CN105992749B

CN105992749B - Alkali-free glass substrate and method for thinning alkali-free glass substrate

Info

Publication number: CN105992749B
Application number: CN201480065338.3A
Authority: CN
Inventors: 德永博文; 小野和孝
Original assignee: Asahi Glass Co Ltd
Current assignee: AGC Inc
Priority date: 2013-11-28
Filing date: 2014-11-26
Publication date: 2020-11-03
Anticipated expiration: 2034-11-26
Also published as: KR102249898B1; WO2015080171A1; KR20160091332A; CN105992749A; JPWO2015080171A1; TW201529518A; TWI639571B; JP6447510B2

Abstract

The present invention relates to an alkali-free glass substrate which is thinned by hydrofluoric acid (HF) etching treatment to a thickness of 5 [ mu ] m or more and a thickness of 0.4mm or less, wherein the alkali-free glass substrate is a predetermined alkali-free glass, and the thinned alkali-free glass substrate has a specific modulus of 31MNm/kg or more and a photoelastic constant of 30nm/MPa/cm or less.

Description

Alkali-free glass substrate and method for thinning alkali-free glass substrate

Technical Field

The present invention relates to an alkali-free glass substrate which is thinned by etching treatment using hydrofluoric acid (HF) and does not substantially contain an alkali metal oxide, and a method for thinning the alkali-free glass substrate, which are suitable as various glass substrates for displays and glass substrates for photomasks.

Background

Conventionally, various glass substrates for displays, particularly glass substrates having a metal, oxide thin film or the like formed on the surface thereof, have been required to have the following characteristics.

(1) When an alkali metal oxide is contained, alkali metal ions are substantially not contained because the alkali metal ions diffuse into the thin film to deteriorate the film characteristics.

(2) The strain point is high so that the shrinkage (thermal shrinkage) associated with the deformation of the glass and the structural stabilization of the glass can be minimized when exposed to high temperatures in the film forming process.

(3) Sufficient chemical durability is required for various chemicals used in semiconductor formation. In particular, it is required to have durability against buffered hydrofluoric acid (BHF: a mixed solution of hydrofluoric acid and ammonium fluoride) used for etching SiOx and SiNx, a chemical solution containing hydrochloric acid used for etching ITO, various acids (nitric acid, sulfuric acid, etc.) used for etching a metal electrode, and an alkali of a resist stripping solution.

(4) The interior and the surface are free from defects (bubbles, striae, inclusions, pits, scars, etc.).

In addition to the above-described requirements, the following situation has arisen in recent years.

(5) The display is required to be lightweight, and it is desirable that the glass itself is also a low-density glass.

(6) The display is required to be lightweight, and thinning of the glass substrate is desired.

(7) In addition to conventional amorphous silicon (a-Si) type liquid crystal displays, polysilicon (p-Si) type liquid crystal displays (a-Si: about 350 ℃ → p-Si: 350 to 550 ℃) having a slightly higher heat treatment temperature were produced.

(8) Glass having a small average thermal expansion coefficient is required for increasing the rate of temperature rise and temperature fall in heat treatment during the production of liquid crystal displays, thereby improving productivity or improving thermal shock resistance.

On the other hand, dry etching has been developed, and the requirement for BHF resistance is reduced. In order to improve the BHF resistance, the glass containing 6 to 10 mol% of B has been used in many cases₂O₃The glass of (2). However, B₂O₃There is a tendency that the strain point is lowered. As containing no B₂O₃Or B₂O₃Examples of the alkali-free glass having a small content include the following alkali-free glasses.

Patent document 1 discloses that B is contained in an amount of 0 to 5 mol%₂O₃The glass of (2) but having an average coefficient of thermal expansion of more than 50X 10 at 50 to 350 DEG C^-7/℃。

The alkali-free glass described in patent document 2 has a high strain point, can be formed by a float process, and is considered to be suitable for applications such as a display substrate and a photomask substrate.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 5-232458

Patent document 2: japanese laid-open patent publication No. 10-45422

Patent document 3: japanese re-publication No. 2009-066624

Disclosure of Invention

Problems to be solved by the invention

On the other hand, in the field of small and medium-sized Liquid Crystal Displays (LCDs), organic EL displays (OELDs), and particularly portable displays such as mobile devices, digital cameras, and mobile phones, weight reduction and thickness reduction of the displays have become important issues. In order to further reduce the thickness of the glass substrate, the following steps are widely adopted: after the array color filter bonding step, the surface of the glass substrate is subjected to etching treatment to reduce the thickness (thickness) of the glass substrate. For example, the following steps are performed: a surface of a glass substrate having a thickness of 0.4mm to 0.7mm is subjected to etching treatment (hereinafter referred to as "hydrofluoric acid etching treatment") using an etching solution containing hydrofluoric acid (HF) to produce a glass substrate having a thickness of 0.1mm to 0.4mm (see patent document 3).

When the glass substrate is thinned by the hydrofluoric acid etching treatment, it is required that: (1) the etching speed is high during the hydrofluoric acid etching treatment; and (2) the glass substrate after the etching treatment should have sufficient strength.

However, although there is a solid-phase crystallization method as a method for manufacturing a high-quality p-Si TFT, in order to implement this method, it is required to further increase the strain point.

In addition, it is necessary to reduce the viscosity of glass, particularly the viscosity of glass by 10, based on the requirements of the glass manufacturing process, particularly melting and forming⁴Temperature T at dPa · s₄。

The object of the present invention is to solve the above-mentioned disadvantages and to provide a glass having a high strain point and a low viscosity, in particular a glass viscosity of up to 10⁴Temperature T at dPa · s₄Low, high etching rate in hydrofluoric acid etching treatment, high strength after hydrofluoric acid etching treatment, less likely to be bent even when it is thin, and high durabilityAn alkali-free glass substrate and a method for thinning an alkali-free glass substrate, wherein the problems of color unevenness and the like are not easily caused by stress.

Means for solving the problems

The present invention provides an alkali-free glass substrate which is thinned by hydrofluoric acid (HF) etching treatment to a thickness of 5 [ mu ] m or more and a thickness of 0.4mm or less, wherein the alkali-free glass substrate is alkali-free glass, and the thinned alkali-free glass substrate has a specific modulus of 31MNm/kg or more and a photoelastic constant of 30nm/MPa/cm or less.

The alkali-free glass has a strain point of 680-735 ℃ and an average thermal expansion coefficient of 30 x 10 at 50-350 DEG C^-7～43×10^-7At/° C, the glass viscosity reaches 10²Temperature T at dPa · s₂The glass viscosity reaches 10 at the temperature of below 1710 DEG C⁴Temperature T at dPa · s₄Is 1310 ℃ or lower, contains in mole% on the basis of oxides:

15.5 to 21 parts of MgO + CaO + SrO + BaO,

MgO/(MgO + CaO + SrO + BaO) is 0.35 or more, CaO/(MgO + CaO + SrO + BaO) is 0.50 or less, and SrO/(MgO + CaO + SrO + BaO) is 0.50 or less.

The alkali-free glass substrate of the present invention preferably has an average breaking load of 300N or more in terms of a thickness of 0.4mm, as measured by a ball and ring (BOR) method using a ring having a diameter of 30mm and an R of 2.5mm and a ball having a diameter of 10 mm.

In addition, the invention provides a thinning method of the alkali-free glass substrate, wherein,

the alkali-free glass substrate is an alkali-free glass in which the amount of elution per unit area and unit time when at least one main surface of the alkali-free glass substrate is immersed in an etching solution (25 ℃, 5% aqueous HF solution) containing hydrofluoric acid (HF) is 0.17 (mg/cm)²) More than minuteUnder the condition, the alkali-free glass substrate is thinned by more than 5 μm.

15.5 to 21 parts of MgO + CaO + SrO + BaO,

Effects of the invention

The alkali-free glass substrate has high strain point and glass viscosity of 10⁴Temperature T at dPa · s₄Low in etching rate during hydrofluoric acid etching treatment, high in strength after hydrofluoric acid etching treatment, hardly flexible even if thin, and hardly causes problems such as color unevenness even if stress is applied, and therefore, is suitable as a thin glass substrate having a thickness of 0.4mm or less used in the fields of small and medium-sized LCDs, OLEDs, and particularly portable displays such as mobile devices, digital cameras, and cellular phones. The alkali-free glass substrate of the present invention can also be used as a glass substrate for a magnetic disk.

Detailed Description

The method for thinning an alkali-free glass substrate of the present invention will be described below.

In the method for thinning an alkali-free glass substrate of the present invention, an alkali-free glass substrate using a glass raw material prepared so as to have a glass composition described below is used.

The strain point of the alkali-free glass is 680 to735 ℃ and has an average thermal expansion coefficient of 30 x 10 at 50-350 DEG C^-7～43×10^-7At/° C, the glass viscosity reaches 10²Temperature T at dPa · s₂The glass viscosity reaches 10 at the temperature of below 1710 DEG C⁴Temperature T at dPa · s₄Is 1310 ℃ or lower, contains in mole% on the basis of oxides:

15.5 to 21 parts of MgO + CaO + SrO + BaO,

The composition ranges of the respective components will be described below. SiO 2₂When the content is less than 63% (mol%, the same applies unless otherwise specified), the strain point cannot be sufficiently increased, the thermal expansion coefficient increases, and the density increases. Preferably 64% or more, more preferably 65% or more, further preferably 66% or more, and particularly preferably 66.5% or more. Preferably 66.5% or more, more preferably 67% or more. When the content exceeds 74%, the etching rate decreases, the meltability of the glass decreases, and the devitrification temperature increases. Preferably 70% or less, more preferably 69% or less, and still more preferably 68% or less.

Al₂O₃The Young's modulus is increased, the deflection after thinning is suppressed, the phase separation property of the glass is suppressed, the thermal expansion coefficient is decreased, the strain point is increased, and the fracture toughness value is increased to improve the glass strength, but when the value is less than 11.5%, this effect is not exhibited, and other components increasing the expansion are increased, and as a result, the thermal expansion is increased. Preferably 12% or more, preferably 12.5% or more, and more preferably 13% or more. When the amount exceeds 16%, the glass may have poor melting properties or the devitrification temperature may be increased. Preferably 15% or less, more preferably 14% or less, and still more preferably 13.5% or less.

B₂O₃The glass has improved melting reactivity, reduced devitrification temperature, and improved BHF resistance, but if the content is 1.5% or less, the effect is not sufficiently exhibited, and the strain point becomes too high, or haze tends to occur after the treatment with BHF. Preferably 2% or more, more preferably 3% or more. However, if the amount is too large, the photoelastic constant becomes large, and when stress is applied, problems such as color unevenness tend to occur. In addition, B₂O₃If the amount exceeds 5%, the surface roughness after thinning becomes large, and the strength after thinning becomes low. Further, the strain point is lowered and the Young's modulus is decreased. Preferably 4.5% or less, more preferably 4% or less.

MgO increases the young's modulus without increasing the specific gravity, and therefore, by increasing the specific modulus, the problem of flexure can be reduced. In addition, alkaline earth metals are characterized by not increasing the expansion and not excessively lowering the strain point, and also by improving the meltability. In addition, the fracture toughness value is improved to improve the glass strength. However, if the content is less than 5.5%, the effect is not sufficiently exhibited, and the density becomes high because the content of other alkaline earth metals becomes high. Preferably 6% or more, further 7% or more, more preferably 7.5% or more, 8% or more, further more than 8%, preferably 8.1% or more, further 8.3% or more, and particularly preferably 8.5% or more. Above 13% devitrification temperature may rise. Preferably 12% or less, more preferably 11% or less, and particularly preferably 10% or less.

Among alkaline earth metals, CaO has a characteristic of increasing the specific modulus, not increasing the expansion, maintaining the density low, and not excessively lowering the strain point, next to MgO, and also improves the meltability. If the content is less than 1.5%, the effect of the addition of CaO as described above is not exhibited. Preferably 2% or more, more preferably 3% or more, still more preferably 3.5% or more, and particularly preferably 4% or more. However, if the amount exceeds 12%, the devitrification temperature may rise or a large amount of limestone (CaCO) as a CaO raw material may be mixed₃) The impurity in (1) is phosphorus. Preferably 10% or less, more preferably 9% or less, still more preferably 8% or less, and particularly preferably 7% or less.

SrO improves the meltability without increasing the devitrification temperature of the glass, but when it is less than 1.5%, the effect is not sufficiently exhibited. Preferably 2% or more, more preferably 2.5% or more, and further preferably 3% or more. However, when it exceeds 9%, the expansion coefficient may increase. Preferably 7% or less, more preferably 6% or less, 5% or less.

BaO is not essential, but may be contained for improving the meltability. However, if too much, the expansion and density of the glass will increase too much, so the amount is set to 1% or less. Preferably less than 1%, more preferably 0.5% or less, and even more preferably substantially none. Substantially free means free from unavoidable impurities.

ZrO may be contained in an amount of at most 2% for the purpose of increasing Young's modulus, lowering glass melting temperature, or promoting crystal precipitation during firing₂. When the amount exceeds 2%, the glass becomes unstable or the relative dielectric constant of the glass increases. Preferably 1.5% or less, more preferably 1.0% or less, still more preferably 0.5% or less, and particularly preferably substantially not contained.

When the total content of MgO, CaO, SrO and BaO is less than 15.5%, the glass viscosity becomes 10⁴Temperature T at dPa · s₄The height of the float bath may be increased to extremely shorten the life of the housing structure and heater of the float bath during float forming. Further, the etching rate becomes slow, the photoelastic constant becomes large, and the meltability is lowered. Preferably 16% or more, and more preferably 17% or more. If it exceeds 21%, the thermal expansion coefficient may not be reduced. Preferably 20% or less, 19% or less, and further 18% or less.

When the total amount of MgO, CaO, SrO and BaO satisfies the above-mentioned conditions and the following conditions, the Young's modulus and the specific modulus can be increased without increasing the devitrification temperature, and the viscosity of the glass, particularly T, can be reduced₄。

MgO/(MgO + CaO + SrO + BaO) is 0.35 or more, preferably 0.37 or more, and more preferably 0.4 or more.

CaO/(MgO + CaO + SrO + BaO) is 0.50 or less, preferably 0.48 or less, and more preferably 0.45 or less.

SrO/(MgO + CaO + SrO + BaO) is 0.50 or less, preferably 0.40 or less, more preferably 0.30 or less, more preferably 0.27 or less, and further preferably 0.25 or less.

In the alkali-free glass of the present invention, Al is contained₂O₃X (MgO/(MgO + CaO + SrO + BaO)) is preferably 4.3 or more because the Young's modulus can be improved. Preferably 4.5 or more, more preferably 4.7 or more, and further preferably 5.0 or more.

Na may be added for the purpose of electrically-assisted heating or the like₂O、K₂And O and the like. When the content of the alkali metal oxide is increased, alkali metal ions diffuse in the thin film to deteriorate film characteristics, and therefore, the alkali metal ions are problematic when used as various display substrate glasses, but when the content of the alkali metal oxide in the glass composition is 2000 molar ppm or less, such a problem is less likely to occur. More preferably 1500 mol ppm or less, 1300 mol ppm or less, 1000 mol ppm or less.

In order to prevent deterioration of the characteristics of the metal or oxide thin film provided on the glass surface when producing a display using the alkali-free glass substrate of the present invention, it is preferable that the glass material contains substantially no P₂O₅. The amount of impurities mixed is preferably 23 mol ppm or less, more preferably 18 mol ppm or less, still more preferably 11 mol ppm or less, and particularly preferably 5 mol ppm or less. In addition, in order to make the glass easily reusable, it is preferable that the glass raw material does not substantially contain PbO or As₂O₃、Sb₂O₃。

In order to improve the melting property, the clarifying property and the formability of the glass, ZnO and Fe may be contained in an amount of 1% or less, preferably 0.5% or less, more preferably 0.3% or less, further preferably 0.15% or less, particularly preferably 0.1% or less, based on the total amount₂O₃、SO₃、F、Cl、SnO₂. Preferably, substantially no ZnO is contained.

The alkali-free glass substrate of the present invention is produced, for example, by the following steps.

The raw materials of each component are blended in a manner of reaching the target component, and the mixture is continuously put into a melting furnace and heated to 1500-1800 ℃ for melting. The forming apparatus for molten glass is used to form a plate-like glass ribbon having a predetermined thickness, and the glass ribbon is annealed and then cut to obtain an alkali-free glass substrate.

In the present invention, a glass ribbon formed into a plate shape by the float process is preferred.

In the method for thinning an alkali-free glass substrate of the present invention, the alkali-free glass substrate is thinned by 5 μm or more by performing hydrofluoric acid (HF) etching treatment on at least one of the two main surfaces of the alkali-free glass substrate. By thinning, the thickness of a display using an alkali-free glass substrate can be reduced, and the display can be made lightweight.

If a thin plate, that is, an alkali-free glass substrate having a small plate thickness is used from the beginning without being thinned by etching, handling of a large thin plate is necessary in a device manufacturing process or the like performed at the time of manufacturing a display, and therefore, problems such as conveyance failure due to self-weight deflection (for example, generation of a flaw on the substrate due to contact at the time of conveyance, the same applies hereinafter), breakage of the substrate, and the like are likely to occur. The thickness is preferably 10 μm or more, more preferably 100 μm or more, and particularly preferably 200 μm or more.

In the method for thinning an alkali-free glass substrate of the present invention, the thickness of the alkali-free glass substrate after thinning is 0.4mm or less. If the thickness is larger than 0.4mm, the effect of making the display light and thin cannot be obtained. More preferably 0.35mm or less, and still more preferably 0.25mm or less.

The thickness of the alkali-free glass substrate before thinning is preferably 0.3mm or more. If the thickness is less than 0.3mm, handling of a large thin plate is necessary in a device manufacturing process or the like, and problems such as conveyance failure and breakage due to deflection by its own weight tend to occur. More preferably 0.4mm or more, and particularly preferably 0.45mm or more. However, if the thickness exceeds 0.75mm, the time required for thinning the display to be light and thin may become too long. More preferably 0.65mm or less, and still more preferably 0.55mm or less.

The chemical liquid used for the etching process uses a chemical liquid containing hydrofluoric acid (HF). The etching treatment may be performed using an alkaline chemical liquid, but the chemical liquid containing hydrofluoric acid has a higher etching rate and can perform smoother etching. The concentration of hydrofluoric acid contained in the chemical liquid is more preferably 1% by mass or more, still more preferably 3% by mass or more, and particularly preferably 5% by mass or more. In addition to hydrofluoric acid, it is preferable to add an acid other than hydrofluoric acid such as hydrochloric acid, nitric acid, or sulfuric acid to the chemical solution.

In the etching treatment, at least one main surface of the alkali-free glass substrate is immersed in a chemical solution containing hydrofluoric acid. The alkali-free glass substrate is thinned by a predetermined amount by immersing for a predetermined time in accordance with the fluorine concentration in the chemical solution.

In the etching treatment, the chemical liquid is preferably fluidized by at least one of stirring, bubbling, ultrasonic wave and spraying. Instead of flowing the chemical liquid, the alkali-free glass substrate may be moved by at least one of shaking and rotation.

In the method for thinning an alkali-free glass substrate of the present invention, when immersed in 5 mass% hydrofluoric acid (HF) at 25 ℃, the amount of elution per unit area and unit time as an index of etching rate is 0.17 (mg/cm)²) The etching treatment is performed under the condition of more than one minute. If it is less than 0.17 (mg/cm)²) The time required for thinning may become too long per minute. More preferably 0.18 (mg/cm)²) More than one minute.

The alkali-free glass substrate thinned by the method of the invention has high strength after thinning. Specifically, the average breaking load measured on the main surface of the thinned alkali-free glass substrate on the side subjected to the etching treatment (the surface on the side to be evaluated) is preferably 300N or more in terms of the sheet thickness of 0.4mm by a ball and ring (BOR) method using a ring having a diameter of 30mm and an R of 2.5mm (the cross-section of the ring is a circle, and R is the radius of the circle) and a ball having a diameter of 10mm (the surface on the side to be evaluated is placed on the ring with the surface on the side to be evaluated facing downward). Here, the diameter of the ring is a diameter of a circle passing through the center of the cross section, and in the case of a ring having a diameter of 30mm and R of 2.5mm, the outermost diameter of the ring is 35mm and the innermost diameter is 25 mm.

The average breaking load is an average value of measurement results obtained by performing measurement of the breaking load by the BOR method a plurality of times. In the examples described later, the breaking load by the BOR method was measured 5 times, and the average value of the measurement results was defined as the average breaking load.

If the average breaking load measured by the BOR method is less than 300N in terms of a sheet thickness of 0.4mm, the surface strength of the alkali-free glass substrate is low, and the glass substrate is broken during handling during display manufacturing (for example, the glass substrate is broken during a step of lifting up the alkali-free glass substrate after device fabrication using support pins or the like), and the strength after thinning may become a problem. More preferably 350N or more.

The plate thickness conversion by the BOR method is performed in accordance with the following procedure.

In the BOR method, since the stress generated on the surface of the glass substrate is inversely proportional to the square of the plate thickness, when the plate thickness of the glass substrate is t (mm) and the breaking load obtained by the BOR method is W (n), the breaking load W (n) in terms of the plate thickness of 0.4mm can be represented by W ═ W × 0.16/t²The relational expression (c) was obtained.

In the alkali-free glass substrate thinned by the method of the present invention, the surface strength by three-point bending of the main surface (surface to be evaluated) on the side subjected to etching treatment of the thinned alkali-free glass substrate is preferably 500MPa or more. If the pressure is less than 500MPa, a display using the thinned alkali-free glass substrate may be easily broken when used as a portable display. More preferably 800MPa or more, still more preferably 1000MPa or more, particularly preferably 1200MPa or more, and most preferably 1500MPa or more.

The surface strength of the main surface (surface to be evaluated) of the thinned alkali-free glass substrate on the side subjected to the etching treatment by three-point bending was measured as follows. The glass substrate was scribed with a point scriber (point scriber) with the evaluation surface protected with a seal, and after cutting, the seal on the evaluation surface was torn off and set on a three-point bending jig with a span of 10mm and an R of 1.5mm with the non-scribed side down. The surface strength by three-point bending was calculated from the breaking load at the time of pressing from the scribe line side of the upper surface with a jig having an R of 1.5 mm.

If the evaluation surface is scratched, the strength is low, and therefore, the evaluation surface needs to be maintained in a state of not being in contact with the evaluation surface after thinning. In the bending test, when the fracture starting point exists on the end face, the end face strength is measured instead of the surface strength, and therefore the average fracture load is determined using only the test result when the starting point is located in the plane.

In the present specification, the environment in which the average breaking load is measured by the BOR method or by three-point bending is set to 22. + -. 2 ℃ and 40. + -. 10% humidity.

In the alkali-free glass substrate thinned by the method of the present invention, the surface roughness of the main surface of the etched side of the thinned alkali-free glass substrate is preferably 0.75nm or less in Ra of 1 μm square in AFM measurement. If the thickness exceeds 0.75nm, the strength of the alkali-free glass substrate may be lowered. More preferably 0.7nm or less.

The alkali-free glass substrate of the present invention has a strain point of 680 ℃ to 735 ℃.

Since the alkali-free glass substrate of the present invention has a strain point of 680 ℃ or higher, thermal shrinkage during panel production can be suppressed. In addition, a method using laser annealing can be applied as a method of manufacturing the p-Si TFT. More preferably 685 ℃ or higher, and still more preferably 690 ℃ or higher.

The alkali-free glass substrate of the present invention has a strain point of 680 ℃ or higher, and is therefore suitable for high strain point applications (for example, a display substrate or an illumination substrate for organic EL having a plate thickness of 0.7mm or less, preferably 0.5mm or less, more preferably 0.3mm or less, or a display substrate or an illumination substrate for a thin plate having a plate thickness of 0.3mm or less, preferably 0.1mm or less).

In the molding of a sheet glass having a thickness of 0.7mm or less, further 0.5mm or less, further 0.3mm or less, further 0.1mm or less, the drawing speed during molding tends to be high, so that the virtual temperature of the glass tends to increase, and the compression (compaction) of the glass tends to increase. In this case, the high strain point glass can suppress the compression.

On the other hand, if the strain point is 735 ℃ or lower, it is not necessary to set the temperature in the float bath and at the outlet of the float bath too high, and the influence on the life of the metal member located in the float bath and on the downstream side of the float bath is small. More preferably 725 ℃ or lower, still more preferably 715 ℃ or lower, and particularly preferably 710 ℃ or lower.

In addition, since the plane strain of the glass is improved, it is necessary to raise the temperature at the portion entering the lehr from the outlet of the float bath, but it is not necessary to set the temperature at this time too high. Therefore, a load is not imposed on the heater used for heating, and the life of the heater is less affected.

The glass transition temperature of the alkali-free glass substrate of the present invention is preferably 730 ℃ or higher, more preferably 740 ℃ or higher, and still more preferably 750 ℃ or higher, for the same reason as the strain point. Further, it is preferably 780 ℃ or lower, more preferably 775 ℃ or lower, and particularly preferably 770 ℃ or lower.

In addition, the alkali-free glass substrate has an average thermal expansion coefficient of 30 multiplied by 10 at 50-350 DEG C^-7～43×10^-7The temperature per DEG C is high in thermal shock resistance, and the productivity in manufacturing the panel can be improved. In the alkali-free glass substrate of the present invention, the average thermal expansion coefficient at 50 to 350 ℃ is preferably 35 × 10^-7Above/° c. The average thermal expansion coefficient at 50-350 ℃ is preferably 42 multiplied by 10^-7/° C or less, more preferably 41X 10^-7Preferably 40X 10 or less/° C^-7Below/° c.

Further, the specific gravity of the alkali-free glass substrate of the present invention is preferably 2.62 or less, more preferably 2.60 or less, and further preferably 2.58 or less.

The viscosity η of the alkali-free glass substrate of the present invention is 10²Temperature T in poise (dPa · s)₂The temperature is 1710 ℃ or lower, more preferably 1700 ℃ or lower, further preferably 1690 ℃ or lower, particularly preferably 1680 ℃ or lower and 1670 ℃ or lower, and therefore melting is easy.

Further, the viscosity η of the alkali-free glass substrate of the present invention is 10⁴Temperature T in poise₄Is 1310 ℃ or lower, preferably 1305 ℃ or lowerMore preferably 1300 ℃ or lower, still more preferably lower than 1300 ℃, 1295 ℃ or lower, and 1290 ℃ or lower, and is suitable for float molding.

In addition, the devitrification temperature of the alkali-free glass substrate of the present invention is preferably 1315 ℃ or lower, from the viewpoint of ease of deformation by the float process. Preferably 1300 ℃ or lower, less than 1300 ℃ or 1290 ℃ or lower, more preferably 1280 ℃ or lower. The temperature T is a reference value for float formability and fusion formability₄(the glass viscosity eta is 10)⁴Temperature at poise, unit: DEG C) and devitrification temperature (T)₄-devitrification temperature) is preferably-20 ℃ or more, -10 ℃ or more, further 0 ℃ or more, more preferably 10 ℃ or more, further preferably 20 ℃ or more, and particularly preferably 30 ℃ or more.

The devitrification temperature in the present specification is an average value of the highest temperature at which crystals are precipitated on the surface and inside of the glass and the lowest temperature at which crystals are not precipitated, as observed by an optical microscope after heat treatment performed for 17 hours in an electric furnace in which glass particles crushed by a platinum dish are charged and controlled to a constant temperature.

The alkali-free glass substrate of the present invention has a specific modulus of 31MNm/kg or more. If the amount is less than 31MNm/kg, problems such as conveyance failure and breakage due to deflection by its own weight tend to occur. Preferably 32MNm/kg or more, and more preferably 33MNm/kg or more.

The alkali-free glass substrate of the present invention has a young's modulus of preferably 78GPa or more, more preferably 79GPa or more, 80GPa or more, further 81GPa or more, and further preferably 82GPa or more.

The alkali-free glass substrate of the present invention preferably has a photoelastic constant of 30nm/MPa/cm or less.

In the liquid crystal display panel manufacturing process and the liquid crystal display device, the glass substrate has birefringence due to stress generated during use, and thus a phenomenon that black display becomes gray and the contrast of the liquid crystal display is lowered may be observed. This phenomenon can be suppressed to a small extent by setting the photoelastic constant to 30nm/MPa/cm or less. Preferably 29nm/MPa/cm or less, more preferably 28.5nm/MPa/cm or less, and still more preferably 28nm/MPa/cm or less.

In the alkali-free glass substrate of the present invention, the photoelastic constant is preferably 23nm/MPa/cm or more, more preferably 25nm/MPa/cm or more, from the viewpoint of easiness of securing other physical properties.

The photoelastic constant can be measured at a measurement wavelength of 546nm by a disk compression method.

The alkali-free glass substrate of the present invention preferably has a relative dielectric constant of 5.6 or more.

In the case of an in-cell touch panel (in which a touch sensor is provided in a liquid crystal display panel) as described in japanese patent application laid-open publication No. 2011-70092, the relative dielectric constant of the glass substrate is preferably high from the viewpoints of improvement in the sensitivity of the touch sensor, reduction in the driving voltage, and power saving. By setting the relative dielectric constant to 5.6 or more, the sensing sensitivity of the touch sensor is improved. Preferably 5.8 or more, more preferably 6.0 or more, further preferably 6.2 or more, and particularly preferably 6.4 or more.

The relative dielectric constant can be measured by the method described in JIS C-2141.

The alkali-free glass substrate of the present invention preferably has a small shrinkage amount during heat treatment. The liquid crystal panel manufacturing process differs from the color filter side thermal processing process on the array side. Therefore, in particular, in the case of a high-definition panel, when the thermal shrinkage rate of glass is large, there is a problem that a dot is shifted at the time of fitting. The thermal shrinkage rate can be evaluated in the following procedure. After the sample was held at a temperature of glass transition temperature +100 ℃ for 10 minutes, it was cooled to room temperature at 40 ℃ per minute. Here, the total length of the sample was measured (denoted as L)₀). Subsequently, the sample was heated at 100 ℃ per hour to 600 ℃, held at 600 ℃ for 80 minutes, cooled at 100 ℃ per hour to room temperature, and the total length of the sample was measured again, and the shrinkage (set to Δ L) of the sample before and after the heat treatment at 600 ℃ was measured. The ratio of the total length of the sample before heat treatment to the shrinkage (. DELTA.L/L)₀) The heat shrinkage rate was determined. In the above evaluation method, the heat shrinkage is preferably 100ppm or less, more preferably 80ppm or less, and further preferablyThe concentration is preferably 60ppm or less, more preferably 55ppm or less, and particularly preferably 50ppm or less.

Examples

(examples 1 to 6, comparative examples 1 and 2)

The raw materials of each component were blended so as to have the target compositions shown in table 1, and were melted in a continuous melting furnace and subjected to flat plate forming by the float method to obtain alkali-free glass substrates.

After mirror polishing of the obtained glass substrate, one surface of the glass substrate was etched while bubbling with a mixed acid of 8 mass% hydrofluoric acid and 10 mass% hydrochloric acid, so that the thickness of the glass substrate was reduced from 0.7mm to 0.4 mm.

Using the thinned glass substrate, 5 times of fracture load measurements were performed by a hoop (BOR) method using SUS rings having a diameter of 30mm and an R of 2.5mm and SUS balls having a diameter of 10mm, and the average fracture load in terms of sheet thickness of 0.4mm obtained from these measurement results is shown in table 2.

Further, the surface roughness of the etched surface was determined by the following method in the case where the plate thickness was etched by 30 μm in the same procedure as described above. The results are shown in table 2 below.

[ method for measuring surface roughness by AFM ]

The etched surface of the glass substrate was measured for surface roughness Ra of 1 μm square by using XE-HDM manufactured by Park Systems, Inc. with the scanning rate set at 1 Hz.

Further, as an index of the etching rate in the hydrofluoric acid etching treatment, the amount of elution per unit area and unit time when the alkali-free glass substrate was immersed in a hydrofluoric acid aqueous solution of 5 mass% at 25 ℃ was evaluated in the following procedure. The results are shown in table 2. Brackets indicate the calculated values.

[ measurement method of elution amount per unit area and unit time ]

The mirror-polished alkali-free glass substrate cut into a 40mm square was cleaned, and then the mass was measured. The sample was immersed in 5 mass% hydrofluoric acid at 25 ℃ for 20 minutes, and the mass after immersion was measured. The amount of elution per unit area and unit time was determined by calculating the surface area from the sample size, dividing the mass reduction by the surface area, and then dividing by the immersion time.

The alkali-free glass substrate obtained in the above-described procedure was also measured for strain point, young's modulus, specific modulus, photoelastic constant, and relative dielectric constant. The results are shown in table 2.

[ Table 1]

[ Table 2]

While the present invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the scope and spirit of the invention.

The present application is based on japanese patent application 2013-246801, filed on 11/28/2013, the contents of which are incorporated in the present specification by reference.

Claims

1. An alkali-free glass substrate which is an alkali-free glass substrate having a thickness of 0.4mm or less and which has been thinned by hydrofluoric acid etching treatment to a thickness of 5 [ mu ] m or more, wherein the alkali-free glass substrate has a specific modulus of 31MNm/kg or more and a photoelastic constant of 30nm/MPa/cm or less after thinning, and wherein the surface roughness of the main surface of the alkali-free glass substrate on the side subjected to etching treatment has an Ra of 1 [ mu ] m of 0.75nm or less in AFM measurement,

the alkali-free glass has a strain point of 680-720 ℃ and an average thermal expansion coefficient of 30 x 10 at 50-350 DEG C^-7～43×10^-7At/° C, the glass viscosity reaches 10²Temperature T at dPa · s₂The glass viscosity reaches 10 at the temperature of below 1710 DEG C⁴Temperature at dPa.sT₄At 1305 ℃ or below, containing, in mol% based on the oxides:

15.5 to 21 parts of MgO + CaO + SrO + BaO,

CaO/(MgO + CaO + SrO + BaO) is 0.50 or less, and SrO/(MgO + CaO + SrO + BaO) is 0.50 or less.

2. The alkali-free glass substrate according to claim 1, wherein the alkali-free glass substrate has an average breaking load of 300N or more in terms of thickness of 0.4mm as measured by a ball and ring method using a ring having a diameter of 30mm and an R of 2.5mm and a ball having a diameter of 10mm

The cross section of the ring is a circle, and R is the radius of the circle.

3. A method for thinning an alkali-free glass substrate,

the alkali-free glass substrate is an alkali-free glass in which the amount of elution per unit area and unit time when at least one main surface of the alkali-free glass substrate is immersed in an etching solution containing hydrofluoric acid is 0.17mg/cm²Thinning the alkali-free glass substrate by 5 [ mu ] m or more under a condition of/min or more, wherein the surface roughness of the main surface of the thinned alkali-free glass substrate on the side subjected to etching treatment has an Ra of 0.75nm or less at 1 [ mu ] m square in AFM measurement, and wherein the etching solution containing hydrofluoric acid is a 5 mass% HF aqueous solution at 25 ℃,

the alkali-free glass has a strain point of 680-720 ℃ and an average thermal expansion coefficient of 30 x 10 at 50-350 DEG C^-7～43×10^-7At/° C, the glass viscosity reaches 10²Temperature T at dPa · s₂The glass viscosity reaches 10 at the temperature of below 1710 DEG C⁴Temperature T at dPa · s₄At 1305 ℃ or below, containing, in mol% based on the oxides:

15.5 to 21 parts of MgO + CaO + SrO + BaO,