JPWO2018056329A1 - Method of manufacturing tempered glass plate, tempered glass plate, and tempered glass plate - Google Patents

Abstract

The method for producing a tempered glass plate according to the present invention is a method for producing a tempered glass plate, wherein the glass plate is tempered using an ion exchange method, and an ion permeation preventive film for preventing ion exchange on a part of the surface of the glass plate. And a selective ion exchange step of selectively ion-exchanging the area other than the film formation area by bringing the formed glass plate into contact with the molten salt bath, and the ion permeation preventive film And an inorganic film containing 50 to 100% by mass of ZrO 2.

Description

  The present invention relates to a method for producing a strengthened glass sheet, a glass sheet for strengthening, and a tempered glass sheet, and more specifically, to a method for producing a tempered glass sheet for chemically strengthening a glass sheet by an ion exchange method.

  Conventionally, a chemically strengthened tempered glass plate is used as a cover glass plate for a touch panel display mounted on an electronic device such as a smartphone or a tablet PC.

  Such a tempered glass sheet is generally manufactured by chemically treating a glass sheet containing an alkali metal as a composition with a reinforcing liquid to form a compressive stress layer on the surface. Such a tempered glass sheet has improved impact resistance and the like because it has a compressive stress layer on the surface. However, even with such a tempered glass plate, the impact resistance at the edge portion and the peripheral portion is lower than the impact resistance at the main surface, which causes the breakage of the tempered glass plate. When the compressive stress layer on the surface of the tempered glass plate is made deep as a whole to prevent such breakage, the tensile stress formed inside the glass plate becomes excessive, and the breakage caused by the tensile stress (so-called self-destruction) Problem is likely to occur.

  In order to solve the above problems, a technology has been developed to selectively form a deep compressive stress layer only on a portion of the surface of a strengthened glass sheet. For example, in the method disclosed in Patent Document 1, by shielding only the central portion of the main surface with the mask material, it is possible to ion-exchange and strengthen only the unshielded peripheral portion. Thereafter, the shielding is removed, and by performing the strengthening treatment again, a deep compressive stress layer can be formed at the edge portion which has been subjected to the reinforcing treatment in advance, and a shallow compressive stress layer can be formed on the main surface which has been shielded.

U.S. Patent Application Publication No. 2012/0236477

  In patent document 1, materials, such as metal foil and a polyimide, are illustrated as a mask material (ion exchange prevention film | membrane) which comprises the said shield. However, ion exchange prevention membranes made of these materials are susceptible to wear, decomposition, or exfoliation due to chemical reaction with molten salt during ion exchange treatment, and ion exchange can not be sufficiently suppressed, and reinforcement with desired reinforcing properties is achieved. There was a case where glass could not be obtained stably. In addition, the wear and the like of the ion exchange preventive film may be more remarkable as the treatment temperature of the ion exchange treatment is higher.

  Therefore, in the case of the conventional ion exchange membrane of material, it is necessary to increase the film thickness to the extent that it can withstand wear, to lower the treatment temperature and to prolong the treatment time, and there is a possibility that the productivity may be lowered.

  The present invention has been made in consideration of such circumstances, and a method for producing a tempered glass sheet capable of stably producing a tempered glass sheet having high strength with high productivity, and a tempered glass sheet , And providing a tempered glass sheet.

The method for producing a tempered glass plate according to the present invention is a method for producing a tempered glass plate, wherein the glass plate is tempered using an ion exchange method, and an ion permeation preventive film for preventing ion exchange on a part of the surface of the glass plate. And a selective ion exchange step of selectively ion-exchanging the area other than the film formation area by bringing the formed glass plate into contact with the molten salt, and the ion permeation preventive film comprising It is characterized by being an inorganic film containing ZrO ₂ .

According to the method for producing a tempered glass sheet of the present invention, since the ion permeation preventive film contains ZrO ₂ , for example, the film is less likely to be worn even when in contact with molten salt such as high temperature potassium nitrate, and a relatively thin film Even the thickness can sufficiently block the permeation of ions. Therefore, it is possible to stably produce a tempered glass sheet having high strength with high productivity.

In the method for producing a tempered glass plate of the present invention, the ion permeation preventive film is preferably an inorganic film containing 50 to 100% by mass of ZrO ₂ .

  In the method for producing a tempered glass sheet of the present invention, it is preferable to immerse the glass sheet in a molten salt bath at a temperature of more than 400 ° C. and less than 500 ° C. in the selective ion exchange step.

In the method for producing a strengthened glass sheet of the present invention, in the film forming step, at least 70 to 99% of ZrO ₂ by mass% as Y ₂ O ₃ , CaO, Al ₂ O ₃ , CeO, HfO ₂ is used as an ion permeation preventive film. It is preferable to form an inorganic film containing 1 to 30% of either in total.

  In the method for producing a strengthened glass plate of the present invention, in the film forming step, it is preferable to form an ion permeation preventive film so as to have a thickness of 400 nm or less.

  In the method for producing a tempered glass sheet according to the present invention, there are a removal step of removing the ion permeation preventive film from the glass plate after the selective ion exchange step, and a total ion exchange step of ion exchange treating the entire surface of the glass plate after the removal step. It is preferable to further include.

  In the method for producing a strengthened glass sheet of the present invention, the surface roughness Ra of the surface of the glass sheet in the film formation region is preferably 0.4 nm or less.

The reinforcing glass plate of the present invention is a reinforcing glass plate to be subjected to a strengthening treatment using an ion exchange method, and is formed by coating an inorganic film containing 50 to 100% by mass of ZrO ₂ on the surface. It has a film part and an exposed part which is not covered with an inorganic membrane in at least one copy of an end face.

The tempered glass plate of the present invention is a tempered glass plate partially tempered using an ion exchange method, and a film-forming portion coated on the surface with an inorganic film containing 50 to 100% by mass of ZrO ₂ And an exposed portion not covered with the inorganic film on at least a part of the end face, and the depth of the compressive stress layer on the glass surface in the film forming portion is smaller than the compressive stress depth in the exposed portion. Do.

It is a figure which shows the manufacturing method of the tempered glass board which concerns on 1st embodiment of this invention. It is a figure which shows the manufacturing method of the tempered glass board which concerns on 1st embodiment of this invention. It is a figure which shows the manufacturing method of the tempered glass board which concerns on 1st embodiment of this invention. It is a figure which shows the manufacturing method of the tempered glass board which concerns on 1st embodiment of this invention. It is a figure which shows the manufacturing method of the tempered glass board which concerns on 1st embodiment of this invention. It is a figure which shows an example of the film-forming area | region in the manufacturing method of the tempered glass board of this invention.

  Hereinafter, the manufacturing method of the tempered glass board of embodiment of this invention is demonstrated. 1A to 1E are views showing an example of the method for producing a tempered glass sheet of the present invention.

  First, the process of the preparation process shown in FIG. 1A is performed. The preparation step is a step of preparing the original glass plate G1. The original glass plate G1 is a plate-like glass plate that can be strengthened using an ion exchange method.

The original glass plate G1 may contain 45 to 75% of SiO ₂ , 1 to 30% of Al ₂ O ₃ , 0 to 20% of Na ₂ O, and 0 to 20% of K ₂ O by mass% as a glass plate composition. preferable. By regulating the glass sheet composition range as described above, it is easy to achieve both ion exchange performance and devitrification resistance at high levels.

  The thickness of the original glass plate G1 is, for example, 1.5 mm or less, preferably 1.3 mm or less, 1.1 mm or less, 1.0 mm or less, 0.8 mm or less, 0.7 mm or less, 0.6 mm or less 0.5 mm or less, 0.4 mm or less, 0.3 mm or less, 0.2 mm or less, particularly 0.1. It is 1 mm or less. The smaller the thickness of the tempered glass plate substrate, the lighter the tempered glass plate substrate can be, and as a result, the thinner and lighter the device can be achieved. The thickness of the original glass plate G1 is preferably 0.01 mm or more in consideration of productivity and the like.

  Although the dimension of the main surface of the original glass plate G1 can be set arbitrarily, it is 480x320 mm-3350x3950 mm, for example.

  The original glass plate G1 is formed, for example, using an overflow downdraw method. In addition, you may select arbitrarily the shaping | molding method and process state of the original glass plate G1. For example, the original glass plate G1 may be formed using a float method, and the main surface S and the end face E may be polished.

  Next, after the above-described preparation process, the process of the selective ion exchange process of FIGS. 1B and 1C is performed. The selective ion exchange step is a step of partially chemically strengthening the surface of the original glass plate G1. Specifically, in the selective ion exchange step, in the selected region (peripheral portion S2 and end surface E) set on a part of the surface of the original glass plate G1, the nonselected region (central portion S1) other than the selected region is selected. This is a process of forming a deep compressive stress layer. The selective ion exchange step includes a film forming step, a selective ion exchange step, and a removal step.

  In the selective ion exchange process, first, the process of the film forming process shown in FIG. 1B is performed. The film forming step is a step of forming the ion permeation preventive film M on the non-selected region set on at least a part of the surface of the original glass plate G1 to obtain the film-coated glass plate G2. In this embodiment, as shown in FIG. 2, the case where center part S1 of front and back main surface S of original glass board G1 is made into a non-selection field is explained as an example. FIG. 1B corresponds to a cross-sectional view taken along the line AA in FIG. Of the surface of the original glass plate G1, a region other than the central portion S1, that is, the peripheral portion S2 and the end face E are selected regions and are in an exposed state. The peripheral portion S2 is a region surrounding the central portion S1 of the main surface S. The ion permeation prevention film M is a film layer which suppresses or blocks the permeation of ions when performing ion exchange of the surface layer of the original glass plate G1 in the selective ion exchange step described later.

The ion permeation prevention film M is an inorganic film containing ZrO ₂ . Preferably, the ion permeation prevention film M contains 50 to 100% by mass of ZrO ₂ . By using such a material as the ion permeation prevention film M, it is possible to suppress wear and the like in the selective ion exchange step described later. Specifically, even in the case of immersion in a molten salt (reinforcing solution) having a temperature higher than 450 ° C., it is extremely difficult to cause peeling or the like of the ion permeation preventive film M from the film-coated glass plate G2.

When forming an ion permeable barrier layer M of the ZrO ₂ as the main, the surface roughness Ra at least in the non-selected region (deposition region) of the surface of the original glass plate G1 is preferably less 0.4 nm. This has an adverse effect on the film quality of the ion permeation preventive film M mainly composed of ZrO ₂ when Ra is large (for example, in the case of a general polishing surface), and the function as the ion permeation preventive film is significantly reduced. There is Therefore, the surface of the original glass plate G1 is preferably an overflow surface (unpolished fire-formed surface) formed by the overflow downdraw method, but may be a polished surface if it is very flat. In addition, it is preferable that surface roughness Ra of the original glass plate G1 is 0.05 nm or more from a viewpoint of manufacturing cost etc.

In addition, the crystallinity of the film of the ion permeation prevention film M mainly composed of ZrO ₂ is changed by being exposed to the molten salt at a high temperature. Specifically, it changes from amorphous to crystalline. Although crystallization does not change the function as an ion permeation preventive film, the volume of the film decreases with crystallization. As a result, a crack may occur on the surface of the ion permeation prevention film M, and ion exchange may be performed from the crack. Since such crystallization is confirmed when the ion exchange temperature is 500 ° C., the ion exchange temperature is preferably less than 500 ° C. and 490 ° C. or less.

The ion permeation preventing film M contains 70 to 99% of ZrO ₂ by mass% as a composition, and 1 to 30% by total amount of at least one of Y ₂ O ₃ , CaO, Al ₂ O ₃ , CeO and HfO _2. Is more preferred. In particular, when containing 0.5 mass% or more of Y ₂ O ₃ , it is preferable because the phase transition of the ion permeation preventive film M can be suppressed at the time of temperature increase.

  The thickness of the ion permeation preventive film M may be any thickness as long as blocking and suppression of ion permeation are possible. However, if the thickness of the ion permeation prevention film M is excessive, the film formation time, material cost, and the like increase, so it is preferable to form the ion permeation prevention film M as thin as possible in a range that can block and suppress ion permeation. The film thickness of the ion permeation prevention film M is preferably 5000 nm or less, 400 nm or less, 350 nm or less, 100 nm or less, 50 nm or less, or 25 nm or less. The film thickness of the ion permeation prevention film M is preferably 1 nm or more, 5 nm or more, or 10 nm or more. Specifically, the film thickness of the ion permeation prevention film M is, for example, preferably 1 to 5000 nm, more preferably 5 to 350 nm, and still more preferably 10 to 100 nm.

  The film formation method of the ion permeation preventing film M is PVD (physical vapor deposition) such as sputtering or vacuum evaporation, CVD (chemical vapor deposition) such as thermal CVD or plasma CVD, dip coating A wet coat method such as a method or a slit coat method can be used. Sputtering and dip coating are particularly preferred. When the sputtering method is used, the ion permeation prevention film M can be easily formed uniformly. The region in which the ion permeation preventive film M is formed may be set by any method. For example, film formation can be performed in a state where the selected region (peripheral portion S2, end surface E) is masked. Alternatively, the ion permeation preventing film M, which is formed in advance in a sheet shape, may be bonded to the main surface of the original glass plate G1 to form a film.

  Next, after the film formation step, the process of the selective ion exchange step shown in FIG. 1C is performed. The selective ion exchange step is a step of chemically strengthening the membrane-coated glass plate G2 by an ion exchange method to obtain a membrane-reinforced glass sheet G3. Specifically, the film-coated glass plate G2 is immersed in the molten salt T1 containing an alkali metal ion for ion exchange. The molten salt T1 in the present embodiment is, for example, a potassium nitrate molten salt.

  The temperature of the molten salt T1 in the selective ion exchange step may be arbitrarily determined. It is preferable that the temperature of molten salt T1 is 350 degreeC or more, 370 degreeC or more, more than 400 degreeC, and 420 degreeC or more. Further, the temperature of the molten salt T1 is preferably 500 ° C. or less, less than 500 ° C., or 480 ° C. or less. Specifically, for example, 350 to 500 ° C., more than 400 ° C. and less than 500 ° C., and 370 to 480 ° C. are preferable. The time for immersing the film-coated glass plate G2 in the molten salt T1 may be arbitrarily determined, but for example, 0.1 to 150 hours, preferably 0.3 to 100 hours, more preferably 0.5 to 50 It's time.

  Then, after the selective ion exchange step, the process of the removal step shown in FIG. 1D is performed.

  The removal step is a step of removing the ion permeation prevention film M from the film-reinforced glass sheet G3. As a method of removing the ion permeation prevention film M, for example, a method such as polishing or etching can be used.

  As a polishing apparatus used for polishing, a known double-sided polishing machine or a single-sided polishing machine can be used. When the ion permeation preventive film M is removed by polishing, only the ion permeation preventive film M may be polished, or the glass plate portion may be polished together with the ion permeation preventive film M.

  As an etching method, a method such as dry etching or wet etching can be used.

When dry etching is used, it is particularly preferable to use a plasma such as Ar, O ₂ , CH ₄ , BC ₁₃ , C ₁₂ , SF ₆ or the like.

  As an etching solution used for wet etching, for example, a solution containing fluorine, TMAH, EDP, KOH, NaOH or the like can be used as the etching solution, and in particular, it is preferable to use a hydrofluoric acid solution as the etching solution. When only the ion permeation prevention film M is removed using a hydrofluoric acid solution without changing the size of the glass, the concentration of HF in the hydrofluoric acid solution is preferably 10% or less.

  The tempered glass sheet G4 obtained as described above has a deep compressive stress layer C at the peripheral edge portion S2 and the end face E. That is, the tempered glass sheet G4 is a glass which can reduce internal tensile stress while having high impact resistance at the edge portion, and is unlikely to be broken due to the tensile stress.

  Since the permeation of ions is blocked by the ion permeation prevention film M in the selective ion exchange step described above, the compressive stress layer C is not formed in the central portion S1 of the strengthened glass plate G4. Therefore, in order to improve the strength of the central portion S1, it is preferable to form the compressive stress layer C also in the central portion S1 by performing the following overall ion exchange step following the treatment of the removal step.

  The whole ion exchange step is a step of bringing the molten salt into contact with the entire surface of the strengthened glass plate G4 to exchange ions in the surface layer, as shown in FIG. 1E. Specifically, the tempered glass plate G4 is immersed in molten salt T2 containing alkali metal ions for ion exchange, and a tempered glass plate G5 having a compressive stress layer C shallower than the peripheral portion S2 and the end face E in the central portion S1 is obtained . The molten salt T2 is, for example, potassium nitrate molten salt. It is preferable that DOL of a non-film-forming area | region (end face E and peripheral part S2) is 1/4 or less of the plate thickness of tempered glass board G5. It is preferable that DOL of a film-forming area | region (central part S1) is 1/8 or less of the plate thickness of the tempered glass board G5.

  Although the temperature of molten salt T2 in a whole ion exchange process may be decided arbitrarily, it is 350-500 ° C, preferably 370-480 ° C, for example. The time for which the tempered glass sheet G4 is immersed in the molten salt T2 may be arbitrarily determined, but for example, 0.1 to 72 hours, preferably 0.3 to 50 hours, more preferably 0.5 to 24 hours It is.

  The molten salt T2 may be similar to the above-described molten salt T1. That is, the tempered glass plate G4 may be dipped again in the salt bath used in the selective ion exchange step. In this case, since a plurality of processes can be performed in a single salt bath, the manufacturing cost can be suppressed.

  The molten salt T2 may be different from the molten salt T1, and the treatment temperature and treatment time in the overall ion exchange step may be different from the treatment temperature and treatment time in the selective ion exchange step. For example, the treatment time of ion exchange in the overall ion exchange step is preferably shorter than the treatment time in the selective ion exchange step. According to such a process, the depth of the compressive stress layer C in the central portion S2 does not become excessive, and an increase in tensile stress can be suppressed.

  In addition, after the whole ion exchange process, you may implement the process of a finishing process further (not shown). In the finishing process, the surface of the tempered glass sheet G5, for example, at least one of the main surface S and the end face E is polished. If the size and surface condition of the strengthened glass sheet G5 are not in a desired state such as a product specification or the like by the treatment of the overall ion exchange step, the desired state can be achieved by carrying out the treatment of such a finishing process.

  As explained above, according to the method for manufacturing a tempered glass plate according to the embodiment of the present invention, it is possible to stably and efficiently produce the tempered glass plates G4 and G5 with less breakage from the end face.

  Before or after any of the above-described steps, a processing step may be provided in which any one of cutting, end surface processing, and drilling processing is performed. In addition, before and after any of the above-described steps, the glass plate may be appropriately subjected to washing and drying treatments.

  In the above embodiment, although the case where molten salts T1 and T2 are potassium nitrate molten salts has been described as an example, the present invention is not limited to this and may substitute or combine well-known molten salts used for ion exchange of glass plates. You may use it. For example, the molten salts T1 and T2 may be a mixed salt of potassium nitrate molten salt and sodium nitrate molten salt.

Moreover, although the case where it exchanges and ion-exchanges Na ion and K ion was illustrated in the said embodiment, you may carry out chemical strengthening by exchange of arbitrary ions. For example, chemical strengthening may be performed by exchanging Li ions and Na ions or exchanging Li ions and K ions. In this case, the base glass plate preferably contains 0.5 to 7.5% by mass of Li ₂ O as a glass composition, and for example, contains 3.0% or 4.5%.

  Further, the treatment of the selective ion exchange step is not limited to the above method, and for example, the partial deep compressive stress layer C is formed by immersing only the selected region in the molten salt for ion exchange or applying the molten salt. You may.

  Here, the stress characteristics of the tempered glass can be measured, for example, using FSM-6000 manufactured by Orihara Mfg. When the depth of the compressive stress layer of the aluminosilicate glass exceeds 100 μm, or when the ion exchange of Li ions is performed, the stress characteristics of the tempered glass can be measured, for example, using SLP-1000 manufactured by Orihara Seisakusho it can. When a cross-sectional sample can be prepared by cutting tempered glass, etc., it is desirable to observe the internal stress distribution and confirm the stress depth using, for example, WPA-micro manufactured by Photonic Lattice, or Abrio manufactured by Tokyo Instruments. .

  Hereinafter, the present invention will be described in detail based on examples.

  In Table 1, Nos. 1 to 3 show examples of the present invention, and Nos. 4 to 7 show comparative examples.

Each sample of Table 1 was produced as follows. First, a glass composition containing 61.6% SiO ₂ , 19.6% Al ₂ O ₃ , 0.8% B ₂ O ₃ , 16% Na ₂ O, and 2% K ₂ O in mass% The glass raw materials were compounded and melted, and formed into a plate shape using an overflow down draw method to obtain a reinforcing glass having a thickness of 0.7 mm. Next, after forming an ion exchange inhibition film having each composition and film thickness described in Table 1 on both main surfaces of the above-mentioned reinforcing glass using a sputtering method, it is cut and the end face is not formed (glass Film-coated glass was obtained. Next, the obtained film-coated glass is immersed in the molten salt temperature of molten salt shown in Table 1 for the immersion time shown in Table 1, washed with pure water and naturally dried, and then the ion exchange inhibiting membrane is removed by polishing No. 1 described in Table 1 1 to 7 tempered glass plate samples were obtained.

  About each glass sample obtained as mentioned above, stress depth DOL of each of a film-forming area (main surface) and a non-film-forming area (end face) was measured with a stress meter (FSM-6000LE and FsmXP made by Orihara Seisakusho) . When the DOL value of the film formation region (main surface) is zero, it is shown that the compressive stress layer is not formed under the film formation region, and that the ion exchange inhibition film sufficiently blocks the ion exchange.

As shown in Table 1, in the sample Nos. 1 to 3 which are examples, since the ion exchange inhibiting membrane contained an appropriate amount of ZrO ₂ , no wear occurred and it was possible to preferably block the ion exchange. In particular, even at relatively high molten salt temperatures and relatively thin film thicknesses, excessive wear did not occur, and ion exchange could be suitably blocked.

On the other hand, sample Nos. 4, ₅ and 7 use an ion exchange inhibiting membrane consisting of SiO ₂ and Nb ₂ O ₅ , so the membrane is worn away at a molten salt temperature of 430 ° C. or higher, and the ion exchange Could not shut off. Also, for sample no. In No. 6, although the temperature of the molten salt was relatively low, the ion exchange could be blocked, but it was necessary to make the film thickness of the ion exchange suppression membrane thicker than in the example. That is, compared with the example, the film formation time was long and the productivity was low.

  The tempered glass sheet of the present invention and the method for producing the same are useful as a tempered glass sheet used for a touch panel display or the like, a method for producing the same, and the like.

G1 original glass plate G2 glass plate with film G3, tempered glass plate with film G4, G5 tempered glass plate M ion permeation preventive film T1 first molten salt T2 second molten salt

Claims (9)

A method for producing a strengthened glass sheet, wherein the glass sheet is strengthened using an ion exchange method,
Forming an ion permeation preventive film for preventing the ion exchange on a part of the surface of the glass plate;
And a selective ion exchange step of bringing the glass plate formed into a film into contact with a molten salt to selectively ion exchange the region other than the film formation region.
The method for producing a strengthened glass plate, wherein the ion permeation preventive film is an inorganic film containing ZrO ₂ . The method for producing a strengthened glass sheet according to claim 1, wherein the ion permeation preventive film is an inorganic film containing 50 to 100% by mass of ZrO ₂ .   The method for producing a strengthened glass sheet according to claim 1 or 2, wherein the glass sheet is immersed in a molten salt bath at a temperature of more than 400 ° C and less than 500 ° C in the selective ion exchange step. In the film forming step, as the ion permeation preventing film, 70 to 99% by mass of ZrO ₂ and at least one of Y ₂ O ₃ , CaO, Al ₂ O ₃ , CeO and HfO _{2 in} a total amount of 1 to 30 The method for producing a tempered glass sheet according to any one of claims 1 to 3, wherein an inorganic film containing% is formed.   The method for producing a strengthened glass plate according to any one of claims 1 to 4, wherein the ion permeation preventing film is formed so as to have a thickness of 400 nm or less in the film forming step. Removing the ion permeation preventive film from the glass plate after the selective ion exchange step;
The manufacturing method of the tempered glass board in any one of Claims 1-5 further equipped with the whole ion exchange process which ion-exchange-treats the whole surface of the said glass board after the said removal process.   Surface roughness Ra of the said surface of the said glass plate in the said film-forming area | region is 0.4 nm or less, The manufacturing method of the tempered glass board in any one of Claims 1-6 characterized by the above-mentioned. A reinforcing glass plate to be subjected to a strengthening treatment using an ion exchange method,
On the surface
A film forming portion coated with an inorganic film containing 50 to 100% by mass of ZrO ₂ ;
And a exposed glass portion not covered with the inorganic film on at least a part of the end face. A tempered glass plate partially strengthened using an ion exchange method,
On the surface
A film forming portion coated with an inorganic film containing 50 to 100% by mass of ZrO ₂ ;
An exposed portion not coated with the inorganic film on at least a part of the end face;
The depth of the compressive stress layer of the glass surface in the said film-forming part is smaller than the compressive stress depth in the said exposed part, The tempered glass board characterized by the above-mentioned.