JP2015175830A - Measurement method of surface characteristic of reinforced glass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow a surface characteristic of reinforced glass to be measured by an ultrasonic material characteristic analysis device.SOLUTION: Reinforcing processing is performed under mutually-different conditions on a plurality of reinforced glass samples for calibration curve creation manufactured in the same process as reinforced glass to be measured. Surface stress and stress layer depth are measured. An LSAW speed and an LSSCW speed are measured by an ultrasonic material characteristic analysis device. Relations between the surface stress and the stress layer depth and the LSAW speed and the LSSCW speed are obtained as an approximate line form. The LSAW speed or the LSSCW speed of the reinforced glass sample to be measured is measured, and the surface stress and the stress layer depth are calculated by using the approximate line form from a measured sound speed.

Description

  The present invention relates to a propagation characteristic of leaky elastic waves and bulk waves measured by an ultrasonic material characteristic analyzer, and more particularly to a method for measuring surface characteristics of tempered glass using phase velocity.

Tempered glass is a glass in which compressive stress is applied to the surface of a substrate to improve resistance to breakage, and has been conventionally used for window glass, watches, tableware, furniture, etc. for automobiles, high-speed railways, and buildings. Tempered glass is heated to near the softening point and then rapidly cooled by air blow, etc., and is produced by air-cooled tempered glass (physically tempered glass) and molten salt (typically KNO ₃ ), from Na ⁺ ions to K ⁺ ions. It is divided roughly into chemically strengthened glass produced by ion exchange.

  Recently, thinning of cover glass is required for smartphones and tablet terminals, and tempered glass is required to be thin and highly reliable. Since incomplete reinforcement processing can lead to major accidents, reliable and highly accurate evaluation technology is required.

  Parameters to be evaluated for tempered glass are surface stress (CS) as well as stress layer depth (DOL). These parameters for chemically strengthened glass depend on the chemical composition ratio of the substrate, the concentration of strengthening salt, and the strengthening process conditions (temperature and time). In the case of physically strengthened glass, the stress layer depth is about 1/6 of the thickness of the substrate, so the only parameter to be evaluated is CS. This CS depends on the chemical composition ratio of the substrate and the strengthening processing conditions (processing temperature and wind pressure).

  Evaluation of the surface stress of tempered glass includes mechanical methods such as an indentation method and a bending strength test method, a method “Patent Document 1” using the optical waveguide effect, an optical method such as a bias corp method and a scattered light photoelasticity method. Has been done by law. However, the indentation method and the bending strength test method are destructive and cannot be used for quality control. On the other hand, the optical method is nondestructive, but the refractive index and photoelastic constant must be obtained separately. Furthermore, the method using the optical waveguide effect can be applied only to the case where the refractive index of the surface is high (the tin surface of chemically strengthened glass and float glass). There is a problem that cannot be applied.

JP-A-53-136886

  The present invention solves the above-mentioned problems of the prior art, and measures non-destructively the surface characteristics of the tempered glass including the surface stress and the stress layer depth by the leaky elastic wave characteristics measured by the ultrasonic material characteristic analyzer. It is an object to provide a method.

The method for measuring the surface properties of the tempered glass according to the present invention is as follows.
(1-A) measuring a leaky surface acoustic wave (LSAW) velocity or a leaky pseudo longitudinal wave (LSSCW) velocity of a sample to be measured made of tempered glass;
(1-B) From the measured LSAW speed or LSSCW speed, the LSAW speed or LSSCW speed created in advance for the calibration curve creation glass sample produced in the same process as the sample to be measured, the surface stress (CS) and Using a calibration curve representing the relationship between the stress layer depth (DOL), determining the surface characteristics including CS and DOL,
including.

  According to the present invention, it is possible to measure surface stress and stress layer depth with non-destructive and non-contact and with an accuracy one digit higher than that of the conventional method. And a method for measuring the surface stress and stress layer depth of tempered glass capable of measuring the surface stress of the sample to be measured and the in-plane distribution of the stress layer depth. be able to.

For aluminosilicate glass, A shows the relationship between the processing time and the surface stress and stress layer depth determined by the optical method, B shows the relationship between the processing time and the LSAW speed and LSSCW speed, and C shows the LSAW The figure which shows the relationship between the stress layer depth calculated | required with the speed change and the LSSCW speed change, and the optical method. Sectional drawing of a tempered glass sample. A is a diagram showing frequency characteristics of LSAW speed, and B is a diagram showing frequency characteristics of LSSCW speed, with respect to aluminosilicate glass. Table 1 showing longitudinal wave velocity, shear wave velocity, density, and elastic constants c ₁₁ and c ₄₄ for aluminosilicate glass. For soda lime glass, A is a diagram showing the relationship between wind pressure and surface stress determined by optical method, B is a diagram showing the relationship between wind pressure and LSAW velocity, C is a diagram showing the relationship between wind pressure and LSSCW velocity, D FIG. 4 is a graph showing the relationship between the LSAW speed change and the LSSCW speed change and the surface stress obtained by the optical method. For borosilicate glass, A is a diagram showing the relationship between wind pressure and surface stress obtained by optical method, B is a diagram showing the relationship between wind pressure and LSAW velocity, C is a diagram showing the relationship between wind pressure and LSSCW velocity, D FIG. 4 is a graph showing the relationship between the LSAW speed change and the LSSCW speed change and the surface stress obtained by the optical method. Table 2 shows the sensitivity and resolution to surface stress of leaky elastic wave velocity for physically strengthened glass. It is a flowchart which shows the procedure which calculates | requires the surface characteristic of the tempered glass by this invention.

[Chemical tempered glass]
Five aluminosilicate glasses were prepared as chemically strengthened glass samples. The sample size is 50 mm × 50 mm, and the sample thickness is 0.7 mm. Four samples were strengthened in KNO ₃ at 425 ° C. for 0.5 h, 1 h, 3 h, and 8 h, respectively. Further, no strengthening treatment was performed on one sample (unreinforced sample). Moreover, the commercially available aluminosilicate glass (sample H) which performed the normal reinforcement | strengthening process, and the unstrengthened sample (sample N) were also prepared. The sample size is 100 mm × 50 mm, and the sample thickness is 0.7 mm. The chemical composition ratio of another sample (40 mm x 30 mm, sample thickness 0.7 mm) in the same lot as sample N was analyzed by X-ray fluorescence analysis. As a result, SiO ₂ was 68.7 wt%, Al ₂ O ₃ was 15.5 wt%, Na ₂ O ₃ was 11.8 wt%, MgO was 3.3 wt%, and SnO was 0.4 wt%.

  The surface stress and the stress layer depth were measured with a surface stress meter (FSM-6000LE, Orihara Seisakusho) for the sample subjected to the strengthening treatment. The measurement results are shown in FIG. 1A. As the processing time increased, the stress layer became deeper. On the other hand, when the treatment time was longer than 3 hours, the surface stress was reduced. This is because stress relaxation occurs as the treatment time increases.

  Next, the LSAW velocity and LSSCW velocity were measured using a linear focused beam ultrasonic material analysis (LFB-UMC) system with an ultrasonic frequency of 225 MHz. The measurement principle and method of LSAW speed and LSSCW speed are detailed in “Reference 1” and “Reference 2”. LSAW and LSSCW are surface acoustic waves, and the resolution in the depth direction is about one wavelength. When the ultrasonic frequency is 225 MHz, the wavelengths of LSAW and LSSCW are 14 μm and 26 μm, respectively. Since the wavelengths of LSAW and LSSCW are in the same order as the stress layer depth shown in FIG. 1A, the tempered glass substrate can be handled as a layered structure sample having a compressive stress layer of depth x as shown in FIG.

  FIG. 1B shows the relationship between processing time and LSAW and LSSCW rates. By performing the strengthening process, the LSAW speed and the LSSCW speed became higher than those of the untreated substrate. This is because the elastic constant of the reinforced layer is larger than that of the unreinforced layer.

  For each sample, the difference between the measured value of the LSAW speed or LSSCW speed for the tempered glass sample and the measured value for the untreated substrate was determined, and the result of determining the relationship between them and the stress layer depth is shown in FIG. 1C. As data corresponding to about one wavelength, an approximate straight line was drawn using the untreated substrate and 0.5h for the LSAW speed, and the untreated substrate and 0.5h, 1h, and 3h samples for the LSSCW speed. . From the slope of the approximate line, the sensitivity of the LSAW velocity and LSSCW velocity to the stress layer depth is 0.46 μm / (m / s) and 0.18 μm / (m / s), respectively. The measurement reproducibility of LSAW speed and LSSCW speed is within ± 0.25 m / s and ± 2.9 m / s, respectively, with ± 2σ (σ: standard deviation). Therefore, the resolution of the LSAW speed and the LSSCW speed with respect to the stress layer depth is ± 0.11 μm and ± 0.52 μm, respectively.

  In FIG. 1C, the relationship between the speed change and the stress layer depth is linear up to the region of approximately one wavelength, but it deviates from the approximate line when the stress layer becomes deeper than that. This is because when the stress layer becomes deeper than the wavelength of LSAW or LSSCW, the region where LSAW or LSSCW exists becomes only the stress layer portion, and the speed change is saturated. In order to evaluate the depth of the deeper compressive stress layer, the ultrasonic frequency of measurement should be set lower than 225 MHz and the wavelength increased.

  Next, the LSAW speed and LSSCW speed were measured while changing the frequency every 5 MHz from 100 MHz to 300 MHz. Differences between the LSAW speed and the LSSCW speed from the measured values for the untreated substrates are shown in FIGS. 3A and 3B, respectively.

  Looking at the results of the LSAW speed, as the frequency increased, the sample treated with 0.5 h and 1 h increased in speed, and the sample treated with 3 h and 8 h decreased in speed. The wavelengths of 100 MHz and 300 MHz LSAW are 32 μm and 11 μm, respectively. As the frequency becomes higher, the wavelength becomes shorter, which reflects more surface characteristics. That is, the elastic modulus distribution in the depth direction of the surface stress layer is not uniform, and the sample treated with 0.5 h for 1 h has a lower elastic modulus as it gets deeper from the surface, and the sample treated with 3 h, 8 h It is considered that the elastic modulus increases as the depth from the surface increases.

  Looking at the LSSCW speed results, the speed increased with increasing frequency in all samples. The wavelengths of LSSCW at 100 MHz and 300 MHz are 58 μm and 19 μm, respectively. Since LSSCW has a longer wavelength than LSAW and propagates while radiating energy to both water and the substrate, the surface concentration rate is lower than LSAW. The LSAW particle displacement is mainly a component perpendicular to the substrate, and the LSSCW particle displacement is mainly a component parallel to the propagation direction, which is close to a transverse wave and a longitudinal wave, respectively. For these reasons, the trend of frequency characteristics of LSSCW speed is different from that of LSAW speed.

  The change in sound speed is due to the change in elastic constant and density. In order to examine the cause, the sample H and the sample N were evaluated by measuring the bulk acoustic characteristics. In the sample model as shown in FIG. 2, the bulk wave (longitudinal wave / transverse wave) sound velocity measurement is performed in the thickness direction of the sample and the density is performed on the entire sample. The measured value is obtained by combining the compressive stress layer and the unreinforced layer of thickness h-2x. As a result of evaluation by a surface stress meter (FSM-6000LE, Orihara Seisakusho) using the optical waveguide effect, the compressive stress to the sample H was 762 MPa, and the stress layer depth was 49 μm.

The ultrasonic device of the LFB-UMC system was changed from an LFB device to a planar device, and longitudinal wave velocity V _l and transverse wave velocity V _s were measured in the substrate thickness direction. The measurement method is detailed in “Reference 3”. Also, “Reference 4” in which density ρ was measured based on Archimedes' principle. The elastic constants c ₁₁ and c ₄₄ were obtained from the following formulas (1) and (2), respectively.
c ₁₁ = ρV _l ² (1)
c ₄₄ = ρV _s ² (2)

The measurement results are shown in Table 1 in FIG. A value of 225 MHz was indicated for both the unreinforced sample and the reinforced sample, which showed velocity dispersion in this frequency band. V _l , V _s , ρ, c ₁₁ , and c ₄₄ of the reinforced sample were 0.55%, 0.40%, 0.16%, 1.3%, and 1.0% larger than those of the unreinforced sample, respectively.

Based on the model of FIG. 2, it is assumed that the compressive stress layer is a single layer, the stress layer depth is a measured value by an optical method, and the difference in acoustic characteristics between the sample H and the sample N is due to only the enhancement layer. The thickness of the sample is h, the stress layer depth is x, the density of the unreinforced sample is ρ _N , the density of the reinforced sample is ρ _H , and the density of the compressive stress layer is ρ _C. Since the reinforced sample can be expressed as a combination of the reinforced layer having a thickness of 2x and the unreinforced layer having a thickness (h-2x), Equation (3) is obtained.

By transforming Equation (3), Equation (4) is obtained, and the density ρ _C of the compressive stress layer can be extracted from the measurements on the unreinforced sample and the reinforced sample.

Similarly, for longitudinal wave velocity and shear wave velocity, the sound velocity of the unreinforced sample is V _N , the sound velocity of the reinforced sample is V _H , and the sound velocity of the enhancement layer is V _C. the speed of sound V _C be extracted of.

Furthermore, if the elastic constant of the reinforcing layer is c _C , the elastic constant c _C of the reinforcing layer can be obtained from the following equation (6).
c _C = ρ _C V _C ² (6)

The results of estimating V ₁ , V _s , ρ, c ₁₁ , and c ₄₄ of the compressive stress layer of the reinforcing layer are also shown in Table 1 of FIG. The changes in V _l , V _s , ρ, c ₁₁ , and c ₄₄ were + 3.9%, + 2.8%, + 1.2%, + 9.1%, and + 6.9%, respectively. The changes in c ₁₁ and c ₄₄ are 7.8 times and 5.9 times larger than the change in ρ, respectively. For this reason, it can be seen that the change in the sound velocity of the surface stress layer due to the strengthening treatment is mainly due to the change in the elastic constant.

[Physical tempered glass]
Four and three soda lime glasses and borosilicate glasses were prepared as physically strengthened glass samples, respectively. The soda lime glass has a sample size of 150 mm × 150 mm and a thickness of 3.7 mm, and the borosilicate glass has a sample size of 200 mm × 200 mm and a thickness of 3.7 mm. The three soda lime glasses were held at 650 ° C. for 4 minutes and then rapidly cooled with a wind pressure of 150 mmAq, 300 mmAq, and 450 mmAq, respectively. Against two borosilicate glass, after holding for 4 minutes at 670 ° C., respectively 0.7 kg / cm ^2, and quenched with wind pressure of 1.4 kg / cm ^2. The soda-lime glass and the borosilicate glass were each subjected to no tempering treatment (unreinforced sample). As a result of analyzing the chemical composition ratio of another unreinforced sample by fluorescent X-ray analysis, it was found that for soda lime glass, SiO ₂ was 75.5 wt%, Al ₂ O ₃ was 1.7 wt%, Na ₂ O ₃ is 9.1 wt%, MgO is 3.2 wt%, CaO is 8.9wt%, K ₂ O is 1.3 wt%, BaO is next 0.1 wt%, relative to the borosilicate glass, SiO ₂ is 83.9wt%, B ₂ O ₃ was 10.6 wt%, Al ₂ O ₃ was 2.4 wt%, Na ₂ O ₃ was 2.4 wt%, and K ₂ O was 0.6 wt%.

  Since the depth of the surface stress layer of the physically strengthened glass is about 1/6 of the substrate, the surface stress layer depth of these samples is about 0.6 mm. Since this value is sufficiently larger than the wavelength of LSAW or LSSCW at 225 MHz for these glasses, it is possible to measure the reinforcing layer as a bulk substrate.

  For soda lime glass, the surface stress was measured with a surface stress meter (FSM-6000LE) on the back surface, which is the tin surface. Since borosilicate glass could not be measured with a surface stress meter, surface stress was measured on both sides of the sample with a glass cross-sectional stress meter (SCALP-04, Glasstress, Ltd.). The measurement results are shown in FIGS. 5A and 6A. In both glasses, the higher the wind pressure, the higher the surface stress.

  The LSAW speed and LSSCW speed were measured for each sample at an ultrasonic frequency of 225 MHz. The measurement results for soda lime glass are shown in FIGS. 5B and 5C, and the measurement results for borosilicate glass are shown in FIGS. 6B and 6C. In both samples, the velocity decreased with increasing wind pressure for both modes.

  Soda lime glass is produced by a float process, and a raw material melted in a float bath is floated on Sn, which is a molten metal. For this reason, in the vicinity of the sample surface, the concentration of Na and Ca on the surface (surface in contact with air) decreases, and the concentration of Sn on the back surface (surface in contact with molten metal) increases (Reference 5). For this reason, in both glasses, the LSAW speed and the LSSCW speed were lower on the back surface than on the front surface.

  FIG. 5D and FIG. 6D show the relationship between the difference between the LSAW speed and the value of the LSSCW speed for the untreated substrate and the surface stress. The smaller the speed difference, the higher the surface stress.

  Table 2 in FIG. 7 shows the sensitivity and resolution of the LSAW speed and LSSCW speed with respect to the surface stress. When the LSAW speed was used, the resolution of this method was within ± 0.8 MPa for soda-lime glass and within ± 0.5 MPa for borosilicate glass. The resolution of surface stress by optical method is ± 20MPa. For this reason, the resolution of this method is more than 25 times higher than the optical method.

[Flow chart for obtaining surface characteristics]
Based on the first and second embodiments described above, the basic processing procedure for determining the surface characteristics of the tempered glass according to the present invention will be described below with reference to the flowchart shown in FIG.
Step S1: Reinforcing treatment is performed under different conditions for a plurality of calibration curve creating glass samples prepared in the same process as the sample to be measured.
Step S2: CS and DOL and LSAW speed or LSSCW speed are measured for the sample obtained in step S1.
Step S3: A relationship between the LSAW speed or the LSSCW speed and CS and DOL, that is, a calibration curve is obtained from the measurement result of step S2.
Step S4: The LSAW speed or LSSCW speed is measured for the sample to be measured.
Step S5: The LSAW speed or LSSCW speed obtained in step S4 is substituted into the calibration curve obtained in step S3 to obtain CS and DOL.

  If an approximate linear equation is obtained in advance for a calibration curve creation sample prepared in the same process as the sample to be measured, CS and DOL can be obtained from steps S4 and S5.

By using the present invention, it is possible to obtain the surface stress, the stress layer depth, and their distribution of the tempered glass in a non-destructive / non-contact manner and with higher accuracy than the conventional method. By utilizing the glass manufacturer, it is possible to evaluate the surface stress, the stress layer depth and the distribution of the produced glass, and the glass production process. When the chemical strengthening treatment is performed, the K ⁺ ion concentration of the strengthening salt decreases and the Na ⁺ ion concentration increases. Therefore, the characteristics of the glass after strengthening are different even at the same treatment temperature and treatment time. It can be used for 100% inspection and sampling inspection of glass before the tempering treatment, 100% inspection and sampling inspection of glass after tempering treatment. By using this evaluation result, it can be used to improve the glass production process conditions in which the tempering treatment conditions are controlled so as to have desired characteristics. Moreover, it is also possible to manufacture tempered glass while performing quality control by this evaluation method. In addition, when used by a glass user, it can be used for quality control and sorting of received samples.

1 Tempered glass substrate 2 Compressive stress layer

[Reference 1]
J. Kushibiki and N. Chubachi, "Material characterization by line-focus-beam acoustic microscope," IEEE Trans. Sonics Ultrason., Vol. SU-32, pp. 189-212 (1985).
[Reference 2]
J. Kushibiki, Y. Ono, Y. Ohashi, and M. Arakawa, "Development of the line-focus-beam ultrasonic material characterization system," IEEE Trans. Ultrason., Ferroelect., Freq. Contr., Vol. 49, pp. 99-113 (2002).
[Reference 3]
J. Kushibiki, and M. Arakawa, "Diffraction effects on bulk-wave ultrasonic velocity and attenuation measurements," J. Acoust. Soc. Am., Vol. 108, pp. 564-573 (2000).
[Reference 4]
HA Bowman, RM Schoonover, and MW Jones, “Procedure for high precision density determinations by hydrostatic weighing,” J. Res. Natl. Bur. Stand., Vol. 71C, pp. 179-198 (1967).
[Reference 5]
Owada, Kakuda, "Glass Cleaning Technology," NEW GLASS, Vol. 23, pp. 7-20 (2008).

Claims (5)

It is a method for measuring the surface characteristics of tempered glass,
(1-A) measuring a leaky surface acoustic wave (LSAW) velocity or a leaky pseudo longitudinal wave (LSSCW) velocity of a sample to be measured made of tempered glass;
(1-B) From the measured LSAW speed or LSSCW speed, the LSAW speed or LSSCW speed created in advance for the calibration curve creation glass sample produced in the same process as the sample to be measured, the surface stress (CS) and Using a calibration curve representing the relationship between the stress layer depth (DOL), determining the surface characteristics including CS and DOL,
Method for measuring surface characteristics of tempered glass including The method for measuring surface characteristics of tempered glass according to claim 1 further comprises:
(2-A) A step of performing a strengthening process under different conditions for a plurality of calibration curve preparation glass samples prepared in the same process as the sample to be measured;
(2-B) For the sample obtained in the step (2-A), surface stress (CS) and stress layer depth (DOL), leakage surface acoustic wave (LSAW) velocity or leakage pseudo longitudinal wave ( LSSCW) measuring the speed,
(2-C) From the result obtained in the step (2-B), obtaining a calibration curve representing the relationship between the LSAW speed or LSSCW speed and CS and DOL;
Method for measuring surface characteristics of tempered glass including   3. The method for measuring surface characteristics of tempered glass according to claim 1 or 2, wherein the step (1-A) is performed by measuring LSAW speed or LSSCW speed at two or more points on the surface of the sample to be measured. A method for measuring the surface characteristics of tempered glass, comprising a step of obtaining an in-plane distribution of surface stress and stress layer depth by performing.   3. The method of measuring surface characteristics of tempered glass according to claim 1 or 2, wherein the step (1-A) further comprises a step of measuring the frequency characteristics of the LSAW speed or LSSCW speed of the sample to be measured, and the measured frequency characteristics. A method for measuring the surface characteristics of tempered glass, including the step of obtaining the depth direction distribution of the surface characteristics of the compressive stress layer.   5. The method for measuring surface characteristics of tempered glass according to claim 1, further comprising preparing an untempered glass substrate sample and a tempered glass substrate sample, wherein both the glass substrate samples are oriented in a direction perpendicular to the substrate. The elastic constant of the reinforcing layer is calculated by calculating the sound velocity of the propagating bulk wave and the density of the sample, the sound velocity and density of the measured bulk wave, and the thickness of the compressive stress layer of the sample to be measured. A method for measuring surface characteristics of tempered glass including a process.