CN114538793A

CN114538793A - Method for producing tempered glass

Info

Publication number: CN114538793A
Application number: CN202111372654.3A
Authority: CN
Inventors: 木下清贵; 长田康生
Original assignee: Nippon Electric Glass Co Ltd
Current assignee: Nippon Electric Glass Co Ltd
Priority date: 2020-11-24
Filing date: 2021-11-18
Publication date: 2022-05-27

Abstract

The present invention provides a method for producing a tempered glass, which comprises a first ion exchange step (S2), a second ion exchange step (S3), a removal step (S5), and a post-removal ion exchange step (S7). In the post-removal ion exchange step (S7), Na ions in the glass and K ions in the molten salt are ion exchanged, whereby the maximum compressive stress CS3 of the compressive stress layer (2) in the new surface (1a) formed in the removal step (S5) is 700MPa or more.

Description

Method for producing tempered glass

Technical Field

The present invention relates to a method of manufacturing a tempered glass suitable for a cover glass of, for example, a mobile phone, a digital camera, a PDA (mobile terminal), a touch panel display.

Background

Mobile phones (particularly smart phones), digital cameras, PDAs, touch panel displays, large-sized televisions, non-contact power supplies, and the like are becoming increasingly popular. In these applications, ion-exchange treated strengthened glass is used. In recent years, the use of tempered glass for exterior parts such as digital signage, mice, and smartphones has been increasing.

The tempered glass has a compressive stress layer formed by ion exchange treatment on the surface thereof, and thereby suppresses the formation and development of cracks on the surface and attains high strength. The strength of the tempered glass can be improved by adjusting the formation mode of the compressive stress layer.

By the ion exchange treatment, defects may be generated or fine irregularities may remain on the surface of the tempered glass. Therefore, it is necessary to remove the defects and the irregularities. For example, patent document 1 discloses a method for producing a tempered glass, which includes a post-tempering polishing step of polishing the surface of a glass plate after a chemical tempering step.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2015-137224

Disclosure of Invention

Problems to be solved by the invention

When the surface of the glass sheet is polished in the post-strengthening polishing step, a part of the compressive stress layer is removed. Therefore, the value of the compressive stress in the compressive stress layer on the surface of the tempered glass sheet may decrease.

Therefore, a technical object of the present invention is to improve the strength of glass reduced by removing a part of the surface after ion exchange treatment.

Means for solving the problems

In order to solve the above problems, the present invention is a method for producing a tempered glass by subjecting a glass having a surface to an ion exchange treatment to obtain a tempered glass having a compressive stress layer in the surface layer, the method comprising: a first ion exchange step of bringing the surface of the glass into contact with a first molten salt to exchange Li ions in the glass with Na ions in the first molten salt; a second ion exchange step of bringing the surface of the glass into contact with a second molten salt to exchange Na ions in the glass with K ions and Li ions in the second molten salt; a removing step of removing at least a part of the surface of the strengthened glass after the first ion exchange step and the second ion exchange step are performed, thereby forming a new surface on the strengthened glass; and a post-removal ion exchange step of ion-exchanging Na ions in the tempered glass after the removal step with K ions in the molten salt to set a maximum compressive stress CS3 of the compressive stress layer in the new surface to 700MPa or more.

According to this configuration, the removal step removes the surface of the tempered glass after the first ion exchange step and the second ion exchange step, thereby removing minute defects and the like formed on the surface. This makes it possible to produce a strengthened glass having defects and the like, and to improve the yield. The compressive stress value formed on the new surface of the tempered glass in the removing step is lower than the compressive stress value of the surface before the removing step, but the compressive stress value can be sufficiently increased by performing the post-removing ion exchange step on the new surface. This makes it possible to produce a high-strength tempered glass.

The method may further include a post-removal preliminary ion exchange step performed after the removal step and before the post-removal ion exchange step, wherein in the post-removal preliminary ion exchange step, the strengthened glass after the removal step is brought into contact with a third molten salt, and Li ions in the strengthened glass after the removal step are ion-exchanged with Na ions in the molten salt.

In the method, NaNO is contained in the third molten salt used in the preliminary ion exchange step after the removal₃The concentration of NaNO in the first molten salt can be the same as that of NaNO in the first molten salt₃The occupied concentrations are substantially equal.

In the method, KNO in the molten salt used in the post-removal ion exchange step is₃The concentration of KNO in the second molten salt may be the same as that of KNO in the second molten salt₃The occupied concentrations are substantially equal.

The ion exchange treatment time in the post-removal preliminary ion exchange step may be 10 to 100% of the ion exchange treatment time in the first ion exchange step.

The ion exchange treatment time in the post-removal ion exchange step may be 50 to 200% of the ion exchange treatment time in the second ion exchange step.

Can be as follows: the glass may be a plate-like or sheet-like glass having a thickness of 0.05 to 2.0mm, and the front and back main surfaces of the tempered glass before the post-removal ion exchange step may be removed to a shallower extent than the compressive stress layer, so that the maximum compressive stress CS2 of the compressive stress layer in the new surface after the removal step may be 100MPa or more.

Can be as follows: in the removing step, the surface of the tempered glass after the first ion exchange step and the second ion exchange step is removed by polishing or etching, and the amount Δ t of removal of the surface in the removing step is smaller than the diffusion depth DOL of the K ions introduced in the second ion exchange step.

Can be as follows: in the method, the removal amount Δ t in the removal step is 20 μm or less, the compressive stress CS2 of the compressive stress layer in the new surface after the removal step and before the post-removal ion exchange step is set to be less than 700MPa, and the maximum compressive stress CS3 of the compressive stress layer after the post-removal ion exchange step is set to be 700 to 1200 MPa.

Can be as follows: in the tempered glass after the post-removal ion exchange step, a stress curve (stress distribution) obtained by measuring stress in a depth direction from the new surface includes: a first peak at which the compressive stress becomes maximum on the surface; a first valley which decreases in the depth direction from the first peak to minimize stress; a second peak which increases in depth from the first valley to maximize the compressive stress; and a second valley which decreases in the depth direction from the second peak to minimize the tensile stress, wherein in the post-removal ion exchange step, Na ions in the strengthened glass and K ions in the molten salt are ion-exchanged so that the compressive stress CSb of the first valley becomes 10MPa or more.

LiNO in the molten salt used in the post-removal ion exchange step₃The concentration of the surfactant may be 0.1 to 2% by mass. Further, the concentration of Na ions in the molten salt used in the post-removal ion exchange step is calculated as NaNO₃In the case of (3), the content may be 5.0% by mass or less.

The temperature of the ion exchange treatment in the post-removal ion exchange step is 350 to 450 ℃, and the time of the ion exchange treatment in the post-removal ion exchange step is equal to or shorter than the time of the ion exchange treatment in the second ion exchange step.

In the method, the following steps can be adopted: in the second ion exchange step, Na ions in the glass are ion-exchanged with K ions in the second molten salt, and Na ions in the glass are ion-exchanged with Li ions in the second molten salt, so that NaNO is produced₃The concentration of KNO in the first molten salt is 50 mass% or more₃The concentration of the first molten salt is less than 50 mass%, and LiNO₃The concentration of the second molten salt is 0.5-5 mass%, KNO₃The concentration of the second molten salt is 95 to 99.5 mass%, the ion exchange treatment temperature in the first ion exchange step is 350 to 480 ℃, the ion exchange treatment temperature in the second ion exchange step is 350 to 480 ℃, the ion exchange treatment time in the first ion exchange step is 1 to 20 hours, and the ion exchange treatment time in the second ion exchange step is shorter than the ion exchange treatment time in the first ion exchange step.

The glass may contain 40 to 70 mass% of SiO ₂10 to 30 percent of Al₂O₃0 to 3 percent of B₂O₃5 to 25 percent of Na₂O, 0 to 5.5 percent of K₂O, 0.1-10% of Li₂O, 0-6% of MgO and 0-15% of P₂O₅As a glass composition.

The method may further include an inspection step of inspecting the surface of the strengthened glass for defects after the first ion exchange step and the second ion exchange step are performed and before the removal step, and removing at least a part of the surface together with the defects in the removal step when the defects on the surface of the strengthened glass are detected.

The present invention is a method for producing a strengthened glass, which is intended to solve the above problems and to obtain a strengthened glass having a surface whose compressive stress is adjusted, the method comprising: a removing step of removing at least a part of the surface of a tempered glass having a compressive stress layer formed on the surface thereof in advance to a depth shallower than the depth of the compressive stress layer, thereby forming a new surface on the tempered glass; and a post-removal ion exchange step of performing an ion exchange treatment on the tempered glass in which the maximum compressive stress CS2 of the compressive stress layer in the new surface is less than 700MPa, wherein in the post-removal ion exchange step, Na ions in the tempered glass are ion-exchanged with K ions in the molten salt, so that the maximum compressive stress CS3 of the compressive stress layer in the new surface is 700MPa or more.

According to this configuration, the compressive stress of the compressive stress layer is reduced in the new surface formed by removing the surface of the tempered glass after the ion exchange treatment, but the compressive stress value can be sufficiently increased by performing the post-removal ion exchange step on the new surface. This makes it possible to produce a high-strength tempered glass.

The method may further include a step of measuring, by a measuring device, information relating to the stress of the tempered glass after the removal step and before the post-removal ion exchange step, and an ion exchange condition setting step of setting the ion exchange condition in the post-removal ion exchange step based on the information measured by the measuring device.

In the method, the following steps can be adopted: the measuring device is a device that generates optical interference fringes for the tempered glass after the removal step and before the ion exchange step after the removal step, and measures a stress distribution by capturing an interference fringe image including the optical interference fringes, the information on the stress includes the interference fringe image, the ion exchange condition includes an ion exchange processing time in the ion exchange step after the removal, and the ion exchange condition setting step sets the ion exchange processing time based on the interference fringe image.

The method may include: a step of measuring, by the measuring device, a diffusion depth DOL1 of the K ions introduced in the second ion exchange step before the removal step; and a removal amount determining step of determining a removal amount Δ t of the surface of the tempered glass removed in the removing step, wherein in the ion exchange condition setting step, the ion exchange condition is set based on a function prepared in advance, a diffusion depth DOL1 of K ions measured by the measuring device, and the removal amount Δ t determined in the removal amount determining step.

In the method, the ion exchange condition may include an ion exchange treatment time Tx in the post-removal ion exchange step, and the function may include the following formula (1).

Tx＝a(1-e^-b×x)...(1)

Here, a and b are constants, and x is a ratio (Δ t/DOL1) between the removal amount Δ t and the diffusion depth DOL1 of the K ions introduced in the second ion exchange step.

The method may comprise: an inspection step of acquiring defect information of the tempered glass after the first ion exchange step and the second ion exchange step are performed and before the removal step; and a predetermined removal amount setting step of setting a predetermined removal amount to be removed from the surface of the tempered glass after the first ion exchange step and the second ion exchange step are performed, based on the defect information acquired in the inspection step.

In the method, the information on the stress includes a diffusion depth DOL2 of K ions remaining in the tempered glass after the removal step and before the post-removal ion exchange step, and in the removal amount determination step, the removal amount Δ t is determined by a difference (DOL1-DOL2) between the diffusion depth DOL1 of K ions introduced in the second ion exchange step and the diffusion depth DOL2 of K ions remaining in the tempered glass.

In order to solve the above problems, the present invention provides a method for producing a tempered glass by subjecting a glass having a surface to an ion exchange treatment to obtain a tempered glass having a compressive stress layer in the surface layer, the method comprising: a first ion exchange step of bringing the surface of the glass into contact with a first molten salt to exchange Li ions in the glass with Na ions in the first molten salt; a second ion exchange step of bringing the surface of the glass into contact with a second molten salt to exchange Na ions in the glass with K ions in the second molten salt; a removing step of removing at least a part of the surface of the strengthened glass after the first ion exchange step and the second ion exchange step are performed, thereby forming a new surface on the strengthened glass; a measuring step of measuring information on the stress of the tempered glass after the removing step by using a measuring device; and a post-removal ion exchange step of increasing the maximum compressive stress of the compressive stress layer on the new surface by ion-exchanging Na ions in the tempered glass after the measurement step with K ions in the molten salt, wherein the method for producing tempered glass further comprises an ion exchange condition setting step of setting the ion exchange conditions in the post-removal ion exchange step based on the information on the stress obtained from the measurement device in the measurement step.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, the strength of the glass reduced by removing a part of the surface after the ion exchange treatment can be improved.

Drawings

FIG. 1 is a schematic view showing a cross section of a tempered glass.

Fig. 2 is a graph showing a stress curve in the thickness direction of the tempered glass.

Fig. 3 is a flowchart showing a method for producing tempered glass according to a first embodiment.

FIG. 4 is a sectional view of the glass in the removal step.

Fig. 5 is a flowchart showing a method for producing tempered glass according to a second embodiment.

FIG. 6 is a flowchart showing a method for producing a tempered glass according to a third embodiment.

Fig. 7 is a diagram schematically showing an interference fringe image of the tempered glass.

Fig. 8 is a diagram schematically showing an interference fringe image of the tempered glass.

Fig. 9 is a diagram schematically showing an interference fringe image of the strengthened glass.

Fig. 10 is a diagram schematically showing an interference fringe image of the strengthened glass.

FIG. 11 shows stress curves of the tempered glass of the examples.

FIG. 12 shows the stress curve of the tempered glass of the example.

Description of the reference numerals

1 tempered glass

1a0 removed surface of glass

1a new surface of glass

3 layer of compressive stress

B1 first valley

B2 second valley

Maximum compressive stress of compressive stress layer after CS2 removal step

CS3 removal of maximum compressive stress of compressive stress layer after post ion exchange process

Compressive stress of first valley of CSb

Diffusion depth of K ions introduced in DOL1 second ion exchange step

First peak of P1

Second peak of P2

S2 first ion exchange Process

S3 second ion exchange Process

S4 first inspection step

S5 removing step

Preliminary ion exchange step after removal of S7a

Ion exchange step after removal of S7

S41 first measurement step

S42 scheduled removal setting process

S61 second measurement step

S62 removal amount determination step

S63 procedure for setting ion exchange conditions

Δ t0 predetermined removal amount

Δ t removal amount

Detailed Description

< first embodiment >

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. Fig. 1 to 4 show a first embodiment of the method for producing tempered glass of the present invention.

As shown in fig. 1, a tempered glass 1 of the present invention is a plate-like or sheet-like chemically tempered glass that is chemically tempered by ion exchange. The tempered glass 1 includes surfaces 1a and 1b, a compressive stress layer 2, and a tensile stress layer 3.

The thickness T of the tempered glass 1 can be arbitrarily determined, and is preferably 2.0mm or less, more preferably 1.8mm or less, 1.6mm or less, 1.4mm or less, 1.2mm or less, 1.0mm or less, 0.9mm or less, 0.85mm or less, further preferably 0.8mm or less, preferably 0.03mm or more, 0.05mm or more, 0.1mm or more, 0.15mm or more, 0.2mm or more, 0.25mm or more, 0.3mm or more, 0.35mm or more, 0.4mm or more, 0.45mm or more, 0.5mm or more, 0.6mm or more, further preferably 0.65mm or more.

The surfaces 1a and 1b of the tempered glass 1 include a main surface 1a forming the front and back surfaces and an end surface 1 b. The compressive stress layer 2 is formed in a surface layer portion including the main surface 1a and the end surface 1b of the tempered glass 1. The compressive stress layer 2 includes a compressive stress layer caused by K ions introduced by the ion exchange treatment and a compressive stress layer caused by Na ions introduced by the ion exchange treatment. The compressive stress layer due to K ions is formed on the surfaces 1a and 1b of the tempered glass 1 and in relatively shallow positions in the vicinity thereof. The depth of the compressive stress layer due to K ions, that is, the diffusion depth DOL1 (not shown) of K ions introduced by ion exchange is preferably 0.02% to 3.00% of the thickness T of the tempered glass 1, and more preferably 0.05% to 2.00% of the thickness T. The compressive stress layer caused by Na ions is formed at a position deeper than the compressive stress layer caused by K ions. The tensile stress layer 3 is formed inside the tempered glass 1, i.e., at a position deeper than the compressive stress layer 2.

The stress curve (stress distribution) of the tempered glass 1 is obtained by measuring the stress in the depth direction (direction orthogonal to the main surface 1a) from the main surface 1a side, with the compressive stress being positive and the tensile stress being negative. The stress curve of the tempered glass 1 thus obtained is shown in fig. 2, for example. In the graph of fig. 2, the vertical axis represents stress, and the horizontal axis represents a position (depth) in the thickness direction with respect to the one main surface 1 a. In the graph of fig. 2, a positive value of stress indicates compressive stress, and a negative value of stress indicates tensile stress. That is, the larger the absolute value of the stress in the graph of fig. 2 is, the larger the stress is. Fig. 2 is a schematic diagram exaggerated for the sake of understanding, and the stress curve of the tempered glass 1 is not limited to this embodiment.

The stress profile of the tempered glass 1 includes a first peak P1, a first valley B1, a second peak P2, and a second valley B2 in this order from the main surface 1a side in the depth direction (direction orthogonal to the main surface 1 a).

The first peak P1 is a position where the maximum value of the compressive stress is obtained, and exists on the main surface 1 a. The first peak P1 has a compressive stress CS1(CSmax) of 700MPa or more, preferably 700MPa to 900MPa, and more preferably 750MPa to 850 MPa.

The stress decreases in the depth direction from the first peak P1, and the stress assumes a minimum value at the first valley B1. The stress CSb in the first valley B1 is illustrated in fig. 2 as a compressive stress (positive value), but may be a tensile stress (negative value). The lower the stress CSb of the first valley B1, the lower the tensile stress CTmax of the second valley B2, and the slower the behavior at the time of breakage.

The stress CSb at the first valley B1 is preferably +100MPa or less, more preferably +90MPa or less, +80MPa or less, +70MPa or less, +60MPa or less. However, if the stress CSb in the first valley B1 is too low, cracks are generated on the surface in the strengthening step, and visibility is deteriorated. The stress CSb of the first valley B1 is preferably-50 MPa or more, more preferably-45 MPa or more, -40MPa or more, -35MPa or more, -30MPa or more, 0MPa or more, and particularly preferably +10MPa or more. The stress CSb of the first valley B1 may be 0MPa or more and +65MPa or less, or-30 MPa or more and less than 0 MPa. The depth DOLb of the first valley B1 is preferably 0.5% to 12% of the thickness T, and more preferably 1% to 7% of the thickness T. The depth DOLb of the first valley B1 is substantially equal to the depth (diffusion depth of K ions) DOL1 of the compressive stress layer due to K ions in the compressive stress layer 2, or slightly deeper than DOL 1. More specifically, DOLb is within a range of ± 10 μm with DOL1 as a reference.

The stress increases in the depth direction from the first valley B1, and the stress has a maximum at the second peak P2. The stress CSp of the second peak P2 is a compressive stress. The compressive stress CSp of the second peak P2 is 15MPa to 250MPa, preferably 15MPa to 240MPa, 15MPa to 230MPa, 15MPa to 220MPa, 15MPa to 210MPa, 15MPa to 200MPa, 15MPa to 190MPa, 15MPa to 180MPa, 15MPa to 175MPa, 15MPa to 170MPa, 15MPa to 165MPa, 15MPa to 160MPa, 18MPa to 100MPa, more preferably 20MPa to 80 MPa.

The depth DOLp of the second peak P2 is 4% to 20% of the thickness T, preferably 4% to 19%, 4% to 18.5%, 4% to 18%, 4% to 17.5%, 4% to 17%, more preferably 4.5% to 17%, 5% to 17%, 6% to 17%, 7.3% to 17%, 8% to 15% of the thickness T.

The distance in the depth direction from the first valley B1 to the second peak P2, that is, DOLp-DOLb, is 3% or more of the thickness T, preferably 4% or more of the thickness T, and more preferably 5% to 13% of the thickness T.

The stress decreases in the depth direction from the second peak P2, and the minimum value (maximum value) of the tensile stress is taken at the second valley B2. The absolute value of the tensile stress CTmax of the second valley B2 is 70MPa or less, preferably 65MPa or less, 60MPa or less, and more preferably 40MPa to 55 MPa.

The product of the tensile stress CTmax and the thickness T of the second valley B2 is preferably-70 MPa · mm or more, more preferably-65 MPa · mm or more, -60MPa · mm or more, -55MPa · mm or more. The product of the tensile stress CTmax and the thickness T of the second valley B2 is preferably-5 MPa · mm or less, -10MPa · mm or less, -15MPa · mm or less, -20MPa · mm or less, -25MPa · mm or less, -30 · mmMPa or less.

There is a zero point Z of stress where the stress is zero between the second peak P2 and the second trough B2. Normally, the depth DOLzero of the stress zero point Z hardly exceeds 20% of the thickness T, and is physically about 22% and the limit, but DOLzero exceeding the limit value can be obtained in the present embodiment.

The larger the depth DOLzero of the stress zero point Z is, the higher the strength of the projection penetration is, the more preferably 10% or more, 10.5% or more, 11% or more, 11.5% or more, 12% or more, 12.5% or more, 13% or more, 13.5% or more, 14% or more, 14.5% or more, 15% or more, 15.5% or more, 16% or more, 16.5% or more, 17% or more, 17.5% or more, 18% or more, more preferably 18.5% or more, 19% or more, 19.5% or more, 20% or more, 20.5% or more, 21% or more, 21.5% or more, 22.0% or more, 22.5% or more, 23% or more, 23.5% or more, and most preferably 24% or more of the thickness T.

However, if the depth DOLzero of the stress zero point Z is too large, an excessive tensile stress may be generated in the first valley B1 and the second valley B2. Therefore, the depth DOLzero of the stress zero point Z is preferably 35% or less, 34.5% or less, 34% or less, 33.5% or less, 33% or less, 32.5% or less, 32% or less, 31.5% or less, 31% or less, 30.5% or less, 30% or less, 29.5% or less, 29% or less, 28.5% or less, and more preferably 27% or less of the thickness T.

Here, in the present embodiment, the tempered glass 1 also has the same stress profile at the end face 1 b. That is, the stress curve of the tempered glass 1 includes: a first peak at which the compressive stress becomes maximum at the end face 1 b; a first valley which decreases in the depth direction from the first peak to minimize the stress; a second peak that increases in depth from the first valley to maximize the compressive stress; and a second valley which decreases in the depth direction from the second peak to minimize the tensile stress, wherein the compressive stress at the first peak is 700MPa or more, the compressive stress at the second peak is 15MPa to 250MPa, and the second peak is present at a depth of 4% to 20% of the thickness T. In addition, as for the preferable range of the stress curve of the end face 1b, the preferable range of the stress curve relating to the main surface 1a can be similarly applied.

The stress and the distribution of the strengthened glass 1 can be measured and synthesized, for example, using FSM-6000LE and SLP-1000 manufactured by kyowski corporation.

The tempered glass 1 configured as above is manufactured by: a plate-shaped glass (hereinafter referred to as a glass for reinforcement) containing an alkali metal oxide as a composition is prepared, and the glass for reinforcement is subjected to a reinforcement treatment.

The glass for reinforcement preferably contains 40 to 70 mass% of SiO ₂10 to 30 percent of Al₂O₃0 to 3 percent of B₂O₃5 to 25 percent of Na₂O, 0 to 5.5 percent of K₂O, 0.1-10% of Li₂O, 0-6% of MgO and 0-15% of P₂O₅As a glass composition.

The reason why the above composition is preferable is shown below. In the description of the content range of each component,% expression means mass% unless otherwise specified.

SiO₂Is a component forming the network of the glass. If SiO₂If the content of (b) is too small, vitrification is difficult and acid resistance is liable to decrease. Thus, SiO₂The lower limit of (3) is preferably 40% by mass or more, more preferably 45% by mass or more, and particularly preferably 50% by mass or more. On the other hand, if SiO₂When the content (b) is too large, the meltability and moldability are liable to be lowered, and the thermal expansion coefficient is too low to be matched with that of the peripheral material. Thus, SiO₂A suitable upper limit range of (b) is 70% or less, preferably 65% or less, 57% or less, 56% or less, 55% or less,particularly preferably 54% or less.

Al₂O₃Is a component for increasing the ion exchange rate and is a component for increasing the Vickers hardness by increasing the Young's modulus. Further, the viscosity of the phase separation is increased. If Al is present₂O₃When the content of (b) is too small, the ion exchange rate and Young's modulus are liable to decrease. Thus, Al₂O₃The lower limit of (b) is preferably 10% or more, more preferably 15% or more, 18% or more, 24% or more, 25% or more, and particularly preferably 26% or more, in mass%. On the other hand, if Al₂O₃When the content of (b) is too large, devitrified crystals are likely to precipitate on the glass, and it is difficult to form a sheet by an overflow down-draw method or the like. In particular, when an alumina refractory is used as a formed refractory and plate-shaped forming is performed by the overflow downdraw method, devitrified crystals of spinel are likely to precipitate at the interface with the alumina refractory. In addition, the acid resistance is also lowered, and it is difficult to apply the acid treatment process. Further, the high-temperature viscosity becomes high, and the meltability tends to be low. Thus, Al₂O₃The upper limit of the range of (3) is 30% or less, preferably 29% or less, 28% or less, and 27% or less, by mass%.

B₂O₃Is a component that reduces high-temperature viscosity and density and improves resistance to devitrification. However, if B₂O₃If the content of (b) is too large, the ion exchange rate (particularly, the stress depth) tends to be low. Further, the ion exchange tends to cause coloring of the glass surface called scorching, or to reduce the acid resistance and water resistance. Thus, B₂O₃The lower limit of (B) is preferably 0% or more, 0.01% or more, or 0.05% or more by mass₂O₃The upper limit of (b) is preferably 3% or less, 2% or less, 1% or less, and particularly preferably less than 0.3% by mass.

Na₂O is an ion exchange component and is a component that lowers the high-temperature viscosity and improves the meltability and moldability. In addition, Na₂O is also a component for improving resistance to devitrification and improving reaction devitrification with a formed refractory, particularly an alumina refractory. Such asFruit Na₂When the content of O is too small, the meltability decreases, the thermal expansion coefficient decreases too much, or the ion exchange rate tends to decrease. Thus, Na₂The lower limit of O is preferably 5% or more, 7% or more, 8% or more, 8.5% or more, 9% or more, 9.5% or more, 10% or more, 11% or more, 12% or more, and particularly 12.5% or more. On the other hand, if Na₂When the content of O is too large, the viscosity of the resulting phase separation tends to decrease. Further, the acid resistance may be lowered or the balance of the components of the glass composition may be lost, whereby the devitrification resistance may be lowered. Thus, Na₂Suitable upper limit ranges of O are 20% or less, 19.5% or less, 19% or less, 18% or less, 17% or less, 16.5% or less, 16% or less, 15.5% or less, and particularly 15% or less.

K₂O is a component for lowering the high-temperature viscosity and improving the meltability and moldability. Further, the composition is also a component for improving resistance to devitrification or increasing vickers hardness. However, if K₂When the content of O is too large, the viscosity of the resulting phase separation tends to decrease. Further, the acid resistance is lowered, or the balance of the components of the glass composition is lost, and the devitrification resistance tends to be lowered conversely. Thus, K₂A suitable lower limit range of O is 0% or more, 0.01% or more, 0.02% or more, 0.1% or more, 0.5% or more, 1% or more, 1.5% or more, 2% or more, 2.5% or more, 3% or more, particularly 3.5% or more, and a suitable upper limit range is 5.5% or less, 5% or less, particularly 4.5% or less, in mass%.

Li₂O is an ion exchange component and is a component that lowers the high-temperature viscosity and improves the meltability and moldability. Or a component for increasing the young's modulus. Li₂A suitable lower limit range of O is 0.1% or more, 0.5% or more, 1.0% or more, 1.5% or more, 2.0% or more, particularly 2.5% or more in terms of mass%, and a suitable upper limit range is 10% or less, 8% or less, 5% or less, 4.5% or less, 4.0% or less, particularly less than 3.5%.

MgO is a component that lowers the high-temperature viscosity and improves the meltability and moldability. Further, the composition is also a component for increasing the Young's modulus, increasing the Vickers hardness, or improving the acid resistance. Therefore, a suitable lower limit range of MgO is 0% or more, 0.1% or more, 0.5% or more, 1% or more, 1.5% or more, and particularly 2% or more. However, if the content of MgO is too large, the ion exchange rate tends to be low, and the glass tends to be devitrified. In particular, when a plate-like shaped refractory is formed by the overflow downdraw method using an alumina refractory as a shaped refractory, devitrified crystals of spinel are likely to precipitate at the interface with the alumina refractory. Therefore, a suitable upper limit range of MgO is 6% or less, 5.5% or less, 4.5% or less, 4% or less, 3.5% or less, 3% or less, and particularly 2.5% or less.

P₂O₅Is a component for increasing the ion exchange rate while maintaining the compression stress value. Thus, P₂O₅The lower limit of the preferable range is 0% or more, 2% or more, 2.1% or more, 2.5% or more, 3% or more, 4% or more, and particularly 4.5% or more. However, if P₂O₅When the content of (b) is too large, cloudiness due to phase separation of the glass tends to occur, or water resistance tends to be lowered. Thus, P₂O₅Suitable upper limit ranges of (a) are 15% or less, 10% or less, 9.5% or less, 9% or less, 8.5% or less, 8% or less, 7.5% or less, 7% or less, 6.5% or less, 6.3% or less, particularly 6% or less.

As the fining agent, 0ppm to 30000ppm (0% to 3%) of SnO selected from SnO may be added in mass% to₂、As₂O₃、Cl、SO₃、CeO₂Group (preferably Cl, SO)₃Group(s) of (a).

Particular preference is given to the inclusion of SnO as a fining agent₂，SnO₂The preferable content range of (b) is 0 to 10000ppm, 0 to 7000ppm, particularly 50 to 6000ppm in mass%. Cl is preferably contained in a range of 0 to 1500ppm, 0 to 1200ppm, 0 to 800ppm, 0 to 500ppm, particularly 50 to 300 ppm. SO (SO)₃The content of (B) is preferably in the range of 0 to 1000ppm, 0 to 800ppm, particularly 10 to 500 ppm.

Fe₂O₃Preferably less than 1000ppm (less than 0.1%), less than 800%ppm, less than 600ppm, less than 400ppm, in particular less than 300 ppm. Thus, the transmittance (400nm to 770nm) at a thickness of 1mm is easily improved.

Nb₂O₅、La₂O₃The rare earth oxide is a component for improving the Young's modulus. However, the cost of the raw material itself is high, and if a large amount of the raw material is added, the devitrification resistance is liable to be lowered. Therefore, the content of the rare earth oxide is preferably 3% or less, 2% or less, 1% or less, 0.5% or less, and particularly preferably 0.1% or less.

In addition, from the viewpoint of environmental considerations, the reinforcing glass preferably contains substantially no As₂O₃、Sb₂O₃PbO as a glass composition. In addition, from the viewpoint of environment, it is also preferable that Bi is not substantially contained₂O₃、F。

The composition of the above-mentioned glass for strengthening is an example, and a glass for strengthening having a known composition can be used as long as it can be chemically strengthened by ion exchange. The composition of the tempered glass obtained by subjecting the above-mentioned tempered glass to ion exchange treatment is the same as the composition of the tempered glass before the ion exchange treatment.

A method for producing the tempered glass 1 (tempered glass sheet) having the above-described structure will be described below.

As shown in fig. 3, the method includes a preparation step S1, a first ion exchange step S2, a second ion exchange step S3, a first inspection step S4, a removal step S5, a second inspection step S6, a post-removal ion exchange step S7, and a third inspection step S8.

The preparation step S1 is a step of preparing a glass for reinforcement. In preparation step S1, a glass raw material prepared so as to have the above glass composition is charged into a continuous melting furnace, heated and melted at 1500 to 1600 ℃, clarified, supplied to a forming apparatus, formed into a sheet shape or the like, and gradually cooled, whereby a reinforcing glass can be produced.

As a method of forming a glass sheet, an overflow down-draw method is preferably employed. The overflow down-draw method is a method that can produce a large amount of high-quality glass sheets, can also easily produce large-sized glass sheets, and can reduce damage to the surfaces of the glass sheets as much as possible. In the overflow downdraw method, alumina or dense zircon is used as a constituent material of the molded body, for example. The glass for reinforcement of the present invention has good compatibility with alumina and dense zircon, and particularly with alumina (the components of molten glass are less likely to react with the components of the molded body, and bubbles, pits, and the like are less likely to be generated).

In addition to the overflow downdraw process, various forming methods may be employed. For example, a forming method such as a float method, a down-draw method (slit down-draw method, redraw method, or the like), a roll-out method, or a press method can be used.

The glass for reinforcement may be bent after or simultaneously with the forming, as necessary. Further, cutting, drilling, surface polishing, chamfering, end face polishing, etching, and the like may be performed as necessary.

The size of the glass for reinforcement can be arbitrarily determined, and the thickness T is preferably 2.0mm or less, more preferably 0.05 to 1.0mm, still more preferably 0.1 to 0.9mm, 0.3 to 0.85mm, and 0.5 to 0.8 mm.

In the first ion exchange step S2, the surface of the glass for reinforcement is ion-exchanged by immersing the glass for reinforcement in a treatment tank filled with a first molten salt containing Na having a larger ionic radius than Li ions contained in the glass for reinforcement and holding the glass for a predetermined time at a predetermined temperature. Thereby, the strengthening glass is brought into contact with the first molten salt, Li ions in the strengthening glass are ion-exchanged with Na ions in the first molten salt, and Na ions are introduced into the vicinity of the surface (main surface and end surface) of the strengthening glass. Further, Na ions in the strengthening glass are ion-exchanged with K ions in the first molten salt. As a result, the compressive stress layer 2 is formed in the surface layer portion of the glass for tempering, and the glass for tempering is tempered.

In the first ion exchange step S2, the region where Na ions are introduced into the reinforcing glass is preferably a region from the surface of the reinforcing glass to a depth of 10% or more of the thickness T, and more preferably a region from the surface of the reinforcing glass to a depth of 12% or more, 14% or more, 15% or more, and 40% or less of the thickness T.

The first molten salt used in the first ion exchange step S2 is preferably NaNO₃And KNO₃The mixed salt of (1). If the first molten salt contains K ions, the stress and the distribution of the glass for reinforcement can be easily measured after the first ion exchange step S2, and therefore, the method is suitable for quality control of the obtained reinforced glass. Preferably NaNO₃The concentration of KNO in the first molten salt is preferably 50% by mass or more₃The concentration in the first molten salt is preferably less than 90% by mass. But is not limited thereto, NaNO₃The concentration of the first molten salt is preferably 100 to 10%, 100 to 20%, 100 to 30%, 100 to 40%, 100 to 50% by mass, and the balance is preferably KNO₃. The first molten salt may contain NaNO alone₃Without comprising KNO₃The composition of (1). In addition, the first molten salt may comprise LiNO₃。

The ion exchange treatment temperature in the first ion exchange step S2 is preferably 350 to 480 ℃, more preferably 360 to 430 ℃, further preferably 370 to 400 ℃, and 370 to 390 ℃. The ion exchange treatment time in the first ion exchange step S2 is preferably 1 to 20 hours, more preferably 1.5 to 15 hours, and still more preferably 2 to 10 hours.

In the second ion exchange step S3, the surface of the glass for reinforcement is ion-exchanged by immersing the glass for reinforcement in a treatment tank filled with a second molten salt containing K ions and Li ions and holding the glass for a predetermined time at a predetermined temperature.

Thereby, the second molten salt is brought into contact with the glass for tempering, and Li ions in the second molten salt and Na ions in the glass for tempering are subjected to reverse ion exchange, whereby at least a part of the Na ions is released from the glass for tempering. At the same time, K ions are ion-exchanged with Li ions or Na ions contained in the glass for strengthening, so that K ions are introduced into the glass for strengthening in a region shallower than 7% of the thickness T from the surface. That is, the compressive stress formed in the surface layer portion of the glass for reinforcement is relaxed by the reverse ion exchange, and the glass for reinforcement is reinforced by the ion exchange, so that a high compressive stress is formed only in the vicinity of the surface in the surface layer portion.

In the second ion exchange step S3, the region where Na ions are desorbed from the reinforcing glass is preferably a region from the surface of the reinforcing glass to a depth of 15% or less of the thickness T, and more preferably a region from the surface of the reinforcing glass to a depth of 14% or less, 13% or less, 12% or less, 11% or less, 10% or less, 1% or more and 10% or less, 2% or more and 10% or less, 3% or more and 10% or less, 4% or more and 10% or less, and 5% or more and 10% or less of the thickness T. In the second ion exchange step S3, the region in which K ions are introduced into the glass for strengthening is preferably a region extending from the surface of the glass for strengthening to a depth of 7% or less of the thickness T, and more preferably a region extending from the surface of the glass for strengthening to a depth of 6.5% or less, 6% or less, 5.5% or less, or 5% or less of the thickness T.

The second molten salt used in the second ion exchange step S3 is preferably LiNO₃And KNO₃The mixed salt of (1). LiNO₃The concentration in the second molten salt is preferably lower than KNO₃The concentration in the second molten salt. In detail, LiNO₃The concentration of the second molten salt is preferably 0.1 to 5%, 0.2 to 5%, 0.3 to 5%, 0.4 to 5%, 0.5 to 4%, 0.5 to 3%, 0.5 to 2.5%, 0.5 to 2%, 1 to 2% by mass. KNO₃The concentration of the second molten salt is preferably 95 to 99.8%, 97 to 99.6%, 98 to 99.5%, or 99 to 99.7% by mass.

The concentration of Li ions in the second molten salt is preferably 100 ppm by mass or more. At this time, the concentration of Li ions in the second molten salt is determined by expressing LiNO in mass%₃And multiplying the result by 0.101.

The ion exchange treatment temperature in the second ion exchange step S3 is preferably 350 to 480 ℃, more preferably 360 to 430 ℃, further preferably 370 to 400 ℃, and 370 to 390 ℃. The ion exchange treatment time in the second ion exchange step S3 is preferably shorter than the ion exchange treatment time in the first ion exchange step S2. The ion exchange treatment time in the second ion exchange step S3 is preferably 0.2 hours or more, more preferably 0.3 to 2 hours, 0.4 to 1.5 hours, and further preferably 0.5 to 1 hour.

The reinforcing glass immersed in the molten salt in each of the ion exchange steps S2 and S3 may be preheated to the temperature of the molten salt in the ion exchange treatment in each of the ion exchange steps S2 and S3, or may be immersed in each of the molten salts at normal temperature (e.g., 1 to 40 ℃).

It is preferable to provide a cleaning step of cleaning the glass for strengthening drawn out from the molten salt between the first ion exchange step S2 and the second ion exchange step S3. By performing the cleaning, the substances adhering to the reinforcing glass can be easily removed, and the ion exchange treatment can be performed more uniformly in the second ion exchange step S2.

In the first inspection step S4, before the removal step S5, the strengthened glass 1 formed through the first ion exchange step S2 and the second ion exchange step S3 is inspected for superiority and inferiority (presence of defects, irregularities, and the like). In the first inspection step S4, when a minute defect such as a flaw is found on the surface, for example, the main surface 1a of the tempered glass 1, the next removal step S5 is performed on the tempered glass 1. On the other hand, if no minute defect is found and the glass meets the standard of other products, the tempered glass 1 becomes a product.

As shown in fig. 4, in the removing step S5, the front and back main surfaces 1a of the tempered glass 1 are removed in a range shallower than the compressive stress layer 2. Specifically, a portion from the surface 1a0 of the strengthened glass 1 in which the defect is found to a predetermined depth Δ t is removed. As a method for removing the surface 1a0 of the tempered glass 1, it is preferable to polish the surface 1a0 of the tempered glass 1 with a polishing tool such as a polishing pad. However, the surface 1a0 may be removed by etching the tempered glass 1.

In the removal step S5, when any removal method is used, it is preferable that the removal amounts of the front and back main surfaces 1a are equal to each other. More specifically, the difference in the amount of removal of front and back main surfaces 1a is preferably 1 μm or less, more preferably 0.5 μm or less and 0.3 μm or less. By limiting the difference in the amount of removal of front and back main surfaces 1a to a small value, the occurrence of warpage in strengthened glass 1 due to removal can be suppressed. Therefore, when the removal is performed by polishing, it is preferable to perform polishing using a double-side polishing apparatus.

The amount (removal amount) Δ t of removal from the tempered glass 1 is preferably 0.5 to 20 μm. The removal amount Δ t is preferably set to be constant over the entire main surface 1a, but may remain without removing a portion of main surface 1a0 where no defect is present. That is, in removing step S5, at least a part of main surface 1a0 of strengthened glass 1 can be removed. The removal amount Δ t is preferably smaller than the depth DOLzero of the compressive stress layer 2, and more preferably smaller than the diffusion depth DOL1 of the K ions introduced in the second ion exchange step S3. When a defect occurs in the end face 1b, the end face 1b may be subjected to a polishing process or an etching process to remove a part of the end face 1 b.

In the removing step S5, the surface 1a0 of the tempered glass 1 is removed, whereby a new surface 1a is formed on the tempered glass 1. Hereinafter, the glass having the new surface 1a formed thereon is referred to as "second glass for reinforcement". As described above, when the removal amount Δ t is made smaller than the diffusion depth DOL1 of the K ions introduced in the second ion exchange step S3, a part of the compressive stress layer due to the K ions remains on the new surface 1 a.

In the removing step S5, the compressive stress value (maximum compressive stress value) CS2 of the compressive stress layer 2 on the new surface 1a of the second glass for reinforcement is lower than the compressive stress value on the surface 1a0 before the removing step S5. The compressive stress value CS2 of the new surface 1a after the removal step S5 and before the ion exchange step S7 after the removal is 80MPa or more, preferably 100MPa or more, and more preferably 150MPa or more and 200MPa or more. The compressive stress value of the new surface 1a is less than 700MPa, 600MPa or less, 500MPa or less, and 400MPa or less depending on the removal amount Δ t of the reinforcing glass 1 in the removal step S5.

In the removal step S5, a new surface 1a is formed on the second glass for reinforcement, and thereby the depth (diffusion depth) of the compressive stress layer due to K ions formed in the second glass for reinforcement is reduced by the removal amount Δ t. The diffusion depth DOL2 of K ions remaining in the compressive stress layer 2 of the second glass for tempering after the removal step S5 (before the post-removal ion exchange step S7) is preferably 0.02% to 3.00% of the thickness T1 of the second glass for tempering, and more preferably 0.05% to 2.00% of the thickness T1.

In the second inspection step S6, it is inspected whether or not a defect remains on the new surface 1a formed on the second reinforcing glass. In the second inspection step S6, it is also possible to inspect whether or not the dimensions such as the thickness of the second reinforcing glass meet predetermined criteria, in addition to the presence or absence of defects. If a defect remains in the second glass for reinforcement, the removal step S5 is performed again on the second glass for reinforcement, and then the second inspection step S6 is performed again. The second strengthening glass that meets the criteria for defects and sizes set in the second inspection step S6 is subjected to the post-removal ion exchange step S7. On the other hand, if the defect or size criterion set in the second inspection step S6 is not met, the second reinforcing glass is subjected to the removal step S5 again, and then to the second inspection step S6 again.

In the post-removal ion exchange step S7, the second reinforcing glass is reinforced so that the first peak P1, the first trough B1, the second peak P2, the second trough B2, and other reinforcing characteristics of the stress curve fall within the above numerical ranges.

In the post-removal ion exchange step S7, the second strengthening glass that has passed through the second inspection step S6 is subjected to an ion exchange treatment. Specifically, in the post-removal ion exchange step S7, the second reinforcing glass having the new surface 1a formed in the removal step S5 is immersed in a treatment tank filled with a molten salt containing K ions and Li ions. The second glass for reinforcement is immersed (contacted) in the molten salt and kept at a predetermined temperature for a predetermined time, thereby performing an ion exchange treatment on the new surface 1a of the second glass for reinforcement.

In this way, Li ions in the molten salt and Na ions in the second glass for reinforcement are subjected to reverse ion exchange, and at least a part of the Na ions are released from the second glass for reinforcement. At the same time, the K ions are ion-exchanged with Li ions or Na ions in the second strengthening glass. That is, the compressive stress formed in the surface layer portion of the second glass for reinforcement is relaxed by the reverse ion exchange, and the second glass for reinforcement is reinforced by the ion exchange, so that a high compressive stress is formed only in the vicinity of the surface in the surface layer portion.

The molten salt used in the post-removal ion exchange step S7 is preferably LiNO₃With KNO₃The mixed salt of (1). LiNO in molten salts₃Preferably in a concentration lower than KNO in the molten salt₃The concentration of the active ingredient. In detail, LiNO in molten salt₃The content is preferably 0.1-2%, 0.2-2%, 0.3-2%, 0.4-2%, 0.5-2% by mass%, and the balance is preferably KNO₃. The molten salt may comprise NaNO₃. In this case, the Na ion concentration in the molten salt is converted to NaNO₃In the case of (3), it is preferably 5% by mass or less, more preferably 1.8% by mass or less. Further, the concentration of Na ions in the molten salt is preferably 5000 mass ppm or less with respect to the total amount of the molten salt.

The Li ion concentration in the molten salt is preferably 100 mass ppm or more with respect to the total amount of the molten salt. In this case, the concentration of Li ions in the molten salt is represented by LiNO in mass%₃And multiplying the result by 0.101.

The ion exchange treatment temperature in the post-removal ion exchange step S7 is preferably 350 to 480 ℃, 350 to 450 ℃, more preferably 360 to 430 ℃, and still more preferably 370 to 400 ℃, and 370 to 390 ℃.

The ion exchange treatment time in the post-removal ion exchange step S7 is preferably shorter than the ion exchange treatment time in the first ion exchange step S2 and is preferably equal to or shorter than the ion exchange treatment time in the second ion exchange step S3. The ion exchange treatment time in the post-removal ion exchange step S7 is preferably 0.2 hours or more, more preferably 0.3 to 2 hours, 0.4 to 1 hour, and further preferably 0.5 to 0.75 hour. The ion exchange treatment time in the post-removal ion exchange step S7 may be 0.1 to 200%, preferably 1 to 200%, 10 to 200%, 50 to 100% of the ion exchange treatment time in the second ion exchange step S3. In other words, the ion exchange treatment time in the post-removal ion exchange step S7 may be set shorter than the ion exchange treatment time in the second ion exchange step S3.

The compressive stress value (maximum compressive stress value) CS3 of the compressive stress layer 2 on the surface 1a of the tempered glass 1 formed in the post-removal ion exchange step S7 is a value that increases from the compressive stress value CS2 of the surface 1a0 before the removal step S5. The compressive stress value CS3 of the surface 1a after the post-removal ion exchange step S7 is 700MPa or more, preferably 700 to 1200 MPa.

In the post-removal ion exchange step S7, the ion exchange conditions are preferably adjusted so that the absolute value of the difference between the compressive stress value CS3 and the compressive stress CS1 is preferably 100MPa or less, preferably 50MPa or less, more preferably 30MPa or less, or 20MPa or less.

In the post-removal ion exchange step S7, the ion exchange conditions are preferably adjusted so that the compressive stress value CS3 is 0.7 to 1.3 times, preferably 0.8 to 1.2 times, and particularly preferably 0.9 to 1.1 times the compressive stress CS 1. If the strength of the tempered glass 1 is increased, CS3 is allowed to be CS1 or more.

In the post-removal ion exchange step S7, the depth of the compressive stress layer 2 in the tempered glass 1 increases. The diffusion depth DOL3 of K ions in the compressive stress layer 2 of the tempered glass 1 after the post ion exchange step S7 is preferably 0.02% to 3.00% of the thickness T1 of the tempered glass 1, and more preferably 0.05% to 2.00% of the thickness T1.

In the third inspection step S8, for example, an inspection and a measurement of a stress curve relating to the presence or absence of defects and the like are performed on the tempered glass 1 formed in the post-removal ion exchange step S7. The tempered glass 1 is a product by meeting the standard specified in the third inspection step S8.

According to the method for producing strengthened glass 1 of the present embodiment described above, by removing the surface (main surface 1a0) of strengthened glass 1 in removing step S5, it is possible to remove minute defects formed on the surface. The compressive stress value of the compressive stress layer 2 on the new surface (new main surface 1a) formed in the removal step S5 is reduced, but the compressive stress value of the surface (main surface 1a) of the tempered glass 1 can be adjusted to 700MPa or more by performing the post-removal ion exchange step S7.

< second embodiment >

Fig. 5 shows a second embodiment of the present invention. The method for producing the tempered glass 1 of the present embodiment is different from the first embodiment in that it includes the post-removal preliminary ion exchange step S7a performed after the second inspection step S6 and before the post-removal ion exchange step S7.

In the post-removal preliminary ion exchange step S7a, the second reinforcing glass having passed through the removal step S5 and the second inspection step S6 is immersed in a treatment tank filled with the third molten salt. That is, the second reinforcing glass is brought into contact with the third molten salt, and Li ions in the second reinforcing glass are ion-exchanged with Na ions in the third molten salt. Further, Na ions in the second glass for strengthening are ion-exchanged with K ions in the third molten salt.

In the post-removal preliminary ion exchange step S7a, the region in which Na ions are introduced into the second glass for reinforcement is preferably a region from the new surface 1a of the second glass for reinforcement to a depth of 10% or more of the thickness T1, and more preferably a region from the surface of the second glass for reinforcement to a depth of 12% or more, 14% or more, 15% or more, and 40% or less of the thickness T1.

The third molten salt used in the post-removal preliminary ion exchange step S7a is preferably NaNO₃And KNO₃The mixed salt of (4). NaNO₃The concentration in the third molten salt is preferably determined by the presence of NaNO₃The concentrations in the first molten salt are substantially equal. Here, "the concentrations are substantially equal" means that the difference (absolute value) between the concentrations is 1% or less. Likewise, KNO₃The concentration in the third molten salt is preferably equal to KNO₃In the first molten saltAre substantially equal.

In the present embodiment, the second reinforcing glass is immersed in the treatment tank containing the third molten salt as described above, but the embodiment of the post-removal preliminary ion exchange step S7a is not limited to the present embodiment. For example, in the post-removal preliminary ion exchange step S7a, the second reinforcing glass that has undergone the second inspection step S6 may be immersed in a treatment tank that contains the first molten salt used in the first ion exchange step.

In this way, NaNO is used in the preliminary ion exchange step S7a after removal₃、KNO₃With the concentration of NaNO in the third molten salt₃、KNO₃The post-removal preliminary ion exchange step S7a can be performed without preparing a treatment tank containing the third molten salt. This can reduce the cost of the facility for manufacturing the tempered glass 1, and can save space. The ion exchange conditions (time and temperature) in the post-removal preliminary ion exchange step S7a may be the same as those in the first ion exchange step S2.

NaNO in third molten salt₃The concentration is preferably 20% or more by mass%, and KNO is preferable₃The concentration in the first molten salt is preferably less than 90% by mass. But not limited thereto, NaNO in the third molten salt₃The concentration is preferably 100 to 10%, 100 to 20%, 100 to 30%, 100 to 40%, 100 to 50% by mass%, and the remaining is preferably KNO₃. The third molten salt may contain NaNO alone₃Without comprising KNO₃The composition of (1). Additionally, the third molten salt may comprise LiNO₃。

The Li ion concentration in the third molten salt is preferably ± 2000ppm in terms of the Li ion monomer.

The ion exchange treatment temperature in the post-removal preliminary ion exchange step S7a is preferably 350 to 480 ℃, more preferably 360 to 430 ℃, still more preferably 370 to 400 ℃, and yet more preferably 370 to 390 ℃.

The ion exchange treatment time in the post-removal preliminary ion exchange step S7a is preferably 10 to 100%, more preferably 50 to 100%, of the ion exchange treatment time in the first ion exchange step S2.

The post-removal ion exchange step S7 of the present embodiment is performed after the post-removal preliminary ion exchange step S7 a. In the post-removal ion exchange step S7, the second reinforcing glass is immersed in the treatment tank containing the molten salt, as in the first embodiment. In this case, KNO is preferable₃Concentration of KNO in molten salt used in post-removal ion exchange step S7₃The concentrations in the second molten salt are substantially equal. Further, LiNO is preferred₃The concentration of LiNO in the molten salt used in the post-removal ion exchange step S7₃The concentrations in the second molten salt are substantially equal.

In the present embodiment, as described above, in the post-removal ion exchange step S7, the second reinforcing glass is immersed in the treatment tank containing the predetermined molten salt, but the form of the post-removal ion exchange step S7 is not limited to the present embodiment. For example, in the post-removal ion exchange step S7, the second reinforcing glass that has undergone the post-removal preliminary ion exchange step S7a may be immersed in a treatment tank that contains the second molten salt used in the second ion exchange step.

In this way, in the post-removal ion exchange step S7, LiNO is used as a catalyst₃、KNO₃LiNO in a molten salt at a substantially equal concentration₃、KNO₃The second molten salt having a concentration of (2) enables the post-removal ion exchange step S7 to be performed even if a dedicated treatment tank is not prepared for the post-removal ion exchange step S7. This can reduce the cost of the facility for manufacturing the tempered glass 1 and save space.

In this case, the ion exchange treatment time in the post-removal ion exchange step S7 is preferably 0.1 to 200%, preferably 1 to 200%, 10 to 200%, 50 to 100% of the ion exchange treatment time in the second ion exchange step S3.

The third inspection step S8 performed after the post-removal ion exchange step S7 is performed in the same manner as the third inspection step S8 in the first embodiment.

In the present embodiment, the ion exchange conditions in the ion exchange step after the removal step S5 (the post-removal preliminary ion exchange step S7a and/or the post-removal ion exchange step S7) are preferably adjusted so that the absolute value of the difference between the stress CSb at the first valley of the strengthened glass 1 obtained after the removal of the post-ion exchange step S7 and the stress CSb at the first valley of the strengthened glass 1 after the second ion exchange step S3 and before the removal step S5 is preferably 50MPa or less, more preferably 40MPa or less and 30MPa or less.

CSb may employ compressive stress in the potassium ion diffusion tips or DOLs without explicitly observing valleys.

Further, the ion exchange conditions in the ion exchange step after the removal step S5 (the post-removal preliminary ion exchange step S7a and/or the post-removal ion exchange step S7) are preferably adjusted so that the stress CSb at the first valley of the strengthened glass 1 obtained after the post-removal ion exchange step S7 becomes 0.5 to 2.0 times, preferably 0.7 to 1.5 times, more preferably 0.7 to 1.5 times, and particularly preferably 0.8 to 1.3 times the stress CSb at the first valley of the strengthened glass 1 after the second ion exchange step S3 and before the removal step S5.

If the strength of the strengthened glass 1 is improved, the stress CSb at the first valley of the strengthened glass 1 obtained after the removal of the post-ion exchange step S7 is allowed to be equal to or higher than the stress CSb at the first valley of the strengthened glass 1 after the second ion exchange step S3 and before the removal step S5.

In the present embodiment, the ion exchange conditions in the ion exchange step after the removal step S5 (the post-removal preliminary ion exchange step S7a and/or the post-removal ion exchange step S7) are preferably adjusted so that the absolute value of the difference between the stress CSp at the second peak of the strengthened glass 1 obtained after the removal of the post-ion exchange step S7 and the stress CSp at the second peak of the strengthened glass 1 after the second ion exchange step S3 and before the removal step S5 is preferably 50MPa or less, more preferably 30MPa or less and 20MPa or less.

When the peak is not clearly observed, the difference between the average stress values up to the depth positions DOL to DOC is compared, thereby enabling calculation of the difference between the csps.

Further, the ion exchange conditions in the ion exchange step after the removal step S5 (the post-removal preliminary ion exchange step S7a and/or the post-removal ion exchange step S7) are preferably adjusted so that the stress CSp at the first peak of the strengthened glass 1 obtained after the post-removal ion exchange step S7 becomes 0.5 to 2.0 times, preferably 0.7 to 1.5 times, more preferably 0.7 to 1.5 times, and particularly preferably 0.8 to 1.3 times the stress CSp at the second peak of the strengthened glass 1 after the second ion exchange step S3 and before the removal step S5.

If the strength of the strengthened glass 1 is increased, the stress CSp at the second peak of the strengthened glass 1 obtained after the removal of the post-ion exchange step S7 is allowed to be equal to or higher than the stress CSp at the second peak of the strengthened glass 1 after the second ion exchange step S3 and before the removal step S5.

According to the method for producing the strengthened glass 1 of the second embodiment described above, for example, even when the removal step S5 is performed to the deep portion of the glass, not only the compressive stress CS1 of the surface layer is reduced, but also the compressive stress CSb of the first valley B1 and the compressive stress CSp of the stress P2 are reduced, the post-removal preliminary ion exchange step S7a is provided, whereby the ion exchange can be performed again to the deep portion, and the compressive stresses of the CSb and the CSp can be regenerated. As a result, the strength characteristics of the tempered glass 1 lost in the removing step S5 can be appropriately restored (reproduced).

< modification example >

The present invention is not limited to the configuration of the above embodiment, and is not limited to the above operation and effects. The present invention can be variously modified within a scope not departing from the gist of the present invention.

In the above embodiment, the example in which the second ion exchange step S3 is performed after the first ion exchange step S2 is performed has been described, but the present invention is not limited to this configuration. The first ion exchange process S2 and the second ion exchange process S3 may be performed simultaneously.

In the above embodiment, the case where Li ions in the glass for reinforcement and Na ions in the first molten salt are ion-exchanged in the first ion exchange step S2 has been exemplified, but the Na ions in the glass for reinforcement and K ions in the molten salt may be ion-exchanged in the first ion exchange step S2.

In the above embodiment, the case where 1 time of the ion exchange treatment is performed as the post-removal ion exchange step after the removal step is exemplified, but a preliminary ion exchange treatment (post-removal preliminary ion exchange step) may be added after the removal step and before the post-removal ion exchange step. That is, after the removal step and before the post-removal ion exchange step, a plurality of ion exchange treatments including a post-removal preliminary ion exchange step may be performed. The composition and temperature of the molten salt used in the ion exchange step prepared after the removal may be, for example, the same as those in the first ion exchange step, and the ion exchange treatment time may be equal to or shorter than that in the first ion exchange step.

In the above embodiment, the compressive stress value in the compressive stress layer 2 of the tempered glass 1 is reduced by removing the surface 1a0 of the tempered glass 1 in the removing step S5. As another method for reducing the compressive stress value, there is a technique of performing a reverse ion exchange treatment on the tempered glass 1 subjected to the first ion exchange step S2 and the second ion exchange step S3. The removing step S5 of the present invention does not include a method of removing the compressive stress of the tempered glass 1 by the reverse ion exchange treatment.

In the second embodiment, the NaNO occupied by the third molten salt in the post-removal preliminary ion exchange step S7a is treated₃And KNO₃With the concentration of NaNO in the first molten salt₃And KNO₃The concentration of (b) is substantially equal to each other, but the concentration of (b) is not limited to this.

In the second embodiment, LiNO occupied by the molten salt in the post-removal ion exchange step S7 is replaced with LiNO₃And KNO₃And the concentration of the first molten salt and the LiNO occupied by the first molten salt₃And KNO₃The concentration of (A) is substantially equal, but not limited theretoMay also be different.

< third embodiment >

The first embodiment described above can be modified to a third embodiment as follows. Fig. 6 is a flowchart showing a method for producing tempered glass according to a third embodiment. In the method for producing a tempered glass according to the third embodiment, information on the tempered glass 1 after the second ion exchange step S3 and information on the second tempered glass after the removal step S5 can be acquired before the post-removal ion exchange step S7, and based on these information, ion exchange conditions in the post-removal ion exchange step S7 can be set. The ion exchange conditions include, for example, the ion exchange treatment time and the ion exchange treatment temperature in the post-removal ion exchange step S7. Hereinafter, a case where an ion exchange treatment time as an ion exchange condition is set will be described.

The first inspection step S4 in the method for producing the tempered glass 1 includes a first measurement step S41 of acquiring information on the stress of the tempered glass 1, and a predetermined removal amount setting step S42 of setting a predetermined removal amount Δ t0 to be removed from the tempered glass 1, in addition to inspecting the tempered glass 1 formed through the first ion exchange step S2 and the second ion exchange step S3 for the presence or absence of defects, and the like.

The second inspection step S6 of the method includes, in addition to the step of inspecting whether or not a defect remains on the new surface 1a formed on the second glass for reinforcement, a second measurement step S61 of acquiring information on the stress of the second glass for reinforcement, a removal amount determination step S62 of determining the removal amount Δ t of the glass for reinforcement 1 actually removed in the removal step S5, and an ion exchange condition setting step S63 of setting the ion exchange conditions in the post-removal ion exchange step S7.

The third inspection step S8 of the present method is provided with a third measurement step S81 of acquiring information on the stress of the tempered glass 1, in addition to inspecting whether or not the tempered glass 1 formed in the post-removal ion exchange step S7 has defects.

In the first measurement step S41 of the first inspection step S4, information on the stress of the tempered glass 1 after the second ion exchange step S3 is measured by a measuring apparatus. As the measuring apparatus used in the first measuring step S41, a surface stress meter (for example, FSM-6000LE, SLP-1000 manufactured by TOYOBO Co., Ltd.) is preferably used.

The surface stress meter can generate optical interference fringes with respect to the tempered glass 1, and can capture an interference fringe image including the optical interference fringes and store the image as image data. The surface stress meter can determine a stress curve (stress distribution) of the strengthened glass 1 based on the image data. The information on the stress of the strengthened glass 1 includes the diffusion depth DOL1 of the K ions introduced into the strengthened glass 1 in addition to the interference fringe image. The information on the stress of the tempered glass 1 may include information on the first peak P1, the first valley B1, the second peak P2, the second valley B2, the depth thereof, and the like in the stress curve.

In the first measurement step S41, the thickness of the tempered glass 1 is measured. The thickness of the tempered glass 1 is measured by a measuring device such as a micrometer or a laser displacement meter.

In the scheduled removal amount setting step S42, for example, in the first inspection step S4, when a defect is detected in the tempered glass 1, a scheduled removal amount Δ t0 to be removed from the tempered glass 1 for removing the defect is set based on the defect information (information such as the type, size, and depth of the defect) and the information such as the thickness of the tempered glass 1.

In addition, in the predetermined removal amount setting step S42, the predetermined removal amount Δ t0 can be set regardless of the result of the first measurement step S41. For example, in the preparation step (the step of producing the tempered glass), when it is clear that the occurrence of defects in the tempered glass tends to be constant, the predetermined removal amount Δ t0 may be uniformly set for the plurality of tempered glasses 1 without using the measurement result of the first measurement step S41.

In the second measurement step S61 of the second inspection step S6, information on the stress of the second reinforcing glass is measured by the measurement device (surface stress meter) used in the first measurement step S41. That is, the measuring device generates optical interference fringes with respect to the second reinforcing glass, takes an image of the interference fringes, and stores the image data as information relating to the stress, in the same manner as in the first measuring step S41. The information on the stress of the second glass for reinforcement includes, in addition to the interference fringe image, the diffusion depth DOL2 of K ions remaining in the second glass for reinforcement, and the like.

In the second measurement step S61, the thickness of the second reinforcing glass may be measured by the same method as in the first measurement step S41.

In the removal amount determining step S62, the amount (removal amount) Δ t actually removed from the tempered glass 1 in the removing step S5 can be calculated from the difference between the thickness of the second tempered glass and the thickness of the tempered glass 1 measured in the first measuring step S41.

The determination of the removal amount Δ t is not limited to the above-described method. In the removal amount determination step S62, for example, the difference (DOL1-DOL2) between the diffusion depth DOL2 of K ions of the second reinforcing glass measured in the second measurement step S61 and the diffusion depth DOL1 of K ions measured in the first measurement step S41 can be determined as the removal amount Δ t.

In the ion exchange condition setting step S63, the ion exchange conditions in the post-removal ion exchange step S7 are set based on the measurement results of the first measurement step S41 and the second measurement step S61. In the ion exchange condition setting step S63, the ion exchange processing time as the ion exchange condition is set based on a function prepared in advance. The function is represented by the following formula (1).

Tx＝a(1-e^-b×x)…(1)

Tx in the formula (1) is an ion exchange treatment time, and a and b are constants different depending on the respective strengthening conditions such as the second ion exchange treatment time and the strengthening temperature and the thickness of the strengthened glass 1. The preferable range of a is, for example, a range from the ion effect treatment time in the second ion exchange step to a number 2 times the ion exchange treatment time in the second ion exchange step. The preferable range of b is, for example, 1 to 5.

The variable x in the formula (1) is the ratio (Δ t/DOL1) of the removal amount Δ t of one (one side) of the front and back main surfaces in the second reinforcing glass determined in the removal amount determination step S62 to the diffusion depth DOL1 of the K ions introduced in the second ion exchange step S3.

The formula (1) is prepared by performing a manufacturing test on a plurality of samples of the glass for tempering prepared in advance. The manufacturing test was carried out as follows.

First, a first ion exchange step and a second ion exchange step were performed on each sample to produce a strengthened glass. Next, information on the stress of each tempered glass and the like are acquired.

Then, a predetermined removal amount different from each other is set for each tempered glass, and a removal step is performed. Next, information on the stress of the second glass for reinforcement and the like are acquired. Then, different ion exchange conditions (ion exchange treatment time) were set for each second strengthening glass, and the post-removal ion exchange step was performed. Finally, information relating to the stress of the strengthened glass after the post-removal ion exchange process is obtained.

Then, information on the stress obtained for the tempered glass after the post-removal ion exchange step was verified. That is, it is checked whether or not the information on the stress of each tempered glass satisfies a predetermined criterion. Next, based on the data of the tempered glass satisfying the standard, the functions of the removal amount Δ t of each sample, DOL1 after the second ion exchange step, DOL2 after the removal step, and ion exchange processing time of the ion exchange step S7 after the removal step were created by analysis software of an arithmetic processing device (for example, a computer such as a PC). The formula (1) is obtained by the above steps.

The ion exchange condition setting step S63 is executed by an arithmetic processing device capable of performing the arithmetic processing of the formula (1).

In the third measurement step S81 of the third inspection step S8, information on the stress of the tempered glass 1 after the post-ion exchange step S7 is removed is measured by a measurement device (surface stress meter). Then, in the third inspection step S8, it is determined whether or not the information on the measured stress satisfies a reference value (determination step). The determination step is executed by, for example, an arithmetic processing unit.

The removal amount Δ t is not limited to the methods of the above embodiments and modifications, and may not be set based on the presence or absence of a defect. In this case, the removal amount Δ t may be set based on various information acquired in the manufacturing process (preparation process) of the reinforcing glass.

< fourth embodiment >

In the third embodiment, the case where the removal amount Δ t is determined and the ion exchange processing time is set based on the removal amount Δ t is exemplified, but a modification may be made such that the ion exchange processing time is set without determining the removal amount Δ t as follows. That is, in the ion exchange condition setting step S63, the ion exchange conditions can be set without using the above formula (1). Specifically, in the ion exchange condition setting step S63, the ion exchange processing time may be set based on the interference fringe image, for example.

In the ion exchange condition setting step S63, the ion exchange processing time in the post-removal ion exchange step S7 may be set based on the data of the interference fringe image of the strengthened glass 1 acquired in the first measurement step S41 and the data of the interference fringe image acquired in the second measurement step S61. In this case, the removal amount determining step S62 may be omitted. A specific embodiment of the ion exchange condition setting step S63 will be described below with reference to fig. 7 to 10.

Fig. 7 is a schematic view of an interference fringe image (hereinafter referred to as "first interference fringe image") of the tempered glass 1 after the second ion exchange step S3. Fig. 8 to 10 are schematic diagrams of interference fringe images (hereinafter, referred to as "second interference fringe images") of the second reinforcing glass, which are acquired after the removal step S5.

As shown in fig. 7, the first interference fringe image includes a first area Al and a second area a2 (the same in the second interference fringe image). Each of the regions a1 and a2 includes a plurality of bright and dark lines L1a to L1c, L2a to L2c, and a boundary portion BP of light interference fringes. The measurement device can create the first interference fringe image and calculate the stress value, depth, and the like of the compressive stress layer of the tempered glass based on the distance D0 between the dark lines L1a to L1c (or bright lines) of the first region a1 and the dark lines L2a to L2c of the second region a 2.

Each of the regions a1 and a2 includes, for example, 3 dark lines L1a to L1c and L2a to L2 c. Hereinafter, the 3 dark lines L1a to L1c and L2a to L2c in the regions a1 and a2 are referred to as first dark lines L1a and L2a, second dark lines L1b and L2b, and third dark lines L1c and L2c, respectively.

In fig. 7, the distance between the boundary BP of the first region a1 and the first dark line L1a (hereinafter referred to as "first distance") is denoted by reference numeral D11, the distance between the first dark line L1a and the second dark line L1b (hereinafter referred to as "second distance") is denoted by reference numeral D12, and the distance between the second dark line L1b and the third dark line L1c (hereinafter referred to as "third distance") is denoted by reference numeral D13. Similarly, a first distance between the boundary BP of the second region a2 and the first dark line L2a is denoted by a reference D21, a second distance between the first dark line L2a and the second dark line L2b is denoted by a reference D22, and a third distance between the second dark line L2b and the third dark line L2c is denoted by a reference D23.

As shown in fig. 8, the first area a1 and the second area a2 of the second interference fringe image include the first dark lines L1a, L2a to third dark lines L1c, L2c, and the boundary portion BP, as in the first interference fringe image. In the second interference fringe image, the first distances D11, D21 to D13, and D23 between the dark lines L1a to L1c and L2a to L2c are different from the first distances D11, D21 to D11, and D23 of the first interference fringe image.

In this case, the distances D11 to D13 and D21 to D23 in the second interference fringe image are changed by performing the post-removal ion exchange step S7. In the ion exchange condition setting step S63, the ion exchange processing time in the post-removal ion exchange step S7 is set so that the distances D11 to D13 and D21 to D23 in the second interference fringe image are equal to the distances D11 to D13 and D21 to D23 in the first interference fringe image. When the number of dark lines included in the second interference fringe image is 3, the ion exchange processing time in the post-removal ion exchange step S7 is preferably 0.1 to 50%, more preferably 10 to 50%, and even more preferably 20 to 45% of the ion exchange processing time in the second ion exchange step S3.

In the example of fig. 8, if the ion exchange processing time in the post-removal ion exchange step S7 exceeds 50% of the ion exchange processing time in the second ion exchange step S3, the number of dark lines included in the interference fringe image of the tempered glass 1 after the post-removal ion exchange step S7 is preferably larger than the number of dark lines (3 lines) in the first interference fringe image.

In the example shown in fig. 9, each of the regions a1 and a2 of the second fringe image includes 2 dark lines L1a, L1b, L2a, and L2 b. In the ion exchange condition setting step S63, the ion exchange conditions (ion exchange processing time) are set so that the 2 dark lines L1a, L1b, L2a, and L2b become 3 dark lines by the post-removal ion exchange step S7, and the 3 dark lines match the positions of the 3 dark lines L1a to L1c and L2a to L2c in the first interference fringe image. In other words, in this example, by performing the post-removal ion exchange step S7, the dark lines in the interference fringe image of the tempered glass 1 are changed from 2 to 3, and the ion exchange conditions (ion exchange processing time) are set so that the first distance, the second distance, and the third distance of the 3 dark lines are equal to the first distances D11, D21, the second distances D12, D22, and the third distances D13, D23 in the corresponding first interference fringe image, respectively.

As in the example of fig. 9, when the number of dark lines L1a, L1b, L2a, and L2b included in the second interference fringe image is 2, the ion exchange processing time in the post-removal ion exchange step S7 is preferably 50 to 100% of the ion exchange processing time in the second ion exchange step S3.

In the example shown in fig. 10, each of the regions a1, a2 of the second interference fringe image includes 1 dark line L1a, L2 a. In the ion exchange condition setting step S63, the ion exchange conditions (ion exchange processing time) are set so that the 1 dark line L1a and L2a become 3 dark lines by the post-removal ion exchange step S7, and the positions of the 3 dark lines coincide with the positions of the 3 dark lines L1a to L1c and L2a to L2c in the first interference fringe image.

As in the example of fig. 10, when the number of dark lines included in the second interference fringe image is 1, the ion exchange processing time in the post-removal ion exchange step S7 is preferably 100 to 150% of the ion exchange processing time in the second ion exchange step S3.

As described above, in the ion exchange condition setting step S63, the optimum ion exchange processing time can be set based on the interference fringe image of the second reinforcing glass after the removal step S5. The ion exchange treatment time is obtained by performing a manufacturing test on a plurality of samples of the glass for tempering prepared in advance.

The manufacturing test was carried out as follows. First, a first ion exchange step and a second ion exchange step were performed on each sample to produce a strengthened glass. Next, information on the stress of each tempered glass and the like are acquired.

Then, a different removal amount is set for each tempered glass, and a removal step is performed. Next, information on the stress of the second reinforcing glass after the removal step is acquired. Then, different ion exchange conditions (ion exchange treatment time) were set for each second strengthening glass, and the post-removal ion exchange step was performed. Next, information on the stress of the strengthened glass after the post-removal ion exchange step is acquired.

Then, the positions and distances of the dark lines of the respective optical interference fringes are compared and verified in the first interference fringe image, the second interference fringe image, and the interference fringe image after the post-removal ion exchange step. If the state of the optical interference fringes of the first interference fringe image matches the state of the optical interference fringes of the interference fringe image after the post-removal ion exchange step, it can be said that the ion exchange processing time in the post-removal ion exchange step is optimal with respect to the removal amount Δ t. The relation between the removal amount Δ t thus obtained and the optimum ion exchange conditions can be constructed as a database. The database is stored in an arithmetic processing device (for example, a computer such as a PC) capable of executing the ion exchange condition setting step S63. By operating this arithmetic processing device, in the ion exchange condition setting step S63, the ion exchange conditions in the post-removal ion exchange step can be set based on the second interference fringe image.

Examples

The tempered glass of the present invention will be described below based on examples. The following examples are merely illustrative, and the present invention is not limited to the following examples.

Samples were prepared as follows. First, a glass plate for strengthening to be subjected to ion exchange treatment is prepared. The glass plate for reinforcement contains SiO in mass%₂ 51.6％、Al₂O₃ 27.9％、B₂O₃ 0.3％、K₂O 0.6％、Na₂O 7.5％、Li₂O 3.3％、MgO 0.3％、P₂O₅ 8.4％、SnO₂0.1% as glass composition.

The glass raw materials were prepared so as to have the above composition, and melted at 1600 ℃ for 21 hours using a platinum kettle. Then, the obtained molten glass is formed by an overflow down-draw method by flowing down the molten glass from the refractory molding. The glass ribbon thus formed was cut into a predetermined size to obtain a glass plate for reinforcing as a test piece. The thickness of the glass plate for strengthening is 0.55, 0.7, or 0.8 mm. Next, the glass for reinforcement is immersed in a molten salt bath, and ion exchange treatment is performed in a first ion exchange step and a second ion exchange step, thereby obtaining a reinforced glass plate.

In the first ion exchange step, KNO in the molten salt is subjected to ion exchange₃With NaNO₃The weight concentration ratio of (a): 60 (%) or 70 (%): 30 (%). The ion exchange treatment temperature of the molten salt in the first ion exchange step was 380 ℃. The ion exchange treatment time in the first ion exchange step is 90 minutes or 180 minutes.

In the second ion exchange step, KNO is used₃、NaNO₃、LiNO₃The ion exchange treatment was performed on each test piece with molten salts having different weight concentration ratios. In this case, the ion exchange treatment time in the second ion exchange step was varied for each test piece. The ion exchange treatment temperature of the molten salt in the second ion exchange step was 380 ℃.

Then, each test piece was subjected to a removal step. In the removal step, both main surfaces of each test piece were removed by polishing. At this time, the removal amount (polishing amount) of each main surface was varied for each test piece.

Then, a preliminary ion exchange step was performed after removing a part of the test piece. In the preliminary ion exchange step after removal, KNO in the molten salt is caused to be present₃With NaNO₃The weight concentration ratio of (A) to (B) is 40 (%): 60 (%). In this case, the ion exchange treatment time in the post-removal preliminary ion exchange step was made different for each test piece. The ion exchange treatment temperature of the molten salt in the preliminary ion exchange step after removal was 380 ℃.

Then, the post-removal ion exchange step was performed on each test piece. In the post-removal ion exchange step, the ion exchange treatment time was varied for each test piece. The ion exchange treatment temperature of the molten salt in the ion exchange step after removal was 380 ℃.

Then, the stress curve of each test piece was measured. The stress curve was measured using FSM-6000LE and SLP-1000, surface stress meters manufactured by TOYO CORPORATION. In the measurement, the refractive index of each test piece was set to 1.50, and the optical elastic constant was set to 28.9[ (nm/cm)/MPa ].

The conditions of the above steps and the results of measurement of the reinforcing properties are shown in tables 1 to 23. Of sample nos. 1 to 174 shown in tables 1 to 23, nos. 1 to 8, 11, 12, 15, 16, 19, 20, 23 to 47, 84 to 110, 112 to 115, 117 to 164, 166 to 174 are examples in which the post-removal ion exchange step was performed without performing the post-removal preliminary ion exchange step after the second ion exchange step, and nos. 52 to 83 are examples in which the post-removal ion exchange step was performed after the post-removal preliminary ion exchange step. Nos. 9, 10, 13, 14, 17, 18, 21, 22, 48 to 51, 111, 116, 165 and 170 are comparative examples. The test pieces of sample nos. 48 to 51 as comparative examples were not subjected to polishing (removal step) after the second ion exchange step. In tables 1 to 23, "polishing amount" is a value obtained by summing up the polishing amounts of the respective main surfaces (both surfaces) of the respective test pieces. The amount of abrasion of one major surface is equal to the amount of abrasion of the other major surface. The polishing amounts shown in tables 1 to 11 are theoretical estimated values calculated based on the polishing rate and the polishing time of the sample, and the strict actual polishing amounts may include variations. In tables 1 to 7 and 12 to 20, "Δ t" represents the removal amount of tempered glass in the removal step (DOL1-DOL 2). In addition, the value of "Δ t/DOL 1" is expressed as a percentage.

In samples Nos. 1 to 174, the thickness of the glass for reinforcing of Nos. 1 to 120 was 0.7 mm. The thickness of the glass for tempering Nos. 121 to 144 was 0.55 mm. The thickness of the glass for strengthening Nos. 145 to 174 was 0.8 mm.

"DOC" in the table is a value of DOLzero in the above embodiment. "CT" in the table is the maximum tensile stress value (CTmax) at the center position in the sheet thickness direction of the test piece. "CS 50" in the table is the value of the compressive stress at a depth of 50 μm from the surface of the test piece.

The "DOC reproducibility" in the table is the ratio of DOC of the example or comparative example in which the removal step and the post-removal ion exchange step were performed to DOC of the comparative example in which the removal step was not performed. Specifically, DOC reproductions of Nos. 1 to 10, 23 to 26, 39 to 47, 52 to 55, and 68 to 71 are values obtained by dividing the measured DOC by the DOC (150.5 μm) of No.48, which is a comparative example prepared under the same conditions, in percentage. Similarly, DOC reproductions of Nos. 11 to 14, 27 to 30, 56 to 59, and 72 to 75 were obtained by dividing the measured values by the DOC (146.2 μm) of No.49 of the corresponding comparative example. DOC reproductions of Nos. 15 to 18, 31 to 34, 60 to 63, and 76 to 79 were values obtained by dividing measured values by DOC (143.0 μm) of No.50 of the corresponding comparative example. DOC reproductions of Nos. 19 to 22, 35 to 38, 64 to 67, and 80 to 83 were values obtained by dividing measured values by DOC (140.4 μm) of No.51 of the corresponding comparative example. Similarly, DOC reproductions of Nos. 84 to 110, 112 to 115, 117 to 164, 166 to 169, and 171 to 174 are values obtained by dividing measured values thereof by DOCs of corresponding comparative examples (not shown).

The "CT reproducibility" in the table is the ratio of the CT of the example or comparative example in which the removal step and the post-removal ion exchange step were performed to the CT of the comparative example in which the removal step was not performed. Specifically, the CT reproductions of Nos. 1 to 10, 23 to 26, 39 to 47, 52 to 55, and 68 to 71 are values obtained by dividing the measured DOC by the CT (-60.0MPa) of No.48, which is a comparative example prepared under the same conditions, in percentage. The CT reproduction ratios of Nos. 11 to 14, 27 to 30, 56 to 59, and 72 to 75 were obtained by dividing the measured values by the CT (-63.4MPa) of No.49 of the corresponding comparative example. The CT reproduction ratios of Nos. 15 to 18, 31 to 34, 60 to 63, and 76 to 79 were obtained by dividing the measured values by the CT (-63.6MPa) of No.50 of the corresponding comparative example. The CT reproduction ratios of Nos. 19 to 22, 35 to 38, 64 to 67, and 80 to 83 are values obtained by dividing the measured values by the CT (-66.7MPa) of No.51 of the corresponding comparative example. Similarly, the CT reproduction ratios of Nos. 84 to 110, 112 to 115, 117 to 164, 166 to 169, and 171 to 174 are values obtained by dividing the measured values by the CT values of the corresponding comparative examples (not shown).

[ TABLE 1 ]

[ TABLE 2 ]

[ TABLE 3 ]

[ TABLE 4 ]

[ TABLE 5 ]

[ TABLE 6 ]

[ TABLE 7 ]

[ TABLE 8 ]

[ TABLE 9 ]

[ TABLE 10 ]

[ TABLE 11 ]

[ TABLE 12 ]

[ TABLE 13 ]

[ TABLE 14 ]

[ TABLE 15 ]

[ TABLE 16 ]

[ TABLE 17 ]

[ TABLE 18 ]

[ TABLE 19 ]

[ TABLE 20 ]

[ TABLE 21 ]

[ TABLE 22 ]

[ TABLE 23 ]

As a result of the measurement, in any of the examples, the same degree of strengthening characteristics as those of the comparative example, which is a product not subjected to polishing, can be obtained by performing the post-removal ion exchange step. In particular, in the example in which the preliminary ion exchange step after removal was performed, even when the polishing amount was increased to 10 μm or more, each strengthening characteristic could be measured, and the DOC reproducibility and the CT reproducibility also showed relatively high values.

As an example, stress curves of the samples No.1, No.4 and No.48 are shown in FIG. 11. The stress curves of the tempered glasses of samples No.1 and No.4 as examples clearly have a first peak, a first valley, a second peak, and a second valley, as in sample No.48 of the comparative example in which the removing step was not performed. As shown in fig. 11, it is understood that the examples are sufficiently strengthened as much as or more than the comparative examples by performing the post-removal ion exchange step.

The stress curves of the samples No.6, No.48, No.57 and No.73 are shown in FIG. 12. As shown in fig. 12, in the stress curve of sample No.57 which is an example in which the post-removal preliminary ion exchange step and the post-removal ion exchange step were performed, the stress curve clearly had the first valley and the second peak larger than those of sample No.6 which is an example in which the post-removal ion exchange step was performed without performing the post-removal preliminary ion exchange step, and the compressive stress in the deep portion was appropriately recovered. Therefore, by performing the post-removal preliminary ion exchange step, the strength of the glass reduced by polishing (removal step) can be suitably increased.

Claims

1. A method for producing a tempered glass having a surface layer provided with a compressive stress layer by subjecting a glass having a surface to an ion exchange treatment, the method comprising:

a first ion exchange step of bringing the surface of the glass into contact with a first molten salt to perform ion exchange between Li ions in the glass and Na ions in the first molten salt;

a second ion exchange step of bringing the surface of the glass into contact with a second molten salt to exchange Na ions in the glass with K ions in the second molten salt;

a removing step of removing at least a part of the surface of the strengthened glass after the first ion exchange step and the second ion exchange step are performed, thereby forming a new surface on the strengthened glass; and

and a post-removal ion exchange step of ion-exchanging Na ions in the tempered glass and K ions in the molten salt after the removal step, thereby setting a maximum compressive stress CS3 of the compressive stress layer in the new surface to 700MPa or more.

2. The method for producing a strengthened glass according to claim 1, further comprising a post-removal preliminary ion exchange step performed after the removal step and before the post-removal ion exchange step,

in the post-removal preliminary ion exchange step, the strengthened glass after the removal step is brought into contact with a third molten salt, and Li ions in the strengthened glass after the removal step and Na ions in the molten salt are ion-exchanged.

3. The method for producing a strengthened glass according to claim 2, wherein NaNO is contained in the third molten salt used in the post-removal preliminary ion exchange step₃In a concentration corresponding to the NaNO concentration in the first molten salt₃The occupied concentrations are substantially equal.

4. The method for producing a strengthened glass according to claim 2 or 3, wherein KNO is contained in the molten salt used in the post-removal ion exchange step₃The concentration of KNO in the second molten salt₃The occupied concentrations are substantially equal.

5. The method for producing a strengthened glass according to any one of claims 2 to 4, wherein the ion exchange treatment time in the post-removal preliminary ion exchange step is 10% to 100% of the ion exchange treatment time in the first ion exchange step.

6. The method for producing a strengthened glass according to any one of claims 2 to 5, wherein the ion exchange treatment time in the post-removal ion exchange step is 50% to 200% of the ion exchange treatment time in the second ion exchange step.

7. The method for producing a strengthened glass according to any one of claims 1 to 6, wherein the glass is a plate-like or sheet-like glass having a thickness of 0.05mm to 2.0mm,

removing the front and back main surfaces of the tempered glass before the post-removal ion exchange step in a range shallower than the compressive stress layer, whereby the maximum compressive stress CS2 of the compressive stress layer in the new surface after the removal step is 100MPa or more.

8. The method for producing a strengthened glass according to any one of claims 1 to 7, wherein in the removing step, the surface of the strengthened glass after the first ion exchange step and the second ion exchange step is removed by polishing or etching,

the amount Δ t of removal of the surface in the removal step is smaller than the diffusion depth DOL1 of the K ions introduced in the second ion exchange step.

9. The method for producing a strengthened glass according to any one of claims 1 to 8, wherein a removal amount Δ t in the removal step is 20 μm or less,

setting a compressive stress CS2 of the compressive stress layer in the new surface after the removing step and before the post-removing ion exchange step to be less than 700MPa,

the maximum compressive stress CS3 of the compressive stress layer after the post-removal ion exchange step is set to 700MPa to 1200 MPa.

10. The method for producing a strengthened glass according to any one of claims 1 to 9, wherein a stress distribution obtained by measuring a stress in a depth direction from the new surface in the strengthened glass after the post-removal ion exchange step includes:

a first peak at which a compressive stress becomes a maximum on the surface;

a first valley which decreases in the depth direction from the first peak to minimize stress;

a second peak that increases in depth from the first valley and that has a maximum compressive stress; and

a second valley which decreases in the depth direction from the second peak to minimize the tensile stress,

in the post-removal ion exchange step, Na ions in the strengthened glass and K ions in the molten salt are ion-exchanged so that the compressive stress CSb of the first valley becomes 10MPa or more.

11. The method for producing a strengthened glass according to any one of claims 1 to 10, wherein LiNO in the molten salt used in the post-removal ion exchange step is₃The concentration of the surfactant is 0.1 to 2 mass%.

12. The method for producing a strengthened glass according to any one of claims 1 to 11, wherein the concentration of Na ions in the molten salt used in the post-removal ion exchange step is calculated as NaNO₃In the case of (3), 5% by mass or less.

13. The method for producing a strengthened glass according to any one of claims 1 to 12, wherein the ion exchange treatment temperature in the post-removal ion exchange step is 350 ℃ to 450 ℃,

the ion exchange treatment time in the post-removal ion exchange step is equal to or shorter than the ion exchange treatment time in the second ion exchange step.

14. The method for producing a strengthened glass according to any one of claims 1 to 13, wherein in the second ion exchange step, Na ions in the glass are ion-exchanged with K ions in the second molten salt, and Na ions in the glass are ion-exchanged with Li ions in the second molten salt,

NaNO₃the concentration of the first molten salt in the first molten salt is 50 mass% or more,

KNO₃the concentration in the first molten salt is less than 50 mass%,

LiNO₃the concentration of the second molten salt in the second molten salt is 0.5 to 5% by mass,

KNO₃the concentration of the second molten salt in the second molten salt is 95 to 99.5 mass%,

the ion exchange treatment temperature of the first ion exchange process is 350-480 ℃,

the ion exchange treatment temperature of the second ion exchange process is 350-480 ℃,

the ion exchange treatment time in the first ion exchange step is 1 to 20 hours,

the ion exchange treatment time of the second ion exchange step is shorter than the ion exchange treatment time of the first ion exchange step.

15. The method for producing a strengthened glass according to any one of claims 1 to 14, wherein the glass contains 40 to 70% by mass of SiO₂10 to 30 percent of Al₂O₃0 to 3 percent of B₂O₃5 to 25 percent of Na₂O, 0 to 5.5 percent of K₂O, 0.1-10% of Li₂O, 0-6% of MgO and 0-15% of P₂O₅As a glass composition.

16. The method for producing a strengthened glass according to any one of claims 1 to 15, wherein an inspection step of inspecting the surface of the strengthened glass for the presence or absence of defects is provided after the first ion exchange step and the second ion exchange step are performed and before the removal step,

when a defect is detected on the surface of the tempered glass, at least a part of the surface is removed together with the defect in the removing step.

17. A method for producing a strengthened glass having a surface whose compressive stress is adjusted, the method comprising:

a removing step of removing at least a part of the surface of a tempered glass having a compressive stress layer formed on the surface thereof in advance to a depth shallower than the depth of the compressive stress layer, thereby forming a new surface on the tempered glass; and

a post-removal ion exchange step of performing ion exchange treatment on the tempered glass having a maximum compressive stress CS2 of the compressive stress layer in the new surface of less than 700MPa,

in the post-removal ion exchange step, Na ions in the tempered glass are ion-exchanged with K ions in the molten salt, whereby the maximum compressive stress CS3 of the compressive stress layer in the new surface is 700MPa or more.

18. The method for producing a strengthened glass according to claim 1, comprising:

measuring information relating to the stress of the tempered glass after the removing step and before the ion exchange step after the removing step by using a measuring device; and

and an ion exchange condition setting step of setting an ion exchange condition in the post-removal ion exchange step based on the information measured by the measuring device.

19. The method for producing a strengthened glass according to claim 18, wherein the measuring device generates an optical interference fringe on the strengthened glass after the removing step and before the ion exchange step after the removing step, and measures the stress distribution by capturing an interference fringe image including the optical interference fringe,

the information related to the stress includes the interference fringe image,

the ion exchange conditions include an ion exchange treatment time in the post-removal ion exchange step,

in the ion exchange condition setting step, the ion exchange processing time is set based on the interference fringe image.

20. The method for producing a strengthened glass according to claim 18, comprising:

a step of measuring, by the measuring device, a diffusion depth DOL1 of the K ions introduced in the second ion exchange step before the removal step; and

a removal amount determining step of determining a removal amount Δ t of the surface of the tempered glass removed in the removing step,

in the ion exchange condition setting step, the ion exchange condition is set based on a function prepared in advance, the diffusion depth DOL1 of the K ions measured by the measuring device, and the removal amount Δ t determined in the removal amount determining step.

21. The method for producing a strengthened glass according to claim 20, wherein the ion exchange conditions include an ion exchange treatment time Tx in the post-removal ion exchange step,

the function includes the following equation (1),

Tx＝a(1-e^-b×x)…(1)

here, a and b are constants, and x is Δ t/DOL1 which is a ratio of the removal amount Δ t to the diffusion depth DOL1 of the K ions introduced in the second ion exchange step.

22. The method for producing a strengthened glass according to claim 20 or 21, wherein the method comprises:

an inspection step of acquiring defect information of the tempered glass after the first ion exchange step and the second ion exchange step are performed and before the removal step;

and a predetermined removal amount setting step of setting a predetermined removal amount to be removed from the surface of the strengthened glass after the first ion exchange step and the second ion exchange step are performed, based on the defect information acquired in the inspection step.

23. The method for producing a strengthened glass according to any one of claims 20 to 22, wherein the information on the stress includes a diffusion depth DOL2 of K ions remaining in the strengthened glass after the removing step and before the post-removing ion exchange step,

in the removal amount determination step, the removal amount Δ t is determined by DOL1-DOL2 which is the difference between the diffusion depth DOL1 of the K ions introduced in the second ion exchange step and the diffusion depth DOL2 of the K ions remaining in the strengthened glass.

24. A method for producing a tempered glass, wherein a glass having a surface is subjected to an ion exchange treatment to obtain a tempered glass having a compressive stress layer in the surface layer, the method comprising:

a removing step of removing at least a part of the surface of the strengthened glass after the first ion exchange step and the second ion exchange step are performed, thereby forming a new surface on the strengthened glass;

a measuring step of measuring information on the stress of the tempered glass after the removing step by using a measuring device; and

a post-removal ion exchange step of increasing the maximum compressive stress of the compressive stress layer on the new surface by ion-exchanging Na ions in the strengthened glass and K ions in the molten salt after the measurement step,

the method for producing a strengthened glass further includes an ion exchange condition setting step of setting an ion exchange condition in the post-removal ion exchange step based on the information on the stress obtained from the measuring device in the measuring step.