JP2016028987A - Glass blank, method for producing glass blank and method for producing chemically strengthened glass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glass blank, a method for producing a glass blank and a method for producing a chemically strengthened glass which can prevent flaws during conveyance or processing.SOLUTION: A glass blank is obtained by continuously molding melting glass into a tabular shape, and then cooling it slowly and cutting. The glass blank has a compressive stress layer, where depth of the compressive stress layer is 12 μm or less, and compression stress of the outermost surface is 600 MPa or more.SELECTED DRAWING: Figure 2

Description

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

  In recent years, display devices such as mobile phones, personal digital assistants (PDAs), and tablet PCs have become widespread. A chemically strengthened glass is attached as a cover glass on the front surface of the display device, and functions to protect a liquid crystal display (LCD).

  This chemically strengthened glass is manufactured by a manufacturing method such as a float method, a fusion method, etc., and after performing processing such as cutting processing and chamfering processing to cut into a desired shape on a glass base plate cut into a predetermined shape, Manufactured by chemical strengthening treatment.

JP 2011-197708 A

  However, the glass base plate cut into a predetermined shape may be damaged during transportation or processing. Such a flaw is called a flaw, and once the flaw is generated, there is a possibility that the final product may be affected even if a chemical strengthening treatment is performed thereafter.

  Then, an object of this invention is to provide the manufacturing method of the glass base plate which can suppress a handling flaw, a glass base plate, and the chemically strengthened glass.

  The inventors have found that the effects of handling flaws formed prior to chemical strengthening can affect the final product. First, in order to understand the crack generation behavior with respect to the stress profile, the compressive stress depth of the compressive stress layer (hereinafter sometimes referred to as the compressive stress depth) and the outermost compressive stress (hereinafter referred to as the surface) in a wide range. The rate of occurrence of cracks in soda lime glass that was chemically strengthened was evaluated by changing the stress (sometimes referred to as compressive stress).

  Evaluation was performed on 18 samples while changing the chemical strengthening time and molten salt temperature of the soda lime glass listed in Table 1, and cracks occurred at a rate of 50% when using a Vickers diamond indenter. The load to be obtained was obtained from the graph of FIG. 1 and mapped to the graph of FIG. The graph of FIG. 1 is obtained by performing 20 indentations for each sample at each load. Each sample was polished with cerium oxide before chemical strengthening treatment.

  As shown in FIG. 1, the load at which cracks are generated at a rate of 50% (hereinafter also referred to as 50% crack generation load) takes the probability of crack occurrence (%) on the vertical axis and the load (kgf) on the horizontal axis. , Defined as a load at which the probability of occurrence of cracks is 50%.

FIG. 2 is a graph showing the 50% crack generation load at the compressive stress depth and surface compressive stress of each sample as a circle.
From FIG. 2, it can be seen that the 50% crack generation load at the same compressive stress depth is significantly increased when a predetermined surface compressive stress is exceeded. For example, when the compressive stress depth is about 10 μm, the 50% crack generation load is 0.5 kgf when the surface compressive stress is 100 to 500 MPa, whereas 50% crack generation occurs when the surface compressive stress is about 600 MPa. The load is 1.0 kgf. Further, it can be seen from FIG. 2 that the deeper the compressive stress depth, the smaller the surface compressive stress at which the 50% crack generation load is significantly increased. For example, when the compressive stress depth is about 10 μm, the surface compressive stress is about 600 MPa, and the 50% crack generation load is significantly increased. However, when the compressive stress depth is about 20 μm, the surface compressive stress is about 500 MPa. When the compressive stress depth is about 40 μm, the surface compressive stress is about 400 MPa, and when the compressive stress depth is about 50 μm, the surface compressive stress is about 300 MPa and the 50% crack generation load is remarkably increased. However, at any compressive stress depth, unless the surface compressive stress is increased to some extent, 50% crack generation load is higher than that of glass not subjected to chemical strengthening treatment (compressive stress depth = 0 μm, surface compressive stress = 0 MPa). It became clear that cracks were easily generated and the strength was weakened. On the other hand, it is also known that if the depth of the compressive stress layer is deep, there is a high possibility of breaking into glass powder during subsequent processing.

  The present inventors have found a new problem of suppression of handling flaws that have not been attracting attention so far, while effectively suppressing the handling flaws, a glass base plate capable of suppressing the cracking of the glass during subsequent processing, It came to the manufacturing method of chemically strengthened glass, and the manufacturing method of chemically strengthened glass.

The present invention provides the following aspects.
(1) A glass base plate obtained by continuously forming molten glass into a plate shape, then slowly cooling and cutting the glass,
A glass base plate having a compressive stress layer, wherein the depth of the compressive stress layer is 12 μm or less, and the compressive stress on the outermost surface is 600 MPa or more.
(2) The glass base plate according to (1), wherein the size is 300 mm × 300 mm or more.
(3) In the step of slowly cooling a glass ribbon obtained by continuously forming molten glass into a plate shape, the depth of the compressive stress layer after slow cooling is 12 μm or less, and the compressive stress on the outermost surface is 600 MPa. A method for producing a glass base plate, which is chemically strengthened as described above and then cuts the glass ribbon.
(4) The method for producing a glass base plate according to (3), wherein the size of the glass base plate is 300 mm × 300 mm or more.
(5) The method for producing a glass base plate according to (3) or (4), wherein the glass ribbon is chemically strengthened by immersing the glass ribbon in a molten salt for 0.5 to 3 minutes.
(6) The method for producing a glass base plate according to (3) or (4), wherein the glass ribbon is chemically strengthened by spraying the molten salt and exposing the glass ribbon to the molten salt for 0.5 to 3 minutes. .
(7) The method for producing a glass base plate according to (5) or (6), wherein the temperature of the molten salt is 400 ° C to 530 ° C.
(8) The method for producing a glass base 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 primary chemical strengthening step of chemically strengthening the glass plate such that the depth of the compressive stress layer is 12 μm or less and the compressive stress of the outermost surface is 600 MPa or more;
A method for producing chemically strengthened glass, comprising: a secondary chemical strengthening step for further chemically strengthening the glass plate chemically strengthened in the primary chemical strengthening step.
(10) The glass plate is manufactured by a float forming method,
The method for producing chemically tempered glass according to (9), wherein the primary chemical tempering step is performed on-line.
(11) The chemical strengthening glass according to (9) or (10), wherein the primary chemical strengthening step chemically strengthens the molten ribbon by immersing the glass ribbon in a molten salt for 0.5 to 3 minutes. Method.
(12) The primary chemical strengthening step includes chemical strengthening by spraying molten salt and exposing the glass ribbon to the molten salt for 0.5 to 3 minutes. Of manufacturing chemically strengthened glass.
(13) The method for producing chemically strengthened glass moth according to (11) or (12), wherein the temperature of the molten salt is 400 ° C to 530 ° C.
(14) A processing step of processing the glass base plate chemically strengthened in the primary chemical strengthening step is provided between the primary chemical strengthening step and the secondary chemical strengthening step. The manufacturing method of the chemically strengthened glass in any one of 13).

In this specification, chemically strengthened glass refers to glass that has been subjected to chemical strengthening treatment, and chemically strengthened glass refers to glass that has been subjected to chemical strengthening treatment later, regardless of whether or not chemical strengthening treatment has been performed. Refers to the glass to be made. Therefore, the glass base plate chemically strengthened by the primary chemical strengthening process is chemically strengthened glass as well as chemically strengthened glass, and the glass chemically strengthened by the secondary chemical strengthening process is chemically strengthened glass.
Moreover, a glass base plate means the glass before a processing process obtained by shape | molding molten glass continuously in plate shape, then cooling slowly and cut | disconnecting. The size of the glass base plate is typically 300 mm × 300 mm or more, and usually has a short side of 500 mm or more or 700 mm or more.

  According to the glass base plate and the glass base plate manufacturing method of the present invention, since the depth of the compressive stress layer of the glass base plate is 12 μm or less and the compressive stress of the outermost surface is 600 MPa or more, there are cracks on the glass surface. It is difficult to occur and handling damage can be suppressed. In addition, since the compressive stress layer is shallow, the glass is prevented from cracking during subsequent processing, and subsequent processing can be performed smoothly while suppressing the occurrence of handling flaws. Furthermore, since it has already been chemically strengthened at the stage of the glass base plate, it is possible to suppress handling flaws in the transport process until the glass ribbon is cut into the glass base plate.

  Further, according to the method for producing chemically strengthened glass of the present invention, a glass plate having a compressive stress layer depth of 12 μm or less and an outermost compressive stress of 600 MPa or more is obtained by the primary chemical strengthening step. Cracks are less likely to occur, and handling flaws can be suppressed. In addition, since the compressive stress layer is shallow, the glass is prevented from cracking during subsequent processing, and subsequent processing can be performed smoothly while suppressing the occurrence of handling flaws. Further, the depth of the compressive stress layer as the final product and the compressive stress on the outermost surface can be appropriately adjusted by the secondary chemical strengthening step.

It is a graph which shows the relationship between a crack generation probability and a load for demonstrating a 50% crack generation load. It is a graph which shows the relationship between compression stress depth and surface compressive stress, and 50% crack generation load. It is the graph which showed the relationship between the compressive-stress layer depth and surface compressive stress of the soda-lime glass and aluminosilicate glass chemically strengthened at 400-450 degreeC for 10 hours. It is a figure which shows an example of the glass manufacturing apparatus at the time of performing a chemical strengthening process on-line. It is a figure which shows the other example of the glass manufacturing apparatus at the time of performing a chemical strengthening process on-line.

Hereinafter, the manufacturing method of the glass base plate and glass base plate of one Embodiment of this invention is demonstrated.
The glass base plate of the present invention is a chemically strengthened glass having a compressive stress layer, the depth of the compressive stress layer is 12 μm or less, and the compressive stress of the outermost surface is 600 MPa or more. 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 smaller the influence of subsequent processing such as cutting or chamfering. The compressive stress on the outermost surface is preferably 650 MPa or more, and more preferably 700 MPa or more. As the compressive stress on the outermost surface increases, the generation of handling flaws can be suppressed. The depth of the compressive stress layer and the compressive stress on the outermost surface can be measured using a surface stress measuring device (FSM-6000 manufactured by Orihara Seisakusho). Moreover, it can obtain | require from the retardation obtained by observing a cross section with a birefringence microscope.

In order to obtain such a glass base plate, it is effective to perform chemical strengthening (primary chemical strengthening) by immersing or exposing the glass base plate to the molten salt for a very short time. In the chemical strengthening treatment, alkali metal ions (typically Li ions, Na ions) having a small ion radius on the glass surface are exchanged with ions having a larger ion radius (typically K) by ion exchange at a temperature below the glass transition point. This is a process for forming a compressive stress layer on the glass surface and a tensile stress layer inside the glass. Specifically, for example, chemical strengthening is performed by immersing or exposing to a molten salt at 400 ° C. to 530 ° C. for 0.5 to 3 minutes. Thereby, glass with a small compressive stress depth and a large surface compressive stress can be obtained. If the temperature exceeds 500 ° C., the surface compressive stress becomes small and the desired scratch resistance cannot be obtained. As the molten salt, a molten salt mainly composed of potassium nitrate (KNO ₃ ) is preferable, and the temperature of the molten salt is preferably 400 ° C to 500 ° C, and more preferably 400 ° C to 450 ° C. When the temperature of the molten salt is higher than 530 ° C., alkali ions are likely to diffuse and the depth of compressive stress tends to be deep, but a desired surface compressive stress cannot be obtained. On the other hand, when the temperature of the molten salt is lower than 400 ° C., it takes a long time for chemical strengthening because alkali ions hardly diffuse.

As the glass for the glass base plate, soda lime glass, aluminosilicate glass, or the like can be used. FIG. 3 is a graph showing the relationship between the compressive stress layer depth and surface compressive stress of soda lime glass and aluminosilicate glass chemically strengthened at 400 to 450 ° C. for 10 hours.
Since the compressive stress depth is proportional to the 1/2 power of the strengthening time, the compressive force depth when chemically strengthened at 400 to 450 ° C. for 1 minute is theoretically about 1/25 when chemically strengthened for 10 hours. It becomes. Therefore, from FIG. 3, when chemically strengthened at 400 to 450 ° C. for 1 minute, it is assumed that soda-lime glass is about 1 μm and aluminosilicate glass is about 3 μm.

As the aluminosilicate glass, for example, a glass having 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, K ₂ O with a composition expressed in mol% 0 to 10%, MgO 0 to 15%, CaO 0 to 5% and ZrO ₂ 0 to 5%. Here, for example, range up but 10% K _{2 O} are not essential "comprising 0-10% of K _{2 O",} and object may include a range that does not impair the present invention, in the meaning of is there.
(Ii) The composition expressed in mol% is SiO ₂ 50-74%, Al ₂ O ₃ 1-10%, Na ₂ O 6-14%, K ₂ O 3-11%, MgO 2 15%, the CaO less than six% and ZrO ₂ and containing 0 to 5%, the total content of SiO ₂ and _Al 2 _{O 3} 75% or less, the total content of Na ₂ O and _{K 2} O Is 12 to 25%, and the total content of MgO and CaO is 7 to 15%.
(Iii) The composition expressed in mol% is SiO ₂ 68-80%, Al ₂ O ₃ 4-10%, Na ₂ O 5-15%, K ₂ O 0-1%, MgO 4 15% and glass containing ZrO ₂ 0 to 1%.
Composition viewed in (iv) mol%, a SiO ₂ 67 to 75%, the _{Al 2 O 3 0~4%, 7~15} % of Na ₂ O, 1 to 9% of _{K 2} O, MgO 6 14 to 15% and ZrO ₂ to 0 to 1.5%, the total content of SiO ₂ and Al ₂ O ₃ is 71 to 75%, the total content of Na ₂ O and K ₂ O is 12 to 20 %, And when it contains CaO, its content is less than 1%.

  The glass base plate preferably has a thickness of 1.5 mm or less, more preferably 0.3 to 1.1 mm. Further, the glass base plate preferably has a size of 300 mm × 300 mm or more.

  The glass base plate is preferably manufactured by a float process, but is not necessarily limited thereto, and may be manufactured by another manufacturing method such as a fusion method. Chemically strengthened glass in which the depth of the compressive stress layer is 12 μm or less and the compressive stress on the outermost surface is 600 MPa or more by subjecting the glass ribbon manufactured by any one of the manufacturing methods to chemical strengthening treatment as described above. A glass base plate can be manufactured. In particular, by manufacturing a glass base plate by the float process, it is possible to perform chemical strengthening treatment on-line, and the generation of handling flaws can be suppressed at the earliest stage. Moreover, since it is not necessary to reheat the glass base plate once cooled by this, a manufacturing process can be simplified and manufacturing cost can be suppressed. 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 diagrams illustrating an example of a glass manufacturing apparatus when performing chemical strengthening treatment on-line.
The glass manufacturing apparatus 10 includes a melting furnace (not shown) for melting glass raw materials, a float bath 11 for floating the molten glass on molten tin to form a flat glass ribbon G, and a lift-out roll 12. And a slow cooling furnace 13 for gradually cooling the glass ribbon G by gradually lowering the temperature of the glass ribbon G after the glass ribbon G is pulled out of the float bath 11.

  The slow cooling furnace 13 is, for example, supplying an amount of heat whose output is controlled by an electric heater H to a required position in the furnace and slowly cooling the glass ribbon conveyed by the conveying roller 14 to a temperature range close to room temperature. Residual stress inherent in the glass ribbon G is eliminated, and the glass has a function of suppressing warping and cracking. The above-described chemical strengthening treatment can be performed in the slow cooling furnace 13. That is, the glass base plate is manufactured through a forming step of forming a glass ribbon with the float bath 11 and a slow cooling step of gradually cooling the glass ribbon with the slow cooling furnace 13. In the slow cooling step, the above-described chemical strengthening treatment is applied to the glass ribbon. Is done.

For example, as shown in FIG. 4, a molten salt bath 15 is provided at a position corresponding to a temperature of the glass ribbon G of the slow cooling furnace 13 corresponding to about 400 ° C. to 530 ° C., and is conveyed by adjusting the position of the conveying roller 14. The glass ribbon G may pass through the molten salt stored in the molten salt bath 15. As shown in FIG. 5, the glass ribbon G in the slow cooling furnace 13 has a temperature corresponding to about 400 ° C. to 530 ° C. The injection device 16 for spraying the molten salt may be provided on the top surface side and the bottom surface side of the glass ribbon G so that the conveyed glass ribbon G is exposed to the molten salt injected from the injection device 16. Reference numeral 20 denotes an atmospheric gas supply device for keeping the region where chemical strengthening is performed in an air atmosphere, an N ₂ atmosphere, and the like, and reference numeral 21 denotes an air supply device that blows away the molten salt.

The glass base plate subjected to the above-described chemical strengthening treatment is subjected to a processing treatment such as a cutting treatment or a chamfering treatment for cutting into a desired shape, and further subjected to a chemical strengthening treatment (secondary chemical strengthening) to obtain a desired This is a chemically strengthened glass having the following strength. By the chemical strengthening treatment (secondary chemical strengthening) after the chemical strengthening treatment (primary chemical strengthening) for suppressing handling scratches, the compressive stress layer depth in the chemically strengthened glass is preferably 30 μm or more, and more preferably 40 μm or more. Further, the surface compressive stress is preferably 600 MPa or more, and more preferably 700 MPa or more. Specifically, for example, it is immersed in a potassium nitrate (KNO ₃ ) molten salt at 425 to 465 ° C. for 2 to 4 hours. The glass base plate does not necessarily need to be subjected to the secondary chemical strengthening treatment. In other words, the glass base plate may be chemically strengthened glass or not chemically strengthened glass.

Examples of the present invention will be described below.
For the glass shown in Table 2, a 0.7 mm thick float plate was cut into a 40 mm square and subjected to chemical strengthening treatment with potassium nitrate (KNO ₃ ) for 1 minute or 3 minutes, and the values of compressive stress depth and surface compressive stress were determined. One point was measured for each surface (A, B) with a surface stress measuring device (FSM-6000 manufactured by Orihara Seisakusho). The results are shown in Table 3.

  From the results in Table 3, it was demonstrated that a chemically strengthened glass having a shallow compressive stress layer depth and a large surface compressive stress can be obtained by adjusting the temperature of the molten salt and the immersion time. In addition, the compressive stress layer depth of Sample 1 is considered to be difficult to measure because the compressive stress layer depth is shallow.

  Sample 4 is chemically strengthened by holding it in 500 ° C. potassium nitrate for 3 minutes, so the compressive stress layer depth is 12 μm. For example, it is chemically strengthened while cooling from 500 ° C. to 450 ° C. Thus, the depth of the compressive stress layer can be reduced. That is, in this case, the sample 4 is held for 3 minutes in the temperature range of 500 ° C. to 450 ° C., and the compressive stress is about intermediate between the case of holding at 500 ° C. for 3 minutes and the case of holding at 450 ° C. for 3 minutes. It is assumed that the layer depth will be reached.

  As described above, according to the glass base plate obtained by continuously forming the molten glass of the present embodiment into a plate shape, then gradually cooling and cutting, the depth of the compressive stress layer is 12 μm or less, and Since the compressive stress on the outermost surface is 600 MPa or more, cracks are hardly generated on the glass surface, and handling flaws can be suppressed. In addition, since the compressive stress layer is shallow, the glass is prevented from cracking during subsequent processing, and subsequent processing can be performed smoothly while suppressing the occurrence of handling flaws. Furthermore, since it has already been chemically strengthened at the stage of the glass base plate, it is possible to suppress handling flaws in the transport process until the glass ribbon is cut into the glass base plate. Even if the glass ribbon is chemically strengthened before the glass ribbon is chemically strengthened, for example, even if scratches occur on the glass surface due to a lift-out roll, the chemical strengthening treatment is performed afterwards, so that the handling scratches have a large effect on the final product. Strengthening can be carried out before it becomes necessary, and subsequent generation of handling flaws can be suppressed.

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

  In addition, the occurrence of handling flaws can be suppressed at the earliest stage by performing the chemical strengthening process online. Moreover, since it is not necessary to reheat the glass base plate once cooled, a manufacturing process can be simplified and manufacturing cost can be suppressed.

  In addition, after the chemical strengthening treatment (primary chemical strengthening), the depth of the compressive stress layer as the final product and the compressive stress on the outermost surface can be appropriately adjusted by further chemical strengthening treatment (secondary chemical strengthening). it can.

The present invention is not limited to the embodiment described above, and can be implemented in various forms without departing from the gist of the present invention.
For example, the glass base plate (chemically tempered glass) of the present invention is not limited to a cover glass of a display device, but can be applied to various uses such as an automobile windshield.

DESCRIPTION OF SYMBOLS 10 Glass manufacturing apparatus 11 Float bath 12 Lift-out roll 13 Slow cooling furnace 14 Conveying roller 15 Molten salt bath 16 Injection apparatus G Glass ribbon H Electric heater

Claims (8)

A glass base plate obtained by continuously forming a molten glass into a plate shape, and then slowly cooling and cutting the glass,
A glass base plate having a compressive stress layer, wherein the depth of the compressive stress layer is 12 μm or less, and the compressive stress on the outermost surface is 600 MPa or more.   The glass base plate according to claim 1, wherein the glass base plate has a size of 300 mm × 300 mm or more.   In the step of slowly cooling a glass ribbon obtained by continuously forming molten glass into a plate shape, the depth of the compressive stress layer after slow cooling is 12 μm or less, and the compressive stress on the outermost surface is 600 MPa or more. A method for producing a glass base plate characterized by chemically strengthening and then cutting the glass ribbon.   The method for producing a glass base plate according to claim 3, wherein the size of the glass base plate is 300 mm x 300 mm or more.   The method for producing a glass base plate according to claim 3 or 4, wherein the molten glass is floated on a molten metal and formed into a plate shape to obtain the glass ribbon. A primary chemical strengthening step of chemically strengthening the glass plate so that the depth of the compressive stress layer is 12 μm or less and the compressive stress of the outermost surface is 600 MPa or more;
A method for producing chemically strengthened glass, comprising: a secondary chemical strengthening step for further chemically strengthening the glass plate chemically strengthened in the primary chemical strengthening step. The glass plate is manufactured by a float forming method,
The method for producing chemically strengthened glass according to claim 6, wherein the primary chemical strengthening step is performed on-line.   The chemistry according to claim 6 or 7, further comprising a processing step of processing the glass plate chemically strengthened in the primary chemical strengthening step between the primary chemical strengthening step and the secondary chemical strengthening step. A method for producing tempered glass.

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