Glass composition for chemical strengthening and chemically strengthened glass article

Abstract

The present invention provides a glass composition for chemical strengthening that makes it possible to produce a glass plate by the float method and that is suitable in terms of both surface compressive stress and compressive stress layer depth. A glass composition according to the present invention includes, in mol%, 60-80% of SiO2, 1-5% of Al2O3, 5-25% of MgO, 0-5% of CaO, 10-20% of Na2O, and 0-10% of K2O as components. The use of this glass composition makes it possible to provide, for example, a chemically reinforced glass article having a compressive surface stress of 500 MPa or more and a compressive stress layer depth of 10 μm or more.

Description

Technical Field

[0001] The present invention relates to a glass composition suitable for chemical strengthening, particularly a glass composition suitable for a cover glass of a display. The present invention also relates to a chemically strengthened glass article composed of the glass composition, and further to a portable information device (such as a smartphone or a tablet), digital signage, an in-vehicle display, and a protective case for a portable information device including the glass article.

Background Art

[0002] High strength against bending and impact has been continuously required for the cover glass of a display. One of the means to achieve this is known to use an aluminosilicate glass composition containing a large amount of Al 2 O 3 . However, since the viscosity of the known aluminosilicate glass composition is high, a high temperature exceeding 1600°C is required during melting, and it has been difficult to adopt the float process suitable for mass production of glass plates. In addition, due to the high viscosity of the glass melt, the difficulty of homogenizing the glass melt is high, it is difficult to increase the yield as a glass article, a large amount of expensive raw materials are required as components of the glass, and a large amount of heating energy is required due to the above-mentioned requirement of high-temperature operation, resulting in high costs. Patent Document 1 discloses a glass composition for chemical strengthening that can be melted at a temperature of less than 1600°C.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Generally, for chemically strengthened glass articles, when the depth of the compressive stress layer is large, the surface compressive stress is not so large, and when the surface compressive stress is large, the depth of the compressive stress layer is not so large.

[0005] In view of the above, an object of the present invention is to provide a glass composition for chemical strengthening suitable for manufacturing a glass plate by a general float process and achieving both a surface compressive stress and a depth of the compressive stress layer within an appropriate range. Further, an object of the present invention is to provide a chemically strengthened glass article in which the surface compressive stress and the depth of the compressive stress layer are appropriately compatible.

Means for Solving the Problems

[0006] As a result of intensive research on the content of components and physical properties in aluminosilicate glass, the present inventor has succeeded in achieving the above object.

[0007] The present invention is expressed in mol%, SiO 2 60 to 80%, Al 2 O 3 1 to 5%, MgO 5 to 25%, CaO 0 to 5%, Na 2 O 10 to 20%, K 2 O 0 to 10%, a glass composition for chemical strengthening containing the above as components, and using the glass composition for chemical strengthening, a chemically strengthened glass article having a surface compressive stress of 500 MPa or more, further 550 MPa or more, and a depth of the compressive stress layer of 10 μm or more, is provided.

Effects of the Invention

[0008] According to the present invention, it becomes possible to manufacture a glass plate by a general float manufacturing method and to provide a glass composition for chemical strengthening suitable for achieving both a surface compressive stress and a compressive stress layer depth within appropriate ranges. Further, according to the present invention, it becomes possible to provide a chemically strengthened glass article in which the surface compressive stress and the compressive stress layer depth are appropriately compatible.

Mode for Carrying Out the Invention

[0009] Hereinafter, % indicating the content of components of the glass composition is "mol%" unless otherwise specified. The preferred ranges for the content of each component, its total, the ratio according to a predetermined calculation formula, the characteristic values of the glass, etc. can be obtained by arbitrarily combining the preferred upper and lower limits individually described below. Hereinafter, for the sake of simplifying the notation, the content of the component in mol% may be shown in the form of [X]. X is a component constituting the glass composition. Therefore, for example, [SiO 2 +[Al 2 O 3 means the total of the content of SiO 2 in mol% and the mol% of Al 2 O 3 . [R 2 O] means the total of [Li 2 O], [Na 2 O] and [K 2 O] ([R 2 O]=[Li 2 O]+[Na 2 O]+[K 2 O]), and [RO] means the total of [MgO], [CaO], [SrO] and [BaO] ([RO]=[MgO]+[CaO]+[SrO]+[BaO]).

[0010] Hereinafter, "substantially not contained" means that the content rate is limited to less than 0.1 mol%, preferably less than 0.07 mol%, more preferably less than 0.05 mol%. Industrially manufactured glass compositions often contain trace amounts of impurities derived from industrial raw materials and the like. "Substantially" means that inevitable impurities are allowed within the above content rate limit. Also, the following description of the embodiments of the present invention is not intended to limit the present invention to a specific form.

[0011] SiO 2 is a component that constitutes the network structure of the glass. SiO 2 The content rate is preferably 80% or less, 75% or less, 72% or less, 68% or less, and in some cases may be 67% or less, or 66% or less depending on the content rates of other components. SiO 2 The content rate is preferably 60% or more, 61% or more, 62% or more, 63% or more, and in some cases may be 64% or more, or 65% or more depending on the content rates of other components. SiO 2 If the content rate of SiO is too high, the viscosity of the glass increases, and T2, which is indicated by the temperature at which the viscosity becomes 10 2 dPa·s, becomes very high, and the meltability of the glass decreases. On the other hand, if it is too low, the glass devitrifies or the weather resistance decreases.

[0012] Al 2 O 3 is a component that enhances the ion exchange performance of the glass and improves the surface compressive stress after chemical strengthening. Al 2 O 3 If the content rate of AlO is too high, the viscosity and devitrification temperature of the glass increase, and the meltability decreases. On the other hand, if it is too low, a high surface compressive stress cannot be obtained after chemical strengthening. Al 2 O 3 The content rate is preferably 5% or less, 4.9% or less, 4.5% or less, and in some cases may be 4% or less. Al 2 O 3 The content rate is preferably 1% or more, 2.5% or more, 3% or more, and in some cases may be 3.5% or more.

[0013] Molar ratio [Al2 O 3 / ([SiO 2 +[Al 2 O 3 ) is a parameter that affects the hydrofluoric acid resistance of the glass composition. When this ratio is large, the hydrofluoric acid resistance tends to decrease, while when it is too small, the viscosity tends to increase. From this perspective, [Al 2 O 3 / ([SiO 2 +[Al 2 O 3 ) is preferably 0.015 or more, 0.02 or more, particularly 0.04 or more, and may be 0.05 or more in some cases. [Al 2 O 3 / ([SiO 2 +[Al 2 O 3 ) is preferably 0.072 or less, 0.07 or less, particularly 0.067 or less, and may be 0.06 or less in some cases.

[0014] MgO is a component that makes the glass difficult to devitrify and is also a component that improves the glass transition point and the surface compressive stress after chemical strengthening. Al 2 O 3 which has the effect of increasing the surface compressive stress after chemical strengthening increases the viscosity of the glass melt, while MgO also has the effect of decreasing the viscosity of the glass melt. However, if the content of MgO is too high, the glass is likely to devitrify. On the other hand, if the content is too low, the chemical resistance such as acid resistance and alkali resistance and the water resistance of the glass will decrease. The content of MgO is preferably 5% or more, 7% or more, 9.5% or more, 10% or more, 12% or more, particularly 13% or more. The content of MgO is preferably 25% or less, 20% or less, 18% or less, 17% or less, particularly 15% or less, and may be 10% or less in some cases.

[0015] CaO is a component that makes it difficult for the glass to devitrify. However, unlike MgO, it has the effect of reducing the surface compressive stress after chemical strengthening. Also, if the CaO content is too high, devitrification is likely to occur. On the other hand, if the content is too low, the chemical resistance such as the alkali resistance of the glass will decrease. The CaO content may be 0% or more, 0.01% or more, 0.05% or more. The CaO content is preferably 1% or less, 0.7% or less, 0.5% or less, particularly preferably 0.1% or less.

[0016] [MgO] + [CaO], that is, the total content of MgO + CaO, is preferably in the range of 9 to 20%, more preferably in the range of 10 to 19%.

[0017] When the molar ratio [MgO] / ([CaO] + [MgO]) is 0.8 or more, the depth of the compressive stress layer after chemical strengthening can be increased. This effect is preferably manifested when it is 0.9 or more, 0.91 or more, particularly 0.92 or more. On the other hand, if this molar ratio is too low, the devitrification temperature of the glass will increase. [MgO] / ([CaO] + [MgO]) is preferably 1 or less, particularly preferably 0.97 or less. The preferred range of the molar ratio [MgO] / [RO] is the same as the preferred range described for the molar ratio [MgO] / ([CaO] + [MgO]).

[0018] Na 2 O is a component that lowers the viscosity of the glass. However, when the content of Na 2 O is too high, the water resistance of the glass becomes too low. On the other hand, if the content is too low, the viscosity of the glass increases and the meltability decreases. The content of Na 2 O is preferably 10% or more, 12.5% or more, 15% or more, particularly 15.5% or more, and in some cases 16% or more. The content of Na 2 O is preferably 20% or less, 19% or less, 18% or less.

[0019] K 2 O is an optional component that suppresses devitrification by adding a small amount. However, when the content of K 2 O is too high, the desired surface compressive stress cannot be obtained after chemical strengthening. K 2The content rate of O is 0% or more, particularly 0.01% or more, and may be 0.05% or more in some cases. K 2 The content rate of O is 10% or less, 5% or less, 1.5% or less, 1% or less, and may be 0.1% or less in some cases.

[0020] [Na 2 O] + [K 2 O] is preferably adjusted to 10 - 30% so as to keep the viscosity of the glass within an appropriate range and prevent the melting property from deteriorating. [Na 2 O] + [K 2 O], if too low, will cause the viscosity of the glass melt to become extremely high and the devitrification resistance of the glass to deteriorate. On the other hand, if too high, the water resistance of the glass will deteriorate. [Na 2 O] + [K 2 O] is preferably 12% or more, 15% or more, particularly 15.5% or more. [Na 2 O] + [K 2 O] is preferably 25% or less, 22% or less, particularly 20% or less, and may be 19% or less, 18% or less in some cases.

[0021] Li 2 O is an optional component and may be added in the range of 1% or less, further 0.5% or less, but may not be substantially contained.

[0022] Also, if the molar ratio [Na 2 O] / ([Na 2 O] + [K 2 O]) is too small, the viscosity of the glass melt will become unnecessarily low, and the deterioration of the molten salt for dipping in chemical strengthening will be severe, resulting in poor productivity of the chemically strengthened glass article and an increase in manufacturing cost. Therefore, this ratio is preferably 0.5 or more, 0.61 or more, particularly 0.75 or more, and may be 0.9 or more in some cases. On the other hand, if this molar ratio is too large, the surface compressive stress after chemical strengthening may become low. Therefore, this ratio is preferably 1 or less, particularly 0.97 or less.

[0023] SrO and BaO significantly hinder the movement of sodium ions in the glass, greatly reducing the surface compressive stress after chemical strengthening and significantly decreasing the depth of the compressive stress layer. Therefore, it is preferable that SrO and BaO are not substantially contained, respectively.

[0024] ZrO 2 promotes the movement of sodium ions in the glass and increases the surface compressive stress after chemical strengthening. With the addition of ZrO 2 , the depth of the compressive stress layer may become shallower. Also, ZrO 2 may inadvertently increase the devitrification temperature of the glass. ZrO 2 may not be substantially contained, but its content may be greater than 0%. The content of ZrO 2 may be 0.01% or more, 0.05% or more, 0.1% or more, and further 0.5% or more, and may also be 2.5% or less, 2% or less, and further 1.5% or less.

[0025] ZrO 2 When the content of ZrO is greater than 0%, it is preferable to add SrO to suppress the increase in the devitrification temperature of the glass. In this case, the content of SrO may be in a range greater than 0%, but may also be 0.01% or more, 0.05% or more, and further 0.1% or more. The content of SrO may also be 3.5% or less, 3% or less, and further 2.5% or less.

[0026] P 2 O 5 , B 2 O 3 are optional components that promote the melting of the raw materials. However, these components may facilitate the erosion of the refractories in the melting furnace, condense on the furnace wall after volatilization, and may mix into the glass melt as foreign substances. P 2 O 5 , B 2 O 3 are preferably not substantially contained, respectively.

[0027] It is known that it may be advisable to add a part of the raw materials as sulfates for clarification. In this case, SO generated from the sulfates3 often remains in the glass. Therefore, SO 3 is an optional component and may not be substantially contained, but the content of SO 3 is preferably 0.5% or less, more preferably 0.3% or less.

[0028] Other optional components that can exhibit a clarification effect include As 2 O 5 , Sb 2 O 5 , F, and Cl. However, these components have a great impact on the environment. When F is contained, it is preferably 0.1% or less, more preferably 0.06% or less, still more preferably 0.05% or less, and most preferably not substantially contained. Also, As 2 O 5 , Sb 2 O 5 and Cl are preferably not substantially contained.

[0029] Iron oxide is an optional component that acts as a colorant and is also a typical impurity inevitably mixed from the industrial raw materials of glass. Iron oxide exists in the glass composition as a divalent oxide (FeO) or a trivalent oxide (Fe 2 O 3 ). When the glass composition is used as a cover glass for a display, since it is required that the coloring is not conspicuous, the content of Fe 2 O 3 is preferably small. The content of iron oxide is expressed by the content [T-Fe 2 O 3 converted to a trivalent oxide, and is preferably 0.5% or less, 0.3% or less, 0.2% or less, and particularly preferably 0.02% or less or 0.01% or less when coloring is severely disliked.

[0030] The glass composition of this embodiment may contain other optional components, but it is preferably not substantially contained other than the above.

[0031] The glass composition of this embodiment can have a low density. A glass plate composed of a glass composition with a low density contributes to the weight reduction of the product in which the glass plate is used.

[0032] In a preferred embodiment, the properties that the glass composition according to the present invention can have, specifically, the elastic modulus, density, and temperature characteristics, are as follows.

[0033] The Young's modulus is preferably 65 GPa or more, more preferably 68 GPa or more. The Young's modulus may be 75 GPa or less. The density is 2.6 g / cm 3 Hereinafter, 2.57 g / cm 3 Hereinafter, 2.5 g / cm 3 Hereinafter, 2.48 g / cm 3 Hereinafter, 2.47 g / cm 3 Hereinafter, more preferably 2.46 g / cm 3 Hereinafter is preferred. The specific elastic modulus is 26×10 6 Nm / kg or more, 27×10 6 Nm / kg or more, 27.5×10 6 Nm / kg or more, 28×10 6 Nm / kg or more, particularly 28.5×10 6 Nm / kg or more, is preferred. The specific elastic modulus may be 31×10 6 Nm / kg or less. The specific elastic modulus is a value calculated by dividing the Young's modulus by the density. A relatively high specific elastic modulus as described above is advantageous for reducing the deflection of a product using a glass plate composed of this glass composition.

[0034] Focusing on the density and the specific elastic modulus, a preferred form of the glass composition according to the present invention can have the following characteristics. Density: 2.6 g / cm 3 Hereinafter, and specific elastic modulus: 27.5×10 6 Nm / kg or more, Or density: 2.48 g / cm 3 Hereinafter, and specific elastic modulus: 27×10 6 Nm / kg or more, Furthermore, density: 2.57 g / cm 3 Hereinafter, and specific elastic modulus: 28.5×10 6Above Nm / kg, or density: 2.47 g / cm 3 Below, and specific elastic modulus: 28×10 6 Above Nm / kg, In particular, density: 2.465 g / cm 3 Below, and specific elastic modulus: 29×10 6 Above Nm / kg.

[0035] The devitrification temperature TL is preferably 1050 °C or lower, more preferably 1000 °C or lower. The forming temperature T4 is preferably 1100 °C or lower, and may be 1000 °C or higher, more preferably 1040 °C or higher. Further, the difference ΔT (ΔT = T4 - TL) obtained by subtracting the devitrification temperature TL from the forming temperature T4 is preferably 0 °C or higher, more preferably 5 °C or higher, further preferably 10 °C or higher, still more preferably 15 °C or higher, particularly preferably 18 °C or higher, and may be 25 °C or higher. Here, the forming temperature T4 is the temperature at which the viscosity measured by the platinum ball pulling-up method is 10 4 dPa·s. The devitrification temperature TL is the highest temperature at which devitrification is observed inside the glass taken out of the furnace after pulverizing the sample glass and holding it in a temperature gradient electric furnace for 2 hours. In a preferred embodiment, the glass according to the present invention can have a devitrification temperature as low as the above level and a positive ΔT. A glass composition having ΔT of 0 °C or higher is suitable for production by the float process.

[0036] Note that T2 of the glass composition of the present embodiment, that is, the temperature at which the viscosity becomes 10 2 dPa·s is preferably 1550 °C or lower, more preferably 1500 °C or lower. The glass transition point Tg may be 500 to 600 °C, more preferably 510 to 595 °C. When T2 and Tg are too high, the difficulty of manufacturing a glass plate by the float process particularly increases. On the other hand, when Tg is too low, the stress relaxation during chemical strengthening treatment increases, and the surface compressive stress after chemical strengthening tends to be low.

[0037] The preferred linear thermal expansion coefficient is 85×10 -7 ~110×10 -7 / °C, more preferably 90×10 -7 ~130×10 -7 / °C. Here, the linear thermal expansion coefficient means the average linear thermal expansion coefficient from 50 to 350 °C. This value is larger than that of general soda-lime glass used for building windows, vehicle windows, etc. A large linear thermal expansion coefficient is effective in shortening the time required for chemical strengthening treatment and suppressing peeling when a glass article composed of the glass composition of the present invention is used by being adhered to a member composed of metal or plastic.

[0038] The glass composition of this embodiment is suitable for mass production by the float process. In this case, it will be manufactured as a glass plate called float glass. As is well known, the float process includes a step of melting glass raw materials in a melting furnace and a step of forming the molten glass raw materials introduced into a float bath into a glass plate on the molten tin in the float bath. In one form of the present invention, float glass is manufactured by preparing glass raw materials so that the glass composition constituting the obtained glass plate has the desired composition described above. Float glass is formed in a float bath with one main surface in contact with molten tin, and tin diffuses into that main surface. Therefore, float glass has a surface layer in which tin has diffused on one main surface called the bottom surface, and this surface layer does not exist on the other main surface called the top surface. From another perspective, in float glass, the concentration of tin on one main surface is higher than the concentration of tin on the other main surface.

[0039] The glass plate may be chemically strengthened glass. As is well known, the chemical strengthening treatment is a treatment for introducing compressive stress to the surface of glass by substituting alkali ions contained in the glass with alkali ions having a larger ionic radius, for example, substituting lithium ions with sodium ions or sodium ions with potassium ions.

[0040] The chemical strengthening treatment of a glass plate is usually carried out by bringing the glass plate into contact with a molten salt containing alkali ions. Examples of the molten salt include potassium nitrate and a mixed salt of potassium nitrate and sodium nitrate. When using a molten salt of potassium nitrate alone, considering the thermal decomposition of potassium nitrate and the heat resistance of the glass, the temperature of the molten salt is appropriately about 460°C to 500°C. The time for bringing the glass into contact with the molten salt is appropriately, for example, 4 hours to 12 hours.

[0041] The chemically strengthened glass article of this embodiment thus obtained can have a very high surface compressive stress and a very deep depth of the compressive stress layer. Specifically, the surface compressive stress is 500 MPa or more, particularly 550 MPa or more, and the depth of the compressive stress layer is 10 μm or more. Preferably, the surface compressive stress is 800 MPa or more and the depth of the compressive stress layer is 15 μm or more. More preferably, the surface compressive stress is 900 MPa or more and the depth of the compressive stress layer is 15 μm or more.

[0042] Therefore, since the chemically strengthened glass article of this embodiment has a very high surface compressive stress, it is difficult for scratches to occur on the surface. Also, since the depth of the compressive stress layer is deep, even when a scratch occurs on the surface, it is less likely for the scratch to reach inside the glass article from the compressive stress layer. The chemically strengthened glass article of this embodiment can satisfy the following relationship between the surface compressive stress CS expressed in MPa and the depth of the compressive stress layer DOL expressed in μm. -0.05×CS + 57 ≤ DOL ≤ -0.05×CS + 76 500 ≤ CS ≤ 1200 In the above, CS may be in the range of 500 ≤ CS ≤ 1100.

[0043] Generally, in a glass article having a compressive stress layer near the surface, the elastic energy due to the compressive stress balances the elastic energy due to the tensile stress (internal tensile stress) generated inside the glass article. Therefore, even with the same surface compressive stress and compressive stress layer depth, the internal tensile stress increases as the thickness of the article decreases. When an external force is applied to such a glass article and exceeds the limit value of the internal tensile stress, the glass article will break, and instead, the strength of the glass article will deteriorate.

[0044] The chemically strengthened glass article of this embodiment has a depth of the compressive stress layer that is not too deep at the same time, so the value of the internal tensile stress is not too high, and thus the chemically strengthened glass article has excellent strength.

[0045] Therefore, the chemically strengthened glass article of this embodiment, specifically the glass plate, is particularly suitable as a cover glass for a display. However, the glass plate according to this embodiment can also be used for other applications, such as window glass for automobiles.

Examples

[0046] Hereinafter, the present invention will be described in more detail with specific examples, but the following examples do not limit the present invention either.

[0047] Batches were prepared using normal glass raw materials such as silica, alumina, sodium carbonate, magnesium oxide, calcium carbonate, potassium carbonate, etc. so as to have the compositions shown in Tables 1 to 4. The prepared batches were put into a platinum crucible, held at 1580 °C for 4 hours, and poured onto an iron plate. This glass was held in an electric furnace at 650 °C for 30 minutes, then the power of the furnace was turned off, and it was allowed to cool to room temperature to obtain sample glasses. The properties of each obtained sample glass were measured as follows. The results are shown in Tables 1 to 4. Note that Examples 24 to 46 are examples described in Patent Document 1.

[0048] 〔Density ρ, Young's modulus E〕 The sample glass was cut, and each surface was mirror-polished to prepare a plate-shaped sample of 25×25×5 mm. The density ρ of each sample was measured by the Archimedes method. Also, the Young's modulus was measured in accordance with the ultrasonic pulse method of JIS R1602-1995. Specifically, using the sample used for the above density measurement, the sound velocities at which ultrasonic pulses propagate were measured for longitudinal waves and transverse waves, and the Young's modulus E was calculated by substituting them into the formula described in the JIS together with the above density. The propagation velocity was calculated by dividing the time from when an ultrasonic pulse with a frequency of 20 kHz propagated in the thickness direction of the sample, reflected, and returned by the propagation distance (twice the thickness of the sample) using an ultrasonic thickness gauge MODEL 25DL PLUS manufactured by Olympus Corporation.

[0049] [Glass transition temperature Tg, linear thermal expansion coefficient α] A cylindrical sample with a diameter of 5 mm and a length of 18 mm was prepared from the sample glass, and the thermal expansion curve when heated at 5 °C / min by a TMA apparatus was measured. Based on this curve, the glass transition temperature Tg and the average linear thermal expansion coefficient α from 50 to 350 °C were obtained.

[0050] [Measurement of devitrification temperature TL] The sample glass was pulverized, passed through a sieve with an aperture of 2.83 mm, and the particles remaining on a sieve with an aperture of 1.00 mm were sieved. These particles were washed to remove the fine powder adhering to the particles, dried, and a sample for measuring the devitrification temperature was prepared. 25 g of the sample for measuring the devitrification temperature was placed in a platinum boat (a rectangular platinum vessel without a lid) so that the thickness was substantially uniform, held in a temperature gradient furnace for 2 hours, then taken out of the furnace, and the highest temperature at which devitrification was observed inside the glass was defined as the devitrification temperature TL.

[0051] [Measurement of melting temperature T2, forming temperature T4] The viscosity was measured by the platinum ball pulling-up method, and the temperatures at which the viscosity became 10 2 dPa·s and 10 4 dPa·s were defined as the melting temperature T2 and the forming temperature T4, respectively.

[0052] [Chemical strengthening] The chemical strengthening treatment of the glass plate was usually carried out by bringing the glass plate into contact with a molten salt containing alkali ions. The sample glass was cut, and the main surface was mirror-polished to prepare two plate-shaped samples of 25×25×0.7 mm. Potassium nitrate was used as the molten salt. The chemical strengthening treatment was carried out under the following conditions. Molten salt temperature 420 °C, contact time between glass and molten salt 2 hours 30 minutes, 4 hours or 6 hours Molten salt temperature 400 °C, contact time between glass and molten salt 4 hours

[0053] [Surface compressive stress CS, depth of compressive stress layer DOL] For the chemically strengthened glass articles obtained as described above, the surface compressive stress CS and the depth of the compressive stress layer DOL were measured. A surface stress meter (manufactured by Orihara Seisakusho, SM-6000LE) was used for the measurement. Specifically, the number and interval of interference fringes observed using the above surface stress meter were observed and calculated using the attached software. For this calculation, not only the interference fringes but also the refractive index and photoelastic constant are required. The refractive index was determined to be 1.511, and the photoelastic constant was obtained by substituting the content of each component into well-known prediction formulas (described on pages 169-174 and 289-292 of M. B. Volf, (1988), "Mathematical Approach to Glass (Glass Science and Technology, Vol9)", Elsevier Science Ltd.).

[0054] In Tables 1 to 4, the content of component X is described simply as X instead of [X], but all the contents are in mol%.

[0055] Examples 41 to 43, 46 to 48 are comparative examples. In Examples 41 and 46, CS was slightly low at 550 MPa or less. In Examples 42, 43, 46, and 47, the depth of the compressive stress layer DOL was small at less than 10 μm. In Example 48, T2 exceeded 1550 °C. On the other hand, in the other examples, both CS and DOL were large, and T2 was also a value not exceeding 1550 °C.

[0056] Furthermore, Examples 1 to 25 are all The difference ΔT (ΔT = T4 - TL) obtained by subtracting the devitrification temperature TL from the forming temperature T4 is 0 °C or higher, and the surface compressive stress CS is 500 to 1200 MPa, the depth DOL of the compressive stress layer is 10 μm or more, furthermore the surface compressive stress CS expressed in MPa and the depth DOL of the compressive stress layer expressed in μm satisfy -0.05 × CS + 57 ≤ DOL ≤ -0.05 × CS + 76 within the range.

[0057] On the other hand, in Examples 26 to 41 and 44 to 45, DOL exceeded 10 μm and T2 was also 1550 °C or lower, but -0.05 × CS + 57 ≤ DOL ≤ -0.05 × CS + 76 did not satisfy the relational expression.

[0058] Although desirable results were obtained in all of Examples 1 to 25, when comparing among Examples 1 to 25, Examples 19 to 22 had a slightly lower specific elastic modulus, and Example 23 had a slightly lower DOL than other examples with the same CS. Examples 1 to 18 were particularly excellent in the balance of characteristics. Example 24 was advantageous in that the devitrification temperature TL was low. Example 25 was advantageous in that it was easy to achieve a high CS.

[0059]

Table 1

[0060]

Table 2

[0061]

Table 3

[0062]

Table 4

Claims

1. Expressed in mol%, SiO 2 62 - 68%, Al 2 O 3 2 to 5%, MgO 12 - 25%, CaO 0 - 1%, Na 2 O 15.5 to 19%, K 2 O 0 to 10%, A glass composition for chemical strengthening containing the above as components.

2. The glass composition for chemical strengthening according to Claim 1, Expressed in mol%, SiO 2 62 to 68%, Al 2 O 3 2 to 4.9%, MgO 12 - 20%, CaO 0 - 1%, Na 2 O 15.5 to 19%, K 2 O 0 to 10%, Containing the above as components, The density is 2.50 g / cm 3 or less A glass composition for chemical strengthening.

3. The glass composition for chemical strengthening according to Claim 1 or 2, Expressed in mol%, SiO 2 62 to 68%, Al 2 O 3 2.5 to 4.9%, MgO 12 - 18%, CaO 0 - 1%, Na 2 O 15.5 to 19%, K 2 O 0 to 1.5%, Containing the above as components, A glass composition for chemical strengthening.

4. The glass composition for chemical strengthening according to any one of Claims 1 to 3, SiO 2 63 to 68%, Al 2 O 3 3 to 4.9%, Expressed in mol%, MgO 12 - 17%, Na 2 O 16 - 19%, K 2 O 0 to 0.1%, CaO 0 - 0.5%, Containing the above as components, A glass composition for chemical strengthening.

5. SiO 2 63 to 68%, Al 2 O 3 2.5 to 4.9%, The glass composition for chemical strengthening according to any one of Claims 1 to 3, Expressed in mol%, Na 2 O 15.5 to 18%, K 2 O 0 to 1.5%, MgO 13 - 15%, The density is 2.48 g / cm 3 or less CaO 0 - 0.1%, Containing the above as components, A glass composition for chemical strengthening.

6. SiO 2 62 to 65%, Al 2 O 3 2 to 4.9%, The glass composition for chemical strengthening according to Claim 1, Expressed in mol%, Na 2 O 15.5 to 19%, MgO 12 - 13%, ZrO 2 greater than 0 and less than or equal to 2.5%, CaO 0 - 0.5%, The density is 2.6 g / cm 3 or less SrO greater than 0 and 3.5% or less, Containing the above as components, A glass composition for chemical strengthening.

7. The glass composition for chemical strengthening according to any one of Claims 1 to 5, A glass composition for chemical strengthening substantially free of SrO and BaO respectively.

8. The glass composition for chemical strengthening according to any one of Claims 1 to 7, Expressed in mol%, MgO + CaO is in the range of 9 - 20%, A glass composition for chemical strengthening.

9. The glass composition for chemical strengthening according to any one of Claims 1 to 8, The molar ratio MgO / (MgO + CaO) is in the range of 0.91 - 1, A glass composition for chemical strengthening.

10. Na 2 O + K 2 wherein O is in the range of 15.5 to 25%, The glass composition for chemical strengthening according to any one of Claims 1 to 9, Expressed in mol%, A glass composition for chemical strengthening. Molar ratio of Na 2 O / (Na 2 O + K 2 O) is in the range of 0.61 to 1,

11. The glass composition for chemical strengthening according to any one of Claims 1 to 10, A glass composition for chemical strengthening. Molar ratio of Al 2 O 3 / (SiO 2 + Al 2 O 3 is in the range of 0.015 to 0.072

12. The glass composition for chemical strengthening according to any one of Claims 1 to 11, A glass composition for chemical strengthening.

13. The specific modulus is in the range of 26 to 31×10 6 N·m / kg, The glass composition for chemical strengthening according to any one of Claims 1 to 12, The Young's modulus is 65 - 75 GPa, A glass composition for chemical strengthening.

14. The chemically strengthened glass composition according to any one of claims 1 to 13, The temperature T2 at which the viscosity becomes 10 2 dPa·s is 1550°C or lower which is the chemically strengthened glass composition.

15. The chemically strengthened glass composition according to any one of claims 1 to 14, The temperature T4 at which the viscosity becomes 10 4 dPa·s is 1100°C or lower, wherein the devitrification temperature TL of T4 is 0 °C or higher, which is the chemically strengthened glass composition.

16. The chemically strengthened glass composition according to any one of claims 1 to 15, The average coefficient of thermal expansion between 50 and 350 °C is in the range of 85 to 110×10 -7 °C -1 . which is the chemically strengthened glass composition.

17. The chemically strengthened glass composition according to any one of claims 1 to 16, wherein the glass transition point Tg is in the range of 510 to 595 °C, which is the chemically strengthened glass composition.

18. A chemically strengthened glass article using the chemically strengthened glass composition according to any one of claims 1 to 17, wherein the surface compressive stress is 500 MPa or more, and the depth of the compressive stress layer is 10 μm or more, which is the chemically strengthened glass article.

19. The chemically strengthened glass article according to claim 18, wherein the surface compressive stress is 800 MPa or more, and the depth of the compressive stress layer is 15 μm or more, which is the chemically strengthened glass article.

20. The chemically strengthened glass article according to claim 19, wherein the surface compressive stress is 900 MPa or more, and the depth of the compressive stress layer is 15 μm or more, which is the chemically strengthened glass article.

21. The chemically strengthened glass article according to any one of claims 18 to 20, wherein the surface compressive stress CS expressed in MPa and the depth of the compressive stress layer DOL expressed in μm satisfy -0.05 × CS + 57 ≤ DOL ≤ -0.05 × CS + 76 500 ≤ CS ≤ 1200 which is the chemically strengthened glass article.

Images