TWI579252B - Cover glass for flat panel display and manufacturing method - Google Patents

Description

Cover glass for flat panel display and manufacturing method

The present invention relates to a cover glass for a flat panel display, a method of manufacturing the same, and a display device using the same.

In recent years, in a flat panel display (hereinafter also referred to as an FPD (Flat Panel Display)), a thin plate-shaped glass is placed in front of the display so as to be a wider area than the image display portion. This eliminates the convex portion of the frame and improves the aesthetics. In order to be disposed at the front, a method of separating the cover glass from the FPD panel is adopted, but in this method, since the appearance is impaired due to reflection between the glass and the air layer, it is preferable to use a resin or an adhesive sheet to glass and The FPD panel is joined to reduce the reflection on the interface.

In recent years, as a home TV set, a large-sized TV set has been favored. When a FPD panel and a cover glass are directly joined to a large FPD of 32 以上 or more, the area of the cover glass becomes large, so if used In the soda-lime glass of 2.5 mm, the weight of the body itself becomes large, and the load during transportation or installation becomes large.

Therefore, a thinned, lightweight glass such as 1.5 mm, 1.1 mm, and 0.7 mm glass can be used. When the glass is made thinner, the strength is lowered. In order to solve this problem, it is necessary to use a glass which is strengthened by a chemical strengthening method (for example, Patent Documents 1 and 2).

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. SHO 57-205343

[Patent Document 2] Japanese Patent Laid-Open No. Hei 9-236792

However, when chemically strengthening a large-area glass plate as described above, if it is soda-lime glass, sufficient stress layer depth cannot be obtained within a required time, and if it is to increase the speed of ion exchange. When the temperature is set to a high temperature, there is a disadvantage that the desired surface compressive stress cannot be obtained due to stress relaxation.

In particular, when a large-area glass plate is to be chemically strengthened, the temperature distribution in the glass surface becomes large, and stress unevenness is likely to occur on the chemically strengthened glass surface. As a result, there is a problem that warpage or undulation is likely to occur on the chemically strengthened glass plate.

The present invention has been made to solve the above problems, and an object of the invention is to provide a glass for a cover glass for a large-sized display device, which has a glass for covering glass even when chemically strengthened at a high temperature. Since the surface compressive stress is the same as that in the case where the chemical strengthening is performed at a low temperature, even when a temperature fluctuation occurs, the change in the compressive stress is small, and the productivity is excellent.

That is, the present invention is as follows.

A cover glass for a flat panel display obtained by chemically strengthening a glass, and a molar ratio of Na ₂ O, Al ₂ O ₃ , MgO, and ZrO ₂ in the glass before chemical strengthening satisfies the formula (1) : (Na ₂ O/2)/(Al ₂ O ₃ /2+MgO+ZrO ₂ )≦0.85... Formula (1).

2. The cover glass for a flat panel display according to the above 1, wherein the surface compressive stress of the glass which is chemically strengthened by KNO ₃ at 450 ° C for 6 hours is the surface of the glass which is chemically strengthened by KNO ₃ at 400 ° C for 6 hours. More than 75% of the compressive stress.

3. The cover glass for a flat panel display according to the above 1 or 2, wherein the strain point of the glass before the chemical strengthening is 530 ° C or higher.

4. The cover glass for a flat panel display according to the above 1 or 2, which has a thickness of 1.5 mm or less and a size of 22 Å or more.

5. The cover glass for a flat panel display according to any one of the above 1 to 4, wherein the glass before the chemical strengthening is a glass having a composition of 50% to 80% of SiO ₂ and 2 to 25%. Al ₂ O ₃ , 0 to 10% Li ₂ O, 0 to 18% Na ₂ O, 0 to 10% K ₂ O, 0 to 15% MgO, 0 to 5% CaO, and 0 to 5 % of ZrO ₂ .

6. The cover glass for a flat panel display according to any one of the above 1 to 5, wherein the glass before the chemical strengthening comprises an aluminosilicate glass of SiO ₂ , Al ₂ O ₃ , Na ₂ O and MgO.

7. The cover glass for a flat panel display according to any one of the above 1 to 5, wherein the glass before the chemical strengthening is a glass having a composition of 50% to 74% of SiO ₂ and 1 to 10%. Al ₂ O ₃ , 6 to 14% Na ₂ O, 3 to 11% K ₂ O, 2 to 15% MgO, 0 to 6% CaO, and 0 to 5% ZrO ₂ , and SiO ₂ and The total content of Al ₂ O ₃ is 75% or less, and the total content of Na ₂ O and K ₂ O is 12 to 25%, and the total content of MgO and CaO is 7 to 15%.

8. The cover glass for a flat panel display according to any one of the above 1 to 5, wherein the glass before the chemical strengthening is a glass having a composition of 80% to 80% of SiO ₂ and 4 to 10%. Al ₂ O ₃ , 5 to 15% Na ₂ O, 0 to 1% K ₂ O, 4 to 15% MgO, and 0 to 1% ZrO ₂ .

9. The cover glass for a flat panel display according to any one of the above 1 to 4, wherein the glass before the chemical strengthening is a glass having a composition represented by mol% and containing 67 to 75% of SiO ₂ and 0 to 4%. The total content of Al ₂ O ₃ , 7 to 15% Na ₂ O, 1 to 9% K ₂ O, 6 to 14% MgO, and 0 to 1.5% ZrO ₂ , SiO ₂ and Al ₂ O ₃ It is 71 to 75%, and the total content of Na ₂ O and K ₂ O is 12 to 20%, and if it contains CaO, the content is less than 1%.

A flat panel display device using the cover glass for a flat panel display according to any one of the above 1 to 9 as a cover glass.

A method for chemically strengthening glass to produce a cover glass for a flat panel display, and a molar ratio of Na ₂ O, Al ₂ O ₃ , MgO, and ZrO ₂ in the glass before chemical strengthening ( 1): (Na ₂ O/2) / (Al ₂ O ₃ / 2 + MgO + ZrO ₂ ) ≦ 0.85... Formula (1)

12. The method according to the above 11, wherein the chemical strengthening of the glass is carried out at 400 to 450 °C.

13. The method according to the above 11 or 12, wherein the strain point of the glass before the chemical strengthening is 530 ° C or higher.

14. The method according to any one of the above 11 to 13, wherein the glass before the chemical strengthening is any one of (i) to (iv) below:

(i) The composition expressed in mole % contains 50 to 80% of SiO ₂ , 2 to 25% of Al ₂ O ₃ , 0 to 10% of Li ₂ O, 0 to 18% of Na ₂ O, 0 to 10 % K ₂ O, 0~15% MgO, 0~5% CaO and 0~5% ZrO ₂ glass

(ii) The composition expressed in mole % contains 50 to 74% of SiO ₂ , 1 to 10% of Al ₂ O ₃ , 6 to 14% of Na ₂ O, 3 to 11% of K ₂ O, 2 to 15 % of MgO, 0 to 6% of CaO and 0 to 5% of ZrO ₂ , and the total content of SiO ₂ and Al ₂ O ₃ is 75% or less, and the total content of Na ₂ O and K ₂ O is 12~ 25%, the total content of MgO and CaO is 7~15% glass

(iii) The composition expressed in mole % contains 68 to 80% of SiO ₂ , 4 to 10% of Al ₂ O ₃ , 5 to 15% of Na ₂ O, 0 to 1% of K ₂ O, 4 to 15 % of MgO and 0~1% of ZrO ₂ glass

(iv) The composition expressed in mole % contains 67 to 75% of SiO ₂ , 0 to 4% of Al ₂ O ₃ , 7 to 15% of Na ₂ O, 1 to 9% of K ₂ O, and 6 to 14 The total content of MgO and 0 to 1.5% of ZrO ₂ , SiO ₂ and Al ₂ O ₃ is 71 to 75%, and the total content of Na ₂ O and K ₂ O is 12 to 20%, if CaO is contained. Glass with a content of less than 1%.

According to the present invention, it is possible to provide a surface compressive stress temperature even in the case of chemical strengthening at a high temperature of, for example, 400 ° C or higher. The time variation is also small, and the cover glass for flat panel displays which exhibits stable strengthening characteristics and is excellent in productivity.

Hereinafter, the present invention will be described in detail.

The method for producing a cover glass for a flat panel display according to the present invention is not particularly limited, except for the composition of the glass subjected to the chemical strengthening treatment and the chemical strengthening treatment step, and may be appropriately selected as long as it is appropriately selected. Previously known steps.

For example, the raw materials of the respective components are blended into a composition described later, and then heated and melted in a glass melting furnace. The glass is homogenized by foaming, stirring, addition of a clarifying agent, etc., and formed into a glass plate of a specific thickness by a conventionally known forming method, followed by slow cooling.

Examples of the glass forming method include a float method, a press method, a melting method, and a down-draw method. It is a super float method suitable for mass production. Further, a continuous molding method other than the floating method, that is, a melting method and a down-draw method is also preferable.

The formed glass is ground and polished as needed, and after chemical strengthening treatment, it is washed and dried.

1. Glass before chemical strengthening

As the glass for chemical strengthening treatment, a glass containing an alkali ion having a small ionic radius (for example, an alkali metal ion having a smaller ionic radius than potassium) is used. The composition of the glass sufficiently imparts surface compressive stress and preferably contains SiO ₂ , Na ₂ O, K ₂ O, Al ₂ O ₃ and MgO from the viewpoint of accommodating the thickness of the compressive stress layer in a short time. .

SiO ₂ forms an essential component of the glass skeleton.

Na ₂ O is a component which is mainly substituted with potassium ions in the ion exchange treatment, thereby chemically strengthening the glass, and controlling the coefficient of thermal expansion to lower the high-temperature viscosity of the glass and to improve the meltability or formability.

K ₂ O is a component which improves the meltability, and when it coexists with Na ₂ O, the compressive stress layer can be accommodated deep in a short time. Therefore, it is preferable to contain K ₂ O when it is desired to impart a deeper compressive stress layer.

The Al ₂ O ₃ system has a effect of improving the Tg, the weather resistance, and the Young's modulus, and further improving the ion exchange performance of the glass surface.

The MgO system makes the glass less susceptible to damage and enhances the melting properties of the glass.

The ZrO ₂ system enhances the ion exchange rate and enhances the chemical durability or hardness of the glass, and sometimes contains ZrO ₂ .

The present inventors have made it possible to obtain a glass having a small decrease in surface compressive stress even when chemically strengthened at a high temperature by changing the composition of the glass before chemical strengthening, and before the chemical strengthening. The correlation between the composition of the glass and the change in surface compressive stress upon chemical strengthening was investigated.

As also explained in the examples, it was found that, as shown in FIG. 4, the vertical axis (y) was set to the surface compressive stress ( _S450 ) of the glass which was chemically strengthened by KNO ₃ at 450 ° C for 6 hours. The ratio of the surface compressive stress (S ₄₀₀ ) of the glass which was chemically strengthened by KNO ₃ at 400 ° C for 6 hours (S ₄₅₀ /S ₄₀₀ ), and the horizontal axis (x) was set to Na in the composition of the glass before chemical strengthening. The molar ratio of ₂ O, Al ₂ O ₃ , MgO and ZrO ₂ [(Na ₂ O/2)/(Al ₂ O ₃ /2+MgO+ZrO ₂ )] is expressed by the formula (y=-0.4374x +1.1035) The relationship represented.

The present inventors have focused on the fact that if the total content of Al ₂ O ₃ and MgO in the composition of the glass before chemical strengthening is large, the surface compressive stress is less reduced even when chemical strengthening is performed at a high temperature. In this regard, various composition ratios were further studied, and in the above correlation, the ratio of the components with the highest correlation was found.

The molar ratio of Na ₂ O, Al ₂ O ₃ , MgO, and ZrO ₂ in the glass before chemical strengthening is such that the glass exhibiting the following formula (1) exhibits a change in surface compressive stress even when chemical strengthening is performed. Smaller features.

(Na ₂ O/2)/(Al ₂ O ₃ /2+MgO+ZrO ₂ )≦0.85...(1)

The above formula (1) has the following technical significance: when the number of intermediate acid ions is relatively strong, the stress drop is small, and when the number of sodium ions increasing the compressive stress is large, it is easy. A drop in stress occurs.

(Na ₂ O/2)/(Al ₂ O ₃ /2+MgO+ZrO ₂ ) of the above formula (1) (hereinafter, referred to as x) may be 0.85 or less, preferably 0.75 or less. By setting x to this range, it is possible to obtain a effect of maintaining a sufficient compressive stress value while reducing a change in surface compressive stress when the temperature has changed.

In other words, when x is 0.85 or less, (S ₄₅₀ /S ₄₀₀ ) becomes 0.75 or more according to the above-described correlation formula (y=-0.4374x+1.1035), which is larger than 0.72 of soda lime glass (described later in the examples). In the case of Example 12), the warpage or the undulation is reduced even in the case of a glass plate having a large area of 22 inches or more.

Further, x is preferably 0.4 or more. By setting x to 0.4 or more, the Na ₂ O content in the glass becomes sufficient, sufficient compressive stress can be obtained, and the strength of the glass can be increased.

The glass for chemical strengthening in the present invention is preferably a surface compressive stress of glass which is chemically strengthened by KNO ₃ at 450 ° C for 6 hours, and is a surface compressive stress of glass which is chemically strengthened by KNO ₃ at 400 ° C for 6 hours. More than 75%, more preferably 80% or more, especially better than 85%.

The surface compressive stress of the glass which was chemically strengthened by KNO ₃ at 450 ° C for 6 hours was set to 75% or more of the surface compressive stress of the glass which was chemically strengthened by KNO ₃ at 400 ° C for 6 hours. That is, the temperature at which the surface compresses the stress when the chemical strengthening is performed at a high temperature of 400 ° C or higher. A cover glass having a small change in time and excellent productivity with stable reinforcing properties.

In the present invention, the strain point of the glass before chemical strengthening is preferably 530 ° C or higher. The reason for this is that by setting the strain point of the glass before chemical strengthening to 530 ° C or more, the relaxation of the surface compressive stress is less likely to occur.

The surface molar compressive stress of the glass which satisfies the above formula (1) as Na ₂ O, Al ₂ O ₃ , MgO, and ZrO ₂ and which is chemically strengthened by KNO ₃ at 450 ° C for 6 hours is represented by KNO ₃ Examples of the glass having a surface compressive stress of 75% or more of the glass which is chemically strengthened at 400 ° C for 6 hours include the following (i) to (iv).

(i) The composition expressed in mole % contains 50 to 80% of SiO ₂ , 2 to 25% of Al ₂ O ₃ , 0 to 10% of Li ₂ O, 0 to 18% of Na ₂ O, 0 to 10 % K ₂ O, 0~15% MgO, 0~5% CaO and 0~5% ZrO ₂ glass

(ii) The composition expressed in mole % contains 50 to 74% of SiO ₂ , 1 to 10% of Al ₂ O ₃ , 6 to 14% of Na ₂ O, 3 to 11% of K ₂ O, 2 to 15 % of MgO, 0 to 6% of CaO and 0 to 5% of ZrO ₂ , and the total content of SiO ₂ and Al ₂ O ₃ is 75% or less, and the total content of Na ₂ O and K ₂ O is 12~ 25%, the total content of MgO and CaO is 7~15% glass

(iii) The composition expressed in mole % contains 68 to 80% of SiO ₂ , 4 to 10% of Al ₂ O ₃ , 5 to 15% of Na ₂ O, 0 to 1% of K ₂ O, 4 to 15 % of MgO and 0~1% of ZrO ₂ glass

(iv) The composition expressed in mole % contains 67 to 75% of SiO ₂ , 0 to 4% of Al ₂ O ₃ , 7 to 15% of Na ₂ O, 1 to 9% of K ₂ O, and 6 to 14 The total content of MgO and 0 to 1.5% of ZrO ₂ , SiO ₂ and Al ₂ O ₃ is 71 to 75%, and the total content of Na ₂ O and K ₂ O is 12 to 20%, if CaO is contained. Glass with less than 1% content

Further, in the glass of the above (iii), the total content of SiO ₂ and Al ₂ O ₃ is preferably 80% or less.

2. Chemical strengthening

The chemical strengthening treatment refers to a treatment in which an alkali ion (for example, sodium ion) having a small ionic radius on the surface of the glass is substituted with an alkali ion (for example, potassium ion) having a large ionic radius. For example, the chemical strengthening treatment can be carried out by treating a glass containing sodium ions with a molten salt containing potassium ions. By performing such ion exchange treatment, the composition of the compressive stress layer on the surface of the glass is slightly different from that before the ion exchange treatment, but the composition of the deep portion of the substrate is substantially the same as that before the ion exchange treatment.

(molten salt)

In the case where the above-mentioned component is used as the glass for chemically strengthening, the molten salt used for the chemical strengthening treatment is preferably a treated salt containing at least potassium ions. As such a treatment salt, potassium nitrate is preferably exemplified. In addition, unless otherwise indicated, the content of each component is represented by mass percentage.

Further, it may contain sodium nitrate. However, there is a case where the surface compressive stress value is lowered by sodium ions. Therefore, in order to obtain sufficient surface compressive stress, the content of sodium nitrate in the molten salt is preferably 10% or less. Further, it is more preferably 8% or less, and still more preferably 5% or less.

Further, other components may be contained in the mixed molten salt. As other For example, an alkali metal sulfate such as sodium sulfate or potassium sulfate, and an alkali metal chloride such as sodium chloride or potassium chloride may be mentioned.

(conditions for chemical strengthening treatment)

In the present invention, the treatment conditions of the chemical strengthening treatment are not particularly limited, and can be appropriately selected from previously known methods.

(1) Heating temperature of molten salt

The heating temperature of the molten salt is preferably 350 ° C or higher, more preferably 380 ° C or higher, still more preferably 400 ° C or higher, further preferably 500 ° C or lower, more preferably 480 ° C or lower, and even more preferably 450 ° C or lower. .

By setting the heating temperature of the molten salt to 350 ° C or higher, it is difficult to prevent chemical strengthening due to a decrease in the ion exchange rate. Moreover, by setting the heating temperature of the molten salt to 500 ° C or lower, decomposition and deterioration of the molten salt can be suppressed.

(2) Processing time

In order to impart sufficient compressive stress, the time for bringing the glass into contact with the molten salt is preferably 1 hour or longer, more preferably 2 hours or longer. Further, in the ion exchange for a long period of time, productivity is lowered, and the compressive stress value is lowered by relaxation, and therefore it is preferably 24 hours or shorter, more preferably 20 hours or shorter.

The cover glass of the present invention preferably has a thickness of 1.5 mm or less and a size of preferably 22 Å or more. That is, the cover glass of the present invention has the advantage that even if the thickness is as thin as 1.5 mm or less and the size is set to a large area of 22 对 or more, it has sufficient strength, is not easily deformed by its own weight, and can be improved. The aesthetics or display quality of the display device. Typical sizes are 32 对 or more.

The cover glass of the present invention is used as a cover glass for a flat panel display device.

Fig. 1 is a schematic side view showing a flat panel display device (hereinafter sometimes simply referred to as a display device) according to an embodiment of the present invention. As shown in FIG. 1, the display device 10 includes a display panel 20 and a cover glass 30.

The cover glass 30 is mainly provided for the purpose of improving the appearance or strength of the display device 10, preventing impact damage, and the like. The cover glass 30 is disposed in front of the display panel 20.

For example, the cover glass 30 may be disposed away from the display side (front side) of the display panel 20 (in the manner of having an air layer) as shown in FIG. In this case, the cover glass 30 and the display panel 20 can be integrated via the frame 12.

Moreover, the cover glass 30 may be attached to the display side (front side) of the display panel 20 as shown in FIG. For example, the cover glass 30 may be attached to the display side of the display panel 20 via a translucent adhesive film (not shown). The film may then be of a general construction, the material or shape of which is suitably selected.

As shown in FIG. 3, by providing a configuration in which no gap exists between the cover glass 30 and the display panel 20, reflection of light at the interface between the cover glass 30 (or the display panel 20) and the gap can be suppressed. As a result, the image quality of the display device 10 can be improved. Moreover, it is also possible to contribute to the thinning of the display device 10.

The cover glass 30 has a front surface 31 for emitting light from the display panel 20 and a rear surface 32 for allowing light from the display panel 20 to enter. The functional film 40 can also be provided on the front face 31 or/and the back face 32. Further, the functional film 40 is disposed on the front surface 31 and the back surface 32 in FIG. 1, and is disposed on the front surface 31 in FIG.

The functional film 40 has, for example, preventing reflection of ambient light, preventing impact damage, The function of shielding electromagnetic waves, shielding near infrared rays, correcting color tone, or/or improving damage resistance. The functional film 40 is formed by attaching, for example, a film made of a resin to the cover glass 30. Alternatively, the functional film 40 may be formed by a thin film formation method such as a vapor deposition method, a sputtering method, or a CVD (Chemical Vapor Deposition) method. The functional film 40 can be of a general configuration, and its thickness, shape, and the like are appropriately selected depending on the use.

On the back surface 32 of the cover glass 30, a decorative layer 50 is provided along at least a part of the peripheral portion. The decorative layer 50 can also be disposed to surround the outer periphery of the display panel 20. The decorative layer 50 is provided for the purpose of improving the cover glass sheet 30, and even the design or decorativeness of the display device 10.

For example, when the decorative layer 50 is colored black, when the display device 10 is in the closed state, the front surface 31 of the cover glass 30 is not exposed to light from the front surface 31 of the cover glass 30. Therefore, the appearance of the display device 10 gives the user a clear impression and the appearance is improved.

The method of forming the decorative layer 50 is not limited. For example, there is a method in which an ink containing pigment particles is applied onto a cover glass 30, irradiated with ultraviolet rays or heated, and then cooled to form a decorative layer. 50. The pigment particles are composed of an organic pigment, an inorganic pigment, or the like, and are prepared by mixing and dispersing the pigment particles in an organic vehicle.

[Examples]

The invention is illustrated by the following examples, but the invention is not limited by the examples.

(Manufacture of chemically strengthened glass)

In the platinum crucible, the glass of the composition shown in Tables 1 and 2 as a percentage of moles The glass raw material is heated to 1400 to 1650 ° C to be melted, clarified, and then cast into a mold to produce glass. After the glass is solidified, the glass is transferred to an electric furnace heated to near the slow cooling point of the glass, and slowly cooled to room temperature to obtain a glass block. The glass was polished from both sides of the glass block to a thickness of 1.0 mm and 5.0 cm x 5.0 cm.

The glass was immersed in KNO ₃ maintained at 400 ° C or 450 ° C for 6 hours to carry out chemical strengthening treatment to obtain tempered glass. The results of evaluation of the glass before the chemical strengthening treatment and the glass after the chemical strengthening treatment by the following evaluation methods are shown in Tables 1 and 2. In addition, in Tables 1 and 2, the calculated value is shown in (). In Tables 1 and 2, Examples 1 to 11 are examples, and Examples 12 to 15 are Comparative Examples.

(evaluation method)

The glass having the composition shown in Tables 1 and 2 corresponds to the change point T _Str (unit: ° C), the glass transition point Tg (unit: ° C), the specific gravity d, and the thermal expansion coefficient α (unit: 10) by the method shown below. ^-7 / ° C), Yang type modulus E (unit: GPa), Passon ratio σ is measured or evaluated.

● strain point

The strain point was measured by the fiber elongation method according to JISR3103-2 (2001).

●Glass transfer point

Using a differential thermal dilatometer, quartz glass was used as a reference sample to measure the elongation of the glass at a temperature of 5 ° C /min from room temperature until the glass was softened and the temperature of stretching was not observed, that is, the deformation point. The temperature corresponding to the critical point in the thermal expansion curve is taken as the glass transition point.

● Specific gravity

The measurement was carried out by the Archimedes method.

● Thermal expansion rate

The coefficient of thermal expansion at 50 to 350 ° C was calculated from the thermal expansion curve obtained by the same measurement method as the above Tg.

●Yang type modulus and Passon ratio

The Yang-type modulus and the Passon ratio were measured by ultrasonic pulse method on a glass plate having a thickness of 4 to 10 mm and a size of about 4 cm × 4 cm.

Further, the surface compressive stress S ₄₀₀ (unit: MPa) and S ₄₅₀ (unit: MPa) at the time of chemical strengthening of the glass at 400 ° C and 450 ° C were measured as follows, and S ₄₅₀ and S ₄₀₀ were calculated. Ratio S ₄₅₀ /S ₄₀₀ .

●Surface compression stress

The surface compressive stress of the glass was measured using a surface stress meter FSM-6000 manufactured by Ohara.

4 shows that the composition shown in Tables 1 and 2, ie, (Na ₂ O/2)/(Al ₂ O ₃ /2+MgO+ZrO ₂ ), is taken as the horizontal axis, and by KNO ₃ at 450 ° C. The ratio of the surface compressive stress (S ₄₅₀ ) of the glass which was chemically strengthened for 6 hours to the surface compressive stress (S ₄₀₀ ) of the glass which was chemically strengthened by KNO ₃ at 400 ° C for 6 hours was taken as (S ₄₅₀ /S ₄₀₀ ) as The chart of the vertical axis.

As shown in FIG. 4, the molar ratio of Na ₂ O, Al ₂ O ₃ , MgO, and ZrO ₂ in the composition of the glass before chemical strengthening [(Na ₂ O/2)/(Al ₂ O ₃ /2+MgO) +ZrO ₂ )] is the horizontal axis (x), the surface compressive stress (S ₄₀₀ ) of the glass chemically strengthened by KNO ₃ at 400 ° C for 6 hours, and the chemical strengthening by KNO ₃ at 450 ° C for 6 hours. The ratio of the surface compressive stress (S ₄₅₀ ) of the glass (S ₄₅₀ /S ₄₀₀ ), that is, the vertical axis (y), exhibits a correlation expressed by the formula (y=-0.4374x+1.1035).

As shown in Tables 1 and 2, the molar ratio of Na ₂ O, Al ₂ O ₃ , MgO, and ZrO ₂ in the composition of the glass before chemical strengthening satisfies the above formula (1), and x is 0.85 or less. The surface compressive stress of the glass of ~11 glass which was chemically strengthened by KNO ₃ at 450 ° C for 6 hours was 75% or more of the surface compressive stress of the glass which was chemically strengthened by KNO ₃ at 400 ° C for 6 hours.

On the other hand, the glass of the examples 12 to 15 in which the molar ratio of Na ₂ O, Al ₂ O ₃ , MgO, and ZrO ₂ in the composition of the glass before chemical strengthening does not satisfy the above formula (1) and x exceeds 0.85 The surface compressive stress of the glass which was chemically strengthened by KNO ₃ at 450 ° C for 6 hours did not reach 75% of the surface compressive stress of the glass which was chemically strengthened by KNO ₃ at 400 ° C for 6 hours.

According to the results, it is understood that the molar ratio of Na ₂ O, Al ₂ O ₃ , MgO, and ZrO ₂ in the composition of the glass before chemical strengthening satisfies the above formula (1), and it is possible to obtain a temperature of 400 ° C or higher. The temperature at which the surface compresses the stress when the high temperature is chemically strengthened. The glass has a small change in time and a stable strengthening property.

The present invention has been described in detail with reference to the particular embodiments of the invention. In addition, the present application is based on Japanese Patent Application No. 2010-187523, filed on Jan.

10‧‧‧Display device

12‧‧‧ frame

20‧‧‧ display panel

30‧‧‧ Covering glass

31‧‧‧ front

32‧‧‧Back

40‧‧‧ functional film

50‧‧‧Adding layer

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a side cross-sectional view showing a display device in an embodiment of the present invention.

Figure 2 is a front view of Figure 1.

Figure 3 is a side cross-sectional view showing a modification of Figure 1.

Fig. 4 is a graph showing the correlation between the composition of the glass before chemical strengthening and the change in surface compressive stress at the time of chemical strengthening.

Claims (15)

A cover glass for flat panel displays obtained by chemically strengthening glass, wherein the glass before chemical strengthening is a glass having a composition of 50% to 73% SiO ₂ and 2 to 8%. Al ₂ O ₃ , 0 to 10% Li ₂ O, 5 to 18% Na ₂ O, 0 to 4.6% K ₂ O, 0 to 15% MgO, 0 to 5% CaO, and 0 to 0.5% The thermal expansion coefficient of ZrO ₂ at 50-350 ° C is 98×10 ^-7 /° C., and the molar ratio of Na ₂ O, Al ₂ O ₃ , MgO. and ZrO ₂ in the glass before chemical strengthening [ (Na ₂ O/2)/(Al ₂ O ₃ /2+MgO+ZrO ₂ )] is 0.4 to 0.85. The cover glass for a flat panel display according to claim 1, wherein the glass transition point of the glass before the chemical strengthening is 527 ° C or higher. The cover glass for a flat panel display according to claim 1 or 2, wherein the glass before the chemical strengthening comprises 50 to 71.3% of SiO ₂ and 0.1 to 5% of CaO, and the glass transition point is 547 ° C or more. The cover glass for a flat panel display according to claim 1 or 2, wherein the glass before the chemical strengthening comprises 10.8 to 18% of Na ₂ O. The cover glass for a flat panel display according to claim 1 or 2, wherein the surface compressive stress of the glass which is chemically strengthened by KNO ₃ at 450 ° C for 6 hours is glass which is chemically strengthened by KNO ₃ at 400 ° C for 6 hours. More than 75% of the surface compressive stress. The cover glass for a flat panel display according to claim 1 or 2, wherein the strain point of the glass before the chemical strengthening is 530 ° C or higher. The cover glass for a flat panel display according to claim 1 or 2, which has a thickness of 1.5 mm or less and a size of 22 Å or more. The cover glass for a flat panel display according to claim 1 or 2, wherein the glass before the chemical strengthening comprises an aluminosilicate glass of SiO ₂ , Al ₂ O ₃ , Na ₂ O and MgO. A flat panel display device using a cover glass for a flat panel display according to claim 1 or 2 as a cover glass. A method for chemically strengthening glass to produce a cover glass for a flat panel display, wherein the glass before chemical strengthening is a glass having a composition of 50% to 73% of SiO ₂ and 2 to 8 % Al ₂ O ₃ , 0~10% Li ₂ O, 5-18% Na ₂ O, 0~4.6% K ₂ O, 0~15% MgO, 0~5% CaO and 0~ 0.5% ZrO ₂ , the thermal expansion coefficient at ^50-350 ° C is 98×10 ^-7 /° C., and the molar ratio of Na ₂ O, Al ₂ O ₃ , MgO and ZrO ₂ in the glass before chemical strengthening [(Na ₂ O/2)/(Al ₂ O ₃ /2+MgO+ZrO ₂ )] is 0.4 to 0.85. The method of claim 10, wherein the glass transition point of the glass before the chemical strengthening is 527 ° C or higher. The method of claim 10 or 11, wherein the glass before the chemical strengthening comprises 50 to 71.3% SiO ₂ and 0.1 to 5% CaO, and the glass transition point is 547 ° C or higher. The method of claim 10 or 11, wherein the glass before the chemical strengthening comprises 10.8 to 18% of Na ₂ O. The method of claim 10 or 11, wherein the chemical strengthening of the glass is carried out at 400 to 450 °C. The method of claim 10 or 11, wherein the strain point of the glass before the chemical strengthening is 530 ° C or higher.