JP7544070B2 - Lithium silicate glass plate with sulfate, lithium silicate glass plate, and manufacturing method thereof - Google Patents

Description

The present disclosure relates to a sulfate-containing lithium silicate glass plate, a lithium silicate glass plate, and a method for manufacturing the same.

The method for producing a glass sheet includes a forming step of forming molten glass into a sheet shape to obtain a glass ribbon, and an annealing step of annealing the glass ribbon while conveying it with a plurality of conveyor rollers. The annealing step includes spraying sulfurous acid (SO ₂ ) gas onto a main surface of the glass ribbon that is in contact with the conveyor rollers during conveyance to form a sulfate coating (see, for example, Patent Document 1).

The sulfate coating is dispersed on the main surface of the glass ribbon to soften the collision between the glass ribbon and the conveying rollers and prevent the glass ribbon from being damaged. When the glass is soda-lime glass, sulfates containing mainly Na are formed. Sulfates are inorganic compounds containing sulfate ions (SO ₄ ²⁻ ).

Lithium silicate glass has been attracting attention as a type of glass for chemical strengthening. Glass for chemical strengthening that has been chemically strengthened is called chemically strengthened glass. Chemically strengthened glass is used, for example, as cover glass for image display devices.

Chemical strengthening involves ion exchange between alkali metal ions with a small ionic radius contained on the glass surface and alkali metal ions with a large ionic radius contained in the molten salt, forming a compressive stress layer on the glass surface. Examples of alkali metals include Li, Na, and K. The ionic radii of Li, Na, and K increase in this order.

Lithium silicate glass contains Li ions, which have the smallest ionic radius of all alkali metal ions. Therefore, not only K ions but also Na ions, which have a smaller ionic radius than K ions, can be selected as the alkali metal ions in the molten salt. This allows for a wide range of alkali metal ions to be selected for the molten salt, and a wide range of control over chemical strengthening.

After being chemically strengthened, lithium silicate glass is used in mobile phones, personal data assistants (PDAs), personal computers, televisions, car navigation systems, etc.

International Publication No. 2002/051767

In the manufacture of lithium silicate glass sheets, a sulfate coating is formed on the glass surface, just as in the manufacture of soda-lime glass sheets. However, lithium silicate glass sheets are more likely to have foreign matter mixed into the glass surface than soda-lime glass sheets.

The inventors have investigated foreign matter that has been mixed into lithium silicate glass sheets in the past and found that the cause of the foreign matter is sulfate. The inventors found that sulfate formed on the glass surface adheres to the transport rollers, and when the adhered sulfate melts, the metal transport rollers corrode, causing rust, which then becomes mixed into the glass sheet as a foreign matter.

One aspect of the present disclosure provides technology that can suppress the intrusion of foreign matter into lithium silicate glass sheets.

A sulfate-containing lithium silicate glass plate according to one embodiment of the present disclosure includes a lithium silicate glass plate and a sulfate containing an alkali metal ion formed on a main surface of the lithium silicate glass plate. The melting point of the sulfate is 40° C. or more higher than the glass transition point (Tg) of the lithium silicate glass.

In a lithium silicate glass plate according to one embodiment of the present disclosure, the depthwise distribution of the Li concentration (unit: mol %) in the glass plate before chemical strengthening is such that the average Li concentration in a region from 0 nm to 100 nm deep from the main surface where sulfate is formed is 88% or less of the average Li concentration in a region from 400 nm to 600 nm deep from the main surface.

A method for producing a lithium silicate glass sheet according to one aspect of the present disclosure includes forming molten glass into a sheet shape to obtain a glass ribbon, and slowly cooling the glass ribbon while transporting it with a plurality of transport rollers. The method also includes spraying sulfur oxide gas onto a main surface of the glass ribbon that is in contact with the transport rollers during transport to form sulfates. At the position where the sulfur oxide gas is sprayed, the temperature of the glass ribbon is -30°C or more and less than 40°C based on the glass transition point (Tg) of the lithium silicate glass. The melting point of the sulfate is 40°C or more higher than the glass transition point (Tg).

According to one aspect of the present disclosure, the intrusion of foreign matter into a lithium silicate glass plate can be suppressed.

FIG. 1 is a side cross-sectional view showing an apparatus for producing a lithium silicate glass plate according to one embodiment. FIG. 2 is a plan view showing an example of the arrangement of the nozzles and the second transport roller. FIG. 3A is a diagram showing an example of the relationship between M5 and M2/M1. FIG. 3B is a diagram showing an example of the relationship between M5 and M4/M3. FIG. 4 is a diagram showing the Li concentration distribution in the depth direction in the glass plate of Example 3. FIG. 5 is an SEM photograph of the principal surface of the glass plate of Example 5 on which sulfate salts were formed. FIG. 6 is a phase diagram of sulfate when M4/M3=0.0050. FIG. 7 is a phase diagram of sulfate when M4/M3=0.0100. FIG. 8 is a phase diagram of sulfate when M4/M3=0.0150. FIG. 9 is a phase diagram of sulfate when M4/M3=0.0200. FIG. 10 is a phase diagram of sulfate when M4/M3=0.0250.

Below, an embodiment of the present disclosure will be described with reference to the drawings. Note that in each drawing, the same or corresponding configurations are given the same reference symbols, and descriptions thereof may be omitted. In each drawing, the X-axis direction, Y-axis direction, and Z-axis direction are mutually perpendicular, the X-axis direction and Y-axis direction are horizontal directions, and the Z-axis direction is vertical. The X-axis direction is the conveying direction of the glass ribbon G, and the Y-axis direction is the width direction of the glass ribbon G.

In the specification, the suffix "~" indicating a range of values means that the values before and after it are included as the lower and upper limits. In addition, in the specification, the melting point means the temperature at which a solid begins to melt. In cases where a solidus temperature and a liquidus temperature exist, the melting point means the solidus temperature.

As shown in FIG. 1, the manufacturing apparatus 1 has a forming apparatus 2 and a heat treatment apparatus 3. The forming apparatus 2 forms the molten glass into a plate shape to obtain a glass ribbon G. The heat treatment apparatus 3 slowly cools the glass ribbon G while transporting it with a first transport roller 41 and a second transport roller 51. After being removed from the forming apparatus 2, the glass ribbon G is slowly cooled in the heat treatment apparatus 3 and then cut by a processing apparatus (not shown). As a result, a lithium silicate glass plate is obtained as a product. Hereinafter, the lithium silicate glass plate is also simply referred to as a glass plate.

The glass plate may be for chemical strengthening. Chemical strengthening involves ion exchange between alkali metal ions with a small ionic radius contained on the glass surface and alkali metal ions with a large ionic radius contained in the molten salt, forming a compressive stress layer on the glass surface. Examples of alkali metals include Li, Na, and K. The ionic radii of Li, Na, and K increase in this order.

Lithium silicate glass contains Li ions, which have the smallest ionic radius of all alkali metal ions. Therefore, not only K ions but also Na ions, which have a smaller ionic radius than K ions, can be selected as the alkali metal ions in the molten salt. This allows for a wide range of alkali metal ions to be selected for the molten salt, and a wide range of control over chemical strengthening.

After being chemically strengthened, the glass plates are used in mobile phones, personal data assistants (PDAs), personal computers, televisions, car navigation systems, etc.

Lithium silicate glass contains, for example, in mole percent on an oxide basis, 50 to 75% SiO ₂ , 2 to 25% Al ₂ O ₃ , 5 to 20% Li ₂ O, and 0.5 to 15% Na ₂ O + K ₂ O. Preferably, it contains, in mole percent on an oxide basis, 55 to 75% SiO ₂ , 8 to 25% Al ₂ O ₃ , 5 to 20% Li ₂ O, and 0.5 to 15% Na ₂ O + K ₂ O.

More preferably, the lithium silicate glass contains, in mole percent based on oxides, 60 to 73% _SiO2 , 8 to 22% _{Al2O3 ,} 9 to 15% _Li2O , 1.2 to 3.0% _K2O , and 0.5 to 10% _Na2O + _K2O .

The glass transition temperature Tg of the lithium silicate glass is, for example, 510°C or higher, preferably 540°C or higher. The glass transition temperature Tg of the lithium silicate glass is, for example, 650°C or lower, preferably 630°C or lower, more preferably 600°C or lower.

The forming device 2 obtains the glass ribbon G, for example, by the float method. In the float method, molten glass is continuously supplied onto the liquid surface of the molten metal M, and the supplied molten glass is formed into a strip shape while flowing from the negative side in the X-axis direction to the positive side in the X-axis direction above the liquid surface of the molten metal M.

The molding device 2 has a bath 21 for storing molten metal M. For example, molten tin or a molten tin alloy is used as the molten metal M. The inside of the molding device 2 is filled with a reducing atmosphere to suppress oxidation of the molten metal M. The reducing atmosphere contains, for example, nitrogen gas and hydrogen gas. Furthermore, the inside of the molding device 2 is kept at a positive pressure higher than atmospheric pressure to suppress the intrusion of air from outside the molding device 2.

The forming device 2 uses the liquid surface of the molten metal M to obtain a plate-shaped glass ribbon G. The glass ribbon G gradually cools and hardens as it flows on the liquid surface of the molten metal M. The glass ribbon G is pulled up from the molten metal M in the downstream area of the bath 21 and discharged from the outlet 22 of the forming device 2. The temperature of the glass ribbon G at the outlet 22 is less than a first temperature T1. The first temperature T1 is a temperature that is +40°C based on the glass transition point Tg (T1 = Tg + 40).

The heat treatment device 3 is adjacent to the outlet 22 of the forming device 2. The heat treatment device 3 has a dross box 4 and an annealing furnace 5 provided downstream in the conveying direction from the dross box 4. Inside the heat treatment device 3, the temperature of the glass ribbon G decreases from the upstream side in the conveying direction to the downstream side in the conveying direction.

The heat treatment device 3 has a first transport roller 41 made of metal inside the dross box 4. The first transport roller 41 pulls the glass ribbon G diagonally upward from the liquid surface of the molten metal M and transports the glass ribbon G from the forming device 2 to the dross box 4. A plurality of first transport rollers 41 are provided at intervals in the transport direction of the glass ribbon G. The first transport roller 41 contacts the underside of the glass ribbon G and transports the glass ribbon G by rotating.

The heat treatment device 3 further has a carbon block 42 inside the dross box 4. The carbon block 42 is provided for each first conveyor roller 41, contacts the first conveyor roller 41 from below, and forms a carbon protective film on the outer circumferential surface of the first conveyor roller 41. The carbon protective film functions as a buffer material that cushions the collision between the first conveyor roller 41 and the glass ribbon G, thereby preventing the glass ribbon G from being damaged.

The inside of the dross box 4 is filled with a reducing atmosphere flowing in from the outlet 22 of the molding device 2 to prevent the carbon block 42 from burning due to oxidation. The inside of the dross box 4 is also kept at a positive pressure higher than atmospheric pressure by introducing nitrogen gas or the like to prevent the intrusion of air from outside the dross box 4.

The heat treatment device 3 has a metallic second transport roller 51 inside the annealing furnace 5. The second transport roller 51 transports the glass ribbon G horizontally from the entrance 52 to the exit 53 of the annealing furnace 5. A plurality of second transport rollers 51 are provided at intervals in the transport direction of the glass ribbon G. The second transport rollers 51 contact the underside of the glass ribbon G and transport the glass ribbon G by rotating.

The heat treatment device 3 has a nozzle 54 inside the annealing furnace 5. The nozzle 54 sprays sulfur oxide gas ( _SOx gas) onto the lower surface of the glass ribbon G to form sulfates. _{The SOx} gas is at least one selected from _SO2 gas and _SO3 gas. The sulfates refer to inorganic compounds containing sulfate ions ( _SO42- ). The sulfates function as ^a buffer material that cushions the collision between the second conveyor roller 51 and the glass ribbon G, and therefore can prevent the glass ribbon G from being damaged.

The nozzle 54 is disposed near the entrance 52 of the annealing furnace 5 to minimize damage to the glass ribbon G. However, the position of the nozzle 54 is not limited to near the entrance 52 of the annealing furnace 5. In addition, although the number of nozzles 54 is one in this embodiment, there may be more than one. The multiple nozzles 54 are provided at intervals in the conveying direction of the glass ribbon G.

The nozzle 54 has an outlet 541 for discharging the _SOx gas. As shown in Fig. 2, a plurality of the outlets 541 are arranged at intervals in the Y-axis direction so as to form sulfates over the entire width direction of the glass ribbon G. The plurality of outlets 541 are formed in a horizontal pipe 542 parallel to the Y-axis direction.

1, the nozzle 54 is connected to a first gas supply source 64 via a first pipe 63 in which a first on-off valve 61 and a first flow control valve 62 are provided. When the first on-off valve 61 opens the flow path of the first pipe 63, the first gas supply source 64 supplies _SOX gas to the nozzle 54, and the nozzle 54 discharges the _SOX gas. The flow rate of the _SOX gas is controlled by the first flow control valve 62. On the other hand, when the first on-off valve 61 closes the flow path of the first pipe 63, the supply of _SOX gas from the first gas supply source 64 to the nozzle 54 is stopped, and the nozzle 54 stops discharging the _SOX gas.

When the nozzle 54 discharges _SO2 gas, the _SO2 gas is oxidized to _SO3 gas inside the annealing furnace 5. Since it is presumed that the _SO3 gas contributes to the generation of sulfate crystals, the inside of the annealing furnace 5 is made to be an oxidizing atmosphere so that the _SO3 gas can exist stably. The oxidizing atmosphere is formed by the air flowing in from the outlet 53 of the annealing furnace 5. Therefore, the oxygen gas concentration in the internal atmosphere of the annealing furnace 5 decreases from the outlet 53 to the inlet 52 of the annealing furnace 5.

As described above, the nozzle 54 is disposed near the inlet 52 of the annealing furnace 5. Thus, the nozzle 54 may discharge an oxygen-containing gas in order to increase the oxygen gas concentration. The oxygen-containing gas may be any gas that contains oxygen gas, and may be pure oxygen gas, but in this embodiment, it is air. The air may be discharged simultaneously with the _SOx gas, or may be discharged alternately with the _SOx gas.

The nozzle 54 is connected to the second gas supply source 74 via a second pipe 73 in which a second on-off valve 71 and a second flow control valve 72 are provided. When the second on-off valve 71 opens the flow path of the second pipe 73, the second gas supply source 74 supplies air to the nozzle 54, and the nozzle 54 discharges the air. The flow rate of the air is controlled by the second flow control valve 72. On the other hand, when the second on-off valve 71 closes the flow path of the second pipe 73, the supply of air from the second gas supply source 74 to the nozzle 54 is stopped, and the nozzle 54 stops discharging air.

In this embodiment, one nozzle 54 discharges both _SOx gas and air, but a nozzle for _SOx gas and a nozzle for air may be provided separately.

The sulfate is usually formed by a reaction between an alkali metal contained in the glass ribbon G and _SO3 gas. Therefore, the sulfate contains an alkali metal ion. Note that the sulfate can also be formed by a reaction between an alkaline earth metal contained in the glass ribbon G and _SO3 gas, and therefore can further contain an alkaline earth metal ion.

Since lithium silicate glass contains Li, sulfates also contain Li. Sulfates may further contain one or more of Na and _K. The melting point of (Li _{(1-A-B) 2} SO ₄ depends on _A and B. A is 0 to 1, and B is also 0 to 1. For example, the solidus temperature of (Li _0.9 , Na _0.1 ) ₂ SO ₄ is 732°C, but there are also combinations of A and B whose solidus temperatures are 530°C or lower.

The inventors have investigated foreign matter that has been mixed into lithium silicate glass sheets in the past and found that the cause of the foreign matter is sulfate. The inventors have found that when sulfate melts, it corrodes the second metal conveyor roller 51, causing rust, which then mixes into the glass sheet as foreign matter. The inventors have also found that when sulfate melts or, even if it does not melt, it softens, the sulfate loses its function as a buffer material, causing more scratches on the glass ribbon G.

The melting point T _M of the sulfate in this embodiment is higher than Tg by 40° C. or more and is equal to or higher than the first temperature T1 (T _M ≧Tg+40=T1). As described above, the temperature of the glass ribbon G is lower than the first temperature T1 at the outlet 22 of the forming device 2, and therefore is lower than the first temperature T1 at the inlet 52 of the annealing furnace 5, and decreases from the inlet 52 to the outlet 53 of the annealing furnace 5.

Therefore, the temperature of the glass ribbon G is lower than the melting point T _M of the sulfate throughout the entire interior of the annealing furnace 5. This makes it possible to prevent the sulfate from melting inside the annealing furnace 5. As a result, it is possible to prevent the corrosion of the metallic second conveyor rollers 51 and the generation of rust, thereby making it possible to prevent the rust from being mixed into the glass sheet as a foreign matter.

The melting point T _M of the sulfate is at least 40° C. higher than Tg (T _M ≧Tg+40), preferably at least 50° C. higher than Tg (T _M ≧Tg+50). The melting point T _M of the sulfate is, for example, 550° C. or higher, preferably 580° C. or higher, more preferably 600° C. or higher. The melting point T _M of the sulfate is, for example, 860° C. or lower, preferably 720° C. or lower.

The alkali metal ions of the sulfate have a ratio (M2/M1=A/(1-B)) of the number of moles of Na ions (M2) to the total number of moles of Li ions and Na ions (M1) that is, for example, less than 0.1, preferably 0.09 or less, and more preferably 0.07 or less. The smaller the ratio (M2/M1), the higher the melting point T _M of the sulfate. M2/M1 is preferably 0.01 or more.

In addition, the ratio (M4/M3=B) of the moles of K ions (M4) to the total moles of alkali metal ions (M3) of the sulfate is, for example, 0.018 or less, preferably 0.015 or less, and more preferably 0.012 or less. The smaller the ratio (M4/M3), the higher the melting point T _M of the sulfate. M4/M3 is preferably 0.005 or more.

When the ratio (M2/M1) is less than 0.1 and the ratio (M4/M3) is 0.018 or less, the proportion of Li ions in the alkali metal ions is high, and the solidus temperature of (Li _(1-A-B) , _NaA , _KB ) _2SO4 exceeds 600° C. In this case, when the temperature of the glass ribbon _G inside the annealing furnace 5 is 600° C. or less, melting of the sulfate can be suppressed.

The present inventors have found through experiments that, when the glass composition of the lithium silicate glass is the same and the temperature T2 of the glass ribbon G at the position where the _SOx gas is blown is the same, the ratio (M2/M1) and the ratio (M4/M3) both decrease as the amount of sulfate per unit area (1 ^m2 ) increases.

The amount of sulfate per unit area is expressed as the number of moles of sulfur per unit area, M5. The relationship between M5 and M2/M1 is shown in Figure 3A, and the relationship between M5 and M4/M3 is shown in Figure 3B. As shown in Figure 3A, the more M5 increases, the smaller M2/M1 becomes. Also, as shown in Figure 3B, the more M5 increases, the smaller M4/M3 becomes.

As M5 increases, both M2/M1 and M4/M3 decrease. The fact that both M2/M1 and M4/M3 decrease means that the ratio of Li among the alkali metals in the sulfate increases, and this means that the melting point T _M of the sulfate increases.

M5 is, for example, 5.1×10 ⁻⁵ mol or more, preferably 6.0×10 ⁻⁵ mol or more, more preferably 7.5×10 ⁻⁵ mol or more. If M5 is 5.1×10 ⁻⁵ mol or more, the ratio of Li to the alkali metals in the sulfate is high, and the melting point T _M of the sulfate is high, so that melting of the sulfate can be suppressed. M5 is preferably 15×10 ⁻⁵ mol or less.

In the examples described below, M2/M1, M4/M3, and M5 were measured by scrubbing the sulfate-contaminated main surface of a glass plate (30 cm x 30 cm) with 20 ml of 1N hydrochloric acid solution, then rinsing with warm water, and analyzing the 100 ml of liquid obtained.

M2/M1 and M4/M3 were measured by atomic absorption spectrometry. A polarized Zeeman atomic absorption spectrophotometer (Z-2310) manufactured by Hitachi High-Tech Science was used for the measurements.

M5 was measured using ICP optical emission spectrometry. A Hitachi High-Tech Science ICP optical emission spectrometry analyzer (ICP-OES SPS3100HV UV) was used for the measurements. Each element was quantified using the calibration curve method.

As described above, sulfates are formed by a reaction between an alkali metal contained in the glass ribbon G and _SO3 gas. At that time, the alkali metal escapes from the glass ribbon G and generates sulfates on the main surface of the glass sheet. As shown in Fig. 4, the shallower the depth from the glass surface, the smaller the Li concentration (unit: mol%) in the glass.

The average Li concentration in the region from 0 nm to 100 nm deep from the main surface of the glass plate is denoted as D1, and the average Li concentration in the region from 400 nm to 600 nm deep from the main surface of the glass plate is denoted as D2. Here, the main surface of the glass plate is the main surface on which sulfate is formed. D1 is, for example, 88% or less of D2, and preferably 86% or less of D2. D1 is preferably 65% or more of D2.

When the glass composition of the lithium silicate glass is the same and the temperature T2 of the glass ribbon G at the blowing position of the _SOx gas is the same, a small D1/D2 means that the amount of Li ions that escape from the glass ribbon G and become part of the sulfate increases. The amount of Li ions is proportional to the amount of sulfate formed on the lithium silicate glass and is proportional to M5. As M5 increases, the melting point T _M of the sulfate increases, as described above. Therefore, a small D1/D2 means that the melting point T _M of the sulfate is high.

Note that D1/D2 also depends on the glass composition of the lithium silicate glass and the temperature T2 of the glass ribbon G at the position where the _SOx gas is blown. The temperature T2 is −30° C. or more and less than 40° C. with respect to the glass transition point (Tg) (Tg−30≦T2<Tg+40).

D1/D2 is measured on unstrengthened glass plates because chemical strengthening also changes the depth distribution of Li concentration.

In the examples described below, the depth distribution of the Li concentration in the glass plate was measured by X-ray photoelectron spectroscopy (XPS) using C60 ion sputtering. For the measurement, an ESCA5500 manufactured by ULVAC-PHI was used. The abundance ratio of each element contained in the glass was measured from the peaks of Si (2p), Al (2p), Na (2s), K (2p), Li (1s), Ca (2s), Mg (2s), Zr (3d), Sn (3d5), and O (1s). The peak measurement conditions were a pass energy of 117.4 eV, an energy step of 0.5 eV/step, and a detection angle (angle between the sample surface and the detector) of 75°. Analysis software MultiPak was used to analyze the spectrum. The background of the spectrum was removed by the Shirley method.

We will explain Examples 1 to 5. Examples 1 to 4 are working examples, and Example 5 is a comparative example.

(Example 1)
In Example 1, molten glass was formed into a sheet by the float process to obtain a glass ribbon G, and then _SOx gas was blown onto the glass ribbon G near the inlet 52 of the annealing furnace 5 to form sulfates on the lower surface of the glass ribbon G. The temperature T2 of the glass ribbon G at the position where the _SOx gas was blown onto the glass ribbon G was 540° C. After annealing, a glass plate was cut out from the glass ribbon G.

The glass of the glass plate was a lithium silicate glass, containing, in mole percent based on oxides, _66.2 % _SiO2 , 11.2% _Al2O3 , 10.4% _Li2O , 5.6% _Na2O , 1.5% _K2O , 3.1% MgO, 0.2% CaO, _1.3 % ZrO2, and _0.5 % _Y2O3 . This glass had a glass transition point Tg of 558°C and an annealing point of 552°C. The glass composition was measured at the center of the glass plate in the thickness direction.

The alkali metal ion ratios of the sulfate salts were M2/M1 0.09 and M4/M3 0.0178. The number of moles of sulfur per unit area M5 was 5.1×10 ⁻⁵ mol. The melting point T _M of the sulfate salts was 600° C. or higher. The Li concentration distribution in the depth direction of the glass plate was 88% of D2 in D1.

The melting point T _M of the sulfate was 600° C. or higher, which was higher than the temperature T2 of the glass ribbon G at the position where the _SOx gas was blown. Therefore, it is presumed that the sulfate did not melt inside the annealing furnace 5. No foreign matter was mixed into the glass surface on which the sulfate was formed. There were some scratches due to contact with the second conveyor roller 51, but these were not of any concern.

(Example 2)
In Example 2, a glass plate was produced under the same conditions as in Example 1, except that the flow rate of the _SOx gas was increased in order to increase the amount of sulfate per unit area. The temperature T2 of the glass ribbon G at the position where the _SOx gas was blown was 540° C. The obtained glass had a glass transition point Tg of 558° C. and an annealing point of 552° C.

The alkali metal ion ratios of the sulfate salts were M2/M1 0.08 and M4/M3 0.0156. The number of moles of sulfur per unit area M5 was 5.8×10 ⁻⁵ mol. The melting point T _M of the sulfate salts was 600° C. or higher. The Li concentration distribution in the depth direction of the glass plate was 86% of D2 in D1.

The melting point TM of the sulfate was 600° C. or higher, which was higher than the temperature T2 of the glass ribbon G at the position where the _SOx gas was blown. Therefore, it is presumed that the sulfate did not melt inside the annealing furnace 5. The glass surface on which the sulfate was formed was free of foreign matter and had no contact scratches with the second conveyor roller 51.

(Example 3)
In Example 3, a glass sheet was produced under the same conditions as in Example 1, except that the flow rate of _SOx gas was increased in order to increase the amount of sulfate per unit area. The temperature T2 of the glass ribbon G at the _SOx gas blowing position was 540° C. The obtained glass had a glass transition point Tg of 558° C. and an annealing point of 552° C.

The ratio of alkali metal ions in the sulfate was M2/M1 0.03 and M4/M3 0.0070. The number of moles of sulfur per unit area M5 was 12.9×10 ⁻⁵ mol. The melting point T _M of the sulfate was 600° C. or higher. The Li concentration distribution in the depth direction of the glass plate obtained in Example 3 is shown in FIG. 4. D1 was 69% of D2.

The melting point T _M of the sulfate was 600° C. or higher, which was higher than the temperature T2 of the glass ribbon G at the position where the _SOx gas was blown. Therefore, it is presumed that the sulfate did not melt inside the annealing furnace 5. The glass surface on which the sulfate was formed was free of foreign matter and had no contact scratches with the second conveyor roller 51.

(Example 4)
In Example 4, glass raw materials having a different compounding ratio from those in Examples 1 to 3 were melted to obtain molten glass, and the molten glass was then formed into a sheet shape by a float method in the same manner as in Examples 1 to 3 to obtain a glass ribbon G. Thereafter, _SOx gas was blown near the inlet 52 of the annealing furnace 5 to form sulfates on the lower surface of the glass ribbon G. The temperature T2 of the glass ribbon G at the position where the _SOx gas was blown was 570° C. After annealing, a glass plate was cut out from the glass ribbon G.

The glass of the glass plate was a lithium silicate glass, containing, in mole percent based on oxides, 70.0% _{SiO2 ,} 7.5% _Al2O3 , 8.0% _Li2O , 5.3% _Na2O , 1.0% _K2O , 7.0% MgO, 0.2% CaO, and _1.0 % ZrO2. This glass had a glass transition point Tg of 548°C and an annealing point of 542°C. The glass composition was measured at the center of the glass plate in the thickness direction.

The alkali metal ion ratios of the sulfate salts were M2/M1 0.08 and M4/M3 0.0120. The number of moles of sulfur per unit area M5 was 5.2×10 ⁻⁵ moles. The melting point T _M of the sulfate salts was 600° C. or higher. The Li concentration distribution in the depth direction of the glass plate was 78% of D2 in D1.

The melting point T _M of the sulfate was 600° C. or higher, which was higher than the temperature T2 of the glass ribbon G at the position where the _SOx gas was blown. Therefore, it is presumed that the sulfate did not melt inside the annealing furnace 5. The glass surface on which the sulfate was formed was free of foreign matter and had no contact scratches with the second conveyor roller 51.

(Example 5)
In Example 5, a glass plate was produced in the same manner as in Example 1, except that the temperature T2 of the glass ribbon G at the _SOx gas blowing position was changed from 540° C. to 560° C. The temperature T2 of the glass ribbon G at the _SOx gas blowing position was 560° C. The obtained glass had a glass transition point Tg of 558° C. and an annealing point of 552° C.

The alkali metal ion ratio of the sulfate was M2/M1 0.12 and M4/M3 0.0244. The number of moles of sulfur per unit area M5 was 4.2×10 ⁻⁵ mol. The melting point T _M of the sulfate was 557° C. The Li concentration distribution in the depth direction of the glass plate was 91% of D2 in D1.

The melting point T _M of the sulfate was 557° C., which was lower than the temperature T2 of the glass ribbon G at the position where the _SOx gas was blown. Therefore, it is presumed that the sulfate melted inside the annealing furnace 5. On the glass surface on which the sulfate was formed, the inclusion of foreign matter C was recognized as shown in FIG. 5, and there were also scratches due to contact with the second conveying roller 51.

Analysis of the composition of foreign matter C shown in Figure 5 revealed that foreign matter C contained sulfur and iron. Therefore, it is presumed that sulfate melted, corroded the stainless steel second conveyor roller 51, and rust was generated, which was then mixed in as foreign matter C.

(summary)
The experimental results of Examples 1 to 5 are summarized in Table 1.

ところで、例１のガラスは、例４のガラスに比べて、カリウム濃度が大きい。ガラス中のカリウム濃度が大きいほど、ガラスから抜けるカリウム量が多く、硫酸塩のカリウム濃度が大きくなり、硫酸塩が溶けやすくなる。従って、例１のガラスのように、酸化物基準のモル％表示でＳｉＯ_２を６０～７３％、Ａｌ_２Ｏ_３を８～２２％、Ｌｉ_２Ｏを９～１５％、Ｋ_２Ｏを１．２～３．０％、Ｎａ_２Ｏ＋Ｋ_２Ｏを０．５～１０％含有するガラスに本願発明を適用する技術的な意義が大きい。

The glass of Example 1 has a higher potassium concentration than the glass of Example 4. The higher the potassium concentration in the glass, the more potassium is removed from the glass, the higher the potassium concentration of the sulfate, and the easier it is to dissolve the sulfate. Therefore, there is a great technical significance in applying the present invention to glass such as the glass of Example ₁ , which contains, in mole percent on an oxide basis, 60 to 73% _{SiO2 ,} 8 to 22% _Al2O3 , 9 to 15% _Li2O , 1.2 to 3.0% K2O, and 0.5 to 10% _Na2O + _K2O .

Figures 6 to 10 show phase diagrams of sulfate when M4/M3 = 0.0050, 0.0100, 0.0150, 0.0200, and 0.0250. In Figures 6 to 10, the areas indicated by dotted patterns are the areas where a liquid phase is produced. As is clear from Figures 6 to 10, the larger M4/M3 (the ratio of K ions to the alkali metal ions in the sulfate), the larger the area where a liquid phase is produced, and therefore the more easily the sulfate dissolves.

The sulfate-containing lithium silicate glass plate, lithium silicate glass plate, and manufacturing method thereof according to the present disclosure have been described above, but the present disclosure is not limited to the above-described embodiments. Various changes, modifications, substitutions, additions, deletions, and combinations are possible within the scope of the claims. Naturally, these also fall within the technical scope of the present disclosure.

This application claims priority to Patent Application No. 2020-007091, filed with the Japan Patent Office on January 20, 2020, the entire contents of which are incorporated herein by reference.

G Glass ribbon 51 Second conveying roller

Claims (13)

A lithium silicate glass plate with sulfate, comprising: a lithium silicate glass plate; and a sulfate containing an alkali metal ion formed on a main surface of the lithium silicate glass plate,
A lithium silicate glass plate with sulfate, wherein the melting point of the sulfate is 40° C. or more higher than the glass transition point (Tg) of the lithium silicate glass. The lithium silicate glass plate with sulfate according to claim 1, wherein the ratio (M2/M1) of the number of moles of Na ions (M2) to the total number of moles of Li ions and Na ions (M1) of the alkali metal ions of the sulfate is less than 0.1. The lithium silicate glass plate with sulfate according to claim 1 or 2, wherein the ratio (M4/M3) of the number of moles of K ions (M4) to the total number of moles of alkali metal ions (M3) of the sulfate is 0.018 or less. The sulfate-attached lithium silicate glass plate according to any one of claims 1 to 3, wherein the amount of sulfur in the sulfate is 5.1 x 10 ^-5 mol or more per m ² of the main surface. The sulfate-containing lithium silicate glass sheet according to any one of claims 1 to 4, wherein the glass transition point (Tg) is 510°C or higher. The lithium silicate glass has, in mole percent on an oxide basis,
_SiO2 50-75%,
_{Al2O3 2-25} %
5-20% Li ₂ O
0.5-15% Na ₂ O + K ₂ O
The sulfate-containing lithium silicate glass plate according to any one of claims 1 to 5, A lithium silicate glass plate in which the depth distribution of the Li concentration (unit: mol %) in the glass plate before chemical strengthening is such that the average Li concentration in the region from 0 nm to 100 nm deep from the main surface where sulfate is formed is 88% or less of the average Li concentration in the region from 400 nm to 600 nm deep from the main surface. The lithium silicate glass plate according to claim 7, wherein the depth distribution of the Li concentration (unit: mol %) in the glass plate before chemical strengthening is such that the average Li concentration in a region from 0 nm to 100 nm deep from the main surface is 86% or less of the average Li concentration in a region from 400 nm to 600 nm deep from the main surface. The lithium silicate glass sheet according to claim 7 or 8, having a glass transition point (Tg) of 510°C or higher. In mole percent based on oxide,
_SiO2 50-75%,
_{Al2O3 2-25} %
5-20% Li ₂ O
0.5-15% Na ₂ O + K ₂ O
The lithium silicate glass plate according to any one of claims 7 to 9, comprising: A method for producing a lithium silicate glass sheet, comprising forming molten glass into a sheet shape to obtain a glass ribbon, and gradually cooling the glass ribbon while conveying it by a plurality of conveying rollers,
A sulfur oxide gas is sprayed onto a main surface of the glass ribbon that is in contact with the conveying roller during conveyance to form sulfates;
At the position where the sulfur oxide gas is blown, the temperature of the glass ribbon is −30° C. or more and less than 40° C. based on the glass transition point (Tg) of lithium silicate glass,
The melting point of the sulfate is higher than the glass transition point (Tg) by 40° C. or more. The method for producing a lithium silicate glass sheet according to claim 11, wherein the glass transition point (Tg) is 510°C or higher. The lithium silicate glass has, in mole percent on an oxide basis,
_SiO2 50-75%,
_{Al2O3 2-25} %
5-20% Li ₂ O
0.5-15% Na ₂ O + K ₂ O
The method for producing a lithium silicate glass plate according to claim 11 or 12, comprising:

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