TW201504170A - Method for manufacturing reinforced glass and reinforced glass - Google Patents

Abstract

A method for manufacturing a bent reinforced glass 1 of the invention includes: a bonding step in which a plurality of glass plat 4, glass plat 5 are laminated and bonded to each other to form a glass plat laminate 6; and a reinforce step in which the glass plat laminate 6 are chemically strengthened by an ion exchange method. The chemically strengthened properties of the glass plat 4 and the glass plat 5 are different from each other. Therefore, a dimensional change difference resulting from ion exchange is generated between the glass plat 4 and the glass plat 5 so that the glass plat laminate 6 are bent.

Description

Method for manufacturing tempered glass and tempered glass

The present invention relates to a method for producing tempered glass, for example, as a cover glass for a portable electronic device, and a tempered glass.

In recent years, a portable display device such as a mobile phone has been widely used as a screen display unit having a touch sensor function. Such an image display portion is usually protected in a state covered with a cover glass containing tempered glass.

Further, in recent years, portable electronic devices are advancing design diversification, and the image display portion is not limited to a plane. Accordingly, the cover glass including the tempered glass is not limited to a flat surface, and it is required to realize a curved shape such as a part of a cylinder or a spherical surface.

Further, the present invention is not limited to a portable electronic device, and even if it has a relatively large screen display unit such as a digital signage, a curved image display unit is also used. Therefore, the actual situation requires curved tempered glass of various sizes.

Here, as a method of manufacturing a curved tempered glass, chemical strengthening is usually performed after bending a glass plate into a predetermined shape.

Specifically, there is the following method: before strengthening the glass plate, the glass is The glass plate is heated to the vicinity of the softening point of the glass, and is press-formed by a mold including an upper mold and a lower mold (see, for example, Patent Document 1 and Patent Document 2).

Further, Patent Document 3 discloses a method of performing local heating in a state where a glass plate is placed on a mold (lower mold) before strengthening the glass sheet, thereby making it possible without performing press molding. The glass sheet is deformed along the mold by its own weight.

[Prior Art Literature] [Patent Literature]

Patent Document 1: Japanese Patent Publication No. Sho 64-10042

Patent Document 2: Japanese Patent Laid-Open No. 64-24034

Patent Document 3: Japanese Patent Laid-Open Publication No. 2012-101975

However, as disclosed in Patent Document 1 to Patent Document 3, when a glass plate is bent using a mold, it is easy to form a contact mark of the mold on the glass plate. If such a contact mark exists, there is a concern that the glass plate may be damaged due to the contact mark at the time of chemical strengthening.

Therefore, there is also a case where the contact marks of the mold are removed by grinding or a special release agent which is difficult to adhere to the contact marks of the mold, but in any case, the manufacturing cost has to be increased.

Further, when the glass sheet is bent by using a mold, if the required curved shape is different, a dedicated mold corresponding to each shape is required, and the manufacturing cost is inevitably increased. In particular, in a portable electronic device such as a mobile phone, since the shape is varied due to the diversity of designs, the increase in manufacturing cost becomes more remarkable.

The present invention has been made in view of the above circumstances, and a technical object thereof is to manufacture a curved tempered glass at low cost.

A method for producing a tempered glass according to the present invention for solving the above problems is a method for producing a tempered glass which is characterized by comprising a joining step of laminating a plurality of glass sheets and bonding them to each other to form a glass sheet laminate; and strengthening a step of chemically strengthening the glass plate laminate by an ion exchange method; and using a glass plate having different chemical strengthening characteristics in the bonding step as the outermost glass plate of the glass plate laminate and the glass The glass plate of the rearmost side of the laminate is bent, and the glass laminate is bent in the above-described strengthening step.

Here, the present invention also includes a case where one of the outermost surface and the rearmost glass sheet is not chemically strengthened (the same applies hereinafter). In addition, the chemical strengthening property is the easiness of ion exchange (chemical strengthening) at the time of chemical strengthening by the ion exchange method, and means that the glass plate having a good chemical strengthening property is more easily ion-exchanged (the same applies hereinafter).

In the above configuration, the compressive stress layer is formed on the surface layer portion of the glass sheet laminate by chemical strengthening (ion exchange treatment) by the ion exchange method. The ion exchange treatment is a method of introducing an alkali ion having a large ionic radius into the surface of the glass at a temperature lower than the strain point of the glass plate for reinforcement. In the case of ion exchange treatment, when the thickness of the glass is small, the compressive stress layer can be appropriately formed.

The ion exchange solution (fortified liquid), the ion exchange temperature (temperature of the strengthening liquid), and the ion exchange time (immersion time in the reinforcing liquid) in the ion exchange treatment may be determined in consideration of the viscosity characteristics of the glass for reinforcement. In particular, when the Na component in the glass plate for reinforcement and the K ion in the potassium nitrate solution are subjected to ion exchange treatment, the compressive stress layer can be formed on the surface with high efficiency.

According to the above configuration, the chemical strengthening characteristics of the glass sheet constituting the outermost surface of the glass sheet laminate and the glass sheet of the rearmost surface are different from each other. Therefore, in the strengthening step, a compressive stress layer is formed on the surface layer portion of at least the chemically strengthened glass sheet in the outermost surface and the rearmost glass sheet. Further, the compressive stress value of the surface layer portion of the glass plate which is easily chemically strengthened is larger than the compressive stress value of the surface layer portion of the other glass plate. Thereby, the surface layer portion of the glass plate which is easily chemically strengthened expands (expands) more than the surface layer portion of the other glass plate, and a dimensional change difference caused by ion exchange occurs between the two. As a result, the entire glass sheet laminate is curved so that the glass plate side which is easily chemically strengthened in the outermost surface and the rearmost glass sheet becomes a convex portion.

Therefore, in the manufacturing method of the above configuration, the glass plate is not required to be processed into a curved shape by using a mold, and the glass plate laminate can be processed into a predetermined curved shape by strengthening.

In other words, the method for producing a tempered glass sheet having the above-described configuration is a method in which, in the bonding step, a glass plate having different magnitudes of compressive stress values of the surface layer portion of the glass when chemically strengthened by the ion exchange method is used as the glass. The glass plate on the outermost surface of the laminate body and the glass plate on the rearmost side of the laminate of the above glass plate. Here, the present invention also includes a case where one of the outermost surface and the rearmost glass sheet does not form a compressive stress layer in the surface layer portion, and the compressive stress value of the surface layer portion is substantially zero (the same applies hereinafter).

In the method for producing a tempered glass sheet according to any one of the above aspects, it is preferable that the outermost glass sheet and the outermost glass sheet have different Al ₂ O ₃ contents. Here, in the present invention, the case where the content ratio of Al ₂ O ₃ of one of the outermost surface and the rearmost glass plate is substantially 0, that is, less than 0.3% by mass, or the case where no alkali component is contained ( The same as below).

If so, the chemical strengthening characteristics of the outermost surface and the rearmost glass sheet can be easily and surely different. Further, since the difference in expansion at the time of chemical strengthening due to the difference in chemical strengthening characteristics can be managed intensively, it is easy to control the curved shape of the produced tempered glass.

In the method for producing a tempered glass sheet according to any one of the above aspects, in the joining step, the plurality of glass sheets may be heated in a state of being laminated.

According to this configuration, the glass sheets in the glass sheet laminate body are reliably adhered to each other by heating, so that the glass sheet peeling can be effectively suppressed, and stable chemical strengthening can be achieved in the strengthening step.

In this case, the surface roughness Ra of the glass plate is preferably 2.0 nm or less. Further, the average surface roughness (Ra) may be measured by a method according to SEMI D7-97 "Measurement method of surface roughness of a flat panel display (FPD) glass plate" (the same applies hereinafter).

According to this configuration, the glass sheets are detachable from each other due to the surface roughness of the glass sheet before heating, but are still in close contact without an adhesive or the like. Further, when the glass sheets in the close contact state are heated to each other, the glass sheets can be completely joined to each other at a temperature lower than the softening point (for example, 300 ° C to 700 ° C) to form a glass sheet laminate. Therefore, large shape deformation of the glass sheet accompanying heating can be avoided. Further, it is considered that the adhesion before heating is caused by hydrogen bonding between the hydrazine-hydroxyl groups formed by adsorbing moisture in the air, and it is considered that the bonding occurring below the softening point is due to the following reason: On the surface of the glass, a dehydration reaction occurs between the hydrazine-hydrogen groups forming a hydrogen bond to become a stronger covalent bond.

Further, in the method for producing a tempered glass sheet of the present invention, it is preferred that a part or all of the surface of the tempered glass sheet is not polished, in particular, the surface is not It is more preferable that all of the polishing is performed, and it is preferable that the average surface roughness (Ra) of the unpolished surface is preferably 2.0 nm or less. The theoretical strength of glass is originally very high, but in most cases even stresses that are much lower than the theoretical strength can cause damage. The reason for this is that a small defect called a Griffith flaw is generated on the surface of the glass in a step after forming, for example, a polishing step or the like. Therefore, if the surface of the tempered glass sheet is not polished, the mechanical strength of the tempered glass sheet is maintained after the ion exchange treatment, and the tempered glass sheet is hardly broken. Further, when the scribe line is cut after the ion exchange treatment, if the surface is not polished, it is difficult to cause improper cracks, breakage, or the like at the time of scribe line cutting. Further, if the surface of the tempered glass sheet is not polished, the polishing step can be omitted, so that the production cost of the tempered glass sheet can be reduced. Further, in order to obtain an unpolished surface, the glass plate for reinforcement may be formed by an overflow downdraw method.

In the method for producing a tempered glass sheet according to any one of the above aspects, the chamfering step may be further performed by chamfering the end surface of the glass sheet alone or the glass sheet laminate before the strengthening step.

According to this configuration, when the glass sheet laminate is chemically strengthened, the glass sheet laminate can be prevented from being broken from the end surface.

Further, the tempered glass of the present invention for solving the above problems is a curved tempered glass in which a plurality of glass sheets are laminated in a state of being joined to each other, and at least the outermost surface of the glass sheet is chemically strengthened. The compressive stress layer is formed, and the compressive stress value of the surface layer portion of the outermost glass plate is different from the compressive stress value of the surface layer portion of the outermost glass plate.

Here, the present invention also includes one of the outermost surface and the rearmost glass sheet which is not chemically strengthened, but is in a state in which a compressive stress layer is not formed in the surface layer portion (Table The case where the compressive stress value of the layer portion is substantially 0) (the same applies hereinafter).

According to the above configuration, the compressive stress value of the surface layer portion of the outermost glass sheet is different from the compressive stress value of the surface layer portion of the outermost glass sheet. In other words, the outermost glass plate and the rearmost glass plate are in a state of being different in ion exchange, thereby maintaining the state in which the strengthened glass is bent. That is, since the bending of the tempered glass is formed by chemical strengthening, the step of processing the glass sheet into a curved shape using a mold can be omitted as in the production method described above.

In the tempered glass having the above configuration, a compressive stress layer can be formed on the surface layer portion of both the outermost glass plate and the rearmost glass plate by chemical strengthening.

Further, the tempered glass of the present invention for solving the above problems is a curved tempered glass in which a plurality of glass sheets are laminated in a state of being joined to each other, and at least the outermost surface of the glass sheet is chemically strengthened. form a compression stress layer, and the outermost surface of the glass plate of Al ₂ O ₃ content higher than most of the back surface of the glass plate in the content of Al ₂ O _3.

In the tempered glass of any of the above configurations, the difference in refractive index nd between mutually adjacent glass sheets among the plurality of laminated glass sheets may be within ±0.02.

According to this configuration, light reflection at the joint interface of the mutually adjacent glass sheets can be prevented.

As described above, according to the present invention, it is not necessary to use a mold to process the glass sheet into a curved shape, and the curved tempered glass can be produced by chemically strengthening the glass sheet laminate. Therefore, the curved tempered glass can be manufactured at low cost.

1‧‧‧ tempered glass

1a‧‧‧Long side of tempered glass

1b‧‧‧ Short side of tempered glass

1c‧‧‧End face of tempered glass

2, 3‧‧‧ glass plate

4, 5‧‧‧ glass plate

2a, 3a, 4a, 5a‧‧‧ compressive stress layer

2b, 3b‧‧‧ tensile stress layer

4x, 5x‧‧‧ joints

6‧‧‧ glass laminate

A, B‧‧ arrows

The maximum value of the gap between the L‧‧‧ stone plate and the end face of the long side

The maximum value of the gap between the S‧‧‧ stone plate and the end face of the short side

S1a, S1b‧‧‧ cutting steps

S2a, S2b‧‧‧Chamfering steps

S3a, S3b‧‧‧ cleaning steps

S4‧‧‧Lamination step (joining step)

S5‧‧‧Preheating step (joining step)

S6‧‧‧Chemical strengthening steps

S11a, S11b‧‧‧ cleaning steps

S12‧‧‧Lamination step (joining step)

S13‧‧‧heating step (joining step)

S14‧‧‧cutting steps

S15‧‧‧Chamfering step

S16‧‧‧Preheating step

S17‧‧‧Chemical strengthening steps

Fig. 1 is a perspective view showing a tempered glass according to a first embodiment of the present invention.

Fig. 2 is an enlarged cross-sectional view showing the tempered glass of Fig. 1.

3A is a view for explaining a method of manufacturing the tempered glass according to the first embodiment.

3B is a view for explaining a method of manufacturing the tempered glass according to the first embodiment.

3C is a view for explaining a method of manufacturing the tempered glass according to the first embodiment.

Fig. 4 is a view for explaining the principle of bending the glass sheet laminate in Fig. 3C.

Fig. 5 is a flowchart showing a method of producing tempered glass according to a second embodiment of the present invention.

Fig. 6 is a flowchart showing another embodiment of a method of producing tempered glass according to a third embodiment of the present invention.

Hereinafter, embodiments for carrying out the invention will be described based on the drawings.

<First Embodiment>

Fig. 1 is a perspective view showing a tempered glass according to a first embodiment of the present invention. The central portion of the tempered glass 1 is the most convex portion, and is gently draped from the central portion to the respective sides, and is integrally bent in a dome shape. The tempered glass 1 is used, for example, as a cover glass for a portable electronic machine. Further, in the present embodiment, for the sake of convenience, the side bent into the convex portion is referred to as the front side, and the side bent into the depressed portion is referred to as the back side.

The tempered glass 1 is, for example, 50 mm to 300 mm on one side, and is a rectangle having a long side 1a and a short side 1b in this embodiment. In addition, the tempered glass 1 can also be Other shapes such as squares. Further, the total thickness of the tempered glass 1 is, for example, 0.3 mm to 2 mm.

As shown in FIG. 2, in the tempered glass 1, two glass plates 2 and glass plates 3 are directly laminated in a state of being joined to each other. Moreover, for the sake of convenience, the glass plate 2 on the front side is referred to as a first glass plate, and the glass plate 3 on the back side is referred to as a second glass plate.

The tempered glass 1 is chemically strengthened by an ion exchange method. The chemical strengthening state of the first glass plate 2 and the second glass plate 3 is different from each other, and the first glass plate 2 is easier to exchange ion ions of alkali ions in the glass than the second glass plate 3.

Specifically, as shown in FIG. 2, the tempered glass 1 is formed by compressively forming a compressive stress layer 2a and a compressive stress layer 3a in the surface layer portion of the first glass sheet 2 and the surface layer portion of the second glass sheet 3 by chemical strengthening, respectively. A tensile stress layer 2b and a tensile stress layer 3b are formed between the stress layer 2a and the compressive stress layer 3a. Further, the compressive stress value of the compressive stress layer 2a formed on the first glass sheet 2 is larger than the compressive stress value of the compressive stress layer 3a formed on the second glass sheet 3. Specifically, for example, a compressive stress of 680 MPa to 950 MPa is generated in the compressive stress layer 2a formed on the first glass sheet 2, and a compressive stress of 200 MPa to 680 MPa is generated in the compressive stress layer 3a formed in the second glass sheet 3. In addition, the state in which the entire tempered glass 1 is bent is maintained so that the first glass sheet 3 side becomes a convex portion by the difference in the compressive stress values.

In this embodiment, the end surface 1c of the tempered glass 1 is curved by chamfering (the cross section is a single arc shape).

Further, in the case where the refractive index difference between the first glass plate 2 and the second glass plate 3 included in the tempered glass 1 is large, light reflection at the joint interface is increased. Therefore, if the refractive index difference between the first glass plate 2 and the second glass plate 3 is increased, the tempered glass can be strengthened. The glass 1 is used as a mirror. Further, when the mirror-finished tempered glass 1 is used as the cover glass of the display device, the anti-peep effect can be expected. On the other hand, in order to prevent light reflection at the joint interface, it is desirable to reduce the difference in refractive index of the first glass sheet 2 and the second glass sheet 3 included in the tempered glass 1 (for example, the difference in refractive index nd is within ±0.02).

Next, a method of manufacturing the tempered glass 1 will be described.

First, as shown in FIG. 3A, two flat glass plates 4 and glass plates 5 are prepared.

The flat glass plate 4 becomes the first glass plate 2 of the tempered glass 1 after chemical strengthening, and the content of Al ₂ O ₃ is relatively large. On the other hand, the flat glass plate 5 becomes the second glass plate 3 of the tempered glass 1 after chemical strengthening, and the content of Al ₂ O ₃ is relatively small.

The bonding surface 4x of the flat glass plate 4, the flat glass plate 5, and the surface roughness Ra of the bonding surface 5x are both 2.0 nm or less, more preferably 1.0 nm or less, further preferably 0.5 nm or less. It is preferably 0.2 nm, and in this embodiment, it is 0.2 nm or less. Further, the GI value of the joint surface 4x and the joint surface 5x of the flat glass plate 4 and the flat glass plate 5 is preferably 1000 pcs/m ² or less.

Then, as shown in FIG. 3B, the flat glass plate 4 and the flat glass plate 5 as described above are directly laminated and joined to each other to form a flat glass plate laminate 6. Here, the joint surface 4x and the joint surface 5x of the flat glass plate 4 and the flat glass plate 5 are directly joined without passing through other members such as an adhesive. In the state in which the bonding surface 4x and the bonding surface 5x of the flat glass plate 4 and the flat glass plate 5 are in close contact with each other, the temperature below the softening point (for example, 300 ° C - 700) is exemplified. °C) Heating. In this manner, a firm joint state due to the surface state of the joint surface 4x of the flat glass plate 4 and the flat glass plate 5 and the joint surface 5x can be achieved. In addition, the flat glass can also be used with an adhesive. The bonding surface 4x of the plate 4 and the flat glass plate 5 and the bonding surface 5x are joined.

When the glass plate laminate 6 thus configured is immersed in the strengthening liquid for chemical strengthening, as shown in FIG. 3C, the flat glass plate laminate 6 is bent to obtain a curved tempered glass 1 (flat plate shape). The glass plate 4 and the glass plate 5 are respectively bent to become a glass plate 2 and a glass plate 3). The reason why the flat glass plate laminate 6 is bent as described above is as follows.

In other words, in the chemical strengthening by the ion exchange method, in the surface layer portion of the glass sheet laminate 6, alkali ions having a small ion radius are exchanged for alkali ions having a larger ionic radius. As a result, as shown in FIG. 4, compressive stress is generated on the front side and the back side of the glass sheet laminate 6, and the compressive stress layer 4a and the compressive stress layer 5a are formed. At this time, since the glass plate 4 on the front side has more Al ₂ O ₃ than the glass plate 5 on the back side, ion exchange is facilitated. Therefore, the compressive stress value of the compressive stress layer 4a on the front side is relatively larger than the compressive stress layer 5a on the back side. Thereby, as shown by the one-dot chain line in the figure, the compressive stress layer 4a on the front side expands relatively larger than the compressive stress layer 5a on the back side (see an arrow A in the drawing). As a result, the force indicated by the arrow B in the figure acts on the glass sheet laminate 6, and the entire glass laminate body 6 is curved so that the flat glass plate 4 side (front side) becomes a convex portion. Further, the expansion portion indicated by the one-dot chain line in the drawing is exaggerated.

Therefore, according to such a manufacturing method, it is not necessary to use a mold to process the glass sheet into a curved shape, and the curved tempered glass 1 can be produced by chemically strengthening the glass sheet laminate 6. Therefore, the curved tempered glass 1 can be manufactured at low cost.

Here, the degree of curvature (curvature) of the tempered glass 1 can be adjusted by the chemical strengthening characteristics of the flat glass plate 4 and the flat glass plate 5. Specifically, for example, the difference in the content of Al ₂ O ₃ between the flat glass plate 4 and the flat glass plate 5 is adjusted. Further, the degree of bending of the tempered glass 1 does not depend on the thickness of the original glass plate 4 or the glass plate 5, but depends on the total thickness of the glass plate laminate 6. Therefore, the degree of bending of the tempered glass 1 can also be adjusted by the thickness (total thickness) of the glass laminate body 6.

The flat glass plate 4 and the flat glass plate 5 preferably contain SiO ₂ 50% to 80% by mass, Al ₂ O ₃ 5% to 25%, B ₂ O ₃ 0% to 15%, and Na ₂ O. 1%~20%, K ₂ O 0%~10% as the glass composition. However, the flat glass plate 5 having poor chemical strengthening properties may also be an alkali-free glass (not chemically strengthened).

The reason for limiting the content range of each component as described above is as follows. In addition, in the description of the content range of each component, % means the mass %.

SiO ₂ is a component that forms a network structure of glass. The content of SiO ₂ is preferably 50% to 80%, 52% to 75%, 55% to 72%, 55% to 70%, and particularly preferably 55% to 67.5%. When the content of SiO ₂ is too small, it is difficult to vitrify, and the coefficient of thermal expansion becomes too high, and the thermal shock resistance is liable to lower. On the other hand, when the content of SiO ₂ is too large, the meltability or moldability is liable to lower.

Al ₂ O ₃ is a component that enhances ion exchange performance and is a component that increases the strain point or Young's modulus. The content of Al ₂ O ₃ is preferably 5% to 25%. When the content of Al ₂ O ₃ is too small, the coefficient of thermal expansion becomes too high, and the thermal shock resistance is likely to be lowered, and the ion exchange performance may not be sufficiently exhibited. Therefore, the preferred lower limit of the Al ₂ O ₃ of the flat glass plate 4 is 12% or more, 14% or more, 15% or more, and particularly preferably 16% or more. The lower limit of the preferable range of Al ₂ O ₃ of the flat glass plate 5 is 7% or more, 8% or more, 10% or more, and particularly preferably 12% or more. The difference in Al ₂ O ₃ content between the flat glass plate 4 and the flat glass plate 5 is preferably 0.5% or more, 1% or more, 2% or more, or 3% or more, and particularly preferably 4% or more. On the other hand, when the content of Al ₂ O ₃ is too large, devitrified crystals are easily precipitated in the glass, and it is difficult to form the glass sheet by an overflow down-draw method or the like. Further, the coefficient of thermal expansion becomes too low, and it is difficult to match the coefficient of thermal expansion of the peripheral material, and the viscosity at high temperature becomes high, and the meltability is liable to lower. Therefore, the preferred upper limit of Al ₂ O ₃ is 22% or less and 20% or less, and particularly preferably 19% or less.

B ₂ O ₃ is a component which lowers the viscosity or density at a high temperature and stabilizes the glass to make it difficult to precipitate crystals and lower the liquidus temperature. And to improve the crack resistance of the ingredients. However, if the content of B ₂ O ₃ is too large, surface coloration called weathering may occur due to ion exchange treatment, or water resistance may be lowered, or compressive stress value of a compressive stress layer may be lowered, or stress depth of a compressive stress layer may be changed. Small tendency. Therefore, the content of B ₂ O ₃ is preferably 0% to 15%, 0.1% to 12%, 1% to 10%, more than 1% to 8%, 1.5% to 6%, and particularly preferably 2% to 5%. .

Na ₂ O is a main ion exchange component and is a component which lowers the high temperature viscosity and improves the meltability or formability. Further, Na ₂ O is also a component for improving resistance to devitrification. The content of Na ₂ O is 1% to 20%. When the content of Na ₂ O is too small, the meltability is lowered, the coefficient of thermal expansion is lowered, or the ion exchange performance is liable to lower. Therefore, in the case of introducing Na ₂ O, the preferred lower limit of Na ₂ O is 10% or more and 11% or more, and particularly preferably 12% or more. On the other hand, when the content of Na ₂ O is too large, the thermal expansion coefficient becomes too high, the thermal shock resistance is lowered, or it is difficult to match the thermal expansion coefficient of the peripheral material. Further, there is a case where the strain point is excessively lowered, or the composition of the glass composition is lacking, and the devitrification resistance is lowered. Therefore, the preferred upper limit of Na ₂ O is 17% or less, and particularly preferably 16% or less.

K ₂ O is a component that promotes ion exchange, and is a component having a large effect of increasing the stress depth of the compressive stress layer in the alkali metal oxide. Further, in order to lower the high-temperature viscosity, the composition of the meltability or formability is improved. Further, it is also a component for improving resistance to devitrification. The content of K ₂ O is 0% to 10%. When the content of K ₂ O is too large, the coefficient of thermal expansion becomes too high, the thermal shock resistance is lowered, or it is difficult to match the thermal expansion coefficient of the peripheral material. Further, there is a tendency that the strain point is excessively lowered or the composition of the glass composition is lacking, and the devitrification resistance is lowered. Therefore, the preferred upper limit of K ₂ O is 8% or less, 6% or less, 4% or less, and particularly preferably less than 2%.

In addition to the above components, for example, the following components may be introduced.

Li ₂ O is an ion exchange component and is a component that lowers high temperature viscosity and improves meltability or formability. And to improve the composition of Young's modulus. Further, the effect of increasing the compressive stress value in the alkali metal oxide is large. However, if the content of Li ₂ O is too large, the viscosity of the liquid phase is lowered, and the glass is easily devitrified. Further, the coefficient of thermal expansion becomes too high, the thermal shock resistance is lowered, or it is difficult to match the thermal expansion coefficient of the peripheral material. Further, if the low-temperature viscosity is excessively lowered and stress relaxation is likely to occur, the compressive stress value may be decreased. Therefore, the content of Li ₂ O is preferably 0% to 3.5%, 0% to 2%, 0% to 1%, 0% to 0.5%, and particularly preferably 0.01% to 0.2%.

The preferred content of Li ₂ O+Na ₂ O+K ₂ O is 5% to 25%, 10% to 22%, 15% to 22%, and particularly preferably 17% to 22%. When the content of Li ₂ O+Na ₂ O+K ₂ O is too small, the ion exchange performance or the meltability is liable to lower. On the other hand, when the content of Li ₂ O+Na ₂ O+K ₂ O is too large, the glass is easily devitrified, and the thermal expansion coefficient is too high, the thermal shock resistance is lowered, or it is difficult to match the thermal expansion coefficient of the peripheral material. Further, there is a case where the strain point is excessively lowered, and it is difficult to obtain a high compressive stress value. Further, there is a case where the viscosity in the vicinity of the liquidus temperature is lowered, and it is difficult to ensure a high liquidus viscosity. Further, "Li ₂ O+Na ₂ O+K ₂ O" is the total amount of Li ₂ O, Na ₂ O, and K ₂ O.

MgO is a component which lowers the high-temperature viscosity, improves the meltability or formability, or increases the strain point or Young's modulus, and has a large effect of improving the ion exchange performance in the alkaline earth metal oxide. However, if the content of MgO is too much, density or thermal expansion The coefficient tends to become high and the glass is easily devitrified. Therefore, the preferred upper limit of MgO is 12% or less, 10% or less, 8% or less, 5% or less, and particularly preferably 4% or less. Further, when MgO is introduced into the glass composition, the preferred lower limit of MgO is 0.1% or more, 0.5% or more, 1% or more, and particularly preferably 2% or more.

Compared with other components, CaO has a high effect of lowering the high-temperature viscosity without increasing the resistance to devitrification, improving the meltability or formability, or increasing the strain point or the Young's modulus. The content of CaO is preferably from 0% to 10%. However, when the content of CaO is too large, the density or the coefficient of thermal expansion becomes high, and the composition of the glass composition is not balanced, and the glass is easily devitrified, or the ion exchange performance is liable to lower. Therefore, the preferred content of CaO is 0% to 5%, 0.01% to 4%, 0.1% to 3%, and particularly preferably 1% to 2.5%.

SrO is a component which lowers the high-temperature viscosity without increasing the resistance to devitrification, improves the meltability or formability, or increases the strain point or Young's modulus. However, if the content of SrO is too large, the density or thermal expansion coefficient becomes high, or the ion exchange performance is lowered, or the composition of the glass composition is lacking, and the glass is easily devitrified. The preferred range of SrO is 0% to 5%, 0% to 3%, 0% to 1%, and more preferably 0% to less than 0.1%.

BaO is a component which lowers the high-temperature viscosity without increasing the resistance to devitrification, improves the meltability or formability, or increases the strain point or Young's modulus. However, if the content of BaO is too large, the density or the coefficient of thermal expansion becomes high, or the ion exchange performance is lowered, or the composition of the glass composition is not balanced, and the glass is easily devitrified. The preferred range of BaO is 0% to 5%, 0% to 3%, 0% to 1%, and particularly preferably 0% to less than 0.1%.

ZnO is a component that enhances ion exchange performance, and is particularly a component that has a large effect of increasing the compressive stress value. And to reduce the low temperature viscosity, and reduce the high temperature viscosity Ingredients. However, when the content of ZnO is too large, the glass may be phase-separated, or the devitrification resistance may be lowered, or the density may be increased, or the stress depth of the compressive stress layer may be small. Therefore, the content of ZnO is preferably 0% to 6%, 0% to 5%, 0% to 1%, 0% to 0.5%, and particularly preferably 0% to less than 0.1%.

ZrO ₂ is a component that significantly improves the ion exchange performance, and is a component that increases the viscosity or strain point in the vicinity of the liquid phase viscosity. However, if the content is too large, there is a fear that the resistance to devitrification is remarkably lowered, and the density becomes excessive. High worry. Therefore, the preferred upper limit of ZrO ₂ is 10% or less, 8% or less, 6% or less, and particularly preferably 5% or less. Further, when it is desired to improve the ion exchange performance, it is preferred to introduce ZrO ₂ into the glass composition. In this case, the preferred lower limit of ZrO ₂ is 0.01% or more and 0.5%, and particularly preferably 1% or more.

P ₂ O ₅ is a component that enhances ion exchange performance, especially a component that increases the stress depth of the compressive stress layer. However, if the content of P ₂ O ₅ is too large, the glass tends to be phase-separated. Therefore, the preferred upper limit of P ₂ O ₅ is 10% or less, 8% or less, 6% or less, 4% or less, 2% or less, 1% or less, and particularly preferably less than 0.1%.

One or more kinds selected from the group consisting of As ₂ O ₃ , Sb ₂ O ₃ , SnO ₂ , F, Cl, and SO ₃ (preferably, a group of SnO ₂ , Cl, and SO ₃ ) may be introduced, and 0 ppm to 30000 ppm may be introduced. (3%) as a clarifying agent. The content of SnO ₂ +SO ₃ +Cl is preferably 0 ppm to 10000 ppm, 50 ppm to 5000 ppm, 80 ppm to 4000 ppm, 100 ppm to 3000 ppm, and more preferably 300 ppm to 3000 ppm from the viewpoint of obtaining the clarification effect. Here, "SnO ₂ +SO ₃ +Cl" means the total amount of SnO ₂ , SO ₃ and Cl.

The preferred range of SnO ₂ is 0 ppm to 10000 ppm, 0 ppm to 7000 ppm, and particularly preferably 50 ppm to 6000 ppm, and the preferred range of Cl is 0 ppm to 1500 ppm, 0 ppm to 1200 ppm, 0 ppm to 800 ppm, 0 ppm to 500 ppm, and particularly preferably 50 ppm. ~300ppm. The preferred range of SO ₃ is 0 ppm to 1000 ppm, 0 ppm to 800 ppm, and particularly preferably 10 ppm to 500 ppm.

A rare earth oxide such as Nd ₂ O ₃ or La ₂ O ₃ is a component that increases the Young's modulus, and is a component that can control the color tone of the glass by adding a color that is a complementary color. However, the cost of the raw material itself is high, and if it is introduced in a large amount, the devitrification resistance is liable to lower. Therefore, the content of the rare earth oxide is preferably 4% or less, 3% or less, 2% or less, or 1% or less, and particularly preferably 0.5% or less.

In view of environmental considerations, the flat glass plate 4 and the flat glass plate 5 preferably do not substantially contain As ₂ O ₃ , F, PbO, or Bi ₂ O ₃ . Here, "substantially does not contain As ₂ O ₃ " is intended to prevent the addition of As ₂ O ₃ as a glass component, but it is allowed to be mixed at an impurity level, specifically, the content of As ₂ O ₃ is smaller than 500ppm. The term "substantially does not contain F" is intended to prevent F from being actively added as a glass component, but it is allowed to be mixed at an impurity level, specifically, the content of F is less than 500 ppm. The phrase "substantially does not contain PbO" is intended to prevent PbO from being actively added as a glass component, but it is allowed to be mixed at an impurity level, specifically, the content of PbO is less than 500 ppm. The so-called "containing substantially no Bi ₂ O _3", aimed not actively adding Bi ₂ O ₃ as a glass component, but to allow the case to the level of impurities mixed, and specifically refers to the content of Bi ₂ O ₃ is less than 500ppm.

Further, the flat glass plate 4 and the flat glass plate 5 preferably have the following characteristics.

The density is preferably 2.6 g/cm ³ or less, and particularly preferably 2.55 g/cm ³ or less. The lower the density, the lighter the tempered glass 1 can be. Further, when the content of SiO ₂ , B ₂ O ₃ , or P ₂ O ₅ in the glass composition is increased, or the content of the alkali metal oxide, the alkaline earth metal oxide, ZnO, ZrO ₂ , or TiO ₂ is decreased, the density is liable to lower. Further, "density" can be measured by the well-known Archimedes method.

The coefficient of thermal expansion is preferably 80 × 10 ^-7 / ° C ~ 120 × 10 ^-7 / ° C, 85 × 10 ^-7 / ° C ~ 110 × 10 ^-7 / ° C, 90 × 10 ^-7 / ° C ~ 110 × 10 ^-7 / ° C, especially preferably 90 × 10 ^-7 / ° C ~ 105 × 10 ^-7 / ° C. When the thermal expansion coefficient is limited to the above range, it is easy to match the thermal expansion coefficient of a member such as a metal or an organic adhesive, and it is easy to prevent peeling of members such as a metal or an organic adhesive. Here, the "thermal expansion coefficient" means a value obtained by measuring an average thermal expansion coefficient in a temperature range of 30 ° C to 380 ° C using a thermal dilatometer. Further, when the content of SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , alkali metal oxide, or alkaline earth metal oxide in the glass composition is increased, the coefficient of thermal expansion tends to be high, and conversely, if the alkali metal oxide or alkaline earth is lowered, The content of the metal oxide is likely to lower the coefficient of thermal expansion.

The strain point is preferably 500 ° C or more, 520 ° C or more, 530 ° C or more, and more preferably 550 ° C or more. The higher the strain point, the higher the heat resistance, and the more difficult it is to warp the tempered glass 1. Further, it is easy to form a high-quality film when patterning a touch panel sensor or the like. Here, "strain point" means a value measured based on the method of ASTM C336. Further, when the content of the alkaline earth metal oxide, Al ₂ O ₃ , ZrO ₂ , or P ₂ O ₅ in the glass composition is increased, or the content of the alkali metal oxide is decreased, the strain point tends to be high.

The liquid viscosity is preferably 10 ^4.0 dpa‧s or more, 10 ^4.4 dPa‧s or more, 10 ^4.8 dPa‧s or more, 10 ^5.0 dPa‧s or more, 10 ^5.4 dPa‧s or more, 10 ^5.6 dPa‧s or more, 10 ^6.0 Above dPa‧s, above 10 ^6.2 dPa‧s, especially preferably above 10 ^6.3 dPa‧s. Here, the "liquid phase viscosity" means a value obtained by measuring the viscosity at a liquidus temperature by a platinum ball pulling method. "Liquid phase temperature" means that glass powder which has passed through a 30-mesh standard sieve (500 μm mesh) and remains in a 50-mesh standard sieve (300 μm mesh) is placed in a platinum boat and precipitated in a temperature gradient furnace for 24 hours. The temperature of crystallization. Further, the lower the liquidus temperature, the more the devitrification resistance or formability is improved. Further, the higher the liquid phase viscosity, the higher the resistance to devitrification or formability. Further, when the content of Na ₂ O or K ₂ O in the glass composition is increased or the content of Al ₂ O ₃ , Li ₂ O, MgO, ZnO, TiO ₂ or ZrO ₂ is decreased, the liquidus viscosity tends to be high.

Further, it is preferable that the flat glass plate 4 and the flat glass plate 5 are formed by an overflow down-draw method. In this case, it is easy to form a glass plate which is not polished and has a good surface quality, and as a result, it is easy to increase the mechanical strength of the surface of the tempered glass 1. The reason for this is that in the case of the overflow down-draw method, the surface to be the surface is not in contact with a gutter-shaped refractory, and the surface is formed in a state of a free surface. The structure or material of the groove-like structure is not particularly limited as long as the desired size or surface quality can be achieved. Further, the method of applying a force to the glass ribbon in order to perform the stretch forming below is not particularly limited as long as the desired size or surface quality can be achieved. For example, a method in which a heat-resistant roller having a sufficiently large width is rotated while being in contact with the glass ribbon may be used, or a plurality of pairs of heat-resistant rollers may be brought into contact with only the vicinity of the end faces of the glass ribbon. The method of extension.

In addition to the overflow down-draw method, the flat glass plate 4 and the flat glass plate 5 may also utilize a slot down draw method, a float method, or a roll-out method. Forming by a redraw method or the like.

In the present invention, the compressive stress value of the compressive stress layer is preferably 400 MPa or more (preferably 500 MPa or more, 600 MPa or more, 650 MPa or more, and particularly preferably 700 MPa or more), and the stress depth of the compressive stress layer is 15 μm or more (more preferably The glass plate laminate 6 is subjected to ion exchange treatment so as to preferably be 20 μm or more, 25 μm or more, 30 μm or more, and more preferably 35 μm or more. The larger the compressive stress value, the higher the mechanical strength of the tempered glass 1 is. On the other hand, if the compressive stress value is too large, it is difficult to cut the tempered glass 1 into a scribe line. Therefore, the compressive stress value of the compressive stress layer is preferably 1,500 MPa or less and 1200 MPa or less, and particularly preferably 1000 MPa or less. Further, when the content of Al ₂ O ₃ , TiO ₂ , ZrO ₂ , MgO, or ZnO in the glass composition is increased or the content of SrO or BaO is decreased, the compressive stress value tends to increase. Further, when the ion exchange time is shortened or the temperature of the ion exchange solution is lowered, the compressive stress value tends to increase. The difference between the compressive stress values of the first glass sheet 2 and the second glass sheet 3 is preferably 40 MPa or more, 60 MPa or more, 80 MPa or more, and more preferably 100 MPa or more. The difference in stress depth between the first glass plate 2 and the second glass plate 3 is preferably 1 μm or more, 4 μm or more, or 7 μm or more, and more preferably 10 μm or more.

The greater the stress depth, the more difficult it is to rupture the tempered glass 1 even if the tempered glass 1 is deeply damaged, and the unevenness of the mechanical strength becomes smaller. On the other hand, if the stress depth is too large, it is difficult to cut the tempered glass 1 by scribe lines. The stress depth is preferably 100 μm or less, less than 80 μm, 60 μm or less, and particularly preferably less than 52 μm. Further, when the content of K ₂ O or P ₂ O ₅ in the glass composition is increased or the content of SrO or BaO is decreased, the stress depth tends to increase. Further, if the ion exchange time is prolonged or the temperature of the ion exchange solution is increased, the stress depth tends to increase.

Further, the tempered glass produced by chemically strengthening the unreinforced glass by the ion exchange method and the tempered glass produced by the ion exchange method in the surface layer portion of the glass have different microscopic glass compositions, but in the case of the glass as a whole, The glass composition and glass properties are substantially the same. That is, the glass composition and the glass characteristics of the flat glass plate 4 and the first glass plate 2 are substantially the same, and the glass composition and the glass characteristics of the flat glass plate 5 and the second glass plate 3 are substantially the same.

<Second Embodiment>

Fig. 5 is a flowchart showing a method of producing tempered glass according to a second embodiment of the present invention. The method for producing tempered glass according to the second embodiment includes a cutting step S1a, a cutting step S1b, a chamfering step S2a, a chamfering step S2b, a washing step S3a, a washing step S3b, a laminating step S4, a preheating step S5, and Chemical strengthening step S6. In addition, the respective characteristics of the flat glass plate 4 and the flat glass plate 5 are the same as those of the first embodiment.

In the cutting step S1a and the cutting step S1b, the original large glass plate (mother plate) is cut, and the flat glass plate 4 and the flat glass plate 5 of the final product size are respectively formed.

In the chamfering step S2a and the chamfering step S2b, the glass sheet 4 formed in the cutting step S1a and the cutting step S1b is respectively formed so that the chamfered end faces are generated when the glass sheet laminate 6 is formed later. The end faces of the glass sheets 5 are chamfered. The chamfering in this case is, for example, for the respective end faces of the glass plate 4 and the glass plate 5, and one of the end edges forms a micro chamfered surface. Needless to say, the present invention is not limited thereto. For example, as shown in FIG. 2, when the glass laminate layer 6 is formed, the cross section is formed into a single arc shape. Further, the cross section of each of the end faces of the glass plate 4 and the glass plate 5 may be a single arc shape. By the chamfering, when the tempering liquid is immersed in the subsequent chemical strengthening step S6, the glass sheet laminate 6 can be prevented from being broken from the end surface.

In the washing step S3a and the washing step S3b, the chamfered glass plate 4 and the glass plate 5 are respectively cleaned in the chamfering step. In this case, it is preferable to wash the bonding surface 4x of the flat glass plate 4, the flat glass plate 5, and the GI value of the bonding surface 5x to 1000 pcs/m<^2> or less.

In the laminating step S4, the glass plate 4 and the glass plate 5 which have been washed in the washing step S3a and the washing step S3b are directly laminated. Due to glass plate 4, glass plate 5 After washing, and the surface roughness Ra is 2.0 nm or less, they are in close contact with each other as long as they are directly laminated.

In the preheating step S5, the glass plate 4 and the glass plate 5 laminated in the lamination step S4 are preheated. The preheating temperature is, for example, set to 250 ° C to 450 ° C. Thereby, the glass plate 4 and the glass plate 5 in the close contact state are reliably joined, and the glass plate laminated body 6 is formed. That is, in this embodiment, the laminating step S4 and the preheating step S5 constitute a joining step of forming the glass sheet laminate 6.

In the chemical strengthening step S6, the preheated glass sheet laminate 6 is immersed in the strengthening liquid, and chemically strengthened by an ion exchange method. Then, according to the principle described in the first embodiment, the glass sheet laminate 6 is bent to form the tempered glass 1.

<Third embodiment>

Fig. 6 is a flowchart showing a method of producing tempered glass according to a third embodiment of the present invention. The method for producing tempered glass according to the third embodiment includes a washing step S11a, a washing step S11b, a laminating step S12, a heating step S13, a cutting step S14, a chamfering step S15, a preheating step S16, and a chemical strengthening step S17.

In the third embodiment, the cutting step S14 and the chamfering step S15 of the glass sheet laminate 6 are greatly different from the second embodiment in which these steps are performed in a state where the glass sheet 4 and the glass sheet 5 are separate bodies. .

In the washing step S11a and the washing step S11b, the glass plate 4 and the glass plate 5 are respectively washed in the state of the mother board. Then, in the laminating step S12, the glass plate 4 and the glass plate 5 which have been washed in the cleaning step are directly laminated in the state of the mother board. Since the glass plate 4 and the glass plate 5 are cleaned and the surface roughness Ra is 2.0 nm or less, they are adhered to each other as long as they are directly laminated.

In the heating step S13, the glass plate 4 and the glass plate 5 in the laminated state formed in the lamination step S12 are heated. Thereby, the glass plate 4 and the glass plate 5 in the laminated state are reliably joined to each other, and the glass plate laminated body 6 is formed. By strengthening the joining, it is possible to effectively suppress peeling of the glass sheet 4 and the glass sheet 5 in the next cutting step S14 and the chamfering step S15.

In the cutting step S14, the glass sheet laminate 6 in the mother sheet state is cut to form the glass sheet laminate 6 of the final product size.

In the chamfering step S15, the end surface of the glass sheet laminate 6 cut in the cutting step S14 is chamfered.

In the preheating step S16, the chamfered glass sheet laminate 6 in the chamfering step S15 is preheated.

In the chemical strengthening step S17, the preheated glass sheet laminate 6 is immersed in a strengthening liquid, and chemically strengthened by an ion exchange method. Then, according to the principle described in the first embodiment, the glass sheet laminate 6 is bent to form the tempered glass 1. Further, in this embodiment, the laminating step S12 and the heating step S13 are bonding steps of forming the glass sheet laminate 6.

In the third embodiment, the glass sheet laminate 6 is cut into the final product size, and the glass sheet 4 and the glass sheet 5 are cut into the final product size in the state of the glass sheet 5 as in the second embodiment. In comparison with the situation, production efficiency is improved.

[Example 1]

The inventors evaluated the bending of the tempered glass of the examples of the present invention. For the evaluation, a glass plate laminate having a two-layer structure was produced using two glass plates.

The glass plate used for the positive side (the content of Al ₂ O ₃ is large, and the degree of chemical strengthening is large) is formed by an overflow down-draw method, and contains SiO ₂ 61.5%, Al ₂ O ₃ 18%, and B ₂ by mass%. O ₃ 0.5%, MgO 3%, Li ₂ O 0.1%, Na ₂ O 14.5%, K ₂ O 2%, SnO ₂ 0.4% as a glass composition, and a density of 2.45 g/cm ³ and a strain point of 564 ° C, The softening point is 863 ° C, the thermal expansion coefficient is 91.2 × 10 ^-7 / ° C, and the liquid viscosity is 10 ^6.2 dPa ‧ s.

The glass plate for the back side (the content of Al ₂ O ₃ is small, and the degree of chemical strengthening is small) is formed by an overflow down-draw method, and contains SiO ₂ 57.4%, Al ₂ O ₃ 13%, and B ₂ by mass%. O ₃ 2%, MgO 2.1%, CaO 1.8%, Li ₂ O 0.1%, Na ₂ O 14.5%, K ₂ O 5%, ZrO ₂ 4%, SnO ₂ 0.3% as a glass composition, and a density of 2.54 g/ Cm ³ , strain point is 517 ° C, softening point is 762 ° C, thermal expansion coefficient is 99.9×10 ^-7 /° C., liquid viscosity is 10 ^5.5 dPa ‧ s.

First, the case where the original glass plate was square (100 mm × 100 mm) and each plate thickness was 0.7 mm was evaluated. The original glass plate is washed in a clean room and laminated to form a glass plate laminate. The glass plate laminate was heated to 300 ° C to bond the glass plates to each other, and then immersed in a potassium nitrate solution at 440 ° C for 6 hours to carry out ion exchange (chemical strengthening). Thereafter, the bending of the glass sheet laminate was measured, and as a result, it was curved (spherical shape) with a radius of curvature equal to 1500 mm in all directions.

Then, the case where the original glass plate was rectangular (60 mm × 120 mm) and each plate thickness was 0.55 mm and 0.7 mm was evaluated. The original glass plate is washed in a clean room and laminated to form a glass plate laminate. The glass plate laminate was heated to 300 ° C to bond the glass plates to each other, and then immersed in a potassium nitrate solution at 430 ° C for 4 hours to carry out ion exchange (chemical strengthening).

Then, the reinforced glass plate laminate is placed on the stone plate, and the maximum value (L) of the gap between the stone plate and the end face of the long side is measured by a clearance gauge, and the stone plate is short and short. The maximum value (S) of the gap at the end face of the side (see Fig. 1). The measurement results are shown in Table 1. Then, the results obtained by re-sampling Table 1 based on the total thickness of the glass-clad laminate are shown in Table 2.

It is understood from Tables 1 and 2 that the degree of curvature (curvature) does not depend on the thickness of the original glass sheet, but depends on the total thickness of the glass sheet laminate. The reason for this is considered to be that the degree of chemical strengthening of the front side and the back side of the glass sheet laminate is fixed irrespective of the thickness of the original glass sheet.

Further, the same results were obtained for the glass described in Table 3 from the content of Al ₂ O ₃ .

Further, in the above description, the glass sheet laminate is formed by laminating two sheets of glass. However, the present invention is not limited thereto, and three or more sheets of glass may be laminated. In this case, the chemical strengthening characteristics of the pair of glass sheets which are the outermost surface side and the rearmost side of the glass sheet laminate are different from each other, and the chemical strengthening property of the glass sheet sandwiched between the glass sheets is not Special restrictions.

1‧‧‧ tempered glass

1a‧‧‧Long side of tempered glass

1b‧‧‧ Short side of tempered glass

The maximum value of the gap between the L‧‧‧ stone plate and the end face of the long side

The maximum value of the gap between the S‧‧‧ stone plate and the end face of the short side

Claims (10)

A method for producing tempered glass, which is a method for producing a tempered glass, comprising: a bonding step of laminating a plurality of glass sheets and bonding each other to form a glass sheet laminate; and a strengthening step by ion exchange The glass plate laminate is chemically strengthened by the method; and a glass plate having different chemical strengthening characteristics is used as the outermost glass plate of the glass plate laminate and the rearmost surface of the glass laminate. The glass plate is bent while the glass plate laminate is bent in the above-described strengthening step. The method for producing a tempered glass according to claim 1, wherein in the joining step, a glass plate having different compressive stress values of the surface layer portion of the glass when chemically strengthened by the ion exchange method is used is used. The glass plate on the outermost surface of the glass plate laminate and the glass plate on the back surface of the glass laminate. The method for producing tempered glass according to the first or second aspect of the invention, wherein the outermost glass plate and the outermost glass plate have different Al ₂ O ₃ contents. The method for producing tempered glass according to any one of the preceding claims, wherein in the joining step, the plurality of glass sheets are heated in a layered state. The method for producing tempered glass according to the fourth aspect of the invention, wherein the glass sheet has a surface roughness Ra of 2.0 nm or less. The tempered glass according to any one of claims 1 to 5 The manufacturing method further includes a chamfering step of chamfering the end surface of the glass sheet alone or the glass sheet laminate before the strengthening step. A tempered glass which is a curved tempered glass, characterized in that a plurality of glass sheets are laminated in a state of being joined to each other, and a compressive stress layer is formed on a surface portion of at least the outermost glass sheet by chemical strengthening, and the above The compressive stress value of the surface layer portion of the outermost glass plate is different from the compressive stress value of the surface layer portion of the outermost glass plate. The tempered glass according to claim 7, wherein a compressive stress layer is formed on the surface layer portion of both the outermost glass plate and the rearmost glass plate by chemical strengthening. A tempered glass which is a curved tempered glass, characterized in that a plurality of glass sheets are laminated in a state of being joined to each other, and a compressive stress layer is formed on a surface portion of at least the outermost glass sheet by chemical strengthening, and the above the outermost surface of the glass sheet in Al ₂ O ₃ content higher than most of the back surface of the glass plate in the content of Al ₂ O _3. The tempered glass according to any one of claims 7 to 9, wherein a difference in refractive index nd of the mutually adjacent glass sheets among the plurality of sheets of the plurality of sheets of the laminated layer is within ±0.02.