free volume inside the glass may be reduced, making chemical toughening difficult. If the content of CaO is out of the above-mentioned range, a compressive stress relaxation phenomenon may occur during chemical toughening, lowering the compressive stress, and thus, bendability and impact resistance may deteriorate.

[0028] The glass composition of the present invention includes ZrO2. When alkali ions are contained in a large amount compared to Al2O3 and ZrO2, ZrO2 has 6 coordinations. On the other hand, when the ZrO2 content is higher than the number of alkali ions, ZrO2 has 8 coordinations. When there are many alkali ions, Al2O3 has [AlO4] - In the form of [ZrO6], there is only one ion that can trap Na ions, but ZrO2 can trap two Na ions, so more Na participates in ion exchange, or 2- Even if Zr does not participate in ion exchange, the binding of Na to Zr causes an increase in the [Al2O3 / R2O] ratio. However, an excess of ZrO2 can induce crystallization of the glass article or increase the melting point of the glass.

[0029] With respect to the total content of the glass composition, ZrO2 may be included in an amount of 0.1 to 3 mol%, for example, 0.1 to 1.5 mol%. If the content of ZrO2 is less than the aforementioned range, it may be difficult to improve the compressive stress by chemical toughening, which may result in a decrease in bendability and impact resistance, and if it exceeds the aforementioned range, it may cause crystallization of the glass article or increase the melting point of the glass material.

[0030] The glass composition of the present invention includes SnO2. When glass is melted, bubbles may be formed due to gases generated by the decomposition of batch components, moisture attached to the interface of raw materials, atmospheric gases, etc. If bubbles exist in the manufactured glass article, the strength of the glass article is significantly reduced, and in particular, in the case of glass articles for display, defects are caused by bubbles. Therefore, bubble removal (fining) is an important process during glass manufacturing. SnO2 is a fining agent that can be used at high temperatures and can be used in the manufacture of alkali aluminosilicate glass having a melting point of 1,500°C or higher. In particular, SnO2 undergoes a reduction reaction (SnO2 → SnO + 1 / 2O2) at high temperatures of 1,500°C or higher, strongly releasing oxygen, and the released oxygen absorbs gaseous contents such as CO2, SO2, and N2 remaining in the glass melt and discharges them from the glass article. On the other hand, when the temperature of the glass melt is lowered, SnO undergoes an oxidation reaction (SnO + 1 / 2O2 → SnO2) and strongly absorbs oxygen. Thus, at high temperatures, it removes air bubbles by releasing oxygen, and at relatively low temperatures, it absorbs oxygen and removes air bubbles remaining in the glass melt, effectively removing air bubbles from glass products. In addition, SnO2 has less toxicity than other high-temperature fining agents (e.g., As2O3, Sb2O3, etc.), so there are fewer restrictions on its use.

[0031] With respect to the total content of the glass composition, SnO2 may be included in an amount of 0.01 to 0.5 mol%, for example, 0.01 to 0.3 mol%. If the content of SnO2 is less than the above-mentioned range, the clearing effect within the glass may be insufficient, and if it exceeds the above-mentioned range, a haze phenomenon may occur on the glass surface, or Sn crystals may be formed, causing a glass devitrification phenomenon.

[0032] The glass composition of the present invention may further include SrO, BaO, Ba2O3, and mixtures thereof in addition to the above-described oxides. For example, the glass composition may include 0.01 to 3 mol% of SrO, for example, 0.5 to 1.7 mol%, 0.01 to 3 mol% of BaO, for example, 0.5 to 1.7 mol%, and 0.01 to 3 mol% of Ba2O3, for example, 0.5 to 1.7 mol%, based on the total content of the glass composition.

[0033] In the present invention, [MgO] / ([MgO]+[CaO]) is 0.65 to 0.95. For example, [MgO] / ([MgO]+[CaO]) may be 0.7 to 0.95, or as another example, 0.75 to 0.9. In the above formula, [MgO] is the content (mol%) of MgO with respect to the total content of the glass composition, and [CaO] is the content (mol%) of CaO with respect to the total content of the glass composition.

[0034] MgO causes violation of Al avoidance in glass, which is beneficial for chemical toughening. 4+ Reduce the number, Al 5+ Increase the number. Al 5+can act as a glass network modifier and increase the number of non-bridging oxygens in the glass. CaO can improve Al-O-Si in Si-O-Si, Al-O-Al bonds due to violation of Al avoidance by Mg, thereby suppressing the increase in glass liquidus temperature and improving chemical toughening properties. In the present invention, by controlling [MgO] / ([MgO]+[CaO]) within the above-mentioned range, the compressive stress can be increased while preventing the increase in liquidus temperature. Specifically, when [MgO] / ([MgO]+[CaO]) is less than the above-mentioned range, the compressive stress after chemical toughening can be lowered, and when it exceeds the above-mentioned range, the compressive stress after chemical toughening can be lowered and the liquidus temperature can be improved.

[0035] In the present invention, [Al2O3] / [R2O] may be 0.6 to 0.75. In the above formula, [Al2O3] is the content (mol%) of Al2O3 with respect to the total content of the glass composition, and [R2O] is the content (mol%) of an alkali metal oxide (R2O) with respect to the total content of the glass composition.

[0036] When [Al2O3] / [R2O] is greater than 1, Al can take a 5 or 6 coordination form, which can cause crystallization of the glass as the liquid fragility index increases. When [Al2O3] / [R2O] is less than 1, Al2O3 is arranged by substitution at the Si position, and at this time, depending on the ratio of Al and Na, Al 3+ is in the four-coordinated form ([AlO4] - ) and at this time, to satisfy charge neutrality, [AlO4] - Wow Na +When a bond is formed, the bonding energy is lower than that of Na combined with non-bridging oxygen, which is advantageous for ion movement. In addition, the number of non-bridging oxygens in the glass decreases and the number of bridging oxygens increases, in which case the charge density decreases, making it relatively easy for cations to move, which is advantageous for chemical strengthening. In addition, as the number of non-bridging oxygens decreases, the free volume of the glass increases, which is advantageous for alkali movement. However, as [Al2O3] / [R2O] approaches 1, the temperature required for melting and working increases, which may cause a rapid increase in viscosity during glass manufacturing. On the other hand, when [Al2O3] / [R2O] is less than 0.6, an excessive amount of R2O can cleave the Si-O bond and generate a large amount of non-bridging oxygen, which may result in a lower charge density, which may be disadvantageous for chemical strengthening. In the present invention, by controlling [Al2O3] / [R2O] within the aforementioned range, it is possible to increase the compressive stress by promoting chemical toughening while preventing crystallization of the glass. Specifically, if [Al2O3] / [R2O] is less than the above-mentioned range, the number of non-bridging oxygen atoms may increase, which may lower the compressive stress, and if it exceeds the above-mentioned range, the liquidus temperature may increase, which may cause difficulties in glass manufacturing.

[0037] In the present invention, [Al2O3] / [SiO2] may be 0.15 to 0.2. In the above formula, [Al2O3] is the content (mol%) of Al2O3 with respect to the total content of the glass composition, and [SiO2] is the content (mol%) of SiO2 with respect to the total content of the glass composition.

[0038] The distribution of TOT (T = Al, Si) bond angles changes depending on [Al2O3] / [SiO2], which affects the compressive stress in chemical toughening. As the [Al2O3] / [SiO2] ratio increases, the compressive stress increases. However, if it is excessively high, the liquidus temperature of the glass may increase, which may violate Al-avoidance and cause the formation of Si-O-Si, Al-O-Al bonds. In the present invention, by controlling [Al2O3] / [SiO2] within the above-mentioned range, the increase in the liquidus temperature can be prevented, while the compressive stress after chemical toughening can be increased. Specifically, when [Al2O3] / [SiO2] is less than the above-mentioned range, the compressive stress may decrease, and when it exceeds the above-mentioned range, the liquidus temperature may increase or the compressive stress may decrease.

[0039] In the present invention, [K2O] / [R2O] may be 0.01 to 0.15. In the above formula, [K2O] is the content (mol%) of K2O with respect to the total content of the glass composition, and [R2O] is the content (mol%) of an alkali metal oxide (R2O) with respect to the total content of the glass composition.

[0040] K ions have a larger atomic radius than Na ions or Na ions, and thus contribute more to the packing effect occurring inside the glass during ion exchange than other alkali metal ions. The driving force during ion exchange is generated from the difference in the concentration of K ions in the KNO3 salt bath and the concentration of K ions inside the glass, and the stress occurring inside the glass due to the packing effect is related to the volume change occurring before and after the ion exchange and the K ion concentration causing the volume change. The greater the difference in the content of K ions between the KNO3 salt bath and inside the glass, the higher the driving force required for ion exchange can be. When [K2O] / [R2O] inside the glass is 0, the increase in volume change due to the difference in ionic radius is maximized and the compressive stress increases. However, when [K2O] / [R2O] is 0, the liquidus temperature increases dramatically. In the present invention, by controlling [K2O] / [R2O] within the aforementioned range, the increase in the liquidus temperature can be suppressed, while the compressive stress after chemical toughening can be increased. Specifically, when [K2O] / [R2O] is below the above-mentioned range, the liquidus temperature can increase dramatically, and when it exceeds the above-mentioned range, the compressive stress can decrease.

[0041] In the present invention, [CaO]+[MgO] may be 3.8 to 6.8. In the above formula, [CaO] is the content (mol%) of CaO relative to the total content of the glass composition, and [MgO] is the content (mol%) of MgO relative to the total content of the glass composition.

[0042] Alkaline earth metal compounds can significantly improve the melting property of glass by lowering the high-temperature viscosity of the glass. However, if a large amount of alkaline earth metal compounds is included, it can cause crystal precipitation within the glass. In addition, alkaline earth metal compounds have a high ionic field strength, which reduces the free volume within the glass, resulting in the Na contained within the glass. + K has a larger atomic radius than + It is difficult to penetrate inside this glass, K +The compressive stress generated by this may be lowered or the ion exchange depth may be lowered. In the present invention, by controlling [CaO]+[MgO] within the aforementioned range, the increase in the liquidus temperature may be suppressed while the compressive stress may be increased. Specifically, when [CaO]+[MgO] is below the aforementioned range, the compressive stress may be lowered, and when it exceeds the aforementioned range, the liquidus temperature may be increased, which may cause difficulties in manufacturing glass products.

[0043]

[0044] Hereinafter, the present invention will be described in more detail through experimental examples. However, the following examples are intended only to aid understanding of the present invention and are not intended to limit the scope of the present invention in any way.

[0045]

[0046] [Example 1-8]

[0047] According to Table 1 below, glass compositions for each example were prepared.

[0048]

[0049] [Comparative Example 1-21]

[0050] According to Table 2-4 below, glass compositions for each comparative example were prepared.

[0051]

[0052]

[0053]

[0054]

[0055]

[0056]

[0057] [Measurement of physical properties]

[0058] Using glass articles manufactured using the glass compositions of each example and comparative example, the physical properties were measured using the following method, and the results are shown in Table 5-8 below.

[0059]

[0060] chemical toughening

[0061] Glass articles manufactured with the glass compositions of each example and comparative example were immersed in a KNO3 molten salt bath (390°C or 430°C) for 1 hour or 6 hours.

[0062]

[0063] compressive stress

[0064] For each glass article of the examples and comparative examples after chemical toughening, compressive stress was measured according to ASTM 1422C-99 and ASTM 1279.19779 (measuring device: FSM-6000 of Orihara, Tokyo Japan).

[0065]

[0066] Liquidus temperature

[0067] According to ASTM C 829 (Measurement of liquidus temperature of glass by the gradient furnace method), the glass articles of each example and comparative example were powdered and heated in an electric furnace having a temperature gradient of 800-1,200 ℃ for 24 hours, and the temperature at which crystals precipitated (liquidus temperature) was measured. The liquidus temperature is preferably 1,200 ℃ or lower, more preferably 1,100 ℃ or lower. If no crystals were precipitated during 24 hours of heating under the above conditions, it was indicated as “not detected.” If crystals were formed throughout the glass article at 1,200 ℃, the temperature at which crystal formation started was considered to be higher than 1,200 ℃ and was described as “out of measurement range.”

[0068]

[0069] Glass silt

[0070] The glass products of each example and comparative example were visually observed to determine whether devitrification (unmelted material, crystals) occurred. If devitrification occurred, it was evaluated as Fail, and if no devitrification occurred, it was evaluated as Pass.

[0071]

[0072] Bending Test

[0073] Using a universal testing machine, the glass articles of each example and comparative example were placed between the upper and lower plate surfaces of the UTM, and the gap (bending radius) between the upper and lower plates just before the glass article broke was measured while lowering the upper plate. A bending radius of 1.5 mm or less was evaluated as Pass, and a bending radius exceeding 1.5 mm was evaluated as Fail.

[0074]

[0075] Impact resistance (Pen drop test)

[0076] A pen was dropped 10 mm from the surface of the glass article of each example and comparative example, and the presence or absence of cracks on the glass surface was checked. If no cracks occurred, the pen was dropped from a higher position by 5 mm in increments, and the presence or absence of cracks was checked, and the highest height without cracks was measured. A score of 40 mm or more was evaluated as Pass, and a score of less than 40 mm was evaluated as Fail.

[0077]

[0078]

[0079]

[0080]

[0081]

[0082]

[0083] As shown in Table 5-8 above, the glass articles manufactured with the glass compositions of Examples 1-8 according to the present invention exhibited excellent physical properties across all measured items. On the other hand, the glass articles manufactured with the glass compositions of Comparative Examples 1-21 in which one or more components were used in an amount outside the range of the present invention or in which [MgO] / ([MgO]+[CaO]) outside the range of the present invention exhibited inferior physical properties compared to Examples 1-8. In particular, in the cases of Comparative Examples 2, 3, 15, and 16, unmelted matter was detected (glass devitrification), and physical property measurements were not performed on these.

[0084]

[0085] The present invention provides a glass composition capable of forming an ultra-thin glass product having excellent bendability and impact resistance.

Claims

1. With respect to the total content of the glass composition, it includes SiO2 60 to 75 mol%, Al2O3 10 to 15 mol%, Na2O 10 to 20 mol%, K2O 0.01 to 5 mol%, MgO 3 to 10 mol%, CaO 0.01 to 3 mol%, ZrO2 0.1 to 3 mol%, and SnO2 0.01 to 0.5 mol%, Glass composition having [MgO] / ([MgO]+[CaO]) of 0.65 to 0.95: In the above formula, [MgO] is the content of MgO (mol%) relative to the total content of the glass composition, [CaO] is the content of CaO (mol%) relative to the total content of the glass composition.

2. A glass composition in paragraph 1, wherein [Al2O3] / [R2O] is 0.6 to 0.75: In the above formula, [Al2O3] is the content of Al2O3 (mol%) relative to the total content of the glass composition, [R2O] is the content (mol%) of alkali metal oxide (R2O) relative to the total content of the glass composition.

3. A glass composition in paragraph 1, wherein [Al2O3] / [SiO2] is 0.15 to 0.2: In the above formula, [Al2O3] is the content of Al2O3 (mol%) relative to the total content of the glass composition, [SiO2] is the content of SiO2 (mol%) relative to the total content of the glass composition.

4. A glass composition in paragraph 1, wherein [K2O] / [R2O] is 0.01 to 0.15: In the above formula, [K2O] is the content of K2O (mol%) relative to the total content of the glass composition, [R2O] is the content (mol%) of alkali metal oxide (R2O) relative to the total content of the glass composition.

5. A glass composition in paragraph 1, wherein [CaO]+[MgO] is 3.8 to 6.8: In the above formula, [CaO] is the content of CaO (mol%) relative to the total content of the glass composition, [MgO] is the content of MgO (mol%) relative to the total content of the glass composition.

6. A glass article manufactured from the glass composition of any one of claims 1 to 5.

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