JP2005043165A - Evaluation method of double-strength glass - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an evaluation method capable of removing double-strength glass which has a fear of producing a large broken piece by eliminating a problem wherein there is a possibility of producing the large broken piece called an island in a part of double-strength glass even when it is a JIS accepted product. <P>SOLUTION: Double-strength glass is evaluated by a stress evaluating step for confirming that the surface compressive stress of the double-strength glass is within a range prescribed by JIS R 3222, a stress difference evaluating step for confirming that the difference between the maximum and minimum values of surface compressive stress measured over the whole surface of the double-strength glass is not higher than a predetermined value and a stress balance ratio evaluating step for investigating the balanced part and unbalanced part of compressive stress and tensile stress in the thickness direction of the double-strength glass to confirm that the ratio of the balanced part occupied in a measuring frame is not higher than the predetermined value. By making the evaluation of the double-strength glass severe as mentioned above, the double-strength glass having possibility to produce a large broken piece can be preliminarily removed to more enhance safety. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for evaluating double strength glass.
[0002]
[Prior art]
Glass that has been increased in strength (wind pressure resistance, thermal cracking strength) by about twice as much as that of float plate glass of the same thickness is called double strength glass. Since this double strength glass is suitable for the window glass of a high floor of a building, the demand has been increasing in recent years. Double strength glass is manufactured and managed in accordance with the following Japanese Industrial Standard (for example, Non-Patent Document 1).
[0003]
[Non-Patent Document 1]
Japanese Industrial Standard JIS R 3222-1996 “Double Strength Glass”
[0004]
Non-Patent Document 1 Note that “double-strength glass” refers to the method of cracking near the sheet glass of the material when the sheet glass is heat-treated to form a compressive stress layer of an appropriate size on the surface of the glass sheet, increasing the fracture strength, and breaking. There is a description of ".
[0005]
Further, Non-Patent Document 1 specifies the following rules.
3.3 "surface compressive stress surface compressive stress was measured by 6.4, each measured value is 20 mN / ^{m 2} or more, and must kicked such a 60 mN / ^{m 2} or less."
In 6.4 (1), “... the surface compressive stress at the four intersections of the straight line and the diagonal line shall be measured.”
[0006]
6.4 (2) In lines 8 to 11, “In double-strength glass, birefringence occurs between light in the direction of the vibration surface along the glass surface and light in a direction perpendicular thereto due to surface compressive stress. Measures the difference in refractive index proportional to the surface compressive stress by measuring the distance (D) between the ... dark line (A) and ... the dark line (B). Value. "
A specific calculation formula is shown in 6.4 (4).
[0007]
On the other hand, a phenomenon called natural breakage may be a problem with glass plates. This natural breakage refers to breaking despite being used below the allowable stress.
This destruction is considered to proceed starting from scratches on the surface and NiS (nickel sulfide) phase transition.
[0008]
[Problems to be solved by the invention]
9 (a) and 9 (b) are broken shape diagrams of a conventional glass plate.
(A) shows a state in which cracks 103 have entered substantially radially from a point 102 where the float plate glass 101 is located. Since there is the window frame 104, there is no fear that the broken glass will come off immediately or fall. This corresponds to “It becomes a cracking method close to a sheet glass of material” noted in JIS.
[0009]
(B) shows the phenomenon seen in some double-strength glass 111. That is, the point 112 with the double-strength glass 111 is shown as a starting point, and a state in which the crack 113 is almost round is shown. Since the window frame 114 is present, the edge of the double-strength glass 111 remains, but there is a possibility that a round piece called an island 115 falls as indicated by an imaginary line.
It is necessary to avoid such an island 115 falling from the high part of the building.
[0010]
However, most of the double-strength glass that has passed the JIS has a cracking manner as described in (a) above. However, although it is a small part, the round crack 113 may enter into the double-strength glass 111 in spite of passing the said JIS. However, the destruction is not as remarkable as described in (b) above. However, it is necessary to prevent the round crack 113 even if it is mild.
[0011]
[Means for Solving the Problems]
There are two methods for improving the reliability of double-strength glass: (1) improving manufacturing technology and (2) improving the evaluation method while maintaining the existing manufacturing technology. Although (1) is preferred, there are a wide variety of items to be solved, so the evaluation method (2) was established first. If an evaluation method is established, by using this evaluation method, the manufacturing technique (1) can be easily evaluated and the manufacturing technique can be improved efficiently.
[0012]
In order to establish the evaluation method (2), the present inventors first examined the influence of NiS, and then examined the number of cracks and the size of the island.
FIG. 1 is a graph in which the relationship between surface compressive stress and NiS particle size is examined, and the range of 20 to 60 (MN / m ² ) on the horizontal axis is the JIS pass range. The area C is an area where natural damage is likely to occur, the area A is an area where there is no fear of natural damage, and the area B is an intermediate area.
[0013]
For example, the point P1 is a point where the surface compressive stress is 40 (MN / m ² ) and the particle size of NiS is 100 μm. There is no natural damage at this point.
On the other hand, the point P2 is a point where the surface compressive stress is 40 (MN / m ² ) and the particle size of NiS is 400 μm. Natural damage is likely to occur at this point.
[0014]
It can be easily recognized that the larger the particle size of NiS, the easier it is to become the starting point and the stronger the action of promoting destruction. As a result, it was confirmed that there is a possibility that natural breakage may occur even though it is a JIS-accepted product.
[0015]
FIG. 2 is a diagram showing an example of how to crack.
(A) shows that one crack 12 entered the double-strength glass 10 from the starting point 11. In this double-strength glass 10, the surface compressive stresses σ1 to σn are measured in advance before the crack 12 is generated. These surface compressive stresses σ1 to σn can be measured by a measuring method defined in JIS R 3222-1996.
When the maximum value σmax and the minimum value σmin were selected from the surface compressive stresses σ1 to σn and the stress difference Δσ = (σmax−σmin) was determined, it was 18 MN / m ² .
[0016]
(B) shows that the crack 22 and the crack 23 entered the double strength glass 20 from the starting point 21. This double-strength glass 20 had a stress difference Δσ of 20 MN / m ² .
(C) shows that the crack 32 and the cracks 33 and 34 entered the double-strength glass 30 from the starting point 31, and the island 35 was generated. This double-strength glass 20 had a stress difference Δσ of 24 MN / m ² .
[0017]
From the above example, it is expected that the more the number of cracks increases, the more easily islands are generated and the risk of falling off the window frame increases. The number of cracks is considered to depend on the magnitude of the stress difference Δσ, that is, the maximum surface compressive stress difference Δσ.
This is because when the surface compressive stress is non-uniform, it can be estimated that the larger the difference between the maximum value and the minimum value, the larger the strain remains, which affects the fracture. Therefore, an experiment was performed with an increased number of samples. The result is shown in the following figure.
[0018]
FIG. 3 is a graph in which the relationship between the stress difference and the crack is examined. The horizontal axis indicates the maximum surface compressive stress difference Δσ, and the vertical axis indicates the number of cracks. Black dots indicate acquired data, and a broken line B can be drawn from these black circles.
From the graph, it can be seen that when the maximum surface compressive stress difference Δσ exceeds 20 MN / m ² , the broken line B rises rapidly and the number of cracks increases rapidly.
[0019]
Assuming that the glass plate is cracked, if the number of cracks is 1-2, islands are unlikely to occur. Since the horizontal axis corresponding to “2” on the vertical axis is “15”, it can be said that the degree of risk is very small if the maximum surface compressive stress difference Δσ is 15 MN / m ² or less.
[0020]
Although it is ideal to keep the number of cracks to two, according to the observations by the present inventors, it has been found that when the number of cracks is up to four, the generation of islands can be substantially prevented. Since the horizontal axis corresponding to “4” on the vertical axis is “20”, the maximum surface compressive stress difference Δσ is allowable up to 20 MN / m ² .
[0021]
Therefore, when evaluated in the number of cracks, the maximum surface compressive stress difference Δσ is 20 mN / ^{m 2} or less, desirably a 15 mN / ^{m 2} or less times strength glass, and acceptable product.
[0022]
Next, consider the size of the island.
Note that a double strength glass is sandwiched between two polarizing plates, and a balance between compressive stress and tensile stress in the thickness direction can be observed using a light source. The balanced part becomes black and the unbalanced part becomes white, so that it can be optically observed.
[0023]
FIG. 4 is a diagram showing an example when the relationship between the optical observation and the island is examined. For the convenience of drawing, the balanced part was left blank and the unbalanced part was hatched.
(A) shows the double-strength glass 40 including the unbalanced portion 41 and the balanced portion 42. A rectangular measurement frame 46 having a side of 150 mm or more is disposed at a position where the unbalanced portion 41 of the double-strength glass 40 is maximized, and the area inside the measurement frame 46 is S1, and the area of the balance portion 42 in the measurement frame 46 is S2. For example, the proportion of the balanced portion occupying the area in the measurement frame 46 can be represented by S2 / S1.
The ratio of the balance portion expressed as a percentage is referred to as “plate thickness direction residual stress balance ratio” (= 100 × S2 / S1).
[0024]
In (b), the crack starting point 43 is artificially generated. Specifically, a small hole is drilled to the center of the plate thickness with a drill. If left in this state for a while, a crack 44 entered and an island 45 was formed.
[0025]
For comparison, (c) and (d) were tried.
The double-strength glass 50 in FIG.
In (d), a crack 54 entered from the starting point 53, but no island was formed.
[0026]
From the above, it is expected that the presence or absence of the unbalanced portion 41 is related to the occurrence of islands, and the size of the unbalanced portion 41, that is, the size of the balanced portion 42 is related to the size of the island.
Therefore, the number of samples was increased and the relationship was examined in detail. The results will be described with reference to the next figure.
[0027]
FIG. 5 is a graph showing the relationship between the plate thickness direction residual stress balance ratio and the total area of the island, the horizontal axis is the plate thickness direction residual stress balance ratio (= 100 × S2 / S1), and the vertical axis is the island. Total area is shown. If there are multiple islands, the total area of the islands is the total. The horizontal axis is an equally spaced scale, and the vertical axis is a logarithmic scale.
[0028]
On the horizontal axis, “100” is all a balanced part and the unbalanced part is 0, so no island is generated. On the other hand, since “50” on the horizontal axis is 50% of the balanced portion and 50% of the unbalanced portion, an island having a small area of 10 mm ² or less is generated. Since 90% of “10” on the horizontal axis is an unbalanced portion, an island with a total area of 10 ⁶ mm ² is generated.
[0029]
According to the study by the present inventors, if the island is 10 ³ mm ² (a circle having a diameter of 35 mm or a corner having a size of 32 mm × 32 mm), even if it is dropped, human and property damage is minimized. Can be fastened. 10 ³ mm ^{2 on the} vertical axis of the graph corresponds to 30% of the horizontal axis.
That is, from the size of the islands, it can be said that if the residual stress balance ratio in the thickness direction is 30% or more, the problem that is concerned with the conventional double-strength glass can be solved.
[0030]
Based on the above description, the present invention can be summarized as follows.
Claim 1 is a stress evaluation step for confirming that the surface compressive stress of double-strength glass is within the range defined by Japanese Industrial Standard JIS R 3222;
A stress difference evaluation step for confirming that the difference between the maximum value and the minimum value of the surface compressive stress measured over the entire surface of the double-strength glass is equal to or less than a predetermined value, and evaluating by a plurality of evaluation steps .
[0031]
The standard is cleared in the stress evaluation step. In the stress difference evaluation step, the number of cracks generated is suppressed to a level that does not cause actual damage.
Therefore, according to the first aspect, since the number of cracks is small even if cracks occur in the double-strength glass, the actual damage such as dropout can be kept to a minimum. Glass can be provided.
[0032]
Claim 2 is a stress evaluation step for confirming that the surface compressive stress of the double-strength glass is within the range defined by Japanese Industrial Standard JIS R 3222;
Examine the balance and unbalance of compressive stress and tensile stress in the plate thickness direction, install a rectangular measurement frame with a side of 150 mm or more where the unbalance is maximized, and the proportion of the balance in the measurement frame is Evaluation is performed by a plurality of evaluation steps including a stress balance rate evaluation step for confirming that the value is equal to or greater than a predetermined value.
[0033]
The standard is cleared in the stress evaluation step. Then, in the stress balance rate evaluation step, the size of the island is suppressed to a level where there is no actual harm.
Therefore, according to the second aspect, even if a double-strength glass is cracked or an island is generated, since the island is small, the actual damage can be kept to a minimum. Strength glass can be provided.
[0034]
Claim 3 is a stress evaluation step for confirming that the surface compressive stress of the double-strength glass is within the range defined by Japanese Industrial Standard JIS R 3222;
A stress difference evaluation step for confirming that the difference between the maximum value and the minimum value of the surface compressive stress measured over the entire surface of the double-strength glass is not more than a predetermined value;
Examine the balance and unbalance of compressive stress and tensile stress in the plate thickness direction, install a rectangular measurement frame with a side of 150 mm or more where the unbalance is maximized, and the proportion of the balance in the measurement frame is Evaluation is performed by a plurality of evaluation steps including a stress balance rate evaluation step for confirming that the value is equal to or greater than a predetermined value.
[0035]
The standard is cleared in the stress evaluation step. In the stress difference evaluation step, the number of cracks generated is suppressed to a level that does not cause actual damage. Furthermore, in the stress balance rate evaluation step, the size of the island is suppressed to a level that does not cause actual damage.
[0036]
Therefore, according to the third aspect, since the number of cracks is small even if cracks occur in the double-strength glass, it is possible to minimize the actual damage such as falling off, and even if cracks occur, islands can be prevented. Even if it occurs, since the islands are small, the actual damage can be kept to a minimum, so that it is possible to provide extremely safe double-strength glass.
[0037]
According to a fourth aspect of the present invention, the predetermined value used in the stress difference evaluation step is 20 MN / m ² .
If the stress difference is 20 MN / m ² or less, the number of cracks can be reduced to 4 or less.
[0038]
According to a fifth aspect of the present invention, the predetermined value used in the stress balance rate evaluation step is 30%.
If the stress balance ratio is 30% or more, the total area of the generated islands can be 1000 mm ² or less.
[0039]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 6 is a flow chart of the double strength glass evaluation method according to the first embodiment of the present invention. STxx indicates a step number. same as below.
ST01: Based on JIS R 3222, surface compressive stresses σ1 to σ4 in the vicinity of corners (four points in total) of the rectangular double strength glass are measured.
[0040]
ST02: Check whether σ1 is within a range of ²⁰ to 60 MN / m ² . It is examined whether or not σ2 is within a range of ²⁰ to 60 MN / m ² . It is examined whether or not σ3 is in the range of ²⁰ to 60 MN / m ² . It is examined whether or not σ4 is in the range of ²⁰ to 60 MN / m ² . If any one of σ1 to σ4 is not acceptable, it is determined to be unacceptable and the evaluation flow ends.
[0041]
ST03: The surface of the rectangular double-strength glass is finely divided into a lattice shape, and the surface compressive stresses σ1 to σm at the intersections of the vertical and horizontal lines are measured. The number of measurement points is several tens to several hundreds. The surface compressive stress is measured based on JIS as in ST01. Σ1 to σ4 in ST01 and σ1 to σm in this step can be measured simultaneously.
[0042]
ST04: The maximum value σmax is selected from the surface compressive stresses σ1 to σm. This operation can be performed instantly by using an electronic computer.
ST05: A minimum value σmin is selected from the surface compressive stresses σ1 to σm. This operation can also be performed instantly by using an electronic computer.
[0043]
ST06: Check whether the stress difference (σmax−σmin) is 20 MN / m ² or less. If it is no, it is determined as rejected. If it is YES, it will determine with the double strength glass of evaluation object being an acceptable product.
[0044]
To summarize the above, the first example is a stress evaluation step (ST01 to ST02) for confirming that the surface compressive stress of the double-strength glass is within the range defined by Japanese Industrial Standard JIS R 3222;
A stress difference evaluation step (ST03 to ST06) for confirming that the difference between the maximum value and the minimum value of the surface compressive stress measured over the entire surface of the double-strength glass is a predetermined value or less (for example, 20 MN / m ² or less); The evaluation is performed by a plurality of evaluation steps.
[0045]
The standard is cleared in the stress evaluation step. In the stress difference evaluation step, the number of cracks generated is suppressed to a level that does not cause actual damage.
Accordingly, even if cracks occur in the double strength glass, since the number of cracks is small, it is possible to minimize the actual damage such as dropout, and therefore it is possible to provide a safer double strength glass. .
[0046]
FIG. 7 is a flowchart of a method for evaluating double strength glass according to the second embodiment of the present invention.
ST11: Based on JIS R 3222, surface compressive stresses σ1 to σ4 near the corners (four points in total) of the rectangular double-strength glass are measured.
[0047]
ST12: Check whether σ1 is within a range of ²⁰ to 60 MN / m ² . It is examined whether or not σ2 is within a range of ²⁰ to 60 MN / m ² . It is examined whether or not σ3 is in the range of ²⁰ to 60 MN / m ² . It is examined whether or not σ4 is in the range of ²⁰ to 60 MN / m ² . If any one of σ1 to σ4 is not acceptable, it is determined to be unacceptable and the evaluation flow ends.
[0048]
ST13: A double-strength glass is sandwiched between two polarizing plates, and a balance between compressive stress and tensile stress in the thickness direction is observed using a light source. The balanced part becomes black and the unbalanced part becomes white, so that it can be optically observed.
[0049]
ST14: If a rectangular measurement frame with a side of 150 mm or more is placed at a location where the unbalanced portion of the double-strength glass is maximized, the area in the measurement frame is S1, and the area of the balance portion in the measurement frame is S2, the measurement frame The proportion of the balanced portion in the inner area can be represented by S2 / S1. The ratio of the balance portion expressed as a percentage is referred to as “plate thickness direction residual stress balance ratio” (= 100 × S2 / S1). It is checked whether (S2 / S1) × 100 is 30% or more.
If it is NO in ST14, it is determined to be a failure. If it is YES, it will determine with a pass.
[0050]
Summarizing the above, in the second example, the stress evaluation step (ST11 to ST12) for confirming that the surface compressive stress of the double-strength glass is within the range defined by Japanese Industrial Standard JIS R 3222, and
Examine the balance and unbalance of compressive stress and tensile stress in the plate thickness direction, install a rectangular measurement frame with a side of 150 mm or more where the unbalance is maximized, and the proportion of the balance in the measurement frame is Evaluation is performed by a plurality of evaluation steps including a stress balance rate evaluation step (ST13 to ST14) for confirming that the value is a predetermined value or more (for example, 30% or more).
[0051]
The standard is cleared in the stress evaluation step. Then, in the stress balance rate evaluation step, the size of the island is suppressed to a level where there is no actual harm.
Therefore, even if a crack occurs or an island occurs in the double-strength glass, since the island is small and the actual damage can be minimized, it is possible to provide a safer double-strength glass. it can.
[0052]
FIG. 8 is a flow chart of the double strength glass evaluation method according to the third embodiment of the present invention. ST21: Based on JIS R 3222, surface compressive stresses σ1 to σ4 near the corners (four points in total) of the rectangular double-strength glass are measured.
[0053]
ST22: It is checked whether or not σ1 is within a range of ²⁰ to 60 MN / m ² . It is examined whether or not σ2 is within a range of ²⁰ to 60 MN / m ² . It is examined whether or not σ3 is in the range of ²⁰ to 60 MN / m ² . It is examined whether or not σ4 is in the range of ²⁰ to 60 MN / m ² . If any one of σ1 to σ4 is not acceptable, it is determined to be unacceptable and the evaluation flow ends.
[0054]
ST23: The surface of the rectangular double-strength glass is finely divided into a lattice shape, and the surface compressive stresses σ1 to σm at the intersections of the vertical and horizontal lines are measured. The number of measurement points is several tens to several hundreds.
ST24: The maximum value σmax is selected from the surface compressive stresses σ1 to σm. This operation can be performed instantly by using an electronic computer.
[0055]
ST25: A minimum value σmin is selected from the surface compressive stresses σ1 to σm. This operation can also be performed instantly by using an electronic computer.
ST26: It is examined whether the stress difference (σmax−σmin) is 20 MN / m ² or less. If it is no, it is determined as rejected. If yes, continue.
[0056]
ST27: A double-strength glass is sandwiched between two polarizing plates, and a balance between compressive stress and tensile stress in the thickness direction is observed using a light source. The balanced part becomes black and the unbalanced part becomes white, so that it can be optically observed.
[0057]
ST28: If a rectangular measurement frame with a side of 150 mm or more is placed at the location where the unbalanced portion of the double-strength glass is maximized, the area in the measurement frame is S1, and the area of the balance portion in the measurement frame is S2, the measurement frame The proportion of the balanced portion in the inner area can be represented by S2 / S1. The ratio of the balance portion expressed as a percentage is referred to as “plate thickness direction residual stress balance ratio” (= 100 × S2 / S1). It is checked whether (S2 / S1) × 100 is 30% or more.
If it is NO in ST28, it is determined to be a failure. If it is YES, it will determine with a pass.
[0058]
To summarize the above, the third example is a stress evaluation step (ST21 to ST22) for confirming that the surface compressive stress of the double-strength glass is within the range defined by Japanese Industrial Standard JIS R 3222;
A stress difference evaluation step (ST23 to ST26) for confirming that the difference between the maximum value and the minimum value of the surface compressive stress measured over the entire surface of the double-strength glass is a predetermined value or less (for example, 20 MN / m ² or less);
Examine the balance and unbalance of compressive stress and tensile stress in the plate thickness direction, install a rectangular measurement frame with a side of 150 mm or more where the unbalance is maximized, and the proportion of the balance in the measurement frame is Evaluation is performed by a plurality of evaluation steps including a stress balance rate evaluation step (ST27 to ST28) for confirming that the value is a predetermined value or more (for example, 30% or more).
[0059]
The standard is cleared in the stress evaluation step. In the stress difference evaluation step, the number of cracks generated is suppressed to a level that does not cause actual damage. Furthermore, in the stress balance rate evaluation step, the size of the island is suppressed to a level that does not cause actual damage.
[0060]
Therefore, even if cracks occur in the double-strength glass, the number of cracks is small, so it is possible to minimize the actual damage such as falling off, and even if cracks occur and islands occur, Since it is small, the actual damage can be kept to a minimum, and thus extremely strong double-strength glass can be provided.
[0061]
Note that the stress evaluation step may be performed after the stress difference evaluation step in FIG. 6, and the stress evaluation step may be performed after the stress balance evaluation step in FIG. 7.
In FIG. 8, the execution order of the stress evaluation step, the stress difference evaluation step, and the stress balance evaluation step may be changed.
[0062]
Furthermore, in claim 1, the predetermined value in the stress difference evaluation step is not limited to 20 MN / m ^2, and it is not possible to reset the value with improvement or change in the manufacturing method of double-strength glass. There is no problem.
Similarly, in claim 2, the predetermined value in the stress balance evaluation step is not limited to 30%, and the value may be reset according to improvement or change of the manufacturing method of the double strength glass. .
[0063]
【The invention's effect】
The present invention exhibits the following effects by the above configuration.
In claim 1, the standard is cleared in the stress evaluation step. In the stress difference evaluation step, the number of cracks generated is suppressed to a level that does not cause actual damage.
Therefore, according to the first aspect, since the number of cracks is small even if cracks occur in the double-strength glass, the actual damage such as dropout can be kept to a minimum. Glass can be provided.
[0064]
In claim 2, the standard is cleared in the stress evaluation step. Then, in the stress balance rate evaluation step, the size of the island is suppressed to a level where there is no actual harm.
Therefore, according to the second aspect, even if a double-strength glass is cracked or an island is generated, since the island is small, the actual damage can be kept to a minimum. Strength glass can be provided.
[0065]
In claim 3, the standard is cleared in the stress evaluation step. In the stress difference evaluation step, the number of cracks generated is suppressed to a level that does not cause actual damage. Furthermore, in the stress balance rate evaluation step, the size of the island is suppressed to a level that does not cause actual damage.
[0066]
Therefore, according to the third aspect, since the number of cracks is small even if cracks occur in the double-strength glass, it is possible to minimize the actual damage such as falling off, and even if cracks occur, islands can be prevented. Even if it occurs, since the islands are small, the actual damage can be kept to a minimum, so that it is possible to provide extremely safe double-strength glass.
[0067]
Claim 4 is characterized in that the predetermined value used in the stress difference evaluation step is 20 MN / m ² , and if the stress difference is 20 MN / m ² or less, the number of cracks is set to 4 or less. be able to.
[0068]
Claim 5 is characterized in that the predetermined value used in the stress balance rate evaluation step is 30%, and if the stress balance rate is 30% or more, the total area of the generated islands is 1000 mm ² or less. Can be.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between surface compressive stress and NiS grain size. FIG. 2 is a diagram showing an example of how cracks enter. FIG. 3 is a graph showing the relationship between stress difference and cracks. FIG. 5 is a graph showing an example of the relationship between the optical observation and the island. FIG. 5 is a graph showing the relationship between the thickness direction residual stress balance ratio and the total area of the island. FIG. Flow diagram of evaluation method of double strength glass according to example [FIG. 7] Flow diagram of evaluation method of double strength glass according to second embodiment of the present invention [FIG. 8] Double strength glass according to third embodiment of the present invention Flow diagram of the evaluation method of the glass [Fig. 9] Figure of damage shape of the conventional glass plate [Explanation of symbols]
10, 20, 30, 40, 50, 111 ... double strength glass, 12, 22, 23, 32, 33, 34, 44, 54, 103, 113 ... crack, 35, 45, 115 ... island, 46 ... rectangular measurement Frame (measurement frame), 41 ... unbalanced part, 42, 52 ... balanced part.

Claims (5)

A stress evaluation step for confirming that the surface compressive stress of the double-strength glass is within the range defined by Japanese Industrial Standard JIS R 3222;
A stress difference evaluation step for confirming that the difference between the maximum value and the minimum value of the surface compressive stress measured over the entire surface of the double-strength glass is equal to or less than a predetermined value, and evaluating by a plurality of evaluation steps Evaluation method of double strength glass. A stress evaluation step for confirming that the surface compressive stress of the double-strength glass is within the range defined by Japanese Industrial Standard JIS R 3222;
A stress balance rate evaluation step that checks the balance portion and unbalance portion of the compressive stress and tensile stress in the plate thickness direction and confirms that the proportion of the balance portion in the measurement frame is equal to or greater than a predetermined value. An evaluation method for double-strength glass, characterized in that evaluation is performed by a plurality of evaluation steps. A stress evaluation step for confirming that the surface compressive stress of the double-strength glass is within the range defined by Japanese Industrial Standard JIS R 3222;
A stress difference evaluation step for confirming that the difference between the maximum value and the minimum value of the surface compressive stress measured over the entire surface of the double-strength glass is not more than a predetermined value;
A stress balance rate evaluation step that checks the balance portion and unbalance portion of the compressive stress and tensile stress in the plate thickness direction and confirms that the proportion of the balance portion in the measurement frame is equal to or greater than a predetermined value. An evaluation method for double-strength glass, characterized in that evaluation is performed by a plurality of evaluation steps. Predetermined values used in the stress difference evaluation step, according to claim 1 or claim 3 Evaluation double strength glass, wherein it is 20 mN / m ^2. The method for evaluating double-strength glass according to claim 2 or 3, wherein the predetermined value used in the stress balance rate evaluation step is 30%.

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