JP4363637B2 - Tempered glass with heterogeneous phase formed by laser irradiation and glass composition suitable for the tempering method - Google Patents

Description

  The present invention relates to a tempered glass, particularly a tempered glass in which a heterogeneous phase is formed by laser irradiation.

  As a method for producing tempered glass for increasing the mechanical strength of plate glass, air-cooled tempering method, chemical tempering method and the like are carried out, and the tempered glass obtained by the method is used as a glass member in various products. .

  In the air-cooling tempering method, it is necessary to heat the plate glass at a high temperature near the glass softening point temperature, so the shape control of the plate glass may be a problem. In the case of a high glass composition, there is a problem that it is necessary to make the heating temperature considerably high, which increases the cost of equipment and the like, and it is difficult to strengthen the glass having a thinner thickness (for example, 2 mm or less).

  Since the chemical strengthening method requires ion exchange treatment, the composition of the plate glass is limited, management of the chemical solution for performing ion exchange is costly, and partial strengthening is difficult.

Recently, Patent Document 1 has proposed a method that can reinforce glass without depending on glass composition, glass thickness, and the like. According to this method, a heterogeneous phase is formed in the shape of dots, lines, or meshes inside a plate glass by focused irradiation of ultrashort pulse laser light. In Patent Document 1, it is confirmed that the mechanical strength is improved up to 1.5 times by laser treatment of soda-lime silicate glass.
JP 2003-286048 A

  In recent years, various products have been in a trend of weight reduction, and naturally, glass members also need to be lightened. In particular, in a display device in which a glass member such as a plasma display (PDP), a liquid crystal display, or an organic EL display occupies most, it is inevitable to reduce the glass member in order to achieve a reduction in weight. In order to reduce the weight of the glass member, it is necessary to satisfy that the glass thickness is reduced while maintaining the mechanical strength. An object of the present invention is to provide a tempered glass that has improved mechanical strength even if it is a thin plate glass and that can maintain mechanical strength even after heat treatment during manufacturing of a display device or the like.

  The inventor has improved the mechanical strength of the tempered glass in which a heterogeneous phase is formed in the shape of dots, lines, or meshes in a plan view of the plate glass by condensing irradiation with an ultrashort pulse laser beam. We found a glass system with great effect.

The tempered glass of the present invention is a tempered glass (hereinafter referred to as super The method of strengthening a plate glass by condensing irradiation of a short pulse laser beam is “laser strengthening”, and the plate glass strengthened by the method is called “laser strengthened glass”). The linear expansion coefficient from 560 ° C. to room temperature to 300 ° C. is 84 to 88 (× 10 ⁻⁷ / ° C.) or more. The ultrashort pulse laser light is preferably a picosecond to femtosecond pulse laser light.

  The plate glass having the above properties is so-called high strain point glass. The factor of whether the glass sheet having the properties exhibits an effect of improving the strength by laser strengthening is unclear, but heat shrinkage occurs locally in the local area when a dense heterogeneous phase is formed inside the glass by laser irradiation. Presumably because it is small.

Since the plate glass has the above-mentioned properties, the composition of the plate glass is expressed by weight%, SiO ₂ 52 to 54%, Al ₂ O ₃ 7 to 11%, ZrO ₂ 0 to 5%, MgO 1 to 5%, CaO 5 to 5%. 9%, SrO 0-5%, BaO 8-14%, MgO + CaO + SrO + BaO 20-25%, TiO ₂ 0-1%, Li ₂ O 0-5%, Na ₂ O 2-6%, K ₂ O 7-11 %, And Li ₂ O + Na ₂ O + K ₂ O 13-15%.

  Since the laser tempered glass of the present invention is not easily affected by the heterogeneous phase being relaxed by heating (for example, the heterogeneous phase remains in the plate glass even when the plate glass on which the heterogeneous phase is formed is heated at 550 ° C.). There is an advantage that the mechanical strength is easily maintained even after a heating step in manufacturing the display device.

  Even if the tempered glass obtained by the laser irradiation of the present invention is a thin glass plate, the mechanical strength is improved, contributing to the weight reduction of glass parts, for example, the weight reduction of display devices and the like. To be successful.

  The tempered glass of the present invention is a laser tempered glass in which a heterogeneous phase is formed in a dot shape, a line shape, or a mesh shape inside a plate glass by focused irradiation of an ultrashort pulse laser beam. The said laser tempered glass is obtained by condensing a laser beam to the target depth from the surface.

  The laser beam is preferably an ultrashort pulse laser beam of picosecond to femtosecond, for example, by a Ti sapphire laser excited by Nd-YAG laser. The pulse width of the pulse laser beam is preferably several hundred femtoseconds or less.

  The wavelength of the laser light is preferably in the range from visible to near infrared, and the wavelength at which the glass sheet absorbs little is used. Preferably it is the range of 400 nm to 1000 nm. Further, the energy of the pulse laser beam is preferably several nJ to 1 mJ, and it is desirable that the energy is as high as possible without causing ablation on the plate glass.

  The laser light is condensed inside the plate glass by a lens or the like. Although depending on the energy per unit area of the laser light, in order to form a heterogeneous phase, it is preferable that the condensed light is spot-shaped with a diameter of 100 μm or less. The heterogeneous phase is continuously formed on the plate glass by moving the condensing point of the laser light inside the plate glass. Or the condensing point of a laser beam is fixed, plate glass is moved, and a heterogeneous phase is formed in plate glass.

  The position for condensing the laser beam can be selected at an arbitrary position between the incident surface and the back surface of the plate glass, and is preferably set to a position of 250 μm to 500 μm in the vertical direction from the glass surface. In the glass composition system of the present invention, when the center position in the glass thickness direction of the heterogeneous phase formed by laser irradiation is formed at a position of 250 μm to 500 μm in the vertical direction from the plate glass surface, it is particularly effective for improving the mechanical strength. Found it expensive. Considering the improvement in mechanical strength, this position is preferably set in the range of 260 to 330 μm, more preferably in the range of 270 μm to 310 μm.

  In the cross-sectional view of the plate glass, the mechanical strength of the plate glass is improved by setting the average distance between the nearest heterogeneous phases to a distance of 50 μm or less. By setting this average distance to 50 μm or less, it is presumed that the effect of changing the crack propagation direction at the time of breaking the plate glass by the heterogeneous phase is increased, and the mechanical strength of the plate glass is improved. If this average distance is shortened, the mechanical strength is improved. However, the manufacturing cost of tempered glass is increased, and therefore this average distance is preferably 0.1 μm or more.

  The average distance is defined as that obtained by the next measurement. When the cross-section of the plate glass is observed with a microscope at a magnification of 100 to 500 times, the heterogeneous phases appearing in the image are averaged from the values obtained by measuring the distance from each of the closest heterogeneous phases. The same measurement was performed for other cross-sectional positions, and the average values obtained at the average of the cross-sectional positions of at least 10 locations were further averaged, and the average distance between the adjacent heterogeneous phases in the cross-sectional view of the plate glass was obtained. And And the cross section is a surface cut so that the adjacent heterogeneous phase is included when the heterogeneous phase when the plate glass is viewed in plan is a dot pattern, and in the case of a linear and mesh pattern, A plane cut perpendicular to the line.

  Furthermore, it has been found that when the length of the heterogeneous phase formed by laser irradiation in the thickness direction of the glass is 50 μm to 500 μm, the effect of improving the mechanical strength is particularly high. When the length of the heterogeneous phase is less than 50 μm, the effect of improving the mechanical strength is small. On the other hand, when the heterogeneous phase exceeds 500 μm, the heterogeneous phase is formed by using a condensing lens having a longer focal depth, and thus the high energy for altering the glass. In some cases, laser light having a density irradiates the surface. In this case, mechanical damage is reduced because the glass surface is subjected to large damage such as rough grinding. And considering the mechanical strength improvement, it is preferable that the length of the heterogeneous phase in the glass thickness direction is 60 to 330 μm.

  The heterogeneous phase is preferably formed inside the plate glass in the shape of dots, lines, or meshes in plan view of the plate glass. Further, it may be formed three-dimensionally.

The glass used in the laser strengthening of the present invention has a strain point of 560 ° C. or higher and a linear expansion coefficient from room temperature to 300 ° C. of 84 to 88 (× 10 ⁻⁷ / ° C.). In consideration of application, the volume resistivity at 250 ° C. is preferably 10 ⁹ Ω · cm or more.

The glass composition of the glass sheet having the properties, in weight _{percentages, SiO 2 52~54%, Al 2} O 3 7~11%, ZrO 2 0~5%, 1~5% MgO, CaO 5~9 %, SrO 0-5%, BaO 8-14%, MgO + CaO + SrO + BaO 20-25%, TiO ₂ 0-1%, Li ₂ O 0-5%, Na ₂ O 2-6%, K ₂ O 7-11% And Li ₂ O + Na ₂ O + K ₂ O preferably have a composition of 13-15%.

In the above glass composition, SiO ₂ is a main component of glass. If the weight percentage is less than 52%, the strain point of the glass tends to be lowered and the chemical durability tends to deteriorate. On the other hand, if it exceeds 54%, the high-temperature viscosity of the glass melt increases, and float molding becomes difficult. Therefore, it is good to set it as 52 to 54%, preferably 53 to 54%.

Al ₂ O ₃ strain point of the glass is less than 7% tends to decrease. On the other hand, if it exceeds 11%, the high-temperature viscosity of the glass melt increases, the tendency to devitrification increases, and float molding becomes difficult. Therefore, it is 7 to 11%, preferably 8 to 11%.

ZrO ₂ is not an essential component, but it has an effect of raising the strain point of the glass and suppressing the occurrence of devitrification, so it is preferably contained in a range of 5% or less. If the component exceeds 5%, the tendency to devitrification increases, so that it becomes difficult to melt the glass or form the float process.

  MgO has an effect of increasing the strain point as compared with other divalent component oxides, but if less than 1%, the effect is insufficient. On the other hand, if it exceeds 5%, the tendency of devitrification increases. Therefore, the content should be in the range of 1 to 5%, preferably 2 to 4%.

  CaO has the effect of lowering the high-temperature viscosity of the glass melt in the presence of BaO, but if it is less than 5%, the effect is insufficient, while if it exceeds 9%, the tendency to devitrification tends to increase. Therefore, it is good to set it as 5 to 9%, Preferably it is 6 to 8% of range.

  BaO has the effect of reducing the high-temperature viscosity of the glass melt and suppressing the occurrence of devitrification in the presence of CaO as described above, but if it is less than 8%, the effect of suppressing devitrification is insufficient, while the other 14% If it exceeds 1, the strain point of the glass tends to decrease too much. Therefore, it is good to set it as 8 to 14%, preferably 9 to 13%.

  SrO is not an essential component, but has the effect of lowering the high-temperature viscosity of the glass melt in the presence of CaO and BaO. The SrO content is preferably in the range of 5% or less, and if it exceeds 5%, the strain point tends to be too low and the linear expansion coefficient tends to be excessive.

  Furthermore, within the above composition range, by keeping the total of alkaline earth metal oxides (CaO, MgO, BaO, SrO) in the range of 20 to 25%, while maintaining the glass meltability in a good range, A glass having a suitable viscosity-temperature gradient, good moldability, excellent heat resistance, chemical durability, and the like, and an appropriate range of linear expansion coefficient can be obtained. When the total of the alkaline earth metal oxides exceeds 25%, the linear expansion coefficient increases, the tendency to devitrification increases, and the chemical durability tends to decrease. If it is less than 20%, the high-temperature viscosity tends to increase, making melting and molding difficult, and the linear expansion coefficient tends to decrease.

Although TiO ₂ is not an essential component, it is preferably introduced in an amount of 1% or less in order to improve the chemical durability of the glass and reduce the tendency to devitrification when the glass is melted. However, if it exceeds 1%, the glass tends to be colored, which is not preferable. Na ₂ O acts as a glass melting agent together with K ₂ O, and is indispensable for maintaining the linear expansion coefficient of the glass at an appropriate size. When Na ₂ O is less than 2%, the linear expansion coefficient tends to be too low, and when it exceeds 6%, the strain point tends to be too low. Therefore, it is good to set it as 2 to 6%, Preferably it is 3 to 5% of range.

K ₂ O suppresses the migration of alkali ions due to the above reasons and the mixed alkali effect with Na ₂ O, and increases the volume resistivity of the glass. If it is less than 7%, these effects are insufficient, and if it exceeds 11%, the linear expansion coefficient becomes excessive and the strain point tends to decrease too much, so that it is 7 to 11%, preferably 8 to 10%. It is good to be in the range.

Li ₂ O is not an essential component, but lowers the high temperature viscosity of the glass and promotes melting of the glass raw material. However, if the content exceeds 5%, the strain point of the glass tends to be lowered too much, so it is desirable to introduce it in a range of 5% or less.

Regarding the amount of the alkali components (Na ₂ O, K ₂ O, Li ₂ O), the total amount is set to 13 to 15%, so that the strain point, linear expansion coefficient, high temperature viscosity, and devitrification temperature are in an appropriate range. Can be maintained. When the total amount of the alkali components is less than 13%, the linear expansion coefficient decreases and the tendency to devitrification tends to increase. If it exceeds 15%, the strain point is lowered too much and the volume resistivity is lowered. Therefore, it is good to set it as 13 to 15% of range.

Further, in the alkaline component and the K 2 _{O /} Na 2 _O weight ratio is 2.0 or more, the movement of the alkali ions in the glass is suppressed, preferably it takes on the effect of increasing the volume resistivity.

Example 1
The plate glass has properties such that the linear expansion coefficient from room temperature to 300 ° C. is 85.4 (× 10 ⁻⁷ / ° C.), the strain point is 603 ° C., and the volume resistivity is 10 ^9.9 Ω · cm. In terms of weight percent, SiO ₂ is 54%, Al ₂ O ₃ is 9%, ZrO ₂ is 3.7%, MgO is 3.0%, CaO is 7.7%, BaO is 9.6%, Na ₂ O is 4.2% _{K 2} O has a composition of 8.8%, at 10 mm × 50 mm square was prepared ones 2.3mm thickness size.

  The ultrashort pulse laser beam is a femtosecond laser beam with a pulse width of 100 femtoseconds, a repetition period of 1 kHz, and a center wavelength of 800 nm oscillated from an Nd-YAG laser-excited Ti sapphire laser. Was adjusted to about 100 mW.

  The position where the femtosecond laser beam is focused is fixed to 300 μm in the vertical direction from the glass surface, and the ultrashort pulse laser beam is approximately 5 μmφ with a focusing lens (Olympus objective lens, magnification 10 ×, numerical aperture 0.25). The light was condensed into a spot shape.

  The position where the femtosecond laser beam was focused was fixed to the inside of 300 μm from the glass surface, and the plate glass was moved at a speed of 25 mm / sec using an automatic stage, thereby forming point-like heterogeneous phases at 25 μm intervals. And the operation | work which forms a dotted | punctate heterogeneous phase was repeated and the laser tempered glass in which the heterogeneous phase was formed in the cross-sectional view of plate glass on the average of 25 micrometers was obtained.

Example 2
The sheet glass has properties such that the linear expansion coefficient from room temperature to 300 ° C. is 87.6 (× 10 ⁻⁷ / ° C.), the strain point is 602 ° C., and the volume resistivity is 10 ^9.4 Ω · cm. SiO ₂ 53.8%, Al ₂ O ₃ 9.6%, ZrO ₂ 2.3%, MgO 2.4%, CaO 7.8%, BaO 10.0%, Na ₂ Except for using O having a composition of 4.6% and K ₂ O of 9.5%, in the same manner as in Example 1, in the cross-sectional view of the plate glass, the interval was 25 μm on average and was dotted A laser tempered glass in which a heterogeneous phase was formed was obtained.

Example 3
The sheet glass has properties such that the linear expansion coefficient from room temperature to 300 ° C. is 86.7 (× 10 ⁻⁷ / ° C.), the strain point is 610 ° C., the volume resistivity is 10 ^9.7 Ω · cm, and the weight percentage is SiO ₂ is 53.2%, Al ₂ O ₃ is 9.3%, ZrO ₂ is 3.9%, MgO is 3.4%, CaO is 6.8%, BaO is 9.8%, Na _2. Except for using O having a composition of 4.5% and K ₂ O of 9.1%, in the same procedure as in Example 1, in the cross-sectional view of the plate glass, the interval was 25 μm on average and dotted A laser tempered glass in which a heterogeneous phase was formed was obtained.

Example 4
The plate glass has properties such that the linear expansion coefficient from room temperature to 300 ° C. is 87.3 (× 10 ⁻⁷ / ° C.), the strain point is 595 ° C., the volume resistivity is 10 ^9.8 Ω · cm, and the weight% SiO ₂ 53.6%, Al ₂ O ₃ 10.4%, MgO 3.6%, CaO 8.0%, BaO 11.2%, Na ₂ O 4.2%, K except _{that 2 O} was used having a composition of 8.8% at the same manner as in example 1, in a cross-sectional view of the glass sheet, a laser distance on average 25 [mu] m, dotted heterogeneous phase is formed A tempered glass was obtained.

Example 5
The plate glass has properties such that the linear expansion coefficient from room temperature to 300 ° C. is 86.2 (× 10 ⁻⁷ / ° C.), the strain point is 600 ° C., and the volume resistivity is 10 ^9.2 Ω · cm. SiO ₂ 53.9%, Al ₂ O ₃ 10.5%, ZrO ₂ 1.0%, MgO 3.0%, CaO 7.9%, BaO 9.1%, Na ₂ Except for using O having a composition of 4.8% and K ₂ O having a composition of 9.8%, the same procedure as in Example 1 was used, and the interval was 25 μm on average in the cross-sectional view of the plate glass. A laser tempered glass in which a heterogeneous phase was formed was obtained.

Comparative Example 1
The plate glass has properties such that the thermal expansion coefficient from room temperature to 300 ° C. is 88.0 (× 10 ⁻⁷ / ° C.), the strain point is 520 ° C., and the volume resistivity is 10 ^7.1 Ω · cm. And having a composition of 70.6% SiO ₂ , 2.0% Al ₂ O ₃ , 3.6% MgO, 9.5% CaO and 14.3% Na ₂ O + K ₂ O Using.

  The ultrashort pulse laser beam is a femtosecond laser beam with a pulse width of 100 femtoseconds, a repetition period of 1 kHz, and a center wavelength of 800 nm oscillated from an Nd-YAG laser-excited Ti sapphire laser. Was adjusted to about 9 mW.

  The position where the femtosecond laser beam is focused is fixed to 200 μm inside in the vertical direction from the glass surface, and the ultrashort pulse laser beam is approximately 5 μmφ with a focusing lens (Olympus objective lens, magnification 40 ×, numerical aperture 0.55). The light was condensed into a spot shape.

A spot-like heterogeneous phase was formed at intervals of 25 μm by fixing the position where the femtosecond laser beam was focused to 200 μm inside from the glass surface and moving the plate glass at a speed of 25 mm / sec using an automatic stage. . And the operation | work which forms a dotted | punctate heterogeneous phase was repeated and the laser tempered glass in which the dotted | punctate heterogeneous phase was formed in the space | interval of 25 micrometers on average was obtained in the cross sectional view of plate glass.
[Evaluation of mechanical strength of laser tempered glass]
The laser tempered glass obtained in Examples 1 to 5 and Comparative Example 1 was subjected to a 4-point bending strength test under the conditions of a distance between fulcrums of 30 mm, a distance between load points of 10 mm, and a load speed of 0.5 mm / min. The load was measured and compared with the plate glass before laser strengthening to determine the rate of increase in mechanical strength due to laser strengthening. The results are shown in Table 1.

  In each of Examples 1 to 5 and Comparative Example 1, improvement in mechanical strength was confirmed by laser strengthening. And it was confirmed that the laser-strengthened glass of Examples 1 to 5 has improved mechanical strength as compared with Comparative Example 1.

[Laser tempered glass heat treatment]
The laser tempered glass obtained in Example 1 and Comparative Example 1 was heated to 550 ° C. in a heating furnace, held for 30 minutes, and then cooled to room temperature. FIGS. 1 to 4 show photographs substituted for drawings when the heterogeneous phase portion is magnified and observed with a reflection differential interference microscope. 1 shows the tempered glass obtained in Example 1 before the heat treatment, FIG. 2 shows the tempered glass obtained in Example 1 after the heat treatment, and FIG. 3 shows the tempered glass obtained in Comparative Example 1. FIG. 4 shows the tempered glass obtained in Comparative Example 1 after the heat treatment before the heat treatment.

  In the laser tempered glass obtained in Example 1, the point-like heterogeneous phase did not disappear even after the heat treatment, and its shape was almost the same as that before the heat treatment, whereas the laser tempered glass obtained in Comparative Example 1 In the glass, the point-like heterogeneous phase almost disappeared after the heat treatment. It was confirmed that the laser tempered glass of the present invention is suitable as a substrate of a display device accompanied by a heating process such as PDP.

It is a photograph for drawing substitutes when the surface of the laser tempered glass of this Example 1 is magnified 200 times with a reflection differential interference microscope. It is the photograph instead of drawing when the surface after heat-treating the laser tempered glass of the present Example 1 at 550 degreeC is magnified 200 times with the reflection differential interference microscope. It is the photograph instead of drawing when the surface of the laser tempered glass of this comparative example 1 is magnified 200 times and observed with the reflection differential interference microscope. It is the photograph instead of drawing when the surface after heat-treating the laser tempered glass of this comparative example 1 at 550 degreeC is magnified 200 times with the reflection differential interference microscope.

Claims (2)

It is a method for improving the mechanical strength of a plate glass, which is a method for producing a heterogeneous phase inside a plate glass by focused irradiation of an ultrashort pulse laser beam of picoseconds to femtoseconds. Jo, or is intended to form a reticulated, the flat glass laser is irradiated, the strain point of 560 ° C. or higher, linear expansion coefficient at 300 ° C. from room temperature properties of 84~88 (× 10 -7 ^/ ℃) has, and, by weight _{percentages, SiO 2 52~54%, Al 2} O 3 7~11%, ZrO 2 0~5%, MgO 1~5%, CaO 5~9%, SrO 0~5% BaO 8-14%, MgO + CaO + SrO + BaO 20-25%, TiO ₂ 0-1%, Li ₂ O 0-5%, Na ₂ O 2-6%, K ₂ O 7-11%, and Li ₂ O + Na ₂ O + K. ₂ O 13-15% A method for improving the mechanical strength of plate glass, characterized by having a composition . A method for producing a display device, comprising: a step of improving the mechanical strength of a plate glass by the method according to claim 1; and a step of heating the plate glass whose mechanical strength has been improved in the step at 550 ° C. or higher. .