TW201429898A - Raw glass plate, method for producing raw glass plate, and method for producing chemically reinforced glass - Google Patents

Abstract

A raw glass plate produced by shaping a molten glass into a plate continuously, subsequently gradually cooling and, at the same time, chemically reinforcing the plate, and subsequently cutting the plate. The raw glass plate has a compression stress layer, wherein the compression stress layer has a depth of 12 [mu]m or less and the outermost surface of the compression stress layer has a compressive stress of more than 500 MPa.

Description

Glass original plate, method for producing glass original plate and method for producing chemically strengthened glass

The present invention relates to a glass original plate subjected to chemical strengthening treatment, a method for producing a glass original plate, and a method for producing chemically strengthened glass.

In recent years, display devices such as mobile phones, personal digital assistants (PDAs, personal handy-phone systems), and tablet computers have become popular. On the front side of the display device, chemically strengthened glass is mounted as a cover glass to protect the liquid crystal display (LCD).

The chemically strengthened glass is produced by a production method such as a float method or a melt method, and is produced by cutting or chamfering a glass original plate cut into a specific shape into a desired shape. After the processing, chemical strengthening treatment is performed.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2011-197708

However, the original glass plate cut into a specific shape is damaged during transportation or processing. Such damage is called an operational damage. If an operational damage occurs, then the chemical strengthening treatment is followed, and the final product is also affected.

Accordingly, an object of the present invention is to provide a glass original plate capable of suppressing operational damage, a method for producing a glass original plate, and a method for producing a chemically strengthened glass.

The present inventors have found that the influence of the operational damage sometimes formed before chemical strengthening affects the final product. Further, first, in order to understand the crack generation behavior for the stress distribution, the depth of the compressive stress of the compressive stress layer (hereinafter, sometimes referred to as the compressive stress depth) and the compressive stress at the outermost surface are changed over a wide range (hereinafter, there are The surface compression stress is referred to as an evaluation of the crack occurrence rate of the chemically strengthened soda lime glass.

For the evaluation, the soda lime glass described in Table 1 was changed in chemical strengthening time and the temperature of the molten salt, and 18 samples were subjected to chemical strengthening treatment, and the case of using the Vickers diamond indenter was determined according to the graph of Fig. 1 . The load of the crack was generated at a ratio of 50%, and the graph of Fig. 2 was analyzed by the size of the circle. The graph of Fig. 1 is obtained by performing 20 indentations for each sample with each load. Each sample was polished with yttrium oxide prior to chemical strengthening treatment.

The load generated by the crack at a ratio of 50% (hereinafter, also referred to as 50% crack generation load) is defined as: as shown in Fig. 1, the probability of occurrence of cracks (%) on the vertical axis is taken on the horizontal axis. The load (kgf), the probability of cracking is 50%.

Fig. 2 is a graph showing the compressive stress depth of each sample and the 50% crack generation load of the surface compressive stress by the size of the circle.

According to Fig. 2, it is found that 50% of the same compressive stress depth generates a load, and if it exceeds a specific surface compressive stress, it becomes remarkably large. For example, when the compressive stress depth is about 10 μm, the 50% cracking load is 0.5 kgf when the surface compressive stress is between 100 and 500 MPa. On the other hand, if the surface compressive stress exceeds 500 MPa, 50% of the crack is generated. The load is 1.0kgf. Further, from Fig. 2, it is seen that the deeper the compressive stress depth, the more the 50% crack generating load becomes larger, and the surface compressive stress tends to become smaller. For example, when the compressive stress depth is about 10 μm, if the surface compressive stress exceeds 500 MPa, the 50% crack generating load becomes remarkably large, and if the compressive stress depth is about 20 μm, the surface compressive stress exceeds about 450 MPa. When the compressive stress depth is about 40 μm, the surface compressive stress exceeds about 400 MPa, and when the compressive stress depth is about 50 μm, when the surface compressive stress exceeds about 300 MPa, the 50% crack generating load becomes remarkably large. However, it can be seen that for any compressive stress depth, if the surface compressive stress is not increased to some extent, the 50% cracking load becomes more than that of the glass which is not subjected to chemical strengthening treatment (compressive stress depth = 0 μm, surface compressive stress = 0 MPa). ) is smaller, prone to cracking, and weaker. On the other hand, it is also known that if the depth of the compressive stress layer is deep, the glass is broken into a powdery shape during the subsequent processing.

The inventors of the present invention have discovered a new problem of suppressing operational damage that has not been noticed so far, and have found that a glass original plate, a method for producing chemically strengthened glass, and a chemical which can suppress glass damage at the subsequent processing while effectively suppressing operational damage. A method of manufacturing tempered glass.

The present invention provides the following aspects.

(1) A glass original plate characterized in that a molten glass is continuously formed into a plate shape, and then chemically strengthened simultaneously with slow cooling, and obtained by cutting, and having a compressive stress layer, the compressive stress layer The depth is 12 μm or less, and the compressive stress at the outermost surface exceeds 500 MPa.

(2) The original glass plate of (1), which has a size of 300 mm × 300 mm or more.

(3) A method for producing a glass raw plate, characterized in that in the step of slowly cooling the glass ribbon obtained by continuously forming the molten glass into a plate shape, the depth of the compressive stress layer after the slow cooling is 12 μm or less. The chemical strengthening is carried out in such a manner that the compressive stress at the outermost surface exceeds 500 MPa, and then the glass ribbon is cut.

(4) The method for producing a glass original plate according to (3), wherein the size of the glass original plate is 300 mm × 300 mm or more.

(5) The method for producing a glass raw plate according to (3) or (4), wherein the glass ribbon is immersed in the molten salt for 0.5 to 3 minutes to carry out chemical strengthening.

(6) The method for producing a glass blank according to (3) or (4), wherein the glass ribbon is subjected to chemical strengthening by exposing the molten glass to the molten salt for 0.5 to 3 minutes by spraying the molten salt.

(7) The method for producing a glass raw plate according to (5) or (6), wherein the molten salt has a temperature of from 400 ° C to 530 ° C.

(8) The method for producing a glass raw plate according to any one of (3) to (7) wherein the molten glass is floated on a molten metal and formed into a plate shape to obtain the glass ribbon.

(9) A method for producing a chemically strengthened glass, comprising: a primary chemical strengthening step of chemically strengthening a glass sheet such that a depth of the compressive stress layer is 12 μm or less and a compressive stress at the outermost surface exceeds 500 MPa; A chemical strengthening step of further chemically strengthening the glass plate chemically strengthened in the above-described one chemical strengthening step.

(10) The method for producing a chemically strengthened glass according to (9), wherein the glass plate is produced by a float molding method, and the primary chemical strengthening step is performed on a line.

(11) The method for producing a chemically strengthened glass according to (9) or (10), wherein the primary chemical strengthening step is chemically strengthened by immersing the glass ribbon in a molten salt for 0.5 to 3 minutes.

(12) The method for producing a chemically strengthened glass according to (9) or (10), wherein the above primary chemical The strengthening step is chemically strengthened by spraying the molten salt and exposing the glass ribbon to the molten salt for 0.5 to 3 minutes.

(13) The method for producing a chemically strengthened glass according to (11) or (12), wherein the molten salt has a temperature of from 400 ° C to 530 ° C.

(14) The method for producing a chemically strengthened glass according to any one of (9) to (13), wherein between the one-time chemical strengthening step and the second chemical strengthening step, including the one-time chemical strengthening step The processing step of processing the chemically strengthened glass original plate.

In the present specification, the term "chemically strengthened glass" means a glass which has been subjected to chemical strengthening treatment, and the glass for chemical strengthening means a glass which is subjected to chemical strengthening treatment regardless of whether or not chemical strengthening treatment is carried out. Therefore, the glass original plate chemically strengthened by one chemical strengthening step is a chemically strengthened glass, and is a glass for chemical strengthening, and the glass chemically strengthened by the secondary chemical strengthening step is chemically strengthened glass.

In addition, the glass original plate means a glass which is formed by continuously forming a molten glass into a plate shape, and then slowly cooling and cutting it to obtain a process before the processing. The size of the original glass plate is typically 300 mm × 300 mm or more, and usually the short side is 500 mm or more or 700 mm or more.

According to the method for producing a glass original plate and a glass original plate of the present invention, the depth of the compressive stress layer of the glass original plate is 12 μm or less, and the compressive stress at the outermost surface exceeds 500 MPa, so that cracking of the glass surface is not easy, and operation damage can be suppressed. Further, since the compressive stress layer is shallow, the glass breakage during the subsequent processing can be suppressed, and the subsequent processing can be smoothly performed while suppressing the occurrence of the operational damage. Further, since chemical strengthening is performed at the stage of the glass original plate, it is possible to suppress the operation damage in the transfer step before the glass ribbon is cut into the glass original plate.

Further, according to the method for producing a chemically strengthened glass of the present invention, a glass plate having a depth of a compressive stress layer of 12 μm or less and a compressive stress of the outermost surface exceeding 500 MPa can be obtained by one chemical strengthening step, so that cracking of the glass surface is not easy. Can suppress operation Make damage. Further, since the compressive stress layer is shallow, the glass breakage during the subsequent processing can be suppressed, and the subsequent processing can be smoothly performed while suppressing the occurrence of the operational damage. Further, by the secondary chemical strengthening step, the depth of the compressive stress layer as the final product and the compressive stress at the outermost surface can be appropriately adjusted.

10‧‧‧Glass manufacturing equipment

11‧‧‧metal tank

12‧‧‧ lifting roller

13‧‧‧ Slow cooling furnace

14‧‧‧Transport roller

15‧‧‧Molten salt tank

16‧‧‧Spray device

20‧‧‧Environmental gas supply device

21‧‧‧Air supply unit

G‧‧‧glass ribbon

H‧‧‧Electric heater

Fig. 1 is a graph showing the relationship between the probability of occurrence of cracks and the load of a 50% crack generating load.

Figure 2 is a graph showing the relationship between the compressive stress depth and the surface compressive stress and the 50% crack generation load.

Fig. 3 is a graph showing the relationship between the compressive stress layer depth and the surface compressive stress of soda lime glass and aluminosilicate glass which were chemically strengthened at 400 to 450 ° C for 10 hours.

Fig. 4 is a view showing an example of a glass manufacturing apparatus at the time of chemical strengthening treatment on the line.

Fig. 5 is a view showing another example of the glass manufacturing apparatus when the chemical strengthening treatment is performed on the line.

Hereinafter, a method for producing a glass original plate and a glass original plate according to an embodiment of the present invention will be described.

The glass original plate of the present invention is a chemically strengthened glass having a compressive stress layer having a depth of 12 μm or less and a compressive stress at the outermost surface exceeding 500 MPa. The depth of the compressive stress layer is preferably 10 μm or less, more preferably 8 μm or less, and particularly preferably 7 μm or less. The shallower the depth of the compressive stress layer, the more the effect of the subsequent processing such as cutting or chamfering can be suppressed to a small extent. The compressive stress at the outermost surface is preferably 550 MPa or more, more preferably 600 MPa or more, further preferably 650 MPa or more, and particularly preferably 700 MPa or more. The greater the compressive stress at the outermost surface, the more the occurrence of operational damage can be suppressed. The surface stress measuring device can be used for the depth of the compressive stress layer and the compressive stress at the outermost surface. (FSM-6000 manufactured by Ohara Seisakusho Co., Ltd.) was measured. Moreover, the cross section can be observed by a birefringence microscope, and can be obtained from the phase delay obtained thereby.

In order to obtain such a glass original plate, it is more effective to perform chemical strengthening (primary chemical strengthening) by merely immersing or exposing the glass original plate in a molten salt for a very short time. The chemical strengthening treatment exchanges alkali metal ions (typically Li ions, Na ions) having a small ionic radius on the surface of the glass to a base ion having a larger ionic radius by ion exchange at a temperature below the glass transition point ( Typically, K ion) is a process of forming a compressive stress layer on the surface of the glass and forming a tensile stress layer on the inside of the glass. Specifically, for example, chemical strengthening is performed by immersion or exposure to a molten salt of 400 ° C to 530 ° C for 0.5 to 3 minutes. Thereby, a glass having a small compressive stress depth and a large surface compressive stress can be obtained. At a temperature exceeding 500 ° C, the surface compressive stress becomes small, and the desired scratch resistance cannot be obtained. The molten salt is preferably a molten salt containing potassium nitrate (KNO ₃ ) as a main component, and the temperature of the molten salt is preferably from 400 ° C to 500 ° C, more preferably from 400 ° C to 450 ° C. When the temperature of the molten salt is higher than 530 ° C, the alkali ions are easily diffused, so that the depth of the compressive stress tends to be deep, but the desired surface compressive stress cannot be obtained. On the other hand, if the temperature of the molten salt is lower than 400 ° C, the alkali ions are not easily diffused, so chemical strengthening takes a long time.

As the glass for the glass original plate, soda lime glass, aluminum silicate glass, or the like can be used. Fig. 3 is a graph showing the relationship between the compressive stress layer depth and the surface compressive stress of soda lime glass and aluminosilicate glass which were chemically strengthened at 400 to 450 ° C for 10 hours.

The depth of the compressive stress is proportional to the 1/2 power of the strengthening time. Therefore, the compressive force depth in the case of chemical strengthening for 1 minute at 400 to 450 ° C is theoretically about 1/25 of that in the case of chemical strengthening for 10 hours. Therefore, according to Fig. 3, it can be assumed that when the chemical strengthening is performed at 400 to 450 ° C for 1 minute, the soda lime glass is about 1 μm, and the aluminosilicate glass is about 3 μm.

As the soda lime glass, for example, a glass having the following composition is used.

(i) SiO ₂ 60-80%, Al ₂ O ₃ 0.01-8%, Na ₂ O 8-22%, K ₂ O 0-7%, RO (R=Mg, in terms of composition by mass %) Ca, Sr, Ba) is 5 to 25% by total, and ZrO ₂ 0 to 5% of glass.

(ii) SiO ₂ is 64 to 77%, Al ₂ O ₃ is 0.01 to 7%, Na ₂ O is 10 to 18%, K ₂ O is 0 to 5%, and MgO is 1 in terms of mass %. ~10%, CaO is 1~12%, SrO is 0~5%, BaO is 0~5%, and ZrO ₂ is 0~3% glass.

(iii) SiO ₂ 60-80%, Al ₂ O ₃ 0.01-8%, Na ₂ O 8-22%, K ₂ O 0-7%, ZrO ₂ 0-5%, in terms of mass % , in the containing case MgO, CaO, SrO or BaO of MgO, the total content of CaO, SrO and BaO of 5-25% over Na content of Na ₂ O and Al ₂ O ₃ of ₂ O / Al ₂ O ₃ It is a glass of 1.5 or more.

(iv) SiO ₂ 60-80%, Al ₂ O ₃ 0.01-8%, Na ₂ O 8-22%, K ₂ O 0-7%, ZrO ₂ 0-5%, in terms of mass % In the case of containing MgO, CaO, SrO or BaO, the total content of MgO, CaO, SrO and BaO is 5 to 25%, and the total content of CaO, SrO and BaO is 1 to 7%, Na ₂ O and Al. A glass having a ratio of ₂ O ₃ to Na ₂ O/Al ₂ O ₃ of 1.5 or more.

(v) SiO ₂ is 60 to 75%, Al ₂ O ₃ is 3 to 12%, MgO is 2 to 10%, CaO is 0 to 10%, and SrO is 0 to 3%, in terms of composition by mass %. BaO is 0 to 3%, Na ₂ O is 10 to 18%, K ₂ O is 0 to 8%, and ZrO ₂ is 0 to 3%.

As the aluminosilicate glass, for example, a glass of the following composition is used.

(i) 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, and K ₂ O 0~ 10%, MgO 0~15%, CaO 0~5% and ZrO ₂ 0~5% glass. Here, for example, "containing K ₂ O 0 to 10%" means that K ₂ O is not essential, but may be in the range of up to 10%, and is contained within a range not impairing the object of the present invention.

(ii) 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, and 2 to 15% of MgO. , CaO 0~6% and ZrO ₂ 0~5%, 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 to 25%, MgO and CaO. The total content is 7 to 15% glass.

(iii) a composition expressed in mole %, containing SiO ₂ 68-80%, Al ₂ O ₃ 4-10%, Na ₂ O 5-15%, K ₂ O 0~1%, MgO 4-15% and ZrO ₂ 0~1% glass.

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

Further, the thickness of the original glass plate is preferably 1.5 mm or less, more preferably 0.3 to 1.1 mm. Further, the size of the original glass plate is preferably 300 mm × 300 mm or more.

The glass original plate is preferably produced by a floating method, but is not necessarily limited thereto, and may be produced by another manufacturing method such as a melting method. The glass ribbon produced by any production method is subjected to chemical strengthening treatment as described above, whereby a glass original sheet which is a chemically strengthened glass having a depth of a compressive stress layer of 12 μm or less and a compressive stress of the outermost surface exceeding 500 MPa can be produced. In particular, by using a floating method to produce a glass original plate, chemical strengthening treatment can be performed on the line, and the occurrence of operational damage can be suppressed at the earliest stage. Moreover, since it is not necessary to reheat the glass original plate which is cooled once, the manufacturing process can be simplified, and the manufacturing cost can be suppressed. Further, the width of the glass ribbon is typically 2 m or more, 3 m or more, or 4 m or more.

4 and 5 are views showing an example of a glass manufacturing apparatus at the time of chemical strengthening treatment on the line.

The glass manufacturing apparatus 10 is configured to include a melting furnace (not shown) that melts a raw material of glass, and a molten metal tank 11 that floats the molten glass on the molten tin to form a flat glass ribbon G; The slow cooling furnace 13 draws the glass ribbon G from the molten metal tank 11 by the lift roller 12, and gradually lowers the temperature of the glass ribbon G to be slowly cooled.

The slow cooling furnace 13 has, for example, an effect of supplying the controlled heat of the output to the necessary position in the furnace by the electric heater H, and slowly cooling the glass ribbon conveyed by the conveying roller 14. However, it is close to the temperature range of normal temperature, whereby the residual stress inherent in the glass ribbon G is eliminated, and warpage or cracking of the glass is suppressed. The above chemical strengthening treatment can be carried out in the slow cooling furnace 13. That is, the glass original plate is produced by a molding step of molding the glass ribbon by the molten metal tank 11, and a slow cooling step of slowly cooling the glass ribbon by the slow cooling furnace 13, and performing the chemical strengthening treatment on the glass ribbon in the slow cooling step. .

For example, as shown in FIG. 4, the molten salt tank 15 may be provided at a position of the slow cooling furnace 13 corresponding to the temperature of the glass ribbon G of about 400 ° C to 530 ° C, and the conveyed glass may be adjusted by adjusting the position of the conveying roller 14 The belt G passes through the molten salt stored in the molten salt tank 15, and as shown in FIG. 5, at the temperature of the slow cooling furnace 13 corresponding to the glass ribbon G at a temperature of about 400 ° C to 530 ° C, at the top of the glass ribbon G The spray device 16 for spraying molten salt is provided on the surface side and the bottom surface side, and the conveyed glass ribbon G is exposed to the molten salt sprayed from the spray device 16. Reference numeral 20 is an environmental gas supply device for maintaining a chemically strengthened region in an atmospheric environment, an N ₂ atmosphere, and the like, and reference numeral 21 is an air supply device that blows molten salt.

The glass original plate subjected to the chemical strengthening treatment is subjected to a chemical treatment (secondary chemical strengthening) to perform a chemical treatment (secondary chemical strengthening) after performing a cutting treatment such as a cutting process or a chamfering process of a desired shape to obtain a chemical having a desired strength. Tempered glass. The chemical strengthening treatment (secondary chemical strengthening) after the chemical strengthening treatment (primary chemical strengthening) for suppressing the operational damage, the depth of the compressive stress layer of the chemically strengthened glass is preferably 15 μm or more, more preferably 20 μm or more, and further It is preferably 30 μm or more, and particularly preferably 40 μm or more. Further, the surface compressive stress is preferably more than 500 MPa, more preferably 550 MPa or more, still more preferably 600 MPa or more, and particularly preferably 700 MPa or more. Specifically, for example, it is immersed in a molten salt of potassium nitrate (KNO ₃ ) at 425 to 465 ° C for 2 to 4 hours. Furthermore, the glass original plate does not necessarily need to be subjected to secondary chemical strengthening treatment. In other words, the glass original plate may be a glass for chemical strengthening, or may not be a glass for chemical strengthening.

[Examples]

Hereinafter, embodiments of the invention will be described.

Regarding the glass shown in Table 2, a floating plate having a thickness of 0.7 mm was cut into a 40 mm square, and a chemical strengthening treatment was performed for 1 minute or 3 minutes using potassium nitrate (KNO ₃ ) to form a surface (A, B). The stress measuring device (FSM-6000 manufactured by Ohara Seisakusho Co., Ltd.) measures the value of the compressive stress depth and the surface compressive stress at each point. The results are shown in Table 3.

From the results of Table 3, it was confirmed that by adjusting the temperature of the molten salt and the immersion time, it is possible to obtain a chemically strengthened glass having a shallow depth of the compressive stress layer and a large surface compressive stress. Further, regarding the depth of the compressive stress layer of the sample 1, it is considered that the depth of the compressive stress layer is shallow, so that it is difficult to measure, and it is considered to be slightly shallow.

Further, since the sample 4 was chemically strengthened by being held in potassium nitrate at 500 ° C for 3 minutes, the depth of the compressive stress layer was 12 μm, and for example, chemical strengthening was performed while cooling from 500 ° C to 450 ° C. The depth of the compressive stress layer becomes smaller. That is, in this case, it can be assumed that the sample 4 is maintained in the temperature region of 500 ° C to 450 ° C for 3 minutes, and is a compressive stress intermediate between the case of maintaining at 500 ° C for 3 minutes and the case of maintaining at 450 ° C for 3 minutes. Layer depth.

Regarding the soda-lime glass shown in Table 1, a floating plate having a thickness of 0.7 mm was cut out to a thickness of 40 mm square, and chemically strengthened by potassium nitrate (KNO ₃ ) for 1 minute or 3 minutes, and the respective faces (A, B) were The value of the compressive stress depth and the surface compressive stress at each point was measured by a surface stress measuring device (FSM-6000 manufactured by Ohara Seisakusho Co., Ltd.). When the device is used, since the depth of the compressive stress layer is shallow, the surface compressive stress and the depth of the compressive stress layer cannot be measured. However, according to the observation of the streaks by the surface stress meter, it was confirmed that the stress was applied.

On the other hand, in the soda-lime glass, a floating plate having a thickness of 0.7 mm was cut out to a thickness of 40 mm square, and chemical strengthening treatment was carried out by potassium nitrate (KNO ₃ ) for 2 hours, and the surface was measured by the surface (A, B). The device (FSM-6000 manufactured by Ohara Seisakusho Co., Ltd.) measures the value of the compressive stress depth and the surface compressive stress at each point. As a result, the average value of both surfaces was 572 MPa, and the depth of the compressive stress layer was 15.4 μm. If the time is delayed, the chemical strengthening is relieved by the stress, and the surface compressive stress tends to decrease. Therefore, it can be estimated that the surface compressive stress after the chemical strengthening treatment for 1 minute or 3 minutes is compared with the chemical strengthening treatment after 2 hours. The surface compressive stress is 572 MPa higher. Further, since the depth of the compressive stress is proportional to the 1/2 power of the strengthening time, it is presumed that the depth of the compressive stress layer after the chemical strengthening treatment for 1 minute or 3 minutes is deeper than the depth of the compressive stress layer after the chemical strengthening treatment for 2 hours. 15.4 μm, respectively, 1.4 μm, 2.4 μm.

As described above, according to the present embodiment, the molten glass is continuously molded into a plate shape, and then the glass original plate is chemically strengthened and diced at the same time as the slow cooling, and the depth of the compressive stress layer is 12 μm or less. Surface compressive stress exceeds 500 MPa, so it is not easy to cause cracks on the surface of the glass, and the operation damage can be suppressed. Further, since the compressive stress layer is shallow, the glass breakage during the subsequent processing can be suppressed, and the subsequent processing can be smoothly performed while suppressing the occurrence of the operational damage. Further, since the chemical strengthening is performed at the stage of the glass original plate, the operation damage in the transfer step before the glass ribbon is cut into the glass original plate can be suppressed. It is assumed that even before the glass ribbon is subjected to chemical strengthening, for example, when the glass surface is damaged by the lifting roller, the chemical strengthening treatment is performed thereafter, before the operation damage is not increased until the final product is affected. Strengthening can suppress the subsequent operational damage.

The glass original plate can be produced, for example, by chemically strengthening by immersing or exposing the glass original plate to a molten salt of 400 ° C to 530 ° C for 0.5 to 3 minutes.

Moreover, by performing chemical strengthening treatment on the line, the occurrence of operational damage can be suppressed at the earliest stage. Further, since it is not necessary to reheat the glass original plate which is cooled once, the manufacturing steps can be simplified, and the manufacturing cost can be suppressed.

Further, by the chemical strengthening treatment (primary chemical strengthening) and further chemical strengthening treatment (secondary chemical strengthening), the depth of the compressive stress layer as the final product and the compressive stress at the outermost surface can be appropriately adjusted.

In addition, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit and scope of the invention.

For example, the glass original plate (chemically strengthened glass) of the present invention is not limited to the cover glass of the display device, and can be applied to various uses such as a windshield of an automobile.

The present application is based on Japanese Patent Application No. 2012-276839, filed on Dec.

Claims (8)

A glass original plate characterized in that the molten glass is continuously formed into a plate shape, and then chemically strengthened simultaneously with slow cooling, and obtained by cutting, and has a compressive stress layer having a depth of 12 μm. Below, and the compressive stress at the outermost surface exceeds 500 MPa. The original glass plate of claim 1 has a size of 300 mm × 300 mm or more. A method for producing a glass raw plate, characterized in that in the step of slowly cooling the glass ribbon obtained by continuously forming the molten glass into a plate shape, the depth of the compressive stress layer after the slow cooling is 12 μm or less, and the outermost surface The chemical stress is strengthened in such a manner that the compressive stress exceeds 500 MPa, and then the glass ribbon is cut. The method for producing a glass original plate according to claim 3, wherein the size of the glass original plate is 300 mm × 300 mm or more. The method for producing a glass raw plate according to claim 3, wherein the molten glass is floated on the molten metal and formed into a plate shape to obtain the glass ribbon. A method for producing a chemically strengthened glass, comprising: a primary chemical strengthening step of chemically strengthening a glass sheet in such a manner that a depth of the compressive stress layer is 12 μm or less and a compressive stress of the outermost surface exceeds 500 MPa; a secondary chemical strengthening step It will be further chemically strengthened by chemically strengthened glass sheets in the above chemical strengthening step. The method for producing a chemically strengthened glass according to claim 6, wherein the glass sheet is produced by a float molding method, and the primary chemical strengthening step is performed on a line. The method for producing a chemically strengthened glass according to claim 6 or 7, wherein between the first chemical strengthening step and the second chemical strengthening step, the processing of the chemically strengthened glass sheet in the one chemical strengthening step is processed. step.