JP2013177253A - Method of improving strength of glass substrate for front face plate of display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of furthermore improving the strength of a glass substrate for display device.SOLUTION: A method for improving the strength of a glass substrate for a front face plate of a display device, includes: (a) preparing a glass substrate including an alkali metal; (b) physically reinforcing the glass substrate; (c) chemically reinforcing the glass substrate treated by the physical reinforcement treatment, whereby a compression stress layer is formed on at least a part of the surface of the glass substrate, and the compression stress layer has a thickness of at least 1/6 times the thickness of the glass substrate, and the compression stress value Pon the outermost surface of the compression stress layer is at least the same as the compression stress value Pon the outermost surface of the compression stress layer obtained by practising only the chemical reinforcement treatment to the glass substrate.

Description

  The present invention relates to a glass substrate used for a front plate or the like of a display device.

  In general, a front plate formed of a glass substrate or the like is widely used in display devices such as a liquid crystal display (LCD), a plasma display panel (PDP), and an organic EL (Electroluminescent) display (OELD). Recently, in order to meet demands for further thinning and weight reduction of display devices, it has been required to use a glass substrate having a thin plate thickness for the front plate.

  In general, the strength of a glass substrate decreases as the plate thickness decreases. Therefore, in order to actually apply a thin glass substrate to a front plate or the like of a display device, it is important to improve the strength of the glass substrate. For this reason, it has been proposed to perform a chemical strengthening process on a glass substrate (Patent Document 1).

Japanese Patent Publication No. 5-3420

  By performing a chemical strengthening process with respect to a glass substrate, a compressive-stress layer is provided to the surface of a glass substrate, and, thereby, the intensity | strength of a glass substrate can be raised.

  However, generally, the compressive stress layer formed by the chemical strengthening treatment method is formed only on the extreme surface of the glass substrate and is in a very thin state.

  For this reason, the chemically strengthened glass substrate may be relatively easily broken (self-destructed) by a small (shallow) scratch. That is, since the compressive stress layer formed by the chemical strengthening treatment method is relatively thin, if the glass substrate is damaged to a degree exceeding the thickness of the compressive stress layer, the glass substrate is relatively easily damaged. There is a risk that.

  In particular, the front plate of the display device tends to become larger and thinner in the future. In this case, it is expected that the surface of the glass substrate for the front plate is more likely to be damaged (for increasing the size), and more likely to be damaged (self-destructing) than (for reducing the thickness).

  The present invention has been made in view of such a background, and an object of the present invention is to provide a method capable of further increasing the strength of a glass substrate for a front plate of a display device.

In the present invention, a method for increasing the strength of a glass substrate for a front plate of a display device (a method for producing a glass substrate with increased strength),
(A) preparing a glass substrate containing an alkali metal;
(B) Physically strengthening the glass substrate;
(C) chemically strengthening the glass substrate subjected to the physical strengthening treatment,
Thereby, a compressive stress layer is formed on at least a part of the surface of the glass substrate,
The compressive stress layer has a thickness of 1/6 or more of the thickness of the glass substrate,
In the compression stress value P _E in the uppermost surface of the compression stress layer, the compressive stress value at the outermost surface of the compressive stress layer obtained when carrying out the only chemical strengthening processing on the glass substrate P _A equal to or higher than A method is provided that is characterized.

  Here, the compressive stress value at the outermost surface of the glass substrate can be obtained by measuring a phenomenon in which an optical path difference is generated in light passing through the stress value by the Babinet correction method.

  In the method according to the present invention, the compressive stress layer may have a thickness in the range of 50 μm to 350 μm.

Further, in the process according to the present invention, the compression stress value _{P E} in the uppermost surface of the compressive stress layer may be in the range of 400MPa～950MPa.

  In the method according to the present invention, the glass substrate may have a thickness in the range of 0.3 mm to 2 mm.

  In the method according to the present invention, the step (b) may be performed by rapidly cooling the glass substrate after the glass substrate is heated to a temperature range of 650 ° C. to 690 ° C.

  In the method according to the present invention, the process of rapidly cooling the glass substrate may be performed locally in the plane of the glass substrate.

  In this case, the process of rapidly cooling the glass substrate may be performed only on the outer periphery of the glass substrate.

  In the method according to the present invention, the step (c) may be performed by immersing the glass substrate in a molten salt containing an alkali metal in a temperature range of 400 ° C to 450 ° C.

  In the method according to the present invention, the step (c) is carried out continuously to the step (b) when the temperature of the glass substrate is in the range of 400 ° C. to 450 ° C. after the step (b). May be.

  In the method according to the present invention, the glass substrate may be used for a front plate of a display device having a size of 32 inches or more.

  The present invention can provide a method capable of further increasing the strength of a glass substrate for a front plate for a display device.

It is the figure which showed an example of the schematic cross section of a display apparatus. It is the figure which showed an example of the schematic cross section of a front board. It is the schematic diagram which showed the residual stress profile in the glass substrate after performing a chemical strengthening process with the cross section of the glass substrate. It is the schematic diagram which showed the residual stress profile in the glass substrate after performing a physical strengthening process with the cross section of the glass substrate. It is the schematic diagram which showed the residual stress profile in the glass substrate to which the method by this invention was applied with the cross section of the glass substrate. FIG. 2 is a flow diagram schematically illustrating an example of a method according to the present invention. It is a temperature change curve of the glass substrate in the case of a physical strengthening process. It is a temperature change curve of a glass substrate at the time of implementing a physical strengthening process and a chemical strengthening process continuously. It is the figure which showed roughly the example of 1 structure of the apparatus used when applying the method by this invention to a glass substrate.

  The present invention will be described below.

  First, a configuration of a display device to which the method according to the present invention can be applied will be briefly described.

  FIG. 1 shows an example of a schematic cross section of a display device. FIG. 2 shows an example of a schematic cross section of the front plate.

  As shown in FIG. 1, the display device 50 includes a front plate 60, an adhesive layer 80, and a display panel 90 from the viewing side.

  The display device 50 may be various FPD devices, for example, display devices such as a liquid crystal display (LCD), a plasma display (PDP), and an organic electroluminescent display (OELD).

  Therefore, the display panel 90 may be for LCD, PDP, and OELD, for example. The structure of the display panel 90 is not particularly limited, and a wide variety of conventional structures can be provided. The display panel 90 emits a predetermined image (light) upward in FIG.

  The front plate 60 is installed “front” of the display panel 90 and has a role of shielding electromagnetic waves, blocking near infrared rays, preventing reflection, and the like.

  The adhesive layer 80 has a role of bonding the front plate 60 to the display panel 90 (so-called “direct bonding”).

  FIG. 2 shows an example of a schematic cross section of the front plate 60.

  As shown in FIG. 2, the front plate 60 includes a glass substrate 69 having a first surface 61A and a second surface 61B. As shown in FIGS. 1 and 2, the first functional film 70 may be provided on the first surface 61 </ b> A of the glass substrate 69. The first functional film 70 is installed to obtain functions such as impact damage prevention, ambient light reflection prevention, electromagnetic wave shielding, near infrared shielding, color tone correction, and / or scratch resistance improvement, for example. However, the first functional film 70 may be omitted.

  In the normal case, in the front plate 60, the side of the glass substrate 69 having the first surface 61 </ b> A is the front side 71 </ b> A of the front plate 60, and the side of the glass substrate 69 having the second surface 61 </ b> B is the back of the front plate 60. Side 71B. The front side 71A of the front plate 60 is the side from which light (image) is emitted from the front plate 60 (ie, the viewer side), and the rear side 71B of the front plate 60 is the display panel 90 side (ie, the light source side). Become.

  Although not shown in the drawing, a second functional film similar to or different from the first functional film 70 may be provided on the second surface 61B of the glass substrate 69.

  A ceramic layer 75 is provided on the second surface 71B of the glass substrate 69 along the peripheral edge.

  The ceramic layer 75 is installed to improve the design and decoration of the front plate 60 and various devices including the front plate 60. For example, when a black ceramic layer is employed as the ceramic layer 75, no light is emitted from the front side 71A of the front plate 60 including the outer peripheral portion of the front plate 60 when the display device 50 is in the off state. Accordingly, the appearance of the display device 50 gives a sharp impression, and the aesthetics of the display device 50 are improved.

  Here, as described above, in order to increase the strength of a thin glass substrate, it has been proposed to apply a chemical strengthening treatment to the glass substrate.

  “Chemical strengthening treatment (method)” means that a glass substrate is immersed in a molten salt containing an alkali metal, and an alkali metal (ion) having a small atomic diameter present on the outermost surface of the glass substrate is introduced into the molten salt. This is a generic term for technologies that replace existing alkali metals (ions) with a large atomic diameter. In the “chemical strengthening treatment (method)”, an alkali metal (ion) having an atomic diameter larger than that of the original atom is arranged on the surface of the treated glass substrate. For this reason, a compressive stress layer can be formed on the surface of the glass substrate, thereby improving the strength of the glass substrate.

  For example, when the glass substrate contains sodium (Na), this sodium is replaced with, for example, potassium (Ka) in the molten salt (for example, nitrate) during the chemical strengthening treatment. Alternatively, for example, when the glass substrate contains lithium (Li), during the chemical strengthening treatment, the lithium is replaced with, for example, sodium (Na) and / or potassium (Ka) in a molten salt (eg, nitrate). Also good.

  By performing such a chemical strengthening process on the glass substrate, a residual stress profile as shown in FIG. 3 is obtained in the glass substrate.

  In FIG. 3, the profile of the residual stress in the depth direction of the glass substrate after a chemical strengthening process is typically shown with sectional drawing of a glass substrate.

As shown in this figure, extremely thin compressive stress layers 12A and 12B are formed on the outermost surface of the glass substrate 10 after the chemical strengthening treatment. Compressive stress layer 12A is a thickness of theta _A, the compression stress layer 12B has a thickness of theta _B. Note that in FIG. 3, the scale is not shown, and in particular, it should be noted that the compressive stress layers 12 </ b> A and 12 </ b> B are drawn exaggeratedly thick.

Although the thicknesses θ _A and θ _B of the compressive stress layers 12A and 12B vary depending on the time of the chemical strengthening treatment, the thickness of the compressive stress layers 12A and 12B formed in a practical and realistic time is, for example, It is about 5 μm to 30 μm. The compressive stress values _{P A} and _{P B} of the outermost surface of the compressive stress layer 12A and 12B, for example, about 400MPa～950MPa (e.g. 800 MPa).

  Thus, by performing a chemical strengthening process with respect to a glass substrate, a compressive-stress layer is formed in the surface and, thereby, the intensity | strength of a glass substrate can be raised.

However, the thickness of the compressive stress layers 12A and 12B introduced into the glass substrate 10 by the chemical strengthening treatment is at most about 30 μm as described above, and is not so thick. For this reason, the chemically strengthened glass substrate 10 may “self-destruct” relatively easily due to small (shallow) scratches and may be damaged. Note that “self-destruction” refers to a phenomenon in which cracks or cracks that are first generated in a glass substrate are the starting point, cracks and cracks are spontaneously developed, and the glass substrate is eventually damaged. For example, in the glass substrate 10 of FIG. 3, when a scratch having a depth exceeding the thickness θ _A (or θ _B ) of the compressive stress layer 12A (or 12B) occurs on the surface, the scratch causes the glass substrate to There is a risk of “self-destruction” relatively easily. In addition, fragments generated from a broken glass substrate usually have a sharp surface, which is dangerous when touched.

  In particular, the front plate of the display device tends to become larger and thinner in the future. In this case, it is expected that the surface of the glass substrate for the front plate is more likely to be scratched (due to an increase in size) and further susceptible to self-destruction (due to a reduction in thickness).

  On the other hand, the method for increasing the strength of the glass substrate according to the present invention is characterized in that the glass substrate is physically strengthened before the glass substrate is chemically strengthened.

  In such a method, as will be described later, the compressive stress layer can be formed further into the glass substrate. Therefore, the glass substrate obtained by the method according to the present invention has significant resistance to small scratches, and the effect that self-destruction and breakage are less likely to occur is obtained.

  Moreover, since the method by this invention includes the process of applying a chemical strengthening process to a glass substrate, the advantage of the conventional chemical strengthening process can be utilized as it is. For example, in the glass substrate obtained by the present invention, a compressive stress layer having a compressive residual stress equal to or higher than that obtained when only the conventional chemical strengthening treatment is performed is formed on the outermost surface. For this reason, the glass substrate obtained by the method of the present invention can be given strength equal to or higher than the strength obtained by the conventional chemical strengthening treatment.

  Here, “physical strengthening treatment (method)” refers to a technique of forming a residual stress distribution in a glass substrate by rapidly cooling the glass substrate from a high-temperature “飴” state. In a normal case, the inside of the glass substrate is less susceptible to rapid cooling than the surface, and is cooled and solidified relatively slowly. For this reason, during rapid cooling, the residual compressive stress increases from the inside to the surface of the glass substrate, and a depth profile of the residual compressive stress is obtained. On the surface of the glass substrate finally obtained, a compressive stress layer is formed with a relatively deep thickness, whereby the strength of the glass substrate is improved as compared with that before the physical strengthening treatment.

  In FIG. 4, the profile of the residual stress in the depth direction of the glass substrate after a physical strengthening process is typically shown with sectional drawing of a glass substrate.

As shown in this figure, relatively thick compressive stress layers 22C and 22D are formed on the outermost surface of the glass substrate 20. Compressive stress layer 22C has a thickness of theta _C, compressive stress layer 22D has a thickness of theta _D. In FIG. 4, the scale is not shown, and in particular, it should be noted that the compressive stress layers 22C and 22D are exaggerated and drawn thickly.

The thicknesses θ _C and θ _D of the compressive stress layers 22C and 22D vary depending on the thickness of the glass substrate. In a normal case, the thicknesses θ _C and θ _D of the compressive stress layers 22C and 22D are about 1/4 to 1/8 (for example, 1/6) of the thickness of the glass substrate 20. For example, when the thickness of the glass substrate 20 is 0.7 mm, the thicknesses θ _C and θ _D are about 100 μm or more. Further, the compression stress value _{P C} and _{P D} at the outermost surface of the compressive stress layer 22C and 22D are, for example, about 50MPa～150MPa (e.g. 100 MPa).

  As apparent from the comparison between FIG. 3 and FIG. 4, in the physical strengthening process, the thickness of the compressive stress layers 22 </ b> C and 22 </ b> D formed on the surface of the glass substrate 20 is the same as the compressive stress layer 12 </ b> A obtained by the chemical strengthening process. It becomes thicker than the thickness of 12B. Therefore, in the physical strengthening treatment, a glass substrate having significant resistance to scratches can be obtained as compared with the glass substrate subjected to the chemical strengthening treatment. Further, since the physically strengthened glass substrate has relatively thick compressive stress layers 22C and 22D, when the glass substrate is broken like a windshield of a vehicle, sharp broken materials are scattered around. Can be significantly suppressed.

In the “physical strengthening treatment”, the compressive stress values P _C and P _D (see FIG. 4) of the outermost surfaces of the compressive stress layers 22C and 22D formed on the surface of the glass substrate 20 are obtained by a chemical strengthening treatment method. compared to the compression stress value of the outermost surface of the compressive stress layer 12A and 12B _{P a} and _{P B} (see FIG. 3), it becomes small. Therefore, there is a problem that it is difficult to impart sufficient strength to the glass substrate simply by performing “physical strengthening treatment” on the glass substrate.

  On the other hand, the present invention is characterized in that the glass substrate is physically strengthened as described above and then chemically strengthened. Therefore, in the present invention, both advantages can be taken in, and a glass substrate that is resistant to scratches and has a large compressive stress on the surface can be obtained.

  In FIG. 5, the profile of the residual stress in the depth direction of the glass substrate to which the method by this invention was applied is shown typically with sectional drawing of a glass substrate.

As shown in this figure, on the outermost surface of the glass substrate 100, relatively thick compressive stress layers 112E and 112F are formed. Compressive stress layer 112E has a thickness of theta _E, compressive stress layer 112F has a thickness of theta _F. Note that in FIG. 5, the scale is not shown, and in particular, it should be noted that the compressive stress layers 112E and 112F are exaggerated.

  Here, from FIG. 5, in the glass substrate 100 to which the method according to the present invention is applied, a glass substrate having a residual stress profile that combines the characteristics of a general chemical strengthening treatment method and the characteristics of a general physical strengthening treatment method. It can be seen that 100 is obtained.

In other words, the compressive stress layers 112E and 112F are formed on the surface of the glass substrate 100, and these are equivalent to the thicknesses θ _C and θ _D of the compressive stress layers 22C and 22D of the glass substrate 20 subjected to only the physical strengthening process. The thicknesses θ _E and θ _F are as described above. The thicknesses θ _E and θ _F of the compressive stress layers 112E and 112F vary depending on physical strengthening processing conditions and conditions such as the thickness of the glass substrate 100, for example, 1/4 to 1/8 of the thickness of the glass substrate 100. Degree (for example, 1/6).

Further, the outermost surface of the compressive stress layer 112E and 112F are chemical strengthening treatment only performed the compressive stress at the outermost surface of the compressive stress layer 12A and 12B of the glass substrate 10 values _{P A} and _{P B} equal or compressive stress _{P E} and a _{P F.} Compressive stress value _{P E} and _{P F} of the outermost surface of the compressive stress layer 112E and 112F may vary by a chemical strengthening treatment conditions, for example about 400MPa～950MPa (e.g. 850 MPa).

  Thus, in the method according to the present invention, the advantages of the chemical strengthening treatment method and the physical strengthening treatment method can be taken in, and a glass substrate that is resistant to scratches and has a large compressive stress on the surface can be obtained. Moreover, when a glass substrate is damaged, it can suppress that a sharp broken material scatters around. This is a feature of physical strengthening employed in safety glass such as automobile side glass.

(About the flow of the method according to the present invention)
Hereinafter, the method according to the present invention will be described in more detail with reference to FIG.

  FIG. 6 shows an example of a method for increasing the strength of the glass substrate according to the present invention.

As shown in FIG. 6, the method of the present invention
(A) preparing a glass substrate containing an alkali metal (step S110);
(B) a step of physically strengthening the glass substrate (step S120);
(C) a step of chemically strengthening the glass substrate subjected to the physical strengthening treatment (Step S130);
Have

  Hereinafter, each step will be described.

(Step S110)
First, a glass substrate 100 containing an alkali metal is prepared. The composition of the glass substrate 100 is not particularly limited as long as it contains an alkali metal, and the glass substrate 100 may be, for example, a soda lime glass substrate.

Glass substrate 100 is, for example, in terms of oxide, 60 mol% 80 mol% of _SiO 2, 0.5mol% _~7mol% of _{Al 2 O 3, 3mol% ~10mol} % of MgO, 6mol% ~9mol% of CaO, 0 to 5 mol% of SrO, have 0～4Mol% of BaO, _ZrO 2 of 0~2mol%, 4mol% ~13mol% of _Na 2 O, and the composition of 0.1mol% ~7mol% of _{K 2} O Also good.

  The thickness of the glass substrate 100 is not particularly limited, but if the plate thickness becomes too thick, the problem of strength is relatively reduced, and the advantage of applying the present invention is reduced. Further, if the plate thickness is too thin, there is a possibility that a compressive stress distribution cannot be obtained in the thickness direction of the glass substrate after the physical strengthening treatment. In a normal case, the thickness of the glass substrate 100 is in the range of 0.3 mm to 2 mm, and preferably in the range of 0.7 mm to 1.5 mm.

  Note that the end surface of the glass substrate 100 may be chamfered.

(Step S120)
Next, the above-mentioned glass substrate is physically strengthened. The conditions for the physical strengthening process are not particularly limited. Physical strengthening process, for example, quenched while heating the glass substrate to a first temperature T _1, it may be implemented by lowering the glass substrate to a second temperature T _2.

  FIG. 7 shows a typical temperature change curve of the glass substrate during the physical strengthening treatment.

7, first, the glass substrate 100 is heated to a first temperature T _1. For example, T ₁ may be in the range of 650 ° C. to 690 ° C., or may be 120 ° C. to 160 ° C. higher than the strain point of the glass substrate 100. The temperature increase rate v ₁ when the temperature of the glass substrate is increased to the first temperature T ₁ is not particularly limited.

Then, the glass substrate 100 is rapidly cooled, the temperature of the glass substrate 100 is lowered to _{T 2.} T ₂ may be in the range of 400 ° C. to 450 ° C., for example. The rapid cooling rate v ₂ may be, for example, about 60 ° C./second to 25 ° C./second, and in this case, the rapid cooling time t ₂ is about 5 seconds to 8 seconds (for example, about 6 seconds). . The method of rapid cooling is not particularly limited. For example, the glass substrate may be rapidly cooled by forcibly supplying cold air to both surfaces of the glass substrate 100.

  Thereafter, the glass substrate 100 is gradually cooled to room temperature.

By the physical strengthening process of the glass substrate 100, a residual stress profile as shown in FIG. 4 is obtained in the glass substrate 100, and compressive stress layers (22C, 22D) are formed on both surfaces. The thickness (θ _C , θ _D ) of the compressive stress layer is not particularly limited, but is usually about 1/4 to 1/8 (for example, 1/6) of the thickness of the glass substrate 100.

(Step S130)
Next, the chemically strengthened glass substrate is chemically strengthened. Conditions for the chemical strengthening treatment are not particularly limited, and a conventional chemical strengthening treatment method can be used. The chemical strengthening treatment may be performed, for example, by dipping a glass substrate in a molten nitric acid salt at 400 ° C. to 450 ° C. for a predetermined time. When the glass substrate contains sodium (Na), for example, potassium nitrate (KNO ₃ ) is used as the nitric acid molten salt. When the glass substrate contains lithium (Li), for example, sodium nitrate (NaNO ₃ ) and / or potassium nitrate (KNO ₃ ) is used as the nitric acid molten salt. Further, when the glass substrate contains lithium (Li) and sodium (Na), for example, potassium nitrate (KNO ₃ ) is used as the nitric acid molten salt. Although the time of a chemical strengthening process is not specifically limited, Usually, it implements about 1 hour-4 hours.

Thereby, the residual stress profile as shown in FIG. 5 is obtained in the glass substrate 100, and the compressive stress layers 112E and 112F are formed on both surfaces. The thicknesses θ _E and θ _F of the compressive stress layers 112E and 112F are not particularly limited, but are usually about 1/4 to 1/8 (for example, 1/6) of the thickness of the glass substrate 100, For example, it is 50 micrometers-350 micrometers.

Further, in the normal case, the compressive stress values P _E and P _{F on} the outermost surface of the obtained compressive stress layers 112E and 112F are the compressive stress values P _C and P _{D on the} outermost surface obtained when only the chemical strengthening treatment is performed. (For example, compressive stress value ≧ 850 MPa). This is due to a synergistic effect of the compressive stress imparting effect obtained by the physical strengthening treatment and the compressive stress imparting effect obtained by the chemical strengthening treatment.

However, depending on the processing conditions, such a synergistic effect may not be clearly recognized. However, even in such a case, the compressive stress layer 112E provided by the present invention, 112F is simply compared with the case where only physical strengthening, a large compressive stress value P _C on the outermost _surface, a P _D Have. Moreover, the compressive stress layers 112E and 112F obtained by the present invention have a larger thickness than when only the chemical strengthening process is performed. Therefore, the glass substrate obtained by the method according to the present invention can be clearly distinguished between a glass substrate subjected to only chemical strengthening treatment and a glass substrate subjected to only physical strengthening treatment.

  The chemical strengthening process may be performed separately from the physical strengthening process or may be performed “continuously” with the physical strengthening process.

  FIG. 8 shows a typical temperature change curve of the glass substrate when the physical strengthening process in step S120 and the chemical strengthening process in step S130 are performed “continuously”.

As shown in FIG. 8, in this method, first, a glass substrate is heated to temperature T ₁ of the first. T ₁ may be, for example, in the range of 650 ° C. to 690 ° C., or may be a temperature 120 ° C. to 160 ° C. higher than the strain point of the glass substrate. The temperature increase rate v ₁ when the temperature of the glass substrate is increased to the first temperature T ₁ is not particularly limited.

Next, a glass substrate is rapidly cooled, the temperature of the glass substrate is lowered to T _2. T ₂ may be in the range of 400 ° C. to 450 ° C., for example. The rapid cooling rate v ₂ may be, for example, about 60 ° C./second to 25 ° C./second, and in this case, the rapid cooling time t ₂ is about 5 seconds to 8 seconds (for example, about 6 seconds). .

Subsequently, the glass substrate is chemically strengthened “continuously”. In other words, in this case, the glass substrate is subjected to a chemical strengthening treatment while the temperature is kept at T ₂ before being cooled to room temperature.

During the chemical strengthening treatment, the temperature of the glass substrate is constant at T _2. During the time t _3, the glass substrate is immersed in the molten salt. Time _{t 3} may be, for example, about 1 to 10 hours. Thereafter, the glass substrate is pulled up from the molten salt and gradually cooled to room temperature.

  In such a “continuous” method, it is not necessary to heat the glass substrate again at the time of the chemical strengthening process, and the processing time and energy cost can be suppressed.

  By the way, in the above description, the flow of the method according to the present invention has been described by taking as an example the case where the method according to the present invention is applied to the entire surface of the glass substrate. However, the method according to the present invention is not necessarily applied to the entire surface of the glass substrate. For example, the method according to the present invention may be applied only to a portion of the surface of the glass substrate.

  Applying the present invention “non-uniformly” within the plane of such a glass substrate is particularly preferable when there is a local area in the glass substrate where it is desired to improve the strength.

  For example, in general, a front panel of a display device requires a greater strength at the peripheral edge than at the center of the front panel. This is because the normal front plate needs to be supported at the peripheral edge when combined with other members such as a display panel, and there is a higher risk of breakage at the peripheral edge. In such a case, by applying the method according to the present invention only to the peripheral portion of the glass substrate for the front plate, a glass substrate having an improved strength at the peripheral portion as compared with the central portion can be obtained. For example, such a glass substrate can be easily provided by applying the above-described physical strengthening process (step S120) only to the peripheral portion of the glass substrate.

(On a device for carrying out the method according to the invention)
Next, an example of an apparatus used when the above-described method according to the present invention is applied to a glass substrate will be described.

  FIG. 9 shows an apparatus used in applying the method according to the present invention to a glass substrate.

  The apparatus 200 is configured to be able to continuously perform the above-described steps S120 and S130. The apparatus 200 includes a heating unit 210, a quenching unit 240, an immersion unit 260, and a slow cooling unit 280. Have.

  The heating unit 210 is a part that heats the glass substrate 202 serving as a front plate for physical strengthening processing. The heating unit 210 includes a heating chamber 212, and the heating chamber 212 can be heated to, for example, 650 ° C. to 690 ° C. with a heater (not shown). The heating unit 210 is provided with a plurality of rollers 214 in order to introduce the glass substrate 202 into the heating chamber and carry the glass substrate 202 out of the heating chamber 212. By rotating the roller 214 in the same direction, the glass substrate 202 can be conveyed in a desired direction (rightward in the example in the figure).

  The quenching unit 240 has a role of quenching the glass substrate 202 heated in the heating chamber 212 and physically strengthening the glass substrate 202. A set of coolers 242 are installed in the quenching section 240 so as to face each other. The glass substrate 202 is rapidly cooled from both sides by the cooling air from the cooler 242. Note that the glass substrate 202 is also transported by the plurality of rollers 214 in the rapid cooling unit 240.

  In the rapid cooling unit 240, the temperature of the glass substrate 202 is lowered to about 400 ° C to 450 ° C.

  The immersion part 260 is an area for chemically strengthening the glass substrate 202 that has been physically strengthened. The immersion unit 260 includes a molten salt tank 262, and an alkali metal molten nitrate 263 is accommodated in the molten salt tank 262. The molten nitrate 263 includes, for example, potassium nitrate (when the glass substrate 202 includes sodium) or sodium nitrate (when the glass substrate 202 includes lithium).

  The molten salt tank 262 is maintained at a temperature of 400 ° C. to 450 ° C., for example.

  The slow cooling unit 280 has a role of gradually cooling the chemically strengthened glass substrate 202 to room temperature, and includes a plurality of rollers 214.

  When the glass substrate 202 to be reinforced is introduced into such an apparatus 200, the glass substrate 202 is first carried into the heating chamber 212 of the heating unit 210 by the roller 214. The glass substrate 202 carried into the heating chamber 212 is heated to a desired temperature (for example, 650 ° C.) before the physical strengthening process.

  Next, the glass substrate 202 is introduced into the quenching unit 240 by the roller 214. In the rapid cooling unit 240, the glass substrate 202 is cooled to a temperature of 400 to 450 ° C. in a few seconds by forced cooling by the cooler 242. Thereby, the glass substrate 202 is physically strengthened.

  Here, the “non-uniform” glass substrate as described above, that is, a region in which the strength is improved by physical strengthening treatment and a region in which the strength is not changed without physical strengthening treatment in the plane of the glass substrate 202 If it is desired to form the air conditioner, the arrangement of the cooler 242 may be adjusted. For example, the physical strengthening process can be performed only on the outer peripheral portion of the glass substrate 202 by arranging the cooler 242 so that the cooling air hits only the outer peripheral portion of the glass substrate 202.

  Next, the glass substrate 202 is conveyed by the roller 214 to the immersion unit 260 for chemical strengthening treatment. In the immersion unit 260, the glass substrate 202 is immersed in the molten salt bath 262 while being placed on the roller 214. Therefore, the glass substrate 202 is chemically strengthened here at a temperature of 400 ° C. to 450 ° C.

  Thereafter, the glass substrate 202 is pulled up from the molten salt bath 262 and gradually cooled to room temperature in the slow cooling unit 280. Thereby, a glass substrate with increased strength is obtained.

  In the above description, the apparatus configuration has been described by taking as an example the case where both the physical strengthening process and the chemical strengthening process are applied “continuously” to the glass substrate 202. However, in the present invention, the physical strengthening process and the chemical strengthening process may be performed separately (discontinuously) on the glass substrate. In this case, after the temperature of the glass substrate is once lowered to room temperature after the physical strengthening process in one apparatus, the glass substrate is chemically strengthened in another apparatus.

  Thus, the present invention can provide a method capable of further increasing the strength of the glass substrate for the front plate of the display device. The method according to the present invention is particularly useful for large display devices (for example, display devices of 32 inches or more) and thin display devices.

  The front plate according to the present invention can be applied to FPD devices such as a liquid crystal display, a plasma display, an organic EL display, and a mobile display.

DESCRIPTION OF SYMBOLS 10 Glass substrate after chemical strengthening process 12A, 12B Compressive stress layer 20 Glass substrate after physical strengthening process 22C, 22D Compressive stress layer 50 Display device 60 Front plate 61A First surface 61B Second surface 69 Glass substrate 70 First Functional film 71A Front side 71B Rear side 75 Ceramic layer 80 Adhesive layer 90 Display panel 100 Glass substrate 112E compressive stress layer 112F compressive stress layer 200 device 202 glass substrate 210 heating unit 212 heating chamber 214 roller 240 Rapid cooling part 242 Cooler 260 Immersion part 262 Molten salt tank 263 Molten nitrate 280 Slow cooling part

Claims (10)

A method for increasing the strength of a glass substrate for a front plate of a display device,
(A) preparing a glass substrate containing an alkali metal;
(B) Physically strengthening the glass substrate;
(C) chemically strengthening the glass substrate subjected to the physical strengthening treatment,
Thereby, a compressive stress layer is formed on at least a part of the surface of the glass substrate,
The compressive stress layer has a thickness of 1/6 or more of the thickness of the glass substrate,
In the compression stress value P _E in the uppermost surface of the compression stress layer, the compressive stress value at the outermost surface of the compressive stress layer obtained when carrying out the only chemical strengthening processing on the glass substrate P _A equal to or higher than A method characterized by being.   The method of claim 1, wherein the compressive stress layer has a thickness in the range of 50 μm to 350 μm. The compressive stress value _{P E} in the uppermost surface of the compression stress layer, the method according to claim 1 or 2, characterized in that in the range of 800MPa～850MPa.   The method according to claim 1, wherein the glass substrate has a thickness in the range of 0.3 mm to 2 mm.   5. The method (b) is carried out by heating the glass substrate to a temperature range of 650 ° C. to 690 ° C. and then rapidly cooling the glass substrate. The method described in 1.   The method according to claim 5, wherein the process of rapidly cooling the glass substrate is performed locally in a plane of the glass substrate.   The method according to claim 6, wherein the process of rapidly cooling the glass substrate is performed only on an outer peripheral portion of the glass substrate.   Said (c) is implemented by immersing the said glass substrate in the molten salt containing the alkali metal of the temperature range of 400 to 450 degreeC, The any one of Claim 1 thru | or 7 characterized by the above-mentioned. The method described in 1.   The step (c) is carried out continuously to the step (b) when the temperature of the glass substrate is in the range of 400 ° C to 450 ° C after the step (b). The method according to any one of 1 to 8.   10. The method according to claim 1, wherein the glass substrate is for a front plate of a display device having a size of 32 inches or more.

Images