TW202128583A - glass substrate - Google Patents

Abstract

The present invention provides a glass substrate with low chargeability. The glass substrate of the present invention is characterized in that: as the glass composition, it contains less than 0.03% of _{Li 2} O, 0.001 to 0.1% of _{Na 2 O, and 0.001 to 1% of K 2} O in terms of mass %, and in terms of mass ratio, Na ₂ O/K ₂ O is less than 1.

Description

Glass base board

The present invention relates to a glass substrate, in particular to a glass substrate that is generally applicable to display substrates including organic EL (Electroluminescence) displays.

Since electronic devices such as organic EL displays are thin and have excellent animation display and consume less power, they are used for displays such as TVs and smartphones.

As the substrate of organic EL displays, glass substrates are widely used in the industry. For the glass substrate for this purpose, the following characteristics are mainly required. (1) In order to prevent the diffusion of alkali metal ions in the semiconductor material formed in the heat treatment step, the content of alkali metal oxide is small; (2) In order to reduce the cost of the glass substrate, it has excellent productivity, especially resistance to devitrification or melting; (3) In the manufacturing steps of p-Si/a-Si·TFT (Thin Film Transistor, thin film transistor), the deformation of the glass substrate due to thermal shrinkage is less; (4) In the manufacturing steps of p-Si/a-Si·TFT, the chargeability of the glass substrate is low; (5) It has a smooth surface suitable for p-Si/a-Si·TFT manufacturing steps.

[The problem to be solved by the invention]

If the above (4) and (5) are described in detail, since the glass substrate is an insulator, in the p-Si/a-Si·TFT manufacturing steps, it is caused by the contact between the glass substrate and the exposure table, etc., the glass substrate Will be charged. The charging is one of the major factors that cause the deviation between the film formation distances used in TFT pixels.

As described in (5), in order to form a high-quality TFT, it is desirable to have a smooth surface. Even if the glass substrate used as a display substrate is a glass substrate that uses a float process that requires grinding, it requires a surface quality close to a relatively smooth free surface. . However, the smoother the surface of the glass substrate, the easier it is to charge the glass substrate. That is, the subject of (4) and the subject of (5) are in a trade-off relationship.

The current situation is to roughen the back surface of the exposure table or the glass substrate in order to suppress charging. However, even if the exposure table is roughened, the roughened surface will be smoothed during repeated use. Moreover, in order to roughen the back surface of the glass substrate, it is necessary to perform chemical etching or gas etching, which may cause problems such as mixing of etching residue on the film formation surface. In addition, the above-mentioned process must be added to the manufacturing process, which will inevitably lead to an increase in cost.

Furthermore, with the thinning of displays in recent years, the reduction in yield due to charging has become a major problem. The reason is that if the glass substrate is made thinner, the affinity with the exposure table or the like becomes better, and as a result, the contact area between the glass substrate and the exposure table or the like increases, and it becomes easy to charge.

In view of the above, the object of the present invention is to provide a glass substrate with low chargeability. [Technical means to solve the problem]

The inventors of the present invention have repeatedly conducted various experiments and found that the above technical problem can be solved by strictly controlling the content of the trace amount of alkali metal oxide contained in the glass substrate, and this is proposed as the present invention. That is, the glass substrate of the present invention is characterized in that as a glass composition, it contains 0.03% or less of _{Li 2} O, 0.001 to 0.1% of _{Na 2 O, and 0.001 to 1% of K 2} O in mass %, and Na ₂ O/K ₂ O is 1 or less. Here, "Na ₂ O/K ₂ O" refers to the value obtained _{by dividing the content of Na 2} O by the content of K _{2 O.}

The glass substrate of the present invention is preferably used as a glass composition, and contains B ₂ O ₃ 9% or less in terms of mass %.

The glass substrate of the present invention is preferably used as a glass composition and contains 2% or less of _{TiO 2 in terms of mass %.}

The glass substrate of the present invention preferably has a surface potential after 300 seconds/initial surface potential of 0.8 or less. Here, "surface potential after 300 seconds" refers to the surface potential of the glass substrate 300 seconds after the fluororubber is brought into contact with the glass substrate. "Initial surface potential" refers to the surface potential of the glass substrate just after the fluororubber is brought into contact with the glass substrate. "Surface potential after 300 seconds/initial surface potential" refers to the value obtained by dividing the surface potential after 300 seconds by the initial surface potential. The smaller the value, the easier the charge diffuses from the surface of the glass substrate, and the lower the chargeability. Furthermore, a surface potential sensor or the like can be used in the measurement of surface potential.

The glass substrate of the present invention preferably has a heat shrinkage rate of 30 ppm or less when heat-treated at 500°C for 1 hour. "The heat shrinkage rate when heat-treated at 500°C for 1 hour" is measured by the following method. First, as shown in Figure 1(a), prepare a short strip specimen G of 160 mm × 30 mm as a measurement specimen. Use #1000 water sandpaper on both ends of the short strip sample G in the longitudinal direction to form marks M at positions 20-40 mm away from the edge. Thereafter, as shown in FIG. 1(b), the short strip-shaped sample G on which the mark M is formed is broken into two pieces in a direction orthogonal to the mark M to produce sample pieces Ga and Gb. Then, only one of the sample pieces Gb was heat-treated as follows: the temperature was raised from room temperature to 500°C at 5°C/min, and after holding at 500°C for 1 hour, the temperature was lowered at 5°C/min. After the above heat treatment, as shown in Fig. 1(c), in the state where the unheated sample piece Ga and the heat-treated sample piece Gb are arranged in parallel, the two sample pieces Ga are read from the laser microscope , Gb mark M position offset (ΔL ₁ , ΔL ₂ ), the thermal shrinkage rate is calculated by the following formula. Furthermore, 10 mm in the following formula is the distance between the initial marks M. Furthermore, if the thermal shrinkage rate is high, the pixel pitch of the TFT will shift, which may cause poor display.

Thermal shrinkage (ppm)=[{ΔL ₁ (μm)+ΔL ₂ (μm)}×10 ³ ]/10(mm)

The glass substrate of the present invention preferably has a strain point of 700°C or higher. The "strain point" is the value measured based on the method of ASTM C336 and C338. Furthermore, the higher the strain point, the less likely it is to generate thermal shrinkage during the manufacturing steps of p-Si·TFT.

The glass substrate of the present invention preferably has an average thermal expansion coefficient of 45×10 ^-7 /°C or less at 30 to 380°C. "Average thermal expansion coefficient at 30～380℃" is the value measured by a thermal dilatometer.

The glass substrate of the present invention preferably has a Young's modulus of 73 GPa or more. "Young's modulus" refers to the value measured by the dynamic elastic modulus measurement method (resonance method) based on JIS R1602.

The glass substrate of the present invention preferably has a liquid phase viscosity of 10 ^4.0 dPa·s or more. The "liquid viscosity" means that the glass powder that has passed through a standard sieve of 30 mesh (mesh mesh 500 μm) and remains in 50 mesh (mesh mesh 300 μm) is added to the platinum boat and kept in a temperature gradient furnace for 24 hours. The well-known platinum ball pulling method calculates the value of the viscosity at the temperature when the crystal (primary phase) precipitates.

The glass substrate of the present invention preferably has a β-OH value of 0.30/mm or less. "Β-OH value" refers to the value obtained by measuring the transmittance of glass using FT-IR (Fourier Transform Infrared Radiation, Fourier Transform Infrared Spectroscopy), and using the following formula. β-OH value = (1 / X) log ( T 1 / T 2) X: glass thickness (mm) T _1: reference wavelength of 3846 cm transmittance (%) of ^-1 T _2: hydroxyl absorption wavelength of 3600 cm ^{- 1} Minimum transmittance when nearby (%)

The glass substrate of the present invention preferably has a thickness of 0.01 to 1.0 mm.

The manufacturing method of the glass substrate of the present invention is characterized in that the above-mentioned glass is manufactured by a fusion method, a down-draw method, or a float method. [Effects of Invention]

According to the present invention, it is possible to provide a glass substrate with low chargeability.

The glass substrate of the present invention is characterized in that: as the glass composition, it contains less than 0.03% of _{Li 2} O, 0.001 to 0.1% of _{Na 2 O, and 0.001 to 1% of K 2} O in terms of mass %, and Na ₂ O /K ₂ O is less than 1. The reason for limiting the content of each component as described above is shown below. In addition, in the description of the content of each component, as long as there is no special description,% display means mass%.

Li is the smallest element among alkali metals. Therefore, Li is easy to move in the glass, which is most helpful for the diffusion of electric charge. Therefore, from the viewpoint of reduction in chargeability, Li can be said to be the most effective element. However, because of its ease of movement, Li is most easily diffused in the semiconductor material in the steps of TFT fabrication including heat treatment, and there is a tendency to reduce the performance of the TFT. Therefore, _{the content of Li 2} O is preferably 0.03% or less, 0.02% or less, 0.01% or less, 0.005% or less, 0.001% or less, especially 0.0005% or less.

Na is second only to Li in the alkali metals, and it is more beneficial to the diffusion of charges. In addition, it is also second only to Li and is likely to cause diffusion into the semiconductor material during the TFT manufacturing step. Therefore, since Na reduces the chargeability and is less likely to reduce the performance of the TFT _{than Li, it is preferable to contain more Na 2} O than Li ₂ O. Specifically, _{the preferred upper limit content of Na 2} O is 0.1%, 0.09%, 0.08%, 0.07%, especially 0.06%, and the preferred lower limit content is 0.001%, 0.005%, 0.01%, 0.02%, especially 0.03. %.

Compared with Li and Na, K has a larger ion radius and is not easy to move in glass. However, since the outermost surface of the glass substrate is charged, K, which is not easy to move, can also sufficiently diffuse the charge and reduce the chargeability. Furthermore, since K is less likely to degrade the performance of the TFT than Li and Na, it is preferable to contain _{more K 2} O than Li ₂ O and Na ₂ O. Specifically, _{the preferred upper limit content of K 2} O is 1%, 0.9%, 0.8%, 0.7%, 0.6%, especially 0.4%, and the preferred lower limit content is 0.001%, 0.01%, 0.1%, 0.15%, 0.2%, 0.25%, especially 0.3%.

In addition, Na is not easily moved because it is contained together with K. Furthermore, in order to reduce the chargeability and prevent the performance of the TFT from degrading, Na ₂ O/K ₂ O is preferably 1.0 or less, 0.9 or less, 0.8 or less, 0.7 or less, especially 0.6 or less.

Table 1 shows the alkali content of glass A, B, and C.

[Table 1] quality% A B C Li ₂ O 0.0006 0.0014 0.0006 Na ₂ O 0.011 0.06 0.023 K ₂ O 0.001 0.26 0.0009

Figure 2 shows the measurement results of the electrification properties of glasses A, B, and C. According to Fig. 2, it can be seen that the _{surface potential of glass B containing more K 2} O decreases significantly with the passage of time. Furthermore, it can be seen that glasses A, B, and C are glasses that can be used in the TFT step. In order to reduce the chargeability, it is very effective to specify the amount of alkali.

In addition to the above-mentioned components, for example, the following components may also be contained.

B ₂ O ₃ is a component that improves meltability and resistance to devitrification. On the other hand, since the strain point and Young's modulus are lowered, it is likely to cause an increase in the thermal shrinkage rate or a shift in the distance between the panel manufacturing steps. Therefore, _{the content of B 2} O ₃ is preferably 9% or less, 8% or less, 7% or less, 6% or less, 5% or less, 4% or less, 3% or less, especially 2% or less.

TiO ₂ has the effect of increasing Young's modulus. On the other hand, the devitrification resistance may deteriorate and the glass may be colored. Therefore, _{the content of TiO 2} is preferably 2% or less, 1% or less, 0.5% or less, especially 0.1% or less.

SiO ₂ is a component that forms the framework of the glass, and is a component that increases the strain point, and further is a component that improves acid resistance. On the other hand, if _{the content of SiO 2} is large, the viscosity at high temperature will increase and the meltability will decrease, devitrification crystals such as cristobalite are likely to be precipitated, and the liquidus temperature will increase. In addition, the etching rate using HF (Hydrofluoric Acid) will also decrease. Therefore, _{the content of SiO 2} is preferably 55 to 70%, 58 to 65%, especially 59 to 62%.

Al ₂ O ₃ is a component that forms the framework of the glass, and it is a component that increases the strain point, and further is a component that increases the Young's modulus. On the other hand, if _{the content of Al 2} O ₃ is large, devitrification crystals of mullite or feldspar are likely to be precipitated, and the liquidus temperature becomes higher. Therefore, _{the content of Al 2} O ₃ is preferably 8-30%, 15-25%, 17-23%, 18-22%, 18-21%, especially 18-20%.

MgO is a component that reduces high temperature viscosity, improves meltability, and improves Young's modulus. On the other hand, if the content of MgO is large, it will promote the precipitation of mullite or crystals derived from Mg and Ba and cristobalite. In addition, the strain point will be significantly reduced. Therefore, the content of MgO is preferably 0-10%, 2-6%, 2-5%, 2.5-5%, especially 2.5-4.5%.

CaO is a component that reduces high temperature viscosity and significantly improves meltability without lowering the strain point. In addition, since CaO is introduced into alkaline earth metal oxides and the raw material is relatively inexpensive, it is a component that reduces the cost of raw materials. Furthermore, it is to improve the composition of Young's modulus. In addition, CaO has the effect of suppressing the precipitation of the above-mentioned devitrified crystals containing Mg. On the other hand, if the content of CaO is large, devitrification crystals of anorthite are likely to be precipitated, and the density is likely to increase. Therefore, the content of CaO is preferably 0-10%, 2-8%, 3-7%, 3.5-6%, especially 3.5-5.5%.

MgO/CaO is an important component ratio used to have both high resistance to devitrification and high specific Young's modulus. If the MgO/CaO is small, the Young's modulus tends to decrease. On the other hand, if the MgO/CaO is large, the liquidus temperature tends to rise along with the devitrification crystals containing Mg. Therefore, MgO/CaO is preferably 0 to 3, 0.4 to 1.5, 0.5 to 1.0, 0.5 to 0.9, especially 0.6 to 0.8. Here, "MgO/CaO" refers to the value obtained by dividing the content of MgO by the content of CaO.

SrO is a component that inhibits phase separation and improves resistance to devitrification. Furthermore, it reduces the high temperature viscosity and improves the meltability without lowering the strain point components. On the other hand, if the content of SrO is large, feldspar-based devitrification crystals are likely to precipitate in a glass system containing more CaO, and the devitrification resistance is likely to decrease. Furthermore, there is a tendency for the density to increase and the Young's modulus to decrease. Therefore, the content of SrO is preferably 0 to 15%, 0 to 10%, 0 to 5%, 0 to 4%, 0 to 3%, 0 to 2%, 0 to 1.5%, 0 to 1%, especially 0 to less than 1%.

BaO is a component in alkaline earth metal oxides that has a higher effect on inhibiting the precipitation of devitrified crystals of mullite or anorthite series. On the other hand, if the content of BaO is large, the density will increase, or the Young's modulus will tend to decrease, and the high temperature viscosity will become too high, and the meltability will tend to decrease. Therefore, the content of BaO is 0-15%, 6-12%, 7-11%, 8-10.7%, especially 9-10.5%.

Alkaline earth metal oxides are very important components for improving strain point, resistance to devitrification, and melting. If there are few alkaline earth metal oxides, the strain point will rise, but it is not easy to suppress _{the precipitation of devitrified crystals of the Al 2} O ₃ system, and the high temperature viscosity will increase and the meltability will tend to decrease. On the other hand, if there are more alkaline earth metal oxides, the meltability is improved, but the strain point tends to be lowered, and the viscosity of the liquid phase is lowered due to the lowering of the high-temperature viscosity. Therefore, MgO+CaO+SrO+BaO is preferably 10-40%, 16-20%, 17-20%, 17-19.5%, especially 18-19.3%. Here, "MgO+CaO+SrO+BaO" refers to the total amount of MgO, CaO, SrO, and BaO.

ZnO is a component that improves the meltability. However, if ZnO is contained in a large amount, the glass tends to devitrify and the strain point tends to decrease. Therefore, the content of ZnO is preferably 0-5%, 0-3%, 0-0.5%, especially 0-0.2%.

ZrO ₂ , Y ₂ O ₃ , Nb ₂ O ₅ , and La ₂ O ₃ have the effects of increasing the strain point and Young's modulus. However, if the content of these ingredients is large, the density is likely to increase. Therefore, _{the contents of ZrO 2} , Y ₂ O ₃ , Nb ₂ O ₅ , and La ₂ O ₃ are preferably 0 to 5%, 0 to 3%, 0 to 1%, 0 to less than 0.1%, especially 0. ~ Less than 0.05%.

SnO ₂ is a component that has a good clarification effect in the high temperature range, and it is a component that increases the strain point, and it is a component that reduces the high-temperature viscosity. On the other hand, if _{the content of SnO 2} is large, devitrification crystals of _{SnO 2} are likely to be precipitated. Therefore, _{the content of SnO 2} is preferably 0 to 1%, 0.001 to 1%, 0.01 to 0.5%, especially 0.05 to 0.3%.

In the range that does not impair the properties of the glass, F ₂ , Cl ₂ , SO ₃ , C, or up to 5% of metal powders such as Al and Si can be added as a clarifying agent. In addition, CeO ₂ or the like may be added up to 1% as a clarifying agent.

As ₂ O ₃ and Sb ₂ O ₃ are effective as fining agents. The glass substrate of the present invention does not completely exclude the introduction of these components, but from an environmental point of view, it is preferable not to use these components as much as possible. Furthermore, if a large amount of As ₂ O ₃ is contained in the glass, the exposure resistance tends to decrease, so the content thereof is preferably 0.1% or less, and in particular, it is not contained substantially. Here, "substantially not containing As ₂ O _{3 "means that the content of As 2} O ₃ in the glass composition is less than 0.05%. In addition, _{the content of Sb 2} O ₃ is preferably 0.2% or less and 0.1% or less, and especially not substantially contained. Here, "substantially not containing Sb ₂ O _{3 "means that the content of Sb 2} O ₃ in the glass composition is less than 0.05%.

Fe ₂ O ₃ is a component that is not easy to avoid mixing as impurities from glass raw materials. Therefore, the introduction of Fe ₂ O ₃ components cannot be completely excluded. Since it can also function as a fining agent, it may also be actively contained. However, in order to maintain the transmittance of the glass in the ultraviolet region as high as possible, the glass of the present invention preferably does not contain Fe ₂ O ₃ as much as possible. By increasing the transmittance in the ultraviolet region, the efficiency when using the laser in the ultraviolet region in the customer step can be improved. Specifically, the Fe ₂ O ₃ content in the glass composition is 0.020% or less, preferably 0.015% or less, more preferably 0.011% or less, and particularly preferably 0.010% or less.

Cl has the effect of promoting the melting of low-alkali glass. If Cl is added, the melting temperature can be lowered and the effect of the clarifier can be promoted. In addition, it has the effect of reducing the β-OH value of molten glass. On the other hand, if the content of Cl is large, it is easy to lower the strain point. Therefore, the content of Cl is preferably 0.5% or less, especially 0.001 to 0.2%. Furthermore, chlorides of alkaline earth metal oxides such as strontium chloride, or raw materials such as aluminum chloride can be used as Cl introduction materials.

The glass substrate of the present invention preferably has the following glass characteristics.

The surface potential after 300 seconds/initial surface potential is preferably 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.38 or less, 0.36 or less, 0.34 or less, 0.32 or less, especially 0.30 or less. In this way, the electric charge is easily diffused from the surface of the glass substrate, and the chargeability becomes low. As a result, abnormalities such as pattern shift are less likely to occur.

The heat shrinkage rate when the heat treatment is performed at 500°C for 1 hour is preferably 30 ppm or less, 20 ppm or less, especially 15 ppm or less. In this way, abnormalities such as pattern shift are less likely to occur. Furthermore, if the thermal shrinkage rate is too low, the production efficiency of the glass substrate is likely to decrease. Therefore, the thermal shrinkage rate is preferably 1 ppm or more, 2 ppm or more, 3 ppm or more, 4 ppm or more, especially 5 ppm or more.

The strain point is preferably 700°C or higher, 710°C or higher, especially 720°C or higher. If the strain point is low, the glass substrate is likely to heat shrink during the manufacturing process. Furthermore, the upper limit of the strain point is not particularly limited, but it is preferably 800°C or lower in consideration of the burden of manufacturing equipment.

Average thermal expansion coefficient in a temperature range of 30 ~ 380 ℃ of preferably 45 × 10 ^-7 / ℃ ^{less, 34 × 10 -7 ~ 43 ×} 10 -7 / ℃, especially ^{38 × 10 -7 ~ 41 × 10} - ⁷ /℃. If the average thermal expansion coefficient in the temperature range of 30-380°C is outside the above range, it will not match the thermal expansion coefficient of the surrounding components, and it is easy to cause peeling of the surrounding components or warping of the glass substrate. In addition, if the value is large, it is likely to cause a deviation of the pitch due to temperature unevenness during the heat treatment.

The higher the Young's modulus, the less deformable the glass substrate. The Young's modulus is preferably 73 GPa or more, 75 GPa or more, especially 77 GPa or more. On the other hand, a composition with a higher Young's modulus tends to deteriorate chemical resistance. Therefore, the Young's modulus is preferably 120 GPa or less, 110 GPa or less, 100 GPa or less, 95 GPa or less, 90 GPa or less, especially 88 GPa or less.

The Young’s modulus is preferably more than 29.5 GPa/g·cm ^-3 , 30 GPa/g·cm ^-3 or more, 30.5 GPa/g·cm ^-3 or more, 31 GPa/g·cm ^-3 or more, 31.5 GPa /g·cm ^-3 or more, especially 32 GPa/g·cm ^-3 or more. If it is higher than the Young's modulus, the glass substrate is likely to bend due to its own weight.

The liquidus temperature is preferably lower than 1350°C, 1300°C or lower, 1280°C or lower, especially 1260°C or lower. If the liquidus temperature is high, devitrification crystals will be generated during forming by the overflow down-draw method, etc., which tends to reduce the productivity of the glass substrate.

The liquid phase viscosity is preferably 10 ^4.0 dPa·s or more, 10 ^4.2 dPa·s or more, 10 ^4.4 dPa·s or more, 10 ^4.6 dPa·s or more, especially 10 ^4.8 dPa·s or more. If the viscosity of the liquid phase is low, devitrification crystals will be generated during forming by the overflow down-draw method, etc., which tends to reduce the productivity of the glass substrate.

The temperature when the high temperature viscosity is 10 ^2.5 dPa·s is preferably 1660°C or lower, 1640°C or lower, 1630°C or lower, especially 1620°C or lower. If the temperature becomes higher when the high-temperature viscosity is 10 ^2.5 dPa·s, it will be difficult for the glass to melt, and the manufacturing cost of the glass substrate will soar.

In the glass of the present invention, if the β-OH value is reduced, in addition to increasing the strain point, the thermal shrinkage rate can also be greatly reduced. The β-OH value is preferably 0.30/mm or less, 0.25/mm or less, 0.20/mm or less, 0.15/mm or less, especially 0.10/mm or less. If the β-OH value is too large, the strain point tends to decrease. Furthermore, if the β-OH value is too small, the meltability tends to decrease. Therefore, the β-OH value is preferably 0.01/mm or more, especially 0.02/mm or more.

As a method of reducing the β-OH value, the following methods can be cited. (1) Choose raw materials with lower water content. (2) Adding ingredients (Cl, SO _3, etc.) that reduce the amount of water in the glass. (3) Reduce the amount of moisture in the atmosphere in the furnace. (4) Pour N ₂ into the molten glass. (5) Use a small melting furnace. (6) Speed up the flow of molten glass. (7) The electrofusion method is adopted.

Here, "β-OH value" refers to the value obtained by measuring the transmittance of glass using FT-IR and using the following formula.

β-OH value = (1 / X) log ( T 1 / T 2) X: glass thickness (mm) T _1: reference wavelength of 3846 cm transmittance (%) of ^-1 T _2: hydroxyl absorption wavelength of 3600 cm ^{- 1} Minimum transmittance when nearby (%)

The etching rate using HF is preferably 0.8 μm/min or more, 0.9 μm/min or more, especially 1 μm/min or more. If the etching rate using HF is low, it is difficult to thin the glass substrate in the thinning step. Here, "HF etching rate" refers to the etching depth when a part of the mirror-polished glass surface is masked with polyimide tape and then etched with a 5 mass% HF aqueous solution at 20°C for 30 minutes Calculated value.

The glass substrate of the present invention preferably has a flat plate shape, and has an overflow confluence surface at the center part in the thickness direction of the plate. That is, it is preferable to form by an overflow down-draw method. The overflow down-draw method refers to a method in which molten glass is overflowed from both sides of a wedge-shaped refractory, while the overflowing molten glass is merged at the lower end of the wedge, and the side is stretched below to form a flat plate shape. In the overflow down-draw method, the surface that should be the surface of the glass substrate is not in contact with the refractory, and it is shaped as a free surface. Therefore, an unpolished glass substrate with good surface quality can be manufactured inexpensively, and it is easy to increase the area or reduce the thickness.

In addition to the overflow down-drawing method, for example, the orifice down-drawing method, the redrawing method, the float method, and the rolling method may be used to shape the glass substrate.

The thickness of the glass substrate is not particularly limited, but in order to make the device easier to reduce the weight, it is preferably 1.0 mm or less, 0.5 mm or less, 0.4 mm or less, 0.35 mm or less, especially 0.3 mm or less. On the other hand, if the plate thickness is too small, the glass substrate is likely to bend. Therefore, the thickness of the glass substrate is preferably 0.001 mm or more, especially 0.01 mm or more. Furthermore, the plate thickness can be adjusted by the flow rate during glass manufacturing or the drawing speed.

Next, the manufacturing method of a glass substrate is demonstrated.

The manufacturing steps of the glass substrate generally include: a melting step, a clarification step, a supply step, a stirring step, and a forming step. The melting step is a step of melting the glass batch material for preparing the glass raw material to obtain molten glass. The clarification step is a step in which the molten glass obtained in the melting step is clarified by the action of a clarifying agent. The supply step is a step of transferring molten glass between each step. The stirring step is a step of stirring the molten glass to homogenize it. The forming step is a step of forming molten glass into flat-plate-shaped glass. Furthermore, if necessary, a step other than the above, for example, a state adjustment step for adjusting the molten glass to a state suitable for molding may be introduced after the stirring step.

In the case of industrial production of the previous low-alkali glass, generally speaking, it is melted by heating with the combustion flame of a burner. The burner is usually arranged above the melting kiln, and uses fossil fuels, specifically liquid fuels such as heavy oil, or gas fuels such as LPG (Liquefied Petroleum Gas) as fuel. Combustion flames can be obtained by mixing fossil fuels with oxygen. However, in this method, since a large amount of water is mixed in the molten glass during melting, the β-OH value tends to increase. Therefore, when manufacturing the glass of the present invention, it is preferable to perform energization heating using a heating electrode, and it is preferable not to perform heating using a combustion flame of a burner, but to perform melting by energization heating using a heating electrode. Thereby, since it is difficult to mix moisture into the molten glass during melting, it is easy to lower the β-OH value. Furthermore, if energization heating using a heating electrode is performed, the energy per unit mass used to obtain the molten glass will be reduced, and the molten volatile matter will be reduced, so the environmental load can be reduced.

The energized heating using the heating electrode is preferably performed by applying an AC voltage to the heating electrode provided at the bottom or side of the melting furnace by contacting the molten glass in the melting furnace. The material used for the heating electrode is preferably one having heat resistance and corrosion resistance to molten glass. For example, tin oxide, molybdenum, platinum, rhodium, etc. can be used, and molybdenum is particularly preferred.

The glass substrate of the present invention does not contain a low-alkali glass containing more alkali metal oxides, and therefore has a higher resistivity. Therefore, when the energization heating using the heating electrode is applied to low-alkali glass, not only the molten glass, but also the refractory constituting the melting furnace may have current flowing, and the refractory constituting the melting furnace may be damaged at an early stage. In order to prevent this, as the refractory in the furnace, it is preferable to use a zirconia refractory with a higher resistivity, especially a zirconia electroformed brick, and the content _{of ZrO 2 in the zirconia refractory is preferably 85} Mass% or more, more preferably 90% by mass or more. [Example]

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

Tables 2 and 3 show examples (sample Nos. 1 to 23) and comparative examples (sample No. 24) of the present invention. Furthermore, in the table, "N.A." means not determined.

[Table 2] quality% 1 2 3 4 5 6 7 8 9 10 11 12 SiO ₂ 58.9 58.6 62.0 63.8 61.2 61.0 61.1 60.4 59.5 60.0 59.4 60.3 Al ₂ O ₃ 16.5 19.3 19.0 16.9 15.8 18.7 18.6 20.1 18.5 19.1 19.5 19.1 B ₂ O ₃ 10.3 6.5 6.2 0.3 0.0 0.7 0.7 3.4 2.9 2.9 2.9 3.1 MgO 0.3 2.5 0.8 1.8 0.0 3.2 3.4 3.7 4.2 3.7 3.3 3.7 CaO 8.0 6.3 7.2 5.9 8.7 5.0 3.8 5.5 4.8 5.5 5.4 5.5 SrO 4.5 0.5 2.5 0.8 1.9 0.6 3.2 2.5 2.0 3.1 0.8 2.7 BaO 0.5 5.7 1.5 10.0 11.4 10.1 8.7 3.9 7.2 4.6 7.9 4.6 TiO ₂ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.02 0.01 0.00 Li ₂ O 0.0001 0.0007 0.0001 0.0003 0.0001 0.0003 0.0009 0.0002 0.0005 0.0004 0.0007 0.0003 Na ₂ O 0.030 0.055 0.011 0.080 0.043 0.046 0.047 0.041 0.021 0.080 0.007 0.047 K ₂ O 0.74 0.35 0.57 0.26 0.78 0.45 0.30 0.40 0.55 0.83 0.55 0.81 SnO ₂ 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Na ₂ O/K ₂ O 0.04 0.16 0.02 0.31 0.06 0.10 0.16 0.10 0.04 0.10 0.01 0.06 Surface potential after 300 seconds/initial surface potential 0.12 0.31 0.20 0.41 0.25 0.35 0.38 0.24 0.30 0.28 0.31 0.23 Heat shrinkage rate [ppm] twenty one 19 18 13 12 12 13 15 17 17 16 16 Ps[℃] 654 687 708 742 747 749 746 725 718 722 727 726 Ta[℃] 709 743 768 802 804 808 806 782 775 778 784 783 Ts[℃] 944 977 1017 1051 1034 1043 1042 1007 1002 1006 1013 1010 α[x10 ^-7 /℃] 37.8 36.8 34.8 39.3 45.4 39.0 39.1 36.3 38.8 38.2 38.1 37.7 Density [g/cm ³ ] 2.459 2.521 2.466 2.617 2.643 2.638 2.686 2.551 2.596 2.569 2.588 2.561 Young's modulus [GPa] 73.0 78.0 77.0 81.0 83.3 83.4 80.0 83.0 82.4 82.3 82.1 82.4 Young’s modulus [Gpa·cm ³ /g] 29.7 30.9 31.2 31.0 31.5 31.6 29.8 32.5 31.7 32.1 31.7 32.2 TL[℃] 1084 1123 1174 1225 1221 1220 1213 1184 1158 1188 1181 1201 Log η[dPa·s] in TL 5.7 5.6 5.5 5.5 5.2 5.3 5.3 5.2 5.4 5.2 5.3 5.1 10 ^{Temperature at 4.5} dPa·s [℃] NA NA NA NA NA NA NA 1255 1250 1255 1262 1258 10 ^{Temperature at 4.0} dPa·s [℃] 1268 1285 1334 1401 1368 1365 1365 1314 1310 1314 1322 1318 10 ^{Temperature at 3.0} dPa·s [℃] 1428 1440 1497 1574 1542 1529 1528 1469 1465 1472 1481 1476 10 ^{Temperature at 2.5} dPa·s [℃] 1532 1540 1602 1682 1654 1634 1632 1567 1566 1572 1584 1576

[table 3] quality% 13 14 15 16 17 18 19 20 twenty one twenty two twenty three twenty four SiO ₂ 60.0 60.8 59.4 60.4 59.4 59.9 59.1 59.1 60.3 59.2 60.3 64.1 Al ₂ O ₃ 19.3 19.4 17.5 18.1 18.9 18.7 10.0 21.0 22.3 20.9 22.1 16.9 B ₂ O ₃ 3.0 4.6 5.6 2.7 3.7 1.9 25.0 3.1 0.0 3.1 0.0 0.3 MgO 3.7 3.0 1.8 2.7 2.9 3.2 1.0 3.6 4.7 3.5 4.7 1.8 CaO 5.3 4.3 5.9 4.6 5.0 4.3 4.0 5.0 0.0 4.9 0.0 5.9 SrO 2.6 4.9 3.9 3.5 1.9 2.7 0.0 3.1 12.1 3.0 12.0 0.8 BaO 5.2 1.8 4.8 7.3 7.4 8.3 0.0 4.5 0.0 4.5 0.0 10.0 TiO ₂ 0.00 0.00 0.01 0.02 0.03 0.02 0.00 0.00 0.00 0.00 0.00 0.00 Li ₂ O 0.0008 0.0002 0.0001 0.0007 0.0005 0.0000 0.0008 0.0001 0.0003 0.0008 0.0008 0.0006 Na ₂ O 0.034 0.073 0.098 0.072 0.045 0.083 0.027 0.088 0.067 0.005 0.013 0.023 K ₂ O 0.60 0.87 0.88 0.28 0.61 0.73 0.67 0.42 0.27 0.69 0.68 0.0009 SnO ₂ 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Na ₂ O/K ₂ O 0.06 0.08 0.11 0.26 0.07 0.11 0.04 0.21 0.25 0.01 0.02 25.56 Surface potential after 300 seconds/initial surface potential 0.17 0.26 0.16 0.32 0.21 0.24 0.18 0.25 0.39 0.29 0.21 0.87 Heat shrinkage rate [ppm] 16 16 19 15 16 14 28 15 11 18 12 13 Ps[℃] 723 722 695 721 716 733 573 724 772 708 757 742 Ta[℃] 780 780 753 780 774 791 630 780 829 764 813 802 Ts[℃] 1008 1013 988 1016 1008 1027 NA 1005 1048 992 1037 1051 α[x10 ^-7 /℃] 38.1 35.2 38.8 39.2 NA NA 32.2 38.6 37.2 40.6 39.6 39.3 Density [g/cm ³ ] 2.572 2.520 NA NA NA NA 2.217 2.573 2.631 2.576 2.628 2.617 Young's modulus [GPa] 82.5 80.3 NA NA NA NA 54.0 NA NA NA NA 81.0 Young’s modulus [Gpa·cm ³ /g] 32.1 31.9 NA NA NA NA NA NA NA NA NA 31.0 TL[℃] 1196 1208 1185 1195 1201 1200 1072 1181 1333 1210 1375 1225 Log η[dPa·s] in TL 5.1 5.1 5.1 5.3 5.0 5.2 5.6 5.2 4.1 4.8 3.8 5.5 10 ^{Temperature at 4.5} dPa·s [℃] 1256 1271 1251 1278 1260 1286 NA NA NA NA NA NA 10 ^{Temperature at 4.0} dPa·s [℃] 1316 1333 1314 1341 1320 1348 1266 1304 1350 1303 1346 1401 10 ^{Temperature at 3.0} dPa·s [℃] 1473 1495 1479 1505 1480 1513 1451 1457 1503 1463 1502 1574 10 ^{Temperature at 2.5} dPa·s [℃] 1575 1601 1586 1608 1584 1620 1565 1556 1600 1570 1602 1682

First, add the glass batch material of the prepared glass raw material to the platinum crucible so as to become the glass composition in the table, and melt it at 1600-1650°C for 24 hours. When the glass batch is melted, use a platinum stirrer to stir and homogenize. Then, the molten glass was flowed out onto the carbon plate and formed into a plate shape, and then slowly cooled at a temperature near the cooling point for 30 minutes. The following evaluations were performed on each sample obtained: surface potential after 300 seconds/initial surface potential, heat shrinkage rate, strain point Ps, slow cooling point Ta, softening point Ts, average in the temperature range of 30 to 380°C Thermal expansion coefficient α, density, Young's modulus, specific Young's modulus, liquidus temperature TL, liquid viscosity at TL log η, high temperature viscosity at 10 ^4.5 dPa·s, high temperature viscosity at 10 ^4.0 dPa·s Temperature, high temperature viscosity 10 ^3.0 dPa·s temperature, high temperature viscosity 10 ^2.5 dPa·s temperature.

The surface potential after 300 seconds/initial surface potential is measured by the method described above.

The heat shrinkage rate is measured by the method already mentioned.

The strain point Ps, the slow cooling point Ta, and the softening point Ts are values measured based on the methods of ASTM C336 and C338.

The average coefficient of thermal expansion α in the temperature range of 30～380℃ is the value measured with a thermal dilatometer.

The density is a value measured according to the well-known Archimedes method.

Young's modulus is a value measured using the well-known resonance method. The Young's modulus is the value obtained by dividing the Young's modulus by the density.

Liquid phase temperature TL is to add glass powder that has passed through a standard sieve of 30 mesh (mesh mesh 500 μm) and remains on 50 mesh (mesh mesh 300 μm) into a platinum boat, and kept in a temperature gradient furnace for 24 hours to measure crystallization (Early phase) The value of the temperature at the time of precipitation.

The liquidus viscosity log ₁₀ ηTL is the value of the viscosity of the glass when the liquidus temperature TL is measured by the platinum ball pulling method.

The high temperature viscosity at 10 ^4.5 dPa·s, 10 ^4.0 dPa·s, 10 ^3.0 dPa·s and 10 ^2.5 dPa·s is the value measured by the platinum ball pulling method.

According to the table, it can be seen that the surface potential after 300 seconds/initial surface potential of sample Nos. 1 to 23 is 0.74 or less, and the chargeability is low, and it is considered that it can be preferably used as a substrate for organic EL displays. On the other hand, since _{the content of K 2} O in sample No. 24 is relatively small, the surface potential after 300 seconds/the initial surface potential is 0.87, and the chargeability is high.

For reference, other glass composition examples of the glass substrate of the present invention are shown in Tables 4 and 5.

[Table 4] quality% 25 26 27 28 29 30 31 32 33 34 35 36 SiO ₂ 60.4 60.8 60.6 60.5 62.7 62.6 62.2 61.5 63.1 63.1 62.5 62.0 Al ₂ O ₃ 18.5 18.5 18.5 18.5 17.6 17.7 17.6 17.7 17.5 16.2 17.6 17.6 B ₂ O ₃ 0.7 0.6 0.5 0.5 0.0 0.0 0.8 0.8 0.0 0.0 0.9 0.8 MgO 3.4 3.4 3.4 3.4 3.3 3.3 3.3 3.3 3.1 3.2 2.8 2.8 CaO 3.8 3.8 3.8 3.8 4.5 4.5 4.5 4.5 4.6 4.9 4.6 4.5 SrO 3.3 3.3 3.3 3.4 1.9 1.9 1.9 1.9 2.2 2.4 2.1 1.9 BaO 9.0 9.0 9.0 9.0 9.4 9.4 9.4 9.4 9.1 9.6 8.9 9.4 TiO ₂ 0.00 0.01 0.04 0.03 0.02 0.01 0.00 0.00 0.00 0.00 0.00 0.00 Li ₂ O 0.0004 0.0008 0.0009 0.0005 0.0000 0.0001 0.0002 0.0008 0.0010 0.0003 0.0004 0.0009 Na ₂ O 0.017 0.065 0.055 0.022 0.016 0.047 0.039 0.051 0.035 0.055 0.070 0.044 K ₂ O 0.78 0.41 0.66 0.79 0.30 0.26 0.06 0.54 0.19 0.27 0.37 0.76 SnO ₂ 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.3 0.4 0.3 0.2 Na ₂ O/K ₂ O 0.02 0.16 0.08 0.03 0.05 0.18 0.61 0.09 0.18 0.20 0.19 0.06 Surface potential after 300 seconds/initial surface potential NA NA NA NA NA NA NA NA NA NA NA NA Heat shrinkage rate [ppm] NA NA NA NA NA NA NA NA NA NA NA NA Ps[℃] NA NA NA NA NA NA NA NA NA NA NA NA Ta[℃] NA NA NA NA NA NA NA NA NA NA NA NA Ts[℃] NA NA NA NA NA NA NA NA NA NA NA NA α[x10 ^-7 /℃] NA NA NA NA NA NA NA NA NA NA NA NA Density [g/cm ³ ] NA NA NA NA NA NA NA NA NA NA NA NA Young's modulus [GPa] NA NA NA NA NA NA NA NA NA NA NA NA Young’s modulus [Gpa·cm ³ /g] NA NA NA NA NA NA NA NA NA NA NA NA TL[℃] NA NA NA NA NA NA NA NA NA NA NA NA Log η[dPa·s] in TL NA NA NA NA NA NA NA NA NA NA NA NA 10 ^{Temperature at 4.5} dPa·s [℃] NA NA NA NA NA NA NA NA NA NA NA NA 10 ^{Temperature at 4.0} dPa·s [℃] NA NA NA NA NA NA NA NA NA NA NA NA 10 ^{Temperature at 3.0} dPa·s [℃] NA NA NA NA NA NA NA NA NA NA NA NA 10 ^{Temperature at 2.5} dPa·s [℃] NA NA NA NA NA NA NA NA NA NA NA NA

[table 5] quality% 37 38 39 40 41 42 43 44 SiO ₂ 60.2 62.0 62.2 60.7 62.3 62.5 62.2 61.9 Al ₂ O ₃ 19.0 17.5 17.7 19.1 17.6 17.6 17.6 19.2 B ₂ O ₃ 0.8 0.8 0.8 0.8 0.8 0.8 0.8 1.8 MgO 3.2 3.2 2.8 3.2 3.2 2.8 2.8 2.9 CaO 4.5 4.5 4.5 4.5 4.5 4.6 4.6 4.0 SrO 1.9 1.9 1.9 1.9 1.9 2.1 2.1 2.1 BaO 9.3 9.3 9.4 9.4 9.4 8.9 8.9 7.9 TiO ₂ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Li ₂ O 0.0005 0.0006 0.0006 0.0008 0.0006 0.0005 0.0004 0.0009 Na ₂ O 0.098 0.093 0.044 0.032 0.025 0.026 0.065 0.071 K ₂ O 0.72 0.43 0.46 0.14 0.09 0.72 0.53 0.29 SnO ₂ 0.2 0.2 0.2 0.2 0.2 0.3 0.3 0.2 Na ₂ O/K ₂ O 0.14 0.22 0.09 0.23 0.28 0.04 0.12 0.25 Surface potential after 300 seconds/initial surface potential NA NA NA NA NA NA NA NA Heat shrinkage rate [ppm] NA NA NA NA NA NA NA NA Ps[℃] NA NA NA NA NA NA NA NA Ta[℃] NA NA NA NA NA NA NA NA Ts[℃] NA NA NA NA NA NA NA NA α[x10 ^-7 /℃] NA NA NA NA NA NA NA NA Density [g/cm ³ ] NA NA NA NA NA NA NA NA Young's modulus [GPa] NA NA NA NA NA NA NA NA Young’s modulus [Gpa·cm ³ /g] NA NA NA NA NA NA NA NA TL[℃] NA NA NA NA NA NA NA NA Log η[dPa·s] in TL NA NA NA NA NA NA NA NA 10 ^{Temperature at 4.5} dPa·s [℃] NA NA NA NA NA NA NA NA 10 ^{Temperature at 4.0} dPa·s [℃] NA NA NA NA NA NA NA NA 10 ^{Temperature at 3.0} dPa·s [℃] NA NA NA NA NA NA NA NA 10 ^{Temperature at 2.5} dPa·s [℃] NA NA NA NA NA NA NA NA

Figure 1 (a) ~ (c) are explanatory diagrams for explaining the method of measuring thermal shrinkage. Figure 2 shows the measurement results of the electrification of glass A, B, and C.

Claims (12)

A glass substrate, characterized in that: as a glass composition, it contains less than 0.03% of _{Li 2} O, 0.001 to 0.1% of _{Na 2 O, and 0.001 to 1% of K 2} O in terms of mass %, and in terms of mass ratio, Na ₂ O /K ₂ O is less than 1. Such as the glass substrate of claim 1, as a glass composition, it contains B ₂ O ₃ 9% or less in mass %. Such as the glass substrate of claim 1 or 2, as a glass composition, it contains 2% or less of _{TiO 2 in terms of mass %.} For the glass substrate of any one of claims 1 to 3, its surface potential after 300 seconds/initial surface potential is 0.8 or less. The glass substrate of any one of claims 1 to 4 has a heat shrinkage rate of 30 ppm or less when it is heat-treated at 500°C for 1 hour. For the glass substrate of any one of claims 1 to 5, its strain point is 700°C or higher. Such as the glass substrate of any one of claims 1 to 6, the average coefficient of thermal expansion at 30 to 380°C is 45×10 ^-7 /°C or less. For example, the glass substrate of any one of claims 1 to 7 has a Young's modulus of 73 GPa or more. For example, the glass substrate of any one of claims 1 to 8 has a liquid phase viscosity of 10 ^4.0 dPa·s or more. For example, the glass substrate of any one of claims 1 to 9 has a β-OH value of 0.30/mm or less. For example, the glass substrate of any one of claims 1 to 10 has a plate thickness of 0.01 to 1.0 mm. A method for manufacturing a glass substrate, which is characterized in that the glass substrate according to any one of claims 1 to 11 is manufactured by an overflow down-draw method.

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