WO2013065648A1

WO2013065648A1 - Glass substrate, method for producing glass substrate, and cover glass

Info

Publication number: WO2013065648A1
Application number: PCT/JP2012/077918
Authority: WO
Inventors: 則史大森; 若月　博; 増田　賢一; 浩司中川; 拓海矢倉
Original assignee: 旭硝子株式会社
Priority date: 2011-10-31
Filing date: 2012-10-29
Publication date: 2013-05-10
Also published as: JP2015006959A; TW201326060A

Abstract

Provided is a glass substrate which has both excellent scratch strength and excellent bending strength. A glass substrate having a laminate configuration wherein a high expansion layer and a low expansion layer, which is thinner than the high expansion layer and has a lower thermal expansion coefficient than the high expansion layer, are laminated and the low expansion layer serves as a surface layer. This glass substrate comprises: a tensile stress layer that is formed of the high expansion layer in which a tensile stress is generated due to the laminate configuration; a laminate reinforcing layer that is formed of the low expansion layer in which a compressive stress is generated due to the laminate configuration; and a chemical reinforcing layer that is the outermost part of the low expansion layer serving as the surface layer, in said outermost part a compressive stress being generated by a chemical reinforcing treatment. The thickness of the chemical reinforcing layer is not more than the thickness of the laminate reinforcing layer.

Description

Glass substrate, method for producing glass substrate, and cover glass

The present invention relates to a glass substrate, a glass substrate manufacturing method, and a cover glass.

Conventionally, as tempered glass with increased mechanical strength, for example, [Claim 1] of Patent Document 1 states that “the inner layer having a thickness of 20 to 2000 μm and the thicknesses provided on both surface sides of the inner layer”. The surface layer has a thickness smaller than that of the inner layer, the thermal expansion coefficient of the surface layer is smaller than that of the inner layer, and at least the surface layer is substantially Without containing an alkali metal oxide, the surface layer and the inner layer are fused together to form a compressive stress of 50 MPa to 500 MPa on the surface layer, and a tensile stress of 30 to 200 MPa on the inner layer. The tempered glass sheet is characterized in that is formed.

Such a tempered glass in which a surface layer and an inner layer are laminated (hereinafter, this type of glass is referred to as a laminated type tempered glass) is also described in [0009] of Patent Document 1. The surface layer (that is, the surface layer made of glass having a relatively small thermal expansion coefficient) and the inner layer (that is, the inner layer made of glass having a relatively large thermal expansion coefficient) are fused to each other. As a result, compressive stress is generated in the surface layer and tensile stress is generated in the inner layer.

Japanese Unexamined Patent Publication No. 2011-93728

In recent years, mobile devices such as smartphones and tablet PCs have been widely used, and tempered glass with increased mechanical strength is expected to be used as a cover glass mounted on such mobile devices.

携帯 Portable devices such as smartphones may be carried in clothes pockets such as pants. Such a cover glass mounted on a portable device is required to have resistance to bending (that is, high bending strength) in addition to resistance to scratches caused by impacts and the like (that is, high scratch strength).

By the way, in the laminated type tempered glass as disclosed in Patent Document 1, the compressive stress layer formed on the surface layer is generally thick. That is, the depth of the compressive stress layer from the glass surface is large.
Therefore, it is said that this laminated type tempered glass is excellent in scratch strength. For example, even if a scratch of depth X ₁ μm is attached to the surface of the laminated type tempered glass, if the thickness X ₂ μm of the compressive stress layer is thicker than the scratch (X ₂ > X ₁ ), the scratch is tensile. Does not reach the stress layer. In this way, it is possible to prevent the laminate type tempered glass from cracking due to the scratches being extended by the tensile stress of the tensile stress layer.

However, the compression stress layer of laminated type tempered glass shows a constant stress value in the thickness direction, but its absolute value is relatively low, and the value is not high even in the vicinity of the outermost layer.
Therefore, this laminated type tempered glass is said to have insufficient bending strength. For example, when this type of tempered glass is bent, a tensile stress is applied to the compressive stress layer on one side. The tensile stress value (Y ₁ MPa) is the stress value of the compressive stress layer (Y ₂ MPa). If larger than (Y ₁ > Y ₂ ), the laminated type tempered glass will break.

The present invention has been made in view of the above points, and an object of the present invention is to provide a glass substrate excellent in both scratching strength and bending strength.

The present inventors have intensively studied to achieve the above object. As a result, the present inventors have found that the bending strength is excellent by forming another compressive stress layer having a high maximum stress value near the outermost surface of the laminated type tempered glass, thereby completing the present invention.

That is, the present invention provides a glass substrate having the following constitutions (1) to (16), a method for producing the glass substrate, and a cover glass.
(1) A high expansion layer (that is, a high expansion layer made of high expansion glass) and a low expansion layer that is thinner than the high expansion layer and has a smaller thermal expansion coefficient (that is, a low expansion layer made of low expansion glass). A glass substrate having a laminated structure in which the low expansion layer is a surface layer, the tensile stress layer formed by generating tensile stress in the high expansion layer by the laminated structure, and the laminated structure A laminated reinforcing layer formed by generating a compressive stress in the low expansion layer, and a chemical strengthening layer formed by generating a compressive stress by a chemical strengthening treatment in the vicinity of the outermost surface of the low expansion layer, which is a surface layer. , And the thickness of the chemical strengthening layer is equal to or less than the thickness of the laminated reinforcing layer.

(2) The glass substrate according to (1), wherein a difference in thermal expansion coefficient between the high expansion layer and the low expansion layer is 5 × 10 ⁻⁷ to 70 × 10 ⁻⁷ / K.

(3) It is composed of two low-expansion layers that are surface layers and one high-expansion layer that is an internal layer, and the total thickness (T _l ) of the low-expansion layers (2T _l ) and the above The glass substrate according to the above (1) or (2), wherein the ratio (2T ₁ / T _h ) to the thickness (T _h ) of the highly expanded layer is 0.05 to 1.5.

(4) The rate of change of the stress value with respect to the thickness direction of the chemical strengthening layer is greater than the rate of change of the stress value with respect to the thickness direction of the laminated reinforcing layer excluding the chemical strengthening layer. The glass substrate as described in any one of).

(5) The glass substrate according to any one of (1) to (4), wherein the maximum value of compressive stress in the chemical strengthening layer is 600 MPa or more in the low expansion layer which is a surface layer.
(6) The glass substrate according to any one of (1) to (5), wherein in the low expansion layer which is a surface layer, the maximum value of compressive stress in the chemical strengthening layer is 1200 MPa or less.

(7) In the low expansion layer which is a surface layer, the maximum value of the compressive stress in the laminated reinforcing layer excluding the chemical reinforcing layer is 400 MPa or less, according to any one of (1) to (6) above Glass substrate.
(8) The low expansion layer which is a surface layer, according to any one of (1) to (7), wherein the maximum value of compressive stress in the laminated reinforcing layer excluding the chemical strengthening layer is 5 MPa or more. Glass substrate.

(9) The glass substrate according to any one of (1) to (8), wherein the maximum value of tensile stress in the tensile stress layer is 200 MPa or less.

(10) The glass substrate according to any one of (1) to (9), wherein the low expansion layer is an alkali aluminosilicate glass layer.

(11) The glass substrate according to any one of (1) to (10), wherein a difference in refractive index between the high expansion layer and the low expansion layer is 0.1 or less.

(12) A method for producing a glass substrate, wherein the glass substrate according to any one of (1) to (11) above is obtained,
A laminating step of laminating the high expansion layer and the low expansion layer (that is, a laminating step of laminating the glass to be the high expansion layer and the glass to be the low expansion layer);
A chemical strengthening step for performing the chemical strengthening treatment on the low expansion layer which is a surface layer;
A method for producing a glass substrate comprising:

(13) It has a lamination process which manufactures a layered product whose inner layer is one high expansion layer, and the surface layer formed on both sides of the high expansion layer is a low expansion layer, The manufacturing method of the glass substrate as described in said (12) including the process of laminating | stacking the glass used as the said low expansion layer on the both surfaces side of the glass used as a high expansion layer.
(14) The chemical strengthening treatment includes pre-heat treatment, and the temperature of the chemical strengthening treatment is lower than the higher one of the glass transition temperatures of the high expansion layer and the low expansion layer, (12) or The manufacturing method of the glass substrate as described in (13).

(15) The method for producing a glass substrate according to (14), wherein the temperature of the chemical strengthening treatment is less than the lower one of the glass transition temperatures of the high expansion layer and the low expansion layer.

(16) A cover glass using the glass substrate according to any one of (1) to (11) above.
The term “to” indicating the above numerical range is used in the sense that the numerical values described before and after it are used as the lower limit value and the upper limit value. Unless otherwise specified, “to” is the same in the following specification. Used with meaning.

According to the present invention, it is possible to provide a glass substrate having excellent scratch strength and bending strength.

It is a conceptual diagram which shows the stress distribution state seen from the side surface side in the plate | board thickness direction of the glass substrate 1. FIG. 3 is a graph schematically showing a stress profile of the glass substrate 1. It is a graph which shows roughly the stress profile of the glass substrate of the comparative examples 1 and 2. FIG. It is a graph which shows roughly the stress profile of the glass substrate of the comparative examples 3 and 4. FIG.

[Glass substrate]
First, an aspect of the glass substrate of the present invention will be described. However, it goes without saying that the glass substrate of the present invention is not limited to the glass substrate 1 described below.

FIG. 1 is a conceptual diagram showing a stress distribution state in the plate thickness direction of the glass substrate 1. As shown in FIG. 1, the glass substrate 1 has a three-layer structure, and an inner layer 2 is disposed between a pair of surface layers 3. The thermal expansion coefficient of the glass layer of the surface layer 3 is smaller than the thermal expansion coefficient of the inner layer 2. That is, the surface layer 3 is a low expansion layer made of glass having a relatively low thermal expansion coefficient, and the inner layer 2 is a high expansion layer made of glass having a relatively high thermal expansion coefficient. Hereinafter, in this specification, the low expansion layer which is a glass layer on the surface side of the glass substrate is also simply referred to as a surface layer, and the high expansion layer which is an inner glass layer sandwiched between the surface layers is also simply referred to as an inner layer. Moreover, each thickness ( _Tl ) of the surface layer 3 which is a low expansion layer is thinner than the thickness ( _Th ) of the inner layer 2 which is a high expansion layer.

The glass of the inner layer 2 and the glass of the surface layer 3 are bonded and laminated together by fusion or adhesion. Due to this laminated structure, a tensile stress as indicated by a white arrow in FIG. 1 is generated in the inner layer 2, and a compressive stress (hereinafter referred to as “laminate” as indicated by a black arrow in FIG. 1 is generated on the surface layer 3. Also referred to as “enhanced compressive stress”.
As described above, a region where a tensile stress is generated by the above-described stacked configuration is referred to as a “tensile stress layer”, and a region where a compressive stress (stacked reinforcing compressive stress) is generated is also referred to as a “stacked reinforcing layer”. In the present invention, the inner layer 2 and the tensile stress layer are substantially synonymous, and the surface layer 3 and the laminated reinforcing layer are substantially synonymous.

In addition, in the glass substrate of the present invention, each of the surface layers 3 is subjected to a chemical strengthening treatment. Even by this chemical strengthening treatment, a compressive stress (hereinafter referred to as “chemical strengthening” is applied to the vicinity of the outermost surface of the surface layer 3. Also referred to as “compressive stress”).
Hereinafter, in the surface layer 3, a region where the chemically strengthened compressive stress is generated is also referred to as “chemically strengthened layer”. The chemical strengthening layer partially overlaps the laminated reinforcing layer, but at least the thickness of the chemical reinforcing layer is equal to or less than the thickness of the laminated reinforcing layer.

The chemical strengthening treatment applied to the surface layer 3 is roughly an alkali component (for example, an alkali metal ion such as Li ion or Na ion) present in the glass layer of the surface layer 3, hereinafter referred to as “small-diameter alkali”. This is a so-called ion exchange strengthening treatment in which the component (also referred to as “component”) is replaced with an alkali component having a larger ionic radius (for example, an alkali metal ion such as K ion, hereinafter also referred to as “large-diameter alkali component”).
Therefore, in the glass layer of the surface layer 3, the concentration of the large-diameter alkaline component in the chemically strengthened layer is higher than that of the laminated strengthened layer excluding this chemically strengthened layer. That is, the chemical strengthening layer and the laminated reinforcing layer excluding the chemical strengthening layer can be clearly distinguished by the difference in the concentration of the large-diameter alkaline component.

More specifically, the average value of the large-diameter alkali component amount (for example, the K element amount (unit: cps)) in the laminated reinforcing layer (that is, the surface layer 3) before the chemical strengthening treatment is set to “μ”. When the standard deviation is “σ”, the chemical strengthening layer is defined as “a layer having a large-diameter alkali component amount of“ μ + 2σ ”or more”, and the laminated reinforcing layer excluding the chemical strengthening layer is defined as “the large-diameter alkali component amount is It is defined as “a layer less than“ μ + 2σ ””. The amount of alkali components can be measured with an electron beam microanalyzer (EPMA).
In an ideal state with no error, the chemically strengthened layer can be simply defined as “a layer having a large-diameter alkaline component amount of“ μ ”or more”. However, in reality, an error occurs depending on the element amount and measurement accuracy of the glass layer before the chemical strengthening treatment. Therefore, it is necessary to define the increment of the large-diameter alkaline component amount after the chemical strengthening treatment as a value that is not less than a significant difference that does not include the error region. Therefore, in the present invention, this significant difference is defined as “2σ”, and the chemically strengthened layer is defined as “a layer having a large alkali component amount of“ μ + 2σ ”or more” as described above.

Further, as a simpler method, for example, the thickness of the chemically strengthened layer can be measured using a surface stress meter FSM-6000LE manufactured by Orihara Seisakusho Co., Ltd.

FIG. 2 is a graph schematically showing a stress profile of the glass substrate 1. In the graph of FIG. 2, the horizontal axis represents the thickness (unit: μm), and the vertical axis represents the stress value (unit: MPa). The upper side of the vertical axis is a tensile stress profile, and the lower side is a compressive stress profile.
The stress profile is calculated by measuring the birefringence of the cross section of the glass substrate 1. For the measurement of birefringence, for example, a birefringence imaging system Abrio-IM manufactured by Tokyo Instruments Inc. is used.

In the inner layer 2, a tensile stress layer is formed as described above. The stress profile of the tensile stress layer is substantially constant in the thickness direction. The maximum value of the tensile stress in the tensile stress layer (indicated by “CT” in FIG. 2) is preferably 200 MPa or less, more preferably 100 MPa or less, because the scratches are self-propelled if they are too high and cracks are likely to occur. preferable.

On the other hand, in the surface layer 3, as described above, the laminated reinforcing layer and the chemical reinforcing layer are formed. The thickness of the chemical strengthening layer (indicated by “DOL2” in FIG. 2) is equal to or less than the thickness of the laminated reinforcing layer (indicated by “DOL1” in FIG. 2).
The stress profile of the chemically strengthened layer has a larger inclination with respect to the thickness direction than the stress profile of the laminated strengthened layer excluding the chemically strengthened layer. That is, the rate of change of the stress value with respect to the thickness direction of the chemically strengthened layer is larger than the rate of change of the stress value with respect to the thickness direction of the laminated strengthened layer excluding the chemically strengthened layer. More specifically, the stress profile is substantially constant in the thickness direction in the laminated reinforcing layer excluding the chemically strengthened layer, but in the chemically strengthened layer, the stress profile is inclined with respect to the thickness direction, and the stress value toward the outermost surface. Is rising.

Thus, in each surface layer 3 of the glass substrate 1, the compressive stress value is not high, but is a thick compressive stress layer (that is, a laminated reinforcing layer excluding the chemical strengthening layer. In other words, before applying the chemical strengthening treatment. A compressive stress layer (that is, a chemically strengthened layer) having a high stress value is formed near the outermost surface. Therefore, the glass substrate 1 is less likely to crack even if it is deeply scratched by impact or the like (that is, the scratching strength is high), and it is difficult to crack even if a high tensile stress is applied to one surface by bending. (That is, the bending strength is high).

The maximum value (indicated by “CS1” in FIG. 2) of the compressive stress (that is, the laminate reinforcing compressive stress) in the laminated reinforcing layer excluding the chemically strengthened layer is preferably 400 MPa or less, and more preferably 350 MPa or less. If the lamination strengthening compressive stress is too high, ion exchange may be hindered in the chemical strengthening treatment (details will be described later), but within this range, ion exchange is appropriately performed and the chemically strengthened compression of the chemically strengthened layer is performed. Excellent stress.
Further, if the lamination strengthening compressive stress is too high, there is a risk that the tensile stress (CT) is increased and cracking is likely to occur, but the tensile stress does not become too high within this range.

In addition, CS1 is preferably 5 MPa or more, and more preferably 20 MPa or more.

In the surface layer 3, the maximum value of the chemical strengthening compressive stress in the chemically strengthened layer (indicated by “CS2” in FIG. 2) is preferably 600 MPa or more, and more preferably 700 MPa or more, because the bending strength is more excellent. .
In addition, 1200 MPa or less is preferable and 1000 MPa or less is more preferable because the tensile stress (CT) is also increased when CS2 becomes excessively high and cracks are easily generated.

In this specification, the numerical values of CT, CS1, and CS2 described above all indicate absolute values.

The thicknesses of the inner layer 2 and the surface layer 3 are not particularly limited as long as the surface layer 3 is thinner than the inner layer 2 as described above. However, the total thickness (2T _l ) of the surface layer 3 and the inner layer 2 are not limited. The ratio (2T ₁ / T _h ) to the thickness (T _h ) is preferably 0.05 to 1.5, more preferably 0.1 to 1.0.
Within thickness ratio (2T l / _T _h) is the range described above, excellent balance between tensile stress and the laminated reinforcing compressive stress in the glass substrate 1.

As specific thicknesses of the inner layer 2 and the surface layer 3, for example, when the plate thickness of the glass substrate is 0.1 to 4 mm, the thickness (T _h ) of the inner layer 2 is 0.07 to 2 mm is preferable, and 0.1 to 2 mm is more preferable. Further, the thickness (T _l ) of the surface layer 3 is preferably 0.05 to 0.5 mm, more preferably 0.05 to 0.4 mm.

The inner layer 2 and the surface layer 3 are both glass layers, but the surface layer 3 is a glass layer containing an alkali component because it is subjected to a chemical strengthening treatment, and is an alkali aluminosilicate glass layer. Is preferred.

Since the inner layer 2 is not subjected to chemical strengthening treatment, it may be a glass layer containing an alkali component or a glass layer not containing an alkali component.

The difference in thermal expansion coefficient (ΔCTE) between the inner layer 2 and the surface layer 3 is preferably 5 × 10 ⁻⁷ to 70 × 10 ⁻⁷ / K from the viewpoint of bringing CS1 and CT within the above ranges, and 5 × 10 ^−7. More preferably, it is ^˜60 × 10 ⁻⁷ / K.

In the present invention, the “thermal expansion coefficient” of glass is a linear expansion coefficient at 50 to 350 ° C., and is measured at a rate of temperature increase of 5 ° C./min using a thermal dilatometer.

As will be described later, the glass transition temperatures of the inner layer 2 and the surface layer 3 are related to the temperature of the chemical strengthening process, but specifically, the inner layer 2 which is a high expansion layer and the surface which is a low expansion layer. The glass transition temperature of the layer 3 is preferably 450 ° C. or higher, and more preferably 500 ° C. or higher.

The difference in refractive index (Δn) between the inner layer 2 and the surface layer 3 is preferably 0.1 or less, and more preferably 0.05 or less. If (DELTA) n is this range, the glass substrate 1 is excellent in permeability | transmittance and becomes suitable for a cover glass use.

In the present invention, “refractive index” is a refractive index with respect to the d-line, and is measured by a precision refractometer KPR-2000 manufactured by Shimadzu Device Manufacturing Co., Ltd.

[Glass substrate manufacturing method]
Next, taking the glass substrate 1 as an example, a method for producing a glass substrate for obtaining the glass substrate of the present invention (hereinafter also referred to as “the production method of the present invention”) will be described.
The production method of the present invention for obtaining a glass substrate 1 is generally a lamination in which glass forming an inner layer 2 (high expansion layer) and glass forming a pair of surface layers 3 (low expansion layer) are stacked. A process and a chemical strengthening process for performing a chemical strengthening process on the surface layer 3 that is a surface layer of the laminated glass.

[Lamination process]
As described above, as described above, the glass for forming the inner layer 2 and the glass for forming the surface layer 3 are bonded to each other by fusing, bonding, or the like, and the inner layer 2 and the surface layer 3 are laminated. There is no particular limitation as long as it is a step of obtaining a laminated body (hereinafter also simply referred to as “laminated body”).
As a method for obtaining the laminate, a conventionally known method can be used. For example, the molten glass to be the inner layer 2 and the molten glass to be the surface layer 3 are overflowed from both sides of the heat-resistant bowl-like structure, and the overflowed molten glass is joined together at the lower end of the bowl-like structure. The inner layer 2 is disposed between the pair of surface layers 3 and heated to a temperature equal to or higher than the softening point of the inner layer 2 and the surface layer 3. And the like.

After such a laminating step, the obtained laminate is gradually cooled as necessary, processed into an appropriate size, and then transferred to a chemical strengthening step.

[Chemical strengthening process]
The chemical strengthening step is a step of performing a chemical strengthening process on the surface layer 3.
As the chemical strengthening treatment, an alkali component (for example, alkali metal ions such as Li ions and Na ions) existing in the surface layer 3 is replaced with an alkali component having a larger ionic radius (for example, alkali metal ions such as K ions). is not particularly limited as long as the process of, for example, a method of immersing the laminate potassium nitrate (KNO ₃₎ in molten salts. The immersion conditions vary depending on the thickness of the surface layer 3, the stress value, and the like, but examples of the immersion time include 0.25 to 5 hours.

By the way, if a chemical strengthening treatment represented by such immersion is performed for a long time (for example, 2 days) on a single-layer glass substrate that is not a laminated type, it is considered that the chemical strengthened layer can be formed thick. .
However, the chemical strengthening treatment is not practical because the manufacturing cost becomes extremely high by performing for a long time, and the chemical strengthening layer having a high compressive stress value is formed thick to balance the compressive stress. The resulting tensile stress is also increased, and there is a risk that cracks are likely to occur.
In that regard, in the glass substrate (glass substrate 1) of the present invention, since the thick laminated reinforcing layer has already been formed, it is not necessary to form the chemical reinforcing layer thickly, and the immersion time in the chemical strengthening treatment can be shortened, Manufacturing cost can be reduced.
And in the glass substrate (glass substrate 1) of this invention, since a chemically strengthened layer with a high stress value does not become thicker than necessary, it is suppressed that tensile stress becomes high and generation | occurrence | production of a crack can also be suppressed.

Further, the chemical strengthening treatment may include a preheat treatment for preheating the laminate as a pretreatment such as the immersion. The method for the preheat treatment is not particularly limited, and examples thereof include a method for heating the laminate using a heater.

At this time, the temperature of the chemical strengthening treatment is preferably lower than the higher one of the glass transition temperatures of the inner layer 2 and the surface layer 3, and is lower than the glass transition temperature of the inner layer 2 and the surface layer 3. It is more preferable that the temperature is lower than that. In addition, the temperature of the pre-heat treatment of the laminate prior to the chemical strengthening treatment is appropriately selected within a temperature range in which the laminate is not damaged or deformed when immersed in a molten salt such as KNO _3. Good.
Incidentally, here, the temperature of the chemical strengthening treatment, specifically, for example, a temperature of KNO ₃ molten salt.

By the way, as the temperature of the chemical strengthening treatment, it is generally considered that the higher one is more efficient, but when the present inventors have studied, the temperature of the chemical strengthening treatment is high in the present invention. It was found that the alkali component after substitution with alkali ions diffuses, and as a result, the chemically strengthened compressive stress of the chemically strengthened layer may be weakened.
That is, when the temperature of the chemical strengthening treatment satisfies the above conditions, the maximum value of the chemical strengthening compressive stress of the chemical strengthening layer is in the above-described range.

In addition, although it depends on the glass transition temperature of the inner layer 2 and the surface layer 3 as described above, the temperature of the chemical strengthening treatment is specifically preferably 550 ° C. or less, and more preferably 500 ° C. or less. Further, specifically, the lower limit temperature of the chemical strengthening treatment is preferably, for example, 350 ° C. or higher, and more preferably 400 ° C. or higher.

Since the glass substrate of the present invention obtained by such a production method of the present invention is excellent in both scratching strength and bending strength, for example, it is suitably used as a cover glass mounted on a mobile device such as a smartphone or a tablet PC. It is done.

As described above, the glass substrate of the present invention is not limited to the three-layer glass substrate 1 of “low expansion layer / high expansion layer / low expansion layer”. For example, “low expansion layer / high expansion layer” A glass substrate having a five-layer structure of “/ low expansion layer / high expansion layer / low expansion layer” may be used.

Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to these.

<Glass type>
The details of the glass layer used in the following examples and the like are as follows.

(Glass 1: Glass forming a high expansion layer on a glass substrate)
- _Composition: SiO 2 64.5 mole%, _Al 2 _{O 3} 6 mol%, MgO 11 mol%, CaO 0.1 mol%, SrO 0.1 mol%, _Na 2 O 12 _{mol%, K} 2 O 4 moles %, ZrO ₂ 2.5 mol%
Thermal expansion coefficient: 91 × 10 ⁻⁷ / K
Glass transition temperature: 620 ° C
Softening point: 842 ° C
-Refractive index: 1.52
・ Young's modulus: 78GPa
-Poisson's ratio: 0.22

(Glass 2: Glass that forms a low expansion layer on a glass substrate)
Composition: SiO ₂ 73 mol%, Al ₂ O ₃ 7 mol%, MgO 6 mol%, Na ₂ O 14 mol%
-Thermal expansion coefficient: 79 × 10 ⁻⁷ / K
Glass transition temperature: 617 ° C
・ Softening point: 850 ° C
-Refractive index: 1.5
-Young's modulus: 71 GPa
・ Poisson's ratio: 0.2

<Examples 1 to 3>
First, one glass 1 (high-expansion glass substrate for forming an inner layer (high expansion layer)) and glass 2 (low-expansion glass for forming a surface layer (low expansion layer) having the same size except the thickness Substrate) Prepare two sheets, place one glass 1 between the two glasses 2, and after heating to a temperature at which both the glass 1 and the glass 2 are above the softening point, by slowly cooling, A laminate having a three-layer structure in which each glass was fused was obtained. In this laminate, the difference in thermal expansion coefficient between the high expansion layer and the low expansion layer is 12 × 10 ⁻⁷ / K. The glass types and thicknesses (T _h , T _l ) used for the inner layer and the surface layer are shown in Table 1 below. The thickness T ₁ of the surface layer shown in Table 1, of the surface layer formed on both sides of the inner layer, while the thickness of the side of the surface layer, also the one thickness of the other side of the surface layer It is the same value as the thickness of the surface layer on the side.

Next, the obtained laminate was subjected to a chemical strengthening treatment to obtain a glass substrate. Specifically, the obtained laminate was preheated using a heater, and then immersed in KNO ₃ molten salt (immersion time and immersion temperature are shown in Table 1 below), and in KNO ₃ molten salt A chemical strengthening treatment by ion exchange was performed, and then the laminate subjected to the chemical strengthening treatment was dried after washing with pure water to obtain a glass substrate. In addition, the temperature of the preheat treatment of the laminated body was set to the same temperature as the temperature of the molten salt to be immersed (immersion temperature).

Each of the glass substrates of Examples 1 to 3 exhibited a stress profile similar to that of the graph of FIG. Based on the stress profile, CT (maximum value of tensile stress in the tensile stress layer, unit: MPa), DOL1 (thickness of the laminated reinforcing layer, unit: μm), DOL2 (thickness of the chemical reinforcing layer, unit: μm), CS1 (maximum value of compressive stress in the laminated reinforcing layer excluding the chemically strengthened layer (ie, laminated strengthened compressive stress). Unit: MPa) and CS2 (maximum value of chemically strengthened compressive stress in the chemically strengthened layer. Unit: MPa) Is shown in Table 1 below. Note that the numerical values of CT, CS1, and CS2 are all absolute values.
CT is measured using a birefringence imaging system Abrio-IM manufactured by Tokyo Instruments Inc., DOL1 is measured by the above-mentioned EPMA, and DOL2, CS1, and CS2 are surface stress meters manufactured by Orihara Seisakusho Co., Ltd. Measurement was performed using FSM-6000LE (hereinafter the same).
The thickness ratio (2T ₁ / T _h ) between the surface layer and the inner layer, the thermal expansion coefficient difference (ΔCTE), and the refractive index difference (Δn) are also shown in Table 1 below.

In the glass substrates of Examples 1 to 3, the amount of K element in the surface layer before chemical strengthening treatment was measured using the above-mentioned EPMA. In Examples 1 to 3, the average value (μ) was 1437 cps. And the standard deviation (σ) was 38. After the chemical strengthening treatment, the amount of K element in the chemically strengthened layer in the surface layer was measured. As a result, the maximum in Example 1 was 4955 cps, and in Examples 2 and 3, the maximum was 6352 cps, both of which were “μ + 2σ” or more. That is, it was “1437 + 2 × 38 = 1513” or more.

<Comparative Examples 1 and 2>
Except that the chemical strengthening treatment was not performed, Comparative Example 1 was the same as Example 1, and Comparative Example 2 was the same as Example 3, to obtain a glass substrate. FIG. 3 is a graph schematically showing the stress profile of the glass substrates of Comparative Examples 1 and 2. As shown in FIG. 3, in Comparative Examples 1 and 2, the chemical strengthening layer is not formed on the surface layer, and only the laminated reinforcing layer showing a certain stress value is formed.

<Comparative Examples 3 and 4>
In Comparative Examples 3 and 4, a glass substrate was obtained by subjecting a single layer glass (that is, a 1 mm thick single glass substrate made of glass 2) to a chemical strengthening treatment. Specifically, Comparative Example 3 was subjected to the same treatment as in Example 1, and Comparative Example 4 was subjected to the same treatment as in Example 2 or 3. FIG. 4 is a graph schematically showing the stress profile of the glass substrates of Comparative Examples 3 and 4. As shown in FIG. 4, in Comparative Examples 3 and 4, the lamination reinforcing layer is not formed on the surface layer, and only the chemical strengthening layer is formed near the outermost surface of the surface layer.

<Evaluation>
(Injury strength)
A diamond square pyramid indenter (Vickers indenter) having a facing angle of 136 ° was driven into the surface of the obtained glass substrate and held for 15 seconds, and then the load was removed to confirm the presence or absence of crushing. The load applied to the indenter was increased stepwise, and the load value when the glass substrate was crushed was measured. When the load value when the glass substrate is crushed is more than 10 kgf, it is evaluated as “A” as having excellent scratch strength, and when it is 10 kgf or less, “B” is determined as having poor scratch strength. It was evaluated.

(Bending strength)
A glass substrate was sandwiched between two rings with a diameter of 30 mm and a diameter of 10 mm, a load was applied to the ring with a diameter of 10 mm, the load value when a crack occurred in the glass substrate was measured, and the test was repeated 15 times. When the average load value when the glass substrate is cracked is 150 kgf or more, the bending strength is evaluated as “A”, and when it is less than 150 kgf, the bending strength is inferior. ".

As is clear from the results shown in Table 1, it was found that all of the glass substrates of Examples 1 to 3 were excellent in scratch strength and bending strength.
In contrast, the glass substrates of Comparative Examples 1 and 2 that were not chemically strengthened were inferior in bending strength, and the glass substrates of Comparative Examples 3 and 4 that did not have a laminated structure were inferior in scratch strength. It was.

According to the present invention, it is possible to provide a glass substrate that is excellent in both scratching strength and bending strength. The tempered glass plate of the present invention is remarkably widespread in portable devices such as smartphones and tablet PCs, and is useful as a cover glass mounted on such portable devices.
The entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2011-239034 filed on October 31, 2011 are incorporated herein by reference. .

1: Glass substrate 2: Inner layer (high expansion layer)
3: Surface layer (low expansion layer)
CS1: Maximum value of compressive stress in the laminated reinforcing layer excluding the chemically strengthened layer CS2: Maximum value of compressive stress in the chemically strengthened layer CT: Maximum value of tensile stress DOL1: Thickness of the laminated reinforcing layer DOL2: Thickness of the chemically strengthened layer T _h : thickness of the inner layer (high expansion layer) T _l : thickness of the surface layer (low expansion layer)

Claims

It has a laminated structure in which a high expansion layer and a low expansion layer having a smaller thermal expansion coefficient than the high expansion layer are laminated, and the low expansion layer is a glass substrate,
A tensile stress layer formed by generating a tensile stress in the high expansion layer by the laminated configuration;
A laminated reinforcing layer formed by generating a compressive stress in the low expansion layer by the laminated configuration;
A chemical strengthening layer formed by compressive stress generated by a chemical strengthening treatment near the outermost surface of the low expansion layer which is a surface layer, and
The glass substrate whose thickness of the said chemical strengthening layer is below the thickness of the said laminated strengthening layer.
The glass substrate according to claim 1, wherein a difference in thermal expansion coefficient between the high expansion layer and the low expansion layer is 5 × 10 −7 to 70 × 10 −7 / K.
It is composed of two low expansion layers that are surface layers and one high expansion layer that is an internal layer,
The ratio (2T l / T h ) of the sum (2T l ) of the thickness (T l ) of the low expansion layer to the thickness (T h ) of the high expansion layer is 0.05 to 1.5 The glass substrate according to claim 1 or 2.
The rate of change of the stress value with respect to the thickness direction of the chemical strengthening layer is larger than the rate of change of the stress value with respect to the thickness direction of the laminated reinforcing layer excluding the chemical strengthening layer. A glass substrate as described in 1.
The glass substrate according to any one of claims 1 to 4, wherein in the low expansion layer which is a surface layer, the maximum value of compressive stress in the chemical strengthening layer is 600 MPa or more.
6. The glass substrate according to claim 1, wherein in the low expansion layer which is a surface layer, the maximum value of compressive stress in the chemical strengthening layer is 1200 MPa or less.
The glass substrate according to any one of claims 1 to 6, wherein in the low expansion layer which is a surface layer, a maximum value of compressive stress in the laminated reinforcing layer excluding the chemical strengthening layer is 400 MPa or less.
The glass substrate according to any one of claims 1 to 7, wherein in the low expansion layer which is a surface layer, a maximum value of compressive stress in the laminated reinforcing layer excluding the chemical reinforcing layer is 5 MPa or more.
The glass substrate according to any one of claims 1 to 8, wherein a maximum value of tensile stress in the tensile stress layer is 200 MPa or less.
The glass substrate according to any one of claims 1 to 9, wherein the low expansion layer is an alkali aluminosilicate glass layer.
The glass substrate according to any one of claims 1 to 10, wherein a difference in refractive index between the high expansion layer and the low expansion layer is 0.1 or less.
A method for producing a glass substrate, wherein the glass substrate according to any one of claims 1 to 11 is obtained,
A laminating step of laminating the high expansion layer and the low expansion layer;
A chemical strengthening step for performing the chemical strengthening treatment on the low expansion layer which is a surface layer;
A method for producing a glass substrate comprising:
An inner layer is a single layer of high expansion, and a layering step of manufacturing a laminate in which the surface layers formed on both sides of the layer of high expansion are low expansion layers, the layering step includes the layer of high expansion The manufacturing method of the glass substrate of Claim 12 including the process of laminating | stacking the glass used as the said low expansion layer on the both surfaces side of glass used as this.
The chemical strengthening treatment includes pre-heat treatment, and the temperature of the chemical strengthening treatment is lower than the higher one of the glass transition temperatures of the high expansion layer and the low expansion layer. A method for producing a glass substrate.
The method for producing a glass substrate according to claim 14, wherein the temperature of the chemical strengthening treatment is lower than the lower one of the glass transition temperatures of the high expansion layer and the low expansion layer.
A cover glass using the glass substrate according to any one of claims 1 to 11.