JP2016016996A - Glass plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glass plate suitable for laminating with a sapphire sheet by applying heat.SOLUTION: A glass plate comprises, as represented by mol percentage based on the following oxides, a total 96% or more of SiO, AlO, BO, NaO and MgO, 50% or more of SiO, 3% or more of NaO and 0 to 1% of CaO and has a yield point of 850°C or less, wherein when the average thermal expansion coefficient at 50 to 350°C is defined as α, the average thermal expansion coefficient αis 60×10to 90×10/°C and when the average thermal expansion coefficient from the glass transition point to the yield point is defined as α, a value of L represented by the ratio α/αis 5 or less and the number of particles having a particle diameter of 10 μm or less on the surface is 2500 pieces/mor less.SELECTED DRAWING: Figure 1

Description

  Embodiments of the present invention relate to a glass plate suitable for bonding to a sapphire sheet, and more particularly to a glass plate suitable for bonding to a sapphire sheet by applying heat.

Currently, mobile terminals such as mobile phones and tablet PCs are widely used. A cover material for protecting the display is necessary on the surface of the display of the portable terminal, and chemically tempered glass that has high designability and can achieve high scratch resistance and strength is adopted.
However, chemically tempered glass is generally vulnerable to impacts such as sharpened objects with high hardness. For example, when a portable terminal is dropped on a gravel road or the like and the cover glass collides with a hard, pointed member or an uneven surface, the cover glass is easily broken. As described above, there is a problem that the cover glass is easily broken at the time of use in daily life, leading to a failure of the mobile terminal.
For example, in patent document 1, the laminated body of a sapphire sheet and a glass plate is proposed as a cover glass of a portable terminal. Patent Document 1 shows that a surface having higher hardness and elastic modulus than glass can be used as a display surface by changing the crystal plane of the sapphire sheet. By doing in this way, it is expected that a portable terminal that is unlikely to break the cover material due to impact damage such as the above-mentioned high-hardness acute-angled objects can be expected.

  Patent Document 1 describes that a sapphire-glass laminate suitable for a cover glass can be obtained by laminating a sapphire sheet and a glass plate. Various methods can be considered for bonding the glass and the sapphire sheet. As an example, bonding by heat can be considered. However, bonding of glass and sapphire sheet by heat is a high-temperature process, and what kind of glass plate is suitable for lamination with sapphire sheet has not been studied.

US Patent Application Publication No. 2013/0236699

  Provided is a glass plate suitable for applying heat to bond with a sapphire sheet.

The glass plate of the embodiment of the present invention contains SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , Na ₂ O, and MgO in total of 96% or more in terms of the molar percentage based on the following oxides, and SiO ₂ 50% or more, Na ₂ O 3% or more, CaO 0 to 1%, the yield point is 850 ° C. or less, and the average thermal expansion coefficient at 50 ° C. to 350 ° C. is α ₁ , the average When the coefficient of thermal expansion α ₁ is 60 × 10 ^{−7 to} 90 × 10 ⁻⁷ / ° C., and the average coefficient of thermal expansion from the glass transition point to the yield point or less is α ₂ , the ratio is expressed by a ratio α ₂ / α _1. The value of L is 5 or less, and the number of particles of 10 μm or less on the surface is 2500 / m ² or less.

  A glass plate suitable for applying heat to be bonded to the sapphire sheet can be provided.

It is sectional drawing which showed typically bonding of the glass plate and sapphire sheet of embodiment of this invention. It is a schematic diagram for measuring the size of a particle. It is a schematic diagram which shows an example of the washing | cleaning apparatus which wash | cleans the glass plate of this embodiment.

Below, based on the preferred embodiment shown in an accompanying drawing, the glass plate of this invention is demonstrated in detail.
FIG. 1 is a cross-sectional view schematically showing bonding of a glass plate and a sapphire sheet according to an embodiment of the present invention.
As shown in FIG. 1, the glass plate 10 is bonded to the sapphire sheet 12 by applying heat, for example. The glass plate 10 is suitable for obtaining a sapphire-glass laminate. The surface 10a of the glass plate 10 becomes an adhesive interface.

The glass plate 10 basically contains 96 mol% or more in total of SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , Na ₂ O and MgO as a composition, and 50 mol% or more of SiO ₂ and Na. ₂ O 3 mol% or more, containing CaO 0 to 1 mol%.
The glass plate 10 has a glass transition point of 750 ° C. or less, a bending point of 850 ° C. or less, and a refractive index of 1.47 or more and 1.75 or less as physical property values.
The glass plate 10 has an average thermal expansion coefficient α ₁ of 60 to 90 × 10 ⁻⁷ / ° C. when the average thermal expansion coefficient at 50 ° C. to 350 ° C. is α ₁ . When the average thermal expansion coefficient below the yield point from the glass transition point is α ₂ , the value of L represented by the ratio α ₂ / α ₁ is 5 or less.
The number of particles of 10 μm or less on the surface 10a of the glass plate 10 is 2500 / m ² or less.

Hereinafter, the composition, physical properties, thickness, and surface state of the glass plate 10 will be described.
First, the composition of the glass plate will be described using the mole percentage display content.
SiO ₂ is a component that constitutes the skeleton of the glass and is essential, and is a component that reduces the occurrence of cracks when the surface 10a of the glass plate 10 is scratched (indented). If the SiO ₂ content is less than 50 mol%, the stability as glass, acid resistance, weather resistance or chipping resistance will decrease. SiO ₂ is preferably 55 mol% or more, more preferably 60 mol% or more, still more preferably 62 mol% or more, 64 mol% or more, or 66 mol% or more.
SiO ₂ is lowered viscosity increases melting property of the glass exceeds 72 mol%. The upper limit is preferably 69 mol% or less, more preferably 67 mol% or less, and typically 65 mol% or less.

When the content of Na ₂ O is moderate, it does not increase the coefficient of thermal expansion, improves the melting property of the glass, and lowers the glass transition point and the yield point to reduce the load of the heat welding process. It is an essential component and essential. If Na ₂ O is less than 3 mol%, the glass transition point and yield point increase. Preferably it is 4 mol% or more, More preferably, it is 5 mol% or more. If Na ₂ O exceeds 25 mol%, the thermal expansion coefficient increases, and bonding failure due to a difference in expansion from the sapphire sheet tends to occur. Moreover, weather resistance or acid resistance falls. Or, when it is damaged, cracks are likely to occur. Therefore, the upper limit of the content of Na 2 _O is preferably not more than 25 mol%, 22 mol% and more preferably less, still more preferably not more than 21 mol%.

  CaO is contained in an amount of 1 mol% or less in order to improve the meltability at high temperature or to prevent devitrification. CaO has the feature of increasing the thermal expansion coefficient of glass at a high temperature. If the content exceeds 1 mol%, poor bonding due to a difference in expansion from the sapphire sheet tends to occur. In addition, resistance to cracking is reduced.

Al ₂ O ₃ is a component that improves the durability of the glass, and is a component that reduces the occurrence of cracks when scratched, and is essential. When Al ₂ O ₃ is less than 2 mol%, cracks are likely to occur when scratched, so it is preferable to contain 2 mol% or more. More preferably, it is 5% or more, and further preferably 8% or more. If Al ₂ O ₃ exceeds 25 mol%, the viscosity of the glass becomes high and homogeneous melting becomes difficult, or the acid resistance decreases. The upper limit of the content of Al ₂ O ₃ is preferably 25 mol% or less, more preferably 23 mol% or less, 20 mol% or less, 16 mol% or less, and even more preferably 15 mol% or less. Typically, it is 14 mol% or less.

B ₂ O ₃ has the effect of improving the durability of the glass, is a component that improves the meltability at high temperature or the glass strength, and may be contained in a range of up to 15 mol%. If B ₂ O ₃ exceeds 15 mol%, it is difficult to obtain a homogeneous glass, which may make it difficult to mold the glass, or may reduce crack resistance. The upper limit of the content of B ₂ O ₃ is preferably 15 mol% or less, more preferably 10 mol% or less, still more preferably 7 mol% or less, and typically 5 mol% or less.

  MgO is a component that improves the durability of the glass, has a feature of maintaining the coefficient of thermal expansion of the glass moderately, and is a component that improves the meltability. When the glass plate 10 contains MgO, the content thereof is preferably 1 mol% or more, more preferably 2 mol% or more, more preferably 3 mol% or more. Further, if the content of MgO exceeds 15 mol%, the glass tends to be devitrified. The upper limit of the content of MgO is preferably 15 mol% or less, more preferably 10 mol% or less, still more preferably 8 mol% or less, 7 mol% or less, or 6 mol% or less.

The total content of SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , Na ₂ O and MgO is 96 mol% or more. Thereby, while maintaining high durability such as crack resistance, chipping resistance, and acid resistance of glass, it is possible to obtain a glass plate having appropriate meltability and thermophysical properties suitable for bonding with a sapphire sheet. When the total is less than 96 mol%, it is difficult to achieve necessary durability such as crack resistance while maintaining suitable thermophysical properties. The total content of SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , Na ₂ O and MgO is preferably 97 mol% or more, 98 mol% or more, and 98.3 mol% or more.

ZrO ₂ is not essential, but may be contained in a range of up to 4 mol% in order to reduce the viscosity at high temperature, to improve acid resistance, or to improve the refractive index of the glass. If ZrO ₂ exceeds 10 mol%, there is a possibility that the possibility of cracks generated from the indentation is increased. Preferably it is 2 mol% or less, More preferably, it is 1.5 mol% or less, Most preferably, it is 1 mol% or less.

Li ₂ O and K ₂ O are not essential, but may be added up to 4 mol% in order to adjust the thermal expansion coefficient. The contents of Li ₂ O and K ₂ O are preferably 4 mol% or less, 3 mol% or less, 2 mol% or less, 1.5 mol% or less, and 1 mol% or less, respectively.

  Similar to MgO, SrO has the feature of maintaining the thermal expansion coefficient of glass moderately and may be contained in a range of up to 4 mol%. The content of SrO is more preferably 3 mol% or less, 2 mol% or less, and 1 mol% or less.

Although the glass plate of this embodiment contains the said component substantially, you may contain a total of 4 mol% of another component in the range which does not impair the objective of this invention. Examples of the other components include BaO, ZrO ₂ , TiO ₂ , Y ₂ O ₃ , and CeO ₂ . Further, as a refining agent in melting of the glass, SO _3, chlorides, fluorides, _{halogen, SnO 2, Sb 2 O 3} , the _As 2 _{O 3} or the like may be contained as appropriate. Furthermore, Ni, Co, Cr, Mn, V, Se, Au, Ag, Cd, etc. may be contained for adjusting the color.

Next, the physical property value of the glass plate of this embodiment is demonstrated.
In this embodiment, a thermal expansion coefficient, a glass transition point, and a yield point are measured as follows. A cylindrical sample having a diameter of 5 mm and a length of 20 mm was prepared, measured at a temperature increase rate of 5 ° C./min using a thermal dilatometer, and an average thermal expansion coefficient α ₁ , glass transition point, yield point at 50 to 350 ° C. Then, an average coefficient of thermal expansion α ₂ at a temperature from the glass transition point to the yield point is obtained.

Regarding the glass transition point Tg, if the glass transition point Tg is large, the temperature of the lamination process with sapphire becomes high. Therefore, the glass transition point Tg is preferably 750 ° C. or lower, more preferably 700 ° C. or lower, further preferably 600 ° C. or lower, and particularly preferably 550 ° C. or lower. Moreover, even if it is too low, there exists a possibility that the reactivity with sapphire may worsen. For this reason, the glass transition point Tg is preferably 450 ° C. or higher, more preferably 500 ° C. or higher.
Furthermore, if the yield point of the glass plate is large, the temperature of the lamination process with sapphire becomes high. The yield point is preferably 850 ° C. or lower, more preferably 800 ° C. or lower, further preferably 700 ° C. or lower, particularly preferably 650 ° C. or lower, and the temperature is preferably lower.

Sapphire - when the glass laminate bonded by heat, the difference between the average coefficient of thermal expansion below the glass transition point Tg alpha ₁ and linear thermal expansion coefficient of sapphire (0 to 200 ° C.) is too large, stacked - after annealing Distortion generated at the bonding interface is increased and adhesion failure is likely to occur. For this reason, it is desirable that the thermal expansion coefficient of glass is as close as possible to the linear thermal expansion coefficient (0 to 200 ° C.) of sapphire. Here, the linear thermal expansion coefficient (0 to 200 ° C.) of sapphire is about 69 × 10 ^{−7 to} 76 × 10 ⁻⁷ / ° C. Therefore, it is preferable that the average thermal expansion coefficient alpha ₁ at 50 ° C. to 350 ° C. is ^{60 × 10 -7 ~90 × 10 -7} / ℃. More preferably ^{60 × 10 -7 ~80 × 10 -7} / ℃, more preferably ^{65 × 10 -7 ~75 × 10 -7} / ℃.

Further, the linear thermal expansion coefficient (0 to 1000 ° C.) of sapphire is about 100 × 10 ⁻⁷ / ° C., and it is desirable that the average thermal expansion coefficient α ₂ below the yield point from the glass transition point of the glass is as close as possible. For this reason, it is preferable that average thermal expansion coefficient (alpha) ₂ is 400x10 < ^-7 > / degrees C or less. The average thermal expansion coefficient α ₂ is more preferably 300 × 10 ⁻⁷ / ° C. or less, further preferably 200 × 10 ⁻⁷ / ° C. or less, and particularly preferably 150 × 10 ⁻⁷ / ° C. or less.

The value of L, represented by the average coefficient of thermal expansion alpha ₁ and the average thermal expansion coefficient alpha ₂ ratio α _{2 /} α ₁ is 5 or less.
When the sapphire-glass laminate is bonded by heat, it is necessary to heat the glass to a temperature higher than the glass transition point, and generally the thermal expansion coefficient of the glass greatly changes at the glass transition point. The above-mentioned average linear expansion coefficient α ₂ and average linear expansion coefficient α ₁ represent the thermal expansion coefficient in the high temperature region and the thermal expansion coefficient in the low temperature region during cooling, respectively, and the ratio L = α ₂ / α ₁ is large. As a result, the strain generated at the bonding interface after lamination-slow cooling becomes larger and adhesion failure tends to occur. For this reason, in this embodiment, the value of L is set to 5 or less. Preferably the value of L is 1-5. When the value of L exceeds 5, adhesion failure tends to occur.

In the glass plate of this embodiment, the temperature T _{2 at} which the viscosity of the glass becomes 10 ² dPa · s is preferably 1800 ° C. or less, more preferably 1700 ° C. or less, further preferably 1600 ° C. or less, and particularly preferably 1500 ° C. or less. is there.
The temperature T _{4 at} which the viscosity of the glass of the present embodiment is 10 ⁴ dPa · s is 1350 ° C. or less, more preferably 1200 ° C. or less, and further preferably 1100 ° C. or less.

  The Young's modulus of the glass plate of this embodiment is an important parameter for obtaining a high-strength sapphire-glass laminate, and the bending strength is low when it is lower than 60 GPa, and the impact strength is weak when it is higher than 95 GPa. . The Young's modulus is preferably 60 to 95 GPa. More preferably, it is 60-85 GPa, More preferably, it is 70-85 GPa.

  When the refractive index of the glass plate of the present embodiment is smaller than the sapphire sheet, the larger the difference in refractive index, the more the display display light is reflected at the interface and the transparency is reduced, which may reduce the brightness of the display light. Also, it is better that the refractive index is as high as possible. For this reason, in this embodiment, the refractive index of a glass plate shall be 1.47 or more and 1.75 or less. More preferably, it is 1.5 or more and 1.6 or less, More preferably, it is 1.5 or more and 1.56 or less.

When glass is heat-treated, the redox state of the components changes and the color changes. Therefore, it is preferable that the glass plate of this embodiment is glass with little change in color even after a process of bonding with heat with sapphire.
By determining the permissible range of the perceived color difference, the permissible range of the color change of the glass after the heat treatment can be managed. Generally, the color tolerance is a level of color difference that is hardly noticed in the color separation comparison if it is a class A tolerance, and is a level considered to be the same color. The color difference in the class A tolerance is 3.2 or less (JIS Z 8721, JIS L 0809, etc.). The color difference is preferably 1.6 or less, more preferably 0.8 or less, and still more preferably 0.4 or less.
The color difference value ΔE ^* ab can be calculated as follows: ΔE ^* ab = ((ΔL ^* ) ² + (Δa ^* ) ² + (Δb ^* ) ² ) ^1/2 The L ^* value, a ^* value, and b ^* value are standardized by the CIE (International Lighting Commission), and are also compliant with the L ^* a ^* b ^* color system measurement standardized by JIS (JISX8729) in Japan. , colorimeter: at (Konica Minolta color color difference meter CR400), in the light source _{^{D 65, L * = 98.44,}} a * = -0.20, b * = 0.23 of white standard plate (LTD It can be measured by placing a 1 mm thick glass on Evers, Ever-WHlTE (Code No. 9582)).

When the glass plate of this embodiment is used for a cover glass of a display or the like, display light visibility is better when the dispersion in the visible light region is smaller. The larger the Abbe number (νd), the smaller the dispersion in the visible region. For this reason, the Abbe number νd of the glass plate is preferably 35 or more. More preferably, it is 40 or more, More preferably, it is 50 or more, Most preferably, it is 55 or more. If it is 35 or less, the dispersion becomes large, and the display light visibility decreases.
The Abbe number (νd) can be obtained by the calculation formula {(nd−1) / (nF−nC)}.
Refractive indexes nd, nF, and nC are respectively
nd: refractive index with respect to Fraunhofer d-line (587.56 nm) nF: refractive index with respect to Fraunhofer F-line (486.1 nm) nC: refractive index with respect to Fraunhofer C-line (656.3 nm).

Moreover, when the photoelastic constant is large, the distortion of the display when the glass plate is distorted increases. For this reason, the photoelastic constant of the glass plate of this embodiment is preferably 3.5 (× 10 ⁻⁷ cm ² / kg) or less, and 3.0 (× 10 ⁻⁷ cm ² / kg) or less, 2 0.9 (× 10 ⁻⁷ cm ² / kg) or less and 2.8 (× 10 ⁻⁷ cm ² / kg) or less. The photoelastic constant can be measured by a disk compression method.
Moreover, it is not preferable that the haze value deteriorates after heat treatment and after lamination. Therefore, the haze value of the glass plate is preferably 1.5% or less, more preferably 1% or less, and still more preferably 0.6% or less.
The haze value H (%) is the ratio of diffusely transmitted light to the total light transmitted light when light is incident on the glass sample, and is represented by the following formula.
H (%) = Td / Tt × 100
Td: Diffuse transmittance Tt: Total light transmittance The haze value can be measured using, for example, a haze meter HZ-2 type.

As shown in FIG. 1, when manufacturing a laminated body by applying heat and bonding the sapphire 12 and the glass plate 10, it is necessary to pay particular attention to the cleanliness of the glass plate surface. The number of particles of 10 μm or more on the bonding surface (main surface) 10a of the glass plate of the present embodiment is 2500 / m 2 or less. This is because if the number of particles exceeds 2500 / m ² , defects such as bubble defects are likely to occur during bonding. When the number of particles is 1000 / m ² or less, defects can be more effectively suppressed, and when the number is 100 / m ² , a high effect can be obtained. As a method for increasing the cleanliness of the glass plate surface, it is preferable to rinse with pure water or ion-exchanged water after cleaning with a cleaning liquid. The number of particles can be reduced by adjusting the type of cleaning liquid, cleaning time, rinsing time, and the like.

  In addition, it is preferable that the glass plate of this embodiment is glass for chemical strengthening. Conventional glass for chemical strengthening has not been required to have a high level of cleanliness on the surface of the glass plate in the cleaning before the strengthening process. The glass plate of this embodiment is unstrengthened glass. In the case of chemically strengthened glass, when the sapphire-glass laminate is produced by applying heat, the strengthening is relaxed by heat. Therefore, when strengthening, it strengthens after bonding with sapphire. In the present embodiment, the number of particles having a size of 10 μm or more can be measured using, for example, a substrate appearance inspection method described in JP2013-228232A.

  Here, the particle size refers to the diameter x μm of a circle in contact with the outer shape of the particle 14 as shown in FIG. The size can be measured by an optical microscope with a scale, a laser microscope, a general surface defect inspection machine for substrates, and the like. Types of particles include organic substances, inorganic substances, and minute glass pieces.

For cleaning the glass plate, for example, a sheet-type cleaning experiment apparatus manufactured by Speed Fem Clean System can be used in a class 100 clean room. For example, a cleaning device 20 shown in FIG. 3 is used for cleaning the glass plate 10. The cleaning method is not limited to using the cleaning apparatus 20 shown in FIG.
In the cleaning device 20 shown in FIG. 3, first, the glass plate 10 is cleaned by a high pressure shower using pure water in the first unit 22. Next, the second unit 24 performs cleaning of both surfaces of the glass plate with a triple brush in combination with a pure water shower. Next, a high pressure shower using pure water is applied in the third unit 26, a shower using pure water is then applied in the fourth unit 28, and finally the fourth unit 40 is dried by an air knife. In this way, the glass plate 10 can be cleaned.

If the surface 10a of the surface 10a of the glass plate 10 has a lot of OH groups or the surface 10a of the glass plate 10 containing a large amount of alkali cations, it becomes easy to form an interdiffusion layer of each component at the glass plate-sapphire sheet interface, so a sapphire sheet It is suitable for obtaining a laminate of sapphire-glass because of the high reactivity at the time of bonding the glass plate.
For this reason, the β-OH value on the surface of the glass plate is preferably 0.1 to 1.0 / mm, more preferably 0.1 to 0.75 / mm, and 0.1 to 0.5 / mm. Is more preferable.
The “β-OH value” is a value obtained by measuring the transmittance of glass using FT-IR and using the following mathematical formula. β-OH value = (1 / t) log 10 (T ₁₁ / T ₂₁ )
Here, t: glass plate thickness, T ₁₁ : transmittance (%) at a wavelength of 4000 cm ⁻¹ , T ₂₁ : transmittance (%) at a wavelength of 3500 cm ⁻¹ .

  Moreover, when the arithmetic mean roughness (JIS B0601-2001) of the surface 10a of the glass plate 10 is too large, it is easy to produce bonding defects, such as a bubble defect at the time of adhesion | attachment, and the smaller one is suitable for obtaining the laminated body of sapphire-glass. Yes. The arithmetic average roughness Ra is preferably 100 nm or less, more preferably 50 nm or less, and still more preferably 10 nm or less.

  The manufacturing method of the glass plate of the present embodiment is not particularly limited. For example, an appropriate amount of various raw materials are prepared, heated to about 1400 to 1800 ° C. and melted, and then homogenized by defoaming, stirring, etc. It is produced by forming into a plate shape by the method, down draw method, pressing method, etc., and cooling to a desired size after slow cooling. A plate-like manufacturing method that can be produced in large quantities at low cost, such as the above-described float method, fusion, down-draw method, etc., is desirable.

If the glass plate or sapphire sheet is too thick, the weight increases and is unsuitable for mobile use such as a portable terminal. Therefore, the thickness h (see FIG. 1) of the glass plate 10 of this embodiment may be 2 mm or less. preferable.
As a combination of a glass plate and a sapphire sheet, for example, the thickness of the glass plate is 0.2 to 1.5 mm, the thickness of the sapphire sheet is 1 μm to 1.0 mm, and the thickness of the glass plate is 0.2. More preferably, the thickness of the sapphire sheet is 1 μm to 1.0 mm, and more preferably the thickness of the glass plate is 0.2 to 0.5 mm, and the thickness of the sapphire sheet is 1 μm to 0 mm. .5 mm.

  The glass plate of the present embodiment is capable of suppressing the occurrence of distortion and bonding defects at the bonding interface when the sapphire sheet is bonded by heat by regulating the composition, physical property values and form. Bonding can be performed without causing defects, and a high-strength sapphire-glass laminate can be obtained.

  The present embodiment is basically configured as described above. As mentioned above, although the glass plate of this embodiment was demonstrated in detail, this invention is not limited to the said embodiment, Of course, in the range which does not deviate from the main point of this invention, you may make a various improvement or change. is there.

Hereinafter, the effect of the glass plate of this embodiment is demonstrated.
The composition and content of the glass plate of the Example (No. 1-14) shown in Table 1, and the comparative example (No. 1-9) shown in Table 2 are shown.
The raw materials of each component were prepared so that the glass plate after molding had the composition and content shown in Tables 1 and 2, and were melted at a temperature of 1500 to 1660 ° C. using a platinum crucible. In melting, the mixture was stirred using a platinum stirrer to homogenize the glass. Next, the molten glass was poured out as it was, formed into a plate having a desired thickness, and then slowly cooled to obtain glass plates of Examples and Comparative Examples.
Of the glass plates of Examples and Comparative Examples, Comparative Example No. Except for the 6 glass plate, the glass plate surface was cleaned by the glass plate cleaning method using the cleaning apparatus shown in FIG. 3 as described above.

Example No. 1 to 14 and comparative example No. About the glass plates of 1-9, as shown in the following Tables 1 and 2, average thermal expansion coefficients α ₁ and α ₂ , glass transition point (Tg), yield point, Young's modulus, refractive index, photoelastic constant, and number of particles Was measured.

[Average thermal expansion coefficient α ₁ , α ₂ , glass transition point (Tg), yield point]
An average linear expansion coefficient α _{1 of} 50 ° C. to 350 ° C., a glass transition point (Tg), a yield point, and an average thermal expansion coefficient α ₂ below the yield point from the glass transition point are expressed by a differential thermal dilatometer (TMA ).
Based average linear expansion coefficient alpha ₁ and the average thermal expansion coefficient alpha ₂ the measurement results was calculated the value of L, represented by the ratio α _{2 /} α _1.
[Young's modulus]
Young's modulus was measured by an ultrasonic pulse method (JIS R1602).
[Refractive index]
The refractive index (nd) at a wavelength of 587.6 nm (d-line) was measured as follows.
A sample processed into a rectangular parallelepiped shape having a side of 20 mm and a thickness of 10 mm was measured using a precision refractometer (manufactured by Shimadzu Corporation, trade name: KPR-2000).
[Photoelastic constant]
A mercury lamp (wavelength 546.1 nm) was used as a light source, and a sample processed into a cylindrical shape of Φ20 to 15 mm × 10 to 15 mm was used, and measurement was performed by a disk compression method.
[Number of particles]
The number of particles (pieces / m ² ) was measured using the substrate appearance inspection method described in JP2013-228232A.

In Example No. 1 shown in Table 1 above. The glass plates 1 to 14 are within the scope of the present invention, and when bonded to the sapphire sheet by thermal bonding, the distortion at the bonding interface and the occurrence of bonding defects can be suppressed. There is no defect.
On the other hand, Comparative Example No. 1 and 2 have a large CaO content, a small total amount of SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , Na ₂ O and MgO, and a value of α ₂ / α ₁ exceeds 5. , Crack resistance is poor and adhesion failure tends to occur. For this reason, it is unsuitable for lamination with a sapphire sheet.
Comparative Example No. _No. 3 has a high CaO content, the value of α ₁ is less than the lower limit, and the value of α ₂ / α ₁ exceeds 5, so that the crack resistance is poor and adhesion failure is more likely to occur. For this reason, it is unsuitable for lamination with a sapphire sheet.
Comparative Example No. 4 has a large CaO content, a small total amount of SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , Na ₂ O, and MgO, the value of α ₁ exceeds the upper limit, and α ₂ / α ₁ Since the value exceeds 5, crack resistance is poor and adhesion failure is more likely to occur. For this reason, it is unsuitable for lamination with a sapphire sheet.
Comparative Example No. 5 and 6 have a high CaO content and a small total amount of SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , Na ₂ O, and MgO, so that they have poor crack resistance and are not suitable for lamination with a sapphire sheet. .
Comparative Example No. _No. 7 has a low α ₁ value and a large difference in thermal expansion coefficient from that of the sapphire sheet, so that adhesion failure tends to occur. For this reason, it is unsuitable for lamination with a sapphire sheet.
Since Comparative Example No. 8 has a value of α ₂ / α ₁ exceeding 5, adhesion failure tends to occur. Not suitable for lamination with sapphire sheets.
In Comparative Example No. 9, the value of the yield point exceeds 850 ° C., so the load on the heat welding process is large and unsuitable for lamination with the sapphire sheet.

10 Glass plate 12 Sapphire sheet 14 Particle 20 Cleaning device

Claims (4)

A molar percentage based on the following _{oxides, SiO 2, Al 2 O 3} , B 2 O 3, Na 2 O, containing 96% or more of MgO in total, and SiO ₂ 50% or more, the Na ₂ O 3 % Or more, containing 0 to 1% CaO,
When the yield point is 850 ° C. or lower and the average thermal expansion coefficient at 50 ° C. to 350 ° C. is α ₁ , the average thermal expansion coefficient α ₁ is 60 × 10 ^{−7 to} 90 × 10 ⁻⁷ / ° C., glass transition When the average coefficient of thermal expansion below the yield point is α ₂ , the value of L represented by the ratio α ₂ / α ₁ is 5 or less,
A glass plate, wherein the number of particles of 10 μm or less on the surface is 2500 / m ² or less.   The glass plate according to claim 1, which is untempered glass.   The glass plate according to claim 1 or 2, wherein the plate thickness is 2 mm or less. Glass plate according to any one of claims 1 to 3 ₂ average coefficient of thermal expansion below the yield point of the glass transition point α is 400 × 10 -7 ^/ ℃ or less.

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