阅读说明：本技术 锂铝硅玻璃的制造方法和浮法玻璃板 (Method for producing lithium aluminosilicate glass and float glass plate ) 是由 白井正信 今北健二 于 2020-08-18 设计创作，主要内容包括：本发明涉及锂铝硅玻璃的制造方法和浮法玻璃板。本发明涉及一种锂铝硅玻璃的制造方法,其为使熔融玻璃流入到熔融金属浴上而将其成形为板状的锂铝硅玻璃的制造方法,其中,以氧化物基准的摩尔百分率表示,所述锂铝硅玻璃含有45％～75％的SiO_2、1％～30％的Al_2O_3、以及1％～20％的Li_2O,并且将所述熔融玻璃的流动方向上的所述熔融金属浴的长度设为L,距离其上游端0.2L～0.4L的下游区域中的所述熔融玻璃的平均粘度η2(dPa·s)与所述锂铝硅玻璃的锂辉石的晶体生长速度为0时的粘度ηB(dPa·s)满足下述式(1)和(2),logη2-logηB＜0.7 (1)；logη2-logηB＞0 (2)。(The present invention relates to a method for producing lithium aluminosilicate glass and a float glass sheet. The present invention relates to a method for producing a lithium aluminosilicate glass, which is a method for producing a lithium aluminosilicate glass by flowing a molten glass onto a molten metal bath to form the molten glass into a sheet, wherein the lithium aluminosilicate glass contains 45 to 75% of SiO, as represented by a molar percentage based on an oxide 2 1 to 30 percent of Al 2 O 3 And 1% to 20% of Li 2 O, and L is a length of the molten metal bath in a flow direction of the molten glass and is a distance from an upstream thereofAn average viscosity η 2(dPa · s) of the molten glass in a downstream region of the end 0.2L to 0.4L and a viscosity η B (dPa · s) when a crystal growth rate of spodumene of the lithium aluminosilicate glass is 0 satisfy the following expressions (1) and (2), and log η 2-log η B < 0.7 (1); log η 2-log η B > 0 (2).)

1. A method for producing a lithium aluminosilicate glass, which comprises flowing a molten glass onto a molten metal bath to form the molten glass into a plate-like shape,

the lithium aluminosilicate glass contains SiO in a proportion of 45-75 mol% based on oxide₂1 to 30 percent of Al₂O₃And 1% to 20% of Li₂O, and

l is the length of the molten metal bath in the flow direction of the molten glass, and the average viscosity eta 2(dPa · s) of the molten glass in a downstream region from the upstream end thereof by 0.2L to 0.4L and the viscosity eta B (dPa · s) when the crystal growth rate of spodumene of the lithium aluminosilicate glass is 0 satisfy the following expressions (1) and (2),

logη2-logηB＜0.7 (1)

logη2-logηB＞0 (2)。

2. the method of manufacturing lithium aluminosilicate glass according to claim 1, wherein a conveyance speed in the annealing furnace is 300 m/hr or more.

3. The method of manufacturing lithium aluminosilicate glass according to claim 1 or 2, wherein the oxide is usedThe lithium aluminosilicate glass contains 55 to 75 percent of SiO in terms of mole percentage₂8 to 20 percent of Al₂O₃7 to 20 percent of Li₂O and 0 to 8 percent of Na₂O, and Na₂O and K₂The total content of O is 5 to 10 percent.

4. The method of manufacturing lithium aluminosilicate glass according to any one of claims 1 to 3, wherein the molten glass is molten glass obtained by melting a glass raw material in a melting tank of a melting furnace, and a portion of the melting tank that is in contact with the molten glass contains high zirconia bricks.

5. The method for producing a lithium aluminosilicate glass according to any one of claims 1 to 4, wherein a viscosity η 1 of the molten glass when supplied onto the molten metal and a devitrification viscosity η A of the molten glass satisfy log η 1 < log η A.

6. A float glass sheet comprising lithium aluminosilicate glass having a SiO content of 45% to 75%, expressed as a molar percentage on an oxide basis₂1 to 30 percent of Al₂O₃And 1% to 20% of Li₂O, wherein,

the devitrification number density obtained by dividing the number of all precipitated crystals counted by observing one main surface of the float glass plate with an optical microscope by the area of the one main surface of the float glass plate is 100 pieces/m²The following.

Technical Field

The present invention relates to a method for producing lithium aluminosilicate glass and a float glass sheet.

Background

A chemically strengthened glass is used for a cover glass of a display device of a mobile device such as a mobile phone, a smart phone, a Personal Digital Assistant (PDA), or a tablet terminal, because the cover glass is required to have high strength so as not to be easily broken even when dropped. As a glass suitable for chemical strengthening, a lithium aluminosilicate glass has been proposed (for example, patent document 1). By subjecting lithium aluminosilicate glass to an ion exchange treatment using a sodium-containing strengthening salt and a potassium-containing strengthening salt, an excellent chemically strengthened glass having a large surface compressive stress value (CS) and a large depth of compressive stress layer (DOL) can be obtained.

As a method for efficiently producing a glass sheet, a float process is known. The float process is a method of forming a molten glass into a flat plate shape by flowing out the molten glass onto a molten metal layer, and is also used for producing a glass (glass for chemical strengthening) subjected to a chemical strengthening treatment (for example, patent document 2).

Documents of the prior art

Patent document

Patent document 1: international publication No. 2018/074335

Patent document 2: international publication No. 2013/183449

Disclosure of Invention

Problems to be solved by the invention

However, lithium aluminosilicate glass has a problem that devitrification is more likely to occur during production by the float process than soda lime glass and the like. This is because the growth rate of the precipitated spodumene crystals is high during the production of the lithium aluminosilicate glass.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for producing a lithium aluminosilicate glass having less devitrification by a float process.

Another object of the present invention is to provide a lithium aluminosilicate glass which is less devitrified and produced by the float process.

Means for solving the problems

The method for producing a lithium aluminosilicate glass according to the present invention for solving the above problems is a method for producing a lithium aluminosilicate glass by flowing a molten glass onto a molten metal bath to form the molten glass into a plate shape, wherein the lithium aluminosilicate glass contains, as represented by a molar percentage based on an oxide, lithium aluminosilicate glassHas 45 to 75 percent of SiO₂1 to 30 percent of Al₂O₃And 1% to 20% of Li₂And O, wherein L represents the length of the molten metal bath in the flow direction of the molten glass, and the average viscosity eta 2(dPa · s) of the molten glass in a downstream region from the upstream end by 0.2L to 0.4L and the viscosity eta B (dPa · s) when the crystal growth rate of spodumene in the lithium aluminosilicate glass is 0 satisfy the following expressions (1) and (2).

logη2-logηB＜0.7 (1)

logη2-logηB＞0 (2)

In one embodiment of the method for producing lithium aluminosilicate glass of the present invention, the conveyance speed in the annealing furnace may be 300 m/hr or more.

In one embodiment of the method for producing lithium aluminosilicate glass of the present invention, the lithium aluminosilicate glass may contain 55% to 75% of SiO, as represented by a molar percentage based on an oxide₂8 to 20 percent of Al₂O₃7 to 20 percent of Li₂O and 0 to 8 percent of Na₂O, and Na₂O and K₂The total content of O is 5 to 10 percent.

In one embodiment of the method for producing lithium aluminosilicate glass of the present invention, the molten glass is obtained by melting a glass raw material in a melting tank of a melting furnace, and a portion of the melting tank that contacts the molten glass may contain high zirconia bricks.

In one embodiment of the method for producing a lithium aluminosilicate glass of the present invention, the viscosity η 1 of the molten glass when supplied onto the molten metal and the devitrification viscosity η a of the molten glass may satisfy log η 1 < log η a.

The float glass sheet of the present invention comprises a lithium aluminosilicate glass containing 45 to 75% of SiO in terms of mole percentage based on oxides₂1 to 30 percent of Al₂O₃And 1% to 20% of Li₂O, wherein the devitrification number density obtained by dividing the number of all precipitated crystals counted by observing one main surface of the float glass sheet with an optical microscope by the area of the one main surface of the float glass sheet is 100 pieces/m²The following.

Effects of the invention

According to the present invention, there is provided a method for producing a lithium aluminosilicate glass having less devitrification by a float process. Further, the present invention provides a lithium aluminosilicate glass which is produced by the float process and has less devitrification.

Drawings

FIG. 1 is a schematic view of a manufacturing apparatus for manufacturing glass by a float process.

FIG. 2 is a schematic view of a float furnace of a glass manufacturing apparatus for manufacturing glass by a float process, as viewed from above.

Description of the reference symbols

1, glass raw materials;

2 melting the glass;

3, a glass ribbon;

10 melting furnace;

11 a melting kiln;

12 a melting tank;

13 a cooling tank;

14 neck (ネック);

20, floating and polishing the kiln;

21 a bath of molten metal;

22 an upper roller;

23, a restrictor;

30 slow cooling furnace (annealing furnace)

Detailed Description

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited to the embodiments described below. In the following drawings, members and portions having the same function are sometimes described with the same reference numerals, and redundant description may be omitted or simplified. In addition, the embodiments shown in the drawings are schematically illustrated for the sake of clarity of the present invention, and do not necessarily indicate actual dimensions or scales accurately.

Method for producing lithium aluminosilicate glass

The method for producing lithium aluminosilicate glass according to the present embodiment (hereinafter also simply referred to as "the method for producing glass according to the present embodiment") is performed byThe oxide-based molar percentage of SiO contained in the composition is 45 to 75%₂1 to 30 percent of Al₂O₃And 1% to 20% of Li₂A process for producing O-containing lithium aluminosilicate glass.

The method for producing a glass according to the present embodiment is a method for producing a lithium aluminosilicate glass by flowing a molten glass onto a molten metal bath to form a sheet, wherein the following expressions (1) and (2) are satisfied where L is a length of the molten metal bath in a flow direction of the molten glass, η 2(dPa · s) is an average viscosity of the molten glass in a downstream region from an upstream end by 0.2L to 0.4L, and η B (dPa · s) is a viscosity when a crystal growth rate of spodumene of the lithium aluminosilicate glass is 0.

logη2-logηB＜0.7 (1)

logη2-logηB＞0 (2)

In this manner, a manufacturing method in which molten glass is poured onto a molten metal bath to form a sheet is called a float process. Hereinafter, a method for producing glass according to the present embodiment will be described with reference to the drawings.

In the present specification, the upstream of the molten metal bath refers to a side into which molten glass flows, and the downstream refers to a side from which glass formed into a belt shape is carried out.

Fig. 1 is a schematic view of a glass manufacturing apparatus using the float method. In addition, fig. 2 shows a schematic view of the floating kiln as viewed from above.

As shown in fig. 1, the glass manufacturing apparatus using the float process includes a melting furnace 10, a float furnace 20, and a slow cooling furnace (annealing furnace) 30.

In the production of glass by the float process, first, a glass raw material is melted in a melting furnace 10 to obtain molten glass.

The melting furnace 10 has a melting furnace 11, and the glass raw material 1 charged into the melting furnace 11 is melted to obtain molten glass 2. More specifically, the melting furnace 11 has a structure in which an upstream-side melting tank 12 and a downstream-side cooling tank 13 are connected by a neck 14 (or throat portion), and the glass raw material 1 is melted on the upstream side (i.e., melting tank) to form molten glass 2, and the temperature of the molten glass 2 is adjusted on the downstream side.

The portion of the melting furnace 11 that contacts the molten glass may contain 45 mass% or more of Al₂O₃And bricks of alumina, mullite, zircon alumina and the like. However, in the case of producing a lithium aluminosilicate glass, particularly in the upstream side of the melting furnace (i.e., the melting tank), the molten glass easily reacts with the bricks, and spodumene crystals are formed in the reaction, which may cause devitrification. Therefore, it is particularly preferable that the melting furnace 11 used in the glass manufacturing method of the present embodiment includes a high zirconia brick in a portion that contacts molten glass on the upstream side (i.e., the melting tank). The high zirconia bricks have low reactivity with lithium aluminosilicate glass, and are less likely to cause the above-described problems. The high zirconia brick is a brick having a zirconia content of 90 mass% or more, preferably 95 mass% or more.

Since the temperature of the molten glass is lower as the downstream side of the melting furnace and the vicinity of the inlet of the float glass furnace (for example, the periphery of the throttle 23) are closer to the upstream side of the melting furnace, expensive high zirconia bricks can be omitted. However, in this case, Al is contained in an amount of 45 mass% or more₂O₃Since the bricks of (1) are also liable to cause devitrification due to precipitation of spodumene crystals, it is preferable to use Al₂O₃The brick with low content. In the presence of Al₂O₃In the case of a brick having a large content, it is preferable to suppress the formation of spodumene crystals by, for example, adding a high polysiloxane protective layer to a portion which is in direct contact with molten glass.

Subsequently, the molten glass 2 is continuously supplied from the upstream side to the surface of the molten metal bath 21 stored in the float furnace 20, and the glass ribbon 3 is formed. Then, the formed glass ribbon 3 is drawn out from the downstream end of the float furnace 20, introduced into a slow cooling furnace (lehr) 30, and slowly cooled, thereby producing plate-like glass. The glass ribbon 3 introduced into the lehr 30 is slowly cooled while being conveyed by a conveying mechanism such as a roller conveyor. Since the molten glass 2 on the molten metal bath 21 and the glass ribbon 3 in the lehr 30 are continuous, the conveyance speed in the lehr 30 (lehr speed (レアー speed)) depends on the speed at which the molten glass 2 flows from upstream to downstream on the molten metal bath 21. Although the glass ribbon 3 in the lehr 30 is already solidified, since the molten glass 2 is flowing, the speed of the molten glass 2 is slower than the lehr speed (レアー speed), and the speed of the molten glass 2 on the molten metal bath 21 tends to be faster toward the downstream.

The kind of the molten metal is not particularly limited, but molten tin is generally used.

In order to prevent the width of the glass ribbon 3 from being shrunk by surface tension or drawing by conveyance of the glass ribbon on the downstream side, an upper roll 22 is appropriately provided in the float furnace 20.

In glass production by the float method, generally, a glass raw material 1 is heated in a melting furnace 11 to become molten glass 2, and the molten glass 2 is supplied onto a molten metal 21 through a channel and a spout while throttling a flow path. Note that, in some cases, the molten glass 2 is supplied onto the molten metal 21 without passing through the grooves and the spout ports, in a state where the flow path is not constricted.

When the viscosity η 1(dPa · s) of the molten glass 2 when supplied onto the molten metal 21 is equal to or higher than the devitrification viscosity (liquid phase viscosity) η a (dPa · s) of the molten glass 2, there is a possibility that the glass may devitrify. Therefore, when glass is produced by the float method, it is preferable to set the value of log η 1 < log η a.

The devitrification viscosity η a of the glass is a viscosity of the molten glass at a devitrification temperature (liquidus temperature) TA which is a temperature at which crystals most easily precipitate in the glass (i.e., crystals that precipitate at the highest temperature when the molten glass is cooled) precipitate. The most easily precipitated crystals vary depending on the composition of the glass, e.g. ZrO is included in the glass₂In the case of (2), most of the crystals that are most likely to precipitate are crystals of zirconia. That is, the glass contains ZrO₂The devitrification viscosity η a in the case of (3) is a viscosity of the molten glass at a temperature at which crystals of zirconia precipitate when the temperature of the molten glass is lowered in many cases.

η 1 can be adjusted by adjusting the temperature of the molten glass when supplied onto the molten metal. Typically log η 1 is about 4. For suppressing devitrification, it is preferably 3.8 or less, and more preferably 3.6 or less. However, if η 1 is too small, it is difficult to adjust the thickness and width of the glass ribbon by using a roller. For easy molding, log η 1 is preferably 3 or more.

Eta a depends on the composition of the molten glass.

In order to adjust the temperature of the molten glass, a heater may be provided near the inlet of the float furnace, for example, near the inlet of the float furnace surrounded by a flow restricting brick, to heat the glass. When the temperature at the inlet of the float kiln is raised, η 1 becomes small, and therefore, log η 1 < log η a is likely to occur.

The viscosity of the glass can be measured by, for example, a rotating cylinder method. However, the viscosity of the molten glass in the float furnace cannot be directly measured. Since the relationship between the temperature and the viscosity of the molten glass is constant if the glass composition is the same, the viscosity of the molten glass in the float furnace can be determined from the glass composition and the temperature of the molten glass.

According to the study of the present inventors, it is found that: when the length of the molten metal bath is L and the temperature reduction rate of the molten glass is low in the downstream region (region indicated by (a) in fig. 2) from the upstream end by 0.2L to 0.4L, devitrification is likely to occur when the viscosity of the molten glass in this region is a viscosity at which crystals of spodumene having a particularly high crystal growth rate are likely to grow. In view of this situation, the present inventors have found that: by appropriately controlling the viscosity of the molten glass in this region, a glass sheet with less devitrification can be obtained even in the case of producing lithium aluminosilicate glass by the float process.

Specifically, for example, in the case where a heater is provided near the inlet of the float kiln to perform heating, the viscosity can be adjusted by rapidly lowering the temperature using a cooler or the like.

Specifically, it was found that: when the logarithm (log η 2) of the average viscosity η 2(dPa · s) of the molten glass in a downstream region of 0.2L to 0.4L from the upstream end of the molten metal bath is greater than the logarithm (log η B) of the viscosity η B (dPa · s) at a crystal growth rate of 0 of spodumene in the spodumene glass to be produced by 0.7 or more, the crystal of spodumene is likely to grow and devitrification is likely to occur. Therefore, in the method for producing glass of the present embodiment, η 2 and η B are set to satisfy the following formula (1).

logη2-logηB＜0.7 (1)

On the other hand, when log η 2 is equal to or less than log η B, the glass is poor in formability, and thus a plate-like glass is not easily obtained. Therefore, in the method for producing glass of the present embodiment, η 2 and η B are set so as to satisfy the following expression (2).

logη2-logηB＞0 (2)

η 2 can be adjusted by adjusting the heater arrangement and the annealing furnace speed (レアー speed), for example.

In addition, η B can be adjusted by adjusting the composition of the molten glass.

η B can be measured by the following method.

(method of measuring. eta.B)

First, a glass to be measured is melted and solidified in a state where a spodumene crystal is precipitated. Then, the temperature is raised while observing it with a microscope or the like, and the temperature TB at which the precipitated spodumene crystals disappear is recorded. The viscosity of the glass at this temperature TB is a viscosity η B at which the crystal growth rate of spodumene is 0.

Further, when the lehr speed (レアー speed) is high, the glass tends not to be devitrified easily. Therefore, the annealing furnace speed (レアー speed) is preferably 300 m/hr or more, more preferably 400 m/hr or more, and still more preferably 500 m/hr or more. When the lehr speed (レアー speed) is too high, the quality of the glass tends to be deteriorated, and therefore 1000 m/hr or less is preferable.

< LiAlSiCglass >

Next, a lithium aluminosilicate glass (hereinafter, also referred to as "present glass") produced by the glass production method of the present embodiment will be described. The glass is produced by the float process as described above, i.e., float glass.

First, the composition of the glass will be described. The lithium aluminosilicate glass in the present embodiment contains 45 to 75% of SiO, as represented by mole percentage based on oxide₂1 to 30 percent of Al₂O₃And 1% -20%Li of (2)₂And O. Hereinafter, each component will be described in detail. In the following description, the contents of the respective components are expressed by mole percentages based on oxides.

SiO₂Are components that form a network of glass and are essential components. SiO 2₂The content of (b) is 45% or more, preferably 55% or more, more preferably 60% or more, further preferably 63% or more, and particularly preferably 65% or more. On the other hand, SiO is used for improving the meltability₂The content of (b) is 75% or less, preferably 72% or less, more preferably 70% or less, and particularly preferably 68% or less.

For chemically strengthened glass having high CS and large DOL obtained by chemical strengthening, Al₂O₃Is an essential component. This is because Al is present in the glass₂O₃Particularly large CS is generated when Li ions in the vicinity of (a) are exchanged for Na ions.

To obtain this effect, Al of the present glass₂O₃The content of (B) is set to 1% or more. Al of the glass for improving Young's modulus₂O₃The content of (b) is preferably 8% or more, more preferably 9% or more, further preferably 10% or more, particularly preferably 11% or more, and most preferably 12% or more.

On the other hand, Al₂O₃When the content of (b) is too large, the crystal growth rate of spodumene becomes high, so devitrification is likely to occur at the time of melting of the glass, and the viscosity increases to lower the meltability. Therefore, Al of the present glass₂O₃The content of (b) is 30% or less, preferably 20% or less, more preferably 18% or less, and further preferably 16% or less.

Li₂O is a component for forming surface compressive stress by ion exchange, is a component for improving the meltability of the glass, and is an essential component. By adding Li₂The Li ion on the surface of the O glass is exchanged with Na ion, and further, the Na ion is exchanged with K ion, thereby obtaining a stress distribution having a large surface compressive stress and a large compressive stress layer.

To through the implementation of the glassHigh CS and large DOL are realized in chemically strengthened glass obtained by chemical strengthening treatment, and Li of the glass₂The content of O is 1% or more, preferably 5% or more, more preferably 7% or more, further preferably 9% or more, and particularly preferably 10% or more.

On the other hand, Li₂When the content of O is too large, the crystal growth rate of spodumene becomes high, and thus devitrification is likely to occur at the time of glass melting. Thus, Li of the present glass₂The content of O is 20% or less, preferably 15% or less, more preferably 13% or less, and further preferably 12% or less.

Although Na is present₂O and K₂O is not an essential component, but is a component for improving the meltability of the glass and reducing the crystal growth rate, and Na may be added for improving the ion exchange performance₂O and K₂O。

Na₂O is a component that forms a surface compressive stress layer in the chemical strengthening treatment using a potassium salt, and is a component that can improve the meltability of glass. To obtain this effect, Na of the present glass₂The content of O is preferably 1% or more, more preferably 2% or more, further preferably 3% or more, particularly preferably 4% or more, and most preferably 5% or more.

On the other hand, Na of the present glass is used in order to avoid a decrease in surface Compressive Stress (CS) in the strengthening treatment due to sodium salt₂The content of O is preferably 10% or less, more preferably 8% or less, further preferably 6% or less, and particularly preferably 5% or less.

K may be contained for the purpose of improving ion exchange performance or the like₂And O. The glass contains K₂In case of O, K₂The content of O is preferably 0.5% or more, more preferably 1% or more, further preferably 1.5% or more, particularly preferably 2% or more, and may be 3% or more.

On the other hand, in order to avoid the decrease of the surface Compressive Stress (CS) in the strengthening treatment due to the potassium salt, K is contained in the present glass₂In case of O, K₂The content of O is preferably 10% or less, more preferably 5% or less, further preferably 3% or less, and particularly preferably 2% or less.

Na of the glass₂O and K₂Total of O content ([ Na ]₂O]+[K₂O]) Preferably 0% to 10%. [ Na ]₂O]+[K₂O]More preferably 5% or more, further preferably 6% or more, further preferably 8% or less, further preferably 7% or less.

Although MgO, CaO, SrO and BaO are not essential components, it is preferable that the present glass contains any one or more of these components in order to improve stability. The total content of these components ([ MgO ] + [ CaO ] + [ SrO ] + [ BaO ]) in the glass is preferably 1% or more, more preferably 2% or more, still more preferably 3% or more, and particularly preferably 4% or more. On the other hand, the total content of these components in the present glass is preferably 20% or less, more preferably 15% or less, still more preferably 10% or less, and still more preferably 8% or less, from the viewpoint of improving the ion exchange ability of chemical strengthening.

In particular, from the viewpoint of increasing the meltability and reducing the crystal growth rate, it is preferable that MgO be contained in the present glass. The content of MgO in the glass is preferably 1% or more, more preferably 2% or more, further preferably 3% or more, particularly preferably 4% or more, and most preferably 5% or more. On the other hand, if the content of MgO is too large, it is difficult to increase the compressive stress layer during the chemical strengthening treatment. The MgO content of the glass of the present invention is preferably 15% or less, more preferably 10% or less, further preferably 8% or less, and particularly preferably 6% or less.

In the case where the glass of the present embodiment contains MgO and any one or more of CaO, SrO, and BaO, the ratio of the content of MgO to the total of the contents of CaO, SrO, and BaO ([ MgO ]/([ CaO ] + [ SrO ] + [ BaO ])) is preferably 10 or more, more preferably 15 or more, further preferably 20 or more, and particularly preferably 25 or more, from the viewpoint of reducing the surface reflectance of the glass. This is because CaO, SrO, and BaO increase the refractive index as compared with MgO. From the viewpoint of lowering the devitrification temperature, [ MgO ]/([ CaO ] + [ SrO ] + [ BaO ]) is preferably 60 or less, more preferably 55 or less, still more preferably 50 or less, and particularly preferably 45 or less.

CaO is a component for improving meltability, and may be contained. When CaO is contained, the content of CaO is preferably 0.1% or more, more preferably 0.15% or more, and further preferably 0.5% or more. On the other hand, if the content of CaO is excessive, it is difficult to increase the compressive stress value during the chemical strengthening treatment. The content of CaO is preferably 5% or less, more preferably 3% or less, further preferably 1% or less, and particularly preferably 0.5% or less.

SrO is also a component for improving the meltability, and may be contained. When SrO is contained, the SrO content is preferably 0.1% or more, more preferably 0.15% or more, and still more preferably 0.5% or more. On the other hand, when the SrO content is excessive, it is difficult to increase the compressive stress value during the chemical strengthening treatment. The SrO content is preferably 3% or less, more preferably 2% or less, still more preferably 1% or less, and particularly preferably 0.5% or less.

BaO is also a component for improving the meltability, and BaO may be contained. When BaO is contained, the content of BaO is preferably 0.1% or more, more preferably 0.15% or more, and further preferably 0.5% or more. On the other hand, when the content of BaO is excessive, it is difficult to increase the compressive stress value at the time of chemical strengthening treatment. The content of BaO is preferably 3% or less, more preferably 2% or less, further preferably 1% or less, and particularly preferably 0.5% or less.

ZnO is also a component for improving the meltability, and may contain ZnO. When ZnO is contained, the content of ZnO is preferably 0.1% or more, more preferably 0.15% or more, and still more preferably 0.5% or more. On the other hand, if the content of ZnO is excessive, it is difficult to increase the compressive stress value during the chemical strengthening treatment. The content of ZnO is preferably 3% or less, more preferably 2% or less, still more preferably 1% or less, and particularly preferably 0.5% or less.

May not contain ZrO₂However, from the viewpoint of increasing the surface compressive stress of chemically strengthened glass obtained by subjecting this glass to a chemical strengthening treatment, it is preferable to contain ZrO₂。ZrO₂The content of (b) is preferably 0.1% or more, more preferably 0.2% or more, further preferably 0.5% or more, particularly preferably 0.8% or more, and typically 1% or more. On the other hand, ZrO₂In an amount ofIn many cases, it is difficult to increase the compressive stress value during the chemical strengthening treatment. ZrO (ZrO)₂The content of (b) is preferably 5% or less, more preferably 3% or less, still more preferably 2% or less, and particularly preferably 1.5% or less.

TiO₂Is component for inhibiting solarization effect (ソラリゼーション), and may contain TiO₂. Containing TiO₂In the case of (2) TiO₂The content of (b) is preferably 0.02% or more, more preferably 0.05% or more, still more preferably 0.1% or more, particularly preferably 0.12% or more, and typically 0.15% or more. On the other hand, TiO₂When the content of (b) is more than 1%, devitrification easily occurs. TiO 2₂The content of (b) is preferably 1% or less, more preferably 0.5% or less, and still more preferably 0.25% or less.

Y₂O₃The chemical strengthening agent is a component that increases the surface compressive stress of a chemically strengthened glass obtained by subjecting the glass to a chemical strengthening treatment and at the same time decreases the crystal growth rate. Y is₂O₃The content of (b) is preferably 0.1% or more, more preferably 0.2% or more, further preferably 0.5% or more, particularly preferably 0.8% or more, and typically 1% or more. On the other hand, Y₂O₃If the content of (b) is too large, it is difficult to increase the compressive stress layer during the chemical strengthening treatment. Y is₂O₃The content of (b) is preferably 5% or less, more preferably 3% or less, still more preferably 2% or less, and particularly preferably 1.5% or less.

Although B is₂O₃B is not an essential component, but B may be contained for the purpose of reducing brittleness, improving chipping resistance and improving meltability₂O₃. Containing B₂O₃In case of (B)₂O₃The content of (b) is preferably 0.5% or more, preferably 1% or more, and more preferably 2% or more. On the other hand, B₂O₃If the content of (B) is too large, the acid resistance is liable to deteriorate, so that B is contained₂O₃In case of (B)₂O₃The content of (b) is preferably 10% or less, more preferably 6% or less, further preferably 4% or less, and typically 2% or less. From the viewpoint of preventing the generation of striae at the time of melting, it is more preferableSubstantially does not contain B₂O₃。

Although P is₂O₅P may be contained in order to increase the compressive stress layer of the chemically strengthened glass obtained by subjecting the glass to the chemical strengthening treatment, although it is not an essential component₂O₅. Containing P₂O₅In case of (2) P₂O₅The content of (b) is preferably 0.5% or more, preferably 1% or more, and more preferably 2% or more. On the other hand, from the viewpoint of improving acid resistance, P is₂O₅The content of (b) is preferably 6% or less, more preferably 4% or less, and further preferably 2% or less. From the viewpoint of preventing the formation of striae during melting, it is more preferable that P is not substantially contained₂O₅。

B₂O₃And P₂O₅The total content of (b) is preferably 0% to 10%, and the lower limit is preferably 1% or more, and more preferably 2% or more. In addition, B₂O₃And P₂O₅The total content of (b) is more preferably 6% or less, and still more preferably 4% or less.

La₂O₃、Nb₂O₅、Ta₂O₅、Gd₂O₃Is a component for reducing the crystal growth rate and improving the meltability, and may contain La₂O₃、Nb₂O₅、Ta₂O₅、Gd₂O₃. When these components are contained, the content of each component is preferably 0.1% or more, more preferably 0.2% or more, further preferably 0.5% or more, and may be 0.8% or more, or may be 1% or more. On the other hand, when the content is too large, it is difficult to increase the compressive stress value in the chemical strengthening treatment, and therefore the respective contents are preferably 3% or less, more preferably 2% or less, further preferably 1% or less, and may be 0.5% or less.

Fe₂O₃Since it absorbs heat rays and has an effect of improving meltability, it preferably contains Fe₂O₃. The glass contains Fe₂O₃In the case of (2) Fe₂O₃In an amount of (C) to oxidizeThe content of the compound is preferably 0.002% or more, more preferably 0.005% or more, still more preferably 0.007% or more, and particularly preferably 0.01% or more. On the other hand, Fe is contained in excess₂O₃In this case, since coloring occurs, Fe is contained in the glass from the viewpoint of improving the transparency of the glass₂O₃In the case of (2) Fe₂O₃The content of (b) is preferably 0.3% or less, more preferably 0.04% or less, further preferably 0.025% or less, and particularly preferably 0.015% or less, in terms of weight% based on the oxide.

Here, the iron oxide in the glass is entirely Fe₂O₃Although the form of (b) is illustrated, in practice, Fe (III) in an oxidized state and Fe (II) in a reduced state are generally present in a mixture. In this case, fe (iii) produces a yellow coloration, fe (ii) produces a blue coloration, and in the balance of the two, a green coloration is produced in the glass.

In addition, components other than the above may be added within a range not hindering achievement of the desired chemical strengthening properties. For example, coloring components may be added. The coloring component may be, for example, Co₃O₄、MnO₂、NiO、CuO、Cr₂O₃、V₂O₅、Bi₂O₃、SeO₂、CeO₂、Er₂O₃、Nd₂O₃And the like as appropriate coloring components.

The content of the coloring component is preferably 5% or less in total, as represented by a molar percentage based on the oxide. When the content of the coloring component is more than 5%, the glass may be easily devitrified. The content of the coloring component is preferably 3% or less, and more preferably 1% or less. When it is desired to improve the transmittance, it is preferable that these components are not substantially contained.

In addition, SO may be added appropriately₃Chlorides and fluorides as fining agents in glass melting. Preferably not containing As₂O₃. In the presence of Sb₂O₃In the case of (3), the content is preferably 0.3% or less, more preferably 0.1% or less, and most preferably not contained.

Next, the physical properties of the glass will be described.

The viscosity of the glass reaches 10²The temperature (T2) at dPa · s is preferably 1750 ℃ or less, more preferably 1700 ℃ or less, still more preferably 1650 ℃ or less, and particularly preferably 1600 ℃ or less. T2 is a temperature that is a standard for the melting temperature of glass, and glass tends to be produced more easily as T2 is lower. The lower limit of T2 is not particularly limited, and since glass having a low T2 may lack stability, T2 is usually 1400 ℃ or higher, preferably 1450 ℃ or higher.

In addition, the viscosity of the glass reaches 10⁴The temperature (T4) at dPa · s is preferably 1350 ℃ or less, more preferably 1250 ℃ or less, still more preferably 1200 ℃ or less, and particularly preferably 1150 ℃ or less. T4 is a standard temperature for forming glass into a plate shape, and glass having a high T4 tends to increase the load on the forming equipment. The lower limit of T4 is not particularly limited, and since glass having a low T4 may lack stability, T4 is usually 900 ℃ or higher, preferably 950 ℃ or higher, and more preferably 1000 ℃ or higher.

The softening point of the glass is preferably 850 ℃ or lower, more preferably 820 ℃ or lower, and still more preferably 790 ℃ or lower. This is because the lower the softening point of the glass, the lower the heat treatment temperature at the time of bending, the lower the energy consumption, and the smaller the load on the equipment. The lower the softening point is, the more preferable the lower the bending temperature is, but the softening point is 700 ℃ or higher in a general glass for chemical strengthening. Since the glass having an excessively low softening point tends to be easily relaxed and to have a low strength due to stress induced during the chemical strengthening treatment, the softening point is preferably 700 ℃ or higher, more preferably 720 ℃ or higher, and still more preferably 740 ℃ or higher.

The softening point can be measured by the fiber elongation method described in JIS R3103-1: 2001.

From the viewpoint of reducing warpage after chemical strengthening, the glass transition temperature (Tg) of the present glass is preferably 500 ℃ or higher, more preferably 520 ℃ or higher, and still more preferably 540 ℃ or higher. From the viewpoint of moldability in float molding, the glass transition temperature (Tg) is preferably 750 ℃ or less, more preferably 700 ℃ or less, further preferably 650 ℃ or less, particularly preferably 600 ℃ or less, and most preferably 580 ℃ or less.

The devitrification of the present glass produced by the method for producing a glass of the present embodiment is suppressed. The degree of devitrification can be evaluated by various methods, for example, by the number density of devitrification measured by the method described in the column of examples.

The devitrification number density of the glass is preferably 100/m²Hereinafter, more preferably 10/m²Hereinafter, more preferably 1 piece/m²The number of molecules is preferably 0.1/m²Hereinafter, 0 is most preferable.

[ examples ]

The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto.

< example 1 > (production of glass plate)

Glass raw materials were mixed so as to have the composition shown in the column of example 1 of table 1, placed in a platinum crucible, melted at 1650 ℃, and then cooled, thereby obtaining a glass gob. This glass block was used for evaluation of viscosity described later. Further, a part of the glass gob was pulverized, and the devitrification temperature TA and the temperature TB at which the crystal growth rate of spodumene was 0 were evaluated. Further, the glass block was placed in a platinum crucible and remelted at 1650 ℃ to obtain molten glass. The obtained molten glass was supplied to a molten metal bath of a glass manufacturing apparatus shown in fig. 1, and a glass sheet was manufactured by a float method. The conditions of the production process are shown in table 1.

(measurement and evaluation of physical Properties)

The obtained glass plate was measured for T2 and T4, devitrification temperature TA, devitrification viscosity η a, temperature TB when the crystal growth rate of spodumene was 0, and viscosity η B as follows. The devitrification number density of the obtained glass sheet was evaluated in the following manner. The results are shown in table 1. The blank column in the table indicates that no measurement is performed.

In addition, the following describes a method of measuring η 1 and η 2 in the production of the above glass plate.

< T2 and T4 >)

Temperature-dependent data of the viscosity of the glass were obtained using a rotational viscometer according to the method specified in ASTM C965-96 (2012). The viscosity is up to 10²The temperature at dPa · s was T2, and the viscosity was adjusted to 10⁴The temperature at dPa · s is T4.

< TA and η A >

5g of glass pulverized so that the average particle size became about 500 μm was placed in a 35mL platinum dish, kept in an electric furnace at a predetermined temperature for 17 hours, and then taken out, observed with a polarizing microscope at a magnification of 10 to 50 times, and observed for the presence or absence of crystal precipitation. The operation of observing the presence or absence of crystal precipitation while changing the temperature to be maintained was repeated in the temperature range of 800 to 1500 ℃, and the lowest temperature at which crystals were not precipitated was set as the liquid phase temperature TA. The viscosity at this temperature is defined as η a.

< TB and η B >

The temperature at which the crystal growth rate of spodumene was 0 was TB. The crystal growth rate of spodumene was evaluated by the following method.

First, the glass pieces were pulverized and classified in a mortar, passed through a sieve having a mesh size of 3.35mm (メッシュ), and the glass particles which did not pass through the sieve having a mesh size of 2.36mm were washed with ion-exchanged water, and the dried glass particles were used for the test. A glass particle is placed in each concave portion of an elongated platinum pool having a plurality of concave portions, and heated in an electric furnace at 1000 to 1100 ℃ until the surface of the glass particle is melted and smoothed. Next, the glass was put into a temperature gradient furnace maintained at a predetermined temperature, heat-treated for a predetermined time (t), and then taken out to room temperature and quenched. According to this method, since the plurality of glass particles can be simultaneously heat-treated while providing the elongated container in the temperature gradient furnace, the devitrification growth rate of spodumene in the predetermined temperature range can be measured.

The glass after the heat treatment was observed with a polarizing microscope (manufactured by Nikon corporation: ECLIPSE LV100ND), and the diameter (expressed as/. mu.m) of the largest crystal in the observed spodumene crystals was measured. Observation is performed under the conditions of 10 times of an eyepiece, 5 to 100 times of an objective lens, transmitted light and polarized light observation. It is considered that the spodumene crystal grows isotropically, and therefore the crystal growth rate thereof is l/(2t) [ unit: μ m/hr ]. However, the crystal to be measured is selected from crystals that do not precipitate from the interface with the container. This is because crystal growth at the metal interface has a different tendency from devitrification growth behavior occurring at the glass-atmosphere interface inside the glass.

The temperature dependence of the spodumene crystal growth rate was evaluated by the above method, and the temperature at which the growth rate was 0 was defined as TB. The viscosity at this temperature is referred to as η B.

< devitrification number density >

One main surface of a glass plate formed by the float method was observed by an optical microscope at a magnification of 10 to 50 times, and the presence or absence of crystal precipitation was observed.

The number of devitrification (precipitated crystal) observed was divided by the area of the principal surface of the glass sheet observed, thereby obtaining the density of devitrification number per unit area shown in table 1. In addition, the average diameter of devitrification (precipitated crystals) was also investigated. The results are shown in table 1.

＜η1＞

The viscosity of the glass at the temperature of the molten glass at the point where the molten glass flowing out of the melting furnace first contacts the molten metal bath is defined as η 1. Note that the blank column in η 1 in table 1 indicates that no measurement was performed.

＜η2＞

The length of the molten metal bath was set to L, the average temperature of the molten glass in the downstream region from the upstream end by 0.2L to 0.4L was measured, and the viscosity of the glass at this temperature was defined as η 2. The average temperature of the molten glass can be measured using a plurality of radiation thermometers provided in the float apparatus.

< examples 2 to 8 >

Glass sheets of examples 2 to 8 were produced in the same manner as in example 1, except that the composition of the glass and the conditions of the production method were changed as shown in table 1. The physical properties of the obtained glass sheets of examples 2 to 8 were measured and evaluated in the same manner as in example 1. The results are shown in table 1.

TABLE 1

Examples 4 and 5, in which log η 2-log η B is 0.7 or more, show much higher devitrification.

On the other hand, in examples 1 to 3 and 6 to 8 in which log η 2-log η B was more than 0 and less than 0.7, glasses with less devitrification were obtained.

The present application is based on the japanese patent application filed on 8/20/2019 (japanese patent application 2019-150480), the contents of which are incorporated herein by reference.