JP2015091737A - Laminated tempered glass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide laminated tempered glass excellent in end surface strength.SOLUTION: Laminated tempered glass is formed by laminating a high-expansion layer and a low-expansion layer smaller in plate thickness and thermal expansion coefficient than the high-expansion layer, with the low-expansion layer as the surface layer, so as to produce tensile stress in the high-expansion layer and compression stress in the low-expansion layer. The high-expansion layer has, in its end surface part, a chemically strengthened layer in which compression stress is generated by a chemically strengthening treatment.

Description

  The present invention relates to laminated tempered glass.

Conventionally, a so-called laminated tempered glass has been known as a glass substrate with increased mechanical strength (see, for example, Patent Document 1).
In the laminated tempered glass, as described in [0009] of Patent Document 1, a surface layer having a relatively small thermal expansion coefficient and an inner layer (having a relatively large thermal expansion coefficient) are mutually connected. By having the fused structure, compressive stress is generated in the surface layer (formation of compressive stress layer), and tensile stress is generated in the inner layer (formation of tensile stress layer).

JP 2011-93728 A

In the laminated tempered glass having the above-described configuration, the tensile stress layer is exposed at the end face portion, so that the end face strength is weak and may cause cracking.
In addition, as an attempt to increase the end face strength of the laminated tempered glass, for example, a method has been proposed in which the end face is melted by heat to extinguish the tensile stress, but it is difficult to maintain the original shape, and dimensional accuracy Another problem occurs that is reduced.

  This invention is made | formed in view of the above point, and aims at providing the laminated tempered glass which has the outstanding end surface intensity | strength.

As a result of intensive studies by the present inventors to achieve the above object, in the laminated tempered glass, by exposing the end surface portion of the high expansion layer where the tensile stress is generated, the tensile stress layer is exposed. The present invention has been completed.
That is, the present invention provides the following (1) to (2).

  (1) By laminating a high expansion layer and a low expansion layer having a smaller plate thickness and a smaller thermal expansion coefficient than the high expansion layer so that the low expansion layer becomes a surface layer, A laminated tempered glass in which a tensile stress is generated and a compressive stress is generated in the low expansion layer, wherein the high expansion layer has a chemical strengthening layer in which a compressive stress is generated by a chemical strengthening process at an end surface portion thereof. A laminated tempered glass characterized by that.

  (2) The laminated tempered glass according to (1), wherein the low expansion layer has a chemically strengthened layer in which compressive stress is generated by a chemical strengthening treatment on the end surface portion and the surface portion.

  According to the present invention, it is possible to provide a laminated tempered glass having excellent end face strength.

1 is a side sectional view schematically showing an example of a laminated tempered glass 1. It is a sectional side view showing typically another example of lamination strengthening glass 1.

[Laminated tempered glass]
The laminated tempered glass of the present invention will be described with reference to FIGS. 1 and 2, but the present invention is not limited to this.

FIG. 1 is a side sectional view schematically showing an example of a laminated tempered glass 1. In the laminated tempered glass 1 having a three-layer structure shown in FIG. 1, a high expansion layer 2 that is an internal layer is disposed between a low expansion layer 3 that is a pair of surface layers. The thermal expansion coefficient of the low expansion layer 3 is smaller than that of the high expansion layer 2. The plate thickness (T _L ) of the low expansion layer 3 is thinner than the plate thickness (T _H ) of the high expansion layer 2.

The high expansion layer 2 and the low expansion layer 3 are bonded and laminated together by fusion, adhesion, or the like. Due to such a laminated structure, a tensile stress as indicated by an open arrow in FIG. 1 is generated in the high expansion layer 2, and a compressive stress (hereinafter referred to as a black arrow in FIG. 1) is generated in the low expansion layer 3. Also referred to as “laminate strengthening compressive stress”).
A region where a tensile stress is generated by the above-described laminated structure is also referred to as a “tensile stress layer”, and a region where a stacked reinforcing compressive stress is generated is also referred to as a “laminated reinforcing layer”. The high expansion layer 2 and the tensile stress layer are substantially synonymous, and the low expansion layer 3 and the lamination reinforcing layer are substantially synonymous.

The tensile stress of the high expansion layer 2 is preferably 100 MPa or less, and more preferably 50 MPa or less. If the tensile stress is too high, the scratches are self-propelled and cracks are likely to occur. However, if the tensile stress is within this range, the occurrence of cracks is easily suppressed.
The tensile stress is an absolute value of the maximum value, and can be measured using, for example, a birefringence imaging system Abrio-IM manufactured by Tokyo Instruments Incorporated.

The lamination strengthening compressive stress of the low expansion layer 3 is preferably 500 MPa or less, and more preferably 400 MPa or less. If the lamination strengthening compressive stress is too high, there is a risk that the tensile stress is increased and cracking is likely to occur. However, if it is within this range, the tensile stress will not be too high.
In addition, as will be described later, when the low expansion layer 3 is also subjected to chemical strengthening treatment, if the lamination strengthening compressive stress is too high, ion exchange may be hindered. Done.
On the other hand, the lamination strengthening compressive stress of the low expansion layer 3 is preferably 30 MPa or more, and more preferably 100 MPa or more, because the glass strength can be increased.
In addition, lamination | stacking reinforcement | strengthening compression stress is an absolute value of the maximum value, for example, can be measured using the surface stress meter FSM-6000LE by a limited company Orihara Seisakusho.

  In the laminated tempered glass 1, the end face portion of the high expansion layer 2 is subjected to a chemical strengthening process described later. By this chemical strengthening process, the end face portion of the high expansion layer 2 is subjected to compressive stress (hereinafter referred to as a compressive stress). , Also referred to as “chemically reinforced compressive stress”). Hereinafter, the region where the chemically strengthened compressive stress is generated is also referred to as “chemically strengthened layer”. 1 a in FIG. 1 indicates a chemically strengthened layer formed in the high expansion layer 2.

  As described above, in the laminated tempered glass 1, the chemical strengthening layer 2a is formed on the end surface portion of the high expansion layer 2 where the tensile stress is generated, so that the tensile stress layer formed on the high expansion layer 2 is exposed to the outside. Exposure can be suppressed. For this reason, the fall of the end surface strength by the tensile stress layer being exposed to the end surface portion is suppressed, and the laminated tempered glass 1 has excellent end surface strength.

  The “end surface portion” of the high expansion layer 2 refers to a portion including exposed surfaces (the left and right end surfaces of the high expansion layer 2 in FIG. 1) that are exposed to the outside without being in contact with the low expansion layer 3. Specifically, it means a portion from the exposed surface to a depth of 200 μm.

Here, another example of the laminated tempered glass 1 will be described.
FIG. 2 is a side sectional view schematically showing another example of the laminated tempered glass 1. As shown in FIG. 2, in the present invention, the chemical strengthening layer is formed on the end surface portion and the surface portion of the low expansion layer 3 in the same manner as the end surface portion of the high expansion layer 2. May be. 2a in FIG. 2 indicates a chemically strengthened layer formed in the low expansion layer 3. In this case, the chemical strengthening layer 3a of the low expansion layer 3 partially overlaps with the laminated reinforcing layer.

The “end face portion” of the low expansion layer 3 refers to a portion including exposed surfaces (in FIG. 2, the left and right end faces of the low expansion layer 3) exposed to the outside without being in contact with the high expansion layer 2. Say.
Similarly, the “surface portion” of the low expansion layer 3 is an exposed surface exposed to the outside without being in contact with the high expansion layer 2, and is an exposed surface other than the exposed surface defining the “end surface portion” ( In FIG. 2, it refers to a part including the upper or lower end face of the low expansion layer 3.
Specifically, any means a part from the exposed surface to a depth of 200 μm.

The chemical tempering treatment applied to the laminated tempered glass 1 generally includes an alkali component (for example, Li ion, Na ion, etc.) present in the high expansion layer 2 (or the high expansion layer 2 and the low expansion layer 3). An alkali metal ion (hereinafter also referred to as “small-diameter alkali 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”). This is a so-called ion exchange treatment.
Therefore, in the high expansion layer 2, the concentration of the large-diameter alkaline component in the chemically strengthened layer 2a is higher than that in the portion excluding the chemically strengthened layer 2a. That is, the chemical strengthening layer 2a and the portion excluding the chemical strengthening layer 2a can be clearly distinguished by the difference in the concentration of the large-diameter alkaline component (the same applies to the chemical strengthening layer 3a in the low expansion layer 3).

More specifically, when the average value of the large-diameter alkaline component amount (for example, the K element amount (unit: cps)) before chemical strengthening is “μ” and the standard deviation is “σ” The chemical strengthening layer 2a and the chemical strengthening layer 3a are defined as “the large diameter alkali component amount is“ μ + 2σ ”or more”, and the portion excluding the chemical strengthening layer 2a and the chemical strengthening layer 3a is defined as “the large diameter alkali component amount is“ μ + 2σ ”. Less than ". 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 2a and the chemically strengthened layer 3a can be simply defined as “a layer having a large-diameter alkali 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, this significant difference is defined as “2σ”, and the chemical strengthening layer 2a and the chemical strengthening layer 3a are defined as “a layer having a large-diameter alkali component amount of“ μ + 2σ ”or more” as described above.

The depth of the chemically strengthened layer 2a of the high expansion layer 2 (indicated by _DH in FIGS. 1 and 2) is 10 for the reason that cracking due to an increase in tensile stress can be suppressed while improving the end face strength. It is preferably ˜100 μm, more preferably 20 to 80 μm.
The depth of the chemical strengthening layer 2a can be measured using, for example, a birefringence imaging system Abrio-IM manufactured by Tokyo Instruments Inc.

The chemical strengthening compressive stress of the chemical strengthening layer 2a is preferably 400 MPa or more, and more preferably 600 MPa or more, because the end face strength is more excellent.
On the other hand, the chemical strengthening compressive stress of the chemical strengthening layer 2a is preferably 2000 MPa or less, and more preferably 1500 MPa or less, because if the stress is too high, the balance is increased and the tensile stress becomes high and cracking easily occurs.
The numerical value of the chemical strengthening compressive stress of the chemical strengthening layer 2a is an absolute value of the maximum value, and can be calculated from, for example, a birefringence measured using a birefringence imaging system Abrio-IM manufactured by Tokyo Instruments Inc.

When forming a chemical strengthening layer 3a in the low expansion layer 3, because its depth (in FIG. 2, indicated by D _L), while improving the scratching strength is suppressing the occurrence of cracks due to the increase in tensile stress Therefore, the thickness is preferably 10 to 100 μm, more preferably 20 to 80 μm.

The chemically strengthened compressive stress of the chemically strengthened layer 3a is preferably 400 MPa or more, and more preferably 600 MPa or more, because it is excellent in bending strength and scratch strength.
On the other hand, the chemical strengthening compressive stress of the chemical strengthening layer 3a is preferably 2000 MPa or less, and more preferably 1500 MPa or less, because the tensile stress is increased and cracks are easily generated when the chemical strengthening layer 3a becomes too high.

The depth of the chemical strengthening layer 3a can be measured using, for example, a surface stress meter FSM-6000LE manufactured by Orihara Seisakusho Co., Ltd.
Moreover, the numerical value of the chemical strengthening compressive stress of the chemical strengthening layer 3a is the absolute value of the maximum value, and can be measured using, for example, a surface stress meter FSM-6000LE manufactured by Orihara Seisakusho Co., Ltd.

The plate thickness of the high expansion layer 2 and the low expansion layer 3 is not particularly limited as long as the low expansion layer 3 is thinner than the high expansion layer 2, but the total plate thickness (2T _L ) of the low expansion layer 3 and the high expansion layer are not limited. The ratio (2T _L / T _H ) to the plate thickness (T _H ) of 2 is preferably 0.05 to 1.5, and more preferably 0.1 to 1.0.
Within the above plate thickness ratio (2T L / _{T H)} is within this range, excellent balance between tensile stress and the laminated reinforcing compressive stress in the laminated tempered glass 1.

As a specific thickness of the high expansion layer 2 and the low expansion layer 3, for example, the thickness of the high expansion layer 2 _{(T H)} is, 0.05 to 2 mm is preferred, 0.1 to 2 mm Gayori preferable. In addition, the plate thickness (T _L ) of the low expansion layer 3 is preferably 0.05 to 0.5 mm, and more preferably 0.05 to 0.4 mm.

Although both the high expansion layer 2 and the low expansion layer 3 are glass layers, the high expansion layer 2 is a glass layer containing an alkali component because it is subjected to a chemical strengthening treatment, and an alkali aluminosilicate glass layer. Is preferred.
The low expansion layer 3 may be a glass layer containing an alkali component or a glass layer not containing an alkali component, but in the case of the laminated tempered glass 1 described with reference to FIG. Since it is subjected to chemical strengthening treatment, it is a glass layer containing an alkali component, and is preferably an alkali aluminosilicate glass layer.

The thermal expansion coefficient difference (ΔCTE) between the high expansion layer 2 and the low expansion layer 3 is preferably 5 × 10 ⁻⁷ to 70 × 10 ⁻⁷ / K from the viewpoint of bringing the lamination reinforcing compressive stress and the tensile stress within the above ranges. 5 × 10 ^{−7 to} 60 × 10 ⁻⁷ / K is more preferable.
In the present invention, the “thermal expansion coefficient” 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.

  The glass transition temperatures of the high expansion layer 2 and the low expansion layer 3 are each preferably 450 ° C. or higher, and more preferably 500 ° C. or higher.

The refractive index difference (Δn) between the high expansion layer 2 and the low expansion layer 3 is preferably 0.1 or less, and more preferably 0.05 or less. When Δn is within this range, the laminated tempered glass 1 has excellent permeability, and is suitable for, for example, a cover glass application mounted on a portable device.
In the present invention, the “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.

The laminated tempered glass of the present invention is not limited to the laminated tempered glass 1 described with reference to FIG. 1 and FIG. 2. For example, “low expansion layer / high expansion layer / low expansion layer / high expansion layer” It may be a laminated tempered glass of five or more layers called “/ low expansion layer”.
In this case, the thermal expansion coefficients of the plurality of high expansion layers may be larger than the thermal expansion coefficient of the low expansion layer. For example, the plurality of high expansion layers may have different thermal expansion coefficients.

  As described above, since the laminated tempered glass of the present invention is excellent in end face strength, for example, a cover mounted on a portable device (for example, a smartphone or a tablet PC) that is easily impacted on the end face because it is portable. It is suitably used as glass.

[Production method]
Next, the manufacturing method of the laminated tempered glass for obtaining the laminated tempered glass 1 will be described. The method generally includes a stacking step in which the high expansion layer 2 and the low expansion layer 3 are stacked, and a chemical strengthening treatment for the low expansion layer 3 (or the high expansion layer 2 and the low expansion layer 3). A chemical strengthening step to be performed.

[Lamination process]
In the laminating step, the high expansion layer 2 and the low expansion layer 3 are laminated by being bonded to each other by fusion, adhesion, or the like, and a laminated body of the high expansion layer 2 and the low expansion layer 3 (hereinafter simply referred to as “laminated body”). The process is not particularly limited as long as it is a process for obtaining "."
As a method for obtaining the laminate, a conventionally known method can be used. For example, the molten glass of the high expansion layer 2 and the molten glass of the low expansion layer 3 overflow from both sides of the heat-resistant cage structure, respectively. A method in which the molten glass overflowed and joined at the lower end of the bowl-shaped structure is drawn downward; A method of fusing the high expansion layer 2 and the low expansion layer 3 by heating; and the like.

  After such a laminating step, the obtained laminated body is gradually cooled (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 low expansion layer 3 (or the high expansion layer 2 and the low expansion layer 3).
As the chemical strengthening treatment, alkali components (for example, alkali metal ions such as Li ions and Na ions) existing in the low expansion layer 3 (or the high expansion layer 2 and the low expansion layer 3) are alkali components having a larger ionic radius. (e.g., alkali metal ions such as K ion), but it if not particularly limited processing be substituted with, for example, a method of immersing the laminate potassium nitrate (KNO ₃₎ in molten salts. Although the conditions for immersion differ depending on the size of the high expansion layer 2 and the low expansion layer 3, etc., examples of the immersion time include 0.25 to 5 hours.

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

The temperature of the chemical strengthening treatment (including the preheat treatment) is preferably less than the higher one of the glass transition temperatures of the high expansion layer 2 and the low expansion layer 3, and the high expansion layer 2 and the low expansion layer 3 It is more preferable that the glass transition temperature is lower than the lower one.
Note that the temperature of the chemical strengthening treatment referred to here is, for example, the heating temperature by the heater in the preheat treatment, the temperature of the KNO ₃ molten salt, or the like.

  As described above, although depending on the glass transition temperatures of the high expansion layer 2 and the low expansion layer 3, the temperature of the chemical strengthening treatment (including preheat treatment) is specifically preferably 550 ° C. or less, for example, 500 ° C. The following is more preferable.

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

<Glass composition>
Details of the glass layer used in the following examples and the like are as follows.

(Glass A)
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

(Glass B)
- _Composition: SiO 2 66.2 _{mole%, Al} 2 O 3 11.3 _{mol%, B 2} O 3 7.6 mol%, MgO 5.3 mol%, CaO 4.7 mol%, SrO 4.9 mol %
-Thermal expansion coefficient: 38 × 10 ⁻⁷ / K
Glass transition temperature: 720 ° C
Softening point: 950 ° C
-Refractive index: 1.52
・ Young's modulus: 75Pa
-Poisson's ratio: 0.21

<Example 1>
First, glass A and glass B having the same size (65 mm × 65 mm) except for the plate thickness were prepared. Next, one glass A which is a high expansion layer (inner layer) is disposed between two glasses B which are low expansion layers (surface layers), and both the glass A and the glass B are above the softening point. After being heated to a certain temperature, it was gradually cooled to obtain a laminate having a three-layer structure in which each glass was fused. The glass composition and the plate thickness (T _H , T _L ) used for the high expansion layer and the low expansion layer are shown in Table 1 below.
Next, it grind | polished with respect to the end surface part of the obtained laminated body, it was set as the size of 63 mm x 63 mm, and C chamfering was performed by the dimension of 0.15 mm over the perimeter. Furthermore, chemical strengthening treatment was performed to obtain laminated tempered glass. Specifically, the obtained laminate was preheated using a heater, then immersed in KNO ₃ molten salt (immersion time: 1 hour, immersion temperature: 435 ° C.), dried after washing with pure water, A laminated tempered glass was obtained. The preheating temperature was the same as the immersion temperature.

<Comparative Example 1>
A laminated tempered glass was obtained in the same manner as in Example 1 except that the chemical strengthening treatment was not performed. Since chemical strengthening treatment was not performed, “−” was described in Table 1 below for the chemically strengthened compressive stress and depth of the chemically strengthened layer.

<Evaluation>
(End face strength)
The end face strength of the obtained laminated tempered glass was evaluated by a four-point bending test according to “JIS R 1601 Bending strength test method of fine ceramics”. The test was repeated 20 times, and the average load value when cracking occurred was measured.
Based on the average load value of Comparative Example 1, when the average load value is less than or equal to the value of Comparative Example 1, it is evaluated as “B”, and when the average load value is larger than the Comparative Example 1 value, A ”. If it is "A", it can be evaluated as having excellent end face strength. The results are shown in Table 1 below.

  As is clear from the results shown in Table 1 above, the laminated tempered glass of Example 1 is superior in end face strength, whereas the laminated tempered glass in Comparative Example 1 that has not been subjected to chemical strengthening treatment has improved end face strength. I found it inferior.

DESCRIPTION OF SYMBOLS 1 Laminated tempered glass 2 High expansion layer 2a Chemical strengthening layer 3 Low expansion layer 3a Chemical strengthening layer _DH Depth of chemical strengthening layer of high expansion layer D _L Depth of chemical strengthening layer of low expansion layer _TH High expansion layer Thickness _TL Thickness of low expansion layer

Claims (2)

By laminating a high expansion layer and a low expansion layer having a smaller plate thickness and a smaller thermal expansion coefficient than the high expansion layer so that the low expansion layer becomes a surface layer, tensile stress is applied to the high expansion layer. A laminated tempered glass that generates and generates compressive stress in the low expansion layer,
Laminated tempered glass, wherein the high expansion layer has a chemically strengthened layer in which compressive stress is generated by chemical strengthening treatment at an end surface portion thereof.   The laminated tempered glass according to claim 1, wherein the low expansion layer has a chemically strengthened layer in which a compressive stress is generated by a chemical strengthening treatment on an end surface portion and a surface portion thereof.