JP2016024002A - Stress measurement method of transparent article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of measuring stress of a glass article with high accuracy even in a case of a thin glass article.SOLUTION: A stress measurement method of a transparent article, after making measurement light incident and propagate to a portion to be measured of a tabular transparent article from a first main surface side of the transparent article that has the first main surface and a second main surface formed into a front-to-rear relation, measures stress of the transparent article on the basis of measurement light emitted to the outside of the transparent article. In a state of contacting a solid or liquid medium having a light permeability to the second surface in advance, the stress measurement method makes measurement light incident or propagate.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a stress measurement method for transparent articles.

  For example, in order to suppress damage to the surface of a display such as a smartphone, a tempered glass plate is used as a cover glass. The strength of the tempered glass sheet against impact, scratching, and the like includes, for example, compressive stress (CS) and compressive stress depth (DOL) as tempering characteristics that depend on the tempering characteristics of the tempered glass plate.

  Conventionally, as a method of measuring the compressive stress and compressive stress depth of the tempered glass plate as described above, the compressive stress and the compressive stress depth are measured by cutting the tempered glass plate and observing the cross section with a polarizing microscope or the like. How to do is known. However, in this method, the compressive stress and the compressive stress depth cannot be measured unless the glass plate is broken.

  In order to solve such a problem, a method for measuring the amount of compressive stress of a tempered glass sheet in a nondestructive manner has been developed (for example, Patent Document 1). In the method described in Patent Document 1, light is incident on the surface layer of the tempered glass plate, and light propagated in the surface layer is emitted out of the tempered glass plate. The light propagating in the surface layer has a photoelastic effect corresponding to the compressive stress of the layer. Therefore, the speed and phase of each of the two types of light components that vibrate along directions parallel and perpendicular to the surface of the tempered glass plate change according to the compressive stress. Therefore, the amount of compressive stress of the tempered glass sheet can be obtained by separating the two light components of the emitted light, converting them into bright line arrays or dark line arrays, and comparing them.

International Publication No. 2012/128184

  By the way, in recent years, a tempered glass plate as a cover glass has been made thinner from the viewpoint of reducing the weight or thickness of the display. However, when the tempered glass plate is thin, the method described in Patent Document 1 may not be able to accurately measure the compressive stress of the tempered glass plate.

  More specifically, when the tempered glass plate is thin, as shown in FIG. 4, the reflected light L3 generated on the second main surface S2 opposite to the first surface layer S1 to be measured is the first reflected light L3. It becomes easy to interfere with the measurement light L4 propagating through the surface layer. When the reflected light L3 interferes with the measurement light L4, it becomes difficult to clearly observe the bright line array and the black line array as shown in FIG. When the bright line array and the black line array cannot be clearly observed, the measurement accuracy of the stress based on the line array is greatly reduced or cannot be measured.

  A main object of the present invention is to provide a method capable of measuring the stress of a transparent article such as glass with high accuracy.

  In the stress measurement method for a transparent article according to the present invention, the plate-shaped transparent article having a first principal surface and a second principal surface that are in a front-back relation is measured from the first principal surface side to the measurement target portion of the transparent article. A method for measuring a stress of a transparent article, wherein the stress of the transparent article is measured based on the measurement light emitted to the outside of the transparent article after the measurement light is incident and propagated. The measurement light is incident and propagated in a state in which a solid or liquid medium having a contact is previously brought into contact.

  According to the stress measurement method for a transparent article of the present invention, by suppressing reflection from the second main surface, interference between the reflected light and the measurement light can be suppressed, and stress measurement accuracy can be improved. In addition, in this invention, a refractive index refers to the absolute refractive index peculiar to each substance when a vacuum is set to 1. Further, the solid or liquid medium includes a sol or gel medium.

In the method for measuring stress of a transparent article according to the present invention, it is preferable to satisfy the formula (A) when the refractive index of air is n ₀ , the refractive index of the transparent article is n ₁ , and the refractive index of the medium is n ₂ .
| N ₁ -n ₀ |> | n ₂ -n ₁ | (A)

  According to such a structure, it can suppress that the measurement light which propagates the inside of a transparent article reflects in the 2nd main surface of a transparent article. Therefore, unnecessary interference between the measurement light propagated through the transparent article and the above-described reflected light can be suppressed. As a result, the measurement light can be observed well, and the stress of the transparent article can be measured with high accuracy.

In the method for measuring stress of a transparent article according to the present invention, when the refractive index of the transparent article is n ₁ and the refractive index of the medium is n ₂ , it is preferable that the formula (B) is satisfied.
n ₂ > n ₁ (B)

  According to such a configuration, it is possible to suppress light once entering the medium from entering the glass article. Therefore, unnecessary interference between the measurement light and the light from the medium can be suppressed.

  In the method for measuring stress of a transparent article according to the present invention, the medium is in contact with the second main surface of the transparent article via the first medium and the liquid first medium that is in contact with the second main surface. And a solid second medium.

  According to such a configuration, the transparent article and the medium are easily brought into close contact with each other, so that the reflection of the measurement light at the boundary between the transparent article and the medium can be more reliably suppressed.

  In the stress measurement method for a transparent article according to the present invention, it is preferable that the medium is made of substantially the same material as the transparent article.

  According to such a configuration, when there are a plurality of transparent articles, the stress of the transparent article can be easily and accurately measured without separately preparing a medium.

  In the stress measurement method for a transparent article according to the present invention, the thickness of the medium is preferably 0.1 mm or more.

  In the range of the thickness of the medium, it is particularly easy to obtain an effect of improving measurement accuracy. In addition, the thickness of a medium means the thickness in the direction perpendicular | vertical with respect to the 1st main surface of a transparent article.

  In the stress measurement method for a transparent article according to the present invention, the thickness of the transparent article is preferably 1 mm or less.

  If it is the range of the thickness of the said transparent article, it will be easy to acquire the effect of a measurement precision improvement especially.

  In the stress measurement method for a transparent article according to the present invention, it is preferable that the transparent article is a tempered glass that has been chemically strengthened, and the surface layer of the first main surface is composed of a compressive stress layer.

  According to such a structure, the compressive stress of the compressive stress layer of chemically strengthened glass can be accurately measured.

  A stress measurement apparatus for a glass article according to the present invention is a stress measurement apparatus for a transparent article that measures the stress of a plate-shaped transparent article having a first main surface and a second main surface that are in a front-back relationship, A support unit that can support the transparent article in a state in which a solid or liquid medium having optical transparency is in contact with the second main surface; and a measurement target portion of the transparent article from the first main surface side. A light source unit that makes measurement light incident thereon, a light receiving unit that receives measurement light emitted after propagating through the transparent article, and a calculation unit that calculates stress of the transparent article based on the measurement light received by the light receiving unit .

  ADVANTAGE OF THE INVENTION According to this invention, even if a glass article is thin, the method which can measure the surface stress etc. of a glass article with high precision can be provided.

It is a typical sectional view of the stress measuring device of the glass article concerning a 1st embodiment. It is a typical sectional view of the stress measuring device of the glass article concerning a 2nd embodiment. It is the image of the bright line row imaged in the Example of this invention. It is typical sectional drawing which shows the stress measuring method of the transparent article which concerns on a prior art. It is the image of the bright line row imaged in the stress measuring method of the transparent article which concerns on a prior art.

  Hereinafter, an example of the preferable form which implemented this invention is demonstrated. However, the following embodiment is merely an example. The present invention is not limited to the following embodiments.

  Moreover, in each drawing referred in embodiment etc., the member which has a substantially the same function shall be referred with the same code | symbol. The drawings referred to in the embodiments and the like are schematically described. A ratio of dimensions of an object drawn in a drawing may be different from a ratio of dimensions of an actual object. The dimensional ratio of the object may be different between the drawings. The specific dimensional ratio of the object should be determined in consideration of the following description.

(First embodiment)
In the following embodiments, a case where the surface stress of the glass article 10 is measured as a transparent article will be described as an example. FIG. 1 is a schematic cross-sectional view of a stress measuring apparatus 1 for a transparent article according to the first embodiment. The stress measuring device 1 is a device that measures the stress of the glass article 10 with the glass article 10 in contact with the medium 12. Hereinafter, the structure of the glass article 10, the medium 12, and the stress measuring device 1 will be described.

  The glass article 10 is, for example, a rectangular flat plate tempered glass plate. The glass article 10 has a first main surface 10a and a second main surface 10b. The first main surface 10a and the second main surface 10b are in a front-back relationship. The glass article 10 has a first surface layer 10A on the first main surface 10a side and a second surface layer 10B on the second main surface 10b side. Each of the first surface layer 10A and the second surface layer 10B is composed of a compressive stress layer having a compressive stress.

The glass article 10 made of a tempered glass article is obtained as follows, for example. First, in mass%, SiO ₂ is 50% to 80%, Al ₂ O ₃ is 5% to 35%, B ₂ O _{3 is 0} to 15%, Na ₂ O is 1% to 20%, and K ₂ O is A glass raw material is measured and prepared so as to have a glass composition containing 0% to 10% and MgO from 0% to 10%, and melted in a melting furnace to obtain a molten glass. Next, the molten glass is formed into a glass article using a forming method such as an overflow down draw method or a float method. Next, a tempered glass article is obtained by performing chemical strengthening treatment by bringing the reinforcing liquid into contact with the surface of the obtained glass article and performing ion exchange. Specifically, the chemical strengthening treatment is performed by immersing the glass plate in a strengthening tank filled with a strengthening solution such as a potassium nitrate solution at 330 ° C. to 480 ° C. for 0.5 to 8 hours. Thereby, the glass article 10 which consists of a chemically strengthened glass plate can be manufactured.

  The medium 12 is a light-transmitting solid or liquid medium, such as a glass plate, a transparent resin plate, or water. The medium 12 has a higher refractive index than air. If the medium 12 is solid, the medium 12 can be easily separated and removed from the glass article 10 after measurement. In the present embodiment, a case where the medium 12 is a glass plate will be described as an example. When the glass article 10 and the medium 12 are both plate-shaped, the shape of the medium 12 is preferably the same as the shape of the glass article 10. The area of the main surface of the medium 12 is preferably equal to or larger than the area of the main surface of the glass article 10. According to such a configuration, the glass article 10 can be easily overlaid on the medium 12, and the entire main surface of the glass article 10 can be easily covered with the medium 12.

  The stress measuring device 1 includes a support unit 11, a light source unit 14, an incident unit 15, an emitting unit 16, a light receiving unit 17, and a calculation unit 18.

  The support part 11 is a member that can be supported in a state where the glass article 10 is in contact with the medium 12, and is a metal or resin stage, for example. When measuring the stress of the glass article 10, for example, the glass article 10 and the medium 12 are stacked on the support portion 11 in a state where the laminated body 13 is formed.

  The light source 14 is a device that emits measurement light for measuring the stress of the glass article 10, and is, for example, a laser light source. The wavelength of the light emitted from the light source 14 can be appropriately determined according to the type of the glass article 10 to be measured. The light source 14 preferably emits light of a single wavelength, but may emit light of a plurality of wavelength bands. The light source 14 may emit light in the visible wavelength range, and may be, for example, an LED or a metal halide lamp.

  The incident part 15 is a member for introducing the measurement light from the light source 14 into the glass article 10 and is, for example, a glass prism. The emission unit 16 is a member for leading the measurement light introduced into the glass article 10 to the light receiving unit 17, and is, for example, a glass prism. The incident part 15 and the emission part 16 are each disposed on the first main surface 10 a of the glass article 10.

  The light receiving unit 17 is a device that receives measurement light emitted from the glass article 10 via the emitting unit 16. More specifically, the light receiving unit 17 is an apparatus that converts each component of the measurement light into a bright line array or a dark line array and captures an image. The light receiving unit 17 includes a lens 17a, a polarizer 17b, and a light receiving element 17d. The lens 17a and the polarizer 17b are an optical system device group for separating the measurement light into two types of components that vibrate along directions parallel and perpendicular to the first surface layer 10A of the glass article 10. The lens 17a is a member that condenses measurement light, and is a lens having positive optical power, for example. The polarizer 17b is a member that polarizes the measurement light collected by the lens 17a. The light receiving element 17d is an element that images a bright line or a dark line of measurement light obtained by passing through the lens 17a and the polarizer 17b, and is, for example, a CCD sensor or a CMOS sensor. The light receiving element 17d outputs the captured image to the calculation unit 18. The light receiving unit 17 may include a plurality of sets of lenses 17a, polarizers 17b, and light receiving elements 17d for each component of the measurement light to be imaged, and the components to be imaged can be switched by rotating the polarizer 17b. It may be configured.

  The calculation unit 18 is a device that calculates the stress of the glass article 10 based on the measurement light received by the light receiving unit 17. The computing unit 18 is, for example, a computer including a processing device such as a CPU and a storage device such as a memory. The calculation unit 18 is preferably configured to be connected to a display device (not shown) such as a display so that the measurement result can be output. Moreover, it is preferable that the calculating part 18 is comprised so that the data of a measurement result can be preserve | saved at a storage device.

  Hereinafter, a method for measuring the stress of the glass article 10 using the stress measuring apparatus 1 will be described. Specifically, a method for measuring the compressive stress of the first surface layer 10A on the first main surface 10a side of the glass article 10 will be described as an example.

  First, the medium 12 is brought into contact with the second main surface 10 b of the glass article 10. At this time, the medium 12 is brought into contact with at least a part of the region corresponding to the measurement target region R (that is, the region through which the measurement light is propagated) for measuring the stress of the first surface layer 10A in the second main surface 10b. Is preferred. In the present embodiment, the glass article 10 and the medium 12 are laminated so that the medium 12 contacts substantially the entire second main surface 10b. More preferably, the glass article 10 and the medium 12 are joined by optical contact. According to such a configuration, an air gap is not easily generated between the glass article 10 and the medium 12, so that the light that has reached the second main surface 10 b inside the glass article 10 is not reflected by the main surface. It can be introduced into the medium 12.

  Next, the glass article 10 and the medium 12 brought into contact with each other as described above are supported by the support portion 11. Specifically, the medium 12 and the glass article 10 are stacked and placed on the support unit 11 so that the glass article 10 side faces the light source unit 14 and the medium 12 side faces the support unit 11. Next, the incident part 15 and the emission part 16 are placed on the glass article 10 (on the first main surface 10a).

  Next, the measurement light is propagated in the glass article 10 arranged as described above. Specifically, the measurement light is irradiated from the light source 14 to the incident portion 15. The measurement light incident on the incident portion 15 is refracted by the incident portion 15 and introduced into the glass article 10.

  At least a part of the measurement light incident on the glass article 10 propagates in the first surface layer 10A (L1 in FIG. 1). On the other hand, part of the measurement light incident on the glass article 10 reaches the second main surface 10b of the glass article 10 (L2 in FIG. 1). Here, since the glass article 10 is in contact with the medium 12 on the second main surface 10b, at least a part of the measurement light L2 reaching the second main surface 10b is reflected on the second main surface 10b. Without entering the inside of the medium 12.

In addition, when the refractive index of air is n ₀ , the refractive index of the glass article 10 is n ₁ , and the refractive index of the medium 12 is n ₂ , the formula (A) is preferably satisfied.
| N ₁ -n ₀ |> | n ₂ -n ₁ | (A)
According to such a configuration, it is possible to more reliably suppress the measurement light from being reflected at the second main surface 10b.

Further, the refractive index of the glass article 10 _{n 1,} the refractive index of the medium 12 _{n 2} is preferably further satisfies the formula (B).
n ₂ > n ₁ (B)
According to such a configuration, the measurement light L2 that has entered the inside of the medium 12 is easily reflected at the interface between the medium 12 and the glass article 10, so that the measurement light L2 can be prevented from returning to the glass article 10 again. That is, measurement light that has not propagated in the first surface layer 10A can be confined in the medium 12 and attenuated. Therefore, it is possible to suppress unnecessary light from interfering with the measurement light L1 propagating in the first surface layer 10A.

  In order to prevent the reflected light of the medium 12 from returning to the glass article 10, it is preferable that the thickness of the medium 12 is set to a certain level or more. Specifically, the thickness of the medium 12 is preferably 0.1 mm or more, more preferably 0.5 mm or more, and further preferably 0.7 mm or more. From the viewpoint of handling, the thickness of the medium 12 is preferably 5 mm or less. Further, an antireflection film or an uneven structure for preventing reflection may be provided on the surface of the medium 12 opposite to the glass article 10 to suppress reflection on the surface.

  The measurement light L1 that has propagated through the first surface layer 10A is led out of the glass article 10 by the emitting portion 16.

The light emitted from the glass article 10 by the emitting unit 16 is guided to the light receiving unit 17. The measurement light introduced into the light receiving unit 17 passes through the lens 17a and the polarizer 17b, and then converges on the light receiving surface 17c of the light receiving element 17d. The light receiving element 17d captures an image including the bright line array and the black line array formed on the light receiving surface 17c, and outputs the image to the calculation unit 18. The computing unit 18 measures the stress of the glass article 10 based on the obtained image. Specifically, the calculation unit 18 calculates stress based on the interval between bright lines and black lines.

  The thinner the glass article 10 is, the easier it is for the reflected light from the second main surface 10b to reach the first surface layer 10A, and the measurement accuracy of stress due to the interference between the reflected light and the measuring light. Tends to decrease. Therefore, when the stress is measured using the method of the present invention, it is more effective when the thickness of the glass article 10 is 1 mm or less, more effective when it is 0.5 mm or less, and 0.2 mm. It is particularly effective when In addition, from the viewpoint of workability, the thickness of the glass article 10 is preferably 0.01 mm or more.

  Hereinafter, other examples of preferred embodiments of the present invention will be described. In the following description, members having substantially the same functions as those of the first embodiment are referred to by the same reference numerals, and description thereof is omitted.

(Second Embodiment)
FIG. 2 is a schematic cross-sectional view of a stress measuring apparatus for a glass article according to the second embodiment.

  In the first embodiment, the example in which the medium 12 is configured by one medium has been described. However, the present invention is not limited to this configuration. The medium 12 may be configured by a stacked body of a plurality of media.

  For example, as illustrated in FIG. 2, the glass article 10 may be configured so that the medium 12 including the first medium 12 a and the second medium 12 b is in contact with the glass article 10. The first medium 12 a is in contact with the second main surface 10 b of the glass article 10. The second medium 12b is in contact with the surface of the first medium 12a opposite to the glass article 10. The first medium 12a is a liquid such as water, alcohol, or an organic solvent. The second medium 12b is a solid member such as a glass plate, for example. According to such a configuration, for example, even when there are minute irregularities or the like on the contact surface of the second medium 12b with the glass article 10, the liquid first medium 12a enters the irregularities, The formation of a gap between the second medium 12b and the glass article 10 can be suppressed, and the solid second medium 12b and the glass article 10 can be easily and reliably adhered to each other.

When the refractive index of air is n ₀ , the refractive index of the glass article 10 is n ₁ , and the refractive index of the first medium 12 a is n ₃ , it is preferable to satisfy the formula (C).

| N ₁ −n ₀ |> | n ₃ −n ₁ | (C)
According to such a configuration, it is possible to more reliably suppress the measurement light from being reflected at the second main surface 10b. Further, when the refractive index of the first medium 12a is n ₃ and the refractive index of the second medium 12b is n ₄ , it is preferable to satisfy the formula (D).

n ₄ > n ₃ (B)
According to such a configuration, it is possible to suppress the measurement light that has entered the second medium 12b from returning to the first medium 12a and the glass article 10 again.

  However, both the first medium 12a and the second medium 12b may be solid or both may be liquid.

  In addition, the structure of the glass article 10 shown to the said embodiment is an example, and can deform | transform suitably. For example, in the glass article 10, at least one of the first and second surface layers 10 </ b> A and 10 </ b> B may not be configured by a compressive stress layer. Further, a compressive stress layer may be formed on the end face of the glass article 10. Moreover, the composition of the glass article 10 is an example, and the glass article of the present invention may be configured using a glass article having an arbitrary composition. Further, the glass article 10 may have any shape as long as it has front and back main surfaces, and may be, for example, a curved plate shape.

  Moreover, in each said embodiment, although the case where the glass article 10 was tempered glass was demonstrated as an example, the glass article 10 may be a glass article which is not strengthened, and is a strengthened glass article, Also good. Further, the glass article 10 may be a glass article that has been chemically strengthened by air cooling strengthening or an ion exchange method. Moreover, the glass article 10 is suitably used as a front plate of a display such as a smartphone, a tablet personal computer (tablet PC), or a notebook computer. The present invention is not limited to the glass article 10 and can be applied to any article as long as it is a transparent article. For example, you may measure the stress of a transparent resin board as a transparent article.

  In the above embodiment, the medium 12 may be made of glass having substantially the same composition as the glass article 10. “Having substantially the same composition” means that the main compositions excluding inevitable impurities are equal. According to such a configuration, for example, a spare sample of the glass article 10 can be used as the medium 12, and it is not necessary to prepare a separate article as the medium 12.

  Moreover, the structure of the said light-receiving part 17 and the calculating part 18 is an example, and as long as it can measure the aspect from which measurement light changes according to the stress of the glass article 10, you may employ | adopt well-known arbitrary structures.

  Moreover, you may arrange | position each structure of the stress measuring device 1 shown in the said embodiment in reverse. That is, it is good also as a structure which irradiates measurement light from the downward direction in the state which mounted the glass article 10 on it, and also mounted the medium 12 on the glass article on the entrance part 15 and the output part 16 as a base. In this case, the incident part 15 and the emission part 16 are constituent members that bear the function of the support part 11.

  Hereinafter, the present invention will be described in more detail on the basis of specific examples. However, the present invention is not limited to the following examples, and may be appropriately modified and implemented without departing from the scope of the present invention. Is possible.

(Example)
As a glass composition, SiO ₂ is 66%, Al ₂ O ₃ is 14.2%, Na ₂ O is 13.4%, K ₂ O is 0.6%, Li ₂ O is 0.1% by mass%. A glass plate having a composition containing 2.3% B ₂ O ₃ , 3.0% MgO and 0.4% SnO ₂ was polished to a thickness of 0.4 mm. Thereafter, a plurality of tempered glass samples were produced by immersing the obtained glass plate in a potassium nitrate solution. FIG. 3 shows an image obtained by laminating the obtained tempered glass samples as the glass article 10 and the medium 12, respectively, and picking up the bright line array by a method substantially similar to the method described in the first embodiment. As can be seen from the image shown in FIG. 3, according to the stress measurement method of the present invention, bright line arrays were clearly observed.

(Comparative example)
FIG. 5 shows the result of imaging the bright line array under the same conditions as in the above example except that the medium 12 was removed. As can be seen from the image shown in FIG. 5, the bright line array could not be clearly observed.

DESCRIPTION OF SYMBOLS 1 Stress measuring apparatus 10 Glass article 10A 1st surface layer 10B 2nd surface layer 10a 1st main surface 10b 2nd main surface 11 Support part 12 Medium 12a 1st medium 12b 2nd medium 13 Laminated body 14 Light source 15 Incident unit 16 Outgoing unit 17 Light receiving unit 17a Lens 17b Polarizer 17c Light receiving surface 17d Light receiving element 18 Calculation unit

Claims (9)

After allowing the measurement light to enter and propagate from the first main surface side of the plate-shaped transparent article having the first main surface and the second main surface in a front-back relationship to the measurement target portion of the transparent article, A stress measurement method for a transparent article, which measures the stress of the transparent article based on the measurement light emitted to the outside of the transparent article,
A stress measurement method for a transparent article, wherein the measurement light is incident and propagated in a state in which a solid or liquid medium having optical transparency is in contact with the second main surface in advance. 2. The transparent article according to claim ₁ , wherein when the refractive index of air is n ₀ , the refractive index of the transparent article is n ₁ , and the refractive index of the medium is n ₂ , the formula (A) is satisfied. Stress measurement method.
| N ₁ -n ₀ |> | n ₂ -n ₁ | (A) 3. The method for measuring stress of a transparent article according to claim ₁ , wherein when the refractive index of the transparent article is n ₁ and the refractive index of the medium is n ₂ , the formula (B) is satisfied.
n ₂ > n ₁ (B) The medium is
A liquid first medium in contact with the second main surface;
A solid second medium in contact with the second main surface of the transparent article via the first medium;
The method for measuring a stress of a transparent article according to any one of claims 1 to 3, wherein:   The method for measuring a stress in a transparent article according to any one of claims 1 to 3, wherein the medium is made of substantially the same material as the transparent article.   The method for measuring a stress of a transparent article according to any one of claims 1 to 5, wherein the thickness of the medium is 0.1 mm or more.   The thickness of the said transparent article is 1 mm or less, The stress measuring method of the transparent article as described in any one of Claims 1-6 characterized by the above-mentioned. The transparent article is a chemically strengthened tempered glass;
The method for measuring stress of a transparent article according to any one of claims 1 to 7, wherein the surface layer of the first main surface is constituted by a compressive stress layer. A stress measuring device for a transparent article for measuring a stress of a plate-like transparent article having a first main surface and a second main surface in a front-back relationship,
A support part capable of supporting the transparent article in a state where at least a part of the second main surface is in contact with a light-transmitting solid or liquid medium;
A light source unit that causes measurement light to enter the measurement target portion of the transparent article from the first main surface side;
A light receiving unit that receives the measurement light emitted after propagating through the transparent article;
A stress measuring apparatus for a transparent article, comprising: an arithmetic unit that measures the stress of the transparent article based on the measurement light received by the light receiving section.